Carbyne complexes nucleophilic displacement

Dihalocarbene complexes are useful precursors to new carbenes by nucleophilic displacement of the chlorine substituents. This has been nicely illustrated for Fe(TPP)(=CCl2) by its reaction with two equivalents of Re(CO)5J to give the unusual /t-carbido complex Fe(TPP)=C=Re(CO)4Re(CO)5 which also contains a rhenium-rhenium bond. " The carbido carbon resonance was observed at 211.7 ppm in the C NMR spectrum. An X-ray crystal structure showed a very short Fe=C bond (1.605(13) A, shorter than comparable carbyne complexes) and a relatively long Re=C bond (1.957( 12) A) (Fig. 4, Table III). " ... 

It was noted in Section V,B that the chlorophenyl carbene complex 85 can be prepared by chlorine addition to carbyne complex 80. Treatment of 85 with one equivalent of PhLi does not afford 80, suggesting that the reaction sequence is reduction/substitution rather than substitution/reduc-tion. The recent report (127) of a nucleophilic displacement reaction of the molybdenum chlorocarbyne complex 87 with PhLi to generate phenylcar-byne complex 88 suggests that the intermediacy of the chlorocarbyne complex 86 in the above mechanism is not unreasonable. 

Deviating from the route via nucleophilic attack of the carbanion at the carbon atom of a CO ligand and then reaction of the acylmetallate with an electrophile are those methods which involve (a) addition of the carbanion to the carbon atom of a carbyne ligand, (b) displacement of halides from transition-metal carbonyl halides by cyclohepta-trienyllithium, or derivatives thereof, followed by hydride abstraction or (c) substitution of a coordinated solvent from a metal-carbonyl complex (see also reaction of LiR with carbene complexes). 

Nucleophilic displacement at the carbyne carbon of the terminal halomethyli-dynes Tp M( = CCl)(CO)2 (M = Mo, W) with alkyl and aryl thiolates and phenylselenolate produces thiolatomethylidyne and selenolatomethylidyne complexes (Scheme 17). 

Aryloxides similarly displace chloride from Tp M( = CCl)(CO)2 (M = Mo, W) with the formation of (aryloxy)carbyne complexes Tp M( = COAr)(CO)2 (Ar = Ph, C6H4Me-4, C6H40Me-4), which are of interest in that they provide models for the elusive hydroxycarbyne ligand that is implicated in Fischer-Tropsch processes. The neutral PR3 substituent in the cationic phosphoniocarbyne salts [Tp W( = CPR2Ph) (C0)2][PF6] (R = Me, Ph) has proven to be an excellent leaving group, with electron-rich aryloxides (ArO ) replacing the phosphine to afford (aryloxy)alkylidyne products Tp W( = COAr)(CO)2. With electron-poor aryloxide nucleophiles, f/ -ketenyl complexes are also formed (Scheme 21). ... 

Nucleophiles react with carbyne complexes to promote (or trap) carbyne-carbonyl coupling products, attack the metal-carbon triple bond, or displace a substituent on the carbyne carbon. Complexes of the form Tp M( = CR)(CO)2 are coordinatively saturated and in the case of Tp = Tp, the metal also enjoys a substantial degree of steric protection. Accordingly, the reaction of these complexes with nucleophiles does not, in general, involve attack at the metal but rather at a coligand. Attempted synthesis of Tp W( = CMe)(CO)2 via reaction of MeLi with the... 

The methoxycarbyne complex Tp W( = COMe)(CO)2 also reacts at the carbyne substituent with nucleophiles attacking the methoxide Me group, delivering Me and generating [Tp W(CO)3] via an Sn2 reaction.The reactivity of the methoxycarbyne complex Tp W( = COMe)(CO)2 thus differs considerably from that of the methylthiocarbyne complex Tp W( = CSMe)(CO)2, which reacts with phosphines at the carbyne carbon to undergo nucleophilic displacement of the methylthiolate substituent to produce phosphoniocarbyne complexes.The... 

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