Degree Name

Master of Science (MS)

Semester of Degree Completion

2000

Thesis Director

Richard L. Keiter

Abstract

Unsymmetrical diphosphine tungsten complexes, (CO)5W[η1-PPh2CH2P(p-tol)2] and (CO)5W[η1-P(p-tol)2CH2PPh2], were prepared from (CO)5W(NH2Ph) and Ph2PCH2P(p-tol)2. Two approaches were successfully used to synthesize Ph2PCH2P(p-tol)2. The first utilized PPh2CH2Cl, prepared from PPh2H, CH2Cl2, and KOH under phase transfer conditions, from which Ph2PCH2P(p-tol)2 was synthesized by reaction of the intermediate with LiP(p-tol)2. The second approach for the synthesis of PPh2CH2P(p-tol)2 was based on the reaction of PPh2CH2SiMe3 with ClP(p-tol)2. The starting materials, PPh2CH2SiMe3 and ClP(p-tol)2, were made from HPPh2 and Me3SiCH2Cl in the presence of NaNH2/NH3, and from HOP(p-tol)2 and PCl3. The isomerization of (CO)5W[η1-PPh2CH2P(p-tol)2] and (CO)5W[η1-P(p-tol)2CH2PPh2] at different temperatures (328 K, 313 K, 298 K) was monitored by 31P{1H} NMR spectroscopy. The rate constants k1, k-1, half-lives to equilibrium and the equilbrium constants at 328 K, 313 K, and 298 K were determined. The isomerization rates are about 100 times slower than those of (OC)5W[η1-Ph2PCH2CH2-P(p-tol)2]. The data support the idea that an interaction between the short dangling phosphine arm and the cis carbonyl groups stabilizes the transition state and accelerates isomerization. The synthesis of (OC)5W[η1-Ph2PCH2CH(PPh2)(P{p-tol}2) and its linkage isomers was unsuccessful. The most promising approach for synthesis of Ph2PCH2-CH(PPh2)P(p-tol)2 appeared to be through nucleophilic addition of HP(p-tol)2 to cis-(Ph2P)CH=CH(PPh2). However, in the presence of base, HP(p-tol)2 reacts with cis-(Ph2P)CH=CH(PPh2) to produce not only Ph2PCH2CH(PPh2)P(p-tol)2, but also many by-products that are difficult to remove from the desired product.

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