Transition Metal Catalysis

Experiment 5: Transition Metal Catalysis

1. Introduction

This experiment aims to give transition metal palladium catalyst for diarylacetylenes synthesis. In general, the procedures constitute of 2 steps: the synthesis of catalyst precursor for dynamical species Pd(PPh3)4 and the preparation of alkyne.

Bases on the previous studies, there are two well-known reactions to synthesize diarylacetylenes.

The first method discovered by Castro involves the use of copper acetylides. These reagents are prepared by discourse of an aqueous ammonia ascendent of cuprous iodide with an fermentation alcohol solution of monosubstituted aryl acetylenes. (eq.1)

(1)

The cuprous acetylides are because treated with aryl iodides in refluxing pyridine under nitrogen atmosphere to stoichiometrically generate diaryl acetylenes.
(eq. 2)

(2)

By using amines as solvents and CuI as a co-catalyst, the method was improved to enable introducing alkyl group substitutent to the triple bond at room temperature.

The second method, which was use in this experiment, was introduced by Cassar and Heck by utilizing palladium colonial to turn the reaction.
(eq. 3)


(3)


2. Experimental Section

2.



1The Catalytic Precursor Preparation
A mixture of palladous chloride (0.0384 g, 0.216 mmol) and sodium chloride (0.0303 g, 0.518 mmol) in water (1.5 ml) was stirred and warmed to about 50ºC. The solution was allowed to cool down. A solution of triphenylphosphine (0.1280 g, 0.488 mmol) in ethanol (20 ml) was then prepared. The palladous chloride solution was added dropwise to the triphenylphosphine solution and stirred simultaneously. The resultant slurry was then warmed to about 50ºC over 30 transactions to coagulate the precipitate. The mixture was cooled, filtered, and washed with water, acetone, and ether. The product was dried-out in a 50ºC oven for 3 minutes to finally generate yellow solid palladium complex product (0.1302 g, 86%).

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