SYNTHESIS AND CHARACTERIZATION OF NOVEL ALUMINUM ARSENIC COMPOUNDS - CRYSTAL-STRUCTURE OF [ET2ALAS(SIME3)2]2

The viability of dehalosilylation and lithium chloride elimination reactions for use in the preparation of compounds containing core rings of the type activated Al-As-Al-As and activated Al-As-Al-Cl was investigated. The second fully characterized aluminum-arsenic dimer, [Et2AlAs-(SiMe3)2]2 (1), was isolated from a coupling reaction between Et2AlCl and LiAs(SiMe3)3 carried out at -78-degrees-C. Reactions between Et2AlCl and As(SiMe3)3 in 1:1 and 2:1 mole ratios at ambient temperature failed to give the expected dehalosilylation products, instead yielding the adduct Et2(Cl)Al.As(SiMe3)3 (2). As evidenced by H-1 NMR spectra, an NMR tube sample of 2 in benzene-d6 did undergo internal dehalosilylation to give 1 when heated to 87-degrees-C in an oil bath. X-ray crystallographic analysis of 1 confirms its dimeric solid-state structure and shows the activated Al-As-Al-As ring to be planar. Compound 1 crystallizes in the monoclinic system, space group C2/c (C2h6), with four molecules in a unit cell of dimensions a = 18.214 (2) angstrom, b = 9.542 (1) angstrom, c = 20.453 (2) angstrom, and beta = 99.89 (1)-degrees.