Synthesis of Organometallic Compounds

1
Synthesis of Organometallic Compounds

• Advanced Inorganic Chemistry 92/2

2
Ruthenium Complexes

• Recently, the chemistry of ruthenium complexes
  has been extensively explored.
• less application in organic synthesis than
  palladium compounds, probably because their
  chemistry is more complicated.

3
Ruthenium Complexes

• Ruthenium complexes generally have 5- or
  6-coordinated geometry and their oxidation state
  can vary between -2 to 6.
• This complexity, however, leads to many
  interesting reactions and further developments in
  this field are expected.

4
Ruthenium Complexes

• A wide variety of organoruthenium complexes is
  known.
• They can be roughly divided into 4 groups
  according to their supporting ligands.

5
1. Ru3(CO)12

• Carbonyl complexes which are generally derived
  from Ru3(CO)12.
• Air stable compound, easy to handle
• The precursor of an active catalyst for reduction
  of nitro groups, CH bond activation or
  carbonylation.

6
2. Ruthenium complexes with tertiary phosphine
ligands

• RuCl2L4, RuHClL4, or RuH2L4
• useful for organic synthesis, catalytic
  reactions, asymmetric reactions.

7
3. Cyclopentadienyl complexes

• Cyclopentadienyl and pentamethylcyclopentadienyl
  ligands effectively stabilize alkyl-ruthenium
  bonds, whereas in phosphine complexes the alkyl
  group tends to undergo b-hydrogen elimination.

8
Ruthenium complexes having arenes or dienes

• Low valent ruthenium starting materials via
  replacement of arene or diene ligands
• Catalysts for olefin dimerization, hydrogenation
  of arenes, or CC bond cleavage reaction.

9
Preparation of these ruthenium complexes

• RuCl3.3H2O and Ru3(CO)12
• They are relatively inexpensive and stable
  against oxygen.

10
Dichlororuthenium Complexes

• RuCl2(PPh3)3
• Coordinatively unsaturated.
• Agostic C-H bond
• A common Ru precursor

11
Dichlororuthenium complexes

• Dichlororuthenium complexes are formed by the
  reduction of RuCl3.3H2O in the presence of the
  ligand.
• RuCl2(PPh3)3 is obtained by treatment of
  RuCl3.3H2O with an excess of PPh3 in methanol as
  air-stable shiny black crystals.
• Reaction of RuCl3.3H2O with PRR2 or PR2R (R
  phenyl, R alkyl) gives cationic dinuclear
  complexes Ru2Cl3(PRnR3-n)6Cl under similar
  conditions.

12
RuCl2(PPh3)3

• The X-ray crystallography of RuCl2(PPh3)3 showed
  that it has a distorted octahedral geometry with
  a vacant site which is occupied by an agostic
  proton of a phenyl group.

13
Reactivities of RuCl2(PPh3)3
14
N-Alkylation of Amines by Primary Alcohols

• RuCl2(PPh3)3 or RuCl3.3H2O/P(OBu)3 effectively
  catalyze the N-alkylation of aromatic amines.
• N-alkylation of aliphatic amines with a primary
  alcohol is carried out in high yield by the use
  of RuH2(PPh3)4 as catalyst.

15
Preparation of heterocycles
N-alkyl piperidine
pyrrolidine
pyrrole
16
Oxidation of Amines, Amides, and Diols

• RuCl2(PPh3)3 is also a catalyst for the oxidation
  of nitriles, amides and lactams under moderate
  conditions.

17
A coordinatively unsaturated 16e- ruthenium(0)
complex

• Reduction of RuCl2(CO)2(PtBu2Me)2 with magnesium
  affords an isolable 16e ruthenium(0) complex
  Ru(CO)2(PtBu2Me)2.
• Highly reactive toward hydrogen, acetylenes and
  phosphines to give coordinatively saturated
  complexes.

Trans phosphines Two COs are bent.
18
RuHCl(CO)(PPh3)3

• Formed by the reduction of RuCl3.3H2O with
  alcohol in the presence of tertiary phosphines.
• Similarly prepared as Vaska's complex,
  IrCl(CO)(PPh3)2
• Where does the CO ligand come from?
• Mechansim?
• Stereochemistry Cl trans to CO

19

• Recent developments

20
C-H Bond activation

• The generation of coordinatively unsaturated
  species play an important role.
• These species are usually produced by thermal or
  photo-mediated reductive elimination of
  dihydrogen, alkanes, alkenes or arenes.

21

• Mechanistic expect

22
Dihydridoruthenium Complexes

• Dihydridoruthenum complexes are reported to be
  catalysts for either the direct or transfer
  hydrogenation of olefins.
• Ruthenium hydride complexes are also catalysts
  for organic reactions such as the coupling
  reaction of alkenes with terminal alkynes, the 2
  2 cycloaddition of norbornene with alkynes,
  Tishchenko-type reactions, and the catalytic
  insertion of olefins into the ortho CH bond of
  aromatic ketones.

23
Preparation of RuH2(PPh3)4

• RuH2(PPh3)4 is prepared by the reaction of
  RuCl2(PPh3)3 with NaBH4 in the presence of PPh3
  in refluxing methanol.
• Or by the direct reaction of RuCl3.3H2O with
  NaBH4 and PPh3 in refluxing ethanol.
• It is formed as an off-yellow powder and should
  be kept under argon, not nitrogen, because a PPh3
  ligand is readily replaced by dinitrogen.

24
Reactivities of RuH2(PPh3)4
25
Chemoselective aldol reactions
26
Coupling reactions of acetylenes with dienes

• The reaction of l-octyne with 1,3-butadiene
  catalyzed by RuH2(PBu3)4 affords 2-
  dodecen-5-yne. A similar coupling reaction is
  also catalyzed by RuCl(C5H5)(C8H12).

Mechanism?
27
Tishchenko-type dimerization.

• RuH2(PPh3)4 reacts with aldehydes to give esters
  via Tishchenko-type dimerization. For example,
  benzaldehyde is converted to benzyl benzoate by
  RuH2(PPh3)4. This reaction involves CH bond
  activation of the formyl proton followed by
  formation of a ruthenium acyl alkoxide complex
  Ru(OCH2Ph)(COPh)(PPh3)4.

Mechanism?
28
RuH2(CO)(PPh3)3 catalyze olefin coupling
reactions of aromatic ketones via CH bond
activation
29
A possible intermediate in theolefin coupling rea
ction ofaromatic ketone catalyzed byRuH2(CO)(PPh
3)3. Other ligandsare omitted.
30
Reactivities of RuH2(PPh3)4
31
Catalytic reactions
Intermediate
32
Ruthenium Complexes with Chiral Ligand

• the chemistry of ruthenium complexes with the
  chiral ligands BINAP and PYBOX are described.

Atropisomers of the BINAP Ligand
33
(No Transcript)
34
Ruthenium Complexes Having Cyclopentadienyl
Ligands

• Ruthenocene is relatively un-reactive

• The dinuclear complex RuCl2(C5Me5)2 is a
  versatile reagent.
• prepared by the reaction of RuCl3.3H2O with
  pentamethylcyclopentadiene in ethanol

35
(No Transcript)
36
Treatment of Ru2H4(C5Me5)2 with ethylene results
in the formation of a divinyl(ethylene)diruthenium
complex under ambient conditions. This is an
interesting reaction because there are few
examples of vinylic CH bond activation with
metal polyhydride complexes.
37
A unique reaction probably proceeds via an
acetylide-vinylidene intermediate.
38
Ruthenium Complexes with Arene/Diene Ligands

• Ru(cod)(cot) is prepared by the reduction of
  RuCl3.3H2O with zinc powder in the presence of
  1,5-cyclooctadiene in methanol 192.

It is used in several catalytic reactions and as
a convenient precursor to various zero- or
multi-valent ruthenium complexes
39
Reactivities of Ru(cod)(cot)
40

• Dimerization of NBD

41
For example, ruthenium complexes sometimes show
ambiphilic reactivity
allyl carbonate
42

• Ruthenium-catalyzed allylations are often show
  quite different reactivities and selectivities
  from those of palladium-catalyzed allylations.

The detailed mechanism of the regiocontrolling
step is still unclear.
43
Useful Ru precursors
44
(No Transcript)