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A Vanadium Methylidene
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DOI：10.1021/jacs.4c01906.png)
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Abstract
En 中文
Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH2)] (PNP = N[2-(PPr2)-Pr-i-4-methylphenyl](-), Ar = 2,6-(Pr2C6H3)-Pr-i), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH3)] or [(PNP)V(=NAr)(CH3)] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, H2CPPh3. Structural and spectroscopic analysis, including C-13 enriched labeling of the methylidene ligand, unequivocally confirmed the terminal nature of a rare 3d methylidene complex, featuring a V=CH2 bond distance of 1.908(2) & Aring; and a highly downfield C-13 NMR spectral shift at 298 ppm. In the absence of the ylide, intermediate [(PNP)V=NAr] activates dinitrogen to form an end-on bridging N-2 complex, [(PNP)V(=NAr)](2)(mu(2)-eta(1):eta(1)-N-2), having a singlet ground state. Complex [(PNP)V(=NAr)(=CH2)] reacts with H3COTf to form [(PNP)V(=NAr)(OTf)], accompanied by the release of ethylene as evidenced by H-1 NMR spectroscopy, and reactivity studies suggest a beta-hydride elimination pathway.
Keywords:
OLEFIN METATHESIS CATALYSTS
ALKYLIDENE COMPLEXES
TANTALUM METHYLIDENE
METHYLENE
TUNGSTEN
ACTIVATION
CHEMISTRY
LIGAND
MONONUCLEAR
MOLYBDENUM
Journal
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15.6
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20.0W
Citations:
60.2W