Compounds of the type [(SCR)M(μ-tpbz)M(SCR)] (R = CN, Me, Ph, p-anisyl; M = Ni, Pd, Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene) have been prepared by transmetalation with [(SCR)SnR'] reagents, by direct displacement of dithiolene ligand from [M(SCR)] with 0.5 equiv of tpbz, or by salt metathesis using Na[SC(CN)] in conjunction with XM(μ-tpbz)MX (X = halide). X-ray crystallography reveals a range of topologies (undulating, chair, bowed) for the (SC)M(PCP)M(SC) core. The [(SCR)M(μ-tpbz)M(SCR)] (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 [(SSCR)M(μ-tpbz)M(SSCR)]. The R = Ph and p-anisyl compounds support a second, reversible oxidation of the dithiolene ligands to their α-dithione form. In contrast, [(SC(CN))Ni(tpbz)Ni(SC(CN))] sustains only reversible, metal-centered reductions. Spectroscopic examination of [(SSC( p-anisyl))Ni(μ-tpbz)Ni(SSC( p-anisyl))] by EPR reveals a near degenerate singlet-triplet ground state, with spectral simulation revealing a remarkably small dipolar coupling constant of 18 × 10 cm 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.

The scope of direct substitution of the dithiolene ligand from [M(SCPh)] [M = Ni (1), Pd (2), Pt (3)] to produce heteroleptic species [M(SCPh)L] (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(SCPh)L], 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(SCPh)(CNMe)] 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, SSCPh, to enedithiolate and dithione, the latter of which is an enhanced leaving group that is subject to further irreversible reactions.

Irradiation at 460 nm of [Mo 3 (μ 3 -S)(μ 2 -S 2 ) 3 (S 2 CNR 2 ) 3 ]I ([2a]I, R = Me; [2b]I, R = Et; [2c]I, R = i Bu; [2d]I, R = CH 2 C 6 H 5 ) in a mixed aqueous−polar organic medium with [Ru(bipy) 3 ] 2+ as photosensitizer and Et 3 N as electron donor leads to H 2 evolution. Maximum activity (300 turnovers, 3 h) is found with R = i Bu in 1:9 H 2 O:MeCN; diminished activity is attributed to deterioration of [Ru(bipy) 3 ] 2+ . Monitoring of the photolysis mixture by mass spectrometry suggests transformation of [Mo 3 (μ 3 -S)(μ 2 -S 2 ) 3 (S 2 CNR 2 ) 3 ] + to [Mo 3 (μ 3 -S)(μ 2 -S) 3 (S 2 CNR 2 ) 3 ] + via extrusion of sulfur on a time scale of minutes without accumulation of the intermediate [Mo 3 S 6 (S 2 CNR 2 ) 3 ] + or [Mo 3 S 5 (S 2 CNR 2 ) 3 ] + species. Deliberate preparation of [Mo 3 S 4 (S 2 CNEt 2 ) 3 ] + ([3] + ) and treatment with Et 2 NCS 2 1− yields [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] ( 4), where the fourth dithiocarbamate ligand bridges one edge of the Mo 3 triangle. Photolysis of 4 leads to H 2 evolution but at ∼25% the level observed for [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + . Early time monitoring of the photolyses shows that [Mo 3 S 4 (S 2 CNEt 2 ) 4 ] evolves H 2 immediately and at constant rate, while [Mo 3 S 7 (S 2 CNEt 2 ) 3 ] + shows a distinctive incubation prior to a more rapid H 2 evolution rate. This observation implies the operation of catalysts of different identity in the two cases.

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).