Unsaturated rh(i) and rh(iii) naphthyl-based pcp complexes. major steric effect on reactivity

Christian M. Freeh, Linda J W Shimon, David Milstein

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The addition of an equimolar amount of hydrochloric acid (-4.0 M in dioxane) to THF solutions of the binuclear Rh(I) complex [(C10H 5(CH2Pr2)2)Rh(η1- N2)]2 (1a) at room temperature led to an inseparable mixture of 1a, [(C10H5(CH2PPr2) 2)Rh(Cl)(H)] (2a), and [(C10H5(CH 2PPr2)2)Rh(Cl)2 (dioxane)], (3a). Exclusive formation of 2a was achieved by slow addition of an equimolar amount of hydrochloric acid (-0.4 M in dioxane) to a THF solution of la at -35 °C, whereas exclusive formation of 3a was obtained when a second equivalent or an excess (-10 equiv) of hydrochloric acid (-4.0 M in dioxane) was added to THF solutions of 2a (or to reaction mixtures, which consist of la, 2a, and 3a). 3a was structurally characterized. In striking difference to the reactivity pattern of la, treatment of THF solutions of the bulky tBu derivative lb with an equimolar amount or even a large excess (-25 equiv) of hydrochloric acid (-4.0 M in dioxane) exclusively yielded the hydrido chloro complex [(C 10H5(CH2PBu2)2)Rh(Cl)(H)] (2b). Chloride abstraction from 2a and 2b with AgBF4 exclusively yielded the hydrido rhodiurn(ITi) complexes [(C10H 5(CH2PR2)2)Rh(H)(F-BF3)] (9a and 9b) with coordination of the counteranion. On the other hand, when an equimolar amount of AgBArF 4 was added to methylene chloride (or diethyl ether) solutions of 2a and 2b the cationic, the solvent-stabilized rhodium hydride complexes of type [(C10H 5(CH2PR2)2)Rh(solv)(H)][BAr F 4] (10a and 10b) were formed. If the electron density of the metal centers of 9 (and 10) is reduced further by substitution of the coordinated anion of 9 (or the solvent molecule of 10) with a carbonyl ligand, instant migration of the hydride ligand to the aromatic unit toyield the stable carbonyl complexes of type [(C10H5(CH2PR 2)2)2(H)Rh(CO)][X] (X = BArF4 11a,11b; X = BF411a ,11b) with η2 Cary1- H agostic interactions was observed. Treatment of 2b with CO gas yielded both isomeric forms of [(C10H5(CH2P'Bu2) 2)Rh(H)(Cl)(CO)] 14b (CO trans to he hydride ligand) and 14b (CO trans to the aromatic pincer core). In contrast, when an excess of CO gas was added to THF (or methylene chloride), solutions of 2a, 14a was exclusively formed within 20 min at room temperature.

Original languageEnglish
Pages (from-to)1900-1908
Number of pages9
Issue number6
Publication statusPublished - Mar 23 2009


ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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