Donald A. Krogstad1, Joon Cho1, Andrew J. DeBoer1, William R. Sanow1, and Jason Halfen2. (1) Concordia College, Moorhead, MN, (2) University of Wisconsin-Eau Claire, Eau Claire, WI
The cis-[MX2(PTA)2] (PTA=1,3,5-triaza-7-phosphaadamantane; M=Pd; X=Cl, Br and M=Pt; X=Cl, Br, I) catalyzed intramolecular hydroamination of 4-pentyn-1-amine in water was previously studied. This aqueous process was found to be viable, and the rates generally exceeded those examined in organic solvents. A kinetic and spectroscopic investigation was recently undertaken to better understand this important reaction in water. Cyclization by the catalytic precursor cis-[PdCl2(PTA)2] in D2O was first-order in metal complex and zero-order in substrate with H‡ = 20.0 ± 2.1 kcal/mol, S‡ = -7.4 ± 6.3 cal/mol.K, and Ea = 20.6 ± 2.1 kcal/mol. The square planar complex, trans-[Pt(C≡C(CH2)3NH2)2(PTA)2], was fortuitously isolated from a catalytic mixture involving cis-[PtBr2(PTA)2] . 31P NMR studies indicated that this acetylide complex, and its cis analog, were the predominant species in solution. Kinetic investigations showed that both compounds were active catalysts for the cyclization reaction. These data, in conjunction with previous rate data, 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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