Chemistry of [(trimethylsilyl)methyl]carbene complexes of chromium. : Thermolysis of oxido-carbene salts

Abstract

The synthesis and characterisation of the compounds (CO) 5CrC(X)CH 2SiMe 3 [X = O −NR 4 + (R = Me, Et) and OEt] is reported. The ethoxy-carbene complex is highly susceptible to nucleophilic attack (water, alcohols, NH 3) leading to rupture of the SiCH 2 bond, but is not affected by HCl. The oxido-carbene complex reacts with acetyl chloride in CH 2Cl 2 and in MeCN to give Me 4N[(CO) 5CrCl] and (CO) 5CrNCMe respectively as a consequence of rupture of the CrC(carbene) bond. The formation of [Cr(CO) 5] as an intermediate in these reactions is proposed. With iodine the oxido-carbene gives Me 4N[(CO) 5CrI]. Thermolysis of the oxidocarbene salts (CO) 5CrC(ONMe 4)Y (Y = CH 2SiMe 3, 2-thienyl, cyclopropyl) results in fission of the YC(carbene) bond in each case. When Y is CH 2SiMe 3, or cyclopropyl the solid product of the reaction is a zwitterion carbene complex, (CO) 5CrC(O −)CH 2NMe 3 +. The mechanism of these reactions is discussed. No product could be isolated from the reaction between Cr(CO) 6 and the ylide, Me 3NCH 2.