Direct platination as a route to conformationally restricted enantiopure C-2-symmetric bisoxazoline pincer complexes

(S)-3-Amino-4-cyclohexyl-2-methylbutan-2-ol 10 was synthesised in four-steps front (S)-2-amino-3-cyclohexanepropanoic acid (47% overall yield). Reaction of 10 with 1,3-bis(ethyl carboximidate)benzene gave (S,S)-1,3-bis(4'-cyclohexylmethyl-5',5'-dimethyl-2'-oxazolinyl)benzene 13 in 53% yield. Heating 13 at reflux in acetic acid with K2PtCl4 gave (S,S)-chloro[2,6-bis(5',5'-dimethyl-4'-methylenecyclohexyl-2'-oxazolinyl )phenyl-N, C-1,N']platinum(11) 5 (22% yield). Similarly prepared were (S,S)-chloro[2,6-bis(4'-methylenecyclohexyl-2'-oxazolinyl)phenyl-N,C-1,N ']platinum(II) 6 (9%)) and (S,S)-chloro[2,6-bis(4'-methylethyl-2'-oxazolinyl)-4-nitrophenyl-N, C-1.N']platinum (II) 18 (21%). Chloride abstraction frorn 5 with AgOTf and 6 with AgOTf or AgSbF6, resulted in isolation of the corresponding salts of (S,S)-aqua[2,6-bis(5',5'-dimethyl-4'-methylenecyclohexyl-2'-oxazolinyl)p henyl-N,C-1,N']platinum(II) or (S,S)-aqua[2 6-bis(4'-methylenecyclohexyl-T-oxazolinyl)phenyl-N,C-1,N']platinum(II), respectively. The X-ray crystal structures of 5 and 6 are reported and compared. (C) 2004 Elsevier Ltd. All rights reserved.