SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF BINUCLEAR AND MONONUCLEAR IRON SYSTEMS.

Abstract

The photochemical fragmentation of Fp(η¹-CH₂C₆H₅) and Me₂Si[C₅H₄Fe(CO)₂(η¹- CH₂C₆H₅)]₂ (2) to give metal-metal bonded species and bibenzyl as products has been explored. Several singly-bridged binuclear iron complexes have been prepared, namely Me₂Si[η⁵-C₅H₄Fe(CO)(L)I]₂(L = CO; L = PPh₃; L = P(OPh)₃) and [η⁵-C₅H₅Fe(CO)I]₂[(PhO)₂PC₂H₄P(OPh)₂], and their structure explored by both spectroscopic means and X-ray analysis. The preparation of the new metal-metal bonded complex, [η⁵-C₅H₅Fe(CO)]₂[(PhO)₂PC₂H₄P(OPh)₂], is also reported. Selective alkylations and reductions of the diiodide were L = PPh₃ with n-BuLi, benzylmagnesium chloride, and LiAlH₄ have led to the preparation of mixed alkyl-iodide and alkyl-hydride compounds. Molecular and crystal structures are determined for Me₂Si[η⁵-C₅H₄Fe(CO)]₂[dppm], Me₂Si[η⁵-C₅H₄Fe(CO)]₂[dppp], and Me₂Si[(η⁵- C₅H₄)₂Fe₂(CO)₃][dppm]. Full details on the synthesis, characterization, and the electrochemistry of the binuclear complexes Me₂Si[η⁵-C₅H₄Fe(CO)]₂[L] (where L = dppm, dppe, dppp) is reported. Also complexes of the type Me₂Si[(η⁵-C₅H₄)₂Fe₂(CO)₃][L] have been isolated in the case of L = dppm and dppe. A series of tetranuclear complexes for L = dppe and dppp is presented. A variety of activated unsaturated compounds, including acrylonitrile, react with Fp(η¹- C₅H₅), where Fp = η⁵- C₅H₅Fe(CO)₂, to give [3+2]-cycloadducts in good yield. Stereospecific replacement of the Fp moiety in these cycloadducts by a -CO₂Me group with retention of configuration occurs in good yield by oxidation with ammonium cerium (IV) nitrate in carbon monoxide saturated methanol. This two-step sequence: (3+2)-cycloaddition followed by oxidation, renders Fp(η¹- C₅H₅) a synthetic equivalent of methyl 1,3-cyclopentadiene-5-carboxylate in cycloaddition reactions. Sequential reaction of η⁵-C₅Me₅Fe(CO)₂I with AgBF₄, cyclopentadiene, and finally triethylamine affords the new compound η⁵- C₅Me₅Fe(CO)₂(η¹- C₅H₅) in 75% yield. This complex has been characterized by X-ray diffraction and low temperature NMR spectroscopy.