Stereospecific syntheses of functionalised iron alkyl complexes with a stereogenic metal center from an iron formyl precursor

Article abstract of DOI:10.1016/0022-328X(95)06026-S

Treatment of the stable formyl complex Fe(C₅Ph₅)(CO)(PMe₃)CHO (1) with an excess of methyl triflate and subsequent addition of NH₄PF₆ produces the secondary carbene complex [Fe(η⁵-C₅Ph₅)(CO)(PMe₃)(=CHOMe)][PF₆] (2, 93%). Methyl lithium acts as a dealkylating reagent with 2 to regenerate 1 (81%). Treatment of methoxycarbene complex 2 with LiAlH₄ gives the methoxymethyl complex Fe(η⁵-C₅Ph₅)(CO)(PMe₃)(CH₂OMe) (3) in 95% yield. Similarly, reaction of 2 with LiAlD₄ gives a 90: 10 mixture of Fe(η⁵-C₅Ph₅)(CO)(PMe₃)(CHDOMe) (3 d₁, 80%) diastereoisomers. The carbene complex 2 reacts with MeONa to give the iron dimethylacetal complex Fe(η⁵-C₅Ph₅)(CO)(PMe₃){CH(OMe)₂} (4, 55%). The cyano(methoxy)methyl complex Fe(η⁵-C₅Ph₅)(CO)(PMe₃){CH(CN)(OMe)} (5, 85%) is obtained from the reaction of 2 with 1 equivalent of KCN. NMR analyses of the crude product revealed that complex 5 was formed as a 85: 15 mixture of diastereoisomers. The carbene complex 2 reacts with TMSC≡CLi to afford a 90: 10 mixture of diastereoisomers of the stable methoxy(trimethylsilylethynyl)methyl iron complexes Fe(C₅Ph₅)(CO)(PMe₃) {CH(OMe)(C≡CTMS)} (6). After extraction and filtration 6 is isolated as a pure diastereoisomer in 63% yield.