Synthesis and reactivity of cyclopentadienyl chloro, imido and alkylidene tungsten(VI) complexes

This paper describes the synthesis and characterization of alkylidene pentamethylcyclopentadienyl imido tungsten(VI) complexes via alpha-hydrogen abstraction processes from suitable alkyl derivatives. Reaction of WCp*Cl-4 with one equivalent of NH2R (R = Bu-t, 2,6-Me-2-C6H3), two equivalents of NEt3 and subsequent oxidation with PCl5 affords the pentamethylcyclopentadienyl imido tungsten derivatives, WCp*((NBu)-Bu-t)Cl-3 2 and WCp*(N-2,6-(Me-2)-C6H3)Cl-3 4. Alkylation of complexes 2 and 4 with 1.5 equivalents of ZnMe2 under appropriate conditions yields the trimethyl derivatives WCp*((NBu)-Bu-t)Me-3 5 and WCp*(N-2,6-(Me-2)-C6H3)Me-3 6. Exposure of complex 6 to sun-light leads to the formation of WCp*(N-2,6-(Me-2)-C6H3)(=CH2)Me 7 through a alpha-hydrogen abstraction process. Analogously, complex 2 reacts with 1.5 equivalents of Mg(CH2Ph)-(thf)(2) or three equivalents of LiCH2SiMe3 to give the alkylidene complexes, WCp*((NBu)-Bu-t)(=CHPh)(CH2Ph) 8 and WCp*((NBu)-Bu-t)(=CHSiMe3)Cl 9, through a spontaneous a-hydrogen abstraction process in these cases. (C) 1998 Elsevier Science S.A. All rights reserved.