Synthesis, structural characterization, and reactivity of Cp*Ru(N -phosphinoamidinate) complexes

Article abstract of DOI:10.1139/cjc-2013-0474

We report herein on the synthesis and spectroscopic/crystallographic characterization of the first isolable, formally 16-electron Cp*Ru(κ²-P～N) species, which are supported by N-phosphinoamidinate ligands. Despite the stability of such complexe

Full text of DOI:10.1139/cjc-2013-0474

194
ARTICLE
Synthesis, structural characterization, and reactivity of
Cp*Ru(N-phosphinoamidinate) complexes
Colin M. Kelly, Adam J. Ruddy, Craig A. Wheaton, Orson L. Sydora, Brooke L. Small, Mark Stradiotto,
and Laura Turculet
Abstract: We report herein on the synthesis and spectroscopic/crystallographic characterization of the first isolable, formally
16-electron Cp*Ru(␬2-PϳN) species, which are supported by N-phosphinoamidinate ligands. Despite the stability of such com-
plexes, they have been shown to readily coordinate two-electron (L) donors including carbon monoxide and 2,6-xylylisocyanide,
affording crystallographically characterized 18-electron Cp*Ru(L)(␬2-PϳN) adducts. Preliminary reactivity studies confirm that
such complexes are capable of extruding hydrogen from ammonia borane.
Key words: N-phosphinoamidinate, ruthenium, ligand design, coordinative unsaturation.
Résumé : Nous décrivons la synthèse et la caractérisation spectroscopique/cristallographique des premières espèces isolables
Cp*Ru(␬2-PϳN) formellement a` 16 électrons, qui sont supportées par des ligands N-phosphinoamidinate. Malgré leur stabilité, on
a montré que ces complexes forment facilement une liaison de coordination avec des donneurs de doublet d'électrons (L), y
compris le monoxyde de carbone et le 2,6-xylylisocyanure, pour donner des adduits Cp*Ru(L)(␬2-PϳN) a` 18 électrons caractérisés
par cristallographie. Les études de réactivité préliminaires confirment que ces complexes sont capables d'extraire l'hydrogène de
l'ammonia borane. [Traduit par la Rédaction]
Mots-clés : N-phosphinoamidinate, ruthénium, conception de ligands, insaturation coordinative.
Control experiments featured in these reports confirm the impor-
tance of tethered phosphino and primary/secondary amine moi-
Introduction
Coordinatively unsaturated Cp*RuLn (Cp* = ␩5-C5Me5) and re-
eties as a means of achieving optimal catalytic performance via
lated complexes have a well-established track record of exhibiting
Ru/NH bifunctional catalysis.22,23 However, despite recent re-
new and unusual metal-centered reactivity,1,2 with diverse appli-
search efforts,24,25 neither [Cp*Ru(␬2-PϳN)]+X− nor related neutral
cations in organic synthesis including but not restricted to redox
isomerization/reductions, alkene−alkyne coupling, and cycloaddition
Cp*Ru(␬2-PϳN) species of the type invoked by Ikariya and co-
workers featuring a tethered amido-phosphine ancillary ligand
chemistry.3–5 As such, considerable focus continues to be directed
have proven isolable prior to our work reported herein.
toward developing new and isolable classes of such complexes
Inspired by the challenge of preparing the first examples of
and exploring their stoichiometric reactivity. Collectively, such
studies serve to enhance our understanding of the substrate trans-
formations that can occur within the coordination sphere of co-
formally 16-electron Cp*Ru(␬2-PϳN) species, we focused our atten-
tion on the application of N-phosphinoamidinate ligands.26
This new P,N-ligand class was developed recently with an aim
ordinatively unsaturated Cp*RuLn species and can represent an
toward supporting highly active chromium-based ethylene tri-/
tetramerization catalysts;26 we have since shown that three-
coordinate (N-phosphinoamidinate)iron(amido) species are highly
effective precatalysts for the hydrosilylation of carbonyl compounds
under mild conditions.27 We report herein on the synthesis and
spectroscopic/crystallographic characterization of the first isolable,
formally 16-electron Cp*Ru(␬2-PϳN) species, along with a brief stoi-
chiometric reactivity survey involving these new complexes.
initial step toward the establishment of new metal-catalyzed
transformations.
Although considerable attention has been paid to the study of
both neutral Cp*RuL(X) complexes 1,6–8 and [Cp*RuL2] + X− salts (A)
(Fig. 1),1,9–12 reports documenting the preparation of isolable, co-
ordinatively unsaturated, and formally 16-electron Cp*Ru(␬2-LϳX)
chelate complexes supported by monoanionic, LX-type ligands are
rare and involve primarily synthetic investigations of ␬2-N,N
amidinate (B)1,2,13 or ␤-diketiminate (C)14,15 complexes. It is wor-
thy of mention that analogous Cp*Ru(␬2-PϳN) species,16 derived
from 2-(diphenylphosphino)ethylamine and related ligands (D),
have been implicated by Ikariya and co-workers as key intermedi-
ates in a diversity of synthetically useful metal-catalyzed trans-
formations including the chemoselective hydrogenolysis of
epoxides,17 the isomerization of allylic alcohols,18 the oxidative
lactonization of 1,4-diols,19 and the hydrogenation of imides.20,21
Results and discussion
Having previously reported on the synthesis of the phos-
phinoamidine ligands 1a and 1b,27 we considered that the reac-
tion of such species with [Cp*RuCl]4 in the presence of a suitable
base could provide access to 16-electron Cp*Ru(N-phosphinoamidinate)
complexes (Scheme 1). Treatment of 1a or 1b with 0.25 equiv. of
[Cp*RuCl]4 in the presence of excess Cs2CO3 afforded the corre-
sponding 16-electron Ru complex 2a or 2b as a blue or dark green
Received 17 October 2013. Accepted 28 November 2013.
C.M. Kelly, A.J. Ruddy, C.A. Wheaton, M. Stradiotto, and L. Turculet. Department of Chemistry, Dalhousie University, 6274 Coburg Road, P.O. Box
15000, Halifax, NS B3H 4R2, Canada.
O.L. Sydora and B.L. Small. Research and Technology, Chevron Phillips Chemical Company, 1862 Kingwood Drive, Kingwood, TX 77339, USA.
Corresponding authors: Orson L. Sydora (e-mail: sydorol@cpchem.com), Mark Stradiotto (e-mail: mark.stradiotto@dal.ca), and Laura Turculet (e-mail:
laura.turculet@dal.ca).
Can. J. Chem. 92: 194–200 (2014) dx.doi.org/10.1139/cjc-2013-0474
Published at www.nrcresearchpress.com/cjc on 23 February 2014.

Kelly et al.
195
Fig. 1. Previously studied [Cp*RuL2]+X− and Cp*Ru(␬2-LϳX) complexes and the new Cp*Ru(N-phosphinoamidinate) complexes featured herein
(Ar = substituted aryl).
Scheme 1. Synthesis of Cp*Ru(N-phosphinoamidinate) complexes 2a and 2b. Conditions: 1a, 0.25 [Cp*RuCl]4, excess Cs2CO3 (for 2a); 1b, nBuLi
(1 equiv., −35 °C) and then 0.25 [Cp*RuCl]4 (for 2b).
solid, respectively (quantitative on the basis of 31P NMR spectros-
copy). Alternatively, treatment of 1b with nBuLi followed by reac-
tion of the ensuing lithium salt with [Cp*RuCl]4 cleanly afforded
dimethyl substituted N-aryl group in 2a gives rise to a single
C(aryl)Me H NMR resonance at 2.27 ppm. In the case of 2b, the
1
2,6-diisopropyl substituted N-aryl group gives rise to a single set
of C(aryl)iPr2 resonances, where the methyl groups on these
substituents are diastereotopic, as indicated by their appearance
as two doublets that integrate to six protons each at 1.37 and
0.80 ppm. The spectroscopic signature of these formally 16-electron,
Cs-symmetric species 2a and 2b differ significantly from their
C1-symmetric 18-electron adducts (vide infra).
The solid-state structures of both 2a and 2b were determined by
using single-crystal X-ray diffraction techniques (Fig. 2; Tables 1
and 2). In both cases, the complexes adopt a monomeric two-
legged piano stool structure that is analogous to that previously
observed for related crystallographically characterized Cp*RuL(X)
complexes1,6–8 as well as complexes of the type Cp*Ru(amidinate)1,13
and Cp*Ru(diketiminate).14,15 The Ru−P distances of 2.3679(5) and
2.3599(5) Å for 2a and 2b, respectively, are slightly shorter than
that of 2.395(2) Å reported for Cp*Ru(PiPr3)Cl,6 possibly due to the
rigid chelating structure of the N-phosphinoamidinate com-
plexes. The Ru−N(2) distance of 2.0734(16) Å in 2b is somewhat
elongated relative to that of 2.0458(13) Å in 2a, which can most
n
2b; in contrast, the use of BuLi in place of Cs2CO3 in the prepa-
ration of 2a afforded multiple phosphorus-containing products,
on the basis of 31P NMR data. Both complexes 2a (67%) and 2b
(using nBuLi, 82%) were readily isolated and appear to be stable at
room temperature under a nitrogen atmosphere both in solution
and in the solid state. The highly colored nature of 2a and 2b is
consistent with previously reported 16-electron Cp*Ru comp-
lexes, including Cp*RuL(X),1,6–8 Cp*Ru(amidinate),1,13 and Cp*Ru
(diketiminate),14,15 which are typically blue or purple in color. The
solution NMR (1H, 13C, 31P) spectra of 2a and 2b (benzene-d6) are
consistent with their formulation as Cs-symmetric, diamagnetic,
N-phosphinoamidinate complexes. The 31P NMR spectra of 2a and
2b feature resonances at 128.2 and 124.9 ppm, which are signifi-
cantly downfield relative to 1a (61.9 ppm) and 1b (61.4 ppm). The
1H NMR spectra (benzene-d6) of 2a and 2b feature a resonance
attributed to the Cp* ligand at 1.21 and 1.19 ppm, respectively, as
well as a resonance at 1.45 and 1.46 ppm, respectively, correspond-
ing to the magnetically equivalent PtBu2 substituents. The 2,6-
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Can. J. Chem. Vol. 92, 2014
Fig. 2. Crystallographically determined structures of 2a (left) and 2b (right) employing 50% ellipsoids and with hydrogen atoms omitted for clarity.
Table 1. Crystallographic solution and refinement data for 2a, 2b, 3, and 4.
2a
2b
3
4
Empirical formula
Wavelength (Å)
Temperature (K)
Formula weight
Crystal dimensions
Crystal system
Space group
a (Å)
b (Å)
c (Å)
␣ (deg)
␤ (°)
C33H47N2PRu
0.71073
173(2)
C37H55N2PRu
0.71073
173(2)
C40H55N2O1.5PRu
1.54178
173(2)
C42H56N3PRu
0.71073
173(2)
603.77
659.87
719.90
734.94
0.40 × 0.29 × 0.17
Triclinic
P(−1)
0.34 × 0.07 × 0.04
Monoclinic
P21/n
14.4690(5)
16.2674(5)
14.9573(5)
90
102.87(1)
90
3432.0(2)
4
0.25 × 0.23 × 0.14
Monoclinic
P21/n
12.1772(5)
15.7345(7)
19.4462(8)
90
94.405(2)
90
3714.9(3)
4
0.44 × 0.31 × 0.07
Triclinic
P(−1)
9.5189(5)
10.5877(5)
15.5381(8)
101.607(1)
98.993(1)
92.575(1)
1510.37(13)
2
9.6910(6)
10.7791(7)
18.5223(12)
82.126(1)
89.982(1)
73.472(1)
1835.9(2)
2
␥ (°)
V (Å3)
Z
␳
calcd. (Mg m−3
)
1.328
0.596
1.277
0.530
1.287
4.072
1.329
0.504
␮ (mm−1
)
Range of trans.
␪ limit (°)
0.9076−0.7949
27.59
0.979−0.8416
27.52
0.5917−0.4353
71.32
0.9656−0.8083
27.54
−12 ≤ h ≤ 12
−13 ≤ k ≤ 13
−20 ≤ l ≤ 20
28597
6961
0.0289
−18 ≤ h ≤ 18
−21 ≤ k ≤ 21
−19 ≤ l ≤ 19
30526
7893
0.0414
−14 ≤ h ≤ 14
−19 ≤ k ≤ 19
−23 ≤ l ≤ 23
24246
7204
0.0439
−12 ≤ h ≤ 12
−13 ≤ k ≤ 14
−23 ≤ l ≤ 24
24290
8369
0.0453
Total data collected
Independent reflections
Rint
Data/restraints/parameters
6961/0/347
1.055
0.0242
0.0558
0.350, −0.394
7893/0/385
1.038
0.0303
0.0699
0.442, −0.377
7204/0/439
1.059
0.0418
0.1110
2.747, −0.560
8369/0/439
1.031
0.0383
0.0757
0.731, −0.644
Goodness-of-fit
R1 [Fo2 ≥ 2␴(Fo2)]a
wR2 [Fo2 ≥ −3␴(Fo2)]a
Largest peak, hole (eÅ−3
)
aR1 = Α| |Fo| − |Fc| |/Α|Fo|. wR2 = [Α[w(Fo2 − Fc2)2]/Α[w(Fo2)2]]1/2. w = 1/[␴2(Fo2) + (mP)2 + nP], where P = (Fo2 + 2Fc2)/3.
Table 2. Selected interatomic distances (Å) and angles (°) for 2a, 2b, 3,
and 4.
likely be ascribed to the greater steric demands of the isopropyl-
functionalized ligand in 2b. Nonetheless, these Ru−N distances
fall within the range observed for crystallographically character-
ized Cp*Ru(amidinate) (2.073(3) Å)13 and Cp*Ru(diketiminate)
(2.025(6)−2.071(2) Å)14,15 complexes. The solid-state structures of 2a
and 2b are consistent with the Cs-symmetric species observed in
solution, as indicated by the perpendicular orientation of the
P−Ru−N(2) plane relative to the plane of the Cp* ligand.
Despite the apparent stability of the coordinatively unsaturated
species 2a and 2b, these complexes proved highly reactive to-
wards two-electron donor ligands, leading to the formation of
18-electron adducts (Scheme 2). Thus, 2b was found to react readily
2a
2b
3a
4b
Ru−P
2.3679(5)
2.3599(5)
2.3652(6)
2.3578(7)
Ru−N(2)
P−N(1)
N(1)−C(9)
(aryl)N(2)−C(9)
P−Ru−N(2)
2.0458(13)
1.7059(15)
1.305(2)
1.369(2)
77.00(4)
2.0734(16)
1.6964(17)
1.308(2)
1.374(3)
77.76(5)
2.199(2)
1.668(2)
1.322(3)
1.349(3)
76.20(6)
2.1823(19)
1.668(2)
1.318(3)
1.348(3)
77.32(5)
aRu−CO 1.844(3); RuC−O 1.147(4).
bRu−CN(xylyl) 1.878(3); bRuC−N(xylyl) 1.182(3).
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Kelly et al.
197
Scheme 2. Reactivity of Cp*Ru(N-phosphinoamidinate) complexes 2a and 2b with two-electron (L) donors.
with an atmosphere of CO to form the corresponding adduct 3,
while 2a reacted with 1 equiv. of 2,6-xylylisocyanide to form 4. In
the case of 3, the identity of this product as being a CO adduct of
2b was confirmed initially on the basis of NMR data, whereby a
diagnostic 13C NMR resonance for the CO group was detected
(212.4 ppm), along with the observation of distinct resonances
attributable to magnetically nonequivalent tBu and isopropyl
groups in both the 1H and 13C NMR spectra. Similarly for 4, unique
resonances in keeping with diastereotopic pairs of aryl-Me and
tBu groups were observed in both the 1H and 13C NMR spectra. The
proposed connectivity in 3 and 4 was confirmed in the solid state
on the basis of single-crystal X-ray diffraction data (Fig. 3; Tables 1
and 2). While for both 3 and 4, the Ru−P bond distances (2.3652(6)
and 2.3578(7) Å) and the P−Ru−N(2) bite angles (76.20(6)° and
77.32(5)°) do not differ significantly from those observed in the
precursor 16-electron complexes, other more notable variations
in interatomic distances are observed upon adduct formation. A
significant lengthening of the Ru−N(2) distance occurs on going
from 2a/2b to 4/3, possibly owing to a combination of increased
congestion on forming a three-legged piano stool structure as well
as a reduction in Ru−N ␲-bonding in the 18-electron adducts in
keeping with concepts described by Caulton and co-workers.8 Fur-
thermore, the observed P−N(1) and N(2)−C(9) distances are shorter,
while the N(1)−C(9) distances are modestly longer in the adducts
relative to 2a and 2b, thereby suggesting that adduct formation
induces changes in the electronic structure of the coordinated
N-phosphinoamidinate ligands. The Ru−CO (1.844(3) Å) distance in
3 is statistically equivalent to the related distances found in
Cp*Ru(CO)(amidinate) (1.828(7) Å)13 and Cp*Ru(CO)(diketiminate)
(1.837(2) Å)14 complexes. Furthermore, the carbonyl stretch in 3
(1902 cm−1) is intermediate between those reported for Cp*Ru(CO)
(amidinate) (1888 cm−1)13 and Cp*Ru(CO)(diketiminate) (1910 cm−1)14
species.
Encouraged by the ability of 2a and 2b to bind two-electron
L-type donor ligands, we turned our attention to exploring the
reactivity of these complexes with E−H bonds (E = main group
element). Our initial efforts in this regard focused on exploring
the reactivity of 2a and 2b with ammonia borane at room temper-
ature, given current interest in the use of ammonia borane as a
material from which hydrogen may be generated under mild con-
ditions.28,29 No reaction was observed upon combination of
5 equiv. of ammonia borane with 2b in THF (approximately 3 mL)
over the course of 24 h on the basis of 31P NMR data obtained from
the reaction mixtures. However, under similar conditions using
2a, the consumption of 2a and formation of a new organometallic
product (5) was observed over the course of 4 h by use of 31P NMR
methods, accompanied by a change in color of the solution from
blue to dark red. Upon workup, 5 was obtained in 93% isolated
yield. The structure of 5 depicted in Scheme 3 was elucidated on
the basis of NMR spectroscopic data. Notably, 1H NMR resonances
(benzene-d6) at 5.38 and −12.16 ppm suggest the presence of NH
and RuH groups, respectively, and the location of the NH group
was confirmed on the basis of nOe interactions observed between
the NH and the PtBu2 group. Moreover, both the 1H and 13C NMR
spectra of 5 feature diastereotopic pairs of aryl-Me and tBu groups,
in keeping with the proposed structural formulation. Our efforts
to monitor the progress of the reaction by use of NMR methods
failed to detect any intermediates en route to 5, and in this regard,
we are unable to comment whether 5 represents the first-formed
product of the reaction. Nonetheless, it is feasible that the initial
site of protonation is at the Ru-N(aryl) nitrogen followed by a net
1,3-proton shift to afford the observed product 5.
While the formation of 5 from 2a corresponds to the net dehy-
drogenation of ammonia borane as desired, continued monitor-
1
ing of the reaction by use of H and 11B NMR methods over the
course of 24 h confirmed the modest consumption of ammo-
nia borane along with the formation of small amounts of cy-
clotriborazane (and (or) cross-linked oligomers) and borazine,30
with minimal hydrogen evolution detected. In an effort to assess
the ability of 5 to release hydrogen and regenerate 2a, benzene-d6
solutions of 5 were heated at 75 °C and were monitored by use of
31P NMR methods. Over the course of 5 days, the clean conversion
of 5 to 2a was observed. The rate of this conversion could be
accelerated through the addition of norbornene (1–2 equiv.),
whereby the clean conversion to 2a was observed after only 4 h at
75 °C (Scheme 3).
Conclusions
In summary, we have described the synthesis and characteriza-
tion of the first isolable, formally 16-electron Cp*Ru(␬2-PϳN) spe-
cies (2a and 2b), which are supported by N-phosphinoamidinate
ligands. These diamagnetic complexes exhibit a Cs-symmetric
structure in both solution and the solid state, as determined on
the basis of NMR spectroscopic and X-ray crystallographic data.
Despite the stability of such complexes, they have been shown
to readily coordinate two-electron (L) donors including CO and
2,6-xylylisocyanide, affording crystallographically characterized
C1-symmetric 18-electron Cp*Ru(L)(␬2-PϳN) adducts (3 and 4). Pre-
liminary reactivity studies confirmed that such complexes are
capable of extruding hydrogen from ammonia borane. Whereas
no reaction was observed upon combination of ammonia borane
and 2b at room temperature, under similar conditions, the less
sterically hindered Cp*Ru(N-phosphinoamidinate) complex 2a
was cleanly transformed into 5, a process that corresponds to the
net transfer of hydrogen from ammonia borane to 2a.
Experimental details
General considerations
All experiments were conducted under nitrogen in an MBraun
glovebox or using standard Schlenk techniques. Dry, oxygen-free
solvents were used unless otherwise indicated. Benzene, toluene,
and pentane were deoxygenated and dried by sparging with ni-
trogen and subsequent passage through a double-column solvent
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Can. J. Chem. Vol. 92, 2014
Fig. 3. Crystallographically determined structures of 3 (left) and 4 (right) employing 50% ellipsoids and with hydrogen atoms omitted for clarity.
Scheme 3. Reactivity of Cp*Ru(N-phosphinoamidinate) complex 2a with ammonia borane and loss of dihydrogen from the resulting product 5.
purification system purchased from MBraun Inc. Tetrahydrofuran
and diethyl ether were purified by distillation from Na/benzophe-
none. All purified solvents were stored over 4 Å molecular sieves.
Benzene-d6 was degassed via three freeze−pump−thaw cycles and
stored over 4 Å molecular sieves. The ligands 1a and 1b27 and
mixture was stirred for 5 h at 45 °C. A gradual color change from
brown to blue was observed. The solvent was removed under vac-
uum and the resulting blue solid was dissolved in approximately
10 mL of benzene. The benzene solution was subsequently filtered
through Celite to remove any residual salts. The solvent was again
removed under vacuum to yield 2a as a blue solid (0.22 g, 67%).
1H NMR (500 MHz, benzene-d6) ␦: 7.42 (d, 2H, J = 7 Hz, Harom), 7.03
(m, 2H, Harom), 6.95–6.82 (overlapping resonances, 4H, Harom), 2.27
31
[Cp*RuCl]4 were prepared according to literature procedures.
Ammonia borane was purchased from Aldrich and sublimed prior
to use. All other reagents were used without further purification.
1H, 13C, and 31P NMR characterization data were collected at 300 K
on a Bruker AV-500 spectrometer operating at 500.1, 125.7, and
202.5 MHz (respectively) with chemical shifts reported in parts per
million downfield of SiMe4 for 1H and 13C and 85% H3PO4 in D2O
for 31P. 1H and 13C NMR chemical shift assignments are based on
data obtained from 13C-DEPTQ135, 1H-1H COSY, 1H-13C HSQC, and
1H-13C HMBC NMR experiments. In some cases, fewer than ex-
pected unique 13C NMR resonances were observed, despite pro-
longed acquisition times. X-ray data collection was carried out by
Dr. Robert MacDonald and Dr. Michael J. Ferguson at the Univer-
sity of Alberta X-ray Crystallography Laboratory, Edmonton, Al-
berta. Infrared spectra were recorded as thin films between NaCl
plates using a Bruker Tensor 27 FT-IR spectrometer at a resolution
of 4 cm−1.
3
(s, 6 H, Me), 1.45 (d, 18H, PtBu2, JPH = 13 Hz), 1.21 (s, 15H, Cp*).
13C{1H} NMR (125.7 MHz, benzene-d6) ␦: 182.1 (NCN), 155.3 (Carom),
139.8 (Carom), 133.4 (Carom), 128.8 (CHarom), 128.6 (CHarom), 128.0
(CHarom), 127.0 (CHarom), 123.7 (CHarom), 75.5 (Cp*), 35.9 (d, PCMe3,
1JPC = 20 Hz), 29.4 (PtBu), 21.0 (CMe), 11.3 (Cp*). 31P{1H} NMR
(202.5 MHz, benzene-d6) ␦: 128.2. Anal. calcd. for C33H47N2PRu:
C 65.64, H 7.85, N 4.64; found: C 65.29, H 7.91, N 4.34. Crystals of 2a
suitable for X-ray diffraction analysis were grown from Et2O at
−35 °C.
Synthesis of 2b
A solution of 1b (0.36 g, 0.85 mmol) in approximately 20 mL of
pentane was cooled to −35 °C and a slight excess of 2.5 mol L−1
nBuLi (375 ␮L, 0.94 mmol) was added slowly by syringe. The reac-
tion mixture was then allowed to warm to room temperature over
the course of 15 min, during which time a white precipitate was
observed. The supernatant was then carefully decanted and the
remaining residue was dried under vacuum to yield the lithium
salt of 1b (0.35 g; 31P NMR, 202.5 MHz, THF-d8: ␦ 74.8, br), which
was used subsequently without further purification. A solution of
Synthesis of 2a
A solution of 1a (0.20 g, 0.54 mmol) in approximately 5 mL of
THF was added by pipette to a solution of [Cp*RuCl]4 (0.15 g,
0.14 mmol) in approximately 5 mL of THF. An excess of Cs2CO3
(0.91 g, 2.79 mmol) was added to the resulting solution and the
Published by NRC Research Press

Kelly et al.
199
the so-formed lithium salt of 1b (0.31 g, 0.72 mmol) in approxi-
mately 5 mL of THF was added by pipette to a solution of
[Cp*RuCl]4 (0.20 g, 0.18 mmol) in approximately 5 mL of THF. An
immediate color change from brown to dark green was observed.
After approximately 20 min, the solvent was removed under vac-
uum and the remaining green solid was taken up in approxi-
mately 10 mL of benzene. The benzene solution was filtered
through Celite and the filtrate was collected. The filtrate solution
was evaporated under vacuum to yield 2b as a dark green solid
(0.39 g, 82%). 1H NMR (500 MHz, benzene-d6) ␦: 7.62 (broad appar-
ent doublet, 2H, Harom), 7.29–7.27 (overlapping resonances, 3H,
31P{1H} NMR (500 MHz, benzene-d6) ␦: 149.1. Anal. calcd. for
C42H56N3PRu: C 68.64, H 7.68, N 5.72; found: C 68.59, H 7.54,
N 5.66. Crystals of 4 suitable for X-ray diffraction analysis were
grown from Et2O at −35 °C.
Synthesis of 5
A solution of ammonia borane(0.15 g, 4.9 mmol) in approxi-
mately 2 mL of THF was added by pipette to a solution of 2a
(0.057 g, 0.094 mmol) in approximately 1 mL of THF. A slow color
change from blue to dark red was observed over a period of 4 h.
The solvent was removed under vacuum and the remaining red
residue was redissolved in approximately 5 mL of pentane and
filtered through Celite. The filtrate solution was collected and was
evaporated to dryness to yield 5 as a dark red solid (0.053 g, 93%).
1H NMR (500 MHz, benzene-d6) ␦: 7.02 (m, 2H, Harom), 6.92 (d, 1H, J =
7 Hz, Harom), 6.78–6.73 (overlapping resonances, 4H, Harom), 6.69
(d, 1H, J = 8 Hz, Harom), 5.38 (br d, 1H, J = 5 Hz, NH), 2.68 (s, 3H, CMe),
H
arom), 6.91–6.85 (overlapping resonances, 3H, Harom), 3.46 (sept,
2H, 3JHH = 7 Hz, CHMe2), 1.46 (d, 18H, PtBu2, 3JPH = 13 Hz), 1.37 (d, 3H,
3JHH = 7 Hz, CHMe2), 1.19 (s, 15H, Cp*), 0.80 (d, 3H, JHH = 7 Hz,
3
CHMe2). 13C{1H} NMR (125.7 MHz, benzene-d6) ␦: 181.7 (d, JCP = 9 Hz,
NCN), 154.7 (Carom), 142.8 (Carom), 138.6 (d, JCP = 18 Hz, Carom), 133.1
(CHarom), 129.3 (CHarom), 127.4 (CHarom), 124.9 (CHarom), 124.7
3
1.94 (s, 3H, CMe), 1.75 (s, 15H, Cp*), 1.36 (d, 9H, PtBu, JPH = 13 Hz),
(CHarom), 76.1 (Cp*), 36.8 (d, JCP = 20 Hz, PCMe3), 29.8 (PtBu), 29.5
1
3
2
1.30 (d, 9H, PtBu, JPH = 13 Hz), −12.16 (d, 1H, JHP = 42 Hz, RuH).
13C{1H} NMR (125.7 MHz, benzene-d6) ␦: 158.3 (d, NCN, J = 14 Hz),
149.4 (Carom), 134.7 (Carom), 133.1 (Carom), 131.0 (Carom), 129.0
(CHarom), 128.9 (CHarom), 127.4 (CHarom), 124.5 (CHarom), 87.9 (Cp*),
40.2 (PCMe3), 39.0 (d, PCMe3, 1JPC = 26 Hz), 30.4 (d, PtBu, 3JCP = 5 Hz),
(CHMe2), 25.3 (CHMe2), 25.0 (CHMe2), 12.3 (Cp*). 31P{1H} NMR
(202.5 MHz, benzene-d6) ␦: 124.9. Anal. calcd. for C37H55N2PRu:
C 67.34, H 8.40, N 4.25; found: C 67.55, H 8.32, N 4.41. Crystals of 2b
suitable for X-ray diffraction analysis were grown from pentane at
−35 °C.
29.5 (d, PtBu, JCP = 8 Hz), 19.5 (CMe), 19.4 (CMe), 12.4 (Cp*).
3
31P{1H} NMR (202.5 MHz, benzene-d6) ␦: 160.8. IR (cm−1): 3404 (w,
Synthesis of 3
A solution of 2b (0.025 g, 0.038 mmol) in approximately 1 mL
of benzene was transferred to a J. Young NMR tube. The solution
was degassed via three freeze−pump−thaw cycles and the tube
was subsequently exposed to approximately 1 atm of CO. A color
change from dark green to amber brown was observed within
5 min after vigorous shaking. After approximately 20 min, the
solvent was removed under vacuum to yield 3 as a pale yellow
solid (0.026 g, 99%). 1H NMR (500 MHz, benzene-d6) ␦: 7.58 (d, 2H, J =
8 Hz, Harom), 7.12–7.07 (overlapping resonances, 3H, Harom), 6.94–
6.87 (overlapping resonances, 3H, Harom), 3.52 (sept, 1H, 3JHH = 7 Hz,
CHMe2), 3.08 (sept, 1H, 3JHH = 7 Hz, CHMe2), 1.56 (d, 9H, 3JPH = 13 Hz,
PtBu), 1.40–1.29 (overlapping resonances, 27H, Cp*, PtBu, CHMe2),
␯
NH), 1981 (m, ␯RuH). Anal. calcd. for C33H49N2PRu: C 65.43, H 8.15,
N 4.62; found: C 65.51, H 8.27, N 4.48.
Details of crystallographic studies
Crystallographic data were obtained at 173(2) K on a Bruker
PLATFORM/SMART 1000 CCD diffractometer or a Bruker D8/APEX
II CCD diffractometer using graphite-monochromated Mo K␣ (␭ =
0.71073 Å) radiation for 2a, 2b, and 4 or CuK␣ (␭ = 1.54178 Å) for 3.
Unit cell parameters were determined and refined on all reflec-
tions. Data reduction and correction for Lorentz polarization were
performed using Saint-plus, and scaling and absorption correc-
tion were performed using the SADABS software package. Struc-
ture solution by direct methods and least-squares refinement on
F2 were performed using the SHELXTL software suite. Except
where noted, nonhydrogen atoms were refined with anisotropic
displacement parameters, while hydrogen atoms were placed in
calculated positions and refined with a riding model. Structural
figures were generated with ORTEP-3. During the refinement of 3,
the asymmetric unit was found to contain half an equivalent of
diethyl ether, which was found to exhibit positional disorder that
was treated satisfactorily. Due to this disorder within this solvate,
hydrogen atoms on the solvate were omitted in the solution and
refinement process.
3
3
1.29 (d, 3H, JHH = 7 Hz, CHMe2), 1.07 (d, 3H, JHH = 7 Hz, CHMe2),
0.55 (d, 3H, 3JHH = 7 Hz, CHMe2). 13C{1H} NMR (125.7 MHz, benzene-
d6) ␦: 212.4 (d, 2JCP = 20 Hz, CO), 175.1 (NCN), 149.9 (Carom), 144.8 (d,
J
CP = 15 Hz, Carom), 138.3 (d, JCP = 19 Hz, Carom), 132.7 (CHarom), 127.1
(CHarom), 125.8 (CHarom), 125.4 (CHarom), 123.3 (CHarom), 96.0 (Cp*),
40.4–39.9 (overlapping resonances, PCMe3), 30.8 (PtBu), 29.6 (PtBu),
28.4 (CHMe2), 28.3 (CHMe2), 26.7 (CHMe2), 25.9 (CHMe2), 24.9
(CHMe2), 23.8 (CHMe2), 10.9 (Cp*). 31P{1H} NMR (202.5 MHz,
benzene-d6) ␦: 139.9. IR (cm−1): 1902 (␯CO). Anal. calcd. for
C38H55N2OPRu: C 66.35, H 8.06, N 4.07; found: C 66.24, H 8.21,
N 4.36. Crystals of 3 suitable for X-ray diffraction analysis were
grown from Et2O at −35 °C.
Supplementary material
Synthesis of 4
Supplementary material is available with the article through
the journal Web site at http://nrcresearchpress.com/doi/suppl/
10.1139/cjc-2013-0474. CCDC 948974−948977 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained, free of charge, via http://www.ccdc.cam.ac.uk/products/
csd/request/ (or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK (fax: 44-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk)).
A solution of 2,6-xylylisocyanide(0.012 g, 0.094 mmol) in ap-
proximately 1 mL of Et2O was added by pipette to a solution of 2a
(0.057 g, 0.094 mmol) in approximately 1 mL of Et2O. An immedi-
ate color change from blue to orange−yellow was observed. After
approximately 20 min, the solvent was removed under vacuum to
yield 4 as a bright yellow solid (0.027 g, 99%). H NMR (500 MHz,
benzene-d6) ␦: 7.68 (d, 2H, J = 7 Hz, Harom), 6.99–6.88 (overlapping
resonances, 4H, Harom), 6.85–6.77 (overlapping resonances, 4H,
1
Notes: The authors declare no competing financial interest.
H
arom), 6.66 (m, 1H, Harom), 2.67 (s, 3H, Me), 2.42 (s, 6H, xylylNC), 1.98
(s, 3H, Me), 1.58 (d, 9H, PtBu, JPH = 13 Hz), 1.43–1.39 (overlapping
resonances, 24H, Cp* + PtBu). 13C{1H} NMR (125.8 MHz, benzene-d6)
␦: 182.5 (d, JCP = 20 Hz, xylylNC), 176.5 (NCN), 153.2 (Carom), 141.1 (d,
J = 19 Hz, Carom), 135.9 (Carom), 135.4 (Carom), 134.2 (Carom), 133.1
(Carom), 130.6 (CHarom), 129.6 (CHarom), 129.5 (CHarom), 129.1 (CHarom),
128.0 (CHarom), 127.3 (CHarom), 125.7 (CHarom), 123.8 (CHarom), 93.6
(Cp*), 40.9 (d, PCMe3, 1JCP = 14 Hz), 39.2 (d, 1JCP = 31 Hz, PCMe3), 31.8
(PtBu), 30.5 (PtBu), 23.4 (CMe), 22.8 (CMe), 21.1 (xylylNC), 11.4 (Cp*).
3
Acknowledgements
We thank the Chevron Phillips Chemical Company for support-
ing this research and permission to publish. Mark Stradiotto and
Laura Turculet are also grateful to the Natural Sciences and Engi-
neering Research Council of Canada and Dalhousie University for
their support of this work. Craig A. Wheaton thanks the Killam
Foundation for a Postdoctoral Fellowship. Dr. Michael Lumsden
Published by NRC Research Press

200
Can. J. Chem. Vol. 92, 2014
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Severin, K.; Schreiber, D. F.; Dyson, P. J. Organometallics 2011, 30, 6119. doi:
10.1021/om2006479.
(NMR-3, Dalhousie) is thanked for on-going technical assistance in
the acquisition of NMR data.
(16) Ito, M.; Osaku, A.; Kobayashi, C.; Shiibashi, A.; Ikariya, T. Organometallics
2009, 28, 390. doi:10.1021/om801042b.
(17) Ito, M.; Hirakawa, M.; Osaku, A.; Ikariya, T. Organometallics 2003, 22, 4190.
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