Duane Choquesillo-Lazarte

Three new modes of adenine-copper(II) coordination: interligand interactions controlling the selective N3-, N7- and bridging μ-N3,N7metal-bonding of adenine to different N-substituted iminodiacetato-copper(II) chelates

Abstract The reaction of Cu2CO3(OH)2, various N-substituted-iminodiacetic acids [RN(CH2CO2H)2)] and adenine (AdeH) in water yields crystalline samples of mixed-ligand copper(II) complexes of formulas [Cu(A)(N7AdeH)(H2O)]·H2O (A=N-methyl- or N-ethyl-iminodiacetato(2−); compounds 1 and 2, respectively), [Cu(B)(N3AdeH)(H2O)]·H2O (B=N-benzyl- or N-(p-methylbenzyl)-iminodiacetato(2−); compounds 3 and 4, respectively) as well as [Cu4(pheida)4(μ-N3,N7AdeH)2(H2O)4]·2H2O (pheida=N-phenethyl-iminodiacetato(2−)). Crystal structures of the acid H2pheida and compounds 1–5 are reported. H2pheida acid exhibits a typical zwitterionic structure. Copper(II) compounds were also studied by TG analysis (with FT-IR study of the evolved gasses), IR, electronic and ESR spectra and magnetic susceptibility data. The N-alkyl- or N-benzyl-like-iminodiacetato(2−) ligands (A or B) give complexes with Cu(II)/(A or B)/AdeH equimolar ratio, whereas pheida yields an unexpected tetranuclear compound with a 2:2:1 Cu(II)/pheida/AdeH molar ratio. In 1 and 2 AdeH binds to the metal by N7, whereas in 3 and 4 the N3 atom is used. An unexpected bridging μ-N3,N7AdeHdicopper(II) binding mode is found in the tetra-nuclear compound 5 (without interligand π,π-stacking interactions). These AdeHCu(II) binding modes have not been referred in the literature before. The difference in AdeHCu(II) binding modes in compounds 1 or 2 and 3 or 4 is rationalised on the basis of the absence or presence of a flexible N-benzyl-like substituent in the iminodiacetato(2−) ligand skeleton, which prevents or permits the interligand π,π-stacking interactions.

Ti‐Catalyzed Barbier‐Type Allylations and Related Reactions

Titanocene(III) complexes, easily generated in situ from commercial Ti(IV) precursors, catalyze Barbier-type allylations, intramolecular crotylations (cyclizations), and prenylations of a wide range of aldehydes and ketones. The reaction displays surprising and unprecedented mechanistic subtleties. In cyclizations a fast and irreversible addition of an allyl radical to a Ti(III)-coordinated carbonyl group seems to occur. Intermolecular additions to conjugated aldehydes proceed through a coupling of a Ti(IV)-bound ketyl radical with an allyl radical. Reactions of ketones with allylic halides take place by the classical addition of an allylic organometallic reagent. The radical coupling processes enable transformations such as the highly regioselective alpha-prenylation that are otherwise difficult to achieve. The mild reaction conditions and the possibility to employ titanocene complexes in only catalytic quantities are highly attractive features of our protocol. These unusual properties have been taken advantage of for the straightforward synthesis of the natural products rosiridol, shikalkin, and 12-hydroxysqualene.

Structure, magnetism and DFT studies of dinuclear and chain complexes containing the tetrazolate-5-carboxylate multidentate bridging ligand.

The reaction of K(2)TzC (H(2)TzC = tetrazole-5-carboxylic acid) and either MnCl(2) x 4 H(2)O or CuCl(2) x 2 H(2)O under hydrothermal conditions leads to the formation of three new polynuclear complexes of formula [Mn(TzC)(H(2)O)(2)](n) 1 and [M(2)(TzC)(2)(H(2)O)(6)] x nH(2)O (M = Mn(II) 2, n = 4 and Cu(II) 3, n = 2). Complex 1 displays a 1D planar zig-zag chain structure where the ligand is disorderd into two positions and exhibits two mu(3)-chelating/bridging tetradentate coordination modes, one through the two carboxylate oxygen atoms and the neighbouring nitrogen atom of the tetrazolate ring and the other one through three neighboring nitrogen atoms belonging to the tetrazole ring and one of the carboxylate oxygen atoms. The structure of 2 and 3 consists of centrosymmetric dinuclear molecules, in which the ligands exhibit a mu(2)-chelating/bridging coordination mode through one of the carboxylate oxygen atoms and two neighbouring nitrogen atoms of the tetrazolate ring, generating a planar M(N-N)(2)M hexagon. Variable-temperature magnetic susceptibility studies reveal a weak antiferromagnetic interaction for 1 (J = -1.5 cm(-1)). In spite of the coplanarity of the tetrazolate and metal coordination planes in 2 and 3, they exhibit very weak antiferromagnetic interactions. DFT calculations have been performed in order to explain this unexpected magnetic behaviour.

A critical look on the nature of the intra-molecular interligand π,π-stacking interaction in mixed-ligand copper(II) complexes of aromatic side-chain amino acidates and α,α′-diimines

The mixed ligand complexes {[Cu(4Cl-Phe)(bpy)(H2O)]Cl·[Cu(4Cl-Phe)(bpy)Cl]·2H2O} (1) and [Cu(4HPG)(bpy)]·2H2O (2) were synthesized and their crystal structures determined by X-ray crystallography (4Cl-Phe = D,L-4-chlorophenylalaninato, 4HPG = D-4-hydroxyphenylglycinato, bpy = 2,2′-bipyridine). The asymmetric unit of crystals of 1 consists of two slightly different Cu(II) complexes-one contains an axial water ligand, whereas the second one has a chloride anion at that position. By contrast, 2 exhibits two close similar molecules, both having axial chloride ligands, and non coordinated water. The geometrical parameters for π,π-stacking interactions were determined by an application of PLATON program. Intermolecular π,π-interaction between bpy ligands on adjacent Cu(II) moieties results in homo pairs of complexes in the case of 1. In addition, both species of compound 1 exhibit intramolecular interligand π,π-interaction between the 4Cl-phenyl ring of 4Cl-Phe and the metalloaromatic Cu–bpy chelate ring. In crystal 2, multi-stacked homo chains are formed. Analogous calculations for previously reported, related compounds, similar to those presented here, revealed that in most cases with intra-molecular interligand π,π-interaction there is an efficient “aryl–metal chelate ring” π,π-stacking instead of an aryl–aryl interligand π,π-interaction, which indeed is not observed. These findings let us to take a critical look at the nature of the intramolecular interligand π,π-stacking interaction in the referred copper(II) mixed-ligand complexes.

Synthesis, Structure, and Catalytic Applications for ortho- and meta-Carboranyl Based NBN Pincer-Pd Complexes

o- and m-Carborane-based NBN pincer palladium complexes (oCB-L1)Pd, (oCB-L2)Pd, and (mCB-L1)Pd are synthesized in two steps from commercially available starting materials. The pincer complexes were prepared by the reaction of bis-[R(hydroxy)methyl]-1,2-dicarba-closo-dodecaborane (R = 2-pyridyl oCB-L1, 6-methyl-2-pyridyl oCB-L2) or bis-[2-pyridyl (hydroxy)methyl]-1,2-dicarba-meta-dodecaborane (mCB-L1) with [PdCl2(MeCN)2] under mild conditions. The X-ray structure determination of all carboranyl pincer complexes shows unambiguously B-H activation of the carborane cages. The results agree with the Pd-B bonds in all complexes exhibiting strong σ-electron donation. Theoretical calculations reveal the importance of considering the solid state intermolecular hydrogen bonding when investigating the trans influence in organometallic chemistry. A localized orbitals approach has also been applied to analyze the metal oxidation state in the carboranyl pincer complexes. Catalytic applications of (oCB-L1)Pd and (mCB-L1)Pd have shown the complexes are good catalyst precursors in Suzuki coupling in water and with very low amounts of catalyst loadings.

Inter-ligand interactions and the selective formation of the unusual metal–N3(adenine) bond in ternary copper(II) complexes with N-benzyliminodiacetato(2−) ligands

A novel mixed-ligand copper(II) complex with N-(p-methoxybenzyl)-iminodiacetato(2)) ligand (MOBIDA) and adenine (AdeH) of formula ½CuðMOBIDAÞðAdeHÞðH2OÞ� � H2O has been obtained. Its crystal structure reveals the selective formation of a rare Cu– N3(AdeH) bond, closely related to those reported by first time for compounds of general formula ½CuðBÞðAdeHÞðH2OÞ� � H2O, with B ¼ N-benzyl- or N-(p-methylbenzyl)-iminodiacetato(2)) ligands. Appropriate structural comparison reveals that the copper(II) coordination by less basic N3 heterocyclic donor of the nucleobase is controlled by a molecular recognition process involving the formation of an intra-molecular inter-ligand N7(imidazole-like)–H ��� O(carboxyl) bond and the inter-molecular inter-ligand p,p-stacking interaction between six membered rings of benzyl (MOBIDA) and AdeH. This stack generates multi-stacked infinite chains along the b-axis of the crystal. 2002 Elsevier Science B.V. All rights reserved.

New (RS)-benzoxazepin-purines with antitumour activity: The chiral switch from (RS)-2,6-dichloro-9-[1-(p-nitrobenzenesulfonyl)-1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl]-9H-purine.

Completing an SAR study, a series of (RS)-6-substituted-7- or 9-(1,2,3,5-tetrahydro-4,1-benzoxazepine-3-yl)-7H or 9H-purines has been prepared under microwave-assisted conditions. Their antiproliferative activities on MCF-7 and MDA-MB-231 cancerous cell lines are presented, being the majority of the IC(50) values below 1μM. The most active compound (RS)-2,6-dichloro-9-[1-(p-nitrobenzenesulfonyl)-1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl]-9H-purine (14) presents an IC(50) of 0.166μM against the human cancerous cell line MDA-MB-231. Compound 14 was the most selective against the human breast adenocarcinoma MCF-7 and MDA-MB-231 cancer cell lines (Therapeutic Indexes, TIs=5.1 and 11.0, respectively) in relation to the normal one MCF-10A. (RS)-14 was resolved into its enantiomers. Both enantiomers are equally potent, but more potent than the corresponding racemic mixture. (R)-14 induces apoptosis against MCF-7 up to 52.50% of cell population after 48h, being more potent than the clinical-used drug paclitaxel (43%). (RS)-14 induces no acute toxicity in mice after two weeks of treatment.

Metal chelates of N-(2-pyridylmethyl)iminodiacetate(2-) ion (pmda). Part I. Two mixed-ligand copper(II) complexes of pmda with N,N-chelating bases. Synthesis, crystal structure and properties of H2pmda·0.5H2O, [Cu(pmda)(pca)]·3H2O (pca=α-picolylamine) and [Cu(pmda)(Hpb)]·5H2O (Hpb=2-(2′-pyridyl)benzimidazole)

N -(2-Pyridylmethyl)iminodiacetic acid hemi-hydrate (H2pmda/0.5H2O) was prepared and characterized by X-ray crystallography (final R 1 � /0.042). The zwitterion H2pmda 9 is intra -stabilized by a trifurcated hydrogen bond. Intermolecular carboxyliccarboxylate hydrogen bonds and the parallel inter-ligand p,p-stacking (3.57(2) A u ) between pyridyl rings from pairs of adjacent zwitterions generate 2D frameworks (bi-layers with the carboxyl groups towards the external surfaces and py � /pmda rings towards the inside). In the crystal, the bi-layered structures are connected by equivalent hydrogen bonds, which link each water molecule to two symmetry related O-carboxylate atoms from the adjacent external faces of two 2D frameworks. The compounds [Cu(pmda)(pca)]/3H2 O( 1) and [Cu(pmda)(Hpb)]/5H2 O( 2) were obtained by stoichiometric reaction of Cu2(CO3)(OH)2, H2pmda/0.5H2O and a-picolylamine (pca) or 2-(2?-pyridyl)benzimidazole (Hpb), respectively, and characterized by single crystal X-ray diffractometry. Compound 2 was also studied by TG analysis (with FTIR study of the evolved gasses in the pyrolysis), magnetic susceptibility at 80 � /300 K range, and FTIR, electronic, ESR spectra. In 1 and 2 the copper(II) atom exhibits a distorted octahedral coordination (type 4� /1� /1) and pmda acts as tripodal tetra-dentate ligand. However, pmda displays different coordination roles. The pmda supplies two N ,O -meridional and two trans -apical N (py),O -donors in 1, whereas links the metal by three N ,N (py),O -meridional and one O -apical atoms in 2 .N op,p-stacking of pyridyl � /(pmda) rings is observed in these complexes. The pyridyl � /(pca) ring of 1 is not involved in ring � /ring stacking interactions, but compound 2 recognizes itself by a roughly antiparallel p,p-stacking of adjacent Hpb ligands (5.38, 3.41(2) A u ) forming pairs of complex units. # 2002 Elsevier Science Ltd. All

Ring–ring or nitro-ring π,π-interactions in N-(p-nitrobenzyl)iminodiacetic acid (H2NBIDA) and mixed-ligand copper(II) complexes of NBIDA and imidazole (Him), 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen). Crystal structures of H2NBIDA, [Cu(NBIDA)(Him)(H2O)], [Cu(NBIDA)(bipy)]·3H2O and [Cu(NBIDA)(phen)]·2H2O

Abstract N-(p-nitrobenzyl)iminodiacetic acid (H2NBIDA) and the mixed-ligand copper(II) complexes with NBIDA and imidazole (Him), 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) were prepared and characterised by thermal, spectral, magnetic and X-ray diffraction methods. Our aim is to study various possibilities of the N-(p-nitrobenzyl) arm in the iminodiacetate(2−) ion (IDA) skeleton to be involved in π,π-interactions which contribute to molecular recognition processes and crystal building. Analysis of the shortest aromatic ring–ring interactions were carried out with platon program and let us conclude that in free H2NBIDA acid (1) and [Cu(NBIDA)(Him)(H2O)] (2) only inter-molecular benzyl–benzyl π,π-stacks occur, whereas in [Cu(NBIDA)(bipy)]·3H2O (3) and [Cu(NBIDA)(phen)]·2H2O (4) there are both inter-molecular nitro-benzyl π,π-interactions (instead of benzyl–benzyl π,π-stacks) and α,α′-diimine-α,α′-diimine ring–ring π,π-interactions. In compound 2 NBIDA ligand has a typical mer-NO2 tridentate conformation, whereas in 3 or 4 it exhibits an unusual fac-O2+N(apical) conformation. The molecular recognition pathway in 3 and 4 is discussed on a structural basis, considering a variety of interligand interactions involved in molecular recognition processes to build these and closely related crystals. We conclude that both the presence of a non-coordinating N-substituent in the IDA-like ligand and the chelation of Cu(II) by an aromatic α,α′-diimine (bipy or phen) display active roles for promote a fac-O2+N(apical) conformation and various modes of interligand π,π-stacking interactions.

Divalent metal vinylphosphonate layered materials: compositional variability, structural peculiarities, dehydration behavior, and photoluminescent properties

A family of M-VP (M = Ni, Co, Cd, Mn, Zn, Fe, Cu, Pb; VP = vinylphosphonate) and M-PVP (M = Co, Cd; PVP = phenylvinylphosphonate) materials have been synthesized by hydrothermal methods and characterized by FT-IR, elemental analysis, and thermogravimetric analysis (TGA). Their structures were determined either by single crystal X-ray crystallography or from laboratory X-ray powder diffraction data. The crystal structure of some M-VP and M-PVP materials is two-dimensional (2D) layered, with the organic groups (vinyl or phenylvinyl) protruding into the interlamellar space. However, the Pb-VP and Cu-VP materials show dramatically different structural features. The porous, three-dimensional (3D) structure of Pb-VP contains the Pb center in a pentagonal pyramid. A Cu-VP variant of the common 2D layered structure shows a very peculiar structure. The structure of the material is 2D with the layers based upon three crystallographically distinct Cu atoms; an octahedrally coordinated Cu(2+) atom, a square planar Cu(2+) atom and a Cu(+) atom. The latter has an unusual co-ordination environment as it is 3-coordinated to two oxygen atoms with the third bond across the double bond of the vinyl group. Metal-coordinated water loss was studied by TGA and thermodiffractometry. The rehydration of the anhydrous phases to give the initial phase takes place rapidly for Cd-PVP but it takes several days for Co-PVP. The M-VP materials exhibit variable dehydration-rehydration behavior, with most of them losing crystallinity during the process.