Dithioether ligands

Scheme 1.3 Test reaction with dithioether ligands.

Scheme 1.4 Pd-catalysed allylic alkylations with dithioether ligands.

Scheme 1.36 Test reaction with pyridine thioether and dithioether ligands.

In 1998, Ruiz et al. reported the synthesis of new chiral dithioether ligands based on a pyrrolidine backbone from (+ )-L-tartaric acid. Their corresponding cationic iridium complexes were further evaluated as catalysts for the asymmetric hydrogenation of prochiral dehydroamino acid derivatives and itaconic acid, providing enantioselectivities of up to 68% ee, as shown in Scheme 8.18. 

In 1999, these authors reported the synthesis of the first family of sugar-derivative dithioethers containing sulfur as a unique donor atom. These chiral Ci-symmetric dithioether ligands were tested in the iridium-catalysed... 

Scheme 8.17 Hydrogenation of A -acetyl-l-phenylethyleneamine with tartrate-derived dithioether ligands.

In 2004, Dieguez et al. reported the development of novel C2-symmetric dithioether ligands derived from the corresponding binaphthyl or biphenanthryl diols. Thus, various (i )-binaphthyl dithiols substituted by alkyl groups on the sulfur atom in order to increase the steric bulk were synthesised, and the corresponding mononuclear cationic Ir(I) -cyclooctadiene complexes were prepared and characterised (Scheme 8.20). NMR studies demonstrated that, in all cases, the coordination of the ligands proceeded with complete stereoselectivity at the... 

Scheme 8.19 Hydrogenations of acrylic acid derivatives with sugar dithioether ligands.

Scheme 8.20 Hydrogenations of olefins with dithioether ligands derived from BINOL.

Scheme 8.22 Hydrogenation of acetamidoacrylic acid with iridium complexes containing dithioether ligands.

A number of dithioethers 169-173 (Fig. 27.16) based on the chiral skeleton of some well-known phosphines such as DIOP, Deguphos and BINAP, have been reported. The use of 1,4-dithioether ligands which lack contiguous chiral centers such as (+)-DiopsR2 169 [130], BINASR2 172 [131] and 173 [132] in the Ir- or... 

B. Copper Polymers Assembled by Aromatic Dithioether Ligands 105... 

Reaction of Cul with bis(phenylthio)methane in acetonitrile in a 2 1 molar ratio gave air-stable colorless crystals of general formula [ Cu4(p,3-I)4 [ i-PhSCH2SPh j2] 9 (Scheme 8). Modification of the molar ratio—for example, a 1 1 or 1 2 molar ratio—had no influence on the composition of the resulting material and only compound 9 was formed.145 The crystal structure of 9 (Fig. 13) consists of cubane-like Cu4I4 clusters linked by bridging dithioether ligands to... 

The spacer rigidity of the dithioether ligand influences the resulting framework in a spectacular manner. Indeed, the unsaturated dithioether ligand l,4-bis(phenythio)butyne, including a linear alkyne -CH2-C=C-CH2- array, reacts with Cul in MeCN to afford the colorless 3D polymer... 

FIGURE 28. (a) Hexanuclear Cu6(g3-I)6 core of 17 ligated by six unsaturated dithioether ligands. H atoms are omitted for clarity, (b) View on the 3D network of 17 along the a,b plane. The phenyl groups are omitted for clarity. 

If the self-assembly reaction of Cul with bis(phenylthio)pentane is conducted in a 1 1 ratio, elemental analyses of the colorless blocks isolated from a concentrated MeCN solution were in accordance with the ligation of one dithioether ligand per copper center with composition [(CuI)2 g-PhS (Cl hfsSPhj2] 22 (Scheme 11). Alternatively, compound 22 is formed after addition of second equivalent of bis(phenylthio)pentane to a solution of 21. 

Crystallographic examination of 22 revealed the existence of infinite ID ribbons (Fig. 39). These corrugated ribbons are constituted by two bridging dithioether ligands, with span rhomboid Cu2l2 units. Each copper center of... 

What are the limits of the number of spacer units between the two sulfur atoms of ArS(CH2)nSAr dithioether ligands that still allow the self-assembly copper iodide and the build-up of metal-organic materials To answer this question, we reacted Cul with both 1,6 bis(phenylthio)hexane and 1,7-bis (phenylthio)heptane in acetonitrile solution in a 2 1 ratio. In both cases,... 

Parallel to our work with RS(CH2)nSR ligands in this domain, the Li group underwent an interesting investigation of the reactivity of pyrimidine-functionalized dithioether ligands toward various copper(I) salts.151,152 The ditopic ligands L25—L28 incorporating an aromatic cycle in the spacer are illustrated in Scheme 12. 

Like for polymer 9, the framework of [Cu2I2 i,-L29 2] 29 (Fig. 43) is monodimensional, but the dithioether ligand L29 assembles dinuclear Cu( i,-I)2Cu motifs (d Cu Cu 3.131(2) A) exclusively through the pyrimidine nitrogen atoms with formation of 16-membered macrocycles. 

Several metal-organic polymers assembled by dithioether ligands, which are functionalized by heteroelements such as O, N, or Si in the spacer unit, have been recently described and reacted with Cu(I) salts. For example, the 2D square-grid coordination polymer 37 incorporating the 16-membered dithiaoxa crown-ether L37 has been prepared by a self-assembly process involving the interaction of the dithiaoxa macrocycle with CuCN (Scheme 17) the parallel reaction of the dithiaoxa crown-ether with Cul afforded the ID double-stranded coordination polymer 37 . This example demonstrates, how the nature of the counterion can control the form of the network.157... 

The same group also explored the reactivity of the two asymmetric dithioether ligands with cyclohexyl (L45) and phenyl (L46) end groups toward Cul.164 Reaction of 2 (cyclohexylmethylthio)-l-thiomorpholinoethanone L45 with copper(I) iodide afforded a ID channel-type coordination polymer [Cu4I4(L45)2]n 45, interconnected by cubane-like tetranuclear Cu4I4 cluster units (Scheme 24). The mean Cu-Cu distance within the cluster cubes amounts to 2.749 A at 173 K. 

Another dithioether ligand system, whose coordination chemistry and photophysics are currently being developed in our laboratory, is based on a Tr-conjugated 2-azabutadiene array.173 For example, ligand L50 has been coordinated to Re(I) leading to luminescent Re(I) S,N chelate complexes.174 This ligand reacts with Cul to produce the dinuclear complex 50, which is luminescent both in solution and in the solid state (Scheme 27). A recent X-ray diffraction study revealed that the Cu - Cu distance in the rhomboid motif is much beyond that of the related dinuclear compound 48 (2.673(6) vs. 2.7964(6) A). Treatment of [Cu(MeCN)4] PF6] with two equivalents L50 afforded the... 

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