Unexpected Reactivity Patterns of Ruthenium Alkylidenes
with N‑Phosphino-Functionalized N‑Heterocyclic Carbene
Ligands (NHCPs)
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Abstract
N-phosphino-functionalized
N-heterocyclic carbene (NHCP) ligands
have been evaluated as potential supporting ligands in ruthenium-catalyzed
olefin metathesis. Initial density functional theory (DFT) calculations
suggested that these NHCP ligands may allow access to neutral 14 valence
electron (VE) speciesequivalents of the active 14 VE species
formed by phosphine dissociation from Grubbs II precatalystsvia
facile decoordination of the NHCP phosphino donor of the strained
four-membered [RuPNC] chelate systems. Their attempted synthesis from
NHCPs and Grubbs-type Ru carbenes revealed addition of an NHCP donor
atom (P or C) to the alkylidene fragment, forming a new C–P
or C–C bond in five-membered chelate structures. DFT investigations
showed that these reactions are controlled kinetically and must not
be neglected as important possible deactivation routes in olefin metathesis