BINAP monoxide

Treatment of a benzene solution of Pd(OAc)2 and 3 equivalents of (/ )-BINAP with an excess amount of Et3N resulted in change in the color of the solution from yellow to red. 31P lYL] NMR study of the resulting solution revealed the formation of [Pd (/ )-BINAP 2] and (/ )-BINAP monoxide ((fl)-BINAP(O)) in a 1 1 ratio. Labeling experiments showed the participation of 1 equivalent of residual water in the reduction system. Thus, the reaction carried out in solution saturated with 18OH2 gave lsO-labeled (fl)-BINAP(l80). 

The role of water in the Heck reaction, as well as in other reactions catalyzed by Pd(0) in the presence of phosphine ligands, can be many-fold. Recent studies confirmed that it may play an important role in the transformation of catalyst precursor into Pd(0) species driving the catalytic cycle. The generation of zero-valent palladium species capable of oxidative addition by oxidation of phosphine ligands by the Pd(ll) catalyst precursor can be strongly affected by the water content in the reaction mixture, as is shown below for the reaction with BINAP ligand (BINAP-0 is BINAP monoxide) [91] ... 

Under a pressure (20 bar) of carbon monoxide, carbonylative silylcarbocyclization of enyne 92 was examined in the presence of a cationic rhodium-BINAP catalyst (Scheme 31).86 Although the enantioselectivity is low, the five-membered carbocycle functionalized with an alkenylsilane moiety and a formyl group was obtained with high selectivity. 

Analysis of Reagent Purity GLC analysis (OV-101, capillary column, 5 m, 200-280 °C) and TLC analysis (E. Merck Kieselgel 60 PF254,1 19 methanol-chloroform) Rf 0.42 (BINAPO, dioxide of BINAP), 0.67 (monoxide of BINAP), and 0.83 (BINAP). 

Handling, Storage, and Precautions solid BINAP is substantially stable to air, but bottles of BINAP should be flushed with N2 or Ar and kept tightly closed for prolonged storage. BINAP is slowly air oxidized to the monoxide in solution. 

Another closely related palladium(O) structure is found in the complex Pd BINAP(0))2, where BINAP(O) is the monoxide of the diphosphine BINAP. The complex is produced by reduction of PdCl2 BINAP(0)J in the presence of BINAP(O), Equation (11). Its X-ray structure shows that one of the ligands is only P-coordinated, and the second is a chelate with the P atom and an 7 -arene coordination to the naphthalene ring adjacent to the uncoordinated phosphynyl group.This closes again a 5.5-membered palladacycle. The P-Pd-P angle is 117.6°, and the Pd-C distances are 2.228 and 2.160 A. 

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