P(CH)P pincer rhodium(I) complexes: the key role of electron-poor imidazoliophosphine extremities - Archive ouverte HAL
Article Dans Une Revue Inorganic Chemistry Année : 2013

P(CH)P pincer rhodium(I) complexes: the key role of electron-poor imidazoliophosphine extremities

Résumé

The coordination chemistry of a potentially pincer-type dicationic meta-phenylene-bis(imidazoliophosphine) ligand 3 to neutral and cationic carbonylrhodium(I) centers has been investigated. Similarly to what was observed previously for its ortho-phenylene counterpart, 3 was found to bind to the RhCl(CO) fragment in a trans-chelating manner that makes possible a weak Rh-C(H) interaction, inferred from the nonbonding but relatively short Rh-C and Rh-H contacts observed in the solid state structure of the dicationic adduct (3)RhCl(CO) (5). Formation of the target PCP-type pincer complex could not be triggered despite multiple attempts to deprotonate the central C-H moiety in the initial dicationic adduct 5, or in the tricationic species [(3)Rh(CO)]+ (8) generated by abstraction of the chloride ion from 5. Complex 8 was identified on the basis of NMR and IR analyses as a Rh(I)-stabilized P(CH)P-intermediate en route to the anticipated classical PCP-type pincer complex. Analysis of the electronic structure of this intermediate computed at the density functional level of theory (DFT level) revealed a bonding overlap between a Rh d-orbital and π-orbitals of the m-phenylene ring. NBO analyses and calculated Wiberg indices confirm that this interaction comprises an η1-C-Rh bonding mode, with only secondary contributions from the geminal C and H atoms. Although the target PCP-type pincer complex could not be generated, treatment of the tricationic intermediate with methanol induced a P-CN2 bond cleavage at both imidazoliophosphine moieties, resulting in the formation of a dicationic "open pincer" species, that is, a nonchelated bis((MeO)PPh2)-stabilized aryl-Rhodium complex that is the κC-only analogue of the putative κP,κC,κP-PCP complex sought initially. Theoretical studies at the DFT level of experimental or putative species relevant to the final C-H activation process ruled out the oxidative addition pathway. Two alternative pathways are proposed to explain the formation of the "open pincer" complex, one based on an organometallic α-elimination step, the other based on an organic aromatization-driven β-elimination process.
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Dates et versions

hal-00993872 , version 1 (20-05-2014)

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Cécile Barthes, Christine Lepetit, Yves Canac, Carine Guyard-Duhayon, Davit Zargarian, et al.. P(CH)P pincer rhodium(I) complexes: the key role of electron-poor imidazoliophosphine extremities. Inorganic Chemistry, 2013, 52 (1), pp.48-58. ⟨10.1021/ic3006508⟩. ⟨hal-00993872⟩
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