Utilising a Proton-Responsive 1,8-Naphthyridine Ligand for the Synthesis of Bimetallic Palladium and Platinum Complexes.

We present four proton-responsive palladium and platinum complexes, [MCl 2 ( R PONNHO)] (M=Pd, Pt; R= i Pr, t Bu) synthesised by complexation of PdCl 2 or PtCl 2 (COD) with the 1,8-naphthyridine ligand R PONNHO. Deprotonation of [MCl 2 ( tBu PONNHO)] switches ligand coordination from mono- to dinucleating, offering a synthetic pathway to bimetallic Pd II and Pt II complexes [M 2 Cl 2 ( tBu PONNO) 2 ]. Two-electron reduction gives planar M I -M I complexes [M 2 ( tBu PONNO) 2 ] (M=Pd, Pt) containing a metal-metal bond. In contrast to the related nickel system that forms a metallophosphorane [Ni 2 ( tBu PONNOPONNO)], an unusual phosphinite binding mode is observed in [M 2 ( tBu PONNO) 2 ] containing close phosphinite-naphthyridinone P⋅⋅⋅O interactions, which is investigated spectroscopically, crystallographically and computationally. The presented proton-responsive and structurally-responsive R PONNHO and bimetallic R PONNO complexes offer a novel platform for future explorations of metal-ligand and metal-metal cooperativity with palladium and platinum.