Applications of the Laddering Principle — A Two-Stage Approach to Describe Lithium Heterocarboxylates

Abstract

Since the development of the laddering principle in the mid‐1980s, it has become a useful concept for describing structural features in a wide variety of organoalkali metal (particularly organolithium) and other main‐group element oligomers. Here a brief account of the laddering principle is given, and a two‐stage approach to understanding structural diversity is described for several lithium heterocarboxylates. “Primary laddering” describes the initial aggregation of monomeric units, whereas “secondary laddering” deals with the assembly of these primary laddered units into larger structures. Both homo‐ and heteromolecular clusters can be formed by these processes. In this context, several examples are discussed, with particular emphasis on the effects of solvation and heteroatoms.

New Lanthanide Alkynylamidinates and Diiminophosphinates

“…In the solid state, both lithium propiolamidinates crystallize in the triclinic space group P-1 with one dimeric molecule in the unit cell. The bond lengths and bond angles are in good agreement with similar structures of amidinate ligands [48][49][50][51][52][53][54][55][56][57][58]. The N-C distances in the amidinate N-C-N unit are 1.321(2) and 1.330(2) Å in 1 and 1.3201 (13) …”

“…Full crystallographic data can be found in the Supplementary Information. The crystal structure determinations of Li[Ph-C≡C-C(N i Pr)2] THF (1) and Li[Ph-C≡C-C(NCy)2] THF (2) in both cases revealed the presence of a ladder-type dimeric structure, which is the most characteristic structural motif of most previously characterized lithium amidinates and guanidinates [48][49][50][51][52][53][54][55][56][57][58]. The dimers are centrosymmetric with the central Li2N2 ring being strictly planar.…”

Backbone-Substituted β-Ketoimines and Ketoiminate Clusters: Transoid Li2O2 Squares and D2-Symmetric Li4O4 Cubanes. Synthesis, Crystallography and DFT Calculations

“…Conceptually, the clusters, whether they adopt the observed D2 or the much more commonly observed S4 geometry in the tetramers, are the results of combining the molecular squares discussed above for 2a-c-the primary laddered units [18]-as diagrammed in Scheme 3. Since the dimers are all transoid, the face to face combination requires not only the displacement of the two coordinated THF molecules ("L" in Scheme 3) but also folding back of one of the two chelate rings because the observed cubane structures contain cisoid rings.…”

“…Rings, ladders and higher aggregates have been obtained [15][16][17][18]. To date, there are several structurally characterised examples of lithium β-ketoiminates.…”

“…The structural chemistry of lithiated organoelement species has seen enormous development over 30 years of active investigation and is known to show great diversity of structures due to aggregation and Lewis base coordination. Rings, ladders and higher aggregates have been obtained [15][16][17][18]. To date, there are several structurally characterised examples of lithium β-ketoiminates.…”