Terminal Phosphido Complexes of the Ru(n5-Cp?) Fragment

Article abstract of DOI:10.1021/acs.organomet.9b00266

In situ generation of the five-coordinate complex Ru(n⁵-Cp?)(PR₂)(PPh₃) (2), via dehydrohalogenation of Ru(n⁵-Cp?)Cl(PR₂H)(PPh₃), has allowed its reactivity toward a range of small molecules to be compared with that of its well-studied analogue Ru(n⁵-indenyl)(PR₂)(PPh₃) (1), in a study designed to assess the likelihood of variable hapticity in the chemistry of complex 1. Reactions of 2 with hydrogen, carbon monoxide, phenylacetylene, ethylene, acrylonitrile, and 1-hexene demonstrate enhanced nucleophilicity/basicity of the terminal phosphido ligand in 2 relative to that in complex 1. Complex 2 also exhibits greater lability of the PPh₃ ligand, leading to substitutional product mixtures that were not observed for 1. Both of these features are consistent with the more electron-rich and sterically imposing nature of the Cp? ligand in 2 relative to the indenyl ligand in 1. Nevertheless, the fundamental transformations of the phosphido ligand are comparable for the two complexes. This suggests that variable hapticity does not play a role in reactions of indenyl complex 1, since n⁵-n³ shifts are unlikely to occur for Cp? complex 2. The implications of these reactivity studies for the design of highly active, yet stable, ruthenium half-sandwich catalysts for hydrophosphination are discussed.

Full text of DOI:10.1021/acs.organomet.9b00266

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Terminal Phosphido Complexes of the Ru(η5‑Cp*) Fragment
Jin Yang,† Sophie Langis-Barsetti,† Hayley C. Parkin,† Robert McDonald,‡
and Lisa Rosenberg*,†
†Department of Chemistry, University of Victoria, P.O. Box 1700 STN CSC, Victoria, British Columbia V8W 2Y2, Canada
‡X-ray Crystallography Laboratory, Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
S
* Supporting Information
ABSTRACT: In situ generation of the five-coordinate complex Ru(η5-
Cp*)(PR2)(PPh3) (2), via dehydrohalogenation of Ru(η5-Cp*)Cl(PR2H)-
(PPh3), has allowed its reactivity toward a range of small molecules to be
compared with that of its well-studied analogue Ru(η5-indenyl)(PR2)(PPh3)
(1), in a study designed to assess the likelihood of variable hapticity in the
chemistry of complex 1. Reactions of 2 with hydrogen, carbon monoxide,
phenylacetylene, ethylene, acrylonitrile, and 1-hexene demonstrate enhanced
nucleophilicity/basicity of the terminal phosphido ligand in 2 relative to that
in complex 1. Complex 2 also exhibits greater lability of the PPh3 ligand,
leading to substitutional product mixtures that were not observed for 1. Both
of these features are consistent with the more electron-rich and sterically
imposing nature of the Cp* ligand in 2 relative to the indenyl ligand in 1.
Nevertheless, the fundamental transformations of the phosphido ligand are comparable for the two complexes. This suggests
that variable hapticity does not play a role in reactions of indenyl complex 1, since η5−η3 shifts are unlikely to occur for Cp*
complex 2. The implications of these reactivity studies for the design of highly active, yet stable, ruthenium half-sandwich
catalysts for hydrophosphination are discussed.
Scheme 1. Reactivity of Indenyl Phosphido Complex 1
INTRODUCTION
■
Metal complexes with terminal phosphido ligands have been
implicated as intermediates in catalytic hydrophosphination
(addition) and phosphination (cross-coupling) reactions.1
Their participation in both of these processes is often proposed
to rely on the established nucleophilicity of the M-PR2
fragment, for example in outer-sphere nucleophilic attack of
the phosphido ligand at activated substrates (e.g. RX or
Michael-type alkenes) or inner-sphere migratory insertion
processes.1e Our studies of phosphido complexes of a
ruthenium indenyl half-sandwich fragment have demonstrated
both inner- and outer-sphere reactivities,2 and we have
reported the activity of this system for the catalytic
hydrophosphination of activated alkenes, which apparently
relies on outer-sphere P−C bond formation.3
Two key features of the low-coordinate phosphido complex
Ru(η5-indenyl)(PR2)(PPh3) (1) drive its reactivity (e.g.
Scheme 1). One is Lewis acidity at Ru; adducts with L-donors
such as CO form readily (a), which disrupts the Ru = P double
bond, changing the geometry at phosphorus from planar to
pyramidal.2a,d,4 The other is nucleophilicity/basicity at P; for
example, polar addenda such as MeI or HCl react to place
electropositive Me+ or H+ at P (b).2a,d,4 The strength of this P-
basicity is illustrated by the addition of acetonitrile to 1 when
R = Cy or Pri: instead of an N-bound nitrile adduct, the
metalated complex Ru(η5-indenyl)(CH2CN)(PR2H)(PPh3)
results (c).2a These two features appear to work in concert
in the addition of H2 and in the insertion of unactivated
alkenes such as ethylene and 1-hexene into the Ru−P bond in
1 (d).2d,e
We have been asked whether variable (η5 → η3) hapticity of
the indenyl ligand is important in the reactions described
above. We are reasonably certain that it is not, since we have
found no evidence for ring-slippage in our studies so far, and
because the change of phosphido geometry from planar to
pyramidal apparently provides ready access to a vacant
coordination site at Ru, for example in the insertion of
ethylene into the Ru-PR2 bond.2e Also, kinetic studies of
phosphine substitution at the parent complex Ru(η5-indenyl)-
(Cl)(PPh3)2 and a cationic derivative [Ru(η5-indenyl)-
(NCPh)(PPh3)2]+ point to a dissociative mechanism, rather
than the associative mechanism that would belie the
Received: April 24, 2019
© XXXX American Chemical Society
A
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participation of variable hapticity.5 Nevertheless, we initiated
study of the analogous Cp* system to address this issue, since
pathways relying on variable hapticity should be disfavored for
this η5-ligand.6,7
The 1H and 13C NMR spectra for complexes 3a−d are very
similar to those for their η5-indenyl analogues, including
significant broadening of the H signals for PPh3 in 3a,c,d,
1
which is attributed to slowed rotation around the Ru-PPh3
bond on the NMR time scale for these sterically congested
complexes.10 31P{1H} NMR spectra show comparable shifts for
signals due to the PPh3 ligand (δ 45−50 ppm), but signals due
to the secondary phosphines, which for the indenyl complexes
appear at lower field than the PPh3 signals (δ 50−68 ppm), all
appear at higher field (δ 34−48 ppm) for the Cp* complexes.
This corresponds to a smaller Δδ 31P relative to the chemical
shifts for the free secondary phosphines. These 31P{1H} signals
Further incentive to take a closer look at the behavior of
phosphido ligands at the Ru(η5-Cp*) fragment relative to
Ru(η5-indenyl) comes from the report of Morris and co-
workers of the activity of Ru(η5-Cp*)(PPh2)(PP) complexes,
where “PP” is 1,2-bis(diphenylphosphino)ethene or -benzene,
in the catalytic hydrophosphination of acrylonitrile.8 These
complexes show initial activities an order of magnitude greater
than we observe for our indenyl system, for which the
structurally similar Ru(η5-indenyl)(PPh2)(PPh2H)(PPh3) has
been implicated as an active species.3 However, unlike the
indenyl system, these Cp* catalysts deactivate rapidly, via an
unknown mechanism, so the reaction does not go to
completion.
Here we report in situ generation of the highly reactive
planar phosphido complex Ru(η5-Cp*)(PR2)(PPh3) (2) and
an examination of its reactivity with a variety of small
molecules. These studies show sufficient similarities to the
established chemistry of the indenyl complex 1 to suggest that
ring-slippage does not play an important role in these half-
sandwich systems. However, they also highlight some striking
differences in reactivity that can be attributed to increased
steric crowding at the Ru(η5-Cp*) fragment and enhanced P-
basicity of its phosphido complexes. The implications of these
results for harnessing the Cp*Ru core in catalytic hydro-
phosphination are discussed.
2
for 3a−d also exhibit slightly lower JPP values (40−43 Hz,
compared to 42−49 Hz for the indenyl complexes).
We presume that the greater substitutional lability leading to
oversubstitution in these complexes derives primarily from
increased steric hindrance associated with the bulky Cp*
ligand. Substitution and oversubstitution is driven by the loss
of relatively bulky PPh3. Some evidence for the importance of
this steric hindrance in solution comes from the observation of
ligand redistribution when analytically pure, crystalline 3a (R =
Cy) is dissolved in C6D6; 31P{1H} NMR shows trace (1.3%),
equimolar amounts of both Ru(η5-Cp*)Cl(PPh3)2 and 4a in
solution, in addition to 3a. PCy2H is about the same size as
PPh3 (cone angles 148° and 145°, respectively); no such
redistribution is seen for the η5-indenyl analogue of 3a (3ai),10
or for complexes 3b−d, which contain smaller phosphines.
Solid state structures of 3a,b (Figures 1, 2) also give some
indication of the impact of the steric bulk of the Cp* ligand.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Secondary Phos-
phine Precursors. We prepared secondary phosphine
complexes 3a−d from Ru(η5-Cp*)Cl(PPh3)2 (Scheme 2).
Scheme 2. Synthesis of Complex 3
These substitution reactions occur rapidly at RT in toluene,
and, unlike the analogous indenyl chemistry, inevitably give
small to significant amounts of the disubstituted products 4a−
d. Lubian and Paz-Sandoval previously reported the synthesis
of the diphenylphosphine complex 3c; they too describe the
ease of formation of 4c in this reaction.9 For the indenyl
system, the issue of unintended oversubstitution arose only for
smallest of the secondary phosphines examined, PEt2H.10 In
that case the Cl− was substituted to give [Ru(η5-indenyl)-
(PEt2H)2(PPh3)]Cl as the major product; we see no evidence
for analogous substitution of the chloride ligand in these
reactions of the Ru(η5-Cp*) fragment.
The high solubility of these Cp* complexes in even nonpolar
hydrocarbons posed challenges in the isolation and purification
of 3. However, the slightly higher solubility of 4 allowed the
fractional crystallization of 3 from toluene layered with pentane
in all cases except for 3c (R = Ph), which typically contained
about 4% 4c. (The literature synthesis of 3c also leads to an
impurity of 5% 4c in the isolated complex.9)
Figure 1. Molecular structure of Ru(η5-Cp*)Cl(PCy2H)(PPh3) (3a)
showing the atom-labeling scheme. Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 30% probability level. The
hydrogen atom attached to P1 is shown with arbitrarily small thermal
parameters.
While the Ru−C5(centroid) and Ru−PPh3 distances are close
to those previously observed for the indenyl analogue of 3a
(see Supporting Information), the Ru-PR2H distances are
significantly longer for the two Cp* complexes: 2.33 Å (R =
Cy) and 2.29 Å (R = Et), compared with 2.26 Å for Ru(η5-
indenyl)Cl(PCy2H)(PPh3).10 These longer Ru−P bonds,
2
along with the solution 31P{1H} chemical shift and JPP data,
are consistent with weaker coordinate bonding of the
secondary phosphines in 3 relative to their indenyl analogues.
Dehydrohalogenation Reactions of 3a−d. Complexes
3a−d react with ∼1.2 equiv of KOBut in C6D6 to give a color
change from clear orange to dark red (3a,b) or dark blue
(3c,d), consistent with the formation of the five-coordinate
B
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Figure 2. Molecular structure of Ru(η5-Cp*)Cl(PEt2H)(PPh3) (3b)
showing the atom-labeling scheme. Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 30% probability level. The
hydrogen atom attached to P1 is shown with arbitrarily small thermal
parameters.
complexes Ru(η5-Cp*)(PR2)(PPh3) (2a−d) (Scheme 3).
While NMR analysis of these mixtures confirms the presence
Figure 3. Time-dependent speciation plots for the reactions of two
dialkylphosphine complexes, 3ai and 3b, with KOBut (300.27 MHz
1H NMR, C6D6).
Scheme 3. Dehydrohalogenation of 3 Using KOBut
Ru(η5-Cp*)H(PCy2H)(PPh3) (6a, vide infra), as determined
by 1H and 31P{1H} NMR, apparently resulting from β-H
elimination from an intermediate butyl complex (Scheme 4;
of 2 (diagnostic 31P{1H} signals for the planar PR2 ligand
appear as doublets at low field (δ 156−211 ppm) with
relatively large coupling to PPh3 (δ 56−63 ppm, 2JPP 67−72)),
during the time taken for consumption of 3 the reactions give
significant amounts of a second product, 5, resulting from
irreversible orthometalation of the PPh3 ligand in 2 (e.g.,
Scheme 3). Complexes 5a−d show upfield 31P{1H} NMR
signals for the κ2-(o-C6H4)PPh2 ligand at −10 to −19 ppm,
similar to the shifts we observe for their η5-indenyl
analogues.2d,4 We have been unable to isolate pure 2a−d
free of orthometalated 5a−d due to the high solubility of both
complexes and the steady conversion from 2 to 5 during
workup. Longer reaction times give the orthometalated
complexes 5a−d as the major products of all these
dehydrohalogenation reactions, and 5b−d can be isolated.
For 3a (R = Cy) the presence of other products in the reaction
mixture (Figure S15, Scheme S2) has precluded isolation of
pure 5a.
Monitoring the progress of these dehydrohalogenation
reactions provided insight into the steric and electronic
characteristics of this Ru(η5-Cp*) system. Time-dependent
speciation (Figure 3a) shows that indenyl complex 3ai (R =
Cy) is consumed quite rapidly over 1 h in its reaction with
KOBut, and that subsequent decomposition to orthometalated
5ai is very slow (the reaction takes days at RT). The analogous
Cp* complex 3a reacts much more slowly, showing just 40%
consumption over 4 h (Figure S15). The particular steric
congestion at 3a must play some role in the slow rate of
deprotonation, since the less hindered but comparably
electron-rich diethylphosphine complex 3b is consumed in
this reaction within 2 h (Figure 3b). However, attempted
dehydrohalogenation of 3a using the less sterically hindered
base n-BuLi gave butene and the ruthenium hydride complex
Scheme 4. Dehydrohalogenation of 3a Using n-BuLi
transient 31P{1H} signals due to the putative intermediate were
observed (Figure S19)). This selectivity for chloride
substitution and β-H elimination, rather than dehydrohaloge-
nation, is consistent with the previously observed reaction of
3ai with the comparably small base NaOMe, which gives the
hydride complex Ru(η5-indenyl)H(PCy2H)(PPh3).10
Progress of the dehydrohalogenation of 3a is complicated by
the competing ligand redistribution chemistry described above,
but complex 3b (Figure 3b) reacts cleanly, and serves to
highlight the apparent impact of greater electron density in the
Cp* system, since the steric impact is probably balanced by the
small size of the PEt2H ligand. The consumption of 3b takes
approximately twice as long as 3ai; this is consistent with rate-
limiting proton transfer that is slowed by less facile polarization
of the P−H bond in the more electron-rich Cp* complex. This
impact of the electron-rich Cp* ligand is notably offset by the
more acidic diarylphosphines in complexes 3c,d (1H δPH ∼
6.9 ppm, relative to ∼4.1 ppm for the dialkyl complexes 3a,b)
during dehydrohalogenation; these complexes are consumed in
under 30 min (Figures S17−S18), even faster than 3ai is
consumed under identical conditions.
For all four phosphido products 2a−d, orthometalation
occurs much faster than for the indenyl phosphido complex 1,
giving 60−80% 5a−d over 4 h (Figures 3, S15−S18). This
result is consistent both with higher P-basicities of 2 relative to
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1, which favors this intramolecular deprotonation reaction
(accordingly, the diaryl complexes 2c,d orthometalate slightly
more slowly than the dialkyl complexes 2a,b), and with steric
compression of the non-Cp* ligands in 2 relative to 1, which
places the ortho-C−H bonds of PPh3 in 2 closer to the
phosphido P.
Scheme 6. Product Distribution after 3 h for Reaction of
Dihydrogen with 2a Generated in Situ
Reactions of Phosphido Complexes 2 with Small
Molecules. To limit the rapid conversion of phosphido
complexes 2 to orthometalated 5 during NMR-scale reactions
of 2 with a variety of different reagents, we generated 2 in situ
under trapping conditions, adding the reagents of interest to
complex 3 in the presence of base. As described below, this
worked well for the reactions of complexes 3b−d, giving
relatively clean product mixtures, for which the major products
1
have been completely spectroscopically characterized via H,
13C, and 31P NMR (see below and Supporting Information).
More complex mixtures were observed for the reactions of
complex 3a (R = Cy), due partly to the presence of
equilibrium amounts of phosphine redistribution products
(vide supra) and partly to the extreme steric crowding in this
complex; the latter slows the rate of intermolecular reactions
relative to intramolecular orthometalation to give complex 5a,
and also allows the formation of some unusual low coordinate
species and substitution products.
Figure 4. Partial 202.51 MHz 31P{1H} NMR showing product
mixture resulting from addition of H2(g) to in situ-generated 2a in
C7D8. Inset: hydride region of 500.27 MHz 1H NMR. [Ru] = Ru(η5-
Cp*).
Hydrogen. Similar to their indenyl analogues,2d,4 com-
plexes 2b−d react rapidly with dihydrogen to give yellow-
orange solutions in which the major products are Ru(η5-
Cp*)H(PR2H)(PPh3), 6b−d, resulting from 1,2-addition
across the Ru−P double bond (Scheme 5). These complexes
phosphine analogue Ru(η5-Cp*)H3(PCy2H). These doublets
(2JHP ∼ 20 Hz) are consistent with the trigonal bipyramidal
geometry shown in Figure 4, in which all three hydride ligands
are in equivalent equatorial sites.12 However, adjacent to each
of the 31P{1H} singlets for these complexes is an additional
singlet of lower intensity, which we attribute to the presence of
square-based pyramidal isomers.13 Variable, low temperature
1H NMR confirms the presence of additional hydride signals
due to these isomers and points to fluxionality of these less
symmetric complexes on the NMR time scale (see Supporting
Information). These trihydride complexes probably form via
the substitution of PPh3 by η2-H2 (and subsequent oxidative
addition), for example during dehydrohalogenation of the
halide precursors Ru(η5-Cp*)Cl(PPh3)2 and 3a. (We see
signal due to free PPh3 in the 31P{1H} NMR spectra of this
mixture but do not see any free PCy2H.) We do not observe
this oxidative addition chemistry during the 1,2-addition of
hydrogen to the analogous indenyl complex 1,4 probably
because the PPh3 in that complex is not labile toward
substitution by H2, and possibly also because 1 is less electron-
rich than 2a.
Scheme 5. Reaction of Dihydrogen with 2b−d Generated in
Situ
show triplets (2JHP ∼ 35 Hz) in the hydride region of their 1H
NMR spectra (−12 to −13 ppm). For the diaryl phosphine
complexes these 1,2-addition reactions are complete within 30
min, while for the diethylphosphine complex, which is
generated more slowly via dehydrohalogenation, the reaction
is complete within 3 h at room temperature. Small amounts of
complex 5b−d also form in these reactions, and complex 6c (R
= Ph) is also accompanied by ∼2% of Ru(η5-Cp*)H(PR2H)2,
which forms from the small amount of 4c present in the
starting material. Complexes 6b−d are stable in the absence of
H2, and can be isolated as yellow powders.
Carbon Monoxide. Complexes 2a−d react readily with
CO in sealed NMR tube experiments to give bright orange
Ru(η5-Cp*)(PR2)(CO)(PPh3), 7a−d (Scheme 7). As for their
indenyl analogues,2d,4 31P{1H} NMR signals for these carbonyl
adducts show very small (negligible, in this case) 2JPP coupling
between the pyramidal PR2 ligand and PPh3. For 7b−d,
Although the orthometalated complex 5a (R = Cy)
dominates the reaction mixture after 3 h when hydrogen is
1
added to in situ-generated 2a, 31P{1H} and H NMR signals
for a small amount of the expected hydride complex 6a are also
1
observed (Scheme 6, Figure 4). In addition, the H NMR
Scheme 7. Reaction of Carbon Monoxide with 2 Generated
in Situ
spectrum shows signals due to three other hydride-containing
products, each of which correlates with a singlet in the 62−72
ppm region of the 31P{1H} NMR spectrum (1H/31P HMBC).
One hydride signal is a triplet that corresponds to Ru(η5-
Cp*)H(PCy2H)2, which forms from the small equilibrium
amount of 4a present in the starting material. The two other
hydride signals are doublets that correspond to the known
trihydride complex Ru(η5-Cp*)H3(PPh3)11 and its secondary
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slightly broadened singlets (ω1/2 ∼ 15 Hz) are observed for
both ligands (δPR2 15−30 ppm, δPPh3 54−61 ppm). For 7a
the Ru-PPh3 signal at 57 ppm is also a singlet, but the Ru-PCy2
is significantly broadened (ω1/2 58 Hz) and shifted downfield
to 63 ppm. This probably indicates a solution equilibrium
between the planar phosphido complex 2a (δPCy2 211 ppm)
and the pyramidal CO adduct 7a. The relative instability of 7a
with respect to 2a again reflects the amplification of steric
congestion at this Cp*Ru core with PCy2 or PCy2H ligands.
We previously observed a similar equilibrium for the pyridine
adduct of the indenyl analogue 2ai, but not for the adduct of
the smaller CO ligand.2a Although complexes 7b−d can be
isolated as bright yellow (7b) or orange (7c,d) powders, they
show some decomposition to as-yet unidentified products
during workup, as determined by IR (for 7c, which showed the
most decomposition, ∼30%) and 31P{1H} NMR (Figures
S51−S52). This data suggests the new complexes still contain
terminal CO and phosphido ligands, but further work is
required to characterize these products.
The Ru-PPh3 ligand in carbonyl adducts 7a−d can be
substituted by excess CO in the sealed NMR samples to give
the yellow bis-carbonyl adducts Ru(η5-Cp*)(PR2)(CO)2, 8a−
d (Scheme 7). This reaction occurs for the indenyl analogues
only when samples are left under an atmosphere of CO for 15
d or longer,14 but for complexes 7b−d we see impurities of 5−
13% 8b−d, respectively, after 3 h. The added steric congestion
in 7a facilitates this further substitution; 7a is the major
product observed after 30 min, but it is completely consumed
within 3 h to give 85% 8a, along with 8% 5a and some other,
unidentified products.
diethylphosphido ligand at the Cp*Ru core in 2b, relative to
the dicyclohexylphosphido ligand in 1. The diarylphosphido
complexes 2c,d are slightly less P-basic than 2b, based on their
slower decomposition via orthometalation (vide supra).
However, the reactions of 2c,d with phenylacetylene gave
the alkynyl products 10c,d as the major products (82−
85%),15,16 accompanied by 15−18% of the insertion products
9c,d. Since the diarylphosphido ligands in 2c,d are bulkier than
the diethylphosphido ligand in 2b, these results may represent
a balance point in terms of the ability of the phenylacetylene to
approach closely enough to Cp*Ru to allow insertion (an
inner-sphere process) and the basicity and availability of the
lone pair at the phosphido P.17 In this context, we might expect
the reaction of phenylacetylene with the very P-basic and
sterically hindered 2a to strongly favor formation of the alkynyl
complex 10a over the insertion product 9a. This selectivity is
indeed observed, in that we see some (∼20%) 10a and no 9a
at all, but the reaction is once again dominated by
intramolecular decomposition to the orthometalated complex
5a (57%), and small amounts of some other products are
observed (Figure S56).
Reduced steric congestion in the PEt2-containing complex
2b also permits its low catalytic activity for alkyne dimerization
(Scheme 9). When ∼10 equiv phenylacetylene is added to 2b
Scheme 9. Dimerization of Phenylacetylene Catalyzed by 2b
Phenylacetylene. The relatively sterically unhindered 2b
(R = Et) undergoes insertion of phenylacetylene to give a
phosphametallacyclobutene complex 9b as the major product
(80%, Scheme 8). The metallacyclic PEt2 group in 9b shows a
Scheme 8. Reaction of Phenylacetylene with 2b−d
Generated in Situ
we observe signals due to the E and Z isomers of the dimer 1,4-
1
diphenyl-1-buten-3-yne, as determined by H COSY NMR
(Figure S65), in addition to signals due to 9b and 10b.
Dimerization of terminal alkynes is known to be catalyzed by a
variety of half-sandwich Ru complexes.18 In this system, the
reaction probably involves substitution of PPh3 in 10b by
PhCCH to give an intermediate η2-alkyne complex, which
subsequently rearranges to two conformers of a vinylidene/
alkynyl complex, followed by insertion of the carbene portion
of the vinylidene ligand into the Ru−Cα bond of the alkynyl
ligand (Scheme 9).19 We do not observe this dimerization
chemistry for the other, more sterically crowded phosphido
complexes 2a,c,d, or for the (less labile) indenyl system.
Ethylene. Complexes 2a−d react with ethylene to give
mixtures of two insertion products (Scheme 10). One of these
diagnostic upfield 31P{1H} NMR signal at −41.9 ppm. The
regiochemistry of phenylacetylene insertion in 9b is confirmed
by correlation of the β-H signal at 7.45 ppm with the PEt2
phosphorus in the 1H/31P HMBC spectrum, and with the β-C
1
signal at 125.0 ppm in the H/13C HSQC spectrum. This 13C
signal shows larger coupling to PEt2 (1JCP = 43 Hz) than to
PPh3 (3JCP = 2 Hz). The quaternary α-C signal in 9b could not
1
be detected directly, but is observed indirectly in the H/13C
HMBC spectrum at ∼193 ppm, through its correlation with
signals due to the ortho protons on the adjacent phenyl group.
31P{1H} signals for a minor product (20%) of this reaction
include a doublet (2JPP = 38 Hz) due to PEt2H at 41.5 ppm,
Scheme 10. Reaction of Ethylene with 2 Generated in Situ
1
which shows JPH = 343 Hz in the 31P spectrum; we presume
this product is the terminal alkynyl complex 10b that results
from deprotonation of the alkyne by RuPEt2.
The reaction of indenyl complex 1 with phenylacetylene
gave analogous products to 9b and 10b,2b but the product
distribution leaned more heavily toward insertion (95%) than
deprotonation (5%). This points to higher basicity of the
E
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is the metallacyclic complex 11, analogous to the ethylene
insertion product obtained for the reaction of indenyl complex
1a with ethylene.2c,e For 2b−d, a second metallacyclic product,
12, results from the replacement of PPh3 in 11 by an η2-
ethylene ligand. Complexes 2b−d are consumed within 2 h in
these reactions with ethylene and give small amounts of the
orthometalation byproducts 5b−d (1−7%), while complex 2a
reacts more slowly (3−4 h) to give 5a as the major product,
along with just 14% 11a, 5% 12a, and other minor,
unidentified products (Figure S66). Complex 11b dominates
the product mixture for R = Et (82%), while the η2-ethylene
adducts 12c,d are the major products (74−83%) for the
reactions of diaryl phosphido complexes 2c,d with ethylene.
We did not observe substitution of PPh3 by ethylene for the
indenyl analogue of 11.
Complexes 11 and 12 show diagnostic high field 31P{1H}
NMR signals for the PR2 moiety incorporated into the
phosphametallacyclobutane (e.g. −13.0 ppm and −15.3 ppm
for the PCy2 group in 11a and 12a, respectively). Relatively
high field 13C{1H} shifts for the metallacycle carbon α- to Ru
(Figure 5) are also diagnostic of these structures (e.g. −16.1
Figure 6. 202.51 MHz 31P{1H} NMR of a sample of 2b in C7D8 that
was cooled to 0 °C in an ice bath while being sealed under an
atmosphere of ethylene. The bottom spectrum was run immediately
after the sample was sealed; the top spectrum was obtained 3 h later,
after the sample had warmed to RT.
occurred via an η2-ethylene adduct (e.g. Figure 6), and were
able to identify this intermediate both visually (it is a deep red
color, while 1 is deep blue) and spectroscopically, by
monitoring the reaction at −80 °C by NMR.2e In the current
studies we have been able to detect the formation of a
comparable intermediate by monitoring the reactions of
ethylene with samples of 2b−d that have been cooled to 0
°C. As for the indenyl system, an intense red color is associated
with formation of the adduct, which then changes to yellow-
orange as the mixture is warmed to RT. 31P{1H} NMR signals
attributable to this intermediate in formation of the PEt2
metallacycle 11b are marked with red dots in the bottom
spectrum in Figure 6. The relatively sharp signal at 53 ppm is
assigned to PPh3 and a broad singlet at −1 ppm is assigned to
the pyramidal PEt2 ligand. As for the analogous indenyl
complex, the breadth and relatively high field shift of the PEt2
signal probably result from an equilibrium between the η2-
adduct and the final 1,2-insertion product, 11b.
Acrylonitrile and 1-Hexene. Since the indenyl phosphido
complex 1 reacts with a wide range of alkenes to give
substituted metallacyclic products analogous to 11, we
screened two representative terminal alkenes for their reactivity
with 2, electron-deficient acrylonitrile and the simple, electron-
rich 1-hexene. Unfortunately, in the presence of the KOBut
used to generate 2 in situ, the activated acrylonitrile apparently
polymerizes;20 these attempted reactions gave pale yellow
precipitates, and 31P{1H} NMR indicated only unreacted 3 was
present in solution.
Figure 5. Positional labeling scheme for metallacycles 11 and 12.
ppm for the PEt2 complex 11b), while the 13C signal for the β-
carbon is typically shifted downfield (e.g. 36.3 ppm for 11b).
The metallacycle protons HA‑D show distinct 1H NMR
multiplets that were assigned through multinuclear two-
dimensional correlation and NOE experiments (see Support-
ing Information); the signal for HD is shifted downfield relative
to the other protons on the ring, typically appearing between 3
and 4 ppm. Two broad signals of equal intensity due to the η2-
ethylene ligand in complexes 12c,d appear between 1.6 and 2.0
1
ppm in the H NMR. These show NOE interactions with HC
on the metallacycle, correlations in the 1H/31P HMBC spectra
with the metallacycle PAr2 phosphorus, and correlations with
each other in the 2D 1H/1H TOCSY spectra. Cooling a sample
of 12c to −70 °C causes decoalescence of the two ethylene 1H
signals to four multiplets of equal intensity, consistent with
slowed rotation around the ethylene-Ru bond (Figure S72).
However, we see no signal due to the η2-ethylene carbons in
the 13C{1H} NMR spectra of these complexes, even at −70 °C.
1
Likewise, in H and 13C{1H} spectra of the reaction mixture
resulting from addition of ethylene to 2b (R = Et), we were
unable to find signals for the η2-ethylene ligand in 12b, even
when the sample was cooled to −70 °C. Since this species
comprises just 11% of the product mixture we presume these
signals are lost in the baseline or (for the 1H spectrum) overlap
with other signals in the busy alkyl region. Nevertheless, we are
confident of the structural assignment for complex 12b, based
on the 1:1 intensity of the 31P{1H} signals for 12b and free
PPh3 in the reaction mixture (consistent with substitution of
PPh3 by ethylene (Figure 6, top), and our ability to identify the
The most striking difference in reactivity that we observe for
the Cp*Ru phosphido complex 2 relative to the indenyl
complex 1 occurs for the addition of 1-hexene to 2. We
anticipated alkene insertion comparable to the ethylene
insertion reactions described above, to yield n-butyl-
substituted phosphametallacylobutanes. Instead, though, the
diaryl complexes 2c,d are consumed within 3 h in the presence
of this electron-rich, terminal alkene to give mixtures of the η3-
allyl complexes 13c,d and the orthometalated complexes 5c,d
1
metallacycle protons by in 12b by H/31P HMBC (Figure
1
S69).
(Scheme 11). 31P NMR signals for 13c,d show large JPH
1
In our studies of the reaction of ethylene with the indenyl
complex 1 we established computationally that 1,2-insertion
(324−325 Hz) for the secondary phosphine, while H spectra
show diagnostic downfield multiplets due to the central proton
F
DOI: 10.1021/acs.organomet.9b00266
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
catalysts, in which the PPh3 ligand in 2 is replaced with
substrate phosphine PR2H (Ru(η5-Cp*)(PR2)(PR2H)): de-
protonation of the coordinated secondary phosphine in this
putative complex would simply regenerate the reactive
Scheme 11. Reaction of 1-Hexene with 2c−d Generated in
Situ
−
phosphido ligand PR2 . We are currently exploring synthetic
routes to this complex and the related, coordinatively saturated
Ru(η5-Cp*)(PR2)(PR2H)2, in order to assess their stability
with respect to orthometalation and their activity in the
hydrophosphination of activated alkenes.
in the allyl group (e.g. δ 3.14−3.05 ppm for 13c), and signals
for all protons of allyl moiety correlate with the 31P signal in
the 1H/31P HMBC spectra. 13C signals for both terminal
carbons of the allyl moiety correlate with 1H P−H signals from
EXPERIMENTAL SECTION
■
General Details. Unless otherwise noted, all procedures were
carried out under nitrogen in a glovebox or using conventional
Schlenk techniques. Solvents (except methanol and ethanol, see
Supporting Information) were degassed by sparging with nitrogen for
25 min and dried by passing through columns of activated alumina in
a solvent purification system. Deuterated solvents (C7D8, C6D6,
Sigma-Aldrich) were dried over Na/benzophenone, degassed by three
freeze−pump−thaw cycles, and vacuum-transferred before use.
Unless otherwise specified, reagents were purchased from Sigma-
Aldrich Canada or Praxair Canada and used as received or dried and
degassed using established procedures. Ru(η5-Cp*)Cl(PPh3)2 was
prepared by a modified literature procedure (see Supporting
Information) and Ru(η5-indenyl)Cl(PCy2H)PPh3 (3ai)10 was pre-
pared using the literature procedure.
1
the secondary phosphine (2JCP = 4−5 Hz) in the H/13C
HMBC spectra; no correlation with the central carbon is
2
observed but a JCP of 2 Hz is observed in the 13C NMR.
Although complexes 13c,d are stable and can be prepared on a
larger scale, they could not be isolated free of 5c,d and PPh3,
due to their high solubility even in cold pentane.
Under the same conditions (Scheme 11), dialkyl phosphido
complexes 2a,b do not react at all with 1-hexene, giving only
the orthometalation product 5a,b.21 Thus, for these more P-
basic complexes, intramolecular deprotonation leading to
orthometalation is faster than intermolecular reaction with 1-
hexene to give 13. Formation of the η3-allyl group in 13
requires substitution of the PPh3 ligand in 2 by the terminal
alkene moiety of 1-hexene, in addition to deprotonation of the
allylic C−H bond. We note that the reactions of 2a−d with
ethylene shown above (Scheme 10) suggest this substitution
occurs more readily for the diaryl phosphido complexes 2c,d
than for 2a,b, which probably contributes to the observed
reactivity differences with 1-hexene.
NMR spectra were recorded at ambient temperature, unless
otherwise noted, on a Bruker AVANCE 500 spectrometer (500.27
1
MHz for H, 125.79 MHz for 13C, and 202.51 MHz for 31P), on a
1
Bruker AVANCE 360 spectrometer (360.13 MHz for H and 145.78
MHz for 31P) or on a Bruker AVANCE 300 spectrometer (300.27
MHz for 1H and 121.55 MHz for 31P). Chemical shifts are reported in
ppm and referenced to residual protonated solvent peaks: 7.26
1
(CHCl3), 7.16 ppm (C6D5H), 2.08 ppm (C7D7H) for H; 128.39
ppm (C6D6), 20.43 ppm (C7D8) for 13C. All H and 13C chemical
1
shifts are reported relative to tetramethylsilane (TMS), and 31P shifts
CONCLUSIONS
1
are relative to 85% H3PO4(aq). H, 13C, and 31P NMR assignments
■
The Ru(η5-Cp*) phosphido complex 2 participates in a rich
variety of chemistry with small molecules that mostly parallels
that of the analogous indenyl complex 1. Given the similarity
of most of the addition, insertion, and deprotonation products
we observe for this rigidly η5-system to those observed for 1,
we feel confident that variable hapticity is not critical to the
chemistry of the indenyl system.
for all identified products are included in the Supporting Information.
31P NMR data is also included below for isolated complexes.
Melting temperatures were recorded using a Gallenkamp apparatus
for capillary samples. IR spectra were recorded on PerkinElmer FTIR
Spectrum One spectrophotometer using KBr pellets under a nitrogen
atmosphere. Microanalysis was performed by Canadian Micro-
analytical Service Ltd. (Delta, BC, Canada).
General Method for Synthesis of Ru(η5-Cp*)Cl(PR2H)(PPh3)
(3a−d). This method is adapted slightly from a procedure previously
reported for the synthesis of 3c (R = Ph).9 Toluene (20 mL) was
added to a flask containing Ru(η5-Cp*)Cl(PPh3)2 (0.61−0.65 mmol)
and a solution of PR2H in hexanes (0.76−1.6 mmol). (In some cases,
excess phosphine was added to offset equilibria including starting
material 3 and the bis(phosphine) complex 4.) The orange
suspension was stirred at RT until it became a homogeneous orange
solution (1−2.5 h). The solvent was removed under vacuum. The
residue was dissolved in a minimum volume of toluene (∼2−3 mL),
layered with pentane (∼10−15 mL), and left to stand overnight. The
supernatant was decanted from the resulting solid product, which was
washed with pentane (at least 3 × 10 mL) and dried under vacuum.
Ru(η5-Cp*)Cl(PCy2H)(PPh3) (3a). Ru(η5-Cp*)Cl(PPh3)2 (0.52 g,
0.65 mmol) and PCy2H in hexanes (0.33 M, 2.3 mL, 0.78 mmol)
were used. The mixture was stirred for 2.5 h. An orange-red powder
was obtained (0.24 g, 0.33 mmol, 50% yield). Melting point: 199−
201 °C. IR (KBr, cm−1) 2329 (w, νPH). Anal. found (calcd for
C40H53P2ClRu) C, 65.65 (65.60); H, 7.72 (7.30). 31P{1H} NMR
(202.51 MHz, C6D6) δ 49.6 (d, 40, PPh3), 48.2 (d, PCy2H).
Ru(η5-Cp*)Cl(PEt2H)(PPh3) (3b). Ru(η5-Cp*)Cl(PPh3)2 (0.52g,
0.65 mmol) and PEt2H in hexane (0.75 M, 2.0 mL, 1.5 mmol)
were used. The suspension was stirred for 2 h. An orange-red
microcrystalline solid was obtained (0.11 g, 0.18 mmol, 27% yield).
Melting point: 196−198 °C. IR (KBr, cm−1) 2327 (w, νPH). Anal.
At the same time we are intrigued by the implications of the
higher phosphido P-basicity in this electron-rich system and
the substitutional lability of the PPh3 ligands, in the context of
possible catalytic hydrophosphination activity. For example,
the phosphido ligand in 2 should participate very readily in
conjugate addition at activated alkenes, the proposed P−C
bond-forming step in hydrophosphination catalyzed by both
our Ru indenyl system and the Ru Cp* system reported by
Morris.8 However, the presence of PPh3 in 2 is a liability, since
rapid orthometalation precludes isolation of this complex and
limits further reactivity, even when 2 is generated in situ.
Indeed, Morris comments on the challenges in identifying both
ancillary ligands and unsaturated hydrophosphination sub-
strates that will not be susceptible to deprotonation in the
presence of the potent Ru(η5-Cp*) phosphido base or the
basic carbanion generated during a conjugate addition step in
catalysis. We suspect that orthometalation or some other
ligand aryl group deprotonation may be responsible for the
deactivation observed for the Morris system during catalysis. In
this context, the high substitutional lability of the PPh3 ligand
in our Ru(η5-Cp*) complexes presents an alternative strategy
for the generation of highly active hydrophosphination
G
DOI: 10.1021/acs.organomet.9b00266
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Organometallics
Article
found (calcd for C32H41P2ClRu) C, 61.26 (61.58); H, 6.70 (6.62).
31P{1H} NMR (202.51 MHz, C6D6) δ 50.5 (d, 43, PPh3), 38.7 (d,
PEt2H).
yellow powder (0.030 g, 0.042 mmol, 32% yield). Dec. point: 178−
180 °C. IR (KBr, cm−1) 2304 (w, νPH). 31P{1H} NMR (202.51 MHz,
C6D6) δ 46.9 (d, 33, PTolp H), −13.3 (d, -PPh2-).
2
Ru(η5-Cp*)Cl(PPh2H)(PPh3) (3c). Ru(η5-Cp*)Cl(PPh3)2 (0.50 g,
0.63 mmol) and PPh2H in hexanes (0.54 M, 1.4 mL, 0.76 mmol)
were used. The mixture was stirred for 1 h. Orange microcrystals were
obtained (0.31 g, 0.43 mmol, 68% yield). The product contained an
impurity of ∼4% of the disubstituted product 4c. Melting point: 217−
219 °C. IR (KBr, cm−1) 2343 (w, νPH). 31P{1H} NMR (202.51 MHz,
C6D6) δ 45.3 (d, 42, PPh3), 36.5 (d, PPh2H).
NMR-Scale Reactions of Complex 2. These trapping reactions
were carried out for complex 2 generated in situ from the
combination of complexes 3a−d with base.
General Procedure for Gaseous Reagents. C7D8 (1 mL) was
added to a mixture of KOBut (2 mg, 0.02 mmol) and metal complex
(3a: 12 mg, 0.016 mmol; 3b: 10 mg, 0.016 mmol; 3c: 12 mg, 0.017
mmol; 3d: 12 mg, 0.016 mmol) in a flame-sealable NMR tube. The
sample was degassed by three freeze−pump−thaw cycles before ∼0.9
atm of gas (hydrogen, carbon monoxide or ethylene) was introduced.
The tube was sealed and cooled to 0 °C in an ice bath. The sealed
orange sample with a thin dark red (for 3a,b) or blue (for 3c,d)
bottom layer was inverted to mix the reagents and then quickly placed
in NMR spectrometer. The samples were also shaken to mix reagents
between NMR experiments.
Ru(η5-Cp*)Cl(PTolp H)(PPh3) (3d). Ru(η5-Cp*)Cl(PPh3)2 (0.61 g,
2
0.77 mmol) and PTolp H in hexanes (0.45 M, 3.5 mL, 1.6 mmol)
2
were used. The solution was stirred for 1 h. Orange-red microcrystals
were obtained (0.38 g, 0.51 mmol, 66% yield). Melting point: 218−
220 °C. IR (KBr, cm−1) 2339 (w, νPH). Anal. found (calcd for
C42H45P2ClRu) C, 67.12 (67.41); H, 6.07 (6.06). 31P{1H} NMR
(202.51 MHz, C6D6) δ 45.5 (d, 42, PPh3), 34.6 (d, PTolp H).
2
Hydrogen. The solutions became yellow/orange after the samples
were inverted.
Carbon Monoxide. The solutions became red after the samples
were inverted, and eventually turned yellow.
Ethylene. The solutions became orange after the samples were
inverted.
General Procedure for Liquid Reagents. C6D6 (1 mL) was added
to KOBut (2 mg, 0.02 mmol) in a small vial, which was allowed to
dissolve completely (24 h). The metal complex (3a: 12 mg, 0.016
mmol; 3b: 10 mg, 0.016 mmol; 3c: 10 mg, 0.016 mmol; 3d: 12 mg,
0.016 mmol) and liquid reagent (phenylacetylene, acrylonitrile and 1-
hexene) were added to the base solution in this vial. The sample was
swirled for 30 s before being transferred to an NMR tube for analysis.
Phenylacetylene. The solutions became yellow-orange immedi-
ately after adding phenylacetylene (3 μL, 0.03 mmol).
Acrylonitrile. The solutions stayed orange and a pale yellow
precipitate formed immediately upon addition of acrylonitrile (2 μL,
0.03 mmol). Only 3 was observed in 31P{1H} spectra.
1-Hexene. The dark red (for 3a,b) or blue (for 3c,d) solution
slowly changed to yellow-orange after addition of 1-hexene (10 μL,
0.08 mmol).
X-ray Diffraction Studies of Complexes 3a,b. Crystals of 3a,b
were grown by layering pentane onto a toluene solution of the
compound. Suitable crystals were coated with a thin layer of Paratone-
N.
Dehydrohalogenation Reactions Monitored by NMR.
Reactions with KOBut. Solid KOBut (2 mg, 0.02 mmol) was
dissolved in 1 mL of C6D6 in a small vial; this happened slowly, so the
mixture was left to stand for 24 h. The metal complex (3ai: 10 mg,
0.014 mmol; 3a: 12 mg, 0.016 mmol; 3b: 10 mg, 0.016 mmol; 3c: 10
mg, 0.016 mmol; 3d: 12 mg, 0.016 mmol) was added to this solution
and the mixture was transferred to an NMR tube. The reaction was
monitored by 1H and 31P{1H} NMR spectroscopy. The tube was
shaken between each measurement. Relative amounts of phosphorus-
containing species in solution were estimated from 31P{1H} NMR.
Reaction of 3a with n-BuLi. Solid 3a (12 mg, 0.016 mmol) was
dissolved in 1 mL of C6D6 in a J. Young NMR tube to give an orange
solution. A slight excess of n-BuLi (8 μL, 0.020 mmol, 2.5 M in
hexanes) was added by syringe, which caused a layer of dark red to
appear at the top of the sample. When the tube was inverted to mix
prior to placing the sample in the spectrometer, the entire solution
turned yellow. The reaction was monitored by 1H and 31P{1H} NMR
spectroscopy. The tube was inverted between each measurement. In
the initial spectra, recorded after 0.5 h, signals due to hydride complex
6a dominate (Figure S19). Spectra recorded after 24 h showed the
same product distribution.
General Method for Synthesis of Ru(η5-Cp*)H(PR2H)(PPh3)
(6b−d). Toluene (10 mL) was added to a Schlenk flask containing
complex 3b−d and KOBut (∼1.3 equiv). The solution was degassed
by three freeze−pump−thaw cycles before H2 gas (∼0.9 atm) was
introduced. The solution was stirred overnight. The resulting yellow
solution was filtered through Celite to remove solid (KCl, excess
KOBut) and gelatinous HOBut. Solvent was removed under vacuum
from the filtrate. The resulting yellow residue was dissolved in 3 mL of
pentane and stored at −22 °C to afford yellow solid 6b−d, which was
washed with cold pentane (3 × 1 mL). The high solubility of 6b−d
even in cold pentane precluded washing to give analytically pure
product, so no microanalysis was obtained. NMR spectra show small
amounts of solvent, grease, and/or unidentified products (see
Supporting Information).
General Method for Synthesis of Ru(η5-Cp*){κ2-(o-C6H4)-
PPh2}(PR2H) (5b−d). Benzene or toluene (10 mL) was added to a
Schlenk flask containing complex 3b−d and KOBut (∼1.1 equiv).
The solution was stirred for 24 h to ensure complete conversion to
the orthometalated complex. The resulting cloudy orange-brown
mixture was filtered through Celite to remove solid KCl and
gelatinous HOBut. Solvent was removed under vacuum from the
filtrate, and the resulting paste was dissolved in pentane (10 mL) and
worked up as described below. The high solubility of 5b−d in pentane
precluded washing to give analytically pure product, so no
microanalysis was obtained. The compounds appear pure by
Ru(η5-Cp*)H(PEt2H)(PPh3) (6b). Ru(η5-Cp*)Cl(PEt2H)(PPh3)
(3b, 0.15 g, 0.24 mmol) and KOBut (0.035 g, 0.31 mmol) were
used. A yellow powder was obtained (0.052 g, 0.088 mmol, 37%).
Melting point: 152−155 °C. IR (KBr, cm−1) 2309 (m, νPH), 1877 (m,
νRuH). 31P{1H} NMR (202.51 MHz, C6D6) δ 74.7 (d, 33, PPh3), 43.9
(d, PEt2H).
1
31P{1H} NMR but show some solvent and grease impurities by H
NMR (see Supporting Information).
Ru(η5-Cp*){κ2-(o-C6H4)PPh2}(PEt2H) (5b). Ru(η5-Cp*)Cl(PEt2H)-
(PPh3) (3b, 0.060 g, 0.096 mmol) and KOBut (0.012 g, 0.11 mmol)
were used. Pentane was removed under vacuum to give an orange
paste. The product was triturated with pentane (8 × 10 mL), but
remained a paste (0.036 g, 0.061 mmol, 64% yield). 31P{1H} NMR
(202.51 MHz, C6D6) δ 43.6 (d, 34, PEt2H), −10.0 (d, -PPh2-).
Ru(η5-Cp*){κ2-(o-C6H4)PPh2}(PPh2H) (5c). Ru(η5-Cp*)Cl(PPh2H)-
(PPh3) (3c, 0.10 g, 0.14 mmol) and KOBut (0.018 g, 0.16 mmol)
were used. Pentane was removed under vacuum to give a brownish
yellow powder (0.028 g, 0.041 mmol, 29% yield). Dec. point: 169−
172 °C. IR (KBr, cm−1) 2302 (w, νPH). 31P{1H} NMR (202.51 MHz,
C6D6) δ 48.6 (d, 31, PPh2H), −13.6 (d, -PPh2-).
Ru(η5-Cp*)H(PPh2H)(PPh3) (6c). Ru(η5-Cp*)Cl(PPh2H)(PPh3)
(3c, 0.20 g, 0.28 mmol) and KOBut (0.040 g, 0.36 mmol) were
used. A yellow powder was obtained (0.075 g, 0.11 mmol, 39%).
Melting point: 130−134 °C. IR (KBr, cm−1) 2299 (m, νPH), 1908 (m,
νRuH). 31P{1H} NMR (202.51 MHz, C6D6) δ 74.5 (d, 31, PPh3), 45.0
(d, PPh2H).
Ru(η5-Cp*)H(PTolp H)(PPh3) (6d). Ru(η5-Cp*)Cl(PTolp H)(PPh3)
2
2
(3d, 0.15 g, 0.20 mmol) and KOBut (0.029 g, 0.26 mmol) were used.
A yellow powder was obtained (0.044 g, 0.062 mmol, 31%). Melting
point: 158−160 °C. IR (KBr, cm−1) 2242 (m, νPH), 1925 (m, νRuH).
31P{1H} NMR (202.51 MHz, C6D6) δ 74.6 (d, 33, PPh3), 43.0 (d,
Ru(η5-Cp*){κ2-(o-C6H4)PPh2}(PTolp2H) (5d). Ru(η5-Cp*)Cl-
(PTolp H)(PPh3) (3d, 0.10 g, 0.13 mmol) and KOBut (0.018 g,
2
0.16 mmol) were used. Pentane was removed under vacuum to give a
PTolp H).
2
H
DOI: 10.1021/acs.organomet.9b00266
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Organometallics
Article
General Method for Synthesis of Ru(η5-Cp*) (PR2)(CO)(PPh3)
(7b−d). Toluene (10 mL) was added to a Schlenk flask containing
complex 3b−d and KOBut (∼1.4−1.5 equiv). The solution was
degassed by three freeze−pump−thaw cycles before CO gas (∼0.9
atm) was introduced. The solution was stirred overnight, at which
point NMR analysis showed the product mixture was comparable to
that described for the NMR-scale reactions above. The resulting
intense orange (for 3b) or red (for 3c,d) solution was filtered through
Celite to remove solid (KCl, excess KOBut) and gelatinous HOBut.
Solvent was removed under vacuum from the filtrate, and the resulting
bright orange or red paste was dissolved in 10 mL of hexanes. The
solvent was removed under vacuum to give a yellow or orange
powder, which was washed with cold hexanes (3 × 1 mL). Isolated
7b−d contained impurities of as-yet unidentified products that
formed during workup; for solution NMR samples we also noted the
slow growth of signal due to free PPh3 (see Supporting Information).
Ru(η5-Cp*)(PEt2)(CO)(PPh3) (7b). Ru(η5-Cp*)Cl(PEt2H)(PPh3)
(3b, 0.15 g, 0.24 mmol) and KOBut (0.040 g, 0.36 mmol) were
used. A bright yellow powder was obtained (0.045 g, 0.073 mmol,
30%) in 97% purity by 31P{1H} NMR. Dec. point: 158−162 °C. IR
(KBr, cm−1) 1899 (s, νCO). 31P{1H} NMR (121.55 MHz, C6D6) δ
61.5 (d, 5, PPh3), 29.7 (d, PEt2).
Accession Codes
CCDC 1911831−1911832 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: lisarose@uvic.ca.
■
ORCID
Jin Yang: 0000-0001-8004-4668
Sophie Langis-Barsetti: 0000-0001-5455-666X
Hayley C. Parkin: 0000-0002-3218-1411
Robert McDonald: 0000-0002-4065-6181
Lisa Rosenberg: 0000-0003-4917-184X
Notes
Ru(η5-Cp*)(PPh2)(CO)(PPh3) (7c). Ru(η5-Cp*)Cl(PPh2H)(PPh3)
(3c, 0.20 g, 0.28 mmol) and KOBut (0.046 g, 0.40 mmol) were used.
A bright orange powder was obtained (0.051 g), which contained 7c
(∼70%) and unidentified product (∼30%), as determined by 31P{1H}
NMR. Dec. point: 190−196 °C. IR (KBr, cm−1) 1929 (s, νCO), 1902
(s, νCO). The extra CO IR stretch band is attributed to the
unidentified product. 31P{1H} NMR (121.55 MHz, C6D6) δ 53.8 (d,
4, PPh3), 14.8 (d, PPh2).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank NSERC of Canada for financial support (Discovery
Grant to LR).
■
REFERENCES
■
Ru(η5-Cp*)(PTolp )(CO)(PPh3) (7d). Ru(η5-Cp*)Cl(PTolp H)-
(1) Leading references for metal-catalyzed hydrophosphination and
phosphination that describe the participation of M-PR2 intermediates
include (a) Glueck, D. S. Recent advances in metal-catalyzed C-P
bond formation. Top. Organomet. Chem. 2010, 31, 65−100.
(b) Tappe, F. M. J.; Trepohl, V. T.; Oestreich, M. Transition-
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2
2
(PPh3) (3d, 0.15 g, 0.20 mmol) and KOBut (0.033 g, 0.29 mmol)
were used. A bright orange powder was obtained (0.062 g, 0.084
mmol, 42%) in 96% purity by 31P{1H} NMR. Dec. point: 160−164
°C. IR (KBr, cm−1) 1909 (s, νCO). 31P{1H} NMR (121.55 MHz,
C6D6) δ 54.3 (d, 4, PPh3), 17.9 (d, PTolp ).
2
Attempted Isolation of Ru(η5-Cp*)(η3-hexenyl)(PR2H)
(13c,d). Toluene (10 mL) was added to a Schlenk flask containing
metal complex, KOBut (∼1.1−1.2 equiv) and 1-hexene (5 equiv).
The solution was stirred overnight to ensure complete conversion.
The resulting yellow mixture was filtered through Celite to remove
solid KCl and gelatinous HOBut. The filtrate was removed under
vacuum, and the resulting bright yellow paste was triturated with
pentane (5 × 10 mL). The pentane was removed under vacuum to
give an oily yellow paste. 31P{1H} NMR indicates this paste contains
the same products (13, 5, PPh3) as those observed in the NMR scale
reactions. The high solubility of this paste in pentane precluded
isolating pure product 13c,d.
Ru(η5-Cp*)(η3-hexenyl)(PPh2H) (13c). Ru(η5-Cp*)Cl(PPh2H)-
(PPh3) (3c, 0.11 g, 0.15 mmol), KOBut (0.019 g, 0.17 mmol) and
1-hexene (83 μL, 0.67 mmol) were used. A bright yellow paste was
obtained (0.020 g), which contains 13c (62%), 5c (33%), free PPh3
and an unidentified Ru product (5%).
Ru(η5-Cp*)(η3-hexenyl)(PTolp H) (13d). Ru(η5-Cp*)Cl(PTolp H)-
2
2
(PPh3) (3d, 0.10 g, 0.13 mmol), KOBut (0.017 g, 0.16 mmol) and 1-
hexene (89 μL, 0.71 mmol) were used. A bright yellow paste was
obtained (0.1 g), which contained 13d (66%), 5d (31%), free PPh3
and an unidentified Ru product (3%).
(2) (a) Derrah, E. J.; Giesbrecht, K. E.; McDonald, R.; Rosenberg, L.
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solvent. Organometallics 2008, 27, 5025−5032. (b) Derrah, E. J.;
McDonald, R.; Rosenberg, L. The 2 + 2 cycloaddition of alkynes at a
Ru-P π-bond. Chem. Commun. 2010, 46, 4592−4594. (c) Derrah, E.
J.; Pantazis, D. A.; McDonald, R.; Rosenberg, L. Concerted 2 + 2
cycloaddition of alkenes to a ruthenium-phosphorus double bond.
Angew. Chem., Int. Ed. 2010, 49, 3367−3370. (d) Hoyle, M. A. M.;
Pantazis, D. A.; Burton, H. M.; McDonald, R.; Rosenberg, L.
Benzonitrile adducts of terminal diarylphosphido complexes:
preparative sources Of “Ru = PR2. Organometallics 2011, 30, 6458−
6465. (e) Burton, K. M. E.; Pantazis, D. A.; Belli, R. G.; McDonald,
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00266.
Modified procedure for the synthesis of Ru(η5-Cp*)Cl-
(PPh3)2, NMR spectroscopic data and representative
spectra for new complexes and reaction mixtures, X-ray
crystallographic data (PDF)
I
DOI: 10.1021/acs.organomet.9b00266
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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1
1JHP (∼380 Hz) for Ru-PR2H observed in their H and 31P NMR
spectra. 13C signals for the alkynyl carbons C to Ru were not
1
observed, but those for the carbons (δ 112.3 ppm) showed H/13C
1
HMBC correlations with the relatively sharp H signals for the ortho
protons on the alkynyl phenyl group for both complexes. This shift is
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similar complexes Ru(η5-indenyl)(CCPh)(PCy2H)(PPh3) (δ 113.3
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(17) Given our “one pot” reaction conditions, we cannot rule out the
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(20) The polymerization of acrylonitrile catalyzed by metal alkoxides
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DOI: 10.1021/acs.organomet.9b00266
Organometallics XXXX, XXX, XXX−XXX