CF3–Ph reductive elimination from [(Xantphos)Pd(Ph)(CF3)] (1) and [(i-Pr-Xantphos)Pd(Ph)(CF3)] (2) has been studied by experimental and computational methods. Complex 1 is cis in the solid state and predominantly cis in solution, undergoing degenerate cis–cis isomerization (ΔG ≠ exp = 13.4 kcal mol–1; ΔG ≠ calc = 12.8 kcal mol–1 in toluene) and slower cis–trans isomerization (ΔG calc = +0.9 kcal mol–1; ΔG ≠ calc = 21.9 kcal mol–1). In contrast, 2 is only trans in both solution and the solid state with trans-2 computed to be 10.2 kcal mol–1 lower in energy than cis-2. Kinetic and computational studies of the previously communicated (J. Am. Chem. Soc. 2006, 128, 12644), remarkably facile CF3–Ph reductive elimination from 1 suggest that the process does not require P–Pd bond dissociation but rather occurs directly from cis-1. The experimentally determined activation parameters (ΔH ≠ = 25.9 ± 2.6 kcal mol–1; ΔS ≠ = 6.4 ± 7.8 e.u.) are in excellent agreement with the computed data (ΔH ≠ calc = 24.8 kcal mol–1; ΔG ≠ calc = 25.0 kcal mol–1). ΔG ≠ calc for CF3–Ph reductive elimination from cis-2 is only 24.0 kcal mol–1; however, the overall barrier relative to trans-2 is much higher (ΔG ≠ calc = 34.2 kcal mol–1) due to the need to include the energetic cost of trans–cis isomerization. This is consistent with the higher thermal stability of 2 that decomposes to PhCF3 only at 100 °C and even then only in a sluggish and less selective manner. The presence of excess Xantphos has a minor decelerating effect on the decomposition of 1. A steady slight decrease in k obs in the presence of 1 and 2 equiv of Xantphos then plateaus at [Xantphos]:1 = 5, 10, and 20. Specific molecular interactions between 1 and Xantphos are not involved in this kinetic effect (NMR, T 1 measurements). A deduced kinetic scheme accounting for the influence of extra Xantphos involves the formation of cis-[(η1-Xantphos)2Pd(Ph)(CF3)] that, by computation, is predicted to access reductive elimination of CF3–Ph with ΔG ≠ calc = 22.8 kcal mol–1.

Within all the eukaryotic cells there is an important group of biomolecules that has been potentially related to signalling functions: the myo-inositol phosphates (InsPs). In nature, the most abundant member of this family is the so called InsP6 (phytate, L(12-)), for which our group has strived in the past to elucidate its intricate chemical behaviour. In this work we expand on our earlier findings, shedding light on the inframolecular details of its protonation and complexation processes. We evaluate systematically the chemical performance of InsP6 in the presence and absence of alkali and alkaline earth metal ions, through (31)P NMR measurements, in a non-interacting medium and over a wide pH range. The analysis of the titration curves by means of a model based on the cluster expansion method allows us to describe in detail the distribution of the different protonated microspecies of the ligand. With the aid of molecular modelling tools, we assess the energetic and geometrical characteristics of the protonation sequence and the conformational transition suffered by InsP6 as the pH changes. By completely characterizing the protonation pattern, conformation and geometry of the metal complexes, we unveil the chemical and structural basis behind the influence that the physiologically relevant cations, Na(+), K(+), Mg(2+) and Ca(2+) have over the phytate chemical reactivity. This information is essential in the process of gaining reliable structural knowledge about the most important InsP6 species in the in vitro and in vivo experiments, and how these features modulate their probable biological functions.

The reaction of compound cis-[Pt(C6F5)2(SEt2)2] with the imine ligands ArCHNCH2CH2NMe2 (Ar = 2-BrC6H4 (1a) or 2,6-Cl2C6H3 (1b)) in toluene produces coordination compounds cis-[Pt(C6F5)2(ArCH N CH2CH2 N Me2)] (2a, 2b) containing a bidentate [N,N′] ligand. No further reactivity has been observed from this point. Compound 2b has been characterized by single-crystal XRD. Under analogous conditions, imine ligand 2-BrC6H4CHNCH2(4′-ClC6H4) (1c) produced the PtII-metalated compound [PtBr{6-(C6F5)(2- C )C5H3CH N CH2(4′-ClC6H4)SEt2] (2c), which contains a five-membered metallacycle with a biaryl linkage involving a C6F5 group. The derivative compounds [PtBr{6-(C6F5)(2- C )C5H3CH N CH2(4′-ClC6H4)L] (L = SMe2 (3c), L = PPh3 (4c)) were also prepared, and compound 4c has also been characterized by XRD. The kinetico-mechanistic study of the formation of compound 2c has also been pursued in view of the previously published data, leading to seven-membered metallacycles. The time monitoring via UV−vis of the full process allowed the detection and NMR characterization of two intermediate species. An initial PtIV complex is present in steady-state low-concentration conditions, and formation of a non-cyclometalated intermediate PtII compound is also detected during the process. The latter already contains the C−C coupled ligand arising from a reductive elimination of the former. Intramolecular C−H activation from the latter produces the final characterized compound 2c along with C6F5H. The full process has been studied as a function of temperature and pressure as well as at varying nonstoichiometric concentrations of SEt2 and free imine ligand. The results agree with the quenching of the process at important excesses of SEt2 (for stoichiometric reasons) or free imine (avoiding the formation of the final complex from the C−C reductively coupled intermediate). The thermal and pressure activation parameters measured indicate that the mechanism operating in this case lies out of the continuum existing for the series of C−H bond activations studied so far. The more than probable associative shift of the reactivity of the PtII complex containing the electron-withdrawing C6F5 ligands is held responsible for this fact.

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The cyclometallation reactions of dinuclear μ-acetato complexes of the type [Pd(AcO)(μ-AcO)L]2 (L = 4-RC6H4CH2NH2, R = H, Cl, F, CF3), a process found to occur readily even in the solid state, have been studied from a kinetico-mechanistic perspective. Data indicate that the dinuclear acetato bridged derivatives are excellent starting materials to activate carbon-hydrogen bonds in a facile way. In all cases the established concerted ambiphilic proton abstraction by a coordinated acetato ligand has been proved. The metallation has also been found to occur in a cooperative manner, with the metallation of the first palladium unit of the dimeric complex being rate determining; no intermediate mono-metallated compounds are observed in any of the processes. The kinetically favoured bis-cyclopalladated compound obtained after complete C-H bond activation does not correspond to the final isolated XRD-characterized complexes. This species, bearing the classical open-book dimeric form, has a much more complex structure than the final isolated compound, with different types of acetato ligands.