[Tris(2-pyridylthio)methyl]zinc hydride, [κ(3)-Tptm]ZnH, is a multifunctional catalyst that is capable of achieving (i) rapid release of hydrogen by protolytic cleavage of silanes with either water or methanol and (ii) hydrosilylation of aldehydes, ketones, and carbon dioxide. For example, [κ(3)-Tptm]ZnH catalyzes the release of 3 equivalents of H(2) by methanolysis of phenylsilane, with a turnover number of 10(5) and a turnover frequency surpassing 10(6) h(-1) for the first 2 equivalents. Furthermore, [κ(3)-Tptm]ZnH also catalyzes the formation of triethoxysilyl formate by hydrosilylation of carbon dioxide with triethoxysilane. Triethoxysilyl formate may be converted into ethyl formate and N,N-dimethylformamide, thereby providing a means for utilizing carbon dioxide as a C(1) feedstock for the synthesis of useful chemicals.

S1 S2 EXPERIMENTAL SECTION Synthesis of N-formyl-4-bromo-2,6-diisopropylaniline. Acetic anhydride (40 mL, 422.7 mmol) was cooled to 0 °C and formic acid (20 mL, 530.1 mmol) was added via syringe over 10 minutes. The colorless solution was allowed to warm to room temperature, then heated at 50 °C for 2 hours. The solution was then allowed to cool to room temperature and then cooled to 0 °C. 4-bromo-2,6-diisopropylaniline was added via syringe, and the mixture was then allowed to warm to room temperature. The mixture was allowed to stir for 30 minutes, then cooled to 0 °C, followed by the addition of 0 °C H2O (ca. 300 mL), resulting in the formation of a light pink suspension. The mixture was filtered, and the precipitate was washed with H2O (ca. 1 L). The white precipitate was dried in vacuo overnight to give N-formyl-4-bromo-2,6diisopropylaniline (5.05 g, 76%) as a white solid. Mixture of isomers 1 H NMR (CDCl3): 1.16 [d, 3 JH-H = 7 Hz, 12H,

The homoleptic arylisocyanide tungsten complexes, W(CNXy) 6 and W(CNIph) 6 (Xy = 2,6dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400−550 nm). MLCT emission (λ max ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy) 6 and W(CNIph) 6 with lifetimes of 17 and 73 ns, respectively. Diffusioncontrolled energy transfer from electronically excited W(CNIph) 6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bu n 4 N][PF 6 ], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph) 6 ] + and [anth] •− . ET from *W to benzophenone and cobalticenium also is observed in [Bu n 4 N][PF 6 ]/THF solutions. The estimated reduction potential for the [W(CNIph) 6 ] + /*W couple is −2.8 V vs Cp 2 Fe +/0 , establishing W(CNIph) 6 as one of the most powerful photoreductants that has been generated with visible light.

Tris(2-pyridylthio)methane, [Tptm]H, has been employed to synthesize the mononuclear alkyl zinc hydride complex, [κ(3)-Tptm]ZnH, which has been structurally characterized by X-ray diffraction. [κ(3)-Tptm]ZnH provides access to a variety of other [Tptm]ZnX derivatives. For example, [κ(3)-Tptm]ZnH reacts with (i) R(3)SiOH (R = Me, Ph) to give [κ(4)-Tptm]ZnOSiR(3), (ii) Me(3)SiX (X = Cl, Br, I) to give [κ(4)-Tptm]ZnX, and (iii) CO(2) to give the formate complex, [κ(4)-Tptm]ZnO(2)CH. The bis(trimethylsilyl)amide complex [κ(3)-Tptm]ZnN(SiMe(3))(2) also reacts with CO(2), but the product obtained is the isocyanate complex, [κ(4)-Tptm]ZnNCO. The formation of [κ(4)-Tptm]ZnNCO is proposed to involve initial insertion of CO(2) into the Zn-N(SiMe(3))(2) bond, followed by migration of a trimethylsilyl group from nitrogen to oxygen to generate [κ(4)-Tptm]ZnOSiMe(3) and Me(3)SiNCO, which subsequently undergo CO(2)-promoted metathesis to give [κ(4)-Tptm]ZnNCO and (Me(3)SiO)(2)CO.

No abstract

Two new iridium hydride complexes, Cp*Ir(2-phenylpyridine)H (Cp* = pentamethylcyclopentadienyl) and Cp*Ir(benzo[h]quinoline)H, and their rhodium analogues Cp*Rh(2-phenylpyridine)H and Cp*Rh(benzo[h]quinoline)H have been prepared from the corresponding chlorides. The X-ray structures of Cp*Ir(2-phenylpyridine)H and Cp*Rh(2-phenylpyridine)H have been determined. The electrochemistry of all four hydride complexes and the corresponding chlorides has been studied by cyclic voltammetry; all exhibit irreversible M(III/IV) (M = Ir, Rh) oxidations. The hydride complexes are more easily oxidized than their chloride analogues, and the rhodium hydrides are more easily oxidized than their iridium analogues. The hydride complexes transfer H– to the N-carbophenoxypyridinium cation at room temperature, giving mixtures of the 1,2- and 1,4-dihydropyridine products. In CD3CN all four hydrides give these products in nearly the same ratio, which results from kinetic control; the thermodynamic ratio of the products has been calculated, and isomerization in that direction has been observed. In weakly coordinating solvents the cations left after H– transfer catalyze this isomerization. Acetonitrile can trap these cations, slowing isomerization substantially. The X-ray structures of [Cp*Ir(2-phenylpyridine)(CH3CN)][PF6] and [Cp*Rh(2-phenylpyridine)(CH3CN)][PF6] have also been determined.

The octahedral core of 84-electron LCuH hexamers does not dissociate appreciably in solution, although their hydride ligands undergo rapid intramolecular rearrangement. The single-electron transfer proposed as an initial step in the reaction of these hexamers with certain substrates has been observed by stopped-flow techniques when [(Ph3P)CuH]6 is treated with a pyridinium cation. The same radical cation has been prepared by the oxidation of [(Ph3P)CuH]6 with Cp*2Fe(+) and its reversible formation observed by cyclic voltammetry; its UV-vis spectrum has been confirmed by spectroelectrochemistry. The 48-electron trimer [(dppbz)CuH]3 has been prepared by use of the chelating ligand 1,2-bis(diphenylphosphino)benzene (dppbz).

W(CNAryl)6 complexes containing 2,6-diisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited states. These properties are enhanced upon appending another aryl ring, e.g., W(CNdippPh(OMe2))6; CNdippPh(OMe2) = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide (Sattler et al. J. Am. Chem. Soc. 2015, 137, 1198-1205). Electronic transitions and low-lying excited states of these complexes were investigated by time-dependent density functional theory (TDDFT); the lowest triplet state was characterized by time-resolved infrared spectroscopy (TRIR) supported by density functional theory (DFT). The intense absorption band of W(CNdipp)6 at 460 nm and that of W(CNdippPh(OMe2))6 at 500 nm originate from transitions of mixed ππ*(C≡N-C)/MLCT(W → Aryl) character, whereby W is depopulated by ca. 0.4 e(-) and the electron-density changes are predominantly localized along two equatorial molecular axes. The red shift and intensity rise on going from W(CNdipp)6 to W(CNdippPh(OMe2))6 are attributable to more extensive delocalization of the MLCT component. The complexes also exhibit absorptions in the 300-320 nm region, owing to W → C≡N MLCT transitions. Electronic absorptions in the spectrum of W(CNXy)6 (Xy = 2,6-dimethylphenyl), a complex with orthogonal aryl orientation, have similar characteristics, although shifted to higher energies. The relaxed lowest W(CNAryl)6 triplet state combines ππ* excitation of a trans pair of C≡N-C moieties with MLCT (0.21 e(-)) and ligand-to-ligand charge transfer (LLCT, 0.24-0.27 e(-)) from the other four CNAryl ligands to the axial aryl and, less, to C≡N groups; the spin density is localized along a single Aryl-N≡C-W-C≡N-Aryl axis. Delocalization of excited electron density on outer aryl rings in W(CNdippPh(OMe2))6 likely promotes photoinduced electron-transfer reactions to acceptor molecules. TRIR spectra show an intense broad bleach due to ν(C≡N), a prominent transient upshifted by 60-65 cm(-1), and a weak down-shifted feature due to antisymmetric C≡N stretch along the axis of high spin density. The TRIR spectral pattern remains unchanged on the femtosecond-nanosecond time scale, indicating that intersystem crossing and electron-density localization are ultrafast (<100 fs).