Vanadium(V) Oxo and imido calix[8]arene complexes: synthesis, structural studies, and ethylene homo/copolymerisation capability.

Interaction of p-tert-butylcalix[8]areneH8 (L(8) H8 ) with [NaVO(OtBu)4 ] (formed in situ from VOCl3 ) afforded the complex [Na(NCMe)5 ][(VO)2 L(8) H]⋅4 MeCN (1⋅4 MeCN). Increasing [NaVO(OtBu)4 ] to 4 equiv led to [Na(NCMe)6 ]2 [(Na(VO)4 L(8) )(Na(NCMe))3 ]2 ⋅10 MeCN (2⋅10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)3 ] with L(8) H8 afforded the alkali-metal-free complex [(VO)4 L(8) (µ(3) -O)2 ] (3); solvates 3⋅3 MeCN and 3⋅3 CH2 Cl2 were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert-butoxide was added to L(8) H8 and then treated with 2 equiv of VOCl3 ; crystallisation afforded [(VO2 )2 Li6 [L(8) ](thf)2 (OtBu)2 (Et2 O)2 ]⋅Et2 O (4⋅Et2 O). Upon extraction into acetonitrile, [Li(NCMe)4 ][(VO)2 L(8) H]⋅8 MeCN (5⋅8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)3 ] and [V(Np-tolyl)(OtBu)3 ] and L(8) H8 , afforded [tBuNH3 ][{V(p-tolylN)}2 L(8) H]⋅3 1/2 MeCN (6⋅3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1, 3, and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)(-1) were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl2 ]. For copolymerisation, incorporation of propylene was 7.1-10.9 mol % (compare 10 mol % for [VO(OEt)Cl2 ]), although catalytic activities were lower than [VO(OEt)Cl2 ].

Vanadyl complexes bearing bi-dentate phenoxyimine ligands: synthesis, structural studies and ethylene polymerization capability.

Reaction of [VO(OnPr)3] with the Schiff bases 3,5-(tBu)2-2-OH-C6H2CH(N(x-OR-C6H4)) (R = Me; x = 2, L(1)H; x = 3, L(2)H; x = 4, L(3)H; R = Et (L(4)H), CF3 (L(5)H), Ph (L(6)H)) or 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2'-(2''-(OR1)C6H4)C6H4) (R = adamantyl, R(1) = Ph (L(7)H) or R = C(Me)2Ph, R(1) = Ph (L(8)H)) afforded the bis(chelate) vanadium(iv) complexes [VO(L(n))2] (n = 1 (1·2MeCN); n = 2 (2); n = 3 (3·2MeCN); n = 4 (4); n = 5 (5); n = 6 (6); n = 6, (7·1.5MeCN); n = 7, (8); n = 8, (9)); in the case of L(6)H, the oxo-bridged vanadium(v) complexes [VO(µ-O)(L(6))]2 (10) was also isolated. By contrast, interaction of 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2'-(2''-(OR1)C6H4)C6H4) (R = adamantyl, R(1) = Me (L(9)H); R = tBu, R(1) = Me (L(10)H); R = C(Me)2Ph, R(1) = Me (L(11)H)) with [VO(OnPr)3] led to the isolation of the dinuclear complexes [VO(µ-OH)(µ-OnPr)(L(n))]2 (n = 9, (·4MeCN); 10, (12); 11, (13)), respectively. The molecular structures of 1 to 13 are reported. All complexes have been screened as pre-catalysts for the polymerization of ethylene in the presence of the co-catalyst diethylaluminium chloride (DEAC) with or without ethyltrichloroacetate (ETA) present at 1 or 10 bar of ethylene. Under high pressure, all pre-catalysts exhibited high activity and afforded high molecular weight (Mw ≈ 200 000 to 675 000 g mol(-1)), linear polyethylene with activities (in the presence of ETA) in the range 4960-16 400 g mmol(-1) h(-1); at one bar, the products were generally of lower molecular weight. The use of methylaluminoxane (MAO) or modified MAO (MMAO) as co-catalyst led to trace or poor (≤110 g mmol(-1) h(-1)) activity, respectively.