INSERTION REACTIONS OF [REH(CO)(5-N)(PME(3))(N)] COMPLEXES (N=2-4) WITH ALDEHYDES, CO2, AND ACTIVATED ACETYLENES

The complexes of the type [ReH(CO)(5-n)(PMe(3))(n)] (n = 2, 1; n = 3, 2; n = 4, 3) were reacted with aldehydes, CO2, and RC=CCOOMe (R = H, Me) to establish a phosphine-substitutional effect on the reactivity of the Re-II bond. In the series 1-3, benzaldehyde showed conversion with only 3 to afford a (benzyloxy)carbonyltetrakis(trimethylphosphine)rhenium complex 4. Pyridine-2-carbaldehyde allowed reaction with all hydrides 1-3. With 1 and 2, the same dicarbonyl[(pyridin-2-yl)methoxy-O,N]bis(trimethylphosphine)rhenium 5b was formed with the intermediacy of a [(pyridin-2-yl)methoxy-O]-ligated species and extrusion of CO or PMe(3), respectively. The analogous conversion of 3 afforded the carbonyl[(pyridin-2-yl)methoxy-O,N]tris(trimethylphosphine)rhenium(I) 7b. While 1 did not react with CO2, 2 and 3 yielded under relatively mild conditions the formato-ligated [Re(HCO2)(CO)(L)(PMe(3))3] species (8 (L = CO) and 9 (L = PMe(3))). Methyl propiolate and methyl butynoate were transformed, in the presence of 1, to [Re{C(CO(2)Me)=CHR}(CO)(3)(PMe(3))2] systems (10a (R = H), and 10b (R = Me)), with prevailing alpha-metallation and trans-insertion stereochemistry. Similarly, HC=CCO(2)Me afforded with 2 and 3, the alpha-metallation products [Re{C(CO(2)Me)=CH2}(CO)(L)(PMe(3))(3)] 11 (L = CO) and 12 (L = PMe(3)). The methyl butyonale insertion into 2 resulted in formation of a mixture of the (Z)- and (E)-isomers of [Re{C(CO(2)Me)=CHMe}(CO)(2)(PMe(3))(3)] (13a, b). In the case of the conversion of 3 with MeC=CCO(2)Me, a Re-H cis-addition product [Re{(E)-C(CO(2)Me)=CHMe}(CO)(PMe(3))(4)] (14) was selectively obtained. Complex 11 was characterized by an X-ray crystal-structure analysis.