Molekül- und kristallstruktur von μ-hydroxy-cyclooctadien(1,5)-rhodium(I)-dimer bei 173 K. Zur reaktion von [μ-OH)R(COD-1,5)]2mit [η5-C5(CH3)5]2Ti(VI)(CH)3)2 und (η5-C5H5)2Ti(II)[P(CH)3)3]2

Titanium thiosalicylate complexes: functional metalloligands for the construction of redox-active heterometallic architectures

The titanium complex [TiCp*(thiosal)(thiosalH)] (1) has been synthesised by reaction of [TiCp*Me₃], Cp* = η⁵-C₅Me₅, with thiosalicylic acid (H₂thiosal). Complex 1 reacts with [M(μ-OH)(COD)]₂ (M = Rh, Ir) to yield the corresponding early-late heterobimetallic complexes [TiCp*(thiosal)₂M(COD)] (M = Rh (2); Ir (3)). Carbon monoxide replaces the COD ligand in 2 and 3 leading to the respective dicarbonyl complexes [TiCp*(thiosal)₂M(CO)₂] (M = Rh (4); Ir (5)). Compound 4 reacts with PPh₃ to yield the monocarbonyl derivative [TiCp*(thiosal)₂Rh(CO)(PPh₃)] (6). The reaction of compound 1 with LiⁿBu yields the tetrametallic complex [{TiCp*(thiosal)₂Li}₂(THF)₃(H₂O)] (7). Compound 7 reacts with [RuCp*Cl(COD)] yielding the heterometallic complex [TiCp*(thiosal)₂RuCp*] (8). The molecular structures of compounds 4, 5 and 7 have been studied by X-ray diffraction. From cyclic voltammetric (CV) and square wave voltammetric (SWV) experiments, we observed that attachment of the titanium moiety of precursor 1 to a late transition metal moiety through the sulfur atoms has a significant influence on the reduction behaviour of the Ti(iv) metal centre. Thus, monometallic 1 exhibits an irreversible reduction process at -1.15 V vs. SCE, whereas the CVs of heterobimetallic compounds 2-6 are characterized by the reversible or quasi-reversible one-electron reduction of the Ti(iv)/Ti(iii) system, suggesting a significant stabilization of the Ti(iii) reduced species. Likewise, substitution of the M(COD) diolefin fragment in 2 and 3 by the M(CO)₂ carbonyl-containing moiety (in compounds 4 and 5) leads to a significant anodic shift in the titanium E_1/2 reduction redox potentials.

Selective Co-Encapsulation Inside an M6 L4 Cage

There is broad interest in molecular encapsulation as such systems can be utilized to stabilize guests, facilitate reactions inside a cavity, or give rise to energy-transfer processes in a confined space. Detailed understanding of encapsulation events is required to facilitate functional molecular encapsulation. In this contribution, it is demonstrated that Ir and Rh-Cp-type metal complexes can be encapsulated inside a self-assembled M6 L4 metallocage only in the presence of an aromatic compound as a second guest. The individual guests are not encapsulated, suggesting that only the pair of guests can fill the void of the cage. Hence, selective co-encapsulation is observed. This principle is demonstrated by co-encapsulation of a variety of combinations of metal complexes and aromatic guests, leading to several ternary complexes. These experiments demonstrate that the efficiency of formation of the ternary complexes depends on the individual components. Moreover, selective exchange of the components is possible, leading to formation of the most favorable complex. Besides the obvious size effect, a charge-transfer interaction may also contribute to this effect. Charge-transfer bands are clearly observed by UV/Vis spectrophotometry. A change in the oxidation potential of the encapsulated electron donor also leads to a shift in the charge-transfer energy bands. As expected, metal complexes with a higher oxidation potential give rise to a higher charge-transfer energy and a larger hypsochromic shift in the UV/Vis spectrum. These subtle energy differences may potentially be used to control the binding and reactivity of the complexes bound in a confined space.

Di-μ-methanolato-bis[(η4-tetrafluorobenzobarrelene)rhodium(I)]

The versatile synthetic precursor methanolate-bridged title rhodium complex, [Rh(2)(CH(3)O)(2)(C(12)H(6)F(4))(2)] or [Rh(μ-OCH(3))(tfbb)](2) [tfbb = tetrafluorobenzobarrelene or 3,4,5,6-tetrafluorotricyclo[6.2.2.0(2,7)]dodeca-2(7),3,5,9,11-pentaene], has been structurally characterized. The asymmetric unit contains half a molecule that can be expanded via a twofold axis. The title compound has been shown to be a dinuclear rhodium complex where each metal centre is coordinated by two O atoms from two bridging methanolate groups and by the olefinic bonds of a tfbb ligand. Comparison of the bite angles of tfbb, norbornadiene (nbd) and cyclooctadiene (cod) olefins in their η(4)-coordination to rhodium reveals similarities between the tfbb and nbd ligands, which are much more rigid than cod. The short distance found between the distorted square-planar metal centres [2.8351 (4) Å] has been related to the syn conformation of the folded core `RhORhO' ring.

Chelating Dialkoxide Titanium Complex: A Versatile Building Block for the Construction of Heterometallic Derivatives

The heterometallic complex [TiCp*(O(2)Bz)(2)AlMe(2)] (2) has been synthesised by reaction of [TiCp*(O(2)Bz)(OBzOH)] (1) with AlMe(3) (Cp*=eta(5)-C(5)Me(5); Bz=benzyl). Complex 1 reacts with HOTf to yield the cationic derivative [TiCp*(OBzOH)(2)]OTf (3) (HOTf=HSO(3)CF(3)). Compound 3 reacts with [{M(mu-OH)(cod)}(2)] (M=Rh, Ir; cod=cyclooctadiene) to render the early-late heterometallic complexes [TiCp*(O(2)Bz)(2){M(cod)}(2)]OTf (M=Rh (4); Ir (5)). The molecular structure of complex 4 has been established by single-crystal X-ray diffraction studies.

A new titanium building block for early–late heterometallic complexes; preparation of a new tetrameric metallomacrocycle by self assembly

The new titanium dicarboxylate complex Cp*TiMe(OOC)2py (2) [Cp*=eta5-C5Me5; (OOC)2py = 2,6-pyridinedicarboxylate] has been synthesized. The reaction of complex 2 with water renders [Cp*Ti(OOC)2py]2O (3). The molecular structure of 3 has been studied by X-ray diffraction methods. Complex 2 reacts with isocyanides to yield the respective iminoacyl derivatives Cp*Ti(eta2-MeCNR)(OOC)2py [R=tBu (4), 2,6-dimethylphenyl (xylyl) (5)]. The molecular structure of complex4 has been established by X-ray diffraction. Compound 2 has been employed as a new building block for the preparation of new early-late heterometallic compounds; it reacts with [M(mu-OH)(COD)]2 (M = Rh, Ir) to give the corresponding tetranuclear metallomacrocycle derivatives [Cp*Ti{(OOC)(2)py}(mu-O)M(COD)]2 [M = Rh (6); Ir (7)]. The molecular structure of 6 has been established by X-ray diffraction.