The earth-metal olefin complex [GaI (COD)2 ]+ [Al(ORF )4 ]- (COD=1,5-cyclooctadiene; RF =C(CF3 )3 ) constitutes the first homoleptic olefin complex of any main-group metal accessible as a bulk compound. It is straight forward to prepare in good yield and constitutes an olefin complex of a main-group metal that-similar to many transition-metals-may adopt the +1 and +3 oxidation states opening potential applications. Crystallographic-, vibrational- and computational investigations give an insight to the atypical bonding between an olefin and a main-group metal. They are compared to classical transition-metal relatives.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/ange.202011466

A Simple Homoleptic Gallium(I) Olefin Complex: Mimicking Transition-Metal Chemistry at a Main-Group Metal?

Various possible structures for neutral ML complexes (M = Al, Ga; L = CO2, CS2, and COS) are investigated using density functional methods and the Moller−Plesset perturbation approach. Formation of C2v and Cs species is observed. Obtained vibrational frequencies are compared with experimental data. Differences between CO2 and CS2 adducts are discussed. Absence of C2v species for MCS2 complexes, as seen in experiments, is consistent with calculated relative energies. Erratic behavior of the MP2 method when excluding core electrons from correlation suggests that for gallium 3d semi-core electrons of GaCO2 complex play an important role in complex formation. Very small (ca. −3 kcal/mol) binding energies explain major difficulties in experimental observation of GaCO2 complexes. To investigate this matter further, calculations for experimentally unknown MCOS complexes have been performed.

Theoretical Study of Aluminum and Gallium Atom Complexes with CO2, CS2, and COS

One of the themes of modern molecular reaction dynamics is to characterize elementary chemical reactions from “quantum state to quantum state”, and the study of molecular reaction dynamics in excited states can help test the validity of modern chemical theories and provide methods to control chemical reactions. The subject of this review is to describe the recent experimental techniques used to study the reaction dynamics of metal atoms in the gas phase. Through these techniques, information such as the internal energy distribution and angular distribution of the nascent products or the three-dimensional stereodynamic reactivity can be obtained. In addition, by preparing metal atoms with specific excited electronic states or orbital arrangements, information about the reactivity of the electronic states enriches the relevant understanding of the electron transfer mechanism in metal reaction dynamics.

Advanced techniques for quantum-state specific reaction dynamics of gas phase metal atoms

The reactions of Al, Ga and In atoms with C2H4 and CO2 have been investigated by matrix isolation infrared spectroscopy. Reactions with ethylene yield a series of C2v symmetry π complexes with comparable geometries. The C-C bond is similarly weakened (- 30 % in C=C force constant) in the complexes of the three metals. The strengthes of the metal-carbon interactions and the relative IR intensities are more sensitive to finer differences in the metal-ethylene bonding and vary continuously from one metal to the other. Reactions with CO2, on the other hand reveal large variation of reactivity from one group III metal atom to the other. Only Al and Ga atoms form complexes in the ground state and both AlCO2 and GaCO2 have two isomeric froms, one of C2v and one of CS or C1 symmetry. The most stable configuration is nevertheless not the same for AlCO2 (CS symmetry) as for GaCO2 (C2v).

T. Burkholder

Papers

Reactions of group iii metal atom with ethylene and carbon dioxide molecules: a matrix isolation study