Pentadienyl Complexes of Alkali Metals: Structure and Bonding

One-Step Synthesis and Schlenk-Type Equilibrium of Cyclopentadienylmagnesium Bromides

In the in situ Grignard metalation method (iGMM), the addition of bromoethane to a suspension of magnesium turnings and cyclopentadienes [C5 H6 (HCp), C5 H5 -Si(iPr)3 (HCpTIPS )] in diethyl ether smoothly yields heteroleptic [(Et2 O)Mg(CpR )(μ-Br)]2 (CpR =Cp (1), CpTIPS (2)). The Schlenk equilibrium of 2 in toluene leads to ligand exchange and formation of homoleptic [Mg(CpR )2 ] (3) and [(Et2 O)MgBr(μ-Br)]2 (4). Interfering solvation and aggregation as well as ligand redistribution equilibria hamper a quantitative elucidation of thermodynamic data for the Schlenk equilibrium of 2 in toluene. In ethereal solvents, mononuclear species [(Et2 O)2 Mg(CpTIPS )Br] (2'), [(Et2 O)n Mg(CpTIPS )2 ] (3'), and [(Et2 O)2 MgBr2 ] (4') coexist. Larger coordination numbers can be realized with cyclic ethers like tetrahydropyran allowing crystallization of [(thp)4 MgBr2 ] (5). The interpretation of the temperature-dependency of the Schlenk equilibrium constant in diethyl ether gives a reaction enthalpy ΔH and reaction entropy ΔS of -11.5 kJ mol-1 and 60 J mol-1 , respectively.

10-π-Electron arenes à la carte: structure and bonding of the [E-(CnHn)-E](n-6) (E = Ca, Sr, Ba; n = 6-8) complexes

In this paper, we provide solid evidence to show that among an overwhelming structural diversity, alkaline earth metals (Ca, Sr, Ba) have the ability to form inverted sandwich compounds with C6H6, C7H7(+), and C8H8(2+) of Dnh symmetry and general formula [E-(CnHn)-E](n-6) (n = 6-8) with planar 10-π-electron aromatic cores by virtue of transferring two electrons per metal atom to the ring. However, the origin of the orbital interaction between the metals and the carbon ring is quite different; while [E-(C6H6)-E] complexes are dominated by δ-interactions, both π- and δ-interactions are important in [E-(C7H7)-E](+) and [E-(C8H8)-E](2+) complexes.

Delocalized and localized donating–accepting Mn–C interactions in half-sandwich cyclopentadienyl and pentadienyl complexes

The flexibility of the Pdl ligand allows a more energetic M–Pdl interaction but also destabilizes the ligand moiety.

Theoretical study of penta- and heteropentadienyl beryllium complexes coordinated to hydrogen molecules

A series of penta- and heteropentadienyl [CH₂CHCHCHXBe]⁺, (X = CH₂, O, NH, S) complexes has been theoretically studied. All calculated complexes show beryllium atoms with two, three, and five coordination numbers. The density functional theory (DFT) was used to determine the electron and structural behavior of those beryllium complexes. The nature of the ligands plays an important role in the form of binding to the beryllium atom. Beryllium structures 1-4 are able to coordinate only one hydrogen molecule. A molecular orbital analysis for all complexes was performed in order to know more about the nature of their bonding scheme.

Construction of double- and triple-decker sandwich compounds from half-sandwich compounds: a theoretical assessment

The viability and properties of double- (Cp2M) and triple-decker (Cp3M2) sandwiches formed from half-sandwiches (CpM, Cp = C5H5; M = Li, Na, K, Be, Mg, Ca, Fe, Co, Ni, Cu, and Zn) are discussed based on the geometry, energy, HOMO-LUMO gap, and topological properties. The calculated results show that the alkali metals and transitional metals (Fe, Co, Ni) with more unpaired electron are more inclined to form high-symmetry sandwich complexes than the alkaline earth metals. The Cp2M and Cp3M2 symmetries for M = Cu and Zn are low. In Cp2M and Cp3M2, the electrostatic and π orbital interactions are dominant. For Cp3M2, the contributions of orbital interaction to the total M-C interaction and of σ-type interaction to the orbital interaction are larger than those in Cp2M. The nature of the M-C bond is well correlated to its bond length. The shorter the M-C bond, the more covalent it is.

Second hyperpolarizability of multimetallocenes [Cp–Mn–Cp] of Be, Mg and Ca

Multimetallocene complexes ( Cp – M n– Cp ) of Be , Mg and Ca have been considered for the theoretical study of static second hyperpolarizability using a number of DFT functionals. Owing to the cooperative effect in bonding, beryllium forms multiberyllocene complexes ( Cp – Be n– Cp ) which have sufficient thermal stability with respect to dissociation into neutral fragments up to n = 10. On the other hand, multimetallocene complexes of Mg and Ca are found to be stable for n ≤ 5 which may be due to the weaker covalent bonding interaction between the larger metal atoms. The rather small variation of linear and cubic polarizabilities of Cp – Be n– Cp complexes beyond n = 5 arises from the rather weaker charge transfer transitions. The difference in NLO property among the investigated metal complexes arises from the extent of charge transfer from the terminal metal atoms and the distance between them. The charge transfer at longer distances in the ground state of Mg and Ca complexes leads to more intense electronic transition — the spectroscopic parameters of which strongly favors the enhancement of second hyperpolarizability.

Molecular and electronic structures of donor-functionalized dysprosium pentadienyl complexes

The molecular structures of two dysprosium complexes of donor-functionalized pentadienyl ligands are described. Electronic structure calculations reveal that the W-shaped pentadienyl ligand strongly influences the orientation of the main magnetic axis of the ground Kramers doublets in both complexes.

Beryllium-cyclobutadiene multidecker inverse sandwiches: electronic structure and second-hyperpolarizability

Beryllium forms stable sandwich and inverse sandwich complexes with the cyclobutadiene molecule. Two types of multidecker complexes are designed. Multidecker inverse sandwiches are found to be thermally more stable than the corresponding sandwich complexes. The average distance between two consecutive metals and the two consecutive cyclobutadiene rings increase gradually on increasing size of the chosen inverse sandwich complexes. The density functional theory functionals B3LYP, BHHLYP, BLYP, M06, CAM-B3LYP, and B2PLYP in conjunction with the 6-311++G (d, p) basis set have been employed for calculating the third-order electric response properties of the chosen beryllium-cyclobutadiene complexes and the results obtained for each functional are found to have a consistent trend. Compared to the normal sandwich compounds the second-hyperpolarizability of inverse sandwiches is predicated to be larger, which fairly correlates with the extent of ground-state polarization. The significant enhancement of cubic polarizability of higher-order multidecker inverse sandwiches arises from the strong coupling between the ground and the low lying charge transfer excited states. The rather strong enhancement of second-hyperpolarizability on increasing size of the beryllium-multidecker inverse sandwiches may provide a new route to design efficient nonlinear optical materials.