Strong interactions between copper halides and unsaturated systems: new metallocycles? Or the importance of deformation

What's Next for First Row Fluorometallacycles?

Hydrocarbon-derived metallacycles have been identified as key intermediates in a host of catalyzed transformations of unsaturated organic substrates. In contrast, our knowledge of analogous reactivity of fluorometallacycles is underdeveloped and largely confined to first row metals. Our summary of recent advances aims to inform young investigators of the exciting challenges offered by this pursuit.

Study of Beryllium, Magnesium, and Spodium Bonds to Carbenes and Carbodiphosphoranes

The aim of this article is to present results of theoretical study on the properties of C⋯M bonds, where C is either a carbene or carbodiphosphorane carbon atom and M is an acidic center of MX2 (M = Be, Mg, Zn). Due to the rarity of theoretical data regarding the C⋯Zn bond (i.e., the zinc bond), the main focus is placed on comparing the characteristics of this interaction with C⋯Be (beryllium bond) and C⋯Mg (magnesium bond). For this purpose, theoretical studies (ωB97X-D/6-311++G(2df,2p)) have been performed for a large group of dimers formed by MX2 (X = H, F, Cl, Br, Me) and either a carbene ((NH2)2C, imidazol-2-ylidene, imidazolidin-2-ylidene, tetrahydropyrymid-2-ylidene, cyclopropenylidene) or carbodiphosphorane ((PH3)2C, (NH3)2C) molecule. The investigated dimers are characterized by a very strong charge transfer effect from either the carbene or carbodiphosphorane molecule to the MX2 one. This may even be over six times as strong as in the water dimer. According to the QTAIM and NCI method, the zinc bond is not very different than the beryllium bond, with both featuring a significant covalent contribution. However, the zinc bond should be definitely stronger if delocalization index is considered.

Rivalry between Regium and Hydrogen Bonds Established within Diatomic Coinage Molecules and Lewis Acids/Bases

A theoretical study of the complexes formed by Ag₂ and Cu₂ with different molecules, XH (FH, ClH, OH₂ , SH₂ , HCN, HNC, HCCH, NH₃ and PH₃ ) that can act as hydrogen-bond donors (Lewis acids) or regium-bond acceptors (Lewis bases) was carried out at the CCSD(T)/CBS computational level. The heteronuclear diatomic coinage molecules (AuAg, AuCu, and AgCu) have also been considered. With the exception of some of the hydrogen-bonded complexes with FH, the regium-bonded binary complexes are more stable. The AuAg and AuCu molecules show large dipole moments that weaken the regium bond (RB) with Au and favour those through the Ag and Cu atoms, respectively.

Regium Bonds between Silver(I) Pyrazolates Dinuclear Complexes and Lewis Bases (N2, OH2, NCH, SH2, NH3, PH3, CO and CNH)

A theoretical study and Cambridge Structural Database (CSD) search of dinuclear Ag(I) pyrazolates interactions with Lewis bases were carried out and the effect of the substituents and ligands on the structure and on the aromaticity were analyzed. A relationship between the intramolecular Ag–Ag distance and stability was found in the unsubstituted system, which indicates a destabilization at longer distances compensated by ligands upon complexation. It was also observed that the asymmetrical interaction with phosphines as ligands increases the Ag–Ag distance. This increase is dramatically higher when two simultaneous PH3 ligands are taken into account. The calculated 109Ag chemical shielding shows variation up to 1200 ppm due to the complexation. Calculations showed that six-membered rings possessed non-aromatic character while pyrazole rings do not change their aromatic character significantly upon complexation.

On the nature of the interaction of copper hydride and halide with substituted ethylene and acetylene

The association of Cu-X (X = -H, -Cl, and -F) with H₂CCHCH_mY_n and HCCCH_mY_n (Y = -Cl, -F, -OH, -CH3) has been studied at a high level of theory. The density functional theory (DFT) at B3LYP/6-311G(d,p)//B3LYP/6-311 + G(3df,2p) level has been chosen to calculate the structure and the relative stability of 24 different complexes. The interaction of Cu-F with the derivatives of ethylene and acetylene was found very strong, with interaction energies close to those of conventional covalent bonds. In all complexes, the most stable structure was found when Cu-X is positioned on the unsaturated CC bond, forming a three-membered ring that leads to longer CC bond distances. Both ethylene and acetylene complexes show similar trends of interaction energies with respect to the same moiety. All electronic indexes analyzed by means of the QTAIM, ELF, and NBO formalisms indicate that the strength of the interaction should increase with the number of withdrawing substituents in both series of compounds. Graphical abstractThe p-Interaction of ethylene and acetylene derivative with fluoride copper. The ELF graphs and its 2D projection show the disynaptic basins of the electrostatic binding.

Understanding Regium Bonds and their Competition with Hydrogen Bonds in Au2 :HX Complexes

A theoretical study of the regium and hydrogen bonds (RB and HB, respectively) in Au₂ :HX complexes has been carried out by means of CCSD(T) calculations. The theoretical study shows as overall outcome that in all cases the complexes exhibiting RB are more stable that those with HB. The binding energies for RB complexes range between -24 and -180 kJ ⋅ mol^-1, whereas those of the HB complexes are between -6 and -19 kJ ⋅ mol^-1 . DFT-SAPT also indicated that HB complexes are governed by electrostatics, but RB complexes present larger contribution of the induction term to the total attractive forces. ¹⁹⁷ Au chemical shifts have been calculated using the relativistic ZORA Hamiltonian.

On the existence and characteristics of π-beryllium bonds

The existence of π-beryllium bonds explains the stability of the complexes between ethylene and acetylene and BeX2 (X = H, F, and Cl) derivatives. These linkers involve a significant charge transfer from the π(CC) bonding orbitals into the empty p orbitals of Be and to a much smaller degree into the σ(BeH)* antibonding orbitals. The significant deformation of the BeX2 moiety and the slight deformation of the unsaturated hydrocarbon result in distortion energies as high as the dissociation energy of the complex. The π-beryllium bonds are about four times stronger than conventional π-hydrogen bonds and even stronger than the strongest π-hydrogen bond reported to date in the literature. The topology of their electron density is characterized as being very flat in the bonding region between the π-system and Be, which leads to topologically unstable structures close to catastrophe points. Among the functionals considered in our study M06 is the one that leads to values in better agreement with CCSD(T)/aug-cc-pVTZ calculations used as a reference. B3LYP underestimates some interactions, whereas M06-2X overestimates all of them. MP2 also yields good agreement with the CCSD(T) method.

A computational study of the effects of ancillary ligands on copper(i)–ethylene interaction

Structural and electronic calculations on a ligand database are used to quantify the influence of the ancillary ligands and coordination mode on the electronic structure of Cu(i) ethylene complexes.

Acidity enhancement of unsaturated bases of group 15 by association with borane and beryllium dihydride. Unexpected boron and beryllium Brønsted acids

BeH₂and BH₃association with unsaturated bases of group 15 increases their acidity and changes the trend. Ethynyl : BeH₂complexes unexpectedly behave as Be acids.

Complicated synergistic effects between metal–π interaction and halogen bonding involving MCCX

Complicated synergistic effects have been found between metal–π interaction and halogen bond in the complexes FCCF⋯MCCX⋯NCH (M = Li, Cu, Ag, and Au; X = Cl, Br, and I).

Cooperativity between hydrogen bonds and beryllium bonds in (H2O)(n)BeX2 (n = 1-3, X = H, F) complexes. A new perspective

The interaction of BeX(2) (X = H, F) with water molecules has been analyzed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory. The formation of strong beryllium bonds between water molecules and the BeX(2) derivative triggers significant electron density redistribution within the whole system, resulting in significant changes in the proton donor and proton acceptor capacity of the water molecules involved. Hence, significant cooperative and anti-cooperative effects are present, explaining why there is no case in which the global minimum corresponds to a tetracoordinated beryllium atom. In fact, the most stable clusters can be viewed as the result of the attachment of BeX(2) to the water trimer and the water dimer, respectively, and not as the result of the solvation of the BeX(2) molecule. We have also shown that the decomposition of the interaction energy into atomic components is a reliable quantitative tool to describe all the closed-shell interactions present in the clusters investigated herein, namely hydrogen bonds, beryllium bonds and dihydrogen bonds. Indeed, we have shown that the changes in the atomic energy components are correlated with the changes in the strength of these interactions, and they provide a quantitative measure of cooperative effects directly in terms of energies.