Synthesis and Characterization of Chair and Boat Forms offac-Re(CO)3(P3)(X) [P3= η2-CH3C(CH2PPh2)3, X = Br, Cl]

The syntheses of complexes having the general formula fac -Re(CO) 3 (η 2 -triphos)X (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane; 1 and 2, X = Br; 5 and 6, X = Cl) from reactions of Re(CO) 5 X and triphos are described. The X-ray structure of 1 shows that the six-membered metallacyclic ring (ReP 2 C 3 ) adopts a chair conformation like the known complex 5, while structural data for 2 and 6 indicate boat forms for the metallacyclic rings. This represents the first identification of boat forms of these complexes. The pendant phosphines in compounds 1 and 2 can be oxidized, yielding compounds 3 and 4, respectively. The X-ray structure of 4 retains the boat form of its precursor and the properties of 3 are different, suggesting that the ring conformation was retained here also. Thermolysis reactions of 5 and 6 were conducted to probe for differences in the ease of decarbonylation and conversion to the known η 3 -coordinated complex, 7 . The boat complex 6 is converted more readily to 7; there is no evidence for any thermal conversion of 6 to 5 .