Synthesis and reactivity studies of palladium(II) complexes containing the N-phosphorylated iminophosphorane-phosphine ligands Ph2PCH2P{=NP(=O)(OR)(2)}Ph-2 (R = Et, Ph): application to the catalytic synthesis of 2,3-dimethylfuran

摘要

Reactions of [PdCl2(COD)] with 1 equiv. of the iminophosphorane-phosphine ligands Ph2PCH2P{=NP(=O)(OR)(2)}Ph-2 (R = Et 1, Ph 2) lead to the novel Pd(II) derivatives cis-[PdCl2(kappa(2)- (P,N)-Ph2PCH2P{ =NP(=O)(OR)(2)}Ph-2)] (R = Et 3, Ph 4). Pd-N bond cleavage readily takes place upon treatment of these species with a variety of two-electron donor ligands. By this way, complexes cis-[PdCl2(kappa'-(P)-Ph2PCH2P{=NP(=O)(OR)(2)}Ph-2)(L)] (R = Et, L = (CNBu)-Bu-t 5a, CN-2,6-C6H3Me2 5b, py 5c, P(OMe)(3) 5d, P(OEt), 5e; R = Ph, L = (CNBu)-Bu-t 6a, CN-2,6-C6H3Me2 6b, py 6c, P(OMe)(3) 6d, P(OEt)(3) 6e) have been synthesized in high yields. The addition of two equivalents of ligands 1/2 to dichloromethane solutions of [PdCl2(COD)] results in the formation of complexes trans-[PdCl2(kappa(1)(P)-Ph2PCH2P =NP(=O)(OR)(2)}Ph-2)(2)] (R = Et 7, Ph 8), which can be converted into the dicationic species [Pd(Ph2PCH2P{=NP(=O)(OR)(2)}Ph-2)(2)][SbF6](2) (R = Et 9, Ph 10) by treatment with AgSbF6. Complex 10 also reacts with (CNBu)-Bu-t to afford trans-[Pd(kappa(1)(P)-Ph2PCH2P{=NP(=O)(OPh)(2)}Ph-2)(2)((CNBu)-Bu-t)(2)][SbF6](2) 11. The structures of 4, 5b, 7 and 9 have been determined by single-crystal X-ray diffraction methods. In addition, the ability of these Pd(II) complexes to promote the catalytic cycloisomerization of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran has also been studied.