Synthesis, Stereochemistry and Molecular Structures of Chiral-at-Metal (Cycloheptatrienyl)molybdenum Complexes Containing the Diphosphane Prophos

Brunner, Henri; Klankermayer, Jürgen; Zabel, Manfred

doi:10.1002/1099-0682(200209)2002:9<2494::aid-ejic2494>3.0.co;2-7

Cited by 7 publications

(3 citation statements)

References 23 publications

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“…Concomitantly with the line broadening, the quartets of the methyl signal of the Prophos ligand in the 1 H NMR spectra became doublets, because the coupling to phosphorus was lost. Addition of a small amount of the strongly reducing agent Cp 2 Co removed the radical cation [CpRu(Prophos)Cl] + • , allowing for good 1 H NMR spectra including a regaining of the phosphorus coupling to the H atoms in the Prophos ligand. – Measurements in the presence and absence of Cp 2 Co gave the same rate constants (Table ), although in the presence of Cp 2 Co the signals of ( S Ru , R C )- and ( R Ru , R C )-[CpRu(Prophos)D] appeared in low intensity.…”

Section: Halide Exchange In [Cpru(prophos)cl] and [Cpru(norphos)cl]mentioning

confidence: 93%

Pyramidal Stability of Chiral-at-Metal Half-Sandwich 16-Electron Fragments [CpRu(P−P′)]

et al. 2008

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The chiral-at-metal diastereomers (R Ru,R C)- and (S Ru,R C)-[CpRu(P−P′)Hal] (P−P′ = (R)-Prophos and (R,R)-Norphos, Hal = Cl, Br, and I) were synthesized, separated, and characterized by X-ray crystallography. Halide exchange and epimerization reactions were studied in 9:1 and 1:1 chloroform/methanol mixtures proceeding at room temperature or slightly above according to first-order. The rate-determining step in the Hal exchange reactions was the dissociation of the Ru−Hal bond, forming the pyramidal 16-electron intermediates (R Ru,R C)- and (S Ru,R C)-[CpRu(P−P′)]+, which maintain the metal configuration. These intermediates can invert their metal configuration or react with nucleophiles with retention of the metal configuration. The measured competition ratios showed that the inversion of the intermediates was slow compared to quenching with nucleophiles, indicating a high pyramidal stability of the 16-electron fragments (R Ru,R C)- and (S Ru,R C)-[CpRu(P−P′)]+ toward inversion in agreement with a basilica-type energy profile. Stereochemically this implies that substitution reactions in (R Ru,R C)- and (S Ru,R C)-[CpRu(P−P′)Hal] occur with predominant retention of configuration, however, accompanied by a well-defined share of inversion, a point overlooked when (R Ru,R C)- and (S Ru,R C)-[CpRu(Prophos)Cl] were extensively used as starting materials in the synthesis of a variety of organometallic derivatives. The rates of the approach to the epimerization equilibrium were much smaller than those of the Hal exchange reactions, because in the basilica-type energy profile the intermediates (R Ru,R C)-/(S Ru,R C)-[CpRu(P−P′)]+, formed in the cleavage of the Ru−Cl bond, have to cross another barrier of appreciable height for inversion. Increasing the methanol content of the solvent increased the rates of the Hal exchange and epimerization reactions. Obviously, the pyramidality of the fragments [CpRu(P−P′)]+ is enforced by the small P−Ru−P angles (83° in the Prophos derivatives and 86° in the Norphos derivatives of (R Ru,R C)- and (S Ru,R C)-[CpRu(P−P′)Hal]). Due to these small angles, intermediates (R Ru,R C)- and (S Ru,R C)-[CpRu(P−P′)]+ resist planarization and thus inversion of the metal configuration.

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Section: Halide Exchange In [Cpru(prophos)cl] and [Cpru(norphos)cl]mentioning

confidence: 93%

Pyramidal Stability of Chiral-at-Metal Half-Sandwich 16-Electron Fragments [CpRu(P−P′)]

et al. 2008

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“…Actually, compounds [CpFe(Diphos)Hal] + X − are stable and can be isolated . To get good NMR spectra, the addition of the strongly reducing agent Cp 2 Co has proven beneficial. ,, Therefore, all the NMR spectra of [CpFe(Prophos)I] were measured in the presence of a small amount of Cp 2 Co. The air sensitivity of [CpFe(Prophos)Cl] (Figure 2S, Supporting Information) is much higher than that of [CpFe(Prophos)I].…”

Section: Synthesis and Characterization Of (R Fer C)-/(s Fer C)-[cpfe...mentioning

confidence: 99%

Chiral-at-Metal Compounds [CpFe(Prophos)L] (L = Cl, I, CN), [CpFe(Prophos)CO]X (X = I, PF₆), and [IndFe(Prophos)CO]I

et al. 2011

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The compounds [CpFe(Prophos)Cl] and [CpFe(Prophos)I] were prepared in photochemical reactions of [CpFe(CO)2Cl] and [CpFe(CO)2I] with (R)-Prophos. They consist of pairs of R Fe,R C and S Fe,R C diastereomers which only differ in the configuration at the metal atom. The diastereomerically pure compounds (S Fe,R C)-[CpFe(Prophos)Cl] and (R Fe,R C)-[CpFe(Prophos)I], which have the same relative configurations, were isolated. They epimerize via change of the Fe configuration and approach the equilibria (R Fe,R C)-/(S Fe,R C)-[CpFe(Prophos)Cl] = 5/95 and (R Fe,R C)-/(S Fe,R C)-[CpFe(Prophos)I] = 95/5 in first-order reactions with half-lives of 43 min at 20 °C and 50 min at 50 °C in C6D6, respectively. The reaction of (R Fe,R C)-/(S Fe,R C)-[CpFe(Prophos)I] = 95/5 with KCN afforded the cyano complex [CpFe(Prophos)CN] in the diastereomer ratio R Fe,R C/S Fe,R C = 50/50. Both diastereomers (R Fe,R C)- and (S Fe,R C)-[CpFe(Prophos)CN] could be isolated diastereomerically pure. The compounds (R Fe,R C)- and (S Fe,R C)-[CpFe(Prophos)CN] are configurationally stable at the metal center. There is no diastereomer interconversion, not even at higher temperatures. The carbonyl complexes [CpFe(Prophos)CO]I, [CpFe(Prophos)CO]PF6, and [IndFe(Prophos)CO]I were prepared in thermal reactions of [CpFe(CO)2I] and [IndFe(CO2)I] with (R)-Prophos or in an autoclave reaction of [CpFe(Prophos)I]/NH4PF6 with CO under pressure. All the carbonyl complexes are configurationally stable at the metal center. Seven diastereomers were characterized by X-ray crystallography. Including the two diastereomers (R Fe,R C)-[CpRu(Prophos)Br] and (R Fe,R C)-[CpRu(Prophos)I], a conformational analysis of the M-Prophos chelate ring was carried out, resulting in characteristic differences between major and minor diastereomers.

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“…As ruthenium has two electrons more than molybdenum, the isoelectronic fragments (η 5 -C 5 H 5 )Ru and (η 7 -C 7 H 7 )Mo should be closely related (Chart ). This was demonstrated in a comparison of the stereochemistry of the new [(η 7 -C 7 H 7 )Mo(prophos)X] (X = Cl, I, CN, H, Me) complexes with their known counterparts [(η 5 -C 5 H 5 )Ru(prophos)X] . On the other hand, with ∼154° the cone angle of the η 7 -C 7 H 7 ligand is much larger than the cone angle of the η 5 -C 5 H 5 ligand (∼110°) .…”

Section: Introductionmentioning

confidence: 92%

Optically Active Transition Metal Complexes. 129.¹ Novel Cycloheptatrienyl−Molybdenum and Cyclopentadienyl−Ruthenium Complexes with Chiral Pyridinecarbaldiminato Chelate Ligands: Syntheses, Molecular Structures, Properties, and Stereochemistry at the Metal Atom

2002

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The reaction of [(η 7 -C 7 H 7 )Mo(η 6 -C 6 H 5 CH 3 )]BF 4 with the optically active Schiff base ligands LL 1 -LL 3 (LL 1 ) pyridine-2-carbald-(S)-1-phenylethylimine, LL 2 ) 6-methylpyridine-2-carbald-(S)-1-phenylethylimine, LL 3 ) pyridine-2-carbald-(S)-1-cyclohexylethylimine) in acetonitrile afforded the diastereomers (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 1-3 )(NCMe)]-BF 4 (1a,b, 3a,b, and 5a,b). Reaction with carbon monoxide resulted in a mixture of the diastereomers (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 1-3 )(CO)]BF 4 (2a,b, 4a,b, and 6a,b). The ligand LL 4 ) (S)-2-(4,5-dihydro-4-isopropyloxazol-2-yl)pyridine gave the pure diastereomer 9b. In both series a and b the diastereomers only differed in the configuration of the metal atom. Complex 1a,b reacted with CN t Bu and PPh 3 to give (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 1 )(CN t Bu)]BF 4 (7a,b) and (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 1 )(PPh 3 )]BF 4 (8a,b). Substitution experiments of 8a,b with PPhMe 2 revealed a significantly different reactivity of the two diastereomers. The neutral complexes (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )-Mo(LL 1 )I] (10a,b) were obtained by refluxing [(η 7 -C 7 H 7 )Mo(CO) 2 I] with LL 1 in toluene. The isoelectronic ruthenium diastereomers (R Ru ,S C )-and (S Ru ,S C )-[(η 5 -C 5 R 5 )Ru(LL 1,4 )(L′)]PF 6 (R ) H, Me, L′ ) CO, PPh 3 ) (11a,b-14a,b) were prepared analogously to their (η 7 -C 7 H 7 )Mo counterparts by starting from [(η 5 -C 5 R 5 )Ru(NCMe) 3 ]PF 6 . The diastereomers were separated by fractional crystallization. X-ray structure analyses established the conspicuously similar molecular structures of the isoelectronic molybdenum and ruthenium complexes and the absolute configurations of 2a, 7b, 8b, 9b, 10a, 12a, and 13b. In the diastereomers (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 1 )(CO)]BF 4 (2a,b), the molybdenum configuration was configurationally labile at room temperature. The epimerization 2a / 2b was a clean first-order reaction in acetone-d 6 solution (τ 1/2 ) 335 min at 21.8°C; ∆H q ) 93 ( 14 kJ mol -1 and ∆S q ) -20 ( 20 J K -1 mol -1 ). Additional experiments with the sterically more hindered 6-methylpyridine complexes (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 2 )(CO)]BF 4 (4a,b) indicated that the mechanism of the epimerization involved a chelate ring opening at the imine side of LL 1 and LL 2 . For the carbonyl complexes 2a,b the diastereomer ratio at equilibrium was 2a:2b ) 76:24, whereas for the corresponding triphenylphosphane complexes (R Mo ,S C )-and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(LL 1 )(PPh 3 )]BF 4 (8a,b) it was 8a:8b ) 4:96. These diastereomer ratios reflected the thermodynamic chiral induction from the stable ligand configuration to the labile metal configuration. In contrast to the molybdenum complexes 2a,b and 8a,b, which were configurationally labile at room temperature in acetone solution, the related ruthenium complexes (R Ru ,S C )-and (S Ru ,S C )-[(η 5 -C 5 Me 5 )Ru(LL 1,4 )(CO)]PF 6 (12a,b and 14...

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Synthesis, Stereochemistry and Molecular Structures of Chiral-at-Metal (Cycloheptatrienyl)molybdenum Complexes Containing the Diphosphane Prophos

Cited by 7 publications

References 23 publications

Pyramidal Stability of Chiral-at-Metal Half-Sandwich 16-Electron Fragments [CpRu(P−P′)]

Pyramidal Stability of Chiral-at-Metal Half-Sandwich 16-Electron Fragments [CpRu(P−P′)]

Chiral-at-Metal Compounds [CpFe(Prophos)L] (L = Cl, I, CN), [CpFe(Prophos)CO]X (X = I, PF₆), and [IndFe(Prophos)CO]I

Optically Active Transition Metal Complexes. 129.¹ Novel Cycloheptatrienyl−Molybdenum and Cyclopentadienyl−Ruthenium Complexes with Chiral Pyridinecarbaldiminato Chelate Ligands: Syntheses, Molecular Structures, Properties, and Stereochemistry at the Metal Atom

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Synthesis, Stereochemistry and Molecular Structures of Chiral-at-Metal (Cycloheptatrienyl)molybdenum Complexes Containing the Diphosphane Prophos

Cited by 7 publications

References 23 publications

Pyramidal Stability of Chiral-at-Metal Half-Sandwich 16-Electron Fragments [CpRu(P−P′)]

Pyramidal Stability of Chiral-at-Metal Half-Sandwich 16-Electron Fragments [CpRu(P−P′)]

Chiral-at-Metal Compounds [CpFe(Prophos)L] (L = Cl, I, CN), [CpFe(Prophos)CO]X (X = I, PF6), and [IndFe(Prophos)CO]I

Optically Active Transition Metal Complexes. 129.1 Novel Cycloheptatrienyl−Molybdenum and Cyclopentadienyl−Ruthenium Complexes with Chiral Pyridinecarbaldiminato Chelate Ligands: Syntheses, Molecular Structures, Properties, and Stereochemistry at the Metal Atom

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Chiral-at-Metal Compounds [CpFe(Prophos)L] (L = Cl, I, CN), [CpFe(Prophos)CO]X (X = I, PF₆), and [IndFe(Prophos)CO]I

Optically Active Transition Metal Complexes. 129.¹ Novel Cycloheptatrienyl−Molybdenum and Cyclopentadienyl−Ruthenium Complexes with Chiral Pyridinecarbaldiminato Chelate Ligands: Syntheses, Molecular Structures, Properties, and Stereochemistry at the Metal Atom