Cp Ring Research Articles

Dominant changes in centre Fe atom of decamethyl-ferrocene from ferrocene in methylation

Staggered decamethyl-ferrocene (*Fc) becomes the lower energy conformer at low temperature, whereas the eclipsed conformer of ferrocene (Fc) is more stable. The powerful infrared (IR) spectroscopy which has remarkably provided signatures of ferrocene (Fc) in eclipsed and staggered conformers recently is employed to investigate methylation of Fc. The most significant consequences of the full methylation of Fc in the IR spectra are the blue shift of the band at ~ 800 cm−1 in Fc to ~ 1500 cm−1 in *Fc, and the enhancement of the C–H stretch band at ~ 3200 cm−1 region in *Fc. Further analysis reveals large impact of Fc methylation on core electron energies of the centre Fe atom (1s22s22p63s23p6). The Fe core electron energy changes can be as large as ~ 10 kcal mol−1 and are directional—the Fe 2pz and 3pz orbitals along the *Cp–Fe–*Cp axis (Cp centroids, vertical) change more strongly than other Fe core electrons in px and py orbitals. The directional inner shell energy changes are evidenced by larger inner shell reorganization energy. Energy decomposition analysis (EDA) indicates that methyl groups in *Fc apparently change the physical energy components with respect to Fc. The large steric energy of *Fc evidences that the closest hydrogens on adjacent methyl groups of the same *Cp ring in crystal structure are 0.2–0.4 Å closer than the hydrogens on nearest-neighbour methyl groups on opposing rings in *Fc. A significant increase in Pauli repulsive energy contributes to the large repulsive steric energy in *Fc.

Stereoselective Synthesis of 1,1’,2,2’‐Tetrasubstituted Ferrocenes by Double Lithiation of a 1,1’‐Disubstituted Ferrocenyl Pyrroloimidazolone

AbstractA 1,1’‐disubstituted ferrocenyl pyrroloimidazolone with syn stereochemistry undergoes double lithiation–electrophile quench in a one‐pot procedure to give C2‐symmetric 1,1’,2,2’‐tetrasubstituted products in >95 : 5 diastereomeric ratio (dr). These results represent an extension of double lithiation to access tetrasubstituted planar chiral ferrocenes for the first time to a nitrogen‐linked (pyrroloimidazolone) chiral directing group. The stereochemistry of the products was determined by X‐ray crystallography of distannane and dibromide adducts in combination with deuteration, elimination, and transmetalation experiments. Results support that products arise from selective deprotonation of the pro‐Sp position of each cyclopentadienyl (Cp) ring.

Bending Ferrocenes with Low Coordinated Bridging Units: The Investigation of Carbenes and Their Analogues with a Ferrocenophane Backbone

[3]ferrocenophanes with X–E–X ansa moieties containing a low coordinated center E stabilized by adjacent donor units X were studied by density functional theory methods. The cyclopentadienyl (Cp) rings favor an eclipsed position in most cases and exhibit a shortened C(1)–C(1′) distance compared to parent ferrocene. In case of bridges with the second row elements, the tilt of the Cp rings is more significant than that in case of third row elements; however, the estimated strain does not exceed 6 kcal/mol. The ansa unit has similar structural characteristics to the X–E–X-fragment in a six-membered saturated ring, with bond angles larger than that in the well-known heterocycles featuring five-membered cyclic systems. For compounds with X = PMe and E = C, Si, Ge, the non-planar coordination of the phosphorus atoms yields two symmetric minimum structures that are distinguished by trans and cis alignment of the PMe groups and are connected by a low-energy asymmetric transition structure with one planarized and one highly pyramidal phosphorus. In case of the analogous species with E = P+, this asymmetric structure was located as the sole minimum. A detailed analysis of the Kohn–Sham orbitals and the analysis of the electron density show that the electronic system of the ferrocene fragment is not mixing considerably with that of the low coordinated center of the ansa unit.

Rh(III)‐Catalyzed Enantioselective Intermolecular Aryl C—H Bond Addition to Aldehydes

Comprehensive SummaryThe direct addition of aryl C—H bond to carbon‐heteroatom double bond by transition‐metal‐catalyzed C—H activation has been extensively investigated in the past decade. However, the enantioselective intermolecular C—H addition to aldehyde has not yet been reported and is of significant challenge. Rh(III)‐catalyzed highly enantioselective intermolecular C—H addition of aryl oxime ethers to glyoxylates is reported. Chiral mandelic acid esters were obtained in excellent yields (up to 98%) and enantioselectivity (up to 99% ee) in the presence of a chiral CpRh(III) catalyst under mild conditions. The substituents on the Cp ring and BINOL skeleton were responsible for the high enantioselectivity observed. The method displays a broad substrate scope and good functionality tolerance. These results provide not only a promising C—H addition approach but also a proof of concept for developing broader asymmetric C—H addition reactions.

Asymmetrically Difunctionalized 1,1′‐Ferrocenyl Metalloligands and Their Transition Metal Complexes

AbstractThe synthesis and full characterization of novel 1,1′‐difunctionalized ferrocene metalloligands is described. While one cyclopentadienyl ring has been functionalized with 2,2′‐bipyridine for secondary coordination, the second Cp ring has been decorated with different aryl moieties containing electron withdrawing groups such as 4‐(CF3)C6H4 (2A) 3,5‐(CF3)2C6H3 (2B) or 4‐(NO2)C6H4 (2C). The newly developed metalloligands were reacted with [Pd(cod)Cl2] (3A–C), CuCl2 (4A–C) and trans‐[(PPh3)2Ni(Mes)Br] (5A,B) to obtain the corresponding square‐planar and dimeric square‐pyramidal complexes. The electrochemical behaviour of the ligands and complexes was investigated with the aid of cyclic voltammetry and compared with the corresponding monofunctionalized derivatives. The influence of the implemented functional groups on the nickel complexes was then confirmed for the reductive elimination reaction of an aryl ether induced by oxidation of the corresponding methoxides (6A,B,D). The experimental findings are supported by quantum chemical calculations.

A free boratriptycene-type Lewis superacid.

Bicyclic pyrazabole-bridged ferrocenes with BH groups at their bridgehead positions were prepared from [Li(thf)]2[1,1′-fc(BH3)2] and pyrazole or 3,5-dimethylpyrazole in the presence of Me3SiCl (1 or 1Me, respectively; 1,1′-fc = 1,1′-ferrocenylene); Me3SiH and H2 are released as byproducts. Treatment of 1 or 1Me with 1 eq. of the hydride scavenger [Ph3C][B(C6F5)4] afforded the borenium salts [2][B(C6F5)4] (72%) and [2Me][B(C6F5)4] (77%). According to X-ray crystallography, [2Me]+ contains one trigonal-planar borenium cation, the cyclopentadienyl (Cp) rings of the 1,1′-fc fragment remain parallel to each other, but the Cp–B bond vector is bent out of the Cp plane by an unprecedentedly large dip angle α* of 40.6°. The Fe⋯B(sp2) distance is very short (2.365(4) Å) and the 11B NMR signal of the cationic B(sp2) center is remarkably upfield shifted (23.4 ppm), suggesting a direct Fe(3d) → B(2p) donor–acceptor interaction. Although this interpretation is confirmed by quantum-chemical calculations, the coupling between the associated orbitals corresponds to an energy of only 12 kJ mol−1. Accordingly, both the experimental (e.g., Gutmann–Beckett acceptor number AN = 111) and theoretical assessment (e.g., Et3PO and F−-ion affinities) of the Lewis acidity proves that [2]+ is among the strongest boron-based Lewis acids available to date.

Synthesis and Oligomerization of CpM(CO)2.

We showcase efficient synthetic protocols of cyclopentadienyl metal dicarbonyl, CpM(CO)2 (M = Rh and Ir). Reflecting the relativistic effect, the 1H and 13C signals of the Cp ring in CpIr(CO)2 were upfield shifted when compared with the Rh analogue. A missing dinuclear complex, (CpIr)2(μ-CO)(CO)2, was spontaneously generated together with [CpIr(CO)]3 by the loss of CO. The crystallographic analyses unambiguously determined their unique structures with one and three Ir–Ir bonds, respectively.

Mechanically Induced Switching between Two Discrete Conductance States: A Potential Single-Molecule Variable Resistor.

The fabrication of solid-state single-molecule switches with high on-off conductance ratios has been proposed to advance conventional technology in areas such as molecular electronics. Herein, we employed the scanning tunneling microscope break junction (STM-BJ) technique to modulate conductance in single-molecule junctions using mechanically induced stretching. Compound 1a possesses two dihydrobenzothiophene (DHBT) anchoring groups at the opposite ends linked with rigid alkyne side arms to form a gold-molecule-gold junction, while 1b contains 4-pyridine-anchoring groups. The incorporation of ferrocene into the backbone of each compound allows rotational freedom to the cyclopentadienyl (Cp) rings to give two distinct conductance states (high and low) for each. Various control experiments and suspended junction compression/retraction measurements indicate that these high- and low-conductance plateaus are the results of conformational changes within the junctions (extended and folded states) brought about by mechanically induced stretching. A high-low switching factor of 42 was achieved for 1a, whereas an exceptional conductance ratio in excess of 2 orders of magnitude (205) was observed for 1b. To the best of our knowledge, this is the highest experimental on-off conductance switching ratio for a single-molecule junction exploiting the mechanically induced STM-BJ method. Computational studies indicated that the two disparate conductance states observed for 1a and 1b result from mechanically induced conformational changes due to an interplay between conductance and the dihedral angles associated with the electrode-molecule interfaces. Our study reveals the structure-function relationship that determines conductance in such flexible and dynamic systems and promotes the development of a single-molecule variable resistor with high on-off switching factors.

Pentaisopropyl Cyclopentadienyl: An Overview across the Periodic Table

AbstractCyclopentadienide (Cp) groups are among the most popular ligands in organometallic chemistry. Sterically demanding substitution patterns on the Cp ring can have an important effect on the ligand properties and there are many examples of metal complex which are only stable and isolatable with sterically demanding Cp ligands, carrying alkyl or aryl groups. Among these sterically demanding Cp ligands, pentaisopropylcyclopentadienide is the bulkiest pentaalkyl derivative and has been utilized in main group, as well as transition metal and rare‐earth element chemistry for several decades.

Protonation of Group 9 Metal (Co, Rh, Ir) Coordinated Bicyclo-[2.2.1]-hepta-2,5-diene and Bicyclo[2.2.2]octa-2,5-diene complexes: Facile Activation of Carbon-Carbon Bond in Bicyclo-[2.2.1]hepta-2,5-diene via M-H or M-H-C interactions

The activation of C-C bond in coordinated M (η4 bicyclo [2.2.1]-hepta-diene) or 2,5-NBD via protonation for 3d,4d and 5d transition metals have been examined. Monoprotonation of the diolefin complexes [M(η5C5R5)(η4- NBD] (R = H, CH3) M = Co, Rh,with CF3COOH or CF3SO3H forms transient agostic metal hydrides (M-H-C) at -80°C. Similar reaction with HPF6 (60% aq), the Ir analogues give terminal hydrides [IrH(η5-C5Me4R)(η4-2,5-NBD)]+PF6 (R=Me, or Et) as isolable solids at room temperature. All these hydride complexes coordinated to NBD subsequently undergo ligand migration to give stable η2-vinyl η3cyclopentenyl cations [M(η5C5R5) (C7H9)]+ (M=Co Rh, Ir). Protonation of the cobalt and rhodium coordinated bicyclo-[2.2.2]-octa 2,5- diene gives unstable M-H-C ground state structures at -80°C, which decompose upon warming to room temp. Protonation reactions of the 2,5-BCOD complexes of Ir also give terminal hydrides [IrH(η5-C5Me5)(η4-2,5-BCOD)]+PF6 as solids. Thermolysis of [IrH(η5-C5Me5)(η4-2,5-BCOD)]+PF6 did not give the expected, isomerized or C-C bond activated product, probably because 2,5-BCOD is less strained than 2,5-NBD. Coupling constant [JCH] and stretching frequency [ν M-H] data indicate the electron density donation from the methyl groups in the Cp ring favors agostic structures. The C-C bond activation in the coordinated norbornadiene, via hydride migration is slower for the terminal hydride, M-H (M= Ir) compared to agostic hydrides for (M=Co, Rh) compounds. The vinyl cyclopentenyl cations of Rh,Ir undergo further isomerization in CF3COOH to give corresponding η6-toluene cations [M(η5-C5R5)(η6-C6H5CH3)]+ At 50 °C in vacuo the salt [(η5C5Me5)Ir(H)(η4nbd]+PF6 forms a neutral tetramethylfulvenyliridium (1) complex η5C5Me4=CH2)Ir(η4NBD) by C-H activation of a methyl group in the C5Me5 ring.

Energy-Level Alignment and Orbital-Selective Femtosecond Charge Transfer Dynamics of Redox-Active Molecules on Au, Ag, and Pt Metal Surfaces.

Charge transfer (CT) dynamics across metal–molecule interfaces has important implications for performance and function of molecular electronic devices. CT times, on the order of femtoseconds, can be precisely measured using synchrotron-based core-hole clock (CHC) spectroscopy, but little is known about the impact on CT times of the metal work function and the bond dipole created by metals and the anchoring group. To address this, here we measure CT dynamics across self-assembled monolayers bound by thiolate anchoring groups to Ag, Au, and Pt. The molecules have a terminal ferrocene (Fc) group connected by varying numbers of methylene units to a diphenylacetylene (DPA) wire. CT times measured using CHC with resonant photoemission spectroscopy (RPES) show that conjugated DPA wires conduct electricity faster than aliphatic carbon wires of a similar length. Shorter methylene connectors exhibit increased conjugation between Fc and DPA, facilitating CT by providing greater orbital mixing. We find nearly 10-fold increase in the CT time on Pt compared to Ag due to a larger bond dipole generated by partial electron transfer from the metal–sulfur bond to the carbon–sulfur bond, which creates an electrostatic field that impedes CT from the molecules. By fitting the RPES signal, we distinguish electrons coming from the Fe center and from cyclopentadienyl (Cp) rings. The latter shows faster CT rates because of the delocalized Cp orbitals. Our study demonstrates the fine tuning of CT rates across junctions by careful engineering of several parts of the molecule and the molecule–metal interface.

Lattice-Strain Coupled to Molecular Conformation and Disorder in Compressed Nickelocene

Isothermal compression of nickelocene (NiCp2, where Cp denotes cyclopentadienyl ring C5H5–) to 1.3 GPa leads to the ordered phase I′, highly isostructural with that obtained at 0.1 MPa by isobaric cooling to 170 K and with phase I′ of ferrocene (FeCp2) above 3.24 GPa. However, the gradual ordering of Cp rings in NiCp2 and its anomalous crystal strain considerably differs from that in FeCp2. The disorder in NiCp2 molecules can be represented as various combinations of achiral staggered and eclipsed conformers, as well as R-/S-rotamers, which are differently stabilized by the crystal environment. The anomalous lattice strain has been correlated with the molecular conformation, represented as the convolution of disordered Cp rings. The coincidence of the phase transition at 1.3 GPa/296 K with the monoclinic angle assuming 90° value does not occur on lowering temperature at 170 K/0.1 MPa, which is due to a weaker coupling between the lattice strain and the molecular disorder. Compared to FeCp2, the energetic preference in NiCp2 for the eclipsed conformation is lower and the stronger crystal field, favoring the staggered conformation. Therefore, phase I′ of NiCp2 is stable below 170 K, while at 300 K NiCp2 transforms to phase I′ at much lower pressure than FeCp2.

Formation of Metallic Polyferrocene Chains under Pressure.

The effect of pressure on the structural reorganization of ferrocene, Fc = (C5H5)2Fe, is studied using density functional theory (DFT) calculations assisted by evolutionary crystal structure prediction algorithms based on USPEX code. Pressure brings the individual molecules in close contact, and above 220 GPa, the 18-electron closed-shell molecular unit undergoes polymerization through the formation of quasi-one-dimensional (1D) chains, [(C5H5)2Fe]∞, termed as polyferrocene (p-Fc). Pressure induced polymerization (PIP) of Fc causes significant deviations from the 5-fold symmetry of the cyclopentadiene (Cp, C5H5 rings) and loss of planarity due to the onset of envelope-like distortions. This triggers distortions within the multidecker sandwich structures and σ(C-C) bond formation between the otherwise weak noncovalently interacting Cp rings in Fc crystals. Pressure gradually reduces the band gap of Fc, and for p-Fc, metallic states are found due to increased electronic coupling between the covalently linked Cp rings. Polyferrocene is significantly more rigid than ferrocene as evident from the 5-fold increase in its bulk modulus. Pressure dependent Raman spectra show a clear onset of polymerization in Fc at P = 220 GPa. Higher mechanical strength coupled with its metallicity makes p-Fc an interesting candidate for high pressure synthesis.

Cyclopentadienyl‐Based Anticancer Drugs: Improvement of Cytotoxic Activity through Functionalisation of the π Ligand

Molybdenum-composed cytotoxiccomplexes are widely studied as a potential substitution for commercially used drugs which often suffer from pronounced side effects and cellular resistance. Compounds of the type [(η 5 -Cp')Mo(CO) 2 ( N, N L)][BF 4 ], where Cp is cyclopentadienyl and N , N L is a bidentate ligand, are well-known for their strong anti-cancer activity. It is generally accepted paradigm, that nature of coordinated N, N Lligand have major impact on the cytotoxicity. In this study, a series of new functionalized Cp complexes of molybdenum were synthesized using derivatized fulvenes asπ-ligand precursors . Indeed, the coordination sphere's modulation via various N , N -chelating ligands afforded species active toward leukemic cell line MOLT-4 with IC 50 value depending on the character of used N , N -chelator. However, the following study further clearly shows that functionalization of Cp ring with amine moiety improves cytotoxicity considerably. These results are of crucial importance for the future design of highly active cytotoxic drugs as modification of cyclopentadienyl is believed to have minor effect on biological activity.

Redox-Induced Structural Reorganization Dictates Kinetics of Cobalt(III) Hydride Formation via Proton-Coupled Electron Transfer.

Two-electron, one-proton reactions of a family of [CoCp(dxpe)(NCCH3)]2+ complexes (Cp = cyclopentadienyl, dxpe = 1,2-bis(di(aryl/alkyl)phosphino)ethane) form the corresponding hydride species [HCoCp(dxpe)]+ (dxpe = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), and dcpe (1,2-bis(dicyclohexylphosphino)ethane)) through a stepwise proton-coupled electron transfer process. For three [CoCp(dxpe)(NCCH3)]2+ complexes, peak shift analysis was employed to quantify apparent proton transfer rate constants from cyclic voltammograms recorded with acids ranging 22 pKa units. The apparent proton transfer rate constants correlate with the strength of the proton source for weak acids, but these apparent proton transfer rate constants curiously plateau (kpl) as the reaction becomes increasingly exergonic. The absolute apparent proton transfer rate constants across both these regions correlate with the steric bulk of the chelating diphosphine ligand, with bulkier ligands leading to slower kinetics (kplateau,depe = 3.5 × 107 M-1 s-1, kplateau,dppe = 1.7 × 107 M-1 s-1, kplateau,dcpe = 7.1 × 104 M-1 s-1). Mechanistic studies were conducted to identify the cause of the aberrant kPTapp-ΔpKa trends. When deuterated acids are employed, deuterium incorporation in the Cp ring is observed, indicating protonation of the CoCp(dxpe) species to form the corresponding hydride proceeds via initial ligand protonation. Digital simulations of cyclic voltammograms show ligand loss accompanying initial reduction gates subsequent PCET activity at higher driving forces. Together, these experiments reveal the details of the reaction mechanism: reduction of the Co(III) species is followed by dissociation of the bound acetonitrile ligand, subsequent reduction of the unligated Co(II) species to form a Co(I) species is followed by protonation, which occurs at the Cp ring, followed by tautomerization to generate the stable Co(III)-hydride product [HCoCp(dxpe)]+. Analysis as a function of chelating disphosphine ligand, solvent, and acid strength reveals that the ligand dissociation equilibrium is directly influenced by the steric bulk of the phosphine ligands and gates protonation, giving rise to the plateau of the apparent proton transfer rate constant with strong acids. The complexity of the reaction mechanism underpinning hydride formation, encompassing dynamic behavior of the entire ligand set, highlights the critical need to understand elementary reaction steps in proton-coupled electron transfer reactions.

Synthetic, spectroscopic, structural, and electrochemical investigations of ferricenium derivatives with weakly coordinating anions: ion pairing, substituent, and solvent effects.

A facile and effective strategy for the preparation of a series of ferricenium complexes bearing either electron-donating or electron-withdrawing substituents with weakly coordinating anions such as [B(C6F5)4]- or SbF6- is reported. These systems were thoroughly investigated for their ground state electronic structures in both solution and solid states using infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies as well as single crystal X-ray crystallography and electrochemical measurements. The X-ray structures of the six electron-deficient ferricenium derivatives are of particular interest as only a handful (∼5) of such derivatives have been structurally characterized to date. Comparison of the structural data for both neutral and oxidized derivatives reveals that the nature of the substituents on the cyclopentadienyl (Cp) ligands displays a more significant impact on the metal-ligand separations (FeCt) in the oxidized species than in their neutral analogs. Our 1H-NMR measurements corroborate that in the neutral ferrocene derivatives, electron-donating ring substitutions lead to a greater shielding of the ring protons while electron-withdrawing groups via induction deshield the nearby ring protons. However, the data for the paramagnetic ferricenium derivatives reveals that this substitutional behavior is more complex and fundamentally reversed, which is further supported by our structural studies. We ascribe this reversal of behavior in the ferricenium derivatives to the δ back-donation from the iron atom into the Cp rings which can lead to the overall shielding of the ring protons. Interestingly, our NMR results for the electron-deficient ferricenium derivatives in solution also indicate a direct correlation between the solvent dielectric constant and the energy barrier for rotation around the metal-ligand bond in these systems, whereas such a correlation is absent or not significant in the case of the electron-rich ferricenium species or the corresponding neutral ferrocene analogs. In this work, we also present the electrochemical behavior of the corresponding ferricenium/ferrocene redox couples including potential values (E1/2), peak-to-peak separation (ΔE1/2), and diffusion coefficients (D) of the redox active species in order to provide a concise outline of these data in one place. Our electrochemical studies involved three different solvents and two supporting electrolytes. Notably, our findings point to the significant effect of ion-pairing in lowering the energy necessary for reduction of the ferricenium ion and E1/2 in lower-polarity media. This has significant implications in applications of the ferrocene or ferricenium derivatives as redox agents in low-polarity solvents where an accurate determination of redox potential is critical.

In silico design to enhance the barrier height for magnetization reversal in Dy(iii) sandwich complexes by stitching them under the umbrella of corannulene.

Lanthanide based single molecular magnets (SMMs), particularly dysprocenium based SIMs, are well known for their high energy barrier for spin reversal (Ueff) and blocking temperatures (TB). Enhancing these two parameters and at the same time obtaining ambient stability is key to realising end-user applications such as compact storage or as qubits in quantum computing. In this work, by employing an array of theoretical tools (DFT, ab initio CASSCF and molecular dynamics), we have modelled six complexes [(η5-corannulene)Dy(Cp)] (1), [(η5-corannulene)Dy(C6H6)] (2), [(η6-corannulene)Dy(Cp)] (3), [(η6-corannulene)Dy(C6H6)] (4), [(exo-η5-corannulene)Dy(endo-η5-corannulene)] (5), and [(endo-η5-corannulene)Dy(endo-η5-corannulene)] (6) containing corannulene as a capping ligand to stabilise Dy(iii) half-sandwich complexes. Our calculations predict a strong axiality exerted by the Dy–C interactions in all complexes. Ab initio calculations predict a very large barrier height for all six molecules in the order 1 (919 cm−1) ≈ 3 (913 cm−1) > 2 (847 cm−1) > 4 (608 cm−1) ≈ 5 (603 cm−1) ≈ 6 (599 cm−1), suggesting larger barrier heights for Cp ring systems, followed by six-membered arene systems and then corannulene. DFT based molecular dynamics calculations were performed on complexes 3, 5 and 6. For complexes 3 and 5, the geometries that are dynamically accessible are far fewer. The range of Ueff computed for molecular dynamics snapshots is high, indicating a possibility of translating the large Ueff obtained into attractive blocking temperatures in these complexes, but the converse is found for 6. Furthermore, an in-depth C–H bond vibrational analysis performed on complex 3 suggests that the vibration responsible for reducing the blocking temperature in dysprocenium SIMs is absent here as the C–H bonds are stronger and corannulene steric strain prevents the C(Cp)–Dy–C(Cor) bending. As [(η6-corannulene)TM(X)]+ (TM = Ru, Zr, Os, Rh, Ir and X = C5Me5, C6Me6) are known, the predictions made here have a higher prospect of yielding stability under ambient conditions, a very large Ueff value and a high blocking temperature – a life-giving combination to new generation SMMs.

Cyclometalation in the (η3-C5H5)Co(η2-C2H2)(PMe3) and (η3-C9H7)Co(η2-C2H2) (PMe3) complexes: A computational investigation

This research examined the cyclometalation in the (η3-C5H5)Co(η2-C2H2)(PMe3) and (η3-C9H7)Co(η2-C2H2)(PMe3) complexes by using mPW1PW91 functional. Thermodynamic and kinetic parameters of this reaction were computed. The solvent effects were studied by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects were explored on the energy barrier, frontier orbitals energies, and reactivity parameters (hardness, chemical potential, electrophilicity). The Hirshfeld population analysis was performed based on optimized structures. The rate constant of the cyclometalation reaction was computed from 300 to 1200 K, in the gas phase. In addition, the synchronicity values of this reaction were determined. Our findings revealed, this reaction was favorable energetically in both gas and solution phases. The larger rate constant values were in the presence of Cp ring than In ring.

Protruding hydrogen atoms as markers for the molecular orientation of a metallocene.

A distinct dumbbell shape is observed as the dominant contrast feature in the experimental data when imaging 1,1’-ferrocene dicarboxylic acid (FDCA) molecules on bulk and thin film CaF2(111) surfaces with non-contact atomic force microscopy (NC-AFM). We use NC-AFM image calculations with the probe particle model to interpret this distinct shape by repulsive interactions between the NC-AFM tip and the top hydrogen atoms of the cyclopentadienyl (Cp) rings. Simulated NC-AFM images show an excellent agreement with experimental constant-height NC-AFM data of FDCA molecules at several tip–sample distances. By measuring this distinct dumbbell shape together with the molecular orientation, a strategy is proposed to determine the conformation of the ferrocene moiety, herein on CaF2(111) surfaces, by using the protruding hydrogen atoms as markers.

Di-aqua-bis-(4-ferrocenyl-1,1,1-tri-fluoro-4-oxobutan-2-olato)cobalt(II).

In the title compound, [CoFe2(C5H5)2(C9H5F3O2)2(H2O)2], the central Co atom has an octa-hedral coordination geometry defined by two chelating tri-fluoro-methyl-β-diketone ferrocene ligands and two aqua ligands, with the latter in a cis disposition. The Cp rings in both ferrocene groupings are close to eclipsed. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into [100] chains.