Syntheses and Properties of Dinuclear Group 6 Metal Complexes with the Zwitterionic Sulfur Donor Ligand Bis(N,N-diethylamino)carbeniumdithiocarboxylate

Abstract

A class of dinuclear group 6 metal complexes [{M0(CO)5}2(μ-S,S′-EtL)] (M = Cr, Mo, W) with the asymmetrically bridged zwitterionic sulfur donor bis(N,N-diethylamino)carbeniumdithiocarboxylate (EtL) was prepared by photoreaction of [M0(CO)6] with EtL in hexane–CH2Cl2 for Cr and Mo or THF for W. The same structure in a syn–anti coordination mode was revealed by X-ray analyses for chromium(0) and tungsten(0) complexes, 1 and 3, respectively, and speculated from various analytical data for the molybdenum(0) complex 2. The pertinent criteria for the coordination mode are found to be the wavenumber of the asymmetric stretching vibration of the −CS2 moiety in the solid state and the ligand-based reduction potential in solution. Complexes 1 and 3 showed quasi-reversible reduction waves, which are assigned to a two-step, one-electron reduction process derived from the bridging EtL. In a series of [Cr(CO)5L] complexes (L = monodentate ligand), the 13C NMR chemical shifts of the trans-to-L carbonyl group showed the order of increasing σ-donor/π-acceptor ratio of the ligands. The sulfur donor ligands, including EtL and thione, are positioned in the middle of this range. All complexes exhibited negative solvatochromism: the wavelength of the absorption maximum shifted to the blue side in the range 500–600 nm with an increase in the Reichardt solvent polarity parameters E T(30), except for protic solvents. Quantum chemical calculations by time-dependent density functional theory–polarized continuum model were employed for understanding the excited states and solvatochromic properties of complex 3. The calculated vertical excitation energies in solution are consistent with the experimental data, suggesting that the transition is a metal-to-ligand charge-transfer transition. In addition, UV–vis, NMR, and cyclic voltammetry data showed that complex 3 dissociates into two mononuclear species in polar solvents: [W(CO)5(EtL)] and [W(CO)5(solvent)].

Observation of the First Spin Crossover in an Iron(II) Complex with an S6 Coordination Environment: Tris[bis(N,N‐diethylamino)carbeniumdithiocarboxylato]iron(II) Hexafluorophosphate

“…Reduction of Fe III by EtL might take place upon the mixing of reactants or during the synthesis process (reduction of Fe III , E °=0.56 V; oxidation of EtL, E °=0.17 V versus Fc/Fc + , in CH 3 CN). The stability of the Fe II complex is due to a suitable electron configuration in which metal t 2g orbitals are filled with six electrons that are used for enhanced π back‐donation to the ligand . As we have reported, π back‐donation from the metal center to the sulfur atoms in EtL plays a more important role in the stabilization of the complex than it does in the dithiocarbamate ligand.…”

“…We have synthesized various transitionmetal complexes with EtL and studied their spectroscopic and electrochemical properties in relationt ot heir structures. [13] The coordination mode of the complex essentially depends on the electron configurationo ft he central metal,w hich is responsible for the spectroscopic ande lectrochemical properties.…”