From: Andre Rebelo
Department of Chemistry
Chem 342L Advanced Inorganic Chemistry Date: March 2015 CC:
Experiment 4: Synthesis of P h2CH 2CH 2Ph2 in Liquid Ammonia and H and P NMR and Melting Point
In this experiment, the preparation of a solution containing solvated electrons is achieved by dissolving sodium metal (2.3g, 0.1 mol) in liquid ammonia. This sodiumammonia solution was used to induce the reductive cleavage of a phenyl group from triphenylphosphine to form sodium diphenylphosphide, which under our reaction conditions will precipitate from the solution as a yellow solid. Further additions of 1,2dichloroethane produces
1,2bis(diphenylphosphino)ethane. The synthesized compound can act as a chelating bidentate ligand and be used in organometallic chemistry to stabilize lowvalent transitionmetal centres.
The verification of formation was conducted by taking a melting point and NMR ( H ). The literature value states1,2bis(diphenylphosphino)ethane melts at 137142 C. The synthesized product (shiney white crystal solid) had a melting point range of 139142 C strongly indicating the formation of dppe. Roughly, 0.169 g of 1,2bis(diphenylphosphino)ethane was formed correlating to a percent yield of 0.4 %. Of course, additional data was need and thus, the NMR taken present show peaks at 1.3 ppm, 2.3 ppm and 7.18.0 ppm, which is the necessary evidence to prove the formation of 1,2bis(diphenylphosphino)ethane. Introduction: In chemical laboratories, liquid ammonia can extensively be utilized as a nonaqueous solvent, as a medium for reductions. Since, liquid ammonia contains hydrogen bonding interactions it will have unusual properties that allow it to dissolve compounds not readily soluble in water. Anhydrous liquid ammonia, for example has the chemical properties to dissolve certain high reducing metals including alkali, alkaline and lanthanide metals. The addition of electropositive metals to liquid NH3 creates a deep blue color characteristic of solvated electrons. It is important to mention at high concentration of electropositive metals such as sodium a color change can occur from deep blue to a bronze brought out by the solvent electrons. In a reaction with sodium metal any indication of transformation of reagents is apparent when the intense blue color disappears. In our experiment, sodium metal is used along with liquid ammonia to create a sodiumammonia solution to acts as a strong reducing agent to add two electrons to triphenylphosphine. In that process of moving electrons a cleavage occurs between a C − P bond in triphenylphosphine producing sodium diphenylphosphide by which a reaction with 1,2dichloroethane synthesizes 1,2Bis(diphenylphosphino)ethane. The reaction sequence can be seen below in figure one.
Figure 1: Reaction Scheme: 1 Formation of SodiumAmmonia Solution: Na(s) + NH3(L) → N aNH2 + H2 Used as a reducing agent to add two electrons to triphenylphosphine. Intense deep blue solution. 2. Cleavage of Carbon Phosphorus Bond: P (C6H5)3 + 2Na → NaP(C6H5)2 + NaC6H5
N aC6H5 conjuga te base of benzene quickly deprotonates ammonia to N aNH2 must be neutralized. via N H4Br forming a sodium salt and additional liquid ammonia color change occurs: Deep blue to an intense redorange.
Color fluctuates to a bronzered orange orange
N aP(C6H5)2 Product Two
Yellow carney salt
Soluble in polar solvents. (dichloromethane) 3. Addition of 1,2Dichloroethane 2NaP(C6H5)2 + C2H2Cl2 → (C6H5)2PCH2CH2P(C6H5)2
In conducting the experiment, we hope to gain familiarity with the nonaqueous solvents and bidentate ligands. In addition, familiarity in laboratory techniques