Ruthenium cyclophanes

Cyclophane ruthenium complexes are of interest as possible monomeric components in the construction of multilayered organometallic polymers such as 262, which might show extended ir-electron delocalization (Scheme 25). 

Cyclophane ruthenium complexes have been prepared by the methods developed to make arene ruthenium complexes (Section II,A). Treatment of the solvated complexes of type 7, obtained from the dimers 1 and silver tetrafluoroborate in acetone, with 1 equiv of cyclophanes a-j in the presence of trifluoroacetic acid gives the double-layered (i76-arene)-(i76-cyclophane)ruthenium(II) complexes 263 in good yield (Scheme 26, p. 222). When 7 is used in excess, the triple-layered complex 264 is formed (159-162). 

A bis(cyclophane)ruthenium(II) complex has been prepared by using Bennett s procedure reaction of diene 265, obtained by Birch reduction of 4,5,7,8-tetramethyl[22](l,4)cyclophane 266, with ruthenium chloride gives the dimeric chloride complex 267 (Scheme 27, p. 223). Treatment of the solvated complex 268 with 266 in the presence of trifluoroacetic acid leads to 269 (163). The structures of complexes 267, 268, and 269 are based on ... 

A more general route to make bis(cyclophane)ruthenium(II) complexes involves a reduction of 263 (arene = benzene) with Red-Al to afford the [ 174-1,3-cyclohexadiene)(tf-cyclophane)]ruthenium(O) derivatives 271 (Scheme 28, p. 224). Treatment of 271 with hydrochloric acid gives the dimeric chloride complexes 272, which lead the desired bis(r)6-[2 ]cyclo-phane)ruthenium(II) complexes 274 via Bennett s procedure (145). Synthesis of the oligomer 275a is also achieved in quantitative yield by heating 274 with the solvated complex 7 (arene = C6Me6) in neat trifluoroacetic acid. 

An attempt to achieve the complexation of the cyclophane iron complex 276 by treatment with the solvated (p-cymene)ruthenium derivative 7 results in disruption of the arene-iron bond and formation of the (p-cymene)[[22](l,4)cyclophane]ruthenium(II) salt 277 as the only-product (164) (Scheme 29, p. 224). 

An electrochemical study of the reduction of the double-layered (arene)-(cyclophane)ruthenium complexes 263 and of bis(arene)ruthenium complexes 235c has been reported (160,166). The compounds show in... 

Monolayered cyclophane complexes of type 263 are also reduced by sodium bis(methoxyethoxy)aluminum hydride (Red-Al) to give (i74-diene)-(i76-cyclophane)ruthenium(0) complexes (Scheme 33). If the benzene ring of 263 (arene = benzene) is converted to the (1,3-cyclohexadiene)-ruthenium(O) derivative 271, however, when the corresponding rj6-hexa-methylbenzene is reduced with Red-Al, the product is the (if-1, 4-cyclohexadiene)ruthenium(0) complex 288. Synthesis of 271 can... 

A special issue devoted to molecular machines appeared in Accounts of Chemical Research in 2001. It reflects the current interest for this field in which ruthenium complexes act as important tools. Molecular machines are characterized by a mobile part and a stationary part. Photochemical and electrochemical inputs can make a machine work, offering the advantage of being switched on and off easily and rapidly. Mechanically interlocked molecules, such as rotaxanes and catenanes, are suitable candidates. Crown ethers, cyclophanes, and calixarenes are representative families of the cyclic... 

Interesting electrical properties are to be expected with the stepwise extension of this TT-system. The preparation of multilayered cyclophanes proved to be laborious [6] nevertheless new synthetic methods in transition metal chemistry of arenes have opened up a promising alternative approach via preparation of multidecker sandwich complexes (structure type D in Fig. 3). First row transition metals like chromium, iron and cobalt [51] form strong coordinative bonds with arenes when their oxidation state is low [48a] whereas second and third row elements like ruthenium, rhodium and iridium are strongly bonded towards arenes in higher oxidation states [48a, 51]. Sandwich complexes of cyclophanes can be divided into two groups ... 

The number of complexes of this type is considerably higher than for inclusion-and carbonyl complexes, because the components of the complexes can be varied much more Substituted cyclophanes from [22]- up to [26]cyclophanes, as well as indenophanes are used as ligands for metal fragments, which may consist of chromium, iron, ruthenium, rhodium, iridium or cobalt as metal units, and Cp-, Cp - and C R -units as stabilizing co-ligands. From Fig. 21 the importance of the oxidation state and position in the periodic table of the individual metals can be seen [48a] cobalt-III forms monocomplexes only, whereas the lower sited iridium-IIl also forms the biscomplexes for cobalt. 

Monomeric building units of structure type D in this series (Fig. 3) are known only for ruthenium (complex 88 in Fig. 21). Method c [82b, 90] is particularly well suited for the preparation of such complexes, whereas method d [83] is limited to the few cyclophanes that can be reduced via Birch s method (Fig. 22). The halogen dimers [( -Cp )MX2]2 are known (X = Cl, I M = Co-... 

Mori [30, 31, 81, 98, 145] pointed out, that the highfield shift of the ligand carbons in complexed [2 ]cyclophanes is dependent on their geometry. On the basis of the boatlike distorted conformation of the bridged benzene rings, the distances of the respective ligand carbons to the metal atom vary. In carbon NMR-spectra of iron-[30, 98], chromium-[30, 145] and ruthenium-complexes [81] the complexation shifts (AS) increase with decreasing distance, independent of the metal (Fig. 41). 

Cyclophanes are suitable ligands for such mixed valence ions of iron and ruthenium in particular, because of the ease of preparation and its stronger n-bonding ability with arenes [169]. 

Complex chemistry of cyclophanes links the two best examined two-layered molecules of organic and organometallic chemistry, namely [22 ]para-cyclophane and ferrocene. The rich redox chemistry of ruthenium, cobalt, rhodium and iridium therefore provides a basis for constructing polymeric structures, of which some oligomeric building units are already known. 

Simple derivatives such as (p-cymene)OsCl2(DMSO) have been reported and the substitution chemistry of [(arene)RuL3l2+ complexes explored. The synthesis of cyclophane ruthenium sandwich complexes has been achieved to give mononuclear and triple-decker-sandwich complexes(52). 

Iron, Ruthenium, and Osmium.—Reactions of [(t7-arene)RuCl2]2 with AgBF followed by [2.2]paracyclophane have afforded salts of cationic sandwich complexes in which one (or both) of the arene rings of the cyclophane is(are) n-complexed with an [(j -arene)Ru] + residue. Kinetic studies have been reported of reversible nucleophilic additions of phosphines and phosphites to a benzene ligand of [( -PhH)2M] + (M=Fe, Ru, and Os) reactivity towards addition decreases through the series M = Fe>Ru>Os. ... 

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