Enantiomeric haloruthenocenium salts: synthesis of the first representatives with the use of asymmetric reduction and asymmetric cyclopalladation

doi:10.1016/S0022-328X(96)06335-8

Journal of Organometallic Chemistry

Volume 524, Issues 1–2, 1 November 1996, Pages 181-186

https://doi.org/10.1016/S0022-328X(96)06335-8 Get rights and content

Abstract

Optically active substituted ruthenocenes, (+)-RcCH(OH)Ph (I), (−)-RcCH(Me)Ph (II) and (+)-1-hydroxymethyl-2-methylruthenocene (VIII) react with molecular iodine to yield the corresponding iodoruthenocenium saltsIa, IIa, VIIIa with I₃⁻ anions. Reduction of these salts using, for example, NaBH₄ regenerates the optically active starting compounds. Ruthenocenes with electron-withdrawing substituents (COMe, COPh, COOMe) remain intact when treated with I₂, Fe(III), or Ce(IV). Asymmetric cyclopalladation of RcCH₂NMe₂ is described for the first time as the initial step of the reaction sequence leading to (+)-VIII.

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Enantiopurity determination of CN-palladacycles using 31P NMR spectroscopy with (1R,2S,5R)-menthyloxydiphenylphosphine as chiral derivatizing agent
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The known readily available phosphinite, (1R,2S,5R)-menthyloxydiphenylphosphine, was introduced as a chiral derivatizing agent for the enantiomeric purity determination of the optically active CN-palladacycles using ³¹P NMR spectroscopy. The advantages of the methodology proposed include opportunity of the in situ analysis, without any complications from geometric isomerism or palladacycle dechelation, with a rather high level of the palladacycle enantiomers spectral recognition. In addition, the valuable palladacycle may be recovered after its testing from the phosphinite adduct, and this phosphinite reagent may be also used for the racemic palladacycle optical resolution or for the enantiopurity increasing of the scalemic dimer.
Synthesis and 2D NMR spectra of (CO)<inf>2</inf>(NO)Cr[(η5- C<inf>5</inf>H<inf>4</inf>)CH+(BF<inf>4</inf>-) (η5-C<inf>5</inf>H<inf>4</inf>)]Ru(η5-C <inf>5</inf>H<inf>5</inf>) α-cynichrodenyl-α-ruthenocenylmethylium tetrafluoroborate
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Citation Excerpt :
The vast majority of these studies have been conducted on ferrocene analogs [6,7]. Carbonium ions located adjacent to ruthenocene [8,9], osmocene [9], cymantrene [10], (η6-benzene)tricarbonylchromium [10,11] and cynichrodene [12] have also been investigated, but to a lesser extent. The availability of cynichrodenylmetallocenylketone, 12, from the Friedel–Crafts acylation of cynichrodenoylchloride with ruthenocene [13] makes it interesting to synthesize a new dimetallocenyl-stabilized carbonium ion, α-cynichrodenyl-α-ruthenocenylmethylium tetrafluoroborate 10, by the reaction of the corresponding cynichrodenyl metallocenyl methanol 8 with fluoroboric acid in acetic anhydride/ether.
Reduction of (CO)₂(NO)Cr[(η⁵-C₅H₄)C(O)(η⁵-C₅H₄)]RuCp (hereafter called cynichrodenylruthenocenylketone) (12) with sodium borohydride gives cynichrodenyl ruthenocenyl methanol (8). Protonation of 8 with fluoroboric acid produces α-cynichrodenyl-α-ruthenocenylmethylium tetrafluoroborate (10). Diastereotopism of the ¹H and ¹³C nuclei was observed in all the complexes (7–10). C(2,5) and C(3,4) were unequivocally assigned on the Cp(Cr) ring of the cynichrodene moiety in the ¹³C NMR spectrum of the carbocation derivative 10, and an opposite correlation was observed for the chemical shift assignments of C(2)–C(5) of the Cp ring between ruthenocene and cynichrodene.
First enantiopure imine CN-palladacycle of non-metallocenic planar chirality with the [2.2]paracyclophane backbone
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Herein the preparation of a planar chiral imine CN-palladacycle free of redox activity is reported. The direct cyclopalladation of a [2.2]paracyclophane-derived imine (HL) afforded the racemic dimer {Pd(η²-L)(-Cl)}₂ 1; its ortho-palladated structure was confirmed by spectroscopic (¹H and ³¹P NMR) data for mononuclear derivatives and the X-ray study of the phosphane adduct (η²-L)PdCl(PPh₃) 4. Both the (S_pl,S_pl)- and (R_pl,R_pl)-enantiomers of dimer 1 were isolated by the diastereoselective decoordination of the (R_C)-valinate auxiliary ligand (Val) from the adduct (η²-L)Pd(κ²-Val) 5 using column chromatography on silica gel. The absolute configuration of these new CN-palladacycles was established by the independent synthesis of the (R_pl,R_pl)-enantiomer of dimer 1 from the pre-resolved (S_pl)-4-formyl[2.2]paracyclophane.
Cyclopalladation of enantiopure oxazolines having the prochiral CMe<inf>2</inf> moiety at position 2 of the heterocycle
2009, Polyhedron
(R)-4-Ethyl-2-(1,1-dimethylpropyl)-2-oxazoline (1) and (S)-4-tert-butyl-2-(1,1-dimethylbutyl)-2-oxazoline (2) were synthesized in two steps from the corresponding enantiopure amino alcohols and acid chlorides in a total yield of 95% and 72%, respectively. (S)-2-(1-Adamantyl-1-methylethyl)-4-isobutyl-2-oxazoline (3) was obtained from adamantyl bromide and l-leucinol in five steps in a total yield of 82%. Reactions of oxazolines 1–3 with Pd(OAc)₂ in AcOH or CH₂Cl₂ followed by treatment with LiCl afforded the corresponding μ-Cl dimeric cyclopalladated complexes 15, 17, and 20 in good yield. Compounds 15, 17, and 20 reacted with PPh₃ to furnish the corresponding mononuclear complexes 16, 19, and 21. The ³¹P NMR spectra of trans(N,P) adducts 16, 19, and 21 contained signals of two diastereomers in a ratio of ca. 1.3:1.
New principle for palladacycle resolution: Diastereoselective monomer to dimer conversion
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A new approach to optically active palladacycles was elaborated based on diastereoselective monomer to dimer transformation on an achiral sorbent. This methodology was illustrated by the preparation of both enantiomers of a cyclopalladated derivative of primary α-tert-butylbenzylamine through its (S)-prolinate complex. The advantages of the combined using of the new methodology with classical recrystallization of diastereomers and their chromatographic separation are discussed.
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The first P,C-cyclopalladated complex with planar chirality was prepared by direct cyclopalladation of prochiral di-tert-butyl(ferrocenylmethyl)phosphine. Resolution of the racemic dimer was achieved through separation of its diastereomeric (S)-prolinate derivatives. The palladacycle structure was confirmed by the ¹H NMR spectra of the dimer and its triphenylphosphine adduct and an X-ray diffraction study of the racemic dimeric complex. The absolute configuration of the planar chirality was determined by an X-ray diffraction investigation of one of two diastereomers of the (S)-prolinate derivative.

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Journal of Organometallic Chemistry

Abstract

Reference (12)

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

Cited by (22)

Enantiopurity determination of CN-palladacycles using <sup>31</sup>P NMR spectroscopy with (1R,2S,5R)-menthyloxydiphenylphosphine as chiral derivatizing agent

Synthesis and 2D NMR spectra of (CO)<inf>2</inf>(NO)Cr[(η<sup>5</sup>- C<inf>5</inf>H<inf>4</inf>)CH<sup>+</sup>(BF<inf>4</inf><sup>-</sup>) (η<sup>5</sup>-C<inf>5</inf>H<inf>4</inf>)]Ru(η<sup>5</sup>-C <inf>5</inf>H<inf>5</inf>) α-cynichrodenyl-α-ruthenocenylmethylium tetrafluoroborate

First enantiopure imine CN-palladacycle of non-metallocenic planar chirality with the [2.2]paracyclophane backbone

Cyclopalladation of enantiopure oxazolines having the prochiral CMe<inf>2</inf> moiety at position 2 of the heterocycle

New principle for palladacycle resolution: Diastereoselective monomer to dimer conversion

First enantiopure phosphapalladacycle with planar chirality. X-Ray study of the racemic dimer and (S(pl),S(C)S(N))-diastereomer of its prolinate derivative

Regular paperEnantiomeric haloruthenocenium salts: synthesis of the first representatives with the use of asymmetric reduction and asymmetric cyclopalladation

Abstract

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

Regular paper
Enantiomeric haloruthenocenium salts: synthesis of the first representatives with the use of asymmetric reduction and asymmetric cyclopalladation