Metal complexes of di-phosphorus imines. An exploration of multifunctionalphosphorus-nitrogen ligand-metal chemistry

The development of a hard-soft ligand system, R(2)PQPR(2)=NR' (where Q repr esents a backbone moiety such as CH2, NR, o-C6H4, etc.), by partial oxidati on of bis(phosphines) with azides is described. These systems form a variet y of complexes and compounds with transition metals depending on the nature of the metal. Bidentate chelation of the P and N centers is common with so ft metals but hard centers such as Ti coordinate only through the N. Some e xamples show only coordination of the soft P center. When the imine is form ed with a trimethylsilyl group, elimination of trimethylsilyl chloride from metal chlorides occurs to yield derivatives with a metal-N sigma bond. In these systems, the soft metals further coordinate through P whereas the har der Ti leaves the P free for further coordination. The silyl group may also migrate to the terminal oxygen of metal-ore precursors thus forming bound iminato ligands. Bimetallic systems can be accessed. The bis(phosphoranimin es), H2C(R2P=NR)(2), formed by uncontrolled complete oxidation of a bis(pho sphine), have been explored and show, with hard transition metals and main group metal alkyls, interesting new methanide and methandiide derivatives i n which the methylene group is deprotonated and the metal center is bound t o the carbon. A suite of complexes in which there is clearly a M=C double b ond between Ti, Zr or Hf and the carbon has been discovered; Easy access to these systems is provided by the novel dilithium salt, Li2C(R2P=NR)(2). Br idging dimeric carbene complexes have also been characterized.