Thermodynamic Studies of HRh(depx) 2 and [(H) 2Rh(depx) 2](CF 3so 3)

Relationships between Five-Coordinate Monohydrides and Six-Coordinate Dihydrides

James W. Raebiger, Daniel L DuBois

Research output: Contribution to journalArticle

45 Citations (Scopus)

Abstract

Four new rhodium complexes, [Rh(depx) 2](CF 3SO 3), [(H) 2Rh(depx) 2](CF 3SO 3), [HRh(depx) 2(CH 3CN)](CF 3SO 3) 2, and HRh(depx) 2 (where depx = α,α′-bis(diethylphosphino)xylene), have been synthesized and characterized. The pK a values of [(H) 2Rh(depx) 2] + (30.6 ± 0.3) and [HRh(depx) 2(CH 3CN)] 2+ (11.5 ± 0.4) in acetonitrile were determined by equilibrium reactions with appropriate bases. The hydride donor ability of [(H) 2Rh(depx) 2] + (71.6 ± 1.0 kcal/mol) was determined by the heterolytic cleavage of hydrogen by [HRh(depx) 2(CH 3CN)] 2+ to form [(H) 2Rh(depx) 2] + in the presence of thioacetamide or benzamide. These equilibrium measurements, the half-wave potentials for the Rh(+l/0) and Kh(0/-l) couples of [Rh(depx) 2] +, and the reversible one-electron oxidation of HRh(depx) 2 (all measured at 22 ± 1.5 °C) were used to establish nine heterolytic and homolytic bond-dissociation free energies in acetonitrile. From these relationships, and those established previously for analogous cobalt and platinum complexes, we conclude that the homolytic bond-dissociation free energies of six-coordinate dihydride species are approximately 2 kcal/mol less than those of the corresponding five-coordinate monohydride species derived by deprotonation. Similarly, the pK a values of six-coordinate dihydride complexes are approximately 2 units lower than the corresponding five-coordinate species formally derived by homolytic bond cleavage.

Original languageEnglish
Pages (from-to)110-118
Number of pages9
JournalOrganometallics
Volume24
Issue number1
DOIs
Publication statusPublished - Jan 3 2005

Fingerprint

dihydrides
Free energy
Thermodynamics
Thioacetamide
Xylenes
thermodynamics
Rhodium
Deprotonation
methylidyne
Cobalt
Platinum
Hydrides
acetonitrile
cleavage
Hydrogen
free energy
dissociation
Oxidation
Electrons
xylene

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

@article{d3c4922c1cec4b91a6cf13725d10cffb,
title = "Thermodynamic Studies of HRh(depx) 2 and [(H) 2Rh(depx) 2](CF 3so 3): Relationships between Five-Coordinate Monohydrides and Six-Coordinate Dihydrides",
abstract = "Four new rhodium complexes, [Rh(depx) 2](CF 3SO 3), [(H) 2Rh(depx) 2](CF 3SO 3), [HRh(depx) 2(CH 3CN)](CF 3SO 3) 2, and HRh(depx) 2 (where depx = α,α′-bis(diethylphosphino)xylene), have been synthesized and characterized. The pK a values of [(H) 2Rh(depx) 2] + (30.6 ± 0.3) and [HRh(depx) 2(CH 3CN)] 2+ (11.5 ± 0.4) in acetonitrile were determined by equilibrium reactions with appropriate bases. The hydride donor ability of [(H) 2Rh(depx) 2] + (71.6 ± 1.0 kcal/mol) was determined by the heterolytic cleavage of hydrogen by [HRh(depx) 2(CH 3CN)] 2+ to form [(H) 2Rh(depx) 2] + in the presence of thioacetamide or benzamide. These equilibrium measurements, the half-wave potentials for the Rh(+l/0) and Kh(0/-l) couples of [Rh(depx) 2] +, and the reversible one-electron oxidation of HRh(depx) 2 (all measured at 22 ± 1.5 °C) were used to establish nine heterolytic and homolytic bond-dissociation free energies in acetonitrile. From these relationships, and those established previously for analogous cobalt and platinum complexes, we conclude that the homolytic bond-dissociation free energies of six-coordinate dihydride species are approximately 2 kcal/mol less than those of the corresponding five-coordinate monohydride species derived by deprotonation. Similarly, the pK a values of six-coordinate dihydride complexes are approximately 2 units lower than the corresponding five-coordinate species formally derived by homolytic bond cleavage.",
author = "Raebiger, {James W.} and DuBois, {Daniel L}",
year = "2005",
month = "1",
day = "3",
doi = "10.1021/om049437w",
language = "English",
volume = "24",
pages = "110--118",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "1",

}

TY - JOUR

T1 - Thermodynamic Studies of HRh(depx) 2 and [(H) 2Rh(depx) 2](CF 3so 3)

T2 - Relationships between Five-Coordinate Monohydrides and Six-Coordinate Dihydrides

AU - Raebiger, James W.

AU - DuBois, Daniel L

PY - 2005/1/3

Y1 - 2005/1/3

N2 - Four new rhodium complexes, [Rh(depx) 2](CF 3SO 3), [(H) 2Rh(depx) 2](CF 3SO 3), [HRh(depx) 2(CH 3CN)](CF 3SO 3) 2, and HRh(depx) 2 (where depx = α,α′-bis(diethylphosphino)xylene), have been synthesized and characterized. The pK a values of [(H) 2Rh(depx) 2] + (30.6 ± 0.3) and [HRh(depx) 2(CH 3CN)] 2+ (11.5 ± 0.4) in acetonitrile were determined by equilibrium reactions with appropriate bases. The hydride donor ability of [(H) 2Rh(depx) 2] + (71.6 ± 1.0 kcal/mol) was determined by the heterolytic cleavage of hydrogen by [HRh(depx) 2(CH 3CN)] 2+ to form [(H) 2Rh(depx) 2] + in the presence of thioacetamide or benzamide. These equilibrium measurements, the half-wave potentials for the Rh(+l/0) and Kh(0/-l) couples of [Rh(depx) 2] +, and the reversible one-electron oxidation of HRh(depx) 2 (all measured at 22 ± 1.5 °C) were used to establish nine heterolytic and homolytic bond-dissociation free energies in acetonitrile. From these relationships, and those established previously for analogous cobalt and platinum complexes, we conclude that the homolytic bond-dissociation free energies of six-coordinate dihydride species are approximately 2 kcal/mol less than those of the corresponding five-coordinate monohydride species derived by deprotonation. Similarly, the pK a values of six-coordinate dihydride complexes are approximately 2 units lower than the corresponding five-coordinate species formally derived by homolytic bond cleavage.

AB - Four new rhodium complexes, [Rh(depx) 2](CF 3SO 3), [(H) 2Rh(depx) 2](CF 3SO 3), [HRh(depx) 2(CH 3CN)](CF 3SO 3) 2, and HRh(depx) 2 (where depx = α,α′-bis(diethylphosphino)xylene), have been synthesized and characterized. The pK a values of [(H) 2Rh(depx) 2] + (30.6 ± 0.3) and [HRh(depx) 2(CH 3CN)] 2+ (11.5 ± 0.4) in acetonitrile were determined by equilibrium reactions with appropriate bases. The hydride donor ability of [(H) 2Rh(depx) 2] + (71.6 ± 1.0 kcal/mol) was determined by the heterolytic cleavage of hydrogen by [HRh(depx) 2(CH 3CN)] 2+ to form [(H) 2Rh(depx) 2] + in the presence of thioacetamide or benzamide. These equilibrium measurements, the half-wave potentials for the Rh(+l/0) and Kh(0/-l) couples of [Rh(depx) 2] +, and the reversible one-electron oxidation of HRh(depx) 2 (all measured at 22 ± 1.5 °C) were used to establish nine heterolytic and homolytic bond-dissociation free energies in acetonitrile. From these relationships, and those established previously for analogous cobalt and platinum complexes, we conclude that the homolytic bond-dissociation free energies of six-coordinate dihydride species are approximately 2 kcal/mol less than those of the corresponding five-coordinate monohydride species derived by deprotonation. Similarly, the pK a values of six-coordinate dihydride complexes are approximately 2 units lower than the corresponding five-coordinate species formally derived by homolytic bond cleavage.

UR - http://www.scopus.com/inward/record.url?scp=12344323448&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=12344323448&partnerID=8YFLogxK

U2 - 10.1021/om049437w

DO - 10.1021/om049437w

M3 - Article

VL - 24

SP - 110

EP - 118

JO - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 1

ER -