Uranyl bis-iminophosphorane complexes with in- and out-of-plane equatorial coordination

The new bis-iminophosphorane complexes [UO2Cl {eta(3)-CH(Ph2PNSiMe3)(2)} (thf)] (1) and [UO2Cl {eta(3)-N(Ph2PNSiMe3)(2)}(thf)] (2) are synthesised from the reaction of [UO2Cl2(thf)(3)] with Na[CH(Ph2PNSiMe3)(2)] (Nal) and Na[N(Ph2PNSiMe3)(2)] (NaII), respectively. Both 1 and 2 form dinuclear complexes in the absence of a coordinating solvent. The reactivity of 1 has been explored. The crystal structures of I and 2 have been determined. They display distorted pentagonal bipyramidal geometry with ligands I and II both bonding in a tridentate chelating manner which is shown to remain intact in solution. Complex 1 contains a U-C bond that is out of the equatorial plane by 0.842(3) Angstrom in contrast to 2 where the U-N bond is close to the equatorial plane (0.154(3) Angstrom). This difference in geometry results in an unusual low energy electronic absorption band for 1 originating from C --> U LMCT supported by molecular orbital calculations at the DFT level.