Structural alternatives in R-2(Cl)P:GaCl3 systems (R = alkyl, phenyl), including examples of intermolecular P->P coordination

Systematic NMR studies of (dialkyl/diaryl)chlorophosphine-gallium chloride reaction mixtures reveal three structural alternatives, which are related by equilibria in solution, and their relative stability is dependent on the nature of the substituent (R = Me, Et, Pr-i, Bu-t, Ph) and the reaction stoichiometry. The coordination complex R-2(Cl)P-->GaCl3 is observed in all cases, and a derivative (R = Pr-i) has been crystallographically characterized. Tetrachlorogallate salts of the diphosphorus cations [R-2(Cl)P-PR2](+) are observed for smaller R substituents (R = Me, Et, Pr-i, Ph), consistent with a previous report. Solid-state P-31 CPMAS NMR spectra distinguish the methyl derivative from the novel salt [Me-2(Cl)P-P(Me-2)GaCl3][GaCl4], containing a phosphine-phosphenium-gallium chloride cation, which has been crystallographically characterized. Factors governing the relative stabilities of the structural alternatives are discussed, and comparisons are made between the isomeric forms for R-2(Cl)P:GaCl3.