Isomerisation of 2-(alkenyl)pyridines by Group 6 metals

Abstract

Reactions of 2-(alkenyl)pyridines with Group 6A hexacarbonyls and [M(CO)₄(nbd)](M = Cr, Mo, or W; nbd = norbornadiene) are described. Isomerisation of the alkenyl side chain occurs with 2-(CR¹MeCR²)-, 2-(CH₂CR¹CH₂CH₂)- and 2-(CH₂CHCH₂CH₂CH₂)-C₅H₄N (R¹, R²= H or Me) to give complexes of the type [M(CO)₄L][L = 2-(prop-2′-enyl)- or 2-(substituted prop-2′-enyl)-pyridine] which have, in some cases, also been prepared directly from L; L is always bidentate. The mechanism of isomerisation is discussed. Spectroscopic studies provide no evidence for conformational isomerism involving the plane of the co-ordinated olefin. Related reactions with Ph₂P[CH₂]₂CHCH₂ and Ph₂P[CH₂]₃CHCH₂ give [Mo(CO)₄(Ph₂PCH₂CH₂CHCH₂)] and [Mo(CO)₄(Ph₂PCH₂CH₂CH₂CHCH₂)₂] respectively.