Ruthenium + agostic

The silanol complex 57 exhibits a Si H M agostic interaction characterized by a /(Si-H) of 41 Hz and a Si-H distance of 1.70(7) It would be incautious to interpret such a low value of the Si-H coupling in terms of a significant Si-H bond activation, because the Si-H bond forms rather acute angles with the Si-C and Si-Si bonds (about 82 and 101°, respectively) and thus must have a considerable p character on silicon, which should contribute to the decrease of /(Si-H). The silanol ligand is -coordinate to ruthenium and the Ru-Si bond of 2.441(3) A is not exceptional, but the Si(SiMe3)3 deviates from the silanol plane by 19.0°, probably as a result of the Si-H interaction. Deprotonation of 57 by strong bases affords a neutral ruthenocene-like product. 

An interesting compound is (N-phenyloctaethylporphyrinato) phenyl-ruthenium(II) (entry 10) in which an agostic hydrogen of the N-phenyl group completes the heavily distored octahedral coordination sphere of the Ru(II) ion. The Ru ion protrudes by 14 pm towards the axial phenyl anion. 

Mononuclear ruthenium compounds acyl complexes, 6, 398 agostic complexes, 6, 392 alkenyl complexes... 

The cationic hexamethylbenzene ruthenium complex 254 can be depro-tonated by treatment with t-BuOK to give the ruthenium complexes 255 and 256 in which the r 4-o-xylylene ligand is coordinated via its exocyclic diene (Scheme 23). Protonation of 255 gives the dication 15c, whereas protonation of 256 produces the fluxional tj3-benzyl derivative 257 which is stabilized by an agostic C—H bond (156,157). 

Figure 4.73 Agostic H-M interactions in a ruthenium(ll) carbene complex that do not result in C-hi activation.

Suresh and Koga DFT (B3LYP) Analogue of (2a) Nearly flat potential energy surface going from Ru-alkylidene with coordinated olefin to ruthenacyclobutane to ruthenium alkylidene with coordinated olefin caused by C-C agostic interactions... 

These reactions have also been studied by DFT. When the set of four ruthenium isomers is considered (Scheme 51), it becomes clear that the [Ru(H)F(PH3)2(GO)(=GF2)] is almost equienergetic with [RuH(GF3)(PH3)2(GO)]. However, the fluorocarbene complex, [RuF2(PH3)2(GO)(=GFH)], is substantially more stable, and the difluoromethyl complex, [Ru(GF2H)F(PH3)2(GO)], is the most stable of all in accord with experiment. The calculated structure of [RuH(GF3)(PH3)2(GO)] shows a remarkable distortion of the GF3 group in which one fluorine is brought close to the metal (2.626 A) while extending its G-F bond (Scheme 51). This structure resembles that of an agostic alkyl, and clearly assists the a-fluorine elimination. " ... 

Although complex 1 presented an important agostic distortion, the oxidative addition from this species is disfavoured (Scheme 1, pathway a). The introduction of HCO3 in the system results in the coordination of the carbonate to the ruthenium and the formation of adduct 4 which evolves to product 5. The transformation from 3 to 5 is exothermic by 13.7 kcai moi making the proton abstraction mechanism more plausible (Scheme 1, pathway b). 

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. 

In the iron, ruthenium, and osmium derivatives, there are cases of q q re-switch on thermolysis followed by the elimination of small ligands. Organo-ruthenium species containing pyrazol-l-ylborate or -methane ligands with bulky substituents often have uncoordinated pyrazol-l-yl moieties and agostic R—B(C) M interaction. The latter sometimes influences the properties of the / -coordinated species as well. 

Scheme 10.13 Direct synthesis of NHCP ruthenium alkylidene complexes. The clashed line in complex 58a does not indicate an agostic interaction but implies the steric shielding of the free coordination site as a consequence of the distinct topology of the NHC group.

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