Exploiting the Electronic Tuneability of Carboranes as Supports for Frustrated Lewis Pairs

The first example of a carborane with a catecholborolyl substituent, [1-Bcat-2-Ph-closo-1,2-C(2)B(10)H(10)] (1), has been prepared and characterized and shown to act as the Lewis acid component of an intermolecular frustrated Lewis pair in catalyzing a Michael addition. In combination with B(C(6)F(5))(3) the C-carboranylphosphine [1-PPh(2)-closo-1,2-C(2)B(10)H(11)] (IVa) is found to be comparable with PPh(2)(C(6)F(5)) in its ability to catalyze hydrosilylation, whilst the more strongly basic B-carboranylphosphine [9-PPh(2)-closo-1,7-C(2)B(10)H(11)] (V) is less effective and the very weakly basic species [μ-2,2′-PPh-{1-(1′-1′,2′-closo-C(2)B(10)H(10))-1,2-closo-C(2)B(10)H(10)}] (IX) is completely ineffective. Base strengths are rank-ordered via measurement of the (1)J (31)P-(77)Se coupling constants of the phosphineselenides [1-SePPh(2)-closo-1,2-C(2)B(10)H(11)] (2), [9-SePPh(2)-closo-1,7-C(2)B(10)H(11)] (3), and [SePPh(2)(C(6)F(5))] (4).