Carbidos, Carbonyls, Carbynes and Carbenes: Reactivity of the Bridging C1 Ligand

Abstract

The u-carbido ligand consists simply of a single carbon atom that acts as a bridging ligand between two transtion metal termini. The bonding of bimetallic u-carbido complexes may be described by one of four bonding scenarios that vary in the number (1, 2 or 3) of valence electrons required by each of the similar (Classes A and D) or disparate (Classes B and C) metal termini, so as to acquire satisfactory effective atomic numbers (16 or 18 valence electrons). As examples from each class have been sporadically identified, an understanding of the more complex bonding within 'MCM' spines has begun to emerge. The reactivity of binuclear u-carbido complexes however remains essentially uncharted, being limited to various co-ligand substitutions prior to the start of this body of work.

This body of work focusses on the cumulenic (Class A) type bonding mode, where the often symmetrical metal compelxes are bound to the u-carbido through two double bonds. This work focusses on the dirhodium complex [Rh2(u-C)Cl2(PPh3)4], and the subsequent ligand/metal reactivity, focussing largely on the carbido ligand itself.

The u-carbido ligand has previously untouched reactivity, but we have successfuly been able to functionalise it into a number of useful carbon-based ligands, such as halocarbynes, chalcocarbonyls, and the very first stable dimetallacarbene. This thesis works through the carbido reactivity, including the further uncharted reactivity of the halocarbyne and dimetallacarbene ligands respectively. Alongside this synthetic program, the nature of the 13C and 103Rh NMR environments have been of interest, and work has been carried out on multi-dimensional NMR studies (31P-13C, 31P-103Rh) in addition to 13C labelling, in order to properly characterise and begin to understand the nature of this largely unknown u-carbido ligand.