Exchange of isonitrile ligands in the complex [Mo(O)Cl(CNMe)4] by the tetraphos ligand prP4: Stereochemical influences on the reaction course

Reaction of [Mo(O)Cl(CNMe)₄]⁺ with the linear tetraphos ligand meso and rac prP₄ leads to a mixture of [Mo(O)Cl(κ⁴-meso-prP₄)]⁺ and [Mo(O)Cl(CNMe)(κ³-rac-prP₄)]⁺ which are identified by X-ray structural analysis and/or ³¹P NMR spectroscopy. In the meso κ⁴-product both of the phenyl groups of the central phosphorus atoms are oriented towards the oxo ligand whereas in the rac κ³-product one of these phenyl groups is oriented to the oxo and the other to the chloro ligand. The origin of the different coordination modes lies in the different steric demands of the oxo and chloro ligands. The influences of the steric interactions are enhanced by the fact that exchange of the fourth isonitrile is difficult. This hypothesis is supported by the preparation of the complex [Mo(O)Cl(CNMe)(dpepp)]PF₆ whose isonitrile ligand is inert towards exchange by monophosphines, even under drastic conditions.