Immobilized Chiral ortho-Metalated Dirhodium(II) Compounds as Catalysts in the Asymmetric Cyclopropanation of Styrene with Ethyl Diazoacetate
Immobilization of ortho-metalated dirhodium(II) compounds has been achieved by a carboxylate interchange reaction between (M)-Rh2(l-protos)2[(p-XC6H3)P(p-XC6H4)2]2 diastereoisomers and carboxyethylpolystyrene polymer (PS-C6H4(CH2)2CO2H). The immobilized chiral catalysts have been tested in the standard reaction of asymmetric cyclopropanation of styrene with ethyl diazoacetate, giving higher yields than homogeneous chiral trifluoroacetate derivatives, but their diastereo- and enantioselectivities were lower. Some of the immobilized catalysts have proved to be very robust. The catalytic behavior of (M)-Rh2(O2C(CH2)2C6H5)2[(p-XC6H3)P(p-XC6H5)2]2 compounds has been studied as a model for the im…
Synthesis of Dirhodium(II) Complexes with Several Cyclometalated Thienylphosphines
The thermal reaction of dirhodium tetraacetate with tris(3-thienyl)phosphine (3TP), diphenyl(3-thienyl)phosphine (3TPPh2), and diphenyl(2-thienyl)phosphine (2TPPh2) gives rise to mono-cyclometalated and bis-cyclometalated compounds; the latter can have a head-to-head (H−H) or head-to-tail (H−T) configuration. Bis-cyclometalated compounds with H−T configuration can be prepared in high yield under photochemical conditions or by combining irradiation with subsequent thermal treatment in acetic acid. The reactivity order of aromatic ring C−H activation is phenyl < 2-thienyl ≪ 3-thienyl, which leads to a selective activation of the thienyl ring. Thus, only one mono-cyclometalated compound is obt…
Reaction of Tris(2-thienyl)phosphine with Dirhodium(II) Acetate. Orthometalation of a Heteroaromatic π-System and an Unusual Ring Rearrangement
The reaction of tris (2-thienyl)phosphine (1) with dirhodium(II) acetate in a 9:1 refluxing toluene/ acetic acid mixture for 2 h leads to the formation of two metalated compounds. The structure of one of them contained two new orthometalated phosphines in a head-to-head arrangement, and, surprisingly, the metalated thiophene rings, but not the nonmetalated ones, were rearranged to a 3-thienyl structure. Both types of dirhodium compounds were assessed in a catalytic α-diazo ester transformation.