Indenylnickel Imidato Complexes:  Synthesis, Characterization, and Reactivities

The complex (1-Me-indenyl)Ni(PPh3)(phthalimidate) has been prepared and fully characterized by IR and H-1, C-13{H-1},and P-31{H-1} NNLR spectroscopy and single-crystal X-ray diffraction. The analogous 4,5-dichlorophthalimidato, maleimidato, and succinimidato complexes have also been prepared and characterized spectroscopically. These complexes are thermally stable, in contrast to the analogous Ni-amido species, which could not be prepared. Reactivity studies have shown that the Ni-imidato bond is fairly unreactive in insertion 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 showed that the P, N, C1, and C3 atoms are arranged around the Ni atom in a distorted-square-planar coordination environment, while the C2 atom is within 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) Angstrom), 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 with respect to each other. The hapticity of the indenyl ligand is characterized 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 indenyl ligand, which can be attributed to the different trans influences of the phthalimidato and PPh3 ligands, is maintained in the solution. The character of the Ni-imidato bond has been discussed in terms of electrostatic-covalent and pi-bonding interactions.