Oxygenation of Ruthenium Carbene Complexes Containing Naphthothiophene or Naphthofuran: Spectroscopic and DFT Studies. Issue 11 (8th August 2013)

• Record Type: Journal Article
• Authors: Tsai, Fu‐Yuan; Lo, Ji‐Xian; Hsu, Hsin‐Tzu; Lin, Ying‐Chih; Huang, Shou‐Ling; Wang, Ju‐Chun; Liu, Yi‐Hong
• Is Part Of: Chemistry, an Asian journal. Volume 8:Issue 11(2013:Nov.)
• Page Start: 2833
• Page End: 2842
• Publication Date: 2013-08-08
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201300726
• Languages: English
• ISSNs: 1861-4728

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The aryl propargylic alcohol 1‐[2‐(thiophen‐3‐yl)phenyl]prop‐2‐yn‐1‐ol (<bold>1a</bold>) is readily prepared from 2‐(thiophen‐3‐yl)benzaldehyde. In the presence of visible light, treatment of <bold>1a</bold> with one‐half mole equivalent of [Ru]Cl ([Ru]Cp(dppe)Ru) (dppe=1, 2‐bis(diphenylphosphino)ethane) and NH<sub>4</sub>PF<sub>6</sub> in O<sub>2</sub> affords the naphtha[2, 1‐<italic>b</italic>]thiophene‐4‐carbaldehyde (<bold>4a</bold>) in high yields. The <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">cyclization</named-content> reaction of <bold>1a</bold> proceeds through the formation of the carbene complex <bold>2a</bold> that contains the naphtha[2, 1‐<italic>b</italic>]thiophene ring, which is isolated in a 1:1 stoichiometric reaction. The CC bond formation between the inner carbon of the terminal triple bond and the heterocyclic ring is confirmed by <named-content content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">structure determination</named-content> of <bold>2a</bold> using single‐crystal X‐ray diffraction analysis. Facile <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">oxygenation</named-content> of <bold>2a</bold> by O<sub>2</sub> yields the aldehyde product <bold>4a</bold> accompanied by the formation of phosphine oxide of dppe. Oxygen is most likely activated by coordination to the ruthenium center when one PPh<sub>2</sub> unit of the dppe ligand dissociates. This dissociated PPh<sub>2</sub> unit then reacts with the coordinated oxygen nearby to generate half‐oxidized dppe ligand and an unobserved oxo–carbene <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">intermediate</named-content>. Coupling of the oxo/carbene ligands followed by <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">demetalation</named-content> then yields <bold>4a</bold>. Presumably the resulting complex with the half‐oxidized dppe ligand continuously promotes cyclization/oxygenation of <bold>1a</bold> to yield the second aldehyde molecule. In alcohol such as MeOH or EtOH, the <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">oxygenation</named-content> reaction affords a mixture of <bold>4a</bold> and the corresponding esters <bold>5a</bold> or <bold>5a'</bold>. Four other aryl propargylic alcohols <bold>1b</bold>, <bold>1c</bold>, <bold>1d</bold>, <bold>1e</bold>, which contain thiophen‐2‐yl, isopropenyl, fur‐3‐yl, and fur‐2‐yl, respectively, on the aryl ring are also prepared. Analogous aldehydes <bold>4b</bold>, <bold>4c</bold>, <bold>4d</bold>, <bold>4e</bold> are similarly prepared from <bold>1b</bold>, <bold>1c</bold>, <bold>1d</bold>, <bold>1e</bold>, respectively. For oxygenations of <bold>1b</bold>, <bold>1d</bold>, and <bold>1e</bold> in alcohol, mixtures of aldehyde <bold>4</bold>, ester <bold>5</bold>, and acetal <bold>8</bold> are obtained. The carbene complex <bold>2b</bold> obtained from <bold>1b</bold> was also characterized by single‐crystal X‐ray diffraction analysis. The UV/Vis spectra of <bold>2a</bold> and <bold>2b</bold> consist of absorption bands with a high extinction coefficient. From DFT calculations on <bold>2a</bold> and <bold>2b</bold>, the visible light is found to populate the LUMO antibonding orbital of mainly RuC bonds, thereby weakening the RuC bond and promoting the oxygenation/demetalation reactions of <bold>2</bold>.</p> </abstract>