Zirconocene-benzyne complexes

The need for Cp2ZrMeCl as a reagent in the above method may be avoided by using in sim-generated Cp2ZrBu Cl although overall yields are lower. 

Preparation of diphenylzirconocene (Structure 62), thermolysis in the presence of propionitrile, and iodinolysis 

Caution All procedures should be carried out in an efficient fume hood. Disposable vinyl or latex gloves and safety glasses should be worn. 

Carefully allow argon to enter the apparatus from the manifold avoiding blowing the zirconocene dichloride around. Repeat the evacuate/refill cycle twice. The apparatus should be left with stopcock A open so that the manifold maintains a positive pressure of argon in the flask. Stopcock B should be kept closed except when adding reagents. 

Place a B14 septum over the end of the side-arm of the 50 mL flask and flush the space between the septum and the stopcock with argon by inserting a vent needle (Fig. 5.1C) and opening stopcock B slightly for a few seconds. 

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The reagent is prepared by reaction of (Cp2ZrCl)20 with A1(CH3)3 (75% yield).1 Benzyne zirconocene complexes.1 This reagent reacts with an aryllithium at - 50° to form an intermediate a that loses methane at 25° to give a zirconocene... 

Naphthalyne drconocene complex. Buchwald1 has extended the preparation and use of benzyne zirconocene complexes (14, 133-134) to a similar naphthalyne complex as a route to substituted naphthalenes and naphthoquinones. 

The precise mechanisms of the conversion of zirconacycloptt nes into five-membered zirconacycles are still unclear. For the reactions of alkynes and alkenes, a concerted carbometallation mechanism earlier proposed appears to be plausible, but remains only a reasonable working hypothesis. One useful piece of information is that the reaction of an in situ generated benzyne-zirconocene complex with stil-bene is stereospecific, as shown in equation (46), suggesting that, in contrast to the formation of some three-membered zirconacycles, this and other related reactions may be concerted. 

Since 1986, the following zirconacyclopropenes as well as one zirconacyclopropane, i.e. (43), have been characterized by X-ray and other spectroscopic means. The compound (44) represents a benzyne-zirconocene complex, and (45) is an example of a cycloalkyne-zirconocene complex. Although these compounds are interesting and significant in their own right, they do not provide support for the formation of zirconacyclopropenes from alkynes and ZrCp , because the alkyne components are generated in situ and have probably never been free. 

Keywords. tf-Benzyne-zirconocene, )j2-Phosphabenzyne-zirconocene, a-Zirconated phosphines, Phosphorus heterocycles, Zwitterionic [phosphonium anionic zirconocene (IV)] complexes... 

In the past decade, reports on the interactions between main group elements, including phosphorus derivatives, and zirconium species such as [Cp2ZrHCl]n [7], Cp2ZrMe2 [8],[Cp2Zr] [9,10], or others [11,12] have appeared in the literature. The present review is focused on the use of /]2-benzyne-zirconocene and the parent rf-phosphabenzyne-zirconocene in phosphorus chemistry. The versatile behavior of these complexes towards unsaturated phosphorus reagents and the versatile behavior of the resulting products will be more precisely reported. 

Photolysis or thermolysis of diarylzirconocenes or arylalkylzirconocenes lead to reactive aryne-zirconocene complexes which can be trapped with several types of electron-donating ligands including dienes, phosphines, and carbon monoxide [13-15]. After being postulated by VoPpin et al. [14] and Erker [13], benzyne-zirconocene 1 (Eq. 1) was fully characterized by Buchwald et al. [16] by X-ray crystallographic studies of its trimethylphosphine complex adduct ... 

Remarkably the use of benzyne-zirconocene allows the formation of unexpected new complexes as the first q1 -iminozirconocene 48, the unprecedented phosphazide and iminophosphoranes complexes 34-46, or the unique so far stable pentacoordinated organo zirconocene-ate complexes 20,21,22-G4,22-G8, 24-G3-G2,25-31. 

Lithiation of commercially available bromoarenes (281) followed by treatment with zirconocene (methyl) chloride affords zirconocene complexes of substituted benzynes (283), which react with symmetric alkynes and l-(trimethylsilyl)propyne to give single regioisomeric zirconacycles, (284) and (285), respectively (Scheme 66). Both (284) and (285) react with disulfur dichloride to produce benzothiophenes (286) and (287), respectively, in 60-80% isolated yields in a one-pot procedure <89JOC2793>. Protodesilylation of (287) can be accomplished in >90% yield to give the corresponding 2-unsubstituted benzothiophenes by treatment with tetrabutylammonium fluoride in tetrahydrofuran. Application of the procedure to the preparation of 2,3-dihydrobenzo[6]thiophenes was also reported <9iOM537>. 

The in i /V -generated CpeZ Bu Cl converts the arene into a zirconocene-benzyne complex which undergoes C-C bond formation with a nitrile to form an intermediary azazirconacycle (Equation (14)). The acidic hydrolysis of the latter species provides the corresponding 3-acyl-l-substituted benzene derivatives. 

Thermolysis of diphenylzirconocene (9) affords the zirconocene—benzyne complex (10), which can provide zirconaindene complexes (11) (Eq. 2.6) [17]. 

Zirconocene 1,9-anthracenediyl complex 69 presumably undergoes rearrangement to an isomeric benzyne complex prior to the insertion of external alkyne (Equation 26). The isomerization can be understood as a /3-hydrogen elimination/reductive elimination process, resulting in a formal reduction to Zr(ll), followed by a typical alkyne/ alkyne oxidative cyclization to the observed zirconacyclopentadiene product 70. The coordinated benzyne intermediate can be observed spectroscopically as a trimethylphosphine adduct <2000JA9880>. 

The use of )j2-benzyne and )j2-phosphabenzyne zirconocene in phosphorus chemistry is reviewed. The regiospecific reactions of these complexes with small unsaturated organic molecules incorporating phosphorus or not led to a variety of cyclic neutral or zwitterionic complexes showing a versatile behavior. New methodologies of synthesis of phosphorus heterocycles and of phosphorus ligands are described, as well as strategies of C-H and M-H (M=N, O, P, S) bond activations. 

As described in the definition of Buchwald indoline synthesis, this reaction involves the formation of a zirconocene-stabilized benzyne complex that intramolecularly inserts to an A-allyl group to give a tricyclic indoline zirconacycle. In the presence of oxidating reagent or electrophiles, the indoline zirconacycle decomposes into indoline derivatives. ... 

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