Science of Synthesis

Kündig, E. P.; Pache, S. H., Science of Synthesis, (2003) 2, 159.

The preferred method for the synthesis of (arene)tricarbonylchromium(0) complexes ‌6‌ (M = Cr) is thermolysis of hexacarbonylchromium(0) under an inert atmosphere (nitrogen or argon) in the presence of an excess of the arene, in a high-boiling solvent (‌Scheme 4‌). This can be the arene itself, dibutyl ether/tetrahydrofuran,[‌31‌] 1,2-dimethoxyethane,[‌32‌] diglyme/tetrahydrofuran,[‌33‌] heptane/diglyme,[‌34‌] α-picoline,[‌35‌] Decalin/ethyl formate, or Decalin/butyl acetate.[‌36‌,‌37‌] For aryl amino acids, a mixture of water and tetrahydrofuran (80:20) has been successfully applied.[‌38‌] The polar ether and ester additives (or solvents) promote carbonyl dissociation, stabilize intermediates, and the vigorous reflux of lower boiling additives washes sublimed hexacarbonylchromium(0) back into the reaction. The most widely used solvent combination is dibutyl ether/tetrahydrofuran (9:1).[‌31‌] This allows the preparation of a wide range of complexes in good yields with reaction times typically in the 1–4 day range. Higher temperatures shorten the reaction times but increase the risk of decomposition, which, once started, can lead to rapid product loss. Special apparatus (double condenser system[‌36‌] or distillative recycling of hexacarbonylchromium[‌39‌]) is advantageous or required in some of the procedures. Complexes of condensed aromatics are unstable toward polar solvents (tetrahydrofuran, dimethyl sulfoxide, acetone) and their synthesis requires special care[‌40‌–‌42‌] or the use of more labile [Cr(CO)3L3] precursors (vide infra). A selection (‌7‌–‌17‌) from the hundreds of mono- and polysubstituted chromium–arene complexes made by this method is shown in ‌Scheme 4‌. Condensed aromatics coordinate the metal in a terminal ring (e.g., in the phenanthrene complex ‌16‌). This can be attributed to a minimum disruption of aromaticity.[‌43‌] Regioselectivity favors the arene over the heteroarene ring (e.g., in the indole complex ‌12‌) and the nonsubstituted arene ring in 1-mono- and 1,4-disubstituted naphthalenes (e.g., in ‌15‌).

‌Meeeee 8‌ Meeeeeeee ee Meeeeeeeeeeeeeee–Meeee Meeeeeeee ee Meeeeeeeeee ee Meee­eeeeeeeeeeeee Meeeeeeee

‌Meeeeeeeeee 8‌

Meeeee eeeeeeeee ee [M(MM)8(eeeee)] eeeeeeeee ‌8‌ (M = Me, M; M8 = M, Me, MMe8, MeMe8) eeee ee eeeee eee [M(MM)8] eeeeeeeee ee eeee eeee eeeeeee eeee eee eeeeeeee.[‌88‌,‌88‌] Mee eeee eeeeeeee eeeee ee eeeeeeee eeeeeeeeeee eee eee eeee eeeeeeeeeee ee eeeeee eeeee eeeeeee ee eee eeeeee eee eeeeeeeeeee eeeeee. M eeee eeeeee eeeeeeeee ee eeeee eeeee ee eeeee eeeeeeee (eee eeeeeeeeee) ee eeeeee eeeeeeeeeeee ee [M(MM)8M8] eeeeeeeee (eee Meeeeeee ‌8.8.8.8‌ eee ‌8.8.8.8‌). (Meeeeee)eeeeeeeeeeeeeeeeeeeee(8) eee eeee eeeeeeee ee eeee eeeeeeeeeeee eeeee.[‌88‌] Mee eeee eeeeeeee eeee (88 eeee) eee ee eeeeeeeee ee eeeeeeee eeeeeeeeeeeeeeeeeeeeee(8) ee eeeeeee ee eee eeeeeeee ee eeeeeeee ee ee eeeeeeeee.[‌88‌] Mee eee eeeeeeee eeeeeeee, eeeeeeee eeeeeeeeeeeeeeeee ee e eeeeee eeeeeeeee eeee eeeeeeee.[‌88‌] (Meeee)eeeeeeeeeeeeeeeeeee(8) eeeeeeeee eeee eeee eeee eeeeeeee ee eee ee eeeeeeee eeeeee ee eeeeeeeeee ee eeeeeeeeeeeeeeeeeeee(8) ee eee eeeeeeee ee eee eeeee.[‌88‌]

Meeeeeeeeeee Meeeeeeee

(η8-Meeeeee)eeeeeeeeeeeeeeeeeee(8) (‌8‌, M = Me; M8 = MMe):[‌88‌]

M 888-eM, eeeee-eeeeeeee eeeee eeeeee eeee e eeee, eeeeeeee-eeee eeeee-eeeeee eeeeeeeee ee 88-ee eeeeee eee eeeeeee eeee Me(MM)8 (8.88 e, 88 eeee), eeeeeee (8.88 e, 88 eeee), eee Me8M (888 eM). Mee eeeeeee eee eeeeeeeee ee eeeee eeeeee–eeee–eeee eeeeee. Meeeeee eeeeeeeee, eee, M8-eee. MMM (88 eM) eee eeeee eeee eee eee eeeeeeeeeeee eeeeeee eeeeeee eee eeeeee ee eeeeee ee eee eeee eeeee M8 eee 88 e. [Mee eeeeeeee eeeeeeeee eeee 8 eeeee ee eeeeeee. M eeeeee eeeee eee eeeeeeee ee eee eeeeeee ee eeeee 8 eeeee eee ee eeeeeeeee eeeeeeee eeee; eeee eeee eeeeeee eeeeeeee eee eeeeeeeeee ee eeeeeeeee Me(MM)8.] Meeee eeeeeee ee ee, eee eeeeeeeee eeee eeeeeeeee eee ee e eeeeee eeeeeeeeee eeee e eeeee eeee eeee ee 88°M (ee eee eeee eee ee eeeeeeee ee eeeeee eee eeeeeee eeeeeeeeee). Mee eeeeee eeeeeee eee eeeeeeeee ee eee, eeeeeeee Me8M eee eeeeeeee eeee Meeeee eeeee e M8 eeeeeeeeee. Meeeeeeeeeeeeee (Me8M/eeeeee) eeee eee eeeeee eeeeeeeeeee eeeeeee; eeeee: 8.88 e (88%); ee 88–88°M (Me8M/eeeeee); MM (eeeeeeeeeee) νMM: 8888, 8888 ee–8; 8M MMM (MMMe8, δ): 8.88 (e, 8M), 8.88 (e, 8M), 8.88 (e, 8M), 8.88 (e, 8M).

Meeeeeeeeee(η8-eeeeeeeeeee)eeeeeeee(8) (‌88‌):[‌88‌]

Me e 888-eM, eeeee-eeeeeeee eeeee eeeeeeee eeee e eee-eeeee eeeeeeeee eeee eeeeee eeeeeeeeeee (88 e, 888 eeee), Me(MM)8 (88 e, 88 eeee), eeeee eeeeeee (88 eM), eee Meeeeee (888 eM). Mee eeeeeee eee eeeeeeee eeeee eeeee eee eeeeee ee eee eeee eeeee M8 ee 888°M eee 8 e. [Me eee eee-eeeee eeeeeeeee, eee eeeee eeeee ee eeeeee ee eeeeeee (eeeeee). Meeeeeeeeee eee Me(MM)8 eeeeeee ee eeee eeeee. Mee eeeee eeeee ee eeeeee ee eeeee (eeeeeeee eeeeeeee eeee eee eeee eeee eeee eee eeeeeeee eeeeee).] Mee eeeeeee eee eeee eeeeee ee 88°M, eeeeeeee ee Meeeee eeeee M8, eeeeeee eeee eee eeeeee (888 eM), eee eeee ee −88°M eeeeeeeee. Mee eeeee eeeeeeee eee eeeeeeee ee eeeeeeeeeee eee eeeee eeeee eeeeee. Meeeeeeeeee ee eeeeee eeeeeeeeeee eeee eee eeeeeee ee e eee eeeeeeeeeee eeeee; eeeee: 8.88 e (88%) [Mee eeeeeeeeee eeeeee, eeeeeee eee eeee eeeeeeeee eeeee Me(MM)8, eeeeeeeeee eeee e eeeee ee 88%.[‌88‌] Meee Me(MM)8 eee eeeeeeee eeeeeeeee eeeeeeeee eeee eeeeee ee eee 88–88% eeeee.]; 8M MMM (eeeeeee-e8, δ): 8.88–8.88 (e, 8M), 8.88–8.88 (e, 8M), 8.88–8.88 (e, 8M), 8.88–8.88 (e, 8M).

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 88-8, 888.
• 8.Meeeee-Meee, (8888) M 88e, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 888.