Acid-free nickel catalyst for stereo- and regioselective hydrophosphorylation of alkynes: Synthetic procedure and combined experimental and theoretical mechanistic study

Article abstract of DOI:10.1002/adsc.201000606

The nickel catalyst prepared in situ from nickel bis(acetylacetonate) [Ni(acac)₂] precursor and bis(diphenylphosphino)ethane (DPPE) ligand has shown excellent performance in the hydrophosphorylation of alkynes. Markovnikov-type regioselective a

Full text of DOI:10.1002/adsc.201000606

FULL PAPERS
DOI: 10.1002/adsc.201000606
Acid-Free Nickel Catalyst for Stereo- and Regioselective
Hydrophosphorylation of Alkynes: Synthetic Procedure and
Combined Experimental and Theoretical Mechanistic Study
Valentine P. Ananikov,a,* Levon L. Khemchyan,a Irina P. Beletskaya,b,*
and Zoya A. Starikovac
a
Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, Moscow 119991, Russia
Fax : (+7)-499-135-5328; e-mail: val@ioc.ac.ru
Lomonosov Moscow State University, Chemistry Department, Vorob’evy gory, Moscow 119899, Russia
b
Fax : (+7)-495-939-3618; e-mail: beletska@org.chem.msu.ru
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
c
Vavilova str. 28, Moscow, 119991, Russia
Received: July 29, 2010; Published online: November 17, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000606.
Abstract: The nickel catalyst prepared in situ from developed catalytic system with up to 99% yield.
ꢀ
nickel bis(acetylacetonate) [Ni
G
bis(diphenylphosphino)ethane (DPPE) ligand has formation were revealed by experimental (NMR,
shown excellent performance in the hydrophosphory- ESI-MS, X-ray) and theoretical (density functional
lation of alkynes. Markovnikov-type regioselective calculations) studies. Two different pathways of the
addition to terminal alkynes and stereoselective ad- alkyne insertion in the coordination sphere of the
dition to internal alkynes were carried out with high metal are reported for the first time.
selectivity without an acidic co-catalyst (in contrast
to the palladium/acid catalytic system). Various H- Keywords: alkynes; homogeneous catalysis; nickel
phosphonates and alkynes reacted smoothly in the complexes; phosphorylation; selectivity
ꢀ
Introduction
The addition of P H bonds to unsaturated species
is a topic of special interest as far as the synthesized
Transition metal-catalyzed addition reactions fulfill organic phosphorus derivatives are in demand as li-
green chemistry requirements in developing sustaina- gands in catalysis,[4] as biologically active com-
ble synthetic procedures.[1] The addition reaction is pounds,[5,6] as useful derivatives in nucleic acid
characterized with 100% atom efficiency and maxi- chemistry,[7] as versatile reagents in synthesis,[8] as
mizes the incorporation of all reactants into the prod- building blocks in polymer sciences,[9] as well as sever-
ucts. Catalytic transformation ensures high selectivity al material science applications including fuel cell
of the synthesis and avoids the formation of by-prod- membranes, optical materials and flame retard-
ucts.
The development of catalytic systems for carrying
out hydrofunctionalization of unsaturated organic rise to the studies of PACTHNUGTREN(NUG III) H and P(V) H addition
ants.[10,11]
The unique nature of the phosphorus atom gave
ꢀ
ꢀ
compounds has experienced an outstanding growth in reactions. These three- and five-valent phosphorus
recent years.[2] Addition of E H bonds to unsaturated substrates possess rather different properties in the
ꢀ
organic molecules has unambiguously proven the re- addition reactions with a strong dependence on the
markable potential of this approach for carbon-heter- nature of the substituents.[12,13,14] Particularly, the addi-
ꢀ
oatom (C E) bond formation. Several excellent cata- tion reactions operate according to different mecha-
lytic systems were reported to carry out hydroalkoxy- nistic frameworks and require special catalytic sys-
lation, hydrothiolation, hydroamination, and other ad- tems to be designed for each combination of reagents.
dition reactions.[3]
Hydrophosphination of unsaturated organic mole-
ꢀ
cules [addition of the P
(III) H bond] appears to
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Scheme 1. Alkyne hydrophosphorylation reaction towards the formation of Markovnikov product 3 (terminal alkynes), syn-
addition product 4 (internal alkynes) and possible by-products.[19]
be an actively developing area with several bright
achievements in the mechanistic studies and synthetic system for the Markovnikov-type hydrophosphoryla-
applications.[13,15]
tion of alkynes. Under optimized conditions a cheap
In the present study we report an acid-free catalytic
In contrast, the mechanistic nature of the addition and easily available Ni catalyst was found to be supe-
ꢀ
of the P(O) H bond is scarcely understood. The reac- rior for this transformation. The mechanistic study re-
tion is rather difficult to carry out with high selectivity vealed the unusual nature of the studied catalytic
ꢀ
since
a
variety of products may be formed system with two possible pathways for C P bond for-
(Scheme 1).[12] The field was pioneered by Tanaka and mation.
co-workers, who reported the catalytic Markovnikov
hydrophosphorylation of alkynes by application of
transition metal catalysts and described the effect of Results and Discussion
the Ph2P(O)OH acid.[16] Recently we have studied the
Pd/CF3COOH catalytic system for the selective hy- The performance of the catalytic reaction was evalu-
drophosphorylation of alkynes using different types of ated using the model hydrophosphorylation reaction
H-phosphonates.[17] In these catalytic systems the ad- of 1-heptyne (1a) with (i-PrO)2P(O)H (2a). The over-
dition of acid was necessary to avoid side-reactions, all selectivity was calculated as the ratio between the
without the acid poor selectivity and yields of the Markovnikov product 3a and the total amount of all
Markovnikov product were observed.
other by-products.[20] Cheap and air-stable Ni
ACHTUNGTRENNUNG(acac)2
Several disadvantages of the available catalytic sys- was chosen as a catalyst precursor and the reaction
tems were noticed. The acid could not be recycled was carried out in THF at 1008C (Scheme 2).
(waste) and, in addition, it imposed a serious draw-
back for commercial implementation,[18] as well as the and steric properties did not lead to the formation of
high cost of the palladium catalyst. product 3a (Entry 1, Table 1). Quantitative recovery
Several phosphine ligands with different electronic
Recent advances in catalytic hydrofunctionalization of starting material 2a indicated that no reaction took
encouraged us to develop a more practical catalyst place under the studied conditions. Neither did most
beyond the Pd/acid system.
of the studied chelate bidentate ligands result in the
Table 1. Ligand effect in the Ni-mediated addition of (i-PrO)2P(O)H (2a) to 1-heptyne (1a).[a]
Entry
Ligand[b]
Yield of
Unreacted
By-products
[%][c,d]
3a [%][c]
2a [%][c]
1
2
3
PPh3, P(o-MeC6H4)3, PPh2Me, PMe2Ph, PCy3, P
DPPM, DPPB, BINAP, DCPM
DPPE
G
E
(O-i-Pr)3
0
0
14
100
100
84
0
0
2
[a]
1 mmol of 1a, 1 mmol of 2a, 3 mol% of Ni
1008C, 3 h.
DPPM: bis(diphenylphosphino)methane; DPPB: 1,4-bis(diphenylphosphino)butane; BINAP: 2,2’-bis(diphenylphos-
ACHTUNGTERN(NUGN acac)2, 12 mol% of ligand (6 mol% of bidentate ligand), 0.5 mL of THF,
[b]
ACHTUNGTRENNUNGphino)-1,1’-binaphthyl; DCPM: bis(dicyclohexylphosphino)methane; DPPE: 1,2-bis(diphenylphosphino)ethane.
[c]
[d]
Determined by 31P NMR.
Overall amount of phosphorus-containing by-products.
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Acid-Free Nickel Catalyst for Stereo- and Regioselective Hydrophosphorylation of Alkynes
Table 3. Additive effects in the NiACHTNUTRGNEUNG(acac)2/DPPE-catalyzed
addition of (i-PrO)2P(O)H (2a) to 1-heptyne (1a).[a]
Entry Additive
Yield of
Unreacted Other prod-
3a [%][b] 2a [%][b]
ucts [%][b,c]
ꢀ
Scheme 2. Model P(O) H bond addition reaction.
1
2
3
4
5
none
62
33
57
100
47
34
5
7
0
5
5
Ph2P(O)OH[d] 36
CF3COOH[d]
Et3N[d]
0
48
formation of 3a (entry 2, Table 1). Surprisingly, a 14%
yield of Markovnikov product 3a was observed with
DPPE. The starting material was recovered with 84%
yield and only 2% of by-products were formed.
Optimization studies of the reaction conditions
with the NiACHTUNGTRENNUNG(acac)2/DPPE catalytic system have shown
that a 53% product yield may be achieved with
6 mol% of the catalyst at 1008C for 6 h. The reaction
was highly selective, the overall amount of by-prod-
ucts was as small as 3%.
g-terpinene[e] 61
[a]
1 mmol of 1a, 1 mmol of 2a, 6 mol% of Ni
12 mol% of DPPE, 0.5 mL of THF, 1008C, 24 h.
Determined by 31P NMR.
ACHTUNGTRENNUNG(acac)2,
[b]
[c]
[d]
[e]
Overall amount of phosphorus-containing by-products.
10 mol% of the additive.
20 mol% of the radical trap[21] additive.
Stimulated with the exciting results with this
NiACHTUNGTRENNUNG(acac)2 system we have studied other nickel precur- creased at longer reaction times – 62% in 24 h
sors in the catalytic system with the DPPE ligand (entry 1, Table 3), compared to 53% in 6 h (entry 4,
(Table 2). The formation of product 3a was not ob- Table 2). At this point we have analyzed the influence
served with NiCl2 and Ni
ACHTUNGTREN(NNUG ClO4)2, while conversion of of various additives on the performance of the cata-
the substrates to by-products was found, 30% and lytic system (Table 3).
43%, respectively (entries 1 and 2; Table 2). A minor
Addition of acids did not improve the performance
amount of 3a was detected in the reaction with of the catalytic reaction. Moreover, the yield was de-
Ni
by-products (entry 3, Table 2). The Ni
zerovalent Ni(COD)2 have shown a similar perfor- Table 3). The result is in sharp contrast with previous-
mance with 52–53% product yields (entries 4 and 5; ly reported catalytic systems, where these acids were
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Table 2) and trace amounts of by-products (~3%).
necessary to increase the yield and selectivity of prod-
Two important points concerning the study of cata- uct 3 formation.[16c,17] Addition of base demonstrated
lyst precursors deserve particular notes. First, the re- a negative effect on the studied hydrophosphorylation
action was extremely sensitive to the nature of the reaction (entry 4, Table 3). A radical trap (g-terpi-
Ni(II) source – a dramatic difference in the yield and nene) did not influence the outcome of the addition
selectivity was observed between rather similar nickel reaction, indicating the absence of radical pathways in
salts. Second, Ni
replacement for the air-sensitive and difficult to pre-
pare zerovalent Ni(COD)2 complex.
ACHTUNGTRENNUNG(acac)2 was confirmed as an excellent the studied system (entry 5, Table 3).
With the optimized parameters of the catalytic re-
action in hands we have designed the synthetic proce-
AHCTUNGTRENNUNG
The further optimization of reaction conditions dure for the selective hydrophosphorylation of al-
with Ni(acac)2 has shown that the yield can be in- kynes. The cheap and easily available catalyst precur-
sor – Ni(acac)2 – allowed the use of 9 mol% of the
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
catalyst and increased the yield of product 3. For the
terminal alkynes it was important to carry out slow
addition to the reaction mixture to minimize the side-
reaction of triple bond polymerization.[22] The scope
of designed synthetic procedure was evaluated with
different H-phosphonates and alkynes (Table 4).
Terminal alkynes 1a–1c smoothly reacted with 2a at
1008C and resulted in product formation in good
yields of 61–89% (entries 1–3, Table 4). The reaction
proceeded with high regioselectivity. The more chal-
lenging reaction with internal alkynes required higher
temperatures of 120–1408C to account for the slower
reactivity of the alkynes. However, even at this high
temperature high product yields of 80–99% and excel-
lent E/Z stereoselectivity of >99/1 were observed
(entries 4 and 5; Table 4).[23]
Table 2. Different metal precursors in the [Ni]/DPPE-cata-
lyzed addition of (i-PrO)2P(O)H (2a) to 1-heptyne (1).[a]
Entry Catalyst
Yield of 3a Unreacted
By-products
[%][b,c]
[%][b]
2a [%][b]
1
2
3
4
5
NiCl2
0
0
70
57
72
44
45
30
43
18
3
Ni
Ni
Ni
Ni
ACHTUNGTRENNUNG(ClO4)2
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
3
[a]
1 mmol of 1a, 1 mmol of 2a, 6 mol% of catalyst precur-
sor, Ni:DPPE=1:2 (except 1:1 ratio for entry 5), 0.5 mL
of THF, 1008C, 6 h.
[b]
[c]
Determined by 31P NMR.
Overall amount of phosphorus-containing by-products.
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Table 4. The scope of the Ni-catalyzed (R3O)2P(O)H (2) addition to alkynes 1.[a]
Entry
Alkyne
(R3O)2P(O)H
Product
Yield [%][b]
70 (63)
1
1a
1b
2a
2a
3a
3b
2
61 (53)
3
4
5
1c
1d
1e
2a
2a
2a
3c
4a
4b
89 (81)
80 (69)
99 (94)
6
7
8
1e
1e
1e
1e
2b
2c
2d
2e
4c
4d
4e
4f
99 (89)
99 (96)
99 (98)
99 (98)
9
[a]
See Experimental Section for details and conditions.
[b]
Determined by 31P NMR and isolated yield (in parenthesis); overall amount of impurities in all cases <10%.
The developed catalytic system was tolerant to the
The catalyst precursor activation step was studied
nature of the H-phosphonates (R3O)2P(O)H. Sub- in THF-d8 solution containing NiX2, DPPE and (i-
stituents with different electronic and steric effects PrO)2P(O)H 2a (Table 5). In the case of NiCl2
a
R3 =iP-r, Ph, benzyl (entries 5–7), a cyclic H-phos- yellow solution was obtained with a brown insoluble
phonate (entry 8) and the large n-C12H25 group precipitate (Entry 1, Table 5). The signals belonging
(entry 9, Table 4) reacted in excellent 99% yield and to 2a and DPPE remained in the THF-d8 solution as
1
>99/1 E/Z selectivity. Worthy of mention again is resolved by H and 31P NMR. The precipitate was iso-
that a quantitative yield of the branched Markovni- lated and ESI-MS characterization showed the forma-
kov-type product (3) was achieved without any acidic tion of the [NiCl
co-catalyst.
MꢀCl=491.0385 Da, calculated: 491.0390 Da). Disso-
After observing this fascinating synthetic applica- lution of the precipitate in chloroform-d1 showed a
tion, we were interested to unravel the key steps of single resonance at d
(31P)=57.7 ppm, which agrees
the catalytic reaction mechanism. First, we have ad- with the literature data for this complex.
2ACHTUNGTNER(NUNG DPPE)] complex (observed peak
AHCTUNGTRENNUNG
dressed the question on the role of catalyst precursor
and the dramatic differences between the nickel salts NiACHTUNGTRENNUNG
A similar procedure was carried out for the
(ClO4)2 precursor and showed only the signals of 2a
(Table 2). Chemical transformations involving all in the THF-d8 solution (entry 2, Table 5). Combined
studied NiX2 precursors (X=Cl, ClO4, OAc, acac, ESI-MS and NMR characterization indicated forma-
1
COD) were investigated by H and 31P NMR spec- tion of a mixture of the complexes [Ni
(ClO4)2
troscopy, and electrospray ionization-mass spectrome-
try (ESI-MS).
(DPPE)2].[24]
ACHTUNGRTEN(NUGN DPPE)] and [NiACHTUNRTGEG(NNUN ClO4)2ACHTNGUTRENNGUN
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Acid-Free Nickel Catalyst for Stereo- and Regioselective Hydrophosphorylation of Alkynes
Table 5. Chemical transformations on the catalyst activation step with different nickel precursors.[a]
Entry Catalyst
Reaction mixture
Compounds
in solution[b]
Precipitate
structure[b]
1
2
NiCl2
Yellow solution and brown precipitate
Light yellow solution and yellow precipitate 2a
2a, DPPE
G
2ACHTUNGTRENNUNG
Ni
(ClO4)2
G
U
AHCTUNGTRENNUNG
3
4
5
Ni
Ni
Ni
U
Light brown solution and green precipitate
Dark brown solution and white precipitate
2a, DPPE
ACHTUNGERTN(NUNG OAc)2
–
[a]
Conditions: THF-d8, metal salt, DPPE (Ni:DPPE=1:2) and (i-PrO)2P(O)H (2a); for NiACTHNUGTRNE(NUG COD)2 the ratio Ni:DPPE=1:1
was used.
[b]
[c]
1
Determined with H and 31P NMR, and ESI-MS.
Broad signal in 31P NMR.
With the NiACHTUNGTRENNUNG(OAc)2 salt both 2a and DPPE re- such an in situ reduction by phosphines and further
mained in the THF-d8 solution, as well as most of the involvement in the catalytic cycle has scarcely been
unreacted nickel acetate as a green precipitate studied. The present study provides evidence for the
(entry 3, Table 5). The light-brown color of the solu- possibility of such a generation of catalytically active
tion indicated that some trace amounts of the nickel nickel species from NiACTHNUTRGENUGN(acac)2.
complexes were dissolved, although it was not possi-
ble to detect them by NMR.
Thus, at the first stage the reaction mechanism in-
volved formation of zero-valent metal species via the
In the case of Ni
ACHUTGTNRNE(UNG acac)2 the salt was completely dis- reduction of divalent nickel precursor NiACTHUNGTRENNUNG
solved, accompanied with formation of a white pre- direct formation via COD replacement in NiAHCUTNGTRENNUNG
cipitate (entry 4, Table 5). In the THF-d8 a broad According to the generally accepted mechanistic
ꢀ
signal corresponding to 2a, i.e., a broad signal at d- framework, oxidative addition of the P H bond fol-
A
(31P)=31.5 ppm and the signal of the dioxide of lowed by alkyne insertion (5) led to the formation of
ꢀ
DPPE were detected. The white precipitate formed complex 6, which furnished product 4 after C H
was characterized as the dioxide of DPPE, which is bond formation (Scheme 3). Taking into account that
only partially soluble in tetrahydrofuran.
Using Ni(COD)2 as a metal source the same broad (RO)2P(O)H and (RO)2POH, the second pathway for
signal at d
(31P)=31.5 ppm as well as the broad signal P H bond addition may involve alkyne coordination
of 2a were observed.[25] The solutions obtained with and external attack by the phosphorus compound
Ni(acac)2 and Ni
(COD)2 possessed identical dark (7).[28] Intermediate zwitterionic complexes 8a and 8b
brown colors. and nickel complex 8c (double bond isomer of 6) may
H-phosphonate 2 may exist in two tautomeric forms,
ACHTUNGTRENNUNG
ꢀ
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
The experiments have clearly highlighted the be expected at this stage. Formation of compound 9
nature of the transformation on the catalyst activation should be accomplished as a final product for this
step from the NiX2 precursors. Stable insoluble com- pathway.
plexes of Ni(II) with DPPE ligand were formed with
It should be noted that both mechanisms – intramo-
X=Cl and ClO4. The nickel complexes were not in- lecular insertion and external attack – are well known
ꢀ
volved in the reaction of interest, thus, showing no in E H bond addition reactions catalyzed by transi-
product formation (entries 1 and 2; Table 2).[26] Trace tion metals.[2] Either of the mechanisms may take
amounts of the nickel species were in solution for the place depending on the metal, the nature of the ele-
X=OAc precursor and showed a small yield in the ment E and the conditions. In the case of terminal al-
catalytic reaction (entry 3, Table 2). Complete dissolu- kynes (R’=H) it is not possible to distinguish these
tion of the NiACHTUNGTRENNUNG(acac)2 and NiACHUTGNTREN(NGUN COD)2 and formation of mechanisms based on the product structure. However,
a homogeneous catalytic system are in excellent for the internal alkynes the structure of the product
agreement with the performance demonstrated in the strongly depends on the reaction pathway: intra-
addition reaction (entries 4 and 5; Table 2).
ACHTUNGTRENmNGNU olecular insertion led to stereoselective formation
The formation of the dioxide of DPPE is important, of syn-addition product 4, while external attack gave
since it indicated in situ reduction of the Ni(II) salt to anti-addition product 9.
zero-valent nickel species. Such an in situ reduction of
For an unambiguous determination of the structure
divalent metal salts by phosphines is well-known in of the product synthesized in the studied catalytic
the case of palladium complexes and it was shown to system we have prepared single crystals of 4e and car-
produce phosphine oxides.[27] For the Ni(II) species ried out an X-ray analysis (Figure 1). The molecular
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Valentine P. Ananikov et al.
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structures of the other products 4a–4d and 4f were
confirmed by measuring NMR coupling constant
ACTHNUTRGNEUNG
3J(31P, 1H)=20–26 Hz, which is known to be sensitive
to the geometry of the double bond. Therefore, com-
paring both pathways shown in Scheme 3, we may
conclude that alkyne insertion is the most likely way
of product formation. The high E/Z selectivity of the
reaction >99/1 gave no evidence for the second path-
way to make a noticeable contribution.
To reveal details of the alkyne insertion in the stud-
ied catalytic system we have performed theoretical
calculations at the B3LYP/DZ(d) level.[29] The model
system used in the theoretical calculations and calcu-
lated potential energy surface are shown on Figure 2,
optimized geometries of intermediate complexes and
transition states are given in Figure 3.[30]
Alkyne coordination to compound I gave a weakly
bound complex and led to II with an energy gain of
5.2 kcalmolꢀ1. Starting from complex II the transition
state of alkyne insertion III-TS was located with the
calculated energy barrier of 12.2 kcalmolꢀ1. Interest-
ingly, movement along the reaction coordinate to-
wards formation of product IV facilitated dissociation
of one of the phosphorus atoms of the bidentate
ꢀ
ligand. In the product IV two s-bonds, Ni C and
C P, were formed, and the oxygen atom of the P=O
ꢀ
group was coordinated to the metal. The reaction was
highly exothermic with the energy gain of 40.1 kcal
molꢀ1 compared to the initial point I and 34.9 kcal
molꢀ1 compared to point II.
Tautomerization of H-phosphonates inspired us to
investigate the possibility of this transformation in the
metal complex I. Indeed, conversion of the phosphor-
ꢀ
Scheme 3. Various mechanistic pathways of addition of P H
bond of H-phosphonates to alkynes.
us(V) center in I to a phosphorusACTHNUTRGNE(NUG III) center in VI
was feasible with a 14.9 kcalmolꢀ1 activation barrier
through the V-TS. Compound VI was found to be less
stable than I by 8.7 kcalmolꢀ1. This finding was in
agreement with the literature data for the free H-
phosphonate, where the (RO)2P(O)H form was also
found to be more stable compared to the (RO)2POH
tautomer.[31]
Alkyne coordination to VI led to the weakly bound
complex VII with an energy gain of 6.2 kcalmolꢀ1. To
our great surprise, quantum chemical calculations of
the further reaction pathway led to discovery of tran-
sition state VIII-TS corresponding to the reaction
with alkyne. A cyclic five-membered structure was
obtained and the movement along reaction coordi-
ꢀ
nate involved breakage of the Ni O bond and forma-
tion of the Ni C and C P bonds in product IX. Con-
ꢀ
ꢀ
Figure 1. Molecular structure of 4e determined by X-ray
version of phosphorusACTHNUTRGNE(NUG III) to phosphorus(V) took
analysis.
place in the phosphonate residue during this stage.
The activation barrier of 23.0 kcalmolꢀ1 was calculat-
ed for VIII-TS starting from complex VII. The forma-
structure of 4e has clearly proven the syn-addition re- tion of IX was highly exothermic with an energy gain
action, the hydrogen atom and phosphorus group of 37.7 kcalmolꢀ1 compared to the initial point I and
were located in a cis relationship to each other. The 40.2 kcalmolꢀ1 compared to point VII.
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Acid-Free Nickel Catalyst for Stereo- and Regioselective Hydrophosphorylation of Alkynes
Figure 2. Calculated potential energy surface of the alkyne insertion in the nickel complexes at B3LYP/DZ(d) level (energy
data for X=H is shown).
Both phosphorus atoms of the bidentate ligand re- was calculated to be 15.4 kcalmolꢀ1 (only structure II
mained coordinated to the nickel center during the is shown on Figure 2 for clarity).
VI!IX pathway, in contrast to the I!IV pathway,
Starting from IIa the transition state III-TS was lo-
which required dissociation of one the phosphorus cated corresponding to the alkyne insertion into the
ꢀ
ꢀ
atoms of the ligand. If the Ni P bonds lengths were Ni P1(O) bond. Movement along the reaction coordi-
fixed during geometry optimization of the I!IV nate towards the transition state caused elongation of
ꢀ
pathway (dissociation restricted calculations), it was the of the Ni P2 bond with complete dissociation of
not possible to reach the transition state of alkyne in- this metal-ligand bond in the optimized structure of
sertion.
Here we briefly discuss the optimized molecular phosphonate ligand in the chelate fashion (Ni C1=
structures of I–IX to get a better insight into the 1.905 and Ni O1=2.033 ꢁ) restored the square-
ꢀ
product IV (Ni P2=4.212 ꢁ). Binding of the vinyl
ꢀ
ꢀ
mechanistic aspects of these transformations (struc- planar geometry of the Ni(II) complex in IV.
tures and selected geometry parameters are provided
Another pathway involved isomerization of the ini-
in Figure 3). Initial complex I possessed the geometry tial nickel complex with the P(V) center to the corre-
typical for a square planar Ni(II) derivative with sponding nickel derivative containing P
2.23–2.24 ꢁ length for the Ni Pligand bonds and stead. The transformation was calculated to take
G
ꢀ
ꢀ
2.188 ꢁ for the Ni P1(O) bond. Approach of the place via the transition state V-TS. During this tauto-
alkyne towards the metal complex first led to weakly merization the Ni P1 bond was broken and a new
ꢀ
ꢀ
ꢀ
ꢀ
bound derivative II, the distances Ni C2=2.351 ꢁ Ni O1 bond was formed in VI (Ni O1=1.835 ꢁ).
and H1 O3=2.266 ꢁ were found in the optimized The geometry arrangement of the phosphorus atom
geometry. Coordination of the alkyne in II only slight- in VI was typical for the P
ly effected the lengths of the Ni P bonds. While in bond was elongated from 1.501 ꢁ (I) to 1.598 ꢁ (VI)
the p-complex IIa (Ni C1=2.146 ꢁ, Ni C2= indicating transition from a double to a single phos-
2.175 ꢁ) coordination of the alkyne distorted the ge- phorus-oxygen bond.
ꢀ
(III) derivative, the P1 O1
ꢀ
ꢀ
ꢀ
ometry and resulted in formation of a five-coordinat-
Surprisingly, the very unusual transition state VIII-
ed complex. Stronger binding of the alkyne activated TS of the alkyne insertion was located starting direct-
ꢀ
ꢀ
both the C1 C2 triple bond and Ni P1(O) bond, ly from the complex VII. The unique nature of this
ꢀ
which became longer by 0.021 and 0.071 ꢁ, respec- transition state involved formation of the Ni C1 and
ꢀ
tively (cf. complexes II and IIa). The energy gain due C2 P1 bonds via the five-membered structure in con-
to alkyne coordination compensated for some de- trast to III-TS, where a four-membered transition
ꢀ
ꢀ
crease of stability originating from the disfavored state was adopted. The longer Ni C1 and C2 P1
geometry. As a result of both of these effects, a simi- bonds were calculated for the VIII-TS compared to
lar relative stability was found for the IIa (ꢀ8.4 kcal the III-TS.
molꢀ1) and the activation energy from IIa to III-TS
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Valentine P. Ananikov et al.
FULL PAPERS
Figure 3. Optimized molecular structures of intermediate complexes and transition states at B3LYP/DZ(d) level.
Overcoming the transition state VIII-TS resulted in view the pathways cannot be distinguished based on
ꢀ
ꢀ
formation of two new s-bonds, Ni C1 and C2 P1 as the product structure, since both operate as a syn-ad-
ꢀ
ꢀ
well as a p-bond P1 O1, accompanied with synchro- dition of the P H bond to alkyne. Both pathways
ꢀ
nous breakage of the Ni O1 bond and one of the ace- were found to be highly exothermic (Figure 2) and
tylenic p-bonds. According to the geometry arrange- complexes IV and IX can be interconverted between
ment of the phosphorus atom in the product IX a typ- each other through intermolecular dissociation/associ-
ꢀ
ical P(V) center was formed (P1 O1=1.498 ꢁ, ation of phosphorus and oxygen heteroatoms to the
ꢀ
ꢀ
P1 O2=1.636 ꢁ, P1 O3=1.618 ꢁ). The vinyl phos- metal center. Thus, it would be hardly possible to dis-
phonate ligand in IX was not bound in the chelate tinguish the pathways with kinetic measurements. It is
fashion like in IV, although some weak interaction be- a valuable advantage of theoretical calculations that
ꢀ
tween the Ni and O1 may take place (Ni O1= allowed us to unravel the mechanistic data, which was
2.860 ꢁ; see side view). In both products IX and IV not evident from the experiment alone.
the same vinyl group was formed with a standard
double bond length C1 C2=1.35 ꢁ.
According to calculated energy surface both path- metal phosphorus species and revealed a previously
ways may contribute to product formation in the stud- unknown pathway of alkyne insertion through the
ied catalytic system.[32] From an experimental point of five-membered transition state. Another important
To summarize, the theoretical calculations clearly
highlighted the importance of tautomerization of the
ꢀ
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Adv. Synth. Catal. 2010, 352, 2979 – 2992

Acid-Free Nickel Catalyst for Stereo- and Regioselective Hydrophosphorylation of Alkynes
ꢀ
Scheme 4. Plausible catalytic cycles of the P H bond addition to alkynes (L and L* denote different coordination types of
the bidentate ligand; see Figure 2 and text for details).
point is destabilization of the well-known pathway in-
The strong ligand effect and catalyst precursor
volving III-TS by the strongly bound bidentate ligand. effect observed in the studied reaction arose from
Combining experimental and theoretical data, the several specific requirements both on the catalyst acti-
following plausible catalytic cycle with NiACTHNUTRGNE(NUG acac)2 as vation step and the catalytic cycle itself. A detailed
precursor may be proposed (Scheme 4).[33] Catalyst mechanistic study unveiled the nature of chemical
activation to form zero-valent nickel species, followed transformations on the catalyst activation step. For-
by reaction with H-phosphonate led to complexes 10 mation of stable unreactive NiX2Ln complexes, solu-
and 13 with the equilibrium shifted to the left. Start- bility and in situ reduction by the phosphine ligand
ing with complex 10 the reaction mechanism includes are the key factors responsible for selection of the
alkyne insertion to form 11 and repeats the catalytic catalyst precursor. NiACHTNUTRGNEUNG(acac)2 was found to be superior
cycle after release of product 4 from complex 12. The to fulfill the above criteria among the studied nickel
second possible cycle uncovered in the present study salts.
involves tautomerization of 10 to form complex 13,
The present study for the first time pointed out the
followed by reaction with alkyne via structure 14. Re- importance of the tautomerization of pentavalent and
lease of the same product 4 from complex 15 com- trivalent phosphorus directly in the coordination
pletes the cycle and regenerates catalytically active sphere of the metal complex. The reaction pathway
ꢀ ꢀ
nickel species.
dealing with the Ni(II) O PACTHNGUTERNNU(G III) tautomeric form
In the present study we addressed the mechanism was discovered by theoretical calculations and the
of alkyne insertion into the metal-phosphorus bond, unique role of a bidentate ligand to control alkyne in-
since this pathway is most often discussed in the liter- sertion step was highlighted. Undoubtedly, the further
ature.[12,16,18] However, it should be pointed out that studies should be anticipated to get more insight into
insertion of the alkyne into the metal-hydrogen bond the mechanistic picture of these transformations and
is also a possible option,[17b] which requires further at- their possible application in carbon-phosphorus bond
tention and more detailed elaboration.
formation.
Conclusions
Experimental Section
We have developed the first acid-free, Ni-catalyzed
synthetic procedure for the selective hydrophosphory-
lation of C C bonds. Addition of H-phosphonates to
internal alkynes was performed with excellent stereo-
selectivity, and the addition reaction involving termi-
nal alkynes was highly regioselective. Cheap and
General Description
All manipulations with Ni
glovebox under an argon atmosphere. In all other cases re-
action vessels were argon flushed before heating. [Ni(acac)2]
ACHTUNGRTEN(NUNG COD)2 were carried out in a
ꢁ
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
was dried under vacuum (0.1–0.05 Torr, 608C, 0.5 h) before
use. Other reagents were obtained from Acros and Aldrich
and used as supplied (checked by NMR spectroscopy before
use). THF was purified by distillation over the Na/benzo-
phenone system, maintaining the intense blue color of ben-
zophenone ketyl. Other solvents were purified according to
easily available NiACTHNUTRGNEUNG(acac)2 salt was utilized as catalyst
precursor. Markovnikov-type vinyl phosphonates
were prepared in high yields using the developed cat-
alytic system and isolated as pure products.
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Valentine P. Ananikov et al.
FULL PAPERS
published methods. Unless otherwise noted, the reactions
were carried out in PTFE screw capped tubes, equipped
with a magnetic stirrer bar.
only a small amount of silica required, 2) quick elution, and
3) economy of solvents. However, slightly better isolated
yields (by ꢂ5–10%) may be achieved using conventional
column chromatography.
All NMR measurements were performed by using a
three-channel Bruker AVANCE 500 spectrometer operating
After drying in vacuum the pure products were obtained.
The isolated yields were calculated based on the initial
amount of H-phosphonate 2.
1
at 500.1, 202.5 and 125.8 MHz for H, 31P and 13C nuclei, re-
spectively. The spectra were processed on a Linux work-
1
Diisopropyl (1-pentylvinyl)phosphonate (3a): 1H NMR
(500 MHz, CDCl3): d=0.90 (t, JH,H =6.78 Hz, 3H), 1.27–1.36
(m, 16H), 1.54 (m, 2H), 2.23 (m, 2H), 4.67 (m, 2H), 5.68 (d,
G
cal shifts are reported relative to external TMS. The 13C
chemical shifts are reported relative to the corresponding
solvent signals used as internal reference. The 31P chemical
shifts are reported relative to external H3PO4/H2O.
J
P, H =49.10 Hz, 1H), 6.01 (d, JP,H =23.20 Hz, 1H); 13C{1H}
NMR (126 MHz, CDCl3): d=13.90, 22.40, 23.78, 23.81,
24.02, 24.05, 27.40, 27.50, 31.30, 31.80, 31.90, 70.10, 70.20,
127.80 (JP, C =9.57 Hz), 140.80 (JP, C =172.40 Hz); 31P{1H}
NMR (202 MHz, CDCl3): d=18.40; MS (EI): m/e (%)=262
(4) [M+]; elemental analysis calcd. (%) for C13H27O3P: C
59.52, H 10.37, P 11.81; found: C 59.63, H 10.31, P 11.84;
yield: 0.166 g (63%).
Evaluation of the Ligand Effect (Table 1)
[NiACHTUNGTRENNUNG
(acac)2] (3.0ꢂ10ꢀ5 mol, 7.7 mg), the ligand (6.0ꢂ10ꢀ5 mol
for bidentate, 1.2ꢂ10ꢀ4 mol for monodentate) and THF
(0.5 mL) were placed into the reaction vessel and stirred at
room temperature for 5 min. 2a (1.0ꢂ10ꢀ3 mol, 166.6ꢂ
10ꢀ3 mL) and 1a (1.0ꢂ10ꢀ3 mol, 131.7ꢂ10ꢀ3 mL) were
added to the mixture and the reaction was carried out at
1008C for 3 h under stirring.
Diisopropyl [1-(3-cyanopropyl)vinyl]phosphonate (3b):
1H NMR (300 MHz, CDCl3): d=1.31 (d, JH,H =6.20 Hz,
6H), 1.35 (d, JH,H =6.20 Hz, 6H), 1.93 (m, 2H), 2.34–2.50
(m, 4H), 4.70 (m, 2H), 5.77 (d, JP, H =47.90 Hz, 1H), 6.09 (d,
J
P, H =22.60 Hz, 1H); 13C{1H} NMR (75 MHz, CDCl3): d=
Evaluation of Activity of Different Metal Precursors
(Table 2)
16.30, 23.70, 23.82, 23.85, 23.93, 23.98, 31.30, 31.40, 70.60,
70.70, 119.20, 129.80 (JP, C =9.61 Hz), 138.70 (JP, C
=
175.50 Hz); 31P{1H} NMR (121 MHz, CDCl3): d=16.50; MS
(EI): m/e (%)=218 (77) [M+ꢀCH3CN]; elemental analysis
calcd. (%) for C12H22NO3P: C 55.59, H 8.55, N 5.40, P 11.95;
found: C 55.72, H 8.51, N 5.86, P 11.63; yield: 0.137 g
(53%).
The Ni compound (see Table 2 for details) used as metal
precursor (6.0ꢂ10ꢀ5 mol), DPPE (12.0ꢂ10ꢀ5 mol, 47.8 mg)
and THF (0.5 mL) were placed into the reaction vesꢀse3 l and
stirred at room temperature for 5 min. 2a (1.0ꢂ10 mol,
166.6ꢂ10ꢀ3 mL) and 1a (1.0ꢂ10ꢀ3 mol, 131.7ꢂ10ꢀ3 mL)
were added to the obtained mixture and the reaction was
carried out at 1008C for 6 h under stirring.
Diisopropyl (1-phenylvinyl)phosphonate (3c): 1H NMR
(500 MHz, CDCl3): d=1.20 (d, JH,H =6.20 Hz, 6H), 1.33 (d,
J
H,H =6.20 Hz, 6H), 4.70 (m, 2H), 6.13 (d, JP, H =45.53 Hz,
1H), 6.34 (d, JP, H =22.0 Hz, 1H), 7.30–7.36 (m, 3H), 7.53–
7.56 (m, 2H); 13C{1H} NMR (126 MHz, CDCl3): d=23.72,
23.75, 24.14, 71.0, 71.05, 127.64, 127.68, 128.15, 128.35,
131.09, 137.15 (JP, C =11.41 Hz), 141.25 (JP, C =175.45 Hz);
31P{1H} NMR (202 MHz, CDCl3): d=15.45; HR-MS (ESI):
Analysis of the Influence of Additives (Table 3)
(acac)2] (6.0ꢂ10ꢀ5 mol, 15.4 mg), DPPE (12.0ꢂ10ꢀ5 mol,
[NiACHTUNGTRENNUNG
47.8 mg) and THF (0.5 mL) were placed into the reaction
vessel and stirred at room temperature for 5 min until a het-
erogeneous dark brown solution was formed (white precipi-
tate was observed). 2a (1.0ꢂ10ꢀ3 mol, 166.6ꢂ10ꢀ3 mL), 1a
(1.0ꢂ10ꢀ3 mol, 131.7ꢂ10ꢀ3 mL) and additive (see Table 3
for details) were transferred to the reaction vessel and the
reaction was carried out at 1008C for 24 h under stirring.
m/z=286.1574, calcd. for [M
+
NH4]+: 286.1567 (D=
2.40 ppm); elemental analysis calcd. (%) for C14H21O3P: C
62.67, H 7.89, P 11.54; found: C 62.59, H 8.16, P 11.24;
yield: 0.217 g (81%).
Diisopropyl [(1E)-1-ethylbut-1-en-1-yl]phosphonate (4a):
1H NMR (500 MHz, CDCl3): d=1.05 (m, 6H), 1.28 (d,
J
H,H =6.20 Hz, 6H), 1.33 (d, JH,H =6.20 Hz, 6H), 2.15–2.29
General Synthetic Procedure (Table 4), Purification
and Characterization of Products
(acac)2] (9.0ꢂ10ꢀ5 mol, 23.1 mg), DPPE (18.0ꢂ10ꢀ5 mol,
[NiACHTUNGTRENNUNG
(m, 4H), 4.65 (m, 2H), 6.51 (dt, JH,H =7.30 Hz, JP, H
=
cis
23.80 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3): d=13.10,
13.90, 20.40, 20.50, 21.40, 21.50, 23.70, 23.80, 23.90, 24.00,
69.70, 69.71, 69.74, 69.80, 131.60 (JP, C =178.10 Hz), 147.00
(JP,C =10.30 Hz); 31P{1H} NMR (202 MHz, CDCl3): d=20.60;
MS (EI): m/e (%)=248 (6) [M+]; elemental analysis calcd.
(%) for C12H25O3P: C 58.05, H 10.15, P 12.47; found: C
58.29, H 9.83, P 12.49; yield: 0.171 g (69%).
71.7 mg) and THF (1.0 mL) were placed into the reaction
vessel and stirred at room temperature for 5 min until a het-
erogeneous dark brown solution was formed (formation of a
white precipitate was also observed). H-phosphonate 2
(1.0ꢂ10ꢀ3 mol), alkyne 1 (1.0ꢂ10ꢀ3 mol) were added to the
obtained solution and the reaction was carried out at 1008C
(1a–c), 1408C (1d), 1208C (1e) for 24 h (1a–c), 30 h (1d),
20 h (1e) under stirring. Alkynes 1a–c were added slowly
using syringe pump (or by small portions manually) during
6 h from heating start.
Diisopropyl [(E)-1,2-diphenylvinyl]phosphonate (4b):
1H NMR (500 MHz, CDCl3): d=1.23 (d, JH,H =6.23 Hz,
6H), 1.30 (d, JH,H =6.23 Hz, 6H), 4.70 (m, 2H), 7.04–7.08
(m, 2H), 7.11–7.19 (m, 3H), 7.27–7.35 (m, 5H), 7.62 (d,
J
P, H cis =24.56 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3): d=
23.86, 23.89, 24.10, 70.89, 70.93, 127.70, 128.20, 128.60,
128.80, 129.52, 129.55, 130.32, 132.77 (JP, C =180.74 Hz),
135.00, 135.15, 135.91, 135.97, 142.70 (JP, C =10.79 Hz);
31P{1H} NMR (202 MHz, CDCl3): d=16.43; HR-MS (ESI):
After completion of the reaction the products were puri-
fied by dry column flash chromatography on silica. A hex-
anes/ethyl acetate gradient elution was applied. Dry column
flash chromatography has several practical advantages: 1)
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Acid-Free Nickel Catalyst for Stereo- and Regioselective Hydrophosphorylation of Alkynes
m/z=367.1438, calcd. for [M+Na]+: 367.1434 (D=
1.10 ppm); elemental analysis calcd. (%) for C20H25O3P: C
69.75, H 7.32, P 8.99; found: C 69.54, H 7.54, P 8.98; yield:
0.324 g (94%).
All precipitates were isolated by centrifugation and dried
under vacuum. Compounds [NiCl2A(DPPE)], [Ni(ClO4)2
(DPPE)], [Ni(ClO4)2A(DPPE)2] and Ni(OAc)2 were washed
thrice with 2 mL of degassed THF, the dioxide of DPPE was
washed thrice with 2 mL of degassed hexane.
G
ACHTUNGTRENNUNG
E
R
G
ACHTUNGTRENNUNG
Diphenyl
[(E)-1,2-diphenylvinyl]phosphonate
(4c):
1H NMR (500 MHz, CDCl3): d=7.06–7.41 (m, 20H), 7.87
(d, JP, H cis =26.21 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3):
d=120.57, 120.60, 125.05, 128.35, 128.42, 129.10, 129.68,
X-Ray Structural Study of 4e
Isolated product 4e was dissolved in 2 mL of THF. Yellowish
crystals were obtained after slow evaporation of the solvent
at room temperature for a few days.
Single crystal X-ray diffraction experiments were carried
out with a Bruker APEX2 1000 CCD area detector at 120 K
using graphite monochromated Mo-Ka radiation (l=
0.71073 ꢁ). Experimental data have been corrected for ab-
sorption effects with the SADABS program.[34]
The structures were solved by direct methods and refined
by the full-matrix least-squares against F2 in anisotropic (for
non-hydrogen atoms) approximation. All hydrogen atoms
were placed in geometrically calculated positions and re-
fined in isotropic approximation in a riding model. All cal-
culations were performed using the SHELXTL software.[35]
Crystallographic data, refinement parameters and geomet-
ric parameters are provided in the Supporting Information,
the molecular structure is shown on Figure 1. Crystallo-
graphic data for the structure reported in this study have
been deposited with the Cambridge Crystallographic Data
Centre under CCDC 784455. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
129.76, 130.70, 134.27, 134.46, 134.97, 146.45 (JP, C
=
12.39 Hz), 150.63, 150.69; 31P{1H} NMR (202 MHz, CDCl3):
d=11.39; HR-MS (ESI): m/z=435.1117, calcd. for [M+
Na]+: 435.1121 (D=0.90 ppm); elemental analysis calcd.
(%) for C26H21O3P: C 75.72, H 5.13, P 7.51; found: C 75.65,
H 5.15, P 7.48; yield: 0.367 g (89%).
Dibenzyl
[(E)-1,2-diphenylvinyl]phosphonate
(4d):
1H NMR (500 MHz, CDCl3): d=5.05 (d, JP, H =7.69 Hz ,4H),
7.0–7.33 (m, 20H), 7.65 (d, JP, H cis =25.05 Hz, 1H); 13C{1H}
NMR (126 MHz, CDCl3): d=67.69, 67.74, 127.87, 127.94,
128.26, 128.29, 128.52, 128.91, 129.15, 129.43, 129.47, 130.44,
130.88 (JP, C =179.25 Hz), 134.59, 134.77, 135.34, 135.40,
136.35, 136.40, 144.06 (JP, C =11.58 Hz); 31P{1H} NMR
(202 MHz, CDCl3): d=19.35; HR-MS (ESI): m/z=441.1611,
calcd. for [M+H]+: 441.1614 (D=0.70 ppm); elemental
analysis calcd. (%) for C28H25O3P: C 76.35, H 5.72, P 7.03;
found: C 76.31, H 5.88, P 7.21; yield: 0.423 g (96%).
2-[(E)-1,2-Diphenylvinyl]-4,5-dimethyl-1,3,2-dioxaphos-
1
pholane 2-oxide (4e): H NMR (500 MHz, CDCl3): d=0.96
(d, JH,H =6.05 Hz, 3H), 1.28 (d, JH,H =6.13 Hz, 3H), 3.22 (m,
1H), 4.21 (m, 1H), 7.04–7.46 (m, 10H), 7.81 (d, JP, H
=
cis
25.85 Hz, 1H); 13C{1H} NMR (126 MHz, CDCl3): d=17.21,
17.29, 17.89, 17.94, 80.06, 83.24, 128.23, 128.31, 129.04,
129.51, 129.84, 129.88, 130.48, 134.36, 134.55, 135.07, 135.14,
146.61 (JP, C =11.81 Hz); 31P{1H} NMR (202 MHz, CDCl3):
d=33.11; HR-MS (ESI): m/z=337.0964, calcd. for [M+
Na]+: 337.0964 (D=0 ppm); elemental analysis calcd. (%)
for C18H19O3P: C 68.78, H 6.09, P 9.85; found: C 68.44, H
6.23, P 9.82; yield: 0.308 g (98%).
Theoretical Calculations
Geometry and energy of the reactants, intermediates, transi-
tion states and products of the reactions were calculated
using the B3LYP hybrid density functional method[36] in con-
junction with the standard 6-31G(d) basis set[37] for H, C, P,
O and Lanl2dz basis set with effective core potentials[38] for
the metal [denoted as B3LYP/DZ(d) level]. In previous
studies it was established that this level of theory reasonably
describes the energy and geometry parameters of the sys-
tems involving transition metal complexes.[39]
For all studied structures normal coordinate analysis was
performed to characterize the nature of the stationary
points and to calculate thermodynamic properties (298.15 K
and 1 atm). Transition states were confirmed with IRC (in-
trinsic reaction coordinate) calculations using the standard
method.[40] All calculations were performed without any
symmetry constraints using the Gaussian 03 program.[41]
Didodecyl
[(E)-1,2-diphenylvinyl]phosphonate
(4f):
1H NMR (500 MHz, CDCl3): d=0.88 (t, 6H), 1.20–1.33 (m,
36H), 1.57–1.65 (m, 4H), 3.97–4.07 (m, 4H), 7.03–7.37 (m,
10H), 7.62 (d, JP, H cis =24.54 Hz, 1H); 13C{1H} NMR
(126 MHz; CDCl3): d=14.16, 22.75, 25.58, 29.22, 29.42,
29.62, 29.72, 30.50, 30.55, 31.99, 66.19, 66.24, 127.79, 128.21,
128.80, 128.95, 129.31, 130.39, 131.34 (JP, C =179.97 Hz),
134.77, 134.95, 135.86, 143.52 (JP, C =10.64 Hz); 31P{1H} NMR
(202 MHz, CDCl3): d=18.61; HR-MS (ESI): m/z=619.4226,
calcd. for [M+Na]+: 619.4251 (D=4.00 ppm); elemental
analysis calcd. (%) for C38H61O3P: C 76.47, H 10.30, P 5.19;
found: C 76.51, H 10.20, P 5.21; yield: 0.585 g (98%).
Acknowledgements
Mechanistic Study of Catalyst Activation (Table 5).
DPPE (12.0ꢂ10ꢀ5 mol, 47.8 mg), 2a (1.0ꢂ10ꢀ3 mol, 166.6ꢂ
10ꢀ3 mL) and degassed THF-d8 (0.5 mL) were transferred to
an NMR tube. The Ni-containing (see Table 5 for details)
metal precursor (6.0ꢂ10ꢀ5 mol) was added to obtained a
colorless homogeneous solution, and the mixture was
The research was supported in part by the Russian Founda-
tion for Basic Research (Project No. 07-03-00851), Program
No 1 of Division of Chemistry and Material Sciences of RAS
and Program No 20 of RAS.
1
heated to 508C for 5 min and shaken. The H and 31P NMR
spectra were recorded directly for the mixture (sample cen-
trifugation was necessary in some cases to get better quality
spectra).
Adv. Synth. Catal. 2010, 352, 2979 – 2992
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2989

Valentine P. Ananikov et al.
FULL PAPERS
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Acid-Free Nickel Catalyst for Stereo- and Regioselective Hydrophosphorylation of Alkynes
Zakeeruddin, M. K. Nazeeruddin, P. Pechy, F. P. Rot-
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are neglected. Although such calculations gave higher
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lower isolated yields due to formation of other by-
products. Throughout the present study the material
balance on phosphorus species was verified in each ex-
periment (the product, unreacted H-phosphonate and
overall amount of by-products).
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ref.[22]).
[24] Observed [MꢀClO4] peaks in ESI-MS at 555.0192 and
953.1553 Da,
calculated
peaks:
555.0186
and
953.1540 Da, respectively. 31P NMR (DMSO): d=56.3,
30.4, 30.2, ꢀ13.9, ꢀ14.2.
[25] Formation of a broad signal is an indication of com-
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[26] In the present study we did not investigate the influ-
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in the optimized conditions high product yields were
obtained.
[27] Reduction of Pd(II) in catalytic reactions (in situ): N.
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[28] External nucleophilic attack is more common for p-
complexes of divalent metal derivatives, although in-
volvement of p-complexes of zero-valent metal deriva-
tives can not be excluded. In the studied system Ni(II)
and Ni(0) centers can be readily interconverted by oxi-
ꢀ
dative addition/reductive elimination of the P H bond
(in Scheme 3 ligands on Ni are omitted for clarity).
ꢀ
[29] Alkyne insertion into the M P bond was studied in
detail, this insertion reaction was assumed as the key
stage of reaction mechanism in a number of studies
(see refs.[12,16,18]).
[30] Under the experimental conditions formation of com-
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(see refs.[12,16–18]), for the calculations here the simple
model with X=H was utilized.
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in the reaction, see the NMR spectrum of crude prod-
uct in the Supporting Information to ref.[17a] and discus-
sion therein.
Adv. Synth. Catal. 2010, 352, 2979 – 2992
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2991

Valentine P. Ananikov et al.
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2010, 352, 2979 – 2992