6 research outputs found
<i>cis</i>-1,3,5-Triaminocyclohexane as a Facially Capping Ligand for Ruthenium(II)
Reaction
of <i>cis-</i>[RuCl<sub>2</sub>(DMSO-<i>S</i>)<sub>3</sub>(DMSO-<i>O</i>)] with <i>cis</i>-1,3,5-triaminocyclohexane
(tach) results in the formation of [RuClÂ(tach)Â(DMSO-<i>S</i>)<sub>2</sub>]ÂCl, a valuable precursor for a wide range of other
tach-containing Ru complexes. Reaction of [RuClÂ(tach)Â(DMSO-<i>S</i>)<sub>2</sub>]Cl with the chelating nitrogen-based ligands
(N–N = bipyridine, phenanthroline, and ethylenediamine) affords
[RuÂ(N–N)Â(DMSO-<i>S</i>)<sub>2</sub>(tach)]Â[Cl]<sub>2</sub>. A similar reaction between [RuClÂ(tach)Â(DMSO-<i>S</i>)]Cl with the chelating phosphorus-based ligands (P–P = dppm,
dppe, dppp, dppb, dppv, and dppben) leads to the formation of [RuClÂ(P–P)Â(tach)]ÂCl.
The structures of 10 examples of the tach-containing complexes have
been determined by single crystal X-ray diffraction. An examination
of the structural metrics obtained from these studies indicates that
the tach ligand is a strong sigma donor. In addition, the presence
of the NH<sub>2</sub> groups in the tach ligand allow for participation
in hydrogen bonding further modulating the coordinative properties
of the ligand
Mapping the Elimination of Water from Hydroxyvinylidene Complexes of Ruthenium(II): Access to Allenylidene and Vinylvinylidene Complexes in a Stepwise Fashion
Reaction
of hydroxyvinylidene complexes [RuÂ(κ<sup>1</sup>-OAc)Â(κ<sup>2</sup>-OAc)Â(î—»Cî—»CHCÂ{OH}ÂR<sup>1</sup>R<sup>2</sup>)Â(PPh<sub>3</sub>)<sub>2</sub>] (R<sup>1</sup> = R<sup>2</sup> = Ph; R<sup>1</sup> = R<sup>2</sup> = Me; R<sup>1</sup> = Ph, R<sup>2</sup> =
Me) with [CPh<sub>3</sub>]ÂBF<sub>4</sub> results in the formation
of the cationic carbene species [RuÂ(κ<sup>2</sup>-OAc)Â(OCÂ{Me}ÂOCCÂ{H}î—»CR<sup>1</sup>R<sup>2</sup>)Â(PPh<sub>3</sub>)<sub>2</sub>]ÂBF<sub>4</sub>. In these complexes, the κ<sup>1</sup>-acetate ligand has changed its binding mode in order to stabilize
the resulting cationic species. The carbene complexes may be deprotonated,
although the outcome of the reaction depends markedly on the substituent
present. In the case in which R<sup>1</sup> = R<sup>2</sup> = Ph,
the hydrogen on the β-carbon of the organic ligand is removed
to afford an allenylidene complex [RuÂ(κ<sup>1</sup>-OAc)Â(κ<sup>2</sup>-OAc)Â(î—»Cî—»Cî—»CPh<sub>2</sub>)Â(PPh<sub>3</sub>)<sub>2</sub>]. An examination of the structural and spectroscopic
parameters for the allenylidene complex indicates that the electronic
influence of this ligand is very similar to the corresponding vinylidene
and isonitrile analogues. In the cases where R<sup>1</sup> = R<sup>2</sup> = Me and R<sup>1</sup> = Me, R<sup>2</sup> = Ph deprotonation
occurs at a methyl group to afford vinylvinylidene complexes [RuÂ(κ<sup>1</sup>-OAc)Â(κ<sup>2</sup>-OAc)Â(î—»Cî—»CÂ{H}-CR<sup>2</sup>î—»CH<sub>2</sub>)Â(PPh<sub>3</sub>)<sub>2</sub>] (R<sup>2</sup> = Me, Ph). No interconversion between vinylvinylidene and
allenylidene complexes was observed. The overall process is analogous
to a formal <i>E</i><sub>1</sub>-type elimination in which
the cationic carbene complex may be viewed as a stabilized carbocation
intermediate. A DFT study provided insight into selectivity of the
deprotonation step indicating that the greatest relative difference
in energy between all the possible isomers of the vinylvinylidene
and allenylidene complexes was <i>ca.</i> 20 kJ mol<sup>–1</sup>. Interconversion between the two forms of the complex
by a [1,3]-hydrogen shift appears to be unlikely due to the higher
energy of the corresponding transition state; hence the selectivity
in the formation of the vinylvinylidene complexes may be due the site
of deprotonation being kinetically controlled. An alternative mechanism
for this interconversion between vinylvinylidene and allenylidene
complexes in cationic half sandwich metal complexes is proposed, which
proceeds via a deprotonation/reprotonation pathway
Mapping the Elimination of Water from Hydroxyvinylidene Complexes of Ruthenium(II): Access to Allenylidene and Vinylvinylidene Complexes in a Stepwise Fashion
Reaction
of hydroxyvinylidene complexes [RuÂ(κ<sup>1</sup>-OAc)Â(κ<sup>2</sup>-OAc)Â(î—»Cî—»CHCÂ{OH}ÂR<sup>1</sup>R<sup>2</sup>)Â(PPh<sub>3</sub>)<sub>2</sub>] (R<sup>1</sup> = R<sup>2</sup> = Ph; R<sup>1</sup> = R<sup>2</sup> = Me; R<sup>1</sup> = Ph, R<sup>2</sup> =
Me) with [CPh<sub>3</sub>]ÂBF<sub>4</sub> results in the formation
of the cationic carbene species [RuÂ(κ<sup>2</sup>-OAc)Â(OCÂ{Me}ÂOCCÂ{H}î—»CR<sup>1</sup>R<sup>2</sup>)Â(PPh<sub>3</sub>)<sub>2</sub>]ÂBF<sub>4</sub>. In these complexes, the κ<sup>1</sup>-acetate ligand has changed its binding mode in order to stabilize
the resulting cationic species. The carbene complexes may be deprotonated,
although the outcome of the reaction depends markedly on the substituent
present. In the case in which R<sup>1</sup> = R<sup>2</sup> = Ph,
the hydrogen on the β-carbon of the organic ligand is removed
to afford an allenylidene complex [RuÂ(κ<sup>1</sup>-OAc)Â(κ<sup>2</sup>-OAc)Â(î—»Cî—»Cî—»CPh<sub>2</sub>)Â(PPh<sub>3</sub>)<sub>2</sub>]. An examination of the structural and spectroscopic
parameters for the allenylidene complex indicates that the electronic
influence of this ligand is very similar to the corresponding vinylidene
and isonitrile analogues. In the cases where R<sup>1</sup> = R<sup>2</sup> = Me and R<sup>1</sup> = Me, R<sup>2</sup> = Ph deprotonation
occurs at a methyl group to afford vinylvinylidene complexes [RuÂ(κ<sup>1</sup>-OAc)Â(κ<sup>2</sup>-OAc)Â(î—»Cî—»CÂ{H}-CR<sup>2</sup>î—»CH<sub>2</sub>)Â(PPh<sub>3</sub>)<sub>2</sub>] (R<sup>2</sup> = Me, Ph). No interconversion between vinylvinylidene and
allenylidene complexes was observed. The overall process is analogous
to a formal <i>E</i><sub>1</sub>-type elimination in which
the cationic carbene complex may be viewed as a stabilized carbocation
intermediate. A DFT study provided insight into selectivity of the
deprotonation step indicating that the greatest relative difference
in energy between all the possible isomers of the vinylvinylidene
and allenylidene complexes was <i>ca.</i> 20 kJ mol<sup>–1</sup>. Interconversion between the two forms of the complex
by a [1,3]-hydrogen shift appears to be unlikely due to the higher
energy of the corresponding transition state; hence the selectivity
in the formation of the vinylvinylidene complexes may be due the site
of deprotonation being kinetically controlled. An alternative mechanism
for this interconversion between vinylvinylidene and allenylidene
complexes in cationic half sandwich metal complexes is proposed, which
proceeds via a deprotonation/reprotonation pathway
<i>cis</i>-1,3,5-Triaminocyclohexane as a Facially Capping Ligand for Ruthenium(II)
Reaction
of <i>cis-</i>[RuCl<sub>2</sub>(DMSO-<i>S</i>)<sub>3</sub>(DMSO-<i>O</i>)] with <i>cis</i>-1,3,5-triaminocyclohexane
(tach) results in the formation of [RuClÂ(tach)Â(DMSO-<i>S</i>)<sub>2</sub>]ÂCl, a valuable precursor for a wide range of other
tach-containing Ru complexes. Reaction of [RuClÂ(tach)Â(DMSO-<i>S</i>)<sub>2</sub>]Cl with the chelating nitrogen-based ligands
(N–N = bipyridine, phenanthroline, and ethylenediamine) affords
[RuÂ(N–N)Â(DMSO-<i>S</i>)<sub>2</sub>(tach)]Â[Cl]<sub>2</sub>. A similar reaction between [RuClÂ(tach)Â(DMSO-<i>S</i>)]Cl with the chelating phosphorus-based ligands (P–P = dppm,
dppe, dppp, dppb, dppv, and dppben) leads to the formation of [RuClÂ(P–P)Â(tach)]ÂCl.
The structures of 10 examples of the tach-containing complexes have
been determined by single crystal X-ray diffraction. An examination
of the structural metrics obtained from these studies indicates that
the tach ligand is a strong sigma donor. In addition, the presence
of the NH<sub>2</sub> groups in the tach ligand allow for participation
in hydrogen bonding further modulating the coordinative properties
of the ligand
Selective Photochemistry at Stereogenic Metal and Ligand Centers of <i>cis</i>-[Ru(diphosphine)<sub>2</sub>(H)<sub>2</sub>]: Preparative, NMR, Solid State, and Laser Flash Studies
Three ruthenium complexes Λ-[<i>cis</i>-RuÂ((<i>R</i>,<i>R</i>)-Me-BPE)<sub>2</sub>(H)<sub>2</sub>] Λ-<i>R</i>,<i>R</i>-Ru1H<sub>2</sub>,
Δ-[<i>cis</i>-RuÂ((<i>S</i>,<i>S</i>)-Me-DuPHOS)<sub>2</sub>(H)<sub>2</sub>] Δ-<i>S</i>,<i>S</i>-Ru2H<sub>2</sub>, and Λ-[<i>cis</i>-RuÂ((<i>R</i>,<i>R</i>)-Me-DuPHOS)<sub>2</sub>(H)<sub>2</sub>] Λ-<i>R</i>,<i>R</i>-Ru2H<sub>2</sub> (<b>1</b> = (Me-BPE)<sub>2</sub>, <b>2</b> =
(Me-DuPHOS)<sub>2</sub>) were characterized by multinuclear NMR and
CD spectroscopy in solution and by X-ray crystallography. The chiral
ligands allow the full control of stereochemistry and enable mechanistic
studies not otherwise available. Oxidative addition of E–H
bonds (E = H, B, Si, C) was studied by steady state and laser flash
photolysis in the presence of substrates. Steady state photolysis
shows formation of single products with one stereoisomer. Solid state
structures and circular dichroism spectra reveal a change in configuration
at ruthenium for some Δ-<i>S</i>,<i>S</i>-Ru2H<sub>2</sub>/Λ-<i>R</i>,<i>R</i>-Ru2H<sub>2</sub> photoproducts from Λ to Δ (or vice versa) while
the configuration for Λ-<i>R</i>,<i>R</i>-Ru1H<sub>2</sub> products remains unchanged as Λ. The X-ray
structure of silyl hydride photoproducts suggests a residual H(1)···Si(1)
interaction for Δ-[<i>cis</i>-RuÂ((<i>R</i>,<i>R</i>)-Me-DuPHOS)<sub>2</sub>(Et<sub>2</sub>SiH)Â(H)]
and Δ-[<i>cis</i>-RuÂ((<i>R</i>,<i>R</i>)-Me-DuPHOS)<sub>2</sub>(PhSiH<sub>2</sub>)Â(H)] but not for their
RuÂ(<i>R</i>,<i>R</i>-BPE)<sub>2</sub> analogues.
Molecular structures were also determined for Λ-[<i>cis</i>-RuÂ((<i>R</i>,<i>R</i>)-Me-BPE)<sub>2</sub>(Bpin)Â(H)],
Λ-[RuÂ((<i>S</i>,<i>S</i>)-Me-DuPHOS)<sub>2</sub>(η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>)], Δ-[RuÂ((<i>R</i>,<i>R</i>)-Me-DuPHOS)<sub>2</sub>(η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>)], and <i>trans</i>-[RuÂ((<i>R</i>,<i>R</i>)-Me-DuPHOS)<sub>2</sub>(C<sub>6</sub>F<sub>5</sub>)Â(H)]. In situ laser photolysis in the presence of <i>p</i>-H<sub>2</sub> generates hyperpolarized NMR spectra because
of magnetically inequivalent hydrides; these experiments and low temperature
photolysis with D<sub>2</sub> reveal that the loss of hydride ligands
is concerted. The reaction intermediates [RuÂ(DuPHOS)<sub>2</sub>]
and [RuÂ(BPE)<sub>2</sub>] were detected by laser flash photolysis
and have spectra consistent with approximate square-planar Ru(0) structures.
The rates of their reactions with H<sub>2</sub>, D<sub>2</sub>, HBpin,
and PhSiH<sub>3</sub> were measured by transient kinetics. Rate constants
are significantly faster for [RuÂ(BPE)<sub>2</sub>] than for [RuÂ(DuPHOS)<sub>2</sub>] and follow the substrate order H<sub>2</sub> > D<sub>2</sub> > PhSiH<sub>3</sub> > HBpin
Ruthenium-Mediated C–H Functionalization of Pyridine: The Role of Vinylidene and Pyridylidene Ligands
A combined experimental and theoretical study has demonstrated
that [RuÂ(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Â(py)<sub>2</sub>(PPh<sub>3</sub>)]<sup>+</sup> is a key intermediate, and active
catalyst for, the formation of 2-substituted <i>E</i>-styrylpyridines
from pyridine and terminal alkynes HCî—¼CR (R = Ph, C<sub>6</sub>H<sub>4</sub>-4-CF<sub>3</sub>) in a 100% atom efficient manner under
mild conditions. A catalyst deactivation pathway involving formation
of the pyridylidene-containing complex [RuÂ(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Â(κ<sup>3</sup>-<i>C</i><sub>3</sub>-C<sub>5</sub>H<sub>4</sub>NCHî—»CHR)Â(PPh<sub>3</sub>)]<sup>+</sup> and subsequently a 1-ruthanaindolizine complex has
been identified. Mechanistic studies using <sup>13</sup>C- and D-labeling
and DFT calculations suggest that a vinylidene-containing intermediate
[RuÂ(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Â(py)Â(î—»Cî—»CHR)Â(PPh<sub>3</sub>)]<sup>+</sup> is formed, which can then proceed to the pyridylidene-containing
deactivation product or the desired product depending on the reaction
conditions. Nucleophilic attack by free pyridine at the α-carbon
in this complex subsequently leads to formation of a C–H agostic
complex that is the branching point for the productive and unproductive
pathways. The formation of the desired products relies on C–H
bond cleavage from this agostic complex in the presence of free pyridine
to give the pyridyl complex [RuÂ(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Â(C<sub>5</sub>H<sub>4</sub>N)Â(î—»Cî—»CHR)Â(PPh<sub>3</sub>)]. Migration of the pyridyl ligand (or its pyridylidene tautomer)
to the α-carbon of the vinylidene, followed by protonation,
results in the formation of the 2-styrylpyridine. These studies demonstrate
that pyridylidene ligands play an important role in both the productive
and nonproductive pathways in this catalyst system