Ring Puckering in Group 14 -diketiminate β Chlorometallylenes is of Quantum-mechanical Origin Víctor M. Rosas-García* and Victor M. Jiménez-Pérez Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León C.P. 66451, México, e-mail:rosas.victor@gmail.com Abstract The ring in cyclic β-diketiminate group 14 chlorometallylenes puckers, pushing the metal out of the β-diketiminate plane, while the rings in metallylene cations are planar. Several hypotheses have been advanced in the past to explain this puckering, such as steric interactions, η 5 bonding or cavity size. We have investigated the origin of this ring puckering by calculations at the B3LYP/LANL2DZdp level of theory using a variety of substituents on nitrogen, and found that the ring puckers even with hydrogen on the nitrogen atoms. Analysis of the resulting wavefunction by Natural Energy Decomposition reveals that the puckering is mainly due to an interplay between electrostatics and electronic exchange. Keywords Heterocycles, carbene analogs, DFT calculations, ring deformation. Introduction β-diketiminate chlorometallylenes show a puckered ring, usually attributed to steric crowding around the metal, but a systematic examination of the relevant factors reveals the paramount role of electrostatics and electronic exchange. β-diketiminate forms part of the family of N-based monoanionic bidentate ligands, which have routinely been used for stabilization of low-valent and carbene centers. The simplest ligand of this family—N,N'-ethenylidenate, which supplies 4 electrons to the metal it binds—was employed by Arduengo et al. [1] to produce the first stable carbene: imidazol- 2-ylidene (Arduengo's carbene). β-diketiminate, which is able to supply six electrons, is another widely used ligand employed to stabilize carbene-analogs. Chlorometallylenes stabilized by β-diketiminate have been previously synthesized for Ge [2], Sn [3] and Pb [4]. These chloro- derivatives are key intermediates in the synthesis of a variety of substituted metallylenes [5,6]. Arduengo's carbene [1] is planar and shows aromatic stabilization through π-delocalization. This aromatic stabilization is reduced in the silylene analogs [7] and further reduced in the Ge and Sn analogs [8]. Even with the lowered stabilization, all these compounds are planar. According to Hayes— 1/28