Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Abstract

A water-soluble self-assembled supramolecular host molecule catalyzes the hydrolysis of orthoformates in basic solution. Comparison of the rate constants of the catalyzed and uncatalyzed reactions for hydrolysis displays rate accelerations of up to 3900 for tri-n-propyl orthoformate. Kinetic analysis shows that the mechanism of hydrolysis with the supramolecular host obeys the Michaelis-Menten model.Mechanistic studies, including 13 C-labeling experiments, revealed that the resting state of the catalytic system is the neutral substrate encapsulated in the host. Activation parameters for the k cat step of the reaction revealed that upon encapsulation in the assembly, the entropy of activation becomes more negative in contrast to the uncatalyzed reaction. Furthermore, solvent isotope effects reveal a normal k(H 2 O)/k(D 2 O) = 1.6, confirming that proton transfer is occurring in the transition state and is rate limiting in the catalyzed reaction. In comparison to the uncatalyzed reaction, which operates by an A-1 mechanism in which the decomposition of the protonated substrate is rate limiting, the encapsulated reaction proceeds through an A-S E 2 mechanism in which proton transfer from protonated water to the substrate is rate limiting.

N-Heterocyclic carbene adducts to [Cp′FeI]2: synthesis and molecular and electronic structure

“…The steric influence of alkyl substitution is also nicely demonstrated in the electronic properties of the corresponding manganocene systems; [Cp* 2 Mn] (S = 1/2) is a low-spin molecule, 16 while [Cp′ 2 Mn] (S = 5/2) adopts the high-spin state. 17 The Fe-C(NHC) bond distances in complexes 2-5 are significantly longer than those found in the related [Cp*FeX(NHC)] (X = monoanionic ligand) derivatives, 9a but are in the range of those observed for threecoordinate, high-spin Fe-NHC complexes (2.096 (2)…”

Paramagnetic Chromium(II) Complexes and Chromium(IV) Nitrides with Bulky Alkylcyclopentadienyl Ligands

“…Crystal structures were obtained by XRD measurements with an Oxford Diffraction Gemini Ultra diffractometer, with an Agilent Supernova diffractometer with a microfocus source and an Atlas S2 detector, or on a Bruker Smart Apex2 diffractometer with CCD area detector, D8 goniometer and an Incoatec Mo‐microfocus source iµS. The compounds [Cr 2 (µ‐OOCCH 3 ) 4 ],, Na 4 Cp,, NaCp′′′, and Li 5 Cp have been prepared according to the literature citations.…”

Tuning the Magnetic Moment of [Ru2(DPhF)3(O2CMe)L]+ Complexes (DPhF=N,N′‐Diphenylformamidinate): A Theoretical Explanation of the Axial Ligand Influence

“…[32][33][34][35][36][37] However, the examples with the second-and thirdrow transition metals are known only for the above-mentioned diruthenium complexes. [25,[29][30][31]38] In some of these compounds the S = 1 = 2 and S = 3 = 2 spin states are sufficiently close in energy that either can be obtained by variation of the axial ligand.…”