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

Article abstract of DOI:10.1016/S0022-328X(01)00879-8

The five-coordinate rhodium(I) stibine complexes Rh(SbPh₃)₃(CO)X (X=Cl (1), Br (2)) react with HCCCH₂Y (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 MeCCCH₂Y yield the η¹-propargyl Rh(SbPh₃)₂(CO)Cl(OTs)(η¹-CH ₂CCMe) (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(η ¹-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)CH ₂) (5d) and Rh(SbPh₃)₃(OTs)(η²-C(O)CH=C(Cl)CH ₂) (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(η ¹-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)CH ₂) (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.