The reaction between [Et4N]2[ReOCl5] and (C6F5NHCH2CH2)3N (H3[N3NF]) in CH3CN at room temperature in the presence of NEt3 yielded air stable, emerald green, diamagnetic [(C6F5NCH2CH2)2NCH2CH2NHC6F5]Re(O)Cl (1). The reaction between 1 and Ta(CH-t-Bu)(THF)2Br3 gave paramagnetic [N3NF]ReBr (2). An X-ray structure of a sample of 2 showed it to be analogous to that of [N3NF]MoCl. Reduction of 2 by methyllithium (or more conveniently by Mg) in the presence of a variety of two-electron ligands gave complexes of the type [N3NF]Re(L) (L = H2, ethylene, propylene, CO, N2, phosphines, pyridine, tetrahydrothiophene, acetonitrile, or silanes). An X-ray structure of [N3NF]Re(ethylene) showed η2-ethylene to be bound in the apical “pocket” with its C−C axis lying in one of the Nax−Re−Neq planes. Protonation of the PMe3 complex gave an authentic hydrido phosphine complex, {[N3NF]Re(H)(PMe3)}+, but protonation of other phosphine complexes gave species in which coupling between H and P is relatively large (∼60 Hz) and therefore that are believed to have some {[N3NF]Re(η2-HPR x H3 - x )}+ character. An X-ray study of {[N3NF]Re(H)(PHPh2)}+ confirmed that one proton is terminally bound to phosphorus and that the phosphorus is “off-axis” in order to accommodate the “hydride” in the same plane.

2,6-Dimethyl-N-(2,2,5,5-tetramethylcyclopentylidene)aniline (4h) is obtained by permethylation; it forms salts (5) by Nprotonation. Its CN double bond is strongly shielded against nucleophilic attack and cannot be hydrolyzed. Nitration and bromination occur smoothly in the aromatic p-position (12,13),showing the directing power of the lone electron pair of the imino function. This x-donor quality is assessed by probing weaker electrophiles and by qualitative competition experiments.The plans to construct sterically strongly hindered Schiff bases arose from projects to develop suitable isoelectronic and isosteric model substances for the non-observable carbanions of vinyllithium compounds. We also hoped that the emerging structural system would allow an unequivocal elucidation of the mechanism of anti/ syn stereomutation[21 for both classes of compounds. Such stereomutation is sterically accelerated[*] in the tetramethyl-2-indanylidene series 1; it was expected that increased front strain along the CN double bond"] should cause a larger acceleration in the system 2. This was indeed observedr41 and explained by increased internal pressure of the 5,s-dimethyl group against the N-aryl moiety, because the 3,4-single bond[31 of t is longer than the C-8/C-9 bond of 1. For easier interpretation of such data, we had chosen the Ncyclopentylidene derivatives 2 rather than the corresponding Ncyclohexylidene analogues in order to avoid stereodynamic complications by chair inversion. Our synthetic route involves permethylation of lithiated imines 3, as described in Section A.

E/Z) Equilibria. Part 16. Lone Electron Pair Donor Quality of the Imino Function: Synthesis and Reactivity of Sterically Strongly Congested Iminocyclopentanes.-Sterically strongly hindered Schiff bases are constructed in order to develop suitable isoelectronic and isosteric model substances for the non-observable carbanions of vinyllithium compounds. (V) is obtained by permethylation; it forms salts such as (VI) by N-protonation. The C= N double bond is strongly shielded against nucleophilic attack and cannot be hydrolyzed. Nitration (and bromination) occur in the aromatic ring showing strongly the directing power of the lone pair of the imino function. This π-donor quality is assessed by probing weaker electrophiles and qualitative competition experiments. -(KNORR, R.; HINTERMEYER-HILPERT, M.; MEHLSTAEUBL, J.; HOANG THI PHUNG; NEUNER, B.; BOEHRER, P.; Chem.

The title compound (1) was chosen as a model for the α/α′‐regioselectivity of deprotonation and subsequent alkylation adjacent to the C=N bond. With the bulky base lithium N,N‐diisopropylamide (LDA) as a catalyst, the one‐pot deprotonation steps can be performed through titration with methyllithium, using gas‐volumetric observation of the liberated methane. In the first step with ensuing methylation by iodomethane, the primary product is born at −40 °C in its metastable (Z) configuration (kinetic control) and may be either isolated or converted in situ at 30 °C into its thermodynamically favored (E)‐isomer via cis to trans stereoinversion at the N‐atom. Being slow enough on the laboratory time scale, this stereoinversion process can serve to control the regioselectivity of the second deprotonation/alkylation sequence as follows. The α,α′‐products are formed from the intermediate (Z)‐imine, whereas α,α‐products result from the intermediate (E)‐imine; in either case, syn deprotonation (cis to tBu at nitrogen) by LDA is apparently disfavored by the tBu group, so that anti deprotonation becomes obligatory. If a third one‐pot deprotonation step is too slow with LDA, it may be performed with the stronger base butyllithium/HMPA which, however, reacts regio‐unselectively. Regioselective one‐pot, LDA‐catalyzed deprotonation with alkylation by oxiranes (alone, or alternatingly with iodomethane) opens a short access to spiro‐[2.4]heptan‐4‐ones.