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

Abstract

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)° 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 d¹ 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 d² 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-Prⁱ-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.