Elevated‐Temperature Metathesis Syntheses of Structurally Novel Alkali‐Metal Tetrakis(3,5‐di‐tert‐butylpyrazolato)lanthanoidate(III) Complexes: Toluene‐Coordinated Discrete Bimetallic Complexes and Supramolecular Chains

Abstract

Sodium and potassium tetrakis(3,5-di-tert-butylpyrazolato)lanthanoidate(III) complexes [M[Ln(tBu(2)pz)(4)]] have been prepared by reaction of anhydrous lanthanoid trihalides with alkali metal 3,5-di-tert-butylpyrazolates at 200-300 degrees C, and a 1,2,4,5-tetramethylbenzene flux for M=K. On extraction with toluene (or occasionally directly from the reaction tube) the following complexes were isolated: [Na(PhMe)[Ln(tBu(2)pz)(4)]] (1 Ln; 1 Ln=1 Tb, 1 Ho, 1 Er, 1 Yb), [K(PhMe)[Ln(tBu(2)pz)(4)]].2 PhMe (2 Ln; 2 Ln=2 La, 2 Sm, 2 Tb, 2 Ho, 2 Yb, 2 Lu), [Na[Ln(tBu(2)pz)(4)]](n) (3 Ln; 3 Ln=3 La, 3 Tb, 3 Ho, 3 Er, 3 Yb), [K[Ln(tBu(2)pz)(4)]](n) (4 Ln; 4 Ln=4 La, 4 Nd, 4 Sm, 4 Tb, 4 Ho, 4 Er, 4 Yb, 4 Lu), with the last two classes generally being obtained by loss of toluene from 1 Ln or 2 Ln, and [Na(tBu(2)pzH)[Ln(tBu(2)pz)(4)]].PhMe (5 Ln; 5 Ln=5 Nd, 5 Er, 5 Yb). Extraction with 1,2-dimethoxyethane (DME) after isolation of 2 Ho yielded [K(dme)[Ho(tBu(2)pz)(4)]] (6 Ho). X-ray crystal structures of 1 Ln (=1 Tb, 1 Ho; P2(1)/c), 2 Ln (=2 La, 2 Sm, 2 Tb, 2 Yb, 2 Lu; Pnma), 3,4 Ln (=3 La, 3 Er, 4 Sm; P2(1)/m), and 5 Ln (=5 Nd, 5 Er, and 5 Yb; P1) show each group to be isomorphous regardless of the size of the Ln(3+) ion. All complexes contain eight-coordinate [Ln(eta(2)-tBu(2)pz)(4)] units. These are further linked to the alkali metal by bridging through two (1,2,5 Ln) or three (3,4 Ln) tBu(2)pz groups which show striking coordination versatility. Sodium is coordinated by an eta(4)-PhMe, a micro-eta(2):eta(2)-tBu(2)pz, and a micro-eta(4)(Na):eta(2)(Ln)-tBu(2)pz ligand in 1 Ln, and by one eta(1)-tBu(2)pzH and two micro-eta(3)(Na):eta(2)(Ln) ligands in 5 Ln. By contrast, potassium has one eta(6)-PhMe and two micro-eta(5)(K):eta(2)(Ln) ligands in 2 Ln. Classes 3,4 Ln form polymeric chains with the alkali metal bonded by two micro-eta(3)(NNC-M):eta(2)(Ln)-tBu(2)pz ligands within [MLn(tBu(2)pz)(4)] units which are joined together by eta(1)(C)-tBu(2)pz-Na, K linkages.

The Synthesis, Structures and Polymorphism of the Dimeric Trivalent Rare‐Earth 3,5‐Dimethylpyrazolate Complexes [Ln(Me2pz)3(thf)]2

“…Indeed, it is surprising that a complex with this bridging array can be crystallised from thf without cleavage of the bridge. Previous examples of this coordination found in rare‐earth chemistry5c,5d come from solventless syntheses or from the use of nonpolar solvents.…”

“…[2e–2g,2k] Of particular interest is the observation of μ‐η 2 :η 5 coordination in complexes of the larger lanthanoids. This binding mode is quite uncommon, but has been observed for lanthanoid complexes with bulkier pyrazolate substituents, such as [Eu( t Bu 2 pz) 2 ] 4 ,5a [Ln 3 (Ph 2 pz) 9 ] (Ln = La, Nd),5d and [K(PhMe)Ln( t Bu 2 pz) 4 ] (Ln = La, Sm, Tb, Yb) {η 5 (K):η 2 (Ln)},5c and has also been observed in some alkaline earth pyrazolate complexes 4c,4d,11. It should be noted that η 5 ‐pz‐Nd binding has been observed in [Nd 3 (pz) 9 (pzH) 2 ] as part of a unique μ 3 ‐η 5 :η 1 :η 1 binding mode,5e and there is η 5 ‐binding of pyrazole ligand (pzH) in [Eu(pz) 2 (pzH) 2 ] ∞ 5e,6c.…”

Alkali Metal/Lanthanoid Heterobimetallic Complexes of 8‐Hydroxyquinolines Accessed by Pseudo‐Solid‐State Reactions

“…[25] Complexes 5 and 6 have structures reminiscent of the [AMLn(tBu 2 pz) 4 ] n class of complex (AM = Na, Ln = La, Tb, Ho, Er, Yb; AM = K, Ln = La, Nd, Sm, Tb, Ho, Er, Yb, Lu; tBu 2 pz = 3,5-di-tert-butylpyrazolate), which were synthesised by metathesis, solventless or in an inert flux, at elevated temperatures (200-300°C). [24] The high symmetry of complexes 1-4 leads to the small number of unique bond lengths (Table 1). In the lithium derivatives, Ln-O bond lengths are 0.018 Å shorter in 3 than in 1; in the potassium derivative 4, the bond lengths are 0.037 Å shorter than in 1, with the difference being close to that expected from the lanthanoid contraction when changing from terbium to erbium.…”

“…The higher coordination number is achieved by involvement of the π-system of the ligands [C(8 and 9)-Rb Ͻ 3.5 Å] and bridging by nitrogen atoms (see below; Figure 2). This cut-off is supported by ranges for π-bonding of arenes to potassium [24] adjusted by the differences between the ionic radii of K + and Rb + . [25,26] The average distance between carbon atoms of π-bonded arenes and potassium is 3.14 Å, and for rubidium this distance is 3.35 Å.…”

“…Similar K-C bond lengths (3.09-3.41 Å) have been reported for [K(PhMe)(Ln(tBu 2 pz) 4 )]·2PhMe. [24] In addition, interaction distances between the ipso carbon atoms of the aryloxide and potassium in [KY(OAr) 4 (thf) 5 ] [31] (OAr = 2,6-dimethylphenolate; thf = tetrahydrofuran) range between 3.288(9)-3.400(10) Å, similar to the analogous K[Nd(Odip) 4 ] [32] (Odip = 2,6-bis(isopropyl)phenolate) [3.256(9) Å] and [KSm(OArЈ) 3 ] n [33] (OArЈ = 2,6-di-tert-butyl-4-methylphenolate) [3.310(10) and 3.534(13) Å]. Crystallographic and refinement data for 8 are given in Table 8.…”