Half-sandwich complexes of osmium containing guanidine-derived ligands. Issue 39 (25th September 2020)

• Record Type: Journal Article
• Authors: Parker, Amie; Lamata, Pilar; Viguri, Fernando; Rodríguez, Ricardo; López, José A.; Lahoz, Fernando J.; García-Orduña, Pilar; Carmona, Daniel
• Is Part Of: Dalton transactions. Volume 49:Issue 39(2020)
• Page Start: 13601
• Page End: 13617
• Publication Date: 2020-09-25
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt02713h
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : The osmium chemistry of guanidine derivatives is explored. The resulting complexes are active Brønsted-acid catalysts for the Friedel–Crafts reaction. Abstract : Pyridinyl- and phosphano-guanidino complexes of formula [(η 6 - p -cymene)OsCl(H2 L )][SbF6 ] (cymene = MeC6 H4 iPr; H2 L = N, N ′-bis( p -Tolyl)- N ′′-(2-pyridinylmethyl)guanidine, H2 L1 (1 ) and N, N ′-bis( p -Tolyl)- N ′′-(2-diphenylphosphanoethyl)guanidine, H2 L2 (2 )) have been prepared from the dimer [{(η 6 - p -cymene)OsCl}2 (μ-Cl)2 ] and H2 L in the presence of NaSbF6 . Treatment of complex 2 with HCl renders the phosphano–guanidinium complex [(η 6 - p -cymene)OsCl2 (H3 L2 )][SbF6 ] (3 ). Compounds 1 and 2 react with AgSbF6 rendering the cationic aqua complexes [(η 6 - p -cymene)Os(H2 L )(OH2 )][SbF6 ]2 (H2 L = H2 L1 (4 ), H2 L2 (5 )). Addition of monodentate ligands L to compound 4 affords complexes of formula [(η 6 - p -cymene)Os(H2 L1 )L ][SbF6 ]2 (L = py (6 ), 4-(NHMe)py (7 ), CO (8 ), P(OMe)3 (9 )). Treatment of complexes 4 and 5 with NaHCO3 renders the monocationic complexes [(η 6 - p -cymene)Os(κ 3 N, N ′, N ′′-HL1 )][SbF6 ] (10 ) and [(η 6 - p -cymene)Os(κ 3 N, N ′, P -HL2 )][SbF6 ] (11 ), respectively, in which the HL ligand adopts a fac -κ 3 coordination mode. The new complexes have been characterised by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1–4, 6, 8, and 11, by X-ray diffractometric methods. The phosphano–guanidino complexes 2 and 5 exhibit a temperature dependent fluxional process in solution. The new 18 electron complexes 1, 2, 6, and 8–10 are active catalysts for the Friedel–Crafts reaction between trans -β-nitrostyrene and N -methyl-2-methylindole. Conversions greater than 90% were obtained. Proton NMR studies support a mechanism involving the Brønsted-acid activation of trans -β-nitrostyrene through the NH functionalities of the coordinated guanidine ligands.