On the Prospects of Polynuclear Complexes with Acetylenedithiolate Bridging Units

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.