Chelating phosphines with low coordinated phosphorus atoms: Part I. Phosphaalkenes associated with phosphine moieties — X-ray structure of cis-(CO)4Mo[ortho-Ph2PC6H4CHP(t-Bu3C6H2)]·C7H16

Condensation of ortho-diphenylphosphinobenzaldehyde with 2,4,6-tri-t-butyl-phenylphosphine yields the λ2,λ3-diphosphorus chelating agent 2a with an E-configurated phosphaalkene unit as indicated by the analysis of the NMR data. On irradiation with UV light 2a is transformed to the Z-isomer (2b). E-2a forms stable Mo(0), Pd(II) and Pt(II) chelate complexes (3–5). The X-ray structure of the molybdenum complex 3·C7H16 (space group P212121) has been determined showing the phosphaalkene moiety to be coordinated in a η1-mode to molybdenum within a distorted six-membered chelate ring.