HRh(dppb)2, a powerful hydride donor

Andrew J. Price, Rebecca Ciancanelli, Bruce C. Noll, Calvin J. Curtis, Daniel L. DuBois, M. Rakowski DuBois

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Abstract

The Rh(I) and Rh(III) hydrides HRh(dppb)2 and [HRh(dppb)2(NCCH3)](BF4)2 (where dppb is 1,2-(bis(diphenylphosphino)benzene) have been prepared, and a structural study of [HRh-(dppb)2(NCCH3)](BF4)2 has been completed. The latter complex is an octahedral complex with a trans arrangement of the hydride and acetonitrile ligands. A pKa value of 9.4 was measured for this complex by equilibration of [Rh(dppb)2](BF4) with 4-bromoanilinium tetrafluoroborate in acetonitrile. [Rh(dppb)2](BF4) reacts with H2 in the presence of Pt(dmpp)2, which acts as a base, to form HRh(dppb)2 and [HPt(dmpp)2](BF4) (where dmpp = 1,2-bis-(dimethylphosphino)propane). An equilibrium constant of 0.42 ± 0.2 was measured for this reaction. Using this equilibrium measurement and a thermodynamic cycle, the hydride donor ability (δG°H-H-) of HRh(dppb)2 was determined to be 34 kcal/mol. This value indicates that HRh(diphosphine)2 complexes are powerful hydride donors. Similarly the pKa value of HRh-(dppb)2 was calculated to be 35 from a thermodynamic cycle that included the potential of the Rh(I/-I) couple (E1/2 = -2.02 V vs ferrocene). These results combined with results from the literature suggest the following order of hydricity for five-coordinate, 18-electron hydrides: second row > third row > first row. Similarly an acidity order of second row ≥ first row > third row is deduced.

Original languageEnglish
Pages (from-to)4833-4839
Number of pages7
JournalOrganometallics
Volume21
Issue number22
DOIs
Publication statusPublished - Oct 28 2002

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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    Price, A. J., Ciancanelli, R., Noll, B. C., Curtis, C. J., DuBois, D. L., & Rakowski DuBois, M. (2002). HRh(dppb)2, a powerful hydride donor. Organometallics, 21(22), 4833-4839. https://doi.org/10.1021/om020421k