Leveraging Metal and Ligand Reactive Sites for One Pot Reactions: Ligand-Centered Borenium Ions for Tandem Catalysis with Palladium

Accelerating σ-Bond Metathesis at Sn(II) Centers

Molecular main-group hydride catalysts are attractive as cheap and Earth-abundant alternatives to transition-metal analogues. In the case of the latter, specific steric and electronic tuning of the metal center through ligand choice has enabled the iterative and rational development of superior catalysts. Analogously, a deeper understanding of electronic structure-activity relationships for molecular main-group hydrides should facilitate the development of superior main-group hydride catalysts. Herein, we report a modular Sn-Ni bimetallic system in which we systematically vary the ancillary ligand on Ni, which, in turn, tunes the Sn center. This tuning is probed using Sn L1 XAS as a measure of electron density at the Sn center. We demonstrate that increased electron density at Sn centers accelerates the rate of σ-bond metathesis, and we employ this understanding to develop a highly active Sn-based catalyst for the hydroboration of CO2 using pinacolborane. Additionally, we demonstrate that engineering London dispersion interactions within the secondary coordination sphere of Sn allows for further rate acceleration. These results show that the electronics of main-group catalysts can be controlled without the competing effects of geometry perturbations and that this manifests in substantial reactivity differences.

Metal-Ligand Role Reversal: Hydride-Transfer Catalysis by a Functional Phosphorus Ligand with a Spectator Metal

Hydride transfer catalysis is shown to be enabled by the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand. Complex 1·[Ru]+, comprising a nontrigonal phosphorus chelate (1, P(N(o-N(2-pyridyl)C6H4)2) and an inert metal fragment ([Ru] = (Me5C5)Ru), reacts with NaBH4 to give a metallohydridophosphorane (1H·[Ru]) by P-H bond formation. Complex 1H·[Ru] is revealed to be a potent hydride donor (ΔG°H-,exp < 41 kcal/mol, ΔG°H-,calc = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the 1·[Ru]+/1H·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.