STABLE TERTIARY PHOSPHINE ADDUCTS OF ALANE

Treatment of LiAlH4/OEt2 solutions with bulky trialkylphosphine hydrochloride salts or phosphine and then ethereal HCl yields thermally stable phosphine-alane adducts, viz. [H3Al.P(C6H11)3] (10), (H-3Al)n.(PPri2CH2)2 (n = 1 (11), 2 (12)), and [(H3Al)2.{P(C6H11)2CH2}2] (13), which have been shown to be four-coordinate (10 and 13, Al-P = 2.467 (1), 2.460 (2) angstrom) or polymeric (13) with trigonal-bipyramidal aluminum centers (P apical) with exceptionally long Al-P bonds (2.732 angstrom (mean)). Ab initio calculations on the model species H3Al.PH3 (Al-P = 2.605 angstrom) give a stabilization energy of 13.2 kcal/mol relative to AlH3 and PH3, and dimerization to dialane, H2Al(mu-H)2AlH2, and PH3 is favored by 5.84 kcal/mol.