Experimental Charge Density Studies of Cyclotetrasilazane and Metal Complexes Containing the Di‐ and Tetraanion

Abstract

The homologous series of parent octamethylcyclotetrasilazane (c‐NH‐SiMe2‐)4, (1), the lithium complex [(THF)2Li2(c‐N‐SiMe2‐NH‐SiMe2‐)2]2, (2), containing the cyclic dianion, and [(THF)2LiAl(c‐N‐SiMe2‐)4]2, (3), accommodating the unprecedented tetraanion [Me2SiN]4‐ was synthesized to investigate the nature of the covalent Si‐N single bond in the presence of various metals. These model compounds show a wide diversity of Si‐N(H), Si‐N(M), Si‐N(H, M) and M‐N bonds and serve as bench‐mark systems to study polar bonds by high‐resolution low‐temperature X‐ray structure analysis. Experimental charge density studies reveal highly polar Si‐N bonds with remarkable ionic contribution, even in the non‐metallated starting material 1. The Li‐N and Li‐O bonds have to be classified as almost purely ionic bonds with topological properties not far from those determined for NaCl.

Spontaneous vs. Base‐Induced Dehydrochlorination of Group 14 ortho‐Carboranylamidinates

“…In 8 and 9, both the Si-C and the Si-N distances are in the typical range of covalently bonded silicon. [24,27,29,32,33] The geometric parameters around the Si atom and within the carboranylamidinate ligand are virtually equal to those in the previously reported compound Ph 2 Si[L′]. [18] The molecular structure of Cl 2 Si[L] (7) is very similar, even though the crystal quality was not good enough for a complete structural refinement.…”

Octahedral Adducts of Dichlorosilane with Substituted Pyridines: Synthesis, Reactivity and a Comparison of Their Structures and 29Si NMR Chemical Shifts

“…Topological analysis of the electron-density distribution is a powerful tool for that purpose, and this analysis can be carried out using the atoms-in-molecules theory (AIM) developed by Bader and others. [22][23][24][25] This method partitions the electron density of a molecule 1(r) into individual non-overlapping atomic fragments by rigorously defined interatomic surfaces. [23] The bond critical points (BCPs) between the atoms of the molecules 1 a-f and 2 represent the topology one would expect for a classical Lewis structure.…”

The crystal structure of 2-chloro-1,3-bis(2,4,6-trimethylphenyl)-4,4-dimethyl-1,3,2λ3,4-diazaphosphasiletidine

“…The unusually acute N1-Si1-N2 angle in the title compound is associated with Si-N distances of 1.7436(17) Å (Si1-N1) and 1.7445(17) Å (Si1-N2). The latter are remarkably longer than the value reported for a Si-N single bond (1.724(4) Å [13]), but correspond to those in related cyclodisilazanes [14][15][16][17][18][19][20][21][22]. Consequently, the P-N bonds are shorter than expected for a single bond (1.6857(17) Å (P1-N1) and 1.6854(17) Å (P1-N2) vs. 1.704(4) Å [13]).…”