Publications [#233974] of Michael J. Therien
Papers Published
- Baker, RT; Calabrese, JC; Krusic, PJ; Therien, MJ; Trogler, WC, "Spectroscopic, Structural, Electrochemical, and Kinetic Studies of Ligand Substitution in the 33e Dinuclear Radical Fe2(CO)7(μ-PPh2) and the 34e Analogues [Fe2(CO)7(μ-PPh2)]_and FeCo(CO)7(μ-PPh2)", Journal of the American Chemical SocietyJanuary,, 1988, 110(25), 8392-8412, American Chemical Society (ACS) [doi].
(last updated on 2026/01/19)Abstract:
The 33e dinuclear radical Fe2 (CO)7 (μ-PPh2 ) undergoes rapid CO ligand substitution with a variety of tertiary phosphorus ligands, L, to give mono- and disubstituted 33e products, which were characterized by elemental analysis and by IR and ESR spectroscopy. While the first substitution gives a single product, with L on the six-coordinate Fe center trans to the PPh2 bridge (confirmed by X-ray diffraction for L = P(OMe)3 ), further substitution (observed for L = PMe3 , PEt3 , P(OMe)3 ) is complex, giving two isomeric 33e disubstituted radicals, minor amounts of 35e addition products Fe2 (CO)6 L2 (μ-PPh2 ), and diamagnetic disproportionation products [Fe2 (CO)5 L3 (μ-PPh2 )]+[Fe2 (CO)8- n Ln (μ-PPh2 )]_(L = PMe3 , n = 0; L = P(OMe)3 , n = 2), as confirmed by an X-ray diffraction study of the PMe3 derivative. The 34e anion [Fe2 (CO)6 (μ-CO)(μ-PPh2 )]-, as the (Et4 N)+ salt, adds two ligands in THF to give the 36e anions [Fe2 (CO)6 L2 (μ-PPh2 )]-(L = PMe3 , PPh3 , P(OMe)3 ), which have one L on each Fe, both trans to the PPh2 bridge (confirmed by X-ray diffraction for L = PPh3 ). The intermediacy of the monosubstituted 34e anion was ruled out. The 34e heterobimetallic complex FeCo(CO)7 (μ-PPh2 ) reacts with PPh3 to give a 34e kinetic product with L on Co trans to the PPh2 bridge; this product rearranges at 25 °C to the thermodynamic product with L on Fe. With P(OMe)3 , monosubstitution occurs as above and disubstitution gives both 34e and 36e products, both with one L on each metal (confirmed for the 34e product by X-ray diffraction). With PMe3 , ligand addition gives 36e FeCo(CO)7 L(μ-PPh2 ), with L on Co. Electrochemical studies show that the 33e unsubstituted and monosubstituted diiron radicals exhibit chemically reversible le reductions to give the 34e CO-bridged anions. A le oxidation of the disubstituted 36e anion [Fe2 (CO)6 (PPh3 )2 (μ-PPh2 )]_ leads to the monosubstituted 33e radical, via loss of PPh3 . While oxidation of 34e FeCo(CO)7 (μ-PPh2 ) is chemically irreversible, le reduction leads to CO loss to give the 33e radical anion [FeCo(CO)6 (μ-PPh2 )]-, which undergoes a further chemically reversible reduction to the 34e dianion. Similarly, 1 e reduction of monosubstituted FeCo(CO)6 (PPh3 )(μ-PPh2 ) gives the 33e monosubstituted radical anion via CO loss, while a chemically reversible le oxidation gives the 33e radical cation [FeCo(CO)6 (PPh3 )(μ-PPh2 )]+. Kinetic studies of ligand monosubstitution in the 33e diiron radical Fe2 (CO)7 (μ-PPh2 ) using transient electrochemical techniques are consistent with an associative mechanism involving a 35e radical intermediate. Activation parameters obtained support the proposed associative pathway. Comparison of the reactivities of 33e Fe2 (CO)7 (μ-PPh2 ) and its 34e analogues [Fe2 (CO)6 (μ-CO)(μ-PPh2 )]- and FeCo(CO)7 (μ-PPh2 ) show that the radical complex is about 105–106 times more reactive toward PPh3 than the diamagnetic 34e compounds. The mono- and disubstituted 35e radicals have been observed by ESR spectroscopy for various L's and are proposed to have a (CO)2 -bridged structure, with two six-coordinate metal centers. Analogous 36e intermediates in the [Fe2 ]- and FeCo systems have the all-terminal-CO structure, with two five-coordinate metal centers. © 1988, American Chemical Society. All rights reserved.