Ir-acceptor properties

It is probable that the greater isomer shift of AUX4 (X= Cl, Br, I) relative to AuF is due to the poor IT donor ability of Cl, Br, and I relative to F. Alternatively, the availability of d orbitals of the valence-shell quantum number in Cl, Br, and I is often cited in arguing for ir acceptor properties for these atoms. F atoms, in contrast, do not have this facility... 

The ligands, NCCH3 and pip, have negligible 7r-acid properties. Pyridine, on the other hand, can potentially v back-bond via its 7r -orbitals but this is considered unlikely. " Thus, for the monodentate nitrogen ligands, ir-acceptor properties are not important but the balance of relative positions... 

To study the reactivity of the Ti-C bond in the Cp TiR compounds we investigated reactions with unsaturated substrate molecules, L, which expose a (or tt) donor and ir-acceptor properties (Scheme 1). These sub-... 

The complex [(cp )IrCl(2,2 -bpy-4,4 -COO(CH2)3-pyrrole)]C104 has a typical three-legged piano-stool structure, with short Ir-cp distances due to the strong 7r-acceptor properties of the bpy ligands.540... 

The trarax-dichloro and dithiocyanate complexes show MLCT transitions in the entire visible and near IR region. The lowest energy MLCT transition band of the trara-dichloro complexes is around 700 nm in DMF solution, and the complexes show weak and broad emission signals above 950 nm. The absorption and emission maxima of the Zrarax-dithiocyanate complexes are blue shifted compared to its trarax-dichloro analogues due to the strong -k acceptor property of the NCS- ligands compared to Cl-, which is consistent with the electrochemical properties of these complexes. 

A remarkable result is the position of (Proto-DME) between (TPP) and (TpivPP) in Series b, Table 15. The vco values originate from various sources and the observed differences between the three porphyrins may thus be meaningless. (Note the enormous solvent dependence of the infrared spectra of various hemes that has been reported recently (29).) Anyway, the three porphyrins have approximately the same ir-acceptor capacity. Therefore, the tetraarylporphyrin moiety, especially in the picket fence hemes, e.g., Fe(TpivPP)LX [33], is comparable with the natural hemes Fe(Proto-DME)LX ([14], M = Fe), and its use as a model porphyrin for the study of hemoprotein properties is well justified, despite the very different substitution pattern. 

At present, most studies on new photochemically active systems concentrate on poly-chromophoric, dendritic, supramolecular systems and novel materials. For example, theoretical calculations indicate that the development of related nanotubes will result in materials with excellent electron-acceptor properties and highly red-shifted bands in the near-IR region17. 

From i CO) spectra of [M(CO)5 E=C(Aryl)H ] (M = Cr, W E = S, Se) it follows that the heteroaldehyde ligand acts essentially as a coordination mode. The acceptor properties and thus v(CO) spectra are similar to those of [M(CO)s(thioether)] and [M(CO)s (phosphine)] complexes. In the 7/2-bonding mode the heteroaldehyde ligands are strong rr acceptors and their IR spectra resemble those of, e.g., alkyne and olefin complexes. Because [W(CO)5 Se = C(Aryl)H ] complexes are present in solution as rapidly interconverting mixtures of the 771 isomers and the if isomer their IR spectra are composed of both types of i CO) spectra. The intensity ratio of the v(CO) absorptions depends on the temperature due to the temperature dependence of the 17V172 equilibrium. 

Xem = 371—430 nm). Clearly, changing from a ir-acceptor anionic ligand in (CyNC)AuICN to a ir-donor anionic ligand in (CyNC)AuIX alters the electronic properties of these complexes and, consequently, their luminescence behavior. Note that the luminescence and absorption characteristics of (CyNC) Au X are rather similar to those communicated for the related compound (CO) Auta.67... 

The four-electron ligand 11 (57), obtained from 12 (X = CH3) and [(CH3)3Sn]2NCH3, is a weak ligand in comparison with borole (2) and thiadiborolene (12). Due to the reduced donor and acceptor properties of 11, complexes 48, 49, and 50 are only accessible, photochemically or thermally, in moderate yields. From the upfield UB-NMR shift (A8 = 28-34 ppm), it is obvious that the 1,2,5-azadiborolene ligand is pentahapto-bonded to the metal (57). In the IR spectrum, the at mode for the Fe(CO)3 group in 48 is found at KCO) 2045 cm 1, which indicates the weaker electron-acceptor properties of 11 in comparison with 12 (a, = 2058 cm-1 in 41 X = CH3). The complexes 48-50 exhibit lower thermal stability than the analogous thiadiborolene compounds. (See Fig. 12.)... 

Analogous compounds with olefins having stronger 7r-acceptor properties, such as tetrafiuoroethylene 152) or tricyanophenylethylene 169) y have been isolated and studied. They are diamagnetic and stable in air from IR and fiuorine NMR spectra evidence, Parshall 152) considers the structure of Ni(PPh3)2(C2F4) more apt to be Formula 2. 

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