Original palladium pincer complexes deriving from 1,3-bis(thiophosphinoyl)indene proligands: C(sp3)-H versus C(sp2)-H bond activation |
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Authors: | Nebra Noel Lisena Jérôme Saffon Nathalie Maron Laurent Martin-Vaca Blanca Bourissou Didier |
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Affiliation: | University of Toulouse, UPS, LHFA, 118 route de Narbonne, F-31062 Toulouse, France. |
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Abstract: | A series of original 2-indenylidene palladium pincer complexes {PdL[Ind(Ph(2)P==S)(2)]} (L = HNCy(2), PPh(3), Cl(-)) have been prepared by double C-H activation of a 1,3-bis(thiophosphinoyl)indene proligand. Crystallographic analyses and DFT calculations indicate that the bonding situation of the {Pd[Ind(Ph(2)P==S)(2)]} fragment is essentially governed by the conjugated and rigid nature of the dianionic pincer ligand, the nature of the coligand having little influence. The formation of the 2-indenylidene complexes involves either a 2-indenyl pincer or a four-membered cyclometalated complex as an intermediate, suggesting that C(sp(2))-H or C(sp(3))-H bond activation takes place. However, deuterium labelling experiences show that in all cases, C(sp(3))-H bond activation occurs followed eventually by a Pd/H exchange. Nevertheless, evidence for direct C(sp(2))-H bond activation under mild conditions is obtained when a methyl group is introduced at the indene proligand to prevent C(sp(3))-H bond activation. The ensuing dissymmetrical 2-indenyl palladium pincer complex has been fully characterized. |
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