Synthesis and catalytic properties of cationic palladium(II) and rhodium(I) complexes bearing diphosphinidinecyclobutene ligands

Cationic palladium(II) and rhodium(l) complexes bearing 1,2-diaryl-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene ligands (DPCB-Y) were prepared and their structures and catalytic activity were examined (aryl = phenyl (DPCB), 4-methoxyphenyl (DPCB-OMe), 4-(trifluoromethyl)phenyl (DPCB-CF3)). The palladium complexes [Pd(McCN)(2)(DPCB-Y)]X-2 (X = OTf, BF4, BAr4 (Ar = 3,5-bis(trifluoromethyl)phenyt)) were prepared by the reactions of DPCB-Y with [Pd(MeCN)(4)]X-2, which were generated from Pd(OAc)(2) and HX in MeCN. On the other hand, the rhodium complexes [Rh(MeCN)(2)(DPCB-Y)]OTf were prepared by the treatment of [Rh(mu-Cl)(cyclooctene)(2)](2) with DPCB-Y in CH2Cl2, followed by treatment with AgOTf in the presence of MeCN. The cationic complexes catalyzed conjugate addition of benzyl carbarnate to alpha,beta-unsaturated ketones. (c) 2006 Elsevier B.V. All rights reserved.