19 research outputs found

    Single-crystal to cingle-crystal addition of H2to [Ir(iPr-PONOP)(propene)][BArF4] and comparison between solid-state and solution reactivity

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    The EPSRC (EP/M024210/2, EP/T019867/1), SCG Chemicals, The Clarendon Trust, The Leverhulme Trust (RPG-2020-184), Diamond Light Source for funding (PhD studentship to AM).The reactivity of the Ir(I) PONOP pincer complex [Ir(iPr-PONOP)(η2-propene)][BArF4], 6, [iPr-PONOP = 2,6-(iPr2PO)2C6H3N, ArF= 3,5-(CF3)2C6H3] 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 H2and propene, and then the application of vacuum, to [Ir(iPr-PONOP)(η2-COD)][BArF4], 1, a reaction manifold that proceeds via the Ir(III) dihydrogen/dihydride complex [Ir(iPr-PONOP)(H2)H2][BArF4], 2, and the Ir(III) dihydride propene complex [Ir(iPr-PONOP)(η2-propene)H2][BArF4], 7, respectively. In solution (CD2Cl2) 6 undergoes rapid reaction with H2to 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 H2in an SC-SC reaction, but unlike in solution the onward reaction (i.e., insertion) does not occur, as confirmed by labeling studies using D2. The solid-state structure of 7 reveals that, on addition of H2to 6, the PONOP ligand moves by 90° within a cavity of [BArF4]-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. H2addition 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(iPr-PONOP)H2(η1-H3B·NMe3)][BArF4], 5, is also reported as part of these studies.Peer reviewe

    Bonding and reactivity of a pair of neutral and cationic heterobimetallic RuZn complexes

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    A combined experimental and computational study of the structure and reactivity of two [RuZn2Me2] complexes, neutral [Ru(PPh3)(Ph2PC6H4)2(ZnMe)2] (2) and cationic [Ru(PPh3)2(Ph2PC6H4)(ZnMe)2][BArF4] ([BArF4] = [B{3,5-(CF3)2C6H3}4]) (3), is presented. Structural and computational analyses indicate these complexes are best formulated as containing discrete ZnMe ligands in which direct Ru–Zn bonding is complemented by weaker Zn···Zn interactions. The latter are stronger in 2, and both complexes exhibit an additional Zn···Caryl interaction with a cyclometalated phosphine ligand, this being stronger in 3. Both 2 and 3 show diverse reactivity under thermolysis and with Lewis bases (PnBu3, PCy3, and IMes). With 3, all three Lewis bases result in the loss of [ZnMe]+. In contrast, 2 undergoes PPh3 substitution with PnBu3, but with IMes, loss of ZnMe2 occurs to form [Ru(PPh3)(C6H4PPh2)(C6H4PPhC6H4Zn(IMes))H] (7). The reaction of 3 with H2 affords the cationic trihydride complex [Ru(PPh3)2(ZnMe)2(H)3][BArF4] (12). Computational analyses indicate that both 12 and 7 feature bridging hydrides that are biased toward Ru over Zn

    Transition Metal-Free Catalytic C−H Zincation and C−H Alumination

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    C−H metalation is the most efficient method to prepare aryl–zinc and –aluminum complexes that are highly useful nucleophiles. Virtually all C–H metalation routes to form Al or Zn organometallic reagents require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported, to our knowledge. Herein we present a catalytic C–H metalation process to form aryl-zinc and aryl-aluminum complexes that uses only simple amine bases (e.g., Et3N) in sub-stoichiometric quantity (10 mol%). Key to this approach is coupling an endergonic C–H metalation step using a [(-diketiminate)MNR3]+ (M = Zn or Al–Me) electrophile with a sufficiently exergonic dehydrocoupling step between the acidic ammonium salt by-product of C–H metalation ([(R3N)H]+) and a Zn–H or Al–Me containing complex. This step, forming H2/MeH, makes the overall cycle exergonic while also generating more of the key cationic metal electrophile. Mechanistic studies supported by DFT calculations revealed metal-specific dehydrocoupling pathways, with the divergent reactivity shown to be due to the different metal valency (which impacts the accessibility of amine-free cationic complexes) and steric environment. Notably, dehydrocoupling in the zinc system proceeds through a ligand-mediated pathway involving protonation of the -diketiminate C position. In this step the magnitude of the key barrier is dependent on the steric bulk of the spectator ligand, with bulkier ligands actually affording lower barriers. This catalytic approach to arene C−H metalation has the potential to be applicable to other main group metals and ligands, thus will facilitate the synthesis of these important organometallic compounds

    CCDC 2083544: Experimental Crystal Structure Determination

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    RAMBEQ : tris(μ-hydrido)-bis(methyl)-tris(triphenylphosphine)-ruthenium-di-zinc tetrakis[3,5-bis(trifluoromethyl)phenyl]borat
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