Effect of Pyramidalization of the M₂(SR)₂ Center: The Case of (C₅H₅)₂Ni₂(SR)₂

Abstract

The effects of simple thiolates vs chelating dithiolates on M−M bonding, redox potentials, and synthetic outcomes have been probed experimentally and computationally. Nickelocene (Cp 2 Ni) has long been known to react with simple thiols to give diamagnetic Cp 2 Ni 2 (SR) 2 with planar Ni 2 S 2 cores and long Ni---Ni distances. Ethane-and propanedithiol (edtH 2 and pdtH 2 , respectively) instead give di-, tri-, and pentanickel complexes, with nonplanar Ni 2 S 2 cores. The 36e Cp 2 Ni 2 (pdt) (1 pdt ) adopts a symmetrical butterfly Ni 2 S 2 structure. Variable-temperature NMR spectra indicate that 1 pdt possesses a thermally accessible triplet state (ΔG = 2.65(5) kcal/mol) in equilibrium with a diamagnetic ground state. DFT calculations indicate that the singlet−triplet gap is highly sensitive to the nonplanarity of the Ni 2 S 2 core. The calculations further reveal that only the high-spin form of 1 pdt features Ni−Ni bonding, which is unprecedented. Cp 2 Ni 3 (pdt) 2 (2 pdt ), which derives from 1 pdt , crystallized as cis and trans isomers, both with a central Ni(pdt) 2 2− unit that is S,Schelated to two CpNi + centers. Reaction of Cp 2 Ni with 1,2-ethanedithiol (H 2 edt) and 1,2-benzenedithiol (bdtH 2 ) exclusively gave the trinickel species 2 edt and 2 bdt , which are structurally analogous to cis-2 pdt . Solutions of 2 edt are unstable, depositing crystals of Cp 2 Ni 5 (edt) 4 (3 edt ). Cyclic voltammetric studies show that the Ni 2 species oxidize readily to give the mixed-valence cations [1 pdt ] + and [1 edt ] + . Crystallographic and EPR analyses indicate that these cations are delocalized mixed-valence Ni(II)− Ni(III) species. Oxidation of Cp 2 Ni 2 (SEt) 2 , which features a planar Ni 2 S 2 core, afforded a mixed-valence cation, showing the pyramidal Ni 2 S 2 core observed in [1 pdt ] 0/+ and [1 edt ] 0/+ . Although not obtained from the Cp 2 Ni/H 2 edt reaction, the neutral complex 1 edt was obtained by reduction of [1 edt ] + . Variable-temperature NMR measurements and DFT calculations indicate that the triplet is further stabilized in this highly pyramidalized species.

Rational Design of Fe2(μ‐PR2)2(L)6 Coordination Compounds Featuring Tailored Potential Inversion

“…In agreement with previous observations, [42,43] the LUMO of 1 has both an FeÀ Fe and FeÀ P (σ*) character, and therefore reduction results in an increase of both the FeÀ Fe distance and (albeit to a lesser extent) the FeÀ P distance. Reduction leads also to an increase in the Fe-PÀ P-Fe torsion angle (θ; often referred to as "hinge" or "flap" angle, [43,[64][65][66] i. e. a decreased pyramidalization; Figure 1, top).…”

Phosphine Functionalized NHC Ligands and Their Cyclopentadienide Nickel(II) Complexes

“…Additionally, there are no longer resonances belonging to diastereotopic methylene protons in the 1 H NMR spectrum and of the diasteareotopic phenyl groups in the 1 H and the 13 C NMR spectrum. The 13 C NMR signal of the coordinated cyanido ligand is found at 125.6 ppm, which corroborates bonding to the nickel(II) site via the carbon atom …”

“…The classical synthesis of the nickel(II) tripledecker cation [Cp 3 Ni 2 ] + follows this sequence: Treatment of nickelocene with HBF 4 splits one cyclopentadienido ligand and leaves behind the reactive [CpNi] + cation, which gets stabilized by binding to another nickelocene molecule. Dinuclear nickel(II) complexes are obtained with (weak) acids containing only one donor atom such as phosphines (HPR 2 ) and sulfides (HSR) or with pyrazoles . Mononuclear compounds have been obtained e.g.…”

Electron-Rich, Diiron Bis(monothiolato) Carbonyls: C–S Bond Homolysis in a Mixed Valence Diiron Dithiolate

“…Density Functional Theory (DFT) computations have been carried out with the TURBOMOLE 7.2 programs suite, 44 by using the pure functional BP86 45,46 and an all-electron valence triple- ζ basis set with polarization functions on all atoms (TZVP). 47 This level of theory, which has proved to reliably reproduce structures, spectroscopic properties, and reactivity of hydrogenase-mimics, 21–25 has been further validated by reproducing experimental IR bands and redox potential for the [ 3 ] +/0 (vide infra). In addition, computations regarding the S–C bond homolysis process have been also performed with the GGA functional B97-D, developed by Grimme to account for noncovalent interactions.…”