Hydrocarbyl Ligands Research Articles

Mixed valence triiron complexes from the conjugation of [FeIFeI] and [FeII] complexes via intermolecular carbyne/alkyne coupling.

We present a new synthetic strategy for obtaining mixed-valence triiron complexes where the metal centers are bridged by a novel, highly functionalized hydrocarbyl ligand. The alkynyl-vinyliminium complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(X-CCH)CHCNMe2}]CF3SO3 (X = 4-C6H4, [2a1]CF3SO3; X = (CH2)3, [2a2]CF3SO3) were synthesized in almost quantitative yields from the aminocarbyne precursor [Fe2Cp2(CO)2(μ-CO){μ-CNMe2}]CF3SO3, [1a]CF3SO3, and the di-alkynes HCC-X-CCH. Then, the ferracycle [Fe(Cp)(CO){C(NMe2)CHC(4-C6H4CCH)C(O)}], 4a1, was produced in 47% yield from the cleavage of [2a1]CF3SO3 promoted by pyrrolidine. Subsequent reactions of the acetonitrile adducts [Fe2Cp2(CO)(μ-CO)(NCMe){μ-CNMe(R)}]CF3SO3 (R = Me, [1aACN]CF3SO3; R = Xyl, [1bACN]CF3SO3) ([FeIFeI]) with 4a1 ([FeII]) at room temperature resulted in the formation of [FeIFeIFeII] complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(X-CCHC(NMe2)FeCp(CO)CO)CHCNMe(R)}]CF3SO3 (R = Me, [5a1]CF3SO3; R = Xyl, [5b1]CF3SO3) in yields ranging from 56% to 64%. The new products were characterized by IR and multinuclear NMR spectroscopy, and the structures of [2a2]CF3SO3 and 4a1 were confirmed by single crystal X-ray diffraction. Cyclic voltammetry and spectroelectrochemical studies on [5a1]+ have revealed that reduction and oxidation events occur almost independently at the [FeIFeI] and [FeII] units, respectively. This observation underscores a minimal electronic interaction between the two fragments within the triiron complex. Accordingly, DFT studies pointed out that the HOMO and LUMO orbitals are predominantly localized in the two distinct compartments of [5a1]+.

Anticancer Potential of Diruthenium Complexes with Bridging Hydrocarbyl Ligands from Bioactive Alkynols.

Diruthenacyclopentenone complexes of the general composition [Ru2Cp2(CO)2{μ-η1:η3-CH═C(C(OH)(R))C(═O)}] (2a-c; Cp = η5-C5H5) were synthesized in 94-96% yields from the reactions of [Ru2Cp2(CO)2{μ-η1:η3-C(Ph)═C(Ph)C(═O)}] (1) with 1-ethynylcyclopentanol, 17α-ethynylestradiol, and 17-ethynyltestosterone, respectively, in toluene at reflux. Protonation of 2a-c by HBF4 afforded the corresponding allenyl derivatives [Ru2Cp2(CO)3{μ-η1:η2-CH═C═R}]BF4 (3a-c) in 85-93% yields. All products were thoroughly characterized by elemental analysis, mass spectrometry, and IR, UV-vis, and nuclear magnetic resonance spectroscopy. Additionally, 2a and 3a were investigated by cyclic voltammetry, and the single-crystal diffraction method was employed to establish the X-ray structures of 2b and 3a. The cytotoxicity in vitro of 2b and 3a-c was evaluated against nine human cancer cell lines (A2780, A2780R, MCF-7, HOS, A549, PANC-1, Caco-2, PC-3, and HeLa), while the selectivity was assessed on normal human lung fibroblast (MRC-5). Overall, complexes exert stronger cytotoxicity than cisplatin, and 3b (comprising 17α-estradiol derived ligand) emerged as the best-performing complex. Inductively coupled plasma mass spectrometry cellular uptake studies in A2780 cells revealed a higher level of internalization for 3b and 3c compared to 2b, 3a, and the reference compound RAPTA-C. Experiments conducted on A2780 cells demonstrated a noteworthy impact of 3a and 3b on the cell cycle, leading to the majority of the cells being arrested in the G0/G1 phase. Moreover, 3a moderately induced apoptosis and oxidative stress, while 3b triggered autophagy and mitochondrial membrane potential depletion.

Alkyne-alkenyl coupling at a diruthenium complex.

Dimetallic complexes are suitable platforms for the assembly of small molecular units, and the reactivity of bridging alkenyl ligands has been widely investigated to model C-C bond forming processes. Here, we report the unusual coupling of an alkenyl ligand, bridging coordinated on a diruthenium scaffold, with a series of alkynes, revealing two possible outcomes. The diruthenium complex [Ru2Cp2(Cl)(CO)(μ-CO){μ-η1:η2-C(Ph)CH(Ph)}], 2, was prepared in two steps from [Ru2Cp2(CO)2(μ-CO){μ-η1:η2-C(Ph)CH(Ph)}]BF4, [1]BF4, in 69% yield. Then, the reaction of 2 with C2(CO2Me)2, promoted by AgCF3SO3 in dichloromethane, afforded in 51% yield the complex [Ru2Cp2(CO)2{μ-η3:η2-C(Ph)CH(Ph)C(CO2Me)C(CO2Me)}]CF3SO3, [3]CF3SO3, containing a ruthenacyclopentene-based hydrocarbyl ligand. On the other hand, 2 reacted with other alkynes and AgX salts to give the butadienyl complexes [Ru2Cp2(CO)2{μ-η3:η2-C(R)CH(R')C(Ph)C(Ph)}]X (R = R' = H, [4]BF4; R = R' = Me, [5]CF3SO3; R = R' = Ph, [6]CF3SO3; R = Ph, R' = H, [7]CF3SO3), in 42-56% yields. All products were characterized by IR and NMR spectroscopy, and by single crystal X-ray diffraction in the cases of 2, [3]CF3SO3 and [6]BF4. DFT calculations highlighted the higher stability of [4-7]+-like structures with respect to the corresponding [3]+-like isomers. It is presumable that [3]+-like isomers initially form as kinetic intermediates, then undergo H-migration which is disfavoured in the presence of carboxylato substituents on the alkyne. Such hypothesis was supported by the computational optimization of the transition states for H-migration in the cases of R = R' = H and R = R' = CO2Me.

α‐ and β‐Eliminations in Transition Metal Complexes: Strategies to Cleave Unstrained C−C and C−F Bonds

AbstractOxidative addition is the standard process for single‐bond activation in transition metal catalysis and it is known to operate for many types of bonds, but challenging σ‐bonds e. g. C(sp3)−F and C(sp3)−C(sp3) bonds are the exceptions in this respect. This short review aims at demonstrating how both α‐ and β‐eliminations may be better options for activation of unstrained C−F and C−C single bonds. Selected examples of such eliminations are presented with a mechanistic focus indicating how unstrained and unactivated C−C and C−F bonds can be broken by employing α‐ and β‐eliminations in transition metal hydrocarbyl ligands. Our examples show that the reaction barrier in β‐eliminations is controlled by the s‐character of the participating bonds where a higher s‐character gives a better overlap in the multi‐center transition state thereby increasing the reactivity; still β‐aryl eliminations can compete with the classical β‐hydrogen eliminations in certain cases.

Insight into the Scope and Mechanism for Transmetalation of Hydrocarbyl Ligands on Complexes Relevant to C–H Activation

We report the transmetalation of hydrocarbyl fragments (Me, Bn, Ph) from a variety of organometallic complexes relevant to C–H activation (Ir, Rh, W, Mo) to Pt(II) electrophiles. The scope of suitable hydrocarbyl donors is remarkable in that three different classes of organometallics with widely varying reactivity all undergo the same general reaction with Pt(II) electrophiles. A competitive substituent effect experiment reveals faster transmetalation of more electron-rich hydrocarbyl groups. This study suggests that transmetalation could provide a viable path for catalytic functionalization of stable complexes resulting from C–H bond activation and other processes.

Characterization of Cr-Hydrocarbyl Species via Pulse EPR in the Study of Ethylene Tetramerization Catalysis

The characterization of complexes involved in chromium catalysis is challenging due to the paramagnetism of Cr in its common oxidation states. Here, we demonstrate the utility of pulse electron paramagnetic resonance (pulse EPR) techniques in assigning structural features of Cr organometallic complexes relevant to ethylene tetramerization. An S = 3/2, Cr(III) bisaryl-methyl ethylene tetramerization precatalyst (1) has been selected for characterization by CW and pulse EPR spectroscopies. Using an isotopically labeled Cr-CD3 complex (1-d3), the methyl ligand was confirmed to remain bound to Cr in solution by detection of 2H couplings in X-band hyperfine sublevel correlation (HYSCORE) spectroscopy. Protonolysis of 1-d3 led to an S = 3/2, Cr(III) product (2-d3) that maintained spectroscopic features in HYSCORE for the CD3 group, indicative of retention of the Cr-alkyl bond. Following protonolysis of 1-h3 and subsequent reaction with ethylene, an S = 1/2 Cr(I) species with an ethylene-derived ligand was generated, supporting a mechanism involving this Cr oxidation state. Additionally, the pulse EPR characterization of a Cr(I) allyl-diene complex was performed for comparison. This is the first direct observation of hydrocarbyl ligands on Cr using pulse EPR methods. The methods described here are broadly applicable to Cr, first-row transition metals and other open-shell organometallic catalytic systems.

The Mechanism of the Intramolecular Hydrocarbyl Metathesis within a Planar Triruthenium Cluster: Combining Core Flexibility with Hydride Mobility.

The transition metal catalysed formation and cleavage of C-C bonds is of utmost importance in synthetic chemistry. While most of the existing homogeneous catalysts are mononuclear, knowledge of the behaviour of polynuclear species is much more limited. By using computational methods, here we shed light into the mechanistic details of the thermally-induced isomerization of Cp*3 Ru3 (μ-H)2 (μ3 -η2 -pentyne)(μ3 -pentylidyne) (2) into Cp*3 Ru3 (μ-H)2 (μ3 -η2 -octyne)(μ3 -ethylidyne) (3), a process that involves the migration of a C3 fragment between the hydrocarbyl ligands and across the plane formed by the three Ru centres. Our results show this to be a complex transformation that comprises of five individual rearrangements in an A→B→A→B→A order. Each so-called rearrangement A consists of the CH migration from the μ3 -η2 -alkyne into the μ3 -alkylidine ligand in the other side of the Ru3 plane. This process is facilitated by the cluster's ability to adopt open-core structures in which one Ru-Ru bond is broken and a new C-C bond is formed. In contrast, rearrangements B do not involve the formation or cleavage of C-C bonds, nor do they require the opening of the cluster core. Instead, they consist of the isomerization of the μ3 -η2 -alkyne and μ3 -alkylidyne ligands on each side of the triruthenium plane into μ3 -alkylidyne and μ3 -η2 -alkyne, respectively. Such transformation implies the migration of three H atoms within the hydrocarbyl ligands, and in this case, it is aided by the cluster's ability to behave as a H reservoir. All in all, this study highlights the plasticity of these Ru3 clusters, whereby Ru-Ru, Ru-C, Ru-H, C-C, and C-H bonds are formed and broken with surprising ease.

Exploring the Anticancer Potential of Diiron Bis-cyclopentadienyl Complexes with Bridging Hydrocarbyl Ligands: Behavior in Aqueous Media and In Vitro Cytotoxicity

A series of diiron complexes based on the [Fe2Cp2(CO)x] skeleton (Cp = η5-C5H5, x = 2, 3; η4-C5H5Ph in place of one Cp in one case) and containing different bridging hydrocarbyl ligands (aminocarby...

Unexpected Precatalyst σ-Ligand Effects in Phenoxyimine Zr-Catalyzed Ethylene/1-Octene Copolymerizations.

Recent decades have witnessed intense research efforts aimed at developing new homogeneous olefin polymerization catalysts, with a primary focus on metal-Cl or metal-hydrocarbyl precursors. Curiously, metal-NR2 precursors have received far less attention. In this contribution, the Zr-amido complex FI2ZrX2 (FI = 2,4-di- tert-butyl-6-((isobutylimino)methyl)phenolate, X = NMe2) is found to exhibit high ethylene polymerization activity and relatively high 1-octene coenchainment selectivity (up to 7.2 mol%) after sequential activation with trimethylaluminum, then Ph3C+B(C6F5)4-. In sharp contrast, catalysts with traditional hydrocarbyl ligands such as benzyl and methyl give low 1-octene incorporation (0-1.0 mol%). This unexpected selectivity persists under scaled/industrial operating conditions and was previously inaccessible with traditional metal-Cl or -hydrocarbyl precursors. NMR, X-ray diffraction, and catalytic control experiments indicate that in this case an FI ligand is abstracted from FI2Zr(NMe2)2 by trimethylaluminum in the activation process to yield a catalytically active cationic mono-FIZr species. Heretofore this process was believed to serve only as a major catalyst deactivation pathway to be avoided. This work demonstrates the importance of investigating diverse precatalyst monodentate σ-ligands in developing new catalyst systems, especially for group 4 olefin polymerization catalysts.

Dimethylcalcium.

The salt metathesis reaction between homoleptic calcium bis(trimethylsilyl)amide [Ca{N(SiMe3)2}2]2 and "halide-free" methyllithium allowed for the isolation of X-ray-amorphous dimethylcalcium [CaMe2]n in good yields and purities. The formation of [CaMe2]n was proven by microanalysis and NMR/FTIR spectroscopic methods as well as a series of derivatization reactions. Despite slowly decomposing thf, [CaMe2]n could be crystallized from chilled thf solutions as the heptametallic adduct [(thf)10Ca7Me14]. Reaction of [CaMe2]n with CaI2 in thf led to the dimeric complex [(thf)3Ca(Me)(I)]2, whereas in tetrahydropyran (thp) the trinuclear complex [(thp)5Ca3(Me)5(I)] was obtained, both representing the first crystallographically characterized heavy-Grignard compounds with methyl groups as the hydrocarbyl ligand. While protonolysis of [CaMe2]n with the superbulky proligand HTptBu,Me in nonpolar solvents gave homoleptic (TptBu,Me)2Ca, reaction in donor solvents (thf, thp) afforded the monomeric complexes [(TptBu,Me)Ca(Me)(thf)] and [(TptBu,Me)Ca(Me)(thp)], which are the first examples bearing terminal Ca-CH3 functionalities. Grignard-type nucleophilic methyl-group transfer to hexamethylacetone gave access to the dimeric alkoxide complexes [(thf)Ca(OCtBu2Me)2]2 and [(tBu2CO)Ca(μ2-OCtBu2Me)3Ca(OCtBu2Me)]. Finally, addition of the Lewis acid GaMe3 to [CaMe2]n led to the corresponding tetramethylgallate compound [Ca(GaMe4)2]n.

Exclusive Csp(3)-Csp(3) vs Csp(2)-Csp(3) Reductive Elimination from Pt(IV) Governed by Ligand Constraints.

Selective reductive elimination of ethane (Csp(3)-Csp(3) RE) was observed following bromide abstraction and subsequent thermolysis of a Pt(IV) complex bearing both Csp(3)- and Csp(2)-hybridized hydrocarbyl ligands. Through a comparative experimental and theoretical study with two other Pt(IV) complexes featuring greater conformational flexibility of the ligand scaffold, we show that the rigidity of a meridionally coordinating ligand raises the barrier for Csp(2)-Csp(3) RE, resulting in unprecedented reactivity.

Diiron Complexes Bearing Bridging Hydrocarbyl Ligands as Electrocatalysts for Proton Reduction

Diiron complexes with bridging hydrocarbyl ligands and containing CO and Cp ligands (Cp = η5-C5H5) have been investigated as possible electrocatalysts for H2 production. In particular, studies included the vinyliminium complexes [Fe2{μ-η1:η3-C(R′)=CRC═NMe2}(μ-CO)(CO)(Cp)2][SO3CF3] (R′ = Tol (4-MeC6H4), R = H, 1a; R′ = CH2OH, R = H, 1b; R′ = CH2OH, R = SPh, 1c), the vinylalkylidene [Fe2{μ-η1:η3-C(Tol)CH═CHNMe2}(μ-CO)(CO)(Cp)2] (2), the aminoalkylidyne [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)(L)(Cp)2][SO3CF3] (R = Me, L = CO, 3a; R = Me, L = NCMe, 3b; R = Xyl (2,6-Me2C6H3), L = CO, 3c), [Fe2{μ-CN(Me)2}(μ-L′)(CO)(L)(Cp)2] (L′ = CO, L = CN, 4; L′ = H, L = CO, 5), the thiocarbyne complexes [Fe2(μ-CSEt)(μ-CO)(CO)2(Cp)2][BF4], (6) and [Fe2(μ-CSMe)(μ-CO)(CO)(CN)(Cp)2] (7), and the alkylidene complexes [Fe2{μ-C(CN)(SMe)}(μ-CO)(CO)2(Cp)2][SO3CF3] (8) and [Fe2{μ-C(CN)(PMe2Ph)}(μ-CO)(CO)2(Cp)2][SO3CF3] (9). Cyclic voltammograms (CV) of the above complexes in CH3CN have been recorded in the presence of increasing amounts of acetic acid to evidence electrocatalytic proton reduction. In spite of the fact that the above diiron complexes do not resemble the typical diiron dithiolate model systems, the aminocarbyne 4 and the thiocarbyne complex 7 exhibit significant electrocatalytic properties for proton reduction (e.g., for 4, the turnover number (TON) is 15.5).

Activation of Linear Alkanes by a Hydrido Triruthenium Cluster and Associated Skeletal Rearrangements

Abstract We explored polyhydrido cluster reaction chemistry for over two decades, developing rational syntheses of di-, tri-, tetra-, and pentanuclear clusters of ruthenium. In our study of cluster chemistry, we found that triruthenium pentahydrido complex [{Cp*Ru(µ-H)}3(µ3-H)2] (1) (Cp*: η5-C5Me5) reacts with linear alkanes to exclusively afford a closo-ruthenacyclopentadiene complex 2. The reaction mechanism has been elucidated by the isolation and alternative preparation of several important intermediates by the reaction of 1 with other hydrocarbons, such as alkynes, dienes, and alkenes. The mechanism is shown to consist of two reversible and four irreversible steps involving dihydrogen elimination, where the cooperative interaction of neighboring metal centers with hydrocarbons on the cluster is clearly seen. Facile migration of a hydride from a metal center to the carbon atom is also observed during the reaction, which emphasizes the crucial role of hydrido ligands in the skeletal rearrangement of hydrocarbyl ligands on a polyhydrido cluster. In addition, coupling reaction between two hydrocarbyl ligands placed on each face of the triruthenium core with concomitant partial cleavage of the cluster skeleton has also been observed. Such a flexible cluster skeleton enables unusual transformation of hydrocarbons on the cluster.

Transmetalation of Alkyl Ligands from Cp*(PMe3)IrR1R2 to (cod)PtR3X

Transmetalation of alkyl and carboxylate ligands between Cp*(PMe3)Ir complexes and d8 Pt and Pd complexes is described. Studies on the scope and kinetics of this reaction support a mechanism in which carboxylate dissociation from the Pt or Pd center precedes alkyl transfer from Ir. Subsequent reaction of the resulting Pt or Pd alkyl complex enables functionalization of the hydrocarbyl ligands and suggests new opportunities for catalytic, nondirected C–C and C–H bond functionalization reactions.

Electrochemical, EPR and computational results on [Fe 2Cp 2(CO) 2]-based complexes with a bridging hydrocarbyl ligand

The dimetallacyclopentenone complexes [Fe 2Cp 2(CO)(μ−CO){μ−η 1:η 3−C αH C β(R)C( O)}] (R = CH 2OH, 1a; R = CMe 2OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe 2Cp 2(CO) 4] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The μ-allenyl compound [Fe 2Cp 2(CO) 2(μ−CO){μ−η 1:η 2 α,β−C αH C β CMe 2][BF 4] ([ 2][BF 4]), obtained by reaction of 1b with HBF 4, underwent monoelectron reduction to give a radical species which was detected by EPR at room temperature. The EPR signal has been assigned to [Fe 2Cp 2(CO) 2(μ−CO){μ−η 1:η 2 α,β–C αH C β CMe 2}], [ 2] • . The molecular structures of [ 2] + and [ 2] • were optimized by DFT calculations. The unpaired electron in [ 2] • is localized mainly at the metal centers and, coherently, [ 2] • does not undergo carbon–carbon dimerization, by contrast with what previously observed for the μ-vinyl radical complex [Fe 2Cp 2(CO) 2(μ−CO){μ−η 1:η 2–CH CH(Ph)}] • , [ 3] • . Electron spin density distributions similar to the one of [ 2] • were found for the μ-allenyl radical complexes [Fe 2Cp 2(CO) 2(μ–CO){μ–η 1:η 2 α,β–C αH C β C(R 1)(R 2)}] • (R 1 = R 2 = H, [ 4] • ; R 1 = H, R 2 = Ph, [ 5] • ; R 1 = R 2 = Ph, [ 6] • ).

ChemInform Abstract: Phosphine Complexes of the Early Metals and the Lanthanoids

The coordination chemistry of the mixed-donor tridentate ligand -N(SiMezCH2PR2)2 with the early transition metals of groups 3 and 4 and the lanthanide elements will be presented. This ancillary ligand has allowed for the formation of phosphine complexes of these hard elements which has in turn induced new reactivity patterns for hydrocarbyl ligands. The stability and reactivity of metal complexes are a function of both the position of the metal in the periodic table and the nature of the ligands. While the former provides for diverse chemical reactivity, it is

Metathesis Reaction of Hydrocarbyl Ligands across the Triruthenium Plane

Trains and boats and planes: The thermolysis of a triruthenium complex having μ3-pentylidyne and μ3-pentyne ligands on each face of the trimetallic plane exclusively afforded the μ3-ethylidyne-μ3-octyne complex. In this reaction, a C3 fragment migrated from one face of the Ru3 plane to the other. This corresponds to the selective redistribution of two C5 molecules into C2 and C8 molecules.

Metathesis Reaction of Hydrocarbyl Ligands across the Triruthenium Plane

C3 wechselt die Seite: Die Thermolyse eines Trirutheniumkomplexes mit einem μ3-Pentylidin- und einem μ3-Pentin-Liganden zu beiden Seiten der von den Metallatomen gebildeten Ebene führt ausschließlich zu einem μ3-Ethylidin-μ3-octin-Komplex. Bei dieser Reaktion wandert ein C3-Fragment von einer Seite der Ru3-Ebene auf die andere, was in einer Umverteilung von zwei C5- in ein C2- und ein C8-Molekül resultiert. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Arylation of Hydrocarbyl Ligands Formed from n‐Alkanes through C–H Bond Activation of Benzene Using a Triruthenium Cluster

AbstractTriruthenium complex 2 containing a perpendicularly coordinated 1‐pentyne ligand, which is one of the key intermediates of the reaction of triruthenium pentahydrido complex 1 with n‐pentane, reacts with benzene to yield μ3‐benzyne–μ3‐pentylidyne complex 5 by C–H bond activation. β‐H elimination form the μ3‐penytylidyne ligand occurred upon heating to yield μ3‐pentenylidene complex 6, which was followed by the formation of closo‐ruthenacyclopentadiene complex 8 by the connection of the two hydrocarbyl moieties placed on each face of the triruthenium plane with partial metal–metal bond breaking. Treatment of 8 with pressurized hydrogen resulted in exclusive liberation of n‐pentylbenzene, which is difficult to synthesize by conventional Friedel–Crafts alkylation. These sequential transformations correspond to the formation of linear alkylbenzene by the reaction of pentane with benzene on a trimetallic plane. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Introduction of a Methoxy Group into a Hydrocarbyl Ligand Derived from a Linear Alkane on a Triruthenium Cluster via Chemical Oxidation

The two-electron oxidation of a closo-ruthenacyclopentadiene complex, [(Cp*Ru)2{Cp*Ru(μ3-CMe═CHCH═CH−)}(μ-H)] (2a), derived from the reaction of a triruthenium complex, {Cp*Ru(μ-H)}3(μ3-H)2 (1), wi...