Indenyl Ligand Research Articles

2.2]Benzoindenophane-Based Chiral Indenyl Ligands: Design, Synthesis, and Applications in Asymmetric C-H Activation.

Development of chiral indenyl ligands for asymmetric C-H activation is a longstanding challenge, and extremely few successes have been achieved. In this paper, we describe a class of readily accessible, facilely tunable and user-friendly chiral indenyl ligands featuring a [2.2]benzoindenophane skeleton via a divergent synthesis strategy. The corresponding chiral indenyl rhodium catalysts were successfully applied in the asymmetric C-H activation reaction of O-Boc hydroxybenzamide with alkenes to give various chiral dihydroisoquinolone products (up to 97 % yield, up to 98 % ee). Moreover, the asymmetric C-H activation reaction of carboxylic acids with alkynes was also successfully accomplished, providing a range of axially chiral isocoumarins (up to 99 % yield, up to 94 % ee). Notably, this represents the first example of enantioselective transition metal catalyzed C(sp2)-H activation/oxidative coupling of benzoic acids with internal alkynes to construct isocoumarins. Given many attractive features of this class of indenyl ligands, such as convenient synthesis, high tunability and exclusive face-selectivity of coordination, its applications in more catalytic asymmetric C-H activation and in other asymmetric catalysis are foreseen.

2.2]Benzoindenophane‐Based Chiral Indenyl Ligands: Design, Synthesis, and Applications in Asymmetric C−H Activation

AbstractDevelopment of chiral indenyl ligands for asymmetric C−H activation is a longstanding challenge, and extremely few successes have been achieved. In this paper, we describe a class of readily accessible, facilely tunable and user‐friendly chiral indenyl ligands featuring a [2.2]benzoindenophane skeleton via a divergent synthesis strategy. The corresponding chiral indenyl rhodium catalysts were successfully applied in the asymmetric C−H activation reaction of O‐Boc hydroxybenzamide with alkenes to give various chiral dihydroisoquinolone products (up to 97 % yield, up to 98 % ee). Moreover, the asymmetric C−H activation reaction of carboxylic acids with alkynes was also successfully accomplished, providing a range of axially chiral isocoumarins (up to 99 % yield, up to 94 % ee). Notably, this represents the first example of enantioselective transition metal catalyzed C(sp2)−H activation/oxidative coupling of benzoic acids with internal alkynes to construct isocoumarins. Given many attractive features of this class of indenyl ligands, such as convenient synthesis, high tunability and exclusive face‐selectivity of coordination, its applications in more catalytic asymmetric C−H activation and in other asymmetric catalysis are foreseen.

Cationic Bis(Gold) Indenyl Complexes.

Reaction of (P)AuOTf [P=P(t-Bu)2o-biphenyl] with indenyl- or 3-methylindenyl lithium led to isolation of gold η1-indenyl complexes (P)Au(η1-inden-1-yl) (1 a) and (P)Au(η1-3-methylinden-1-yl) (1 b), respectively, in >65 % yield. Whereas complex 1 b is static, complex 1 a undergoes facile, degenerate 1,3-migration of gold about the indenyl ligand (ΔG≠ 153K=9.1±1.1 kcal/mol). Treatment of complexes 1 a and 1 b with (P)AuNTf2 led to formation of the corresponding cationic bis(gold) indenyl complexes trans-[(P)Au]2(η1,η1-inden-1,3-yl) (2 a) and trans-[(P)Au]2(η1,η2-3-methylinden-1-yl) (2 b), respectively, which were characterized spectroscopically and modeled computationally. Despite the absence of aurophilic stabilization in complexes 2 a and 2 b, the binding affinity of mono(gold) complex 1 a toward exogenous (P)Au+ exceed that of free indene by ~350-fold and similarly the binding affinity of 1 b toward exogenous (P)Au+ exceed that of 3-methylindene by ~50-fold. The energy barrier for protodeauration of bis(gold) indenyl complex 2 a with HOAc was ≥8 kcal/mol higher than for protodeauration of mono(gold) complex 1 a.

Terminal and bridging ligand effects on M(I)M(I) multiple bonding: ADFTinvestigation of the coordination in (X)[M2Cl]L2complexes (M = Cr,Fe,L = CO,PEt3,X = Cl, allyl,Cp, and indenyl)

AbstractA theoretical DFT investigation has been achieved on (X)[M2Cl]L2(M = Cr, Fe, L = CO, PEt3, and X = allyl, cyclopentadienyl, and indenyl) complexes by means of BP86 and B3LYP* functionals. The geometry optimizations showed an η3‐coordination for the allyl, while Cp and indenyl ligands adopt the same η5‐coordination mode and the chloride acts as bridging ligand. The metal–metal bond distances are very sensitive to the replacement of the CO with PEt3(triethylphosphine) with regard to the electron‐donation and electron π‐backdonation properties for the former and only to the electron‐donation for the later. This replacement impacts drastically the metal–metal bonding. Changing the metal from Cr to Fe increases the metal–metal bond distance, decreases the bond order and the oxidation sate of Fe, in agreement with the decrease of Wiberg bond indices (WBI) and Mayer bond order values (MBO). The findings showed that the Cl−and allyl−behave as 4‐electron donors, while Cp−and Ind−behave as 6–electron donors leading to outstanding electron properties stemming from different coordination, which are clarified by the σ‐donation and π‐backdonation properties, which are highlighted by the orbitals' populations and the energy decomposition analysis (EDA). Based on the aforementioned information, the chromium and iron complexes of Cl−and allyl−are of 22‐ and 24‐metal valence electrons (MVE), where those of Cp−and Ind−are of 26‐ and 28‐MVE, respectively. It is well noted that the metal–metal multiple bonding overcomes the electrons' deficiency.

Benz[e]indenyl and benz[f]indenyl molybdenum compounds: evidence of the η3-coordination mode

The capability of benz[e]indenyl and benz[f]indenyl ligands to undergo η5-to-η3 haptotropic rearrangement was evidenced on new molybdenum compounds.

Explaining the High Catalytic Activity in Bis(indenyl)methyl Zirconium Cation Using Combined EDA-NOCV/QTAIM Approach.

The main purpose of this study is to elucidate some discrepancies already observed in the catalytic activity values of some zirconocene methyl cations. The EDA-NOCV scheme was employed for a theoretical description of the interactions between an ethylene molecule and five catalysts of zirconocene methyl cation. The nature of the chemical interactions has been elucidated through the QTAIM topological analysis. The steric hindrance due to the ligands was evaluated qualitatively by means of an IRI-based analysis and quantitively through Fisher information. The findings prove that the indenyl ligand seems to favor the orbital interaction between the ethylene molecule and the metal centre of zirconocene methyl cation. Both electrostatic and orbital contributions play a crucial role in stabilising the studied complexes. Based on the NOCV deformation density contributions, the strongest orbital interaction is reached with the bis(indenyl)methyl zirconium cation, which is the only one exhibiting covalent interactions. Especially, the strong contribution of π-back donation (occurring from the occupied orbitals of the zirconium atom to the π* anti-bonding orbital of ethylene) may be a key to understand why this catalyst has a higher polymerisation yield than the other studied catalysts. This work suggests a perspective for predicting values of catalytic activity when theoretically designing novel catalysts of zirconocene type.

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

We synthesized a series of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands (Me2Si(2-R1-3-R2-4,5-Me2C7S)(2,7-R32C13H6))ZrMe2 (R1 = Me or H, R2 = H or Me, R3 = H, tBu, or Cl) for the subsequent preparation of supported catalysts. We determined that the fluorenyl ligand adopts an η3-binding mode in 9 (R1 = Me, R2 = H, R3 = H) by X-ray crystallography. Further, we synthesized a derivative 15 by substituting the fluorenyl ligand in 9 with a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand, derivatives 20 and 23 by substituting the Me2Si bridge in 12 (R1 = Me, R2 = H, R3 = tBu) and 15 with a tBuO(CH2)6(Me)Si bridge, and the dinuclear congener 26 by connecting two complexes with a –(Me)Si(CH2)6Si(Me)– spacer. The silica-supported catalysts prepared using 12, 20, and 26 demonstrated up to two times higher productivity in ethylene/1-hexene copolymerization than that prepared with conventional (THI)ZrCl2 (21–26 vs. 12 kg-PE/g-(supported catalyst)), producing polymers with comparable molecular weight (Mw, 330–370 vs. 300 kDa), at a higher 1-hexene content (1.3 vs. 1.0 mol%) but a lower bulk density of polymer particles (0.35 vs. 0.42 g/mL).

In-Reactor Polypropylene Functionalization─The Influence of Catalyst Structures and Reaction Conditions on the Catalytic Performance

To unravel the relationship between silylene-bridged metallocene catalyst structures and polymerization conditions and their effect on the performance in in-reactor functionalization of polypropylene, the behaviors of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(2-Me-4-Ph-Ind)2HfCl2, and rac-Me2Si(Ind)2HfCl2 in propylene/aluminum alkyl-passivated 10-undecen-1-ol copolymerization were compared. Kinetic analysis revealed higher catalytic activities for zirconocenes compared to analogous hafnocenes. Both the zirconocene and hafnocene with substituted indenyl ligands afforded a higher molecular weight capability, improved stereo-selectivity, and enhanced ability to incorporate functionalized comonomers compared to their non-substituted congeners. An in-depth study of polypropylene functionalization using the best performing catalyst system, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, at temperatures ranging from 40 to 100 °C, revealed a linear inversely proportional correlation of polymerization temperature with functionalized comonomer reactivity (↑Tp → ↓ r1), copolymer molecular weight (↑Tp → ↓Mn), and melting temperature (↑Tp → ↓Tm). While performing well under standard laboratory polymerization conditions, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO showed limited molecular weight and stereo-selectivity capabilities under high-temperature (130–150 °C) solution process conditions. Although immobilization of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 onto silica, allowing it to be used under industrially relevant slurry and gas-phase conditions, led to an active catalyst, it failed to incorporate any functionalized comonomer.

Di(indenyl)beryllium.

The bonding in beryllocene, [BeCp2 ], took decades to establish, owing to its unexpected mixed hapticity structure (i.e., [Be(η5 -Cp)(η1 -Cp)]). Beryllium complexes containing the indenyl ligand, which is a close relative of the cyclopentadienyl anion, but which is also known to exhibit its own bonding peculiarities (e.g., facile η5 ⇄ η3 shifts), have remained unknown. Standard metathetical approaches to their synthesis (e.g., with K[Ind'] + BeX2 in an ether solvent) give rise to intractable oils from which nothing identifiable can be isolated. In contrast, mechanochemical preparation, involving the solvent-free grinding of BeBr2 and potassium indenides, leads to the production of discrete (indenyl)beryllium complexes, including [Be(C9 H7 )2 ] (1) and [Be{1,3-(SiMe3 )2 C9 H5 }Br] (2). The former displays η5 /η1 -coordinated ligands in the solid state, but DFT calculations indicate that an η5 /η5 -conformation is less than 5 kcal mol-1 higher in energy.

Di(indenyl)beryllium

AbstractThe bonding in beryllocene, [BeCp2], took decades to establish, owing to its unexpected mixed hapticity structure (i.e., [Be(η5‐Cp)(η1‐Cp)]). Beryllium complexes containing the indenyl ligand, which is a close relative of the cyclopentadienyl anion, but which is also known to exhibit its own bonding peculiarities (e.g., facile η5 ⇄ η3 shifts), have remained unknown. Standard metathetical approaches to their synthesis (e.g., with K[Ind′] + BeX2 in an ether solvent) give rise to intractable oils from which nothing identifiable can be isolated. In contrast, mechanochemical preparation, involving the solvent‐free grinding of BeBr2 and potassium indenides, leads to the production of discrete (indenyl)beryllium complexes, including [Be(C9H7)2] (1) and [Be{1,3‐(SiMe3)2C9H5}Br] (2). The former displays η5/η1‐coordinated ligands in the solid state, but DFT calculations indicate that an η5/η5‐conformation is less than 5 kcal mol−1 higher in energy.

Experimental and DFT study on titanium-based half-sandwich metallocene catalysts and their application for production of 1-hexene from ethylene

• The Ti metallocene catalysis guides selectively the trimerization from ethylene to 1-hexene. • Synthesis of [Ind-C(R)-Phenyl]TiCl 3 catalysts based on indenyl with various types of bridges (R) bearing an indenyl ring. • Selective catalysts for ethylene trimerization to 1-hexene using mild conditions. • Reaction mechanism and selectivity described by DFT calculations. • The highest catalytic activity with the catalyst with a cyclohexane middle bridge. Different types of [Ind-C(R)-Phenyl]TiCl 3 catalysts based on pendant arene containing indenyl (Ind) ligand bearing various types of bridges (R= cyclo ‐C 5 H 10 (C1), (CH 3 ) 2 (C2), 4- t Bu- cyclo ‐C 5 H 9 (C3), and cyclo ‐C 6 H 12 (C4)) have been synthesized, and used in the ethylene trimerization to 1-hexene in the presence of methyl aluminoxane (MAO) as co-catalyst. The reaction conditions were first optimized in C2 catalyst case, where the highest 1-hexene product was achieved at the catalyst concentration, temperature and ethylene pressure of 1.5 × 10 −3 M, 40 °C, and 8 bar, respectively. During this optimization and under specific reaction conditions, a switching behavior from ethylene trimerization to polymerization was also detected, as an undesired reaction. At the optimized conditions, synthesized catalysts showed the following trend toward both 1-hexene yield and selectivity: C1>C2>C3>C4. Then, to shed light on the possible reaction mechanisms and to confirm the activity trend obtained in experimental section, density functional theory (DFT) calculations were employed. In this line, obtained results for activity trend in the simulation studies fit well with the experiments. According to both experimental and DFT results, the highest catalytic activity was observed in the presence of the catalyst with a cyclohexane middle bridge (C1).

Improved Single‐Site Chromium Catalysts with Electron Rich Indenyl Ligands for the Formation of Ultrahigh Molecular Weight Polyethylene

AbstractQuinolyl functionalized indenyl chromium complexes with different substitution patterns were synthesized and evaluated as single site catalysts in ethylene polymerization. Adding substituents like a fused cyclohexyl ring or a Si(CH3)3 group to the indenyl moiety improve complex stability, solubility and catalytic activity compared to the unsubstituted analogues. Furthermore, the ability to incorporate 1‐hexene into the polymer chain increased. Ultrahigh molecular weight polyethylene (UHMW‐PE) or linear low density polyethylene (LLD‐PE) with very high molecular weight was obtained. Although other catalysts are able to incorporate more 1‐hexene only a few systems are known, that combine substantial 1‐hexene incorporation with very high activity and such high molecular weights. Consequently, these catalytic systems are attractive candidates in industrial processes for the production of improved polyethylene materials.

Structure, electronic properties and slippage of cyclopentadienyl and indenyl ligands in the (η5-C5H5) (η3-C5H5) W(CO)2 and (η5-C9H7) (η3-C9H7)W(CO)2 complexes: A C-PCM investigation

The structure, electronic properties, and the slippage of cyclopentadienyl and indenyl ligands in the (η5-C5H5) (η3-C5H5)W(CO)2 and (η5-C9H7)(η3-C9H7)W(CO)2 were illustrated by applying the mPW1PW91 functional. The solvent impacts were surveyed by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM).The behavior of these compounds was investigated by studying the dipole moment and carbonyl stretching frequencies in solvents of different polarities such as tetrahydrofuran (THF), dichloromethane (DCM), cyclohexanone (CH), ortho-nitrotoluene (NT), Propanonitrile (PN), Acetonitrile (AN), Dimethylsulfoxide (DMSO). The correlations of dipole moment values with Lippert–Mataga polarity function, Bakhshiev polarity function and Bilot and Kawski were illustrated. Also, correlations of the calculated carbonyl stretching frequencies (ν(CO)) with the Kirkwood–Bauer–Magat equation (KBM) were explored. Natural bond orbital analysis (NBO) was utilized for illustration of the W–C bonds in the studied complexes.

Controlling the spin-crossover behavior of the [Cr(indenyl)2] family via ligand functionalization.

In this work, a computational method to study the spin-crossover (SCO) behavior of the [Cr(n-Meindenyl)2] family was carried out. Using the TPSSh/Def2TZVP method with the GD3BJ dispersion correction scheme, we computed the thermochemistry and transition temperatures (T1/2) for all members of this family, which are in excellent agreement with the available experimental data. Moreover, the computed data allow us to build a model that describes the effect of functionalizing the indenyl ligand in different positions on the spin-state energy gap and transition temperature. Our results show that the C4 and C7 positions of the indenyl ligand have a greater effect on tuning the SCO properties of such complexes. The model quantitatively reproduces the DFT calculations, thus providing a powerful tool to analyze and predict the SCO properties in any member of the [Cr(n-Meindenyl)2] family.

Quantum‐chemical calculations on the slippage of cyclopentadienyl and indenyl ligands in the (η3‐dienyl)Ir(PX3)3; (X = H, F, Cl, Me) complexes

AbstractThe structure, electronic properties, and the slippage of cyclopentadienyl (Cp) and indenyl (In) ligands in the (η3‐dienyl)Ir(PX3)3; (X = H, F, Cl, Me) complexes were illustrated using the hybrid density functional MPW1PW91 theory. The characteristics of chemical bond among the [Ir(PX3)3]+ and mono‐anionic dienyl ligands (Cp and In) fragments was surveyed by the energy decomposition analysis (EDA). Charge decomposition analysis (CDA) and extended charge decomposition analysis (ECDA) were utilized to investigate the electron transfer among the fragments in the studying complexes. The correlations among the computed parameters and Tolman cone angles (θ), Tolman's Electronic Parameter (TEP), as well as the Crabtree's DFT Electronic Parameter (CEP) of the phosphine ligands were explained.

Stacking Interactions between Indenyl Ligands of Transition Metal Complexes: Crystallographic and Density Functional Study

The analysis of crystal structures deposited in the Cambridge Structural Database showed that indenyl ligands of transition metal complexes prefer to form stacking interactions with one of the thre...

Bonding and electronic structures in dinuclear (X)[(Ind)M2L2] complexes (M = Ni, Pd, L = CO, PEt3, X = Cl, Allyl, Ind = indenyl, Cp = cyclopentadienyl): analogy between four-electron donor ligands

The calculations of bimetallic complexes of the type (X)[(Ind)M2(L)2] (M = Ni, Pd, L = CO, (PEt3) and X = Allyl, Cp and indenyl) have been done using two DFT functionals, namely BP86 and B3LYP*. The allyl, Cp and indenyl ligands adopt the same η3-coordination mode with a π bond and can be considered to be isolobal, while the chloride acts as σ- and π-donor. The computed structural and energetic parameters and energy decomposition yield chemically useful information. We report that the metal–metal bond distances are slightly sensitive to the electron donation and electron π-backdonation as the isolobal prediction suggests. Changing the metal from Ni to Pd has the result of increasing the metal–metal bond distance, decreasing the natural population of Pd and the weakness interactions between the X− ligand and the [(Ind)M2(L)2]+ fragment. The results showed that the four ligands behave quite similarly in terms of bonding, coordination mode and donation and π-backdonation properties highlighted by the orbitals’ populations and the energy decomposition. However, the strength of interactions can be classified as follows: Cl < Cp ≈ Ind < Allyl. In all the complexes studied, the M22+ moiety adopts a single metal–metal bonding attributing the 16-MVE configuration to each M(I) cation.

Terminal Phosphido Complexes of the Ru(η5-Cp*) Fragment

In situ generation of the five-coordinate complex Ru(η5-Cp*)(PR2)(PPh3) (2), via dehydrohalogenation of Ru(η5-Cp*)Cl(PR2H)(PPh3), has allowed its reactivity toward a range of small molecules to be compared with that of its well-studied analogue Ru(η5-indenyl)(PR2)(PPh3) (1), in a study designed to assess the likelihood of variable hapticity in the chemistry of complex 1. Reactions of 2 with hydrogen, carbon monoxide, phenylacetylene, ethylene, acrylonitrile, and 1-hexene demonstrate enhanced nucleophilicity/basicity of the terminal phosphido ligand in 2 relative to that in complex 1. Complex 2 also exhibits greater lability of the PPh3 ligand, leading to substitutional product mixtures that were not observed for 1. Both of these features are consistent with the more electron-rich and sterically imposing nature of the Cp* ligand in 2 relative to the indenyl ligand in 1. Nevertheless, the fundamental transformations of the phosphido ligand are comparable for the two complexes. This suggests that variable hapticity does not play a role in reactions of indenyl complex 1, since η5–η3 shifts are unlikely to occur for Cp* complex 2. The implications of these reactivity studies for the design of highly active, yet stable, ruthenium half-sandwich catalysts for hydrophosphination are discussed.

μ-Carbonyl-bis(carbonyl{η5-[tricarbonyl(η6-2-methylindenyl)chromium(0)]rhodium(III)})(Rh—Rh)

The structure of the title complex, [Cr2Rh2(C10H9)2(CO)9], was solved by single-crystal X-ray diffraction analysis in the P21/c space group. The crystal shows two units of the tetrametallic complex in the asymmetric unit. The most remarkable features of this new compound are the asymmetric bonding of the RhIII atom to the indenyl ligand, which can be formulated in terms of an η2;η3 coordination rather than η5, and the Rh—Rh distances of 2.6756 (6) and 2.6737 (6) Å that are characteristic of an intermetallic interaction supported by a bridging carbonyl ligand. The infrared spectroscopic signature informs of its clear bridging feature characterized by a significantly elongated C=O bond length compared to those in the two Rh-bound `terminal' carbonyl ligands.

Structural, bonding and redox properties of 34-electron bimetallic complexes and their oxidized 32- and 33-electron and reduced 35- and 36-electron derivatives containing the indenyl fused π-system: A DFT overview

DFT calculations with the BP86, OPBE and hybrid B3LYP* functionals have been performed on a series of homo- and heterobimetallic compounds of the type [(RuCp)2(Ind)]+, [(CoCb)2(Ind)]+ and [(RuCp)(CoCb)(Ind)]+ (Ind = indenyl, Cp = cyclopentadienyl and Cb = cyclobutadiene) of 34-TNE (Total number of electrons), their oxidized 32- and 33-TNEs and their reduced 35- and 36-TNEs species. Depending on the ancillary Cp or Cb ligand to the metal, the electronic and molecular structures and the metal–metal bonding of this family of compounds have been analyzed. The syn and anti-configurations are possible for the studied binuclear complexes, which are related to the metal nature, where mostly steric constraints of the Cp or the Cb ligand appear to control its spatial disposition favouring the anti configuration, despite its electronic deficiency for the 32- and 33-TNEs species. The flexibility of the indenyl ligand, which is related to the metal hapticity, favors the possibility of existence of several syn and anti isomers of close energies. This study showed quite similar behaviours of the (RuCp)+ and (CoCb)+ fragments of 12-electrons regarding their change or their permutation. The current study shows the ease of reduction with regard to oxidation, particularly that by the loss of two electrons. The used three functionals gave comparable tendencies of the stability sequences between isomers, favouring the low-spin structures, and provided comparable findings regarding the low-spin/high-spin energy splittings.