Metal-carbene complexes decomplexation

Cyclopropyl-substituted transition-metal carbene and carbyne complexes, especially as cyclo-propylidene- or as cyclopropylcarbene complexes, have been used as synthetic building blocks with or without ring opening. Examples of cyclopropane synthesis via decomplexation are described in Section 1.A.5.2.6. 

Indenes, like cyclobutenones and furans, are common side-products in the reaction of chromium arylalkoxycarbene complexes with alkynes, especially internal alkynes [9]. The in-dene structure comes about by a process that is very similar to naphthol formation annula-tion to the aryl ring still occurs, but without carbon monoxide insertion, and, instead, bond formation takes place directly between an alkyne carbon and the aryl carbon ortho to the metal carbene substituent [Eq. (18)] [4]. Scheme 5-1 shows two pathways that have been suggested for this transformation beginning from the vinylcarbene intermediate 3, naphthol formation can be diverted to intermediate 8, either by direct cyclization (3 -+ 8) or through the chromacyclohexadiene (3->6- 8). Aromatization and decomplexation yield the indene [7 b, d, 43], More detailed mechanistic analyses consider the roles of the stereochemistry of 3, as an ( )- or (Z)-vinylcarbene, as well as the coordination of external ligands, in the production of indenes, naphthols, furans, cyclobutenones, and other common side-products [8 a, 9, 13, 44],... 

MO calculations suggest that, in nucleophilic addition reactions of substituted benchrotrenes [( -PhX)Cr(CO)3] (see Vol. 9, ref. 412), the preferred orientation of addition is influenced more by the conformation of the Cr(CO)a residue than by the electronic character of the substituent X. Whereas lithiation (with BuLi-TMED) of 3-methoxybenzyl alcohol occurs very predominantly at the 2-position of the arene ring, similar treatment of the corresponding n-Cr(CO)3 complex gives a mixture of the 2- and 4-lithio derivatives in the ratio 23 77, respectively these products were characterized by isolation of carboxylic acid derivatives following carbonation (COg) and metal decomplexation hv 0. Experimental details for the preparation of [(iy-PhX)Cr(CO)3] (X=I and SiMes) from [( -PhLi)Cr(CO)3] have been reported. This lithio derivative has also been used to prepare the carbene complexes [(OC)3Cr(i7-Ph)C(OEt)M(CO)5] (M=Cr, Mo, and W), which react with BX, (X=C1 and Br) to give the carbyne products [(OC)3Cr( Ph)C=M(CO)4X] (M=Cr and W only). ... 

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