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Intervalent Bis(μ‐aziridinato)M II M I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?
Author(s) -
Tejel Cristina,
Ciriano Miguel A.,
Passarelli Vincenzo,
López José A.,
de Bruin Bas
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801615
Subject(s) - delocalized electron , radical , chemistry , electron delocalization , photochemistry , organic chemistry
Reactions of the methoxo complexes [{M(μ‐OMe)(cod)} 2 ] (cod=1,5‐cyclooctadiene, M=Rh, Ir) with 2,2‐dimethylaziridine (Haz) give the mixed‐bridged complexes [{M 2 (μ‐az)(μ‐OMe)(cod) 2 }] [(M=Rh, 1 ; M=Ir, 2 ). These compounds are isolated intermediates in the stereospecific synthesis of the amido‐bridged complexes [{M(μ‐az)(cod)} 2 ] (M=Rh, 3 ; M=Ir, 4 ). The electrochemical behavior of 3 and 4 in CH 2 Cl 2 and CH 3 CN is greatly influenced by the solvent. On a preparative scale, the chemical oxidation of 3 and 4 with [FeCp 2 ] + gives the paramagnetic cationic species [{M(μ‐az)(cod)} 2 ] + (M=Rh, [ 3 ] + ; M=Ir, [ 4 ] + ). The Rh complex [ 3 ] + is stable in dichloromethane, whereas the Ir complex [ 4 ] + transforms slowly, but quantitatively, into a 1:1 mixture of the allyl compound [(η 3 ,η 2 ‐C 8 H 11 )Ir(μ‐az) 2 Ir(cod)] ([ 5 ] + ) and the hydride compound [(cod)(H)Ir(μ‐az) 2 Ir(cod)] ([ 6 ] + ). Addition of small amounts of acetonitrile to dichloromethane solutions of [ 3 ] + and [ 4 ] + triggers a fast disproportionation reaction in both cases to produce equimolecular amounts of the starting materials 3 and 4 and metalmetal bonded M II M II species. These new compounds are isolated by oxidation of 3 and 4 with [FeCp 2 ] + in acetonitrile as the mixed‐ligand complexes [(MeCN) 3 M(μ‐az) 2 M(NCMe)(cod)](PF 6 ) 2 (M=Rh, [ 8 ] 2+ ; M=Ir, [ 9 ] 2+ ). The electronic structures of [ 3 ] + and [ 4 ] + have been elucidated through EPR measurements and DFT calculations showing that their unpaired electron is primarily delocalized over the two metal centers, with minor spin densities at the two bridging amido nitrogen groups. The HOMO of 3 and 4 and the SOMO of [ 3 ] + and [ 4 ] + are essentially MM d–d σ*‐antibonding orbitals, explaining the formation of a net bonding interaction between the metals upon oxidation of 3 and 4 . Mechanisms for the observed allylic H‐atom abstraction reactions from the paramagnetic (radical) complexes are proposed.