Syntheses and structures of chiral rhenium-containing phosphonium salts and phosphines with ReCH₂P̈Ar₂ or ReCH(R)P̈Ar₂ linkages; enantioselective catalysis of intramolecular Morita–Baylis–Hillman and Rauhut–Currier reactions

Abstract

Easily accessed (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) (2) is treated with Ph₃C⁺ PF₆⁻ (−78 °C) to generate the methylidene cation [(η⁵-C₅H₅)Re(NO)(PPh₃)(=CH₂)]⁺ and then secondary phosphines PAr₂H (Ar = a, Ph; b, p-tol; c, p-C₆H₄OCH₃; d, p-C₆H₄N(CH₃)₂; e, 2-biphen; f, α-naph) to give the phosphonium salts [(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂PAr₂H)]⁺ PF₆⁻ ([1a–f-H]⁺ PF₆⁻, 87–94%). Additions of t-BuOK yield the phosphines 1a–f (64–91%). Analogous procedures starting with (S)-2 give enantiopure (S)-1a–d in comparable yields. The ethyl complex (S)-(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂CH₃) is similarly treated with Ph₃C⁺ PF₆⁻ to generate the ethylidene cation (S)-(sc)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(=CHCH₃)]⁺ and then PPh₂H to give enantiopure and diastereopure (S_ReS_C)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH(CH₃)PPh₂H)]⁺ PF₆⁻ (51%). Addition of t-BuOK yields the corresponding ReCH(CH₃)PPh₂ adduct. The crystal structures of [1c,d-1 PF₆⁻] are determined and analyzed. Most of the ReCH₂PAr₂ species catalyze intramolecular Morita–Baylis–Hillman reactions of R(CO)CH=CH(CH₂)_nCH₂CHO (n/R = 1/Ph, 1/S-i-Pr, 2/p-tol 2/Me) in C₆H₆ or C₆H₅Cl (20 °C) to give R(CO)[upper bond 1 start]CH=CH(CH₂)_nCH₂C[upper bond 1 end]HOH (99–86%, 74–38% ee with (S)-1a) or Rauhut–Currier reactions of R(CO)CH=CHCH₂CH₂CH=CH(CO)R (R = Ph, S-i-Pr) to give R(CO)C=C[upper bond 1 start][upper bond 1 start]HCH₂CH₂C[upper bond 1 end]HCH₂(CO)R (87–82%, 56–42% ee with (S)-1a).

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Introduction

There are now an immense number of phosphine catalyzed organic reactions,^1,2 and many enantioselective transformations have been developed with enantiopure chiral phosphines.³ Two examples, both intramolecular, are illustrated in Scheme 1: a Morita–Baylis–Hillman reaction (top), and a vinylogous version known as the Rauhut–Currier reaction (bottom).^1,4 At the time our work commenced, the former had been studied by Murphy,⁵ Koo,⁶ and a few others.⁷ Murphy found the phosphine PBu₃ (20 mol%) to be a moderately effective catalyst with two substrates (up to four turnovers), but inferior to other types of Lewis bases. Under Koo's conditions, stoichiometric quantities of PPh₃ were required. Then Miller developed a phosphorus-free chiral pipecolinic acid/N-methylimidazole cocatalyst system for effecting closely related cyclizations.⁸ This afforded an average ee value of 73% (high/low 80%/51%, five substrates).⁹

Scheme 1 Intramolecular Morita–Bayliss–Hillman (top) or Rauhut–Currier reactions (bottom); A, B: key stereocenter generating steps.

We have sought to synthesize and study the catalytic properties of enantiopure phosphines in which a “chiral-at-metal” fragment serves as the sole stereogenic center, in particular the sixteen-valence electron pyramidal rhenium moiety (η⁵-C₅H₅)Re(NO)(PPh₃).^10–12 The phosphorus donor group may be directly bound to rhenium (ReP̈R₂ or ReP̈Ar₂), separated by a methylene or similar spacer (ReCH₂P̈R₂ or ReCH₂P̈Ar₂), or attached to the cyclopentadienyl ligand (η⁵-C₅H₄P̈R₂ or η⁵-C₅H₄P̈Ar₂).¹⁰ As will be described later, analogous species that are furthermore “chiral-at-phosphorus” are easily accessed.¹³ At the time our work began, there was only a single example of an enantiopure phosphine being applied to an intramolecular Morita–Baylis–Hillman reaction ((S)-CAMP, 18 mol%, 75% GLC yield), and the enantioselectivity was poor (14% ee).^7a

In a preliminary communication, we established the viability of catalyzing the reactions in Scheme 1 with chiral rhenium-containing phosphines.¹² However, data were provided for only two catalysts, racemic or enantiopure (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂PAr₂) with Ar = Ph (1a) or p-C₆H₄OCH₃ (1c).^10,14 Furthermore, the publisher required that the full set of ESI† be replaced by two footnotes describing representative protocols. This introduced a number of gaps in the documentation. In subsequent efforts, several related catalysts were synthesized and evaluated, some of which exhibited improved performance characteristics. Accordingly, this full paper combines all of these themes into a cohesive, comprehensive narrative.⁹

Results

Chiral-at-rhenium catalysts

The starting material in Scheme 2, methyl complex (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) (2), can be prepared from Re₂(CO)₁₀ in six steps in 44% overall yield (racemic)¹⁵ or nine steps in 36% overall yield (enantiopure).¹⁵ The racemate and the hydride abstracting reagent Ph₃C⁺ PF₆⁻ were combined at −78 °C. The electrophilic methylidene complex¹⁶ [(η⁵-C₅H₅)Re(NO)(PPh₃)(=CH₂)]⁺ PF₆⁻ formed in situ and was subsequently treated with a symmetrically substituted secondary phosphine PAr₂H (Ar = Ph (a), p-tol (b), p-C₆H₄OCH₃ (c), p-C₆H₄N(CH₃)₂ (d), 2-biphenyl (e), α-naphthyl (f)). The phosphines a,b are commercially available, and c,d,f have been previously reported.^17,18 However, e is a new compound, and its preparation is described in the ESI.†

Scheme 2 Preparation of rhenium-containing phosphonium salts and phosphines.

Workups gave the protonated rhenium-containing phosphines [(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂PAr₂H)]⁺ PF₆⁻ ([1a–f-H]⁺ PF₆⁻) as air-stable orange to red powders in 87–95% yields. The parent ReCH₂PPh₂H species [1a-H]⁺ PF₆⁻, enantiopure salts thereof, and phosphines derived therefrom have been described earlier.^10,14 The other complexes were new, and were characterized by NMR (¹H, ¹³C{¹H}, ³¹P{¹H}) and IR spectroscopy, elemental analysis, and mass spectrometry, as summarized in the Experimental section. Since the PAr₂ groups are diastereotopic, two sets of ¹H and ¹³C{¹H} NMR signals were seen, including those of the para substituents in [1b–d-H]⁺ PF₆⁻.

As shown in Scheme 2, the phosphonium salts [1-H]⁺ PF₆⁻ were deprotonated with t-BuOK under heterogeneous conditions in benzene. The red suspensions were filtered (Celite), and additions of pentane precipitated the target rhenium-containing phosphines 1a–f as orange to red solids in 91–64% yields. These were slightly air sensitive and characterized analogously to [1-H]⁺ PF₆⁻. The ¹H and ¹³C{¹H} spectra again showed separate signals for the diastereotopic PAr₂ groups, consistent with the appreciable pyramidal inversion barriers of most triorganophosphines.¹⁹ The ³¹P{¹H} NMR data for all compounds are summarized in Table s1 (ESI).†

The new enantiopure complexes (S)-[1b–d-H]⁺ PF₆⁻ and (S)-1b–d were synthesized analogously to the racemates, although due to their generally higher solubilities, some workups were slightly modified. Additions of carbon, nitrogen, phosphorus and sulfur nucleophiles to the methylidene complex [(η⁵-C₅H₅)Re(NO)(PPh₃)(=CH₂)]⁺ PF₆⁻ have been shown to proceed with retention at rhenium.^20,21 Since racemic 1e,f proved to be poor catalysts (vide infra), enantiopure analogs were not sought.

Chiral-at-rhenium-and-carbon catalysts

The phosphorus donor atoms in 1a–f are separated from the stereogenic rhenium by a CH₂ spacer. Complexes that lack the CH₂ spacer – i.e., feature a direct RePR₂ linkage – have not been effective in any phosphine-catalyzed reaction examined to date. These are exceptionally nucleophilic systems²² that appear to have a number of facile deactivation pathways. Therefore, we sought to replace the CH₂ spacer by a CHR spacer, thereby introducing a stereocenter proximal to the reactive site of the catalyst.

As shown in Scheme 3, the enantiopure rhenium ethyl complex (S)-(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂CH₃)²³ and Ph₃C⁺ PF₆⁻ were combined in CH₂Cl₂ at −78 °C. A hydride moiety was regiospecifically (α ≫ β) and diasteroselectively (pro-R ≫ pro-S) abstracted to give the ethylidene complex (S)-(sc)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(=CHCH₃)]⁺ PF₆⁻. This species is generated in the Re=C conformation III,²³ and PPh₂H was added at low temperature to preclude isomerization. Workup gave the phosphonium salt (S_ReS_C)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH(CH₃)PPh₂H)]⁺ PF₆⁻ ((S_ReS_C)-[9a-H]⁺ PF₆⁻) as a pale yellow powder in 51% yield, which was characterized as the other new complexes. The carbon configuration was assigned by analogy to addition products of ethylidene and benzylidene complexes that have been crystallographically characterized.²⁴

Scheme 3 Preparation of the diastereopure rhenium-containing phosphine (S_ReS_C)-9a.

The (S_ReS_C)-[9a-H]⁺ PF₆⁻ was subsequently treated with t-BuOK in benzene. An abbreviated workup (filtration/precipitation) gave crude (S_ReS_C)-9a, which was employed without further purification or characterization for catalysis. The analogous benzylidene-derived complex (S_ReS_C)-10a (Scheme 3), which has been previously reported and fully characterized,²⁴ was similarly synthesized.

Crystallography

In the course of the preceding studies, the phosphonium salts [1c,d-H]⁺ PF₆⁻ crystallized. X-ray data were collected as summarized in Table 1 and the Experimental section. Key metrical parameters are supplied in Table 2, together with previously reported data for a benzene monosolvate of a related deprotonation product, (S)-1a.¹⁰ Views of the cations are presented in Fig. 1. Both feature the typical octahedral coordination geometries of d⁶ piano-stool type complexes, as reflected by the ca. 90° L–Re–L bond angles between the non-cyclopentadienyl ligands.

Fig. 1 Structures of the cations of [1c-H]⁺ PF₆⁻ (bottom) and [1d-H]⁺ PF₆⁻ (top) with thermal ellipsoids at the 50% probability level. Some of the atom labels have been changed from those in the CIF files to facilitate comparisons.

Table 1 Crystallographic data for [1c-H]⁺ PF₆⁻ and [1d-H]⁺ PF₆⁻

	[1c-H]^+ PF6^−	[1d-H]^+ PF6^−
Empirical formula	C38H37F6NO3P3Re	C40H43F6N3OP3Re
Formula weight	948.80	974.88
Temperature [K]	173(2)	173(2)
Diffractometer	Nonius KappaCCD	Nonius KappaCCD
Wavelength [Å]	0.71073	0.71073
Crystal system	Monoclinic	Monoclinic
Space group	P2(1)/c	P21/n
a [Å]	12.7618(3)	11.84610(1)
b [Å]	15.3419(5)	16.04480(1)
c [Å]	19.2417(5)	21.0727(2)
α [°]	90	90
β [°]	97.260(2)	91.033(1)
γ [°]	90	90
Volume [Å^3]	3737.13(18)	4004.60(6)
Z	4	4
ρ calc [Mg m^−3]	1.686	1.617
μ [mm^−1]	3.448	3.218
F(000)	1880	1944
Crystal size [mm]	0.20 × 0.15 × 0.01	0.20 × 0.15 × 0.15
Θ range [°]	2.43 to 27.46	1.96 to 27.47
Index ranges	−16 ≤ h ≤ 16, −19 ≤ k ≤ 19, −24 ≤ l ≤ 24	−15 ≤ h ≤ 15, −20 ≤ k ≤ 20, −27 ≤ l ≤ 27
Reflections collected	15 172	17 867
Independent reflections	8539 [R(int) = 0.0470]	9171 [R(int) = 0.0157]
Reflections [I > 2σ(I)]	5978	7969
Max. and min. transmission	0.9663 and 0.5455	0.6439 and 0.5654
Data/restraints/parameters	8539/0/470	9171/0/491
Goodness-of-fit on F^2	1.008	1.043
Final R indices [I > 2σ(I)]	R 1 = 0.0384, wR^2 = 0.0814	R 1 = 0.0228, wR^2 = 0.0579
R indices (all data)	R 1 = 0.0714, wR^2 = 0.0920	R 1 = 0.0290, wR^2 = 0.0606
Largest diff. peak/hole [e Å^−3]	1.221 and −1.001	1.128 and −1.062

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Table 2 Key distances [Å] and angles [°] in [1c,d-H]⁺ PF₆⁻ and (S)-1a·C₆H₆ ^a

a Some atom labels used in this table, Fig. 1, and elsewhere in the main text have been changed from those in the CIF files to facilitate comparisons. b Data for this complex from ref. 10.
	[1c-H]^+ PF6^−	[1d-H]^+ PF6^−	(S)-1a·C6H6 ^b
Re–N(1)	1.745(4)	1.760(2)	1.773(7)
Re–P(1)	2.3531(13)	2.3487(6)	2.352(2)
Re–C(1)	2.192(5)	2.197(2)	2.170(8)
C(1)–P(2)	1.757(5)	1.770(3)	1.845(8)
Re–Cp(centroid)	1.953	1.942	1.949
N(1)–Re–P(1)	92.33(14)	93.53(7)	92.5(2)
Re–N(1)–O(1)	173.7(4)	170.8(2)	174.5(6)
N(1)–Re–C(1)	99.81(18)	100.87(10)	97.2(3)
P(1)–Re–C(1)	86.38(14)	88.78(7)	87.6(2)
Re–C(1)–P(2)	111.5(3)	109.75(13)	112.1(4)
P(1)–Re–C(1)–P(2)	131.9(2)	123.08(12)	159.9
N(1)–Re–C(1)–P(2)	40.2(3)	29.71(14)	67.6
Re–C(1)–P(2)–H or LP	50.0	59.3	49.1
Re–C(1)–P(2)–C(50)	176.1(2)	172.22(11)	176.9
Re–C(1)–P(2)–C(60)	60.9(3)	59.13(15)	78.8

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Both cations also exhibit similar conformations, as can be gauged by the torsion angles in Table 2. In particular, the Newman-type projections (Fig. 1, right) show that the CH₂–P (C1–P2) linkages are directed into the most spacious interstice between the cyclopentadienyl and nitrosyl ligands.²⁵ This is reflected by the P1–Re–C1–P2 and N1–Re–C1–P2 torsion angles (131.9–123.1° and 40.2–29.7°, respectively). Turning to the conformations about the CH₂–P bonds, the large rhenium substituents on C1 are anti to one P–C_ipso group (torsion angles 176.1–172.2°) and gauche to the other (60.9–59.1°) as well as the smaller P–H moiety (50.0–59.3°). In general, (S)-1a exhibits similar torsion angles, the major difference being a 28–38° rotation about the Re–CH₂ linkage. Hence, the structures of [1-H]⁺ PF₆⁻ do not significantly change upon deprotonation.

Catalysis

Next, the rhenium-containing phosphines in Schemes 2 and 3 were applied as catalysts to the reactions in Schemes 1 and 4. The substrates were easily prepared from succinaldehyde or glutaraldehyde and either one (3j,k, 4l,m) or two (5j,k) equivalents of the appropriate phosphorus ylide X(C=O)CHPPh₃. Two were new compounds when this work was carried out (3k, 4l), and characterization is supplied in the ESI.†

Scheme 4 Catalysis of intramolecular Morita–Baylis–Hillman and Rauhut–Currier reactions by chiral rhenium-containing phosphines 1a–c.

In the prototype for one series of reactions, a 0.0100 M benzene solution of racemic catalyst 1a was added dropwise to an equal volume of a 0.100 M benzene solution of 3j. This corresponds to a 10 mol% catalyst loading and 0.0050 M and 0.050 M catalyst and substrate concentrations, parameters that were kept constant throughout this work. After 1.5 h at 20 °C, a chromatographic workup gave the known carbocycle 2-benzoylcyclopent-2-en-1-ol (6j; Scheme 4)⁵ in 91% yield as a spectroscopically pure oil. NMR monitoring versus an internal standard (CH₂ClCH₂Cl, 3.73 δ/ppm; used throughout this work) showed a nearly quantitative conversion, with significant amounts of catalyst remaining.

An analogous but slightly slower reaction of the thioester 3k (6 h) gave the corresponding carbocycle 6k in 99% yield. This new compound was fully characterized as described in the Experimental section. The substrates 4l,m gave still slower cyclizations, but after 3 d, chromatography afforded the six-membered ring products 7l,m (Scheme 4) in 91–86% yields. However, preliminary experiments with related esters, which would be less electrophilic, gave much slower reactions and lower product yields.

The preceding reactions were repeated on 0.010–0.020 g scales using the enantiopure catalyst (S)-1a. As summarized in Scheme 4, the Morita–Baylis–Hillman products 6j,k and 7m were obtained with quite high enantioselectivities (74–62% ee, or er 87 : 13 to 81 : 19), as analyzed by HPLC. The enantiomeric purity of 7l was somewhat lower (38% ee, or er 69 : 31). NMR analyses indicated yields comparable to those with racemic 1a. The Rauhut–Currier products 8j,k were isolated in 87% and 82% yields, and 42% ee (er 71 : 29) and 52% ee (er 76 : 24), respectively. These reactions required 5–6 h and 100–120 h, respectively, to go to completion (NMR monitoring).

Other solvents were screened. In chlorobenzene, the reactions of 3j,k were slower, but those of 4l,m were comparable. With 8j, the enantioselectivity increased from 42% ee (er 71 : 29) to 56% ee (er 78 : 22). However, with the other substrates, values decreased versus benzene (62–38% ee; avg. 50% vs. 56% in benzene). Since chlorobenzene has a lower freezing point, the reaction of (S)-1a and 3j was repeated at −25 °C. Surprisingly, byproducts formed that were not evident in the room temperature reactions. Rates and conversions were much lower in acetonitrile (e.g., ca. 45% conversion of 3j to 6j, racemic 1a, 160 h). Many of these trends and generalizations are illustrated graphically, often with additional data, elsewhere.²⁶

Donor groups in para positions (e.g., Me, MeO, Me₂N) normally increase the basicities of aryl phosphines.^27,28 This should accelerate the formation of the intermediates A and B in Scheme 1. Accordingly, the racemic and enantiopure catalysts 1b–d were similarly studied. Indeed, racemic 1b gave faster cyclizations with all six substrates. With (S)-1b, enantioselectivities averaged marginally higher than those with (S)-1a (57% vs. 56% in benzene), with superior results with 6j,k. However, a few product yields appeared lower as compared to 1a or (S)-1a. Disappointingly, 1c, with still more electron donating p-methoxy substituents, gave lower product yields (Scheme 4), and byproducts were evident by NMR. When (S)-1c was used, enantioselectivities nosedived to 41–0% ee. Such low ee values suggest that an achiral catalyst may be generated. The complexes 1d and (S)-1d gave still poorer results.

The bis(2-biphenyl)phosphine adduct 1e gave no reactions with all substrates examined. The bis(α-naphthyl) catalyst 1f gave very slow reactions with 3j,k (90% conversion to 6j over 168 h) and essentially none with the other substrates. Perhaps these aryl substituents are simply too bulky for efficient catalysis. The phosphido complex (η⁵-C₅H₅)Re(NO)(PPh₃)(PPh₂)^4a is the most basic of all the types of rhenium-containing phosphines surveyed in the introduction.^4a It was rapidly consumed under conditions of Scheme 4, and no catalysis occurred. NMR data strongly suggest the formation of phosphine oxides in some reactions, particularly with the poorer catalysts.

The Re,C stereogenic phosphine (S_Re,S_C)-9a (Scheme 3) proved to be another slow catalyst, giving a ca. 86% conversion of 3j to 6j over the course of 168 h. It was much less effective with other substrates, and the related species (S_Re,S_C)-10a gave only 10% conversion to 6j over 120 h. Along the same lines, the previously reported diphosphine (S_Re,S_C)-11a (Scheme 5)²⁴ gave no reaction with 3j and other substrates. The diphosphine (S_Re)-12a (Scheme 5),¹⁰ which lacks a carbon stereocenter, did slowly convert 3j to 6j (27%, 72 h; 41%, 168–240 h), but the ee value was only 3%.

Scheme 5 Other complexes used in this study (top) and additional relevant catalysts and reactions (middle, bottom).

Discussion

A variety of racemic and enantiopure rhenium-containing phosphine catalysts has been described above. Those in Scheme 2 are easily accessed in two steps from the methyl complexes 2 or (S)-2, and if desired the second step can be carried out in situ. Thus, had a “privileged catalyst” been discovered during this work, it could well have been practical economically. However, in line with observations of other researchers, the optimum catalysts and conditions for intramolecular Morita–Baylis–Hillman and Rauhut–Currier reactions can vary greatly from substrate to substrate.^4–6

Nonetheless, there are discernable trends in our data. The substrates are more rapidly consumed as the donor strengths of the PAr₂ groups in 1 increase (1a < 1b < 1c < 1d). However, with methoxy- and dimethylamino-substituted 1c,d, product yields also greatly decrease, reflecting some combination of side-reactions and catalyst deactivation. Similarly, when phenyl is replaced by the much bulkier aryl groups 2-biphenyl and α-naphthyl (1e,f), little or very slow turnover is seen, perhaps for steric reasons. Related catalysts with an added ReCH(R)PPh₂ stereocenter (Scheme 3) or cyclopentadienyl-based PPh₂ group (Scheme 5), are essentially ineffective, for reasons that can only be speculated about.

Since our communication, several other chiral phosphorus-containing catalysts have been developed for intramolecular Morita–Baylis–Hillman or Rauhut–Currier reactions.⁴ Those that have been applied to substrates used in this study are illustrated in Scheme 5 (middle).^29–32 Under highly optimized conditions in CH₂Cl₂, the thiourea-containing phosphine 13 effects the Rauhut–Currier cyclization of 5j to 8k in 80–88% isolated yields and ≥99% ee at 20 mol% loadings.^29a The related catalyst 14a was comparably effective at 10 mol% loadings.^29b The binapthol-containing phosphine 15 gave 8k in only 44–38% isolated yields and 82–94% ee at 20 mol% loadings, although it was much more effective for cyclizations producing six-membered rings.³⁰ A reviewer has suggested that the non-phosphorus-containing catalyst system 16, which has been applied to 5j, also be highlighted.^32d

The thiourea 14b, which features an electronegative aryl NH substituent, effected the Morita–Baylis–Hillman cyclization of 4l to 7l in 79% isolated yield and 78% ee at 10 mol% loadings.^29c The catalyst 17, in which a squaramide unit has been introduced on nitrogen, gave 7l in 94% isolated yield and 92% ee at 3 mol% loadings.^29d A variant of 14a,b with a mannose-derived NH substituent, 14c, catalyzed the conversion of 3a to 6k in 93% isolated yield and 97% ee at only 2 mol% loadings.^29e The ferrocene and squaramide-containing phosphine 18 catalyzed the same cyclization in 68% isolated yield and 88% ee at 20 mol% loadings (CH₂Cl₂, 7 d).³¹ All of these catalysts are bifunctional, with extensively employed hydrogen bond donors or acceptors. Protic solvents or additives are often used in phosphine catalyzed reactions,^4,5,7b but when the reactions in Scheme 4 were doped with t-BuOH, CF₃CH₂OH, or binaphthol, poorer results were always obtained.

In another study, we found that the fluorous aliphatic phosphine P[(CH₂)₃(CF₂)₇CF₃]₃ is a good achiral catalyst for the conversion of substrates 3j,k, 4l, and 5k to 6j,k, 7l, and 8k, respectively.³³ The basicity of the phosphorus atom can be modulated by varying the lengths of the methylene spacers and perfluoroalkyl segments, and three methylene groups proved to be the “sweet spot” in these cases. Probably the most obvious way to optimize the catalysts in Schemes 2 and 3 is to introduce chirality at the phosphorus donor atom. Another approach would be to mimic the bifunctionality of catalysts 13–18 (Scheme 5) in the rhenium coordination sphere.

Nonetheless, the phosphines 1 have other types of applications. For example, (S)-1a is a good catalyst for the enantioselective cycloaddition of allenes and tosylated aryl imines (Scheme 5, bottom),¹¹ and when combined with [Pd(allyl)Cl]₂, for the kinetic resolution of racemic esters of chiral alcohols, such as cyclohex-2-en-1-yl acetate.¹³ Alternatively, they may serve as springboards to diphosphines of the types (S_Re)-12a and (S_Re,S_C)-11a (Scheme 5, top).^10,24 Such diphosphines chelate to rhodium, giving excellent catalysts for enantioselective hydrogenations of olefins and hydrosilylations of ketones.³⁴ This study provides a library of building blocks for further developing this catalyst family.

In conclusion, this investigation has greatly expanded the range of racemic and enantiopure rhenium-containing phosphorus donor ligands. Among these, 1a,b and (S)-1a,b have clearly emerged as the best catalysts for (enantioselective) intramolecular Morita–Baylis–Hillman and Rauhut–Currier reactions. While several researchers have also made significant contributions to catalyst development, including bifunctional phosphorus Lewis bases that sometimes exhibit superior efficacy,^29–31 there is still much room for improvement regarding generality, enantioselectivity, catalyst loading, and other performance factors. Parallel efforts involving rhenium-containing P-stereogenic catalysts will be reported in a subsequent paper.¹³

Experimental section

General data

All reactions were conducted under N₂. The Ph₃C⁺ PF₆⁻ (≥95%, Fluka)³⁵ was stored under argon at −30 °C. Other (mostly routine) details are provided in the ESI.†

[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(p-tol)₂H)]⁺ PF₆⁻ ([1b-H]⁺ PF₆⁻)

A Schlenk flask was charged with racemic (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) (2, 0.244 g, 0.437 mmol)¹⁵ and CH₂Cl₂ (15 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.187 g, 0.481 mmol) added with stirring. After 1 h, P(p-tol)₂H (b, 0.112 g, 0.787 mmol) dissolved in CH₂Cl₂ (1 mL) was added. After 20 min, the cold bath was removed. After 1 h, the mixture was concentrated by oil pump vacuum (to ca. 2.5 mL) and added dropwise to stirred hexanes (25 mL). An orange powder precipitated, which was collected by filtration and washed with pentane (3 × 5 mL). The powder was dissolved in CH₂Cl₂ (3 mL) and benzene (15 mL). Hexanes (15 mL) were added with stirring and again an orange powder precipitated, which was collected by filtration, washed with hexanes (2 × 5 mL) and pentane (5 × 5 mL), and dried by oil pump vacuum to give [1b-H]⁺ PF₆⁻ (0.376 g, 0.411 mmol, 94%), mp 179–181 °C, dec. Anal. calcd (%) for C₃₈H₃₇F₆NOP₃Re (917.2): C 49.78, H 4.07, N 1.53; found: C 49.45, H 3.98, N 1.50.

NMR (CD₂Cl₂, δ/ppm): ¹H (400 MHz) 7.73–7.65, 7.51–7.43, 7.37–7.30 (3 m, C₆H̲₅ and C₆H̲₄, 23H), 6.91 (dd, ¹J(H,P) = 484 Hz, ³J(H,H) = 13.3 Hz, PH̲, 1H), 4.87 (s, C₅H̲₅, 5H), 2.65–2.54 (m, CH̲H′, 1H), 2.50, 2.40 (2 s, CH̲₃ and CH̲₃′, 2 × 3H), 2.32–2.18 (m, CHH̲′, 1H); ¹³C{¹H} (101 MHz) 91.0 (s, C̲₅H₅), −34.9 (dd, ¹J(C,P) = 29.8 Hz, ²J(C,P) = 4.1 Hz, C̲HH′); PPh₃ at³⁶ 134.4 (d, ¹J(C,P) = 54.0 Hz, i), 134.0 (d, ²J(C,P) = 10.6 Hz, o), 131.6 (d, ⁴J(C,P) = 2.1 Hz, p), 129.5 (d, ³J(C,P) = 10.4 Hz, m); P(p-tol)(p-tol)′ at 146.1 (d, ⁴J(C,P) = 2.8 Hz, p to P), 145.5 (d, ⁴J(C,P) = 2.8 Hz, p′ to P), 132.6 (d, ²J(C,P) = 10.6 Hz, o to P), 131.9 (d, ²J(C,P) = 10.5 Hz, o′ to P), 131.2 (d, ³J(C,P) = 12.9 Hz, m to P), 130.9 (d, ³J(C,P) = 12.2 Hz, m′ to P), 121.5 (d, ¹J(C,P) = 71.8 Hz, i to P), 119.2 (d, ¹J(C,P) = 88.2 Hz, i′ to P), 22.1, 22.0 (2 s, C̲H₃ and CH̲₃′); ³¹P{¹H} (162 MHz) 28.8 (d, ³J(P,P) = 10.9 Hz, P̲H), 21.7 (d, ³J(P,P) = 10.9 Hz, P̲Ph₃), −144.0 (sept, ¹J(P,F) = 708 Hz, P̲F₆).

IR (thin film, cm⁻¹): 1668 (s, ν_NO). MS:³⁷ 772 (90) [1b-H]⁺, 558 (100) [1b-P(p-tol)₂H]⁺.

(S)-[1b-H]⁺ PF₆⁻

A Schlenk flask was charged with (S)-2 (0.250 g, 0.448 mmol)¹⁵ and CH₂Cl₂ (15 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.191 g, 0.493 mmol) added with stirring. After 1 h, b (0.115 g, 0.787 mmol) dissolved in CH₂Cl₂ (1 mL) was added. After 20 min, the cold bath was removed. After 1 h, the mixture was concentrated by oil pump vacuum (to ca. 2.5 mL) and EtOH (7 mL) added with stirring. A yellow powder precipitated, and the solvent volume was reduced by oil pump vacuum (to ca. 6 mL). The mixture was kept at −20 °C. After 2 h, the yellow powder was collected by filtration, washed with EtOH (1 mL) and hexanes (2 × 5 mL), and dried by oil pump vacuum to give (S)-[1b-H]⁺ PF₆⁻ (0.353 g, 0.385 mmol, 86%), mp 179–180 °C, dec. Anal. calcd (%) for C₃₈H₃₇F₆NOP₃Re (917.2): C 49.78, H 4.07, N 1.53; found: C 49.50, H 4.12, N 1.54. [α]⁵⁸⁹₂₆ = 257° ± 2° (c = 2.00 mg mL⁻¹, CH₂Cl₂). Spectroscopic data were similar to those of the racemate.

(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(p-tol)₂) (1b)

A Schlenk flask was charged with [1b-H]⁺ PF₆⁻ (0.161 g, 0.191 mmol) and benzene (20 mL). The suspension was vigorously stirred and t-BuOK (0.0321 g, 0.287 mmol) added. After 1 h, the orange suspension was filtered through a plug of Celite. The plug was rinsed with benzene until the filtrate became colorless. The filtrate was concentrated by oil pump vacuum (to ca. 2 mL), layered with pentane (15 mL), and kept at 4 °C. After 48 h, the orange crystals were collected by filtration and dried by oil pump vacuum to give 1b (0.118 g, 0.153 mmol, 80%), Dec. pt. 160–162 °C. Anal. calcd (%) for C₃₈H₃₆NOP₂Re (770.9): C 59.21 H 4.71, N 1.82; found: C 58.98, H 4.98, N 1.81.

NMR (C₆D₆, δ/ppm): ¹H (300 MHz) 7.74 (apparent t, ³J(H,H) = ³J(H,P) = 7.0 Hz, C₆H̲₄, o to P, 2H), 7.66 (apparent t, ³J(H,H) = ³J(H,P) = 7.0 Hz, C₆H̲₄′, o to P, 2H), 7.53 (dd, ³J(H,P) = 11.6 Hz, ³J(H,H) = 9.6, o-C₆H̲₅, 6H), 7.12–6.93 (m, m-, p-C₆H̲₅ and C₆H̲₄, m to P, 13H), 4.55 (s, C₅H̲₅, 5H), 2.83 (dd, ²J(H,H) = 11.6 Hz, J(H,P) = 9.7 Hz, CH̲H′, 1H), 2.12, 2.08 (2 s, CH̲₃ and CH̲₃′, 2 × 3H), 2.15–2.05 (m, CHH̲′, 1H); ¹³C{¹H} (76 MHz) 89.9 (s, C̲₅H₅), −18.1 (dd, ¹J(C,P) = 37.2 Hz, ²J(C,P) = 4.7 Hz C̲HH′); PPh₃ at 136.6 (d, ¹J(C,P) = 50.8 Hz, i), 134.0 (d, ²J(C,P) = 10.2 Hz, o), 130.1 (s, p), 128.5 (d, ³J(C,P) = 10.2 Hz, m); P(p-tol)(p-tol)′ at 144.7 (d, ¹J(C,P) = 20.6 Hz, i to P), 143.4 (d, ¹J(C,P) = 19.8 Hz, i′ to P), 137.0, 136.6 (2 s, p and p′ to P), 133.7 (d, ²J(C,P) = 18.6 Hz, o to P), 133.1 (d, ²J(C,P) = 17.6 Hz, o′ to P), 128.9 (d, ³J(C,P) = 4.9 Hz, m to P), 128.9 (d, ³J(C,P) = 5.8 Hz, m′ to P), 21.3, 21.2 (2 s, C̲H₃ and CH̲₃′); ³¹P{¹H} (121 MHz) 26.8 (d, ³J(P,P) = 6.7 Hz, P̲Ph₃), 5.8 (d, ³J(P,P) = 6.7 Hz, P̲(p-tol)₂).

IR (thin film, cm⁻¹): 1644 (s, ν_NO). MS:³⁷ 771 (11) [1b]⁺, 558 (100) [1b-P(p-tol)₂]⁺.

(S)-1b

(S)-[1b-H]⁺ PF₆⁻ (0.187 g, 0.204 mmol), t-BuOK (0.0343 g, 0.306 mmol), and benzene (20 mL) were combined in a procedure analogous to that given for the racemate. An identical workup gave (S)-1b as an orange powder (0.138 g, 0.180 mmol, 88%). Dec. pt. 125–130 °C. Spectroscopic data were similar to those of the racemate.

[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(p-C₆H₄OCH₃)₂H)]⁺ PF₆⁻ ([1c-H]⁺ PF₆⁻)

A Schlenk flask was charged with racemic 2 (0.246 g, 0.441 mmol)¹⁵ and CH₂Cl₂ (15 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.188 g, 0.485 mmol) added with stirring. After 1 h, P(p-C₆H₄OCH₃)₂H (c, 0.141 g, 0.573 mmol)¹⁷ dissolved in CH₂Cl₂ (1 mL) was added dropwise. After 20 min, the cold bath was removed. After 1 h, the sample was concentrated by oil pump vacuum (to ca. 4 mL). A CH₃OH/EtOH mixture (2.5 mL, 2 : 3 v/v) was added, followed by CH₂Cl₂ until the sample became homogeneous. Hexanes (ca. 20 mL) were added with stirring and an orange powder precipitated, which was collected by filtration, washed with hexanes (3 × 3 mL), and dried by oil pump vacuum to give [1c-H]⁺ PF₆⁻ (0.369 g, 0.389 mmol, 88%), mp 207–208 °C, dec. Anal. calcd (%) for C₃₈H₃₇F₆NO₃P₃Re (949.1): C 48.10, H 3.93, N 1.48; found: C 47.76, H 3.84, N 1.45.

NMR (δ/ppm): ¹H (400 MHz, CDCl₃) 7.78 (dd, ³J(H,P) = 13.0, ³J(H,H) = 8.5 Hz, C₆H̲₄, o to P, 2H), 7.31–7.49 (m, C₆H̲₅ and C₆H̲₄′, o to P, 17H), 7.12 (d, ³J(H,H) = 8.8 Hz, C₆H̲₄, m to P, 2H), 6.96 (d, ³J(H,H) = 8.5 Hz, C₆H̲₄′, m to P, 2H), 6.90 (dd, ¹J(H,P) = 478 Hz, ³J(H,H) = 12.0 Hz, PH̲, 1H), 4.90 (s, C₅H̲₅, 5H), 3.89, 3.83 (2 s, OCH̲₃ and OCH̲₃′, 2 × 3H), 2.68 (apparent dt, ²J(H,H) = 19.8 Hz, J(H,P) = ³J(H,H) = 14.5 Hz, CH̲H′, 1H), 2.50 (dd, ²J(H,H) = 19.8 Hz, J(H,P) = 12.2 Hz CHH̲′, 1H); ¹³C{¹H} (101 MHz, CD₂Cl₂) 90.9 (s, C̲₅H₅), −34.0 (dd, ¹J(C,P) = 30.8 Hz, ²J(C,P) = 4.4 Hz, C̲HH′); PPh₃ at 134.4 (d, ¹J(C,P) = 40.0 Hz, i), 134.0 (d, ²J(C,P) = 10.4 Hz, o), 131.6 (d, ⁴J(C,P) = 2.4 Hz, p), 129.5 (d, ³J(C,P) = 10.4 Hz, m); P(C̲₆H₄OCH₃)(C̲₆H₄OCH₃)′ at 164.8 (d, ⁴J(C,P) = 2.8 Hz, p to P), 164.4 (d, ⁴J(C,P) = 2.4 Hz, p′ to P), 134.71, 134.70 (2 s, m and m′ to P), 116.2 (d, ²J(C,P) = 13.6 Hz, o to P), 115.8 (d, ²J(C,P) = 12.8 Hz, o′ to P), 115.5 (d, ¹J(C,P) = 75.9 Hz, i to P), 113.0 (d, ¹J(C,P) = 92.7 Hz, i′ to P), 56.3, 55.2 (2 s, OC̲H₃ and OC̲H₃′); ³¹P{¹H} (162 MHz, CDCl₃) 29.2 (d, ³J(P,P) = 10.9 Hz, P̲H), 23.1 (d, ³J(P,P) = 10.9 Hz, P̲Ph₃), −142.9 (sept, ¹J(P,F) = 708 Hz, P̲F₆).

IR (thin film, cm⁻¹): 1640 (s, ν_NO). MS:³⁷ 804 (100) [1b-H]⁺, 558 (90) [1b-P(p-C₆H₄OCH₃)₂H]⁺.

(S)-[1c-H]⁺ PF₆⁻

Complex (S)-2 (0.399 g, 0.715 mmol),¹⁵ CH₂Cl₂ (20 mL), Ph₃C⁺ PF₆⁻ (0.305 g, 0.787 mmol), c (0.211 g, 0.858 mmol),¹⁷ and CH₂Cl₂ (1 mL) were combined in a procedure analogous to that given for the racemate. An identical workup gave (S)-[1c-H]⁺ PF₆⁻ as an orange powder (0.645 g, 0.680 mmol, 95%), mp 204–205 °C, dec. Anal. calcd (%) for C₃₈H₃₇F₆NO₃P₃Re (949.1): C 48.10, H 3.93, N 1.48; found: C 47.98, H 3.67, N 1.45. [α]⁵⁸⁹₂₅ = 248° ± 2° (c = 2.00 mg mL⁻¹, CH₂Cl₂). Spectroscopic data were similar to those of the racemate.

(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(p-C₆H₄OCH₃)₂) (1c)

A Schlenk flask was charged with [1c-H]⁺ PF₆⁻ (0.154 g, 0.162 mmol) and benzene (10 mL). The suspension was vigorously stirred and t-BuOK (0.0273 g, 0.243 mmol) added. After 1 h, the orange suspension was filtered through a plug of Celite. The plug was rinsed with benzene until the filtrate became colorless. The filtrate was concentrated by oil pump vacuum (to ca. 2 mL), layered with pentane (15 mL), and kept at 4 °C. After 48 h, the orange crystals were collected by filtration and dried by oil pump vacuum to give 1c (0.100 g, 0.125 mmol, 77%), Dec. pt. 162 °C. Anal. calcd (%) for C₃₈H₃₆NO₃P₂Re (802.9): C 56.85, H 4.52, N 1.74; found: C 56.38, H 4.46, N 1.74.

NMR (δ/ppm): ¹H (400 MHz, C₆D₆) 7.74 (dd, ³J(H,H) = 8.6 Hz, ³J(H,P) = 5.8 Hz, C₆H̲₄, o to P, 2H), 7.68 (dd, ³J(H,H) = 8.6, ³J(H,P) = 5.8 Hz, C₆H̲₄′, o to P, 2H), 7.56–7.50 (m, o-C₆H̲₅, 6H), 7.07–7.01, 7.00–6.95 (2 m, m-, p-C₆H̲₅, 9H), 6.91 (d, ³J(H,H) = 8.6 Hz, C₆H̲₄, m to P, 2H), 6.79 (d, ³J(H,H) = 8.6 Hz, C₆H̲₄′, m to P, 2H), 4.59 (s, C₅H̲₅, 5H), 3.30, 3.27 (2 s, OCH̲₃ and OCH̲₃′, 2 × 3H), 2.83 (dd, ²J(H,H) = 11.9 Hz, J(H,P) = 9.7 Hz, CH̲H′, 1H), 2.09 (dd, ²J(H,H) = 11.9 Hz, J(H,P) = 2.5 Hz, CHH̲′, 1H); ¹³C{¹H} (101 MHz, CD₂Cl₂) 90.3 (s, C̲₅H₅), −18.1 (dd, ¹J(C,P) = 35.4 Hz, ²J(C,P) = 5.2 Hz, C̲HH′); PPh₃ at 136.3 (d, ¹J(C,P) = 51.6 Hz, i), 134.1 (d, ²J(C,P) = 10.7 Hz, o), 130.5 (s, p), 128.8 (d, ³J(C,P) = 10.4 Hz, m); P(C̲₆H₄OCH₃)(C̲₆H₄OCH₃)′ at 159.8, 159.5 (2 s, p and p′ to P), 138.4 (d, ¹J(C,P) = 18.8 Hz, i to P), 137.4 (d, ¹J(C,P) = 18.1 Hz, i′ to P), 134.2 (d, ²J(C,P) = 20.6 Hz, o to P), 134.0 (d, ²J(C,P) = 18.4 Hz, o′ to P), 113.7 (d, ³J(C,P) = 7.0 Hz, m to P), 113.6 (d, ³J(C,P) = 5.9 Hz, m′ to P), 55.5, 55.4 (2 s, OC̲H₃ and OC̲H₃′); ³¹P{¹H} (162 MHz, C₆D₆) 27.6 (d, ³J(P,P) = 6.9 Hz, P̲Ph₃), 5.1 (d, ³J(P,P) = 6.9 Hz, P̲(C₆H₄OCH₃)₂).

IR (thin film, cm⁻¹): 1633 (s, ν_NO). MS:³⁷ 803 (10) [1c]⁺, 558 (100) [1c-P(p-C₆H₄OCH₃)₂H]⁺.

(S)-1c

(S)-[1c-H]⁺ PF₆⁻ (0.225 g, 0.237 mmol), t-BuOK (0.0398 g, 0.356 mmol), and benzene (20 mL) were combined in a procedure analogous to that given for the racemate. An identical workup gave (S)-1c as an orange-red powder (0.166 g, 0.206 mmol, 87%), mp 125–130 °C, dec. Spectroscopic data were similar to those of the racemate.

[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(p-C₆H₄N(CH₃)₂)₂H)]⁺ PF₆⁻ ([1d-H]⁺ PF₆⁻)

A Schlenk flask was charged with racemic 2 (0.212 g, 0.380 mmol)¹⁵ and CH₂Cl₂ (15 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.162 g, 0.418 mmol) added with stirring. After 1 h, P(p-C₆H₄N(CH₃))₂H (d, 0.134 g, 0.494 mmol)¹⁷ dissolved in CH₂Cl₂ (1 mL) was added dropwise. After 20 min, the cold bath was removed. After 1 h, the sample was concentrated by oil pump vacuum (to ca. 4 mL). A CH₃OH/EtOH mixture (5.5 mL, 4 : 5 v/v) was added, followed by CH₂Cl₂ until the sample became homogeneous. Then hexanes (ca. 20 mL) were added with stirring. The precipitate was washed with EtOH (2 × 1 mL) and hexanes (2 × 3 mL). After drying by oil pump vacuum [1d-H]⁺ PF₆⁻ was obtained as an orange powder (0.345 g, 0.349 mmol, 93%), mp 230–232 °C, dec. Anal. calcd (%) for C₄₁H₄₅F₆N₃OP₃Re (989.2): C 49.28, H 4.45, N 4.31; found: C 48.91, H 4.39, N 4.22.

NMR (δ/ppm): ¹H (400 MHz, CDCl₃) 7.61 (dd, ³J(H,P) = 12.6 Hz, ³J(H,H) = 8.5 Hz, C₆H̲₄, o to P, 2H), 7.49–7.42, 7.38–7.31 (2 m, C₆H̲₅, 15H), 7.26 (dd, ¹J(H,P) = 472 Hz, ³J(H,H) = 10.7 Hz, PH̲, 1H), 7.18 (dd, ³J(H,P) = 12.1, ³J(H,H) = 8.6 Hz, C₆H̲₄′, o to P, 2H), 6.80 (d, ³J(H,H) = 8.6 Hz, C₆H̲₄, m to P, 2H), 6.62 (d, ³J(H,H) = 8.6 Hz, C₆H̲₄′, m to P, 2H), 4.87 (s, C₅H̲₅, 5H), 3.07, 2.99 (2 s, CH̲₃ and CH̲₃′, 2 × 6H), 2.52–2.37 (m, CH̲H̲′, 2H); ¹³C{¹H} (101 MHz, CD₂Cl₂) 90.8 (s, C̲₅H₅), −32.0 (dd, ¹J(C,P) = 33.3 Hz, ²J(C,P) = 3.4 Hz, C̲HH′); PPh₃ at 134.7 (d, ¹J(C,P) = 53.7 Hz, i), 134.0 (d, ²J(C,P) = 10.5 Hz, o), 131.5 (d, ⁴J(C,P) = 2.0 Hz, p), 129.5 (d, ³J(C,P) = 10.4 Hz, m); P(C̲₆H₄N(CH₃)₂)(C̲₆H₄N(CH₃)₂)′ at 154.2 (d, ⁴J(C,P) = 1.9 Hz, p to P), 153.7 (d, ⁴J(C,P) = 2.0 Hz, p′ to P), 134.0 (d, ³J(C,P) = 11.5 Hz, m to P), 133.3 (d, ³J(C,P) = 11.5 Hz, m′ to P), 112.6 (d, ²J(C,P) = 13.3 Hz, o to P), 112.3 (d, ²J(C,P) = 12.5 Hz, o′ to P), 108.2 (d, ¹J(C,P) = 79.9 Hz, i to P), 104.7 (d, ¹J(C,P) = 98.9 Hz, i′ to P), 40.3, 40.2 (2 s, C̲H₃ and C̲H₃′); ³¹P{¹H} (162 MHz, CD₂Cl₂) 28.7 (d, ³J(P,P) = 11.9 Hz, P̲H) 23.9 (d, ³J(P,P) = 11.9 Hz, P̲Ph₃), −142.9 (sept, ¹J(P,F) = 714 Hz, P̲F₆).

IR (thin film, cm⁻¹): 1645 (s, ν_NO). MS:³⁷ 830 (100) [1d-H]⁺, 558 (62) [1d-P(p-C₆H₄N(CH₃)₂)₂H]⁺.

(S)-[1d-H]⁺ PF₆⁻

Complex (S)-2 (0.300 g, 0.538 mmol),¹⁵ CH₂Cl₂ (15 mL), Ph₃C⁺ PF₆⁻ (0.234 g, 0.603 mmol), d (0.175 g, 0.646 mmol),¹⁷ and CH₂Cl₂ (1 mL) were combined in a procedure analogous to that given for the racemate. After the reaction mixture was stirred at room temperature for 1 h, the sample was concentrated by oil pump vacuum (to ca. 3 mL). Then EtOH (7 mL) was added, and the mixture kept at −20 °C. After 2 h, the precipitate was collected by filtration, washed with EtOH (1 mL) and hexanes (2 × 3 mL), and dried by oil pump vacuum to give (S)-[1d-H]⁺ PF₆⁻ as a yellow powder (0.400 g, 0.410 mmol, 76%), mp 180–182 °C, dec. Anal. calcd (%) for C₄₀H₄₃F₆N₃OP₃Re (975.2): C 49.28, H 4.45, N 4.31; found: C 48.79, H 4.71, N 4.21. [α]⁵⁸⁹₂₅ = 202° ± 2° (c = 2.00 mg mL⁻¹, CH₂Cl₂). Spectroscopic data were similar to those of the racemate.

(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(p-C₆H₄N(CH₃)₂)) (1d)

A Schlenk flask was charged with [1d-H]⁺ PF₆⁻ (0.212 g, 0.217 mmol) and benzene (20 mL). The suspension was vigorously stirred and t-BuOK (0.0365 g, 0.326 mmol) added. After 1 h, the orange suspension was filtered through a plug of Celite. The plug was rinsed with benzene until the filtrate became colorless. The filtrate was concentrated by oil pump vacuum (to ca. 4 mL), layered with pentane (15 mL), and kept at 4 °C. After 48 h, the orange crystals were collected by filtration and dried by oil pump vacuum to give 1d as a red solid (0.153 g, 0.185 mmol, 85%). Dec. pt. 157–158 °C. Anal. calcd (%) for C₄₁H₄₄N₃OP₂Re (829.2): C 57.96, H 5.11, N 5.07; found: C 58.07, H 4.89, N 4.97.

NMR (C₆D₆, δ/ppm): ¹H (300 MHz) 7.82 (dd, ³J(H,H) = 8.6 Hz, ³J(H,P) = 6.3 Hz, C₆H̲₄, o to P, 2H), 7.76 (dd, ³J(H,H) = 8.6 Hz, ³J(H,P) = 6.0 Hz, C₆H̲₄′, o to P, 2H), 7.65–7.55 (m, o-C₆H̲₅, 6H), 7.11–6.95 (m, m-, p-C₆H̲₅, 9H), 6.72 (d, ³J(H,H) = 8.6 Hz, C₆H̲₄, m to P, 2H), 6.60 (d, ³J(H,H) = 8.6 Hz, C₆H̲₄′, m to P, 2H), 4.63 (s, C₅H̲₅, 5H), 2.94 (dd, ²J(H,H) = 11.5 Hz, J(H,P) = 9.7 Hz, CH̲H′, 1H), 2.52, 2.50 (2 s, CH̲₃ and CH̲₃′, 2 × 6H), 2.25 (dd, ²J(H,H) = 11.5 Hz, J(H,P) = 2.5 Hz, CHH̲′, 1H); ¹³C{¹H} (76 MHz) 89.9 (s, C̲₅H₅), −16.6 (dd, ¹J(C,P) = 36.6 Hz, ²J(C,P) = 4.8 Hz C̲HH′); PPh₃ at 136.8 (d, ¹J(C,P) = 50.9 Hz, i), 134.1 (d, ²J(C,P) = 10.4 Hz, o), 130.0 (d, ⁴J(C,P) = 1.6 Hz, p), 128.5 (d, ³J(C,P) = 10.0 Hz, m); P(C̲₆H₄N(CH₃)₂)(C̲₆H₄N(CH₃)₂)′ at 150.5, 150.2 (2 s, p and p′ to P), 134.8 (d, ¹J(C,P) = 19.8 Hz, i to P), 133.9 (d, ¹J(C,P) = 18.4 Hz, i′ to P), 134.4 (s (other line of expected d obscured), o to P), 133.8 (d, ²J(C,P) = 15.9 Hz, o′ to P), 113.0 (d, ³J(C,P) = 6.0 Hz, m to P), 112.7 (d, ³J(C,P) = 7.1 Hz, m′ to P), 40.4, 40.3 (2 s, C̲H₃ and C̲H₃′); ³¹P{¹H} (121 MHz) 27.2 (d, ³J(P,P) = 6.7 Hz, P̲Ph₃), 2.8 (d, ³J(P,P) = 6.7 Hz, P̲(p-C₆H₄N(CH₃)₂)₂).

IR (thin film, cm⁻¹): 1633 (s, ν_NO). MS:³⁷ 830 (51) [1d]⁺, 558 (100) [1d-P(p-C₆H₄N(CH₃)₂)₂H]⁺.

(S)-1d

(S)-[1d-H]⁺ PF₆⁻ (0.196 g, 0.201 mmol), t-BuOK (0.0338 g, 0.302 mmol), and benzene (20 mL) were combined in a procedure analogous to that given for the racemate. An identical workup gave (S)-1d as a red powder (0.149 g, 0.179 mmol, 89%), mp 130–135 °C, dec. Spectroscopic data were similar to those of the racemate.

[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(2-biphen)₂H)]⁺ PF₆⁻ ([1e-H]⁺ PF₆⁻)

A Schlenk flask was charged with racemic 2 (0.212 g, 0.380 mmol)¹⁵ and CH₂Cl₂ (15 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.162 g, 0.418 mmol) added with stirring. After 1 h, P(2-biphen)₂H (e, 0.167 g, 0.494 mmol) dissolved in CH₂Cl₂ (1.5 mL) was added dropwise. After 20 min, the cold bath was removed. After 1 h, the sample was concentrated by oil pump vacuum (to ca. 4 mL). A CH₃OH/EtOH mixture (4 mL, 1 : 1 v/v) was added. The solution was added dropwise to vigorously stirred hexanes (75 mL). The precipitate was collected by filtration, washed with hexanes (3 × 3 mL), and dried by oil pump vacuum to give [1e-H]⁺ PF₆⁻ as an orange powder (0.376 g, 0.361 mmol, 95%), mp 236 °C, dec. Anal. calcd (%) for C₄₈H₄₁F₆NOP₃Re (1041.2): C 55.38, H 3.97, N 1.35; found: C 55.28, H 4.05, N 1.37.

NMR (CD₂Cl₂, δ/ppm): ¹H (400 MHz) 7.79–7.67, 7.62–7.35, 7.26–7.17, 7.11–7.00 (4 m, aryl-H̲, 33H), 6.48 (dd (other part of expected ddd obscured), ³J(H,H) = 12.4 Hz, ³J(H,H′) 3.1 Hz, PH̲, 1H), 4.46 (s, C₅H̲₅, 5H), 2.30–2.16 (m, CH̲H′, 1H), 1.61–1.50 (m, CHH̲′, 1H); ¹³C{¹H} (101 MHz) 90.7 (s, C̲₅H₅), −30.9 (dd, ¹J(C,P) = 28.8 Hz, ²J(C,P) = 3.8 Hz, C̲HH′); PPh₃ at 134.4 (d, ¹J(C,P) = 53.7 Hz, i), 133.8 (d, ²J(C,P) = 10.7 Hz, o), 131.6 (d, ⁴J(C,P) = 1.9 Hz, p), 129.4 (d, ³J(C,P) = 10.7 Hz, m); P(2-biphen)(2-biphen)′ at³⁸ 147.8, (d, J(C,P) = 6.5 Hz), 146.6 (d, J(C,P) = 9.2 Hz), 139.6 (d, J(C,P) = 5.0 Hz), 139.5 (d, J(C,P) = 4.6 Hz), 134.3 (d, J(C,P) = 2.3 Hz), 134.0 (d, J(C,P) = 2.7 Hz), 133.5 (d, J(C,P) = 10.7 Hz), 132.7 (d, J(C,P) = 10.0 Hz), 132.4 (d, J(C,P) = 8.8 Hz), 132.1 (d, J(C,P) = 8.1 Hz), 129.78, 129.76, 129.7, 129.5, 129.4 (5 s), 129.2 (d, J(C,P) = 10.7 Hz), 128.7 (d, J(C,P) = 11.9 Hz), 125.4 (d, ¹J(C,P) = 65.2 Hz, i to P), 118.7 (d, ¹J(C,P) = 87.4 Hz, i′ to P); ³¹P{¹H} (162 MHz) 24.0 (d, ³J(P,P) = 20.8 Hz, P̲H), 20.5 (d, ³J(P,P) = 20.8 Hz, P̲Ph₃), −142.9 (sept, ¹J(P,F) = 708 Hz, P̲F₆).

IR (thin film, cm⁻¹): 1660 (s, ν_NO). MS:³⁷ 896 (80) [1e-H]⁺, 558 (100) [1e-P(2-biphen)₂H]⁺.

(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(2-biphen)₂) (1e)

A Schlenk flask was charged with racemic [1e-H]⁺ PF₆⁻ (0.520 g, 0.500 mmol) and benzene (30 mL). The suspension was vigorously stirred and solid t-BuOK (0.0840 g, 0.749 mmol) added. After 1 h, the orange suspension was filtered through a plug of Celite. The plug was rinsed with benzene until the filtrate became colorless. The filtrate was concentrated by oil pump vacuum to ca. 5 mL and layered with pentane (35 mL). The orange precipitate was collected by filtration and dried by oil pump vacuum to give 1e (0.406 g, 0.453 mmol, 91%), Dec. pt. 205 °C. Anal. calcd (%) for C₄₈H₄₀NOP₂Re (895.2): C 64.42, H 4.50, N 1.57; found: C 64.15, H 4.11, N 1.64.

NMR (CD₂Cl₂, δ/ppm): ¹H (400 MHz) 7.41–7.33, 7.31–7.20, 7.14–6.98 (3 m, aryl-H̲, 32H), 4.39 (s, C₅H̲₅, 5H), 1.89 (apparent dt, ²J(H,H) = 12.6 Hz, ²J(H,P) = ³J(H,P) = 8.6 Hz, CH̲H′, 1H), 1.32 (ddd, ²J(H,H) = 12.6 Hz, ²J(H,P) = 8.6 Hz, ³J(H,P) = 2.5 Hz, CHH̲′, 1H); ¹³C{¹H} (76 MHz) 90.9 (dd, ²J(C,P) = 4.4 Hz, ³J(C,P) = 1.2 Hz, C̲₅H₅), −16.3 (dd, ¹J(C,P) = 39.6 Hz, ²J(C,P) = 5.1 Hz, C̲HH′); PPh₃ at 136.7 (d, ¹J(C,P) = 51.4 Hz, i), 134.1 (d, ²J(C,P) = 10.5 Hz, o), 130.5 (d, ⁴J(C,P) = 2.0 Hz, p), 128.8 (d, ³J(C,P) = 10.1 Hz, m); P(2-biphen)(2-biphen)′ at³⁸ 149.2, 149.2, 148.8, 148.7, 146.5, 146.2, 144.3, 144.2, 144.0, 144.0, 139.8, 139.6, 135.8, 135.7, 131.3, 131.0, 131.0, 130.7, 130.7, 130.5, 130.4, 130.4, 130.3, 128.2, 128.1, 127.4, 127.3, 127.0, 126.9, 126.7; ³¹P{¹H} (162 MHz) 24.6 (d, ³J(P,P) = 6.9 Hz, P̲Ph₃), −5.7 (d, ³J(P,P) = 6.9 Hz, P̲(2-biphen)₂).

IR (thin film, cm⁻¹): 1621 (s, ν_NO). MS:³⁷m/z (%): 896 (80) [1e-H]⁺, 558 (100) [1e-P(2-biphen)₂]⁺.

[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(α-naph)₂H)]⁺ PF₆⁻ ([1f-H]⁺ PF₆⁻)

A Schlenk flask was charged with racemic 2 (0.500 g, 0.896 mmol)¹⁵ and CH₂Cl₂ (25 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.382 g, 0.986 mmol)¹⁸ added with stirring. After 1 h, P(α-naph)₂H (f, 0.308 g, 1.075 mmol) dissolved in CH₂Cl₂ (5 mL) was added. After 20 min, the cold bath was removed. After 1 h, the sample was concentrated by oil pump vacuum (to ca. 4 mL). A CH₃OH/EtOH mixture (4 mL, 1 : 1 v/v) was added. Then hexanes (ca. 20 mL) were added dropwise with vigorous stirring. The precipitate was collected by filtration, washed with hexanes (3 × 3 mL), and dried by oil pump vacuum to give [1f-H]⁺ PF₆⁻ as an orange powder (0.772 g, 0.781 mmol, 87%), Dec. pt. 181–183 °C. Anal. calcd (%) for C₄₄H₃₇F₆NOP₃Re (989.2): C 53.44, H 3.77, N 1.42; found: C 53.20, H 3.72, N 1.39.

NMR (CD₂Cl₂, δ/ppm): ¹H (400 MHz) 6.48 (dd; other part of expected ddd obscured), (³J(H,H) = 12.3 Hz, ³J(H,H′) = 3.0 Hz, PH̲, 1H), 8.45 (dd, ³J(H,P) = 17.3 Hz, ³J(H,H) = 7.1 Hz, 2-C₁₀H̲₇, 1H), 8.34 (dd, ³J(H,P) = 16.0 Hz, ³J(H,H) = 7.2 Hz, 2-C₁₀H̲₇′, 1H), 8.25, 8.17, 8.12, 8.02, 7.95, 7.82 (6 d, ³J(H,H) = 8.2, 8.4, 8.4, 8.0, 8.0, and 8.3 Hz, 4-, 5-, 8-C₁₀H̲₇ and 4-, 5-, 8-C₁₀H̲₇′, 6 × 1H), 7.80–7.71, 7.69–7.60 (2 m, 6-, 7-C₁₀H̲₇ and 6-, 7-C₁₀H̲₇′, 2 × 2H), 7.55 (apparent t, ³J(H,H) = 7.0 and 7.0 Hz, 3-C₁₀H̲₇, 1H), 7.49 (apparent t, ³J(H,H) = 7.2 and 7.2 Hz, 3-C₁₀H̲₇′, 1H), 7.47–7.31 (m, C₆H̲₅, 15H), 4.62 (s, C₅H̲₅, 5H), 3.06–2.96, 2.87–2.74 (2 m, CH̲H̲′, 2 × 1H); ¹³C{¹H} (101 MHz) 90.6 (s, C̲₅H₅), −33.9 (d, ¹J(C,P) = 27.4 Hz, C̲HH′); PPh₃ at 134.1 (d, ¹J(C,P) = 54.8 Hz, i), 133.8 (d, ²J(C,P) = 10.5 Hz, o), 131.4 (d, ⁴J(C,P) = 2.1 Hz, p), 129.4 (d, ³J(C,P) = 10.5 Hz, m); P(α-naph)(α-naph)′ at³⁸ 135.8 (d, J(C,P) = 2.9), 135.6 (d, J(C,P) = 2.9 Hz), 135.5 (d, J(C,P) = 10.5 Hz), 135.2 (d, J(C,P) = 11.8 Hz), 134.0 (d, J(C,P) = 4.6 Hz), 133.9 (d, J(C,P) = 3.4 Hz), 132.8 (d, J(C,P) = 8.4 Hz), 132.3 (d, J(C,P) = 5.9 Hz), 130.4, 130.2, 129.6, 128.8, 128.1, 127.5 (6 s), 126.0 (d, J(C,P) = 11.4 Hz), 125.9 (d, J(C,P) = 11.4 Hz), 124.1 (d, J(C,P) = 8.0 Hz), 123.5 (d, J(C,P) = 8.0 Hz), 120.5 (d, ¹J(C,P) = 65.3 Hz, 1-C̲₁₀H₇), 119.6 (d, ¹J(C,P) = 83.5 Hz, 1-C̲₁₀H₇′); ³¹P{¹H} (162 MHz) 22.7 (d, ³J(P,P) = 12.9 Hz, P̲H), 20.3 (d, ³J(P,P) = 12.9 Hz, P̲Ph₃), −142.9 (sept, ¹J(P,F) = 708 Hz, P̲F₆).

IR (thin film, cm⁻¹): 1656 (s, ν_NO). MS:³⁷ 844 (45) [1f-H]⁺, 558 (100) [1f-P(α-naph)₂H]⁺.

(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂P(α-naph)₂) (1f)

A Schlenk flask was charged with [1f-H]⁺ PF₆⁻ (0.361 g, 0.365 mmol) and benzene (22 mL). The suspension was vigorously stirred and solid t-BuOK (0.0613 g, 0.548 mmol) added. After 1 h, the orange suspension was filtered through a plug of Celite. The plug was rinsed with benzene until the filtrate became colorless. The filtrate was concentrated by oil pump vacuum (to ca. 5 mL), and pentane (35 mL) added dropwise with vigorous stirring. The precipitate was collected by filtration and dried by oil pump vacuum to give 1f as a pale yellow powder (0.197 g, 0.234 mmol, 64%), mp 187–189 °C, dec. Anal. calcd (%) for C₄₄H₃₆NOP₂Re (843.2): C 62.70, H 4.30, N 1.66; found: C 62.80, H 4.50, N 1.76.

NMR (CD₂Cl₂, δ/ppm): ¹H (400 MHz) 8.87–8.82, 8.78–8.72, 7.82–7.69, 7.52–7.28 (4 m, aryl-H̲, 29H), 4.62 (s, C₅H̲₅, 5H), 2.63 (dd, ²J(H,H) = 11.5 Hz, J(H,P) = 9.6 Hz, CH̲H′, 1H), 1.91 (d, ²J(H,H) = 11.5 Hz, CHH̲′, 1H); ¹³C{¹H} (76 MHz) 90.4 (s, C̲₅H₅), −19.1 (dd, ¹J(C,P) = 36.8 Hz, ²J(C,P) = 4.8 Hz, C̲HH′); PPh₃ at 136.3 (d, ¹J(C,P) = 51.9 Hz, i), 134.2 (d, ²J(C,P) = 10.4 Hz, o), 130.7 (d, ⁴J(C,P) = 2.1 Hz, p), 128.9 (d, ³J(C,P) = 10.1 Hz, m); P(α-naph)(α-naph)′ at³⁸ 145.9, 145.5, 143.5, 143.2, 136.5, 136.5, 136.3, 136.2, 134.2, 133.9, 133.8, 130.8, 130.3, 129.1, 128.4, 128.4, 127.6, 127.3, 127.2, 126.9, 126.1, 126.0, 125.8, 125.8, 125.7; ³¹P{¹H} (162 MHz) 26.5 (d, ³J(P,P) = 6.9 Hz, P̲Ph₃), −21.2 (d, ³J(P,P) = 6.9 Hz, P̲(α-naph)₂).

IR (thin film, cm⁻¹): 1644 (s, ν_NO). MS:³⁷ 842 (30) [1f-H]⁺, 558 (100) [1f-P(α-naph)₂]⁺.

(S_ReS_C)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH(CH₃)PPh₂H)]⁺ PF₆⁻ ((S_ReS_C)-[9a-H]⁺ PF₆⁻)

A Schlenk flask was charged with (S)-(η-C₅H₅)Re(NO)(PPh₃)(CH₂CH₃) (0.114 g, 0.199 mmol)²³ and CH₂Cl₂ (5 mL). The solution was cooled to −78 °C and Ph₃C⁺ PF₆⁻ (0.0722 g, 0.219 mmol) added with stirring. After 1 h, the orange mixture had turned bright yellow. Then PPh₂H (0.0555 g, 0.299 mmol) dissolved in CH₂Cl₂ (0.6 mL) was added. After 1 h, the mixture was allowed to warm to room temperature over the course of 1 h. The solution was concentrated (to ca. 1 mL) and pentane added. The oil-like precipitate was isolated by decantation and dissolved in CH₂Cl₂/t-BuOH (7 mL, 2 : 5 v/v). The solvent was concentrated by oil pump vacuum with vigorous stirring. A yellow powder precipitated, which was collected by filtration, washed with pentane (2 × 0.5 mL), and dried by oil pump vacuum to give (S_ReS_C)-[9a-H]⁺ PF₆⁻ as a pale yellow powder (0.0920 g, 0.102 mmol, 51%), Dec. pt. 125–128 °C. Anal. calcd (%) for C₃₇H₃₅F₆NOP₃Re (902.8): C 49.22, H 3.91, N 1.55; found: C 49.17, H 4.06, N 1.52. [α]⁵⁸⁹₂₅ = 105° ± 1° (c = 1.00 mg mL⁻¹, CH₂Cl₂).

NMR (δ/ppm): ¹H (400 MHz, CDCl₃) 7.79–7.30 (m, C₆H̲₅, 25H), 7.48 (dd, ¹J(H,P) = 493 Hz, ³J(H,H) = 9.0 Hz, PH̲, 1H), 5.06 (s, C₅H̲₅, 5H), 3.46–3.35 (m, CH̲CH₃, 1H), 1.27 (dd, J(H,P) = 24.5 Hz, ³J(H,H) = 7.5 Hz, CHCH̲₃, 3H); ¹³C{¹H} (76 MHz, CD₂Cl₂; the ReC̲H signal was not observed) 91.6 (s, C̲₅H₅); PPh₃ at 133.9 (d, ¹J(C,P) = 54.0 Hz, i), 133.7 (d, ²J(C,P) = 10.6 Hz, o), 131.5 (d, ⁴J(C,P) = 2.2 Hz, p), 129.5 (d, ³J(C,P) = 10.4 Hz, m); PPhPh′ at 134.6 (d, ⁴J(C,P) = 2.6 Hz, p to P), 134.1 (d, ⁴J(C,P) = 2.6 Hz, p′ to P), 133.2 (d, ²J(C,P) = 9.1 Hz, o to P), 132.6 (d, ²J(C,P) = 9.1 Hz, o′ to P), 130.5 (d, ³J(C,P) = 11.5 Hz, m to P), 130.3 (d, ³J(C,P) = 11.7 Hz, m′ to P), 122.4 (d, ¹J(C,P) = 57.7 Hz, i to P), 121.5 (d, ¹J(C,P) = 68.1 Hz, i′ to P), 20.4 (s, C̲H₃); ³¹P{¹H} (122 MHz, CD₂Cl₂) 22.7 (d, ³J(P,P) = 14.9 Hz, P̲Ph₃), 31.9 (d, ³J(P,P) = 14.6 Hz, P̲H), −142.8 (sept, ¹J(P,F) = 713 Hz, P̲F₆).

IR (thin film, cm⁻¹): 1668 (s, ν_NO). MS:³⁷ 758 (18) [9a-H]⁺, 572 (100) [9a-PPh₂H]⁺.

(S_ReS_C)-(η⁵-C₅H₅)Re(NO)(PPh₃)(CH(CH₃)PPh₂H) ((S_ReS_C)-9a)

This complex was generated by first treating (S_ReS_C)-[9a-H]⁺ PF₆⁻ with t-BuOK (1.5 equiv.) in benzene. The mixture was filtered through a plug of Celite. The filtrate was concentrated and pentane added. The (S_ReS_C)-9a precipitated and was collected by filtration, dried by oil pump vacuum, and used without further characterization.

Crystallography

(A) Racemic [1c-H^+]PF₆⁻ was dissolved in CH₂Cl₂ and layered with pentane. After 7 d at 4 °C, orange prisms had formed. Data were collected as outlined in Table 1. Cell parameters were obtained from 10 frames using a 10° scan and refined with 8286 reflections. Lorentz, polarization, and absorption corrections³⁹ were applied. The space group was determined from systematic absences and subsequent least-squares refinement. The structure was solved by direct methods. The parameters were refined with all data by full-matrix-least-squares on F² using SHELXL-97.⁴⁰ Non-hydrogen atoms were refined with anisotropic thermal parameters. The hydrogen atoms were fixed in idealized positions using a riding model. Scattering factors were taken from literature.⁴¹ (B) Orange prisms of [1d-H⁺]PF₆⁻ were similarly obtained, and the structure was solved analogously (10 frames using a 10° scan and refined with 9467 reflections). The PH hydrogen atom (P2) was located and free isotropically refined.

Catalytic reactions

(A) Racemic catalysts. A Schlenk flask was charged with the substrate (typically 0.060–0.080 g). Then benzene or chlorobenzene solutions that were 0.0125 M in ClCH₂CH₂Cl (internal standard, ¹H NMR integration) were added to give 0.100 M substrate solutions. These were equilibrated to 20 °C using a cryostat. Solutions of benzene or chlorobenzene that were 0.0100 M in catalyst and 0.0125 M in ClCH₂CH₂Cl were cooled to 0 °C. Equal volumes, corresponding to 10 mol% loading, were added dropwise over ca. 5 min to the substrate solutions. An aliquot (0.6 mL) was transferred to an NMR tube, and ¹H NMR spectra were periodically recorded. When the reaction was complete (or no further reaction took place), five volumes of hexane were added with stirring. The mixture was filtered through a short plug of silica gel (removing catalyst), which was washed with hexane/ethyl acetate (9 : 1 v/v). The solvent was removed from the filtrates by rotary evaporation to give the product, characterized as summarized in the ESI.† Yields: see text and Scheme 4. Reactions conducted in chlorobenzene were further purified by silica gel column chromatography, except in the case of 6j. (B) Enantiopure catalysts. The preceding reactions were repeated on 0.0010–0.0020 g scales. The products were analyzed by HPLC using Chiralcel OD, Chiralpak AD-H or Chiralpak AS-H columns and a Thermo Quest instrument package (pump/autosampler/detector P4000/AS3000/UV6000LP).

Data availability

Electronic supplementary information (ESI) available: General procedures, syntheses of secondary phosphines and organic substrates and products, additional NMR data, and ee determinations. CCDC 2423133 ([1c-H]⁺ PF₆⁻) and 2423134 ([1d-H]⁺ PF₆⁻).† For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d2dt02680e.

Conflicts of interest

There are none to declare.

Acknowledgements

The authors thank the Deutsche Forschungsgemeinschaft (DFG, GL 300/4-3, 300/8-1), the Alexander von Humboldt Stiftung, and the Welch Foundation (A-2189) for support.

References

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2. H. Guo, Y. C. Fan, Z. Sun, Y. Wu and O. Kwon, Phosphine Organocatalysis, Chem. Rev., 2018, 118, 10049–10293.
3. H. Ni, W.-L. Chan and Y. Lu, Phosphine-Catalyzed Asymmetric Organic Reactions, Chem. Rev., 2018, 118, 9344–9411.
4. Reviews of intramolecular Morita–Baylis–Hillman and/or Rauhut–Currier reactions: (a) K. C. Bharadwaj, Intramolecular Morita-Baylis-Hillman and Rauhut-Currier reactions. A catalytic and atom economic route for carbocycles and heterocycles, RSC Adv., 2015, 5, 75923–75946; (b) D. Basavaiah and G. C. Reddy, Intramolecular Baylis-Hillman reaction: synthesis of heterocyclic molecules, ARKIVOC, 2016, 172–205.
5. E. L. Richards, P. J. Murphy, F. Dinon, S. Fratucello, P. M. Brown, T. Gelbrich and M. B. Hursthouse, Assessing the scope of the tandem Michael/intramolecular aldol reaction mediated by secondary amines, thiols and phosphines, Tetrahedron, 2001, 57, 7771–7784.
6. J. E. Yeo, X. Yang, H. J. Kim and S. Koo, The intramolecular Baylis–Hillman reaction: easy preparation of versatile substrates, facile reactions, and synthetic applications, Chem. Commun., 2004, 236–237.
7. There are additional early reports of intramolecular Morita–Baylis–Hillman reactions, but to our knowledge ref. 5 and 6 are the only that feature substrates in common with this study. For examples with different substrates, see: (a) F. Roth, P. Gygax and G. Fráter, An intramolecular Baylis-Hillman reaction, Tetrahedron Lett., 1992, 33, 1045–1048; (b) G. E. Keck and D. S. Welch, Intramolecular Baylis-Hillman and Morita Reactions Using Unsaturated Thiol Ester Substrates Containing Enolizable Aldehydes, Org. Lett., 2002, 4, 3687–3690.
8. C. E. Aroyan, M. M. Vasbinder and S. J. Miller, Dual Catalyst Control in the Enantioselective Intramolecular Morita−Baylis−Hillman Reaction, Org. Lett., 2005, 7, 3849–3851.
9. Intramolecular Morita–Baylis–Hillman and Rauhut–Currier reactions and chiral phosphine-containing catalysts that have appeared subsequent to our communication are cited and analyzed in the Discussion section.
10. K. Kromm, B. D. Zwick, O. Meyer, F. Hampel and J. A. Gladysz, A new family of chelating diphosphines with a transition metal stereocenter in the backbone: novel applications of “chiral-at-rhenium” complexes in rhodium-catalyzed enantioselective alkene hydrogenations, Chem. – Eur. J., 2001, 7, 2015–2027.
11. A. Scherer and J. A. Gladysz, A Promising New Catalyst Family for Enantioselective Cycloadditions Involving Allenes and Imines: Chiral Phosphines with Transition Metal-CH₂-P: Linkages, Tetrahedron Lett., 2006, 47, 6335–6337.
12. F. Seidel and J. A. Gladysz, Enantioselective Catalysis of Intramolecular Morita-Baylis-Hillman and Related Reactions by Chiral Rhenium-Containing Phosphines of the Formula (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂PAr₂), Synlett, 2007, 986–988.
13. D. A. Castillo Molina, F. O. Seidel, K. Pathak, S. A. Williams, F. Hampel and J. A. Gladysz, Syntheses, Structures, Reactivity, and Catalytic Applications of Enantiopure Rhenium-Containing P-Stereogenic Phosphonium Salts, Phosphines, Phosphine Boranes, and Phosphine Oxides. Submitted to Organometallics.
14. S. Eichenseher, O. Delacroix, K. Kromm, F. Hampel and J. A. Gladysz, Rhenium-Containing Phosphorus Donor Ligands for Palladium-Catalyzed Suzuki Cross-Coupling Reactions: A New Strategy for High-Activity Systems, Organometallics, 2005, 24, 245–255.
15. (a) F. Agbossou, E. J. O'Connor, C. M. Garner, N. Q. Méndez, J. M. Fernández, A. T. Patton, J. A. Ramsden and J. A. Gladysz, Cyclopentadienyl Rhenium Complexes, Inorg. Synth., 1992, 29, 211–225; (b) For a procedural improvement in one step, see the last experimental in: Y. Zhou, M. A. Dewey and J. A. Gladysz, Synthesis and Reactivity of Chiral Rhenium Indenyl Complexes of the Formula [(η⁵-C₉H₇)Re(NO)(PPh₃)(X)]ⁿ⁺, Organometallics, 1993, 12, 3918–3923.
16. (a) W. Tam, G.-Y. Lin, W.-K. Wong, W. A. Kiel, V. K. Wong and J. A. Gladysz, Synthesis and Electrophile-Induced Disproportionation of the Neutral Formyl (η- C₅H₅)Re(NO)(PPh₃)(CHO), J. Am. Chem. Soc., 1982, 104, 141–152; (b) T. Wititsuwannakul, M. B. Hall and J. A. Gladysz, Mechanism of Coupling of Methylidene to Ethylene Ligands in a Dimetallic Assemblies; Computational Investigation of a Model for a Key Step in Catalytic C₁ Chemistry, J. Am. Chem. Soc., 2022, 144, 18672–18687.
17. C. A. Busacca, J. C. Lorenz, N. Grinberg, N. Haddad, M. Hrapchak, B. Latli, H. Lee, P. Sabila, A. Saha, M. Sarvestani, S. Shen, R. Varsolona, X. Wei and C. H. Senanayake, A Superior Method for the Reduction of Secondary Phosphine Oxides, Org. Lett., 2005, 7, 4277–4280.
18. C. F. Hobbs and W. S. Knowles, Asymmetric hydroformylation of vinyl acetate with DIOP-type ligands, J. Org. Chem., 1981, 46, 4422–4427.
19. J. Holz, H. Jiao, M. Gandelman and A. Börner, About the Inversion Barriers of P-Chirogenic Triaryl-Substituted Phosphanes, Eur. J. Org. Chem., 2018, 2984–2994.
20. L. J. Alvey, O. Delacroix, C. Wallner, O. Meyer, F. Hampel, S. Szafert, T. Lis and J. A. Gladysz, A New Family of Chiral Chelating Diamines with Transition-Metal Stereocenters: Synthesis, Structure, and Reactivity of the Enantiomerically Pure Dirhenium-Substituted 1,2-Diamine (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂N(CH₃)CH₂CH₂(H₃C)NCH₂)(Ph₃P)(ON)Re(η⁵-C₅H₅), Organometallics, 2001, 20, 3087–3096.
21. J. H. Merrifield, C. E. Strouse and J. A. Gladysz, Synthesis, Optical Resolution, and Absolute Configuration of Pseudotetrahedral Organorhenium Complexes (η-C₅H₅)Re(NO)(PPh₃)(X), Organometallics, 1982, 1, 1204–1211.
22. W. E. Buhro, B. D. Zwick, S. Georgiou, J. P. Hutchinson and J. A. Gladysz, Synthesis, Structure, Dynamic Behavior, and Reactivity of Rhenium Phosphide Complexes (η⁵-C₅H₅)Re(NO)(PPh₃)(P̈R₂): The “Gauche Effect” in Transition-Metal Chemistry, J. Am. Chem. Soc., 1988, 110, 2427–2439.
23. W. A. Kiel, G.-Y. Lin, G. S. Bodner and J. A. Gladysz, Regiospecific and stereospecific reactions of triphenylmethyl hexafluorophosphate with rhenium alkyls (η-C₅H₅)Re(NO)(PPh₃)(R). α- vs. β-Hydride abstraction, J. Am. Chem. Soc., 1983, 105, 4958–4972.
24. K. Kromm, F. Hampel and J. A. Gladysz, A New Family of Chelating Diphosphines with Transition-Metal and Carbon Stereocenters in the Backbone: A Second-Generation Rhenium-Containing System, Organometallics, 2002, 21, 4264–4274.
25. S. Georgiou and J. A. Gladysz, Reactions of Organorhenium Complexes (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂R) with Ph₃C⁺ PF₆⁻; Analysis of the Energetics of α-Hydride Abstraction, Tetrahedron, 1986, 42, 1109–1116.
26. F. O. Seidel, Doctoral dissertation, University of Erlangen-Nürnberg, 2009.
27. T. Allman and R. G. Goel, The basicity of phosphines, Can. J. Chem., 1982, 60, 716–772.
28. R. C. Bush and R. J. Angelici, Phosphine Basicities as Determined by Enthalpies of Protonation, Inorg. Chem., 1988, 27, 681–686.
29. (a) J.-J. Gong, T.-Z. Li, K. Pan and X.-Y. Wu, Enantioselective intramolecular Rauhut-Currier reaction catalyzed by chiral phosphinothiourea, Chem. Commun., 2011, 47, 1491–1493; (b) X. Zhao, J.-J. Gong, K. Yuan, F. Sha and X.-Y. Wu, Highly enantioselective intramolecular Rauhut-Currier reaction catalyzed by chiral thiourea-phosphine, Tetrahedron Lett., 2015, 56, 2526–2528; (c) J.-J. Gong, K. Yuan, H.-L. Song and X.-Y. Wu, The enantioselective intramolecular Morita-Baylis Hillman reaction catalyzed by amino-acid-derived phosphinothiourea, Tetrahedron, 2010, 66, 2439–2443; (d) H. L. Song, K. Yuan and X.-Y. Wu, Chiral phosphine-squaramides as enantioselective catalysts for the intramolecular Morita-Baylis-Hillman reaction, Chem. Commun., 2011, 47, 1012–1014; (e) W. Yang, K. Yuan, H. Song, F. Sha and X. Wu, Highly Enantioselective Intramolecular Morita-Baylis-Hillman Reaction Catalyzed by Mannose-Based Thiourea-phosphine, Chin. J. Chem., 2015, 33, 1111–1114; (f) See also: K. Yuan, H.-L. Song, Y. Hu, J.-F. Fang and X.-Y. Wu, Enantioselective intramolecular Morita-Baylis-Hillman reaction using chiral bifunctional phosphinothiourea as an organocatalyst, Tetrahedron: Asymmetry, 2010, 21, 903–908.
30. (a) X.-N. Zhang and M. Shi, A Highly Nucleophilic Multifunctional Chiral Phosphane-Catalyzed Asymmetric Intramolecular Rauhut-Currier Reaction, Eur. J. Org. Chem., 2012, 6271–6279.
31. X. Zhang, P. Ma, D. Zhang, Y. Lei, S. Zhang, R. Jiang and W. Chen, Bifunctional ferrocene-based squaramide-phosphine as an organocatalyst for highly enantioselective intramolecular Morita-Baylis-Hillman reaction, Org. Biomol. Chem., 2014, 12, 2423–2428.
32. Additional related literature: (a) S. Takizawa, T. M.-N. Nguyen, A. Grossmann, D. Enders and H. Sasai, Enantioselective Synthesis of α-Alkylidene-γ-Butyrolactones: Intramolecular Rauhut-Currier Reaction Promoted by Acid/Base Organocatalysts, Angew. Chem., Int. Ed., 2012, 51, 5423–5426; (b) B. Satpathi, S. V. Waguide and S. S. V. Ramasastry, An enantioselective organocatalytic intramolecular Morita-Baylis-Hillman (IMBH) reaction of dienones, and elaboration of the IMBH adducts to fluorenones, Chem. Commun., 2017, 53, 8042–8045; (c) Y. Jiang, Y. Yang, Q. He, W. Du and Y.-C. Chen, Asymmetric Intramolecular Rauhut-Currier Reaction and Its Desymmetric Version via Double Thiol/Phase-Transfer Catalysis, J. Org. Chem., 2020, 85, 10760–10771; (d) G. Całka-Kuc, S. Żubrowski and S. Buda, Catalytic Enantioselective Rauhut-Currier Reaction Mediated by Lithium Selenolates, ACS Omega, 2025, 10, 11854–11860.
33. F. O. Seidel and J. A. Gladysz, Catalysis of Intramolecular Morita-Baylis-Hillman and Rauhut-Currier Reactions by Fluorous Phosphines; Facile Recovery by Liquid/Solid Organic/Fluorous Biphase Protocols Involving Precipitation, Teflon® Tape, and Gore-Rastex® Fibers, Adv. Synth. Catal., 2008, 350, 2443–2449.
34. K. Kromm, P. L. Osburn and J. A. Gladysz, Chelating Diphosphines that Contain a Rhenium Stereocenter in the Backbone: Applications in Rhodium-Catalyzed Enantioselective Ketone Hydrosilylations and Alkene Hydrogenations, Organometallics, 2002, 21, 4275–4280.
35. The quality of commercial Ph₃C+ X⁻ can vary, and crystallization from CH₂Cl₂/hexanes or CH₂Cl₂/benzene is recommended. See: A. T. Patton, C. E. Strouse, C. B. Knobler and J. A. Gladysz, Syntheses, Properties, and X-ray Crystal Structures of Stable Methylidene Complexes of the Formula [(η-C₅Me₅)Re(NO)(L)(=CH₂)]⁺ PF₆⁻, J. Am. Chem. Soc., 1983, 105, 5804–5811.
36. Assignments of the PPh₃ carbon signals were made as follows. Both ipso (i) and para (p) carbon resonances were easily distinguished on the basis of intensity and the J(C,P) value. The meta (m) signal was assigned as that closest to benzene: B. E. Mann, J. Chem. Soc., Perkin Trans. 2, 1972, 30.
37. FAB, 3-NBA, m/z (%); the peaks correspond to the most intense signal of the isotope envelope.
38. Due to the complexity of this set of signals, no assignments were attempted.
39. (a) "Collect" data collection software, B.V., Nonius 1998. ; (b) "Scalepack" data pro-cessing, Z. software and W. Minor, Methods in Enzymology, 1997, 276, 307 , (Macromol-ecular Crystallography, Part A).
40. G. M. Sheldrick, SHELX-97, Program for refinement of crystal structures, University of Göttingen, 1997.
41. D. T. Cromer and J. T. Waber, in International Tables for X-ray Crystallography, ed. J. A. Ibers and W. C. Hamilton, Kynoch, Birmingham, England, 1974.

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Footnote

† Electronic supplementary information (ESI) available: General procedures, syntheses of secondary phosphines and organic substrates and products, additional NMR data, and ee determinations. CCDC 2423133([1c-H]⁺ PF₆⁻) and 2423134 ([1d-H]⁺ PF₆⁻). For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d5dt01102g

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