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

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The reaction of (Phebox)RhCl 2 (H 2 O) complexes 3 (Phebox ) 2,6-bis(oxazolinyl)phenyl) with methyl isocyanoacetate (1) and (p-tolylsulfonyl)methyl isocyanide (TosMIC; 2) provided the corresponding isocyanide complexes (Phebox)RhCl 2 (L) (4, L ) methyl isocyanoacetate; 5, L ) TosMIC) in almost quantitative yields. These isocyanide complexes 4 and 5 readily reacted with aldehydes in the presence of t-BuOK to give the aldol adducts as diastereomeric mixtures of chiral Fischer carbene complexes 6-9. NMR study and X-ray crystallography of these carbene complexes revealed that (1) the aldol reactions proceed with trans stereoselectivity with modest to good diastereofacial selectivities on the (Phebox)RhCl 2 fragments, (2) the carbene fragments act as basic σ-donor ligands, and (3) the hybridization of the carbene carbon atoms is sp 2 and the electron-deficient carbene carbon centers are π-conjugated with both neighboring nitrogen and oxygen atoms. We also succeeded in the isolation of both enantiomers of 2-oxazoline derivative 14 from the corresponding chiral carbene complexes 8 by treatment with AgBF 4 .

Bis(oxazolinyl)phenylrhodium(III) aqua complexes, (Phebox)RhX2(H2O) [X = Cl, Br], were found to be efficient Lewis acid catalysts for the enantioselective addition of allyl- and methallyltributyltin reagents to amino aldehydes. The reactions proceed smoothly in the presence of 5–10 mol % of (Phebox)RhX2(H2O) complex at ambient temperature to give the corresponding amino alcohols with modest to good enantioselectivity (up to 94% ee).

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