Dimerization 2+2, solid state

A detailed investigation of the structure of amorphous PcRu by large-angle X-ray scattering (LAXS)269 showed that in the solid state dimeric species exist with a Ru-Ru distance in the magnitude of a double bond. Current experiments using the extended X-ray absorption fine structure (EXAFS) method confirm these results.279... 

Topochemical control of solid state dimerizations is well illustrated by the example of the frows-cinnamic acids.(112) The a form of ftmv-cinnamic acid is known to have a molecular separation of 3.6 A between double bonds and the molecules are arranged in a head-to-tail fashion. -Cinnamic acid has approximately the same intermolecular distance in the crystal but the molecules are arranged in a parallel head-to-head manner. a-Truxillic (101) and /3-truxinic (102) acids are the products expected and observed ... 

Electron donor groups (EDG) on the aromatic ring favour its displacement to the right while electron withdrawing group (EWG) favours its displacement to the left. Selenobenzophenone monomer in solution is isolated as a dimer in the solid state. Dimerization of the stable 12 to the 1,3-ditelluretane was observed in the solid state, in solution the dimer reforms 12.25 26 Contrary to the reaction in the solid state dimerization does not take place in solution. 

Ultraviolet (UV) data for several structural types were reported in <1996CHEC-II(7)921>. Solid-state dimerization (see Section 10.23.9.1.1) of 11 at an excitation of A iax 308nm gives caged dimers via ry -dimers 12 however, the corresponding a -dimer 13, with Amax 282 nm, is photostable <1999H(51)2367>. 

Marubayashi et al. <1997J(P2)1309> have also shown that solid-state dimerization is possible and propose that there is a buffer zone in the crystal structure of 1,4-dihydropyridines that governs the solid-state photodimerization process. This is exemplified by the fact that dimethyl l,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicar-boxylate 83 cannot undergo solid-state photodimerization (Equation 21), whereas the structurally related (4/ 3, l / 3 )-methyl-l-phenyl-2-piperidinoethyl-l,4-dihydro-2,6-dimethyl-4-(2-thienyl)pyridine-3,5-dicarboxylate 84 affords a single product 5 (Scheme 2). Interestingly, when the photodimerization conditions are applied to the corresponding solution-phase reaction, the sole product is that of aromatization giving product 85. 

Wilkes, J. S., and Zaworotko, M. J., Manifestations of noncovalent interactions in the solid state. Dimeric and polymeric self-assembly in imidazolium salts via face-to-face cation-cation Il-stacking, Supramolec. Chem., 1,191-193, 1993. 

Scheme 4 CpCo dithiolenes solid state dimerization...

The stereochemistry of photodimerization in the solid state and solution has been reported for several halogenated derivatives of t-1 (Table 2) (59-62). Solid state photodimerization of stilbenes, like other alkenes, is subject to topochem-ical control viz, the two reactive double bonds must be parallel and separated by < 4.2 A (63). The photostability of t-1 in the solid state (39b,59) is consistent with its reported crystal packing (64). The halogenated stilbenes 15-20 serve to illustrate the variety of stereochemical outcomes observed for solution and solid state dimerization (eq. 11). 

Heterocyclic thiazyl radicals hold considerable potential in the design of both conductive and magnetic materials. In the pursuit of improved conductivity, a series of resonance-stabilized radicals based on diselenadiazoles, sulfaselenazoles, and diselenazoles were obtained (185-188) (Fig. 17) [298-303], Structural analyses of 187 and 188 (R1 = Me, R2 = H) confirm that lattice and n-delocalization energies are sufficient to prevent solid state dimerization of the radicals. Incorporation of selenium leads to a dramatic increase in conductivity and reduction in thermal activation energy relative to sulfur-based radicals [300],... 

Specific Interactions in Solid State Dimers of Push-Pull Molecules Motivations and Model... 

Fullerenes have also been chemically modified. The reactivity of Ceo is closer to that of an olefin rather than a benzene ring. Solid-state reaction of the fullerene with potassium cyanite results in a fullerene dimer (a dumbbellshaped fullerene see Fig. 3.3). Because the fullerene intermediate anion (with a CN substituent) is reactive in the solid state, dimerization of the fullerene occurs. In contrast, this anion is stabilized by solvation, and so dimerization does not proceed. 

All three species are copolymerizable with styrene. The three species were prepared in interesting solid-state dimerizations involving their salts and mixed salts.453-455... 

Benzo[c]cinnoline is a weakly basic compound (Section IV,A), crystallizing from water or cyclohexane in yellow, monoclinic needles of m.p. 156" C. It is very soluble in alcohols, ether, etc. An X-ray crystallographic study has shown the molecule to be only approximately planar, forming molecular pairs with opposed dipoles in the solid state dimerization also takes place in solution at low temperature. It is found that bonds 1—2, 3—4, 7—8, and 9—10 are shorter than the others of the benzene rings, indicating a degree of bond fixation with 1 as the preferred Kekule structure. 

In the solid state, dimers (18.28) supported by hydride bridges (Sn Sn = 312 pm) are present. The orange solid dissolves in Et20, hexane or toluene to give blue solutions, indicating that RSnH monomers exist in solution. This conclusion is based on the electronic spectroscopic properties (Aj x = 608 nm) which are similar to those of monomeric R2Sn compounds. 

For as long as studies are carried out in which no more than the correspondence between the general level of reactivity and the total dislocation content is examined, little real advance will be accomplished in our understanding of the role of defects in chemical reactivity. An effort has to be made to characterize more fully the nature of the dislocations, and to exclude wherever possible effects which may arise from extraneous factors such as the presence of impurities. Quite clearly, model systems need to be investigated using techniques which readily reveal the presence and influence of the dislocations. In this subsection we shall concentrate, in detail, on three major model systems the oxidation of graphite, the thermal decomposition of calcium carbonate, and the solid-state dimerization of anthracene. Related systems will also be discussed where appropriate. 

The solid state dimerization of three polymorphic forms of (24) has been reported. From these irradiations, the dimer (25) is obtained when light in the range 320-400 nm is used. The principal product (25) is obtained in 58% yield and is accompanied by several minor products. Another report of the photochemical reactivity of (24) has shown that irradiation in solution brings about aromatiza-tion quantitatively.In the crystal, however, irradiation of the (4R",TRS)-(24) affords the dimer (25). Apparently this dimerization in the crystalline phase is possible because of extra space within the crystal, but this is not so with crystals... 

Molecular-weight determination revealed dimeric self-assembly of diorganogallium thiolates [R2GaSR ]2, 75, (R = Me, R = Me, Ph, P-CIC6H4) [190]. Several structurally characterized solid-state dimers are known. Some Ga-S interatomic distances in associated organogallium thiolates are collected in Table 3.4 [204-209]. 

Unusual modes of dimerization of cinnamic acids have been found in the solid state photodimerization of the octadecyl esters of these acids. Bolt and co-workers have crystallized this ester of cinnamic acid in three different forms, one of which cyclized to an a-truxilic acid type of dimer, one of which was photo-inert, and one of which gave the 6-truxinic acid dimer. Two crystal forms of the ester of trans-p-chloro-cinnamic acid were isolated, one of which cyclized to an a-truxillic acid, the other being photo-inert. The long-chain ester group presumably modifies the crystal structure, and use of orienting groups of this type may allow the formation of other dimers not usually obtained in solid state dimerizations. 

The X-ray structures of lithiated Af,Af-diisopropylbenzamide and 1-naphthamide revealed for the first time that the oxygen coordination of the lithinm center is maintained in ortho-lithiated aromatic tertiary amides [156] like lV,lV-diisopropyl benzamide and naphthamide, giving species that have been characterized as solid-state dimers (Fig. 26.10). In a (CLi) core, each Li-ion is further stabilized by one solvent molecnle (Et O or THF) and an amide O-center [157]. These solid-state strnctnres are coherent with a CIPE-induced lithiation of benzamides through amide(0)-Li coordination. 

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