Synthesis and chemistry of cationic alkyl, alkenyl, and allyl complexes derived from the soluble, cationic hydride (C5H4Me)2Zr(H)(THF)+

Article abstract of DOI:10.1021/om00114a026

Reaction of Cp′₂Zr(CH₂Ph)₂ (Cp′ = C₅H₄Me) with [Cp′₂Fe] [BPh₄] in THF produces the cationic benzyl complex [Cp′₂Zr(CH₂Ph)(THF)] [BPh₄] (4) which contains a normal η¹-benzyl ligand. Hydrogenolysis of 4 in THF solution (1 atm of H₂, 23°C) produces the soluble cationic hydride complex [Cp′₂Zr(H)-(THF)][BPh₄] (5). Hydride 5 reacts with olefins H₂C=CH₂R to yield cationic alkyl complexes [Cp′₂Zr-(CH₂CH₂R)(THF)][BPh₄] (8a, R = H; 8b, R = Me; 8c, R = Et), with 2-butyne to give the cationic 2-butenyl complex [Cp′₂Zr(CE)-C(Me)=C(H)(Me)}(THF)][BPh₄] (9), and with allene to give the allyl complex [Cp′₂Zr(η³-C₃H ₆)(THF)][BPh₄] (13). Solutions of 4, 5, or 13 in CH₂Cl₂ catalyze the polymerization of ethylene to polyethylene. Solutions of 5 and of 8a,c in THF catalyze the oligomerization of ethylene to butene, hexene, and octene. Alkyl complexes 8a-c also insert 2-butyne to give cationic alkenyl complexes [Cp′₂Zr{(Z)-C(Me)=C(Me)(R)}(THF)][BPh₄] (10a, R = Et; 10b, R = ⁿPr; 10c, R = ⁿBu). No evidence for multiple 2-butyne insertion or for competing β-H elimination reactions is observed. The structure of the cationic alkenyl complex [Cp′₂Zr{(Z)-C(Me)=C(Me)(ⁿPr)}(THF)] [BPh₄] (10b) has been determined by X-ray diffraction. Complex 10b crystallizes in space group P2₁/n with a = 12.084 (4) A?, b = 20.469 (9) A?, c = 16.436 (2) A?, β= 100.26 (2)°, V = 4000 (2) A?³, and Z = 4. The alkenyl ligand lies in the plane between the two Cp′ ligands in the exo conformation, and the THF ligand is rotated 50° from the optimum conformation for Zr-O π bonding.