Functionalizing Heterocycles by Electron-Deficient Bonding to a Triosmium Cluster

Abstract

A new synthetic methodology for adding carbon-based nucleophiles to the carbocyclic ring of quinolines has been developed, based on the electron-deficient bonding of the C(8) carbon and the protective coordination of the nitrogen atom to the metal core in the complexes Os 3 (CO) 9 (µ 3 -η 2 -C 9 H 5 (R)N)(µ-H), 1a-1h. These compounds react with a wide range of carbanions (e.g., R′Li) to give the nucleophilic addition products Os 3 (CO) 9 (µ 3 -η 3 -C 9 H 7 (5-R′)N)(µ-H), 2a-2l, and Os 3 (CO) 9 (µ 3 -η 3 -C 9 H 6 (3-, 4-, or 6-R)(5-R′)N)(µ-H), 3b-3g, after quenching with trifluoroacetic acid, in isolated yields of 25-86%. In the 6-substituted derivatives, this addition is stereoselective, forming only the cis-diastereomer. In the case the 6-chloro derivative, a second product is obtained, Os 3 (CO) 9 (µ 3 -η 2 -C 9 H 5 (6-Cl)(5-C(CH 3 ) 2 CN)N)(µ-H) 2 , 4, the result of protonation at the metal core and rearrangement of the carbocyclic ring. The trans-diastereomer of the 6-substituted derivatives can be obtained by quenching the intermediate anion of the unsubstituted complex with (CH 3 O) 2 SO 2 or acetic anhydride. Nucleophilic addition to the 5-chloro complex occurs across the 3,4-bond to give Os 3 (CO) 9 (µ 3η 2 -C 9 H 6 (5-Cl)(4-C(CH 3 ) 2 CN)N)(µ-H), 5. The addition products, types 2 and 3, can be rearomatized by reaction with diazobicyclononane (DBU)/dichlorodicyanoquinone (DDQ) or by reaction of the intermediate anion with trityl cation or DDQ. The resulting rearomatized complexes can be cleanly cleaved from the cluster by heating in acetonitrile under a CO atmosphere, yielding the functionalized quinoline and Os 3 (CO) 12 as the only two products. Solid structures of cis-3e, trans-3e, 4, and 5 are reported.

Spectroscopic and Computational Investigations of Stable Radical Anions of Triosmium Benzoheterocycle Clusters

“…[6] Nevertheless, in the case of the phenanthridine and 5,6-benzoquinoline complexes, 1 and 2, respectively, very stable radical anions are obtained [Eqs. (3) and (4)]. …”

Cationic Heterocycles as Ligands: Synthesis and Reactivity with Anionic Nucleophiles of Cationic Triruthenium Clusters Containing C‐Metalated N‐Methylquinoxalinium or N‐Methylpyrazinium Ligands

“…[24] It has been shown that coordinatively unsaturated triosmium clusters that have neutral N-heterocyclic bridging ligands undergo addition of anionic carbon nucleophiles at a C atom of the bridging ligand, [25] but that chemistry has no parallel in ruthenium cluster chemistry.…”

Cluster-mediated alkenyl isomerism and carbon–carbon bond formation: The reaction of the unsaturated benzothiazole cluster [Os3(CO)9(μ3-C7H4NS)(μ-H)] with dimethyl acetylenedicarboxylate

“…The benzoheterocyclic clusters [Os 3 (CO) 9 (l 3 -benzoheterocycle)(l-H)] represent further examples of unsaturated 46-electron triosmium hydride complexes and over the past 10 years they have been shown to show to be reactive towards a wide range of substrates [10][11][12][13][14][15][16][17]. We have now investigated the reaction of one of these complexes, namely [Os 3 (CO) 9 (l 3 -C 7 H 4 NS)(l-H)] (1) [10], towards the activated alkyne dmad.…”