Inorganic, Organometallic, Organic, and Computational Chemistry

Ph.D. 1986, Kazan State University, Russia
Doctor of Sci. 2000, Kazan State University, Russia
Postdoctoral Research Fellow 2001-2003, Indiana University, Bloomington

Department of Chemistry & Biochemistry
Room 2353
Phone: (301) 405 2784
E-mail: avederni@umd.edu

Aerobic Organoplatinum(II) Chemistry 
Our semi-labile facially chelating ligands of the di(2-pyridyl)methanesulfonate (dpms) family allow to control reactivity of d⁸/d⁶ metal species in oxidative addition / reductive elimination reactions in various solvents including water. These ligands allow for facile oxidation of monohydrocarbyl Pt^II complexes (dpms)Pt^IIR(HX) with O₂ in water or alcohols to produce (dpms)Pt^IVR(OH)X species (R = alkyl, aryl; HX = H₂O, alcohols, primary amines). Due to the presence of the sulfonate which is a good leaving group the dpms ligand allows for clean and facile C(sp³)-O reductive elimination from (dpms)Pt^IVR(OH)X complexes leading to alcohols, ethers and epoxides in acidic, neutral or basic aqueous solutions. Some examples are given below:
a) Oxidation of (dpms)Pt^IIMe(OH₂) complex under air in water leads ultimately to methanol:

b) (dpms)Pt^II(ethene)OH complex reacts cleanly with O₂ in water at room temperature via 2-hydroxyethyl Pt^II intermediate to produce (dpms)Pt^IV(C₂H₄OH)(OH)₂ complex. The latter eliminates ethylene oxide at 80^oC: 

 c) Analogous cycloolefin complexes produce readily Pt^II- and Pt^IV-oxetanes. The latter eliminate corresponding epoxides:

Available data indicates that anionic intermediates (dpms)Pt^IIR(X)^- are responsible for dioxygen activation. 

New Mechanisms of C(sp³)-O Reductive Elimination from Pt^IV
We discovered that several mechanisms of C(sp³)-O elimination from (dpms)Pt^IV complexes may be operational in aqueous solutions:
a) C-O coupling involving nucleophilic hydroxo or alkoxo Pt^IV complexes that can compete successfully with water (solvent) even in dilute (few mM) solutions. For instance, formation of Me¹⁶OH is observed in H₂¹⁸O solutions of (dpms)Pt^IVMe(OH)₂ along with Me¹⁸OH which is the expected product of an S_N2 reaction involving the solvent. Me¹⁶OH results from nucleophilic attack of Pt^IV(OH) at the methyl group of Pt^IVMe species; this reaction is 2^nd order in Pt^IV:

b) In certain cases an unprecedented for Pt^IV direct intramolecular C-O elimination is observed (see elimination of epoxides from Pt^IV oxetanes above). This reaction is fundamentally different from S_N2 mechanism typical for Pt^IVMe complexes and is also stereospecific. The order of reactivity of Pt^IV alkyls in direct C-O elimination is as follows: 2^o alkyl > 1^o alkyl > Me. The opposite order of reactivity is observed in S_N2 reactions.

The observations above may be valuable for designing Pt-mediated selective hydrocarbon functionalization reactions in hydroxylic solvents including water.

Catalytic Aerobic Organopalladium(II) Chemistry 
Similar to monohydrocarbyl platinum(II) complexes, alkylpalladium(II) complexes are inert toward O₂ but when dpms or some other anionic pyridine ligand is installed, aerobic oxidation of AlkPd^II becomes possible in such solvents as acetic acid. When 2,6-pyridinedicarboxylic acid is used as a ligand (H₂pda), CH activation of some aromatic amines N-CH by Pd^II(pda)L (L = solvent or substrate) and O₂ activation by derived alkylpalladium(II) intermediates Pd^II(Hpda)(N-C) can be realized in a single catalytic cycle: 

The catalytic oxidation reaction is selective; a number of functional groups are tolerated. One of the suggested reaction mechanisms involves direct aerobic oxidation of alkypalladium(II) species, Pd^II(Hpda)(N-C), to produce reactive alkylpalladium(IV) intermediates.  

Financial support to this work from the Donors of the American Chemical Society Petroleum Research Fund (PRF#42307-AC3), National Science Foundation (CHE-0614798), the US-Israel Binational Science Foundation and the Center for Catalytic Hydrocarbon Functionalization (CCHF), an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award Number DE-SC0001298) is gratefully acknowledged.