Syntheses and crystal structures of intramolecularly stabilized organogallium compounds containing an o-carboranyl C,N-chelating ligand system

The reaction of HCab(N) (1; HCab(N) = closo-1-[(dimethylamino)methyl]-o-car borane) with GaCl3 yielded the simple Lewis acid-base adduct complex HCab(N ). GaCl3 (3). The reaction of LiCab(N) (2; LiCab(N) = closo-1-[( dimethylam ino)methyl]-2-lithio-o-carborane) with GaCl3 in a 1:1 ratio produced the fo ur-coordinated metallacyclic organogallium compound Cab(N)GaCl(2) (4), in w hich the gallium atom was stabilized via intramolecular C,N-coordination. A similar intramolecularly base-stabilized four-coordinated gallane, Cab(N)G aMe(2) (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 Cab(N)GaCl(2). NC5H5 (6). The trigon al-bipyramidal coordination of the metal center was proven by the single-cr ystal X-ray determination of the complex 6. The reaction of LiCab(N) (2) wi th GaCl3 in a 2:1 ratio afforded the bis[((dimethylamino)methyl)-o-carboran yl]gallium compound (Cab(N))(2)GaCl(7). The NMR spectra revealed that intra molecular Ga-N coordination occurs in solution, resulting in a pentacoordin ate (Cab(N))(2)GaCl structure. Crystals of (Cab(N))(2)GaCl(H2O) (8) were ob tained 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 w ater-coordinated bis[((dimethylamino)methyl)-o-carboranyl]gallane structure .