Aryl halides monodentate ligands

Platinum (II) complexes of the type (COD)PtRX (COD = jj -l,5-cyclooctadiene R, X = alkyl, aryl, halide) are known for many combinations of R and X, and then-reaction chemistry is well developed see Platinum Organometallic Chemistr. The lability of the COD-Pt interaction renders these compounds convenient sources of organoplatinum fragments for coordination to Lewis bases such as phosphines, according to equation (27). In an effort to better understand the factors that influence the stability of bis(phosphine)platinum(II) species, a thermodynamical study of the reaction in equation (27) was undertaken for a series of monodentate and bidentate phosphine ligands of varying steric and electronic character. 

The similar reaction of diarylphosphine oxides with aryl halides and triflates has been used more recently to prepare a variety of ligands for asymmetric catalysis. Many of these reactions involve additions of secondary phosphine oxides to di- or monotriflates derived from binaphthol because the triflates are more accessible than 2,2 -l,l -dibro-mobinaphthol. Workers at Syntex described a procedure to use the ditriflate of binaphthol to prepare mixed phosphine oxide, hydroxo ligands, and the monophosphine oxide, bi-naphthyldiphenylphosphine oxide. Hayashi then developed a route to a number of chiral monodentate phosphine ligands with a 2-(diphenylphosphino)-2 -alkoxy-l,l -binaphthyl structure (Eq. Reaction of the ditriflate with diphenylphosphine oxide in the... 

The palladium-catalyzed reaction of olefins with aryl or vinyl halides or pseudohalides in the presence of base (the Heck reaction) follows a different course from the other crosscoupling reactions after the oxidative addition step. As shown in Scheme 19.5, the olefin coordinates to the palladium after oxidative addition of the aryl or vinyl halide. Tliis coordination of olefin may occur by associative displacement of a monodentate ligand from the palladium, or it may occur by replacement of halide by the olefin to generate a cationic olefin complex. In some cases, these reactions are conducted with aryl or vinyl triflates. In this case, the olefin readily displaces the triflate to generate a cationic palladium-olefin... 

Four classes of catalysts have been used for the coupling of amines and related nitrogen nucleophiles witii aryl halides. Initially, complexes of the hindered monodentate aromatic tri-ortlio-tolylphosphine catalyzed the reaction of aryl bromides with secondary amines in the presence of an alkoxide or silylamide base. The use of this catalyst for this type of coupling to form C-N bonds was based on an earlier report of the reaction of aryl bromides with tin amides in the presence of a palladium complex of the same ligand as catalyst. - Later, complexes containing aromatic bisphosphines, such as BINAP and dppf, were... 

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