Coordination Modes of 2,5-Di(tert-butyl)pyrrolide – Crystal Structures of HPyr*, Pyr*H·thf, (thf)2LiPyr*, and [(Me3Si)3C-Zn]2(μ-Cl)(μ-Pyr*) (Pyr* = 2,5-tBu2NC4H2)

Abstract

The lithiation of 2,5‐di(tert‐butyl)pyrrole (1) yields bis(tetrahydrofuran)lithium 2,5‐di(tert‐butyl)pyrrolide (2), which is monomeric in solution as well as in the solid state. Due to the coordination number of three for the lithium atom, short Li–O and Li–N bond lengths of 193 pm are observed. The metathesis reaction of 2 with tris(trimethylsilyl)‐methylzinc chloride (3) gives colorless bis[tris(trimethyl‐silyl)methylzinc] chloride 2,5‐di(tert‐butyl)pyrrolide (4). The pyrrolide ligand and the chlorine atom bridge the zinc atoms. One of the zinc atoms is bonded to the nitrogen atom of the pyrrolide substituent, while the other bonds to the opposite C–C bond. At 215 pm, the Zn–N bond is very long compared to those in alkylzinc amides, whereas the Zn–C distances lie in the range of Zn–C bond lengths found between zinc and η5‐bonded cyclopentadienide ligands. The molecular structures of 1 and of the low‐melting THF adduct 1·thf show a similar 2,5‐di(tert‐butyl)pyrrole molecule, but in the latter case a weak N–H···O bond is observed (N–H 97 pm, O···H 199 pm).

3-Phenyl-5-(2-pyridyl)pyrazolato Complexes of Lithium, Magnesium, Calcium, and Zinc

“…214.1 pm). A smaller value of 193.2(7) pm was observed for bis(thf)lithium 2,5-di(tert-butyl)pyrrolide with a three-coordinate lithium atom [23]. Lithium amides represent an extensively investigated class of compounds due to their enormous importance as nucleophiles in deprotonation and transamination reactions.…”

Structural Diversity in Alkali Metal Complexes of Sterically Demanding Carbazol-9-yl Ligands

“…In the solid state structure of 1 ·2THF the lithium cation is coordinated to the nitrogen atom of the 1,3,6,8-tetra- tert -butylcarbazol-9-yl ligand and two THF moieties in a trigonal planar arrangement (Σ angles around Li = 359.8°). The Li–N distance for 1 ·2THF [2.030(6) Å], which is relatively long compared to other monomeric complexes of the formula R 2 NLi(THF) 2 , ,, but is similar to those distances measured for the Li–N σ-bonds in [ 1 ] 2 and [C 12 H 8 NLi(THF) 2 ] 2 . The Li···C distances for the α-carbon atoms are 2.701(6) and 2.737(6) Å; such distances are shorter than in N -lithiopyrrole·TMEDA (2.76 Å), indicating the presence of an additional weak C···Li interaction .…”

Phosphine-substituted sterically encumbered pyrrolyl ligands – synthesis and reactivity studies

“…The H1⋯O distance is somewhat longer than the 1.99(3) Å in 1-H•THF. 20 The ring C-C bond lengths show the typical short-long-short pattern as previously observed for 1-H 20 and Pyr tBu2Me 2 H. 37 The electron delocalization within the pyrrole system can be deduced from the individual CC bond distances, which are intermediate between the distances of isolated single (d 0 (C-C) = 1.54 Å) 40 and double (d 0 (CvC) = 1.34 Å) 40 bonds. The extent of delocalization within the heterocyclic ring can be described by the parameter τ, the normalized quotient of the single and double bond length (eqn (1)) [41][42][43]…”