THE COORDINATION CHEMISTRY OF THE AMIDINE LIGAND

Amidines, R'NH-C(R)=NR', as for the isoelectronic carboxylic acids, form a large number of transition metal derivatives, the metals varying from early metals in high oxidation states to the later metals in lower oxidation states. Various bonding modes for the amidino group are involved, and are reviewed with reference to other aza-allyl systems. Much current interest arises from the ability of the ligand to bridge between metals, facilitating metal-metal bonding, and from the use of unsymmetrically substituted amidino groups to produce chiral complexes. Methods of synthesis are reviewed, together with infrared and NMR spectroscopic, mass spectrometric and thermal analysis data. The complexes are introduced systematically according to their Period Group, making easy access to information on specific metal complexes. Mixed-metal complexes containing amidino groups bridging between different metals are considered separately. X-ray crystallographic data is collated in a table, thus providing an accessible source for reference purposes. Source material for the review amounts to about 300 references.