Chemistry of Vanadaboranes: Synthesis, Structures, and Characterization of Organovanadium Sulfide Clusters with Disulfido Linkage

Polyhedral and Macropolyhedral Metal-Rich Cobaltaboranes: A 25-Vertex Hourglass-Shaped Cluster

In an effort to break the single-cage 16-vertex supraicosahedral barrier, we have explored the reaction of [Cp*CoCl2], 1 with [LiBH4·THF], followed by thermolysis with [BH3·SMe2] [Cp* = η5-C5Me5]. Although our objective to synthesize a high-nuclearity single-cage cluster was not achieved, we have isolated a 25-vertex macropolyhedral cluster [(Cp*Co)5Co2B18H17(CH3)S] (2). Cluster 2 is an exceptional fused hourglass-shaped macropolyhedral cluster composing two icosahedral cores ([Co3B9] and [Co4B8]) and three tetrahedral cores [Co2B2]. Although the fusion in cluster 2 is very complex, it follows Mingos fusion formalism, leading to an attractive hourglass-shaped cluster. Through subtle changes in reaction conditions, two new cobaltaborane clusters, nido-4,5,7-[(Cp*Co)3B7H11] (3) and nido-2,9-[(Cp*Co)2B8H12] (4), have been isolated. The observed core geometries of clusters 3 and 4 are similar to the parent deltahedra [B10H14] with (n + 2) SEP (SEP = skeletal electron pair, n = no. of vertices). All the synthesized cobaltaboranes have been characterized in solution by ESI-mass, nuclear magnetic resonance spectroscopy, infrared spectroscopy and structurally solved by single-crystal X-ray diffraction analysis.

Chemistry of CS2 and CS3 Bridged Decaborane Analogues: Regular Coordination Versus Cluster Expansion

In an effort to synthesize metallaheteroborane clusters of higher nuclearity, the reactivity of metallaheteroboranes, nido-[(Cp*M)₂B₆S₂H₄(CS₃)] (Cp* = C₅Me₅) (1: M = Co; 2: M = Rh) with various metal carbonyls have been investigated. Photolysis of nido-1 and nido-2 with group 6 metal carbonyls, M'(CO)₅.THF (M' = Mo or W) were performed that led to the formation of a series of adducts [(Cp*M)₂B₆S₂H₄(CS₃){M'(CO)₅}] (3: M = Co, M' = Mo; 4: M = Co, M' = W; 5: M = Rh, M' = Mo; 6: M = Rh, M' = W) instead of cluster expansion reactions. In these adducts, the S atom of C=S group of di(thioboralane)thione {B₂CS₃} moiety is coordinated to M'(CO)₅ (M = Mo or W) in η¹-fashion. On the other hand, thermolysis of nido-1 with Ru₃(CO)₁₂ yielded one fused metallaheteroborane cluster [{Ru(CO)₃}₃S{Ru(CO)}{Ru(CO)₂}Co₂B₆SH₄(CH₂S₂){Ru(CO)₃}₂S], 7. This 20-vertex-fused cluster is composed of two tetrahedral {Ru₃S} and {Ru₂B₂}, a flat butterfly {Ru₃S} and one octadecahedron {Co₂RuB₇S} core with one missing vertex, coordinated to {Ru₂SCH₂S₂} through two boron and one ruthenium atom. On the other hand, the room temperature reaction of nido-2 with Co₂(CO)₈ produced one 19-vertex fused metallaheteroborane cluster [(Cp*Rh)₂B₆H₄S₄{Co(CO)}₂{Co(CO)₂}₂(μ-CO)S{Co(CO)₃}₂], 8. Cluster 8 contains one nido-decaborane {Rh₂B₆S₂}, one butterfly {Co₂S₂} and one bicapped square pyramidal {Co₆S} unit that exhibits an intercluster fusion with two sulfur atoms in common. Clusters 3-6 have been characterized by multinuclear NMR and IR spectroscopy, mass spectrometry and structurally determined by XRD analyses. Furthermore, the DFT calculations have been carried out to gain insight into electronic, structural and bonding patterns of the synthesized clusters.

Metal-Rich Metallaboranes: Synthesis, Structures and Bonding of Bi- and Trimetallic Open-Faced Cobaltaboranes

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]2 with [LiBH4·THF] and subsequent photolysis with excess [BH3·THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane nido-[(Cp*Co)3B8H10] (1, Cp* = η5-C5Me5). The reaction of Li[BH2S3] with the dicobaltaoctaborane(12) [(Cp*Co)2B6H10] yielded the 10-vertex nido-2,4-[(Cp*Co)2B8H12] cluster (2), extending the library of dicobaltadecaborane(14) analogues. Although cluster 1 adopts a classical 11-vertex-nido-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 adopts a perfectly symmetrical 10-vertex-nido framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB3} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes.

Chemistry of group 5 metallaboranes with heterocyclic thiol ligands: a combined experimental and theoretical study

Thermolysis of [(Cp*Nb)₂(B₂H₆)₂], 1b (Cp* = η⁵-C₅Me₅), with 2-mercaptobenzothiazole, C₆H₄NSCSH (MBT), and 2-mercaptobenzoxazole, C₆H₄NOCSH (MBO), yielded hydrogen substituted compounds 2 and 3 with a general formula [(Cp*Nb)₂(B₂H₆)(B₂H₅L)] (2: L = C₆H₄NSCS and 3: L = C₆H₄NOCS). A similar reaction of 1b with Ph₂Se₂ yielded the monosubstituted derivative [(Cp*Nb)₂(B₂H₆){B₂H₅(PhSe)}], 4. All further efforts towards persubstitution of 1b under various drastic conditions were unfruitful. In parallel, in an effort to find a better synthetic route to the known Ta-aziridine complex [Cp*TaBH(C₇H₄NS₂)CH₂S₂NC₆H₄], Cp*TaCl₄ was treated with a 2-mercaptobenzothiazolyl-based borate ligand Na[H₂B(C₆H₄NSCS)₂]. Surprisingly, the reaction led to the formation of the half-sandwich trichloroaryltantalum(v) complex [Cp*TaCl₃{κ²-N,S-C₆H₄NSCS}], 5, containing a heterocyclic thiol ligand. Using an alternative method complex 5 was isolated in good yield when Cp*TaCl₄ was treated with the potassium salt of 2-mercaptobenzothiazole K[C₆H₄NSCS]. All the compounds were characterized by ¹H, ¹¹B{¹H}, and ¹³C{¹H} NMR spectroscopy, and their structures were unequivocally established by crystallographic analysis.

Selective oxo ligand functionalisation and substitution reactivity in an oxo/catecholate-bridged UIV/UIV Pacman complex

The oxo- and catecholate-bridged U^IV/U^IV Pacman complex [{(py)U^IVOU^IV(μ-O₂C₆H₄)(py)}(L^A)] A (L^A = a macrocyclic "Pacman" ligand; anthracenylene hinge between N₄-donor pockets, ethyl substituents on meso-carbon atom of each N₄-donor pocket) featuring a bent U^IV-O-U^IV oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. Complex A reacts with H₂O or MeOH to afford [{(py)U^IV(μ-OH)₂U^IV(μ-O₂C₆H₄)(py)}(L^A)] (1) and [{(py)U^IV(μ-OH)(μ-OMe)U^IV(μ-O₂C₆H₄)(py)}(L^A)] (2), respectively, in which the bridging oxo ligand in A is substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively, A reacts with either 0.5 equiv. of S₈ or 4 equiv. of Se to provide [{(py)U^IV(μ-η²:η²-E₂)U^IV(μ-O₂C₆H₄)(py)}(L^A)] (E = S (3), Se (4)) respectively, in which the [E₂]^2- ion bridges the two U^IV centres. To the best of our knowledge, complex A is the first example of either a d- or f-block bimetallic μ-oxo complex that activates elemental chalcogens. Complex A also reacts with XeF₂ or 2 equiv. of Me₃SiCl to provide [{(py)U^IV(μ-X)₂U^IV(μ-O₂C₆H₄)(py)}(L^A)] (X = F (5), Cl (6)), in which the oxo ligand has been substituted for two bridging halido ligands. Reacting A with either XeF₂ or Me₃SiCl in the presence of O(Bcat)₂ at room temperature forms [{(py)U^IV(μ-X)(μ-OBcat)U^IV(μ-O₂C₆H₄)(py)}(L^A)] (X = F (5A), Cl (6A)), which upon heating to 80 °C is converted to 5 and 6, respectively. In order to probe the importance of the bent U^IV-O-U^IV motif in A on the observed reactivity, the bis(boroxido)-U^IV/U^IV complex, [{(py)(pinBO)U^IVOU^IV(OBpin)(py)}(L^A)] (B), featuring a linear U^IV-O-U^IV bond angle was treated with H₂O and Me₃SiCl. Complex B reacts with two equiv. of either H₂O or Me₃SiCl to provide [{(py)HOU^IVOU^IVOH(py)}(L^A)] (7) and [{(py)ClU^IVOU^IVCl(py)}(L^A)] (8), respectively, in which reactions occur preferentially at the boroxido ligands, with the μ-oxo ligand unchanged. The formal U^IV oxidation state is retained in all of the products 1-8, and selective reactions at the bridging oxo ligand in A is facilitated by: (1) its highly nucleophilic character which is a result of a non-linear U^IV-O-U^IV bond angle causing an increase in U-O bond covalency and localisation of the lone pairs of electrons on the μ-oxo group, and (2) the presence of the bridging catecholate ligand, which destabilises a linear oxo-bridging geometry and stabilises the resulting products.

Homocubane Chemistry: Synthesis and Structures of Mono- and Dicobaltaheteroborane Analogues of Tris- and Tetrahomocubanes

Room-temperature reactions between [Cp*CoCl]2 (Cp* = η5-C5Me5) and large excess of [BH2E3]Li (E = S or Se) led to the formation of homocubane derivatives, 1-7. These species are bimetallic tetrahomocubane, [(Cp*Co)2(μ-S)4(μ3-S)4B2H2], 1; bimetallic trishomocubane isomers, [(Cp*Co)2(μ-S)3(μ3-S)4B2H2], 2 and 3; monometallic trishomocubanes, [M(μ-E)3(μ3-E)4B3H3] [4: M = Cp*Co, E = S; 5: M = Cp*Co, E = Se and 6: M = {(Cp*Co)2(μ-H)(μ3-Se)2}Co, E = Se], and bimetallic homocubane, [(Cp*Co)2(μ-Se)(μ3-Se)4B2H2], 7. As per our knowledge, 1 is the first isolated and structurally characterized parent prototype of the 1,2,2',4 isomer of tetrahomocubane, while 3, 4, and 5 are the analogues of parent D 3-trishomocubane. Compounds 2 and 3 are the structural isomers in which the positions of the μ-S ligands in the trishomocubane framework are altered. Compound 6 is an example of a unique vertex-fused trishomocubane derivative, in which the D 3-trishomocubane [Co(μ-Se)3(μ3-Se)4B3H3] moiety is fused with an exopolyhedral trigonal bipyramid (tbp) moiety [(Cp*Co)2(μ-H)(μ3-Se)2}Co]. Multinuclear NMR and infrared spectroscopy, mass spectrometry, and single crystal X-ray diffraction analyses were employed to characterize all the compounds in solution. Bonding in these homocubane analogues has been elucidated computationally by density functional theory methods.

Chalcogen stabilized trimetallic clusters: synthesis, structures, and bonding of [(Cp*M)3(E)6+m(BH)n] (M = Nb or Ta; E = S or Se; m = 0 or 1 or 2; n = 0 or 1)

An unusual trimetallic octaselenide complex, [(Cp*Ta)₃(μ-Se)₄{μ-Se₂(Se₂)}], has been synthesized and structurally characterized.

Metal-Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc

This survey of metal-metal (MM) bond distances in binuclear complexes of the first row 3d-block elements reviews experimental and computational research on a wide range of such systems. The metals surveyed are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, representing the only comprehensive presentation of such results to date. Factors impacting MM bond lengths that are discussed here include (a) the formal MM bond order, (b) size of the metal ion present in the bimetallic core (M₂) ⁿ⁺, (c) the metal oxidation state, (d) effects of ligand basicity, coordination mode and number, and (e) steric effects of bulky ligands. Correlations between experimental and computational findings are examined wherever possible, often yielding good agreement for MM bond lengths. The formal bond order provides a key basis for assessing experimental and computationally derived MM bond lengths. The effects of change in the metal upon MM bond length ranges in binuclear complexes suggest trends for single, double, triple, and quadruple MM bonds which are related to the available information on metal atomic radii. It emerges that while specific factors for a limited range of complexes are found to have their expected impact in many cases, the assessment of the net effect of these factors is challenging. The combination of experimental and computational results leads us to propose for the first time the ranges and "best" estimates for MM bond distances of all types (Ti-Ti through Zn-Zn, single through quintuple).

Heterometallic boride clusters: synthesis and characterization of butterfly and square pyramidal boride clusters*

A number of heterometallic boride clusters have been synthesized and structurally characterized using various spectroscopic and crystallographic analyses. Thermolysis of [Ru3(CO)12] with [Cp*WH3(B4H8)] (1) yielded [{Cp*W(CO)2}2(μ 4-B){Ru(CO)3}2(μ-H)] (2), [{Cp*W(CO)2}2(μ 5-B){Ru(CO)3}2{Ru(CO)2}(μ-H)] (3), [{Cp*W(CO)2}(μ 5-B){Ru(CO)3}4] (4) and a ditungstaborane cluster [(Cp*W)2B4H8Ru(CO)3] (5) (Cp*=η 5-C5Me5). Compound 2 contains 62 cluster valence-electrons, in which the boron atom occupies the semi-interstitial position of a M4-butterfly core, composed of two tungsten and two ruthenium atoms. Compounds 3 and 4 can be described as hetero-metallic boride clusters that contain 74-cluster valence electrons (cve), in which the boron atom is at the basal position of the M5-square pyramidal geometry. Cluster 5 is analogous to known [(Cp*W)2B5H9] where one of the BH vertices has been replaced by isolobal {Ru(CO)3} fragment. Computational studies with density functional theory (DFT) methods at the B3LYP level have been used to analyze the bonding of the synthesized molecules. The optimized geometries and computed 11B NMR chemical shifts satisfactorily corroborate with the experimental data. All the compounds have been characterized by mass spectrometry, IR, 1H, 11B and 13C NMR spectroscopy, and the structural architectures were unequivocally established by crystallographic analyses of clusters 2–5.

Hypoelectronic 8-11-Vertex Irida- and Rhodaboranes

A series of novel isocloso-diiridaboranes [(Cp*Ir)2B6H6], 1, 2; [1,7-(Cp*Ir)2B8H8], 4; [1,4-(Cp*Ir)2B8H8], 5; [(Cp*Ir)2B9H9], 8; isonido-[(Cp*Ir)2B7H7], 3; and 10-vertex cluster [5,7-(Cp*Ir)2B8H12], 6 (Cp* = η(5)-C5Me5) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl2]2 and BH3·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)B9H13)], 7, and [(Cp*Rh)2B9H9], 9, respectively. Clusters 1 and 2 are topological isomers. The geometry of 1 is dodecahedral, similar to that of its parent borane [B8H8](2-), in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of 2 can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds 4 and 5 are 10-vertex isocloso clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal-metal bond in 5. The solid-state structures of 8 and 9 attain an 11-vertex geometry in which a unique six-membered B6H6 moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. All the compounds have been characterized by IR and (1)H, (11)B, and (13)C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis.

Non-oxido divanadium(IV) and divanadium(V) thiolate complexes with a new type of chalcogenide bridging motif

In our effort to study vanadium chalcogenide chemistry, we have synthesized and characterized a class of non-oxido divanadium(IV) and divanadium(V) complexes with chalcogenide and dichalcogenide as bridges. All structures consist of a similar divanadium motif, in which two metal centers are bridged by one μ-chalcogenide and one μ-η(2):η(2)-dichalcogenide, forming a V2(μ-E)(μ-η(2):η(2)-E2) (E = S or Se) core structure. These compounds are [V(IV)2(PS3)2(μ-Se2)(μ-Se)][PPh4]2 (1), [V(V)2(PS3'')2(μ-Se2)(μ-Se)] (2), [V(V)2(PS3'')2(μ-S2)(μ-S)] (3a) and [V(V)2(PS3)2(μ-S2)(μ-S)] (3b) ([PS3](3-) = P(C6H4-2-S)3 and [PS3''](3-) = P(C6H3-3-SiMe3-2-S)3). Compound 1 exhibits diamagnetic behavior, indicating strong antiferromagnetic coupling between two d(1) centers. Compounds 2 and 3a-b have the highest oxidation states for vanadium ions (+5/+5) among those reported divanadium chalcogenide clusters. The work demonstrates that high-valent divanadium chalcogenide clusters can be obtained with the activation of elemental chalcogens by low-valent vanadium ions.

In search for new bonding modes of the methylenedithiolato ligand: novel tri- and tetra-metallic clusters

Photolysis ofarachno-[(Cp*Ru)₂(B₃H₈)(CS₂H)] in the presence of [Re₂(CO)₁₀] produced [(Cp*Ru)₂B₃H₅(CH₂S₂){Re(CO)₄}₂], with a planar 8-membered ring containing heavier transition metals and a main group element.

Synthesis and chemistry of the open-cage cobaltaheteroborane cluster [{(η5-C5Me5)Co}2B2H2Se2]: a combined experimental and theoretical study

An open cage triple-decker molecule with three planar rings almost parallel to each other (see the picture).

Chemistry of group 9 dimetallaborane analogues of octaborane(12)

Reaction of octaborane(12) analogue with metal carbonyl compounds yielded condensed metallaborane (A) and boride cluster (B).

Synthesis, characterization and crystal structure analysis of cobaltaborane and cobaltaheteroborane clusters

A novel class of cobaltaborane and cobaltaheteroborane clusters, isocloso-[(Cp*Co)₃B₆H₇Co(CO)₂], closo-[(Cp*Co)₂B₂H₅Mo₂(CO)₆I], nido-[(Cp*Co)₂B₂H₂S₂], and closo-[(Cp*Co)₂B₄H₂Br₄] were investigated (see picture).