摘要：

This chapter discusses the developments and up-to-date review of trimethylenemethane metal complexes. Tris(carbonyl)-n 4 -trimethylenemethaneiron(0) was the first trimethylenemethane metal complex to be synthesized and was obtained from the reaction of 3-chloro-2-chloromethylprop-1-ene with [Fez 2 (CO) 9 ] or Na 2 [Fe(CO) 4 ]. The thermal extrusion of a simple molecule from an n 3 -allyl complex, to generate an n 4 -trimethylenemethane metal complex, was originally observed by Emerson. The ability of [Pd(PPh 3 ) 4 ] to promote the elimination of trimethylsilyl acetate from the allyl silane 31a and generate a highly reactive n 3 -trimethylenemethane palladium intermediate, which is considered to be of the form [Pd{n 3 -C(CH 2 ) 3 }(PPh 3 )w 2 ], was first observed by Trost and Chan. The structure of this complex has been substantiated by a single crystal X-ray study. A gas-phase electron diffraction study of tris(carbonyl)-n 4 -trimethylenemethaneiron establishes that the carbonyl ligands and a trigonalpyramidal trimethylenemethane ligand are in a staggered conformation about the iron with the central carbon being closer to the iron center than the outer methylene carbons. Initial studies have shown that iron trimethylenemethane complexes are susceptible to electrophilic attack. The cycloaddition of trimethylenemethane to alkenes can be envisaged as the Diels–Alder (471 + 2 π) reaction for the synthesis of five-membered rings. In the special cases of substituents that are good anion-stabilizing groups, the allyl carbonate 77 (Z = CN) serves as a suitable trimethylenemethane precursor.

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