Alkali-metal pyrazolate complexes with unusual pyrazolate coordination modes and pseudocubane motifs

The dimeric complex [Li(Ph(2)pz)(OEt2)](2) (1) and tetrameric cluster [Na(Ph(2)pz)(thf)](4) (2) were prepared by treatment of alkali-metal reagents (nBuLi and Na(N(SiMe3)(2)}, respectively) with 3,5-diphenylpyrazole (Ph(2)pzH) in Et2O (1) or THF (2). The polymer [Na(tBu(2)pz)](n) center dot (3) was obtained from reaction at elevated temperature in a sealed tube between Na metal and 3,5-di-tert-butylpyrazole (tBu(2)pzH). The complex [Na-4(tBu(2)pz)(2) (thf)(3)(obds)](2) (4; obds=(OSiMe2)(2)O) was obtained as a minor product from prolonged treatment of tBu(2)pzH with elemental sodium in a silicone-greased flask. All four alkali-metal pyrazolato complexes were characterized by IR and H-1 NMR spectroscopy and X-ray crystallography. The Li dimer 1 displays mu-eta(2):eta(1) lithium-pyrazolato binding, in which both lithium atoms are four-coordinate. Room- and variable-temperature NMR studies (H-1, C-13, and Li-7) of 1 suggest similar behavior in solution, with peaks coalescing at low temperatures. Complexes 2 and 4 display distorted cubane structures. In 2, all the sodium atoms are five-coordinate, whereas 4 contains two sodium/pyrazolate/thf clusters (4:2:3 ratio) bridged by two obds(2-) units, as well as two four-coordinate and two five-coordinate sodium atoms. Compound 3 is composed of two independent chains with the unusual coordination modes eta(5):eta(2):eta(2), mu(3)-eta(5):eta(2) :eta(1), and mu(3)-eta(4):eta(2):eta(1), with five-, six-, and seven-coordinate sodium atoms. Two oxo-centered M-8 cage complexes [(tBu(2)pz)(6)Li8O] (5) and [(tBu(2)pz)(6)Na8O] (6) were obtained as by-products from attempted preparation of [Li(tBu(2)pz)] and [Na(tBu(2)pz)], respectively, and their structures were determined.