Noemí Andrade-López

Versatile behavior of 2‐guanidinobenzimidazole nitrogen atoms toward protonation, coordination and methylation

The structure, dynamic behavior, protonation, methylation, and coordination sites of 2-guanidinobenzimidazole la were investigated. Structures of compounds [2-guanidinium-1,3,10-trihydrobenzimidazole]sulfate lb, [2-guanidinium-l,3-dihydro-benzimidazole]sulfate lc-ld, [2-guanidinium-l,3-dihydro-benzimidazole]tetrafluoroborate le, [2-guanidinium-l,3-dihydro-benzimidazole]chbride If, [2-guanidinium-1,3dihydro-benzimidazole] perchlorate 1% 2-guanidinoI-methyl-benzimidazole 2a, [2-guanidinium-l,3-dimethyl-benzimidazole]iodide 2b, [2-guanidinium-1methyl-3-hydro-benzimidazole]chloride 2c, [2

Benzazole‐N(SINGLE BOND)BH3 adducts. Reductive transposition of 2‐benzimidazole, 2‐benzothiazole, and 2‐benzoxazole N(SINGLE BOND)BH3 adducts to 1,3,2‐benzimidazaborole, 1,3,2‐benzoxaborole, and 1,3,2‐benzothiazaborole

1,3,2-Benzimidazaborole, 1,3,2-benzoxaborole, and 1,3,2-benzothiazaborole were synthesized from the corresponding 2-benzazole N(SINGLE BOND)BH3 and 2-benzazole S(SINGLE BOND)BH3 adducts through a reductive transposition from the isolobal fragment X(SINGLE BOND)C(sp2) (DOUBLE BOND) N(sp2) (SINGLE BOND) B(sp3) (X (DOUBLE BOND) N, O, S) to the fragment X(SINGLE BOND)B(sp2) (DOUBLE BOND) N(sp2) (SINGLE BOND) C(sp3). N(SINGLE BOND)BH3 substitution shifts to lower frequencies 4-H, C-3a, and C-7a resonances. The X-ray diffraction analysis of 2-(o-methoxyphenyl)benzothiazole N(SINGLE BOND)BH3 adduct is reported. Two new tetracyclic boron-bridged compounds were observed as by-products (6,9-(ethyl)-diaza-2-oxa-1-bora[3,4,7,8]-dibenzobycyclo[4.3.0]-nona-3,7-diene, 6d, and 8-aza-9-oxa-2-thia-1-bora-[3,4,7,8]dibenzobycyclo[3.4.0]nona-3,7-diene, 15d, when 2-(o-methoxyphenyl)-1-ethylbenzimidazole-BH36b and 2-(o-methoxyphenyl)-benzothiazole-BH315b adducts were heated.

Organometallic tin complexes derived from 2‐guanidinobenzimidazole

Coordination compounds derived from 2-guanidinobenzimidazole 1 and R2SnCl2 (2 R = Me, 3 R = Bu, 4 R = Ph), and SnCl4 7 were prepared and their structures investigated by 1H, 13C, 119Sn, 15N NMR, mass spectrometry (FAB or EI), infrared, and elemental analysis. The NMR data suggest pentacoordinated (5 and 6) or hexacoordinated tin atoms 2–4 and 7. In all cases, 2-guanidinobenzimidazole acts as a bidentate ligand. In the solid state, 2–4 and 7 are associated by bridging chlorine atoms in polymeric chains.

Boron and Transition Metal Compounds Derived from 2-Uroylbenzimidazole

The coordination sites of 2-uroylben- zimidazole 1 toward diphenylborinic acid, as well as zinc, cadmium, copper, nickel and cobalt chlorides, bromides, and nitrates were investigated. The ligand is bonded in monodentate mode to ZnCl2, ZnBr2, CdCl2, CdBr2, and Cd(NO3)2, and in bidentate mode to all oth- ers. With diphenylborinic acid, two heterocycles are formed; in one, the boron is bonded to imidazole and the terminal NH2 group, and in the other the boron is bonded to imidazole and to the oxygen atom. Boron, zinc, and cadmium derivatives were studied by NMR spectroscopy. The X-ray diffraction structure of 2- uroylbenzimidazole is reported. q 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 577-584, 1999

Synthesis and structural characterization of mono- and dinuclear NiII and PdII complexes derived from tetradentate 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene

The reaction of Schiff base 1,7-bis-(pyridin-2-yl)-2,6-diaza-1,6-heptadiene (L) with either NiCl2·6H2O or [PdIICl2(CH3CN)2]/Na[BF4] in 1 : 1 stoichiometry yielded mononuclear ionic complexes, trans-[NiII(L)(H2O)2]Cl2·3H2O (1·3H2O) and [PdII(L)][BF4]2 (2), respectively; the reaction of L with [PdIICl2(CH3CN)2] in 1 : 2 ratio yielded dinuclear cis-[PdII 2(μ-L)Cl4] (3). Complexes 1–3 were characterized by vibrational spectroscopy and X-ray diffraction; diamagnetic 2 and 3 were also characterized by NMR in solution. The molecular structures of 1 and 2 displayed tetradentate coordination of L with formation of two five-membered and one six-membered chelate rings for both complexes. In 3, L showed bidentate coordination mode for each pyridylimine toward PdII. Complex 1 has distorted octahedral geometry around NiII and an extended hydrogen-bond network; distorted square planar geometry around PdII in 2 and 3 was observed.

Selective Liquid-Liquid Extraction of Mercury(II) from Aqueous Solution by N-Alkyldithiophosphate Compounds CH3(CH2)nS2P(OC6H4)2 (n = 0 to 4)

The extraction of mercury(II) from nitric acid solutions by the dithiophosphate compounds CH3(CH2)nS2P(OC6H4)2 (n = 0 to 4) has been examined. The best extracting properties were displayed by the liquid compound containing the longest alkyl chain CH3(CH2)4S2P(OC6H4)2 (Pen-DTP) in acidic media. The results indicate the stability of Pen-DTPA in nitric and sulphuric media. Pen-DTP selectively extracted Hg(II) in the presence of some interfering ions such as Cd(II), Pb(II) and Bi(III). The Hg(II) recovery from back-extraction experiments with chloridric acid is higher than 70%. Mostly, this extractant shows a remarkable selectivity in the extraction of mercury (76.6%) in the presence of Ag(I) (9.2%) without using a masking agent.

Activation of aldehydes by exocyclic iridium(I)-η4:π2-diene complexes derived from 1,3-oxazolidin-2-ones

The Ir(i) complexes [TpMe2Ir(η4-1,4-diene)] 2b and 2c react thermally with a variety of aromatic aldehydes, 3a-e, to generate the metallabicyclic compounds 4e-k and the Fischer-type carbenes 5a-b in moderate yields. These reactions are proposed to take place with the initial formation of η1-aldehyde adducts as key intermediates. The formation of the metallabicyclic compounds 4e-k involves a formal decarboxylation process at the exo-2-oxazolidinone diene and an ortho metallation of the aromatic ring. The generation of the Fischer-type carbenes 5a-b is the result of a series of metal-based rearranged intermediates with no decarboxylation observed. Treatment of the η4-diene complex 2b with a variety of Lewis bases induces a change in the binding mode of the diene ligand from η4:π2 to η2:σ2 to form the Ir(iii) derivatives 6b-d of composition TpMe2Ir-(η4:π2-1,4-diene)(L) (L = CO, MeCN, and C5H5N). A study of reactions of complex 2b with either mono- or poly-deuterated aldehydes was performed to understand the mechanisms of such processes. The results of these studies were used to determine plausible formation mechanisms of the metallabicyclic compounds 4e-4k and Fischer-type carbenes 5a-b compound series. These mechanisms were corroborated by density functional theory (DFT) calculations of the free energy profiles.

Pentacoordination at antimony via endocyclic and exocyclic intramolecular interactions in dibenzostibocine diorganodithiophosphates [{D(C6H4S)2}Sb{S2P(OR)2}] (D=O, S)

Abstract Treatment of [{D(C6H4S)2}SbCl] (D=O, 1; D=S, 2) with MS2P(OR)2 afforded the stable dibenzostibocine dithiophosphate compounds [{D(C6H4S)2}Sb{S2P(OR)2}] with D=O, R=1,2-C6H4 (3); for D=S, R=1,2-C6H4 (4), Et (5), nPr (6), iPr (7), and Ph (8). The compounds were characterized by IR and 1H, 13C{1H}, and 31P{1H} NMR spectroscopy in solution. The 31P{1H} NMR data are consistent with an anisobidentate coordination mode of the dithiophosphate ligand to the Sb atom. Single crystal X-ray diffraction analyses of compounds 3, 4, 7, and 8 revealed that the antimony atom acts as an acceptor atom exhibiting endocyclic and exocyclic intramolecular interactions with the donor D atom and with both sulfur atoms of the dithiophosphate ligand, expanding its coordination sphere from four in the starting materials to five and displaying a skew-trapezoidal pyramidal local geometry.

Coordination diversity in tin compounds with bis(benzoxazole)phenol as a polydentate ligand: Synthesis and crystal structure studies

Abstract The reaction of 2,6-bis(benzoxazolyl)-4-tert-butylphenol (HL) with [nBuxSnCl4−x] (x = 0, 1) in 1:1 stoichiometry yielded the tin coordination complexes [(HL)SnnBuxCl4−x] [x = 0 (1); x = 1 (2)]. Deprotonation of HL was performed using reagents having groups with high basicity such as nBuLi or [Sn{N(SiMe3)2}2]. These basic reagents prompted the coordination of the ligand in its anionic form, yielding the complexes [(thf)2Li(L)SnCl4] (3) and [(L)Sn{N(SiMe3)2}] (4), respectively. The molecular structure of HL displayed an intramolecular hydrogen bond OH—N and a planar arrangement of the bis(benzoxazolyl)phenolic system. In the molecular structures of both complexes containing HL an intramolecular hydrogen bond of NH—O type was also present. The coordination of the ligand in either neutral or anionic form is described by a κO,κN chelate mode toward Sn. All complexes displayed bis(benzoxazolyl)phenolic moieties close to planar; the least planar system was observed in 4 that was also studied by DFT methods. Graphical abstract