Isocyanide derivatives of tungstenocene

Abstract

The synthesis and reactions of the tungstenocene isocyanide complexes [CP 2WCNR] ( 2a: R=1cr Et; 2b: R=1cr tBu; 2c: R=1cr Me) with electrophiles are reported. Complexes 2a and 2b are obtained from Cp 2WCl 2 in two steps. The first involves chloride abstraction from CP 2WCl 2 by TlPF 6 in the presence of RNC and affords the W IV isocyanide complexes [Cp 2WCl(CNR)]PF 6 ( 1a: R=1cr Et; 1b: R=1cr tBu). 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 Et 3OBF 4 affords the W IV ethyl complex [Cp 2WEt(CNEt)]BF 4 ( 3a). Similarly alkylation of 2b and 2c with MeI gives the methyl complexes [Cp 2WMe(CNR)]I ( 4b: R=1cr tBu; 4c: R=1cr Me). The crystal structure of 1a 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 Cp 2W IV derivatives, with the ethylisocyanide ligand adopting a linear coordination mode.