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Superhydrophobic coatings find important applications in consumer, commercial and advanced materials industries. Despite the existing approaches, the variety of substrates and different coating compositions necessitates the availability of several simple and versatile strategies for creating these functional coatings. This work demonstrates a facile and versatile strategy for achieving superhydrophobic coatings via deposition of modified polyvinylidene fluoride (m-PVDF) microparticles and subsequent thiol-ene surface functionalization of the microparticles with perfluorodecyl-1-thiol. The “ene” functionalities of the m-PVDF microparticles are achieved via dehydrofluorination of PVDF. The obtained coatings exhibit up to 160° static water contact angle. We show that the hydrophobic properties of the coatings are dependent upon the surface coverage of the substrate with the microparticles and the functionalization with the perfluorodecyl groups. Raman spectroscopy was used to provide insight into the thiol-ene functionalization of the superhydrophobic coatings.

The first highly enantioselective catalytic protocol for the reductive coupling of ketones and hydrazones is reported. These reactions proceed through neutral ketyl radical intermediates generated via a concerted proton-coupled electron transfer (PCET) event jointly mediated by a chiral phosphoric acid catalyst and the photoredox catalyst Ir(ppy)2(dtbpy)PF6. Remarkably, these neutral ketyl radicals appear to remain H-bonded to the chiral conjugate base of the Brønsted acid during the course of a subsequent C-C bond-forming step, furnishing syn 1,2-amino alcohol derivatives with excellent levels of diastereo- and enantioselectivity. This work provides the first demonstration of the feasibility and potential benefits of concerted PCET activation in asymmetric catalysis.

Aryl alkyl ethers, which are widely used throughout the chemical industry, are typically produced via the Williamson ether synthesis. Olefin hydroaryloxylation potentially offers a much more atom-economical alternative. Known acidic catalysts for hydroaryloxylation, however, afford very poor selectivity. We report the organometallic-catalyzed intermolecular hydroaryloxylation of unactivated olefins by iridium "pincer" complexes. These catalysts do not operate via the hidden Brønsted acid pathway common to previously developed transition-metal-based catalysts. The reaction is proposed to proceed via olefin insertion into an iridium-alkoxide bond, followed by rate-determining C-H reductive elimination to yield the ether product. The reaction is highly chemo- and regioselective and offers a new approach to the atom-economical synthesis of industrially important ethers and, potentially, a wide range of other oxygenates.

A pincer-ligated iridium complex, (PCP)Ir (PCP = κ(3)-C6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp(3))-O bonds of methyl esters (CH3-O2CR'), methyl tosylate (CH3-OTs), and certain electron-poor methyl aryl ethers (CH3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H)[κ(2)-CH2OC(O)Me] which then affords (PCP-CH2)Ir(H)(κ(2)-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ(2)-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

The isomerization of olefins by complexes of the pincer-ligated iridium species ((tBu)PCP)Ir ((tBu)PCP = κ(3)-C(6)H(3)-2,6-(CH(2)P(t)Bu(2))(2)) and ((tBu)POCOP)Ir ((tBu)POCOP = κ(3)-C(6)H(3)-2,6-(OP(t)Bu(2))(2)) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH(2), are known to hydrogenate olefins via initial Ir-H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for olefin isomerization (the "hydride addition pathway"); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η(2)-olefin) species undergo isomerization via the formation of (pincer)Ir(η(3)-allyl)(H) intermediates; one example of such a species, ((tBu)POCOP)Ir(η(3)-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to ((tBu)POCOP)Ir(η(2)-propene). Surprisingly, the DFT calculations indicate that the conversion of the η(2)-olefin complex to the η(3)-allyl hydride takes place via initial dissociation of the Ir-olefin π-bond to give a σ-complex of the allylic C-H bond; this intermediate then undergoes C-H bond oxidative cleavage to give an iridium η(1)-allyl hydride which "closes" to give the η(3)-allyl hydride. Subsequently, the η(3)-allyl group "opens" in the opposite sense to give a new η(1)-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C-H elimination and π-coordination to give a coordinated olefin that has undergone double-bond migration.

A study of electronic factors governing the thermodynamics of C-H and N-H bond addition to Ir(I) complexes was conducted. DFT calculations were performed on an extensive series of trans-(PH3)2IrXL complexes (L = NH3 and CO; X = various monodentate ligands) to parametrize the relative σ- and π-donating/withdrawing properties of the various ligands, X. Computed energies of oxidative addition of methane to a series of three- and four-coordinate Ir(I) complexes bearing an ancillary ligand, X, were correlated with the resulting (σ(X), π(X)) parameter set. Regression analysis indicates that the thermodynamics of addition of methane to trans-(PH3)2IrX are generally strongly disfavored by increased σ-donation from the ligand X, in contradiction to widely held views on oxidative addition. The trend for oxidative addition of methane to four-coordinate Ir(I) was closely related to that observed for the three-coordinate complexes, albeit slightly more complicated. The computational analysis was found to be consistent with the rates of reductive elimination of benzene from a series of isoelectronic Ir(III) phenyl hydride complexes, measured experimentally in this work and previously reported. Extending the analysis of ancillary ligand energetic effects to the oxidative addition of ammonia to three-coordinate Ir(I) complexes leads to the conclusion that increasing σ-donation by X also disfavors oxidative addition of N-H bonds to trans-(PH3)2IrX. However, coordination of NH3 to the Ir(I) center is disfavored even more strongly by increasing σ-donation by X, which explains why the few documented examples of H-NH2 oxidative addition to transition metals involve complexes with strongly σ-donating ligands situated trans to the site of addition. An orbital-based rationale for the observed results is presented.

New carbazolide-based iridium pincer complexes ((carb)PNP)Ir(C2H4), 3a, and ((carb)PNP)Ir(H)2, 3b, have been prepared and characterized. The dihydride, 3b, reacts with ethylene to yield the cis-dihydride ethylene complex cis-((carb)PNP)Ir(C2H4)(H)2. Under ethylene this complex reacts slowly at 70 °C to yield ethane and the ethylene complex, 3a. Kinetic analysis establishes that the reaction rate is dependent on ethylene concentration and labeling studies show reversible migratory insertion to form an ethyl hydride complex prior to formation of 3a. Exposure of cis-((carb)PNP)Ir(C2H4)(H)2 to hydrogen results in very rapid formation of ethane and dihydride, 3b. DFT analysis suggests that ethane elimination from the ethyl hydride complex is assisted by ethylene through formation of ((carb)PNP)Ir(H)(Et)(C2H4) and by H2 through formation of ((carb)PNP)Ir(H)(Et)(H2). Elimination of ethane from Ir(III) complex ((carb)PNP)Ir(H)(Et)(H2) is calculated to proceed through an Ir(V) complex ((carb)PNP)Ir(H)3(Et) which reductively eliminates ethane with a very low barrier to return to the Ir(III) dihydride, 3b. Under catalytic hydrogenation conditions (C2H4/H2), cis-((carb)PNP)Ir(C2H4)(H)2 is the catalyst resting state, and the catalysis proceeds via an Ir(III)/Ir(V)/Ir(III) cycle. This is in sharp contrast to isoelectronic (PCP)Ir systems in which hydrogenation proceeds through an Ir(III)/Ir(I)/Ir(III) cycle. The basis for this remarkable difference is discussed.

We report on the synthesis and reactivity of rhodium complexes featuring bulky, neutral pincer ligands with a “POP” coordinating motif, tBuxanPOP, iPrxanPOP, and tBufurPOP (tBuxanPOP = 4,5-bis(di-tert-butylphosphino)-9,9-dimethyl-9H-xanthene; iPrxanPOP = 4,5-bis(diisopropylphosphino)-9,9-dimethyl-9H-xanthene; tBufurPOP = 2,5-bis((di-tert-butylphosphino)methyl)furan). The (POP)Rh complexes described in this work are, in general, more reactive than their (PNP)Rh and (PCP)Rh analogues, which allows for the generation of several new species under relatively mild conditions. Thus, monomeric (POP)RhCl complexes oxidatively add H2 to form (POP)Rh(H)2Cl, from which the coordinatively unsaturated hydride complexes (POP)Rh(H)2+ and (tBuxanPOP)Rh(H) can be obtained. In the case of the new ligand tBufurPOP, a major kinetic product of the reaction with H2 is, surprisingly, the trans dihydride, i.e. trans-(tBufurPOP)Rh(H)2Cl; this is most likely attributable to reversible decoordination of one of the pincer coordinating groups, followed by addition of H2 to a highly reactive three-coordinate species. Ethylene is hydrogenated by (tBuxanPOP)Rh(H)2+ at 25 °C, but propylene is not, even at elevated temperatures. Ethylene undergoes insertion into the Rh–H bond of (tBuxanPOP)RhH; this reaction is reversible, allowing for an experimental determination of the equilibrium constant for this hydrometalation. The less bulky iPrxanPOP ligand affords a dihydride complex which functions as a modestly active alkane dehydrogenation catalyst, the first such example for a cationic pincer complex of any metal.