Ruthenium catalyzed regioselective hydrophosphination of propargyl alcohols

Article abstract of DOI:10.1039/b212408d

Catalytic hydrophosphination of propargyl alcohols by ruthenium complexes RuCl(cod)(C₅Me₅) and RuCl(PPh₃)₂(C₅Me₅) leads to the formation of functionalized vinylphosphines, with linkage of the phosphorus atom to the terminal alkyne carbon, via a ruthenium vinylidene intermediate.

Full text of DOI:10.1039/b212408d

Ruthenium catalyzed regioselective hydrophosphination of propargyl
alcohols
François Jéroˆme, Florian Monnier, Hania Lawicka, Sylvie Dérien and Pierre H. Dixneuf*
Institut de Chimie de Rennes, UMR 6509—CNRS—Université de Rennes, Organométalliques et Catalyse,
Campus de Beaulieu 35042, Rennes, France. E-mail: pierre.dixneuf@univ-rennes1.fr; Fax: 33 2 23 23 69
39; Tel: 33 2 23 23 62 80
Received (in Cambridge, UK) 17th December 2002, Accepted 5th February 2003
First published as an Advance Article on the web 17th February 2003
Catalytic hydrophosphination of propargyl alcohols by
ruthenium
complexes
RuCl(cod)(C5Me5)
and
RuCl(PPh3)2(C5Me5) leads to the formation of function-
alized vinylphosphines, with linkage of the phosphorus atom
to the terminal alkyne carbon, via a ruthenium vinylidene
intermediate.
Alkenylphosphines are attracting interest as building blocks in
organic synthesis and as useful ligand precursors for cataly-
sis.1,2 The synthesis of vinylphosphines is generally achieved
by the reaction of halophosphines with vinylmagnesium or
lithium derivatives which do not tolerate functional groups.3
Two alternatives have been described: the direct addition of
secondary phosphines to alkynes which requires prolonged
heating and leads to isomer mixtures, and radical chains
reactions.3 Recently, metal-catalysed additions of P–H bonds to
alkynes have offered control over both regio- and ster-
eoselectivity leading to alkenylphosphines.4 Palladium and
platinum catalysts favour the anti-Markovnikov addition of
diphenylphosphine oxide to alkynes,5 and the regioselectivity is
reversed by addition of phosphinic acid R2P(O)OH,6 whereas
Scheme 2
conversion of 1a led to a mixture of the stereoisomers 2a and 3a
(Z/E = 85/15).
Several catalytic systems such as RuCl(L)2(C5R5) (R = H,
Me) (L = PPh3, cod) and diphenylphosphine with NaPF6,
NH4PF6 or Na2CO3 were tested, and we rapidly observed that
RuCl(cod)(C5Me5), with diphenylphosphine in the presence of
Na2CO3 in chloroform, generated the best catalyst system for
this hydrophosphination.
The reaction of propargyl alcohols 1a–d with diphenylphos-
phine in CHCl3, in the presence of catalytic amounts of
RuCl(cod)(C5Me5) (B) (5 mol%) and Na2CO3 (10 mol%), leads
after 20–24 h at reflux to complete conversion of 1 and the
production of the two stereoisomer vinylphosphines 2a–d (Z)
and 3a–d (E) (Scheme 2).13 The ratio Z/E was determined by 1H
NMR. Only P–CHN bond formation was observed demonstrat-
rhodium( ) catalysts lead to the formation of E-alkenylphos-
I
phine oxides or phosphonates.7 The catalytic addition of
secondary phosphines HPR2 to non-functional alkynes is just
emerging. It is performed by lanthanides,8 palladium and nickel
catalysts,9 for the preferred production of alkenylphosphines
with addition of the phosphorus atom to the internal alkyne
carbon. All the above hydrophosphinylation and hydrophosphi-
nation processes were shown to take place via insertion of the
alkyne into M–H or M–PR2 bonds. To our knowledge, no
example of catalytic hydrophosphination of functional alkynes
has been reported in spite of its potential for a new direct route
to a wide range of polydentate ligands.
ing the selective anti-Markovnikov addition of the H–P(III
)
We now report the first example of direct hydrophosphina-
tion of propargyl alcohols in the presence of diphenylphosphine
catalysed by ruthenium complexes RuCl(PPh3)2(C5Me5) (A)
and RuCl(cod)(C5Me5) (B). This highly regioselective reaction
affords in one step functionalised vinylphosphines with P–CHN
bond formation via a vinylidene ruthenium intermediate
(Scheme 1).
bond across the alkyne. The reaction is also stereoselective as
the Z isomer is always preferentially formed. For the derivative
2 with Z configuration, 1H NMR spectroscopy indicates an O–
H…P interaction between the hydroxy group proton and the
phosphorus atom (2a, d = 3.18 ppm and J(H,P) = 11.7 Hz for
the hydroxy proton). Chromatography of the 2–3 mixture led to
an increase of the E/Z ratio, and by using silica gel or basic and
neutral alumina a fast complete isomerisation of 2 to 3 was
observed. Monitoring the transformation of 2d/3d by 1H NMR
showed that a Z/E ratio of 4/1 is approximately constant during
the reaction.
In order to gather information about the reaction mechanism
several experiments were carried out. RuCl(cod)(C5Me5) (B) in
the presence of two equivalents of HPPh2 and NH4PF6 in
chloroform at room temperature has its cod ligand displaced and
gives [Ru(C5Me5)(Ph2PH)2]+PF62 (C)+. The intermediate (C)+
formation was monitored by 31P NMR: after a few minutes of
reaction in chloroform, we observed the complete coordination
of the two secondary phosphines on the ruthenium center (d =
+37.8 ppm vs. d = 239 ppm for the free secondary phosphine).
The stoichiometric reaction of (A) with 1a and NH4PF6 in
chloroform led to the isolation of vinylidene complex (4)
resulting from the dehydration of the ruthenium activated
propargyl alcohol (Scheme 3).
Whereas most ruthenium(II) complexes activate propargyl
alcohols via metal allenylidene intermediates RuNCNCNCR2,10
RuCl(PPh3)2(C5Me5) (A), in the presence of NH4PF6, stoi-
chiometrically reacts with propargyl alcohols to give the
vinylidene derivative Ru(NCNCHCR2OH)(PPh3)2(C5Me5)-
11
PF6 and ruthenium vinylidene intermediates are well known
to favour nucleophilic addition to the RuNC carbon atom.12
Consequently, the addition of diphenyphosphine to in situ
generated vinylidene has been attempted.
1-Ethynyl-1-cyclohexanol 1a was reacted with 1.2 equiva-
lents of diphenylphosphine in previously neutralised chloro-
form, by treatment with Na2CO3, in the presence of 5 mol% of
complex (A) and NH4PF6. After 24 hours at reflux, complete
Scheme 1
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CHEM. COMMUN., 2003, 696–697
This journal is © The Royal Society of Chemistry 2003

Table 1 Influence of the catalyst on the hydrophosphination of 1aa
Catalyst
Selectivity 2a/3ab
RuCl(C5Me5)(cod)
95/5
Ru(C5Me5)(CH3CN)3PF6
RuCl(C5Me5)(PPh3)2
Ru(C5H5)(CH3CN)3PF6
RuCl(C5H5)(PPh3)2
80/20
85/15
35/65
45/55
Scheme 3
This observation shows the role of Na2CO3 is simply to
inhibit dehydration of the vinylidene intermediate in the
catalytic cycle. The complex (4) is also catalytically active
under the general reaction conditions (Scheme 2) with 10%
Na2CO3.
a Conditions as in Scheme 2. Complete GC conversion after 20–24 h.
b Ratio Z/E was determined by 1H NMR.
Based on these results, the catalytic cycle from precursor (B)
is likely to proceed as indicated in Scheme 4: i) formation of
intermediate [Ru(C5Me5)(Ph2PH)2]+X2 (C)+, identified by
spectroscopy for X2 = PF62, ii) formation of the unstable
vinylidene (D), analogous to the dehydrated isolated complex
(4) arising from (A), iii) addition of an external Ph2PH to the
electrophilic vinylidene carbon of (D).
The stereoselectivity of the reaction dramatically depends on
the nature of the propargylic alcohol substituents R1 and R2 and
on the nature of the ruthenium(II) catalyst precursors. With the
Cp*RuXL2 catalyst precursors (A) and (B), the Z isomer is
always obtained as the major product, whereas in the case of
CpRuXL2 precursors we observed by contrast the major
formation of the E isomer (Table 1).
This work was supported by the CNRS and the Ministère de
la Recherche. The authors are grateful to the latter for a PhD
grant to F. M. and to the European Union for support via the
Cost Program D17 and Socrates Program Exchange for H. L.
with the University of Poznan (Poland).
Notes and references
1 D. G. Gilheany and C. M. Mitchell, in The Chemistry of Organophos-
phorus Compounds, vol. 1, ed. F. R. Hartley, J. Wiley and Sons,
Chichester, 1990, pp. 151–190.
2 H. Brunner and J. Furst, Tetrahedron, 1994, 50, 4303; Y. Yamanoi and
T. Imamoto, J. Org. Chem., 1999, 64, 2988; Y. Gimbert, F. Robert, A.
Durif, M.-T. Averbuch, N. Kann and A. E. Greene, J. Org. Chem., 1999,
64, 3492.
This difference of stereoselectivity is likely due to the steric
hindrance of the C5R5 group and also of the propargyl alcohol
groups. Indeed, the Scheme 2 results indicate that the bulkier
cyclohexyl substituent leads to the higher 2a/3a ratio (95/5).
In order to show that the reaction is not restricted to propargyl
alcohols but can also be performed with vinylidene precursors,
an initial study of the hydrophosphination of terminal alkynes
RC·CH (R = Ph, Bu, SiMe3) has been carried out. It also leads
to the corresponding alkenylphosphines Ph2PCHNCHR with
stereoselective formation of the Z isomer (Z/E = 93/7 for R =
Ph).
However the corresponding hydrophosphination of alkynes
with internal C·C bonds cannot be achieved (e.g. CH3–C·C–
C6H5), thus again supporting the vinylidene intermediate.
The above results show a novel catalytic method to prepare
alkenylphosphines with hydroxy functionality via regiose-
lective hydrophosphination of propargyl alcohols. This reac-
tion, that is catalysed by RuX(L)2C5Me5 complexes and
proceeds via the formation of a vinylidene intermediate, has
potential for access to new bifunctional phosphorus ligands.
3 H. R. Hudson, in The Chemistry of Organophosphorus Compounds, vol.
1, ed. F. R. Hartley, J. Wiley and Sons, Chichester, 1990, pp. 309–401;
N. Dankowski, in The Chemistry of Organophosphorus Compounds,
vol. 1, ed. F. R. Hartley, J. Wiley and Sons, Chichester, 1990, pp.
496–499; T. N. Mitchell and K. Heesche, J. Organomet. Chem., 1991,
409, 163; K. Heesche-Wagner and T. N. Mitchell, J. Organomet. Chem.,
1994, 468, 99.
4 D. K. Wicht and D. S. Glueck, in Catalytic Heterofunctionalization, vol.
5, eds. A. Togni and H. Grützmacher, Wiley-VCH, Weinheim, 2001, pp.
143–170.
5 L.-B. Han, N. Choi and M. Tanaka, Organometallics, 1996, 15, 3259;
L.-H. Han and M. Tanaka, Chem. Commun., 1999, 395; L.-B. Han, C.-
Q. Zhao, S.-Y. Onozawa, M. Goto and M. Tanaka, J. Am. Chem. Soc.,
2002, 124, 3842.
6 L.-B. Han, R. Hua and M. Tanaka, Angew. Chem., Int. Ed., 1998, 37,
94.
7 L.-B. Han, C.-Q. Zhao and M. Tanaka, J. Org. Chem., 2001, 66, 5929;
C.-Q. Zhao, L.-B. Han, M. Goto and M. Tanaka, Angew. Chem., Int. Ed.,
2001, 40, 1929.
8 M. R. Douglass and T. J. Marks, J. Am. Chem. Soc., 2000, 122, 1824; K.
Takaki, M. Takeda, G. Koshoji, T. Shishido and K. Takeira, Tetra-
hedron Lett., 2001, 42, 6357; M. R. Douglass, C. L. Stern and T. J.
Marks, J. Am. Chem. Soc., 2001, 123, 10221.
9 M. A. Kazankova, I. V. Efimova, A. N. Kochetkov, V. V. Afanas’ev, I.
P. Beletskaya and P. H. Dixneuf, Synlett, 2001, 4, 497.
10 M. I. Bruce, Chem. Rev., 1998, 98, 2797; Y. Nishibayashi, I. Wakiji, Y.
Ishii, S. Uemura and M. Hidai, J. Am. Chem. Soc., 2001, 123, 3393; Y.
Nishibayashi, Y. Inada, M. Hidai and S. Uemura, J. Am. Chem. Soc.,
2002, 124, 7900–7901.
11 R. Le Lagadec, E. Roman, L. Toupet, U. Mueller and P. H. Dixneuf,
Organometallics, 1994, 13, 5030–5039.
12 C. Bruneau and P. H. Dixneuf, Acc. Chem. Res., 1999, 32, 311.
13 Selected data: 2a :1H NMR (200 MHz, CDCl3, 25 °C): d = 7.23–7.44
(m, 10H, Ph), 6.58 (dd, J(H,H) = 12.3 Hz, J(H,P) = 27.5 Hz, 1H; CH),
6.19 (dd, J(H,H) = 12.3 Hz, J(H,P) = 3.4 Hz, 1H; CH), 3.18 (d, J(H,P)
= 12.1 Hz, 1H; OH), 1.38–1.79 (m, 10H, (CH2)5). 31P NMR (81 MHz,
CDCl3, 25 °C) d = 228.3 ppm. 13C NMR (50 MHz, CDCl3, 25 °C) d
= 21.9 (s, CH2), 25.3(s, CH2), 38.9 (s, CH2), 74.2 (s, C–OH), 125.3 (d,
J(C,P) = 12.2 Hz; CHN), 128.6 (d, J(C,P) = 7.2 Hz; Ph), 128.6 (s, Ph),
132.6 (d, J(C,P) = 18.3 Hz; Ph), 138.9 (d, J(C,P) = 7.3 Hz; Ph), 154.3
(d, J(C,P) = 16.0 Hz; –CHN). 3a: 1H NMR (200 MHz, CDCl3, 25 °C)
d = 7.22–7.50 (m, 10H, Ph), 6.49 (dd, J(H,H) = 16.8 Hz, J(H,P) = 6.9
Hz, 1H; CH), 6.27 (dd, J(H,H) = 16.8 Hz, J(H,P) = 14.8 Hz, 1H; CH),
1.39–1.81 (m, 10H, (CH2)5). 31P NMR (81 MHz, CDCl3, 25 °C) d =
212.9 ppm. HRMS calcd. for C20H23OP 310.14865, found
310.14794.
Scheme 4
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