On the Basicity of Carboranylphosphines.

Three new carboranylphosphines, [1-(1'--1',7'-CBH)-7-PPh--1,7-CBH], [1-(1'-7'-PPh--1',7'-CBH)-7-PPh--1,7-CBH], and [1-{PPh-(1'--1',2'-CBH)}--1,2-CBH], have been prepared, and from a combination of these and literature compounds, eight new carboranylphosphine selenides were subsequently synthesized. The relative basicities of the carboranylphosphines were established by (i) measurement of the NMR coupling constant of the selenide and (ii) calculation of the proton affinity of the phosphine, in an attempt to establish which of several factors are the most important in controlling the basicity. It is found that the basicity of the carboranylphosphines is significantly influenced by the nature of other substituents on the P atom, the nature of the carborane cage vertex (C or B) to which the P atom is attached, and the charge on the carboranylphosphine.

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--1,2-C₂BH] (), 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(C₆F₅)₃ the -carboranylphosphine [1-PPh₂--1,2-C₂BH] () is found to be comparable with PPh₂(C₆F₅) in its ability to catalyze hydrosilylation, whilst the more strongly basic -carboranylphosphine [9-PPh₂--1,7-C₂BH] () is less effective and the very weakly basic species [μ-2,2'-PPh-{1-(1'-1',2'--C₂BH)-1,2--C₂BH}] () is completely ineffective. Base strengths are rank-ordered via measurement of the ¹ P-Se coupling constants of the phosphineselenides [1-SePPh₂--1,2-C₂BH] (), [9-SePPh₂--1,7-C₂BH] (), and [SePPh₂(C₆F₅)] ().