Unequivocal Characterization of an Osmium Complex with a Terminal Sulfide Ligand and Its Transformation into Hydrosulfide and Methylsulfide.

Deprotonation of the thioamidate group of [OsH{κ2-N,S-[NHC(CH3)S]}(≡CPh)(IPr)(PiPr3)]OTf [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene; OTf = CF3SO3] results in the release of acetonitrile and formation of the terminal sulfide complex OsH(S)(≡CPh)(IPr)(PiPr3) (2), which has been transformed into the hydrosulfide [OsH(SH)(≡CPh)(IPr)(PiPr3)]OTf (3) and the methylsulfide [OsH(SMe)(≡CPh)(IPr)(PiPr3)]OTf (4) through protonation and methylation reactions, respectively. The structure, spectroscopic characteristics, and reactivity of these compounds are compared. Reactions of 3 and 4 with 2-hydroxypyridine and 2-mercaptopyridine afford [OsH{κ2-X,N-[X-py]}(≡CPh)(IPr)(PiPr3)]OTf [X = O (5), S(6)].

C-H, N-H, and O-H Bond Activations to Prepare Phosphorescent Hydride-Iridium(III)-Phosphine Emitters with Photocatalytic Achievement in C-C Coupling Reactions.

Complex IrH5(PiPr3)2 (1) activates two different σ-bonds of 3-phenoxy-1-phenylisoquinoline, 2-(1H-benzimidazol-2-yl)-6-phenylpyridine, 2-(1H-indol-2-yl)-6-phenylpyridine, 2-(2-hydroxyphenyl)-6-phenylpyridine, N-(2-hydroxyphenyl)-N'-phenylimidazolylidene, and 1,3-di(2-pyridyl)-4,6-dimethylbenzene to give IrH{κ3-C,N,C-[C6H4-isoqui-O-C6H4]}(PiPr3)2 (2), IrH{κ3-N,N,C-[NBzim-py-C6H4]}(PiPr3)2 (3), IrH{κ3-N,N,C-[Ind-py-C6H4]}(PiPr3)2 (4), IrH{κ3-C,N,O-[C6H4-py-C6H4O]}(PiPr3)2 (5), IrH{κ3-C,C,O-[C6H4-Im-C6H4O]}(PiPr3)2 (6), and IrH{κ3-N,C,C-[py-C6HMe2-C5H3N]}(PiPr3)2 (7), respectively. The activations are sequential, with the second generally being the slowest. Accordingly, dihydride intermediates IrH2{κ2-C,N-[C6H4-isoqui-O-C6H5]}(PiPr3)2 (2d), IrH2{κ2-N,N-[NBzim-py-C6H5]}(PiPr3)2 (3d), IrH2{κ2-N,N-[Ind-py-C6H5]}(PiPr3)2 (4d), and IrH2{κ2-N,C-[py-C6HMe2-py]}(PiPr3)2 (7d) were characterized spectroscopically. Complexes 3 and 5 are green phosphorescent emitters upon photoexcitation, exhibiting good absorption over a wide range of wavelengths, emission quantum yields about 0.70 in solution, long enough lifetimes (10-17 µs), and reversible electrochemical behavior. In agreement with these features, complex 3 promotes the photocatalytic α-amino C(sp3)-H arylation of N,N-dimethylaniline and N-phenylpiperidine with 1,4-dicyanobenzene and 4-cyanopyridine under blue LED light irradiation. The C-C coupling products are isolated in high yields with only 2 mol % of photocatalyst after 24 h.

Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and N,C(sp3),C(sp2),O-Tetradentate Ligands.

The preparation of three families of phosphorescent iridium(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and N,C(sp3),C(sp2),O-tetradentate containing complexes, has been performed starting from dimers cis-[Ir(µ2-η2-C≡CR){κ2-C,N-(MeC6H3-py)}2]2 (R = tBu (1a), Ph (1b)). Reactions of 1a with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir{κ2-C,O-[C(CH2tBu)NC(R)O]}{κ2-C,N-(MeC6H3-py)}2 (R = Ph (2), Me (3), CH2Ph (4), CF3 (5)) with a fac disposition of carbons and heteroatoms around the metal center. In 2-methyltetrahydrofuran and dichloromethane, water promotes the C-N rupture of the IrC-N bond of the iridaoxazole ring of 3-5 to form amidate-iridium(III)-hydroxycarbene derivatives Ir{κ1-N-[NHC(R)O]}{κ2-C,N-(MeC6H3-py)}2{═C(CH2tBu)OH} (R = Me (6), CH2Ph (7), CF3 (8)). In contrast to 1a, dimer 1b reacts with benzamide and acetamide to give Ir{κ4-N,C,C',O-[py-MeC6H3-C(CH2-C6H4)NHC(R)O]}{κ2-C,N-(MeC6H3-py)}(R = Ph (9), Me (10)), which bear a N,C(sp3),C(sp2),O-tetradentate ligand resulting from a triple coupling (an alkynyl ligand, an amide, and a coordinated aryl group) and a C-H bond activation at the metal coordination sphere. Complexes 2-4 and 6-10 are emissive upon photoexcitation, in orange (2-4), green (6-8), and yellow (9 and 10) regions, with quantum yields between low and moderate (0.01-0.50) and short lifetimes (0.2-9.0 µs).

Alkynyl Ligands as Building Blocks for the Preparation of Phosphorescent Iridium(III) Emitters: Alternative Synthetic Precursors and Procedures.

Alkynyl ligands stabilize dimers [Ir(µ-X)(3b)2]2 with a cis disposition of the heterocycles of the 3b ligands, in contrast to chloride. Thus, the complexes of this class─cis-[Ir(µ2-η2-C≡CPh){κ2-C,N-(C6H4-Isoqui)}2]2 (Isoqui = isoquinoline) and cis-[Ir(µ2-η2-C≡CR){κ2-C,N-(MeC6H3-py)}2]2 (R = Ph, tBu)─have been prepared in high yields, starting from the dihydroxo-bridged dimers trans-[Ir(µ-OH){κ2-C,N-(C6H4-Isoqui)}2]2 and trans-[Ir(µ-OH){κ2-C,N-(MeC6H3-py)}2]2 and terminal alkynes. Subsequently, the acetylide ligands have been employed as building blocks to prepare the orange and green iridium(III) phosphorescent emitters, Ir{κ2-C,N-[C(CH2Ph)Npy]}{κ2-C,N-(C6H4-Isoqui)}2 and Ir{κ2-C,N-[C(CH2R)Npy]}{κ2-C,N-(MeC6H3-py)}2 (R = Ph, tBu), respectively, with an octahedral structure of fac carbon and nitrogen atoms. The green emitter Ir{κ2-C,N-[C(CH2tBu)Npy]}{κ2-C,N-(MeC6H3-py)}2 reaches 100% of quantum yield in both the poly(methyl methacrylate) (PMMA) film and 2-MeTHF at room temperature. In organic light-emitting diode (OLED) devices, it demonstrates very saturated green emission at a peak wavelength of 500 nm, with an external quantum efficiency (EQE) of over 12% or luminous efficacy of 30.7 cd/A.

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.

Square-Planar Alkylidyne-Osmium and Five-Coordinate Alkylidene-Osmium Complexes: Controlling the Transformation from Hydride-Alkylidyne to Alkylidene.

Square-planar alkylidyne and five-coordinate alkylidene mixed (i)Pr3P-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)(P(i)Pr3)]OTf (X = Cl (1), F (4); OTf = CF3SO3) undergo deprotonation with KO(t)Bu to afford the trans-halide-alkylidyne square-planar derivatives OsX(≡CPh)(IPr)(P(i)Pr3) (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)(P(i)Pr3) (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)(P(i)Pr3) (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)(P(i)Pr3) (10), which is also stable.

An Entry to Stable Mixed Phosphine-Osmium-NHC Polyhydrides.

An entry to mixed phosphine-osmium-NHC polyhydride complexes is described, starting from the five-coordinate hydrido-alkylidyne compounds [OsHCl(≡CPh)(IPr)(PR3)]OTf (IPr = 1,3-bis(2,6-disopropylphenyl)imidazolylidene; OTf = CF3SO3; PR3 = P(i)Pr3 (1), PPh3 (2)). The experimental procedure involves the borylation of the Os-C triple bond of 1 and 2 with NaBH4 and the subsequent alcoholysis of the borylation products OsH2Cl(η(2)-H-BCH2Ph)(IPr)(PR3) (PR3 = P(i)Pr3 (3), PPh3 (4)) or OsH2(η(2):η(2):H2BCH2Ph)(IPr)(P(i)Pr3) (5). Stirring of 3 in 2-propanol affords the five coordinate chloride-trihydride OsH3Cl(IPr)(P(i)Pr3)2 (6), which reacts with NaBH4 to give OsH3(κ(2)-H2BH2)(IPr)(P(i)Pr3) (7). This trihydride-tetrahydrideborate derivative and its PPh3 counterpart OsH3(κ(2)-H2BH2)(IPr)(PPh3) (8) can be also obtained in a one-pot procedure, starting from 1 and 2 and using methanol at -60 °C instead of 2-propanol as alcoholysis agent. The bonding situation in 7 and 8, analyzed by DFT calculations using AIM and NBO methods, resembles that found in B2H6 and contrasts with the bonding situation in the bis-σ-borane derivative 5. Stirring of 7 and 8 in 2-propanol leads to the corresponding d(2)-hexahydride derivatives OsH6(IPr)(PR3) (PR3 = P(i)Pr3 (9), PPh3 (10)), which reduce the C≡N triple bond of benzonitrile and promote the subsequent chelate-assisted ortho-CH bond activation of the resulting phenylmethanimine, to form the trihydride compounds OsH3{κ(2)-N,C-(NH═CH-C6H4)}(IPr)(PR3)2 (PR3 = P(i)Pr3 (11), PPh3 (12)), containing a stabilized orthometalated aldimine.

Osmathiazole Ring: Extrapolation of an Aromatic Purely Organic System to Organometallic Chemistry.

An osmathiazole skeleton has been generated starting from the cation of the salt [OsH(OH)(≡CPh)(IPr)(PiPr3)]OTf (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene; OTf = CF3SO3) and thioacetamide; its aromaticity degree was compared with that of thiazole, and its aromatic reactivity was confirmed through a reaction with phenylacetylene. Salt 1 reacts with the thioamide to initially afford the synthetic intermediate [OsH{κ2-N,S-[NHC(CH3)S]}(≡CPh)(IPr)(PiPr3)]OTf (2). Thioamidate and alkylidyne ligands of 2 couple in acetonitrile at 70 °C, forming a 1:1 mixture of the salts [OsH{κ2-C,S-[C(Ph)NHC(CH3)S]}(CH3CN)(IPr)(PiPr3)]OTf (3) and [Os{κ2-C,S-[CH(Ph)NHC(CH3)S]}(CH3CN)3(IPr)]OTf (4). Treatment of 3 with potassium tert-butoxide produces the NH-deprotonation of its five-membered ring and gives OsH{κ2-C,S-[C(Ph)NC(CH3)S]}(IPr)(PiPr3) (5). The osmathiazole ring of 5 is slightly less aromatic than the osmathiazolium cycle of 3 and the purely organic thiazole. However, it is more aromatic than related osmaoxazoles and osmaoxazoliums. There are significant differences in behavior between 3 and 5 toward phenylacetylene. In acetonitrile, the cation of 3 loses the phosphine and adds the alkyne to afford [Os{η3-C3,κ1-S-[CH2C(Ph)C(Ph)NHC(CH3)S]}(CH3CN)2(IPr)]OTf (6), bearing a functionalized allyl ligand. In contrast, the osmathiazole ring of 5 undergoes a vicarious nucleophilic substitution of hydride, by acetylide, via the dihydride OsH2(C≡CPh){κ2-C,S-[C(Ph)NC(CH3)S]}(IPr)(PiPr3) (7), which releases H2 to yield Os(C≡CPh){κ2-C,S-[C(Ph)NC(CH3)S]}(IPr)(PiPr3) (8).

From tetrahydroborate- to aminoborylvinylidene-osmium complexes via alkynyl-aminoboryl intermediates.

The tetrahydroborate OsH(η(2)-H(2)BH(2))(CO)(P(i)Pr(3))(2) (1) reacts with aniline and p-toluidine to give the aminoboryl derivatives [chemical structure: see text] (R = H (2), CH(3) (3)) and four H(2) molecules. Treatment of 2 and 3 with phenylacetylene gives Os{B(NHC(6)H(4)R)(2)}(C≡CPh)(CO)(P(i)Pr(3))(2) (R = H (4), CH(3) (5)), which react with HBF(4) to afford the amino(fluoro)boryl species Os{BF(NHC(6)H(4)R)}(C≡CPh)(CO)(P(i)Pr(3))(2) (R = H (6), CH(3) (7)). In contrast to HBF(4), the addition of acetic acid to 4 and 5 induces the release of phenylacetylene and the formation of the six-coordinate derivatives Os{B(NHC(6)H(4)R)(2)}(κ(2)-O(2)CCH(3))(CO)(P(i)Pr(3))(2) (R = H (8), CH(3) (9)). The coordination number six for 4 and 5 can be also achieved by addition of CO. Under this gas Os{B(NHC(6)H(4)R)(2)}(C≡CPh)(CO)(2)(P(i)Pr(3))(2) (R = H (10), CH(3) (11)) are formed. In toluene, these alkynyl-aminoboryl compounds evolve into the aminoborylvinylidenes Os{═C═C(Ph)B(NHC(6)H(4)R)(2)}(CO)(2)(P(i)Pr(3))(2) (R = H (12), CH(3) (13)) via a unimolecular 1,3-boryl migration from the metal to the C(ß) atom of the alkynyl ligand. Similarly to 4 and 5, complexes 6 and 7 coordinate CO to give Os{BF(NHC(6)H(4)R)}(C≡CPh)(CO)(2)(P(i)Pr(3))(2) (R = H (15), CH(3) (16)), which evolve to Os{═C═C(Ph)BF(NHC(6)H(4)R)}(CO)(2)(P(i)Pr(3))(2) (R = H (17), CH(3) (18)).

Dissimilarity in the Chemical Behavior of Osmaoxazolium Salts and Osmaoxazoles: Two Different Aromatic Metalladiheterocycles.

The preparation of aromatic hydride-osmaoxazolium and hydride-oxazole compounds is reported and their reactivity toward phenylacetylene investigated. Complex [OsH(OH)(≡CPh)(IPr)(PiPr3)]OTf (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene, OTf = CF3SO3) reacts with acetonitrile and benzonitrile to give [OsH{κ2-C,O-[C(Ph)NHC(R)O]}(NCR)(IPr)(PiPr3)]OTf (R = Me (2), Ph (3)) via amidate intermediates, which are generated by addition of the hydroxide ligand to the nitrile. In agreement with this, the addition of 2-phenylacetamide to acetonitrile solutions of 1 gives [OsH{κ2-C,O-[C(Ph)NHC(CH2Ph)O]}(NCCH3)(IPr)(PiPr3)]OTf (4). The deprotonation of the osmaoxazolium ring of 2 and 4 leads to the oxazole derivatives OsH{κ2-C,O-[C(Ph)NC(R)O]}(IPr)(PiPr3) (R = Me (5), CH2Ph (6)). Complexes 2 and 4 add their Os-H and Os-C bonds to the C-C triple bond of phenylacetylene to afford [Os{η3-C 3 ,κ1-O-[CH2C(Ph)C(Ph)NHC(R)O]}(NCCH3)2(IPr)]OTf (R = Me (7), CH2Ph (8)), bearing a tridentate amide-N-functionalized allyl ligand, while complexes 5 and 6 undergo a vicarious nucleophilic substitution of the hydride at the metal center with the alkyne, via the compressed dihydride adduct intermediates OsH2(C≡CPh){κ2-C,O-[C(Ph)NC(R)O]}(IPr)(PiPr3) (R = Me (9), CH2Ph (10)), which reductively eliminate H2 to yield the acetylide-osmaoxazoles Os(C≡CPh){κ2-C,O-[C(Ph)NC(R)O]}(IPr)(PiPr3) (R = Me (11), CH2Ph (12)).

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-N py-(HBMePHI)} (5), and the binuclear species [RhCl(η4-C8H12)]2{µ-N py,N py-(HBMePHI)} (6). Under the same conditions, complex 2 affords the iridium counterparts IrCl(η4-C8H12){κ1-N py-(HBMePHI)} (7) and [IrCl(η4-C8H12)]2{µ-N py,N py-(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-N py,N iso-(BMePHI)} (M = Rh (9), Ir (10)), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KO t Bu, 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.

Oxidative Addition of Group 14 Element Hydrido Compounds to OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2): Synthesis and Characterization of the First Trihydrido-Silyl, Trihydrido-Germyl, and Trihydrido-Stannyl Derivatives of Osmium(IV).

The dihydrido-olefin complex OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2) (2) reacts with H(2)SiPh(2) to give OsH(3)(SiHPh(2))(CO)(P(i)Pr(3))(2) (3). The molecular structure of 3 has been determined by X-ray diffraction (monoclinic, space group P2(1)/c with a = 16.375(2) Å, b = 11.670(1) Å, c =18.806(2) Å, beta = 107.67(1) degrees, and Z = 4) together with ab initio calculations on the model compound OsH(3)(SiH(3))(CO)(PH(3))(2). The coordination geometry around the osmium center can be rationalized as a heavily distorted pentagonal bipyramid with one hydrido ligand and the carbonyl group in the axial positions. The two other hydrido ligands lie in the equatorial plane, one between the phosphine ligands and the other between the SiHPh(2) group and one of the phosphine ligands. Complex 3 can also be prepared by reaction of OsH(eta(2)-H(2)BH(2))(CO)(P(i)Pr(3))(2) (4) with H(2)SiPh(2). Similarly, the treatment of 4 with HSiPh(3) affords OsH(3)(SiPh(3))(CO)(P(i)Pr(3))(2) (5), while the addition of H(3)SiPh to 4 in methanol yields OsH(3){Si(OMe)(2)Ph}(CO)(P(i)Pr(3))(2) (6). Complex 2 also reacts with HGeR(3) and HSnR(3) to give OsH(3)(GeR(3))(CO)(P(i)Pr(3))(2) (GeR(3) = GeHPh(2) (7), GePh(3) (8), GeEt(3) (9)) and OsH(3)(SnR(3))(CO)(P(i)Pr(3))(2) (R = Ph (10), (n)Bu (11)), respectively. In solution, compounds 3 and 5-11 are fluxional and display similar (1)H and (31)P{(1)H} NMR spectra, suggesting that they possess a similar arrangement of ligands around the osmium atom.