Gold-Catalysed Heck Reaction: Fact or Fiction?

Two recent high-profile publications described the formation of Heck-type arylated alkenes catalysed by MeDalPhosAuCl / AgOTf (J. Am. Chem. Soc. 2023, 145, 8810) and their cyclisation to tetralines (Angew. Chem. Int. Ed. 2023, e202312786), claiming that these were the first demonstrations of alkene insertion into Au-aryl bonds, β-H elimination and chain-walking by Au-H cations under catalytic conditions. We show here that in fact this chemistry is a two-stage process. Only the first step, the production of an alkyl triflate ester as primary product by the well-known alkene heteroarylation sequence, involves gold. The subsequent formation of Heck-type olefins and their cyclisation to tetralines represent are classical H+-triggered carbocationic chemistry. These steps proceed in the absence of gold with identical results. Literature claims of new gold reactivity such as chain walking by the putative [LAuH]2+ dication have no basis in fact

Application of multipoles expansion technique to two-dimensional nonlinear free-surface flows

The original idea by Rokhlin (1985) to rapidly solve the Laplace equation is applied here for studying nonlinear free-surface flows. The boundary integral equations for the velocity field are discretized through the Euler-McLaurin quadrature formula, which, in spite of its simplicity, displays spectral convergence properties for regular boundary data. In order to solve the discretized boundary integral equations, an iterative solver for algebraic systems is coupled to a fast summation technique based on the multipoles expansion of the influence coefficients. The resulting algorithm allows for a small size of the code (O(N)) and fast computation (O(Nlog N)) without affecting the original convergence properties. Typical long-time evolution and large-scale computations, which often arise in nonlinear free-surface flows, are discussed to show the effectiveness of the developed approach

Application of multipole expansion technique to two-dimensional nonlinear free surface flows.

The original idea by Rokhlin (1985) to rapidly solve the Laplace equation is applied here for studying nonlinear free-surface flows. The boundary integral equations for the velocity field are discretized through the Euler-McLaurin quadrature formula, which, in spite of its simplicity, displays spectral convergence properties for regular boundary data. In order to solve the discretized boundary integral equations, an iterative solver for algebraic systems is coupled to a fast summation technique based on the multipoles expansion of the influence coefficients. The resulting algorithm allows for a small size of the code (O(N)) and fast computation (O(Nlog N)) without affecting the original convergence properties. Typical long-time evolution and large-scale computations, which often arise in nonlinear free-surface flows, are discussed to show the effectiveness of the developed approach

Flow induced by the forced roll motion of a hull section

Rapporto Tecnico INSEAN 2000--23, 2000

Non--linear Long Waves Generated by a Moving Pressure Disturbance

The evolution of long waves generated by a pressure disturbance acting on an initially unperturbed free surface in a channel of finite depth is analysed. Both off-critical and transcritical conditions are considered in the context of the fully nonlinear inviscid problem. The solution is achieved by using an accurate boundary integral approach and a time-stepping procedure for the free-surface dynamics. The discussion emphasizes the comparison between the present results and those provided by both the Boussinesq and the related Korteweg-de Vries model. For small amplitudes of the forcing, the predictions of the asymptotic theories are essentially confirmed. However, for finite intensities of the disturbance, several new features significantly affect the physical results. In particular, the interaction among different wave components, neglected in the Korteweg-de Vries approximation, is crucial in determining the evolution of the wave system. A substantial difference is indeed observed between the solutions of the Korteweg-de Vries equation and those of both the fully nonlinear and the Boussinesq model. For increasing dispersion and fixed nonlinearity the agreement between the Boussinesq and fully nonlinear description is lost, indicating a regime where dispersion becomes dominant. Consistently with the long-wave modelling, the transcritical regime is characterized by an unsteady flow and a periodic emission of forward-running waves. However, also in this case, quantitative differences are observed between the three models. For larger amplitudes, wave steepening is almost invariably observed as a precursor of the localized breaking commonly detected in the experiments. The process occurs at the crests of either the trailing or the upstream-emitted wave system for Froude numbers slightly sub- and super-critical respectively

Studio e sviluppo di un algoritmo "Viscous Vortex Method" per la soluzione delle equazioni di Navier-Stokes in presenza di superficie libera.

Rapporto Tecnico INSEAN 2000-0

Aspetti numerici della simulazione del flusso attorno ad una carena investita da onde

Sien