Naphthalenes dianion

The lithium naphthalene was prepared in THF from lithium metal and a 25 mole % excess of naphthalene to minimize formation of the dilithium naphthalene dianion (18,19). A sample of a,w-dilithiumpolystyrene was quenched with methanol for molecular weight characterization (see Table II). 

The much larger rate constant (9) for naphthalene dianion plus diphenylethylene undoubtedly reflects the greater ease of overlap for the ring orbitals. Part of the effect also may be caused by the fact that anions will have larger orbitals than cations. 

The hydrolysis products of the potassium naphthalene dianion have been analyzed by proton NMR spectroscopy. As reported elsewhere (19), they agree with eq [l], whereas the ratio between the forms I and II is close to 3. 

Eq (3] takes into account the behavior of the potassium naphthalene dianion in the presence of an excess of naphthalene. 

In contrast to the potassium naphthalene dianion, EN gives rise to a dianionic species at concentrations higher than 0.03 mol.l- (Table II). Furthermore the EN dianion is unable to transfer one electron to another naphthalene molecule. These sharp differences are to be attributed to the participation of the -ethyl group in the metalation process. 

Figure 1. Visible and 11V spectra of (A) naphthalene radical anion (NRA) (THF, 25°C) (B) naphthalene dianion (OD values shifted upward by 0.2 unit) (C) naphthalene dianion after neutral naphthalene addition (OD values shifted upward by 1 unit the NRA concentration is the same in A and ).

Figure 2. The fi-ethylnaphthalene metalation by in THF at RT. VV spectra after (A) 10 min, NRA spectrum (B) 10 h, naphthalene dianion spectrum (OD shifted upward by 0.4 unit) (C) 50 h, isomerized fi-substituted naphthalene dianion (OD shifted upward by 0.25 unit) (D) compound corresponding to Spec-trum C, water deactivated, purified, and again metalated by (OD shifted upward...

The metalation of naphthalene 8-substituted by both an ethyl group or polyisoprene chain (PIP) is completely similar as established by the titration of the carbanions formed and the UV analysis of the reaction medium (21, 22, 25). Accordingly the naphthalene radical anion, naphthalene dianion and its further isomerization by hydrogen transfer sure successively observed and the final stage of the metalation can be represented by the following structure ... 

In the second step, oxirane has been added at -30°C to an isomerized and stable naphthalene dianion fixed at the end of the PA chain. Oxirane is completely polymerized at RT, and the crude product obtained is separated into block copolymer, starting homopolymer PA and homopolyether. The separation scheme is described in Table IV and the results obtained for a great lot of PA (PIP, PS, and PTBS) based copolymers agree with a ratio of about 90 block copolymer, 10 homo PA and only traces of homopolyether. 

The knowledge and good control of new dianionic species like 8 substituted naphthalene dianions is a very attractive tool to tailor block copolymers with the new molecular structure. This approach can be applied to develop new materials enjoying original and useful sets of properties. 

Coal Alkylation with Butyl-1- C Iodide. Potassium (26.1 mmol) was added to a stirred solution of naphthalene (3.14 mmol) in tetrahydrofuran (45 mL) under argon. After 45 min, -325 mesh coal (1.00 g) and an additional wash quantity of tetrahydrofuran (10 mL) were added. The mixture was stirred for 5 days. The excess potassium (2.98 mmol) was removed. A small quantity of insoluble coal (0.041 g) was unavoidably lost in the removal of the metal. A solution of 90%-enriched butyl-1- C iodide (6.88 g) in tetrahydrofuran (10 mL) was added to the stirred solution in 15 min. This quantity corresponds to a twofold excess of the amount of reagent needed for the alkylation of a coal polyanion with 21 negative charges per 100 carbon atoms and naphthalene dianion. Potassium iodide began to precipitate from the reaction mixture almost immediately. The alkylation reaction was allowed to proceed for 2 days. Potassium iodide rapidly settled from the reaction mixture when stirring was interrupted. 

The Alkylation Reaction. Ether solvents and naphthalene often are employed in the Sternberg alkylation reaction. Inasmuch as these substances are reactive in strongly basic solution, concern has been expressed about their polymerization reactions and about their incorporation into the alkylation product. In view of these potential problems we examined the reaction of potassium with carefully purified tetrahydrofuran at 25 C. The results shown in Figure 1, Curve A, indicate that the reaction is insignificant. On the other hand, the results shown in Figure 1, Curve B, indicate that potassium reacts rapidly with naphthalene to form naphthalene anion radical and naphthalene dianion. The reduction to the dianion is about 80% complete after 4.5 hr. 

Apart from the wide range of NMR chemical shifts of the 4njt dianions discussed in the previous section there are also variations in the line shape of the condensed polycyclic dianions. An extreme case is the naphthalene dianion (552 ) 18,150 l58) which was very rigorously studied and characterized by UV-Vis-spectroscopy 1 2,150 158)... 

In general, however, one must be concerned with the possible dominance of chemistry by small amounts of dianions. Although not seen in electrochemistry, the naphthalene dianion has been reported in the literature ll l5°-159 167) and could dictate the results of quench reactions. In the specific case of sodium naphthalene in tetrahydro-furan, kinetic analysis of a water quench directly implicites the radical anion as the chemically dominant species 150 -158-167>. In the case of the larger aromatic molecule, perylene, however, the dianion and not the radical anion is the species quenched167a). 

Removing hydrogen atoms from adjacent carbon atoms, as shown above for stilbene, is generally difficult synthetically. Preliminary work (28) has shown that dianions of acenaphthalene can be prepared by treating acenaphthene with n-BuLi in THF. Unfortunately the technique has limited applicability—for example, similar treatment of 9,10-dihydrophenanthrene does not give dianion formation (28). We have routinely used a modified version of this reaction with the base TMED for years (24, 25)—as above in the synthesis of naphthalene dianion. The dianion of phenanthrene with TMED can also be readily prepared by this reaction ... 

The bond lengths in the radical anion of naphthalene are probably intermediate between those of the naphthalene dianion and the naphthalene molecule. The lower-energy angular distortions of the molecule from planarity may however be similar in the radical and dianion species. 

Like the naphthalene dianion, the anthracene dianion is distinctly nonplanar (Figure 6). However, there is some indication from the results obtained for this complex that the angular distortions observed in both the naphthalene and anthracene dianions may be caused by interactions of the unsaturated carbanion with the LiTMED group. There are three preferred sites in anthracene to which the lithium atom is most likely to... 

Figure 32. Potential energy distribution for the naphthalene dianion electrostatic attraction between a positive point charge and the naphthalene anion where the positive charge is 3 A above the nuclear plane of naphthalene. Energy in units of f3°00 (100).

Two Methods for Preparation of Highly Reactive Uranium and Thorium Use of a Novel Reducing Agent Naphthalene Dianion... 

The UV/vis spectrum of complex 2 shows an absorption at 444nm, which disappears in the presence of air. The metalation of naphthalene by potassium has been studied previously, and a visible absorption around 450 nm vras attributed to the naphthalene dianion [80]. 

The presence of dihydronaphthalenes, especially 1,4-dihy-dronaphthalene, shows that a naphthalene dianion is present. After 2 equiv of complex 2 was stirred with 1 equiv of UCI4 in benzene for 1 h, followed by quenching with water or saturated aqueous NH4CI, only naphthalene is observed. This shows that 2 has been completely consumed in reducing the UCI4 within 1 h at room temperature. 

A considerable amount of 2 remained in the supernatant solution, and no attempt was made to isolate more crystals from this. The crystals of 2 were stored in the argon-filled dry box and were found to be stable indefinitely. Visible absorption at 444 nm of a less than 0.7 mM solution (e > 4000) confirms the presence of a naphthalene dianion [80]. 

The molecular structure of Sc2-naph (Fig. 11) was reminiscent of previously reported yttrium naphthalene complexes (Fryzuk et al., 2000). The naphthalene is distorted from planarity with C2/C3 and C2A/C3A bending in opposite directions from the plane composed of the other six carbon atoms (ca. 20° torsion angle). The C-C bonds within the naphthalene are best described as two isolated double bonds (C2=C3 and C2A=C3A), with short distances averaging 1.37 A, and a 6C, 871-electron system for the six coplanar center carbon atoms. Each scandium ion binds to Cl through C4 (or CIA through C4A) with similar distances averaging 2.51 A. These features are also reminiscent of those of the lithium naphthalene dianion [Li(TMEDA)]2(p-ri ri -CioH8) (TMEDA = tetramethylethylenediamine) (Melero et al., 2009). 

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