Synthesis, structures and catalytic properties of chelating N,N ′-bis(silylated) 1,2-benzenediamidozirconium(IV) chlorides [and a titanium(IV) analogue] and dimethylamides 

Abstract

Chelating diamido ligands of formula [C₆H₄{N(SiMe₂X)}₂-1,2]²⁻, abbreviated as L′²⁻ (X = CH[double bond, length half m-dash]CH₂) or L²⁻ (X = Me), were used to prepare di(amido)metal(IV) chlorides [{M(Cl)L′(μ-Cl)(thf )}₂] (M = Zr 2 or Ti 3), ZrCl₂(L′) 5 and [ZrCl₂(L)(tmen)] 6 and the heteroleptic amides [{Zr(NMe₂)(L^x)(μ-NMe₂)}₂] (L^x = L′ 4 or L 7). Complexes 2 and 3 were obtained from equivalent proportions of Li₂L′ (prepared in situ from H₂L′ 1) and the appropriate metal chloride [MCl₄(thf )₂], while [Li₂(L)(tmen)₂] and ZrCl₄ furnished 6. Treatment of Zr(NMe₂)₄ with an equivalent portion of H₂L′ or H₂L gave 4 and 7, respectively. Complex 5 was obtained from 4 and Si(Cl)Me₃, and with thf yielded 2. The crystal structures of 2, 4, 6 and 7 have been determined. Compounds 2 and 4–6, unlike the less active titanium complex 3, were active catalysts with methylaluminoxane (AlMeO)_n for polymerisation of ethene and the resulting polymers were shown to have extremely high average molecular weights, as determined by viscosity measurements.

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We have a long-standing interest in the chemistry of metal and non-metal amides,¹ including those of the Group 4 metals; for example, [Ti(NMe₂)₄] was examined as an initiator of acrylonitrile polymerisation.² As an extension, we are exploring some aspects of the chemistry of complexes derived from diamido ligands. The first studies involved ligands such as A (R¹ = a primary alkyl or an unhindered aryl group), mainly in the context of derived carbene ligands [upper bond 1 start]CN(R¹)(CH₂)₂N[upper bond 1 end]R¹.³ The ligand B (R¹ = SiMe₃ = R; [≡ L²⁻]) was used to generate the compounds [Mg(L)]₂,⁴ [(SnL)₂(μ-tmen)] ⁵ and Ge(L).⁶ The related ligand B′ (≡ B with R¹ = CH₂Bu^t) having N,N ′-neopentyl, rather than SiMe₃, substituents became prominent with the discovery of the thermally stable silylene SiB′; ⁷ isoleptic Group 14 element compounds EB′ (E = C, Ge, Sn or Pb) as well as their adducts CB′·E′B′ (E′ = Si, Ge, Sn or Pb) have also been obtained.⁸ The 1,3 and 1,4 isomers of L²⁻ are being investigated; relevant to the present study are the zirconium(IV) complexes C and D and their 1,4 isomers.⁹

A recent review on new olefin polymerisation catalysts identified various types of spectator ligands, other than those of cyclopentadienyl type, many of which are nitrogen-centred.¹⁰ In the context of the present paper, Group 4 metal complexes containing diamido ligands without (as in E ¹¹ or F ¹²) or with (as in G ¹³) an additional donor site have been prominent (see also refs. 14–16), and several of them have been active polymerisation catalysts.^11–14 For example, E ¹¹ or G ¹³ with methylaluminoxane (AlMeO)_n (MAO) was a catalyst for both ethene and propene polymerisation, while F with B(C₆F₅)₃ induced the living polymerisation of hex-1-ene.¹²

A ligand B′′ of type B (R¹ = SiPrⁱ₃) has featured in the complexes [Ti(B′′)X₂] (X = Cl or Me) and [Zr(B′′)X₂] (X = OBu^t, or X₂ = B′′),¹⁶ while a ligand [L′′]²⁻ related to ligand L²⁻ has been a component of the complexes [M(L′′){η⁵-C₅H₃(SiMe₃)₂-1,3}(η³-C₃H₅)] {M = Zr or Hf; [L′′]²⁻ = [N(Ph)C(Me)[double bond, length half m-dash]C(Me)NPh]²⁻}.¹⁷ The L²⁻ ligand has also been employed in the chemistry of Ta^V,¹⁷ Mo^VI,¹⁸ and W^VI.¹⁹

Results and discussion

Our initial aim was to obtain new chelated bis(amido)-zirconium(IV) and -titanium(IV) complexes, with a view to employing them as procatalysts for alkene polymerisation. For this purpose, we first selected a ligand of type B ([C₆H₄(N{SiMe₂(CH[double bond, length half m-dash]CH₂)})₂-1,2]²⁻ ≡ [L′]²⁻), with R¹ chosen as a dimethylvinylsilyl group. The presence of a pendant vinyl (Vi) group was considered to have the potential to protect a zirconium atom site but readily be displaceable by an incoming untethered alkene. This strategy had been effective for hydrosilylation of terminal alkenes using various vinyl-silane- or -siloxy-rhodium(I), -nickel(0) and -platinum(0) catalysts.²⁰

The syntheses in good yield of a number of L′²⁻ complexes of Ti^IV and Zr^IV are summarised in Scheme 1. 1,2-Bis[dimethylvinylsilylamino]benzene 1 was obtained (step i of Scheme 1) from 1,2-diaminobenzene by successive N,N ′-dilithiation and quenching with the chlorosilane Si(Cl)Me₂Vi. The diamine 1 was converted (step ii of Scheme 1) into each of the binuclear complexes [{M(Cl)L′(μ-Cl)(thf )}₂] (M = Zr 2 or Ti 3) by treatment successively with 2LiBuⁿ and the appropriate complex [MCl₄(thf )₂]. The diamine 1 with tetrakis(dimethylamido)zirconium gave (step iii of Scheme 1) the binuclear heteroleptic zirconium(IV) amide [{Zr(NMe₂)L′(μ-NMe₂)}₂] 4, which in turn was transformed (step iv of Scheme 1) into the neutral donor-free zirconium(IV) chloride ZrCl₂(L′) 5, by reaction with (chloro)trimethylsilane. Complex 5 with tetrahydrofuran provided (step v of Scheme 1) an alternative route to the dinuclear thf adduct 2.

Scheme 1 Synthesis of compounds 1–5 (R′ = SiMe₂Vi). Reagents: i, successively 2LiBuⁿ and 2Si(Cl)Me₂Vi; ii, successively 2LiBuⁿ and [MCl₄(thf)₂]; iii, 2Zr(NMe₂)₄; iv, 4Si(Cl)Me₃; v, thf (M = Zr, 100%).

Attempts to make complex 5 directly from zirconium(IV) chloride and Li₂L′ in toluene yielded a product which from microanalytical data was assigned as being a mixture of ZrL′₂ and ZrCl₂(L′) in a ratio of 0.6∶1. This observation is consistent with the finding that ZrCl₄ and Li₂(B′′) in benzene, irrespective of stoichiometry, had yielded [Zr(B′′)₂].¹⁶

A further set of experiments relating to B-type zirconium(IV) complexes was undertaken using the ligand ([C₆H₄(NSiMe₃)₂-1,2]²⁻ ≡ L²⁻). Thus, the crystalline diamidodilithium compound [Li₂(L)(tmen)₂] ²¹ with an equivalent portion of zirconium(IV) chloride in toluene at ambient temperature yielded the mononuclear zirconium(IV) chloride 6, eqn. (1). By a procedure similar to that of step iii of Scheme 1 for the preparation of the amide 4, its isoleptic analogue [{Zr(NMe₂)L(μ-NMe₂)}₂] 7 was obtained from Zr(NMe₂)₄ and H₂L in toluene at ambient temperature, eqn. (2).

Each of the yellow-to-brown (2–6) or colourless (7) crystalline metal(IV) complexes gave satisfactory microanalyses, as did the pale yellow liquid diamine 1. The highest m/z peak in the EI mass spectrum corresponded to the monomeric molecular ion M⁺ (1), [M − 1]⁺ (2, 4 and 7) or [M − 2Cl]⁺ (6); for 5 a metal-containing fragment was not detected.

The molecular structure of the dinuclear zirconium(IV) chloride [{Zr(Cl)L′(μ-Cl)(thf )}₂] 2 is illustrated in Fig. 1. Selected geometric parameters are in Tables 1 and 2; the latter shows comparative data for the ZrC₆H₄(NR¹)₂-1,2 moiety (R¹ = SiMe₂Vi) of 2 and the related Zr(B′′) of [Zr(B′′)X₂] ¹⁶ and ZrL′′ of [Zr(L′′){η⁵-C₅H₃(SiMe₃)₂-1,3}(η³-C₃H₅)] 9 [L′′ = {N(Ph)C(Me)[double bond, length half m-dash]C(Me)N(Ph)}].¹⁷ The molecule 2 lies on a crystallographic inversion centre having similar Zr–Cl(2) and Zr–Cl(2)′ bond lengths of 2.670(2) and 2.687(2) Å [compared with 2.403(2) Å for the terminal Zr–Cl(1) bond]; the endocyclic angles at the Cl atoms are wider [99.17(6)°] than those at the Zr atoms, 80.83(6)°. Each zirconium atom is at the centre of a distorted octahedron: N(1), N(2) and O(1) are trans to Cl(2)′, Cl(2) and Cl(1), respectively; the corresponding angles subtended at the Zr atom are 167.72(13), 169.29(13) and 166.05(10)°. The [L′]²⁻ ligand is folded along the N(1) ⋯ N(2) vector. Similar folding H (as also in that of 4, 6 and 7) has previously ^16,17 been interpreted in terms of κ⁴-bonding, which however we consider to be unlikely. The vinyl groups, as in 4, are bent away from the Zr atoms.

Table 1 Some important geometric data (bond lengths in Å, angles in °) on compound 2 (see also Table 2)

Zr ⋯ Zr′	4.078(6)			Cl(1)–Zr–Cl(2)	88.29(6)	Cl(2)–Zr–Cl(2)′	80.83(6)
Zr–Cl(1)	2.403(2)	Zr–Cl(2)	2.670(2)	N(1)–Zr–Cl(1)	101.53(14)	N(1)–Zr–Cl(2)′	167.72(13)
Zr–Cl(2)′	2.687(2)	Zr–O(1)	2.249(4)	N(1)–Zr–Cl(2)	99.37(13)	N(2)–Zr–Cl(2)′	94.26(13)
N(1)–C(1)	1.430(6)	C(1)–C(2)	1.405(8)	N(2)–Zr–Cl(1)	101.35(14)	N(1)–Zr–O(1)	87.9(2)
N(2)–C(2)	1.422(7)			N(2)–Zr–Cl(2)	169.29(13)	N(2)–Zr–O(1)	89.8(2)
N(1)–Si(1)	1.740(5)	N(2)–Si(2)	1.753(5)	Zr–Cl(2)–Zr′	99.17(6)	O(1)–Zr–Cl(2)	79.96(11)
				O(1)–Zr–Cl(1)	166.05(10)	O(1)–Zr–Cl(2)′	80.85(11)

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Table 2 Some important geometric data (bond lengths in Å, angles in °) for the L²⁻, L′²⁻, B′′ or L′′²⁻ ligand in the compounds 2, 4, 6, 7, [Zr(B′′)₂] 8 ¹⁶ and [Zr(L′′){η⁵-C₅H₃(SiMe₃)₂-1,3}(η³-C₃H₅)] 9 [B′′ = B with R¹ = SiPrⁱ₃; L′′ = {N(Ph)C(Me)[double bond, length half m-dash]C(Me)N(Ph)}] ¹⁷

	2	4	6	7	8	9
a The fold of the ligand L^2−, L′^2− or L′′^2− along the N(1) ⋯ N(2) vector.
Zr–N(1)	2.053(5)	2.112(4)	2.118(6)	2.1444(14)	2.072(6)	2.105(4)
Zr–N(2)	2.044(5)	2.116(4)	2.050(6)	2.0702(13)	2.087(6)	2.100(4)
N(1)–Zr–N(2)	83.4(2)	80.4(2)	82.0(2)	81.4(5)	86.1(2)	81.5(2)
Zr–N(1)–C(1)	102.9(3)	100.4(2)	100.6(4)	98.85(4)	92.8(2)	92.9(3)
					91.6(2)
Zr–N(2)–C(2)	103.1(4)	100.2(3)	102.7(4)	98.64(9)	93.7(2)	93.4(3)
					94.8(2)
Fold angle ^a	38	43	42	49	51 (53)	60

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Fig. 1 Molecular structure of compound 2.

The molecular structure of the binuclear zirconium(IV) amide [{Zr(NMe₂)L′(μ-NMe₂)}₂] 4 is shown in Fig. 2. Selected geometric parameters, other than those of the ZrL′ moiety (see Table 2), are listed in Table 3. The central Zr(1)N(5)Zr(2)N(6) ring is puckered; the mean Zr(1 or 2)–N(5 or 6) bond lengths range from 2.263(4) to 2.369(4) Å and the endocyclic angles at N(5) or N(6) are wider (103.5 ± 1.4°) than those at Zr(1) or Zr(2), 74.0 ± 0.5°. As for 2, the vinyl groups in 4 are bent away from each of the five-co-ordinate Zr atoms, which are situated in an environment intermediate between trigonal bipyramidal (TBPY) and square pyramidal. On the basis of TBPY, the atoms N(1), N(5) and N(7) occupy the “equatorial” sites; the “axial” N(2) and N(6) atoms subtend an angle of 142.2(2)° at Zr(1). Angles at Zr(1) involving N(2) and N(5) or N(7) are 89.1(2) and 111.4(2)°, respectively, and those involving N(6) and N(7) or N(1) are 106.2(2) or 88.4(2)°, respectively. The Zr(2) environment is similar to that of Zr(1).

Table 3 Some important geometric data (bond lengths in Å, angles in °) on compound 4 (see also Table 2)

Zr(1) ⋯ Zr(2)	3.621(5)			Zr(1)–N(5)–Zr(2)	102.4(2)	Zr(1)–N(6)–Zr(2)	104.9(2)
Zr(1)–N(1)	2.112(4)	Zr(2)–N(3)	2.120(4)	N(5)–Zr(1)–N(6)	74.5(2)	N(5)–Zr(2)–N(6)	73.5(2)
Zr(1)–N(2)	2.116(4)	Zr(2)–N(4)	2.102(4)	N(1)–Zr(1)–N(2)	80.4(2)	N(3)–Zr(2)–N(4)	80.1(2)
Zr(1)–N(7)	2.021(5)	Zr(2)–N(8)	2.024(4)	N(1)–Zr(1)–N(6)	88.4(2)	N(3)–Zr(2)–N(6)	88.6(2)
Zr(1)–N(5)	2.276(4)	Zr(2)–N(5)	2.369(4)	N(2)–Zr(1)–N(5)	89.1(2)	N(4)–Zr(2)–N(5)	94.1(2)
Zr(1)–N(6)	2.304(4)	Zr(2)–N(6)	2.263(4)	N(7)–Zr(1)–N(1)	113.2(2)	N(8)–Zr(2)–N(3)	103.9(2)
N(1)–C(1)	1.409(7)	N(3)–C(15)	1.404(7)	N(7)–Zr(1)–N(2)	111.4(2)	N(8)–Zr(2)–N(4)	113.4(2)
N(2)–C(2)	1.405(7)	N(4)–C(16)	1.425(7)	N(7)–Zr(1)–N(5)	110.0(2)	N(8)–Zr(2)–N(5)	102.8(2)
N(1)–Si(1)	1.734(4)	N(2)–Si(2)	1.732(4)	N(7)–Zr(1)–N(6)	106.2(2)	N(8)–Zr(2)–N(6)	120.1(2)
N(3)–Si(3)	1.737(4)	N(4)–Si(4)	1.736(4)	N(2)–Zr(1)–N(6)	114.2(2)
C(1)–C(2)	1.426(4)	C(15)–C(16)	1.432(4)

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Fig. 2 Molecular structure of compound 4.

Related to 4 is the isoleptic complex [{Zr(NMe₂)L(μ-NMe)}₂] 7, see Fig. 3 and Tables 2 and 4. The two complexes are structurally similar except that the molecule 7 lies on an inversion centre, the midpoint of the ZrN(3)Zr′N(3)′ rhombus (cf. the puckered ring in 4), having Zr–N bond lengths of 2.294 ± 0.041 Å [compared with 2.037(2) Å for the terminal Zr–N(4) bond distance]. The endocyclic angles at the N atoms are wider at 104.24(6)° than those at the Zr atoms, 75.76(6)°. Each zirconium atom is in a pseudo-TBPY environment, the atoms N(1), N(3) and N(4) being “equatorial”; the “axial” N(2) and N(3)′ atoms subtend an angle of 152.69(5)° at Zr. Angles at Zr involving N(2) and N(3) or N(4) are 89.75(5) or 106.44(6)°, respectively and those involving N(3)′ and N(1) or N(4) are 89.22(5) or 100.78(6)°, respectively.

Table 4 Some important geometric data (bond lengths in Å, angles in °) on compound 7 (see also Table 2)

Zr–N(1)	2.0702(13)	Zr–N(3)	2.2528(14)	Zr–N(3)–Zr′	104.24(6)	N(3)–Zr–N(3)′	75.76(6)
Zr–N(2)	2.1444(14)	Zr–N(4)	2.0370(16)	N(1)–Zr–N(2)	81.14(5)
N(1)–C(1)	1.419(2)	Zr–N(3)′	2.3551(14)	N(1)–Zr–N(3)	127.05(5)	N(2)–Zr–N(3)	89.75(5)
N(2)–C(2)	1.4080(19)			N(1)–Zr–N(3)′	89.22(5)	N(2)–Zr–N(3)′	152.69(5)
N(1)–Si(1)	1.7419(14)	N(2)–Si(2)	1.7358(14)	N(1)–Zr–N(4)	115.42(7)	N(2)–Zr–N(4)	106.44(6)
Zr ⋯ Zr′	3.638(2)	C(1)–C(2)	1.430(2)	N(4)–Zr–N(3)	117.18(7)	N(4)–Zr–N(3)′	100.78(6)

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Fig. 3 Molecular structure of compound 7.

The molecular structure of the mononuclear zirconium(IV) chloride [ZrCl₂(L)(tmen)] 6 is shown in Fig. 4. Selected geometric parameters are in Tables 2 and 5. There are three independent molecules in the unit cell, each of which is closely similar and hence data for only one are here cited. The molecule has the six-co-ordinate zirconium atom in a distorted octahedral environment: N(1), N(2) and N(4) are trans to Cl(1), N(3) and Cl(2), respectively; the corresponding angles subtended at the Zr atom are 173.01(16), 165.0(2) and 156.09(15)°, respectively. The Zr–N(1 or 2) or Zr–N(3 or 4) bond distances are 2.084 ± 0.034 or 2.481 ± 0.017 Å, respectively, the latter corresponding to the Zr–N(tmen) bonds. The Zr–Cl(1) bond of 2.537(2) Å is significantly longer than Zr–Cl(2) of 2.432(2) Å. The Zr–X bonds lengths indicate that the trans-influence order is Cl⁻ > L²⁻ > tmen. The tmen bite angle at Zr, N(3)–Zr–N(4) of 71.8(2)°, and the N(2)–Zr–Cl(2) angle of 103.37(16)° deviate most markedly from the twelve idealised orthogonal angles of an octahedron; the others range from 83.06(15) [N(4)–Zr–Cl(1)] to 97.9(2)° [N(4)–Zr–N(1)].

Table 5 Some important geometric data (bond lengths in Å, angles in °) on compound 6 (see also Table 2)

Zr–Cl(1)	2.537(2)	Zr–Cl(2)	2.432(2)	Cl–Zr–Cl(2)	86.41(8)
Zr–N(1)	2.118(6)	Zr–N(3)	2.497(6)	N(1)–Zr–Cl(1)	173.01(16)	N(3)–Zr–Cl(1)	89.11(15)
Zr–N(2)	2.050(6)	Zr–N(4)	2.464(6)	N(1)–Zr–Cl(2)	95.13(17)	N(3)–Zr–Cl(2)	86.65(15)
N(1)–C(1)	1.438(9)	N(1)–Si(1)	1.753(6)	N(2)–Zr–Cl(1)	91.03(16)	N(4)–Zr–Cl(1)	83.06(15)
N(2)–C(2)	1.428(9)	N(2)–Si(2)	1.742(6)	N(2)–Zr–Cl(2)	103.37(16)	N(4)–Zr–Cl(2)	156.09(15)
C(1)–C(2)	1.412(10)			N(1)–Zr–N(2)	82.0(2)	N(2)–Zr–N(3)	165.0(2)
				N(1)–Zr–N(3)	97.8(2)	N(3)–Zr–N(4)	71.8(2)
				N(1)–Zr–N(4)	97.9(2)	N(4)–Zr–N(2)	93.3(2)

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Fig. 4 Molecular structure of compound 6.

The ¹H and ¹³C-{¹H} NMR spectra of compound 2 in aromatic solvents were more complicated than expected. Thus the ¹H NMR spectrum in C₆D₆ at 293 K displayed two sets of resonances for each of the C₆H₄, CH[double bond, length half m-dash]CH₂, and the diastereotopic SiMe₂ groups and the thf ligand, consistent with there being a major and a minor product in a 2∶1 ratio. The ²⁹Si-{¹H} NMR spectrum in toluene-d₈ showed signals at δ −3.1 and −8.6 in a ratio of 1∶2. These data are consistent with the presence in solution of two isomers or oligomers, possibly a dimer as in the solid and a monomer.

The ¹H NMR spectrum of compound 4 in C₆D₆ at 293 K likewise showed two sets of resonances, possibly due to an equilibrium as shown in eqn. (3) between a monomeric and a dimeric (solid state) complex in a 4∶1 ratio. On cooling the sample in C₆D₅CD₃ to 188 K the singlet at δ 2.52 was split into two separate signals (δ 2.54 and 2.41) in a 1∶1 ratio; these correspond to bridging and terminal NMe₂ groups that interconvert, possibly via the monomer. The coalescence temperature was 239 K, corresponding to ΔG ^‡_{239 K} = ca. 50 kJ mol⁻¹.

The ¹H NMR spectrum of complex 7 in C₆D₆ at 293 K gave only one set of resonances; the broad signal at δ 2.53 is attributed to the NMe₂ groups, although the ¹³C-{¹H} spectrum under the same conditions showed the two expected signals at δ 45.0 and 41.9 for the terminal and the bridging NMe₂ units, respectively.

Attempts to obtain a dialkyl derivative containing the Zr(L′) moiety were carried out using, in the first instance, the standard methylating reagent LiMe or Mg(Cl)Me with [{Zr(Cl)L′(μ-Cl)(thf )}₂] 2. Elemental analysis of the product was consistent with the composition Zr(L′)Me₂(thf ). The ¹H NMR spectrum in C₆D₆ revealed the absence of vinyl resonances suggesting that an intermediate Zr(L′)Me₂ complex had undergone a bis(cyclometallation); thus the product is tentatively formulated as I. Similarly, a dibenzyl complex was not obtained from the equimolar reaction between [Zr(CH₂C₆H₅)₄] and H₂L′.

Details of ethene polymerisation experiments, using compounds 2–5 activated by an excess of methylaluminoxane as catalyst, are shown in Table 6. In a typical reaction (footnote a in Table 6) a solution of metal complex (6 × 10⁻⁴ mol l⁻¹ in toluene) and MAO (500∶1 Al∶Zr ratio) at 20 °C was pressurised with ethene (2.4 bar) for 15 min. The polymerisation was quenched by addition of a methanolic hydrogen chloride (MeOH–concentrated aqueous HCl 1∶1 by volume) solution. The polymer was filtered off, washed and dried; its insolubility precluded examination by GLC, but viscosity measurements showed that the average molecular weight of the polymer was very high.

Table 6 Data for polymerisation of ethene

Entry	Catalyst/mg	Conditions	Yield of polymer/mg	Activity × 10^3/g polymer (mol cat)^−1 h^−1 bar^−1	Viscosity number/×10^3 cm^3 g^−1
a Unless otherwise stated, the Al∶Zr ratio was 500∶1, the Al being provided in the form of MAO as a 10% solution in toluene; [catalyst] = 6 × 10^−4 mol l^−1; pressure of C2H4 2.4 bar; t = 15 min. b As a, but Al∶Zr 1200∶1. c As a, but [cat] = 10^−4 mol l^−1. d As a, but pressure of C2H4 1.4 bar. e As d, but t = 6 h. f As a, but CH2Cl2–C6H5Me (6∶1).
1	2 (53)	a	1250	20.0	750
2	4 (61)	a	1020	12.7	500
3	5 (36)	a	705	14.2	450
4	3 (26)	a	26	1.1	2000
5	2 (20)	b	505	21.6
6	2 (7)	c	50	6.2
7	2 (34)	d	146	5.9
8	2 (19)	e	1700	5.4	900
9	2 (11)	f	49	3.8
10	[Zn(η^5-C5H5)2Cl2]	a	13100	266

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The new zirconium catalysts showed lower activity (entries 1–3 in Table 6) than [Zr(η⁵-C₅H₅)₂Cl₂] by an order of magnitude (entry 10) under similar conditions, but similar to those of related bis(amido)zirconium(IV) complexes; ^11,14 they were significantly more active than the titanium catalyst 3 (entry 4). The catalyst derived from [{Zr(Cl)L′(μ-Cl)(thf )}₂] 2 was next examined under changed conditions. Its catalytic activity remained relatively constant as a function of (i) time [up to 6 h; entry 8; cf. zirconocene(IV) chloride generally loses its activity after ca. 1 h] and (ii) use of an excess of MAO (entry 5); but was adversely affected by lowering (iii) the concentration of 2 (entry 6) or (iv) pressure of C₂H₄ (entry 7). Using a mixed CH₂Cl₂–C₆H₅Me solvent system (entry 9) drastically reduced the catalytic activity. Items (i)–(iv) and the high average molecular weight of the polymers are indicative of there being a low concentration of active species.

Experimental

All experiments were carried out under argon in flamed Schlenk-type glassware on a dual manifold Schlenk line. Solvents were pre-dried over sodium wire. Hydrocarbons (pentane, hexane and toluene) and thf were distilled from sodium–potassium alloy and sodium–benzophenone, respectively, and stored over potassium mirrors or molecular sieves. Deuteriated solvents (benzene-d₆, toluene-d₈ and thf-d₈) were distilled or dried on molecular sieves and degassed prior to use. n-Butyllithium in hexanes (1.6 mol dm⁻³), 1,2-diaminobenzene, MCl₄ (M = Ti or Zr), Si(Cl)Me₂(CH[double bond, length half m-dash]CH₂) and Si(Cl)Me₃ were purchased from Aldrich and used without further purification. The compounds Zr(NMe₂)₄ ²² and B(C₆F₅)₃ ²³ were prepared according to literature methods. The NMR spectra were recorded on Bruker, DPX 300 or AMX 500 instruments at 293 K unless otherwise stated, and were referenced internally (¹H and ¹³C) to residual solvent resonances or externally (²⁹Si) to SiMe₄. The IR spectra were measured on solid samples as “Nujol” mulls using a Perkin-Elmer 1720 instrument, electron impact mass spectra using a Kratos MS 80 RF instrument (M denotes the mass number of the monomeric compound). Elemental analyses were carried out by Medac Ltd, UK. Average molecular weights of polyethylene were determined by BASF (Ludwigshafen).

Preparations

C₆H₄(NH{SiMe₂(CH[double bond, length half m-dash]CH₂)})₂-1,2] (≡ H₂L′) 1. n-Butyllithium (60 cm³, 96 mmol in hexanes) was added dropwise during ca. 20 min at 0 °C to 1,2-diaminobenzene (5.40 g, 50 mmol) in thf (100 cm³). The mixture was warmed to room temperature and stirred for ca. 20 h. The resulting green suspension was cooled to 0 °C and a solution of Si(Cl)Me₂(CH[double bond, length half m-dash]CH₂) (15 cm³, 109 mmol) in thf (20 cm³) added dropwise during ca. 30 min. The mixture was refluxed for 2 h and stirred at room temperature for ca. 20 h. The solvent was removed in vacuo and pentane (100 cm³) added to give an orange solution and a white precipitate. Filtration and evaporation of the solvent from the filtrate led to an orange oil. Distillation at bp ca. 90 °C/0.5 mmHg gave pale yellow oil 1 (9.5 g, 72%). ¹H NMR (C₆D₆): δ 6.96 (m, 2 H, C₆H₄), 6.81 (m, 2 H, C₆H₄), 6.19 (dd, 2 H, ³J_HHtrans 20.0, ³J_HHcis 14.8, CH[double bond, length half m-dash]CH₂), 5.92 (dd, 2 H, ³J_HHcis 14.7, ²J_HH 4.0, CH[double bond, length half m-dash]CH₂), 5.75 (dd, 2 H, ³J_HHtrans 20.0, ²J_HH 4.0 Hz, CH[double bond, length half m-dash]CH₂), 3.05 (s, 2 H, NH), 0.18 and 0.17 (s, 12 H, SiMe₂). ¹³C-{¹H} NMR (C₆D₆): δ 138.8, 137.5, 132.8 (C₆H₄), 121.1 (C H[double bond, length half m-dash]CH₂) 120.7 (CH[double bond, length half m-dash]C H₂) and −1.8 (SiMe₂). ²⁹Si-{¹H} NMR (C₆D₆): δ −6.6. IR: 3370m [ν(N–H)], 1599m, 1584w [ν(C[double bond, length half m-dash]C)], 1251s cm⁻¹ [ν(Si–C)]. MS: m/z 276 (100, [M]⁺), 261 (17, [M − Me]⁺) and 234 (11%, [M − Me − Vi]⁺).

[{Zr(Cl)L′(μ-Cl)(thf )}₂] 2.
Procedure a. A mixture of compound 1 (0.77 g, 2.6 mmol) and LiBuⁿ (3.2 cm³ of a 1.6 mmol dm⁻³ solution in hexanes, 5.12 mmol) was added dropwise during ca. 30 min at 0 °C to a solution of [ZrCl₄(thf )₂] (1.0 g, 2.65 mmol) in thf (100 cm³). The mixture changed from colourless to deep orange. It was allowed to warm to room temperature and stirred for 20 h. Solvent was removed in vacuo and hexane (80 cm³) added. The resulting suspension was stirred for 4 h at ambient temperature and filtered. The filtrate was concentrated and cooled at −35 °C to give deep orange crystals of compound 2 (0.90 g, 67%).
Procedure b. Complex 2 (Found: C, 41.75; H, 5.80; N, 5.75. C₁₈H₃₀Cl₂N₂OSi₂Zr requires C, 42.5; H, 5.91; N, 5.51%) was obtained quantitatively by dissolving [ZrCl₂(L′)] 5 (see below) in thf and removing excess of thf in vacuo. ¹H NMR (C₆D₆): δ 7.06–6.96 (m, 5 H, C₆H₄), 6.85 (m, 1 H, C₆H₄), 6.52 (m, 2 H, CH[double bond, length half m-dash]CH₂), 6.21 (m, 1 H, CH[double bond, length half m-dash]CH₂), 6.00–5.75 (m, 6 H, CH[double bond, length half m-dash]CH₂), 4.15 (br s, 2 H, OCH₂CH₂), 3.69 (br s, 4 H, OCH₂CH₂), 1.30 (br s, 4 H, OCH₂CH₂), 1.09 (br s, 2 H, OCH₂CH₂), 0.84 (s, 6 H, SiMe₂), 0.52 (s, 6 H, SiMe₂), 0.28 (s, 3 H, SiMe₂) and 0.18 (s, 3 H, SiMe₂). ²⁹Si-{¹H} NMR (C₆D₆): δ −3.1 and −8.6. MS: m/z 436 (15, [M − 1]⁺), 386 (12, M − 1 − MeCl)⁺] and 360 (74%, [M − Ph]⁺).

[{Ti(Cl)L′(μ-Cl)(thf )}₂] 3. Deep brown crystals of complex 3 (0.66 g, 62%) (Found: C, 45.85; H, 6.22; N, 5.96. C₁₈H₃₀Cl₂N₂OSi₂Ti requires C, 46.45; H, 6.45; N, 6.02%) were obtained from the diamine 1 (0.63 g, 2.28 mmol) and LiBuⁿ (5.56 mmol) in hexanes (30 cm³) and [TiCl₄(thf )₂] (0.76 g, 2.28 mmol) at −35 °C, using a procedure similar to that of (a) for complex 2. ¹H NMR (C₅D₆CD₃): δ 6.92–6.71 (m, 8 H, C₆H₄), 6.13 (m, 4 H, CH[double bond, length half m-dash]CH₂), 6.01–5.62 (m, 8 H, CH[double bond, length half m-dash]CH₂), 3.53 (br s, 4 H, OCH₂CH₂), 3.24 (br s, 4 H, OCH₂CH₂) 1.59 (br s, 4 H, OCH₂CH₂), 1.40 (br s, 4 H, OCH₂CH₂), 1.24 (br s, 3 H, SiMe₂), 0.82 (s, 3 H, SiMe₂), 0.21, 0.19 (s, 15 H, SiMe₂), 0.14, 0.10 (s, 3 H, SiMe₂). ¹³C-{¹H} NMR (C₆D₅CD₃): δ 139.1, 133.4, 132.5, 131.9 (C₆H₄), 124.5, 120.9, 120.6, 119.8 (CH[double bond, length half m-dash]CH₂), 70.4 (OC H₂CH₂), 26.8 (OCH₂C H₂), 1.4, 0.9, 0.4, −2.1 (SiMe₂). ²⁹Si-{¹H} NMR (C₆D₅CD₃): δ −4.4 and −7.6. MS: m/z 367 (15, [M − Vi]⁺).

[{Zr(NMe₂)L′(μ-NMe₂)}₂] 4. The diamine 1 (0.72 g, 2.61 mmol) in toluene (20 cm³) was added dropwise at 0 °C during ca. 10 min to Zr(NMe₂)₄ (0.70 g, 2.62 mmol) in toluene (30 cm³). The mixture became orange. It was stirred at room temperature for ca. 20 h. The solvent was removed in vacuo and pentane (30 cm³) added. After filtration, the volume of the filtrate was reduced to ca. 5 cm³ and cooled to 4 °C. The pale yellow crystalline complex 4 (0.97 g, 82%) (Found: C, 46.7 (duplicate analyses); H, 7.36; N, 11.91. C₁₈H₃₄N₄Si₂Zr requires C, 47.6; H, 7.55; N, 12.34%) was isolated by filtration and dried in vacuo. ¹H NMR (C₅D₆CD₃): δ 7.16 (m, 4 H, C₆H₄), 6.87 (m, 4 H, C₆H₄), 6.73 (m, 1 H, C₆H₄), 6.62 (m, 1 H, C₆H₄), 6.31 (m, 4 H, CH[double bond, length half m-dash]CH₂), 6.05 (m, 1 H, CH[double bond, length half m-dash]CH₂), 5.74 (m, 8 H, CH[double bond, length half m-dash]CH₂), 5.77 (m, 2 H, CH[double bond, length half m-dash]CH₂), 2.58 (s, 6 H, NMe₂), 2.52 (s, 24 H, NMe₂), 0.30 (s, 6 H, SiMe₂), 0.27 (s, 12 H, SiMe₂) and 0.25 (s, 12 H, SiMe₂). ¹³C-{¹H} NMR (C₆D₅CD₃): δ 142.0, 137.4, 134.6, 131.0 (C₆H₄), 124.8, 122.5, 118.7, 116.1 (CH[double bond, length half m-dash]CH₂), 45.1, 42.1, 41.4 (NMe₂), 0.9, 0.4, −0.6 (SiMe₂). ²⁹Si-{¹H} NMR (C₆D₅CD₃): δ −10.8 and −18.3. MS: m/z 452 (100, [M − 1]⁺), 407 (65, [M − 2 − NMe₂]⁺) and 364 (50%, [M − 1 − 2NMe₂]⁺).

ZrCl₂(L′) 5. The zirconium(IV) amide 4 (0.85 g, 1.9 mmol) was dissolved in hexane (100 cm³), an excess of chloro(trimethyl)silane (2.4 cm³, 19 mmol) was added dropwise at room temperature and the mixture stirred overnight. A fine yellow precipitate began to appear after ca. 10 min. The precipitate was collected by filtration and washed with pentane. The residue, a yellow microcrystalline powder after recrystallisation from toluene at 4 °C, was identified as complex 5 (0.72 g, 87%) (Found: C, 38.35; H, 4.91; N, 6.99. C₁₄H₂₂Cl₂N₂Si₂Zr requires C, 38.5; H, 5.08; N, 6.41%). ¹H NMR (C₅D₆CD₃): δ 6.87 (m, 2 H, C₆H₄), 6.73 (m, 2 H, C₆H₄), 6.13 (m, 2 H, CH[double bond, length half m-dash]CH₂), 5.79 (m, 4 H, CH[double bond, length half m-dash]CH₂), 0.49 (br s, 3 H, SiMe₂), 0.19 to −0.02 (5 peaks, 9 H, SiMe₂). ¹³C-{¹H} NMR (C₆D₅CD₃): δ 138.9, 137.5, 133.9, 132.8 (C₆H₄), 121.1 (C H[double bond, length half m-dash]CH₂), 120.8 (CH[double bond, length half m-dash]C H₂), 1.4, −1.6 (SiMe₂). No ²⁹Si-{¹H} NMR signals were observed due to the low solubility of the compound in toluene. MS: m/z 276 (100, [H₂L′]⁺).

[ZrCl₂{C₆H₄(NSiMe₃)₂-1,2}(tmen)] 6. Zirconium(IV) chloride (1.17 g, 5.03 mmol) was added in portions during ca. 10 min to an orange solution of [Li₂{C₆H₄(NSiMe₃)₂-1,2}(tmen)₂] ²¹ (1.62 g, 3.26 mmol) in toluene (20 cm³). The resulting mixture initially contained a green solid, which became yellow after ca. 12 h. Volatiles were removed in vacuo. The residual brown solid was extracted into pentane (20 cm³). The extract was filtered and the filtrate evaporated in vacuo, yielding a yellow-brown solid which, upon crystallisation from toluene, gave at −30 °C yellow-brown crystals of complex 6 (1.73 g, 70%) (Found: C, 39.2; H, 7.02; N, 10.61. C₁₈H₃₈Cl₂N₄Si₂Zr requires C, 40.9; H, 7.19; N, 10.60%), mp 260–264 °C. ¹H NMR (C₆D₆): δ 7.02 (br s, 4 H, C₆H₄), 2.18 (s, 12 H, NMe), 1.73 (s, 4 H, CH₂N) and 0.53 (s, 18 H, SiMe₃). ¹³C-{¹H} NMR (C₆D₆): δ 136.8 (ipso-C), 125.4 (m-C), 123.4 (o-C), 58.4 (NMe), 50.6 (CH₂N) and 2.7 (SiMe₃). ²⁹Si-{¹H} NMR (C₆D₆): δ −2.6. MS: m/z 459 (20, [M − 2Cl]⁺), 385 (25, [M − tmen − 2Me]⁺), 315 (20, [M − tmen − 2Me − 2Cl]⁺), 281 (30), 323 (60), 197 (75), 73 (60, [SiMe₃]⁺) and 58 (100, [SiMe₂]⁺).

[Zr(NMe₂){C₆H₄(NSiMe₃)₂-1,2}(μ-NMe₂)] 7. A solution of the diamine C₆H₄(NHSiMe₃)₂-1,2 (2.76 g, 10.90 mmol) in toluene (20 cm³) was added dropwise during ca. 10 min to Zr(NMe₂)₄ (2.84 g, 10.78 mmol) in toluene (80 cm³) at 0 °C. The mixture was set aside at ambient temperature for ca. 12 h. Volatiles were removed in vacuo. The residual solid was extracted into pentane (100 cm³). The extract was filtered; concentration of the filtrate to ca. 30 cm³ yielded colourless crystals of compound 7 (4.40 g, 95%) (Found: C, 42.8; H, 7.70; N, 12.58. C₁₆H₃₄N₄Si₂Zr requires C, 41.9; H, 7.97; N, 13.04%), mp 197–199 °C. ¹H NMR (C₆D₆): δ 7.01–7.19 (m, 2 H, m-H), 6.97–7.00 (m, 2 H, o-H), 2.53 (s, 12 H, NMe₂) and 0.29 (s, 18 H, SiMe₃). ¹³C-{¹H} NMR (C₆D₆): δ 137.7 (ipso-C), 124.9 (m-C), 122.4 (o-C), 45.0 and 41.9 (NMe₂) and 2.8 (SiMe₃). ²⁹Si-{¹H} NMR (C₆D₆): δ −1.8. MS: m/z 428 (100, [M − H]⁺), 383 (90, [M − NMe₂]⁺), 368 (25, [M − NMe₂ − Me]⁺), 340 (40), 323 (30), 307 (60), 252 (30, [H₂L]⁺), 149 (20), 73 (55, [SiMe₃]⁺) and 58 (100, [SiMe₂]⁺).

Reaction of LiMe with [{Zr(Cl)L′(μ-Cl)(thf )}₂] 2. Methyllithium (4.7 cm³ of a 1.6 mmol dm⁻³ solution in diethyl ether, 7.0 mmol) was added dropwise at 0 °C during ca. 10 min to complex 2 (1.33 g, 3.53 mmol) in thf (50 cm³). The mixture, which became deep orange, was stirred at ambient temperature for ca. 48 h. Volatiles were removed in vacuo and hexane (80 cm³) was added. After filtration, the filtrate was concentrated and cooled at −25 °C. An orange amorphous solid (0.80 g) was separated and dried in vacuo. It is believed to have been a compound of composition Zr(L′)Me₂(thf ) (Found: C, 50.35; H, 7.77; N, 5.36. C₂₀H₃₆Cl₂N₂OSi₂Zr requires C, 51.4; H, 7.70; N, 5.99%). MS: the highest peak observed had m/z 276 (100%).

Crystallography

Data were collected on an Enraf-Nonius CAD4 (compounds 2, 4 and 6) or KappaCCD (7) diffractometer using monochromated Mo-Kα radiation [λ 0.71073 Å]. Crystals were either sealed in a Lindemann capillary under argon (2) or else directly mounted on the diffractometer under a stream of cold nitrogen gas. Refinement was based on all F ² using SHELXL 93 ²⁴ (2 and 4) or SHELXL 97 ²⁵ (6 and 7). Further details are in Table 7.

Table 7 Crystal data and refinement for compounds 2, 4, 6 and 7

	2	4	6	7
Formula	C36H60Cl4N4O2Si4Zr2	C36H68N8Si4Zr2	C18H38Cl2N4Si2Zr	C32H68N8Si4Zr2
M	1017.5	907.8	528.8	859.7
T/K	293(2)	173(2)	173(2)	173(2)
Crystal system	Monoclinic	Monoclinic	Monoclinic	Monoclinic
Space group	P21/n (no. 14)	P21/c (no. 14)	Cc (no. 9)	C2/c (no. 15)
a/Å	9.836(4)	18.596(11)	30.39(2)	25.7431(4)
b/Å	13.669(4)	10.248(4)	18.203(5)	10.1941(2)
c/Å	18.534(7)	25.869(13)	14.315(5)	18.7501(4)
β/°	93.90(3)	111.00(4)	102.52(4)	116.877(1)
U/Å^3	2486(2)	4603(4)	7731(6)	4389.0(1)
Z	2	4	12	4
μ/mm^−1	0.76	0.59	0.74	0.615
Unique reflections, Rint	3449, 0.03	6398, 0.05	5487	5216, 0.04
Reflections with I > 2σ(I )	2212	5575	4994	4722
R1 (I > 2σ(I ))	0.048	0.070	0.033	0.026
wR2 (all data)	0.107	0.200	0.072	0.069

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CCDC reference number 186/2264.

See http://www.rsc.org/suppdata/dt/b0/b006596j/ for crystallographic files in .cif format.

Acknowledgements

We thank the European Commission for the award of Marie Curie fellowships to P. G. M. and S. D., BASF (Ludwigshafen) for polymer evaluation and EPSRC for other support.

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Footnote

† In memoriam Ron Snaith.

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