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

Cationic palladium(II) and rhodium(I) 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(MeCN)2(DPCB–Y)]X2 (X = OTf, BF4, BAr4 (Ar = 3,5-bis(trifluoromethyl)phenyl)) were prepared by the reactions of DPCB–Y with [Pd(MeCN)4]X2, 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(μ-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 carbamate to α,β-unsaturated ketones.