Methoxycarbene complex

While the first transition metal carbene complex was reported in 1964134, the first cyclopropylcarbene complex salt [(CO)5Cr=C(chromium hexacarbonyl, followed by tetramethylammonium bromide135. Subsequent reaction with trimethyloxonium fluoro-borate gave methoxycarbene complex (CO)5Cr=C(OMe)(c-Pr) (equation 62)136. 

For most methoxycarbene complexes a one pot modification of the above method is utilized. This involves direct alkylation of the initially formed lithium acylate carbene complex with trifluoromethanesulfonate or with methyl fluorosulfonate. The method is successfully employed for preparation of chromium140 as well as molybdenum and tungsten monocyclic uation 65), bicyclic (equation 66) and tricyclic carbene complexes... 

The vast majority of work exploring the reactivity of ruthenium viny-lidene complexes has focused on the attack of alcohols at the electrophilic a carbon of monosubstituted vinylidenes, resulting in the formation of ruthenium alkoxycarbene complexes. Bruce and co-workers have determined, for example, that the phenylvinylidene complex 80 is slowly transformed in refluxing MeOH to the methoxycarbene complex 82 in good yield (73,83). The mechanism for this reaction must involve initial attack of the alcohol at the electrophilic Ca to form a transient vinyl intermediate 81 which is rapidly protonated at the nucleophilic Cp, generating the product carbene 82 [Eq. (79)]. In contrast to monosubstituted vinylidene complexes, disubstituted vinylidene complexes are generally unreactive to nucleophiles even the relatively small dimethylvinylidene complex 83 shows no reaction with MeOH after 70 hours at reflux [Eq. (80)]. 

Consiglio et al. (88) have reported that the reaction of LiAlH4 with the methoxycarbene complex 99 gives the completely reduced 2-phenylethyl complex (100) as the exclusive product [Eq. (90)]. The reaction probably involves initial hydride attack at C , elimination of methoxide, and a second hydride attack to give the final product. 

Alkylation of iron acyl complexes also provides access to iron carbenes. Thus, the neutral iron acyl complex will react with acid, with alkylating agents, or with trifluoromethanesul-fonic anhydride to afford cationic hydroxy- or aUcoxycarbene complexes (52) and (53) or the cationic vinylidene complex (54, L = CO) (Scheme 20). The vinylidene complex can be used to prepare a more substituted analog of (51) by treatment with a thiol. The enantiomerically pure iron acyl complex (R)-(45a) can be converted to the corresponding enantiopure methoxycarbene complex with Me30Bp4 as well. Finally,... 

The methoxycarbene complex Cr(CO)5[C(OCH3)C6H5], Figure 6-4, illustrates some important characteristics of bonding in transition metal carbene complexes.11 Evidence for double bonding between chromium and carbon is provided by X-ray... 

In Fischer s original synthesis, carbyne complexes were obtained fortuitously as products of the reactions of carbene complexes with Lewis acids. For example, the methoxycarbene complex Cr(CO)5[C(OCH3)C6H5] reacts with the Lewis acids BX3 (X = Cl, Br, or I). 

The vinylidene complexes 8 also react with nucleophiles such as water and methanol. Hydration of the unsubstituted vinylidene complex 8a leads to the formation of the rj -acetyl complex 13, whereas the corresponding reactions of 8b and 8c result in the C-C bond cleavage, giving the cationic carbonyl complex 14 and organocarbonyl products R COMe(R = OMe or Me). On the other hand, the reactions of 8 with methanol afford the methoxycarbene complex 15 and the vinyl complex 16, depending upon the substituent of the vinylidene complexes 8. Intramolecular nucleophilic attack takes place in the reaction of 4 with 3-butyn-l-ol, giving the cyclic alkoxycarbene complex [Cp RuCl(p-SPr%Ru =C(CH2)30 Cp ](OTf). ... 

Whereas no stereocontrol of the configuration of the double bond formed was observed with methoxycarbene complex 105, its menthyloxycarbene analogue 108 afforded exclusively the E stereoisomer. The chemoselectivity of the reaction strongly depends on the nature of the catalyst In the presence of 15 mol-% of [Cu(MeCN)4][PFg], a dimerization of the methoxycarbene ligand was observed favouring the E isomer in a 10 1 ratio. (Scheme 46). [98]... 

Vinyl- and phenyl-methoxycarbene complexes condense with alkynes to form benzene or naphthalene derivatives respectively. One carbonyl ligand is also incorporated into the new ring as a phenolic group. The reaction is a key step in a recent synthesis of Vitamin E. 

The alkoxycarbene complex, [FeGp (G0)2 =G(0Me)Me ][GF3S03], undergoes substitution of one or two carbonyl ligands to produce various mono- and disubstituted methoxycarbene complexes, providing a convenient method for the generation of cationic iron-carbene complexes. 

Hydride abstraction with Ph C PFg from the methoxymethyl complex [(CjMe )(C0)2Fe(CH20Me)] affords the methoxycarbene complex [(C Me )(CO)2Pe =C(H)0Me ][PFg], which undergoes an addition... 

Pr", Ph Ri = Me, SiMea, CPha and others), react with vinyl methoxycarbene complexes, [(OC)5Cr=C(OMe)C(R2)=CHR3] (R2 = H, Me R = H, Me) to give arene chromium tricarbonyl complexes with high asymmetric induction. oo... 

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