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.
The first 4d/4f polyphosphides were obtained from reactions of the divalent metallocenes [Cp*2Ln(thf)2] (Ln = Sm, Yb) with [{CpMo(CO)2}2(μ,η2:2-P2)] or [Cp*Mo(CO)2(η3-P3)]. New aggregation of the central phosphorus scaffold in combination with P–P bond formation within the coordination sphere of the transition metal was observed.
The reduction of [(Cp‴Co) 2 (μ,η 2:2 -P 2 ) 2 ] (Cp‴ = 1,2,4-tBu 3 C 5 H 2 ) with the samarocenes, [(C 5 Me 4 R) 2 Sm-(THF) n ] (R = Me or n-propyl), gives [(Cp‴Co) 2 P 4 Sm(C 5 Me 4 R) 2 ]. This is the first example of an intramolecular P−P coupling in a polyphosphide complex upon reduction of the transition metal. The formation of the P−P bond is not a result of the direct reduction of the phosphorus atoms but is induced by a rearrangement of the positive charges between the metal atoms.
The reactions of the divalent lanthanide metallocenes [Cp*2Ln(thf)2] (Cp* = η(5)-C5Me5; Ln = Sm, Yb) with realgar (As4S4) gave the open cage tetrametallic complex [(Cp*2Sm)(Cp*Sm)3AsS3(Cp*AsS2)2(thf)3] (1) or the trimetallic cage compound [(Cp*Yb)3As2S4(Cp*AsS2)(thf)2] (2), respectively, by reductive cleavage of the inorganic cage. As result of a Cp* transfer, the novel Cp*AsS2(2-) anion is formed. Moreover, the As2S4(4-) anion, which is bound in 2, is observed for the first time in coordination chemistry. Closed cage compounds are formed by either using bulkier ligands or a different As/S cage. The reaction of [Cp‴2Sm] (Cp‴ = (1,2,4-(t-Bu)3C5H2)) with As4S4 and the reaction of [Cp*2Yb(thf)2] with dimorphite (As4S3) gave the closed 11-vertex cage clusters [(Cp‴Sm)3(AsS3)2] (3) and [(Cp*Yb)3(AsS3)2] (4), respectively. The reaction of 3 with [CuMes] resulted in the formation of the Sm/S/Cu cluster [(Cp‴Sm(thf))4Cu4S6] (5), in which the Sm atoms encapsulate a classical Cu4S6(8-) cluster core. This is the first transition metal chalcogenide cluster encapsulated by f-elements. Alternatively, the endohedral cluster can thus be described as [Cu4@{(Cp‴Sm(thf))4S6}], in which a Cu4 tetrahedron is encapsulated by the samarium sulfido cluster {(Cp‴Sm(thf))4S6}.
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