Synthesis, structure, and properties of chiral titanium and zirconium complexes bearing biaryl strapped substituted cyclopentadienyl ligands

Ellis, William W.; Hollis, T. Keith; Odenkirk, W.; Whelan, John; Ostrander, Robert L.; Rheingold, Arnold L.; Bosnich, B.

doi:10.1021/om00035a026

Cited by 79 publications

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“…5 This linker contains both planar and central elements of chirality which we wish to harness in our new ligand system. Figure 1An attractive retrosynthesis for planar chiral bis(2-indenyl)ligand in 2 followed from the related work by Bosnich et al 3 The indenyl groups could be built onto the cyclopentadienyl rings by reaction of the bis-Grignard of orthobis(chloromethyl) benzene (5) with N,N-dimethyl-2,1¢-bis(methylcarboxyl)ferrocene 6 followed by dehydration. …”

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confidence: 99%

Synthesis of Ferrocene Bridgedbis(2-Indenyl) Ligands

Anderson¹,

White²,

Stenson³

2002

Synlett

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An optimised synthesis of 1,1¢-bis(2-indenyl)ferrocene in 47% yield from the Pd(0)-catalysed cross coupling between 1,1¢-zincated ferrocene and 2-bromo-indene is described along with the formation of (2-indenyl) ferrocene in 40% yield. The analogous synthesis of planar chiral derivatives gave either pure N, 1¢-bis(2-indenyl)ferrocenyl]ethylamine (26%) dependent upon the amount of Pd(0) catalyst used.The design and development of catalytic enantioselective reactions is an important area of synthetic chemical research. Organometallic systems have featured prominently in this area as they can be made to possess well-defined three dimensional structures. 1 More specifically chiral ansa-metallocenes, also known as bridged metallocenes, have found wide use as catalysts that effect enantioselective bond forming processes. 2 The formation of chiral ansa-metallocenes can be complicated by the formation of meso and asymmetric metallocene isomers. 2 With the incorporation of a chiral bridging group it is possible to selectively form a single stereoisomer. An example of the use of this strategy is Bosnich's Ti[(S)-biphenacene]Cl 2 complex (1) 3 which has been used in asymmetric Lewis acid-catalysed Diels-Alder reactions. 4 We wish to extend these types of systems by investigating the effect planar chirality can impose on the arrangement of indenyl systems around a Lewis acid metal centre. This paper describes our first steps towards synthesising planar chiral metallocene ligands for assay in asymmetric catalysis.We decided initially to synthesise a novel range of planar chiral ansa-bis(indenyl) based metallocenes of type 2 as this ligand system would not suffer from the potential formation of meso isomers as the more complicated pseudo-C 2 symmetric 3 could (Figure 1). The corresponding tetrahydroindenyl complexes could be prepared by standard hydrogenation if necessary. An important feature of our systems is that they contain the readily available N,N-dimethyl-1-ferrocenylethylamine unit as the chiral bridging group which has proved highly effective for the synthesis of chiral ligands in asymmetric catalysis. 5 This linker contains both planar and central elements of chirality which we wish to harness in our new ligand system. Figure 1An attractive retrosynthesis for planar chiral bis(2-indenyl)ligand in 2 followed from the related work by Bosnich et al. 3 The indenyl groups could be built onto the cyclopentadienyl rings by reaction of the bis-Grignard of orthobis(chloromethyl) benzene (5) with N,N-dimethyl-2,1¢-bis(methylcarboxyl)ferrocene 6 followed by dehydration. Scheme 1We decided first to conduct model studies with ferrocene. The dimethyl ester 7 was synthesised by treating the corresponding known diacid 6 with SO 2 Cl 2 in MeOH (quant.). 7 Treatment of 7 with the bis-Grignard reagent 5, 8 gave the bis-carbinol 8 in 44% yield after trituration with MeOH (Scheme 1). Dehydration with p-TsOH followed by recrystallation from toluene/methanol gave the pure 1,1¢-bis(2-indenyl)ferrocene (9) in 17% unoptimised yield.With the ...

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confidence: 99%

Synthesis of Ferrocene Bridgedbis(2-Indenyl) Ligands

Anderson¹,

White²,

Stenson³

2002

Synlett

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“…In particular, their dynamic behaviour and the chiral character of their zirconium complexes play a role in determining the tacticity of the polymers [55]. Molecules such as (indenyl) 2 SiMe 2 can exist not only as a d,l mixture, 29, but also as the meso isomer 30.…”

Section: Silatropic Shifts Over Indenyl Surfacesmentioning

confidence: 99%

Symmetry Breaking in NMR Spectroscopy: The Elucidation of Hidden Molecular Rearrangement Processes

McGlinchey¹

2014

Symmetry

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Variable-temperature NMR spectroscopy is probably the most convenient and sensitive technique to monitor changes in molecular structure in solution. Rearrangements that are rapid on the NMR time-scale exhibit simplified spectra, whereby non-equivalent nuclear environments yield time-averaged resonances. At lower temperatures, when the rate of exchange is sufficiently reduced, these degeneracies are split and the underlying "static" molecular symmetry, as seen by X-ray crystallography, becomes apparent. Frequently, however, such rearrangement processes are hidden, even when they become slow on the NMR time-scale, because the molecular point group remains unchanged. Judicious symmetry breaking, such as by substitution of a molecular fragment by a similar, but not identical moiety, or by the incorporation of potentially diastereotopic (chemically non-equivalent) nuclei, allows the elucidation of the kinetics and energetics of such processes. Examples are chosen that include a wide range of rotations, migrations and other rearrangements in organic, inorganic and organometallic chemistry.

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“…Bosnich and coworkers [9] described the synthesis of biaryl-strapped bis-2-indenyl ligands (e.g. the binaphthyl-strapped ligand precursor 10 prepared from 9 (Fig.…”

Section: Preparation Of the Ligands 21 Formation Of Aryl-substitutementioning

confidence: 99%

Synthesis of Aryl- and Heteroaryl-Substituted Cyclopentadienes and Indenes and their Use in Transition Metal Chemistry

Enders¹,

Robert

2006

COC

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Synthesis, structure, and properties of chiral titanium and zirconium complexes bearing biaryl strapped substituted cyclopentadienyl ligands

Cited by 79 publications

References 0 publications

Synthesis of Ferrocene Bridgedbis(2-Indenyl) Ligands

Synthesis of Ferrocene Bridgedbis(2-Indenyl) Ligands

Symmetry Breaking in NMR Spectroscopy: The Elucidation of Hidden Molecular Rearrangement Processes

Synthesis of Aryl- and Heteroaryl-Substituted Cyclopentadienes and Indenes and their Use in Transition Metal Chemistry

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