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ChemComm
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COMMUNICATION
The four-coordinate magnesium(II) centre in 3 adopts a
distorted tetrahedral geometry ( = 0.76)27 in the solid state
with the coordination sphere consisting of one dithiolene
Conflicts of interest
There are no conflicts to declare.
DOI: 10.1039/C9CC03427G
ligand and two carbenes ([:C{N(Pri)CMe}2]) (Fig. 1). The CNHC
–
Mg bond distances in 3 [2.228(3) Å, av] are comparable to
those in the 3-Me model (2.297 Å)24 and in N-heterocyclic
Acknowledgements
We are grateful to the National Science Foundation for support:
CHE-1565676 (G.H.R., Y.W.) and CHE-1855641 (G.H.R., Y.W.) and
CHE-1661604 (H.F.S.).
carbene complex of Mg(II)Cp* (Cp* = Me5C5) [2.194(2) Å].28
2
Natural bond orbital (NBO) analysis shows that the CNHC–Mg
bonds (WBIs = 0.34) in 3-Me are strongly polarized (90.0%)
toward the carbene carbon atoms (which has 45.4% s-, 54.6%
p-, 0.0% d-character). The strong electron-donating capability
of the NHC ligand favours the increase of the electron density
at the Mg(II) centre. Consequently, the Mg–S bonds (WBIs =
0.47) in 3 [2.4501(12) Å, av] are approximately 0.08 Å shorter
than that in 2 [2.5339(12) Å], whereas the S–Mg–S bond angle
in 3 [94.23(4)] is larger than that in 2 [89.82(5)].
While crystallographically disordered around an inversion
centre, the five-coordinate magnesium atom in 4 adopts a
slightly distorted square-pyramidal geometry ( = 0.01),29 with
one THF oxygen atom occupying the apical position and the
Mg(II) centre residing 0.617 Å above the S4 basal plane of bis-
dithiolene ligands (Fig. 1). Consequently, the MgS2C2 rings in 4
are obviously bent ( = 18.7). However, the two C2S2 planes
are somewhat twisted in the [4]2- model, rendering the four
sulphur atoms non-coplanar.24 In addition, the value (3.2,
av) of [4]2- is considerably smaller than that in 4 ( = 18.7).
These structural differences between 4 and the [4]2- model
may be mainly attributed to crystal packing. The elongated
sulphur-carbon bonds [1.724(3)–1.739(2) Å vs. 1.677(3) Å (av)
(1•)]15 and concomitant shortening of the carbon-carbon bond
distances [1.341(5)– 1.360(6) Å vs. 1.417(3) Å (1•)]15 of the C2S2
units in complexes 2-4 are consistent with the HOMOs of 2-4
model compounds (Fig. 2 and Fig. S524), which is primarily
ligand-based, involving C–C -bonding and C–S -antibonding
character.
Notes and references
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Fig. 2 HOMOs of 3-Me, and [4]2- optimized models.
Reaction of the lithium dithiolene radical 1• with a Grignard
reagent afforded the first magnesium monodithiolene complex
2, which was subsequently utilized to synthesize a carbene-
complexed magnesium monodithiolene 3 by reaction with
[:C{N(Pri)CMe}2] in toluene. Compound 3 may undergo partial
hydrolytic reaction in polar solvents (THF/MeCN), giving a five-
coordinate magnesium bis-dithiolene dianion 4. The intriguing
redox chemistry of 2 and 3 is being investigated in this
laboratory.
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