Nonphosphine ligands

Chelating ligands with both phosphine and nonphosphine binding sites 343... 

Catalysts can also be immobilized through nonphosphine ligands. A new type of immobilized Pd° complex with a macrocyclic triolefin ligand (L30) has been successfully used for simple crosscoupling reactions of aryl iodides and allyl bromide with arylboronic acids, in both aqueous and anhydrous media.498... 

As was the case in the other coupling reactions, nonphosphine-based catalysts have also been applied in amination chemistry. In particular, N-heterocyclic carbenes such as (9) have provided successful results for a wide variety of amination transformations. Similarly, catalysts based upon phosphinous acid ligands (e g. (11)) have also found success in the amination of aryl chloride substrates. ... 

Hydrosilylation of acetophenone to give silyl ether (M R = Me) can also be achieved using copper(I) complexes with the chiral phosphine ligands (-)-DIOP (87) or (+)-NORPHOS (88). The enantioselectiv-ity is rather low, but a nonphosphine auxiliary, PYTHIA (89) with a Rh(COD)Ch catalyst using neat diphenylsilane reduces aryl ketones to (R)-l-phenylethyl alcohol silyl ethers in high yield and with high enantiomeric excess (Scheme 18). " ... 

Yao described stable and soluble poly(ethylene glycol)-bormd Ru catalysts (10) for the ring-closing metathesis (RCM) of a variety of dienes. Bidentate nonphosphine ligands are in fact promising candidates for the recycling of Ru-carbene complexes, since the formation of chelates is entropicaUy favored at the end of the reaction [Eq. (8)] [20]. 

RuH2(ttp) is the active catalyst in the presence of base (Figure 8.2). In the presence of acid, the catalytic species is probably cationic, e.g., [RuH(sol-vent)jc(ttp)]". The isolated, stable, 18-electron cationic complexes [RuH(CH3CN)2(ttp)]BF4 and [RuH(P(OMe)3)2(ttp)]BF4 are not effective catalysts this difference in the catalysis rates may simply reflect the need for one of the nonphosphine ligands to dissociate to generate a vacant... 

Despite electron-rich bulky side-arms as in phosphine pincers 190,191 [245] or 192 [246] (Figure 2.24), these complexes behave strikingly different from their respective dialkyl or trialkylphosphine palladium complexes the latter complexes show t)q)e3 activtity (cf. Hartwig-Fu protocol see above). PCP-pincer complexes 190-192, however, are typical SRPCs exclusively suitable for type 1 reactions of aryl iodides and activated aryl bromides (Table 2.9, entries 1-6). Ligand-acceleration effects are not observed, which unequivocally underlines that the cleavage of these pincer complexes under the reacation conditions occurs to release nonphosphine palladium complexes with indeterminate coordination shell. 

Figure 2.27 Nonphosphine bidentate ligands and respective SRPC.

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