Zur reaktion von metall-koordiniertem kohlenmonoxid mit yliden : VIII. Trimethyl(methylen)phosphoran-katalysierte isomerisierung eines eisenacyl-phosphorylids. übertragung der Cp(CO) 2FeC(O)-einheit zwischen ylidischen zentren

Abstract

The addition of MeI to the ironacyl phosphorusylide Cp(CO) 2FeC(O)CH PMe 3 (I) gives the phosphonium salt [Cp(CO) 2FeC(O)(Me)CHPMe 3]I (II), which can be dehydrohalogenated with Me 3PCH 2 to the corresponding ylide Cp(CO) 2FeC(O)(Me)CPPMe 3 (III). III is thermally stable in the pure state, but rearranges irreversibly with the addition of a trace of Me 3PCH 2 to the thermodynamically favored isomer Cp(CO) 2FeC(O)HCPEtMe 2 (IV). A plausible mechanism for the rearrangement is established, involving the intermolecular transfer of the Cp(CO) 2FeC(O)-group between the tautomeric ylides Me 3PCHMe and EtMe 2PCH 2. It is proved by the simple reaction of Cp(CO) 2FeC(O)(Me)CPEt 3 (V) with Me 3PCH 2 to give quantitatively I and Et 3PCHMe. The first ylide rearrangement involving the shift of a transition metal group is mainly induced by the better electronic stabilization of the ylidic function, when the Cp(CO) 2FeC(O) moiety is combined with a hydrogen atom.