Allyl Isomerization Mediated by Cyclopentadienyl Group 6 Metal Compounds

Reactions at mild temperatures of the acetonitrile adducts [M(CO) 3 (NCMe) 3 ] (M = Mo ( 1 ), W ( 2 )) with various substituted cyclopentadienes in THF give the hydrido derivatives [MH{η 5 -C 5 R 4 Si(CH 3 ) 2 -(CH 2 CH CH 2 )}(CO) 3 ] (M = Mo, R = H ( 5a ), R = CH 3 ( 6 ), M = W, R = H ( 7a ), R = CH 3 ( 8a )) and [MoH{η 5 -C 5 R 4 R‘}(CO) 3 ] (R = CH 3, R‘ = H ( 16 ); R = H, R‘ = SiMe 3 ( 17 )) in isolated yields of 60−70%. THF solutions of derivatives 5a, 7a, and 8a undergo isomerization of the cyclopentadienyl-tethered-allyl unit to give the corresponding methyl-vinyl-dimethylsilyl-η 5 -cyclopentadienyl hydrido compounds [MH{η 5 -C 5 R 4 Si(CH 3 ) 2 (CH CHCH 3 )}(CO) 3 ] (M = Mo, R = H ( 5b ), M = W, R = H ( 7b ), R = CH 3 ( 8b )) in final a: b ratios of ca. 2:1, 2:1, and 1:1, respectively. Solvent polarity seems to be crucial in these transformations. Dehydrogenation and desilylation of 5a in THF solutions to give the dinuclear derivative [Mo{η 5 -C 5 H 4 Si(CH 3 ) 2 (CH 2 CH CH 2 )}(CO) 3 ] 2 ( 9 ) and [MoH(η 5 -C 5 H 5 )(CO) 3 ] ( 15 ), respectively, are processes competitive with the allyl isomerization. Treatment of 5a and 7a with equimolar amounts of ONMe 3 permits isolation of pure compound 9 and [W{η 5 -C 5 H 4 Si(CH 3 ) 2 (CH 2 CH CH 2 )}(CO) 3 ] 2 ( 10 ) in isolated yields of 80−90%. Coordination of the olefin pendant unit to the metal was detectable only by reaction of 5a and 7a with [CPh 3 ][B(C 6 F 5 ) 4 ] to give the cationic species [M{η 5 -C 5 H 4 Si-(CH 3 ) 2 (CH 2 CH CH 2 )}(CO) 3 ][B(C 6 F 5 ) 4 ] (M = Mo ( 18 ), W ( 19 )). Molecular structure determinations by X-ray diffraction methods for derivatives 8a and 9 are also reported.