Rhodium Disulfur and Dioxygen Complexes: Examination of Boron Secondary Coordination Sphere Effects

Abstract

A series of diphosphine-ligated rhodium(III) h2-peroxo and -persulfido compounds are targeted with one subset containing a boron-rich secondary coordination sphere (SCS). A systematic investigation using both experimental and theoretical methods has been performed to assess whether peripheral boranes can be used to engage with rhodium(III)-bound chalcogenides. For the model compound, [RhI(dnppe)2]BPh4 (dnppe = 1,2-bis(di-n-propylphosphino)ethane), adducts of the form [RhI(dnppe)2(h2-Ch2)]BPh4 (Ch = O or S) were characterized. For the octaboranyl compound, [RhI(P2BCy4)2]BPh4 (P2BCy4 = 1,2-bis(di(3-dicyclohexylboranyl)propylphosphino)ethane), however, treatment with O2 resulted in SCS decomposition via B—O bond formation, while reaction with 0.25 equivs. S8 provided [RhI(P2BCy4)2(2-S2)]BPh4, which based on variable-temperature 31P NMR spectroscopic measurements, does not exhibit a B—S interaction. Using a compound with a single pendant borane as a model, potential energy surface (PES) scans were found to suggest kinetic and thermodynamic feasibility of a B—O interaction with DG(B—O) = —2.5 kcal mol-1; a stationary point for the related B—S system was not located.

A Borane Lewis Acid in the Secondary Coordination Sphere of a Ni(II) Imido Imparts Distinct C–H Activation Selectivity

“…Our group has recently explored a series of ligands containing tunable secondary coordination sphere environments with nitrogen-based and NHC ligands, ,,,− and our previous studies showed that the appended 9-BBN (BBN = borabicyclo[3.3.1]­nonyl) group provides moderate Lewis acidity, enabling unique reactivity that is facilitated by reversible borane-substrate bond formation . Our prior efforts demonstrated that when coordinated to low valent metals, depe (depe = Et 2 PCH 2 CH 2 PEt 2 ) provides sufficient electron density to activate nitrogenous substrates, without precluding interactions to a Lewis acid. , Herein, we establish the synthesis and reactivity of depe derivatives containing a single appended Lewis acidic borane (Figure ) to evaluate the extent that acidic groups modulate the reactivity of late transition metal (Ni) imidos. , …”

“…7,15 Herein, we establish the synthesis and reactivity of depe derivatives containing a single appended Lewis acidic borane (Figure 1) to evaluate the extent that acidic groups modulate the reactivity of late transition metal (Ni) imidos. 57,58 ■ RESULTS AND DISCUSSION Synthesis of Borane-Functionalized Bisphosphine Ligands. Key to our synthetic approach was access to Et 2 PCH 2 CH 2 P(Et)(Cl).…”