New donor-acceptor chromophores by formal [2+2] cycloaddition of donor-substituted alkynes to dicyanovinyl derivatives.

The efficient methodology of the cycloaddition between electron-rich alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), followed by retro-electrocyclisation, is extended to dicyanovinyl derivatives to produce new donor-acceptor push-pull 1,1-dicyanobutadienyl chromophores in excellent to quantitative yield (63-98%) that express strong charge-transfer (CT) absorptions from 300 to 600 nm. The scope of this reaction is established by both varying the nucleophilic and electrophilic components. Electrochemical studies show that the CT properties of these systems are readily tunable by substitution on the electrophile, which has the largest effect on the lowest unoccupied molecular orbital (LUMO). Non-reversible reduction potentials range from ca. -1.2 to -1.9 V in CH(2)Cl(2), against the ferricinium/ferrocene couple (Fc(+)/Fc) according to cyclovoltammetry (CV) and rotating disk voltammetry (RDV). The chromophores show a significant non-planarity between the N,N-dimethylanilino donor and the 1,1-dicyanovinyl acceptor moieties, with torsional angles around 40 degrees from X-ray analysis, but retain strong quinoidal character. The mechanism of this reaction has been studied computational using density functional methods in the gas-phase and using the polarizable continuum model (PCM) for addressing solvent effects. The complete reaction free-energy profile has been determined for the reaction of 1,1-dicyanoethene and 4-ethynyl-N,N-dimethylaniline. The process proceeds through formal [2+2] cycloaddition followed by retro-electrocyclisation. The formation of a zwitterionic intermediate in the cycloaddition step is shown.

[1]  Ivan Biaggio,et al.  A High‐Optical Quality Supramolecular Assembly for Third‐Order Integrated Nonlinear Optics , 2008 .

[2]  F. Diederich,et al.  1,2,3-triazoles as conjugative pi-linkers in push-pull chromophores: importance of substituent positioning on intramolecular charge-transfer. , 2008, Organic letters.

[3]  F. Diederich,et al.  New strong organic acceptors by cycloaddition of TCNE and TCNQ to donor-substituted cyanoalkynes. , 2007, Chemical communications.

[4]  F. Diederich,et al.  A novel reaction of 7,7,8,8-tetracyanoquinodimethane (TCNQ): charge-transfer chromophores by [2 + 2] cycloaddition with alkynes. , 2007, Chemical communications.

[5]  F. Diederich,et al.  Donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDS): new chromophores with efficient intramolecular charge-transfer interactions by atom-economic synthesis. , 2006, Chemistry.

[6]  K. Houk,et al.  Diels-Alder reactions of cyclopentadiene and 9,10-dimethylanthracene with cyanoalkenes: the performance of density functional theory and Hartree-Fock calculations for the prediction of substituent effects. , 2006, The journal of physical chemistry. A.

[7]  Ivan Biaggio,et al.  A new class of organic donor-acceptor molecules with large third-order optical nonlinearities. , 2005, Chemical communications.

[8]  J. Brédas,et al.  Donor-acceptor diphenylacetylenes : geometric structure, electronic structure, and second-order nonlinear optical properties , 1993 .

[9]  Corwin Hansch,et al.  A survey of Hammett substituent constants and resonance and field parameters , 1991 .

[10]  G. Himbert,et al.  (Aminoethinyl)metallierungen, 121), Umsetzungen von Inaminen mit Olefinen vom (Methylen)malonsäure‐Typ , 1984 .

[11]  M. R. Snow,et al.  Cyclopentadienyl-ruthenium and -osmium chemistry. Cleavage of tetracyanoethylene under mild conditions: X-ray crystal structures of [Ru{η3-C(CN)2CPhCC(CN)2}(PPh3)(η-C5H5)] and [Ru{C[C(CN)2]CPhC(CN)2}-(CNBut)(PPh3)(η-C5H5)] , 1981 .

[12]  Y. Kai,et al.  The Crystal and Molecular Structure of trans-Bis(trimethylphosphine)propynyl-1-(4′-dicyanomethylene-cyclohexa-2′-5′-dien-1-ylidenl-3,3-dicyano-2-methyl-prop-2-en-1-ylplatinum, a Reaction Product of trans-Bis(trimethylphosphine)bis(propynyl)platinum and 7,7,8,8-Tetracyanoquinodimethane , 1975 .

[13]  Günter Szeimies,et al.  1.3-Dipolare Cycloadditionen, XXXII. Kinetik der Additionen organischer Azide an CC-Mehrfachbindungen , 1967 .