Reaction of terminal phosphinidene complexes with dihydrogen

Article abstract of DOI:10.1021/om2009974

The reaction of H₂ with [RP-W(CO)₅] (R = Ph, Me) above 120 °C leads, first, to the secondary diphosphine complex (RPH-PHR)(W(CO)₅)₂ and then to the primary phosphine complex (RPH₂)(W(CO)₅). On the basis of DFT calculations, the mechanism most likely involves the addition of H₂ to the P-W bond, followed by the formation of the radical [RPH-W(CO)₅] ^? by homolysis of the W-H bond. In the case of [PhNHP-W(CO) ₅], the hydrogenolysis takes place at the P-N bond and ultimately produces the secondary diaminophosphine complex ((PhNH)₂PH)(W(CO) ₅).

Full text of DOI:10.1021/om2009974

Note
pubs.acs.org/Organometallics
Reaction of Terminal Phosphinidene Complexes with Dihydrogen
Matthew P. Duffy, Liow Yu Ting, Leo Nicholls, Yongxin Li, Rakesh Ganguly, and Franco̧ is Mathey*
Division of Chemistry & Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
S
* Supporting Information
ABSTRACT: The reaction of H2 with [RP-W(CO)5] (R = Ph,
Me) above 120 °C leads, first, to the secondary diphosphine
complex (RPH-PHR)(W(CO)5)2 and then to the primary
phosphine complex (RPH2)(W(CO)5). On the basis of DFT
calculations, the mechanism most likely involves the addition of H2 to the P−W bond, followed by the formation of the radical
[RPH-W(CO)5]• by homolysis of the W−H bond. In the case of [PhNHP-W(CO)5], the hydrogenolysis takes place at the P−N
bond and ultimately produces the secondary diaminophosphine complex ((PhNH)2PH)(W(CO)5).
he carbene-like chemistry of terminal phosphinidene
complexes [RP-M(CO)5] (M = Cr, Mo, W) is now
T
well established,1 but their reaction with dihydrogen has not
been investigated up to now. Two recent reports led us to get a
closer look at it. The first paper by Bertrand and co-workers2
described the insertion of reactive singlet carbenes into the H−
H bond of dihydrogen. It must be stressed that [RP-M(CO)5]
is strictly isolobal with a singlet carbene. The second paper by
Ruiz and co-workers3 described the reaction of H2 with a
bridging η2-phosphinidene complex leading to a primary
phosphine η1 complex with the breaking of one P−M bond.
We were thus curious to see whether it would be possible to
duplicate these reactions with [RP-M(CO)5]. To some extent,
the answer is positive, although the reaction conditions are
harsher and the mechanism of the reaction is quite different.
mixture of two diastereomers. The structure of the rac isomer
was fully established by X-ray crystal structure analysis (Figure
RESULTS AND DISCUSSION
■
Our initial experiments were performed with [PhP-W(CO)5].
Accordingly, the 7-phosphanorbornadiene precursor 14 was
heated in an autoclave with hydrogen at variable temperature
and pressure. A complete conversion into the expected
phenylphosphine complex 2 was observed at 150 °C under
20 bar of H2 (eq 1).
Figure 1. X-ray crystal structure of rac-diphosphine complex 3. Main
distances (Å) and angles (deg): W1−P1 = 2.4931(9), W2−P2 =
2.4961(9), P1−C6 = 1.820(4), P2−C12 = 1.817(4), P1−P2 =
2.2352(13); P2−P1−W1 = 119.04(4), P2−P1−H = 97(2), P2−P1−
C6 = 105.38(12), W1−P1−P2−W2 = 166.77, C6−P1−P2−C12 =
78.23, H−P1−P2−H = 82.3.
As can be noticed, these conditions are significantly harsher
than those used with carbenes2 and bridging phosphinidenes,3
where the reactions take place around room temperature.
However, it must be stressed that the precursor yields the
phosphinidene only above 100−110 °C. In order to have an
insight into the possible mechanism, we repeated the
experiment at 120 °C, with unexpected results (eq 2).
1). When 3a,b is heated at 150 °C under 20 bar of H2, it is
completely transformed into 2 and, thus, appears as the initial
The trace product 4 has already been described5 and comes
from the addition of traces of water, present in the solvent, to
the phosphinidene. The major product 3a,b is formed as a
Special Issue: F. Gordon A. Stone Commemorative Issue
Received: October 16, 2011
Published: November 30, 2011
© 2011 American Chemical Society
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Note
product of the reaction of hydrogen with [PhP-W(CO)5]. An
obvious explanation for the formation of 3 would be the
addition of H2 onto the diphosphene [(PhPPPh)(W-
(CO)5)3] resulting from the dimerization of [PhP-W(CO)5].6
We have indeed demonstrated that this reaction cleanly
proceeds at 90 °C under 20 bar of H2 (reaction time 16 h,
yield of 3a,b 32%). However, this pathway appears to be
unlikely, because the thermolysis of 1 does not produce the
diphosphene in the absence of copper chloride. Another
possibility (as suggested by one of the reviewers) would be the
insertion of [PhP-W(CO)5] into the P−H bonds of 2. In order
to check this possibility, we allowed 2 to react with 1 at 120 °C
in toluene and in the absence of H2. Only traces of 3a,b were
observed. These observations lead us to propose the
Figure 3. SOMO (Kohn−Sham) of radical 5.
converted into 2 at 150 °C under 20 bar of H2 (see the
Experimental Section). Many phosphites are used as ligands in
catalytic reactions where hydrogen is present, such as the
hydroformylation reaction. Their industrial use has been
hampered by their sensitivity to hydrolysis. It is interesting to
know that hydrogenation of the P−O bond is another possible
pathway for their decomposition.
Then, we repeated similar experiments with [MeP-W(CO)5].
The conditions were slightly different, but the products were
similar. Just above the decomposition temperature of the 7-
phosphanorbornadiene precursor, we obtained mainly the
diphosphine complex (eq 4).
mechanism given in eq 3 for the reaction of H2 with [PhP-
W(CO)5].
This mechanism is closely related to the well-known
conversion of [H−Co(CO)4] into [Co2(CO)8] via the
intermediate radical [Co(CO)4]• formed by homolysis of the
metal−hydrogen bond.7 In order to check if this mechanism is
likely, we decided to perform a DFT analysis of 5. The
calculations were performed at the uB3PW91/6-31G(d)-
Lanl2dz(W) level.8 The structure is shown in Figure 2. It
The primary phosphine complex 8 is the sole product at 150
°C for 6.5 h. We have been able to crystallize the meso isomer
of 7. Its X-ray crystal structure is shown in Figure 4. It displays
Figure 2. Structure of radical 5 as computed by DFT. Main distances
(Å) and angles (deg): P1−W23 = 2.4682, P1−C12 = 1.7891, P1−H24
= 1.4138; C12−P1−W23 = 130.14, C12−P1−H24 = 100.84, H24−
P1−W23 = 122.95.
Figure 4. X-ray crystal structure of meso-diphosphine complex 7. Main
distances (Å) and angles (deg): W1−P1 = 2.4940(6), P1−C6 =
1.823(3), P1−P1A = 2.2061(11); P1A−P1−W1 = 119.83(4), P1A−
P1−H = 97.9(15), P1A−P1−C6 = 102.06(9), W1−P1−P1A−W1A =
C6−P1−P1A−C6A = H−P1−P1A−H = 180.00.
corresponds to a local minimum on the energy hypersurface
(no negative frequency). At 2.468 Å, the P−W bond is
relatively short (compare with the structure of 3) and has
probably some multiple-bond character. However, the P atom
retains some pyramidality (∑(C−P−C) = 354°). The SOMO
(Figure 3) shows a high localization at phosphorus. According
to the calculations, 75% of the spin is localized at P and only 5%
at W. This explains why the dimerization takes place at P and
supports the proposed mechanism. Another interesting
observation was also made. The side product 4 is completely
an all-trans conformation. The most striking difference with the
structure of rac-3 is the much shorter P−P bond at 2.2061(11)
Å vs 2.2352(13) Å for 3. This probably reflects the steric
repulsion that exists between the two P subunits in rac-3.
Bertrand2 has stressed the fact that the reactivity of carbenes
toward hydrogen is heavily dependent on their substitution
pattern. We, therefore, decided to check whether the use of an
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Note
was purified by column chromatography (0 °C) with 90/10 hexane/
methylene chloride solution as the eluent, to give a white film of 2
(0.0383 g, 28.8% yield).
aminophosphinidene such as [PhNHP-W(CO)5] would change
the course of the reaction with hydrogen. In this case, the
precursor is the phosphirane complex9 9 and the phosphini-
dene is generated at lower temperature than in the preceding
cases. The outcome of the reaction was unexpected. The sole
product is the secondary diaminophosphine complex 10 (eq 5).
31P NMR (CD2Cl2): δ −86.2, 1JPW = 220 Hz, 1JPH = 343 Hz (t). 1H
NMR (CD2Cl2): δ 5.80 (d, 1JPH = 343 Hz, H−P), 7.47−7.64 (m, Ph).
HRMS: m/z 433.9539 (calcd for C11H7O5P184W 433.9541).
Complex 2 has been previously described.10
Reaction of Dihydrogen with 3 at 150 °C. In the Parr reactor
were added the two inseparable isomers of 3 (0.0418 g, 0.048 mmol)
and toluene (6 mL). Next the reactor was filled with hydrogen gas
(20.0 bar) and heated for 3 h at 150 °C. The reactor was cooled to
room temperature, the pressure was released, and the reaction mixture
was transferred to another flask, where the solvent was removed by
vacuum. The product was purified by column chromatography (0 °C)
with 90/10 hexane/methylene chloride solution as the eluent, to give a
white film of 2 (0.0227 g, 54.2% yield).
Reaction of Dihydrogen with 4 at 150 °C. In the Parr reactor
were added compound 4 (0.1116 g, 0.25 mmol) and toluene (6 mL).
Next the reactor was filled with hydrogen gas (20.0 bar) and heated for
10 h at 150 °C. The reactor was cooled to room temperature, the
pressure was released, and the reaction mixture was transferred to
another flask where the solvent was removed by vacuum. The product
was purified by column chromatography (−5 °C) with 90/10 hexane/
methylene chloride solution as the eluent, to give a white film of 2
(0.0484 g, 45.0% yield).
Complex 10 has been fully characterized by X-ray crystal
structure analysis (see the Supporting Information). The
mechanism of its formation is quite obvious. The hydro-
genolysis of the P−N bond produces aniline, which reacts with
the aminophosphinidene complex to yield 10. On the basis of
this result, we can expect a number of different outcomes with
functional phosphinidene complexes and, in some cases, we
might get interesting products for further synthetic applications.
EXPERIMENTAL SECTION
Reaction of Dihydrogen with [MeP-W(CO)5] at 120 °C. In the
Parr reactor were added 7-methylphosphanorbornadiene tungsten
pentacarbonyl complex (0.1994 g, 0.34 mmol) and toluene (7 mL).
Next the reactor was filled with hydrogen gas (20.0 bar) and heated for
7 h at 120 °C. The reactor was cooled to room temperature, the
pressure was released, and the reaction mixture was transferred to
another flask where the solvent was removed by vacuum. The product
was purified by column chromatography (−15 °C) with 80/20
hexane/methylene chloride solution as the eluent, to give a light
yellow solid containing two inseparable isomers of 7 (0.0273 g, 21.9%
yield). Crystals were grown from a 50/50 hexane/methylene chloride
solution at −25 °C.
■
All reactions were carried out with distilled dry solvents. Silica gel
(230−400 mesh) was used for the chromatographic separations. NMR
spectra were recorded on either a JEOL ECA 400 or JEOL ECA
400SL spectrometer. All spectra were recorded at 298 K. Proton
decoupling was applied for 13C and 31P spectra. HRMS were obtained
on a Water Q-Tof Premier MS. X-ray crystallographic analyses were
performed on a Bruker X8 APEX CCD diffractometer or a Bruker
Kappa CCD diffractometer. Purified hydrogen (99.9995%) was used
for all reactions. All reactions were performed inside a glass line in a
Parr Instrument Co. 4560 mini bench top reactor, using a Parr
Instrument Co. 4848 reactor controller.
Isomer A. 31P NMR (C6D6): δ −62.6, 1JPH = 342 Hz, ∑JPW = 156
Reaction of Dihydrogen with [PhP-W(CO)5] at 120 °C. In the
Parr reactor were added 7-phenylphosphanorbornadiene tungsten
pentacarbonyl complex (0.1075 g, 0.16 mmol) and toluene (6 mL).
Next the reactor was filled with hydrogen gas (20.0 bar) and heated for
3 h at 120 °C. The reactor was cooled to room temperature, the
pressure was released, and the reaction mixture was transferred to
another flask where the solvent was removed by vacuum. The product
was purified by column chromatography (0 °C) with 90/10 hexane/
methylene chloride solution as the eluent, to give a colorless film
containing two inseparable isomers (0.0223 g, 31.3% yield). Crystals
were grown from a 50/50 hexane/methylene chloride solution at −25
1
Hz. H NMR (C6D6): δ 1.01 (m, CH3), 4.12 (dm, H−P) 13C NMR
(C6D6): δ 12.21 (pseudo-t, ∑JCP = 12.5 Hz, CH3), 195.76 (pseudo-t,
∑JCP = 2.9 Hz, cis CO), 197.75 (pseudo-t, ∑JCP = 12.4 Hz, trans
CO). HRMS: m/z 742.8691 (calcd for C12H9O10P2184W2 742.8690).
Isomer B. 31P NMR (C6D6): δ −67.0, 1JPH = 341 Hz, ∑JPW = 156
1
Hz. H NMR (C6D6): δ 1.01 (m, CH3), 4.42 (dm, H−P). 13C NMR
(C6D6): δ 10.28 (pseudo-t, ∑JCP = 14.4 Hz, CH3), 195.76 (pseudo-t,
∑JCP = 2.9 Hz, cis CO), 197.72 (pseudo-t, ∑JCP = 12.4 Hz, trans
CO). HRMS: m/z 742..8691 (calcd for C12H9O10P2184W2 742.8690).
Reaction of Dihydrogen with [MeP-W(CO)5] at 150 °C. In the
Parr reactor were added the 7-methylphosphanorbornadiene tungsten
pentacarbonyl complex (0.2286 g, 0.39 mmol) and toluene (7 mL).
Next the reactor was filled with hydrogen gas (20.0 bar) and heated for
5 h at 150 °C. The reactor was cooled to room temperature, the
pressure was released, and the reaction mixture was transferred to
another flask where the solvent was removed by vacuum. The product
was purified by column chromatography (−15 °C) with 90/10
hexane/methylene chloride solution as the eluent, to give a white film
of 8 (0.0519 g, 36.1% yield).
°C.
1
Isomer A. 31P NMR (CD2Cl2): δ −19.7, JPH = 345 Hz, ∑JPW
=
1
1
152 Hz. H NMR (CD2Cl2): δ 6.40 (d, JPH = 345 Hz, H−P), 7.33−
7.58 (m, Ph). 13C NMR (CD2Cl2): δ 130.24 (pseudo-t, ∑JCP = 3.8
Hz, meta C), 130.60 (pseudo-t, ∑JCP = 18.1 Hz, ipso C), 132.44 (s,
para C), 133.71 (pseudo-t, ∑JCP = 6.7 Hz, ortho C), 195.64 (s, cis
CO), 198.12 (pseudo-t, ∑JCP = 12.4 Hz, trans CO). HRMS: m/z
866.8997 (calcd for C22H13O10P2184W2 866.9003).
Isomer B. 31P NMR (CD2Cl2): δ −22.8, JPH = 352 Hz, ∑JPW
=
1
1
1
31P NMR (C6D6): δ −122.1, JPW = 221 Hz. H NMR (C6D6): δ
1
1
161 Hz. H NMR (CD2Cl2): δ 6.41 (d, JPH= 352 Hz, H−P), 7.33−
7.58 (m, Ph). 13C NMR (CD2Cl2): δ 128.78 (pseudo-t, ∑JCP = 18.1
Hz, ipso C), 129.90 (pseudo-t, ∑JCP = 3.8 Hz, meta C), 132.19 (s,
para C), 134.38 (pseudo-t, ∑JCP = 6.7 Hz, ortho C), 195.89 (s, cis
CO), 198.33 (pseudo-t, ∑JCP = 12.4 Hz, trans CO). HRMS: m/z
866.8997 (calcd for C22H13O10P2184W2 866.9003).
0.57 (m, CH3), 3.37 (dq, JPH = 340 Hz, H−P). 13C NMR (C6D6): δ
4.40 (d, JCP = 31.6 Hz, CH3), 196.33 (d, JCP = 6.7 Hz, cis CO),
1
1
199.00 (d, JCP = 21.1 Hz, trans CO). HRMS: m/z 371.9386 (calcd for
C6H5O5P184W 371.9384).
Complex 8 has been previously described.11
Reaction of Dihydrogen with [PhNHP-W(CO)5]. In the Parr
reactor were added the 1-phenylaminophosphirane tungsten penta-
carbonyl complex12 (0.1152 g, 0.24 mmol) and toluene (6 mL). Next
the reactor was filled with hydrogen gas (20.0 bar) and heated for 4 h
at 90 °C. The reactor was cooled to room temperature, the pressure
was released, and the reaction mixture was transferred to another flask,
where the solvent was removed by vacuum. The product was purified
Reaction of Dihydrogen with [PhP-W(CO)5] at 150 °C. In the
Parr reactor were added 7-phenylphosphanorbornadiene tungsten
pentacarbonyl complex (0.2006 g, 0.31 mmol) and toluene (6 mL).
Next the reactor was filled with hydrogen gas (20.0 bar) and heated for
4 h at 150 °C. The reactor was cooled to room temperature, the
pressure was released, and the reaction mixture was transferred to
another flask, where the solvent was removed by vacuum. The product
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Note
by column chromatography (−10 °C) with 70/30 hexane/methylene
chloride solution as the eluent, to give 10 as a faint yellow solid
(0.0424 g, 64.7% yield). Colorless crystals were grown from a 50/50
hexane/methylene chloride solution at −25 °C.
1
1
31P NMR (CD2Cl2): δ 29.8, JPW = 289 Hz. H NMR (CD2Cl2): δ
2
3
5.05 (dd, JHP = 14.2 Hz, JHH = 6.4 Hz, H−N), 6.98−7.27 (m, H−
Ph), 8.02 (dt, 1JHP = 401 Hz, 3J = 6.4 Hz, H−P). 13C NMR (CD2Cl2):
3
δ 119.52 (d, JCP = 5.7 Hz, ortho C), 123.19 (s, para C), 129.93 (s,
2
2
meta C), 143.30 (d, JCP = 5.8 Hz, ipso C), 196.24 (d, JCP = 7.7 Hz,
cis CO), 198.77 (d, 2JCP = 26.9 Hz, trans CO). HRMS: m/z 540.0070
(calcd for C17H13N2O5P184W, 540.0072)
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files and figures giving X-ray crystal structure analysis and
NMR spectra of compounds 3, 7, and 10. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
* E-mail: fmathey@ntu.edu.sg.
■
ACKNOWLEDGMENTS
We thank the Nanyang Technological University in Singapore
for financial support of this work.
■
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