Metal alkyls programmed to generate metal alkylidenes by ?-H abstraction: prognosis from NMR chemical shift.
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ABSTRACT: Metal alkylidenes, which are key organometallic intermediates in reactions such as olefination or alkene and alkane metathesis, are typically generated from metal dialkyl compounds [M](CH2R)2 that show distinctively deshielded chemical shifts for their ?-carbons. Experimental solid-state NMR measurements combined with DFT/ZORA calculations and a chemical shift tensor analysis reveal that this remarkable deshielding originates from an empty metal d-orbital oriented in the M-C?-C?' plane, interacting with the C? p-orbital lying in the same plane. This ?-type interaction inscribes some alkylidene character into C? that favors alkylidene generation via ?-H abstraction. The extent of the deshielding and the anisotropy of the alkyl chemical shift tensors distinguishes [M](CH2R)2 compounds that form alkylidenes from those that do not, relating the reactivity to molecular orbitals of the respective molecules. The ?-carbon chemical shifts and tensor orientations thus predict the reactivity of metal alkyl compounds towards alkylidene generation.
SUBMITTER: Gordon CP
PROVIDER: S-EPMC5890791 | biostudies-literature |
REPOSITORIES: biostudies-literature
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