Reactions of Rh(SbPh3)3(CO)X (X=Cl, Br) with organic propargyl compounds. Synthesis, structure and reactivity of rhodiacyclopent-3-ene-2-one complexes

The five-coordinate rhodium(I) stibine complexes Rh(SbPh3)3(CO)X (X=Cl (1), Br (2)) react with HCCCH2Y (Y=Cl, Br, OTs, OBs) in CH2Cl2 at ambient temperature to afford the η1-allenyl Rh(SbPh3)2(CO)X(Y)(η1-CHCCH2) (X=Cl, Y=OTs (3a), OBs (3b); X=Y=Br (3c)) and the rhodiacyclopent-3-ene-2-one Rh(SbPh3)3Cl(η2-C(O)CHC(Cl)CH2) (5a) and Rh(SbPh3)3Br(η2-C(O)CHC(X or Y)CH2) (X or Y=Cl (5b), Br (5c)) products. The corresponding reactions of Rh(SbPh3)3(CO)X with MeCCCH2Y yield the η1-propargyl Rh(SbPh3)2(CO)Cl(OTs)(η1-CH2CCMe) (4) and the rhodiacyclic Rh(SbPh3)3(X or Y)(η2-C(O)C(Me)C(Y or X)CH2) (6) complexes. The rhodiacycles 5a and 5c were converted to the η1-allenyls Rh(SbPh3)2(CO)Cl2(η1-CHCCH2) (3d) and 3c, respectively, upon heating at 60 °C in THF, with the relative rates being 5c>5a. Treatment of 5a and 5b with one equivalent of AgOTf or AgOTs results in replacement of the halide bonded to Rh and formation of Rh(SbPh3)3(OTf)(η2-C(O)CHC(Cl)CH2) (5d) and Rh(SbPh3)3(OTs)(η2-C(O)CHC(Cl)CH2) (5e), respectively. The structure of 5d (as 5d·0.5C7H8) was determined by single-crystal X-ray diffraction analysis. Addition of two equivalents of AgOTf to 5a and 5b, or of one equivalent of AgOTf to 5d, leads to the replacement of the remaining halide to afford the η1-allenyl Rh(SbPh3)2(CO)(OTf)2(η1-CHCCH2) (3e). The reverse of the 5a to 3e conversion can be effected with chloride and SbPh3; however, without added SbPh3, the reaction affords the substitution product 3d instead. Addition of excess pyridine or PPh3 to 5a yields the substitution products Rh(SbPh3)2(py)Cl(η2-C(O)CHC(Cl)CH2) (9) and five-coordinate, 16-electron Rh(PPh3)2Cl(η2-C(O)CHC(Cl)CH2) (7), respectively. A mechanism is proposed for the conversion of 1 and 2 to 5 and for the transformations between 5 and 3.