Luca Rocchigiani

Iridium‐EDTA as an Efficient and Readily Available Catalyst for Water Oxidation

It′s so easy: The readily available and highly water‐soluble [IrCl(Hedta)]Na complex is an efficient and robust catalyst for water oxidation to molecular oxygen. The reaction is driven by the reduction of Ce4+ to Ce3+. Its performances (TOF=6.8 min−1 and TON>12 000) are derived by UV/Vis spectroscopic, volumetric and electrochemical measurements, and compare favorably with those of the best catalysts reported so far.

Self‐Aggregation Tendency of Zirconocenium Ion Pairs Which Model Polymer‐Chain‐Carrying Species in Aromatic and Aliphatic Solvents with Low Polarity

From pairs to double pairs: Zirconocene ion pairs bearing an aliphatic chain of variable length were synthesized and investigated by means of NOE and diffusion NMR spectroscopy experiments. The presence of long aliphatic chains allowed an unprecedented investigation of their self‐aggregation tendency in cyclohexane (see figure), which has a dielectric constant similar to that of isoparaffins used in industrial plants.

Anion‐Dependent Tendency of Di‐Long‐Chain Quaternary Ammonium Salts to Form Ion Quadruples and Higher Aggregates in Benzene

The self-aggregation tendency of [N(CH(3))(2)(C(18)H(37))(2)]X [1X; X(-)=BF(4) (-), PF(6) (-), OTf(-), NTf(2) (-), BPh(4) (-), BTol(4) (-), BAr(F-), and B(C(6)F(5))(4) (-)] salts to form ion quadruples (IQs) and higher aggregates (HAggs) in [D(6)]benzene is investigated by means of diffusion NMR spectroscopy. The experimental results indicate that salts containing small anions (1BF(4), 1PF(6), and 1OTf) are present in solution as IQs even at the lowest investigated concentration of C=5×10(-5) M and show a limited tendency to further self-aggregate, reaching a maximum average aggregation number (N=V(H)/V(H)(0IP), where V(H)=measured hydrodynamic volume and V{H}{0IP}=hydrodynamic volume of the ion pair) of about 6-8 (C=0.050-0.100 M). Salts with larger counterions [1BPh(4), 1BTol(4), 1BAr(F), and 1B(C(6)F(5))(4)] form instead ion pairs at low concentration but steadily self-aggregate (especially the non-fluorinated ones) on increasing their concentration up to N values exceeding 50 (C=0.030-0.050 M). 1NTf(2) behaves in an intermediate fashion. The self-aggregation tendency of salts is quantified by formulating the dependence of V(H) on C by means of the equations of indefinitive aggregation models. The following rankings for the formation of IQs and HAggs are obtained: IQs: 1BF(4)≈1PF(6)≈1OTf> 1NTf(2)>1B(C(6)F(5))(4)≥1BPh(4)≥1BTol(4)≥1BAr(F); HAggs: 1BTol(4)>1BPh(4)> 1NTf(2)>1B(C(6)F(5))(4)> 1BAr(F)>1BF(4)≈1PF(6)≈1OTf. Interionic NOE NMR studies and DFT calculations were conducted in order to determine the relative anion-cation orientation in the self-aggregating units.

Unusual hafnium-pyridylamido/ER(n) heterobimetallic adducts (ER(n) = ZnR2 or AlR3).

NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)-pyridylamido catalytic system for olefin polymerization, [{N(-),N,CNph(-)}HfMe][B(C6F5)4] (1, Nph = naphthyl), interacts with ER(n) (E = Al or Zn, R = alkyl group) to afford unusual heterobimetallic adducts [{N(-),N}HfMe(μ-CNph)(μ-R)ER(n-1)][B(C6F5)4 in which the cyclometalated Nph acts as a bridge between Hf and E. (1)H VT (variable-temperature) EXSY NMR spectroscopy provides direct evidence of reversible alkyl exchanges in heterobimetallic adducts, with ZnR2 showing a higher tendency to participate in this exchange than AlR3. 1-Hexene/ERn competitive reactions with 1 at 240 K reveal that the formation of adducts is strongly favored over 1-hexene polymerization. Nevertheless, a slight increase in the temperature (to >265 K) initiates 1-hexene polymerization.

Low-temperature kinetic NMR studies on the insertion of a single olefin molecule into a Zr-C bond: assessing the counterion-solvent interplay.

Sticky counterions: Low‐temperature kinetic NMR studies were performed to determine ΔH≠ and ΔS≠ values for the insertion of a single 2‐methyl‐1‐heptene molecule into a Zr-C bond of [Cp2Zr(η2‐CH2NMePh)][X] (1a: X−=MeB(C6F5)3−, 1b: B(C6F5)4−) in [D8]toluene and a 1:1 mixture of [D8]toluene and [D5]chlorobenzene. Both activation parameters critically depend on the interplay of the counterion and the solvent.

An Integrated NMR and DFT Study on the Single Insertion of α-Olefins into the MC Bond of Group 4 Metallaaziridinium Ion Pairs

The reactions of metallaaziridinium ion pairs [Cp2M(η2‐CH2NMePh)][B(C6F5)4] [M=Zr (1), Hf (2)] with 1‐hexene and 2‐methyl‐1‐heptene were investigated by means of NMR spectroscopy and DFT calculations. We found that a single insertion of the olefin into the MC bond led to the formation of stable five‐membered heterocycles (3–6). The reactions were 1,2‐regioselective and afforded two diastereoisomers whose ratio was mainly controlled by the nature of the olefin, whilst the nature of the metal only played a marginal role. In particular, the reaction with 1‐hexene was found to be not only more favored than that with 2‐methyl‐1‐heptene from a thermodynamic point of view but it was also more diastereoselective. In all cases, the observed diastereoisomeric ratio was dictated by thermodynamics because the products interconverted into each other, as indicated by EXSY NMR spectroscopy and by DFT calculations.