Bulky Ytterbium Formamidinates Stabilise Complexes with Radical Ligands, and Related Samarium "Tetracyclone" Chemistry. Issue 9 (16th January 2017) - Werner, Daniel
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 either1 a or1 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 . ‐ O 2 )] (5 ), [Yb(DippForm)2 (phen . ‐ O 2 )] (6 ), and [Yb(DippForm)2 (acen . ‐ O 2 )(thf)] (7 ). An unsolvated derivative of7, namely [Yb(DippForm)2 (acen . ‐ O 2 )] (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 of3, 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 ]). Thus3 was oxidised to tpc by Se. Treatment of3 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 ofSm13 with iodine in situ provided access to [{SmI({C5 Ph4 }‐ O )(thf)2 }2 ] (Sm11 ), in good yield. Abstract : Radical new discoveries : 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 a range of ketones and in several cases, rare stabilised ketyl radical complexes were isolated; in other cases, unusual reactivity was noted. To investigate the reactivity of the 2, 3, 4, 5‐tetraphenylcyclopentadienone‐ O ketyl radical species, we report the outcome upon treatment with oxidants (CS2, Se) and reducing agents (Mg 0, [SmI2 (thf)2 ] and KH).