Tetramethylammonium cation

It is interesting to note that although the first examples of template effects were observed in nitrogen macrocycles (see chapter 2) no template effect appears to operate in the synthesis of 72. Richman and Atkins note this in their original report . The authors replaced the sodium cation with tetramethylammonium cations and still obtained greater than 50% yield of tetra-N-tosyl-72. Shaw considered this problem and suggested that because of the bulky N-tosyl groups, .. . the loss of internal entropy on cyclization is small He offered this as an explanation for the apparent lack of a template effect in the cyclization. 

The formation of novel silicon-rich synthetic zeolites has been facilitated by the use of templates, such as large quaternary ammonium cations instead of Na+. For instance, the tetramethylammonium cation, [(CH3)4N], is used in the synthesis of ZK-4. The aluminosilicate framework condenses around this large cation, which can subsequently be removed by chemical or thermal decomposition. ZSM-5 is produced in a similar way using the tetra-.n-propyl ammonium ion. Only a limited number of large cations can fit into the zeolite framework, and this severely reduces the number of [AIO4] tetrahedra that can be present, producing a silicon-rich structure. 

In an attempt to demonstrate the existence of pentavalent nitrogen, Schlenk and Holtz studied the reaction of triphenylmethyl sodium with tetramethylammonium chloride (52). The highly colored material was strongly conducting in polar solvents and could be identified as a salt, the stability of which is due to the resonance stabilization of the triphenyl-methide anion. In the absence of such stabilizing substituent effects (53), as with n-butyl or another alkyllithium reagent, a metalation of the tetramethylammonium cation occurs, which leads to type I products (18) ... 

The addition compounds (I) are insoluble in diethyl ether, and the slurries obtained are quite stable. In more strongly solvating media, such as tetrahydrofuran or dimethoxyethane, the compounds are soluble but show rapid decomposition, with trimethylamine and polymethylene as the main products. These experiments indicate (9, 40) that when the lithium salt is trapped by donor solvent molecules, the free ylide quickly undergoes decomposition (40). No free trialkylammonium ylide has yet been prepared, even under very mild conditions (35). On the other hand, it has been shown, that the tetramethylammonium cation can even be metalated twice by organolithium reagents (102) to afford dimethyl-ammonium bismethylides ... 

As mentioned in Section 13.5.1, the transient species [BO(OH)2]-has been stabilized by hydrogen-bonding interactions with the nearest urea molecules in the host framework of the inclusion compound [(CH3)4N]+[B0(0H)2]--2(NH2)2C0-H20. A perspective view of the crystal structure along the [010] direction is presented in Fig. 20.4.16. The host lattice consists of a parallel arrangement of unidirectional channels whose cross section has the shape of a peanut. The diameter of each spheroidal half is about 704 pm, and the separation between two opposite walls at the waist of the channel is about 585 pm. The well-ordered tetramethylammonium cations are accommodated in double columns within each channel. 

Ion radius is given in parentheses, a Decomposition temperature, [Nuu]+, tetramethylammonium cation [N2222]+, tetraethylammonium cation [EMIM]+, l-ethyl-3-methylimidazolium cation. 

When considering the results obtained in the present investigation, it seems quite difficult to account for the occurrence of stacking faults in the framework of pentasils simply by the different molecular size of the tetralkylammonium cations trapped within the pores. In fact, the phenomenon occurs in the presence of tetrabutylammonium or tetramethylammonium cations which have the largest and the smallest molecular size, respectively, among the organic bases investigated. It is possible that crystallization kinetics or hydrophilicity of the quaternary ammonium cations play some role. In any case, additional experiments are needed to provide a reasonable explanation. 

There is one report of a three-dimensional actinide sulfate, [C4NH12]2[(U02)6(H20)2(S04)7], MUS-1 XXIII,83 formed by the bridging of the uranium centres by the sulfate tetrahedra. Each sulfate tetrahedron binds to four different uranium atoms to form the three-dimensional network (Fig. 7b). MUS-1 is structurally similar to Mg(U02)6(Mo04)7(H20)15 and Sr-(U02)6(Mo04)7(H20) 9.84 Channels run along the c-axis of the unit cell and are occupied by the tetramethylammonium cations. 

The third family of superconductors is based on dmit nickelate complex ion as the acceptor, which gives a CT complex with TTF [103], or anion-radical superconducting salt with tetramethylammonium cation [104]. 

Figure 24.5b Relative contributions of the predominant modes of cation rotation within the tetramethylammonium dicyanamide salt across a range of temperatures. The static state decreases rapidly with increasing temperature, as does the methyl group spinning. Isotropic tumbling begins to a very small degree at 240 K and increases dramaticaiiy above 315 K. These rotational transitions are unusual for the tetramethylammonium cation.

The vibrational spectrum of the tetramethylammonium cation in the region 150 -550 cm l contains botii torsional and vibrational modes. The vg and V19 vibrational modes of E and T2 symmetry involve C-N-C bond angle bending. These modes are Raman active and have been studied for TMA+ in several zeolite environments, although little change in frequency is observed (51). The V4 and V12 torsional modes involve partial rotation about C - N bonds and form respectively a singlet (A2) and a triplet (Ti) which are both Raman inactive. These torsional modes are directly observed in the HNS spectra and prove to be sensitive to the character of the TMA+ cation (see Table 1) environment(52). 

Wu et al. (74) found that the thermal decomposition of intracrystalline tetramethylammonium cations (A) at 150°—400°C in Y-type fauja-site, (Na)28.4(TTMA) 17.7(H)6.o(A102)52(Si02) 140, proceeds by a number of different pathways (Scheme 3). One path involves nucleophilic... 

In G, the methyl disproportionation reaction observed in thermal decomposition of tetramethylammonium cations, the hydride receiver may be a surface methoxyl group, v hile the hydrogen-deficient ( oxidized ) moiety is a formaldehyde-like species, and ultimately, C=0 and H2. Ethane was detected (H) as a minor product during the alkylation of isobutane with ethylene over REHX catalyst assuming a classical... 

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