Synthesis and reactivity studies of palladium(ii) complexes containing the N-phosphorylated iminophosphorane-phosphine ligands Ph2PCH2P{NP(O)(OR)2}Ph2 (R = Et, Ph): application to the catalytic synthesis of 2,3-dimethylfuran

Abstract

Reactions of [PdCl₂(COD)] with 1 equiv. of the iminophosphorane-phosphine ligands Ph₂PCH₂P{NP(O)(OR)₂}Ph₂ (R = Et 1, Ph 2) lead to the novel Pd(II) derivatives cis-[PdCl₂(κ²-(P,N)-Ph₂PCH₂P{NP(O)(OR)₂}Ph₂)] (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(κ¹-(P)-Ph₂PCH₂P{NP(O)(OR)₂}Ph₂)(L)] (R = Et, L = CN^tBu 5a, CN-2,6-C₆H₃Me₂5b, py 5c, P(OMe)₃5d, P(OEt)₃5e; R = Ph, L = CN^tBu 6a, CN-2,6-C₆H₃Me₂6b, py 6c, P(OMe)₃6d, P(OEt)₃6e) 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(κ¹-(P)-Ph₂PCH₂P{NP(O)(OR)₂}Ph₂)₂] (R = Et 7, Ph 8), which can be converted into the dicationic species [Pd(Ph₂PCH₂P{NP(O)(OR)₂}Ph₂)₂][SbF₆]₂ (R = Et 9, Ph 10) by treatment with AgSbF₆. Complex 10 also reacts with CN^tBu to afford trans-[Pd(κ¹(P)-Ph₂PCH₂P{NP(O)(OPh)₂}Ph₂)₂(CN^tBu)₂][SbF₆]₂11. 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.