Syn−anti Conversion in Octahedral Bis(β-diketonato)diorganotin(IV) Derivatives Containing Fluorinated 4-Acyl-5-pyrazolonato Donors

Abstract

Six-coordinate organotin derivatives L2SnR2 [L = 3-methyl-1-(4-trifluoromethylphenyl)-4-R3-C=O-5-pyrazolonato (R3 = CH3, L = L1; R3 = C6H5, L = L2; R3 = CF3, L = L3; R = CH3, n-C4H9, C6H5)] have been synthesized and characterized by analytical and spectroscopic (1H, 13C, 119Sn, and 19F NMR, IR) techniques. Partial dissociation of one ligand in chloro-hydrocarbon solvents gives rise to cationic five-coordinate L-(solvent)-diorganotin(IV) complexes. The X-ray crystal structure of bis[4-benzoyl-3-methyl-1-(4-trifluoromethylphenyl)pyrazolon-5-ato]diphenyltin (6) shows the metal in a distorted octahedron (skewed trapezoidal bipyramidal) with the two β-diketonato donors in syn positions, a C−Sn−C bond angle of 165.2(2)° and two sets of tin−oxygen bonds [2.141(5) and 2.139(3) A for Sn−O(pyrazolonato) and 2.250(4) and 2.272(5) A for Sn−O(acyl)]. Surprisingly, the recently reported dimethyltin derivative has the anti configuration, in contrast to expectations based on all previous experience. Large scale Hartree−Fock (HF) and Density Functional Theory (DFT) calculated structures for the anti configuration of bis[4-benzoyl3-methyl-1-(4-trifluoromethylphenyl)pyrazolon-5-ato]dimethyltin show good agreement with the experimental structure obtained from X-ray methods. The hypothetical syn configuration of bis[4-benzoyl-3-methyl-1-(4-trifluoromethylphenyl)pyrazolon-5-ato]dimethyltin was also studied theoretically and both methods also predict characteristic structural features, such as: (from HF) a C−Sn−C bond angle of 150.0°, Sn−O(pyrazolonato) bond lengths of 2.088 and 2.084 A and Sn−O(acyl) bond lengths of 2.385 and 2.401 A. Results from the syn calculated structures suggest that intramolecular repulsive F···F interactions contribute to the syn−anti conversion.