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Reactions of phenylacetylene with nickel POCOP-pincer hydride complexes resulting in different outcomes from their palladium analogues†
Gleason L. O. Wilson,Medhanei Abraha,Jeanette A. Krause,Hairong Guan
Dalton Transactions Pub Date : 03/06/2015 00:00:00 , DOI:10.1039/C5DT00161G
Abstract

Nickel POCOP-pincer hydride complexes [2,6-(R2PO)2C6H3]NiH (R = iPr, 4a; R = cPe = cyclopentyl, 4b) react with phenylacetylene to generate [2,6-(R2PO)2C6H3]NiC(Ph)[double bond, length as m-dash]CH2 (5a–b) as the major product and (E)-[2,6-(R2PO)2C6H3]NiCH[double bond, length as m-dash]CHPh (6a–b) as the minor product. The 2,1-insertion is more favorable than the 1,2-insertion and both pathways involve cis addition of Ni–H across the C[triple bond, length as m-dash]C bond. Unlike the palladium case, alkynyl complexes [2,6-(R2PO)2C6H3]NiC[triple bond, length as m-dash]CPh (7a–b) and H2 are not produced in the nickel system. The more bulky hydride complex [2,6-(tBu2PO)2C6H3]NiH (4c) shows no reactivity towards phenylacetylene. Catalytic hydrogenation of phenylacetylene with 4a–b takes place at an elevated temperature (70–100 °C) and proves to be heterogeneous. The structures of 5b, 6a, 7a and 7b have been studied by X-ray crystallography.

Graphical abstract: Reactions of phenylacetylene with nickel POCOP-pincer hydride complexes resulting in different outcomes from their palladium analogues
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