Syntheses of Cationic Lead(II) and Tin(II) Complexes Containing Tris(pyrazolyl)methane Ligands. Control of Stereochemistry by Variation in Ligand Substitution

The addition of 2 equiv of HBF 4 ·Et 2 O to a THF suspension of Pb(acac) 2 (acac = acetylacetonate) followed by addition of 1 molar equiv of the tris(pyrazolyl)methane ligand HC(3,5-Me 2 pz) 3 (pz = pyrazolyl ring) results in the immediate precipitation of {[HC(3,5-Me 2 pz) 3 ]Pb}(BF 4 ) 2 ( 1 ). The complex {[HC(3,5-Me 2 pz) 3 ] 2 Pb}(BF 4 ) 2 ( 2 ) was prepared by precipitation from an acetone solution of 1 containing an excess of HC(3,5-Me 2 pz) 3 . Both {[HC(pz) 3 ] 2 Pb}(BF 4 ) 2 ( 3 ) and {[HC(pz) 3 ]Pb}(BF 4 ) 2 ( 4 ) are prepared by the addition of the respective equivalent amounts of HC(pz) 3 to the HBF 4 ·Et 2 O−Pb(acac) 2 THF solution. The lead ion in 1 is three coordinate with normal Pb−N distances ranging from 2.379(14) to 2.434(16) Å (average = 2.41 Å). The six-coordinate lead ion in 2 is in a trigonally distorted octahedral environment with equivalent Pb−N bond distances (2.635(7) Å). The lone pair on lead is stereochemically inactive and does not appear to influence the structure. The lead ion in 3 is in an asymmetric six-coordinate environment with disparate Pb−N bond distances ranging from 2.609(5) to 2.789(5) Å (average = 2.69 Å) and very different interligand N−Pb−N bond angles. Reactions of equal molar amounts of 1 with either K[HB(3,5-Me 2 pz) 3 ] or K[HB(pz) 3 ] yield {[HC(3,5-Me 2 pz) 3 ]Pb[HB(3,5-Me 2 pz) 3 ]}(BF 4 ) ( 5 ) and {[HC(3,5-Me 2 pz) 3 ]Pb[HB(pz) 3 ]}(BF 4 ) ( 6 ). The highly asymmetric structure of 5 is best described as a distorted square base pyramid. The [HB(3,5-Me 2 pz) 3 ] - ligand is tridentate with Pb−N distances ranging from 2.375(7) to 2.475(8) Å (average = 2.43 Å), whereas the HC(3,5-Me 2 pz) 3 ligand is bidentate with long Pb−N distances of 2.745(7) and 2.827(7) Å. Reaction of Sn(O 3 SCF 3 ) 2 with 1 molar equiv of HC(3,5-Me 2 pz) 3 in THF yields the complex {[HC(3,5-Me 2 pz) 3 ]Sn}(O 3 SCF 3 ) 2 ( 7 ).