Redox-Transmetalation Reactions: Easy Access to Homo- and Heterodimetallic d⁸,d¹⁰ Complexes

The ability of the imine PyCH═N-CH₂Py (Py = 2-pyridyl, bpi) to behave as a heteroditopic ligand, which is suitable for creating two separate compartments to host metals in different oxidation states, has been developed by studying the reactions of the mixed-valence complexes [(cod)M^-Ι(μ-bpi)M^Ι(cod)] (M = Rh, Ir) with [M'(Cl)₂(PPh₃)₂] (M' = Pd, Ni). The results depend on the molar ratio of the reagents used (1:1 or 1:2) to give the heterometallic complexes {d¹⁰-M',d⁸-M}-[(PPh₃)(Cl)M'⁰(μ-bpi)M^Ι(cod)] (Pd,Rh, 4; Pd,Ir, 5; Ni,Rh, 8; Ni,Ir, 9) and the two-electron mixed-valent compounds [(PPh₃)(Cl)M'⁰(μ-bpi)M'^ΙΙ(Cl)] (M' = Ni, 10; Pd, 11), respectively. A redox process occurs in the replacement of the low-valent [(cod)M^-I] fragment, whereas the exchange of the [(cod)M^I] fragment is redox-neutral. The metal with a d⁸ configuration in the products exhibits a square-planar geometry coordinated to two (Rh/Ir) or three (Ni/Pd) nitrogen atoms of the bridging bpi ligand. Conversely, the metal with a d¹⁰ configuration adopts trigonal-planar geometries, π-bonded to the imine C═N bond. The isolated complexes 4/5 and 10/11, along with the hypothetical heterometallic Pd,Ni compound (12), were studied by DFT methods. Additionally, the T-shaped moiety 'M'^ΙΙ(PPh₃)(Cl)(η¹-CH-N(bpi))', stabilized by a secondary γ-agostic interaction, and the 'M'^II(Cl)(κ³N-bpi)' fragment was found to be accessible redoxomers of complexes 10 and 11 by DFT calculations.