Air-Stable Platinum and Palladium Complexes Featuring Bis[2,4-bis(trifluoromethyl)phenyl]phosphinous Acid Ligands

作者：Kurscheid Boris; Neumann Beate; Stammler Hans Georg; Hoge Berthold^*

来源：Chemistry - A European Journal, 2011, 17(52): 14935-14941.

DOI：10.1002/chem.201102347

• ligand effects
• palladium
• phosphane oxides
• phosphinous acid
• platinum

Secondary phosphane oxides, R2P(O)H, are commonly used as preligands for transition-metal complexes of phosphinous acids, R2P-OH (R=alkyl, aryl), which are relevant as efficient catalysts in cross-coupling processes. In contrast to previous work by other groups, we are interested in the ligating properties of an electron-deficient phosphinous acid, (Rf)2P-OH, bearing the strongly electron-withdrawing and sterically demanding 2,4-bis(trifluoromethyl)phenyl group towards catalysis-relevant metals, such as palladium and platinum. The preligand bis[2,4-bis(trifluoromethyl)phenyl]phosphane oxide, (Rf)2P(O)H, reacts smoothly with solid platinum(II) dichloride yielding the trans-configured phosphinous acid platinum complex trans-[PtCl2({2,4-(CF3)2C6H3}2POH)2]. The deprotonation of one phosphinous acid ligand with an appropriate base leads to the cis-configured monoanion complex cis-[PtCl2({2,4-(CF3)2C6H3}2- PO)2H]-, featuring the quasi-chelating phosphinous acid phosphinito unit, (Rf)2P-O-H center dot center dot center dot O=P(Rf)2, which exhibits a strong hydrogen bridge substantiated by an O center dot center dot center dot O distance of 245.1(4) pm. The second deprotonation step is accompanied by a rearrangement to afford the trans-configured dianion trans-[PtCl2({2,4-(CF3)2C6H3}2PO)2]2-. The reaction of (Rf)2P(O)H with solid palladium(II) dichloride initially yields a mononuclear palladium complex [PdCl2({2,4-(CF3)2C6H3}2POH)2], which condenses under liberation of HCl to the neutral dinuclear palladium complex [Pd2(mu-Cl)2{({2,4-(CF3)2C6H3}2PO)2H}2]. The equilibrium between the mononuclear [PdCl2({2,4-(CF3)2C6H3}2POH)2] and dinuclear [Pd2(mu-Cl)2{({2,4-(CF3)2C6H3}2PO)2H}2] palladium complexes is reversible and can be shifted in each direction by the addition of base or HCl, respectively. Treatment of palladium(II) hexafluoroacetylacetonate, [Pd(F6acac)2], with a slight excess of (Rf)2P(O)H yields the complex [Pd(F6acac)({2,4-(CF3)2C6H3}2- PO)2H]. The quasi-chelating phosphinous acid phosphinito unit, which is formed by the liberation of HF6acac, is characterized by a O center dot center dot center dot O distance of 244.1(3) pm. These transition metal complexes are stable towards air and moisture and can be stored for months without any evidence of decomposition.

• 出版日期2011-12