Alkylation and acylation of the iron carbonyl anion [(CO)4FeSi(CH3)3]-. Evidence for 1,3-silatropic shifts from iron to acyl oxygen

Article abstract of DOI:10.1021/om00087a001

Anions K⁺[(CO)₄FeSi(CH₃)₃]^- (K⁺-I) 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 CH₂C₆H2 (2c), room-temperature reductive elimination of RSi(CH₃)₃ occurs. Reactions of K⁺-1 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 carbene 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.