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Neutral and Cationic Group 4 Metal Compounds Containing Octamethyldibenzotetraazaannulene (Me8taa2-) Ligands. Synthesis and Reactivity of (Me8taa)MX2 and (Me8taa)MX+ Complexes (M = Zr, Hf; X = Cl, Hydrocarbyl, NR2, OR)

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journal contribution
posted on 1998-01-06, 00:00 authored by Alfredo Martin, Roger Uhrhammer, Thomas G. Gardner, Richard F. Jordan, Robin D. Rogers
The synthesis and reactivity of out-of-plane (Me8taa)MX2 and (Me8taa)MX+ complexes (M= Zr, Hf; X= Cl, hydrocarbyl, NR2, OR) containing the dianionic tetraaza-macrocycle ligand octamethyldibenzotetraazaannulene (Me8taa2-) are described. The reaction of [Li(Et2O)]2[Me8taa] (1) with MCl4(THF)2 yields (Me8taa)MCl2 complexes (2a, M = Zr; 2b, M = Hf). Alkylation of 2a,b with LiCH2SiMe3 or LiMe in hydrocarbon solvents yields (Me8taa)M(CH2SiMe3)2 (3a, M = Zr; 4a, M = Hf) or (Me8taa)MMe2 (3b, M = Zr; 4b, M = Hf) complexes. Compound 3b rearranges by migration of a Me group from Zr to a Me8taa imine carbon in coordinating solvents. The reaction of (Me8taa)H2 with the appropriate ZrR4 compound yields (Me8taa)Zr(CH2Ph)2 (3c) and (Me8taa)Zr(CH2CMe3)2 (3d). The reaction of (Me8taa)H2 and Zr(NR2)4 yields (Me8taa)Zr(NR2)2 (6a, R = Me; 6b, R = Et). Spectroscopic data for (Me8taa)MX2 compounds 2, 3, 4, and 6 are consistent with cis, C2v-symmetric structures. Dialkyl complexes 3 and 4 and bis(amide) complexes 6 react with chlorinated solvents (1,1,2,2-tetrachloroethane, CH2Cl2) to yield 2. Compound 6a reacts with AlMe3 to afford the heterobimetallic μ-amido complex [(Me8taa)Zr(μ-NMe2)2AlMe2][AlMe4] (8), which does not undergo further reaction to yield 3b. The reaction of dialkyl complexes 3 and 4a with HNR3+ reagents yields cationic [(Me8taa)MR][B(C6F5)4] compounds (10a, M = Zr, R = η2-CH2Ph; 10b, M = Zr, R = CH2SiMe3; 10c, M = Zr, R = CH2CMe3; 10d, M = Hf, R = Me). These species form labile adducts with PMe2Ph and THF. Cation 10a polymerizes ethylene to a linear polymer with low activity, while 10d is unreactive with ethylene. 10a reacts with HOCMe2CH2CH2CHCH2 to yield the mononuclear alkoxide complex (Me8taa)Zr(OCMe2CH2CH2CHCH2)+ (13), in which the pendant alkene is not coordinated. 10a also reacts with water or ethanol to yield binuclear complexes [{(Me8taa)Zr(μ-OR)}2]2+ (14a, R = H; 14b, R = Et). An X-ray structural analysis of 14a reveals that one of the (Me8taa)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 [(Me8taa)Hf(CMeCMeCMeCMe2)]+ (15) and with MeC⋮CSiMe3 to afford [(Me8taa)Hf(C(SiMe3)CMe2)]+ (16), while 10a and 10b are unreactive with these alkynes. 10a and 10c react with terminal alkynes by protonolysis to afford binuclear [{(Me8taa)Zr(μ-C⋮CR)}2]2+ complexes (17a, R = Ph; 17b, R = Pr). Complex 17a reacts reversibly with PMe3 to yield the mononuclear cation (Me8taa)Zr(C⋮CPh)(PMe3)+ (18a). (Me8taa)MR+ species are less reactive for alkene and alkyne insertion than are Cp2MR+ species.