Complexes of the heavier alkaline earth metals containing β-diketiminato and iodide ligand sets

Abstract

Treatment of [ ( 2 , 6 - i Pr 2 C 6 H 3 ) NC ( t Bu ) CH 2 C ( t Bu ) N ( 2 , 6 - i Pr 2 C 6 H 3 ) ] ( L Ar ′ H ) with potassium hydride in tetrahydrofuran afforded K ( η 1 - L Ar ′ ) ( THF ) 3 (89%) as a yellow crystalline solid after workup. The crystal structure of K ( η 1 - L Ar ′ ) ( THF ) 3 revealed an open monomeric molecule in which the potassium ion is bonded to three tetrahydrofuran ligands and one η 1-β-diketiminato ligand through one of the nitrogen atoms. Treatment of K ( η 1 - L Ar ′ ) ( THF ) 3 with equimolar amounts of MI 2 (M = Ca, Ba) afforded [ Ca ( η 5 - L Ar ′ ) ( μ - I ) ( THF ) ] 2 (62%) and [ Ba ( η 2 - L Ar ′ ) ( μ - I ) ] 2 (27%) as yellow crystalline solids. Treatment of M(η 5-L tBu ) 2 (M = Ca, Sr, Ba, L tBu = tBuNC(CH 3)CHC(CH 3)N tBu −) with the corresponding metal iodide in tetrahydrofuran afforded [Ca(η 5-L tBu )(μ-I)(THF)] 2 (68%), [Sr(η 5-L tBu )(μ-I)(THF)] 2 (53%), and [(η 5-L tBu )Ba(μ-I)(μ-η 2:η 5-L tBu )Ba(η 5-L tBu )] 2(24%). Structural assignments for these complexes were based on spectral and analytical data as well as X-ray crystallography. [Ca(η 5-L tBu )(μ-I)(THF)] 2 and [Sr(η 5-L tBu )(μ-I)(THF)] 2 are dimers that are held together by bridging iodide ligands, while [Ba(η 5-L tBu )(μ-I)(μ-η 2:η 5-L tBu )Ba(η 5-L tBu )] 2 is a tetramer containing two symmetrical dimeric units that are linked by two bridging iodide ligands. In benzene- d 6 solution, [ Ca ( η 5 - L Ar ′ ) ( μ - I ) ( THF ) ] 2 and [ Ba ( η 2 - L Ar ′ ) ( μ - I ) ] 2 are stable toward ligand redistribution. [Ca(η 5-L tBu )(μ-I)(THF)] 2 exists as mixtures of three species in toluene- d 8, but the mixed ligand complex is strongly favored under the conditions studied. At 31.3 °C, the equilibrium constant for ligand redistribution of [Sr(η 5-L tBu )(μ-I)(THF)] 2 to Sr(η 5-L tBu ) 2 and SrI 2(THF) 2 in toluene- d 8 was 5.3 × 10 −5 M.