1、第三章 氧化加成反應(yīng) Chapter 3 Oxidative Addition,氧化加成反應(yīng)是指基團(tuán)A-B對(duì)過(guò)渡金屬絡(luò)合物中心金屬加成的反應(yīng)。,從電子變化看：可以有雙電子和單電子的氧化加成，加成的結(jié)果是使金屬中心發(fā)生氧化：,氧化加成是描寫(xiě)反應(yīng)過(guò)程的化學(xué)計(jì)量關(guān)系，還沒(méi)有指明特定的機(jī)理,氧化加成反應(yīng)是生成金屬-碳和金屬-氫鍵的重要方法，也是C-H鍵活化所涉及到的重要基元反應(yīng)。因此對(duì)這類基元反應(yīng)的范圍和歷程的討論是過(guò)渡金屬有機(jī)化學(xué)的重要內(nèi)容。,一、反應(yīng)的范圍及影響因素,1. 價(jià)電子構(gòu)型,對(duì)所有具有價(jià)電子數(shù)2, 4, 6, 7, 8, 10構(gòu)型的過(guò)渡金屬絡(luò)合物都存在氧化加成，不過(guò)對(duì)中心金屬具有d8,

2、d10電子構(gòu)型的絡(luò)合物最為普遍。,2. 配合物類型,配位飽和的和配位不飽和的絡(luò)合物都可以發(fā)生氧化加成反應(yīng)，但是配位不飽和絡(luò)合物更為活潑。,配位飽和的d8電子構(gòu)型的配合物采取三角雙錐構(gòu)型,3. 加成物的分類,（1）極性的親電試劑：X2, H-Y, RSCl, RSO2Cl, R-X, RCOX, RfI, R-CN, SnCl4, HgX2,這類試劑的加成方式與對(duì)烯烴的加成類似，可以按極性的兩步歷程或鏈?zhǔn)阶杂苫鶜v程進(jìn)行。,（2）加成試劑在加成后仍有鍵的連接,O2, S2, Se2, 鄰笨醌，RCCR, RN=NR, RCH=CHR, S=C=S, CH2=O, 環(huán)丙烷，1，3-偶極加成物，如：R

3、CON3, RN3,第二類試劑，因在加成后保留有鍵，所以新形成的兩個(gè)鍵必須是順式的。底物限于配位不飽和的絡(luò)合物，或加成前失去一個(gè)配位體得到配位不飽和的絡(luò)合物。,（3）非極性加成試劑,此類試劑有：H2, R3Si-H, R3Ge-H, RSH, RCHO, Ar-H, R-H, 活化的C-H基團(tuán)的氧化加成,這類試劑通常僅與配位不飽和的絡(luò)合物進(jìn)行加成，并且總的立體化學(xué)是立體專一的順式加成。但也有例外：在質(zhì)子堿存在下的配位飽和絡(luò)合物的氫化。,4. 金屬中心,不同金屬的d8絡(luò)合物對(duì)氧化加成的相對(duì)活性與其發(fā)生氧化加成形成d6電子構(gòu)型的傾向性有關(guān),5. 配體,配體改變時(shí)，相對(duì)活性會(huì)有變化。釋電子配位體如瞵

4、增加氧化加成的傾向，而-授體如CO或烯烴減低氧化加成的傾向。,二、各類氧化加成反應(yīng)的歷程,（一）生成M-C鍵的氧化加成反應(yīng),A. 雙電子過(guò)程機(jī)理,反應(yīng)的特點(diǎn)： 需要金屬配合物配位不飽和 碳的構(gòu)型保持不變 氧化加成的兩個(gè)基團(tuán)在金屬中心保持順式 常見(jiàn)的是鹵代烴的加成,1. 協(xié)同機(jī)理(concerted mechanism),2. SN2機(jī)理,反應(yīng)的特點(diǎn)： 碳構(gòu)型的翻轉(zhuǎn) 陽(yáng)離子型的中間體 遵循二級(jí)反應(yīng)動(dòng)力學(xué) 具有典型的SN2反應(yīng)特征,B. 單電子機(jī)理,1. 原子的攫取及另外一個(gè)金屬中心的結(jié)合,反應(yīng)的特點(diǎn)： Mn與RX的化學(xué)計(jì)量關(guān)系為2：1 氧化加成試劑碳的外消旋化 Rate = KobsMRX te

5、rtiary C secondary C primary C Methyl EPR 可以檢測(cè)到R.,2. 自由基鏈?zhǔn)綒v程(Radical chain pathway),反應(yīng)的特點(diǎn) evidence for R (racemization, homocoupling, traping) Initiation and inhibition.,3. 內(nèi)界電子轉(zhuǎn)移（或籠狀自由基對(duì)）機(jī)理,反應(yīng)特點(diǎn)： Similar to SN2, but should give racemization at carbon,4. 外界電子轉(zhuǎn)移機(jī)理,反應(yīng)特點(diǎn)： 發(fā)生反應(yīng)時(shí)的能壘較高 只有在內(nèi)界電子時(shí)的配位受阻，SN2反應(yīng)

6、相對(duì)較慢。,1. 平面d8電子構(gòu)型IrI絡(luò)合物,L為有機(jī)膦配體,JACS, 1966, 88, 3511,(1) 絡(luò)合物中的膦配體不同反應(yīng)速度有下列降低次序,PMe2Ph PEt3 PEt2Ph PEtPh2 P(p-C6H4CH3)3 PPh3 P(OPh)3,PMe2Ph PEt3 反應(yīng)速度相差1.5倍,從PEt3到PPh3反應(yīng)速度相差30倍,PPh3 P(OPh)3之間反應(yīng)速度相差20倍,給電子能力越強(qiáng)，增加金屬中心發(fā)生氧化加成轉(zhuǎn)變成d6電子構(gòu)型的傾向,給電子能力強(qiáng)的膦配體增加中心金屬的活性，給電子能力弱的配體降低活性。,（2）絡(luò)合物中基團(tuán)Y為F Cl Br I時(shí)反應(yīng)速度依次降低。,說(shuō)明

7、空間因素起重要作用。,（3）CH3-X中X為I Br Cl速度也依次降低。 CH3-X中X越易離去反應(yīng)速度越快。 CH3I CH3CH2I R2CHI R3CI,（4）溶劑極性對(duì)反應(yīng)速度的影響的次序 DMF CH3CN THF C6H5Cl C6H6 極性越大，C-X中X越易離去。,（5）反應(yīng)不受自由基清除劑的影響，動(dòng)力學(xué)研究表明反應(yīng)服從二級(jí)速率公式,（6）二級(jí)鹵代烷對(duì)這個(gè)反應(yīng)不活潑,（7）反應(yīng)過(guò)程中觀察不到X與外加鹵負(fù)離子的交換。說(shuō)明反應(yīng)是受動(dòng)力學(xué)控制的。 （8）手性的鹵代烷R*X在反應(yīng)過(guò)程中發(fā)生構(gòu)型的翻轉(zhuǎn)。是SN2歷程的重要證據(jù)之一。,極性溶劑使反式產(chǎn)物重排為熱力學(xué)穩(wěn)定的順式產(chǎn)物,手性R*

8、-X在這樣的加成中發(fā)生構(gòu)型翻轉(zhuǎn)。,二級(jí)鹵代烷對(duì)平面四方d8IrI絡(luò)合物的氧化加成是按照自由基歷程進(jìn)行，可以從手性的R*-X發(fā)生外消旋化得到證明。,L =PMe3, or PMe2Ph,這個(gè)反應(yīng)給出了(R, R) 和(R, S)-兩種構(gòu)型的產(chǎn)物,下式為自由基引發(fā)的各步驟，每個(gè)過(guò)程相當(dāng)于單電子變化的自由基加成。,由上述情況可以看出：d8IrI絡(luò)合物的氧化加成有SN2歷程和鏈?zhǔn)阶杂苫鶜v程。 與CH3I的反應(yīng)按照SN2歷程進(jìn)行，而二級(jí)鹵代烷和其它一級(jí)鹵代烷的活性都不足以按照SN2歷程進(jìn)行。,Relative reactivity: ROTs RBr initiated by O2, benzoyl p

9、eroxide, etc. inhibited by radical traps.,2. d8RhI絡(luò)合物（平面大環(huán)）,平面大環(huán)d8RhI絡(luò)合物極易與鹵代烷進(jìn)行氧化加成反應(yīng)。,上述RhI絡(luò)合物與CH3I的加成速度比Ir(CO)Cl(PMe2Ph)2與CH3I的加成速度快104,中性的RhI絡(luò)合物和鹵代烷的反應(yīng)是按照SN2的二級(jí)歷程進(jìn)行。,烴基不同時(shí)有下列活性次序,實(shí)際上R為(CH3)3C-和 時(shí)反應(yīng)已不能進(jìn)行。,3. d8PtII配合物的氧化加成,在黑暗的條件下無(wú)反應(yīng)發(fā)生 reaction inhibited by pyrene, and activated by benzophenone 量

10、子效率取決于Pr only Pr was trapped by radical trap.,JACS, 1985, 107, 1218-1225,4. d10絡(luò)合物的氧化加成,C-X鍵對(duì)d10電子構(gòu)型的絡(luò)合物M(PR3)4 ( M = Pt, Pd, Ni, R = Ph, Et等）的氧化加成歷程比d8電子構(gòu)型的絡(luò)合物還要復(fù)雜，但也有一些結(jié)果明確的例子。,(1) d10Pd絡(luò)合物,ACC. Chem. Res. 1977, 10, 434. JACS, 1975, 100, 838, 845,Reactivity: PhI (r.t.) PhBr (80 0C PhCl (no reactio

11、n at 135 0C),Electron donating groups slow down the rate of oxidative addition, electron withdrawing groups accelerate the reaction.,PhCl (no reaction at 135 0C) p-Clbenzophenone (89%, 135 0C) p-chlorobenzonitrile (97%, 100 0C) 4-chloronitrobenzene (86%, 80 0C),反應(yīng)開(kāi)始給出順式加成物，但是分離得到的是反式加成物。,J. Organome

12、t. Chem. 1971, 28, 287-291.,下列反應(yīng)的順式加成物可以觀測(cè)和分離得到，但是慢慢地轉(zhuǎn)變?yōu)榉词疆a(chǎn)物。,Organometallics, 1998, 17, 954-959.,(2) d10Pt絡(luò)合物的氧化加成,d10Pt絡(luò)合物PtL3 ( L = PPh3, PEt3)與烷基鹵化物的氧化加成過(guò)程可按自由基歷程進(jìn)行。通過(guò)加入自由基自旋捕捉劑證明有自由基中間體存在。,鏈?zhǔn)綒v程,（3）d10有機(jī)銅鋰絡(luò)合物,有機(jī)銅鋰試劑參與的烷基偶聯(lián)反應(yīng)的第一步是CuI副離子絡(luò)合物與烷基鹵化物或類鹵代物的氧化加成，此時(shí)碳原子的構(gòu)型發(fā)生翻轉(zhuǎn)，第二步是生成的CuIII中間體的還原消除給出烷基偶聯(lián)的產(chǎn)

13、物，這一步碳的構(gòu)型不變?？偟牧Ⅲw化學(xué)由上式可以看出。,動(dòng)力學(xué)研究：反應(yīng)服從二級(jí)速率公式，第一步是速率決定步驟； 速率：R = 一級(jí)烷基 二級(jí)烷基 新戊基 X = OTs I Br Cl 立體化學(xué)：氧化加成試劑碳立體構(gòu)型發(fā)生翻轉(zhuǎn) 反應(yīng)屬于SN2歷程,（二）生成M-H鍵的氧化加成反應(yīng),H2對(duì)過(guò)渡金屬絡(luò)合物的氧化加成是不飽和烴的氫化，氫甲酰化，費(fèi)-托反應(yīng)等催化循環(huán)中必不可少的步驟。 H2的氧化加成大多數(shù)是可逆的。,1. Concerted mechanism,Vaskas complex (JACS, 1985, 107, 8049),Rate = KobsIrH2 kH/kD = 1.09,Ste

14、reochemistry of oxidative addition: When H2 adds to a square planar complex, it can add along two different L-M-L axes.,In the case of a chelated version of Vaskas complex, a stereoselective addition was seen. The H2 approaches along the P-M-CO axis.,H2,The -acceptor orbital of CO helps to stabilize

15、 the H2 complex promoting oxidative addition along that axis.,The Kubas dihydrogen complex undergoes reversible oxidative addition to give the dihydride (JACS, 1986, 133, 9). A variable temperature NMR study showed that at 50 C, the 1JH-D disappears reversibly.,Serena Fantasia, et al, Angew. Chem. I

16、nt. Ed. 2009, DOI: 10.1002/anie.200900463,2. Homolytic Cleavage of Hydrogen,Although less common, there are examples of 17 e metal complexes oxidatively adding H2 by a homolytic mechanism.,rate = kobs(CN)5Co3-2H2 Halpern, Inorg. Chem. 1970, 9, 2616; Inorg. Chim. Act. 1983, 77, L105-L106,3. Heterolyt

17、ic Cleavage,Activation of H2 by heterolytic cleavage is not formally an oxidative addition. The metal retains the same oxidation state and coordination number in the product. A base, either external or one of the ligands, promotes the heterolytic cleavage by deprotonating the bound H2 ligand.,An exa

18、mple is this hydride bridged Ru dimer, where the oxygen acts as a base to promote H2 addition to give the hydroxy Ru-H. C.P. Casey, JACS, 2001, 123, 1092.,Heterolytic oxidative addition of H2 promoted by an external base is a key step in many ionic hydrogenation catalysts.,Participation by an intern

19、al ligand is very Common for early transition metals, activation by an external base is less commonly observed.,H2,Sc(III) is d0 metal, so this reaction cannot involve oxidative addition of dihydrogen. Instead the reaction occurs by a process called -bond metathesis.,(三) Oxidative addition of Silane

20、s (Si-H),Silanes typically undergo oxidative addition by a concerted mechanism and show similar reactivity to H2. Oxidative addition of silanes is a general method for the preparation of metal-silyl complexes and is the initial step in hydrosilylation catalysts.,JACS, 1985, 107, 1794,(四) Oxidative a

21、ddition of Alkanes (C-H),Same mechanisms as H2 Oxidative addition,Heterolytic: M-Z + H-CR3 M-CR3 + HZ,Homolytic: 2 Mn + H-CR3 Mn+1-CR3 + Mn+1-H,Concerted: Mn- + H-CR3 (alkane complex) H-Mn+2-CR3,General trend: sp2 C-H bonds are usually activated more readily than sp3 C-H bonds.,1. Heterolytic cleava

22、ge: -bond metathesis,Early transition metals (usually d0) with basic ligands (H-, R-) will heterolytically activate C-H bonds. For d0 metals, oxidative addition is not possible, so the reaction must proceed by -bond metathesis.,Acc. Chem. Res., 1985, 51,Is the mechanism simply electrophilic aromatic

23、 substitution?,2. Homolytic Activation,2 (TMP)Rh + CH4 (TMP)RhH + (TMP)RhCH3,Proposed mechanism,J. Am. Chem. Soc. 1991, 113, 5305,3. Concerted Oxidative Addition,a. Intramolecular C-H oxidative addition,Intramolecular oxidative addition, which is often called cyclometallation, is very common.,J. Am.

24、 Chem. Soc. 1969, 91, 6983,Prior coordination (agostic) allows the weakly binding C-H species to be held in close proximity to the metal center facilitating oxidative addition.,b. Intermolecular C-H oxidative addition,The first examples of intermolecular oxidative addition of alkanes was reported by

25、 Bergman (J. Am. Chem. Soc., 1982, 104, 352 and 1983, 105, 7190) using coordinatively unsaturated iridium(I) complexes formed by expulsion of H2.,Cp*Ir(PMe3) + H-Cy,For alkanes, less sterically hindered C-H bonds add at faster rate.,This presumably is due to the greater stability of less sterically demanding alkane c