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Chemistry (Weinheim an der Bergstrasse, Germany)

Bulky Ytterbium Formamidinates Stabilise Complexes with Radical Ligands, and Related Samarium "Tetracyclone" Chemistry.


PMID 27897349

Abstract

Divalent [Yb(DippForm)2 (thf)n ] (n=2 (1 a), or 1 (1 b), DippForm=N,N'-bis(2,6-diisopropylphenyl)formamidinate) complexes were treated with the ketones: 9-fluorenone (fn), or 2,3,4,5-tetraphenylcyclopentadienone (tpc, tetracyclone), giving ketyl complexes: [Yb(DippForm)2 (fn(.) -O)(thf)] (2), and [Yb(DippForm)2 (tpc(.) -O)] (3), respectively (ketyl=a radical anion containing a C(.) -O((-)) group. By contrast, when perfluorobenzophenone (pfb) was treated with either 1 a or 1 b, transitory ketyl formation was followed by rapid decomposition through a C-F activation pathway, giving [YbF(DippForm)2 (thf)] (4 a) and a highly unusual fluoride/oxide-bridged species: [Yb5 F6 O2 (DippForm)5 ] (4 b). The reduction of diketones: 3,5-di-tert-butyl-1,2-benzoquinone (tbbq), 9,10-phenanthrenequinone (phen), or 1,2-acenaphthenequinone (acen), was also examined giving ketyl complexes: [Yb(DippForm)2 (tbbq(.) -O2 )] (5), [Yb(DippForm)2 (phen(.) -O2 )] (6), and [Yb(DippForm)2 (acen(.) -O2 )(thf)] (7). An unsolvated derivative of 7, namely [Yb(DippForm)2 (acen(.) -O2 )] (8), was obtained from PhMe. All ketyl complexes had suitably elongated C(.) -O bonds, were stable in both polar and non-polar solvents-an uncommon trait for rare-earth ketyl complexes-and, with the exception of 3, showed radical signals in ESR spectra. To investigate the reactivity of the tpc(.) -O ketyl complex, 3 was treated with oxidants (CS2 , Se) and reducing agents (Mg(0) , KH, or [SmI2 (thf)2 ]). Thus 3 was oxidised to tpc by Se. Treatment of 3 with KH led to a ligand exchange process giving an unusual diketyl species [Yb(DippForm)(tpc(.) -O)2 (thf)2 ] (10), which has two cisoid tpc(.) -O(-) ligands in very close proximity. When treated with [SmI2 (thf)2 ], the tpc(.) -O ketyl was further reduced to a dianion (1-oxido-2,3,4,5-tetraphenylcyclopentadianide(2-) ), ({C5 Ph4 }-O)(2-) by [SmI2 (thf)2 ], giving dimeric [{SmI({C5 Ph4 }-O)(thf)2 }2 ] (Sm11) and monomeric complexes [YbI(DippForm)2 (thf)] (11 b) and [YbI2 (DippForm)(thf)2 ] (11 c). Activated Sm metal reduced neutral tetracyclone to the dianion, ({C5 Ph4 }-O)(2-) , in THF, giving tetranuclear [{Sm(II)2 ({C5 Ph4 }-O)2 (thf)3 }2 ] (Sm13). Treatment of Sm13 with iodine in situ provided access to [{SmI({C5 Ph4 }-O)(thf)2 }2 ] (Sm11), in good yield.