Reactivity of an Iron Carbonyl Dianion Dictated by a Lewis Basic Appendant

Reactions of an Fe(-II) carbonyl dianion bearing an amino appendant with diverse electrophiles generated a range of unprecedented products, most notably a diphenylstannylene complex formed via chelate-assisted oxidative addition of Sn−Ph bond. The amino appendant is proposed to play a pivotal role in differentiating the reactivity of this dianion to the basic [Fe(CO)₄]²⁻ species.

Abstract

Studies toward transition metals in negative oxidation states are much less explored compared to those in zero or positive oxidation states. In this study, we present the synthesis and reactivity studies of an Fe(-II) carbonyl dianion (3) featuring an appended Lewis base, [(L)Fe(CO)₃]²⁻ (L=Ph₂PCH₂CH₂NMe₂). Unlike the well-known reactivity of [Fe(CO)₄]²⁻ with common electrophiles (E ⁺) which typically forms [(E)₂Fe(CO)₄], 3 reacted with 2 equiv. of Ph₃SnCl to afford a mixture of two products: one being an Fe(II) bis(triphenylstannyl) product (4), and the other an Fe stannylene product (5). Further insights into the reactivity of 3 was elucidated through its reactions with 2 equiv. of Cy₃SnCl or Me₃SiCl, producing an Fe(II) bis(tricyclohexylstannyl) product (8) and a zwitterionic complex (11), respectively, the latter emerging via THF ring-opening. Intermediates generated from reactions of 3 with 1 equiv. of each electrophile were isolated to shed light on the reaction mechanisms, highlighting the influence of appended Lewis base on the reactivity of metal carbonyl dianions, especially the generation of the novel stannylene complex 5. The electronic structure of this paramagnetic stannylene complex was also investigated by computational studies.

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