Contrasting Binding Modes in Lanthanoid Pyrazolate and Pseudo-pyrazolates Prepared by Oxidation of Lanthanoid(II) Complexes and Lanthanoid Metals with Thallium(I) Reagents

Oxidation of Yb(C5Me5)(2) with [Tl(Ph(2)pz)] and [Tl(azin)] (Ph(2)pz = 3,5-diphenylpyrazolate, azin = 7-azaindolate) yields [Yb(C5Me5)(2)(Ph(2)pz)] (1) and [Yb(C5Me5)(2)(azin)] (2). X-ray crystal structures of 1 and 2 reveal monomeric eight-coordinate complexes with eta(2)-Ph(2)pz or azin ligands. Treatment of neodymium metal with [Tl(Ph(2)pz)] yields [Nd(Ph(2)pz)(3)(dme)(2)] (3), which is a nine-coordinate monomer with three y2-pyrazolate ligands and a chelating and a unidentate dme ligand. Oxidation of Sm(C5Me5)(2) with [Tl( 1,4,2-P2SbC2Bu2t)/[Tl(1,2,4-P3C2-Bu-2(t))] (approximately 4:1) gave a mixture of [Sm(C5Me5)(2)(1,2,4-P3C2Bu2t)] (4) and [Sm(C-5-Me-5)(2)(1,4,2-P2SbC2Bu2t)]. The former was shown to be a nine-coordinate monomer with novel pseudo-pyrazolate eta(2)-(P-2)-[1,2,4-P3C2Bu2t] coordination of the triphosphacyclopentadienide ligand. After metathesis routes to Ln(1,4,2-P2SbC2Bu2t)(n) complexes failed, redox transmetalation between ytterbium metal and [Tl( 1,4,2-P2EC2Bu2t) (E = Sb, P) containing a substantial impurity of [Li(tmeda)(2)][1,4,2-P2EC2Bu2t] yielded the first lanthanoid diphosphastibacyclopentadienide complex in a mixture with [1,2,4-P3C2Bu2t] species. An X-ray investigation of single crystals containing an isomerically diverse mixture enabled the structure of[li(thf)(4)]-[Yb(1,4,2-P2SbC2Bu2t)(3)] (5) to be determined, and it was shown to contain a pi-eta(2) and two eta(5)-[1,4,2-P2SbC2Bu2t] ligands. In the series 1, 4, and 5, the eta(2)-ring varies from edge-on to side-on, reflecting a progression from sigma to pi coordination. [Li(tmeda)(2)][1,4,2-P(2)SbC(2)But(2)(t)] (6) has been successfully crystallized from a [Li(tmeda)(2)][P2EC2Bu2t] mixture and structurally characterized.