Novel Anionic Heterocyclic Thiolate Complexes of Group VIB Metal Carbonyls: Synthesis and Reactivity

Abstract

The syntheses and characterization of novel Group VIB metal carbonyl complexes containing heterocyclic thiolate ligands is described. The reactions of the photogenerated intermediate, M(CO) 5 THF (M = W, Mo, Cr), with the thiolate anions RS À in [(n-Bu) 4 N][SR] [SR À = 2mercaptobenzimidazolyl (a), 2-mercaptobenzothiazolyl (b), 2-mercaptobenzoxazolyl (c)], afforded exclusively [(n-Bu) 4 N][M(CO) 5 SR] in fairly good yields. Homo-and heterobimetallic complexes of the type [(n-Bu) 4 N][M(CO) 5 (m-SR)M'(CO) 5 ] (M, M' = W, Mo, Cr), in which both the exocyclic S-atom and the endocyclic N-atom are involved in coordination to two metal centers, have been prepared by the reaction of [(n-Bu) 4 N][M(CO) 5 SR] with M'(CO) 5 ÁTHF at ambient temperatures. The methods of preparation and characterization of these complexes are described. CO-substitution reactions in [(n-Bu) 4 N][W(CO) 5 SR] [SR À = (b) and (c)] with tri(iso-propyl)phosphite (L) afforded the complexes [(n-Bu) 4 N][cis-W(CO) 4 (SR){P(OPr-i) 3 }] as the sole reaction product.The kinetics of CO dissociation from the pentacarbonyl anions under pseudo-first-order conditions confirm that these reactions are firstorder in substrate and independent of the entering group (L) concentration. The facile CO dissociation in these complexes is another example of neighboring-group participation in assisting cis-CO loss in octahedral metal carbonyls. From the kinetics data, the anionic ligands (b) and (c) are classified as cis-CO labilizing groups. Rate constants and activation parameters for the CO-substitution reactions in these complexes are reported.

A Combined Patch-Clamp and Electrorotation Study of the Voltage- and Frequency-Dependent Membrane Capacitance Caused by Structurally Dissimilar Lipophilic Anions

“…The synthesis of the tetrabutylammonium salts of WO − , WN − and WS − by a somewhat different route has been recently described by Asali, El-Khateeb & Battaineh ( 2003 ). These authors assumed that the heterocycles are coordinated to the W(CO) 5 unit through the sulfur atom.…”