# Presentation: 516219

## Selectivity of Aldehyde C-H Activation Reactions in Nanovessels

**Selectivity of Aldehyde C-H Activation Reactions in Nanovessels**

***Encapsulated***

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***Not encapsulated***

***Challenges in nanovessel recognition and chemistry:***
**Understanding physical factors that control size and shape selectivity in host-guest systems**
**Installation and reactivity of functional groups inside nanovessels**
**Understanding “intravessel” stereochemical relationships and isomerization reactions**
**Developing efficient enantiorecognition in host-guest systems**
**Developing efficient nanovessel-catalyzed reactions**

## Membranes: Potentially, an efficient method for improved selectivity

**	****1) Ionically conductive membranes for achieving **
**	****selectivity for hydrogen production; potentially also **
**	****for electrochemical production of other chemicals.**
**	****	**
**	****2) Membranes for fine **
**	****chemicals**
**	**
**	****3) Development of membranes with well-defined pore structures (zeolites, microporous materials)**
**	****4) “Strong” Pd membranes (supported in or on another structure to allow thin, cost-effective use of Pd.)**

- Figure from report by Air Products Inc.

## Spin control of selectivity

- Establish whether spin changes can indeed significantly effect reactivity - need more unambiguous examples of ‘two state reactivity’ (notion is still controversial)
- Emphasize study of reactions featuring open shell compounds as reagents, intermediates, or products
- Identify chemical system and circumstances under which ‘spin blocking’ is expected to be important (e. g. reaction types, metals etc.)
- Demonstrate that spin change can be used to control selectivity and offers a dimension of catalyst design
- Develop better computational methods for characterizing reactions involving multiple spin surfaces (i. e. location of ‘minimum energy crossing points’ and calculation of crossing probabilities)

*Potential energy surface of an oxygen atom transfer *
*reaction involving crossing from a doublet to a quartet*
*surface*

***Future challenges:***

## Microwave Control of Catalysis: an example

- Microwave Energy
- Suppresses SO2 poisoning (selective desorption)
- Lowers Lightoff Temp. (selective heating of sites)
- Changes Selectivity     (selective desoprtion)
- CAN Also:
- Enhance Catalyst Synthesis (zeolites & other: more uniform morphology)

- Auto-exhaust Catalyst lightoff

- SO2

- μwave

-  Conner et al., Catalysis Letters 71, 3-4, 133-8 (2001)

## Origins of Surface Chirality

**Natural chirality**
**Originates from the surface structure of the substrate.**

**2. Chirally modified surface**
**Isolated chiral modifiers induce 1:1 enantiospecific interactions with chiral adsorbate.**

**3. Chirally templated surface**
**Chiral modifiers form structures with long-range chiral order.**

**Challenges**
**Preparation of high surface area, naturally chiral materials.**
**Predictive control of enantio-specific modifier-adsorbate interactions. **

## CO2

- X.V. Zhang, Scot T. Martin, & C.M. Friend, Harvard University
- Funded by NASA

_**Rationale**_**:  **
**Heterogeneous photoelectrochemistry provides paths to important chemical syntheses **
***Example *****CO****2**** Fixation promoted by MnS**

- _Future Challenges_:
- Understand how to design photocatalysts for specific applications
- Control of selectivity promoted by understanding of mechanism

## How Do Coordination and Redox Properties of Active Surface Sites Affect Selectivity?

**Rationale:**
** ****Selectivity Controlled by Relative Rates of**
**   ****Competing Pathways**
** ****Relative Rates Influenced by Coordination and**
**   ****Redox Properties**
** ****Optimizing Selectivity Requires Controlling**
**   ****Coordination and Redox Properties**

**Future Work:**
** ****Establish Relationship Between Coordination and**
**    ****Redox Properties**
** ****Establish Relationship Between Coordination/Redox**
**   ****Properties and Kinetics of Competing Pathways**

** ****More Active Surface Redox Sites are More Selective**

## How Does Synthesis Method Affect Structure/Function Properties?

**Future Work:**
** ****Establish Relationship Between Structure/Function Properties and**
**   ****Synthesis Method**
** ****Establish Relationship Between Structure/Function Properties and**
**   ****Kinetics of Competing Pathways**

**Rationale:**
** ****Selectivity Controlled by Relative Rates of Competing**
**   ****Pathways**
** ****Relative Rates Influenced by Structure/Function**
**   ****Properties**
** ****Optimizing Selectivity Requires Controlling the Specific**
**   ****Structures/Functions of Active Surface Sites**

** ****Synthesis Method Controls Distribution of Active Surface Sites**

**Structure of Active Surface Site**

## Tandem Catalysis in Alkene Polymerization

*Non-statistical oligomerization reactions.*  There are no catalysts that allow for the selective formation of pentamers
- or higher condensation products for any substrate available at the present moment.  For example, in the production
- of decene from ethylene, one oligomerizes ethylene with a suitable catalysts to generate a Schultz-Flory distribution
- of products.  Distillation into size specific products is then required, which results in the generation of waste and
- undesirable fractions.  A “dream” set of reactions is shown below, in which Cat1, Cat2, etc. correspond to
- size-specific oligomerization catalysts.

**Tandem Catalysis in Alkene Polymerization**

## Supported catalysts may alter reactivity by suppressing certain bimolecular reactions and favoring others

- Example:     Single-site metal catalysts that form polyesters by ring-opening polymerization also enter into bimolecular trans-esterification.      Supported single-site catalysts grow chains that are released into the solution as exclusively cyclic polymers/oligomers by intrachain trans-esterification

- Potential: New classes of cyclic polyesters and polycarbonates