Carla Bisi Castellani

Insertion of isocyanides into the palladium—carbon bond of C2-palladated heterocycles. Synthesis of trans-[PdCl{C(RN)NR}(PPh3)2] complexes (RN = 2-pyridyl, 2-pyrazyl; R = alkyl or aryl group)

The titles complexes trans-[PdCl{C(RN)NR}(PPh3)2] (RN = 2-pyridyl (2-py), R = p-C6H4OMe, Me; RN = 2-pyrazyl (2-pyz), R = p-C6H4OMe) can be prepared by reaction of the N-protonated compounds, cis-[PdCl2(RNH)(PPh3] (RNH = 2-pyridylium (2-pyH) or 2-pyrazylium (2-pyzH) group), with PPh3, followed by addition of the isocyanide CNR and deprotonation with triethylamine, in a molar ratio Pd/PPh3/CNR/NEt3 of 1/1/1/1.1. The reaction sequence involves the successive formation of the cationic intermediates trans-[PdCl(RNH)(PPh3)2]+, trans-[Pd(RNH)(CNR)(PPh3)2]2+ and trans-[Pd(RN)(CNR)(PPh3)2]+, which were isolated and characterized as perchlorate salts for RN = 2-pyridyl. In the final step the coordinated isocyanide of trans-[Pd(RN)(CNR)(PPh3)2]+ undergoes migratory insertion into the Pd-RN σ bond, promoted by the chloride ions progressively displaced by the entering neutral ligands from cis-[PdCl2(RNH)(PPh3)]. The resulting products were characterized by conventional spectroscopic techniques and, for RN = 2-pyridyl and R = p-C6H4OMe, also by ligand substitution reaction at the palladium center and by protonation and coordination of the p-methoxyphenylimino(2-pyridyl)methyl group with strong mineral acids (HClO4, HCl) and ZnCl2, respectively.

Insertion of isocyanides into the 2-one-1-propyl-palladium(II) bond: a convenient synthetic route to C1-palladated 1-amino-3-one-1-butene compounds

Abstract Migratory insertion of isocyanides CNR (R = p -C 6 H 4 OMe, Me) into the palladium—carbon σ bond of trans -[PdCl(CH 2 COMe)(PPh 3 ) 2 ] (I) yields the 1-amino-3-one-1-butenyl complexes trans -[PdCl{C(NHR)CHCOMe}(PPh 3 ) 2 ] (IIa, R = p -C 6 H 4 OMe; IIb, R = Me), which have been characterized by IR, 1 H and 31 P NMR spectra. The reaction of IIa with nickel acetate gives a diamagnetic bischelate complex of the type [Ni(ON) 2 ] , in which the deprotonated 1-amino-3-one-1-butenyl moiety acts as a bidentate O,N ligand.

Scandium trifluoromethanesulphonate as an active catalyst in the decarbonylation of aromatic aldehydes

Abstract Scandium trifluoromethanesulphonate efficiently catalyzes the decarbonylation of 2,4,6-trimethoxybenzaldehyde ( 1 ) which, on heating in MeOH solution, is deformylated neatly and completely in a few minutes, yielding 1,3,5 trimethoxybenzene and methyl formate. The reaction was studied by UV and NMR spectroscopy, which gave evidence for the reaction mechanism. Aromatic aldehydes less electron rich than 1 were decarbonylated more sluggishly. The unique catalytic properties of Sc(OTf) 3 were compared with other non transition metal triflates.

Studies on copper(II) complexes of o-quinone monooximes. 8. Penta and hexacoordinated adducts of bis(4-chloro-1,2-benzaquinone 2-oximato)copper(II), [Cu(Clqo)2], with imidazole and N-methylimidazole

Abstract Bis(4-chloro-1,2-benzaquinone 2-oximato)copper(II) [Cu(Clqo)2] reacts with imidazole (Im) and with N-methylimidazole (MeIm) forming penta and hexacoordinated adducts. The X-ray crystal structure determination showed that the Cu(II) ion is in a distorted trigonal bipyramidal geometry in Cu(Clqo)2 ·MeIm and in a tetragonally distorted octahedral geometry in Cu(Clqo)2·2L (L = Im, MeIm). In all cases the Clqo quinonic oxygen atoms are in the axial positions while in the parent compound Cu(Clqo)2 they are in the equatorial ones. IR and electronic spectra were recorded in order to obtain some correlation between structure and spectroscopic features.

Synthesis and luminescence studies on the lanthanide(III) complexes of a novel schiff base derivative of dehydroacetic acid

Abstract A novel, potentially heptadentated ligand (dhatren) has been obtained by condensation of dehydroacetic acid and tris(2-aminoethyl)amine. Its lanthanide(III) complexes of the formula Ln(dhatren)(NO3)3·2H2O have been isolated for Ln = La, Eu and Tb. Their stability constants in methanol have been determined and their photophysical properties studied. The 1H NMR and the IR spectra of both the dhatren ligand and its complexes are reported.

Covalent and electrostatic contributions to the bonds involving lanthanoid(III) cations: a new look based on parametric correlation of complexation constants

Abstract The formation constants of 308 lanthanoid(III) complexes with (poly)aminopolycarboxylate ligands are correlated by the equation log K1=CACB+EAEB. The C and E parameters indicate the tendency of each cation A and anion B to undergo covalent or ionic bonding; the ratio H=E/C indicates the charge control on the bond formation tendency of each species A or B. Steric effects are found to be negligible. A break in the H values occurs between the first (La-Gd) and the second half (Gd-Lu) of the lanthanoid series. This feature is interpreted in terms of the LUMO energy of the Ln3+ ions.

Structural chemistry of actinide compounds with different coordination numbers: The crystal and molecular structures of tetrachlorotris(N,N-diethylpropionamide)thorium(IV) and tetra-N-thiocyanato tetrakis(N,N-dimethylpropionamide)thorium(IV)

Abstract The crystal and molecular structures of ThCl 4 (depa) 3 (1) (depa = N,N-diethylpropionamide) and Th(NCS) 4 (dmpa) 4 (2) (dmpa = N,N-dimethylpropionamide) have been determined from three-dimensional X-ray diffraction data. The compounds crystallize in space group P2 1 /n (1) and P2 1 /a (2), with a = 18.107(5), b = 10.347(3), c = 17.867(5) A , β = 108.5(1)°, Z = 4 (1) and a = 22.759(6), b = 13.763(4), c = 11.910(3) A , β = 91.4(1)° and Z = 4 (2). Full matrix least-squares refinement of both structures gave for (1) with 3126 intensity data R = 0.046 and Rw 0.046 and for (2) with 3480 intensity data R = 0.050, Rw 0.054. The different steric constraints imposed by the ligand give rise to different coordination numbers. In (1) the coordination polyhedron about the seven co-ordinate thorium atom is a pentagonal bipyramid with two chlorine atoms in the axial positions, an unusual geometry for Th(IV) species. The average bonding distances are ThO = 2.340(9), ThCl eq = 2.754(3) and ThCl ax = 2.692(3) A . In (2) the less hindering dmpa ligand favours the presence of four of them in the metal coordination sphere in a distorted square antiprismatic coordination geometry. ThO and ThN average 2.37(1) and 2.49(2) A respectively.

Scandium Trifluoromethanesulfonate as Catalyst in the Hydrogen/Deuterium Exchange of 1,3,5-Trimethoxybenzene: Evidence for a Direct Interaction of Scandium with the Aromatic Ring

Abstract Scandium trifluoromethanesulfonate in CD3OD is a very active catalyst for hydrogen/deuterium exchange at the aromatic nucleus of 1,3,5-trimethoxybenzene. The very low proticity of the system, spectrophotometric evidence, and easy iodination of the substrate point to the formation of a transient unprecedented arylscandium species as a plausible intermediate of the reaction.

Rare earth trifluoromethanesulphonates as catalysts in some Meerwein—Ponndorf—Verley type reductions

Abstract Rare earth cations catalyze the reduction of aldehydes and ketones by isopropanol. The reaction rate constants have been determined by 1H NMR spectroscopy in the presence of La3+, Y3+, Lu3+, Sc3+, using Cl−, ClO4− and TfO− as counterions; the values obtained indicate that the reaction rates increase as the cation size decreases and with the use of poorly co-ordinating counterions. Scandium trifluoromethanesulphonate turned out to be by far the best catalyst for these reactions. By comparison of strictly analogous aldehydes and ketones it has been found that the former compounds are more easily reduced than the latter. The formation of mixed ethers with isopropanol was observed during the reduction of aromatic carbonyl compounds substituted with electron donating groups.

Metal complexes of pyrazole-4,5-dione-4-oximes: crystallographic characterization and their reactions with dimethyl acetylenedicarboxylate

Abstract Complexes of type ML2, ML2(H2O)2 and ML2(py)2 (LH = pyrazole-4,5-dione-4-oximes) have been prepared and their IR and LSIMS spectra, magnetic susceptibilities and behaviour towards triphenylphosphine and dimethyl acetylenedicarboxylate (DMAD) have been investigated. The structures of Zn(Mpo)2(H2O)2 (MpoH = 1,3-dimethyl-1 H-pyrazole-4,5-dione-4-oxime and Mn(1-Ppo)2(py)2 (1-PpoH = 3-methyl-1-phenyl-1 H-pyrazole-4,5-dione-4-oxime) were determined by X-ray crystallography. In all the complexes, the ligands chelate to the metal, forming six-membered rings. The adducts are monomeric, whereas the ML2 complexes are associated in the solid state. All the complexes and their respective ligands react with DMAD at 80°C to give the condensation product, whereas at 20°C, the ligands and their lithium complex give the open chain adduct.