A Selective and Convenient Method for the Synthesis of 2-Phenylaminothiazolines

A series of 2-phenylaminothiazolines have been prepared from the corresponding N-(2-hydroxyethyl)-N′-phenylthioureas under mild reaction conditions using either thio-CDI (1,1′-thiocarbonyldiimidazole) or CDI (1,1′-carbonyldiimidazole) to promote the cyclization. This protocol provides the desired cyclization products in good yield with excellent selectivity. The scope and selectivity of this methodology are also described

New Reactions of Terminal Hydrides on a Diiron Dithiolate

Mechanisms for biological and bioinspired dihydrogen activation and production often invoke the intermediacy of diiron dithiolato dihydrides. The first example of such a Fe2(SR)2H2 species is provided by the complex [(term-H)­(μ-H)­Fe2(pdt)­(CO)­(dppv)2] ([H1H]0). Spectroscopic and computational studies indicate that [H1H]0 contains both a bridging hydride and a terminal hydride, which, notably, occupies a basal site. The synthesis begins with [(μ-H)­Fe2(pdt)­(CO)2(dppv)2]+ ([H1(CO)]+), which undergoes substitution to afford [(μ-H)­Fe2(pdt)­(CO)­(NCMe)­(dppv)2]+ ([H1(NCMe)]+). Upon treatment of [H1(NCMe)]+ with borohydride salts, the MeCN ligand is displaced to afford [H1H]0. DNMR (EXSY, SST) experiments on this complex show that the terminal and bridging hydride ligands interchange intramolecularly at a rate of 1 s–1 at −40 °C. The compound reacts with D2 to afford [D1D]0, but not mixed isotopomers such as [H1D]0. The dihydride undergoes oxidation with Fc+ under CO to give [1(CO)]+ and H2. Protonation in MeCN solution gives [H1(NCMe)]+ and H2. Carbonylation converts [H1H]0 into [1(CO)]0

¹³C NMR Signal Enhancement Using Parahydrogen-Induced Polarization Mediated by a Cobalt Hydrogenation Catalyst

The use of a cobalt-based catalyst for the generation of hyperpolarized 13C NMR resonances by parahydrogenation of ethyl acrylate is presented herein. Comparisons of the carboxylate 13C NMR signal enhancement factor of ethyl propionate between using (MesCCC)­Co-py and a commonly utilized cationic diphosphine rhodium complex demonstrates that the cobalt system is a viable PHIP catalyst alternative. Furthermore, the operative hydrogenation mechanism of the cobalt system was examined by using 1H, 13C, and parahydrogen-induced polarization NMR spectroscopies to elucidate reaction intermediates affiliated with the observed 1H and 13C NMR signal enhancements in ethyl propionate

Spectroscopic Investigation of Phosphorus Mineralization as Affected by the Calcite–Water Interfacial Chemistry

The mineralization and bioavailability of phytic acid, the predominant organic phosphorus (OP) species in many soils, have generally been rendered limited due to its interaction with soil minerals. In particularly calcareous and neutral to slightly alkaline soils, phytic acid is known to actively react with calcite, although how this interaction affects phytic acid mineralization is still unknown. This study, therefore, investigated the mechanisms regarding how the calcite–water interface influences phytic acid mineralization by phytase, at pHs 6 and 8 using in situ spectroscopic techniques including solution nuclear magnetic resonance and attenuated total reflection Fourier transform infrared spectroscopy. The findings indicated a pH-specific effect of the calcite–water interface. Inhibited phytase activity and thus impaired phytic acid mineralization were induced by calcite at pH 6, while the opposite effect was observed at pH 8. How the interaction between phytic acid and calcite and between phytase and calcite differed between the two pH values contributed to the pH-specific effect. The results demonstrate the importance of soil pH, enzyme–, and OP–clay mineral interactions in controlling the mineralization and transformation of OP and, consequently, the release of phosphate in soils. The findings can also provide implications for the management of calcite-rich and limed soils

New Reactions of Terminal Hydrides on a Diiron Dithiolate

Mechanisms for biological and bioinspired dihydrogen activation and production often invoke the intermediacy of diiron dithiolato dihydrides. The first example of such a Fe₂(SR)₂H₂ species is provided by the complex [(<i>term</i>-H)­(μ-H)­Fe₂(pdt)­(CO)­(dppv)₂] ([H<b>1</b>H]⁰). Spectroscopic and computational studies indicate that [H<b>1</b>H]⁰ contains both a bridging hydride and a terminal hydride, which, notably, occupies a basal site. The synthesis begins with [(μ-H)­Fe₂(pdt)­(CO)₂(dppv)₂]⁺ ([H<b>1</b>(CO)]⁺), which undergoes substitution to afford [(μ-H)­Fe₂(pdt)­(CO)­(NCMe)­(dppv)₂]⁺ ([H<b>1</b>(NCMe)]⁺). Upon treatment of [H<b>1</b>(NCMe)]⁺ with borohydride salts, the MeCN ligand is displaced to afford [H<b>1</b>H]⁰. DNMR (EXSY, SST) experiments on this complex show that the terminal and bridging hydride ligands interchange intramolecularly at a rate of 1 s^–1 at −40 °C. The compound reacts with D₂ to afford [D<b>1</b>D]⁰, but not mixed isotopomers such as [H<b>1</b>D]⁰. The dihydride undergoes oxidation with Fc⁺ under CO to give [<b>1</b>(CO)]⁺ and H₂. Protonation in MeCN solution gives [H<b>1</b>(NCMe)]⁺ and H₂. Carbonylation converts [H<b>1</b>H]⁰ into [<b>1</b>(CO)]⁰

Well-Defined Cobalt(I) Dihydrogen Catalyst: Experimental Evidence for a Co(I)/Co(III) Redox Process in Olefin Hydrogenation

The synthesis of a cobalt dihydrogen Co^I-(H₂) complex prepared from a Co^I-(N₂) precursor supported by a monoanionic pincer bis­(carbene) ligand, ^MesCCC (^MesCCC = bis­(mesityl-benzimidazol-2-ylidene)­phenyl), is described. This species is capable of H₂/D₂ scrambling and hydrogenating alkenes at room temperature. Stoichiometric addition of HCl to the Co^I-(N₂) cleanly affords the Co^III hydridochloride complex, which, upon the addition of Cp₂ZrHCl, evolves hydrogen gas and regenerates the Co^I-(N₂) complex. Furthermore, the catalytic olefin hydrogenation activity of the Co^I species was studied by using multinuclear and parahydrogen (<i>p</i>-H₂) induced polarization (PHIP) transfer NMR studies to elucidate catalytically relevant intermediates, as well as to establish the role of the Co^I-(H₂) in the Co^I/Co^III redox cycle

Well-Defined Cobalt(I) Dihydrogen Catalyst: Experimental Evidence for a Co(I)/Co(III) Redox Process in Olefin Hydrogenation

The synthesis of a cobalt dihydrogen Co^I-(H₂) complex prepared from a Co^I-(N₂) precursor supported by a monoanionic pincer bis­(carbene) ligand, ^MesCCC (^MesCCC = bis­(mesityl-benzimidazol-2-ylidene)­phenyl), is described. This species is capable of H₂/D₂ scrambling and hydrogenating alkenes at room temperature. Stoichiometric addition of HCl to the Co^I-(N₂) cleanly affords the Co^III hydridochloride complex, which, upon the addition of Cp₂ZrHCl, evolves hydrogen gas and regenerates the Co^I-(N₂) complex. Furthermore, the catalytic olefin hydrogenation activity of the Co^I species was studied by using multinuclear and parahydrogen (<i>p</i>-H₂) induced polarization (PHIP) transfer NMR studies to elucidate catalytically relevant intermediates, as well as to establish the role of the Co^I-(H₂) in the Co^I/Co^III redox cycle

A Highly Chemoselective Cobalt Catalyst for the Hydrosilylation of Alkenes using Tertiary Silanes and Hydrosiloxanes

The hydrosilylation of alkene substrates bearing additional functionalities is difficult to achieve using earth-abundant catalysts and has not been extensively realized with both earth-abundant transition metals and tertiary silanes or hydrosiloxanes. Reported herein is a well-defined bis­(carbene) cobalt­(I)-dinitrogen complex for the efficient, catalytic anti-Markovnikov hydrosilylation of terminal alkenes, featuring a broad substrate scope. Alkenes containing hydroxyl, amino, ester, epoxide, ketone, formyl, and nitrile groups are selectively hydrosilylated in this reaction sequence. Multinuclear NMR studies of reactive intermediates gave insights into the mechanism