Submitted by Adam Johnson / Harvey Mudd College on Fri, 01/04/2008 - 13:26
My Notes
Description

Relative metal-hydrogen, -oxygen, -nitrogen, and -carbon bond strengths for organoruthenium and organoplatinum compounds; equilibrium studies of Cp*(PMe3)2RuX and (DPPE)MePtX systems
Henry E. Bryndza, Lawrence K. Fong, Rocco A. Paciello, Wilson Tam, John E. Bercaw
J. Am. Chem. Soc.; 1987 ; 109(5); 1444-1456.

Monomeric Cyclopentadienylnickel Methoxo and Amido Complexes: Synthesis, Characterization, Reactivity, and Use for Exploring the Relationship between H-X and M-X Bond Energies
Holland, P. L.; Andersen, R. A.; Bergman, R. G.; Huang, J.; Nolan, S. P.
J. Am. Chem. Soc.; 1997; 119(52); 12800-12814.

These 2 papers are a good introduction to bond strength thermodynamics, and show that good ideas can be proven wrong, though it may take time.  Bercaw studied M-H, M-O, M-N and M-C bond strengths for Ru and Pt compounds and found a 1:1 correspondence of M-X vs H-X bond strengths (slope is 1:1 plotting M-X vs H-X).  A decade later, Bergman found that the 1:1 rule, as it had come to be known, didn't hold generally, as shown for Ni complexes.  The main problem is that substitution of M-N with H-O is not as simple as replacing M-N with H-N, and the data best fit a qualitative E-C model.  Bergman used (among other things) Hammet parameters and a wider range of ligands than Bercaw.

 I use this paper in a senior level organometallics discussion course where we study "classic" papers. 

Learning Goals

Upon completing this LO students will be able to

1) recognize that trends in transition metal chemistry are harder to extrapolate than in main group chemistry

2) count electrons using the CBC method to describe transition metal complexes

3) understand and describe the trend in M-X bond strengths observed by Bercaw for Ru and Pt

4) Understand and describe the breakdown in the trend Bergman showed for Ni

Related activities
Time Required
1 or 2 75 minutes class periods
Evaluation
Evaluation Methods

Students are expected to present the paper at a high level. I assess on preparation, and ability to lead a discussion.

Evaluation Results

A lively discussion ensues.

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