NOVEL MOLECULAR CLUSTERS HAVING ALUMINUM-PHOSPHORUS, ALUMINUM-ARSENIC, AND GALLIUM-ARSENIC SKELETONS, AND SYNTHESIS OF AN AL4AS6LI4 RHOMBODODECAHEDRON

The cyclocondensation reaction of the primary silylarsanes 4a,b, with the trimethylamine adducts of alane (5a) leads, under liberation of H- 2, to the four-membered 1,3-diarsa-2,4-dialuminetane heterocycles 2a, b. The latter derivatives were characterized by NMR spectroscopy and a single-crystal X-ray diffraction analysis, Compound 2a consists of a puckered four-membered Al2As2 ring, which contains three-coordinate As and four-coordinate Al centers and, surprisingly, the NMe3 groups are cis oriented. Upon heating of 2a, b in toluene, the NMe3 groups at th e Al centers are readily cleaved and the resulting unsolvated Al2As2 r ings trimerize, affording the novel hexagonal prismatic Al6As6 cluster compounds 1a, b, The latter were characterized by (H-1, Al-27) NMR an d IR spectroscopy, and the structure of 1a was established by a X-ray diffraction analysis. The conversion of the silylarsane 4a with the am ine-gallane 5b and of the silyl-phosphane 4c with the amine - alane 5a , respectively, gives directly, that is, without NMR-spectroscopically detectable intermediates, the hexameric arsagallane and phosphaalane clusters if and 1d, respectively They are isostructural with 1a, Inter estingly, the delta (Al-27) values of 1a (48), 1b ( 10). and 1d (46) a re relatively small compared to that of 2a (127) and 2b (140), althoug h the Al centers are in all cases four-coordinate, due to the ring str ain in 1a, b, and 1d. The reaction of the silylarsane 4a with [LiAlH4] in the molar ratio of 1:1 in Et2O as solvent gives, under elimination of H-2. access to the unusual novel heteroaggregate 3, which has a rh ombododecahedral Al4As6Li6 skeleton. The structure of 3 was establishe d by X-ray diffraction. Surprisingly, the same reaction of the startin g materials in 1,2- dimethoxyethane instead of Et2O as solvent leads t o an unusual triple ion pair compound.