Synthesis, mechanism and ethylene polymerization catalysis of Ge(IV), Sn(II) and Zr(IV) complexes derived from substituted β-diketiminates

Abstract

Insertion of LiCH(SiMe₃)₂ into the CN bond of the appropriate nitriles RCN afforded dimeric β-diketiminato lithium complexes [Li{N(SiMe₃)C(R)C(H)C(R′)N(SiMe₃)}]₂ (1a, R = R′ = NMe₂; 1b, R = Bu^t, R′ = o-C₅H₄N). Lithium salt 1a was used as a precursor to react with SnCl₂ and GeCl₄, respectively, and complexes [ClSn{N(SiMe₃)C(NMe₂)C(H)C(NMe₂)N(SiMe₃)}] (2) and [Cl₂Ge{NC(NMe₂)C(H)C(NMe₂)N(GeCl₃)}] (3) were obtained in good yields. By β-diketiminato lithium 1b ligand transfer, the cyclo-1,3-diazasilane heterocyclic complex (4) was prepared using 1b and ZrCl₄. Unexpectedly, the chelating β-diketiminato backbone in 3 acts as a dianionic ligand, whereas in 4, the ligand acts as a neutral cyclo-1,3-diazasilane heterocyclic ring to coordinate with the Zr center. The X-ray structures of 2–4 are presented, and reaction pathways for each complex are proposed. Upon activation with methylaluminoxane, complex 4 exhibits good activity for ethylene polymerization.

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Introduction

Metal complexes supported by monoanionic β-diketiminato ligands have been widely explored¹ mainly due to the modification in steric and electronic demands.² The steric bulk of β-diketiminato ligands can be easily tuned by substituents on the nitrogen atoms or on the carbon framework. However, the variation of substituents attached to the carbon backbone of the ligands is rather limited.³ Thus, modification of the ligand skeleton can provide an opportunity to change their steric and electronic properties by coordination chemistry. In our former publications, we described the synthesis and structures of the β-diketiminato lithium compounds, in which the β-diketiminato ligands were prepared via insertion of various nitriles into the Li–C bond of LiCH(SiMe₃)₂.^4–6 These β-diketiminato lithium compounds were ligand-transfer reagents when reacted with metal halides.^7,8

In this paper, we report the insertion products [Li{N(SiMe₃)C(R)C(H)C(R′)N(SiMe₃)}]₂ (1a, R = R′ = NMe₂; 1b, R = Bu^t, R′ = o-C₅H₄N) via LiCH(SiMe₃)₂ with nitriles,^4,5 were used as ligand transfer reagents to react with metal chlorides. The precursor complexes 1a reacted with SnCl₂ and GeCl₄, respectively, to provide [ClSn{N(SiMe₃)C(NMe₂)C(H)C(NMe₂)N(SiMe₃)}] (2) and [Cl₂Ge{NC(NMe₂)C(H)C(NMe₂)N(GeCl₃)}] (3). The reaction of 1b with ZrCl₄ afforded a cyclo-1,3-diazasilane Zr complex (4). Interestingly, complex 3 contains a novel dianionic β-diketiminato ligand and 4 has a neutral cyclo-1,3-diazasilane heterocyclic ring, which is a new type of stable silicon compound. Complex 4 can initiate ethylene polymerization. Herein, the detailed investigations and discussions are described.

Results and discussion

Synthesis and characterization of complexes 2 and 3

The β-diketiminato lithium salt (1a) was synthesized following the procedure reported in our previous publication.⁴ The reaction mechanism involves two consecutive nucleophilic attacks on a nitrile molecule, and each one is followed by a 1,3-shift of a trimethylsilyl group. Reaction of SnCl₂ and GeCl₄ with an equivalent of 1a in diethyl ether at −78 °C afforded the corresponding complex 2 (86%) as a white solid and 3 (65%) as a red solid, respectively. Complexes 2 and 3 are soluble in THF and Et₂O but show poor solubility in hexanes (Scheme 1).

Scheme 1 Synthetic pathway of complexes 2 and 3.

We noticed that the reaction of 1a with GeCl₄ afforded an unanticipated β-diketiminate 3, in which the end groups at the nitrogen atoms are not trimethylsilyl substituents. It was suggested that the silyl group is quite labile in the presence of Lewis acid GeCl₄. Scheme 2 depicts a possible mechanism for the formation of 3. We hypothesized two steps to the formation of 3 from reactant 1a: (i) the Li compound 1a reacted with GeCl₄ to form the corresponding β-diketiminate 3′ via a metathesis reaction; (ii) in the presence of excess GeCl₄, an intermolecular reaction between 3′ and GeCl₄ yields 3 via elimination of 2 equiv. Me₃SiCl due to the Si–N bond being weaker than the Ge–N bond. For the elimination reaction of the chlorotrimethylsilane, it has been reported that the reaction of lithium amidinate [Me₃SiNC(Ph)N(CH₂)₃N(Me)SiMe₃]Li(THF) with TiCl₄(THF)₂ gave titanium amidinato amide dichloride complex [η²,η¹-Me₃SiNC(Ph)N(CH₂)₃NMe]TiCl₂ by the elimination of LiCl and Me₃SiCl.⁹ Our group demonstrated that lithium silylquinolylamide reacted with (MeC₅H₄)TiCl₃ to afford titanium(IV) complex [{8-(C₉H₆N)NC(NMe₂)N}Ti(MeC₅H₄)Cl]₂ via a metathesis reaction and the elimination of SiMe₃Cl.¹⁰ Apparently, in the presence of a stronger Lewis acid, the formation of a new metal–amido bond was thermodynamically favored by elimination of SiMe₃Cl.

Scheme 2 Possible mechanism for the formation of 3.

Crystals of 2 and 3 suitable for X-ray diffraction study were grown from a concentrated diethyl ether solution at −30 °C. The structures of 2 and 3, along with selected bond lengths and angles, are depicted in Fig. 1 and 2, respectively; the crystal and structural refinement data are summarized in Table 2.

Fig. 1 ORTEP (30% probability) diagram of 2. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Sn(1)–N(1) 2.154(6), Sn(1)–N(2) 2.187(6), Sn(1)–Cl(1) 2.471(2), N(1)–C(1) 1.362(9), N(2)–C(3) 1.350(9), C(1)–C(2) 1.408(9), C(2)–C(3) 1.396(9), N(1)–Sn(1)–N(2) 87.5(2), N(1)–Sn(1)–Cl(1) 95.51(17), N(2)–Sn(1)–Cl(1) 93.24(14).

Fig. 2 ORTEP (30% probability) diagram of 3. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Ge(1)–N(2) 1.765(3), Ge(1)–N(1) 1.844(3), Ge(2)–N(1) 1.838(3), N(1)–C(1) 1.371(5), N(2)–C(3) 1.297(5), C(1)–C(2) 1.329(6), C(2)–C(3) 1.472(5), N(2)–Ge(1)–N(1) 106.03(15), N(2)–Ge(1)–Cl(1) 112.23(12), N(1)–Ge(1)–Cl(1) 111.77(11), N(2)–Ge(1)–Cl(2) 112.81(12), N(1)–Ge(1)–Cl(2) 108.78(12), Cl(1)–Ge(1)–Cl(2) 105.30(5).

In complex 2, the backbone of the chelating ligand (N1C1C2C3N2) is essentially planar (mean deviation: 0.0139 Å) and the tin atom is out of the plane (1.0601 Å); whereas the skeletal atoms including Ge (N1C1C2C3N2Ge six-membered ring) in complex 3, are almost coplanar with a mean deviation of 0.0282 Å. For β-diketiminato N1C1C2C3N2 moieties: in 2, the distances of C1–C2 and C2–C3 [1.408(9) and 1.396(9) Å] are rather the same, and the distances of N1–C1 and N2–C3 [1.362(9) and 1.350(9) Å] are between the bond lengths of C–N and C=N bonds, indicating that a significant π-electron delocalization present as a η⁵ anion; in 3, the distances of C1–C2 and C2–C3 are 1.329(6) and 1.472(5) Å, and the distances of N(1)–C(1) and N(2)–C(3) are 1.371(5) and 1.297(5), which is consistent with localized β-diketiminate bonding over these atoms.

Analogues of 2 are reported in the following compounds: [HC(CMeNAr)₂]SnCl (Ar = 2,6-i-Pr₂C₆H₃),¹¹ [HC{CPhN(SiMe₃)}₂]SnCl,¹² [(Mes)₂DAP]SnCl (where [(Mes)₂DAP] = 2,4-dimethyl-N,1-N′-bis(2,4,6-trimethylphenyl)-1,5-diazapentadienyl),¹³ [{N(C₆H₃Prⁱ₂-2,6)C(H)}₂CPh]SnCl,¹⁴ which were obtained from SnCl₂ and the appropriate Li β-diketiminate. The fragment ClSnNN in 2 is similar to those analogues and the Sn–N bond lengths [2.154(6) and 2.187(6) Å] are in the normal range (2.121–2.397 Å).¹⁵

Complex 3 consists of two germanium atoms, both of them are in a distorted tetrahedral environment. It was worth noting that the distances of Ge(IV) to the amido nitrogen atom N1 [Ge(1)–N(1) = 1.844(3) and Ge(2)–N(1) = 1.838(3) Å] are longer than the distance of germanium to the imino nitrogen atom [Ge(1)–N(2) = 1.765(3) Å]; however, both of them are shorter than those of the corresponding Ge(II)–N_av in [CH{(CMe)(2,6-i-Pr₂C₆H₃N)}₂]GeCl (1.993 Å)¹⁶ or [CH{(CMe)(2,4,6-Me₃C₆H₂N)}₂]GeCl (1.993 Å).¹⁷

Synthesis and catalytic behavior of complex 4

The aza-allyl lithium starting material was obtained by the insertion of Bu^tCN into LiCH(SiMe₃)₂.^8,18–20 The synthetic procedure for zirconium complex 4 is illustrated in Scheme 3. The β-diketiminato lithium [Li{N(R)C(Bu^t)C(H)C(o-C₅H₄N)N(R)}]₂ (R = SiMe₃) (1b) is prepared from treatment of aza-allyl lithium with o-PyCN in a 1 : 1 molar ratio in diethyl ether.⁵

Scheme 3 Synthetic pathway for complex 4.

Treatment of lithium precursor 1b (ref. 5) with an equimolar amount of ZrCl₄ in toluene at −78 °C to room temperature for 24 h unexpectedly yielded the cyclo-1,3-diazasilane product (4) instead of the β-diketiminato zirconium. Zr compound 4 was isolated in good yield (59%) as an orange solid by filtration of the resulting mixture to remove insoluble residue followed by recrystallization from toluene.

The formation of the silicon heterocyclic complex 4 involved Lewis-acid assisted cleavage of a Si–C bond and the formation of a new Si–N bond. The similar reaction was also reported by Leung and co-workers, in which the reaction of 2,3-pyrazyl-linked bis(1-aza-allyl) dilithium complex [Li₂-{{N(SiMe₃)C(Bu^t)C(H)}₂C₄H₂N₂-2,3}(THF)₂]₂ with CdCl₂ afforded the silicon cyclized product .²¹ The Lewis-acid assisted Si–C bond cleavage reaction was also applied in a methyl/chlorine exchange reaction triggered by the action of GaCl₃.²² Herein, the unexpected formation of 4 in the reaction of 1b with ZrCl₄ is presumably that of an intermolecular interaction of the weak acceptor, zirconium, with the anionic imido-nitrogen leading to the cleavage of an Si–C bond and the formation of a new Si–N bond with concomitant elimination of MeLi, which is a possible pathway to form the cyclized compound 4 (Scheme 4).

Scheme 4 Plausible mechanism for the formation of 4.

The ¹H NMR spectrum of 4 shows that the silylic CH₃ protons are diastereotopic, appearing as two singlets at δ 0.05 and 0.91 ppm. As expected, the proton signals for SiMe₂ are more deshielded than SiMe₃. Likewise, the ¹³C NMR spectrum of 2 also indicates that the carbon chemical shift of SiMe₂ (δ 3.81) is substantially more deshielded than SiMe₃ (δ 3.30).

Single crystals of 4 suitable for X-ray diffraction were obtained at −30 °C after two weeks. In compound 2, the neutral ligand is coordinated to the metal in a κ²-fashion with the two nitrogen atoms from the cyclo-1,3-diazasilane and pyridyl (Fig. 3). The zirconium atom exhibits a distorted octahedral geometry furnished with two N atoms of ligand and four chlorine atoms. Both dative Zr1–N1 and Zr1–N2 bond distances of 2.328(4) and 2.283(4) Å, respectively, are comparable to those dative Zr–N interactions in bis{3-(2-pyridyl)-1-azaallyl}zirconium system [Zr{N(SiMe₃)C(Bu^t)C(H)(C₅H₄N-2)}₂Cl₂] (2.322(3) Å) and [Zr{N(SiMe₃)C(Ph)C(SiMe₃)(C₅H₄N-2)}₂Cl₂] (2.354(3) Å),²³ and pyridyl imido zirconium complexes [Zr{(2-C₅H₄N)C-(CH₃){CH₂NSi(CH₃)₂^tBu}₂(=N^DIPP)(Py)}] (Zr–N_Py = 2.315(2) Å) and [Zr{(2-C₅H₄N)C-(CH₃){CH₂NSi(CH₃)₂^tBu}₂(N^MesN₂N(Ph))}] (Zr–N_Py = 2.338(2) Å).²⁴ These dative bond distances are significantly longer than the Zr–N covalent bond in the pyridyl imido zirconium complexes (Zr–N_imido = 2.096(2) and 2.104(2) Å),²³ and amido complex (Zr–N_amido = 2.141(2)–2.231(3) Å).²² For the cyclo-1,3-diazasilane skeleton, the bond lengths of N(2)–C(6) [1.309(6) Å] and C(7)–C(8) [1.362(6) Å] are significantly shorter than N(3)–C(8) [1.407(6) Å] and C(6)–C(7) [1.441(6) Å], indicating the presence of localized C=C and C=N double bonds; a similar phenomenon is also found in .²¹

Fig. 3 ORTEP (30% probability) diagram of 4. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Zr(1)–N(1) 2.328(4), Zr(1)–N(2) 2.283(4), N(1)–C(4) 1.355(6), N(2)–C(6) 1.309(6), C(4)–C(6) 1.494(6), C(6)–C(7) 1.441(6), C(7)–C(8) 1.362(6), N(3)–C(8) 1.407(6), Si(1)–N(2) 1.810(4), Si(1)–N(3) 1.756(4), N(2)–Zr(1)–N(1) 70.25(13), Cl(1)–Zr(1)–Cl(4) 92.05(5), N(2)–Zr(1)–Cl(1) 160.33(10), N(1)–Zr(1)–Cl(3) 168.24(9), Cl(2)–Zr(1)–Cl(4) 167.43(5), N(1)–Zr(1)–Cl(1) 90.33(11), N(2)–Zr(1)–Cl(3) 98.00(11).

Compound 4 was investigated for its catalytic behavior of ethylene polymerization with methylaluminoxane (MAO) as a co-catalyst under atmospheric pressure. The results of the optimization conditions are summarized in Table 1.

Table 1 Ethylene polymerization with complex 4/MAO^a

Entry	Al/Zr	Cat. (μmol)	T (°C)	Time (h)	Yield (mg PE)	Activity^b	Tm^h (°C)	10^5Mw^i	Mw/Mn
a Conditions: complex, 5 μmol; solvent, toluene; Vtotal = 100 mL; ethylene pressure, 1 atm.b Activity in units of 10^4 g of PE (mol of Zr)^−1 h^−1 atm^−1.c The complex is ZrCl4. 5 atm of ethylene pressure.^25d The complex is ZrCl4(THF)2.^25e The complex is ZrCl4(Et2O)2.^25f The complex is Cp2Zr2Cl2.^26g The complex is dimethyl-β-IAM–ZrCl3. 6.8 atm of ethylene pressure.^27h Determined by DSC.i Determined by GPC.
1	200	5	25	0.5	43.1	1.72	138.2	8.78	3.17
2	500	5	25	0.5	64.5	2.58	138.0	10.5	3.6
3	1000	5	25	0.5	38.2	1.52	136.2	9.28	5.7
4	500	5	25	1.0	108	2.16	138.8	11.5	5.7
5	500	5	50	0.5	560	22.4	137.8	12.4	6.7
6^c	500	10	50	1.0	950	0.37	n.d.	n.d.
7^d	500	10	50	0.5	1100	22.0	140.6	12.3	5.9
8^e	500	10	50	0.5	1200	24.0	142.8	13.8	5.9
9^f	500	10	50	1.0	4500	45.8	137.5	n.d.
10^g	1000	2.0	25	1.0	560	4.51	138.1	n.d.

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At the temperature of 25 °C, with an increase of the molar ratios of Al to Zr from 200 to 1000 (entries 1–3), the catalytic ability of 4 achieved the maximum activity of 2.58 × 10⁴ g of PE (mol of Zr)⁻¹ h⁻¹ atm⁻¹ at a Al/Zr molar ratio of 500 (entry 2) and then decreased to a lower value of 1.52 × 10⁴ g of PE (mol of Zr)⁻¹ h⁻¹ atm⁻¹ at a Al/Zr molar ratio of 1000 (entry 3). At different times (0.5 to 1 h, entries 2 and 4), the yield increased with the increase of polymerization time. This behavior indicated that the catalyst had a catalytic lifetime of at least 1 h. The reaction temperature also influenced the catalytic performance significantly, the activities were increased from 2.58 × 10⁴ to 22.4 × 10⁴ g of PE (mol of Zr)⁻¹ h⁻¹ atm⁻¹ at 50 °C (entry 5). This result showed that raising the temperature could accelerate the formation of the active species.

The activity of 4 (entry 5) is about a hundred times higher than ZrCl₄ (entry 6), but comparable to those complexes of ZrCl₄ incorporating donor reagents such as ZrCl₄(THF)₂ (entry 7) or ZrCl₄(Et₂O)₂ (entry 8).²⁵ As can be noted, 4/MAO is only two times less active than metallocene pre-catalyst Cp₂ZrCl₂ (entries 5 and 9) under similar conditions;²⁶ therefore, this catalyst mixture can be described as high activity according to the Gibson classification.^27a Comparison with β-diketiminate Zr complexes, such as dimethyl-β-iminoaminate (IAM)–ZrCl₃ [4.51 × 104 g of PE (mol of Zr)⁻¹ h⁻¹ atm⁻¹, entry 10]^27b and [(2-Pyr)C(H)C(Bu^t)N(SiMe₃)]ZrCl₃ [7.50 × 10⁴ g of PE (mol of Zr)⁻¹ h⁻¹ atm⁻¹],^27a the activity of complex 4 is an order of magnitude higher than those of β-diketiminates. The PEs produced by 4/MAO have high melting temperatures in the range of 136.2–138.8 °C, typical for high-density polyethylene, which are lower than those of the polyethylenes obtained by ZrCl₄(THF)₂ and ZrCl₄(Et₂O)₂ (entries 7 and 8),²⁵ and comparable to those of the polyethylenes formed with zirconocenes (entries 9 and 10). The GPC analyses show a wide molecular weight distribution because of the formation of more than one active species in the reaction of 4 with MAO.

Conclusion

In summary, the unusual X-ray characterized crystalline Sn(II), Ge(IV) and Zr(IV) complexes have been prepared via a salt metathesis and elimination reaction. Their novelty lies in the phenomenon that a β-diketiminato ligand in each complex is very different: (i) for the Sn(II) compound, the β-diketiminato ligand is monoanionic in η⁵-fashion; (ii) for the Ge(IV) compound, the β-diketiminato ligand is dianionic with localized bonding over these atoms of backbone. And (iii) for the Zr(IV) compound, the ligand is a neutral cyclo-1,3-diazasilane heterocyclic ring, which represents a new type of silicon-bridged compound. The possible mechanistic pathways for the formation of complexes 3 and 4 have been proposed. The catalytic behavior of complex 4 was investigated in the presence of MAO as a co-catalyst, and the results showed that pre-catalyst 4 has high activity for ethylene polymerization up to 22.4 × 10⁴ g of PE (mol of Zr)⁻¹ h⁻¹.

Experimental section

Materials and procedures

All manipulations were carried out under an inert nitrogen atmosphere using standard Schlenk techniques. Solvents were dried with sodium, distilled from sodium/potassium alloy (toluene), sodium/benzophenone (diethyl ether) and stored over molecular sieves (4 Å). Deuterated C₆D₆ was dried over activated molecular sieves (4 Å). All solvents were degassed prior to use. Chemicals were purified by distillation before use. The β-diketiminato lithium [Li{N(SiMe₃)C(NMe₂)C(H)C(NMe₂)N(SiMe₃)}]₂ (1a)⁴ and [Li{N(SiMe₃)C(Bu^t)C(H)C(o-C₅H₄N)N(SiMe₃)}]₂ (1b)⁵ were prepared according to the reported procedures. ¹H and ¹³C NMR spectra were recorded on a Bruker DRX-300. Elemental analyses were carried out with a Vario EL-III instrument. The molecular weights of polyethylene were measured by a PL-GPC at 150 °C using 1,2,4-trichlorobenzene as the eluent and calibrated by polystyrene standards. Transition melting temperatures (T_m) were measured on a Perkin-Elmer DSC-7 differential scanning calorimeter, measured upon reheating the polymer sample to 180 °C at a heating rate of 20 °C min⁻¹.

[ClSn{N(SiMe₃)C(NMe₂)C(H)C(NMe₂)N(SiMe₃)}] (2). SnCl₂ (0.73 g, 3.86 mmol) was added to a solution of complex 1a (1.18 g, 3.86 mmol) in Et₂O (20 mL) at −78 °C. The resulting mixture was warmed to room temperature and stirred for a further 16 h. The resulting pale yellow solution was filtered and concentrated to approximately 10 mL. The product was isolated by crystallization from diethyl ether for 3 d at −30 °C to give colorless crystals 2. Yield: 1.51 g (86%). ¹H NMR (C₆D₆, 300 MHz): δ 4.43 (s, 1H, CH), 2.81 (s, 12H, N(CH₃)₂), 0.17 (s, 18H, Si(CH₃)₃). ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 173.3, 83.4, 41.3, −3.4. Anal. calcd for C₁₃H₃₁ClN₄Si₂Sn: C, 34.41; H, 6.89; N, 12.35. Found: C, 34.18; H, 7.17; N, 12.34.

[Cl₂Ge{NC(NMe₂)C(H)C(NMe₂)N(GeCl₃)}] (3). GeCl₄ (0.75 g, 3.5 mmol) was added to a solution of complex 1a (0.56 g, 2.3 mmol) in Et₂O (20 mL) at −78 °C. The mixture was warmed to room temperature and stirred for a further 16 h. The resulting solution was filtered and concentrated. The product was isolated by crystallization from diethyl ether for 7 d at −30 °C to give red crystals 3. Yield: 1.21 g (65%). ¹H NMR (C₆D₆, 300 MHz): δ 5.33 (s, 1H, CH), 3.30 (s, 6H, N(CH₃)₂), 2.84 (s, 6H, N(CH₃)₂). ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 170.3, 162.9, 83.4, 41.3. Anal. calcd for C₇H₁₃Cl₅Ge₂N₄: C, 17.67; H, 2.75; N, 11.78. Found: C, 17.53; H, 2.80; N, 11.69.

(4). ZrCl₄ (0.71 g, 3.03 mmol) was added to a solution of 1b (1.12 g, 3.02 mmol) in toluene at −78 °C. The mixture was warmed to room temperature and stirred for a further 24 h. Then, the solution was filtered off and concentrated. The product was isolated by crystallization from toluene for 7 d at −30 °C to give yellow crystals 4. Yield: 1.01 g (59%). ¹H NMR (C₆D₆, 300 MHz): δ 9.58 (s, 1H, o-py), 8.17 (d, 1H, J = 8.7 Hz, o-py), 7.93 (s, 1H, o-py), 7.09 (s, 1H, o-py), 2.34 (s, 1H, CH), 1.47 (s, 9H, C(CH₃)₃), 0.91 (s, 6H, Si(CH₃)₂), 0.05 (s, 9H, Si(CH₃)₃). ¹³C{¹H} NMR (C₆D₆, 75 MHz): δ 181.1, 161.5, 149.7, 138.7, 122.8, 96.8, 99.7, 98.6, 44.5, 29.4, 3.8, 3.3. Anal. calcd for C₁₇H₂₉Cl₄N₃Si₂Zr: C, 36.16; H, 5.18; N, 7.44. Found: C, 36.08; H, 5.08; N, 7.40.

General procedure for ethylene polymerization

Ethylene polymerization. A 250 mL flask was equipped with an ethylene inlet, a magnetic stirrer, and a Schlenk line. The flask was filled with 50 mL of freshly distilled toluene, MAO (10 wt% in toluene) was added, and the flask was placed in a bath at the desired polymerization temperature for 10 min. The polymerization reaction was started by adding a toluene solution of the desired catalyst precursor with a syringe. Then, the solvent toluene was added to bring the total volume of the solution to 100 mL. The polymerization was carried out for the desired time and temperature and then quenched with 5% HCl in ethanol (250 mL). The precipitated polymer was filtered and dried overnight in a vacuum oven at 50 °C.

X-ray crystallography

Data collection of 2, 3 and 4 was performed with Mo-Kα radiation (λ = 0.71073 Å) on a Bruker Smart Apex CCD diffractometer. The structures were solved by direct methods (SHELXS-97)²⁸ and refined against F² by full-matrix least squares using SHELXL-97.²⁹ All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were placed in calculated positions. Crystal data and experimental details of the structure determinations are listed in Table 2.

Table 2 Details of the X-ray structure determination of complexes 2, 3, 4

Complex	2	3	4
Formula	C13H31ClN4Si2Sn	C7H13Cl5Ge2N4	C17H29Cl4N3Si2Zr
Mw (g mol^−1)	455.75	475.64	564.63
T (K)	183(2) K	456(2) K	293(2) K
Crystal system	Monoclinic	Triclinic	Triclinic
Space group	P21/n	P1̄	P1̄
a (Å)	11.7137(17)	8.7293(16)	10.139(2)
b (Å)	15.426(2)	9.6018(18)	12.050(2)
c (Å)	11.7657(17)	10.0436(19)	12.659(3)
α (°)	90	91.651(2)	118.34(3)
β (°)	91.121(2)	98.999(2)	110.25(3)
γ (°)	90	102.452(2)	91.62(3)
V (Å^3)	2125.6(5)	810.2(3)	1241.9(4)
Z, Dcalcd (g cm^−3)	4, 1.424	2, 1.950	2, 1.510
μ (mm^−1)	1.441	4.522	0.978
F(000)	936	464	576
Reflections collected	8605	3339	5135
Independent (Rint) reflections	3697(0.0427)	2782(0.0166)	4291(0.0255)
Goodness of fit on F^2	1.015	1.010	1.048
Final R indices [I > 2σ(I)] R1, wR2	0.0517, 0.1577	0.0326, 0.0780	0.0545, 0.1120
R indices (all data) R1, wR2	0.0626, 0.1745	0.0402, 0.0803	0.0674, 0.1181
Largest diff. peak and hole [e Å^−3]	0.580 and −1.024	0.580 and −1.024	1.064 and −0.411

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Acknowledgements

We thank the National Natural Science Foundation of China (grant no. 21072120), Shanxi International Science and Technology Cooperation Program (2015081050) and Shanxi Patent Promotion Implementation Project (20161001).

References

1. (a) Y. C. Tsai, Coord. Chem. Rev., 2012, 256, 722; (b) L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem. Rev., 2002, 102, 3031.
2. P. H. M. Budzelaar, A. B. Van Oort and A. G. Orpen, Eur. J. Inorg. Chem., 1998, 1485.
3. S. Yokota, Y. Tachi, N. Nishiwaki, M. Ariga and S. Itoh, Inorg. Chem., 2001, 40, 5316.
4. X. Chen, C. X. Du, J. P. Guo, X. H. Wei and D. S. Liu, J. Organomet. Chem., 2002, 655, 89.
5. X. Chen, L. Wang, J. P. Guo, S. P. Huang and D. S. Liu, Mendeleev Commun., 2005, 4, 160.
6. X. Chen, L. Wang, S. P. Huang and D. S. Liu, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2004, 60, o473.
7. X. Chen, L. L. Guan, M. S. Eisen, H. F. Li, H. B. Tong, L. P. Zhang and D. S. Liu, Eur. J. Inorg. Chem., 2009, 3488.
8. P. B. Hitchcock, M. F. Lappert and D. S. Liu, J. Chem. Soc., Chem. Commun., 1994, 2637.
9. W. J. Meerendonk, K. Schröder, E. A. C. Brussee, A. Meetsma, B. Hessen and J. H. Teuben, Eur. J. Inorg. Chem., 2003, 427.
10. P. Wang, H. Li, X. Xue and X. Chen, Dalton Trans., 2015, 44, 4718.
11. Y. Ding, H. W. Roesky, M. Noltemeyer, H.-G. Schmidt and P. P. Power, Organometallics, 2001, 20, 1190.
12. P. B. Hitchcock, M. F. Lappert and J. R. Severn, Dalton Trans., 2004, 4193.
13. A. E. Ayers, T. M. Klapötke and H. R. V. Dias, Inorg. Chem., 2001, 40, 1000.
14. D. J. Doyle, P. B. Hitchcock, M. F. Lappert and G. Li, J. Organomet. Chem., 2009, 694, 2611.
15. C. Cui, H. W. Roesky, H. Hao, H.-G. Schmidt and M. Noltemeyer, Angew. Chem., 2000, 112, 1888 (Angew. Chem., Int. Ed., 2000, 39, 1815).
16. Y. Ding, H. W. Roesky, M. Noltemeyer and H.-G. Schmidt, Organometallics, 2001, 20, 1190.
17. A. E. Ayers, T. M. Klapötke and H. V. R. Dias, Inorg. Chem., 2001, 40, 1000.
18. P. B. Hitchcock, M. F. Lappert, W. P. Leung, D. S. Liu, T. C. W. Mak and Z. X. Wang, J. Chem. Soc., Dalton Trans., 1999, 1263.
19. M. F. Lappert and D. S. Liu, J. Organomet. Chem., 1995, 500, 203.
20. P. B. Hitchcock, M. F. Lappert, M. Layh, D. S. Liu, R. Sablong and T. Shun, J. Chem. Soc., Dalton Trans., 2000, 14, 2301.
21. W. P. Leung, W. Y. I. Queenie, T. W. Lam and T. C. W. Mak, Organometallics, 2004, 23, 1284.
22. D. Michalik, A. Schulz and A. Villinger, Inorg. Chem., 2008, 47, 11798.
23. B. J. Deelman, P. B. Hitchcock, M. F. Lappert, W. P. Leung, H. K. Lee and T. C. W. Mak, Organometallics, 1999, 18, 1444.
24. T. Gehrmann, J. L. Fillol, H. Wadepohl and L. H. Gade, Organometallics, 2012, 31, 4504.
25. A. Proto, C. Capacchione, O. Motta and F. D. Carlo, Macromolecules, 2003, 36, 5942.
26. (a) W. Kaminsky and R. Steiger, Polyhedron, 1988, 4, 2357; (b) W. Kaminsky, Macromol. Chem. Phys., 1996, 197, 3907.
27. (a) V. C. Gibson and S. K. Spitzmesser, Chem. Rev., 2003, 103, 283; (b) X. Jin and B. M. Novak, Macromolecules, 2002, 33, 6205.
28. G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 1990, 46, 467.
29. G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 2008, 64, 112.

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Footnote

† CCDC 1450544–1450546. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra11097e

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