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.