Degree Name

Master of Science (MS)

Semester of Degree Completion

2003

Thesis Director

Richard L. Keiter

Abstract

Di(p-tol)phosphido-bridged complexes, (OC)4M[μ-P(p-tol)2]2M(CO)4 (M = Mo, W), have been synthesized for the first time. These have been obtained from the reaction of (OC)5MP(p-tol)2H with BuLi, followed by air oxidation. The choice of solvent is very important as the intermediate anion, [(OC)5MP(p-tol)2] is unstable in THF. An ideal solvent for these preparations is CH3OCH2CH2OCH3 (monoglyme) from which yields of 68% and 76% were realized for the tungsten and molybdenum complexes, respectively.

Reaction of (OC)4M[μ-P(p-tol)2]2M(CO)4 with Ph2PC≡CPPh2 or trans-Ph2PCH=CHPPh2 led to the loss of CO and formation of tetrametallic complexes, (OC)4M[μ-P(p-tol)2]2M(CO)3(μ-PPh2C≡CPPh2)(OC)3M[μ-P(p-tol)2]2M(CO)4 and (OC)4M[μ-P(p-tol)2]2M(CO)3(μ-trans-PPh2CH=CHPPh2)(OC)3M[μ-P(p-tol)2]2M(CO)4 in which two dimetallic units are bridged by the ditertiary phosphine. These complexes, which may be thought of as precursors for molecular wires, were characterized by IR, 31P{1H} NMR, and cyclic voltammetry.

Oxidation of the tetrametallic complexes occurs in two steps indicating that electronic communication between the dimetallic units and through the ditertiary phosphine bridging ligand takes place. The difference in potential between the two steps was small for both tetrameric complexes, 0.12 and 0.09 volts for Ph2PC≡CPPh2 and trans-PPh2CH=CHPPh2 complexes, respectively. Furthermore, a comparison of the difference in potential for P(p-tol)2 and PPh2 bridged complexes linked by Ph2PC≡CPPh2 indicates that there is very little difference between the two, 0.12 and 0.11 volts, respectively.

Attempts to prepare tetrametallic complexes in which Ph2PCH2CH2PPh2 bridges the two dimetallic units were unsuccessful. The reaction of (OC)4W(μ-PPh2)2W(CO)3PPh2H and (OC)4W(μ-PPh2)2W(CO)3PPh2CH=CH2 in the presence of base did not lead to the desired complex, but rather a mixture of (OC)4W(μ-PPh2)2W(CO)4 and (OC)4W(μ-PPh2)2W(CO)2(κ2-PPh2CH2CH2PPh2). The ditertiary phosphine in the latter complex is present as a chelating ligand.

Attempts were made to separate cis and trans isomers of (HPPh2)(OC)3W(μ-PPh2)2W(CO)3(PPh2H) but were unsuccessful.

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