POLY(PYRAZOLYL)BORATE COMPLEXES OF TIN(II) - CRYSTAL AND MOLECULAR-STRUCTURES OF [H2B(PZ)2]SNCL AND [B(PZ)4]2SN (PZ = PYRAZOLYL RING)

The complexes [H(n)B(pz)4-n](m)SnCl2-m (n = 0-2; m = 1, 2; pz = pyrazolyl ring) have been prepared by the reaction of SnCl2 and the ligand salts in the appropriate stoichiometries. The complexes are air stable in the solid phase with solution stability increasing with the number of poly(pyrazolyl)borate ligands and the number of pyrazolyl rings present in the ligand. The structure of [H2B(pz)2]SnCl (1) has been determined by X-ray crystallography: monoclinic, P2(1)/n, a = 4.894 (5) angstrom, b = 27.079 (23) angstrom, c = 7.744 (6) angstrom, beta = 100.32 (7) degrees, V = 1009.8 (16) angstrom 3, Z = 4, R(F) = 5.67%. The basic geometry about the three-coordinate tin is trigonal pyramidal. The donor atom angles through the tin atom average 86-degrees, and the lone pair on tin presumably occupies the fourth vertex. There are also weak tin-chlorine bridging interactions forming centrosymmetric dimeric units. In both the solution and solid phases, [H2B(pz)2]2Sn (2) has a trigonal-bipyramidal geometry with each ligand spanning an axial and equatorial site. The tin lone pair presumably occupies the remaining equatorial vertex. The molecule shows two types of dynamic processes in solution. The axial and equatorial positions equilibrate with a barrier of 10.2 kcal/mol at -58-degrees-C. Also, the barrier to the boat-boat flip of the SnN4B rings formed by each ligand is determined to be 10.3 kcal/mol at -52-degrees-C. [HB(pz)3]SnCl (3) and [B(pz)4]SnCl (5) are believed to have a similar trigonal-bipyramidal geometry, and both are fluxional in solution. An X-ray crystallographic study of [B(pz)4]2Sn (6) shows it to be four-coordinate with a highly distorted trigonal-bipyramidal structure: monoclinic, P2(1)/n, a = 10.754 (3) angstrom, b = 17.109 (4) angstrom, c = 15.566 (3) angstrom, beta = 91.236 (20)degrees, V = 2863.6 (12) angstrom 3, Z = 4, R(F) = 3.63%. Each ligand is bidentate with one of the noncoordinated pyrazolyl rings located fairly close to the tin. Correlations from the Sn-119 NMR chemical shifts of these complexes indicate that 6 is also four-coordinate in solution. The H-1 NMR spectra show that 6 is dynamic in solution. All of the pyrazolyl rings are equivalent at ambient temperatures with a 3/1 pattern observed at -80-degrees-C. The low-temperature spectrum can be explained by a low-energy process that equilibrates the three pyrazolyl rings in each ligand close to tin, but the fourth ring remains unique. At higher temperatures, the fourth ring also equilibrates by a boat-boat flip of the six-membered ring (10.5 kcal/mol barrier). The Sn-119 data indicate that [HB(pz)3]2Sn (4) may be five-coordinate in solution.