Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes – Utilization of the Liberated Imines for Further Syntheses of Mixed Imine-Diazadiene Complexes and of (E)-Cyanoalkenes

Authors

  • Jamal Lasri,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal, Fax: +351-218464455
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  • M. Fátima C. Guedes da Silva,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal, Fax: +351-218464455
    2. Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Av. Campo Grande 376, 1749-024 Lisboa, Portugal
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  • M. Adília Januário Charmier,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal, Fax: +351-218464455
    2. Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Av. Campo Grande 376, 1749-024 Lisboa, Portugal
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  • Armando J. L. Pombeiro

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal, Fax: +351-218464455
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Abstract

Treatment of trans-[PtCl2(NCR)2] (1) {R = CH2CO2Me (1a), Ph (1b)} with (R*)-camphor oxime (C9H16)C=NOH (2) gives access to the optically active mixed imine-nitrile complexes trans-(R*)-[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4), which, on reaction with ketoximes R1R2C=NOH (3) {R1 = R2 = Me (3a), C4H8 (3b)}, give the chiral unsymmetric bis(imine) complexes trans-(R*)-[PtCl2{NH=C(R)ON=C(C9H16)}{NH=C(R)ON=CR1R2}] (6) in moderate yields. An alternative route involves the reaction of the starting complexes 1 with ketoximes 3 to give the mixed imine-nitrile complexes trans-[PtCl2{NH=C(R)ON=CR1R2}(NCR)] (5), followed by reaction of the latter with (R*)-camphor oxime (2) to afford products 6 in similar yields. Treatment of complexes 1 or 4 with two or one equivalent of 2, respectively, gives the symmetrical bis(imine) complexes trans-[PtCl2{NH=C(R)ON=C(C9H16)}2] (7). These reactions are accelerated by microwave irradiation to afford, in better yields (71–50 %), the same products. The new optically active diimine compounds NH=C(R)ON=C(C9H16) (8) are quantitatively liberated upon reaction of complexes 7 with a diphosphane. The chiral diimino ester 8a (R = CH2CO2Me) acts as a protic nucleophile and efficiently couples with the coordinated nitrile in 4 to give the new optically active, mixed, unsymmetric imine-1,3-diaza-1,3-diene complexes trans-(R*,R*)-[PtCl2{NH=C(R)ON=C(C9H16)}{NH=C(R)N=C(CH2CO2Me)ON=C(C9H16)}] (9). Diimino ester 8a with an acidic α-methylene group also reacts with acyclic nitrones O+N(Me)=C(H)R′ (10) to afford stereoselectively the (E)-cyanoalkenes (N≡C)C(CO2Me)=C(H)R′ (11) {R′ = 4-MeC6H4 (11a), 2,4,6-Me3C6H2 (11b)}. All of these compounds were characterized by IR and NMR (1H, 13C, and 195Pt for metal complexes) spectroscopy, ESI-MS or FAB-MS, elemental analysis, and X-ray diffraction analysis (for 5c and 7b). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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