Reactivity of fullerene epoxide: preparation of fullerene-fused thiirane, tetrahydrothiazolidin-2-one, and 1,3-dioxolane

The epoxide moiety in the fullerene-mixed peroxide C60(O)(OOtBu)4 1 reacts readily with aryl isocyanates ArNCS (Ar = Ph, Naph) to form both the thiirane derivative C60(S)(OOtBu)4 and fullerene-fused tetrahydrothiazolidin-2-one. The reaction of 1 with trimethylsilyl isothiocyanate TMSNCS yields the isothiocyanate derivative C60(NCS)(OH)(OOtBu)4, the isothiocyanate and hydroxyl moieties of which could be converted to a fullerene-fused tetrahydrothiazolidin-2-one ring with alumina quantitatively. Treating 1 with BF3.Et2O yields the fullerene-fused [1,3,2]-dioxoborolane derivative C60(O2BOH)(OOtBu)4. In the presence of aldehyde or acetone, BF3.Et2O catalyzes the conversion of epoxide to fullerene-fused 1,3-dioxolane derivatives. The products are characterized by spectroscopic data. Two of the compounds are also characterized by single-crystal X-ray analysis.     

Palladium(0)-catalyzed intramolecular [2+2+2] alkyne cyclotrimerizations with electron-deficient diynes and triynes

In the presence of 2.5 mol % of [Pd(2)(dba)(3)] (dba=dibenzylideneacetone) and 5 mol % of PPh(3), nearly equimolar amounts of dimethyl nona-2,7-diyne-1,9-dioate derivatives (diyne diesters) and dialkyl acetylenedicarboxylates were allowed to react in toluene at 110 degrees C to afford [2+2+2] cycloadducts in moderate-to-good yields. Similarly, dimethyl trideca-2,7,12-triyne-1,13-dioate derivatives (triyne diesters) were catalytically transformed into phthalic acid ester analogues in excellent yields. To gain insight into the mechanism of these intramolecular alkyne cyclotrimerizations, stoichiometric reactions of [Pd(2)(dba)(3)] with a diyne diester and a triyne diester bearing ether tethers were conducted in acetone at room temperature to furnish an oligomeric bicyclopalladacyclopentadiene and a Pd(0) triyne complex, respectively. The structures of these novel complexes were unequivocally determined by Xray structure analysis. The isolated triyne complex was heated at 50 degrees C or treated with PPh(3) in acetone at room temperature to afford the arene product. Furthermore, the same complex catalyzed the triyne cyclization with or without PPh(3).     

Poly(trifluoromethyl)fullerene radical anions. An ESR/Vis-NIR Spectroelectrochemical Study of C60F2,4 and C60(CF3)2,10

Cyclic voltammograms are reported for C(60)(CF(3))(n) derivatives for the first time. The compounds studied were 1,9-C(60)(CF(3))(2) and 3 isomers of C(60)(CF(3))(10), including the structurally characterized derivative 1,3,7,10,14,17,23,28,31,40-C(60)(CF(3))(10) (C(60)(CF(3))(10)-3). The compound 1,9-C(60)(CF(3))(2) exhibited 3 reversible reductions; C(60)(CF(3))(10)-3 exhibited 2 reversible reductions; the other 2 isomers of C(60)(CF(3))(10) each exhibited 1 reversible reduction. ESR and near-IR spectroelectrochemical experiments were performed to characterize some of the C(60)(CF(3))(n)(-) and C(60)(CF(3))(n)(2-) species generated by cyclic voltammetry. The ESR spectrum of the C(60)(CF(3))(10)-3(-) radical anion consisted of an envelope of 25 lines centered at g = 2.0032 (the apparent a value is ca. 0.5 G), evidence of coupling between the unpaired electron and a significant number of the CF(3) fluorine atoms. The most significant finding is that this radical anion has a half-life in solution at 25 degrees C of about 7 min.     

Acylation of 2,5-dimethoxycarbonyl[60]fulleropyrrolidine and synthesis of its multifullerene derivatives

2,5-Dimethoxycarbonyl[60]fulleropyrrolidine (1) is acylated with various chlorocarbonyl compounds to give fullerene derivatives with the general formula C(60)(MeOOCCH)(2)NC(O)R, R = (CH(2))(5)Br, (CH(2))(8)C(O)Cl (3), (CH(2))(4)C(O)Cl, or cis-C(6)H(4)(C(O)Cl. The monoacylated sebacoyl derivative 3 readily reacts with alcohols and amines such as methanol, diethylamine, glycine methyl ester, and aza-18-crown-6 through the remaining chlorocarbonyl group. Chromatography of 3 on silica gel converts it into the corresponding acid C(60)(MeOOCCH)(2)NC(O)(CH(2))(8)COOH (4). Treating 4 with PCl(5) regenerates the precursor 3 quantitatively. Piperazine reacts with 4 in the presence of DCC and BtOH to form a bisfullerene derivative in which two sebacoyl chains and the piperazine act as the bridge between two molecules of 1. Other molecules with multifunctional groups react with 4 similarly to form multifullerene derivatives. NMR data indicate that the rotation of the relatively bulky phthaloyl group is hindered around the amide bond N [bond] C(O), the rotation barrier of which is 15.06 kcal/mol. The relative stereochemistry of the 2,5-dimethoxycarbonyl groups is established by (1)H NMR spectra and further confirmed by resolution of the enantiomeric 2,5-trans-isomer of the starting material 1.     

Synthesis of 18-membered open-cage fullerenes through controlled stepwise fullerene skeleton bond cleavage processes and substituent-mediated tuning of the redox potential of open-cage fullerenes

Oxidation of the fullerenediol C(60)(OH)(2)(O)(OAc)(OOtBu)(3) with PhI(OAc)(2) yields the open-cage fullerene derivative C(60)(O)(2)(O)(OAc)(OOtBu)(3)2 with an 11-membered orifice. Compound 2 reacts with aniline to form a new open-cage derivative with a 14-membered orifice, which yields an 18-membered open-cage fullerene derivative upon addition of another molecule of aniline. Two different types of aniline derivatives with either electron-donating or electron-withdrawing substituents can be added sequentially, affording an unsymmetrical moiety in the open-cage structure. Reduction potentials of the 18-membered open-cage fullerene derivatives can be fine-tuned by changing the substituents on the aniline. The results provide new insights about the mechanism of open-cage reactions of fullerene-mixed peroxide.     

Synthesis and photophysical properties of fullerene-phthalocyanine-porphyrin triads and pentads

The synthesis and photophysical properties of several fullerene-phthalocyanine-porphyrin triads (1-3) and pentads (4-6) are described. The three photoactive moieties were covalently connected in an one-step synthesis through 1,3-dipolar cycloaddition to C(60) of the corresponding azomethine ylides generated in situ by condensation reaction of a substituted N-porphyrinylmethylglycine derivative and an appropriated formyl phthalocyanine or a diformyl phthalocyanine derivative, respectively. ZnP-C(60)-ZnPc (3), (ZnP)(2)-ZnPc-(C(60))(2) (6), and (H(2)P)(2)-ZnPc-(C(60))(2) (5) give rise upon excitation of their ZnP or H(2)P components to a sequence of energy and charge-transfer reactions with, however, fundamentally different outcomes. With (ZnP)(2)-ZnPc-(C(60))(2) (6) the major pathway is an highly exothermic charge transfer to afford (ZnP)(ZnP(.+))-ZnPc-(C(60)(.-))(C(60)). The lower singlet excited state energy of H(2)P (i.e., ca. 0.2 eV) and likewise its more anodic oxidation (i.e., ca. 0.2 V) renders the direct charge transfer in (H(2)P)(2)-ZnPc-(C(60))(2) (5) not competitive. Instead, a transduction of singlet excited state energy prevails to form the ZnPc singlet excited state. This triggers then an intramolecular charge transfer reaction to form exclusively (H(2)P)(2)-ZnPc(.+)-(C(60)(.-))(C(60)). A similar sequence is found for ZnP-C(60)-ZnPc (3).     

Selective synthesis of fullerenol derivatives with terminal alkyne and crown ether addends

A series of isomerically pure alkynyl-substituted fullerenol derivatives such as C(60)(OH)(6)(O(CH(2))(3)CCH)(2) were synthesized through Lewis acid catalyzed epoxy ring opening and/or S(N)1 replacement reactions starting from the fullerene-mixed peroxide C(60)(O)(t-BuOO)(4). Copper-catalyzed azide-alkyne cycloaddition readily converted the terminal alkynyl groups into triazole groups. Intramolecular oxidative alkyne coupling afforded a fullerenyl crown ether derivative.     

Synthesis of seven-membered ring diazepin-2-ones via palladium-catalyzed highly regioselective cyclization of 2-vinylpyrrolidines with aryl isocyanates

The first palladium-catalyzed ring-expansion reaction of 2-vinylpyrrolidines with aryl isocyanates to form seven-membered ring heterocycles is described. This regioselective reaction requires 5 mol % of Pd(2)(dba)(3).CHCl(3) and 10 mol % of dppp at 40-60 degrees C in THF and results in the formation of 1,3-diazepin-2-ones in good isolated yields. When Pd(OAc)(2) and PPh(3) were utilized in the reaction, an intramolecular hydrogen migration occurs resulting in the formation of conjugated diene derivatives of urea.     

Strong interfullerene electronic communication in a bisfullerene-hexarhodium sandwich complex

Reaction of Rh(6)(CO)(12)(dppm)(2) (dppm = 1,2-bis(diphenylphosphino)methane) with 1.4 equiv. of C(60) in chlorobenzene at 120 degrees C affords a face-capping C(60) derivative Rh(6)(CO)(9)(dppm)(2)(micro(3)-eta(2),eta(2),eta(2)-C(60)) (1) in 73% yield. Treatment of 1 with excess CNR (10 equiv., R = CH(2)C(6)H(5)) at 80 degrees C provides a bisbenzylisocyanide-substituted compound Rh(6)(CO)(7)(dppm)(2)(CNR)(2)(micro(3)-eta(2),eta(2),eta(2)-C(60)) (2) in 59% yield. Reaction of 1 with excess C(60) (4 equiv.) in refluxing chlorobenzene followed by treatment with 1 equiv. of CNR at room temperature gives a bisfullerene sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(micro(3)-eta(2),eta(2),eta(2)-C(60))(2) (3) in 31% yield. Compounds 1, 2, and 3 have been characterized by spectroscopic and microanalytical methods as well as by X-ray crystallographic studies. Electrochemical properties of 1, 2, and 3 have been examined by cyclic voltammetry. The cyclic voltammograms (CVs) of 1 and 2 show two reversible one-electron redox waves, a reversible one-step two-electron redox wave, and a reversible one-electron redox wave, respectively, within the solvent cutoff window. This observation suggests that compounds 1 and 2 undergo similar C(60)-localized electrochemical pathways up to 1(5)(-) and 2(5)(-). Each redox wave of 2 appears at more negative potentials compared to that of 1 because of the donor effect of the benzylisocyanide ligand. The CV of compound 3 reveals six reversible well-separated redox waves due to strong interfullerene electronic communication via the Rh(6) metal cluster bridge. The electrochemical properties of 1, 2, and 3 have been rationalized by molecular orbital calculations using the density functional theory (DFT) method. In particular, the molecular orbital (MO) calculation reveals significant contribution of the metal cluster center to the unoccupied molecular orbitals in 3, which is consistent with the experimental result of strong interfullerene electronic communication via the Rh(6) metal cluster spacer.     

Synthesis and structural characterization of some new porphyrin-fullerene dyads and their application in photoinduced H2 evolution

The [3 + 2] cycloaddition reaction of C(60) with ethyl isonicotinoylacetate in the presence of piperidine in PhCl at room temperature or in the presence of Mn(OAc)(3) in refluxing PhCl gave the pyridyl-containing dihydrofuran-fused C(60) derivative (4-C(5)H(4)N)C(O)═C(C(60))CO(2)Et (1), whereas the phenyl-containing C(60) derivative PhC(O)═C(C(60))CO(2)Et (2) was similarly prepared by [3 + 2] cycloaddition reaction of C(60) with ethyl benzoylacetate in the presence of piperidine or Mn(OAc)(3). More interestingly, one of the new porphyrin-fullerene dyads, i.e., [4-C(5)H(4)NC(O)═C(C(60))CO(2)Et]·ZnTPPH (3, ZnTPPH = tetraphenylporphyrinozinc), could be prepared by coordination reaction of the pyridyl-containing C(60) derivative 1 with equimolar ZnTPPH in CS(2)/hexane at room temperature. In addition, the β-keto ester-substituted porphyrin derivative H(2)TPPC(O)CH(2)CO(2)Et (4) was prepared by a sequential reaction of HO(2)CCH(2)CO(2)Et with n-BuLi in 1:2 molar ratio followed by treatment with H(2)TPPC(O)Cl in the presence of Et(3)N and then hydrolysis with diluted HCl, whereas the porphyrinozinc derivative ZnTPPC(O)CH(2)CO(2)Et (5) could be prepared by coordination reaction of 4 with Zn(OAc)(2) in refluxing CHCl(3)/MeOH. Particularly interesting is that the second new porphyrin-fullerene dyad H(2)TPPC(O)═C(C(60))CO(2)Et (6) could be prepared by [3 + 2] cycloaddition reaction of 4 with C(60) in the presence of piperidine in PhCl at room temperature. In addition, treatment of 6 with Zn(OAc)(2) in refluxing CHCl(3)/MeOH afforded the third new dyad ZnTPPC(O)═C(C(60))CO(2)Et (7). All the new compounds 1-7 were characterized by elemental analysis and various spectroscopic methods and particularly for 2, 3, and 5 by X-ray crystallography. The five-component system consisting of an electron donor EDTA, dyad 3, an electron mediator methylviologen (MV(2+)), the catalyst colloidal Pt, and a proton source HOAc was proved to be effective for photoinduced H(2) evolution. A possible pathway for such a type of H(2) evolution was proposed.     

Fullerene- and pyromellitdiimide-appended tripodal ligands embedded in light-harvesting porphyrin macrorings

Three new tripyridyl tripodal ligands appended with either fullerene or pyromellitdiimide moieties, named C(60)-s-Tripod, C(60)-l-Tripod, and PI-Tripod, were synthesized and introduced into a porphyrin macroring N-(1-Zn)(3) (where 1-Zn = trisporphyrinatozinc(II)). From UV-vis absorption and fluorescence titration data, the binding constants of C(60)-s-Tripod, C(60)-l-Tripod, and PI-Tripod with N-(1-Zn)(3) in benzonitrile were estimated to be 3 × 10(8), 1 × 10(7), and 2 × 10(7) M(-1), respectively. These large binding constants denote multiple interactions of the ligands to N-(1-Zn)(3). The binding constants of the longer ligand (C(60)-l-Tripod) and the pyromellitdiimide ligand (PI-Tripod) are almost the same as those without the fullerene or pyromellitdiimide groups, indicating that they interact via three pyridyl groups to the porphyrinatozinc(II) coordination. In contrast, the larger binding constants and the almost complete fluorescence quenching in the case of the shorter ligand (C(60)-s-Tripod) indicate that the interaction with N-(1-Zn)(3) is via two pyridyl groups to the porphyrinatozinc(II) coordination and a π-π interaction of the fullerene to the porphyrin(s). The fluorescence of N-(1-Zn)(3) was quenched by up to 80% by the interaction of C(60)-l-Tripod. The nanosecond transient absorption spectra showed only the excited triplet peak of the fullerene on selective excitation of the macrocyclic porphyrins, indicating that energy transfer from the excited N-(1-Zn)(3) group to the fullerenyl moiety occurs in the C(60)-l-Tripod/N-(1-Zn)(3) composite. In the case of PI-Tripod, the fluorescence of N-(1-Zn)(3) was quenched by 45%. It seems that the fluorescence quenching probably originates from electron transfer from the excited N-(1-Zn)(3) group to the pyromellitdiimide moiety.     

Thermally stable perfluoroalkylfullerenes with the skew-pentagonal-pyramid pattern: C60(C2F5)4O, C60(CF3)4O, and C60(CF3)6

Reaction of C(60) with CF(3)I at 550 degrees C, which is known to produce a single isomer of C(60)(CF(3))(2,4,6) and multiple isomers of C(60)(CF(3))(8,10), has now been found to produce an isomer of C(60)(CF(3))(6) with the C(s)-C(60)X(6) skew-pentagonal-pyramid (SPP) addition pattern and an epoxide with the C(s)-C(60)X(4)O variation of the SPP addition pattern, C(s)-C(60)(CF(3))(4)O. The structurally similar epoxide C(s)-C(60)(C(2)F(5))(4)O is one of the products of the reaction of C(60) with C(2)F(5)I at 430 degrees C. The three compounds have been characterized by mass spectrometry, DFT quantum chemical calculations, Raman, visible, and (19)F NMR spectroscopy, and, in the case of the two epoxides, single-crystal X-ray diffraction. The compound C(s)-C(60)(CF(3))(6) is the first [60]fullerene derivative with adjacent R(f) groups that are sufficiently sterically hindered to cause the (DFT-predicted) lengthening of the cage (CF(3))C-C(CF(3)) bond to 1.60 A as well as to give rise to a rare, non-fast-exchange-limit (19)F NMR spectrum at 20 degrees C. The compounds C(s)-C(60)(CF(3))(4)O and C(s)-C(60)(C(2)F(5))(4)O are the first poly(perfluoroalkyl)fullerene derivatives with a non-fluorine-containing exohedral substituent and the first fullerene epoxides known to be stable at elevated temperatures. All three compounds demonstrate that the SPP addition pattern is at least kinetically stable, if not thermodynamically stable, at temperatures exceeding 400 degrees C. The high-temperature synthesis of the two epoxides also indicates that perfluoroalkyl substituents can enhance the thermal stability of fullerene derivatives with other substituents.     

Scratching the surface of buckminsterfullerene: the barriers for Stone-Wales transformation through symmetric and asymmetric transition states

General-gradient approximation (PBE) and hybrid Hartree-Fock density functional theories (B3LYP) in conjunction with basis sets of up to polarized triple-zeta quality have been applied to study the Stone-Wales transformation of buckminsterfullerene (BF) to yield a C(60) isomer of C(2)(v) symmetry with two adjacent pentagons (#1809). In agreement with earlier investigations, two different transition states and reaction pathways could be identified for the rearrangement from BF to C(60)-C(2)(v) on the C(60) potential energy surface (PES). One has C(2) molecular point group symmetry with the two migrating carbon atoms remaining close to the fullerene surface. The other one has a high-energy carbene-like (sp(3)) structure where a single carbon atom is significantly moved away from the C(60) surface. The carbene intermediate and the second transition state along the stepwise reaction path characterized previously at lower levels of theory do not exist as stationary points with the density functionals utilized here. The classical barriers of both mechanisms are essentially identical, 6.9 eV using PBE and 7.3 eV with B3LYP.     

Synthesis and properties of oligodeoxynucleotides incorporating a conformationally rigid uridine unit having a cyclic structure at the 5'-terminal site

A 2'-O-methyluridylic acid derivative 3 having a cyclic structure linked between the 5-position of the uracil residue and the 5'-phosphate group was synthesized. The NMR analysis suggests that this cyclouridylic acid derivative has exclusively the C3'-endo conformation that is in favor of duplex formation with RNA. Two oligonucleotides ?pc3Um(pT)(9) and pc3Um(pU)(9) incorporating this cyclouridylic acid unit at the 5'-terminal site were synthesized by using the fully protected cyclouridylic acid 3'-phosphoramidite derivative 11 in the solid-phase synthesis. To examine the actual effect of this cyclic structure on the thermal stability of duplexes between the modified oligonucleotides and their complementary oligonucleotides, two oligonucleotides ?pUm(pT)(9) and pUm(pU)(9) having an acyclic structure were also synthesized. As the complementary oligonucleotides, dA(pdA)(9) and A(pA)(9) were used for T(m) experiments with these 5'-terminal modified oligonucleotides. The T(m) values of all the possible duplexes were measured. These results clearly show that the duplex of pc3Um(pT)(9)-A(pA)(9) has a higher T(m) value by 5.5 degrees C than that of A(pA)(9)-T(pT)(9). This is rather significant compared with all other cases. Moreover, the T(m) value of pc3Um(pT)(9)-A(pA)(9) is 4.5 degrees C higher than that of pUm(pT)(9)-A(pA)(9). This result suggests that the cyclic structure can considerably contribute to stabilization of the duplex only in the case of the modified oligomer (DNA) and decaadenylate (RNA).     

Synthesis of the phosphino-fullerene PPh2(o-C6H4)(CH2NMeCH)C60 and its function as an η1-P or η3-P,C2 ligand

Following the method of Prato et al., reaction of C(60), N-methylglycine and o-(diphenylphosphino)benzaldehyde affords PPh(2)(o-C(6)H(4))(CH(2)NMeCH)C(60) (1) in moderate yield. Compound 1 reacts with W(CO)(4)(NCMe)(2) to produce W(CO)(4)(η(3)-PPh(2)(o-C(6)H(4))(CH(2)NMeCH)C(60)) (2), through coordination of the phosphine group and one 6 : 6-ring junction of fullerene. Reaction of 1 and Os(3)(CO)(11)(NCMe) affords Os(3)(CO)(11)(PPh(2)(o-C(6)H(4))(CH(2)NMeCH)C(60)) (3), which undergoes a cluster fragmentation reaction in refluxing toluene to produce Os(CO)(3)(η(3)-PPh(2)(o-C(6)H(4))(CH(2)NMeCH)C(60)) (4). Thermal reaction of 1 and Os(3)(CO)(12) affords 3 and 4. On the other hand, reaction of 1 and Ru(3)(CO)(12) yields only the mononuclear complex Ru(CO)(3)(η(3)-PPh(2)(o-C(6)H(4))(CH(2)NMeCH)C(60)) (5). The structures of 1-3 and 5 were determined by an X-ray diffraction study.     

Homoleptic imidazolate frameworks [Sr(1-x)Eu(x)(Im)2]--hybrid materials with efficient and tuneable luminescence

Homoleptic frameworks of the formula [Sr(1-x)Eu(x)(Im)(2)] (1) (x = 0.01-1.0; Im(-) = imidazolate anion, C(3)H(3)N(2)(-)) are hybrid materials that exhibit an intensive green luminescence. Tuning of both emission wavelength and quantum yield is achieved by europium/strontium substitution so that a QE of 80% is reached at a Eu content of 5%. Even 100% pure europium imidazolate still shows 60% absolute quantum efficiency. Substitution of Sr/Eu shows that doping with metal cations can also be utilized for coordination compounds to optimize materials properties. The emission is finely tuneable in the region 495-508 nm via variation of the europium content. The series of frameworks [Sr(1-x)Eu(x)(Im)(2)] presents dense MOFs with the highest quantum yields reported for MOFs so far.     

Synthesis of a green [60]fullerene derivative through cage-opening reactions

Open-cage derivative C(60)(O)(4)(OH)(2)(NC(6)H(4)(t)Bu)(2) reacts with ICl to form a Baeyer-Villiger type product, which yields an intense green product upon treatment with HI.     

BH3 as a protecting group for phosphonic acid: a novel method for the synthesis of dinucleoside H-phosphonate

A BH₃ group is found to be an effective protecting group for phosphonic acid esters. This new phosphonic acid protecting group was applied to the synthesis of a dithymidine H-phosphonate derivative from a dithymidine boranophosphate derivative. Triarylmethyl cations were found to be effective for the deprotection of the BH₃ group in the dithymidine boranophosphate diester to afford the corresponding H-phosphonate derivative in excellent yield.     

Electrosynthesis of Rh2(dpf)4(R) where dpf = N,N'-diphenylformamidinate anion and R = CH3, C2H5, C3H7, C4H9 or C5H11

The electrosynthesis of Rh(2)(dpf)(4)(R) where dpf is the N,N'-diphenylformamidinate anion and R = CH(3), C(2)H(5), C(3)H(7), C(4)H(9) or C(5)H(11) was carried out in THF containing 0.2 M tetra-n-butylammonium perchlorate (TBAP) and one of several alkyl iodides represented as RI. The initial step in the reaction involved a one-electron reduction of the Rh(2)(4+) unit in Rh(2)(dpf)(4) to its Rh(2)(3+) form followed by a homogeneous reaction involving electrogenerated [Rh(2)(dpf)(4)](-) and the alkyl iodide in solution to give Rh(2)(dpf)(4)(R). The homogeneously generated Rh(2)(5+) product was then immediately reduced by a second electron at the potential where [Rh(2)(dpf)(4)(R)](-) is generated, giving [Rh(2)(dpf)(4)(R)](-) which contains a Rh(2)(4+) center as a final product of an electrochemical ECE mechanism. The electrosynthesized [Rh(2)(dpf)(4)(CH(3))](-) derivative could be reoxidized to Rh(2)(dpf)(4)(CH(3)) on the reverse potential sweep and both forms of the CH(3) bonded derivative were in situ characterized by cyclic voltammetry combined with UV-visible and/or ESR spectroscopy. The reversible Rh(2)(4+/3+) process of Rh(2)(dpf)(4) is located at E(1/2) = -1.11 V in THF, 0.2 M TBAP while the electrogenerated Rh(2)(dpf)(4)(R) products are substantially easier to reduce, with E(p) values for the Rh(2)(5+/4+) couples ranging from -0.50 to -0.54 V vs. SCE depending upon the specific R group.     

C-H and P-C(Ph) activation competitive processes caused by interaction with the solvate [cis-Pt(C6F5)2(thf)2

The study of the reaction between the ethylene [Pt(eta-H2C = CH2)(PPh3)2] or alkyne [Pt(eta2-HC [triple bond] CR)(PPh3)2] (R = SiMe3 1, Bu(t) 2) complexes with [cis-Pt(C6F5)2(thf)2] (thf = tetrahydrofuran) has enabled us to observe the existence of competitive processes between the activation of a P-C(Ph) bond on the PPh3 ligand, to give the binuclear derivative [cis-(C6F5)2Pt(mu-Ph)(mu-PPh2)Pt(PPh3)] 3, and the activation of a C-H bond of the unsaturated group, to give the corresponding (mu-hydride)(mu-vinyl) [cis, cis-(PPh3)2Pt(mu-H)(mu-1kappaC(alpha):eta2-CH = CH2)Pt(C6F5)2] 4 or (mu-hydride)(mu-alkynyl) [cis,cis-(PPh3)2Pt(mu-H)(mu-1kappaC(alpha):eta2-C [triple bond]CR)Pt(C6F5)2] (R = SiMe3 5, Bu(t) 6) compounds, respectively. The monitoring of these reactions by NMR spectroscopy has allowed us to detect several intermediates, and to propose a mechanism for the C-H bond activation. In addition, the structures of the (muo-hydride)(mu-alkynyl) complex 5 and the unprecedented (mu-hydride)(mu-vinyl) derivative 4 have been obtained by X-ray crystallographic analyses.