Cyclobutadienes mass spectra

Cyclobutadiene(cyclopentadienyl)cobalt has been prepared by Amiet and Pettit (4) from dichlorocyclobutene and sodium tetracarbonyl cobaltate, while Rosenblum and North (177) prepared it from photo-a-pyrene and C5H5Co(CO)2. The mass spectrum shows that fragmentation of the cyclobutadiene ring occurs before loss of the cyclopentadienyl ring, and the major ions in the spectrum correspond to M+ m/e 176, [M — C2H2]+ m/e 150, and [M — C4H4]+ m/e 124 (4, 177). Metastable peaks have been reported by Rosenblum and North for the transitions 176 150,... 

The mass spectrum of tricarbonyliron cyclobutadiene derivative 282 shows fragments corresponding to the stepwise loss of four CO molecules and finally of C2H2 (78AJC1607). 

The photoisomer of a-pyrone was synthesized in order to prepare a cyclobutadiene.64 It was pyrophoric in air at room temperature and its mass spectrum was similar to that of furan. Flash thermolysis was reported to give many compounds, as shown in Scheme 26.65 No evidence for the formation of cyclobutadiene was obtained, but carbon dioxide and acetylene products seem to support its intervention. 

Photoreaction of a-pyridones give [2 + 2] dimers. The photolysis of N-methyl-a-pyridone in a dilute solution gives a bicyclic isomer, which has a mass spectrum showing m/e 52, perhaps due to cyclobutadiene (Scheme 30).64... 

Excess iron nonacarbonylFe2(CO)9 was stirred with 3-chloro-(2-chloromethyl) propene in ether at room temperature for 12 hr. The pale yellow complex, mp 28-29°, was isolated from the reaction mixture. Propose a plausible structure from the following data Analysis C, 43.29 and H, 2.90 mass spectrum m/e 194, 166, 138, and 110 IR 1998 and 2064 cm NMR 8.00t(s) 7r-cyclobutadiene iron tricarbonyl 6.09t 7r-allyl-7r-cyclopentadienyl iron monocarbonyl 7.33t (syn), and 9.32t (anti). 

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