Ligand displacement reactions of fac-(eta(2)-buckminsterfullerene)(eta(2)-phen)M-tricarbonyl (M = molybdenum, chromium, and tungsten)

A mechanistic description of the ligand exchange reactions of fac-(eta2-C60)(eta2-phen)M(CO) 3 (M = Cr, W and Mo); phen = 1,10-phenanthroline) will be presented in this work.;The Lewis bases (L) piperidine (pip), triphenyl phosphine (PPh3 ) and tricyclohexyl phosphine (P(Cy)3) displace [60]fullerene (C60) from fac-(eta2-C60 )(eta2-phen)M(CO)3 to produce fac -(eta2-phen)(eta1-L)M(CO) 3 and fac-(eta1-L)3M(CO) 3, depending on M. The progress of the reactions were followed by observing the change of absorbance values at various wavelengths, depending on M and entering ligand (L). The reactions were also monitored by observing the stretching carbonyl region from 1700 to 2100cm-1 to establish the nature of non-steady-state intermediate species and products.;The reactions of fac-(eta2-phen)(eta 2-C60)W(CO)3 produced fac-(eta 2-phen)(eta1-L)W(CO)3 as the only product. For M = Mo, the formation of fac-(eta2-phen)(eta 1-L)Mo(CO)3 was followed by thermal decomposition. For, M = Cr, the formation of fac-(eta2-phen)(eta 1-L)Cr(CO)3 was followed displacement of phen producing fac-(eta1-L)3Cr(CO)3.;The reactions of fac-(eta2-phen)(eta 2-C60)Cr(CO)3 were biphasic depending on L. For example, plots of absorbance vs. time were biexponential for reactions under conditions where [L] >> [fac-(eta2-C 60)(eta2-phen)Cr(CO)3]. The plots of absorbance vs. time consisted of two consecutive segments. The first segment (increasing) of the plot was assigned to step-wise additions of piperidine to uncoordinated C60. The second segment (decreasing) was ascribed to solvent-assisted displacement of C60 from fac-(eta2-C 60)(eta2-phen)Cr(CO)3. The observation of an experimentally-accessible isokinetic temperature suggests that the seemingly different mechanistic path for the systems investigated is actually limiting cases of the general mechanism that will be presented.