Metal Coordinated Tri‐ and Tetraborane Analogues

Abstract

A series of triborane and tetraborane analogues have been isolated and structurally characterized utilizing chalcogenatoborate ligands Li[BH3(EPh)] (E=S or Se). Thermolysis of [Cp*TaCl4] in the presence of Li[BH3(SPh)] afforded bimetallic tantallaheteroborane [(Cp*Ta)2(μ-η3:η3-B2H4S)(μ-η2:η2-SBH3)] (1) and hexasulfido trimetallic complex [(Cp*Ta)3(μ-S)4(μ-SPh)2] (2). Compound 1 is a fused ditantallaheteroborane, in which both di- and triborane analogues are stabilized by two tantalum atoms. In an attempt to synthesize the selenium analogues of 1 and 2, room-temperature reaction of [Cp*TaCl4] with Li[BH3(SePh)] was carried out, which afforded bimetallic tantallaheteroborane [(Cp*Ta)2{μ-η3:η3-B3H6(SePh)}{μ-SePh}2] (3), monometallic tantallaheteroboranes [Cp*Ta(SePh)2{B4H8-n(SePh)n}] (4: n=0, 5: n=1), and trimetallic species [(Cp*Ta)3(μ-Se)4{μ-Se2(Se)}] (6). Compound 3 is the rarest example of triborane analogue {B3H6(SePh)} in the coordination sphere of two tantalum atoms. Whereas compounds 4 and 5 are examples of unsaturated metallaheteroboranes, in which the tetraborane analogues are stabilized in the coordination sphere of tantalum. One of the unique features of 3 and 5 is the presence of terminal B-SePh. Compound 6 has similar Ta3Se6 trisbutterfly core as that of 2 with additional bridging selenide unit. All the compounds have been characterized by NMR spectroscopy, mass spectrometry, IR spectroscopy and single-crystal X-ray diffraction studies.