Paul J Chirik

Princeton University, Princeton, New Jersey, United States

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Publications (158)1329.94 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Cycloadditions, such as the [4+2] Diels-Alder reaction to form six-membered rings, are among the most powerful and widely used methods in synthetic chemistry. The analogous [2+2] alkene cycloaddition to synthesize cyclobutanes is kinetically accessible by photochemical methods, but the substrate scope and functional group tolerance are limited. Here, we report iron-catalyzed intermolecular [2+2] cycloaddition of unactivated alkenes and cross cycloaddition of alkenes and dienes as regio- and stereoselective routes to cyclobutanes. Through rational ligand design, development of this base metal-catalyzed method expands the chemical space accessible from abundant hydrocarbon feedstocks. Copyright © 2015, American Association for the Advancement of Science.
    Science 08/2015; 349(6251):960-3. DOI:10.1126/science.aac7440 · 33.61 Impact Factor
  • Paul J Chirik ·
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    ABSTRACT: The hydrogenation of alkenes is one of the most impactful reactions catalyzed by homogeneous transition metal complexes finding application in the pharmaceutical, agrochemical, and commodity chemical industries. For decades, catalyst technology has relied on precious metal catalysts supported by strong field ligands to enable highly predictable two-electron redox chemistry that constitutes key bond breaking and forming steps during turnover. Alternative catalysts based on earth abundant transition metals such as iron and cobalt not only offer potential environmental and economic advantages but also provide an opportunity to explore catalysis in a new chemical space. The kinetically and thermodynamically accessible oxidation and spin states may enable new mechanistic pathways, unique substrate scope, or altogether new reactivity. This Account describes my group's efforts over the past decade to develop iron and cobalt catalysts for alkene hydrogenation. Particular emphasis is devoted to the interplay of the electronic structure of the base metal compounds and their catalytic performance. First generation, aryl-substituted pyridine(diimine) iron dinitrogen catalysts exhibited high turnover frequencies at low catalyst loadings and hydrogen pressures for the hydrogenation of unactivated terminal and disubstituted alkenes. Exploration of structure-reactivity relationships established smaller aryl substituents and more electron donating ligands resulted in improved performance. Second generation iron and cobalt catalysts where the imine donors were replaced by N-heterocyclic carbenes resulted in dramatically improved activity and enabled hydrogenation of more challenging unactivated, tri- and tetrasubstituted alkenes. Optimized cobalt catalysts have been discovered that are among the most active homogeneous hydrogenation catalysts known. Synthesis of enantiopure, C1 symmetric pyridine(diimine) cobalt complexes have enabled rare examples of highly enantioselective hydrogenation of a family of substituted styrene derivatives. Because improved hydrogenation performance was observed with more electron rich supporting ligands, phosphine cobalt(II) dialkyl complexes were synthesized and found to be active for the diastereoselective hydrogenation of various substituted alkenes. Notably, this class of catalysts was activated by hydroxyl functionality, representing a significant advance in the functional group tolerance of base metal hydrogenation catalysts. Through collaboration with Merck, enantioselective variants of these catalysts were discovered by high throughput experimentation. Catalysts for the hydrogenation of functionalized and essentially unfunctionalized alkenes have been discovered using this approach. Development of reliable, readily accessible cobalt precursors facilitated catalyst discovery and may, along with lessons learned from electronic structure studies, provide fundamental design principles for catalysis with earth abundant transition metals beyond alkene hydrogenation.
    Accounts of Chemical Research 06/2015; 48(6). DOI:10.1021/acs.accounts.5b00134 · 22.32 Impact Factor
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    ABSTRACT: Aryl-substituted bis(imino)pyridine cobalt dinitrogen compounds, (RPDI)CoN2 are effective pre-catalysts for the intramolecular [2π+2π] cycloaddition of α,ω-dienes to yield the corresponding bicyclo [3.2.0]heptane derivatives. The reactions proceed under mild thermal conditions with unactivated alkenes, tolerating both amine and ether functional groups. The overall second order rate law for the reaction, first order with respect to both cobalt pre-catalyst and substrate, in combination with EPR spectroscopic studies established the catalyst resting state as the starting cobalt dinitrogen compounds. Planar, S = ½ κ3-bis(imino)pyridine cobalt alkene and tetrahedral κ2-bis(imino)pyridine cobalt diene complexes were observed by EPR spectroscopy and in the latter case, structurally characterized. The electronic structure of these intermediates highlights the role of metal-ligand cooperativity during catalytic turnover. The hemilabile chelate facilitates conversion of a principally ligand-based SOMO in the cobalt dinitrogen and alkene compounds to a metal-based SOMO in the diene intermediates, generating a sufficiently reducing metal center to promote C-C bond forming oxidative cyclization. Structure-activity relationships on bis(imino)pyridine substitution were also established with 2,4,6-tricyclopentyl aryl groups, resulting in optimized catalytic [2π+2π] cycloaddition. The cyclopentyl groups provide a sufficiently open metal coordination sphere that encourages substrate coordination while remaining large enough to promote a challenging, turnover limiting C(sp3)-C(sp3) reductive elimination.
    Journal of the American Chemical Society 06/2015; 137(24). DOI:10.1021/jacs.5b04034 · 12.11 Impact Factor
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    ABSTRACT: Generated in situ from air-stable cobalt precursors or readily synthesized using NaHBEt3, (PPh3)3CoH(N2) was found to be an effective catalyst for the hydroboration of alkenes. Unlike previous base-metal catalysts for alkene isomerization-hydroboration which favor the incorporation of boron at terminal positions, (PPh3)3CoH(N2) promotes boron incorporation adjacent to π-systems even in substrates where the alkene is at a remote position, enabling a unique route to 1,1-diboron compounds from α,ω-dienes.
    Organic Letters 05/2015; 17(11). DOI:10.1021/acs.orglett.5b01135 · 6.36 Impact Factor
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    ABSTRACT: A bis(imino)pyridine cobalt-catalyzed hydroboration of terminal alkynes with HBPin (Pin = pinacolate) with high yield and (Z)-selectivity for synthetically valuable vinylboronates is described. Deuterium labeling studies, stoichiometric experiments and isolation of catalytically relevant intermediates support a mechanism involving selective insertion of an alkynylboronate ester into a Co-H bond, a pathway distinct from known precious metal catalysts where metal vinylidene intermediates have been proposed to account for the observed (Z)-selectivity.
    Journal of the American Chemical Society 04/2015; 137(18). DOI:10.1021/jacs.5b00936 · 12.11 Impact Factor
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    ABSTRACT: Cobalt(II) dichloride complexes supported by a variety of neutral, tridentate pincer ligands have been prepared and, following in situ activation with NaBEt3H, evaluated for the catalytic borylation of 2-methylfuran, 2,6-lutidine, and benzene using both HBPin and B2Pin2 (Pin = pinacolate) as boron sources. Preparation of well-defined organometallic compounds in combination with stoichiometric experiments with HBPin and B2Pin2 provided insight into the nature and kinetic stability of the catalytically relevant species. In cases where sufficiently electron donating pincers are present, such as with bis(phosphino)pyridine chelates, Co(III) resting states are preferred and catalytic C-H borylation is efficient. Introduction of a redox-active subunit into the pincer reduces its donating ability and, as a consequence, the accessibility of a Co(III) resting state. In these cases, unusual mixed-valent μ-hydride cobalt complexes have been crystallographically and spectroscopically characterized. These studies have also shed light on the active species formed during in situ activated cobalt alkene hydroboration catalysis and provide important design criteria in base metal catalyzed C-B bond forming reactions.
    Organometallics 04/2015; 34(7):1307-1320. DOI:10.1021/acs.organomet.5b00044 · 4.13 Impact Factor
  • Iraklis Pappas · Paul J Chirik ·
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    ABSTRACT: The catalytic hydrogenolysis of the titanium-amide bond in (η5-C5Me4SiMe3)2Ti(Cl)NH2 to yield free ammonia is described. The rhodium hydride, (η5-C5Me5)(py-Ph)RhH (py-Ph = 2-phenylpyridine), serves as the catalyst and promotes N-H bond formation via hydrogen atom transfer. The N-H bond dissociation free energies of ammonia ligands have also been determined for titanocene and zirconocene complexes and reveal a stark dependence on metal identity and oxidation state. In all cases, the N-H BDFEs of coordinated NH3 decreases by >40 kcal/mol from the value in the free gas phase molecule.
    Journal of the American Chemical Society 02/2015; 137(10). DOI:10.1021/jacs.5b01047 · 12.11 Impact Factor
  • Peter T Wolczanski · Paul J. Chirik ·
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    ABSTRACT: On the occasion of Professor John Bercaw’s 70th birthday, we reflect and highlight his distinguished career in organometallic chemistry and homogeneous catalysis. What began as a fundamental interest in the chemistry bis(cyclopentadienyl)titanium compounds and their interaction with molecular nitrogen evolved into a vibrant and di-verse program tackling some of the most important problems in catalysis. Using well-defined organometallic compounds, fundamental insights were gained in the mechanism of CO reduction, basic transformations of organometallic chemistry such as alkene insertion and alkyl β-hydrogen elimination, the origin of stereocontrol in metallocene-catalyzed polymeri-zation and in the activation of hydrocarbons by electrophilic late transition metals.
    ACS Catalysis 02/2015; 5(3):150209095624001. DOI:10.1021/acscatal.5b00076 · 9.31 Impact Factor
  • W. Neil Palmer · Tianning Diao · Iraklis Pappas · Paul J. Chirik ·
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    ABSTRACT: Cobalt alkyl complexes bearing readily available and redox-active 2,2′:6′,2″-terpyridine and α-diimine ligands have been synthesized, and their electronic structures have been elucidated. In each case, the supporting chelate is reduced to the monoanionic, radical form that is engaged in antiferromagnetic coupling with the cobalt(II) center. Both classes of cobalt alkyls proved to be effective for the isomerization-hydroboration of sterically hindered alkenes. An α-diimine-substituted cobalt allyl complex proved exceptionally active for the reduction of hindered tri-, tetra-, and geminally substituted alkenes, representing one of the most active homogeneous catalysts known for hydroboration. With limonene, formation of an η3-allyl complex with a C-H agostic interaction was identified and accounts for the sluggish reactivity observed with diene substrates. For the terpyridine derivative, unique Markovnikov selectivity with styrene was also observed with HBPin.Keywords: cobalt; hydroboration; catalysis; redox-active ligands; boronates
    ACS Catalysis 02/2015; 5(2):622-626. DOI:10.1021/cs501639r · 9.31 Impact Factor
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    Paul J. Chirik ·

    Organometallics 01/2015; 34(1):1-2. DOI:10.1021/om5012984 · 4.13 Impact Factor
  • Iraklis Pappas · Paul J. Chirik ·
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    ABSTRACT: Cycloaddition of monosubstituted allenes with a monomeric, base free titanocene oxide resulted in isolation and crystallographic characterization of the corresponding oxatitanacyclobutanes. In solution these compounds are a mixture of (E) and (Z) isomers and interconvert by mechanisms that are dependent on the specific substitution of the allene. Facile carbonylation of the oxatitanacyclobutanes was also observed to yield rare examples of structurally characterized oxatitanacyclopentanones. Isomerization of these species was observed in the presence of proton sources. These studies highlight the new chemistry available from synthesis of base free titanocene oxide compounds enabled by appropriate cyclopentadienyl substitution.
    Polyhedron 12/2014; 84:67-73. DOI:10.1016/j.poly.2014.06.023 · 2.01 Impact Factor
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    ABSTRACT: The activity of bis(phosphine) iron dialkyl complexes for the asymmetric hydrogenation of alkenes has been evaluated. High-throughput experimentation was used to identify suitable ironphosphine combinations using the displacement of pyridine from py(2)Fe(CH2SiMe3)(2) for precatalyst formation. Preparative-scale synthesis of a family of bis(phosphine) iron dialkyl complexes was also achieved using both ligand substitution and salt metathesis methods. Each of the isolated organometallic iron complexes was established as a tetrahedral and hence high-spin ferrous compound, as determined by Mossbauer spectroscopy, magnetic measurements, and, in many cases, X-ray diffraction. One example containing a Josiphos-type ligand, (SL-J212-1)Fe(CH2SiMe3)(2), proved more active than other isolated iron dialkyl precatalysts. Filtration experiments and the lack of observed enantioselectivity support dissociation of the phosphine ligand upon activation with dihydrogen and formation of catalytically active heterogeneous iron. The larger six-membered chelate is believed to reduce the coordination affinity of the phosphine for the iron center, enabling metal particle formation.
    Organometallics 10/2014; 33(20):5781-5790. DOI:10.1021/om500329q · 4.13 Impact Factor
  • Jennifer V. Obligacion · Scott P. Semproni · Paul J. Chirik ·

    ChemInform 10/2014; 45(43). DOI:10.1002/chin.201443184
  • Grant W. Margulieux · Zoë R. Turner · Paul J. Chirik ·
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    ABSTRACT: The bis(imino)pyridine 2,6-(2,6-iPr2-C6H3NCPh)2-C5H3N (iPrBPDI) molybdenum dinitrogen complex, [{(iPrBPDI)Mo(N2)}2(μ2,η1,η1-N2)] has been prepared and contains both weakly (terminal) and modestly (bridging) activated N2 ligands. Addition of ammonia resulted in sequential NH bond activations, thus forming bridging parent imido (μ-NH) ligands with concomitant reduction of one of the imines of the supporting chelate. Using primary and secondary amines, model intermediates have been isolated that highlight the role of metal–ligand cooperativity in NH3 oxidation.
    Angewandte Chemie 10/2014; 53(51). DOI:10.1002/ange.201408725
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    ABSTRACT: The electronic structures of pyridine N-heterocyclic dicarbene ((iPr)CNC) iron complexes have been studied by a combination of spectroscopic and computational methods. The goal of these studies was to determine if this chelate engages in radical chemistry in reduced base metal compounds. The iron dinitrogen example ((iPr)CNC)Fe(N2)2 and the related pyridine derivative ((iPr)CNC)Fe(DMAP)(N2) were studied by NMR, Mössbauer, and X-ray absorption spectroscopy and are best described as redox non-innocent compounds with the (iPr)CNC chelate functioning as a classical π acceptor and the iron being viewed as a hybrid between low-spin Fe(0) and Fe(II) oxidation states. This electronic description has been supported by spectroscopic data and DFT calculations. Addition of N,N-diallyl-tert-butylamine to ((iPr)CNC)Fe(N2)2 yielded the corresponding iron diene complex. Elucidation of the electronic structure again revealed the CNC chelate acting as a π acceptor with no evidence for ligand-centered radicals. This ground state is in contrast with the case for the analogous bis(imino)pyridine iron complexes and may account for the lack of catalytic [2π + 2π] cycloaddition reactivity.
    Organometallics 10/2014; 33(19):5423-5433. DOI:10.1021/om500727t · 4.13 Impact Factor
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    ABSTRACT: The addition of carbon dioxide to ((tBu)PNP)CoH [(tBu)PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine] resulted in rapid insertion into the Co-H bond to form the corresponding κ(1)-formate complex, which has been structurally characterized. Treatment of ((tBu)PNP)CoH with PhSiH3 resulted in oxidative addition to form trans-((tBu)PNP)CoH2(SiH2Ph), which undergoes rapid exchange with excess free silane. With 0.5 mol % ((tBu)PNP)CoH, the catalytic hydrosilylation of CO2 with PhSiH3 to a mixture of oligomers containing silyl formate, bis(silyl)acetyl, and silyl ether subunits has been observed.
    Inorganic Chemistry 08/2014; 53(18). DOI:10.1021/ic501901n · 4.76 Impact Factor
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    ABSTRACT: Planar, low-spin cobalt(II) dialkyl complexes bearing bidentate phosphine ligands, (P-P)Co(CH2SiMe3)2 are active for the hydrogenation of geminal and 1,2-disubstituted alkenes. Hydrogenation of more hindered linear and endocyclic trisubstituted alkenes was achieved through hydroxyl group activation, an approach that also enables directed hydrogenations to yield contrasteric isomers of cyclic alkenes.
    Journal of the American Chemical Society 08/2014; 136(38). DOI:10.1021/ja507902z · 12.11 Impact Factor
  • Grant W Margulieux · Scott P Semproni · Paul J Chirik ·
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    ABSTRACT: The zirconocene dinitrogen complex [{(η(5) -C5 Me4 H)2 Zr}2 (μ2 ,η(2) ,η(2) -N2 )] was synthesized by photochemical reductive elimination from the corresponding zirconium bis(aryl) or aryl hydride complexes, providing a high-yielding, alkali metal-free route to strongly activated early-metal N2 complexes. Mechanistic studies support the intermediacy of zirconocene arene complexes that in the absence of sufficient dinitrogen promote CH activation or undergo comproportion to formally Zr(III) complexes. When N2 is in excess arene displacement gives rise to strong dinitrogen activation.
    Angewandte Chemie International Edition 08/2014; 53(35). DOI:10.1002/anie.201402401 · 11.26 Impact Factor
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    ABSTRACT: The aryl substituted bis(imino)pyridine cobalt methyl complex, (MesPDI)CoCH3 (MesPDI = 2,6-(2,4,6-Me3C6H2-N=CMe)2C5H3N) promotes the selective catalytic dehydrogenative silylation of linear α-olefins to form the corresponding allylsilanes with commercially relevant tertiary silanes such as (Me3SiO)2MeSiH and (EtO)3SiH. Dehydrogenative silylation of internal olefins such as cis- and trans-4-octene also exclusively produce the allylsilane with the silicon located at the terminus of the hydrocarbon chain resulting in a highly selective base metal catalyzed method for the remote functionalization of C-H bonds with retention of unsaturation. The cobalt-catalyzed reactions also enable inexpensive α-olefins to serve as functional equivalents of more valuable αω-dienes and offers a unique method for the cross linking of silicone fluids with well-defined carbon spacers. Stoichiometric experiments and deuterium labeling studies support activation of the cobalt alkyl precursor to form a putative cobalt silyl, which undergoes 2,1-insertion of the alkene followed by selective β-hydrogen elimination from the carbon distal from the large tertiary silyl group and accounts for the observed selectivity for allylsilane formation.
    Journal of the American Chemical Society 07/2014; 136(34). DOI:10.1021/ja5060884 · 12.11 Impact Factor
  • Carsten Milsmann · Scott P Semproni · Paul J Chirik ·
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    ABSTRACT: Addition of stoichiometric quantites of 1,2-diaryl hydrazines to the bis(imino)pyridine vanadium dinitrogen complex, [{(iPrBPDI)V(THF)}2(μ2-N2)] (iPrBPDI = 2,6-(2,6-iPr2-C6H3N=CPh)2C5H3N) resulted in N-N bond cleavage to yield the corresponding vanadium bis(amido) derivatives, (iPrBPDI)V(NHAr)2 (Ar = Ph, Tol). Spectroscopic, structural and computational studies support an assignment as vanadium(III) complexes with chelate radical anions, [BPDI]•-. With ex-cess 1,2-diarylhydrazine, formation of the bis(imino)pyridine vanadium imide amide compounds, (iPrBPDI)V(NHAr)NAr were observed along with the corresponding aryldiazene and aniline. A DFT-computed N-H bond dissociation free energy of 69.2 kcal/mol was obtained for (iPrBPDI)V(NHPh)NPh and interconversion between this compound and (iPrBPDI)V(NHPh)2 with (2,2,6,6-Tetramethylpiperidin-1-yl)oxidanyl (TEMPO), 1,2-diphenylhydrazine and xanthene ex-perimentally bracketed this value between 67.1-73.3 kcal/mol. For (iPrBPDI)V(NHPh)2, the N-H BDFE was DFT-calculated to be 64.1 kcal/mol, consistent with experimental observations. Catalytic disproportionation of 1,2-diaryl hydrazines pro-moted by (iPrBPDI)V(NHAr)NAr was observed and crossover experiments established exchange of anilide (but not imido) ligands in the presence of free hydrazine. These studies demonstrate the promising role of redox-active active ligands in promoting N-N bond cleavage with concomitant N-H bond formation and how the electronic properties of the metal-ligand combination influence N-H bond dissocation free energies and related hydrogen atom transfer processes.
    Journal of the American Chemical Society 07/2014; 136(34). DOI:10.1021/ja5062196 · 12.11 Impact Factor

Publication Stats

6k Citations
1,329.94 Total Impact Points


  • 2011-2015
    • Princeton University
      • Department of Chemistry
      Princeton, New Jersey, United States
  • 2002-2012
    • Cornell University
      • Department of Chemistry and Chemical Biology
      Итак, New York, United States
  • 1999-2005
    • California Institute of Technology
      • Division of Chemistry and Chemical Engineering
      Pasadena, California, United States