Mercè Font-Bardia

Unique Single-Atom Binding of Pseudohalogeno Ligands to Four Metal Ions Induced by Their Trapping into High-Nuclearity Cages

μ4 end-on coordination (through the N atom) of the pseudohalogeno ligands X- =N3- and NCO- has been observed in the isostructural nonanuclear CoII cages with the general formula [Co9 {(2-C5 H4 N)2 CO2 }4 (O2 CMe)8 X2 ]; this mode is imposed by the trapping of anions X- into cavities formed inside the cage. The change of X- modulates the magnetic behavior of the cage from antiferromagnetic coupling to a ferrimagnetic high-spin ground state.

Three new dinuclear copper(II) complexes with [Cu(μ1,3-N3)2Cu]2+ and [Cu(μ1,1-N3)2Cu]2+ asymmetrical cores: syntheses, structures and magnetic behaviour

Three new dinuclear copper(II) complexes, derived from end-to-end and end-on azido bridging ligands and triamine derivatives, have been synthesized and their crystal structures have been determined by X-ray diffraction methods. These are the dinuclear end-to-end compounds, [Cu2(μ1,3-N3)2(Et3dien)2](ClO4)2 (1) and [Cu2(μ1,3-N3)2(Medpt)2](ClO4)2 (2), and the dinuclear end-on compound [Cu2(μ1,1-N3)2(Medien)2](ClO4)2 (3) (Et3dien is triethyldiethylenetriamine, Medpt is methyldipropylenetriamine and Medien is methyldiethylenetriamine). The [Cu(μ-N3)2Cu]2+ cores are asymmetrical in all 3 compounds. Variable temperature magnetic susceptibility data were collected and fitted to the appropriate equation derived from the Hamiltonian H = −JS1S2. 1 shows unusual ferromagnetic interactions with J = 9 cm−1 through the end-to-end azido bridges while 2 shows an antiferromagnetic interaction through the end-to-end azido bridges with the highest reported absolute magnitude of J = −105 cm−1. The magnetic data of 1 and 2 have been correlated with the Addison parameter, τ, and mainly with the Cu–N3–Cu torsion angle, Δ. 3 shows an unusual antiferromagnetic interaction with J = −16.8 cm−1 through the end-on azido bridges.

Enantioselective Organocatalytic Addition of Azlactones to Maleimides: A Highly Stereocontrolled Entry to 2,2‐Disubstituted‐2H‐oxazol‐5‐ones

The first highly diastereo- and enantioselective organocatalytic synthesis of 2,2-disubstituted-2H-oxazol-5-ones is described. The addition of oxazolones to maleimides is promoted by bifunctional thiourea catalysts, which afford the corresponding 2,2-disubstituted-2H-oxazol-5-ones with total regio- and stereocontrol.

Two new nickel(II) cubane compounds derived from pyridine-2-methoxide (Pym): {Ni4(Pym)4Cl4(CH3OH)4} and {Ni4(Pym)4(N3)4(CH3OH)4}. Crystal structures and magnetic properties

Abstract The pyridine-2-methoxide anion (Pym) allows the two new nickel(II) cubane compounds: {Ni 4 (Pym) 4 Cl 4 (CH 3 OH) 4 } ( 1 ) and {Ni 4 (Pym) 4 (N 3 ) 4 (CH 3 OH) 4 } ( 2 ), to be easily synthesized. 1 and 2 are structurally characterised. Complexes 1 and 2 crystallise in the tetragonal system. 1 and 2 have similar structures that consist of tetrameric cubane complexes with the alkoxide oxygen atoms of the pyridine-2-methoxide ligand and octahedrally co-ordinated nickel(II) atoms placed alternately at the corners of the cube. Magnetic susceptibility data, measured from 2 to 260 K show ferromagnetic behaviour for 1 and 2 . These data were fitted by using the equation derived from the Hamiltonian H =−2 J 1 ( S 1 S 2 + S 3 S 4 )−2 J 2 ( S 1 S 3 + S 1 S 4 + S 2 S 3 + S 2 S 4 ) including the Zero Field Splitting for the ground state S =4, giving the parameters J 1 =0.43, J 2 =5.28, D =−0.47 cm −1 , g =2.11 for 1 and J 1 =9.78, J 2 =2.42, D =−0.10 cm −1 , g =2.21 for 2 .

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.

Benzoate as terminal ligand in the defective double-cubane, tetranuclear cobalt(II) complex [Co4(N3)2(O2CPh)2{(py)2C(OH)O}4].2DMF with simultaneous μ1,1-azido and μ-o bridges [(py)2C(OH)O = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone]

The reaction of Co(O2CPh)2 with di-2-pyridyl ketone, (py)2CO, and NaN3 in DMF allows isolation of the tetranuclear compound [Co4(N3)2(O2CPh)2{(py)2C(OH)O}4]/2DMF (2) instead of the expected nonanuclear cage [Co9(N3)2(O2CPh)8{(py)2CO2}4]. The Xray diffraction analysis reveals a defective double-cubane, tetrameric entity in which the Co II atoms are linked by h 1 ,m2-N3 azide ligand and two kinds of O-bridges. The molar magnetic susceptibility measurements of 2 in the 2 � /300 K range indicate bulk ferromagnetic coupling. Some synthetic aspects of the Co II /(py)2CO/N3 � reaction system are also discussed. # 2002 Elsevier

Structural and cytotoxic study of new Pt(II) and Pd(II) complexes with the bi-heterocyclic ligand mepirizole

Pd(II) and Pt(II) complexes of formulae [MLCl2], where L = mepirizole, were synthesized and characterized. Two complexes were obtained and studied by different techniques: IR, 1H and 13C NMR and XPS spectroscopies and mass spectrometry (electrospray). The crystal structure of the complex cis-dichloro-4-methoxy-2-(5-methoxy-3-methyl- pyrazol-1-yl)-6-methyl-pyrimidinepalladium(II), [Pd(mep)Cl2], was studied by crystal X-ray diffraction. It consists of discrete molecules with planar geometry. Pd(II) ions are four-coordinated by two mepirizole nitrogen atoms (N1 from the pyrazole ring and N4 from the pyrimidine ring) and two chlorine atoms. The geometry of the PdN2Cl2 chromophore is a distortion of the square-planar coordination. Data from powder pattern X-ray diffraction of cis-dichloro-4-methoxy-2-(5-methoxy-3-methyl-pyrazol-1-yl)-6-methyl- pyrimidineplatinum(II), [Pt(mep)Cl2], demonstrated that the two complexes are isostructural. The cytotoxic activity of both Pd and Pt complexes was checked for six different tumor cell lines and was lower than that of cisplatin. The Pt bound to DNA was also checked and only a low percentage is able to cross the cell membrane.

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.

Structure and magnetic behaviour of the first singly bridged nickel cyanate chain and a new dinuclear complex: an approximation to the superexchange mechanism for the nickel pseudohalide system

Two new nickel(II) bridging-cyanate complexes of formula [{Ni(323-tet)(µ-OCN)}n][ClO4]n1[323-tet =N,N′-bis(3-aminopropyl)ethane-1,2-diamine] and [{Ni(Me6[14]aneN4)}2(µ-OCN)2][ClO4]22(Me6[14]aneN4=DL-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) have been synthesized and characterized. The crystal structures of 1 and 2 have been solved and in both compounds the cyanate ligand acts as an end-to-end bridge with the nickel atoms in a NiN5O octahedral environment. Compounds 1 is a chain in which the Ni(323-tet)fragments are linked by single cyanate bridges in a trans position, whereas compound 2 consists of dinuclear units with two cyanate bridges in a cis arrangement. Magnetic measurements in the 2–300 K range indicate weak ferromagnetism for 1 and antiferromagnetic behaviour for 2. Magneto-structural correlations have been obtained by Extended-Huckel calculations and a generic superexchange model for the nickel(II) pseudohalogen system is proposed.

Synthesis, structural determination and magnetic properties of three new di-μ1,3-azido copper(II) dimers derived from tridentate amines: magneto-structural correlations

Abstract Three new copper(II) dinuclear complexes, derived from the μ1,3-azido bridging ligand and tridentate amines, were synthesised and their crystal structures determined by X-ray diffraction methods. [Cu2(μ-N3)2(Me5dien)2](ClO4)2 (1), [Cu2(μ-N3)2(Et5dien)2](ClO4)2 (2), and [Cu2(μ-N3)2(EtMe4dien)2](ClO4)2 (3). Me5dien is 1,1,4,7,7-pentamethyldiethylenetriamine, Et5dien is 1,1,4,7,7-pentaethyldiethylenetriamine and EtMe4dien is 4-ethyl-1,1,7,7-tetramethyldiethylenetriamine. The three new dinuclear compounds are asymmetrical double bridging μ2-1,3 azido pentacoordinate copper(II) compounds. Variable temperature magnetic susceptibility data showed antiferromagnetic coupling for all of them. These data were fitted to the appropriate equation derived from the Hamiltonian H=−JS1S2 giving the parameters J=−7.5(6) cm−1, g=2.048(14) for 1; J=−28(3) cm−1, g=2.09(8) for 2; and J=−3.6(4) cm−1, g=2.062(8) for 3.