α–βAlkenyl isomerisation at diiron centres
Abstract
α-Substituted CH2)(μ-PPh2)] 1a–1e (R = Ph, Me, Prn, Bun or But) have been prepared via regioselective hydrodimetallation of primary
CHR)(μ-PPh2)] 2a–2e. Isomerisation is accelerated in the presence of a range of
CHR)(μ-PPh2)] 3a–3e in which the
CH2)(μ-PPh2)] 1a at 60–70 °C affords mono- and di-substituted α-alkenyl complexes [Fe2(CO)5{P(OMe)3}(μ-PhC
CH2)(μ-PPh2)] 4 and [Fe2(CO)4{P(OMe)3}2(μ-PhC
CH2)(μ-PPh2)] 5 respectively. Above 100 °C, conversion into the β-substituted isomers [Fe2(CO)5{P(OMe)3}(μ-HC
CHPh)(μ-PPh2)] 6 and [Fe2(CO)4{P(OMe)3}2(μ-HC
CHPh)(μ-PPh2)] 7 occurs cleanly. Crystallographic studies have been carried out on 1a, [Fe2(CO)6(μ-PrnC
CH2)(μ-PPh2)] 1c, [Fe2(CO)6(μ-HC
CHPh)(μ-PPh2)] 2a, [Fe2(CO)5(PPh3)(μ-HC
CHPh)(μ-PPh2)] 3a, 6 and 7 and compared with related structures. Different structural characteristics are seen between isomers, β isomers being characterised by a longer Feπ–Cβ interaction and a more obtuse Feσ–Cα–Cβ angle. The mechanisms of
∶
1 mixture of [Fe2(CO)6(μ-DC
CHPh)(μ-PPh2)] 2a-d1α and [Fe2(CO)6(μ-HC
CDPh)(μ-PPh2)] 2a-d1β. A mechanism for α–β