The versatile chemistry of niobium pentachloride with aliphatic amines: Aminolysis, metal reduction and C–H activation

The reactions of NbCl5 with limited amounts (1-2 molar equivalents) of a series of primary, secondary and tertiary amines were investigated in dichloromethane as solvent. The 1:1 reaction of NbCl5 with NHEt2 cleanly afforded an equimolar mixture of [NbCl4(NEt2)]2, 1, and [NH2Et2][NbCl6], 2a; the former product constitutes the first example of structurally characterized Nb(V) chlorido-amido complex. The ammonium salts [NH3nPr][NbCl6], 2b, and [NH2iPr2][NbCl6], 2c, were isolated in 20-30% yields from the 1:1 reactions of NbCl5 with NH2nPr and NHiPr2, respectively. Cα-H bond activation and Nb(V) to Nb(IV) reduction took place in the reactions of NbCl5 with NR3 (R = Bz, Et; Bz = CH2Ph). The iminium salt [(PhCH2)2N=CHPh][NbCl6], 3, and the ammonium ion [NH(CH2Ph)3]+ were identified as the prevalent species generated from the 1:1 NbCl5/NBz3 interaction. [NHEt3][NbCl6], 4, and [NHEt3]2[NbCl6], 5, were isolated in moderate yields from, respectively, the 1:1 and 1:2 molar reactions of NbCl5 with NEt3. The solid state structures of 1, 2a, 3, 4 and 5 were ascertained by single crystal X-ray studies.