The Complexed 1,3‐Diphospha‐2‐Arsaallyl Radical and Its Cationic and Anionic Derivatives

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.