Pyridyl‐Functionalised Cyclopentadienyl Ligands: Building Blocks for Oligonuclear Organometallic Assemblies

Lithiated 2‐methylpyridine reacts with 2,3,4,5‐tetramethylfulvene (TMF) to give 2‐[2‐(2,3,4,5‐tetramethylcyclopenta‐1,4‐dien‐1‐yl)ethyl]pyridine (2H) after aqueous work‐up. Similarly, a mixture of 2‐methyl‐6‐[2‐(2,3,4,5‐tetramethylcyclopenta‐1,4‐dien‐1‐yl)ethyl]pyridine (3H) and 2,6‐bis[2‐(2,3,4,5‐tetramethylcyclopenta‐1,4‐dien‐1‐yl)ethyl]pyridine (4H2) was obtained from monolithiated 2,6‐dimethylpyridine and TMF. All three compounds were obtained as a roughly statistical mixture of double‐bond isomers. 2‐Lithiopyridine reacts with 2,3,4,5‐tetramethylcyclopent‐2‐enone to yield 2‐(2,3,4,5‐tetramethylcyclopenta‐1,3‐dien‐1‐yl)pyridine (5H) after acidic work‐up. This compound was obtained as a non‐statistical mixture of double‐bond isomers, which is presumably due to intramolecular hydrogen‐bond interactions. The lithiated derivatives 2Li, 3Li and 5Li react with iron(II) chloride to afford the respective ferrocenes (2)2Fe (8), (3)2Fe (9) and (5)2Fe (10). The structure of 10 was determined by a single‐crystal X‐ray diffraction study. The cyclopentadienyl ligands adopt a staggered conformation; the pyridyl rings are arranged in a stacked fashion with the closest ring‐ring contact being 3.16 Å. The distance between the iron atom and the cyclopentadienyl ring centroids is 1.66 Å.