Reactivity of RuCl2(CO)(PtBu2Me)2 toward H2 and Br?nsted Acids: Aggregation Triggered by Protonation and Phosphine Loss

Article abstract of DOI:10.1021/ic9605837

Reaction of H₂ with RuCl₂(CO)L₂ (L = P^tBu₂Me) in benzene forms RuHCl(CO)L₂ and HCl. The latter reacts with RuCl₂(CO)L₂ to give [LH][Ru₂Cl₅(CO)₂L₂] and [LH]Cl. The Ru₂Cl₅(CO)₂L₂^- ion is detected (NMR) as several isomers, and is shown by X-ray diffraction to have a face-shared bioctahedral structure: LCl(OC)Ru(μ-Cl)₂Ru(CO)ClL^-. The loss of phosphine from Ru(II) is triggered by electrophilic attack, but not directly on P or on the Ru-P bond. It is shown (low-temperature NMR studies) that HCl reacts with RuHCl(CO)L₂ to give initially RuCl₂(H₂)(CO)L₂, in which H₂ is trans to Cl. From this study, and also direct observation of the reaction of HCl with RuCl₂(CO)L₂ to produce Ru₂Cl₅(CO)₂L₂^-, the Br?nsted basicity of chloride in RuCl₂(CO)L₂ is established. This accounts for its reaction with PhC₂H and NEt₂ to give Ru(C₂Ph)Cl(CO)L₂. Crystallographic data (-173 °C) for [P^tBu₂MeH][Ru₂Cl₅(CO) ₂(P^tBu₂Me)₂]: a = 16.418(2)A?, c = 12.578(2)A?, c = 20.044(3)A?, β = 103.38(1)° with Z = 4 in space group P2_1/a.

Full text of DOI:10.1021/ic9605837

Inorg. Chem. 1996, 35, 7035-7040
7035
Reactivity of RuCl2(CO)(PtBu2Me)2 toward H2 and Brønsted Acids: Aggregation Triggered
by Protonation and Phosphine Loss
Dejian Huang, Kirsten Folting, and Kenneth G. Caulton*
Department of Chemistry and Molecular Structure Center, Indiana University,
Bloomington, Indiana 47405-4001
ReceiVed May 21, 1996X
Reaction of H2 with RuCl2(CO)L2 (L ) PtBu2Me) in benzene forms RuHCl(CO)L2 and HCl. The latter reacts
-
with RuCl2(CO)L2 to give [LH][Ru2Cl5(CO)2L2] and [LH]Cl. The Ru2Cl5(CO)2L2 ion is detected (NMR) as
several isomers, and is shown by X-ray diffraction to have a face-shared bioctahedral structure: LCl(OC)Ru(µ-
Cl)3Ru(CO)ClL-. The loss of phosphine from Ru(II) is triggered by electrophilic attack, but not directly on P or
on the Ru-P bond. It is shown (low-temperature NMR studies) that HCl reacts with RuHCl(CO)L2 to give
initially RuCl2(H2)(CO)L2, in which H2 is trans to Cl. From this study, and also direct observation of the reaction
of HCl with RuCl2(CO)L2 to produce Ru2Cl5(CO)2L2-, the Brønsted basicity of chloride in RuCl2(CO)L2 is
established. This accounts for its reaction with PhC2H and NEt3 to give Ru(C2Ph)Cl(CO)L2. Crystallographic
data (-173 °C) for [PtBu2MeH][Ru2Cl5(CO)2(PtBu2Me)2]: a ) 16.418(2)Å, b ) 12.578(2)Å, c ) 20.044(3)Å,
â ) 103.38(1)° with Z ) 4 in space group P21/a.
Introduction
(especially if it is not a π-acid ligand) to any of these 16-electron
complexes will leave chloride particularly Brønsted basic. Even
the above fiVe-coordinate molecules will have Brønsted basic
chloride, since there are more chloride lone pairs than can be
donated to the one empty metal orbital. We have tested some
of these ideas by reacting RuCl2(CO)(PtBu2Me)2 with anhydrous
HCl and even with H2, and report here the outcome of this study.
Transition metal complexes containing one or more hydride
ligands are normally synthesized1 by halide replacement (eq 1)
EH4- + MCl f MH + ...
(1)
with EH4- (E ) B, Al) reagents (and subsequent transformation
of the M(EH4) primary product with ROH) or by oxidative
addition of H2 to a low-valent metal (eq 2). Only poorly
Experimental Section
All manipulations were performed under inert atmosphere or in Vacuo
using standard Schlenk and glovebox techniques. Solvents were
distilled from drying agents and stored in bulbs with Teflon valves.
Infrared spectra were recorded on a Nicolet 510P FT-IR spectrometer.
NMR spectra were recorded on either a Nicolet 360 MHz or a Varian
XL 300 MHz instrument with chemical shifts in ppm referenced to
residual solvent peaks (1H) or external H3PO4 (31P). Elemental analysis
was performed by Desert Analytics, Tucson, AZ, or in this department
on a Perkin-Elmer 2400 CHNS analyzer.
M0 + H2 f M(H)2
(2)
understood are the reactions of later transition elements with
metal halides where H2 formally disproportionates into H+ and
H- (eq 3). Such heterolytic splitting of H2 is usually “pro-
MCl + H2 f MH + HCl
(3)
RuHCl(CO)(PtBu2Me)2. The following is an improved procedure
compared to the one reported,6 based on using NEt3 to scavenge evolved
HCl. To a mixture of RuCl3‚3H2O (4.0 g; 15 mmol), triethylamine
(3.4 g; 33 mmol), and 2-methoxyethanol (80 mL) was added via cannula
PtBu2Me (7.6 g; 47.4 mmol) in methoxyethanol (20 mL). The resulting
solution was heated to 130 °C for 12 h. Volatiles were evaporated,
and the residue was extracted with benzene (4 × 50 mL). The benzene
solution was evaporated in Vacuo to give a crude product. Recrystal-
lization from methoxyethanol gave orange-yellow crystals, which were
filtered off and washed with cold (-20 °C) methanol. Yield: 6.6 g
moted” by a Brønsted base (e.g., NEt3), which functions to
absorb HCl. The detailed mechanism of this heterolysis of H2
is not understood,2 and is the subject of this report.
Divalent ruthenium compounds are normally six-coordinate,
with an 18-valence-electron count. With sufficiently bulky
phosphines, five-coordinate 16-electron complexes become
isolable: RuCl2(PPh3)3,3 RuHCl(PPh3)3,4 and RuCl2(CO)-
(PCy3)2.5 These are all square-pyramidal with the anionic and
two trans phosphine ligands in the basal positions. We have
pursued the idea that there can be destabilizing interactions
between halide ligand lone pairs and the filled dπ orbitals of an
18-electron metal center. Thus, coordination of a sixth ligand
1
(89%). The purity of the products was checked by H and 31P NMR.
RuCl2(CO)(PtBu2Me)2. A solution of RuHCl(CO)(PtBu2Me)2 (2.0
g; 4 mmol) in CHCl3 (20 mL) was refluxed for 4.5 h. The color of the
solution changed from orange to dark brown. After the solution was
cooled to room temperature, CHCl3 was removed in Vacuo. The residue
was extracted four times with pentane. The combined pentane extracts
were evaporated, yielding a brown solid which was recrystallized from
toluene (-40 °C) to obtain 1.25 g (58%) of dark brown crystals. 31P-
{1H} NMR (C6D6): 39.0 ppm. 1H NMR (C6D6): 1.44 (vt, N ) 6.6
Hz, 6 H, PCH3), 1.30 (vt, N ) 12.9 Hz, 36 H, PtBu) ppm. IR (C6D6):
ν(CO) ) 1937 cm-1. Anal. Calc (found) for C19H42Cl2OP2Ru: C,
43.84 (43.81); H, 8.14 (8.24). MS (EI): m/z 520 (M), with isotopic
peaks consistent with the computer-simulated result for the formula
* Corresponding author. E-mail: caulton@indiana.edu.
X Abstract published in AdVance ACS Abstracts, October 15, 1996.
(1) Inorganic Reactions and Methods; Zuckerman, J. J., Ed.; VCH:
Weinheim: Germany, 1987; Vol. 2, p 173.
(2) Brothers, P. J. Prog. Inorg. Chem. 1981, 28, 1. Grushin, V. V. Acc.
Chem. Res. 1993, 26, 279.
(3) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
945.
(4) Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J. Chem. Soc. A 1968,
3143.
(5) Moers, F. G.; Buerskens, P. T.; Noordik, J. H. Cryst. Struct. Commun.
1982, 11, 1655.
(6) Gill, D. F.; Shaw, B. L. Inorg. Chim. Acta 1979, 32, 19.
S0020-1669(96)00583-6 CCC: $12.00 © 1996 American Chemical Society

7036 Inorganic Chemistry, Vol. 35, No. 24, 1996
Huang et al.
C19H42Cl2OP2Ru. RuCl2(CO)L2 has two rotamers at temperature <
-30 °C; the 31P chemical shifts are 38.5 and 37.8 ppm with a ratio of
1:0.7 at -70 °C.
Table 1. Crystallographic Data for
[PtBu2MeH][Ru2Cl5(CO)2(PtBu2Me)2]
formula C29H63Cl5O2P3Ru2
fw ) 916.14
space group: P21/a
trans,trans,trans-RuCl2(CO)2(PtBu2Me)2 and cis,cis,trans-RuCl2-
(CO)2(PtBu2Me)2. In an NMR tube with a Teflon stopcock, 10 mg of
RuCl2(CO)(PtBu2Me)2 was dissolved in toluene-d8. After three freeze-
pump-thaw cycles, 1 atm of CO was introduced, and the brown
solution changed to light yellow within the time of mixing. 31P{1H}
NMR: 42.05 ppm (trans isomer). 1H NMR: 1.47 (vt, N ) 5.7 Hz, 6
H, PCH3), 1.35 (vt, N ) 12.3 Hz, 36 H, PCCH3) ppm. IR: ν(CO) )
1981 cm-1. The solution was then kept at 80 °C in an oil bath for 2
h, during which the solution became colorless. 31P{1H} NMR: 44.8
ppm (cis, trans isomer). 1H NMR: 1.65 (vt, N ) 8.1 Hz, 6 H, PCH3),
1.29 (vt, N ) 12 Hz, 36 H, PCCH3) ppm. IR: ν(CO) ) 2029, 1964
T ) -173 °C
a ) 16.418(2) Å
b ) 12.578(2) Å
c ) 20.044(3) Å
â ) 103.38(1)°
V ) 4026.69 Å3
Z ) 4
λ ) 0.710 69 Åa
Fcalc ) 1.511 g cm-3
µ ) 12.1 cm-1
R(Fo)b ) 0.0583
Rw(Fo)c ) 0.0601
a Graphite monochromator. b R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw
)
2
[∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2 where w ) 1/σ2(|Fo|).
Table 2. Selected Distances (Å) and Angles (deg) for
[PtBu2MeH][Ru2Cl5(CO)2(PtBu2Me)2]
cm-1
.
[HPtBu2Me][Ru2Cl5(CO)2(PtBu2Me)2]. A Schlenk flask was charged
with RuCl2(CO)(PtBu2Me)2 (50 mg; 0.096 mmol) and toluene (5 mL).
After three freeze-pump-thaw cycles, 0.096 mmol of HCl gas was
condensed (-196 °C) into the flask via a gas manifold. The solution
was warmed to room temperature, and some white precipitate formed.
The solution was filtered, and the solid was washed with toluene. The
combined toluene solution was evaporated to dryness, and the residue
was recrystallized from CH2Cl2 and ether to give red crystals. Anal.
Calc (found) for C29H63Cl5O2P3Ru2: C, 38.02 (37.78); H, 6.93 (7.01).
31P{1H} NMR (C6D6): 64.3, 62.5, 28.7 ppm. 1H NMR (C6D6), ppm:
for the cation 0.94 (d, JHP ) 15.3 Hz, PCCH3), 1.54 (d, JHP ) 9.3 Hz,
PCH3); for the major anion isomer 1.43 (d, JHP ) 12.9 Hz, PCCH3),
1.45 (d, JHP ) 12.9 Hz, PCCH3), 1.48 (d, JHP ) 6.6 Hz, PCH3); for the
Distances
Ru(1)-Ru(2)
Ru(1)-Cl(3)
Ru(1)-Cl(4)
Ru(1)-Cl(5)
Ru(1)-Cl(6)
Ru(1)-P(9)
Ru(1)-C(7)
Ru(2)-Cl(3)
Ru(2)-Cl(4)
3.2988(10)
2.4264(22)
2.5144(25)
2.4857(21)
2.359(3)
2.3389(25)
1.858(12)
2.4205(22)
2.4996(23)
Ru(2)-Cl(5)
Ru(2)-Cl(19)
Ru(2)-P(22)
Ru(2)-C(20)
O(8)-C(7)
O(21)-C(20)
P(32)-Cl(19)
P(32)-Cl(4)
2.4890(22)
2.3952(27)
2.3453(23)
1.828(11)
1.088(14)
1.142(14)
3.857(3)
4.176(3)
Angles
Cl(3)-Ru(1)-Cl(4)
Cl(3)-Ru(1)-Cl(5)
80.33(8) Cl(3)-Ru(2)-P(22)
97.06(8)
98.8(3)
79.18(8)
90.13(8)
81.26(7) Cl(3)-Ru(2)-C(20)
minor anion isomer 1.37 (d, JHP ) 12.9 Hz, PCCH3), 1.51 (d, JHP
12.2 Hz, PCCH3), 1.61 (d, JHP ) 5.4 Hz, PCH3). IR (C6D6): ν(CO) )
1948, 1957 (sh) (weak) cm-1
)
Cl(3)-Ru(1)-Cl(6) 167.40(10) Cl(4)-Ru(2)-Cl(5)
Cl(3)-Ru(1)-P(9)
Cl(3)-Ru(1)-C(7)
Cl(4)-Ru(1)-Cl(5)
Cl(4)-Ru(1)-Cl(6)
Cl(4)-Ru(1)-P(9)
Cl(4)-Ru(1)-C(7)
Cl(5)-Ru(1)-Cl(6)
Cl(5)-Ru(1)-P(9)
Cl(5)-Ru(1)-C(7)
Cl(6)-Ru(1)-P(9)
Cl(6)-Ru(1)-C(7)
P(9)-Ru(1)-C(7)
Cl(3)-Ru(2)-Cl(4)
Cl(3)-Ru(2)-Cl(5)
99.10(8) Cl(4)-Ru(2)-Cl(19)
97.5(4)
Cl(4)-Ru(2)-P(22) 177.25(8)
.
78.96(8) Cl(4)-Ru(2)-C(20)
87.81(11) Cl(5)-Ru(2)-Cl(19)
92.1(4)
91.18(9)
Search for Intermediates by Low-Temperature Reactions. Typi-
cal method: An NMR tube was charged with RuHCl(CO)(PtBu2Me)2
(10 mg; 0.020 mmol) and toluene-d8 (0.5 mL). It was degassed by
three freeze-pump-thaw cycles. One equivalent of HCl gas was
introduced at -196 °C, and the tube was flame-sealed. The sealed
tube was kept in a dry ice-acetone bath with most of the tube immersed
in the bath. After the tube was shaken several times to allow mixing
of the gas and liquid, it was transferred to a precooled NMR probe.
Certain low-temperature experiments seeking to detect an adduct
between H2 and RuCl2(CO)L2 gave artifactual results due to formation
of an adduct with H2O impurity. This adduct, at -27 ppm in its 31P
178.27(8) Cl(5)-Ru(2)-P(22) 102.19(8)
91.4(4)
Cl(5)-Ru(2)-C(20) 171.1(4)
92.37(9) Cl(19)-Ru(2)-P(22) 92.23(8)
102.59(8) Cl(19)-Ru(2)-C(20) 87.4(3)
170.3(4)
92.87(10) Ru(1)-Cl(3)-Ru(2)
86.9(4)
87.1(4)
P(22)-Ru(2)-C(20)
86.6(4)
85.78(7)
82.28(7)
83.07(6)
177.4(11)
Ru(1)-Cl(4)-Ru(2)
Ru(1)-Cl(5)-Ru(2)
80.75(8) Ru(1)-C(7)-O(8)
81.31(7) Ru(2)-C(20)-O(21) 175.2(10)
1
Cl(3)-Ru(2)-Cl(19) 169.10(9)
NMR, showed a temperature-dependent H NMR signal in the range
3.14-3.42 ppm for the water protons. In contrast, dry sources of H2
gave no change in the 31P NMR spectrum in the temperature range
-50 to -120 °C (in Freons).
correction was applied (range 0.71-0.91). The structure was solved
by locating the Ru atoms in the best E map from MULTAN-78. The
remaining non-hydrogen atoms were located in successive iterations
of least-squares refinement followed by difference Fourier calculations.
Following initial refinement, many of the hydrogen atoms were evident,
at least one on each methyl group. Hydrogen atoms were then
introduced in fixed idealized positions and assigned a thermal parameter
of 1.0 plus the isotropic equivalent of the parent atom. During the
refinement, abnormally short C-O distances were noticed in the two
carbonyl groups (C(7)-O(8) and C(20)-O(21)), as well as elongated
thermal ellipsoids on the carbon atoms in these groups. A disorder
between CO and Cl was suspected and resolved. At the predominantly
CO site, the disorder is 85% CO and 15% Cl for Cl(42) and Cl(43). A
similar disorder would then be expected at the terminal Cl sites (Cl(6)
and Cl(19)); however, it was not possible to observe the 15% C and O
positions in a difference map computed after the occupancy of the Cl
atoms had been refined to approximately 85%. The final cycles of
full-matrix least-squares refinement were then completed using aniso-
tropic thermal parameters on non-hydrogen atoms, except for C(7),
O(8), C(20), O(21), Cl(42), and Cl(43), which were refined with
isotropic thermal parameters. Hydrogen atoms were fixed, and the final
R(F) was 0.058 for the full unique data. The final difference map was
essentially featureless, the largest peak was 1.33 e/Å3 in the vicinity of
Ru(1), and the deepest hole was -1.35 e/Å3. The results of the structure
determination are shown in Table 2 and Figure 1.
Reaction of RuCl2(CO)(PtBu2Me)2 with 0.5 equiv of HCl. To a
benzene solution of 10 mg of RuCl2(CO)(PtBu2Me)2 was added 0.01
mmol of HCl gas. The color changed from brown to orange. 31P{1H}
NMR: 64.3, 62.6 ([Ru2Cl5(CO)2(PtBu2Me)2]-) 22.0 ppm (coalesced
peak of [HPtBu2Me]+ and PtBu2Me).
Reaction of RuCl2(CO)(PtBu2Me)2 with H2 in the Presence of
NEt3. Into a degassed benzene solution of 10 mg of RuCl2(CO)-
(PtBu2Me)2 and 3 µL of NEt3 was introduced 1 atm of H2. After
mixing,
a
white precipitate formed. 31P{1H} NMR showed
RuHCl(CO)(PtBu2Me)2 as the only phosphine-containing product (50.1
1
ppm); this was further confirmed by H NMR.
X-ray Structure Determination of [HPtBu2Me][Ru2Cl5(CO)2-
(PtBu2Me)2]. A suitable single crystal (plate) was selected from the
bulk sample using inert-atmosphere handling techniques (nitrogen-filled
glovebag).7 The crystal was attached to a glass fiber using silicone
grease and then transferred to a goniostat where it was cooled to -173
°C for characterization and data collection. A systematic search of
selected regions of reciprocal space yielded a set of reflections which
exhibited 2/m diffraction symmetry. The systematic extinctions of h0l
for h ) 2n + 1 and of 0k0 for k ) 2n + 1 uniquely identified the
space group as P21/a (No. 14). This choice was confirmed by the
subsequent solution and refinement of the structure. Data collection
(6 < 2θ < 45°) was undertaken as detailed in Table 1; an absorption
Reaction of RuCl2(CO)(PtBu2Me)2 with PhCCH. To a benzene
solution of 10 mg (0.02 mmol) of RuCl2(CO)(PtBu2Me)2 was added 3
µL (0.02 mmol) of PhCCH. After 5 min at room temperature, 31P{1H}
(7) Huffman, J. C.; Lewis, L. N.; Caulton, K. G. Inorg. Chem. 1980, 19,
2755.

Reactivity of RuCl2(CO)(PtBu2Me)2
Inorganic Chemistry, Vol. 35, No. 24, 1996 7037
accord with the correctness of the structure for RuCl2(CO)L2:
it reacts (rapidly) with CO to give the all-trans isomer (only
one ν(CO)). Since this has fewer push/pull interactions from
Cl lone pairs to π*(CO), this isomer is expected to be less stable
than the cis-dicarbonyl. Indeed, the kinetic isomer is observed
to isomerize completely to the cis-dicarbonyl in toluene solution.
Figure 1. ORTEP drawing of the non-hydrogen atoms of (HPtBu2-
Me)Ru2Cl5(CO)2(PtBu2Me)2, showing selected atom labeling. Hydrogen
bonding from the (undetected) hydrogen on P(32) of the phosphonium
cation is shown as a dashed line to Cl(19).
In agreement with the expectation that back bonding will be
greater in the cis-dicarbonyl, its asymmetric ν(CO) value is 17
cm-1 lower than that of the trans-dicarbonyl. Both the cis and
the trans isomers show only a single 31P{1H} NMR chemical
NMR revealed [HPtBu2Me][Ru2Cl5(CO)2(PtBu2Me)2] (64.3, 62.6, 28.7
ppm), RuCl(C2Ph)(CO)(PtBu2Me)2 (41.1 ppm), Ru(C2Ph)2(CO)(PtBu2-
Me)2 (47.0 ppm), and PtBu2Me (11.8 ppm).
t
shift and a single Bu proton virtual triplet.
Hydrogenolysis of RuCl2(CO)L2. Reaction of RuCl2(CO)L2
(L ) PtBu2Me) with 1 atm of H2 in toluene at 25 °C gives,
with the time of our first NMR observation (20 min), complete
consumption of the dichloride complex with production of some
RuHCl(CO)L2. Also evident by 31P{1H} NMR spectroscopy
RuCl(C2Ph)(CO)(PtBu2Me)2. PhCCH (30 mg; 0.30 mmol) in
toluene (2 mL) was added via a cannula to a 10 mL toluene solution
of RuCl2(CO)(PtBu2Me)2 (150 mg; 0.30 mmol) and NEt3 (90 mg; 0.90
mmol) at -40 °C. The mixture was stirred for 24 h at room
temperature, during which a white solid formed. The brown mixture
was filtered through a Celite pad. The filtrate was evaporated to
dryness, and the residue was extracted with pentane. The pentane
solution was concentrated to 3 mL. After 1 day at -40 °C, dark brown
crystals precipitated and were filtered off, washed with a small amount
of pentane, and dried in Vacuo. Yield: 125 mg (74%). 31P{1H} NMR
(C6D6, 25 °C): 41.0 ppm. 1H NMR (C6D6, room temperature): 1.34
(two overlapping vt, J ) 13.8 Hz, 36 H, PCCH3), 1.55 (vt, J ) 6.6
Hz, 6 H, PCH3), 7.00 (m, 1 H C6H5-p-H), 7.17 (m, 2 H, C6H5 m-H),
7.50 (dd, 2 H, C6H5-o-H) ppm. IR (C6D6): 2095 (ν(CtC)), 1937
-
are a group of signals due to isomers of Ru2Cl5(CO)2L2 (see
below) and the resonance due to protonated phosphine, HPt-
Bu2Me+. The reactions forming these two products are those
in eqs 4 and 5, which show that the relative amounts of RuHCl-
RuCl2(CO)L2 + H2 f RuHCl(CO)L2 + HCl
2RuCl2(CO)L2 + HCl f [LH][Ru2Cl5(CO)2L2] + L (5a)
L + HCl H [LH]Cl (5b)
(4)
(ν(CtO) cm-1
. Anal. Calc (found) for C27H47ClOP2Ru: C, 55.32
(55.37); H, 8.08 (7.95).
trans,trans- and cis,trans-RuCl(C2Ph)(CO)2(PtBu2Me)2. Into a
toluene solution of 10 mg of RuCl(C2Ph)(CO)(PtBu2Me)2 was intro-
duced 1 atm of CO at -78 °C. After mixing, the solution color changed
from brown to pale orange. 31P{1H} NMR at -80 °C showed one
peak at 47.0 ppm assigned to trans,trans-RuCl(C2Ph)(CO)2(PtBu2Me)2,
which, at room temperature, was completely isomerized to the cis,-
trans isomer. 31P{1H} NMR: 48.0 ppm. 1H NMR: 1.34 and 1.33
(vt, J ) 13 Hz, PCCH3), 1.78 (vt, J ) 6.6 Hz, PCH3), 7.00 (tt, J ) 7
Hz, 2 Hz, 1 H, C6H5 p-H), 7.16 (dd, J ) 8 Hz, 7 Hz, 2 H, C6H5), 7.58
(dd, J ) 8 Hz, 2 Hz, 2 H, C6H5) ppm. IR (C6D6): 2027 and 1960
cm-1 with equal intensities.
(CO)L2 and Ru2Cl5(CO)2L2- will be influenced by stirring rate,
by the rates of the reactions in eqs 4 and 5, and by the
concentrations of dissolved H2 and HCl.
[LH][Ru2Cl5(CO)2L2]. This compound crystallizes well in
any of the reactions described in this report where it is formed
in toluene. It can be conveniently recrystallized from CH2Cl2/
Et2O. The 31P{1H} NMR of recrystallized material shows (25
°C) two resonances of unequal intensity at 64.2 ppm (intensity
37) and 62.3 ppm (intensity 30) and a third, due to LH+, at
29.2 ppm (intensity 33). The intensity ratio of cation to the
sum of the 60-70 ppm resonances is ∼1:2, consistent with a
formula [LH][Ru2Cl5(CO)2L2]. The 1H NMR spectrum of this
Results
t
product in C6D6 shows Bu and Me doublets for HPtBu2Me+
The synthesis of RuCl2(CO)L2 (L ) PtBu2Me) is conveniently
accomplished by refluxing RuHCl(CO)L2 in chloroform for 4
h. A number of other reagents were tried, without success.
These include CH3COCl, PhCH2Cl, N-chlorosuccinimide, and
CCl4. This reaction is also quite specific, since it fails to convert
either RuHCl(CO)(PiPr3)2 or OsHCl(CO)(PtBu2Me)2 to the
corresponding dichloride.
The structure of RuCl2CO(PCy3)2 shows it to be square-
pyramidal with CO apical.8 The ν(CO) value (1937 cm-1) for
RuCl2(CO)L2 is distinctly higher than that for RuHCl(CO)L2
(where CO is trans to Cl); this frequency indicates CO in a site
trans to no ligand. We also offer a reactivity result which is in
t
and four Bu doublets for phosphines attached to Ru. There
are also two PMe doublets. If it is formed according to eq
5a (which has been independently verified), consumption of
RuCl2(CO)L2 is complete at an HCl:Ru ratio of 0.5 (see eq 5a
and also see below). The resulting product has a ν(CO)
stretching pattern in its infrared spectrum (in C6D6) composed
of one strong band (1948 cm-1) with a weak shoulder at ∼1957
cm-1. All of these spectra suggest two isomeric forms for
-
Ru2Cl5(CO)2L2
.
The formula of one crystal from solid samples which repro-
ducibly give a three-line 31P{1H} NMR spectrum was estab-
lished by single-crystal X-ray diffraction to be [LH][Ru2Cl5-
(CO)2L2], as shown in Figure 1. It is a face-shared bioctahedron
with three bridging halides, which is a common way for Ru(II)
(8) Moers, F. G.; Beurskens, P. T.; Noordijk, J. H. Cryst. Struct. Commun.
1982, 11, 1655.

7038 Inorganic Chemistry, Vol. 35, No. 24, 1996
Huang et al.
Chart 1
Scheme 1
less, T1 of H2 in the presence of RuCl2(CO)L2 is 110 ms at
-60 °C, much shorter than that of free dissolved H2, and
indicating weak interaction of H2 with RuCl2(CO)L2. The
reaction of H2 and RuCl2(CO)L2 occurs at temperatures >-40
°C to form L, [HL][Ru2Cl5(CO)2L2], and RuHCl(CO)L2. The
proposed reaction mechanism is depicted in Scheme 1 (the
compound in quotation marks is unobserved). H2 binds to
RuCl2(CO)L2 to form an unobservable trans-RuCl2(H2)-
(CO)L2 transient, which generates RuHCl(CO)L2 by dissociation
of HCl. The Brønsted acidity of coordinated H2 is well
established.12 The generated HCl reacts with RuCl2(CO)L2 to
form [HL][Ru2Cl5(CO)2L2] and L. This could be confirmed in
two ways. First, reaction of RuCl2(CO)L2 with H2 in the
presence of the HCl scavenger NEt3 (which does not bind
detectably to RuCl2(CO)L2) at room temperature in benzene
gives 100% yield (31P{1H} and 1H NMR) of RuHCl(CO)L2 and
[HNEt3]Cl. In addition, reaction of HCl with RuCl2(CO)L2 at
a 1:2 mole ratio at room temperature in benzene gives a
100% yield (31P{1H} NMR) of [HL][Ru2Cl5(CO)2L2] and
equimolar L.
to achieve coordination number 6 when ligands are in short
supply (i.e., HCl has consumed phosphine ligands under our
reaction conditions). There are five possible isomers, based on
the configuration of the two Ru(CO)LCl units. They are shown
in Chart 1, together with their symmetry, followed by the
expected number of 31P NMR chemical shifts. The crystal
selected for the X-ray study contains primarily the mirror-
symmetric structure in Chart 1. There is however an 85:15
disorder of CO and Cl in the crystal selected. The disorder is
consistent with a 70:15:15 occupation by isomer m and the two
enantiomers of the isomer marked with an asterisk in Chart 1.
The overall structure of the major (and also the minor) anion
has phosphine ligands eclipsed at opposite ends, although it is
clear that there are no significant repulsions between the eclipsed
bulky phosphines. It is of course significant that Ru(II)
molecules with two bulky PtBu2Me ligands are always five-
coordinate monomers (i.e., halide bridging is absent), yet here,
with only one PtBu2Me ligand per Ru, a face-shared bioctahe-
dron is adopted. Ru-Cl bond lengths are longer to µ-Cl
(average 2.473(3) Å) than to terminal Cl (average 2.377(4) Å),
and Ru-(µ-Cl) distances lengthen systematically according to
the ligand in the trans site according to Cl < CO < PtBu2Me.
The Ru-CO distances are short (average 1.843(15) Å), and Ru-
C-O angles are essentially linear (angles exceed 175.2°).
Angles at µ-Cl range from 82.3(7) to 85.8(7)°, and (µ-Cl)-
Ru-(µ-Cl) angles are much less than 90° (79.0(1)-81.3(1)°).
This furnishes more room for the bulky phosphines, but angles
involving terminal ligands are all less than 92.9°. An analogous
anion, Ru2(µ-Cl)3Cl2(CO)2(PPh3)2-, was isolated following
protonation (CH2ClCO2H) of RuHCl(CO)(PPh3)3.9 The face-
shared octahedron is of extremely common occurrence for
Ru(II).10
Characterization and Decomposition Pathways of cis-
RuCl2(H2)(CO)L2. We sought to evaluate whether the Ru2
anion was formed only from HCl attack on RuCl2(CO)L2 or
also from HCl reacting with the primary product RuHCl(CO)-
L2. Our early attempts to synthesize RuCl2(CO)L2 according
to eq 6 at 25 °C were completely unsuccessful (the 31P{1H}
RuHCl(CO)L2 + HCl
9
?8 RuCl2(CO)L2 + H2
(6)
NMR spectrum of the product solution contained numerous
resonances, indicative of an unselective reaction). This sug-
gested that simple chloride-for-hydride replacement was not
viable. Our results also showed that 2.5 equiv of HCl had to
be used to completely consume the hydride. When slightly less
than 1 equiv of HCl gas is combined with RuHCl(CO)L2 in
toluene at -70 °C (Figure 2), 31P{1H} NMR revealed a broad
peak at 54 ppm for one rotamer of RuHCl(CO)L2 (A),13 a major
peak at 48.4 ppm (B) (cis-RuCl2(H2)(CO)L2), and a trace amount
of RuCl2(CO)L2 (C). The assignment of the 48.4 ppm peak is
further supported by the 1H NMR data obtained under the same
conditions: a broad peak at -9 ppm, which has T1min ) 6.9 ms
at -70 °C, for η2-H2. The calculated rH-H distance is 0.891 Å
for slow-spinning H2 (JHD for Ru(η2-HD)Cl2(CO)L2 is measured
as 28 Hz). In addition, two virtual triplets for diastereotopic
tBu groups on the phosphine ligands confirm a cis geometry.
When the sample was warmed to -50 °C, the major signal
sharpened while the RuHCl(CO)L2 peak broadened. Trace
amounts of RuCl2(CO)L2 (C) and free H2 (in the 1H NMR) were
also observed. A dramatic change occurred at -40 °C. The
intensity of the RuCl2(CO)L2 peak (38 ppm) increased signifi-
The phosphonium proton appears to be involved in a
hydrogen bond to chloride in the solid state. The P-H vector
points in the direction of terminal Cl(19), and bridging chloride
Cl(4), with the P(32)/Cl(19) contact the shorter at 3.86 Å. This
is only 0.25 Å longer (after correction for P Vs N single-bond
radii) than found for strong N-H‚‚‚Cl hydrogen bonds.11 Such
hydrogen bonding helps to explain the benzene solubility of
this salt.
Search for Reaction Intermediates. Although reaction of
RuCl2(CO)L2 with H2 at room temperature is complete within
20 min, attempts to detect its H2 adduct were unsuccessful even
at -120 °C because of a low equilibrium constant. Neverthe-
(9) Sanchez-Delgado, R. A.; Thewalt, U.; Valencia, N.; Andriollo, A.;
Ma´rquez-Silva, R. Inorg. Chem. 1986, 25, 1097.
(10) Ohta, T.; Tonomura, Y.; Nozaki, K.; Takaya, H.; Mashima, K.
Organometallics 1996, 15, 1521. Joshi, A. M.; Thorburn, I. S.; Rettig,
S. J.; James, B. R. Inorg. Chim. Acta 1992, 198-200, 283. Seddon,
E. A.; Seddon, K. R. The Chemistry of Ruthenium; Elsevier: Am-
sterdam, 1984; p 497.
(12) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155.
(13) Notheis, J. U.; Heyn, R. H.; Caulton, K. G. Inorg. Chim. Acta 1995,
229, 187. RuHCl(CO)L2 exhibits three rotamers at -70 °C. Major
isomer (>90%) is at 54 ppm (singlet) (31P{1H} NMR). Two minor
isomers are at 42 and 40 ppm.
(11) Halepoto, D. M.; Larkworthy, L. F.; Povey, D. C.; Smith, G. W.;
Ramdas, V. Polyhedron 1995, 14, 1453.

Reactivity of RuCl2(CO)(PtBu2Me)2
Inorganic Chemistry, Vol. 35, No. 24, 1996 7039
reaction of LiC2Ph with RuCl2(CO)L2 (1:1 mole ratio) gives
mainly Ru(C2Ph)2(CO)L2 and a small amount of Ru(C2Ph)Cl-
(CO)L2, together with unreacted RuCl2(CO)L2. Apparently,
LiC2Ph reacts more rapidly with (the more electrophilic) RuCl-
(C2Ph)(CO)L2 than with RuCl2(CO)L2.
The product RuCl(C2Ph)(CO)L2 shows two 1H NMR virtual
t
triplets for the (diastereotopic) Bu groups, a virtual triplet for
the PMe groups, and a ν(CO) value essentially identical to that
of RuCl2(CO)L2. This strongly suggests that CO occupies the
apical site that it does in RuCl2(CO)L2, since CO in a basal site
has a lower ν(CO) value due to more efficient (trans) back-
donation. At 25 °C, Ru(C2Ph)Cl(CO)(PtBu2Me)2 absorbs 1
equiv of CO (eq 7) to give Ru(C2Ph)Cl(CO)2(PtBu2Me)2, which
(7)
shows two ν(CO) bands (2027, 1960 cm-1; intensities 1:1). This
indicates that the cis isomer is formed. However, on repetition
of this reaction at -80 °C in toluene, a kinetic product is
observed (31P{1H} NMR signal at 47 ppm). This isomerizes
within 20 min at 25 °C to the cis isomer. We assign the kinetic
product to be the isomer with the two CO ligands mutually trans,
which is clearly the product of approach of dissolved CO to
the open site of this square-pyramidal monocarbonyl.
Base-induced elimination of HCl has been employed14 to form
Pt/C bonds in the polymerization of (HCtC-aryl)PtCl. Brøn-
sted basic halide on late transition metals may thus be of rather
general occurrence.
Other Reactions. In the course of our attempts at halide
metathesis of RuCl2(CO)L2 with NaI, LiBr, and CsF in acetone,
we have observed the production of free PtBu2Me and several
31P{1H} NMR singlets between 60 and 70 ppm. These we
propose to be a species analogous to that arising from HCl:
MI[Ru2(halide)5(CO)2L2].
We consider that these results, taken together, show that
RuCl2(CO)L2, when it adds a sixth ligand, shows a tendency to
lose one of its bulky phosphine ligands, with subsequent halide-
bridged aggregation of the resulting unsaturated RuCl2(CO)-
(Nu)L (Nu ) H2, Cl-, ClH, F-, or I-). This aggregation
becomes possible (while it was not for RuCl2(CO)L2) because
of the diminished steric encumbrance of the metal after loss of
phosphine. This is shown in Scheme 2.
Figure 2. Variable-temperature 31P{1H} NMR spectra for the reaction
of RuHCl(CO)L2 with less than equimolar HCl. Reactants were
combined below -70 °C, and the progress of the reaction was
monitored as the temperature (shown at left) was raised.
cantly along with the RuHCl(CO)L2 peak. Several peaks in
the region 63-65 ppm (E) are attributed to many possible
isomers of Ru2Cl5(CO)2L2-. The counterion HL+ appears at
30 ppm (D). On 1H NMR integration, the ratio of free H2, the
proton of RuHCl(CO)L2, and bound H2 on Ru(H2)Cl2(CO)L2
is 1:1.2:1. At -30 °C, Ru(H2)Cl2(CO)L2 and RuCl2(CO)L2
were transformed to [Ru2Cl5(CO)2Cl2]-, RuHCl(CO)L2, HL+,
and L (10 ppm) (F). Detection of free L at this temperature
indicates that it is dissociated from ruthenium spontaneously
and is not induced by direct protonation of phosphorus itself.
The conclusion is that eq 5a may be initiated by protonation of
Cl on Ru. Consumption of RuCl2(CO)L2 can be caused either
by reaction with H2 in the solution or by HCl dissociated
from cis-RuCl2(H2)(CO)L2; both routes produce RuHCl(CO)-
1
L2. The H NMR intensity of the free H2 signal decreases,
indicating reaction of H2 with RuCl2(CO)L2. However, no
evidence can be obtained to rule out the dissociation of HCl
from cis-RuCl2(H2)(CO)L2. Above -30 °C, rearrangements of
Conclusions
While we have established that the thermodynamic isomer
cis-RuCl2(H2)(CO)L2 (A) is a dihydrogen complex, its trans
isomer (B) is not observable in NMR. This is consistent with
-
the isomers of Ru2Cl5(CO)2L2 and coalescence of HL+ and
L are the only changes (Scheme 1). The RuHCl(CO)L2
which remains is due to the substoichiometric amount of HCl
used. It is clear that the failure to synthesize RuCl2(CO)L2 by
this reaction is due to the competing dissociation of H2 and
HCl, which reacts immediately with RuCl2(CO)L2 to form
-
Ru2Cl5(CO)2L2
.
Reaction of PhC2H as a Brønsted Acid toward RuCl2-
(CO)L2. Additional evidence for the Brønsted basicity of the
chloride ligands in RuCl2(CO)L2 comes from its reaction with
a terminal alkyne. In the presence of NEt3 as a proton acceptor,
PhC2H reacts cleanly with RuCl2(CO)L2 to give RuCl(C2Ph)-
(CO)L2 and [HNEt3]Cl as the only products. In the absence of
NEt3, the liberated HCl reacts with RuCl2(CO)L2 to give some
Ru2Cl5(CO)2L2-. This is an effective synthetic route to this
halo/acetylide compound not only because it does not require
an electropositive metal acetylide reagent but also because the
the trans effect of CO in B preventing a close approach of H2
to Ru and therefore minimal back-donation to σ*(H-H). The
formation constant for B is thus very low. In contrast, H2 in
isomer A is trans to a weaker σ ligand Cl, and thus H2 can
approach closer to Ru, where dπ to σ*(H-H) overlap is more
(14) James, S. L.; Verspui, G.; Spek, A. L.; van Koten, G. Chem. Commun.
1996, 1309.

7040 Inorganic Chemistry, Vol. 35, No. 24, 1996
Huang et al.
Scheme 2
+ Os(H)2Cl2L216), protonation of the metal (cf. protonation of
W(CO)3(PCy3)2),17 or coordination of the molecular ClH to Ru
(compare η1-ClH bound to Pt(II)18).
The reactivity of RuXCl(CO)L2 with H2 is very different for
X ) H (only weak adduct formation, to give an η2-H2 complex)
and for X ) Cl (hydrogenolysis of an Ru-Cl bond, with
liberation of HCl). The latter case is an unusual example of
simple (i.e., two-component) heterolytic splitting of H2,2 without
the necessity of added base. However, it is clear from the work
reported here that the liberation of HCl can be dangerous (here,
it reacts with RuCl2(CO)L2 to give a diruthenium species). The
distinct reactivity of these two RuXCl(CO)L2 species may
originate in part because of their different structures (H and
CO apical, respectively), but the occurrence of proton transfer
by coordinated H2 to Cl suggests that the enhanced Brønsted
basicity of chloride when X ) Cl is a significant contributor to
the observed reactivity. RuCl2(CO)L2 also shows unusual
reactivity with PhC2H: the alkyne acts like a Brønsted acid
toward the chloride. RuHCl(CO)L2, in contrast, adds the Ru-H
bond across the alkyne triple bond.19
efficient. Back-donation is even more effective in A because
the filled-filled repulsion of Cl trans to H2 raises the energy
of the filled dπ orbital toward that of σ*(H-H). Consistent
with these observations, the cis isomer OsCl2(H2)CO(PiPr3)2 (the
trans isomer is unknown) binds H2 so well that it is not removed
under vacuum,15 either in toluene solution or as a solid.
The results reported here show the dramatic influence of
synthetic approach (HCl and RuHCl(CO)L2 Vs H2 and RuCl2-
(CO)L2) on the isomeric products obtained. Our study also
reveals that, in spite of the square-pyramidal geometry of RuCl2-
(CO)L2 with CO trans to a vacant site, the activation energy
for H2 addition is high enough that no cis RuCl2(H2)(CO)L2
(A) can be formed by mixing H2 and RuCl2(CO)L2 at low
temperature. In contrast, HCl reacts with RuHCl(CO)L2 to
produce a product (A) which appears as if it has added within
the H-Ru-Cl angle to produce coordinated H2 and mutually
cis chlorides (C, path a). This could be a concerted reaction,
It was recently reported20 that a solution containing a
dichlororuthenium species (RuHnCl2(PiPr3)2?) reacts with CO
to give the monochloro species RuHCl(CO)2(PiPr3)2. We
suggest that this reaction involves loss of HCl (compare eq 4
here) and is thus closely related to the behavior of RuH2Cl2-
(CO)L2 we report here. Moreover, the original report6 isolated
an otherwise unidentified product of reaction of HCl with
RuHCl(CO)[PtBu2Me]2; this product is that shown in Figure 1.
Acknowledgment. This work was supported by funds from
the National Science Foundation and by material from Johnson
Matthey/Aesar. We thank Dr. D. G. Gusev for crucial contribu-
tions to our understanding of these results.
Supporting Information Available: Tables of full crystallographic
details, fractional coordinates, and anisotropic thermal parameters (3
pages). Ordering information is given on any current masthead page.
IC9605837
initiated by hydrogen bonding of HCl to coordinated hydride
(or chloride), but it may also proceed via a nonconcerted path,
involving Ru(H2)Cl(CO)L2 and free chloride, or by an
intermediate with HCl added trans to the hydride (C, path b).
Finally, we cannot be certain whether the HCl reaction with
RuCl2(CO)L2 begins with protonation of coordinated Cl (cf. H+
(16) Kuhlman, R.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 1995, 34,
1788.
(17) Van Der Sluys, L. S.; Kubat-Martin, K. A.; Kubas, G. J.; Caulton, K.
G. Inorg. Chem. 1991, 30, 306.
(18) Kuhlman, R.; Rothfuss, H.; Gusev, D. G.; Streib, W. E.; Caulton, K.
G. Abstr. PapsAm. Chem. Soc. 1995, 209th, INOR 497.
(19) Poulton, J. T.; Sigalas, M. P.; Eisenstein, O.; Caulton, K. G. Inorg.
Chem. 1993, 32, 5490.
+
(15) Esteruelas, M. A.; Lahoz, F. J.; On˜ate, E.; Oro, L. A.; Valero, C.;
(20) Gru¨nwald, C.; Gevert, O.; Wolf, J.; Gonza´lez-Herrero, P.; Werner,
H. Organometallics 1996, 15, 1960.
Zeier, B. J. Am. Chem. Soc. 1995, 117, 7935.