Cyclopentadiene Alkylation and Nickel Complexes with Tri-, Tetra-, or Pentaisopropylcyclopentadienide or an Even Bulkier Lithium Alkylcyclopentadienide

Abstract

Phase transfer catalysis has been adapted to the synthesis of triisopropylcyclopentadiene isomers 1 in high yield and purity. Alkylation of sodium triisopropylcyclopentadienides with isopropyl bromide in tetrahydrofuran has been shown to be the currently most efficient way to generate tetraisopropylcyclopentadiene isomers 2, which give sodium tetraisopropylcyclopentadienide (3) upon metalation. The crucial step for the introduction of the fifth isopropyl group, the selective attack of an iminium salt at the tetraisopropylcyclopentadienide anion in the 5-position with generation of the corresponding 1,2,3,4-tetraisopropyl(6-dimethylamino)fulvene ( 4), has been carried out according to a published procedure. Addition of 1-naphthyllithium to the dimethylaminofulvene 4 yielded extremely bulky lithium dimethylamino-(1-naphthyl)methyltetraisopropylcyclopentadienide (7). Pure 1,2,4,1′,2′,4′-hexaisopropylnickelocene (8) was obtained from sodium triisopropylcyclopentadienide and nickel(II) bromide. The tetraisopropylcyclopentadienylnickel(II) bromide [(C 5

Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

“…81 The closely related nickel complex [{(C 5 H i Pr 4 )Ni} 2 (μ-CH 2 )], obtained in a very similar reaction from the corresponding tetraisopropylcyclopentadienylnickel bromide dimer [(C 5 H i Pr 4 )Ni(μ-Br)] 2 and methylmagnesium chloride, has been discussed in terms of the 18 valence electron rule. 82 The conversion of two methyl anions to methane, methylidyne, and hydride as seen in the reaction of 4 to 5 (Scheme 4) obviously involves oxidative addition of one C−H bond to the dicobalt core and could be rationalized as a consequence of the lower electron count of cobalt compared to nickel. Again the results of DFT calculations are not supporting the assumption of a direct cobalt−cobalt bond, as has been outlined in the following section on DFT calculations.…”

Coordination Chemistry of Polynitriles, I. Syntheses and Crystal Structures of [Ag(PCC)(DMF)], [Ni(DMF)6](PCC)2 and [Co(DMF)6](PCC)2 (PCC = [C5(CN)5]-, DMF = N,N-Dimethylformamide) [1]

“…Recrystallization of Ag [C 5 (CN) 5 ] from dimethylformamide gives brownish-yellow needles of the mono-solvato complex [Ag{C 5 (CN) 5 }(HCONMe 2 )], ([Ag(PCC)(DMF)]), 1, which slowly become opaque when taken out of the solvent. However, when left in contact with a drop of solvent, they can be examined by X-ray diffraction.…”

“…Ag[C 5 (CN) 5 ] was prepared according to the literature [16]. N, NDimethylformamide was obtained in analytical grade from Aldrich and used as received.…”

“…The cyclopentadienide anion [C 5 H 5 ] − and its pentaalkyl-substituted derivatives [C 5 R 5 ] − (R = Me, Et, iPr) coordinate usually to most metals via their π systems in an η 5 fashion due to the high electron density in the carbon ring [2 -5]. When the electron-donating alkyl groups are substituted by electron-withdrawing substituents like halides or ester groups either no coordination occurs at all upon treatment of appropriate metal precursors (R = halide) [6] or coordination via the donor atoms present in the substituent dominates [7].…”

“…For the preparation of η 5 -coordinated complexes of these electron-poor cyclopentadienides either the substituents have to be introduced to already η 5 -coordinated ligands or special experimental tricks have to be applied. Thus, it was possible to prepare η 5 complexes of [C 5 5 ] − (PCC) has been proven so far. The "decacyanoferrocene" reported over 40 years ago most likely contains Fe 2+ coordinated to one or more N atoms of the polynitrile ligand.…”