RESUMO
Transition metal triple-decker complexes are an interesting class of sandwich complexes that engrossed great attention due to their structures and properties. Over the decades, synthesis of triple-decker complexes featuring homocyclic, heterocyclic or π-conjugated rings as middle decks have been abundantly reported. In this regard, the chemistry of such complexes bearing boron in the middle deck are well explored due to the ability of boron-containing cycles to readily coordinate bifacially with metal atoms thereby forming triple-decker complexes. On the other hand, electron counting rules and theoretical calculations have strengthened our knowledge of the structure and bonding in these complexes. Further, these complexes can be used as synthons to generate organometallic polymers having interesting electronic, optical and magnetic properties that can be appropriately tuned to cater to a wide range of applications. In our quest for novel metallaboranes and metallaheteroboranes, we have been successful in isolating various triple-decker complexes that feature boron in the middle deck. This review explained elaborately the synthesis, structures, and bonding in such complexes reported by us and others.
RESUMO
In an attempt to isolate boron-containing tri-niobium polychalcogenide species, we have carried out prolonged thermolysis reactions of [Cp*NbCl4] (Cp* = ɳ5-C5Me5) with four equivalents of Li[BH2E3] (E = Se or S). In the case of the heavier chalcogen (Se), the reaction led to the isolation of the tri-niobium cubane-like cluster [(NbCp*)3(µ3-Se)3(BH)(µ-Se)3] (1) and the homocubane-like cluster [(NbCp*)3(µ3-Se)3(µ-Se)3(BH)(µ-Se)] (2). Interestingly, the tri-niobium framework of 1 stabilizes a selenaborate {Se3BH}- ligand. A selenium atom is further introduced between boron and one of the selenium atoms of 1 to yield cluster 2. On the other hand, the reaction with the sulfur-containing borate adduct [LiBH2S3] afforded the trimetallic clusters [(NbCp*)3(µ-S)4{µ-S2(BH)}] (3) and [(NbCp*)3(µ-S)4{µ-S2(S)}] (4). Both clusters 3 and 4 have an Nb3S6 core, which further stabilizes {BH} and mono-sulfur units, respectively, through bi-chalcogen coordination. All of these species were characterized by 11B{1H}, 1H, and 13C{1H} NMR spectroscopy, mass spectrometry, infrared (IR) spectroscopy, and single-crystal X-ray crystallography. Moreover, theoretical investigations revealed that the triangular Nb3 framework is aromatic in nature and plays a vital role in the stabilization of the borate, borane, and chalcogen units.
