Osmium-mediated direct C–H bond activation at the 8-position of quinolines

Metal-mediated direct C–H bond activation at the 8-position of quinolines, which is the essential step for the functionalization of this bond, is promoted by the hexahydride OsH6(PiPr3)2. This complex activates quinoline and 2-, 3-, 6-, and 7-methylquinoline to afford the classical trihydride derivatives OsH3{κ2-C8,N-(quinolinyl)}(PiPr3)2 and OsH3{κ2-C8,N-(quinolinyl-n-Me)}(PiPr3)2 (n = 2, 3, 6, 7), containing a four-membered heterometalla ring.Financial support from the MINECO of Spain (Projects CTQ2014-52799-P and CTQ2014-51912-REDC), the Diputación General de Aragón (E-35), FEDER, and the European Social Fund is acknowledged.Peer reviewe

Azolium Control of the Osmium-Promoted Aromatic C-H Bond Activation in 1, 3-Disubstituted Substrates

The hexahydride complex OsH6((PPr3)-Pr-i)(2) promotes the C-H bond activation of the 1, 3-disubstituted phenyl group of the [BF4](-) and [BPh4](-) salts of the cations 1-(3-(isoquinolin-1-yl)phenyl)-3-methylimidazolium and 1-(3-(isoquinolin-1-yl)phenyl)-3-meth-ylbenzimidazolium. The reactions selectively afford neutral and cationic trihydride-osmium(IV) derivatives bearing kappa(2)-C, N- or kappa(2)-C, C-chelating ligands, a cationic dihydride-osmium(IV) complex stabilized by a kappa(3)-C, C, N-pincer group, and a bimetallic hexahydride formed by two trihydride-osmium(IV) fragments. The metal centers of the hexahydride are separated by a bridging ligand, composed of kappa(2)-C, N- and kappa(2)-C, C-chelating moieties, which allows electronic communication between the metal centers. The wide variety of obtained compounds and the high selectivity observed in their formation is a consequence of the main role of the azolium group during the activation and of the existence of significant differences in behavior between the azolium groups. The azolium role is governed by the anion of the salt, whereas the azolium behavior depends upon its imidazolium or benzimidazolium nature. While [BF4](-) inhibits the azolium reactions, [BPh4](-) favors the azolium participation in the activation process. In contrast to benzimidazolylidene, the imidazolylidene resulting from the deprotonation of the imidazolium substituent coordinates in an abnormal fashion to direct the phenyl C-H bond activation to the 2-position. The hydride ligands of the cationic dihydride-osmium(IV) pincer complex display intense quantum mechanical exchange coupling. Furthermore, this salt is a red phosphorescent emitter upon photoexcitation and displays a noticeable catalytic activity for the dehydrogenation of 1-phenylethanol to acetophenone and of 1, 2-phenylenedimethanol to 1-isobenzofuranone. The bimetallic hexahydride shows catalytic synergism between the metals, in the dehydrogenation of 1, 2, 3, 4-tetrahydroisoquinoline and alcohols

mer, fac, and bidentate coordination of an alkyl-POP ligand in the chemistry of nonclassical osmium hydrides

Nonclassical and classical osmium polyhydrides containing the diphosphine 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(PiPr2)2), coordinated in κ3-mer, κ3-fac, and κ2-P,P fashions, have been isolated during the cyclic formation of H2 by means of the sequential addition of H+ and H– or H– and H+ to the classical trihydride OsH3Cl{xant(PiPr2)2} (1). This complex adds H+ to form the compressed dihydride dihydrogen complex [OsCl(H···H)(η2-H2){xant(PiPr2)2}]+ (2). Under argon, cation 2 loses H2 and the resulting unsaturated fragment dimerizes to give [(Os(H···H){xant(PiPr2)2})2(μ-Cl)2]2+ (3). During the transformation the phosphine changes its coordination mode from mer to fac. The benzofuran counterpart of 1, OsH3Cl{dbf(PiPr2)2} (4; dbf(PiPr2)2 = 4,6-bis(diisopropylphosphino)dibenzofuran), also adds H+ to afford the benzofuran counterpart of 2, [OsCl(H···H)(η2-H2){xant(PiPr2)2}]+ (5), which in contrast to the latter is stable and does not dimerize. Acetonitrile breaks the chloride bridge of 3 to form the dihydrogen [OsCl(η2-H2)(CH3CN){xant(PiPr2)2}]+ (6), regenerating the mer coordination of the diphosphine. The hydride ion also breaks the chloride bridge of 3. The addition of KH to 3 leads to 1, closing a cycle for the formation of H2. Complex 1 reacts with a second hydride ion to give OsH4{xant(PiPr2)2} (7) as consequence of the displacement of the chloride. Similarly to the latter, the oxygen atom of the mer-coordinated diphosphine of 7 has a tendency to be displaced by the hydride ion. Thus, the addition of KH to 7 yields [OsH5{xant(PiPr2)2}]− (8), containing a κ2-P,P-diphosphine. Complex 8 is easily protonated to afford OsH6{xant(PiPr2)2} (9), which releases H2 to regenerate 7, closing a second cycle for the formation of molecular hydrogen.Financial support from the MINECO of Spain (Projects CTQ2014-52799-P and CTQ2014-51912-REDC), Gobierno de Aragon (E35), FEDER, and the European Social Fund is acknowledged.Peer reviewe

Square-planar alkylidyne–osmium and five-coordinate alkylidene–osmium complexes: controlling the transformation from hydride-alkylidyne to alkylidene

This is an open access article published under an ACS AuthorChoice License.Square-planar alkylidyne and five-coordinate alkylidene mixed iPr3P–Os–IPr (IPr = 1,3-bis(diisopropylphenyl)imidazolylidene) complexes have been discovered and characterized, and their formation has been rationalized. The cationic five-coordinate hydride-alkylidyne compounds [OsHX(≡CPh)(IPr)(PiPr3)]OTf (X = Cl (1), F (4); OTf = CF3SO3) undergo deprotonation with KOtBu to afford the trans-halide-alkylidyne square-planar derivatives OsX(≡CPh)(IPr)(PiPr3) (X = Cl (2), F (5)). Oxidative addition of the C(sp)–H bond of phenylacetylene and methyl propiolate along the Cl–Os–CPh axis of 2 with the hydrogen atom directed to the alkylidyne leads to alkynyl-cis-hydride-alkylidyne intermediates, which rapidly evolve into the five-coordinate alkylidene complexes Os(C≡CR)Cl(═CHPh)(IPr)(PiPr3) (R = Ph (6), CO2Me (7)) as a consequence of the migration of the hydride from the metal center to the Cα atom of the alkylidyne. Oxidative addition of the C(sp)–H bond of methyl propiolate along the X–Os–CPh axis of 2 and 5 with the hydrogen atom directed to the halide gives the alkynyl-trans-hydride-alkylidyne derivatives OsH(C≡CCO2Me)X(≡CPh)(IPr)(PiPr3) (X = Cl (8), F (9)). Complex 8 evolves into 7. However, complex 9 containing the stronger π-donor fluoride is stable. The oxidative addition of HCl to 2 selectively yields the cis-hydride-alkylidyne compound OsHCl2(≡CPh)(IPr)(PiPr3) (10), which is also stable.Financial support from the Spanish MINECO (Projects CTQ2014-52799-P, Red de Excelencia Consolider CTQ2014-51912-REDC), the DGA (E35), and the European Social Fund (FSE) is acknowledged. J.J.F.C. acknowledges support via a predoctoral fellowship from the DGA.Peer reviewe

An Acyl-NHC Osmium Cooperative System: Coordination of Small Molecules and Heterolytic B–H and O–H Bond Activation

The hexahydride complex OsH6(PiPr3)2 (1) activates the C–OMe bond of 1-(2-methoxy-2-oxoethyl)-3-methylimidazolium chloride (2), in addition to promoting the direct metalation of the imidazolium group, to afford a five-coordinate OsCl(acyl-NHC)(PiPr3)2 (3) compound. The latter coordinates carbon monoxide, oxygen, and molecular hydrogen to give the corresponding carbonyl (4), dioxygen (5), and dihydrogen (6) derivatives. Complex 3 also promotes the heterolytic bond activation of pinacolborane (HBpin), using the acyl oxygen atom as a pendant Lewis base. The hydride ligand and the Bpin substituent of the Fischer-type carbene of the resulting complex 7 activate the O–H bond of alcohols and water. As a consequence, complex 3 is a metal ligand cooperating catalyst for the generation of molecular hydrogen, by means of both the alcoholysis and hydrolysis of pinacolborane, via the intermediates 7 and 6.Financial support from the MINECO of Spain (Projects CTQ2014-52799-P and CTQ2014-51912-REDC), the Diputación General de Aragón (E-35), and the European Social Fund (FSE) and FEDER. M.P.G. thanks the Spanish MINECO for her FPI fellowship. T.B. thanks the Spanish MINECO for funding through the Juan de la Cierva program

Preparation of capped octahedral OsHC6 complexes by sequential carbon-directed C–H bond activation reactions

A synthetic procedure based on sequential C-directed C–H bond activation reactions is reported for the preparation of capped octahedral OsHC6 complexes. Reactions of the dimer [OsCl2(η6-p-cymene)]2 (1) with PhMeLAgI (PhMeL = 1-phenyl-3-methyl-1H-benzimidazolylidene (PhMeBIm), 1-phenyl-3,5,6-trimethyl-1H-benzimidazolylidene (PhMeBIm*)) afford OsCl2(η6-p-cymene)(PhMeL) (L = BIm (2), BIm* (3)), which undergo cyclization to give OsCl{κ2-C,C-(MeL-C6H4)}(η6-p-cymene) (L = BIm (4), BIm* (5)) by stirring in dichloromethane suspensions of Al2O3. Complexes 4 and 5 exchange the anion with AgOTf (OTf = CF3SO3). In acetonitrile, at 75 °C, the resulting OTf derivatives Os(OTf){κ2-C,C-(MeL-C6H4)}(η6-p-cymene) (L = BIm (6), BIm* (7)) release the arene to yield the tetra(solvento) compounds [Os{κ2-C,C-(MeL-C6H4)(CH3CN)4]OTf (L = BIm (8), BIm* (9)). Complexes 8 and 9 react with PhMeLAgI to coordinate a second NHC ligand. The generated species Os{κ2-C,C-(MeL-C6H4)(PhMeL)(CH3CN)3]OTf (L = BIm (10), BIm* (11)), containing a C,C-chelate NHC-C6H4 ligand and a monodentate NHC group, exist as a mixture of mer (a and b) and fac (c) acetonitrile isomers. The X-ray diffraction structure of 10c reveals aromatic–aromatic interactions between the N-phenyl substituent of the monodentate NHC group and aromatic rings of the chelate ligand. The π–π stacking has been analyzed by means of DFT calculations by using the AIM approach. Treatment of 10 and 11 with [PhMeLH]I, in the presence of an excess of Et3N, leads to the capped octahedral target compounds OsH{κ2-C,C-(MeL-C6H4)}3 (L = BIm (12), BIm* (13)), as a result of the coordination of a third NHC group and the orthometalation of the N-phenyl substituents of the second and third NHC ligands.Financial support from the MINECO of Spain (Projects CTQ2014-52799-P and CTQ2014-51912-REDC), Gobierno de Aragón (E35), FEDER, and the European Social Fund is acknowledged.Peer reviewe

Selective C–Cl bond oxidative addition of chloroarenes to a POP–rhodium complex

The C–Cl bond cis oxidative addition of 12 chloroarenes, including chlorobenzene, chlorotoluenes, chlorofluorobenzenes, and di- and trichlorobenzenes to RhH{xant(PiPr2)2} (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) and the ability of the resulting rhodium(III) species to undergo reductive elimination reactions are reported. Complex 1 reacts with chlorobenzene to give RhHCl(C6H5){xant(PiPr2)2} (2), which eliminates benzene to afford RhCl{xant(PiPr2)2} (3). On the other hand, in the presence of potassium tert-butoxide (KOtBu), it undergoes dehydrodechlorination to yield Rh(C6H5){xant(PiPr2)2} (4). The reactions of 1 with 3- and 4-chlorotoluenes lead to RhHCl(C6H4-3-Me){xant(PiPr2)2} (5) and RhHCl(C6H4-4-Me){xant(PiPr2)2} (6), respectively. Treatment of the acetone solutions of both compounds with KOtBu also results in their dehydrodechlorination to give Rh(C6H4-3-Me){xant(PiPr2)2} (7) and Rh(C6H4-4-Me){xant(PiPr2)2} (8). Chlorofluorobenzenes undergo both C–Cl oxidative addition and C–H bond activation in a competitive manner. The amount of the C–H activation product increases as fluorine and chlorine are separated. Complex 1 reacts with o-chlorofluorobenzene to afford the C–Cl oxidative addition product RhHCl(C6H4-2-F){xant(PiPr2)2} (9). The reaction of 1 with m-chlorofluorobenzene leads to RhHCl(C6H4-3-F){xant(PiPr2)2} (10; 91%) and the C–H bond activation product Rh(C6H3-2-Cl-6-F){xant(PiPr2)2} (12; 9%), whereas p-chlorofluorobenzene gives a mixture of RhHCl(C6H4-4-F){xant(PiPr2)2} (13; 61%) and Rh(C6H3-3-Cl-6-F){xant(PiPr2)2} (15; 39%). The addition of KOtBu to the acetone solutions of 9, 10, and 13 produces the HCl abstraction and the formation of Rh(C6H4-2-F){xant(PiPr2)2} (16), Rh(C6H4-3-F){xant(PiPr2)2} (17), and Rh(C6H4-4-F){xant(PiPr2)2} (18). In contrast to o-chlorofluorobenzene, 1,2-dichlorobenzene reacts with 1 to give RhHCl(C6H4-2-Cl){xant(PiPr2)2} (19; 32%), Rh(C6H4-2-Cl){xant(PiPr2)2} (20; 51%) and Rh(C6H3-2,3-Cl2){xant(PiPr2)2} (22; 17%). The reactions of 1 with 1,3- and 1,4-dichlorobenzene lead to the respective C–Cl bond oxidative addition products RhHCl(C6H4-3-Cl){xant(PiPr2)2} (23) and RhHCl(C6H4-4-Cl){xant(PiPr2)2} (24), which afford Rh(C6H4-3-Cl){xant(PiPr2)2} (25) and Rh(C6H4-4-Cl){xant(PiPr2)2} (26) by dehydrodechlorination with KOtBu in acetone. Treatment of 1 with 1,2,3-, 1,2,4-, and 1,3,5-trichlorobenzenes leads to RhHCl(C6H3-2,3-Cl2){xant(PiPr2)2} (27), RhHCl(C6H3-3,4-Cl2){xant(PiPr2)2} (28), and RhHCl(C6H3-3,5-Cl2){xant(PiPr2)2} (29). The addition of KOtBu to acetone solutions of 27-29 affords 22, Rh(C6H3-3,4-Cl2){xant(PiPr2)2} (30) and Rh(C6H3-3,5-Cl2){xant(PiPr2)2} (31).Financial support from the MINECO of Spain (Projects CTQ2014-52799-P and CTQ2014-51912-REDC), the Diputacion General de Aragon (E-35), FEDER, and the European Social Fund is acknowledged.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(PiPr3)2 (1) and OsH(OH)(CO)(PiPr3)2 (2) react with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePI) to give OsH3{¿2-Npy,Nimine-(BMePI)}(PiPr3)2 (3) and OsH{¿2-Npy,Nimine-(BMePI)}(CO)(PiPr3)2 (4). The unprecedented ¿2-Npy,Nimine 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(PiPr3)2 (5) with 0.5 equiv of HBMePI in the presence of KOtBu affords the chloride salt of the bis(osmium(IV)) dinuclear cation [{OsH3(PiPr3)2}2{µ-(¿2-Npy,Nimine)2-BMePI}]+ (6). Related homoleptic bis(osmium(II)) complexes have been also synthesized. Complex 4 reacts with the bis(solvento) [OsH(CO){¿1-O-[OCMe2]2}(PiPr3)2]BF4 to give [{OsH(CO)(PiPr3)2}2{µ-(¿2-Npy,Nimine)2-BMePI}]BF4 (7), whereas the addition of 0.5 equiv of HBMePI to {OsCl(¿6-C6H6)}2(µ–Cl)2 (8) affords [{OsCl(¿6-C6H6)}2{µ-(¿2-Npy,Nimine)2-BMePI}]Cl (9). The reactions of 4 with 8 and {OsCl(¿6-p-cymene)}2(µ–Cl)2 (10) lead to the heteroleptic cations [(PiPr3)2(CO)HOs{µ-(¿2-Npy,Nimine)2-BMePI}OsCl(¿6-arene)]+ (arene = C6H6 (11), p-cymene (12)). The electronic structrure and electrochemical properties of the dinuclear complexes were also studied. Complexes 3 and 4 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

Amide-Directed Formation of Five-Coordinate Osmium Alkylidenes from Alkynes

The amide-directed synthesis of five-coordinate osmium alkylidene derivatives from alkynes is reported. These types of complexes, which have been elusive until now because of the tendency of osmium to give hydride alkylidyne species, are prepared by reaction of the dihydride OsH2Cl2(PiPr3)2 (1) with terminal alkynes containing a distal amide group. Complex 1 reacts with N-phenylhex-5-ynamide and N-phenylhepta-6-ynamide to give OsCl2{═C(CH3)(CH2)nNH(CO)Ph}(PiPr3)2 (n = 3 (2), 4 (3)). The relative position of carbonyl and NH groups in the organic substrates has no influence on the reaction. Thus, treatment of 1 with N-(pent-4-yn-1-yl)benzamide leads to OsCl2{═C(CH3)(CH2)3NHC(O)Ph}(PiPr3)2 (4). The new compounds are intermediate species in the cleavage of the C–C triple bond of the alkynes. Under mild conditions, they undergo the rupture of the Cα–CH3 bond of the alkylidene, which comes from the alkyne triple bond, to afford six-coordinate hydride–alkylidyne derivatives. In dichloromethane, complex 2 gives a 10:7 mixture of OsHCl2{≡C(CH2)3C(O)NHPh}(PiPr3)2 (5) and OsHCl2{≡CCH(CH3)(CH2)2C(O)NHPh}(PiPr3)2 (6). The first complex contains a linear separation between the alkylidyne Cα atom and the amide group, whereas the spacer is branched in the second complex. In contrast to the case for 2, complex 4 selectively affords OsHCl2{≡C(CH2)3NHC(O)Ph}(PiPr3)2 (7). In spite of their instability, these compounds give the alkylidene–allene metathesis, being a useful entry to five-coordinate vinylidene complexes, including the dicarbon-disubstituted OsCl2(═C═CMe2)(PiPr3)2 (8) and the monosubstituted OsCl2(═C═CHCy)(PiPr3)2 (9)Financial support from the Spanish MINECO (Projects CTQ2014-52799-P, SAF2013-41943-R, and CTQ2014-51912-REDC), the DGA (E35), the ERDF, the European Research Council (Advanced Grant No. 340055) and the European Social Fund (FSE), and the Xunta de Galicia (grants GRC2013-041, EM2013/036, 2015-CP082 and a Parga Pondal contract to M.G.) is acknowledge