Structure and reactivity of homoleptic samarium(II) and thulium(II) phospholyl complexes.

Potassium 2,5-di-tert-butyl-3,4-dimethylphospholide K(dtp) (9) was synthesised in 45 % yield from commercially available starting materials by using zirconacyclopentadiene chemistry. Reaction of the K salt of this bulky anion and of the previously described potassium 2,5-bis(trimethylsilyl)-3,4-dimethylphospholide K(dsp) (8) with SmI(2) in diethyl ether afforded the homoleptic samarium(II) complexes 7 and 6, respectively, whose solid-state structures, [[Sm(dtp)(2)](2)] (7 a) and [[Sm(dsp)(2)](2)] (6 a), are dimeric owing to coordination of the phosphorus lone pairs to samarium, as shown by X-ray crystallography. Reaction of 8 with TmI(2) in diethyl ether afforded [Tm(dsp)(2)(Et(2)O)], which could not be desolvated without decomposition. In contrast, the coordinated ether group of the solvate [Tm(dtp)(2)(Et(2)O)], obtained from 9 and TmI(2), could easily be removed by evaporation of the solvent and extraction with pentane at room temperature, and the monomer [Tm(dtp)(2)] (5) could be isolated and was characterised by X-ray crystallography. Presumably, steric crowding in 5 is too high for dimerisation to occur. Compound 5, the first Tm(II) homoleptic sandwich complex, is remarkably stable at room temperature in solution and did not noticeably react with nitrogen, in sharp contrast with other thulium(II) species. As expected, 5, 6 and 7 all reacted with azobenzene to give the trivalent complexes [Tm(dtp)(2)(N(2)Ph(2))] (13), [Sm(dsp)(2)(N(2)Ph(2))], (14) and [Sm(dtp)(2)(N(2)Ph(2))] (15), respectively; 13 and 14 were characterised by X-ray crystallography. Complex 5 immediately reacted with triphenylphosphane sulfide at room temperature to give [[Tm(dtp)(2)](2)(mu-S)] (16), which was characterised by X-ray crystallography, whereas samarium(II) complexes 6 and 7 did not noticeably react with Ph(3)PS over 24 h under the same conditions.

Synthesis and structure of phospholyl- and arsolylthulium(II) complexes.

Reaction of thulium diiodide with substituted phospholide and arsolide salts respectively afforded stable bis(phospholyl)- and bis(arsolyl)thulium(II) complexes, that were characterised by multinuclear NMR and X-ray crystal structures, thus showing the beneficial effects of the steric and electronic properties of crowded phospholyl and arsolyl ligands for the stabilisation of divalent thulium.