Hydrogenolysis of palladium(II) hydroxide, phenoxide, and alkoxide complexes

J Am Chem Soc. 2011 Nov 9;133(44):17713-26. doi: 10.1021/ja205824q. Epub 2011 Oct 19.

Abstract

A series of pincer ((tBu)PCP)Pd(II)-OR complexes ((tBu)PCP = 2,6-bis(CH(2)P(t)Bu(2))C(6)H(3), R = H, CH(3), C(6)H(5), CH(2)C(CH(3))(3), CH(2)CH(2)F, CH(2)CHF(2), CH(2)CF(3)) were synthesized to explore the generality of hydrogenolysis reactions of palladium-oxygen bonds. Hydrogenolysis of the Pd hydroxide complex to generate the Pd hydride complex and water was shown to be inhibited by formation of a water-bridged, hydrogen-bonded Pd(II) hydroxide dimer. The Pd alkoxide and aryloxide complexes exhibited more diverse reactivity. Depending on the characteristics of the -OR ligand (steric bulk, electron-donating ability, and/or the presence of β-hydrogen atoms), hydrogenolysis was complicated by hydrolysis by adventitious water, a lack of reactivity with hydrogen, or a competing dissociative β-hydride abstraction reaction pathway. Full selectivity for hydrogenolysis was observed with the partially fluorinated Pd(II) 2-fluoroethoxide complex. The wide range of Pd-OR substrates examined helps to clarify the variety of reaction pathways available to late-transition-metal alkoxides as well as the conditions necessary to tune the reactivity to hydrogenolysis, hydrolysis, or dissociative β-hydride abstraction.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Crystallography, X-Ray
  • Hydrogenation
  • Hydroxides / chemistry*
  • Models, Molecular
  • Molecular Structure
  • Organometallic Compounds / chemical synthesis
  • Organometallic Compounds / chemistry*
  • Oxides / chemistry*
  • Palladium / chemistry*

Substances

  • Hydroxides
  • Organometallic Compounds
  • Oxides
  • Palladium