Steric and electronic factor comparisons in hydrotris(3-phenylpyrazolyl)borate nickel(II) aryloxides.

Hydrotris(pyrazolyl)borate (Tp) ligands, also known as scorpionates, are potent tridentate donors that effectively bind metal ions in a face-capping array. Hydrotris(3-phenylpyrazolyl)borate enforces a tetrahedral environment on NiII to model metalloenzymes. The syntheses and structural characterizations of a number of [hydrotris(3-phenylpyrazolyl)borato]nickel(II) aryloxides were performed to provide insight into the environment of the model active site; these compounds are chlorido[hydrotris(3-phenylpyrazolyl-κN2)borato](3-phenyl-1H-pyrazole-κN2)nickel(II) chloroform monosolvate, [Ni(C27H22BN6)Cl(C9H8N2)]·CHCl3, (2), [hydrotris(3-phenylpyrazolyl-κN2)borato](phenolato-κO)nickel(II), [Ni(C27H22BN6)(C6H5O)], (3), (2,6-dimethylphenolato-κO)[hydrotris(3-phenylpyrazolyl-κN2)borato]nickel(II) [Ni(C27H22BN6)(C8H9O)], (4), (4-tert-butylphenolato-κO)[hydrotris(3-phenylpyrazolyl-κN2)borato]nickel(II), [Ni(C27H22BN6)(C10H13O)], (5), and [hydrotris(3-phenylpyrazolyl-κN2)borato](phenolato-κO)(tetrahydrofuran-κO)nickel(II) tetrahydrofuran monosolvate, [Ni(C27H22BN6)(C6H5O)(C4H8O)]·C4H8O, (6). Alkyl groups, e.g. tert-butyl in (5) and methyl in (4), electronically activate the aryloxide group to intramolecular π-π stacking but can be frustrated by steric encumbrance at the interacting ring faces. The flexibility at the nickel coordination site, afforded by the uncrowded B atom of the TpPh ligand, allows tetrahydrofuran coordination in the phenolate compound.

FcTp(R) (R = iPr or tBu): third-generation ferrocenyl scorpionates.

Scorpionate (or trispyrazolylborate) ligands have seen much structural variation due to the relative ease of modifying their electronic and steric effects. Second-generation scorpionates were created by increasing the bulk in the 3-position of the pyrazole (pz) ring. A new class of third-generation scorpionates was obtained by modifying the remaining boron substituent. A series of thallium(I) and cobalt(II) complexes of the ferrocenyltris(3-R-pyrazolyl)borate ligand [FcTpR; R = isopropyl (iPr) or tert-butyl (tBu)] have been synthesized in order to expand the range of redox-active third-generation scorpionates. These are [ferrocenyltris(3-tert-butylpyrazol-1-yl-κN2)borato]thallium(I), [FeTl(C5H5)(C26H37BN6)], [ferrocenyltris(3-isopropylpyrazol-1-yl-κN2)borato]thallium(I), [FeTl(C5H5)(C23H31BN6)], chlorido[ferrocenyltris(3-tert-butylpyrazol-1-yl-κN2)borato]cobalt(II), [CoFe(C5H5)(C26H37BN6)Cl], [ferrocenyltris(3-tert-butylpyrazol-1-yl-κN2)borato]iodidocobalt(II) benzene disolvate, [CoFe(C5H5)(C26H37BN6)I]·2C6H6, and [ferrocenyltris(3-isopropylpyrazol-1-yl-κN2)borato]iodidocobalt(II), [CoFe(C5H5)(C23H31BN6)I]. The structures demonstrate that the metal coordination site can easily be modified by using bulkier substituents at the pz 3-position.

Ferrocenyl-substituted tris(pyrazolyl)borates--a new ligand type combining redox activity with resistance to hydrogen atom abstraction.

The low-temperature syntheses of ferrocenyl-substituted tris(pyrazolyl)borate ligands Tp(Fc*) (hydrobis(3-ferrocenylpyrazolyl)mono(5-ferrocenylpyrazolyl)borate), Tp(Fc,Me*) (hydrobis(3-ferrocenyl-5-methylpyrazolyl)mono(5-ferrocenyl-3-methylpyrazolyl)borate), and Tp(Fc,iPr) (hydrotris(3-ferrocenyl-5-isopropylpyrazolyl)borate) are reported. The Tl salts of Tp(Fc*) and Tp(Fc,Me*) can be thermally isomerized to the symmetric Tp(Fc) (hydrotris(3-ferrocenylpyrazolyl)borate) and Tp(Fc,Me) (hydrotris(3-ferrocenyl-5-methylpyrazolyl)borate) species, respectively. Conversely, upon heating, the thermal isomerization of Tp(Fc,iPr) results in the generation of a mixture of regioisomers. These ligands display a reversible three-electron oxidation. The preparations of Tp(CF3,Fc)Tl (hydrotris(3-trifluoromethyl-5-ferrocenylpyrazolyl)borate) and PhTp(Fc) (phenyltris(3-ferrocenylpyrazolyl)borate) are also reported.

Improved syntheses, and structural and electronic characterization of carboxamide-substituted Tp(CONHPh,Me) and Tp(CONHt-Bu,Me) ligands.

Improvements in the syntheses of the carboxamide-substituted tris(pyrazolyl)borate ligands Tp(CONHPh,Me) [tris(3-anilinocarbonyl-5-methylpyrazol-1-yl)borate] and Tp(CONHt-Bu,Me) [tris(3-tert-butylaminocarbonyl-5-methylpyrazol-1-yl)borate] are reported. Their Tl(I) salts, namely [tris(3-anilinocarbonyl-5-methylpyrazol-1-yl-κN(2))borato]thallium(I), [Tl(C33H31BN9O3)], (II), and [tris(3-tert-butylaminocarbonyl-5-methylpyrazol-1-yl-κN(2))borato]thallium(I), [Tl(C27H43BN9O3)], (III), as well as the Cu(I) carbonyl complexes (Tp(CONHPh,Me))Cu(CO), namely carbonyl[tris(3-anilinocarbonyl-5-methylpyrazol-1-yl-κN(2))borato]copper(I) tetrahydrofuran trisolvate, [Cu(C33H31BN9O3)(CO)]·3C4H8O, (IV), and (Tp(CONHt-Bu,Me))Cu(CO), namely carbonyl[tris(3-tert-butylaminocarbonyl-5-methylpyrazol-1-yl-κN(2))borato]copper(I) tetrahydrofuran hemisolvate, [Cu(C27H43BN9O3)(CO)]·0.5C4H8O, (V), have been prepared. Their spectroscopic properties and structures are compared with those of related compounds. The molecules of (II)-(V) show hydrogen bonding to either solvent molecules or neighboring complex molecules via amide groups. The title compounds feature the ability to engage other ligands in hydrogen bonding and they show strong electron-withdrawing character. Compound (V) displays voids of ca 800 Å(3) in the crystal structure.

Copper iminopyrrolidinates: a study of thermal and surface chemistry.

Several copper(I) iminopyrrolidinates have been evaluated by thermogravimetric analysis (TGA) and solution based (1)H NMR studies to determine their thermal stability and decomposition mechanisms. Iminopyrrolidinates were used as a ligand for copper(I) to block previously identified decomposition routes of carbodiimide deinsertion and ß-hydrogen abstraction. The compounds copper(I) isopropyl-iminopyrrolidinate (1) and copper(I) tert-butyl-iminopyrrolidinate (2) were synthesized for this study, and compared to the previously reported copper(I) tert-butyl-imino-2,2-dimethylpyrrolidinate (3) and the copper(I) guanidinate [Me(2)NC((i)PrN)(2)Cu](2) (4). Compounds 1 and 2 were found to be volatile yet susceptible to decomposition during TGA. At 165 °C in C(6)D(6), they had half-lives of 181.7 h and 23.7 h, respectively. The main thermolysis product of 1 and 2 was their respective protonated iminopyrrolidine ligand. ß-Hydrogen abstraction was proposed for the mechanism of thermal decomposition. Since compound 3 showed no thermolysis at 165 °C, it was further studied by chemisorption on high surface area silica. It was found to eliminate an isobutene upon chemisoption at 275 °C. Annealing the sample at 350 °C showed further evidence of the decomposition of the surface species, likely eliminating ethene, and producing a surface bound methylene diamine.

Phenylcyanamidoruthenium scorpionate complexes.

Nine [Ru(Tp)(dppe)L] complexes, where Tp is hydrotris(pyrazol-1-yl)borate, dppe is ethylenebis(diphenylphosphine), and L is (4-nitrophenyl)cyanamide (NO(2)pcyd(-)), (2-chlorophenyl)cyanamide (2-Clpcyd(-)), (3-chlorophenyl)cyanamide (3-Clpcyd(-)), (2,4-dichlorophenyl)cyanamide (2,4-Cl(2)pcyd(-)), (2,3-dichlorophenyl)cyanamide (2,3-Cl(2)pcyd(-)), (2,5-dichlorophenyl)cyanamide (2,5-Cl(2)pcyd(-)), (2,4,5-trichlorophenyl)cyanamide (2,4,5-Cl(3)pcyd(-)), (2,3,5,6-tetrachlorophenyl)cyanamide (2,3,5,6-Cl(4)pcyd(-)), and (pentachlorophenyl)cyanamide (Cl(5)pcyd(-)), and the dinuclear complex [{Ru(Tp)(dppe)}(2)(µ-adpc)], where adpc(2-) is azo-4,4-diphenylcyanamide, have been prepared and characterized. The crystal structures of [Ru(Tp)(dppe)(Cl(5)pcyd)] and [{Ru(Tp)(dppe)}(2)(µ-adpc)] reveal the Ru(II) ion to occupy a pseudooctahedral coordination sphere in which the cyanamide ligand coordinates to Ru(II) by its terminal nitrogen atom. For both complexes, the cyanamide ligands are planar, indicating significant π mixing between the cyanamide and phenyl moieties as well as the azo group in the case of adpc(2-). The optical spectra of the nominally ruthenium(III) species [Ru(Tp)(dppe)L](+) were obtained through spectroelectrochemistry measurements and showed an intense near-IR absorption band. Time-dependent density functional theory calculations of these species revealed that oxidation of the ruthenium(II) species led to species where partial oxidation of the cyanamide ligand had occurred, indicative of noninnocent character for these ligands. The spin densities reveal that while the 3-Clpycd species has substantial Ru(II)(3-Clpycd(0)) character, the Cl(5)pycd species is a much more localized ruthenium(III) complex of the Cl(5)pycd monoanion. Some bond order and charge distribution data are derived for these ruthenium(III) species. The near-IR band is assigned as a quite complex mixture of d-d, 4d(π) to L(NCN) MLCT, and L(NCN) to Ru 4d LMCT with even a scorpionate ligand component. Spectroelectrochemistry was also performed on [{Ru(Tp)(dppe)}(2)(µ-adpc)] to generate the mixed-valence state. The intense intervalence transition that is observed in the near-IR is very similar to that previously reported for [{Ru(trpy)(bpy)}(2)(µ-adpc)](2+), where trpy is 2,2':6',2"-terpyridine and bpy is 2,2'-bipyridine, and by analogy identifies [{Ru(Tp)(dppe)}(2)(µ-adpc)](+) as a delocalized mixed-valence complex.

Nickel-catalyzed cross couplings of benzylic ammonium salts and boronic acids: stereospecific formation of diarylethanes via C-N bond activation.

We have developed a nickel-catalyzed cross coupling of benzylic ammonium triflates with aryl boronic acids to afford diarylmethanes and diarylethanes. This reaction proceeds under mild reaction conditions and with exceptional functional group tolerance. Further, it transforms branched benzylic ammonium salts to diarylethanes with excellent chirality transfer, offering a new strategy for the synthesis of highly enantioenriched diarylethanes from readily available chiral benzylic amines.

Preventing thermolysis: precursor design for volatile copper compounds.

A copper(I) iminopyrrolidinate was synthesized and evaluated by thermal gravimetric analysis (TGA), solution based (1)H NMR studies and surface chemistry to determine its thermal stability and decomposition mechanism. Copper(I) tert-butyl-imino-2,2-dimethylpyrrolidinate (1) demonstrated superior thermal stability and showed negligible decomposition in TGA experiments up to 300 °C as well as no decomposition in solutions at 165 °C over 3 weeks.

Guanidinium 2-(myristoylsulfanyl)ethane-sulfonate.

In the title compound, CH(6)N(3) (+)·C(16)H(31)O(4)S(2) (-) [systematic name: guanidinium 2-(tetra-deca-noylsulfan-yl)ethane-sulfon-ate], each 2-(myristoyl-thio)-ethane-sulfonate ion displays hydrogen bonding to three guanidinium counter-ions, which themselves display hydrogen bonding to two symmetry-related 2-(myristoylthio)ethanesulfonate ions. Thus each cation forms six N-H⋯O bonds to neighboring anions, thereby self-assembling an extended ladder-type network. The average hydrogen-bond donor-acceptor distance is 2.931 (5) Å. The alkyl chains form the rungs of a ladder with hydrogen-bonding inter-actions forming the side rails.