H. Miessner, SURFACE-CHEMISTRY IN A ZEOLITE MATRIX - WELL-DEFINED DINITROGEN COMPLEXES OF RHODIUM SUPPORTED ON DEALUMINATED Y-ZEOLITE, Journal of the American Chemical Society, 116(25), 1994, pp. 11522-11530
Surface reactions of well-defined Rh dicarbonyl Rh-I(CO)(2)(+) support
ed on highly dealuminated Y zeolites (Si:Al greater than or equal to 1
00) have been monitored by time-resolved FTIR spectroscopy. Rh-I(CO)(2
)(+) is partly decarbonylated in an atmosphere of diluted hydrogen at
200-250 degrees C, yielding a reactive monocarbonyl with v(CO) = 2096
cm(-1). In a gas flow of pure nitrogen this monocarbonyl transforms in
dinitrogen complexes of Rh attached to the zeolite framework. Two wel
l-defined dinitrogen complexes of Rh have been identified on the surfa
ce: a bis-dinitrogen complex Rh-I(N-2)(2)(+) with v(N-2) = 2244 and 22
18 cm(-1) and a mixed carbonyl-dinitrogen complex Rh-I(CO)(N-2)(+) wit
h v(N-2) = 2252 and v(CO) = 2062 cm(-1). The composition of these surf
ace species has been verified by ligand exchange with N-15(2) and (CO)
-O-18 and a corresponding force field calculation. The force constants
of the CO and the N-2 stretchings are lower and higher, respectively,
in the mixed carbonyl-dinitrogen complex Rh-I(CO)(N-2)(+) compared wi
th those of the dicarbonyl and the bis-dinitrogen species, reflecting
the weaker pi-acceptor ability of N-2 compared with CO. The new comple
xes are stable in flowing pure nitrogen at temperatures up to 250 degr
ees C. They react with CO, yielding the dicarbonyl, and with H-2/N-2,
forming reversibly the intermediate monocarbonyl.