Alkali-Metal Complexes of a Tetramethylcyclopentadienyl-Functionalized Pyrazolylborate Ligand. Structures of [Li2(THF)3B(3-Mepz)3(C5Me4)] and [K2(THF)2B(3-Mepz)3(C5Me4)]∞

The new dianionic ligand [B(3-Mepz) 3 (C 5 Me 4 )] 2 - was prepared and structurally characterized as its lithium and potassium salts. In the solid state, [Li 2 (THF) 3 {B(3-Mepz) 3 }(C 5 Me 4 )] is monomeric, while [K 2 (THF) 2 {B(3-Mepz) 3 }(C 5 Me 4 )] ∞ consists of infinite puckered chains. The compounds were synthesized by reaction of B(NMe 2 ) 2 (C 5 Me 4 H) with 2 equiv of 3-methylpyrazole and 1 equiv of M(3-Mepz) (M = Li, K) followed by deprotonation with n-BuLi or KH. The crystal structure of the intermediate monoanion, [Li(THF) 2 {B(3-Mepz) 3 }(C 5 Me 4 H)], is also presented.