Neutral and Cationic Group 4 Metal Compounds Containing Octamethyldibenzotetraazaannulene (Me₈taa²⁻) Ligands. Synthesis and Reactivity of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes (M = Zr, Hf; X = Cl, Hydrocarbyl, NR₂, OR)

The synthesis and reactivity of out-of-plane (Me 8 taa)MX 2 and (Me 8 taa)MX + complexes (M= Zr, Hf; X= Cl, hydrocarbyl, NR 2, OR) containing the dianionic tetraaza-macrocycle ligand octamethyldibenzotetraazaannulene (Me 8 taa 2- ) are described. The reaction of [Li(Et 2 O)] 2 [Me 8 taa] ( 1 ) with MCl 4 (THF) 2 yields (Me 8 taa)MCl 2 complexes ( 2a, M = Zr; 2b, M = Hf). Alkylation of 2a, b with LiCH 2 SiMe 3 or LiMe in hydrocarbon solvents yields (Me 8 taa)M(CH 2 SiMe 3 ) 2 ( 3a, M = Zr; 4a, M = Hf) or (Me 8 taa)MMe 2 ( 3b, M = Zr; 4b, M = Hf) complexes. Compound 3b rearranges by migration of a Me group from Zr to a Me 8 taa imine carbon in coordinating solvents. The reaction of (Me 8 taa)H 2 with the appropriate ZrR 4 compound yields (Me 8 taa)Zr(CH 2 Ph) 2 ( 3c ) and (Me 8 taa)Zr(CH 2 CMe 3 ) 2 ( 3d ). The reaction of (Me 8 taa)H 2 and Zr(NR 2 ) 4 yields (Me 8 taa)Zr(NR 2 ) 2 ( 6a, R = Me; 6b, R = Et). Spectroscopic data for (Me 8 taa)MX 2 compounds 2, 3, 4, and 6 are consistent with cis, C 2 v -symmetric structures. Dialkyl complexes 3 and 4 and bis(amide) complexes 6 react with chlorinated solvents (1,1,2,2-tetrachloroethane, CH 2 Cl 2 ) to yield 2 . Compound 6a reacts with AlMe 3 to afford the heterobimetallic μ-amido complex [(Me 8 taa)Zr(μ-NMe 2 ) 2 AlMe 2 ][AlMe 4 ] ( 8 ), which does not undergo further reaction to yield 3b . The reaction of dialkyl complexes 3 and 4a with HNR 3 + reagents yields cationic [(Me 8 taa)MR][B(C 6 F 5 ) 4 ] compounds ( 10a, M = Zr, R = η 2 -CH 2 Ph; 10b, M = Zr, R = CH 2 SiMe 3; 10c, M = Zr, R = CH 2 CMe 3; 10d, M = Hf, R = Me). These species form labile adducts with PMe 2 Ph and THF. Cation 10a polymerizes ethylene to a linear polymer with low activity, while 10d is unreactive with ethylene. 10a reacts with HOCMe 2 CH 2 CH 2 CH CH 2 to yield the mononuclear alkoxide complex (Me 8 taa)Zr(OCMe 2 CH 2 CH 2 CH CH 2 ) + ( 13 ), in which the pendant alkene is not coordinated. 10a also reacts with water or ethanol to yield binuclear complexes [{(Me 8 taa)Zr(μ-OR)} 2 ] 2+ ( 14a, R = H; 14b, R = Et). An X-ray structural analysis of 14a reveals that one of the (Me 8 taa)Zr units has an unusual inverted conformation, and NMR data suggest that 14a, b adopt similar structures in solution. 10d reacts with 2-butyne to yield the double insertion product [(Me 8 taa)Hf(CMe CMeCMe CMe 2 )] + ( 15 ) and with MeC⋮CSiMe 3 to afford [(Me 8 taa)Hf(C(SiMe 3 ) CMe 2 )] + ( 16 ), while 10a and 10b are unreactive with these alkynes. 10a and 10c react with terminal alkynes by protonolysis to afford binuclear [{(Me 8 taa)Zr(μ-C⋮CR)} 2 ] 2+ complexes ( 17a, R = Ph; 17b, R = Pr). Complex 17a reacts reversibly with PMe 3 to yield the mononuclear cation (Me 8 taa)Zr(C⋮CPh)(PMe 3 ) + ( 18a ). (Me 8 taa)MR + species are less reactive for alkene and alkyne insertion than are Cp 2 MR + species.