Metal alkyls programmed to generate metal alkylidenes by α-H abstraction: Prognosis from NMR chemical shift
- Author(s): Gordon, CP
- Yamamoto, K
- Searles, K
- Shirase, S
- Andersen, RA
- Eisenstein, O
- Copéret, C
- et al.
Published Web Locationhttp://doi.org/10.1039/c7sc05039a
© The Royal Society of Chemistry 2018. 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)2that show distinctively deshielded chemical shifts for their α-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-Cα-Cα′plane, interacting with the Cαp-orbital lying in the same plane. This π-type interaction inscribes some alkylidene character into Cαthat favors alkylidene generation via α-H abstraction. The extent of the deshielding and the anisotropy of the alkyl chemical shift tensors distinguishes [M](CH2R)2compounds that form alkylidenes from those that do not, relating the reactivity to molecular orbitals of the respective molecules. The α-carbon chemical shifts and tensor orientations thus predict the reactivity of metal alkyl compounds towards alkylidene generation.
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