Theoretical Studies on the Mechanism of Iridium-Catalyzed Alkene Hydrogenation by the Cationic Complex [IrH₂(NCMe)₃(P^<i>i</i>Pr₃)]⁺

A mechanistic DFT study has been carried out on the ethene hydrogenation catalyzed by the [IrH₂­(NCMe)₃­(P^<i>i</i>Pr₃)]⁺ complex (<b>1</b>). First, the reaction of (<b>1</b>) with ethene has been theoretically characterized, and three mechanistic proposals (<b>A</b>–<b>C</b>) have been made for an identification of the preferred pathways for the alkene hydrogenation catalytic cycle considering Ir­(I)/Ir­(III) and Ir­(III)/Ir­(V) intermediate species. Theoretical calculations reveal that the reaction path with the lowest energy starts at an initial ethene migratory insertion into the metal–hydride bond, followed by dihydrogen coordination into the vacancy. Ethane is formed via σ-bond metathesis between the bound H₂ and the Ir-ethyl moiety, being the rate-determining step, in agreement with the experimental data available. The calculated energetic span associated with the catalytic cycle is 21.4 kcal mol^–1. Although no Ir­(V) intermediate has been found along the reaction path, the Ir­(V) nature of the transition state for the proposed key σ-bond metathesis step has been determined by electron localization function and geometrical analysis

Cubane-Type Mo₃FeS₄^4+,5+ Complexes Containing Outer Diphosphane Ligands: Ligand Substitution Reactions, Spectroscopic Studies, and Electronic Structure

A general protocol to access Mo₃FeS₄⁴⁺ clusters selectively modified at the Fe coordination site is presented starting from the all-chlorine Mo₃(FeCl)­S₄(dmpe)₃Cl₃ (<b>1</b>) [dmpe = 1,2-bis­(dimethylphosphane-ethane)] cluster and tetrabutylammonium salts (<i>n</i>-Bu₄NX) (X = CN^–, N₃^–, and PhS^–). Clusters Mo₃(FeX)­S₄(dmpe)₃Cl₃ [X = CN^– (<b>2</b>), N₃^– (<b>3</b>), and PhS^– (<b>4</b>)] are prepared in high yield, and comparison of geometric and redox features upon modification of the coordination environment at the Fe site at parity of ligands at the Mo sites is also presented. The existence of the cubane-type Mo₃FeS₄^4+,5+ redox couple is demonstrated by cyclic voltammetry and for compound <b>1</b> by cluster synthesis and X-ray structure determinations. Ground states for the <b>1</b>/<b>1</b>⁺ redox couple are evaluated on the basis of magnetic susceptibility measurements, electron paramagnetic resonance, and ⁵⁷Fe Mössbauer spectroscopy aimed at providing an input of experimental data for electronic structure determination based on density functional theory calculations

Cubane-Type Mo₃FeS₄^4+,5+ Complexes Containing Outer Diphosphane Ligands: Ligand Substitution Reactions, Spectroscopic Studies, and Electronic Structure

A general protocol to access Mo₃FeS₄⁴⁺ clusters selectively modified at the Fe coordination site is presented starting from the all-chlorine Mo₃(FeCl)­S₄(dmpe)₃Cl₃ (<b>1</b>) [dmpe = 1,2-bis­(dimethylphosphane-ethane)] cluster and tetrabutylammonium salts (<i>n</i>-Bu₄NX) (X = CN^–, N₃^–, and PhS^–). Clusters Mo₃(FeX)­S₄(dmpe)₃Cl₃ [X = CN^– (<b>2</b>), N₃^– (<b>3</b>), and PhS^– (<b>4</b>)] are prepared in high yield, and comparison of geometric and redox features upon modification of the coordination environment at the Fe site at parity of ligands at the Mo sites is also presented. The existence of the cubane-type Mo₃FeS₄^4+,5+ redox couple is demonstrated by cyclic voltammetry and for compound <b>1</b> by cluster synthesis and X-ray structure determinations. Ground states for the <b>1</b>/<b>1</b>⁺ redox couple are evaluated on the basis of magnetic susceptibility measurements, electron paramagnetic resonance, and ⁵⁷Fe Mössbauer spectroscopy aimed at providing an input of experimental data for electronic structure determination based on density functional theory calculations

Halogen-Bonding Complexes Based on Bis(iodoethynyl)benzene Units: A New Versatile Route to Supramolecular Materials

Iodoalkynes [1,4-bis­(iodoethynyl)­benzene (<i><b>p</b></i><b>-BIB</b>) and 1,3-bis­(iodoethynyl)­benzene (<i><b>m</b></i><b>-BIB</b>)] have been used successfully to prepare halogen bonding complexes with a range of 4-pyridine derivatives showing liquid crystalline organizations. The trimeric halogen-bonded complexes obtained from <i><b>p</b></i><b>-BIB</b> have a rod-like structure and exhibited high order calamitic phases (SmB and G). In contrast, <i><b>m</b></i><b>-BIB</b> gives rise to bent-shaped structures that display SmAP-like mesophases. Furthermore it was found that the presence of three and five aromatic rings in these halogen-bonding complexes promotes calamitic mesophases while seven rings are required to stabilize bent-core mesophases. The formation of halogen bonding in the complexes was confirmed by several techniques, including FT-IR, XPS, and single crystal X-ray diffraction and the strength of the bonds was evaluated by DFT calculation

Halogen-Bonding Complexes Based on Bis(iodoethynyl)benzene Units: A New Versatile Route to Supramolecular Materials

Iodoalkynes [1,4-bis­(iodoethynyl)­benzene (<i><b>p</b></i><b>-BIB</b>) and 1,3-bis­(iodoethynyl)­benzene (<i><b>m</b></i><b>-BIB</b>)] have been used successfully to prepare halogen bonding complexes with a range of 4-pyridine derivatives showing liquid crystalline organizations. The trimeric halogen-bonded complexes obtained from <i><b>p</b></i><b>-BIB</b> have a rod-like structure and exhibited high order calamitic phases (SmB and G). In contrast, <i><b>m</b></i><b>-BIB</b> gives rise to bent-shaped structures that display SmAP-like mesophases. Furthermore it was found that the presence of three and five aromatic rings in these halogen-bonding complexes promotes calamitic mesophases while seven rings are required to stabilize bent-core mesophases. The formation of halogen bonding in the complexes was confirmed by several techniques, including FT-IR, XPS, and single crystal X-ray diffraction and the strength of the bonds was evaluated by DFT calculation

Halogen-Bonding Complexes Based on Bis(iodoethynyl)benzene Units: A New Versatile Route to Supramolecular Materials

Iodoalkynes [1,4-bis­(iodoethynyl)­benzene (<i><b>p</b></i><b>-BIB</b>) and 1,3-bis­(iodoethynyl)­benzene (<i><b>m</b></i><b>-BIB</b>)] have been used successfully to prepare halogen bonding complexes with a range of 4-pyridine derivatives showing liquid crystalline organizations. The trimeric halogen-bonded complexes obtained from <i><b>p</b></i><b>-BIB</b> have a rod-like structure and exhibited high order calamitic phases (SmB and G). In contrast, <i><b>m</b></i><b>-BIB</b> gives rise to bent-shaped structures that display SmAP-like mesophases. Furthermore it was found that the presence of three and five aromatic rings in these halogen-bonding complexes promotes calamitic mesophases while seven rings are required to stabilize bent-core mesophases. The formation of halogen bonding in the complexes was confirmed by several techniques, including FT-IR, XPS, and single crystal X-ray diffraction and the strength of the bonds was evaluated by DFT calculation

Hydroxo–Rhodium–N-Heterocyclic Carbene Complexes as Efficient Catalyst Precursors for Alkyne Hydrothiolation

The new Rh–hydroxo dinuclear complexes stabilized by an N-heterocyclic carbene (NHC) ligand of type [Rh­(μ-OH)­(NHC)­(η²-olefin)]₂ (coe, IPr (<b>3</b>), IMes (<b>4</b>); ethylene, IPr (<b>5</b>)) are efficient catalyst precursors for alkyne hydrothiolation under mild conditions, presenting high selectivity toward α-vinyl sulfides for a varied set of substrates, which is enhanced by pyridine addition. The structure of complex <b>3</b> has been determined by X-ray diffraction analysis. Several intermediates relevant for the catalytic process have been identified, including Rh^I-thiolato species Rh­(SCH₂Ph)­(IPr)­(η²-coe)­(py) (<b>6</b>) and Rh­(SCH₂Ph)­(IPr)­(η²-HCCCH₂Ph)­(py) (<b>7</b>), and the Rh^III-hydride-dithiolato derivative RhH­(SCH₂Ph)₂(IPr)­(py) (<b>8</b>) as the catalytically active species. Computational DFT studies reveal an operational mechanism consisting of sequential thiol deprotonation by the hydroxo ligand, subsequent S–H oxidative addition, alkyne insertion, and reductive elimination. The insertion step is rate-limiting with a 1,2 thiometalation of the alkyne as the more favorable pathway in accordance with the observed Markovnikov-type selectivity

Hydroxo–Rhodium–N-Heterocyclic Carbene Complexes as Efficient Catalyst Precursors for Alkyne Hydrothiolation

The new Rh–hydroxo dinuclear complexes stabilized by an N-heterocyclic carbene (NHC) ligand of type [Rh­(μ-OH)­(NHC)­(η²-olefin)]₂ (coe, IPr (<b>3</b>), IMes (<b>4</b>); ethylene, IPr (<b>5</b>)) are efficient catalyst precursors for alkyne hydrothiolation under mild conditions, presenting high selectivity toward α-vinyl sulfides for a varied set of substrates, which is enhanced by pyridine addition. The structure of complex <b>3</b> has been determined by X-ray diffraction analysis. Several intermediates relevant for the catalytic process have been identified, including Rh^I-thiolato species Rh­(SCH₂Ph)­(IPr)­(η²-coe)­(py) (<b>6</b>) and Rh­(SCH₂Ph)­(IPr)­(η²-HCCCH₂Ph)­(py) (<b>7</b>), and the Rh^III-hydride-dithiolato derivative RhH­(SCH₂Ph)₂(IPr)­(py) (<b>8</b>) as the catalytically active species. Computational DFT studies reveal an operational mechanism consisting of sequential thiol deprotonation by the hydroxo ligand, subsequent S–H oxidative addition, alkyne insertion, and reductive elimination. The insertion step is rate-limiting with a 1,2 thiometalation of the alkyne as the more favorable pathway in accordance with the observed Markovnikov-type selectivity

Ligand-Controlled Regioselectivity in the Hydrothiolation of Alkynes by Rhodium N-Heterocyclic Carbene Catalysts

Rh–N-heterocyclic carbene compounds [Rh­(μ-Cl)­(IPr)­(η²-olefin)]₂ and RhCl­(IPr)­(py)­(η²-olefin) (IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl­(IPr)­(py)­(η²-olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate–hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate–alkyne disposition, favoring formation of 2,2-disubstituted metal–alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl–hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium–thiolate bond is the rate-determining step

Ligand-Controlled Regioselectivity in the Hydrothiolation of Alkynes by Rhodium N-Heterocyclic Carbene Catalysts

Rh–N-heterocyclic carbene compounds [Rh­(μ-Cl)­(IPr)­(η²-olefin)]₂ and RhCl­(IPr)­(py)­(η²-olefin) (IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl­(IPr)­(py)­(η²-olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate–hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate–alkyne disposition, favoring formation of 2,2-disubstituted metal–alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl–hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium–thiolate bond is the rate-determining step