A pentamethylcyclopentadienyl (Cp*) iridium water-oxidation precatalyst was modified to include a silatrane functional group for covalent attachment to metal oxide semiconductor surfaces. The heterogenized catalyst was found to perform electrochemically driven water oxidation at an overpotential of 462 mV with a turnover number of 304 and turnover frequency of 0.035 s–1 in a 0.1 M KNO3 electrolyte at pH 5.8. Computational modeling of the experimental IR spectra suggests that the catalyst retains its Cp* group during the first hour of catalysis and likely remains monomeric.

Activation of organometallic Ir precatalysts can yield either homogeneous or heterogeneous water-oxidation catalysts with very high activity.

Aniline joins the club: A β-diketiminato copper(I) catalyst enables C-H amination of anilines employing low catalyst loadings to preclude oxidation to the diazene ArN=NAr. Electron-poor anilines are particularly resistant towards diazene formation and participate in the amination of strong and unactivated C-H bonds. N-alkyl anilines also take part in C-H amination.

A series of Cp*IrIII dimers have been synthesized to elucidate the mechanistic viability of radical oxo-coupling pathways in iridium-catalyzed O2 evolution. The oxidative stability of the precursors toward nanoparticle formation and their oxygen evolution activity have been investigated and compared to suitable monomeric analogues. We found that precursors bearing monodentate NHC ligands degraded to form nanoparticles (NPs), and accordingly their O2 evolution rates were not significantly influenced by their nuclearity or distance between the two metals in the dimeric precursors. A doubly chelating bis-pyridine–pyrazolide ligand provided an oxidation-resistant ligand framework that allowed a more meaningful comparison of catalytic performance of dimers with their corresponding monomers. With sodium periodate (NaIO4) as the oxidant, the dimers provided significantly lower O2 evolution rates per [Ir] than the monomer, suggesting a negative interaction instead of cooperativity in the catalytic cycle. Electrochemical analysis of the dimers further substantiates the notion that no radical oxyl-coupling pathways are accessible. We thus conclude that the alternative path, nucleophilic attack of water on high-valent Ir-oxo species, may be the preferred mechanistic pathway of water oxidation with these catalysts, and bimolecular oxo-coupling is not a valid mechanistic alternative as in the related ruthenium chemistry, at least in the present system.

This paper introduces Ir(I)(CO)2(pyalc) (pyalc = (2-pyridyl)-2-propanoate) as an atom-efficient precursor for Ir-based homogeneous oxidation catalysis. This compound was chosen to simplify analysis of the water oxidation catalyst species formed by the previously reported Cp*Ir(III)(pyalc)OH water oxidation precatalyst. Here, we present a comparative study on the chemical and catalytic properties of these two precursors. Previous studies show that oxidative activation of Cp*Ir-based precursors with NaIO4 results in formation of a blue Ir(IV) species. This activation is concomitant with the loss of the placeholder Cp* ligand which oxidatively degrades to form acetic acid, iodate, and other obligatory byproducts. The activation process requires substantial amounts of primary oxidant, and the degradation products complicate analysis of the resulting Ir(IV) species. The species formed from oxidation of the Ir(CO)2(pyalc) precursor, on the other hand, lacks these degradation products (the CO ligands are easily lost upon oxidation) which allows for more detailed examination of the resulting Ir(pyalc) active species both catalytically and spectroscopically, although complete structural analysis is still elusive. Once Ir(CO)2(pyalc) is activated, the system requires acetic acid or acetate to prevent the formation of nanoparticles. Investigation of the activated bis-carbonyl complex also suggests several Ir(pyalc) isomers may exist in solution. By (1)H NMR, activated Ir(CO)2(pyalc) has fewer isomers than activated Cp*Ir complexes, allowing for advanced characterization. Future research in this direction is expected to contribute to a better structural understanding of the active species. A diol crystallization agent was needed for the structure determination of 3.

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The prevalence of basic nitrogen atoms in myriads of small molecules of biological interest motivates the development of methodologies to streamline the introduction of nitrogen atoms into organic molecules. CÀH amination offers a potentially highly atom-economical approach, directly converting C À H into C À N bonds. [1] Prototypical nitrene-based routes [2] for C sp 3 À H amination typically employ the iminoiodinanes PhI = N(EWG) (EWG = SO 2 R' or C(O)OR') as nitrene transfer reagents with a range of catalysts to aminate CÀH bonds in the substrates R-H to provide the corresponding secondary amines RNH(EWG). Though rhodium- [1e, 3] and rutheniumbased [4] catalysts are perhaps most common, a growing number of catalyst systems employing Earth abundant firstrow transition metals such as Mn, [5] Fe, [6,7] Co, [8] and Cu, [9] have been developed.CÀH amination with secondary amines HNR 1 R 2 requires non-nitrene-based routes. Liu and co-workers [10] and White and co-workers [11] independently described allylic CÀH amination with sulfonyl carbamates MeOC(O)NHSO 2 R in which cationic Pd-allyl complexes serve as key intermediates. Mildly basic diarylamines such as HNAr 2 also participate in allylic CÀH amination, [12a] and N-fluorobis(phenylsulfonyl)imide (NFSI) may be used for palladium-catalyzed CÀH amidation of substrates which possess directing donor groups. [12b] A 1,10-phenanthroline-based copper(I) catalyst employs MeNHSO 2 Ph with tBuOOR (R = O 2 CMe, O 2 CAr) as an oxidant to give tertiary sulfonylamines derived from allylic and benzylic substrates. [13,14] The near ubiquitous requirement of very strong electron-withdrawing groups on the nitrogen atom, however, severely limits the range of Nbased functionalities that may be directly incorporated through C À H amination, though in some cases simple organic amides [9d] or imidazoles [7b] may be employed.We recently showed that the b-diketiminato copper(I) complex [{(Cl 2 NN)Cu} 2 (m-benzene)] (1) catalyzes the amination of C sp 3 ÀH bonds of ethylbenzene, indane, and even the completely unactivated substrate cyclohexane with the primary alkylamines 1-adamantylamine, cyclohexylamine, and phenethylamine employing tBuOOtBu as an oxidant (Scheme 1). [9b] Emphasizing the non-nitrene nature of this protocol, the secondary amines morpholine and piperidine may also be used. Through its isolation and reactivity studies, the copper(II) amide [(Cl 2 NN)Cu-NHAd] serves as a key intermediate that participates in both hydrogen atom abstraction (HAA) of the substrates R-H and capture of the resulting radical RC to give the CÀH amination product R-NHAd. [9b] Aiming to extend our CÀH amination protocol to aromatic amines H 2 NAr, we were quite concerned that our system would instead catalyze their oxidation to diazenes ArN = NAr. Although first reported in 1955, [15] the use of copper(I) halides in pyridine for the aerobic oxidation of anilines into azobenzenes recently has been rediscovered as a versatile method for the synthesis of aromatic diazenes. [16] Indeed, early...

We previously reported a dimeric Ir IV -oxo species as the active water oxidation catalyst formed from a Cp*Ir(pyalc)Cl {pyalc = 2-(2′-pyridyl)-2-propanoate} precursor, where the Cp* is lost to oxidative degradation during catalyst activation; this system can also oxidize unactivated CH bonds. We now show that the same Cp*Ir(pyalc)Cl precursor leads to two distinct active catalysts for CH oxidation. In the presence of external CH substrate, the Cp* remains ligated to the Ir center during catalysis; the active specieslikely a highvalent Cp*Ir(pyalc) specieswill oxidize the substrate instead of its own Cp*. If there is no external CH substrate in the reaction mixture, the Cp* will be oxidized and lost, and the active species is then an iridium-μ-oxo dimer. Additionally, the recently reported Ir(CO) 2 (pyalc) water oxidation precatalyst is now found to be an efficient, stereoretentive CH oxidation precursor. We compare the reactivity of Ir(CO) 2 (pyalc) and Cp*Ir(pyalc)Cl precursors and show that both can lose their placeholder ligands, CO or Cp*, to form substantially similar dimeric Ir IV -oxo catalyst resting states. The more efficient activation of the bis-carbonyl precursor makes it less inhibited by obligatory byproducts formed from Cp* degradation, and therefore the dicarbonyl is our preferred precatalyst for oxidation catalysis.