Complexes of a gallium heterocycle with transition metal dicyclopentadienyl and cyclopentadienylcarbonyl fragments, and with a dialkylmanganese compound

Abstract

The reactivity of several transition metal half sandwich complexes towards an anionic gallium(I) heterocyclic complex, [K(tmeda)][Ga{[N(Ar)C(H)]₂}] (Ar = C₆H₃Prⁱ₂-2,6), has been investigated. This has led to the anionic half sandwich complexes, [K(tmeda)][(C₅H₄R)M(CO)_n[Ga{[N(Ar)C(H)]₂}]] (M = V, R = H, n = 3; M = Mn, R = Me, n = 2; M = Co, R = H, n = 1), which crystallographic studies show to form dimers (M = Mn and Co) or a polymer (M = V) through bridging potassium cations. The metal–gallium bond lengths in all complexes are very short which, combined with some spectroscopic evidence, is suggestive of M–Ga π-bonding. Density functional theory studies of models of all complexes indicate that the level of back-bonding in these complexes is, however, minimal and of a similar order to that seen in analogous complexes incorporating neutral N-heterocyclic carbene ligands. Reactions of the metallocenes, [M(C₅H₄Me)₂] (M = V or Cr), with the digallane(4), [Ga{[N(Ar)C(H)]₂}]₂, have afforded the neutral complexes, [M(C₅H₄Me)₂[Ga{[N(Ar)C(H)]₂}]], which are thought to be formed via an initial oxidative insertion of the transition metal centre into the Ga–Ga bond of the digallane. X-Ray crystallography shows the complexes to be monomeric. One (M = V) reacts with one equivalent of [K(tmeda)][Ga{[N(Ar)C(H)]₂}] to give the crystallographically characterised, anionic bis(gallyl)-complex, [K(tmeda)][V(C₅H₄Me)₂[Ga{[N(Ar)C(H)]₂}]₂]. For comparison, the reaction of [K(tmeda)][Ga{[N(Ar)C(H)]₂}] with [Mn{CH(SiMe₃)₂}₂] was carried out and gave the monomeric, anionic complex, [K(tmeda)][Mn{CH(SiMe₃)₂}₂[Ga{[N(Ar)C(H)]₂}]].