Synthesis and dehydrocoupling reactivity of iron and ruthenium phosphine-borane complexes

Article abstract of DOI:10.1039/b718918d

The Fe and Ru phosphine-borane complexes CpM(CO)₂PPh ₂?BH₃ (1, M = Fe, 4, M = Ru) were synthesized utilizing the reaction of the phosphine-borane anion Li[PPh₂? BH₃] with the iodo complexes CpM(CO)₂I. The Fe complex 1 reacted with PMe₃ to yield CpFe(CO)(PMe₃)(PPh ₂?BH₃) (2) and CpFe(PMe₃) ₂(PPh₂?BH₃) (3) whereas the Ru species 4 gave only CpRu(CO)(PMe₃)(PPh₂?BH₃) (5). The complexes 1-5 were characterized by ¹H, ¹¹B, ¹³C and ³¹P NMR spectroscopy, MS, IR and X-ray crystallography for 1 to 4, and EA for 1, 2 and 4. The reactivity of 1 and 4 towards PPh₂H?BH₃ was explored. Although no stoichiometric reactions were detected under mild conditions, both 1 and 4 were found to function as dehydrocoupling catalysts to afford Ph₂PH? BH₂?PPh₂?BH₃ in the melt at elevated temperature (120 °C). The carbonyl Fe₂(CO)₉ also functioned as a dehydrocoupling catalyst under similar conditions. Complex 1 and Fe₂(CO)₉ represent the first reported active Fe complexes for the catalytic dehydrocoupling of phosphine-borane adducts. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b718918d

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Synthesis and dehydrocoupling reactivity of iron and ruthenium
phosphine–borane complexes†‡
Kajin Lee,a Timothy J. Clark,b Alan J. Loughb and Ian Manners*a,b
Received 7th December 2007, Accepted 28th February 2008
First published as an Advance Article on the web 21st April 2008
DOI: 10.1039/b718918d
The Fe and Ru phosphine–borane complexes CpM(CO)2PPh2·BH3 (1, M = Fe, 4, M = Ru) were
synthesized utilizing the reaction of the phosphine–borane anion Li[PPh2·BH3] with the iodo complexes
CpM(CO)2I. The Fe complex 1 reacted with PMe3 to yield CpFe(CO)(PMe3)(PPh2·BH3) (2) and
CpFe(PMe3)2(PPh2·BH3) (3) whereas the Ru species 4 gave only CpRu(CO)(PMe3)(PPh2·BH3) (5). The
complexes 1–5 were characterized by 1H, 11B, 13C and 31P NMR spectroscopy, MS, IR and X-ray
crystallography for 1 to 4, and EA for 1, 2 and 4. The reactivity of 1 and 4 towards PPh2H·BH3 was
explored. Although no stoichiometric reactions were detected under mild conditions, both 1 and 4 were
found to function as dehydrocoupling catalysts to afford Ph2PH·BH2·PPh2·BH3 in the melt at elevated
temperature (120 ◦C). The carbonyl Fe2(CO)9 also functioned as a dehydrocoupling catalyst under
similar conditions. Complex 1 and Fe2(CO)9 represent the first reported active Fe complexes for the
catalytic dehydrocoupling of phosphine–borane adducts.
in the phosphin◦e–borane, the catalytic dehydrocoupling reaction
Introduction
proceeded at 60 C.4d Early and late transition metal-catalyzed de-
hydrocoupling of primary and secondary amine–borane adducts
results in cyclic aminoboranes and borazines under mild reaction
conditions (eqn (4) and (5)).6 This process has been applied to
transfer hydrogenation using Rh catalysts and Me2NH·BH3 as a
stoichiometric hydrogen source for the hydrogenation of alkenes
Metal-catalyzed dehydrocoupling to form bonds between inor-
ganic elements is emerging as a convenient, mild and versatile
synthetic method.1 Since the initial reports of Si–Si and B–B
bond formation via catalytic dehydrocoupling in the mid 1980s2,
many other bonds between main group elements have been suc-
cessfully mediated by transition metal catalysts.3 Both homo-and
heterodehydrocoupling reactions involving main-group hydride
species havebeendemonstrated with earlyand late transition metal
catalysts.1–3
The catalytic dehydrocoupling of phosphine–borane and
amine–borane adducts has been developed to produce rings,
chains and high molecular weight polymers under relatively
mild reaction conditions. For example, using Rh catalysts, such
processes proceed at 60–120 ◦C for secondary phosphine–borane
adducts such as Ph2PH·BH3.4 In contrast, in the absence of
catalyst, thermal dehydrocoupling ◦of phosphine–borane adducts
requires temperatures of 180–200 C.5 Dehydrocoupling of pri-
mary and secondary phosphine–borane adducts catalyzed by
late transition metals has been shown to yield linear oligomeric
species, six- and eight-membered rings, and high molecular weight
polyphosphinoboranes (eqn (1)–(3)).4 For example, PhPH2·BH3
can be polymerized using RhI complexes at 130 ◦C whereas in the
absence of catalyst only low molecular weight materials are formed
(eqn (3)).4 With electron-withdrawing substituents at phosphorus
◦
at 25 C.7 Recently, in addition to the Rh, Ir, and Ru catalysts
described earlier, other (and in some cases more efficient) metal
catalysts for the dehydrocoupling of amine–boranes have been
reported as well.8 The ammonia–borane adduct NH3·BH3 has
recently attracted great interest for hydrogen storage applications
as a result of possessing one of the highest densities of hydrogen
available (ca. 20% by weight).9
aSchool of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK
BS8 1TS. E-mail: ian.manners@bristol.ac.uk; Fax: +44 (0)117 929 0509;
Tel: +44 (0) 117 928 7650
bDepartment of Chemistry, University of Toronto, 80 St. George Street,
Toronto, ON, Canada M5S 3H6
† Dedicated to Prof. Ken Wade on the occasion of his 75th birthday.
1
‡ Electronic supplementary information (ESI) available: 1H, 13C{ H} and
proton-coupled 11B NMR spectra of compound 5 in CDCl3. CCDC
reference numbers 670259–670262. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b718918d
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It has also been reported that B(C6F5)3 can catalyze formation
of B–P bonds by dehydrocoupling of phosphine–borane adducts
at 20 C; however, the molecular weight of the polymer was low
and the reaction time was 3 days.10
we focussed on the subsequent steps. In particular, we were
interested in detecting a stoichiometric reaction of a phosphine
borane complex with a phosphine–borane adduct (i.e. step 2 in
Scheme 1) rather than the ligand exchange reactions observed
in the case of Pt.15a We prepared the Fe and Ru complexes
utilized in this study via a convenient nucleophilic substitution
route. The targeted phosphine–borane complexes were chosen
such that the generation of additional vacant coordination sites
around the metal via ligand dissociation would be possible. This
was anticipated to facilitate further reactivity towards phosphine–
borane adducts within the metal coordination sphere.
◦
Mechanistic studies have indicated that the dehydrocoupling of
phosphine–borane adducts using [Rh(l-Cl)(1,5-cod)]2 involves a
homogeneous process whereas that for amine–borane adducts is
predominantly heterogeneous.11 It has also been suggested that
the dehydrocoupling of amine–borane adducts involves a key
homogeneous catalytic component according to XAFS studies.12
Further insights into the mechanism of the Rh catalyzed dehy-
drocoupling of phosphine–borane adducts such as Ph2PH·BH3
can be anticipated from studies of model complexes related to the
proposed intermediates in the catalytic cycle. A possible first step
in the dehydrocoupling of phosphine–borane adducts may involve
insertion of the transition metal into either the P–H or B–H bond
of the adduct. The following steps may involve r-bond metathesis
and/or oxidative addition/reductive elimination processes.13 One
of the plausible processes involving initial P–H bond activation is
shown in Scheme 1.14
Synthesis of CpFe(CO)2PPh2BH3 (1)
The iron phosphine–borane complex CpFe(CO)2(PPh2·BH3) (1)
was targeted to utilize the CO ligands that might dissociate to
generate vacant coordination space around the central metal
atom to enable subsequent reaction with phosphine–borane
adducts. Complex 1 was synthesized by reacting CpFe(CO)2I and
LiPPh2·BH3 at −30 ◦C in THF for 1 h (eqn (6)). The product
1 was purified by column chromatography and recrystallization
from toluene at −40 ◦C to yield amber crystals (50% yield).
(6)
Complex 1 was characterized by EA, IR, NMR, MS and X-
1
ray crystallography. The 31P{ H} spectrum showed a quartet at
◦
◦
d 31.5 at 60 C which appears as a broad doublet at 25 C. The
broad signal is characteristic of P bound to B with the broadening
1
arising from unresolved quadrupolar coupling. The 11B{ H}
NMR spectrum showed a doublet at d −30.4 ppm (1JPB = 45 Hz).
This doublet also resolved better like the broad signal in the
31P{ H} NMR spectrum at higher temperature. The H NMR
showed multiplets for phenyl resonances around d 7.75 ppm and
d 7.33 ppm as well as a singlet for the Cp resonance at d 4.99 ppm
and a broad quartet for a boron hydride resonance at d 1.45 ppm
(1JHB = ca. 100 Hz). The IR spectrum showed carbonyl peaks
at 2029 and 1980 cm−1 which are lower frequency than those
for CpFe(CO)2I at 2037 and 1994 cm−1.16 This data indicated
that the phosphine–borane substituent is more electron donating
compared to iodide and increases the back-bonding of the electron
density from the Fe centre to the CO ligand. Complex 1 was
reported recently by Wagner and co-workers who◦similarly treated
CpFe(CO)2I with KPPh2BH3 in THF at −78 C.17 The X-ray
structure (Fig. 1) is in monoclinic crystal system with a P21/n
space group whereas Wagner and co-workers reported a structure
in orthorhombic crystal system with P212121 space group. The
bond length and bond angle data are comparable for the two struc-
tures. The same group also recently reported the first bidentate
phosphanylborohydride Fe complex, rac/meso-[(CpFe(CO)2)2{l-
(P(BH3)(Ph)CH2)2}], using a similar synthetic method.18
1
1
Scheme 1
As an illustration of the first step in Scheme 1, we
have previously studied the oxidative-addition of the P–H
bond in the adducts RPhPH·BH3 (R = H or Ph) at Pt(0)
15a
centers on addition of Pt(PEt3)3.
However, upon treat-
ment of the resulting complexes with a further equivalent
of adduct, phosphine–borane ligand-exchange reactions rather
than dehydrocoupling (step 2 in Scheme 1) were detected
at the Pt centre of cis-[PtH(PPh2·BH3)(depe)] (depe = 1,2-
bis(diethylphosphino)ethane).15a Model complexes such as cis-
[PtH(PPhH·BH3)(dcype)] (dcype = 1,2-bis(dicyclohexylphos-
phino)ethane) were also successfully prepared via dehydrocou-
pling reactions between the Pt–H and P–H bonds of cis-
[PtH2(dcype)] and PhPH2·BH3, respectively.15b The absence of de-
hydrocoupling reactivity with Pt phosphine–borane complexes15
has prompted us to explore the corresponding chemistry of other
metals. In this paper we describe our analogous studies of Fe and
Ru phosphine–borane complexes.
Results and discussion
Reaction of 1 with PMe3
As step 1 in Scheme 1 involving the oxidative-addition of a
P–H bond of a phosphine–borane adduct at a metal center
has been amply demonstrated in the case of Pt, in this work
Next, we explored the reactivity of 1 with PMe3 in order to
examine if the P–B bond was stable to the presence of a strong
donor ligand and also to explore if the CO ligands are easy to
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Fig. 2 Molecular structure of CpFe(CO)(PMe3)(PPh2·BH3) 2. Selected
◦
˚
bond lengths (A) and angles ( ): C21–Fe1 1.729(5), C21–O1 1.168(5),
P1–Fe1 2.2106(13), P2–Fe1 2.2718(12), C21–O1 1.168(5), P2–B1 1.949(5);
C21–Fe1–P1 91.95(15), C21–Fe1–P2 98.83(15), P1–Fe1–P2 94.23(5),
C9–P2–B1 108.7(2), C9–P2–C15 96.87(18).
Fig. 1 Molecular structure of CpFe(CO)2(PPh2·BH3) 1. Selected bond
◦
˚
lengths (A) and angles ( ): C5–Fe1 2.102(2), C6–O1 1.145(3), C6–Fe1
1.766(2), C7–O2 1.144(3), P1–C8 1.837(2), P1–C14 1.831(2), P1–B1
1.953(3), P1–Fe1 2.2822(6); C6–Fe1–P1 89.22(7), C7–Fe1–P1 92.33(7),
C8–P1–C14 101.89(9), C8–P1–B1 107.23(11), C8–P1–Fe1 113.26(7),
C14–P1–B1 109.26(11), C14–P1–Fe1 107.58(7).
displace. The latter situation would facilitate further reaction with
phosphine–borane adducts at the metal center, as required for
step 2 in Scheme 1. Upon the addition of two equivalents of PMe3
to a THF solution of 1 at 20 ◦C, the CO-substitution products
CpFe(CO)(PMe3)(PPh2·BH3) (2) and CpFe(PMe3)2(PPh2·BH3) (3)
1
were formed (eqn (7)). The 31P{ H} NMR spectrum of the reaction
solution showed two resonances consistent with these products:
a doublet at d 31.2 and a broad multiplet at d 26.9 for 2 and a
doublet at d 24.1 and a broad multiplet at d 18.8 for 3. Complex
2 was isolated in pure form by column chromatography and
recrystallization from THF. Both compounds were characterized
by X-ray crystallography (Fig. 2 and 3). The complexes 2 and 3
crystallize in the monoclinic crystal system with Cc and P21/n
space group respectively. The P–B bond length of 2 is not
significantly different to that of 1. However, the P–B bond length
Fig. 3 Molecular structure of CpFe(PMe3)2(PPh2·BH3) 3. Selected bond
◦
˚
lengths (A) and angles ( ) P1–Fe1 2.2124(6), P2–Fe1 2.2160(6), P3–Fe1
2.3119(6), P3–B1 1.980(3); P3–Fe1–P1 94.99(2), P3–Fe1–P2 95.39(2),
C18–P3–C12 100.70(9), B1–P3–Fe1 127.34(8).
˚
of 3 is significantly (0.03 A) longer than that of 2. In addition, the
The 1H NMR spectrum showed multiplets for phenyl resonances
around d 7.95 ppm and d 7.10 ppm as well as a singlet for the Cp
resonance at d 4.54 ppm and a broad quartet for the boron hydride
resonance at d 2.39 ppm (1JHB = ca. 100 Hz). The IR spectrum
showed carbonyl peaks at 2040 and 1985 cm−1 which, as for the
case of 1, are at lower wavenumber than the peaks for CpRu(CO)2I
at 2044 and 1995 cm−1.16 This is attributed to the more electron
donating phosphine–borane ligand. In comparison with the IR
data of compound 1 of 2037 and 1994 cm−1, the values were similar.
Complex 4 crystallized in the monoclinic crystal system with P21/n
space group (Fig. 4).
Fe–P(Ph2·BH3) bond length of 2 and that of 1 are similar whereas
˚
the Fe–P(Ph2·BH3) bond length of 3 is significantly (0.04 A) longer.
(7)
Synthesis of CpRu(CO)2(PPh2·BH3) (4)
We also attempted to prepare a phosphine–borane complex of
Ru analogous to 1. The compound CpRu(CO)2(PPh2·BH3) (4)
was synthesized analogously to 1 by reacting CpRu(CO)2I and
LiPPh2·BH3 at −30 ◦C in THF (eqn (6)). This compound was also
characterized by EA, IR, NMR, MS and X-ray crystallograp◦hy.
Reaction of 4 with PMe3
As with the case of Fe complex 1, the reactivity of 4 with PMe3 was
investigated. Upon the addition of two equivalents of PMe3 to a
THF solution of 4, CpRu(CO)(PMe3)(PPh2·BH3) (5) was formed
at 20 ◦C. The product was found to be not as soluble in THF as
1
The 31P{ H} NMR spectrum showed a quartet at d 18.7 at 60 C
◦
1
which had the appearance of a broad doublet at 20 C. The 11B{ H}
NMR spectrum showed a doublet at d −28.5 ppm (1JPB = 42 Hz).
2734 | Dalton Trans., 2008, 2732–2740
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consistent with additional back-bonding to the CO moiety due to
the electron-donating PMe3 ligand.
Dehydrocoupling reactivity of Fe and Ru complexes 1 and 4 with
Ph2PH·BH3
The dehydrocoupling reactivity of complexes 1 and 4 toward
Ph2PH·BH3 was explored both in the melt and in solution
(Table 1). We have previously shown that the conversion of
Ph2PH·BH3 to Ph2PH·BH2·PPh2·BH3 (eqn (8)), is less than 5% at
120 ◦C in the melt after 15 h (Table 1, entry 3).4b In toluene solution
at 110 ◦C the conversion was also very low but was detectable with
1
1
a value of ca. 10% after 15 h by 11B{ H} and 31P{ H} NMR in
toluene (entry 1). A significant amount of free PPh2H was also
observed.
(8)
No stoichiometric reaction was detected between equimolar
amounts of 1 and Ph2PH·BH3 in solution at 25 ◦C. However, on
heating the 1 : 1 reaction at 110 ◦C, Ph2PH·BH3 dehydrocoupled
to form Ph2PH·BH2·PPh2·BH3 with 75% conversion after 15 h
(Table 1, entry 4). Dehydrocoupling also did not proceed when a
solution of Ph2PH·BH3 and 1 (10 mol%) was irradiated by UV,
which can often promote CO dissociation (entry 6). When 10
mol% of 1 was used at 110 ◦C (entry 7), the conversion was only
slightly higher than when no complex was added in toluene (entry
1). There was only 5% conversion at 60 ◦C (entry 8). In contrast,
in the absence of solvent, the adduct Ph2PH·BH3 dehydrocoupled
to Ph2PH·BH2·PPh2·BH3 with 65% conversion using 1.5 mol% of
Fig.
4
Molecular structure of CpRu(CO)2(PPh2·BH3) 4. Selected
◦
˚
bond lengths (A) and angles ( ): C5–Ru1 2.251(5), C6–O1 1.150(5),
C6–Ru1 1.875(5), C7–O2 1.139(5), P1–C8 1.835(4), P1–C14 1.846(4),
P1–B1 1.965(5), P1–Ru1 2.3760(11); C6–Ru1–P1 87.47(13), C7–Ru1–P1
91.51(12), C8–P1–C14 102.28(19), C8–P1–B1 110.0(2), C8–P1–Ru1
108.40(13), C14–P1–B1 107.4(2), C14–P1–Ru1 112.87(14).
CpRu(CO)2(PPh2·BH3), and gradually precipitated out as a white
solid. Unlike the reactivity of 1 with PMe3, the bisphosphine Ru
analogue of 3 was not detectable. The 31P{ H} NMR spectrum
1
◦
of 5 showed two resonances as expected: a broad multiplet at d
1 at 120 C after 15 h (entry 9) whereas only 5% conversion was
noted for the reaction at 60 ◦C and no conversion was detected at
1
13.5 and a doublet at d 9.5. The H NMR spectrum resembled
that of 4 along with a doublet at d 1.23 for the PMe3 ligand. The
IR peak of 1939 cm−1 for complex 5 is at lower frequency than
the stretching vibrations at 2039 and 1985 cm−1 for complex 4,
20 ◦C (entry 10 and 11).
When the Ru complex 4 was treated with a stoichiometric
amount of Ph2PH·BH3 at 110 ◦C for 4 days in toluene, no
a
Table 1 Dehydrocoupling of Ph2PH·BH3 to Ph2PH·BH2·PPh2·BH3
Entry
Potential catalyst
Mol%
Solvent
T/◦C
% Conversionb
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
—
—
—
—
—
—
100
25
10
10
10
1.5
1.5
1.5
100
1.5
1.5
1.5
1.5
0.3
10
Toluene
Toluene
None
Toluene
Toluene
Toluene
Toluene
Toluene
None
110
5 (UV)
120
110
110
5 (UV)
110
60
120
60
20
110
120
120
120
90
5 (UV)
110
60
10
0
0c
1
75
50
0
1
1
1
20
5
1
1
65d
5
1
None
1
Toluene
Toluene
None
None
None
None
THF
Toluene
Toluene
None
0
0
4
4
60d
15c
5d
100c
0
Ru3(CO)12
Ru/Al2O3
[Rh(l-Cl)(1,5-cod)]2
[Rh(l-Cl)(1,5-cod)]2
Fe2(CO)9
Fe2(CO)9
Fe2(CO)9
Fe2(CO)9
10
0
10
1.5
1.5
120
60
80d
0
None
1
a A ca. 0.10 M solution of PPh2H·BH3 was used where appropriate. b After 15 h reaction and estimated by 11B{ H} NMR spectroscopy and averaged
from 2 or 3 trials. c See ref. 4b. d These are upper limit estimates due to sublimation effects outlined in the Experimental section. The true values may be
ca. 10% lower.
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dehydrocoupled product was observed (entry 12), but no unre-
acted Ph2PH·BH3 was detected either. However, when 1.5 mol% of
4 was used without solvent at 120 ◦C, there was 60% conversion to
Ph2PH·BH2·PPh2·BH3 (entry 13). In comparison, with 1.5 mol%
of Ru3(CO)12 or Ru/Al2O3 under the same conditions, 15 or 5%
conversion was observed, respectively (entry 14 and 15).4b
313, 302, 297, 289, 280, 270, 265, 254 nm (Photochemical Reactors
Ltd.).
NMR spectra were recorded at 20 ◦C on a Delta/GX 270,
Eclipse 300/400 and Lambda300 MHz spectrometer unless oth-
erwise indicated. Chemical shifts are reported relative to residual
protonated solvent peaks (1H and 13C) or external BF3·Et2O
(11B) or H3PO4 (31P) standards. NMR spectra were obtained at
300 MHz (1H), 96 MHz (11B) or 75 or 101 MHz (13C). Infrared
spectra were obtained on a Perkin Elmer Spectrum One FT-
IR spectrometer using KBr windows. Elemental analysis was
performed by the Laboratory for Microanalysis, University of
Bristol. Mass spectrometry analyses (electron impact (EI) and
chemical impact (CI), 70 eV) were carried out on a VG AutoSpec
by the Mass Spectrometry service, University of Bristol.
The percentage conversion of Ph2PH·BH3 to Ph2PH·BH2·
PPh2·BH3 was averaged from two or three trials.
For comparative purposes, we explored the use of Fe2(CO)9 as
a catalyst. With 10 mol% of Fe2(CO)9 in toluene, the dehydrocou-
◦
pling activity of Ph2PH·BH3 was not significant at 60 or 110 C
(entries 18 and 19), but with 1.5 mol% of Fe2(CO)9 in the absence
of solvent, 80% conversion to Ph2PH·BH2·PPh2 BH3 was detected
at 120 ◦C (entry 20). No dehydrocoupling activity was detected at
◦
60 C (entry 21). Interestingly, Fe2(CO)9 is a better catalyst than
Ru3(CO)12 (entries 20 and 14, respectively).
Complex 1 is the first Fe complex that catalyzes the dehy-
drocoupling of phosphine–borane adducts. The observation that
Fe2(CO)9 also catalyzes the dehydrocoupling reaction shows that
compound 1 is not unique among Fe complexes in possessing the
catalytic ability to promote the phosphine–borane dehydrocou-
pling reaction.
The proton coupled 11B spectra for compounds 1–5 are only par-
tially resolved because they are not completely first-order. Higher
temperatures of 35–60 ◦C showed no significant improvement,
therefore, only approximate values of coupling constants are given.
A representative spectrum is given in the ESI.‡
X-Ray structural characterization
Conclusions
Diffraction data were collected on a Bruker-Nonius Kappa-CCD
diffractometer using graphite-monochromated Mo-Ka radiation
The iron phosphine–borane complex CpFe(CO)2(PPh2·BH3) (1)
and the ruthenium analogue CpRu(CO)2(PPh2·BH3) (4) have been
prepared. No stoichiometric P–B bond-formation chemistry was
detected on treatment of these complexes with Ph2PH·BH3 under
mild conditions despite the observation that CO substitution with
PMe3 is facile. However, at 120 ◦C in the melt, complexes 1, 4 and
Fe2(CO)9 were shown to promote the catalytic dehydrocoupling of
Ph2PH·BH3 to Ph2PH·BH2·PPh2·BH3 Although no clear mecha-
nistic conclusions can be been drawn from the results, complex 1
and Fe2(CO)9 represent the first Fe dehydrocoupling catalysts for
phosphine–borane adducts.
˚
(k = 0.71073 A) and were measured using a combination of φ
scans and x scans with j offsets, to fill the Ewald sphere. The
data were integrated and scaled using the Denzo-SMN package.21
Absorption corrections were carried out using SORTAV.22 The
structures were solved and refined with the SHELXTL V6.13
software package.23 Refinement was by full-matrix least squares on
F2 using all data (negative intensities included). Molecular struc-
tures are presented with thermal ellipsoids at a 30% probability
level and most hydrogen atoms attached to carbon are omitted
for clarity. In all structures, hydrogen atoms bonded to carbon
were included in calculated positions and treated as riding atoms,
whereas those attached to boron or nitrogen were located and
refined with isotropic thermal parameters. Crystallographic data
for the compounds is given in Table 2.
Experimental
General considerations
All air-and moisture-sensitive manipulations were carried out
using standard vacuum line, Schlenk, and cannula techniques or
in an MBraun inert atmosphere drybox containing an atmosphere
of Ar. All solvents were dried and distilled prior to use, or vacuum
transferred directly from the appropriate drying agent except
Et2O and hexanes which were dried via the Grubbsꢀ method.19
Deuterated solvents were purchased from Cambridge Isotope
Laboratories and then degassed and vacuum-transferred from Na
(C6D6) or CaH2 (CDCl3 and CD2Cl2) and stored over activated
Synthesis of CpFe(CO)2(PPh2·BH3) (1). The complex
CpFe(CO)2I (1.000 g, 3.29 mmol) was dissolved in 30 mL THF in
a round-bottom Schlenk flask and cooled to −30 ◦C. A similarly
chilled (−30 ◦C) LiPPh2·BH3 (23 mL, 0.149 M in THF) was added
dropwise. The reaction temperature was maintained between −30
and −20 ◦C for 1.5 h, and then the volatile components of the
reaction mixture were removed in vacuo to obtain burgundy oil.
The product was chromatographed on silica (2 × 5 cm) supported
on a medium porosity frit with diethyl ether (250 mL) to obtain
a yellowish brown eluant. The solution volume was reduced to
50 mL in vacuo and the product crystallized at −40 ◦C for 2 days,
affording amber yellow crystals (0.615 g, 50% yield) of 1. In the
case of having obtained only sticky brown crystals, these can
be redissolved into Et2O and chromatographed again on silica
and recrystallized as described above to yield yellow crystals.
Alternatively, the work-up can also be performed in toluene
instead of Et2O.
˚
4A molecular sieves. CpRu(CO)2I was synthesized according to
published procedures.20 CpFe(CO)2I, Fe2(CO)9, [Rh(l-Cl)(1,5-
cod)]2 and Ru/Al2O3 were purchased from Aldrich. PPh2H·BH3
was prepared using a procedure analogous to that used for
PhPH2·BH3.4b Ph2PH was purchased from Strem and PMe3 was
purchased from Alfa Aesar.
Photoirradiation experiments were carried out with Pyrex-glass
filtered emission from a 125 W medium-pressure mercury lamp
(Photochemical Reactors Ltd.). The emission lines of the mercury
lamps were as follows: 577–579, 546, 436, 408–405, 366–365, 334,
IR (Toluene): 2029 (s, CO), 1980 (s, CO) cm−1.
IR (THF): 2028 (s, CO), 1978 (s, CO) cm−1.
2736 | Dalton Trans., 2008, 2732–2740
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Table 2 Crystallographic data for 1, 2, 3 and 4
1
2
3
4
Empirical formula
C19H18BFeO2P
375.96
150(2)
C21H27BFeOP2
424.03
150(2)
C23H36BFeP3
472.09
150(2)
C19H18BO2PRu
421.18
150(1)
Mr
T/K
˚
k/A
0.71073
0.71073
0.71073
0.71073
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
Cc
Monoclinic
P21/n
Monoclinic
P21/n
˚
a/A
13.1693(3)
9.8830(4)
13.8078(5)
102.900(2)
1751.76(10)
4
15.5704(6)
9.2138(4)
15.2599(7)
107.608(3)
2086.66(15)
4
9.6143(2)
13.9049(2)
18.1670(4)
90.5310(11)
2428.57(8)
4
13.4151(5)
9.7058(3)
14.0420(5)
101.7740(19)
1789.86(11)
4
˚
b/A
˚
c/A
b/◦
3
˚
VA
Z
Dc/g cm−3
1.426
0.959
1.350
0.883
1.291
0.826
1.563
0.972
l/mm−1
F(000)
776
888
1000
848
Crystal size/mm3
h Range for data collection/◦
Index ranges, hkl
0.30 × 0.26 × 0.18
0.10 × 0.09 × 0.08
0.28 × 0.26 × 0.24
0.30 × 0.30 × 0.14
2.56–27.50
2.60–27.47
2.58–27.50
2.57–27.52
−17 to 17, −12 to 12, −17 −19 to 18, −11 to 11, −19 −12 to 12, −17 to 17, −16 −17 to 17, −11 to 12, −18
to 17
to 16
to 23
to 18
Reflections collected
12104
3982 (Rint = 0.0538)
10243
13404
11118
Independent reflections
3898 (Rint = 0.0697)
5489 (Rint = 0.0369)
4085 (Rint = 0.0442)
Completeness to h = 27.50◦ (%) 99.1
99.5
99.1
99.1
Max., min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.847, 0.644
3982/0/229
1.044
0.935, 0.802
3898/12/250
1.042
0.825, 0.735
5489/0/271
1.039
0.874, 0.803
4085/0/230
1.086
Final R indices [I > 2r(I)]
R Indices (all data)
R1 = 0.0377, wR2 = 0.0943 R1 = 0.0443, wR2 = 0.0774 R1 = 0.0375, wR2 = 0.0879 R1 = 0.0395, wR2 = 0.0889
R1 = 0.0518, wR2 = 0.1033 R1 = 0.0733, wR2 = 0.0886 R1 = 0.0566, wR2 = 0.0983 R1 = 0.0638, wR2 = 0.1168
Absolute structure parameter
—
−0.02(2)
—
0.0033(7)
−3
˚
Dq/e A
0.413, −0.574
0.706, −0.497
0.529, −0.367
1.730, −1.551
Absorption correction: semi-empirical from equivalents; refinement method: full-matrix least-squares on F2.
MS (CI, m/z): 375 (M+, 13%), 347 (M+ − CO, 10%), 79 (C6H7,
HR-MS (CI): 423.0902 (M+) − 1H−, 100%, calc. mass for
C21H2611B56FeO1P2 423.0901.
100%).
1H NMR (300 MHz, CDCl3): d 7.69–7.75 (m, 4 H, Ph), 7.33–
7.37 (m, 6H, Ph), 4.99 (s, 5H, Cp), 1.45 (br q, 3H, BH3, 1JHB = ca.
100 Hz)
1H NMR (300 MHz, CDCl3): d 7.17–8.03 (m, 10 H, Ph), 4.63
1
(m, 5H, Cp), 1.43 (q, 3H, BH3, JHB = ca. 80 Hz), 1.13 (d, 9H,
PMe3, 2JPH = 9.0 Hz).
1
1
2
31P{ H} NMR (121 MHz, CDCl3): d 31.5 (br q, 1JPB = ca. 45 Hz,
31P{ H} NMR (121 MHz, CDCl3): d 31.2 (d, Jpp = 43 Hz,
coupling is clearer at 60 ◦C)
PMe3), 26.9 (br m, PPh2BH3)
1
1
11B{ H} NMR (96 MHz, CDCl3): d −30.4 (d, 1JPB = ca. 45 Hz).
11B{ H} NMR (96 MHz, CDCl3): d −31.5 (d, 1JPB = ca. 55 Hz).
11B NMR (96 MHz, THF): d−29.6 (br partially resolved q of d,
at 50 ◦C, 1JHB = ca. 100 Hz, 1JPB = ca. 45 Hz).
11B NMR (96 MHz, CDCl3): d −31.4 (br partially resolved q of
d, at 60 ◦C, 1JHB = ca. 90 Hz, 1JPB = ca. 55 Hz).
1
1
13C{ H} NMR (75 MHz, CDCl3): d 212.5 (d, CO, 2JCP = 18 Hz),
13C{ H} NMR (101 MHz, CDCl3): d 218.1 (dd, CO, 2JCP = 33,
139.01 (d, Ph, JCP = 29 Hz), 132.6 (d, Ph, JCP = 8 Hz), 129.1 (d,
Ph, JCP = 2 Hz), 128.0 (d, Ph, JCP = 9 Hz), 86.8 (s, Cp).
Anal. Calc. for C19H18O2PBFe: C, 60.71; H, 4.82. Found: C,
60.57; H, 4.72%.
20 Hz), 141.5 (m, ipso-C of Ph), 132.0 (m, Ph), 126.7 (m, Ph),
126.4 (m, Ph, JCP = ca. 10 Hz), 83.9 (s, Cp), 19.3 (d, PMe3, 1JCP
=
30 Hz).
1
2
13C{ H} NMR (101 MHz, CD2Cl2): d 219.9 (dd, CO, JCP
=
33, 20 Hz), 143.5 (m, ipso-C of Ph), 133.7 (m, Ph), 128.3 (dd, Ph,
JCP = 11, 2 Hz), 127.9 (m, Ph, JCP = 12, 8 Hz), 85.1 (s, Cp), 20.0
(d, PMe3, 1JCP = 30 Hz).
Synthesis of CpFe(CO)(PMe3)(PPh2BH3) (2). Complex 1
(300 mg, 0.798 mmol) was dissolved in 1.8 mL THF in a round-
bottom Schlenk flask. PMe3 (82 lL, 0.798 mmol) was added to the
Anal. Calc. for C21H27OP2BFe: C, 59.48; H, 6.42. Found: C,
59.01; H, 5.99%.
solution which was stirred at 20 ◦C and monitored by 11B and 31
P
NMR. The pale yellow solution turned orange. After 2 days, the
volatile components of the reaction mixture were removed in vacuo
overnight. The product was chromatographed on silica (0.5 ×
5 cm) with hexanes, Et2O and then THF. The orange solutions
were recrystallized at −40 ◦C for 15 days, affording orange crystals
of 2 which were of X-ray quality. Only the crystals obtained from
the THF eluant were pure with a yield of 41 mg (12% yield).
IR (THF): 1928 (s, CO) cm−1.
Synthesis of CpFe(PMe3)2(PPh2BH3) (3). Complex 1 (100 mg,
0.266 mmol) was dissolved in 1.8 mL THF in a round bottom
Schlenk flask. PMe3 (55 lL, 0.53 mmol) was added to the
solution which was stirred at 20 ◦C and monitored by 11B and 31
P
NMR. The pale yellow solution turned orange. After 15 days, the
volatile components of the reaction mixture were removed in vacuo
overnight. The product was washed by filtering through Celite
supported on glass wool with Et2O to yield an orange solution.
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◦
The solution was recrystallized at −40 C for 15 days, affording
and 31P NMR. The pale yellow solution slowly deposited a white
precipitate. After 3 days, the volatile components of the reaction
mixture were removed in vacuo overnight to yield a yellow powder.
The product was washed by filtration through celite supported
on glass wool with Et2O–THF (5 : 1) solution to yield a yellow
solution which was stored at −40 ◦C for 2 days. This afforded
a white precipitate (20 mg, 16% yield) consisting of 5 which was
not readily soluble in benzene. Even after silica chromatography
and multiple recrystallizations for attempted further purification,
this compound was isolated only ca. 97% pure with an unknown
red needles of 3 and orange crystals of 2.
Despite the fact that compound 3 crystallizes out in Et2O
along with 2 and that the red needles of 3 were hand-picked,
on dissolution the red needles were still found to be contaminated
with the residue of 2, as detected by NMR spectroscopy. Other
methods of purification such as silica chromatography and partial
fraction crystallization failed to give pure 3. Therefore, it was not
possible to determine the yield. The NMR data were given by
subtracting the signals from those of 2. Compound 3 decomposes
in CDCl3 faster than compound 2. Therefore, it was essential to
1
1
impurity indicated by the arrows in the H and 13C{ H} NMR
spectra in the ESI.‡ Therefore, accurate EA was not possible.
IR (THF): 1939 (s, CO) cm−1.
run the 13C{ H} NMR in CD2Cl2 for the overnight scan.
1
MS (EI, m/z): 382 (M+ − BH3 − PMe3, 10%), 306 (M+ − BH3 −
2PMe3, 18%), 72 (THF, 100%).
MS (EI, m/z): 456 (M+ − CO, 66%), 72 (THF, 100%).
1H NMR (300 MHz, CDCl3): d 7.64–7.92 (m, 4 H, Ph), 7.14–
7.35 (m, 6H, Ph), 5.09 (s, 5H, Cp), 1.43 (br q, 3H, BH3, 1JHB = ca.
93 Hz), 1.23 (d, 9H, PMe3, 2JPH = 9.0 Hz)
1H NMR (300 MHz, CDCl3): d 7.17–8.03 (m, 10 H, Ph), 4.01
(m, 5H, Cp), 1.43 (br q, 3H, BH3), 1.43 (m, 18H, PMe3).
31P{ H} NMR (121 MHz, CDCl3): d 24.1 (d, Jpp = 40 Hz,
1
2
1
PMe3) and 18.8 (br m, PPh2BH3)
31P{ H} NMR (121 MHz, CDCl3): d 13.5 (br m, PPh2BH3), 9.48
11B{ H} NMR (96 MHz, CDCl3): d −28.4 (d, 1JPB = ca. 52 Hz)
(d, 1Jpp = 26 Hz, PMe3)
1
11B NMR (96 MHz, CDCl3): d −28.2 (br partially resolved q of
d, at 60 ◦C, 1JHB = ca. 80 Hz, 1JPB = ca. 50 Hz).
11B{ H} NMR (96 MHz, CDCl3): d −30.7 (br d, JPB = ca.
1
1
57 Hz).
13C{ H} NMR (101 MHz, CD2Cl2): d 147.9 (dt, ipso-C of Ph,
11B NMR (96 MHz, CDCl3): d −30.7 (br partially resolved q of
1
JCP = 18 Hz, 2 Hz), 133.7 (m, Ph, JCP = 8 Hz), 127.4 (d, Ph, JCP
7 Hz), 127.0 (d, Ph, JCP = 2 Hz), 78.7 (s, Cp), 22.9 (m, PMe3, JCP
13 Hz).
=
=
d, at 60 ◦C, 1JHB = ca. 92 Hz, 1JPB = ca. 57 Hz).
1
13C{ H} NMR (75 MHz, CDCl3): d 204.6 (dd, CO, 2JCP = 20,
2
11 Hz), 143.0 (dd, ipso-C of Ph, JCP = 63.9, 31 Hz), 133.4 (dd,
Ph, JCP = 61, 8 Hz), 127.9 (dd, Ph, JCP = 16, 2 Hz), 127.5 (dd, Ph,
Synthesis of CpRu(CO)2(PPh2·BH3) (4). The complex
JCP = 16, 9 Hz), 87.9 (s, Cp), 21.3 (d, 2JCP = 33 Hz).
CpRu(CO)2I (250 mg, 0.716 mmol) was dissolved in 10 mL THF
◦
in a round-bottom Schlenk flask and cooled to −30 C. Chilled
Thermal dehydrocoupling of Ph2PH·BH3. The adduct
Ph2PH·BH3 (40 mg, 0.20 mmol) in toluene (1.8 mL) was stirred at
110 ◦C. After 16 h, 10% conversion to Ph2PH·BH2·PPh2·BH3 was
(−30 ◦C) LiPPh2·BH3 (4.5 mL, 0.18 M in THF) was added
dropwise. The reaction temperature was maintained between −30
and −20 ◦C for 2 h, and then the volatile components of the
reaction mixture were removed in vacuo in the cold bath to obtain
yellow oil. The oily product was purified by chromatography with
a column of celite (0.5 × 1.5 cm) supported on glass wool with
hexanes and then with toluene to obtain an orange solution which
was stored at −40 ◦C for 3 days, affording pale yellow crystals
(190 mg, 63% yield) of 4.
1
1
observed by 11B{ H} and 31P{ H} NMR. A new unidentified peak
was detected by 11B{ H} NMR at d 17 ppm (10%). After 40 h, 16%
1
conversion was detected. PPh2H was also observed at d −40.1 by
1
31P{ H} NMR.
Thermal reaction of complex 1. Complex 1 (50 mg, 0.13 mmol)
in toluene (1.8 mL) was stirred at 110 ◦C for 19 h.
1
31P{ H} (toluene) d 194 (s, 17%), 187 (1%), 57 (d, J = 40 Hz,
IR (Toluene): 2040 (s, CO), 1986 (s, CO) cm−1.
IR (THF): 2039 (s, CO), 1985 (s, CO) cm−1.
20%), 34 (br d) and 33 (br., 1, 51%), 12 (br s, 10%).
1
11B{ H} (toluene) d −16 (s, 4%), −29 (d, 96%, 1)
MS (EI, m/z): 421 (M+, 44%), 408 (M+ − BH3, 60%), 352 (M+ −
BH3 − 2CO, 100%).
Thermal dehydrocoupling of PPh2H·BH3 in the presence of 1.
(a) Complex 1 (56 mg, 0.15 mmol, 100 mol%) was added to a
toluene (0.9 mL) solution of PPh2H·BH3 (30 mg, 0.15 mmol) and
the solution was stirred at 110 ◦C. After 15 h, 75% conversion of
1H NMR (300 MHz, C6D6): d 7.92–7.99 (m, 4 H, Ph), 7.00–7.19
(m, 6H, Ph), 4.54 (s, 5H, Cp), 2.39 (br q, 3H, BH3, JHB = ca.
1
100 Hz)
◦
31P{ H} NMR (121 MHz, C6D6): d 18.7 (br q, at 60 C, 1JPB
=
1
1
PPh2H·BH3 to Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H}
ca. 45 Hz)
NMR.
11B{ H} NMR (96 MHz, C6D6): d −28.5 (br d, 1JPB = ca. 45 Hz).
11B NMR (96 MHz, THF): d −29.1 (br partially resolved q of
d, at 50 ◦C, 1JHB = ca. 100 Hz, 1JPB = ca. 45 Hz).
1
1
31P{ H} (toluene) d 194.7 (s), 56.1 (d, JPP = 21 Hz), 32 (1), 30
(br. s), 2.0 (d, Ph2PH·BH3), −3 (br. s, Ph2PH·BH2·PPh2·BH3), −16
(br. s, Ph2PH·BH2·PPh2·BH3).
13C{ H} NMR (75 MHz, C6D6): d 199.3 (d, CO, 2JCP = 11 Hz),
1
1
11B{ H} (toluene) d −30.9 (s, 52%), −34.4 and −38.6 (s,
141.2 (d, Ph, JCP = 35 Hz), 133.6 (d, Ph, JCP = 10 Hz), 129.5 (d,
Ph, JCP = 2 Hz), 128.6 (d, Ph, JCP = 9 Hz), 89.9 (s, Cp).
Anal. Calc. for C19H18O2PBRu: C, 54.19; H, 4.31. Found: C,
54.49; H, 4.33%.
1
34%. Ph2PH·BH2·PPh2·BH3), −41.4 (d, JPB = 35 Hz, 14%,
PPh2H·BH3).
(b) Complex 1 (28 mg, 0.074 mmol, 25 mol%) was added to
a toluene (1.8 mL) solution of PPh2H·BH3 (60 mg, 0.300 mmol)
and the solution was stirred at 110 ◦C. After 15 h, 50% con-
version of PPh2H·BH3 to Ph2PH·BH2·PPh2·BH3 was observed
Synthesis of CpRu(CO)(PMe3)(PPh2BH3) (5). Complex 4
(110 mg, 0.261 mmol) was dissolved in 1.8 mL THF in a round-
bottom Schlenk flask. PMe3 (54 lL, 0.52 mmol) was added to
the solution which was stirred at 20 ◦C and monitored by 11B
1
by 11B{ H} NMR. The same reaction with complex 1 (11 mg,
0.029 mmol, 10 mol%) yielded 20% conversion of PPh2H·BH3
2738 | Dalton Trans., 2008, 2732–2740
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1
to Ph2PH·BH2·PPh2·BH3, observed by 11B{ H} NMR. The same
(a) Complex Fe2(CO)9 (1 mg, 0.005 mmol, 1.5 mol% Fe)
was added to PPh2H·BH3 (60 mg, 0.300 mmol) and the neat
mixture was heated at 120 ◦C. The reaction was stopped ev-
ery 2–3 h to return the sublimed PPh2H·BH3 back into the
reaction mixture. After 15 h, 70% conversion of PPh2H·BH3 to
reaction heated at 60 ◦C for 15 h yielded 0% conversion.
(c) Complex 1 (2 mg, 0.005 mmol, 1.5 mol%) was added
to PPh2H·BH3 (60 mg, 0.300 mmol) and the neat mixture was
◦
heated at 120 C. After 15 h, 65% conversion of PPh2H·BH3 to
1
Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H} NMR. This is
1
Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H} NMR. When the
same reaction was performed at 60 ◦C, 5% conversion was noted
and there was no conversion at 20 ◦C with 1.8 mL of toluene.
10% less than entry 20 in Table 1, suggesting an error of ca. 10%.
Acknowledgements
Attempted UV induced dehydrocoupling of PPh2H·BH3. (a)
The complex CpFe(CO)2PPh2BH3 (1) (6 mg, 10 mol%) was added
to a toluene (0.9 mL) solution of PPh2H·BH3 (30 mg, 0.15 mmol)
and stirred under UV lamp at 5 ◦C. After 15 h, 0% conversion of
I. M. thanks EPSRC, the University of Bristol for start-up funds,
the European Union for a Marie Curie Chair and the Royal Society
for a Wolfson Research Merit Award for financial support. We
thank Drs George R. Whittell and Anne Staubitz for helpful
discussions. We thank Drs Craig Butts and Martin Murray for
the contribution of their expertise in the NMR spectroscopy.
Initial experiments were performed at the University of Toronto,
Toronto, ON, Canada with the funding from NSERC.
1
PPh2H·BH3 to Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H}
NMR.
(b) The complex [Rh(l-Cl)(1,5-cod)]2 (1 mg, 0.8 mol% Rh)
was added to a THF (1.8 mL) solution of PPh2H·BH3 (100 mg,
0.500 mmol) and stirred under UV lamp at 5 ◦C. After 15 h, 0%
conversion of PPh2H·BH3 to Ph2PH·BH2·PPh2·BH3 was observed
1
by 11B{ H} NMR.
(c) A toluene (0.9 mL) solution of PPh2H·BH3 (50 mg,
Notes and references
◦
0.25 mmol) was stirred under UV lamp at 5 C. After 15 h, 0%
1 (a) T. D. Tilley, Acc. Chem. Res., 1993, 26, 22; (b) F. Gauvin, J. F.
Harrod and H. G. Woo, Adv. Organomet. Chem., 1998, 42, 363; (c) J. A.
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I. Manners, Chem.–Eur. J., 2006, 12, 8634.
conversion of PPh2H·BH3 to Ph2PH·BH2·PPh2·BH3 was observed
1
by 11B{ H} NMR and a new peak, d 18.6 (s), was detected by
1
31P{ H} NMR.
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0.16 mmol, 100 mol%) was added to a toluene (1.8 mL) solution
◦
of PPh2H·BH3 (33 mg, 0.16 mmol) and stirred at 110 C. After
4 days, PPh2H·BH3 was completely consumed.
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1844.
1
31P{ H} (toluene) d 38.0 (d, J = 26 Hz), 20.0 (br s), 17.4 (s),
−40.1 (s, PPh2H).
1
11B{ H} (toluene) d −29.1 (s).
(b) Complex 4 (2 mg, 5 lmol, 1.5 mol%) was added PPh2H·BH3
(60 mg, 0.30 mmol) and stirred at 120 ◦C. After 15 h, 60%
conversion of PPh2H·BH3 to Ph2PH·BH2·PPh2·BH3 was observed
1
by 11B{ H} NMR.
Reaction of Ph2PH·BH3 with Ru/Al2O3. Ru/Al2O3 (9 mg,
1.5 mol%) was added PPh2H·BH3 (60 mg, 0.30 mmol) and
stirred at 120 ◦C. After 15 h, 5% conversion of PPh2H·BH3 to
1
Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H} NMR.
Reaction of Ph2PH·BH3 with Fe2(CO)9. (a) Complex Fe2(CO)9
(5 mg, 0.027 mmol, 10 mol% Fe) was added to a toluene (1.8 mL)
solution of PPh2H·BH3 (60 mg, 0.300 mmol) and the solution was
◦
stirred at 110 C. After 15 h, 10% conversion of PPh2H·BH3 to
1
Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H} NMR. The same
reaction mixture heated at 60 ◦C for 15 h yielded 0% conversion.
(b) Complex Fe2(CO)9 (1 mg, 0.005 mmol, 1.5 mol% Fe) was
added to PPh2H·BH3 (60 mg, 0.300 mmol) and the neat mixture
was heated at 120 ◦C. After 15 h, 80% conversion of PPh2H·BH3 to
1
Ph2PH·BH2·PPh2·BH3 was observed by 11B{ H} NMR. When the
same experiment was done at 60 ◦C, 0% conversion was detected.
Experiments of entries 9, 13, 15 and 20 in Table 1. In
these experiments the conversion is an upper-limit estimate due
to sublimation of mostly PPh2H·BH3 and a small amount of
Ph2PH·BH2·PPh2·BH3 during the reaction onto the top of the
reaction flask. The following experiment was conducted to assess
the effect of the sublimation.
9 (a) A. Gutowska, L. Li, Y. Shin, C. M. Wang, X. S. Li, J. C.
Linehan, R. S. Smith, B. D. Kay, B. Schmid, W. Shaw, M. Gutowski
and T. Autrey, Angew. Chem., Int. Ed., 2005, 44, 3578; (b) M.
Jacoby, Chem. Eng. News, 2005, 83, 42; (c) M. S. Dresselhaus and
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Dalton Trans., 2008, 2732–2740 | 2739
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17 While our studies were in progress, complex 1 was reported by Wagner
and co-workers using a similar route, see: T. I. Ku¨ckmann, F. Dornhaus,
M. Bolte, H.-W. Lerner, M. C. Holthausen and M. Wagner, Eur. J. Inorg.
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18 F. Dornhaus, B. Michael, H.-W. Lerner and M. Wagner, J. Organomet.
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13 C. A. Jaska, PhD thesis, University of Toronto, 2004.
14 An analogous possible mechanism involves initial B–H bond activation.
In the case of amine–borane adducts this mechanism has been
considered in some detail, see: A. Paul and C. B. Musgrave, Angew.
Chem., Int. Ed., 2007, 46, 8153.
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2740 | Dalton Trans., 2008, 2732–2740
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