First-Row Transition Metals in Binuclear Cyclopentadienylmetal Derivatives of Tetramethyleneethane: 畏3,畏3 versus 畏4,畏4 Ligand鈥揗etal Bonding Related to Spin

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• 作者：Huidong Li ; Hao Feng ; Weiguo Sun ; Qunchao Fan ; R. Bruce King ; Henry F. Schaefer ; III
• 刊名：Organometallics
• 出版年：2014
• 出版时间：July 14, 2014
• 年：2014
• 卷：33
• 期：13
• 页码：3489-3499
• 全文大小：645K
• ISSN：1520-6041

文摘

The tetramethyleneethane (TME) ligand is found in the 畏³,畏³ complex trans-(畏³,畏³-TME)Ni₂Cp₂ and the 畏⁴,畏⁴ complex trans-(畏⁴,畏⁴-TME)Co₂Cp₂, which have both been synthesized and structurally characterized by X-ray crystallography. The structures of the complete series of (TME)M₂Cp₂ derivatives of the first-row transition metals from Ti to Ni have now been investigated by density functional theory. The experimentally known nickel and cobalt complexes are found to have closed-shell electronic ground states. The lowest energy structure for the iron complex is the triplet spin state trans-(畏⁴,畏⁴-TME)Fe₂Cp₂ structure with geometry similar to that of the lowest energy cobalt structure. All of the low-energy (TME)M₂Cp₂ structures for manganese and the first-row transition metals to the left of manganese (Cr, V, and Ti) exhibit cis-(畏⁴,畏⁴-TME)M₂Cp₂ stereochemistry, thereby providing the possibility for direct metal鈥搈etal interactions. Vanadium is the only first-row transition metal to the left of cobalt where the lowest energy (TME)M₂Cp₂ structure is a singlet spin state, suggesting limited applicability of the 18-electron rule in these systems. The frontier molecular orbitals of these cis-(畏⁴,畏⁴-TME)M₂Cp₂ systems have been examined in order to provide insight regarding metal鈥搈etal bonding. Thus, low-energy cis-(畏⁴,畏⁴-TME)Mn₂Cp₂ structures are found in both quintet and triplet spin states with formal Mn鈺怣n double bonds. The lowest energy cis-(畏⁴,畏⁴-TME)Cr₂Cp₂ and cis-(畏⁴,畏⁴-TME)Ti₂Cp₂ structures have triplet spin states with a formal Cr鈮r triple bond and a formal Ti鈺怲i double bond, respectively. The lowest energy cis-(畏⁴,畏⁴-TME)V₂Cp₂ structure is a singlet structure with a formal V鈮 triple bond.