Fakultät für Chemie, Anorganische Chemie, Universität Bielefeld, Universitätsstrasse 25, 33615 Bielefeld, Germany.
Chemistry. 2011 Dec 23;17(52):14935-41. doi: 10.1002/chem.201102347. Epub 2011 Dec 6.
Secondary phosphane oxides, R(2)P(O)H, are commonly used as preligands for transition-metal complexes of phosphinous acids, R(2)P-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, (R(f))(2)P-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, (R(f))(2)P(O)H, reacts smoothly with solid platinum(II) dichloride yielding the trans-configured phosphinous acid platinum complex trans-[PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)]. The deprotonation of one phosphinous acid ligand with an appropriate base leads to the cis-configured monoanion complex cis-PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H, featuring the quasi-chelating phosphinous acid phosphinito unit, (R(f))(2)P-O-H···O=P(R(f))(2), which exhibits a strong hydrogen bridge substantiated by an O···O distance of 245.1(4) pm. The second deprotonation step is accompanied by a rearrangement to afford the trans-configured dianion trans-PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2). The reaction of (R(f))(2)P(O)H with solid palladium(II) dichloride initially yields a mononuclear palladium complex [PdCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)], which condenses under liberation of HCl to the neutral dinuclear palladium complex [Pd(2)(μ-Cl)(2){({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H}(2)]. The equilibrium between the mononuclear [PdCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)] and dinuclear [Pd(2)(μ-Cl)(2){({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H}(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(F(6)acac)(2)], with a slight excess of (R(f))(2)P(O)H yields the complex [Pd(F(6)acac)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H]. The quasi-chelating phosphinous acid phosphinito unit, which is formed by the liberation of HF(6)acac, is characterized by a O···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.
仲膦氧化物，R(2)P(O)H，通常被用作膦酸的预配体，R(2)P-OH（R=烷基，芳基），这些配体在交叉偶联反应中是有效的催化剂。与其他小组之前的工作不同，我们对含有强吸电子和空间位阻的 2,4-双（三氟甲基）苯基的缺电子膦酸，(R(f))(2)P-OH，与催化相关的金属（如钯和铂）的配位性质感兴趣。预配体双[2,4-双（三氟甲基）苯基]氧化膦，(R(f))(2)P(O)H，与固体铂(II)二氯化物反应顺利，生成反式构型的膦酸铂配合物反式-[PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)]。用适当的碱对一个膦酸配体进行去质子化，导致顺式构型的单阴离子配合物顺式-PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H，其中含有准螯合膦酸亚膦酸单元，(R(f))(2)P-O-H···O=P(R(f))(2)，其具有强烈的氢键，由 245.1(4) pm 的 O···O 距离证实。第二步去质子化伴随着重排，生成反式构型的二阴离子反式-PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)。(R(f))(2)P(O)H与固体钯(II)二氯化物的反应最初生成单核钯配合物[PdCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)]，在释放 HCl 下缩合为中性双核钯配合物[Pd(2)(μ-Cl)(2){({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H}(2)]。单核[PdCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)]和双核[Pd(2)(μ-Cl)(2){({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H}(2)]钯配合物之间的平衡是可逆的，可以通过分别加入碱或 HCl 来向每个方向移动。用稍过量的(R(f))(2)P(O)H处理六氟乙酰丙酮钯，[Pd(F(6)acac)(2)]，生成配合物[Pd(F(6)acac)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H]。由 HF(6)acac 释放形成的准螯合膦酸亚膦酸单元，其 O···O 距离为 244.1(3) pm。这些过渡金属配合物对空气和水分稳定，可以在没有任何分解迹象的情况下储存数月。
