Ruthenium complex with chiral arene ligand [(camphor-arene)RuCl2]2 was synthesized by the reaction of RuCl3∙nH2O with the chiral diene, which was obtained from natural camphor in 3 steps. This complex catalyzed asymmetric hydrogenation of acetophenone (64-85% ee), but decomposed in the catalytic reactions involving C-H activation of 2-phenyl-pyridine or benzoic acid derivatives.
Dedicated to Prof. Ken Tanaka in recognition of his studies of rhodium-catalyzed cyclization of alkynes.Reaction of two molecules of o-diphenylphosphino-tolane with RhCl(PPh 3 ) 3 produces the metallacycle complex with C 4 Rh(P 3 )Cl core. Further addition of tolane leads to 2 + 2 + 2-cycloaddition and gives the cationic complex [Rh(Ph 2 PÀ C 6 H 4 À C 6 Ph 4 À C 6 H 4 À PPh 2 )]Cl, in which the metal is coordinated to C 6 Ph 4 aromatic ring as well to two chelating PPh 2 groups. The resulting bulky terphenyl-diphosphine ligand with phosphorous atoms locked in cis-position can be decoordinated from rhodium by a strong and non-hindered ligand tBuNC. Peculiar structures of all the compounds were studied by the X-ray diffraction.Biaryl phosphine ligands (Buchwald-type ligands) are widely used in palladium and gold chemistry, due to stabilizing effect of the metal-arene π-interaction. Similar ligands with two phosphorous atoms have also attracted some attention because such chelating systems allow for a variable metal-arene coordination while maintaining the stability of the complex through the strong MÀ P bonds. [1][2][3][4] To the best of our knowledge, almost all of these ligands have been synthesized by reactions of the corresponding lithium or magnesium aromatic derivatives with R 2 PCl. However, long time ago, Dr. Winter has reported an intriguing alternative approach based on the metal-promoted 2 + 2 + 2-cycloaddition of the phosphoroussubstituted alkyne 1 (Scheme 1). [5,6] Unfortunately, these results were published only as the short communication with little experimental details and no crystal structures. Recently, we and others have synthesized a variety of catalytically active rhodium complexes by cyclization of alkynes into cyclobutadiene and cyclopentadienyl ligands in the coordination sphere of the metal. [7][8][9][10][11] Therefore, we became interested in the detailed reinvestigation of the results reported by Dr. Winter.The starting ortho-diphenylphisphino-tolane (1) was obtained by the literature procedure from 2-bromo-iodobenzene in two steps. [12] Further reaction of 1 with Rh(PPh 3 ) 3 Cl proceeded at room temperature and gave the metallacycle 2, which was isolated in 92 % yield as air-stable orange crystals.Unfortunately, the analogous reaction of 1 with Co(PPh 3 ) 3 Cl led to a complex mixture of products according to 31 P NMR. The formation of 5-membered metallacycles from alkynes is quite typical, [13][14][15] although in the case of phosphorous-substituted alkynes more complex dinuclear structures are often formed [a]
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