SYNTHESIS OF TRIIRON CARBONYL CLUSTER COMPLEXES CONTAINING ISOMERIC TRIPLY BRIDGING ACIMIDOYL OR ALKYLIDENIMIDO GROUP DERIVED FROM THE REDUCTION OF ORGANIC NITRILES

Reaction of various iron carbonyls such as [Fe2(CO)8]2- (1) in the presence of [W(CO)5I]-, [HFe3(CO)11]- (2), or Fe(CO)5 in the presence of Nal with refluxing nitriles gives [Fe3(RC=NH)(CO)9]- (3) and [Fe3(N=CHR)(CO)9]- (4) (a, R = CH3; b, R = Ph; c, R = n-Pr). These products contain triply bridging acimidoyl or alkylidenimido groups and may be protonated to give the neutral complexes HFe3(RC=NH)(CO)9 (5) and HFe3(N=CHR)(CO)9 (6), respectively. Deprotonation of 6a gives pure 4a but deprotonation of 5a gives either pure 3a or a mixture of both 3a and 4a, depending on the base employed. Anions 3a and 4a do not interconvert but the neutral complex 5a isomerizes irreversibly to 6a at 65 °C. The complexes have been characterized by infrared, 1H NMR, mass spectroscopy, and single-crystal X-ray structure determination (see paper immediately following). The C-N stretching absorptions of 5a and 6a have been identified at 1353 and 1325 cm-1, respectively. An intramolecular H/D exchange is observed for monodeuterated complex 6a: DFe3(N=CHCH3)(CO)9 -HFe3(N=CDCH3)(CO)9 (CDC13, 35°C). For this exchange, kf = 6 × 10-4 s-1 and Keq = 1.2 ± 0.2. Complex 5a forms hydrogen-bonded adducts via the N-H hydrogen with a variety of bases. The average shift in VCO upon adduct formation is correlated with the base strength. © 1979, American Chemical Society. All rights reserved.