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

The five-coordinate rhodium(I) stibine complexes Ph(SbPh3)(3)(CO)X (X = Cl (1), Br (2)) react with HC=CCH2Y (Y = Cl, Br, OTs, OBs) in CH2Cl2 at ambien t temperature to afford the eta (1)-allenyl Rh(SbPh3)(2)(CO)X(Y)(eta (1)-CH =C=CH2) (X = Cl, Y = OTs (3a), OBs (3b); X = Y = Br (3c)) and the rhodiacyc lopent-3-ene-2-one Rh(SbPh3)(3)Cl(eta (2)-C(O)CH=C(Cl)CH2) (5a) and Rh(SbPh 3)(3)Br(eta (2)-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 e ta (1)-propargyl Rh(SbPh3)2(CO)Cl(OTs)(eta (1)-CH2C-CMe) (4) and the rhodia cyclic Rh(SbPh3)(3)(X or Y)(eta (2)-C(O)C(Me)=C(Y or X)CH2) (6) complexes. The rhodiacycles 5a and 5c were converted to the eta (1)-allenyls Rh(SbPh3) (2)(CO)Cl-2(eta (1)-CH=C=CH2) (3d) and 3c, respectively, upon heating at 60 degreesC in THF, with the relative rates being 5c > 5a. Treatment of 5a an d 5b with one equivalent of AgOTf or AgOTs results in replacement of the ha lide bonded to Rh and formation of Rh(SbPh3)(3)(OTf)(eta (2)-C(O)CH=C(Cl)CH 2) (5d) and Rh(SbPh3)(3)(OTs)(eta (2)-C(O)CH=C(Cl)CH2) (5e), respectively. The structure of 5d (as 5d.0.5C(7)H(8)) 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 rema ining halide to afford the eta (1)-allenyl Rh(SbPh3)(2)(CO)(OTf)(2)(eta (1) -CH=C=CH2) (3e). The reverse of the 5a to 3e conversion can be effected wit h chloride and SbPh3; however, without added SbPh3, the reaction affords th e substitution product 3d instead. Addition of excess pyridine or PPh3 to 5 a yields the substitution products Rh(SbPh3)(2)(py)Cl(eta (2)-C(O)CH=C(Cl)C H2) (9) and five-coordinate, 16-electron Rh(PPh3)(2)Cl(eta (2)-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. (C) 2001 Elsevier Scie nce B.V. All rights reserved.