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

Abstract

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 NbF with a selection of α-diimines afforded the ionic compounds [NbF(DAD)][NbF] (DAD = DAD, 1a; DAD, 1b; DAD, 1c) in 80-90% yields. The addition of DAD to NbOCl gave NbOCl(DAD), 7 (62% yield). [MBr(DAD)][MBr] (M = Nb, 7a; M = Ta, 7b) were afforded in moderate yields from MBr and DAD. The reactions of NbCl with DAD and DAD proceeded with non-selective activation of the organic substrate affording complex mixtures of products, including the quinoxalinium salt [{2,6-CH(CHMe)}N(CH)NCC(CHMe)(CH)C][NbCl], 2, the Nb(iv) coordination complex NbCl(DAD), 3, the N-(monoprotonated) α-diimine salts [DAD(H)][MCl], 4a-b, and the iminomethyl-imidazolium [(2,6-CHMe)NCHCHN(2,6-CHMe)CCHN(2,6-CHMe)][NbCl], 5.

Niobium(V) oxido tris-carbamate as easily available and robust catalytic precursor for the selective sulfide to sulfone oxidation

“…The minor stability of 5 is presumably ascribable to the presence of Nb V -chlorides, which represent acidic sites favouring the attack by protic species and the consequent rupture of the carbamato moieties [5c,35]. Note that the lower Lewis acidity and activating power of [NbOCl3] towards hard donors, compared to [NbCl5], has been clearly established previously [36].…”

Tantalum Recycling by Solvent Extraction: Chloride Is Better than Fluoride

“…In contrast, amide L is a poor reagent of choice when attempting to transport TaF 5 under high chloride conditions, likely due to a combination of competitive chloride extraction and significantly weaker interactions between [HL 2 ] + and more charge-dense species in the aqueous phase, such as [TaF 5 Cl] − . This latter aspect is evident from a comparison of the X-ray crystal data for [TaCl 6 ] − and [TaF 6 ] − , which shows a 1 A decrease in the diameter of the Ta complex moving from chloride to fluoride [28,29]. It is therefore anticipated that L would be a poor extractant for Ta when employed under solely fluoride conditions, in which species such as [TaF 6 ] − and even the dianion [TaF 7 ] 2− may be present.…”

Serendipitous Formation of a Zwitterionic Imidazolium Molecule from α‐Diimine with Glyoxal as Unusual Cyclization Agent

“…In the framework of our research on the coordination chemistry of α-diimines, [18][19][20][21] and in their derivatization with bioactive groups via esterification reactions, [22,23] we became interested in obtaining the α-diimine compound D1 bearing two 4-cyclohexanecarboxylic acid groups as nitrogen substituents. Using the classical procedure (see Scheme 1A), (1S,4S)-4-aminocyclohexanecarboxylic acid and glyoxal were refluxed in methanol in the presence of a catalytic amount of acetic acid.…”