Synthesis and reactivity of iron carbene complexes

McCormick, Fred
Journal Title
Journal ISSN
Volume Title
Research Projects
Organizational Units
Organizational Unit
Journal Issue

A variety of Cp(CO)(,2)FeC(XR)YR('+) (X = S, Y = O, S, Se) carbene complexes are readily available from Cp(CO)(,2)Fe(CS)('+) by reaction with RY('-) to form Cp(CO)(,2)FeC(=S)YR, followed by alkylation with CH(,3)SO(,3)F or CH(,3)SO(,3)CF(,3). Similar treatment of CpFe(CO)(,3)('+) leads to Cp(CO)(,2)FeY(CH(,3))Ph('+) compounds rather than carbene complexes. The reactions of Cp(CO)(,2)FeC(SCH(,3))OCH(,3)('+) with alcohols and;Cp(CO)(,2)FeC(SCH(,3))(,2)('+) with dithiols yield Cp(CO)(,2)FeC(OR)OCH(,3)('+) and Cp(CO)(,2)FeCS(CH(,2))(,n)S('+) (n = 2, 3) carbene complexes, respectively. Several Cp(CO) (L)FeC(SCH(,3))(,2)('+) (L = CH(,3)NC, P(OPh)(,3), P(OCH(,3))(,3), PPh(,3), AsPh(,3), SbPh(,3), C(,5)H(,5)N) carbene complexes are easily prepared from the reactions of the photochemically generated Cp(CO) (CH(,3)CN)FeC(SCH(,3))(,2)('+) complex with the appropriate ligands. These;carbene complexes appear to react with amines by initial formation of ylide intermediates which collapse to the observed products according to the leaving group abilities of the carbene substituents (PhSe('-) (DBLTURN) Phs('-) > PhO('-) > CH(,3)S('-) > CH(,3)O('-)). Carbene complexes with two good leaving groups give isocyanide products, Cp(CO) (L)FeCNR('+), upon reaction with primary amines and aminocarbene complexes upon reaction with diamines, amino alcohols, amino thiols, and secondary amines. Complexes with only one good leaving group react with primary and secondary amines to form aminocarbene complexes, Cp(CO)(,2)FeC(XR)NRR'('+) (R' = R, H). Carbene complexes with two poor leaving groups generally yield uncharacterizable products upon reaction with amines. The;Cp(CO)(,2)FeC(SCH(,3))(,2)('+) complex reacts with RS('-) to form Cp(CO)(,2)FeC(SCH(,3))(,2)SR derivatives, and an X-ray diffraction study of Cp(CO)(,2)FeC(SCH(,3))(,3) is reported. The Cp(CO)(,2)FeC(SR)(,3) complexes react with CF(,3)SO(,3)H to give nearly quantitative yields of cationic dithiocarbene complexes. The Cp(CO)(,2)FeC(SCH(,3))(,2)('+) complex also reacts with LiAlH(,4) to produce Cp(CO)(,2)FeC(SCH(,3))(,2)H which is converted to the very moisture sensitive secondary carbene complex,;Cp(CO)(,2)FeC(SCH(,3))H('+), by reaction with CF(,3)SO(,3)H. The reactivity of the carbene carbon towards nucleophilic amines appears to decrease as (pi)-donation from the metal or the XR and YR substituents increases. Infrared studies indicate the order of decreasing (pi)-donor ability is N >> Se (GREATERTHEQ) S > O. The ('13)C-NMR resonances of C(carbene) occur in characteristic ranges for the various Cp(CO)(,2)FeC(XR)YR('+) carbene complexes. For the Cp(CO)(,2)FeC(OCH(,3))NRR' complexes, correlations between the ('13)C-NMR chemical shifts of C(carbene), the (upsilon)(CO) force constants, and the gas-phase basicities of the amine substituents suggest that N(--->)C(carbene) (pi)-donation increases as the basicity of the amine group increases. In the Cp(CO) (L)FeC(SCH(,3))(,2)('+) carbene complexes, Fe(--->)C(carbene) (pi)-backbonding increases and S(--->)C(carbene) (pi)-donation decreases as the (pi)-acceptor/(sigma)-donor ratio of the ligand, L, decreases;*DOE Report IS-T-913. This work was performed under Contract W-7405-eng-82 with the Department of Energy.

Chemistry, Chemistry (Inorganic-organic)