Author :
Amirnasr, Mehdi,Hoel, Elvin L.,Hawthorne, M. F
Descriptors :
Deuterium exchange,Metallocarboranes,Selectivity,Mechanism
Abstract :
A wide variety of substrates, including caboranes, metallocarboranes, and boron hydrides, were found to undergo catalytic isotopic exchange of terminal hydrogen with deuterium gas in the presence of various transition metal complexes. With (pph***3)***3 RuHCI as catalyst, exchange was found to proceed with stereoselectivity indicative of nucleophilic attack at boron; e.g., the order of rates for deuterium incorporation at chemically nonequivalent sites in 1.2,C***2B***10H***12 was B(3.6) > B(4,5,7,11) > B(8,10) > B(9,12). Other catalysts, most notably the series of hydridometallocarboranes. (pph***3)***2HMC***2B***9H***11 (M=Rh, Ir), showed little or no stereoselectivity during deuterium exchange. Intermediate stereoselectivity was found with (pph***3)2(CO)IrCl and (pph***3)***2IrC1 species as catalysts, while exchange catalyzed by (Asph***3)***2IrCl exhibited the stereoselectivity found with (pph***3)***3RuHCI, A mechanism is postulated which rationalizes the varied results and which involves oxidative addition of boron-hydrogen bonds to catalytic species.
