Optimizing ligand structure for low-loading and fast catalysis for alkynyl-alcohol and-amine cyclization

Authors

James M. Stubbs, The University of Western Ontario
Benjamin J. Bridge, The University of Western Ontario
Johanna M. Blacquiere, The University of Western OntarioFollow

Document Type

Article

Publication Date

1-1-2019

Journal

Dalton Transactions

Volume

48

Issue

22

First Page

7928

Last Page

7937

URL with Digital Object Identifier

10.1039/c9dt01870k

Abstract

A series of [Ru(Cp/Cp∗)(PR2NR′2)(MeCN)]PF6 complexes were prepared, in which the steric and electronic properties of the primary coordination sphere were varied (R = Ph, t-Bu, Bn; and Cp vs. Cp∗). These complexes were catalytically active in the cyclization of alkyne substrates with an intramolecular nucleophile (amine or alcohol) to produce 5-and 6-membered heterocycles. The effect of the 1° coordination sphere structure on catalyst performance was evaluated. Steric bulk around the metal centre was a key feature to achieve rapid catalysis at low temperatures. The catalyst [Ru(Cp)(Pt-Bu2NPh2)(MeCN)]PF6 gave a turnover number that was >1 order of magnitude more active than previous catalysts in the cyclization of the benchmark substrate 2-ethynylaniline. This catalyst is tolerant of a diversity of functional groups and is competent at the formation of various substituted indoles.