Main-group metal cyclophane complexes with high coordination numbers.

Yasir Altaf,Muhammad Yar,Muhammad Ali Hashmi

doi:10.1039/d0ra05303a

Abstract

Density functional theory calculations using the PBE0-D3BJ hybrid functional have been employed to investigate the complexation of main-group metal-cations with [2.2.2]paracyclophane and deltaphane. Geometry optimization under symmetry constraints was performed to observe the mode of coordination that a metal-cation adopts when it resides inside the cyclophane cavity. Thermodynamic properties were investigated to note the trends of stability along a group of metals. To further investigate the bonding properties, Morokuma–Ziegler energy decomposition analysis, natural bond orbital analysis and Bader's analysis were employed. It was observed that most of the main-group metal complexes with cyclophanes prefer an η6η6η6 coordination mode where the metal-cation sits in the centre of the cyclophane cavity. There is an increased thermodynamic stability in [2.2.2]paracyclophane complexes compared to their deltaphane analogues while the reverse is true regarding the strength of coordination based on interaction energy.

Highlights

Cyclophanes consist of two or more aromatic rings connected through aliphatic bridges, to form a cyclic cavity.[1]
We propose in these two cases that only p2 and p3 of the cyclophane cavity coordinate with ns orbital and one of the np sub-orbitals, respectively leaving behind p1 without any interaction as in Fig. S2(b).† This is supported by the comparison of the amount of ligand to metal charge transfer (LMCT) in these two complexes (Table 7) with h6h6h6-coordinated pCp– Ga+ where LMCT is double the amount of that in its other two counterparts
Geometry optimization under symmetry constraints shows that an h6h6h6 mode of coordination is preferred in most of the cases

Summary

Introduction

Cyclophanes consist of two or more aromatic rings connected through aliphatic bridges, to form a cyclic cavity.[1]. During the same period (mid to late 1980s), Schmidbaur and coworkers reported the groundbreaking complexes of pCp with some of the main-group metals.[17,18,19] Despite these contributions in synthesis of metallacyclophanes of pCp and Dp, a lot of effort is still required to explore the bonding properties of these complexes to make use of these promising p-donating ligands on industrial scale In this regard, we previously reported the bonding properties of coinage metal complexes of pCp and Dp.[20] Earlier, the groups of Frenking and Castro carried out a computational study on the coordination mode and bonding properties of inclusion complexes of Sn2+ and Ag+ with pCp.[21] They further extended the concept to computationally understand the role of formal charge of a cation in p–cation interactions by comparing the complexes of isoelectronic In+ and Cd2+ with pCp.[22] In further instances, Castro et al investigated helicenes[23] and Dp24 as potential p-donors to form various p–cation interactions through relativistic DFT approach. NBO analysis was carried out with NBO 6.0 program[37] as interfaced with Gaussian[09]

Results and discussion

D3 C3 D3 C3 D3 C3 D3 C3 D3 C3 D3 C3 D3 C3 D3 C3 D3 C3 D3

Conclusion