A New Family of Organometallic Rhodium Complexes with [Rh(PiPr2Ph)2] and [Rh(PiPrPh2)2] as Molecular Units

Abstract

The π-allyl complexes [Rh(η3-C3H5)(PR3)2] [PR3 = PiPr2Ph (4), PiPrPh2 (5)], prepared from [RhCl(C8H14)2]2, PR3 and the Grignard reagent C3H5MgBr, react with carboxylic acids and p-toluenesulfonic acid to give the chelate compounds [Rh(κ2-O2CR′)(PR3)2] (8−10) and [Rh{κ2-O2S(O)-p-Tol}(PR3)2] (11, 12), respectively. While the reactions of 8, 10 and 12 with CO afford the square-planar rhodium(I) complexes 13−15 with monodentate carboxylato and tosylato ligands, treatment of 8−10 and 11, 12 with H2 leads to the formation of the octahedral dihydridorhodium(III) derivatives [RhH2(κ2-O2CR′)(PR3)2] (16−18) and [RhH2{κ2-O2S(O)-p-Tol}(PR3)2] (19, 20). Similarly to CO, internal alkynes RC≡CCO2Me (R = CO2Me, Me) react with 8 and 9 by partial opening of the chelate bond to yield the π-alkyne complexes 21−23, of which 23 with R = Me is quite labile and smoothly regenerates the starting material. In contrast, the reactions of 8 and 9 with terminal alkynes HC≡CR (R = Ph, CO2Me) afford six-coordinate alkynyl(vinyl)rhodium(III) compounds 24−26 with a different stereochemistry at the C=C double bond depending on the substituent R. From 8 and HC≡CCH(Cl)Me the octahedral allenyl complex [RhCl(CH=C=CHMe)(κ2-O2CR′)(PiPrPh2)2] (27) is obtained, the molecular structure of which has been determined by X-ray crystallography. The reaction of [Rh(κ1-O2CR){η2-C2(CO2Me)2}(PiPrPh2)2] (21, 22) with HC≡CPh also leads to the six-coordinate alkynyl(vinyl)rhodium(III) compounds 28, 29, which upon treatment with Me3SiCl and thermolysis are stepwise converted into the four-coordinate π-enyne complex trans-[RhCl{η2-PhC≡CC(CO2Me)=CHCO2Me}(PiPrPh2)2] (31). The reaction of 31 with CO generates the uncoordinated substituted enyne. The rhodium(I) vinylidene complexes trans-[Rh(C≡CR′)(=C=CHR)(PiPrPh2)2] (36−38) were prepared in two steps from the tosylato complex 12 and terminal alkynes; they react with CO via migratory insertion to give the square-planar enynyl compounds trans-[Rh{η1-C(C≡CR)=CHR′}(CO)(PiPrPh2)2] (39−41). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)