Dante Masi

Toward a novel metal based chemotherapy against tropical diseases 4. Synthesis and characterization of new metal-clotrimazole complexes and evaluation of their activity against Trypanosoma cruzi

Abstract The syntheses and characterization of metal imidazole complexes showing activity against Trypanosoma cruzi, the causative agent of Chagas disease, are presented, RuCl2(CTZ)2 (2) and RuCl2(BTZ)2 (4) were prepared by reaction of RuCl2(NCCH3)4 (1) with the appropriate ligand (CTZ, clotrimazole = 1-[(2-chlorophenyl)diphenylmethyl]-1H-imidazole; BTZ = 1-[(2-bromophenyl)diphenylmethyl]-1H-imidazole) [Ru(bipy)(CTZ)2](PF6)2 (3) (bipy=2,2′-bipyridyl) was obtained by reaction of 2 with bipy and NH4PF6 in MeCN. Reaction of [RhCl(COD)]2 with CTZ yielded RhCl(COD)(CTZ) (5) (COD=1,5-cyclooctadiene), while AuCl1CTZ (6), K2[PtCl4(CTZ)2] (7) and [Cu(CTZ)2]PF6 (8) were obtained by interaction of CTZ with AuCl1·HCl, K2PtCl4 and [Cu(CH3CN)4]PF6, respectively. All the new complexes were characterized by NMR and other appropriate techniques, X-ray diffraction studies of 4·3H2O, 5 and 6 were also carried out. The structure of 4·3H2O consists of a distorted tetrahedral arrangement of two N atoms from the BTZ ligands and two Cl atoms around the Ru(II) ion; 4·3H2O crystallizes in the orthorhombic space group Puma (No. 62) with a=12.818(5), b=29.115(5), c=12.040(5) A , V=4493.2(8) A and Z=4. Complex 5 displayed a square planar structure typical for Rh(1) bound to N from CTZ, Cl, and the two CC bonds of COD; 5 crystallized in the triclinic space group (P(= l) (No. 2) with a=12.407(3), b=12.876(4), c=10.069(3) A , α=111.59(2)°, β=107.80(2)°, γ=103.28(2)°, V=1313.4(8) A 3 and Z=2. Complex 6 also displayed a square arrangement of N from CTZ, plus three Cl atoms around the Au(III) ion; 6 crystallized in the monoclinic space group P21/n (No. 14) with a=9.507(1), b=18.280(4), c=12.877(1) A , β=100.59(1)°, V=2199.7(5) A 3 and Z=4. All the new compounds were found to be active against in vitro cultures of Trypanosoma cruzi, following the trend 3 = 7

Trimethylsilyl-substituted ligands as solubilizers of metal complexes in supercritical carbon dioxide

The SiMe3 group (TMS), introduced as a substituent at the cyclopentadienyl ligand, is found to magnify the solubility of the corresponding metal complexes in supercritical carbon dioxide (scCO2). This is verified from comparative solubility measurements of the species (η5-Me3SiC5H4)MoO2Cl, 1a, (η5-Me3SiC5H4)2ZrCl2, 2a, and (η5-Me3SiC5H4)Co(CO)I2·0.5(I2), 3a (newly synthesised), and of their unsubstituted precursors 1b–3b, respectively. In spite of the increased solubility, the chemical, structural and reactivity properties of the TMS derivatives are scarcely affected. Confirmation comes from a detailed study of the cobalt complex 3a that includes X-ray structural determination. The geometry is most similar to that of the precursor 3b while an apparently different Co–CO interaction is observed in the carboxylated analogue [(η5–PhCH2CO2C5H4)Co(CO)I2, 3c]. The problem is computationally tackled by using the DFT B3LYP method. The optimised geometries of the simplified models of 3a–3c are all very similar. In particular, the computed stretching frequency of the unique CO ligand is consistent with the insignificant influence of the TMS group while it suggests a reduced amount of metal back-donation in 3c. It is inferred that the TMS complexes 1a–3a, while having higher solubility in scCO2, maintain almost unaltered the electronic and chemical features of their parent compounds. In particular, the role of 1a–3a as catalysts, that is well documented for homogeneous solutions, remains unaltered in the very different scCO2 environment. The assumption is experimentally validated for 1a by performing with the latter two classic catalytic processes. The first process is the oxidation of PPh3 that is achieved by using molecular oxygen as an oxidant. The second example concerns the epoxidation of cyclohexene achieved in presence of tert-butyl hydroperoxide (TBHP).

Synthesis and Structural Characterization of (Carbene)ruthenium Complexes Binding Nucleobases

The new (carbene)ruthenium(II) nucleobase derivatives fac,cis-[(PNP)RuCl{C(NHC4H3N2O2)(CH2Ph)}]Cl (5) and fac,cis-[(PNP)RuCl{C(NHC5H3N4)(CH2Ph)}]Cl (6) [PNP = CH3CH2CH2N(CH2CH2PPh2)2] were synthesised by treating (vinylidene)ruthenium(II) complex fac,cis-[(PNP)RuCl2{C=C(H)Ph}] (1) with 5-aminouracil or adenine, respectively. Both complexes were characterized by spectroscopic techniques (IR and NMR) and elemental analyses, which confirmed the formation of the aminocarbene moieties incorporating 1 equiv. of the nucleobase in the complex framework. Crystal and molecular structure determination by X-ray diffraction analysis of the uracil derivative 5 revealed a very unusual O-coordination of the exocyclic C=O group on the C(4) atom of the uracil ring to the ruthenium atom leading to an unprecedented six-membered aminocarbene metallacycle. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

2-Oxacyclopentylidene, 2-Oxacyclohexylidene, and 2-Oxacycloheptylidene Rhenium Complexes by Reaction of ω-Alkynols with the [{MeC(CH2PPh2)3}Re(CO)2]+ Auxiliary

Various β-, γ-, and δ-alkynols have been reacted with the 16e− fragment [(triphos)Re(CO)2]+ generated in situ by H2 elimination from [(triphos)Re(CO)2(η2-H2)]BF4 [triphos = MeC(CH2PPh2)3]. Irrespective of the length of the alkyl chain between the C≡C and OH functional groups in the ω-alkynol, 2-oxacyclocarbene complexes are obtained. These include the 2-oxacyclopentylidene derivatives [(triphos)Re(CO)2{=CCH2CH2CH2O}]BF4 and [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4, the 2-oxacyclohexylidene dervivatives [(triphos)Re(CO)2{=CCH2CH2CH2CH2O}]BF4 and[(triphos)Re(CO)2{=CCH2CH2CH2CH(Me)O}]BF4, and the 2-oxacycloheptylidene complex [(triphos)Re(CO)2{=CCH2CH2- CH2CH2CH2O}]BF4. The latter compound contains a unprecedented seven-membered oxacarbene ring. The rhenium-assisted δ-alkynol to 2-oxacyloheptylidene rearrangement proceeds via the hydroxybutylvinylidene kinetic intermediate [(triphos)Re(CO)2{C=C(H)CH2CH2CH2CH2OH}]BF4, which has been characterized in both the solid state and solution. An X-ray analysis has been carried out on a single crystal of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]BF4. The structure of this complex consists of [(triphos)Re(CO)2{=CCH2CH2CH(Me)O}]+ cations and tetrafluoroborate anions with no interspersed solvent molecules. A facial triphos ligand, two cis-disposed carbonyl groups and a 2-oxacyclopentylidene ligand coordinate the Re centre in a slightly distorted octahedral environment.

Synthesis, molecular structure and properties of oxo-vanadium(IV) complexes containing the oxydiacetate ligand

The complex [V(O)(oda)(H2O)2] 1 [oda = O(CH2COO−)2] has been obtained by reaction of aqueous solutions of [V(O)(acac)2] with oxydiacetic acid. The coordination geometry around the vanadium in 1 is distorted octahedral with mutually trans water ligands and a planar conformation of the oda ligand (mer). The relative stability of the experimentally determined structure and that of the alternative isomer with a puckered oda conformation (fac) has been investigated by DFT calculations. The latter confirms that the mer geometry is more stable by 35.6 kJ mol−1. The complex [V(O)(oda)(μ-OMe)]2[Na(H2O)]22a is obtained by reaction of 1 with NaOH in methanol. The anions feature two V(O)(oda) units symmetrically bridged by methoxy groups in a syn-orthogonal arrangement, while the oda ligands have the fac conformation. Similar complexes [V(O)(oda)(μ-OMe)]2[K(H2O)]22b and [V(O)(oda)(μ-OMe)]2[HL]22c–2g are obtained from reaction with KOH or with selected N-donor bases (L), respectively. An excess of pyridine, however, causes the simple substitution of the water molecules in 1 and generates the monomer [V(O)(oda)(py)2] 3. Antiferromagnetic behaviour of binuclear compounds 2a, 2d and 2e is suggested by a variable-temperature study. Finally, the reaction of 1 with bidentate N-donor ligands allows the synthesis of the complexes [V(O)(oda)(N–N)]·H2O (N–N = 2,2′-bipyridine, 4; o-phenanthroline, 5). X-Ray characterization of 4 shows that the conformation of oda has changed from mer (as in the reactant 1) to fac.

Stereochemistry of hypervalent tin(IV) compounds. NMR and crystallographic studies of organoyltin(IV) complexes with 1,1-dithiolate ligands

Abstract Tin-119 NMR data have been used to examine the effective coordination spheres in dichloromethane solution of a series of organoyltin(IV) 1,1-dithiolate compounds RSnXn(SS)3−n (where R Ph, Me; X  Cl, Br; n=0, 1,2), for SS S2CNEt2, S2COEt, S2P(OEt)2. Intermolecular halide and 1,1-dithiolate exchange are slow on the NMR timescale however the tin-119 chemical shifts are temperature dependent due to the intramolecular equilibrium between monodentate and bidentate coordinated 1,1-dithiolate ligand. The magnitude of the temperature dependence of the tin-119 chemical shifts for the series RSn(SS)3 indicates that the order of 1,1-dithiolate ligand donor strength is Et2dtc > Etxan > Et2dtp. Mixed ligand complexes PhSn(SS)(SS)2 may be formed either by redistribution reactions of PhSn(SS)3 and PhSn(SS)3 or by addition of 1,1-dithiolate salt to solutions of PhSnCln,(SS)3−n, (n=1,2). The crystal structure of PhSn(S2CNEt2)3 has been determined. The geometry about tin in PhSn(S2CNEt2)3 is a distorted pentagonal bipyramid with tin-sulfur distances ranging from 2.487(1) to 2.794(2) A.

Insertion of iridium into C-H and C-S bonds of 2,5-dimethylthiophene 2-methylbenzothiophene and 4,6-dimethyldibenzothiophene

Abstract C-H insertion thienyl products are selectively formed at early times of the interaction of the unsaturated 16e − fragment [(triphos)IrH]with 2,5-dimethylthiophene (Me 2 T), 2-methylbenzothiophene (MeBT) and 4,6-dimethyldibenzothiophene (Me 2 DBT) [triphos = MeC(CH 2 PPh 2 ) 3 ]. C-S insertion to give six-membered metallathiacycle products occurs as a thermal step only for Me 2 T and MeBT. The C-S insertion products are isolated as both kinetic and thermodynamic stereoisomers. The thermodynamic C-S insertion product of MeBT, endo-[(triphos)Ir(η 3 - S,C,C -S(C 6 H 4 )CH=C(Me)H)], has been characterized by X-ray diffraction studies.

Reductive elimination of dimethylcarbonate from (dimethoxycarbonyl) tricarbonyl cobaltates. Isolation and crystal structures of Cs[Co(COOCH3)2(CO)3] and K[(dibenzo-18-crown-6)][Co(COOCH3)2(CO)3]

Abstract Salts of the anion [Co(COOCH 3 ) 2 (CO) 3 ] − with Cs + and K + (with the latter cation complexed by dibenzo-18-crown-6 ether) have been isolated and structurally characterized. In the trigonal bipyramidal cobaltate two C-coordinated COOCH 3 groups occupy trans -axial positions. There are ionic interactions between the cation and the terminal oxygen atoms of methoxycarbonyl involving both of the coordinated COOCH 3 groups in the case of the Cs salt but only one of them in the case of the K salt. One methoxy group of the anion [Co(COOCH 3 ) 2 (CO) 3 ] − is strongly nucleophilic, as shown by the reactions with Co 2 (CO) 8 or CO 2 . Under an inert atmosphere [Co(COOCH 3 ) 2 (CO) 3 ] − undergoes elimination of dimethylcarbonate.

CONFIGURATIONAL ISOMERISM OF COORDINATED TETRAAZAMACROCYCLES. CRYSTAL AND MOLECULAR STRUCTURE OF CARBONATO(1,7-DIMETHYL-1,4,7,10-TETRAAZACYCLODODECANE)COBALT(III) PERCHLORATE

Abstract The title compound was prepared according to three different procedures and was characterized by ion-exchange chromatography, NMR spectroscopy and X-ray crystallography. The compound crystallizes in the orthorhombic space group Imcb with a = 18.458(4), b = 13.608(3) and c = 13.436(3) A. The structure was solved by heavy-atom methods and refined to an R of 0.061. The geometry of the complex cation is octahedral with the macrocyclic ligand bonded through its four nitrogen atoms. Ion-exchange chromatography and NMR spectroscopy give no evidence of more than one stable configurational isomer of this complex.

Uracil and thiouracil complexes of dicyclopentadienyl molybdenum and tungsten: Preparation and electrochemistry. The structures of [M(η5-C5H5)2(2-SN2OC4H3)][PF6], [M(η5-C5H5)2{2-S(CH3)N2OC4H2}][PF6], [Mo(η5-C5H5)2 (4-SN2OC4H3)][PF6] and [Mo(η5-C5H5)2{4-S(CH3)N2OC4H2}][PF6] (M Mo and W)

Abstract Cationic complexes [MoCp2(U)][PF6] (1), [MCp2(2TU)][PF6] (2, 2′), [MCp2(4TU)][PF6] (3, 3′), [MoCp2(2,4-DTU)]Cl (4), [MCp2(2MTU)][PF6] (5, 5′) and [MCp2(4MTU)][PF6] (6, 6′) (M  Mo, W; Cp = η5-C5H5; U = uracilato; 2TU = 2-thiouracilato; 4TU = 4-thiouracilato; 2,4-DTU = 2,4-dithiouracilato; 2MTU = 2-methylthiouracilato and 4MTU = 4-methylthiouracilato) have been prepared from the reaction of [MCp2Cl2] with the corresponding uracil in the presence of triethylamine. All the uracilato derivatives act as bidentate ligands and experimental evidence (X-ray and IR) shows the following preference for binding atoms in this system: N(3) > N(1), = S > = O, O(2) > O(4); although there is no clear evidence it is also likely that S(2) > S(4). Electrochemical studies, by cyclic voltammetry carried out in acetonitrile or dimethylformamide, showed that compounds where ligands coordinate through N,S atoms are more stable upon oxidation than compounds where ligands coordinate through N,O donor atoms. The molecular structures of [MoCp2(2TU)][PF6](2), [WCp2(2TU)][PF6](2′), [MoCp2(4TU)][PF6](3), [MoCp2(2MTU)][PF6](5), [WCp2(2MTU)][PF6](5′) and [MoCp2(4MTU)][PF6](6) have been determined by X-ray crystallography.