The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry

Article abstract of DOI:10.1016/j.jorganchem.2008.06.013

The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl₂(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (E = Bu₄N⁺: R = Ph, 1a, ⁱPr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or PNP⁺: R = Ph, 1a′, ⁱPr, 1b′ or Cy, 1c′) are reported. X-ray crystallographic studies of 1a′ and 1b′ confirmed the three-legged piano-stool coordination geometry. In solution, complexes 1a-c and 1a′-c′ are proposed to form monomer-dimer equilibria as a result of chloride ligand dissociation. Complexes 1a-c and 1a′-c′ also form the formally neutral zwitterionic complexes [RuCl(L)(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (L = pyridine: R = Ph, 2a, ⁱPr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, ⁱPr, 3b or Cy, 3c) via chloride ligand abstraction using AgNO₃ or MeOTf.

Full text of DOI:10.1016/j.jorganchem.2008.06.013

Journal of Organometallic Chemistry 693 (2008) 2921–2928
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry
Michael T. Beach a, Jesse M. Walker a, Timothy G. Larocque a, Justin L. Deagle a, Ruiyao Wang b,
Gregory J. Spivak a,
*
a Department of Chemistry, Lakehead University, Thunder Bay, Ontario, Canada P7B 5E1
b Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6
a r t i c l e i n f o
a b s t r a c t
6-p-cyme-
Article history:
Received 16 May 2008
Received in revised form 6 June 2008
Accepted 6 June 2008
Available online 13 June 2008
The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl2(
g
i
ne){PR2(p-Ph3BC6H4)}] (E = Bu4N+: R = Ph, 1a, Pr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or
i
PNP+: R = Ph, 1a0, Pr, 1b0 or Cy, 1c0) are reported. X-ray crystallographic studies of 1a0 and 1b0 confirmed
the three-legged piano-stool coordination geometry. In solution, complexes 1a–c and 1a0–c0 are proposed
to form monomer–dimer equilibria as a result of chloride ligand dissociation. Complexes 1a–c and 1a0–c0
also form the formally neutral zwitterionic complexes [RuCl(L)(g
6-p-cymene){PR2(p-Ph3BC6H4)}]
Keywords:
Ruthenium
Zwitterionic
Arene
i
i
(L = pyridine: R = Ph, 2a, Pr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, Pr, 3b or Cy, 3c) via chloride ligand
abstraction using AgNO3 or MeOTf.
Ó 2008 Elsevier B.V. All rights reserved.
Half-sandwich
(Phosphino)tetraphenylborate
Anionic phosphine
1. Introduction
might offer several advantages, including enhanced solubilities in
low polarity solvents, an increase in tolerance towards coordinat-
Phosphorus-based ligands continue to play a dominating role as
co-ligands in organometallic chemistry. Indeed, tertiary phos-
phines are especially important and have been studied quite exten-
sively, with considerable attention being directed towards
developing novel structural variants possessing unique electronic,
steric and coordination behaviours [1]. Recent reports describing
the synthesis, properties and coordination chemistry of several
new classes of anionic phosphines [2], in particular the monoden-
tate (phosphino)tetraphenylborate ligands [PR2(p-Ph3BC6H4)]ꢀ [3]
(Structure I), are quite intriguing. Conceptually, they may be re-
garded as a tertiary phosphine ligand tethered to a tetraphenylbo-
rate anion. The strategic positioning of the triphenylborane group
on the phenyl substituent, which projects away from the phospho-
rus donor atom, might suggest these phosphines are essentially
isosteric with their neutral counterparts, and thus only their elec-
tronic profile has been altered. In fact, it has been suggested that
anionic phosphines exhibit enhanced electron-donor properties
vs. their neutral counterparts [2a,2b]. Equally intriguing, anionic
phosphine ligands have also proven to be useful in developing
new catalytically active zwitterionic complexes [2b]. While many
cationic complexes are effective in catalyzing a variety of organic
transformations, their charge-neutral zwitterionic analogues
ing solvents and substrate functional groups, and eliminating com-
petition for the active site between the substrate and a counterion.
We found it surprising that the coordination chemistry of this
novel class of phosphine ligand remains underdeveloped, particu-
larly for catalytically important ruthenium. We report here some
of our preliminary investigations involving the synthesis of ruthe-
nium-arene complexes containing these anionic phosphine
ligands.
2. Experimental
Unless otherwise stated, all experiments and manipulations
were conducted under an inert atmosphere of prepurified N2 using
standard Schlenk techniques. Distilled, deionized water was stored
in a bulb with a Teflon tap, and purged with N2 prior to use. Meth-
anol, acetonitrile and pyridine were each stored over activated 4A
molecular sieves in a bulb with a Teflon tap, and purged with N2
before use. All other bulk solvents used in large-scale preparations
were pre-dried over activated 4A molecular sieves, passed through
a column of alumina, purged with N2 and stored over 4A molecular
sieves in bulbs with Teflon taps [4]. NMR solvents used in solution
structure elucidations were dried with appropriate drying agents,
vacuum distilled, freeze-pump-thaw degassed three times, and
stored in bulbs with Teflon taps: CDCl3 and C2D4Cl2 (anhydrous
CaCl2); CD2Cl2 (CaH2); acetone-d6 (activated 4A sieves). NMR
* Corresponding author. Tel.: +1 807 343 8297; fax: +1 807 346 7775.
E-mail address: greg.spivak@lakeheadu.ca (G.J. Spivak).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.06.013

2922
M.T. Beach et al. / Journal of Organometallic Chemistry 693 (2008) 2921–2928
Found: C, 66.32; H, 8.03; N, 1.02%. 1H NMR (499.9 MHz, CDCl3,
-
BPh3
22 °C): 7.43–6.93 (m, Ph and PC6H4B), 5.09–4.84 (m, p-cymene),
R = Ph, iPr or Cy
+ = Bu4N+ or PNP+
i
E+
3.49 (d, Cy of phosphine), 2.84 (m, Pr of p-cymene), 2.69 (m, 8H,
R
E
R
i
Bu), 2.58 (m, Pr of p-cymene), 2.14–1.24 (m, Bu and Cy of phos-
P
phine), 1.81 (s, Me of p-cymene), 1.76 (s, Me of p-cymene), 1.74
I
i
(s, Me of p-cymene), 1.09 (br d, Pr of p-cymene), 0.99 (t, 12H,
Structure I
Bu). 31P{1H} (202.3 MHz, CDCl3, 22 °C): 21.4, 19.9, 18.6
(ꢁ1.5:2.5:1, all s, PCy2).
spectra (1H and 31P{1H}) were obtained using a Varian Unity INOVA
500 MHz spectrometer, with chemical shifts (in ppm) referenced to
residual protio solvent peaks (1H) or external 85% H3PO4 (31P). Ele-
mental analyses were performed on a CEC 240XA analyzer by the
Lakehead University Instrumentation Laboratory. The ruthenium
2.3. Synthesis of [PNP][RuCl2(g
6-p-cymene){PR2(p-Ph3BC6H4)}]
i
(R = Ph, 1a0, Pr, 1b0 or Cy, 1c0)
Complexes 1a0–c0 were prepared in a manner analogous to that
described for the synthesis of 1a–c, except using [PNP][PR2(p-
Ph3BC6H4)]. Yields were typically >75%. Combustion and NMR
spectroscopic data for complexes 1a0-c0 follow. Complex 1a0
(R = Ph): Anal. Calc. for C82H73BCl2NP3Ru: C, 73.00; H, 5.46; N,
1.04. Found: C, 72.96; H, 5.41; N, 0.95%. 1H NMR (499.9 MHz,
CDCl3, 22 °C): 7.81–6.81 (m, Ph and PC6H4B), 5.08 (d, p-cymene),
4.96 (d, p-cymene), 4.91 (d, p-cymene), 4.88 (d, p-cymene), 2.76
precursor [RuCl2(
g
6-p-cymene)]2 [5] and the ligands [E][PR2(p-
Ph3BC6H4)] (E = Bu4N+ or PNP+; R = Ph or Pr) [3] were prepared
according to the literature procedures; the ligands were recrystal-
lized from THF/hexanes.
i
2.1. Synthesis of [E][PCy2(p-Ph3BC6H4)] (E = Bu4N+ or PNP+)
i
i
(septet, Pr of p-cymene), 1.80 (s, Me of p-cymene), 1.06 (d, Pr of
p-cymene). 31P{1H} (202.3 MHz, CDCl3, 22 °C): 25.6, 24.4 (ꢁ7:1,
both s, PPh2), 22.1 (PNP+). Complex 1b0 (R = iPr): Anal. Calc. for
The ligands [E][PCy2(p-Ph3BC6H4)] were prepared in a manner
analogous to the literature procedure [3] except using ClPCy2 as
a precursor, and isolated either as the Bu4N+ salt (using [Bu4N]Br)
or PNP+ salt (using [PNP]Cl) in 84% and 78% yield, respectively.
NMR spectroscopic data for the Bu4N+ salt follows. 1H NMR
(499.9 MHz, acetone-d6, 22 °C): 7.38–6.78 (m, 19 H, Ph and
PC6H4B), 3.44 (m, 8H, Bu), 2.05 (m, 8H, Bu), 1.86–1.60, 1.33–1.08
(m, 22H, Cy), 1.43 (m, 8H, Bu), 0.97 (t, 12H, Bu). 31P{1H}
(202.3 MHz, acetone-d6, 22 °C): 6.70 (PCy2). The 1H and 31P{1H}
NMR spectroscopic data (acetone-d6, 22 °C) of the anion of the
PNP+ salt were identical to the Bu4N+ salt.
C
76H77BCl2NP3RuX3MeOH (the MeOH was confirmed via 1H NMR
spectroscopy): C, 68.70; H, 6.51; N, 1.02. Found: C, 68.51; H,
6.04; N, 0.89%. 1H NMR (499.9 MHz, CDCl3, 22 °C): 7.56–6.82 (m,
i
Ph and PC6H4B), 5.06–4.78 (m, p-cymene), 3.08 (m, Pr of phos-
i
i
phine), 3.00 (m, Pr of phosphine), 2.58 (m, Pr of p-cymene), 2.49
i
(septet, Pr of p-cymene), 1.80 (s, Me of p-cymene), 1.76 (s, Me of
i
i
p-cymene), 1.34 (m, Pr of phosphine), 1.22 (m, Pr of phosphine),
1.04 (d, Pr of p-cymene). 31P{1H} (202.3 MHz, CDCl3, 22 °C): 29.8,
i
28.2, 26.5 (ꢁ11:7:1, all s, PiPr2), 22.2 (PNP+). Complex 1c0
(R = Cy): Anal. Calc. for C82H85BCl2NP3Ru: C, 72.24; H, 6.24; N,
1.03. Found: C, 71.98; H, 6.75; N, 0.94%. 1H NMR (499.9 MHz,
CDCl3, 22 °C): 7.61–6.85 (m, Ph and PC6H4B), 5.05–4.81 (m, p-cym-
2.2. Synthesis of [Bu4N][RuCl2(
(R = Ph, 1a, Pr, 1b or Cy, 1c)
g
6-p-cymene){PR2(p-Ph3BC6H4)}]
i
i
ene), 3.49 (d, Cy of phosphine), 2.75 (m, Pr of p-cymene), 2.50 (m,
In a typical procedure, a Schlenk tube was charged with
[RuCl2(
6-p-cymene)]2 (0.95 mmol) and [Bu4N][PR2(p-Ph3BC6H4)]
iPr of p-cymene), 2.10–1.16 (m, Cy of phosphine), 1.84 (s, Me of p-
cymene), 1.79 (s, Me of p-cymene), 1.77 (s, Me of p-cymene), 1.06
(d, iPr of p-cymene). 31P{1H} (202.3 MHz, CDCl3, 22 °C): 22.1 (PNP+),
21.9, 20.5, 19.1 (ꢁ6:4:1, all s, PCy2).
g
(1.90 mmol). Next, CH2Cl2 (30 mL) was added via syringe and the
deep, dark red solution was allowed to stir for 1.5 h. After this time,
the volatiles were removed under reduced pressure to yield an or-
ange-red product, which was recrystallized from CH2Cl2/hexanes
via slow diffusion. The products were isolated as orange-red pow-
ders in yields >90% after drying under reduced pressure. Analyti-
cally pure samples could be obtained by cooling saturated MeOH
solutions to ꢀ78 °C for several hours, filtering the microcrystalline
product, and washing with MeOH. Combustion and NMR spectro-
scopic data for complexes 1a–c follow. Complex 1a (R = Ph): Anal.
Calc. for C62H79BCl2NPRu: C, 70.92; H, 7.60; N, 1.33. Found: C,
71.04; H, 7.15; N, 0.94%. 1H NMR (499.9 MHz, CDCl3, 22 °C):
7.81–6.75 (m, Ph and PC6H4B), 5.06 (d, p-cymene), 4.94 (d, p-cym-
2.4. Synthesis of [RuCl(py)(g
6-p-cymene){PPh2(p-Ph3BC6H4)}], 2a
In a Schlenk tube, complex 1a (0.279 g, 0.265 mmol) was dis-
solved in CH2Cl2 (20 mL). Excess pyridine (1.1 mL, 13.3 mmol)
was added via syringe, followed by AgNO3 (0.050 g, 0.292 mmol).
Almost immediately an orange mixture was produced, which grad-
ually turned yellow and deposited a white precipitate of AgCl. After
stirring for 1.5 h, the mixture was filtered through Celite, and the
orange filtrate was extracted with water (6 ꢂ 30 mL) with vigorous
shaking. The combined organic layers were dried over MgSO4 and
filtered through Celite. Removal of the volatiles under reduced
pressure yielded an orange-yellow solid. The solid was recrystal-
lized from CH2Cl2/diethyl ether via slow diffusion. Yield: 90%. Anal.
Calc. for C51H48BClNPRu: C, 71.18; H, 5.63; N, 1.63. Found: C, 70.99;
H, 5.76; N, 1.56%. 1H NMR (499.9 MHz, acetone-d6, 22 °C): 8.91 (m,
2H, o-H of py), 7.79–6.82 (m, 32H, py, Ph and PC6H4B), 5.94, 5.70,
i
ene), 4.91 (d, p-cymene), 4.86 (d, p-cymene) 2.62 (septet, Pr of p-
cymene), 2.58 (m, 8H, Bu), 1.78 (s, Me of p-cymene), 1.20 (m, 8H,
i
Bu), 1.09 (m, 8H, Bu), 1.03 (d, Pr of p-cymene), 0.83 (t, 12H, Bu).
31P{1H} (202.3 MHz, CDCl3, 22 °C): 24.5, 23.1 (ꢁ9:1, both s, PPh2).
Complex 1b (R = iPr): Despite numerous attempts, satisfactory car-
bon, hydrogen and nitrogen analyses could not be obtained for 1b.
1H NMR (499.9 MHz, CDCl3, 22 °C): 7.49–6.95 (m, Ph and PC6H4B),
5.13–4.87 (m, p-cymene), 3.15 (m, iPr of phosphine), 3.04 (m, iPr of
i
5.59, 5.49 (each m, each 1H, p-cymene), 2.36 (septet, 1H, Pr of p-
i
cymene), 1.82 (s, 3H, Me of p-cymene), 1.12 (d, 3H, Pr of p-cym-
i
i
phosphine), 2.62 (m, 8H, Bu), 2.56 (m, Pr of p-cymene), 2.45 (sep-
tet, Pr of p-cymene), 1.79 (s, Me of p-cymene), 1.75 (s, Me of p-
ene), 1.05 (d, 3H, Pr of p-cymene). 31P{1H} (202.3 MHz, acetone-
i
d6 , 22 °C): 40.1 (s, PPh2).
i
cymene), 1.41 (m, Pr of phosphine), 1.30 (m, 16H, Bu), 1.04 (d,
iPr of p-cymene), 0.98 (t, 12H, Bu). 31P{1H} (202.3 MHz, CDCl3,
22 °C): 29.2, 27.4, 25.9 (ꢁ2:2.5:1, all s, PiPr2). Complex 1c
(R = Cy): Anal. Calc. for C62H91BCl2NPRuX3MeOH (the MeOH was
confirmed via 1H NMR spectroscopy): C, 66.95; H, 8.84; N, 1.20.
2.5. Synthesis of [RuCl(py)(g
6-p-cymene){PiPr2(p-Ph3BC6H4)}], 2b
Complex 1b (0.200 g, 0.203 mmol) was dissolved in CH2Cl2
(10 mL) in a Schlenk tube. Next, excess pyridine (1.6 mL, 19.3 mmol)

M.T. Beach et al. / Journal of Organometallic Chemistry 693 (2008) 2921–2928
2923
was added via syringe, followed by a slight excess of MeOTf (25
lL,
2.9. Synthesis of [RuCl(MeCN)(
g
6-p-cymene){PCy2(p-Ph3BC6H4)}], 3c
0.224 mmol). After stirring for 1 h a yellow solution was obtained.
The solution was then filtered through a short plug of silica gel
(ꢁ2 cm W ꢂ 1 cm H), and then the volatiles were removed under re-
duced pressure to yield a bright yellow solid. Yield: 86%. Anal. Calc.
for C45H52BClNPRu: C, 68.82; H, 6.69; N, 1.78. Found: C, 68.94; H,
6.27; N, 1.50%. 1H NMR (499.9 MHz, CDCl3, 22 °C): 8.67 (br, 2H, o-
H of py), 7.77–6.92 (m, 22H, py, Ph and PC6H4B), 5.37, 5.28, 5.00,
Complex 3c was prepared in a manner analogous to that
described for 3b using complex 1c0 as the precursor. Yield: 30%.
Anal. Calc. for C48H58BClNPRu: C, 69.67; H, 7.08; N, 1.69%. Found:
C, 69.67; H, 7.01; N, 1.39%. 1H NMR (499.9 MHz, CDCl3, 22 °C):
7.70–6.98 (m, 19H, Ph and PC6H4B), 5.41, 5.60, 5.00, 4.82 (each
i
m, each 1H, p-cymene), 2.69 (septet, 1H, Pr of p-cymene), 1.84
i
i
4.90 (each m, each 1H, p-cymene), 2.90 (m, 1H, Pr of phosphine),
(s, 3H, Me of p-cymene), 1.54 (s, 3H, MeCN), 1.14 (d, 3H, Pr of p-
i
i
i
2.42 (m, 1H, Pr of phosphine), 2.07 (septet, 1H, Pr of p-cymene),
cymene), 1.09 (d, 3H, Pr of p-cymene) 2.34–0.88 (m, 22H, Cy of
i
1.47 (m, 6H, Pr of phosphine), 1.35 (s, 3H, Me of p-cymene), 1.13
phosphine). 31P{1H} (202.3 MHz, CDCl3, 22 °C): 29.72 (s, PCy2).
(d, 3H, iPr of p-cymene), 1.03 (d, 3H, iPr of p-cymene), 0.79 (m, 6H,
iPr of phosphine). 31P{1H} (202.3 MHz, CDCl3, 22 °C): 34.1 (s, PiPr2).
2.10. X-ray crystallographic studies
2.6. Synthesis of [RuCl(py)(g
6-p-cymene){PCy2(p-Ph3BC6H4)}], 2c
Diffraction quality crystals were grown over a period of days at
room temperature via slow diffusion of hexanes into saturated
CH2Cl2 solutions of either 1a0 or 1b0. The crystals were mounted
on a glass fibre with grease and cooled to ꢀ93 °C in a stream of
nitrogen gas controlled with a Cryostream Controller 700. Data
collection was performed on a Bruker SMART APEX II X-ray
Complex 2c was prepared in a manner analogous to that de-
scribed for 2a using complex 1c0 as the precursor. Yield: 21%. Anal.
Calc. for C51H60BClNPRu: C, 70.34; H, 6.89; N, 1.61. Found: C, 69.79;
H, 6.79; N, 1.14%. 1H NMR (499.9 MHz, CDCl3, 22 °C): 8.86 (br, 2H,
o-H of py), 7.88–6.97 (m, 22H, py, Ph and PC6H4B), 5.33, 5.22, 5.04,
diffractometer with graphite-monochromated MoK
a radiation
i
(k = 0.71073 Å), operating at 50 kV and 30 mA over 22 ranges of
2.50–52.00° (1a0) or 2.94–52.00°. No significant decay was observed
during the data collection. Data were processed using the Bruker
AXS Crystal Structure Analysis Package [6]: Data collection: APEX2;
cell refinement: SAINT; data reduction: SAINT; structure solution: XPREP
and SHELXTL; structure refinement: SHELXTL. Neutral atom scattering
factors were taken from Cromer and Waber [7]. The structures were
4.96 (each m, each 1H, p-cymene), 2.44 (septet, 1H, Pr of p-cym-
i
ene), 1.38 (s, 3H, Me of p-cymene), 1.17 (d, 3H, Pr of p-cymene),
1.16 (d, 3H, iPr of p-cymene), 2.26–1.08 (m, 22H, Cy of phosphine).
31P{1H} (202.3 MHz, CDCl3, 22 °C): 27.51 (s, PCy2).
2.7. Synthesis of [RuCl(MeCN)(g
6-p-cymene){PPh2(p-Ph3BC6H4)}], 3a
solved by direct methods. Full-matrix least-square refinements
Complex 1a (0.234 g, 0.222 mmol) in CH2Cl2 (15 mL) was trea-
ted with excess MeCN (580 L, 11.1 mmol) via syringe. Next, a
slight excess of MeOTf (30 L, 0.266 mmol) was then added via
P
minimizing the function w(Fo2 ꢀ Fc2)2 were applied to each com-
pound. All non-hydrogen atoms were refined anisotropically. All of
the H atoms were placed in geometrically calculated positions. For
l
l
syringe. The solution was allowed to stir for 3 h whereupon a col-
our change from red to orange was observed. The solvent was re-
moved under reduced pressure to yield an orange solid. The
product was redissolved in CH2Cl2 (ꢁ75 mL) and filtered through
a plug of silica gel (2 cm W ꢂ 1 cm H), discarding the first 50 mL.
The volatiles were removed under reduced pressure to yield an or-
ange solid. Yield: 89%. Anal. Calc. for C48H46BClNPRuX1 ꢃ 75CH2Cl2
(the CH2Cl2 was confirmed via 1H NMR spectroscopy): C, 61.98; H,
5.18; N, 1.45. Found: C, 62.06; H, 5.90; N, 1.31%. 1H NMR
(499.9 MHz, CDCl3, 22 °C): 7.75–6.89 (m, 29H, Ph and PC6H4B),
5.73, 5.25, 4.87, 4.67 (each m, each 1H, p-cymene), 2.54 (septet,
i
1b0, one of the Pr groups and one of the Ph groups are disordered.
The SHELX commands EDPA, DFIX and SUMP were applied to resolve
the disorder of the structure. Graphical representations of the struc-
tures were produced using ORTEP-3 [8].
2.10.1. X-ray data for 1a0
C82H73BCl2NP3Ru, M = 1348.1 g/mol, monoclinic, P2(1)/n,
a = 10.0396(3) Å, b = 18.0768(6) Å, c = 38.2871(12) Å,
b = 95.773(2)°,
= 90°, Z = 4, V = 6913.2(4) Å3, Dcalc = 1.295 g/cm3,
(MoK
a = 90°,
c
l
a
) = 0.419 mmꢀ1
,
crystal dimensions 0.10 ꢂ 0.08 ꢂ 0.08
mm3. The structure was refined by full matrix least-squares on
i
1H, Pr of p-cymene), 1.91 (s, 3H, Me of p-cymene), 1.54 (s, 3H,
F2. Convergence to final R1 = 0.0657 and wR2 = 0.0953 for 6315
MeCN), 1.19 (d, 3H, iPr of p-cymene), 1.13 (d, 3H, iPr of p-cymene).
31P{1H} (202.3 MHz, CDCl3, 22 °C): 31.6 (s, PPh2).
(I > 2U(I)) independent reflections, and R1 = 0.1721 and
wR2 = 0.1298 for all 13,589 (R(int) = 0.1181) independent reflec-
2.8. Synthesis of [RuCl(MeCN)(g
6-p-cymene){PiPr2(p-Ph3BC6H4)}], 3b
tions, with 808 parameters and 0 restraints, were achieved.
2.10.2. X-ray data for 1b0
Complex 1b (0.201 g, 0.204 mmol) was dissolved in CH2Cl2
(20 mL) and treated with excess MeCN (533 L, 10.2 mmol) via
ꢀ
C77H78BCl4NP3Ru, M = 1363.99 g/mol, triclinic, P1, a = 11.0955
l
(2) Å, b = 14.1779(3) Å, c = 22.9304(4) Å,
a = 79.4280(10)°, b =
syringe. Next, a slight excess of AgNO3 (0.042 g, 0.245 mmol) was
added and the mixture was allowed to stir for 1 h. During this time,
the mixture turned orange and a white precipitate deposited. The
mixture was filtered through Celite and the orange filtrate was ex-
tracted with water (6 ꢂ 30 mL) with vigorous shaking. The com-
bined organic layers were dried over MgSO4 and filtered.
Removal of the volatiles under reduced pressure yielded a bright
orange solid. Yield: 86%. Anal. Calc. for C42H50BClNPRu: C, 67.71;
H, 6.78; N, 1.88. Found: C, 67.94; H, 7.05; N, 1.62%. 1H NMR
(499.9 MHz, CDCl3, 22 °C): 7.70–6.95 (m, 19H, Ph and PC6H4B),
5.39, 5.34, 4.97, 4.83 (each m, each 1H, p-cymene), 3.01 (m, 1H,
77.2810(10)°,
c =
= 80.7990(10)°, Z = 2, V = 3431.99(11) Å3, Dcalc
1.320 g/cm3,
l
(MoKa
) = 0.498 mmꢀ1, crystal dimensions 0.24 ꢂ
0.12 ꢂ 0.09 mm3. Convergence to final R1 = 0.0652 and wR2 =
0.1457 for 7964 (I > 2U(I)) independent reflections, and R1 = 0.1276
and wR2 = 0.1778 for all 13,483 (R(int) = 0.0791) independent
reflections, with 779 parameters and 11 restraints, were achieved.
3. Results and discussion
3.1. Synthesis of [E][RuCl2(
g
6-p-cymene){PR2(p-Ph3BC6H4)}]
i
iPr of phosphine), 2.62 (m, 1H, Pr of phosphine), 2.27 (septet, 1H,
(E = Bu4N+ or PNP+; R = Ph, Pr or Cy)
i
iPr of p-cymene), 2.01 (s, 3H, Me of p-cymene), 1.83 (s, 3H, MeCN),
i
1.41 (m, 6H, Pr of phosphine), 1.32 (m, 6H, iPr of phosphine), 1.11
The anionic tertiary phosphines examined as part of this work
each contain as a common design element a BPh3 group tethered
to a general PR2 framework via an aryl linker (see Structure I). In
i
i
(d, 3H, Pr of p-cymene), 1.09 (d, 3H, Pr of p-cymene). 31P{1H}
(202.3 MHz, CDCl3, 22 °C): 37.0 (s, PiPr2).

2924
M.T. Beach et al. / Journal of Organometallic Chemistry 693 (2008) 2921–2928
this way, they represent structurally similar, yet anionic analogues
of their neutral counterparts phenyldiarylphosphines and phen-
yldialkylphosphines. Accordingly, lithiation of (p-BrC6H4)PR2, fol-
lowed by addition of electrophilic BPh3 provides the anionic
monodentate (phosphino)tetraphenylborate ligands [PR2(p-
Ph3BC6H4)]ꢀ [3] in relatively good yields. This convenient synthetic
strategy allowed us to expand the series to include the synthesis of
the desirable cyclohexyl analogue. Although the general procedure
permits the isolation of the tetrabutylammonium salts of these li-
gands, [Bu4N][PR2(p-Ph3BC6H4)], we found it could easily be
adapted to include the bis(triphenylphosphine)iminium (PNP+)
imately bisecting C(2)–C(3) in 1a0 and C(5)–C(6) in 1b0 when
viewed down the ruthenium-arene centroid axis; this presumably
permits minimal steric interactions with the arene methyl and iso-
propyl substituents. An approximately staggered conformation of
the phosphine substituents is observed about the ruthenium–
phosphorus axis in each complex. Remarkably, the substituent
bearing the bulky BPh3 group is positioned near the arene ligand
in both cases. The pseudo-octahedral geometry about the metal
in each complex is evidenced by the approximately 90° angles ob-
served for the angles P(1)–Ru(1)–Cl(1), P(1)–Ru(1)–Cl(2) and
Cl(1)–Ru(1)–Cl(2), with the
facial coordination sites.
g
6-p-cymene ligand occupying three
i
analogues, [PNP][PR2(p-Ph3BC6H4)] (R = Ph, Pr or Cy), since PNP+
is known to form crystalline salts with anions that are often diffi-
cult to crystallize (vide infra).
The bond distances and angles observed in the solid-state struc-
tures of 1a0 and 1b0 resemble those determined for other structurally
characterized analogues. The ruthenium–phosphorus and ruthe-
nium-chloride bond distances (see captions of Figs. 1 and 2) in both
complexes compare well with those observed for the neutral com-
As anticipated, the ligands [Bu4N][PR2(p-Ph3BC6H4)] readily
cleave the chloride bridge of [RuCl2(
the monomeric half-sandwich adducts [Bu4N][RuCl2(
g
6-p-cymene)]2 to provide
g
6-p-cyme-
i
ne){PR2(p-Ph3BC6H4)}] (R = Ph, 1a, Pr, 1b or Cy, 1c) in good yields
as orange-red, air-stable powders (Scheme 1). The corresponding
PNP+ analogues (1a0–c0) could be isolated in a similar fashion start-
ing from [PNP][PR2(p-Ph3BC6H4)]. Alternatively, they could also be
prepared via cation exchange simply by stirring the Bu4N+ salts 1a–
c in methanol in the presence of a twofold excess of [PNP]Cl.
plexes [RuCl2(
anions in [Ph4P][RuCl3(
6)K( -Cl)3Ru(
6-p-cymene)] [11], [RuCl(N-butylimidazole)2(
cymene)][RuCl3(
6-p-cymene)] [12], and [N,N-bis(6-methylpyrid-
2-ylium)-(1R,2R)-1,2-diaminocyclohexane][RuCl3(
6-p-cymene)]2
g
6-arene)(PR3)] [9], and for the trichlororuthenate
6-p-cymene)] [10], [(dibenzo-18-crown-
6-p-
g
l
g
g
g
g
[13]. However, these same distances in 1a0 are somewhat shorter
than those observed in 1b0, and this may be related to the compara-
tively smaller size of the phosphine in 1a0. The longer Ru(1)-centroid
distance in 1b0 (1.704 Å) compared to 1a0 (1.683 Å) would also seem
to suggest the phosphine [PiPr2(p-Ph3BC6H4)]ꢀ has a greater steric
profile compared to [PPh2(p-Ph3BC6H4)]ꢀ. The distances between
the metal and the arene carbon atoms are asymmetric in both com-
plexes (2.175(6)–2.251(5) Å for 1a0; 2.182(6)–2.242(6) Å for 1b0). In
fact, the Ru(1)–C(arene) distances trans to the phosphine ligand in
each complex are slightly longer than those trans to the Ru(1)–
Cl(1) or Ru(1)–Cl(2) distances. This is likely linked to the large trans
influence exerted by the phosphine ligands [9]. Indeed, it has been
suggested that the anionic ligands [PR2(p-Ph3BC6H4)]ꢀ in general
may exert a greater trans influence over their neutral analogues [3].
3.2. Solid-state structures of 1a0 and 1b0
In order to confirm the proposed structures of complexes 1a–c
and 1a0–c0, and to gain a better insight into the impact these new
ligands may have on their solid-state structures, we attempted to
grow single crystals for X-ray crystallographic studies. Unfortu-
nately, our attempts involving the Bu4N+ salts were often frus-
trated by the production of oily products despite investigating a
variety of crystal-growing conditions. However, the PNP+ salts
proved to be better candidates, and after employing conventional
slow-diffusion techniques, we were immediately successful in
growing single crystals of 1a0 and 1b0 for crystallographic studies.
The ruthenate(II) anions of 1a0 and 1b0 are displayed in Figs. 1
and 2, respectively, along with selected bond distances and angles
in the captions. The ruthenium centres of 1a0 and 1b0 adopt the ex-
pected three-legged piano-stool coordination geometry typically
observed for these complexes. The phosphine ligand in each com-
plex projects between the substituents of the arene ligand, approx-
3.3. Solution NMR spectroscopic studies
In contrast to their neutral counterparts, the solution NMR
spectra of complexes 1a–c and 1a0–c0 unexpectedly proved to be
somewhat more complex. For example, multiple sets of ortho and
meta arene hydrogen signals of varying intensities were observed
in the 1H NMR spectra of these complexes, rather than the single
pair of doublets typically observed for (ideal Cs-symmetric)
1/2 [RuCl2(p-cymene)]2
[E][PR2(p-Ph3BC6H4)]
+
[RuCl2(g
6-p-cymene)(PR3)] [5a]. Perhaps more revealing, the
E = Bu4N+ or PNP+
31P{1H} NMR spectrum of each complex displays several signals
attributed to the single phosphine ligand, compared to the lone
singlet observed for the neutral complexes bearing more conven-
tional phosphines [9,14]. Moreover, the number and the relative
intensities of the signals vary with the R group on the phosphine,
and to a certain extent, the identity of the counterion. Thus, the
room temperature 31P{1H} NMR spectra of the R = Ph complexes
each reveal two closely spaced singlets with substantially different
intensities (1a:d = 24.5 and 23.1 ppm, ꢁ9:1; 1a0:d = 25.6 and 24.4
R = Ph, iPr or Cy
-
Ph3B
Ph iPr Cy
E+
Bu4N+
PNP+
1c
Ru
1a 1b
1a' 1b'
Cl
Cl
P
1c'
R
ppm, ꢁ7:1; for comparison, the PPh3 ligand of [RuCl2(
g
6-p-cyme-
R
ne)(PPh3)] appears at d = 25.3 ppm [14a]), while under the same
Ag+ or Me+, excess L
i
- AgCl or MeCl
conditions, the R = Pr and Cy analogues (for example, see Fig. 3)
each yield three closely spaced singlets (1b:d = 29.2, 27.4 and
25.9 ppm, ꢁ2:2.5:1; 1b0:d = 29.8, 28.2 and 26.5 ppm, ꢁ11:7:1;
1c:d = 21.4, 19.9 and 18.6 ppm, ꢁ1.5:2.5:1; 1c0:d = 21.9, 20.5 and
19.1 ppm, ꢁ6:4:1).
Ph iPr Cy
Ph3B
Ru
py
MeCN
2c
2a 2b
Cl
P
3c
3a 3b
The accumulated NMR evidence seemed to suggest several dis-
tinct ruthenium species exist in solution for each complex, despite
only one structure being observed in the solid state (at least for 1a0
and 1b0). There are two possible scenarios we might propose to ex-
L
R
R
Scheme 1.

M.T. Beach et al. / Journal of Organometallic Chemistry 693 (2008) 2921–2928
2925
C10
C6
C3
C5
C1
C7
C9
C8
C4
C2
Cl1
Ru1
Cl2
P1
C23
C11
C17
Fig. 1. ORTEP representation of the ruthenate anion of 1a0. Selected bond lengths (Å) and angles (°): Ru(1)–P(1), 2.3534(16); Ru(1)–Cl(1), 2.4149(15); Ru(1)–Cl(2), 2.4149(14);
Ru(1)–C(1), 2.212(6); Ru(1)–C(2), 2.201(5); Ru(1)–C(3), 2.175(6); Ru(1)–C(4), 2.231(6); Ru(1)–C(5), 2.228(6); Ru(1)–C(6), 2.251(5); P(1)–Ru(1)–Cl(1), 83.86(5); P(1)–Ru(1)–
Cl(2), 89.48(5); Cl(1)–Ru(1)–Cl(2), 87.58(5).
C10a
C9a
C3
C6
C2
C1
C8
C4
C5
C7
Ru1
Cl1
Cl2
C11
P1
C17
C20
Fig. 2. ORTEP representation of the ruthenate anion of 1b0. Selected bond lengths (Å) and angles (°): Ru(1)–P(1), 2.3897(15); Ru(1)–Cl(1), 2.4380(13); Ru(1)–Cl(2), 2.4382(13);
Ru(1)–C(1), 2.217(5); Ru(1)–C(2), 2.242(6); Ru(1)–C(3), 2.231(6); Ru(1)–C(4), 2.214(6); Ru(1)–C(5), 2.188(5); Ru(1)–C(6), 2.182(6); P(1)–Ru(1)–Cl(1), 88.95(5); P(1)–Ru(1)–
Cl(2), 87.11(5); Cl(1)–Ru(1)–Cl(2), 89.75(5).
plain these observations. The first involves the formation of rota-
tional isomers in solution, a result of hindered rotation about the
ruthenium–phosphorus bond. The origin of these rotamers in solu-
tion would likely be linked to the bulky BPh3 group tethered to the
phosphine. Indeed, hindered rotation about metal–phosphorus
bonds has been observed in the arene-metal complexes [Os(g6
C6H6)(
2-ON@CMe2)(PMetBu2)]PF6 and [OsX2( 6-C6R3H3)(PHtBu2)]
(R = H or Me; X = Cl or I) [15]. However, no signal coalescence or
-
g
g

2926
M.T. Beach et al. / Journal of Organometallic Chemistry 693 (2008) 2921–2928
Fig. 3. 31P{1H} NMR spectra (CDCl3) of complex 1b, and 1b in the presence of excess chloride ion (inset).
even signal broadening was observed in the 31P{1H} NMR spectra of
complexes 1a–c up to 80 °C in C2D4Cl2, suggesting these different
ruthenium species in solution do not originate from the formation
of rotational isomers.
31P{1H} spectra revealed the complete consumption of the com-
plexes with downfield signals at d = 29.2 ppm and d = 27.4 ppm,
and a single albeit broad signal at d 26 ppm dominated the spec-
trum (ꢁ75%). Similarly, for 1c, the complexes with signals down-
field at d = 21.4 and d = 19.9 ppm disappeared completely, with
the main product now appearing at d 19 ppm (ꢁ80%). In both cases,
a sharp resonance at d = 3.03 ppm in the 1H NMR spectrum re-
vealed the evolution of chloromethane [16].
A second plausible, and perhaps more likely scenario which
could account for the unusual NMR spectroscopic behaviour in
solution is the formation of monomer–dimer equilibria. We see
no evidence of phosphine dissociation in the 31P{1H} NMR spectra
of 1a–c and 1a0–c0. However, dynamic equilibria involving halide
dissociation have been observed for other anionic (p-cymene)ruth-
enate(II) complexes [10,11]. Accordingly, we examined the effects
of added chloride ion to CDCl3 solutions (ꢁ0.04 M) of 1a–c. In all
cases, the reactions proceeded very cleanly, and we noticed (in
some instances a dramatic) change in the 31P{1H} NMR spectrum
of each complex, with generally only one main peak observed in
the presence of excess chloride. When a threefold excess of [Et4N]Cl
was added to 1a, we observed only a marginal change in the inten-
sities of the two 31P signals, and the peak downfield at d = 24.5 ppm
remained dominant. In contrast, complexes 1b and 1c responded
more dramatically towards adding excess [Et4N]Cl. Thus, with com-
plex 1b (inset, Fig. 3) one dominant signal at d = 29.2 ppm was ob-
served; of the other two original upfield signals, one (d = 27.4 ppm)
substantially decreased in intensity, while the other (d = 25.9 ppm)
disappeared completely. An almost identical response was also wit-
nessed for complex 1c: a single dominant peak at d = 21.4 ppm was
observed, while the remaining two signals upfield became consid-
erably less intense (d = 19.9 ppm) or completely disappeared
(d = 18.6 ppm). The 1H NMR spectra of 1a–c, particularly in the
coordinated arene region, also became dramatically simplified
upon adding excess chloride ion, with each now revealing a prom-
inent pair of doublets corresponding to the ortho and meta hydro-
gens of the arene ring (1a, d = 5.11 and 4.97 ppm; 1b, d = 4.94 and
4.89; 1c, d = 4.89 and 4.83), consistent with that observed for
Although we cannot unequivocally assign structures to all of the
species observed in solution for 1a–c and 1a0–c0, we might propose
the equilibrium structures depicted in Scheme 2. Thus, complex 1a,
and presumably 1a0, appear to favour monomeric species A in solu-
tion, since little response was observed to the addition of excess
chloride ion. In contrast, complexes 1b/b0 and 1c/c0 appear to show
a greater tendency towards chloride dissociation yielding bridged
species, B and C, and only favour monomeric species A in the pres-
ence of excess chloride ion. Interestingly, the 31P peak ratios re-
mained essentially unchanged in CDCl3, CD2Cl2 or C2D4Cl2,
suggesting the equilibria at least were not strongly dependent on
the identity of the chlorinated solvent. Unfortunately, we were
unsuccessful in isolating any bridged species from solutions of
1a–c or 1a0–c0. Nonetheless, similar complexes have been identi-
fied or isolated for other ruthenium(II)-arene complexes [9d,17].
The extent of unassisted spontaneous chloride loss from complexes
1a–c and 1a0–c0 in solution is intriguing, and perhaps is linked to
phosphine basicity here. Indeed, complexes 1a and 1a0 bearing
the comparatively weaker donor phosphine [PPh2(p-Ph3BC6H4)]ꢀ
appear to show little tendency toward chloride dissociation since
species A dominates in solution. However, bridged species (B and
C) appear to form more readily in solutions containing complexes
1b/1b0 and 1c/1c0 which bear the stronger donor phosphines
i
[PR2(p-Ph3BC6H4)]ꢀ (R = Pr or Cy).
[RuCl2(
g
6-p-cymene)(PR3)] [9a].
3.4. Synthesis of [RuCl(L)(
iPr or Cy; L = MeCN or py)
g
6-p-cymene){PR2(p-Ph3BC6H4)}] (R = Ph ,
We also explored how the equilibria responded to the addition
of an excess of a chloride scavenger. Unfortunately, the NMR spec-
tra were not as clean (e.g., reactions involving 1a yielded unappeal-
ing mixtures of products). Nonetheless, when solutions of complex
1b in CD2Cl2 were treated with a twofold excess of MeOTf, the
Intrigued by these results, we next turned our attention to-
wards exploring the possibility of complexes 1a–c or 1a0–c0 func-
tioning as precursors to formally neutral, zwitterionic complexes

M.T. Beach et al. / Journal of Organometallic Chemistry 693 (2008) 2921–2928
2927
R
-
BPh3
R
Ph3B
P
Cl
Ru
Ru
R
Ru
P
Cl
Cl
Cl
P
R
Ph3B
R
R
A
C
-Cl-
-Cl-
+Cl-
+Cl-
-
R
BPh3
R
P
Cl
Cl
Ru
Ru
Cl
P
Ph3B
R
R
B
Scheme 2.
by way of chloride ligand removal (Scheme 1). Our initial efforts
centred on trapping the zwitterions with suitable ligands with
the anticipation of forming stable 18-electron complexes. Interest-
ingly, the choice of Lewis acid was critical in effecting halide re-
moval, however we found AgNO3 or MeOTf were effective in all
reactions examined (AgNO3 was usually favoured in order to facil-
itate aqueous extraction of [Bu4N]NO3). Thus, treating either 1a–c
or 1a0–c0 with AgNO3 or MeOTf in the presence of excess pyridine
or acetonitrile yielded the 18-electron zwitterionic complexes
mally neutral zwitterionic complexes via chloride ligand removal,
which are readily trapped as their solvated adducts. We are cur-
rently exploring further the role of these novel phosphine ligands
in ruthenium half-sandwich chemistry, and hope to report these
results at a later date.
Acknowledgements
We are very grateful for the financial support provided by the
Natural Sciences and Engineering Research Council (NSERC) of
Canada.
[RuCl(py)(
2b; R = Cy, 2c) and [RuCl(MeCN)(
(R = Ph, 3a; R = Pr, 3b; R = Cy, 3c) as air-stable, orange-yellow
g
6-p-cymene){PR2(p-Ph3BC6H4)}] (R = Ph, 2a; R = iPr,
g
6-p-cymene){PR2(p-Ph3BC6H4)}]
i
Appendix A. Supplementary material
powders.
Complexes 2a–c and 3a–c were characterized in solution using
1H and 31P{1H} NMR spectroscopy, and the proposed formulae
were confirmed by microanalytical data. The chirality of the metal
centres was clearly demonstrated in their respective 1H NMR spec-
tra, and revealed diastereotopic methyl signals for the arene iso-
propyl substituent (and, for 2b and 3b, the isopropyl substituents
of the phosphine ligands), as well as four individual arene hydro-
gen atom signals [18]. The 1H NMR spectra of the pyridine adducts
also revealed signals corresponding to the ortho-pyridine hydro-
gens with chemical shifts diagnostic of coordinated pyridine [19]
(for 2a, d = 8.91 ppm; for 2b, d = 8.67 ppm; for 2c, d = 8.86), while
the acetonitrile adducts showed signals corresponding to coordi-
nated acetonitrile (for 3a, d = 1.54 ppm; for 3b, d = 1.83 ppm; for
3c, d = 1.54 ppm). We note that neutral complexes 2a–c and 3a–c
produce only one sharp signal in their 31P{1H} NMR spectra, possi-
bly suggesting the importance of complex charge on chloride dis-
sociation in solution for 1a–c and 1a0–c0.
CCDC 687100 and 687101 contain the supplementary crystallo-
graphic data for complexes 1a0 and 1b0. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.06.013.
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