Issue 46, 2014

Mixed amido-/imido-/guanidinato niobium complexes: synthesis and the effect of ligands on insertion reactions

Abstract

The new monoguanidinato complexes [Nb(NMe2)2{N(2,6-iPr2C6H3)}{(NR)(NR′)C(NMe2)}] (R = R′ = iPr, 2; R = tBu, R′ = Et, 3) were obtained by the insertion reaction of either diisopropylcarbodiimide or 1-tert-butyl-3-ethylcarbodiimide with the triamido precursor [Nb(NMe2)3(N-2,6-iPr2C6H3)] (1) bearing a bulky imido moiety. The μ-oxo derivative [{N(2,6-iPr2C6H3)}{(NiPr)2C(NMe2)}(NMe2)Nb]2(μ-O) (2a) was formed by an unexpected hydrolysis reaction of the amido niobium compound 2. Alternatively, monoguanidinato complexes [Nb(NMe2)2{N(2,6-iPr2C6H3)}{(NiPr)2C(NHR)}] (R = iPr, 4, nBu, 5) can be obtained by protonolysis of 1 with N,N′,N′′-alkylguanidines [(NHiPr)2C(NR)] (R = iPr, nBu). Compound 1 also reacts with either tert-butylisocyanide or 2,6-xylylisocyanide to give, by a migratory insertion reaction, the corresponding iminocarbamoyl compounds [Nb(NMe2)2{(NMe2)C[double bond, length as m-dash]NR}{N(2,6-iPr2C6H3)}] (R = tBu, 6, Xy, 7). Addition of the neutral alkylguanidines to complex 6 results in a facile C–N bond cleavage at room temperature in a process directed by the formation of the stable chelate complex 4 or 5. Complex 1 reacts with heterocumulenic CS2 to produce new imido dithiocarbamato complexes [Nb(NMe2){S2C(NMe2)}2{N(2,6-iPr2C6H3)}] (8) and [Nb{S2C(NMe2)}3{N(2,6-iPr2C6H3)}] (9). These complexes do not react with alkylguanines, although new mixed guanidinato dithiocarbamato complexes [Nb(NMe2){S2C(NMe2)}{(NiPr)2C(NHiPr)}{N(2,6-iPr2C6H3)}] (10) and [Nb{(S2C(NMe2)}2{(NiPr)2C(NHiPr)}{N(2,6-iPr2C6H3)}] (11) can be obtained by reaction of complex 4 with one or two equivalents of CS2, respectively. All of the complexes were characterized spectroscopically and the dynamic behaviour of some of them was studied by variable-temperature NMR. The molecular structures of 2a, 3, 6 and 10 were also established by X-ray diffraction studies.

Graphical abstract: Mixed amido-/imido-/guanidinato niobium complexes: synthesis and the effect of ligands on insertion reactions

Supplementary files

Article information

Article type
Paper
Submitted
30 Jun 2014
Accepted
22 Sep 2014
First published
26 Sep 2014

Dalton Trans., 2014,43, 17434-17444

Mixed amido-/imido-/guanidinato niobium complexes: synthesis and the effect of ligands on insertion reactions

D. Elorriaga, F. Carrillo-Hermosilla, A. Antiñolo, I. López-Solera, R. Fernández-Galán and E. Villaseñor, Dalton Trans., 2014, 43, 17434 DOI: 10.1039/C4DT01975J

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