Metal–carbonyl and metal–nitrosyl complexes. Part X. Photochemical generation of organometallic nitrenes and the crystal structure of a carbonylation product, isocyanatocarbonyl-π-cyclopentadienylbis(triphenylphosphine)molybdenum

Abstract

U.v. irradiation of a benzene solution of triphenylphosphine and dicarbonyl-π-cyclopentadienylnitrosylmolybdenum yields approximately equal quantities of the simple substitution product carbonyl-π-cyclopentadienylnitrosyl(triphenylphosphine)molybdenum, [(π-C₅H₅)Mo(CO)(NO)(PPh₃)](I), and a complex shown by a three-dimensional X-ray crystal-structure analysis to be isocyanatocarbonyl-π-cyclopentadienylbis(triphenylphosphine)molybdenum, [(π-C₅H₅)Mo(CO)(PPh₃)₂(NCO)](II). Irradiation of the azide [(π-C₅H₅)Mo(CO)(PPh₃)₂N₃] under an atmosphere of carbon monoxide, and of the azide [(π-C₅H₅)Mo(CO)₂(PPh₃)N₃] in the presence of triphenylphosphine, gives mixtures of [(π-C₅H₅)Mo(CO)(PPh₃)₂(NCO)] and [(π-C₅H₅)Mo(CO)₂(PPh₃)(NCO)]. These reactions are consistent with the formation of organometallic nitrenes which capture carbon monoxide to produce the isocyanate ligand. The methylene chloride solvate of (II) crystallizes in the monoclinic space group P2₁/c, with a= 16·65, b= 13·21, c= 18·14 Å, β= 90°12′, and Z= 4, and has ca. 0·5 molecule of CH₂Cl₂ to each molecule of (II). The atoms were located in electron-density distributions and the co-ordinates and isotropic thermal parameters adjusted by least-squares calculations, the final value of R being 0·114 over 5606 independent reflections. The molybdenum atom, formally seven-co-ordinate, may be described as being at the central position of a distorted square pyramid, with the cyclopentadienyl ring at the apex and the other ligands at the corners of the base. The MoNCO grouping is closely linear, the Mo–M–C and N–C–O angles being 178·3 ± 0·9° and 179·1 ± 1·2°, respectively. The Mo–NCO distance is 2·127 ± 0·008 Å and the Mo–CO distance 1·934 ± 0·010 Å. The Mo–P bond lengths are 2·497 and 2·500 (±0·003)Å. The Mo–C(cyclopentadienyl) distances range from 2·267–2·425 Å(±0·012 Å) and the mean value is 2·333 Å. In the single crystal subjected to X-ray analysis the phosphine ligands of (II) are in a trans relationship. The ¹H n.m.r. measurements indicate that the bulk sample of photochemically generated complex (II) consists of a mixture of the cis- and trans-isomers.