title: Chiral triaryl phosphite-based palladacycles and platinacycles: synthesis and application to asymmetric Lewis acid catalysis.
abstract: The optically pure monophosphites P(OAr)(BINOLate) (7, where Ar = 2,4-di-tert-butylphenyl) have been prepared by treatment of PCl2(OAr) with R- or S-BINOL. Treatment of [PdCl2(NCMe)2] with 7 gave [PdCl2(7)2] (9) or the binuclear orthometallated complex [Pd2Cl2(7-H)2] (8) depending on the reaction conditions. Bridge cleavage reactions of 8 gave [PdCl(7-H)(L)] with L trans to carbon when L = PPh3 or 7 and cis to carbon when L = N-heterocyclic carbene. Treatment of [PtCl2(NCtBu)2] with 7 gave [PtCl2(7)2] (18) which upon further reaction with PtCl2 furnished a mixture of binuclear [Pt2Cl2(7-H)2] (17) and cis-[PtCl(7-H)(7)] (19). The palladium complexes containing cyclometallated 7 were screened for catalysis of 1,4-conjugate addition of phenylboronic acid to cyclohexen-2-one and the allylation of benzaldehyde with allyltributyltin. Conversions were generally high in each case but enantioselectivities were low (15% e.e. at best). The X-ray crystal structures of 8, 17 and [PdCl(7-H)(NHC)] (10a, where NHC = 1,3-(dimesityl)imidazolidin-2-ylidene) have been determined.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, UKBS8 1TS. r.bedford@bristol.ac.uk
authors.forename: Robin B
authors.initials: RB
authors.lastname: Bedford
authors.forename: Helena
authors.initials: H
authors.lastname: Dumycz
authors.forename: Mairi F
authors.initials: MF
authors.lastname: Haddow
authors.forename: Lukasz T
authors.initials: LT
authors.lastname: Pilarski
authors.forename: A Guy
authors.initials: AG
authors.lastname: Orpen
authors.forename: Paul G
authors.initials: PG
authors.lastname: Pringle
authors.forename: Richard L
authors.initials: RL
authors.lastname: Wingad