Regiospecific influences of phenyl ring substituents in monoimido complexes of tantalum and tungsten and bis imido complexes of molybdenum

Imido exchange of [TaCl3(NCMe3)(py)(2)] with 2-tert-butylaniline in refluxing benzene and crystallisation of the product from CH2Cl2 gave the anionic complex [Hpy][TaCl4(C6H4CMe3-2)(py)] 1. X-Ray structural analysis shows that with the Ta-N-C bond angle at 165.1(5)degrees two of the tert-butyl substituent methyl groups sit above two meridional chloro ligands but NMR spectroscopy indicates that the tert-butyl group can still rotate in solution. Reaction of isocyanates ArNCO [Ar=C10H7 (naphthyl), C6H4CMe3-2 or C6H4Ph-2] with WOCl4 in refluxing benzene gave [{WCl4(NC10H7)}(x)] 2, [{WCl4(NC6H4CMe3-2)}(x)] 3, and [{WCl4(NC6H4Ph-2)}(x)] 4 which NMR spectra show convert from two species into one in CDCl3. In refluxing toluene, 2-tert-butylphenyl isocyanate also forms the metallacyclic amido complex [WCl4{NHC6H4(CMe2CH2)-2(C,N)}] 5. The d(1) complexes [WCl3(NC10H7)(PMe3)(2)] 6, [WCl3(NC6H4CMe3-2)(PMe3)(2)] 7, [WCl3(NC6H4Ph-2)(PMe3)(2)] 8, [WCl3(NC10H7)(PMe2Ph)(2)] 9 and [WCl3(NC10H7)(PMePh2)(2)] 10 were prepared, and show hindered imido ligand aryl C-N bond rotation. A crystal structure determination of 6 shows the naphthyl ring C-8 proton positioned between a chloro and phosphine ligand. Also prepared to demonstrate hindered aryl C-N bond rotation were the d(2) complexes [WCl2(NC10H7)(PMe3)(3)] 11, [WCl2(NC6H4CMe3-2)(PMe3)(3)] 12, [WCl2(NC6H4Ph-2)(PMe3)(3)] 13 and [WCl2(NC10H7)(PMe2Ph)(3)] 14. Crystal stucture determinations show the tert-butyl group in 12 located above a chloro ligand and the phenyl group in 13 located between a chloro and phosphine ligand. They also show the methyl and isopropyl substituents in [MoCl2(NC6H3Me-2-Pr-i-6)(2)(dme)] 15 form an anti configuration and in [MoCl2(NC6H4CMe3-2)(2)(dme)] 16 a syn configuration is identified where the Mo-N-C bond angles are determined by steric effects and crystal packing forces.