Synthesis and characterization of organometallic derivatives of $C_{60}$

Abstract

The present study involves the synthesis, structure, and electrochemical properties of metallofullerene compounds. The reaction of (triphos)$RhH_3$ (triphos = $CH_3C(CH_2PPh_2)_3$) with $C_{60}$ yields an $\eta^2$- $C_{60}$ compound (triphos)RhH($\eta^2-C_{60}$) (Ⅱ-2). The likely steps for the formation of Ⅱ-2 involve insertion of a $C_{60}$ molecule into a Rh-H bond followed by dihydrogen elimination and coordination of the $C_{60}$ ligands. Compound Ⅱ-2 shows a remarkable electrochemical stability compared to other known $\eta^2-C_{60}$ complexes. The first metal cluster derivatives of $C_{60}$, $Os_3(CO)_{11}(\eta^2- C_{60})$ (Ⅲ-1) and $Os_3(CO)_10(NCMe)(\eta^2-C{60})$ (Ⅲ-2), are prepared from the reaction of $Os_3(CO)_{12-n}(NCMe)_n$ (n = 1, 2) with $C_{60}$. Complexes Ⅲ-1 and Ⅲ-2 are interconvertible either by decarbonylation of Ⅲ-1 with $Me_3NO$/MeCN or by exposure of Ⅲ-2 to CO gas. Complex Ⅲ-2 reacts with $PPh_3$ to afford $Os_3(CO)_10(PPh_3)(\eta^2-C_{60})$ (Ⅲ-3), which undergoes further reaction with $PPh_3$ to produce $Os_3(CO)_9(PPh_3)_2(\eta^2 -C_{60})$ (Ⅲ-4) upon decarbonylation with $Me_3NO$. The molecular structure of Ⅲ-1 is derived from that of $Os_3(CO)_{12}$ by replacing an equatorial carbonyl group on the osmium atom with the $C_{60}$ ligand. The C-C bond directly bonded to the metal center is the shortest (1.42(2) Å) observed for $\eta^2-C_{60}$metallofullerenes, implying that the π-back- donation in Ⅲ-1 may be significantly suppressed by strong $\pi$-acid carbonyl ligands on the osmium atoms. Complexes Ⅲ-2 and $Os_3(CO)_9(PMe_3)_2 (\eta^2-C_{60})$ (Ⅲ-5) show a fluxional process ($\DeltaG_c^{\ddagger}=12.7\pm0.1kcal/mol$) of the equatorial ligand exchange among three metal centers via a triply bridged intermediate. Thermolysis of Ⅲ-2 in refluxing chlorobenzene affords $Os_3(CO)_9(\mu_3-\eta^2,\eta^2,\eta^2-C_{60})$ (Ⅳ-1) in 23% yield by loss of both acetonitrile and a carbonyl ligand. A better yield (32%) has been obtained from the react...