New [M(R,R‘timdt)2] Metal-Dithiolenes and Related Compounds (M = Ni, Pd, Pt; R,R‘timdt = Monoanion of Disubstituted Imidazolidine-2,4,5-trithiones): An Experimental and Theoretical Investigation

Abstract

Several new Ni (7a−i), Pd (8a−j), and Pt (9a−j) dithiolenes belonging to the general class [M(R,R‘timdt)2] (R,R‘timdt = monoanion of di-substituted imidazolidine-2,4,5-trithione) have been synthesized by sulfuring the disubstituted imidazolidine-2-thione-4,5-diones (4) with Lawesson's reagent (5) in the presence of the appropriate metal either as powder or as chloride. The obtained compounds have been characterized by UV−vis−NIR, FT-IR, and FT-Raman spectroscopies, CP-MAS 13C NMR, and cyclic voltammetry, while [Ni(Me,Pritimdt)2] (7c) was also characterized by X-ray diffraction on a single crystal. Isolation from the reaction mixtures of the complex trans-bis[O-ethyl(4-methoxyphenyl)phosphonodithioato]Ni(II) (10a) and of 4,5,6,7-tetrathiocino[1,2-b:3,4-b‘]diimidazolyl-1,10-diphenyl-3,8-diethyl-2,9-dithione (6a) as byproducts supports a radical mechanism for the one-pot reaction leading to the title dithiolenes. All these complexes absorb in the NIR region in the range 991−1030 nm with extinction coefficients of rarely encountered magnitudes (up to 80000 M-1 cm-1). They are therefore ideal candidates for applications on Nd:YAG laser technology for which the excitation wavelength is 1064 nm. Hybrid-DFT calculations have been used to gain an insight on the properties of this class of dithiolenes compared with those of the simplest [M(S2C2H2)2] [M = Ni (1); M = Pd (2); M = Pt (3)] and of the well-known [M(dmit)2] [dmit = C3S52-, 1,3-dithiole-2-thione-4,5-dithiolate; M = Ni (11); M = Pd (12); M = Pt (13)] dithiolenes.