Structural Diversity and Dynamics of Nickel Complexes with Ambidentate Phosphorus Heterocycles

The reaction of [Ni­(C2H4)­(dtbpe)] with 1-alkyl-1,2-diphospholes afforded [Ni­(1-alkyl-1,2-diphosphole)­(dtbpe)] complexes. Both DNMR experimental and DFT calculation results have shown that in solution these complexes are in an equilibrium of two P–P side-on η2-coordinated 1-alkyl-1,2-diphosphole isomers. In one form, unusual η2 bonding occurred at a P2–P1 side, presumably at the expense of a vicinal P2–C1 π bond, and it could be characterized as a phosphametallacycle with the formal oxidation state of Ni­(II). In the second isomer with the Ni(0) state, Ni bonds to the ligand through two σ interactions with phosphorus lone pairs. The P2 chemical shift, being heavily dependent on structure, can be used to monitor these isomer populations.