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 SmI2 in diethyl ether afforded the homoleptic samarium(H) complexes 7 and 6, respectively, whose solid-state structures, [(Sm(dtp)(2)}(2)] (7a) and [[Sm(dsp)(2)}(2)] (6a), are dimeric owing to coordination of the phosphorus lone pairs to samarium, as shown by X-ray crystallography. Reaction of 8 with TmI2 in diethyl ether afforded [Tm(dsp)(2)(Et2O)], which could not be desolvated without decomposition. In contrast, the coordinated ether group of the solvate [Tm(dtP)(2)(Et2O)], obtained from 9 and TmI2, 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)(N2Ph2)] (13), [Sm(dsp)(2)(N2Ph2)], (14) and [Sm(dtp)(2)(N2Ph2)] (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 Ph3PS over 24 h under the same conditions.