Naphthalene‐Bridged ansa‐Nickelocene: Synthesis, Structure, Electrochemical, and Magnetic Measurements

Abstract

The reaction of naphthalene‐1,8‐diylbis(cyclopentadienylsodium) (1) with the nickel triple‐decker compound [Ni2Cp3]BF4 affords the paramagnetic ansa‐nickelocene 1,1′‐(naphthalene‐1″,8″‐diyl)nickelocene (2). Alternatively, 2 can directly be obtained by a salt metathesis reaction of the disodium salt 1 with hexaammine nickel(II) dichloride [Ni(NH3)6]Cl2. For magnetic dilution experiments, the corresponding but diamagnetic ansa‐ruthenocene 3 was synthesized by reaction of the disodium salt 1 with dichloridotetrakis(dimethyl sulfoxide)ruthenium(II). The solid‐state molecular structures of 2 and 3 were determined by single‐crystal X‐ray diffraction analysis and revealed bent sandwich complexes. Cyclic voltammetry studies of 2 indicate three oxidation states. The electronic structure of complex 2 has been investigated by variable‐temperature 1H NMR spectroscopy, magnetic measurements, and DFT calculations. Superconducting quantum interference device (SQUID) magnetometry has been performed for the neat and diluted samples of 2. The neat crystalline material of 2 displays antiferromagnetic behavior, whereas the susceptibility of the magnetically diluted sample runs into saturation at T < 4 K. This property is in agreement with an intermolecular antiferromagnetic interaction in the bulk material of compound 2 and the triplet ground state calculated by broken‐symmetry (BS)‐DFT calculations.

Ring‐Opening Polymerisation of Low‐Strain Nickelocenophanes: Synthesis and Magnetic Properties of Polynickelocenes with Carbon and Silicon Main Chain Spacers

“…The μ eff values for 13 a and 14 a (2.94 and 3.01 μ B respectively) agree well with the value previously reported for 6 x / 7 (2.94 μ B ) in the Curie–Weiss regime . These are slightly greater than μ eff values reported for monomeric nickelocenes (2.88–2.92 μ B ) …”

“…2019, 25,1044 -1054 www.chemeurj.org m eff values reportedf or monomeric nickelocenes (2.88-2.92 m B ). [25,39] In aC urie-Weiss model,i nteractions between magnetic centres are considered in am ean field approach, parameterised by the Weiss temperature (V). All complexes studied showed negative valueso fV,c haracteristic of antiferromagnetic spinspin interactions.…”

“…[16a, 21] As ar esult of the 20 valence electron configuration of nickelocene, two electrons are accommodated in antibonding e'' 1 orbitals, resulting in the elongation and weakening of the nickel-cyclopentadienyl (NiÀCp) bond [22] and as ubsequenti ncreasei nt he Cp ligand tilt-angle, a,c omparative to iron and cobalt metallocene analogues. [23] This weaker MÀCp bond is reflected in the low number of reported [n]nickelocenophane structures compared to well-studied [n]ferrocenophanes;c urrently reported species are limited to those bridged with unsubstituted alkylene chainsw here n is greater than 2, namely 5 and 8-10 naphthalene, 11, [25] and disila linkers, 12, [23c] (Figure 2). Currently,t he only reported highm olar mass polynickelocene, poly(nickelocenylpropylene) 7,r esults from the ROP of tricarba [3]nickelocenophane 5 [a = 16.6(1)8]i np yridine (and a number of other polar organic solvents), Scheme1.…”

Toward an automated analysis of exchange pathways in spin‐coupled systems

“…Although the attempt to synthesize this compound was not successful and instead lead to the formation of ansa‐nickelocene, it was possible to obtain the permethylated analogue of this complex . Such types of complexes are interesting, because there are two potential exchange pathways contributing to the spin coupling.…”

Recent developments with strained metallocenophanes

“…The weaker MeCp bond is reflected in the low number of [n]nickelocenophanes reported in the literature, and thus are currently limited to species bridged with unsubstituted alkyls [34], naphthalene [35], and disila linkers (29) [26a,36]. An interesting reactivity mode was reported for species 29, where upon addition of [Ni(CNtBu) 4 ] cleavage of the Si 2 bridge occurs with concomitant formation of two SieNi bonds to afford new dimer 30 (Scheme 9).…”