Mild and selective Pd-Ar protonolysis and C-H activation promoted by a ligand aryloxide group

Authors

Ava Behnia, The University of Western Ontario
Mahmood A. Fard, The University of Western Ontario
Johanna M. Blacquiere, The University of Western OntarioFollow
Richard J. Puddephatt, The University of Western Ontario

Document Type

Article

Publication Date

1-1-2018

Journal

Dalton Transactions

Volume

47

Issue

10

First Page

3538

Last Page

3548

URL with Digital Object Identifier

10.1039/c8dt00437d

Abstract

A bidentate nitrogen-donor ligand with an appended phenol group, C5H4NCHN-2-C6H4OH, H(L1) was treated with a palladium cycloneophyl complex [Pd(CH2CMe2C6H4)(COD)], with both Pd-aryl and Pd-alkyl bonds, to give a Pd-alkyl complex, [Pd(CH2CMe2C6H5)(κ3-N,N′,O-OC6H4NCH(2-C5H4N))], 1. The cleavage of the Pd-aryl bond and the deprotonation of the ligand phenol to afford a bound aryloxide, indicates facile Pd-aryl bond protonolysis. Deuterium labelling experiments confirmed that the ligand phenol promotes protonolysis and that the reverse, aryl C-H activation, occurs under very mild reaction conditions (within 10 min at room temperature). An unusual isomerization of the Pd-alkyl complex 1 to a Pd-aryl complex, [Pd(C6H4(2-t-Bu))(κ3-N,N′,O-OC6H4NCH(2-C5H4N))], 2, was observed to give an equilibrium with [2]/[1] = 9 after 5 days in methanol. The isomerization requires that both aryl C-H activation and Pd-alkyl protonolysis steps occur. The very large KIE value (kH/kD = ca. 40) for isomerization of 1 to 2, suggests a concerted SE2-type mechanism for the Pd-alkyl protonolysis step.