skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Thursday, February 13 until 2:00 AM ET on Friday, February 14 due to maintenance. We apologize for the inconvenience.


Title: Group 13 ion coordination to pyridyl breaks the reduction potential vs hydricity scaling relationship for NADH models

The relationshipEpvs. ΔGH− correlates the applied potential (Ep) needed to drive organohydride formation with the strength of the hydride donor that is formed: hydride transfer catalysis - as in enzymes like LarA - will be more energy efficient ifEpis shifted anodically using kinetic effect.

 
more » « less
Award ID(s):
2054529
PAR ID:
10538842
Author(s) / Creator(s):
; ;
Publisher / Repository:
Royal Society of Chemistry
Date Published:
Journal Name:
Chemical Science
Volume:
14
Issue:
47
ISSN:
2041-6520
Page Range / eLocation ID:
13944 to 13950
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The catalytic one‐bond isomerization (transposition) of 1‐alkenes is an emerging approach toZ‐2‐alkenes. Design of more selective catalysts would benefit from a mechanistic understanding of factors controllingZselectivity. We propose here a reaction pathway forcis‐Mo(CO)4(PCy3)(piperidine) (3), a precatalyst that shows highZselectivity for transposition of alpha olefins (e. g., 1‐octene to 2‐octene, 18 : 1Z : Eat 74 % conversion). Computational modeling of reaction pathways and isotopic labeling suggests the isomerization takes place via an allyl (1,3‐hydride shift) pathway, where oxidative addition offac‐(CO)3Mo(PCy3)(η2‐alkene) is followed by hydride migration from one position (cisto allyl C3carbon) to another (cisto allyl C1carbon) via hydride/CO exchanges. Calculated barriers for the hydride migration pathway are lower than explored alternative mechanisms (e. g., change of allyl hapticity, allyl rotation). To our knowledge, this is the first study to propose such a hydride migration in alkene isomerization.

     
    more » « less
  2. Abstract

    N‐Heterocyclic carbene (NHC) ligands possess the ability to stabilize metal‐based nanomaterials for a broad range of applications. With respect to metal‐hydride nanomaterials, however, carbenes are rare, which is surprising if one considers the importance of metal‐hydride bonds across the chemical sciences. In this study, we introduce a bottom‐up approach that leverages preexisting metal‐metal m‐center‐n‐electron (mc‐ne) bonds to access a highly stable cyclic(alkyl)amino carbene (CAAC) copper‐hydride nanocluster, [(CAAC)6Cu14H12][OTf]2with superior stability compared to Stryker's reagent, a popular commercial phosphine‐based copper hydride catalyst. Density functional theory (DFT) calculations reveal that the enhanced stability stems from hydride‐to‐ligand backbonding with the π‐accepting carbene. This new cluster emerges as an efficient and selective copper‐hydride pre‐catalyst, thereby providing a bench‐stable alternative for catalytic applications.

     
    more » « less
  3. Abstract

    Membrane bound nicotinamide nucleotide transhydrogenase (TH) catalyses the hydride transfer from NADH to NADP+. Under physiological conditions, this reaction is endergonic and must be energized by thepmf, coupled to transmembrane proton transport. Recent structures of transhydrogenase holoenzymes suggest new mechanistic details, how the long-distance coupling between hydride transfer in the peripheral nucleotide binding sites and the membrane-localized proton transfer occurs that now must be tested experimentally. Here, we provide protocols for the efficient expression and purification of theEscherichia colitranshydrogenase and its reconstitution into liposomes, alone or together with theEscherichia coliF1F0ATP synthase. We show thatE. colitranshydrogenase is a reversible enzyme that can also work as a NADPH-driven proton pump. In liposomes containing both enzymes, NADPH driven H+-transport by TH is sufficient to instantly fuel ATP synthesis, which adds TH to the pool ofpmfgenerating enzymes. If the same liposomes are energized with ATP, NADPH production by TH is stimulated > sixfold both by a pH gradient or a membrane potential. The presented protocols and results reinforce the tight coupling between hydride transfer in the peripheral nucleotide binding sites and transmembrane proton transport and provide powerful tools to investigate their coupling mechanism.

     
    more » « less
  4. Abstract

    Dinuclear manganese hydride complexes of the form [Mn2(CO)8(μ‐H)(μ‐PR2)] (R=Ph,1; R=iPr,2) were used inE‐selective alkyne semi‐hydrogenation (E‐SASH) catalysis. Catalyst speciation studies revealed rich coordination chemistry and the complexes thus formed were isolated and in turn tested as catalysts; the results underscore the importance of dinuclearity in engendering the observedE‐selectivity and provide insights into the nature of the active catalyst. The insertion product obtained from treating2with (cyclopropylethynyl)benzene contains acis‐alkenyl bridging ligand with the cyclopropyl ring being intact. Treatment of this complex with H2affords exclusivelytrans‐(2‐cyclopropylvinyl)benzene. These results, in addition to other control experiments, indicate a non‐radical mechanism forE‐SASH, which is highly unusual for Mn−H catalysts. The catalytically active species are virtually inactive towardscistotransalkene isomerization indicating that theE‐selective process is intrinsic and dinuclear complexes play a critical role. A reaction mechanism is proposed accounting for the observed reactivity which is fully consistent with a kinetic analysis of the rate limiting step and is further supported by DFT computations.

     
    more » « less
  5. Abstract

    Molecular design ultimately furnishes improvements in performance over time, and this has been the case for Rh‐ and Ir‐based molecular catalysts currently used in transfer hydrogenation (TH) reactions for fine chemical synthesis. In this report, we describe a molecular pincer ligand Al catalyst for TH, (I2P2−)Al(THF)Cl (I2P=diiminopyridine; THF=tetrahydrofuran). The mechanism for TH is initiated by two successive Al‐ligand cooperative bond activations of the O−H bonds in two molecules of isopropanol (iPrOH) to afford six‐coordinate (H2I2P)Al(OiPr)2Cl. Stoichiometric chemical reactions and kinetic experiments suggest an ordered transition state, supported by polar solvents, for concerted hydride transfer fromiPrOto substrate. Metal‐ligand cooperative hydrogen bonding in a cyclic transition state is a likely support for the concerted hydride transfer event. The available data does not support involvement of an intermediate Al‐hydride in the TH. Proof‐of‐principle reactions including the conversion of isopropanol and benzophenone to acetone and diphenylmethanol with 90 % conversion in 1 h are described. The analogous hydride compound, (I2P2−)Al(THF)H, also cleaves the O−H bond iniPrOH to afford (HI2P)Al(OiPr)H and (HI2P)Al(OiPr)2, but no activity for catalytic TH was observed.

     
    more » « less