Chemistry of phosphine-borane adducts at platinum centers: Dehydrocoupling reactivity of Pt(II) dihydrides with P-H bonds

Article abstract of DOI:10.1039/b416114a

The reaction of the Pt(II) dihydride complex cis-[PtH₂(dcype)] (dcype = 1,2-bis(dicyclohexylphosphino)ethane) with the primary or secondary phosphine-borane adducts PhRPH·BH₃ (R = H, Ph) was found to exclusively afford the mono-substituted complexes cis-[PtH(PPhR·BH ₃)(dcype)] (1: R = H; 2: R = Ph) via a dehydrocoupling reaction between Pt-H and P-H bonds. Similar reactivity was observed between the uncoordinated phosphines PhRPH (R = H, Ph) and cis-[PtH₂(dcype)], which gave cis-[PtH(PPhR)(dcype)] (4: R = H; 5: R = Ph). The complexes were characterized by ¹H, ¹¹B, ¹³C and ³¹P NMR spectroscopy, IR, MS and, in the case of 2, X-ray crystallography that confirmed the cis geometries. The di-substituted complex cis-[Pt(PhPH·BH₃)₂(dcype)] 3) was prepared from the reaction of cis-[PtCl₂(dcype)] with two equivalents of Li[PPhH·BH₃]. This suggested that steric reasons alone cannot be used to explain the lack of reactivity with respect to a second dehydrocoupling reaction involving the remaining Pt-H bond in complexes 1, 2, 4 and 5.

Full text of DOI:10.1039/b416114a

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F U L L P A P E R
Chemistry of phosphine–borane adducts at platinum centers:
dehydrocoupling reactivity of Pt(II) dihydrides with P–H bonds
Cory A. Jaska, Alan J. Lough and Ian Manners*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario,
Canada M5S 3H6. E-mail: imanners@chem.utoronto.ca
Received 25th October 2004, Accepted 11th November 2004
First published as an Advance Article on the web 7th December 2004
The reaction of the Pt(II) dihydride complex cis-[PtH2(dcype)] (dcype = 1,2-bis(dicyclohexylphosphino)ethane) with
the primary or secondary phosphine–borane adducts PhRPH·BH3 (R = H, Ph) was found to exclusively afford the
mono-substituted complexes cis-[PtH(PPhR·BH3)(dcype)] (1: R = H; 2: R = Ph) via a dehydrocoupling reaction
between Pt–H and P–H bonds. Similar reactivity was observed between the uncoordinated phosphines PhRPH (R =
H, Ph) and cis-[PtH2(dcype)], which gave cis-[PtH(PPhR)(dcype)] (4: R = H; 5: R = Ph). The complexes were
characterized by 1H, 11B, 13C and 31P NMR spectroscopy, IR, MS and, in the case of 2, X-ray crystallography that
confirmed the cis geometries. The di-substituted complex cis-[Pt(PhPH·BH3)2(dcype)] (3) was prepared from the
reaction of cis-[PtCl2(dcype)] with two equivalents of Li[PPhH·BH3]. This suggested that steric reasons alone cannot
be used to explain the lack of reactivity with respect to a second dehydrocoupling reaction involving the remaining
Pt–H bond in complexes 1, 2, 4 and 5.
Introduction
Catalytic dehydrocoupling has recently emerged as a convenient,
mild and versatile route for the formation of new bonds
between inorganic elements.1 In particular, a range of main
group hydride species have been shown to undergo both homo-
and heterodehydrocoupling reactions in the presence of a
variety of early and late transition metal-catalysts. Catalytic
dehydrocoupling reactions to form new Si–Si bonds were first
discovered in the mid 1980s.2 Subsequent work has extended
this type of method to include, for example, Ge–Ge,3 Sn–Sn,4 P–
P,5 Si–P,6 Si–N7 and B–C8 bond forming reactions. Research
in our group has focussed on the dehydrocoupling of pri-
mary and secondary phosphine–borane adducts (RRꢀPH·BH3)
in the presence of late transition metal-catalysts, which has
afforded six- and eight-membered rings [RRꢀP–BH2]x (x =
3, 4), linear oligomeric species RRꢀPH–BH2–RRꢀP–BH3 and
high molecular weight poly(phosphinoboranes) [RPH–BH2]n
(eqns. (1) and (2)).9,10 This method was extended to the
(2)
(3)
(4)
(5)
To date, there are only a few known examples of “dehy-
drocoupling type” reactions involving either Pt or Pd hydride
complexes. For example, Fink and co-workers have reported
the reaction of cis-[PtH2(dcype)] with the disilane H3Si–
SiH3 which afforded a mixture of cis-[Pt(SiH2SiH3)2(dcype)]
and [Pt(l-SiH2SiH2)(dcype)]2.16 Puddephatt and cowork-
ers have reported the reaction of the dinuclear complex
[Pt2Me6(l-H)(bu2bpy)2]OTf (bu2bpy = 4,4ꢀ-di-tert-butyl-2,2ꢀ-
bipyridine) with HSPh to form the substituted complex
[PtMe3(bu2bpy)(SPh)] and H2.17 Recently, Glueck and co-
workers have reported the reaction of the bridging Pd hy-
dride complex [Pd2I2(l-dppf)(l-H)(l-PPh2)] (dppf = 1,1ꢀ-
bis(diphenylphosphino)ferrocene) with Ph2PH to yield [PdI(l-
PPh2)(Ph2PH)]2.18 However, more detailed investigations into
the dehydrocoupling reactivity of Pt hydrides with main group
compounds containing E–H bonds have not been performed.
In this paper, we report on our detailed investigations of the
reactivity of platinum(II) dihydride complexes with phosphines
and phosphine–borane adducts bearing P–H bonds.
metal-catalyzed dehydrocoupling of primary and secondary
amine–borane adducts (RRꢀNH·BH3), which has afforded cyclic
aminoboranes [RRꢀN–BH2]2 and borazines [RN–BH]3 under
mild reaction conditions (eqns. (3) and (4)).10,11 In addition,
a tandem catalytic dehydrocoupling–hydrogenation reaction
involving a variety of Rh (pre)catalysts and Me2NH·BH3 as
a stoichiomet◦ric hydrogen source for the hydrogenation of
alkenes at 25 C has also been recently developed (eqn. (5)).12
Recent comparative work between the two systems has indicated
the presence of a homogeneous mechanism for phosphine–
borane adducts and a heterogeneous mechanism involving Rh(0)
colloids in the case of amine–borane analogs.13 Our attempts
to further explore the homogeneous mechanism of phosphine–
borane dehydrocoupling involved studies of the chemistry of
phosphine–borane adducts at platinum centers.14,15 During this
work an unusual reaction between cis-[PtH(PPhH·BH3)(depe)]
(depe = 1,2-bis(diethylphosphino)ethane) and PhPH2·BH3 was
observed, which afforded the di-substituted complex cis-
14b
[Pt(PPhH·BH3)2(depe)]. This was formally considered to be
a dehydrocoupling reaction involving Pt–H and P–H bonds.
Results and discussion
The first Pt(II) hydride complexes (e.g. trans-[PtHCl(PEt3)2])
were discovered by Chatt and Shaw in 1957.19 While Pt(IV)
hydride species are relevant with respect to C–H bond activation
and Pt-catalyzed hydrosilation reactions, they are less well-
known than their Pt(II) counterparts.20 A variety of stable Pt(II)
(1)
3 2 6
D a l t o n T r a n s . , 2 0 0 5 , 3 2 6 – 3 3 1
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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dihydride complexes containing tertiary phosphine ligands have
been synthesized with both cis and trans geometries.21 However,
steric protection in the form of bulky phosphine ligands is
usually required to help stabilize these complexes.22 In addition,
the reversible loss of dihydrogen has been observed but can
be avoided by exposure of these complexes to a hydrogen
atmosphere.23 The complex trans-[PtH2(PMe3)2] is one of the
first structurally characterized examples of a mononuclear Pt(II)
dihydride complex, which was reported by Trogler and co-
workers in 1985.24 Therefore, for their combination of stability
and reactivity, platinum(II) dihydride complexes with both cis
and trans geometries were chosen for preliminary dehydrocou-
pling studies.
PCy2 group (JPP = 2.6 Hz) with associated 195Pt satellites (JPPt
=
1823 Hz). Finally, a broad doublet was observed at d −50.6 ppm,
which is due to the phosphine–borane moiety with a large trans
coupling to one PCy2 group (JPP = 266 Hz) and associated Pt
satellites (JPPt = 1887 Hz). The 1H NMR spectrum displayed two
key resonances associated with 1. A broad doublet was observed
at d 4.7 ppm, which is due to the PH of the phosphine–borane
moiety (JHP = 323 Hz) while a doublet of doublet of doublets was
observed at d −2.63 ppm, which is due to the PtH hydrogen atom
with coupling to a trans PCy2 group (JHP = 164 Hz) and cis PCy2
and PPhH·BH3 groups (JHP = 26 and 13 Hz), with associated Pt
satellites (JHPt = 913 Hz) (Fig. 1(b)). The 11B NMR spectrum of
1 displayed only a broad signal at d −33.6 ppm. The IR spectrum
of 1 in CH2Cl2 showed absorptions at 2358, 2197 and 2004 cm−1
due to B–H, P–H and Pt–H stretches, respectively.
t
Reaction of trans-[PtH2(PR3)2] (R = Bu, Me) with PhPH2·BH3
Our first attempts to explore the reactivity of platinum hy-
drides with the primary phosphine–borane adduct PhPH2·BH3
were performed using the trans dihydride complexes trans-
t
[PtH2(PR3)2] (R = Bu, Me). The reaction of trans-[PtH2(PtBu3)2]
with 2 equivalents of PhPH2·BH3 was found to result in
partial decomposition of the metal complex with the formation
of Bu3P·BH3 after 5 h at 25 ◦C, in addition to unreacted
t
starting materials. The reaction of trans-[PtH2(PMe3)2] with 2
equivalents of PhPH2·BH3 was performed under an atmosphere
of hydrogen, as the dihydride complex has been shown to
slowly decompose to eliminate hydrogen under a nitrogen
atmosphere.24 However, displacement of the phosphine ligands
was again observed with the formation of Me3P·BH3. The
(6)
t
formation of R3P·BH3 (R = Bu, Me) in these reactions likely
arises due to the fact that the trialkylphosphines are much
stronger bases than PhPH2, and thus will undergo exchange with
PhPH2·BH3 to afford the tertiary phosphine–borane adducts. In
order to avoid this complication, reactions involving platinum
dihydrides containing a chelating bis(phosphine) were investi-
gated, as dissociation from the metal center would be inhibited.
Synthesis of cis-[PtH(PhRP·BH3)(dcype)] (1: R = H; 2: R = Ph)
It is known that platinum dihydride complexes with a cis
geometry are prone to hydrogen elimination. However, the use
of ligands with bulky substituents can help to stabilize these
complexes and prevent decomposition.22 For this reason, the
chelating ligand 1,2-bis(dicyclohexylphosphino)ethane (dcype)
was employed as the large cyclohexyl groups should ensure
sufficient steric protection. The complex cis-[PtH2(dcype)] was
readily prepared from the reaction of the corresponding dichlo-
ride cis-[PtCl2(dcype)] with 2 equivalents of “superhydride”
Li[BEt3H]. It has been previously shown that cis-[PtH2(dcype)]
undergoes slow, reversible loss of hydrogen to afford the binu-
clear complex [(dcype)Pt(l-H)]2 under a nitrogen atmosphere.23
However, in our case [(dcype)Pt(l-H)]2 was either not observed,
or was formed only in very small quantities (<5%) when the
reaction was performed under an atmosphere of nitrogen (1 h,
25 ◦C). The addition of 1 equivalent of PhPH2·BH3 to a solution
of cis-[PtH2(dcype)] (prepared in situ) was found to result in a
rapid colour change from red to yellow along with the formation
Fig. 1 Selected NMR spectra of cis-[PtH(PPhH·BH3)(dcype)] 1. (a)
1
31P{ H} NMR: For Pa: JPPcis = 2.6 Hz, JPPtrans = 264 Hz, JPtP = 2282 Hz.
Pb: JPPcis = 2.6 Hz, JPPcis = 15 Hz, JPtP = 1823 Hz. Pc: JPPtrans = 266 Hz,
JPtP = 1887 Hz. A small amount of unreacted PhPH2·BH3 at ca. d
−49 ppm overlaps with the signal due to Pc yielding the observed unequal
doublet. (b) 1H NMR (hydride region): JHPcis = 13 and 26 Hz, JHPtrans
=
164 Hz, JPtH = 913 Hz. The increasing baseline at the left edge of the
spectrum is due to the impending intense resonances of the protons in
the cyclohexyl groups.
of gas bubbles. The gas released was determined to be H2, as
5c,25
indicated by a resonance at d 4.46 ppm (lit. d 4.5 ppm)
in
1
the H NMR spectrum of the reaction mixture. After 24 h,
the H, 11B and 31P NMR spectra all indicated the formation
The reaction of cis-[PtH2(dcype)] with Ph2PH·BH3 was found
to afford the corresponding secondary phosphine–borane com-
plex cis-[PtH(PPh2·BH3)(dcype)] (2), which has many analogous
spectroscopic characteristics to those of 1. For example, the
1
of cis-[PtH(PPhH·BH3)(dcype)] (1) (eqn. (6)). For example,
1
the 31P{ H} NMR spectrum showed three distinct resonances
(Fig. 1(a)), suggesting inequivalency of the phosphorus nuclei
in the dcype ligand. A doublet of doublets was observed at d
77.9 ppm, which is due to the PCy2 group that is arranged trans
to the phosphine–borane moiety (JPP = 264 Hz) and cis to the
other PCy2 group (JPP = 2.6 Hz) with additional 195Pt satellites
(JPPt = 2282 Hz). A second doublet of doublets was observed at
d 66.5 ppm, which is due the PCy2 group that is arranged cis to
both the phosphine–borane moiety (JPP = 15 Hz) and the other
1
31P{ H} NMR spectrum again showed three different res-
onances due to the inequivalent PCy2 groups (d 77.5 and
67.3 ppm) and the PPh2·BH3 moiety (d −5.8 ppm). The hydride
region of the 1H NMR spectrum displayed a doublet of doublet
of doublets at d −1.84 ppm due to coupling with three different
phosphorus nuclei, while the 11B NMR spectrum consisted of a
broad resonance at d −30.5 ppm.
D a l t o n T r a n s . , 2 0 0 5 , 3 2 6 – 3 3 1
3 2 7

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X-Ray quality crystals of 2 were grown from THF–hexanes,26
and the molecular structure is shown in Fig. 2. The geometry
around the Pt center is distorted square planar, with the
hydride and the phosphine–borane moiety in a cis arrangement.
Large angles of 170(2) and 176.10(8)◦ were observed between
the trans substituents (H–Pt–P and P–Pt–P, respectively). The
S,R) diastereomers due to the four different substituents on
phosphorus (Pt, H, B and Ph). Based on the previous assignment
of cis-[Pt(PPhH·BH3)2(depe)] and the trend in the 31P chemical
shifts, we can tentatively assign 3ꢀ to be the rac diastereomer
14b
and 3ꢀꢀ to be the meso diastereomer. However, structural deter-
mination by X-ray crystallography would be required to confirm
this assignment. In addition, the complex multiplets observed at
d 64.6 and 65.3 ppm occur as a result of a non-first order AAꢀXXꢀ
˚
Pt–H bond length was determined to be 1.70(7) A, slightly
˚
longer than the 1.59(4) A found in the analogous complex cis-
14b
14b
[PtH(PPh2·BH3)(depe)]. For the phosphine–borane moiety,
spin system due to the chiral phosphorus centers. However,
˚
Pt–P and P–B bond lengths of 2.332(2) and 1.944(11) A were
as 3 was synthesized by a salt metathesis reaction and not by
a consecutive oxidative-addition/reductive-elimination reaction
sequence, steric hindrance can not be completely eliminated as
a valid reason to explain the lack of reactivity. For example, the
insertion of the Pt center in 1 into the P–H bond of PhPH2·BH3
would likely give an intermediate octahedral Pt(IV) complex
[PtH2(PPhH·BH3)2(dcype)], which could reductively eliminate
H2 to give 3. However, if this intermediate complex is too
sterically hindered, the initial oxidative-addition reaction would
not be favoured and only monosubstitution might result. In
addition, reactions involving 1 and PhPH2·BH3 may require
more forcing conditions that were not investigated during the
course of this study.
found, respectively. For the chelating phosphine, Pt–P bond
˚
lengths of 2.269(2) and 2.312(2) A were observed with a P–
Pt–P bite angle of 87.12(7)◦. The Pt–P bond trans to the
hydride ligand was found to be much longer than the Pt–P
bond cis to the hydride, which likely arises from the larger
trans influence exerted by the hydride ligand compared to the
phosphine–borane moiety. Similar bonding behaviour has been
14b
observed in the complexes cis-[PtH(PPh2·BH3)(depe)] and cis-
[PtH{P(O)Ph2}{PPh2(OH)}(PEt3)].27
(7)
Synthesis of cis-[PtH(PhRP)(dcype)] (4: R = H; 5: R = Ph)
With the reactivity of cis-[PtH2(dcype)] with primary and
secondary phosphine–borane adducts established, the reaction
of uncoordinated phosphines bearing P–H bonds was also
investigated. The treatment of cis-[PtH2(dcype)] with PhPH2
was found to result in a colour change from red to yellow and
the formation of H2 gas. Again, the spectroscopic characteristics
were consistent with the formation of cis-[PtH(PhPH)(dcype)]
Fig. 2 Molecular structure of cis-[PtH(PPh2·BH3)(dcype)] 2. Selected
◦
˚
bond lengths (A) and angles ( ): Pt(1)–P(1) 2.269(2), Pt(1)–P(2)
2.312(2), Pt(1)–P(3) 2.332(2), Pt(1)–H(1Pt) 1.70(7), P(3)–B(1)
1.944(11), P(1)–C(1) 1.855(8), P(2)–C(2) 1.839(8), P(1)–C(21) 1.861(7),
P(2)–C(27) 1.832(7), P(3)–C(3) 1.819(8), P(3)–C(9) 1.823(7), C(1)–C(2)
1.554(10); P(1)–Pt(1)–H(1Pt) 83(2), P(2)–Pt(1)–H(1Pt) 170(2),
P(3)–Pt(1)–H(1Pt) 93(2), P(1)–Pt(1)–P(2) 87.12(7), P(1)–Pt(1)–P(3)
176.10(8), P(2)–Pt(1)–P(3) 96.77(8), B(1)–P(3)–Pt(1) 123.7(4).
1
(4) (eqn. (8)). For example, the 31P{ H} NMR spectrum
showed the presence of three resonances due to three different
phosphorus nuclei. The two PCy2 groups displayed resonances
at d 79.3 and 65.5 ppm, while the PPhH group showed a signal
at d −29.5 ppm with a resolved cis coupling of JPP = 13 Hz.
The 1H coupled 31P NMR spectrum of 4 showed that the latter
signal was further split into a doublet of doublets with a large
Synthesis of cis-[Pt(PhPH·BH3)2(dcype)] (3)
1
coupling to the PH hydrogen atom (JPH = 269 Hz). The H
One noteworthy observation for the reactivity of 1 and 2 was
that only mono-substituted complexes were formed during
the dehydrocoupling reactions. For example, the treatment
of 1 with a second equivalent of PhPH2·BH3 was found to
result in no further reaction at 25 ◦C. This reactivity is in
contrast to the initial dehydrocoupling reaction observed in
which the di-substituted complex cis-[Pt(PPhH·BH3)2(depe)]
was formed from the reaction of cis-[PtH(PPhH·BH3)(depe)]
NMR spectrum showed two key resonances associated with
4. A broad doublet at d 6.06 ppm due to the PH hydrogen
atom was observed, as well as a doublet of doublet of doublets
at d −2.63 ppm with associated 195Pt satellites, which is due
to the PtH hydrogen atom. Similarly, the reaction of cis-
[PtH2(dcype)] with Ph2PH was found to result in the formation
of cis-[PtH(PPh2)(dcype)] (5), as evidenced by three 31P NMR
resonances at d 75.8, 61.8 and 13.8 ppm and a 1H NMR hydride
resonance at d −3.38 ppm, which occurred as the expected
doublet of doublet of doublets with associated 195Pt satellites.
14b
with PhPH2·BH3. The larger cyclohexyl substituents on the
dcype ligand in 1 and 2 might be expected to sterically shield the
Pt center and prevent close approach of a second phosphine–
borane adduct. This would explain the lack of reactivity towards
di-substitution compared to the previously reported depe com-
14b
plex that contains smaller ethyl substituents. Contrary to this
explanation, it was found that the di-substituted species cis-
[Pt(PhPH·BH3)2(dcype)] (3) resulted from the reaction of cis-
[PtCl2(dcype)] with 2 equivalents of Li[PPhH·BH3] (eqn. (7)).
1
For complex 3, the 31P{ H} NMR spectrum showed the presence
of two species with resonances at d 64.6 and −36.6 ppm for 3ꢀ
and d 65.3 and -46.3 ppm for 3ꢀꢀ. These isomers are expected
to be a mixture of rac (R,R and S,S) and meso (R,S and
(8)
3 2 8
D a l t o n T r a n s . , 2 0 0 5 , 3 2 6 – 3 3 1

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As the P–H hydrogen substituents in borane-complexed
phosphines would be expected to be more acidic those of
the corresponding free phosphines, phosphine–borane adducts
might be anticipated to undergo more facile reaction with basic
transition metal hydrides to form dihydrogen due to this greater
inherent polarity difference. However, no difference in reactivity
between coordinated and uncoordinated free phosphine was
observed in this study, suggesting that the acidity of the P–H
hydrogen substituents does not affect the reactivity in this case.
or external BF3·Et2O (11B) or H3PO4 (31P) standards. NMR
spectra were obtained at 300 or 400 MHz (1H), 96 MHz (11B),
75 or 100 MHz (13C) or 121 MHz (31P). Mass spectra were
obtained with a VG 70-250S mass spectrometer operating in
electron impact (EI) mode. Melting points were performed in
sealed capillary tubes and are uncorrected. Infrared spectra were
obtained on a Perkin Elmer Spectrum One FT-IR spectrometer
using KBr windows.
X-Ray structural characterization
Mechanism for the formation of 1, 2, 4 and 5
Diffraction data were collected on a Nonius Kappa-CCD using
graphite-monochromated Mo-Ka radiation (k = 0.71073 A).
˚
The formation of complexes 1, 2, 4 and 5 may be expected to
occur by consecutive oxidative-addition/reductive-elimination
reactions. For example, the insertion of the Pt center in cis-
[PtH2(dcype)] into a P–H bond may give an intermediate
octahedral polyhydride complex (e.g. [Pt(H)3(PPh2)(dcype)] in
the case of 5), which could undergo reductive-elimination of
H2 to yield a mono-substituted complex. Alternatively, the
reductive-elimination of H2 from cis-[PtH2(dcype)] may give
[Pt(dcype)], which could undergo oxidative-addition with a P–H
bond to afford the mono-substituted complex. Unfortunately,
no evidence for any intermediate complexes were observed in
the NMR spectra of the reaction mixtures. Notably, Bo¨hm and
Brookhart and co-workers have reported the catalytic dehydro-
coupling of secondary phosphines using the late transition metal
The data were integrated and scaled using the Denzo-SMN
package.31 The structure was solved and refined with the
SHELXTL-PC V5.1 software package.32 Refinement was by full-
matrix least squares on F2 using all data (negative intensities
included). The molecular structure is presented with thermal
ellipsoids at a 30% probability level and all hydrogen atoms
attached to carbon are omitted for clarity. The hydrogen
atoms bonded to carbon were included in calculated positions
and treated as riding atoms, while those attached to boron
or platinum were located and refined with isotropic thermal
parameters.
Crystallographic data and summary of data collection and re-
finement for 2. Empirical formula: C38H62BP3Pt, Mr = 817.69,
5c
=
catalyst [Cp*Rh(CH2 CH(SiMe3))2]. They found that the P–
˚
T = 150(1) K, k = 0.71073 A, monoclinic, space group P21/n,
H bonds of two phosphine ligands underwent oxidative-addition
at the Rh(I) center to afford a detectable Rh(V) dihydride
intermediate [Cp*Rh(H)2(PR2)2]. This intermediate was then
observed to reductively eliminate H2 and R2P–PR2 and return
to the Rh(I) oxidation state. This type of reaction sequence may
parallel the observed reactivity of the phosphine or phosphine–
borane species at the Pt center in our case.
crystal size = 0.10 × 0.10 × 0.06 mm, a = 10.7765(6), b =
◦
˚
20.0924(12), c = 17.4561(12) A, b = 100.571(3) , V = 3715.5(4)
3
−3
−1
˚
A , Z = 4, Dc = 1.462 g cm , l = 3.931 mm , F(000) = 1672,
h range = 2.58–24.99◦, index ranges: −12 ≤ h ≤ 12, −21 ≤ k ≤
23, −20 ≤ l ≤ 20, reflns. collected = 18649, ind. reflns. = 6408,
Rint = 0.0861, GoF on F2 = 1.031, R1 (I > 2r(I)) = 0.0478, wR2
−3
˚
(all data) = 0.1154, peak/hole = 1.609/−2.218 e A .
CCDC reference number 249141. See http://www.rsc.org/
suppdata/dt/b4/b416114a/ for crystallographic data in CIF
or other electronic format.
Summary
The reaction of the dihydride complex cis-[PtH2(dcype)] with
primary and secondary phosphine–borane adducts or phos-
phines has been shown to afford the mono-substituted com-
plexes 1, 2, 4 and 5 via dehydrocoupling between the Pt–H and
P–H bonds. The formation of di-substituted species were not
observed, which may be due to the potentially unfavourable
steric hindrance present in a Pt(IV) intermediate. With further
development, this dehydrocoupling route may prove to be a
general method for the formation of new Pt–P bonds which
does not rely on metathesis-type salt elimination reactions.
Synthesis of cis-[PtCl2(dcype)]
To a solution of (PhCN)2PtCl2 (0.369 g, 0.781 mmol) in CH2Cl2
(5 mL), a solution of dcype (0.329 g, 0.778 mmol) in CH2Cl2
(2 mL) was added dropwise at 25 C. The solution was stirred
◦
for 4 h and the volatiles were removed to give cis-[PtCl2(dcype)]
as a pale yellow solid. Yield: 0.526 g (98%). 1H NMR (300 MHz,
CD2Cl2): d 2.7 (br, PCH2), 2.34 (m, Cy), 2.2 (br, Cy), 2.0–1.6 (m,
1
Cy), 1.4–1.2 (m, Cy). 31P{ H} NMR (CD2Cl2): d 64.7 (s, JPPt
=
3574 Hz).
Reaction of trans-[PtH2(PtBu3)2] with 2 equiv. PhPH2·BH3
Experimental
To a solution of trans-[PtH2(PtBu3)2] (0.054 g, 0.090 mmol) in
C6D6 in a 5 mm NMR tube, a solution of PhPH2·BH3 (0.023 g,
0.19 mmol) in C6D6 was added at 25 ◦C. After 5 h, the 11B and
31P NMR spectra of the reaction mixture showed the presence
of unreacted trans-[PtH2(PtBu3)2] and PhPH2·BH3, and also
tBu3P·BH3 (dP 58.9 (q, JPB = 56 Hz), dB −40.8 (d, JBP = 56 Hz);
lit. dP 58.5 (JPB = 59 Hz), dB −40.8 (JBP = 58 Hz)).33
General procedures and materials
All reactions and product manipulations were performed un-
der an atmosphere of dry nitrogen using standard Schlenk
techniques or in an inert atmosphere glovebox filled with
dry nitrogen unless otherwise specified. Hexanes was dried
via the Grubb’s method28 while THF and CH2Cl2 were dried
over Na/benzophenone and CaH2, respectively, and distilled
prior to use. Li[BEt3H] (1.0 M in THF), Na (Aldrich), dcype,
Ph2PH, PhPH2 (10 wt% in hexanes) (Strem Chemicals) were
purchased and used as received. Naphthalene (Aldrich) was sub-
limed prior to use. trans-[PtH2(PtBu3)2],29 cis-[PtCl2(PMe3)2],24
Reaction of trans-[PtH2(PMe3)2] with 2 equiv. PhPH2·BH3
A green solution of Na[naphthalide] was prepared from the
reaction of Na (0.178 g, 7.74 mmol) and naphthalene (0.277 g,
2.16 mmol) in THF (7.8 mL) at 25 ◦C for 1.5 h. Under a H2
atmosphere, the above solution of Na[naphthalide] (3.6 mL, ca.
1.0 mmol) was added to a solution of cis-[PtCl2(PMe3)2] (0.208 g,
0.497 mmol) in THF (15 mL) at 0 ◦C. The mixture was stirred
for 30 min, then warmed to 25 ◦C to give a brown solution
of trans-[PtH2(PMe3)2]. To this solution, PhPH2·BH3 (0.123 g,
0.992 mmol) in THF (3 mL) was added. After 3.5 h, the 11B and
31P NMR spectra of the reaction mixture showed the presence of
(PhCN)2PtCl2,30 Ph2PH·BH3 and PhPH2·BH3 were synthe-
9b
9b
sized by literature procedures.
Equipment
NMR spectra were recorded on a Varian Gemini 300 MHz
or a Varian Unity 400 MHz spectrometer. Chemical shifts are
reported relative to residual protonated solvent peaks (1H, 13C)
D a l t o n T r a n s . , 2 0 0 5 , 3 2 6 – 3 3 1
3 2 9

View Article Online
Me3P·BH3 (dP −1.1 (q, JPB = 60 Hz), dB −36.9 (d, JBP = 59 Hz);
lit. dP −1.8 (JPB = 59.8 Hz), dB −36.0 (JBP = 59.8 Hz)).34
second equivalent of PhPH2·BH3 (0.007 g, 0.06 mmol) in C6D6
was added. After 24 h, the 31P NMR spectrum indicated the
presence of 1 and unreacted PhPH2·BH3 with no evidence of
any di-substituted species.
Synthesis of cis-[(dcype)PtH(PPhH·BH3)] (1)26
In a 5 mm NMR tube, cis-[PtCl2(dcype)] (0.039 g, 0.057 mmol)
was suspended in C6D6, and a solution of Li[BEt3H] in THF
(0.11 mL, 0.11 mmol) was added via syringe. After 1 h at
25 ◦C, the formation of cis-[PtH2(dcype)] was complete as
Synthesis of cis-[(dcype)Pt(PPhH·BH3)2] (3)
A solution of nBuLi in hexanes (1.05 mL, 1.68 mmol) was added
dropwise to a solution of PhPH2·BH3 (0.209 g, 1.69 mmol) in
THF (14 mL) cooled to 0 ◦C. The mixture was warmed to
25 ◦C, and 3 mL of solution (corresponding to ca. 0.36 mmol of
Li[PPhH·BH3]) was removed and added dropwise to a solution
of cis-[PtCl2(dcype)] (0.123 g, 0.179 mmol) in CH2Cl2 (5 mL)
1
indicated by 31P{ H} NMR: d 77.2 (s, JPPt = 1875 Hz); lit. d
78.2 (s, JPPt = 1822 Hz).23 A solution of PhPH2·BH3 (0.007 g,
0.06 mmol) in C6D6 was added via syringe and the formation of
bubbles were observed. The initia◦l orange–red solution turned
yellow in colour after 24 h at 25 C. The solution was filtered
and the volatiles were removed in vacuo. The residue was
washed with hexanes (4 × 10 mL), and the residual solvent
removed to give 1 as a yellow solid. Crude yield: 0.020 g
(48%). Attempts at recrystallization from THF–hexanes by
vapour diffusion first afforded a dark yellow oil in which pale
yellow crystals of 1 were embedded and could not be cleanly
separated. The crystals were determined to be ca. 95% pure by
1H NMR. Attempts at recrystallization by other methods (slow
evaporation, solvent layering, cooling saturated solutions) all
resulted in the precipitation of either impure powders or oils.
1H NMR (400 MHz, CD2Cl2): d 7.84 (m, Ph), 7.70 (m, Ph), 4.7
(d br, JHP = 323 Hz, PH), 2.0–1.5 (m, PCH2 and Cy), 1.4–1.0
◦
at 25 C. After stirring the mixture for 18 h, the volatiles were
removed, and the yellow oily residue was dissolved in CH2Cl2
(10 mL). The solution was filtered and hexanes (40 mL) added
to precipitate a solid. The supernatant was decanted and the
residual solvent was removed in vacuo to give 3 as a yellow solid.
Pale yellow crystals were obtained by slow evaporation of a
CH2Cl2–hexanes solution (1 : 1) over 3–4 days at 25 ◦C. Despite
1
confirming the purity of 3 by H NMR spectroscopy, suitable
elemental analysis could not be obtained. Yield: 0.096 g (62%).
Mp 129–131 ◦C. IR (Nujol): 2335 (mBH), 2247 (mPH) cm−1. EI-MS
+
(70 eV): m/z 833 (M+ − 2 BH3 − 2H, 4%), 435 (dcypeBH2
,
12%).
3ꢀ (rac diastereomer): 1H NMR (CD2Cl2): d 7.58 (m, Ph), 7.24
(m, Ph), 4.7 (d br, JHP = 341 Hz, PH), 2.68 (m, PCH2), 2.30
(m, Cy), −2.63 (ddd, JHPtrans = 164 Hz, JHPcis = 26 Hz, JHPcis
=
1
13 Hz, JHPt = 913 Hz, PtH). 11B{ H} NMR (C6D6): d −33.6 (br).
(m, PCH2), 1.9–1.6 (m, Cy), 1.4–1.0 (m, Cy). 11B{ H} NMR
1
1
13C{ H} NMR (125 MHz, CD2Cl2): d 135.9 (Ph), 129.5 (Ph),
1
(CD2Cl2): d −36.7 (br). 13C{ H} NMR (CD2Cl2): d 135.2 (d,
128.2 (d, JCP = 8.8 Hz, Ph), 36.5–35.8 (PCH2), 29.6 (m, Cy),
JCP = 8.4 Hz, Ph), 134.1 (d, JCP = 34 Hz, ipso-Ph), 129.4 (s, Ph),
128.3 (d, JCP = 8.3 Hz, Ph), 36.3 (m, PCH2), 33.0 (m, Cy), 30.3
1
27.6–27.0 (m, Cy), 26.6–26.2 (m, Cy). 31P{ H} NMR (C6D6):
d 77.9 (dd, JPPcis = 2.6 Hz, JPPtrans = 264 Hz, JPPt = 2282 Hz,
PCy2), 66.5 (dd, JPPcis = 2.6 Hz, JPPcis = 15 Hz, JPPt = 1823 Hz,
PCy2), −50.6 (d br, JPPtrans = 266 Hz, JPPt = 1887 Hz, PHPh).
IR (CH2Cl2): 2358 (mBH), 2197 (mPH), 2004 (mPtH) cm−1. EI-MS (70
eV): m/z 725 (M+ − BH3 − 2H, 3%).
1
(m, Cy), 27.6–26.8(m, Cy), 26.6(s, Cy). 31P{ H} NMR(CD2Cl2):
d 64.6 (m, JAX = JA X
ꢀ
= 224 Hz, JAX = JA X
ꢀ
ꢀ
= −20 Hz, JXX
ꢀ
=
8.4 Hz, JAA
ꢀ
=ꢀ0 Hz, JPPt = 2170 Hz, PCy2), −36.6 (d br, JPPtrans
=
244 Hz, JPPt = 1725 Hz, PHPh).
3ꢀ (meso diastereomer): H NMR (CD2Cl2): d 7.84 (m, Ph),
1
7.30 (m, Ph), 4.7 (d br, JHP = 341 Hz, PH), 2.68 (m, PCH2), 2.30
Synthesis of cis-[(dcype)PtH(PPh2·BH3)] (2)26
(m, PCH2), 1.9–1.6 (m, Cy), 1.4–1.0 (m, Cy). 11B{ H} NMR
1
1
(CD2Cl2): d −36.7 (br). 13C{ H} NMR (CD2Cl2): d ipso-Ph not
Complex 2 was prepared by a procedure similar to 1 using
cis-[PtCl2(dcype)] (0.039 g, 0.057 mmol), Li[BEt3H] in THF
(0.11 mL, 0.11 mmol) and Ph2PH·BH3 (0.011 g, 0.055 mmol).
Crude yield: 0.016 g (32%). Attempts at recrystallization from
THF/hexanes by vapour diffusion afforded a brown oil in which
colourless, X-ray quality crystals of 2 were embedded and could
not be cleanly separated. The crystals were determined to be ca.
observed, 135.8 (d, JCP = 7.6 Hz, Ph), 129.5 (s, Ph), 128.2 (d,
JCP = 8.4 Hz, Ph), 36.2 (m, PCH2), 30.7 (m, Cy), 29.6 (m, Cy),
1
27.6–26.8 (m, Cy), 26.1 (s, Cy). 31P{ H} NMR (CD2Cl2): d 65.3
= 0 Hz, JPPt = 2135 Hz, PCy2), −46.3 (d br, JPPtransꢀ = 257 Hz,
(m, JAX
JAA
ꢀ
= JA X
ꢀ
= 223 Hz, JAX = JA X = −20 Hz, JXX = 7.0 Hz,
ꢀ
ꢀ
ꢀ
JPPt = 1755 Hz, PHPh).
1
97% pure by H NMR. Similar to that of 1, all other attempts
Synthesis of cis-[(dcype)PtH(PPhH)] (4)26
at recrystallization by different methods (slow evaporation,
solvent layering, cooling saturated solutions) resulted in the
precipitation of either impure powders or oils. 1H NMR
(300 MHz, C6D6): d 8.31 (m, Ph), 7.21 (m, Ph), 7.05 (m, Ph),
2.59 (m, PCH2), 2.24 (m, PCH2), 1.7 -1.4 (m, Cy), 1.23 (m, Cy),
1.03 (m, Cy), −1.84 (ddd, JHPtrans = 171 Hz, JHPcis = 13 Hz,
Complex 4 was prepared by a procedure similar to 1 us-
ing cis-[PtCl2(dcype)] (0.042 g, 0.061 mmol), Li[BEt3H] in
THF (0.12 mL, 0.12 mmol) and PhPH2 in hexanes (0.008 g,
0.073 mmol). Crude yield: 0.024 g (55%). Attempts at recrystal-
lization from THF–hexanes by vapour diffusion afforded small
clusters of pale yellow microcrystals of 4 embedded in a brown
oil which could not be cleanly separated. The crystals were
1
JHPcis = 6.4 Hz, JHPt = 961 Hz, PtH). 11B{ H} NMR (C6D6):
1
d −30.5 (br). 13C{ H} NMR (125 MHz, CD2Cl2): d 134.6 (br,
ipso-Ph), 128.5 (Ph), 128.1 (Ph), 127.7 (d, JCP = 8.4 Hz, Ph), 32.2
1
determined to be ca. 93% pure by H NMR. All attempts to
1
(Cy), 30.3 (Cy), 28–26 (m, PCH2), 23.2 (Cy), 14.4 (Cy). 31P{ H}
recrystallize 4 by other methods (e.g. slow evaporation, solvent
layering, cooling ◦saturated solutions) did not result in pure
samples. Mp 150 C. 1H NMR (400 MHz, CD2Cl2): d 7.69 (m,
Ph), 7.27 (m, Ph), 6.06 (d br, JHP = 250 Hz, PH), 2.1–1.5 (m,
PCH2 and Cy), 1.4–1.0 (m, Cy), −2.63 (ddd, JHPtrans = 122 Hz,
NMR (C6D6): d 77.5 (dd, JPPcis = 3.2 Hz, JPPtrans = 266 Hz, JPPt
2220 Hz, PCy2), 67.3 (dd, JPPcis = 3.2 Hz, JPPcis = 9.7 Hz, JPPt
=
=
1873 Hz, PCy2), −5.8 (d br, JPPtrans = 254 Hz, JPPt = 2121 Hz,
PPh2). IR (CH2Cl2): 2358 (mBH), 2032 (mPtH) cm−1. EI-MS (70 eV):
m/z 817 (M+, 1%), 803 (M+ − BH3, 2%).
JHPcis = 19 Hz, JHPcis = 9 Hz, JHPt = 682 Hz, PtH). 13C{ H}
1
NMR (125 MHz, CD2Cl2): d 128.4 (d, JCP = 9 Hz, Ph), 37–
Attempted reaction of cis-[PtH2(dcype)] with 2 equiv. of
PhPH2·BH3
In a 5 mm NMR tube, cis-[PtCl2(dcype)] (0.021 g, 0.030 mmol)
was dissolved in C6D6, and a solution of Li[BEt3H] in THF
(0.06 mL, 0.06 mmol) was added via syringe. After 1 h at 25 ◦C, a
solution of PhPH2·BH3 (0.008 g, 0.06 mmol) in C6D6 was added
via syringe. Upon complete conversion to 1 (18 h, 25 ◦C), a
35 (m, PCH2), 31–30 (m, Cy), 30–29 (m, Cy), 27.5–27 (m, Cy),
1
26.7–26.3 (m, Cy). 31P{ H} NMR (C6D6): d 79.3 (d, JPPtrans
=
228 Hz, JPPt = 2310 Hz, PCy2), 65.5 (d, JPPcis = 13 Hz, JPPt
=
1806 Hz, PCy2), −29.5 (dd, JPPcis = 13 Hz, JPPtrans = 228 Hz,
JPPt = 1642 Hz, PHPh). Selected 31P NMR (C6D6): d −29.4
(dd br, JPH = 269 Hz). IR (Nujol): 2308 (mPH), 2000 (mPtH) cm−1.
EI-MS (70 eV): m/z 617 (dcypePt, 23%).
3 3 0
D a l t o n T r a n s . , 2 0 0 5 , 3 2 6 – 3 3 1

View Article Online
Synthesis of cis-[(dcype)PtH(PPh2)] (5)26
10 C. A. Jaska, A. Bartole-Scott and I. Manners, Dalton Trans., 2003,
4015.
Complex 5 was prepared by a procedure similar to 1 using
cis-[PtCl2(dcype)] (0.040 g, 0.058 mmol), Li[BEt3H] in THF
(0.12 mL, 0.12 mmol) and Ph2PH (0.011 g, 0.059 mmol).
Crude yield: 0.030 g (64%). Attempts at recrystallization from
THF/hexanes by vapour diffusion occasionally produced pale
brown crystals of 5 that were embedded in a dark brown
oil and could not be cleanly separated. The crystals were
determined to be ca. 90% pure by 1H NMR. All other attempts
at recrystallization by other methods (e.g. slow evaporation,
solvent layering, cooling saturated solutions) did not result
in crystalline material, only impure powders or oils. Mp 149–
153 ◦C. 1H NMR (400 MHz, CD2Cl2): d 7.77 (m, Ph), 7.39 (m,
Ph), 7.30 (m, Ph), 2.2–1.7 (m, PCH2 and Cy), 1.5–1.1 (m, Cy),
−3.38 (ddd, JHPtrans = 121 Hz, JHPcis = 21 Hz, JHPcis = 7.8 Hz,
11 (a) C. A. Jaska, K. Temple, A. J. Lough and I. Manners, Chem.
Commun., 2001, 962; (b) C. A. Jaska, K. Temple, A. J. Lough and I.
Manners, J. Am. Chem. Soc., 2003, 125, 9424.
12 C. A. Jaska and I. Manners, J. Am. Chem. Soc., 2004, 126, 2698.
13 (a) C. A. Jaska and I. Manners, J. Am. Chem. Soc., 2004, 126, 1334;
(b) C. A. Jaska and I. Manners, J. Am. Chem. Soc., 2004, 126, 9776.
14 (a) H. Dorn, C. A. Jaska, R. A. Singh, A. J. Lough and I. Manners,
Chem. Commun., 2000, 1041; (b) C. A. Jaska, H. Dorn, A. J. Lough
and I. Manners, Chem. Eur. J., 2003, 9, 271.
15 For other examples of transition metal phosphine–borane complexes,
see the following: For M–PB complexes: (a) K. Kubo, I. Kane-
mitsu, E. Murakami, T. Mizuta, H. Nakazawa and K. Miyoshi,
J. Organomet. Chem., 2004, 689, 2425; (b) J. R. Moncarz, T. J.
Brunker, D. S. Glueck, R. D. Sommer and A. L. Rheingold, J. Am.
Chem. Soc., 2003, 125, 1180; (c) U. Vogel, P. Hoemensch, K. C.
Schwan, A. Y. Timoshkin and M. Scheer, Chem. Eur. J., 2003, 9, 515;
(d) S. J. Lancaster, A. J. Mountford, D. L. Hughes, M. Schormann
and M. Bochmann, J. Organomet. Chem., 2003, 680, 193; (e) A. C.
Gaumont, M. B. Hursthouse, S. J. Coles and J. M. Brown, Chem.
Commun., 1999, 63; (f) S. Moreton, Inorg. Chim. Acta, 1994, 215,
67; (g) W. Angerer, W. S. Sheldrick and W. Malisch, Chem. Ber.,
1985, 118, 1261. For M–BP complexes; (h) T. Yasue, Y. Kawano and
M. Shimoi, Angew. Chem., Int. Ed., 2003, 42, 1727; (i) T. Yasue, Y.
Kawano and M. Shimoi, Chem. Lett., 2000, 58; (j) Y. Kawano, T.
Yasue and M. Shimoi, J. Am. Chem. Soc., 1999, 121, 11744; (k) M.
Shimoi, S. Ikubo, Y. Kawano, K. Katoh and H. Ogino, J. Am. Chem.
Soc., 1998, 120, 4222; (l) D. J. Elliot, C. J. Levy, R. J. Puddephatt,
D. G. Holah, A. N. Hughes, V. R. Magnuson and I. M. Moser, Inorg.
Chem., 1990, 29, 5014.
1
JHPt = 656 Hz, PtH). 13C{ H} NMR (125 MHz, CD2Cl2): d 128.6
(d, JCP = 11 Hz, Ph), 128.3 (br, Ph), 127.8 (d, JCP = 9 Hz, Ph),
37–36 (m, PCH2), 30.5–29.5 (m, Cy), 28.9–28.6 (m, Cy), 27.7–27
1
(m, Cy), 26.8–26.2 (m, Cy). 31P{ H} NMR (C6D6): d 75.8 (dd,
JPPcis = 5.2 Hz, JPPtrans = 283 Hz, JPPt = 2263 Hz, PCy2), 61.8
(d, JPPcis = 14 Hz, JPPt = 2004 Hz, PCy2), 13.8 (dd, JPPtrans
=
228 Hz, JPPcis = 10 Hz, JPPt = 2006 Hz, PPh2). IR (Nujol): 1997
(mPtH) cm−1. EI-MS (70 eV): m/z 802 (M+ − H, 3%).
Acknowledgements
C. A. J. is grateful for a Natural Sciences and Engineering
Research Council of Canada (NSERC) scholarship (2002–2004)
and I. M. thanks NSERC for a Discovery Grant and the
Canadian Government for a Canada Research Chair.
16 M. J. Michalczyk, C. A. Recatto, J. C. Calabrese and M. J. Fink,
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19 J. Chatt, L. A. Duncanson and B. L. Shaw, Proc. R. Chem. Soc.
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D a l t o n T r a n s . , 2 0 0 5 , 3 2 6 – 3 3 1
3 3 1