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.