Single-Crystal to Single-Crystal Addition of H₂ to [Ir(ⁱPr-PONOP)(propene)][BAr^F₄] and Comparison Between Solid-State and Solution Reactivity

The reactivity of the Ir(I) PONOP pincer complex [Ir(Pr-PONOP)(η-propene)][BAr ], , [Pr-PONOP = 2,6-(PrPO)CHN, Ar = 3,5-(CF)CH] was studied in solution and the solid state, both experimentally, using molecular density functional theory (DFT) and periodic-DFT computational methods, as well as in situ single-crystal to single-crystal (SC-SC) techniques. Complex is synthesized in solution from sequential addition of H and propene, and then the application of vacuum, to [Ir(Pr-PONOP)(η-COD)][BAr ], , a reaction manifold that proceeds via the Ir(III) dihydrogen/dihydride complex [Ir(Pr-PONOP)(H)H][BAr ], , and the Ir(III) dihydride propene complex [Ir(Pr-PONOP)(η-propene)H][BAr ], , respectively. In solution (CDCl) undergoes rapid reaction with H to form dihydride and then a slow (3 d) onward reaction to give dihydrogen/dihydride and propane. DFT calculations on the molecular cation in solution support this slow, but productive, reaction, with a calculated barrier to rate-limiting propene migratory insertion of 24.8 kcal/mol. In the solid state single-crystals of also form complex on addition of H in an SC-SC reaction, but unlike in solution the onward reaction (i.e., insertion) does not occur, as confirmed by labeling studies using D. The solid-state structure of reveals that, on addition of H to , the PONOP ligand moves by 90° within a cavity of [BAr ] anions rather than the alkene moving. Periodic DFT calculations support the higher barrier to insertion in the solid state (Δ = 26.0 kcal/mol), demonstrating that the single-crystal environment gates onward reactivity compared to solution. H addition to to form is reversible in both solution and the solid state, but in the latter crystallinity is lost. A rare example of a sigma amine-borane pincer complex, [Ir(Pr-PONOP)H(η-HB·NMe)][BAr ], , is also reported as part of these studies.