Synthesis and characterization of the octahydrotriborate complexes Cp*V(B3H8)2 and Cp*Cr(B3H8)2 and the unusual cobaltaborane cluster Cp*2Co2(B6H14)

The new compounds CpV(B(3)H(8))(2), CpCr(B(3)H(8))(2), and Cp(2)Co(2)(B(6)H(14)) have been synthesized by treating the pentamethylcyclopentadienyl complexes [CpVCl(2)](3), [CpCrCl(2)](2), and [CpCoCl](2) with NaB(3)H(8). X-ray crystallography shows that CpV(B(3)H(8))(2) and CpCr(B(3)H(8))(2) have the same ligand sets but different molecular structures: the vanadium compound contains two bidentate B(3)H(8) ligands (i.e., bound to the metal center via two vicinal hydrogen atoms), whereas the chromium compound has one bidentate B(3)H(8) ligand and one B(3)H(8) ligand bound in an unprecedented fashion via two geminal hydrogen atoms. The "gem-bound" B(3)H(8) group itself has an atypical structure consisting of a BH(2)-BH(2)-BH(3) triangle with one additional hydrogen atom bridging the unique BH(2)-BH(2) edge. The B-B distances are nearly identical within experimental error at 1.790(5), 1.792(5), and 1.786(6) Angstrom. The relationship between the electronic and molecular structures of the V and Cr compounds is briefly discussed. The structure of Cp(2)Co(2)(B(6)H(14)) can be viewed in two different ways: as a dicobalt complex in which two CpCo units are each bound to four adjacent boron atoms of an S-shaped B(6)H(14) ligand, or as an eight-vertex hypho cluster compound. In the former case, the B(6)H(14) ligand is best regarded as a dianionic bi-borallyl group H(3)B(mu-H)BH(mu-H)BHBH(mu-H)BH(mu-H)BH(3) in which one hydrogen at each end of the chain is involved in an agostic interaction. From a cluster point of view, the structure of Cp(2)Co(2)(B(6)H(14)) can be generated by removing three adjacent high-connectivity vertices from the eleven-vertex closo polyhedron. The Co-B distances vary from 2.008(5) to 2.183(4) Angstrom, and the B-B distances within in the S-shaped chain range from 1.734(8) to 1.889(6) Angstrom. Finally, a new synthesis of the known molybdenum compound Cp(2)Mo(2)(B(5)H(9)) is described; its structure as established by X-ray crystallography closely resembles that of the previously described (C(5)H(4)Me) analogue.     

Structural chemistry of "defect" cyanometalate boxes: (Cs subset [CpCo(CN)3]4[Cp*Ru]3) and (M subset [Cp*Rh(CN)3]4[Cp*Ru]3) (M = NH4, Cs)

A series of heptametallic cyanide cages are described; they represent soluble analogues of defect-containing cyanometalate solid-state polymers. Reaction of 0.75 equiv of [Cp*Ru(NCMe)3]PF6, Et(4)N[Cp*Rh(CN)3], and 0.25 equiv of CsOTf in MeCN solution produced (Cs subset [CpCo(CN)3]4[Cp*Ru]3)(Cs subset Rh4Ru3). 1H and 133Cs NMR measurements show that Cs subset Rh4Ru3 exists as a single Cs isomer. In contrast, (Cs subset [CpCo(CN)3]4[Cp*Ru]3) (Cs subset Co4Ru3), previously lacking crystallographic characterization, adopts both Cs isomers in solution. In situ ESI-MS studies on the synthesis of Cs subset Rh4Ru3 revealed two Cs-containing intermediates, Cs subset Rh2Ru2+ (1239 m/z) and Cs subset Rh3Ru3+ (1791 m/z), which underscore the participation of Cs+ in the mechanism of cage formation. 133Cs NMR shifts for the cages correlated with the number of CN groups bound to Cs+: Cs subset Co4Ru4+ (delta 1 vs delta 34 for CsOTf), Cs subset Rh4Ru3 where Cs+ is surrounded by ten CN ligands (delta 91), Cs subset Co4Ru3, which consists of isomers with 11 and 10 pi-bonded CNs (delta 42 and delta 89, respectively). Although (K subset [Cp*Rh(CN)3]4[Cp*Ru]3) could not be prepared, (NH4 subset [Cp*Rh(CN)3]4[Cp*Ru]3) (NH4 subset Rh4Ru3) forms readily by NH4+-template cage assembly. IR and NMR measurements indicate that NH4+ binding is weak and that the site symmetry is low. CsOTf quantitatively and rapidly converts NH4 subset Rh4Ru3 into Cs subset Rh4Ru3, demonstrating the kinetic advantages of the M7 cages as ion receptors. Crystallographic characterization of CsCo4Ru3 revealed that it crystallizes in the Cs-(exo)1(endo)2 isomer. In addition to the nine mu-CN ligands, two CN(t) ligands are pi-bonded to Cs+. M subset Rh4Ru3 (M = NH4, Cs) crystallizes as the second Cs isomer, that is, (exo)2(endo)1, wherein only one CN(t) ligand interacts with the included cation. The distorted framework of NH4 subset Rh4Ru3 reflects the smaller ionic radius of NH4+. The protons of NH4+ were located crystallographically, allowing precise determination of the novel NH4...CN interaction. A competition experiment between calix[4]arene-bis(benzocrown-6) and NH4 subset Rh4Ru3 reveals NH4 subset Rh4Ru3 has a higher affinity for cesium.     

Stacking reactions of the borole complex Cp*Rh(η5-C4H4BPh) with the dicationic fragments [Cp*M]2+ (M = Rh or Ir)

The reaction of the (borole)rhodium iodide complex [(η-C₄H₄BPh)RhI]₄ with Cp^*Li afforded the sandwich compound Cp^*Rh(η-C₄H₄BPh) (4). The reactions of compound 4 with the solvated complexes [Cp^*M(MeNO₂)₃]²⁺(BF ₄ ⁻ )₂ gave triple-decker cationic complexes with the central borole ligand [Cp^*Rh(η-η⁵:η⁵-C₄H₄BPh)MCp^*]²⁺(BF ₄ ⁻ )₂ (M = Rh (5) or Ir (7)). The structure of complex 4 was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1525–1527, September, 2006.     

Reactions of [Cp*Ru(H2O)(NBD)]+ with alkynes

Formal [2 + 2 + 2] addition reactions of [Cp*Ru(H₂O)(NBD)]BF₄ (NBD = norbornadiene) with PhC?CR (R = H, COOEt) give [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BF₄ (1a, R = H; 2a, R = COOEt). Treatment of [Cp*Ru(H₂O)(NBD)]BF₄ with PhC?C? C?CPh does not give [2 + 2 + 2] addition product, but [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BF₄(3a). Treatment of 1a, 2a, 3a with NaBPh₄ affords [Cp*Ru(η⁶‐C₆H₅? C₉H₈R)] BPh₄ (1b, R = H; 2b, R = COOEt) and [Cp*Ru(η⁶‐C₆H₅? C?C? C?CPh)] BPh₄(3b). The structures of 1b, 2b and 3b were determined by X‐ray crystallography. Copyright © 2007 John Wiley & Sons, Ltd.     

Formation of Isomeric Tetrathiotungstate Clusters [{Cp*Ru(CO)}2(WS4){W(CO)4}] by the Reaction of [Cp*2Ru2S4] with [W(CO)3(MeCN)3]

Thermal and photochemical interconversion occurs between the isomeric pair of tetrathiotungstate [WS₄]²⁻ clusters 1 and 2 , which were formed by thermolysis of [Cp^*₂Ru₂S₄] and [W(CO)₃(MeCN)₃] [Eq. (1)] and then structurally characterized. During synthesis, a dramatic redistribution of ligands between the Ru and W atoms takes place without the loss of any CO and S ligands.     

Condensed tantalaborane clusters: synthesis and structures of [(Cp*Ta)2B5H7{Fe(CO)3}2] and [(Cp*Ta)2B5H9{Fe(CO)3}4

The reaction of [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))] (1; Cp* = η(5)-C(5)Me(5)) with [Fe(2)(CO)(9)] in hexane yielded [(Cp*Ta)(2)B(5)H(7){Fe(CO)(3)}(2)] (2) and [(Cp*Ta)(2)B(5)H(9){Fe(CO)(3)}(4)] (3) in moderate yield. Cluster 2 represents the first example of a bicapped pentagonal-bipyramidal metallaborane with a deformed equatorial plane, and 3 can be described as a fused cluster in which two pentagonal-bipyramidal units are fused through a common 3-vertex triangular face. Compounds 2 and 3 have been characterized by mass spectrometry and IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis.     

Complexes of decamethylsilicocene: Cp2*Si(CO) and Cp2*Si(N2)

The synthesis and IR spectroscopic detection of the monocarbonyl and mononitrogen complex of decamethylsilicocen in liquid xenon (LXe) and liquid nitrogen (LN₂) is reported. The reactions were found to be highly incomplete under a few bar of CO or N₂ and reversibel when the pressure is released. Cp₂*Si(CO) is characterized by three isotopomeres and Cp₂*Si(N₂) was synthesized on two independent routes.     

Multinuclear self-assembly via half-sandwich complexes Cp*M[S2C2(B10H10)] and pyridine-based ligands

The study on transition metal mediated self-assemblies has drawn considerable attention during the past decade. This article focused on the significant progress made in the area of multinuclear supramolecular construction through pseudo-aromatic carboranyl species Cp*M[S(2)C(2)(B(10)H(10))] (M = Co, Rh, Ir) and pyridine-based ligands over the past few years. Structurally pre-defined complexes, from mono-molecules to three-dimensional frameworks, can be obtained in high yields under mild reaction conditions through self-assembly, and the structural features of solid state confirmed by X-ray crystallography are also discussed.     

Reactivity of a coordinatively unsaturated Cp*Ru(kappa2-P,O) complex

Whereas a new coordinatively unsaturated Cp*Ru(kappa(2)-P,O) complex (1a) forms adducts with two-electron donors (including sigma-H(2) and mu-N(2) ligands), double Si-H bond activation is observed upon treatment with Ph(2)SiH(2) or PhSiH(3), leading to the clean formation of products corresponding to the net insertion of a Ph(2)Si: or Ph(H)Si: fragment into the Ru-O bond of 1a.     

Metal-Stabilized [B8H8]2− Derivatives with Dodecahedral Structure in the Solid and Solution States: [(Cp2MBH3)2B8H6] (Cp=η5-C5H5; M=Zr (1-Zr) and Hf (1-Hf)).

Despite the synthesis and structural characterization of closo-hydroborate dianions, [B_nH_n]²⁻ (n=6–12) more than 50 years ago, some ambiguity remains about the structure of [B₈H₈]²⁻. Although the solid-state structure of [B₈H₈]²⁻ was established by single-crystal X-ray studies in 1969, fast rearrangements in solution at accessible temperatures prevented its detailed characterization. We therefore stabilized a derivative of [B₈H₈]²⁻ by using Cp₂MBH₃ and structurally characterized two new octaborane analogues, [(Cp₂MBH₃)₂B₈H₆] (Cp=η⁵-C₅H₅; M=Zr ( 1-Zr ) and Hf ( 1-Hf )), so that the dynamics of the B₈ skeleton were arrested. The solid-state structures of both 1-Zr and 1-Hf comprise a dodecahedron core protected by {Cp₂MBH₃} moieties on both sides of the cluster. Spectroscopic characterization (¹¹B NMR) validates the intactness of the B₈ dodecahedron core in solution as well. Theoretical calculations establish that the two exo-{Cp₂MBH₃} fragments provide structural and electronic structural stability to the B₈ core and its intact dodecahedral dianionic nature. Furthermore, we propose isodesmic equations for the formation of higher analogues of the B_n core (n>8) guarded by different group 4 transition metals. Our analysis suggests that, as we move to higher polyhedra (n>10), the formation becomes unfavourable irrespective of metal.     

The elusive 16-electron Cp*M(NO)Me(2)(M = Mo, W) complexes and their spontaneous conversions to Cp*M(NMe)(O)Me isomers.

Treatment of [Cp*Mo(NO)Cl(mu-Cl)](2) with magnesium (Me(2)Mg.dioxane, MeMgCl) or aluminum (Me(3)Al) methylating reagents affords the known compound [Cp*Mo(NO)Me(mu-Cl)](2) (1). Similar treatment of the dichloro precursor with MeLi in ethereal solvents generates an equimolar mixture of 1 and the trimethyl "ate" complex, Cp*MoMe(3)(NO-Li(OEt(2)(n)), (2-Et(2)O). Reaction of 2-Et(2)O with a source of [Me](+) forms Cp*MoMe(3)(=N-OMe)(3), a rare terminal alkoxylimido complex. Metathesis of the chloro ligands of [Cp*Mo(NO)Cl(mu-Cl)](2) by MeLi in toluene at low temperatures produces the target dimethyl complex, Cp*Mo(NO)Me(2) (4), in 75% isolated yield. In solution, 4 is predominantly a monomeric species, whereas in the solid state it adopts a dimeric or oligomeric structure containing isonitrosyl bridges as indicated by IR and (15)N/(13)C NMR spectroscopies. Hydrolysis of 4 affords meso- and rac-[Cp*Mo(NO)Me](2)(mu-O) (5), and the reactions of 4 with a range of Lewis bases, L, to form the 18e adducts Cp*Mo(NO)(L)Me(2) (e.g., Cp*Mo(NO)(PMe(3))Me(2) (7)), have established it to be the most electrophilic complex of its family. Acidolysis of the methyl groups of 4 is also facile. Most notably, 4 is thermally unstable in solution and undergoes isomerization via nitrosyl N-O bond cleavage to its oxo(imido) form, Cp*Mo(NMe)(O)Me (11), which is isolable from the final reaction mixture as the mu-oxo-bridged adduct formed by 4 and 11, i.e., Cp*Mo(NO)Me(2)(mu-O)Cp*Mo(NMe)Me (4 <-- 11). The rate of this isomerization is significantly faster for the tungsten dimethyl complex; hence, Cp*W(NO)Me(2) (12) is not isolable free of a supporting donor interaction and can only be isolated as Cp*W(NO)Me(2)(mu-O)Cp*W(NMe)Me (12 <-- 13) or Cp*W(NO)Me(2)(PMe(3)) (14) adducts.     

A mechanistic study of the utilization of arachno-diruthenaborane [(Cp*RuCO)2B2H6] as an active alkyne-cyclotrimerization catalyst

The reaction of nido-[1,2-(Cp*RuH)(2)B(3)H(7)] (1a, Cp*=η(5)-C(5)Me(5)) with [Mo(CO)(3)(CH(3)CN)(3)] under mild conditions yields the new metallaborane arachno-[(Cp*RuCO)(2)B(2)H(6)] (2). Compound 2 catalyzes the cyclotrimerization of a variety of internal- and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The reactivities of nido-1a and arachno-2 with alkynes demonstrates that a change in geometry from nido to arachno drives a change in the reaction from alkyne-insertion to catalytic cyclotrimerization, respectively. Density functional calculations have been used to evaluate the reaction pathways of the cyclotrimerization of alkynes catalyzed by compound 2. The reaction involves the formation of a ruthenacyclic intermediate and the subsequent alkyne-insertion step is initiated by a [2+2] cycloaddition between this intermediate and an alkyne. The experimental and quantum-chemical results also show that the stability of the metallacyclic intermediate is strongly dependent on the nature of the substituents that are present on the alkyne.     

TA on Mo(W)/Cu(Ag)/S clusters derived with [Cp*MS3]- Kinetics of [PPh4]2[Cp*WS3(CuBr)3]2 and [PPh4]2[Cp*MoS3(CuBr)3]2

Thermal analysis on two new heterometallic sulfide clusters, [PPh4]2[WS3(CuBr)3]2 and [PPh4]2[MoS3(CuBr)3]2 (where PPh4=tetraphenyl phosphonium, =pentamethylcyclopenta- dienyl), was carried out using a simultaneous TG-DTA unit in an atmosphere of flowing nitrogen and at various heating rates. Supplemented using EDS method, their thermal behavior and properties, together with the composition of their intermediate product, were examined and discussed in connection with their distinctive molecular structure as a dianion, which provided some theoretically and practically significant information. Both clusters decomposed in a two-step mode, but without a stable new phase composed of Mo/W-Cu-S formed during their decomposition process as we expected. Based on TG-DTG data, four methods, i.e. Achar-Brindley-Sharp, Coats-Redfern, Kissinger and Flynn- Wall-Ozawa equation, were used to calculate the non-isothermal kinetic parameters and to determine the most probable mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrosyl Complexes 6.Reactions of Na[Fe(CO)_3NO]with Cp~*M(CO)_3Cl(Cp~*=η~5-CH_3C_5H_4,M=Mo or W):Crystal structures of Cp~*M(CO)_2NO and Cp~*M(μ_3-NH)(μ_2-NO)(μ_2-CO)Fe_2(CO)_6

Sodium nitrosylcarbonyliron reacts with methylcyclopentadienylcarbonylmetal(Mo orW)chloride in CH_3OH/THF at room temperature to give CpMo(CO)_2NO(1a)(Cp=η~5-CH_3C_5H_4)or CpW(CO)_2NO(1b),[CpMo(CO)_3]_2(2a)or[CpW(CO)_3]_2(2b),and CpMo(μ3-NH)(μ2-NO)-(μ2-CO)Fe_2(CO)_6(3a)or CpW(μ3-NH)(μ2-NO)(μ2-CO)Fe_2(CO)_6(3b),respectively.Complexes1a,1b,3a and 3b were analyzed by IR,NMR,MS and elemental analyses,and the crystalstructures of 1b,3a and 3b were determined by X-ray diffraction method.The new clusters 3aand 3b have μ3-NH ligands which were formed by redaction of NO in the synthetic reactions.     

Speciation of [Cp*2M2O5] in Polar and Donor Solvents

The speciation of compounds [Cp*₂M₂O₅] (M=Mo, W; Cp*=pentamethylcyclopentadienyl) in different protic and aprotic polar solvents (methanol, dimethyl sulfoxide, acetone, acetonitrile), in the presence of variable amounts of water or acid/base, has been investigated by ¹H NMR spectrometry and electrical conductivity. Specific hypotheses suggested by the experimental results have been further probed by DFT calculations. The solvent (S)‐assisted ionic dissociation to generate [Cp*MO₂(S)]⁺ and [Cp*MO₃]^? takes place extensively for both metals only in water/methanol mixtures. Equilibrium amounts of the neutral hydroxido species [Cp*MO₂(OH)] are generated in the presence of water, with the relative amount increasing in the order MeCN≈acetone<MeOH<DMSO. Addition of a base (Et₃N) converts [Cp*₂M₂O₅] into [Et₃NH]⁺[Cp*MO₃]^?, for which the presence of a N? H???O?M interaction is revealed by ¹H NMR spectroscopy in comparison with the sodium salts, Na⁺[Cp*MO₃]^?. These are fully dissociated in DMSO and MeOH, but display a slow equilibrium between free ions and the ion pair in MeCN and acetone. Only one resonance is observed for mixtures of [Cp*MO₃]^? and [Cp*MO₂(OH)] because of a rapid self‐exchange. In the presence of extensive ionic dissociation, only one resonance is observed for mixtures of the cationic [Cp*MO₂(S)]⁺ product and the residual undissociated [Cp*₂M₂O₅] because of a rapid associative exchange via the trinuclear [Cp*₃M₃O₇]⁺ intermediate. In neat methanol, complex [Cp*₂W₂O₅] reacts to yield extensive amounts of a new species, formulated as the mononuclear methoxido complex [Cp*WO₂(OMe)] on the basis of the DFT study. An equivalent product is not observed for the Mo system. The addition of increasing amounts of water results in the rapid decrease of this product in favor of [Cp*₂W₂O₅] and [Cp*WO₂(OH)].