Reactions of osmapyridinium with terminal alkynes

Abstract

We have synthesized a new type of ten-membered osmacycles by reaction of osmapyridinium with HC≡CCH(OH)R (R = Ph, Et). We propose that these reactions take place initially by coordination of the alkynes, [2 + 2] cycloaddition, subsequent 1,2-hydrogen migration and a final reductive elimination. The reactions with phenylacetylenes do not afford the corresponding derivatives but rather give η⁴-coordinated cyclopentadiene complexes, which are proposed to derive from a [4 + 2] cycloaddition process. Related reactions of the η⁴-coordinated cyclopentadiene complexes are also discussed.

---

Introduction

The chemistry of metalloaromatic compounds has made significant progress in the past decades.¹ The incorporation of a transition metal fragment into conventional aromatic hydrocarbons has recently attracted much attention from both theoretical and experimental chemists.^2,3 Whereas the synthesis of a variety of metallobenzene derivatives has been reported and allowed further insight into their reactivities,² reports on the isolation of analogues containing nitrogen atoms, e.g. metallopyridines, remain limited.⁴ The first example of metallopyridines is tantalopyridine, which is significant in favoring the localized imido form.^4e,f Another example of metallopyridines are osmapyridines with relatively delocalized structures.^4a,d It is therefore not surprising that, so far, only the nucleophilic addition reactions^4d and the ligand substitution reactions^4b of delocalized metallopyridines have been reported.

As we were interested in the chemistry of metallacycles, we have studied the reactions of osmafuran with PhC≡CH and HC≡CCH(OH)Ph.⁵ As shown in Chart 1, the reactions yielded nine-membered osmacycles, which might be formed through a [2 + 2] cycloaddition process relevant to olefin metathesis and alkyne polymerization. Another related approach is the investigation of the ruthenium vinyl carbene,⁶ which can react with propargyl alcohols to produce a series of ten-membered η²-olefine coordinated ruthenacycles (Chart 1(c)). The proposed mechanism for the reaction involves a regioselective [2 + 2] cycloaddition and 1,2-migration process.^6a In this paper, we report the reactions of osmapyridinium with terminal alkynes to generate new osmacycles.

Chart 1 (a) Reaction of osmafuran with PhC≡CH; (b) reaction of osmafuran with HC≡CCH(OH)Ph; (c) reactions of ruthenium vinyl carbene with propargyl alcohols.

Results and discussion

Reactions of osmapyridinium with HC≡CCH(OH)R

Treatment of osmapyridinium 1^4d with excess HC≡CCH(OH)Ph in dichloromethane under reflux led to the formation of complex 2 (Scheme 1). 2 can be isolated as a purple solid in 68% yield, which was characterized by NMR spectroscopy and elemental analysis, and the structure was further confirmed by single-crystal X-ray diffraction.

Scheme 1 Reactions of 1 with HC≡CCH(OH)R.

The crystallographic details of complex 2 are given in Table 1. As shown in Fig. 1, 2 contains a distorted ten-membered metallacycle (N1, O1, C1, C2, C3, C4, C6, C7, C8, Os1). The osmium centre exhibits a somewhat irregular octahedral geometry, which may be attributed to the coordination of the double bond to the metal centre. The C–C distances within the osmacycle are similar to those in the ten-membered ruthenacycles (Chart 1(c)).^6a Consistent with the X-ray structure, the ¹H NMR (CD₂Cl₂) spectrum shows the signals of the coordinated double bond at 5.9 (C1H) and 5.2 (C6H) ppm. The remaining ¹H signals of the metallacycle are observed at 10.6 (NH), 3.5 (C7H), and 0.9 ppm (C7H). With the aid of ¹H–¹³C HSQC, ¹H–¹³C HMBC and ¹³C-dept 135 spectra, the seven carbon signals of the metallacycle are observed at δ = 219.8 (C8), 166.6 (C4), 156.5 (C3), 124.5 (C2), 61.9 (C6), 52.7 (C1), and 43.7 (C7) ppm in the ¹³C{¹H} NMR spectrum. The ³¹P NMR spectrum shows two signals at 19.7 and −9.5 ppm for CPPh₃ and OsPPh₃, respectively.

Fig. 1 X-ray structure of complex 2 (ellipsoids at the 50% probability level). Some of the hydrogen atoms, phenyl groups and the counteranion are omitted for clarity. Selected bond lengths (Å) and angles (°): Os1–N1 2.012(7), Os1–O1 2.190(5), N1–C4 1.282(11), C3–C4 1.473(12), C2–C3 1.342(11), C1–C2 1.506(11), C1–C6 1.416(11), C6–C7 1.505(11), C7–C8 1.515(11), C8–O1 1.216(9), C4–C5 1.523(12); O1–Os1–N1 82.6(2), C4–N1–Os1 135.4(6), C3–C4–N1 121.8(7), C2–C3–C4 120.7(7), C1–C2–C3 125.8(7), C2–C1–C6 122.6(7), C1–C6–C7 124.7(7), C6–C7–C8 111.7(7), C7–C8–O1 119.2(7), C8–O1–Os1 116.4(5).

Table 1 Crystal data and structure refinement for 2, 5, 6 and 8

	2·2H2O·0.25CHCl3	5·2CH2Cl2	6·CH2Cl2	8·2CH2Cl2
Formula	C56.25H52.25BCl2.75F4NO3OsP2	C58H52BCl6F4NOOsP2	C52H55BCl4F4N3OsP	C50H43BCl5F4N3OOsP
M r	1226.68	1330.65	1171.77	1187.10
crystal system	Monoclinic	Monoclinic	Monoclinic	Monoclinic
space group	P21/c	P21/n	Cc	P21/c
a [Å]	11.9299(3)	16.5731(8)	19.3445(9)	12.0746(3)
b [Å]	14.1946(3)	19.6848(7)	16.8974(6)	18.8448(3)
c [Å]	33.0235(7)	18.1839(9)	16.1902(7)	20.9677(4)
α [°]	90	90	90	90
β [°]	98.5760(10)	112.182(2)	111.0040(10)	90.0230(10)
γ [°]	90	90	90	90
V [Å^3]	5529.7(2)	5493.2(4)	4940.5(4)	4771.06(17)
Z	4	4	4	4
ρ calcd [g cm^−3]	1.473	1.609	1.574	1.653
μ [mm^−1]	2.553	2.727	2.884	3.044
F(000)	2458	2656	2352	2356
crystal size [mm^3]	0.18 × 0.12 × 0.10	0.30 × 0.10 × 0.10	1.00 × 0.60 × 0.40	0.80 × 0.50 × 0.30
θ Range [°]	3.08 to 25.00	3.02 to 27.48	3.25 to 24.99	3.11 to 27.48
Reflns collected	62 557	38 256	18 915	70 908
Independent reflns	9691	9642	7754	10 901
Observed reflns [I ≥ 2σ(I)]	8011	7791	6954	8348
Data/restraints/params	9691/6/667	9642/0/669	7754/47/596	10 901/0/598
GOF on F^2	1.044	1.084	1.091	1.170
R 1/wR2 [I ≥ 2σ(I)]]	0.0566/0.1635	0.0643/0.1710	0.0344/0.0737	0.0526/0.1396
R 1/wR2 (all data)	0.0694/0.1720	0.0779/0.1873	0.0439/0.0858	0.0723/0.1954
Largest peak/hole [e Å^−3]	2.14/−1.30	4.64/−2.06	1.43/−1.15	2.13/−2.64

---

Reaction of osmapyridinium 1 with HC≡CCH(OH)Et was also investigated. As shown in Scheme 1, 1 reacted with HC≡CCH(OH)Et to produce insertion product 3. 3 has been characterized by NMR spectroscopy and elemental analysis. The structure of 3 can be deduced easily, as its NMR data are similar to those of complex 2 (Table 2). The resonances of the osmacycle in the ¹H NMR spectrum (10.5 (N1H), 6.0 (C1H), 5.1 (C6H), 2.8 (C7H), and 0.7 (C7H) ppm) and ¹³C{¹H} NMR spectrum (236.5 (C8), 167.4 (C4), 158.1 (C3), 124.7 (C2), 62.0 (C6), 53.1 (C1), and 48.8 (C7) ppm) are very close to those observed for complex 2.

Table 2 Selected NMR spectroscopic data for 2 and 3

Compound		2	3
δ (^1H) (ppm)	NH	10.6	10.5
	H1	5.9	6.0
	H6	5.2	5.1
	H7	3.5	2.8
		0.9	0.7
δ (^13C) (ppm)	C4	166.6	167.4
	C3	156.5	158.1
	C2	124.5	124.7
	C1	52.7	53.1
	C6	61.9	62.0
	C7	43.7	48.8
	C8	219.8	236.5

---

Similar to our previous reported mechanism for the formation of ten-membered ruthenacycles from ruthenium vinyl carbene,^6a the formation of osmacycles 2 and 3 may also involve a [2 + 2] cycloaddition and 1,2-migration process. As shown in Scheme 2, coordination of the terminal alkyne to the metal center in 1 accompanied by the dissociation of the PPh₃ ligand could generate π-alkyne intermediate A. Then, [2 + 2] cycloaddition of the alkyne with the Os=C in A may lead to the formation of the metallacyclobutene intermediate B, which could undergo cycloreversion to form the nine-membered intermediate C. The following activation of hydroxyl in C could produce the hydride intermediate D. Subsequent 1,2-hydrogen migration, reductive elimination, and coordination of the carbonyl group to metal center could yield the final metallacycle 2/3. It is also possible that the proton on the oxygen may transfer to the carbene carbon without the intermediacy of the Os center. The mechanism shown in Scheme 2 is similar to that for our ten-membered ruthenacycle synthesis from ruthenium vinyl carbene and propargyl alcohols as demonstrated by deuterium labeling experiments.^6a In this context, it should be mentioned that similar [2 + 2] cycloadditions of alkynes with carbene complexes have been described in literature.⁷

Scheme 2 Proposed mechanism of the reaction of 1 with HC≡CCH(OH)R.

Reactions of osmapyridinium with phenylacetylenes

To further study the reactions of osmapyridinium complex 1 with terminal alkynes, we also investigated its reactivity with phenylacetylenes. As shown in Scheme 3, 1 can react with phenylacetylene to produce complex 4 as a yellow solid in 92% yield. Similarly, complex 5 was obtained in 91% yield from the reaction of 1 with a substituted phenylacetylene, i.e. 1-ethynyl-4-methoxybenzene (Scheme 3).

Scheme 3 Reactions of 1 with phenylacetylenes.

These two complexes have been characterized by NMR spectroscopy and elemental analysis. As shown in Table 3, the complexes 4 and 5 must have similar structures as indicated by the similarity in their NMR spectroscopic data. Fortunately, we were able to obtain a single crystal for 5, enabling determination of its solid-state structure. The crystallographic details for 5 are given in Table 1. As shown in Fig. 2, 5 contains a substituted cyclopentadiene unit, which is η⁴-coordinated to the metal centre. The phenyl group and the imido group are located on the sp³ carbon of the cyclopentadiene unit.

Fig. 2 X-ray structure of complex 5 (only the R enantiomer is shown, ellipsoids at the 50% probability level). Some of the hydrogen atoms, phenyl groups and the counteranion are omitted for clarity. Selected bond distances (Å) and angles (°): Os1–N1 2.054(7), Os1–C1 2.206(7), Os1–C2 2.264(7), Os1–C6 2.190(8), Os1–C7 2.307(7), C1–C2 1.395(10), C2–C3 1.595(11), C3–C7 1.577(10), C6–C7 1.419(10), C1–C6 1.424(11), N1–C4 1.258(10), C3–C4 1.520(11), C2–P2 1.805(8); C1–C2–C3 110.1(7), C2–C3–C7 95.4(5), C3–C7–C6 110.1(6), C7–C6–C1 109.1(6), C6–C1–C2 109.1(7), C4–N1–Os1 118.5(6), C3–C4–N1 108.2(7), C3–C4–C5 128.6(7), C2–C3–C4 107.3(6), C7–C3–C4 104.9(6).

Table 3 Selected NMR spectroscopic data for 4, 5, 6, 7 and 8

Compound	δ (^1H) (ppm)			δ (^13C) (ppm)
	NH	H1	H6	C4	C3	C2	C1	C6	C7
4	8.3	6.8	6.9	191.0	88.3	78.6	118.2	83.4	102.9
5	8.3	6.8	6.7	190.7	88.3	77.6	117.4	82.1	105.6
6	11.1	8.2	6.5	180.3	81.9	105.3	170.4	59.2	96.7
7	11.1	8.2	6.5	180.2	82.0	104.9	170.6	59.5	97.1
8	12.2	6.1	4.7	179.6	80.3	76.3	135.4	68.9	133.8

---

Based on the characterized structures, we postulate the reaction mechanism shown in Scheme 4 for the reaction of 1 with phenylacetylenes. The PPh₃ ligand in 1 could initially be displaced by phenylacetylene to give the π-alkyne complex F. Subsequent [4 + 2] cycloaddition of the osmium vinyl carbene fragment with the alkyne in F may lead to the formation of the metallacyclohexadiene intermediate G. Finally, G could undergo reductive elimination to generate complex 4/5 in which the cyclopentadiene is coordinated to the metal center as a ligand. It is interesting to note that, in our previous report, the osmafuran only underwent a head-to-tail double insertion of PhC≡CH to generate nine-membered osmacycles (Chart 1(a)).⁵ We speculated that the difference may be attributed to the delocalized structure of the osmapyridinium 1, which only shows a weak alternating double/single bond character around the metallacycle. A similar [4 + 2] cycloaddition process has been previously proposed in the reactions of metallobenzenes with unsaturated substrates⁸ and the reactions of alkenyl carbene complexes with alkynes or alkenes.⁹ In the case of osmapyridinium 1 with HC≡CCH(OH)R, the [2 + 2] cycloaddition may be aided by the hydroxyl group, which helps stabilize the 16-electron intermediate.

Scheme 4 Proposed mechanism of the reactions of 1 with phenylacetylenes.

Reactions of 4/5 with cyclohexyl isocyanide and 2,2′-bipyridine

The osmium complexes 4 and 5 are reactive towards strong ligands, such as isocyanides and bipyridines. As shown in Scheme 5, reactions of 4 and 5 with cyclohexyl isocyanide produce the ligand substitution products 6 and 7, respectively. The structures of 6 and 7 can be assigned based on the NMR data. In particular, the NMR signals associated with the metallacycle are similar to those of the analogous cyclopentadiene complexes 4 and 5 (see Table 3). The different coordination mode of the substituted cyclopentadiene unit in 6 and 7 is supported by the chemical shifts of C1 and C2 in the ¹³C NMR spectrum.

Scheme 5 Reactions of 4/5 with cyclohexyl isocyanide.

The structure of complex 6 was further confirmed by X-ray diffraction analysis (Fig. 3). As shown in Fig. 3 and Table 4, the structural parameters of complex 6 are similar to those of 5. The two cyclohexyl isocyanide ligands are mutually trans, and the substituted cyclopentadiene fragment in 6 is η²-coordinated to the metal centre. We think that the steric effect of the bulky phosphonium group would account for the observed regioselectivity.

Fig. 3 X-ray structure of complex 6 (only the R enantiomer is shown, ellipsoids at the 50% probability level). Some of the hydrogen atoms, phenyl groups and the counteranion are omitted for clarity.

Table 4 Selected bond distances and angles for 6 and 8

	6	8
Bond distances (Å)
Os1–N1	2.020(6)	2.022(5)
N1–C4	1.280(9)	1.290(7)
C3–C4	1.546(10)	1.532(8)
C1–C2	1.360(10)	1.455(7)
C2–C3	1.552(10)	1.593(7)
C3–C7	1.602(9)	1.535(8)
C6–C7	1.412(10)	1.323(9)
C1–C6	1.454(9)	1.459(8)
Bond angles (°)
Os1–N1–C4	125.6(5)	126.5(4)
N1–C4–C3	113.7(6)	113.1(5)
C4–C3–C2	103.4(5)	106.6(4)
C4–C3–C7	108.0(6)	103.4(5)
C1–C2–C3	109.9(6)	106.0(4)
C2–C3–C7	100.6(5)	101.5(4)
C3–C7–C6	108.2(6)	111.7(6)
C1–C6–C7	108.8(6)	111.9(5)
C2–C1–C6	112.3(6)	108.7(5)

---

The reaction of 5 with 2,2′-bipyridine was also examined. Compound 8 could be readily obtained in 75% isolated yield by the reaction of 5 with 2,2′-bipyridine (Scheme 6). The complex has been characterized by NMR spectroscopy and elemental analysis. The structures of complexes 8 were assigned based on the fact that the NMR data associated with the complex are similar to those of 4, 5, 6 and 7, as illustrated by the data shown in Table 3.

Scheme 6 Reactions of 5 with 2,2′-bipyridine.

The structure of 8 has been confirmed by X-ray diffraction (Fig. 4). Like 6, the cyclopentadiene ligand in 8 is also η²-coordinated to osmium. The complex contains the 2,2′-bipyridine in the equatorial plane, and one of the phenyl groups of the phosphonium ligand bonded to the metal center which may derive from the C–H activation process. We have reported a similar oxidative addition of the phenyl C–H bond of PPh₃ which could give rise to tethered complexes.¹⁰ In this case, the basicity of the 2,2′-bipyridine might facilitate the C–H activation of the phosphonium ligand. Thus, the reaction of 5 with pyridine under the above reaction conditions resulted in the formation of a similar tethered complex, as suggested by in situ NMR.

Fig. 4 X-ray structure of complex 8 (only the R enantiomer is shown, ellipsoids at the 50% probability level). Some of the hydrogen atoms, phenyl groups and the counteranion are omitted for clarity.

Conclusions

The reactions of osmapyridinium with terminal alkynes were studied, which led to the formation of new osmium complexes. For propargyl alcohols, the [2 + 2] cycloaddition and 1,2-hydrogen migration process was proposed for the formation of the final ten-membered osmacycles. For phenylacetylenes, η⁴-coordinated cyclopentadiene complexes can be obtained, which may be attributed to a [4 + 2] cycloaddition process.

Experimental

General comments

All manipulations were carried out at room temperature under a nitrogen atmosphere using standard Schlenk techniques, unless otherwise stated. Solvents were distilled under nitrogen from sodium benzophenone (diethyl ether) or calcium hydride (dichloromethane). Column chromatography was performed on neutral alumina gel (200–300 mesh) or silica gel (200–300 mesh). NMR experiments were performed on a Bruker AV-400 spectrometer (¹H 400.1 MHz; ¹³C 101.6 MHz; ³¹P 162.0 MHz) at room temperature unless otherwise stated. ¹H and ¹³C NMR chemical shifts are relative to TMS, and ³¹P NMR chemical shifts are relative to 85% H₃PO₄. Elemental analysis data were obtained on an Elementar Analysensystem GmbH Vario EL III instrument.

Preparation and characterization of complex 2. A solution of compound 1 (229 mg, 0.18 mmol) in CH₂ClCH₂Cl (30 mL) was heated under reflux for 5 h in the presence of 1-phenyl-2-propyn-1-ol (28 mg, 0.21 mmol). The solution was concentrated to about 3 mL. Subsequent addition of Et₂O (25 mL) gave a purple precipitate, which was washed with Et₂O (25 mL) and dried under vacuum. Yield: 140 mg, 68%.

¹H NMR (400.1 MHz, CD₂Cl₂): δ = 10.6 (s, 1 H, NH), 7.7–6.5 (39 H, other aromatic carbon atoms), 5.9 (dd, ³J(P, H) = 9.6 Hz, ³J(H, H) = 9.6 Hz, 1 H, H¹), 5.2 (m, 1 H, H⁶), 3.5 (dd, ²J(H, H) = 18.3 Hz, ³J(H, H) = 6.0 Hz, 1 H, H⁷), 1.8 (s, 3 H, H⁵), 0.9 ppm (dd, ²J(H, H) = 18.5 Hz, ³J(H, H) = 8.2 Hz, 1 H, H⁷). ³¹P{¹H} NMR (162.0 MHz, CD₂Cl₂): δ = 19.7 (s, CPPh₃), −9.5 ppm (s, OsPPh₃). ¹³C{¹H} NMR (101.6 MHz, CD₂Cl₂, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 219.8 (s, C⁸), 166.6 (d, ³J(P, C) = 13.1 Hz, C⁴), 156.5 (d, ²J(P, C) = 14.9 Hz, C³), 135.4–118.8 (other aromatic carbon atoms), 124.5 (d, ¹J(P, C) = 66.6 Hz, C²), 61.9 (s, C⁶), 52.7 (d, ²J(P, C) = 10.0 Hz, C¹), 43.7 (s, C⁷), 28.2 ppm (s, C⁵). Elemental analysis calcd (%) for C₅₆H₄₈Cl₂P₂BF₄NOOs: C, 57.94; H, 4.17; N, 1.21. Found: C, 57.88; H, 4.08; N, 1.06.

Preparation and characterization of complex 3. A solution of compound 1 (138 mg, 0.11 mmol) in CH₂ClCH₂Cl (30 mL) was heated under reflux for 5 h in the presence of 1-pentyn-3-ol (20 mg, 0.24 mmol). The solution was concentrated to about 3 mL. Subsequent addition of Et₂O (25 mL) gave a purple precipitate, which was washed with Et₂O (25 mL) and dried under vacuum. Yield: 65.4 mg, 55%.

¹H NMR (400.1 MHz, CDCl₃): δ = 10.5 (s,1 H, NH), 7.8–6.6 (35 H, other aromatic carbon atoms), 6.0 (dd, ³J(P, H) = 10.0 Hz, ³J(H, H) = 10.0 Hz, 1 H, H¹), 5.1 (m, 1 H, H⁶), 2.8 (dd, ²J(H, H) = 18.4 Hz, ³J(H, H) = 4.1 Hz, 1 H, H⁷), 2.5 (m, 2 H, H⁹), 1.7 (s, 3 H, H⁵), 1.0 (dd, ³J(H, H) = 6.1 Hz, ³J(H, H) = 6.1 Hz, 3 H, H¹⁰), 0.7 ppm (dd, ²J(H, H) = 18.6 Hz, ³J(H, H) = 8.1 Hz, 1 H, H⁷). ³¹P{¹H} NMR (162.0 MHz, CDCl₃): δ = 19.0 (s, CPPh₃), −10.7 ppm (s, OsPPh₃). ¹³C{¹H} NMR (101.6 MHz, CDCl₃, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 236.5 (s, C⁸), 167.4 (d, ³J(P, C) = 12.4 Hz, C⁴), 158.1 (d, ²J(P, C) = 15.0 Hz, C³), 135.0–119.7 (other aromatic carbon atoms), 124.7 (d, ¹J(P, C) = 66.7 Hz, C²), 62.0 (s, C⁶), 53.1 (d, ²J(P, C) = 10.2 Hz, C¹), 48.8 (s, C⁷), 35.7 (s, C⁹), 28.8 (s, C⁵), 7.8 ppm (s, C¹⁰). Elemental analysis calcd (%) for C₅₂H₄₈Cl₂P₂BF₄NOOs: C, 56.12; H, 4.35; N, 1.26. Found: C, 56.41; H, 4.65; N, 1.52.

Preparation and characterization of complex 4. A solution of compound 1 (230 mg, 0.18 mmol) in CH₂ClCH₂Cl (30 mL) was heated under reflux for 2 h in the presence of phenylacetylene (200 mg, 1.9 mmol). The solution was concentrated to about 3 mL. Subsequent addition of Et₂O (25 mL) gave a yellow precipitate, which was washed with Et₂O (25 mL) and dried under vacuum. Yield: 186 mg, 92%.

¹H NMR (400.1 MHz, CD₂Cl₂): δ = 8.3 (s,1 H, NH), 6. 9 (d, ³J(H, H) = 2.8 Hz, 1 H, H⁶), 6.8 (d, ³J(H, H) = 2.8 Hz, 1 H, H¹), 7.8–7.1 and 6.8–6.3 (40 H, other aromatic carbon atoms), 1.5 ppm (s, 3 H, H⁵). ³¹P{¹H} NMR (162.0 MHz, CD₂Cl₂): δ = 25.7 (s, CPPh₃), −13.6 ppm (s, OsPPh₃). ¹³C{¹H} NMR (101.6 MHz, CD₂Cl₂, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 191.0 (s, C⁴), 137.5–126.7 (other aromatic carbon atoms), 118.2 (dd, ²J(P, C) = 12.6 Hz, ²J(P, C) = 5.2 Hz, C¹), 102.9 (d, ²J(P, C) = 10.0 Hz, C⁷), 88.3 (d, ²J(P, C) = 8.7 Hz, C³), 83.4 (d, ²J(P, C) = 9.6 Hz, C⁶), 78.6 (dd, ¹J(P, C) = 71.6 Hz, ²J(P, C) = 26.5 Hz, C²), 26.0 ppm (s, C⁵). Elemental analysis calcd (%) for C₅₅H₄₆Cl₂P₂BF₄NOs: C, 58.42; H, 4.10; N, 1.24. Found: C, 58.03; H, 4.53; N, 1.49.

Preparation and characterization of complex 5. A solution of compound 1 (500 mg, 0.39 mmol) in CH₂ClCH₂Cl (50 mL) was heated under reflux for 2 h in the presence of 4-ethynylanisole (510 mg, 3.9 mmol). The solution was concentrated to about 3 mL. Subsequent addition of Et₂O (30 mL) gave an orange precipitate, which was washed with Et₂O (30 mL) and dried under vacuum. Yield: 411 mg, 91%.

¹H NMR (400.1 MHz, CD₂Cl₂): δ = 8.3 (s,1 H, NH), 6.8 (d, ³J(H, H) = 2.6 Hz, 1 H, H¹), 6.7 (d, ³J(H, H) = 2.6 Hz, 1 H, H⁶), 7.7–7.0 and 6.6–6.3 (39 H, other aromatic carbon atoms), 3.7 (s, 3 H, OCH₃), 1.4 ppm (s, 3 H, H⁵). ³¹P{¹H} NMR (162.0 MHz, CD₂Cl₂): δ = 25.9 (s, CPPh₃), −13.1 ppm (s, OsPPh₃). ¹³C{¹H} NMR (101.6 MHz, CD₂Cl₂, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 190.7 (s, C⁴), 159.3(s, C²⁴), 137.6–113.8 (other aromatic carbon atoms), 117.4 (dd, ²J(P, C) = 13.9 Hz, ²J(P, C) = 6.3 Hz, C¹), 105.6 (d, ²J(P, C) = 10.1 Hz, C⁷), 88.3 (d, ²J(P, C) = 8.7 Hz, C³), 82.1 (d, ²J(P, C) = 9.9 Hz, C⁶), 77.6 (dd, ¹J(P, C) = 71.9 Hz, ²J(P, C) = 26.5 Hz, C²), 54.7 (s, OCH₃), 26.1 ppm (s, C⁵). Elemental analysis calcd (%) for C₅₆H₄₈Cl₂P₂BF₄NOOs: C, 57.94; H, 4.17; N, 1.21. Found: C, 58.04; H, 4.44; N, 1.25.

Preparation and characterization of complex 6. A solution of compound 4 (172 mg, 0.15 mmol) in DCM (30 mL) was stirred for 1 day in the presence of isocyanocyclohexane (80 mg, 0.73 mmol). The solution was concentrated to about 3 mL, Subsequent addition of Et₂O (25 mL) gave an orange precipitate, which was washed with Et₂O (25 mL) and dried under vacuum. Yield: 97 mg, 59%.

¹H NMR (400.1 MHz, CD₂Cl₂): δ = 11.1 (s, 1 H, NH), 8.2 (dd, ³J(H, H) = 10.1 Hz, ³J(P, H) = 4.0 Hz, 1 H, H¹), 7.8–6.6 (20 H, other aromatic carbon atoms), 6.5 (br, 1 H, H⁶), 3.8–3.4 (m, 2 H, C≡NCH), 2.0 (s, 3 H, H⁵), 2.0–1.0 ppm (20 H, other alkyl carbon atoms). ³¹P{¹H} NMR (162.0 MHz, CD₂Cl₂): δ = 18.1 ppm (s, CPPh₃). ¹³C{¹H} NMR (101.6 MHz, CD₂Cl₂, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 180.3 (s, C⁴), 170.4 (d, ²J(P, C) = 11.3 Hz, C¹), 140.5–116.8 (other aromatic carbon atoms), 105.3 (d, ¹J(P, C) = 85.8 Hz, C²), 96.7 (d, ³J(P, C) = 6.9 Hz, C⁷), 81.9 (d, ²J(P, C) = 8.1 Hz, C³), 59.2 (d, ³J(P, C) = 16.2 Hz, C⁶), 54.3 (s, CNCH), 52.8 (s, CNCH), 31.9–21.3 (other alkyl carbon atoms), 25.6 ppm (s, C⁵). Elemental analysis calcd (%) for C₅₁H₅₂Cl₂PBF₄N₃Os: C, 56.41; H, 4.83; N, 3.87. Found: C, 56.80; H, 5.10; N, 3.76.

Preparation and characterization of complex 7. A solution of compound 5 (186 mg, 0.16 mmol) in DCM (30 mL) was stirred for 1 day in the presence of isocyanocyclohexane (88 mg, 0.81 mmol). The solution was concentrated to about 3 mL, subsequent addition of Et₂O (25 mL) gave an orange precipitate, which was washed with Et₂O (25 mL) and dried under vacuum. Yield: 100 mg, 56%.

¹H NMR (400.1 MHz, CD₂Cl₂): δ = 11.1 (s, 1 H, NH), 8.2 (dd, ³J(H, H) = 10.2 Hz, ³J(P, H) = 2.7 Hz, 1 H, H¹), 7.8–6.4 (19 H, other aromatic carbon atoms), 6.5 (br, 1 H, H⁶), 3.8–3.5 (m, 2 H, C≡NCH), 3.6 (s, 3 H, OCH₃), 2.0 (s, 3 H, H⁵), 1.9–1.1 ppm (20 H, other alkyl carbon atoms). ³¹P{¹H} NMR (162.0 MHz, CD₂Cl₂): δ = 18.0 ppm (s, CPPh₃). ¹³C{¹H} NMR (101.6 MHz, CD₂Cl₂, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 180.2 (s, C⁴), 170.6 (d, ²J(P, C) = 11.1 Hz, C¹), 157.2 (s, CN), 134.8–111.5 (other aromatic carbon atoms), 104.9 (d, ¹J(P, C) = 85.6 Hz, C²), 97.1 (d, ³J(P, C) = 7.5 Hz, C⁷), 82.0 (d, ²J(P, C) = 7.5 Hz, C³), 59.5 (d, ³J(P, C) = 16.2 Hz, C⁶), 54.3 (s, OCH₃), 54.3 (s, CNCH), 31.9–21.3 (other alkyl carbon atoms), 25.6 ppm (s, C⁵). Elemental analysis calcd (%) for C₅₂H₅₅Cl₂PBF₄N₃OOs: C, 55.92; H, 4.96; N, 3.76. Found: C, 55.99; H, 4.98; N, 3.48.

Preparation and characterization of complex 8. A solution of compound 5 (70 mg, 0.06 mmol) in CH₂ClCH₂Cl (30 mL) was heated under reflux for 2 day in the presence of 2,2′-dipyridyl (70 mg, 0.45 mmol). The solution was concentrated to about 3 mL, and then purified by column chromatography (silica gel, acetone) to give a red solution. The brown solid of 8 was collected after the solvent was evaporated to dryness under vacuum. Yield: 46 mg, 75%.

¹H NMR (400.1 MHz, DMSO-D6): δ = 12.2 (s,1 H, NH), 9.2–6.6 (31 H, other aromatic carbon atoms), 6.1 (s, 1 H, H¹), 4.7 (d, ³J(H, H) = 8.2 Hz, 1 H, H⁶), 3.7 (s, 3 H, OCH₃), 2.5 ppm (s, 3 H, H⁵). ³¹P{¹H} NMR (162.0 MHz, DMSO-D6): δ = 43.3 ppm (s, CPPh₂). ¹³C{¹H} NMR (101.6 MHz, DMSO-D6, plus ¹H–¹³C HSQC and ¹H–¹³C HMBC and ¹³C-dept 135): δ = 179.6 (s, C⁴), 171.4–114.4 (other aromatic carbon atoms), 135.4 (d, ²J(P, C) = 4.4 Hz, C¹), 133.8 (s C⁷), 80.3 (d, ²J(P, C) = 12.3 Hz, C³), 76.3 (d, ¹J(P, C) = 70.9 Hz, C²), 68.9 (d, ³J(P, C) = 3.8 Hz, C⁶), 55.9 (s, OCH₃), 25.3 ppm (s, C⁵). Elemental analysis calcd (%) for C₄₈H₄₀ClPBF₄N₃OOs: C, 56.61; H, 3.96; N, 4.13. Found: C, 56.84; H, 4.35; N, 3.88.

Crystallographic details

Single-crystal X-ray diffraction data were collected on an Oxford Gemini S Ultra CCD Area Detector or a Rigaku R-AXIS SPIDER IP CCD Area Detector with graphite-monochromated MoKa radiation (λ = 0.71073 Å). All of the data were corrected for absorption effects using the multi-scan technique. The structures were solved by direct methods, expanded by difference Fourier syntheses and refined by full matrix least-squares on F² using Bruker SHELXTL (Version 6.10) program package. Non-H atoms were refined anisotropically unless otherwise stated. Hydrogen atoms were introduced at their geometric positions and refined as riding atoms unless otherwise stated. For complexes 5, 6 and 8, the crystal suitable for X-ray diffraction was grown from a CH₂Cl₂ solution layered with hexane. For complex 2, the crystal suitable for X-ray diffraction was grown from a CHCl₃ solution layered with hexane. Solvent molecules CHCl₃ in 2 are disordered and were refined with suitable restraints. Isocyanocyclohexane ligand molecules in 6 were refined isotropically using fixed C–C or C–N length. CCDC-1038534 (2), CCDC-1038533 (5), CCDC-1038537 (6), CCDC-1038535 (8), please see the supplementary crystallographic data for this paper.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (21272193, 21490573) and the program for Changjiang Scholars and Innovative Research Team in University.

Notes and references

1. For recent reviews on the chemistry of metalloaromatics, see: (a) B. J. Frogley and L. J. Wright, Coord. Chem. Rev., 2014, 270–271, 151–166; (b) X.-Y. Cao, Q. Zhao, Z. Lin and H. Xia, Acc. Chem. Res., 2014, 47, 341–354; (c) C. Zhu, X. Cao and H. Xia, Chin. J. Org. Chem., 2013, 33, 657–662; (d) G. Jia, Organometallics, 2013, 32, 6852–6866; (e) J. Chen and G. Jia, Coord. Chem. Rev., 2013, 257, 2491–2521; (f) J. Chen, G. He and G. Jia, Chin. J. Org. Chem., 2013, 33, 792–798; (g) A. F. Dalebrook and L. J. Wright, Adv. Organomet. Chem., 2012, 60, 93–177; (h) M. Paneque, M. L. Poveda and N. Rendón, Eur. J. Inorg. Chem., 2011, 19–33; (i) A. T. Balaban, Top. Heterocycl. Chem., 2009, 19, 203–246; (j) G. Jia, Coord. Chem. Rev., 2007, 251, 2167–2187; (k) J. R. Bleeke, Acc. Chem. Res., 2007, 40, 1035–1047; (l) L. J. Wright, Dalton Trans., 2006, 1821–1827; (m) C. W. Landorf and M. M. Haley, Angew. Chem., Int. Ed., 2006, 45, 3914–3936; (n) G. Jia, Acc. Chem. Res., 2004, 37, 479–486; (o) G. He, H. Xia and G. Jia, Chin. Sci. Bull., 2004, 49, 1543–1553; (p) J. R. Bleeke, Chem. Rev., 2001, 101, 1205–1227.
2. For very recent reports on metallobenzenes: (a) F. Han, J. Li, H. Zhang, T. Wang, Z. Lin and H. Xia, Chem. – Eur. J., 2015, 21, 565–567; (b) R. Lin, K.-H. Lee, K. C. Poon, H. H. Y. Sung, I. D. Williams, Z. Lin and G. Jia, Chemistry, 2014, 20, 14885–14899; (c) F. Han, T. Wang, J. Li, H. Zhang and H. Xia, Chem. – Eur. J., 2014, 20, 4363–4372; (d) Q. Zhao, X.-Y. Cao, T. B. Wen and H. Xia, Chem. – Asian J., 2013, 8, 269–275; (e) T. Wang, J. Zhu, F. Han, C. Zhou, H. Chen, H. Zhang and H. Xia, Angew. Chem., Int. Ed., 2013, 52, 13361–13364; (f) T. Wang, H. Zhang, F. Han, L. Long, Z. Lin and H. Xia, Chem. – Eur. J., 2013, 19, 10982–10991; (g) T. Wang, H. Zhang, F. Han, L. Long, Z. Lin and H. Xia, Angew. Chem., Int. Ed., 2013, 52, 9251–9255; (h) Á. Vivancos, M. Paneque, M. L. Poveda and E. Álvarez, Angew. Chem., Int. Ed., 2013, 52, 10068–10071; (i) J. Chen, C. Zhang, T. Xie, T. B. Wen, H. Zhang and H. Xia, Organometallics, 2013, 32, 3993–4001; (j) Q. Zhao, J. Zhu, Z.-A. Huang, X.-Y. Cao and H. Xia, Chem. – Eur. J., 2012, 18, 11597–11603; (k) R. Lin, J. Zhao, H. Chen, H. Zhang and H. Xia, Chem. – Asian J., 2012, 7, 1915–1924; (l) M. Hernández-Juárez, V. Salazar, E. V. García-Báez, I. I. Padilla-Martínez, H. Höpfl and M. d. J. Rosales-Hoz, Organometallics, 2012, 31, 5438–5451; (m) Q. Zhao, L. Gong, C. Xu, J. Zhu, X. He and H. Xia, Angew. Chem., Int. Ed., 2011, 50, 1354–1358; (n) C. Shi, T. Guo, K. C. Poon, Z. Lin and G. Jia, Dalton Trans., 2011, 40, 11315–11320; (o) R. Lin, H. Zhang, S. Li, J. Wang and H. Xia, Chem. – Eur. J., 2011, 17, 4223–4231; (p) R. Lin, H. Zhang, S. Li, L. Chen, W. Zhang, T. B. Wen, H. Zhang and H. Xia, Chem. – Eur. J., 2011, 17, 2420–2427; (q) H. Zhang, R. Lin, G. Hong, T. Wang, T. B. Wen and H. Xia, Chem. – Eur. J., 2010, 16, 6999–7007; (r) K. C. Poon, L. Liu, T. Guo, J. Li, H. H. Y. Sung, I. D. Williams, Z. Lin and G. Jia, Angew. Chem., Int. Ed., 2010, 49, 2759–2762; (s) P. M. Johns, W. R. Roper, S. D. Woodgate and L. J. Wright, Organometallics, 2010, 29, 5358–5365; (t) J. Huang, R. Lin, L. Wu, Q. Zhao, C. Zhu, T. B. Wen and H. Xia, Organometallics, 2010, 29, 2916–2925; (u) G. R. Clark, L. A. Ferguson, A. E. McIntosh, T. Söhnel and L. J. Wright, J. Am. Chem. Soc., 2010, 132, 13443–13452.
3. For very recent reports on other metalloaromatics: (a) Y. Huang and J. Zhu, Chem. – Asian J., 2015, 10, 405–410; (b) Y. Zeng, H. Feng, R. B. King and H. F. Schaefer III, Organometallics, 2014, 33, 7193–7198; (c) C. Huang, Y. Hao, Y. Zhao and J. Zhu, Organometallics, 2014, 33, 817–822; (d) J. Fan, X. Wang and J. Zhu, Organometallics, 2014, 33, 2336–2340; (e) M. El-Hamdi, O. El Bakouri, E. Farri, P. Salvador, B. A. Abdelouahid, M. S. El Begrani, J. Poater and M. Solà, Organometallics, 2013, 32, 4892–4903; (f) R. W. A. Havenith, F. De Proft, L. W. Jenneskens and P. W. Fowler, Phys. Chem. Chem. Phys., 2012, 14, 9897–9905; (g) M. Lin, P. Li and Z. Cao, J. Theor. Comput. Chem., 2011, 10, 861–874; (h) M. Mauksch and S. B. Tsogoeva, Chem. – Eur. J., 2010, 16, 7843–7851; (i) Z. Lin, Acc. Chem. Res., 2010, 43, 602–611.
4. Metallopyridines: (a) T. Wang, H. Zhang, F. Han, R. Lin, Z. Lin and H. Xia, Angew. Chem., Int. Ed., 2012, 51, 9838–9841; (b) B. Liu, Q. Zhao, H. Wang, J. Chen, X. Cao, Z. Cao and H. Xia, Chin. J. Chem., 2012, 30, 2158–2168; (c) H. Zhang, R. Lin, G. Hong, T. Wang, T. B. Wen and H. Xia, Chem. – Eur. J., 2010, 16, 6999–7007; (d) B. Liu, H. Wang, H. Xie, B. Zeng, J. Chen, J. Tao, T. B. Wen, Z. Cao and H. Xia, Angew. Chem., Int. Ed., 2009, 48, 5430–5434; (e) K. J. Weller, I. Filippov, P. M. Briggs and D. E. Wigley, Organometallics, 1998, 17, 322–329; (f) K. J. Weller, I. Filippov, P. M. Briggs and D. E. Wigley, J. Organomet. Chem., 1997, 528, 225–228.
5. Y. Lin, L. Gong, H. Xu, X. He, T. B. Wen and H. Xia, Organometallics, 2009, 28, 1524–1533.
6. (a) X. Zhou, C. Zhang, Y. Lin, X. He, Y. Zhang, J. Wang and H. Xia, Org. Chem. Front., 2014, 1, 1077–1082; (b) C. Zhang, H. Zhang, L. Zhang, T. B. Wen, X. He and H. Xia, Organometallics, 2013, 32, 3738–3743; (c) C. Zhang, H. Zhang, A. Wei, X. He and H. Xia, Acta Chim. Sin., 2013, 71, 1373–1378.
7. See for example: (a) K. H. Ng, Y. Li, R. Ganguly and F. Mathey, Organometallics, 2013, 32, 7482–7486; (b) H. Park and T.-L. Choi, J. Am. Chem. Soc., 2012, 134, 7270–7273; (c) M. Yamaguchi, Y. Arikawa, Y. Nishimura, K. Umakoshi and M. Onishi, Chem. Commun., 2009, 2911–2913; (d) W. Zhang, J. Yamada and K. Nomura, Organometallics, 2008, 27, 5353–5536.
8. (a) V. Jacob, C. W. Landorf, L. N. Zakharov, T. J. R. Weakley and M. M. Haley, Organometallics, 2009, 28, 5183–5190; (b) J. R. Bleeke, Acc. Chem. Res., 2007, 40, 1035–1047; (c) M. A. Iron, A. C. B. Lucassen, H. Cohen, M. E. van der Boom and J. M. L. Martin, J. Am. Chem. Soc., 2004, 126, 11699–11710; (d) M. A. Iron, J. M. L. Martin and M. E. van der Boom, J. Am. Chem. Soc., 2003, 125, 11702–11709.
9. (a) J. Barluenga, R. Vicente, L. A. López, E. Rubio, M. Tomás and C. Álvarez-Rúa, J. Am. Chem. Soc., 2004, 126, 470–471; (b) J. Barluenga, S. López and J. Flórez, Angew. Chem., Int. Ed., 2003, 42, 231–233; (c) H. Kagoshima, T. Okamura and T. Akiyama, J. Am. Chem. Soc., 2001, 123, 7182–7183; (d) M. Hoffmann, M. Buchert and H.-U. Reißig, Chem. – Eur. J., 1999, 5, 876–882; (e) B. L. Flynn, F. J. Funke, C. C. Silveira and A. d. Meijere, Synlett, 1995, 1007–1010; (f) B. M. Trost and A. S. K. Hashmi, J. Am. Chem. Soc., 1994, 116, 2183–2184.
10. (a) F. Han, T. Wang, J. Li, H. Zhang, L. Zhang, X. He and H. Xia, Organometallics, 2014, 33, 5301–5307; (b) Y. Lin, H. Xu, L. Gong, T. B. Wen, X.-M. He and H. Xia, Organometallics, 2010, 29, 2904–2910.

---

Footnote

† Electronic supplementary information (ESI) available: Material including copies of ¹H and ¹³C NMR spectra of all new products and crystallographic data for 2, 5, 6, 8. CCDC 1038534, 1038533, 1038537 and 1038535. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5qo00052a

---