The interaction of organotin(IV) acceptors with a benzoic acid containing two pyrazolone groups

Abstract

A new polydentate ligand, namely 2-[(5-hydroxy-1-phenyl-3-methylpyrazol-4-yl)(5-oxo-1,5-dihydro-4-phenyl-2-methylpyrazol-4-ylidene)methyl]benzoic acid (H₂QBz), has been prepared and characterized. The structure of the ligand H₂QBz consists of discrete molecules linked to one another by an extensive H-bonding network. The reactivity of H₂QBz towards [R₃Sn]₂O (R = Ph or Buⁿ) and R_nSnCl_4 − n (R = Me, Buⁿ, Bu^t, Ph, n = 2; R = Me, n = 3) has been investigated. Mono- and di-nuclear derivatives have been obtained depending on the nature of the starting acceptor and reaction conditions. [Ph₃Sn(HQBz)] 1 contains the HQBz ligand coordinated to Ph₃Sn through the deprotonated carboxylic group. In the complex [(H₂O)Ph₃Sn(HQBz)] 2, obtained by hydration of 1, the coordination sphere of tin is completed by bonding to a water molecule. The compounds [(R₃Sn)₂(QBz)] (R = Me, 3; Buⁿ, 4) contain the dianionic ligand bridged to two triorganotin(IV) fragments. In solution the mononuclear triorganotin(IV) aqua complexes [(H₂O)R₃Sn(HQBz)] (R = Ph, 2; Buⁿ, 5) loose the molecule of water and slowly decompose, yielding the free ligand and the R₃SnOH species. The diorganotin(IV) derivatives [R₂Sn(QBz)]₂ (R = Me, 6; Bu^t, 7; Buⁿ, 8; Ph, 9) are dinuclear both in the solid state and in solution. In the structure of [Me₂Sn(QBz)]₂6 both acidic H atoms of the ligand are substituted by tin: a dimeric centrosymmetric structure forms, involving two [QBz]²⁻ ligands acting as bridges between two tin atoms through both pyrazolone and benzoate moieties. Sn centers in the dimer are five-coordinated in a strongly distorted trigonal bypiramidal environment.