A Convergent Approach to the Synthesis of Multimetallic Dithiolene Complexes

Controlled base hydrolysis of one or both of the protected 1,2-dithiolene chelates of 1,3,5,7-tetrathia-s-indacene-2,6-dione (OCS2C6H2S2CO) enables the stepwise synthesis of di- and trimetallic complexes with 1,2,4,5-benzenetetrathiolate as the connector. Treatment of OCS2C6H2S2CO with MeO−, followed by [NiBr2(dcpe)] [dcpe = 1,2-bis(dicyclohexylphosphino)ethane], yields [(dcpe)Ni(S2C6H2S2CO)] (4). The reaction of 4 with EtO−, followed by [MX2(dcpe)] (X = halide), yields [(dcpe)Ni(S2C6H2S2)M(dcpe)] [M = Ni (5a), Pd (5b)]. Deprotection of the 1,3-dithiol-2-one group of 4, followed by introduction of 1/2 equiv of MX2 and then I2, yields the neutral trimetallic compounds [(dcpe)Ni(S2C6H2S2)]2M [M = Ni (6a), Pt (6b)]. Tetrahedralization at nickel is observed in 5a, which density functional theory calculations attribute to second-order Jahn−Teller effects, while 6a and 6b display an end-to-end folding of ∼46°. A color darkening is observed in moving from 4 to compounds 6 due to the increasing size of the conjugated metal−organic π system. Intense, broad absorptions in the near-IR are observed for 6a and 6b.