Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, Ohio 45221-0172, United States.
Published: July 2022
AI Article Synopsis
Article Abstract
PNP-pincer-stabilized iron carbonyl dihydride complexes are key intermediates in catalytic hydrogenation and dehydrogenation reactions; however, decomposition through these intermediates has been observed. This inspires the development of a PPP-pincer system that may show improved catalyst stability. In this work, bis[2-(diisopropylphosphino)phenyl]phosphine (or PPP) is used to react with FeCl under a carbon monoxide (CO) atmosphere to yield -(PPP)Fe(CO)Cl. A subsequent reaction with NaBH produces /-(PPP)FeH(CO)Cl or ,-(PPP)Fe(CO)H, depending on the amount of NaBH employed. The -dihydride complex shows catalytic activity for the conversion of PhCHO to PhCHOH (under H) or PhCOCHPh (under Ar). It also catalyzes the dehydrogenation of PhCHOH to PhCHO and PhCOCHPh, albeit with limited turnover numbers. A more efficient catalytic process is the dehydrogenation of formic acid to carbon dioxide (CO), which can operate under additive-free conditions. Mechanistic investigation suggests that the -dihydride complex undergoes protonation with formic acid to release H while forming -(PPP)FeH(CO)(OCHO)·HCOH, in which the CO ligand has shifted and the formate is hydrogen-bonded to formic acid. The hydrido formate complex loses CO under ambient conditions, completing the catalytic cycle by reforming the -dihydride complex.
State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.
The homogeneous catalytic hydrogenation of benzo-fused heteroarenes generally provides partially hydrogenated products wherein the heteroaryl ring is preferentially reduced, such as quinoline hydrogenation, leading to 1,2,3,4-tetrahydroquinoline. Herein, we report a carbocycle-selective hydrogenation of fused -heteroarenes (quinoline, isoquinoline, quinoxaline, etc.) using the Ru complex of a chiral spiroketal-based diphosphine (SKP) as the catalyst, affording the corresponding 5,6,7,8-tetrahydro products in high chemoselectivities.
State Key Laboratory of Supramolecular Structure and Materials, Institute of Theoretical Chemistry, College of Chemistry, Jilin University, Changchun 130021, China.
Silyl-phenanthroline (NN'Si) ligand ancillary iridium-catalyzed C(sp)-H borylation is investigated theoretically. Density functional theory calculations clearly disclose that the (NN'Si)Ir(H)(Bpin) (NN'Si = 6-[(di--butylsilyl)methyl]-1,10-phenanthroline) complex is a resting state, and the (NN'Si)Ir(Bpin) complex serves as an active species in the catalytic cycle. The remarkably high activity of this type of a catalyst arises from the rapid reductive elimination of HBpin from (NN'Si)Ir(H)(Bpin) to generate the active species (NN'Si)Ir(Bpin).
The reaction of [Ir(IPr)H][BAr] (; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; BAr = B{CH(3,5-CF)}) with ZnMe proceeds with CH elimination to give [Ir(IPr)(IPr')(ZnMe)H][BAr] (, where (IPr') is a cyclometalated IPr ligand). reacts with H to form tetrahydride [Ir(IPr)(ZnMe)H][BAr], , that loses H under forcing conditions to form [Ir(IPr)(ZnMe)H][BAr], . Crystallization of also results in the formation of its noncyclometalated isomer, [Ir(IPr)(ZnMe)][BAr], , in the solid state.
Unsymmetric dinuclear Ir(I) complexes, [IrCl(L)(-dpmppp)] (L = XylNC (), BuNC (), CO ()), were synthesized using -PhPCHP(Ph)(CH)P(Ph)CHPPh (-dpmppp), which supports - (M) and (M) metal sites, and exhibited high reactivity for O, H, and HCl. The IrRh heterodinuclear complexes, [MMCl(L)(-dpmppp)] () (MM = IrRh, RhIr; L = XylNC, CO ( = , )), were also synthesized and used together with the Rh complexes () to elucidate the role of each metal site. For the reactions of O, and showed higher reactivity than those of and , giving η-peroxide complexes [{MCl}{M(η-O)(XylNC)}(-dpmppp)] (, ), from which O would not dissociate.
Direct dehydrogenation of carboxylic acids to their unsaturated counterparts represents a valuable transformation for complex molecule synthesis, which, however, has been challenging to achieve. In addition, the current carbonyl desaturation methods are almost all based on oxidative conditions. Here we report an Ir-catalyzed redox-neutral transfer dehydrogenation approach to directly convert carboxylic acids to either α,β- or β,γ-unsaturated counterparts.
