Control of the stereochemical impact of the lone pair in lead(II) tris(pyrazolyl)methane complexes.: Improved preparation of Na{B[3,5-(CF3)2C6H3]4}

The reaction of Pb(acac)(2) with 2 equiv of [H(Et2O)(2)]{B[3,5-(CF3)(2)C6H3]4} (HBArf) in CH2Cl2 followed by addition of 2 equiv of either HC(pz)(3) or HC(3,5-Me(2)pz)(3) (pz = pyrazolyl ring) leads to the formation of {Pb[HC(pz)(3)](2)}-{B[3,5-(CF3)(2)C6H3](4)}(2) (1) and {Pb[HC(3,5-Me(2)pz)(3)](2)}{B [3,5-(CF3)(2)C6H3](4)}(2) (2), respectively. The cation in 1 has a distorted octahedral structure with a stereochemically active lone pair on lead(II). In contrast, the cation in 2 is trigonally distorted octahedral with the lone pair on the lead(II) clearly stereochemically inactive. The driving force for this cation to have a stereochemically inactive lone pair is that in this geometric arrangement the interligand distances between adjacent 3-position methyl groups are close to 4.0 Angstrom, the sum of the van der Waals radii of two methyl groups. To facilitate this chemistry, the synthesis of Na{B [3,5-(CF3)(2)C6H3](4)}, needed to prepare HBArf, has been dramatically improved. The main change is to add NaBF4 to the reaction mixture before forming the Grignard from the reaction of magnesium and 3,5-(CF3)(2)C6H3Br. The Grignard reacts with the NaBF4 as it forms, reducing the danger of explosion and leading to a higher isolated yield of the product. Crystallographic information: 1 is triclinic, P (1) over bar, a 13.0133(6) Angstrom, b = 17.2210(7) Angstrom, c = 24.7634(11) Angstrom, alpha = 71.7300(10)degrees, beta = 82.3630(10)degrees, gamma = 70.5120(10)degrees, Z = 2; 2 is triclinic, P (1) over bar, a = 12.756(4) Angstrom, b = 13.469(4) Angstrom, c = 17.160(5) Angstrom, alpha = 82.454(7)degrees, beta = 89.904(8)degrees, gamma = 72.995(7)degrees Z = 1.