Aryl oxide ligands

Fig. 25. ORTEP drawing of Sr(OC6H2- -Bu1)2(THF) 0.5 THF showing the trigonal bipyramidal ligand arrangement around the metal center. The more spatially demanding aryl oxide ligands are located at the equatorial sites. (Redrawn from Ref. I32.)...

Within this topic may be included agostic interactions and cyclometalation. A general review concerning the latter topic has appeared,as has a more mechanistically oriented review on the cyclometalation chemistry of aryl oxide ligands. ... 

Scheme 20 Imprinted polymer P-32 is bathed in a racemic solution of BINOL, which displaces the aryl oxide ligands of the platinum center. Removal of BINOL from the polymer matrix and determination of the % ee of BINOL is used to gauge the polymer s selective rebinding ability.

They doubtless owe their stability to the bulk of the aryl thiolate ligand they have tbp structures with equatorial nitrile that can be displaced by CO to give rare carbonyls of a metal in the +4 oxidation state. 

Fluorous ligands introduce an ease of purification in that the tagged phosphine ligand, the palladium catalyst complexed ligand, and the oxidized ligand can be completely removed by direct fluorous solid-phase separation (F-SPE) prior to product isolation. Similarly, an example of a fluorous palladium-catalyzed microwave-induced synthesis of aryl sulfides has been reported, whereby the product purification was aided by fluorous solid-phase extraction [91]. 

Arnold et alP reported the synthesis and structural characterization of an aryl-oxide-functionalized samarium silsesquioxane complex. Steric protection of 2 by one SiMe2tBu group generated a new disilanol ligand, (c-C5H9)7Si709(0H)2(0SiMe2tBu)... 

Aryl diazonium ions can also be used to form certain types of carbon-carbon bonds. The copper-catalyzed reaction of diazonium ions with conjugated alkenes results in arylation of the alkene. This is known as the Meerwein arylation reaction 01 The reaction sequence is initiated by reduction of the diazonium ion by Cu(I). The aryl radical adds to the alkene to give a new /Caryl radical. The final step is an oxidation/ligand transfer which takes place in the copper coordination sphere. An alternative course is oxidation/ deprotonation, which gives a styrene derivative. 

Chiral N-arylated imidazolinylidene ligands have been employed in the palladium(II) catalyzed aerobic oxidation of secondary alcohols to the corresponding ketones [55]. The chiral variant of this reaction, which does not generate a new element of chirality, is again based on the kinetic resolution of racemic mixtures. The active catalyst is formed in situ by a combination of two precursors, a dinuclear NHC-palladium(II) complex and an achiral (acetate) or chiral base ((-)-sparteine) (Scheme 18). 

Hu et al. [104] disclosed that the spiro phosphine oxide ligand (/ )-30a is highly efficient for the Pd-catalyzed Heck reaction of cyclic and heterocyclic olefins with aryl triflates. An asymmetric domino Heck cyclization was established using catalyst Pd/(/ )-30a to form fused carbo- and heterocycles with excellent stereoselectivity (Scheme 42) [105]. This method was used in a short synthesis of (-)-martinellic acid, a primary ingredient in traditional eye medicine in South America. 

GY Li. The First Phosphine Oxide Ligand Precursors for Transition Metal Catalyzed Cross-Coupling Reactions C-C, C-N, and C-S Bond Formation on Unactivated Aryl Chlorides. Angew Chem 113 1561-1564, 2001 Angew Chem Int Ed 40 1513-1516, 2001. 

The formation of the first monomeric heavy group 2 element alkoxides has been postulated based on oligoether ligands (14), the molecularity of which is supported by cryoscopic molecular weight data. This contrasts with the initial publications of Ba(OR)2 preparations. When a saturated hydrocarbon is the parent alcohol, apparently only involatile and insoluble alkoxides are formed. Quite recently, a benzene soluble bis (aryl oxide), Ba(bht)2(THF)2, has been prepared however, no volatility was reported. ... 

The reaction of metal halides with an alkoxide or aryl oxide (most commonly an alkali metal alkoxide), can result in metathetic exchange to give the required complex (equation 6). Such reactions can also result in the formation of heterometallic species (such as NaZr2(OR)4) this can be a problem when homometallic alkoxides are desired, but it is an important route to heterometallic alkoxides and aryloxides. The nature of the product can be influenced by the alkali metal, the alkoxide ligand, and the relative amounts of the... 

Iron complexes containing bidentate alkyl and aryl phosphorus ligands cleave a variety of C-H bonds under mild conditions, Hydrido acetylide complexes were prepared by oxidative addition of primary acetylenes in the Fe(DPPE)2 and the Fe(DMPE)2 systems [DPPE = bis(diphenylphos-phino)ethane, DMPE = bis(dimethylphosphino)ethane]. The Fe(DMPE)2 system also cleaves C-H bonds of activated methyl groups, aromatic compounds, and certain other sp hybridized molecules. The C-H cleavage reactions are reversible, resulting in equilibrium mixtures of isomeric products in many cases. Studies of substituted benzenes show that while product stability is favored by electron withdrawing substituents, steric effects play a predominant role in the determination of product distribution. 

---