The reactivity of gallium-(i), -(ii) and -(iii) heterocycles towards Group 15 substrates: Attempts to prepare gallium-terminal pnictinidene complexes

The reactivity of a series of Ga(i), Ga(ii) and Ga(iii) heterocyclic compounds towards a number of Group 15 substrates has been investigated with a view to prepare examples of gallium-terminal pnictinidene complexes. Although no examples of such complexes were isolated, a number of novel complexes have been prepared. The reactions of the gallium(i) N-heterocyclic carbene analogue, [K(tmeda)][:Ga([N(Ar)C(H)]2)] (Ar = 2,6-diisopropylphenyl) with cyclo-(PPh)5 and PhNNPh led to the unusual anionic spirocyclic complexes, [(κ2P,P′-(PhP)4)Ga([N(Ar)C(H)] 2)]- and [(κ2N,C-PhNN(H)(C 6H4))Ga([N(Ar)C(H)]2)]-, via formal reductions of the Group 15 substrate. The reaction of the digallane(4), [Ga([N(Ar)C(H)]2)]2, with (Me3Si)N3 afforded the paramagnetic, dimeric imido-gallane complex, [([N(Ar)C(H)] 2)Ga(μ-N(SiMe3))]2, via a Ga-Ga bond insertion process. In addition, the new gallium(iii) phosphide, [GaI(P(H)Mes*)([N(Ar)C(H)]2)], Mes* = C6H 2But3-2,4,6; was prepared and treated with diazabicycloundecane (DBU) to give [Ga(DBU)(P(H)Mes*)([N(Ar)C(H)] 2)], presumably via a gallium-terminal phosphinidene intermediate, [Ga(PMes*)([N(Ar)C(H)]2)]. The possible mechanisms of all reactions are discussed, all new complexes have been crystallographically characterised and all paramagnetic complexes have been studied by ENDOR and/or EPR spectroscopy. © The Royal Society of Chemistry 2006.