Ruthenium complexes bidentate

Z)-Enol esters. The stereoselective addition of carboxylic acid to a terminal alkyne linkage is catalyzed by ruthenium complexes. Bidentate phosphine ligands separated by 2, 3, or 4 methylene groups are all effective. 

There are more examples of a second type in which the chirality of the metal center is the result of the coordination of polydentate ligands. The easiest case is that of octahedral complexes with at least two achiral bidentate ligands coordinated to the metal ion. The prototype complex with chirality exclusively at the metal site is the octahedral tris-diimine ruthenium complex [Ru(diimine)3 with diimine = bipyridine or phenanthroline. As shown in Fig. 2 such a complex can exist in two enantiomeric forms named A and A [6,7]. The bidentate ligands are achiral and the stereoisomery results from the hehcal chirality of the coordination and the propeller shape of the complex. The absolute configuration is related to the handness of the hehx formed by the hgands when rotated... 

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

Ruthenium complexes of formula [(ri -arene)Ru(LL )(H20)](SbF6)2 (arene = CeHg, p-MeC6H4 Pr, CeMee LL = bidentate chelate chiral ligand with PN, PP, or... 

An anti-Markovnikov hydration of terminal alkynes could be a convenient way of preparing aldehydes, but so far only a few ruthenium-complexes have been identified that catalyze this unusual hydration mode ]16]. The presence of bidentate phosphine ligands ]16b], the coordination of a water molecule stabilized by hydrogen bonding ]16e] and the use of phosphinopyridine ligands ]16f] seem to be of major importance in these processes. 

Bernhard and coworkers [58] have addressed the discovery of ionic iridium(III) and ruthenium(II) complexes by combinatorial luminophore synthesis and screening (Scheme 5.9). Starting from iridium trichloride, cyclometalation with (hetero)arylpyridyl ligands 45 (Fig. 5.17) gives rise to the formation of binuclear iridium complexes 46. Upon complexation with bidentate N,N- or P,P-ligands 47 (Fig. 5.17), the cationic complex 48 is formed, which upon anion metathesis with hexafluorophosphate is transformed into the target complex 49. In this sequence, the step from 46 to 48 was performed in a traditional and a parallel manner, the latter leading to a library of 100 iridium and 10 ruthenium complexes. 

The derivative of 1,4-diphosphepane 158 was obtained from the hydroxylmethyl-alkynyl ruthenium complex 157, which underwent dehydratation upon treatment with HBF4 in CH2CI2. Subsequently, the generated alkene endured a double nucleophilic attack by bidentate (diphenylphosphino) ethane to give cationic cluster 158 in 94% yield <2006IGA(359)938>. The structure of 158 was confirmed by the X-ray data. 

Finally, the structural characteristics of the 1,8-naphthyridines favour their behavior as bidentate and dinucleating ligands, thus leading to short metal-metal separations in late transition-metal complexes,24"26 and to the stabilization of mixed-valence complexes.27,28 The dinuclear ruthenium complex [ Ru(napy)(H20)2 (/i-Cl)(/i-0H)](C104)2 is a stable and active catalyst for the oxidation of alcohols and the epoxidation of alkenes, while its mononuclear precursor is much less active.29... 

Bridging ligands capable of binding more than two metal centers are less studied. Some examples were highlighted earlier. Polymetallic ruthenium complexes have been synthesized using the tetra-bidentate ligands (62) and (63) as multi-electron transfer agents.181,182... 

For [(BINAP)Pd(3-picoline)2] +, AG 50 kj mol was determined for restricted rotation about the Pd-N bonds. The barrier in the analogous platinum complexes were higher, AG 58 kJ mol . The general trend is that the barriers for the Pd-N bonds are somewhat lower than those for Pd-C bonds in analogous covalently bonded aryl complexes. This type of phenomena can also be flowed by P NMR. It would appear that one of the anti isomers is generally preferred in systems with a chiral bidentate ligand. Barriers are also observed in octahedral complexes and have been studied in ruthenium complexes. 

Several arene-ruthenium complexes containing bidentate phosphine ligands have been shown to be useful catalyst precursors for the hydration of terminal aryl alkynes 105 to afford acetophenones 106 (Scheme 29) [52]. For example, the cationic complex 104, when activated by AgSbH5, promoted addition of water to a carbon-carbon triple bond. It was found that such reactions proceeded slowly but in good to excellent yields. It is remarkable, that the water in commercial acetone was sufficient to achieve complete conversion to the product. 

Ruthenium complexes bearing bidentate Schiff base ligands as efficient catalysts for organic and polymer syntheses 05CCR(249)3055. 

More recently, Chatani and his researchers developed the ruthenium-catalyzed carbonylation at the ortho-C-H bonds of aromatic amides [65] to give phthali-mides as their products. Analogously, this reaction can also be transferred to even inactivated C(sp )-H bonds and yield the corresponding succinimides. (Scheme 6.20) [66] In both cases, the presence of 2-pyridinylmethylamino moiety is necessary for these transformations, because it plays an important role as a N,N-bidentate ligand to form a dinuclear ruthenium complex with Ru3(CO)i2. Interestingly, in the absence of ethylene, no carbonylation product could be detected while the efficiency of the reaction decreased in the absence of water. In the latter case, a long reaction time (5 days) is still needed. 

Figure 11.33 Chiral bidentate NHC-bearing ruthenium complexes 160-166.

Figure 12.11 Ruthenium complexes with S-chelated carbene ligand (46, 47), phosphene chelated carbene ligand (48), and bidentate isopropoxy-indenylidene ligand (49, 50).

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