Abstract
Novel tin(II) β‐diketonate Sn(Q)~2~ complexes [HQ = 1‐R^1^‐3‐R^3^‐4‐R^4^(C=O)‐pyrazol‐5‐one; HQ^C^: R^1^ = Ph, R^3^ = Me, R^4^ = Cy; HQ^S^: R^1^ = Ph, R^3^ = Me, R^4^ = CHPh~2~; HQ^L^: R^1^ = Ph, R^3^ = Me, R^4^ = CH~2~Ph; HQ^T^: R^1^ = Ph, R^3^ = Me, R^4^ = CH~2~__t__Bu; HQ^E^: R^1^ = Ph, R^3^ = Me, R^4^ = Et; HQ^B^: R^1^ = Ph, R^3^ = Me, R^4^ = __t__Bu; HQ^W^: R^1^ = Ph, R^3^ = Me, R^4^ = p‐(__t__Bu)Ph; HQ^R^: R^1^ = Ph, R^3^ = Me, R^4^ = p‐[(CH~2~)~5~CH~3~]Ph; HQ^N^: R^1^ = p‐NO~2~Ph, R^3^ = Me, R^4^ = Ph; HQ^M^: R^1^ = Me, R^3^ = Me, R^4^ = Ph; HQ^D^: R^1^ = Me, R^3^ = Me, R^4^ = Me; HQ^P^: R^1^ = Ph, R^3^ = Ph, R^4^ = Ph; HQ^G^: R^1^ = Ph, R^3^ = Ph, R^4^ = Me; HQ^F^: R^1^ = p‐CF~3~Ph, R^3^ = Me, R^4^ = Ph; HQ^H^: R^1^ = p‐CF~3~Ph, R^3^ = Me, R^4^ = Me] have been isolated and characterized by single‐crystal X‐ray diffraction analyses, IR, ^1^H, ^13^C, ^119^Sn NMR and ^119^Sn Mössbauer spectroscopy, ESI mass spectrometry, conductivity and molecular weight measurements. The tin complexes SnQ~2~ are air‐stable, contrary to equivalent compounds of classical β‐diketones, and adopt mononuclear pseudo‐trigonal‐bipyramidal structures (pSnO~4~, where p is a stereochemically active lone electron pair) in which both ligands chelate a single metal center, as confirmed in the X‐ray crystal structure of Sn(Q^L^)~2~. This structure fits a trend for all “SnO~4~” compounds: Sn−O(primary) and Sn−O(secondary) bonds are associated with small O(primary)−Sn−O(primary) and wide O(secondary)−Sn−O(secondary) bond angles. The reactivity of Sn(Q^T^)~2~ toward RI (R = Me or Et) and CrCO~6~ has been investigated. The compounds PbQ~2~ (HQ = HQ^T^, HQ^B^, HQ^W^, HQ^D^) have been also synthesized and the X‐ray structures of Pb(Q^B^)~2~ and Pb(Q^T^)~2~ in the solid state determined. These are different from SnQ~2~ and are composed of “PbO~4~” moieties with additional interactions from neighboring units to produce polymeric forms. Compound Pb(Q^T^)~2~ is unusual in having the metal−O(pyrazolonato) bond longer than the metal−O(acyl) one, probably due to a Pb−arene interaction with a neighboring phenyl ring. The sterically less hindered Pb(Q^D^)~2~ reacts with phen (1,10‐phenanthroline) yielding the mixed ligand complex [Pb(Q^D^)~2~(phen)]. In this work, in addition to the different coordination numbers expressed by Sn and Pb, associated with the larger covalent radius of the latter, the binding mode of 4‐acyl‐5‐pyrazolonates to Pb is syn whereas for Sn it is anti. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)