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In this comprehensive study, we report the syntheses and crystal structures of 6 fused oxazolidine (FOX) bicycles and 22 complexes with FOX ligands. The structures are compared to the few FOX complexes found in literature. For our investigations, we developed synthetic strategies to selectively synthesize chiral or achiral FOX bicycles with pyridyl substituents. The coordination chemistry of the chiral and achiral FOX compounds with first-row transition metals is discussed in an indepth analysis of the crystal structures. We found that the binding modes of the ligands are dependent on the configuration of the FOX backbone and on the steric demand of the substituents which were introduced to the pyridyl groups. The configuration of the FOX ligands is retained during the coordination of metal(II) ions such as Mn2+, Fe2+, Co2+, Ni2+, Cu2+. Reactions of these metal ions with chiral FOX ligands lead to the formation of chiral complexes. In contrast, stronger Lewis acidic metal(III) ions, such as Fe3+ or Al3+, induce an isomerization of the chiral FOX ligands to their achiral diastereomers. [ABSTRACT FROM AUTHOR]

We report that pincer-ligated iridium complexes undergo oxidative addition of the strained C-C bond of biphenylene. The sterically crowded species (tBuPCP)Ir (RPCP = ³-1,3-C6H3(CH2PR2)2) initially reacts with biphenylene to selectively add the C(1)-H bond, to give a relatively stable aryl hydride complex. Upon heating at 125 °C for 24 h, full conversion to the C-C addition product, (tBuPCP)Ir(2,2'-biphenyl), is observed. The much less crowded (iPrPCP)Ir undergoes relatively rapid C-C addition at room temperature. The large difference in the apparent barriers to C-C addition is notable in view of the fact that the addition products are not particularly crowded, since the planar biphenyl unit adopts an orientation perpendicular to the plane of the RPCP ligands. Based on DFT calculations the large difference in the barriers to C-C addition can be explained in terms of a "tilted" transition state. In the transition state the biphenylene cyclobutadiene core is calculated to be strongly tilted (ca. 50°-60°) relative to its orientation in the product in the plane perpendicular to that of the PCP ligand; this tilt results in very short, unfavorable, non-bonding contacts with the t-butyl groups in the case of the tBuPCP ligand. The conclusions of the biphenylene studies are applied to interpret computational results for cleavage of the unstrained C-C bond of biphenyl by (RPCP)Ir. [ABSTRACT FROM AUTHOR]

The unique dinuclear Ir(III) complex (Cp*IrCl)(μ-H)[μ-(η:η-CHS)](IrCp*) ( 1) has been synthesized and characterized by NMR spectroscopy (H and C), elemental analysis, and single crystal X-ray diffraction. It is the first structurally determined complex in which an activated thiophene ligand displays an η-allylic interaction. 1 appears to form from successive C-H bond activations of 2,5-dimethylthiophene, resulting in its bridging the two iridium centers. The η-allylic interaction occurs with one of the Ir centers and has Ir-C bond lengths ranging from 2.133(5)-2.207(5) Å; the C-C double bond involved in the interaction has a bond length of 1.438(7) Å compared to 1.348(8) Å for the uncoordinated C-C double bond. The 3-carbon of the thiophene ring bridges both iridium centers with bond lengths of 2.036(5) Å and 2.208(5) Å. 1 crystallizes in space group P−1 with cell constants a = 8.6303(6) Å, b = 9.0153(6) Å, c = 18.1089(12) Å, α = 84.728(1)°, β = 87.534(1)°, γ = 64.373(1)°, and Z = 2. The structure was solved by direct methods and refined to R = 0.0363 ( F > 2 σ( F)) and wR = 0.0851 ( F). The NMR data indicate the solution state structure is consistent with the solid state structure. Graphical Abstract: The reaction of 2,5-dimethylthiophene with [Cp*IrHCl] leads to the formation of a unique double C-H activation product displaying a unique μ-η:η coordination of the thiophene [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A well-defined iron complex (3) supported by a bis(phosphino)amine pincer ligand efficiently catalyzes both acceptorless dehydrogenation and hydrogenation of N-heterocycles. The products from these reactions are isolated in good yields. Complex 3, the active catalytic species in the dehydrogenation reaction, is independently synthesized and characterized, and its structure is confirmed by X-ray crystallography. A transdihydride intermediate (4) is proposed to be involved in the hydrogenation reaction, and its existence is verified by NMR and trapping experiments. [ABSTRACT FROM AUTHOR]

Abstract: A cationic rhodium aquo methyl complex, [Rh(bpy)(CH3)(H2O)3]2+·2[BF4]−, was prepared and examined for activity related to the Shilov PtII system, specifically the formation of methanol. Instead, the complex exhibited interesting behavior under basic conditions, with rare double “rollover” metalation of the coordinated bipyridine ligand and deuterium incorporation into the rhodium methyl group. [Copyright &y& Elsevier]

Synthesis and characterization of new (PONOP) [2,6-bis(di-tert-butylphosphinito)pyridine] metal (Ni, Pd, Pt) complexes are reported. Surprisingly, these compounds [(PONOP)MCl]Cl in the presence of 1 equiv of superhydride (LiEt3BH) formed a new class of complexes (H-PONOP)MCl, in which the pyridine ring in the PONOP ligand lost its aromaticity as a result of hydride attack at the para position of the ring. The new Ni-H compound [(H-PONOP)NiH] was synthesized by reacting (H-PONOP)NiCl with 1 equiv of superhydride. Analogous Pd and Pt compounds were prepared. Reactivity of these new pincer complexes toward MeLi and PhLi also has been studied. These Ni complexes catalyzed the hydrosilylation of aldehyde. In some cases characterization of new (PONOP)M complexes was difficult because of high instability due to degradation of the P-O bond. [ABSTRACT FROM AUTHOR]

Abstract: Treatment of Rh(acac)(CO)2 (acac=acetoacetonate) with perchloric acid followed by addition of an α-diimine (α-diimine=1,4-bis(Ar)-2,3-dimethyl-1,4-diaza-1,3-butadiene, Ar=3,5-dimethylphenyl, 1; 3,5-di-tert-butylphenyl, 2; and 3,4,5-trimethoxyphenyl, 3; phenyl, 4; and 4-chlorophenyl, 5) generates a series of complexes of the type [Rh(α-diimine)(CO)2][ClO4] 6–10 with varying electronic properties of the supporting diimine ligand. X-ray crystal structures have been determined for the α-diimine ligands 1–5, and complexes 6, 8, and 10. [Copyright &y& Elsevier]

A new series of molybdenum and tungsten tricarbonyl pincer complexes, bearing pyridine-based PONOP-type pincer ligands, have been synthesized and fully characterized. Addition of HBF4·Et2O to these tricarbonyl complexes generated seven-coordinate molybdenum and tungsten hydride complexes, and these compounds have been isolated in good yields. These metal hydrides show fluxional behavior in solution. The hydride ligands on these metal complexes are acidic in nature and are readily deprotonated by bases. The molybdenum hydride complex is shown to catalyze isomerization of 1-hexene to internal isomers under mild conditions. [ABSTRACT FROM AUTHOR]

The (dippe)palladium(0) fragment generated from [(dippe)Pd(μ-H)]2 (1) has been shown to form an intermediate η2-nitrile complex with acetonitrile (dippe)Pd(η2-C,N-CH3CN-BEt3) (2a) in the presence of BEt3 [(dippe = bis-diisopropylphosphino)ethane)]. On introducing a solution of 2a to 1 equiv of BPh3, rapid formation of (dippe)Pd(η2-C,N-CH3CNBPh3) (2a') is observed. Heating 2a' at 100 °C in THF-d8 results in the C-CN activation product 3a', (dippe)Pd(CH3)(CNBPh3). Reaction of 1 with benzonitrile in the presence of BEt3 gives the C-CN activation product (dippe)Pd(Ph)(CN-BEt3) (3b) exclusively. The complexes 2a, 2a', 3a', and 3b were characterized by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy, elemental analysis, IR spectroscopy, and X-ray diffraction. [ABSTRACT FROM AUTHOR]

• A series of four half-sandwich ruthenium (II) complexes supported by pyrazolyl ligands is reported. • Molecular structure of the complexes was determined by various spectro-analytical techniques, including single crystal X-ray crystallographic studies. • Profound influence of the steric factors of the ligand substituents on the coordination chemistry and molecular structure of the complexes is profiled. • An interesting, solvent induced geometrical transformation was observed in the scorpionate supported half sandwich complex. Energetics and electronic structure of both the complexes were analyzed with the help of DFT calculations. Four half-sandwich ruthenium(II) complexes were prepared by reacting dichloro(p -cymene)ruthenium(II) dimer or dichloro(benzene)ruthenium(II) dimer with 3,5-dimethylpyrazole (L1), bis(3,5-dimethylpyrazolyl)methane (L2), tris(3,5-dimethylpyrazolyl)methane (L3) and potassium tris(3,5-dimethylpyrazolyl)borate (L4) under air free conditions in good yields. All of the complexes were duly characterized by molar conductivity measurement, IR, UV, NMR spectroscopy, and elemental analysis. Solid state molecular structures of the complexes C2 and C4 were determined by single crystal X-ray crystallographic studies. Profound influence of the steric factors of the ligand substituents on the coordination chemistry and molecular structure of the complexes was profiled and compared with the related complexes in literature. An interesting solvent induced geometrical change was documented in the case of complex C4 , bearing κ2-tris(3,5-dimethylpyrazolyl)borate and η6-p-cymene ligands. DFT calculations were used to understand the energetics and electronic structures of the polymorphic structures C4 and C4´. [Display omitted] [ABSTRACT FROM AUTHOR]