Two isomers of a bis(diphenylphosphino)phosphinine, and the synthesis and reactivity of Ru arene/Cp* phosphinophosphinine complexes

Article abstract of DOI:10.1039/c8nj03632b

The reaction of 4,6-di(tert-butyl)-1,3,2-diazaphosphinine (3) with two equivalents of MeCCPPh₂ gave two isomeric products, 2,6-bis(diphenylphosphino)-3,5-dimethylphosphinine (5) and 2,5-bis(diphenylphosphino)-3,6-dimethylphosphinine (6), which were successfully separated and their molecular structures determined by X-ray crystallography. Although the 2,6-bis(iminophosphorano)phosphinine 7 was readily synthesised from 5 using mesityl azide, its coordination to late transition metals was not achieved. The reaction of 2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (1) with [{Ru(Cl)(μ-Cl)(p-cymene)}₂] generated two products: cis-[Ru(Cl)₂(1)₂] (2) and the dinuclear species [Ru(μ-Cl)₃(p-cymene)Ru(Cl)(1)] (8), which was characterised by single crystal X-ray diffraction. The reaction of 1 with [{Ru(Cl)(μ-Cl)(C₆Me₆)}₂]/NH₄PF₆ led to cleavage of the SiMe₃ group and addition of H₂O across a P═C bond to generate [Ru(C₆Me₆)(1-OH-2-PPh₂-3-MePC₅H₄)][PF₆] (9). The reaction of 1 with [{Ru(Cp*)(μ₃-Cl)}₄] yielded [Ru(Cp*)(Cl)(1)] (10) which readily reacted with H₂O across a P═C bond to form [Ru(Cp*)(Cl)(1-OH-2-PPh₂-3-Me-6-SiMe₃PC₅H₃)] (11). Neither 9, 10, 11 or cis-[Ru(Cl)₂(dppm)₂] were effective precatalysts for the transfer hydrogenation (TH) of acetophenone, unlike 2 which in addition was also found to catalyse the TH of benzophenone at 82 °C (0.1 mol% 2 with 0.5 mol% KO^tBu in ⁱPrOH), with much lower activity for 2-fluorobenzaldehyde and 4-methylcyclohexanone. 11 was a competent precatalyst for the hydrogen-borrowing upgrading of EtOH/MeOH to isobutanol, albeit in lower yields compared to 2.

Full text of DOI:10.1039/c8nj03632b

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Two isomers of a bis(diphenylphosphino)-
phosphinine, and the synthesis and reactivity of
Ru arene/Cp* phosphinophosphinine complexes†‡
Cite this: New J. Chem., 2018,
42, 19625
a
b
Robert J. Newland,
Stephen M. Mansell
Matthew P. Delve,a Richard L. Wingad
and
a
*
The reaction of 4,6-di(tert-butyl)-1,3,2-diazaphosphinine (3) with two equivalents of MeCRCPPh2 gave two
isomeric products, 2,6-bis(diphenylphosphino)-3,5-dimethylphosphinine (5) and 2,5-bis(diphenylphosphino)-
3,6-dimethylphosphinine (6), which were successfully separated and their molecular structures determined
by X-ray crystallography. Although the 2,6-bis(iminophosphorano)phosphinine 7 was readily synthesised
from 5 using mesityl azide, its coordination to late transition metals was not achieved. The reaction of
2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (1) with [{Ru(Cl)(m-Cl)(p-cymene)}2] generated
two products: cis-[Ru(Cl)2(1)2] (2) and the dinuclear species [Ru(m-Cl)3(p-cymene)Ru(Cl)(1)] (8), which was
characterised by single crystal X-ray diffraction. The reaction of 1 with [{Ru(Cl)(m-Cl)(C6Me6)}2]/NH4PF6 led
to cleavage of the SiMe3 group and addition of H2O across a PQC bond to generate [Ru(C6Me6)(1-OH-2-
PPh2-3-MePC5H4)][PF6] (9). The reaction of 1 with [{Ru(Cp*)(m3-Cl)}4] yielded [Ru(Cp*)(Cl)(1)] (10) which
readily reacted with H2O across a PQC bond to form [Ru(Cp*)(Cl)(1-OH-2-PPh2-3-Me-6-SiMe3PC5H3)]
(11). Neither 9, 10, 11 or cis-[Ru(Cl)2(dppm)2] were effective precatalysts for the transfer hydrogenation
(TH) of acetophenone, unlike 2 which in addition was also found to catalyse the TH of benzophenone
Received 20th July 2018,
Accepted 31st October 2018
at 82 1C (0.1 mol% 2 with 0.5 mol% KOtBu in PrOH), with much lower activity for 2-fluorobenzaldehyde
i
DOI: 10.1039/c8nj03632b
and 4-methylcyclohexanone. 11 was a competent precatalyst for the hydrogen-borrowing upgrading of
EtOH/MeOH to isobutanol, albeit in lower yields compared to 2.
rsc.li/njc
Introduction
Phosphinines (the phosphorus analogue of pyridine) are aromatic
heterocycles that are of interest due to their unique properties1
and for their use as ligands in homogeneous catalysis.2
Functionalising phosphinines with an additional donor can
generate chelating ligands,3 and much of the recent progress in
this area has focused on the development of 2-pyridylphosphinines
(the mono-phosphorus analogues of bipyridine).4 The synthesis
of phosphinines with an additional phosphorus donor has
also been explored, and chiral ligands containing a phosphine
(Chart 1, A)5 or phosphite donor (B)6 have been successfully syn-
thesised along with phosphinines that contain a phosphinite (C)7
a Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
E-mail: s.mansell@hw.ac.uk; Web: www.mansellresearch.org.uk
b School of Chemistry, University of Bristol, Cantock’s Close, Bristol, BS8 1TS, UK
† Additional research data supporting this publication are available from Heriot-
Watt University’s research data repository at DOI: 10.17861/594df3c3-3002-412b-
a224-0614d1b378b2.
‡ Electronic supplementary information (ESI) available. CCDC 1838426–1838431.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c8nj03632b
Chart 1 Phosphinines with additional phosphorus substituents.
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or phosphonite donor (D).7b,8 Additionally, several diphos-
phinines,1d,9 triphosphinines7a,10 and tetraphosphinine macro-
cycles11 are also known.
There are a handful of synthetic methods that give access
to 2-phosphinophosphinines,12 but the diazaphosphinine
methodology reported by Mathey and Le Floch represents a
simple and versatile route to mono-, di- and tetra-diphenyl-
phosphino-substituted phosphinines.13 2,6-(PPh2)2-3,5-Ph2PC5H
has exclusively been used in reactions with sulfur followed by a
nucleophile in order to generate anionic phosphacyclohexadienyl
ligands (E),14 which have shown extensive coordination
chemistry,15 although the aromaticity in the phosphinine ring
is lost. We are interested in applying phosphine-substituted
phosphinine ligands in homogeneous catalysis, and have previously
shown that 2-PPh2-3-Me-6-SiMe3PC5H2 (1) can be used as a chelating
ligand to generate cis-[Ru(Cl)2(1)2] (2).16 2 was an effective precatalyst
for the room temperature transfer-hydrogenation of acetophenone
derivatives and the H-borrowing upgrading of EtOH/MeOH to
Scheme 1 Synthesis of bis(phosphino)phosphinines and
phosphorano)phosphinine.
a bis(imino-
isobutanol.16 Prior to this study, 2-phosphinophosphinine 51% yield as a colourless powder that is air-stable in the solid
ligands were only characterised as bridging ligands.8,17 Further state but decomposes under air within hours in solution.
examples of 1 as a small-bite angle18 chelating ligand were 31P{1H} NMR spectroscopy was used to identify the 2,6-isomer,
subsequently described in a series of group 6 tetracarbonyl with a triplet resonance at d = 244.8 ppm for the phosphinine P
complexes, with 1 also able to influence the selectivity of atom and a doublet resonance of greater intensity at d = 8.1 ppm
Cr-catalysed ethylene oligomerisation reactions,19 as well as for the equivalent PPh2 groups. Purification of the 2,5-isomer
in the Rh-catalysed hydroboration of carbonyls.20 We now was achieved by Soxhlet extraction of the remaining residue from
describe the extension of the synthetic route used to synthesise the diazaphosphinine reaction using n-hexane heated under
1 to give bis(diphenylphosphino)phosphinines. In addition, the reflux over seven days. The 2,5-isomer is more stable to atmo-
coordination chemistry of phosphinophosphinines using addi- spheric air and moisture than the 2,6 isomer and the extraction
tional Ru starting materials was explored because this area is still was successfully carried out under air. Recrystallisation from
very limited; the only structurally characterised Ru phosphinine toluene at ꢀ25 1C yielded 6 as a colourless solid in moderate
complexes are trans-[Ru(Cl)2(PC5H5)4],21 [Ru(Cp*)(2,6-(SiMe3)2- yield (22%). 31P{1H} NMR spectroscopy demonstrated the
PC5H3)][BF4]22 and Ru complexes containing 2,20-biphosphinines.23 inequivalence of the two PPh2 groups as two resonances at
F, containing a 2-(phosphinesulfide)phosphacyclohexadienyl ligand, low chemical shift; a doublet-of-doublets at d = ꢀ9.1 ppm and
has also been characterised.13c
another at d = ꢀ10.4 ppm with much smaller coupling constants.
The phosphinine P atom was also observed at d = 220.8 ppm as a
doublet-of-doublets. Single crystals of the 2,6-isomer suitable for
X-ray diffraction were grown from a mixture of THF and pet.
ether at ꢀ25 1C, and the 2,5-isomer from a THF solution layered
with Et2O. The solid-state structure of 5 shows a C2-symmetric
Results and discussion
Bis(phosphino)phosphinines
As was observed in the synthesis of 1,16 the reaction of one structure with one Ph group in each PPh2 unit pointing towards
equivalent of MeCRCPPh2 with the diazaphosphinine 313 the open space around the phosphinine P atom, with the other
regioselectively formed one azaphosphinine isomer containing two orientated anti to each other (Fig. 1, left). Analysis of the ring
an ortho-phosphine substituent within two hours in toluene at bond lengths and angles confirmed that the ring is symmetric
120 1C in a sealed vessel (Scheme 1, 4). However, reaction with a and is in agreement with the aromatic nature of the phosphinine
second equivalent of MeCRCPPh2 proceeded considerably ring (Table 1). The P(1)–C(1)/P(1)–C(5) bond lengths are slightly
more slowly, requiring two weeks at 120 1C for complete con- contracted with respect to the P(1)–C(1) bond length of 1
sumption of the azaphosphinine. 31P{1H} NMR spectroscopy (1.741(1) versus 1.754(3) Å for 1).16 The solid-state structure of
revealed that two isomeric phosphinines, 5 and 6, were produced the 2,5-isomer showed disorder in the central phosphinine ring
in an approximately 60: 40 ratio respectively (Scheme 1), unlike (P1 and C1–C7), which was successfully modelled over two
the analogous reaction for PhCRCPPh2 which was reported to positions. Although the location of the PPh2 groups in the
cleanly generate the 2,6-isomer after 20 h at 120 1C.13a,13b 2,5-positions was established (Fig. 1, right), the disorder makes
Separation of the two regioisomers was readily achieved without discussion of the bond lengths and angles unwarranted.
the need for chromatographic purification due to their different
The derivatisation of the 2,6-isomer into its bis(iminophos-
solubilities. 5 is relatively soluble in aliphatic solvents, and was phorano)phosphinine analogue was successfully achieved by the
extracted using petroleum ether at 20 1C. After recrystallisation Staudinger reaction using mesityl azide in 85% yield (Scheme 1).
from toluene at ꢀ25 1C, analytically pure 5 was obtained in 7 is structurally related to the well-known bis(imino)pyridine
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Me groups were observed as two singlets in a 12 : 6 ratio by
1H NMR spectroscopy, and the Me substituents on the phos-
phinine ring appeared as a singlet in the same region. Many of
the aryl-H signals appeared as overlapping multiplets, but the
4-H atom on the phosphinine ring was observed as a singlet at
d = 6.71 ppm.
Many reactions aimed at exploring the coordination chem-
istry of 7 with late transition metals were attempted without
success. No reaction was observed with [Rh(Cl)(PPh3)3] and
[{Rh(m-Cl)(COD)}2], and multiple products were observed in reactions
with [Pt(Cl)2(COD)], [{Rh(m-Cl)(CO)2}2] and cis-[Ru(Cl)2(dmso)4]
which could not be characterised further. Ultimately, simple
coordination of 7 has not yet been achieved with these metals,
with the formation of multiple products and loss of aromaticity
in the phosphinine ring observed instead. The reaction with
FeCl2 gave similar results, as indicated by 31P{1H} NMR spectro-
scopy, however, single crystals of one of the products were
grown from the reaction mixture. X-ray diffraction confirmed
the basic framework of ligand 7, but also highlighted additional
reactivity of this ligand with protonation of both PQN bonds
and functionalisation of the phosphinine P atom with both
O and H (7Fe, see ESI‡). The reason for this lack of success is
not known, but the unusual combination of two types of polar-
opposite donors (a soft, p-accepting phosphinine with two hard,
Fig. 1 Molecular structure of 5 (left) and 6 (right; thermal ellipsoids at
50%). All H-atoms and the 2nd positions of the phosphinine ring in 6 have
been removed for clarity.
Table 1 Selected bond lengths and angles for 5
Bond lengths (Å)
Bond angles (1)
P(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–P(1)
C(1)–P(2)
1.741(1)
1.409(1)
1.394(2)
1.399(2)
1.406(2)
1.742(1)
1.836(1)
P(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(4)–C(5)–P(1)
C(5)–P(1)–C(1)
P(1)–C(1)–P(2)
124.01(9)
121.5(1)
126.1(1)
121.8(1)
123.73(9)
102.76(5)
118.52(6)
ligands that have been extensively applied in homogeneous s-donating iminophosphoranes) could result in a ‘‘mismatched’’
catalysis,24 although the ligand properties are very different as ligand with little propensity to coordinate to late transition
it incorporates two ‘hard’ iminophosphorane donors25 along metals. However, the coordination chemistry with other ‘harder’
with a ‘soft’, p-accepting central phosphinine donor (using the Lewis acids may prove more fruitful because Zn and Mg
HSAB classification). 7 is very moisture-sensitive and must be complexes with neutral iminophosphorane ligands based on
handled using rigorously dried solvents and under careful exclu- dibenzofuran scaffolds are well known.26
sion of air. Unfortunately, single crystals suitable for X-ray
diffraction could not be obtained, but 1H, 13C and 31P{1H}
Ru coordination chemistry
NMR spectroscopic data, as well as HRMS and elemental The coordination of 1 to Ru was readily achieved by the reaction
analysis, were in agreement with the proposed structure. The of 1 with cis-[Ru(Cl)2(dmso)4],16 so reactions using this Ru pre-
phosphinine P resonance was clearly observed at d = 246.9 ppm cursor with the two bis(phosphino)phosphinines were attempted.
as a triplet (2JP–P = 99.7 Hz) and the two iminophosphorane P The reaction of two equivalents of 5 or 6 with cis-[Ru(Cl)2(dmso)4]
atoms were observed as a doublet at d = ꢀ9.4 ppm. The mesityl was anticipated to yield the bis-chelating complex that would
Scheme 2 Synthesis of Ru phosphinophosphinine complexes.
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Table 2 Selected bond lengths and angles for the Ru phosphinophos-
phinine complexes. Values for only one molecule in the asymmetric unit
are given due to the similar values observed for the other molecule
feature uncoordinated PPh2 donors with great potential for
further reactivity and coordination chemistry. Unfortunately,
reactions with both of the isomers generated multiple products,
as observed by 31P{1H} NMR spectroscopy, and clean conversion
to a single product was not achieved. Purification by crystalli-
sation was also unsuccessful, so our efforts instead focused on
extending the coordination chemistry of 1 with additional Ru
complexes (Scheme 2). The reaction of 1 with 0.5 equivalents of
the para-cymene dimer [{Ru(Cl)(m-Cl)(p-cymene)}2] at 50 1C for
5 min was carried out and the reaction was analysed by 31P{1H}
NMR spectroscopy. It was observed that all of the proligand 1
had been consumed and that two products had been formed in
an approximately 1 : 1 ratio, with the characteristic signals of 2
allowing it to be readily assigned as one of these products.16
Initially, it was expected that the second product (d = 231.4 (d)
and 21.7 (d) ppm) would be mononuclear and possess a half-
sandwich geometry (cf. 9), but analysis by single crystal X-ray
diffraction of the dark red crystals formed from layering the
reaction mixture with pet. ether showed a dinuclear compound
8 (Fig. 2). The structure that was obtained was the result of
displacement of one p-cymene ligand instead of separation of
the dimer by breaking the two dative Cl - Ru bonds.27 Ru1 is
in a distorted octahedral geometry with one chelating diphos-
phinophosphinine ligand and four bonds to Cl atoms, one of
which is a terminal ligand. Ru2 has an Z6-cymene ligand and
bonds to three bridging Cl ligands. The bond lengths and
angles for the phosphinophosphinine ligand are similar to that
previously described in complex 2 with the Ru–phosphinine
bond distance shorter than the Ru–PPh2 distance (Table 2). The
P(1)–C(5)–P(2) angle is more acute than in 2 (93.1(1)1 versus
97.7(3)1 in 2), although the P(1)–Ru(1)–P(2) bite-angle has not
changed significantly. Unfortunately, insufficient material could
be separated from samples of 8, due to co-crystallised 2, to allow
for complete characterisation. Attempts were made to optimise
the reaction conditions to favour the exclusive formation of 8,
however, varying the equivalents of 1 (including a 1 : 1 reaction)
Bond lengths (Å)
Bond angles (1)
Compound
8
P(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–P(1)
C(5)–P(2)
P(1)–Ru(1)
P(2)–Ru(1)
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–Cl(3)
Ru(1)–Cl(4)
Ru(2)–Cl(2)
Ru(2)–Cl(3)
Ru(2)–Cl(4)
1.713(3)
P(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(4)–C(5)–P(1)
C(5)–P(1)–C(1)
P(1)–C(5)–P(2)
P(1)–Ru(1)–P(2)
Cl(1)–Ru(1)–Cl(3)
114.9(2)
128.9(3)
125.2(3)
117.8(3)
125.1(3)
108.2(1)
93.1(1)
1.409(4)
1.397(4)
1.405(4)
1.396(4)
1.717(3)
1.837(3)
2.184(1)
2.283(1)
2.395(1)
2.495(1)
2.428(1)
2.484(1)
2.422(1)
2.458(1)
2.447(1)
70.56(3)
169.60(2)
9
P(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–P(1)
C(1)–P(2)
P(1)–O(1)
P(1)–Ru(1)
P(2)–Ru(1)
Ru(1)–Cl(1)
1.861(3)
1.505(4)
1.328(6)
1.453(6)
1.338(5)
1.774(3)
1.880(3)
1.667(3)
2.286(1)
2.326(1)
2.401(1)
P(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(4)–C(5)–P(1)
C(5)–P(1)–C(1)
P(1)–C(1)–P(2)
P(1)–Ru(1)–P(2)
118.9(2)
121.4(3)
126.2(4)
126.5(4)
121.8(3)
102.5(2)
92.2(1)
71.53(3)
11
P(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–P(1)
C(1)–P(2)
P(1)–O(1)
P(1)–Ru(1)
P(2)–Ru(1)
Ru(1)–Cl(1)
1.860(4)
1.504(5)
1.346(6)
1.463(6)
1.358(6)
1.783(4)
1.884(4)
1.628(3)
2.280(1)
2.276(1)
2.450(1)
P(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(4)-C(5)-P(1)
C(5)–P(1)–C(1)
P(1)–C(1)–P(2)
P(1)–Ru(1)–P(2)
118.5(3)
121.9(4)
126.2(4)
127.8(4)
118.6(3)
105.7(2)
91.1(2)
71.84(3)
and the reaction temperature did not result in anything other
than a mixture of two products. A 4 : 1 reaction of 1:[{Ru(Cl)(m-Cl)-
(p-cymene)}2] resulted in the selective formation of 2, and 8 could
represent an intermediate in this synthetic pathway.
In order to circumvent the issue of the lability of the
p-cymene ligand, the reaction was repeated with the hexa-
methylbenzene dimer [{Ru(Cl)(m-Cl)(C6Me6)}2] using strictly
anhydrous salts of non-coordinating anions to exchange the
Cl counteranion that would be formed upon chelation of 1
(Scheme 2). AgBF4, AgSbF6 and Na[B{3,5-(CF3)2C6H3}4] generated
multiple products, however, NH4PF6 cleanly produced a single
product by 31P{1H} NMR spectroscopy, although the observed
chemical shifts (d = 11.6 (d) and 8.8 (d) ppm) indicated that the
phosphinine ligand was no longer aromatic. NH4PF6 is hygro-
scopic, but attempts to repeat the reaction with dried NH4PF6
led to multiple products indicating an important role for the
adsorbed water in selectively yielding one product. Additionally,
without NH4PF6, displacement of C6Me6 occurs and complex 2
is formed (see ESI‡). Single crystals of the product were grown
by slow diffusion of petroleum ether into a CH2Cl2 solution of
Fig. 2 Molecular structure of 8 with thermal ellipsoids at 50% probability.
All H-atoms removed for clarity.
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Fig. 4 Molecular structure of 11 with thermal ellipsoids at 50% probability.
Only one molecule present in the asymmetric unit is shown and all of the H
atoms except those resulting from reaction with H2O removed for clarity.
Fig. 3 Molecular structure of 9 with thermal ellipsoids at 50% probability.
All H-atoms except those resulting from the reaction with H2O removed
for clarity along with the other cation and anion in the asymmetric unit.
rapidly in THF, with a colour change to deep red observed
within seconds. The resulting complex proved to be very soluble,
the product in good yield (78%), and the resulting orange however, upon storing a concentrated pet. ether solution at 0 1C,
needles were analysed by X-ray diffraction, revealing 9 to be the product precipitated and was collected as an orange solid in
the product of the syn-reaction of the phosphinine with H2O, 70% yield. 31P{1H} NMR showed two doublets at d = 240.1 and
1
and the unexpected cleavage of the SiMe3 group (Fig. 3). The Ru 18.2 ppm, and the H NMR spectroscopic data was also in-line
atom is bonded to Cl, an Z6-C6Me6 and a chelating phospha- with the anticipated half-sandwich compound. The 4-H phos-
cyclohexadiene ligand which has formed from the addition of phinine resonance was observed at d = 6.46 ppm as an apparent
4
H2O across a PQC double bond. As ammonium salts are hygro- doublet-of-triplets due to two similar JH–P couplings, and the
scopic, it is likely that the NH4PF6 was the source of the water. It 5-H resonance at d = 7.63 ppm as a doublet-of-doublets. HRMS
was also observed that the trimethylsilyl substituent had been confirmed the anticipated formula, but the compound readily
cleaved, possibly through reaction with Fꢀ arising from disso- reacted with trace moisture which precluded successful
ciation from the PF6 anion. Cleavage of SiMe3 using HCl has elemental analysis. This was definitively established when the
been observed previously.19,28
compound was exposed to atmospheric moisture and then
The molecular structure of 9 shows P(1) in a distorted crystallised from petroleum ether at 5 1C. Single crystal X-ray
tetrahedral geometry, resulting from sp3 hybridisation. As diffraction proved that, similarly to the synthesis of 9, 10 had
expected, the loss of aromaticity in the phosphacyclohexadiene reacted with water in a syn-manner, although the trimethylsilyl
ligand has had a notable effect on the bond lengths and angles group had not been cleaved (Fig. 4). Analogous reactivity with
around the ring. The C(1)–C(2) bond has lengthened signifi- isoelectronic [M(Cp*)(pyridylphosphinine)][Cl] (M = Rh, Ir)
cantly (1.505(4) Å) in line with a bond order of one, whilst the complexes has previously been established,30 and subsequent
C(2)–C(3) and C(4)–C(5) bonds (1.328(6) and 1.338(5) Å respec- work demonstrated the catalytic potential of a cyclometalated
tively) are shorter than in 1 (1.404(4) and 1.396(4) Å respectively) phosphinine iridium(III) complex for water oxidation.3d A Pd
due to localisation of the CQC double bonds. Both P(1)–C(1) complex of 2-diphenylphosphinito-phosphinine also recently
and P(1)–C(5) bonds have lengthened (1.861(3) and 1.774(3) Å showed facile hydrolysis in a similar manner to 10.7a 11 was
respectively) compared to 1 (1.754(3) and 1.749(3) Å respectively obtained in 12% yield (31P{1H} d = 78.3 (d), 18.0 (d) ppm). As
in 1). The reaction of coordinated phosphinine ligands with with 9, the structure of 11 shows that P(1) has a distorted tetra-
water is well precedented.1d,7a,29 Pyridylphosphinine ligands hedral geometry, with the H and OH groups in a syn orientation.
coordinated to Pd, Pt,29 Rh and Ir30 readily react with water or The bond lengths and angles in 11 are very similar to 9 due to
alcohols across a localised PQC double bond, with Pd/Pt their similar structures. There are few substantial differences
complexes demonstrating syn-addition31 but anti-addition for in the bond lengths, although the P(2)–Ru(1) bond length
Ir and Rh.30 We have explored the chemistry of BH3-protected (Ru–PPh2) has decreased slightly (2.276(1) Å in 11 compared
phosphinophosphinine ligands,16,19 and BH3 protection of the to 2.326(1) Å in 9). This was unexpected considering that the
PPh2 does not increase the reactivity of the phosphinine unit. P(1)–Ru(1) bond lengths (2.280(1) Å compared to 2.286(1) Å
BH3 does not coordinate to the phosphinine, and hence does for 9) are nearly identical despite the different electronics of
not lead to enhanced reactivity of the phosphinine with H2O, the phosphacyclohexadienyl ligand due to the lack of a SiMe3
because phosphinines are not basic (pKa E ꢀ16)2b and so substituent in 9.
protonation is also not a feature of their chemistry as it is for
phosphines.
Transfer hydrogenation and hydrogen-borrowing catalysis
In order to prepare a half-sandwich complex with an aro- Octahedral Ru bis(phosphinophosphinine) complex 2 displayed
matic phosphinine ligand, 1 was reacted with 0.25 equivalents high activity in the room temperature transfer hydrogenation of
of [{Ru(Cp*)(m3-Cl)}4] (Scheme 2). The reaction proceeded acetophenones (12) at 0.1 mol% loading with 0.5 mol% KOtBu
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Table 3 Transfer hydrogenation of ketones
Table 4 Catalytic upgrading of ethanol and methanol to isobutanol
T
Ethanol con- Isobutanol Isobutanol
Catalyst
(h) versiona (%) yielda (%) selectivitya (%) Ref.
trans-
2
88.4
64.6
92.8
34a
[Ru(Cl)2(dppm)2]
2
9
2
2
51.4
40.8
38.1
11.1
87.7
73.1
16
Substrate
2 (mol%)
Temp. (1C)
Time (h)
Yielda (%)
Ref.
16
Conditions: catalyst (0.1 mol%), EtOH (1 cm3), MeOH (10 cm3,
14.4 equiv.), NaOMe (2 equiv.).a Percentages for the liquid phase,
analysed by GC.
12
13
0.1
0.1
0.1
0.1
0.1
1
20
20
82
20
82
82
82
1
24
4
24
96
24
1
94
70
95
0
6
24
63
14
phosphinophosphinine 1. cis-[Ru(Cl)2(dppm)2] showed no cata-
lytic activity at 0.1 mol% loading with KOtBu (0.5 mol%) in
iPrOH, and heating the reaction mixture to 82 1C for 16 h still
did not show any reaction. This was not anticipated because cis/
trans-[Ru(Cl)2(dppm)2] are reported to be highly-active catalysts
for the related hydrogen-borrowing reaction where ethanol and
methanol is ‘‘upgraded’’ to isobutanol,34 a reaction which com-
plex 2 catalyses.16 The Guerbet-type upgrading of EtOH to
n-butanol and EtOH/MeOH to isobutanol is of considerable
recent interest35 because of their use as advanced biofuels.36
To extend our initial study on the use of phosphinophosphinine
1 in the ‘hydrogen-borrowing’ production of isobutanol, complex 9
was evaluated to facilitate comparison with trans-[Ru(Cl)2(dppm)2]
and 2 (Table 4). In comparison to complex 2, 9 produced a lower
conversion (40.8%) of ethanol and gave a lower yield of the desired
isobutanol in two hours with moderate selectivity (73.1%). How-
ever, GC analysis of the reaction mixture revealed the presence of
n-propanol (4.1% yield), which is an intermediate in the formation
of isobutanol, indicating that the reaction was not complete.16,34
A similar result was observed for 2, with 5.3% n-propanol still left
after 2 h.16
15
1
Conditions: 2, KOtBu (0.5 mol%), PrOH (0.4 M [substrate]).a Conver-
sion determined by 1H NMR spectroscopy using 1,3,5-trimethoxy-
benzene as an internal standard.
i
after 1 hour.16 In an extension to this initial study, several other
common substrates were tested (Table 3): benzophenone (13) as
an example of a diaryl ketone, an aldehyde (14) and a dialkyl
ketone (15). Whilst good conversions were achieved for several
acetophenones using 0.1 mol% 2 within one hour,16 decreased
reactivity was observed for 13–15. The room temperature transfer
hydrogenation of benzophenone required 24 h to reach the
maximum yield (70%), but this could be increased to 95%
upon heating to 82 1C for four hours. 2-Fluorobenzaldehyde
was tested as a representative aldehyde because electron-poor
acetophenones were previously found to be better substrates,16
but no conversion was observed at room temperature. An
increase in catalyst loading (1 mol%), reaction time (24 h)
and temperature (82 1C) still only gave low yields of the alcohol
(24%). For 4-methylcyclohexanone, using 1 mol% 2 at 82 1C, a
63% yield of 4-methylcyclohexanol was observed within one
hour. There is evidence that cyclohexanone can be a more
Conclusions
challenging substrate than acetophenone,32 but the excellent Contrary to the reaction of PhCRCPPh2 with diazaphos-
activities observed for 2 at room temperature appear to be limited phinine 3, the reaction of MeCRCPPh2 with 3 yielded both the
to aryl-substituted ketones.
2,6- and 2,5-bis(diphenylphosphino)phosphinine regioisomers.
The catalytic activity of 9, 10 and 11 was then evaluated These isomeric compounds were separated based on their different
using acetophenone under the same conditions as reported for solubilities and recrystallisation allowed the determination of
2,16 but no activity was found for these three complexes. Either their molecular structures by X-ray crystallography. Although the
the presence of an arene or Cp* co-ligand does not produce an reaction of the 2,6-isomer with mesityl azide generated the
active catalyst, or a phosphacyclohexdiene ligand, resulting analogous bis(iminophosphorane) compound 7, its coordina-
from the addition of H2O, is not conducive for catalysis. As tion chemistry to late transition metals was not successful,
limited examples of transfer hydrogenation catalysts with possibly due to the widely contrasting donor-properties of the
P-donor ligands have been reported in the literature,§ 33 cis- iminophosphorane and phosphinine donors. Extending the
[Ru(Cl)2(dppm)2] (dppm = bis(diphenylphosphino)methane) coordination chemistry of the 2-phosphinophosphinine 1 with
was investigated as a precatalyst in order to probe whether or additional Ru precursors revealed the preferential displace-
not the activity of 2 was due to the narrow bite-angle of ment of para-cymene over displacement of the Ru–Cl dative
bonds to form an asymmetric dinuclear intermediate. Coordi-
nation of 1 to [Ru(Z6-C6Me6)] and [RuCp*] fragments exposed
§ cis-[Ru(Cl)2(PPh3)3] is a known precatalyst for the transfer hydrogenation of
the coordinated phosphinine to reaction with trace quantities
of water, revealing in both cases the syn-addition of H2O across
ketones, however, it is not as active as 2, only achieving a 75% yield with aceto-
phenone as the substrate after six hours at 82 1C.48
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a localised PQC double bond. None of the Ru complexes, or cis- 2,6-bis(diphenylphosphino)-3,5-dimethylphosphinine, 5
[Ru(Cl)2(dppm)2], functioned as precatalysts for the transfer
hydrogenation of acetophenone, although the cationic Z6-C6Me6
complex 9 was active in the hydrogen-borrowing upgrading of
EtOH/MeOH to isobutanol, with lower yields observed compared
to those found previously for 2.
To a solution of diazaphosphinine (374 mg, 1.78 mmol) in
20 cm3 toluene was added a solution of diphenyl(prop-1-ynyl)-
phosphine (798 mg, 3.56 mmol, 2 equiv.) in toluene (5 cm3).
Experimental
The solution was heated at 120 1C in an ampoule sealed with a
Young’s tap until 31P{1H} NMR spectroscopy showed complete
All reactions and product isolations were performed under an
conversion of the diazaphosphinine to two isomeric products
oxygen-free nitrogen atmosphere using standard Schlenk line
in a 60 : 40 ratio (ca. 14 d). All volatiles were removed under
techniques or by using an MBRAUN UNIlab Plus glovebox,
unless otherwise noted. Anhydrous toluene, dichloromethane,
acetonitrile and THF were obtained from an MBRAUN SPS-800
solvent purification system. 40–60 petroleum ether was dis-
reduced pressure and the resulting oil was extracted with 40–60 pet.
ether (ca. 150 cm3) and filtered through a glass frit under air
before concentration on a rotary evaporator. This extraction was
repeated until a signal at d = 244.8 ppm was not observed by
tilled from sodium wire under nitrogen. Chloroform, CDCl3,
31P{1H} NMR spectroscopy in the solid material. All solvent was
hexamethyldisiloxane (HMDSO), pivalonitrile, and triethyla-
removed under reduced pressure and the resulting dark oil was
mine were distilled from calcium hydride. Isopropanol and
dissolved in the minimum volume of CH2Cl2 (ca. 5 cm3).
CD2Cl2 were dried over 4 Å molecular sieves. Benzene-d6 was
Pentane (10 cm3) was layered on top of the solution causing
dried over molten potassium, distilled under a static vacuum
the slow precipitation of a brown crystalline solid. If precipita-
and stored in the glovebox. Anhydrous ethanol and methanol
tion did not occur, more pentane (50 cm3) was added and the
were purchased from Sigma-Aldrich. All anhydrous solvents
mixture agitated. The resulting brown precipitate was isolated
were degassed before use and stored over activated molecular
sieves. Non-dry solvents were used as received from Fisher
Scientific. AgBF4 and AgSbF6 were purchased from commercial
by filtration and washed with pentane (3 ꢂ 10 cm3), then dried
under vacuum. Recrystallisation from a minimum volume of
toluene at ꢀ25 1C gave the pure product as a colourless solid
sources and used in the glovebox as anhydrous salts; Na[B{3,5-
(450 mg, 0.91 mmol, 51%). Once isolated, the product is air-stable
(CF3)2C6H3}4] was synthesised and thoroughly dried as des-
in the solid state. Crystals suitable for X-ray diffraction were grown
cribed in the literature.37 NH4PF6 was purchased and used in
from a 10 : 1 solution of anhydrous THF and 40–60 petroleum
its hydrated state because reactions with dried NH4PF6 led to
ether at ꢀ25 1C.
the formation of multiple products. NMR spectra were recorded
1H NMR (400 MHz, CDCl3): d = 7.32–7.20 (m, 20H, 2 ꢂ PPh2),
at 25 1C, unless otherwise stated, on a Bruker AVIII300, AVIII400
7.18–7.14 (m, 1H, HC), 2.48 (s, 6H, HD); 31P{1H} NMR (162 MHz,
and AVI400, spectrometer using the internal protio resonance as
2
2
CDCl3): d = 244.8 (t, P1, JP–P = 38.9 Hz), ꢀ8.1 (d, 2P, P2, JP–P
=
a reference (1H and 13C{1H} NMR spectra). 11B, 29Si, 19F and 31
P
38.9 Hz); 13C{1H} NMR (100 MHz, CDCl3): d = 164.22 (dd, 2C, CA,
were referenced to external samples of BF3ꢁOEt2, SiMe4, CFCl3
and 85% H3PO4 in H2O respectively as 0 ppm. 4,6-Di(tert-butyl)-
1,3,2-diazaphosphinine,13a diphenyl(1-prop-1-ynyl)phosphine,38
mesityl azide,39 [Ru(Cl)2(dmso)4],40 [Ru(Cl)2(Cp*)]n,41 [{Ru(m3-
1JCA–P1 = 84.5 Hz, JCA–P2 = 24.1 Hz), 147.38 (dd, 2C, CB, JCB–P1
=
1
2
23.1 Hz, 2JCB–P2 = 11.1 Hz), 136.1 (t, CC, 3JCC–P2 = 9.8 Hz) 134.1 (m,
2 ꢂ PPh2), 128.7 (s, 2 ꢂ PPh2), 128.3 (d, 2 ꢂ PPh2), 23.5 (d, 2C, CD,
3JCD-P = 23.1 Hz); EI: m/z: 492.1 ([M]+); elemental analysis: Anal.
calcd for C31H27P3: C 75.61, H 5.53. Found: C 75.50, H 5.49.
Cl)(Cp*)}4],42
[{Ru(Cl)(m-Cl)(p-cymene)}2],43
[{Ru(Cl)(m-Cl)-
(C6Me6)}2],44 and cis-[Ru(Cl)2(dppm)2]45 were prepared according
to literature procedures. Mass spectrometry analysis was per-
formed at the EPSRC UK National Mass Spectrometry Facility
at Swansea University using an Atmospheric Solids Analysis
Probe. Electron ionisation mass spectrometry (EI-MS) was
carried out using a Finnigan (Thermo) LCQ Classic ion trap
mass spectrometer at the University of Edinburgh. FTIR
2,5-Bis(diphenylphosphino)-3,6-dimethylphosphinine, 6
was performed on a Thermo Scientific Nicolet iS5/iD5 ATR The pet. ether insoluble solid from the previous procedure was
spectrometer. GC-FID analysis of EtOH/MeOH upgrading mixed with sand and transferred to a Soxhlet thimble. This was then
catalytic samples was carried out on an Agilent 7820A GC extracted with boiling n-hexane (300 cm3) using a Soxhlet apparatus
fitted with DB-WAX column 30 m ꢂ 320 mm, I.D. 0.25 mm. for one week under air. Over the course of the extraction, a white
Method: oven temperature starts at 35 1C for 5 minutes, heat to precipitate formed that was isolated by filtration and washed with
250 1C at 50 1C minꢀ1 then hold at 250 1C for 5 minutes. Flow hexane (3 ꢂ 10 cm3), then dried under reduced pressure. The
rate 6.5 cm3 minꢀ1. Elemental analyses were conducted by product was then recrystallized from a minimum volume of toluene
Dr Brian Hutton using an Exeter CE-440 elemental analyser at at ꢀ25 1C, yielding the pure product as a colourless solid (190 mg,
Heriot-Watt University or by Mr Stephen Boyer at London 0.39 mmol, 22%). Single crystals suitable for X-ray diffraction were
Metropolitan University.
grown by slow diffusion of ether into a THF solution.
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1H-NMR (300 MHz, CDCl3): d = 7.45–7.31 (m, 20H, 2 ꢂ PPh2) (20 mg, 0.05 mmol, 1 equiv.), [{Ru(Cl)(m-Cl)(p-cymene)}2] (17 mg,
6.74 (bs, 1H, HC), 2.61 (d, 3H, HF, 3JHF–P1 = 16.0 Hz), 2.29 (s, 3H, 0.03 mmol, 0.5 equiv.) and C6D6 (0.6 cm3) then sealed under N2.
HG); 31P{1H}-NMR (162 MHz, CDCl3): d = 220.3 (dd, P1, 2JP1–P2
29.2 Hz, 3JP1–P3 = 4.9 Hz), ꢀ9.2 (dd, P2, 2JP2–P1 = 29.2 Hz, 5JP2–P3
=
=
The reaction was heated to 50 1C for 5 min then layered with
40–60 pet. ether (1.2 cm3). Dark red crystals of 8 were then
2.3 Hz), ꢀ10.8 (dd, P3, 3JP3–P1 = 4.9 Hz, 5JP3–P2 = 2.3 Hz); 13C{1H}- manually separated from the yellow crystals of 2 for X-ray
1
NMR (100 MHz, CDCl3): d = 169.6 (dd, CE, JCE–P1 = 59.9 Hz, analysis.
1
2
2
2JCE–P3 = 19.2 Hz), 167.1 (dd, CA, JCA–P1 = 75.1 Hz, JCA–P2
=
31P{1H}-NMR (162 MHz, CDCl3): d = 231.4 (d, P1, JP1–P2
=
2
2
2
24.0 Hz), 145.3 (dd, CB, JCB–P1 = 22.4 Hz, JCB–P2 = 12.8 Hz), 55.5 Hz), 21.7 (d, P2, JP2–P1 = 55.5 Hz).
142.6 (dd, CD, 1JCD–P1 = 22.4 Hz, 2JCD–P3 = 12.8 Hz), 136.5 (m, CC,
3JCC–P1 = 15.2 Hz), 136.0 (t, PPh2, J = 8.8 Hz), 135.7 (d, PPh2, J =
11.2 Hz), 134.3(t, PPh2, J = 20.0 Hz), 129.1–128.5 (m, PPh2), 23.8
Chloro(hexamethylbenzene)(1-hydroxy-2-diphenylphosphino-3-
methylphosphacyclohexa-3,5-diene)ruthenium(II)
hexafluorophosphate, 9
(d, CG, 3JCG-P1 = 24.1 Hz), 23.5 (dd, CF, 2JCF–P1 = 43.3 Hz, 3JCF–P3
=
24.1 Hz); EI: m/z: 492.1 ([M]+); Elemental analysis: Anal. calcd
for C31H27P3: C 75.61, H 5.53. Found: C 75.47, H 5.71.
2,6-Bis{diphenyl(N-mesityl)iminophosphorano}-3,5-
dimethylphosphinine, 7
To a Schlenk flask containing 2-diphenylphosphino-3-methyl-
6-trimethylsilylphosphinine, 1 (71 mg, 0.19 mmol, 1 equiv.),
[{Ru(Cl)(m-Cl)(C6Me6)}2] (65 mg, 0.1 mmol, 0.5 equiv.) and
NH4PF6 (32 mg, 0.19 mmol, 1 equiv.) was added anhydrous
CH2Cl2 (15 cm3) and the resulting heterogeneous mixture was
vigorously stirred for 64 h. The solution was filtered to remove
NH4Cl and then concentrated to ca. 1 cm3 under reduced
pressure before being layered with 40–60 pet. ether (10 cm3).
Once crystallisation was complete, the supernatant solvent was
removed by cannula filtration and the orange needles of pro-
duct (113 mg, 0.15 mmol, 78%) manually separated from a
white solid.
To a Schlenk flask containing freshly recrystallized 2,6-bis(diphenyl-
phosphino)-3,5-dimethylphosphinine, 5 (432 mg, 0.88 mmol,
1 equiv.) was added sequentially anhydrous HMDSO (15 cm3)
and mesityl azide (311 mg, 1.93 mmol, 2.2 equiv.). The hetero-
geneous mixture was heated under reflux for 24 h, forming a
bright yellow precipitate. Once cool, the precipitate was isolated by
cannula filtration and washed with anhydrous HMDSO (10 cm3).
The product was dried overnight under high vacuum, yielding a
yellow solid (564 mg, 0.74 mmol, 85%). An analytically pure
sample was obtained by recrystallization from toluene at ꢀ25 1C.
1H-NMR (400 MHz, CDCl3): d = 7.75–7.70 (m, 8H, 2 ꢂ o-PPh2)
7.05–6.83 (m, 16H, 2 ꢂ m,p-PPh2, HI), 6.71 (s, 1H, HC), 2.49 (s,
6H, HF), 2.32 (s, 6H, HH), 2.24 (s, 12H, HG); 31P{1H}-NMR (162
MHz, CDCl3): d = 246.9 (t, P1, 2JP1–P2 = 99.7 Hz), ꢀ9.4 (d, 2P, P2,
2JP2–P1 = 99.7 Hz); 13C{1H}-NMR (100 MHz, CDCl3): d = 160.0–
158.4 (m, 2C, CA), 151.5–151.2 (m, 2C, CB), 145.1 (s, 2C, CJ),
139.3–138.9 (m, CC), 134.0–129.0 (m, CI & 2 ꢂ PPh2), 24.3 (m,
2C, CF), 21.1 (s, 4C, CG), 20.6 (s, 2C, CH); HRMS (ASAP/QTof):
m/z: ([M + H]+) calcd for C49H50N2P3: 759.3187; found: 759.3196;
Elemental analysis: Anal. calcd for C49H49N2P3: C 77.56, H 6.51,
N 3.69. Found: C 77.55, H 6.42, 3.68.
1H-NMR (400 MHz, CD2Cl2): d = 7.79–7.60 (m, 7H, PPh2 &
HE), 7.54–7.50 (m, 2H, PPh2), 7.24–7.19 (m, 2H, PPh2), 6.96
3
(ddd, 1H, HD, 3JHD–P1 = 33.75 Hz, 3JHD–HE = 12.32 Hz, JHD–HC
=
7.04 Hz), 6.59 (dd, 1H, HH, 2JHH–P1 = 24.06 Hz, 2JHH–HE = 12.32 Hz),
5.89 (bs, 1H, HC), 5.32 (t, 1H, HG, 2JHG–P1 = 15.55 Hz), 2.20 (s, 18H,
HI), 1.65 (s, 3H, HF); 31P{1H}-NMR (162 MHz, CD2Cl2): d = 11.6 (d,
P1, 2JP1–P2 = 97.1 Hz), 8.8 (d, P2, 2JP2–P1 = 97.1 Hz), ꢀ144.5 (sept, P3,
1JP3-F = 711.4 Hz); 19F{1H}-NMR (79 MHz, CD2Cl2): d = ꢀ73.3 (d, 6F,
PF6, 2JF–P3 = 709.5 Hz); HRMS (ASAP/QTof): m/z: ([M ꢀ PF6]+) calcd
for C30H36ClOP2Ru: 611.0978; found: 611.0983; Elemental analy-
sis: Anal. calcd. for C30H36ClF6OP3Ru: C 47.66, H 4.80; found:
C 47.89, H 5.17.
Chloro(pentamethylcyclopentadienyl)(2-diphenylphosphino-3-
methyl-6-trimethylsilylphosphinine)ruthenium(II), 10
Compound 8
An NMR tube equipped with a J. Young tap was charged with To a Schlenk flask containing 2-diphenylphosphino-3-methyl-6-
2-diphenylphosphino-3-methyl-6-trimethylsilylphosphinine, trimethylsilylphosphinine, 1 (30 mg, 0.08 mmol, 1 equiv.) and
1
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[{Ru(m3-Cl)(Cp*)}4] (22 mg, 0.02 mmol, 0.25 equiv.) was 2JCI–P1 = 2.6 Hz, 2JCI–P2 = 2.5 Hz), 21.6 (ap. t, CF, 3JCF–P1 = 6.7 Hz,
added anhydrous THF (2 cm3). The resulting deep red solu- 3JCF–P2 = 6.7 Hz) 10.4 (s, 5C, CH), 0.0 (d, 3C, CG, 3JCG–P1 = 3.5 Hz);
2
tion was stirred for 5 minutes before the solvent was removed 29Si{1H}-NMR (79 MHz, CDCl3): d = ꢀ2.4 (dd, SiMe3, JSi–P1
=
4
under reduced pressure. The resulting oily solid was then 22.0 Hz, JSi–P2 = 3.0 Hz); HRMS (ASAP/QTof): m/z: ([M ꢀ Cl]+)
dissolved in 40–60 pet. ether (5 cm3) and the solution cooled calcd for C31H39P2RuSi: 603.1348; found: 603.1347.
to 0 1C until an orange precipitate was observed. The preci-
Chloro(pentamethylcyclopentadienyl)(1-hydroxy-2-
diphenylphosphino-3-methyl-6-trimethylsilylphospha-
cyclohexa-3,5-diene) ruthenium(II), 11
pitate was isolated by cannula filtration and dried under high
vacuum yielding a highly air-sensitive orange powder, (36 mg,
0.06 mmol, 70%).
1H-NMR (400 MHz, C6D6): d = 8.24–8.19 (m, 2H, PPh2), 7.63
3
3
(dd, 1H, HD, JHD–P1 = 22.51 Hz, JHD–HC = 8.48 Hz), 7.41–7.36
(m, 2H, PPh2), 7.22–6.93 (m, 6H, PPh2), 6.46 (app. dt, 1H, HC,
3JHC–HD = 8.48 Hz, 4JHC–P1 = 2.92 Hz, 4JHC–P2 = 2.63 Hz), 1.74 (s,
3
3H, HF), 1.62 (t, 15H, HH, JHH–P1 = 2.05 Hz), 0.47 (s, 9H, HF);
31P{1H}-NMR (162 MHz, C6D6): d = 240.1 (d, P1, 2JP1–P2 = 6.9 Hz),
18.2 (d, P2, 2JP2–P1 = 6.9 Hz); 13C{1H}-NMR (126 MHz, CDCl3): d =
168.8 (d, CE, 1JCE–P1 = 18.0 Hz), 151.3 (dd, CA, 1JCA–P1 = 61.4 Hz,
2
2
1JCA–P2 = 19.1 Hz), 146.6 (dd, CB, JCB–P1 = 11.1 Hz, JCB–P2
=
2-Diphenylphosphino-3-methyl-6-trimethylsilylphosphinine (76 mg,
7.9 Hz), 144.1 (dd, CD, 2JCD–P1 = 17.1 Hz, 4JCD–P2 = 3.4 Hz), 135.5 0.2 mmol, 1 equiv.) and [{Ru(m3-Cl)(Cp*)}4] (56 mg, 0.05 mmol,
(d, PPh2, J = 12.0 Hz), 134.2 (dd, PPh2, J = 37.9, 6.5 Hz), 132.0 (d, 0.25 equiv.) were dissolved in THF (5 cm3). After removal of the
PPh2, J = 9.9 Hz), 130.3 (dd, PPh2, J = 23.4 Hz, 14.6 Hz), 129.9 solvent, the residue was dissolved in 40–60 pet. ether (5 cm3)
(d, PPh2, J = 2.4 Hz), 129.1 (d, PPh2, J = 2.1 Hz), 123.6 (dd, and stored at 5 1C in the presence of atmospheric moisture for
3
3
CC, JCC–P1 = 32.7 Hz, JCC–P2 = 6.1 Hz), 89.1 (ap. t, 5C, CI, 30 days. Small red crystals formed, which were isolated by
Table 5 Crystallographic data for compounds 5, 6, 7Fe, 8, 9 and 11
Compound
5
6
7Feꢁ4(CH2Cl2)
8
9ꢁ0.5(CH2Cl2)
11
Empirical
formula
Formula weight 492.43
Temperature/K 100
C
31H27P3
C31H27P3
C53H60Cl11FeN2OP3 C31H38Cl4P2Ru2Si C30.5H37Cl2F6OP3Ru C31H41ClOP2RuSi
492.43
100
1279.74
100
844.58
100
798.48
150
656.19
120
Crystal system
Space group
Triclinic
P1
Monoclinic
P21/n
Triclinic
P1
Triclinic
P1
Monoclinic
P21/n
Triclinic
P1
%
%
%
%
a/Å
b/Å
c/Å
a/1
7.5692(9)
12.6145(16)
15.2354(17)
69.228(5)
76.539(5)
73.790(5)
1291.5(3)
2
9.9671(13)
8.0650(11)
15.9450(18)
90
99.576(9)
90
1263.9(3)
2
1.294
12.3741(5)
14.0430(5)
19.6151(7)
104.833(2)
93.541(2)
114.316(2)
2948.1(2)
2
9.8194(5)
10.9184(6)
16.7816(9)
99.502(3)
94.824(3)
105.119(3)
1697.74(16)
2
8.8172(4)
37.4359(16)
19.6657(9)
90
90.340(2)
90
6491.1(5)
8
1.634
14.6758(5)
14.7658(4)
15.2176(3)
92.281(2)
105.461(2)
101.298(2)
3101.93(15)
4
b/1
g/1
Volume/Å3
Z
rcalc g cmꢀ3
m/mmꢀ1
F(000)
1.266
0.248
516
1.442
0.875
1316
1.652
1.355
848
1.405
6.394
1360
0.254
516
0.855
3240
Crystal size/mm3 0.40 ꢂ 0.40 ꢂ 0.15 0.17 ꢂ 0.10 ꢂ 0.10 0.38 ꢂ 0.22 ꢂ 0.10 0.20 ꢂ 0.20 ꢂ 0.20 0.27 ꢂ 0.27 ꢂ 0.19 0.20 ꢂ 0.05 ꢂ 0.02
Radiation
MoKa (l = 0.71073) MoKa (l = 0.71073) MoKa (l = 0.71073) MoKa (l = 0.71073) MoKa (l = 0.71073) CuKa (l = 1.54184)
2Y range for
data collection/1
Index ranges
3.536 to 60.984
5.24 to 55.118
3.678 to 55.62
5.276 to 55.356
4.68 to 56.784
7.478 to 152.286
ꢀ10 r h r 10,
ꢀ17 r k r 17,
ꢀ21 r l r 20
34 832
ꢀ12 r h r 11,
ꢀ10 r k r 8,
ꢀ20 r l r 20
9164
ꢀ16 r h r 15,
ꢀ18 r k r 18,
ꢀ25 r l r 25
51 076
ꢀ12 r h r 12,
ꢀ14 r k r 14,
ꢀ21 r l r 21
50 022
ꢀ11 r h r 11,
ꢀ50 r k r 49,
ꢀ26 r l r 26
222 582
ꢀ18 r h r 17,
ꢀ18 r k r 17,
ꢀ18 r l r 19
49 418
Reflections
collected
Independent
reflections
Data/restraints/ 7806/0/309
parameters
7806 [Rint = 0.0276, 2854 [Rint = 0.0756, 13 575 [Rint = 0.0345, 7730 [Rint = 0.0489, 16 043 [Rint = 0.0388, 12 852 [Rint = 0.0820,
Rsigma = 0.0291]
Rsigma = 0.1155]
2854/54/192
Rsigma = 0.0395]
13 575/2/657
Rsigma = 0.0403]
7730/0/368
Rsigma = 0.0188]
16 043/2/810
Rsigma = 0.0664]
12 852/1/697
Goodness-of-fit 1.044
1.051
1.158
1.062
1.127
1.045
on F2
Final R indexes R1 = 0.0331,
R1 = 0.0779,
wR2 = 0.1361
R1 = 0.1452,
wR2 = 0.1601
0.81/ꢀ0.53
R1 = 0.0525,
wR2 = 0.1045
R1 = 0.0605,
wR2 = 0.1081
0.62/ꢀ0.84
R1 = 0.0308,
wR2 = 0.0618
R1 = 0.0445,
wR2 = 0.0659
0.56/ꢀ0.76
R1 = 0.0422,
wR2 = 0.0973
R1 = 0.0493,
wR2 = 0.1009
1.25/ꢀ0.94
R1 = 0.0516,
wR2 = 0.1277
R1 = 0.0635,
wR2 = 0.1358
1.04/ꢀ1.39
[I r 2s(I)]
wR2 = 0.0823
Final R indexes R1 = 0.0424,
[all data]
wR2 = 0.0873
0.37/ꢀ0.24
Largest diff.
peak/hole/e Åꢀ3
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018 New J. Chem., 2018, 42, 19625--19636 | 19633

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Paper
NJC
cannula filtration and dried under high vacuum yielding a red Conflicts of interest
crystalline powder (16 mg, 0.02 mmol, 12%).
There are no conflicts to declare.
1H-NMR (400 MHz, CD2Cl2): d = 7.76–7.14 (m, 10H, PPh2),
3
3
6.67 (dd, 1H, HD, JHD–P1 = 36.68 Hz, JHD–HC = 6.75 Hz), 6.48
3
(bs, 1H, HH), 5.81 (d, 1H, HC, JHC–HD = 6.46 Hz), 5.08 (app. t,
Acknowledgements
1H, HG, 2JHG–P1 = 12.32 Hz, 2JHG–P2 = 12.03 Hz), 1.59 (t, 15H, HI,
3JHI–P1 = 2.05 Hz), 1.39 (s, 3H, HF), 0.37 (s, 9H, HK); 31P{1H}-NMR
(162 MHz, CD2Cl2): d = 78.3 (d, P1, 2JP1–P2 = 59.5 Hz), 18.0 (d, P2,
2JP2–P1 = 59.5 Hz);29Si{1H}-NMR (79 MHz, CD2Cl2): d = ꢀ2.7 (d,
The authors would like to acknowledge the EPSRC UK National
Mass Spectrometry Facility at Swansea University for collecting
the MS data and Dr Gary Nichol (University of Edinburgh) for
collecting X-ray diffraction data for 9 and 11. Financial support is
gratefully acknowledged from the EPSRC (DTP studentship to RJN),
the Royal Society (Research grant: RG130436) and Heriot-Watt
University as well as the UK Catalysis Hub Consortium (funded
by EPSRC grants EP/K014706/2, EP/K014668/1, EP/K014854/1,
EP/K014714/1 and EP/M013219/1) for providing travel funding
to SMM and RJN.
2
SiMe3, JSi–P1 = 15.6 Hz); HRMS (ASAP/QTof): m/z: ([M ꢀ Cl ꢀ
H2O]+) calcd for C31H39P2RuSi: 603.1348; found: 603.1360;
Elemental analysis: Anal. calcd for C31H41ClOP2RuSi: C 56.73,
H 6.30; found: C 56.73, H 6.52.
Procedure for transfer hydrogenation catalysis
To a dry Schlenk flask, under N2 and equipped with a stirrer bar,
was added a known amount of 1,3,5-trimethoxybenzene, iPrOH,
the substrate (1 mmol) and a stock solution of 2 (0.1 mol%) and
KOtBu (0.5 mol%) in iPrOH, to a total solvent volume of 2.3 cm3.
Notes and references
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19636 | New J. Chem., 2018, 42, 19625--19636 This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018