ISOCYANIDE DERIVATIVES OF TUNGSTENOCENE

The synthesis and reactions of the tungstenocene isocyanide complexes [Cp2WCNR] (2a: R = Et; 2b: R = (t)Bu; 2c: R = Me) with electrophiles are reported. Complexes 2a and 2b are obtained from Cp2WCl2 in two steps. The first involves chloride abstraction from CP2WCl2 by TIPF6 in the presence of RNC and affords the W(IV) isocyanide complexes [Cp2WCl(CNR)]PF6 (1a: R = Et; 1b: R = (t)Bu). The second step is the reductive dehalogenation of 1a and 1b by sodium amalgam to give 2a and 2b in high yields. The electron-rich tungstenocene complexes 2a-2c undergo electrophilic addition exclusively at the metal centre. Thus, treatment of 2a with Et3OBF4 affords the W(IV) ethyl complex [Cp2WEt(CNEt)]BF4 (3a). Similarly alkylation of 2b and 2c with MeI gives the methyl complexes [Cp2WMe(CNR)]I (4b: R = tBu; 4c: R = Me). The crystal structure of la reveals a pseudotetrahedral coordination geometry around the tungsten center with the Cp ligands adopting an eclipsed conformation. The structural parameters of 1a exhibit values close to those for other Cp2W(IV) derivatives, with the ethylisocyanide ligand adopting a linear coordination mode.