Synthesis and properties of some gallium amidine complexes [GaXyL3–y][X = Me, Et or Cl; L = RNCR′NR (R, R′= H, alkyl or aryl); y= 0–2]. Crystal structures of [GaMe2(PhNCPhNPh)] and [GaMe(PhNCPhNPh)2]

Abstract

The amidinato compounds [GaMe₂L][L = RNCR′NR (R,R′= H, alkyl or aryl)], [GaMe(PhNCPhNPh)₂], [GaEt(PhNCMeNPh)₂] and [Ga(PhNCRNPh)₃](R = Me or Ph) have been isolated from the reaction of the appropriate gallium trialkyl with 1, 2 and 3 mol of amidine RNCR′N(H)R, respectively. The chloro derivatives [GaCl₃{RNCR′N(H)R}](R = Ph or p-ClC₆H₄; R′= Me) and [GaCl₂(p-ClC₆H₄NCMeNC₆H₄Cl-p)] have also been prepared. The compounds have been fully characterised, and mass spectrometric data indicate that the volatile dimethylgallium derivatives exist as either monomers or dimers in the gas phase. X-Ray crystallographic studies on [GaMe₂(PhNCPhNPh)] and [GaMe(PhNCPhNPh)₂] revealed monomeric structures and the presence of chelating amidinate ligands, with distorted tetrahedral and trigonal-bipyramidal co-ordination respectively at the metal centres. Cleavage of the Ga–Me bond occurs on photolysis in the presence of a spin-trapping agent, and thermal decomposition of the solids leads to the formation of gallium nitride.