Over the past two decades, considerable attention has been given to the development of new ligands for the palladium-catalyzed arylation of amines and related NH-containing substrates (i.e., Buchwald-Hartwig amination). The generation of structurally diverse ligands, by research groups in both academia and industry, has facilitated the accommodation of sterically and electronically divergent substrates including ammonia, hydrazine, amines, amides, and NH heterocycles. Despite these achievements, problems with catalyst generality persist and access to multiple ligands is necessary to accommodate all of these NH-containing substrates. In our quest to address this significant limitation we identified the BippyPhos/[Pd(cinnamyl)Cl]2 catalyst system as being capable of catalyzing the amination of a variety of functionalized (hetero)aryl chlorides, as well as bromides and tosylates, at moderate to low catalyst loadings. The successful transformations described herein include primary and secondary amines, NH heterocycles, amides, ammonia and hydrazine, thus demonstrating the largest scope in the NH-containing coupling partner reported for a single Pd/ligand catalyst system. We also established BippyPhos/[Pd(cinnamyl)Cl]2 as exhibiting the broadest demonstrated substrate scope for metal-catalyzed cross-coupling of (hetero)aryl chlorides with NH indoles. Furthermore, the remarkable ability of BippyPhos/[Pd(cinnamyl)Cl]2 to catalyze both the selective monoarylation of ammonia and the N-arylation of indoles was exploited in the development of a new one-pot, two-step synthesis of N-aryl heterocycles from ammonia, ortho-alkynylhalo(hetero)arenes and (hetero) aryl halides through tandem N-arylation/hydroamination reactions. Although the scope in the NH-containing coupling partner is broad, BippyPhos/[Pd(cinnamyl)Cl]2 also displays a marked selectivity profile that was exploited in the chemoselective monoarylation of substrates featuring two chemically distinct NH-containing moieties.
Peroxidase (EC 1.11.1.7) from horseradish ( Armoracia rusticana ) roots was purified using a simple, rapid, three-step procedure: ultrasonication, ammonium sulfate salt precipitation, and hydrophobic interaction chromatography on phenyl Sepharose CL-4B. The preparation gave an overall yield of 71%, 291-fold purification, and a high specific activity of 772 U mg(-1) protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the purified enzyme was homogeneous and had a molecular weight of approximately 40 kDa. The isolated enzyme had an isoelectric point of 8.8 and a Reinheitszahl value of 3.39 and was stable when stored in the presence of glycerol at -20 degrees C, with >95% retention of original enzyme activity for at least 6 months. Maximal activity of purified horseradish peroxidase (HRP) was obtained under different optimized conditions: substrate (guaiacol and H(2)O(2)) concentrations (0.5 and 0.3 mM, respectively), type of buffer (50 mM phosphate buffer), pH (7.0), time (1.0 min), and temperature of incubation (30 degrees C). In addition, the effect of HRP and H(2)O(2) in a neutral-buffered aqueous solution for the oxidation of phenol and 2-chlorophenol substrates was also studied. Different conditions including concentrations of phenol/2-chlorophenol, H(2)O(2), and enzyme, time, pH, and temperature were standardized for the maximal activity of HRP with these substrates; under these optimal conditions 89.6 and 91.4% oxidations of phenol and 2-chlorophenol were obtained, respectively. The data generated from this work could have direct implications in studies on the commercial production of this biotechnologically important enzyme and its stability in different media.
A mixture of tris(dibenzylideneacetone)dipalladium(0) (Pd 2 dba 3 ) and 5-(di-tert-butylphos-is shown to be a robust and efficient catalyst system for the hydroxylation of structurally diverse (hetero)aryl halides under mild conditions and with broad substrate scope. Included in this reactivity survey is the successful synthesis of substituted benzofurans and related heteroatomic derivatives, which are formed via the hydroxylation of 2-haloalkynylarenes. Notably, a significant number of the reactions reported herein proceed at room temperature, and we have demonstrated that it is possible to conduct reactions on the benchtop under air using unpurified solvents with negligible loss in reactivity versus related transformations conducted under inert atmosphere conditions. We also report herein the first crystallographically characterized (Bippyphos)Pd(II) complex, which confirms the ability of this synthetically useful ligand to adopt a bidentate binding motif in a manner similar to Buchwalds biarylphosphine ligand class.
The new and easily prepared OTips-DalPhos ligand (L1) offers broad substrate scope at relatively low loadings in the palladium-catalyzed C-N cross-coupling/cyclization of o-alkynylhalo(hetero)arenes with primary amines, affording indoles and related heterocyclic derivatives in high yield.
The efficacy of phosphine-free Pt precatalysts including PtCl 2 and (COD)PtCl 2 in promoting the cyclohydroamination of primary as well as secondary alkyl/arylamines tethered to R-olefins is demonstrated for the first time. Further catalytic studies examining the use of phenylene-P,N co-ligands, as well as neutral, cationic, and formally zwitterionic complexes derived from the new ligand precursor 1-PPh 2 -2-P(tBu) 2 -indene, revealed comparable reactivity in Pt-catalyzed cyclohydroamination catalysis relative to these phosphine-free catalysts.
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