Synthesis and characterization of terminal [Re(XCO)(CO)2(triphos)] (X=N, P): isocyanate versus phosphaethynolate complexes.

The terminal rhenium(I) phosphaethynolate complex [Re(PCO)(CO)(2)(triphos)] has been prepared in a salt metathesis reaction from Na(OCP) and [Re(OTf)(CO)(2)(triphos)]. The analogous isocyanato complex [Re(NCO)(CO)(2)(triphos)] has been likewise prepared for comparison. The structure of both complexes was elucidated by X-ray diffraction studies. While the isocyanato complex is linear, the phosphaethynolate complex is strongly bent around the pnictogen center. Computations including natural bond orbital (NBO) theory, natural resonance theory (NRT), and natural population analysis (NPA) indicate that the isocyanato complex can be viewed as a classic Werner-type complex, that is, with an electrostatic interaction between the Re(I) and the NCO group. The phosphaethynolate complex [Re(P=C=O)(CO)(2)(triphos)] is best described as a metallaphosphaketene with a Re(I)-phosphorus bond of highly covalent character.