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PubMed2005

Synthesis and properties of electrophosphorescent chelating polymers with iridium complexes in the conjugated backbone.

The synthesis of electrophosphorescent chelating polymers by Suzuki polycondensation of A-A- and B-B-type monomers is described, in which the fluorene-alt-carbazole (PFCz) segment is used as polymer backbone. By using alkyl-substituted ligands of iridium complex monomers, chelating copolymers with higher contents of iridium complex can be synthesized. Chemical and photophysical characterization confirm that the Ir complex is incorporated into the polymer backbone as one of the monomer repeat units by means of two 5-bromotolylpyridine ligands. Chelating polymers with Ir complexes in the conjugated polymer backbone show highly efficient energy transfer of excitons from the PFCz host segment to the Ir complex by an intramolecular trapping mechanism. The external quantum and luminous efficiencies of a device made with PFCzMppyIrhm4 copolymer reach 4.1 % ph/el (photons/electron) and 5.4 cd A(-1), respectively, at a current density of 32.2 mA cm(-2), an emission peak of 577 nm, and a luminance of 1730 cd cm(-2). Most important, the devices made from the chelating copolymers show no notable efficiency decay with increasing current density due to reduced concentration quenching and triplet-triplet (T-T) annihilation. This indicates that incorporation of the phosphorescent complex into the rigid conjugated polymer main chain is a new way to simultaneously realize high efficiency, long-term stability, and simple processing of phosphorescent polymer light-emitting diodes.

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PubMed2006

pi-Conjugated chelating polymers with charged iridium complexes in the backbones: synthesis, characterization, energy transfer, and electrochemical properties.

A series of pi-conjugated chelating polymers with charged iridium (Ir) complexes in the backbones were synthesized by a Suzuki polycondensation reaction, leading to homogeneous polymeric materials that phosphoresce red light. The fluorene and bipyridine (bpy) segments were used as polymer backbones. 5,5'-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligand. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5,5'-dibromobipyridine ligand. Chelating polymers showed almost complete energy transfer from the host fluorene segments to the guest Ir complexes in the solid state when the feed ratio was 2 mol %. In the films of the corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol %. Both intra- and intermolecular energy-transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film formation. These chelating polymers also showed more efficient energy transfer than the corresponding blended system and the mechanism of incorporation of the charged Ir complexes into the pi-conjugated polymer backbones efficiently avoided the intrinsic problems associated with the blend system, thus offering promise in optoelectronic applications.

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PubMed2006

Mechanistic investigations of imine hydrogenation catalyzed by dinuclear iridium complexes.

Treatment of [Ir2(mu-H)(mu-Pz)2H3(NCMe)(PiPr3)2] (1) with one equivalent of HBF4 or [PhNH=CHPh]BF4 affords efficient catalysts for the homogeneous hydrogenation of N-benzylideneaniline. The reaction of 1 with HBF4 leads to the trihydride-dihydrogen complex [Ir2(mu-H)(mu-Pz)2H2(eta2-H2)(NCMe)(PiPr3)2]BF4 (2), which has been characterized by NMR spectroscopy and DFT calculations on a model complex. Complex 2 reacts with imines such as tBuN=CHPh or PhN=CHPh to afford amine complexes [Ir2(mu-H)(mu-Pz)2H2(NCMe){L}(PiPr3)2]BF4 (L = NH(tBu)CH2Ph, 3; NH(Ph)CH2Ph, 4) through a sequence of proton- and hydride-transfer steps. Dihydrogen partially displaces the amine ligand of 4 to form 2; this complements a possible catalytic cycle for the N-benzylideneaniline hydrogenation in which the amine-by-dihydrogen substitution is the turnover-determining step. The rates of ligand substitution in 4 and its analogues with labile ligands other than amine are dependent upon the nature of the leaving ligand and independent on the incoming ligand concentration, in agreement with dissociative substitutions. Water complex [Ir2(mu-H)(mu-Pz)2H2(NCMe)(OH2)(PiPr3)2]BF4 (7) hydrolyzes N-benzylideneaniline, which eventually affords the poor hydrogenation catalyst [Ir2(mu-H)(mu-Pz)2H2(NCMe)(NH2Ph)(PiPr3)2]BF4 (11). The rate law for the catalytic hydrogenation in 1,2-dichloroethane with complex [Ir2(mu-H)(mu-Pz)2H2(OSO2CF3)(NCMe)(PiPr3)2] (8) as catalyst precursor is rate = k[8]{p(H2)}; this is in agreement with the catalytic cycle deduced from the stochiometric experiments. The hydrogenation reaction takes place at a single iridium center of the dinuclear catalyst, although ligand modifications at the neighboring iridium center provoke changes in the hydrogenation rate. Even though this catalyst system is also capable of effectively hydrogenating alkenes, N-benzylideneaniline can be selectively hydrogenated in the presence of simple alkenes.

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PubMed2006

Synthetically tailored excited states: phosphorescent, cyclometalated iridium(III) complexes and their applications.

Phosphorescent iridium(III) complexes are being widely explored for their utility in diverse photophysical applications. The performance of these materials in such roles depends heavily on their excited-state properties, which can be tuned through ligand and substituent effects. This concept article focuses on methods for synthetically tailoring the properties of bis-cyclometalated iridium(III) materials, and explores the factors governing the nature of their lowest excited state.

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PubMed2003

Improved electrodeposited iridium oxide pH sensor fabricated on etched titanium substrates.

In the present paper, the preparation and characterization of an improved solid-state pH sensor are described. The sensor is based on anodically electrodeposited iridium oxide film, as a pH-sensing layer. Merits of the present sensor include (i) excellent adhesion of the pH sensitive layer to the substrate, (ii) excellent reproducibility of sensor fabrication, (iii) faster preparation procedure, and (iv) low cost of the titanium substrate. These advantages are realized by combining acid-etched titanium as the electrode substrate with an optimized electrodeposition solution consisting of IrCl4 as an iridium source, hydrogen peroxide, potassium oxalate, and potassium carbonate. Heating the electrodeposition solution to 90 degrees C reduced the time required for solution development from approximately 3 days to 10 min. The pH-sensing layer is protected with a layer of Nafion and a microporous polyester membrane. The improved sensor showed a super-Nernstian response (-73.7 +/- 1.2 mV/pH unit) in the pH range of 1.5-11.5. The present pH sensor, fabricated in a tubular form, is used as a detector in a flow injection analysis (FIA) system for pH measurements. Optimization of the FIA experimental parameters resulted in a linear dependence of peak heights on the pH of the injected samples in the pH range of 2-11.

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PubMed2002

Synthesis of heteroleptic anthryl-substituted beta-ketoenolates of rhodium(III) and iridium(III): photophysical, electrochemical, and EPR study of the fluorophore-metal interaction.

The anthryl-substituted rhodium(III) and iridium(III) heteroleptic beta-ketoenolato derivatives of general formula [M(acac)(2)(anCOacac)] [acac = pentane-2,4-dionate; anCOacac = 3-(9-anthroyl)pentane-2,4-dionate], 3 (M = Rh) and 4 (M = Ir), and [M(acac)(2)(anCH(2)acac)] [anCH(2)acac = 3-(9-anthrylmethyl)pentane-2,4-dionate], 5 (M = Rh) and 6 (M = Ir), were prepared by reacting the corresponding tris(pentane-2,4-dionate)metal complexes, [M(acac)(3)], with 9-anthroyl chloride and 9-chloromethylanthracene, respectively, under Friedel-Crafts conditions. 3-6 were characterized by elemental analysis, ion spray mass spectrometry (IS-MS), (1)H NMR, and UV-vis spectroscopy. The structure of 3 was also elucidated by single-crystal X-ray analysis. When excited at 365 nm, 3-6 result to be poorly luminescent compounds; while the free diketone, i.e., 3-(9-anthrylmethyl)pentane-2,4-dione 1, whose structure was established also by single-crystal X-ray analysis, results to be a strongly light emitting molecule. The study of the electrochemical behavior of 3-6 as well as of the corresponding tris-acetylacetonates of rhodium(III) and iridium(III) allows a satisfactory interpretation of their electrode process mechanism, and gives information about the location of the redox sites along with the thermodynamic and kinetic characterization of the corresponding redox processes. All data are in agreement with the hypothesis that the quenching of the anthracene fluorescence, observed for compounds 3-6, can be due to an intramolecular electron transfer process between the anthryl moiety and the metal-beta-ketoenolato component. Moreover, a study was carried out of the redox behavior of the dyads 3-6 under chemical activation. The one-electron oxidation of compounds 3-6 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, 3(+)-6(+), whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribution.

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PubMed2002

Parahydrogen induced polarization and the oxidative addition of hydrogen to iridium tribromostannyl carbonylate anions.

Activation of dihydrogen by a system composed of (Bu(4)N)[IrBr(2)(CO)(2)] (1) and tin dibromide in varying ratios was studied using parahydrogen induced polarization (PHIP) which allows the detection of transient dihydrides not observable in conventional (1)H NMR spectra. While the oxidative addition of dihydrogen to neutral and cationic Ir(I) species is common, there are only a few examples of H(2) addition to anionic complexes. Tin dibromide reacts with iridium(I) complex 1 in acetone forming equilibrium mixtures of cis- and trans-tribromostannyl derivatives [IrBr(n)()(SnBr(3))(2)(-)(n)()(CO)(2)](-), n = 0,1, the existence of which is inferred from the stereochemistries of the dihydrogen addition products determined using PHIP. The sigma-donating effect of the SnBr(3)(-) ligand facilitates the oxidative addition to the iridium center. The structures of the dihydrides formed upon addition of dihydrogen are assigned on the basis of hydride chemical shifts and values of (2)J((1)H-(117,119)Sn). The only dihydride observed in conventional (1)H NMR spectra is cis-trans-cis-[IrH(2)(SnBr(3))(2)(CO)(2)](-), the identity of which was confirmed using the (13)C labeled Ir(I) precursor. Both [IrBr(2)(CO)(2)](-) and its tribromostannyl derivatives catalyze cis-pairwise addition of dihydrogen to phenylacetylene.

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PubMed2002

Novel intramolecular C-H bond activation in an iridium dppm complex.

Reaction of TpIr(C(2)H(4))(2) (Tp = tris-pyrazolylborate) with various chelating phosphine ligands has been explored. Reaction with bis-diphenylphosphinoethane leads to complete displacement of the Tp ligand. With bis-diphenylphosphinomethane, an intramolecular proton transfer from the methylene bridge to the iridium center occurs to give an iridium hydride complex formally resulting from oxidative C-H bond activation. Reaction with 2,2-bis(diphenylphosphino)propane (dppip) affords an Ir(I) complex formulated as kappa(2)-TpIr(dppip). Protonation of this Ir(I) complex gives a six coordinate Ir(III) hydride species.

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PubMed2004

Iridium(III) complexes formed by O-H and/Or C-H activation of 2-(arylazo)phenols.

Reaction of 2-(arylazo)phenols with [Ir(PPh(3))(3)Cl] in refluxing ethanol in the presence of a base (NEt(3)) affords complexes of three different types, viz. [Ir(PPh(3))(2)(NO-R)(H)Cl] (R = OCH(3), CH(3), H, Cl and NO(2)), [Ir(PPh(3))(2)(NO-R)(H)(2)] and [Ir(PPh(3))(2)(CNO-R)(H)]. Structures of the [Ir(PPh(3))(2)(NO-Cl)(H)Cl], [Ir(PPh(3))(2)(NO-Cl)(H)(2)] and [Ir(PPh(3))(2)(CNO-Cl)(H)] complexes have been determined by X-ray crystallography. In the [Ir(PPh(3))(2)(NO-R)(H)Cl] and [Ir(PPh(3))(2)(NO-R)(H)(2)] complexes, the 2-(arylazo)phenolate ligands are coordinated to the metal center as monoanionic bidentate N,O-donors, whereas in the [Ir(PPh(3))(2)(CNO-R)(H)] complexes, they are coordinated to iridium as dianionic tridentate C,N,O-donors. In all three products formed in ethanol, the two PPh(3) ligands are trans. Reaction of 2-(arylazo)phenols with [Ir(PPh(3))(3)Cl] in refluxing toluene in the presence of NEt(3) affords complexes of two types, viz. [Ir(PPh(3))(2)(CNO-R)(H)] and [Ir(PPh(3))(2)(CNO-R)Cl]. Structure of the [Ir(PPh(3))(2)(CNO-Cl)Cl] complex has been determined by X-ray crystallography, and the 2-(arylazo)phenolate ligand is coordinated to the metal center as a dianionic tridentate C,N,O-donor and the two PPh(3) ligands are cis. All of the iridium(III) complexes show intense MLCT transitions in the visible region. Cyclic voltammetry shows an Ir(III)-Ir(IV) oxidation on the positive side of SCE and an Ir(III)-Ir(II) reduction on the negative side for all of the products.

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PubMed2004

Dyads containing iridium(III) bis-terpyridine as photoactive center: synthesis and electron transfer study.

A series of Ir(III)-D dyads based on an iridium(III) bis-terpyridine complex as a photoactive center and tertiary amines as donor groups, as well as their individual components, have been designed to generate photoinduced charge separation. Depending on the donor group, a modular approach or a "chemistry-on-the-complex" approach has been used to prepare three different Ir(III)-D dyads. A detailed photophysical study has been performed on one Ir(III)-D dyad in which a triarylamine is linked to the iridium bis-terpyridine complex with an amido-phenyl group used as a spacer. In acetonitrile at room temperature, steady-state and time-resolved methods gave evidence of a photoinduced charge-separated state Ir(-)-D(+) with a lifetime of 70 ps. This relatively short lifetime could be due to the close proximity between the negative charge, likely localized in the bridging terpyridine, and the oxidized donor group.

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PubMed2005

Novel eta1-N,eta2-C,C-binding mode between pyridinyl-functionalized cyclopentadienyl ligands and iridium.

The reaction between 2-(2,3,4,5-tetramethyl-cyclopenta-1,3-dienyl)-pyridine 1 and IrCl3 was performed in an attempt to synthesize a cyclometalated system with decreased pi conjugation in the ligand. An unexpected reduction and rearrangement of bis-pyridinyl-cyclopentadienyl cyclometalated Ir(III) intermediate 2 took place yielding bis-pyridinyl-fulvene Ir(I) complex 4, which exhibits a novel bis-eta1-N,eta2-C,C-binding mode between the pyridinyl-functionalized fulvene ligand and iridium. The iridium atom in 4 is not sandwiched between two cyclopentadienyl moieties; rather, the two cyclopentadienyl groups adopt a pi-pi stacking arrangement with a centroid-centroid distance of 3.494 A. The Cl/P(wedge)O ligand-exchange reaction between 4 and 2-[(diphenylphosphanyl)-methyl]-1,1,1,3,3,3-hexafluoro-propan-2-ol 5 led to loss of one pyridinyl-functionalized fulvene ligand and produced complex 6, in which the remaining pyridinyl-functionalized fulvene ligand exhibits the mono-eta1-N,eta2-C,C-binding mode.

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PubMed2006

Series of new cationic iridium(III) complexes with tunable emission wavelength and excited state properties: structures, theoretical calculations, and photophysical and electrochemical properties.

A series of new cationic iridium(III) complexes [Ir(piq)2(N/\N)]+PF6- (1-6) (piq =1-phenyl-isoquinoline) containing N/\N ligands with different conjugated lengths were synthesized, where the six N/\N ligands were bipyridine, phenanthroline, 2-pyridyl-quinoline, 2,2'-biquinoline, 1,1'-biisoquinoline, and 2-(2-quniolinyl)quinoxaline. Single-crystal X-ray diffraction spectra of three complexes were studied, and the iridium(III) centers were found to adopt a distorted octahedral coordination geometry with cis metalated carbons and trans nitrogen atoms. UV-vis, photoluminescence, cyclic voltammetry, and theoretical calculations were employed for studying the photophysical and electrochemical properties. And the excited-state properties were investigated in detail. The excited state of complexes is complicated and contains triplet metal-to-ligand charge transfer (3MLCT), triplet ligand-to-ligand charge transfer (3LLCT), and ligand-centered (cyclometalated) (3LC) transitions simultaneously. Importantly, the emission wavelength can be tuned significantly from 586 to 732 nm by changing the conjugated length of N/\N ligands.

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PubMed2006

Dinuclear iridium(III) complexes consisting of back-to-back tpy-(ph)n-tpy bridging ligands (n = 0, 1, or 2) and terminal cyclometallating tridentate N-C-N ligands.

Three dinuclear iridium(III) complexes consisting of a conjugated bis-tpy type bridging ligand and cyclometallating capping tridentate ligands of the 1,3-di-2-pyridylbenzene family have been prepared (tpy, 2,2',6',2' '-terpyridine). The two tpy units of the bridge are connected via their back-positions (4') either directly or with a p-phenylene or p-biphenylene spacer. The synthesis relies on the reaction between the dinuclear [Ir(dpb)Cl2]2 complex (dpb-H =1,3-dipyridyl-4,6-dimethylbenzene) and the corresponding bis-tpy ligand. Electrochemical measurements afford metal-centered oxidation and ligand-centered reduction potentials; from the oxidation steps, no evidence is obtained for a strong coupling between the two iridium(III) subunits of the dinuclear species. For all complexes, ground-state absorption data in the 380 nm to visible region show a trend which is consistent with the presence of charge-transfer (CT) transitions involving different degrees of electronic delocalization at the bridging ligands. (dpb)Ir(tpy-tpy)Ir(dpb)4+ exhibits an appreciable luminescence at room temperature (phi = 3.0 x 10(-3); tau = 3.3 ns), whereas no emission from the other binuclear complexes is detected. All binuclear complexes luminesce at 77 K, and a metal-to-ligand CT nature for (dpb)Ir(tpy-tpy)Ir(dpb)4+ is suggested, whereas a ligand-centered (LC) emission is proposed for (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+ on the basis of the comparison with the phosphorescence properties of the free bridging ligand, tpy-(ph)2-tpy. Transient absorbance experiments at room temperature afford the absorption spectra and lifetimes of the non-emissive excited states. For (dpb)Ir(tpy-ph-tpy)Ir(dpb)4+ and (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+, the spectra exhibit a broad profile peaking around 780 nm, quite intense in the case of (dpb)Ir(tpy-(ph)2-tpy)Ir(dpb)4+, and lifetimes of 160 and 440 ps, respectively.

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PubMed1996

Reactions of Singlet Oxygen with Organometallic Compounds. 4. Photooxidation of Cationic Iridium(I) and Rhodium(I) Complexes with Weakly Bonded Ligands.

Cationic complexes of the type [M(CO)S(PPh(3))(2)](+) (M = Ir, Rh; S = CH(3)CN) react with singlet oxygen to form the corresponding peroxo complexes [M(CO)S(PPh(3))(2)(O(2))](+). The solvent molecule remains coordinated to the metal in the oxygen adducts. The novel cationic iridium-peroxo complex is stable at room temperature, while the rhodium-peroxo complex is only stable below 0 degrees C. Rate constants for physical and chemical interaction of the complexes with singlet oxygen are somewhat smaller than those for related neutral complexes. Upon addition of alkenes (tetramethylethylene or 1-octene) to the peroxo complexes, neither oxidation of the olefins nor substitution of the acetonitrile ligand was observed. 1-Octene was isomerized to give mostly 2- and 3-octene by the cationic rhodium(I) complex. A cationic iridium complex which already possesses a coordinated diene ligand ([Ir(COD)(PPh(3))(2)](+)) did not react with or quench singlet oxygen.

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PubMed1999

Iridium(III, 0, and -I) Complexes Stabilized by 1,1'-Bis(diphenylphosphino)ferrocene (dppf): Synthesis and Characterization. Crystal Structures of [Na(THF)(5)][Ir(dppf)(2)].THF and [Ir(dppf)(2)].

The iridium(I) complex stabilized by the organometallic ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf), [Ir(dppf)(2)](+), 1, undergoes a cyclometalation reaction in solution to give the iridium(III) hydride [IrH(dppf(-H))(dppf)](+), 2, which has been isolated and characterized by spectroscopic methods. The compound is the final product of the intramolecular oxidative addition of the ortho C-H bond of a phenyl substituent of the diphosphine and is formed through an intermediate hydride, which has also been spectroscopically characterized. 1 can be electrochemically reduced to the Ir(0) and Ir(-I) species, [Ir(dppf)(2]), 3, and [Ir(dppf)(2)](-), 4, respectively, in two reversible single-electron processes. These low-valent metal complexes have been obtained by chemical reduction of 1 with sodium naphthalenide in tetrahydrofuran solution and their crystal and molecular structures determined by single-crystal X-ray analyses. 3 crystallizes in the triclinic system, space group P&onemacr;, with a = 13.019(4) Å, b = 13.765(6) Å, c = 15.549(5) Å, alpha = 93.74(3) degrees, beta = 90.35(3) degrees, gamma = 92.07(3) degrees, V = 2779(2) Å(3), and Z = 2. Anionic complex 4 crystallizes as sodium-solvated salt [Na(THF)(5)][Ir(dppf)(2)].THF, 4b, in which the sodium cation is surrounded by five molecules of THF in a slightly distorted trigonal-bipyramidal environment. 4b crystallizes in the monoclinic system, space group P2(1)/n, with a = 13.325(3) Å, b = 23.976(5) Å, c = 26.774(7) Å, beta = 98.77(2) degrees, V = 8454(4) Å(3), and Z = 4. The coordination geometry around the metal in neutral d(9) complex 3 is intermediate between the highly distorted square-planar geometry, found earlier in cationic d(8) species 1, and the almost regular tetrahedral arrangement of the two diphosphines in the anionic d(10) complex 4. Reduction of Ir(I) to Ir(0) and Ir(-I) causes a stepwise decrease of the Ir-P bond length of 0.04 Å (average) and 0.05 Å, respectively, with a concomitant increase of the bite angle of the diphosphine which ranges from 94.3 degrees (average) in [Ir(dppf)(2)](+) to 102.3 degrees in [Ir(dppf)(2)](-).

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PubMed2001

Mechanism of beta-hydrogen elimination from square planar iridium(I) alkoxide complexes with labile dative ligands.

Mechanistic studies were conducted on beta-hydrogen elimination from complexes of the general formula [Ir(CO)(PPh(3))(2)(OR)], which are square planar alkoxo complexes with labile ligands. The dependence of rate, isotope effect, and alkoxide racemization on phosphine concentration revealed unusually detailed information on the reaction pathway. The alkoxo complexes were remarkably stable, including those with a variety of electronically and sterically distinct groups at the beta-carbon. These complexes were much more stable than the corresponding alkyl complexes. Thermolysis of these complexes in the presence of PPh(3) yielded the iridium hydride [Ir(CO)(PPh(3))(3)H] and the corresponding aldehyde or ketone with rate constants that were affected little by the groups at the beta-carbon. The reactions were first order in iridium complexes. At low [PPh(3)], the reaction rate was nearly zero order in PPh(3), but reactions at high [PPh(3)] revealed an inverse dependence of reaction rate on PPh(3). The rate constants were similar in toluene, THF, and chlorobenzene. The y-intercept of a 1/k(obs) vs [PPh(3)] plot displayed a primary isotope effect, indicating that the y-intercept did not simply correspond to phosphine dissociation. These data and a dependence of alkoxide racemization on [PPh(3)] showed that the elementary beta-hydrogen elimination step was reversible. A mechanism involving reversible beta-hydrogen elimination followed by associative displacement of the coordinated ketone or aldehyde by PPh(3) was consistent with all of our data. This mechanism stands in contrast with the pathways proposed recently for alkoxide beta-hydrogen elimination involving direct elimination, protic catalysts, or binuclear mechanisms and shows that alkoxide elimination can follow pathways similar to those for beta-hydrogen elimination from alkyl complexes.

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PubMed2002

Combined computational and experimental study of substituent effects on the thermodynamics of H(2), CO, arene, and alkane addition to iridium.

The thermodynamics of small-molecule (H(2), arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d(8), four-coordinate d(8), and five-coordinate d(6)) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = eta(3)-1,3,5-C(6)H(2)[CH(2)PR(2)](2)Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H(2), C-H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)(2). Para substituents on arenes undergoing C-H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)(2), disfavors addition of H-H or C-H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron complexes is also disfavored by increased electron donation from Y. By contrast, addition of H-H and C-H bonds or CO to the three-coordinate parent species (Y-PCP)Ir is favored by increased electron donation. In general, the effects of varying Y are markedly similar for H(2), C-H, and CO addition. The trends can be fully rationalized in terms of simple molecular orbital interactions but not in terms of concepts related to oxidation, such as charge-transfer or electronegativity differences.

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PubMed2005

High nuclearity iridium-platinum clusters: synthesis, structures, bonding, and reactivity.

The reaction of Ir4(CO)12 with an excess of Pt(PBu(t)3)2 at room temperature yielded the bis-Pt(PBu(t)3) adduct Ir4(CO)12[Pt(PBu(t)3)]2 (9), which contains two Pt(PBu(t)3) groups bridging opposite edges of a central Ir4 pseudotetrahedron. The same reaction at 110 degrees C yielded two new higher nuclearity complexes, Ir8(CO)12[Pt(PBu(t)3)]4 (10) and Ir6(CO)10[Pt(PBu(t)3)]4 (11). Compound 10 consists of a central Ir4(CO)4 tetrahedron with four edge-bridging Ir(CO)2 groups and four Pt(PBu(t)3) groups that are each bonded to Ir3 triangles of the Ir4 tetrahedron and two of the Ir(CO)2 groups. Compound 11 consists of a central Ir4(CO)4 pseudotetrahedron with two edge-bridging Ir(CO)2 groups and four Pt(PBu(t)3) groups; one Pt(PBu(t)3) group is bonded to five iridium atoms as found in 10; two are bonded to four iridium atoms, and one is bonded to one of the outer Ir2Pt triangles. Compound 11 reacted with hydrogen at 97 degrees C to give the new tetrahydrido complex Ir6(CO)8[Pt(PBu(t)3)]4(mu-H)4 (12). Compound 12 is formed by the loss of the two bridging carbonyl ligands from 11 and the addition of four hydrido ligands. All four new compounds were characterized by both 1H and 31P NMR and by single-crystal X-ray diffraction analyses. The bonding in 9 was studied by Fenske-Hall molecular orbital calculations, which in this case provides a delocalized bonding description for the Ir-Ir and Ir-Pt bonding, where the attachment of the 0 e- fragments of Pt(PR3) use Ir-Ir bonding orbitals of the Ir4(CO)12 cluster to form multicenter Pt-Ir bonds.

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