Reactions of a Dicarboxylate-Substituted Allene with Activated Dirhenium Carbonyl Complexes

The compound Re(CO)₄[C(CH₂CO₂Me)C(H)CO₂Me], 1, was obtained in 83% yield when a mixture of Re₂(CO)₉(NCMe) and MeO₂C(H)CCC(H)CO₂Me in a hexane solution was heated to reflux for 1.5 h. The addition of one hydrogen atom to the allene grouping was shown to be derived from adventitious water. The reaction of 1 with PMe₂Ph yielded the derivative fac-Re(CO)₃(PMe₂Ph)[C(CH₂CO₂Me)C(H)CO₂Me], 2, in 98% yield. The reaction of Re₂(CO)₈(PMe₂Ph)(NCMe) with MeO₂C(H)CCC(H)CO₂Me yielded two isomeric products mer-Re₂(CO)₆(PMe₂Ph)[μ-η³-η¹-MeO₂C(H)CCC(H)CO₂Me], 3 (31%), and fac-Re₂(CO)₆(PMe₂Ph)[μ-η³-η¹-MeO₂C(H)CCC(H)CO₂Me], 4 (22%), which contain bridging η³-η¹-MeO₂C(H)CCC(H)CO₂Me dicarboxylateallene ligands and small amounts of three mononuclear nuclear products:  fac-Re(CO)₃(PMe₂Ph)[MeO₂CCH₂CC(H)CO₂Me], 2 (8%), mer-Re(CO)₃(PMe₂Ph)(MeO₂CCH₂CCHCO₂Me), 5 (5%), and a trace of 1. The carbonyl oxygen atom of one of the carboxylate groups is coordinated to one of the metal atoms in 3 and 4. Compound 3 slowly isomerizes to 4 at 25 °C, and compound 5 isomerizes to 2 when heated. The reaction of 4 with EtO₂CNCS produced two products:  2 (20%) and fac-Re(CO)₃(PMe₂Ph)[MeO₂CCH₂CC(CO₂Me)CSN(H)CO₂Et], 6 (28%). Water may be involved in the formation of both products. Compound 6 contains a MeO₂CCH₂CC(CO₂Me)CS)N(H)CO₂Et grouping that is chelated to the rhenium atom by the sulfur and alkenyl carbon atom to form a five-membered Re-CCCS ring, with Re−S = 2.443(3) Å and Re−C(1) = 2.12(1) Å.