Synthesis and properties of Fischer carbene complexes of N,N-Dimethylaniline (cas 121-69-7) and anisole π-coordinated to chromium tricarbonyl

Add time:09/25/2019    Source:sciencedirect.com

The reaction of lithiated N,N-Dimethylaniline (cas 121-69-7) π-coordinated to Cr(CO)3 with W(CO)6 and alkylation with [Et3O][BF4] afforded the o-, m- and p-isomers of the σ,π-bimetallic complexes {η6-Me2NC6H4C(OEt)W(CO)5}Cr(CO)3 (o-, 1, m-, 2 and p-isomer, 3). A by-product of the reaction is found by the substitution of a carbonyl ligand in 1 by the aniline nitrogen atom to give {η6-C,N-o-Me2NC6H4C(OEt)W(CO)4}Cr(CO)3 (4). As a result, the W-chelate ring dominates the HOMO rather than the{η6-arene Cr(CO)3} fragment, affecting the site of the first oxidation. Enhanced activation of anisole by π-coordination to Cr(CO)3, and subsequent reactions with nBuLi, W(CO)6 and [Et3O][BF4] gave only o-substituted products {μ,η6:1-o-MeOC6H4C(OEt)W(CO)5}Cr(CO)3 (5), the monocarbene chelate {μ,η6:2-C,O-o-MeOC6H4C(OEt)W(CO)4}Cr(CO)3 (6) by carbonyl substitution, and by reaction of two molar equivalents of these reagents, the unique σ,π-heterotrimetallic biscarbene complex {μ3,η6:1:1-o,o-MeOC6H3(C(OEt)W(CO)5)2}Cr(CO)3 (7). Attempts to synthesise the m- and p-isomers of 5 were unsuccessful due to transmetallation of the lithiated precursors. NMR data confirmed that lithiation and subsequent reactions of m- or p-bromoanisole chromiumtricarbonyl afforded only the o-isomer 5 and {η6-MeOC6H5}Cr(CO)3. Crystal structure determinations of complexes 1–7 confirmed their molecular structures. Spectroscopic data, electrochemistry studies and DFT calculations of the complexes are reported and are in line with a shifting of the HOMO from the Cr(CO)3 to the W(CO)4 chelate entity and with an unusually large delocalization of the HOMO of the other complexes onto the π-coordinated arene ligand and the carbene-bonded metal atom.

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