Amidinate–carboxylate complexes of dimolybdenum and ditungsten: M2(O2CR)2((NiPr)2CR′)2. Preparations, molecular and electronic structures and reactions

Abstract

The compounds M₂(O₂CMe)₄ and the lithium amidinates Li[(NⁱPr)₂CR] react to give the new compounds trans-M₂(O₂CMe)₂[(NⁱPr)₂CR]₂ where M = Mo or W and R = Me (M = Mo only), –CC^tBu, –CCPh and –CC–Fc where Fc = 1-ferrocenyl. The limitations of this type of reaction are described based on steric considerations together with the preparation and characterization of the compound Mo₂(µ-O₂C-9-anthracene)₂[η²-(NⁱPr)₂CMe]₂. The electronic structures of the bis-amidinate–bis-carboxylate M₂ complexes are described based on model compounds employing density functional theory and are correlated with the experimental observations of their physicochemical properties and in particular their observed electronic absorption spectra which show intense MLCT absorption bands. Preliminary studies of the reactions of these bis-amidinate–bis-carboxylate complexes in the preparation of 1-D oligomers are also described along with the preparation and molecular structures of the compounds [Li(NⁱPr)₂CR·THF]₂ where R = 2-thienyl or –CC–Ph. The kinetic lability of these new M₂-containing compounds toward ligand exchange is also noted.