金属有机化学课件课件.ppt

advantageous (a) normally no homocoupling or so little. (b) borons are not toxic.(c) organoborons are stable to air and moisture, and can be purified, stored and used as and when required. (d) couplings tolerate a wide range of functional groups, esters, nitriles, carbonyls, nitros, alcohols and phenols (e) consistently high yields for a wide range of substrates. (f) very efficient even for sterically hindered couplings. disadvantages (a) some boronic acid species are easily hydrodeboronated. (b) selectivity between iodo and bromo leaving groups is not as good as for zinc couplings. although a stronger base is required, sterically hindered boronic acids couple very efficiently, even to sterically hindered halides - note that in many cases it is best to use a milder base to prevent hydrodeboronation -loss of boron unit for a proton - stronger bases do enhance coupling, but they also enhance hydrodeboronation - sometimes a strong base helps, other times a weak base helps!! Selective Cross-couplings involving Organoborons Alkenyl Couplings involving Organoborons alkenyl couplings are little different to the successful aryl-aryl couplings as they both involve the same type of carbon - and conditions can be similar to aryl-aryl couplings discussed previously. Alkyl Couplings involving Organoborons Couplings involving alkyl species are particularly poor because of b-hydride elimination, which can take place at any time throughout the catalytic cycle - straight after oxidative addition if an alkyl halide is used, or straight after transmetallation if an alkyl metal is used. 与酰氯反应生成酮 不影响羰基和腈基，芳基酰氯收率低，加入正丁基膦后收率改善。 与?,?-不饱和羰基化物加成 VIII族金属有机化合物和催化反应 实验室规模的均相催化反应 Catalyst Reaction type Typical condition comments RhCl(PPh3)3 25?C Excellent selectivity, insensitive to functional groups. RhCl3?H2O 50-100 ?C,1 bar RhCl3?H2O in the presence of ehanol is a powerful catalyst for forming conjugated systems. Pd(CH3CO2)2 100 ?C With bromides it is necessary to use PdCl2(PPh3)2 PdCl2(PP