Superamidines 2.: Synthesis of the bulky ligand N,N′-bis-(2,6-diisopropylphenyl)-trifluoroacetamidine and its molybdenum carbonyl complex

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 Z-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 eta(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)(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-2(amidinate)(4) as observed previously in a redox reaction between N,N'-diphenylbenzamidine and Mo(CO)(6) under similar thermal reaction conditions.