Preparation and Characterization of a 19-Electron Ni(I) Complex Bearing a Cyclopentadienyl-Phosphine Ligand

A series of Ni complexes bearing cyclopentadienyl-phosphine (L) ligands have been synthesized and structurally characterized. 18-electron LNi­(II)­X complex 1 with the halogen atom was stable and could not be reduced by common reducing agents. By introducing a PMe3 ligand, the bromine atom dissociated from the Ni center, enabling the isolation of separated ion-pair complex 2 ([LNi-PMe3]+X–). Complex 2 could be efficiently reduced by KC8, and the corresponding 19-electron formal Ni­(I) complex (3) was obtained as dark green crystals. Our L ligand stabilized the Ni­(I) center in 3 and provided sufficient steric hindrances to avoid the dimerization of 3. All complexes were fully characterized, including single-crystal X-ray crystallography and spectroscopic investigations coupled with theoretical computations. Electron paramagnetic resonance (EPR) measurements indicated that the unpaired electron is considerably delocalized from the Ni center to the ligand. DFT calculations successfully reproduced the geometric structures and the EPR parameters and further revealed that complex 3 possesses a fairly covalent Ni–Cp interaction.