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A chiral ruthenium(II)–bis(2-oxazolin-2-yl)pyridine catalyst prepared in situ from optically active bis(2-oxazolin-2-yl)pyridine (Pybox-ip) (2) and [RuCl2(p-cymene)]2 (1) exhibited efficient activity for the asymmetric cyclopropanation (ACP) of styrene and several diazoacetates to give the corresponding trans- and cis-2-phenylcyclopropane-1-carboxylates (3 and 4) in good yields (66—87%). A mixture of 1 and 2 in an atmosphere of ethylene produced the trans-RuCl2(Pybox-ip)(ethylene) complex (5), which also proved to be a powerful catalyst for ACP. The stereoselectivity of the trans- and cis-cyclopropanes were from 90 : 10 up to 98 : 2, and their enantioselectivities reached 97%. A catalytic system with 5 could be used for several olefins and internal olefins. A concerted mechanism of ACP with the Ru–Pybox catalyst was postulated on the basis of the stereospecificity with deuterated styrene. Other substituents, such as ethyl, s-butyl, benzyl, and phenyl on the oxazoline rings of Pybox in place of the isopropyl group were also examined, and were found to exhibit a similar high trans-stereoselection and a high enantioselectivity of the cyclopropane products; ex. with Ru–Pybox-ethyl 91 : 9 of 3 : 4 and 82% ee for 3. The non-chiral Ru–Pybox-dihydro catalyst exhibited asymmetric induction with 39% ees of 3 with d- and l-menthyl diazoacetates, and kept a high trans- and cis-stereoselection of 97 : 3.

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The transmetalation of (Phebox)SnMe 3 (3; Phebox ) 2,6-bis(oxazolinyl)phenyl) with PdCl 2 -(PhCN) 2 or K[PtCl 3 (C 2 H 4 )](H 2 O) gave (Phebox)M II Cl complexes (4, M ) Pd; 5, M ) Pt) in modest to good yields. The (Phebox)Pt IV Cl 3 complexes 8 were also synthesized by the reaction of 5 with CuCl 2 (H 2 O) 2 as an oxidant. These chloride complexes, 4, 5, and 8, were in turn converted to the cationic complexes by treatment with the corresponding silver salts (AgX: X ) BF 4 , OTf, OCOCF 3 ). X-ray structure studies revealed that the octahedral structure of (Phebox)Pt IV Cl 2 fragment G is isosteric with the (Phebox)Rh III Cl 2 fragment D, and the (Phebox)M II fragment H (M ) Pd, Pt) is almost the same configuration with a square-planar structure. In these complexes, the cationic BF 4 aqua complexes (9, M ) Pd II ; 10, M ) Pt II ; 11, M ) Pt IV ) were found to act as chiral catalysts for the aldol-type condensation of isocyanides and aldehydes in the presence of i-Pr 2 NEt. Excellent trans diastereoselectivities and modest to good enantioselectivities were obtained in the reaction of tosylmethyl isocyanide (TosMIC, 1) by the use of [(i-Pr-Phebox)Pt II (H 2 O)](BF 4 ) (i-Pr-10). Scheme 2Scheme 3