Insertion of Terminal and Internal Acetylenes into the Zr−μ-Methylene Bond of the Dinuclear Cationic Zirconium Complex [{Zr(η⁵-C₅H₅)}₂(μ-CH₂)(μ-Cl)(μ-η⁵-C₅H₄-η⁵-C₅H₄)][BMe(C₆F₅)₃]. Synthetic Aspects, NMR Spectroscopic Study, and Dynamic Behavior in Solution

The dinuclear cationic zirconium species [{Zr(η 5 -C 5 H 5 )} 2 (μ-CH 2 )(μ-Cl)(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] ( 1 ) reacts in dichloromethane at −78 °C with terminal alkynes, via insertion into the Zr−μ-methylene bond, to give various dinuclear cationic derivatives. Reaction of 1 with Me 3 SiC⋮CH gives the hydrido complex [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl)(μ-H)(CH 2 C⋮CSiMe 3 )(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] ( 2 ), whereas 1-pentyne and 3,3-dimethyl-1-butyne give the μ-η 1 -η 3 -(2-alkyl)allyl derivatives [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl){μ-[η 1 -η 3 -CHC( n Pr)CH 2 ]}(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] ( 3 ) and [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl){μ-[η 1 -η 3 -CHC( t Bu)CH 2 ]}(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )] [BMe(C 6 F 5 ) 3 ] ( 4 ). Compounds 3 and 4 show dynamic behavior in solution involving an interchange between two enantiomeric structures through a suprafacial migration of the “−RC CH 2 ” moiety. When compound 1 was treated with a molar equivalent of internal alkynes RC⋮CR (R = Et, n Pr), formation of [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl){μ-CH 2 C(Et) C(Et)}(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] ( 5 ) and [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl){μ-CH 2 C( n Pr) C( n Pr)}(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] ( 6 ) was observed, which were isomerized to the [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl){μ-CH 2 C(Et)CH CHMe}(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )] [BMe(C 6 F 5 ) 3 ] ( 7 ) and [{Zr(η 5 -C 5 H 5 )} 2 (μ-Cl){μ-CH 2 C( n Pr)CH CHEt}(μ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] ( 8 ) derivatives at room temperature, through a β−α hydrogen migration. The new complexes reported were characterized by elemental analysis and IR and NMR spectroscopy.