Computational Analysis of n鈫捪€* Back-Bonding in Metallylene鈥揑socyanide Complexes R2MCNR鈥?(M = Si, Ge, Sn; R = tBu, Ph; R鈥?= Me, tBu, Ph)

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• 作者：Akseli Mansikkam盲ki ; Philip P. Power ; Heikki M. Tuononen
• 刊名：Organometallics
• 出版年：2013
• 出版时间：November 25, 2013
• 年：2013
• 卷：32
• 期：22
• 页码：6690-6700
• 全文大小：373K
• 年卷期：v.32,no.22(November 25, 2013)
• ISSN：1520-6041

文摘

A detailed computational investigation of orbital interactions in metal鈥揷arbon bonds of metallylene鈥搃socyanide adducts of the type R₂MCNR鈥?(M = Si, Ge, Sn; R, R鈥?= alkyl, aryl) was performed using density functional theory and different methods based on energy decomposition analysis. Similar analyses have not been carried out before for metal complexes of isocyanides, even though the related carbonyl complexes have been under intense investigations throughout the years. The results of our work reveal that the relative importance of 蟺-type back-bonding interactions in these systems increases in the sequence Sn < Ge Si, and in contrast to some earlier assumptions, the 蟺-component cannot be neglected for any of the systems investigated. While the fundamental ligand properties of isocyanides are very similar to those of carbonyl, there are significant variations in the magnitudes of different effects observed. Most notably, on coordination to metals, both ligands can display positive or negative shifts in their characteristic stretching frequencies. However, because isocyanides are stronger 蟽 donors, the metal-induced changes in the CN bonding framework are greater than those observed for carbonyl. Consequently, isocyanides readily exhibit positive CN stretching frequency shifts even in complexes where they function as 蟺-acceptors, and the sign of these shifts is alone a poor indicator of the nature of the metal鈥揷arbon interaction. On the other hand, the relative 蟺-character of the metal鈥揷arbon bond in metallylene鈥搃socyanide adducts, as judged by the natural orbitals of chemical valence as well as by partitions of the orbital interaction energy, was shown to have a linear correlation with the shift in CN stretching frequency upon complex formation. The details of this correlation show that 蟺-back-donation contributions to total orbital interaction energy need to exceed 100 kJ mol^鈥? in order for the shift in the CN stretching frequency of metallylene鈥搃socyanide adducts to be negative.