Platinum (II) and palladium (II) 1,3,5-triaza-7-phosphaadamantane (PTA) complexes as intramolecular hydroamination catalysts in aqueous and organic media |
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Authors: | Donald Alan Krogstad Joonhyung Cho Justin A Klitzke Heidi A Williams |
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Institution: | a Concordia College, Department of Chemistry, 901 8th Street South, Moorhead, MN 56562, United States b Minnesota State University-Moorhead, Department of Chemistry, Moorhead, MN, 56563, United States c University of Wisconsin-Eau Claire, Department of Chemistry, Eau Claire, WI 54702, United States |
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Abstract: | Complexes of the general formula cis-MX2(PTA)2] (M = Pd, Pt; X = Cl, Br, I; PTA = 1,3,5-triaza-7-phosphaadamantane) were used to study the catalytic intramolecular hydroamination/cyclization of 4-pentyn-1-amine into 2-methyl-pyrroline in water, methanol, and dimethyl sulfoxide (DMSO). Kinetic data were measured via 1H NMR under homogeneous conditions at 50 °C and showed the following trends in rate: (i) Fastest rates were observed in D2O. (ii) The Pd complexes of this study produced faster rates than the Pt complexes. (iii) The identity of the halide had no effect on the catalytic rate. Cyclization by the catalytic precursor cis-PdCl2(PTA)2] (4) in D2O was zero-order in substrate and first-order in metal complex with ΔH‡ = 20.0 ± 2.1 kcal/mol, ΔS‡ = −7.4 ± 6.3 cal/mol K, and Ea = 20.6 ± 2.1 kcal/mol. The acetylide complex, trans-Pt(C C(CH2)3NH2)2(PTA)2] (6) precipitated from a catalytic mixture involving cis-PtBr2(PTA)2] (2). Spectroscopic and kinetic studies indicated that 6 and its cis analog, 7, were the predominant species in solution and that they were both active catalysts for the cyclization reaction. These data, in conjunction with the rate trends, indicated that the mechanism of the Pd(II) and Pt(II) catalyzed hydroamination of terminal alkynylamines in aqueous solution followed a unique mechanism with cyclization of an acetylenic-amine ligand being rate determining. |
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Keywords: | Intramolecular hydroamination Water Palladium Platinum 1 3 5-triaza-7-phosphaadamantane |
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