Date of Award

1982

Document Type

Dissertation - Pacific Access Restricted

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Graduate School

First Advisor

Patrick R. Jones

First Committee Member

Herschel Frye

Second Committee Member

Donald K. Wedegaertner

Third Committee Member

Silvio Rodriguez

Fourth Committee Member

Andres F. Rodriguez

Abstract

A series of monosubstituted tungsten(0)pentacarbonyl complexes, W(CO)5L (L = water, hydrogen sulfide, pyrazine, pyrimidine, 4,4'-bipyridine, 4-cyanopyridine, isonicotinamide, and methanol) were synthesized and characterized. The purpose of this project was to determine the effect of the W(CO)5 moiety on the coordinated ligand, L.

The visible spectra of the synthesized W(CO)5L complexes typically exhibited a maximum around 400 nm ((epsilon) (TURN) 4000). The infrared spectra of these complexes exhibited the characteristic three band pattern (2A1 + E) in the carbonyl region ((TURN)2070 cm-1, (TURN)1930 cm-1, (TURN)1900 cm-1. The pKa's of the ligands coordinated to the W(CO)5 moiety were determined. When the ligand was basic, the pKa of the ligand's conjugate acid was determined. The pKa's of water changed from 15.8 to 4.8 upon coordination. The rest of the ligand pKa's changed in a similar fashion upon coordination; from 0.6 to -0.4 for coordinated pyrazine; from 1.3 to -0.4 for coordinated pyrimidine; from 1.9 to -0.3 for coordinated 4-cyanopyridine; and from 4.8 to -0.7 for coordinated 4,4'-bipyridine. The effect of the W(CO)5 moiety on coordinated ligands is to make the ligands more acidic. This result is explained by the presence of strong (pi)-back bonding between tungsten and the carbonyls.

The methanoltungsten(0)pentacarbonyl complex was very labile at room temperature in the presence of acetonitrile. The substitution reaction followed the rate law -d{complex}/dt = k(,1){complex} + k(,2){CH(,3)CN}{complex}. At 24.6(DEGREES)C, k(,1) = 1.4 x 10('-3) sec('-1) and k(,2) = 3.6 x 10('-2) M('-1)sec('-1). The activation parameters were calculated: (DELTA)H(,1)('(DAG)) = 9 kcal/mole; (DELTA)S(,1)('(DAG)) = -42 eu; (DELTA)H(,2)('(DAG)) = 9 kcal/mole; and (DELTA)S(,2)('(DAG)) = -34 eu.

Since the substitution of methanol occurs so readily at room temperature, W(CO)5 (methanol) should be very useful as a synthetic intermediate. The use of this complex would avoid the problems involved in direct synthesis of W(CO)5L complexes such as disubstituted products or bridged binuclear complexes.

Pages

121

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