Towards the Limit of Atropochiral Stability: H-MIOP, an N-Heterocyclic Carbene Precursor and Cationic Analogue of the H-MOP Ligand

Authors

  • Dr. Ibrahim Abdellah,

    1. CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
    2. Université de Toulouse, UPS, INP, LCC (Laboratoire de Chimie de Coordination), 31077 Toulouse (France)
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  • Dr. Martial Boggio-Pasqua,

    1. Laboratoire de Chimie et Physique Quantiques, IRSAMC, CNRS et Université de Toulouse, 31062 Toulouse (France)
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  • Dr. Yves Canac,

    Corresponding author
    1. CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
    2. Université de Toulouse, UPS, INP, LCC (Laboratoire de Chimie de Coordination), 31077 Toulouse (France)
    • CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
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  • Dr. Christine Lepetit,

    1. CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
    2. Université de Toulouse, UPS, INP, LCC (Laboratoire de Chimie de Coordination), 31077 Toulouse (France)
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  • Carine Duhayon,

    1. CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
    2. Université de Toulouse, UPS, INP, LCC (Laboratoire de Chimie de Coordination), 31077 Toulouse (France)
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  • Prof. Remi Chauvin

    Corresponding author
    1. CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
    2. Université de Toulouse, UPS, INP, LCC (Laboratoire de Chimie de Coordination), 31077 Toulouse (France)
    • CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse (France), Fax: (+33) 561-55-30-03
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Abstract

The configurational stability of biaryl motifs is addressed for the 1-naphthyl-N-benzimidazolyl motif substituted by a single diphenylphosphinyl group at the 2-position. The atropoenantiomers of the N-methylated cation H-MIOP, a less sterically locked analogue of the neutral H-MOP ligand, were resolved by enantiospecific cleavage of the N2C[BOND]P bond of the resolved enantiomers of BIMIONAP. The latter were obtained by enantiospecific N-methylation of the previously resolved enantiomers of neutral BIMINAP. PdCl2 complexes of the P,C-chelating N-heterocyclic carbene (NHC)–phosphine ligands derived from (R)- and (S)-H-MIOP were prepared by two enantiospecific routes: by N2C[BOND]P bond cleavage from the (R)- and (S)-BIMIONAP–PdCl2 complexes, or by simultaneous coordination of the P and C atoms of the in situ generated free NHC–phosphine. The enantiomerization pathways of H-MOP, H-MIOP, and corresponding NHC–phosphine have been investigated at the B3PW91/6-31G(d,p) level of theory. The calculated enantiomerization barriers of H-MOP and H-MIOP in acetonitrile are equal to 176.0 and 146.4 kJ mol−1, respectively, and are mainly determined by the distortion of the naphthalene and/or benzimidazole motifs in the transition state. Beyond the stability of their optical rotation at room temperature, the respective calculated Oki’s racemization temperatures of 334 and 225 °C allowed us to consider both ligands as configurationally stable.

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