Trimethylenemethane-Fe

Iron, Ruthenium, and Osmium.—Acyclic Olefins. Matrix u.v. photolysis of (trimethylenemethane)Fe(CO)3 results in photodissociation of CO to yield the Fe(CO)2 species similar reactions are observed for (cbd)Fe(CO)3, (CeH6)Cr-(CO)3, and CpMn(CO)3. ESCA studies on (trimethylenemethane)Fe(CO)3 indicate a very positively charged central carbon in the trimethylenemethane group, consistent with previous calculations. ... 

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. 

In trimethylenemethane complexes, the metal stabilizes an unusual and highly reactive ligand which cannot be obtained in free form. Trimethylenemethanetricar-bonyliron (R=H) was the first complex of this kind described in 1966 by Emerson and coworkers (Figure 1.2) [38]. It can be obtained by reaction of bromomethallyl alcohol with Fe(CO)5. Trimethylenemethaneiron complexes have been applied for [3+2]-cycloaddition reactions with alkenes [39]. 

Phenyl-substituted trimethylenemethane iron complexes can be obtained from the methylenecyclopropanes, XLVIIa and b, when reacted with Fe(CO)j [alternatively. 

The systems studied fall into three classes. The Fe(CO)3 moiety is well known for forming many stable compounds with dienes it also forms complexes with the unstable radicals cyclobutadiene and trimethylenemethane. Few binary metal diene systems are known, but those of Mo(C4H6)3 and W(C4H6)3 have been studied. The third class is the group of compounds M(cp)L, where M = Co, Rh or Ir, cp = cyclopentadienyl group and L = conjugated or non conjugated diene. 

The analysis of the diagram representing the interaction of Fe(CO)3 with 1,3-butadiene leads to the conclusion that conformation (8.2) of Fe(C4H6)(CO)3 is the most stable (Figure 8.3). Experiments show that in the case of trimethylenemethane complexes of the type Fe(tmm)(CO)3 (tmm = trimethylenemethane and its derivatives). 

The first trimethylenemethane compound [Fe C(CH2)3 (CO)3] was obtained by reaction of 3-chloro-2-chloromethylpropene with nonacarbonyldiiron [equation (8.45)]. The carbonyl [Cr(CO)s] also reacts in an analogous manner [equation (8.46)]. A... 

The complex [Fe C(CH2)3 (CO)3] reacts with bromine to afford a 2-bromo-methylallyl iron complex [equation (8.88)]. The addition of HCl may also take place [equation (8.89)]. Some other trimethylenemethane complexes may also react in a similar manner " [equation (8.90)]. 

Oxidation of the iron compound [Fe C(CH2)3 (CO)3] by Ce(IV) causes loss of trimethylenemethane which gives an adduct with tetracyanoethylene. The HCl addition, similarly to other electrophilic substitution reactions (e.g., acylation) ... 

The complex [Fe(CO)3(ri" -13-cyclohexadiene)], useful in organic synthesis, is obtained by complexation-isomerization of the 1,4-isomer by reaction with [Fe(CO)5]. There are also other robust 18-electron complexes of unsaturated hydrocarbons as L2 ligands that are related to dienes but are instable in the free state cyclobutadiene, orthoxylylene (orthoquinodimethane) and trimethylenemethane (below). 

The reactions of various iron carbonyl complexes, such as Fe(GO)4(NMe3), with allene compounds under photo-lytic conditions, yield chelated 77 -allyliron complexes. Two brief reviews discussing the chemistry and application to organic synthesis of these (7r-allyl)tricarbonyl iron lactone complexes have appeared recently. Reaction of the iron lactone complexes with trimethyloxonium tetrafluoroborate yields the carbene complex 23 in good yields. Treatment of the cationic carbene complex with triphenylphosphine results in substitution at the terminal end of the allyl ligand of the trimethylenemethane complex 24. 

The relative steric and electronic contributions to the rotational barriers in trimethylenemethane complexes of the type [Fe(CO)2(L)( n -TMM)] (L = CO, PH3, PF3) have been determined303 using density functional calculations. 

---