Chlorobenzene, tricarbonylchromium

The isolation of the first halobenzene complex, (q6-chlorobenzene)tricarbonylchromium(0), allowed a test for a direct analog of classical SNAr reactivity.15 The activating effect of the Cr(CO>3 unit was found to be comparable to a single p-nitro substituent in reaction with methoxide in methanol and the substituted arene ligand was detached with mild oxidation (equation 2). 

Arylation of N, N-dimethylhydrazone 77 with ( fl-chlorobenzene)tricarbonylchromium complex lb can be achieved in 64 % yield. The copper lithium azaenolate 78 is trapped with the chromium complex at 70 °C to give a-phenyl ketone 80 as a result of an ipso substitution (Scheme 35) [59]. This represents an easy access to a-aryl carbonyl compounds, some of which may exhibit anti-inflammatory properties. 

Formation of aldehydes. Aldehydes can be prepared by the carbonylation of halides in the presence of various hydride sources. The carbonylation of aryl and alkenyl iodides and bromides with CO and H (1 1) in aprotic solvents in the presence of tertiary amines affords aldehydes[373,374]. Aryl chlorides, as tricarbonylchromium derivatives, are converted into aldehydes at 130 C[366], Sodium formate can be used as a hydride source to afford aldehydes. Chlorobenzene (514) was carbonylated at 150 °C to give benzaldehyde with CO and sodium formate by using dippp as a ligand[375,376]. 

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