Trapping the Dirhenium Alkynyl Fischer Type Carbene through Michael Addition. Unexpected Room-Temperature E/Z Isomerization of (CO)₅Re(CO)₄Re(C(OMe)CHC(NMe₂)TMS)

Abstract

The reaction of Re 2 (CO) 10 with LiCtCTMS and Me 3 O + BF 4results in a low-stability Fischer type alkynyl carbene complex, (CO) 5 Re(CO) 4 Re(dC(OMe)CtCTMS). This easily reacts with HNMe 2 to giVe the stable (CO) 5 Re(CO) 4 Re-(dC(OMe)CHdC(NMe 2 )TMS) in 82% yield, which exhibits unrestrained rotation around the carbon-carbon "double bond", resulting in room-temperature E/Z isomerization. The aminolysis product (CO) 5 Re(CO) 4 Re(dC(NMe 2 )CtCTMS) was also generated from (CO) 5 Re(CO) 4 Re(dC(OMe)CtCTMS) and could be desilylated to form the acetylene carbene (CO) 5 Re-(CO) 4 Re(dC(NMe 2 )CtCH).

Synthesis of Rhenabenzenes from the Reactions of Rhenacyclobutadienes with Ethoxyethyne

“…The similarity in the chemical shifts of the C H signals of the rhenabenzenes and 1,3‐dimethoxybenzene may also be taken as an indication of aromaticity of the rhenabenzenes. However, we notice that the β‐C H of alkoxy complex 29 has a chemical shift of δ =6.25 ppm 52. Thus, we feel that the NMR evidence is not conclusive for their aromatic character.…”

“…However, we notice that the b-CH of alkoxy complex 29 has a chemical shift of d = 6.25 ppm. [52] Thus, we feel that the NMR evidence is not conclusive for their aromatic character. In this regard, Schleyer et al recently pointed out that proton chemical shifts are not generally reliable aromaticity indicators.…”

Organometallic chemistry of bi- and poly-metallic complexes

“…The facile synthesis of dirhenium alkynyl Fischer-type carbenes via the original Fischer protocol and subsequent hydroamination has been developed (Scheme 3). 36 Interestingly, the alkenyl alkoxo complex [Re 2 (CO) 9 {QC(OMe)C(H)Q C(SiMe 3 )NMe 2 }] undergoes an unusual room temperature E/Z isomerisation.…”