Arene complexes of ruthenium

A tridentate (r 6 ri1 r 1) strapped arene complex of ruthenium(II), 20, containing a pair of auxiliary nitrogen donor atoms derived from (R, R)-1,2-diphenylethylenedi-amine, has been prepared by a sequence in which the functionalized arene is first coordinated to ruthenium(II), as shown in Scheme 5.25 The structure of 20 has been... 

A large number of strapped arene complexes of ruthenium(ll) have been prepared by treatment of [RuCl2(il6-arene)]2 complexes with tertiary phosphines of the type R2P Ar in which an aromatic group is separated from the phosphorus atom by a two- or three-atom chain. In the first step, which usually occurs at or just above... 

Tethered arene complexes of ruthenium(II) are also formed readily when the conformational freedom of the tether is restricted, for which purpose the biphenyl unit has proved ideal. Thus, (2-dicyclohexylphosphino)biphenyl and its derivatives react with [RuCl2(r 6-C6H6)]2 in DMF at 100 °C to give directly the tethered complexes 67-69 in yields of 31-96% without detection or isolation of the presumed P-coordinated intermediates.65... 

An example of a tethered arene complex of ruthenium(II) in which the auxiliary ligand is a a-bonded carbon atom is complex 80, which is formed by the action of AgBF4 and P(OMe)3 on the r 4-tetraphenylcyclobutadiene r 3-allyl complex 79 [Eq. (13)]. In the proposed mechanism, the allyl group migrates to the four-membered ring, which opens to generate an intermediate cation 81, the pendant arene of which coordinates to the metal.74... 

A series of cationic, strapped, r)6 ri1 ri1-arene complexes of ruthenium(II) (82) containing both carbon and phosphorus as the auxiliary atoms has been obtained by a coupling reaction of the iminophosphorane complexes 83 with an excess of 1, l-diphenyl-2-propyn-l-ol, the p-cymene in 83 being displaced by one of the phenyl... 

Bis(arene) complexes of ruthenium (99), first prepared in relatively low yield by the Fischer-Hafiier synthesis (see Fischer-Hafner Synthesis) (MCb/AlCb/arene) are now readily available through solvento cations [(arene)RuS] + (S = acetone, nitromethane), which in turn are made from the dimeric half-sandwich halides [(arene)RuCl2]2 (Section 6.3) with Ag+ with the appropriate arene as solvent (Scheme 23). This method allows a whole range of functionalities to be incorporated to at least one of the arenes. The dications (99) + are of relatively high solvolytic stability and are decomposed by DMSO only to form [(arene)Ru(DMSO)3] +. 

Bennett, M.A., Recent advances in the chemistry of arene complexes of ruthenium(0) and ruthenium(II), Coord. Chem. Rev. 1997,166 225-254. 

Several other versions of these catalysts have been developed. Arene complexes of monotosyl-l,2-diphenylethylenediamine ruthenium chloride give good results with a,(3-ynones.55 The active catalysts are generated by KOH. These catalysts also function by hydrogen transfer, with isopropanol serving as the hydrogen source. Entries 6 to 8 in Scheme 5.3 are examples. 

The complexed arene rings in tethered complexes of ruthenium(II) are close to planar, though the ipso-carbon atom is often pulled slightly towards the metal atom. In the phosphine complexes, the Ru-C(arene) distances trans to the P-donor (2.22-2.29 A) are significantly greater than those trans to the Ru-Cl bonds (2.15-2.25 A). This feature is also evident in non-tethered complexes of the type [RuCl2(r 6-arene)(PR3)] and can be attributed to the higher trans-influence of PR3 relative to that of Cl-.88... 

Redox Potentials (vs FcH/FcH+) of Selected Tethered Arene-Phosphine Complexes of Ruthenium (II)... 

J. Chatt, and J. M. Davidson, The Tautomerism of Arene and Ditertiary Phosphine Complexes of Ruthenium(O), and the Preparation of New Types of Hydrido-Complexes of Ruthenium(II), J. Chem. Soc. 1965, 843-855. 

Star-shaped molecules containing cationic arene complexes of iron and ruthenium have been reported by Astruc and co-workers.298 Utilizing the activating nature of the cyclopentadienyliron moiety on the complexed arene, 260 was converted into 262 via bromobenzylation. The photolysis of 262 gave 263, which was subsequently reacted with 264 to give the hexametallic complex 265. Further nucleophilic aromatic substitution reactions with phenol 266 gave the allyl-substituted complex 267 (Scheme 2.70). 

Ruthenium complexes also catalyze the anti-Markovnikov hydroamination of vinylarenes. In this case, the combination of l,5-bis(diphenylphosphino)pentane (DPPPent), triflic acid, and a ruthenium(II) precursor generates a catalyst for the additions of secondary amines to vinylarenes (Equation 16.72). This mixture of catalyst components has been shown to generate a cationic Ti -arene complex of a PCP pincer ligand generated from the DPPPent ligand. The mechanism of this reaction involves nucleophilic attack of the amine on an Ti -vinylarene complex, as described in more detail in the section on the mechanisms of hydroamination. 

The reaction of ( n -arene)(ti - 2.21paracyclophane)-complexes of nithenium(II) with hydride afforded (q6-l,3-diene)(Tj -(2.2]paracyclophane)-complexes of ruthenium(0) whidi on protonation with HBF4 gave a series of highly fluxional endocyclic agostic compounds. 

It will be important to gain more knowledge of the in vivo metabolism of ruthenium(II) arene complexes of potential interest as drugs. Little is currently known, but some studies on metal cyclopentadienyl (Cp) complexes have been reported. For ferrocene, [(Cp)2Fe], a coordinated Cp ring is hydroxylated in the liver via the P-450 system (Fig. 2.11) [78]. 

Chatt J, Davidson JM (1965) The tautomerism of arene and ditertiary phosphine complexes of Ruthenium(O), and the preparation of new types of hydrido-complexes of ruthenium(II). J Chem Soc 843-855... 

Astruc has also reported the use of arene complexes of iron and ruthenium in the design of star-shaped complexes. The cyclopentadienyliron moiety in 93 (Scheme 25) was utilized to activate the complexed arene toward bromobenzyla-tion to produce 95. Following photolytic demetallation, 96 was reacted with 97 to yield the /jexa-metallic complex 98. These complexed arenes were then subjected to nucleophilic aromatic substitution reactions with 99 allowing for the isolation of 100. 

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