Pincer-type complexes preparation

ROMP polymerization (Eq. 28) of norbornene esters containing SCS-Pd(II) pincer-type complexes useful in Heck, Suzuki, and Sonogashira couplings have been reported by Week s group [111, 112]. The SCS-Pd(II) complexes in the polymer 74 prepared by this chemistry are competent catalysts in iodoarene couplings. The product polymer 74 is soluble and recoverable by precipitation using hexanes. 

For this purpose, a series of Frechet-type polyether dendrons of zeroth-to third-generation containing an NCN-pincer metal complex (M = Pt, Ni) at the focal point of the wedge were prepared [69]. Their synthesis was either... 

Cyclometallation, which provides multidentate ligands containing carbon donors, has been known as a useful synthetic method for preparing organometallic complexes. A noticeable extension in such a category, which substantially facilitates the recent development of organoplatinum chemistry, is the pincer-type ligands, which allow tridentate meridional chelation with various donor combinations to the metal. ... 

It was shown that palladacydes 1 [3c, 24] prepared from palladium] I) acetate and tris(o-tolyl)- or trimesitylphosphine are excellent catalysts for the Heck coupHng of triflates and halides including certain aryl chlorides. In some of these cases, a possible involvement of oxidation states +II and +IV in the catalytic cycle has been considered [25]. Similarly, other palladacydes such as 3 [26e,h] or 6 [27] have been used in the Heck reactions (Figure 8.1) [24, 26, 28]. It has been proposed that, at least for NC palladacydes, the reaction proceeds through the classical phosphine-free Pd(0)/Pd(II) catalytic cycle and that the active catalysts are actually slowly formed palladium clusters [29]. Besides classical palladacydes, complexes with pincer-type ligands such as 2 [30] have become very popular in palladium catalysis [31]. 

A chloro complex 599 with an optically active NGN pincer-type ligand, having two chiral imidazole groups ((, )-Phebox), has been prepared via the reaction of the stannyl derivative of the ligand with Zeise s complex (Equation (131))V ... 

Pincer-type figands with more complex central moieties have also been prepared. For example, figands with a central 1,8-naphthyridine moiety... 

Preparation of pincer-type ligand SiNSi 102 Preparation of [SiNSi]FeCl2 complex 103... 

Fig. 12 b Preparation of chiral molecular nanocapsules 15 and 16 with Bis(2,3-di-hydroxypropyl)-10-undecenylamine and trimethylolpropane (TMP), Respectively, and a schematic encapsulation of sulfonated platinum pincer complexes of type 3 in the hydrophilic compartment of the nanocapsules... 

Finally, late-metal-amido complexes have been prepared by the oxidative addition of amines. These oxidative additions are included in Chapter 7. In brief, the oxidative addition of aniline is favored for several different types of metals. This reaction of electron-poor pentafluoroaniline to Pt(0) was reported many years ago by Stone (Equation 4.7), and the reaction of the parent aniline with Ir(PEt3)3Cl was reported later by Casalnuovo and Mil-stein. More recently, the oxidative addition of ammonia to an iridium(I) complex containing an electron-rich pincer ligand was observed (Equation 4.8). ... 

Bis-NHC CNC-type pincer ligands were first used with Pd and, later on, coordinated onto early-transition metal complexes. The titanium (III) complex 35 was readily prepared from (THF)3TiCl3 and the free bis(carbene)pyridine, whereas the imido Ti complex 36 was obtained from Ti(NtBu)Cl2(pyridine)3 (Scheme 14.19) [66,67]. The pincer complex 35 was tested in ethylene polymerization. With 500 equivalents of MAO cocatalyst, an activity of 791kgmor bar h was observed. 

The particular features of phosphonium salts were exploited for a number of synthetic applications in 2014. Phosphonium chloride salts found applications as chlorine source and as modifiers for homogeneous catalyst systems. As an example, Muller, Rosenthal and co-workers reported the study of a chromium-based catalyst for the selective tri-merization of ethylene. A phosphonium precursor of the type i cyclo-(PR2CH2CH(OH) )2][Br]2) was used for the preparation of iron(n) complexes containing unsymmetrical P-N-P pincer ligands (Scheme 5). The group of Prof. Morris tested these compounds as catalysts for the asymmetric hydrogenation of ketones and imines. ... 

---