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Article

Synthesis and Asymmetric Mono-cyclopalladation of 1,1’-Di(α-dimethylamino)ethylferrocene

“Nesmeyanov” Institute of Organoelement Compounds, Russian Academy of Sciences, Russian Federation
*
Author to whom correspondence should be addressed.
Molecules 2005, 10(6), 649-652; https://doi.org/10.3390/10060649
Submission received: 11 November 2004 / Accepted: 20 December 2004 / Published: 14 July 2005
(This article belongs to the Special Issue Synthesis and Chemistry of Chiral Metallocenes)

Abstract

:
Two-step synthesis of 1,1’-di(α-dimethylamino)ethylferrocene is described in details. Cyclopalladation of this diamine involving one or two amino groups is reported and the product of asymmetric mono-cyclopalladation is fully characterized.

Introduction

Cyclopalladation is one of the most studied organometallic reactions [1]. In the ferrocene series, it was first carried out with acetate anion as nucleophilic catalyst [2]. Shortly after that we had developed the efficient asymmetric version using salts of optically active acids as catalysts [3,4].

Results and Discussion

The goal of this study was to synthesize 1,1’-bis-derivative of ferrocene which is able to give products of the double cyclopalladation and to demonstrate the optical activity of the product of asymmetric mono-cyclopalladation. 1,1’-di(α-dimethylamino)ethylferrocene was prepared in two steps starting from 1,1’-diacetylferrocene (Scheme 1). It is well-known that during cyclopalladation of ferrocenes the planar chirality arises [5,6]. Diastereoselectivity during the cyclopalladation of enantiomeric 1-dimethylaminoethylferrocene was previously [7] found to be about 70%. Therefore one can expect that a very complicated mixture of 16 (24) diastereoisomers would form as a result of double cyclopalladation of 1 because 2 chiral centres and 2 chiral planes will be present in monomeric species and even more in the primarily formed dimer 2.
Scheme 1.
Scheme 1.
Molecules 10 00649 g001
For characterization purposes, racemic dimer 2 was converted into the monomeric acetylacetonate or triphenylphosphine derivatives 3 and 4. When the reaction was carried out using an asymmetric catalyst (Na salt of N-acetyl-D-valine) the dimeric mono-cyclopalladation product 5 was isolated and converted into acetylacetonate 6, which appeared to be optical active; the (+) sign suggests the Rp configuration of chiral plane. All reactions performed are shown in Scheme 2.
Scheme 2.
Scheme 2.
Molecules 10 00649 g002

Conclusions

We have presented the synthesis of 1,1’-di(α-dimethylamino)ethylferrocene and its cyclo-palladation in non-asymmetric and asymmetric versions.

Experimental

General

1H-NMR spectra were obtained using a BRUKER 200 NMR instrument. Optical rotations were measured with a Perkin-Elmer 141 instrument. Reagents were commercial (Aldrich and other companies) and were used as received. All reactions were performed under argon.

Synthesis of 1,1’-di(α-dimethylamino)ethylferrocene (1)

LiAlH4 (1.5 g, 40 mmol) was added in portions to a red solution of 1,1’-diacetylferrocene (17.9 g, 66 mmol) in a mixture of benzene (200 mL) and anhydrous ether (150 mL). After 2 hrs of additional stirring the starting ketone had disappeared (TLC). Water (200 mL) and several drops of H2SO4 were added to the yellow solution, the organic layer was separated and the aqueous solution was extracted twice with ether. Usual work-up afforded crude 1,1’-di(α-hydroxy)ethylferrocene as a yellow oil (20 g). It was dissolved in CH2Cl2 (100 mL), mixed with NEt3 under argon, chilled and reacted immediately at –70oC with EtSO2Cl (31.6 g, 247 mmol) in CH2Cl2 (25 mL) added over 30 min. The reaction mixture was stirred during 2.5 hr, then it was allowed to warm to –50oC, poured into a solution of dimethylamine (28 g, 620 mmol) in isopropanol (100 mL) kept at the same temperature and left overnight. The reaction mixture was evaporated in vacuo at +50oC, the residue was treated with 10% H3PO4 (150 mL) and CH2Cl2 (150 mL), then the organic phase was extracted with 2% H3PO4 (2 x 50 mL). The acidic extract was washed with CH2Cl2 (100 ml) and solid Na2CO3 was added to pH 9-10. Free amine separated was taken into CH2Cl2 and usual work-up afforded 1,1’-di(α-dimethylamino)ethylferrocene (1) as a dark-orange oil (19.5 g, 89% from 1,1’-diacetylferrocene). Found, %: C 64.80; H 8.53; N 8.55. Calcd. for C18H28N2Fe, %: C 65.86; H 8.60; N 8.53; 1H-NMR (CDCl3) δ: 1.44 (d, 6H, J = 7.0, CH3-C), 2.09 (s, 12H, CH3-N), 3.60 (q, 2H, J = 7.0, CH), 4.09 (m, 8H, Cp).

Non-asymmetric double cyclopalladation of 1

Compound 1 (1.18 g, 3.6 mmol) in MeOH (8 mL) was added over 10 min to a solution of Na2PdCl4 (2.22 g, 7.55 mmol) and NaOAc·3H2O (0.98 g, 7.2 mmol) in MeOH (14 mL), stirred for 1 hr and filtered. The brown precipitate was washed with MeOH and dried over CaCl2 to obtain 1.96 g (88%) of crude dimer 2. To prepare pure acetylacetonate 3, this amount of 2 in benzene (50 mL) was mixed with solution of Na(acac) (1.56 g, 13 mmol) in MeOH (10 mL) and stirred for 30 min. After evaporation the dark residue was extracted with benzene, the solvent evaporated and the oil was triturated with small volume of pentane to give 1.6 g of orange solid 3. Found, %: C 44.51; H 5.49; N 3.24; Pd 31.08. Calcd. for C28H40N2O4FePd2, %: C 45.50; H 5.47; N 3.15; Pd 29.9. Dimer 2 (1.50 g, 2.45 mmol) and PPh3 (2.0 g, 7.6 mmol) were refluxed under argon in benzene (25 mL) during 4 hrs. Precipitate was separated and extracted with benzene. Addition of hexane to the united benzene solution afforded 1.03 g of orange triphenylphosphine complex 4, which was purified by chromatography (SiO2, benzene - NEt3). Found, %: C 58.92; H 5.20; Cl 6.03; P 5.16. Calcd. for C54H56N2Cl2FeP2Pd2.C6H6, %: C 59.43; H 5.15; Cl 5.85; P 5.11.; 1H-NMR (CDCl3) δ: 1.27 (d, 6H, J = 6.5, CH3-C), 2.64 (s, 6H, CH3-N), 3.05 (s, 3H, CH3-N), 3.07 (s, 3H, CH3-N), 4.07 (q, 2H, CH-CH3); 2.10 (d), 3.08 (d), 3.41 (t) – J = 2.2, 6H (2Cp); 7.34-7.70 (m, 30H, arenes).

Asymmetric cyclopalladation of 1

Na metal (75 mg, 3.23 mmol) was dissolved in MeOH (7 mL), N-acetyl-D-valine (515 mg, 3.23 mmol) was added, followed by a solution of 1 (1.05 g, 3.20 mmol) in MeOH (6 mL). The reaction mixture was stirred for 2.5 hrs, then water (60 mL) was added and after that the reaction mixture was extracted with CHCl3. The chloroform layer was washed with aqueous K2CO3 and usual work-up afforded 1.1 g of red oil. Trituration with methanol gave 430 mg of a brick-red coloured solid (bis-product 2) while 650 mg of dark-red oil obtained from methanolic solution was the dimeric product of mono-cyclopalladation 5 (yield 43%). It was treated with Na(acac) in MeOH to give after chromatography on SiO2 analytically pure optically active acetylacetonate 6 as yellow-orange solid in 35% yield. [α]546 + 17.4o (c = 0.01, CH2Cl2). Found, %: C 51.71; H 6.58; N 5.13. Calcd. for C23H34N2O2FePd, %: C 51.80; H 6.43; N 5.26; 1H- NMR (CDCl3) δ: 1.16 (d, 3H, J = 7.0, CH3-C), [1.44 (d, J = 7.0) 1.55 (d, J = 7.0) – 3H together, CH3-C – diastereomers], [1.95 (s, CH3(acac)), 1.98 (s, CH3(acac))], [2.08 (s, 6H, CH3-N), 2.52 (s, 3H, CH3-N), 2.80 (s, 3H, CH3-N) – diastereomers], 3.68 (q, 2H, J = 7.0, CH-C), 3.87 – 4.47 (m, 7H, 2Cp), [5.22 (s, 1H), 5.27 (s, 1H), CH(acac) – diastereomers].

References

  1. Omae, I. Organometallic Intramolecular-coordination Compounds; Elsevier: Amsterdam, 1986. [Google Scholar]
  2. Gaunt, J.C.; Shaw, B.L. J. Organomet. Chem. 1975, 19, 229.
  3. Sokolov, V.I.; Troitskaya, L.L. Chimia 1978, 32, 122–123.
  4. Sokolov, V.I.; Troitskaya, L.L.; Reutov, O.A. J. Organomet. Chem. 1979, 182, 537–540.
  5. Sokolov, V.I. Chirality and Optical Activity in Organometallics; Gordon & Breach: London, 1991. [Google Scholar]
  6. Togni, A.; Hayashi, T. Ferrocenes; VCH: Weinheim, 1995. [Google Scholar]
  7. Sokolov, V.I.; Troitskaya, L.L.; Reutov, O.A. J. Organomet. Chem. 1977, 133, C28–C30.
  • Samples availability: available from authors

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MDPI and ACS Style

Sokolov, V.; Troitskaya, L.; Bondareva-Don, V. Synthesis and Asymmetric Mono-cyclopalladation of 1,1’-Di(α-dimethylamino)ethylferrocene. Molecules 2005, 10, 649-652. https://doi.org/10.3390/10060649

AMA Style

Sokolov V, Troitskaya L, Bondareva-Don V. Synthesis and Asymmetric Mono-cyclopalladation of 1,1’-Di(α-dimethylamino)ethylferrocene. Molecules. 2005; 10(6):649-652. https://doi.org/10.3390/10060649

Chicago/Turabian Style

Sokolov, V., L. Troitskaya, and V. Bondareva-Don. 2005. "Synthesis and Asymmetric Mono-cyclopalladation of 1,1’-Di(α-dimethylamino)ethylferrocene" Molecules 10, no. 6: 649-652. https://doi.org/10.3390/10060649

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