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.…”

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]…”

“…[11][12][13] However, sterically encumbered groups in the 2,5-positions increase their stability by destabilizing the κN-coordination mode, and [(η 5 -Pyr tBu2 ) 2 Fe] (Pyr tBu2 = 2,5-(Me 3 C) 2 C 4 H 2 N, 1-Fe) was the first successfully isolated and structurally characterized diazaferrocene. 14,15 Thereafter, bulky pyrrolyl ligands were employed to prepare various main-group-, [16][17][18][19][20] transition- [21][22][23][24][25] and rare-earth-metal complexes. [26][27][28][29] However, the price of increased stability was that the inherent property of the pyrrolyl system to act simultaneously as η 5 -/κN-ligand is lost.…”

Synthesis and structure of η5-bonded pyrrolyl complexes of calcium and strontium

“…Another coordination mode of the pyr* ligand was established for a binuclear zinc complex in which a pyr* ligand is bridging the two metal centers by forming a s-N donor bond to one zinc atom and coordinating the other zinc atom by the 3,4-carbon atoms of the pyr* ring in an h 2 -fashion. 3 Whereas a series of homoleptic alkyl-substituted cyclopentadienyl complexes of alkaline earth metals have been synthesized in recent years, 4 corresponding pyrrolyl (synonymous with azacyclopentadienyl) complexes of these metals have not been described until now. For this reason, we started to examine the coordination behaviour of pyr* towards alkaline earth metals and report here, the results we obtained for calcium and strontium.…”