18 electron rule EAN rule Effective Atomic Number

18 electron rule: EAN rule (Effective Atomic Number) In 1927, developed by Sidgwick d electrons of metal + electrons of ligand = 18 electrons 3 4 5 6 7 8 9 10 11 12 d 3 d 4 d 10 Sc Ni Y Rh Au Ti Cu Zr Pd Ta Hg d 5 d 6 d 7 V Zn Nb Ag Cr Mn Mo Tc Cd W Re d 8 d 9 Fe Co Ru Os Ir Pt

Ni: 1 s 22 p 63 d 84 s 2 : it is better to promote 4 s electron to 3 d, therefore Ni(0) is d 10. Cu(I), Ag(I), and Au(I) is d 10, Zn 2+, Cd 2+, and Hg 2+ is d 10 Ti(IV) serves as a good index for memorizing the d electrons Because it is a d 0 metal ion. Ti. Cl 4 is colorless, diamagnetic liquid Ti. Cl 3 is violet color

octahedral Trigonal bipyramid tetrahedral Square planar

Electrons Ligand 1 수소라디칼(H radical), 알킬 라디칼(alkyl radical), 아릴 라디 칼(aryl radical) , 할로겐 라디칼(halogen radical), NO (굽은 형태) 2 CO, CS, RCN, R 3 P, R 3 As, RCN, R 2 S, 수소음이온(H-), 알킬음이온(R-), 알켄 (alkene), η 3 -알릴 양이온(η 3 -allyl+), 알 킨(alkyne), 니트로실 양이온(NO+), 할로겐 음이온(X-) 3 η 3 -알릴 라디칼(η 3 -allyl), NO (직선형) 4 η 3 -알릴 음이온(η 3 -allyl-), η 4 -C 4 R 4(η 4 -cyclobutadiene), η 4비 공 액 디 엔 (nonconjugate diene), η 4 -공 액 디 엔 (conjugate diene) 5 η 5 -C 5 R 5 라디칼(η 5 -cyclopentadienyl radical) 6 η 5 -C 5 R 5 음 이 온 (η 5 -cyclopentadienyl anion), η 6 -C 6 R 6, η 7 C 7 R 7 양이온(cycloheptatrienyl cation) 7 η 7 -C 7 R 7 라디칼(cycloheptatrienyl radical) 8 η 8 -C 8 R 8 (cyclooctatetraene)

Ni(CO)4, Fe(CO)5, Cr(CO)6, Ni(CO)4, For Mn, Mn(CO)5: 17 electrons Mn(CO)6: 19 electrons Mn(CO)5 (CO)5 Mn-Mn(CO)5 HMn(CO)5, CH 3 Mn(CO)5, Cl. Mn(CO)5 CH 3 - + Mn(CO)5+

18 Electron Rule: strong field ligand such as CO, Hydride, Cycanide anion. Not good for Aqua complex: Weak Field Ligand such as H 2 O is not matched with 18 electron rule. Late transition metal is better than early transition metals.

Exceptions Early trantion metals (η 5 -C 5 H 5)2 Zr. Cl 2: 5 ex 2+4 e+2 e=16 e, (CH 3)3 Ta. Cl 2는 1 ex 3+5 e+2 e=10 e (CH 3)6 W는 1 ex 6+6 e=12 e For early transition metals, there is not enough room to attach many ligands to satisfy 18 electron rule. Coordination number: number of ligand to bind to metal. Coordination number cannot be larger than the maximun oxidation number or the group number of element. For Late transition Metals (PPh 3)3 Pt: 2 ex 3+10 e=16 e (η 5 -C 5 H 5)2 Ni: 5 ex 2+10 e=20 e

d 8 complex: 16 electrons Pt(II), Pd(II), Cu(III), Ir(I), Rh(I): square planar For example, Cl(PPh 3)3 Rh(I) (Wilkinson’s complex), Cl(PPh 3)2(CO)Ir(I) (Vaska’ complex), (PPh 3)2(CCPh)2 Pt(II) even though they contains strong field ligand

1. 3 Mechanism in Organometallic Chemistry 1. oxidative addition (산화성부가반응) and reductive elimination (환원성 제거반응 ) 2. insertion (삽입반응) and deinsertion (이탈반응) 3. Oxidative coupling (산화성결합반응)and Reductive Cleavage (환원성결합분열)

1. oxidative addition (산화성부가반응) and reductive elimination (환원성 제거반응 ) two electron oxidative addtion (이전자 산화성부가반응) and one electron oxidative addition (일전자 산화성부가반응) A; 16 electron complexes B: 18 electron complexes

H 2 Fe(CO)2 -4 20 electron complex Na 2 Fe(CO)4 18 electron complex [RFe(CO)4]+X 18 electron complex

Rh(II), Co(II) d 7 complex

1965, Chatt and Davidson Kinetic Factor Thermodynamic Factor

In 1982, Bergman, Graham, Jones

Endo methyl migration: aromatic stablization energy

Reductive Elimination: spontaneous To do reductive elimination, two ligands should be placed at cis-position Concerted Mechanism

Transphos Ligand: Pd(II) is dsp 2 (square planar): no reductive elimination Addition of CH 3 I allows to make cis-dimethyl to undergo reductive elimination.

2. Elimination of one of ligand to make T-shape to Y shape. 3. Reduce the electron density of central metal Ligand off from metal by heat or light, oxidize the metal, addition of strong pi-acceptor ligand such as CO, maleic anhydride, quinone, tetracyanoethylene

1. Insertion (삽입반응) and Deinsertion (이탈 반응)

Migratory Insertion: cis position and concerted mechanism Order: h 3 -allyl ≥ Et 〉Me 〉Ph. CH 2 〉vinyl ≥aryl, ROCH 2 〉HOCH 2 Hard to migrate to CO: Hydride(H-), acyl (CH 3 CO), CF 3 , Heteroatome: RO-, R 2 N

Decarbonylation

Hydride Insertion: cis-addition, 4 -centered transition state For example: hydroboration, hydrosilylation, hydroformylation Reverse Reaction: b-Hydride Elimination The reason why it is hard to make a long chain alkylmetal complex

Alkyl Migration into olefin: olefin polymerization

Order of Migration of sigma liand-metal complex to Olefin: H >> R, vinyl, aryl> RCO>>RO, R 2 N Heteroatom is hard to migrate because of strong bond of heteroatom bearing lone pair to metal

Alkyne undergoes migratory insertion, but further successive reaction make polymer compounds, which make complication. Other Insertion, deinsertion substrate; isocyanide (: C≡NR), carbene(: CR 2), SO 2 , etc

Nucleophilic Addition Reaction (친핵부가반응) reverse sterechemistry to migratory insertion High valent metal species: electron deficient metal

Trans-Addition Product

Order of Reactivity 1. 4. 3 Oxidative coupling (산화성결합반응) Reductive Cleavage (환원성결합분열) M: +2 Increase

Electron withdrawing or strained molecules For alkyne, electron-withdrawing is no necessary