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)2C6H3]4} (HBArf) in CH2Cl2 followed by addition of 2 equiv of either HC(pz)3 or HC(3,5-Me2pz)3 (pz = pyrazolyl ring) leads to the formation of {Pb[HC(pz)3]2}{B[3,5-(CF3)2C6H3]4}2 (1) and {Pb[HC(3,5-Me2pz)3]2}{B[3,5-(CF3)2C6H3]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 Å, the sum of the van der Waals radii of two methyl groups. To facilitate this chemistry, the synthesis of Na{B[3,5-(CF3)2C6H3]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)2C6H3Br. 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, P1̄, a = 13.0133(6) Å, b = 17.2210(7) Å, c = 24.7634(11) Å, α = 71.7300(10)°, β = 82.3630(10)°, γ = 70.5120(10)°, Z = 2; 2 is triclinic, P1̄, a = 12.756(4) Å, b = 13.469(4) Å, c = 17.160(5) Å, α = 82.454(7)°, β = 89.904(8)°, γ = 72.995(7)°, Z = 1.