Crystal structures of two closely related compounds of molybdenum-(II) and -(IV): carbonylcyclopentadienylhexafluorobut-2-yne(pentafluorophenylthio)molybdenum and cyclopentadienyl(hexafluorobut-2-yne)oxo(pentafluorophenylthio)molybdenum

Abstract

The co-ordinatively unsaturated species [Mo(CO)(η⁵-C₅H₅)(CF₃C₂CF₃)(SC₆F₅)](I) undergoes slow oxidation in diethyl ether to give [Mo(O)(η⁵-C₅H₅)(CF₃C₂CF₃)(SC₆F₅)], (II). X-Ray diffraction studies show that the co-ordinated hexafluorobut-2-yne moiety has its bond axis approximately parallel to the Mo–C–O bonds in the Mo^II carbonyl compound but that this has turned through 90° to become parallel to the Mo–S bond in the Mo^IV oxo-compound. Crystals of (I) are triclinic, space group P, with Z= 2 in a unit cell of dimensions: a= 8.267(4), b= 13.548(5), c= 8.337(3)Å, α= 99.16(3), β= 97.08(4), γ= 86.61(4)° the structure was solved by heavy-atom methods from 2 722 independent diffracted intensities measured on a diffractometer, and refined to R 0.038. Crystals of (II) are orthorhombic, space group Pbca, with Z= 8 in a unit cell of dimensions: a= 25.130(6), b= 10.933(4), c= 13.210(4)Å, and the structure has been similarly elucidated from 2 251 independent reflections (R 0.050).

In both compounds the co-ordinated acetylene is non-linear, with CF₃–C–C angles of 136 and 138°(I), 138 and 142°(II), and C–C 1.29 (I), 1.27 (II), but all four carbon atoms are approximately coplanar with the molybdenum atom, the Mo–O distance in (II) is 1.678 Å, and Mo–S distances are 2.366 (I) and 2.403 (II). The co-ordination around the Mo atom is approximately octahedral with the cyclopentadienyl ligand occupying three facial sites.