Angular Distortions at Benzylic Carbons Due to Intramolecular Polarization-Induced Metal-Arene Interactions: A Case Study with Open-Shell Chromium(II) NHC Complexes

作者：Danopoulos Andreas A^*; Monakhov Kirill Yu; Robert Vincent; Braunstein Pierre; Pattacini Roberto; Conde Guadano Susana; Hanton Martin; Tooze Robert P

来源：Organometallics, 2013, 32(6): 1842-1850.

DOI：10.1021/om3012568

The synthesis and full characterization of the unprecedented open-shell Cr(II) benzyl organometallic complexes [Cr(NHC)(2)(benzyl)(2)] (2) and [Cr(NHC*)(benzyl)(2)] (3) (NHC = N,N%26apos;-diisopropylimidazol-2-ylidene; NHC* = N,N%26apos;-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) from [Cr(benzyl)(3)(THF)(3)] and [CrCl2(THF)(2)]/[Mg(benzyl)(2)], respectively, uncovered unusually acute angles (93 degrees in 2 and 76 degrees in 3) at the sp(3) benzylic C of the coordinated benzyl ligands. Detailed theoretical analyses (DFT and CASPT2) of the four- and three-coordinate Cr(II) species were performed to elucidate the physical origin of the benzyl bending and led to the recognition of a noncovalent, intramolecular polarization-induced metal arene (PIMA) interaction as being responsible for it. The energetic contribution from a single PIMA interaction is estimated to be ca. 50 kJ/mol. A comparison with the origin of the angular distortions in the d(0) [Zr(benzyl)(4)] complex will also be presented. Sharing the common origin of an induced-dipole charge density scheme with intermolecular anion-pi interactions, the intramolecular PIMA interaction concept involving a transition metal unpaired d electron and arene-pi orbitals can be viewed as an extension of intermolecular anion-pi interactions and leads to remarkable quantitative prediction of the observed structural distortions. PIMA interactions may manifest themselves in diverse structural and dynamic phenomena and have broad implications in chemical sciences.

• 出版日期2013-3-25