Bis “sandwich” complex

The above study has been extended to the synthesis of 4 which was prepared in a similar fashion to 1 and 3 starting from tris(l,4,7-triazacyclonon-l-ylmethyl)benzene [12], The X-ray structure of the [Ni2(4)(H20)3]4+ cation shows that both nickel ions adopt distorted octahedral coordination geometries, with one nickel being sandwiched between two tacn residues while the other is coordinated to the third tacn residue with the coordination sphere being completed by three water ligands. Electrochemical studies indicate that the sandwiched Ni(II) centres in this and the related nickel complexes mentioned above may the be reversibly oxidised to the Ni(III) state. In the case of the dinuclear bis-sandwich complex, [Ni2(4)](C104)4, the electrochemical results indicate that the two nickel centres behave in an essentially independent manner. 

Arsenin will form bis-sandwich complexes 22, 23, and 14 when it is condensed with vapors of the metals Cr, V, and Ti, respectively (Equation 6). When Cr is condensed with arsenin and a 25-fold excess of benzene, it forms 22, the mixed arsenin/benzene sandwich 24, and bis(benzene)chromium in the ratio of 6 3 1 (Equation 7) <19990M1495>. Clearly arsenin complex formation is favored over the benzene complexes even when the benzene is in large excess. Another example of the preference for it-complexation of an arsenin ring versus a benzocyclic ring is shown in Equation (8). The reaction of 18 with (Py)3Mo(CO)3 gives exclusively 15. No product with metal complexation to the benzocyclic ring was detected <20010M2109>. 

Reaction of [Fe(OH2)e] (C104)2 or FeCl2 4H20 with two molar equivalents of [9]aneS3 in refluxing CH3OH affords the bis-sandwich complex... 

Also in the case of ruthenium-ferrocene complexes, we would like to start with the bis-sandwich complexes illustrated in Scheme 7-12. 

Classic A/-heterocychc ligands, eg, bipyridyl (bipy), terpyridyl, imidazole, pyrazine, phenanthroline, piperazine (including alkyl- and aryl-substituted derivatives), and polypyrazol-l-yl-borates (bis, tris, and tetra), have all been found to coordinate Th(IV) chlorides, perchlorates, and nitrates. The tripodal hydrotris(pyrazolyl)borates, HBPz, have been used to stabilize organometaHic complexes (31). Bis-porphyrin Th(IV) "sandwich" complexes have been... 

MetaHacarborane dicarboUide complexes are generaUy more robust than the corresponding cyclopentadiene complexes. The bis-dicarboUide sandwich complexes of general formula [M(C2Bg)H )2] , where M is Fe ", Co ", and exhibit great thermal, chemical, redox, and radiolytic stabUity. 

The remarkable 19-electron molybdenum half-sandwich complex Mo(r 5-C5HPh4)(CO)2L2 (L2 = 2,3-bis(diphenylphosphino)maleic anhydride) (44) was prepared from [Mo(r)5-C5HPh4)(CO)3]2 and L2 and its structure in the solid state determined [65]. The average distance from molybdenum to the ring ligand is... 

The five-membered heterocycle Et2C2B2Mc2S reacts with 17 -CpM fragments (M = Ni, Co) from [Tj -CpNi(CO)2]2 and i) -CpCo(CO)2 to form mixed sandwich complexes of the type rj -CpM(Et2C2B2MeS) , whereas Ni(CO>4 yields the bis(di-hydrothiadiborol) complex. The (Et2C2B2Me2S)Ni(CO)2 is formed in the first step. 

Mixed arene-2,5-dihydro-l,2,5-thiadiborole-iron complexes have been synthesized by a novel route thermally unstable bis(arene)iron sandwich complexes, prepared by cocondensation of iron atoms with arene, react in the temperature range of -100 to -60°C with free Et2C2B2Mc2S to form reactive intermediates that decom-... 

Consequently, in Figures 5-11 are shown the appropriate Tanabe-Sugano type diagrams for dx systems (x = 2 — 8) in pseudo-axial, CmV, symmetry, the parameters DtjDs = 0.55 and C/B = 4.0 being adopted throughout. As indicated above this parameteri-sation is most appropriate for the metallocenes, for which the d-d spectra are now considered in more detail. Thereafter a brief survey is made of the limited data relating to bis-arene species, and to various mixed sandwich complexes. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

Sandwich complexes of porphyrazines are prepared by direct intercalation of lanthanides between two pz ligands, the route commonly utilized for the preparation of porphyrin sandwich complexes. Interestingly, the synthetic method used for the preparation of bis(phthalocyanines), starting from the dinitrile or the dilithium substituted monophthalocyanine, has never been successfully implemented for the synthesis of porphyrazines (77). 

The crystal structure of the cerium sandwich complex (31) (34) shows it to be similar to that of the related Cclv bis(octaethylporphyrinate) complex (Fig. 7) (83, 84). 

For the neutral lutetium pz sandwich complexes, which exist as jr-cation radicals, ring oxidation to the bis 71-radical is easier for the pz than for its pc analogue, while ring reduction is harder, suggesting that the lutetium pz... 

Proton nmr titration experiments of [26] and [27] with KPF6 in acetonitrile revealed that in solution both compounds form 1 1 intramolecular sandwich complexes with the potassium cation. A number of alkyl-, vinyl- and azo-linked bis(benzo-15-crown-5) ligands are well known to exhibit this mode of K+ coordination. In the case of [26], a solid-state potassium complex was isolated whose elemental analysis and fast-atom bombardment mass spectrum ([26] K+ = 1083 complex ion) was in agreement with 1 1 complex stoichiometry (Fig. 20). 

We synthesized bis crown-ethers 1 and 2 in which cations can be well accomodated between the two ligand units, thus giving rise to sandwich complexes ( ) which can be expected to have complexation constants higher than those of crown-ethers. 

It is interesting to compare these actinide(IV) cyclooctatetraene complexes with similar compounds of the group IVB transition elements Ti, Zr and Hf. Bis (cyclooctatetraene) complexes of aU three are known although structural data is only available for the first two. All would appear to involve both planar and non-planar COT rings and to exhibit a sHpped sandwich structure rather than the true sandwich structure of uranocene. 

Formula (C5H5)2Fe or (ri-C5H5)2Fe MW 186.04 a metal n sandwich complex in which the six n electron system of the cyclopentadienidide ion CsHf is bound to Fe2+ ion Fe—C distance 2.045 A and C—C bond distance 1.4 A. Synonyms bis(cyclopentadienyl)iron ferrocene dicyclopentadienyliron... 

Ruthenium reacts with cyclopentadiene in ether to form a sandwich complex, a yellow crystalline compound, bis(cyclopentadiene) ruthenium(0), also known as ruthenocene. 

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