Contribution of the o-carboranyl fragment to the chemical stability and the P-31-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 reacti ng with a nucleophile such as OH- with hydrolysis of the C-P bond. On the o ther hand, they are less basic than similar organophosphorus compounds, and less reactive both towards oxygen and some metal ions. Many or all of thes e characteristics can be attributed to the carborane cluster. Its influence on the phosphorus has been revealed by studying the P-31 chemical shifts o f a series of P(L)R-2 and P(L)(2)R phosphines, where L are different carbor anyl fragments. If the series P(L)Ph, is considered, where a phosphorus ato m is surrounded by two phenyl groups and one o-carboranyl moiety carbon bon ded to the phosphorus, it is observed that the capacity to shift the P-31-N MR resonances of P(L)Ph-3 to lower field follows the trend: 1-yl-1,2-dicarb a-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 )R-2 series tested so far. It is also found that the absolute value of the (1)J(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) is presented in this paper. (C) 19 99 Elsevier Science S.A. All rights reserved.