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Published on: November 27, 2015
Catalytic double-bond metathesis without the transition metal
Stephen A Bell1, Tara Y Meyer, Steven J Geib
1Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Journal of the American Chemical Society
|September 5, 2002
Summary
Iminophosphoranes catalyze the metathesis of carbodiimide C=N bonds, mimicking metal-catalyzed olefin metathesis. Isolated diazaphosphetidine intermediates reveal the reaction mechanism and kinetics.
Area of Science:
- Organophosphorus Chemistry
- Catalysis
- Organic Synthesis
Background:
- Metal-catalyzed olefin metathesis is a cornerstone of organic synthesis.
- Developing non-metal catalysts for similar transformations is highly desirable.
- Iminophosphoranes offer a unique platform for exploring novel catalytic pathways.
Purpose of the Study:
- To investigate the catalytic activity of iminophosphoranes in carbodiimide C=N bond metathesis.
- To elucidate the mechanism of this novel catalytic process.
- To characterize reaction intermediates and determine kinetic parameters.
Main Methods:
- Synthesis and characterization of iminophosphoranes (X(3)P=NR).
- Reaction of iminophosphoranes with carbodiimides to study C=N bond metathesis.
- Isolation and structural determination of diazaphosphetidine intermediates.
- Kinetic studies of the addition and elimination steps.
Main Results:
- Iminophosphoranes effectively catalyze C=N bond metathesis of carbodiimides.
- Diazaphosphetidine intermediates were successfully isolated and characterized.
- A detailed addition/elimination mechanism, analogous to olefin metathesis, was proposed.
- Rate constants for addition (k(add) = 1.7 x 10(-3) M s(-1)) and elimination (k(elim) = 4.0 x 10(-4) s(-1)) were determined.
- The catalytic turnover frequency (TOF) of 1.44 TO/P/h was consistent with kinetic data.
Conclusions:
- Iminophosphoranes provide a viable non-metal alternative for carbodiimide metathesis.
- The reaction proceeds via a [2+2] cycloaddition followed by elimination, conserving key metathesis features.
- Understanding the mechanism and kinetics facilitates catalyst optimization and development of new synthetic methodologies.
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