Publications (4)6.05 Total impact
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Article: The Remote Activation of Chemical Bonds via Metal Coordination
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ABSTRACT: The activation of chemical bonds to cleavage by mild metal nucleophiles can be achieved by precoordination of a transition metal fragment to a site remote from the bond in question. The following bonds have been activated in this manner by η6-coordination to an internal arene ring: CC in biphenylene, CS in benzothiophene and dibenzothiophene, CSe in benzoselenophene, CO in benzofuran, and NH in indole.Advanced Synthesis & Catalysis 08/2003; 345(9‐10):1053 - 1060. · 6.05 Impact Factor -
Article: Models for Deep Hydrodesulfurization of Alkylated Benzothiophenes. Reductive Cleavage of C−S Bonds Mediated by Precoordination of Manganese Tricarbonyl to the Carbocyclic Ring
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ABSTRACT: The reduction of (η6-benzothiophene)Mn(CO)3+ with cobaltocene under CO leads to insertion of the Mn(CO)4- fragment into the C(aryl)−S bond to afford a neutral bimetallic complex. When there are methyl substituents at the 2,3-, 2,7-, or 3,7-positions, the regioselectivity and product distribution in the reductive insertion reactions are significantly affected, and several new types of complexes are formed. Low-temperature chemical reduction of (η6-benzothiophene)Mn(CO)3+ complexes affords unstable η4-species, (η4-BT)Mn(CO)3-, which do not react with the η6-cation to give insertion products. Similarly, electrochemical reduction of (η6-benzothiophene)Mn(CO)3+ changes from a one-electron chemically irreversible process at room temperature to a two-electron chemically reversible but electrochemically irreversible process at −90 °C. It is concluded from these results that the room-temperature reductive cleavage of a C−S bond in (η6-benzothiophene)Mn(CO)3+ occurs by a radical mechanism. Crystallographic data and density function theory (DFT) calculations indicate that insertion into the C(aryl)−S and not the C(vinyl)−S bond of (η6-benzothiophene)Mn(CO)3+ is favored. A redetermination of the crystal structure of the η1-S complex (η1-3-MeBT)Re(Cp*)(CO)2 revealed that the C(aryl)−S and C(vinyl)−S bonds are of similar lengths, suggesting that an η1-S intermediate is not predisposed to insert into the latter bond, as was previously thought. DFT calculations of (η6-BT)Mn(CO)3+ bonded in an η1-S fashion to Mn(CO)4- indicated that an intermediate of this sort is viable in the C−S insertion reactions.02/2002; -
Article: Models for Deep Hydrodesulfurization (HDS). Remote Activation of C−S Bonds in Alkylated Benzothiophenes and Dibenzothiophenes by Metal Coordination to a Carbocyclic Ring
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ABSTRACT: A series of alkylated benzothiophene and dibenzothiophene complexes containing a manganese tricarbonyl moiety coordinated to a carbocyclic ring have been synthesized. Reaction of these with the mild nucleophile Pt(PPh3)2(C2H4) leads to rapid room-temperature insertion of Pt(PPh3)2 into a C−S bond to afford metallathiacyclic complexes. With benzothiophene complexes bearing no substitutent at the 2- or at the 3-position, it is shown that initial rapid coordination of the platinum to the CC bond in the heterocyclic ring takes place prior to insertion into the C(vinyl)−S bond. When a substituent is present at the benzothiophene 2- and/or 3-position, formation of the η2-(CC) intermediate is blocked, the reaction rate slows, and insertion into the C(aryl)−S bond becomes possible or even dominant. An η1-S intermediate is suggested in these cases. Insertion into the C−S bond nearer the coordinated ring in dibenzothiophene complexes, even ones alkylated at the 4- and/or 6-positions, occurs rapidly at rates similar to those found for alkylated benzothiphene complexes. Even the normally intractable 4,6-Me2DBT is “remotely activated” to rapid C−S bond cleavage by Pt(PPh3)2 when precoordinated to the Mn(CO)3+ moiety. On the basis of observed regioselectivities, low-temperature infrared studies, and room-temperature stopped-flow kinetics, a mechanism is proposed for the insertion of platinum into precoordinated benzothiophenes and dibenzothiophenes. The palladium complex Pd(PPh3)2(C2H4) is capable of inserting into C−C, C−S, and C−Se bonds in coordinated biphenylene, thiophenes, and selenophenes. The X-ray structure of the biphenylene insertion product is reported. It is concluded that the metallacycles formed from Pd(PPh3)2(C2H4) are in general not as rapidly formed or as stable as those obtained with Pt(PPh3)2(C2H4). X-ray structures are reported for (η5-selenophene)Mn(CO)3+ and its Pt(PPh3)2 insertion product.07/2001; -
Article: The Remote Activation of Chemical Bonds via Metal Coordination
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ABSTRACT: The activation of chemical bonds to cleav-age by mild metal nucleophiles can be achieved by precoordination of a transition metal fragment to a site remote from the bond in question.
