Single-Crystal to Single-Crystal Addition of H(2) to [Ir((i)Pr-PONOP)(propene)][BAr(F)(4)] and Comparison Between Solid-State and Solution Reactivity

[Image: see text] The reactivity of the Ir(I) PONOP pincer complex [Ir((i)Pr-PONOP)(η(2)-propene)][BAr(F)(4)], 6, [(i)Pr-PONOP = 2,6-((i)Pr(2)PO)(2)C(6)H(3)N, Ar(F) = 3,5-(CF(3))(2)C(6)H(3)] 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 6 is synthesized in solution from sequential addition of H(2) and propene, and then the application of vacuum, to [Ir((i)Pr-PONOP)(η(2)-COD)][BAr(F)(4)], 1, a reaction manifold that proceeds via the Ir(III) dihydrogen/dihydride complex [Ir((i)Pr-PONOP)(H(2))H(2)][BAr(F)(4)], 2, and the Ir(III) dihydride propene complex [Ir((i)Pr-PONOP)(η(2)-propene)H(2)][BAr(F)(4)], 7, respectively. In solution (CD(2)Cl(2)) 6 undergoes rapid reaction with H(2) to form dihydride 7 and then a slow (3 d) onward reaction to give dihydrogen/dihydride 2 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 6 also form complex 7 on addition of H(2) 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(2). The solid-state structure of 7 reveals that, on addition of H(2) to 6, the PONOP ligand moves by 90° within a cavity of [BAr(F)(4)](−) anions rather than the alkene moving. Periodic DFT calculations support the higher barrier to insertion in the solid state (ΔG(‡) = 26.0 kcal/mol), demonstrating that the single-crystal environment gates onward reactivity compared to solution. H(2) addition to 6 to form 7 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((i)Pr-PONOP)H(2)(η(1)-H(3)B·NMe(3))][BAr(F)(4)], 5, is also reported as part of these studies.