RADICAL PROCESSES IN THE REDUCTION OF NITROBENZENE PROMOTED BY IRON CARBONYL CLUSTERS - X-RAY CRYSTAL-STRUCTURES OF [FE-3(CO)(9)(MU(3)-NPH)](2-), [HFE3(CO)(9)(MU(3)-NPH)](-), AND THE RADICAL-ANION [FE-3(CO)(11)](-CENTER-DOT)

The halides Cl-, Br-, and I- and the pseudo-halide NCO- react with Fe-3(CO)12 (1) in aprotic solvents to induce a disproportionation reaction yielding the radical anion [Fe-3(CO)(11)](-.) (3). This species has been fully characterized by single-crystal X-ray diffraction studies of its PPh(4)(+) and PPN+ salts, although the latter was disordered. Crystal data for PPh(4).3: C35H20- Fe3O11P, monoclinic, P2(1)/n, a 11.313(2), b = 12.966(3), and c = 23.682(5) Angstrom, beta = 91.380(9)degrees, V = 3472.8(9) Angstrom(3), Z = 4, R(F) = 6.73%. In contrast to other related Fe-3 carbonyl clusters, the structures show that the anion has one semibridging CO and ten terminal CO ligands. Cluster 3 also forms upon reaction of [Fe-3(CO)(11)](2-) with ArNO2, and it disproportionates under a CO atmosphere to yield Fe(CO)(5) and [Fe3(CO)(11)](2-). The mixed-metal cluster Fe-2-Ru(CO)(12) also reads with [PPN]Cl to yield [PPN][Fe2Ru(Cl)(CO)10], a reaction which is similar to that previously observed for RU(3)(CO)(12). Reaction af[Fe-3(CO)(11)](-.) with PhNO and PhNO(2) yields a mixture of clusters which, after workup, gives azo- and azoxybenzene. When Cl5C6- NO2 was used in place of PhNO(2), the cluster [Fe-3(CO)(9)(mu(3)-NC6Cl5)]2(-) (5) was Obtained together with other products. Cluster 5 can be protonated by HBF4 to yield [HFe3(CO)(9) mu(3)-NC6Cl5)](6). The non-chlorinated analogue of 5, [PPh(4)](2)[Fe-3(Co)(9)(mu(3)-NPh)].2CH(2)Cl(2) (PPh(4).8. .2CH(2-) Cl-2), has been characterized by an X-ray diffraction study. Crystal data for PPh(4).8.2CH(2-)Cl(2): P2(1), a = 13.065(3), b = 18.114(4), and c = 13.618(3) Angstrom, beta = 98.93(2)degrees, Z = 2, R(F) = 6.94%, R(wF) = 7.30%. The cluster [HFe3(CO)(11)](-) (2) has been found to react with PhNO and ArNO2 by an initial electron-transfer process to form [HFe3(CO)(9)(mu 3-NPh](-) (7), with PhNO giving higher yields. This species has been crystallographically characterized as its PPN+ salt: Crystal data for PPN.7: P2(1)/c, a = 15.03(3), b = 21.22(3), and c = 16.12(3) Angstrom, beta = 106.71(2)degrees, Z = 4, R(F) = 10.05%, R(wF) = 11.34%, Cluster 7 reacts with PhNO in the presence of radical activators to yield azo- and azoxybenzene. The use of 2-Me-C6H4NO in this reaction gave only symmetrical ate; and azoxyarenes, implying that these products do not derive from a coupling of the imido fragment in 7 with free ArNO. Cluster 7 reacts with water to yield aniline in the presence of[Cp(2)Fe][PF6] but not in its absence. Competition experiments show that 7 is not a kinetically significant intermediate in the phase-transfer catalyzed reduction of ArNO2 by Fe-3(CO)(12)) and imply that radical intermediates are also involved in this reaction.