The photochemistry of N-p-toluenesulfonyl peptides: the peptide bond as an electron donor

The scope of photobiological processes that involve absorbers within a protein matrix may be limited by the vulnerability of the peptide group to attack by highly reactive redox centers consequent upon electronic excitation. We have explored the nature of this vulnerability by undertaking comprehensive product analyses of aqueous photolysates of 12 N-p-toluene-sulfonyl peptides with systematically selected structures. The results indicate that degradation includes a major pathway that is initiated by intramolecular electron transfer in which the peptide bond serves as electron donor, and the data support the likelihood of a relay process in dipeptide derivatives

Solution thermochemical study of tertiary phosphine ligand substitution reactions in the RhCl(CO)(PR3)2 system

The enthalpies of reaction of [Rh(CO)(2)Cl](2) (1) with a series of monodentate tertiary phosphine ligands, leading to the formation of RhCl(CO)(PR(3))(2) complexes, have been measured by anaerobic solution calorimetry in CH2Cl2 at 30.0 degrees C. These reactions are rapid and quantitative. The measured reaction enthalpies span a range of 43 kcal/mol. The relative stability scale established is as follows: P(NC4H4)(3) < P(NC4H4)(2)(C6H5) < P(OPh)(3) < P(p-CF3C6H4)(3) < P(NC4H4)(C6H5)(2) < P(p-ClC6H4)(3) < AsEt(3) < P(p-FC6H4)(3) < PPh(3) < P(p-CH3C6H4)(3) < P(p-CH3OC6H4)(3) < PPh(2)Me < P(OMe)(3) < PPhMe(2) < PEt(3). The relative importance of phosphine electronic ligand parameters is closely examined in terms of the presented quantitative thermochemical information. Comparisons with enthalpy data in related organometallic systems are also presented

Solution thermochemical study of tertiary phosphine ligand substitution reactions in the Rh(acac)(CO)(PR3) system

The enthalpies of reaction of Rh(acac)(CO)(2) (1) with a series monodentate tertiary phosphine ligands, leading to the formation of Rh(acac)(CO)(PR3) complexes, have been measured by anaerobic solution calorimetry in CH2Cl2 at 30.0 degrees C. These reactions are rapid and quantitative. The measured reaction enthalpies span a range of 12 kcal/mol. The relative stability scale established is as follows: PPh2(o-Tol) < P(p-CF3C6H4)(3) approximate to P(p-ClC6H4)(3) < P(p-FC6H4)(3) < P(NC4H4)(3) < P(NC4H4)(2)(C6H5) < P(m-CH3OC6H4)(3) < P(NC4H4)(C6H5)(2) < P(OPh)(3) approximate to PPh2(p-Tol) approximate to P(m-Tol)(3) < P(p-CH3C6H4)(3) < PPh3 < P(p-CH3OC6H4)(3) < PCy3 < PPh2Me < (PPr3)-Pr-i < PPhMe2. The relative importance of the phosphine stereoelectronic ligand parameters are examined in terms of the presented quantitative thermochemical information. Comparisons with enthalpy data in related organometallic systems are also presented

Enthalpies of reaction of [(p-cymene)OsCl2]2 with monodentate tertiary phosphine ligands : importance of steric and electronic ligand factors in an omium(II) system

The enthalpies of reaction of [OsCl2(p-cymene)](2) (1) (p-cymene = eta(6)-CH3C6H4CH(CH3)(2)) with a series of monodentate phosphines (PR3), leading to the formation of OsCl2(p-cymene)(PR3) complexes, have been measured by anaerobic calorimetry in CH2Cl2 at 30 degrees C. These reactions are rapid and quantitative. The overall relative order of stability established is as follows: PPh(NC4H4)(2) < P(NC4H4)(3) < P(p-CF3C6H4)(3) < PPh2(NC4H4) < PPh3 < P(p-ClC6H4)(3) < P(p-CH3C6H4)(3) < P(p-FC6H4)(3) < PCy3 < PBz(3) < (PPr3)-Pr-i < P(p-CH3OC6H4)(3) < P(NC4H8)(3) < PPh2Me < PPhMe2 < PEt3 < PMe3. A quantitative analysis of ligand effects for the present data helps clarify the exact steric versus electronic ligand contributions to the enthalpy of reaction in this system. Both steric and electronic factors appear to play an important role in dictating the magnitude of the enthalpy of reaction. The data are compared to the previously studied RuCl2(p-cymene)(PR3) system

Solution thermochemical and structural studies of ligand substitution of N-pyrrolyl-substituted phosphine ligands in the Cp'Ru(PR3)2Cl (Cp'=η5-C5H5 and η5-C5Me5) systems

The enthalpies of reaction of Cp'Ru(COD)Cl (1) (Cp' = eta(5)-C5H5 and eta(5)-C(5)Me(5); COD = cyclooctadiene) with a series of N-pyrrolyl-substituted monodentate tertiary phosphine ligands, leading to the formation of Cp'Ru(PR(3))(2)Cl (PR(3) = P(NC4H4)(3); P(NC4H4)(2)(C6H5), P(NC4H4)(C6H5)(2), P(NC4H8)(3)), have been measured by anaerobic solution calorimetry in THF at 30.0 degrees C. These reactions are rapid and quantitative. Structural studies have been carried out on five complexes in this series, and a discussion of bond length-bond strength relationships is presented, The measured reaction enthalpies span a range of 5 kcal/mol. This series of ligands include some of the most weakly bound phosphines calorimetrically investigated within these two related organometallic systems. Relative importance of phosphine steric vs electronic ligand parameters is more closely examined in terms of the presented quantitative thermochemical and structural information. Comparisons with enthalpy data in related organometallic systems are also presented