Bitopic bis- and tris(1-pyrazolyl)borate ligands: Syntheses and structural characterization

Starting from 1,4- and 1,3-diborylated benzene derivatives, bitopic bis(1-pyrazolyl)borates (K-2[1,4-(tBuBpz(2))(2)C6H4]; (Li,K)(2)[1,3-(tBuBpz(2))(2)C6H4]) and tris(l-pyrazolyl)borates (K-2[1,4-(Bpz(3))(2)C6H4]) have been synthesized (pz = pyrazolyl). X-ray single-crystal structure analyses revealed K-2[1,3-(tBuBpz(2))(2)C6H4] to establish a polymeric structure in the solid state. In contrast, the unsymmetrically substituted hydrolysis product Li-2[1,3-(tBuBpz(2))(tBuB(OH)pz)C6H4] forms discrete dimers in which four lithium cations are encapsulated by their organic ligands. As a representative of bitopic 1,2-diboryl benzene-based scorpionates, the 9,10-dihydro-9,10-diboraanthracene derivative K-2[(Bpz(2))(2)(C6H4)(2)] is described, which bears two pyrazolyl substituents at each of its boron atoms and stands out due to its stereorigidity.