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

Sodium and potassium tetrakis(3,5-di-tert-butylpyrazolato)lanthanoidate(III) complexes [M{Ln(tBu2pz)4}] have been prepared by reaction of anhydrous lanthanoid trihalides with alkali metal 3,5-di-tert-butylpyrazolates at 200–300 °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(tBu2pz)4}] (1 Ln; 1 Ln=1 Tb, 1 Ho, 1 Er, 1 Yb), [K(PhMe){Ln(tBu2pz)4}]⋅2 PhMe (2 Ln; 2 Ln=2 La, 2 Sm, 2 Tb, 2 Ho, 2 Yb, 2 Lu), [Na{Ln(tBu2pz)4}]n (3 Ln; 3 Ln=3 La, 3 Tb, 3 Ho, 3 Er, 3 Yb), [K{Ln(tBu2pz)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(tBu2pzH){Ln(tBu2pz)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(tBu2pz)4}] (6 Ho). X-ray crystal structures of 1 Ln (=1 Tb, 1 Ho; P21/c), 2 Ln (=2 La, 2 Sm, 2 Tb, 2 Yb, 2 Lu; Pnma), 3,4 Ln (=3 La, 3 Er, 4 Sm; P21/m), and 5 Ln (=5 Nd, 5 Er, and 5 Yb; Pequation image) show each group to be isomorphous regardless of the size of the Ln3+ ion. All complexes contain eight-coordinate {Ln(η2-tBu2pz)4} units. These are further linked to the alkali metal by bridging through two (1,2,5 Ln) or three (3,4 Ln) tBu2pz groups which show striking coordination versatility. Sodium is coordinated by an η4-PhMe, a μ-η2:η2-tBu2pz, and a μ-η4(Na):η2(Ln)-tBu2pz ligand in 1 Ln, and by one η1-tBu2pzH and two μ-η3(Na):η2(Ln) ligands in 5 Ln. By contrast, potassium has one η6-PhMe and two μ-η5(K):η2(Ln) ligands in 2 Ln. Classes 3,4 Ln form polymeric chains with the alkali metal bonded by two μ-η3(NNC-M):η2(Ln)-tBu2pz ligands within [MLn(tBu2pz)4] units which are joined together by η1(C)-tBu2pz-Na, K linkages.