Characterization and reactivity of an unprecedented unsaturated zero-valent ruthenium species: Isolable, yet highly reactive

Article abstract of DOI:10.1021/ja960967w

Magnesium reduction of cis,cis,trans-RuCl₂(CO)₂L₂ (L = P(t)Bu₂Me) yields isolable Ru(CO)₂L₂, shown by solution spectroscopies and X-ray diffraction to have trans phosphines but cis carbonyls, in a nonplanar structure which resembles a trigonal bipyramid with one equatorial ligand missing. This unusual geometric structure is traced by ab initio (MP2) study to enhanced back-donation to CO by zero-valent Ru. This molecule reacts in time of mixing to add CO, MeNC, O₂, CS₂, C₂H₄, or PhC≡CPh. Rapid oxidative addition occurs with H₂, HCl, Cl₂, and PhC≡CH. Oxidative addition is slower with MeCl, Me₃SiH, and MeOH, which leads to more complicated reaction schemes. Reaction with PPh₂H gives not oxidative addition but addition and displacement, yielding Ru(CO)₂(PPh₂H)₂(P(t)Bu₂Me) and equimolar free P(t)Bu₂Me. Magnesium reduction of cis,cis,trans-RuCl₂(CO)₂L'₂ proceeds analogously for L' = P(i)Pr₃, but for L' = PPh₃, decomposition and ligand scavenging give Ru(CO)₂(PPh₃)₃. Reduction of cis,trans-RuCl₂(CO)(CNMe)L₂ gives the product of oxidative addition of a (t)Bu C-H bond: RuH(CO)(CNMe)[η²-P(CMe₂CH₂)(t)BuMe]L, showing the influence of electron density at unsaturated Ru(0) on its persistence.

Full text of DOI:10.1021/ja960967w

J. Am. Chem. Soc. 1996, 118, 10189 10199
10189
Characterization and Reactivity of an Unprecedented
Unsaturated Zero-Valent Ruthenium Species: Isolable, Yet
Highly Reactive
Masamichi Ogasawara,† Stuart A. Macgregor,‡ William E. Streib,† Kirsten Folting,†
Odile Eisenstein,*,‡,§ and Kenneth G. Caulton*,†
Contribution from the Department of Chemistry and Molecular Structure Center, Indiana
Uni ersity, Bloomington, Indiana 47405-4001, Laboratoire de Chimie The´orique, Baˆtiment 490,
Uni ersite´ de Paris-Sud, 91405 Orsay, France, and LSDSMS, Case Courrier 014, Baˆtiment 15,
Uni ersite´ de Montpellier 2, 34095 Montpellier Cedex 5, France
Recei ed March 25, 1996X
Abstract: Magnesium reduction of cis,cis,trans-RuCl2(CO)2L2 (L
PtBu2Me) yields isolable Ru(CO)2L2, shown
by solution spectroscopies and X-ray diffraction to have trans phosphines but cis carbonyls, in a nonplanar structure
which resembles a trigonal bipyramid with one equatorial ligand missing. This unusual geometric structure is traced
by ab initio (MP2) study to enhanced back-donation to CO by zero-valent Ru. This molecule reacts in time of
mixing to add CO, MeNC, O2, CS2, C2H4, or PhCtCPh. Rapid oxidative addition occurs with H2, HCl, Cl2, and
PhCtCH. Oxidative addition is slower with MeCl, Me3SiH, and MeOH, which leads to more complicated reaction
schemes. Reaction with PPh2H gives not oxidative addition but addition and displacement, yielding Ru(CO)2-
(PPh2H)2(PtBu2Me) and equimolar free PtBu2Me. Magnesium reduction of cis,cis,trans-RuCl2(CO)2L′2 proceeds
analogously for L′ PiPr3, but for L′ PPh3, decomposition and ligand scavenging give Ru(CO)2(PPh3)3. Reduction
t
of cis,trans-RuCl2(CO)(CNMe)L2 gives the product of oxidative addition of a Bu C H bond: RuH(CO)(CNMe)-
[η2-P(CMe2CH2)tBuMe]L, showing the influence of electron density at unsaturated Ru(0) on its persistence.
were degassed under vacuum and used without further purification.
Benzene-d6 and toluene-d8 were dried over sodium metal and vacuum-
distilled prior to use. Phosphines (PiPr3 and PPh2H) and 1,2-
dibromoethane were purchased from Aldrich Chemical Co. and used
without purification. Diphenylacetylene, phenylacetylene, and carbon
disulfide were purchased from Aldrich and used after purifying by
appropriate methods (sublimation or distillation). Gaseous reagents
(H2, O2, CO, HCl, Cl2, C2H4, and MeCl) were purchased from Air
Products and used as received. Trimethylsilane was purchased from
Petrarch Systems and used as received. Formaldehyde (37% in water)
was purchased from Baker Analyzed and used as received. Methyl-
lithium (in diethyl ether, Aldrich) was used after its concentration was
determined by appropriate titration prior to use. Methyl isocyanide
was synthesized according to a published method.2 Ruthenium
trichloride hydrate was a generous loan from Johnson Matthey and
used as received. RuHCl(CO)(PtBu2Me)2,3 cis,cis,trans-RuCl2(CO)2-
(PtBu2Me)2,4 RuCl2(CO)(PtBu2Me)2,5 and cis,cis,trans-RuCl2(CO)2-
Introduction
We report here a new aspect to the chemistry of zero-valent
ruthenium; the isolation and characterization of unsaturated
Ru(CO)2(PtBu2Me)2. This permits the determination of the
unusual geometric and thus the electronic structure of this
molecule. In addition, most reactions of saturated Ru(0)
molecules with nucleophiles begin with ligand dissociation, and
thus determining the details of the reactions of the unsaturated
transient with the reagent partner remains difficult. In the work
presented here, since we begin with this persistent unsaturated
species, heretofore unobserved mechanistic detail is within
reach. Since our reactions occur at and below 25 °C, we are
often able to observe the primary (kinetic) products. Finally,
the persistence of Ru(CO)2(PtBu2Me)2 lies in part in its steric
bulk as well as in the resistance of the PtBu2Me to intramolecular
C H oxidative addition. We have tried to modulate the
properties of this unusual species by altering the steric and
electronic properties of the ligands. Part of this work has been
reported in a preliminary communication where we comment
that all other d8 four-coordinate species of RhI, IrI, PdII, and
PtII are planar.1
6
(PPh3)2 were synthesized as reported. 1H (300 MHz) NMR spectra
were recorded on a Varian XL300 spectrometer. 31P NMR spectra
were obtained on a Nicolet NT-360 spectrometer at 146 MHz. 1H NMR
chemical shifts are reported in ppm downfield of tetramethylsilane using
residual solvent resonances as internal standards. 31P NMR chemical
shifts are relative to external 85% H3PO4. Infrared spectra were
recorded on a Nicolet 510P FT-IR spectrometer. Elemental analyses
were performed by Desert Analytics, Tucson, AR, or on a Perkin-Elmer
2400 CHN/S elemental analyzer at the Chemistry Department, Indiana
University.
Experimental Section
General. All manipulations were carried out using standard Schlenk
and glovebox techniques under prepurified argon. Benzene, pentane,
THF, and toluene were dried over sodium benzophenone ketyl, distilled,
and stored in gas tight solvent bulbs. Methanol and 2-methoxyethanol
cis,cis,trans-RuCl2(CO)2(PiPr3)2. Carbon monoxide was passed
through a solution of ruthenium trichloride hydrate (2.31 g, 10.0 mmol)
in 2-methoxyethanol (55 mL) at 130 °C until the solution color changed
to pale yellow (ca. 12 h). After a small amount of insoluble material
* To whom correspondence should be addressed. E-mail: caulton@
indiana.edu; eisenst@lsd.univ-montp2.fr.
(2) Schuster, R. E.; Scott, J. E.; Casanova, J., Jr. Organic Syntheses;
Wiley: New York, 1973; Collect. Vol. V, p 772.
(3) Gill, D. F.; Shaw, B. L. Inorg. Chim. Acta 1979, 32, 19.
(4) Gill, D. F.; Mann, B. E.; Shaw, B. L. J. Chem. Soc., Dalton Trans.
1973, 311.
(5) Huang, D.; Folting, K.; Caulton, K. G., Inorg. Chem., in press.
(6) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
945.
† Indiana University.
‡ Universite´ de Paris-Sud.
§ Universite´ de Montpellier 2.
X Abstract published in Ad ance ACS Abstracts, October 1, 1996.
(1) Ogasawara, M.; Macgregor, S. A.; Streib, W. E.; Folting, K.;
Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1995, 117, 8869.
S0002-7863(96)00967-5 CCC: $12.00 © 1996 American Chemical Society

10190 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Ogasawara et al.
was filtered away, PiPr3 (3.50 g, 21.8 mmol) was added, and then the
solution was refluxed for 10 min. The solution was concentrated to
ca. 15 mL under reduced pressure and cooled to room temperature,
yielding two crops of white crystals; yield 4.75 g (8.62 mmol, 86%).
Ru(η2-O2)(CO)2(PtBu2Me)2 (6). Ru(CO)2(PtBu2Me)2 (100 mg, 0.21
mmol) was dissolved in pentane (5 mL) in a Schlenk flask, and the
flask was freeze/pump/thaw degassed three times. The solution was
cooled to 78 °C, and O2 (1 atm) was admitted to the flask at this
temperature. Immediately, the deep red solution became pale orange.
The remaining O2 gas was removed from the flask with the solvent by
evacuation. The remaining pale orange solid was recrystallized from
pentane to give two crops of the title compound in pure form; yield 92
mg (0.18 mmol, 86%). 1H NMR (toluene-d8, 23 °C): δ 1.15 (vt, JHP
3.2 Hz, 6H, P Me), 1.25 (vt, JHP 6.5 Hz, 36H, P tBu). 31P{1H}
1H NMR (C6D6, 23 °C): δ 1.26 (dvt, JHP ≈ JHH
7.0 Hz, 36H,
PCCH3), 2.79 (sept of vt, JHH 7.0 Hz, JHP 3.9 Hz, 6H, PCHMe2).
31P{1H} NMR (C6D6, 23 °C): δ 38.4 (s). IR: νCO (C6D6) 2029 and
1960 cm 1. Anal. Calcd for RuC20H42Cl2O2P2: C, 43.80; H, 7.72.
Found: C, 44.00; H, 7.69.
Ru(CO)2(PtBu2Me)2 (3). (a) From the Metalated Species.
A
Schlenk flask was charged with RuHCl(CO)(PtBu2Me)2 (303 mg, 0.62
mmol). Toluene (12 mL) was added, and the orange solution was
cooled to 78 °C. MeLi (1.4 M, 0.47 mL, 0.66 mmol) was added via
syringe, and the now darker orange mixture was warmed to 40 °C
with stirring for 20 min. The Schlenk flask was degassed three times
by freeze/pump/thaw cycles, and carbon monoxide (450 Torr in 36
mL at 290 K, 0.90 mmol) was introduced into the flask. After the
solution was stirred for 30 min at 40 °C, the remaining CO was
NMR (toluene-d8, 23 °C): δ 47.7 (s). IR: νCO (pentane) 1991 and
1
1921 cm
. Anal. Calcd for RuC20H42O4P2: C, 47.14; H, 8.31.
Found: C, 47.00; H, 8.17.
Ru(η2-CS2)(CO)2(PtBu2Me)2 (7). A pentane (20 mL) solution of
Ru(CO)2(PtBu2Me)2 (200 mg, 0.42 mmol) was placed in a Schlenk flask
fitted with a rubber septum and cooled to 78 °C. To this solution
was added CS2 (27 µL, 0.45 mmol) via syringe. Immediately, a light
orange precipitate formed from the dark red solution. Removing the
mother liquor and washing the remaining solid with cold pentane (10
mL × 2) gave the title compound in essentially pure form; yield 212
mg (0.38 mmol, 91%). 1H NMR (C6D6, 23 °C) δ 1.13 (vt, JHP 6.6
Hz, 18H, PtBu), 1.16 (vt, JHP 6.6 Hz, 18H, P tBu), 1.19 (vt, JHP
3.0 Hz, 6H, P Me). 31P{1H} NMR (toluene-d8, -80 °C): δ 52.3 (s).
IR: νCO (C6D6) 1993 and 1933 cm 1, νCS (C6D6) 1125 cm 1. Anal.
Calcd for RuC21H42O2P2S2: C, 45.55; H, 7.65. Found: C, 45.76; H,
7.51.
removed from the flask by pumping at low temperature (
40 °C).
The solution was warmed under argon to room temperature and then
kept stirring for 4 h. During this period, the solution color changed
from pale yellow to dark red. The volatiles were removed, and the
red residue was extracted with pentane (5 mL × 3). The combined
solution was concentrated and cooled, yielding very dark red crystals;
yield 137 mg (0.29 mmol, 46%). 1H NMR (C6D6, 23 °C): δ 1.19 (vt,
JHP 6.6 Hz, 36H, P-tBu), 1.38 (vt, JHP 2.1 Hz, 6H, P-Me). 31P-
{1H} NMR (C6D6, 23 °C): δ 65.4 (s). IR: νCO (Nujol) 1902 and 1831
cm 1. Anal. Calcd for RuC20H42O2P2: C, 50.30; H, 8.86; P, 12.97.
Found: C, 50.03; H, 8.88; P, 13.18.
Ru(η2-C2H4)(CO)2(PtBu2Me)2 (8). A solution of Ru(CO)2(PtBu2-
Me)2 (10 mg, 0.021 mmol) in toluene-d8 (0.5 mL) was placed in an
NMR tube fitted with a Teflon stopcock. The solution was frozen in
liquid N2, the headspace was evacuated, and ethylene (1 atm, ca. 0.12
mmol) was introduced into the tube. Upon thawing and vigorous
shaking, the 31P{1H} NMR spectrum showed reversible coordination
of ethylene to the complex (see text for detail). Below 50 °C, the
title compound is the only observable species by NMR. 1H NMR
(toluene-d8, 50 °C): δ 0.59 (br, 6H, P Me), 1.21 (vt, JHP 6.1 Hz,
36H, P tBu), 1.58 (t, JHP 5.6 Hz, 4H, C2H4). 31P{1H} NMR (toluene-
d8, 60 °C): δ 58.4 (s).
(b) Reduction of cis,cis,trans-RuCl2(CO)2(PtBu2Me)2. Magnesium
turnings (52 mg, 2.12 mmol) and THF (1 mL) were placed in a Schlenk
flask, and 1,2-dibromoethane (26 µL, 0.30 mmol) was added via
syringe. The mixture was gently stirred until the evolution of ethylene
ceased. To the flask was added a solution of cis,cis,trans-RuCl2(CO)2-
(PtBu2Me)2 (1.00 g, 1.82 mmol) in THF (30 mL) by means of cannula
transfer. The mixture was stirred at room temperature until all the
magnesium turnings were consumed (ca. 20 h). During this period,
the color of the solution changed from colorless to deep red. The
volatiles were removed, and the dark red residue was extracted with
pentane (20 mL × 3). After the insoluble material was filtered away,
the solution was concentrated and cooled, yielding two crops of dark
red crystals totaling 0.70 g (1.47 mmol, 80%). All the spectroscopic
data are consistent with those described above.
Ru(η2-PhCtCPh)(CO)2(PtBu2Me)2 (9). To a solution of Ru(CO)2(Pt-
Bu2Me)2 (10 mg, 0.021 mmol) in toluene-d8 (0.5 mL) was added
diphenylacetylene (4.0 mg, 0.022 mmol). Immediately, the deep red
solution became yellow. Although the 31P{1H} NMR spectrum showed
complete consumption of Ru(CO)2(PtBu2Me)2, isolation of the title
compound was unsuccessful due to the equilibrium with phosphine
dissociation (see text). 1H NMR (toluene-d8, 40 °C): δ 0.68 (br,
6H, P Me), 1.12 (vt, JHP 5.8 Hz, 36H, P tBu), 7.04 (t, JHH 7.2
Hz, 2H, p-H), 7.29 (t, JHH 7.8 Hz, 4H, m-H), 7.94 (d, JHH 7.2 Hz,
Ru(CO)2(PiPr3)2. This compound was synthesized from cis,cis,-
trans-RuCl2(CO)2(PiPr3)2 and stoichiometric activated magnesium turn-
ings in THF as described above in 83% yield. 1H NMR (C6D6, 23
°C): δ 1.19 (dvt, JHP JHH 6.8 Hz, 36H, PCCH3), 2.07 (sept of vt,
JHH 6.8 Hz, JHP 3.4 Hz, 6H, PCHMe). 31P{1H} NMR (C6D6, 23
°C): δ 71.2 (s). IR: νCO (Nujol) 1898 and 1829 cm 1. Anal. Calcd
for RuC20H42O2P2: C, 50.30; H, 8.86. Found: C, 50.47; H, 8.78.
Ru(CO)3(PtBu2Me)2 (4). A solution of Ru(CO)2(PtBu2Me)2 (10 mg,
0.021 mmol) in C6D6 (0.5 mL) was placed in an NMR tube fitted with
a Teflon stopcock. The solution was frozen in liquid N2, the headspace
was evacuated, and excess CO (1 atm) was introduced into the tube.
When the solution warmed to room temperature and the tube was
shaken, the solution color immediately changed from deep red to pale
yellow. 1H and 31P{1H} NMR and IR spectra showed complete
conversion to Ru(CO)3(PtBu2Me)2, which was previously reported.7
Ru(CNMe)(CO)2(PtBu2Me)2 (5). A pentane (5 mL) solution of
Ru(CO)2(PtBu2Me)2 (100 mg, 0.21 mmol) was placed in a Schlenk flask
fitted with a rubber septum. To this solution was added methyl
isocyanide (8.7 mg, 0.21 mmol) via syringe at room temperature.
Immediately, the dark red solution color changed to yellow. The solution
was concentrated to ca. 2 mL and cooled to 40 °C to give bright
yellow needles; yield 79 mg (0.15 mmol, 73%). 1H NMR (C6D6, 23
°C): δ 1.35 (vt, JHP 6.6 Hz, 36H, P tBu), 1.41 (vt, JHP 2.6 Hz,
6H, P Me), 2.53 (t, JHP 2.0 Hz, 3H, CH3NC). 31P{1H} NMR (C6D6,
23 °C): δ 68.8 (s). IR: νCO (C6D6) 1881 and 1829 cm 1, νCN (C6D6)
2078 cm 1. Anal. Calcd for RuC22H45NO2P2: C, 50.95; H, 8.75; N,
2.70. Found: C, 50.77; H, 8.54; N, 2.67.
4H, o-H). 31P{1H} NMR (toluene-d8, 40 °C): δ 60.9 (s). IR: νCO
1
(pentane) 1960 and 1896 cm 1, νCC (pentane) 1744 cm
.
Ru(CO)2(PPh2H)2(PtBu2Me) (11). To a solution of Ru(CO)2-
(PtBu2Me)2 (10 mg, 0.021 mmol) in C6D6 (0.5 mL) was added 7.4 µL
of diphenylphosphine (8.0 mg, 0.042 mmol). Immediately, the deep
red solution became bright yellow. Although the 31P{1H} NMR
spectrum showed complete conversion into Ru(CO)2(PPh2H)2(PtBu2-
Me) and free PtBu2Me, isolation of Ru(CO)2(PPh2H)2(PtBu2Me) in pure
form was unsuccessful due to the poor crystallinity of the compound.
1H NMR (C6D6, 23 °C): δ 1.23 (d, JHP 13.0 Hz, 18H, P-tBu), 1.34
(d, JHP 5.7 Hz, 3H, P-Me), 6.48 (dm, JHP 280 Hz, 2H, PH), 6.93
7.03 (m, 12H, m- and p-H), 7.55 (m, 8H, o-H). 31P{1H} NMR (C6D6,
23 °C): δ 24.4 (d, JPP 72.3 Hz, 2P, PPh2H), 66.6 (t, JPP 72.3 Hz,
1
1P, PtBu2Me). IR: νCO (pentane) 1858 cm
.
Ru(H)2(CO)2(PtBu2Me)2 (12). A solution of Ru(CO)2(PtBu2Me)2
(100 mg, 0.21 mmol) in pentane (5 mL) was placed in a Schlenk flask
and freeze/pump/thaw degassed three times. The solution was warmed
to room temperature, and H2 (1 atm) was admitted. Immediately, the
deep red solution became pale yellow. After filtration, the solution
was concentrated to ca. 1 mL under reduced pressure and cooled to
78 °C under H2 atmosphere, yielding pale yellow crystals; yield 88
mg (0.18 mmol, 88%). 1H NMR (toluene-d8, 23 °C): δ 7.96 (t, JHP
22.7 Hz, 2H, Ru H), 1.22 (vt, JHP
6.7 Hz, 36H, P tBu), 1.36
(vt, JHP 2.2 Hz, 6H, P Me). 31P{1H} NMR (toluene-d8, 23 °C): δ
1
74.0 (s). IR: νCO (Nujol) 1999 and 1966 cm
. Anal. Calcd for
(7) Heyn, R. H.; Macgregor, S. A.; Nadasdi, T. T.; Ogasawara, M.;
Eisenstein, O.; Caulton, K. G. Inorg. Chim. Acta, in press.
RuC20H44O2P2: C, 50.09; H, 9.25. Found: C, 50.09; H, 9.45.

Characterization of a Zero-Valent Ru Species
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10191
cis,trans-RuHCl(CO)2(PtBu2Me)2 (13). A solution of Ru(CO)2-
(PtBu2Me)2 (10 mg, 0.021 mmol) in C6D6 (0.5 mL) was placed in an
NMR tube fitted with a Teflon stopcock. The solution was frozen in
liquid N2, the headspace was evacuated, and HCl (0.021 mmol) was
condensed into the tube using a calibrated gas manifold. When the
solution warmed to room temperature and the tube was shaken, the
solution color immediately changed from deep red to colorless. 1H
and 31P{1H} NMR and IR spectra showed complete conversion to
RuHCl(CO)2(PtBu2Me)2, which was previously reported.3
RuCl2(CO)2(PtBu2Me)2 (14 and 15). A solution of Ru(CO)2-
(PtBu2Me)2 (10 mg, 0.021 mmol) in toluene-d8 (0.5 mL) was placed in
an NMR tube fitted with a Teflon stopcock. The solution was frozen
in liquid N2, the headspace was evacuated, and Cl2 (0.021 mmol) was
condensed into the tube using a calibrated gas manifold. When the
solution warmed to room temperature and the tube was shaken, the
solution color immediately changed from deep red to pale yellow. The
31P{1H} NMR spectrum showed complete conversion of Ru(CO)2-
(PtBu2Me)2 into cis-RuCl2(CO)2(PtBu2Me)2 and trans-RuCl2(CO)2-
(PtBu2Me)2 in a 2:1 molar ratio. Heating the solution at 70 °C for 2 h
isomerized the trans isomer to the cis isomer completely.
of ethylene ceased. A suspension of cis,cis,trans-RuCl2(CO)2(PPh3)2
(0.41 g, 0.54 mmol) in THF (10 mL) was added to the flask by means
of cannula transfer. The mixture was stirred at room temperature until
all the magnesium turnings were consumed. During this period, the
color of the solution changed from colorless to dark reddish brown.
The volatiles were removed, and the dark red residue was extracted
with benzene (10 mL × 3). After the insoluble material was filtered
away, the solution was evaporated to dryness, leaving a brown solid.
31P{1H} NMR and IR data reveal formation of Ru(CO)2(PPh3)39 as the
main product ( 90% purity based on 31P{1H} NMR); yield 225 mg
(0.24 mmol, 44% based on Ru).
cis,trans-RuCl2(CO)(CNMe)(PtBu2Me)2.10 To an orange solution
of RuCl2(CO)(PtBu2Me)2 (684 mg, 1.31 mmol) in toluene (30 mL) was
added 75 µL of methyl isocyanide (57 mg, 1.38 mmol) by means of
syringe at room temperature. The obtained pale yellow solution was
refluxed for 5 min. After filtration, the solution was concentrated to
ca. 10 mL and recrystallized from hot toluene to give two crops of
colorless crystals; yield 582 mg (1.04 mmol, 79%). 1H NMR (THF-
d8, 23 °C): δ 1.45 (vt, JHP 6.3 Hz, 36H, P tBu), 1.69 (vt, JHP 3.3
Hz, 6H, P Me), 3.52 (s, 3H, CH3NC). 31P{1H} NMR (THF-d8, 23
1
°C): δ 40.9 (s). IR: νCO (C6D6) 1956 cm 1, νCN (C6D6) 2174 cm
.
RuH(CtCPh)(CO)2(PtBu2Me)2 (16). A pentane (5 mL) solution
of Ru(CO)2(PtBu2Me)2 (100 mg, 0.21 mmol) was placed in a Schlenk
flask fitted with a rubber septum. To this solution was added 26 µL
of phenylacetylene (24.2 mg, 0.24 mmol) was added via syringe at
room temperature. Immediately, the dark red solution color changed
to colorless. The solution was concentrated to ca. 2 mL and cooled to
Anal. Calcd for RuC21H45Cl2NOP2: C, 44.92; H, 8.08; N, 2.49.
Found: C, 44.79; H, 8.23; N, 2.71.
RuH(CO)(CNMe)[η2-P(CMe2CH2)tBuMe](PtBu2Me) (17a and
17b). A solution of RuHCl(CO)(PtBu2Me)2 (10 mg, 0.021 mmol) in
toluene-d8 (0.5 mL) was placed in an NMR tube. The solution was
cooled to 78 °C, and MeLi (15 µL in 1.4 M ether solution, 0.021
mmol) was added into the tube by syringe. Warming to 40 °C formed
a diastereomeric mixture of RuH(CO)[η2-P(CMe2CH2)tBuMe](PtBu2-
Me) as reported.7 When methyl isocyanide (1.15 µL, 0.021 mmol)
was added into the NMR tube and the tube was shaken, the solution
color changed immediately from red-orange to pale yellow. 1H and
31P{1H} NMR spectra showed complete conversion to the title
compounds as a diastereomeric mixture. 17a: 31P{1H} NMR (toluene-
d8, 40 °C) δ 23.2 (d, JPP 240 Hz, 1P, metalated P), 65.1 (d, JPP
240 Hz, 1P, PtBu2Me); 1H NMR (toluene-d8, 40 °C) δ 7.29 (t, JPH
21.8 Hz, Ru-H). 17b: 31P{1H} NMR (toluene-d8, 40 °C) δ 13.9
(d, JPP 240 Hz, 1P, metalated P), 64.3 (d, JPP 240 Hz, 1P, PtBu2-
1
40 °C to give colorless needles; yield 92 mg (0.16 mmol, 76%). H
NMR (C6D6, 23 °C): δ 6.63 (t, JHP
19.7 Hz, 1H, Ru H), 1.21
(vt, JHP 6.5 Hz, 18H, P tBu), 1.35 (vt, JHP 6.5 Hz, 18H, P tBu),
1.63 (vt, JHP 3.0 Hz, 6H, P Me), 6.99 (m, 1H, p-H), 7.15 (m, 2H,
m-H), 7.50 (m, 2H, o-H). 31P{1H} NMR (C6D6, 23 °C): δ 60.2 (s).
IR: νCO (C6D6) 2020 and 1958 cm 1, νCC (C6D6) 2103 cm 1, νRuH (C6D6)
1
1919 cm
. Anal. Calcd for RuC28H48O2P2: C, 58.01; H, 8.35.
Found: C, 57.73; H, 8.34.
Reaction of Ru(CO)2(PtBu2Me)2 with MeCl. A solution of
Ru(CO)2(PtBu2Me)2 (10 mg, 0.021 mmol) in C6D6 (0.5 mL) was placed
in an NMR tube fitted with a Teflon stopcock. The solution was frozen
in liquid N2, the headspace was evacuated, and chloromethane (0.032
mmol) was condensed into the tube using a calibrated gas manifold.
After the solution was maintained at 80 °C for 2 h, the 31P{1H} NMR
spectrum showed complete conversion of Ru(CO)2(PtBu2Me)2 into Ru-
(COCH3)Cl(CO)(PtBu2Me)2,8 RuMeCl(CO)(PtBu2Me)2,8 and Ru(CO)3-
(PtBu2Me)2 in a 5:1:1 molar ratio.
1
Me); H NMR (toluene-d8, 40 °C) δ 7.48 (t, JPH 21.7 Hz, Ru
H).
Magnesium Reduction of RuCl2(CO)(CNMe)(PtBu2Me)2. Mag-
nesium turnings (21 mg, 0.84 mmol) and THF (0.5 mL) were placed
in a Schlenk flask, and 1,2-dibromoethane (40 µL, 0.46 mmol) was
added via syringe. The mixture was gently stirred until the evolution
of ethylene ceased. RuCl2(CO)(CNMe)(PtBu2Me)2 (205 mg, 0.37
mmol) in THF (8 mL) was added to the flask by means of cannula
transfer. The mixture was stirred at room temperature until all the
magnesium turnings were consumed (ca. 12 h). During this period,
the color of the solution changed from colorless to dark brown. The
volatiles were removed, and the dark brown residue was extracted with
toluene (5 mL × 3). After the insoluble material was filtered away,
the solution was evaporated to dryness, leaving ca. 150 mg of red-
orange-colored solid. The 31P{1H} NMR spectrum showed formation
of 17a and 17b as main products in addition to a singlet at δ 64.1 ppm
with a small amount of some uncharacterized species.
Reaction of Ru(CO)2(PtBu2Me)2 with Me3SiH. A solution of
Ru(CO)2(PtBu2Me)2 (10 mg, 0.021 mmol) in C6D6 (0.5 mL) was placed
in a Teflon valve NMR tube and freeze/pump/thaw degassed. Tri-
methylsilane (0.21 mmol) was condensed into the tube. After 2 days
at room temperature, Ru(H)2(CO)2(PtBu2Me)2 was produced as the only
phosphorus-containing species detected by 31P{1H} NMR. 1H NMR
revealed Me3Si SiMe3 as the only silicon-containing product.
Reaction of Ru(CO)2(PtBu2Me)2 with CH2O. A C6D6 (0.5 mL)
solution of Ru(CO)2(PtBu2Me)2 (10 mg, 0.021 mmol) was placed in
an NMR tube fitted with a rubber septum. Equimolar aqueous
formaldehyde was added to this solution via syringe at room temper-
ature. After 24 h at room temperature, the solution color changed from
deep red to pale yellow. The 31P{1H} NMR spectrum showed complete
conversion of Ru(CO)2(PtBu2Me)2 into Ru(H)2(CO)2(PtBu2Me)2 and
Ru(CO)3(PtBu2Me)2. The ratio between the two products depends on
the amount of formaldehyde employed (see text for detail).
Reaction of Ru(CO)2(PtBu2Me)2 with MeOH. A solution of
Ru(CO)2(PtBu2Me)2 (10 mg, 0.021 mmol) in a mixture of C6D6 (0.4
mL) and MeOH (0.1 mL) was placed in an NMR tube. After 3 h at
room temperature, the solution color changed from deep red to pale
yellow. The 31P{1H} NMR spectrum showed formation of
Ru(H)2(CO)2(PtBu2Me)2 (ca. 60%) and Ru(CO)3(PtBu2Me)2 (ca. 35%)
with some other small amount of uncharacterized products (ca. 5%).
Magnesium Reduction of cis,cis,trans-RuCl2(CO)2(PPh3)2. Mag-
nesium turnings (18 mg, 0.74 mmol) and THF (0.5 mL) were placed
in a Schlenk flask, and 1,2-dibromoethane (16 µL, 0.19 mmol) was
added via syringe. The mixture was gently stirred until the evolution
X-Ray Structure Determinations. (a) Ru(CO)2(PtBu2Me)2. The
crystal was attached to a glass fiber using silicone grease and was
transferred to the goniostat where it was cooled to 171 °C for
characterization and data collection. A systematic search of selected
ranges of reciprocal space yielded a set of reflections which exhibited
monoclinic (2/m) diffraction symmetry. Data collection was undertaken
as shown in Table 1. Plots of the four standard reflections (6,0,0;
0, 6,0; 0,0,6; 5, 3, 5) measured every 300 reflections showed no
(9) (a) Cavit, B. E.; Grundy, K. R.; Roper, W. R. J. Chem. Soc., Chem.
Commun. 1972, 60. (b) Gaffney, T. R.; Ibers, J. A. Inorg. Chem. 1982, 21,
2851.
t
(10) Although the 1H NMR spectrum shows only one Bu signal, we
propose the conformation of CO and CNMe taking a cis position. Addition
of MeNC to a THF solution of RuCl2(CO)(PtBu2Me)2 gives the yellow
product whose 31P{1H} NMR chemical shift is δ 37.7. This complex
(presumably trans isomer) isomerizes into cis isomer at toluene reflux
temperature within 15 min. This reaction pattern is identical to that which
is shown for two isomers of RuCl2(CO)2(PtBu2Me)2.4,5
(8) Ogasawara, M.; Caulton, K. G. Manuscript in preparation.

10192 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Table 1. Crystallographic Data
Ogasawara et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Ru(CO)2(PtBu2Me)2
Ru(CO)2(PtBu2Me)2
Ru(CO)2(O2)(PtBu2Me)2
Ru(1) P(2)
2.3596(22)
2.3542(22)
1.886(10)
1.854(9)
1.153(11)
1.177(10)
formula
a (Å)
b (Å)
C20H42O2P2Ru
11.601 (3)
14.320(3)
15.404(3)
107.65(1)
2438.47
4
477.6
P21/n
171
0.71069
1.301
C20H42O4P2Ru
16.312(1)
14.686(1)
20.778(2)
106.19(1)
4780.30
8
509.6
P21/c
172
0.71069
1.416
Ru(1) P(12)
Ru(1) C(22)
Ru(1) C(24)
O(23) C(22)
O(25) C(24)
c (Å)
â (deg)
V (Å3)
Z
P(2) Ru(1) P(12)
P(2) Ru(1) C(22)
P(2) Ru(1) C(24)
P(12) Ru(1) C(24)
P(12) Ru(1) C(22)
C(22) Ru(1) C(24)
Ru(1) C(22) O(23)
Ru(1) C(24) O(25)
165.56(8)
96.49(26)
89.91(25)
94.25(25)
90.70(26)
133.3(4)
168.2(8)
168.7(7)
fw (g/mol)
space group
T (°C)
λ (Åa)
calc (g/cm3)
1
µ (cm
)
7.69
0.0666
0.0712
7.95
0.0608
0.0575
R(Fo)b
Rw(Fo)c
a Graphite monochromator. b R
∑||Fo|
|Fc||/∑|Fo|. c Rw
2
[∑w(|Fo| |Fc|)2/w|Fo| ]1/2 where w 1/σ2(|Fo|).
systematic trends. Examination of the 0k0 data showed that 0k0
reflections were systematically extinct for k 2n 1. The h01 zone
was problematic: reflections having h
weak; the average intensity for h
2n. The maximum intensity for a reflection having h
1 was 235 for 6,0, 7, and it should be noted that 156 of the 308
h01 reflections with h 2n 1 had intensities greater than 50.0.
1
2n 1 were, in general,
2n 1 was 24 vs 1731 for h
2n
1
1
1
l
The original assumption was that there were no systematic extinctions
in the h01 zone and the space group was assumed to be P21 (or P21/m)
rather than P21/n. P21: The structure was solved by locating the two
unique Ru atoms using MULTAN-78. The remaining non-hydrogen
atoms were located in successive iterations of least-squares refinement,
followed by difference Fourier calculations. The two independent
molecules in the asymmetric unit were mirror images of each other.
The refinement did not proceed smoothly, several thermal parameters
behaved abnormally and chemically equivalent distances and angles
showed significant differences between the two molecules. This is
typical in cases where the space group is really centrosymmetric rather
than acentric. P21/n: When this space group is chosen, the significant
space group violations must be ignored. The structure was solved again
using MULTAN-78. The identical solution could be obtained by
shifting the center of symmetry between the two molecules in P21 to
the origin. The structure was refined using anisotropic thermal
parameters on all non-hydrogen atoms and with fixed calculated
hydrogen atoms. The number of parameters refined was 227, including
the scale factor and an overall isotropic extinction parameter. The final
difference map contains a peak of 2.9 e/Å3. This peak is located 2.14
Å from C(18) (65501). The next highest peak of 1.1 e/Å3 is located 1
Å from one phosphorus. The deepest hole is 1.7 e/Å3. The space
group violations for space group P21/n are significant. They could
possibly be explained by the presence of a small fragment of different
alignment; however, no abnormalities were noted during the initial
search. The possibility that the crystal might have undergone a phase
transition was investigated by heating the crystal from 171 to 50
°C; the space group violations remained. Another crystal from the same
sample was mounted as above and transferred to the goniostat at 50
°C, a search was carried out, and the identical unit cell was obtained.
Results of the structure determination are shown in Table 2 and Figure
1.
(b) Ru(η2-O2)(CO)2(PtBu2Me)2. A larger crystal was cleaved to
obtain a suitably sized fragment, which was affixed to the end of a
glass fiber using silicone grease. The mounted sample was transferred
to the goniostat where it was cooled to 172 °C for characterization
and data collection. A systematic search of a limited hemisphere of
reciprocal space located a set of reflections with symmetry and
systematic absences corresponding to the unique monoclinic space
group P21/c (Table 1). Subsequent solution and refinement of the
structure confirmed this choice. Data were collected (6° 2θ 45°)
using a standard moving-crystal, moving-detector technique with fixed
background counts at each extreme of the scan. Raw intensities were
corrected for Lorentz and polarization terms and for absorption. The
structure was solved by Patterson and Fourier techniques. A difference
Figure 1. ORTEP view, with selected atom numbering, of Ru(CO)2-
(PtBu2Me)2.
Fourier phased on the non-hydrogen atoms located many of the
hydrogen atoms, and these were placed in idealized fixed positions in
the subsequent least-squares refinements. Two independent molecules
are present in the asymmetric unit. During the refinement, three carbon
atoms (C(26), C(42), and C(51)) refused to properly converge while
being refined anisotropically. Since the crystal used was cleaved from
a larger mass, the behavior of these atoms may be due to a poor
absorption correction. The three atoms were assigned isotropic thermal
parameters for the final refinement. A careful examination was made
to ensure that the cell chosen was indeed proper. The initial
examination revealed several surprising facts. (1) The two molecules
are not only nearly identical but related by an apparent translational
vector of 0.259, 0.746, 0.253 (1/4, 3/4 1/4). (2) The midpoint of the
two Ru atoms lies at 0.370, 0.127, 0.125 (3/8, 1/8, 1/8). (3) Examination
of the intensity data reveals areas in reciprocal space with “pseudoex-
tinctions”; for example h00 exists for only h
4n. In spite of the
above, there does not appear to be an error in space group assignment.
This conclusion is based on the following: (a) P21/c is difficult to
missassign, (b) examination of the Ru Ru vectors fails to show any
missed symmetry, (c) two different cell reduction programs fail to find
a better cell. Results are shown in Table 3 and Figure 2.
Computational Method. Calculations were performed using the
ab initio core-potential (ECP) method and employed the Gaussian 92
package of programs.11 For Ru and Rh, the ECPs of Hay and Wadt,12
(11) Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; Gill, P. M. W.;
Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M.
A.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, K.; Binkley,
J. S.; Gonzales, C.; Martin, R. L.; Fox, D. J.; Defrees, D. J.; Baker, J.;
Stewart, J. J. P.; Pople, J. A. Gaussian 92, Re ision A; Gaussian, Inc.:
Pittsburgh, PA, 1992.

Characterization of a Zero-Valent Ru Species
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10193
Table 3. Selected Bond Distances (Å) and Angles (deg) for
Scheme 1
Ru(CO)2(O2)(PtBu2Me)2
molecule A
molecule B
Ru(1) P(4)
Ru(1) P(14)
Ru(1) O(2)
Ru(1) O(3)
Ru(1) C(24)
Ru(1) C(26)
O(2) O(3)
2.435(3)
2.431(3)
2.042(8)
2.032(8)
1.891(12)
1.860(12)
1.472(10)
1.134(13)
2.433(3)
2.434(3)
2.029(7)
2.028(7)
1.876(12)
1.887(13)
1.467(10)
1.148(13)
C(51) O(52)
P(4) Ru(1) P(14)
P(4) Ru(1) O(2)
P(4) Ru(1) O(3)
P(4) Ru(1) C(24)
P(4) Ru(1) C(26)
P(14) Ru(1) O(2)
P(14) Ru(1) O(3)
P(14) Ru(1) C(24)
P(14) Ru(1) C(26)
O(2) Ru(1) O(3)
O(2) Ru(1) C(24)
O(2) Ru(1) C(26)
O(3) Ru(1) C(24)
O(3) Ru(1) C(26)
C(24) Ru(1) C(26)
Ru(1) O(2) O(3)
Ru(1) O(3) O(2)
Ru(1) C(24) O(25)
Ru(1) C(26) O(27)
163.93(11)
84.22(23)
82.22(23)
97.6(3)
164.38(11)
84.62(23)
82.41(23)
93.2(3)
to minima (i.e., the square-planar structure of Ru(CO)2(PH3)2 and the
bent structure of [Rh(CO)2(PH3)2] ), geometries were optimized with
fixed angles at the metal. The geometry of Ru(CO)2(PH3)2 was
reoptimized with C1 symmetry to confirm the geometry found in C2
symmetry. No significant difference was found. Previous work on
other unsaturated Ru complexes has shown that experimental geometries
can be reproduced at this level of calculation without the need to
incorporate polarization functions on metal-bound atoms.7
93.4(4)
96.6(4)
86.27(23)
82.01(23)
97.7(3)
91.8(4)
42.3(3)
108.4(4)
162.5(4)
150.7(4)
120.2(4)
89.1(5)
68.5(4)
69.2(4)
85.19(22)
82.08(23)
92.5(3)
98.0(4)
42.4(3)
160.7(4)
109.8(4)
118.3(4)
152.2(4)
89.5(5)
68.8(4)
68.8(4)
Results
Preparation and Characterization of Ru(CO)2(PtBu2Me)2.
Addition of methyllithium to a toluene solution of RuHCl(CO)-
(PtBu2Me)2 at 78 °C and warming the solution to 40 °C
give clean conversion to a diastereomeric mixture (Scheme 1,
asterisks indicate chiral centers) of 1a and 1b with approximately
3:1 molar ratio as reported.7 Complexes 1a and 1b absorb 1
equiv of CO at 40 °C to give 2a and 2b with the solution
color change from red-orange to pale yellow. This transforma-
tion was confirmed by NMR measurements.16 31P{1H} NMR
of 2a and 2b shows the two new sets of AM patterns at 40
175.9(11)
177.6(11)
178.4(10)
176.4(10)
2
°C with a large JPP value (220 Hz), which shows a trans
relationship of the two phosphine ligands. The molar ratio
between the two diastereomers 2a and 2b is identical to that of
1a and 1b, suggesting that CO acts purely as a trapping reagent.
In 1H NMR, the hydride resonances of 2a and 2b are observed
in the lower field region (δ 5.9 and 6.2, respectively) at
20 °C in toluene-d8, compared to those of 1a and 1b (δ 25.0
and 26.7 at 40 °C in toluene-d8). This observation is
consistent with the coordination of the second carbonyl at the
position trans to the hydride. The mixture 2a and 2b is only
stable at low temperature. Remarkably (RuII f Ru0), it
undergoes demetalation (i.e., C H reductive elimination) of the
metalated phosphine to form the four-coordinate complex
Ru(CO)2(PtBu2Me)2, 3, at room temperature in 2 h. During
this period, the solution color changes from pale yellow
(saturated) to very deep red (unsaturated). The thermodynamics
of this reaction are quite surprising, i.e., an 18-electron,
coordinatively saturated species (2a and 2b) isomerizes into a
16-electron coordinatively unsaturated complex (3).
Figure 2. ORTEP view, with selected atom numbering, of “molecule
Complex 3 shows one 31P{1H} NMR signal at 23 °C. This
signal is very sharp, and even at 90 °C does not show obvious
broadening. In the 1H NMR, one virtual triplet for tBu protons
and one virtual triplet for its P Me hydrogens are observed.
All these are consistent with the phosphine ligands being
equivalent and taking transoid geometry. Therefore, from these
NMR studies, there is no evidence for an agostic interaction,
which would make the two phosphines in 3 inequivalent. The
31P NMR chemical shift of 3 in benzene, toluene, pentane, or
THF shows no obvious solvent dependency; i.e., there is no
(or no strong) interaction of these solvents with the vacant site
A” of Ru(O2)(CO)2(PtBu2Me)2.
in which the 4s and 4p subvalence shell electrons are included in the
valence shell, were chosen along with a [3111/3111/311] Gaussian basis
set. For P, the ECP and [31/31] basis set of Barthelat et al. were
employed.13 For C and O, we chose the (9s/5p) primitives of Huzinaga
with the contraction scheme of Dunning and Hay.14 H atoms were
described by (4s) primitives contracted into a [1s] basis set.15 PH3
groups were given a fixed geometry (P
H
1.42 Å, M P H
120.0°). All geometries were fully optimized at the MP2 level under
the C2 symmetry constraint. For the structures that did not correspond
(12) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(13) Bouteiller, Y.; Mijoule, C.; Nizam, N.; Barthelat, J.-C.; Daudey,
J.-P.; Pe´lissier, M.; Silvi, B. Mol. Phys. 1988, 65, 295.
(14) Dunning, T. H.; Hay, P. J. In Methods of Electronic Structure
Theory; Schaefer, H. F., III, Ed., Plenum Press: New York, 1977; Vol. 1.
(15) Huzinaga, S. J. Chem. Phys. 1965, 42, 1293.
(16) 2a: 31P{1H} NMR (toluene-d8, 20 °C): δ 17.1 (d, JPP 220 Hz,
1P, metalated P), 63.4 (d, JPP 220 Hz, 1P, PtBu2Me); 1H NMR (toluene-
d8, 20 °C): δ 5.9 (ddt, JPH 25.5 and 17.1 Hz, JHH 2.9 Hz, Ru-H).
2b: 31P{1H} NMR (toluene-d8, 20 °C): δ 11.8 (d, JPP
220 Hz, 1P,
metalated P), 63.1 (d, JPP 220 Hz, 1P, PtBu2Me); 1H NMR (toluene-d8,
20 °C): δ -6.2 (t, JPH 21.8 Hz, Ru-H).

10194 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Ogasawara et al.
of 3. The complex is highly soluble; it dissolves into even
saturated hydrocarbons such as pentane and Nujol. The IR
spectrum of 3 in Nujol gives the two CO stretching vibrations
with unequal intensities at 1831 and 1902 cm 1. These values
are low and consistent with a low oxidation state of ruthenium.
The observation of two infrared CO absorptions indicates that
two carbonyl ligands are not trans. The intensity of the two
ν(CO) bands, together with the equation tan2 θ Ias/Is where
I is the intensity of the appropriate ν(CO) band and 2θ is the
angle between the two CO vectors, gives 2θ
130°. This
generally supports the retention of the nonplanar solid-state
structure ( C Ru C 133°, see below) in solution. However,
in the solid state, the Ru C O moieties are bent to ca. 168°
in a cisoid mode, so the angle of two CO vectors in the crystals
is ca. 110°, indicating some fluxionality of the molecules in
solution.
The four-coordinate complex 3 also can be synthesized from
cis,cis,trans-RuCl2(CO)2(PtBu2Me)2 by reduction with stoichio-
metric activated magnesium in THF according to eq 1.17 The
cis,cis,trans-RuCl2(CO)2L2 Mg f Ru(CO)2L2 MgCl2
L
PtBu2Me or PiPr3
(1)
reaction proceeds almost quantitatively, and the isolated yield
of 3 goes up to 80%. Triisopropylphosphine has electronic and
steric properties similar to those of PtBu2Me. However, reaction
of RuHCl(CO)(PiPr3)2 with MeLi does not give analogous
products to 1a and 1b, which are obtained from RuHCl(CO)-
(PtBu2Me)2 and MeLi. The 31P NMR spectrum of the reaction
mixture of RuHCl(CO)(PiPr3)2 and MeLi (1:1 molar ratio) shows
formation of several uncharacterized species in addition to
remaining RuHCl(CO)(PiPr3)2. Therefore, the original synthetic
route of Ru(CO)2(PtBu2Me)2, successive metalation and de-
metalation, is not applicable to the synthesis of a PiPr3 analogue.
However, the reductive route to Ru(0) using magnesium yields
Ru(CO)2(PiPr3)2 from cis,cis,trans-RuCl2(CO)2(PiPr3)2 in 83%
isolated yield. In Ru(CO)2(PiPr3)2, the phosphorus nuclei are
equivalent, as are the iPr groups. 1H NMR shows one doublet
of virtual triplets for PCHMe2 and multiplet for PCHMe2. All
this is consistent with trans phosphines. Two νCO bands are
seen at 1898 and 1829 cm 1 in the IR spectrum, and the OC
Ru CO angle is calculated as 129° from their intensity.
Both four-coordinate complexes, Ru(CO)2(PtBu2Me)2 and
Ru(CO)2(PiPr3)2, are very air-sensitive, however, they are fairly
thermally stable; a benzene solution of either complex shows
no decomposition at room temperature for up to 10 days.
Refluxing the benzene solution of 3 causes slow decomposition
(ca. 20% in 6 h) into Ru(CO)2(PtBu2Me)3, free phosphine, and
some other uncharacterized compounds. The crystals, which
are kept in the glovebox under argon at room temperature,
do not show any detectable change during 8 months.18
Figure 3. Walsh diagram relating the frontier orbitals of planar and
bent Ru(CO)2(PH3)2, based on ab initio calculations.
Electronic Origin of the Structure. Density functional
studies19 on Ru(CO)4 support this as a singlet ground state with
C2 symmetry (i.e., nonplanar), analogous to Ru(CO)2L2. Earlier
EHT studies20 traced this nonplanar structure to a d8 electron
count, influenced by π-acceptor ligands. Our reported1 core
potential ab initio calculations (MP2) on Ru(CO)2(PH3)2
reproduce well the structural features observed for Ru(CO)2-
(PtBu2Me)2, showing that the observed structure is not caused
by the very bulky ligand PtBu2Me. In addition, the calculations
at the same level showed that isoelectronic Rh(CO)2(PH3)2
prefers a planar structure, in agreement with experiment.
A Walsh diagram (Figure 3) reveals the origin of the structural
preferences. The antibonding a1 orbital is less antibonding upon
bending because of diminished overlap between the 5σ CO
orbital (HOMO) and z2 and because back-donation into π*CO
becomes possible (A) as already suggested.20 This increased
The structure of Ru(CO)2L2 (Table 2) might be described as
a trigonal bipyramid (Figure 1) lacking one equatorial ligand.
The molecule is four-coordinate and nonplanar, but like no
previously observed four-coordinate X-ray structure. The
C Ru C angle (133.3(4)°) is larger than TBP, and the
phosphines bend ( P Ru P 165.56(8)°) almost negligibly
toward the opposite “side” from the carbonyl ligands. There
are no Ru/C or H distances short enough to be interpreted as
stabilizing interaction with z2 is one of the factors which leads
to shorter calculated M (CO) distances in the bent than in the
planar structure. The b1 (xz) orbital is also stabilized by back-
donation which only occurs in the bent structure. The b2 orbital
(angles drawn to scale) is strongly destabilized in the bent
structure because of increased overlap with the 5σ of CO (B)
and diminished overlap with π*CO. However, cisoid bending
of the M C O angle as in B diminishes the destabilization by
minimizing the overlap between b2 and the 5σ of CO. The
t
an agostic interaction with Bu or methyl substituents on P.
(17) Sodium amalgam also can be employed as a reductant of this
reaction. However, large excess of Na/Hg is required and the yield of 3 is
relatively low (ca. 40%).
(18) The complexes are unreactive toward dinitrogen, so N2 gas can be
employed as an inert media instead of Ar gas.
(19) Li, O.; Schreckenbach, G.; Ziegler, T. J. Am. Chem. Soc. 1995,
117, 486.
(20) Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058.

Characterization of a Zero-Valent Ru Species
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10195
lowering of a2 upon bending is unexpected since bending the
C Ru C angle should diminish the overlap between a2 and
π*CO, thus raising the energy of a2. The calculated (opposite)
behavior may be due to two effects: (1) a general field effect
according to which the destabilization of z2 by the four ligands
in the planar structure destabilizes all other (even the nonbond-
ing) d orbitals; (2) the shorter M CO distance in the bent
structure compensating for the smaller overlap due to imperfect
alignment of the a2 and π*CO orbitals.
somewhat larger than that of the X-ray data (89.1°). 1H NMR
spectrum of 6 shows only one virtual triplet for Bu groups,
which is consistent with C2v symmetry of the molecule as shown
in Figure 2. The coordination of O2 to 6 is irreversible;
evacuation to 0.01 mmHg at 50 °C (higher temperature causes
the decomposition of the complex) does not show any dissocia-
tion of the O2 ligand.
t
The spectroscopic features of Ru(η2-CS2)(CO)2(PtBu2Me)2,
7, are consistent with structure 7. The phosphorus nuclei are
equivalent, as indicated by a singlet in the 31P{1H} NMR
spectrum at 80 °C. This equivalence requires that the dangling
S in structure 7 must lie in the Ru(CO)2 plane. The tBu groups
In contrast to the above, the d orbital energies of Rh(I) lie
farther from the π*CO. The calculated stabilization of the a1
and b1 orbitals is therefore less on bending RhI(CO)2(PH3)2
,
and the destabilization of b2 by the now closer 5σ of CO is
greater. In short, it is the greater reducing power of Ru(0) than
Rh(I) which leads to different structures for Ru(CO)2L2 and
(planar) Rh(CO)2L2 . Thus, the presence of a π-acceptor ligand
is a necessary (but not sufficient) condition for a nonplanar d8
ML4 complex.21
Reaction of 3 with Donor Ligands. Compound 3 absorbs
1 equiv of CO quickly and irreversibly to form adduct 4. The
reaction proceeds very cleanly and yields Ru(CO)3(PtBu2Me)2,
quantitatively based on 31P{1H} NMR. All the spectroscopic
data (1H and 31P{1H} NMR and IR) are consistent with those
reported previously.7 Similarly, 3 reacts with methyl isocyanide
quantitatively in the time of mixing to give Ru(CNMe)(CO)2-
of the phosphines appear as two virtually coupled triplets in
the 1H NMR spectrum, consistent with no mirror plane of
symmetry perpendicular to the Ru(CO)2(CS2) plane. This rules
out η1-C and η2-S,S structures for the CS2 ligand. An η2-CS
coordination is thus the most likely.25 A similar structure was
reported for an analogous complex Ru(η2-CS2)(CO)2(PPh3)2.26
The IR spectrum of 7 shows a strong band at 1125 cm 1, as
1
(PtBu2Me)2, 5. It is a bright yellow, crystalline solid, and H
and 31P{1H} NMR and IR data suggest a similar structure to 4,
i.e., two bulky phosphine ligands are taking the apical sites and
the three strong π-acid ligands (two CO and a MeNC) are on
the equatorial plane. Two νCO frequencies (1894 and 1844
cm 1) are low enough to be consistent with Ru(0) oxidation
state.
Complex 3 adds stoichiometric O2 and CS2 in the time of
mixing at 25 °C to give Ru(η2-O2)(CO)2(PtBu2Me)2, 6, and
Ru(η2-CS2)(CO)2(PtBu2Me)2, 7, respectively. The crystals of
6, suitable for X-ray analysis, were obtained by recrystallization
from cold pentane. Figure 2 shows the crystal structure of 6 as
a distorted octahedron with O2 Ru1 O3 42.3(3)°, P4
expected for this type of compound,27 in addition to two CO
1
stretches with equal intensities at 1993 and 1933 cm
.
Remarkably, these are as high as in the O2 complex, 6.
Complex 7 is thermally unstable; its solution in C6D6 darkens
from pale yellow to a blackish color in 2 h, even at room
temperature. The 31P{1H} NMR spectrum reveals decomposi-
tion of 7 into free phosphine and some other uncharacterized
compounds. However, the isolated complex (solid) shows no
obvious decomposition during 10 days at 25 °C under Ar.
Under ethylene atmosphere (1 atm), 3 ligates one molecule
of C2H4 per ruthenium reversibly to form Ru(η2-C2H4)(CO)2-
(PtBu2Me)2, 8. Below 60 °C, it shows a broad signal in the
31P{1H} NMR spectrum at ca. 58 ppm. Above 40 °C,
coordinated ethylene dissociates and the signal of 3 emerges.
The ratio of 3 and 8 is approximately 1:20 at 40 °C, 2:3 at
20 °C, and 7:1 at 0 °C. At and above 20 °C, the signals of
3 and 8 coalesce into one broad signal, indicating rapid
equilibrium between the two complexes. The coordinated
Ru1 P14
163.93(11)°, and C24 Ru1 C26
89.1(5)°.
The O2 O3 distance (1.472(10) Å) is somewhat longer than
in other crystallographically characterized η2-O2 ruthenium
22
complexes, [RuH(O2)(dippe)2]BPh4 (d(O O) 1.360(1) Å)
23
and [Ru(O2)(η5-C5Me5)(dppe)]PF6 (d(O O) 1.398(5) Å).
Note that the oxidation states of the ruthenium centers in these
two complexes are higher than the oxidation state in 6, i.e.,
weaker back-donation to the O2 ligands should be expected in
these molecules than that in 6. The reported O O bond length
in H2O2 is 1.49 Å;24 this value is almost identical with that in
6. Thus the dioxygen ligand in 6 is best considered as a
peroxide ligand. Therefore, 6 must be formally considered as
a Ru(II) complex with a strong back-donation to the coordinated
O2. In the IR spectrum, νCO are detected at relatively higher
frequency (1991 and 1921 cm 1, or about 90 cm 1 above those
of 3), also supporting a 2 oxidation state of the ruthenium
center in 6, although these frequencies are considerably below
those of a typical Ru2 species such as cis,cis,trans-RuCl2-
(CO)2(PtBu2Me)2 (2029 and 1962 cm 1). The angle of OC
Ru CO is calculated as 102° from the intensities of the νCO
bands in the IR spectrum in pentane solution. This value is
1
ethylene is observed at 1.58 ppm as a triplet at 50 °C in H
NMR; this indicates that, even at this temperature, there is a
fast rotation of the ethylene ligand.
Reaction with diphenylacetylene is immediate, giving Ru-
(η2-PhC≡CPh)(CO)2(PtBu2Me)2, 9, which dissociates slightly
( 5%) in an equilibrium process, to release free phosphine
above 40 °C in toluene; the 31P{1H} NMR signal of 9 then
becomes broader. At higher temperatures ( 0 °C), the reso-
nances of 9 and free phosphine coalesce into one very broad
signal (w1/2 ≈ 400 Hz at 23 °C), and its chemical shift at this
temperature (δ 58.9) is slightly higher than that of 9 at 40 °C
(21) Hoffmann, R.; Minot, C.; Gray, H. B. J. Am. Chem. Soc. 1984,
106, 2001.
(22) Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J. Am. Chem. Soc.
1993, 115, 9794.
(23) Kirchner, K.; Mauthner, K.; Mereiter, K.; Schmid, R. J. Chem. Soc.,
Chem. Commun. 1993, 892.
(24) Savariault, J.-M.; Lehmann, M. S. J. Am. Chem. Soc. 1980, 102,
1298.
(25) Mealli, C.; Hoffmann, R.; Stockis, A. Inorg. Chem. 1984, 23, 56.
(26) Grundy, K. R.; Harris, R. O.; Roper, W. R. J. Organomet. Chem.
1975, 90, C34.
(27) Butler, I. S.; Fenster, A. E. J. Organomet. Chem. 1974, 66, 161.

10196 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Ogasawara et al.
(δ 60.9). Although Ru(η2-PhCtCPh)(CO)2(PtBu2Me), 10, is
not detectable by either 31P{1H} NMR or IR, probably due to
its low concentration, we propose the equilibrium as eq 2
Scheme 2
2
Ru(η2-PhCCPh)(CO)2L2 Ru(η -PhCCPh)(CO)2)L
h
L
9
10
(2)
between 9, 10, and free PtBu2Me from these observations. An
analogous complex, Ru(η2-PhC≡CPh)(CO)2(PEt3)2,28 is isolable
and does not show the phosphine dissociation shown for 9, even
at 80 °C in benzene. Since PtBu2Me is more basic than PEt3,
the driving force of this phosphine dissociation from 9 seems
to be a steric repulsion between the bulky phosphines and the
coordinated PhCtCPh. This equilibrium is further supported
by the capacity of the alkyne to change from two-electron donor
character in 9 to four-electron donation in 10. Two νCO bands
are detected for 9 at 1960 and 1896 cm 1, which are ca. 60
cm 1 above those of 3 but below those of 6, indicating weaker
π-acceptor character of diphenylacetylene in 9 than of the O2
ligand in 6.
red to pale yellow and is quantitative by 31P{1H} NMR. The
dihydride complex 12 is isolated in pure form as pale yellow
crystals in 88% yield. It shows a single high field resonance
at δ 7.96 as a triplet in the 1H NMR. The tBu and the methyl
groups of the phosphines show virtual triplets in their 1H NMR
1
signals. Two νCO bands are seen at 1999 and 1966 cm
,
consistent with 12 as cis,cis,trans-RuH2(CO)2(PtBu2Me)2.
At 23 °C in C6D6, 3 reacts with PPh2H (2 equiv) not by P H
oxidative addition, but by displacement of one of PtBu2Me to
give Ru(CO)2(PPh2H)2(PtBu2Me), 11, and free phosphine. The
reaction with 1 equiv of PPh2H shows the same products, in
addition to the remaining 3. Steric hindrance among three
Complex 3 adds 1 equiv of HCl or Cl2 immediately to give
cis,trans-RuHCl(CO)2(PtBu2Me)2, 13, or RuCl2(CO)2(PtBu2-
Me)2, respectively. All the spectroscopic data (1H and 31P{1H}
NMR and IR) agree with those reported previously.3,4 In the
31P{1H} NMR spectrum, RuCl2(CO)2(PtBu2Me)2 is observed as
a mixture of two isomers, 14 (cis,trans) and 15 (trans,trans).
Complex 14 is the thermodynamically favorable species;
complex 15 isomerizes completely into 14 in C6D6 at 70 °C in
2 h. Although the cis isomer 14 is both the kinetically and
thermodynamically expected product from simple oxidative
addition of Cl2 to 3, our observation of forming some trans
isomer 15 suggests that the reaction mechanism (or at least one
mechanism) is not concerted. However, the reaction is too fast
to detect intermediates.
phosphines in the probable intermediate, Ru(CO)2(PPh2H)(Pt-
Bu2Me)2, causes one PtBu2Me to dissociate to form Ru(CO)2-
(PPh2H)(PtBu2Me). This species should be more reactive than
3, adding PPh2H to give 11. This reaction is thus controlled
by steric effects. The 31P{1H} NMR spectrum of 11 shows an
The reaction of 3 with equimolar phenylacetylene occurs in
the time of mixing at room temperature to give the oxidative
addition product, RuH(CtCPh)(CO)2(PtBu2Me)2, 16. Two
2
AM2 pattern with the JPP coupling constant of 72.3 Hz. This
1
tBu signals are detected in its H NMR spectrum. This (and
value is too small for a trans coupling, but is also inconsistent
with a coupling at a 90° P Ru P angle (∼20 Hz expected).
These observations support the structure 11. Indeed, in the IR
spectrum, one strong νCO is detected at relatively low frequency
(1858 cm 1). A similar complex, Ru(CO)2(PPh3)3, with trans
two νCO bands) is consistent with Cs symmetry of 16, i.e., two
bulky phosphines are trans and two carbonyls are cis. This
stereochemistry is consistent with a concerted mechanism. The
rearrangement of 16 to the isomeric vinylidene complex
Ru(dCdCHPh)(CO)2(PtBu2Me)2 cannot be achieved thermally,
even at 110 °C after 24 h in toluene.
carbonyls was reported previously and showed a νCO of 1905
1 9a
cm
.
No reaction is found with CO2 (1 atm), N2 (1 atm), acetonitrile
(10 equiv), or pyridine (10 equiv). There is no reason to
attribute these first two negative results to steric factors.
Acetonitrile can be estimated as isosteric with isocyanide, which
reacts with 3 immediately; however, no reaction was observed
by 31P{1H} NMR even at 90 °C in toluene for each case. In
acetonitrile as a solvent, 3 does not show any obvious line
broadening in the 31P{1H} NMR spectrum at room temperature.
A common feature of these four reagents is weaker π-acidity
than that of all the other reagents described above, which exhibit
great reactivity toward 3. It is concluded from these observa-
tions that Ru(CO)2(PtBu2Me)2 is not a strong σ-Lewis acid (as
might have been anticipated by its 16-electron count), but relies
heavily on its π-basicity for ligand binding. This is consistent
with the idea that the high energy of the HOMO also results in
a LUMO of high energy.
The reaction with MeCl is relatively slow; it is necessary to
heat the reaction mixture. Complex 3 is consumed completely
at 80 °C in 2 h to form three products: the main product, the
acetyl complex 17, and the two minor products, 4 and 18. The
molar ratio between the three products is approximately 17:4:
18 5:1:1 based on the 31P NMR spectrum. The mechanism
of this transformation is explained in Scheme 2. The first step
is an oxidative addition of MeCl to the four-coordinate complex
3 to give an unobservable intermediate, Ru(Me)Cl(CO)2(PtBu2-
Me)2. This intermediate is converted into the final products in
two different manners: one is an insertion of the CO ligand to
the Ru Me bond to give 17 (path A),29 while the other is CO
abstraction from the intermediate by unreacted 3 to give
equimolar (as observed) 4 and 18 (path B). A similar carbonyl
transfer reaction between 3 and 13 to form 4 and RuHCl(CO)-
(PtBu2Me)2 was observed independently,8 supporting the above
mentioned mechanism. The acetyl complex, 17, does not show
thermal transformation into 18 by loss of CO at 80 °C in C6D6.
Reaction of 3 with Oxidants. The reaction of 3 with H2
proceeds quite rapidly with a prompt color change from deep
(28) Ogasawara, M.; Kawamura, K.; Ito, K.; Toyota, K.; Streib, W. E.;
Komiya, S.; Caulton, K. G. Manuscript in preparation.
(29) A similar CO insertion was reported for an analogous complex:
Roper, W. R.; Wright, L. J. J. Organomet. Chem. 1977, 142, C1.

Characterization of a Zero-Valent Ru Species
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10197
Scheme 3
Scheme 4
Scheme 5
Complex 3 reacts with excess Me3SiH (10 equiv) in C6D6 at
room temperature within 2 days to give the dihydride complex
12 and Me3Si SiMe3. The reaction is slow, but quite clean;
at the end of the reaction, 12 is the only phosphorus-containing
species detected by 31P{1H} NMR spectroscopy. However,
during the reaction, the 31P{1H} NMR spectrum of the reaction
mixture shows four signals: remaining 3, 12, free PtBu2Me,
and a species with a singlet at δ 43.7. Note that the final
products do not contain any trace amount of free phosphine or
of the 43.7 ppm species. The 31P{1H} NMR intensities of Pt-
Bu2Me and the signal at δ 43.7 are approximately the same.
From these observations, we propose the mechanism of the
reaction as Scheme 3. Me3SiH is added to 3 to give an
undetectable intermediate, RuH(SiMe3)(CO)2(PtBu2Me)2. The
three bulky ligands (two phosphines and SiMe3) of this species
presumably are thermodynamically unfavorable due to mutual
steric repulsion. Thus, one phosphine dissociates to form
equimolar free phosphine and a coordinatively unsaturated
species, RuH(SiMe3)(CO)2(PtBu2Me). We propose that this is
the species at δ 43.7 in the 31P{1H} NMR. Indeed, the 1H NMR
spectrum of this mixture shows a hydride signal at δ 26.2 in
addition to the hydride signal of 12. Although the signal is
observed as a broad singlet (coupling with a phosphorus is not
resolved), presumably due to the low signal-to-noise ratio of
the spectrum, the very high-field chemical shift of the hydride
signal is consistent with the coordinative unsaturation of RuH-
(SiMe3)(CO)2(PtBu2Me). Dissociation of a carbonyl from RuH-
(SiMe3)(CO)2(PtBu2Me)2 is ruled out by our observations; if
this were the case, released CO should be trapped by remaining
3 to form 4, which is not observed. RuH(SiMe3)(CO)2(PtBu2-
Me) reacts with a second Me3SiH to give Me3Si SiMe3 and
RuH2(CO)2(PtBu2Me), and then the latter traps the free phos-
phine to give 12.
(CO)2L2 and RuH(CHO)(CO)2L2 (see Scheme 4).30 However,
due to its low concentration and short lifetime, we could not
obtain any further information about this intermediate. The
detection, but ultimate disappearance, of free phosphine indicates
that the final step of the reaction, H-migration from the formyl
ligand, proceeds via the dissociation of the phosphine.
Complex 3 is also converted into 4 (ca. 35%), 12 (ca. 60%),
and some other minor products in MeOH and C6D6 mixtures at
room temperatures in several hours. The stoichiometry of the
reaction approximates that of eq 4 and probably begins with
oxidative addition of the O H bond of methanol to 3.31
3Ru(CO)2L2 CH3OH f 2Ru(H)2(CO)2L2 Ru(CO)3L2
(4)
Magnesium Reduction of Other RuCl2(CO)(CX)L2 Com-
plexes. The ruthenium dichloride complex, cis,cis,trans-RuCl2-
(CO)2(PPh3)2, was reduced with activated magnesium, trying
to synthesize a four-coordinate complex analogous to 3 with
smaller phosphines and also with a different electronic character.
9a
The reaction gives Ru(CO)2(PPh3)3 as the main ruthenium-
containing product instead of the target molecule, Ru(CO)2-
(PPh3)2. In addition to Ru(CO)2(PPh3)3, an uncharacterized dark
brown solid, which is insoluble in toluene, is formed. The yield
of Ru(CO)2(PPh3)3 is low (44% based on ruthenium), and it
has one extra phosphine ligand in the molecule. Presumably,
two Ru(CO)2(PPh3)2 molecules are transformed into Ru(CO)2-
(PPh3)3 and the dark brown solid by phosphine disproportion-
ation. It should be noted that no ortho-metalated species is
observed by 31P NMR (see Scheme 5).
Addition of 0.5 equiv of formaldehyde to the C6D6 solution
of 3 gives a mixture of 4 and 12 in approximately 1:1 molar
ratio (eq 3). However, the ratio between the two products
depends on the amount of CH2O employed. When CH2O/3
Ru(CO) L
Ru(H)2(CO)2L2
2Ru(CO)2L2 CH2O f
(3)
3
2
4
12
(mol/mol) 1, 4 forms as a main product in more than 90%
yield with 12 as a minor product.30 In the course of the reaction,
the formation of an intermediate whose 31P{1H} NMR chemical
shift is δ 59.3 and a small amount of free phosphine is observed.
There are two candidates for the intermediate: Ru(η2-CH2O)-
Magnesium reduction of RuCl2(CO)(CNMe)(PtBu2Me)2 in
THF gives a diastereomeric mixture of metalated species, 17a
and 17b, as the main product in approximately 9:1 molar ratio.
In addition to 17a and 17b, a small singlet at δ 64.1 is
observed at room temperature in the 31P{1H} NMR spectrum
(30) The two hydrides in 12 are labile, and 12 reacts with CO to form
4 and H2 gas.7
(31) Brown, K. L.; Clark, G. R.; Headford, C. E. L.; Marsden, K.; Roper,
W. E. J. Am. Chem. Soc. 1979, 101, 503.

10198 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Ogasawara et al.
Scheme 6
ability to isolate Ru(CO)2L2. In contrast, Ru(CO)2(PMe3)2 has
been shown in matrix isolation studies to bind Ar, CH4, and
Xe.36
Ru(CO)2L2 has much of the reactivity which would be
expected of an unsaturated molecule containing a zero-valent,
4d metal. It adds many sterically compact Lewis bases in time
of mixing, and it undergoes two-electron oxidative addition with
H H, sp-C H, Si H, O H, H Cl, and Cl Cl bonds. The
results with Cl2 suggest the reaction is not a concerted addition
of both atoms, which should yield only the cis isomer of RuCl2-
(CO)2L2. Alternatives include a radical reaction or the inter-
mediate RuCl(CO)2L2 and Cl .
The first “slow” (greater than time of mixing) reaction we
encounter is that with MeCl. Acetyl formation and subsequent
CO dissociation of the presumed primary product, Ru(Me)Cl-
(CO)2L2, at a rate faster than that of the slow rate of the primary
reaction permits CO to (rapidly) scavenge unreacted Ru(CO)2L2,
leading to several products in a rational stoichiometry.
The reaction with PHPh2, which was intended as a possible
oxidative addition reaction, is instead probably a simple Lewis
base addition reaction, but steric hindrance in any 1:1 adduct is
so large as to cause dissociation of PtBu2Me, followed by
binding of an additional molecule of PHPh2. The reaction is
thus addition and phosphine substitution: nonredox processes.
Thus, the thermodynamics of this process are probably dictated
by diminishing steric repulsion in the five-coordinate molecule.
of the toluene extract of the magnesium reduction products. 1H
and 31P{1H} NMR characteristics of 17a and 17b are identical
with those prepared from 1a and 1b and methyl isocyanide
(Scheme 6). Addition of MeNC to the cold toluene solution of
1a and 1b gives immediate solution color change from reddish
orange to pale yellow. The molar ratio of 17a and 17b in this
solution at 40 °C is ca. 3:1; it duplicates that of the 1a and
1b employed. When this solution was kept at room temperature,
the solution turned light red in color and the 31P{1H} NMR
spectrum showed an additional singlet at δ 64.1, which was
also observed in the sample prepared from RuCl2(CO)(CNMe)-
(PtBu2Me)2 and Mg as described above. Note the molar ratio
between 17a and 17b changed from 3:1 to 9:1, while the sample
was kept at room temperature for 3 days. However, during this
period, slow decomposition of the complexes into several
uncharacterized species is also observed. The reddish colored
solution, at room temperature, indicates formation of a coor-
dinatively unsaturated species, presumably the species with the
signal at δ 64.1 in the 31P NMR spectrum. This change of the
molar ratio of 17a and 17b between 40 °C and room
temperature suggests an equilibrium between 17a, 17b, and the
species whose 31P NMR chemical shift is δ 64.1. Judging from
our results on the Ru(CO)2(PtBu2Me)2 system, we propose that
this species is an analogous four-coordinate complex, Ru(CO)-
(CNMe)(PtBu2Me)2. Note that the 31P NMR chemical shift of
3 (δ 65.4) is very close to that of Ru(CO)(CNMe)(PtBu2Me)2
(δ 64.1). Methyl isocyanide is a weaker π-acceptor than
carbonyl.32 Substitution of one of the two carbonyls in 3 with
methyl isocyanide apparently increases the electron density of
the ruthenium center and thus enhances the reactivity of the
complex toward oxidative addition. Consequently, Ru(CO)-
(CNMe)(PtBu2Me)2 metalates one of its phosphine ligands to
form 17a and 17b.
The magnesium reduction method of synthesis of Ru(CO)2L2
has some generality for bulky L and is seemingly much more
simple than the zinc reduction of FeX2(CO)2(PEt3)2,37 which
gives first the FeX(CO)2(PEt3)2 radical, and then FeX(CO)2-
(PEt3)2 , by a sequence of apparent one-electron reductions. In
contrast, Mg reduction of MCl2(PMe3)4 (M Ru, Os) leads to
38
MH(η2-CH2PMe2)(PMe3)3 by internal redox from the pre-
sumed intermediate M(PMe3)4. This shows the importance of
the presence of two CO ligands here in maintaining a zero-
valent product. Our original synthesis of Ru(CO)2L2, by
formation of RuH(CO)2[η2-P(CMe2CH2)tBuMe](PtBu2Me), fol-
lowed by its reductive elimination of C with H, displayed
unanticipated thermodynamics. We have examined our spectra
(particularly 31P NMR) for evidence that either species Ru(CO)2L2
(L
PtBu2Me or PiPr3) is in detectable equilibrium with a
species where a phosphine substituent has been metalated. None
was found. However, the reducing power of the metal in the
analogous compound where one CO has been replaced by the
weaker π-acid MeNC is stronger than in the dicarbonyl complex;
the zero-valent and divalent isomers are present at detectable
concentrations. The results of magnesium reduction of RuCl2-
(CO)2(PPh3)2 also support the subtle electronic balance in the
Ru(CO)2L2 system, which prevents the complexes from meta-
lation to form coordinatively saturated species. The metal center
in the presumed intermediate Ru(CO)2(PPh3)2 is not strong
enough as a reductant for ortho-metalation; thus, it transformed
to the final product by an intermolecular ligand disproportion-
ation. The electronic balance in “Ru(CO)2(PPh3)2” is easily
altered by a change of the metal or the ligand; the osmium
analogue, “Os(CO)2(PPh3)2”, and “Ru(CO)(PPh3)3” show oxida-
tive addition of aromatic C H bonds of the ligands to form
OsH(CO)2[PPh2(C6H4)](PPh3)39 and RuH(CO)[PPh2(C6H4)]-
(PPh3)2,40 respectively.
Discussion
Studies33,34 of several reactions of Ru(CO)5 reveal that they
begin with dissociation of one CO to form transient Ru(CO)4
1
with ∆Hq
27.6 kcal/mol (and ∆Sq
15.2 cal K mol 1).
This establishes the approximate Ru CO bond dissociation
energy to form unsaturated Ru(0) unassisted by steric effects,
but also permits determination that the rate of CO loss down
this group is Ru
Os
Fe.35 This helps to understand our
(32) Farrar, D. H.; Grundy, K. R.; Payne, N. C.; Roper, W. R.; Walker,
A. J. Am. Chem. Soc. 1979, 101, 6577.
(33) Huq, R.; Poe¨, A. J.; Chawla, S. Inorg. Chim. Acta 1980, 38, 121.
(34) Hastings, W. R.; Rossel, M. R.; Baird, M. C. J. Chem. Soc., Dalton
Trans. 1990, 203.
(36) Mawby, R. J.; Perutz, R. N.; Whittlesey, M. K. Organometallics
1995, 14, 3268.
(37) Kandler, H.; Gauss, C.; Bidell, W.; Rosenberger, S.; Bu¨rgi, T.;
Eremenko, I. L.; Veghini, D.; Orama, O.; Burger, P.; Berke, H. Chem.sEur.
J. 1995, 1, 541.
(35) Shen, J.-K.; Gao, Y. C.; Shi, Q.-Z.; Basolo, F. Inorg. Chem. 1989,
28, 4304.
(38) Werner, H.; Gotzig, J. Organomet. Chem. 1981, 209, C60; 1985,
284, 73. Werner, H.; Gotzig, J. Organometallics 1983, 2, 547.

Characterization of a Zero-Valent Ru Species
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10199
While, initially, our finding that Ru(CO)2L2 is not isostructural
with isoelectronic Rh(CO)2L2 was surprising, we have been
able to show that this represents a deformation to a (nonplanar)
structure of lower energy as a result of the greater back-bonding
ability of Ru(0) compared to that of Rh(I), in concert with the
presence of two carbonyl ligands to take advantage of the metal
electron density. It is ironic that the distortion away from that
of Rh(CO)2L2 moves Ru(CO)2L2 to a structure which is very
close to that of Ru(CO)3L2, with one equatorial CO removed.
In this way, the Ru(CO)2,3L2 pair are closely analogous to the
Cr(CO)5,6 pair,41 where removal of one CO does not result in
major structural reorganization.
represents the first class of ruthenium complexes of this type
without a π-donor ligand or an agostic interaction.
The ruthenium center in the complex is not a sufficiently
strong reductant to cleave most C H bonds. For example,
intramolecular C H oxidative addition is observed in only
certain of the unsaturated, zero-valent species reported here. This
feature, together with the steric protection by the bulky
phosphine ligands, makes it possible to isolate Ru(CO)2L2 for
L
PiPr3 and PtBu2Me.
Acknowledgment. This work was supported by the U.S.
National Science Foundation and the French CNRS. M.O. held
a JSPS fellowship. We thank Johnson Matthey for material
support. We thank the EPSRC for a Western European NATO
Research Fellowlship and the EU for a grant to S.A.M. within
the Human Capital and Mobility Network No. CHRX CT
930152.
Conclusions
Platinum group metal complexes with d8 16-electron count,
which include RhCl(CO)(PPh3)2 and IrCl(CO)(PPh3)2 play an
important role in organo-transition-metal chemistry. However,
the isolable examples of such compounds of zero-valent
ruthenium are very few. Our new system, Ru(CO)2L2, with its
Supporting Information Available: Full crystallographic
details and positional and thermal parameters for Ru(CO)2-
(PtBu2Me)2 and Ru(O2)(CO)2(PtBu2Me)2 (7 pages). See any
current masthead page for ordering and Internet access
instructions.
unusual geometry not found for isoelectronic Rh(CO)2L2
,
(39) Clark, G. R.; Headford, C. E. L.; Marsden, K.; Roper, W. R. J.
Organomet. Chem. 1982, 231, 335.
(40) Roper, W. R.; Wright, L. J. J. Organomet. Chem. 1982, 234, C5.
(41) Burdett, J. K.; Perutz, R. N.; Poliakoff, M.; Turner, J. J. J. Chem.
Soc., Chem. Commun. 1975, 157.
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