Activation of a catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the catalyst-activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the catalyst in the presence of sufficient substrate can lead to irreversible deactivation consistent with oligomerization of the catalyst molecules. Following catalyst activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyperpolarized 1H spins of the hydride/orthohydrogen spin bath. Importantly, the chemical changes that accompanied the catalyst’s full activation were also found to endow the catalyst with water solubility, here used to demonstrate SABRE hyperpolarization of nicotinamide in water without the need for any organic cosolvent—paving the way to various biomedical applications of SABRE hyperpolarization methods.

Reusable Co-catalyzed coupling of thiols to synthesize S–N/S–S bonds in water.

Organosulfides have great significance and value in synthetic and biological chemistry. To establish a versatile and green methodology for C-S bond generation, we successfully developed a new aerobic cross-dehydrogenative coupling of C-H and S-H to synthesize aryl sulfides in water, utilizing CoPcS as the catalyst and O as the oxidant. This protocol shows great tolerance of a wide range of substrates. A large variety of organosulfur compounds were produced in modest to excellent yields.

Catalytic syntheses of organic sulfenamides and disulfides have great significance and value in synthetic chemistry and bioscience. To establish av ersatile and efficient technology for such reactions, an aerobic oxidative coupling methodf or the formation of SÀNa nd SÀS bonds, using TEMPOa sacatalyst and O 2 as an oxidant, has been successfully developed. Reactions showedg ood tolerance towardv arious amines and thiols. Sulfenamides were produced in up to 99 %y ield, while disulfides were formed in up to 97 %y ield in one-pot syntheses. Activation of the NÀHb ond by 2,2-disbenzothiazoledisulfide showed the great potential in organic synthesis.Organics ulfur-nitrogen and sulfur-sulfur bonds are significant buildingb locks in synthetic chemistry and biology,o wing to their unique structures and reactivity. [1] Organosulfur compoundsb earing SÀNb onds, defined as sulfenamides, [2] have broad applications in manufacturing and the pharmaceutical industry.F or example, N-[(trichloromethyl)thio]phthalimide is one of the most effective fungicides and has been commercialized for decades. [3] Owing to the high liability of the SÀNb ond, some sulfenamides exhibit high effectiveness as rubberv ulcanization accelerators. [4] As the only readily reversible covalent cross-linking bond existing in native proteins, [5] the disulfide bond plays as ignificant role in the protein-folding process and the stabilization of tertiary structures. [1,6] Despite the prominent applications of sulfenamides,t here are only af ew reports about their preparation. [3] Amongt hose, the reactionb etweens ulfenyl chlorides anda mines ac lassical but inefficient method, owing to the low availability of sulfenyl chlorides. [7] Later,t he amination of thiols with N-halo compounds or amines was performed in the presence of copper catalysts. [8] Unfortunately,d isulfides were formed as byproducts, decreasing the yields of the desired sulfenamides. With increasing concerns about environmental awareness and waste control, more efforts are required to investigate more versatile and greener strategies.2,2,6,6-(Tetramethylpiperidin-1-yl)oxyl (TEMPO) and its derivatives are well-studied and widely applied as stoichiometric or catalytic oxidants in organic chemistry. [9] Recently,w ereported an oxidativeh omocoupling of 2-mercaptobenzothiazole leading to 2,2-disbenzothiazoledisulfide in up to 94 %y ield. [10] The reactions used TEMPO as the catalyst and underwent ar adicalmediated process. TEMPO abstracted one hydrogen atom from the SÀHb ond of 2-mercaptobenzothiazole and formed at hiyl radicali ntermediate. Inspired by that finding, we decidedt o try the radical reaction between thiols and amines. Herein, we report aT EMPO-catalyzed aerobic oxidative coupling system, which utilizes environmentally friendly and naturallya bundant O 2 ,p roducing compounds containing SÀNa nd SÀSb onds in high yields.Initially,t he aerobic oxidative coupling of 2-mercaptobenzothiazolew ith tert-butylamine was conducted, using 5.0 mol % TEMPO, 2mLs olvent, and 0.3 MPa O 2 at ...

We demonstrate the preparation of diacenaphthopentalene derivatives via a palladium-catalyzed dimerization of 1-iodo-2-arylethynyl-acenaphthylenes. The resulting 7,14-diarylpentaleno[1,2-a:4,5a']diacenaphthylenes, which contain four linearly fused five-membered rings, are benchtop stable and behave as hole-transporting or ambipolar semiconductors in organic field effect transistors. The X-ray crystal structure shows the important role of the fused naphthalene unit that enforces a formal pentalene subunit at the central five-membered rings and [5]-radialene-like structures at the proximal five-membered rings. Nucleus-independent chemical shift (NICS) calculations show the internal pentalene rings are intermediate in antiaromaticity character between known pentalene and dibenzopentalenes derivatives. The diacenaphthopentalene derivatives give high optical gap materials owing to a forbidden HOMO to LUMO transition, yet have narrow electrochemical gaps and are reduced at small negative potentials giving LUMO energy levels of -3.57 to -3.74 eV.