Stable coordination complexes of α-diimines with Nb(v) and Ta(v) halides

Uncommon examples of coordination compounds of high valent transition metals with α-diimines were obtained and characterized by IR and NMR spectroscopy, X-ray diffraction and/or DFT analysis. The 1:1 molar reactions of NbF5with a selection of α-diimines afforded the ionic compounds [NbF4(DADR)2][NbF6] (DADR= DADDip, 1a; DADXyl, 1b; DADMes, 1c) in 80-90% yields. The addition of DADDipto NbOCl3gave NbOCl3(DADDip), 7 (62% yield). [MBr4(DADDip)][MBr6] (M = Nb, 7a; M = Ta, 7b) were afforded in moderate yields from MBr5and DADDip. The reactions of NbCl5with DADDipand DADXylproceeded with non-selective activation of the organic substrate affording complex mixtures of products, including the quinoxalinium salt [2,6-C6H3(CHMe2)2N(CH)2NCC(CHMe2)(CH)3C][NbCl6], 2, the Nb(iv) coordination complex NbCl4(DADDip), 3, the N-(monoprotonated) α-diimine salts [DADDip(H)][MCl6], 4a-b, and the iminomethyl-imidazolium [(2,6-C6H3Me2)NCHCHN(2,6-C6H3Me2)CCHN(2,6-C6H3Me2)][NbCl6], 5.