Synthesis and spectroscopic properties of the ‘mixed’ seven-co-ordinate complexes [MI2(CO)3L(L′)][M = Mo or W; L,L′= PPh3, PPh2(C6H11), PPh(C6H11)2, AsPh3, or SbPh3] and rearrangement of selected [MI2(CO)3L(L′)] to [HL][MI3(CO)3L′]. X-Ray crystal structure of [PPh2(C6H11)H][WI3(CO)3(SbPh3)]·Et2O

Abstract

Reaction of the complexes [MI₂(CO)₃(NCMe)₂](M = Mo or W) with 1 equivalent of L(L = PPh₃, AsPh₃, or SbPh₃) in CH₂Cl₂ at room temperature followed by 1 equivalent of L′[L′= PPh₃, PPh₂(C₆H₁₁), PPh(C₆H₁₁)₂, AsPh₃, or SbPh₃]in situ affords the ‘mixed’ seven-co-ordinate compounds [MI₂(CO)₃L(L′)]. Low-temperature (-70 °C, CD₂Cl₂)¹³C n.m.r. spectra of the triphenylantimony complexes [MI₂(CO)₃L(SbPh₃)][L = PPh₃, PPh₂(C₆H₁₁), or PPh(C₆H₁₁)₂] showed two carbonyl resonances. This indicated capped octahedral geometry with a carbonyl ligand in the unique capping position. Some of the neutral seven-co-ordinate complexes [MI₂(CO)₃L(L′)] containing phosphines disproportionated in CH₂Cl₂ to give the salts [HL][MI₃(CO)₃L′]. ³¹P N.m.r. spectroscopy and negative ion mass spectrometry confirmed that the more electron-rich phosphine is protonated in [HL][MI₃(CO)₃(PPh₃)][L = PPh₂(C₆H₁₁) or PPh(C₆H₁₁)₂]. The structure of the complex [PPh₂(C₆H₁₁)H][WI₃(CO)₃(SbPh₃)]·Et₂O was determined by X-ray analysis. The co-ordination geometry about the tungsten is capped octahedral with a carbonyl ligand in the unique capping position. The capped face contains two carbonyl groups and the triphenylantimony ligand, with the three iodide ligands occupying the uncapping face. The low-temperature (-70 °C, CD₂Cl₂) spectrum of the related complex [NBuⁿ₄][WI₃(CO)₃(SbPh₃)] prepared by treating [WI₂(CO)₃(NCMe)(SbPh₃)]in situ with 1 equivalent of [NBuⁿ₄]I in CH₂Cl₂showed two carbonyl resonances at δ= 209.68 and 235.50 p.p.m. with an intensity ratio of 2 : 1. The lower-field resonance can be ascribed to the unique capping carbonyl ligand and the higher-field resonance to the two equivalent carbonyl ligands on the octahedron. The low-temperature ¹³C n.m.r. spectrum of [NBuⁿ₄][MoI₃(CO)₃(PPh₃)] shows a single resonance at δ= 222.20 p.p.m. which suggests a different capped octahedral structure with the triphenylphosphine ligand capping the three carbonyl ligands.