Related Experiment Video
Updated: Jul 16, 2026
![The Synthesis of [Sn10(Si(SiMe3)3)4]2- Using a Metastable Sn(I) Halide Solution Synthesized via a Co-condensation Technique](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F54498.jpg&w=3840&q=50)
12:43
The Synthesis of [Sn10(Si(SiMe3)3)4]2- Using a Metastable Sn(I) Halide Solution Synthesized via a Co-condensation Technique
Published on: November 28, 2016
B(C6F5)3- vs Al(C6F5)3-derived metallocenium ion pairs. Structural, thermochemical, and structural dynamic
Nicholas G Stahl1, Michael R Salata, Tobin J Marks
1Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA.
Journal of the American Chemical Society
|August 4, 2005
Summary
Aluminum (Al(C6F5)3) cocatalysts show lower methide affinity than boron (B(C6F5)3) counterparts in group 4 metallocenium ion pairs. This results in stronger bridging methyl group binding and altered epimerization kinetics for Al-derived systems.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Main Group Chemistry
Background:
- Metallocenium ion pairs are crucial in olefin polymerization catalysis.
- The choice of counter-anion significantly influences catalyst activity and stability.
- Boron-based fluoroaryl compounds like B(C6F5)3 are common activators, but their properties are not fully understood in comparison to aluminum analogs.
Purpose of the Study:
- To quantitatively compare the thermodynamic and structural properties of Al(C6F5)3-derived versus B(C6F5)3-derived group 4 metallocenium ion pairs.
- To investigate the impact of the counter-anion on the binding strength of the bridging methyl group and subsequent ion pair epimerization kinetics.
- To elucidate the differences in methide affinity between Al(C6F5)3 and B(C6F5)3.
Main Methods:
- Synthesis of metallocenium ion pairs using rac-C2H4(eta5-Ind)2Zr(CH3)2 and either B(C6F5)3 or Al(C6F5)3.
- X-ray crystallography to determine the structural characteristics of the ion pairs.
- Isoperibol solution calorimetry to measure ion pair formation enthalpies.
- Variable temperature (VT) Nuclear Magnetic Resonance (NMR) spectroscopy to determine kinetic parameters for ion pair epimerization (cocatalyst exchange and anion exchange).
Main Results:
- Al(C6F5)3-derived ion pairs exhibit weaker methide affinity compared to B(C6F5)3-derived ion pairs, as evidenced by lower ion pair formation enthalpies.
- X-ray crystallography reveals that the bridging methyl group in Al(C6F5)3-derived ion pairs is less abstracted, leading to longer Zr-CH3 bridging bond lengths.
- Kinetic studies indicate that the bridging methide is more strongly bound in Al(C6F5)3-derived ion pairs, consistent with higher activation barriers for epimerization.
Conclusions:
- Al(C6F5)3 is a significantly weaker Lewis acid than B(C6F5)3, demonstrating lower methide affinity.
- The structural and thermodynamic differences between Al- and B-derived ion pairs impact the stability and reactivity of metallocenium catalysts.
- These findings provide valuable insights for designing tailored cocatalysts for specific polymerization applications.
More Related Videos
12:02Determination of Thermodynamic Properties of Alkaline Earth-liquid Metal Alloys Using the Electromotive Force Technique
Published on: November 3, 2017
07:20Discovery and Synthesis Optimization of Isoreticular Al(III) Phosphonate-Based Metal-Organic Framework Compounds Using High-Throughput Methods
Published on: October 6, 2023
Related Concept Videos
02:48Ionic Bonding and Electron Transfer
Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence shell, and an anion (a negative ion) forms when a neutral atom gains one or more electrons in its valence shell. Compounds composed of ions are called ionic compounds (or salts), and their constituent ions are held together by ionic bonds: electrostatic forces of attraction between oppositely charged cations and anions.
02:37Metallic Solids
Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability. Many...
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and malleability. Many...
02:45Alkyl Halides
Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
01:23Properties of Organometallic Compounds
Organometallic compounds are compounds that contain a carbon–metal bond. Carbon belongs to an organyl group like alkyl, aryl, allyl, or benzyl groups. The metal can be from Group I or Group II of the periodic table, a transition metal, or a semimetal.
01:04Structures of Aldehydes and Ketones
Vanillin—a flavoring agent in vanilla, cinnamaldehyde—a molecule responsible for the distinct smell of cinnamon, and acetone—a strong-smelling ingredient in nail polish removers, all belong to a class of carbonyl compounds called aldehydes and ketones (Figure 1). Although both aldehydes and ketones contain the characteristic carbonyl (C=O) bond, their chemical structures vary with respect to the groups directly attached to the carbonyl carbon.
In aldehydes (Figures 1a and 1b), the carbonyl...
In aldehydes (Figures 1a and 1b), the carbonyl...