New Trinuclear Complexes of Group 6, 8, and 9 Metals with a Triply Bridging Borylene Ligand

Trinuclear complexes of group 6, 8, and 9 transition metals with a (μ₃‐BH) ligand [(μ₃‐BH)(Cp*Rh)₂(μ‐CO)M′(CO)₅], 3 and 4 ( 3 : M′=Mo; 4 : M′=W) and 5 – 8 , [(Cp*Ru)₃(μ₃‐CO)₂(μ₃‐BH)(μ₃‐E)(μ‐H){M′(CO)₃}] ( 5 : M′=Cr, E=CO; 6 : M′=Mo, E=CO; 7 : M′=Mo, E=BH; 8 : M′=W, E=CO), have been synthesized from the reaction between nido‐[(Cp*M)₂B₃H₇] (nido‐ 1 : M=Rh; nido‐ 2 : M=RuH, Cp*=η⁵‐C₅Me₅) and [M′(CO)₅ ? thf] (M′=Mo and W). Compounds 3 and 4 are isoelectronic and isostructural with [(μ₃‐BH)(Cp*Co)₂(μ‐CO)M′(CO)₅], (M′=Cr, Mo and W) and [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂M′′H(CO)₃], (M′′=Mn and Re). All compounds are composed of a bridging borylene ligand (B?H) that is effectively stabilized by a trinuclear framework. In contrast, the reaction of nido‐ 1 with [Cr(CO)₅ ? thf] gave [(Cp*Rh)₂Cr(CO)₃(μ‐CO)(μ₃‐BH)(B₂H₄)] ( 9 ). The geometry of 9 can be viewed as a condensed polyhedron composed of [Rh₂Cr(μ₃‐BH)] and [Rh₂CrB₂], a tetrahedral and a square pyramidal geometry, respectively. The bonding of 9 can be considered by using the polyhedral fusion formalism of Mingos. All compounds have been characterized by using different spectroscopic studies and the molecular structures were determined by using single‐crystal X‐ray diffraction analysis.     

From Metallaborane to Borylene Complexes: Syntheses and Structures of Triply Bridged Ruthenium and Tantalum Borylene Complexes

Reaction of [1,2‐(Cp*RuH)₂B₃H₇] ( 1 ; Cp*=η⁵‐C₅Me₅) with [Mo(CO)₃(CH₃CN)₃] yielded arachno‐[(Cp*RuCO)₂B₂H₆] ( 2 ), which exhibits a butterfly structure, reminiscent of 7 sep B₄H₁₀. Compound 2 was found to be a very good precursor for the generation of bridged borylene species. Mild pyrolysis of 2 with [Fe₂(CO)₉] yielded a triply bridged heterotrinuclear borylene complex [(μ₃‐BH)(Cp*RuCO)₂(μ‐CO){Fe(CO)₃}] ( 3 ) and bis‐borylene complexes [{(μ₃‐BH)(Cp*Ru)(μ‐CO)}₂Fe₂(CO)₅] ( 4 ) and [{(μ₃‐BH)(Cp*Ru)Fe(CO)₃}₂(μ‐CO)] ( 5 ). In a similar fashion, pyrolysis of 2 with [Mn₂(CO)₁₀] permits the isolation of μ₃‐borylene complex [(μ₃‐BH)(Cp*RuCO)₂(μ‐H)(μ‐CO){Mn(CO)₃}] ( 6 ). Both compounds 3 and 6 have a trigonal‐pyramidal geometry with the μ₃‐BH ligand occupying the apical vertex, whereas 4 and 5 can be viewed as bicapped tetrahedra, with two μ₃‐borylene ligands occupying the capping position. The synthesis of tantalum borylene complex [(μ₃‐BH)(Cp*TaCO)₂(μ‐CO){Fe(CO)₃}] ( 7 ) was achieved by the reaction of [(Cp*Ta)₂B₄H₈(μ‐BH₄)] at ambient temperature with [Fe₂(CO)₉]. Compounds 2 – 7 have been isolated in modest yield as yellow to red crystalline solids. All the new compounds have been characterized in solution by mass spectrometry; IR spectroscopy; and ¹H, ¹¹B, and ¹³C NMR spectroscopy and the structural types were unequivocally established by crystallographic analysis of 2 – 6 .     

Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(eta5-C5Me5)Ta}2BnHm] (n=4, m=10; n=5, m=11), [{(eta5-C5Me5)Ta}2B5H10(C6H4CH3)], and [{(eta5-C5Me5)TaCl}2B5H11

Reaction of [Cp*TaCl4] (Cp*=eta5-C5Me5) with a sixfold excess of LiBH(4)thf followed by BH3thf in toluene at 100 degrees C led to the isolation of hydrogen-rich metallaboranes [(Cp*Ta)2B4H10] (1), [(Cp*Ta)2B5H11] (2), [(Cp*Ta)2B5H10(C6H4CH3)] (3), and [(Cp*TaCl)2B5H11] (4) in modest yield. Compounds 1-3 are air- and moisture-sensitive but 4 is reasonably stable in air. Their structures are predicted by the electron-counting rules to be a bicapped tetrahedron (1), bicapped trigonal bipyramids (2, 3), and a nido structure based on a closo dodecahedron 4. Yellow tantalaborane 1 has a nido geometry with C2v symmetry and is isostructural with [(Cp*M)2B4H8] (M=Cr and Re); whereas 2 and 3 are C3v-symmetric and isostructural with [(Cp*M)2B5H9] (M=Cr, Mo, W) and [(Cp*ReH)2B5Cl5]. The most remarkable feature of 4 is the presence of a hydride ligand bridging the ditantalum center to form a symmetrical tantalaborane cluster with a long Ta--Ta bond (3.22 A). Cluster 4 is a rare example of electronically unsaturated metallaborane containing four TaHB bonds. All these new metallaboranes have been characterized by mass spectrometry, 1H, 11B, and 13C NMR spectroscopy, and elemental analysis, and the structural types were unequivocally established by crystallographic analysis of 1-4.     

Metal-Rich Metallaboranes: Synthesis,Structure, and Bonding of Heteronuclear Trimetallic Clusters containing (μ3-BH) Ligand

Building upon our earlier results on the chemistry of nido-1,2-[(Cp*RuH)₂B₃H₇] (Cp*=ɳ⁵-C₅Me₅) (nido- 1 ) with different transition metal carbonyls, we continued to investigate the reactivity with group 7 metal carbonyls under photolytic condition. Photolysis of nido- 1 with [Mn₂(CO)₁₀] led to the isolation of a trimetallic [(Cp*Ru)₂{Mn(CO)₃}(μ-H)(μ-CO)₃(μ₃-BH)] ( 2 ) cluster with a triply bridging borylene moiety. Cluster 2 is a rare example of a tetrahedral cluster having hydrido(hydroborylene) moiety. In an attempt to synthesize the Re analogue of 2 , a similar reaction was carried out with [Re₂(CO)₁₀] that yielded the trimetallic [(Cp*Ru)₂{Re(CO)₃}(μ-H)(μ-CO)₃(μ₃-BH)] ( 3 ) cluster having a triply bridging borylene unit. Along with 3 , a trimetallic square pyramid cluster [(Cp*Ru)₂{Re(CO)₃}(μ-H)₂(μ-CO)(μ₃,ɳ²-B₂H₅)] ( 4 ), and heterotrimetallic hydride clusters [{Cp*Ru(CO)₂}-{Re(CO)₄}₂(μ-H)] ( 5 ) and [{Cp*Ru(CO)}{Re(CO)₄}₂(μ-H)₃] ( 6 ) were isolated. Cluster 4 is a unique example of a M₂M′B₂ cluster having diboron capped Ru₂Re-triangle. The hydride clusters 5 and 6 have triangular RuRe₂ frameworks with one and three μ-Hs respectively. All the clusters have been characterized by using mass spectrometry, ¹H, ¹¹B{¹H}, ¹³C{¹H} NMR and IR spectroscopies analyses and the structures of clusters 2 – 6 have been unambiguously established by XRD analyses. Furthermore, to understand the electronic, structural, and bonding features of the synthesized metal-rich clusters, DFT calculations have been performed.     

From Intercalation to Groove Binding: Switching the DNA‐Binding Mode of Isostructural Transition‐Metal Complexes

The interaction with duplex DNA of a small library of structurally related complexes that all contain a d⁶‐metal ion coordinated to either the 2,2 ′ :4,4 ′′ :4 ′ ,4 ′′′ ‐quaterpyridyl ligand or its methylated derivative are reported. This library is made up of a mixture of newly synthesised and previously reported systems. Despite their structural similarities the complexes display an almost 20‐fold variation in binding affinities. Although effects due to the overall charge of the complexes are apparent, the differences in binding characteristics are deeper than this; indeed, in a number of cases, changes in overall charge have little effect on binding affinity. Intriguingly, despite interacting with DNA through unfused ring systems, although two of the complexes studied are groove binders, the majority are non‐classical intercalators. A rationale for these effects has been obtained through a combination of experimental and computational studies.     

Dual Esterase‐ and Steroid‐Responsive Energy Transfer Modulation of Ruthenium(II) and Rhenium(I) Complex Functionalized Gold Nanoparticles

A number of adamantane‐containing ruthenium(II) and rhenium(I) complexes have been synthesized, characterized, and noncovalently functionalized with β‐cyclodextrin‐capped gold nanoparticles (β‐CD–GNPs) through the host–guest interaction between cyclodextrin and adamantane. The resultant nanoconjugates have been characterized by transmission electron microscopy (TEM), energy‐dispersive X‐ray analysis (EDX), and 2D ROESY ¹H NMR experiments. The Förster resonance energy transfer (FRET) properties of the nanoconjugates can be modulated by both esterase‐accelerated hydrolysis and competitive displacement of steroid, by monitoring the emission intensity and luminescence lifetime. The FRET efficiencies are found to vary with the nature of the chromophores and the length of the spacer between the transition metal complexes and the GNPs. This work constitutes a “proof‐of‐principle” assay method for the dual‐functional detection of important classes of biomolecules, such as enzymes and steroids.