LIGAND-TRANSFORMATION SYNTHESES AND STEREOPHYSICAL INVESTIGATIONS OF 48-ELECTRON MIXED CP-CP' TRIANGULAR MNFE2 CLUSTERS CONTAINING MNFE2(MU-2-CO)2(MU-2-NO)(MU-3-NX) CORES (WHERE X=O, OH, OME, H) - STRUCTURAL-BONDING CONSEQUENCES DUE TO CONVERSIONS OF A CAPPING NITROSYL (MU-3-NO)LIGAND INTO ELECTRONICALLY EQUIVALENT (MU-3-NOR)-3-NH)+ LIGAND AND TOTHE ONE-ELECTRON REDUCTION OF AN IMIDO-CAPPED MNFE2 CLUSTER( LIGANDS (R=H, ME) AND INTO AN IMIDO (MU)

Ligand-transformation syntheses of a series of 48-electron mixed Cp/Cp ' triangular heterometallic clusters containing MnFe2(mu2-CO)2(mu2-NO) (mu3-NX) cores (where Cp and Cp' denote eta5-C5H5 and eta5-C5H4Me, res pectively; X = O, OH, OMe, and H) are presented herein. These compound s were characterized by single-crystal X-ray diffraction, IR, H-1 NMR, laser-desorption FT mass spectrometric, and electrochemical studies; one reduced 49-electron cluster was additionally characterized by EPR measurements. The (mu3-NH)+-containing imido MnFe2 monocations were ob tained directly (i.e., with no detectable (mu3-NOH)+-containing interm ediates) from their neutral (mu3-NO)-containing nitrosyl analogues in CH2Cl2 either by proton-induced reduction in reactions with HBF4-OR2 ( R = Me, Et) (40% yields) or by oxidation-induced reductive deoxygenati on in reactions with a variety of oxidants (Ag+, NO+, NO2+, Br2, 12) a nd presumably adventitious water as the proton source (10-40% yields). The two electrons required for the formal reduction of each (mu3-NO) ligand into the (mu3-NH)+ ligand are provided by other ''sacrificial' clusters (i.e., most likely by metal atoms in the acid reactions and C O/NO ligands in the oxidation reactions). Methylation reactions conver ted the (mu3-NO)-containing MnFe2 clusters into corresponding (mu3-NOM e)+-containing monocations (40-50% yields); the (mu3-NOH)+-containing MnFe2 monocation was isolated from the reaction of a (mu3-NO)-containi ng cluster with dilute triflic acid formed via the hydrolysis of methy l triflate with adventitious water in the CH2Cl2 solvent. All of these 48-electron MnFe2 clusters, which contain the same MnFe2(mu2-CO)2(mu2 -NO)(mu3-N) fragment exhibit pseudo-C(s)-m symmetry with similar elect ron-pair Fe-Fe (2.44 +/- 0.01 angstrom) and Fe-Mn (2.57 +/- 0.01 angst rom) bonding distances; their core geometries are also not significant ly affected by an interchange of Cp and Cp' ligands. The noncylindrica l (mu3-NOR)+ ligands in these clusters were found to possess a particu lar geometrical orientation relative to the MnFe2 triangle. Observed v ariations in metal-nitrogen distances to the capping ligands are consi stent with the proposed changes in the bonding interactions of the met al atoms with the (mu3-NOR)+ (R = H, Me) and (mu3-NH)+ ligands relativ e to those with the parent (mu3-NO) ligand. The marked changes in geom etry observed upon reduction of the 48-electron imido-capped [Cp'MnFe2 CP'2(mu2-CO)2(mu2-NO)(mu3-NH)]+ monocation to its 49-electron neutral species correspond to the previously determined geometrical difference s between the corresponding members of the closely related 48/49-elect ron nitrosyl-capped [Cp'MnFe2CP2(mu2-CO)2(mu2-NO)(mu3-NO)]n series (n = 0, 1-). The analogous changes in overall core geometries coupled wit h both 49-electron species displaying similar EPR spectra (with no dis cernible hyperfine interactions) provide convincing evidence that the unpaired electron in the imido-capped MnFe2 cluster likewise occupies a nondegenerate HOMO (under C(s) symmetry) of primarily diiron-antibon ding character.