Syntheses, Spectroscopy, Structures, and Reactivity of Neutral Cubic Group 13 Molecular Phosphonates

The syntheses of cubic group 13 molecular phosphonate cages of the formulas [RPO 3 MR‘] 4 (R = Me, Et, t -Bu, Ph; MR‘ = BEt, BBu- s, GaMe, InMe; all combinations, 1 − 16 ), [ t -BuPO 3 AlBu- i ] 4 ( 17 ), and [MePO 3 AlBu- t ] 4 ( 18 ) have been achieved by the facile reactions of alkyl- or arylphosphonic acids with the corresponding alkyl compounds under appropriately chosen reaction conditions. Compounds 1 − 18 have been characterized by analytical and spectroscopic techniques. In all cases, the central M 4 O 12 P 4 inorganic cubic framework is shielded by alkyl/aryl groups. The phosphonates bearing tert -butyl groups on the phosphorus are highly soluble in common organic solvents such as n -hexane, Et 2 O, and THF. The molecular structure of representative examples [ t -BuPO 3 BEt] 4 ( 3 ) and [ t -BuPO 3 BBu- s ] 4 ( 7 ) as determined by single-crystal X-ray diffraction studies reveal the presence of a central cubic M 4 O 12 P 4 framework that is analogous to those found in alumino- and gallophosphate materials. Most of these cubic phosphonates are air and moisture stable. In the presence of excess phenol, it is possible to react one of the M−C bonds at the corners of the cube 3 and prepare its monophenoxy derivative [ t -BuPO 3 BEt] 3 [ t -BuPO 3 B(OPh)] ( 19 ) in very low yields. However, in spite the presence of reactive M−C bonds, these cubic phosphonates are unreactive toward alcohols, amines, carboxylic acids, H 2 O, and air under ambient conditions.