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(1-Ferrocenyl-η6-borabenzene)(η5-cyclopentadienyl)cobalt(1+):  A New Heterobimetallic Basic NLO Chromophore§,

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journal contribution
posted on 18.12.1996, 00:00 by Ute Hagenau, Jürgen Heck, Eric Hendrickx, André Persoons, Thomas Schuld, Hans Wong
The heterobimetallic cationic NLO chromophore (1-ferrocenyl-η6-borabenzene)(η5-cyclopentadienyl)cobalt(1+) ([{1-((η5-C5H5)Fe(η5-C5H4))-η6-BC5H5}Co(η5-C5H5)]+, 1+) has been synthesized by reaction of FcBBr2 and cobaltocene and subsequent oxidation with FeCl3. The neutral bimetallic compound 1 is paramagnetic and exhibits an ESR spectrum similar to that of the mononuclear 19-valence-electron complex Co(1-Ph-η6-borabenzene)2. Complex 1-PF6 crystallizes in monoclinic space group P21/c with a = 10.541(3) Å, b = 17.647(5) Å, c = 10.965(3) Å, β = 96.38(2)°, Z = 4, and V = 2027.0(10) Å3. NMR data for the oxidized diamagnetic cation 1+ indicate that the positive charge is predominantly localized on the (borabenzene)cobalt moiety. The X-ray structure determination of 1-PF6 shows the two sandwich units in mutually trans positions. The structural data denote an increased electronic interaction between the donating ferrocenyl group and the borabenzene unit. A cyclic voltammetric study of 1-PF6 or 1 reveals three reversible redox couples (−1/0, 0/+1, +1/+2), resembling those of the mononuclear parent compounds, although the redox potentials are slightly shifted due to the mutual influence of the electron-donating and -accepting properties of the different sandwich units. The UV−vis spectrum of 1+ confirms the enhanced donor−acceptor interaction by a strong, negative solvatochromic absorption about λ = 600 nm which is assigned to a charge-transfer transition. The determination of the first hyperpolarizability β by means of hyper Rayleigh scattering yields (90 ± 30) × 10-30 esu, which is unexpectedly high in the face of the directly coupled donor−acceptor pair.