Syntheses and Crystal Structures of Intramolecularly Stabilized Organogallium Compounds Containing an <i>o</i>-Carboranyl C,N-Chelating Ligand System

Abstract

The reaction of HCabN (1; HCabN = closo-1-[(dimethylamino)methyl]-o-carborane) with GaCl3 yielded the simple Lewis acid−base adduct complex HCabN·GaCl3 (3). The reaction of LiCabN (2; LiCabN = closo-1-[(dimethylamino)methyl]-2-lithio-o-carborane) with GaCl3 in a 1:1 ratio produced the four-coordinated metallacyclic organogallium compound CabNGaCl2 (4), in which the gallium atom was stabilized via intramolecular C,N-coordination. A similar intramolecularly base-stabilized four-coordinated gallane, CabNGaMe2 (5), was synthesized from the reaction of 2 with Me2GaCl. Complex 5 was also formed upon reaction of the complex 4 with 2 equiv of LiMe. The X-ray structural studies of complexes 4 and 5 indicate that the gallium atom is located in the center of a distorted tetrahedron. The Lewis acid 4 added the base pyridine to yield the adduct CabNGaCl2·NC5H5 (6). The trigonal-bipyramidal coordination of the metal center was proven by the single-crystal X-ray determination of the complex 6. The reaction of LiCabN (2) with GaCl3 in a 2:1 ratio afforded the bis[((dimethylamino)methyl)-o-carboranyl]gallium compound (CabN)2GaCl (7). The NMR spectra revealed that intramolecular Ga−N coordination occurs in solution, resulting in a pentacoordinate (CabN)2GaCl structure. Crystals of (CabN)2GaCl(H2O) (8) were obtained while recrystallizing 7 in toluene over a period of several days. X-ray analysis of this complex 8 provides support for the assignment of the water-coordinated bis[((dimethylamino)methyl)-o-carboranyl]gallane structure.