Rhodium- and iridium-trispyrazolylborate complexes

Organoselenium ligands are building blocks of several transition metal complexes which catalyze various organic reactions efficiently in solution. In this review the survey of developments pertaining to the designing of such complexes (along with their Se-ligands), and their uses as catalysts for various organic reactions has been presented with critical analysis of present status of the subject. Undoubtedly a new family of catalysts or their precursors has been generated by organoselenium ligands. The catalytic activity and selectivity of their metal complexes can sometimes be fine-tuned efficiently by changing the ligand's framework. They show good thermal and air-stability. This, coupled with ease in their handling and synthesis, may make them not only attractive but good alternatives to several popular catalysts.

Organoselenium ligands in catalysis.

Highly Selective Nickel Ethylene Oligomerization Catalysts Based on Sterically Hindered Tris(pyrazolyl)borate Ligands

The selective catalytic oxidation of alkanes using inexpensive and environmentally friendly oxidants is of immense interest to the chemical community and of great potential benefit to the world economy and ecology. Since the earliest reports that the oxidative addition of alkane C-H bonds to transition metal species can occur with high selectivities, substantial research effort has focused on the functionalization of the metal alkyl hydride products. The authors report that Pt(IV) dialkyl hydride complex reacts cleanly with dioxygen to produce a dialkyl Pt(IV) hydroperoxide species. Of potential relevance to the development of alkane oxidation systems is that the Pt(IV) dialkyl hydride reactant is analogous to compounds formed by intermolecular oxidative addition of alkane C-H bonds to Pt(II). The novel Pt(IV) product has been crystallographically characterized and displays an {eta}-hydroperoxide linkage.

Insertion of dioxygen into a platinum-hydride bond to form a novel dialkylhydroperoxo Pt(IV) complex

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

Structural Characterization and Intramolecular Aliphatic C−H Oxidation Ability of MIII(μ-O)2MIII Complexes of Ni and Co with the Hydrotris(3,5-dialkyl-4-X-pyrazolyl)borate Ligands Tp (X=Me, H, Br) and Tp

http://www.res.titech.ac.jp/~smart/OMcitation/97om970352n.pdf

Synthesis and Structure Determination of Rh−diene Complexes with the Hydridotris(3,5-diisopropylpyrazolyl)borate Ligand, TpiPrRh(diene) (diene = cod, nbd): Dependence of the ν(B−H) Values on the Hapticity of the TpiPr Ligand (κ2 vs κ3)1

Synthesis of a Series of Rhodium Complexes, TpiPrRhIL2 and TpiPrRhIII(X)(Y)(MeCN), with the Hydridotris(3,5-diisopropylpyrazolyl)borato Ligand (TpiPr) from a Versatile Precursor, (κ3-TpiPr)Rh(coe)(MeCN), and Dependence of κ2−κ3 Interconversion Rate of the TpiPr Ligand on the Chelate Ring Size

Keisuke Ohta

Papers

Synthesis and Structure Determination of Rh−diene Complexes with the Hydridotris(3,5-diisopropylpyrazolyl)borate Ligand, TpiPrRh(diene) (diene = cod, nbd): Dependence of the ν(B−H) Values on the Hapticity of the TpiPr Ligand (κ2 vs κ3)1

Synthesis of a Series of Rhodium Complexes, TpiPrRhIL2 and TpiPrRhIII(X)(Y)(MeCN), with the Hydridotris(3,5-diisopropylpyrazolyl)borato Ligand (TpiPr) from a Versatile Precursor, (κ3-TpiPr)Rh(coe)(MeCN), and Dependence of κ2−κ3 Interconversion Rate of the TpiPr Ligand on the Chelate Ring Size