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

Several new Ni (7a-i), Pd (8a-j), and Pt (9a-j) dithiolenes belonging to th e 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 disub stituted 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. T he obtained compounds have been characterized by UV-vis-NIR, FT-IR, and FT- Raman spectroscopies, CP-MAS C-13 NMR, and cyclic voltammetry, while [Ni(Me ,Pr(i)timdt)(2)] (7c) was also characterized by X-ray diffraction on a sing le 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-tetra thiocino[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 lea ding to the title dithiolenes. All these complexes absorb in the NIR region in the range 991-1030 nm with extinction coefficients of rarely encountere d magnitudes (up to 80000 M-1 cm(-1)). They are therefore ideal candidates for applications on Nd:YAG laser technology for which the excitation wavele ngth 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 s implest [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.