Markus Stubenhofer

The Complexed Triphosphaallyl Radical, Cation, and Anion Family

Radically complex: The photolytic reaction of [Cp*P{W(CO)(5)}(2)] (Cp* = C(5)Me(5)) with a diphosphene produces, via a radical intermediate, an air-stable complexed triphosphaallyl radical, in which the unpaired electron is evenly distributed over both terminal P atoms. Oxidation of the radical leads to a triphosphaallyl cation, which is only stable at low temperatures in solution, whereas the stable triphosphaallyl anion is formed by reduction (see picture, Mes* = 2,4,6-tri-tert-butylphenyl).

Stepwise Expansion of a Cp* Ring at Pentelidene Complexes and Stereoselective Formation of Triphosphines†

Stepwise opening and final removal of the η1-bound Cp* substituents in the bridged pentelidene complexes [Cp*E{W(CO)5}2] (E=P, As) occurs by the reaction with primary phosphines. Not only novel diphospha- and arsaphosphanorbornenes are obtained, but also diastereomerically pure complexed triphosphines. All reaction steps were monitored by NMR spectroscopy, and compounds structurally characterized.

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

Photolysis of [Cp*As{W(CO)(5)}(2)] (1a) in the presence of Mes*P=PMes* (Mes*=2,4,6-tri-tert-butylphenyl) leads to the novel 1,3-diphospha-2-arsaallyl radical [(CO)(5)W(mu,eta(2):eta(1)-P(2)AsMes*(2))W(CO)(4)] (2a). The frontier orbitals of the radical 2a are indicative of a stable pi-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 2a 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 2a, the complex [(CO)(5)W(mu,eta(2):eta(1)-P(2)As(H)Mes*(2))W(CO)(4)] (6a) is formed during chromatographic workup, whereas the additional products [Mes*P=PMes*{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 2a. Reduction of radical 2a yields the stable anion [(CO)(5)W(mu,eta(2):eta(1)-P(2)AsMes*(2))W(CO)(4)](-) in 7a, whereas upon oxidation the corresponding cationic complex [(CO)(5)W(mu,eta(2):eta(1)-P(2)AsMes*(2))W(CO)(4)][SbF(6)] (8a) is formed, which is only stable at low temperatures in solution. Compounds 2a, 7a, and 8a represent the hitherto elusive complexed redox congeners of the diphospha-arsa-allyl system. The analogous oxidation of the triphosphaallyl radical [(CO)(5)W(mu,eta(2):eta(1)- P(3)Mes*(2))W(CO)(4)] (2b) also leads to an allyl cation, which decomposes under CH activation to the phosphine derivative [(CO)(5)W{mu,eta(2):eta(1)-P(3)(Mes*)(C(5)H(2)tBu(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 2a, 3, 6a, 7a, and 9 by X-ray diffraction analysis.

CCDC 930882: Experimental Crystal Structure Determination

Related Article: Markus Stubenhofer, Christian Kuntz, Michael Bodensteiner, Alexey Y. Timoshkin, and Manfred Scheer|2013|Organometallics|32|3521|doi:10.1021/om400357y