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

Abstract

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]2C=NDip which crystallizes in the triclinic system, space group P[Formula: see text], a = 10.6513(11), b = 10.8997(11), c = 16.2961(17) Å, α = 80.524(12), β = 78.921(13), γ = 70.060(12)°, V = 1735.2(3) Å3, 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°C, and is consistent with three distinct barriers to N-CAr 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]2C=NDip·Mo(CO)3, a complex in which Mo(CO)3 is η6-coordinated to one of the diisopropylphenyl rings.Key words: crystal structure, diisopropylaniline, guanidine, bulky ligands.