(Pentamethylcyclopentadienyl)selenium Derivatives. 5.¹ Bis(pentamethylcyclopentadienyl)selenium and Its Reactions with Transition-Metal Carbonyls

Abstract

The first cyclopentadienylselenium derivative, Se(C 5 Me 5 ) 2 (1), has been prepared by the reaction of LiC 5 Me 5 with selenium bis(diethyldithiocarbamate). Steric crowding about the selenium atom in 1 results in long Se-C bonds and an expanded C-Se-C angle, giving rise to unprecedented reactivity. Treatment of 1 with sources of M(CO) 5 fragments yields the terminal diselenide complexes [M(CO) 5 {Se 2 (C 5 Me 5 ) 2 }] (M ) Cr, W) via reduction within the transition-metal coordination sphere. Reaction of 1 with [Fe 2 (CO) 9 ] leads to loss of both C 5 Me 5 groups and formation of [Fe 3 Se 2 (CO) 9 ].

Synthesis, reactivity and structural studies of selenide bridged carboranyl compounds

“…24 In the diselenide compounds the mutual conformations are quite similar, e.g the absolute values of the C c -C c -Se-Se torsion angles (C c refers to cluster carbon) are very close to each other varying only within 6.5 • . In 1 the C(1)-Se-C(21) angle of 110.11 (11) • is near to the value of 109.6(2) • found in (C 5 Me 5 ) 2 Se (C 5 Me 5 = pentamethylcyclopentadienyl) 25 and also very close to the value of a tetrahedral angle. However, there are several short intramolecular contacts of H atoms between the cages like H(5)…”

Tetramethylcyclopentadienylselenium derivatives

“…Bis(1,2,3,4-tetramethylcyclopentadienyl)selane (1), Cp t 2 Se (Cp t = C 5 Me 4 H), was synthesised in the same way as Cp* 2 Se, via the room temperature reaction of tetramethylcyclopentadienyllithium (Cp t Li) with the convenient Se(II) precursor Se(S 2 CNEt 2 ) 2 , as summarised in eqn (1). The product was obtained as an orange solid after column chromatography, and was recrystallised from diethyl ether at −10 • C. Compound 1 is air-stable for a few days, but is best stored under an inert atmosphere in the dark at −10 • C.…”

“…Bis(pentamethylcyclopentadienyl)selane, Cp* 2 Se (Cp* = C 5 Me 5 ), shows unusual reactivity towards low-valent transition metal fragments, leading to complexes of the diselenide Cp* 2 Se 2 . 1 Two routes to monocyclopentadienylselenium derivatives have been developed: methyl(pentamethylcyclopentadienyl)selane, 2 Cp*SeMe, can be prepared by the reaction of methyl iodide with Cp*Se x Li; treatment of diferrocenyl diselenide with Cp*Li leads to ferrocenyl(pentamethylcyclopentadienyl)selane, 3 Cp*SeFc (Fc = [Fe(g 5 -C 5 H 5 )(g 5…”

Pentamethylcyclopentadienylselenium derivatives VI: Synthesis and characterisation of ferrocenyl(pentamethylcyclopentadienyl)selenium

“…No features are present in this region in the voltammograms of the ferrocenyl alkyl selenides, where the oxidation of the selenium atom does not occur below ca. 1.3 V. On the other hand, the oxidation of 1 occurs at +0.400 V, and the orbital from which the electron is lost has been identified as part of the ring p-system [1].…”

“…Bis(pentamethylcyclopentadienyl)-selenium, Se (C 5 Me 5 ) 2 (1) shows unusual reactivity towards low-valent transition metal fragments, as a result of the steric crowding at the selenium atom [1]. We used the reaction of LiSe x C 5 Me 5 [2] with methyl iodide to prepare methyl(pentamethylcyclopentadienyl)selenium, Se(C 5 -Me 5 )Me (2) in order to compare its behaviour with that of 1 [3].…”