Gas electron diffraction then and now: from trisilyl phosphine to iso-propyl(tert-butyl)(trichlorosilyl)phosphine

The gas-phase molecular structure of iso-propyl(tert-butyl)(trichlorosilyl)phosphine has been determined using a combination of gas electron diffraction and computational methods. The structure presents a conformational challenge that required use of the SARACEN method to combine theoretical observations into the least-squares refinement process, a great advance on the techniques used to solve the structure of the parent trisilyl phosphine. Five conformers were found on the potential-energy surface for iso-propyl(tert-butyl)(trichlorosilyl)phosphine using the UCONGA program, and following a series of individual structure refinements a combined model with the two most abundant confirmers was evaluated. Key structural parameters (r(a)) include rP-Si [225.5(6) pm], rSi-Cl-mean [204.0(1) pm] and rP-C-mean [204.0(1) pm], angle P-C-H 101.5(5)degrees, angle C-C-C (iPr) 110.5(5)degrees, angle C-C-C (tBu) 109.2(5)degrees and angle C-P-C 105.4(5)degrees.