RESUMEN
The preparation of a resin-supported boron-scorpionate ligand and its nickel(II) coordination complexes are reported. The supported ligand is prepared as its potassium salt, making it a general reagent suitable for chelation of any transition metal ion. Resin-immobilized benzotriazole (Bead-btz) reacted cleanly with KTp* (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) by heterocycle metathesis in warm dimethylformamide (DMF) to yield bead-Tp'K, {resin-btz(H)B(pz*)(2)}K. Significantly, bead-Tp'K readily bound nickel(II) from simple salts with minimal leaching of the nickel ion. Bead-Tp'NiNO(3) reacts further with cysteine thiolate (ethyl ester), imparting the deep green color to the beads characteristic of a Tp(R)NiCysEt coordination sphere. Bead-Tp'NiCysEt exhibited an oxygen sensitivity similar to Tp*NiCysEt in solution (Inorg. Chem. 1999, p 5690) and also independently verified for a selenocystamine analogue, Tp*NiSeCysAm. Addition of fresh cysteine thiolate ethyl ester to oxidized bead-Tp'NiCysEt reproduced the original green color. Heterocycle metathesis was also used to prepare KTp' as a white solid. Reaction with nickel(II) gave (Tp')(2)Ni, separable into two different isomers. The air-sensitive molybdenum(0) complex, [PPh(4)][Tp'Mo(CO)(3)], was also prepared and the C(s) complex symmetry demonstrated by infrared and (13)C NMR spectroscopies. Immobilized TpmMo(CO)(3) was prepared from the previously reported resin-supported tris(pyrazolyl)methane. In contrast to its weak coordination of nickel(II) (Inorg. Chem. 2009, p 3535), bead-Tpm proved a strong chelate toward this second row metal. The supported scorpionates described here should find use in studies of selective metal-protein binding, metalloprotein modeling, and heterogeneous catalysis, and render such scorpionate applications amenable to combinatorial methods.
RESUMEN
Single-scorpionates of nickel(II), Tp(R)NiX or Tpm(R)NiX, are kinetic products whose preparation has generally required considerable steric constraints on the ligands (i.e., R = phenyl, tert-butyl, or isopropyl) to prevent formation of intractable two-ligand products like (Tp(R))(2)Ni. It is well established that the facial tridentate chelates hydrotris(3,5-dimethylpyrazolyl)borate (Tp*(-)), tris(3,5-dimethylpyrazolyl)methane (Tpm*), and trispyrazolylmethane (Tpm), all readily form two-ligand complexes as thermodynamic products. For the first time we report a route to the single-ligand complex TpmNiX(2)(OH(2))(n) (X = Cl and Br). We also report a novel method for making single-ligand nickel(II) scorpionate complexes using preformed tetrahalonickelate(II) ion in nitromethane. The complex Tpm*NiCl(2)(OH(2))(n) was also prepared here for the first time utilizing an alternative method first reported by Zargarian and co-workers (Inorg. Chim. Acta 2006, 2592). TpmNiX(2)(OH(2))(n) are kinetic products, and although they are stable indefinitely in the solid state, they readily convert to the thermodynamic product (Tpm)(2)Ni(2+) in solution over the course of several hours at room temperature and in a matter of minutes at 100 degrees C. The new nitromethane/NiX(4)(2-) method offers an alternative route to monoscorpionates of first row transition metals, for which tetrahalometallate ions are common. HOCH(2)Tpm (2,2,2-tris(pyrazolyl)ethanol) was covalently attached to polystyrene synthesis beads and found to bind nickel(II) (from NiX(4)(2-)) in a manner similar to Tpm. Solid state electronic spectra of supported-TpmNiCl(2) are comparable to those measured for their homogeneous complexes. Covalently supported scorpionates are expected to further extend the utility of this rich ligand class in areas of heterogeneous catalysis and metal-protein interactions.