Syntheses of halogenated ethenyl isocyanide chromium complexes as organometallic precursor molecules for ethenyl and ethynyl isocyanides

The radical alkylation of tetraethylammonium pentacarbonyl(cyano)chromate 1 yielded the halogenated ethyl isocyanide complexes [(CO)(5)Cr(CN-CClX-CClY F)] 3 (a, X = Cl, Y= F: b. X = f, Y = F and c. X = Y = Cl) Dehalogenation o f 3 using zinc in diethyl ether gave [(CO)(5)Cr(CN-CX=CFY)] 4. The compound s 4a, b reacted with various nucleophiles exclusively at the difluoromethyl ene group. The unstable phosphorane 5, which is formed on reaction of 4b wi th trimethylphosphane. decomposed thermally and on hydrolysis yielding pent acarbonyl(1,2-difluoroethenyl isocyanide)chromium (6). The cyano substituen t can be introduced in the a position or the isocyanide function by reactio n of 4a, b with potassium cyanide, leading to the formation of [(CO)(5)Cr(C N-CX=CF-CN)] (7). Reactions of 4a, b with organolithium or organomagnesium compounds yielded [(CO)(5)Cr(CN-CX=CF-R)] (8) and [(CO)(5)Cr(CN-CF=CF-C=-C- CF=CF-NC)Cr(CO)(5)] (10). The trimethylsilyl group in 8a, b, d could be rem oved by a solution of potassium carbonate in methanol leading to [(CO)(5)Cr (CN-CX=CF-C-n-H)] (11) (n =2, 4). Octa carbonyldicobalt reacted with 8e und er coordination of the C-C triple bond to the hexacarbonyldicobalt fragment , resulting in the cluster compound 12. The crystal and molecular structure of 8i, 11a, b, and 12 were elucidated by X-ray crystallography. The alkeny l and alkynyl isocyanides CN-CCl=CF2 (13a), CN-CF=CF2 (13b). CN-CCl=CClF (1 3c), CN-CF=CFH (14), CN-CC-H (15), CN-CC-CN (16), and CN-CCl=CF-CN (17) wer e obtained by flash vacuum pyrolysis of 4a. 4b, 4c. 6, and 7a, respectively .