Contribution of the o-carboranyl fragment to the chemical stability and the 31P-NMR chemical shift in closo-carboranylphosphines. Crystal structure of bis(1-yl-2-methyl-1,2-dicarba-closo-dodecaborane)phenylphosphine

Closo-carboranylphosphines behave differently from closo-monothiocarboranes or other organophosphorus compounds. They tend to lose one boron by reacting with a nucleophile such as OH− with hydrolysis of the CP bond. On the other hand, they are less basic than similar organophosphorus compounds, and less reactive both towards oxygen and some metal ions. Many or all of these characteristics can be attributed to the carborane cluster. Its influence on the phosphorus has been revealed by studying the 31P chemical shifts of a series of P(L)R2 and P(L)2R phosphines, where L are different carboranyl fragments. If the series P(L)Ph2 is considered, where a phosphorus atom is surrounded by two phenyl groups and one o-carboranyl moiety carbon bonded to the phosphorus, it is observed that the capacity to shift the 31P-NMR resonances of P(L)Ph2 to lower field follows the trend: 1-yl-1,2-dicarba-closo-dodecaborane>1-yl-2-phenyl-1,2-dicarba-closo-dodecaborane>1-yl-2-methyl-1,2-dicarba-closo-dodecaborane. These trends are valid for any P(L)R2 series tested so far. It is also found that the absolute value of the 1J(PC(1)) coupling constants, where C(1) is the cluster carbon bonded to P atom, also displays the same trend. The molecular structure of bis(1-yl-2-methyl-1,2-dicarba-closo-dodecaborane)phenylphosphine is presented in this paper.