Micro-flow synthesis and structural analysis of sterically crowded diimine ligands with five aryl rings.

Sterically crowded diimine ligands with five aryl rings were prepared in one step in good yields using a micro-flow technique. X-ray crystallographic analysis revealed the detailed structure of the bulky ligands. The nickel complexes prepared from the ligands exerted high polymerization activity in the ethylene homopolymerization and copolymerization of ethylene with polar monomers.

Combinatorial synthesis and evaluation of α-iminocarboxamide-nickel(II) catalysts for the copolymerization of ethylene and a polar monomer.

Late-transition metal catalysts used for olefin polymerization, the so-called postmetallocenes, which includes α-iminocarboxamide-nickel(II) catalysts have attracted a great deal of attention because of many valuable features such as the copolymerization of α-olefins with polar monomers. In this paper, the combinatorial synthesis and evaluation of α-iminocarboxamide-nickel(II) catalysts are discussed for their roles in the discovery of a highly active catalyst and elucidation of its structure-activity relationship. The combinatorial optimization of each reaction condition was performed, then a combinatorial library of α-iminocarboxamides with systematically modified substituents was constructed by amidation of α-keto acid chlorides and subsequent imination of α-keto carboxamides in parallel fashion. As a result, 87 analytically pure α-iminocarboxamide ligands were successfully synthesized. α-Iminocarboxamide-nickel(II) catalysts were prepared from the synthesized α-iminocarboxamide ligands. The catalysts' activities for polymerization of ethylene and copolymerization of ethylene and 5-norbornen-2-ol were evaluated. Results of the present study revealed 9 novel active catalysts for ethylene polymerization and 7 novel active catalysts for copolymerization of ethylene and 5-norbornen-2-ol. It should be noted that the best catalysts for ethylene polymerization and for copolymerization in the present study showed higher activities compared to the known active catalyst. Polymerization activities of the catalysts varied dramatically according to the combination of substituents on the α-iminocarboxamides.

Switchable C- and N-bound isomers of transition-metal cyanocarbanions: synthesis and interconversions of cyclopentadienyl ruthenium complexes of phenylsulfonylacetonitrile anions.

The synthesis, structure, and dynamic behavior of bistable C- and N-bound isomers of transition-metal cyanocarbanions are described. A series of C-bound cyclopentadienyl (Cp) ruthenium phosphane complexes, [Ru{CH(CN)SO2Ph}(Cp)L1L2] (3), and their N-bound isomers, [Ru+(Cp)(NCCH(-)SO2Ph)L1L2] (4), were prepared by treating [RuCl(Cp)(PR3)2] with the sodium salt of phenylsulfonylacetonitrile and performing ligand-exchange reactions with the resulting compounds. Structural characterization by X-ray diffraction indicates that the cyanocarbanion moiety of 3 has an alpha-metalated structure, whereas that of 4 has a zwitterionic, end-on structure. Heating these complexes in aprotic solvents gives rise to irreversible linkage isomerization between C- and N-bound isomers, in which the relative thermal stabilities vary greatly depending on the steric and electronic nature of the ligands. Mechanistic studies of N-to-C isomerization revealed that the reaction proceeds irreversibly in a unimolecular manner without the formation of coordinatively unsaturated species. A metal-sliding process, which occurs over the -C-C triple chemical bond N pi-conjugated surface of the cyanocarbanion moiety, was suggested by results from kinetic studies and density functional theory (DFT) calculations. C-to-N isomerizations proceed by the above-mentioned intramolecular process, with a temperature-dependent contribution from the formation and cleavage of mu2-C,N coordination dimers [{Ru{CH(CN)SO2Ph}(Cp)(PPh3)}2] (15 and 16).

Mechanism of the interconversions between C- and N-bound transition metal alpha-cyanocarbanions.

The first presentation of the intra- and intermolecular mechanisms of the C-N interconversions of transition metal alpha-cyanocarbanions is described. A pair of N- and C-bound isomers of isonitrile complex Ru+Cp(NCCH-SO2Ph)(PPh3)(CN-t-Bu) (1) and RuCp[CH(CN)SO2Ph](PPh3)(CN-t-Bu) (2) was synthesized for the mechanistic studies on the N-to-C isomerizations. Structural characterization by X-ray diffractions of 1 and 2 indicated their typical zwitterionic and alpha-metalated structures. The kinetic studies on the irreversible isomerization of 1 to 2 in benzene-d6 at 333-348 K were carried out using 1H NMR spectroscopy, affording the first-order rate constants k1 and the activation parameters DeltaH = 107 +/- 2 kJ.mol-1 and DeltaS = -22 +/- 5 J.K-1.mol-1. The almost identical values of k1 were obtained upon similar treatment of 1 with 4 equiv of external ligands such as PPh3, CH3CN, and t-BuNC at 333 K, indicating that the N-to-C isomerization proceeds in an intramolecular manner without dissociation of a ligand. As a model system for the C-to-N isomerization, the irreversible transformation of RuCp[CH(CN)SO2Ph](PPh3)2 (3) to Ru+Cp(NCCH-SO2Ph)(PPh3)2 (4) was investigated under various reaction conditions. The reaction of 3 at room temperature in THF affords the coordination dimers (RRu*,SC*,RRu*,SC*)-{RuCp[CH(CN)SO2Ph](PPh3)}2 (5) stereoselectively, and its distorted mu2-C,N-bound structure was determined by X-ray analysis. The reaction profiles for the isomerization of 3 includes the generation- and temperature-dependent decays of dimeric species 5 and its diastereomer 6, which strongly suggests that the intra- and intermolecular pathways are included in the C-to-N isomerization. The intramolecular process of the C-to-N isomerization of 3 has been confirmed by the kinetic studies on the isomerization of 3 with excess amount of PPh3 in benzene-d6 at 333-348 K which afford the first-order kinetics with the activation parameters of DeltaH = 121 +/- 1 kJ.mol-1 and DeltaS = 42 +/- 4 J.K-1.mol-1. Treatment of 5 with PPh3 in boiling benzene gives rise to the quantitative formation of N-bound complex 4. The controlled kinetic experiments on the cleavage of 5 with PPh3 have concluded that the cleavage of 5 with PPh3 proceeds via simultaneous C-Ru and N-Ru bond scissions, indicating the temperature-dependent participation of intermolecular process in the C-to-N isomerization of 3.