196403-69-7Relevant academic research and scientific papers
Comparison of the reactivity of cationic phosphenium complexes of iron containing a group 14 element ligand
Nakazawa, Hiroshi,Yamaguchi, Yoshitaka,Kawamura, Kazumori,Miyoshi, Katsuhiko
, p. 4626 - 4635 (1997)
Reactions of Cp(CO)(EMe3)Fe{PN(Me)CH2CH2NMe(OMe)} (E = Si (2a), Ge (3a), and Sn (4a)) with a Lewis acid (BF3·OEt2 or Me3SiOSO2CF3 (TMSOTf)) have been examined. The silyl complex 2a reacts with BF3·OEt2 to give a stable cationic phosphenium complex [Cp-(CO)(SiMe3)Fe{PN(Me)CH2CH2NMe}]BF 4 by OMe anion abstraction from phosphorus. This reaction is in contrast to that of the corresponding alkyl complex reported earlier showing that the phosphenium complex once formed immediately undergoes migratory insertion of the phosphenium ligand into the Fe-C bond. The X-ray analysis of [Cp(CO)(SiMe3)-Fe{PN(Me)CH2CH2NMe}]BPh 4 reveals that there is considerable double-bond character in the Fe-P bond. The rotation barrier around the Fe-P(phosphenium) bond is estimated (ΔG? (248 K) = 12.7 kcal/mol) from a variable-temperature 1H NMR study. The germyl complex 3a exhibits the same reactivity as that of 2a. In contrast, the stannyl complex 4a reacts with TMSOTf to give a stannylene complex [Cp(CO)(SnMe2)Fe{PN(Me)CH2CH2NMe-(Me)}]OTf (4e). X-ray analysis reveals that 4e is regarded as a stannylene iron complex doubly-base-stabilized by an oxygen of OTf- and one nitrogen of the PN(Me)CH2CH2NMe-(Me) ligand. In solution, there is an equilibrium between a base-stabilized and a base-free stannylene form. The activation parameter (ΔG? (188 K) = 9.0 kcal/mol) is estimated for the methyl group exchange in the stannylene ligand. The reaction of Cp(CO)(Sn-nBu3)Fe{PN(Me)CH2CH 2NMe(OMe)} with TMSOTf verifies that a cationic phosphenium iron complex is formed first and that then an alkyl migration from the Sn to the phosphenium phosphorus takes place.
