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, [MCl2 (R PONNHO)] (M=Pd, Pt; R=i Pr, t Bu) synthesised by complexation of PdCl2 or PtCl2 (COD) with the 1,8-naphthyridine ligand R PONNHO. Deprotonation of [MCl2 (tBu PONNHO)] switches ligand coordination from mono- to dinucleating, offering a synthetic pathway to bimetallic PdII and PtII complexes [M2 Cl2 (tBu PONNO)2 ]. Two-electron reduction gives planar MI -MI complexes [M2 (tBu PONNO)2 ] (M=Pd, Pt) containing a metal-metal bond. In contrast to the related nickel system that forms a metallophosphorane [Ni2 (tBu PONNOPONNO)], an unusual phosphinite binding mode is observed in [M2 (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.

Jellyfish-type Dinuclear Hafnium Azido Complexes: Synthesis and Reactivity

Di- and multinuclear hafnium complexes bridged by ligands have been rarely reported. In this article, a novel 3,5-disubstituted pyrazolate-bridged ligand LH5 with two [N2 N]2- -type chelating side arms was designed and synthesized, which supported a series of dinuclear hafnium complexes. Dinuclear hafnium azides [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(THF)4 ] 3 and [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(2,2,2-Kryptofix)] 4 were further synthesized and structurally characterized, featuring two sets of terminal and bridging azido ligands like jellyfishes. The reactivity of 3 under reduction conditions was conducted, leading to a formation of a tetranuclear hafnium imido complex [L1 Hf2 (μ1 -NH)(N3 ){μ2 -K}]2 5. DFT calculations revealed that the mixed imido azide 5 was generated via an intramolecular C-H insertion from a putative dinuclear HfIV -nitridyl intermediate.

Merging Pincer Motifs and Potential Metal-Metal Cooperativity in Cobalt Dinitrogen Chemistry: Efficient Catalytic Silylation of N2 to N(SiMe3 )3

Using a pyrazolate-bridged dinucleating ligand that provides two proximate pincer-type PNN binding sites ("two-in-one pincer"), different synthetic routes have been developed towards its dicobalt(I) complex 2 that features a twice deprotonated ligand backbone and two weakly activated terminal N2 substrate ligands directed into the bimetallic pocket. Protonation of 2 is shown to occur at the ligand scaffold and to trigger conversion to a tetracobalt(I) complex 4 with two end-on μ1,2 -bridging N2 ; in THF 4 is labile and undergoes temperature-dependent N2 /triflate ligand exchange. These pyrazolate-based systems combine the potential of exhibiting both metal-metal and metal-ligand cooperativity, viz. two concepts that have emerged as promising design motifs for molecular N2 fixation catalysts. Complex 2 serves as an efficient (pre)catalyst for the reductive silylation of N2 into N(SiMe3 )3 (using KC8 and Me3 SiCl), yielding up to 240 equiv N(SiMe3 )3 per catalyst.