Further emphasizing the basic differences between structural relatives (1) and (2) with regard to their ability to sustain bicycloconjugation is the fact that analysis of the I3C-NMR information relating to the oxa counterpart of (2a), i. e. (2c), reveals the actual AJ(6+2)=7 Hz to be significantly greater (ca. 200%) than the additive value, AJ(6+7)+AJ(6+5)=2 Hz! (see Table 1). At this early stage, one can tentatively explain the apparent increase in three-center mobility of the oxygen lone pair of (2c) (originally located at 9.1 eV)I"' chiefly on the basis of the destabilization it is expected to experience through interaction with the lower-energy (9.4 or 9.9 eV)14.61 second highest occupied symmetric131 MO of the naphthalene unit, i. e., & in free naphthalene. It is hoped that careful analysis of pertinent PE-spectroscopic information will allow us to further define the contrasting influences brought to play on the nitrogen and oxygen lone pairs by the molecular environment of (1) and (2).

No abstract

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 230. DOI:10.1002/anie.198202300

Decamethylnickelocen (1) existiert, im Unterschied zum unsubstituierten Nickelocen (2) und ahnlich wie das permethylierte Manganocen,), in drei verschiedenen stabilen Ladungsstufen, namlich als 20-Elektronen-NeutraIkomplex, als 19-Elektronen-Monokation und als 18-ElektronenDikation. -Mit einer groRen Anzahl von Elektrophilen RX reagiert 1 zu den neuartigen, permethylierten (Cyclopentadienyl)(exo-R-cyclopentadien)nickel-Kationen 131 + , ), die in den meisten Permethylmetallocenes, I11 1)Decamethylnickelocene: the Neutral Sandwich Complex, the Monocation, the Dication, and their Addition Reactionsz) Decamethylnickelocene (1) unlike its unsubstituted analog nickelocene (2) and similar to the permethylated manganocene,) exists in three stable differently charged forms, i. e. as the neutral sandwich complex with 20 valence electrons, as the 19-electron monocation, and as the 18-electron dication. -1 reacts with a wide variety of electrophiles RX to yield novel permethylated (cyclopentadienyl)(exo-R-cyc1opentadiene)nickel cations, [3] + , ), which in most cases are isolable as the hexafluorophosphate salts from water (e.g. R = H, CCI,, C,H,CO, C,H,CH,). The same type of cation is obtained from addition of nucleophiles (H-, CN-) to [112+ or of neutral radicals ((CH,),(CN)C*, C,H,-) to [ l ] + . Addition of R from the ex0 side follows in all cases from the 'H NMR spectra of the diamagnetic salts [3]X. The latter are weakly electrophilic but in some cases react with strong nucleophiles like hydride or cyanide to give the neutral (cyclopentadienyl)(cyclopentenyl)nickel complexes 4. From [3 k] + (R = CN) base (tBuOK) abstracts a proton from a methyl group at C-1 of the cyclopentadiene ligand to form neutral (q1-,-4-cyano-1,2,3,4-tetramethyl-5-methylenecyclopentenyl)(pentamethylcyclopentadienyl)nickel (4e). The stereochemical and mechanistic aspects of the above reactions are discussed.

Decamethylcobaltocen (1 b) wird aus Dibromo(l,2-dimethoxyethan)cobalt und Pentamethylcyclopentadienyllithium dargestellt. 1 b zeigt erhOhte Reaktionsbereitschaft in oxidierenden Additionen mil Elektrophilen RX. Mit Chloriodalkanen fiihrt diese Reaktion zu exo-Chloralkyl-Komplexen, Zc, e, diewiederum leichter als die entsprechenden Derivate des Cobaltocens (la) -durch solvolytische Ringerweiterung in permethylierte (Cyclohexadienyl)(cyclopentadienyl)cobalt-Kationen, [3] + , iibergehen. Deren Oxidation mit Salpeterslure fiihrt erstmals zu in beiden Ringen methylierten (Aren)(cyclopentadienyl)cobalt-Dikationen, [6f+ . Permethylmetallocenes, 11') Decsmethylcobaltocene: Preparation and Transformation into Methylated (Arene)(c)clopentadienyl)cobalt CationsDecamethylcobaltocene (1 b) is obtained from dibromo(l,2-dimethoxyethane)cobalt and pentamethylcyclopentadienyllithium. 1 b shows enhanced reactivity in oxidative addition reactions with electrophiles RX. This reaction, when performed with chloroiodoalkanes, leads to exochloroalkyl complexes, which undergo a solvolytic ring expansion reaction, again more smoothly than the analogous derivatives of cobaltocene (1 a), to form permethylated (cyclohexadienyl)(cy-clopentadieny1)cobalt cations [3]+. The latter are oxidized with nitric acid to yield for the first time (arene)(cyclopentadienyl)cobalt dications, [6]" , methylated in both ligand rings.