An increasing number of biological roles are ascribed to S-nitrosothiol compounds. Their inherent instability in multicomponent solutions is recognized as forming the basis for their physiological effects, such as the release of nitric oxide or the posttranslational modification of protein cysteine residues. This reactivity also contributes to the lack of fundamental physical and spectroscopic data that have been reported. We have addressed this issue through characterization of the physical and spectroscopic properties of a group of commonly used S-nitrosothiols. The S-nitrosothiol Ph3CSNO, which is readily prepared by the biphasic nitrosation of Ph3CSH, is characterized by X-ray diffraction, vibrational spectroscopy, electrochemistry, and spectroelectrochemistry. Its behavior is contrasted with that of known S-nitrosothiols derived from glutathione and N-acetyl-d,l-penicillamine, which also are demonstrated to undergo facile electrochemical and chemical denitrosylation. The structure and vibrational data are contrasted with ab initio results calculated with density functional theory, B3LYP/6-311+G*, which indicates that electron transfer populates an orbital that is strongly ON−SR antibonding in character. The bond lengths observed for Ph3CSNO (N−O 1.18 Å, S−N 1.79 Å) indicate a formal nitrogen-to-oxygen double bond and sulfur−oxygen single bond. However, theoretical calculations show a measure of delocalization over the −CSNO framework. This is supported by experimental results that show low ν(NO) vibrational frequencies (1470−1515 cm-1) and a large ΔG ⧧ (10.7 kcal/mol) for syn−anti interconversion determined by variable-temperature 15N NMR. Together these results demonstrate an important new reactivity pattern for this biologically critical class of compounds.

Atom transfer radical polymerization (ATRP) generally requires a catalyst/initiator molar ratio of 0.1 to 1 and catalyst/monomer molar ratio of 0.001 to 0.01 (i.e., catalyst concentration: 1000-10,000 ppm versus monomer). Herein, we report a new copper-based complex CuBr/N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) as a versatile and highly active catalyst for acrylic, methacrylic, and styrenic monomers. The catalyst mediated ATRP at a catalyst/initiator molar ratio of 0.005 and produced polymers with well-controlled molecular weights and low polydispersities. ATRP occurred even at a catalyst/initiator molar ratio as low as 0.001 with copper concentration in the produced polymers as low as 6-8 ppm (catalyst/monomer molar ratio = 10(-5)). The catalyst structures were studied by X-ray diffraction and NMR spectroscopy. The activator CuIBr/TPEN existed in solution as binuclear and mononuclear complexes in equilibrium but as a binuclear complex in its single crystals. The deactivator CuIIBr2/TPEN complex was mononuclear. High stability and appropriate KATRP (ATRP equilibrium constant) were found crucial for the catalyst working under high dilution or in coordinating solvents/monomers. This provides guidance for further design of highly active ATRP catalysts.

0 = CO, C 2 H 4 ; L = PhCN, L 0 = C 2 H 4 ) are highly fluxional, with ligand site interconversion free energy barriers determined by VT NMR of 9.7 kcal mol -1 (L = L 0 = CO), 12.2 kcal mol -1 (L = L 0 = C 2 H 4 ), and 16.1 kcal mol -1 (L = C 2 H 4 , L 0 = PhCN). A dissociative site exchange mechanism is proposed. ( CF 3 PCP)Ir(L) complexes readily undergo oxidative addition reactions. Addition of H 2 to ( CF 3 PCP)-Ir(CO) reversibly forms trans-( CF 3 PCP)Ir(CO)(H) 2 at ambient temperatures. In contrast, addition of H 2 to ( CF 3 PCP)Ir(dfmp) affords fac,cis-( CF 3 PCP)Ir(dfmp)(H) 2 as the major product, with an unusual facially coordinated pincer group. VT NMR monitoring of the reaction of ( CF 3 PCP)Ir(CO) with H 2 established the initial formation of fac,cis-( CF 3 PCP)Ir(CO)(H) 2 followed by conversion to mer, cis-( CF 3 PCP)Ir(CO)(H) 2 prior to isomerization to mer,trans-( CF 3 PCP)Ir(CO)(H) 2 . The unusual stability of ( CF 3 PCP)Ir(L) 2 and fac,cis-( CF 3 PCP)Ir(L)(H) 2 complexes is attributable to the increased stability of nonplanar (PCP)M moieties possessing strongly π-accepting phosphorus groups. (1) (a) Albrecht, M.; van Koten, G. Zhu, K.; Kissin, Y. V.; Cherian, A. E.; Coates, G. W.; Goldman, A. S. Chem. Commun. 2005, 3388-3390. (i) Kuklin, S. A.; Sheloumov, A. M.; Dolgushin, F. M.; Ezernitskaya, M. G.; Peregudov, A. S.; Petrovskii, P. V.; Koridze, A. A. Organometallics 2006, 25, 5466-5476. (3) (a) Goldman, A. S.; Roy, A. H.; Huang, Z.; Ahuja, R.; Schinski, W.; Brookhart, M. Science (Washington, DC, U.S.) 2006, 312, 257-261. (b) Ahuja, R.; Kundu, S.; Goldman, A. S.; Brookhart, M.; Vicente, B. C.; Scott, S. L. Chem. Commun. 2008, 253-255. (c) Bailey, B. C.; Schrock, R. R.; Kundu, S.; Goldman, A. S.; Huang, Z.; Brookhart, M. Rolfe, E.; Carson, E. C.; Brookhart, M.; Goldman, A. S.; El-Khalafy, S. H.; MacArthur, A. H. R. Adv. Synth. Catal. 2010, 352, 125-135. (5) Kundu, S.; Choliy, Y.; Zhuo, G.; Ahuja, R.; Emge, T. J.; Warmuth, R.; Brookhart, M.; Krogh-Jespersen, K.; Goldman, A. S.

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A number of alkylammonium and bipyridinium salts of hyponitrous acid, namely, N,N,N′,N′-tetraethylethylenediammonium (3 and 4), N,N,N′,N′-tetramethylethylenediammonium (5), triethylenediammonium (6), diquinuclidinium (7), 2,2′-bipyridinium (8), 4,4′-bipyridinium (9), 4,4′-trimethylenebis(1-methylpiperidinium) (10), 4,4′trimethylenepiperidinium (11), and bis(triethylammonium) (12) hyponitrite salts, have been synthesized by the reaction of the corresponding amine in either anhydrous diethyl ether or absolute ethanol with hyponitrous acid solution in anhydrous diethyl ether. Single-crystal X-ray crystallographic data were obtained for sodium hyponitrite (1), and the thermal decomposition behavior of the salt was examined. The new salts were characterized by IR and Raman spectroscopic data and elemental analyses. Compounds 4 and 7-9 were also characterized by singlecrystal X-ray crystallography. The hyponitrite anions in 1 and 7-9 exhibit similar structural features. The anions are planar with average NdN and N-O bond distances of 1.237 and 1.380 Å, respectively. The monoprotonated hyponitrite anion and solvated hyponitrous acid molecules present in 4 also exhibit close structural similarity to the dianion in the crystals of 1 and 7-9. Most of these salts are soluble in organic solvents. The UV-vis spectra of the sodium and alkylammonium salts (1, 3-7, and 10-12) in aqueous 0.1 M NaOH exhibit an absorption peak at 248 nm (λ max ) with a molar extinction coefficient of 7033 ( 153 M -1 cm -1 . Differential scanning calorimetric data for the salts reveal exothermic decomposition of the hyponitrite species. Significantly, the pentahydrate and anhydrous forms of Na 2 N 2 O 2 exhibit distinct thermal decomposition behavior. The thermogram of the pentahydrate exhibits two exotherms at ca. 96 and 382 °C, whereas that of the anhydrous Na 2 N 2 O 2 exhibits a single exotherm at ca. 382 °C. The exotherm at 96 °C observed for the pentahydrate is explained in terms of a coupled phase transition-dehydration process. The alkylammonium and bipyridinium salts undergo exothermic decomposition at a considerably lower temperature in the range 67-170 °C. Electrochemistry of the salts in acetonitrile solvent reveal an irreversible oxidation at ∼1.80 V vs an Ag/AgCl reference electrode.

The lithium, barium, ammonium, and guanidinium salts of nitrosodicyanomethanide ([ONC(CN)2]-), and the lithium, sodium, barium, ammonium, guanidinium, and hydrazinium salts of nitrodicyanomethanide ([O2NC(CN)2]-) are synthesized and characterized by infrared, UV−vis and 13C NMR spectroscopy, and elemental analysis. Four of them, namely, [NH4][ONC(CN)2], Ba[ONC(CN)2]2(H2O), [NH4][O2NC(CN)2], and Ba[O2NC(CN)2](Cl)(H2O)2, have also been characterized by single-crystal X-ray diffraction data. The structural data reveal that the two anions possess comparable structural features irrespective of the nature of the cation. The N−O bond distances in [NH4][ONC(CN)2] and Ba[ONC(CN)2]2(H2O) are similar at 1.286(2) and 1.292(4) Å, respectively, and the anion possesses a nearly planar geometry. Nitrodicyanomethanide anions in the crystals of [NH4][O2NC(CN)2] and Ba[O2NC(CN)2](Cl)(H2O)2 are also nearly planar with average N−O bond distances of 1.258(2) and 1.252(5) Å, respectively. In Ba[ONC(CN)2]2(H2O), the nitrosodicyanomethanide anion binds a single metal center through the nitrogen and oxygen atoms of the nitroso group while also binding two other metal centers through the cyano nitrogen atoms. In Ba[O2NC(CN)2](Cl)(H2O)2, the nitrodicyanomethanide anion coordinates to the metal center only through the cyano nitrogen atoms. The thermal properties of the new compounds together with those of the known sodium, potassium, and silver salts of nitrosodicyanomethanide and the potassium and silver salts of nitrodicyanomethanide are examined by differential scanning calorimetry (DSC). The DSC data reveal that the two series of compounds undergo exothermic decomposition releasing 240−690 cal/g. The alkali metal, silver, and barium salts decompose at higher temperatures (>200 °C), whereas the nitrogenous cationic salts decompose at lower temperatures, indicating that the thermal behavior of the two anions can be significantly altered by choosing appropriate cations.

The iridium fluorinated pincer complex ( CF 3 PCP)Ir-(cod) ( CF 3 PCP = 2,6-C 6 H 3 (CH 2 P(CF 3 ) 2 ) 2 ) catalyzes hydrogen transfer from cyclooctane (coa) to tert-butylethylene (tbe) in 1/1 coa/tbe at 200 °C to give cyclooctene (coe) and neohexane (tba) at an initial rate of 40 TO h −1 . In 5/1 coa/tbe, higher initial activity (155 TO h −1 ) and higher turnovers (2580 TON's after 1450 min) are found. Samples of 95% tbe contain significant amounts of isoprene (2-methyl-1,3-butadiene), which reacts with ( CF 3 PCP)Ir(cod) to initially form ( CF 3 PCP)Ir(isoprene). Alkene inhibition studies show that ( CF 3 PCP)Ir is only modestly inhibited (67% reduced initial activity) in the presence of 800 equiv of added coe. Unlike donor pincer systems, no decrease in activity is noted under 1 atm of N 2 or in the presence of excess water. Hydrogenation of ( CF 3 PCP)Ir(L) (L = cod, isoprene) did not produce ( CF 3 PCP)Ir(H) x but instead afforded the first example of the unusual aryl-bridged bimetallic complex [(μ-1κ 2 (P,C),2κ 2 (P′,C)-CF 3 PCP)Ir(H) 2 ] 2 (μ-CF 3 PCPH)(μ-H), which has been isolated and crystallographically characterized. Ir(I) pincer complexes ( CF 3 PCP)Ir(L) (L = MeP(C 2 F 5 ) 2 , CO, dfepe (dfepe = (C 2 F 5 ) 2 PCH 2 CH 2 P(C 2 F 5 ) 2 )) also serve as moderately active aldehyde decarbonylation catalyst precursors for 2-naphthaldehyde with similar activities in diglyme (1.7 TO h −1 , 152 °C) and in 1,4-dioxane (0.052 TO h −1 , 94 °C). The catalyst resting states are the corresponding five-coordinate carbonyl complexes ( CF 3 PCP)Ir(MeP(C 2 F 5 ) 2 )(CO), ( CF 3 PCP)Ir(CO) 2 , and [( CF 3 PCP)Ir-(CO)] 2 (μ-dfepe). DFT studies indicate that the preferred catalyst resting state for alkane dehydrogenation, ( CF 3 PCP)Ir(cod), can be ascribed to the lower steric requirements of the CF 3 -substituted pincer ligand.

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