Synthesis of diorganotin derivatives containing asymmetric disubstituted bis(pyrazol-1-yl)methanes: X-ray crystal structures of (3-isopropylpyrazol-1-yl-5 '-isopropylpyrazol-1-yl)methane diphenyltin(IV) dibromide and bis(5-isopropylpyrazol-1-yl)methane diphenyltin(IV) dibromide

The reaction of 3-tert-butylpyrazole with dibromomethane under phase-transf er catalytic conditions afforded a new ligand, bis(3-tert-butylpyrazol-1-yl )methane [CH2(3-Bu(t)Pz)(2)]. However, the reaction of 3-isopropylpyrazole with dibromomethane under the same conditions yielded three isomers: bis(5- isopropylpyrazol-1-yl)methane [CH2(5-iPrPz)(2)], (3-isopropylpyrazol-1-yl-5 '-isopropylpyrazol-1-yl) methane [CH2(3-iPrPz-5'-iPrPz)] and bis(3-isopropy lpyrazol-1-yl)methane [CH2(5-iPrPz)(2)]. Although CH2(5-iPrPz), suffered th e greatest degree of steric hindrance, this ligand was obtained in highest yield. Upon treating the isomeric mixture with diorganotin halides in petro leum ether (60-90 degrees C), the isomers were isolated in the form of dior ganotin derivatives of bis(pyrazol-1-yl)methanes. The crystal structures of CH2(3-iPrPz-5'-iPrPz) SnPh2Br2 and CH2(5-iPrPz)(2)SnPh2Br2 determined by X -ray crystallography indicated that the isopropyl group in the 3-position o f the pyrazole ring decreased the coordination ability of CH, (3-iPrPz-5'-i PrPz), and the average Sn-N distance in CH2(3-iPrPz 5'-iPrPz) SnPh2Br2 (2.5 2 Angstrom) was longer than that in CH2(5-iPrPz)(2)SnPh2Br2 (2.435 Angstrom ). (C) 2000 Elsevier Science Ltd All rights reserved.