The First Triple-Decker Complex with a Carbenium Center, [CpCo(µ-C3 B2 Me5 )RuC5 Me4 CH2 ]+ : Synthesis, Reactivity, X-Ray Structure, and Bonding.

The first derivative of the methylium cation with the triple-decker substituent, [CpCo(C3 B2 Me5 )RuC5 Me4 CH2 ]PF6 (2PF6 ), was synthesized from the reaction of the triple-decker complex CpCo(C3 B2 Me5 )RuCp* (1) with the salt of the trityl cation [CPh3 ]+ . The X-ray crystal structure of 2PF6 reveals that the methylium carbon is bound to the ruthenium with Ru-C bond length of 2.259 Šand corresponds to the description of its structure as η6 -fulvene-ruthenium. Reactions of 2PF6 with nucleophiles OH- , Ph3 P, Et3 N led to the corresponding derivatives of 1 in high yields. Aromatic amines PhNEt2 and 4-MeC6 H4 NH2 react with 2PF6 to give the electrophilic aromatic substitution products quantitatively. Chemical reduction of 2PF6 with Zn powder in tetrahydrofuran leads to the formation of the bis(triple-decker) derivative (CpCo(C3 B2 Me5 )RuC5 Me4 CH2 )2 (10) with a CH2 CH2 -bridge. The structures of complexes 4, 7-10 were determined by X-ray diffraction. Density functional calculations support the crystallographically determined geometry of 2 and allow rationalization of some characteristics of its structure, spectroscopy, and reactivity.

Electrochemistry and Photoluminescence of Icosahedral Carboranes, Boranes, Metallacarboranes, and Their Derivatives.

Icosahedral boranes, carboranes, and metallacarboranes are extraordinarily robust compounds with desirable properties such as thermal and redox stability, chemical inertness, low nucleophilicity, and high hydrophobicity, making them attractive for several applications such as medicine, nanomaterials, molecular electronics, energy, catalysis, environmental chemistry, and other areas. The hydrogen atoms in these clusters can be replaced by convenient groups that open the way to a chemical alternative to conventional "organic" or "organometallic" realms. Icosahedral boron cluster derivatives have been reviewed from different perspectives; however, there is a need for a review dedicated to the redox and photophysical characteristics of easily accessible borane and carborane derivatives, which are excellent materials for a wide range of applications. This review deals with the redox properties and photoluminescence behavior of this collection of compounds, as well as their influence on the properties of materials and devices whose working principles are related to electron-transfer or electron-promotion phenomena. We hope that this review will be of great value to boron cluster scientists and researchers working in the photoluminescence and electrochemistry fields who are interested in exploring the possibilities of these unique and promising systems.

Cooperative effects of electron donors and acceptors for the stabilization of elusive metal cluster frameworks: synthesis and solid-state structures of [Pt19(CO)24(µ4-AuPPh3)3]- and [Pt19(CO)24{µ4-Au2(PPh3)2}2].

The anionic cluster [Pt(19)(CO)(22)](4-) (1), of pentagonal symmetry, reacts with CO and AuPPh(3)(+) fragments. Upon increasing the Au:Pt(19) molar ratio, different species are sequentially formed, but only the last two members of the series could be characterized by X-ray diffraction, namely, [Pt(19)(CO)(24)(µ(4)-AuPPh(3))(3)](-) (2) and [Pt(19)(CO)(24){µ(4)-Au(2)(PPh(3))(2)}(2)] (3). The metallic framework of the starting cluster is completely modified after the addition of CO and AuL(+), and both products display the same platinum core of trigonal symmetry, with closely packed metal atoms. The three AuL(+) units cap three different square faces in 2, whereas four AuL(+) fragments are grouped in two independent bimetallic units in the neutral cluster 3. Electrochemical and spectroelectrochemical studies on 2 showed that its redox ability is comparable with that of the homometallic 1.

Synthesis, structure, and spectroscopic characterization of [H(8-n)Rh22(CO)35](n-) (n = 4, 5) and [H2Rh13(CO)24{Cu(MeCN)}2](-) clusters: assessment of CV and DPV as techniques to circumstantiate the presence of elusive hydride atoms.

The previously ill-characterized [H(x)Rh(22)(CO)(35)](4-/5-) carbonyl cluster has been obtained as a byproduct of the synthesis of [H(3)Rh(13)(CO)(24)](2-) and effectively separated by metathesis of their sodium salts with [NEt(4)]Cl. Although the yields are modest and never exceed 10-15% (based on Rh), this procedure affords spectroscopically pure [H(3)Rh(22)(CO)(35)](5-) anion. Formation of the latter in mixture with other Rh clusters was also observed by electrospray ionization-mass spectrometry (ESI-MS) in the oxidation of [H(2)Rh(13)(CO)(24)](3-) with Cu(2+) salts. The recovery of further amounts of [H(3)Rh(22)(CO)(35)](5-) was hampered by too similar solubility of the salts composing the mixture. Conversely, the reaction in CH(3)CN of [H(2)Rh(13)(CO)(24)](3-) with [Cu(MeCN)(4)](+)[BF(4)](-) leads to the [H(2)Rh(13)(CO)(24){Cu(MeCN)}(2)](-) bimetallic cluster. The X-ray crystal structures of [H(4)Rh(22)(CO)(35)](4-), [H(3)Rh(22)(CO)(35)](5-), and [H(2)Rh(13)(CO)(24){Cu(MeCN)}(2)](-) are reported. From a formal point of view, the metal frame of the former two species can be derived by interpenetration along two orthogonal axes of two moieties displaying the structure of the latter. The availability of [H(8-n)Rh(22)(CO)(35)](n-) salts prompted their detailed chemical, spectroscopic, and electrochemical characterization. The presence of hydride atoms has been directly proved both by ESI-MS and (1)H NMR. Moreover, both [H(4)Rh(22)(CO)(35)](4-) and [H(3)Rh(22)(CO)(35)](5-) undergo distinctive electrochemically reversible redox changes. This allows to assess electrochemical studies as indisputable though circumstantial evidence of the presence of (1)H NMR-silent hydride atoms in isostructural anions of different charge.

Octanuclear manganese(II,III) clusters stabilized with diamino-alcoxo ligands.

The employment of the 1,3-bis(dimethylamino)-2-propanolate (bdmap) ligand as a chelating/bridging ligand in manganese chemistry is described. The reaction of Mn(R-BzO)(2) and bdmap affords [Mn(8)(O)(4)(R-BzO)(12)(bdmap)(2)(H(2)O)(2)], R = H (1), R = 3-Cl (2) and R = 4-Cl (3), which are mixed-valence Mn(II)(2)Mn(III)(6) clusters. Structural characterization was achieved for 1 and 2, which can be described as a central double defective dicubane Mn(III)(4) subunit, capped by two oxo-bridged Mn(II)-mu(bdmap)-Mn(III) dinuclear units. DC variable-temperature magnetic susceptibility studies were carried out in the 2-300 K range, revealing an overall antiferromagnetic behaviour for 1-3. This work demonstrates for the first time the ability of this kind of polytopic ligands in high nuclearity manganese chemistry.

Nickelacyclic-cobaltocene vs. nickelacyclic-nickelocene. Synthesis, X-ray structures, electron transfer activity, EPR spectroscopy, and theoretical calculations.

Reactions of 9-nickelafluorenyllithium with cobalt and nickel pentamethylcyclopentadienyl-acetylacetonates resulted in the formation of the novel nickelacyclic-cobaltocene 2 and nickelacyclic-nickelocene 3, respectively, in which the central metal atom is bonded to the nickelafluorenyl ring. On the basis of their redox propensity, compounds 2 and 3 were oxidized to the corresponding monocations [2](+) and [3](+). The crystal and molecular structures of both the redox couples were determined by single-crystal X-ray analysis. In spite of their structural similarity, they display a rather different electron transfer ability. To throw light on such an aspect, the pertinent redox couples have been examined by EPR spectroscopy and the nature of the frontier orbitals involved in the redox activity of the neutral precursors has been supported by extended Huckel theoretical calculations.

The electrochemical inspection of the redox activity of sumanene and its concave CpFe complex.

The redox properties of sumanene C(21)H(12) and its concave Fe(II) complex [(eta(5)-C(5)H(5))Fe(eta(6)-C(21)H(12))](+) have been elucidated through an electrochemical study in non-aqueous solvents, i.e. N,N-dimethylformamide (DMF) and acetonitrile (MeCN). The electron transfer activity of sumanene can be depicted as an irreversible oxidation and a partially chemically reversible one-electron reduction, both processes being located in proximity of the respective discharges of the solvents. The Fe(II) complex [(eta(5)-C(5)H(5))Fe(eta(6)-C(21)H(12))](PF(6)) in turn exhibits the Fe(II)/Fe(I) reduction, which in both DMF and MeCN solvents displays features of partial chemical reversibility, coupled to decomposition of the corresponding Fe(I) species [(eta(5)-C(5)H(5))Fe(eta(6)-C(21)H(12))] to fragments which, upon reoxidation, regenerate for the most part the original Fe(II)-sumanene species. In fact, among the fragments produced by exhaustive reduction, ESI measurements allowed the detection of ferrocene, the oxidation of which probably triggers the partial regeneration of the original Fe(II) complex. The pertinent PM6 semiempirical study accounts for the limited chemical reversibility of the redox processes exhibited by both sumanene and its Fe(II) complex.

Site selectivity in the reactions of the hexanuclear platinum cluster [Pt6(mu-PtBu2)4(CO)6][CF3SO3]2.

The previously reported hexanuclear cluster [Pt(6)(mu-PtBu(2))(4)(CO)(6)](2+)[Y](2) (1-Y(2): Y=CF(3)SO(3) (-)) contains a central Pt(4) tetrahedron bridged at each of the opposite edges by another platinum atom; in turn, four phosphido ligands bridge the four Pt-Pt bonds not involved in the tetrahedron, and, finally, one carbonyl ligand is terminally bonded to each metal centre. Interestingly, the two outer carbonyls are more easily substituted or attacked by nucleophiles than the inner four, which are bonded to the tetrahedron vertices. In fact, the reaction of 1-Y(2) with 1 equiv of [nBu(4)N]Cl or with an excess of halide salts gives the monochloride [Pt(6)(mu-PtBu(2))(4)(CO)(5)Cl](+)[Y], 2-Y, or the neutral dihalide derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)X(2)] (3: X=Cl; 4: X=Br; 5: X=I). Moreover, the useful unsymmetrically substituted [Pt(6)(mu-PtBu(2))(4)(CO)(4)ICl] (6) was obtained by reacting equimolar amounts of 2 and [nBu(4)N]I, and the dicationic derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)L(2)](2+)[Y](2) (7-Y(2): L=(13)CO; 8-Y(2): L=CNtBu; 9-Y(2): L=PMe(3)) were obtained by reaction of an excess of the ligand L with 1-Y(2). Weaker nitrogen ligands were introduced by dissolving the dichloride 3 in acetonitrile or pyridyne in the presence of TlPF(6) to afford [Pt(6)(mu-PtBu(2))(4) (CO)(4)L(2)](2+)[Z](2) (Z=PF(6) (-), 10-Z(2): L=MeCN; 11-Z(2): L=Py). The "apical" carbonyls in 1-Y(2) are also prone to nucleophilic addition (Nu(-): H(-), MeO(-)) affording the acyl derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)(CONu)(2)] (12: Nu=H; 13: Nu=OMe). Complex 12 is slowly converted into the dihydride [Pt(6)(mu-PtBu(2))(4)(CO)(4)H(2)] (14), which was more cleanly prepared by reacting 3 with NaBH(4). In a unique case we observed a reaction involving also the inner carbonyls of complex 1, that is, in the reaction with a large excess of the isocyanides R-NC, which form the corresponding persubstituted derivatives [Pt(6)(mu-tPBu(2))(4)(CN-R)(6)](2+)[Y](2), (15-Y(2): R=tBu; 16-Y(2) (2-): R=-C(6)H(4)-4-C triple bond CH). All complexes were characterized by microanalysis, IR and multinuclear NMR spectroscopy. The crystal and molecular structures of complexes 3, 5, 6 and 9-Y(2) are also reported. From the redox viewpoint, all complexes display two reversible one-electron reduction steps, the location of which depends both upon the electronic effects of the substituents, and the overall charge of the original complex.