Tris{(diphenylphosphino)dimethylsilyl}methane: a sterically hindered tripod

Abstract

The synthesis and characterization of a new tripodal tris(phosphine) molecule, HC(Me2SiPPh2)3 (3) is described. The impact of dimethylsilyl "elbows" on the conformational preferences of this tris(dimethylsilyl)methane core in solution and in the solid state was assessed for 3 and its precursor HC(Me2SiBr)3 (2). Hindered rotation around the "arms" of 3, evident from its solid state structure, has been probed in solution by variable temperature, 1H{31P} NMR spectroscopy, and molecular modelling studies based on the solid state structure of 2 also indicate significant barriers to rotation in this molecule. The susceptibility of 3 to cleavage of the P-Si bonds by protic reagents is described.Key words: tripodal tris(phosphine), polyphosphine, trisilylmethane, C3-symmetry.

Fluorous Zirconocene(IV) Complexes and Their Olefin Polymerization Activity in Toluene and Fluorous Biphasic Solvent Systems

“…Å). 15 Also, the tetrahedral hybridization of the Si atoms with angles of 108.37(10)-110.55(9)°is comparable to that in other bromotrialkylsilanes and compounds 4a,c (vide infra). Interestingly, the pentafluorophenyl rings of the two independent molecules of 2d are π-stacked but with significant ring slippage ( Figure 2).…”

“…The asymmetric unit contains one-third of each of the two independent molecules, both of which have crystallographic C 3 symmetry with the symmetry axis along the Si-Br bond. Despite the heavy fluorination at the phenyl rings the Si-Br bond distances of 2.2192 (15) and 2.1971 (14) Å are comparable to those in Me 3 SiBr 13 and 1,4-dibromo-1,4-disilabutane (2.2362(12) Å) 14 but shorter than in tris(bromodimethylsilyl)methane (2.251-2.263…”

“…Symmetry operations: (i) 1 -y, 1 + xy, z; (ii) -x + y, 1 -x, z. Selected bond lengths (Å): Si-Br ) 2.2192 (15), 2.1971 (14); Si-C11 ) 1.864(3), 1.876(3). Selected bond angles (deg): Br-Si-C11 ) 108.37 (10), 109.46(9), C11-Si-C11i ) 110.55(9), 109.48(9); Si-C11-C12 ) 114.41 (19), 115.18 (18).…”

Conformational control by halogen substitution and by crystallisation: a study of the molecular structures of CH(SiMe2H)3 and CH(SiMe2Br)3 by gas-phase electron diffraction, and ab initio molecular orbital calculations †

“…The conformers of 2 are interconverting rapidly on the NMR timescale in toluene-d 8 at Ϫ90 ЊC. 9 The failure of the calculations on the bromo derivative to predict the correct relative populations of the different conformers is probably an artefact of the quality of the calculations, with a larger basis set than that of 6-31G* being required for bromine. Unfortunately calculations of this magnitude are not possible with our current computational resources.…”

“…Meanwhile, an independent account of the solid state structure of 2 has appeared. 9 Although our study gave bond lengths and angles with lower e.s.d.s we have not included the detailed results here.…”