Organosulphur–transition-metal chemistry. Part 3. Methyl thiocyanate complexes: crystal and molecular structure of pentacarbonyl(methyl thiocyanate)chromium

Abstract

Treatment of [N(PPh₃)₂][M(NCS)(CO)₅](M = Cr, MO, or W) with SFO₂(OMe) yields methyl thiocyanate complexes [M(CO)₅(NCSMe)](M = Cr or W) in ca. 50% yield. The molybdenum analogue is unstable and could not be purified. Displacement of acetonitrile from [Cr(CO)₅(NCMe)] by MeSCN also gives [Cr(CO)₅(NCSMe)], while the isocyanide [Cr(CO)₅,(CNMe)] is formed on attempted displacement by MeNCS. Several reactions of [M(CO)₅,(NCSMe)] have been studied, but only that with PPh₃ was successful, affording [M(CO)₅(PPh₃)]. Methylation of a mixture of [Fe(SCN)(CO)₂(η-C₅H₅)] and [Fe(NCS)(CO)₂(η-C₅H₅)] does not yield a cationic complex of either MeNCS or MeSCN, and addition of SFO₂(OMe) to [N(PPh₃)₂][Cr(NCO)(CO)₅] gives only a low yield of unstable [Cr(CO)₅(NCOMe)], identified by its i.r. spectrum. Crystals of the title complex are monoclinic, space group P2₁/n, with Z= 4 in a unit cell of dimensions a= 6.462(6), b= 11.891 (12), c= 13.618(18)Å, and β= 96.46(9)°. The structure has been elucidated by conventional heavy-atom methods from 2 720 independent reflections measured on a four-circle diffractometer at a low temperature (203 K), and refined to R 0.032. The atomic sequence Cr–N–C–S–Me has been established with geometry: Cr–N 2.059, NC 1.145, and C–S 1.688 Å; C–S–C 98.7 °. Chromium is octahedrally co-ordinated, with the carbonyl group trans to the MeSCN ligand having Cr–C shorter (0.073 Å) and C–O longer (0.02 Å) than the four co-planar carbonyl groups, a reflection of the low π-acceptor capacity of MeSCN.