Molecular Polyarsenides of the Rare‐Earth Elements

Abstract

Reduction of [Cp*Fe(η(5)-As5)] with [Cp''2Sm(thf)] (Cp''=η(5)-1,3-(tBu)2C5H3) under various conditions led to [(Cp''2Sm)(μ,η(4):η(4)-As4)(Cp*Fe)] and [(Cp''2Sm)2As7(Cp*Fe)]. Both compounds are the first polyarsenides of the rare-earth metals. [(Cp''2Sm)(μ,η(4):η(4)-As4)(Cp*Fe)] is also the first d/f-triple decker sandwich complex with a purely inorganic planar middle deck. The central As4(2-) unit is isolobal with the 6π-aromatic cyclobutadiene dianion (CH)4(2-). [(Cp''2Sm)2As7(Cp*Fe)] contains an As7(3-) cage, which has a norbornadiene-like structure with two short As-As bonds in the scaffold. DFT calculations confirm all the structural observations. The As-As bond order inside the cyclo As4 ligand in [(Cp''2Sm)(μ,η(4):η(4)-As4)(Cp*Fe)] was estimated to be in between an As-As single bond and a formally aromatic As4(2-) system.

Arsenic‐Rich Polyarsenides Stabilized by Cp*Fe Fragments

“…Molecular structure of the anion of 5 in the solid state. [12b,d] In conclusion, we have reported on electrochemical studies of [Cp*Fe(h 5 -As 5 Furthermore,t he reactivity of 1 towards KH differs significantly from previously reported chemical reductions of 1 with divalent lanthanide complexes or the reaction of the lighter congener [Cp*Fe(h 5 -P 5 )] under similar reaction conditions.While the reaction of 1 with Cp''Sm complexes results in the formation of one favored discrete polyarsenide depending on the used solvent, [10,11] the studied reduction of 1 with KH showed the potential of 1 for the formation of novel arsenic-rich As n ligand complexes,w hich are scarcely known in organometallic chemistry.A ccordingly, 1 is as uitable starting material for the synthesis of novel polyarseniccontaining compounds,a nd its exciting reactivity will continue to be explored. Displacementellipsoids set at 50 %p robability.S elected bond lengths []: As1-As2 2.3545(15), As1-As5 2.4355(11), As2-As6 2.4278(13), As3-As42 .3648 (14), As3-As62 .4203(13), As4-As5 2.4309- (14), As5-As72 .4523 (14),A s6-As72 .4424 (12),A s7-As82 .4434(12), As8-As13 2.4234(13), As8-As9 2.4559(11), As9-As10 2.3819(12), As10-As112 .5738 (13),A s11-As122 .3775(13), As12-As13 2.4384(12), As13-As142 .4438 (11),A s14-As152 .4737 (12), As14-As18 2.4400(11), As15-As162 .3553 (14),A s16-As172 .3696 (14), As17-As18 2.3604- (13).…”

“…[15,21] However,DFT calculations at the BP86/def2-TZVP level of theory suggested multiple-bond character within the individual As 2 dumbbells, which is also reflected by the Wiberg bond indices (WBIs) of 1.20. [10] In contrast, the 31 VE complex 2 is paramagnetic and was additionally characterized by EPR spectroscopy.I nt he X-band EPR spectrum of 2,arather broad anisotropic signal centered at g iso = 2.008 was detected at 77 K. [15] According to DFT calculations,the spin density is mainly localized on the iron center,with only small contributions from arsenic. Interestingly,t he chemical reduction of 1 with [Cp'' 2 Sm(thf)] afforded the triple-decker complex [(Cp''Sm)(m,h 4:4 -As 4 )(Cp*Fe)],w hich contains ac entral cyclo-As 4 2À unit.…”

“…However,f irst reactivity studies [8,9] showed differences,a nd the reduction of 1 by divalent samarium complexes led to ar earrangement of the former cyclo-As 5 ligand of 1 to form either [(Cp''Sm)(m,h 4:4 -As 4 )(Cp*Fe)] or [(Cp''Sm) 2 As 7 -(Cp*Fe)] (Cp'' = h 5 -1,3-t Bu 2 C 5 H 3 ). [10,11] This indicates interesting behavior for this compound as ap otential As source because arsenic-rich polyarsenides in particular are rare to date.Most of them have been obtained from reactions of the Zintl ion As 7 3À with transition-metal and main-group-metal precursors (Scheme 1). [12] were obtained, which are the largest neutral As n ligand complexes that have been structurally characterized thus far.…”

“…Interestingly,t he chemical reduction of 1 with [Cp'' 2 Sm(thf)] afforded the triple-decker complex [(Cp''Sm)(m,h 4:4 -As 4 )(Cp*Fe)],w hich contains ac entral cyclo-As 4 2À unit. [10] In contrast, the 31 VE complex 2 is paramagnetic and was additionally characterized by EPR spectroscopy.I nt he X-band EPR spectrum of 2,arather broad anisotropic signal centered at g iso = 2.008 was detected at 77 K. [15] According to DFT calculations,the spin density is mainly localized on the iron center,with only small contributions from arsenic. [15] In addition, the redox chemistry of 2 was investigated by cyclic voltammetry,e xclusively revealing ar eversible oxidation (E 1/2 = À1.2 Vv s.…”

Durch Cp*Fe‐Fragmente stabilisierte, Arsen‐reiche Polyarsenide

“…[8,9] 2 As 7 (Cp*Fe)] (Cp'' = h 5 -1,3-C 5 H 3 t Bu 2 ). [10,11] Dies lässt auf ein interessantes Verhalten dieser Verbindung als eine mçgliche As-Quelle schließen, zumal bis heute insbesondere Arsen-reiche Polyarsenide selten sind. Die meisten stammen aus den Reaktionen des Zintl-Ions As 7 3À mit Übergangsmetall-oder Hauptgruppenmetall-Ausgangsstoffen (Schema 1).…”