SYNTHESIS AND X-RAY CRYSTAL-STRUCTURE OF [FE-2(CO)(5)(MU-PBU(2)(T))(MU-PCY(2))(DPPM-P)] - A COMPLEX CONTAINING DPPM [DPPM=BIS(DIPHENYLPHOSPHINO)METHANE] IN THE RARE MONODENTATE COORDINATION

The coordinatively unsaturated complex [Fe-2(CO)(5)(mu-PBu(2)(t))(mu-P Cy(2))] (Fe=Fe) (1) adds spontaneously dppm [dppm = bis(diphenylphosph ino)methane] and yields the saturated compound [Fe-2(CO)(5)(mu-PBu(2)( t))(mu-PCy(2))(dppm-P)] (2). Compounds 1 and 2 exist in a reversible t hermal equilibrium; heating 2 in toluene produces 1 together with the free ligand dppm, whereas by cooling to room temperature 2 is recovere d. A conversion of 2 into the known complex [Fe-2(CO)(3)(mu-PBu(2)(t)) (mu-PCy(2))(mu-dppm)] (3) is only possible by photochemical means. Com pound 3 is readily transformed back into 2 by carbon monoxide under no rmal conditions. The molecular structure of 2 determined by X-ray anal ysis is described.