The Ο-allyl complexes [Rh(Ξ· 3 -C 3 H 5 )(PR 3 ) 2 ] [PR 3 = PiPr 2 Ph (4), PiPrPh 2 (5)], prepared from [RhCl(C 8 H 14 ) 2 ] 2 , PR 3 and the Grignard reagent C 3 H 5 MgBr, react with carboxylic acids and p-toluenesulfonic acid to give the chelate compounds [Rh(ΞΊ 2 -O 2 CRΠ)(PR 3 ) 2 ] (8-10) and [Rh{ΞΊ 2 -O 2 S(O)-p-Tol}(PR 3 ) 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 H 2 leads to the formation of the octahedral dihydridorhodium(III) derivatives [RhH 2 (ΞΊ 2 -O 2 CRΠ)-(PR 3 ) 2 ] (16-18) and [RhH 2 {ΞΊ 2 -O 2 S(O)-p-Tol}(PR 3 ) 2 ] (19, 20). Similarly to CO, internal alkynes RCΟ΅CCO 2 Me (R = CO 2 Me, Me) react with 8 and 9 by partial opening of the chelate bond to yield the Ο-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 HCΟ΅CR (R = Ph, CO 2 Me) afford six-coordinate alkynyl(vinyl)rhodium(III) compounds 24-26 with a different stereochemistry at the C=C double bond depending on the [a]