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.