Synthesis, coordination chemistry, and cooperative activation of H 2 with ruthenium complexes of proton-responsive METAMORPhos ligands

Article abstract of DOI:10.1002/ejic.201301215

The synthetic scope of proton-responsive sulfonamidophosphorus (METAMORPhos) ligands is expanded and design principles for the selective formation of particular tautomers, ion pairs, or double condensation products are elucidated. These systems have been introduced in the coordination sphere of Ru for the first time, thereby enabling the exclusive coordination as a monoanionic P,O chelate. Depending on the Ru precursor, halide-bridged dinuclear species 3-5 or cymene-derived piano-stool complexes 6-9 are isolated. The METAMORPhos framework is shown to play a role in the heterolytic cleavage of H₂, with species 7 converted into neutral monohydride 10. Substitution chemistry with cymene complex 7 has also been examined, thereby giving rise to tetrakis(acetonitrile) adduct 11. Introduction of a second equivalent of METAMORPhos ligand to this species yielded the bis(ligated) derivative 13, for which variable-temperature (VT) NMR spectroscopy indicates coalescence of the phosphine donors at high temperature. Solid-state structures of 3, 6, 11, and 13 are presented to establish the precise bonding situation of the inorganic PNSO framework within METAMORPhos upon coordination as a proton-responsive monoanionic P,O chelate. Copyright

Full text of DOI:10.1002/ejic.201301215

FULL PAPER
DOI:10.1002/ejic.201301215
Synthesis, Coordination Chemistry, and Cooperative
Activation of H2 with Ruthenium Complexes of Proton-
Responsive METAMORPhos Ligands
CLUSTER
ISSUE
Frédéric G. Terrade,[a] Martin Lutz,[b] Jarl Ivar van der Vlugt,*[a]
and Joost N. H. Reek*[a]
Keywords: P ligands / Ruthenium / Chelates / Sulfonamides / Dihydrogen activation
The synthetic scope of proton-responsive sulfonamidophos-
phorus (METAMORPhos) ligands is expanded and design
principles for the selective formation of particular tautomers,
ion pairs, or double condensation products are elucidated.
These systems have been introduced in the coordination
sphere of Ru for the first time, thereby enabling the exclusive
coordination as a monoanionic P,O chelate. Depending on
the Ru precursor, halide-bridged dinuclear species 3–5 or
cymene-derived piano-stool complexes 6–9 are isolated. The
METAMORPhos framework is shown to play a role in the
heterolytic cleavage of H2, with species 7 converted into neu-
tral monohydride 10. Substitution chemistry with cymene
complex 7 has also been examined, thereby giving rise to
tetrakis(acetonitrile) adduct 11. Introduction of a second
equivalent of METAMORPhos ligand to this species yielded
the bis(ligated) derivative 13, for which variable-temperature
(VT) NMR spectroscopy indicates coalescence of the phos-
phine donors at high temperature. Solid-state structures of 3,
6, 11, and 13 are presented to establish the precise bonding
situation of the inorganic PNSO framework within
METAMORPhos upon coordination as a proton-responsive
monoanionic P,O chelate.
for “hydrogen-borrowing” reactions wherein the substrate
is dehydrogenated by the catalyst, undergoes a coupling re-
action, and is then hydrogenated.[5]
Introduction
Since Noyori et al. unveiled an outer-sphere mechanism
to be operative for transfer hydrogenation with particular
aminoamide chelate ligands,[1] proton-responsive ligands
have attracted much attention as reactive scaffolds for selec-
tive bond-activation processes and cooperative catalysis.[2]
The proton-responsive character is brought about by acido–
basic moieties that can be reversibly deprotonated during
catalytic turnover, thereby allowing bioinspired bifunctional
substrate activation and conversion.[3]
More recently, dehydrogenations and dehydrogenative
coupling reactions based on the same proton-responsive na-
ture of suitable bifunctional metal–ligand combinations
have been developed. In those reactions, the basic ligand
abstracts a proton, and the metal center abstracts a hydride
from the substrate. The catalytic cycle is then closed by re-
lease of hydrogen and regeneration of the initial complex.
Such catalysts have been used for various atom-efficient
conversions.[4] Proton-responsive ligands can also be used
The proton-responsive feature might involve temporary
dearomatization of functionalized pyridines,[6] the intercon-
version between amino/amido units within the ligand
framework,[7] or pH-responsive pyridonate fragments.[8] In
addition, some other concepts have been explored as well.[9]
Most of these ligands currently lack a high degree of modu-
larity to effectively tune the proton response for specific
(catalytic) purposes. Hence, the applicability of these sys-
tems to address different types of conversions or substrate
classes is limited. Moreover, the possibilities to introduce
elements of chirality for asymmetric transformations are
often hampered by cumbersome synthetic procedures.
Sulfonamidophosphorus “METAMORPhos” ligands
were recently introduced as a family of highly versatile and
modular building blocks for late-transition-metal com-
plexes.[10] Their ability to act as (chiral) proton-responsive
ligands in Rh-catalyzed (asymmetric) hydrogenation of
functionalized
alkenes
was
demonstrated
(Scheme 1).[10a–10c] A novel cooperative mechanism for the
activation of molecular dihydrogen was proposed
(Scheme 2, a).[10a] The unique self-sorting behavior among
complexes bearing chiral derivatives has recently been com-
municated.[11] Furthermore, Ir–METAMORPhos com-
plexes were used for the base-free dehydrogenation of
formic acid (Scheme 2, b). Besides the proton-responsive
character of this ligand, which allowed it to act as internal
[a] van ’t Hoff Institute for Molecular Sciences, Faculty of
Sciences, University of Amsterdam,
Science Park 904, 1098 XH Amsterdam, The Netherlands
E-mail: j.i.vandervlugt@uva.nl
j.n.h.reek@uva.nl
www.science.uva.nl/research/imc/homkat/index.html
[b] Crystal and Structural Chemistry, Bijvoet Center for
Biomolecular Research, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301215.
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Scheme 1. Top: Proton-responsive behavior of known Ru systems[1,6] toward H2. Bottom: Envisioned reactivity of METAMORPhos
ligands.
ligand class have been reported.[10,13] Depending on the
substituents on phosphorus and sulfur, different condensa-
tion products are typically obtained (Scheme 3).
Indeed, when sulfonamides are coupled to chlorophos-
phites, the deprotonated ligand 1– (PN–) is formed (as the
triethylammonium salt) as the sole product, regardless of
the electronic properties of the sulfonamide (Table 1, entries
base, its ability to function as hydrogen-bond acceptor was
found to be crucial for catalyst activity.[10d] Also noteworthy
is the complete inorganic PNSO backbone of these ligands
in these constellations.
I–K).
This
tendency
of
phosphoramidite-based
METAMORPhos systems to form strong ion pairs, which
is related to the enhanced acidity of the –NH group due
to the electron-withdrawing binaphthol (BINOL) auxiliary,
and the resulting dinucleating nature of the PN– scaffolds
was previously exploited in our group.[11] In contrast,
employing chlorophosphines typically results in neutral
METAMORPhos ligands with reduced overall acidity at ni-
trogen (Table 1, entries A–H). These phosphines show taut-
omerism due to prototropic behavior: the proton either re-
sides on the nitrogen (PIII) or on phosphorus (PV). Elec-
tron-donating isopropyl or tert-butyl groups at phosphorus
(Table 1, entries F–H), stabilize the high-oxidation-state PV
tautomer, which is the only detected tautomer in solution.
For chlorodiarylphosphines (Table 1, entries A–E), both
tautomers can be observed by 31P NMR spectroscopy, with
the PIII/PV ratio strongly depending on the nature of the
Scheme 2. (a) METAMORPhos as proton-responsive ligand for
hydrogen splitting and (b) formic acid dehydrogenation.
Encouraged by these results, we decided to thoroughly
investigate and optimize the synthetic procedures for a
range of METAMORPhos ligands to establish a broader
acido-basic scope and to study the coordination behavior
of selected systems with ruthenium, which is often the metal sulfonamide R group. Electron-donating fragments favor
of choice for catalytic transformations that involve proton- the regular PIII tautomer, while the electron-withdrawing
responsive ligands.[12]
bis(trifluoromethyl)phenyl group leads to enhanced acidity
at nitrogen, resulting in almost complete tautomer reversal
to PV as the major component in solution.
When the sulfur atom carries an electron-withdrawing
organic substituent such as bis(trifluoromethyl)phenyl, the
Results and Discussion
double condensation product 2 is also obtained as a by-
Ligand Synthesis
product or even the main product.[13,14] Bulky phosphorus
METAMORPhos ligands 1A–K have been obtained by substituents prevent (Table 1, entries F and G) or suppress
condensation of readily available chlorophosphorus com- (Table 1, entry H) the occurrence of 2. In most cases, re-
pounds (chlorophosphines or chlorophosphites) with moval of this diphosphorus compound was facile, but treat-
sulfonamides (Scheme 3). As the latter are essential building ment of ClPPh2 with bis(trifluoromethyl)phenyl sulfon-
blocks for biologically active molecules, a plethora of pri- amide provided a mixture of 1D and 2D from which only
mary sulfonamides is commercially available, which in prin- 2D was obtained after purification, thus indicating a low
ciple could enable the (high-throughput) synthesis of many energy barrier for self-condensation and potentially higher
ligands, thereby allowing fine-tuning of their proton-re- stability of 2D (Table 1, entry D). Fortunately, replacement
sponsive identity. So far, only a limited number from this of the phenyl substituent by more bulky o-tolyl groups on
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Scheme 3. Condensation of chlorophosphorus compounds with sulfonamides to give species 1H (as the PIII and/or PV tautomer) or the
deprotonated 1– (PN–) derivative thereof and/or 2 (PPN) depending on reaction conditions and the specific substitution patterns at
phosphorus and sulfur.
Table 1. Condensation between chlorophosphorus species and sul- dride precursor that would result in highly volatile H2 as
fonamides.
“conjugate acid”. This concept also underlies recent appli-
cations for dehydrogenative coupling reactions.
R
RЈ
Product(s)
(crude)[a] (isolated)
major
Gratifyingly, when ligand 1FH was treated with
[Ru(H)(Cl)(PPh3)3(CO)] in toluene under reflux conditions
(Scheme 4), two sets of two doublets were observed in a
1:1.7 ratio in the 31P NMR spectrum, each corresponding
to one METAMORPhos [δ = 100.0 (JP,P = 25.5 Hz) and
97.7 ppm (JP,P = 24 Hz)] and one PPh3 ligand [δ = 39.1 (JP,P
= 24.0 Hz)] and 37.4 ppm (JP,P = 25.5 Hz)]. No hydride or –
(minor)
A
B
C
D
E
F
G
H
I
phenyl
phenyl
phenyl
phenyl
o-tolyl
p-butylphenyl
p-tolyl
p-methoxyphenyl
m-bis(trifluoromethyl)phenyl 1 and 2
m-bis(trifluoromethyl)phenyl 1 and 2
1
1
PIII (PV)
PIII (PV)
PIII (PV)
2
1 and 2
P
V (PIII
)
isopropyl p-butylphenyl
isopropyl trifluoromethyl
tert-butyl trifluoromethyl
BINOL
BINOL
BINOL
1 and 2[b] PV
1 and 2
1
1
1
1
1
NH signal was apparent in the H NMR spectrum, thus
PV
indicating the release of H2. The two species are proposed
to be isomers given the strong resemblance in their spectral
features. Single crystals suitable for X-ray diffraction could
be obtained by slow diffusion of diethyl ether into a dichlo-
romethane solution. Surprisingly, the molecular structure
(see Figure 1) was found to be that of chloride-bridged di-
mer 3, which features the METAMORPhos ligand as an-
ionic P,O chelate. Coordination of the oxygen atom leads to
desymmetrization of the sulfonamide fragment and induces
PV
methyl
p-butylphenyl
trifluoromethyl
PN–
PN–
PN–
J
K
[a] After 16 h reaction. [b] Trace amount.
phosphorus and higher temperature for the coupling reac-
tion favored the formation of neutral monophosphine 1H.
Compound 1EH could be isolated in reasonable yield with-
out any contamination of 2E.
Coordination to a RuII Precursor Bearing an Internal Base
To date, the coordination chemistry of METAMORPhos
ligands has only been detailed for group 9 metals with mul-
tiple geometries already established. The ligand can act as
a neutral monodentate P donor or as monoanionic bridging
P,N ligand.[10] However, no mononuclear, monoligated spe-
cies bearing METAMORPhos as bidentate monoanionic
P,O chelate has been established to date. Deprotonation of
the –NH unit can be enforced by the addition of an external
base during complexation or through the use of a metal
precursor bearing an internal base such as the acetylacet-
onate (acac) ligand in [Ir(acac)(cod)] (cod = cyclooctadi-
ene).[10d] We sought to expand this “intramolecular” depro-
tonation strategy and to enforce irreversible deprotonation,
as acetylacetone was found to induce isomerization of di-
meric structures due to reversible proton-transfer phenom-
ena under certain reaction conditions.[10d] Removal of the
“conjugate acid” from the reaction mixture should elimin-
Scheme 4. Coordination of 1FH to [Ru(H)(Cl)(PPh3)3(CO)] to gen-
erate 3 (and/or isomeric 4/5) concomitant with hydrogen release.
The chirality at sulfur, induced by ligand coordination to Ru, is
ate this process. We thus opted to investigate a metal–hy- highlighted.
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chirality at the sulfur atom.[15] The dimer has exact crystal-
lographic C2 symmetry with both sulfur atoms of equal chi-
rality, but the unit cell possesses an inversion center as the
complex crystallizes as a true racemate. The P1–Ru–P2 an-
gle of 100.154(15)° as well as the O1–Ru–C17 angle of
174.02(5)° exemplify the distorted-octahedral geometry
around Ru. The P1–Ru–O1 angle is small at 82.39(3)°. The
N–S bond length of 1.5435(14) Å indicates double-bond
character.[16] The S–O1 [1.4911(11) Å; formal S–O] and S–
O2 [1.4416(12) Å; S=O] bond lengths differ significantly as
a consequence of the coordination of O1 to the metal. The
spectroscopically observed second species is suggested to
correspond to a Ru dimer with ligands of opposite chirality
at the sulfur atom, either with a pseudo-C2 axis (structure
4) or a center of inversion (structure 5).
Scheme 5. Synthesis of piano-stool complexes 6–9.
This geometry was unambiguously corroborated by X-
ray crystal-structure determination; the molecular structure
is depicted in Figure 2. Like for 3, the METAMORPhos
ligand is deprotonated and acts as a P,O chelate. The P–R–
O1 angle of 80.20(4)° is even smaller than in dimer 3,
whereas the Ru–P bond is marginally longer at 2.3240(5) Å.
The N–S bond length of 1.5478(18) Å indicates double-
bond character. Again, the S–O1 [1.5027(13) Å; formal S–
O] and S–O2 [1.4412(15) Å; S=O] bond lengths differ sig-
nificantly due to coordination to Ru. Coordination of the
anionic oxygen donor induces desymmetrization of both
the sulfur and ruthenium center. Interestingly, only one dia-
stereoisomer is observed (RuSSS and its enantiomer RuRSR)
in the racemic crystal structure as the complex crystallizes
as a true racemate. In solution, the configuration of at least
one of the two chiral centers is retained (on the NMR spec-
troscopic timescale), because the two phenyl groups on
phosphorus showed distinct signals in the 13C NMR spec-
trum. Piano-stool complexes with ligands 1BH, 1CH, and
1DH could be synthesized using this protocol, thus exemp-
lifying the possibility to fine-tune such complexes with elec-
tron-donating (7 and 8) or -withdrawing groups (9) at
sulfur.
Figure 1. Solid-state structure of 3. Hydrogen atoms have been
omitted for clarity. Only the major conformation of the disordered
n-butyl chain is shown. Selected bond lengths [Å] and angles [°]:
Ru–P1 2.3096(4), Ru–P2 2.3466(4), Ru–O1 2.1485(11), Ru–C17
1.8293(16), Ru–Cl 2.4673(4), P1–N 1.6597(14), N–S 1.5435(14), S–
O1 1.4911(13), S–O2 1.4416(14); P1–Ru–P2 100.15(2), P1–Ru–Cl
168.320(14), P2–Ru–Cl 86.773(14), O1–Ru–C17 174.02(5), P1–Ru–
O1 82.39(3), P2–Ru–O1 93.54(3), N–S–O1 112.92(7), N–S–O2
113.44(8), Ru–C17–O3 176.64(14), P–N–S 119.30(9). Symmetry
operation i: –x, y, 0.5 – z.
Formation of Ru Complexes with Piano-Stool Geometry
Because a reproducible high-yielding synthesis of 3
turned out to be cumbersome due to purification problems,
we resorted to [{RuCl(cymene)(μ-Cl)}2] as an alternative
Ru precursor. Coordination of 1AH with this cymene dimer
in THF in the presence of triethylamine led to quantitative
formation of a single product, according to 31P NMR spec-
troscopy, with concomitant precipitation of triethylammo-
nium chloride. The cymene fragment is preserved within the
Figure 2. ORTEP plot (50% probability displacement ellipsoids)
of piano-stool complex 6, [RuCl(1A)(η6-cymene)]. Hydrogen atoms
and THF solvent molecule are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Ru–P 2.3240(5), Ru–Cl 2.3943(5), Ru–
O1 2.1419(14), P–N 1.651; O1–Ru–Cl 86.61(4), P–N–S 117.69(11),
N–S–O1 111.29(9), N–S–O2 114.22(10), Ru–O1–S 121.48(8).
1
coordination sphere of ruthenium, as deduced from the H
NMR spectrum, which suggests a piano-stool geometry for
complex 6 (Scheme 5).
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Heterolytic Splitting of Dihydrogen
give neutral complex 10 (Scheme 6). Addition of an excess
amount of HCl (1 m solution in diethyl ether) to 7 also led
to smooth reformation of the coordinated neutral PIII tau-
tomer: the –NH signal was observed at δ = 6.68 ppm (JP,H
= 11.0 Hz). By in situ chloride abstraction with AgBF4 dur-
ing the H2-splitting process we were also able to identify
the cationic complex 10ЈЈBF4, which could be characterized
in solution by 1H and 31P NMR spectroscopy. Interestingly,
10ЈЈ was observed as an equimolar mixture of both dia-
stereoisomers, with the Ru and S atoms as stereogenic cen-
ters.
Notably, the use of complex 9, which bears the electron-
poor bis(trifluoromethyl)phenyl sulfonamide derivative, nei-
ther resulted in full conversion nor in clean formation of a
single hydridic species. After 18 h at 50 bar, two hydrides
could be observed at δ = –7.26 (JP,H = 45 Hz) and
–8.05 ppm (JP,H = 52 Hz) in a ratio of 1:8 and 1:1.7 with
respect to the remaining starting complex, as well as a
cymene species bearing no hydride. Although we did not
characterize this mixture further, the incomplete conversion
might indicate the establishment of an equilibrium with this
particular system that features a more acidic META-
MORPhos ligand. This not only supports the active in-
volvement of the METAMORPhos framework in cleavage
of the H–H bond, but also provides clear indications of the
tunable character of this PNSO scaffold relative to other
types of proton-responsive systems.
In analogy to the activity displayed by Noyori’s complex
and related reversible amido-to-amino switchable ligands,[7]
we were curious as to whether the combination of a Lewis
acidic metal and a Brønsted basic ligand would result in
direct heterolytic H2 cleavage. It should be noted that there
is a pronounced difference in both Ru–amide geometry
(equatorial/meridional versus piano-stool) and Ru–amide
character (inner-sphere coordination versus two-bond sepa-
ration), which might have pronounced differences for amide
protonolysis. When complex 7, a close analogue of 6 that
features ligand 1BH, was kept under 5 bar of H2 in [D8]-
THF, a doublet was obtained at δ = –8.34 ppm (JP,H
=
52 Hz) in the 1H NMR spectrum [33% conversion after
18 h on the basis of 31P NMR spectroscopy: δ = 87.7 ppm
(JP,H = 52 Hz)], which is strongly suggestive of heterolytic
hydrogen splitting and reprotonation of the META-
MORPhos ligand. Full conversion to the hydride complex
could be reached at higher H2 pressure, thereby allowing
the isolation and full characterization of this stable com-
pound. The corresponding expected –NH signal was ob-
served at δ = 7.57 ppm, identified by its coupling with phos-
phorus (JP,H = 10.9 Hz). The addition of KPF6 (1 equiv.)
while applying H2 pressure led to the same NMR spectro-
scopic features with no indication of the PF6 anion (by 31P
and 19F NMR spectroscopy). Hence, complex 10 is formu-
lated as the neutral complex [Ru(H)(Cl)(7H)]. This was evi-
dent from HRMS data (ESI: m/z 666.034 for [M + K] and
592.103 for [M – Cl]). We postulate that the Ru–Cl bond is
sufficiently labilized in polar solvent (KPF6 might further
assist in labilizing the chloride ligand) to allow coordination
Substitution Reactions on Piano-Stool Complex 7
Recently, the group of Bruneau reported arene-free com-
of molecular hydrogen and its subsequent heterolytic cleav- plexes based on a phosphinosulfonate ligand that were gen-
age. Presumably, initial interaction of the Ru–O bond with erated from similar piano-stool complexes as 6–9.[17] Re-
H2 occurs, thus leading to the transient [Ru(H)(κ2-OH,P)] placement of the cymene fragment by acetonitrile led to
species 10Ј that undergoes intramolecular proton shuttling higher catalytic activity in the hydrogenation of ketones.
to afford 10ЈЈ, which bears the PIII tautomer within the Ru Consequently, we were curious to establish similar substitu-
coordination sphere as neutral P,O chelate. The weakly co- tion chemistry on piano-stool complexes bearing the related
ordinating oxygen of the protonated chelating ligand is then monoanionic METAMORPhos scaffold. Stirring complex
displaced by a chloride (KCl is partially soluble in THF) to 7 in acetonitrile with NaPF6 for 2 days at room temperature
Scheme 6. Heterolytic activation of H2 by piano-stool complex 7.
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Figure 3. Solid-state structures of 11 (left) and 13 (right). Hydrogen atoms and PF6 counterion and CH2Cl2 solvent (for 11) have been
omitted for clarity. Selected bond lengths [Å] and angles [°] for 11: Ru–P 2.2637(3), Ru–O1 2.1210(10), Ru–N2 2.0200(13), Ru–N3
1.9991(13), Ru–N4 2.0175(12), Ru–N5 2.1248(13), P–N1 1.6720(12), N1–S 1.5544(12), S–O1 1.4996(10), S–O2 1.4482(10); P–Ru–O1
83.87(3), P–Ru–N2 93.27(4), P–Ru–N3 96.87(4), P–Ru–N5 171.22(4), N2–Ru–N4 175.11(5), O1–Ru–N3 178.70(4), P–N1–S 116.65(7),
N1–S–O1 112.65(6), N1–S–O2 112.05(6), Ru–O1–S 117.44(6), Ru–N2–C20 174.81(15). For 13: Ru–P 2.3230(6), Ru–O1 2.1334(16), Ru–
N2 2.0112(19), P–N1 1.671(2), N1–S 1.552(2), S–O1 1.4978(18), S–O2 1.4387(19); P–Ru–O1 81.31(5), P–Ru–N2 90.41(6), PЈ–Ru–O1
98.69(5), O1–Ru–N2 89.55(7), P–N1–S 115.40(13), N1–S–O1 113.36(11), N1–S–O2 113.00(12), Ru–O1–S 118.55(9). Symmetry operation
i: 1 – x, 1 – y, 1 – z.
(or for one hour at 50°) yielded complex 11 in almost quan- nors and consequently fast intramolecular proton shuttling.
titative yield. 1H NMR spectroscopy clearly illustrated Single crystals suitable for X-ray crystallographic analysis
complete dissociation of the cymene fragment after reac- were grown by slow diffusion of methyl tert-butyl ether
tion, and the 31P NMR spectrum showed only a singlet at (MTBE) into a CH2Cl2 solution of 12. Instead of the antici-
δ = 73.5 ppm (and the PF6 ion). X-ray crystal-structure pated monocationic complex, the resulting molecular struc-
analysis confirmed the displacement of the cymene ligand ture showed neutral complex 13, which contained two de-
by four acetonitrile molecules as well as complete exchange protonated, anionic METAMORPhos ligands (Figure 3,
of chloride for PF6 (Figure 3, left). The Ru–N bond length right). The molecule is located on an exact, crystallographic
varies from 1.9991(13) Å for the NCMe trans to the oxygen inversion center and bears two axial NCMe ligands and two
atom to 2.1248(13) Å for the NCMe trans to P, which fol- P,O chelates, with the strong O donors in a mutually trans
lows the same trend as reported for related compounds.[17] configuration. The P–Ru–O1 angle is slightly smaller
There is slight out-of-plane bending of the two axial NCMe [81.31(5)°] than in parent species 11.
units away from the PNSO side, which might be related to
slight steric hindrance [N2–Ru–N4 175.11(5) Å, Ru–N2– autoprotonolysis process between two molecules of 12, as
C20 174.81(15) Å]. depicted in Scheme 8, which results in formation of dication
We speculate that the formation of 13 originates from an
At least part of the weakly coordinated acetonitrile li- 14 and neutral species 13 that was characterized in the solid
gand set is easily displaced, as complex 11 reacted almost state. The proposed equilibrium might be influenced by sol-
instantaneously at room temperature with one additional vent polarity, but this has not been further investigated to
equivalent
of
1BH
to
yield
complex
12, date. Only complex 12 could be detected by HRMS spec-
[Ru(1B)(1BH)(NCMe)3]PF6 (Scheme 7). The exogenous trometry.
METAMORPhos ligand remained protonated at nitrogen,
because a doublet was observed in the H NMR spectrum MORPhos derivative [HNEt3][1K] (1 equiv.), which bears a
Upon addition of phosphoramidite-based META-
1
at δ = 6.96 ppm (2JP,H = 15.1 Hz) for the –NH group. At chiral binaphthol auxiliary, to complex 11, we observed the
room temperature, two doublets are detected in the 31P formation of two diastereomers (15a and 15b) in the 31P
NMR spectrum at δ = 74.2 and 70.8 ppm (2JP,H = 15 Hz). NMR spectrum due to the presence of a chiral sulfur atom
The –NH group is potentially involved in intramolecular as well as the atropisomeric chirality of the binaphthyl unit.
hydrogen bonding with the anionic oxygen donor of the P,O This implies that the chirality at sulfur is kinetically stable
chelate between the two ligands, as previously suggested for under these ligand substitution conditions, which could
analogous rhodium complexes.[10a] This is supported by the hold promise as an additional ligand design element for ap-
observation of coalescence using 31P variable-temperature plications in asymmetric catalysis. This is currently under
(VT) NMR spectroscopy, which indicates two equal P do- investigation.
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Scheme 7. Synthesis of cymene-free complex 11, [Ru(1B)(NCMe)4]PF6, and derivative 12 bearing two METAMORPhos ligands.
Scheme 8. Proposed autoprotonolysis of 12 to generate neutral complex 13, [Ru(1B)2(NCMe)2], and dicationic 14.
proton-responsive character allows for modulation of the
Conclusion
rate of H2 splitting with these piano-stool Ru species. Cur-
In summary, we have successfully synthesized a range of
rent efforts focus on the utilization of these complexes with
METAMORPhos ligands by coupling sulfonamides with
proton-responsive ligands in catalytic reactions and the po-
chlorophosphorus reagents. The introduction of electron-
tential exploitation of sulfur chirality for asymmetric trans-
donating or -withdrawing substituents is possible at phos-
formations.
phorus and sulfur independently, thus creating a versatile
library of these proton-responsive ligands. The presence of
steric bulk at phosphorus strongly favors formation and iso-
Experimental Section
lation of METAMORPhos ligands over the diphosphorus
(PPN) compound 2, which results from double condensa-
tion. The prototropic behavior of the METAMORPhos li-
gand family is tuned by the electronic character of both
P and S substituents, but to a varying extent. The use of
dialkylchlorophosphines leads to exclusive formation of the
PV tautomer, which features a P–H unit, whereas for chlor-
odiarylphosphines the ratio between the PIII (N–H) and PV
(P–H) tautomers is strongly dependent on the nature of the
organic group at sulfur. The coordination of these META-
MORPhos ligands to ruthenium was investigated by using
two different Ru precursors. The first piano-stool-type com-
plexes with METAMORPhos ligands were prepared and
fully characterized, including X-ray crystal-structure deter-
mination (for 6). Exclusive coordination as the
monoanionic P,O chelate was observed for a range of com-
plexes in the solid state, whereas the corresponding solution
phase also indicated coordination as neutral monodentate
P donor. Upon coordination of the ligand platform as P,O
chelate, the sulfur atom becomes chiral, and this chirality is
retained during subsequent substitution reactions at Ru, as
evidenced by the conversion of [Ru(1B)(NCMe)4]PF6. This
feature was not observed for Rh–METAMORPhos com-
plexes due to their dynamic coordination behavior. The het-
erolytic splitting of dihydrogen occurs in a bifunctional
manner, thereby resulting in reprotonation of the anionic
P,O chelate and formation of the neutral species
Ligand 1E: Commercially available 3,5-bis(trifluoromethyl)phenyl
sulfonamide (1 equiv., 10 mmol) was placed in a Schlenk flask un-
der nitrogen. The compound was azeotropically dried with toluene
and then dissolved in THF (15 mL) and triethylamine (25 mmol).
A
solution of bis(2-methylphenyl)chlorophosphine (10 mmol,
1.0 equiv.) in THF (5 mL) was added dropwise under strong mag-
netic stirring at room temperature. After stirring overnight at 60 °C,
the solution was filtered under a nitrogen atmosphere to remove the
insoluble triethylamonium chloride salt. The solvent was removed
under vacuum to leave a viscous oil. This residue was triturated
with diethyl ether (50 mL) and subsequently filtered. After one day
under dynamic vacuum, the oil solidified to yield a white solid that
1
still contained triethylamine and traces of solvent (55% yield). H
NMR (400 MHz, CD2Cl2): δ = 8.69–7.16 (aromatic region), 2.76
3
(q, 3JH,H = 7.3 Hz, CH2 of NEt3), 2.17 (s), 1.12 (t, JH,H = 7.3 Hz,
CH3 of NEt3) ppm. 1EH to NEt3 ratio of 5 based on proton inte-
gration. 13C{1H} NMR (101 MHz, CD2Cl2): δ = 142.2 (s, Cquat),
142.0 (s, Cquat), 133.8 (s, CH), 133.0 (d, JP,C = 3 Hz, CH), 132.9 (s,
CH), 132.8 (s, CH), 132.7 (s, Cquat), 132.4 (s, Cquat), 132.0 (s, Cquat),
131.9 (br. s, CH), 131.4 (d, JP,C = 3 Hz, CH), 127.1 (br. m, CH),
124.9 (br. m, CH), 124.7 (s, Cquat), 122.0 (s, Cquat), 20.6 (s, CH3),
20.4 (s, CH3) ppm. 19F NMR (282 MHz, CD2Cl2): δ = –63.2 (s)
ppm. 31P NMR (162 MHz, CD2Cl2): δ = 9.5 (s, PIII tautomer), 1.0
(d, 1JP,H = 497 Hz, PV tautomer) ppm. PIII is the major component,
on 31P integration. HRMS (ESI+): m/z calcd. for C28H34F6N2O2PS
(NEt3 adduct): [M + HNEt3]+: 607.19828; found 607.19790.
Ligand 1F: Obtained by means of the same procedure as compound
1B, starting from commercially available chlorodiisopropylphos-
[Ru(H)(Cl)(LH)] with only P-coordination. Tuning of the phine and p-butylphenyl sulfonamide in 75% yield. 1H NMR
Eur. J. Inorg. Chem. 2014, 1826–1835
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FULL PAPER
3
3
(400 MHz, CDCl3): δ = 7.82 (d, JH,H = 8 Hz, 2 H), 7.21 (d, JH,H
(s, CH3, CH3–Ar cymene), 14.0 (s, CH3, butyl) ppm. 31P{1H}
NMR (162 MHz, CDCl3): δ = 73.5 (s) ppm. HRMS (FAB+): m/z
calcd. for C32H38ClNO2PRuS: 668.1093 [M + H]+; found 668.1097.
1
2
= 8 Hz, 2 H), 6.36 (dt, JH,P = 441, JH,H = 4 Hz, 1 H, PH), 2.63
(t, 3JH,H = 7 Hz, 2 H, Ar–CH2–CH2–CH2–CH3), 2.23 (m, 2 H, CH
isopropyl), 1.58 (m, 2 H, Ar–CH2–CH2–CH2–CH3), 1.33 (m, 2 H,
Ar–CH2–CH2–CH2–CH3), 1.24 (m, 12 H, CH3 isopropyl), 0.91 (t,
3JH,H = 7 Hz, 3 H, Ar–CH2–CH2–CH2–CH3) ppm. 13C{1H} NMR
(101 MHz, CDCl3): δ = 145.8 (s), 142.9 (s), 128.2 (s), 125.6 (s), 34.2
(d, 1JP,C = 211 Hz), 23.8 (s), 23.1 (s), 22.1 (s), 16.4 (s), 15.4 (d, 2JP,C
= 4 Hz), 13.8 (s) ppm. 31P NMR (162 MHz, CDCl3): δ = 36.9 (m,
1JH,P = 441 Hz) ppm.
Complex 7: Obtained in 98% yield from ligand 1B. 1H NMR
(400 MHz, CD2Cl2): δ = 7.82–7.39 (aromatic region, 12 H), 7.11 (d,
3JH,H = 8.0 Hz, 2 H, tolyl aromatic CH), 5.70 (m, 3JH,H = 6.3 Hz, 1
3
H, Arcymene CH), 5.42 (d.m., JH,H = 6.3 Hz, 1 H, Arcymene CH),
3
3
5.230 (d.m., JH,H = 5.8 Hz, 1 H, Arcymene CH), 4.80 (m, JH,H
=
5.8 Hz, 1 H, Arcymene CH), 2.49 (m, 1 H, isopropyl cymene CH),
3
2.31 (s, 3 H), 2.07 (s, 3 H), 1.24 (d, JH,H = 6.9 Hz, 3 H, isopropyl
3
CH3), 1.16 (d, JH,H = 6.9 Hz, 3 H, isopropyl CH3) ppm. 31P{1H}
Synthesis of 3 (mixture of diastereoisomers): Ligand 1F (1 equiv.,
0.15 mmol) and [Ru(H)(Cl)(PPh3)3(CO)] (1 equiv., 0.15 mmol) were
heated at reflux overnight in toluene (5 mL) under nitrogen. The
solvent was removed by vacuum and the residue was dissolved in
diethyl ether (2 mL). Hexane (8 mL) was added and the solution
was kept at –20 °C overnight, thus leading to a yellow precipitate
that was filtered and washed with hexane (10 mL). Complex 3 was
obtained in 35% yield. Slow evaporation of a saturated solution of
complex 3 in diethyl ether resulted in the formation of yellow crys-
tals suitable for X-ray analysis after one week at room temp. 1H
NMR (400 MHz, CDCl3): δ = 8.21–6.94 (aromatic region, 38 H),
2.71–2.53 (4 H, Ar–CH2–CH2–CH2–CH3 both diastereoisomers),
2.20–2.02 (alkyl region, 2 H), 1.67–0.67 (alkyl region, 42 H) ppm.
NMR (162 MHz, CD2Cl2): δ = 73.3 (s) ppm. 13C{1H} NMR
1
(101 MHz, CD2Cl2): δ = 142.5 (d, JP,C = 59.5 Hz, Cquat, phenyl),
3
142.4 (s, Cquat, tolyl C–Me), 140.0 (d, JP,C = 3.7 Hz, Cquat, C–S),
1
134.0 (d, JP,C = 67.4 Hz, Cquat, phenyl), 132.4 (d, JP,C = 11.2 Hz,
CH, phenyl), 130.9 (d, JP,C = 2.9 Hz, CH, phenyl), 130.6 (d, JP,C
=
11.2 Hz, CH, phenyl), 130.4 (d, JP,C = 2.7 Hz, CH, phenyl), 129.3
(s, CH, tolyl), 129.1 (d, JP,C = 10.9 Hz, CH, phenyl), 128.4 (d, JP,C
= 11.7 Hz, CH, phenyl), 127.9 (s, CH, tolyl), 105.7 (s, Cquat
,
2
cymene), 95.3 (d, JP,C = 6.3 Hz, CH, cymene), 94.0 (s, Cquat
,
2
2
cymene), 86.9 (d, JP,C = 6.9 Hz, CH, cymene), 86.1 (d, JP,C
=
2
3.3 Hz, CH, cymene), 82.6 (d, JP,C = 2.9 Hz, CH, cymene), 31.1
(s, CH, cymene), 22.6 (s, CH3), 22.2 (s, CH3), 21.6 (s, CH3), 18.8
(s, CH3, CH3–Ar cymene) ppm. HRMS (ESI+): m/z calcd. for
C29H32ClNO2PRuS: 626.06234 [M + H]+; found 626.06409.
31P{1H} NMR (162 MHz, CDCl3): δ = 100.0 (d, JP,P = 25.5 Hz,
diastereoisomer a), 97.7 (d, JP,P = 24.0 Hz, diastereoisomer b),
2
2
39.1 (d, 2JP,P = 24.0 Hz, diastereoisomer b), 37.4 (d, 2JP,P = 25.5 Hz,
diastereoisomer a) ppm. Ratio of diastereoisomer a/b = 1.7 After
purification, based on 31P integrals. HRMS (ESI+): m/z calcd. for
C70H86Cl2N2O6P4Ru2S2: 1512.23418 [M·]+; found 1512.23667.
Heterolytic Cleavage of H2 Using 7 to Yield Complex 10: Method
A: Complex 7 (1 equiv., 12.5 μmol), KPF6 (10 equiv., 125 μmol),
and [D8]THF (0.5 mL) were charged in a high-pressure NMR spec-
troscopy tube. The tube was pressurized with hydrogen (10 bar),
1
stirred, and sonicated for 4 days. H NMR (400 MHz, [D8]THF):
General Synthesis of Piano-Stool Complexes: Ligand 1 (2 mmol,
1 equiv.) and [{RuCl(cymene)(μ-Cl)}2] (2 mmol, 1 equiv.) were dis-
solved in THF (20 mL) at room temperature. Triethylamine (1 mL)
was added, and the solution was stirred at room temperature for
2 h. The solution was filtered, and the THF was evaporated. The
residue was dissolved in dichloromethane (5 mL) and diethyl ether
(35 mL) was added dropwise, thus leading to an orange precipitate.
The precipitate was filtered and washed with diethyl ether (10 mL).
3
δ = 7.94 (m, 2 H, phenyl C–H), 7.85 (d, JP,H = 10.7 Hz, 1 H, N–
H), 7.79 (m, 2 H, phenyl C–H), 7.42–7.32 (6 H, phenyl C–H), 6.96
3
3
(d, JH,H = 8.2 Hz, 2 H, tolyl C–H), 6.89 (d, JH,H = 8.2 Hz, 2 H,
tolyl C–H), 5.63 (d, JH,H = 6.2 Hz, 1 H, Arcymene C–H), 5.39 (d,
JH,H = 5.8 Hz, 1 H, Arcymene C–H), 4.72 (d, JH,H = 6.2 Hz, 1 H,
Arcymene C–H), 4.54 (s, dissolved H2), 4.39 (d, JH,H = 5.8 Hz, 1 H,
Arcymene C–H), 2.25 (s, 3 H), 1.84 (m, 1 H, isopropyl cymene C–
3
H), 1.80 (s, 3 H), 0.98 (d, JH,H = 5.0 Hz, 3 H, isopropyl cymene
3
Complex 6: Obtained in 93% yield from ligand 1A. For crystalli-
zation, a solution of 6 (20 mg) in THF (0.2 mL) was layered with
diethyl ether (1 mL) to give a red crystalline material (suitable for
CH3), 0.96 (d, JH,H = 5.0 Hz, 3 H, isopropyl cymene CH3), –8.34
(d, J = 52.5 Hz, 1 H) ppm. 31P NMR (162 MHz, [D8]THF): δ =
87.7 (m, JP,H = 52 Hz) ppm. Method B: Complex 7 (1 equiv.,
X-ray analysis) after two weeks of slow diffusion at room temp. 1H 125 μmol) and KPF6 (2 equiv., 250 μmol) were suspended in THF
3
NMR (400 MHz, CDCl3): δ = 7.86–7.36 (12 H), 7.08 (d, JH,H
=
(2 mL). The solution was charged into an autoclave and submitted
8.3 Hz, 2 H, CH), 5.68 (d, 3JH,H = 6.3 Hz, 1 H, Arcymene CH), 5.40 to H2 (50 bar) for 10 h. After depressurizing to ambient conditions,
(d, JH,H = 6.4 Hz, 1 H, Arcymene CH), 5.26 (m, JH,H = 5.8 Hz, 1 the solution was filtered and the solvent was evaporated. The resi-
H, Arcymene CH), 4.83 (m, JH,H = 5.7 Hz, 1 H, Arcymene CH), 2.59 due was dissolved in dichloromethane and filtered with an HPLC
(m, 1 H, iPrCymene CH), 2.54 [t, JH,H = 7.0 Hz, 2 H, Ar–CH2– filter. The solvent was evaporated to yield complex 10 in quantita-
3
3
3
3
(CH2)2–CH3], 2.12 (s, 3 H, CH3 cymene), 1.50 (m, 2 H, Ar–CH2– tive yield. Method C: Complex 7 (1 equiv., 12.5 μmol) was dissolved
CH2–CH2–CH3), 1.32–1.18 [8 H, isopropyl cymene CH3 and Ar–
in THF (0.5 mL) and submitted to an atmosphere of H2 (50 bar)
3
(CH2)2–CH2–CH3] 0.87 (t, JH,H = 7.3 Hz, 3 H, butyl CH3) ppm. in an autoclave/NMR spectroscopy tube for 10 h. After depressur-
13C{1H} NMR (101 MHz, CDCl3): δ = 146.7 (s, Cquat, bu-
izing to ambient conditions, the solvent was evaporated to yield
1
3
1
tylphenyl), 142.2 (d, JP,C = 60.0 Hz, Cquat, phenyl), 139.1 (d, JP,C
complex 10 in quantitative yield. H NMR (400 MHz, CD2Cl2): δ
1
= 3.6 Hz, Cquat, butylphenyl), 133.1 (d, JP,C = 67.3 Hz, Cquat
phenyl), 132.2 (d, JP,C = 11.3 Hz, CH, phenyl), 130.627 (d, JP,C
,
=
= 7.92 (dd, JP,H = 11.5, JH,H = 7.5 Hz, 2 H, phenyl C–H), 7.76 (dd,
2
JP,H = 12.0, JH,H = 7.1 Hz, 2 H, phenyl C–H), 7.57 (d, JP,H
=
2.7 Hz, CH, phenyl), 130.4 (d, JP,C = 11.4 Hz, CH, phenyl), 130.047
(d, JP,C = 2.8 Hz, CH, phenyl), 128.7 (d, JP,C = 10.8 Hz, CH,
phenyl), 128.7 (s, CH, butylphenyl), 128.0 (d, JP,C = 11.8 Hz, CH,
10.9 Hz, 1 H, N–H), 7.48–7.35 (6 H), 6.96 (d, 3JH,H = 8.2 Hz, 2 H,
tolyl C–H), 6.91 (d, JH,H = 8.2 Hz, 2 H, tolyl C–H), 5.61 (d, JH,H
3
= 6.2 Hz, 1 H, Arcymene C–H), 5.36 (d, JH,H = 5.9 Hz, 1 H, Arcymene
phenyl), 127.9 (s, CH, butylphenyl), 105.090 (s, Cquat, cymene), C–H), 4.69 (d, JH,H = 6.2 Hz, 1 H, Arcymene C–H), 4.28 (d, J =
2
94.614 (d, JP,C = 6.2 Hz, CH, cymene), 93.4 (s, Cquat, cymene),
5.8 Hz, 1 H, Arcymene C–H), 2.28 (s, 3 H), 1.83 (s, 3 H), 1.81 (m, 1
2
2
3
86.5 (d, JP,C = 6.9 Hz, CH, cymene), 86.0 (d, JP,C = 3.2 Hz, CH,
cymene), 83.2 (d, 2JP,C = 3.2 Hz, CH, cymene), 35.6 (s, CH2, butyl),
33.4 (s, CH2, butyl), 30.7 (s, CH, cymene), 22.4 (s, CH3, CH3–CH
H, isopropyl cymene C–H), 0.99 (d, JH,H = 7.0 Hz, 6 H), –8.45
2
(d, JP,H = 52.0 Hz, 1 H) ppm. 31P NMR (162 MHz, CD2Cl2): δ =
2
89.2 (m, JP,H = 52.0 Hz) ppm. 13C{1H} NMR (75 MHz, CD2Cl2):
cymene), 22.3 (s, CH2, butyl), 22.3 (s, CH3, CH3–CH cymene), 18.7 δ = 143.1 (s, Cquat, tolyl C–Me), 139.5 (s, Cquat, tolyl C–Me), 136.0
Eur. J. Inorg. Chem. 2014, 1826–1835
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1
2
4
(d, JP,C = 44.3 Hz, Cquat, phenyl), 135.2 (d, 1JP,C = 65.3 Hz, Cquat
phenyl), 133.6 (d, JP,C = 13.1 Hz, CH, phenyl), 133.1 (d, JP,C
12.5 Hz, CH, phenyl), 131.4 (d, JP,C = 2.2 Hz, CH, phenyl), 131.1
,
=
6.96 (dd, JP,H = 15.1, JP,H = 3.4 Hz, 1 H, N–H), 2.39 (s, 3 H,
CH3), 2.35 (s, 3 H, CH3), 2.30 (s, 3 H, CH3), 1.64 (s, 3 H, CH3),
1.25 (s, 3 H, CH3) ppm. 13C{1H} NMR (101 MHz, CD2Cl2): δ =
3
(d, JP,C = 2.5 Hz, CH, phenyl), 129.4 (s, CH, tolyl), 128.4 (d, JP,C 144.2 (s, Cquat, tolyl), 142.8 (d, JP,C = 2.7 Hz, Cquat, tolyl), 142.5
= 5.7 Hz, CH, phenyl), 128.2 (d, JP,C = 6.3 Hz, CH, phenyl), 126.4 (s, Cquat, tolyl), 139.2 (s, Cquat, tolyl), 137.9 (dd, JP,C = 48.0, JP,C
(s, CH, tolyl), 110.0 (s, Cquat, cymene), 103.2 (s, Cquat, cymene),
93.2 (d, JP,C = 3.8 Hz, CH, cymene), 90.5 (d, JP,C = 6.6 Hz, CH,
cymene), 89.10 (d, JP,C = 5.5 Hz, CH, cymene), 82.40 (d, JP,C
3.0 Hz, CH, cymene), 31.4 (s, CH, cymene), 24.6 (s, CH3), 22.0 (s,
1
3
1
3
= 9.7 Hz, Cquat, phenyl), 135.5 (dd, JP,C = 47.6, JP,C = 10.3 Hz,
2
2
C
quat, phenyl), 134.0 (dd, 2JP,C = 11.9, 4JP,C = 2.3 Hz, CH, phenyl),
2
2
2
4
=
133.5 (dd, JP,C = 11.7, JP,C = 2.2 Hz, CH, phenyl), 132.0 (br. d,
JP,C = 12.1 Hz, CH, phenyl), 131.6 (dd, 2JP,C = 11.3, 4JP,C = 2.8 Hz,
CH3), 21.7 (s, CH3), 19.0 (s, CH3, CH3–Ar cymene) ppm. HRMS CH, phenyl), 131.3 (br. d, JP,C = 1.2 Hz, CH, phenyl), 130.5–130.4
(ESI+): m/z calcd. for C29H33ClKNO2PRuS: 666.03425 [M + K]+;
found 666.03437; m/z calcd. for C29H33NO2PRuS: 592.10203 [M –
Cl]+; found 592.10311.
(br., CH, overlapping signals), 129.9 (s, Cquat, NCCH3), 129.7 (s,
CH, tolyl), 129.5 (s, CH, tolyl), 129.4 (d, JP,C = 10.7 Hz, CH,
phenyl), 129.1 (d, JP,C = 9.9 Hz, CH, phenyl), 128.9 (d, JP,C
=
,
=
10.3 Hz, CH, phenyl), 128.6 (dd, 1JP,C = 14.2, 3JP,C = 7.1 Hz, Cquat
In Situ Synthesis and Characterization of Complex 10ЈЈ: Complex
10 (1 equiv., 17.5 μmol), AgBF4 (17.5 μmol), and CD2Cl2 (0.7 mL)
were stirred for 2 h under nitrogen. The solution was filtered and
introduced into a screw-cap NMR spectroscopy tube for direct
measurement (31P yield: 87.5%). 1H NMR (500 MHz, MHz,
CD2Cl2): δ = 7.88–7.24, 6.40 (br., Arcymene C–H), 6.33 (d, J =
4.5 Hz, Arcymene C–H), 6.26 (d, J = 6.0 Hz, Arcymene C–H), 6.18
(br., Arcymene C–H), 6.11 (br., Arcymene C–H), 5.82 (br., Arcymene C–
H), 5.68 (d, J = 6.5 Hz, Arcymene C–H), 5.52 (br., Arcymene C–H),
1
phenyl), 128.9 (d, JP,C = 10.1 Hz, CH, phenyl), 128.1 (d, JP,C
7.1 Hz, Cquat, phenyl), 127.3 (s, Cquat, NCCH3), 126.5 (s, CH, tolyl),
126.2 (s, CH, tolyl), 126.1 (s, Cquat, NCCH3), 21.7 (s, CH3, tolyl),
21.6 (s, CH3, tolyl), 4.7 (s, CH3, NCCH3), 3.5 (s, CH3, NCCH3),
2.9 (s, CH3, NCCH3) ppm. 31P{1H} NMR (162 MHz, CD2Cl2): δ
2
2
= 74.2 (d, JP,P = 342 Hz), 70.8 (d, JP,P = 342 Hz), –146.7 (PF6)
ppm. HRMS (ESI+): m/z calcd. for C44H44N5O4P2RuS2: 934.13640
[M – PF6]+; found 934.13248.
2
2
CCDC-960163 (for 3), -960164 (for 6), -960165 (for 11), and
-960166 (for 13) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2.50–0.09 (alkyl region), –9.06 (d, JP,H = 37.8 Hz), –9.16 (d, JP,H
= 35.1 Hz) ppm. 31P{1H} NMR (202 MHz, CD2Cl2): δ = 100.4,
97.1 ppm. Complex 10ЈЈ was formed as a 1:1 mixture of diastereo-
isomers (the eight cymene signals and both hydride signals inte-
grate for 1H each; both phosphorus signals integrate for 1P). The
phosphorus–hydride coupling was not observed in the 31P NMR
spectra due to broadened signals.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details, full characterization of all ligands and
complexes, crystallographic data, NMR spectra.
Complex 11: Complex
7 (1 equiv., 0.8 mmol) and KPF6
(1.05 equiv., 0.84 mmol) were suspended in acetonitrile (50 mL).
The reaction mixture was stirred for 2 h at 50 °C. The solvent was
removed under vacuum, and the residue dissolved in dichlorometh-
ane (5 mL). The solution was filtered through an HPLC filter and
dried. The residue was dissolved in dichloromethane (1 mL), and
diethyl ether (10 mL) was added dropwise while stirring, thus lead-
ing to a pale yellow precipitate that was filtered and washed with
diethyl ether (10 mL). Complex 11 was obtained in quantitative
yield. For crystallization, a solution of 11 (17.5 μmol) in CD2Cl2
(0.7 mL) was filtered with an HPLC filter and layered with methyl
tert-butyl ether (1 mL) to result in pale yellow crystals after two
weeks of slow diffusion at room temp. 1H NMR (400 MHz,
Acknowledgments
This work was funded by the National Research School Combina-
tion – Catalysis (NRSC – Catalysis). The authors thank Prof. Dr.
Bas de Bruin, Pierre Boulens, and Sander Oldenhof for useful dis-
cussions. The X-ray diffractometer was financed by the Nether-
lands Organization for Scientific Research (NWO).
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3
CD2Cl2): δ = 7.82–7.73 (4 H), 7.59 (d, JH,H = 8.2 Hz, 2 H, tolyl),
3
7.51–7.40 (6 H), 7.17 (d, JH,H = 8.2 Hz, 2 H, tolyl), 2.59 (s, 3 H),
2.51 (s, 3 H), 2.35 (s, 3 H), 1.98 (s, 3 H), 1.77 (s, 3 H) ppm. 13C{1H}
NMR (101 MHz, CD2Cl2): δ = 142.3 (s, Cquat, tolyl), 142.2 (d, 3JP,C
1
= 3.7 Hz, Cquat, tolyl), 138.6 (d, JP,C = 62.8 Hz, Cquat, phenyl),
1
136.4 (d, JP,C = 61.2 Hz, Cquat, phenyl), 131.2 (d, JP,C = 11.6 Hz,
CH, phenyl), 131.0 (d, JP,C = 2.5 Hz, CH, phenyl), 130.5 (d, JP,C
=
11.7 Hz, CH, phenyl), 130.3 (d, JP,C = 2.9 Hz, CH, phenyl), 129.5
(s, CH, tolyl), 129.1 (d, JP,C = 11.1 Hz, CH, phenyl), 128.9 (d, JP,C
= 11.0 Hz, CH, phenyl), 127.8 (s, Cquat, NCCH3), 126.5 (s, CH,
tolyl), 125.1 (s, Cquat, NCCH3), 124.3 (s, Cquat, NCCH3), 122.6 (d,
3JP,C = 15.4 Hz, Cquat, NCCH3), 20.8 (s, CH3, tolyl), 4.0 (s, CH3,
NCCH3), 3.3 (s, CH3, NCCH3), 3.1 (s, CH3, NCCH3), 2.7 (s, CH3,
NCCH3) ppm. 31P{1H} NMR (162 MHz, CD2Cl2): δ = 87.5 (s),
–142.3 (PF6) ppm. HRMS (ESI+): m/z calcd. for
C27H29N5O2PRuS: 620.08296 [M + H]+; found 620.08594.
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Received: September 17, 2013
Published Online: November 19, 2013
Eur. J. Inorg. Chem. 2014, 1826–1835
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