Molybdenum chlorocarbyne complexes

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. 

Preparation of the corresponding chlorocarbyne complexes of molybdenum and tungsten was achieved by modification of the classical Fischer synthesis (equation 91), except that the acylmetallate intermediate was isolated as the tetramethylammonium salt, and further reacted with oxalyl chloride in CH2CI2 (equation The carbyne com-... 

When methylene chloride was used as a solvent, it was found that 28 are obtained in minor amounts, while the dominating product is the -coordinated chloro-carbyne species [(> -Tp )Mo(CO)2(=CCl)], whose yield increases abruptly with substitution in the pyrazol-l-yl fragments (3-methyl-, 3,4,5-trimethyl-, and 3,5-dimethyl-4-chloro derivatives) [90AX(C)59,95JCS(D) 1709]. The tungsten analog can be prepared similarly. The chlorocarbyne molybdenum complex follows also from the reaction of the parent anion with triphenylsulfonium cation but conducted in dichloromethane. The bromo- and iodocarbyne derivatives are made similarly. 

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