A New Set of Structurally Related Enantiopure Polypyrazolyl Ligands of Varying Rotational Symmetry: Synthesis, Metal Complexation, and Comparison of Asymmetric Induction

Immobilized boron-centered heteroscorpionates: heterocycle metathesis and coordination chemistry

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.

Applications of chiral C3-symmetric molecules

Throughout history symmetry and chirality have inspired artists and scientists alike. Given that rotational axes are the only elements of symmetry compatible with chirality, it is not surprising that C2- and C3-symmetrical molecules have attracted considerable attention. In recent years, the aesthetic appeal of C2-symmetrical molecules has been translated into many widely-used applications some of which are of commercial importance by its exploitation in the area of asymmetric catalysis. In contrast, exploitation of the arguably greater aesthetic appeal of C3-symmetric molecules is still in its infancy. This review, which surveys the applications of chiral C3-symmetrical molecules in the areas of asymmetric catalysis, molecular recognition and nanoarchitecture, has been designed with a view to identifying some of the most promising areas of application of these very beautiful molecules.

Synthesis of a Macrobicycle Incorporating the Tris(pyrazolyl)methane Ligand

Steric crowding of the 3-position of tris(pyrazolyl)borate and -methane ligands has produced tetrahedral metal complexes with controlled reactivity. As an alternative, we propose to incorporate the tris(pyrazolyl)methane chelate in a macrobicyclic structure in order to create a cavity with well-defined dimensions and shape. Acid-catalyzed equilibration of excess of the new pyrazole 3-(1H-pyrazol-3-yl)benzenemethanethiol acetate with HC(3,5-Me(2)pz)(3) followed by hydrolysis affords a functionalized tris(pyrazolyl)methane, which reacts with 1,3,5-tris(bromomethyl)benzene in K(2)CO(3)/DMF to give the title compound. [structure: see text]

One-Dimensional Copper(I) Coordination Polymers Based on a Tridentate Thioether Ligand

The one-dimensional copper(I) coordination polymers Cu(3){MeSi(CH(2)SMe)(3)}(2)X(3) (X = Cl, Br) and [{MeSi(CH(2)SMe)(3)}Cu(NCMe)]Y (Y = OSO(2)CF(3), BF(4), PF(6)) were readily obtained in very good to excellent yields (80-95%) by reacting CuX or [Cu(NCMe)(4)]Y, respectively, with the tridentate thioether ligand MeSi(CH(2)SMe)(3) in acetonitrile. The new complexes were characterized by a combination of analytical and spectroscopic techniques, including electrospray ionization mass spectrometry and, for the bromo and hexafluorophosphate derivatives, single-crystal X-ray diffraction. Both complexes exhibit one-dimensional chain structures with approximately tetrahedral copper centers and bridging unidentate/bidentate thioether ligands.

Synthesis and Characterization of Copper(I) Complexes with a Fairly Bulky Tris(pyrazolyl)hydroborate Ligand. Probing the Flexibility of the Metal-Containing Pocket Formed by the Ligand

Four copper(I) tris(pyrazolyl)hydroborate complexes are reported with the fairly bulky tris[3-(p-tert-butylphenyl)-5-methylpyrazol-1-yl]hydroborate ligand (Tp()t(Bu-)(Ph,Me)). Tp()t(Bu-)(Ph,Me)Cu(CH(3)CN) (1) was synthesized from CuCl and Tp()t(Bu-)(Ph,Me)Li(CH(3)CN). The acetonitrile ligand in 1 was easily replaced by CO, PPh(3), and P(t)()Bu(3), forming Tp()t(Bu-)(Ph,Me)Cu(CO) (2), Tp()t(Bu-)(Ph,Me)Cu(PPh(3)) (3), and Tp()t(Bu-)(Ph,Me)Cu(P(t)()Bu(3)) (4), respectively. Complexes 1-4 have been crystallographically characterized. 1.4CH(3)CN, 173 K: C(52)H(67)BCuN(11), triclinic, P&onemacr;, a = 13.4201(10) Å, b= 15.132(2) Å, c = 15.2125(13) Å, alpha = 60.743(6) degrees, beta = 73.211(4) degrees, gamma = 74.839(5) degrees, Z = 2, R1 = 6.81% (wR2 = 18.91%). 2, 296 K: C(43)H(52)BCuN(6)O, monoclinic, C2/c, a = 25.592(4) Å, b = 12.434(2) Å, c = 28.044(3) Å, beta = 104.073(9) degrees, Z = 8, R1 = 7.47% (wR2 = 22.08%). 3.CH(2)Cl(2), 173 K: C(61)H(69)BCl(2)CuN(6)P, triclinic, P&onemacr;, a= 12.5080(13) Å, b = 15.159(3) Å, c = 17.151(2) Å, alpha = 64.271(10) degrees, beta = 79.073(7) degrees, gamma = 86.572(8) degrees, Z = 2, R1 = 5.13% (wR2 = 13.28%). 4.0.5 hexane, 298 K: C(57)H(86)BCuN(6)P, triclinic, P&onemacr;, a = 13.337(2) Å, b = 13.435(2) Å, c = 17.386(2) Å, alpha = 88.371(7) degrees, beta = 71.863(8) degrees, gamma = 80.223(9) degrees, Z = 2, R1 = 6.96% (wR2 = 18.62%). The Tp()t(Bu-)(Ph,Me) ligands in 1, 2, and 3 bind in a tridentate fashion; the CH(3)CN and CO ligands fit comfortably within the pocket formed by the tert-butylphenyl substituents and the PPh(3) ligand interleaves between the pyrazole arms. The flexibility of the pocket was probed by calculating the area of the triangle created by connecting the midpoints of the 3-phenyl groups; this parameter increases by 15% for 3 (the largest) over 1 (the smallest). Thus, the pocket exhibits some flexibility, found to be due to both steric and electronic factors. Complex 4 features a bidentate Tp()t(Bu-)(Ph,Me) ligand as the P(t)()Bu(3) apparently exceeds the pocket's flexibility.