Bis(tert-butyldimethylsilyl)(2,6-diisopropylphenyl)phosphane: the first structure of an organophosphane with twotert-butyldimethylsilyl (TBDMS) substituents

Abstract

The title compound, C(24)H(47)PSi(2), is the first organophosphane bearing two tert-butyldimethylsilyl (TBDMS) groups to be crystallographically characterized, even though TBDMS is a very popular bulky silyl group. The structure is a considerably flattened trigonal pyramid, with the sum of the C/Si-P-C/Si angles being 333.35 (6)°, which can be attributed to the steric pressure from the three bulky groups. The P-Si distances [2.2605 (6) and 2.2631 (6) Å] are normal, while the P-C distance [1.8646 (12) Å] is long (outside the s.u. values) compared with related structures. The plane of the aryl ring approximately bisects the Si-P-Si angle, quite unlike the secondary (tert-butyldimethylsilyl)(2,6-diisopropylphenyl)phosphane bearing only one TBDMS group, in which the single Si atom is perpendicular to the aryl ring. The title structure conforms closely to that predicted from B3LYP/6-31G(d) calculations, although the calculations overestimate the degree of planarity. The compound crystallizes centrosymmetrically in the space group P1 as isolated molecules.