MOP-phosphonites: A novel ligand class for asymmetric catalysis

Abstract

Chiral phosphonite ligands (S,R_b)-5a, (S,S_b)-5b, (R,R_b)-6a and (R,S_b)-6b are introduced, comprising a MOP-type backbone with a binol-based binaphthyl group bound to the phosphorus. Their reaction with [Pd(η³-C₄H₇)Cl]₂ affords η³-methallylpalladium chloride complexes 7a/b and 8a/b which have been isolated and structurally characterised. Solid-state and solution studies indicate subtle differences in their coordination behaviour, which ultimately affects their efficacy in the asymmetric hydrosilylation of styrene.

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Introduction

Chiral monophosphorus ligands have attracted considerable attention as their transition metal complexes have been found to be valuable catalysts in a variety of organic transformations.¹ Binaphthyl-derived phosphorus ligands based on phosphine,² phosphoramidite³ and phosphonite⁴ architectures (Chart 1) have all demonstrated their effectiveness in asymmetric catalysis.

Chart 1 Established classes of binaphthyl monophosphorus ligands.

Primary phosphines have a reputation for being difficult compounds to work with owing to their perceived high reactivity towards oxygen.⁵ Hence, they are somewhat under-represented as synthons in synthetic chemistry, despite the two P–H bonds being easily functionalised. A few examples of user-friendly, air-stable primary phosphines have however been reported,⁶ and we were the first to describe enantiopure analogues;⁷ we subsequently published a DFT-based model to help rationalise this stability.⁸ We also recently described how air-stable, chiral primary phosphines (S)-1 and (R)-2 could form novel phosphiranes with unusually high oxidative and thermal stability.⁹ We were therefore keen to establish whether we could transform (S)-1 and (R)-2 into their dichlorophosphines, and ultimately access MOP/XuPhos-type hybrids (Chart 1), or whether their resistance to oxidation would render them unreactive to halogen sources. This work focuses on the synthesis and characterisation of a novel MOP-phosphonite ligand class. The coordination chemistry of their methallylpalladium complexes is described and we have therefore investigated their potential as asymmetric ligands in the catalytic hydrosilylation of styrene.

Results and discussion

Four MOP-phosphonite ligand derivatives have each been synthesised in a straightforward two-step, one-pot reaction approach. The ligands differ in the substituent on the 2′-position of the MOP-backbone (H or OMe) and in the stereochemistry of the affiliated hydroxyl compound ((R)- or (S)-binol). By comparing the two pairs of diastereomeric compounds with each other, we were able to elucidate the effect of the second stereocentre.

Following the synthetic method of Weferling,^10,11 (S)-1 and (R)-2 were treated with phosphorus pentachloride to give the dichlorophosphines (S)-3 and (R)-4 in quantitative conversion. Subsequent addition of (R)-binol under basic conditions afforded the MOP-phosphonite hybrids (S,R_b)-5a and (R,R_b)-6a as white solids (Scheme 1). Their diastereomers (S,S_b)-5b and (R,S_b)-6b were afforded from reactions with (S)-binol, again in high yield.

Scheme 1 The synthesis of phosphonites (S,R_b)-5a and (R,R_b)-6a.

The ³¹P NMR spectroscopic data for the phosphonites are as expected, showing characteristic resonances (δ = 177.4 ppm for (S,R_b)-5a; 177.8 ppm for (R,R_b)-6a; 175.7 ppm for (S,S_b)-5b; 177.9 for (R,S_b)-6b). Notably, all the ligands could conveniently be handled in air; in common reagent grade solvents no hydrolysis products were found after 24 h.¹² We next studied the coordination chemistry of the phosphonites; reaction of two equivalents of the pertinent ligand with [Pd(η³-C₄H₇)Cl]₂ resulted in the rapid, quantitative formation of 7a, 7b, 8a and 8b (Scheme 2) as shown by NMR, HRMS and X-ray crystallography.

Scheme 2 The synthesis of the complexes 7a, 7b, 8a and 8b.

In all four complexes the X-ray crystal structure reveals the methyl group on the allyl fragment points towards the binol component of the ligand (see Fig. 1–4). The torsion angles of the two binaphthyl fragments present are significantly different from each other. The unstrained MOP portion preserves an almost right angle while the torsion of the binol moiety is enforced by the bonding of both oxygen atoms to the phosphorus, and thus appears acutely angled. The ligands coordinate via the phosphorus donor atom in an expected monodentate manner to form a pseudo-square-planar configuration around the palladium. Pd–P bond lengths are similar in all complexes (2.2354(7) to 2.2542(8) Å) and are found to be shorter than for the two MOP-phosphine allylpalladium complexes previously reported (2.3098(9) and 2.328(1) Å);¹³ however, shortened Pd–P bond lengths are anticipated for phosphonite complexes due to their stronger π-acceptor character.¹⁴ Pd–C bond lengths show the dominant trans effect of the P-ligand relative to the chloride; the bonds trans to the phosphorus are about 0.1 Å longer compared to the bonds in the cis position. In all complexes the position of the palladium centre is face-to-face with the lower naphthyl moiety of the MOP fragment of the ligand. However, the exact position of the methallylpalladium moiety is somewhat diverse. When the phosphonite consists of a (R)-binol fragment (7a/8a), the palladium is situated towards the back of the lower napthyl ring (Fig. 1 and Fig. 3); in 7b/8b, as a consequence of the opposite binol stereochemistry, the metal is instead located above the front of this group (Fig. 2 and Fig. 4). The distance of the palladium atom from the naphthyl group ranges from 3.0653(1) Å in 7a to 3.4458(1) in 8b.

Fig. 1 Molecular structure of 7a with 50% probability displacement ellipsoids. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): Pd–P 2.2476(7), Pd–Cl(1) 2.3854(7), Pd–C(44) 2.093(2), Pd–C(43) 2.206(2), C(41)–C(43) 1.384(4), C(41)–C(44) 1.415(4), Pd⋯C(39) 3.0653(1); P–Pd–Cl(1) 93.67(2), P–Pd–C(44) 98.23(9), Cl(1)–Pd–C(43) 101.60(7), C(43)–Pd–C(44) 66.68(11), C(21)–C(30)–C(31)–C(32) −101.2(3), C(1)–C(10)–C(11)–C(20) −51.2(3).

Fig. 2 View of the molecular structure of 7b. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): Pd–P 2.2354(7), Pd–Cl(1) 2.3730(8), Pd–C(44) 2.078(3), Pd–C(42) 2.198(3), C(42)–C(43) 1.387(4), C(43)–C(44) 1.409(4), Pd⋯C(32) 3.1412(1); P–Pd–Cl(1) 94.51(3), P–Pd–C(44) 96.49(9), Cl(1)–Pd–C(42) 101.71(9), C(42)–Pd–C(44) 67.31(13), C(21)–C(30)–C(31)–C(32) −90.5(4), C(1)–C(10)–C(11)–C(20) 52.1(4).

Fig. 3 View of the molecular structure of 8a. Hydrogen atoms and cocrystallised solvent have been omitted for clarity. Selected bond distances (Å) and angles (deg): Pd–P 2.2363(8), Pd–Cl(1) 2.3755(10), Pd–C(42) 2.104(4), Pd–C(44) 2.185(4), C(42)–C(43) 1.415(6), C(43)–C(44) 1.381(7), Pd⋯C(32) 3.4018(1); P–Pd–Cl(1) 93.29(3), P–Pd–C(42) 98.24(12), Cl–Pd–C(44) 101.41(16), C(42)–Pd–C(44) 67.08(19), C(21)–C(30)–C(31)–C(40) −98.0(4), C(1)–C(10)–C(11)–C(20) −52.1(4).

Fig. 4 View of the molecular structure of 8b. Hydrogen atoms and cocrystallised solvent have been omitted for clarity. Selected bond distances (Å) and angles (deg): Pd–P 2.2542(8), Pd–Cl 2.3675(7), Pd–C(43) 2.101(3), Pd–C(42) 2.177(3), C(42)–C(44) 1.402(5), C(43)–C(44) 1.412(4), Pd⋯C(31) 3.4458(1), Pd⋯C(32) 3.4793(0); P–Pd–Cl 98.46(3), P–Pd–C(43) 96.80(8), Cl–Pd–C(42) 97.23(9), C(42)–Pd–C(43) 67.39(12), C(21)–C(30)–C(31)–C(40) −98.9(3), C(1)–C(10)–C(11)–C(20) 53.8(4).

The NMR spectra of complexes 7a and 8a show the presence of two isomers in a 97/3 and 93/7 ratio, respectively, which can be rationalised by a rotation of the allyl moiety. NOE contacts between each pair of syn and anti protons and between the syn allyl protons and the central methyl group, in addition to allyl proton–phosphorus coupling, allowed for a complete NMR assignment of the allyl signals (Table S2†). The protons trans to the phosphorus ligand are deshielded and show coupling with ³¹P whereas the cis protons are observed as singlets at higher field.¹⁵ The ¹³C chemical shifts for the atoms in terminal allyl positions are consistent with those reported for similar complexes:¹⁶ 77–79 ppm (²J_CP ≈ 46 Hz) for the allyl carbons trans to the P-donor, and 56–59 ppm (²J_CP ≈ 5 Hz) for the cis allyl carbons. The phase-sensitive NOESY spectrum of 8a shows exchange peaks due to interconversion of the two isomers (see Fig. S2†). Quantitative analysis of the peak integrals yielded exchange rate constant values of k_AB ≈ 0.12 s⁻¹ and k_BA ≈ 1.5 s⁻¹ at room temperature.

The selective syn/anti exchange of the allyl protons cis to the phosphorus is caused by the well-known η³–η¹–η³ mechanism (Scheme 3); the protons in the trans position exchange syn/syn and anti/anti, while the cis protons exchange syn/anti due to the selective opening of the allyl ligand.^16,17 The selectivity of the process is due to the stronger trans effect of the P-donor ligand compared to the chloro ligand. An apparent allyl rotation mechanism which is often observed in N-donor ligands requires a syn/syn and anti/anti exchange for both cis and trans allyl protons and can be ruled out here.¹⁸ Note that conversely for complexes 7b and 8b, we observe only a single isomer in each case.

Scheme 3 Syn/anti exchange mechanism in allyl palladium complexes.

MOP ligands can display unexpected bonding characteristics upon metal complexation, using their aromatic backbone to coordinate to a vacant metal site, as shown by several groups who observed binding in a chelating P,C-σ-donor or P,C-π-olefin bidentate fashion.^13b,16,19,20 When the chloride counterions of complexes 8a and 8b were exchanged for the non-coordinating BArF anion to give complexes 9a and 9b, the C1′ carbon shifted by −14.3 (9a) or −15.6/−14.5 ppm (for the two isomers of 9b) to lower frequency compared to the free ligand, indicative of greater sp³ character. The chemical shift of the C2′ carbon remains almost unchanged (Table 1).

Table 1 Selected ¹³C NMR data (δ in ppm) for ligands 6a and 6b and their palladium complexes 8a, 8b, 9a and 9b (CD₂Cl₂, 21 °C)

Carbon	6a	8a ^a	9a ^b	6b	8b	9b ^b
a Major isomer. b Two isomers were observed due to allyl rotation. c No distinctive assignment due to signal overlap and peak broadening.
1′	118.9	118.8	104.6/n.d.^c	119.0	118.2	103.4/104.5
2′	156.6	156.4	157.2/159.0	154.9	156.2	156.6/154.8
3′	112.8	113.1	114.9/114.5	113.0	113.5	115.3/115.9
4′	130.8	131.0	134.6/134.6	130.7	129.7	134.9/134.3
9′	134.5	134.2	131.5/131.4	135.0	135.5	132.7/133.7
10′	128.2	127.0	128.4/128.4	128.3	128.2	129.3/130.0

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In agreement with studies made by Pregosin and co-workers^20b we therefore propose a weak η¹ binding mode of the lower naphthyl ring via the C-1′ carbon (Fig. 5, left). The downfield shifts of 3.8 ppm in 9a and 4.2/3.6 ppm in 9b for the C-4′ carbon also suggests it carries some of the associated positive charge of the cation, again matching the aforementioned work. A section of the ¹³C–¹H HMBC spectrum of 9b showing the indirect resonances of the C1′ and C2′ carbons is given (Fig. 5, right).

Fig. 5 Left: Proposed binding mode in 9a/b using ¹³C NMR data. Right: Section of the ¹³C–¹H HMBC spectrum of 9b with key C1′/H3′ and C2′/H4′ data shown; two isomers of 9b (labelled A, B) are present.

The catalytic activity of the newly prepared ligands was tested in the asymmetric hydrosilylation of styrene.²¹ The catalysts were generated in situ from allylpalladium chloride dimer and the appropriate phosphonite. We chose a ligand to palladium ratio of 1 : 1 to form the catalyst precursors as the methallylpalladium complexes 7a/b and 8a/b had been obtained in this way (vide supra). We found that the activity of the catalyst was predominantly dependent on the substituent in the 2′-position of the ligand: H-MOP derivatives 5a/b showed a higher activity (>94% conversion after 6 h) than their corresponding OMe-MOP derivatives 6a/b (completed after 16 h, Table 2). In contrast, the selectivity was mostly determined by the configuration of the adherent binol group. Enantioselectivities of 80 and 79% were achieved with the (S)-binol derivatives 5b and 6b, while (R)-binol compounds 5a and 6a gave lower ee values. In previous studies H-MOP ligands have been found to be more selective in this transformation than their OMe-MOP counterparts,^2a hence our results for 5a (H-MOP derivative, low ee) and 6b (OMe-MOP derivative, high ee) were somewhat surprising. Solid-state analysis of an H-MOP allylpalladium phosphine complex,^13b found to be very selective in the same catalytic reaction,²² shows a similar P/Pd environment to that found in the H-MOP complex 7b. In contrast, the palladium atom in 7a is located more towards the back of the lower naphthyl ring. Thus the subtle differences in the position of the palladium atom relative to the MOP fragment in the catalytically active species could be crucial in determining the reaction enantioselectivity, again emphasising that we are comparing pairs of diastereomers in this study; an examination of the wider implications of these results is now underway.

Table 2 The palladium-catalyzed asymmetric hydrosilylation of styrene

	L^a	Time	Conv.^b	ee ^c
a The catalyst was generated in situ from the ligand (0.25 mol%) and [Pd(allyl)Cl]2 (0.125 mol%), and reacted with styrene (10.0 mmol) and trichlorosilane (12.0 mmol). b Determined by ^1H NMR spectroscopy. c Determined by chiral HPLC; absolute configuration assigned by comparing the retention times to literature data.^23 d Complete conversion after additional 2 h reaction time.
1	5a	6 h	94%^d	7% (R)
2	5b	4 h	95%^d	80% (R)
3	6a	16 h	100%	55% (S)
4	6b	16 h	100%	79% (R)

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Conclusions

In summary, we have demonstrated that the air-stable primary phosphines (S)-1 and (R)-2 readily form their dichlorophosphine counterparts, which react as electrophiles with enantiopure binol to give novel chiral phosphonites. We have characterised each ligand as its methallylpalladium complex by NMR and X-ray crystallography, which together with detailed NMR experiments on related cationic complexes indicate the subtly different metal environment in each case and the P,C ligation of 9a/b. In the hydrosilylation of styrene, enantioselectivities of 80% were achieved in reactions that have not yet been optimised.

Experimental

General

All air- and/or water-sensitive reactions were performed under an N₂ atmosphere using standard Schlenk line techniques. THF and CH₂Cl₂ were dried over Na/benzophenone and CaH₂ respectively, and distilled prior to use. Toluene (Acros) was purchased in an anhydrous state and stored over molecular sieves. The preparations of (S)-1 and (R)-2 were carried out using literature procedures.⁷ All other chemicals were used as received without further purification. Flash chromatography was performed on silica gel from Fluorochem (silica gel, 40–63u, 60A, LC301). Thin-layer-chromatography was performed on Merck aluminium-based plates with silica gel and fluorescent indicator 254 nm. For indicating, UV light or KMnO₄ solution (1.0 g KMnO₄, 6.7 g K₂CO₃, 0.1 g NaOH, 100 mL H₂O) was used. Melting points were determined in open glass capillary tubes on a Stuart SMP3 melting point apparatus. Optical rotation values were determined on an Optical Activity Polaar 2001 device. ¹H NMR, ¹¹B{¹H} NMR, ¹³C{¹H} NMR, ¹⁹F NMR, and ³¹P{¹H} NMR spectra were recorded on a JEOL Lambda 500 (¹H 500.16 MHz) or JEOL ECS-400 (¹H 399.78 MHz) spectrometer at room temperature (21 °C) if not otherwise stated, using the indicated solvent as internal reference. Two-dimensional NMR experiments (COSY, NOESY, HSQC, HMBC) were used for the assignment of proton and carbon resonances, the numbering scheme is given in Fig. S1†. Full range NOESY spectra were acquired with 512 × 1024 data points and a spectral width of 9.0 ppm; mixing times were chosen between 10 and 500 ms. For the measurement of exchange rate constants in 8a, the proton resonances of the methoxy group were used. Peak volumes were determined manually from the NOESY spectrum using MestReNova 6, and the rate constants were calculated with an estimated error of 10% using EXSYCalc.²⁴ Mass spectrometry was carried out by the EPSRC National Mass Spectrometry Service Centre, Swansea. Analytical high performance liquid chromatography (HPLC) was performed on a Varian Pro Star HPLC equipped with a variable wavelength detector.

Synthesis of (S,R_b)-[1,1′-binaphthalene]-2,2′-diyl [1,1′-binaphthalen]-2-ylphosphonite (5a)

PCl₅ (458 mg, 2.20 mmol) was dissolved in toluene (8 mL). (S)-1 (286 mg, 1.00 mmol) was added and the reaction mixture was left to stir for 45 min. The volatiles were removed in vacuo to give (S)-3 (³¹P{¹H} NMR, CDCl₃: δ = 157.1 ppm) as a yellow oil. THF (8 mL), NEt₃ (448 mg, 0.64 mL, 4.40 mmol) and (R)-binol (286 mg, 1.00 mmol) were subsequently added and the solution was left to stir overnight. The volatiles were removed in vacuo and the crude product was filtered through a plug of silica in toluene. The title product was obtained after removal of the solvent as a white solid. Yield: 404 mg (71%). MP: 158 °C. [α]²⁰_D = +238° (c = 1.0 mg mL⁻¹, CHCl₃). IR (neat): ν 3055.4, 2981.3, 1588.6, 1505.9, 1462.5, 1362.2, 1326.4, 1228.2, 1203.1, 1154.9, 1070.0, 949.2, 869.5, 818.8, 782.0, 747.7, 629.4 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) 8.06 (d, ³J_HH = 8.3 Hz, 1H, H4′), 8.01 (d, ³J_HH = 8.3 Hz, 1H, ArH), 7.95–7.91 (m, 3H, H14/ArH), 7.88 (d, ³J_HH = 8.2 Hz, 1H, ArH), 7.84 (dd, ³J_HH = 7.0 Hz, ⁵J_HP = 1.0 Hz, 1H, H2′), 7.73 (d, ³J_HH = 8.7 Hz, 1H, H14′), 7.69 (dd, ³J_HH = 8.3 Hz, ³J_HH = 7.0 Hz, 1H, H3′), 7.61 (d, ³J_HH = 8.6 Hz, 1H, H4), 7.56–7.52, (m, 2H, ArH), 7.49–7.40 (m, 4H, H13/ArH), 7.38–7.31 (m, 5H, ArH), 7.30–7.24 (m, 3H, H3/ArH), 6.91 (d, ³J_HH = 8.7 Hz, 1H, H13′). ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) 150.2 (d, ²J_CP = 2.4 Hz, C12), 149.0 (d, ²J_CP = 6.1 Hz, C12′), 145.0 (d, ²J_CP = 37.2 Hz, C1), 136.2 (d, ¹J_CP = 38.9 Hz, C2), 135.0, 134.8 (d, J_CP = 10.0 Hz), 133.5, 133.3 (d, J_CP = 2.1 Hz), 133.0 (d, J_CP = 4.7 Hz), 132.9 (d, J_CP = 1.5 Hz), 132.8 (d, J_CP = 1.0 Hz), 131.7, 131.2, 130.9 (d, ⁴J_CP = 5.8 Hz, C2′), 130.6 (C14), 129.6 (d, ⁴J_CP = 0.7 Hz, C14′), 129.1 (C4′), 128.5, 128.4, 128.3, 128.2, 127.7, 127.1 (C4), 127.0 (d, J_CP = 2.8 Hz), 126.8, 126.7, 126.6, 126.6, 126.5, 126.3, 126.3, 126.2, 125.0, 124.9 (C3′), 124.9, 124.7 (d, ³J_CP = 5.7 Hz, C11), 124.2 (d, ²J_CP = 2.7 Hz, C3), 123.8 (d, ³J_CP = 2.6 Hz, C11′), 122.2 (C13′), 121.5 (d, ³J_CP = 1.4 Hz, C13). ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) 177.4. HRMS (m/z, ESI⁺, MeOH): found 585.1605, calcd for [M + H₂O]⁺ 585.1614.

Synthesis of (S,S_b)-[1,1′-binaphthalene]-2,2′-diyl [1,1′-binaphthalen]-2-ylphosphonite (5b)

The same procedure was followed as for 5a, except for using (S)-binol as the nucleophile. The title product was obtained as a white solid after removal of the solvent. Yield: 527 mg (93%). MP: 197 °C. [α]²⁰_D = −264° (c = 1.0 mg mL⁻¹, CHCl₃). IR (neat): ν 3060.6, 2981.3, 1588.6, 1506.5, 1466.0, 1366.0, 1330.0, 1262.7, 1232.0, 1204.0, 1141.6, 1141.6, 1072.2, 951.6, 869.5, 822.7, 789.4, 753.7, 684.6, 630.2 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) 8.04 (d, ³J_HH = 8.2 Hz, 1H, H4′), 7.99–7.89 (m, 4H, H14′/ArH), 7.88 (d, ³J_HH = 8.2 Hz, 1H, H5), 7.78 (d, ³J_HH = 8.7 Hz, 1H, H14), 7.68 (dd, ³J_HH = 8.2 Hz, ³J_HH = 7.0 Hz, 1H, H3′), 7.63 (dd, ³J_HH = 7.0 Hz, ⁵J_HP = 1.2 Hz, 1H, H2′), 7.61 (d, ³J_HH = 8.6 Hz, 1H, H4), 7.55 (ddd, ³J_HH = 8.2 Hz, ³J_HH = 5.5 Hz, ⁴J_HH = 2.5 Hz, 1H, H6), 7.53–7.36 (m, 7H, H13′/ArH), 7.35–7.28 (m, 3H, H7/H8/ArH), 7.23–7.21 (m, 3H, H3/ArH), 6.90 (d, ³J_HH = 8.7 Hz, 1H, H13). ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) 150.1 (d, ²J_CP = 1.9 Hz, C12′), 148.9 (d, ²J_CP = 5.7 Hz, C12), 145.4 (d, ²J_CP = 37.0 Hz, C1), 136.5 (d, ¹J_CP = 40.4 Hz, C2), 135.0 (d, J_CP = 7.9 Hz), 134.1 (d, J_CP = 2.9 Hz), 133.5, 133.0 (d, J_CP = 4.3 Hz), 132.9, 132.8, 131.6, 131.4, 131.2, 130.6 (C14′), 129.6 (C14), 129.4 (C2′), 128.7 (C4′), 128.5, 128.4, 128.4, 128.1 (C5), 127.8, 127.4 (d, J_CP = 2.6 Hz), 127.1 (C4), 127.0, 126.9, 126.8, 126.6, 126.5, 126.4, 126.2, 126.1, 125.9, 125.1 (C3′), 124.9, 124.8 (C11′), 124.3 (d, ²J_CP = 2.6 Hz, C3), 123.6 (C11), 122.5 (C13), 121.4 (C13′). ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) 175.7. HRMS (m/z, EI⁺): found: = 567.1514, calcd for [M − H]⁺ 567.1508.

Synthesis of (R,R_b)-[1,1′-binaphthalene]-2,2′-diyl (2′-methoxy-[1,1′-binaphthalen]-2-yl)phosphonite (6a)

PCl₅ (458 mg, 2.20 mmol) was dissolved in toluene (8 mL). (R)-2 (316 mg, 1.00 mmol) was added and the reaction mixture was left to stir for 45 min. The volatiles were removed in vacuo to give (R)-4 (³¹P{¹H} NMR, CDCl₃: δ = 159.1 ppm) as a yellow solid. THF (8 mL), NEt₃ (448 mg, 0.64 mL, 4.40 mmol) and (R)-binol (286 mg, 1.00 mmol) were added subsequently and the solution was left to stir overnight. The volatiles were removed in vacuo and the crude product was dissolved in toluene and filtered through a plug of silica. The title product was obtained after removal of the solvent as a white solid. Yield: 523 mg, (87%). MP: >270 °C. [α]²⁰_D = +444° (c = 1.0 mg mL⁻¹, CHCl₃). IR (neat): ν 2981.2, 1619.8, 1590.0, 1507.0, 1461.8, 1431.0, 1327.7, 1228.2, 1149.5, 1078.1, 947.3, 866.6, 820.5, 799.5, 746.7, 686.7, 630.3 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) 8.09 (d, ³J_HH = 9.1 Hz, 1H, H4′), 7.94–7.90 (m, 4H, H5′/H14/H15′/ArH), 7.89 (d, ³J_HH = 8.2 Hz, 1H, H5), 7.72 (d, ³J_HH = 8.8 Hz, 1H, H14′), 7.59 (d, ³J_HH = 8.5 Hz, 1H, H4), 7.55 (ddd, ³J_HH = 8.2 Hz, ³J_HH = 5.7 Hz, ⁴J_HH = 2.1 Hz, 1H, H6), 7.53 (d, ³J_HH = 9.1 Hz, 1H, H3′), 7.47 (ddd, ³J_HH = 8.2 Hz, ³J_HH = 6.8 Hz, ⁴J_HH = 1.2 Hz, 1H, ArH), 7.44–7.40 (m, 3H, H13/ArH), 7.38 (ddd, ³J_HH = 8.2 Hz, ³J_HH = 6.8 Hz, ⁴J_HH = 1.2 Hz, 1H, ArH), 7.36–7.24 (m, 6H, ArH), 7.23 (dd, ³J_HH = 8.5 Hz, ³J_HP = 1.4 Hz, 1H, H3), 7.02 (d, ³J_HH = 8.5 Hz, 1H, ArH), 6.93 (d, ³J_HH = 8.8 Hz, 1H, H13′), 3.99 (s, 3H, OCH₃). ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) 156.6 (d, ⁴J_CP = 3.5 Hz, C2′), 150.3 (d, ²J_CP = 2.5 Hz, C12), 154.9 (d, ²J_CP = 5.8 Hz, C12′), 141.8 (d, ²J_CP = 37.5 Hz, C1), 136.3 (d, ¹J_CP = 37.7 Hz, C2), 135.3, 134.5 (d, ⁴J_CP = 2.9 Hz, C9′), 132.9, 132.8, 132.7 (d, J_CP = 1.0 Hz), 131.6 (d, J_CP = 0.9 Hz), 131.4, 131.2, 130.8 (C4′), 130.5 (C5′), 129.5 (C14′), 128.7, 128.5, 128.5, 128.3 (C5), 128.2 (C10′), 128.1, 127.7, 127.1, 126.8, 126.7 (C4), 126.6, 126.5, 126.4 (d, J_CP = 2.6 Hz), 126.2, 126.1, 125.2, 124.9, 124.8, 124.5 (d, ²J_CP = 2.0 Hz, C3), 123.8, 122.7 (C13), 121.6 (C13′), 118.9 (d, ³J_CP = 10.2 Hz, C1′), 112.8 (C3′), 56.2 (s, OCH₃). ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) 177.8. HRMS (m/z, ESI⁺, CH₂Cl₂): found 599.1767, calcd for [M + H]⁺ 599.1771.

Synthesis of (R,S_b)-[1,1′-binaphthalene]-2,2′-diyl (2′-methoxy-[1,1′-binaphthalen]-2-yl)phosphonite (6b)

The same procedure was followed as for 6a, except for using (S)-binol as the nucleophile. The title product was obtained as a white solid after removal of the solvent. Yield: 430 mg (72%). MP: 231 °C (decomposition). [α]²⁰_D = −310° (c = 1.0 mg mL⁻¹, CHCl₃). IR (neat): ν 2980.8, 1620.1, 1590.2, 1506.3, 1462.7, 1431.5, 1329.8, 1230.2, 1203.4, 1146.0, 1070.1, 949.5, 867.8, 820.8, 789.7, 747.2, 684.7, 628.8 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) 8.09 (d, ³J_HH = 9.1 Hz, 1H, H4′), 7.97 (d, ³J_HH = 8.8 Hz, 1H, H14′), 7.93–7.90 (m, 3H, H15/H5′/H15′), 7.88 (d, ³J_HH = 8.2 Hz, 1H, H5), 7.76 (d, ³J_HH = 8.7 Hz, 1H, H14), 7.60 (d, ³J_HH = 8.6 Hz, 1H, H4), 7.54 (dd, ³J_HH = 8.0 Hz, ^3/4J_HH = 4.0 Hz, 1H, H6′), 7.52 (d, ³J_HH = 8.8 Hz, 1H, H13′), 7.51 (d, ³J_HH = 9.1 Hz, 1H, H3′), 7.46 (ddd, ³J_HH = 8.0 Hz, ³J_HH = 6.8 Hz, ⁴J_HH = 1.0 Hz, 1H, H16), 7.42–7.35 (m, 4H, H18/ArH), 7.32 (d, ³J_HH = 4.0 Hz, 2H, H7′/H8′), 7.30 (ddd, ³J_HH = 8.4 Hz, ³J_HH = 6.8 Hz, ⁴J_HH = 1.3 Hz, 1H, H17), 7.23–7.18 (m, 4H, H3/ArH), 6.87 (d, ³J_HH = 8.7 Hz, 1H, H13), 3.89 (s, 3H, OCH₃). ¹³C{¹H} NMR (CD₂Cl₂, 101 MHz): δ (ppm) 154.9 (d, ⁴J_CP = 2.9 Hz, C2′), 150.2 (d, ²J_CP = 2.3 Hz, C12′), 149.0 (d, ²J_CP = 5.9 Hz, C12), 141.9 (d, ²J_CP = 39.2 Hz, C1), 136.4 (d, ¹J_CP = 38.3 Hz, C2), 135.3, 135.0 (C9′), 132.8, 132.7, 132.7, 131.6, 131.1, 130.7 (C4′), 130.5 (C14′), 129.5 (C14), 128.8, 128.4 (C15), 128.4 (C15′), 128.3 (C5′), 128.3 (C10′), 128.2 (C5), 127.7, 126.9 (C4), 126.8, 126.7, 126.6, 126.5, 126.4 (d, J_CP = 2.1 Hz), 126.2, 126.1, 125.5, 124.9, 124.8 (C16), 124.6 (d, J_CP = 2.5 Hz), 123.7, 123.6 (d, J_CP = 2.5 Hz), 122.5 (C13), 121.5 (C13′), 119.0 (d, ³J_CP = 10.3 Hz, C1′), 113.0 (C3′), 56.4 (s, OCH₃). ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) 177.9. HRMS (m/z, ESI⁺, CH₂Cl₂): found 599.1766, calcd for [M + H]⁺ 599.1771.

Synthesis of [Pd(5a)(η³-C₄H₇)Cl] (7a)

[Pd(η³-C₄H₇)Cl]₂ (7 mg, 18 μmol) and 5a (20 mg, 35 μmol) were dissolved in CH₂Cl₂ (1 mL) and stirred for 10 min. The intended complex was formed quantitatively. Slow diffusion of diethyl ether into the reaction mixture yielded colorless crystals overnight, which were suitable for X-ray diffraction analysis. Yield: 25 mg (92%). MP: >270 °C. IR (neat): ν 3052.0, 1587.6, 1505.8, 1460.0, 1432.9, 1360.3, 1322.4, 1220.7, 1067.8, 977.3, 942.2, 871.8, 838.4, 810.2, 759.4, 706.9, 677.2, 634.3, 596.8 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) isomer A (97%), 7.97 (d, ³J_HH = 8.1 Hz, 1H, H4′), 7.94–7.90 (m, 4H, H14/H5/H15/H15′), 7.89–7.85 (m, 2H, H2–/H5′), 7.84–7.80 (m, 2H, H13/H4), 7.78 (d, ³J_HH = 8.9 Hz, 1H, H14′), 7.72 (dd, ³J_HH = 8.6 Hz, ³J_HP = 5.5 Hz, 1H, H3), 7.69 (dd, ³J_HH = 8.1 Hz, ³J_HH = 7.2 Hz, 1H, H3′), 7.58–7.55 (m, 1H, ArH), 7.53–7.43 (m, 5H, H6′/ArH), 7.39–7.27 (m, 5H, ArH), 7.18–7.13 (m, 2H, H13′/ArH), 3.75 (dd, ³J_HP = 9.9 Hz, ⁴J_HH = 2.5 Hz, 1H, allyl-Ht_syn), 2.56 (s, 1H, allyl-Hc_syn), 1.57 (d, ³J_HP = 14.1 Hz, 1H, allyl-Ht_anti), 1.00 (s, 3H, allyl-CH₃), 0.83 (s, 1H, allyl-Hc_anti); isomer B (3%), 8.00–6.99 (m, 23H, ArH), 6.92 (m, 1H, ArH), 6.87 (m, 1H, ArH), 3.96 (d, ³J_HP = 6.8 Hz, 1H, allyl-Ht_syn), 2.96 (m, 1H, allyl-Hc_syn), 2.64 (d, ³J_HP = 12.3 Hz, 1H, allyl-Ht_anti), 1.53 (m, 1H, allyl-Hc_anti), 1.42 (s, 3H, allyl-CH₃). ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) isomer A (97%), 149.1 (d, ²J_CP = 5.3 Hz, C12), 148.6 (d, ²J_CP = 13.2 Hz, C12′), 144.7 (d, ²J_CP = 27.2 Hz, C1), 135.2, 134.7 (d, ¹J_CP = 9.3 Hz, C2), 133.5, 133.4, 133.3, 133.1, 132.6 (d, J_CP = 1.4 Hz), 132.2 (d, J_CP = 1.9 Hz), 131.9 (d, J_CP = 1.3 Hz), 131.5 (d, J_CP = 1.3 Hz), 131.1 (C2′), 131.0 (d, J_CP = 28.6 Hz, allyl-C), 130.7 (d, ⁴J_CP = 1.1 Hz, C14), 130.2 (d, ⁴J_CP = 1.4 Hz, C14′), 129.7, 129.2 (C4′), 128.6, 128.5, 128.3, 128.2, 128.2, 127.7 (d, ³J_CP = 5.2 Hz, C4), 127.3, 127.1, 127.1, 127.0 (d, J_CP = 2.3 Hz), 126.9, 126.8, 126.7, 126.6, 126.4, 125.5, 125.4, 125.2 (C3′), 124.9 (d, ²J_CP = 2.8 Hz, C3), 124.2 (d, ³J_CP = 3.8 Hz, C11), 123.7 (d, ³J_CP = 2.9 Hz, C11′), 122.4 (d, ³J_CP = 2.4 Hz, C13), 120.4 (C13′), 76.8 (d, ²J_CP = 45.3 Hz, allyl-Ct), 56.1 (d, ²J_CP = 5.8 Hz, allyl-Cc), 22.4 (allyl-CH₃); signals of isomer B could not be observed. ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) isomer A (97%), 173.4; isomer B (3%), 175.7. HRMS (m/z, ESI⁺, MeOH): found 727.1178, calcd for [M − Cl]⁺ 727.1176.

Synthesis of [Pd(5b)(η³-C₄H₇)Cl] (7b)

The same procedure was followed as for 7a. Yield: 23 mg (83%). MP: >270 °C. IR (neat): ν 3047.7, 1585.8, 1505.6, 1461.1, 1434.2, 1360.9, 1322.9, 1269.3, 1222.1, 1161.0, 1121.5, 1068.7, 1027.5, 977.3, 943.4, 877.1, 839.5, 803.3, 757.5, 729.6, 687.3, 634.8, 598.0, 557.6 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) 8.13 (d, ³J_HH = 7.0 Hz, 1H, H2′), 7.98–7.86 (m, 7H, H4′/H15/H5′/H14′/H5/H15′/H13′), 7.83 (d, ³J_HH = 8.8 Hz, 1H, H14), 7.74 (d, ³J_HH = 8.7 Hz, 1H, H4), 7.69 (dd, ³J_HH = 8.7 Hz, ³J_HH = 7.0 Hz, 1H, H3′), 7.60–7.57 (m, 1H, ArH), 7.53–7.40 (m, 7H, H3/ArH), 7.36–7.23 (m, 5H, ArH), 7.00 (d, ³J_HH = 8.7 Hz, 1H, H13), 4.16 (dd, ³J_HP = 10.2 Hz, ⁴J_HH = 2.8 Hz, 1H, allyl-Ht_syn), 2.56 (d, ³J_HP = 14.8 Hz, 1H, allyl-Ht_anti), 2.31 (s, 1H, allyl-Hc_syn), 0.93 (s, 3H, allyl-CH₃), 0.50 (s, 1H, allyl-Hc_anti). ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) 149.1 (d, ²J_CP = 5.3 Hz, C12′), 148.4 (d, ²J_CP = 13.1 Hz, C12), 145.1 (d, ²J_CP = 29.7 Hz, C1), 135.5, 134.5 (d, ¹J_CP = 9.4 Hz, C2), 134.3, 133.6 (d, J_CP = 4.7 Hz), 133.5 d, J_CP = 4.4 Hz), 133.3, 132.6 (d, J_CP = 1.4 Hz), 132.1, 131.8 (d, J_CP = 0.9 Hz), 131.6, 131.5 (d, ⁴J_CP = 1.0 Hz, C2′), 130.8 (d, J_CP = 28.5 Hz, allyl-C), 130.7 (C14′), 130.2 (d, ⁴J_CP = 1.4 Hz, C14), 128.6, 128.5, 128.5, 128.3, 128.1, 128.1 (C4′), 127.6 (d, ³J_CP = 4.9 Hz, C4), 127.3, 127.2, 127.1, 127.0, 126.6, 126.6, 126.5, 126.3, 126.3, 126.2 (C3′), 125.5, 125.4, 124.5 (C3), 124.1 (d, ³J_CP = 4.2 Hz, C11′), 123.5 (d, ³J_CP = 2.6 Hz, C11), 122.5 (d, ³J_CP = 2.3 Hz, C13′), 121.1 (d, ³J_CP = 0.8 Hz, C13), 77.8 (d, ²J_CP = 46.5 Hz, allyl-Ct), 57.6 (d, ²J_CP = 5.3 Hz, allyl-Cc), 22.5 (allyl-CH₃). ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) 172.1. HRMS (m/z, ESI⁺, MeOH): found 725.1177, calcd for [M − Cl]⁺ 725.1176.

Synthesis of [Pd(6a)(η³-C₄H₇)Cl] (8a)

The same procedure was followed as for 7a. Yield: 26 mg (91%). MP: >270 °C. IR (neat): ν 3065.2, 1620.2, 1589.0, 1507.6, 1463.0, 1431.3, 1327.7, 1247.8, 1223.0, 1194.2, 1151.8, 1068.9, 1021.8, 943.5, 873.9, 839.0, 807.0, 743.7, 677.2, 637.2, 597.2, 597.8, 560.2 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) isomer A (93%), 7.98 (d, ³J_HH = 9.1 Hz, 1H, H4′), 7.93 (dd, ³J_HH = 8.9 Hz, ⁴J_HP = 0.9 Hz, 1H, H13), 7.91–7.86 (m, 4H, H14/H5/H15/H15′), 7.78–7.73 (m, 2H, H5′/H4), 7.72 (d, ³J_HH = 8.9 Hz, 1H, H14′), 7.63 (dd, ³J_HH = 8.6 Hz, ³J_HP = 5.4 Hz, 1H, H3), 7.55 (ddd, ³J_HH = 8.1 Hz, ³J_HH = 6.8 Hz, ⁴J_HH = 1.1 Hz, 1H, ArH), 7.50 (d, ³J_HH = 9.1 Hz, 1H, H3′), 7.47–7.24 (m, 10H, ArH/H6′), 7.19 (d, ³J_HH = 8.9 Hz, ⁴J_HP = 1.0 Hz, 1H, H13′), 7.14 (d, ³J_HH = 8.4 Hz, 1H, ArH), 3.97 (s, 3H, OCH₃), 3.73 (dd, ³J_HP = 10.0 Hz, ⁴J_HH = 3.0 Hz, 1H, allyl-Ht_syn), 2.60 (m, 1H, allyl-Hc_syn), 1.63 (d, ³J_HP = 14.1 Hz, 1H, allyl-Ht_anti), 0.92 (s, 3H, allyl-CH₃), 0.85 (m, 1H, allyl-Hc_anti); isomer B (7%), 8.05 (d, ³J_HH = 9.1 Hz, 1H, H4′), 7.99–7.10 (m, 20H, ArH), 7.07–7.02 (m, 1H, ArH), 6.97 (d, ³J_HH = 8.9 Hz, 1H, H13′), 6.74 (d, ³J_HH = 8.5 Hz, 1H, ArH), 4.12 (s, 3H, OCH₃), 3.87 (m, 1H, allyl-Ht_syn), 3.18 (m, 1H, allyl-Hc_syn), 1.94 (d, ³J_HP = 13.0 Hz, 1H, allyl-Ht_anti), 1.70 (s, 3H, allyl-CH₃), 1.35 (m, 1H, allyl-Hc_anti). ¹³C {¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) isomer A (93%), 156.4 (C2′), 149.3 (d, ²J_CP = 5.3 Hz, C12), 149.1 (d, ²J_CP = 12.9 Hz, C12′), 141.5 (d, ²J_CP = 27.0 Hz, C1), 135.5 (d, ¹J_CP = 1.4 Hz, C2), 134.2 (C9′), 133.2 (d, J_CP = 7.1 Hz), 133.2 (d, J_CP = 8.1 Hz), 132.4 (d, J_CP = 1.3 Hz), 132.1 (d, J_CP = 1.4 Hz), 131.8 (d, J_CP = 8.1 Hz), 131.6 (d, J_CP = 1.1 Hz), 131.3 (d, ²J_CP = 28.8 Hz, allyl-C), 131.0 (C4′), 130.5 (d, ⁴J_CP = 1.1 Hz, C14), 130.1 (d, ⁴J_CP = 1.3 Hz, C14′), 128.6, 128.5, 128.4, 128.4, 128.3, 128.2 (C6), 128.0, 127.5 (d, ³J_CP = 5.3 Hz, C4), 127.0 (C10′), 127.0, 126.9 (C5′), 126.7, 126.4, 126.3 (d, J_CP = 2.3 Hz), 126.2 (C8), 125.4, 125.3, 125.0 (d, ²J_CP = 2.7 Hz, C3), 124.5 (C6′), 124.4 (d, ³J_CP = 3.8 Hz, C11), 123.7 (d, ³J_CP = 3.0 Hz, C11′), 122.9 (d, ³J_CP = 2.4 Hz, C13), 121.5 (C13′), 118.8 (d, ³J_CP = 9.5 Hz, C1′), 113.1 (C3′), 77.3 (d, ²J_CP = 44.9 Hz, allyl-Ct), 56.2 (OCH₃), 56.1 (d, ²J_CP = 5.3 Hz, allyl-Cc), 22.5 (allyl-CH₃); signals of isomer B could not be observed. ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) isomer A (93%), 173.6; isomer B (7%) 175.6. HRMS (m/z, ESI⁺, MeOH): found 755.1301, calcd for [M − Cl]⁺ 755.1296.

Synthesis of [Pd(6b)(η³-C₄H₇)Cl] (8b)

The same procedure was followed as for 7a. Yield: 23 mg (80%). MP: >270 °C. IR (neat): ν 3066.0, 1619.1, 1587.6, 1506.6, 1463.6, 1429.5, 1323.0, 1276.0, 1226.1, 1199.8, 1155.9, 1117.7, 1070.1, 1028.0, 946.1, 867.4, 833.3, 814.2, 751.9, 706.2, 686.6, 634.8, 606.6, 560.1 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) 8.02 (d, ³J_HH = 9.1 Hz, 1H, H4′), 8.00–7.97 (m, 2H, H15/H13′), 7.94 (d, ³J_HH = 8.9 Hz, 1H, H14′), 7.91 (d, ³J_HH = 8.1 Hz, 1H, H5), 7.89 (d, ³J_HH = 8.2 Hz, 1H, H15′), 7.86 (d, ³J_HH = 8.7 Hz, 1H, H14), 7.83 (d, ³J_HH = 8.2 Hz, 1H, H5′), 7.65 (d, ³J_HH = 8.7 Hz, 1H, H4), 7.59 (ddd, ³J_HH = 8.1 Hz, ³J_HH = 6.6 Hz, ⁴J_HH = 1.0 Hz, 1H, H6), 7.54–7.51 (m, 1H, H16), 7.49 (d, ³J_HH = 9.1 Hz, 1H, H3′), 7.46–7.39 (m, 3H, ArH/H16′), 7.37–7.27 (m, 7H, ArH/H17/H7′/H6′/H3/H7/H18′), 7.25–7.22 (m, 1H, H17′), 7.00 (d, ³J_HH = 8.7 Hz, 1H, H13), 4.07 (dd, ³J_HP = 9.9 Hz, ⁴J_HH = 3.8 Hz, 1H, allyl-Ht_syn), 3.87 (s, 3H, OCH₃), 2.35 (s, 1H, allyl-Hc_syn), 2.24 (d, ³J_HP = 13.6 Hz, 1H, allyl-Ht_anti), 0.84 (s, 3H, allyl-CH₃), 0.32 (s, 1H, allyl-Hc_anti). ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) 156.2 (C2′), 149.2 (d, ²J_CP = 5.3 Hz, C12′), 148.5 (d, ²J_CP = 12.4 Hz, C12), 142.6 (d, ²J_CP = 29.8 Hz, C1), 135.6 (d, ¹J_CP = 1.3 Hz, C2), 135.5 (d, ⁴J_CP = 0.9 Hz, C9′), 134.0 (d, J_CP = 9.2 Hz), 133.1 (d, J_CP = 9.8 Hz), 132.7 (d, J_CP = 1.5 Hz), 132.1 (d, J_CP = 1.9 Hz), 131.8 (d, J_CP = 1.3 Hz), 131.6 (d, J_CP = 1.3 Hz), 131.3 (d, ²J_CP = 26.3 Hz, allyl-C), 130.5 (d, ⁴J_CP = 0.9 Hz, C14′), 130.1 (d, ⁴J_CP = 1.3 Hz, C14), 129.7 (C4′), 128.5 (C15), 128.5 (C15′), 128.5 (C6), 128.3 (C5), 128.2 (C10′), 128.0 (C5′), 127.3 (d, ³J_CP = 4.7 Hz, C4), 127.0, 127.0, 126.9, 126.8, 126.6, 126.6, 126.2 (C17′), 125.5 (C16), 125.3 (C16′), 125.3, 125.1 (d, ²J_CP = 1.4 Hz, C3), 124.1 (d, ³J_CP = 3.8 Hz, C11′), 123.5, 123.4 (d, ³J_CP = 2.8 Hz, C11), 123.1 (d, ³J_CP = 2.4 Hz, C13′), 121.4 (C13), 118.2 (d, ³J_CP = 10.5 Hz, C1′), 113.5 (C3′), 79.3 (d, ²J_CP = 46.1 Hz, allyl-Ct), 59.0 (d, ²J_CP = 4.5 Hz, allyl-Cc), 56.0 (OCH₃), 22.3 (allyl-CH₃). ³¹P {¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) 174.4. HRMS (m/z, ESI⁺, MeOH): found 755.1280, calcd for [M − Cl]⁺ 755.1296.

Synthesis of [Pd(6a)(η³-C₄H₇)]BArF (9a)

Sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (33.4 mg, 37.7 μmol) and 8a (30.0 mg, 37.7 μmol) were dissolved in CH₂Cl₂ (2 mL) and stirred for 30 min. The reaction mixture was filtered through a layer of celite and the solvent removed in vacuo; the intended product was obtained as a yellow solid. Yield: 48.9 mg (80%). IR (neat): ν 1612.4, 1588.2, 1506.9, 1464.1, 1353.8, 1273.2, 1220.7, 1116.5, 953.5, 882.6, 836.8, 813.3, 746.2, 711.9, 681.4, 638.0, 599.2 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) isomer A,B, 8.27–7.23 (m, 2H, H4′^B/H4′^A), 8.14–7.98 (m, 10H, H5′/H14/H15′/H15/H14′), 7.93–7.89 (m, 3H, H5′/H3′^B), 7.86–7.80 (m, 3H, H3′^A/H4), 7.74 (br s, 16H, o-BArF), 7.63–7.51 (m, 18H, H6′/H16/H16′/H6/ArH/p-BArF), 7.48–7.38 (m, 10H, H13/ArH), 7.26–7.19 (m, 4H, H7/ArH), 7.13–7.02 (m, 4H, H13′/H3), 6.06 (d, ³J_HH = 8.3 Hz, 2H, H8), 4.06 (s, OCH₃^B), 4.00 (s, OCH₃^A), 3.16 (br d, ³J_HP = 10.7 Hz, allyl-Ht_anti^B), 3.03 (s, allyl-Hc_syn^B), 2.99 (s, allyl-Hc_syn^A), 2.90 (d, ³J_HP = 13.2 Hz, allyl-Ht_anti^A), 2.43 (br d, ³J_HP = 8.2 Hz, allyl-Ht_syn^A), 2.39 (s, allyl-Hc_anti^A), 2.34 (br s, allyl-Ht_syn^B), 2.22 (s, allyl-Hc_anti^B), 1.58 (s, allyl-CH₃^A), 1.30 (s, allyl-CH₃^B); A : B ratio from integration of CH₃ signals: 52 : 48. ¹¹B NMR (CD₂Cl₂, 160 MHz): δ (ppm) −7.6. ¹³C{¹H} NMR (CD₂Cl₂, 101 MHz): δ (ppm) isomer A,B, 161.8 (q, ¹J_CB = 40.8 Hz, ipso-BArF), 159.0 (C2′^B), 157.2 (C2′^A), 148.1 (d, ³J_CP = 10.1 Hz, C11′^B), 148.0 (d, ³J_CP = 11.0 Hz, C11′^A), 147.1 (d, ³J_CP = 7.7 Hz, C11), 142.1 (d, ²J_CP = 41.7 Hz, C1^B), 141.9 (d, ²J_CP = 41.7 Hz, C1^A), 137.9 (d, ²J_CP = 9.5 Hz, allyl-C^A), 137.0 (C2), 134.8 (o-BArF), 134.6 (C4′), 132.8, 132.5, 132.1, 132.0, 131.7, 131.6 (C14), 131.5 (C9′^A), 131.4 (C9′^B), 131.4 (C14′), 130.9, 130.8, 130.4, 130.3 (C4), 130.1 (C5′), 130.0, 129.8, 129.4, 128.9 (qq, ²J_CF = 31.2 Hz, ⁴J_CF = 2.8 Hz, m-BArF), 128.8, 128.4 (C10′), 127.5, 127.4, 127.3, 127.1, 127.0, 126.9, 126.5, 126.4, 126.3, 126.0, 125.0, 124.8, 124.7 (q, ¹J_CF = 273.2 Hz, CF₃), 124.1, 124.0 (d, J_CP = 3.4 Hz), 123.8, 123.7, 123.3, 122.5, 122.3, 120.7 (C3), 120.6 (C13′), 120.3 (C13), 120.1, 117.5 (septet, ³J_CF = 4.0 Hz, p-BArF), 114.9 (C3′^A), 114.5 (C3′^B), 104.6 (C1′^A), 99.6 (d, ²J_CP = 40.1 Hz, allyl-Ct^A), 57.5 (OCH₃^B), 57.4 (OCH₃^A), 53.2 (allyl-Cc^A), 22.4 (allyl-CH₃^A), 21.6 (allyl-CH₃^B); not all signals could be observed due to peak broadening and overlap. ¹⁹F NMR (CD₂Cl₂, 471 MHz): δ (ppm) −62.7. ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) isomer A, 177.5; isomer B, 178.0. HRMS (m/z, ESI⁺, MeCN): found 757.1287, calcd for [M]⁺ 757.1281.

Synthesis of [Pd(6b)(η³-C₄H₇)]BArF (9b)

The same procedure was followed as for 9a; the intended product was obtained as a yellow solid. Yield: 54.0 mg (91%). IR (neat): ν 1612.1, 1588.9, 1506.1, 1463.5, 1353.6, 1273.0, 1219.8, 1116.1, 952.9, 882.4, 836.7, 811.4, 745.5, 711.9, 669.8, 638.6, 602.7 cm⁻¹. ¹H NMR (CD₂Cl₂, 500 MHz): δ (ppm) isomer A,B, 8.22 (d, ³J_HH = 9.2 Hz, 1H, H4′^A), 8.21 (d, ³J_HH = 9.2 Hz, 1H, H4′^B), 8.17–8.01 (m, 10H, H14/H14′/H5′/ArH), 7.99 (d, ³J_HH = 9.2 Hz, 1H, H3′^A), 7.96–7.89 (m, 5H, ArH/H4/H3′^B), 7.76 (br s, 16H, o-BArF), 7.64–7.51 (m, 18H, ArH/p-BArF), 7.49–7.35 (m, 12H, ArH/H13^B/H13′^A/H13^A), 7.30–7.22 (m, 4H, ArH/H7/H13′^B), 7.20 (dd, ³J_HH = 8.5 Hz, ³J_HP = 6.9 Hz, 1H, H3^A), 7.10 (dd, ³J_HH = 8.5 Hz, ³J_HP = 6.9 Hz, 1H, H3^B), 6.09 (br d, 1H, H8^B), 6.00 (d, ³J_HH = 8.6 Hz, 1H, H8^A), 3.98 (s, OCH₃^A), 3.89 (s, OCH₃^B), 3.76 (d, ³J_HP = 13.6 Hz, allyl-Ht_anti^A), 3.00 (br d, allyl-Ht_syn^B), 2.87 (s, allyl-Hc_syn^B), 2.82 (s, allyl-Hc_syn^A), 2.63 (d, ³J_HP = 13.5 Hz, allyl-Ht_anti^B), 2.32 (s, allyl-Hc_anti^A), 2.20 (br s, allyl-Hc_anti^B), 2.19 (d, allyl-Ht_syn^A), 1.79 (br s, allyl-CH₃^B), 0.96 (s, allyl-CH₃^A); A : B ratio of 50 : 50 from integration of OMe resonances (signals of isomer B broadened). ¹¹B NMR (CD₂Cl₂, 128 MHz): δ (ppm) −7.6. ¹³C{¹H} NMR (CD₂Cl₂, 126 MHz): δ (ppm) isomer A,B, 161.8 (q, ¹J_CB = 40.7 Hz, ipso-BArF), 156.6 (C2′^A), 154.8 (d, J_CP = 2.4 Hz, C2′^B), 148.3 (d, ³J_CP = 13.5 Hz, C11^A), 148.3 (d, ³J_CP = 13.3 Hz, C11^B), 147.2 (d, ³J_CP = 7.1 Hz, C11′^A), 147.1 (d, ³J_CP = 7.4 Hz, C11′^B), 142.4 (d, ²J_CP = 43.5 Hz, C1^B), 142.2 (d, ²J_CP = 41.3 Hz, C1^A), 138.9 (d, ²J_CP = 10.4 Hz, allyl-C^A), 138.1 (d, J = 10.0 Hz, allyl-C^B), 137.1 (C2^B), 137.0 (C2^A), 134.9 (C4′^A), 134.9 (o-BArF), 134.3 (C4′^B), 133.7 (C9′^B), 132.8, 132.7 (C9′^A) 132.1, 131.8, 131.7, 131.6, 131.5, 130.7 (d, ³J_CP = 4.7 Hz, C4), 130.0 (C10′^B), 129.8, 129.8, 129.7, 129.3 (C10′^A), 128.9 (qq, ²J_CF = 31.6 Hz, ⁴J_CF = 2.9 Hz, m-BArF), 128.7, 128.6, 128.0, 127.6, 127.4, 127.4, 127.0, 127.0, 126.6, 126.5, 126.4, 125.1, 124.8, 124.7 (q, ¹J_CF = 272.3 Hz, CF₃), 124.3, 124.1, 123.7 (d, ²J_CP = 1.4 Hz, C3^B), 123.7 (d, ²J_CP = 1.4 Hz, C3^A), 123.0, 122.3, 122.1, 120.7 (d, ³J_CP = 1.0 Hz, C13^B), 120.6 (d, ³J_CP = 1.0 Hz, C13^A), 120.1 (d, ³J_CP = 2.1 Hz, C13′^A), 119.8 (C13′^B), 117.5 (septet, ³J_CF = 4.0 Hz, p-BArF), 115.9 (C3′^B), 115.3 (C3′^A), 104.5 (C1′^B), 103.4 (C1′^A), 99.5 (d, ²J_CP = 41.1 Hz, allyl-Ct^A), 96.9 (br, allyl-Ct^B), 57.6 (OCH₃^A), 57.3 (OCH₃^B), 56.4 (allyl-Cc^B), 54.9 (allyl-Cc^A), 22.6 (allyl-CH₃^B), 21.5 (allyl-CH₃^A); not all signals could be observed due to peak broadening and overlap. ¹⁹F NMR (CD₂Cl₂, 471 MHz): δ (ppm) −62.7. ³¹P{¹H} NMR (CD₂Cl₂, 202 MHz): δ (ppm) isomer A, 178.9; isomer B, 179.1. HRMS (m/z, ESI⁺, MeCN): found 757.1296, calcd for [M]⁺ 757.1281.

Asymmetric palladium-catalyzed hydrosilylation of styrene

[Pd(η³-C₃H₄)Cl]₂ (4.6 mg, 0.0125 mmol, 0.125 mol%), ligand (0.25 mol%) and styrene (1.2 mL, 1.0 g, 10.0 mmol) were stirred at room temperature for 20 min. Trichlorosilane (1.2 mL, 1.6 g, 12.0 mmol) was added and the reaction was stirred at room temperature for the appropriate time. The conversion of the reaction was followed by ¹H NMR spectroscopy. The product was purified by Kugelrohr distillation (reduced pressure, 150 °C).

Trichloro(1-phenylethyl)silane (400 mg, 1.67 mmol) was dissolved in MeOH (30 mL) and THF (30 mL). K₂CO₃ (1.40 g, 10.1 mmol), KF (600 mg, 10.3 mmol) and 35% H₂O₂ (1.8 mL) were added subsequently and left to stir overnight. The solution was filtered, water was added and the product was extracted with diethyl ether three times. The combined organic washings were dried over MgSO₄ and the crude product was purified by column chromatography on silica (hexane/ethyl acetate, 4 : 1, R_f = 0.20). The enantiomeric excess was measured by chiral HPLC (Column Daicel Chiralcel OD; flow rate: 0.5 mL min⁻¹; hexane/2-propanol, 95 : 5; retention times: (R) t₁ = 19.3 min, (S) t₂ = 22.3 min). The absolute configuration was assigned by comparing the retention times to literature data.²³

Acknowledgements

We thank the EPSRC for a Career Acceleration Fellowship (L.J.H.), Studentship (A.F.), an Equipment Grant (R.W.H) and its National Mass Spectrometry Service Centre, Swansea, UK, and IRCSET for a Scholarship (R.M.H.).

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: Full experimental and crystallographic data. CCDC reference numbers 840097 (7a), 840098 (7b), 854373 (8a) and 840100 (8b). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt12214f

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