P-C, P-N, and M-N Bond Formation Processes in Reactions of Heterometallic Phosphinidene-Bridged MoMn and MoRe Complexes with Diazoalkanes and Organic Azides to Build Three- to Five-Membered Phosphametallacycles.

Reactions of the heterometallic MoRe complex [MoReCp(μ-PR*)(CO)6] and its MoMn analogue with some small molecules having N-N multiple bonds, such as diazoalkanes and organic azides, were investigated (R* = 2,4,6-C6H2tBu3). Reactions with excess ethyl diazoacetate proceeded slowly and with concomitant denitrogenation to give complexes [MoMCp(μ-η2P,C:κ2P,O-PR*CHCO2Et)(CO)5], which display a bridging phosphaalkene ligand in a novel μ-η2:κ2 coordination mode, while reactions with other diazoalkanes resulted only in the decomposition of the organic reagent. The MoRe complex reacted with benzyl- or p-tolyl azide at room temperature to give the green complexes [MoReCp(μ-η2P,N:κP,N'2-PR*N3R)(CO)6] [R = Bn, p-tol], which display bridging phosphatriazadiene ligands in a novel 6-electron donor coordination mode as a result of a formal [2 + 1] cycloaddition of the terminal N atom of the azide to the Mo-P double bond of the parent complex, followed by coordination of the distal NR nitrogen to the rhenium center. Denitrogenation was only observed for the p-tolyl azide derivative, which upon heating at 333 K yielded [MoReCp{μ-κP:κN-PR*N(p-tol)}(CO)6], a molecule displaying a bridging phosphaimine ligand in a rare κP:κN coordination mode. Analogous reactions of the MoMn phosphinidene complex proceeded similarly at 273 K to give the phosphatriazadiene-bridged derivatives [MoMnCp(μ-η2P,N:κ2P,N'-PR*N3R)(CO)6], but these were thermally unstable and degraded at room temperature to give the mononuclear triazenylphosphanyl complexes [Mn2(κP,N-PR*NHNNR)(CO)3] as major products, along with small amounts of the phosphaimine-bridged complex [MoMnCp{μ-κP:κN-PR*N(p-tol)}(CO)6] in the case of the p-tolyl azide derivative. The structure of the new complexes was analyzed in light of spectroscopic data and single-crystal diffraction studies on selected examples of each type of complex.