Ramón Bosque

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.

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.

Reactivity of cyclometallated compounds of N-benzylideneamines. Synthesis and X-ray crystal structure of [Pd{1-CH2-2-(CHN-C6H5)-3,5-(CH3)2C6H2} (2,4-Me2C5H3N)]ClO4

Abstract The action of Ph2PCH2CH2PPh2 (dpe) on the cyclometallated compounds [{Pd( CN )Br}2] ( CN = 2-(HCNC6H5)-5-ClC6H31a, 2-(CH2NCH-2′,6′-Cl2C6H3)C6H41b, or 1-CH2-2-(CHN-C6H5)-3,5-(CH3)2C6H21c) in a 2:1 molar ratio, gives the novel neutral species [Pd( CN )Br(dpe)] (2a,b) or the ionic compound [ (dpe)]Br (3c). The action of dpe on compound 1 in a 1:1 molar ratio gives the dinuclear cyclometallated compound 4, in which two palladium atoms are bridged by the diphosphine. The ionic compounds[ (lut)(PPh3)]ClO4 6 (lut = 2,4-lutidine) were obtained by reaction between AgClO4 and acetone solutions of the cyclometallated compounds , and subsequent addition of 2,4-lutidine. [P d{1-CH 2 -2-(CHN -C6H5)-3,5-(CH3)2C6H2}(2,4-lut)]ClO4 crystallizes in the orthorhombic space group Pcab with a = 16.331(3) A; b = 18.885(3) A; c = 24.702(4) A, and Z = 8. The endo six-membered ring displays a half-skew-chair conformation, with the palladium atom out of the plane (1.086 A) defined by the other atoms.

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) and platinum (II) compounds containing bi- and terdentate ferrocenyl ligands. X-ray crystal structure of cis-[Pd{(η5-C5H5)Fe{(η5-C5H4)–CHN–CH2–CH2–N(CH3)2]}Cl2]

The synthesis, characterization and study of the three ferrocenyl Schiff bases: [(η 5 -C 5 H 5 )Fe{(η 5 -C 5 H 4 )–CHN–CH 2 –CH 2 –N(CH 3 ) 2 }] ( 1a ), [(η 5 -C 5 H 5 )Fe{(η 5 -C 5 H 4 )–CHN–CH 2 –CH 2 –S–CH 2 –CH 3 }] ( 1b ) and [(η 5 -C 5 H 5 )Fe{(η 5 -C 5 H 4 )–CHN–CH(COOCH 3 )–CH 2 –CH 2 –S–CH 3 }] ( 1c ) are reported. Reactivity studies of these substrates versus palladium (II) and platinum (II) salts have allowed us to isolate and characterize different sorts of complex. The coordination complexes: cis -[M(ligand)Cl 2 ] {where M=Pd ( 2a – 2c ) or Pt ( 3a – 3c )} were prepared by treatment of the corresponding ligand and Na 2 [PdCl 4 ] (for 2a – 2c ) or cis -[PtCl 2 (dmso) 2 ] (for 3a – 3c ) in methanol. In compounds 2 , 3a – c the ligand acts as a neutral bidentate group. The cyclopalladated complex: [Pd{(η 5 -C 5 H 5 )Fe[(η 5 -C 5 H 3 )–CHN–CH 2 –CH 2 –N(CH 3 ) 2 ]}Cl] ( 4a ) can be isolated by reaction of stoichiometric amounts of 1a , Na 2 [PdCl 4 ] and Na(CH 3 COO) · 3H 2 O in methanol for 8 days. In complex 4a the ligand acts as a monoanionic (C, N, N′) − terdentate group. The reaction of compound 4a with an equimolar amount of PPh 3 produces [Pd{(η 5 -C 5 H 5 )Fe[(η 5 -C 5 H 3 )–CHN–CH 2 –CH 2 –N(CH 3 ) 2 ]}Cl(PPh 3 )], in which the ligand acts as a monoanionic (C, N) − bidentate ligand. All the compounds included in this study have been characterized by infrared and NMR spectroscopy and complex 2a has also been characterized structurally: monoclinic, P 2 1 / m , with a =6.034(2) A, b =14.502(2) A, c =10.236(2) A and β =104.61(2)°. The crystal structure of complex 2a reveals that the imine adopts the Z -form.

Synthesis and resolution of benzylisopropylphenylphosphine, a monodentate P-chiral ligand

Abstract The synthesis of benzylisopropylphenylphosphine by reaction between the benzylphenylphosphide anion and isopropyl chloride and its subsequent resolution by means of an optically active palladium metallacycle is reported. The synthesis of the organometallic complex [Pd(η 3 -2-MeC 3 H 4 )Cl(PBn i PrPh)] is also described, as well as the assignment of the absolute configuration of the coordinated phosphine by mono- and bidimensional proton NMR spectra, using the homochiral palladacycle as a reference point. In order to estimate the height of the energy barrier corresponding to the rotation of the phosphine ligand around the PdP bond, several calculations were performed at the semiempirical PM3(tm) level.

Syntheses and characterization of optically active cyclopalladated compounds containing ferrocenyl units

Abstract The diastereoselective cyclopalladation of ( S )-(−)-N,N-dimethyl-1-ferrocenylethylamine 1 produces (R,S,S,R)−(+)−[ {[(n 5 −C 5 H 3 )−CH(CH 3 −N (CH 3 ) 2 ]Fe(n 5 −C 5 H 5 )}{u−C1)] 2 2 . The absolute configuration of this complex has been determined by X-ray diffraction. Reactivity studies on the “Pd(μ-Cl) 2 Pd” units and the σ(PdC) bond in compound 2 have been also undertaken and have allowed to isolate (R,S) −(+)−[ {[(n 5 −C 5 H 3 )−CH(CH 3 −N (CH 3 ) 2 ]Fe(n 5 −C 5 H 5 )}C1(L)=PPh 3 3 or 1-Meimd 4 and Pd{[(PhC=CPh) 2 −(n 5 C 5 H 3 )−CH(CH 3 )−N (CH 3 ) 2 ]Fe{n 5 −C 5 H 5 )}C1] 5 .