Trinuclear complex

These complexes exhibit in dichloromethane solution a first ferrocene-based oxidation with features of chemical reversibility, followed by a second irreversible oxidation, which is thought to be centered on the metal-carbonyl fragment. A poorly reproducible oxidation of the Au moiety is also observable [49]. The relevant redox potentials are summarized in Table 7-35. With respect to the oxidation of free l,T-bis(diphenylphosphino)ferrocene E° = - -0.66 V) [49], the multimetallic com-plexation makes oxidation of the ferrocene fragment significantly more difficult (by about 0.4 V). 

The linear trinuclear molecules can also be formed in the case of the presence in the central octahedron of 2 terminal ligands in trans-configuration because both [M202] cycles are arranged in the equatorial plane in this case. 

The structure of the [M202] cycles in the chain-like trimers is in general analogous to that in the molecules of dimeric alkoxides. 

As seen, [Co3(dpa)4Cl2] (as well as the analogues bearing different axial fragments) undergoes two one-electron oxidations displaying features of chemical reversibility in the cyclic voltammetric time scale, Table 6. 

Such behaviour has been interpreted assuming that in this case the electron removal is localized on one of the two outer Cr atoms, and hence [Cr3(dpa)4Cl2]+ can be viewed as possessing the authentic Cr(l)11— Cr(2)n—Cr(3)in electronic configuration.3041 

The last trinuclear dpa complex we will consider is [Ni3(dpa)4Cl2], the electrochemical behaviour of which is known.31 In fact, complexes such as [M3(dpa)4Cl2] (M = Cu, Ru, Rh) have been structurally characterized,33,34 but nothing has been reported on their redox activity. 

In contrast with the Co and Cr analogues, [Ni3(dpa)4Cl2] has been, up to now, crystallized only in the symmetrical geometry (Ni-Ni bonding,3 la or, alternatively, Ni—Ni nonbonding3 lb distances of 2.43 A, and Ni-Cl 

To conclude the section, we recall that ligands somewhat related to dpa also give rise to linear trinuclear complexes. This is the case of 2,6-bis(phenylamino)pyridine,36 2,6-bis(phenylamino)piperidine,37 and bis (2-pyridyl)formamidine.38 At the moment, however, no (significant) electrochemical investigation has been carried out on their metal complexes. 

The complex ThjlOHlj has been included in models for lutrate media, i.e., 0.5- 

0 M NaNOs [1982MIL/SUR2], 3.0 M LiNOs and 3.0 M Mg(N03)2 [1971MIL2]. Extrapolation of the equilibrium constants in 0.5 to 3.0 M NaNOs [1982MIL/SUR2] and 

Other trinuclear complexes like Th3(OH)3 proposed in models for 3.0 M LiNOs [1971MIL2] and 3.0 M NaCl [1968HIE/SIL], ThsCOH) in 3.0 M NaCl [1968HIE/SIL] or Th3(OH)g in 4.0 M NaNOs [1968DAN/MAG] are not considered to be well established. 

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Isolation and characterization of stereoisomers in di- and trinuclear complexes with N-heterocyclic ligands 98CSR185. 

Imidazole with [(r -C3Hj)2Rh(acac)] gives the trinuclear complex 60 (86JCS(D)2193). 

L = C3H3, C H ) and then [Rh(acac)(CO),] to yield the tetranuclear species 180 (85ICA(i00)L5), where the heterocyclic ligands are tridentate. The product reacts with the rhodium(I) dimer [Rh(CO)2Cl]3 to give the trinuclear complex 181. In the solid state, the molecules of this complex form the intermolecular stacks along the z-axis. 

Tetrazole with [(T) -C3Hj)2Rh(acac)] gives the trinuclear complex 191 (86JCS(D)2193). This product with [Rh( j.-Cl)(CO)2]2 produces the mixed-valence trinuclear species 192. 

Lithium 2-thiolatobenzothiazole with [Pd(/z-Cl)( j -C3H5)2]2 gives the dinuclear complex 84 (91JCS(D)255). The latter has the ligating potential and ability to form the trinuclear complex 85 on reaction with [Pd( , -C3H5)(Me2C0)2]C104. 

A variety of such ternary catalytic systems has been developed for diastereoselective carbon-carbon bond formations (Table). A Cp-substituted vanadium catalyst is superior to the unsubstituted one,3 whereas a reduced species generated from VOCl3 and a co-reductant is an excellent catalyst for the reductive coupling of aromatic aldehydes.4 A trinuclear complex derived from Cp2TiCl2 and MgBr2 is similarly effective for /-selective pinacol coupling.5 The observed /-selectivity may be explained by minimization of steric effects through anti-orientation of the bulky substituents in the intermediate. 

Although there is a severe paucity of vibrational data for the molecular form of O2 chemisorbed on rhodium surfaces, it is possible to visualize the dinuclear and trinuclear complexes as models for the associative chemisorption of O2 on rhodium. The pq-o values of the complexes Rh2(02)i,2 show little... 

An unprecedented stereoselective procedure to obtain enantiomerically pure transition cluster M3Q4 complexes consists of the direct excision of the M3Q7X4 n polymers using chiral diphosphanes, namely (+)-l,2-bis[(2J ,5R)-2,5-(dimethylphospholano)]ethane [(R,R)-Me-BPE] and its respective enantiomer [(S,S)-Me-BPE] to afford the trinuclear complexes (P)-[Mo3S4Cl3(J ,J -Me-BPE)3] and (Af)-[Mo3S4Cl3(S,S-Me-BPE)3] , respectively [30]. The structures of both enantiomers are shown in Fig. 7.3. The symbols (P) and (M) refer to the rotation of the chlorine atoms around the C3 axis, with the capping sulfur pointing towards the viewer. 

These trinuclear complexes can act as metalloligands to afford a whole series of heterobimetallic M3M Q4 cubane-type complexes and several review articles on the topic have been published in the last decade [31, 32]. 

The formation of monomer and dimer of (salen)Co AIX3 complex can be confirmed by Al NMR. Monomer complex la show Al NMR chemical shift on 5=43.1 ppm line width =30.2 Hz and dimer complex lb 5=37.7 ppm line width =12.7 Hz. Further instrumental evidence may be viewed by UV-Vis spectrophotometer. The new synthesized complex showed absorption band at 370 nm. The characteristic absorption band of the precatalyst Co(salen) at 420 nm disappeared (Figure 1). It has long been known that oxygen atoms of the metal complexes of the SchifT bases are able to coordinate to the transition and group 13 metals to form bi- and trinuclear complex [9]. On these proofs the possible structure is shown in Scheme 1. 

Using sterically bulky groups in the ortho positions of the phenyl rings in ArNC(H)NHAr, such as Ar = 2,6-Me2-QH3, led to formation of dinudear and trinuclear complexes. This suggests that steric factors can prevent the formation... 

Cold(l) and Silver(l) Mixed-Metal Trinuclear Complexes 33... 

Au-C bonds, mixed metal gold-silver dimers of planar, trinuclear complexes are readily formed by mixing gold(I) carbeniates and gold(I) benzylimidazolates with silver(I) pyrazolates in stoichiometric ratios. The complexes retain the ligands associated with the metal atoms of the starting materials. 

H-HOESY and PGSE NMR studies of neutral trinuclear complexes of Aul and Hgll evidence for acid-base stacking in solution. Journal of the American Chemical Society, 124, 4570. 

Figure 3.10 Trinuclear complex [(Au2S2CNR2)] (PPh2)3CH Au(C6F5)].

The trinuclear complex [(Au2S2CNR2)] (PPh2)3CH Au(C6F5)] [102] (Figure 3.10) has an IR spectra that confirms the presence of the pentafluorophenyl group bonded to the Au(I) atom. The P H NMR spectrum shows a doublet at 43.6 ppm and a triplet at 41.2 ppm while the F H NMR spectrum shows the typical pattern for the pentafluorophenyl group bonded to the Au(I) atom. 

The two trinuclear complexes [(Au2S2CNR2)(PPh2CH2PPh2CH2PPh2)Au(C6F5)j [103] (Figure 3.11) are synthesized by treatment of [Au3( j,-dpmp)(S2CNMe2)2Cl]... 

When the same reaction is carried out in a 1 2 ratio the trinuclear complexes where R = C Fs (Figure 3.21) and QCI5 are obtained. The crystal structure of the former was solved by X-ray diffraction. The complex where R = QF5 can also be obtained by reaction of [AulCgFsjldppm)] with trows-[Pd(C6F5)(tht)2]... 

Barbera, J., Elduque, A., Gimenez, R., Oro, L.A. and Serrano, J.L. (1996) Pyrazolate Golden Rings Trinuclear Complexes That Form Columnar Mesophases at Room Temperature. Angewandte Chemie... 

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