Transition metal-ligand complex formation

Transition Metal-Ligand Complex Formation - Co(ll) Complexes... 

V. I. Minkin and L. E. Nivorozhkin, Stereodynamics and Degenerated Ligand Exchange in the Solutions of Tetracoordinated Chelate Complexes of Non-Transition Metals in Complex Formation and Stereochemistry of Coordination Compounds , ed. Y. Beslaev, Nova Science Publishers, Commack, New York, 1996, p. 77. 

Desulhirization reactions of transition metal-polysulfido complexes have also been reported. The treatment of a dimetallic complex of titanium, [ Ti(Cp)(OAr) 2(yU-S)(yU-S2)] (Cp=77 -C5H5, Ar=2,6-i-Pr2C6H3), with an equimolar amount of PhsP results in the quantitative formation of [ Ti(Cp)(OAr) 2(yU-S)2] via the transformation of the 1U-S2 ligand to a /t-S ligand (Scheme 44) [93]. The reverse reaction of [ Ti(Cp)(OAr) 2(/t-S)2] with Ss proceeds in a good yield. 

Hi) Formation of transition metal carbonyl complexes Ashe and Colburn have reported (77JA8099) the synthesis of molybdenum carbonyl complexes of arsenin and antimonin but were unable to prepare bismin complexes because of its lability (Scheme 23). As expected for electron-rich aromatic compounds, both formed six-electron 7r-complexes (113) by a ligand displacement mechanism. Arsenin also forms a two-electron complex (114) analogous to those formed by pyridine, whereas antimonin did not give a similar complex under the conditions of this reaction. 

This chapter illustrates that electron-rich transition metal-diene complexes can couple with carbon electrophiles and, thereby, provide unusual methods for carbon-carbon bond formation. These procedures are of interest from a synthetic viewpoint since normally uncomplexed dienes or polyenes are not reactive toward weak carbon electrophiles or, with strong electrophiles, undesirable reactions such as polymerization occur. Furthermore, the metal-mediated route often results in desirable regio- and/or stereo-selectivity. Important to the utility of these methods is the ability to free the organic ligand from the metal. In most instances efficient oxidative procedures have been developed for such cleavage reactions. 

Although terminal oxo complexes of the late-transition-metal elements have been proposed as possible intermediates for oxidations catalyzed by these elements, late-transition-metal-oxo complexes were scarcely known. Hill and coworkers reported the synthesis and characterization of Pt4 + -, Pd4 + - and Au3 + -oxo complexes, [M(0)(0H2) W0(0H2) (PW9034)2]m (M = Pt, Pd and Au, n = 0-2), stabilized by electron-accepting polyoxotungstate ligands [109-111]. The stoichiometric reaction of the Au-oxo complex [Au(0)(0H2) W0(0H2) 2 (PW9034)2]9 with triphenylphosphine led to the formation of triphenylphosphine oxide. 

The formation of transition-metal carbene complexes containing tin substituents on the metal is another example where the tin group is a spectator ligand (equations 169-171)395-401. 

The tantalum-benzyne complex (130) is much less reactive than other early transition-metal aryne complexes. It shows no reaction with acetone, benzophenone, benzaldehyde, acetonitrile, 3-hexyne, or methanol. The lack of reactivity of 130 was attributed to nonlability of the PMe3 ligand. Indeed, no phosphine exchange was observed when 130 was mixed with an excess of PMe3-d9. Refluxing 129 in a mixture of methanol and toluene (3 10 v/v) leads to clean formation of 131. This presumably results from reaction of a 16-electron benzyne complex with the alcohol. 

MetaUacycle formation has also been observed in bis-Cp complexes. Heating Cp 2UR[P(Si(CH3)3)2] (R = Cl [146840-37-1], CH3 [146840-39-3]) results in the metaUation of the phosphido ligand. These complexes are structurally similar to the group 4 and 6 transition-metal metallacyde complexes, but show a dramatically reduced reactivity. 

The authors have previously reported33 a new convenient method of preparing transition metal-acetylide complexes of the type cis- and frans-(PR3)2M(C=CR)2 according to Eq. 10, and have shown that the complex having tri-n-butylphosphine as the ligand is air-stable and highly soluble in a variety of organic solvents. This new M-C bond formation reaction... 

The ligand was then used to form a variety of transition metal carbene complexes [207] (see Figure 3.72). Interestingly, more than one method for the formation of transition metal carbene complexes was successfully employed presence of an inorganic base (IC COj) to deprotonate the imidazolium salt and the silver(I) oxide method with subsequent carbene transfer to rhodium(I), iridium(I) and copperfi), respectively. The silver(I) and copper(I) carbene complexes were used for the cyclopropanation of styrene and indene with 1,1-ethanediol diacetate (EDA) giving very poor conversion with silver (< 5%) and qnantitative yields with copper. The diastereomeric ratio (endolexo) was more favonrable with silver than with copper giving almost a pnre diastereomer for the silver catalysed reaction of indene. 

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