Oxidative Addition Of Dihydrogen Research Articles

Dihydrogen Cleavage by a Zinc-Zinc Bond of a Heteroleptic Dizinc(I) Cation.

Oxidative addition of dihydrogen across a metal-metal bond to form reactive metal hydrides in homogeneous catalysis is known for transition metals but not for zinc(I)-zinc(I) bond as found in Carmona's eponymous dizinconene [Zn2Cp*2] (Cp* = η5-C5Me5). Dihydrogen reacted with the heteroleptic zinc(I)-zinc(I) bonded cation [(L2)Zn-ZnCp*][BAr4F] (L2 = TMEDA, N,N,N',N'-tetramethylethylenediamine, TEEDA, N,N,N',N'-tetraethylethylenediamine; ArF = 3,5-(CF3)2C6H3) under 2 bar at 80 °C to give the zinc(II) hydride cation [(L2)ZnH(thf)][BAr4F] along with zinc metal and Cp*H derived from the intermediate [Cp*ZnH]. DFT calculations show that the cleavage of dihydrogen occurs through a highly unsymmetrical transition state. Mechanistic studies agree with a heterolytic cleavage of dihydrogen as a result of the cationic charge and unsymmetrical ligand coordination. To explore the existence of zinc(I) hydride, thermally unstable hydridotriphenylborate complexes of zinc(I) [(L2)Zn(HBPh3)-ZnCp*] (L2 = TMEDA, TEEDA; TMPDA, N,N,N',N'-tetramethyl-1,3-propylenediamine) have been prepared by salt metathesis and were shown to undergo fast exchange with both BPh3 and [HBPh3]-.

Square Planar Cobalt(II) Hydride versus T-Shaped Cobalt(I): Structural Characterization and Dihydrogen Activation with PNP-Cobalt Pincer Complexes.

The carbazole-based pincer ligand R(CbzPNP)H (R = iPr, tBu) has been used for the synthesis and characterization of various low- and high-spin cobalt complexes. Upon treatment of the high-spin complexes R(CbzPNP)CoCl (2R-CoIICl) with NaHBEt3, the selective formation of cobalt(II) hydride 3 iPr-CoIIH and T-shaped cobalt(I) complex 4 tBu-CoI was observed, depending on the substituents at the phosphorus atoms. For an unambiguous characterization of the reaction products, a density functional theory (DFT) supported paramagnetic NMR analysis was carried out, which established the electron configuration and the oxidation states of the metal atoms, thus demonstrating the significant impact of ligand substitution on the outcome of the reaction. A distinct one-electron reactivity was found for 4 tBu-CoI in the dehalogenation of tBuCl and cleavage of PhSSPh. On the other hand, the CoI species displayed two-electron redox behavior in the oxidative addition of dihydrogen. The resulting dihydride complex 6 tBu-CoIII(H)2 was found to display sluggish reactivity toward alkenes, whereas the cobalt(II) hydride 3 iPr-CoIIH was successfully employed in the catalytic hydrogenation of unhindered alkenes. The stoichiometric hydrogenolysis of 8 iPr-CoIIBn at elevated pressure (10 bar) led to a rapid cleavage of the Co-C bond to yield hydride complex 3 iPr-CoIIH. On the other hand, treatment of 2 iPr-CoIICl with phenethylmagnesium chloride directly resulted in the formation of 3 iPr-CoIIH, indicating facile β-H elimination of the alkene insertion product (reversibly) generated in the catalytic hydrogenation. On the basis of these observations, a mechanistic pathway involving a key σ-bond metathesis step of the CoII-alkyl species is proposed.

Oxidative Addition of Dihydrogen, Boron Compounds, and Aryl Halides to a Cobalt(I) Cation Supported by a Strong-Field Pincer Ligand.

Cationic cobalt(I) dinitrogen complexes with a strong-field tridentate pincer ligand were prepared and the oxidative addition of polar and non-polar bonds was studied. Addition of H2 to [(iPrPNP)Co(N2)]+ (iPrPNP = 2,6-bis((diisopropylphosphaneyl)methyl)pyridine) in THF-d8 resulted in rapid oxidative addition and formation of the cis-Co(III) dihydride complex, cis-[(iPrPNP)Co(H)2L]+ where L = THF or N2. The addition of H2 was reversible as evidenced by the dynamics observed by variable temperature 1H NMR spectroscopy and the regeneration of [(iPrPNP)Co(N2)]+ upon exposure to dinitrogen. In contrast, addition of HBPin, (Pin = pinacolato) B2Pin2 and aryl halides resulted in the formation of net one-electron oxidation products: cationic Co(II)-boryl and Co(II)-halide/aryl complexes, respectively. All products were structurally characterized by X-ray crystallography and the electronic structures were determined by a combination of magnetic moment measurements, EPR spectroscopy and DFT calculations. Monitoring the addition of HBPin to [(iPrPNP)Co(N2)]+ provided evidence for a transient Co(III) oxidative addition product that likely undergoes comproportionation with the cobalt(I) starting material to generate the observed Co(II) products.

Cp*Co(IPr): synthesis and reactivity of an unsaturated Co(i) complex.

Synthesis of coordinatively unsaturated Cp*Co(IPr) (2), is accomplished by addition of free N-heterocyclic carbene IPr to [(Cp*Co)2-μ-(η(4):η(4)-toluene)] (1). Stoichiometric reactivity is consistent with a 16 electron species, as 2 undergoes ligand addition/NHC displacement and reversible reaction with dihydrogen. Cp*Co(IPr) represents an elusive example of a stable Cp*CoL fragment.

Synthesis of a 14-electron iridium(III) complex with a xanthene-based bis(silyl) chelate ligand (xantsil): A distorted seesaw-shaped four-coordinate geometry and reactions leading to 16-electron complexes

Synthesis, structure determination, and reactions of a 14-electron four-coordinate iridium(III) complex bearing a xanthene-based bis(silyl) chelate ligand, i.e., Ir{κ2(Si,Si)-xantsil}(PCy3)Cl (1a, xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)), are reported. A precursor of 1a, the 16-electron (dihydrido)iridium(V) complex Ir{κ2(Si,Si)-xantsil}(H)2(PCy3)Cl (2), was prepared by the reaction of [IrCl-(coe)2]2 (coe = cyclooctene) with 4,5-bis(dimethylsilyl)-9,9-dimethylxanthene (xantsilH2) and PCy3. Dehydrogenation reaction of 2 with 3,3-dimethylbut-1-ene, a hydrogen acceptor, afforded a mixture of 1a and its isomer 1b, abbreviated as 1a + 1b, together with 2,2-dimethylbutane. Single crystals obtained from a CH2Cl2 solution of 1a + 1b contained only isomer 1a. X-ray crystal structure analysis of one of the crystals revealed that 1a adopts a distorted seesaw-shaped four-coordinate geometry where the coordinatively unsaturated metal center is stabilized by weak agostic interaction of two γ-C–H bonds of the PCy3 ligand. On the other hand, NMR spectroscopic analysis of 1a + 1b demonstrated that 1a is in fast equilibrium with a minor amount of 1b in solution. Replacement of the chloro ligand in complexes 1a + 1b by a triflato ligand with AgOTf (OTf = OSO2CF3) afforded quantitatively a single product, i.e., the 16-electron iridium–triflato complex Ir{κ3(Si,O,Si)-xantsil}(PCy3)(OTf) (3). 1a + 1b and 16-electron complex 2 are interconvertible via oxidative addition of dihydrogen (from 1a + 1b to 2) and alkene hydrogenation (from 2 to 1a + 1b). Complexes 1a + 1b and 2 were found to catalyze hydrogenation of 3,3-dimethylbut-1-ene.

Interconversion of Quadruply and Quintuply Bonded Molybdenum Complexes by Reductive Elimination and Oxidative Addition of Dihydrogen

Aus 4 mach 5 (und umgekehrt): UV-Bestrahlung eines Bis(amidinat)-Komplexes mit [(H)MoMo(H)]-Kern induziert die reduktive Eliminierung von H2 unter Bildung einer bekannten Mo-Mo-Spezies mit Fünffachbindung (siehe Schema), die durch Rückreaktion mit H2 wieder [(H)MoMo(H)] bildet. UV-Bestrahlung der Bis(hydrid)-Spezies in Benzol und Toluol ergibt Aren-Komplexe, in denen der aromatische Kohlenwasserstoff die Mo-Atome verbrückt. Dipp=2,6-Diisopropylphenyl. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Interconversion of Quadruply and Quintuply Bonded Molybdenum Complexes by Reductive Elimination and Oxidative Addition of Dihydrogen

Five plus H2 gives four: UV irradiation of a bis(amidinate) complex with a [(H)MoMo(H)] core induces reductive elimination of H2 and formation of a known quintuply bonded MoMo species (see scheme) that reacts back with H2 to restore [(H)MoMo(H)]. UV irradiation of the bis(hydride) species in benzene and toluene gives arene complexes in which the aromatic hydrocarbon bridges the molybdenum atoms. Dipp=2,6-diisopropylphenyl. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Multiple Modes for Coordination of Phenazine to Molybdenum: Ring Fusion Promotes Access to η4-Coordination, Oxidative Addition of Dihydrogen and Hydrogenation of Aromatic Nitrogen Compounds

Mo(PMe(3))(6) reacts with phenazine (PhzH) to give (eta(6)-C(6)-PhzH)Mo(PMe(3))(3), (mu-eta(6),eta(6)-PhzH)[Mo(PMe(3))(3)](2) and (eta(4)-C(4)-PhzH)(2)Mo(PMe(3))(2), each of which displays previously unknown coordination modes for phenazine. Both mononuclear (eta(6)-C(6)-PhzH)Mo(PMe(3))(3) and dinuclear (mu-eta(6),eta(6)-PhzH)[Mo(PMe(3))(3)](2) react with H(2) at room temperature to give the respective dihydride complexes, (eta(4)-C(4)-PhzH)Mo(PMe(3))(3)H(2) and (mu-eta(6),eta(4)-PhzH)[Mo(PMe(3))(3)][Mo(PMe(3))(3)H(2)]. A comparison of (eta(6)-C(6)-PhzH)Mo(PMe(3))(3) with the anthracene (AnH) and acridine (AcrH) counterparts, (eta(6)-AnH)Mo(PMe(3))(3) and (eta(6)-C(6)-AcrH)Mo(PMe(3))(3), indicates that oxidative addition of H(2) is promoted by incorporation of nitrogen substituents into the central ring. Furthermore, comparison of (eta(6)-C(6)-PhzH)Mo(PMe(3))(3) with the quinoxaline (QoxH) analogue, (eta(6)-C(6)-QoxH)Mo(PMe(3))(3), indicates that ring fusion also promotes oxidative addition of H(2). The mononitrogen quinoline (QH) and acridine compounds, (eta(6)-C(6)-QH)Mo(PMe(3))(3) and (eta(6)-C(6)-AcrH)Mo(PMe(3))(3), which respectively possess two and three fused six-membered rings, exhibit a similar trend, with the former being inert towards H(2), while the latter reacts rapidly to yield (eta(4)-C(4)-AcrH)Mo(PMe(3))(3)H(2). Ring fusion also promotes hydrogenation of the heterocyclic ligand, with (eta(6)-C(6)-AcrH)Mo(PMe(3))(3) releasing 9,10-dihydroacridine upon treatment with H(2) in benzene at 95 degrees C. Furthermore, catalytic hydrogenation of acridine to a mixture of 9,10-dihydroacridine and 1,2,3,4-tetrahydroacridine may be achieved by treatment of (eta(6)-C(6)-AcrH)Mo(PMe(3))(3) with acridine and H(2) at 95 degrees C.

FeFe]‐Hydrogenase Models and Hydrogen: Oxidative Addition of Dihydrogen and Silanes

Dieisendithiolate finden sich in der Natur in der [FeFe]-Hydrogenase und dienen der Synthese oder Oxidation von molekularem Wasserstoff. Einblicke in die Wechselwirkung von H2 mit Dieisenkomplexen lassen sich anhand von Carbonylmodellkomplexen (siehe Schema) gewinnen. Die dargestellten Reaktionspfade wurden rechnerisch und durch Synthesen aufgeklärt, wobei Silane anstelle von H2 verwendet wurden. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

FeFe]‐Hydrogenase Models and Hydrogen: Oxidative Addition of Dihydrogen and Silanes

Super model: Diiron dithiolates exist in nature in [FeFe]-hydrogenase, for the purpose of making or oxidizing molecular hydrogen. Evidence for how H2 interacts with diiron complexes has been realized using model diiron dithiolato carbonyl complexes. The pathway for this interaction has been elucidated computationally as well as synthetically, by using silanes in place of H2.

In situ NMR Detection of Dihydrides in the Systems [RhH(SnCl3)5]3–/Tertiary Phosphanes/Parahydrogen

The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3–/PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation of previously unknown dihydride complexes, the 1H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt3 as the phosphane and acetonitrile as the solvent, a complex with a SnCl2L ligand (L = CD3CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the 1H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr3 ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via 1H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr3)nBr6–n]3– has been isolated.

Oxidative addition of dihydrogen to Ni(II) complexes.ab initio MO/MP4 calculations of the electronic structure of NiH2Cl2(PH3)2 complex

Electronic state d6 Ni(IV) in the complex [NiH2Cl2(PH3)2] was studied by means ofab initio MO/MP4 calculations.

ChemInform Abstract: Dihydrogen Complexes of the Transition Metals

The binding and activation of dihydrogen by simple transition metal complexes is of fundamental importance in processes as diverse as the homogeneous or heterogeneous hydrogenation of unsaturated organic molecules(1) and understanding how metalloenzymes such as nitrogenase(2) and the hydrogenases(3) work at the atomic level. Simple consideration of the oxidative-addition of dihydrogen to a coordinatively-unsaturated complex {or its reverse (reductive-elimination)} reveals that the reactions are compelled to proceed via a dihydrogen complex as shown in Equation (1). However until recently it was considered that the dihydrogen complex had only a fleeting existence. Although there had been some reports in the literature such as that by Ashworth and Singleton(4) that the formally RuIV trihydride, [RuH3(PMe2Ph2]+ was better formulated as the Ru11 species [RuH(H2)(PMe2Ph)2]+, these could not be substantiated. In 1984, though, Kubas showed that the apparently innocuous complex [WH2(CO)3(PPr 3 i )2] contained the side-on bonded dihydrogen molecule, established unambiguously by x-ray, and neutron crystallography and spectroscopy(5). In this highlight the current status of dihydrogen complexes, their structure, identification and in particular their reactivity will be discussed.

Further studies on metal-to-metal migration processes. The steric influence of the phosphorus ligands on the oxidative addition of dihydrogen and of hexafluoro-2-butyne to [Ir(.mu.-SCMe3)(CO)[P(OCMe3)3]

Le complexe du titre reagit avec H 2 pour donner [(H 2 (P(O-t-Bu) 3 )(CO)Ir III (μ-S-t-Bu) 2 Ir I (CO)(P(O-t-Bu) 3 )] et [Ir III (H 2 )(μ-S-t-Bu)(CO)(P(O-t-Bu) 3 )] 2 . Avec l'hexafluoro, butyne-2, on obtient un compose d'addition asymetrique et un symetrique. Le coordinat P(O-t-Bu), apparait comme un modulateur efficace de reactivite