Trimethylenemethane complexes structure

A number of investigations have appeared documenting the metal-mediated cleavage of a variety of cyclopropane derivatives, particularly those which are more reactive than ordinary cyclopropanes due to additional structural strain, unsaturation and/or substituents. In a pioneering study, methylene cyclopropane was shown to react with Fe2(CO)9 to furnish trimethylenemethane complex 6 [15]. 

Table 8.2. Structures of Metal Diene, Cyclobutadiene, and Trimethylenemethane Complexes...

In trimethylenemethane complexes, the metal atom is located under the central carbon atom. The terminal carbon atoms of the ligand are located in a plane which is closer to the metal atom than the central carbon, and therefore all metal-carbon distances are the same. Thus, the coordinated trimethylenemethane molecule is bent and possesses symmetry. The structures of complexes containing 4c ligands are represented in Figures 8.5 and 8.6, and the interatomic distances are given in Table 8.2. 

Similar to the first syntheses of cyclobutadiene complexes [2, 9], the first synthesis of a trimethylenemethane complex started from dichloride 2, which was treated with diironenneacarbonyl to give tricarbonyl(trimethylenemethane) iron(O) (3) in 30% yield In addition to iron(II) chloride (Scheme 10.1) [10]. The r -coordination has been confirmed by crystal structure analyses [11, 12]. Very recently, Frenking et al. published a detailed theoretical bonding analysis of some late transition metal sandwich trimethylenemethane complexes [13]. 

Another general way to prepare trimethylenemethane complexes is the reaction of trimethylenmethane dianions with metal halides. By this way. Mills et al. obtained (cyclopentadienyl)(trimethylenemethane)cobalt (21) in 18% yield by dilithiation of isobutene (19) with butyllithium/tetramethylethylenediamine (TMEDA) to dianion 20 [22,23] followed by treatment with 1 equiv. of (cyclopen-tadienyl)diiodo(triphenylphosphane)cobalt (Scheme 10.7). The crystal structure analysis shows a highly symmetric molecule with a slight pyramidalization of the trimethylenemethane ligand away from the cyclopentadienylcobalt... 

Trimethylenemethane is a special type of alkene that does not exist as the free compound. Various synthetic equivalents to the synthon 43 shown below have been reported. Trost, in particular, has exploited these compounds in 1,3-dipolar cycloaddition reactions.138 139 A metal-bound, isolated trimethylenemethane species was recently reported by Ando (Scheme 6). It resulted from the complexation of an ero-methylenesila-cyclopropene with group 8 carbonyls (Fe, Ru).140,140a The structure was proved by X-ray crystal structure analysis.29Si NMR data were consistent with the -structure shown. 

Reactions of mononuclear vinylidene complexes with other reactive metal complexes to give binuclear //-vinylidene complexes have been described above. Addition of Fe2(CO)c, to Mn(C=CHPh)(CO)2(i/-C5H5) also gives 31, by addition of a CO group to the a-carbon structural data are consistent with the delocalized formulation (31b), with its obvious resemblances to trimethylenemethane (60) ... 

In principle, this is a simple process we determine the causes of instability in the target molecule and eliminate them by appropriate transformations (substitution, complex-ation, etc.). Indeed many abnormal molecules with varied structures have now been made.32 For each problem, several solutions are possible. There is not enough space to illustrate every conceivable approach here, so we will merely consider four representative molecules norcaradiene (p. 226), cyclobutadiene, trimethylenemethane and carbene. 

Very recently an X-ray structure of a -conjugated trimethylenemethane dianion derivative complexed to two TMEDA-solvated lithium cations has been described (40). In this n complex the most symmetrical form, with the lithium atoms lying along the threefold axis, is not lowest in energy instead, a less symmetrical structure was found. 

The oxidative addition of an allylic acetate having an allylsilane structure (18) to a Pd(0) complex provides a (trimethylenemethane)palladium species (19), which undergoes [3+2] cycloaddition to a variety of electron-deficient olefins (eqs (115) and (116)) [146]. 

Binger and Weintz studied the reaction of the unsubstituted methylene-cyclopropane with carbon dioxide and obtained the 3-methy1-2-buten-4-olide in yields up to 80 % [25,26]. As shown in Figure 10, parallel to the main reaction, the formation of cotrimers, cotetramers and copentamers can not be avoided. A mechanism is proposed, in which the palladium forms a trimethylenemethane intermediate which exists in two tautomeric structures (Figure 11). By insertion of carbon dioxide palladium carboxylate complexes are formed which release the furanone. 

The addition of a carbanion to an allenyl complex leads to a trimethylenemethane derivative that has been isolated, and its structure determined by X-ray crystallography (Equation (51)). ... 

The first single crystal structure and convenient synthesis of zwitterionic Ti -trimethylenemethane palladium complexes derived from nucleophilic addition of caibanions to an allenyl complex has been reported. ... 

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