Synthesis and Structure of Organic-Soluble Binuclear Molecular Phosphonates of Tantalum, Molybdenum, and Tungsten

The reaction of (η5-C5Me5)TaMe4 with tert-butylphosphonic acid leads to the formation of a mixture of
compounds:  {[(η5-C5Me5)TaMe][t-BuP(O)(OH)][t-BuP(O)(OH)2]}2(t-BuPO3)2 (1) and {[(η5-C5Me5)Ta][t-BuP(O)(OH)2]}2(t-BuPO3)2(μ-O)2 (2). Compound 2 was also obtained by recrystallization of 1 from a THF/hexane
mixture. Reaction of (η5-C5Me5)MCl4 (M = Mo, W) with PhP(O)(OH)2 yields the binuclear phosphonates {[(η5-C5Me5)M][PhP(O)(OH)2]}2(PhPO3)2(μ-O)2 (M = Mo (3); M = W (4)). Compounds 2·THF and 3·2.5THF were
characterized by single-crystal X-ray studies. The tantalum and molybdenum phosphonates 2·THF and 3·2.5THF
have different structures as compared to those of the previously reported titanophosphonate cages.