D-π-A Compounds with Tunable Intramolecular Charge Transfer Achieved by Incorporation of Butenolide Nitriles as Acceptor Moieties.

Chromophores where a polyenic spacer separates a 4H-pyranylidene or benzothiazolylidene donor and three different butenolide nitriles have been synthesized and characterized. The role of 2(5H)-furanones as acceptor units on the polarization and the second-order nonlinear (NLO) properties has been studied. Thus, their incorporation gives rise to moderately polarized structures with NLO responses that compare favorably to those of related compounds featuring more efficient electron-withdrawing moieties. Derivatives of the proaromatic butenolide PhFu show the best nonlinearities. Benzothiazolylidene-containing chromophores present less alternated structures than their pyranylidene analogues, and, unlike most merocyanines, the degree of charge transfer does not decrease on lengthening the π-bridge.

Push-pull systems bearing a quinoid/aromatic thieno[3,2-b]thiophene moiety: synthesis, ground state polarization and second-order nonlinear properties.

Chromophores bearing a 2-dicyanomethylenethieno[3,2-b]thiophene moiety in their quinoidal form have been synthesized, exploring for the first time the reactivity of this system towards aldehydes. Their ground state polarization and linear and second-order nonlinear optical (NLO) properties have been determined by a combined experimental and theoretical study, and compared to those of analogous compounds featuring an aromatic thienothiophene unit. Due to the gaining of aromaticity, quinoid systems have been found to display more polarized electronic ground states and higher NLO responses with respect to their aromatic counterparts.

Cycloaddition reactions of polyenic donor-π-acceptor systems with an electron-rich alkyne: access to new chromophores with second-order optical nonlinearities.

The formal [2 + 2] cycloaddition-cycloreversion (CA-CR) between 4-ethynyl-N,N-dimethylaniline and polyenic Donor-π-Acceptor (D-π-A) systems takes place to yield compounds bearing two donors and one acceptor. Structural, linear and second-order nonlinear optical (NLO) properties of the new molecules reveal the stronger polarization of these systems when compared to analogous merocyanines lacking the dimethylaminophenyl (DMA) ring.

Thiolates vs. halides as pi-donors: the redox-active alkyne complexes [M(SR)L(eta-R'C[triple bond]CR')L'] {M = Mo or W, L = CO or P(OMe)(3), L' = eta-C(5)H(5) and Tp'}.

The cyclic voltammograms of the alkyne complexes [M(SR)L(eta-R'C[triple bond, length as m-dash]CR')(eta-C(5)H(5))] (M = Mo or W, R = Me or Ph, R' = Me or Ph) show two oxidation processes. Both are irreversible for the stereochemically rigid carbonyls (L = CO) but the first is reversible for the fluxional phosphites {L = P(OMe)(3)}; the paramagnetic monocations [M(SPh){P(OMe)(3)}(eta-MeC[triple bond, length as m-dash]CMe)(eta-C(5)H(5))](+) were detected by ESR spectroscopy after in situ chemical one-electron oxidation. By contrast, the hydrotris(pyrazolyl)borate analogues [W(SR)(CO)(eta-PhC[triple bond, length as m-dash]CPh)Tp'] {R = Me or Ph, Tp' = hydrotris(3,5-dimethylpyrazolyl)borate} are oxidised in two reversible steps to the corresponding mono- and dications; the redox pair [W(SPh)(CO)(eta-PhC[triple bond, length as m-dash]CPh)Tp'](z) (z = 0 and 1+) has been structurally characterised. A comparison of the redox potentials for the oxidation of [W(SR)(CO)(eta-PhC[triple bond, length as m-dash]CPh)Tp'] with those of the halide analogues [WX(CO)(eta-PhC[triple bond, length as m-dash]CPh)Tp'] suggests that the factors which give rise to the inverse halide order for the latter may not operate for the thiolates, which appear to be the better pi-donors in all three redox states [WL(CO)(eta-PhC[triple bond, length as m-dash]CPh)Tp'](z) (L = halide or thiolate, z = 0, 1+ and 2+).

Synthesis of binuclear platinum complexes containing the ligands 8-naphthyridine, 2-aminopyridine, and 7-azaindolate. An experimental study of the steric hindrance of the bulky pentafluorophenyl ligands in the synthesis of binuclear complexes.

The bidentate N-donor ligands 2-aminopyridine (2-ampy), 7-azaindolate (aza) and 1,8-naphthyridine (napy) have been used to study the steric effect of pentafluorophenyl groups in the synthesis of binuclear platinum(II) complexes. The 2-ampy and aza ligands bridge two "Pt(C 6F 5) 2" fragments with Pt...Pt distances of 4.1 and 3.4 A, respectively (complexes 1 and 3). Under the same reaction conditions the napy ligand shows chelating behavior and makes the mononuclear complex ( A) highly reactive because of its strained coordination. One of the Pt-N bonds of the chelating complex is broken on reaction with HX {X = Cl ( 4), Br ( 5)} because of protonation while the anion X (-) occupies a created vacant site. The resulting mononuclear complex eliminates C 6F 5H when refluxed, and a binuclear complex ( 6) with two napy ligands bridging two "Pt(C 6F 5)Cl" fragments is obtained. The reaction of A with HPPh 2 affords a mononuclear complex ( 7) analogous to complexes 5 and 6, but reflux gives a binuclear complex ( 8) with the two napy ligands terminally bound and the PPh 2 groups bridging the "Pt(C 6F 5)napy" moieties. The reaction of A with HCCPh gives a binuclear complex; moreover, the final product does not depend on the ratio of complex A to HCCPh. Complexes 1, 4, 6, 9 have been structurally characterized by X-ray diffraction.

Synthesis and in solution and solid state structural study of intramolecular Pt...H interactions in pentafluorophenyl platinum(II) complexes containing the ligands triazene, formamidine, and 2-aminopyridine.

The preparation of the [NBu4][Pt(C6F5)3L] complexes (L=triazene, formamidine, 2-aminopyridine,) have been carried out. These ligands contain a hydrogen atom, with more or less acidic character, in a position suitable for establishing an intramolecular hydrogen bonding interaction with the metal center. This interaction has been detected in solution for; its 1H NMR spectrum shows that the resonance assignable to this hydrogen has platinum satellites. For, this coupling is not observed, and the interaction, if it exists, has to be weaker because of the less acidic character of the hydrogen atom. The 2-aminopyridine ligand is more flexible than the triazene or formamidine, and also in this case, no evidence of the interaction in solution is obtained. Nevertheless, if another potential proton acceptor is present, such as ClO4- in [NBu4]2[Pt(C6F5)3(C5H6N2)](ClO4), a conventional N-H...O-Cl hydrogen bond is formed. The crystal structures of complexes have been determined by X-ray diffraction.

Hydrogen-bond mediation of supramolecular aggregation in neutral bis-(C6F5)Pt complexes with aromatic H-bond donating ligands. A synthetic and structural study.

Six pentafluorophenylplatinum(II) complexes containing proton acceptor atoms (F) and pyridine-like aromatic ligands able to act as proton donors have been synthesized and characterized, with emphasis on the factors that mediate their supramolecular aggregation in the solid state--hydrogen bonds and pi-pi interactions. The crystal structure analyses of the mononuclear complexes cis-[Pt(C6F5)2(napy)](1), cis-[Pt(C6F5)2(CH2napy)](3), cis-[Pt(C6F5)2(2-ammpy)](5), and cis-[Pt(C6F5)2(2-bipym)](6) reveal the influence of D-HPt and D-HF (D=C, N) hydrogen bonding on the organization of molecules into stacks, which can be further interconnected to generate channels. The prevalence of hydrogen bonding over pi-pi interactions between aromatic rings in establishing the nature of the observed supramolecular aggregation is demonstrated.