Novel types of organic S-Fe-CO complexes: Reaction of [SFe ₃(CO)₉]^2- with propargyl bromide

We have synthesized a series of novel organic S-Fe-CO complexes from the reaction of the sulfur-capped triiron carbonyl cluster [SFe₃(CO) ₉]^2- with the bifunctional propargyl bromide and subsequent reactions. When [SFe₃(CO)₉]^2- was treated with 2 equiv of propargyl bromide in MeCN, three new organo-bridged iron-sulfur carbonyl complexes, [Et₄N][Fe₃(CO) ₉(μ₃-η³:η¹: η²-CH₂C(S)CHC(O))] ([Et₄N]-[1]), (μ₃-S)Fe₃(CO)₉(μ₃- η¹:η²:η¹-C(H)=C(CH₃)) (2), and Fe₂(CO)₆(μ₂-η¹: η²:η¹-C(H)=C(CH₃CH)) (3), were obtained. The novel anionic acyl cluster 1 is a CO insertion product and can be considered to display a SFe₃ core bridged by an allylcarbonyl ligand, H₂C=CCHC(O), in μ₂-η³:η¹ fashion. While cluster 2 can be seen to possess a SFe₃ core coordinated with a propyne ligand, CH≡C(CH₃), complex 3 exhibits a SFe₂ core bridged by a α-methylvinylcarbonyl ligand, C(O)C(CH₃)=CH. The anionic cluster 1 could transform to 2 and 3 upon treatment with excess propargyl bromide. When [Et₄N][1] was reacted with the oxidizing agent [Cu(MeCN)₄][BF₄], the neutral diiron complex Fe₂(CO)₆(μ₂- η²:η³-C(O)CHC(S)(CH₃)) (4) was obtained as the major product. Complex 4 is seen to possess a SFe₂ core linked by a β-methylvinylcarbonyl ligand, C(O)CH=C(CH₃). More interestingly, the methylation of the acyl cluster 1 with CF₃SO ₃Me afforded a unique triiron cluster carbene, Fe₃(CO) ₉(μ₃-η¹:η⁴: η²-CH₂C(S)CHC(OCH₃)) (5). This paper describes a rare example of the reaction of a sulfur-capped triiron cluster with the bifunctional propargyl bromide and related reactions, in which a new series of iron-sulfur carbonyl complexes coordinated with novel organic fragments results, and the relative stability of some resultant complexes is discussed on the basis of theoretical calculations.