1,2,4-Diazaphospholide Complexes of Barium: Mechanism of Formation and Crystallographic Characterization

A number of barium 1,2,4-diazaphospholide (dp−) complexes have been prepared by protonolysis of barium bis[bis(trimethylsilyl)]amide (Ba[N(SiMe3)2]2(THF)2) and the corresponding 1,2,4-diazaphospholes. The bis(3,5-diphenyl-1,2,4-diazaphospholide)-tetrakis(tetrahydrofuran)barium [η2(N,N)-3,5-Ph2dp)2Ba(THF)4] (1) and bis(3,5-diphenyl-1,2,4-diazaphospholide)-tetrakis(dimethylsulfoxide)barium [η2(N,N)-3,5-Ph2dp)2Ba(DMSO)4] (2) were prepared by the reactions of Ba[N(SiMe3)2]2(THF)2 and 3,5-diphenyl-1,2,4-diazaphosphole (H[3,5-Ph2dp]) in tetrahydrofuran (THF) or dimethylsulfoxide (DMSO), respectively, while the bis(3,5-disubstituted-1,2,4-diazaphospholide)-(18-crown-6) barium complexes [trans-η2(N,N)-dp)2Ba(18-crown-6)] (3), [cis-η2(N,N)-tBu2dp)2Ba(18-crown-6)] (4), [trans-η2(N,N)-tBu2dp)2Ba(18-crown-6)] (5), [cis-η2(N,N)-Ph2dp)2Ba(18-crown-6)] (6), and [trans-η2(N,N)-Ph2dp)2Ba(18-crown-6)] (7) were synthesized by the reaction of Ba[N(SiMe3)2]2(THF)2 and the corresponding 1,2,4-diazaphospholes in the presence of 18-crown-6 in THF or DMSO. Complexes 1, 2, 3, 4, and 7 have been structurally characterized. Complex 4 is the first structurally characterized barium complex in which the two organic ligands are located on the same side of 18-crown-6 (cis conformation). The 31P{1H} NMR spectra suggested a partial dissociation of the barium 1,2,4-diazaphospholides 2, 4, and 7 into the corresponding ion associated complexes in solutions.