Syntheses, characterisation, and catalytic role of (η5-C5Me5)Rh(iii) guanidinato complexes in transfer hydrogenation (TH) and TH–etherification. Issue 54 (5th July 2017)

• Record Type: Journal Article
• Authors: Kumar, Robin; Thirupathi, Natesan
• Is Part Of: RSC advances. Volume 7:Issue 54(2017)
• Page Start: 33890
• Page End: 33904
• Publication Date: 2017-07-05
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7ra04152g
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Complex3 has been synthesised and its catalytic activity in base assisted and base free transfer hydrogenation (TH) of a variety of carbonyl compounds and TH–etherification of substrates such as 2-hydroxy-1-naphthaldehyde have been achieved. Abstract : A family of air stable half sandwich meal guanidinato complexes ([(η 5 -Cp*)MCl{κ 2 ( N, N ′)((ArN)2 C–N(H)Ar)}]) (M = Rh and Ir; Cp* = C5 Me5 ; Ar = aryl) were synthesized in good yield and characterised by elemental analyses, IR, and NMR ( 1 H, 13 C, and 19 F) spectroscopy. The geometry of the metal and the conformations of the guanidinate ligands in the complexes were studied by single crystal X-ray diffraction. The solution behaviour of representative complexes was investigated by detailed NMR studies including variable temperature and variable concentration 1 H NMR measurements. The new complexes were screened as catalysts for transfer hydrogenation (TH) of acetophenone under basic and base free conditions and from these experiments, ([(η 5 -Cp*)RhCl{κ 2 ( N, N ′)((ArN)2 C–N(H)Ar)}]) (Ar = 3, 5-(CF3 )2 C6 H3 ;3 ) was chosen as the preferred catalyst due to its slightly better catalytic activity than other complexes. The utility of3 in TH of a variety of carbonyl compounds was explored under basic and base free conditions. Tandem catalysis involving TH of a carbonyl group and etherification of the resulting –CH2 OH group in reduction products of salicylaldehyde, 2-hydroxy-1-naphthaldehyde and 5-(hydroxymethyl)furfural was achieved in the presence of3 under base free conditions. The role of the guanidinate ligands in the complexes for basic and base free TH of carbonyl compounds and TH–etherification tandem catalysis is discussed. Plausible mechanisms for TH and TH–etherification are outlined.