Organometallics: Hard to define usefully and completely at the same time, but generally: Compounds containing metal-carbon bond(s).

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1 eady; Catalysis rganometallics: Definitions rganometallics: ard to define usefully and completely at the same time, but generally: Compounds containing metal-carbon bond(s). C C C C C C K 3 o question:???? rganometallic Catalysis further complicates the issue: Inorganic o question: Inorganic C3 ()B Br % d(ac) 3% L CsF, rt e 3C L d L C3 C3 C3 C3 3C L = C3 Cy C3 chwald, JAC, 1998, 97 rganometallic Ln h III 1 mol% (h 3) 3h Wilkinson's Catalyst Inorganic Likely intermediate rganometallic Zhang, JAC, 3, 637 eady; Catalysis rganometallics: layers rganometallics is dominated by d electrons and orbitals e Li Be ost commonly used in B C F e organometallic reactions a g Al i K Ca c V Cr n Co i Cu Zn Ga Ge As e Br Kr b r Y Zr b o Tc u h d Ag Cd In n b Te I Xe Cs Ba La f Ta W e s Ir t Au g Tl b Bi o At n Usually d Transition metals (copper often included) p e- dominate Usually have e- configuration Xd 1 (X1)s n ote: for our purposes, t.m. s will be s eady; Catalysis rganometallics: electronegativity auling Electronegativity (ε) Li a.9 K b Cs Be g Ca r Ba.9 c Y 1. La 1.1 Zr f V b Ta Cr o.1 W.3 n Tc e u s Co h.3 Ir i d t.3 Cu Ag Au.5 Zn 1.7 Cd 1.7 g B Al Ga In Tl C.5 i Ge n b 3. As b Bi Te.1 o F. 3.1 Br.9 I.6 At e e Kr Xe n Lanthanoids and Actinoids: 1.1 Alkali and main group, electronegativity decreases down the column Transition metals: electronegativity increases down the column Consider -C bonds: trength ~ rbital overlap ε-εc T..-Carbon bond covalent, strong (note C-d less polarized than C-i) Alkali metal-carbon bond largely ionic 1

2 eady; Catalysis rganometallics: bonding (n1) p orbitals (n1) s orbital imple bonding: σ p z p x p z n d orbitals - Can be covalent or dative (Lewis base) - ame representation for both L nzr L nd dyz dxz dxy lobes between axes - Centrosymmetric - Lobes 9 o apart - 9 orbitals, 9 bonds possible - ard to fit 9 ligands around most metals - Usually up to 6 ligands, 3 non-bonding orbitals dx -y dz lobes on axes L ns ote: Ln used if we don't know (or don't care) about other ligands on the metal - analogous to "" for organic chemists π Covalent: L ncr e e Dative (metal can accept or donate e-) (C) C (C) C L nd L nd eady; Catalysis rganometallics: bonding Ionic Bonding: Driven by electrostatics Covalent Bonding: Driven by verlap increasing ionization potential -L trongest bond when high opposite charges interact. E i Charge differences are reflected in electronegativity differences. Therefore large electronegativity differences give stronger bonds. L otential energy E i E c -L trongest covalent bond when orbitals of similar energy interact trength of interaction directly proportional to orbital overlap (matching size) trength of interaction inversely proportional to difference in electronegativity. σ* σ L E i = f(-q Q L) = f[-(ε -ε L)] E c = f( orbital overlap ε-εl ) L bonding for early is substantially ionic L bonding for late is substantially covalent eady; Catalysis rganometallics: hard/soft oft ucleophile Li a.9 K b Cs Be g Ca r Ba.9 c Y 1. La 1.1 ard electrophile Zr f V b Ta Cr o.1 W.3 n Tc e u s Co h.3 Ir Increasing electronegativity oft electrophile i d t.3 Cu Ag Au.5 Zn 1.7 Cd 1.7 g Increasing electronegativity B Al Ga In Tl C.5 i Ge n b 3. As b Bi Te.1 o ard nucleophiles (i.e. ligands): Low E, high charge density ard electrophiles (i.e. metals): igh E LU, high charge density ard-ard interactions largely ionic (e.g. CsF) oft nucleophiles: igh E, low charge density oft electrophiles: Low energy LU, low charge denisty oft-oft interactions largely covalent (e.g. ecu) Increasing electronegativity ard ucleophile F. 3.1 Br.9 I.6 At e e Kr Xe n Increasing electronegativity

3 eady; Catalysis rganometallics: hard/soft ard/oft effects on ligand binding Log[K eq ] n Ligand F - - Br - I Zn Cu g eady; Catalysis rganometallics: ligands ligands charge # e- ligands charge # e- C 3,, = F,, Br, I 3, 3, C or C 6 C 3-6 C 3 triplet (chrock) carbene X C 3 singlet (Fischer) carbene - -eterocyclic Carbenes (C) η- peroxo superoxide terminal oxo BF, bf 6, B(C 6F 5) B[C 6 3-(CF 3) ], Tf ~ - - eady; Catalysis rganometallics: phosphines n hosphines Cone Angle trong σ-donors σ-donation 3 3 < () 3 < h 3 < 3 ligand F 3 θ 1 trong π-acceptors (e) 3 e d -> d h t (CF 3) or d -> σ* - rpen Chem. Com. 1985, 131 8A θ he dppe Et 3 h 3 Cy 3 (t) Chiral and modular h 75 e e 9 h h h C Cp BIA Duhos e DIA toleman Chem ev. 1977,313 3

eady; Catalysis rganometallics: C s -eterocyclic Carbenes (C's) eviews: errmann, ACIEE,, 19; gan, ACIEE, 7, 768 Key initial discoveries: lky C's are stable: duengo, JAC, 1991, 361.

4 eady; Catalysis rganometallics: C s -eterocyclic Carbenes (C's) eviews: errmann, ACIEE,, 19; gan, ACIEE, 7, 768 Key initial discoveries: lky C's are stable: duengo, JAC, 1991, 361. Useful as ligands: errmann, ACIEE, 1995, 371 Kt, a or (T) Characteristics: eutral, e- donor trong σ-donor (similar to phosphine) Weak π acceptor odular (C) complexes: often air stable thermally and hydrolytically stable e- rich <A CrLn e (usually not isolated) >.1A Little backbonding - similar to olefin see Bielawski, JAC, 6, 1651 ynthesis: 3 common methods (see errman review) X Δ X - X ' X ' X - X - C(Et)3 X potential for optically active ligands eady; Catalysis rganometallics: C s Applications: lefin metathesis u h (Cy)3 Grubb's nd generation catalyst Almost all d-catalyst reactions work using Cs. eck, uzuki, tille, chwald-artwig, onagashira... i, and Ir chemistry also reported. Like with phosphines, best ligand is case-dependent. Two most popular C precursors: (bulky to prevent dimer formation) ptically active versions have been made - Ies - Ir (cod)ir For asymmetric hydrogenation rgess, JAC, 1, 8878 Asymmetric metathesis Grubbs, ACIEE, 6, 7591; JAC, 6, 18 Conjugate addition oveyda, ACIEE, 7, 197 Ligand Identity Can Dictate eaction Efficiency A typical case: chwald, ACIE, 1, 71 An extreme case: awamura, JAC, 1, 19

5 eady; Catalysis rganometallics: Bond trength Conclusions: -C bond strength correlates with -C bond strength C 3 >1 o > o >3 o sp>sp >sp 3 eady; Catalysis rganometallics: Bond trength lope = 1 Exceptions: - (55 kcal too strong) - too strong in d -, -i too strong in late T s. t: eady; Catalysis rganometallics: Bond trength, neutral ligands 13 C resonance for different L s: tronger ligand uynh, rganomet. 9,

6 eady; Catalysis rganometallics ame ligand, different metal = different reactivity olefin as nucleophile Et (ir) c-c 6 11g δ- δ- e 95% see Chem ev, 835 olefin as electrophile ct C % d Cu DF/ d δ ct d δ d -d C 8 17 C 8 17 ynthesis, 198, 369 ame metal, different ligand = different reactivity electrophilic d(allyl) d II a, cat. d(h 3) δ E E h h Ac E E h Chem ev 1996, 395 E E nucleophilic d(allyl) cat. h n 3 h d h h d h δ- h 88% ACIEE, 3, 3656 eady; Catalysis rganometallics: Electronic effects d h 3 - d h 3 - C C 3 (1) Kurosawa, JAC, 198, 6996 d d Kurosawa, JAC, 1987, 6333 () d d h C 3 = tahl, JAC,, 183 h C 3 (3).5 y = 3.685x LogK 1.5 y = -.19x eq 1 eq eq ( = EDG) σ y =.53x ( = EWG) eady; Catalysis rganometallics Electron Counting and xidation tate 1. Decide what charge a ligand has. Determine # e s donated 3. Assume etal has charge equal in magnitude, opposite in charge to sum of ligands. xidation state = charge on metal 5. d e- count = #e- for neutral element charge 6. Total e- count = d e- sum of ligand electrons e- is stable # of e- (nobel gas configuration), 16 e- for square planar h 3 - h h h 1 3 = h 3 h 3 h 3 h 3 t Wilkinson's catalyst Total ligand charge = Zeise's salt Total ligand charge = - xidation state = 1 xidation state = Total metal e- = 8 Total metal e- = 8 Total ligand e- = 8 Total ligand e- = 8 Total e- count = 16 Total e- count = 16 K u oyori hydrogenation catalyst - - K t - - u - Total ligand charge = - xidation state = Total metal e- = 6 Total ligand e- = 1 Total e- count = 18 6

7 eady; Catalysis rganometallics (Cy) (Cy) Ir Ir 3 CF CF (Cy (Cy 3) 3) Total ligand charge = -3 Crabtree's xidation state = 3 dehydrogenation Total metal e- = 6 catalyst Total ligand e- = 1 Total e- count = 18 Zr Brintzinger's ligand e 5 u u C 3 _ e F e 5 C Ir _ u 3 u 3 Cy 3 JAC, 3, 79 - propargylic alcohol CD: common for i and substitution e 5 C 3 hydrogenation cat (why?) Total ligand charge = -3 Cp* (Cp star) Crabtree catalyst (homogeneous xidation state = 3 hydrogenation) Total metal e- = 5 Total ligand charge = u-u bond = 1e-/u xidation state = 1 Total ligand e- = 1 Total metal e- = 8 Total e- count = 18 F6 contribution = ote: electron count same for each u Total ligand e- = 8 b/c they are equivalent Total e- count = 16 _ - Zr _ - Total ligand charge = - xidation state = Total metal e- = Total ligand e- = 16 Total e- count = 16 C 3 eady; Catalysis rganometallics eady; Catalysis rganometallics Geometries of transition metal complexes, cont. ome less common geometries Trigonal bipyramidal quare pyramidal C C C C C ote both are L5, 18ecomplexes of d8 metals t- i Tf t- Tf- asymmetric aldol catalyst evans, Jacs, 3, 876 Bent giant phosphine precludes th ligand Linear common for Cu, Ag and Au Au h 3 d Br artwig, Jacs,, 936 For a list of geometry by metal and oxidations state, see Jeffrey oore's web site: 7

useful reference, and fun for the whole family: Web page for Jeffrey. oore (U.

8 eady; Catalysis rganometallics: xidation tates Transition metals are such good catalysts because they can change oxidation states: eady; Catalysis rganometallics: xidation tates A useful reference, and fun for the whole family: Web page for Jeffrey. oore (U. Illinois, chemistry) Under the periodic table link I stole the next 3 slides!!! 8

9 9

Chem 634. Introduction to Transition Metal Catalysis. Reading: Heg Ch 1 2 CS-B 7.1, , 11.3 Grossman Ch 6

Chem 634. Introduction to Transition Metal Catalysis. Reading: Heg Ch 1 2 CS-B 7.1, , 11.3 Grossman Ch 6 Chem 634 Introduction to Transition etal Catalysis eading: eg Ch 1 2 CS-B 7.1, 8.2 8.3, 11.3 Grossman Ch 6 Announcements Problem Set 1 due Thurs, 9/24 at beginning of class ffice our: Wed, 10:30-12, 220