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