Ruthenium complexes paths

Irradiation of 1 in moist acetonitrile containing triethylamine leads to no net reduction of the Ru(II) complex addition of water to solutions of reduced 1 in acetonitrile produce a rapid regeneration of the Ru(II) complex. While the products have not yet been determined, it is evident that a net redox reaction between water and the reduced ruthenium complex is occurring. Under these conditions (water, acetonitrile, and triethylamine), sustained irradiation of 1 can be carried out so that appreciable conversion of the triethylamine occurs acetaldehyde, which presumably arises through hydrolysis of the SchiflE base produced in Reaction 15, is easily detected by VPC as a major product. A trace of product having a retention time identical to succinonitrile is also detectable by VPC, but it appears that Reactions 14, 15, and 16 are the predominant paths for rapid depletion of the triethylamine radical cation. 

Although this spectrum does not correspond to any particular ruthenium carbonyl complex, it is consistent with the presence of one or more anionic ruthenium carbonyl complexes, perhaps along with neutral species. Work is in progress with a variable path-length, high pressure infrared cell designed by Prof. A. King, to provide better characterization of species actually present under reaction conditions. 

A most significant advance in the alkyne hydration area during the past decade has been the development of Ru(n) catalyst systems that have enabled the anti-Markovnikov hydration of terminal alkynes (entries 6 and 7). These reactions involve the addition of water to the a-carbon of a ruthenium vinylidene complex, followed by reductive elimination of the resulting hydridoruthenium acyl intermediate (path C).392-395 While the use of GpRuGl(dppm) in aqueous dioxane (entry 6)393-396 and an indenylruthenium catalyst in an aqueous medium including surfactants has proved to be effective (entry 7),397 an Ru(n)/P,N-ligand system (entry 8) has recently been reported that displays enzyme-like rate acceleration (>2.4 x 1011) (dppm = bis(diphenylphosphino)methane).398... 

The hydrative cyclization involves the formation of a ruthenium vinylidene, an anti-Markovnikov addition of vater, and cyclization ofan acylmetal species onto the alkene. Although the cyclization may occur through a hydroacylation [32] (path A) or Michael addition [33] (path B), the requirement for an electron- vithdra ving substituent on the alkene and lack of aldehyde formation indicate the latter path vay to be the more likely mechanism. Notably, acylruthenium complex under vent no decarbonylation in this instance. 

Routes to the important class of well-defined ruthenium initiators of the Grubbs type (20b-22b) are summarized in Eigure 4 for details, see Table 2. COMC (1995) described the first example of this family, vinylalkylidene 20a, prepared by reaction of RuCl2(PPh3)3 with 2,2-diphenylcyclopropene. Subsequent treatment with PCys yields 20b (path (a)). (The corresponding complex 21a was later prepared by reaction of RuHCl(PPh3)3 with propargyl chloride see below). Initiator 20a effected controlled ROMP of and bicyclo[3.2.0]heptene M6, but ROMP of less... 

In contrast to the chelate formation with ligand 4 the reaction of the amino-methyl ligand 3 follows another path and no chelate complex is formed. Instead two molecules of ligand 3 are P-coordinated to the Ru atom while the amino-methyl side-chains remain uncoordinated. Two diastereomeric products were observed, a meso complex 12a and a Cj-symmetric diastereomer 12b, which has two molecules of 3 with identical configurations coordinated to ruthenium (Scheme 1.5.4) [11]. 

The possibility of the practical application of the catalytic photode-composition of water based on the reactivity of the excited states of tris(2,2 -bipyridine) complexes of ruthenium(III) and ruthenium(II) has attracted considerable interest, but it is now clear that the efficiency of this process is limited not only by the lack of efficient catalysts, particularly for the dioxygen-evolving path, but also by both thermal and photochemical ligand oxidation 1,2) and ligand substitution reactions (3) of the 2,2 -bipyridine complexes. The stoichiometrically analogous tris(2,2 -bipyridine) and tris(l,10-phenanthroline) complexes of both... 

Scheme 1. Reaction paths a-o of ruthenium (II) and osmium (II) prophyrins starting from carbonylmetal (II) complexes MCO (P) L (M = Ru, Os). For reaction conditions and references, see Table 4...

Autoxidadon of Bare ruthenium( II) and osmium(II) porphyrins - A resonance Raman study of the intermediates formed during the reaction of Ru(TPP) (which was obtained according Scheme 1, paths — f, — j, — k) in toluene [258] proved the anticipated [205] reaction scheme of the inner-sphere autoxidation, the first step of which is the formation of a p-peroxobis[porphyrinato-ruthenium(III)] complex which is split into two oxoruthenium (IV) fragments. These species precede the formation of /r-oxobisruthenium(IV) porphyrins (reaction 16) for P = TPP, OEP for P = TMP, a disproportionation (17) is indicated, the resulting Ru(P) itself is further autoxidized. 

There are two possible pathways to homologate methanol with carbon dioxide the CO2 insertion path and CO insertion path (Scheme 2). As for the former, Fukuoka et al. reported that the cobalt-ruthenium or nickel bimetallic complex catalyzed acetic acid formation from methyl iodide, carbon dioxide and hydrogen, in which carbon dioxide inserted into the carbon-metal bond to form acetate complex [7]. However, the contribution of this path is rather small because no acetic acid or its derivatives are detected in this reaction. Besides, the time course... 

A pyrene derivative was also used as an anchor to immobilize a ruthenium alkylidene complex onto SWCNTs [94]. The immobilization of the Ru complex was performed by two different paths (1) adsorption of pyrene derivative precursor onto the sidewall of nanotubes by ti-ti interactions, followed by cross-metathesis with the ruthenium alkylidene complex, and (2) adsorption onto the sidewall of SWCNTs of the pyrene-substituted ruthenium alkylidene prepared previously. 

Fig. 21, Reaction paths (a tof) to multidecker sandwich complexes of ruthenium, cobalt, rhodium and iridium with [2.2]paracyclophane (8) as ligand...

Ruthemum(iii).—Ruthenium(iii) complexes [RuX(NH3)s] +, where X = halide or azide, react even in the dark by parallel aquation and redox paths. The latter at least must involve intramolecular electron transfer. For X = chloride, the direct aquation path predominates, but for X = azide, the redox path is more significant, yielding molecular nitrogen complexes of ruthenium(ii). The rate constant for aquation of the dinuclear molecular nitrogen complex [(H3N)5RuN2Ru(NH3)s] + has been determined at 25-0... 

Reaction of CO with the tautomeric mixture of the two aforementioned rhodium complexes (several / flra-substituted imidoaryl groups were tested) afforded a unique bridging isocyanate complex Rh2(CO)2(ii -N,T] -C, x-ArNCO)(p-DPPM)2. The CO insertion is irreversible. Since the two initial tautomers are in equilibrium in solution, insertion of CO may in principle proceed by either of the two (Scheme 20)(next page). However, evidence was given in favour of the amido-path (path b in the Scheme), based on the fact that the cationic complex [Rh2(p-NHPh)(CO)2(DPPM)2] rapidly reacted with CO. No complex could be isolated from this last reaction, but the formation of PhNCO was detected. Two features of this mechanism are worth of note. The first is the contrast between the conclusion reached for this system (amido complex more reactive than imido one in the insertion reaction of CO) and the one reached by Bhaduri et al. [161] for the trinuclear complex Ru3(p-H)(p-NHPh)(CO)io, which, upon deprotonation of the amido group by OH, affords the inserted product [Ru3(p-H)(T] -N,ii -C,p3-PhNCO)(CO)9]. The difference is likely due to the fact that, in this latter case, the complex is trinuclear, so that the inserted CO is already coordinated to the third ruthenium atom and, especially, the formation of the new C-N bond does not require the breaking of any of the pre-existing Ru-N bonds. 

The RCM of 1,6-dienes into cyclopentenes is sometimes accompanied by a cycloisomerisation reaction to give cyclic products with an exo-methylene substituent, especially when ruthenium-arene complexes are used as catalyst precursors (see for instance compounds 32 in Section 7.3.1.6). In many cases, this side reaction was undesired and could be effectively suppressed by the addition of various co-catalysts. It is nevertheless possible to alter the reaction path to obtain the cycloisomerisation products with very high selectivities. Early examples of NHC-Ru complexes suitable for this task included the unstable cationic alle-nylidene complexes 36 prepared in situ from more robust chelated precursors 35 (Equation (7.6)). Alternatively, a combination of IMes-HCl/Cs2C03/[RuCl2(p-cymene)]2 also provided an efficient catalytic system. A mechanism involving oxidative coupling of the 1,6-diene to a ruthenium(II) centre followed by p-elimination to generate a hydrido ruthenium(IV) intermediate and reductive elimination was proposed for the transformation (Scheme 1.9)2 ... 

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