<i>cis</i>-1,3,5-Triaminocyclohexane as a Facially Capping Ligand for Ruthenium(II)

Reaction of <i>cis-</i>[RuCl₂(DMSO-<i>S</i>)₃(DMSO-<i>O</i>)] with <i>cis</i>-1,3,5-triaminocyclohexane (tach) results in the formation of [RuCl­(tach)­(DMSO-<i>S</i>)₂]­Cl, a valuable precursor for a wide range of other tach-containing Ru complexes. Reaction of [RuCl­(tach)­(DMSO-<i>S</i>)₂]Cl with the chelating nitrogen-based ligands (N–N = bipyridine, phenanthroline, and ethylenediamine) affords [Ru­(N–N)­(DMSO-<i>S</i>)₂(tach)]­[Cl]₂. A similar reaction between [RuCl­(tach)­(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 [RuCl­(P–P)­(tach)]­Cl. 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 NH₂ 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 [Ru­(κ¹-OAc)­(κ²-OAc)­(CCHC­{OH}­R¹R²)­(PPh₃)₂] (R¹ = R² = Ph; R¹ = R² = Me; R¹ = Ph, R² = Me) with [CPh₃]­BF₄ results in the formation of the cationic carbene species [Ru­(κ²-OAc)­(OC­{Me}­OCC­{H}CR¹R²)­(PPh₃)₂]­BF₄. In these complexes, the κ¹-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 R¹ = R² = Ph, the hydrogen on the β-carbon of the organic ligand is removed to afford an allenylidene complex [Ru­(κ¹-OAc)­(κ²-OAc)­(CCCPh₂)­(PPh₃)₂]. 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 R¹ = R² = Me and R¹ = Me, R² = Ph deprotonation occurs at a methyl group to afford vinylvinylidene complexes [Ru­(κ¹-OAc)­(κ²-OAc)­(CC­{H}-CR²CH₂)­(PPh₃)₂] (R² = Me, Ph). No interconversion between vinylvinylidene and allenylidene complexes was observed. The overall process is analogous to a formal <i>E</i>₁-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^–1. 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 [Ru­(κ¹-OAc)­(κ²-OAc)­(CCHC­{OH}­R¹R²)­(PPh₃)₂] (R¹ = R² = Ph; R¹ = R² = Me; R¹ = Ph, R² = Me) with [CPh₃]­BF₄ results in the formation of the cationic carbene species [Ru­(κ²-OAc)­(OC­{Me}­OCC­{H}CR¹R²)­(PPh₃)₂]­BF₄. In these complexes, the κ¹-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 R¹ = R² = Ph, the hydrogen on the β-carbon of the organic ligand is removed to afford an allenylidene complex [Ru­(κ¹-OAc)­(κ²-OAc)­(CCCPh₂)­(PPh₃)₂]. 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 R¹ = R² = Me and R¹ = Me, R² = Ph deprotonation occurs at a methyl group to afford vinylvinylidene complexes [Ru­(κ¹-OAc)­(κ²-OAc)­(CC­{H}-CR²CH₂)­(PPh₃)₂] (R² = Me, Ph). No interconversion between vinylvinylidene and allenylidene complexes was observed. The overall process is analogous to a formal <i>E</i>₁-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^–1. 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>[RuCl₂(DMSO-<i>S</i>)₃(DMSO-<i>O</i>)] with <i>cis</i>-1,3,5-triaminocyclohexane (tach) results in the formation of [RuCl­(tach)­(DMSO-<i>S</i>)₂]­Cl, a valuable precursor for a wide range of other tach-containing Ru complexes. Reaction of [RuCl­(tach)­(DMSO-<i>S</i>)₂]Cl with the chelating nitrogen-based ligands (N–N = bipyridine, phenanthroline, and ethylenediamine) affords [Ru­(N–N)­(DMSO-<i>S</i>)₂(tach)]­[Cl]₂. A similar reaction between [RuCl­(tach)­(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 [RuCl­(P–P)­(tach)]­Cl. 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 NH₂ 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)₂(H)₂]: Preparative, NMR, Solid State, and Laser Flash Studies

Three ruthenium complexes Λ-[<i>cis</i>-Ru­((<i>R</i>,<i>R</i>)-Me-BPE)₂(H)₂] Λ-<i>R</i>,<i>R</i>-Ru1H₂, Δ-[<i>cis</i>-Ru­((<i>S</i>,<i>S</i>)-Me-DuPHOS)₂(H)₂] Δ-<i>S</i>,<i>S</i>-Ru2H₂, and Λ-[<i>cis</i>-Ru­((<i>R</i>,<i>R</i>)-Me-DuPHOS)₂(H)₂] Λ-<i>R</i>,<i>R</i>-Ru2H₂ (<b>1</b> = (Me-BPE)₂, <b>2</b> = (Me-DuPHOS)₂) 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>-Ru2H₂/Λ-<i>R</i>,<i>R</i>-Ru2H₂ photoproducts from Λ to Δ (or vice versa) while the configuration for Λ-<i>R</i>,<i>R</i>-Ru1H₂ 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>-Ru­((<i>R</i>,<i>R</i>)-Me-DuPHOS)₂(Et₂SiH)­(H)] and Δ-[<i>cis</i>-Ru­((<i>R</i>,<i>R</i>)-Me-DuPHOS)₂(PhSiH₂)­(H)] but not for their Ru­(<i>R</i>,<i>R</i>-BPE)₂ analogues. Molecular structures were also determined for Λ-[<i>cis</i>-Ru­((<i>R</i>,<i>R</i>)-Me-BPE)₂(Bpin)­(H)], Λ-[Ru­((<i>S</i>,<i>S</i>)-Me-DuPHOS)₂(η²-C₂H₄)], Δ-[Ru­((<i>R</i>,<i>R</i>)-Me-DuPHOS)₂(η²-C₂H₄)], and <i>trans</i>-[Ru­((<i>R</i>,<i>R</i>)-Me-DuPHOS)₂(C₆F₅)­(H)]. In situ laser photolysis in the presence of <i>p</i>-H₂ generates hyperpolarized NMR spectra because of magnetically inequivalent hydrides; these experiments and low temperature photolysis with D₂ reveal that the loss of hydride ligands is concerted. The reaction intermediates [Ru­(DuPHOS)₂] and [Ru­(BPE)₂] were detected by laser flash photolysis and have spectra consistent with approximate square-planar Ru(0) structures. The rates of their reactions with H₂, D₂, HBpin, and PhSiH₃ were measured by transient kinetics. Rate constants are significantly faster for [Ru­(BPE)₂] than for [Ru­(DuPHOS)₂] and follow the substrate order H₂ > D₂ > PhSiH₃ > HBpin

Ruthenium-Mediated C–H Functionalization of Pyridine: The Role of Vinylidene and Pyridylidene Ligands

A combined experimental and theoretical study has demonstrated that [Ru­(η⁵-C₅H₅)­(py)₂(PPh₃)]⁺ is a key intermediate, and active catalyst for, the formation of 2-substituted <i>E</i>-styrylpyridines from pyridine and terminal alkynes HCCR (R = Ph, C₆H₄-4-CF₃) in a 100% atom efficient manner under mild conditions. A catalyst deactivation pathway involving formation of the pyridylidene-containing complex [Ru­(η⁵-C₅H₅)­(κ³-<i>C</i>₃-C₅H₄NCHCHR)­(PPh₃)]⁺ and subsequently a 1-ruthanaindolizine complex has been identified. Mechanistic studies using ¹³C- and D-labeling and DFT calculations suggest that a vinylidene-containing intermediate [Ru­(η⁵-C₅H₅)­(py)­(CCHR)­(PPh₃)]⁺ 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 [Ru­(η⁵-C₅H₅)­(C₅H₄N)­(CCHR)­(PPh₃)]. 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