Bond Disruption Enthalpies Research Articles

Antioxidative and α-glucosidase inhibitory constituents of Polyscias guilfoylei: experimental and computational assessments.

Searching for bioactive agents from medicinal plants, eleven constituents were isolated from Polyscias guilfoylei stem for the first time, including a nucleoside uracil (1), two sterols β-sitosterol (2) and daucosterol (3), a saponin androseptoside A (4), two lignans (+)-pinoresinol (5) and (+)-syringaresinol (6), four phenolic acids protocatechuic acid (7), methyl protocatechuate (8), caffeic acid (9), and 5-O-caffeoylquinic acid (10), and a flavonoid quercitrin (11). Metabolites 1, 4, and 6-11 have never been observed in genus Polyscias before. Phenolic compounds 7 and 9 possessed the respective IC50 values of 21.33 and 13.88µg/mL in DPPH (2,2-diphenyl-1-picrylhydrazyl) antioxidative assay, as compared with that of the positive control resveratrol (IC50 = 13.21µg/mL). From density functional theory (DFT) calculated approach, the DPPH free radical scavenging capacity of two compounds 7 and 9 can be explained by the role of OH groups at carbons C-3 and C-4. Antioxidative actions of these two potential agents are followed HAT (H atom transfer) mechanism by OH bond disruption in gas, but SPLET (sequential proton loss electron transfer) mechanism in solvents water and methanol. Compared to 4-OH group, 3-OH group showed better bond disruption enthalpies and better kinetic energies since it reacted with HOO• and DPPH radicals. Sterols 2-3 and flavonoid 11 induced the IC50 values of < 2.0µg/mL better than the positive control acarbose (IC50 = 184.0µg/mL) in α-glucosidase inhibitory assay. Their interactions with human intestinal C- and N-terminal domains of α-glucosidase were explored using molecular docking study. The obtained results proved that compounds 2, 3, and 11 bind relatively stronger with the C-terminal domain than to the N-terminal domain through pivotal residues in the binding site and could be hypothesized as mixed inhibitors.

The Nature of Unsupported Uranium–Ruthenium Bonds: A Combined Experimental and Theoretical Study

Four new uranium-ruthenium complexes, [(Tren(TMS))URu(η(5)-C(5)H(5))(CO)(2)] (9), [(Tren(DMSB))URu(η(5)-C(5)H(5))(CO)(2)] (10), [(Ts(Tolyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (11), and [(Ts(Xylyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (12) [Tren(TMS)=N(CH(2)CH(2)NSiMe(3))(3); Tren(DMSB)=N(CH(2)CH(2)NSiMe(2)tBu)(3)]; Ts(Tolyl)=HC(SiMe(2)NC(6)H(4)-4-Me)(3); Ts(Xylyl)=HC(SiMe(2)NC(6)H(3)-3,5-Me(2))(3)], were prepared by a salt-elimination strategy. Structural, spectroscopic, and computational analyses of 9-12 shows: i) the formation of unsupported uranium-ruthenium bonds with no isocarbonyl linkages in the solid state; ii) ruthenium-carbonyl backbonding in the [Ru(η(5)-C(5)H(5))(CO)(2)](-) ions that is tempered by polarization of charge within the ruthenium fragments towards uranium; iii) closed-shell uranium-ruthenium interactions that can be classified as predominantly ionic with little covalent character. Comparison of the calculated U-Ru bond interaction energies (BIEs) of 9-12 with the BIE of [(η(5)-C(5)H(5))(3)URu(η(5)-C(5)H(5))(CO)(2)], for which an experimentally determined U-Ru bond disruption enthalpy (BDE) has been reported, suggests BDEs of approximately 150 kJ mol(-1) for 9-12.

Covalent Lanthanide Chemistry Near the Limit of Weak Bonding: Observation of (CpSiMe3)3Ce−ECp* and a Comprehensive Density Functional Theory Analysis of Cp3Ln−ECp (E = Al, Ga)

Experimental evidence for the existence of two new lanthanide-metalloligand adducts (CpSiMe(3))(3)Ce-ECp* (E = Al, Ga) is presented. Paramagnetic (1)H NMR titration experiments were employed to derive thermodynamic parameters for Ce-Ga dative bond formation, and competition experiments with the U analogue were performed. Density functional theory calculations were undertaken using model complexes Cp(3)Ln-ECp where Ln = La-Lu and E = Al, Ga. The Ln-E bond distances were predicted to decrease more sharply across the Ln series than those involving hard Lewis bases; however, local increases were observed at Eu and Yb. Electronic analyses were performed in the natural bond orbital-natural localized molecular orbital (NBO/NLMO) formalism, indicating that the E→Ln acceptor orbital is primarily of d character in all cases. The Cp(-) ligands donate significant electron density to the Ln d manifold and thus in its bonding interactions with a dative ligand the Ln center may be considered to be Ln(2+) in the f((n-3))d(1) electronic configuration (n = 3 for La, etc.). Molecular dipole moments, NLMO and natural population analyses, bond order indices, measures of E→Ln charge transfer, and calculated Ln-E heterolytic bond disruption enthalpies were found to follow saw-tooth trends, which correlate to varying degrees with the ionization potentials of the Ln(+) ions (corrected for their ground state-to-f((n-3))d(2) excitations). It is proposed that a steric-strain component which increases with the lanthanide contraction in this case balances the Ln-E bond stabilizing effect of core-orbital contraction. All data indicate that the Ln-E bonding interactions are predominantly of covalent or nonpolar donor-acceptor character. However, the formation of a strong covalent bond is not observed because of resistance to reduction of an effectively divalent Ln center.

Effect of Ancillary Ligation on the Relative Bond Disruption Enthalpies of Ru−H and Ru−Cl Bonds in Cp(PR3)2RuX (PR3= PMe3, PMe2Ph, PMePh2, PPh3; X = H, Cl)

The ruthenium chloride and hydride complexes Cp(PR3)(2)RuH {X = Cl; PR3 = PMe3 (1), PMe2Ph (2), PMePh2 (3), PPh3 (4); X = H; PR3 = PMe3 (5), PMe2Ph (6), PMePh2 (7), PPh3 (8)} were studied by spectroscopy and solution calorimetry. The structures of 2 and 3 are reported and complete the structural characterization of the series 1-4. In this series, the Ru-Cl distance (2.449 +/- 0.007 Angstrom) remains constant, while the Ru-PR3 distance increases in the order 1 6 > 7 > 8. Enthalpies of reaction for the hydride/chloride metatheses of 5-8 with chlorocarbons (CHCl3 or CCl4) were studied by solution calorimetry and allowed for the determination of Ru-Cl bond disruption enthalpies (BDEs) relative to the corresponding Ru-H BDEs. [BDE(Ru-Cl) - BDE(Ru-H)] values covered a 6 kcal/mol range with an average of 21.4 +/- 2.5 kcal/mol. The magnitude of [BDE(Ru-Cl) - BDE(Ru-H)] correlated with the number of methyl groups on the phosphine and was dependent on the electronic and steric properties of the phosphine.

Absolute Metal−Ligand σ Bond Enthalpies in Group 4 Metallocenes. A Thermochemical, Structural, Photoelectron Spectroscopic, and ab Initio Quantum Chemical Investigation

Absolute metal−ligand σ bond enthalpies have been determined for a series of titanocene, zirconocene, and hafnocene halides and dimethyls by iodinolytic titration calorimetry. Absolute metal−iodine bond disruption enthalpies were measured by iodination of the monomeric trivalent group 4 metallocenes Cptt2TiI, (Me5C5)2TiI, Cptt2ZrI, and Cptt2HfI (Cptt = η5-1,3-di-tert-butylcyclopentadienyl). Iodinolysis of Cptt2ZrMe2 and Cptt2HfMe2 in turn yields absolute Zr−Me and Hf−Me bond enthalpies. Derived values (kcal/mol) are D[Cptt2Ti(I)−I] = 40.6(5); D[(Me5C5)2Ti(I)−I] = 52.3(6); D[Cptt2Zr(I)−I] = 58.0(5); D[Cptt2Hf(I)−I] = 61.2(4); D̄[Cptt2Zr-Me2] = 43(1); and D̄[Cptt2Hf−Me2] = 47.6(9). That D[Cptt2Zr(I)−(I)] ≈ D(I3Zr−I) and D[(Me5C5)2Ti(I)−I] ≈ D(I3Ti−I), while D[Cptt2Ti(I)−I] ≈ D(I3Ti−I) − 12 kcal/mol, argues for more reliable transferability of D(MIV−I) in sterically less congested metallocenes. The molecular structures of Cp2ttZrI2, Cp2ttZrI, and Cp2ttHfI were determined by X-ray diffraction. In Cptt2ZrI2, the Zr ligation is pseudotetrahedral, and the ring tert-butyl groups “straddle” the Zr−I bonds to minimize steric interactions. The geometry about Zr in Cptt2ZrI is pseudotrigonal, with contracted Zr−ring centroid and Zr−I distances versus Cptt2ZrI2, primarily reflecting substantially diminished ligand−ligand repulsive nonbonded interactions in the latter. Cptt2HfI is isomorphous with Cptt2ZrI, and the slightly different metrical parameters are in accord with Hf vs Zr ionic radii. The significant differences in interligand repulsive interactions in the trivalent versus tetravalent complexes are confirmed by van der Waals calculations. High-resolution UV PE spectra combined with ab initio relativistic effective core potential calculations provide details of electronic structure. Absolute ionization energy values indicate that iodine behaves as both a strong σ and π donor. Trends in the large Cp2MXn structural database can be understood in terms of the interplay between electronic and molecular structure factors, which are highly sensitive to the substitution patterns of the cyclopentadienyl ligands and, in particular, to competing σ vs π M−X bonding.

DFT calculations of the binding energy of metallocenes

As recently reported by Klopper and Lüthi, there is a discrepancy between experiment and high-level quantum chemical calculations as to the value of the heterolytic metal–ligand bond disruption enthalpy of ferrocene. Indeed their ab initio calculations lead to a best estimate of 655 kcal/mol, whereas the experimental value is 635 kcal/mol. We report here results obtained using density functional theory. In addition to ferrocene, other metallocenes such as vanadocene, manganocene, nickelocene and ruthenocene, have also been investigated. Gradient-based corrections are crucial for a quantitative description of bond dissociation, our best estimate for ferrocene being 663 kcal/mol.

Organoruthenium Thermochemistry. Enthalpies of Reaction of Cp‘Ru(COD)Cl (Cp‘ = η5-C5H5 and η5-C5Me5) with Tertiary Phosphite Ligands

The enthalpies of reaction of Cp‘Ru(COD)Cl (Cp‘ = η5-C5H5 (Cp), η5-C5Me5 (Cp*); COD = cyclooctadiene) with a series of monodentate phosphite ligands, leading to the formation of Cp‘Ru(P(OR)3)2Cl, have been measured by anaerobic solution calorimetry in THF at 30 °C. The overall relative order of stability established for the preceding complexes is as follows: for the CpRu(P(OR)3)2Cl series, P(O-o-MeC6H4)3 < P(OC6H5)3 < P(OiPr)3 < P(OCH2)3CEt < P(OMe)3; for the Cp*Ru(P(OR)3)2Cl series, P(O-o-MeC6H4)3 < P(OC6H5)3 < P(OCH2)3CEt < P(OiPr)3 < P(OMe)3. Single-crystal diffraction studies were carried out on two members of the Cp*Ru(P(OR)3)2Cl series, P(OR)3 = P(OMe)3 and P(OR)3 = P(OCH2)3CEt (TMPP). Comparisons with other organometallic systems and insight into factors influencing the Ru−P(OR)3 bond disruption enthalpies are discussed.

Towards the accurate computation of properties of transition metal compounds: the binding energy of ferrocene

Recently published ab initio computations on ferrocene in the framework of coupled-cluster as well as multireference perturbation theory are exploited to obtain a theoretical best estimate of 655 ± 15 kcal/mol for the heterolytic bond disruption enthalpy. This best estimate was obtained by establishing the complete atomic orbitals basis set limit at the level of single-reference second-order perturbation theory, and computing corrections for relativistic effects, semicore (3s/3p) electron correlation effects, vibrational zero-point energy corrections, and structural relaxation energies of the fragments. Agreement with the experimental value of 635 ± 6 kcal/mol is unsatisfactory.

Solution Thermochemistry of Ligand Substitution Reactions Involving Organoruthenium Complexes

The solution thermochemistry of ruthenium-based organometallic complexes is outlined. Until recently, very little thermodynamic information was available concerning organogroup VIII systems. Bond enthalpy data for metal-hydride, metal-arene, metal-diene and metal-phosphine bonds have only recently been determined and will be presented and discussed in the following contribution. Developments in organometallic thermochemistry have demonstrated the considerable insight into bonding and reaction chemistry that metal-ligand bond disruption enthalpy data can provide. Such thermodynamic data will prove to be of fundamental importance to both theoretical and applied research in organometallic chemistry and catalysis.

Organoruthenium Thermochemistry. Absolute Metal-Ligand Bond Disruption Enthalpies in the (.eta.5-C5Me5)(CO)2Ru-X System (X = H, Cl, Br, I) and Thermodynamic Influences of Ancillary Ligand Variation on the Ru-X Bond Disruption Enthalpy

The enthalpies of reaction of (eta(5)-C(5)Me(5))(CO)(2)RU-H (1) With CCl4, CBr4, and CH3I leading to the formation of (eta(5)-C(5)Me(5))(CO)(2)Ru-X complexes (X = Cl, Br, I) have been measured by solution calorimetry in THF at 30 degrees C. On the basis of enthalpies of reaction and the recently reported Ru-H in (C5H5)Ru(CO)(2)H (65 +/- 1.0 kcal/mol), an absolute Ru-X bond disruption enthalpy (BDE) scale can be established for ruthenium halide complexes. The absolute BDE scale for ruthenium halide complexes, (eta(5)-C(5)Me(5))(CO)(2)RU-X, is as follows (X, kcal/mol): Cl, 80.7; Br, 61.1; and I, 55.6, respectively. These ruthenium BDE values can be directly compared with other metal-based systems and lead to a clearer understanding of general BDE trends in M-X systems. In addition, a number of enthalpies of reaction were measured involving organoruthenium hydride complexes with varied ancillary ligands in order to examine the ancillary ligand effects on the relative Ru-X bond enthalpies.

Metal-silicon bonding energetics in organo-Group 4 and organo—f-element complexes. Implications for bonding and reactivity

Metal-silicon bond disruption enthalpies have been measured for a series of U, Zr, and Sm metallocene complexes: Cp 3USi(TMS) 3, Cp 2Zr(Cl)Si(TMS) 3, Cp 2Zr(Me)Si(TMS) 3, Cp 2Zr(TMS)Si(TMS) 3, Cp 2Zr(TMS)O tBu, Cp′ 2SmSiH(TMS) 2 (Cp = η 5-C 5H 5, Cp′ = η 5-Me 5C 5, TMS = trimethylsilyl). Data were obtained by anaerobic batch-titration solution calorimetry in toluene. Derived metal-ligand bond enthalpies D(L n M-R) in kcal mol −1 are: D[Cp 3USi(TMS) 3] = 37(3), D[Cp 2(Cl)ZrSi(TMS) 3]=57(3), D[Cp 2(Me)ZrSi(TMS) 3]=56(5), D[Cp 2(Si(TMS) 3)ZrMe] = 66(5), D[Cp 2(O tBu)Zr-TMS] = 60(5), D[Cp 2(TMS)ZrSi(TMS) 3] = 42(11), D[Cp 2(Si(TMS) 3)Zr-TMS] = 45(7), D[Cp′ 2SmSiH(TMS) 2] = 43(5). These results show that metal-silicon bond disruption enthalpies involving these electron-deficient metals are substantially smaller than those of the corresponding metal hydride and hydrocarbyl bonds. These data in combination with previously measured metal-ligand bond enthalpies allow thermodynamic analyses of a variety of stoichiometric and catalytic transformations involving metal silyl functionalities. The latter include potential pathways for dehydrogenative silane polymerization, dehydrogenative silane-hydrocarbon coupling, olefin hydrosilylation, and dehydrogenative silane-amine coupling. It is not uncommon for there to be multiple pathways which effect the same catalytic transformation and which contain no steps having major enthalpic impediments.

Enthalpies of Reaction of (.eta.5-C5H5)Ru(cyclooctadiene)Cl with Tertiary Phosphine Ligands: Ligand Substitution as a Gauge for Metal Basicity and A Linear Correlation of Bond Length and Bond Enthalpy

The enthalpies of reaction of CpRu(COD)Cl (1) (Cp = eta(5)-C5H5; COD = cyclooctadiene) with a series of monodentate ligands, leading to the formation of CpRu(ER(3))(2)Cl (E = P, As), have been measured by anaerobic solution calorimetry in THF at 30.0 degrees C. These reactions are rapid and quantitatively lead to the formation of the corresponding CpRu(ER(3))(2)Cl complexes. The overall relative order of stability established for the preceding complexes is as follows: AsEt(3) < PPh(3) < PPh(2)Me < P(OPh)(3) < PEt(3) < P(n)Bu(3) < PPhMe(2) < PMe(3) < P(OMe)(3). Comparisons with other organometallic systems providing insights into factors influencing the Ru-L bond disruption enthalpies and metal basicity are discussed. Structural studies of two of these CpRu(ER(3))(2)Cl complexes (ER(3) = AsEt(3) (2) and PEt(3) (3)) have also been performed. Data for 2: monoclinic, C2/c; a = 30.549(5); b =. 10.523(2); c = 13.503(3) Angstrom; alpha gamma = 90 degrees; beta = 103.71(2)degrees; V = 4217.1 Angstrom(3); Z = 8; d(calcd) 2 = 1.656g cm(-1);n(obsd) 5328; R = 0.032. Data for 3: monoclinic, P2(1)/c; a 13.553(1); b = 8.283(2); c = 19.359(3) Angstrom; beta = 109.74(1)degrees; V = 2045.5 Angstrom 3; Z = 4; dcalcd = 1.422 g cm(-1); n(obsd) = 5152; R = 0.030. A relationship between bond distances and relative bond energies is made possible by the present data. This correlation is good and represents a rare example of such a relationship.

Organo-f-element thermochemistry. Absolute uraniumligand bond disruption enthalpies of [UL 3SX] complexes (L  C 5H 4tBu, C 5H 4SiMe 3 or C 9H 6SiMe 3 and X  Et or tBu)

The absolute uraniumligand bond disruption enthalpies for the series of compounds U(Cp′) 3SEt, U(Cp★) 3SX (X  Et or tBu) and U(Ind★) 3SEt [Cp′ C 5H 4 tBu, Cp★  C 5H 4SiMe 3 and Ind★  C 9H 6SiMe 3] have been measured by an oxidative addition process involving batch-titration solution calorimetry in toluene. The derived values are as follows (kJ mol −1): 252 ± 8 (Cp′, Et); 266 ± 9 (Cp★, Et); 158 ± 8 (Cp★, tBu) and 158 ± 8 (Ind ★, Et).

Gas-Phase Ionization Energetics, Electron-Transfer Kinetics, and Ion Solvation Thermochemistry of Decamethylmetallocenes, Chromocene, and Cobaltocene

The gas-phase free energies of ionization, [Delta]G[sub i][degrees] for Cp*[sub 2]Mn, Cp*[sub 2]Fe, Cp*[sub 2]Ni, Cp*[sub 2]Os, Cp[sub 2]Cr, and Cp[sub 2]Co (Cp = [eta][sup 5]-cyclopentadienyl, Cp[sup *] = [eta][sup 5]-pentamethylcyclopentadienyl) have been determined by using the electron-transfer equilibrium (ETE) technique and Fourier transform ion cyclotron resonance mass spectrometry. The high-resolution valence photoelectron spectra of bis(benzene)chromium(0), Bz[sub 2]Cr, Cp*[sub 2]Os, and Cp*[sub 2]Ru have also been measured. Most of the [Delta]G[sub i][degrees] values are referenced to the estimated [Delta]G[sub i][degrees] value of Bz[sub 2]Cr, for which the narrow first ionization band at 5.473 [+-] 0.005 eV is assigned as the adiabatic ionization potential. The [Delta]S[sub i][degrees] for ionization of Bz[sub 2]Cr is assumed to be equal to the electronic entropy change, [Delta]S[sub elec][degrees] (=1.4 cal mol[sup [minus]1] K[sup [minus]1]), and the difference between the integrated heat capacities for Bz[sub 2]Cr and Bz[sub 2]Cr[sup +] is also assumed to be negligible near room temperature [Delta]H[sub i,0][degrees] [approx] [Delta]H[sub i,350][degrees], leading to [Delta]G[sub i][degrees] (Bz[sub 2]-Cr) = 125.6 [+-] 1.0 kcal mol[sup [minus]1]. Through the use of thermochemical cycles, estimates are given for the average heterolytic and homolytic M-Cp bond disruption enthalpies of Cp[sub 2]Cr[sup +/0] and Cp[sub 2]Co[sup +/0]. 46 refs.,more » 7 figs., 4 tabs.« less

Organoruthenium thermochemistry. Enthalpies of reaction of (Cp*RuCl)4 and Cp*Ru(COD)Cl (Cp* = .eta.5-C5Me5, COD = cyclooctadiene) with dienes and tertiary phosphine ligands

The enthalpies of reaction of Cp*Ru(COD)Cl(Cp* = eta5-C5Me5, COD = cyclooctadiene) with a series of monodentate ligands, leading to the formation of Cp*Ru(ER3)2Cl (E = P, As), have been measured by anaerobic solution calorimetry in THF at 30-degrees-C. The enthalpies of reaction associated with the rapid and quantitative reaction of the (Cp*RuCl)4 complex with diene ligands in THF at 30-degrees-C, producing Cp*Ru(diene)CI complexes, have also been investigated. Reaction of (Cp*RuCl)4 with excess phosphine ligand, at 30-degrees-C, has been shown to quantitatively yield the corresponding Cp*Ru(PR3)2Cl complex and allows for the design of a thermochemical cycle assuring the internal consistency of the thermochemical data. The overall relative order of stability established for the preceding complexes is as follows: for monodentate ligands, AsEt3 < PPh3 < PnBu3 < PEt3 < PPh2Me < P(OPh)3 < PPhMe2 < PMe3 < P(OMe)3; for dienes, 2,3-dimethyl-1,3-butadiene < 1,3-cyclohexadiene < cyclooctadiene < 1,3-pentadiene < norbornadiene. Comparisons with other organometallic systems and insight into factors influencing the Ru-L bond disruption enthalpies are discussed.

Adiabatic ionization energies, bond disruption enthalpies, and solvation free energies for gas-phase metallocenes and metallocenium ions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdiabatic ionization energies, bond disruption enthalpies, and solvation free energies for gas-phase metallocenes and metallocenium ionsMatthew F. Ryan, John R. Eyler, and David E. RichardsonCite this: J. Am. Chem. Soc. 1992, 114, 22, 8611–8619Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/ja00048a040RIGHTS & PERMISSIONSArticle Views620Altmetric-Citations89LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Enthalpies of reaction of (benzylideneacetone)iron tricarbonyl, (BDA)Fe(CO)3, with phosphine ligands. Thermodynamic insights into iron chemistry

The enthalpies of reaction of (BDA)Fe(CO)3 (BDA = benzylideneacetone) with a series of monodentate phosphine ligands (PR3) leading to the formation of trans-(PR3)2Fe(CO)3 complexes have been measured by solution calorimetry in THF at 50-degrees-C. These enthalpy data help establish the following relative order of stability: PEt3 > P(n)Bu3 > PMe3 > PPhMe2 > PPh2Me > PPh3. The data span a range of 15 kcal/mol. This stability scale sheds light on the relative donating ability of phosphines. These data also allow comparison with other organometallic systems and give insight into factors influencing the Fe-PR3 bond disruption enthalpies in the (PR3)2Fe-(CO)3 system.

Absolute uranium–ligand bond-disruption enthalpies of [U(C5H4R)3X] complexes (X = I or H, R = Butor SiMe3)

The absolute uranium–ligand bond-disruption enthalpies (kJ mol–1) of the series [U(C5H4R)3X](X = H or I, R = But or SiMe3) have been measured by iodinolysis batch-titration solution calorimetry in toluene: R = But, 246.3 ± 5.3 (X = I), 249.7 ± 5.7 (X = H); R = SiMe3, 265.6 ± 4.3 (X = I), 251.7 ± 5.1 (X = H).

Organo- f-element thermochemistry. Uranium(III)Tetrahydrofuran bond disruption enthalpy in an indenyl compound

The UTHF (THF = tetrahydrofuran) bond disruption in tris(indenyl)uranium tetrahydrofuranate has been obtained by iodinolysis batch-titration solution calorimetry. The D[(C 9H 7) 3UTHF] value in toluene solution is (71.3±5.2) kJ mol −1.

Organo-f-element thermochemistry. Actinide-Group 14 element and actinide-transition-element bond disruption enthalpies and stoichiometric/catalytic chemical implications thereof in heterobimetallic tris(cyclopentadienyl)uranium(IV) compounds

Uranium-metal bond disruption enthalpies have been determined in the series of complexes Cp3U-MPh3, where Cp = eta-5-C5H5, Ph = C6H5, and M = Si, Ge, Sn, and in Cp3U-M'(CO)2Cp, where M' = Fe, Ru. Thermochemical data were obtained by anaerobic batch-titration solution calorimetry in toluene from enthalpies of solution and iodinolysis of the aforementioned compounds. Derived U-M/U-M' bond disruption enthalpies in toluene solution are as follows (M/M' moiety, kcal/mol): SiPh3, 37.3 (4.2); GePh3, 38.9 (4.5); SnPh3, 37.2 (4.0); Fe(CO)2Cp, 30.9 (3.0); Ru(CO)2Cp, 40.4 (4.0). These data fall in a relatively narrow range and indicate comparatively weak heterobimetallic bonding. Chemical implications of the present thermochemical results include the general favorability and marked M/M' sensitivity of alkane, hydrogen, and amine elimination synthetic routes to these compounds, the existence of favorable pathways for hydrocarbon and olefin activation, and the observation that no steps in plausible f-element-catalyzed dehydrogenative silane polymerization and olefin hydrosilylation cycles are predicted to have major thermodynamic impediments.