Frustratingly synergic effect of cobalt–nickel heterometallic precatalysts on ethylene reactivity: the cobalt and its heteronickel complexes bearing 2-methyl-2,4-bis(6-aryliminopyridin-2-yl)-1H-1,5-benzodiazepines

Abstract

A series of 2-methyl-2,4-bis(6-aryliminopyridin-2-yl)-1H-1,5-benzodiazepines were reacted with cobalt chloride to form their corresponding cobalt complexes, which were further reacted with nickel chloride to form their binuclear heteronickel complexes. One of the representative cobalt–nickel complexes was unambiguously confirmed using single-crystal X-ray diffraction. Generally all mononuclear cobalt complexes and binuclear cobalt–nickel complexes showed good activities towards ethylene reactivity (oligomerization and polymerization), however, the mononuclear cobalt complexes showed much higher activities than the binuclear cobalt–nickel analogues, and this is described as the frustratingly synergic effect of heterometallic complexes in ethylene oligomerization. In addition, the obtained oligomers sometimes followed a Poisson distribution.

---

1. Introduction

The synergic catalysis of multinuclear systems has become a hot topic in chemistry,¹ and progress has also been made in the area of coordinative polymerization using multinuclear catalysts based on either monometallic or heterometallic complexes.² Targeting olefin polymerization, the multinuclear early-transition metal catalysts have been extensively investigated.² However, there are a limited number of papers on multinuclear late-transition metal precatalysts including α-diimino,³ phenoxyiminato⁴ or multidentate nickel (Ni) complexes⁵ and multi-sp²-nitrogen coordinated iron (Fe) and cobalt (Co) complexes.^6–8 In addition to homo- and multinuclear precatalysts, heteronuclear precatalysts have also been developed^2a including some of the late-transition metal complexes.^9–11 It is academically important to characterise the contributions made by different cations of heteronuclear catalysts in ethylene oligomerization and/or polymerization, reflecting the individual influences concerning the activities and resultant products. Following binuclear Fe and Co complexes containing 2-methyl-2,4-bis(6-aryliminopyridin-2-yl)-1H-1,5-benzodiazepines (Scheme 1),^8a,b these organic compounds were investigated for their mono-Co analogues and Co–Ni heteronuclear complexes (Scheme 1). Both mono- and hetero-nuclear complexes showed good to high activities towards ethylene reactivity in the presence of methylaluminoxane (MMAO). Surprisingly the oligomers obtained using current systems sometimes followed the Poisson distribution. In literature reports, the oligomers created using Fe or Co precatalysts commonly followed the Schulz–Flory distribution,¹² however, it was possible for only Fe precatalysts to oligomerize ethylene following a Poisson distribution with the assistance of diethylzinc (ZnEt₂) as chain transfer agent.¹³ In this research, the Co and Co–Ni complexes were synthesized and characterized, and their catalytic behaviors in ethylene reactivity were found in ethylene oligomerization to follow the Poisson distribution.

Scheme 1 Binuclear complexes (previously M1 = M2 = Fe, Co, Ni;⁸ currently M1 = Co, M2 = Ni).

2. Results and discussion

2.1 Synthesis and characterization of cobalt and cobalt–nickel complexes

Using a previously reported procedure,^8a 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepine derivatives (L1–L5) were prepared and used to react with one equivalent of cobalt(II) dichloride in a mixture of dichloromethane (DCM)/ethanol to give the corresponding mononuclear Co complexes Co1–Co5 in good yields. Then Co1–Co5 was reacted with nickel(II) dichloride (NiCl₂·6H₂O) in ethanol to give the corresponding heteronuclear complexes Co/Ni1–Co/Ni5 as shown in Scheme 2. All the binuclear complexes were consistent with their matrix assisted laser desorption/ionization – time-of-flight (MALDI-TOF) mass spectra, whereas effective coordination to metal centers was reflected in the Fourier-transform – infrared (FT-IR) spectra, where the C=N stretching vibration bands appeared in the range of 1615–1619 cm⁻¹ for binuclear complexes versus 1639–1650 cm⁻¹ for the ligands L1–L5.

Scheme 2 Synthesis of Co–Ni heterometallic complexes Co/Ni1–Co/Ni5.

2.2 X-ray crystallographic study

Single crystals of heteronuclear complex Co/Ni3 were grown from a mixture of DCM and methanol. Its molecular structure was confirmed using single-crystal X-ray diffraction (SC-XRD) and the structure is shown in Fig. 1. The structure of Co/Ni3 consists of one ligand molecule, one Co(II) cation, one Ni(II) cation, four chlorides and one incorporated methanol molecule. The ligand behaves as a bischelate and bridges two metal fragments. The geometry at the Co center can be described as a more distorted trigonal bipyramid. The nitrogen (N5) of the pyridine and the two chlorides form an equatorial plane, whereas the axial plane consists of the other two nitrogen atoms (N4 and N6) and the Co core with a bond angle of 153.08° for N4–Co2–N6. The Co atom deviates by 0.02 Å from the equatorial plane. The Co2–N5 (pyridine) bond (1.994 Å) is shorter by about 0.057 Å than that found in the homobinuclear Co complex. The N4–C15 bond length in the benzodiazepine and the N6–C23 bond length are 1.28 and 1.263 Å, respectively, with the typical characterisation for a C=N double bond, but are shorter than that in the homobinuclear Co complex (1.283 and 1.278 Å, respectively).^8a The coordination geometry of the Ni center is similar to that in the homo-binuclear Ni complex.^8b An inspection of the intermetallic distance of 4.965 Å between the Co and Ni atoms reveals no direct Co⋯Ni interaction, and such a distance is slightly shorter than the distance of the Co⋯Co with a length of 4.979 Å (ref. 8a) but slightly longer than the distance of the Ni⋯Ni with a length of 4.717 Å (ref. 8b) within the homo-binuclear metal complexes, confirming individual presences of two cationic ions without any interaction.

Fig. 1 ORTEP drawing of the Co–Ni heteronuclear complex Co/Ni3. All the hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Ni1–N1 = 2.187(2), Ni1–N2 = 2.061(1), Ni1–N3 = 2.312(1), Co2–N4 = 2.146(1), Co2–N5 = 1.994(1), Co2–N6 = 2.211(1), N3–C8 = 1.467(2), N3–C9 = 1.47(2), N4–C14 = 1.44(2), N4–C15 = 1.28(2), N6–C23 = 1.263(6), Cl1–Ni1–Cl2 = 170.5(2), N1–Ni1–N3 = 145.61(2), Cl3–Co2–Cl4 = 108.08(2), N4–Co2–N6 = 153.08(1).

2.3 Catalytic behavior towards ethylene oligomerization/polymerization

The mononuclear Co complexes Co1–Co5 and Co–Ni heterometallic complexes Co/Ni1–Co/Ni5 were systematically investigated for their effect on ethylene oligomerization/polymerization in the presence of MMAO as cocatalyst. The catalytic activity and the distribution of the oligomers were studied in detail at various aluminium (Al)/Co molar ratios and polymerization temperatures. All the results are summarized in Table 1.

Table 1 Ethylene oligomerization/polymerization by Co1–Co5 or Co/Ni1–Co/Ni5 in the presence of MMAO^a

Entry	Complex	Al/M	T (°C)	Oligomers		Polyethylene (PE)
				Act.^b	α-O^c (%)	Act.^b	PE (wt%)
a General conditions: 2.0 μmol of complex; ethylene pressure: 10 atm; polymerization time: 30 min; 100 mL of toluene as solvent.b 10^6 g mol^−1 (metal) h^−1.c Determined by GC.
1	Co4	500	30	1.0	>99	0.10	9
2	Co4	1000	30	3.8	>99	0.47	11
3	Co4	1500	30	3.2	>99	0.48	13
4	Co4	2000	30	1.2	>99	0.40	25
5	Co4	1000	20	2.8	>99	0.35	11
6	Co4	1000	40	2.9	>99	0.54	16
7	Co4	1000	50	1.5	>99	0.41	22
8	Co1	1000	30	1.4	>99	1.08	44
9	Co2	1000	30	2.1	>99	0.82	28
10	Co3	1000	30	0.8	>99	0.20	20
11	Co5	1000	30	8.9	>99	0.96	10
12	Co/Ni4	500	30	1.6	>99	0.37	19
13	Co/Ni4	1000	30	2.1	>99	0.51	20
14	Co/Ni4	1500	30	2.8	>99	0.36	11
15	Co/Ni4	2000	30	0.3	>98	0.22	42
16	Co/Ni4	1000	20	0.7	>99	0.44	39
17	Co/Ni4	1000	40	1.4	>99	0.36	20
18	Co/Ni4	1000	50	1.0	>99	0.42	30
19	Co/Ni1	1500	30	0.2	>99	0.12	38
20	Co/Ni2	1500	30	0.2	>99	0.12	38
21	Co/Ni3	1500	30	0.2	>99	0.19	49
22	Co/Ni5	1500	30	0.4	>99	0.12	23

---

In the presence of MMAO, Co4 and Co/Ni4 were selected for optimization of the catalytic parameters at various polymerization conditions. With the reaction temperature fixed at 30 °C, variation of the molar ratio of Al/M from 500 to 2000 was investigated at 10 atm of ethylene pressure (entries 1–4 and 12–15, Table 1). As shown in Fig. 2, relatively higher oligomerization and polymerization activities were obtained with an Al/Co molar ratio of 1000/1 by using the Co4/MMAO catalytic system. However, Co/Ni4 displayed higher oligomerization activity when the Al/M molar ratio was fixed at 1500 and there was a higher polymerization activity when the Al/M molar ratio was fixed at 1000. The heteronuclear complex Co/Ni4 exhibited lower oligomerization activity than Co4 if the Al/M molar ratio was fixed between 500 and 1500. These results could be explained by the lower catalytic activity of the Ni center than the Co center and the frustratingly synergic effect of the Ni center on the Co center.

Fig. 2 Ethylene oligomerization/polymerization activity using Co4 or Co/Ni4 at various Al/M molar ratios.

In addition to the effect of the Al/M molar ratio on the catalytic activity, the oligomer distribution was also influenced by the Al/M molar ratio. As shown in Fig. 3, the molar fraction of C₄ and C₆ in the oligomers produced by the Co4/MMAO catalytic system decreased and then increased when the Al/M molar ratio was increased from 500 to 1000. However, the increase of the Al/M molar ratio from 500 to 1000 led to an obvious increased molar fraction of C₄ and C₆ in the oligomers produced using Co/Ni4 in the presence of MMAO. The C₄ and C₆ took 42.8 mol% when the Al/M molar ratio was fixed at 1500. Compared to Co4, where more C₄ and C₆ were produced by Co/Ni4, which could be attributed to the active species formed by the Ni atom. The distribution of oligomers ranged from C₈ to C₃₀ was also affected by the Al/M molar ratio. As shown in Fig. 4(a), the distribution of oligomers produced using Co4 matched a Poisson distribution when the Al/M molar ratio was fixed at 1000 and 1500. This means that chain transfer to aluminum constitutes the major transfer mechanism, and the exchange of the growing polymer chains between the transition metal and the aluminum centers is very fast and reversible.^13a At the Al/M molar ratio of 500 and 2000, the distribution did not follow a Poisson distribution which could be explained that there was more than one active species at a lower or higher amount of cocatalyst. Similarly to oligomers produced using Co4, the distribution of oligomers produced using Co/Ni4 at the Al/M molar ratio ranging from 500 to 1500 also matched a Poisson distribution, as shown in Fig. 4(b). According to previous reports, Fe complexes for ethylene oligomerization in the presence of ZnEt₂ as chain transfer reagent, the peak maximum of the Poisson distribution shifts to a higher carbon number (n) with a decreased amount of chain transfer reagent.¹³ However, this trend was not obvious in this catalytic system when the Al/M molar ratio decreased [trimethylaluminium (AlMe₃) in the cocatalyst was considered as the chain transfer reagent].

Fig. 3 Molar fraction of C₄ and C₆ in the oligomers produced using Co4 or the Co/Ni4/MMAO catalytic system at various Al/M molar ratios.

Fig. 4 Distribution of oligomers (C₈–C₃₀) produced using Co4 (a) and Co/Ni4 (b) at various Al/M molar ratios.

The reaction temperature also played a significant role in the catalytic activity and α-olefin distribution. With the Al/Co molar ratio fixed at 1000, ethylene oligomerization/polymerization at varied reaction temperatures from 20 °C to 50 °C was investigated (entries 2, 5–7 in Table 1 for Co4 and 13, 16–18 in Table 1 for Co/Ni4). As shown in Fig. 5, oligomerization showed its best activity at 30 °C and then decreased because of the instability of the active species (decomposition), together with low ethylene solubility in the reaction solution at higher temperatures. Thus, oligomerization activities as high as 3.8 × 10⁶ g mol⁻¹ (metal) h⁻¹ for Co4 and 2.1 × 10⁶ g mol⁻¹ (metal) h⁻¹ for Co/Ni4 were obtained at the polymerization temperature of 30 °C. The polymerization activities of Co4 and Co/Ni4 were not obviously influenced by the variation of polymerization temperatures. Compared to Co4, the heterometallic complex Co/Ni4 displayed lower oligomerization activity at the polymerization temperatures ranged from 20 to 50 °C. The oligomer distribution was also influenced by the polymerization temperature. Greater production of lower olefins was commonly achieved by increasing the polymerization temperature because of the faster β-H elimination.¹³ However, such a trend did not happen with the current catalytic system, for example of the Co4/MMAO system. As shown in Fig. 6, the minimal C₄ and C₆ were produced by the Co4/MMAO system at 40 °C. The maximum of the oligomer distributions did not shift to the lower carbon numbers as the reaction temperature was increased from 30 to 50 °C, although the shift was observable when the temperature was increased from 20 to 30 °C [as shown in Fig. 7(a)]. More interestingly and importantly, more higher-order oligomers were produced at the higher temperature between 20 and 50 °C by using the Co/Ni4/MMAO system. As shown in Fig. 6 and 7(b), the amount of C₄ and C₆ decreased and the maximum of the oligomer distributions shifted to a higher carbon number with a higher temperature. All of these results indicated the effect of the Ni center on the Co center.

Fig. 5 Ethylene oligomerization/polymerization activity using Co4 or Co/Ni4 at various polymerization temperatures.

Fig. 6 Molar fraction of C₄ and C₆ in the oligomers produced using Co4 or a Co/Ni4/MMAO catalytic system at various polymerization temperatures.

Fig. 7 Distribution of oligomers (C₈–C₃₀) produced using Co4 (a) and Co/Ni4 (b) at various polymerization temperatures.

The coordination environment greatly influences the catalytic behavior of the complex catalysts. In this research, all the mononuclear pre-catalysts Co1–Co5 were evaluated for ethylene oligomerization under the optimum reaction conditions of Al/Co equals 2000 at the temperature of 30 °C (entries 2, 8–11 in Table 1). As shown in Fig. 8, the polymerization activity decreased in the order of Co1 > Co2 > Co3 because of the steric bulkiness of the ligands. However, the oligomerization activity decreased in the order of Co2 > Co1 > Co3, which may be attributed to the steric effect and electronic effect of substitutes at the ortho-position of the aromatic ring. The introduction of a methyl group at the para-position of the aromatic ring could obviously increase the oligomerization activity. All these results indicated that the electronic donating group or less steric bulkiness resulted in higher oligomerization activity in this catalytic system. However, the polymerization activity was not obviously affected by the introduction of a methyl group at the para-position of the aromatic ring. The distributions of the oligomers produced using the monocobalt complexes Co1–Co5 were also affected by the structure of ligands. As shown in Fig. 9, the fraction of C₄ and C₆ increased in the order of Co3 > Co2 > Co1 which indicated that the steric bulky groups at the ortho-position of the aromatic ring led to the formation of shorter α-olefins. This trend could also be observed in the distributions of oligomers from C₈ to C₃₀ shown in Fig. 10. The introduction of a methyl group at the para-position of the aromatic ring could increase the fraction of the longer α-olefins, which could be observed from the decrease of C₄ and C₆ in Fig. 9 and the shift of the maximum of the oligomer distributions in Fig. 10. Compared to Co/Ni4, Co/Ni1–Co/Ni3 and Co/Ni5 displayed a much lower ethylene oligomerization activity because of the electronic effect and steric bulky effect of the ligand. It is worthwhile to note that the heteronuclear complexes Co/Ni1–Co/Ni3 and Co/Ni5 exhibited a much lower oligomerization activity than their mononuclear analogues Co1–Co3 and Co5 because of the frustratingly synergic effects. When compared with typically N,N,N-tridenate Co precatalysts,¹⁴ the current precatalysts showed lower activities, however, the oligomers' distribution distinctly follows the Poisson rules instead of Schluz–Flory rules observed within ethylene oligomerization using most Co catalytic systems.

Fig. 8 Ethylene oligomerization/polymerization activity using the Co1–Co5/MMAO catalytic system.

Fig. 9 Molar fraction of C₄ and C₆ in the oligomers produced using the Co1–Co5/MMAO catalytic system.

Fig. 10 Distribution of oligomers (C₈–C₃₀) produced using the Co1–Co5/MMAO catalytic system.

3. Conclusions

A series of heterometallic Co–Ni complexes ligated using 2,4-di(6-aryliminopyridin-2-yl)-1H-benzazepines has been synthesized and fully characterized. The free C=N bond stretching frequency was clearly detected in the heteronuclear complexes using FT-IR spectroscopy (at about 1620 cm⁻¹). MALDI-TOF mass spectra of these complexes was used to further confirm the complexes. All mono and binuclear complexes showed good catalytic activities towards ethylene oligomerization/polymerization, however, mono-nuclear complexes showed higher activities, indicating the dominant behavior of the active species from the cobalt ion. Therefore, the introduction of the nickel ion resulted in a negative influence on the catalytic performance, which is described as the frustratingly synergic effect of the heterometallic precatalyst. In addition, it was also the first case of late transition precatalysts oligomerizing ethylene without the presence of ZnEt₂ reagent, following the Poisson distribution. However, the introduction of the nickel ion significantly affected the distributions of oligomers with more lower order oligomers by the heteronuclear complexes Co/Ni1–Co/Ni5.

4. Experimental section

4.1 General considerations

All manipulations of air and/or moisture sensitive compounds were carried out under a nitrogen atmosphere using standard Schlenk techniques. Toluene was refluxed over sodium–benzophenone and distilled under nitrogen prior to use. Modified MMAO (1.93 M in heptane, 3A) was purchased from the Akzo Nobel Corporation. High purity ethylene was purchased from the Beijing Yanshan Petrochemical Company and used as received. 2,6-Dimethylaniline, 2,6-diethylaniline, 2,6-diisopropylaniline, 2,4,6-trimethylaniline and 2,6-diethyl-4-methylaniline were purchased from AstaTech (Chengdu) BioPharmaceutical Corporation. Nuclear magnetic resonance spectra were recorded on a Bruker DMX 400 MHz instrument at ambient temperature using trimethylsilane as an internal standard. FT-IR spectra were recorded on a PerkinElmer System 2000 FT-IR spectrometer. Elemental analysis was carried out using an HP-MOD 1106 microanalyzer. Gas chromatography (GC) analysis was performed on an Agilent Technologies 7890A gas chromatograph equipped with a flame ionization detector and a 30 m column (0.2 mm id, 0.25 mm film thickness). MALDI-TOF spectra were recorded on a Bruker autoflex III, using CCA as the substrate.

4.2 Synthesis of complexes

Mononuclear cobalt complex Co1–Co5. The detailed synthesis of Co1 is as follows: the mixture of the ligand L1 (0.21 g) and cobalt chloride (0.04 g) was dissolved in a mixture of DCM (5 mL) and ethanol (5 mL), and then the solution was continually stirred for 24 h. The brown powder (0.198 g) obtained was collected after condensation and washing with diethyl ether with a yield of 79%. FT-IR: 3252.2, 1636.4 (ν_C=N), 1618.5 (ν_C=N), 1584.3, 1466.1, 1366.2, 1209.1, 813.7, 757.6. MS (MALDI-TOF, m/z): calcd 734.62, found 663.2 [M − 2Cl]⁺.

Co2. Brown powder, 55% yield. FT-IR: 3251.4, 1632.4 (ν_C=N), 1619.6 (ν_C=N), 1584.3, 1466.0, 1365.7, 1208.9, 814.1, 753.5. MS (MALDI-TOF, m/z): calcd 790.73, found 673.1 [M − 2Cl + CCA]⁺.

Co3. Brown powder, 65% yield. FT-IR: 3273.8, 1644.9 (ν_C=N), 1622.4 (ν_C=N), 1584.3, 1464.6, 1365.6, 1199.6, 814.5, 766.9. MS (MALDI-TOF, m/z): calcd 846.84, found 774.4 [M − 2Cl]⁺.

Co4. Brown powder, 55% yield. FT-IR: 3248.6, 1619.6 (ν_C=N), 1584.7, 1470.3, 1367.3, 1216.9, 1022.8, 814.1, 749.5. MS (MALDI-TOF, m/z): calcd 762.68, found 690.1 [M − 2Cl]⁺.

Co5. Brown powder, 55% yield. FT-IR: 3248.6, 1622.4 (ν_C=N), 1585.8, 1468.7, 1363.4, 1216.4, 1022.3, 815.1, 751.1. MS (MALDI-TOF, m/z): calcd 818.78, found 687.1 [M − 2Cl − Co]⁺.

Heteronuclear complexes Co/Ni1–Co/Ni5. The detailed synthesis of Co/Ni1 is as follows: the mononuclear complex Co1 (0.10 g) was firstly dissolved in 10 mL ethanol, and then NiCl₂·6H₂O (0.036 g) was added to the solution. The mixture was continually stirred for 12 h. After condensation and addition of diethyl ether, the yellow powder was collected by filtration (0.118 g, 81% yield). FT-IR: 3358.5, 1618.8 (ν_C=N), 1585.0, 1467.4, 1370.6, 1209.8, 814.5, 770.7. MS (MALDI-TOF, m/z): calcd 864.22, found 663.1 [M − 4Cl − Ni]⁺, 720.0 [M − 4Cl]⁺, 656.0 [M − 3Cl]⁺.

Co/Ni2. Yellow powder, 82% yield. FT-IR: 3237.3, 1619.6 (ν_C=N), 1584.6, 1464.2, 1366.3, 1200.7, 812.9, 748.7. MS (MALDI-TOF, m/z): calcd 920.33, found 755.28 [M − 3Cl − Ni]⁺.

Co/Ni3. Yellow powder, 77% yield. FT-IR: 3359.8, 1618.3 (ν_C=N), 1585.0, 1464.1, 1367.6, 1201.6, 801.5, 767.2. MS (MALDI-TOF, m/z): calcd 976.44, found 773.1 [M − 4Cl − Ni]⁺, 830.1[M − 4Cl]⁺, 867.0 [M − 3Cl]⁺.

Co/Ni4. Yellow powder, 76% yield. FT-IR: 3357.7, 1614.0 (ν_C=N), 1587.3, 1467.4, 1366.5, 1216.6, 814.8, 748.1. MS (MALDI-TOF, m/z): calcd 892.28, found 751.9 [M − 4Cl]⁺.

Co/Ni5. Yellow powder, 83% yield. FT-IR: 3331.7, 1616.8 (ν_C=N), 1584.3, 1461.3, 1366.1, 1213.4, 814.1, 750.6. MS (MALDI-TOF, m/z): calcd 948.38, found 687.1 [M − 4Cl − Ni − Co]⁺.

4.3 X-ray crystallographic study

The XRD study was conducted using graphite-monochromatic Mo-Kα radiation (λ = 0.71073 Å) at 293(2) K, and cell parameters were obtained using global refinement of the positions of all the collected reflections. Intensities were corrected for Lorentz and polarization effects and empirical absorption. The structures were solved using direct methods and refined using full matrix least squares on F². All the hydrogen atoms were placed in the calculated positions. Using the SHELXL-97 package,¹⁵ structure solution and refinement was performed. Details of the X-ray structure determinations and refinements are given in Table 2.

Table 2 Crystal data and structure refinement details for Co/Ni3

Empirical formula	C51H62N6CoNiCl4	D calcd (g cm^−3)	1.102
Formula weight	1176.31	μ/mm^−1	1.037
Temperature	293(2) K	F(000)	1218
λ/Å	0.71073	Crystal size/mm	0.33 × 0.16 × 0.11
Crystal system	Triclinic	θ range (°)	2.37–25.01
Space group	P^−1	Limiting indices	−12 ≤ h ≤ 13
			−19 ≤ k ≤ 19
			−19 ≤ l ≤ 19
a/Å	11.080(2)	No. of rflns collected	8457
b/Å	16.393(3)	No. unique rflns [R(int)]	11 503(0.1292)
c/Å	16.352(3)	Completeness to θ (%)	99.0%
α (°)	104.07(3)	Data/restraints/params	8457/0/625
β (°)	96.01(3)	Goodness of fit on F^2	1.152
γ (°)	94.14(3)	Final R indices [I > 2σ(I)]	R1 = 0.2290
			wR2 = 0.3963
V/Å^−3	2850.6(1)	R indices (all data)	R1 = 0.1514
			wR2 = 0.3420
Z	2	Largest diff peak and hole/e Å^−3	0.343 and −0.186

---

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. U1362204).

Notes and references

1. P. Buchwalter, J. Roseé and P. Braunstein, Chem. Rev., 2015, 115, 28.
2. (a) M. Delferro and T. J. Marks, Chem. Rev., 2011, 111, 2450 and references therein; (b) J. P. McInnis, M. Delferro and T. J. Marks, Acc. Chem. Res., 2014, 47, 2545.
3. (a) H. K. Luo and H. Schumann, J. Mol. Catal. A: Chem., 2005, 227, 153; (b) S. Jie, D. Zhang, T. Zhang, W.-H. Sun, J. Chen, Q. Ren, D. Liu, G. Zheng and W. Chen, J. Organomet. Chem., 2005, 690, 1739; (c) J. Yu, Y. Zeng, W. Huang, X. Hao and W.-H. Sun, Dalton Trans., 2011, 40, 8436–8443; (d) X. Hou, Z. Cai, X. Chen, L. Wang, C. Redshaw and W.-H. Sun, Dalton Trans., 2012, 41, 1617–1623; (e) Z. Sun, E. Yue, M. Qu, I. V. Oleynik, I. I. Oleynik, K. Li, T. Liang, W. Zhang and W.-H. Sun, Inorg. Chem. Front., 2015, 2, 223–227; (f) J. Yu, X. Hu, Y. Zeng, L. Zhang, C. Ni, X. Hao and W.-H. Sun, New J. Chem., 2011, 35, 178–183; (g) W. Chai, J. Yu, L. Wang, X. Hu, C. Redshaw and W.-H. Sun, Inorg. Chim. Acta, 2012, 385, 21–26.
4. (a) S. Sujith, D. J. Joe, S. J. Na, Y. W. Park, C. H. Chow and B. Y. Lee, Macromolecules, 2005, 38, 10027; (b) T. Hu, Y. G. Li, Y. S. Li and N. H. Hu, J. Mol. Catal. A: Chem., 2006, 253, 155; (c) B. A. Rodriguez, M. Delferro and T. J. Marks, Organometallics, 2008, 27, 2166; (d) M. R. Radlauer, M. W. Day and T. Agapie, J. Am. Chem. Soc., 2012, 134, 1478; (e) M. R. Radlauer, A. K. Buckley, L. M. Henling and T. Agapie, J. Am. Chem. Soc., 2013, 135, 3784; (f) D. Shu, A. R. Mouat, C. J. Stephenson, A. M. Invergo, M. Delferro and T. J. Marks, ACS Macro Lett., 2015, 4, 1297.
5. (a) A. Tomov and K. Kurtev, J. Mol. Catal. A: Chem., 1995, 103, 95; (b) K. Kurtev and A. Tomov, J. Mol. Catal., 1994, 88, 141.
6. (a) Z. J. Zheng, J. Chen and Y. S. Li, J. Organomet. Chem., 2004, 689, 3040; (b) J. Y. Liu, Y. S. Li, J. Y. Liu and Z. S. Li, Macromolecules, 2005, 38, 255.
7. (a) P. Barbaro, C. Bianchini, G. Giambastiani, I. G. Rios, A. Meli, W. Oberhauser, A. Segarra, M. L. Sorace and A. Toti, Organometallics, 2007, 26, 4639; (b) L. C. Wang and J. Q. Sun, Inorg. Chim. Acta, 2008, 361, 1843; (c) Q. Xing, T. Zhao, Y. Qiao, L. Wang, C. Redshaw and W.-H. Sun, RSC Adv., 2013, 3, 26184; (d) D. Takeuchi, S. Takano, Y. Takeuchi and K. Osakada, Organometallics, 2014, 33, 5316; (e) Q. Xing, T. Zhao, S. Du, W. Yang, T. Liang, C. Redshaw and W.-H. Sun, Organometallics, 2014, 33, 1382.
8. (a) S. Zhang, I. Vystorop, Z. Tang and W.-H. Sun, Organometallics, 2007, 26, 2456; (b) S. Zhang, W. H. Sun, X. Kuang, I. Vystorop and J. Yi, J. Organomet. Chem., 2007, 692, 5307; (c) P. Barbaro, C. Bianchini, G. Giambastiani, I. G. Rios, A. Meli, W. Oberhauser, A. M. Segarra, L. Sorace and A. Toti, Organometallics, 2007, 26, 4639; (d) A. P. Armitage, Y. D. M. Champouret, H. Grigoli, J. D. A. Pelletier, K. Singh and G. A. Solan, Eur. J. Inorg. Chem., 2008, 4597; (e) W.-H. Sun, Q. Xing, J. Yu, E. Novikova, W. Zhao, X. Tang, T. Liang and C. Redshaw, Organometallics, 2013, 32, 2309.
9. J. Kuwabara, D. Takeuchi and K. Osakada, Chem. Commun., 2006, 3815.
10. M. Tanabiki, K. Tsuchiya, Y. Motoyama and H. Nagashima, Chem. Commun., 2005, 3409.
11. T. Sun, Q. Wang and Z. Fan, Polymer, 2010, 51, 3091.
12. V. C. Gibson, C. Redshaw and G. A. Solan, Chem. Rev., 2007, 107, 1745.
13. (a) G. J. P. Britovsek, S. A. Cohen, V. C. Gibson, P. J. Maddox and M. Meurs, Angew. Chem., Int. Ed., 2002, 41, 489; (b) G. J. P. Britovsek, S. A. Cohen, V. C. Gibson and M. Meurs, J. Am. Chem. Soc., 2004, 126, 10701; (c) M. Meurs, G. J. P. Britovsek, V. C. Gibson and S. A. Cohen, J. Am. Chem. Soc., 2005, 127, 9913.
14. (a) B. L. Small, M. Brookhart and A. M. A. Bennett, J. Am. Chem. Soc., 1998, 120, 4049; (b) G. P. J. Britovsek, V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. J. McTavish, G. A. Solan, A. J. P. White and D. J. Williams, Chem. Commun., 1998, 849; (c) R. Gao, Y. Li, F. Wang, W.-H. Sun, C. Redshaw and M. Bochmann, J. Mol. Catal. A: Chem., 2009, 309, 166; (d) L. Xiao, R. Gao, M. Zhang, Y. Li, X. Cao and W.-H. Sun, Organometallics, 2009, 28, 2225; (e) M. Zhang, R. Gao, X. Hao and W.-H. Sun, J. Organomet. Chem., 2008, 693, 3867; (f) S. Jie, S. Zhang and W.-H. Sun, Eur. J. Inorg. Chem., 2007, 5584.
15. G. M. Sheldrick, SHELXL-97, Program for refinement of crystal structures, University of Göttingen, Germany, 1997.

---

Footnotes

† CCDC 1477337. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra13048h

‡ Present address: State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.

---