Propargyl complexes mononuclear

There has been a growing interest in the organometallic chemistry of allenyl-containing complexes. Although mononuclear propargyl complexes have proved to be versatile reagents in the synthesis of heterome-tallic allenyl clusters and nucleophilic attack of diazoalkanes at C carbon atoms of /u.2-i7, i7 -coordinated acetylides is an effective... 

Quite recently, some mononuclear ruthenium complexes such as [(p-cymene)RuX-(CO)(PR3)]OTf (X = Cl, OTf, R = Ph, Cy) have been found to work as catalysts for the propargylation of aromatic compounds such as furans, where some ruthenium complexes were isolated as catalytically active species from the stoichiometric reactions of propargylic alcohols (Scheme 7.27) [31]. The produced active species promoted the propargylation of furans vdth propargylic alcohols bearing not only a terminal alkyne moiety but also an internal alkyne moiety, indicating that this propargylation does not proceed via allenylidene complexes as key intermediates. 

A. Preparation of Mononuclear Propargyl, Allenyl, and Allenylidene Complexes... 

Mononuclear allenylidene complexes have been prepared by either (i) reaction of a deprotonated propargyl alcohol with a binary metal carbonyl or (ii) dehydration of the acetylenic alcohol HC=CCR20H with an appro-... 

Structural Characteristics of Mononuclear tj - and ij -Propargyl and. 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. 

Recently a number of mononuclear ti -propargyl/allenyl complexes have been reported, e.g., 21-24 (Scheme 4-8). These have been produced in a variety of ways including protona-... 

Dehydration of propargyl alcohols occurs commonly on mononuclear ruthenium complexes.[ l Water is formed from the terminal alkynic hydrogen and by the alcoholic OH this is the more common dehydration process (it is denoted Route A). These reactions afford organic intermediates leading to cumulene complexes useful for the synthesis of doped polyacetylenes or of non-linear optic materials. Dehydration of rhodium-coordinated propargyl alcohols " leads to free or coordinated cumulenes and can be catalyzed by alumina and chloride ions, Fig. 16. 

Reverse processes, that is reactions of propargyl or allenylidene ligands coordinated to mononuclear centers with water, methanol, amines, and other ligands are known. Tungsten l and platinum complexes give a series of reactions (some of which are mediated by surfaces) comparable with those discussed for clusters. 

Different reactivity trends on M3(CO)i2 clusters (M = Fe, Ru, Os) have been observed, depending on the nature of the cluster metals. Two dehydration routes have been observed for cluster-bound propargyl alcohols - the less common is similar to the main process observed for mononuclear complexes and involves loss of the terminal alkynic hydrogen and of the alcoholic OH (Route A). The more common, when CH3 groups are available, involves loss of one methyl hydrogen and of the adjacent OH (Route B). The former process leads to allenylidene and the second to ene-yne (or vinylacetylide) derivatives. Examples are given in Fig. 21. 

The homobimetallic, ethylene-ruthenium complex 15, which contains three chloro bridges, was readily obtained from the reaction of [RuCl2(/ -cymene)]2 with 1 atm of ethylene [34]. In 2009, Demonceau and Delaude [34] showed that complex 15 could be a useful precursor to allow subsequent access to the diruthenium vinylidene complex 16, allenylidene complex 17, and indenylidene complex 18 (Scheme 14.8). Upon reaction with propargylic alcohol, complex 15 afforded vinylidene complex 16, which converted into the allenylidene complex 17 in the presence of molecular sieves [34]. As shown in the acid-promoted intramolecular rearrangement of mononuclear ruthenium allenylidene complexes [19, 20, 32], the addition of a stoichiometric amount of TsOH to complex 17 at -50 °C led to the indenylidene binuclear complex 18 [34]. Complex 18 has been well... 

---