Modular chemistry with aluminum phosphanides: Cluster formation of (AlP)(n) (n=3,6,7), Al4P3, and Al4Li4P6 frameworks

The Al3P3 heterocycle 1 is formed in 94% yield by the reaction of the prima ry silylphosphane 6a with Me3Al in toluene at 70 degreesC. While 1 crystall izes in an isomerically pure form, in which the six-membered Al3P3 ring pre fers the chair conformation and the P-H hydrogen atoms adopt exo positions, it isomerizes in solution to give different diastereomers as shown by H-1 and P-31 NMR spectroscopy. Intermolecular cyclocondensation of 1 at 110 deg reesC in toluene leads, under liberation of methane, to the distorted hexam eric-prismatic (AlP)(6) cluster 2 in 98% yield. The capability of 1 to func tion as a building block was further used for the synthesis of the solvent- separated ion pair [Li(thf)(2)](+) [(Me2Al)(4)(PR)(3)](-) (3) which was pre pared by a one-pot reaction of 1 with nBuLi and Me2AlCl in 15% yield. The s tructure of 3 was established by an X-ray diffraction analysis. Double depr otonation at phosphorus in 1 with RPLi2 (R = iPr(3)Si) (molar ratio 1:2), a nd subsequent transformation of the reaction mixture with Me3Al afforded th e novel donor-solvent-free cluster 4 in 62% yield. The latter consists of a rhombododecahedral Al4Li4P6 framework, in which the Li centers are three-c oordinate. The reaction of the silyl-phosphane 6b with the trimethylamine a dduct of alane furnishes not only the hexamer (RPAlH)(6) (R = (iPrMe(2)C)-M e2Si) but also the corresponding heptamer 5, which has a nonregular polyhed ral (AIP)(7) framework and represents the first cluster of this type.