M Strategies to introduce Free coordination sites

Transcription

1 2. emilability u d h eductive limination 3. eighboring group ffect o Strategies to introduce Free coordination sites F 3 C Symmetric estriction Steric estriction F 3 C CF 3 CF 3 Dynamic one air h 5. Cr The Steric Complete estriction h Indenyl ffect 6. Cr 8. Cy 3 u Cy 3 Co 1 Agostic Interactions h 7. seudo-jahn-teller-ffect

2 Steric restrictions e - cat. 2 3 o o +, e , e - 2 o +, e - o +, e - o +, e - o +, e o 2

3 Symmetric restrictions e - 1. cat. 15e-complex rather than 17e-complex o one lone pair is non-bonding! 2 3 3

4 lectron-transfer-catalysis 1. lectronic restrictions C 3 C 3 18e-Complex 3 CC h 3 slow h 3 18e-Complex o =0.19V o =0.52V C 3 C 3 17e-Complex 3 CC h 3 fast h 3 17e-Complex C 3 3 CC The reaction works catalytically, because h 3 is a stronger π-acid than C 3 C. Thus, the substituted complex becomes more precious than the starting compound. 4

5 lectronic restrictions lectron-transfer-catalysis 1. 18e-Complex o h 3 slow o h 3 18e-Complex 17e-Complex o -, +h 3 o h 3 17e-Complex o 5

6 lectronic restrictions 1. o o h 3 o o h 3 o o h 3 o o h 3 A B - A - B A B + A + B metal center in B more electron rich than in A metal center in B less electron rich than in A C 3 C 3 C C 3 C 3 C 3 C C 3 3 CC h 3 A B - h 3 3 CC A - B 3 CC h 3 CC 3 h 3 A B + A + B 6

7 eductive elimination 2. II u C h cat. - h C u 0 u C u C 3 C ed l x Add (C-activation) C u u C α--insertion 7

8 8 cat. C n d C 3 Solv d C 3 d C Solv d C d d d d C d C 3. hemilability

9 Temporary free Coordination Sites (emilabile igands) 3. lectronically (enthalpically): introduction of a -D (hart-soft) or (soft-hard) interaction rather than (hard-hard) or (soft-soft) labile or weak D ntropically: ing size smaller or larger than 5 D stable (or inert) Sterically (enthalpically): introduction of large substituents at D (tbu, Adamantyl) 9

10 Temporary free Coordination Sites (- cis to ) etal hydrides insert in contrast to -Alkyls reversibly! etal hydrides often substitute easier than other similar complexes. They are sensitive to traces of radicals present, because those start a radical reaction by homolysis of the - bond! 4. egel 6 - ad

11 11 18e-complex 18e-complex 18e-complex 18e-complex 16e-complex 16e-complex 16e-complex 16e-complex 18e-complex 16e-complex 4. eighboring group effect

12 Formally an 18e-complex Dynamic lone pair C 1 C 3 5. C 2 C 4 F 3 C F 3 C o CF 3 CF 3 e 3 F 3 C F 3 C o e 3 CF 3 CF 3 F 3 C F 3 C o CF 3 CF 3 cat. C 1 C 3 C 2 C 4 18e-Complex 18e-Complex 18e-Complex e-Complex 18e-Complex 18e-Complex h 3 -h 3 + acemization 12

13 Characterization of metal carbonyl complexes to classic metal-π-donation predominates nonclassic 70 igand-σ-donation predominates 13

14 Characterization of metal nitrosyl complexes to to 74 igand-π-donation predominates igand-σ-donation predominates 14

15 Indenyl effect 6. 18e-complex 18e-complex 16e-complex 2 'C C 2 t h 3 u h 3 h 3 2 C 2 t u - 2 -h 3 Ct h 3 h 3 u h 3 h 3 Ct 2 'C cat. Ct 2 C 2 t h 3 -h 3 u h 3 h 3-2 u C 2 t 2 C 2 t h 3 h 3 18e-complex 18e-complex 15

16 Temporary free Coordination Sites (Charged olyenes) 6. lectron-withdrawing and rearomatizing substituents, annelated to the charged olyene, facilitate the substitution at the etal Center (Indenyl-ffect)! 18e-Komplex 18e-Komplex 18e-Komplex h + h 3 h h + h3 h 3 3 C C 3 2 h C C 3 C 3 > > > > > > C 3 C 3 3 C C 3 3 C C 3 C 3 16

17 Indenyl effect 6. 17

18 seudo-jahn-teller effect 7. 3 X 3 h h 3 3 X d d X d X d X base cat. h 3 d X h 3 d X base*x D 4h C 2v D 3h 18

19 7. Desymmetrization effects Coupling of electronic and vibrational structure (Vibronic) ffect Jahn-Teller 1. order Jahn-Teller 2. order seudo-jahn-teller enner-teller Γ a Γ c Γ b Γ b Γ a Γ c Γ a Γ c Γ c Γ b Γ a Γ c Γ b 19

20 idden Coordination Sites (Jahn-Teller-ffect) 7. D 4h C 2v D 3h - igh T 31 - ow T a b 29 20

21 olecular vibration Dynamic rocess Chemical exchange processes olecular otation acroscopic transport processes slow s ms µs ns ps fs fast Spectroscopic Finding slow exchange ine wideperturbation fast exchange The time scale ongitudinal agnetization exchange elaxation time scale Spectral time scale armortime scale 21

22 seudo-jahn-teller effect 7. h 3 h 3 h 3 h h 3 h 3 h h 3 22

23 18e-Complexes 7. seudo-jahn-teller effect e h seudo-jahn-teller-ffect Jahn-Teller-ffekt in case bei of dd 6 6 -low-spin C 4v a e a e Verlust oss of der + + Stereokontrolle control + e + D 3h a e e e 23

24 seudo-jahn-teller effect 7. T- or Y- shape? π-donors maximize the angle to each other σ-donors and π-aceptors prefer 90 and 180 angles to each other 24

25 Agostic interactions n 8. Zr Zr Zr cat. X= Y=C, B, Si X=B 2e-3c X Y 4e-3c Y=C,,, F X= X=,, F n agostic IA 2e-3c-Bondung anagostic IA ydrogen-bonding IA eason: mainly orbital interaction (IA) eason: mainly electrostatic interanction (IA) Y X X Y VB: Y Y Y B X Y B δ δ δ X Y : π-ückbindung (erfordert d n - Konfiguration) σ-inbindung (immer möglich) bindend nicht-bindend anti-bindend Co B B h i Br Br agostische 2e-3c-Bindung anagostische asserstoffbrücken- h 2 25

26 idden free Coordination Sites (agostic ydrogens) 8. 16e-Complex 16e-Complex 12e-Complex u h h Ti!!! h h h h u quasi-18e-complex quasi-14e-complex Ti quasi-18e-complex 26

27 idden free Coordination Sites (agostic ydrogens, types) 8. α-agostic β-agostic γ-agostic γ α α β α D β α e 2 C Ti e 2 e 2 Ti e 2 h 3 h 2 u h 3 27

28 8. Agostic interaction (experim. evidence) ule: ecessary condition for an agostic interaction are electronic and coordinative undersaturation and steric availability of the metal center. xidative addition Agostic interaction o interaction agostic C C anagostic (preagostic) -bond X Bonding 3c-2e 3c-4e C angle 90 to to to 180 δ () upfield shift downfield shift downfield shift d 1.8 to 2.2 Å 2.3 to 2.9 Å 2.65 to 3.5 Å 1 J Coupling yes no 28

29 Agostic Interactions (influences) 8. Charge on the metal Sterics on the ligand Interaction ~ overlapp/energy gap C- C- ositive charge at the metal center causes orbital contraction, which worsens the overlap abilities of this orbital. The metal center becomes more electrophile. The ligand to metal σ-bonding is stronger, while The metal to ligand π-back bonding is weaker. (The energy of the orbitals at the metal center is lowered by positive charge. In general positive charge at the metal center weakens the agostic interaction (important with Ziegler/atta-Chemistry). rbital polarisation by trans-ligand C- C- Sterically demanding substituents educe the mobility of the C-bond and freezes this bond. In general, this is postive for an agostic interaction. verlap properties and energies of the orbitals are not influenced. Strong σ-donors polarise the towards them, and the U away from them. This is advantageous for the ligand to metal σ-bond part of the agostic interaction, however the U is raised energetically, which increases the energy gap between -C-- rbitals and etal-u-rbitals. This weakens the interaction. Strong π-aczeptors polarise the towards then, and the U away from them. This is disadvantageous for the metal to ligand π-back bonding part of the agostic ineraction. The is lowered decisively in energy, which increases the 29energy gap between U-C--ribtals and etal-- rbitals and, thus, weakens this interaction as well.

30 30 u i-r i-r i-r i-r i-r i-r s i-r i-r i-r i-r i-r i-r u h h h u h e e u i-r i-r i-r i-r i-r i-r u Cy Cy Cy Cy Cy Cy h i-r i-r i-r i-r i-r i-r h h h h h h h u 2,-6e-h 2,-6e-h h h h h Ir h h d h h u h h Agostic Interaction or o Agostic Interaction? 8.

31 Agostic interactions 8. i-r i-r Si Ta Si Si o Si Si e Si Si e Si 1 J C = 80 z 1 J C = 110 z 1 J C = 109 z 1 J C = 159 z 1 J C2 = 124 z 31

32 The Complete Coupling of Coordination Sites t-c Ct Ct Ct Decrease of Coordination number Generation of a idden Coordination Site 2 Kubas-Complex 32