Synthesis and characterization of Group 13 hydrides and metal-metal bonded dimers stabilized by the macrocyclic bis(amidophosphine) ligand [P2N2] ([P2N2] = [PhP(CH2SiMe2NSiMe2CH2)2PPh])

Addition of LiAlH4 to the monomeric chlorides syn-MCl[P2N2] (M = Al (1), Ga (2), In (3)) results in the formation of the aluminum hydride syn-AlH[P2N2] (4). The solution H-1- and P-31{H-1}-NMR spectra are consistent with a C-20 symmetric species in solution. The X-ray crystal structure shows the hydride to be monomeric, and free from interaction with either salt (LiCl) or external base (Et2O). The coordination of both phosphines of the macrocycle to the metal center is found in the solid state. Solution molecular weight measurements are consistent with a monomeric structure. The gallium hydride syn-GaH[P2N2] (5) is synthesized by the addition of LiGaH4 to syn-MCl[P2N2] (M = Ga (2), In (3)). This species is unstable and could only be characterized in solution. Reduction of syn-MCl[P2N2] (M = Ga (2), In (3)) with KC8 yields the reduced, dimeric species {syn-M[P2N2]}(2) (M = Ga (6), In (7)). The solution H-1- and P-31{H-1}-NMR spectra are consistent with C-2v symmetric species in solution. The X-ray crystal structures of the gallium and indium complexes confirm the presence of unsupported metal-metal bonds in both cases. The features of the solution H-1- and P-31{H-1}-NMR spectra suggest that both dimers are fluxional in solution. (C) 1999 Elsevier Science S.A. All rights reserved.