1:45 2:05 T-A06 THE INTERFACE SCIENCE OF PHOTOVOLTAIC SOLAR ENERGY CONVERSION: CHARGE TRANSFER AT INORGANIC-ORGANIC AND INORGANIC-INORGANIC INTERFACES MODULATED BY HOLEAND ELECTRON-SELECTIVE INTERLAYERS [CISSEM] Neal Armstrong, Erin Ratcliff, Brian Zacher, Gordon MacDonald, Laura Schirra, Oliver Monti, Xerxes Steirer, Dana Olson, Jens Meyer, Antoine Kahn, Hyeunseok Cheun, and Bernard Kippelen University of Arizona; National Renewable Energy Laboratory; Princeton University and Georgia Institute of Technology

Benzo[1,2-h: 5,4-h′]diquinoline(1a) represents a new family of tridentate NCN pincer ligand. We report the synthesis of the parent ligand (1a) and its derivatives (1b R = Me, 1c R = t-Butyl, 1d R = Phenyl). The ligands were characterized by 1H and 13C NMR, as well as mass spectral analysis, and X-ray structural determination. They readily undergo cyclometalation with LiPdCl4, Pd(OAc)2, and K2PtCl4 to form the cyclometalated Pd(NCN)Cl (2a–c, 3a), and Pt(NCN)Cl (4a) pincer complexes. These complexes have been characterized through NMR, and mass spectrometry. PdNCNCl (2a) structure was determined by single crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bromobenzene and n-butylacyrlate in NMP at 140 °C, TON of 2506 were observed.

We have synthesized and fully characterized the air-stable complex (κ2-acac-O,O)2OsIV(Ph)Cl (Cl-1-Ph; acac-O,O = acetylacetonate), which reacts with C6D6 to generate Cl-1-Ph-d5 in high yield and catalyzes the H/D exchange reaction between benzene and toluene-d8 upon heating to 140 °C. To our knowledge, this is the first example of stoichiometric and catalytic, homogeneous, intermolecular CH activation of arenes by a discrete Os complex. The reactions show extended induction periods. DFT studies of Cl-1-Ph and cis-(κ2-acac-O,O)2OsIII(C6H5)(C6D6) (cis-(C6D6)-2-Ph) found a mechanism involving CH activation by traces of Os(III) and Cl atom transfer between Cl-1-Ph and cis-(C6D6)-2-Ph. Experimental data showing that addition of reductants eliminates the induction periods suggest that CH activation occurs from an oxidation state lower than OsIV, consistent with the DFT predictions. Consistent with a Cl atom transfer mechanism, the triflate analogue of Cl-1-Ph, OTf-1-Ph, does not undergo a stoichiometric or catalytic reaction with C6D6.

Using tridentate, neutral PyBox ligands, several new osmium and ruthenium complexes [M(PyBox)Cl2(C2H4), where M=Ru, Os] have been prepared, all thermally stable. Some of these PyBox compounds are active for C–H activation of benzene. The Os(PyBox)Cl2(C2H4) complex was characterized by X-ray diffraction. DFT calculations (B3LYP and M06 including Poisson–Boltzmann solvation) corroborate that the Os/PyBox complex in acetic acid (ΔG‡=32.0kcal/mol) is more reactive for benzene C–H activation than Ru/PyBox in basic conditions (ΔG‡=34.8kcal/mol at pH=13). The stability of hydroxide- and chloride-bridged dinuclear resting states determines calculated barriers.

(IPI)Ru(II)(OH)(n)(H(2)O)(m), 2, where IPI is the NNN-pincer ligand, 2,6-diimidizoylpyridine, is shown to catalyze H/D exchange between hydrocarbons and strongly basic solvents at higher rates than in the case of the solvent alone. Significantly, catalysis by 2 is accelerated rather than inhibited by increasing solvent basicity. The evidence is consistent with the reaction proceeding by base modulated nucleophilic CH activation.

Heating the potential tridentate 6-(4-R-phenyl)-2,2'-bipyridine ligand la (R = H), and derivatives 1b (R = CMe3) and 1c (R = OH), with IrCl3 hydrate in 2-methoxyethanol or acetone/H2O gave the unexpected bidentate cyclometalated NC dinuclear complexes [Ir(NC)Cl-2(C5H5N)](2) (2a-cPy), as the major product. Altering the ligand/metal ratio from 1:1 to 2:1 produced a mixture of bis-cyclometalated complexes, Ir(NNC)(NC)Cl (3a,b), with tridentate and bidentate binding modes. Using discrete Ir-I synthons, such as Ir(dmso)(3)Cl or [Ir(cyclooctene)(2)Cl](2), gave a complicated mixture of products. However, when [Ir(C2H4)(2)Cl](2) was used, then the desired tridentate cyclometalated Ir(NNC) complex Ir(NNC)Et(CH4)Cl (4) was synthesized cleanly. The dinuclear complex 2a-Py was converted to the corresponding mononuclear dichloride complexes Ir(NC)(NN)Cl-2 (5a) upon refluxing with 4,4'-di-tert-butylbipyridine in N,N-dimethylacetamide (DMA). Treatment of 5a with ZnMe2 gives Ir(NC)(NNtBu)MeCl (6a). Abstraction of the chloride with AgOTF yields Ir(NC)(NNtBu)MeOTf (7a). Complex 7a undergoes stoichiometric CH activation with arenes and shows catalytic activity for the H/D exchange between benzene and ( trifluoro)acetic acids.

A discrete, air, protic, and thermally stable (NNC) Ir(III) pincer complex was synthesized that catalytically activates the CH bond of methane in trifluoroacetic acid; functionalization using NaIO4 and KIO3 gives the oxy-ester.

We report the Synthesis of the pincer-cyclometalated (NNCt-Bu)Ir(III) dihydroxo pyridyl complex 6, which catalyzes hydrogen-deuterium (H/D) exchange between water and benzene in the presence of base (TOF = similar to 6 x 10(-3) s(-1) at 190 degrees C) Experimental and density functional theory (B3LYP) studies suggest that H/D exchange occurs through loss of pyridine followed by benzene coordination and C-H bond activation by a heterolytic substitution mechanism to give a phenyl aquo complex, which may dimerize. Exchange of H2O for D2O followed by the microscopic reverse of CH activation leads to deuterium incorporation into benzene. Synthesis of the mu-hydroxo phenyl dinuclear complex [(NNCt-Bu)lr(Ph)(mu-OH)](2) (9) also catalyzes H/D exchange with a turnover frequency (TOF = similar to 7 x 10(-3) S-1 at 190 degrees C) similar to that for 6.

A well-defined, thermal-, air-, and protic-stable, bis-bidentate, cyclometalated Ir(III) complex, Ir(NC)(NNtBu)CH3OTf, (2-CH3; NC = κ2-6-phenyl-2,2‘-bipyridine, NNtBu = κ2-4,4‘-di-tert-butyl-2,2‘-bipyridine) has been shown to undergo oxy functionalization with oxidants such as PhI(X)2 (X = OAc, TFA) to generate CH3X (X = OAc, TFA, OTf) in yields ranging from 36 to 67% in CH2Cl2 at ambient temperatures. 2-CH3 is also competent for CH activation, undergoing stoichiometric CH activation in benzene, and catalyzes the H/D exchange reaction between benzene and acids (acetic and trifluoroacetic acid).

We report on the design of more efficient C-H activation catalysts based on DFT calculations. The first examples of well-defined, N,O-donor ligated platinum complexes that are competent for fast C-H activation are detailed. These complexes exhibit thermal and protic stability and are efficient catalysts for H/D exchange reactions with benzene. The C-H activation is shown to benefit from design elements that (A) reduce the barrier for substrate coordination and (B) retain a low barrier for CH cleavage via a novel six-membered transition state involving the carboxylate group of the solvent.

A well-defined, O-donor ligated iridium hydroxide complex is reported that is competent for benzene CH activation and long-lived catalytic H/D exchange between benzene and water. An inverse dependence of the H/D exchange rate on added pyridine, a kinetic isotope effect (KIE) of 2.65 +/- 0.56 for CH activation with 1,3,5-trideuteriobenzene, a KIE of 1.07 +/- 0.24 with C6H6/C6D6, and DFT calculations are consistent with the CH activation proceeding via rate-determining benzene coordination followed by fast CH cleavage via a sigma-bond-metathesis transition state.

The direct, low temperature conversion of hydrocarbons to functionalized products using novel, single site catalysts could lead to technological advances that redefine the landscape of the current materials and energy industries. Natural gas continues to represent a vast source of untapped hydrocarbons around the globe that has the potential to replace or augment petroleum as the raw material for materials and energy. Its abundance has garnered much interest in the scientific community as groups have focused on the catalytic conversion of its major component, methane, to functionalized products. The key requirements is to design new catalysts for the oxidative functionalization of methane that operate at lower temperatures and that also meet the basic requirements of selectivity, rate, and lifetime that characterize useful catalysts. Recent advances in the field of hydrocarbon CH activation have shown the potential for transition metal based coordination catalysts to meet these requirements. Described herein are recent advances in designing catalysts based on the CH activation reaction that address the basic requirements for practical systems with emphasis on the issues that have prevented promising reported systems from becoming commercially viable.