Olefin complexes difunctionalizations

Zirconium-benzyne complexes have been used rather extensively in organic synthesis.8 45 For this purpose, one particularly important characteristic of zirconium-aryne complexes is that olefin insertion into the Zr—C bond occurs stereospecifically. Thus, when generated in situ, the zirconium-benzyne complex (45) reacts with cyclic alkenes to give exclusively the cis-zirconaindanes (46), which upon treatment with electrophiles provide access to a variety of m-difunctionalized cycloalkanes (47-49) (Scheme 5).46 For example, carbonylation of intermediate 46 affords tricyclic ketone 49, reaction with sulfur dichloride gives thiophene 48, and reaction of 46 with tert-butylisocyanide followed by I2 gives 47 via 50 and, presumably, intermediate 51 [Eq. (12)]. 

The topic of outer sphere reductive oxy-de-metallation is also prominent in work on the difunctionalization of alkenes [26]. The reaction of a dinuclear Pt(III) complex with olefin and water gave a hydroxy-alkyl complex next, the dinuclear metal unit serves as an electron sink and leaving group in an oxy-de-metallation at carbon, presumably via double inversion and an epoxide intermediate (Scheme 7) [26]. The process currently remains a stoichiometric oxidation. 

Carbon-heteroatom bond-forming reductive elimination from transient intermediates has been proposed as the product release step of a variety of important Pd-catalyzed transformations, including arene and alkane C-H bond functionahza-tion [1,2], ally lie acetoxylation [3], alkene borylation [4], and olefin difunctionalization [5]. Over the past 25 years, a variety of Pd " model complexes have been synthesized to study reductive elimination reactions at Pd centers. For instance, in 1986, Canty reported the first example of a crystallographically characterized organometallic Pd complex, /ac-[(bpy)Pd (CH3)3(l)] (bpy = 2,2 -bipyridine) (1). In addition, his group has demonstrated that this species undergoes facile C-C bond-forming reductive elimination to release ethane (Eq. 1) [6],... 

In contrast, unactivated olefins and alkynes complexed to organopalladium species generated in situ by oxidative addition of an unsaturated halide to a palladium(0) complex react intramolecularly with stabilized nucleophiles. These reactions that require catalytic quantities of the metal result in overall difunctionalization of the olefinic or acetylenic substrates. 

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