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On the Prospects of Polynuclear Complexes with Acetylenedithiolate Bridging Units

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posted on 2007-11-12, 00:00 authored by Wolfram W. Seidel, Matthias J. Meel, Udo Radius, Markus Schaffrath, Tania Pape
The generation of polynuclear complexes with one, two, or four acetylenedithiolate bridging units via the isolation of η2-alkyne complexes of acetylenedithiolate K[Tp‘M(CO)(L)(C2S2)] (Tp‘ = hydrotris(3,5-dimethylpyrazolyl)borate, M = W, L = CO (K-3a), M = Mo, L = CNC6H3Me2 (K-3b)) is reported. The strong electronic cooperation of Ru and W in the heterobimetallic complexes [(η5-C5H5)(PPh3)Ru(3a)] (4a) and [(η5-C5H5)(Me2C6H3NC)Ru(3a)] (4b) has been elucidated by correlation of the NMR, IR, UV−vis, and EPR-spectroscopic properties of the redox couples 4a/4a+ and 4b/4b+ with results from density functional calculations. Treatment of M(II) (M = Ni, Pd, Pt) with K-3a and K-3b afforded the homoleptic bis complexes [M(3a)2] (M = Ni (5a), Pd (5b), Pt (5c)), and [M(3b)2] (M = Pd (6a) and Pt (6b)), in which the metalla-acetylendithiolates exclusively serve as S,S‘-chelate ligands. The vibrational and electronic spectra as well as the cyclic voltammetry behavior of all the complexes are compared. The structural analogy of 5a/5b/5c and 6a/6b with dithiolene complexes is only partly reflected in the electronic structures. The very intense visible absorptions involve essential d orbital contributions of the central metal, while the redox activity is primarily attributed to the alkyne complex moiety. Accordingly, stoichiometric reduction of 5a/5b/5c yields paramagnetic complex anions with electron-rich alkyne complex moieties being indistinguishable in the IR time scale. K-3a forms with Cu(I) the octanuclear cluster [Cu(3a)]4 (7) exhibiting a Cu4(S2C2)4W4 core. The nonchelating bridging mode of the metalla-acetylenedithiolate 3a- in 7 is recognized by a high-field shift of the alkyne carbon atoms in the 13C NMR spectrum. X-ray diffraction studies of K[Tp‘(CO)(Me3CNC)Mo(η2-C2S2)] (K-3c), 4b, 6a, 6b, and 7 are included. Comparison of the molecular structures of K-3c and 7 on the one hand with 4b and 6a/6b on the other reveals that the small bend-back angles in the latter are a direct consequence of the chelate ring formation.

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