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 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 13 C NMR, and cyclic voltammetry, while [Ni(Me,Pr i timdt) 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(S 2 C 2 H 2 ) 2 ] [M = Ni ( 1 ); M = Pd ( 2 ); M = Pt ( 3 )] and of the well-known [M(dmit) 2 ] [dmit = C 3 S 5 2 -, 1,3-dithiole-2-thione-4,5-dithiolate; M = Ni ( 11 ); M = Pd ( 12 ); M = Pt ( 13 )] dithiolenes.