Crystal and Molecular Structure of (1,1,4,4-Tetrafhioro-2-tert-butyl-1,4-disilabut-2-ene)molybdenum(II) Pentacarbonyl

(1,1,4,4-Tetrafluoro-2-tert-butyl-1,4-disilabut-2-ene)molybdenum(II) pentacarbonyl has been prepared photochemically by reaction of 3-tert-butyl-1,1,2,2-tetrafluoro-1,2-disilacyclobutene with molybdenum hexacarbonyl in pentane. The crystal structure was determined by X-ray diffraction. The crystal is triclinic, of space group PĪ, with Z = 2; a = 12.710 (3) Å, b = 10.236 (2) Å, c = 7.242 (5) Å, α = 86.53 (3)°0, β = 93.78 (3)°, γ = 70.65 (2)°, and D_calcd = 1.568 g cm^-3. The structure was solved by heavy-atom methods and refined by full-matrix least squares with the use of anisotropic temperature factors to an R value of 0.059 for 2897 independent reflections. The central molybdenum atom is seven-coordinated with a pentagonal-bipyramidal environment. The pentagonal base contains the disilabutene ligand and three carbonyl groups. The average bonding distances are 2.041 (13) Å for Mo-C and 2.605 (3) Å for Mo-Si. The five-membered molybdodisilabutene ring is rather strained with endocyclic silicon and carbon valence angles substantially greater and smaller than their tetrahedral and trigonal ideal ones, respectively. The transannular Si-Si distance is 2.861 Å, which is substantially shorter than the sum of van der Waals radii, suggesting there might be direct silicon-silicon cross-ring interaction.