Increased Reactivity of the .Cr(CO)3(C 5Me5) Radical with Thiones Versus Thiols: A Theoretical and Experimental Investigation

Kengkaj Sukcharoenphon, Damian Moran, Paul V R Schleyer, James E. McDonough, Khalil A. Abboud, Carl Hoff

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

2-Pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical .Cr(CO)3Cp* (where Cp* = C5Me 5), yielding hydride H-Cr(CO)3Cp* and thiolate (η1-2mp)Cr(CO)3CP*. In a slower secondary reaction, (η1-2mp)Cr(CO)3CP* loses CO generating the N,S-chelate complex (η2-2mp)Cr(CO) 2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with .Cr(CO) 3Cp* (abbreviated .Cr) in toluene best fits rate = kobs[H-2mp][.Cr]; kobs(288 K) = 22 ± 4 M-1 s-1; ΔH‡ = 4 ± 1 kcal/mol; ΔS‡= - 40 ± 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH = 1.06 ± 0.10). The rate of decarbonylation of (η 1-2mp)Cr(CO)3Cp* forming (η 2)-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K) = 3.1 × 10-4 s-1, ΔH‡ = 23 ± 1 kcal/mol, and ΔS‡ = + 5.0 ± 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with .Cr(CO)3Cp* in THF and CH2Cl 2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [.(S=C5H 4N-H)Cr(CO)3Cp*] versus [.(H-S-C 6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H. radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by ≈30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H. to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H. or HS. without barrier.

Original languageEnglish
Pages (from-to)8494-8503
Number of pages10
JournalInorganic Chemistry
Volume42
Issue number25
DOIs
StatePublished - Dec 15 2003

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Thiones
Carbon Monoxide
Sulfhydryl Compounds
thiols
reactivity
pyridines
disulfides
kinetics
sulfur
Sulfur
Disulfides
tautomers
Kinetics
chelates
isotope effect
attack
hydrides
atoms
toluene
electrons

ASJC Scopus subject areas

  • Inorganic Chemistry

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Increased Reactivity of the .Cr(CO)3(C 5Me5) Radical with Thiones Versus Thiols : A Theoretical and Experimental Investigation. / Sukcharoenphon, Kengkaj; Moran, Damian; Schleyer, Paul V R; McDonough, James E.; Abboud, Khalil A.; Hoff, Carl.

In: Inorganic Chemistry, Vol. 42, No. 25, 15.12.2003, p. 8494-8503.

Research output: Contribution to journalArticle

Sukcharoenphon, Kengkaj ; Moran, Damian ; Schleyer, Paul V R ; McDonough, James E. ; Abboud, Khalil A. ; Hoff, Carl. / Increased Reactivity of the .Cr(CO)3(C 5Me5) Radical with Thiones Versus Thiols : A Theoretical and Experimental Investigation. In: Inorganic Chemistry. 2003 ; Vol. 42, No. 25. pp. 8494-8503.
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abstract = "2-Pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical .Cr(CO)3Cp* (where Cp* = C5Me 5), yielding hydride H-Cr(CO)3Cp* and thiolate (η1-2mp)Cr(CO)3CP*. In a slower secondary reaction, (η1-2mp)Cr(CO)3CP* loses CO generating the N,S-chelate complex (η2-2mp)Cr(CO) 2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with .Cr(CO) 3Cp* (abbreviated .Cr) in toluene best fits rate = kobs[H-2mp][.Cr]; kobs(288 K) = 22 ± 4 M-1 s-1; ΔH‡ = 4 ± 1 kcal/mol; ΔS‡= - 40 ± 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH = 1.06 ± 0.10). The rate of decarbonylation of (η 1-2mp)Cr(CO)3Cp* forming (η 2)-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K) = 3.1 × 10-4 s-1, ΔH‡ = 23 ± 1 kcal/mol, and ΔS‡ = + 5.0 ± 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with .Cr(CO)3Cp* in THF and CH2Cl 2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [.(S=C5H 4N-H)Cr(CO)3Cp*] versus [.(H-S-C 6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H. radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by ≈30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H. to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H. or HS. without barrier.",
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TY - JOUR

T1 - Increased Reactivity of the .Cr(CO)3(C 5Me5) Radical with Thiones Versus Thiols

T2 - A Theoretical and Experimental Investigation

AU - Sukcharoenphon, Kengkaj

AU - Moran, Damian

AU - Schleyer, Paul V R

AU - McDonough, James E.

AU - Abboud, Khalil A.

AU - Hoff, Carl

PY - 2003/12/15

Y1 - 2003/12/15

N2 - 2-Pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical .Cr(CO)3Cp* (where Cp* = C5Me 5), yielding hydride H-Cr(CO)3Cp* and thiolate (η1-2mp)Cr(CO)3CP*. In a slower secondary reaction, (η1-2mp)Cr(CO)3CP* loses CO generating the N,S-chelate complex (η2-2mp)Cr(CO) 2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with .Cr(CO) 3Cp* (abbreviated .Cr) in toluene best fits rate = kobs[H-2mp][.Cr]; kobs(288 K) = 22 ± 4 M-1 s-1; ΔH‡ = 4 ± 1 kcal/mol; ΔS‡= - 40 ± 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH = 1.06 ± 0.10). The rate of decarbonylation of (η 1-2mp)Cr(CO)3Cp* forming (η 2)-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K) = 3.1 × 10-4 s-1, ΔH‡ = 23 ± 1 kcal/mol, and ΔS‡ = + 5.0 ± 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with .Cr(CO)3Cp* in THF and CH2Cl 2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [.(S=C5H 4N-H)Cr(CO)3Cp*] versus [.(H-S-C 6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H. radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by ≈30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H. to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H. or HS. without barrier.

AB - 2-Pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical .Cr(CO)3Cp* (where Cp* = C5Me 5), yielding hydride H-Cr(CO)3Cp* and thiolate (η1-2mp)Cr(CO)3CP*. In a slower secondary reaction, (η1-2mp)Cr(CO)3CP* loses CO generating the N,S-chelate complex (η2-2mp)Cr(CO) 2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with .Cr(CO) 3Cp* (abbreviated .Cr) in toluene best fits rate = kobs[H-2mp][.Cr]; kobs(288 K) = 22 ± 4 M-1 s-1; ΔH‡ = 4 ± 1 kcal/mol; ΔS‡= - 40 ± 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH = 1.06 ± 0.10). The rate of decarbonylation of (η 1-2mp)Cr(CO)3Cp* forming (η 2)-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K) = 3.1 × 10-4 s-1, ΔH‡ = 23 ± 1 kcal/mol, and ΔS‡ = + 5.0 ± 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with .Cr(CO)3Cp* in THF and CH2Cl 2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [.(S=C5H 4N-H)Cr(CO)3Cp*] versus [.(H-S-C 6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H. radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by ≈30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H. to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H. or HS. without barrier.

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