ALKYLATION AND ACYLATION OF THE IRON CARBONYL ANION [(CO)4FESI(CH3)3]- - EVIDENCE FOR 1,3-SILATROPIC SHIFTS FROM IRON TO ACYL OXYGEN
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Anions K+[(CO)4FeSi(CH3)3]- (K+-l) and Na+-1 are treated with CH3OSO2F, CH3OSO2CF3, and CH3CH2OSO2F (2 min, 0 C) and C6H5CH2Br and H2C=CHCH2Br (0.5 h, 25 C). Labile, air-sensitive alkyls cis-(CO)4Fe(R)Si(CH3)3 (2) are subsequently isolated in 34-89% yields. When R = CH3 (2a) or CH2C6H5 (2c), room-temperature reductive elimination of RSi(CH3)3 occurs. Reactions of K+-l or Na+-1 with acylating agents CH3COBr, CH3CH2COBr, and C6H5CH2COBr give H2C=CHOSi(CH3)3, CH3CH= CHOSi(CH3)3, and C6H5CH=CHOSi(CH3)3, respectively. On the basis of low-temperature NMR and IR monitoring and literature precedent, it is proposed that initial acylation of 1 is followed by a rapid 1,3-silatropic shift to give the observable (silyloxy)carbene complex (CO)4Fe=C(CH2R)OSi(CH3)3, followed by a 1,2-hydride shift to give olefin complex (CO)4Fe(RCH=CHOSi(CH3)3), which in turn dissociates RCH=CHOSi(CH3)3. This interpretation is supported by (1) the independent synthesis and rearrangement of (CO)4Fe=C(CH3)OSi(CH3)3 from Li+(CO)4Fe=C(CH3)O- and (CH3)3SiBr, (2) the synthesis of an isolable car bene complex, (CO)4Fe=C(C(CH3)3)OSi(CH3)3, from 1 and (CH3)3CCOBr, and (3) the reaction of 2a with PPh3 to give (Ph3P)(CO)3Fe=C(CH3)OSi(CH3)3. 1984, American Chemical Society. All rights reserved.
