Theoretical Study On The Structuries, Bonding Energies And Aromaticities For The Sandwich Complexes Containing E₄^2- (N, P, As, Sb And Bi) Ligands

The ferrocene and [(η5-P5)2Ti]2-had been successfully synthesized, people have been studying it because of special structure, property and extensive application.The synthesis and theoretical study on sandwich complexes analogous to ferrocenehave become a focus for experimental and theoretical chemists. At present, the structure and property of phospha-five-membered ligand, its half-sandwich complexes and sandwich complexes have been reported largely. P42-(D4h), As42-(D4h), Sb42-(D4h) and Bi42-(D4h) have been successfully synthesized. After that, the structure and aromaticity on tetracoordinate metallocene attract attention. However, recently trans-metal tetraphosphametallocenes having reported less by now, especially, the structure, bonding energy and aromaticity of hetero-decked sandwich complexes containing E42-(N, P, As, Sb and Bi) ligands.All calculations were performed with the Gaussian 03 program.The geometries were first optimized with DFT/B3LYP method and 6-311+G* group. The NICSs and frequencies of all optimized geometry were predicted with the same basis sets. In order to study the total NICS distribution in cyclo-E4 plane and the various bonds NICS contributions, the total NICS has been dissected into NICS contributions of various bonds, core, and lone pairs by NBO.Firstly, the equilibrium geometries and aromaticity of the E42? (E= N-Bi) were predicted. The result showed that the ground states of E42?were in D4h symmetries. All of the center and inner side of E42? rings are anti-aromatic excluding the outer for N42?.Secondly, half-sandwiches [ME4]q( M=Co, Ti, V, Cr and Mn, E= N—Bi, q=0, 1) were desiged based on E42?. The results showed that C4V configurations for the [ME4]q are local minima except for [MnE4]+, [CrP4] and [CrAs4]. All of E4 rings of [CoE4]+, [CrP4] and [CrAs4] have strong center and inner aromaticity, and outer anti-aromaticity, except for [CoN4]+. Large aromaticities for the complexes are attributed mainly to the effects of their E-M bonds, M lone pairs and P long pairs. The rest complexes have center, inner and outer aromacticity which is stronger than the single rings.Finally, the sandwich complexes [P4ME4]q- (M=Co, Ti, V, Cr and Mn, E= N—Bi, q=1, 2) were desiged. The results showed that the ground states of [P4ME4]q- were in C4V(eclipsed)and C4V(staggered)symmetries. The Ti, V species is eclipsed (C4V) conformations as their local minima and the P4 and E4 of Ti, V species have anti-aromaticity, dominated to the contributions of E-Eπbonds. The Cr, Mn, Co species is staggered (C4V) conformations as their stable structures and the P4 and E4 of Cr, Mn, Co species have aromaticity, dominated to the contributions of E-M bonds and E lone pairs. The aromaticity of P4 ring for [P4ME4]q- increases with the order of P, As, Sb and Bi. There areσ,πandδinteractions between the ligands and metal for the all complexes. The binding energies between Co3+ and E4 in [P4CoE4]? increase with the order N, P, As, Bi, Sb. The Co complex is the most stable and the Cr complex is the most non-stable in all the complexes.