Synthesis, reactivity and complexation studies of N,S exo-heterodisubstituted o-carborane ligands. Carborane as a platform to produce the uncommon bidentate chelating (pyridine)N-C-C-C-s(H) motif.

The synthesis of N,S-heterodisubstituted 1-(2'-pyridyl)-2-SR-1,2-closo-C2B10H10 compounds (R = Et, 2; R = (i)Pr, 3) has been accomplished starting from 1-(2'-pyridyl)-l,2-closo-C2B10H11 (1), and their partial deboronation reaction leading to the structurally chiral [7-(2'-pyridyl)-8-SR-7,8-nido-C2B9H10]-derivatives (R = Et, [4]-; R = (i)Pr, [5]-) has been studied. Capillary electrophoresis combined with the chiral selector alpha-cyclodextrin has permitted the separation of the electrophoretically pure racemic [7-(2'-pyridyl)-8-SR-7,8-nido-C2B9H11]- ions into two peaks each one corresponding to the interaction of one enantiomer with the alpha-cyclodextrin. The N,S-heterodisubstituted o-carborane containing a mercapto group, 1-(2'-pyridyl)-2-SH-1,2-closo-C2B10H10, 1, is one of the two examples of a rigid bidentate chelating (pyridine)N-C-C-C-S(H) motif having been structurally fully characterized. To study the potential of such a binding site, 1 has been tested as a ligand with metal ions requiring different coordination numbers, two (Au(+)) and four (Pd2+ and Rh+). The crystal structures of the Pd(II) and Au(I) complexes are reported. For the Pd(II) complex, 1 acts as a bidentate ligand whereas for Au(I), 1 acts as a monodentate ligand through the thiolate.

Eta5-(3)-1-methyl-1,2-dicarbollyl-eta5-2',5'-dimethylpyrrolylcobalt(III).

In the title compound, (eta(5)-2,5-dimethylpyrrolyl)[(7,8,9,10,11-eta)-7-methyl-7,8-dicarba-nido-undecaborato]cobalt(III), [3-Co[eta(5)-[2,5-(CH(3))(2)-NC(4)H(2)]]-1-CH(3)-1,2-C(2)B(9)H(10)] or [Co(C(3)H(13)B(9))(C(6)H(8)N)], the Co(III) atom is sandwiched between the pentagonal faces of the pyrrolyl and dicarbollide ligands, resulting in a neutral molecule. The C-C distance in the dicarbollide cage is 1.649 (3) A.

Comparative study of NS(2)(S-aryl) pyridine-based dithia-containing ligands with different substituent groups. Reactivity toward Cu(II) and Ru(II).

Ligands LX of the type NS(2) with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced. Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results from the reaction of these ligands with Cu(ClO(4))(2).6H(2)O and [RuCl(2)(PPh(3))(3)] have revealed that their coordination capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas [Cu(LX)][ClO(4)](2), except for L5, and [RuCl(2)(LX)(PPh(3))], have been obtained, respectively. The electronic characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-bis[(2'-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl(2)(L5)(PPh(3))].2CCl(4) have been characterized by single-crystal X-ray diffraction methods.

Contribution of the nido-[7,8-C2B9H10]- anion to the chemical stability, basicity, and 31P NMR chemical shift in nido-o-carboranylmonophosphines.

The icosahedral dicarboranes and their decapitated anion, 1-R'-1,2-C(2)B(10)H(10) (closo) and [7-R'-7,8-C(2)B(9)H(10)](-) (nido), exert a distict influence at the alpha position of substituents attached to the cage carbon atom. The closo fragment is electron-withdrawing while the nido anion is electron-releasing. These effects are studied by (31)P NMR, phosphorus oxidation, and phosphorus protonation in [7-PR(2)-8-R'-7,8-C(2)B(9)H(10)](-) species. The (31)P NMR chemical shift dependence is related to the R alkyl or aryl nature of [7-PR(2)-8-R'-7,8-C(2)B(9)H(10)](-). No direct relationship to the nature of the R substituent on the nido-carboranylmonphosphine toward oxidation has been found. The basicity of the nido-alkylcarboranylmonophosphines is the highest while the lowest corresponds to the nido-arylcarboranylmonophosphines. Interpretation can be carried out qualitatively by considering the electronic properties of the cluster and the nature of the R groups. The influence of R' is less relevant. Confirmation of the molecular structure of the oxidated and protonated nido-carboranylmonophosphine compounds was obtained by X-ray diffraction analysis of [NBu(4)][7-P(O)Ph(2)-8-Ph-7,8-C(2)B(9)H(10)] and [7-PH((i)Pr)(2)-8-Me-7,8-C(2)B(9)H(10)].

Unusual 9-->10 rearrangement of the substituted cage carbon in the ferratricarbollide series. Synthesis of the isomeric complexes [2-eta 5-(C5H5)-10-X-closo-2,1,7,10-FeC3B8H10] (where X = H2N, MeHN, Me2N, and ButHN).

Treatment of the zwitterionic amine tricarbollides of general formula 7-L-nido-7,8,9-C3B8H10 (1) (where L = Me2HN (1c) and ButH2N (1d)) with [(eta 5-C5H5)Fe(CO)2]2 in refluxing mesitylene resulted in the formation of a mixture of the known compounds [2-(eta 5-C5H5)-9-X-closo-2,1,7,9-FeC3B8H10] (2) (where X = H2N (2a), Me2N (2c), and ButHN (2d)) and a series of new, isomeric ferratricarbollylamines [2-(eta 5-C5H5)-10-X-closo-2,1,7,10-FeC3B8H10] (3) (where X = H2N (3a), Me2N (3c), and ButHN (3d)) in moderate yields. Complexes of type 3 (where X = H2N (3a), MeHN (3b), Me2N (3c), and ButHN (3d)) were also obtained readily by heating complexes of type 2 (where X = H2N (2a), MeHN (2b), Me2N (2c), ButHN (2d), and Bu(t)(Me)N (2e)) at ca. 300 degrees C for 10 min. All the complexes of type 3 contain reactive amine functions in meta positions with respect to the metal center. The observed 9-->10 rearrangement of the substituted cluster carbon is quite unexpected and is believed to result from higher thermodynamic stability of the 10-substituted isomers. The structures of all compounds of type 3 were established by high-field NMR spectroscopy and mass spectrometry, and that of 3d was determined by an X-ray diffraction study.

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII).

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.

Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions.

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.