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The reaction of N,N'-bis(2,6-diisopropylphenyl)carbodiimide with lithium 2,6-diisopropylanilide, quenching with water and recrystallization from heptane produces the symmetric guanidine [[DipNH].sub.2]C=NDip which crystallizes in the triclinic system, space group P[bar]1, a = 10.6513(11), b = 10.8997(11), c = 16.2961(17) [Angstrom], [alpha] = 80.524(12), [beta] = 78.921(13), [gamma] = 70.060(12)[degrees], V = 1735.2(3) [[Angstrom].sup.3], Z = 2. The molecule crystallizes with three perpendicular 2,6-diisopropylphenyl groups, which surround and shield the central C[N.sub.3] unit, and provide (almost) three-fold symmetry around the central atom. Its dynamic solution behaviour has been studied by VT NMR between -90 and +180[degrees]C, and is consistent with three distinct barriers to N-[C.sub.Ar] rotation. Preliminary estimates of the Gibbs free energy of activation for the lower two barriers are 56 [+ or -] 2 and 73 [+ or -] 2 kJ [mol.sup.-1]. Reaction of the title compound with Mo[(CO).sub.6] in refluxing n-heptane produces [[DipNH].sub.2]C= NDip*Mo[(CO).sub.3], a complex in which Mo[(CO).sub.3] is [[eta].sup.6]-coordinated to one of the diisopropylpbenyl rings. Key words: crystal structure, diisopropylaniline, guanidine, bulky ligands.

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).sub.6] to produce a coordination complex with Mo[(CO).sub.3] in which the ligand is also in the Z-anti geometry, the metal is [[eta].sup.6]-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).sub.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 [Mo.sub.2][(amidinate).sub.4] as observed previously in a redox reaction between N,N'diphenylbenzamidine and Mo[(CO).sub.6] under similar thermal reaction conditions. Key words: trifluoromethyl, superamidine, amidine, molybdenum, carbonyl, coordination.