Synthesis and structural characterization of homochiral 2D coordination polymers of zinc and copper with conformationally flexible ditopic imidazolium-based dicarboxylate ligands

Different novel coordination polymers containing zinc, 1–4, and copper, 5–8, metals, connected via chiral imidazolium-based dicarboxylate ligands, [LR]−, were isolated by reaction between zinc acetate or copper acetate and enantiomerically pure HLR compounds. They were characterised and structurally identified by X-ray diffraction methods (single crystal and powder). These compounds are twodimensional homochiral coordination polymers, [M(LR)2]n, in which the metal ions are coordinated by the two carboxylate groups of [LR]− anions in a general bridging monodentate μ2–κ1-O1,κ1-O3 fashion that afforded tetrahedral metal coordination environments for zinc, 1–4, and square planar for copper, 5–8, complexes. In all the compounds the 3D supramolecular architecture is constructed by non-covalent interactions between the hydrophobic parts (R groups) of the homochiral 2D coordination polymers and, in some cases, by weak C–H⋯O non-classical hydrogen bonds that provided, in general, a dense crystal packing. DFT calculations on the [LR]− anions confirmed their conformational flexibility as ditopic linkers and this fact makes possible the formation of different coordination polymers for four-coordinated metal centers. Preliminary studies on the Zn-catalyzed synthesis of chiral α-aminophosphonates were carried out and, unfortunately, no enantioselectivity was observed in these reactions.Proyecto de la Junta de Andalucía FQM-707

Novel coordination modes of a BPI anion in osmium complexes

Resumen del trabajo presentado a la X International School on Organometallic Chemistry “Marcial Moreno Mañas”, celebrada en Ciudad Real (España) del 5 al 7 de julio de 2017.1,3-Bis(2-pyridylimino)isoindolates (BPIs) are a class of polydentate nitrogen-donor monoanionic ligands which usually form Npy,Niso,Npy-pincer complexes with transition metals, although a few compounds present other coordination modes. BPI complexes are of interest in homogeneous catalysis in different organic reactions including upgrading ethanol to 1-butanol, hydroboration of ketones and nitriles, hydrogenation of alkynes, among others. Recently in our group, the Npy,Nimine-bidentate-chelate and Npy,Nimine,Nimine,Npy-tetradentatebridge coordination modes of the 1,3-bis(6’-methyl-2’-pyridylimino)isoindolinate anion have been discovered. In the present contribution, we will show the preparation of novel BPI osmium complexes and some preliminary studies in catalytic reactions.Peer reviewe

Synthesis and structural characterization of homochiral 2D coordination polymers of zinc and copper with conformationally flexible ditopic imidazolium-based dicarboxylate ligands

Different novel coordination polymers containing zinc, 1-4, and copper, 5-8, metals, connected via chiral imidazolium-based dicarboxylate ligands, [L], were isolated by reaction between zinc acetate or copper acetate and enantiomerically pure HL compounds. They were characterised and structurally identified by X-ray diffraction methods (single crystal and powder). These compounds are two-dimensional homochiral coordination polymers, [M(L)], in which the metal ions are coordinated by the two carboxylate groups of [L] anions in a general bridging monodentate μ-κ-O,κ-O fashion that afforded tetrahedral metal coordination environments for zinc, 1-4, and square planar for copper, 5-8, complexes. In all the compounds the 3D supramolecular architecture is constructed by non-covalent interactions between the hydrophobic parts (R groups) of the homochiral 2D coordination polymers and, in some cases, by weak C-H⋯O non-classical hydrogen bonds that provided, in general, a dense crystal packing. DFT calculations on the [L] anions confirmed their conformational flexibility as ditopic linkers and this fact makes possible the formation of different coordination polymers for four-coordinated metal centers. Preliminary studies on the Zn-catalyzed synthesis of chiral α-aminophosphonates were carried out and, unfortunately, no enantioselectivity was observed in these reactions.Financial support from the Junta de Andalucía (Proyecto de Excelencia FQM-7079) is gratefully acknowledged. R. P. C. acknowledges the Junta de Andalucía for the postdoctoral contract associated with the FQM-7079 project

N–H and C–H Bond Activations of an Isoindoline Promoted by Iridium- and Osmium-Polyhydride Complexes: A Noninnocent Bridge Ligand for Acceptorless and Base-Free Dehydrogenation of Secondary Alcohols

The elusive C–H bond activation of an organic fragment contained in many biologically active molecules and the use of the resulting noninnocent ligand in bimetallic catalysis applied to the acceptorless and base-free dehydrogenation of secondary alcohols has been performed by using the polyhydrides IrH5(PiPr3)2 (1) and OsH6(PiPr3)2 (2). Complex 1 activates the N–H bond of 1,3-bis(6′-methylpyridyl-2′-imino)isoindoline (HBMePHI) to give the mononuclear complex IrH2{κ2-Npy,Nimine(BMePHI)}(PiPr3)2 (3). Both 1 and 2 activate the C(sp2)–H bond at position 4 of the core isoindoline of the BMePHI ligand of 3. The reactions lead to the homobinuclear complex (PiPr3)2H2Ir{μ-(κ2-Npy,Nimine-BMePI-κ2-Nimine,C4iso)}IrH2(PiPr3)2 (4) and the heterobinuclear compound (PiPr3)2H2Ir{μ-(κ2-Npy,Nimine-BMePI-κ2-Nimine,C4iso)}OsH3(PiPr3)2 (5), respectively. The metalated carbon atom of 4 and 5 has a marked nucleophilic character. Thus, it adds the proton of alcohols to afford the respective cations [(PiPr3)2H2Ir{μ-(κ2-Npy,Nimine-BMePHI-κ2-Npy,Nimine)}IrH2(PiPr3)2]+ (6) and [(PiPr3)2H2Ir{μ-(κ2-Npy,Nimine-BMePHI-κ2-Npy,Nimine)}OsH3(PiPr3)2]+ (7), and the corresponding alkoxide. The mononuclear complex 3 and the binuclear compounds 4 and 5 are efficient catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. The binuclear complexes 4 and 5 are significantly more active than 3. The catalytic synergism is a consequence of the mutual electronic influence of the metals through the bridge. X-ray diffraction analysis data of the structures of 3–5 and the reactivity of 4 and 5 support a noninnocent character of the bridging ligand.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P (AEI/FEDER, UE) and RED2018-102387-T), Gobierno de Aragón (Group E06_20R and project LMP148_18), FEDER, and the European Social Fund is acknowledged. A.I.N. thanks the MINECO for his predoctoral fellowship.Peer reviewe

Alternative conceptual approach to the design of bifunctional catalysts: An osmium germylene system for the dehydrogenation of formic acid

The reaction of the hexahydride OsH6(PiPr3)2 with a P,Ge,P-germylene-diphosphine affords an osmium tetrahydride derivative bearing a Ge,P-chelate, which arises from the hydrogenolysis of a P–C(sp3) bond. This Os(IV)–Ge(II) compound is a pioneering example of a bifunctional catalyst based on the coordination of a σ-donor acid, which is active in the dehydrogenation of formic acid to H2 and CO2. The kinetics of the dehydrogenation, the characterization of the resting state of the catalysis, and DFT calculations point out that the hydrogen formation (the fast stage) exclusively occurs on the coordination sphere of the basic metal center, whereas both the metal center and the σ-donor Lewis acid cooperatively participate in the CO2 release (the rate-determining step). During the process, the formate group pivots around the germanium to approach its hydrogen atom to the osmium center, which allows its transfer to the metal and the CO2 release.Financial support was provided by the MICINN of Spain (PID2020-115286GB-I00/AEI/10.13039/501100011033, RED2018-102387-T, and PID2019-104652GB-I00), Gobierno de Aragón (E06_20R and LMP148_18), FEDER, and FSE.Peer reviewe

Preparation and degradation of rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols

Rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols have been prepared, and their degradation has been investigated, during the study of the reactivity of the dimers [M(μ-Cl)(η4-C8H12)]2 (M = Rh (1), Ir (2)) and [M(μ-OH)(η4-C8H12)]2 (M = Rh (3), Ir (4)) with 1,3-bis(6′-methyl-2′-pyridylimino)isoindoline (HBMePHI). Complex 1 reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of 1, the mononuclear derivative RhCl(η4-C8H12){κ1-Npy-(HBMePHI)} (5), and the binuclear species [RhCl(η4-C8H12)]2{μ-Npy,Npy-(HBMePHI)} (6). Under the same conditions, complex 2 affords the iridium counterparts IrCl(η4-C8H12){κ1-Npy-(HBMePHI)} (7) and [IrCl(η4-C8H12)]2{μ-Npy,Npy-(HBMePHI)} (8). In contrast to chloride, one of the hydroxide groups of 3 and 4 promotes the deprotonation of HBMePHI to give [M(η4-C8H12)]2(μ-OH){μ-Npy,Niso-(BMePHI)} (M = Rh (9), Ir (10)), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KOtBu, the [BMePHI]− ligand undergoes three different degradations: alcoholysis of an exocyclic isoindoline-N double bond, alcoholysis of a pyridyl-N bond, and opening of the five-membered ring of the isoindoline core.Financial support from the MCI, projects CTQ2017-82935-P, PID2019-108429RB-I00, and RED2018-102387-T, the Gobierno de Aragón (Group E06_17R), Fundación Ramón Areces (XVIII Concurso Nacional de Ayudas a la Investigación en Ciencias de la Vida y de la Materia CIVP18A3938), Fondo Europeo de Desarrollo Regional (FEDER), and the European Social Fund (FSE) is acknowledged. A.I.N. and A.C. thank the MINECO (Spain) for a predoctoral fellowship and Juan de la Cierva-Incorporación Fellowship, respectively.Peer reviewe

Osmium Catalysts for Acceptorless and Base-Free Dehydrogenation of Alcohols and Amines: Unusual Coordination Modes of a BPI Anion

A novel type of catalyst precursors for the dehydrogenation of hydrogen carriers based on organic liquids has been discovered. Complexes OsH₆(P^<i>i</i>Pr₃)₂ (<b>1</b>) and OsH­(OH)­(CO)­(P^<i>i</i>Pr₃)₂ (<b>2</b>) react with 1,3-bis­(6′-methyl-2′-pyridylimino)­isoindoline (HBMePI) to give OsH₃{κ²-N_py,N_imine-(BMePI)}­(P^<i>i</i>Pr₃)₂ (<b>3</b>) and OsH­{κ²-N_py,N_imine-(BMePI)}­(CO)­(P^<i>i</i>Pr₃)₂ (<b>4</b>). The unprecedented κ²-N_py,N_imine coordination mode of BMePI is thermodynamically preferred with Os­(IV) and Os­(II) metal fragments and allows for preparation of BMePI-based dinuclear metal cations. Treatment of OsH₂Cl₂(P^<i>i</i>Pr₃)₂ (<b>5</b>) with 0.5 equiv of HBMePI in the presence of KO^<i>t</i>Bu affords the chloride salt of the bis­(osmium­(IV)) dinuclear cation [{OsH₃(P^<i>i</i>Pr₃)₂}₂{μ-(κ²-N_py,N_imine)₂-BMePI}]⁺ (<b>6</b>). Related homoleptic bis­(osmium­(II)) complexes have been also synthesized. Complex <b>4</b> reacts with the bis­(solvento) [OsH­(CO)­{κ¹-O-[OCMe₂]₂}­(P^<i>i</i>Pr₃)₂]­BF₄ to give [{OsH­(CO)­(P^<i>i</i>Pr₃)₂}₂{μ-(κ²-N_py,N_imine)₂-BMePI}]­BF₄ (<b>7</b>), whereas the addition of 0.5 equiv of HBMePI to {OsCl­(η⁶-C₆H₆)}₂(μ–Cl)₂ (<b>8</b>) affords [{OsCl­(η⁶-C₆H₆)}₂{μ-(κ²-N_py,N_imine)₂-BMePI}]Cl (<b>9</b>). The reactions of <b>4</b> with <b>8</b> and {OsCl­(η⁶-<i>p</i>-cymene)}₂(μ–Cl)₂ (<b>10</b>) lead to the heteroleptic cations [(P^<i>i</i>Pr₃)₂(CO)­HOs­{μ-(κ²-N_py,N_imine)₂-BMePI}­OsCl­(η⁶-arene)]⁺ (arene = C₆H₆ (<b>11</b>), <i>p</i>-cymene (<b>12</b>)). The electronic structrure and electrochemical properties of the dinuclear complexes were also studied. Complexes <b>3</b> and <b>4</b> are efficient catalyst precursors for the acceptorless and base-free dehydrogenation of secondary and primary alcohols and cyclic and lineal amines. The primary alcohols afford aldehydes. The amount of H₂ released per gram of heterocycle depends upon the presence of a methyl group adjacent to the nitrogen atom, the position of the nitrogen atom in the heterocycle, and the size of the heterocycle

Osmium Catalysts for Acceptorless and Base-Free Dehydrogenation of Alcohols and Amines: Unusual Coordination Modes of a BPI Anion

A novel type of catalyst precursors for the dehydrogenation of hydrogen carriers based on organic liquids has been discovered. Complexes OsH₆(P^<i>i</i>Pr₃)₂ (<b>1</b>) and OsH­(OH)­(CO)­(P^<i>i</i>Pr₃)₂ (<b>2</b>) react with 1,3-bis­(6′-methyl-2′-pyridylimino)­isoindoline (HBMePI) to give OsH₃{κ²-N_py,N_imine-(BMePI)}­(P^<i>i</i>Pr₃)₂ (<b>3</b>) and OsH­{κ²-N_py,N_imine-(BMePI)}­(CO)­(P^<i>i</i>Pr₃)₂ (<b>4</b>). The unprecedented κ²-N_py,N_imine coordination mode of BMePI is thermodynamically preferred with Os­(IV) and Os­(II) metal fragments and allows for preparation of BMePI-based dinuclear metal cations. Treatment of OsH₂Cl₂(P^<i>i</i>Pr₃)₂ (<b>5</b>) with 0.5 equiv of HBMePI in the presence of KO^<i>t</i>Bu affords the chloride salt of the bis­(osmium­(IV)) dinuclear cation [{OsH₃(P^<i>i</i>Pr₃)₂}₂{μ-(κ²-N_py,N_imine)₂-BMePI}]⁺ (<b>6</b>). Related homoleptic bis­(osmium­(II)) complexes have been also synthesized. Complex <b>4</b> reacts with the bis­(solvento) [OsH­(CO)­{κ¹-O-[OCMe₂]₂}­(P^<i>i</i>Pr₃)₂]­BF₄ to give [{OsH­(CO)­(P^<i>i</i>Pr₃)₂}₂{μ-(κ²-N_py,N_imine)₂-BMePI}]­BF₄ (<b>7</b>), whereas the addition of 0.5 equiv of HBMePI to {OsCl­(η⁶-C₆H₆)}₂(μ–Cl)₂ (<b>8</b>) affords [{OsCl­(η⁶-C₆H₆)}₂{μ-(κ²-N_py,N_imine)₂-BMePI}]Cl (<b>9</b>). The reactions of <b>4</b> with <b>8</b> and {OsCl­(η⁶-<i>p</i>-cymene)}₂(μ–Cl)₂ (<b>10</b>) lead to the heteroleptic cations [(P^<i>i</i>Pr₃)₂(CO)­HOs­{μ-(κ²-N_py,N_imine)₂-BMePI}­OsCl­(η⁶-arene)]⁺ (arene = C₆H₆ (<b>11</b>), <i>p</i>-cymene (<b>12</b>)). The electronic structrure and electrochemical properties of the dinuclear complexes were also studied. Complexes <b>3</b> and <b>4</b> are efficient catalyst precursors for the acceptorless and base-free dehydrogenation of secondary and primary alcohols and cyclic and lineal amines. The primary alcohols afford aldehydes. The amount of H₂ released per gram of heterocycle depends upon the presence of a methyl group adjacent to the nitrogen atom, the position of the nitrogen atom in the heterocycle, and the size of the heterocycle