Stable heterocyclic stannylene: The metal, ligand-centered reactivity, and effective catalytic hydroboration of aldehydes

A stable O,N‐heterocyclic stannylene 1 bearing novel tetradentate 2,4‐di‐tert‐butyl‐6‐((2‐(1‐((pyridin‐2‐ylmethyl)imino)ethyl)phenyl)amino)phenolate ligand (^RAPH₂) was synthesized and characterized. Complex 1 is monomeric in crystal and solution due to two additional intramolecular N → Sn donor–acceptor interactions. The diverse reactivity of compound 1 towards various iron carbonyl compounds was studied. Oxidative addition of [Fe₂(μ‐S₂)(CO)₆]₂ to the tin center of 1 resulted in a new six‐coordinate Sn(IV) compound 2 containing two Sn–S bonds. The reaction of 1 with Fe₂(CO)₉ led to the formation of a stable tin(II) adduct 3 – ^RAPSn‐Fe(CO)₄. The interaction between 1 and [(η⁵‐C₅H₅)Fe(CO)₂]₂ resulted in a transformation of the ligand skeleton. During this reaction, the tin center is oxidized to the tetravalent state, and the donor ═N–CH₂–Py group is converted into an anionic one with the loss of the methylene hydrogen atom. The molecular structures of all obtained compounds were determined by single‐crystal X‐ray diffraction. The novel stannylene 1 demonstrates striking activity in benzaldehydes' hydroboration reactions down to 0.02 mole percent of the catalyst loading under mild conditions.