Bis(pyridyl)siloxane Oligomeric Ligands for Palladium(II) Acetate: Synthesis and Binding Properties

Abstract

The complexation of a series of new bis(meta-pyridyl)methylsiloxane ligands with palladium(II) acetate in dilute toluene-d 8 solution was studied by 1H NMR at 233−363 K, measuring the binding affinity and ring−chain distribution as a function of ligand structure, temperature, and concentration. Significant differences in the ring distribution and Pd binding affinity were observed as a function of siloxane chain length, with hexa- and heptasiloxane spacers binding Pd most effectively. The 1H NMR resonance of the singlet ortho aromatic proton was shifted unusually far downfield for the bidentate complex; the effect was strongest for the shortest chains and disappeared for chains with 10 or more siloxane units. Fitting the experimental data to a modified Jacobson−Stockmayer model demonstrated that the bidentate bis(pyridyl)siloxane complexes function as chelates in the concentration range 1−10 mM. Variable-temperature studies showed that all of the observed cyclic coordination oligomers are strainless. Therefore, entropic effects are implicated as the main cause of the observed trends in binding affinity, particularly the loss of conformational freedom of the siloxane chain upon binding.

Room temperature aerobic oxidation of alcohols using CuBr2 with TEMPO and a tetradentate polymer based pyridyl-imine ligand

“…This can be explained by strong coordination of 4 Ndonors to the copper centre and a difficulty in dissociating these to yield a vacant site. Cyclic coordination oligomers might be forming as previously reported for bis(pyridyl)siloxane ligands with palladium acetate [49]. Formation of such cyclic species would mean that coordination of the alcoholate group with the metal centre would be challenging.…”

“…More recently, others have prepared pyridine terminated siloxane-derived ligands for use in a variety of applications including oxidation catalysis [45][46][47][48][49][50]. We have extended this approach to prepare a bis(pyridyl-imine) terminated siloxane ligand and herein, we report the first use of a series of tetradentate N-donor ligands in the aerobic oxidation of alcohols.…”

Three Reactions, One Catalyst: A Multi‐Purpose Platinum(IV) Complex and its Silica‐Supported Homologue for Environmentally Friendly Processes

“…However, as mentioned, one of them (Karstedt's catalyst) is commonly known as one of the most powerful hydrosilylation catalysts, with industrial applications. On the other hand, metal (copper, palladium) complexes of pyridyl‐functionalized siloxanes showed catalytic activity in alcohol oxidation reactions …”

“…On the other hand, metal (copper, palladium) complexes of pyridyl-functionalized siloxanes showed catalytic activity in alcohol oxidation reactions. [40][41][42][43] The present work describes the formation and catalytic properties of platinum(IV) complex of a piridyl-modified disiloxane, in comparison with complexes obtained with other amino-pyridyl compounds, with or without disiloxane moieties. Very high affinity and selectivity for platinum was found for the siloxane-based ligand, which could be of interest for platinum recovery.…”

By‐Product‐Free Siloxane‐Bond Formation and Programmed One‐Pot Oligosiloxane Synthesis

“…[8] Thek ey feature of this reaction is B(C 6 F 5 ) 3 -catalyzed Si À Hb ond activation. [15] Moreover,w hen at rihydrosilane,p henylsilane,w as employed in the boron-catalyzed cross-coupling step,s iloxane-bond formation occurred twice to give the corresponding Table 1: Iridium-catalyzed hydrosilylation of trimethylsilyl acetate. The[ {Ir(coe) 2 Cl} 2 ]-catalyzed hydrosilylation of silyl esters with dihydrosilanes provides the corresponding disilyl acetals with aS i ÀHf unctional group.…”