Modification of aminoallenylidene complexes of chromium via exchange of the C3-bound amino group |
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Authors: | Normen Szesni |
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Institution: | Fachbereich Chemie, Universität Konstanz, Fach M727, D-78457 Konstanz, Germany |
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Abstract: | The aminoallenylidene(pentacarbonyl)chromium complexes (CO)5Cr C C C(NR1R2)Ph] (1a-c) react with dimethylamine by addition of the amine to the C1 C2 bond of the allenylidene ligand to give alkenyl(amino)carbene complexes (CO)5Cr C(NMe2)CH C(NR1R2)Ph] (2a-c) (R1 = Me: R2 = Me (a), Ph (b); R1 = Et: R2 = Ph (c)). In contrast, addition of a large excess (usually 20 equivalents) of ammonia or primary amines, H2NR, to solutions of (CO)5Cr C C C(NMe2)Ph] (1a) affords the aminoallenylidene complexes (CO)5Cr C C C(NHR)Ph] (1d-w) in which the dimethylamino group is replaced by NH2 or NHR, respectively. In addition to simple amines such as methylamine, butylamine, and aniline, amines carrying a functional group (allylamine, propargylamine) and amino acid esters as well as amino terpenes and amino sugars can be used to displace the NMe2 substituent. Usually the Z isomer (with respect to the partial C3-N double bond) is formed exclusively. Products derived from addition of H2NR to the C1 C2 bond of 1a are not observed. The amino group in 1d-w is rapidly deprotonated by excess of amine to form iminium alkynyl chromates 1d-w]−, thus protecting 1d-w from addition of free amine to either C3 or across the C1 C2 bond. The iminium alkynyl chromates are readily reprotonated by acids or by chromatography on wet SiO2 to reform 1d-w. |
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Keywords: | Allenylidene complexes Chromium Carbene complexes Addition Substitution |
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