The complexation potential of mono(borane)diorganophosphides toward lithium and aluminum has been explored in the complexes [{(tmeda)Li}{P(BH3)Me2}] (1), [{((−)-sparteine)Li}{P*(BH3)(Ph)tBu}] (2), [(tmeda)2Li]+[Al{P(BH3)Me2}4]- (3), and [(mtbe)Li]+[Al{P(BH3)Me2}4]- (4) (tmeda = N,N,N ‘,N ‘-tetramethylethylenediamine; mtbe = methyl-tert-butyl ether). In 1 there is competing Li−P and Li−H−B bonding, while in 2 Li−P coordination is absent due to steric hindrance. Compound 2 contains the enantiomerically pure P-chiral anion [P*(BH3)(Ph)tBu]-, which is a valuable building block for the synthesis of P-chirogenic phosphines. The complexes 3 and 4 are the first homoleptic tetraphosphorus aluminates to be structurally characterized.

The bis((dimethylphosphino)methyl)-substituted alcohol (Me 2 PCH 2 ) 2 CHOH (1) was prepared from the respective bis(3,5-dimethylbenzyl)phosphonium dichloride by reductive elimination of mesitylene with lithium alanate in 56% yield. Deprotonation with nbutyllithium or elemental sodium gave the respective alkali metal alcoholates [(Me 2 PCH 2 ) 2 -CHOM] 6 (M ) Li (2), Na (3)). Both compounds have a core consisting of two stacked M 3 O 3 hexagons held together by short M-O bonds. In 2, in addition to three oxygen atoms, each lithium atom is coordinated by one phosphino group of an adjacent ligand in a distorted tetrahedral geometry (Li-P ) 2.60(1) Å). In 3 each sodium atom is coordinated by two phosphino groups from different ligands in addition to the oxygen atoms. The coordination geometry at the sodium atom is a distorted trigonal bipyramid (O 3 P 2 ), the two phosphine donors being in axial and equatorial positions, respectively (Na-P ) 3.083(2), 3.151(2) Å). The tris((dimethylphosphino)methyl)-substituted alcohol (Me 2 PCH 2 ) 3 COH (4) was synthesized from 1-chloro-2,3-epoxy-2-(chloromethyl)propane by reaction with 3 equiv of LiPMe 2 in 69% yield. Its crystal structure contains a O-H‚‚‚P hydrogen bond (O‚‚‚P ) 3.460(1) Å). Reaction of 4 with excess n-butyllithium in the absence of solvent gave the dimeric polylithium mixed-anion aggregate [(Me 2 PCH 2 ) 3 COLi‚2Li-n-Bu] 2 (5), the core of which consists of two stacked LiOLiCLiC hexagons. Each (Me 2 PCH 2 ) 3 COanion is coordinated to three Li + cations via O-Li and P-Li bonds. The same reaction in toluene led to further deprotonation of the methylene groups in 4, subsequent loss of Li 2 O, and formation of the symmetrically tris(phosphino)-substituted trimethylenemethane dianion. It crystallizes as the mixed-anion aggregate [(Me 2 PCH 2 ) 3 CO -‚3Li + ‚(Me 2 PCH) 3 C 2-] (6), consisting of an almost equilateral triangle of lithium atoms sandwiched between the two anions. Each lithium atom has a severly distorted tetrahedral coordination geometry consisting of two phosphino donors, one oxygen atom, and one methylene group.