CHLOROSILYL-SUBSTITUTED MONOCYCLOPENTADIENYL NIOBIUM CHLORO, IMIDO CHLORO, AND BENZYL COMPLEXES - X-RAY MOLECULAR-STRUCTURE OF )(MU-O)(MU-CL)(2))((ETA(5)-C5H4)(2)(ME2SIOSIME2))]

We report the synthesis of 1-(chloromethylphenylsilyl)cyclopentadie. T he reaction of a toluene/CH2Cl2 suspension of NbCl5 with 1-(SiClMeX)-1 -(SiMe3)C5H4 (X = Me, Ph) leads to the monocyclopentadienyl derivative s [M{eta(5)-C5H4(SiClMeX)}Cl-4] (X = Me, Ph) in 90 and 78% yields, res pectively. Reaction of 1 equiv of water with [M(eta(5)-C5H4(SiClMe2))C l-4] in toluene takes place with elimination of HCl, resulting in form ation of the dinuclear niobium oxo derivative (mu-O)(mu-Cl)(2))((eta(5 )-C5H4)(2)(Me2SiOSiMe2)}]. Reaction of the complexes [M{eta(5)-C5H4(Si ClMeX))Cl-4] with (LiNHBu)-Bu-t and NEt3 in toluene leads to the half- sandwich imido complexes [Nb{eta(5)-C5H4(siClMeX))Cl-2((NBu)-Bu-t)] (X = Me, Ph), which react at room temperature with 1 equiv of Mg(CH2Ph)( 2)(THF)(2) to give the imido dibenzyl complexes [Nb{eta(5)-C5H4(siClMe X))(CH2Ph)(2)((NBu)-Bu-t)] (X = Me, Ph). The reaction of the chloro im ido complexes [Nb{eta(5)-C5H4(SiClMeX))Cl-2((NBu)-Bu-t)] with excess M g(CH2Ph)(2)(THF)(2) on heating for 2-3 days to 80-90 and 50-60 degrees C, respectively, takes place, affording the totally alkylated complex es b{eta(5)-C5H4[si(CH2Ph)MeX])(CH2Ph)(2)((NBu)-Bu-t) (X = Me, Ph). Th e chloro benzyl derivative [Nb{eta(5)-C5H4(SiClMe2))(CH2Ph)Cl((NBu)-Bu -t)], which could not be prepared by addition of the stoichiometric am ount of the alkylating agent, was isolated in quantitative yield by he ating a mixture of the dichloro and dibenzyl complexes in toluene at 1 20 degrees C for 4 h. The 18-electron imido eta(2)-iminoacyl derivativ es ta(5)-C5H4(SiMeXY))R((NBu)-Bu-t){eta(2)-C(CH2Ph=N- (2,6-Me2C6H3))] (R = CH2Ph, X = Cl, Y = Me, Ph; R = CH2Ph, X = CH2Ph, Y = Me, Ph; R Cl , X = Cl, Y = Me) are formed when the isocyanide CN(2,6-Me2C6H3) is ad ded to a hexane solution of the benzylimido complexes. The molecular s tructure of the oxo complex )(mu-O)(mu-Cl)(2)){(eta(5)-C5H4)(2)(Me2SiO SiMe2)}] has been determined by X-ray diffraction methods.