Reactions of Transition Metal Complexes with Fullerenes (C(60), C(70), etc.) and Related Materials

Binding Energy of Transition-Metal Complexes with Large π-Conjugate Systems. Density Functional Theory vs Post-Hartree−Fock Methods

We systematically evaluated the binding energies of d10, d8, and d6 transition-metal complexes with various pi-conjugate systems such as Pt(PH3)2{C2H4-n(CH=CH2)n}, Pd(PH3)2{C2H4-n(CH=CH2)n}, [PtCl3{C2H4-n-(CH=CH2)n}]-, [PdCl3{C2H4-n(CH=CH2)n}]-, and [PtCl5{C2H4-n(CH=CH2)n}]- (n = 0-4) using the MP2 to MP4, CCSD(T), and density functional theory (DFT) methods. The MP4(SDQ) and CCSD(T) methods present a reliable binding energy, whereas the DFT method significantly underestimates the binding energy when the size of the pi-conjugate system is large. The underestimation occurs independently of the coordinate bonding nature; the pi-back-donation is stronger than the sigma-donation in the Pt(0) complexes, as expected, they are comparable in the Pt(II) complexes, and only the sigma-donation participates in the coordinate bond of the Pt(IV) complexes. The DFT method provides moderately stronger charge-transfer (CT) interaction than the MP4(SDQ) method, suggesting that the underestimation of the binding energy by the DFT method does not arise from the insufficient description of the CT interaction. From theoretical investigation of several model systems, it is concluded that the underestimation arises from the insufficient description of electron correlation effects.

Inclusion properties of 3-fluoromesotetraphenylporphyrin with C60 and C70

To improve the selectivity ratio of C70 over C60, a new designer molecule, viz., 3-fluoromesotetraphenylporphyrin (1) has been reported in the present investigations. Fluorescence studies reveal that the Q-absorption band of 1 gets sufficient quenching effect upon addition of both C60 and C70. Binding constants (K) of the C60/1 and C70/1 complexes are estimated to be 580 and 10,800 dm3 mol(-1), respectively. Thus, K(C70)/K(C60) is approximately 19 which is very large and even comparable with other macrocyclic host molecules like calix[5]arene, azacalix[m]arene[n]pyridine, cyclotriveratrylenophane and calixarene bisporphyrin. 1H NMR chemical shift measurements show that the -NH- proton of 1 suffers more shifts in presence of C70 compared to C60. This finding also offers a good support in favor of high K value for C70/1 complex as well as large selectivity ratio of C70 over C60.

Cycloaddition Reactions of 16-Electron d4 Metallocene Complexes with C60: A Theoretical Study

The potential-energy surfaces of the cycloaddition reaction Cp(2)M+C60-->Cp(2)M(C60) (Cp=eta5-C(5)H(5); M=Cr, Mo, and W) were studied at the B3LYP/LANL2DZ level of theory. Two competing reaction pathways were found, which can be classified as [6,5] attack (path A) and [6,6] attack (path B). Given the same reaction conditions, the [6,6]-attack pathway for cycloaddition to C60 is more favorable than the [6,5]-attack pathway, both kinetically and thermodynamically. A qualitative model, based on the theory of Pross and Shaik, was used to develop an explanation for the reaction barrier heights. Thus, our theoretical findings suggest that the singlet-triplet splitting DeltaE(st) (=E(triplet)-E(singlet)) of the 16-electron d4 Cp(2)M and C60 species are a guide to predicting their reactivity towards cycloaddition. Our model results demonstrate that the propensity for cycloaddition to C60 increases in the order Cp(2)Cr<Cp(2)Mo<Cp(2)W. We show that both electronic and geometric effects play a decisive role in determining the energy barriers and reaction enthalpies.

Chiral Ruthenium–Allenylidene Complexes That Bear a Fullerene Cyclopentadienyl Ligand: Synthesis, Characterization, and Remote Chirality Transfer

Ruthenium complexes that bear both a fullerene and an allenylidene ligand, [Ru(C60Me5)((R)-prophos)=C=C=CR1R2]PF6 (prophos = 1,2-bis(diphenylphosphanyl)propane), were prepared by the reaction of [Ru(C60Me5)Cl((R)-prophos)] and a propargyl alcohol in better than 90% yields, and characterized by 1H, 13C, and 31P NMR, IR, and UV/Vis/NIR spectroscopy and MS. Cyclic voltammograms of these complexes showed one reversible or irreversible reduction wave due to the allenylidene part, and two reversible reduction waves due to the fullerene core. Nucleophilic addition of RMgBr or RLi proceeded regioselectively at the distal carbon atom of the allenylidene array. The reaction took place with a 60:40-95:5 level of diastereoselectivity with respect to the original chirality in the (R)-prophos ligand, which is located six atoms away from the electrophilic carbon center.

Corannulene vs. C60-fullerene in metal binding reactions: A direct DFT and X-ray structural comparison

DFT calculations and X-ray crystallography were used to directly compare the reactivity of the convex carbon surfaces of C20H10-corannulene and the C60-fullerene toward the diruthenium(I,I) metal cluster.

Molecular and supramolecular C60–oligophenylenevinylene conjugates

Fullerene derivatives are attractive building blocks for the preparation of molecular and supramolecular photoactive devices. As a part of this research, combination of C60 with oligophenylenevinylene (OPV) subunits has generated significant research efforts. These results are summarized in the present account to illustrate the current state-of-the-art of fullerene chemistry for the development of new photoactive materials.

X-ray and density functional theory structural study of 1,3,5,7,9-penta-tert-butylcorannulene, C40H50

The first X-ray structural characterization of an alkyl-substituted corannulene, namely, 1,3,5,7,9-penta-tert-butylcorannulene (C40H50), has been accomplished. The addition of bulky tert-butyl groups to the corannulene core flattens the bowl and affects the solid-state packing. The presence of two enantiomers, in addition to positional disorder of the C40H50 bowls in the solid-state structure, has prevented the acquisition of accurate geometric parameters of this open geodesic polyarene. Therefore, DFT calculations have been used to describe its molecular geometry and to access bond lengths, bond angles, and a bowl depth.

Synthetic, Electrochemical, and Theoretical Studies of Tetrairidium Clusters Bearing Mono- and Bis[60]fullerene Ligands

Heating a mixture of Ir(4)(CO)(9)(PPh(3))(3) (1) and 2 equiv of C(60) in refluxing chlorobenzene (CB) affords a "butterfly" tetrairidium-C(60) complex Ir(4)(CO)(6){mu(3)-kappa(3)-PPh(2)(o-C(6)H(4))P(o-C(6)H(4))PPh(eta(1)-o-C(6)H(4))}(mu(3)-eta(2):eta(2):eta(2)-C(60)) (3, 36%). Brief thermolysis of 1 in refluxing chlorobenzene (CB) gives a "butterfly" complex Ir(4)(CO)(8){mu-k(2)-PPh(2)(o-C(6)H(4))PPh}{mu(3)-PPh(2)(eta(1):eta(2)-o-C(6)H(4))} (2, 64%) that is both ortho-phosphorylated and ortho-metalated. Interestingly, reaction of 2 with 2 equiv of C(60) in refluxing CB produces 3 (41%) by C(60)-assisted ortho-phosphorylation, indicating that 2 is the reaction intermediate for the final product 3. On the other hand, reaction of Ir(4)(CO)(8)(PMe(3))(4) (4) with excess (4 equiv) C(60) in refluxing 1,2-dichlorobenzene, followed by treatment with CNCH(2)Ph at 70 degrees C, affords a square-planar complex with two C(60) ligands and a face-capping methylidyne ligand, Ir(4)(CO)(3)(mu(4)-CH)(PMe(3))(2)(mu-PMe(2))(CNCH(2)Ph)(mu-eta(2):eta(2)-C(60))(mu(4)-eta(1):eta(1):eta(2):eta(2)-C(60)) (5, 13%) as the major product. Compounds 2, 3, and 5 have been characterized by spectroscopic and microanalytical methods, as well as by single-crystal X-ray diffraction studies. Cyclic voltammetry has been used to examine the electrochemical properties of 2, 3, 5, and a related known "butterfly" complex Ir(4)(CO)(6)(mu-CO){mu(3)-k(2)-PPh(2)(o-C(6)H(4))P(eta(1)-o-C(6)H(4))}(mu(3)-eta(2):eta(2):eta(2)-C(60)) (6). These cyclic voltammetry data suggest that a C(60)-mediated electron transfer to the iridium cluster center takes place for the species 3(3)(-) and 6(2)(-) in compounds 3 and 6. The cyclic voltammogram of 5 exhibits six well-separated reversible, one-electron redox waves due to the strong electronic communication between two C(60) cages through a tetrairidium metal cluster spacer. The electrochemical properties of 3, 5, and 6 have been rationalized by molecular orbital calculations using density functional theory and by charge distribution studies employing the Mulliken and Hirshfeld population analyses.

Aggregation of [70]fullerene in presence of acetonitrile: A chemical kinetic experiment

[70]fullerene solutions in carbon tetrachloride and o-xylene exhibit a noteworthy spectral variation with time when acetonitrile is added. This has been ascribed to self-aggregation of [70]fullerene caused by the repulsion between polar acetonitrile and hydrophobic [70]fullerene, and the aggregation numbers have been determined from a kinetic scheme and also from a scanning electron microscopic study. The numbers thus obtained follow a cuboctahedral stacking pattern proposed recently and also agree with the magic formula n=55+3m (m=1 to 14) proposed by Branz et al. for [60]fullerene clusters [Phys. Rev. B. 66, 094107 (2002)].

[60]Fullerene−Pyrrolidine-N-oxides

Eight members of a new family of fullerene derivatives, [60]fulleropyrrolidine-N-oxides, have been synthesized and characterized. Facile oxidation, by a peracid, of the parent [60]fulleropyrrolidine gave clean conversions into the product molecules, in which the tertiary amine is transformed into a quaternary amine bearing an oxygen atom. The reaction is very selective, favoring the nitrogen atom of the pyrrolidine ring in preference to epoxidation of the fullerene cage. The 1H NMR shows an AB quartet splitting pattern, characteristic of nonequivalent hydrogens in the pyrrolidine ring and at a chemical shift displacement of 0.8 ppm downfield. Other methods of characterization are described, including MS, differential scanning calorimetry, thermogravimetric analysis, HPLC, UV/vis, and IR. Conclusive evidence for the formation of an N-oxide moiety is provided by the synthesis, oxidation, and NMR characterization of a novel [60]fulleropyrrolidine containing a 15N isotope, showing an 85 ppm downfield heteroatom chemical shift. Preliminary details of the effects of substitution on the reactivity of the pyrrolidine ring are also reported.

Neutral and Ionic Complexes of C60 with Metal Dibenzyldithiocarbamates. Reversible Dimerization of C60•- in Ionic Multicomponent Complex [CrI(C6H6)2•+]·(C60•-)·0.5[Pd(dbdtc)2]

New molecular complexes of C60 with metal(II) dibenzyldithiocarbamates, M(dbdtc)2.C60.0.5(C6H5Cl), where M=Cu(II), Ni(II), Pd(II), and Pt(II) and an ionic multicomponent complex [Cr(I)(C6H6)2*+].(C60*-).0.5[Pd(dbdtc)2] (Cr(C6H6)2: bis(benzene)chromium) were obtained. According to IR, UV-visible-NIR, and EPR spectra, involve neutral components, whereas 5 comprises neutral Pd(dbdtc)2 and C60*- and Cr(I)(C6H6)2*+ radical ions. The crystal structure of at 90 K reveals strongly puckered fullerene layers alternating with those composed of Pd(dbdtc)2. The Cr(I)(C6H6)2*+ radical cations are arranged between the layers. Fullerene radical anions form pairs within the layer with an interfullerene C...C contact of 3.092(2) A, indicating their monomeric state at 90 K. This contact is essentially shorter than the sum of van der Waals radii of two carbon atoms, and consequently, C60*- can dimerize. According to SQUID and EPR, single-bonded diamagnetic (C60-)2 dimers form in below 150-130 K on slow cooling and dissociate above 150-170 K on heating. The hysteresis was estimated to be 20 K. For the (C60-)2 dimers in, the dissociation temperature is the lowest among those for ionic complexes of C60 (160-250 K). Fast cooling of the crystals within 10 min from room temperature down to 100 K shifts dimerization temperatures to lower than 60 K. This shift is responsible for the retention of a monomeric phase of at 90 K in the X-ray diffraction experiment.

Theoretical Study of M(PH3)2 Complexes of C60, Corannulene (C20H10), and Sumanene (C21H12) (M = Pd or Pt). Unexpectedly Large Binding Energy of M(PH3)2(C60)

DFT and MP2 to MP4(SDQ) methods were applied to M(PH3)2(C60), Pt(PH3)2(C20H10), and Pt(PH3)2(C21H12) (M = Pd or Pt, C20H10 = corannulene, and C21H12 = sumanene). The binding energy considerably fluctuates around MP2 and MP3 levels but much less upon going from MP3 to MP4(SDQ) in Pt(PH3)2(C2H4), Pt(PH3)2(C20H10), and Pt(PH3)2(C21H12). Also, the MP4(SDQ) method presents a binding energy similar to that of the CCSD(T) method in Pt(PH3)2(C2H4). Thus, it is likely that the MP4(SDQ) method is useful to evaluate binding energies of these complexes. The binding energies of Pt(PH3)2(C20H10) and Pt(PH3)2(C21H12) are evaluated to be 24.9 and 26.1 kcal/mol, respectively, by the MP4(SDQ) method and only +5.8 and -2.6 kcal/mol, respectively, by the DFT(B3LYP) method. These MP4(SDQ)-calculated binding energies of Pt(PH3)2(C20H10) and Pt(PH3)2(C21H12) are similar to that of Pt(PH3)2(C2H4), which strongly suggests that these complexes can be successfully synthesized. The binding energy of Pt(PH3)2(C60) is evaluated to be 44.8 and 45.5 kcal/mol with the ONIOM(MP4(SDQ):UFF) and ONIOM(MP4(SDQ):B3LYP) methods, respectively, and that of the Pd analogue is evaluated to be 39.9 kcal/mol with the ONIOM(MP4(SDQ):UFF) method, whereas the DFT(B3LYP), DFT(BVP86), and DFT(BPW91) methods provide much smaller binding energies. It is noted that these binding energies are much larger than those of the ethylene, corannulene, and sumanene analogues. This difference is reasonably interpreted in terms that the LUMO of C60 is at much lower energy than those of ethylene, corannulene, and sumanene. We investigated also how to separate the high level and the low level regions in the ONIOM calculation of M(PH3)2(C60) and proposed here the reasonable way to evaluate the binding energy of transition-metal complexes of C60.