Periodic trends in metal hydride donor thermodynamics

Measurement and comparison of the hydride donor abilities of the series HM(PNP)2 + (M = Ni, Pd, Pt; PNP = Et2PCH2N(Me)CH2PEt2)

Calvin J. Curtis, Alex Miedaner, James W. Raebiger, Daniel L DuBois

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Abstract

The complexes M(PNP)2 2+ (M = Pd, Pt, PNP = Et2PCH2N(Me)CH2PEt2) were synthesized by addition of PNP to Pd(CH3CN)4(BF4)2 and (COD)PtCl2, respectively. Pd(PNP)2 was synthesized by reaction of Pd(PNP)2 2+ with H2 and tetramethylguanidine (TMG) in CH3-CN. The thermodynamic hydride donor ability, ΔG°H -, for HPt(PNP)2 + (54.7 kcal/mol) was measured by heterolytic cleavage of hydrogen in the presence of NEt3 in CH3CN. The hydride donor ability of HPd(PNP)2 + (51.1 kcal/mol) was determined by measuring the equilibrium constant for direct hydride transfer to Pt(PNP)2 2+. The M(II) complexes undergo reversible, two-electron reductions in benzonitrile. The measured reduction potentials were used in a thermodynamic cycle to estimate pKa values of 22.1 and 27.6 for deprotonation of HPd-(PNP)2 + and HPt(PNP)2 +, respectively. The palladium hydride has an acidity equal to that of the nickel hydride and is a better hydride donor than both the nickel and platinum analogues. This shows that it is possible for transition metal hydrides to act simultaneously as both acids and hydride donors.

Original languageEnglish
Pages (from-to)511-516
Number of pages6
JournalOrganometallics
Volume23
Issue number3
DOIs
Publication statusPublished - Feb 2 2004

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metal hydrides
Hydrides
hydrides
Metals
Thermodynamics
trends
thermodynamics
Nickel
nickel
thermodynamic cycles
Deprotonation
crack opening displacement
Equilibrium constants
Platinum
Acidity
acidity
Transition metals
palladium
cleavage
Hydrogen

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

Periodic trends in metal hydride donor thermodynamics : Measurement and comparison of the hydride donor abilities of the series HM(PNP)2 + (M = Ni, Pd, Pt; PNP = Et2PCH2N(Me)CH2PEt2). / Curtis, Calvin J.; Miedaner, Alex; Raebiger, James W.; DuBois, Daniel L.

In: Organometallics, Vol. 23, No. 3, 02.02.2004, p. 511-516.

Research output: Contribution to journalArticle

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AB - The complexes M(PNP)2 2+ (M = Pd, Pt, PNP = Et2PCH2N(Me)CH2PEt2) were synthesized by addition of PNP to Pd(CH3CN)4(BF4)2 and (COD)PtCl2, respectively. Pd(PNP)2 was synthesized by reaction of Pd(PNP)2 2+ with H2 and tetramethylguanidine (TMG) in CH3-CN. The thermodynamic hydride donor ability, ΔG°H -, for HPt(PNP)2 + (54.7 kcal/mol) was measured by heterolytic cleavage of hydrogen in the presence of NEt3 in CH3CN. The hydride donor ability of HPd(PNP)2 + (51.1 kcal/mol) was determined by measuring the equilibrium constant for direct hydride transfer to Pt(PNP)2 2+. The M(II) complexes undergo reversible, two-electron reductions in benzonitrile. The measured reduction potentials were used in a thermodynamic cycle to estimate pKa values of 22.1 and 27.6 for deprotonation of HPd-(PNP)2 + and HPt(PNP)2 +, respectively. The palladium hydride has an acidity equal to that of the nickel hydride and is a better hydride donor than both the nickel and platinum analogues. This shows that it is possible for transition metal hydrides to act simultaneously as both acids and hydride donors.

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