Intramolecular diamination reactions are described which yield cyclic ureas as direct products of an oxidative alkene transformation in the presence of palladium acetate and iodosobenzene diacetate as terminal oxidant. The reaction is truly catalytic in metal catalyst and represents the proof of principle for this elusive type of alkene oxidation.
A first palladium-catalyzed intramolecular diamination of unfunctionalized terminal alkenes has recently been reported. This study investigates the details of its mechanistic course based on NMR titration, kinetic measurements competition experiments, and deuterium labeling. It concludes a two-step procedure consisting of syn-aminopalladation with an unligated palladium(II) catalyst state followed by oxidation to palladium(IV) and subsequent C-N bond formation to give the final products as cyclic diamines. Related reactions employing sulfamides give rise to aminoalkoxy-functionalization of alkenes. This process was investigated employing deuterated alkenes and found to follow an identical mechanism where stereochemistry is concerned. It exemplifies the importance of cationic palladium(IV) intermediates prior to the final reductive elimination from palladium and proves that the nucelophile for this step stems from the immediate coordination sphere of the palladium(IV) precursor. These results have important implications for the general development of alkene 1,2-difunctionalization and for the individual processes of aminopalladation and palladium-catalyzed C(alkyl)-N bond formation.
Controlling the mechanical behavior of novel supramolecular materials is of the utmost importance and requires a fundamental understanding of the underlying physical processes. We present a multimethods approach to the dynamics of entangled transient polyisoprene networks. Small-angle neutron scattering (SANS) on randomly functionalized chains shows homogeneous supramolecular melts with Gaussian chain conformations. The H-bond lifetimes (dielectric α*-process) and the rheological response in terms of the loss modulus G″ differ by 2 orders of magnitude in time. Within the concept of a compact random walk (RW), where the random walker (urazole group acting as a sticker) undergoes multiple returns to its starting point and following the concept of theoretical proposed renormalized sticky bond lifetimes, we quantitatively solve this longstanding and unexplained large discrepancy: While the bond opening gives rise to the dielectric response, for rheological relaxation the association with a new partner is relevant. This takes place only after multiple returns to the original binding partner.
A unique metal-free intramolecular diamination of alkenes based on bromide catalysis is reported that uses only potassium bromide and sodium chlorite avoiding any use of transition metal. This unprecedented halide catalysis is of general applicability, uses economic reagents, can be conveniently up-scaled and proceeds under mild and selective conditions that surpass all conventional transition metals in scope.
In
this work we present a combined analysis of small-angle neutron
scattering, linear rheology and pulsed field gradient nuclear magnetic
resonance spectroscopy experiments on the supramolecular association
and chain structure of well-defined telechelically modified poly(ethylene
glycol) (PEG) in the bulk. Oligomeric PEG was functionalized with
directed heterocomplementary hydrogen-bonding end-groups, thymine
(Thy) and diaminotriazine (DAT). The polarity of the backbone polymer
is comparable to the end groups and avoids clustering of the groups
basing on energetic arguments. Their linear association behavior in
the ideal melt state was investigated on the microscopic/molecular
level as a function of temperature. By means of a selective labeling
scheme, which should ideally lead to the formation of alternating
hydrogeneous-deuterated building block sequences if the hydrogen bonding
reaction is exclusively heterocomplementary, we showed that the Thy–DAT
association is dominant and a Thy–Thy homoassociation is approximately
three times less probable. Latter nondirected association gives rise
to a considerable amount of random-copolymerization without affecting
seriously neither the macroscopic melt viscosity nor the diffusivity
of the supramolecular associates. From the q-dependence
of a multiblock RPA structure factor, the linear association in the
melt is confirmed. Furthermore, this diffusion and viscosity study
reveals simple Rouse dynamics of supramolecular polymer chains with
molecular weight much larger than the entanglement mass M
e. The Rouse-like dynamics of long supramolecular chains
indicates short lifetime hydrogen bonds of the end groups. Our results
are in excellent agreement with the related polycondensation theory.
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