Oligomeric Chain Structures of Substituted (Dialkylaminomethyl)cyclopentadienyllithium Compounds:  Structural Variations Characterized by Different Involvement of the Internal Amino Donor Ligands in the Solid State

Abstract

Treatment of 6-dimethylaminofulvene (8) with propynyllithium (9a) results in a clean nucleophilic addition at the electrophilic fulvene carbon atom C6 to yield the substituted lithium cyclopentadienide system [C5H4CH(C⋮CCH3)N(CH3)2]Li (10). Likewise, the addition of p-tolyllithium, n-butyllithium, or phenyllithium resulted in the analogous substituted lithium cyclopentadienide systems [C5H4CH(R)N(CH3)2]Li, 11 (R = p-tolyl), 12 (R = C4H9), or 13 (R = Ph), respectively. These four Li−cyclopentadienide systems were characterized by single crystal X-ray structural analyses. This has revealed a series of gradually different oligomeric [C5H4CH(R)N(CH3)2]Li structural aggregate types in the solid state. Compound 10 crystallizes with 1 equiv of THF that is coordinated to Li. The metal is η5-coordinated to the Cp ligand and κN-bonded to the −N(CH3)2 substituent of the next ligand (Li−N 2.181(7) Å), thereby constructing an oligomeric chain of a (THF)Li(η5-Cp)(L-κN) type. The compound 11 crystallizes without incorporation of solvent. Here the oligomeric chain is constructed by η5-Cp coordination to lithium and again κN-bonding of the −N(CH3)2 donor of the adjacent ligand to the metal center. In the solvent-free system 11 the resulting Li−N linkage (2.032(5) Å) is much shorter than in 10. In 12 a beginning coordination of the lithium atom to both its neighboring Cp rings is observed. A Li cation is η5-coordinated to one face of the C5H4 ring system, whereas another lithium atom in the oligomeric chain structure is bonded in a η2-fashion from the other face, assisted by κN-coordination of the attached dimethylamino substituent. Eventually, two very different coordination geometries around lithium are characteristic for the oligomeric chain structure of 13: atom Li1 is rather symmetrically η5-coordinated in a metallocene fashion to two cyclopentadienides, whereas the adjacent Li2 atom is coordinated to two −N(CH3)2 groups, assisted by a weaker η2- to η4-Cp coordination to the attached Cp ring systems. Supporting quantum chemical calculations have revealed rather shallow minima and easy conversions between these structural types. The [C5H4CH(R)NR2‘]- ligand is thus suited to experimentally realize a whole family of novel oligomeric (CpLi) n structural types.

New Lithium Phosphonium Diylides: A Methylene and a Cyclopentadienyl Moiety as Ylidic Coordination Sites

“…Compounds 9 and 11 represent lithium cyclopentadienyl derivatives with an additional neutral coordination site attached to the Cp fragment. Complexes known in the literature which also belong to this small class of compounds usually form oligomeric structures in the solid state . Thus, a dimeric arrangement as observed in the case of 9 and 11 is unprecedented for such compounds.…”

Synthesis of an Amino-Functionalized ansa-Zirconocene by Intramolecular Photochemical Enamine [2+2]Cycloaddition

“…We had previously shown that 6-dialkylaminofulvenes 3 are readily deprotonated to yield the enamino-substituted Cp-anion equivalents 4 . ,, Treatment of the examples 4b (diethylamino) and 4c (piperidino) with zirconium tetrachloride under carefully controlled reaction conditions gave the bis(enamino-Cp)ZrCl 2 products 5b and 5c , respectively. Their treatment with a Lewis acid (ZrCl 4 ) or a Bro̷nsted acid (R 3 NH + ) catalyst resulted in a rapid intramolecular Mannich-type condensation reaction to yield the unsaturated C 3 -bridged ansa -metallocenes 6b and 6c , respectively (see Scheme 2).…”

Synthesis and Dynamic Features of (Chloro)zirconocene Cations Stabilised by Pendant (Diarylphosphanyl)alkyl and (Dimethylamino)alkyl Substituents at Their Cyclopentadienyl Ring Systems

“…The synthesis started from 6‐(dimethylamino)‐6‐methylfulvene 23. Hydride addition gave the Li[C 5 H 4 −CHMe−NMe 2 ] reagent,24 which was then transmetallated with zirconium to yield a meso / rac mixture of [(C 5 H 4 −CHMe−NMe 2 ) 2 ZrCl 2 ] ( 6b ). Methyllithium addition to 6‐(dimethylamino)‐6‐methylfulvene25 gave Li[C 5 H 4 −CMe 2 −NMe 2 ].…”