Iron complexes, with trimethylenemethane

While the q -bonding mode in the iron complex 3 has earlier been established crystallographically [11, 12], it is remarkable that this coordination mode is observed in a 17 electron iron(III) complex as well. Dixneuf et al. treated iron(III) chloride with magnesium and dichloride 2 in the presence of phosphane ligands and obtained the respective trimethylenemethane iron(II) complexes, which were then oxidized with silver triflate resulting in the formation of cationic trimethylenemethane complexes with the ligand still being q -coordinated [30]. Bazan et al. reported a distorted coordination to zirconium [31], and... 

First, cis- and trans-2-phenylmethylenecyclopropanes-3-d were shown to give trimethyl-enemethane complexes with the deuterium at a location consistent only with disrotatory ring-opening (Figure 41). Second, reaction of 2,2-diphenylmethylenecyclopropane with a variety of iron carbonyl reagents allowed isolation of the methylenecyclopropane iron tetracarbonyl complex. This compound could be shown to give the trimethylenemethane complex on reaction with trimethylamine-N-oxide or diiron nonacarbonyl, both of which... 

JOM(322)103>. Other more exotic addition reactions of (55) have also appeared including reactions with allenes <90OM289> and phosphinimines <89JA7279,920M2613). The former reaction is an efficient method for the preparation of iron trimethylenemethane complexes. 

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)]. 

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. 

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]. 

In addition to dihalides such as 2, other organohalides can serve as precursors for the synthesis of trimethylenemethane complexes by dehalogenation. This dehalogenation can be afforded not only by iron carbonyls but also by disodium tetracarbonylferrate(-II). For example, the reaction of 2-(bromomethyl)allyliron halide 6 with Fe2(CO)g afforded trimethylenemethane complex 3 in 91% yield (Scheme 10.3) [16]. 

Mitsudo reported the synthesis of the fluoro-substituted trimethylenemethane complex 28 by treatment of the trifluoromethyl-substituted vinylcarbene iron complex 27 with K[B(sec-Bu)3H] in 34% yield (Scheme 10.10) [28]. 

In a similar way, the reaction of carbinol 96 with diironenneacarbonyl afforded heptafulvene complex 97 in 48% yield, showing a trimethylenemethane complex substructure. Further reaction with the iron reagent gave dinuclear complex 98 in 77% yield (Scheme 10.33). The products were characterized by IR, MS, and... 

Scheme 4-99. Reaction of (trimethylenemethane)iron complexes with a,P unsaturated ketones.

Cyclization of an (T -trimethylenemethane)iron complex with a double bond of a diene in an appropriate distance leads to bis(T -allyl)iron complexes (Scheme 4—100), which are presumably also intermediates in the reactions presented in Scheme 4—99. ... 

Methoxybutadiene has been complexed photochemically using Fe2(CO)9, instead of the more conventional thermal conditions. Complexation of acyclic dienes with Fe2(CO)9 constituted the first step toward trimethylenemethane complexes. All details concerning the preparation and spectral properties of tricarbonyl(butadiene)iron complexes are gathered in recent reviews. ... 

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

Substituted methylenecyclopropanes react with diiron nonacarbonyl to give trimethylenemethane and 1,3-diene iron tricarbonyl complexes . Theoretical analysis of the former... 

A tricarbonyl(trimethylenemethane)iron complex containing a cyclopropane subunit 5 was converted photochemically with an acid to give chrysanthemic acid. °... 

In contrast, isolable t/ -transition-metal complexes of trimethylenemethanes, e.g. the iron compounds 8 or 9, usually exhibit almost no tendency to undergo cycloadditions due to their extraordinary stability. Only low yields of cycloaddition products are obtained, even at elevated temperatures and prolonged reaction times, and with highly reactive alkenes such as tetracyanoethene. As in all of these cases, the complexes have to be oxidatively destroyed in order to accomplish any cycloaddition, so that catalytic pathways cannot be generated using these reactants. 

Oxidation of tricarbonyl(trimethylenemethane)iron complexes 25 containing an olefinic side chain, with Me3NO in boiling benzene, affords dibridged dicarbonyl (bis-7r-allyl)iron complexes. 

Kerber et al. succeeded in the synthesis of the first iron complexes of isobenzo-fulvene. Reaction of the dibromide 89 with Collman s reagent (disodiumtetracar-bonylferrate) afforded isobenzofulvene complexes 90 and 91 in 4 and 2% yield, respectively. 90 is a trimethylenemethane system anellated to an intact benzene ring (Scheme 10.31) [83]. 

Alternatively, (trimethylenemethane)iron complexes can be synthesized by disproportionation of tricarbonyl(2-methallyl)ironJ Enantiomerically pure tricarbonyl-(trimethylenemethane)iron complexes can be obtained by resolution of the racemic mixture via diastereomeric esters or amides. (5)-(-)-Ethyl lactate and (/ I)-(+)-a-methyl-benzylamine are employed as resolving reagents for this piupose. The chiral auxiliaries can be removed by a variety of reagents leaving the (trimethylenemethane)iron fragment unaffected. Treatment of both the corresponding Boc-protected amides and the chiral esters with diisobutylaluminum hydride (DIBAL) or methyllithium provides the primary or tertiary alcohols, respectively. Saponification of the ester with lithium hydroxide in methanol and subsequent acidification of the mixture affords the methyl ester. Treatment of the ester with triethylsilane leads to complete reduction of the functionality to leave a methyl group (Scheme 4—85). ... 

Reaction with Electrophilic AUenes. Formation of tricarbonyl(l,3-butadiene)iron(0) complexes from allenes (e.g. 57) is possible via tricarbonyl(trimethylenemethane)iron(0) intermediates (eq 35 ). ... 

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