Some more space-group corrections

A survey of approximately 100 000 entries in recent releases of the Cambridge Structural Database (CSD) has uncovered 156 crystal structures that were apparently described in inappropriate space groups. We have revised these space groups and prepared CIFs containing the new coordinates and brief comments describing the revisions

Zirconium and titanium complexes supported by tridentate LX2 ligands having two phenolates linked to furan, thiophene, and pyridine donors: precatalysts for propylene polymerization and oligomerization

Zirconium and titanium complexes with tridentate bis(phenolate)-donor (donor = pyridine, furan and thiophene) ligands have been prepared and investigated for applications in propylene polymerization. The ligand framework has two X-type phenolates connected to the flat heterocyclic L-type donor at the 2,6- or 2.5- positions via direct ring-ring (sp^2-sp^2)linkages. The zirconium and titanium dibenzyl complexes have been prepared by treatment of the neutral bis(phenol)-donor ligands with M(CH_2Ph)_4 (M = Ti, Zr) with loss of 2 equiv of toluene. Titanium complexes with bis(phenolate)pyridine and -furan ligands and zirconium complexes with bis(phenolate)pyridine and -thiophene ligands have been characterized by single-crystal X-ray diffraction. The solid-state structures of the bis(benzyl)titanium complexes are roughly C_2 symmetric, while the zirconium derivatives display C_s and C^1 symmetry. The bis(phenolate)pyridine titanium complexes are structurally affected by the size of the substituents substituents (CMe_3 or CEt_3) ortho to the oxygens, the larger group leading to a larger C_2 distortion. Both titanium and zirconium dibenzyl complexes were found to be catalyst precursors for the polymerization of propylene upon activation with methylaluminoxane (MAO). The activities observed for the zirconium complexes are particularly notable, exceeding 10^6 g polypropylene/mol Zr center dot h in some cases. The bis(phenolate)pyridine titanium analogues are about 10^3 times less active, but generate polymers of higher molecular weight. When activated with MAO, the titanium bis(phenolate)furan and bis(phenolate)thiophene systems were found to promote propylene oligomerization

Cationic Alkylaluminum-Complexed Zirconocene Hydrides: NMR-Spectroscopic Identification, Crystallographic Structure Determination, and Interconversion with Other Zirconocene Cations

The ansa-zirconocene complex rac-Me_2Si(1-indenyl)_2ZrCl_2 ((SBI)ZrCl_2) reacts with diisobutylaluminum hydride and trityl tetrakis(perfluorophenyl)borate in hydrocarbon solutions to give the cation [(SBI)Zr(μ-H)_3(Al^iBu_2)_2]^+, the identity of which is derived from NMR data and supported by a crystallographic structure determination. Analogous reactions proceed with many other zirconocene dichloride complexes. [(SBI)Zr(μ-H)_3(Al^iBu2)_2]^+ reacts reversibly with ClAl^iBu_2 to give the dichloro-bridged cation [(SBI)Zr(μ-Cl)_2Al^iBu_2]^+. Reaction with AlMe_3 first leads to mixed-alkyl species [(SBI)Zr(μ-H)_3(AlMe_x^iBu_(2−x))_2^]+ by exchange of alkyl groups between aluminum centers. At higher AlMe_3/Zr ratios, [(SBI)Zr(μ-Me)_2AlMe_2]^+, a constituent of methylalumoxane-activated catalyst systems, is formed in an equilibrium, in which the hydride cation [(SBI)Zr(μ-H)_3(AlR_2)_2]^+ strongly predominates at comparable HAl^iBu_2 and AlMe_3 concentrations, thus implicating the presence of this hydride cation in olefin polymerization catalyst systems

Structure of dicarbonylbis-(μ-3,5-dimethylpyrazolyl)-bis(4-tolyl diphenylphosphinite)diiridium(I)–dichloromethane (1/1)

In bis(μ-3,5-dimethylpyrazolyl-N:N')-bis[carbonyl( 4-tolyl diphenylphosphinite-P)iridium(I)] dichloromethane solvate, two Ir^I atoms are joined by two 3,5-dimethylpyrazolyl bridges with one carbonyl and one 4-tolyl diphenylphosphinite ligand completing the square-planar geometry about each Ir atom. The Ir· · ·Ir distance of 3.307 (1) Å is greater than the distance of 3.22 Å found in a similar pyrazolyl-bridged iridium(I) dimer [Fox (1989). PhD dissertation, California Institute of Technology, USA]

Spectral and Structural Characterization of 5,6-Chrysenequinone Diimine Complexes of Rhodium(III): Evidence for a pH-Dependent Ligand Conformational Switch

Rhodium(III) complexes containing 9,10-phenanthrenequinone diimine (phi) ligands have been broadly applied for the construction of DNA binding and recognition molecules, and more recently, derivatives containing the 5,6-chrysenequinone diimine (chrysi) ligand have been shown specifically to recognize base mismatches in DNA. Here the structural properties of [Rh(bpy)_2(chrysi)]Cl_3 and spectroscopic properties of derivatives are examined and compared to those of phi complexes of rhodium. Although similar in many respects, phi and chrysi complexes display distinctly different protonation behavior. The pK_a values of chrysi complexes are as much as 1 unit lower than analogous phi compounds, and visible spectra of the chrysi complexes differ markedly from the phi counterparts in acidic but not basic solution. This protonation behavior is traced to the presence of a steric clash between a proton on the aromatic ring of the chrysi ligand and the acidic immino proton of the metal complex. In avoidance of this steric clash, a significant disruption in the planarity of the chrysi ligand is evident crystallographically in the structure of [Rh(bpy)_2(chrysi)]Cl_3·3CH_3CN·2H_2O (triclinic crystal system, space group P1̄ (No. 2), Z = 2, a = 9.079(3) Å, b = 10.970(3) Å, c = 21.192(8) Å, α = 86.71(3)°, β = 89.21(3)°, γ = 78.58(3)°, V = 2065.4(12) Å^3). Phi complexes, lacking the additional aromatic ring, require no similar distortion from ligand planarity. NMR spectra support this pH-dependent structural distortion for the chrysi complex. Rhodium complexes of chrysenequinone diimine, therefore, not only represent new DNA binding molecules targeted to mismatches but also provide an illustration of a pH “gated” ligand conformational switch

A revision of the structure of (bipyridyl-N,N')-dicyanoplatinum(II)

In a previous X-ray crystallographic study of crystals of Pt(bpy)(CN)_2 (bpy = 2,2'-bipyridine) the planar molecules were reported to be exactly eclipsed, stacked directly on top of one another with a spacing of 3.33 Å so as to form a linear Pt· · ·Pt· · ·Pt chain. A reinvestigation shows this structure to be incorrect. The presence of weak intermediate layer lines indicates that the repeat distance along the stacking direction is 6.66 Å rather than 3.33 Å. Successive molecules within the stack are rotated by 180° and the resulting Pt-atom chain is slightly zigzag with a Pt· · ·Pt· · ·Pt angle of 168.6 (1)°. The implications are discussed of the determination and refinement of an apparently satisfactory, although grossly wrong, structure that was based on an incorrect unit cell and an incorrect space group

Competitive Activation of a Methyl C−H Bond of Dimethylformamide at an Iridium Center

During the synthesis of [AsPh_4][Ir(CO)_2I_3Me] by refluxing IrCl_3·3H_2O in DMF (DMF = dimethylformamide) in the presence of aqueous HCl, followed by sequential treatment with [AsPh_4]Cl, NaI, and methyl iodide and finally recrystallization from methylene chloride/pentane, three crystalline byproducts were obtained: [AsPh4]_2[Ir(CO)I_5], [AsPh_4]_2[trans-Ir(CO)I_4Cl], and [AsPh_4][Ir(CO)(κ^2O,C-CH_2NMeCHO)Cl_2I]. The last of these, whose structure (along with the others) was determined by X-ray diffraction, results from activation of a methyl C−H bond of dimethylformamide, rather than the normally much more reactive aldehydic C−H bond

Synthesis and Reactivity of Neutral and Cationic Ruthenium(II) Tris(pyrazolyl)borate Alkylidenes

A series of neutral and cationic ruthenium(II) alkylidenes containing the hydrotris(pyrazolyl)borate (Tp) ligand have been prepared. The complex Tp(PCy_3)(Cl)Ru=CHPh (2) was obtained by the reaction of (PCy_3)_2(Cl)_2Ru=CHPh (1) and KTp. Treatment of 2 with AgBF_4 or AgSbF_6 in the presence of a variety of coordinating solvents afforded [Tp(PCy_3)(L)Ru=CHPh]^+ (L = H_2O, CH_3CN, pyridine) in high yield. The dynamic NMR behavior of these new complexes is discussed, and the X-ray crystal structure of [Tp(PCy_3)(H_2O)Ru=CHPh]BF_4 (3) is reported. Alkylidenes 2−5 alone do not catalyze olefin metathesis reactions. However, complex 2 is activated for ring-closing metathesis by the addition of HCl, CuCl, and AlCl_3

Bespoke Photoreductants: Tungsten Arylisocyanides

Modular syntheses of oligoarylisocyanide ligands that are derivatives of 2,6-diisopropylphenyl isocyanide (CNdipp) have been developed; tungsten complexes incorporating these oligoarylisocyanide ligands exhibit intense metal-to-ligand charge-transfer visible absorptions that are red-shifted and more intense than those of the parent W(CNdipp)_6 complex. Additionally, these W(CNAr)_6 complexes have enhanced excited-state properties, including longer lifetimes and very high quantum yields. The decay kinetics of electronically excited W(CNAr)_6 complexes (*W(CNAr)_6) show solvent dependences; faster decay is observed in higher dielectric solvents. *W(CNAr)_6 lifetimes are temperature dependent, suggestive of a strong coupling nonradiative decay mechanism that promotes repopulation of the ground state. Notably, *W(CNAr)_6 complexes are exceptionally strong reductants: [W(CNAr)_6]+/*W(CNAr)_6 potentials are more negative than −2.7 V vs [Cp_2Fe]^+/Cp_2Fe

Bimetallic Coordination Insertion Polymerization of Unprotected Polar Monomers: Copolymerization of Amino Olefins and Ethylene by Dinickel Bisphenoxyiminato Catalysts

Dinickel bisphenoxyiminato complexes based on highly substituted p- and m-terphenyl backbones were synthesized, and the corresponding atropisomers were isolated. In the presence of a phosphine scavenger, Ni(COD)_2, the phosphine-ligated syn-dinickel complexes copolymerized α-olefins and ethylene in the presence of amines to afford 0.2–1.3% α-olefin incorporation and copolymerized amino olefins and ethylene with a similar range of incorporation (0.1–0.8%). The present rigid catalysts provide a bimetallic strategy for insertion polymerization of polar monomers without masking of the heteroatom group. The effects of the catalyst structure on the reactivity were studied by comparisons of the syn and anti atropisomers and the p- and m-terphenyl systems