Versatile Coordination and C–C Coupling of Diphosphine-Tethered Imine Ligands with Ni(II) and Ni(0)

Ligands that can adapt their coordination mode to the electronic properties of a metal center are of interest to support catalysis or small molecule activation processes. In this context, the ability of imine moieties to bind in either an η1(N)-fashion via σ-donation of the lone pair or, less commonly, in an η2(C,N)-fashion via π-coordination is potentially attractive for the design of new metal–ligand cooperative systems. Herein, the coordination chemistry of chelating ligands with a diphosphine imine framework (PCNP) to nickel is investigated. The imine moiety binds in an η1(N)-fashion in a Ni­(II)­Cl2 complex. The uncommon η2(C,N)-interaction is obtained in Ni(0) complexes in the presence of a PPh3 coligand. Increasing the bulk on the phosphine side-arms in the Ni(0) complexes, by substituting phenyl for o-tolyl groups, leads to a distinct binding mode in which only one of the phosphorus atoms is coordinated. In the absence of a coligand, a mixture of two different dimeric Ni(0) complexes is formed. In one of them, the imine adopts an uncommon η1(N)­η2(C,N) bridging mode of the ligand to nickel, while the second one may involve reactivity on the ligand by the formation of a new C–C bond by oxidative coupling. The latter is supported by the isolation and structural characterization of a crystalline bis-CO derivative featuring a C–C bond formed by oxidative coupling of two imine moieties