Synthetic and computational studies of organometallic complexes containing low-coordinate group 13 ligands

The work presented in this thesis is concerned with synthetic and computational studies of low coordinate transition metal complexes of boron. New symmetrically bridged boryl complexes of iron and manganese have been prepared and characterised. Information obtained from spectroscopic and structural analyses, together with Density Functional theoretical studies, has been used to investigate the nature of the metal-boron bonds in these complexes. Development of the chemistry of related terminal analogues has also been undertaken. The M-B bonds present in these molecules can be considered mainly o in character, with very little n contribution. Attempts to investigate the chemistry of base-stabilised boryl complexes, using PMe3 and THF as Lewis bases, shows that, while PMe3 adducts with haloboranes are very stable and do not react with metallic fragments, THF complexes give more promising results, especially when THF is also used as a solvent for the reaction. Substitution and abstraction chemistry of the new (mesityloxy)chloroborane (MesO)BCl2 has been analysed. Replacement of the chlorine atom in (ti5-C5H5)Fe(CO)2 B(OMes)Cll by other nucleophiles is possible, thereby generating new asymmetric boryl ligands. Chloride abstraction using NalBAr'J leads to the formation of the fluoroboryl complex (Tf-C5Hs)Fe(CO)2 B(OMes)F possibly via the putative terminal borylene (n5-C5R5XCO)2Fe=B(OMes) Oxidative addition of B-H, B-B and B-X bonds to both d-block (Rh, Pt) and p-block (In, Sn) metals as an alternative pathway to boryl complexes has also been examined. Unfortunately, while many of the reactions appear to give the expected products (on the basis of in situ NMR monitoring), purification difficulties have prevented the isolation of many of these species as pure compounds. DFT studies on terminal boron- aluminium- and gamum containing complexes have been undertaken. Geometry optimisation, molecular orbital composition, bond dissociation energies and bond density partitioning have been investigated in order to probe the nature of the M=E bonds (E = B, Al, Ga) and the dependence of compound stability on both the ancillary metal-bound ligands and on the substituent of the group 13 diyl fragment. The examples considered were diyl complexes of general formula (n5-C5R5KL)2M(EX)1D+, the 'naked' bridging gallium complex ({(CrMes)Fe(CO)2}2Ga + and five gallium carbene complexes of first row transition metals (V, Mn, Fe, Co, Ni), featuring the heterocyclic ligand {:Ga N(Ph)CH 2}