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

Abstract

Lithiated 2-methylpyridine reacts with 2,3,4,5-tetramethylfulvene (TMF) to give 2-[2-(2,3,4,5-tetramethylcyclopenta-1,4-dien-l-yl)ethyl]pyridine (2H) after aqueous work-up. Similarly, a mixture of 2-methyl-6-[2-(2,3,4,5-tetramethylcyclopenta-1,4-dien-l-yl)ethyl]pyridine (3H) and 2,6-bis[2-(2,3,4,5-tetramethylcyclopenta-l,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-l,3-dien-l-yl)pyridine (5H) after acidic work-up. This compound was obtained as a nonstatistical mixture of double-bond isomers, which is presumably due to intramolecular hydrogen-bond interactions. The lithiated derivatives 2Li, 3Li and 5Li react with iron(I1) chloride to afford the respective ferrocenes (2),Fe ( 8 ) , (3),Fe (9) and (5),Fe (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 A. The distance between the iron atom and the cyclopentadienyl ring centroids is 1.66 A.We have recently described the first example of a pentamethylcyclopentadiene functionalised with a pendant pyridyl unit"]; compound 1H could be obtained in 60% yield by the addition of lithiated 4-tert-butyl-2-isopropylpyridine to tetramethylfulvene (TMF)L2] and subsequent aqueous work-up. + (mixture of isomers)Donor-functionalised cyclopentadienyl systems such as 1 are of great current interestI31. They belong to the rapidly growing class of hemilabile ligands['x41 and have, for example, proved useful for the "reversible" stabilisation of reactive metal-ligand fragments (serving, for example, as Results and DiscussionThe strategy for the synthesis of l H , which is based on the use of TMF as synthetic equivalent for the cyclopentadienyl moiety, was extended to the preparation of compounds 2H and 3H. These cyclopentadienes were obtained as yellow oils in 38% (2H) and 45% (3H) yield, respectively, after vacuum distillation. Owing to deprotonation equilibria, the bis(cyc1opentadiene) 4H2 was obtained as a side product (1 ~Y o yield) in the latter case (Scheme 1). Chem Bev 1995,128,481 -485 The steric and electronic properties of cyclopentadienyl ) H20This strategy cannot be extended, however, to the preparation of pyridyl-functionalised cyclopentadienes containing a single methylene spacer group between the pyridine and cyclopentadiene ring: When 2-lithiopyridine (prepared

A Lutetium Allyl Complex That Bears a Pyridyl‐Functionalized Cyclopentadienyl Ligand: Dual Catalysis on Highly Syndiospecific and cis‐1,4‐Selective (Co)Polymerizations of Styrene and Butadiene

“…AFM micrographs of a spin-coated thin film of (cis-1,4-PBD)-block-(syn-PS) diblock copolymer obtained by the concurrent addition of two monomers (Table 2, [17d] The ligand C 5 Me 4 HÀC 5 H 4 N was synthesized as described earlier. [25] [Ph 3 C][BA C H T U N G T R E N N U N G (C 6 F 5 ) 4 ] was synthesized following the literature procedures. [26] X-ray crystallographic studies: Crystals for X-ray analysis were obtained as described in the preparations below.…”

Octamethyl-1, 1′-di(2-pyridyl)ferrocene: A Redox-Active Ligand with a Pronounced Selectivity for Divalent Metal Ions

“…In order to investigate the influence of different positive charges on our system, we have synthesised the N-alkyl- (2) 142.5(7), C(1)ϪC(5) 143.6(6), C (2)ϪC (3) 142.2(7), C(3)ϪC(4) 143.1(6), C(4)ϪC (5) 143.3(6), C(5)ϪC (10) 146.7(6), C(16)ϪC (17) 143.2(6), C (16)ϪC (20) 144.1(6), C(17)ϪC (18) 142.0(6), C(18)ϪC (19) 143.2(6), C (19)ϪC (20) 144.3(6), C (20)ϪC (25) 147.9(6); C (10)ϪN (1)ϪC (14) 120.6(6), C (10)ϪN (1)ϪC (15) 120.0(5), C (14)ϪN (1)ϪC (15) 119.4(5). ated cations 1Me ϩ , 1Me 2 2ϩ , 1Bzl ϩ and 1Bzl 2 2ϩ from 1 and methyl iodide and benzyl bromide, respectively. 1MeI has been characterised by single-crystal X-ray diffraction (Fig.…”

“…The effect of alkylation on the ironϪring centroid distances (166 Ϫ 167 pm) is negligible. The cyclopentadienyl ring tilt [14] and twist angles [15] increase upon alkylation (1 1.1°/ 4.3° [16], 1Me ϩ 4.4°/24.5°). These trends are also observed for the dimethylated 1Me 2 2ϩ , in which case, however, the quality of the crystal structure determination is not sufficient to allow a detailed discussion.…”

“…1MeI: A solution of 1 [16] (0.25 g, 0.55 mmol) and methyl iodide (0.08 g, 0.56 mmol) in acetonitrile (40 mL) was stirred at room temperature for 5 d. Volatile components were removed in vacuo, leaving a violet solid, which was washed with n-hexane (3 ϫ 20 mL) and dried in vacuo. The reaction mixture was allowed to warm to room temperature.…”

“…The two individual molecules present in the unit cell show disordered thiophenyl rings. A striking structural feature is that the two 2-thiophenyl groups are located at opposite ends of each molecule, whereas pronounced intramolecular π-stacking of the 2-pyridyl groups is observed in the case of 1 [16].…”