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N,N'-bis-(2,6-diisopropylphenyl)trifluoroacetamidine has been prepared for the first time from 2,6-diisopropylaniline and the trifluoroacylation reagent TFAP via the imidoylchloride. The crystal structure of the amidine was determined, indicating that it crystallizes in the Z-anti tautomer, in contrast to the nonfluorinated analogue, which is E-anti in the solid state. In solution, as indicated by NMR spectroscopy, it exists in two isomeric forms. The amidine reacts with Mo(CO)6 to produce a coordination complex with Mo(CO)3 in which the ligand is also in the Z-anti geometry, the metal is η6-coordinated to the imino-2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards the metal, as determined by a single-crystal X-ray structure. Unlike the analogous nonfluorinated acetamidine, there is no indication of an intermediate in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)5 unit, which we now attribute to the predominant geometry of the ligand, both in the solid state and in solution, being Z-anti. The high steric bulk of this superamidine ligand apparently prevents the formation of a metal-metal bonded Mo2(amidinate)4 as observed previously in a redox reaction between N,N'-diphenylbenzamidine and Mo(CO)6 under similar thermal reaction conditions.Key words: trifluoromethyl, superamidine, amidine, molybdenum, carbonyl, coordination.

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Abstract:The title compounds have been studied in CH2CI, by cyclic voltammetry. Nonacarbonyldi(p,-methylidyne)triiron, [Fe3(CO),(p3-CX),] (X = F, CI, Br, H), undergo chemically reversible le-reduction (-0.72 to -0.88 V vs. SCE) and irreversible oxidation (+1.59 to +I .72 V); the compound for which X = F displays a second, irreversible reduction (-1.96 V). Using reduction potentials of comparable p,-E (E = S, Se, NPh, PPh) clusters, p,-methylidyne ligands are shown to be strongly basic, comparable to PPh and NPh and more basic than S or Se. The methylidyne clusters are both more difficult to oxidize and reduce than isomeric alkyne clusters [Fe3(C0),(C2R,)], indicative of greater thermodynamic stability. The complexes previously formulated as [Fe2(CO),(S2N2CC6H,X)] (X = H, CF,, OCH,) are reversibly reduced (-1.59 to -1.70 V) and irreversibly oxidized (+1.0 to 1.3 V), unlike free dithiadiazole radicals, which are reversibly oxidized around +0.8 V. This behaviour is not consistent with the ring-centered free radical claimed for the case where X = H; instead we find conclusive evidence that these are diamagnetic complexes of the 3-H-1,2,3,5-dithiadiazolines, [Fe,(CO),(S,N(NHJCC6H,X)] (vNH = 3376-3381 cm-I; fjNH = 6.55-7.1 ppm). Dicyclopentadienyldithiadiazoledinickel, [Ni2Cp2(S,N2CC6H5)], is both reversibly reduced (-0.79 V) and oxidized (+0.45 V);and irreversibly oxidized at + 1.9 V. This is consistent with an unpaired electron, and only the nickel cluster has an ESR signal (g = 2.041 0, no resolved hyperfine splitting). Extended Huckel theory locates the free electron in a SOMO restricted to Ni, C, and S atoms.Key words: electrochemistry, organometallic, methylidyne, dithiadiazole, dithiadiazoline.Received April 6, 1995.