Sodium hydrotris(methimazolyl)borate, a novel soft, tridentate ligand: preparation, structure and comparisons with sodium hydrotris(pyrazolyl)borate †

Structural and Theoretical Insights into Metal–Scorpionate Ligand Complexes

“…Due to the lanthanide contraction and the more efficient overlap of the tungsten d-orbitals with those on sulfur, the M-S distances in the two complexes are similar, with the Mo-S distances in the molybdenum complex being slightly longer than the equivalent W-S distances. Consistent with the other structures obtained from the metal complexes of this ligand, [6][7][8][9][10][11][12][13] the methimazolyl rings of the Tm Me ligand lie at a mean angle of 33.5°to the imaginary H-B-M axis. This has the effect of reducing the symmetry of the M(Tm Me ) fragment from C 3v to approximately C 3 thus minimising the steric strain in the eight-membered chelate rings.…”

“…The three sulfur atoms revert to a position above the BN 3 plane, with the methimazoles adopting a C 3 -symmetric propeller con-formation around the B-O axis reminiscent of the orientation in the crystal structure of the free parent Tm Me anion. [7] The presence of the large DMF unit does however somewhat reduce the angle that the heterocyclic rings adopt to the main B-O axis. Oxidation of the anion and removal of the small negatively charged hydride leaves the borane with less electron density to distribute around the B(mt) 3 moiety, an effect which is evident in the C=S bond lengths, which are much shorter (i.e.…”

“…The introduction of steric bulk was quickly achieved, and latterly more limited attention has been given to their electronic properties. [5] We have sought to extend the scope of the scorpionate ligands by developing "soft" tripodal systems such as the hydrotris(methimazolyl)borate anion (Tm Me ) [6,7] (Scheme 1), replacing the heterocyclic nitrogen donors of hydrotris(pyrazolyl)borate anion (Tp) with thione sulfur donors. Initially, studies using these ligands produced results which were qualitatively in accordance with accepted hard and soft acid/base concepts.…”

Copper Complexes of Mono‐ and Ditopic [(Methylthio)methyl]borates: Missing Links and Linked Systems En Route to Copper Enzyme Models

“…deviation 0.038 ) through Cu(1) and its four N ligands. The four Cu À N bond lengths range from Cu(1)ÀN(42) = 1.980(7) to Cu(1)ÀN(12) = 2.009 (7) and are thus in good agreement with the corresponding values in the related five-coordinate Cu II complexes. [58,59] The molecular structures of K [11] and 12 are distinctly different.…”

“…One way to alter the donor/acceptor properties of scorpionate ligands over a wider range is to replace the pyrazolyl rings by phosphorus-(B [3][4][5] ) or sulfur-containing groups (C, [6,7] D; [8][9][10][11][12] Figure 1). Similar to the parent scorpionates A, ligands B-D provide a monoanionic, tridentate, face-capping coordination mode, but they differ from A with regard to the softness of their donor sets.…”