Phosphorus-containing ruthenacycles: exploring their potential in processes relevant to hydrophosphination.
Date
2012-04-17
Authors
Morrow, Krista Maria Elena
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Abstract
Phosphorus-containing metallacycles formed from the [2+2] cycloaddition of unsaturated substrates at the Ru-P π-bond of [Ru(η5-indenyl)(PCy2)(PPh3)] (2) were examined as possible intermediates relevant to hydrophosphination. Reagents, intermediates, products, and by-products involved in the [2+2] cycloaddition were identified and analyzed for reactivity and stability. The products, metallacycles of the form [Ru(η5-indenyl)(κ2-RCHCH2PCy2)(PPh3)] (4), were found to undergo facile cycloreversion. An ethylene η2-coordination adduct was directly observed by low temperature 31P{1H} NMR as an intermediate in the [2+2] cycloaddition mechanism. Steric and electronic effects of alkene substituents on metallacycle formation and selectivity were investigated in detail through rate constant and activation parameter determination, as well as collaborative computational DFT analyses and the construction of a Hammett plot. Preliminary attempts at releasing phosphinated products from ruthenacycle complexes via protonolysis and phosphine substitution were conducted. An unexpected metallacyclic product of one of these attempts, [Ru(η5-indenyl)(κ2-CHCHPCy2)(PPh3)] (10), was identified and characterized.
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Keywords
cycloaddition, metallacycles, ruthenium, P ligands, hydrophosphination