Alkynes allenyl ligands

The products obtained were diverse and contained, for example, bridging alkyne, allenyl, alkenyl, alkynyl and vinylidene ligands derived from the added alkyne. Compound 125 was obtained after near-UV irradiation of [Ru2(CO)6 i-Ph2PC(H) = C(H)PPh2 ] in the presence of DMAD. The compound [ Cp Ru( i-H)4 2] has been shown to cleave a C-C bond in norbor-nadiene to give compounds like 126. The synthesis and characterisation of compound 127 has been described. ... 

In addition to alcohols, some other nucleophiles such as amines and carbon nucleophiles can be used to trap the acylpalladium intermediates. The o-viny-lidene-/j-lactam 30 is prepared by the carbonylation of the 4-benzylamino-2-alkynyl methyl carbonate derivative 29[16]. The reaction proceeds using TMPP, a cyclic phosphite, as a ligand. When the amino group is protected as the p-toluenesulfonamide, the reaction proceeds in the presence of potassium carbonate, and the f>-alkynyl-/J-lactam 31 is obtained by the isomerization of the allenyl (vinylidene) group to the less strained alkyne. 

A cycloaddition process between the Rh=C bond of the allenylidene derivative 38 and the C=C bond of the terminal alkyne has been evoked in the formation of the zwitterionic 71-aUyl-allenyl complexes 81 (Scheme 28), the initially formed metaUacyclobutenes 80 evolving into 81 by formation of carbene intermediate [RhCl(P/-Pr3)2(=CHCR=C=C=CPh2)] (R = Ph, p-MeC6H4, SiMe3) and subsequent migration of one of the phosphine ligands from the metal to the carbene carbon atom [205]. 

Cydoaddition reactions of allenylidene ligands with alkynes have also been described. Thus, heating a toluene solution of the neutral osmium complex 43 in the presence of dimethylacetylenedicarboxylate leads selectively to the allenyl-vinyli-dene 4S (Scheme 2.18) [31c[. The formal insertion of the alkyne into the Co =Cp... 

The need for a base additive in this reaction implies the intermediacy of acetylide complexes (Scheme 9.10). As in the Rh(III)-catalyzed reaction, vinylidene acetylide S4 undergoes a-insertion to give the vinyl-iridium intermediate 55. A [l,3]-propargyl/ allenyl metallatropic shift can give rise to the cumulene intermediate 56. The individual steps of Miyaura s proposed mechanism have been established in stoichiometric experiments. In the case of ( )-selective head-to-head dimerization, vinylidene intermediates are not invoked. The authors argue that electron-rich phosphine ligands affect stereoselectivity by favoring alkyne C—H oxidative addition, a step often involved in vinylidene formation. 

Extending the carbon chain of vinylidenes by one or three carbons provides linear cumulenated ligands, LwM=(C=C)w=CR2 (n = 1,2). These compounds have been studied in considerable detail, especially allenyl-idenes (n = 1) and arise in most cases from the rearrangement and dehydration (often spontaneous) of hydroxyalkyl alkynes or diynes (Figure 5.51). Various intermediates (Figure 4.18) may be envisaged (and occasionally isolated) which are related by elimination/addition of H+ or hydroxide, e.g. y-hydroxyalkynyl complexes have been isolated and subsequently dehydroxylated with Lewis or Bronsted acids. 

Recently, a series of triruthenium clusters containing allenyl or alkynyl ligands have been investigated electrochemically, and two, subsequent one-electron reduction steps have been observed (471). Further studies of this kind should provide a new insight into the electronic processes which take place in alkyne-substituted cluster systems. 

The allenyl cluster [Ru3H(CO)9(jU,-i7, yj, i7--MeCCC(H)NMe2)] (101). with a hydrocarbyl ligand which closely resembles a zwitterionic alkyne. 

The recently reviewed chemistry of the jj -allenyl and propargyl ligands has significant contributions from Re complexes. jj -propargyl derivatives of the ReCp (CO)2 fragment (80) have been prepared either by abstraction from alkyne complexes ReCp (CO)2(RC=CR0 or... 

X)-alkyne, 3- -diruthenaallyl, /it3- 7 -allenyl, t7oro-/Lt3- 7 -mthenacyclopentadiene, and Hi-rf-.if-.if-benzene complexes, which are also reported for carbonyl clusters. Some of these complexes, for example, a /Lt3- ( )-alkyne-/Lt3-alkylidyne complex, contain a different type of hydrocarbyi ligand on each face of the Ru3 plane. 

CHCRCHCR)(HC(pz )3 ]PF6 (R = Ph, H) with the two alkynes linked head-to-tail when R = Ph. Vinylallenerhodium complexes with three kinds of coordination modes, that is, j -coordination of the terminal TT-bond of the allenyl group, if -coordination of the conjugated diene skeleton, and planar o -coordination, were synthesized by ligand substitution of RhCl(PPh3)3 with vinylallenes of specific substitution patterns (Scheme 35). Coordination preferences were explained in terms of spatial interactions between the vinylallene substituents and the phosphine ligands as well as effective delocalization of the Tt-electrons of the endo- and exocyclic double bonds. ... 

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