Ruthenium allenyl complexes

The formation of allenylidene derivatives from ethynyl-hexanol and alkenyl-vinylidene mononuclear complexes (9), the formation of mononuclear ruthenium allenyl complexes from terminal alkynes (10), the intermediacy of ruthenium-allenylidene complexes in forming propargylic alcohols (II), and in the cyclization of propargyl alcohols (12), and the use of mononuclear ruthenium compounds in allylic alkylation catalysis (13) have also been reported. 

The reaction of [Ru2Cl(PhNpy) ] with [Li(CECPh)] produces [RU2(CECPh)(PhNpy) ], a diruthenium(II, III) compound with an axial n -acetylide ligand.Carbene (N2CR2) addition to [RU2(CO)g(u2-n -CECPh)(u-PPh2)] results in the formation of the u,-n -allenyl complexes [Ru., (CO), (u -n -R C=C-=CPh)(M-PPh ) ] (R=H,Me,Ph). The heteronuclear ruthenium-phenyl... 

In contrast to ruthenium and osmium, the reactivity of iron allenylidenes remains almost unexplored. Only the behavior of the cationic diphenylallenylidene-Fe(II) derivative frans-[FeBr(=C=C=CPh2)(depe)2]" has been studied in detail. Thus, it has been found that this complex reacts exclusively at Cy with both neutral (amines, phosphines) and anionic (H , MeO , CN ) nucleophiles [105-107]. This behavior contrasts with that of the neutral Fe(0) derivative [Fe =C=C=C(f-Bu)2 (CO)5] which undergoes PPhs-attack at Co- to afford the zwitterionic phosphonio-allenyl species [Fe C(PPh3)=C=C(f-Bu)2 (CO)5] [104]. 

Trisubstituted furans were obtained via an unprecedented 1,4-shift of the sulfanyl group of allenyl sulfides in high yields employing ruthenium complexes as catalyst, as depicted below. Furan products can also be provided in a one-pot reaction from a-diazocarbonyls and propargyl sulfide using both rhodium- and ruthenium-complexes or only a ruthenium-complex as catalyst <07AGE1905>. 

The intermolecular coupling of allenes 123 and enones 124 selectively afforded dienones 125 in 53-81% yields (Scheme 4.45) [93]. As a catalyst precursor, [CpRuCl(cod)] was employed with CeCl3 7H20 and an alkynol 126 as activators. The proposed reaction mechanism involves the regioselective oxidative cyclization of the two components on a cationic ruthenium center, leading to the ruthenacyclopentane intermediate 127. When allenyl alcohols 128 were employed under otherwise identical conditions, the final products were cyclic ethers 129 (Scheme 4.46) [94]. As a catalyst precursor, the cationic ruthenium complex 68 can be used in the absence of the alkynol 126. The ether ring was considered to be formed directly via the ruthenacyclopentane 130 or alternatively through its Jt-allyl form 131. 

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