No abstract

We report the selective activation of carbon-fluorine bonds in trifluoroethylene using the diiridium complex [Ir(2)(CH(3))(CO)(2)(dppm)(2)][OTf] (1). Coordination of trifluoroethylene in a bridging position between the two metals in 1 results in facile fluoride ion loss in three different ways. Attack by strong fluorophiles such as Me(3)SiOTf and HOTf results in F(-) removal from one of the geminal fluorines to give the cis-difluorovinyl-bridged product [Ir(2)(CH(3))(OTf)(CO)(2)(μ-κ(1):η(2)-C(F)═CFH)(dppm)(2)][OTf]. A second activation can also be accomplished by addition of excess Me(3)SiOTf to give the fluorovinylidene-bridged product [Ir(2)(CH(3))(OTf)(CO)(2)(μ-C(2)FH)(dppm)(2)][OTf](2). Interestingly, activation of the trifluoroethylene-bridged precursor by water also occurs, yielding [Ir(2)(CH(3))(CO)(2)(κ(1)-C(H)═CF(2))(μ-OH)(dppm)(2)][OTf], in which the lone vicinal fluorine is removed, leaving a geminal arrangement of fluorines in the product. A [1,2]-fluoride shift can also be induced in the trifluoroethylene-bridged precursor upon the addition of CO to give the 2,2,2-trifluoroethylidene-bridged product [Ir(2)(CH(3))(CO)(3)(μ-C(H)CF(3))(dppm)(2)][CF(3)SO(3)]. Addition of hydrogen to the cis-difluorovinyl-bridged product results in the quantitative elimination of cis-difluoroethylene, while its reaction with CO yields a mixture of cis-difluoropropene and 2,3-difluoropropene by reductive elimination of the methyl and difluorovinyl groups with an accompanying isomerization in the case of the second product. Finally, protonation of the 2,2,2-trifluoroethylidene-bridged product liberates 1,1,1-trifluoroethane, in which one hydrogen (H(+)) is from the acid while the other hydrogen (H(-)) is derived from activation of the methyl group.

The synthesis, comprehensive linear photophysical and photochemical study, two-photon absorption (2PA) spectrum, ultrafast relaxation kinetics in the excited states, and efficient superluminescence properties of a new symmetrical three-armed star-shaped squaraine derivative (1) are presented. The steady-state spectral parameters of 1 in a number of organic solvents, including fluorescence excitation anisotropy spectra, revealed a weak interaction between the squaraine branches and the effect of symmetry breaking in the ground electronic state. The degenerate 2PA spectrum of 1 was obtained over a broad spectral range with a maximum cross section of ∼8000 GM using the open aperture Z-scan technique. The nature of the fast dynamic processes in the excited electronic states of 1 was investigated by the femtosecond transient absorption pump−probe method, revealing characteristic relaxation times of ∼3−4 ps. The efficient superluminescence emission of 1 was observed in relatively low concentration solution (≈ 2.3·10 −4 M) under femtosecond transverse pumping. A quantum-chemical study of 1 was performed using ZINDO/S//DFTB theory levels. Simulated 1PA and 2PA absorption spectra were found to be in a good agreement with experimental data. The figure of merit for 1 is ∼10 11 GM, 1 one of the highest values ever reported for two-photon fluorescence molecular probes, suggesting strong potential for its application in two-photon fluorescence microscopy and bioimaging.

The binuclear complex [Ir2(CH3)(CO)(μ-CO)(dppm)2][CF3SO3] (1; dppm = μ-Ph2PCH2PPh2) reacts with allene and methylallene to ultimately yield the vinylcarbene products [Ir2H(CO)2(μ-η1:η3-HCC(CH3)C(H)R)(dppm)2][CF3SO3] (R = H (6), CH3 (7)). Monitoring the reactions by NMR spectroscopy (1H, 13C, 31P) between −78 °C and ambient temperature allows the observation of several intermediates in each of these transformations in which the allene moves from an η2 binding site on one metal, through an η1:η1-bridging geometry in which the cumulene is coordinated through the “H2CC” moiety, to an η1:η3-bridging geometry in which the central carbon of the cumulene is σ-bound to one metal, adjacent to the methyl ligand, while the three cumulene carbons are η3-bound to the adjacent metal. We propose that formation of the respective vinyl carbene products results from migration of the methyl ligand to the central cumulene carbon followed by activation of a cumulene C−H bond. 1,1-Dimethylallene reacts with 1 at −78 °C to yield a methylene hydride product containing an η2-bound cumulene on one metal, much as observed for the first products in the allene and methylallene reactions. Upon warming, this intermediate isomerizes to the final product containing a methyl ligand on one metal and an η2-bound cumulene on the other. No cumulene-bridged products are observed with this disubstituted allene. 1,1-Difluoroallene also yields a methylene hydride product at −78 °C, which is analogous to the first species observed in all cases noted above. In this case, warming results in movement of the cumulene to an η1:η1-bridging position in which this group binds to the metals via the “H2CC” moiety. Unlike the transformations observed with allene and methyl allene, difluoroallene undergoes no additional transformations as the temperature is raised. A rationalization of these transformations is presented together with a perspective on how the cumulene ligand moves over the dimetallic framework leading to the final products.

The reactions of the diiridium methyl complex [Ir 2 (CH 3 )(CO)(µ-CO)(dppm) 2 ][CF 3 SO 3 ] (1) with ethylene, fluoroethylene, Z-1,2-difluoroethylene, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene have been investigated. Reaction of 1 with ethylene at -78 °C yields [Ir 2 H(η 2 -C 2 H 4 )(CO) 2 (µ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (2a), resulting from C-H activation of the methyl group induced by ethylene coordination, whereas reaction at higher temperatures yields the simple ethylene adduct [Ir 2 (CH 3 Reactions of 1 with fluoroethylene and Z-1,2-difluoroethylene yield only the olefin adducts analogous to 2b. At -78 °C reaction with 1,1-difluoroethylene yields the methylene-bridged hydride product [Ir 2 H(η 2 -C 2 F 2 H 2 )(CO) 2 (µ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (5a), which upon warming, yields first the olefin adduct [Ir 2 (CH 3 ). Trifluoro-and tetrafluoroethylene yield only the olefin-bridged products [Ir 2 7)). The structure of the tetrafluoroethylene-bridged, tricarbonyl species [Ir 2 (CH 3 )(CO) 3 (µ-C 2 F 4 )(dppm) 2 ][CF 3 SO 3 ] (8), determined by X-ray techniques, is reported.