The Coordination and Transformations of a Dicarboxylate Substituted Allene on a Dimanganese Carbonyl Grouping

Two products, Mn 2 (CO) 7 (PMe 2 Ph)[μ‐η 2 ‐η 2 ‐MeO 2 C(H)CCC‐(H)CO 2 Me] ( 1 ) in 9% yield and Mn 2 (CO) 6 (PMe 2 Ph)[μ‐η 3 ‐η 1 ‐MeO 2 CC(H)CC(H)CO 2 Me] ( 2 ) in 34% yield, were obtained from the reaction of Mn 2 (CO) 8 (PMe 2 Ph)(MeCN) with MeO 2 C(H)C=C=C(H)CO 2 Me. Compound 1 contains a bridging η 2 ‐η 2 ‐MeO 2 C(H)CCC(H)CO 2 Me allene ligand and compound 2 contains a bridging η 3 ‐η 1 ‐MeO 2 C(H)CCC(H)‐CO 2 Me allene ligand in which the oxygen atom of one of the carbonyl groups is also coordinated. Compound 1 slowly converts to 2 , which establishes that it is a precursor to 2 . Compound 2 reacts with NEtH 2 to give the mononuclear manganese complex fac ‐Mn(CO) 3 (PMe 2 Ph)[MeO 2 CCH 2 ‐C=C(H)CO 2 Me] ( 3 ) in 96% yield. Compound 3 contains a chelating 1,3‐di(methoxycarbonyl)propenyl grouping formed by addition of a hydrogen atom to the allene and the loss of a manganese grouping. Compounds 1–3 were characterized by single crystal x‐ray diffraction methods.