The reaction of Ir4(CO)8(PMe3)4 with excess C60 in refluxing 1,2-dichlorobenzene, followed by treatment by CNR (R = CH2C6H5) at 70 degrees C, affords a fullerene-metal sandwich complex Ir4(CO)3(mu4-CH)(PMe3)2(mu-PMe2)(CNR)(mu-eta2,eta2-C60)(mu4-eta1,eta1,eta2,eta2-C60) (1), which exhibits an interesting structural feature of two metal atoms bridging the two C60 centers as well as the first example of a mu4-eta1,eta1,eta2,eta2-C60 bonding mode. Compound 1 has been characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study. A cyclic voltammetry study reveals strong electronic communication between the two C60 centers in 1, which is due to the presence of a wide channel of two metal centers between the two C60 cages for efficient electronic interaction.
The extensive use of [60]fullerene, the most abundant member of the fullerene family, as a ligand in organometallic chemistry has been attributed to its pivotal role in material science owing to its unique electronic, optical, and magnetic properties. [1] In particular, the interaction of a carbon cluster such as C 60 with metal clusters has been a topic of great interest in exohedral metallofullerene chemistry, [2] because C 60 -metal cluster complexes have a direct analogy to carbon nanotubes decorated with metal nanoparticles.[3] Furthermore, they exhibit very strong electronic communication between C 60 and metal-cluster centers that can be fine-tuned by ligands attached to the metal atoms.[2a] As part of our studies on the chemistry of C 60 -metal cluster complexes, we examined the reaction between the phosphane-substituted iridium carbonyl cluster [Ir 4 (CO) 9 (PPh 3 ) 3 ] (1) [4] and C 60 . We demonstrated a new behavior of C 60 as a noninnocent ligand, stemming from its multifunctionality, for the chemical transformation of ligands on the cluster surface. Here we report a novel C 60 -induced formation of a P-(C) n -P-(C) n -P moiety by a series of ortho-phosphanation and ortho-metalation reactions of phosphanes on a tetrairidium butterfly framework (Scheme 1).Heating a mixture of 1 and 2 equiv of C 60 in refluxing chlorobenzene (CB) for 2 h afforded [Ir 4 (CO) 6 {m 3 -PPh 2 (o-C 6 H 4 )P(o-C 6 H 4 )PPh(h 1 -o-C 6 H 4 )}(m 3 -h 2 :h 2 :h 2 -C 60 )] (3) in moderate yield (36 %). Thermolysis of 1 in refluxing CB gave [Ir 4 (CO) 8 {m-PPh 2 (o-C 6 H 4 )PPh}{m 3 -PPh 2 (h 1 :h 2 -o-C 6 H 4 )}] (2) in 64 % yield. Reaction of 2 with C 60 in refluxing CB produced 3 in 41 % yield, that is, 2 is indeed the reaction intermediate for the final product 3 (see Scheme 1 and Experimental Section). The formulas of 2 and 3 were established by microanalytical data and molecular-ion isotope multiplets at m/z 1624 for 2 and 2210 for 3 in the positive-ion FAB mass spectra.The molecular structures of 2 and 3 are shown in Figures 1 and 2, respectively. Both complexes exhibit a butterfly geometry of four iridium atoms, in which the two wings are nearly perpendicular to each other, as was observed in previously reported wingtip-bridged Ir 4 butterfly complexes.[5]The P1 atom bearing two phenyl groups in 2 is coordinated to the Ir4 center, and the two wingtip Ir atoms are almost symmetrically bridged by the P2 atom. An o-phenylene group bridges the P1 and P2 atoms in the bidentate diphosphane moiety Ph 2 P(o-C 6 H 4 )PPh, which in turn forms a five-membered metallacyclic P1-C301-C306-P2-Ir4 moiety on the cluster. Another interesting structural feature of 2 is the presence of a m 3 -PPh 2 (h 1 :h 2 -o-C 6 H 4 ) ligand (a five-electron donor), which is coordinated through P3 to the Ir3 atom by an IrÀC(phenylene) s bond to the Ir2 center, and by an h
A brief thermolysis of the bis-phosphine-substituted tetrairidium cluster Ir4(CO)10(PPh3)2 (1) in chlorobenzene (CB) converts it rapidly to the diphosphine cluster Ir4(CO)7(μ-CO)3{κ2-Ph2P(o-C6H4)PPh2} (2) in 53% yield, providing evidence for ortho phosphorylation at the tetrairidium cluster framework. Treatment of 2 with excess C60 affords the “butterfly” Ir4−C60 complex Ir4(CO)6(μ-CO){μ3-κ2-Ph2P(o-C6H4)P(η1-o-C6H4)}(μ3-η2:η2:η2-C6 0) (3) in 71% yield. Interestingly, compound 3 can be prepared directly from the thermolysis of 1 with excess C60 in moderate yield (52%). Compounds 2 and 3 have been characterized by microanalysis, spectroscopy, and single-crystal X-ray diffraction studies. A molecular structure determination reveals that complex 2 adopts a regular tetrahedral geometry with three edge-bridging CO groups around the basal triangle and a diphosphine κ2-Ph2P(o-C6H4)PPh2 ligand chelating one of the basal iridium atoms. In contrast, complex 3 possesses a “butterfly” geometry in which the C60 ligand is coordinated to the lower wing of the “butterfly” by an arene type μ3-η2 :η2 :η2-C60 bonding mode. One unique feature of 3 is the presence of both ortho phosphorylated and ortho-metalated phenyl rings forming five-membered [Ir−P−C−C−P] and [Ir−Ir−P−C−C] metallocycles joined in a spiro union at the iridium−iridium-bridged phosphorus atom. A crossover experiment confirms that the conversion of 1 to 2 is intramolecular. Plausible reaction pathways for the formation of 2 and 3 are proposed.
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