Neutral, Radical [CpNi(dithiolene)] Complexes with Flexible, Nonplanar Seven‐Membered Rings: [CpNi{S2C2S2(CH2)2X}] (X = CH2, CF2, C=CH2, S, C=O)

Abstract

AbstractNeutral, radical [CpNi(dithiolene)] complexes fused with seven‐membered rings, formulated as [CpNi{S2C2S2(CH2)2X}] (X = CH2, CF2, C=CH2, S), have been synthesized in 30–60 % yields from the reactions of nickelocene with the corresponding neutral, square‐planar, (dithiolene)nickel complexes [Ni{S2C2S2(CH2)2X}2]. [CpNi{S2C2S2(CH2)2X}] (X = C=O) was prepared from nickelocene and [1,3]dithiolo[4,5‐b][1,4]dithiepine‐2,6‐dione under thermal or photochemical conditions. All complexes exhibit reversible oxidation and reduction waves to the cation and anion form, respectively. The terminal groups (X) in the seven‐membered ring shift their redox potentials to anodic potentials in the following order: CF2 > C=O > S > C=CH2 > CH2. The singlet EPR responses of [CpNi{S2C2S2(CH2)2(X)}] appear at g ≈ 2.0514–2.0529 in dichloromethane solution at room temperature. An NIR absorption is observed at λmax ≈ 798–848 nm (ϵ ≈ 1700–2400 M–1 cm–1) in dichloromethane solution. The X‐ray structures of the five complexes show two‐legged piano‐stool geometries around the central nickel atom (formally NiIII) and strong distortions from planarity of the seven‐membered C2S2(CH2)2X rings. In the solid state, those radical (S = 1/2) species adopt either one‐dimensional alternating chain‐like motifs (X = CH2, C=CH2, S) or dimeric entities characterized by a singlet–triplet magnetic behavior (X = CF2, C=O). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)