Preparation, NMR studies, and X-ray analysis of cis-L2Mo(CO)4 complexes (L = tritylated phosphines) with sterically demanding ligands

The synthesis and characterization of the cis complexes L2Mo(CO)4 with L = Ph3CPF2, Ph3CPH2, Ph3CP(H)Cl, Ph3CP(H)F, Ph3CP(NH2)2 and Ph3CP(H)Ph is described. The compounds were formed when norbornadiene tetracarbonylmolybdenum was allowed to react with two equivalents of L at room temperature, while, presumably due to their increasing steric hindrance, in the case of the ligands Ph3CP(H)t-Bu and Ph3C(H)PP(H)CPh3 no reaction had taken place. The PC-bond of the unstable phosphine Ph3CPH2 showed stabilization and, in contrast, the PC-bond of the stable phosphine Ph3CPCl2 showed destabilization when the PMo-bond was formed. An X-ray structure determination of (Ph3CPF2)2Mo(CO)4 revealed short P–Mo bonds.