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Kinetic and Thermodynamic Aspects of the Regioselective Addition of Bifunctional Hydroxylaminooxime-type HO-Nucleophiles to Pt-Complexed Nitriles
Version 2 2022-07-06, 18:05
Version 1 2016-05-05, 06:42
journal contribution
posted on 2006-03-06, 00:00 authored by Konstantin V. Luzyanin, Vadim Yu. Kukushkin, Maxim L. Kuznetsov, Alexander D. Ryabov, Markus Galanski, Matti Haukka, Eugene V. Tretyakov, Victor I. Ovcharenko, Maximilian N. Kopylovich, Armando J. L. PombeiroThe coupling between coordinated propiononitriles in trans-[PtCln(EtCN)2] (n = 2, 4) and the 1,2-hydroxylaminooximes
HON(H)CMe2C(R)NOH (R = Ph 1, Me 2) proceeds smoothly in CHCl3 at ca. 40−45 °C and gives trans-[PtCln{NHC(Et)ON(H)CMe2C(R)NOH}2] (n = 2, R = Ph 5, Me 6; n = 4, R = Ph 7, Me 8) in 80−85% isolated
yields. The reaction is highly regioselective, and both spectroscopic (IR; FAB+-MS; 1D 1H, 13C{1H}, and 195Pt
NMR; and 2D 1H,13C HMQC, 1H,13C HMBC, and 1H,15N HMQC NMR) and X-ray data for 6−8 suggest that the
addition proceeds exclusively via the hydroxylamine moiety of the 1,2-hydroxylaminooxime species; the existence
of an oxime group remote from the nucleophile was also confirmed. Heating of 6 in air leads to its conversion to
the unusual nitrosoalkane complex [PtCl2{HONC(Me)C(Me)2NO}] (9), whereas in the case of 5, only the metal-free salt [H3NC(Me)2C(Ph)NOH]2(NO3)Cl·H2O (10) was isolated. To compare the kinetic aspects and trends in
the addition of both types of nucleophiles (oximes and hydroxylamines; for the latter, see our recent work: Inorg.
Chem. 2005, 44, 2944) to coordinated nitriles, a kinetic study of the addition of HONC(CH2Ph)2 to [Ph3PCH2Ph][PtCl5(EtCN)] (11) to give [Ph3PCH2Ph][PtCl5{NHC(Et)ONC(CH2Ph)2}] (12) was performed. The calculated
rate constant k2 of 3.9 × 10-6 M-1 s-1 at −20 °C for the addition of the oxime indicates that the hydroxylamine
is, by a factor 1.7 × 104, more reactive toward the addition to nitriles than the oxime. Results of the synthetic,
kinetic, and theoretical (at the B3LYP level of theory) studies have demonstrated that the high regioselectivity of
the reactions of the 1,2-hydroxylaminooximes with ligated nitriles is both kinetically and thermodynamically controlled.