The interaction of organotin(iv) acceptors with 1,4-bis(5-hydroxy-1-phenyl-3-methyl-1H-pyrazol-4-yl)butane-1,4-dione

Abstract

From the interaction of organotin(IV) halides SnR₂Cl₂ with 1,4-bis(5-hydroxy-1-phenyl-3-methyl-1H-pyrazol-4-yl)butane-1,4-dione (Q2QH₂) in methanol in the presence of base the complexes [SnR₂(Q2Q)] (1: R = isobutyl (Buⁱ); 2: R = n-octyl (Ot); 3: R = n-dodecyl (Do)) have been synthesised. The reaction between equimolar quantities of R₂SnO and Q2QH₂ in toluene yields the dinuclear derivatives [SnR₂(Q2Q)]₂4 (R = Me) and 5 (R = Buⁿ) which have a cis-R₂Sn configuration in solution whereas from the reaction of Q2QH₂ with SnMe₂Cl₂ in CH₃OH in the presence of KOH, an insoluble probably polynuclear isomeric form of 4 formed. The reaction between Q2QH₂ and (R₃Sn)₂O produces the derivative [(SnR₃)₂(Q2Q)] (6: R = Buⁿ; 7: R = Ph). 6 reacts with water yielding the aquo complex [(SnBuⁿ₃)₂(Q2Q)(H₂O)] 8. The X-ray crystal structures of [SnBuⁿ₂(Q2Q)]₂5, [(SnBuⁿ₃)₂(Q2Q)] 6 and [(SnPh₃)₂(Q2Q)] 7 have been determined. Compound 5 is a binuclear species with the tin atoms in a distorted octahedral Sn-cis-C₂O₄ environment (skewed trapezoidal bipyramidal) with the C–Sn–C angles ranging from 107.28(14) to 112.4(2)°. The two different carbonyl groups coordinate the metal with different donor abilities (the Sn–O bond lengths range from 2.132(2) to 2.209(2) Å). Compounds 6 and 7 contain a dianionic ligand (Q2Q)²⁻ bridged to two triorganotin(IV) fragments with the tin atoms in a strongly distorted trigonal bipyramidal environment. ¹H, ¹³C and ¹¹⁹Sn NMR (rt and −55 °C) data indicate that the diorganotin(IV) derivatives 1–5 are not fluxional in solution whereas 6–8 slowly undergo disproportionation reaction, affording SnR₄ and [SnR₂(Q2Q)]₂.