Koshino Nobuyoshi, Espenson James H
Ames Laboratory and Department of Chemistry, Iowa State University of Science and Technology, Ames, Iowa 50011, USA.
Inorg Chem. 2003 Sep 8;42(18):5735-42. doi: 10.1021/ic034322q.
An oxorhenium(V) dimer, PMeReO(mtp), D, where mtpH(2) is 2-(mercaptomethyl)thiophenol, catalyzes oxygen atom transfer reaction from methyl phenyl sulfoxide to triarylphosphines. Kinetic studies in benzene-d(6) at 23 degrees C indicate that the reaction takes place through the formation of an adduct between D and sulfoxide. The equilibrium constants, K(DL), for adduct formation were determined by spectrophotometric titration, and the values of K(DL) for MeS(O)C(6)H(4)-4-R were obtained as 14.1(2), 5.7(1), and 2.1(1) for R = Me, H, and Br, respectively. Following sulfoxide binding, oxygen atom transfer occurs with either internal or external nucleophilic assistance. Because MeReO(mtp) is a much more reactive catalyst than its monomerized form, MeReO(mtp)PPh(3), loss of the active catalyst during the time course of the reaction must be taken into account as a part of the kinetic analysis. As it happens, sulfoxide catalyzes monomerization. Monomerization by triarylphosphines was also studied in the presence of sulfoxide, and a mechanism for that reaction was also proposed. Both the phosphine-assisted monomerization and the phosphine-assisted pathway for oxygen atom transfer involve transition states with ternary components, D, sulfoxide, and phosphine, which we suggest are structural isomers of one another.
一种氧代铼（V）二聚体，[PMeReO(mtp)]₂，D，其中mtpH₂为2-(巯基甲基)苯硫酚，可催化氧原子从苯基亚砜转移至三芳基膦。在23℃的氘代苯中进行的动力学研究表明，该反应通过D与亚砜之间形成加合物而发生。通过分光光度滴定法测定了加合物形成的平衡常数K(DL)，对于MeS(O)C₆H₄-4-R，当R = Me、H和Br时，K(DL)的值分别为14.1(2)、5.7(1)和2.1(1)。亚砜结合后，氧原子转移在内源或外源亲核试剂的协助下发生。由于[MeReO(mtp)]₂是比其单体形式MeReO(mtp)PPh₃活性高得多的催化剂，在反应过程中活性催化剂的损失必须作为动力学分析的一部分加以考虑。碰巧的是，亚砜催化单体化。还研究了在亚砜存在下三芳基膦引发的单体化，并提出了该反应的机理。膦辅助的单体化以及膦辅助的氧原子转移途径都涉及具有三元组分D、亚砜和膦的过渡态，我们认为它们是彼此的结构异构体。
