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

Abstract

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)(C₆H₄)}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* = C₆H₂Bu^t₃-2,4,6; 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.