Carbene vs olefin products of C-H activation on ruthenium via competing alpha- and beta-H elimination

Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from the pincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the products and determine the mechanisms of the C-H cleavage, reactions of [RuCl(2)(p-cymene)](2) with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2) were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computational techniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomers of the 16-e monohydride RuHCl[(t)Bu(2)PNHC(3)H(4)NHPBu(t)(2)] (2), whereas the reaction of L2 gave two olefin and two alkylidene isomers of 16-e RuHCl[2,6-(CH(2)PBu(t)(2))(2)C(6)H(8)] (3), all resulting from dehydrogenations of the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactions were identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2. Thus the alpha- and beta-H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH(2)Cl(PCP) distinguished by a large quantum exchange coupling between the hydrides.     

Neutral high-potential nickel triad bisdithiolenes: structure and solid-state NMR properties of Pt[S2C2(CF3)2]2

X-ray crystallography and solid-state NMR techniques were used to determine the structure and 195Pt NMR chemical shift (CS) tensor of Pt[S2C2(CF3)2]2. This is the first reported crystal structure of a highly oxidizing (CN- or CF3-substituted) neutral bis(dithiolene) complex of a Ni triad metal in its pure form. The 195Pt NMR CS tensor is highly anisotropic and asymmetric; the latter property is attributed to the noninnocent nature of the ligand. The tensor components and orientation are determined with density functional theory calculations.     

Easily prepared air- and moisture-stable Pd-NHC (NHC=N-heterocyclic carbene) complexes: a reliable, user-friendly, highly active palladium precatalyst for the Suzuki-Miyaura reaction

The synthesis of NHC-PdCl(2)-3-chloropyridine (NHC=N-heterocyclic carbene) complexes from readily available starting materials in air is described. The 2,6-diisopropylphenyl derivative was found to be highly catalytically active in alkyl-alkyl Suzuki and Negishi cross-coupling reactions. The synthesis, ease-of-use, and activity of this complex are substantial improvements over in situ catalyst generation and all current Pd-NHC complexes. The utilization of complex 4 led to the development of a reliable, easily employed Suzuki-Miyama protocol. Employing various reaction conditions allowed a large array of hindered biaryl and drug-like heteroaromatic compounds to be synthesized without difficulty.     

Bidirectional photocontrol of peptide conformation with a bridged azobenzene derivative

It goes both ways: A thiol-reactive cross-linker based on a bridged azobenzene derivative permits photoreversible control of peptide conformation on irradiation with violet (407?nm) and green (500-550?nm) light (see picture) through isomerization of the cross-linker. The large separation of the absorbance bands of the cis (yellow) and trans (red) isomers enables complete bidirectional photoswitching.     

Bis­(tri­chloro­phosphine)­iminium salts, [Cl3P=N=PCl3]+, with transition metal halide counter‐ions

The structures of four bis­(tri­chloro­phosphine)­iminium {[Cl₃P=N=PCl₃]⁺; systematic name: tri­chloro­[(tri­chloro­phos­phor­an­yl­idene)im­in­io]phos­phor­us(V)} salts, namely bis(tri­chloro­phosphine)­iminium hexa­chloro­niobate, (Cl₆NP₂)[NbCl₆], (I), bis­(tri­chloro­phosphine)­iminium hexa­chloro­tantalate, (Cl₆NP₂)[TaCl₆], (II), bis­(tri­chloro­phosphine)­iminium tri‐μ‐chloro‐bis­[tri­chloro­titanium(IV)], (Cl₆NP₂)[Ti₂Cl₉], (III), and bis­[bis­(tri­chloro­phosphine)­iminium] di‐μ‐chloro‐bis­[tetrachloro­zirconium(IV)], (Cl₆NP₂)₂[Zr₂Cl₁₀], (IV), have been determined. The P=N distances in the discrete [Cl₃P=N=PCl₃]⁺ moieties in structures (I), (II) and (IV) range from 1.5460 (14) to 1.5554 (16) Å, and the P=N=P angles range from 136.8 (3) to 143.4 (4)°. The [Cl₃P=N=PCl₃]⁺ cation in (III) is disordered and the calculated geometries for the cation are therefore less reliable. Compounds (I) and (II) are isostructural and the metal anions have slightly distorted octahedral geometries. The anion in compound (III) consists of two distorted octahedral Ti centres linked by three μ₂‐Cl atoms, while in compound (IV), the dianion is derived from two distorted edge‐shared ZrCl₆ octahedra.     

N,N′‐Dithiobisphthalimide–1,4‐dioxan (1/0.6): a C2/c solvate with disordered solvent molecules localized in channels

N,N′‐Di­thio­bisphthal­imide crystallizes from 1,4‐dioxan solution as a solvate, 3C₁₆H₈N₂O₄S₂·1.8C₄H₈O₂, having space group C2/c. Four of the 12 C₁₆H₈N₂O₄S₂ mol­ecules in the unit cell lie on twofold rotation axes, while the other eight lie in general positions. These mol­ecules are linked by aromatic π–π‐stacking interactions and by C—H?O hydrogen bonds to form a framework enclosing continuous channels running parallel to the [101] direction, which account for ca 20% of the unit‐cell volume. The dioxan mol­ecules lie in these channels disordered across two sets of sites, with one set across an inversion centre and the other across a twofold rotation axis.     

Synthesis, characterization and single crystal structures of one-dimensional coordination polymers formed with [Ni(L)]·2ClO4 and polycarboxylate ligands

Two new one-dimensional coordination polymers {[Ni(L)(maleate)] · H₂O} _n (1) and {[Ni(L)(H₂btc)] · 2DMF} _n (L = cyclam, btc = 1,2,4,5-benzenetetracarboxylate, DMF = N,N-dimethylformamide) (2) have been synthesized and structurally characterized by single crystal X-ray diffraction. In the structures (1) and (2), the carboxylate groups of bridging ligands are coordinated to nickel(II) cyclams resulting in the formation of one-dimensional coordination polymers. In addition to the Ni–O bonds, it is observed that the hydrogen bonding interactions between the pre-organized N–H groups of the cyclams and bridging anions support the formation of coordination polymers in both complexes.