Abstract
Open-ended, singly metalated dithiolene complexes with 1,2,4,5-tetrakis(diphenylphosphino)benzene (tpbz) are prepared either by ligand transfer to [Cl2M(tpbz)] from (R2C2S2)SnR′2 (R = CN, R′ = Me; R = Me, R′ = nBu) or by a direct reaction between tpbz and [M(S2C2R2)2] (M = Ni, Pd, Pt; R = Ph, p-anisyl) in a 1:1 ratio. The formation of dimetallic [(R2C2S2)M(tpbz)M(S2C2R2)] attends these syntheses in modest amounts, but the open-ended compounds are readily separated by silica chromatography. As affirmed by X-ray crystallographic characterization of numerous members of the set, the [(R2C2S2)M(tpbz)] compounds show dithiolene ligands in their fully reduced ene-1,2-dithiolate form conjoined with divalent Group 10 ions. Minor amounts of octahedral [(Ph2C2S2)2PtIV(tpbz)], a presumed intermediate, are isolated from the preparation of [(Ph2C2S2)PtII(tpbz)]. Heterodimetallic [(Ph2C2S2)Pt(tpbz)Ni(S2C2Me2)] is prepared from [(Ph2C2S2)PtII(tpbz)]; its cyclic voltammogram, upon anodic scanning, shows two pairs of closely spaced, but resolved, 1e– oxidations corresponding first to [R2C2S22–] – 1e– → [R2C2S•S–] and then to [R2C2S•S–] – 1e– → [R2(C=S)2]. The open diphosphine of [(R2C2S2)M(tpbz)] can be oxidized to afford open-ended [(R2C2S2)M(tpbzE2)] (E = O, S). Synthesis of the octahedral [(dppbO2)3Ni][I3]2 [dppbO2 = 1,2-bis(diphenylphosphoryl)benzene] suggests that the steric profile of [(R2C2S2)M(tpbzE2)] is moderated enough that three could be accommodated as ligands around a metal ion.
Highlights
In recent work,1,2 we have reported the synthesis, structures, and properties of a set of dimetallic compounds of the type [(R2C2S2)M(tpbz)M(S2C2R2)] [tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene], where R may be CN, Me, Ph, or p-anisyl and, independent of R, M may be varied as Ni2+, Pd2+, or Pt2+
The dithiolene end groups can be concurrently oxidized to radical monoanions (a → b, Scheme 1), providing [(R2C2S−S)M(tpbz)M(S−SC2R2)]2+ dications, which weakly couple to provide nearly isoenergetic S = 1 and 0 states in equilibrium
When the tpbz ligand is introduced to a source of the Group 10 metal bis(dithiolene) complex in an amount that is greater than the 1:2 ratio that is optimal for [(R2C2S2)M(tpbz)M(S2C2R2)], we Received: May 25, 2021
Summary
Redox Levels Available to a Dithiolene Ligand When Bound to a Transition Metal differences among the [(R2C2S2)M(tpbz)M(S2C2R2)]2+ complexes as M and R are varied. Simulations of the EPR spectra of [((MeO-p-C6H4)2C2S2)M(tpbz)M(S2C2(C6H4-p-OMe)2)]2+, where M = Ni2+ or Pd2+, yield D = −18 × 10−4 cm−1 and −15 × 10−4 cm−1, respectively, with the former value indicative of a slightly shorter distance between the spin barycenters because of greater spin delocalization onto the metal from the dithiolene radicals. When the tpbz ligand is introduced to a source of the Group 10 metal bis(dithiolene) complex in an amount that is greater than the 1:2 ratio that is optimal for [(R2C2S2)M(tpbz)M(S2C2R2)], we Received: May 25, 2021 Published: August 9, 2021
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