- 作者: Eisenberg, Richard
- 作者服務機構: Dept. of Chemistry, Univ. of Rochester, Rochester, New York, U.S.A.
- 中文摘要: Parahydrogen-included polarization (PHIP), its occurrence and mechanistic implications in homogeneous hydrogenation chemistry, and its appearance in the oxidative addition of H/sub 2/ to transition metal centers are described and analyzed. The PHIP phenomenon, which is characterized by unusual NMR absorptions and emissions in product spectra, arises when para-enriched H/sub 2/ is employed in hydrogenation of unsaturated organic substrates with a homogeneous metal catalyst or when para-enriched H/sub 2/ is added to a metal complex to form a metal dihydride. Examples of PHIP are found in ruthenium phosphine-catalyzed hydrogenations, catalysis by binuclear rhodium complexes, and in H/sub 2/ oxidative addition to Ir(I) complexes. The decay of polarization has been shown in the case of asymmetric hydrogenation catalyzed by Rh(chiraphos)/sup +/ to correlate well with the measured rate of reaction. For asymmetric hydrogenation of aprotic substrates using Noyori's Ru(BINAP)(OAc)/sub 2/ catalyst, PHIP is observed indicating a pairwise hydrogen transfer mechanism. Through the signal enhancement of PHIP, it has been possible to observe Rh hydride species never previously detected including binuclear complexes in the reaction of H/sub 2/ with RhCl(CO)(PR/sub 3/)/sub 2/(R=Ph, Me) and in hydrogenation catalysis promoted by RhCl(PPh/sub 3/)/sub 3/. Also observed in the hydrogenation catalysis is the putative olefin dihydride catalytic intermediate.
- 英文摘要: --
- 中文關鍵字: Hydrogen; Transition Metal; Hydrogenation; Polarization; Parahydrogen Induced Polarization
- 英文關鍵字: 氫;過渡金屬;氫化;極化