Transitions triaryls

Protonic initiation is also the end result of a large number of other initiating systems. Strong acids are generated in situ by a variety of different chemistries (6). These include initiation by carbenium ions, eg, trityl or diazonium salts (151) by an electric current in the presence of a quartenary ammonium salt (152) by halonium, triaryl sulfonium, and triaryl selenonium salts with uv irradiation (153—155) by mercuric perchlorate, nitrosyl hexafluorophosphate, or nitryl hexafluorophosphate (156) and by interaction of free radicals with certain metal salts (157). Reports of "new" initiating systems are often the result of such secondary reactions. Other reports suggest standard polymerization processes with perhaps novel anions. These latter include (Tf)4Al (158) heteropoly acids, eg, tungstophosphate anion (159,160) transition-metal-based systems, eg, Pt (161) or rare earths (162) and numerous systems based on tri flic acid (158,163—166). Coordination polymerization of THF may be in a different class (167). 

The IR bands in a number of nickel complexes of triaryl formazans have been assigned by Arnold and Schiele.415 A similar assignment of the electronic bands has been carried out.414 LCAO-MO calculations correlate well with these assignments417 and have been extended to include both inner ligand transitions as well as charge transfer bands and d—d transitions.418 EPR spectra have been used to study the nature of bonding in copper complexes of heterocyclic-containing formazans.419 Metal formazan complexes have also been studied by electrochemistry.283,398 420-422... 

The reactions of trialkyl and triaryl phosphines (R3P) with a wide variety of bare transition metal ions have not yet been studied but it is possible to get a phosphine such as Ph3P into the gas phase (145). Figure 6 shows the reaction of Eu+ with Ph3P. The addition of only two phosphine molecules was observed under the conditions used (113) (Ph3P at an uncorrected pressure of 2 x 10-6 Pa). The spectrum also shows the addition of only one Ph3P to [EuO]+. 

Kappe and Stadler have invented a microwave protocol enabling quick access to triaryl phosphines via coupling of diphenylphosphine with aryl halides and triflates [107]. Because of the value of phosphine ligands in assorted transition metal-catalyzed reactions, convenient routes for their pro-... 

After publication of details of the biphasic catalytic hydroformylation system in 1994 many applications of the same concept were found. A variety of fluorous triaryl phosphane ligands was synthesized to enable recycling of precious transition metal catalysts [10b, 18] (Scheme 3.3). 

Trialkyl- and triaryl-phosphines, -arsines and -stibines are all good donors toward rf-group transition metals and chelating di- and tri-phosphines and -arsines have been especially widely used as 7r-acid ligands (Section 22-13). The oxides, R3MO, also form many complexes, but they function simply as donors. Trialkyl- and triaryl-phosphines, -arsines and -stibines generally react with alkyl and aryl halides to form quaternary salts ... 

The oxidation-reduction method, developed initially by Mukaiyama et al. [133] and related to the previously described organophosphorus methods, has permitted a variety of important solid-phase applications. The mechanism of the activation is complex and involves the oxidation of the triaryl/ alkyl-phosphine to the oxide as well as reduction of the disulfide to the mercapto derivative. However, different active species, such as 81 (Fig. 11), the 2-pyridyl thioester, or even the symmetrical anhydride, have been postulated to form. For the intermediate 81, the peptide bond formation may proceed through a (cyclic transition state. The method has been used for conventional stepwise synthesis [134], acylation of the first protected amino acid to a hydroxymethyl resin, and to achieve segment condensation on a solid support in the opposite direction (N C) [135,136]. Lastly, it has been used for efficient grafting of a polyethylene glycol (molecular weight 2000) derivative to an aminomethyl resin to prepare PEG-PS resins [137]. 

Kappe and Stadler have developed an MW procedure for rapid production of triaryl phosphines by coupling diphenylphospine with aryl halides and triflates [134]. Taking into account the importance of phosphine ligands in a variety of transition metal-catalyzed reactions, convenient procedures for their production is valuable. Both homogeneous Pd-Ni and heterogeneous Pd catalysts were explored and the more unusual substrate phenyl triflate could also be coupled swiftly by use of nickel catalysis (Scheme 15.68). Couplings with other aryl halides proceeded in 26-85% yield after 3-30 min microwave irradiation at 180-200 °C. 

We have demonstrated with several of the main group elements that the reactivity of the resulting metal is highly dependent on such factors as the solvent, reducing agent, anion, or in the case of some metals the presence of additional alkali salts [2, 9, 10]. In the case of the transition metals, the presence of a triaryl- or trialkylphosphine during the reduction yields a highly reactive metal slurry. 

Trimethylthallium (Figure 13(b)) has a similar crystal structure, though in solution both thallium trialkyls and triaryls are monomeric. A proton magnetic resonance study of MeaTl in PhCD3 shows that methyl exchange is second-order and consistent with an electron-deficient transition state only 6 kcal/mole above that of two monomers ... 

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