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The reaction of the 11-vertex rhodathiaborane [8,8,8-(H)(PPh 3 ) 2 -3-(NC 5 H 5 )- nido -7,8-RhSB 9 H 10 ] ( 1 ) with 1,2-bis(diphenylphosphine)benzene (dppbz) and ( S )-(-)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (binap) affords [1,1-(η 2 -dppbz)-3-(NC 5 H 5 )- closo -1,2-RhSB 9 H 8 ] ( 2 ) and [1,1-(η 2 -binap)-3-(NC 5 H 5 )- closo -1,2-RhSB 9 H 8 ] ( 3 ). These 11-vertex closo -rhodathiaborane chelates result from PPh 3 ligand substitution at the rhodium center and a nido -to- closo structural cluster transformation driven by H 2 loss. Treating compounds 2 and 3 with triflic acid (TfOH) leads to the formation of cationic clusters 4 and 5 . The hydrons bind to the polyhedral clusters, acquiring hydride character and providing chemical nonrigidity that manifests through metal vertex-to-thiaborane pseudo -rotations and concomitant hydron tautomerisms. The resulting cations react with hydrogen to form mixtures of hydrons, hydrogen, and hydridorhodathiaboranes in equilibrium. The reaction products are the result of heterolytic cleavage of the H-H bond, with full participation of the clusters and the addition of hydrogen atoms to the cages. In these reactions, there is a conversion of electrons and hydrons into hydrogen, and hydrogen into hydride ligands, demonstrating that these boron-based metal compounds act as electron reservoirs, capable of promoting multielectron processes.

The 1,8-bis(dimethylamino)naphthalenium ([PSH] + ) decaborane salt, [PSH][B 10 H 13 ], has been found to react in ethanol to form [PSH][B 9 H 14 ] ( 1 ), affording a simple route to the synthesis of the arachno -nonaborate anion. This new polyhedral salt is characterized by NMR spectroscopy and X-ray diffraction. The measurement of diffusion coefficients by NMR methods demonstrates that the [PSH] + cation and the [B 9 H 14 ] - anion form ion pairs in a non-coordinating solvent such as CH 2 Cl 2 , whereas in CD 3 CN the formation of ion pairs was not observed. Insights into the long-known low-energy dynamic behavior, which involves the bridging and endo -terminal hydrogen atoms, are elucidated using DFT calculations. Salts [PSH][B 9 H 14 ] ( 1 ) and [PSH][B 9 H 14 ]·0.5CHCl 3 (solvated, 1· 0.5CHCl 3 ) have also been studied by X-ray diffraction analysis. A solid-state NMR study has demonstrated that K[B 9 H 14 ] and [PSH][B 9 H 14 ] ( 1 ) undergo significantly different motion regimes, being a low-energy, weakly temperature-dependent process for 1 , which may be ascribed to some type of low-amplitude reorientation of the whole boron cages. This process may be the mechanism for the low- to-room-temperature order-disorder hidden transition found by X-ray analysis.

High yields of novel macropolyhedral selenaboranes are reported. Reactions of the monoanions of the syn - and anti -isomers of B 18 H 22 with powdered selenium in THF variously give new macropolyhedral selenaboranes: 19-vertex [SeB 18 H 19 ] - anion 1 , 19-vertex [SeB 18 H 21 ] - anion 2 , 20-vertex [Se 2 B 18 H 19 ] - anion 3 , and 19-vertex [Se 2 B 17 H 18 ] - anion 4 . Single-cluster [ hypho -Se 2 B 6 H 9 ] - anion 5 and neutral arachno -Se 2 B 7 H 9 6 also result. All of the macropolyhedrals 1 , 2 , 3 , and 4 are characterized by NMR spectroscopy and mass spectrometry, and by single-crystal X-ray diffraction analyses. Anions 1 and 2 each consist of an 11-vertex subcluster joined by a common two-boron edge to a 10-vertex subcluster. Anion 3 consists of an 11-vertex subcluster joined by a common boron atom and an interboron link to an arachno -type 10-vertex subcluster. Unusually, anion 3 incorporates a hexagonal pyramidal intracluster structural motif in its 11-vertex subcluster. Anion 4 entails two arachno -type 10-vertex subclusters joined by a common boron atom, and with an additional intercluster boron-boron link. NMR data for syn -B 18 H 22 and its mono- and dianions 7 and 8 and single-crystal X-ray diffraction results for these anions and also the monoanion 9 of anti -B 18 H 22 are also reported. The oxaborane [μ-(8,9)-O- syn -B 18 H 20 ] 2- dianion 10 was serendipitously formed during the work and also characterized by a single-crystal X-ray diffraction study. Experimental NMR and structural findings are supported by DFT calculations throughout.

The discovery of systems that interact with small molecules plays a vital facilitating role in the development of devices that show sensitivity to their surroundings and an ability to quickly relay chemical and physical information. Herein, we report on the reaction of [NiCl 2 (dppe)] with decaborane that produces in usable yield a new 11-vertex nickelaborane, [7,7-(dppe)- nido -7-NiB 10 H 12 ] ( 1 ), which shows interesting reactivity and functionality toward carbon monoxide and ethylisonitrile. This contribution describes the synthesis and full structural characterization of 1 and its small-molecule EtNC and CO adducts, 2 and 3 , and delineates the dynamic molecular behavior of all of these species in solution. This information sets a foundation from which more advanced work on this and related metallaborane systems can be conceived and provides a more general reference to how NMR spectroscopy, combined with DFT calculations, can be used to analyze the precise locomotion of labile ligands around a metal center held within a borane cluster.

The reaction of K[ arachno- B 9 H 14 ] with [NiCl 2 (dppe)] produces four new 19-vertex macropolyhedral metallaboranes that result from borane cluster fusion: [9'-(dppe)-9'-Ni- anti -B 18 H 20 ] ( 1 ) and isomeric [11'-(dppe)-11'-Ni- syn -B 18 H 20 ] ( 2 ), together with the chlorine-substituted derivative of 1 , [5'-Cl-9'-(dppe)-9'-Ni- anti -B 18 H 19 ] ( 3 ), and the 18-vertex cluster compound [7'-(dppe)-7'- anti -NiB 17 H 21 ] ( 4 ). Two closo 10-vertex single-cluster species, [1-(dppe)-1- closo- NiB 9 H 7 Cl 2 ] ( 5 ) and [1-(dppe)-1- closo -NiB 9 H 7 Cl(OH)] ( 6 ), were also isolated from the reaction. The production of the metalated syn -octadecaborane isomer 2 from the fusion of two arachno -nonaborate clusters is the first such case to be observed; in all other reported cases fusion has resulted in products with the anti- octadecaboranyl bis-nido configuration.

The reaction of the 11-vertex rhodathiaborane, [8,8-(PPh3)2-nido-8,7-RhSB9H10] (1), with NH3 affords inmediately the adduct, [8,8,8-(NH3)(PPh3)2-nido-8,7-RhSB9H10] (4). The NH3-Rh interaction induces the labilization of the PPh3 ligands leading to the dissociation product, [8,8-(NH3)(PPh3)-nido-8,7-RhSB9H10] (5), which can then react with another molecule of NH3 to give [8,8,8-(NH3)2(PPh3)-nido-8,7-RhSB9H10] (6). These clusters have been characterized in situ by multielement NMR spectroscopy at different temeperatures. The variable temperature behavior of the system demonstrates that the intermediates 4-6 are in equilibrium, involving ligand exchange processes. On the basis of low intensity signals present in the (1)H NMR spectra of the reaction mixture, some species are tentatively proposed to be the bis- and tris-NH3 ligated clusters, [8,8-(NH3)2-nido-8,7-RhSB9H10] (7) and [8,8,8-(NH3)3-nido-8,7-RhSB9H10] (8). After evaporation of the solvent and the excess of NH3, the system containing species 4-8 regenerates the starting reactant, 1, thus closing a stoichiometric cycle of ammonia addition and loss. After 40 h at room temperature, the reaction of 1 with NH3 gives the hydridorhodathiaborane, [8,8,8-(H)(PPh3)2-nido-8,7-RhSB9H9] (2), as a single product. The reported rhodathiaboranes show reversible H3N-promoted ligand lability, which implies weak Rh-N interactions, leading to a rare case of metal complexes that circumvent "classical" Werner chemistry.

Reactions of [8,8,8-(H)(PPh(3))(2)-9-(Py)-nido-8,7-RhSB(9)H(9)] (1), [1,1-(PPh(3))(2)-3-(Py)-closo-1,2-RhSB(9)H(8)] (2), and [1,1-(CO)(PPh(3))-3-(Py)-closo-1,2-RhSB(9)H(8)] (4), where Py = Pyridine, with HCl to give the Cl-ligated clusters, [8,8-(Cl)(PPh(3))-9-(Py)-nido-8,7-RhSB(9)H(9)] (3) and [8,8,8-(Cl)(CO)(PPh(3))-9-(Py)-nido-8,7-RhSB(9)H(8)] (5), have recently demonstrated the remarkable nido-to-closo redox flexibility and bifunctional character of this class of 11-vertex rhodathiaboranes. To get a sense of the scope of this chemistry, we report here the reactions of PR(3)-ligated analogues, [8,8,8-(H)(PR(3))(2)-9-(Py)-nido-8,7-RhSB(9)H(9)], where PR(3) = PMePh(2) (6), or PPh(3) and PMe(3) (7); and [1,1-(PR(3))(2)-3-(Py)-closo-1,2-RhSB(9)H(8)], where PR(3) = PPh(3) and PMe(3) (8), PMe(3) (9) or PMe(2)Ph (10), with HCl to give Cl-ligated clusters. The results demonstrate that in contrast to the PPh(3)-ligated compounds, 1, 2, and 3, the reactions with 6-10 are less selective, giving rise to the formation of mixtures that contain monophosphine species, [8,8-(Cl)(PR(3))-9-(Py)-nido-8,7-RhSB(9)H(9)], where PR(3) = PMe(3) (11), PMe(2)Ph (12), or PMePh(2) (15), and bis-ligated derivatives, [8,8,8-(Cl)(PR(3))(2)-9-(Py)-nido-8,7-RhSB(9)H(9)], where PR(3) = PMe(3) (13) or PMe(2)Ph (14). The {RhCl(PR(3))}-containing compounds, 3, 11, 12, and 15, are formally unsaturated 12 skeletal electron pair (sep) clusters with nido-structures. Density functional theory (DFT) calculations demonstrate that the nido-structure is more stable than the predicted closo-isomers. In addition, studies have been carried out that involve the reactivity of 3 with Lewis bases. Thus, it is reported that 3 interacts with MeCN in solution, and it reacts with CO and pyridine to give the corresponding Rh-L adducts, [8,8,8-(Cl)(L)(PPh(3))-9-(Py)-nido-8,7-RhSB(9)H(9)], where L = CO (5) or Py (20). On the other hand, the treatment of 3 and 5 with Proton Sponge (PS) promotes the abstraction of HCl, as [PSH]Cl, from the nido-clusters, and the regeneration of the parent closo-species, completing two new stoichiometric cycles that are driven by Brønsted acid/base chemistry.

Three nido-decaborane thiol cluster compounds, [1-(HS)-nido-B(10)H(13)] 1, [2-(HS)-nido-B(10)H(13)] 2, and [1,2-(HS)(2)-nido-B(10)H(12)] 3 have been characterized using NMR spectroscopy, single-crystal X-ray diffraction analysis, and quantum-chemical calculations. In the solid state, 1, 2, and 3 feature weak intermolecular hydrogen bonding between the sulfur atom and the relatively positive bridging hydrogen atoms on the open face of an adjacent cluster. Density functional theory (DFT) calculations show that the value of the interaction energy is approximately proportional to the number of hydrogen atoms involved in the interaction and that these values are consistent with a related bridging-hydrogen atom interaction calculated for a B(18)H(22)·C(6)H(6) solvate. Self-assembled monolayers (SAMs) of 1, 2, and 3 on gold and silver surfaces have been prepared and characterized using X-ray photoelectron spectroscopy. The variations in the measured sulfur binding energies, as thiolates on the surface, correlate with the (CC2) calculated atomic charge for the relevant boron vertices and for the associated sulfur substituents for the parent B(10)H(13)(SH) compounds. The calculated charges also correlate with the measured and DFT-calculated thiol (1)H chemical shifts. Wetting-angle measurements indicate that the hydrophilic open face of the cluster is directed upward from the substrate surface, allowing the bridging hydrogen atoms to exhibit a similar reactivity to that of the bulk compound. Thus, [PtMe(2)(PMe(2)Ph)(2)] reacts with the exposed and acidic B-H-B bridging hydrogen atoms of a SAM of 1 on a gold substrate, affording the addition of the metal moiety to the cluster. The XPS-derived stoichiometry is very similar to that for a SAM produced directly from the adsorption of [1-(HS)-7,7-(PMe(2)Ph)(2)-nido-7-PtB(10)H(11)] 4. The use of reactive boron hydride SAMs as templates on which further chemistry may be carried out is unprecedented, and the principle may be extended to other binary boron hydride clusters.

Metallaborane compounds containing two adjacent metal atoms, [(PMe(2)Ph)(4)MM'B(10)H(10)] (where MM' = Pt(2), 1; PtPd, 7; Pd(2), 8), have been synthesized, and their propensity to sequester O(2), CO, and SO(2) and to then release them under pulsed and continuous irradiation are described. Only [(PMe(2)Ph)(4)Pt(2)B(10)H(10)], 1, undergoes reversible binding of O(2) to form [(PMe(2)Ph)(4)(O(2))Pt(2)B(10)H(10)] 3, but solutions of 1, 7, and 8 all quantitatively take up CO across their metal-metal vectors to form [(PMe(2)Ph)(4)(CO)Pt(2)B(10)H(10)] 4, [(PMe(2)Ph)(4)(CO)PtPdB(10)H(10)] 10, and [(PMe(2)Ph)(4)(CO)Pd(2)B(10)H(10)] 11, respectively. Crystallographically determined interatomic M-M distances and infrared CO stretching frequencies show that the CO molecule is bound progressively more weakly in the sequence {PtPt} > {PtPd} > {PdPd}. Similarly, SO(2) forms [(PMe(2)Ph)(4)(SO(2))Pt(2)B(10)H(10)] 5, [(PMe(2)Ph)(4)(SO(2))PtPdB(10)H(10)] 12, and [(PMe(2)Ph)(4)(SO(2))Pd(2)B(10)H(10)] 13 with progressively weaker binding of the SO(2) molecule. The uptake and release of gas molecules are accompanied by changes in their absorption spectra. Nanosecond transient absorption spectroscopy clearly shows that the O(2) and CO molecules are liberated from the bimetallic binding site with high quantum yields of about 0.6. For 3, in addition to dioxygen release in the triplet ground state, singlet oxygen O(2)((1)Δ(g)) was also detected with a quantum yield <0.01. In most cases, the release and rebinding of the gas molecules can be cycled with little photodegradation of the compounds. Femtosecond transient absorption spectroscopy further reveals that the photorelease of the O(2) and CO molecules, from 3 and 4 respectively, is an ultrafast process taking place on a time scale of tens of picoseconds. For SO(2), the release is even faster (<1 ps), but only in the case of mixed metal PtPd adducts, most probably because of the metal-metal bonding asymmetry in the mixed metal clusters; for the corresponding symmetric Pt(2) and Pd(2) adducts, 5 and 13, the release of SO(2) is significantly slower (>1 ns). All these compounds may have potential to serve as light-triggered local and instantaneous sources of the studied gases., (© 2011 American Chemical Society)

The reaction between [IrCl(CO)(PMe(3))(2)] and the Cs[arachno-6-SB(9)H(12)] salt in CH(2)Cl(2) yields pale-yellow 11-vertex [8,8,8-(CO)(PMe(3))(2)-nido-8,7-IrSB(9)H(10)] (4). Reaction of this CO-ligated iridathiaborane with Me(3)N=O affords pale-yellow 11-vertex [1,1,1-(H)(PMe(3))(2)-isonido-1,2-IrSB(9)H(9)] (6), which is also formed from the thermal decarbonylation of 4. Compound 4 has a conventional cluster structure based on classical 11-vertex nido geometry, with the iridium center and the sulfur atom in the adjacent 8- and 7-positions on the pentagonal open face. Compound 6 exhibits an 11-vertex isonido structure based on an octadodecahedron with the {Ir(H)(PMe(3))(2)} occupying the apical position of connectivity six, but with one long non-bonding Ir-B distance generating the quadrilateral isonido open-face. Compound 6 reverts to 4 upon reaction with CO, and the Lewis acid character of 6 is further demonstrated in the reaction with EtNC to give [8,8,8-(EtNC)(PMe(3))(2)-nido-8,7-IrSB(9)H(10)] (7). The three new compounds 4, 6, and 7 have been characterized by single-crystal X-ray diffraction analyses and by NMR spectroscopy. Each of the nido iridathiaboranes 4 and 7 exhibits two different {Ir(L)(PMe(3))(2)}-to-{SB(9)H(10)} conformers in solution and in the solid state. Density functional theory (DFT) calculations reveal that the iridium atom inverts the nido-isonido-closo energy profile previously found for the rhodathiaborane congener [8,8-(PPh(3))(2)-nido-8,7-RhSB(9)H(10)] (3), demonstrating how the structure of these 11-vertex clusters can be controlled and fine-tuned by the tailoring of the metal center.

Treatment of [RhCl(eta4-diene)]2 (diene = nbd, cod) with the N-heterocyclic ligands 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), and pyridine (py) followed by addition of Cs[arachno-6-SB9H12] affords the corresponding salts, [Rh(eta4-diene)(L2)][SB9H12] [diene = cod, L2 = bpy (1), Me2bpy (3), phen (5), (py)2 (7); diene = nbd, L2 = bpy (2), Me2bpy (4), phen (6), (py)2 (8)]. These compounds are characterized by NMR spectroscopy and mass spectrometry, and in addition, the cod-Rh species 1 and 3 are studied by X-ray diffraction analysis. These saltlike reagents are stable in the solid state, but in solution the rhodium(I) cations, [Rh(eta4-diene)(L2)]+, react with the polyhedral anion [SB9H12]- leading to a chemistry that is controlled by the d8 transition element chelates. The nbd-Rh(I) complexes react faster than the cod-Rh(I) counterparts, leading, depending on the conditions, to the synthesis of new rhodathiaboranes of general formulas [8,8-(L2)-nido-8,7-RhSB9H10] [L2 = bpy (9), Me2bpy (10), phen (11), (py)2 (12)] and [8,8-(L2)-8-(L')-nido-8,7-RhSB9H10] [L' = PPh3, L2 = bpy (13), Me2bpy (14), phen (15); L' = NCCH3, L2 = bpy (16), Me2bpy (17), phen (18)]. Compound 13 is characterized by X-ray diffraction analysis confirming the 11-vertex nido-structure of the rhodathiaborane analogues 14-18. In dichloromethane, 1 and 3 yield mixtures that contain the 11-vertex rhodathiaboranes 9 and 10 together with new species. In contrast, the cod-Rh(I) reagent 5 affords a single compound, which is proposed to be an organometallic rhodium complex bound exo-polyhedrally to the thiaborane cage. In the presence of H2(g) and stoichiometric amounts of PPh3, the cod-Rh(I) reagents, 1, 3, and 5, afford the salts [Rh(H)2(L2)(PPh3)2][SB9H12] [L2 = bpy (19), Me2bpy (20), phen (21)]. Similarly, in an atmosphere of CO(g) and in the presence of PPh3, compounds 1-6 afford [Rh(L2)(PPh3)2(CO)][SB9H12] (L2 = bpy (22), Me2bpy (23), phen (24)]. The structures of 19 and 24 are studied by X-ray diffraction analysis. The five-coordinate complexes [Rh(L2)(PPh3)2(CO)]+ undergo PPh3 exchange in a process that is characterized as dissociative. The observed differences in the reactivity of the nbd-Rh(I) salts versus the cod-Rh(I) analogues are rationalized on the basis of the higher kinetic lability of the nbd ligand and its faster hydrogenation relative to the cod diene.

The two clusters [8,8-(eta(2)-dppm)-8-(eta(1)-dppm)-nido-8,7-RhSB(9)H(10)] (1) and [9,9-(eta(2)-dppm)-9-(eta(1)-dppm)-nido-9,7,8-RhC(2)B(8)H(11)] (2) (dppm = PPh(2)CH(2)PPh(2)), both of which contain pendant PPh(2) groups, react with BH(3).thf to afford the species [8,8-eta(2)-(eta(2)-(BH(3)).dppm)-nido-8,7-RhSB(9)H(10)] (3) and [9,9-eta(2)-(eta(2)-(BH(3)).dppm))-nido-9,7,8-RhC(2)B(8)H(11)] (4), respectively. These two species are very similar in that they both contain the bidentate ligand [(BH(3)).dppm], which coordinates to the Rh center via a PPh(2) group and also via a eta(2)-BH(3) group. Thus, the B atom in the BH(3) group is four-coordinate, bonded to Rh by two bridging hydrogen atoms, to a terminal H atom, and to a PPh(2) group. At room temperature, the BH(3) group is fluxional; the two bridging H atoms and the terminal H atom are equivalent on the NMR time scale. The motion is arrested at low temperature with DeltaG++ = ca. 37 and 42 kJ mol(-1), respectively, for 3 and 4. Both species are characterized completely by NMR and mass spectral measurements as well as by elemental analysis and single-crystal structure determinations.