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Catalysis > Organometallic Structures > Flashcards

Organometallic Structures Flashcards

1
Q

Electron Counting

A
  1. Count Number of anionic ligands
  2. Determine Oxidation state of Metal
  3. Count donor electrons (mindful of haptic bonding)
  4. sum valence electrons and d electrons
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2
Q

18 electron rule exceptions

A
  1. Steric exceptions
    - high oxidation or early transition
    - small radii increases sterics of ligands
    - steric energy prevents coordination of more ligands to reach 18 electrons
  2. Electronic exceptions
    - late transition or low oxidation
    - high atomic number means stable d orbitals
    - dz2 no longer bonds
    - d8 froms square planar
    - d10 froms trigonal planar
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3
Q

Metal Bonding

A
  1. Assume complex achieves 18 electrons
  2. count valence electrons for each metal
  3. if less tahn 18 add metal metal bonds

one metal bond equals one electron to each metal centre

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4
Q

Molecular orbitals of Geometries

A
  1. Octahedral
    - ligands approach along axes
    - eg bonding sigma
    - t2g non-bonding sigma
  2. Square planar
    - ligands approach along xy axes
    - dx2-y2 bonding
    - dz2 interacts
    - t2g non bonding
  3. Tetrahedral
    - ligands approach in between axes
    - t2g bonding sigma
    - eg non-bonding sigma
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5
Q

Square Planar or Tetrahedral

A

Depends on Electronic configuration then sterics. Config with lowest energy is preferred even if higher sterics.

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6
Q

pi acceptors and pi donors

A
  1. pi donors
    - have filled p orbitals
    - donate electron density via pi interactions
    - eg amines, halides, oxygen
  2. pi acceptors
    - have vacant p orbitals
    - accept electron density from metal d orbitals
    - eg CO, phosphines, alkenes
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7
Q

pi backbonding

A

metal donates electron density into π* orbital of ligand.

  • weakens ligand bond (decreased frequency)
  • increases sigma donation
  • increase metal-ligand bond
  • strong sigma donors (NHC, PPh3) increase electron density and thus π backbonding
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8
Q

Hard Soft Acid Bases

A
  1. Hard
    - small radius
    - high charge density
    - non-polarisable
    - eg F, Cl, amines, O
  2. Soft
    - large
    - low charge density
    - polarisable
    - eg low valent metals, CO, R-, PPh3

like goes with like

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9
Q

Metal Carbonyl Synthesis

A
  1. Direct Ligation of unoxidised metal
  2. Reductive Carbonylation with CO gas
  3. Reductive carbonylation with organic carbonyl
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10
Q

Metal Phosphine Synthesis

A
  1. Coordination to unsaturated metal
  2. Coordination to low valent
  3. ligand substitution
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11
Q

Metal-Alkyl Synthesis

A
  1. Direct ligation with alkylating agent
    e. g AlMe3, SnMe4, Mao, LiMe
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12
Q

Metal-CP synthesis

A
  1. Ligand Exchange and in-situ deprotonation with metal salt
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13
Q

Metal-NHC Synthesis

A
  1. Free carbene metallation
  2. in situ deprotonation and metallation
  3. silver-NHC transmetallation
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14
Q

Substitution Mechanisms

A
  1. Associative
  2. Dissociative
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15
Q

Associative Sub Increase Rate

A
  1. decrease sterics
  2. trans effect
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16
Q

Dissociative Sub increase rate

A
  1. Increase sterics
17
Q

Oxidative Addition non-polar

A
  1. metal coordinates to bond
  2. donation into π* breaks bond
  3. coordinates cis
18
Q

Oxidative Addition Polar

A
  1. metal nucleophilic attacks electrophilic atom, breaking bond froming anion
  2. becomes electrophilic
  3. anion attacks trans due to sterics
19
Q

Oxidative Addition Factors

A
  1. Electron Density
    - donates electron density to ligand
  2. coordinatively unsaturated
20
Q

Oxidative Addition Rate

A
  1. π acceptors reduce electron density and thus rate eg CO, suppress oxidative addition
  2. sigma donors increase electron density and thus increase rate eg NHC, PPh3
21
Q

Reductive Elimination Requirements

A
  1. 2 ligands cis for orbital overlap
  2. product makes sense
22
Q

Reductive elim factors

A
  1. locked cis means faster rate
  2. low valent metals are unstable by reduction
23
Q

Migration Reactions

A
  1. Alkene insertion to form alkyl ligand
  2. CO insertion to from carbonyl
24
Q

Hydride Elimination Requirements

A
  1. Beta hydrogen present
  2. M-C-C-H in syn coplanar
  3. adjacent vacant/psuedo-vacant site
    (4. Metal has d electron density to cleave C-H)
25
Q

Rules for polyenes

A
  1. Even before odd
  2. Open before closed (after even or odd)

(shorter before longer)

(least anionic/most electrophilic carbon/largest orbitals)

26
Q

Direct CO ligation

A

CO ligates to unoxidised metal

27
Q

Reductive carbonylation with CO gas

A
  1. coordination to metal salt
  2. reduction with reducing agent e.g. Al, NaOMe
28
Q

Reductive Carbonylation with organic carbonyl

A
  1. oxidative addition of acyl halide
  2. reverse migration of alkyl
  3. reductive elimination of R-X
29
Q

Metallation of Preformed Carbene

A
  1. form carbene by deprotonation
  2. Metallation
30
Q

In-situ deprotonation metallation of NHC

A

requires metal with basic ligands

e.g OAc

31
Q

Silver-NHC transmetallation

A

labile Ag-NHC bond due to high d electron density

transfers readily to other metals

32
Q

Complex geometry factors

A

Coordination number

electronics

sterics

(metal oxidation state, ligands, sterics)

33
Q

Dative vs Covalent Ligands

A

Dative donates 2 electrons (neutral)

covalent donates 1 electron (anionic)

34
Q

Determining anionic neutral

A

put both dative bond electrons on ligand

determine electron configuration of ligand

35
Q

Enhancing insertion rate

A
  1. increase steric bulk

insertion decreases coordination

  1. lewis acid additives/metals e.g. AlCl3

stabilises metal acyl transition

  1. electrophilic metals

withdraw electron from carbon activating electrophilicity

Catalysis (6 decks)

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