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 α-hydrogen abstraction processes from suitable alkyl derivatives. Reaction of WCp*Cl4 with one equivalent of NH2R (R=tBu, 2,6-Me2–C6H3), two equivalents of NEt3 and subsequent oxidation with PCl5 affords the pentamethylcyclopentadienyl imido tungsten derivatives, WCp*(NtBu)Cl3 2 and WCp*(N-2,6-(Me2)–C6H3)Cl3 4. Alkylation of complexes 2 and 4 with 1.5 equivalents of ZnMe2 under appropriate conditions yields the trimethyl derivatives WCp*(NtBu)Me3 5 and WCp*(N-2,6-(Me2)–C6H3)Me3 6. Exposure of complex 6 to sun-light leads to the formation of WCp*(N-2,6-(Me2)–C6H3)(CH2)Me 7 through a α-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*(NtBu)(CHPh)(CH2Ph) 8 and WCp*(NtBu)(CHSiMe3)Cl 9, through a spontaneous α-hydrogen abstraction process in these cases.