Synthesis and X-ray structures of amidinate, oxoamidate, and thioamidate complexes of boron

The reactions of PhBCl2 with Li[CE((NBu)-Bu-t)(Bu-n)] or Li[CS((NBu)-Bu-t)((NHBu)-Bu-t)] (1:1 molar ratio) in toluene at 23 degrees C produced the heterocycles Ph(Cl)B(mu-(NBu)-Bu-t)(mu-E)C(Bu-n) (1a, E = (NBu)-Bu-t; 1b, E = O; 1c, E = S) or Ph(Cl)B(mu-(NBu)-Bu-t)(mu-S)C((NHBu)-Bu-t) (2), which were characterized by H-1, B-11 and C-13 NMR and by mass spectra. X-ray structural determinations revealed that 1a, 1c and 2 contain four-membered rings. In 2 the thioamidate ligand adopts an N,S bonding mode. Crystal data: 1a, monoclinic, space group P2(1), a = 8.816(3), b = 11.311(2), c = 10.168(3) Angstrom, beta = 98.86(3)degrees, V = 1001.7(5) Angstrom(3), Z = 2, R = 0.042, and R-w = 0.020; 1c, monoclinic, space group P2(1)/n, a = 7.617(2), b = 11.200(1), c = 19.568(2), beta = 90.74(2)degrees, V = 1669.1(5) Angstrom(3), Z = 4, R = 0.046, and R-w = 0.059; 2, monoclinic, space group P2(1)/a, a = 11.357(2), b = 12.289(2), c = 12.620(3) Angstrom, beta = 95.43(2)degrees, V = 1753.4(5) Angstrom(3), Z = 4, R = 0.043, and R-w = 0.027.