Synthesis of monomercurated N-protected pyrroles and the use of these compounds as pyrrolyl group transfer reagents to ruthenium and osmium. Crystal structures of (2-C 4H 3NC[O]CH 3)HgCl, (2-C 4H 3NC[O]CH 3) 2 Hg and

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N-Acetylpyrrole and N-phenylsulfonylpyrrole are each selectively mercurated in the 2-position on treatment with mercuric chloride. The resulting organomercuric chlorides are symmetrized to the corresponding diorganomercury derivatives (2-C 4H 3NC[O]CH 3) 2Hg ( 2) and (2-C 4H 3NSO[O]Ph) 2Hg ( 4) by the action of sodium iodide. The crystal structures of (2-C 4H 3NC[O]CH 3HgCl ( 1) and (2-C 4H 3NC[O]CH 3) 2Hg ( 2) have been determined. The acetyl oxygen atom interacts weakly with the mercury centre in both cases, but more strongly in 1 than 2. Treatment of the hydrido complexes MHCl(CO)(PPh 3) 3 (M  Ru, Os) with the diorganomercurial 2 or 4 affords in good yield the 2-pyrrolyl complexes ▪ CH 3)Cl(CO)(PPh 3) 2 or ▪, respectively. In each case the pyrrolyl group is coordinated in a bidentate fashion through C-2 and an oxygen atom of the N-substituent. The chloride ion in ▪ ▪( 7) is labile, and upon treatment with AgSbF 6 and CO, the cationic complex ▪ ▪ is formed. Treatment of 7 with AgSbF 6 and sodium dimethyldithiocarbamate gives the neutral monophosphine complex ▪ ( 10), the crystal structure of which has been determined.