10 research outputs found
Kinetic and DFT Studies on the Mechanism of CâS Bond Formation by Alkyne Addition to the [Mo<sub>3</sub>S<sub>4</sub>(H<sub>2</sub>O)<sub>9</sub>]<sup>4+</sup> Cluster
Reaction
of [Mo<sub>3</sub>(Îź<sub>3</sub>-S)Â(Îź-S)<sub>3</sub>]
clusters with alkynes usually leads to formation of two CâS
bonds between the alkyne and two of the bridging sulfides. The resulting
compounds contain a bridging alkenedithiolate ligand, and the metal
centers appear to play a passive role despite reactions at those sites
being well illustrated for this kind of cluster. A detailed study
including kinetic measurements and DFT calculations has been carried
out to understand the mechanism of reaction of the [Mo<sub>3</sub>(Îź<sub>3</sub>-S)Â(Îź-S)<sub>3</sub>(H<sub>2</sub>O)<sub>9</sub>]<sup>4+</sup> (<b>1</b>) cluster with two different
alkynes, 2-butyne-1,4-diol and acetylenedicarboxylic acid. Stopped-flow
experiments indicate that the reaction involves the appearance in
a single kinetic step of a band at 855 or 875 nm, depending on the
alkyne used, a position typical of clusters with two CâS bonds.
The effects of the concentrations of the reagents, the acidity, and
the reaction medium on the rate of reaction have been analyzed. DFT
and TD-DFT calculations provide information on the nature of the product
formed, its electronic spectrum and the energy profile for the reaction.
The structure of the transition state indicates that the alkyne approaches
the cluster in a lateral way and both CâS bonds are formed
simultaneously
Influence of the Ligand Alkyl Chain Length on the Solubility, Aqueous Speciation, and Kinetics of Substitution Reactions of Water-Soluble M<sub>3</sub>S<sub>4</sub> (M = Mo, W) Clusters Bearing Hydroxyalkyl Diphosphines
Water-soluble [M<sub>3</sub>S<sub>4</sub>X<sub>3</sub>(dhbupe)<sub>3</sub>]<sup>+</sup> diphosphino
complexes (dhbupe = 1,2-bisÂ(bisÂ(hydroxybutyl)Âphosphino)Âethane), <b>1</b><sup>+</sup> (M = Mo, X = Cl) and <b>2</b><sup>+</sup> (M = W; X = Br), have been synthesized by extending the procedure
used for the preparation of their hydroxypropyl analogues by reaction
of the M<sub>3</sub>S<sub>4</sub>(PPh<sub>3</sub>)<sub>3</sub>X<sub>4</sub>(solvent)<sub><i>x</i></sub> molecular clusters
with the corresponding 1,2-bisÂ(bishydroxyalkyl)Âdiphosphine. The solid
state structure of the [M<sub>3</sub>S<sub>4</sub>X<sub>3</sub>(dhbupe)<sub>3</sub>]<sup>+</sup> cation possesses a <i>C</i><sub>3</sub> symmetry with a cuboidal M<sub>3</sub>S<sub>4</sub> unit, and the
outer positions are occupied by one halogen and two phosphorus atoms
of the diphosphine ligand. At a basic pH, the halide ligands are substituted
by hydroxo groups to afford the corresponding [Mo<sub>3</sub>S<sub>4</sub>(OH)<sub>3</sub>(dhbupe)<sub>3</sub>]<sup>+</sup> (<b>1</b><sub><b>OH</b></sub><sup>+</sup>) and [W<sub>3</sub>S<sub>4</sub>(OH)<sub>3</sub>(dhbupe)<sub>3</sub>]<sup>+</sup> (<b>2</b><sub><b>OH</b></sub><sup>+</sup>) complexes. This behavior
is similar to that found in 1,2-bisÂ(bisÂ(hydroxymethyl)Âphosphino)Âethane
(dhmpe) complexes and differs from that observed for 1,2-bisÂ(bisÂ(hydroxypropyl)Âphosphino)Âethane
(dhprpe) derivatives. In the latter case, an alkylhydroxo group of
the functionalized diphosphine replaces the chlorine ligands to afford
Mo<sub>3</sub>S<sub>4</sub> complexes in which the deprotonated dhprpe
acts in a tridentate fashion. Detailed studies based on stopped-flow, <sup>31</sup>PÂ{<sup>1</sup>H} NMR, and electrospray ionization mass spectrometry
techniques have been carried out in order to understand the solution
behavior and kinetics of interconversion between the different species
formed in solution: <b>1</b> and <b>1</b><sub><b>OH</b></sub><sup>+</sup> or <b>2</b> and <b>2</b><sub><b>OH</b></sub><sup>+</sup>. On the basis of the kinetic results,
a mechanism with two parallel reaction pathways involving water and
OH<sup>â</sup> attacks is proposed for the formal substitution
of halides by hydroxo ligands. On the other hand, reaction of the
hydroxo clusters with HX acids occurs with protonation of the OH<sup>â</sup> ligands followed by substitution of coordinated water
by X<sup>â</sup>
Synthesis and Structure of Trinuclear W<sub>3</sub>S<sub>4</sub> Clusters Bearing Aminophosphine Ligands and Their Reactivity toward Halides and Pseudohalides
The aminophosphine ligand (2-aminoethyl)Âdiphenylphosphine
(edpp)
has been coordinated to the W<sub>3</sub>(Îź-S)Â(Îź-S)<sub>3</sub> cluster unit to afford trimetallic complex [W<sub>3</sub>S<sub>4</sub>Br<sub>3</sub>(edpp)<sub>3</sub>]<sup>+</sup> (<b>1<sup>+</sup></b>) in a one-step synthesis process with high yields.
Related [W<sub>3</sub>S<sub>4</sub>X<sub>3</sub>(edpp)<sub>3</sub>]<sup>+</sup> clusters (X = F<sup>â</sup>, Cl<sup>â</sup>, NCS<sup>â</sup>; <b>2<sup>+</sup></b>â<b>4<sup>+</sup></b>) have been isolated by treating <b>1<sup>+</sup></b> with the corresponding halide or pseudohalide salt.
The structure of complexes <b>1<sup>+</sup></b> to <b>4<sup>+</sup></b> contains an incomplete W<sub>3</sub>S<sub>4</sub> cubane-type
cluster unit, and only one of the possible isomers is formed: the
one with the phosphorus atoms trans to the capping sulfur and the
amino groups trans to the bridging sulphurs. The remaining coordination
position on each metal is occupied by X. Detailed studies using stopped-flow, <sup>31</sup>PÂ{<sup>1</sup>H} NMR, and ESI-MS have been carried out in
order to understand the solution behavior and the kinetics of interconversion
among species <b>1<sup>+</sup></b>, <b>2<sup>+</sup></b>, <b>3<sup>+</sup></b>, and <b>4<sup>+</sup></b> in solution.
Density functional theory (DFT) calculations have been also carried
out on the reactions of cluster <b>1<sup>+</sup></b> with the
different anions. The whole set of experimental and theoretical data
indicate that the actual mechanism of substitutions in these clusters
is strongly dependent on the nature of the leaving and entering anions.
The interaction between an entering F<sup>â</sup> and the amino
group coordinated to the adjacent metal have also been found to be
especially relevant to the kinetics of these reactions
Water-Soluble Mo<sub>3</sub>S<sub>4</sub> Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions
The [Mo<sub>3</sub>S<sub>4</sub>Cl<sub>3</sub>(dhprpe)<sub>3</sub>]<sup>+</sup> (<b>1</b><sup>+</sup>) cluster cation
has been
prepared by reaction between Mo<sub>3</sub>S<sub>4</sub>Cl<sub>4</sub>(PPh<sub>3</sub>)<sub>3</sub> (solvent)<sub>2</sub> and the water-soluble
1,2-bisÂ(bisÂ(hydroxypropyl)Âphosphino)Âethane (dhprpe, L) ligand. The
crystal structure of [<b>1</b>]<sub>2</sub>[Mo<sub>6</sub>Cl<sub>14</sub>] has been determined by X-ray diffraction methods and shows
the typical incomplete cuboidal structure with a capping and three
bridging sulfides. The octahedral coordination around each metal center
is completed with a chlorine and two phosphorus atoms of the diphosphine
ligand. Depending on the pH, the hydroxo group of the functionalized
diphosphine can substitute the chloride ligands and coordinate to
the cluster core to give new clusters with tridentate deprotonated
dhprpe ligands of formula [Mo<sub>3</sub>S<sub>4</sub>(dhprpe-H)<sub>3</sub>]<sup>+</sup> (<b>2</b><sup>+</sup>). A detailed study
based on stopped-flow, <sup>31</sup>PÂ{<sup>1</sup>H} NMR, and electrospray
ionization mass spectrometry techniques has been carried out to understand
the behavior of acidâbase equilibria and the kinetics of interconversion
between the <b>1</b><sup>+</sup> and the <b>2</b><sup>+</sup> forms. Both conversion of <b>1</b><sup>+</sup> to <b>2</b><sup>+</sup> and its reverse process occur in a single kinetic
step, so that reactions proceed at the three metal centers with statistically
controlled kinetics. The values of the rate constants under different
conditions are used to discuss on the mechanisms of opening and closing
of the chelate rings with coordination or dissociation of chloride
Water-Soluble Mo<sub>3</sub>S<sub>4</sub> Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions
The [Mo<sub>3</sub>S<sub>4</sub>Cl<sub>3</sub>(dhprpe)<sub>3</sub>]<sup>+</sup> (<b>1</b><sup>+</sup>) cluster cation
has been
prepared by reaction between Mo<sub>3</sub>S<sub>4</sub>Cl<sub>4</sub>(PPh<sub>3</sub>)<sub>3</sub> (solvent)<sub>2</sub> and the water-soluble
1,2-bisÂ(bisÂ(hydroxypropyl)Âphosphino)Âethane (dhprpe, L) ligand. The
crystal structure of [<b>1</b>]<sub>2</sub>[Mo<sub>6</sub>Cl<sub>14</sub>] has been determined by X-ray diffraction methods and shows
the typical incomplete cuboidal structure with a capping and three
bridging sulfides. The octahedral coordination around each metal center
is completed with a chlorine and two phosphorus atoms of the diphosphine
ligand. Depending on the pH, the hydroxo group of the functionalized
diphosphine can substitute the chloride ligands and coordinate to
the cluster core to give new clusters with tridentate deprotonated
dhprpe ligands of formula [Mo<sub>3</sub>S<sub>4</sub>(dhprpe-H)<sub>3</sub>]<sup>+</sup> (<b>2</b><sup>+</sup>). A detailed study
based on stopped-flow, <sup>31</sup>PÂ{<sup>1</sup>H} NMR, and electrospray
ionization mass spectrometry techniques has been carried out to understand
the behavior of acidâbase equilibria and the kinetics of interconversion
between the <b>1</b><sup>+</sup> and the <b>2</b><sup>+</sup> forms. Both conversion of <b>1</b><sup>+</sup> to <b>2</b><sup>+</sup> and its reverse process occur in a single kinetic
step, so that reactions proceed at the three metal centers with statistically
controlled kinetics. The values of the rate constants under different
conditions are used to discuss on the mechanisms of opening and closing
of the chelate rings with coordination or dissociation of chloride
Cuboidal Mo<sub>3</sub>S<sub>4</sub> Clusters as a Platform for Exploring Catalysis: A Three-Center Sulfur Mechanism for Alkyne Semihydrogenation
We
report a trinuclear Mo<sub>3</sub>S<sub>4</sub> diamino cluster
that promotes the semihydrogenation of alkynes. Based on experimental
and computational results, we propose an unprecedented mechanism in
which only the three bridging sulfurs of the cluster act as the active
site for this transformation. In the first step, two of these Îź-S
ligands react with the alkyne to form a dithiolene adduct; this process
is formally analogous to the olefin adsorption on MoS<sub>2</sub> surfaces.
Then, H<sub>2</sub> activation occurs in an unprecedented way that
involves the third Îź-S center, in cooperation with one of the
dithiolene carbon atoms. Notably, this step does not imply any direct
interaction between H<sub>2</sub> and the metal centers, and directly
results in the formation of an intermediate featuring one (Îź-S)âH
and one CâH bond. Finally, such half-hydrogenated intermediate
can either undergo a reductive elimination step that results in the <i>Z</i>-alkene product, or evolve into an isomerized analogue
whose subsequent reductive elimination generates the <i>E</i>-alkene product. Interestingly, the substituents on the alkynes have
a major impact on the relative barriers of these two processes, with
the semihydrogenation of dimethyl acetylenedicarboxylate (dmad) resulting
in the stereoselective formation of dimethyl maleate, whereas that
of diphenylacetylene (dpa) leads to mixtures of <i>Z</i>- and <i>E</i>-stilbene. The results herein could have
significant implications on the understanding of the catalytic properties
of MoS<sub>2</sub>-based materials
Water-Soluble Mo<sub>3</sub>S<sub>4</sub> Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions
The [Mo<sub>3</sub>S<sub>4</sub>Cl<sub>3</sub>(dhprpe)<sub>3</sub>]<sup>+</sup> (<b>1</b><sup>+</sup>) cluster cation
has been
prepared by reaction between Mo<sub>3</sub>S<sub>4</sub>Cl<sub>4</sub>(PPh<sub>3</sub>)<sub>3</sub> (solvent)<sub>2</sub> and the water-soluble
1,2-bisÂ(bisÂ(hydroxypropyl)Âphosphino)Âethane (dhprpe, L) ligand. The
crystal structure of [<b>1</b>]<sub>2</sub>[Mo<sub>6</sub>Cl<sub>14</sub>] has been determined by X-ray diffraction methods and shows
the typical incomplete cuboidal structure with a capping and three
bridging sulfides. The octahedral coordination around each metal center
is completed with a chlorine and two phosphorus atoms of the diphosphine
ligand. Depending on the pH, the hydroxo group of the functionalized
diphosphine can substitute the chloride ligands and coordinate to
the cluster core to give new clusters with tridentate deprotonated
dhprpe ligands of formula [Mo<sub>3</sub>S<sub>4</sub>(dhprpe-H)<sub>3</sub>]<sup>+</sup> (<b>2</b><sup>+</sup>). A detailed study
based on stopped-flow, <sup>31</sup>PÂ{<sup>1</sup>H} NMR, and electrospray
ionization mass spectrometry techniques has been carried out to understand
the behavior of acidâbase equilibria and the kinetics of interconversion
between the <b>1</b><sup>+</sup> and the <b>2</b><sup>+</sup> forms. Both conversion of <b>1</b><sup>+</sup> to <b>2</b><sup>+</sup> and its reverse process occur in a single kinetic
step, so that reactions proceed at the three metal centers with statistically
controlled kinetics. The values of the rate constants under different
conditions are used to discuss on the mechanisms of opening and closing
of the chelate rings with coordination or dissociation of chloride
Cuboidal Mo<sub>3</sub>S<sub>4</sub> Clusters as a Platform for Exploring Catalysis: A Three-Center Sulfur Mechanism for Alkyne Semihydrogenation
We
report a trinuclear Mo<sub>3</sub>S<sub>4</sub> diamino cluster
that promotes the semihydrogenation of alkynes. Based on experimental
and computational results, we propose an unprecedented mechanism in
which only the three bridging sulfurs of the cluster act as the active
site for this transformation. In the first step, two of these Îź-S
ligands react with the alkyne to form a dithiolene adduct; this process
is formally analogous to the olefin adsorption on MoS<sub>2</sub> surfaces.
Then, H<sub>2</sub> activation occurs in an unprecedented way that
involves the third Îź-S center, in cooperation with one of the
dithiolene carbon atoms. Notably, this step does not imply any direct
interaction between H<sub>2</sub> and the metal centers, and directly
results in the formation of an intermediate featuring one (Îź-S)âH
and one CâH bond. Finally, such half-hydrogenated intermediate
can either undergo a reductive elimination step that results in the <i>Z</i>-alkene product, or evolve into an isomerized analogue
whose subsequent reductive elimination generates the <i>E</i>-alkene product. Interestingly, the substituents on the alkynes have
a major impact on the relative barriers of these two processes, with
the semihydrogenation of dimethyl acetylenedicarboxylate (dmad) resulting
in the stereoselective formation of dimethyl maleate, whereas that
of diphenylacetylene (dpa) leads to mixtures of <i>Z</i>- and <i>E</i>-stilbene. The results herein could have
significant implications on the understanding of the catalytic properties
of MoS<sub>2</sub>-based materials
Kinetics Aspects of the Reversible Assembly of Copper in Heterometallic Mo<sub>3</sub>CuS<sub>4</sub> Clusters with 4,4â˛-Di-<i>tert</i>-butyl-2,2â˛-bipyridine
Treatment
of the triangular [Mo<sub>3</sub>S<sub>4</sub>Cl<sub>3</sub>(dbbpy)<sub>3</sub>]Cl cluster ([<b>1</b>]ÂCl) with CuCl
produces a novel tetrametallic cuboidal cluster [Mo<sub>3</sub>(CuCl)ÂS<sub>4</sub>Cl<sub>3</sub>(dbbpy)<sub>3</sub>]Â[CuCl<sub>2</sub>] ([<b>2</b>]Â[CuCl<sub>2</sub>]), whose crystal structure was determined
by X-ray diffraction (dbbpy = 4,4â˛-di-<i>tert</i>-butyl-2,2â˛-bipyridine). This species, which contains two
distinct types of CuÂ(I), is the first example of a diimine-functionalized
heterometallic M<sub>3</sub>Mâ˛S<sub>4</sub> cluster. Kinetics
studies on both the formation of the cubane from the parent trinuclear
cluster and its dissociation after treatment with halides, supported
by NMR, electrospray ionization mass spectrometry, cyclic voltammetry,
and density functional theory calculations, are provided. On the one
hand, the results indicate that addition of CuÂ(I) to [<b>1</b>]<sup>+</sup> is so fast that its kinetics can be monitored only
by cryo-stopped flow at â85 °C. On the other hand, the
release of the CuCl unit in [<b>2</b>]<sup>+</sup> is also a
fast process, which is unexpectedly assisted by the CuCl<sub>2</sub><sup>â</sup> counteranion in a process triggered by halide
(X<sup>â</sup>) anions. The whole set of results provide a
detailed picture of the assemblyâdisassembly processes in this
kind of cluster. Interconversion between trinuclear M<sub>3</sub>S<sub>4</sub> clusters and their heterometallic M<sub>3</sub>Mâ˛S<sub>4</sub> derivatives can be a fast process occurring readily under
the conditions employed during reactivity and catalytic studies, so
their occurrence is a possibility that must be taken into account
in future studies
Kinetics Aspects of the Reversible Assembly of Copper in Heterometallic Mo<sub>3</sub>CuS<sub>4</sub> Clusters with 4,4â˛-Di-<i>tert</i>-butyl-2,2â˛-bipyridine
Treatment
of the triangular [Mo<sub>3</sub>S<sub>4</sub>Cl<sub>3</sub>(dbbpy)<sub>3</sub>]Cl cluster ([<b>1</b>]ÂCl) with CuCl
produces a novel tetrametallic cuboidal cluster [Mo<sub>3</sub>(CuCl)ÂS<sub>4</sub>Cl<sub>3</sub>(dbbpy)<sub>3</sub>]Â[CuCl<sub>2</sub>] ([<b>2</b>]Â[CuCl<sub>2</sub>]), whose crystal structure was determined
by X-ray diffraction (dbbpy = 4,4â˛-di-<i>tert</i>-butyl-2,2â˛-bipyridine). This species, which contains two
distinct types of CuÂ(I), is the first example of a diimine-functionalized
heterometallic M<sub>3</sub>Mâ˛S<sub>4</sub> cluster. Kinetics
studies on both the formation of the cubane from the parent trinuclear
cluster and its dissociation after treatment with halides, supported
by NMR, electrospray ionization mass spectrometry, cyclic voltammetry,
and density functional theory calculations, are provided. On the one
hand, the results indicate that addition of CuÂ(I) to [<b>1</b>]<sup>+</sup> is so fast that its kinetics can be monitored only
by cryo-stopped flow at â85 °C. On the other hand, the
release of the CuCl unit in [<b>2</b>]<sup>+</sup> is also a
fast process, which is unexpectedly assisted by the CuCl<sub>2</sub><sup>â</sup> counteranion in a process triggered by halide
(X<sup>â</sup>) anions. The whole set of results provide a
detailed picture of the assemblyâdisassembly processes in this
kind of cluster. Interconversion between trinuclear M<sub>3</sub>S<sub>4</sub> clusters and their heterometallic M<sub>3</sub>Mâ˛S<sub>4</sub> derivatives can be a fast process occurring readily under
the conditions employed during reactivity and catalytic studies, so
their occurrence is a possibility that must be taken into account
in future studies