Allenylidene reactions with alkynes

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... 

Allenylidene complexes also undergo [2+2] cycloaddition reactions with alkynes, but in addition to the cycloadducts linear insertion products are also obtained. For example, diarylallenylidene complexes of chromium and tungsten react with MeC NEth2 or PhCMI NEt2 to give both linear adducts 36 and cycloadducts 37. The linear adducts are formed via an initial cycloaddition of the ynamine to the C =C bond in the allenylidene complex, followed by cycloreversion. The cyclobutenylidene complexes are formed by [2+2] cycloaddition of the ynamine to the C =C double bond . 

Reaction of Fe3(CO)12 with 3-pentyn-l-ol gives the hydrido cluster 4, formed by coupling of an allenylidene unit with a coordinated carbonyl ligand and methoxy group. In contrast, reaction with the isomeric alkyne 2-methyl-3-butyn-2-ol affords a binuclear iron complex.18 Treatment of Fe3(p3-S)2(CO)9 with Me3NO affords the vinylferrocene complex 5, whereas the similar reaction with Fe3(p3-Te)2(CO)9 gives no cluster products.19... 

C-C couplings with alkynes. An unprecedented coupling of this type was found in the reaction of the Ir(I) hydroxo-allenylidenes 71 with excess of HC=CR (R - Ph, CO2Me) to afford, under remarkably mild conditions (r.t.), the novel five-coordinate compounds 72 (Scheme 24). The proposed mechanism involves an initial HO /R CsC ligand exchange followed by the oxidative addition of a... 

Formation of allenylidene derivatives comparable with the above is observed in the reaction of (Cp)2Mo2(CO)4 with lithium isopropenylacetylide protonation of the reaction mixture in an alumina column leads to products with coordinated allenylidene or isopropenyl-alkyne ligands, Fig. This process should be... 

Reactions with hetero-substituted alkynes are also examined. The dipropargylamine, MeN(GH2C=GH)2, reacts with Fe3(CO)i2 to provide a mixture of the bicyclic 4- and 5-type ferrole complexes, 9 and 10, as the major products," " while propargyl alcohols give allenylidene complexes, Fe3(GO)io(/x-C=C=CR2) (R2 = Me2, (GH2)s, Me/Ph) (see Section 6.08.2.3) via dehydration together with the 2- and 4-type complexes. " For a thiopropargyl system, see Chapter 6.07.7.2.2.1. 

A number of processes catalyzed by the dithiolate-bridged species have been mentioned already however, the extensive reactivity of alkynes within these systems has led to a number of more recent reports on their use in catalysis. The allenylidene complex 363 (R = Tol, R = Me 864 salt) has been identified as an intermediate in the catalysis of propargylic alcohol substitution reactions with alcohols in high yields and with complete regioselectivities... 

Phosphines, as nucleophiles, add to many unsaturated substrates giving metallated ylides. Scheme 17 collects some representative examples of the addition of phosphines to carbyne complexes, giving (57) [132], to allenylidenes (58) [133], rr-alkenyls (59) [134], or CT-alkynyls (60) [135]. Moreover, reaction of phosphines with jt-aUcenes [136] and n-alkynes (61)-(64) [137-140] have also been reported. It is not possible to explain in depth each reaction, but the variety of resulting products provides an adequate perspective about the synthetic possibilities of this type of reactions. 

Preparation of the pioneering manganese(l) allenylidene derivatives [MnCp(=C= C=C1<2XCO)2 (5) was accomplished by treatment of the Ji-alkyne complex [MnCp (/f-HC CC() A1cXC() i (4) with excess of an organolithium reagent, followed by deoxygenation with HCl or COCb (Scheme 5) [24,42,95]. In essence, this reaction... 

The use of Me3NO to induce substitution of dppm (bis(diphenylphosphino)-methane) for CO molecules on dinuclear iron complexes led to insertion of CO into C-C bonds of alkyne-derived metallacycles. Similar behavior was observed when [PPNJCl salts were used to favor the formation of alkyne-substituted triruthenium dppm-containing clusters.I This behavior should be compared with the insertion of CO into allenylidene and phosphido-bridging ligands occurring when dppm coordinates to binuclear ruthenium complexes as shown in Fig. 3. This reaction is a nucleophilic attack of the coordinated allenylidene and phosphido groups on a coordinated CO (see Section 2.8.2.2). 

Coordination-dehydration reactions of propargyl alcohols have been followed in detail on triosmium clusters an example is given in Fig. 26.1 Protonation of triosmium clusters substituted with parallel alkynes leads to propargyl cationic derivatives which, in turn, can isomerize to allenylidene complexes. Fig. 27.1 ... 

TpRuCl(DMF)(PR3) (crystal structure determined for PPh3), typically prepared in situ by the reaction of TpRuCl(COD) with one equivalent of phosphine in refluxing DMF, reacts readily with terminal alkynes, propargylic alcohols and HC = C(CH2) 0H n = 2, 3, 4) to afford the neutral vinylidene, allenylidene and... 

Some general reviews relating to the chemistry of Ru/Os-r hydrocarbon complexes appear in the literature the reactivity of Ru-H bonds with alkenes and alkynes/ aspects of ruthenium/osmium vinylidene/allenylidene/cumul-enylidene complexes,equilibria of M-R/M=CR2/M=CR complexes, the organometallic chemistry of metal porphyrin complexes, and the reactions of [Os(P Pr3)2(CO)HGl], ruthenium pyrazoly I borate complexes,and metallabenzynes. Other reviews relate more to applications of some of the complexes outlined in this chapter. See, for example, metal vinylidenes in catalysis,the development of Grubbs-type alkene metathesis catalysts, applications of ruthenium/osmium carbene complexes in metathesis polymerization, and the role of Ru /V-hetero-cyclic carbene complexes in metathesis polymerization. ... 

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