Preparation, X-ray structure, and dynamic solution behaviour of N,N′,N"-tris(2,6-diisopropylphenyl)-guanidine, and its reaction with molybdenum carbonyl

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](2)C=NDip which crystallizes in the triclinic system, space group P(1) over bar, 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 (3), Z = 2. The molecule crystallizes with three perpendicular 2,6-diisopropylphenyl groups, which surround and shield the central CN3 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 degreesC, and is consistent with three distinct barriers to N-C-Ar rotation. Preliminary estimates of the Gibbs free energy of activation for the lower two barriers are 56 +/- 2 and 73 +/- 2 kJ mol(-1). Reaction of the title compound with Mo(CO)(6) in refluxing n-heptane produces [DipNH](2)C=NDip.Mo(CO)(3), a complex in which Mo(CO)(3) is eta (6)-coordinated to one of the diisopropylphenyl rings.