1,3-Diphenylamidine and methylaminopyridine compounds of gallium

Article abstract of DOI:10.1016/S0277-5387(97)00205-2

Reaction of Ga(^tBu)₃ with the 1,3-diphenylamidine [PhN(H)C(H)=NPh, H-dpam] yields monomeric (^tBu)₂Ga(dpam) (1). The partial hydrolysis of 1 results in the isolation of (^tBu)₂Ga(μ-dpam)(μ-OH)Ga(^tBu)₂ (2), whose structure consists of a gallium dimer in which the amidine and hydroxide ligands bridge two Ga(^tBu)₂ moieties. Reaction of [Me₂Ga(μ-Cl)]₂ with H-dpam results in the complex [H₂-dpam] [Me₂GaCl₂] (3). The solid state structure of 3 indicates the presence of a hydrogen bonded cation-anion complex, in which the core has a twisted eight-membered ring configuration. The versatility of amidines as both chelating and bridging ligands to gallium is discussed with respect to the predominance of bridging and chelating modes of coordination of carboxylates and triazenides, respectively. Reaction of 2-(methylamino)pyridine (H-map) with Ga(^tBu)₃ allows for the isolation of (^tBu)₂Ga(map) (4). In contrast, reaction with [(^tBu)₂Ga(μ-Cl)]₂ and [Me₂Ga(μ-Cl)]₂ yields the Lewis acid base adducts, (^tBu)₂GaCl(H-map) (5) and Me₂GaCl(H-map) (6), respectively. Reaction of compound 6 with ⁿPrNH₂ does not result in the deprotonation of the H-map ligand, but ligand metathesis and the formation of (^tBu)₂GaCl(NH₂ⁿPr) (7). The structures of 2, 3, 6, and 7 have been determined by X-ray crystallography.