Group 10 Metal Dithiolene Bis(isonitrile) Complexes: Synthesis, Structures, Properties, and Reactivity

Abstract

Reaction of [(Ph2C2S2)2M] (M = Ni 2+ , Pd 2+ , Pt 2+ ) with 2 eq of RN≡C (R = Me (a), Bn (b), Cy (c), t Bu (d), 1-Ad (e), Ph (f)) yields [(Ph2C2S2)M(C≡NR)2] (M= Ni 2+ , 4a-4f; M = Pd 2+ , 5a-5f; M = Pt 2+ , 6a-6f), which are air-stable and amenable to chromatographic purification. All members have been characterized crystallographically. Structurally, progressively greater planarity tends to be manifest as M varies from Ni to Pt, and a modest decrease in the C≡N bond length of coordinated C≡NR appears in moving from Ni toward Pt. Vibrational spectroscopy (CH2Cl2 solution) reveals νC≡N frequencies for [(Ph2C2S2)M(C≡NR)2] that are substantially higher than for free C≡NR and increase as M ranges from Ni to Pt. This trend is interpreted as arising from increasing positive charge at M that stabilizes the linear, charge-separated resonance form of the ligand over the bent form with lowered C-N bond order. UV-vis spectra reveal lowest energy transitions that are assigned as HOMO (dithiolene π) → LUMO (M-L σ*) excitations. Oneelectron oxidations of [(Ph2C2S2)M(C≡NR)2] are observed at ~+0.5 V due to Ph2C2S2 2-→ Ph2C2S -S • + e -. Chemical oxidation of [(Ph2C2S2)Pt(C≡N t Bu)2] with [(Br-p-C6H4)3N][SbCl6] yields [(Ph2C2S -S • )Pt(C≡N t Bu)2] 1+ , identified spectroscopically, but in the crystalline state [[(Ph2C2S -S • )Pt(C≡N t Bu)2]2] 2+ prevails, which forms via axial Pt•••S interactions and pyramidalization at metal. Complete substitution of MeNC from [(Ph2C2S2)Ni(C≡NMe)2] by 2,6-Me2py under forcing conditions yields [(2,6-Me2py)Ni(μ2-η 1 ,η 1 -S',η 1 -S"-C2Ph2)]2 (8), which features a folded Ni2S2 core. In most cases, isonitrile substitution from [(Ph2C2S2)M(C≡NMe)2] with monodentate ligands (L = phosphine, CN -, carbene) typically leads to [(Ph2C2S2)M(L)(C≡NMe)] n (n = 0 or 1 -), wherein νC≡N varies according to the relative σ donating power of L (9 -21). Use of 1,3-bis(2,6diisopropylphenyl)imidazol-2-ylidene (IPr) provides [(Ph2C2S2)M(IPr)(C≡NMe)] for M = Ni (18)or Pd ( 19), but for Pt , attack by IPr at the isonitrile carbon occurs to yield the unusual η 1 ,κCketenimine complex [(Ph2C2S2)Pt(C(NMe)(IPr))(C≡NMe)] (20).

Thiolate Coordination vs C–S Bond Cleavage of Thiolates in Dinickel(II) Complexes

“…In comparison to these large numbers of literature reports on the synthesis and reactivity of mononuclear nickel–thiolates and heterodinuclear Ni–Fe complexes, reports on the synthesis and reactivity of well-defined, dinuclear Ni­(II)–thiolate and dinuclear Ni­(II)–hydrosulfide complexes are relatively less explored. Almost all of the literature reports on dinuclear Ni­(II)–thiolate − complexes used bi-/tri-/tetra-/multidentate chelating ligands which themselves contain one or more S-donor sites. On the other hand, only a handful of reports on discrete mononuclear − and dinuclear − nickel–-hydrosulfide, and dinuclear nickel–sulfide , complexes are available in the literature.…”

Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes

“…Scanning in the opposite direction shows an initial oxidation at −0.25 V assigned to the removal of an electron in the Ni-dithiolene unit denoted as Ni DT 0/+ . This reversible oxidation event shows a greater cathodic shift compared to most heteroleptic Ni-dithiolene complexes ( 26 , 27 ). The reversible redox couples are confirmed to be one-electron events by comparison of current densities with the Fc +/0 couple.…”

“…The (NO)Fe(bme-dame)-NiS 2 C 2 Ph 2 complex [bme-dame = N , N ′-dimethyl- N , N ′-bis(2-mercapto-ethyl)-ethylenediamine] was prepared using the Donahue and coworkers strategy ( Fig. 2 ) ( 25 , 26 ). Similar to the displacement of the labile isomethylnitrile ligands by diimines, reaction with the nitrosylated iron dithiolate yielded the neutral bimetallic complex, FeNi .…”

“…Pursuant of our program in metallodithiolates as ligands to appropriate receivers, we saw opportunity for the synthesis of heterobimetallic complexes of nickel dithiolenes according to the following strategy. A 2017 report by Donahue and coworkers introduced a synthon that provides entry to heteroleptic, square planar nickel and palladium dithiolenes that contain phosphine, isonitrile, and amine ligands and avoids higher S-bridged aggregates ( 24 – 27 ). With the expectation that an analogous synthetic strategy might yield stable molecules rich in redox levels in hybrid dithiolene/nitrosyl complexes, we have pursued heterobimetallic nickel dithiolenes by replacing the traditional ligands such as phosphines or isonitriles with (NO)Fe(bme-dame) ( Fig.…”

Asymmetric by Design: Heteroleptic Coordination Compounds with Redox-Active Dithiolene and 1,2,4,5-Tetrakis(isopropylthio)benzene Ligands

“…35 The comparative binding weakness of tptbz that is implicated by this difference is borne out in the finding that 8 is not directly accessible from [(pdt) 2 Pt] by dithiolene displacement with tptbz, though such an approach is efficacious for the synthesis of a range of other heteroleptic dithiolene complexes of the group 10 metals. 33,35,36 In the crystalline state, the packing arrangement for isostructural 5 and 6 is such that the square planar molecules form orderly, columnar stacks that arrange approximately along the a-axis of the monoclinic cell (Figure S23). Compound 8, however, occurs in triclinic P-1 with an atypical three full molecules in the asymmetric unit such that Z = 6.…”