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

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journal contribution
posted on 1996-10-15, 00:00 authored by Richard D. Adams, Mingsheng Huang
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-η31-MeO2C(H)CCC(H)CO2Me], 3 (31%), and fac-Re2(CO)6(PMe2Ph)[μ-η31-MeO2C(H)CCC(H)CO2Me], 4 (22%), which contain bridging η31-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.