REVERSIBLE HYDROGENATION AND DEHYDROGENATION OF CLUSTER BOUND ACIMIDOYL AND ALKYLIDENIMIDO GROUPS - SYNTHESIS OF COMPLEXES CONTAINING TRIPLY BRIDGING NITRENE AND NITRILE LIGANDS

HFe3(N=CHR)(CO)9 (6a,b)2 reacts with H2or CO to give respectively the nitrene complexes H2Fe3(NR’)(CO)9 (7a,b) or Fe3(NR’)(CO)10 (8a,b) (a, R = CH3, R’ = CH2CH3; b, R = Ph, R’ = CH2Ph). Thermolysis of 7a,b or 8a,b converts them back to 6a,b. Complexes with no hydrogen on the a carbon atom, i.e., 7d or 8d (R’ = Ph), cannot form.derivatives of type 6 but they are interconverted directly, i.e., treatment of 7d with CO yields 8d which can be reversed by heating 8d in H2. Treatment of 7a with base gives [HFe3(NR’)(CO)9]- (9a), which may also be prepared by reduction of 6a with sodium borohydride. Furthermore, complexes 9a,d may be prepared directly by reaction of CH3CH2NO2 or PhNO2, respectively, with [HFe3(CO)11]-. Complex 9a can be thermally dehydrogenated to [Fe3(N=CHCH3)(CO)9]- (4a), but this is suppressed by carbon monoxide. Air oxidation of HFe3(RC=NH)(CO)9 (5a,c) gives Fe3(RC=N)(CO)9 (10a,c) (a, R = CH3; c, R = n-Pr) which possesses the first known triply bridging nitrile ligand. Complex 10a can be reduced with hydrogen to give a mixture of 5a, 6a, and 7a, while 10c is reduced by sodium borohydride to a 1:3 mixture of [Fe3(RC=NH)(CO)9]- (3c) and [Fe3 (N=CHR)(C0)9]- (4c). An attempt to employ 3a and 4a as homogeneous catalysts for the hydrogenation of nitriles resulted in their decomposition to iron metal. Possible pathways for these transformations are discussed. © 1979, American Chemical Society. All rights reserved.