The three-center-four-electron tetrel bond

• We present a thermodynamically stable complex that possesses a three-center-four-electron (3c4e) tetrel bond [1,2], formed by capturing a reactive carbenium ion with a bidentate Lewis base. We report NMR spectroscopic, titration calorimetric and reaction kinetic evidences for the structure of this pentacoordinate species and discuss the properties of its tetrel bond, [N˜˜˜∙∙∙C∙∙∙˜˜˜N]+, in comparison with the analogous halogen, [N˜˜˜∙∙∙X∙∙∙˜˜˜N]+ and hydrogen, [N∙∙∙˜˜˜H∙∙∙˜˜˜N]+, bonds [3]. The necessity of the involvement of a bidentate Lewis base for the formation of a stable 3c4e tetrel bond is demonstrated by providing spectroscopic and crystallographic evidence, that a monodentate Lewis base induces a reaction rather than stabilizing the reactive species. A vastly decreased Lewis basicity of the bidentate ligand or reduced Lewis acidity of the carbenium ion weakens — or even prohibits — the formation of the pentacoordinate species, whereas synthetic modifications facilitating attractive orbital overlaps promote it. As the geometry of the pentacoordinate complex resembles the SN2 transition state, it may provide a model system for the investigation of fundamental reaction mechanisms and chemical bonding theories [4].References1. G.C. Pimentel J. Chem. Phys. 1951, 19, 446-4482. R.H. Crabtree Chem. Soc. Rev. 2017, 46, 1720-1729.3. S.B. Hakkert, M. Erdelyi J. Phys. Org. Chem. 2015, 95, 2572-25784. Karim, N. Schultz, H. Andersson, B. Nekoueishahraki et al, 2018, submitted.

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NATURVETENSKAP  -- Kemi -- Organisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Organic Chemistry (hsv//eng)

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