Sterically Congested Tripodal Phosphites: Conformational Analysis, Solid-State Polymorphism, Metal Complexation, and Application to the Asymmetric Hydrosilation of Ketones1

The synthesis as well as isolation and crystallographic analysis of two solid-state polymorphs of the tripodal ligand tri{2,2‘,2‘ ‘-tris[(2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]ethyl}amine (3) is described. Form I crystallized from ethyl acetate in the space group P21/n with the unit-cell parameters a = 20.070(10) A, b = 17.477(2) A, c = 27.620(3) A, and β = 93.050(10)°, V = 9674.5(14) A3, and Z = 4. Form II crystallized from a mixture of acetone and toluene in the space group P1 with the unit-cell parameters a = 12.493(1) A, b = 19.701(2) A, c = 21.027(2) A, α = 116.23(1)°, β = 100.15(1)°, and γ = 91.07(1)°, V = 4542 A3, and Z = 2. Differences in the relative absolute stereochemistry of the stereoaxes in the seven-membered dibenzo[d,f][1,3,2]dioxaphosphepin ring are discussed. The synthesis and X-ray characterization of enantiomerically pure (S,S,S)-tri{2,2‘,2‘ ‘-tris[(2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]propyl}amine [(...