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The Complexed 1,3‐Diphospha‐2‐Arsaallyl Radical and Its Cationic and Anionic Derivatives
Author(s) -
Stubenhofer Markus,
Kuntz Christian,
Bodensteiner Michael,
Zenneck Ulrich,
Sierka Marek,
Scheer Manfred
Publication year - 2010
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.201000418
Subject(s) - chemistry , cationic polymerization , allylic rearrangement , electron paramagnetic resonance , unpaired electron , medicinal chemistry , protonation , decomposition , photodissociation , hydroxyl radical , atomic orbital , radical , crystallography , photochemistry , stereochemistry , ion , polymer chemistry , catalysis , electron , organic chemistry , physics , nuclear magnetic resonance , quantum mechanics
Photolysis of [Cp*As{W(CO) 5 } 2 ] ( 1 a ) in the presence of Mes*PPMes* (Mes*=2,4,6‐tri‐ tert ‐butylphenyl) leads to the novel 1,3‐diphospha‐2‐arsaallyl radical [(CO) 5 W(μ,η 2 :η 1 ‐P 2 AsMes* 2 )W(CO) 4 ] ( 2 a ). The frontier orbitals of the radical 2 a are indicative of a stable π‐allylic system that is only marginally influenced by the d orbitals of the two tungsten atoms. The SOMO and the corresponding spin density distribution of the radical 2 a show that the unpaired electron is preferentially located at the two equivalent terminal phosphorus atoms, which has been confirmed by EPR spectroscopy. The protonated derivative of 2 a , the complex [(CO) 5 W(μ,η 2 :η 1 ‐P 2 As(H)Mes* 2 )W(CO) 4 ] ( 6 a ) is formed during chromatographic workup, whereas the additional products [Mes*PPMes*{W(CO) 5 }] as the Z ‐isomer ( 3 ) and the E ‐isomer ( 4 ), and [As 2 {W(CO) 5 } 3 ] ( 5 ) are produced as a result of a decomposition reaction of radical 2 a . Reduction of radical 2 a yields the stable anion [(CO) 5 W(μ,η 2 :η 1 ‐P 2 AsMes* 2 )W(CO) 4 ] − in 7 a , whereas upon oxidation the corresponding cationic complex [(CO) 5 W(μ,η 2 :η 1 ‐P 2 AsMes* 2 )W(CO) 4 ][SbF 6 ] ( 8 a ) is formed, which is only stable at low temperatures in solution. Compounds 2 a , 7 a , and 8 a represent the hitherto elusive complexed redox congeners of the diphospha‐arsa‐allyl system. The analogous oxidation of the triphosphaallyl radical [(CO) 5 W(μ,η 2 :η 1 ‐ P 3 Mes* 2 )W(CO) 4 ] ( 2 b ) also leads to an allyl cation, which decomposes under CH activation to the phosphine derivative [(CO) 5 W{μ,η 2 :η 1 ‐P 3 (Mes*)(C 5 H 2 t Bu 2 C(CH 3 ) 2 CH 2 )}W(CO) 4 ] ( 9 ), in which a CH bond of a methyl group of the Mes* substituent has been activated. All new products have been characterized by NMR spectrometry and IR spectroscopy, and compounds 2 a , 3 , 6 a , 7 a , and 9 by X‐ray diffraction analysis.