A Convenient, Safe, and Atom‐Economical Route to a Large Portfolio of Grubbs‐Type Catalysts for Olefin Metathesis via Four‐Coordinate Ruthenium Alkylidynes

Abstract

ABSTRACT p ‐Tolyl(trimethylsilyl)diazomethane is a readily accessible and easy‐to‐handle net carbyne donor reagent. It reacts with [( p ‐cymene)RuCl 2 ] 2 in MeCN to give the phosphine‐free chloride‐bridged dinuclear complex [(MeCN) 2 RuCl 2 ( = C( p ‐tolyl)(SiMe 3 ))] 2 ( 2 ) carrying a silyl group on each of the carbene ligands. Treatment of 2 with either PCy 3 or an N‐heterocyclic carbene (NHC) causes elimination of TMSCl with formation of the corresponding four‐coordinate ruthenium alkylidynes. The non‐bonding electron lone pair of significant d z2 character at their Ru center is prone to protonation; in this way, the alkylidyne unit is converted into a carbene ligand under very mild conditions. The sequence of alkylidyne formation/protonation opens a novel entry into all relevant “generations” of Grubbs and Grubbs‐Hoveyda type catalysts, which is distinguished by a superior ligand‐ and atom economy, a good safety profile, and high overall yields. Moreover, the method is inherently flexible and arguably suitable for parallel screening and reaction optimization purposes.