Chalcogen stabilized trimetallic clusters: Synthesis, structures, and bonding of [(Cp∗M) <inf>3</inf> (E) <inf>6+: M</inf> (BH) <inf>n</inf> ] (M = Nb or Ta; E = S or Se; M = 0 or 1 or 2; N = 0 or 1)

In an effort to isolate the chalcogen-rich niobium analogue of [(Cp∗Ta) 3 (μ-S) 3 (μ 3 -S) 3 BH], the room temperature reaction of [Cp∗NbCl 4 ] (Cp∗ = η 5 -C 5 Me 5 ) with Li[BH 2 S 3 ] was carried out. Although the objective of isolating the niobium analogue was not achieved, the reaction yielded a homocubane-type cluster [(Cp∗Nb) 3 (μ-S) 3 (μ 3 -S) 3 (μ-S)BH], 1, and a hexa-sulfido cluster [(Cp∗Nb) 3 (μ-S) 6 ], 2. Cluster 1 is a notable example of a homocubane-type cluster in which one of the vertices of the homocubane is missing. Compound 1 may be considered as a hypo-electronic cluster with an electron count of 64 cve (cve = cluster valence electrons), whereas compound 2 shows the presence of two doubly bridging η 1 -S around each Nb-Nb bond. On the other hand, the room temperature reaction of [Cp∗TaCl 4 ] with selenaborate ligand, [LiBH 2 Se 3 ], led to the formation of [(Cp∗Ta) 3 (μ-Se) 4 {μ-Se 2 (Se 2 )}], 3. Compound 3 is one of the rarest examples having a Ta 3 Se 6 core structure with a unique diselenide bridging fragment. The presence of a short Se-Se bond of this diselenide unit makes this molecule of further interest. All these compounds were characterized by 1 H, 11 B{ 1 H} and 13 C{ 1 H} NMR spectroscopy, infrared spectroscopy, mass spectrometry, and single-crystal X-ray crystallography. Density functional theory (DFT) calculations were carried out to provide insight into the bonding and electronic structures of these chalcogen-rich trimetallic clusters.