Chemistry and reactivity of dimolybdathiaborane, [(Cp^∗Mo)₂B₄SH₆], 1, obtained from the reaction of 2-mercaptobenzothiazole, [Cp^∗MoCl₄] and [LiBH₄.thf], has been explored with dinuclear metal carbonyl [Fe₂(CO)₉]. As a result, reaction of 1 with [Fe₂(CO)₉] yielded heterometallathiaborane, [(Cp^∗Mo)₂B₄H₆SFe(CO)₃], 2 in good yield. Both the new compounds have been characterized in solution by ¹H, ¹¹B and ¹³C NMR spectroscopy and the structural types were unequivocally established by X-ray crystallographic analysis of compound 2. Cluster 2 has a bicapped octahedral geometry with the {Fe(CO)₃} fragment occupying one of the high-connectivity cluster vertexes rather than a capping position. Interestingly, cluster 1 undergoes geometric changes (bicapped trigonal bipyramid → bicapped octahedron) on the addition of two-electron {Fe(CO)₃} fragment to 1.

Two Cu²⁺-specific colorimetric sensors, based on ferrocene-carbohydrate bioconjugates, 2, C₄₆H₅₆O₂₀N₆Fe and 3, C₂₈H₃₃O₁₀N₃Fe were designed and synthesized in good yields. Both the compounds, 2 and 3, behave as very selective and sensitive chromogenic and electrochemical chemosensor for Cu²⁺ ion in aqueous environment (CH₃CN/H₂O (2:8, $v/v$). The analytical detection limit (ADL) for receptor 2 was $7.5 \times 10^{−7}$ M. The considerable changes in their absorption spectra of 2 and 3 are accompanied by the appearance of a new low energy (LE) peak at 630 nm (2: $\epsilon = 1600$ M^-1 cm^-1 and 3: 822 M^-1 cm^-1). This is further accompanied by a strong colour change from yellow to dark green that allows the prospective for `naked eye’ detection of Cu²⁺ ion.

Recently we described the synthesis and structural characterization of various dimetallaherteroborane clusters, namely nido-[(Cp^∗Mo)₂B₄ECl$_x$H$_{6−x}$], 1-3; (1: E = S, x = 0; 2: E = Se, x = 0; 3: E = Te, x = 1). A combined theoretical and experimental study was also performed, which demonstrated that the clusters 1-3 with their open face are excellent precursors for cluster growth reaction. In this investigation process on the reactivity of dimetallaheteroboranes with metal carbonyls, in addition to [(Cp^∗Mo)₂B₄H₆EFe(CO)₃] (4: E = S, 6: E = Te) reported earlier, reaction of 2 with [Fe₂(CO)₉] yielded mixed-metallaselenaborane [(Cp^∗Mo)₂B₄H₆SeFe(CO)₃], 5 in good yield. The quantum chemical calculation using DFT method has been carried out to probe the bonding, NMR chemical shifts and electronic properties of dimolybdaheteroborane clusters 4-6.

Reactivity of [Cp*Mo(CO)₃Me], 1 with various chalcogenide ligands such as Li[BH₂E₃] andLi[BH₃EFc]] (E = S, Se or Te; Fc = (C₅H₅-Fe-C₅H&#8324)) has been described. Room temperature reaction of 1 with Li[BH₂E₃] (E = S and Se) yielded metal chalcogenide complexes [Cp*Mo(CO)₂(ŋ2-S₂CCH3)], 2 and [Cp*Mo(CO)₂(ŋ1-SeC₂H₅)], 3. In compound 2, {Cp*Mo(CO)2} fragment adopts a four-legged piano-stool geometry with a η2-dithioacetate moiety. In contrast, treatment of 1 with Li[BH3(EFc)] (E = S, Se or Te; Fc = C₅H₅-Fe-C₅H₄) yielded borate complexes [Cp*Mo(CO)₂(μ-H)(μ-EFc)BH₂], 4-6 in moderate yields. Compounds 4-6 are too unstable and gradual conversion to [{Cp*Mo(CO)₂}₂(μ-H)(μ-EFc] (7: E = S; 8: Se) and [{Cp*Mo(CO)₂}₂(μ-TeFc)₂], 9 happened by subsequent release of BH₃. All the compounds have been characterized by mass spectrometry, IR, multinuclear NMR spectroscopy and structures were unequivocally established by crystallographic analysis for compounds 2, 3 and 7.

Treatment of nido-[1,2-(Cp*Ru)₂(μ-H)₂B₃H₇], 1 with five equivalents of Te powder led to the isolation of diruthenium pentalene analogue [(Cp*Ru){(Cp*Ru)₂B₆H₁₄}(RuCp*)], 2 and a metal indenyl complex [(Cp*Ru)₂B₂H₆C₆H₃ CH₃], 3. The [(Cp*Ru)₂B₆H₁₄] fragment in 2 may be considered as a true metal–boron analogue of η⁵-η⁵-pentalene ligand (C₈H₆) and [(Cp*Ru)B₂H₆C₆H₃ CH₃] fragment in 3 is an analogue of η⁵-indenyl ligand. The solid-state X-ray structures were unambiguously determined by crystallographic analysis of compounds 2 and 3. Further, the density functional theory (DFT) calculationswere performed to investigate the bonding and the electronic properties of 2a (Cp analogue of 2). The frontier molecular orbital analysis of both 2a and 2b (Cp analogue of [(Cp*Ru)B₈H₁₄(RuCp*)]) reveals a lower HOMO–LUMO gap indicating less thermodynamic stability

Syntheses and structural elucidations of a series of chalcogen stabilized binuclear complexes of group 5 and 6 transition metals have been described. Room temperature reaction of [Cp^*CrCl]₂ (Cp^* = h⁵- C₅Me₅) with Li[BH₃(SePh)] afforded a Se inserted binuclear chromium complex, [(Cp^*Cr)₂(m-Se₂SePh)₂], 1.In an attempt to make the analogous complexes with heavier group 6 metals, reactions of [Cp^*MCl₄] (M = Mo and W) with Li[BH₃(SePh)] were carried out that yielded Se inserted binuclear complexes [(Cp^*M)₂(m-Se)₂(m-SePh)₂], 2 and 3 (2: M = Mo and 3: M = W) along with known [(Cp^*M)₂B₅H₉], 4a–b (4a: M = Mo and 4b: M = W). Similarly, the reactions of [Cp^*NbCl₄] with Li[BH₃(EPh)] (E = S or Se)followed by thermolysis led to the formation of binuclear chalcogen complexes [(Cp^*Nb)₂(m-E₂)₂], 5 and 6 (5: E = S and 6: E = Se) and known [(Cp^*Nb)₂(B₂H₆)₆], 7. All these complexes have been characterized by ¹H and ¹³C NMR spectroscopy and mass spectrometry. The structural integrity of complexes 1, 3, 5 and 6 was established by the X-ray diffraction studies. The DFT studies further exemplify the bonding interactions present in these complexes, especially the multiple bond character between the metals in 1–3.