Synthesis and characterization of chair and boat forms of fac-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)(eta (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 (ReP2C3) 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 eta (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.