Although Pd(OAc)2-catalysed alkoxylation of the C(sp3)-H bonds mediated by hypervalent iodine(III) reagents (ArIX2) has been developed by several prominent researchers, there is no clear mechanism yet for such crucial transformations....

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Numerous studies have demonstrated that Brønsted acids (HAs), such as HOTf and HOTs, can promote Pd(OAc) 2catalyzed functionalization of C−H bonds. However, the rationale for using these acids as a promoter is not yet completely obvious. The purpose of this work is to provide a detailed explanation for this observation with the aid of density functional theory calculations. This is accomplished by investigating the chlorination mechanism of phenol carbamates (DG∼C−H) with N-chlorosuccinimide (NCS) using HOTf as a promoter and Pd(OAc) 2 as a catalyst. Typically, in order for Pd(OAc) 2 to activate the C−H bond, it is believed that the trinuclear precatalyst Pd 3 (OAc) 6 reacts with the substrate DG∼C−H to generate the chelated complex [Pd(OAc) 2 (DG∼C−H)], from which C−H activation occurs via a concerted metalation−deprotonation mechanism. Because the substrate DG∼C−H binds relatively weak to palladium, the corresponding chelated complex lies much higher in energy than the reference structure Pd 3 (OAc) 6 , resulting in a very high energy barrier for C−H activation. The Brønsted acid HA is capable of undergoing ligand-exchange reactions with both Pd 3 (OAc) 6 and [Pd(OAc) 2 (DG∼C−H)] to form Pd 3 (OAc) 6−x (A) x and [Pd(OAc)(A)(DG∼C−H)], respectively. Our calculations demonstrate that while the formation of [Pd(OAc)(A)(DG∼C−H)] from [Pd(OAc) 2 (DG∼C−H)] is highly exergonic, that of Pd 3 (OAc) 6−x (A) x from Pd 3 (OAc) 6 is either nearly thermoneutral or endergonic. This feature significantly reduces the energy difference between the reference structure and the chelated complex, resulting in a significant decreased energy barrier for C−H activation. We also found that the acidity of the employed HA influences the energy difference between the trinuclear reference structure and the chelated complex [Pd(OAc)(A)(DG∼C−H)]; the more acidic the HA, the smaller the energy difference, and the lower the activation energy of C−H activation. In addition, our calculations show that the presence of HA not only lowers the overall energy barrier for C−H activation but also accelerates the chlorination step by protonating one of the oxygen atoms in NCS rather than the N atom.

Two new one-dimensional metal-organic polymers (MOPs) {[Cu(L) (PPh 2 Py)•I 2 ]•CH 3 Cl} n (I) and {[Cu(L)(PPh 2 Py)•Br 2 ]•CH 3 Cl} n (II) (L = (1E,2E)-1,2-bis(pyridine-4-ylmethylene)hydrazine) (4-bpmh)) have been synthesized and elucidated by single crystal X-ray diffraction. The results of X-ray diffraction analysis unambiguously revealed that the two polymers are isostructural with the major intermolecular CHÁ Á Áπ and πÁ Á Áπ interactions. Microstructures of these polymers were also synthesized using a sonochemical method in different concentrations and reaction times. Field emission scanning electron microscopy, powder X-ray diffraction, thermogravimetric analysis and IR spectroscopy were applied to fully characterize these compounds. The photoluminescent properties of microrod MOPs were also evaluated to add to our understanding of their potential ability for nitro compound sensing. These experiments showed that MOPs I and II are good luminescence sensors for detection of nitro explosives in aqueous media. The probes maintained their high sensitivity and selectivity for 4-nitrophenol (4-NP). The energy transfer process accompanied by electrostatic interactions of 4-NP with these MOPs can be considered as an influential reason for the selectivity of 4-NP. The competitive study of the quenching process has a6lso shown superior operation with microparticles compared with bulky polymers. These results indicate that this method may be useful to synthesize luminescent materials possessing good sensing properties. K E Y W O R D S energy transfer, isostructural, metal-organic polymers, photoluminescent properties, sonochemical 1 | INTRODUCTION Explosive nitroaromatic compounds (NACs) such as nitrotoluene (NT), 4-nitrophenol (4-NP), nitrobenzene (NB), trinitrotoluene (TNT) and 4-nitroaniline (4-NA) are considered highly toxic environmental pollutants (in soils, rivers, groundwater, etc.). [1] Among various NACs, nitrophenols are widely used in the production of