Synthetic hosts for molecular recognition of ureas.

Four hosts (7-10) containing 2,6-bisamidopyridine- and 2,5-bisamidopyrrole-bearing pyridyl or 1,8-naphthyridyl groups have been prepared and their structures studied by a combination of multinuclear NMR spectroscopy and X-ray crystallography. Their behavior in molecular recognition of urea derivatives, including (+)-biotin methyl ester, has been approached by molecular modeling (Monte Carlo conformational search, AMBER force field). The minimum energy values for the complexes are correlated with the experimental binding energies determined by means of (1)H NMR titrations.

A hydridoirida-beta-diketone as an efficient and robust homogeneous catalyst for the hydrolysis of ammonia-borane or amine-borane adducts in air to produce hydrogen.

The first homogeneous metal-catalysed hydrolysis of ammonia-borane or amine-borane adducts for hydrogen generation, using a stable organometallic complex [IrHCl{(PPh(2)(o-C(6)H(4)CO))(2)H}], is reported.

Selective formation of cis-diacyl, cis-PPh(2)R rhodium(III) complexes by the reaction of rhodium(III) cis-diacyl, trans-PPh(2)R complexes with aliphatic diamines.

The cis-diacyl, trans-PPh(2)R complex [RhCl(PPh(2)(o-C(6)H(4)CO))(2)(pyridine)] () reacts with substituted aliphatic diamines to afford selectively cationic cis-diacyl, cis-PPh(2)R, diamine derivatives [Rh(PPh(2)(o-C(6)H(4)CO))(2)(NN')](+) (NN' = 1,2-diphenylethylenediamine, 2; 1,2-propanediamine, 3; N-methylethylenediamine, 4; N,N-dimethylethylenediamine, 5; N,N'-dimethylethylenediamine, 6; N,N,N'-trimethylethylenediamine, 7) with high stereoselectivity depending on the N-donor ligand employed. Complexes 2 and 3 contain a single isomer, while 4 is a mixture of two isomers, 4a and 4b. Formation of 4a occurs first and is followed by isomerisation to 4b until the equilibrium 4a:4b = 1:4 ratio is attained. In contrast, 5 and 6 contain a single isomer. More basic amino groups prefer positions trans to an acyl group while less basic amino groups are trans to a phosphine group. The preferred intramolecular N-H...O hydrogen bond formation between an amino and an acyl coordinated ligands, trans to the phosphorus atoms, appears to be relevant to the selectivity observed. 7 is a mixture of two isomers 7a and 7b in a 7a:7b = 5.7:1 ratio. N,N,N',N'-tetramethylethylenediamine or N,N'-diphenylethylenediamine led to the elimination of the N-donor ligands and the formation of a mixture of isomers of [Rh(2)(mu-Cl)(mu-PPh(2)(o-C(6)H(4)CO))(2)(PPh(2)(o-C(6)H(4)CO))(2)](+) (), where the Rh atoms are triply bridged by two acyl groups in a head-to-tail arrangement and by a chloride. The reaction of [Rh(PPh(2)(o-C(6)H(4)CO))(2)(ndmeen)]ClO(4) (5) with acids led to the displacement of the diamine and the formation of a [8a](+):[8b](+):[8c](+) = 1:1:3 mixture. 8c, containing the weakest sigma-donor oxygen atoms trans to the strongest sigma-donor acyl groups, represents the most electronically favourable geometry for . All the complexes were fully characterized spectroscopically. Single crystal X-ray diffraction analysis was performed on 5, 6, 8a and 8b.

Molecular complexes between pi-excedent heterocycles (indoles and carbazole) and pi-deficient polynitrobenzenes.

Five charge-transfer complexes 1-5 derived from indoles (including a carbazole) and halogenopolynitrobenzenes (ClDNB, FDNB, ClTNB) as well as their individual components have been studied in the solid state by (13)C CPMAS NMR. The stacking effects on the (13)C chemical shifts have been rationalized by means of M05-2X functional and GIAO/B3LYP/6-311 ++G(d,p) calculations. The results, although only semiquantitative, are very promising for studying such structures.

Electrical stimulation combined with exercise increase axonal regeneration after peripheral nerve injury.

Although injured peripheral axons are able to regenerate, functional recovery is usually poor after nerve transection. In this study we aim to elucidate the role of neuronal activity, induced by nerve electrical stimulation and by exercise, in promoting axonal regeneration and modulating plasticity in the spinal cord after nerve injury. Four groups of adult rats were subjected to sciatic nerve transection and suture repair. Two groups received electrical stimulation (3 V, 0.1 ms at 20 Hz) for 1 h, immediately after injury (ESa) or during 4 weeks (1 h daily; ESc). A third group (ES+TR) received 1 h electrical stimulation and was submitted to treadmill running during 4 weeks (5 m/min, 2 h daily). A fourth group performed only exercise (TR), whereas an untreated group served as control (C). Nerve conduction, H reflex and algesimetry tests were performed at 1, 3, 5, 7 and 9 weeks after surgery, to assess muscle reinnervation and changes in excitability of spinal cord circuitry. Histological analysis was made at the end of the follow-up. Groups that received acute ES and/or were forced to exercise in the treadmill showed higher levels of muscle reinnervation and increased numbers of regenerated myelinated axons when compared to control animals or animals that received chronic ES. Combining ESa with treadmill training significantly improved muscle reinnervation during the initial phase. The facilitation of the monosynaptic H reflex in the injured limb was reduced in all treated groups, suggesting that the maintenance of activity helps to prevent the development of hyperreflexia.

New hydridoirida-beta-diketones derived from 8-quinoline-carbaldehyde and o-(diphenylphosphino)benzaldehyde.

8-Quinoline-carbaldehyde (C(9)H(6)NCHO) reacts in methanol with [IrCl(Cod)](2) (Cod = 1,5-cyclooctadiene) to give the acylhydrido complex [IrHCl(C(9)H(6)NCO)(Cod)] (1) or with [IrHCl{PPh(2)(o-C(6)H(4)CO)}(Cod)] to afford the hydridoirida-beta-diketone complex [IrHCl({PPh(2)(o-C(6)H(4)CO)}(C(9)H(6)NCO)H)] (2). Complex 2 reacts with silver perchlorate in the presence of pyridine to afford the cationic [IrH({PPh(2)(o-C(6)H(4)CO)}(C(9)H(6)NCO)H)(py)]ClO(4) (), which in solution transforms slowly into the cationic dinuclear complex [Ir{micro-PPh(2)(o-C(6)H(4)CO)}(C(9)H(6)NCO)(py)](2)(ClO(4))(2) (4) with two acylphosphine chelate-bridging ligands. The reaction of 2 with AgClO(4) in the presence of carbon monoxide affords [IrH({PPh(2)(o-C(6)H(4)CO)}(C(9)H(6)NCO)H)(CO)]ClO(4) (5), which in solution is in equilibrium with the deprotonated diacylhydrido complex [IrH{PPh(2)(o-C(6)H(4)CO)}(C(9)H(6)NCO)(CO)] (6). The reaction of 2 with Et(3)OPF(6) results in the formation of [[IrH({PPh(2)(o-C(6)H(4)CO)}(C(9)H(6)NCO)H)](2)(micro-Cl)]PF(6) (7), containing a cationic dinuclear species with a single chlorine atom bridging two hydridoirida-beta-diketone fragments. The reaction of with [Rh(OMe)(Cod)](2) affords the hydridoirida-beta-diketonaterhodium(I) complex [IrHCl{micro-PPh(2)(o-C(6)H(4)CO)}(micro-C(9)H(6)NCO)Rh(Cod)] (8), which isomerizes to the thermodynamically stable isomer [IrCl{PPh(2)(o-C(6)H(4)CO)}(micro-H)(micro-C(9)H(6)NCO)Rh(Cod)] (9). The catalytic activity of these complexes in the hydrogen transfer from isopropanol to cyclohexanone has been tested. The X-ray diffraction structures of complexes 2, 4 and 9 are reported.

Silver and gold luminescent metallomesogens based on pyrazole ligands.

A series of ionic bis(pyrazole)-silver(I) and -gold(I) complexes [ML(2)][A] (M = Ag, Au; A = BF(4)(-), PF(6)(-), NO(3)(-)), prepared by coordination of the mesomorphic L = Hpz(2R(n)) or non-mesomorphic L = Hpz(R(n)) pyrazole ligands (Hpz(2R(n)) = 3,5-bis(4-alkyloxyphenyl)pyrazole; Hpz(R(n)) = 3-(4-alkyloxyphenyl)pyrazole), has been studied. The complexes exhibit enantiotropic behaviour, showing smectic A (SmA) mesophases. The choice of the ligands allows the achievement of 'H' or 'U' molecular shapes, which appear to be responsible for the attainment of liquid crystal mesophases, these not being dependent on the coordinating or non-coordinating nature of the A counteranions. The new complexes are photoluminescent both in the solid state and in solution at room temperature. In addition, the luminescent behaviour of selected compounds as a function of the temperature indicates that the luminescence is maintained in the mesophase.

Reactivity of hydridoirida-beta-diketones with bases: the selective formation of new di-mu-acyl-mu-hydridodiiridium(III) or dihydridoirida-beta-diketone complexes and heterometallic Ir(III)-Rh(I) derivatives.

The hydridoirida-beta-diketone [IrHCl{(PPh2(o-C6H4CO))2H}] (1a) reacts with bases such as KOH or NaHCO3 in methanol to undergo dehydrodechlorination and acyl-bridge formation affording [Ir2H2(PPh2(o-C6H4CO))2(mu-PPh2(o-C6H4CO))2] (2) with two acylphosphine chelate-bridging ligands, in a head-to-tail disposition, and terminal hydrides. The acyl bridges can be broken by pyridine, PPh3, CO or dimethylsulfoxide affording selectively mononuclear diacylhydrido neutral derivatives [IrH(PPh2(o-C6H4CO))2L] (3-6). la reacts with KOH or NaHCO3 in refluxing methanol to afford a novel dihydridoirida-beta-diketone [IrH2{(PPh2(o-C6H4CO))2H}](7), via dehydrodechlorination to afford 2, which then undergoes hydrogenation and protonation. The reaction of la with NEt3 affords 2 and [NHEt3]Cl. Further reaction affords [Ir2(mu-H){mu-PPh2(o-C6H4CO)}2(PPh2(o-C6H4CO))2] (8), with two acylphosphine chelate-bridging ligands and a bridging hydride. Neutral or cationic hydridoirida-beta-diketone complexes react with [Rh(cod)(OMe)]2 (cod = 1,5-cyclooctadiene) to afford hydridoirida-P-diketonaterhodium(I) complexes [IrHCl(mu-PPh2(o-C6H4CO))2Rh(cod)] (9) or [IrHL(mu-PPh2(o-C6H4CO))2Rh(cod)]ClO4 (L = py, 10; CO, 11), respectively that isomerise to the thermodynamically stable isomers of [IrCl(PPh2(o-C6H4CO))(mu-H))(mu-PPh,2(o-C6H4CO))Rh(cod)] (12) or [Ir(py)(PPh2(o-C6H4CO))(mu-H))(mu-PPh2(o-C6H4CO))Rh(cod)]ClO4(13). The reaction of 7 with [Rh(cod)(OMe)]2 affords [Ir(PPh2(o-C6H4CO))2(mu-H)2Rh(cod)](14). All the complexes were fully characterised spectroscopically. Single-crystal X-ray diffraction analysis was performed on 2, 4, 7, [8]ClO4 and 9.

Structural studies of two Tinuvin P analogs: 2-(2,4-dimethylphenyl)-2H-benzotriazole and 2-phenyl-2H-benzotriazole.

2-(2,4-Dimethylphenyl)-2H-benzotriazole (1) has been synthesized in a three step procedure starting from 2,4-dimethyl-N-(2-nitrophenyl)benzamide via a 5-(2,4- dimethylphenyl)-1-(2-nitrophenyl)-1H-tetrazole intermediate. Its structure and those of Tinuvin P and 2-phenyl-2H-benzotriazole (5) have been studied by multinuclear NMR (1H-, 13C- and 15N-) in solution and in the solid state. X-ray diffraction analysis of 1 and 5 allowed to us establish the molecular conformation around the single bond connecting the two aromatic systems, in agreement with the conclusions drawn from the NMR study. In the case of 1 ab initio geometry optimization was achieved at the Hartree-Fock HF/6- 31G** and DFT B3LYP/6-31G** levels.

The structure of pyrazoles in the solid state: a combined CPMAS, NMR, and crystallographic study.

The structures of six N-unsubstituted pyrazoles, three already known and three newly synthesized, have been studied by a combination of X-ray crystallography, multinuclear NMR (solution and solid state), and density functional theory (DFT) calculations. In those cases where crystal structure and CPMAS NMR were available, the agreement was almost perfect, allowing a prediction of the tautomer (with certitude) and the tetrameric structure (with high probability) in the case of 5-isopropyl-3-phenyl-1H-pyrazole without knowing the X-ray structure. In the case of the 5-(2-benzylphenyl)-3-trifluoromethyl-1H-pyrazole above represented, the DFT calculations at the B3LYP/6-31G level justify the great stability of this tautomer by the presence of an intramolecular N-H...pi interaction, present in solution.

A trinuclear Pt(II) compound with short Pt-Pt-Pt contacts. An analysis of the influence of pi-pi stacking interactions on the strength and length of the Pt-Pt bond.

In this work we report the first example of a trinuclear Pt(II) complex with Pt-Pt-Pt bonds that are not facilitated by direct intervention of bridging ligands but are partially held by the attractive pi-pi stacking interaction between the phenyl units of the 4,4'-dimethyl-2,2'-bipyridyl ligands. The effect of the pi-pi stacking interactions on the strength and length of the Pt-Pt bond has been discussed using reduced models of the interacting moieties in which the aromatic rings have been removed. The nature of the Pt-Pt bonds has been studied through energy decomposition and atoms-in-molecules analyses. The results indicate that the relatively strong (about 40 kcal mol(-1)) Pt-Pt metallic bond has similar covalent and ionic contributions.

Novel hydridoirida-beta-diketones containing small molecules, CO, or ethylene: their behavior in coordinating solvents such as dimethylsulfoxide or acetonitrile.

New hydridoirida-beta-diketones [IrH[(PPh2(o-C6H4CO))2H](CO)]ClO4 2 and [IrH[(PPh2(o-C6H4CO))2H](olefin)]BF4 (olefin = C2H4, 5; 1-hexene, 10) have been prepared. These complexes may afford new diacylhydridoiridium(III) derivatives. In chloroform solution, complex 2 is in equilibrium with the deprotonated diacylhydride trans-[IrH(PPh2(o-C6H4CO))2(CO)] complex 3. In DMSO, deprotonation of 2 occurs to yield the kinetically favored product 3, which isomerizes to the thermodynamically favored complex cis-[IrH(PPh2(o-C6H4CO))2(CO)] 4. Reprotonation of 4 with HBF4 in chlorinated solvents gives the cation in 2. In coordinating solvents such as dimethyl sulfoxide or acetonitrile, complex 5 undergoes displacement of ethylene to afford [IrH{(PPh2(o-C6H4CO))2H](L)]BF4 (L = DMSO, 7; CH3CN, 9). Complexes 5 and 7 undergo deprotonation by NEt3 to give the corresponding diacylhydrides. The ethylene complex gives only trans-[IrH(PPh2(o-C6H4CO))2(C2H4)] 6, while the dimethyl sulfoxide derivative affords a mixture of trans- and cis-[IrH(PPh2(o-C6H4CO))2(DMSO)] 8. Complex 10 shows inhibited alkene rotation around the Ir-olefin axis. All of the complexes were fully characterized spectroscopically. Single-crystal X-ray diffraction analysis was performed on complexes 3, 4, and 9. The 13C NMR and X-ray data point to a carbenoid character in the carbon atoms bonded to iridium in the irida--diketone fragment, so that it can be considered as an acyl(hydroxycarbene) moiety.