Half-sandwich iridium complexes for homogeneous water-oxidation catalysis

Iridium half-sandwich complexes of the types Cp*Ir(N-C)X, [Cp*Ir(N-N)X]X, and [CpIr(N-N)X]X are catalyst precursors for the homogeneous oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H(2)O)(3)]SO(4) and [(Cp*Ir)(2)(μ-OH)(3)]OH can show even higher turnover frequencies (up to 20 min(-1) at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic oxidation at pH > 7; conversely, at low pH, there are no oxidation waves up to 1.5 V vs NHE for the complexes. H(2)(18)O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distinguish the active homogeneous catalyst from heterogeneous nanoparticulate iridium dioxide.     

Distinguishing homogeneous from heterogeneous catalysis in electrode-driven water oxidation with molecular iridium complexes

Molecular water-oxidation catalysts can deactivate by side reactions or decompose to secondary materials over time due to the harsh, oxidizing conditions required to drive oxygen evolution. Distinguishing electrode surface-bound heterogeneous catalysts (such as iridium oxide) from homogeneous molecular catalysts is often difficult. Using an electrochemical quartz crystal nanobalance (EQCN), we report a method for probing electrodeposition of metal oxide materials from molecular precursors. Using the previously reported [Cp*Ir(H(2)O)(3)](2+) complex, we monitor deposition of a heterogeneous water oxidation catalyst by measuring the electrode mass in real time with piezoelectric gravimetry. Conversely, we do not observe deposition for homogeneous catalysts, such as the water-soluble complex Cp*Ir(pyr-CMe(2)O)X reported in this work. Rotating ring-disk electrode electrochemistry and Clark-type electrode studies show that this complex is a catalyst for water oxidation with oxygen produced as the product. For the heterogeneous, surface-attached material generated from [Cp*Ir(H(2)O)(3)](2+), we can estimate the percentage of electroactive metal centers in the surface layer. We monitor electrode composition dynamically during catalytic turnover, providing new information on catalytic performance. Together, these data suggest that EQCN can directly probe the homogeneity of molecular water-oxidation catalysts over short times.     

Doping metal-organic frameworks for water oxidation, carbon dioxide reduction, and organic photocatalysis

Catalytically competent Ir, Re, and Ru complexes H(2)L(1)-H(2)L(6) with dicarboxylic acid functionalities were incorporated into a highly stable and porous Zr(6)O(4)(OH)(4)(bpdc)(6) (UiO-67, bpdc = para-biphenyldicarboxylic acid) framework using a mix-and-match synthetic strategy. The matching ligand lengths between bpdc and L(1)-L(6) ligands allowed the construction of highly crystalline UiO-67 frameworks (metal-organic frameworks (MOFs) 1-6) that were doped with L(1)-L(6) ligands. MOFs 1-6 were isostructural to the parent UiO-67 framework as shown by powder X-ray diffraction (PXRD) and exhibited high surface areas ranging from 1092 to 1497 m(2)/g. MOFs 1-6 were stable in air up to 400 °C and active catalysts in a range of reactions that are relevant to solar energy utilization. MOFs 1-3 containing [Cp*Ir(III)(dcppy)Cl] (H(2)L(1)), [Cp*Ir(III)(dcbpy)Cl]Cl (H(2)L(2)), and [Ir(III)(dcppy)(2)(H(2)O)(2)]OTf (H(2)L(3)) (where Cp* is pentamethylcyclopentadienyl, dcppy is 2-phenylpyridine-5,4'-dicarboxylic acid, and dcbpy is 2,2'-bipyridine-5,5'-dicarboxylic acid) were effective water oxidation catalysts (WOCs), with turnover frequencies (TOFs) of up to 4.8 h(-1). The [Re(I)(CO)(3)(dcbpy)Cl] (H(2)L(4)) derivatized MOF 4 served as an active catalyst for photocatalytic CO(2) reduction with a total turnover number (TON) of 10.9, three times higher than that of the homogeneous complex H(2)L(4). MOFs 5 and 6 contained phosphorescent [Ir(III)(ppy)(2)(dcbpy)]Cl (H(2)L(5)) and [Ru(II)(bpy)(2)(dcbpy)]Cl(2) (H(2)L(6)) (where ppy is 2-phenylpyridine and bpy is 2,2'-bipyridine) and were used in three photocatalytic organic transformations (aza-Henry reaction, aerobic amine coupling, and aerobic oxidation of thioanisole) with very high activities. The inactivity of the parent UiO-67 framework and the reaction supernatants in catalytic water oxidation, CO(2) reduction, and organic transformations indicate both the molecular origin and heterogeneous nature of these catalytic processes. The stability of the doped UiO-67 catalysts under catalytic conditions was also demonstrated by comparing PXRD patterns before and after catalysis. This work illustrates the potential of combining molecular catalysts and MOF structures in developing highly active heterogeneous catalysts for solar energy utilization.     

Iridium(III) molecular catalysts for water oxidation: the simpler the faster

We report on three Ir(iii) molecular catalysts for water oxidation: 1, [Cp*Ir(ppy)Cl]; 2, [Cp*Ir(bzpy)NO(3)]; 3, [Cp*Ir(H(2)O)(3)](NO(3))(2). 2 and 3 are water-soluble and show a long-term activity ca. 2 and 3 times higher than 1. It is remarkable that 3, having the simplest structure, is the catalyst with the highest activity.     

Stepwise formation of a molecular square with bridging NH,O-substituted dicarbene building blocks

The β,β'-bis(triisopropylsiloxy)phenyl-1,4-diisocyanide 3 and [Ir(Cp*)Cl(2)](2) were used for the stepwise assembly of the [Ir(Cp*)Cl] cornered molecular square [6](Cl)(4). Synthesis of the tetrakis(diisocyanide) bridged molecular square [Ir(Cp*)Cl(3)](4)(BF(4))(4) [5](BF(4))(4) followed by cleavage of the O-Si(i-Pr)(3) bonds of the diisocyanide bridges with HCl/i-PrOH led to an intramolecular attack of the liberated hydroxyl groups at the isocyanide carbon atoms with formation of molecular square [6](Cl)(4) featuring four dicarbene linkers.     

Supported-nanoparticle heterogeneous catalyst formation in contact with solution: kinetics and proposed mechanism for the conversion of Ir(1,5-COD)Cl/γ-Al2O3 to Ir(0)(~900)/γ-Al2O3

A current goal in heterogeneous catalysis is to transfer the synthetic, as well as developing mechanistic, insights from the modern revolution in nanoparticle science to the synthesis of supported-nanoparticle heterogeneous catalysts. In a recent study (Mondloch, J. E.; Wang, Q.; Frenkel, A. I.; Finke, R. G. J. Am. Chem. Soc. 2010, 132, 9701-9714), we initialized tests of the global hypothesis that quantitative kinetic and mechanistic studies, of supported-nanoparticle heterogeneous catalyst formation in contact with solution, can provide synthetic and mechanistic insights that can eventually drive improved syntheses of composition-, size-, and possibly shape-controlled catalysts. That study relied on the development of a well-characterized Ir(1,5-COD)Cl/γ-Al(2)O(3) precatalyst, which, when in contact with solution and H(2), turns into a nonaggregated Ir(0)(~900)/γ-Al(2)O(3) supported-nanoparticle heterogeneous catalyst. The kinetics of the Ir(1,5-COD)Cl/γ-Al(2)O(3) to Ir(0)(~900)/γ-Al(2)O(3) conversion were followed and fit by a two-step mechanism consisting of nucleation (A → B, rate constant k(1)) followed by autocatalytic surface growth (A + B → 2B, rate constant k(2)). However, a crucial, but previously unanswered question is whether the nucleation and growth steps occur primarily in solution, on the support, or possibly in both phases for one or more of the catalyst-formation steps. The present work investigates this central question for the prototype Ir(1,5-COD)Cl/γ-Al(2)O(3) to Ir(0)(~900)/γ-Al(2)O(3) system. Solvent variation-, γ-Al(2)O(3)-, and acetone-dependent kinetic data, along with UV-vis spectroscopic and gas-liquid-chromatography (GLC) data, are consistent with and strongly supportive of a supported-nanoparticle formation mechanism consisting of Ir(1,5-COD)Cl(solvent) dissociation from the γ-Al(2)O(3) support (i.e., from Ir(1,5-COD)Cl/γ-Al(2)O(3)), solution-based nucleation from that dissociated Ir(1,5-COD)Cl(solvent) species, fast Ir(0)(n) nanoparticle capture by γ-Al(2)O(3), and then subsequent solid-oxide-based nanoparticle growth from Ir(0)(n)/γ-Al(2)O(3) and with Ir(1,5-COD)Cl(solvent), the first kinetically documented mechanism of this type. Those data disprove a solid-oxide-based nucleation and growth pathway involving only Ir(1,5-COD)Cl/γ-Al(2)O(3) and also disprove a solution-based nanoparticle growth pathway involving Ir(1,5-COD)Cl(solvent) and Ir(0)(n) in solution. The present mechanistic studies allow comparisons of the Ir(1,5-COD)Cl/γ-Al(2)O(3) to Ir(0)(~900)/γ-Al(2)O(3) supported-nanoparticle formation system to the kinetically and mechanistically well-studied, Ir(1,5-COD)·P(2)W(15)Nb(3)O(62)(8-) to Ir(0)(~300)·(P(2)W(15)Nb(3)O(62)(8-))(n)(-8n) solution-based, polyoxoanion-stabilized nanoparticle formation and stabilization system. That comparison reveals closely analogous, solution Ir(1,5-COD)(+) or Ir(1,5-COD)Cl-mediated, mechanisms of nanoparticle formation. Overall, the hypothesis supported by this work is that these and analogous studies hold promise of providing a way to transfer the synthetic and mechanistic insights, from the modern revolution in nanoparticle synthesis and characterization in solution, to the rational, mechanism-directed syntheses of solid oxide-supported nanoparticle heterogeneous catalysts, also in contact with solution.     

C-H activation on a diphosphine and hydrido-bridged diiridium complex: generation and detection of an active IrII-IrII species [(Cp*Ir)2(micro-dmpm)(micro-H)]+

Reaction of [Cp*Ir(micro-H)](2) (5) (Cp* = eta(5)-C(5)Me(5)) with bis(dimethylphosphino)methane (dmpm) gives a new neutral diiridium complex [(Cp*Ir)(2)(micro-dmpm)(micro-H)(2)] (3). Treatment of 3 with methyl triflate at -30 degrees C results in the formation of [(Cp*Ir)(H)(micro-dmpm)(micro-H)(Me)(IrCp*)][OTf] (6). Warming a solution of above 0 degrees C brings about predominant generation of 32e(-) Ir(II)-Ir(II) species [(Cp*Ir)(micro-dmpm)(micro-H)(IrCp*)][OTf] (7). Further heating of the solution of 7 up to 30 degrees C for 14 h leads to quantitative formation of a new complex [(Cp*Ir)(H)(micro-Me(2)PCH(2)PMeCH(2))(micro-H)(IrCp*)][OTf] (8), which is formed by intramolecular oxidative addition of the methyl C-H bond of the dmpm ligand. Intermolecular C-H bond activation reactions with 7 are also examined. Reactions of 7 with aromatic molecules (benzene, toluene, furan, and pyridine) at room temperature result in the smooth sp(2) C-H activation to give [(Cp*Ir)(H)(micro-dmpm)(micro-H)(Ar)(IrCp*)][OTf] (Ar = Ph (9); Ar = m-Tol (10a) or p-Tol (10b); Ar = 2-Fur (11)) and [(Cp*Ir)(H)(micro-dmpm)(micro-C(5)H(4)N)(H)(IrCp*)][OTf] (12), respectively. Complex also reacts with cyclopentene at 0 degrees C to give [(Cp*Ir)(H)(micro-dmpm)(micro-H)(1-cyclopentenyl)(IrCp*)][OTf] (13). Structures of 3, 8 and 12 have been confirmed by X-ray analysis.     

Preparation, characterization, surface modification and redox reactions of silver nanoparticles in the presence of tryptophan

The synthesis and characterization of water-soluble dispersions of Ag nanoparticles by the reduction of AgNO(3) using tryptophan under alkaline synthesis conditions are reported. The Ag nanoparticle formation was very slow at low concentration and rapid at extremes. For surface modification and redox reactions, manipulating the interparticles interaction controlled the size of Ag nanoparticles aggregates. Our results suggest that the replacement of the BH(4)(-) ions adsorbed on the nanoparticle surface by tryptophan destabilizes the particles and further caused aggregation. A mechanism is proposed for the formation of silver nanoparticles by tryptophan. The experimental results are supported by theoretical calculations. The Ag nanoparticles were characterized by UV-vis absorption, dynamic light scattering and transmission electron microscopy techniques.     

Preparation and physical properties of early-late heterobimetallic compounds featuring Ir-M bonds (M = Ti, Zr, Hf)

Treatment of Cp*Ir N(t)Bu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N(t)Bu)MCp(2) (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir-M bond, to afford Cp*Ir(μ-N(t)Bu)(μ-H)MCp(2)OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp(2)Zr(H)Cl in the presence of Me(3)SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S(8) and aryl azides to insert an S-atom or aryl azide fragment into the metal-metal bond, yielding Cp*Ir(μ-N(t)Bu)(μ-S)HfCp(2) (6-Hf) and Cp*Ir(μ-N(t)Bu)(N(3)Ph)HfCp(2) (4-Hf), respectively. Heating 4-Hf results in N(2) extrusion to form Cp*Ir(μ-N(t)Bu)(NPh)HfCp(2) (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir-Zr heterobimetallics.     

Activation and coordination of ammonia at [cp*ir(h)(2) ]: NMR and matrix isolation studies

(1) H?NMR exchange spectroscopy of a reaction mixture of [Cp*Ir(H)(4) ] (1; Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) and ammonia suggests an exchange of hydrogen atoms between the hydrido ligands and ammonia. Treatment of 1 with ND(3) led to an H/D exchange between ND(3) and the hydrido ligands of 1. Subsequent studies showed that photolysis of 1 isolated in frozen argon matrices leads to the formation of the iridium compounds [Cp*Ir(H)(2) ] (2) and [Cp*Ir(H)(3) ] (4), as it was confirmed by IR spectroscopy. In the presence of water the aqua complex [Cp*Ir(H)(2) (OH(2) )] (3) was generated simultaneously. Accordingly, photolysis of 1 in an argon matrix doped with ammonia gave rise to the ammine complex [Cp*Ir(H)(2) (NH(3) )] (5). IR assignments were supported by calculations of the gas-phase IR spectra of 1-5 by DFT methods.     

Acidic iridium hydrides: implications for aerobic and Oppenauer oxidation of alcohols

[Cp*Ir(H)(bpym)]+ and [Cp*Ir(H)(bpy)]+ are the first examples of iridium based catalysts for the aerobic oxidation of alcohols; the catalytic cycle proceeds via acidic hydrides. Deprotonation of the hydride leads to a highly oxygen sensitive Ir I species that regenerate the Ir III complexes upon oxidation with dioxygen.     

Mono(sulfido)-bridged mixed-valence nitrosyl complex: protonation and oxidative addition of iodine across the Ir(II)-Ir(0) bond

Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively.     

Catalytic Water Splitting with an Iridium Carbene Complex: A Theoretical Study

Catalytic water oxidation at Ir (OH)⁺ ( Ir =IrCp*(Me₂NHC), where Cp*=pentamethylcyclopentadienyl and Me₂NHC=N,N′‐dimethylimidazolin‐2‐ylidene) can occur through various competing channels. A potential‐energy surface showing these various multichannel reaction pathways provides a picture of how their importance can be influenced by changes in the oxidant potential. In the most favourable calculated mechanism, water oxidation occurs via a pathway that includes four sequential oxidation steps, prior to formation of the O?O bond. The first three oxidation steps are exothermic upon treatment with cerium ammonium nitrate and lead to formation of Ir ^V(?O)(O ^. )⁺, which is calculated to be the most stabile species under these conditions, whereas the fourth oxidation step is the potential‐energy‐determining step. O?O bond formation takes place by coupling of the two oxo ligands along a direct pathway in the rate‐limiting step. Dissociation of dioxygen occurs in two sequential steps, regenerating the starting material Ir (OH)⁺. The calculated mechanism fits well with the experimentally observed rate law: v=k_obs[ Ir ][oxidant]. The calculated effective barrier of 24.6 kcal mol^?1 fits well with the observed turnover frequency of 0.88 s^?1. Under strongly oxidative conditions, O?O bond formation after four sequential oxidation steps is the preferred pathway, whereas under milder conditions O?O bond formation after three sequential oxidation steps becomes competitive.     

Sulfur-bridged early-late heterobimetallics synthesized by incorporation of titanium,vanadium, and molybdenum into bis(hydrosulfido) templates of group 9 metals

Reactions of the bis(hydrosulfido) complexes [Cp*Rh(SH)(2)(PMe(3))] (1a; Cp* = eta(5)-C(5)Me(5)) with [CpTiCl(3)] (Cp = eta(5)-C(5)H(5)) and [TiCl(4)(thf)(2)] in the presence of triethylamine led to the formation of the sulfido-bridged titanium-rhodium complexes [Cp*Rh(PMe(3))(micro(2)-S)(2)TiClCp] (2a) and [Cp*Rh(PMe(3))(micro2-S)(2)TiCl(2)] (3a), respectively. Complex 3a and its iridium analogue 3b were further converted into the bis(acetylacetonato) complexes [Cp*M(PMe(3))(micro(2)-S)(2)Ti(acac)(2)] (4a, M = Rh; 4b, M = Ir) upon treatment with acetylacetone. The hydrosulfido complexes 1a and [Cp*Ir(SH)(2)(PMe(3))] (1b) also reacted with [VCl(3)(thf)(3)] and [Mo(CO)(4)(nbd)] (nbd = 2,5-norbornadiene) to afford the cationic sulfido-bridged VM2 complexes [(Cp*M(PMe(3))(micro2-S)(2))2V](+) (5a(+), M = Rh; 5b(+), M = Ir) and the hydrosulfido-bridged MoM complexes [Cp*M(PMe(3))(micro2-SH)(2)Mo(CO)(4)] (6a, M = Rh; 6b, M = Ir), respectively.     

Inter- and intramolecular activation of aromatic C-H bonds by diphosphine and hydrido-bridged dinuclear iridium complexes

Reactions of [(Cp*Ir)2(mu-dmpm)(mu-H)2]2+ (1) with NaOtBu in aromatic solvent at room temperature give [(Cp*Ir)(H)(mu-dmpm)(mu-H)(Cp*Ir)(Ar)]+ [Ar = Ph (3), p-Tol (4a), m-Tol (4b), 2-furanyl (5a), 3-furanyl (5b)] via intermolecular aromatic C-H activation. Treatment of [(Cp*Ir)2(mu-dppm)(mu-H)2]2+ (2) with base (Et2NH) results in intramolecular C-H activation of the phenyl group in the dppm ligand to give [(Cp*Ir)(H){mu-PPh(C6H4)CH2PPh2}(mu-H)(Cp*Ir)]+ (6). The structures of 3, 5a, and 6 have been determined by X-ray diffraction methods.     

Hydrogen evolution from aliphatic alcohols and 1,4-selective hydrogenation of NAD+ catalyzed by a [C,N] and a [C,C] cyclometalated organoiridium complex at room temperature in water

A [C,N] cyclometalated Ir complex, [Ir(III)(Cp*)(4-(1H-pyrazol-1-yl-κN(2))benzoic acid-κC(3))(H(2)O)](2)SO(4) [1](2)·SO(4), was reduced by aliphatic alcohols to produce the corresponding hydride complex [Ir(III)(Cp*)(4-(1H-pyrazol-1-yl-κN(2))-benzoate-κC(3))H](-)4 at room temperature in a basic aqueous solution (pH 13.6). Formation of the hydride complex 4 was confirmed by (1)H and (13)C NMR, ESI MS, and UV-vis spectra. The [C,N] cyclometalated Ir-hydride complex 4 reacts with proton to generate a stoichiometric amount of hydrogen when the pH was decreased to pH 0.8 by the addition of diluted sulfuric acid. Photoirradiation (λ > 330 nm) of an aqueous solution of the [C,N] cyclometalated Ir-hydride complex 4 resulted in the quantitative conversion to a unique [C,C] cyclometalated Ir-hydride complex 5 with no byproduct. The complex 5 catalyzed hydrogen evolution from ethanol in a basic aqueous solution (pH 11.9) under ambient conditions. The 1,4-selective catalytic hydrogenation of β-nicotinamide adenine dinucleotide (NAD(+)) by ethanol was also made possible by the complex 1 to produce 1,4-dihydro-β-nicotinamide adenine dinucleotide (1,4-NADH) at room temperature. The overall catalytic mechanism of hydrogenation of NAD(+), accompanied by the oxidation of ethanol, was revealed on the basis of the kinetic analysis and detection of the reaction intermediates.     

Synthesis, structures, and properties of group 9- and group 10-group 6 heterodinuclear nitrosyl complexes

The reaction of the group 9 bis(hydrosulfido) complexes [Cp*M(SH)2(PMe3)] (M=Rh, Ir; Cp*=eta(5)-C 5Me5) with the group 6 nitrosyl complexes [Cp*M'Cl2(NO)] (M'=Mo, W) in the presence of NEt3 affords a series of bis(sulfido)-bridged early-late heterobimetallic (ELHB) complexes [Cp*M(PMe3)(mu-S)2M'(NO)Cp*] (2a, M=Rh, M'=Mo; 2b, M=Rh, M'=W; 3a, M=Ir, M'=Mo; 3b, M=Ir, M'=W). Similar reactions of the group 10 bis(hydrosulfido) complexes [M(SH)2(dppe)] (M=Pd, Pt; dppe=Ph 2P(CH2) 2PPh2), [Pt(SH)2(dppp)] (dppp=Ph2P(CH2) 3PPh2), and [M(SH)2(dpmb)] (dpmb=o-C6H4(CH2PPh2)2) give the group 10-group 6 ELHB complexes [(dppe)M(mu-S)2M'(NO)Cp*] (M=Pd, Pt; M'=Mo, W), [(dppp)Pt(mu-S)2M'(NO)Cp*] (6a, M'=Mo; 6b, M'=W), and [(dpmb)M(mu-S)2M'(NO)Cp*] (M=Pd, Pt; M'=Mo, W), respectively. Cyclic voltammetric measurements reveal that these ELHB complexes undergo reversible one-electron oxidation at the group 6 metal center, which is consistent with isolation of the single-electron oxidation products [Cp*M(PMe3)(mu-S)2M'(NO)Cp*][PF6] (M=Rh, Ir; M'=Mo, W). Upon treatment of 2b and 3b with ROTf (R=Me, Et; OTf=OSO 2CF 3), the O atom of the terminal nitrosyl ligand is readily alkylated to form the alkoxyimido complexes such as [Cp*Rh(PMe3)(mu-S)2W(NOMe)Cp*][OTf]. In contrast, methylation of the Rh-, Ir-, and Pt-Mo complexes 2a, 3a, and 6a results in S-methylation, giving the methanethiolato complexes [Cp*M(PMe3)(mu-SMe)(mu-S)Mo(NO)Cp*][BPh 4] (M=Rh, Ir) and [(dppp)Pt(mu-SMe)(mu-S)Mo(NO)Cp*][OTf], respectively. The Pt-W complex 6b undergoes either S- or O-methylation to form a mixture of [(dppp)Pt(mu-SMe)(mu-S)W(NO)Cp*][OTf] and [(dppp)Pt(mu-S) 2W(NOMe)Cp*][OTf]. These observations indicate that O-alkylation and one-electron oxidation of the dinuclear nitrosyl complexes are facilitated by a common effect, i.e., donation of electrons from the group 9 or 10 metal center, where the group 9 metals behave as the more effective electron donor.     

Silylenediamido [(CH3)2Si(NTs)2(2-); Ts = p-CH3C6H4SO2] complexes of iridium: synthesis, structures and facile Si-N bond cleavage

The N,N'-bis(sulfonyl)diaminosilane TsdmsinH(2) (TsdmsinH(2) = (CH(3))(2)Si(NHTs)(2), Ts = p-CH(3)C(6)H(4)SO(2)) reacted with [Cp*IrCl(2)](2) (Cp* = eta(5)-C(5)(CH(3))(5)) in the presence of a base to give the coordinatively unsaturated (silylenediamido)iridium complex [Cp*Ir(Tsdmsin)] (2), which was further converted to the 18e adducts [Cp*Ir(Tsdmsin)L] (L = P(C(6)H(5))(3) (3a), P(OC(2)H(5))(3), CO); the reactions of 2 and 3a with water led to the formation of the imido-bridged dinuclear complex [Cp*Ir(micro(2)-NTs)(2)IrCp*] and the bis(amido) complex [Cp*Ir(NHTs)(2){P(C(6)H(5))(3)}], respectively.     

Construction of tetranuclear macrocycles through C-H activation and structural transformation induced by [2+2] photocycloaddition reaction

A series of binuclear complexes [{Cp*Ir(OOCCH₂COO)}₂(pyrazine)] ( 1 b ), [{Cp*Ir(OOCCH₂COO)}₂(bpy)] ( 2 b ; bpy=4,4′‐bipyridine), [{Cp*Ir(OOCCH₂COO)}₂(bpe)] ( 3 b ; bpe=trans‐1,2‐bis(4‐pyridyl)ethylene) and tetranuclear metallamacrocycles [{(Cp*Ir)₂(OOC‐C?C‐COO)(pyrazine)}₂] ( 1 c ), [{(Cp*Ir)₂(OOC‐C?C‐COO)(bpy)}₂] ( 2 c ), [{(Cp*Ir)₂(OOC‐C?C‐COO)(bpe)}₂] ( 3 c ), and [{(Cp*Ir)₂[OOC(H₃C₆)‐N?N‐(C₆H₃)COO](pyrazine)}₂] ( 1 d ), [{(Cp*Ir)₂[OOC(H₃C₆)‐N?N‐(C₆H₃)COO](bpy)}₂] ( 2 d ), [{(Cp*Ir)₂[OOC(H₃C₆)‐N?N‐(C₆H₃)COO](bpe)}₂] ( 3 d ) were formed by reactions of 1 a – 3 a {[(Cp*Ir)₂(pyrazine)Cl₂] ( 1 a ), [(Cp*Ir)₂(bpy)Cl₂] ( 2 a ), and [(Cp*Ir)₂(bpe)Cl₂] ( 3 a )} with malonic acid, fumaric acid, or H₂ADB (azobenzene‐4,4′‐chcarboxylic acid), respectively, under mild conditions. The metallamacrocycles were directly self‐assembled by activation of C? H bonds from dicarboxylic acids. Interestingly, after exposure to UV/Vis light, 3 c was converted to [2+2] cycloaddition complex 4 . The molecular structures of 2 b , 1 c , 1 d , and 4 were characterized by single‐crystal x‐ray crystallography. Nanosized tubular channels, which may play important roles for their stability, were also observed in 1 c , 1 d , and 4 . All complexes were well characterized by ¹H NMR and IR spectroscopy, as well as elemental analysis.     

Synthesis and reactivity of Ir(I) and Ir(III) complexes with MeNH2, Me2C=NR (R = H, Me), C,N-C6H4{C(Me)=N(Me)}-2, and N,N'-RN=C(Me)CH2C(Me2)NHR (R = H, Me) ligands

Complexes [Ir(Cp*)Cl(n)(NH2Me)(3-n)]X(m) (n = 2, m = 0 (1), n = 1, m = 1, X = Cl (2a), n = 0, m = 2, X = OTf (3)) are obtained by reacting [Ir(Cp*)Cl(mu-Cl)]2 with MeNH2 (1:2 or 1:8) or with [Ag(NH2Me)2]OTf (1:4), respectively. Complex 2b (n = 1, m = 1, X = ClO 4) is obtained from 2a and NaClO4 x H2O. The reaction of 3 with MeC(O)Ph at 80 degrees C gives [Ir(Cp*){C,N-C6H4{C(Me)=N(Me)}-2}(NH2Me)]OTf (4), which in turn reacts with RNC to give [Ir(Cp*){C,N-C6H4{C(Me)=N(Me)}-2}(CNR)]OTf (R = (t)Bu (5), Xy (6)). [Ir(mu-Cl)(COD)]2 reacts with [Ag{N(R)=CMe2}2]X (1:2) to give [Ir{N(R)=CMe2}2(COD)]X (R = H, X = ClO4 (7); R = Me, X = OTf (8)). Complexes [Ir(CO)2(NH=CMe2)2]ClO4 (9) and [IrCl{N(R)=CMe2}(COD)] (R = H (10), Me (11)) are obtained from the appropriate [Ir{N(R)=CMe2}2(COD)]X and CO or Me4NCl, respectively. [Ir(Cp*)Cl(mu-Cl)]2 reacts with [Au(NH=CMe2)(PPh3)]ClO4 (1:2) to give [Ir(Cp*)(mu-Cl)(NH=CMe2)]2(ClO4)2 (12) which in turn reacts with PPh 3 or Me4NCl (1:2) to give [Ir(Cp*)Cl(NH=CMe2)(PPh3)]ClO4 (13) or [Ir(Cp*)Cl2(NH=CMe2)] (14), respectively. Complex 14 hydrolyzes in a CH2Cl2/Et2O solution to give [Ir(Cp*)Cl2(NH3)] (15). The reaction of [Ir(Cp*)Cl(mu-Cl)]2 with [Ag(NH=CMe2)2]ClO4 (1:4) gives [Ir(Cp*)(NH=CMe2)3](ClO4)2 (16a), which reacts with PPNCl (PPN = Ph3=P=N=PPh3) under different reaction conditions to give [Ir(Cp*)(NH=CMe2)3]XY (X = Cl, Y = ClO4 (16b); X = Y = Cl (16c)). Equimolar amounts of 14 and 16a react to give [Ir(Cp*)Cl(NH=CMe2)2]ClO4 (17), which in turn reacts with PPNCl to give [Ir(Cp*)Cl(H-imam)]Cl (R-imam = N,N'-N(R)=C(Me)CH2C(Me)2NHR (18a)]. Complexes [Ir(Cp*)Cl(R-imam)]ClO4 (R = H (18b), Me (19)) are obtained from 18a and AgClO4 or by refluxing 2b in acetone for 7 h, respectively. They react with AgClO4 and the appropriate neutral ligand or with [Ag(NH=CMe2)2]ClO4 to give [Ir(Cp*)(R-imam)L](ClO4)2 (R = H, L = (t)BuNC (20), XyNC (21); R = Me, L = MeCN (22)) or [Ir(Cp*)(H-imam)(NH=CMe2)](ClO4)2 (23a), respectively. The later reacts with PPNCl to give [Ir(Cp*)(H-imam)(NH=CMe2)]Cl(ClO4) (23b). The reaction of 22 with XyNC gives [Ir(Cp*)(Me-imam)(CNXy)](ClO4)2 (24). The structures of complexes 15, 16c and 18b have been solved by X-ray diffraction methods.