Tetranuclear complexes

Tetranuclear alkyne clusters involving cobalt can adopt a variety of geometries. Reductive dehalogenation of ( Bu)(PhC=C)PCI by [Co2(CO)8] affords 39 in which a chain of four cobalt centers is supported by the functionalized alkyne, as shown in Eq, (15).146-147 

The majority of tetranuclear alkyne clusters containing cobalt adopt butterfly geometries.151152 This is illustrated by the molecular structure of [Co4(/L4-r72-HC2H)(/L-CO)2(CO)8] (Fig. 16), which can be prepared by the 

A variety of cobalt-containing mixed-metal butterfly alkyne clusters are known and will be described in approximate order of decreasing cobalt content. The dehalogenation of [RuCl2(Ph2PC=CBut)(p-cymene)] by [Co2(CO)8] followed by protonation affords fRuCo3(/x4-t -Bu QH)(/i- 

This review has already indicated numerous applications of dicobalt-alkyne complexes in organic synthesis. Like the Nicholas reaction (see Section II,D), the Pauson-Khand reaction has seen widespread use.175 This reaction is a three-component cycloaddition of alkynes with alkenes and carbon monoxide which occurs in the presence of octacarbonyldicobalt to afford cyclopentenones, as shown in Eq. (16). 

Sufficient information about the reaction has been gathered to allow fairly accurate predictions of yield as well as of stereo- and regioselectivity.176177 The reaction proceeds via the formation of hexacarbonylalkyne-dicobalt complexes and is remarkably tolerant of functional groups in both the alkyne and the alkene. The intramolecular Pauson-Khand reaction is an effective way of preparing bi- and polycyclic systems, and the cyclization of 1,6-heptenyne derivatives to give bicyclo[3.3.0]oct-l-en-3-ones has been the most popular application of the Pauson-Khand reaction in natural product synthesis [Eq. (17)]. 

A few linear tetranuclear complexes of ligands related to dpa have been structurally characterised, namely [Ni4(phdpda)4] (phdpda = dianion of A-phenyldipyridylamine),39 [Cu4(dphip)4]2 + (dphip = anion of 2,6-bis(phenylamino)piperidine),37b and [Cr4(dpf)4Cl2]2+ (dpf = anion of bis(2-pyridyl)formamidine),38 but no pertinent electrochemical investigation is available. 

This class of compounds displays a large variety of structural types, which can be generalized as follows  

The regular tetrahedron exists supposedly only in the [Pb4(p4-0)(p.-0Si-Ph) ] molecule, where in addition to the central [l4-0 ligand are present only 

This most widespread type of tetrameric structures is a rhombus of 4 metal atoms, where 4 edges are supported by [l-OR ligands and where both triangles 

This group includes in particular the square planar molecules of [CuOR]4, R = Bu , SiPh3, C6H3Ph2-2,6 (analogs of[Cu404]4- oxocuprates), where the Cu atoms have linear coordination, the vertexes of the squares being occupied by the oxygen atoms [676, 1094, 1027]. In the cluster molecules of Mo, W, and 

A special notice is to be made for the (BaCu[OCMe(CF3)2]3THF 2 structure, where the groups being tridentate in the [Ti4(OMe)16] molecules, turn bidentate and connect only Ba atoms [173] (Fig. 4.8 a). 

Hietanen and Sillen [1968HIE/SIL] tested different speciation models for their data in 3.0 M NaCl, including Th4(OH)g as minor complex. The calculated value of logic A,4 is consistent for the different models. The value of log,o p, = - (21.1 + 0.2) in 3 M NaCl can be used to evaluate the SIT coefficients 

Figrtre VII-8 The stracture of the Zr (OH)g core in the crystal stractures of zirconyl chloride and bromide octahydrates [1956CLEA/AU]. The hydrogen atoms carmot be located, but the bridges are formed by OH groups. The Zr iorts (black) are coplanar. 

Equilibrium constants for the complex Th (OH) j were first calcrrlated by [1968DAN/MAG] -(37.21+0.06) in 4.0 M NaNOs) and later by 

These values are selected by this review. As only these few data are available and the uncertainties given in the original papers, less than +0.1 logio-units, seem to be underestimated, the uncertainty of logn, 4 is increased in the present review to +0.2 logio-units. 

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Molecular examples of trivalent molybdenum are known in mononuclear, dinuclear, and tetranuclear complexes, as illustrated in Figure 5. The hexachloride ion, MoCk (Fig- 5a) is generated by the electrolysis of Mo(VI) in concentrated HCl. Hydrolysis of MoCP in acid gives the hexaaquamolybdenum(III) ion, Mo(H20) g, which is obtainable in solution of poorly coordinating acids, such as triflic acid (17). Several molybdenum(III) organometaUic compounds are known. These contain a single cyclopentadienyl ligand (Cp) attached to Mo (Fig. 5d) (27). 

Pd2L(AN)2l(C104)2 (H2L = /VjV-diethyl-2,6-dialdiminobenzene) and pyrazole form [Pd2L(Hpz)4](C104)2 (91POL1513). With excess pyrazole and in the presence of triethylamine, the tetranuclear complex 248 is formed. 

For nearly two decades TACN-type ligands are of continuing interest for oxidation chemistry. A more recent example is described by ShuFpin and cow-orkers, who prepared novel di- and tetranuclear complexes with TACN ligands 25 bearing pendant acetato arms bridging the iron(lll) centers (Scheme 18) [111]. The... 

Reacting the amidinate salt, K[4-MePh-form], with the dinuclear gold(I) complex, [Au2(2,6-Me2Ph-form)2], in a 1 1 stoichiometry in THF forms the dinuclear-tetra-nuclear complex [Au2(2,6-Me2Ph-form)2][Au4(4-MePh-form)4]-2THF, Figure 1.24, with one tetranuclear and one dinuclear molecule in the same unit cell. Adjusting the reaction ratio to 2 1 formed the tetranuclear complex [Au4(4-MePh-form)4j. 

Figure 3.16 Tetranuclear complex with inequivalent pentafluorophenyl groups.

Herberhold reported activation of water with Re2(CO)io. The reaction proceeded at 200°C to give a tetranuclear complex [Re(CO)3( X -OH)]4 (23) in quantitative yield, and evolution of dihydrogen and CO was observed (Eq. 6.13) [21]. Complex 23 has a pseudo-cubane structure without metal-metal bonds in which the Re(CO)3 groups are linked by triply-bridging OH ligands. Also in this case, no presumed intermediate hydrido(hydroxo) species was detected. 

IC6H4).2348,2349 Amidinato gold(I) complexes have been described and are dinuclear, as [Au2 C(Ph)(NTMS)2 2]475 (398) or tetranuclear as [Au4 CH(NPh)2 4].2350 The triazenido ions RN3R react with Aul in liquid ammonia to form the tetranuclear complex (399), which has an analogous structure to that of the tetranuclear formamidinato compound. 1 The structure of the azido complex [Au(N3)(PPh3)] has been reported.1736... 

A tetranuclear complex is formed with (dimethylamino)ethanethiolate of type [Zn4L4Cl4]. It can be obtained directly from the zinc chloride salt or from zinc acetate in the presence of HC1.852... 

The ligand A-,A--bis(2-niercaptoethyl)benzylaniine complexes zinc in the doubly deprotonated form resulting in a tetranuclear complex, Zn4L4, which has an unusual Zn4S4 metalacyclic structure 875... 

First generation dendrimers (tetranuclear complexes) of the same family with branches containing different metals have also been synthesized and energy migration patterns leading to one or two peripheral units have been obtained [58]. 

In addition to the well-known luminescent Re(NAN)(GO)3 moieties, the electrochemically active ferrocenyl groups were employed as building blocks for the construction of polynuclear silver(i) alkynyl complexes. Yip reported the synthesis, structural characterization, and electrochemistry of a tetranuclear complex, [Ag3(dppm)3(C=CFc)(OTf)]OTf 96 (Figure 43), with the Ag3(dppm)3 skeletal unit being capped by a ferrocenylethynyl ligand on one side and an OTP anion on the other, all in a /Z3-771-bonding mode.170... 

Thiols like pyridine-2-thiol yield (carbene)gold thiolates, and onium salts give cationic (carbene)gold ylide complexes, isolated and characterized as the perchlorates.170 The reaction of dithiocatechol with (cyclohexylisocya-nide)gold chloride affords a carbene complex [(CyNC)AuC(NHCy)2]+Cl-, which co-crystallizes with a neutral tetranuclear complex [(CyNCAu)2Au2(S2C6H4)2].224... 

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