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We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η(2)-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η(2)-alkene complexes but is favored in this case by the strain in the C(3) ring which prevents the decomposition of the key intermediate via loss of cyclopropene.
CNRS, Laboratoire de Chimie de Coordination, 205 Route de Narbonne, F-31077 Toulouse, France.
This article was published in the following journal.
Name: Journal of the American Chemical Society
The ethylene complex (PNP)Ti(eta2-H2C=CH2)(CH2tBu) or (PNP)Ti=CHtBu(CH2tBu) (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) react with H2CPPh3 to form the kappa2-phosphinoalkylidene (PNP)Ti=CHPPh2(Ph) (1), wh...
A formal insertion of two aryne moieties into the carbon-oxygen double bond of cyclopropenone has been realized. Spirocyclic xanthene-cyclopropene scaffolds were obtained. Mechanistically, a sequence ...
The triamidophosphine protioligand 1 reacts with the homoleptic pentakis(dimethylamido) precursors of niobium and tantalum [M(NMe2)5, where M = Nb, Ta] to form cyclometalated complexes of the type [N2...
Trans unsaturated lipids are uncommon in nature. In the human diet, they occur as natural products of ruminal bacteria or from industrial food processing like hydrogenation of vegetable oils. Consumpt...
Low-valent late transition-metal catalysis has become indispensable to chemical synthesis, but homogeneous high-valent transition-metal catalysis is underdeveloped, mainly owing to the reactivity of h...
The research is to evaluate benzene metabolism after exposure at levels that can be found in the environment, such as the higher end concentrations in the air inside cars and buses while b...
The Veterans Health Administration (VHA) has stated the need for a brief screening instrument that can assist with the triage of the enormous number of returning OEF/OIF veterans with conc...
The purpose of this study is to investigate the health effects of benzene exposure in workers in Shanghai, China.
This study compares air pollution exposures of residents in a South Baltimore community next to major industry with those in a comparison community with much less industry nearby. Parents ...
RATIONALE: Exposure to low-level benzene in the work place may affect the risk of developing cancer later in life. Learning about the long-term effects of benzene exposure may help the stu...
Niobium. A metal element atomic number 41, atomic weight 92.906, symbol Nb. (From Dorland, 28th ed)
Complexes of enzymes that catalyze the covalent attachment of UBIQUITIN to other proteins by forming a peptide bond between the C-terminal GLYCINE of UBIQUITIN and the alpha-amino groups of LYSINE residues in the protein. The complexes play an important role in mediating the selective-degradation of short-lived and abnormal proteins. The complex of enzymes can be broken down into three components that involve activation of ubiquitin (UBIQUITIN-ACTIVATING ENZYMES), conjugation of ubiquitin to the ligase complex (UBIQUITIN-CONJUGATING ENZYMES), and ligation of ubiquitin to the substrate protein (UBIQUITIN-PROTEIN LIGASES).
The sequential activation of serum COMPLEMENT PROTEINS to create the COMPLEMENT MEMBRANE ATTACK COMPLEX. Factors initiating complement activation include ANTIGEN-ANTIBODY COMPLEXES, microbial ANTIGENS, or cell surface POLYSACCHARIDES.
UNSATURATED FATTY ACIDS that contain at least one double bond in the trans configuration, which results in a greater bond angle than the cis configuration. This results in a more extended fatty acid chain similar to SATURATED FATTY ACIDS, with closer packing and reduced fluidity. HYDROGENATION of unsaturated fatty acids increases the trans content.
Unsaturated derivatives of the steroid androstane containing at least one double bond at any site in any of the rings.