Indenylnickel imidato complexes: Synthesis, characterization, and reactivities

The complex (1-Me-indenyl)Ni(PPh3)(phthalimidate) has been prepared and ful ly characterized by IR and H-1, C-13{H-1},and P-31{H-1} NNLR spectroscopy a nd single-crystal X-ray diffraction. The analogous 4,5-dichlorophthalimidat o, maleimidato, and succinimidato complexes have also been prepared and cha racterized spectroscopically. These complexes are thermally stable, in cont rast to the analogous Ni-amido species, which could not be prepared. Reacti vity studies have shown that the Ni-imidato bond is fairly unreactive in in sertion and nucleophilic reactions, and VT H-1 NMR studies suggest that the rotation around the Ni-N bond in the maleimidato complex is hindered by ca . 11 kcal/mol. The solid-state structure of the phthalimidato derivative sh owed that the P, N, C1, and C3 atoms are arranged around the Ni atom in a d istorted-square-planar coordination environment, while the C2 atom is withi n bonding distance above the main square plane. The phthalimidato ligand is eta(1)(N)-coordinated to Ni; the Ni-N bond is relatively short (1.845(4) A ngstrom), and the orientation of the imidato ligand is such that the planes bearing the atoms P, Ni, N and C9, N, C16 are rotated by ca. 76 degrees wi th respect to each other. The hapticity of the indenyl ligand is characteri zed by an allyl-ene distortion (eta(5)<->eta(3)) and a partial localization of bonding inside the indenyl ring(eta(3<->)eta(1),eta(2)). H-1 and C-13{H -1} NMR spectra indicate that the nonsymmetrical coordination of the indeny l ligand, which can be attributed to the different trans influences of the phthalimidato and PPh3 ligands, is maintained in the solution. The characte r of the Ni-imidato bond has been discussed in terms of electrostatic-coval ent and pi-bonding interactions.