Literature Seminar

080220 Kenzo YAMATSUGU (D1)π-alkyne metal complex and vinylidene metal complex
in organic synthesis
0. Introduction
R

R' = H

R'[M]
R[M]
π-alkyne metal complex

vinylidene metal complex

Recently, electrophilic activation of alkynes through π-alkyne complex formation has been studied extensively.
ex. Au(I), Au(III), Pt(II), Ru(II), and so on.
More recently, there has been a large number of reactions involving metal vinylidenes as catalytic species.
ex. Cr0, Mn0, W0, Ru(II), Rh(I), Fe(II), and so on.
In this literature seminar, mainly three reports will be introduced in full detail.

Contents
1. W(CO)5(thf)-catalyzed generation of carbonyl ylide and tandem reaction with alkene
2. CpRu+L3-catalyzed anti-Markovnikov hydration of terminal alkynes
3. Control of π-alkyne and vinylidene complex

1. W(CO)5(thf)-catalyzed generation of carbonyl ylide and tandem reaction with alkene
generally studied reactions involving π-alkyne metal complex

*X
M

RX

X

X
R

R

X = OHNH2etc

M

X

M

X
RR

For review of Pt, Au, see ; Angew. Chem. Int. Ed. 2007, 46, 3410.
other metals ; J. Org. Chem. 2007, 72, 7817.

RX=ONHetc

M
1st. report. (Pd) (pyrrole)
Utimoto et al. Tetrahedron Lett. 1981, 22, 4277.

Iwasawa et al. JACS 2001, 123, 5814. (commun.)
JACS 2005, 125, 2709. (full)x-ray

1 / 13

+ postulated mechanism

Scheme 6+ Tungsten-containing carbonyl ylide+ Minute mechanistic consideration is presented below

Table 1R3+ Not only ketene acetal but also alkyl vinyl ether is applicableentry 7, 8+ aryl aldehyde is applicableentry 8+ internal alkyne is applicableNot all the alkenes have a suitable carbon-hydrogen bond for tungsten-carbenoid intermediate to insert.
It is well known that metal-carbenoid can readily insert into a silicon-hydrogen bond of silanes.

+ silicon trapping of intermediate tungsten-carbenoid

H O
H+HH

NOEO

Pr

H5g
17 % yield2 / 13

Table 2. Reaction of 1d with Various Alkenes in the Presence of Silanesa

entry 1 - 4
large silane : C-H insertion occurred predominantly.
entry 5
Small EtMe2SiH was effective.
entry 6 - 9silyl enol ether, allyl silane, styrene were applicable.
1-octene and methyl acrylate : No Rxn.

expansion of substrate scope to ones having no C-H bond to insert+ To gain insight into the reactivity of the tungsten-containing carbonyl ylide
Ab initio calculation(lan12dz basis set was used for the W atom, and the 6-31 basis sets were used for the other atoms)*LUMO of ylide A is considerably lower than that of ylide D.
(probably because of the strong electron-withdrawing natureof the tungsten carbonyl)+ Mechanistic consideration
1. in the presence of H2O

cf. Shceme 6 in page 2
endo-attack

normal carbonyl ylide :react with electron deficient alkene preferentiallytungsten-containing ylide :react with electron rich alkene preferentially

isolation of alkylidene complex

exo-attack

Uemura et al. J. Organomet. Chem. 2002, 645, 228.
12b was directrly
observed in NMR.

In the presence of H2O instead of alkene,
13b was obtained probably through 11b.

3 / 13

3. in the absence of alkene & H2O
vinylidene-metal complex

Scheme 1
2 was isolated by silica gel chromatography and characterized by
13
C NMR (typical carbene carbon δ = 230.9 ppm) andelemental analysis.

In the absence of alkene and H2O,
2 was obtained probably through metalvinylidene
intermediate.
Iwasawa et al. JACS 2000, 122, 10226.

+ Dynamic equilibria to account for these experimental results+ Path (i) and (ii) would be faster than path (iii).
+ Path (i) and path (ii) would be under rapid equilibrium.

exo-attack+ Therefore, in the presence of a reagent capable of trapping
intermediate 11 or 7 (H2O or alkene), the reaction proceeds
through path (i) or (ii).
+ In the absence of such trapping reagents, vinylidene complex
2 would form slowly and to give 3 through an irreversible
electrocyclization.

endo-attack

4 / 13

+ Observation of the tungsten-containing carbonyl ylide
1. 1H NMR time course*in the absence of alkene
1.7 eq.

* New species have much lower electron density thanthe SM ketone* X disappeared and 3 c became a major product after 3.5 h.
SM ketone* singlet at 8.92 ppm

envisioned three X

δ 184.6 ppm

matched with isolated 3c
see Scheme 1

2. HMBCδ 184.6 ppm (13C) : correlation with H(e) and H(f)C3

1.7 eq.

HMBC−40 oC

C 3 : correlation with singlet at δ 8.92 ppm (1H) = H(a)30 minX would be endo-cyclized carbonyl ylide 7 c
3. 13C-183W coupling(20% 13C)

* 183W has 1/2 nuclear spin (other isotopes of tungsten have no nulear spin)* A set of satelite peaks should be observed in 13C NMR spectrum at the carbon directly bonded to tungsten.
* 76.4 Hz (1JC-W) (C1 - W) in 13C NMR spectrum and 17.2 Hz (2JC-H) (Ha - C1) in 1H NMR spectrum were observed.
: direct bonding between C1 and W

5 / 13

+ Other application
HHPhN

OTBS

W(CO)6, hνOEtToluene

PhPhN

NO

W(CO)5
Iwasawa et al. JACS 2002, 124, 11592.

Tungsten-containing azomethine ylide

2. CpRu+L3-catalyzed anti-Markovnikov hydration of terminal alkynes* general features of metal vinylidene complexRH

R

[M]
II000

R'R' = H[M][M]IM : Ru , Cr ,Mo , W , Rh , etc..

Rπ-alkyne metal complex

vinylidene metal complex

Three types of reactions are commonly investigated.
review ; Chem. Asian J. 2008, 3, 164.

1. nucleophilic addition to the α-carbon atom
1st example of a metal vinylidene complex as a catalytic species
2% [Ru3(CO)12]
CO2 (50 atom)

BuO
O
RuLn

toluene, 140 oC
20 h, y. 36%

Et2NH

BuO

Bu

Et2N

O

O
NEt2

NEt2
6O

Bu

Bu:

5:

1

Y. Sasaki, P. H. Dixneuf J. Chem. Soc. Chem. Commun. 1986, 790.
other nucleophiles ; carboxylic acid, alcohol, epoxide, carbonyl, thiol, amine, phosphine, enolate, enamine

2. [1,2]-alkyl migration from the metal center to the α-carbon atom
alkyne dimerization
1% [Ru(-C CTMS){P(CH2CH2PPh2)3}]BPh4

LL

TMS

TMS

Ru

TMS
THF, reflux, 6h, y. 90%TMS

TMS

TMS

TMS
7:93

Bianchini et al. JACS 1991, 113, 5453.
For earlier work by Yamazaki, see ; J. Chem. Soc. Chem. Commun. 1976, 841.

3. Pericyclic reactions
1st example of 6π electrocyclization onto a catalytic vinylidene intermediateOOO

4% [RuCl2(p-cymene)(PPh3)]
CH2Cl2, reflux, 10 h, y. 89%RuLn

C. A. Merlic, M. E. Pauly JACS 1996, 118, 11319.

6 / 13

*CpRu+L3-catalyzed anti-Markovnikov hydration of terminal alkynes
anti-Markovnikov hydration
aldehyde

H2O

[M]
RRHR

H

[M]

H2O
Markovnikov hydration=methyl ketone

acid, mercury, etc..
known

1st report : M. Tokunaga, Y. Wakatsuki Angew. Chem. Int. Ed. 1998, 37, 2867.
* By tuning phosphine ligand, they could produce aldehyde or ketone.
* not so good selectivity* high catalyst loading* Phenylacetylene, tert-butylacetylene were not applicable.

EtOH or 2-propanol

Improvement (use of RuCpCl(dppm))
Wakatsuki et al. Org. Lett. 2001, 3, 735.

proposed bifunctional role

Grotjahn et al. Angew. Chem. Int. Ed. 2001, 40, 3884.
JACS 2004, 126, 12232.
Chem. Euro. J. 2005, 11, 7146.
1st attempt

wet

wet

21, 22 : The same ligand is coordinated in two different environments, one chelating, the other not.
The reaction with alkyne didn't afford aldehyde, but 23 and 24. (2D NMR and X-ray)

7 / 13

* sterical environment tuning

5 eq.

RuCp(CH3CN)OTf

δ = 9.1 ppm(2H, brs)+ To hinder the direct attack of nitrogen at vinylidene carbon,
bulky substituent was introduced.
+ H2O was incorporated.
+ Two hydrogen bond* scope and limitations

NN
1

entry 3, 4, 5
tert-Butylacetylene and phenylacetylene were applicable
although sluggish reaction
entry 8Nitrile didn't inhibit the reaction(Wakatsuki catalyst was inhibited by nitrile.)
entry 11 and 12
Proper placement of imidazole is crucial for efficient catalysis.

8 / 13

* Postulated mechanism

H2O has to be exchanged to alkyne substrate.
(Two phosphine seemed to stay on the metal
because added phosphine did not change thehydration rate)

Imidazole+ facilitate conversion from B to C ?
+ activate H2O ? (C to D)* facilitate conversion from D to E via F (proton shuttle) ?
* stabilize the catalyst by hydrogen bonding ?

so far, not clear*next report* JACS 2004, 126, 12232.

reduced hydrogen bonding to open catalytically
active site for alkyne bindingentry 3, 4, 5
Phenylacetylene and electron-rich arylacetylene
were applicable.
entry 6
Nitrile inhibited the reaction.
entry 10in situ deprotection

9 / 13

Breit et al. Angew. Chem. Int. Ed. 2006, 45, 1599.

6-DPPAP
concept
adenine / thymine in DNA
mimicaminopyridine / isoquinolone
through hydrogen bonding

3-DPICon* Search for appropriate catalyst
LigandHO
PivPh2PN
HO

6-DPPon

NNN

PPh2

PPh2

H

6-DPPAP

3-DPICon

entry 6 and 7
Heterodimer is responsible for the result.

*characterization of catalyst 5+ 31P NMR : two doublet (around 50 Hz, 2J(P-P) = 35.9 Hz)+ 1H NMR : substantial shift of NH signals of two ligands tolower field+ X-ray

10 / 13

* Scope and limitations
Ocatalyst 5, H2O (5 eq.)

RR
acetone, 120 oC

H

The origin of the catalytic activity remains unknown.
Hydrogen bonding network incorporates H2O so that addition proceeds readily and regioselectively ?

11 / 13

3. Control of π-alyne and vinylidene complex

Iwasawa et al. JACS 2008, 130, 802.

RH

dynamic control

[M]
R[M]
π-alkyne metal complex

vinylidene metal complex* condition optimization

Addition of tert-amine controled the product distribution.
The use of N-Ms instead of N-Ts improved the yield.

* scope and limitations

entry 5 and 6
In the case of alkyl substituted diene, small amounts of 2 wereobtained even in the amine-promoted reaction.

12 / 13* deuterium- and 13C-labeling experiments
to support the proposed mechanism* proposed mechanism

without D2O : 46% D incorporation
A to CThe presence of amine would facilitate the formation ofvinylidene complex
E to F
1,2-alkyl migration aided by electron donation from nitrogenF* Effect of amine
Similar effect of amine has been suggested.

PhPh
W(CO)5(thf) (3 eq.)

O

Ph

O

THF, r.t., 24 h[W]

OO

[W]

[W]

Ph

Ph

In the presence of Et3N : y. 72%
In the absence of Et3N : No Rxn.

OH
O

O
[Rh(C2H2)2Cl]2 (5 mol %)P(4-F-C6H4)3 (25 mol %)N

DMF, 24 hO

H

O

Ph

Ph

Ph

Ph

Ohe and Uemura et al. JACS 2002, 124, 526.

Ph
N

O
[Rh]

H

Ph
N

O[Rh]

N[Rh]

PhO

N

In the presence of DABCO : y. 95%
In the absence of DABCO : y. 30%

Lee et al. JACS 2006, 128, 6336.

13 / 13