Intramolecular [4+2] Diels−Alder Cycloaddition of a 2H-Phosphole to Coordinated Unsaturated Phosphines, Phospholes, and an Arsine

Stereoselective [4+2] Diels−Alder cycloadditions occur between unsaturated tertiary phosphine, phosphole, and arsine molybedenum carbonyl complexes, e.g., (Ph 2 E- trans -CH 2 CH CHCH 3 )Mo(CO) 5 [E = P, As] and 3,4-dimethyl-1-phenylphosphole (DMPP). The coordinated DMPP undergoes a [1,5] phenyl migration at about 145 °C prior to or concomitant with the [4+2] intramolecular cycloaddition reaction with the alkene moiety of the dienophile to produce a new class of conformationally rigid bidentate ligands containing the 1-phosphanorbornene bicyclic ring system. The characteristic 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopic features of these compounds are described. Crystal structures of most of the new compounds are reported.