An alkylidene-tethered tantallanorbornadiene from reduction of a tantalum(phenylalkenyl)alkylidene derived from 3,3-diphenylcyclopropene ring opening by (eta-C5Me4R)(2)Ta-2(mu-X)(4) (Ta=Ta)

摘要

The terminal (diphenylalkenyl)alkylidene complexes (C5Me4R)Ta(CHCHCPh2)X-2 (R = Me, Et; X = Cl, Br) are formed in moderate yields from the ring-opening reaction of 3,3-diphenylcyclopropene with the organoditantalum(III) halides (eta-C5Me4R)(2)Ta-2(mu-X)(4), Potassium amalgam reduction of these alkenylalkylidene complexes afforded the alkylidene-tethered tantallanorbornadienes (C5Me4R)Ta[CHCHCPh(sigma(2) -C6H5)], which possess a bent, boat conformation sigma(2)-arene ligand with a fold angle of 19.24(46)degrees (R = Me) in the solid state. C-13 and H-1 NMR spectroscopies are consistent with a rapid flip-flop motion that averages the resonances of the sigma(2)-phenyl group to fewer resonances than expected from the solid-state structure. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 22]