Complex ruthenium, divalent

Ruthenium complexes are active hydrogenation catalysts for the reduction of dienes to monoenes. Both zerovalent and divalent ruthenium complexes containing various (alkene, diene and phosphine) ligands have been employed as catalysts that have met with different degrees of success. 

Reduction of ammonium chlororuthenate with titanous chloride gives a solution containing divalent ruthenium which will absorb ethylene or propylene to give a 1 1 ruthenium-olefin complex which was not isolated (108). Ethylene was previously reported not to form stable complexes on treatment with ruthenium halides (97). 

Acids can also react vith ruthenium complexes by either protonation or oxidative addition. The catalytic addition of acidic compounds is also important for example, a divalent ruthenium complex Ru(>7 -cydooctadienyl)2 catalyzes the addition reaction of carboxylic acid to alkynes in the presence of tertiary phosphines and maleic anhydride (Eq. 14.5) [71]. 

Divalent ruthenium complexes are efficient catalysts for A -alkylation of amines by a primary alcohol. RuCl2(PPh3)3 or RuCl3-3H20/P(0Bu)3 effectively catalyze the A -alkylation of aromatic amines (eq (38)) [133-134]. On the other hand, yV-alkylation of aliphatic amines with a primary alcohol is carried out in high yield by the use of RuH2(PPh3>4as catalyst [135]. 

However, the same ruthenium complex will promote the cleavage of DNA under nonoxidative conditions as well. Barton and coworkers find that divalent metal ions (cobalt, zinc, cadmium, lead), when added to the... 

A singular chiral adduct was formed between C70 and two RujfCOjg units which are known for the complexation of arenes. From the corresponding mono -adduct it was known that the trinuclear ruthenium moieties add preferentially to the hexagons of highest local curvature [143]. Assuming addition of two Ru3(CO)9 units at opposite poles, three constitutional isomers of [[Ru3(CO)9 2(ft-T2, /2, rf-C7o)] are possible in analogy to the addition of achiral divalent addends to a-type bonds (cf. Sect. 4.2.1) [54,131 ] One of them has symmetry and two have C2-symmetry. Of the three formed isomers, the major one afforded crystals suitable for X-ray analysis it has an inherently chiral addition pattern and corresponds to structure ( )-59 [143] (Fig. 9). 

C-0 bond cleavage of alkenyl carboxylates such as vinyl and allyl carboxylates can also be achieved by transition metal hydrides. For example, a divalent ruthenium dihydride complex c 5-RuH2(PPh3)4 reacts with vinyl acetate to give c 5-Ru(H)(OAc)(PPh3)4 accompanied by evolution of ethylene (Scheme 3.31)... 

The UV spectral pattern of the spin-paired tris-bipy and -phen complexes of iron(II), ruthenium(II) and osmium(II) (see ref. (23)) is very similar to that of the complexes of other divalent metal ions. As compared with the latter complexes, the first internal ligand transition is shifted to larger wave numbers, the shift beinggreater for ruthenium(II) and osmium(II) than for iron(II). This shift was associated (23, 69) with the effect of back-donation which tends to push the filled and vacant i-levels of the ligands further apart. 

Given the isoelectronic relationship between [CR] and [NO] and the ubiquity of this latter ligand in the coordination chemistry of later transition metals, the scarcity of mononuclear alkylidyne complexes of metals from groups 8-10 is surprising [1-4]. Isolated examples have been reported for iron [5], cobalt [6], ruthenium [4,7], osmium [4,8-9] and iridium [10]. Most of the examples known employ routes with extensive precedent in early transition metal systems, i.e., either electrophilic attack at the p-atom of a hetero carbonyl (CS [5], CTe [4], or C=CH2 [10]) or the Lewis-acid assisted abstraction of an alkoxide group from a carbene precursor [5] (Scheme 1). The one approach which is, too date, peculiar to group 8 metals involves reduction of a divalent dichlorocarbene complex by lithium aryls [4]. The limitation of this procedure to ruthenium and osmium is presumably not a feature of these metals but rather a result of the present lack of synthetic routes to suitable dihalocarbene precursor complexes of earlier metals. 

Allenylidenes could be considered as divalent radicals derived from allenes. In a similar way to vinylidenes, allenylidenes can be stabilized by coordination with transition metals and again ruthenium is one of the most widely used metals. Metal-allenylidene complexes can be easily obtained from terminal propargylic alcohols by dehydration of the initially formed metal-hydroxyvinylidenes, in which the reactivity of these metal complexes is based on the electrophilic nature of Ca and Cy, while Cp is nucleophilic. Catalytic processes based on nucleophilic additions and pericyclic reactions involving the it system of ruthenium allenylidenes afford interesting new structures with high selectivity and atom economy. 

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