Oxidative addition of vinyl

As described in the preceding sections, many domino reactions start with the formation of vinyl palladium species, these being formed by an oxidative addition of vinylic halides or triflates to Pd°. On the other hand, such an intermediate can also be obtained from the addition of a nucleophile to a divalent palladium-coordinated allene. Usually, some oxidant must be added to regenerate Pd11 from Pd° in order to achieve a catalytic cycle. Lu and coworkers [182] have used a protonolysis reaction of the formed carbon-palladium bond in the presence of excess halide ions to regenerate Pd2+ species. Thus, reaction of 6/1-386 and acrolein in the presence of Pd2+ and LiBr gave mainly 6/1-388. In some reactions 6/1-389 was formed as a side product (Scheme 6/1.98). 

Ruthenium(O) complexes such as Ru(COD)(COT) catalyze the dehydrohalo-genative coupling of vinyl halides with olefins to give substituted conjugated dienes in a Heck-type reaction [11]. Thus, alkenyl halides readily react with activated olefins to produce dienes 16 (Eq. 7). Oxidative addition of vinyl halide, followed by regioselective insertion of an electron-deficient olefin and by -hydrogen elimination leads to the diene. 

Carbonylation of [CoH(CN)5]3- in strongly alkaline media results in the formation of [Co(CN)2-(CO)2]2- and the intermediacy of the short-lived tetracyanocobaltate(I) ion [Co(CN)4]3" in this process has been inferred from mechanistic studies (Scheme 9).15 Under very similar conditions [CoH(CN)s]3- catalyzes the cyanation of vinyl halides to form a,j3-unsaturated nitriles with retention of configuration (equation 6). Oxidative addition of vinyl halide to the intermediate [Co(CN)4]3- ion is stereoselective and in the a complex so produced reductive coupling of the vinyl and cyano ligands gives the stereoretentive organic product and regenerates [Co(CN)4]3-.78... 

The first clear example of oxidative addition of the C-O bond is the reaction of Ru(l,5-COD)(l,3,5-COT) with vinyl acetate in the presence of PEt3, to give mer-Ru(CH=CH2)(0Ac-K 0,0 )(PEt3)3 (Scheme 14.26) [62]. In this reaction, the introduction of a substituent at the alkenyl carbon discourages the reaction, but the bulky carboxylate promotes the oxidative addition. In the oxidative addition of vinyl carboxylate to Ru(l,5-COD)(l,3,5-COT) in the presence of DEPE, an intermediate... 

A step towards more realistic systems in the context of the Heck reaction was taken by Herrmann s group [10]. They have studied the mechanism and activation barriers of oxidative addition of vinyl halides and halobenzenes to Pd° complexes with simple ligands of varying donor/acceptor characteristics (eq. (10)). 

Diiron nonacarbonyl undergoes oxidative addition of vinyl disilanes at room temperature to give oxidative addition product 28, which is isolated by chromatography on silica gel (Eq. 11) [25]. The structure of 28 was determined by H NMR spectroscopy to be (organosilyl)(r 3-l-silapropenyl)iron(II) complexes rather than simple bis(organosilyl)iron(II) complexes. 

In contrast to the diverse chemistry of allylpalladium complexes, vinylpalladium intermediates have been involved mainly in the vinylpalladation of carbon-carbon unsaturated systems and in the insertion into carbon-hydrogen and heteroatom-hydrogen bonds (Scheme 10). It is found that a vinylpalladium species reacts with carbon electrophiles such as aldehydes, ketones, and nitriles (Scheme 11, type a). Oxidative addition of vinyl-halogen and -pseudohalogen bonds to Pd(0) is the common way to generate the vinylpalladium species. Vinyl-... 

Oxidative addition of vinyl carboxylates with the vinyl-0 bond cleavage is much less explored to date than that of allyl carboxylates. Reaction of vinyl... 

This reaction is proposed to involve insertion of the C=C bond into the Ru-H to give a 6-acetoxyethylruthenium(II) intemediate (1,2-addition) followed by the yd-acetate elimination to yield the products. C-0 bond oxidative addition of vinyl acetate to give hydrido(vinyl)ruthenium(IV) followed by reductive elimination of ethylene is also a possible alternative mechanism. 

Oxidative addition of vinylic C-S bond to zero-valent platinum complex has recently been investigated in detail [139], The reaction of Pt(C2H4)(PPh3)2 with... 

Vinyl complexes are typically prepared by the same methods used to prepare aryl complexes. Vinyl mercury compounds, like aryl mercury compoimds, are easily prepared (by the mercuration of acetylenes), and are therefore useful for the preparation of vinyl transition metal complexes by transmetallation. The use of vinyl lithium reagents has permitted the s rnthesis of homoleptic vinyl complexes by transmetallation (Equation 3.35). Reactive low-valent transition metal complexes also form vinyl complexes by the oxidative addition of vinyl halides with retention of stereochemistry about the double bond (Equation 3.36). Vinyl complexes have also been formed by the insertion of alkynes into transition metal hydride bonds (Equation 3.37), by sequential electrophilic and nucleophilic addition to alkynyl ligands (Equation 3.38), and by the addition of nucleophiles to alkyne complexes (Equation 3.39). The insertion of alkynes into transition metal alkyl complexes is presented in Chapter 9 and, when rearrangements are slower than insertion, occurs by s)m addition. In contrast, nucleophilic attack on coordinated alkynes, presented in Chapter 11, generates products from anti addition. 

Me or vice versa X = Br, I) to [L2PtX(COCR =CR22)] for X = Q, oxidative addition of vinyl acyl chloride to [Ptm was used instead.529 The preparation of rrans-[L2Pt(C02R )(CR CR 2)] which eliminates (x, unsaturated esters, has also been described. Treatment of [PtL3(CMe=CHMe)] with [Q)Re(CO)2H]-produced [CpRe(CO)2(Tl-MeCH=CHMe)],531 whereas [CpRe(CX))2Me]-formed (L2ptai-CH2)Rc(CX))2Cp] 532... 

Recently, mechanistic and computational studies aiming to establish whether organic electrophiles bearing halides on a sp -hybridized carbon could indeed undergo an oxidative addition leading to paUadium(IV) complexes, and to uncover alternative pathways that could account for the formation of the observed products, have appeared in the literature. In a representative study, Echavarren reported DPT calculations comparing the feasibility of a direct oxidative addition of vinyl halides to pallada(II)cycles analogous to those proposed in Dyker s and Catellani s... 

The mechanism (Scheme 48) ° is expected to proceed through the acylpalladium species much as in the Rosenmund reduction. Indeed, the acyl complex 56 from oxidative addition of vinyl chloride with Pd(CO)(Ph3P)3 was isolated (Scheme 49). " The reaction of acid chlorides with the same catalyst provides aldehydes. However, aliphatic acid chlorides do not reduce effectively. The phosphine ligands present in the Heck acylpalladium intermediate are thought to be the cause, allowing decarbonylation and elimination to occur. Interestingly, the formylation will not occur with the Rosenmund catalyst. 

The oxidative addition of vinyl triflates to [Pt(PPh3) 3 gives... 

A key step (Eq. 14.2) in a new synthesis of strychnine involves a C-C coupling in 14.6 to give the pentacyclic 14.9. Oxidative addition of vinyl iodide 14.6, together with deprotonation a to the ketone, gives... 

Also using the key intennediates in the Ramage synthesis, the newly developed oxidative addition of vinyl triflates to palladium(II) and the Heck reaction paved a way to lysergic acid (1). 

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