Syntheses, X-ray Crystal Structures, and Spectroscopic Properties of New Nickel Dithiolenes and Related Compounds

The direct addition of nickel powder to the reaction mixtures of
1,3-dialkyl-4,5-dioxoimidazolidine-2-thione (1)
with the thionation Lawesson reagent produces
[NiII(R2timdt-)2]
(R2timdt =
1,3-dialkylmidazolidine-2,4,5-trithione).
These complexes belong to a new class of nickel−dithiolenes,
showing remarkably high absorption (ε ≈ 80 000
dm3 mol-1
cm-1, λ ≈ 1000 nm) in the near-infrared
region (near-IR), accompanied by high photochemical
stability
that makes these complexes promising near-IR dyes. In the absence
of nickel the reaction yields generally the
compounds
4,5,6,7-tetrathiocino[1,2-b:3,4-b‘]diimidazolyl-1,3,8,10-tetraalkane-2,9-dithione
(2) instead of the
expected 1,3-dialkylimidazolidine-2,4,5-trithione. However, with
bulky substituents on the nitrogen atoms, well-characterized reaction products have not been obtained until now.
Only in the R = Pri case, the new
tetrathiocino
isomer
(4,5,9,10-tetrathiocino[1,2-b:5,6-b‘]diimidazolyl-1,3,6,8-tetraisopropane-2,7-dithione
(3) in trace amounts
and the bis(1,3-diisopropyl-2-thioxoimidazolin-4-yl) disulfide
(4) were isolated from the reaction with the
Lawesson
reagent and P4S10, respectively. Reaction
of 5 with different amounts of I2 leads to a
variety of products, and
among them the following derivatives have been characterized: 
[NiII(Pri2timdt-)2]·2I2
(6) a neutral adduct in
which each I2 molecule interacts with each peripheral
thione sulfur atom of 5;
[NiII(Pri2timdt-)2]·2I2·1/2I2
(7),
which differs from 6 with the presence of half diiodine as a
guest; with a larger diiodine excess (starting from a
1:10 molar ratio) a partial oxidation of 5 is achieved and
[NiII(Pri2timdt-)2]
[NiII(I)2(Pri2timdt)2]·5I2
(8) is formed,
a ligand mixed-valence compound in which the square-planar complex
5 and the octahedral complex
[NiII(I)2(Pri2timdt)2] (the ligand in neutral form) are bound by diiodine
molecules in such a way that a sequence of 12 iodine
atoms
(S·I2···I2···I-···I2···I-···I2···I2·S)
is formed. Spectroscopic and X-ray diffractometric studies of
3
(monoclinic, space group P21/n,
a = 13.104(6) Å, b = 15.091(6) Å,
c = 6.067(7) Å, β = 103.00(2)°,
Z = 2), 4
(monoclinic, space group C2/c, a =
18.717(5) Å, b = 8.846(5) Å, c =
14.475(5) Å, β = 97.78(2)°, Z = 4),
5
(orthorhombic, space group Pna21, a
= 18.806(5) Å, b = 5.628(7) Å, c
= 23.665(5) Å, Z = 4), 7 (triclinic,
space
group P1̄, a = 9.126(7) Å,
b = 9.153(7) Å, c = 12.924(6) Å,
α = 82.11(2), β = 70.14(2), γ = 72.51(2)°,
Z =
1), and 8 (monoclinic, space group
C2/c, a = 21.971(6) Å,
b = 28.081(5) Å, c = 12.207(8) Å,
β = 93.57(2)°,
Z = 4) are given.