20 research outputs found
Unprecedented inequivalent metal coordination environments in a mixed-ligand dicobalt complex
Bimetallic complexes of the transition metals containing mixed diimine and dithiolate ligands are of fundamental interest on account of their intriguing electronic properties. Almost always, such complexes are isolated as species in which both the metal centers are in identical coordination environments - this means that the two metals often have identical redox properties. In contrast, mixed-diimine/dithiolate bimetallic complexes of the first row transition metals where the two metals are in dissimilar coordination environments are exceedingly rare, and are only known for nickel. Herein, we report the first ever example of a mixed-diimine/dithiolate dicobalt complex where the two cobalt centers are in different coordination environments. The synthesis of this compound is straightforward, and produces a complex in which the two cobalt centers display very different redox properties
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The activation of N-heterocyclic thiols and disulfides by Group VI organometallic complexes: A kinetic and thermodynamic study
The reaction of 2,2\u27-pyridine disulfide (2-mpd) and 2-mercaptopyridine (2-pyridine thione, H-2mp) with Group VI (Cr, Mo, and W) L3M(CO)3 complexes were studied in comparison to their phenyl analogues: phenyl disulfide and thiophenol. Where L = Py or 1/3 CHPT (CHPT = cycloheptatriene), 18-electron complexes of the type (CHPT)M(CO) 3 or (Py)3M(CO)3 showed oxidative addition of the disulfide bond of 2-mpd to form chelated complexes Cr(eta2-2mp) 3, [(eta2-2mp)Mo(eta2,mu- S-2mp)(CO)]2, and (eta2-2mp)2W(CO) 3. Synthesis and crystal structures of all 3 products are reported. The 7-coordinate W(II) complex (eta2-2mp)2W(CO) 3 undergoes further oxidative addition with additional 2-mpd yielding W(eta2-2mp)4. Whilst the reaction of (eta 2-2mp)2W(CO)3 with •NO forms solely (eta 2-2mp)2W(NO)2, the reaction of (eta 2-2mp)2W(CO)3 with 2-mpd in the presence of •NO yields a mixture of (eta2-2mp)3W(NO) and (eta2-2mp)2W(NO)2, the crystal structures of which are reported. The rate of nitrosylation of (eta 2-2mp)2W(CO)3 was found to be within the rate of substitution with P(Ph2Me), which forms the complex (eta 2-2mp)2W(CO)2(PPh2Me) as characterized by X-ray diffraction.With two moles of the 17-electron organometallic radical •Cr(CO) 3Cp* (where Cp* = C5Me5), 2-Pyridine thione undergoes rapid oxidative addition yielding hydride H-Cr(CO)3Cp* and thiolate (eta1-2mp)Cr(CO)3Cp*.Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with •Cr(CO) 3Cp* in CH2Cl2 also follows second-order kinetics and occurs 2--4 times more rapidly than that of H-2mp under the same conditions.Finally, reaction of the unsaturated 16-electron complex (PiPr 3)2W(CO)3 (referred to as iprW k) with H-2mp in toluene almost instantaneously forms the complex iprWk(H-2mp). This adduct undergoes slow, first-order oxidative addition to yield the W(II) thiolate iprWk(H)(2mp): rate = k[iprWk] where k (288 K) = 3.22 x 10 -5 s-1; DeltaH⁁ = +25.7 kcal/mol, DeltaS⁁ = +10.7 cal/mol K.The gas phase and solvent dependent preference of the tautomerization between 2-pyridine thiol and 2-pyridine thione was assessed using variable temperature FTIR experiments and 1H NMR spectroscopy. (Abstract shortened by UMI.
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Dinuclear oxidative addition of N-H and S-H bonds at chromium. Reaction of ()Cr(CO)(3)(C(5)Me(5)) with [o-(HA)C(6)H(4)S-Cr(CO)(3)(C(5)Me(5))] (A = S, NH) yielding [eta(2)-o-(mu-A)C(6)H(4)S-Cr(C(5)Me(5))](2) and H-Cr(CO)(3)(C(5)Me(5))
Reaction of the 17-electron radical (*)Cr(CO)(3)Cp* (Cp* = C(5)Me(5)) with 0.5 equiv of 2-aminophenyl disulfide [(o-H(2)NC(6)H(4))(2)S(2)] results in rapid oxidative addition to form the initial product (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp*. Addition of a second equivalent of (*)Cr(CO)(3)Cp* to this solution results in the formation of H-Cr(CO)(3)Cp* as well as (1)/(2)[[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2). Spectroscopic data show that (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp* loses CO to form [eta(2)-(o-H(2)N)C(6)H(4)S]Cr(CO)(2)Cp*. Attack on the N-H bond of the coordinated amine by (*)Cr(CO)(3)Cp* provides a reasonable mechanism consistent with the observation that both chelate formation and oxidative addition of the N-H bond are faster under argon than under CO atmosphere. The N-H bonds of uncoordinated aniline do not react with (*)Cr(CO)(3)Cp*. Reaction of the 2 mol of (*)Cr(CO)(3)Cp* with 1,2-benzene dithiol [1,2-C(6)H(4)(SH)(2)] yields the initial product (o-HS)C(6)H(4)S-Cr(CO)(3)Cp and 1 mol of H-Cr(CO)(3)Cp*. Addition of 1 equiv more of (*)Cr(CO)(3)Cp to this solution also results in the formation of 1 equiv of H-Cr(CO)(3)Cp*, as well as the dimeric product (1)/(2)[[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2). This reaction also occurs more rapidly under Ar than under CO, consistent with intramolecular coordination of the second thiol group prior to oxidative addition. The crystal structures of [[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2) and [[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2) are reported
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Synthesis and Structure of W(η2-mp)2(CO)3 (mp = Monoanion of 2-Mercaptopyridine) and Its Reactions with 2,2‘-Pyridine Disulfide and/or NO To Yield W(η2-mp)4, W(η2-mp)2(NO)2, and W(η2-mp)3(NO)
Oxidative addition of the sulfur−sulfur bond of 2,2‘-pyridine disulfide (C5H4NS−SC5H4N) with L3W(CO)3 [L = pyridine, 1/3CHPT; CHPT = cycloheptatriene] in methylene chloride solution yields the seven-coordinate W(II) thiolate complex W(η2-mp)2(CO)3 (mp = monoanion of 2-mercaptopyridine). This complex undergoes slow further oxidative addition with additional pyridine disulfide, yielding W(η2- mp)4. Reaction of W(η2-mp)2(CO)3 with NO results in quantitative formation of the six-coordinate W(0) complex W(η2-mp)2(NO)2. Reaction of W(η2-mp)2(CO)3 with NO in the presence of added pyridine disulfide yields the seven-coordinate W(II) nitrosyl complex W(η2-mp)3(NO) as well as W(η2-mp)2(NO)2 and trace amounts of W(η2-mp)4. The complex W(η2-mp)3(NO) is formed during the course of the reaction and not by reaction of W(η2-mp)4 or W(η2-mp)2(NO)2 with NO under these conditions. The crystal structures of W(η2- mp)2(CO)3, W(η2-mp)2(NO)2, and W(η2-mp)3(NO) are reported
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Increased Reactivity of the •Cr(CO)3(C5Me5) Radical with Thiones versus Thiols:  A Theoretical and Experimental Investigation
2-Pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical •Cr(CO)3Cp* (where Cp* = C5Me5), 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 = k obs[H-2mp][•Cr]; k obs(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 (k D/k H = 1.06 ± 0.10). The rate of decarbonylation of (η1-2mp)Cr(CO)3Cp* forming (η2-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with k obs (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 CH2Cl2 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, [•(SC5H4NH)Cr(CO)3Cp*] versus [•(HSC6H5)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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2-Pyridinethiol/2-pyridinethione tautomeric equilibrium. A comparative experimental and computational study
The gas phase and solvent dependent preference of the tautomerization between 2-pyridinethiol (2SH) and 2-pyridinethione (2S) has been assessed using variable temperature Fourier transform infrared (FTIR) experiments, as well as ab initio and density functional theory computations. No spectroscopic evidence (nu(S)(-)(H) stretch) for 2SH was observed in toluene, C(6)D(6), heptane, or methylene chloride solutions. Although, C(s)() 2SH is 2.61 kcal/mol more stable than C(s)() 2S (CCSD(T)/cc-pVTZ//B3LYP/6-311+G(3df,2p)+ZPE), cyclohexane solvent-field relative energies (IPCM-MP2/6-311+G(3df,2p)) favor 2S by 1.96 kcal/mol. This is in accord with the FTIR observations and in quantitative agreement with the -2.6 kcal/mol solution (toluene or C(6)D(6)) calorimetric enthalpy for the 2S/2SH tautomerization favoring the thione. As the intramolecular transition state for the 2S, 2SH tautomerization (2TS) lies 25 (CBS-Q) to 30 kcal/mol (CCSD/cc-pVTZ) higher in energy than either tautomer, tautomerization probably occurs in the hydrogen bonded dimer. The B3LYP/6-311+G(3df,2p) optimized C(2) 2SH dimer is 10.23 kcal/mol + ZPE higher in energy than the C(2)(h)() 2S dimer and is only 2.95 kcal/mol + ZPE lower in energy than the C(2) 2TS dimer transition state. Dimerization equilibrium measurements (FTIR, C(6)D(6)) over the temperature range 22-63 degrees C agree: K(eq)(298) = 165 +/- 40 M(-)(1), DeltaH = -7.0 +/- 0.7 kcal/mol, and DeltaS = -13.4 +/- 3.0 cal/(mol deg). The difference between experimental and B3LYP/6-311+G(3df,2p) [-34.62 cal/(mol deg)] entropy changes is due to solvent effects. The B3LYP/6-311+G(3df,2p) nucleus independent chemical shifts (NICS) are -8.8 and -3.5 ppm 1 A above the 2SH and 2S ring centers, respectively, and the thiol is aromatic. Although the thione is not aromatic, it is stabilized by the thioamide resonance. In solvent, the large 2S dipole, 2-3 times greater than 2SH, favors the thione tautomer and, in conclusion, 2S is thermodynamically more stable than 2SH in solution