Fischer mono- and biscarbene complexes of tungsten with mono- and dimeric heteroaromatic substituents

Abstract

An electrochemical study of a series of mono- and biscarbene complexes of tungsten pentacarbonyl with mono- and dimeric heteroarene substituents are reported and compared in CH3CN and DCM. Results revealed that the order of oxidation (reduction) depends largely on the aryl substituent attached to the carbene carbon (2-thienyl, 2-furyl or 2-(N-methylpyrrolyl)). The order of oxidation (reduction) for monocarbene complexes containing a monomeric heteroarene substituent ((1)–(3)), a dimeric heteroarene substituent ((4)–(6)) or biscarbene complexes connected with a heteroarene substituent ((7)–(9)) is the same, namely 2-thienyl > 2-furyl > 2-(N-methylpyrrolyl). Carbene complexes containing a larger conjugated heteroarene substituent attached to the carbene carbon reduce more easily than the monomeric analogues. Tungsten biscarbene complexes exhibit two separate oxidation potentials for the two metal centres or one large oxidation peak, consistent with the simultaneous oxidation of the two W metal centres.