The co-ordination chemistry of electron-rich poly(organosulphur) compounds. Part 1. Chromium(0), molybdenum(0), and tungsten(0) complexes having tetrakis(thioalkyl)olefins as two- or four-electron donors: the crystal and molecular structure of tetracarbonyl[tetrakis(methylthio)ethene-SS″]chromium

Abstract

Treatment of [Cr(CO)₆] with C₂(SR)₄(L^SR₂) under photolysis in tetrahydrofuran affords cis-[M(CO)₄(L^SR₂)](9; M = Cr, R = Me); analogues (9; M = Cr, Mo, or W; R = Et) have been obtained in better yield from the appropriate hexacarbonyl and C₂(SEt)₄ in EtOH in the presence of Na[BH₄]. In contrast, the olefin (:[graphic omitted])₂ and [Cr(CO)₆] gave [Cr(CO)₅{[graphic omitted][graphic omitted]}], which on heating reverts to the olefin and [Cr(CO)₆]; a related complex [Cr(CO)₅{C₂(SEt)₄}] can be obtained from [NEt₄][Cr(CO)₅Cl] and the olefin in the presence of [OEt₃][BF₄], but the Mo or W analogue was unstable, affording complex (9). Complexes fac-[M(CO)₃(PPh₃)(L^SEt₂)](10) have been prepared from [M(CO)₃(NCMe)₃] by successive treatment with C₂(SEt)₄ and PPh₃ in toluene. Infrared [ν(CO)] and ¹³C n.m.r. spectra support the assigned configurations for complexes (9) and (10) and indicate some M–S π interaction; ¹H n.m.r. spectra show two sets of inequivalent groups R in these complexes. These features are confirmed by a single-crystal X-ray analysis of the title complex, showing an approximately octahedral geometry around the metal, with Cr–S(av.)= 2.379(2), Cr–CO(trans to S)= 1.886(9), Cr–CO(trans to CO)= 1.833(7), and CC = 1.335(9)Å. Crystals are monoclinic, a= 12.487(1), b= 21.838(2), c= 13.686(1)Å, β= 117.32°, T= 21° C, space group P2₁/c, with two molecules per asymmetric unit. The structure was solved by direct methods and refined to R 0.049 by full-matrix least squares using 3 246 independent terms.