Immobilized Boron-Centered Heteroscorpionates: Heterocycle Metathesis and Coordination Chemistry

Abstract

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.

Amine‐Functionalized Spin Crossover Building Blocks

“…Despite the relative lability of the B–N bond, this reaction usually requires high temperatures and is poorly selective, yielding mixtures of products with varied substitution patterns . However, the reaction of 4‐NO 2 ‐pzH with K[HB(pz) 3 ] in a non‐protic solvent at 60 °C for 2 hours affords K[HB(4‐NO 2 pz)(pz) 2 ] ( K‐1 ) in 70 % yield.…”

Rapid Synthesis of a Functional Resin‐Supported Scorpionate and Its Copper(I, II), Rhodium(I), and Chromium(III) Complexes

“…Here CO is a particularly effective ligand for characterizing supported metal coordination spheres. Distinct CO vibrations helped characterize the fac ‐Mo(CO) 3 sphere in resin‐supported Bd‐TpmMo(CO) 3 , and these vibrations were lost with aerial oxidation of the Mo 0 coordination sphere.…”

“…Evidence with copper(II) suggests that this linear polystyrene system was flexible enough to allow formation of (Ligand) 2 Cu sandwich complexes on the resin . Cases IV and V represent work from our laboratory,, and both offer the benefits of transition‐metal‐free chelates capable of coordinating a wide variety of metal ions. Neither gives any evidence of bis‐chelate sandwich complex formation, regardless of metal ion employed, due to the dispersion of functional groups across the resin and the rigidity of the cross‐linked resin.…”

“…Case IV incorporates the neutral carbon‐based scorpionate, a weaker donor than the anionic boron examples . Case V represents the first boron‐based heteroscorpionate supported to cross‐linked polystyrene, and functional nickel(II) centers were observed for this chelate system …”

Trispyrazolylborate Ligands Supported on Vinyl Addition Polynorbornenes and Their Copper Derivatives as Recyclable Catalysts

“…For the latter,t wo different approaches have been used:1 )the presence of an aryl group, which is part of a polystyrene structure, as the fourth substituent of boron (Scheme 1d); [12,13] 2) the substitution of one of the pyrazolyl groups by ap olymer-boundN -heterocycle (Scheme 1e). [14] None of these supported trispyrazolylborates have been used in catalysis.…”