syn-anti Conversion in octahedral bis(beta-diketonato)diorganotin(IV) derivatives containing fluorinated 4-acyl-5-pyrazolonato donors

Six-coordinate organotin derivatives L2SnR2 [L = 3-methyl-1-(4-trifluoromet hylphenyl)-4-R-3-C=O-5-pyrazoloriato (R-3 = CH3, L = L-1; R-3 = C6H5, L = L -2; R-3 = CF3, L = L-3; R = CH3, n-C4H9, CH5)] have been synthesized and ch aracterized by analytical and spectroscopic (H-1, C-13, Sn-119, and F-19 NM R, IR) techniques. Partial dissociation of one ligand in chlorohydrocarbon 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-trif luoromethylphenyl)p-yrazolon-5-ato]diphenyltin (6) shows the metal in a dis torted octahedron (skewed trapezoidal bipyramidal) with the two beta -diket onato donors in syn positions, a C-Sn-C bond angle of 165.2(2)degrees and t wo sets of tin-oxygen bonds [2.141(5) and 2.139(3) Angstrom for Sn-O(pyrazo lonato) and 2.250(4) and 2.272(5) A for Sn-O(acyl)]. Surprisingly, the rece ntly reported dimethyltin derivative has the anti configuration, in contras t to expectations based on all previous experience. Large scale Hartree-Foc k (HF) and Density Functional Theory (DFT) calculated structures for the an ti configuration of bis[4-benzoyl-3-methyl-1-(4-trifluoromethylphenyl)pyraz olon-5-atoldi- methyltin show good agreement with the experimental structur e obtained from X-ray methods. The hypothetical syn configuration of bis[4- benzoyl-3-methyl-1-(4-trifluoromethyl-phenyl)pyrazolon-5-ato]dimethyltin wa s also studied theoretically and both methods also predict characteristic s tructural features, such as: (from HF) a C-Sn-C bond angle of 150.0 degrees , Sn-O(pyrazolonato) bond lengths of 2.088 and 2.084 Angstrom and Sn-O(acyl ) bond lengths of 2.385 and 2.401 Angstrom. Results from the syn calculated structures suggest that intramolecular repulsive F . . .F interactions con tribute to the syn-anti conversion.