Concepción López

Assembly of cyclopalladated units: synthesis, characterisation, X-ray crystal structure and study of the reactivity of the tetrametallic cyclopalladated complex [Pd{C6H4CHN(C6H42-O)}]4·2CHCl3

The reaction of the equimolar amounts of the Schiff base C 6 H 4 CHN(C 6 H 4 2-OH) ( 1 ) and palladium(II) acetate in refluxing methanol for 2 h produces [Pd{C 6 H 4 CHN(C 6 H 4 2-O)}] 4 ( 2 )·2CHCl 3 . The X-ray crystal structure of 2 ·2CHCl 3 reveals that it contains a central non-planar eight-membered ring “Pd 4 O 4 ” formed by the self-assembly of four cyclopalladated fragments in which the ligand behaves as a [C, N, O] 2− terdentate ligand and the oxygen atoms act as bridges between the monomeric units. The reaction of 2 with triphenylphosphine or 1,1′-bis(diphenylphosphino)ferrocene (dppf) produces the opening of the central “Pd 4 O 4 ” core and the formation of the monomeric derivative [Pd{C 6 H 4 CHN(C 6 H 4 2-O)}(PPh 3 )] ( 3 )·CH 2 Cl 2 and the trimetallic complex [{Pd[C 6 H 4 CHN(C 6 H 4 2-O)]} 2 (μ-dppf)] ( 4 ), respectively. In 3 and 4 , the ligand also behaves as a dianionic and terdentate [C, N, O] 2− group, thus indicating that the PdO bond exhibits remarkable stability. The X-ray crystal structure of 3 ·CH 2 Cl 2 confirmed the mode of binding of the Schiff base and a trans arrangement between the imine nitrogen and the PPh 3 ligand. A comparative study of the spectrochemical properties of compounds 2 – 4 is also reported.

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.

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.

Alcohol activation by [Ir(COD)(tris(pyrazol-1-yl)methane)]+ and [Ir(COD) (tris(pyrazol-1-yl)ethanel+ cations: formation of alkoxycarbonyl derivatives [(tpzm)IrH(CO2R′)(CO)]+ and [(tpze)IrH(CO2R′)]+ (R′ = Me, Et, i-Pr)

The reactions of iridium and rhodium complexes derived from tris(pyrazolyl)-methane (tpzm) and tris(pyrazolyl)ethane (tpze) have been examined. One of the most interesting reactions involves the formation of alkoxycarbonyl derivatives of iridium tris(pyrazolyl)alkanes from carbon monoxide and alcohols. In the case of rhodium derivatives, a dimer of formula [(tpzm)]2Rh2(CO)3](CIO42 has been obtained. A careful 1H and 13C NMR study has allowed assignment of all the signals of the compound [(tpzm)IrH(CO2Me)(CO)]BF4.

Schiff bases derived from aminomethylferrocene and their cyclopalladated derivatives

Abstract Synthesis and characterization of novel Schiff bases derived from aminomethylferrocene of general formula: [(η5-C5H5)Fe{(η5-C5H4)CH2=CH(C6H4-2-R)}] with R = Cl (1a) and H (1b) are reported. These react with Na2[PdCl4] and Na(CH3COO)·3H2O in methanol at room temperature producing di-μ-chloro-bridged cyclopallated compounds (2a, 2b) which contain a σ(PdCsp2phenyl) bond. However, for (1b), the activation of the σ(Csp2,ferrocene−H) bond also takes place giving (2b′). These dinuclear complexes react with triphenylphosphine (PPh3) with cleavage of the μ-Cl bridges, yielding mononuclear derivatives (3). The results obtained show the strong influence of the so-called “endo effect” in cyclopalladation reactions of N-donor ferrocenyl ligands.

Palladium(II) compounds with planar chirality. X-Ray crystal structures of (+)-(R)-[{(η5-C5H4)–CHN–CH(Me)–C10H7}Fe(η5-C5H5)] and (+)-(Rp,R)-[Pd{[(Et–CC–Et)2(η5-C5H3)–CHN–CH(Me)–C10H7]Fe(η5-C5H5)}Cl]

Abstract A wide variety of planar chiral cyclopalladated compounds of general formulae [Pd{[(η5-C5H3)–CHN–CH(Me)–C10H7]Fe(η5-C5H5)}Cl(L)] (with L=py-d5 or PPh3), [Pd{[(η5-C5H3)–CHN–CH(Me)–C10H7]Fe(η5-C5H5)}(acac)] or [Pd{[(R1–CC–R2)2(η5-C5H3)–CHN–CH(Me)–C10H7]Fe(η5-C5H5)}Cl] (with R1=R2=Et; R1=Me, R2=Ph; R1=H, R2=Ph; R1=R2=Ph; R1=R2=CO2Me or R1=CO2Et, R2=Ph) are reported. The diastereomers {(Rp,R) and (Sp,R)} of these compounds have been isolated by either column chromatography or fractional crystallization. The free ligand (R)-(+)-[{(η5-C5H4)–CHN–CH(Me)–C10H7}Fe(η5–C5H5)] (1) and compound (+)-(Rp,R)-[Pd{[(Et–CC–Et)2(η5-C5H3)–CHN–CH(Me)–C10H7]Fe(η5-C5H5)}Cl] (7a) have also been characterized by X-ray diffraction. Electrochemical studies based on cyclic voltammetries of all the compounds are also reported.

Protonation and phase effects on the NMR chemical shifts of imidazoles and pyrazoles: experimental results and GIAO calculationsElectronic supplementary information (ESI) available: absolute and relative shieldings calculated at the B3LYP/6-311++G**//B3LYP/6-311++G** level for compounds V to XXI as well as pyrazole and 3,5-dimethylpyrazole dimers, trimers and tetramers (420 shieldings). See http://www.rsc.org/suppdata/nj/b2/b210251j/

The effects produced on 1H, 13C and 15N chemical shifts by protonation and by hydrogen-bonding solvents on five azoles have been determined experimentally. The following compounds have been studied: imidazole, 4,5-dimethylimidazole, pyrazole, 3,5-dimethylpyrazole and 4,5-dihydro-3-methyl-2H-benz[g]indazole. Phase effects on the 13C chemical shifts of the C-4 atom of pyrazole are discussed based both on empirical models and on GIAO calculations of absolute shieldings in different complexes. The special case of the chemical shifts of pyrazoles in the solid state, where they form multiple N–H⋯N hydrogen bonds, has also been studied theoretically.

An 1H and 13C NMR spectroscopic study of the structure of potassium and thallium salts of tris- and tetrakis-(pyrazol-1-yl) borates in solution. Some 13C11B and 13C205Tl residual coupling constants

Abstract The 1 H and 13 C NMR spectra of 18 tris- and tetrakis-pyrazolylborates in the form of potassium or thallium salts have been recorded. Four of these compounds are new. The results are discussed with regard to two main aspects: coupling constants with 205 Tl and positional isomerism of the pyrazole substituents. Most borates are symmetric compounds (all the pyrazole rings being identical isomers) corresponding to less hindered structures (all 3-aryl, 3-i-propyl-4-bromo, 3-t-butyl-5-methyl or 3-t-butyl-5-i-propyl pyrazoles). Only one derivative, potassium hydrotris(2,4,6-trimethylphenylpyrazol-1-yl)borate 5 , does not fit this pattern, being either a 3/3/3/ or a 3/3/5 isomer.