Insertion Reactions of [ReH(CO) 5– n (PMe 3 ) n ] Complexes ( n = 2–4) with aldehydes, CO 2 , and activated acetylenes

The complexes of the type [ReH(CO) 5– n (PMe 3 ) n ] ( n = 4, 3) were reacted with aldehydes, CO 2 , and RCCCOOMe (R = H, Me) to establish a phosphine‐substitutional effect on the reactivity of the Re–H 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 ( 1 ) 7b . While 1 did not react with CO 2 , 2 and 3 yielded under relatively mild conditions the formato‐ligated [Re(HCO 2 )(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 α‐metallation and trans ‐insertion stereochemistry. Similarly, HC≡CCO 2 Me afforded with 2 and 3 , the α‐metallation products [Re{C(CO 2 Me)CH 2 }(CO)(L)(PMe 3 ) 3 ] 11 (L = CO) and 12 (L = PMe 3 ). The methyl butyonate 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 MeCCCO 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.