The enthalpies of reaction of neat PBu 3 with solid sulfur (-27.1 ( 0.5 kcal/mol), selenium (-20.0 ( 0.6 kcal/ mol), and tellurium (-4.9 ( 0.6 kcal/mol) have been measured by solution calorimetry. The enthalpies of reaction of a series of phosphines with sulfur in toluene solution have been measured as follows (values in kcal/mol): PCy 3 ) -30.9 ( 1.9, PBu 3 ) -28.9 ( 0.3, PMe 3 ) -27.1 ( 0.4, PMe 2 Ph ) -26.0 ( 0.5, PMePh 2 ) -23.8 ( 0.3, PPh 3 ) -21.5 ( 0.3. These values correlate with literature data for enthalpies of protonation and indicate that P to S σ donation is probably the dominant factor in determining the R 3 PdS bond strength, estimates for which range from 88 to 98 kcal/mol. The enthalpies of S atom transfer to PPh 3 by SdAsPPh 3 and SdSbPh 3 in toluene solution are -17.7 ( 1.2 and -21.5 ( 1.0 kcal/mol, respectively. The enthalpy of removal of the central S atom from BzSSSBz by PCy 3 , yielding BzSSBz and SdPCy 3 , is -29.0 ( 1.8 kcal/mol. These data are used to establish a range of enthalpies of S atom transfer in these compounds which spans 31 kcal/mol from SdSbPPh 3 to SdPCy 3 .
Reaction of (RNC)AuCl [R ) tert-butyl (1a), mesityl (1b)] with sodium thiosalicylate in the two-phase system water/dichloromethane gives high yields of the corresponding (isocyanide)gold(I) thiosalicylates (2a,b). The solid-state structures of 2a,b have been determined by X-ray diffraction studies. The supramolecular structure of both compounds is governed by Å; 2b, Au--Au 3.3186( 5) Å] and hydrogen bonding through the carboxylic acid groups.
Hydrogen adds reversibly to the chromium-chromium bond of FvCr 2 (CO) 6 yielding FvCr 2 (CO) 6 (H) 2 (Fv ) fulvalene). Equilibrium data for this process have been measured in toluene and deuteriobenzene in the temperature range 50-80 °C and pressures up to 72 atm H 2 [∆H°) -1.0(0.4) kcal/mol, ∆S°) -14.0(2.0) cal/mol deg]. These data are used to estimate the enthalpy [16.5 (2.0) kcal/mol] and entropy (11 cal/mol deg) for breaking the Cr-Cr bond in FvCr 2 (CO) 6 . A theoretical calculation of the isodesmic process FvCr 2 (CO) 6 (H) 2 + [η 5 -C 5 H 5 Cr-(CO) 3 ] 2 f FvCr 2 (CO) 6 + 2 η 5 -C 5 H 5 Cr(CO) 3 H predicts it to have an enthalpy of -1.74 kcal/mol, very close to the experimental value of -2 kcal/mol. Thus, and assuming that the individual Cr-H bonds in FvCr 2 (CO) 6 (H) 2 and η 5 -C 5 H 5 Cr(CO) 3 H are equal, these results lead to the conclusion that the metal-metal bond in the fulvalene system is 2 ( 2 kcal/mol stronger than that in [η 5 -C 5 H 5 Cr(CO) 3 ] 2 , despite the greater Cr-Cr bond length in the former. This result is also in accord with the measured enthalpy of reaction [FvCr 2 (CO) 6 ] 2-(Na + ) 2 + [η 5 -C 5 H 5 -Cr(CO) 3 ] 2 f FvCr 2 (CO) 6 + 2 [η 5 -C 5 H 5 Cr(CO) 3 ] -Na + , ∆H ) -2.4(0.4) kcal/mol. Deuterium was found to add to FvCr 2 (CO) 6 with a normal equilibrium isotope effect: K eq (H 2 )/K eq (D 2 ) ) 1.45(0.10). A kinetic study of reductive elimination of H 2 in the temperature range 45-75 °C shows that it obeys first-order kinetics: [k -1 45.5 ) 1.0 × 10 -5 s -1 , ∆H q ) 27.8(2.0) kcal/mol, ∆S q ) 5.6(3.0) cal/mol deg]. Similarly, the oxidative addition reaction reveals first-order behavior in both FvCr 2 (CO) 6 and H 2 [∆H q ) 26.8(2.5) kcal/mol, ∆S q ) -19.6 (6.0) cal/mol deg]. The obtained combined kinetic data are in reasonable agreement with the measured equilibrium constant. The rate of hydrogenation under 60 atm of H 2 is not retarded by addition of 15 atm of CO, arguing against a transition state involving CO loss. Studies of the rate of oxidative addition/reductive elimination of D 2 suggest a late transition state for the former which involves cleavage of the D-D (H-H) bond. Substitution of 12 CO in FvCr 2 ( 12 CO) 6 by 13 CO occurs 1-2 orders of magnitude faster than does hydrogenation [k 1 43.7 ) 5.6 × 10 -6 s -1 atm -1 , ∆H q ) 16.7(1.5) kcal/mol, ∆S q ) -30.0(4.0) cal/mol deg] but is much slower than in analogous complexes [η 5 -C 5 R 5 Cr(CO) 3 ] 2 (R ) H, Me). The crystal structure of [FvCr 2 (CO) 6 ] 2-(Na + ) 2 is reported.
Maleic and phthalic acids are found to react with Be(OH)(2), generated in situ from BeSO(4)(aq) and Ba(OH)(2)(aq), in aqueous solution at pH 3.0 or 4.4, respectively (25 degrees C), to give solutions containing the complexes (H(2)O)(2)Be[(OOCCH)(2)] (1) and (H(2)O)(2)Be[(OOC)(2)C(6)H(4)] (3). The products can be isolated in high yield and identified by microanalytical data. With 2 equiv of the dicarboxylic acids and the pH adjusted to 5.5 and 5.9, respectively, by addition of ammonia, the bis-chelate complexes [(NH(4))(+)](2){[Be[(OOCCH)(2)](2)}(2)(-) (2) and [(NH(4))(+)](2){Be[(OOC)(2)C(6)H(4)](2)}(2)(-) (4) are obtained, which can also be isolated. The compounds show distinct (9)Be, (1)H, and (13)C resonances in their NMR spectra in aqueous solutions. Layering of an aqueous solution of compound 4 with acetone at ambient temperature leads to the precipitation of single crystals suitable for an X-ray structure determination. This salt (5) was found to contain the bis-chelated dianion {Be[(OOC)(2)C(6)H(4)](2)}(2)(-) with the beryllium atom in the spiro center of two seven-membered rings and an overall geometry approaching closely C(2) symmetry. These anions are associated with two crystallographically independent but structurally similar counterions [MeC(O)CH(2)CMe(2)NH(3)](+), which are the product of a condensation reaction of the ammonium cation with the acetone solvent. In the crystal the ammonium hydrogen atoms of the cations form N-H.O hydrogen bonds with the oxo functions of the dianion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.