Ruthenium complexes halogens

Ruthenium complexes are capable of catalyzing halogen atom transfer reactions to olefins. This has been illustrated in the enantioselective atom transfer reactions of alkane and arene-sulfonyl chlorides and bro-motrichloromethanes to olefins using chiral ruthenium complexes. Moderate ee s up to 40% can be achieved for these transformations [74-77]. These specific reactions are believed to follow a radical redox transfer chain process. 

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

Transition-metal-mediated C-O bond cleavage reactions are interesting in view of environmentally benign halogen-free chemical processes [59]. Zerovalent ruthenium complexes are also active toward C-O bond-deavage reactions, and a number of catalytic processes have been developed in this respect. For example, Ru(l,5-COD)(l,3,5-COT) catalyzes allylic alkylation of carbon nucleophiles with allylic carbonates in basic solvent (Scheme 14.24) [60]. 

Ru(Tp)I(Ci6Hi7l)]-0.512 (Fig. 2.80) has been obtained as a cocrystal of an iodine-bearing neutral ruthenium complex and diiodine. The centrosymmetric diiodine molecule links a pair of Ru complexes via halogen bonds to the Ru-bound iodide anions, thus forming a linear I- I-I- I chain.349... 

Transition metal catalysts arc characterized by their redox chemistry (catalysts can be considered as one electron oxidants/reductants). They may also be categorized by their halogen affinity. While in the initial reports on ATRP (and in most subsequent work) copper" " or ruthenium complexes" were used, a wide range of transition metal complexes have been used as catalysts in ATRP. 

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-... 

Whereas osmium dithiocarboxylato complexes are very rare, some dithiocar-boxylato iron and ruthenium complexes have been synthesized by substituting into the metal-halogen complex with lithium dithiocarboxylate [77] and by inserting CS2 into the carbon-metal bond [78,79]. The reaction of a vinylidene complex 32 with CS2 and NaOMe has also been reported to undergo a facile loss of HCl, followed by insertion of CS2 to give the dithiocarboxylato complex 33 (Scheme 7) [80]. 

In apparent contradiction with our results, however, no catalyst decomposition was observed over the course of two tandem ROMP-ATRP polymerisations (Scheme 10) mediated by a difunctional ruthenium complex 9 incorporating both a ROMP and an ATRP initiator [27]. Furthermore, halogen exchange has not been reported. In the preparation of these PMMA-PBD diblock copolymers, ROMP and ATRP occurred simultaneously provided that excess PCy3 be added to the reaction mixture. With this in mind, the stability of catalyst 9 over the course of the polymerisations may be related to the observation that additional PCy extends the longevity of the catalyst [25]. 

Five-coordinate d complexes add halogens under very mild conditions, usually with loss of a neutral ligand to form cis dihalo compounds. Comparison with the analogous ruthenium(O) and osmium(O) compounds (XIV) reveals the stepwise nature of halogenation. In the case of the osmium complex a cationic intermediate (XLIV), which has been isolated and characterized, is formed (39). Warming this cationic complex in tetrahydrofuran results in the loss of a mole of CO and the formation of the cis dihalide (XLV). The intermediate ruthenium complex is apparently too... 

The complexes of ruthenium and osmium in the same oxidation state are generally similar and are, therefore, treated together the structural (Table 1.3) and vibrational data (Table 1.4) have been set out in some detail to demonstrate halogen-dependent trends. 

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