Expanding the scope of ligand substitution from [M(S2C2Ph2] (M = Ni2+, Pd2+, Pt2+) to afford new heteroleptic dithiolene complexes

The scope of direct substitution of the dithiolene ligand from [M(S2C2Ph2)2] [M = Ni2+ (1), Pd2+ (2), Pt2+ (3)] to produce heteroleptic species [M(S2C2Ph2)2Ln] (n = 1, 2) has been broadened to include isonitriles and dithiooxamides in addition to phosphines and diimines. Collective observations regarding ligands that cleanly produce [M(S2C2Ph2)Ln], do not react at all, or lead to ill-defined decomposition identify soft σ donors as the ligand type capable of dithiolene substitution. Substitution of MeNC from [Ni(S2C2Ph2)(CNMe)2] by L provides access to a variety of heteroleptic dithiolene complexes not accessible from 1. Substitution of a dithiolene ligand from 1 involves net redox disproportionation of the ligands from radical monoanions, –S•SC2Ph2, to enedithiolate and dithione, the latter of which is an enhanced leaving group that is subject to further irreversible reactions

Group 10 metal dithiolene bis(isonitrile) complexes: synthesis, structures, properties and reactivity

The reaction of [(Ph2C2S2)2M] (M = Ni2+, Pd2+, Pt2+) with 2 equiv of RN≡C (R = Me (a), Bn (b), Cy (c), tBu (d), 1-Ad (e), Ph (f)) yields [(Ph2C2S2)M(C≡NR)2] (M = Ni2+, 4a–f; M = Pd2+, 5a–f; M = Pt2+, 6a–f), which are air-stable and amenable to chromatographic purification. All members have been characterized crystallographically. Structurally, progressively greater planarity tends to be manifested 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 those for free C≡NR and increase as M ranges from Ni to Pt. This trend is interpreted as arising from an increasingly 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. One-electron oxidations of [(Ph2C2S2)M(C≡NR)2] are observed at ∼+0.5 V due to Ph2C2S22– → Ph2C2S–S• + e–. Chemical oxidation of [(Ph2C2S2)Pt(C≡NtBu)2] with [(Br-p-C6H4)3N][SbCl6] yields [(Ph2C2S–S•)Pt(C≡NtBu)2]+, identified spectroscopically, but in the crystalline state [[(Ph2C2S–S•)Pt(C≡NtBu)2]2]2+ prevails, which forms via axial Pt···S interactions and pyramidalization at the metal. Complete substitution of MeNC from [(Ph2C2S2)Ni(C≡NMe)2] by 2,6-Me2py under forcing conditions yields [(2,6-Me2py)Ni(μ2-η1,η1-S′,η1-S″-S2C2Ph2)]2 (8), which features a folded Ni2S2 core. In most cases, isocyanide substitution from [(Ph2C2S2)M(C≡NMe)2] with monodentate ligands (L = phosphine, CN–, carbene) leads to [(Ph2C2S2)M(L)(C≡NMe)]n (n = 0, 1−), wherein νC≡N varies according to the relative σ-donating power of L (9–21). The use of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) provides [(Ph2C2S2)M(IPr)(C≡NMe)] for M = Ni (18), Pd (19), but for Pt, attack by IPr at the isocyanide carbon occurs to yield the unusual η1,κC-ketenimine complex [(Ph2C2S2)Pt(C(NMe)(IPr))(C≡NMe)] (20)

Redox-active metallodithiolene groups separated by insulating tetraphosphinobenzene spacers

Compounds of the type [(S2C2R2)M(μ-tpbz)M(S2C2R2)] (R = CN, Me, Ph, p-anisyl; M = Ni, Pd, Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene) have been prepared by transmetalation with [(S2C2R2)SnR′2] reagents, by direct displacement of dithiolene ligand from [M(S2C2R2)2] with 0.5 equiv of tpbz, or by salt metathesis using Na2[S2C2(CN)2] in conjunction with X2M(μ-tpbz)MX2 (X = halide). X-ray crystallography reveals a range of topologies (undulating, chair, bowed) for the (S2C2)M(P2C6P2)M(S2C2) core. The [(S2C2R2)M(μ-tpbz)M(S2C2R2)] (R = Me, Ph, p-anisyl) compounds support reversible or quasireversible oxidations corresponding to concurrent oxidation of the dithiolene terminal ligands from ene-1,2-dithiolates to radical monoanions, forming [(−S•SC2R2)M(μ-tpbz)M(−S•SC2R2)]2+. The R = Ph and p-anisyl compounds support a second, reversible oxidation of the dithiolene ligands to their α-dithione form. In contrast, [(S2C2(CN)2)Ni(tpbz)Ni(S2C2(CN)2)] sustains only reversible, metal-centered reductions. Spectroscopic examination of [(−S•SC2(p-anisyl)2)Ni(μ-tpbz)Ni(−S•SC2(p-anisyl)2)]2+ by EPR reveals a near degenerate singlet–triplet ground state, with spectral simulation revealing a remarkably small dipolar coupling constant of 18 × 10–4 cm–1 that is representative of an interspin distance of 11.3 Å. This weak interaction is mediated by the rigid tpbz ligand, whose capacity to electronically insulate is an essential quality in the development of molecular-based spintronic devices

Redox-Active Metallodithiolene Groups Separated by Insulating Tetraphosphinobenzene Spacers

Compounds of the type [(S₂C₂R₂)­M­(μ-tpbz)­M­(S₂C₂R₂)] (R = CN, Me, Ph, <i>p</i>-anisyl; M = Ni, Pd, Pt; tpbz = 1,2,4,5-tetrakis­(diphenylphosphino)­benzene) have been prepared by transmetalation with [(S₂C₂R₂)­SnR′₂] reagents, by direct displacement of dithiolene ligand from [M­(S₂C₂R₂)₂] with 0.5 equiv of tpbz, or by salt metathesis using Na₂[S₂C₂(CN)₂] in conjunction with X₂M­(μ-tpbz)­MX₂ (X = halide). X-ray crystallography reveals a range of topologies (undulating, chair, bowed) for the (S₂C₂)­M­(P₂C₆P₂)­M­(S₂C₂) core. The [(S₂C₂R₂)­M­(μ-tpbz)­M­(S₂C₂R₂)] (R = Me, Ph, <i>p</i>-anisyl) compounds support reversible or quasireversible oxidations corresponding to concurrent oxidation of the dithiolene terminal ligands from ene-1,2-dithiolates to radical monoanions, forming [(⁻S^<b>•</b>SC₂R₂)­M­(μ-tpbz)­M­(⁻S^<b>•</b>SC₂R₂)]²⁺. The R = Ph and <i>p</i>-anisyl compounds support a second, reversible oxidation of the dithiolene ligands to their α-dithione form. In contrast, [(S₂C₂(CN)₂)­Ni­(tpbz)­Ni­(S₂C₂(CN)₂)] sustains only reversible, metal-centered reductions. Spectroscopic examination of [(⁻S^<b>•</b>SC₂(<i>p</i>-anisyl)₂)­Ni­(μ-tpbz)­Ni­(⁻S^<b>•</b>SC₂(<i>p</i>-anisyl)₂)]²⁺ by EPR reveals a near degenerate singlet–triplet ground state, with spectral simulation revealing a remarkably small dipolar coupling constant of 18 × 10^–4 cm^–1 that is representative of an interspin distance of 11.3 Å. This weak interaction is mediated by the rigid tpbz ligand, whose capacity to electronically insulate is an essential quality in the development of molecular-based spintronic devices

Expanding the Scope of Ligand Substitution from [M(S₂C₂Ph₂] (M = Ni²⁺, Pd²⁺, Pt²⁺) To Afford New Heteroleptic Dithiolene Complexes

The scope of direct substitution of the dithiolene ligand from [M­(S₂C₂Ph₂)₂] [M = Ni²⁺ (<b>1</b>), Pd²⁺ (<b>2</b>), Pt²⁺ (<b>3</b>)] to produce heteroleptic species [M­(S₂C₂Ph₂)₂L_<i>n</i>] (<i>n</i> = 1, 2) has been broadened to include isonitriles and dithiooxamides in addition to phosphines and diimines. Collective observations regarding ligands that cleanly produce [M­(S₂C₂Ph₂)­L_<i>n</i>], do not react at all, or lead to ill-defined decomposition identify soft σ donors as the ligand type capable of dithiolene substitution. Substitution of MeNC from [Ni­(S₂C₂Ph₂)­(CNMe)₂] by L provides access to a variety of heteroleptic dithiolene complexes not accessible from <b>1</b>. Substitution of a dithiolene ligand from <b>1</b> involves net redox disproportionation of the ligands from radical monoanions, ^–S^•SC₂Ph₂, to enedithiolate and dithione, the latter of which is an enhanced leaving group that is subject to further irreversible reactions