Created by Allegra Liberman-Martin ([email protected]), Drexel Proctor, Levi Moore, and Giselle Sulivan and posted on VIPEr on December 2009

Created by Allegra Liberman-Martin ([email protected]), Drexel Proctor, Levi Moore, and Giselle Sulivan and posted on VIPEr on December 2009. Copyright Allegra Liberman-Martin 2009. This work is licensed under the Creative Commons Attribution Non-commercial Share Alike License. To view a copy of this license visit http://creativecommons.org/about/license/

C-H Functionalization:Shilov Chemistry

Allegra Liberman-Martin, Levi Moore, Drexel Proctor, and Giselle Sullivan

Chem 165: Organometallic Chemistry

Fall 2009

This presentation was created as part of the requirements for Chemistry 165 "Organometallics" at Harvey Mudd College during the fall semester 2009. The authors of this presentation are Allegra Liberman-Martin (Scripps College), Levi Moore (Pomona College), Drexel Proctor (Pomona College) and Giselle Sullivan (Scripps College).


• Current methane conversion methods are indirect• Synthesis gas method

• Goal: Direct conversion of methane to methanol

• Challenging aspect: increasing reactivity of oxidation products

Comparing

Bond

Dissociation

Energies (BDEs):

BDE(C-H, methane) = 104 kcal/molBDE(C-H, methanol) = 93 kcal/mol

Methane Utilization


Radical Chain Oxidation of Alkanes vs. Oxenoid Mechanism

Muradov, N. Z.; Shilov, A. E.; Shteinman, A. A., Reac. Kin. and Cat.Lett. 1975, 2, 417-423.

Shilov, A.E.; Shteinman A.A. Acc. Chem. Res. 1999, 32, 763, 771.

Radical Chain Oxidation

RH + O2 R• + HOO•

R• + O2 ROO•ROO• + RH ROOH + R•

• Dioxygen causes initiation and propagation of chains.ROOH + Mn Mn+1 + RO- + •OH

• Compounds of transition metals can also participate in thepropagation of radicals. The radical mechanism is a 1e- process.

Oxenoid Mechanism

RH + 2e- + 2H+ + O2 ROH + H2O

• Hydroxylation of C-H bond of a hydrocarbon coupled with oxidation of electron donors.

• Requires interaction with a metal core, either in a synthesized catalyst or an enzyme.

• The oxenoid mechanism is a 2e- process, and does not involve the formation of radicals.

• Both major systems currently in use proceed through an oxenoid type mechanism.


Shilov System

First transition metal system for alkane functionalization

Catalytic in Pt(II), but requires stoichiometric Pt(IV)

Because methyl undergoes nucleophilic attack by both water and chloride ions in solution, both CH3OH and CH3Cl are generated

Luinstra, G. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1993, 115, 3004-3005.

Lunistra, G. A.; Wang, L.; Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Organomet. Chem. 1995, 504, 75-91.


Shilov System - Rate Determining Step

• Two steps in question:1. Methane uptake

• methane platinum complex precursor for C–H

2. C-H activation

• Rate Determining Step: methane uptake– Associative vs. dissociative pathway– Ligand dependency (see respective rate laws)

Zhu, H.; Ziegler, T. J. Organomet. Chem. 2006. 691, 4486.


Shilov System: Methane Uptake

Associative mechanism for methane uptake

Dissociative mechanism for methane uptake

Zhu, H.; Ziegler, T. J. Organomet. Chem. 2006. 691, 4486.


Catalytica Systems

• 85% selectivity for methyl bisulfate

• 50% conversion of methane

• 81% selectivity for methyl bisulfate

•89% conversion of methane

Hydrolysis of methyl bisulfate to methanol is necessary.

Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fuhii, H. Science 1998, 280, 560-564.


Vanadate Catalysis

• Vanadate/pyrazine-2-carboxylic acid catalysis– Less extreme reaction conditions

• Industrial impact for C-H functionalization• Forms methanol, formic and acetic acid

Süss-Fink, G.; Stanislas, S.: Shul'pin, G.B.; Nizova, G.V. Appl. Organomet. Chem. 2000, 14, 623-628.


Gold in the Shilov Reaction System

• Au(I) is isoelectronic with Hg(II); Au(III) with Pt(II)

• Selenic acid (H2SeO4) used as oxidant, rather than Pt(IV)

• Methane converts to methyl bisulfate, which is hydrolyzable to methanol

De Vos, D. E.; Sels, B. F. . Angew. Chem. Int. Ed. 2004, 44, 30-32.


Construction of MOF

• Wanted to construct a heterogeneous catalyst for Shilov reaction

• Used Gd and Pt(BPDC)Cl2 in MOF

• Catalytic site structure retained

Szeto, K. C.; Kongshaug, K. O.; Jakobsen, S.; Tiset, M.; and Lillerud, K. P. Royal Soc. Chem. 2008, 2054-60.

Image (Figure 1, p. 2057) from “Design, synthesis, and characterization of a Pt-Gd metal-organic framework containing potentially catalytically active sites.” Szeto, K. C.; Kongshaug, K. O.; Jakobsen, S.; Tiset, M.; and Lillerud, K. P. Royal Soc. Chem. 2008,2054-2060.


Formation of Lactones

• Best with typical Shilov Pt(II) catalyst and Pt(IV) oxidant (60%yield)

• Second best with Cu(II) oxidant (56%yield with 3 eq.)

• Can be monomers for organic synthesis, materials science, polymers, or biological molecules

Lee, J. M., and Chang, S. Tetra. Lett. 2006, 47, 1375-1379.

Documents

Created by Allegra Liberman-Martin ([email protected]), Drexel Proctor, Levi Moore, and Giselle Sulivan and posted on VIPEr on December 2009