Tris(Pyrazolyl)Methane Ligands: The Neutral Analogs of Tris(Pyrazolyl)Borate Ligands

Despite the widespread use of tris(pyrazolyl)borate ligands, their isoelectronic, neutral analogs, tris(pyrazolyl)methane ligands, have not been extensively studied. By use of appropriate starting materials, such as [Cu(NCMe)4]PF6 or [Cd2(thf)5](BF4)4, stable cationic complexes of the ligands HC(3,5-Me2pz)3, HC(3-Phpz)3 and HC(3-Bu1pz)3 can be prepared with the metals copper(I), silver(I), cadmium(II), lead(II) and thallium(I). In many cases isoelectronic groups of complexes, such as [HB(3,5-Me2pz)3]2Cd. {[HC(3,5-Me2pz)3]Cd[HB(3,5-Me2pz)3]}+, and {[HC(3,5-Me2pz)3]2Cd}2+, have been prepared and shown to have very similar structures. The 113Cd NMR chemical shifts of the three complexes are also very similar. The isoelectronic complexes {[HC(pz)3]2Pb}2+ and [HB(pz)3]2Pb have similar distorted six-coordinate structures. The isoelectronic pair {[HC(3,5-Me2pz)3]2Pb}2+ and [HB(3,5-Me2pz)3]2Pb have very similar octahedral structures in which the lone pair on the lead(ll) is stereochemically inactive. Thus, for most cases the tris(pyrazolyl)methane and tris(pyrazolyl)borate ligands bond to these metals in a similar fashion.