Evaluation of bismuth-based dispersion energy donors - synthesis, structure and theoretical study of 2-biphenylbismuth(iii) derivatives.

A series of 2-biphenyl bismuth(iii) compounds of the type (2-PhC6H4)3-nBiXn [n = 0 (1); n = 1, X = Cl (2), Br (3), I (4), Me (5); n = 2, X = Cl (6), Br (7), I (8)] has been synthesized and analyzed with focus on intramolecular London dispersion interactions. The library of the compounds was set up in order to investigate the Biπ arene interaction by systematic variation of X. The structural analysis in the solid state revealed that the triarylbismuth(iii) compound 1 shows an encapsulation of the metal atom but the distances between the bismuth atom and the phenyl centroids amount to values close to or larger than 4.0 Å, which is considered to be a rather week dispersion interaction. In the case of monomeric diorganobismuth(iii) compounds 2-5 the moderate crowding effectively hinders the formation of intermolecular donor-acceptor interactions, but allows for intramolecular dispersion-type interactions with the 2-biphenyl ligand. In contrast, the structures of the monoorganobismuth compounds 6-8 show the formation of Bi-XBi donor-acceptor bonds leading to the formation of 1D ribbons in the solid state. These coordination bonds are accompanied by intermolecular dispersion interactions with BiPhcentroid distances < 4.0 Å. In solution the diorganobismuth(iii) halides 2-4 show a broadening of their NMR signals (H-8, H-8' and H-9, H-9' protons of the 2-biphenyl ligand), which is a result of dynamic processes including ligand rotation. For further elucidation of these processes compounds 2, 4 and 7 were studied by temperature-dependent NMR spectroscopy. Electronic structure calculations at the density functional theory and DLPNO-coupled cluster level of theory were applied to investigate and quantify the intramolecular London dispersion interactions, in an attempt to distinguish between basic intramolecular interactions and packing effects and to shed light on the dynamic behavior in solution.

Balancing Donor-Acceptor and Dispersion Effects in Heavy Main Group Element π Interactions: Effect of Substituents on the Pnictogen⋠⋠⋠π Arene Interaction.

High-level ab initio calculations using the DLPNO-CCSD(T) method in conjunction with the local energy decomposition (LED) were performed to investigate the nature of the intermolecular interaction in bismuth trichloride adducts with π arene systems. Special emphasis was put on the effect of substituents in the aromatic ring. For this purpose, benzene derivatives with one or three substituents (R=NO2 , CF3 , OCHO, OH, and NH2 ) were chosen and their influence on donor-acceptor interaction as well as on the overall interaction strength was examined. Local energy decomposition was performed to gain deeper insight into the composition of the interaction. Additionally, the study was extended to the intermolecular adducts of arsenic and antimony trichloride with benzene derivatives having one substituent (R=NO2 and NH2 ) in order to rationalize trends in the periodic table. The analysis of natural charges and frontier molecular orbitals shows that donor-acceptor interactions are of π→σ* type and that their strength correlates with charge transfer and orbital energy differences. An analysis of different bonding motifs (Bi⋅⋅⋅π arene, Bi⋅⋅⋅R, and Cl⋅⋅⋅π arene) shows that if dispersion and donor-acceptor interaction coincide as the donor highest occupied molecular orbital (HOMO) of the arene is delocalized over the π system, the M⋅⋅⋅π arene motif is preferred. If the donor HOMO is localized on the substituent, R⋅⋅⋅π arene bonding motifs are preferred. The Cl⋅⋅⋅π arene bonding motif is the least favorable with the lowest overall interaction energy.