Anton Vidal-Ferran

Kinetic competition in liquid electrolyte and solid-state cyanine dye sensitized solar cells

The photovoltaic performance of liquid electrolyte and solid-state dye sensitized solar cells, employing a squarilium methoxy cyanide dye, are evaluated in terms of interfacial electron transfer kinetics. Dye adsorption to the metal oxide film resulted in a mixed population of aggregated and monomeric sensitizer dyes. Emission quenching data, coupled with transient absorption studies, indicate that efficient electron injection was only achieved by the monomeric dyes, with the aggregated dye population having an injection yield an order of magnitude lower. In liquid electrolyte devices, transient absorption studies indicate that photocurrent generation is further limited by slow kinetics of the regeneration of monomeric dye cations by the iodide/iodine redox couple. The regeneration dynamics are observed to be too slow (≫ 100 µs) to compete effectively with the recombination of injected electrons with dye cations. In contrast, for solid-state devices employing the organic hole conductor spiro-OMeTAD, the regeneration dynamics are fast enough (≪ 1 µs) to compete effectively with this recombination reaction, resulting in enhanced photocurrent generation.

Interfacial charge recombination between e(-)-TiO2 and the I(-)/I3(-) electrolyte in ruthenium heteroleptic complexes: dye molecular structure-open circuit voltage relationship.

A series of heteroleptic ruthenium(II) polypyridyl complexes containing phenanthroline ligands have been designed, synthesized, and characterized. The spectroscopic and electrochemical properties of the complexes have been studied in solution and adsorbed onto semiconductor nanocrystalline metal oxide particles. The results show that for two of the ruthenium complexes, bearing electron-donating (-NH2) or electron-withdrawing (-NO2) groups, the presence of the redox-active I(-)/I3(-) electrolyte produces important changes in the interfacial charge transfer processes that limit the device performance. For example, those dyes enhanced the electron recombination reaction between the photoinjected electrons at TiO2 and the oxidized redox electrolyte. In an effort to understand the details of such striking observations, we have monitored the charge transfer reactions taking place at the different interfaces of the devices using time-resolved single photon counting, laser transient spectroscopy, and light-induced photovoltage measurements.

Modular bis(oxazoline) ligands for palladium catalyzed allylic alkylation: Unprecedented conformational behaviour of a bis(oxazoline) palladium η3-1,3-diphenylallyl complex

New families of enantiopure bis(oxazolines) with 4,5-trans (5 a-g) or 4,5-cis (6 c) stereochemistry at the individual rings have been prepared in high yield. Their eta(3)-allyl palladium complexes (8 a-g, 9 c and 10) have been used as catalytic precursors in allylic alkylation reactions with excellent enantioselectivities (up to 96 %) for the trans oxazoline derivatives, while Pd/6 c system was inactive. NMR studies on palladium eta(3)-1,3-diphenylallyl intermediates (11 a, c and e) showed the presence of syn/syn- and syn/anti-allyl isomers in solution; this resembles the first example of eta(3)-eta(1)-eta(3) isomerism in Pd allylic complexes containing bis(oxazolines) derived from malonic acid.

Primary and Secondary Aminophosphines as Novel P-Stereogenic Building Blocks for Ligand Synthesis†

Chiral phosphine ligands are central to asymmetric metal catalysis. The effect of the majority of these ligands arises from the chirality of their backbones; however, P-stereogenic (P*) ligands have garnered renewed interest. After the decisive work of Knowles and co-workers with PAMP and DIPAMP ligands, several efficient syntheses of all-carbon P* compounds have been reported. In contrast, P* compounds that contain heteroatoms directly linked to the phosphorus center are scarce, and have found little application in catalysis. This class of substances includes secondary phosphine oxides, which exist in equilibrium with their trivalent phosphinite form. P* aminophosphines, which are the corresponding nitrogen analogues, are even more rare, as free primary aminophosphines tend to dimerize with the evolution of ammonia. However, Kolodiazhnyi et al. have reported that borane aminophosphines of type I are stable and that they can be obtained in diastereomerically pure form using 2-phenylethylamine as a chiral amine (Scheme 1). Nonetheless, type I compounds do not have any reported applications in asymmetric catalysis, nor has their hydrogenolysis been described. We envisioned that reductive cleavage of the arylethyl fragment should provide boraneprotected primary aminophosphines of type II, which would be amenable to further transformations and become useful P* building blocks in catalysis. Herein, we report the synthesis of enantiopure P-chiral primary and secondary aminophosphines (II) and diphosphinoamines (III). We began by investigating the hydrogenolysis of the known compound 1a, which contains a tert-butyl(phenyl)phosphinamine moiety (Scheme 2), under various

[Ir(P-OP)]-catalyzed asymmetric hydrogenation of diversely substituted C═N-containing heterocycles.

Iridium(I) complexes of enantiomerically pure phosphine-phosphite ligands ([Ir(Cl)(cod)(P-OP)]) efficiently catalyze the enantioselective hydrogenation of diverse C═N-containing heterocyclic compounds (benzoxazines, benzoxazinones, benzothiazinones, and quinoxalinones; 25 examples, up to 99% ee). A substrate-to-catalyst ratio as high as 2000:1 was reached.

The reaction of malononitrile with chalcone: a controversial chemical process

Abstract Given the significant discrepancies in the several reported results on the reaction of chalcone (1,3-diphenyl-2-propne-1-one) (1) with malononitrile (2), a careful reinvestigation was carried out. Depending upon the reaction conditions either the open-chain Michael adduct (4), an alkoxypyridine (5), an aminoisophthalonitrile (6) or a cyclohexanol (7) is obtained. However, no 4H-pyran could be isolated from this reaction.

Structural optimization of enantiopure 2-cyclialkylamino-2-aryl-1,1-diphenylethanols as catalytic ligands for enantioselective additions to aldehydes.

The structural optimization of a family of modular, enantiopure beta-amino alcohol ligands with a common 2-amino-2-aryl-1,1-diphenylethanol skeleton, whose stereogenicity was introduced through the Jacobsen epoxidation of 1,1-diphenyl-2-arylethylenes, has led to the identification of a small set of optimal catalysts with enhanced activity and enantioselectivity in the addition of alkylzinc and arylzinc reagents to aldehydes. Criteria for the discrimination between apparently analogous, highly enantioselective ligands are proposed.

Reversing the stereochemistry of a Diels–Alder reaction: use of metalloporphyrin oligomers to control transition state stability

A cyclic Zn-porphyrin trimer with ethyne and butadiyne links stabilises the thermodynamically disfavoured endo transition state and product of a reversible Diels–Alder reaction; at 30°C the endo adduct is formed rapidly and almost exclusively. Linear porphyrin dimers containing ethyne or butadiyne links show related stereochemical preferences to the corresponding cyclic trimers; substantial rate accelerations are observed despite rotational freedom around the linkers. A qualitative correlation is observed between rate acceleration (i.e., transition state binding) and product binding, and the results are rationalised in terms of host geometry and flexibility.

The dual-catalyzed (amino alcoho/Lewis acid) enantioselective addition of diethylzinc to N-diphenylphosphinoyl imines

Abstract Optimal structural characteristics within a family of (2 R ,3 R )-1-alkoxy-3-dialkylamino-3-phenyl-2-propanols have been determined for maximum enantioselectivity in the addition of diethylzinc to N -diphenylphosphinoyl imines (1-alkoxy = trityloxy; 3-dialkylamino = piperidino). The simultaneous use of silylating agents acting as Lewis acids to induce rate acceleration has been investigated, allowing the identification of triisopropylsilyl chloride and tert -butyldiphenylsilyl chloride as the most efficient mediators in terms of rate enhancement and enantiomeric excess of the resulting phosphinamides.

Computer assisted, mechanism directed design of a new ligand for the highly enantioselective catalytic addition of diethylzinc to aldehydes

Abstract A new ligand, (1 R ,2 R )-1-( cis -2,6-dimethylpiperidino)-1-phenyl-3-trityloxypropan-2-ol 1c , designed on the basis of molecular modelling (AM1) studies to increase the energy gap between the re and si attacks in the aminoalcohol promoted addition of diethylzinc to benzaldehyde, has been synthesised in 73% overall yield from enantiomerically pure epoxycinnamyl alcohol. Ligand 1c induces the highly enantioselective addition of Et 2 Zn to a broad range of aromatic and aliphatic aldehydes.