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

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Abstract

A bidentate nitrogen-donor ligand with an appended phenol group, C5H4NCH[double bond, length as m-dash]N-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-OC6H4N[double bond, length as m-dash]CH(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-OC6H4N[double bond, length as m-dash]CH(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.

Graphical abstract: Mild and selective Pd–Ar protonolysis and C–H activation promoted by a ligand aryloxide group

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Publication details

The article was received on 01 Feb 2018, accepted on 05 Feb 2018 and first published on 13 Feb 2018


Article type: Paper
DOI: 10.1039/C8DT00437D
Citation: Dalton Trans., 2018, Advance Article
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    Mild and selective Pd–Ar protonolysis and C–H activation promoted by a ligand aryloxide group

    A. Behnia, M. A. Fard, J. M. Blacquiere and R. J. Puddephatt, Dalton Trans., 2018, Advance Article , DOI: 10.1039/C8DT00437D

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