Isomerisation and Substitution Reactions of Dimolybdenum Complexes

[摘要] The work in this thesis deals with quadruply bonded dimolybdenum compounds. Many new complexes have been synthesised and characterised by various spectroscopic techniques. Complexes of general formula Mo2X4(P~P)2 where X = Cl or Br and P~P is a diphosphine ligand, can exist as two geometric isomers. In many cases the a (chelated) isomer isomerises to the IB (bridged) form in dry dichioromethane solution. This transformation has also been observed for Mo2Cl4(dppe)2 in the solid state. Kinetic parameters have been collected for the solution isomerisation of alpha-Mo2Cl4(dppp)2 and for the solid state isomerisation of alpha-Mo2Cl4(dppe)2. The kinetic data are compared with those obtained for other dimolybdenum complexes. The possible mechanisms for the isomerisation reactions are reviewed and discussed in the light of the new data obtained for the solid state reaction. Many quadruply bonded complexes contain weakly bound ligands which can easily be displaced. The complex Mo2(TFMS)4 contains very labile ligands. Reactions of this complex with ligands such as DMF or acetonitrile lead to total ligand substitution. [Mo2(O2CCH3 )2(CH3CN)6]2+ has labile acetonitrile ligands and partial ligand substitution was observed when the cation was reacted with diphosphine or diamine ligands. The product from the reaction of [MO2(O2CCH3)2(CH3CN)6]2+ and dmpe gives [Mo2(O2CCH3)2(dmpe)2]2+, the latter complex has a trans arrangement of acetate ligands while the former has cis. A mechanism for this reaction is presented. Optical activity in quadruply bonded complexes has generated considerable interest in recent years. The configurations and conformations of a variety of complexes of the general formula B-Mo2Cl4. (P~P)2 and [Mo2(O2CCH3)2(L~L)4-2x(CH3CN)6]2+(x = 1 or 2), where P~P is a chiral diphosphine ligand and L~L can be either a chiral diamine or diphosphine ligand, have been studied.

[发布机构] University:University of Glasgow

[关键词] Inorganic chemistry