Structural Effects of Sodium Cations in Polynuclear, Multicubane‐Type Mixed Na–Ni Complexes

Abstract

Dedicated to Professor Herbert W. Roesky on the occasion of his 75th birthdayThe importance of transition-metal catalysts for ethylene oligo-and polymerization continues to motivate the synthesis of a wide range of heterotopic ligands and metal complexes. [1] Studies of dinuclear Ni II complexes with N,OH chelates as precatalysts for ethylene oligomerization [2] triggered our interest in comparing complexes with (pyridine-2-yl)methanol (HL) and those containing the corresponding anionic chelate, partly because N,O À ligands may lead to systems that do not require any cocatalyst. [3] Furthermore, L À is well known to promote the formation of polynuclear complexes with exciting physical properties, [4] paralleling the rich chemistry of 2-pyridones. [5] We have now obtained unusual mixed nickel/sodium polynuclear complexes and identified remarkable structural effects of the sodium cations associated with the reagent used to deprotonate the alcohol function. In addition to their intrinsic novelty, such observations are relevant to the possible in situ formation of unexpected and possibly overlooked active species in catalytic reactions.The dinuclear complex [Ni(m-Cl)(HL)] 2 Cl 2 (1) and the mononuclear, octahedral mer-[Ni(HL) 3 ]Cl 2 complex (2) have been recently reported. [2a] The reaction of 1 with 10 equivalents of NaH in THF led mainly to a complex catalytically active for ethylene oligomerization formulated as [Ni(HL)(L)Cl], [2a] but a few green crystals were also obtained, which are now shown to correspond to a very unusual mixed Ni-Na cluster (Figures 1 and 2).In this cluster, 3, [20] two fragments are held together through Na + ···O interactions (Figure 2 left): 1) a cationic trinuclear nickel moiety (Ni2, Ni3, Ni4, Figure 1 b), in which two L À ligands N,O-chelate each metal center, the Ni atoms being doubly bridged by the oxygen atoms and further capped by a m 3 -OH group; and 2) a mononuclear anionic unit in which three N,O chelating ligands form a facial arrangement around Ni1 (Figure 1 c). The alcoholate oxygen atoms O5, O7, and O9 each bridge two Na + ions and two Ni centers in the Ni 3 substructure. This generates a pseudo-cubane arrangement for Ni2, Ni3, Ni4, the m 3 -OH group (O10-H), and a missing vertex (Figure 2). The latter is shared with another defective pseudo-cubane entity containing Ni1, the three Na + ions, and O1, O2, and O3, which each bridge two Na + ions. The formation of this unprecedented nickel/sodium polynuclear complex illustrates the remarkable effect of the Na + ions. [5f, 6] A much improved synthesis of 3 was devised by reacting HL, [NiCl 2 (DME)] (DME = 1,2-dimethoxyethane), and NaH in THF in a 3.2:1:5 ratio, respectively. The presence of the m 3 -OH group most likely originates from the presence of NaOH that originates from NaH [Eq. (1), see the Supporting Information for details]. 4 ½NiCl 2 ðDMEÞ þ 9 HL þ 9 NaH þ NaOH ! ½Ni 4 Na 3 ðLÞ 9 OHCl ð3Þ þ 7 NaCl # þ9 H 2 " þ4 DMEWhen HL was stirred in THF with [NiCl 2 (DME)] for 12 h, 1 formed first, irrespective of the L/Ni r...

Breaking the Gordian Knot in the Structural Chemistry of Polyoxometalates: Copper(II)–Oxo/Hydroxo Clusters

“…The heptacuprate skeleton {Cu 7 O 18 } consists of six edge‐sharing {CuO 5 } square‐pyramidal moieties arranged in a cyclic manner through twelve Cu‐O‐Cu bridges; the six inner O atoms coordinate to the central Cu II ion, thus leading to a central {CuO 6 } octahedron (Figure b). Interestingly, this POCu topology is similar to that described, for example, for the iodobismuthate [Bi 7 I 24 ] 3−[52] and heptanuclear wheel complexes of Co II , Ni II , and Zn II ions, the CdI 2 ‐type (brucite) or Anderson‐type structure of which is supported by N,O‐donor pyridyl–methanolate ligands . However, in contrast to the obtained POCu, the peripheral heavy main group and late‐3d transition metal ions in these compounds are coordinatively saturated, being in a (pseudo‐)octahedral coordination environment.…”

Polynuclear Complexes with Alkoxo and Phenoxo Bridges from In Situ Generated Hydroxy‐Rich Schiff Base Ligands: Syntheses, Structures, and Magnetic Properties

“…The c m T product at 300 K is 9.335 cm 3 kmol À1 , which is much higher than the expected spin-only value of 7.7 cm 3 kmol À1 (g = 2.1) for seven uncoupled nickel(II) ions, indicating significant orbital contributions of the distorted octahedral nickel(II) ions. Although several Ni 7 complexes with similar core structures have been reported, [21] magnetic data-fitting has been performed for only one example reported by Braunstein and co-workers, [21a] wherein, the NiA C H T U N G T R E N N U N G (central)ÀA C H T U N G T R E N N U N G (m 3 -O)ÀNi angles range from 95.6(1) to 98.7(1)8, and the peripheral NiÀOÀNi angles range from 102.4(1) to 103.6(1)8, with J 1 and J 2 (Scheme 4 a) values of À2.7 and 12.8 cm À1 , respectively. Then, the product decreases at lower temperatures, which is indicative of weak antiferromagnetic interactions.…”

“…Several similar heptanuclear nickel complexes with Ni@Ni 6 arrangement have been reported, [21] utilizing simple bidentate or tridentate ligands. Each heptanuclear structure contains six or twelve ligands.…”

Facile Self‐Assembly of Intermetallic [Ni2Gd2] Cubane Aggregate for Magnetic Refrigeration

“…A variety of homo‐ and heterometallic metal aggregates using 2‐(hydroxymethyl)pyridine (hmpH) as a ligand have been reported, such as [Mn II 2 Mn III 2 ],9 [Mn 3 Ni],10 [Mn 2 Ln 2 ],11 [Mn 4 ],12 [Gd 4 M 8 ],13 etc. By using hmpH as a ligand, a series of polynuclear metal aggregates such as the [NaNi 6 ] Anderson‐type framework,14 and [Ni 4 ]15 and [Co 3 Ln] cubanes16 have been prepared. Herein, we report a simple one‐pot self‐assembly of a [Ni 2 Gd 2 ] heterometallic cubane at room temperature and its X‐ray crystallographic analysis.…”