Vinylogue Mono‐ and Bimetallic Cationic Sesquifulvalene and Monohydro Sesquifulvalene Complexes for Second Harmonic Generation

Abstract

The donor‐acceptor complexes with a vinylogue monohydro sesquifulvalene and sesquifulvalene backbone of the type [(η5‐C5H5)Ru{µ‐(η5‐C5H4)C2H2(η6‐C7H7)}ML](PF6)n [n = 0: ML = none (1), Cr(CO)3 (2); n = 1: ML = Ru(η5‐C5H5) (3a), Ru(η5‐C5Me5) (3b)] and [(η5‐C5H5)Ru{µ‐(η5‐C5H4)C2H2(η7‐C7H6)}ML](PF6)n [n = 1: ML = none (4), Cr(CO)3 (5); n = 2: ML = Ru(η5‐C5H5) (6a), Ru(η5‐C5Me5) (6b)], respectively, have been synthesised, and spectroscopically and structurally characterised. A charge‐shift correlation was carried out by means of 1H NMR spectroscopic studies and an increased ground‐state donor‐acceptor interaction in the order 5 < 6b < 4 < 6a was found. The corresponding donor‐acceptor interaction in 3a and 3b varies by an insignificant amount. Hyper‐Rayleigh scattering (HRS) was applied to determine the first hyperpolarisability β of the mono‐ and dicationic complexes 3a−6b. The β values obtained for the cationic sesquifulvalene complexes 4−6b are among the largest ever measured for ruthenocenyl containing complexes due to a strong resonance enhancement: the sesquifulvalene complexes 4−6a, 6b show first hyperpolarisabilities which range between 360 and 700 × 10−30 esu, whereas β for the monohydrosesquifulvalene complexes are considerably lower (75 and 162 × 10−30 esu). For the latter complexes the first hyperpolarisability doubles on going from Ru(η5‐C5Me5) (3b) to Ru(η5‐C5H5) (3a) in the acceptor unit. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Trigonal‐Pyramidal Tetra‐Sandwich Complexes as 3D NLOphores

“…In addition, the synthesis of the ruthenocenyl compound 3 has not been reported yet. Therefore, and because of our experience in monolithiation of metallocenes [6,[15][16][17] the Negishi cross-coupling reaction was chosen as the synthetic route to 2 and 3. The use of ruthenocene in addition to ferrocene as electron-donating metallocenes in this research project was motivated by the observation that ferrocene-containing NLOphores very often show fluorescence due to two-photon absorption in contrast to the ruthenocene congeners.…”

“…The use of ruthenocene in addition to ferrocene as electron-donating metallocenes in this research project was motivated by the observation that ferrocene-containing NLOphores very often show fluorescence due to two-photon absorption in contrast to the ruthenocene congeners. [15][16][17] The appropriate metallocene was monolithiated by conducting the method as described. [18] The corresponding zinc compound was generated in situ by adding a thf solution of water-free zinc chloride.…”

“…[17] For 6 the beneficial situation is given that the decrease of charge on the electron-accepting sandwich has to go along with an increase of charge on the ruthenocene donors and thus with a corresponding low-field shift of the Cp resonance signal of the ruthenocenyl donor. The experimental data in Table 3 fulfil this expectation: three times a charge +0.10 for three metallocene units corresponds quite well to a charge reduction to +0.69 on the acceptor sandwich cation.…”

“…[17] The relationship enables the calculation of the actual charge for an Ru sandwich entity in donor-acceptor compounds containing (η 5 -C 5 H 5 )Ru units if the proton shift of the Cp signal is known. The singlet of the unsubstituted cyclopentadienyl ligand of the metallocene donor in 6 and the corresponding Cp ligand of the cationic sandwich unit in 4 and 6 are taken as the monitoring signals.…”

Synthesis and Electrochemical and Spectroscopic Properties of Molybdenum Complexes Bearing 5‐Alkoxythiophene or ‐bithiophene Groups

“…[6,7] These requirements are satisfied in asymmetric conjugated complexes containing electron-acceptor and electron-donor groups connected by a conjugated π system. [8,9] For example, metal complexes based on nitrosylmolybdenum and -tungsten moieties stabilised by tris(3,5-dimethylpyrazolyl)-borate and attached to phenolato or anilido groups are strongly polarised and may therefore be able to act as electron termini of dipolar complexes having second-order NLO properties. [7] Thiophene and bithiophene chromophores exhibit greater β second-order polarisabilities compared to those of biphenyls or stilbenes.…”