Joaquim Sales

Direct production of hydrogen from ethanolic aqueous solutions over oxide catalysts

Steam-reforming of ethanol over ZnO gives highly effective production of CO-free H2: 5.1 mol of H2 per mol of reacted ethanol is formed at 723 K under 100% ethanol conversion.

INFRARED BAND ASSIGNMENTS OF COORDINATED C6CL5 IN COMPOUNDS OF THE TYPE (MX(C6CL5)(PPH3)2)

Abstract A review of the C 6 Cl 6 infrared spectrum is made and some combination bands observed in this spectrum are assigned. On the basis of the C 6 Cl 6 spectrum, band assignments for some new compounds of the [MX (C 6 Cl 5 )(PPh 3 ) type (with M = Ni, Pd; X = C1, Br, I, NCS, NCO, N 3 ) are proposed.

Cyclopalladated compounds derived from ferrocenylimines. Crystal strcuture of [Pd{(η5-C5H5)Fe[η5-C5H3CHN(CH2)2Ph]}Cl(PEt3)]

Reactions of ferrocenylimines of general formula [Fe(η5-C5H5){η5-C5H4CHN(CH2)nPh}](n= 1 1a or 2 1b) with palladium(II) salts have been studied. The dimeric cyclopalladated complexes [{[graphic omitted](CH2)nPh}]Cl}2]2a and 2b were obtained when the reactions were carried out in the presence of sodium acetate and using Na2[PdCl4] as starting material. Addition of phosphine ligands PR3(R = Ph or Et) or 1,2-bis(diphenylphosphino)ethane (dppe) to acetone suspensions of these dinuclear compounds produced the more soluble mononuclear complexes [[graphic omitted](CH2)nPh]}Cl(PR3)] with R = Ph (3a and 3b) and Et (4a and 4b) and [[graphic omitted](CH2)nPh]}(dppe)]Cl (5a and 5b). Proton and 31P NMR spectroscopic studies on these compounds confirm the formations of endo five-membered metallocycles. Mossbauer spectra of compounds 1b–5b have also been recorded. The first crystal structure of a cyclopalladated complex derived from ferrocenylimines has been determined. The compound [[graphic omitted]CH2CH2Ph)}Cl(PEt3)]4b is monoclinic, space group P21/a, with a= 15.944(3), b= 12.425(2), c= 12.682(2)A, β= 100.19(2)° and Z= 4. The structure confirms the formation of an endo five-membered metallocycle on the ferrocene moiety.

Influences of the substituents at the iminic carbon atoms (hydrogen versus methyl) upon the properties of ferrocenylimines and their cyclopalladated derivatives

Ferrocenylimines of general formula [Fe(η5-C5H5)(η5-C5H4CRNR′)](R = Me, R′= Ph 1a, C6H4Me-2 1b, C6H4Me-4 1c, CH2Ph 1d, CH2C6H4Me-2 1e, CH2C6H4Cl-2 1f, CH2CH2Ph 1g or 1-C10H71h; R = H, R′= Ph 1i, C6H4Me-2 1j, C6H4Me-4 1k, CH2C6H4Me-2 1l, CH2C6H4Cl-2 1m or 1-C10H71n) have been prepared and characterized. Addition of these ligands to methanolic solutions of Na2[PdCl4], and sodium acetate trihydrate in a 1 : 1 molar ratio, results in the formation of the di-µ-chloro bridged cyclopalladated complex [{[graphic omitted]R′)](µ-Cl)}2]2a–2n. Reaction of compounds 2a–2n with triphenylphosphine in benzene yields more soluble monocyclopalladated derivatives [[graphic omitted]R′)}Cl(PPh3)]3a–3n. Proton, 13C and 31P NMR spectroscopic studies on these complexes reveal that cyclopalladation occurs on the ferrocenyl moiety, thus producing five-membered metallacycles containing the CN bond (endo-type structures). The crystal structures of compounds 1a, 1i and 3g have been determined. Complex 1a is triclinic, space group P with a= 10.152(3), b= 12.169(3), c= 12.239(3)A, α= 90.45(2), β= 100.56(2) and γ= 102.72(2)°. Compound 1i is monoclinic, space group Cc, with a= 5.876(3), b= 37.298(9), c= 12.640(4)A and β= 103.26(4)°. The complex [[graphic omitted]CH2CH2Ph)}Cl(PPh3)]·CH2Cl23g is monoclinic, space group P21/n with a= 20.343(2), b= 9.133(1), c= 19.714(2)A and β= 97.17(1)°, and its crystal structure confirms the formation of a five-membered palladocycle fused with the ferrocenyl moiety. The influence of the substituents R (H or Me) and R′ upon the spectroscopic and structural properties of the free ligands and the cyclopalladated complexes is also discussed.

Schiff bases derived from benzoylferrocene and their cyclopalladated derivatives. X-Ray crystal structure of [P d{(η5-C5H5) Fe[(η5-C5H3)C(C6H5)NC6H5]} Cl(PPh3)]

We report the syntheses, characterization, and study of cyclopalladated complexes derived from ferrocenylimines [(η5-C5H5)-Fe(η5 C5H4)C(C6H5)NR′] (R′ = C6H5 (1a), C6H4-2-CH3 (1b), C6H4- 4-CH3 (1c), CH2-C6H5 (1d), CH2-C6H4-2-CH3 (1e), or CH2-C6H4-2-Cl (1f)). Addition of these ferrocenylamines to methanolic solutions of Na2[PdCl4] and sodium acetate trihydrate in a 1:1 molar ratio results in the formation of the di-μ-chloro-cyclopalladated complexes [Pd{(η5-C5H5)Fe[(η5-C5H3)C(C6H5N R](μ-Cl)]2 (2a-2f). More soluble complexe [Pd{(η5-C5H5)Fe[(η5-C5H3)C(C6H5) NR])}Cl(PPh3)] (3a-3f) were obtained by the reaction of compounds 2a-2f with triphenylphosphine. 1H, 13C, and 31 P-NMR spectroscopic studies of these complexes reveal that cyclometallation occurs on the ferrocenyl-moiety, producing five-membered metallacycles whic contain the > CN bond (endo-type structures). The X-ray crystal structure of [Pd{(η5-C5H5)Fe[(η5-C5H3)C(C6H5)N -C6H5]}Cl(PPh3)]· 2H2O (3a) is also reported. This complex is monoclinic with a = 18.184(3), b = 11.631(2), c = 19. 499(3)A, β = 112.55(2)°, space group P21/c, and its crystal structure confirms the formation of a five-membered metallacycle, which contains a σ{PdC insp2(ferrocene} bond.

A QSPR study of O-H bond dissociation energy in phenols.

A Quantitative Structure-Property Relationship (QSPR) is developed for the O-H bond dissociation energy (BDE) of a set of 78 phenols. The data set was composed of monosubstituted, disubstituted, and polysubstituted phenolic derivatives containing substituents with different steric and electronic effects in the ortho-, meta-, and para-positions of the aromatic ring. The proposed model, derived from multiple linear regression, contains seven descriptors calculated solely from the molecular structure of compounds. The average absolute relative errors are 1.37% (R(2) = 0.8978; SD: 6.67) and 1.13% (R(2) = 0.9076; SD: 4.26) for the working set (62 compounds) and the prediction set (16 compounds), respectively. These results are better than those obtained from DFT calculations, QSAR approach, and correlations with Hammet parameters.

Cyclometallation reactions of N-(benzylidene)benzylamines with palladium compounds

Abstract The cyclometallation of p-RC6H4CHNCH2C6H2, (R = H, Cl, NO2) by PdX2 (X = Cl, AcO) has been studied. In every case the cyclometallation occurs with formation of a five-membered ring containing the methine group. The structure of these compounds [ PdX( p -RC 6 H 3 CHN CH2C6H5)]2, derived from 1H NMR spectra, are different from those reported previously. Reaction of these compounds with PEt3 gives the compounds [PdX(p-RC6H3CHNCH2C6H5)(PEt3)2] but with an excess of PPh3 only the complexes [ PdX( p -RC 6 H 3 CHN CH2C6H5)(PPh3)] are formed.

Ligand exchange reactions in cyclopalladated complexes of benzylideneanilines. Crystal structure of [Pd(C6H4CHNC6H5)Br(PPh3)2]

The ligand exchange reactions between [{[graphics omitted]C6H5)(O2CMe)}2] and the free imines p-RC6H4CHNC6H5(R = H, Cl, NMe2, or NO2)(N[graphics omitted]CH) in acetic acid have been studied. The substitution process is favoured when the incoming ligand contains electron-withdrawing substituents. From the results obtained a new mechanism involving a bis-cyclometallated complex ([graphics omitted]P[graphics omitted])] as intermediate is proposed. The dimeric cyclopalladated compounds are obtained by metallation of the imines by Pd(O2CMe)2; by reaction with phosphines PR′3 and LiBr, [[graphics omitted]C6H5)Br(PR′3)] and [Pd(p-RC6H3CHNC6H5)Br(PR3′)2] are formed (R′= Ph or Et). All the compounds have been fully characterized and their 1H and 13C n.m.r. spectroscopic data recorded. The molecular structure of [Pd(C6H4CHNC6H5)Br(PPh3)2] has been determined by a single-crystal X-ray analysis. The crystals are monoclinic, space group P21/a, a= 17.427(3), b= 24.790(4), c= 10.424(2)A, β= 98.91(2)°, and Z= 4; R= 0.053 for 6 579 reflections. The palladium atoms are five-co-ordinated, the Pd–N distance being 2.710(6)A.

Substituent effects on the electrochemical behaviour of iron(II) in Schiff bases derived from ferrocene and their cyclopalladated compounds

Abstract Cyclic voltammetries of ferrocenylimines [(η 5 − C 5 H 5 ) Fe ∗(η 5 − C 5 H 4 )− C ( R 1 )= N − R 2 ∗] ( 1–3 ) and [(η 5 − C 5 H 5 ) Fe ∗(η 5 − C 5 H 4 )−( CH 2 ) n − N = CH ( C 6 H 5−x R 3 x )∗] (4, 5), and bis(ferrocenyl)imine [(η 5 − C 5 H 5 ) Fe ∗(η 5 − C 5 H 4 )−( CH 2 ) n − N = C ( R 4 ) (η 5 − C 5 H 4 ) Fe (η 5 − C 5 H 5 ] ( 6 ) are reported. The comparison of the half-wave potentials ( E 1 2 ) shows that the liability of iron(II) to undergo oxidation is highly dependent on the nature of the substituents. For their mono- and dinuclear cyclopalladated compounds, and , the E 1 2 values reveal that the formation of a σ(Pd(sp2, ferrocene)) bond favours the oxidation of the ferrocenyl moiety, while for compounds with a σ(PdC(sp2, phenyl)) bond the trend is the opposite.

A QSPR study of the p solute polarity parameter to estimate retention in HPLC.

A Quantitative Structure-Property Relationship (QSPR) model is developed to calculate the solute polarity parameter p of a set of 233 compounds of a very different chemical nature. The proposed model, derived from multiple linear regression, contains four descriptors calculated from the molecular structure and the well-known hydrophobicity parameter log P(o/w). According to the statistics obtained with the prediction set, the model has a very good prediction capacity (R(2) = 0.954, F = 889, n = 45, and SD = 0.27). The study shows that log P(o/w) and hydrogen bond acidity of the solutes are the most relevant descriptors to predict p values. This p parameter is embodied in a general equation to predict retention in reversed-phase liquid chromatography (RP-HPLC). It describes analyte retention exclusively on the basis of mobile phase/analyte/stationary phase polar interactions. Equations and procedures to determine polarity of both chromatographic phases had been successfully developed previously. Therefore, the proposed QSPR model for p estimation becomes a very useful tool in RP-HPLC optimization of procedures and methods in the everyday analytical work.