SYNTHESIS AND SPECTROSCOPIC STUDIES ON THE THIOPHENE DERIVATIVES OF THE GROUP-13 ELEMENTS ALUMINUM AND INDIUM - CRYSTAL AND MOLECULAR-STRUCTURES OF [ME2M(MU-2-C4H3S)]2 (M=AL, IN) AND ((2-C4H3S)2AL[MU-N(H)C(H)(C6H5)2])2

Trithiophene derivatives (2-C4H3S)3M.nL (M = Al, n = 1, L = OEt2, 1a; M = In, n = 2, L =THF, 1b) have been prepared by the reaction of the G rignard reagent 2-C4H3SMgBr with MCl3 (M = Al, In) in ether solvents. Compounds 1a,b undergo exchange reactions with Me3Al to give a mixture of [Me2M(mu-2-C4H3S)]2 (M = Al, 2a; M = In, 2b) and (2-C4H3S)2-(Me)M. L (M = Al, L = OEt2; M = In, L = THF). The antinolysis of la with a pr imary amine, (C6H5)2C(H)NH2, giveS {(2-C4H3S)2Al[mu-N(H)C(H)(C6H5)2]}2 (3) in excellent yield. The resulting compounds have been characteriz ed by H-1 and C-13 NMR spectroscopy. A single-crystal X-ray study of 2 a established that it crystallizes in the monoclinic cell system, spac e group P2(1)/c (No. 14), with cell constants of a = 14.332(5) angstro m, b = 14.460(3) angstrom, c = 16.226(6) angstrom, beta = 112.43(2)-de grees, and Z = 8 (dimers); R = 5.7% and R(w) = 5.5%, based on 2709 obs erved reflections (I greater-than-or-equal-to 2.5sigma(I)). Compound 2 b crystallizes in the monoclinic space group C2/c (No. 15) with cell c onstants of a = 12.999(5) angstrom, b = 13.421(2) angstrom, c = 9.522( 2) angstrom, beta = 105.86(2)-degrees, and Z = 4 (dimers); R = 2.1% an d R(w) = 2.3%, based on 1179 observed reflections (I greater-than-or-e qual-to 2.5sigma(I)). The molecular unit in 2a consists of two Me2Al m oieties bridged symmetrically by thiophene rings. In 2b the bridge is asymmetric. Compound 3 crystallizes in the triclinic space group P1BAR (No. 2) with cell constants of a = 9.813(5) angstrom, b = 10.126(5) a ngstrom, c = 10.654(5) angstrom, alpha = 87.36(4)-degrees, beta = 74.2 0(4)-degrees, gamma = 72.77(4)-degrees, and Z = 1 (dimer); R = 7.0% an d R(w) = 7.0%, based on 1768 observed reflections (I greater-than-or-e qual-to 2.5sigma(I)). The molecular unit in 3 is a nitrogen-bridged, p lanar dimer with an Al-N bond distance of 1.955(6) angstrom. In soluti on at low temperature, 2a exists as syn and anti conformers which unde rgo rapid exchange on the NMR time scale at room temperature with an a ctivation energy of 12 kcal mol-1. The formation of the compound Me2Al (mu-Me)(mu-2-C4H3S)AlMe2 has been established by low-temperature NMR s pectroscopic studies.