Bridging MCl Bonds with Ambiphilic Phosphine–Borane Ligands

Bridging or pendant? Palladium and rhodium complexes deriving from an ambiphilic phosphine–borane ligand are shown to adopt a bridging P→MCl→B coordination mode in the solid state. DFT calculations provide more insight into the Cl→B interaction and suggest the possible interconversion of the bridging and B‐pendant forms in solution.A combined experimental/theoretical study provides insight into the bridging coordination of MCl bonds with the ambiphilic phosphine–borane ligands i Pr 2 P‐ o (C 6 H 4 )‐BR 2 (PBCy 2 : R=Cy; PBMes 2 : R=Mes). Reaction of [PdCl(allyl)(PBCy 2 )] ( 3 ) with HCl affords the related dinuclear complex [PdCl(μ‐Cl)(PBCy 2 )] 2 ( 5 ). Subsequent cleavage of the chloride bridge by PPh 3 leads to the heteroleptic mononuclear complex trans ‐[PdCl 2 (PPh 3 )(PBCy 2 )] ( 6 ). The solid‐state structures of complexes 5 and 6 substantiate the propensity of the PBCy 2 ligand to bridge Pd‐Cl bonds via P→PdCl→B interactions. DFT calculations carried out on both the model mononuclear complexes 3* and 6* reveal that in each system the energy of the linkage isomer with a Cl→B interaction is very similar to that without. A comparison of the solution and solid‐state 11 B NMR spectroscopic data for complexes 3 and 6 suggests the possible interconversion of the bridging and B‐pendant forms in solution. Bridging coordination of the PBCy 2 ligand across a RhCl bond is observed in the solid‐state structure of the related complex [RhCl(nbd)(PBCy 2 )] ( 7 ). Replacement of the Cy groups at boron by Mes substituents illustrates the role of steric factors on the participation of the Lewis acid upon coordination, no Cl→B interaction being observed in the complex [PdCl(allyl)(PBMes 2 )] ( 8 ).