Unsaturated Ru(0) species with a constrained bis-phosphine ligand: [Ru(CO)2((t)Bu2PCH2CH2P(t)Bu2)]2. Comparison to [Ru(CO)2(P(t)Bu2Me)2]

Article abstract of DOI:10.1021/ic9911320

The synthesis of Ru(C₂H₄)(CO)₂(d(t)bpe) (d(t)bpe = (t)Bu₂PC₂H₄P(t)Bu₂), then green [Ru(CO)₂(d(t)bpe)](n) is described. In solution, n = 1, while in the solid state, n = 2; the dimer has two carbonyl bridges. DFTPW91, MP2, and CCSD(T) calculations show that the potential energy surface for bending one carbonyl out of the RuP₂C(O) plane is essentially flat. Ru(CO)₂(d(t)bpe) reacts rapidly in benzene solution to oxidatively add the H-E bond of H₂, HCl, HCCR (R = H, Ph), [HOEt₂]BF₄, and HSiEt₃. The H-C bond of C₆HF₅ oxidatively adds at 80 °C. CO adds, as does the C=C bond of H₂C=CHX (X = H, F, Me). The following do not add: N₂, THF, acetone, H₃COH, and H₂O.

Full text of DOI:10.1021/ic9911320

Inorg. Chem. 2000, 39, 3957-3962
3957
Unsaturated Ru(0) Species with a Constrained Bis-Phosphine Ligand:
[Ru(CO)2(tBu2PCH2CH2PtBu2)]2. Comparison to [Ru(CO)2(PtBu2Me)2]
Torsten Gottschalk-Gaudig,‡ John C. Huffman,‡ He´le`ne Ge´rard,† Odile Eisenstein,*,† and
Kenneth G. Caulton*,‡
Department of Chemistry and Molecular Structure Center, Indiana University,
Bloomington, Indiana 47405-4001, and LSDSMS (UMR 5636), Universite´ de Montpellier 2,
34095 Montpellier Cedex 5, France
ReceiVed September 22, 1999
The synthesis of Ru(C2H4)(CO)2(dtbpe) (dtbpe ) tBu2PC2H4PtBu2), then green [Ru(CO)2(dtbpe)]n is described. In
solution, n ) 1, while in the solid state, n ) 2; the dimer has two carbonyl bridges. DFTPW91, MP2, and
CCSD(T) calculations show that the potential energy surface for bending one carbonyl out of the RuP2C(O)
plane is essentially flat. Ru(CO)2(dtbpe) reacts rapidly in benzene solution to oxidatively add the H-E bond of
H2, HCl, HCCR (R ) H, Ph), [HOEt2]BF4, and HSiEt3. The H-C bond of C6HF5 oxidatively adds at 80 °C. CO
adds, as does the CdC bond of H2CdCHX (X ) H, F, Me). The following do not add: N2, THF, acetone,
H3COH, and H2O.
Introduction
detailed comparison of the synthesis, structure, and reactivity
to those of the monodentate PtBu2Me analogue.
We have reported earlier on the synthesis, structure, and
reactivity of Ru(CO)2(PtBu2Me)21 and its isoelectronic analogue
Ru(CO)(NO)(PtBu2Me)2+.2 These are rare examples of unsatur-
ated, zerovalent ruthenium complexes. We have moreover
shown that, unlike the typical planar structure of d8 M(CO)Cl-
(PR3)2, M ) Rh or Ir, and M′Cl2(PR3)2, M′ ) Pd or Pt, these
zerovalent ruthenium species with two π-acid ligands adopt a
structure which resembles a trigonal bipyramid with an empty
equatorial site, I. While this has the advantage of minimizing
the inter-phosphine repulsion, ab initio calculations have shown
that the same structure is adopted for L ) PH3; thus, this
structure originates from electronic, not steric, preferences.
Experimental Section
General. All manipulations were carried out with standard Schlenk
and glovebox techniques under purified argon. Benzene, toluene, and
pentane were dried over sodium benzophenone ketyl, distilled, and
stored in gastight solvent bulbs. Benzene-d6 and toluene-d8 were dried
by appropriate methods and vacuum-distilled prior to use. Et3SiH, HCt
CPh, and C6HF5 were purchased from Aldrich and used without further
purification. Gaseous reagents were purchased from Air Products and
used as received. [Ru(H)2(CO)2(dtbpe)] was synthesized as reported.5
1H, 31P, 19F, and 13C NMR spectra were recorded on a Varian Gemini
300 spectrometer (1H, 300 MHz; 31P, 122 MHz; 19F, 282 MHz; 13C,
75 MHz) or on a Varian INOVA 400 spectrometer (1H, 400 MHz; 31P,
161 MHz; 19F, 376 MHz; 13C, 100 MHz). 1H NMR chemical shifts are
reported in parts per million downfield of tetramethylsilane with use
of residual solvent resonances as internal standards. 31P NMR chemical
shifts are relative to external 85% H3PO4. 19F NMR chemical shifts
are externally referenced to CF3COOH/C6D6. Infrared spectra were
recorded on a Nicolet 510P FT-IR spectrometer. UV-vis spectra were
recorded on a HP 8452A UV-vis and a Perkin-Elmer Lambda 19 UV-
vis/near-IR spectrometer. Elemental analyses were performed on a
Perkin-Elmer 2400 CHNS/O elemental analyzer at Indiana University.
All calculations were carried out with the Gaussian 94 package of
programs6 at the DFT(B3PW91),7 MP2,8 and CCSD(T)9 levels.
Effective core potentials were used for replacing the 28 innermost
We explore here the consequences of linking together the
two phosphine donors, via the ligand tBu2PCH2CH2PtBu2. This
makes structure I impossible and, thus, might be anticipated to
create an even more reactive species.3,4 We are interested in
(5) Gottschalk-Gaudig, T.; Folting, K.; Caulton, K. G. Inorg. Chem., in
press.
* Authors to whom correspondence should be addressed. E-mail:
caulton@indiana.edu and eisenste@lsd.univ-montp2.fr.
† Universite´ de Montpellier.
(6) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. H.; Peng, C. Y.; Ayala, P. Y.; Chen,
W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.;
Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian
94; Gaussian, Inc.: Pittsburgh, PA, 1995.
‡ Indiana University.
(1) Ogasawara, M.; Macgregor, S. A.; Streib, W. E.; Folting, K.;
Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1996, 18, 10189.
(2) Ogasawara, M.; Huang, D.; Streib, W. E.; Huffman, J. C.; Gallego-
Planas, N.; Maseras, F.; Eisenstein, O.; Caulton, K. G. J. Am. Chem.
Soc. 1997, 119, 8642.
(3) Hofmann, P.; Heiss, H.; Neiteler, P.; Mu¨ller, G.; Lachmann, J. Angew.
Chem., Int. Ed. Engl. 1990, 29, 880.
(4) Hackett, M.; Ibers, J. A.; Whitesides, G. M. J. Am. Chem. Soc. 1988,
110, 1436.
(7) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(8) Moller, C.; Plesset, M. S. Phys. ReV. 1934, 46, 618.
(9) Pople, J. A.; Head-Gordon, M.; Raghavachari, K. Chem. Phys. Lett.
1987, 87, 5968.
10.1021/ic9911320 CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/10/2000

3958 Inorganic Chemistry, Vol. 39, No. 18, 2000
Gottschalk-Gaudig et al.
Table 1. Crystallographic Data for [Ru(CO)2(tBu2PCH2CH2PtBu2)]2
(m, CH2), 208.24 (dd, CO, J(CPtrans) ) 87 Hz, J(CPcis) ) 15 Hz), 213.80
(m, CO). 31P{1H} NMR (C7D8, 208 K): δ 105.18 (d, J(PP) ) 19 Hz),
86.41 (d, J(PP) ) 19 Hz).
formula
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
C40H80O4P4Ru2
11.353(2)
18.453(4)
11.830(2)
112.92(1)
2282.81
2
space group
T, °C
P21/c
-168
0.71069
1.384
8.4
0.0669
0.0376
[Ru(H)2(CO)2(dtbpe)] was obtained from [Ru(CO)2(dtbpe)]2 (5.0
λ, Å
1
mg, 0.0052 mmol), C6D6, and H2. H and 31P NMR spectra showed
F
calcd, g/cm-3
µ(Mo KR), cm-1
complete conversion to [Ru(H)2(CO)2(dtbpe)], for which independent
synthesis was reported elsewhere.5
Ra
Rw
b
[Ru(CO)3(dtbpe)] was obtained from [Ru(CO)2(dtbpe)]2 (3.9 mg,
fw
951.11
1
0.0040 mmol), C6D6, and CO. H, 31P NMR, and IR spectra showed
complete conversion to [Ru(CO)3(dtbpe)], for which independent
synthesis was reported elsewhere.5
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
where w ) 1/σ2(|Fo|).
[RuHCl(CO)2(dtbpe)] was obtained from [Ru(CO)2(dtbpe)]2 (4.5
electrons of Ru10 and 10 innermost electrons of P.11 A basis set was of
valence double-ú quality10-12 with polarization functions on all
atoms.13,14
1
mg, 0.0047 mmol), C6D6, and HCl (0.0094 mmol). H and 31P NMR
spectra showed complete conversion to [RuHCl(CO)2(dtbpe)], for which
independent synthesis was reported elsewhere.5
[Ru(CO)2(dtbpe)]2. A 100-mL solvent seal flask was charged with
a yellow solution of [Ru(H)2(CO)2(dtbpe)] (190 mg, 0.4 mmol) in
benzene (15 mL). The solution was frozen at -78 °C, the headspace
was evacuated, and the flask was filled with C2H4 (1 atm). The sealed
flask was heated to 55 °C (CAUTION!) with vigorous stirring for 6
h, and the gas atmosphere was changed every 2 h. The resulting orange
solution was evaporated to dryness, giving a dark green residue, which
was recrystallized from toluene/pentane (1:5) at -40 °C, yielding dark
green crystals. Yield: 80 mg (43%). Anal. Calcd for C40H80O4P4Ru2:
C, 50.51; H, 8.48. Found: C, 50.90; H, 8.31. IR (C6D6, cm-1): 1944,
[RuH(CtCH)(CO)2(dtbpe)]. An NMR tube fitted with a Teflon
stopcock was filled with a green solution of [Ru(CO)2(dtbpe)]2 (8.1
mg, 0.0084 mmol) in C6D6 (0.5 mL). The solution was frozen, the
headspace was evacuated, and 1 atm of C2H2 was admitted, giving a
yellow solution in the time of mixing. The solution was filtered, and
the filtrate was evaporated to dryness, giving a yellow solid. Yield:
6.0 mg (71%). IR (C6H6, cm-1): 2031, 1989 (νCO). 1H NMR (C6D6):
δ -7.21 (dd, 1 H, RuH, J(HP) ) 21 Hz, 25 Hz), 0.97-1.47 (m, 40 H,
CH3, CH2), 1.35 (s, 1 H, CH). 13C{1H} NMR (C6D6): δ 23.29 (m,
PC), 23.90 (m, PC), 29.66-30.83 (m, CH3), 36.07-36.56 (m, CH2),
71.84 (s, CH), 96.66 (d, RuCC, J(CP) ) 20 Hz), 201.13, 202.10 (CO,
multiplicity of the signal is not given, due to the weakness of the signal).
31P{1H} NMR (C6D6): δ 108.03 (d, J(PP) ) 13 Hz), 97.79 (d, J(PP)
) 13 Hz). Elemental analysis was not obtained due to the close
similarity to the phenyl analogue, below.
1
1873 ν(CO); (Nujol, cm-1) 1869, 1668 ν(CO). H NMR (C6D6): δ
1.15 (d, 36 H, CH3), 1.36 (d, 4 H, CH2). 13C{1H} NMR (C6D6) δ 23.42
(t, P-C), 30.64 (t, CH3), 36.65 (t, CH2), 208.73 (dd, CO, J(CPtrans) )
72 Hz, J(CPcis) ) 18 Hz). 31P{1H} NMR (C6D6): δ 99 (s). UV-vis
(C6H6): 424 nm (ꢀ ) 4260 L mol-1 cm-1), 672 nm (ꢀ ) 2455 L mol-1
cm-1).
[RuH(CtCPh)(CO)2(dtbpe)]. In an NMR tube, HCCPh (1.55 µL,
0.014 mmol) was added to a green solution of [Ru(CO)2(dtbpe)]2 (7.0
mg, 0.0074 mmol) in C6D6 (0.5 mL), yielding a yellow solution in the
time of mixing. The solution was filtered, and the filtrate was evaporated
to dryness, giving a yellow solid. Yield: 3.0 mg (35%). Anal. Calcd
for C28H46O2P2Ru: C, 58.22; H, 8.03. Found: C, 58.20; H, 8.07. IR
(C6H6, cm-1): 2108 (νCtC), 2027, 1989 (νCO). 1H NMR (C6D6): δ
-7.20 (dd, 1 H, RuH, J(HP) ) 21, 26 Hz), 0.91-1.36 (m, 40 H, CH3,
CH2), 6.90 (t, 1 H, C6H5), 7.10 (t, 2 H, C6H5), 7.65 (d, 2 H, C6H5).
13C{1H} NMR (C6D6): δ 23.35 (m, PC), 23.87 (m, PC), 29.66-30.64
(m, CH3), 35.98-36.50 (m, CH2), 112.03 (d, RuCC, J(CP) ) 20 Hz),
124.35, 127.20, 127.60, 128.12, 131.59 (s, CPh, C(aryl)), 200.98, 202.04
(CO, multiplicity of the signal is not given, due to the weakness of the
signal). 31P{1H} NMR (C6D6): δ 107.74 (d, J(PP) ) 13 Hz), 97.14 (d,
J(PP) ) 13 Hz).
[RuH(FBF3)(CO)2(dtbpe)]. In an NMR tube, HBF4 (2.0 µL, 0.012
mmol, 85% in Et2O) was added to a green solution of [Ru(CO)2-
(dtbpe)]2 (5.6 mg, 0.0059 mmol) in C7D8 (0.5 mL), yielding a bright
orange solution in the time of mixing. 1H and 31P NMR spectra showed
complete conversion to [RuH(FBF3)(CO)2(dtbpe)], for which indepen-
dent synthesis was reported elsewhere.5
X-ray Diffraction Structure Determination of [Ru(CO)2-
(tBu2PC2H4PtBu2)]2. A typical green crystal was selected, affixed to a
glass fiber using silicone grease, and then rapidly transferred to the
goniostat and cooled to -168 °C. A systematic search of a limited
hemisphere of reciprocal space was used to determine that the crystal
possessed monoclinic symmetry and systematic absences corresponding
to the unique space group P21/c (Table 1). Subsequent solution and
refinement confirmed this choice. The data were collected (6° < 2θ <
50°) using a standard moving crystal-moving detector technique with
fixed backgrounds at each extreme of the scan. Data were corrected
for Lorentz and polarization effects and equivalent reflections averaged
after correction for absorption. The structure, which consists of a dimer
located at a center of inversion, was solved with some difficulty using
direct methods (SHELX) and Fourier techniques. Hydrogen atoms were
readily located in a difference Fourier phased on the non-hydrogen
atoms. Since several of the hydrogen atoms tended to converge to
negative isotropic thermal parameters upon refinement, only their
positions were varied in the final cycles of refinement. A final difference
Fourier was featureless, the largest peak of intensity 0.55 e/Å3, lying
adjacent to the Ru atom.
General Procedure for the Reaction of [Ru(CO)2(dtbpe)] with
C2H4, H2, CO, and HCl. An NMR tube fitted with a Teflon stopcock
was filled with a green solution of [Ru(CO)2(dtbpe)]. The solution was
frozen, the headspace was evacuated, and 1 atm of the corresponding
gas (except HCl) was admitted, giving a yellow solution in the time of
mixing.
[RuH(SiEt3)(CO)2(dtbpe)]. In an NMR tube, HSiEt3 (1.7 µ, 0.011
mmol) was added to a green solution of [Ru(CO)2(dtbpe)]2 (5.2 mg,
0.0055 mmol) in C7D8 (0.5 mL), yielding a yellow solution in the time
of mixing. IR (C7D8, cm-1): 1995, 1954 (νCO), 1908 (νRuH). 1H NMR
1
(C7D8, 333 K): δ 1.13 (d, 36 H, CH3), 1.29 (d, 4 H, CH2). H NMR
[Ru(C2H4)(CO)2(dtbpe)] was obtained from [Ru(CO)2(dtbpe)]2 (4.6
(C7D8, 213 K): δ -8.09 (dd, 1 H, RuH, J(HP) ) 21 Hz, 23 Hz), 0.40-
1.80 (m, 55 H, CH3, CH2). 31P{1H} NMR (C7D8, 333 K): δ 102.60
(s). 31P{1H} NMR (C7D8, 213 K): δ 100.99 (d, J(PP) ) 15 Hz), 100.05
(d, J(PP) ) 15 Hz).
mg, 0.005 mmol) and C2H4 (1 atm). C7D8 IR (C7D8, cm-1): 1964, 1892
1
ν(CO). H NMR (C7D8, 293 K) δ 1.14 (d, 36 H, CH3), 1.35 (d, 4 H,
CH2), 2.10 (br, 4 H, C2H4). 1H NMR (C7D8, 208 K): δ 0.82, 1.23 (br,
40 H, CH3, CH2), 1.83, 2.15, 2.34, 2.49 (s, each 1 H, C2H4). 13C{1H}
NMR (C7D8, 208 K): δ 23.80 (m, P-C), 29.91 (m, CH3, C2H4), 37.04
[RuH(C6F5)(CO)2(dtbpe)]. A green solution of [Ru(CO)2(dtbpe)]2
(6.1 mg, 0.0064 mmol) in C6HF5 (0.5 mL) was heated for 4 h at 80
°C, yielding a bright yellow solution. All volatiles were removed in a
vacuum, and the white residue was dried for 12 h in vacuo. IR (C7D8,
(10) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(11) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(12) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257.
(13) Ho¨llwarth, A.; Bo¨hme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi, A.;
Jonas, V.; Ko¨hler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 208, 237.
1
cm-1): 1997, 1941 ν(CO). H NMR (C7D8) δ -6.89 (dt, 1 H, RuH,
J(HF) ) 29 Hz, J(HP) ) 25 Hz), 0.76-1.70 (m, 40 H, CH3, CH2).
31P{1H} NMR (C7D8): δ 89.37 (d, J(PP) ) 11 Hz), 109.99 (m). 19F
NMR (C7D8): -165.47 (m, m-F), -165.06 (m, m-F), -164.01 (m, p-F),
-100.39 (m, o-F), -96.80 (m, o-F). The fluorine content frustrated
satisfactory combustion analysis.
(14) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.

Unsaturated Ru(0) Species with a Bis-Phosphine Ligand
Inorganic Chemistry, Vol. 39, No. 18, 2000 3959
Figure 1. DFT calculated structure of Ru(CO)2(H2PCH2CH2PH2).
Results
Preparation and Characterization of [Ru(CO)2(dtbpe)] (1)
t
(dtbpe ) Bu2PCH2CH2PtBu2). Reaction of [Ru(H)2(CO)2-
(dtbpe)] with C2H4 gave the yellow ethylene complex [Ru-
(C2H4)(CO)2(dtbpe)] (2). The ethylene ligand in 2 is labile and
can be easily removed in a vacuum, yielding dark green [Ru-
(CO)2(dtbpe)] (1) (eq 1).
Figure 2. DFT calculated structure for cis-Ru(CO)2(PH3)2 (hydrogens
omitted) showing the ground state (center) and two transition states
(Cs and C2) for site exchange of carbonyls and of phosphines.
complex in part because the constraint of the five-membered
ring prevents the Ru-P-C (tBu) angle from achieving the small
angle (∼100°) characteristic of agostic donation.
1
The H NMR spectrum of 1 shows one doublet for the four
tBu substituents of the chelate ligand, the 31P{1H} NMR shows
one singlet, and the 13C{1H} NMR spectrum exhibits one
doublet of doublets for the CO ligands. These spectroscopic
data are consistent with a square-planar structure of 1 in solution.
In particular the two J(PC) values in the CO NMR signal have
magnitudes consistent with one being to a trans P (72 Hz) and
one being to a cis P (18 Hz). Furthermore, the CO ligands show
two absorption bands in the IR spectrum in hexane (1944 and
1873 cm-1). From the intensities of these, a C-Ru-C angle of
84° was calculated.15 However, quantum calculations (see
below) show that 1 has a structure II which differs subtly from
square-planar.
In order to determine how the chelate ligand influences the
coordination at the Ru center, we also optimized the geometry
of cis-Ru(CO)2(PH3)2 in its singlet and triplet states. The triplet
state is calculated to be 26.1 kcal‚mol-1 above the singlet
minimum, proving without doubt the preference for a diamag-
netic species. This is consistent with the experimental NMR
evidence for diamagnetism. For the singlet state, the geometrical
structure is found to be very similar to that of the chelate
phosphine system (P-Ru-C ) 151.7° and 168.3°, C-Ru-C
) 90.3°, CO ) 1.158 Å) (Figure 2 (center)). In particular, the
two CO ligands are also not equivalent (C1 symmetry). The
nonplanar coordination and the lack of symmetry elements (Cs
or C2) is thus an intrinsic property of the ground state of the
cis-Ru(CO)2(PH3)2 system. The compound trans-Ru(CO)2(PH3)2
is calculated to be 1.3 kcal‚mol-1 more stable than cis-Ru(CO)2-
(PH3)2.
While the two isomers (trans- and cis-Ru(CO)2(PH3)2) are
nonplanar, they show significant differences. The C-Ru-C
angle (138.8°) of the trans isomer is significantly smaller than
any trans L-Ru-L′ angle in the cis isomer. In contrast, the
P-Ru-P angle (171.0°) is larger than any P-Ru-P angle in
the cis isomer. In addition, the Ru-C-O angle is bent (168.4°),
while no such distortion is obtained in the cis isomer (Ru-
C-O ) 173.3°, 176.0°). The geometry of a d8 ML4 complex is
thus highly sensitive to the nature16 and site occupancy1 of the
π acceptor ligands.
How can this conclusion of inequivalent carbonyls (and thus
inequivalent 31P nuclei) be reconciled with the NMR spectra?
Two nonplanar singlet transition states for equivalencing the
two CO and the two PH3 ligands were located (Figure 2) only
0.2 and 0.3 kcal‚mol-1 above the minimum. The introduction
Computational Study of cis-Ru(PR3)2(CO)2. The structure
of the model complex cis-Ru(CO)2(H2PCH2CH2PH2), 1, was
fully optimized without any symmetry constraint with DFT-
(B3PW91) calculations. The resulting structure (Figure 1) shows
the preference for a nonplanar geometry with two different CO
ligands (P-Ru-C ) 169.3° and 157.6° and equal CO bond
lengths of 1.159 Å). The angle between the two CO ligands
(91.6°) is in very close agreement with that calculated from the
IR measurement. The five-membered ring has the expected
t
envelope shape. Despite the absence of Bu substituents on P,
the calculated structure seems to mimic well the experimental
system. We believe that no agostic interaction is present in this
(15) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London,
1975.
(16) Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058.

3960 Inorganic Chemistry, Vol. 39, No. 18, 2000
Gottschalk-Gaudig et al.
P-Ru-P angle is 83.99(6)°, which is comparable to the
P-Ru-P angle in [RuH(CO)2(dtbpe)]BArF (85.76(7)°).5
4
The dimeric solid-state structure of 1 is supported by the IR
spectrum in Nujol mull, which shows one absorption for a
terminal CO ligand (1869 cm-1) and one band for a bridging
CO ligand (1668 cm-1). Further proof of the different structure
of 1 in solution and the solid state comes from the UV-vis
spectra in solution and in the solid state. While the solution
spectrum (benzene) shows two bands at 424 and 672 nm, in
which the latter one is responsible for the green color, the solid-
state spectrum (Fluorolube) exhibits only one band (665 nm),
supporting the different structure of 1 in solution and in the
solid state. Furthermore, a possible interaction between coor-
dinatively unsaturated monomeric 1 and the solvent could be
excluded by comparison of the UV-vis spectra in benzene and
n-hexanes, which are essentially identical. In order to exclude
that traces of benzene cause the low but observable solubility
and affect the UV-vis spectrum of 1 in n-hexanes, two samples
of 1 were prepared in n-hexanes with identical concentrations
but one sample containing a trace of benzene. The UV-vis
spectra of these samples were essentially identical; in particular
the intensities of the bands were identical, which shows that
the solubility of 1 in n-hexanes is not caused by traces of
benzene breaking up the dimeric structure of solid 1.
Figure 3. ORTEP drawing of the non-hydrogen atoms of centrosym-
metric [Ru(CO)2(tBu2PC2H4PtBu2)]2 in the solid state.
Table 2. Selected Bond Distances (Å) and Angles (deg) in 1
Ru(1)-P(2)
Ru(1)-P(5)
Ru(1)-C(22)
Ru(1)-C(22)′
2.4593(19)
2.4620(19)
2.016(7)
Ru(1)-C(24)
O(23)-C(22)
O(25)-C(24)
Ru(1)-Ru(1)′
1.836(7)
1.198(7)
1.165(8)
2.703
2.050(6)
In retrospect, the comment made earlier here that Ru(CO)2-
(dtbpe) in solution is not planar may seem like splitting hairs.
Despite the fact that all calculations suggest a preference for a
nonplanar structure, the tiny difference in energy from the
calculated planar structure does not allow a definitive decision
for the experimental compound. On the other hand, this is a
situation where, at the level of less than ∼3° or ∼0.02 Å, the
uncertainty here is analogous to the question of FHF- (cen-
trosymmetric or not?),17 (OC)5CrHCr(CO)5- (two equal Cr-H
distances, or not?),18 “stretched” H2 complexes19 (0.6 Å variation
in RH/H alters energy by <1 kcal/mol), and (most contemporary)
P(2)-Ru(1)-P(5)
P(2)-Ru(1)-C(22)
P(2)-Ru(1)-C(22)′
P(2)-Ru(1)-C(24)
P(5)-Ru(1)-C(22)
P(5)-Ru(1)-C(22)
P(5)-Ru(1)-C(24)
C(22)-Ru(1)-C(22)′
83.99(6)
Ru(1)-P(2)-C(3)
106.29(23)
116.11(22)
119.88(22)
105.18(24)
118.32(24)
118.56(23)
83.31(24)
154.08(18) Ru(1)-P(2)-C(6)
86.10(19) Ru(1)-P(2)-C(10)
102.75(23) Ru(1)-P(5)-C(4)
87.18(19) Ru(1)-P(5)-C(14)
164.47(18) Ru(1)-P(5)-C(18)
98.45(23) Ru(1)-C(22)-Ru(1)
96.69(24) Ru(1)-C(22)-O(23) 139.9(5)
C(22)-Ru(1)-C(24) 102.6(3)
C(22)′-Ru(1)-C(24) 95.4(3)
Ru(1)-C(22)′-O(23)′ 136.6(5)
Ru(1)-C(24)-O(25) 169.8(6)
of ZPE correction does not alter the relative energies of the
C1, C2, and Cs structures, thus proving that the C1 structure is
a true minimum. Furthermore, the energy of the square-planar
singlet structure, obtained from optimization under constraints,
is only 0.7 kcal‚mol-1 above the same minimum. The extreme
flatness of this potential energy surface was also established
by MP2 calculations, which find a difference in energy of 0.4
kcal‚mol-1 between planar and nonplanar structures, in favor
of a nonplanar structure. Finally, CCSD(T) calculations on
CH5 .
+ 20 What is true of both Ru(CO)2(dtbpe) and CH5+ is that
seVeral (inequivalent) structures are at energies comparable to
kT at 25 °C. Thus, several nonplanar as well as the planar
structures are populated at 25 °C, which merely describe it as
an exceptionally deformable four-coordinate d8 species (but
compare RhCl(CO)(PtBu3)221 and Rh(PPh2Me)4+ 22 where steric
,
effects are becoming acute). This structural “plasticity” can lead
to atypical interaction (albeit weak interactions) with exception-
ally weak donors (cf. Ru(CO)2(Me2PC2H4PMe2) in inert gas
matrixes), as well as the dimerization observed here which can
be completely destroyed by entropy at 25 °C and below (T∆S
∼3 kcal/mol at, e.g., -60 °C).
MP2 geometries give a difference of energy of 0.3 kcal‚mol-1
.
Thus, quantum calculations all agree on a highly flexible
structure for cis-Ru(CO)2(PH3)2. The flatness of the surface
indicated by all levels of calculations thus accounts for the
NMR spectroscopic observation of two chemically equivalent
t
CO and also of identical Bu substituents on P, all by time
averaging.
Reactivity
Binding of C2H4 to [Ru(CO)2(dtbpe)] (1) in arene solvents is
complete in the time of mixing at 25 °C. The green color of 1
changes to yellow. The ethylene ligand in [Ru(C2H4)(CO)2-
(dtbpe)] (2) is weakly bound. Heating a solution of 2 in benzene
Solid-State Structure. Surprisingly, the solid-state structure
of green crystalline 1 differs from the structure in solution. The
X-ray structure analysis reveals that 1 has a centrosymmetric
dimeric solid-state structure (Figure 3). The two ruthenium
centers are bridged by two CO ligands. The Ru-Ru distance is
2.703 Å (Table 2). Each Ru center is surrounded by two P
atoms, one terminal CO ligand, and two bridging CO ligands,
giving a square-pyramidal geometry. The four apical-to-basal
angles fall into the narrow range 95.4(3)°-102.75(23)°. The
Ru-C (183.6(7) pm) and C-O distances (116.5(8) pm) of the
terminal CO ligand are distinctly different from the correspond-
ing distances of the bridging CO ligands (Ru-C, 201.6(7),
205.0(6) pm; C-O, 119.8(7) pm). The terminal CO ligand is
slightly bent with a Ru-C-O angle of 169.8(6)°. The Ru-
C-Ru angle of the bridging CO ligand is 83.31(24)°. The
(17) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University
Press: New York, 1997; p 34.
(18) Petersen, J. L.; Brown, R. K.; Williams, J. M. Inorg. Chem. 1981, 20,
158.
(19) (a) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789. (b)
Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155.
(20) White, E. T.; Tang, J.; Oka, T. Science 1999, 284, 135. See also: Marx,
D.; Parinello, M. Science 1999, 284, 59.
(21) Harlow, R. L.; Westcott, S. A.; Thorn, D. L.; Baker, R. T. Inorg.
Chem. 1992, 31, 323. See also: Thorn, D. L.; Harlow, R. L. Inorg.
Chem. 1990, 29, 2017.
(22) Lundquist, E. G.; Streib, W. E.; Caulton, K. G. Inorg. Chim. Acta
1989, 159, 23.

Unsaturated Ru(0) Species with a Bis-Phosphine Ligand
Inorganic Chemistry, Vol. 39, No. 18, 2000 3961
1
to 60 °C or removal of the ethylene atmosphere resulted in loss
of the C2H4 ligand and formation of [Ru(CO)2(dtbpe)] (1),
indicated by the green color of the solution. [Ru(C2H4)(CO)2-
(CO) of II. The H NMR spectrum of [Ru(H)2(CO)2(dtbpe)]
recorded at 70 °C shows a small line broadening of the hydride
signals while the 31P NMR signals are unaffected. In no case
was there evidence of thermal loss of H2 by NMR spectroscopy
or by a color change of a solution of [Ru(H)2(CO)2(dtbpe)] at
elevated temperatures.
The oxidative addition of HCl (gas) and HBF4 (solution in
Et2O) gives trans-[RuHCl(CO)2(dtbpe)] and trans-[RuH-
(FBF3)(CO)2(dtbpe)], respectively. The formation of the trans
products indicates a nonconcerted mechanism for these reactions
or a fast rearrangement of the kinetic cis product to the
thermodynamically more stable trans product.
1
(dtbpe)] (2) is rapidly fluxional. The H NMR spectrum at 25
t
°C shows only one doublet for the Bu group, one doublet for
the (CH2)2 bridge of the chelate ligand, and a broad signal for
the ethylene ligand. The ethylene protons decoalesce to four
chemical shifts at 208 K, which excludes structure IV under
the conditions where olefin rotation has been halted. Four
ethylene chemical shifts are consistent with structure III,
regardless of the orientation of the CdC vector. Structure III
Reaction with HCtCR (R ) H, Ph) in the time of mixing
changes the green color to yellow. A hydride signal proves that
these products are formed by oxidative addition of one C-H
bond, and its two different P/H coupling constants show the
molecule to be stereochemically rigid, with inequivalent phos-
phines. The similarity of the two 2JPH values (21 and 25 Hz) is
most consistent with structure VII, which is analogous to the
oxidative addition product with H2. The acetylide â-hydrogen
is also detected when R ) H.
is also supported by the low-temperature 13C{1H} NMR
spectrum, which shows a doublet of doublets and a multiplet
for the inequivalent CO ligands, and the 31P{1H} NMR
spectrum, which shows two chemical shifts. The observation
that only one CO has one large J(PC) (87 Hz) is only consistent
with structure III. The IR spectrum in toluene exhibits two CO
bands, whose intensities permit a C-Ru-C angle of 91° to be
calculated. The νCO values rise by about 20 cm-1 on binding of
C2H4 to 1, which suggests that ethylene is more a π-acid than
a donor in the adduct.
Other olefins, such as H2CdCHF and H2CdCHCH3, are also
only weakly bound. The stability of the adducts decreases
according to H2CdCH2 > H2CdCHF > H2CdCHCH3. This
order has been determined from the temperature dependence
of the color change from orange ([Ru(olefin)(CO)2(dtbpe)]) to
green ([Ru(CO)2(dtbpe)]). [Ru(olefin)(CO)2(dtbpe)] loses H2Cd
CH2 at ca. 60 °C and H2CdCHF at 40 °C, and H2CdCHCH3
is already lost at room temperature.
The green color of [Ru(CO)2(dtbpe)] (1) transforms to yellow
during 4 h at 80 °C in neat C6F5H. The product has structure
VII, and the 19F NMR spectrum shows five chemical shifts,
showing that rotation around the Ru-C(ipso) bond is slow, due
t
apparently to steric pressure from the two nearby Bu groups.
Indeed, all compounds with isomeric form VII are probably
favored because they put the bulkier ligand cis to only one
PtBu2 group. The alternative placement of H and R creates cis
interactions between R and both phosphorus donors.
Reaction with CO in benzene occurs in the time of mixing
at 25 °C to give [Ru(CO)3(dtbpe)], which has an IR spectrum
(three νCO absorptions) consistent with structure V. NMR spectra
The reaction of [Ru(CO)2(dtbpe)] (1) with HSiR3 (R ) Me,
Et) at 25 °C gave a bright yellow solution in the time of mixing.
1
The H NMR spectrum of this solution at 25 °C showed only
a broad signal for the hydride and no signals for the alkyl groups
of the silane. Heating the solution to 60 °C resulted in a green
solution, indicative of equilibrium between the oxidative addition
product [RuH(SiR3)(CO)2(dtbpe)] and [Ru(CO)2(dtbpe)] (1)
which can be shifted toward [Ru(CO)2(dtbpe)] (1) by heating.
1
The H NMR spectrum at 60 °C was nearly identical to the
at 25 °C and at -60 °C show only one 31P{1H} chemical shift,
one tBu 1H NMR chemical shift, and one triplet carbonyl signal
in the 13C{1H} NMR, all consistent with a rapidly fluxional
molecule.
spectrum of [Ru(CO)2(dtbpe)] (1) at room temperature. How-
ever, a resolved 1H NMR spectrum for [RuH(SiR3)(CO)2-
(dtbpe)] obtained at low temperatures showed the expected
hydride doublet of doublets with nearly identical coupling
constants for a hydrido ligand in a coordination sphere according
to structure VII. The 31P{1H} NMR spectrum exhibits two
doublets for the inequivalent P atoms in structure VII. These
spectral features are comparable to those of RuH(SiEt3)(CO)2(Me2-
PCH2CH2PMe2) (which is nonfluxional)23 and to those of FeH-
(SiR3)(CO)2(Ph2PCH2CH2PPh2),24 which shows intramolecular
fluxionality. Neither of these shows the dissociative process (loss
of H-SiR3) observed here for RuH(SiR3)(CO)2(dtbpe).
H2 oxidatively adds in the time of mixing at 25 °C to give a
product of structure VI. The molecule shows inequivalent 31P
When N2 was admitted to a solution of 1, no reaction was
observed at room temperature as judged by NMR spectroscopies
t
1
nuclei, four Bu H NMR chemical shifts, and two hydride
chemical shifts, one with a large coupling to phosphorus. The
fact that the hydrides are cis is consistent with a mechanism in
which H2 approaches perpendicular to the quasi-plane RuP2-
(23) Whittlesey, M. K.; Perutz, R. N.; Virrels, I. G.; George, M. W.
Organometallics 1997, 16, 268.
(24) Knorr, M.; Mu¨ller, J.; Schubert, U. Chem. Ber. 1987, 120, 879.

3962 Inorganic Chemistry, Vol. 39, No. 18, 2000
Gottschalk-Gaudig et al.
and by the absence of any color change. The 31P chemical shift
of 1 in THF is within 1 ppm of that in benzene, indicating no
coordination of THF. Dissolving 1 in acetone-d6 gave no
Chart 1
1
reaction according to H and 31P NMR spectroscopy after 1 h
at room temperature. A solution of 1 in THF is also stable
against a large excess of H2O for 20 h at room temperature,
and CH3OH in C6D6 does not react with 1 at 25 °C. All of
these are consistent with 1 being a strong π-base and reductant,
but not strongly Lewis acidic toward σ-bases.
Discussion
While Cp*Rh(CO)25-27 and Os(CO)428-30 are d8 16-electron
transient species which also dimerize, Ru(CO)2L2 is unique in
doing so reversibly on change from solution to the solid state.
There are two distinct classes of compounds to which to
compare the Ru/Ru distances in [Ru(CO)2L2]2. In the unbridged
long and short Ru-C distances differing by 0.33 Å (R ) Me)
and 0.51 Å (R ) iPr). Associated with this difference is a change
in metal coordination geometry shown in Chart 1. In fact,
neglecting the long (2.3-2.4 Å) Ru/C distance, the geometry
around Ru in [Ru(CO)2{(RO)2PNEtP(OR)2}]2 rather closely
mimics the nonplanar “saw-horse” geometry of Ru(CO)2-
(PtBu2Me)2.
Single and double Ru0/Ru0 bonds bridged by (Ph2P)2CH2
ligands have distances of 2.784 and 2.697 Å, respectively.34
The unbridged single RuI/RuI bond in [Ru(CO)3(dppe)]22+ has
a distance of 3.04 Å.35
The dimerization of [Ru(CO)2(dtbpe)]2 in the solid state stands
also in contrast to the structure of the analogous [Ru(CO)2L2]
complexes of monodentate L, which are monomeric in the solid
state and in solution. One reason for this different behavior is
the more sterically compact cis P2 geometry of [Ru(CO)2-
(dtbpe)]2, which enables dimerization without excessive end-
to-end inter-phosphine repulsions.
31
dimer [Ru(octaethylporphyrin)]2 and in [Ru(tetraazaannu-
32
lene)]2 the RuII/RuII distances are 2.408 and 2.379 Å,
respectively. The 18-electron rule, their diamagnetism, and the
absence of any bridging ligands collectively demand a RudRu
double bond in these species. However, these differ from [Ru-
(CO)2L2]2 in that they are d6/d6 dimers and they represent
square-planar RuN4 species which become apically connected
square pyramids when they dimerize. An authentic (Ru0)2 dimer
is [Ru(CO)2{(RO)2PNEtP(OR)2}]2,33 where the Ru/Ru distance
i
is 2.73 Å (R ) Me) or 2.76 Å (R ) Pr); this is also a case
where the 18-electron rule demands a RudRu double bond. In
this dimer structure, each bidentate ligand bridges the two
metals, in contrast to our chelate; while there are two bridging
carbonyls in this dimer, they are highly asymmetric, with the
Acknowledgment. This work was supported by the National
Science Foundation and by a DFG grant to T.G.-G. We thank
Professor Robin Perutz for useful discussions, advice, and
suggestions.
(25) Green, M.; Hankes, D. R.; Howard, J. A. K.; Louca, P.; Stone, F. G.
A. J. Chem. Soc., Chem. Commun. 1983, 757.
(26) Belt, S. T.; Grevels, F.; Kotzbu¨cher, W. E.; McCamley, A.; Perutz,
R. N. J. Am. Chem. Soc. 1989, 111, 8373.
(27) Nutton, A.; Maitlis, P. M. J. Organomet. Chem. 1979, 166, C21.
(28) Church, S. P.; Grevels, F.; Kiel, G.; Kiel, W. A.; Takats, J.; Schaffner,
K. Angew. Chem., Int. Ed. Engl. 1986, 25, 991.
(29) Poliakoff, M.; Turner, J. J. J. Chem. Soc., Dalton Trans. 1974, 2276.
(30) Haynes, A.; Poliakoff, M.; Turner, J. J.; Bender, B. R.; Norton, J. R.
J. Organomet. Chem. 1990, 383, 497.
Supporting Information Available: An X-ray crystallographic file,
in CIF format, for the structure of [Ru(CO)2(tBu2PCH2CH2PtBu2)]2. This
material is available free of charge via the Internet at http://pubs.acs.org.
IC9911320
(31) Collman, J. P.; Barnes, C. E.; Swepston, P. N.; Ibers, J. A. J. Am.
Chem. Soc. 1984, 106, 3500.
(32) Warren, L. F.; Goedken, V. L. J. Chem. Soc., Chem. Commun. 1978,
909.
(33) Field, J. S.; Haines, R. J.; Stewart, M. W.; Sundermeyer, J.; Woollam,
S. F. J. Chem. Soc., Dalton Trans. 1993, 947.
(34) Bo¨ttcher, H.; Bruhn, C.; Merzwiler, K. Z. Anorg. Allg. Chem. 1999,
625, 586.
(35) Skoog, S. J.; Jorgensen, A. L.; Campbell, P.; Dooskey, M. L.; Munson,
E.; Gladfelter, W. L. J. Organomet. Chem. 1998, 557, 13.