Preparation of a Vaska-Type Rhodium Complex

S. N. Hartley, 2010030670

07 August 2014

CEM324

EXPERIMENT 10

Synthesis of a Tertiary Phosphine and a Vaska-type Rhodium Complex

1. Introduction

In this experiment a tertiary phosphine (triphenylphosphine) will be synthesised using a Grignard reagent and chlorodiphenylphosphine. Following this, a Vaska-type rhodium complex will be prepared using the tertiary phosphine. The experiment is done in a completely anhydrous and inert condition to ensure no oxygen or other combustible compounds are present during the synthesis. Magnesium turnings, Mg(0), will need to be completely dissolved into its Mg(II) form before it can become reactive and form the Grignard reagent. In Figure 1 the formation of the Grignard reagent and the tertiary phosphine is shown. The Grignard complex not only provides another phenyl ring but also lowers the activation energy required for the formation of the tertiary phosphine. 1

Figure 1: Synthesis of a tertiary phosphine.

1

The product formed will be the tertiary phosphine as well as an inorganic salt. The products can then be separated using a separation funnel with both an organic and inorganic solvent. During the synthesis of the Vaska-type rhodium complex a bridged chloro-dimer will form. This formation is important because it alters the oxidation state of rhodium to Rh(III) to Rh(I). This will allow rhodium four available bonds instead of just three as shown in Figure 2.1

Figure 2: Synthesis of a Vaska-type rhodium complex The tetracarbonyldichlororhodium(I) complex will then react with the tertiary phosphine to form the Vaska-type rhodium complex. Tetracarbonyldichlororhodium(I) will break in two at one of the shared chlorine sites, this will produce an empty bond that will be filled by the tertiary phosphine. A high electron density at the rhodium atom will cause the carbonyl rhodium bond to donate electrons towards the double bond forming carbon monoxide gas.

2. Experimental Method

Synthesis of a...