New members of the [Mo2(S)n(S2)6-n]2- series. Synthesis, structural characterization, and properties of the [Mo2S9]2-, [Mo2S7]2-, and [Mo2S6]2- thio anions
Abstract:035ChemInform Abstract The compounds (III), (V), (VI), and (VIII), containing the title anions, are prepared as shown in the scheme. (III) and (VIII) crystallize in the triclinic system, space group P1 with Z=2. Crystals of (V) and (VI) are isostructural and crystallize in the space group P1 with Z=1. In the structure of (V) the thio anions Mo2S72-and Mo2 S62-occupy the same center of symmetry with occupancy factors 0.63 and 0.37, respectively. In (III) and (VIII) the complex assumes a distorted-square-pyramid… Show more
“…All molybdenum enzymes contain sulfur [1e5]. Many sulfur-containing molybdenum complexes were synthesized and structurally characterized [6,7]. Within the various thiomolybdate anions, the molybdenum ions are found in different oxidation states (IV, V, and VI), and they are bound by sulfide and polysulfide ligands in various coordination modes.…”
“…All molybdenum enzymes contain sulfur [1e5]. Many sulfur-containing molybdenum complexes were synthesized and structurally characterized [6,7]. Within the various thiomolybdate anions, the molybdenum ions are found in different oxidation states (IV, V, and VI), and they are bound by sulfide and polysulfide ligands in various coordination modes.…”
“…Second, metal sulfides are thought to undergo disproportionation reactions in solution, via intramolecular electron transfer processes, resulting in S−S bond formation and concomitant reduction of metal centers. For instance, [M(S) 4 ] 2- (M = Mo(VI), W(VI)) are readily transformed to various polythiomolybdate and polythiotungstate anions . Third, reaction of thio ligands with transition metals is often carried out under reducing conditions which facilitates metal−metal bond formation, because sulfurization reagents such as alkali metal sulfides and alkaline earth metal sulfides act as strong bases.…”
A series of mononuclear thio complexes of
pentamethylcyclopentadienyl−molybdenum(VI) and
−tungsten(VI) have been synthesized via C−S bond-cleaving reactions of
thiolates. Use of Li2S2 for sulfurization
of Cp*MoCl4
resulted in the known dinuclear complex,
anti-Cp*2Mo2(S)2(μ-S)2
(1), while the analogous reaction of
Cp*WCl4
gave rise to
anti-Cp*2W2(S)2(μ-S)2
(2) and (PPh4)[Cp*W(S)3]
(3), the latter of which was isolated after the
subsequent
cation exchange reaction with PPh4Br. In
contrast, the reaction of Cp*WCl4 with
Li2edt (edt = SCH2CH2S)
followed
by treatment with PPh4Br generated 3 as the
sole isolable product in high yield. A similar reaction between
Cp*WCl4
and LiStBu afforded
Cp*W(S)2(StBu) (6),
which turned out to be thermally unstable in solution and gradually
degraded
to 2. In these reactions of Cp*WCl4 with
lithium thiolates, a facile C−S bond cleavage took place and the
tungsten
atom was oxidized from W(V) to W(VI). On the other hand, the
Mo(IV) thiolate complexes,
Cp*Mo(StBu)3 (4)
and
(PPh4)[Cp*Mo(edt)2] (5),
were formed from the Cp*MoCl4/LiStBu and
Cp*MoCl4/Li2edt/PPh4Br
reaction systems.
The complex 4 was readily oxidized by dry
O2 producing Cp*Mo(O)2(StBu)
(7) exclusively, while the reactions of
4 with NH2NMe2 and
NH2NHPh occurred slowly to yield
Cp*Mo(S)2(StBu) (8).
The hydrazines acted as oxidants,
presumably by cleaving the N−N bond, and promoted the C−S bond
rupture of tert-butyl thiolate and concomitant
oxidation of molybdenum from Mo(IV) to Mo(VI). Elemental
sulfur S8 and grey selenium also acted as
oxidants
in the reactions with 4, leading to a complex mixture of
products. From the 4 + S8 reaction, the
complexes 1, 8,
and Cp*Mo(O)(S)(StBu) (9) were produced,
and the 4 + Se reaction lead to 8 and
anti-Cp*2Mo2(E)2(μ-E)2
(10; E
= S, Se). Finally treatment of 8 with
Li2S2 and PPh4Br afforded
(PPh4)[Cp*Mo(S)3] (11).
We found that 11 was
synthesized more easily by a one-pot reaction of 4,
1/4 equiv of S8, and
Li2S2 in THF. The trithio complexes,
3 and
11, reacted very cleanly with PhC⋮CPh generating
(PPh4)[Cp*M(S)(S2C2Ph2)]
(M = W (12), Mo (13)),
respectively.
A kinetic study of these reactions showed that they were first
order in PhC⋮CPh and first order in 3 or 11
with
appreciable negative entropies of activation and that the activation
barrier was higher for the molybdenum reaction.
The crystal structures of 3−8 and
11−13 were determined by the X-ray
analysis.
“…The average Mo−S distance to the μ 2 -S bridge of 2.319(8) Å is shorter than the distance from Mo2 to the S atoms in the terminal η 2 -S 2 2- group [2.389(18) Å]. Such a difference is also observed in other binuclear thio- and oxothiomolybdates. , Significantly larger distances of 2.482(2) and 2.463(2) Å are observed between Mo1 and the S atoms of the two μ 3 coordinating S atoms. 1 View of the [Mo 6 O 6 S 14 ] 4- anion with labeling and displacement ellipsoids drawn at the 50% probability level.…”
Reaction of elemental sulfur, sodiummolybdate dihydrate and tetramethylammonium hydroxide under solvothermal conditions leads to the new oxothiomolybdate: [N(CH3)4]4Mo6O6S14. The structure consists of three Mo2O2S4-units which are connected by two μ3-S atoms. The compound is characterized by single-crystal methods and vibrational spectra.
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