Pincer-type complexes

Some other intermolecular C-H activations involving the NHC ligand have been observed during the synthesis of particular NHC-containing pincer -type complexes also called CCC-NHC complexes. In addition to zirconium- and rhodium-based complexes (210) and (211)/ several examples involving palladium of general structure (271) have been synthesized. Whereas Faller... 

K. J. Szabo, O. F. Wendt, Pincer and Pincer-Type Complexes Applications in Organic Synthesis and Catalysis, Wiley-VCH, Weinheim, 2014. 

Espinet et air reported a rather nice series of 2,6-dipicolinate derivatives 84 whose structure is reminiscent of pincer-type complexes. The first thing to note is that none of the Pd complexes of dipicolinate (84a X = 0)... 

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. 

An interesting oxidative addition reaction leading to a pincer-type complex was reported by Matsumura and Inoue et al. [40]. The protocol involves the reaction of a 71-sulfurane (lO-S-3-tetraazapentalene) with Pd(PPh3)4. The hypervalent sulfur is reduced, and at the same time one of the phosphines and Pd(0) are oxidized to triphenylphosphine sulfide and Pd(II), respectively (see Scheme 6). 

Figure 80 Chemical structures of the pincer-type complexes (191).

Pincer and Pincer-Type Complexes Applications in Organic Synthesis and Catalysis, First Edition. 

Poverenov, H., Gandelman, M., Shimon, L.J.W. et al. (2004) Nucleophilic de-coordination and electrophilic regeneration of hemilabile pincer-type complexes formation of anionic dialkyl, diaryl, and dihydride Pt(II) complexes bearing no stabilizing rr-acceptors. Chem. Eur. J., 10, 4673-84. 

Werkmeister, S. Neumann, J. Junge, K. Beller, M. Pincer-type complexes for catalytic (dejhydrogenation and transfer (dejhydrogenation reactions Recent progress. Ghent. 2015,21,12226-12250. 

Ruthenium-Catalyzed Hydrogen Generation from Alcohols and Formic Acid, Including Ru-Pincer-Type Complexes... 

A unique case of the chemistry of pincer-type complexes was the synthesis of the first carbonyl hemilabile pincer complex (PCN)Pt(CO) reported by Milstein and coworkers [15]. Hence, the carbonyl derivatives (32) and (33) were synthesized from the direct reaction of CH2CI2 solutions of the corresponding cationic complexes (30) and (31) with a slight excess of CO. Here, the weakly coordinated Bp4 counteranion is easily displaced by the better coordinating ligand CO (Scheme 2.17). 

Multidentate donor ligands specifically the pincer-type motif [EDE] (D = pyridyl, phenyl E = PR2, NR2, SR) with tridentate coordinating ligand framework have the advantage that they can simultaneously increase the electronic density and stabilize the coordination sphere of a transition metal. This can have suhstantial effects on the catalytic activity of the transition metal complexes. As an example, iron-hased pincer-type complexes present high catalytic activity for different reactions, such as hydrogenation (1—3), hydrosilylation (4,5), and hydroho-ration (6). 

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