Procedure for the degradation of 1,2-(PR2)2-1,2-dicarba-closo-dodecaborane(12) and 1-(PR2)-2-R'-1,2-dicarba-closo-dodecaborane(12)

Article abstract of DOI:10.1016/0022-328X(95)05558-7

Monophosphines and bisphosphines bearing anionic groups derived from the7,8-dicarba-nido-undecaborate unit, such as [7-PR2-8-Me-7,8-C2B9H10](-) and [7,8-(PR2)2-7,8-C2B9H10](-) (R = phenyl, ethyl, isopropyl or ethoxy ), were synthesized from closo-carborane precursors 1-PR2-2-Me-1,2-C2B10H10 and 1,2-(PR2)2-1,2-C2B10H10, respectively. In general, the C(c)-P bond in the closo species is very susceptible degradation reactions, producing C(c)-P cleavage and yielding the [7,8-C2B9H10]2(-) anion. Good degradation conditions which retain the C(c)-P found are toluene with a carborane-to-piperidine ratio of 1:50 and ethanol with carborane-to-piperidine ratio of 1:10. The aryl phosphines keep the C(c)-P bond best and produce the highest yields. Phosphites also retain the C(c)-P bond, but the phosphorus becomes positive and produces a zwitterionic species. Alkylphosphines are intermediate, depending on the bulk and nature of the R group in the -PR2 unit. The crystal structure of [NMe4][7,8-(PPh2)2-7,8-C2B9H10].CH3CH2OH is described.