Synthesis of the five-coordinate ruthenium(II) complexes [(PCP)Ru(CO)(L)][BAr′4

Article abstract of DOI:10.1021/ic051074k

Reaction of (PCP)Ru(CO)(Cl) (1) with NaBAr′₄ yields the bimetallic product [{(PCP)Ru(CO)}₂(μ-Cl)][BAr′₄] (2). The monomeric five-coordinate complexes [(PCP)Ru(CO)(η¹- ClCH₂Cl)][BAr′₄] (3) a

Full text of DOI:10.1021/ic051074k

Inorg. Chem. 2005, 44, 8379−8390
Synthesis of the Five-Coordinate Ruthenium(II) Complexes
[(PCP)Ru(CO)(L)][BAr PCP
2,6-(CH2PtBu2)2C6H3, BAr′4 )
3,5-(CF3)2C6H3, L ) η1-ClCH2Cl, 1-N2, or
-Cl Ru(PCP)(CO)
Reactions with Phenyldiazomethane and Phenylacetylene
′
]
4
{
)
η
µ
−
}:
Jubo Zhang,† Khaldoon A. Barakat,‡ Thomas R. Cundari,‡ T. Brent Gunnoe,*,† Paul D. Boyle,†
Jeffrey L. Petersen,§ and Cynthia S. Day|
Department of Chemistry, North Carolina State UniVersity, Raleigh, North Carolina 27695-8204,
Department of Chemistry, UniVersity of North Texas, Box 305070, Denton, Texas 76203-5070,
C. Eugene Bennett Department of Chemistry, West Virginia UniVersity, Morgantown,
West Virginia 26506-6045, and Department of Chemistry, Wake Forest UniVersity,
Winston Salem, North Carolina 27109-7486
Received June 29, 2005
Reaction of (PCP)Ru(CO)(Cl) (1) with NaBAr
The monomeric five-coordinate complexes [(PCP)Ru(CO)(
(4) are synthesized upon reaction of (PCP)Ru(CO)(OTf) (6) with NaBAr
′
yields the bimetallic product [
{
(PCP)Ru(CO)
4] (3) and [(PCP)Ru(CO)(
in CH2Cl2 or C6H5F, respectively. The
}
(
2 µ-Cl)][BAr
1-N2)][BAr
′ ]
4
′4] (2).
4
η
1-ClCH2Cl)][BAr
′
η
′
4
solid-state structures of 2, 3, and 4 have been determined by X-ray diffraction studies of single crystals. The
reaction of 3 with PhCHN2 or PhC CH affords carbon carbon coupling products involving the aryl group of the
t
−
PCP ligand in transformations that likely proceed via the formation of Ru carbene or vinylidene intermediates.
Density functional theory and hybrid quantum mechanics/molecular mechanics calculations were performed to
investigate the bonding of weak bases to the 14-electron fragment [(PCP)Ru(CO)]+ and the energetics of different
isomers of the product carbene and vinylidene complexes.
Introduction
been extensively studied,6-13 and several unsaturated ruthe-
nium complexes have been synthesized to study C-H agostic
interactions.14-17 Caulton et al. have conducted systematic
studies on the synthesis and reactivity of four-coordinate
Coordinatively and electronically unsaturated divalent
ruthenium complexes with 14- or 16-electron counts are of
interest as possible intermediates in catalytic processes as
well as for the fundamental understanding of structure and
bonding.1,2 For example, 16-electron Grubbs-type ruthenium
catalysts have been successfully applied to olefin metathesis,3-5
coordinatively unsaturated half-sandwich ruthenium com-
plexes with phosphine, amidinate, or carbene ligands have
(6) Nagashima, H.; Kondo, H.; Hayashida, T.; Yamaguchi, Y.; Gondo,
M.; Masuda, S.; Miyazaki, K.; Matsubara, K.; Kirchner, K. Coord.
Chem. ReV. 2003, 245, 177-190.
(7) Aneetha, H.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.;
Sapunov, V. N.; Schmid, R.; Kirchner, K.; Mereiter, K. Organo-
metallics 2002, 21, 5334-5346.
(8) Tenorio, M. J.; Puerta, M. C.; Valerga, P. J. Organomet. Chem. 2000,
609, 161-168.
* To whom correspondence should be addressed. E-mail:
brent_gunnoe@ncsu.edu.
(9) Kolle, U.; Rietmann, C.; Raabe, G. Organometallics 1997, 16, 3273-
3281.
† North Carolina State University.
(10) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J. Chem. Soc., Chem.
Commun. 1988, 278.
(11) Johnson, T. J.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. Soc.
1992, 114, 2725-2726.
(12) Bickford, C. C.; Johnson, T. J.; Davidson, E. R.; Caulton, K. G. Inorg.
Chem. 1994, 33, 1080.
‡ University of North Texas.
§ West Virginia University.
| Wake Forest University.
(1) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University
Science: Mill Valley, CA, 1987.
(2) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; John Wiley and Sons: New York, 1994.
(3) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29.
(4) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413-4450.
(5) Grubbs, R. H. Tetrahedron 2004, 60, 7117-7140.
(13) Huang, J.; Stevens, E. D.; Nolan, S. P.; Petersen, J. L. J. Am. Chem.
Soc. 1999, 121, 2674-2678.
(14) Huang, D.; Streib, W. E.; Eisenstein, O.; Caulton, K. G. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2004-2006.
(15) Tenorio, M. J.; Tenorio, M. A. J.; Puerta, M. C.; Valerga, P. Inorg.
Chim. Acta 1997, 259, 77-84.
10.1021/ic051074k CCC: $30.25
Published on Web 10/06/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 23, 2005 8379

Zhang et al.
complexes of the type [L2Ru(CO)(R)][BAr′4] (R ) H, Me,
or Ph; Ar′ ) 3,5-(CF3)2C6H3; L ) phosphine ligands) as well
as their five-coordinate precursors and have extended their
studies to systems with the chelating PNP (PNP ) N(SiMe2-
ride abstraction from 1 could afford a four-coordinate
ruthenium center; however, the reaction of complex 1 with
1 equiv of NaBAr′4 in CH2Cl2 results in the formation of a
mixture of two products that could not be separated. Given
the possibility of formation of a binuclear species with a
bridging chloride ligand, we reacted complex 1 with 0.5
equiv of NaBAr′4. Clean isolation of the complex [{(PCP)-
Ru(CO)}2(µ-Cl)][BAr′4] (2) in 80% yield was obtained after
workup (eq 1). Complex 2 is air sensitive, as indicated by
t
CH2PR2)2, R ) Cy or Bu) ligands.14,18-23
Our group has been interested in studying the reactivity
of coordinatively unsaturated ruthenium complexes with a
bulky PCP pincer ligand (PCP ) 2,6-(CH2PtBu2)2C6H3), and
we have previously reported the synthesis of the amido
complexes (PCP)Ru(CO)(NHR) (R ) H or Ph) and their
reactivity with substrates that possess polar as well as
nonpolar bonds.24-26 For example, the ruthenium parent
amido complex (PCP)Ru(CO)(NH2) has been demonstrated
to initiate the activation of dihydrogen as well as the
intramolecular activation of C-H bonds.24 The reaction of
(PCP)Ru(CO)(PMe3)(NHPh) with organic substrates such as
nitriles, carbodiimides, and isocyanates likely proceeds via
PMe3 dissociation, coordination of the organic substrate, and
intramolecular nucleophilic addition of the amido nitrogen
to form azametallacyclobutane complexes.25,26 Herein, we
report that efforts to access a four-coordinate ruthenium
complex starting from the five-coordinate precursor (PCP)-
Ru(CO)(Cl) (1) lead to the formation of complexes of the
type [(PCP)Ru(CO)(L)]+ {L ) η1-ClCH2Cl, η1-N2, C6H5F,
or µ-Cl-Ru(PCP)(CO)}.27 We anticipated that the geo-
metrical restriction of the meridional coordinating tridentate
PCP ligand might lead to chemistry that diverges from that
of Caulton et al.’s [L2Ru(CO)(R)]+ systems. Reactions of
[(PCP)Ru(CO)(ClCH2Cl)]+ with a carbene source or a
phenylacetylene yield products that are intermediates for
carbene or vinylidene insertion into the Ru aryl bond of the
PCP ligand. Computational studies of these systems are also
presented and discussed.
slow decomposition of a CD2Cl2 solution of 2 in air. Salient
1
features of the H NMR spectrum of 2 include overlapping
multiplets in the region 1.74-0.85 ppm due to the PCP tert-
butyl groups, as compared to two virtual triplets for 1.27 Also,
doublets at 74.1 and 68.9 ppm (JPP ) 228 Hz) are observed
in the 31P NMR spectrum of 2, while IR spectroscopy reveals
νCO ) 1939 cm-1. Further reaction of 2 with NaBAr′4 or
reaction of 1 with excess NaBAr′4 results in a mixture of
complex 2 and a second product; however, the second
product could not be isolated cleanly.
A single crystal of 2 grown from a methylene chloride
solution layered with pentane was selected for an X-ray
diffraction study. A limited resolution data set revealed the
presence of two {(PCP)Ru(CO)} fragments connected with
a bridging chloride (Figure 1). The low yield of high-
resolution data for this compound is presumably due to the
presence of disordered CH2Cl2 and pentane solvent molecules
of crystallization as well as disordered CF3 groups of the
anion. Nonetheless, the X-ray data are consistent with the
assigned structure based on spectroscopic and elemental
analysis data.
Results and Discussions
Synthesis and Solid-State Structures of [{(PCP)Ru-
(CO)}2(µ-Cl)][BAr′4] (2), [(PCP)Ru(CO)(η1-ClCH2Cl)]-
[BAr′4] (3), and [(PCP)Ru(CO)(η1-N2)][BAr′4] (4). The air
stable 16-electron compound 1 has been synthesized and
structurally characterized by Gusev and co-workers.27 Chlo-
As reported previously, the treatment of complex 1 with
excess trimethylsilyltriflate (TMSOTf) affords (PCP)Ru-
(CO)(OTf) (OTf ) η1-OSO2CF3) (6).25 When 1 equiv of
NaBAr′4 was added to a CH2Cl2 solution of 6, the CO
(16) Baratta, W.; Herdtweck, E.; Rigo, P. Angew. Chem., Int. Ed. 1999,
38, 1629-1631.
(17) Tenorio, M. J.; Mereiter, K.; Puerta, M. C.; Valerga, P. J. Am. Chem.
Soc. 2000, 122, 11230-11231.
(18) Huang, D.; Streib, W. E.; Bollinger, J. C.; Caulton, K. G.; Winter, R.
F.; Scheiring, T. J. Am. Chem. Soc. 1999, 121, 8087-8097.
(19) Huang, D.; Bollinger, J. C.; Streib, W. E.; Folting, K.; Young, V., Jr.;
Eisenstein, O.; Caulton, K. G. Organometallics 2000, 19, 2281-2290.
(20) Watson, L. A.; Coalter, J. N., III; Ozerov, O. V.; Pink, M.; Huffman,
J. C.; Caulton, K. G. New J. Chem. 2003, 263.
(21) Watson, L. A.; Ozerov, O. V.; Pink, M.; Caulton, K. G. J. Am. Chem.
Soc. 2003, 125, 8426-8427.
(22) Walstrom, A. N.; Watson, L. A.; Pink, M.; Caulton, K. G. Organo-
metallics 2004, 23, 4814-4816.
(23) Walstrom, A.; Pink, M.; Yang, X.; Tomaszewski, J.; Baik, M.-H.;
Caulton, K. G. J. Am. Chem. Soc. 2005, 127, 5330-5331.
(24) Conner, D.; Jayaprakash, K. N.; Cundari, T. R.; Gunnoe, T. B.
Organometallics 2004, 23, 2724-2733.
(25) Zhang, J.; Gunnoe, T. B.; Boyle, P. D. Organometallics 2004, 23,
3094-3097.
(26) Zhang, J.; Gunnoe, T. B.; Petersen, J. L. Inorg. Chem. 2005, 44, 2895-
Figure 1. ORTEP diagram (30% probability) of [{(PCP)Ru(CO)}2(µ-Cl)]-
[BAr′4] (2) (hydrogen atoms and the BAr′4 counterion have been omitted
for clarity).
2907.
(27) Gusev, D. G.; Madott, M.; Dolgushin, F. M.; Lyssenko, K. A.; Antipin,
M. Y. Organometallics 2000, 19, 1734-1739.
8380 Inorganic Chemistry, Vol. 44, No. 23, 2005

Synthesis of FiWe-Coordinate Ru(II) Complexes
Scheme 1. Reaction of (PCP)Ru(CO)(OTf) (6) with NaBAr′4 in
CH2Cl2 or in C6H5Fa
a Complex 5 has not been fully characterized, and its identity is suggested
based on evidence from IR spectroscopy and computational studies.
Figure 2. ORTEP diagram (30% probability) of [(PCP)Ru(CO)(η1-
ClCH2Cl)][BAr′4] (3) (hydrogen atoms, except the two on CH2Cl2, and the
BAr′4 counterion have been omitted for clarity). Selected bond lengths (Å)
and bond angles (deg): Ru1-Cl1s, 2.614(1); Ru1-C2, 2.053(3); C1s-
Cl1s, 1.791(5); C1s-Cl2s, 1.695(5); Cl1s-C1s-Cl2s, 115.5(2); Ru1-
Cl1s-C1s, 123.1(2); C2-Ru1-Cl1s, 170.7(2); Ru1-P2-C22, 100.9(1);
Ru1-P2-C18, 127.8(1); Ru1-P1-C14, 113.4(1); Ru1-P1-C10, 121.8(1);
P1-Ru1-P2, 161.5(1).
absorption changed from 1941 to 1964 cm-1 within 30 min,
as determined by IR spectroscopy. A highly air sensitive
product that turns black immediately upon exposure to air
can be isolated after workup. Characterization using 1H, 31P,
and 19F NMR and IR spectroscopy as well as X-ray
crystallography revealed the complex as [(PCP)Ru(CO)(η1-
ClCH2Cl)][BAr′4] (3) (Scheme 1).
state structures of [RuH(CO)(PMetBu2)2(η2-CH2Cl2)][BAr′4],
[Cp*Ir(Me)(η1-ClCH2Cl)][BAr′4], [trans-(PiPr3)2Pt(H)(η1-
ClCH2Cl)][BAr′4], and [cis-Re(CO)4(PPh3)(η1-ClCH2Cl)]-
[BAr′4] have been reported (Cp* ) pentamethylcyclopenta-
dienyl).19,30-32 The ruthenium hydride complex [Ru(H)(η2-
CH2Cl2)(CO)(PtBu2Me)2][BAr′4] with an η2-coordinated
CH2Cl2 has been reported, while the closely related ruthe-
nium phenyl compound [Ru(Ph)(CO)(PtBu2Me)][BAr′4] could
be crystallized from a CH2Cl2 solution without evidence of
CH2Cl2 coordination.14,19 Complexes with other chloroalkanes
or chlorobenzene ligands have been reported.33,37-39
Instead of formation of a four-coordinate complex, a
molecule of CH2Cl2 coordinates to the ruthenium center
through a single chlorine atom. A singlet at 5.35 ppm in the
1H NMR spectrum of 3 in CD2Cl2 is most likely due to free
CH2Cl2 as a result of rapid exchange of coordinated CH2Cl2
with CD2Cl2. The PCP ligand yields two virtual triplets at
1
1.50 and 1.11 ppm (N ) 15 Hz) in the H NMR spectrum
and a broad singlet at 71.0 ppm in the 31P NMR spectrum
of 3.
Although the fragment [(PCP)Ru(CO)]+ has two available
coordination sites, the X-ray structural analysis of 3 con-
firmed the presence of a monohapto coordinated η1-CH2Cl2
ligand (Figure 2). The bond length of Ru1-Cl1s (2.614(1)
Å) is longer than the Ru-Cl bond distance in 1 (2.420(1)
Å). The C-Cl (bound) distance is 1.791(5) Å while the
C-Cl (unbound) distance is 1.695(5) Å. The Cl-C-Cl bond
angle is 115.5(2)° with the unbound Cl oriented toward the
carbonyl group. One agostic interaction is indicated based
on the short Ru/Cagostic distance (Ru1‚‚‚C23, 2.85(1) Å), and
the bond angle Ru1-P2-C22 (100.9(1)°) is significantly
smaller than the other three tert-butyl group bond angles
(113.4(1)°, 121.8(1)°, and 127.8(1)°). Previously, Caulton
et al. observed double agostic interactions for the complex
[Ru(Ph)(CO)(PtBu2Me)2][BAr′4] with Ru/Cagostic bond lengths
of 2.87 and 2.88 Å and Ru-P-C bond angles of 98.1° and
96.6°.14 An agostic interaction has been observed in the solid-
state structure of [(PCP)Ru(CO)2]+ with a reported Ru‚‚‚HC
distance of 2.19(6) Å.28 Although both bidentate and mono-
dentate CH2Cl2 ligands have been reported, examples of
structurally characterized complexes with CH2Cl2 ligands are
relatively rare.19,29-36 For example, the synthesis and solid-
To exclude the possibility of CH2Cl2 coordination, 1 equiv
of NaBAr′4 was reacted with 6 in fluorobenzene. IR
spectroscopy revealed two CO absorptions at 1987 cm-1
(major) and 1953 cm-1 (minor). In addition, an absorption
at 2249 cm-1 was observed and assigned to coordinated
dinitrogen. Free dinitrogen exhibits an absorption at 2331
cm-1 (Raman).1,2 Purging the solution with argon results in
the transformation to a solution with a single CO absorption
at 1953 cm-1 and the disappearance of absorptions previously
(29) Kulawiec, R. J.; Crabtree, R. H. Coord. Chem. ReV. 1990, 99, 89.
(30) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970-1972.
(31) Butts, M. D.; Scott, B. L.; Kubas, G. J. J. Am. Chem. Soc. 1996, 118,
11831-11843.
(32) Huhmann-Vincent, J.; Scott, B. L.; Kubas, G. J. J. Am. Chem. Soc.
1998, 120, 6808-6809.
(33) Peng, T.-S.; Winter, C. H.; Gladysz, J. A. Inorg. Chem. 1994, 33,
2534-2542.
(34) Colsman, M. R.; Newbound, T. D.; Marshall, L. J.; Noirot, M. D.;
Miller, M. M.; Wulfsberg, G. P.; Frye, J. S.; Anderson, O. P.; Strauss,
S. H. J. Am. Chem. Soc. 1990, 112, 2349-2362.
(35) Newbound, T. D.; Colsman, M. R.; Miller, M. M.; Wulfsberg, G. P.;
Anderson, O. P.; Strauss, S. H. J. Am. Chem. Soc. 1989, 111, 3762-
3764.
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(37) Van Seggen, D. M.; Anderson, O. P.; Strauss, S. H. Inorg. Chem.
1992, 31, 2987-2990.
(38) Wu, F.; Dash, A. K.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
15360-15361.
(28) van der Boom, M. E.; Iron, M. A.; Atasoylu, O.; Shimon, L. J. W.;
Rozenberg, H.; Ben-David, Y.; Konstantinovski, L.; Martin, J. M. L.;
Milstein, D. Inorg. Chim. Acta 2004, 357, 1854-1864.
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Milstein, D. J. Am. Chem. Soc. 2003, 125, 4714-4715.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8381

Zhang et al.
observed at 1987 and 2249 cm-1. However, this change is
reversible, as purging the resultant solution with dinitrogen
leads to observation of the three original absorptions at 1987,
1953, and 2249 cm-1. These results suggest an equilibrium
between a five-coordinate dinitrogen complex, [(PCP)Ru-
(CO)(N2)][BAr′4] (4), with a labile N2 ligand, and a second
complex that is likely either the four-coordinate complex
[(PCP)Ru(CO)][BAr′4] or the fluorobenzene complex [(PCP)-
Ru(CO)(FC6H5)][BAr′4]. Repeated attempts to grow crystals
and perform an X-ray diffraction study of this complex have
failed; however, on the basis of IR evidence, we propose
that the coordination of fluorobenzene is more likely, though
not definitively shown, than the formation of a four-
coordinate system. For example, the series of Ru(II) systems
Ru(Ph)(CO)(Cl)L2, Ru(Ph)(CO)(OTf)L2, and [Ru(Ph)(CO)-
L2][BAr′4] (where L ) PtBu2Me and the latter complex is a
four-coordinate system with two agostic interactions) exhibits
CO absorptions (IR spectroscopy) at 1902, 1921, and 1958
cm-1, respectively.14,18,19 The series of systems (PCP)Ru-
(CO)(Cl), (PCP)Ru(CO)(OTf), and the uncharacterized com-
plex has CO absorptions at 1919, 1941, and 1953 cm-1. The
conversion of the (PCP)Ru-Cl complex to the (PCP)Ru-
OTf complex results in an increase in the CO stretching
frequency of 22 cm-1, while the conversion of the Ru(Ph)-
(CO)(Cl)L2 complex to the corresponding triflate complex,
Ru(Ph)(CO)(OTf)L2, results in an increase in the CO
stretching frequency of 19 cm-1. Thus, for the two types of
Ru systems, conversion of a Ru-Cl bond to a Ru-OTf bond
yields quite similar changes in the energy of the CO stretches.
The conversion of the five-coordinate complex Ru(Ph)(CO)-
(OTf)L2 to the four-coordinate complex [Ru(CO)(Ph)L2]-
[BAr′4] increases the CO absorption energy by 37 cm-1,
while the transformation of (PCP)Ru(CO)(OTf) to complex
5 results in an increase of the CO absorption energy of only
12 cm-1. Thus, without confirmation by X-ray crystal-
lography, we assign the identity of this system as [(PCP)-
Ru(CO)(FC6H5)][BAr′4] (5) (Scheme 1), and calculations are
consistent with the notion that the coordination of fluoro-
benzene is favorable to a four-coordinate complex (see
below). The formation of a binuclear species with a bridging
dinitrogen ligand is another possibility for complex 5;
however, the reaction of (PCP)Ru(CO)(OTf) with NaBAr′4
in C6H5F under argon produces complex 5 (as indicated by
IR spectroscopy) and provides evidence against a complex
that possesses a bridging dinitrogen moiety. When an excess
of CH2Cl2 is added to the solution of 4 and 5, conversion to
complex 3 is observed, as indicated by a single CO
absorption at 1964 cm-1 in the IR spectrum (eq 2).
Figure 3. ORTEP diagram (30% probability) of [(PCP)Ru(CO)(η1-N2)]-
[BAr′4] (4) (hydrogen atoms and the BAr′4 counterion have been omitted
for clarity). Selected bond lengths (Å) and bond angles (deg): Ru1-C2,
2.059(2); Ru1-N1, 2.132(1); N1-N2, 1.069(3); Ru1-C1, 1.809(2); C1-
O1, 1.148(2); N1-N2, 1.069(3); C2-Ru1-N1, 175.7(1); Ru1-N1-N2,
179.1(2); Ru1-P2-C22, 101.2(1); P1-Ru1-P2, 162.8(1).
is indicated by a short Ru/Cagostic distance (Ru1‚‚‚C23, 2.89
Å) and a small Ru-P-C bond angle (Ru1-P2-C22,
101.2(1)°). A Ru-N bond length of 2.132(1) Å and a linear
Ru-N-N bond angle (179.1(2)°) are observed. The N1-
N2 bond length (1.069(3) Å) is shorter than that in free N2
(1.0975 Å);40 however, correction of selected bond lengths
for rigid body motion and riding effects resulted in a
corrected N1-N2 bond length of 1.098 Å, which is
indistinguishable from the N-N bond length in free di-
nitrogen (see the Supporting Information for details). A
rhodium dinitrogen complex with an “aliphatic” PCP ligand,
Rh(η1-N2){η1-CH3C(CH2CH2PtBu2)2}, has been reported
with a short N-N bond length of 0.963(14) Å.41 Other
complexes with short N-N bond lengths for dinitrogen
ligands include trans-ReCl(N2)(PMe2Ph)2 (1.055(30) Å),
trans-RhCl(N2)(PiPr3)2 (0.958(5) Å), and trans-RhH(N2)-
(PPhtBu2)2 (1.074(7) Å) with the bond contraction due to
disorder.42-44 For complex 4, the atom N2 displays a
relatively high atomic displacement amplitude perpendicular
to the N-N bond vector. However, there was no evidence
of a multiple site orientational or compositional disorder in
the final difference Fourier map (see the Supporting Infor-
mation). The Ru-N bond distance of 4, 2.132(1) Å, is longer
than the bond distances of related Ru-dinitrogen complexes.
For example, Ru(II) systems with bisphosphine “pincer”
ligands with η1-N2 ligands have Ru-N bond distances in
the range of 1.965(4)-2.014(2) Å.45-47 For all of these
systems, the observed dinitrogen stretching frequencies in
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Eur. J. 1997, 3, 253-260.
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Chem., Int. Ed. 2003, 42, 216-219.
The identity of [(PCP)Ru(CO)(η1-N2)][BAr′4] (4) has been
confirmed by a single-crystal X-ray diffraction study (Figure
3). Similar to the case of complex 3, one agostic interaction
(46) Gusev, D. G.; Lough, A. J. Organometallics 2002, 21, 5091-5099.
(47) Amoroso, D.; Jabri, A.; Yap, G. P. A.; Gusev, D. G.; dos Santos, E.
N.; Fogg, D. E. Organometallics 2004, 23, 4047-4054.
8382 Inorganic Chemistry, Vol. 44, No. 23, 2005

Synthesis of FiWe-Coordinate Ru(II) Complexes
Table 1. Selected Crystallographic Data and Collection Parameters for Complexes 2, 3, 4, 7, and 8
[{(PCP)Ru(CO)}2(µ-
Cl)][BAr′4] (2)
[(PCP)Ru(CO)(η1-
CH2Cl2)][BAr′4] (3)
[(PCP)Ru(CO)(η1-
N2)][BAr′4] (4)
[(PCP-CHPh)Ru(CO)]
[BAr′4] (7)
[(PCP-CCHPh)Ru(CO)]
[BAr′4] (8)
complex
empirical
formula
formula wt
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C93H124B Cl3 F24O2 P4Ru2
C58H57BCl2F24OP2Ru
C66H62.50BF25.50N2OP2Ru
C64H61BF24P2ORu
C66H63BCl2F24OP2Ru
2173.10
monoclinic
P21/c
12.970(4)
27.644(7)
29.174(8)
1470.77
triclinic
P1h
1558.01
triclinic
P1h
1475.95
triclinic
P1h
1572.88
orthorhombic
Pna21
24.883(3)
15.962(2)
17.930(2)
13.4350(4)
13.5298(4)
17.9662(5)
98.7273(11)
106.3306(10)
94.8176(11)
3069.99(15)
2
12.3183(6)
12.6860(6)
22.7533(12)
102.535(3)
94.787(3)
91.770(3)
3454.4(3)
2
12.794(1)
15.129(1)
18.119(1)
73.841(1)
79.979(1)
89.871(1)
3313.1(4)
2
96.932(5)
10383(5)
4
1.390
0.066, 0.114
0.699
7127.7(15)
4
1.467
0.068, 0.159
0.929
Z
D
R, Rw
calcd, g/cm3
1.591
0.049, 0.060
1.84
1.498
0.051, 0.058
1.92
1.480
0.062, 0.164
1.023
a
GOF
a See the Supporting Information for definitions of R and Rw.
the IR spectra are <2143 cm-1. In addition, [TpRu(N2)-
(PEt3)2][BPh4] has been characterized with a Ru-N distance
of 1.91(2) Å and a νNN ) 2163 cm-1.48 [CpRu(N2)(dippe)]-
[BPh4] and [Cp*Ru(N2)(dippe)][BPh4] (dippe ) diiso-
propylphosphinoethane) have been isolated with νNN at 2145
and 2120 cm-1, respectively.49 The relatively long Ru-N
bond distance and high-energy νNN of complex 4 could be
due to the combination of a cationic charge and competition
for Ru-N2 π-back-donation with the strong π-acid CO. The
high-energy νNN (2249 cm-1) of complex 4 compared to
similar Ru systems is consistent with the strong π-acid CO
competing for metal dπ electrons. The combination of
dinitrogen in the same coordination sphere with CO is
rare.50-52 Thus, we suggest that the Ru-N bond is relatively
weak, a proposal that is consistent with the highly labile
nature of the dinitrogen ligand of 4. Several other late
transition metal dinitrogen complexes with pincer ligands
have also been reported with either monodentate η1-N2-M
or M-µ-N2-M coordination.41,46,53-60
Table 2. CO Stretching Frequencies (cm-1) for Complexes of the Type
[(PCP)Ru(CO)(X)]n+ (n ) 0 or 1)
X
νCO
X
νCO
X
νCO
NH2 1890
NHPh
H
CtCPh 1915
Cl 1919
1900
1906
(PCP)(CO)Ru(Cl) 1939
Me
OH
Ph
1893
1896
1900
OTf
1941
1964
1987
η1-ClCH2Cl
η1-N2
stabilization provided by the chloride ligand, and/or the
strong trans effect of the CO ligand. The coordination of a
two-electron donor ligand results in the formation of a
saturated 18-electron complex of the type (PCP)Ru(CO)-
(L)(Cl). For example, (PCP)Ru(CO)2Cl and (PCP)Ru(CO)-
(PMe3)Cl have been isolated and characterized;25,28 however,
(PCP)Ru(CO)(NCMe)Cl and (PCP)Ru(CO)(NH3)Cl can only
be observed in solution, with attempts to isolate them
resulting in the dissociation of NCMe or NH3.24,25 The
electron density of the metal center as influenced by the “X”
ligands of systems of the type [(PCP)Ru(CO)(X)]n+ (n ) 0
or 1) can be approximated by the energy of the CO
absorptions. In addition to the new systems reported herein,
other complexes of the type (PCP)Ru(CO)(X) have been
previously reported.24,25,59,61 The CO absorption energies of
a series of systems are listed in Table 2.
Ligand Donor Ability and Agostic Interaction. The
stability of complex 1 as a five-coordinate, 16-electron
system could be due to the bulky tert-butyl groups, π
(48) Tenorio, M. A. J.; Tenorio, M. J.; Puerta, M. C.; Valerga, P. J. Chem.
Soc., Dalton Trans. 1998, 3601-3608.
Potentially, the unsaturated metal center of 1 could also
be stabilized by a C-H agostic interaction.62,63 Caulton et
al. reported double agostic interactions for the 14-electron
complex [Ru(Ph)(CO)(PtBu2Me)][BAr′4] with an average Ru/
(49) de los R´ıos, I.; Tenorio, M. J.; Padilla, J.; Puerta, M. C.; Valerga, P.
Organometallics 1996, 15, 4565-4574.
(50) Luo, X.-L.; Kubas, G. J.; Burns, C. J.; Eckert, J. Inorg. Chem. 1994,
33, 5219-5229.
C
agostic distance of 2.87 Å.14 In another case, the neutral 14-
(51) Sato, M.; Tatsumi, T.; Kodama, T.; Hidai, M.; Uchida, T.; Uchida,
Y. J. Am. Chem. Soc. 1978, 100, 4447-4452.
electron complex RuCl2{PPh2(2,6-Me2C6H3)}2 with two
agostic interactions with an average Ru/Cagostic distance 2.65
Å has been reported.16 There are several other unsaturated
ruthenium complexes with a single C-H agostic interaction
with Ru/Cagostic distances less than 3 Å.17-19,27,28,59 However,
there is no agostic interaction reported for 1, which is
possibly due to the presence of the π-donating chloride
ligand, which can stabilize the 16-electron ruthenium center;
(52) Kandler, H.; Gauss, C.; Bidell, W.; Rosenberger, S.; Burgi, T.;
Eremenko, I. L.; Veghini, D.; Orama, O.; Burger, P.; Berke, H.
Chem.sEur. J. 1995, 1, 541-548.
(53) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759-
1792.
(54) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Shimon, L. J. W.;
Milstein, D. J. Am. Chem. Soc. 1998, 120, 6531-6541.
(55) Vigalok, A.; Ben-David, Y.; Milstein, D. Organometallics 1996, 15,
1839-1844.
(56) Vigalok, A.; Milstein, D. Organometallics 2000, 19, 2061-2064.
(57) Jensen, C. M. Chem. Commun. 1998, 2443.
(58) Lee, D. W.; Kaska, W. C.; Jensen, C. M. Organometallics 1998, 17,
1.
(59) Gusev, D. G.; Dolgushin, F. M.; Antipin, M. Y. Organometallics 2000,
19, 3429-3434.
(60) Abbenhuis, R. A. T. M.; del Rio, I.; Bergshoef, M. M.; Boersma, J.;
Veldman, N.; Spek, A. L.; van Koten, G. Inorg. Chem. 1998, 37,
1749-1758.
(61) Lail, M.; Bell, C. M.; Conner, D.; Cundari, T. R.; Gunnoe, T. B.;
Petersen, J. L. Organometallics 2004, 23, 5007-5020.
(62) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog. Inorg. Chem.
1988, 36, 1-124.
(63) Brookhart, M.; Green, M. L. H. J. Organomet. Chem. 1983, 250, 395-
408.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8383

Zhang et al.
however, for complexes 3 and 4 with the weak donating
ligands CH2Cl2 or N2, respectively, the unsaturated formal
16-electron metal centers are apparently each stabilized by
a single agostic interaction. Milstein et al. have reported the
agostic interaction for [(PCP)Ru(CO)2]+.28 Thus, an agostic
interaction appears favorable for systems of the type [(PCP)-
Ru(CO)(L)]n+ (n ) 0 or 1) in which “L” is either weakly
coordinating or a strong π-acid. In contrast, for L ) Cl, the
formation of a sixth Ru-ligand bond does not appear to be
highly favorable; hence, an agostic interaction is not observed
and ligands such as NH3, NCMe, and PMe3 very weakly
coordinate to the (PCP)Ru(CO)(Cl) system (see above).
Density Functional Theory (DFT) Calculations for
Comparison of [(PCP)Ru(CO)(L)]+ (L ) η1-ClCH2Cl, η1-
N2, η1-FC6H5, or Agostic) Complexes. Hybrid quantum
mechanics/molecular mechanics (QM/MM) calculations on
full experimental models were performed for the comparison
of the binding of weak bases to [(PCP)Ru(CO)]+ to form
[(PCP)Ru(CO)(L)]+ (L ) η1-ClCH2Cl, η1-N2, η1-FC6H5, or
C-H agostic). For the four-coordinate, 14-electron complex
[(PCP)Ru(CO)]+, both agostic and nonagostic conformers
were investigated. Three of the tert-butyl groups were
modeled classically (using MM); the one with an agostic
interaction was modeled at the same B3LYP/CEP-31G(d)
level of theory as the other quantum atoms. Although
geometry optimizations were started from crystallographic
coordinates, it must be noted that an extensive conformational
analysis of these species was not performed and the reported
energetics must be viewed in this light. Upon geometry
optimization, the complex [(PCP)Ru(CO)]+ had one weak
agostic interaction with a distance Ru‚‚‚Cagostic ) 3.25 Å as
well as a compressed bond angle, Ru-P-C ) 102.1°. The
small Ru-P-C bond angle is akin to that noted in the crystal
structures of the agostic interactions for [(PCP)Ru(CO)(L)]+
complexes (see above). In terms of the calculated binding
energy, the agostic conformer is 6 kcal/mol more stable than
the nonagostic conformer (Figure 4).
Figure 4. QM/MM (B3LYP/CEP-31G(d):UFF) binding energies in kcal/
mol (given in boxes) relative to the nonagostic isomer of [(PCP)Ru(CO)]+.
factors play a secondary role in discrimination among the
various bases for coordination to ruthenium. The calculations,
thus, support the experimental inference made above that
fluorobenzene is a competent base for [(PCP)Ru(CO)(L)]+
and that a 14-electron, four-coordinate species [(PCP)Ru-
(CO)]+ (both agostic and nonagostic conformers) represents
a higher energy state than [(PCP)Ru(CO)(L)]+ for L ) η1-
N2, η1-CH2Cl2, or PhF (Figure 4).
Geometry optimization, followed by vibrational frequency
analysis, was performed on truncated 16-electron [(PCP′)Ru-
(CO)(L)]+ models to ascertain their CO absorptions. The
experimental order of νCO (cm-1) for [(PCP)Ru(CO)(L)]+ is
1987 (L ) η1-N2), 1964 (L ) η1-CH2Cl2), and 1953 (L )
PhF) with the latter being inferred from equilibrium studies;
the calculated νCO (cm-1) values for the corresponding PCP′
models are 2085, 2066, and 2054. Scaling the calculated CO
stretching frequencies by a typical factor of 0.95 yields νCO
) 1981 cm-1 (L ) η1-N2), 1963 cm-1 (L ) η1-CH2Cl2),
and 1951 cm-1 (L ) PhF) for [(PCP′)Ru(CO)(L)]+. The
proposed fluorobenzene complex, 5, has an experimental νCO
of 1953 cm-1. Thus, the calculations support the intermediacy
of a fluorobenzene complex in the solution equilibrium
experiments.
For the five-coordinate, 16-electron complexes [(PCP)-
Ru(CO)(L)]+, binding of the fifth ligand to the nonagostic
conformer of [(PCP)Ru(CO)]+ afforded nonagostic com-
plexes with the following calculated binding energies: ∆E
(kcal/mol) ) -12 (L ) η1-CH2Cl2), -13 (L ) FC6H5), and
-18 (L ) η1-N2) (Figure 4). An agostic conformer for these
five-coordinate complexes was found for two of the ligands
(L ) CH2Cl2, FC6H5) although none could be found for L
) N2. Manually altering the geometry to create agostic
interactions resulted in optimized geometries in which this
interaction was absent. Each of the agostic conformers of
[(PCP)Ru(CO)(L)]+, with L ) CH2Cl2 and FC6H5, had one
The computational studies suggest that the weakly coor-
dinating ligands η1-N2, η1-CH2Cl2, and PhF are preferred over
the four-coordinate complex [(PCP)Ru(CO)]+ with or with-
out an agostic interaction, and these calculations are con-
sistent with experimental observations. The calculations also
indicate that the agostic fragment [(PCP)Ru(CO)]+ has little
preference for binding of η1-N2, η1-CH2Cl2, or PhF with
calculated differences in energies of only 1 kcal/mol (Figure
4).
agostic interaction with calculated distances Ru‚‚‚Cagostic
)
3.20 and 3.22 Å, respectively.
The relative order for the [(PCP)Ru(CO)]+ and [(PCP)-
Ru(CO)(L)]+ complexes in terms of increasing binding
energy is CHagostic < CH2Cl2 ∼ PhF < N2. The same order
is seen in full QM calculations on small models (i.e., PCP
f PCP′, where tert-butyl groups are replaced by hydrogen).
Additionally, binding energies for PCP′ models are of the
same magnitude ((1-2 kcal/mol), implying that steric
Reaction of 3 with PhCHN2. The labile CH2Cl2 ligand
of complex 3 makes it a potentially useful synthetic precur-
8384 Inorganic Chemistry, Vol. 44, No. 23, 2005

Synthesis of FiWe-Coordinate Ru(II) Complexes
Scheme 2. Comparison of Bond Lengths (Å) of C6-Ring Moieties of
Complexes 4, 7, and 8 and Assignment of σ-Arenium for Complexes 7
and 8a
Figure 5. ORTEP diagram (30% probability) of [(PCP-CHPh)Ru(CO)]-
[BAr′4] (7) (hydrogen atoms, except the one on “PhCH”, and the BAr′4
counterion have been omitted for clarity). Selected bond lengths (Å) and
bond angles (deg): Ru1-C2, 2.329(8); Ru1-C10, 2.11(1); C2-C10,
1.47(1); C2-C3, 1.42(1); C2-C7, 1.42(1); C3-C4, 1.37(2); C4-C5,
1.36(2); C5-C6, 1.36(2); C6-C7, 1.398(1); C2-Ru1-C10, 38.2(3); C2-
Ru1-C1, 141.9(4); P1-Ru1-P2, 164.86(9); Ru1-C10-C2, 79.2(6); Ru1-
C10-C11, 128.8(6); C11-C10-C(2), 124.2(9); C10-C2-Ru1, 62.6(5).
sor. A pentane solution of excess phenyldiazomethane,
PhCHN2, was added to a CH2Cl2 solution of 3. A single
ruthenium product was isolated after workup in 80% yield
a The left side shows bond length data, and the right side shows structure
assignments.
1
and was fully characterized by H, 31P, 19F, and 13C NMR
and IR spectroscopy, elemental analysis, and a single-crystal
X-ray diffraction study. Spectral data do not provide evidence
for the presence of a benzylidene ligand, as a resonance
downfield of 10 ppm in the 1H NMR spectrum, which would
be consistent with a carbene proton, is not observed nor is
a resonance consistent with a carbene carbon observed in
the 13C NMR spectrum. Four doublets with JPH ) 14 Hz are
other phenyl carbons are longer than 3 Å. These bonding
interactions have an effect on the aromaticity of the PCP
phenyl ring with the best description being an arenium moiety
based on the bond length analysis (Scheme 2). The bond
lengths of C2-C3 (1.42(1) Å) and C2-C7 (1.42(1) Å) are
slightly longer (∼0.06 Å) than those of C5-C6 (1.36(2) Å)
and C4-C5 (1.36(2) Å). In contrast, a smaller difference
was observed in complex 4 (∼0.02 Å). The C-C bond length
in benzene is 1.394(5) Å.66 Similar structures such as
σ-arenium complexes of Pt, Ir, or Rh and methylene arenium
complexes of Ir or Rh have been reported.53,67-70
1
observed in the region of 0.8-1.6 ppm in the H NMR
spectrum, which can be assigned as tert-butyl groups. Two
doublets at 46.2 and 23.6 ppm with JPP ) 218 Hz are present
in the 31P{1H} NMR spectrum. An absorption due to the
CO ligand is observed at 1931 cm-1 in the IR spectrum.
A possible mechanism for the conversion of 3 and
PhCHN2 to 7 involves the initial formation of a Ru
benzylidene complex followed by an intramolecular C-C
coupling sequence (Scheme 3). If this pathway is operative,
complex 7 is a trapped intermediate of a formal insertion of
a carbene ligand into a Ru-aryl bond. Similar transforma-
tions are important C-C bond forming reactions.71-74 Hybrid
QM/MM calculations on full experimental models suggest
A solid-state X-ray crystal structure analysis was per-
formed and revealed the product as [(PCP-CHPh)Ru(CO)]-
[BAr′4] (PCP-CHPh ) κ4-P,P,C,C-1-CHPh-2,6-(CH2PtBu2)2-
C6H3) (7) (Figure 5). Thus, rather than formation of a stable
and isolable ruthenium alkylidene complex, the coupling of
the carbene moiety “CHPh” with the PCP ipso carbon occurs.
Prominent geometric features include a C2-Ru1-C1 bond
angle of 141.9(4)° and a single weak agostic interaction
(Ru1-C24, 3.06 Å). The Ru1-C2 bond distance (2.329(8)
Å) is longer than typical Ru-Cipso bond distances (e.g.,
2.053(3) Å in complex 3). The C2-C10 bond distance
(1.47(1) Å) is slightly shorter than a carbon-carbon single
bond (∼1.54 Å) but longer than a carbon-carbon double
bond (∼1.34 Å). No evidence for possible η3-allyl or η4-
diene coordination involving the PCP phenyl ring or carbene
phenyl ring is observed.64,65 All distances between Ru and
(66) Schomaker, V.; Pauling, L. J. Am. Chem. Soc. 1939, 61, 1769-1780.
(67) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750-
3781.
(68) Terheijiden, J.; van Koten, G.; Vinke, I. C.; Spek, A. L. J. Am. Chem.
Soc. 1985, 107, 2891-2898.
(69) Vigalok, A.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 1998,
120, 477-483.
(70) Vigalok, A.; Rybtchinski, B.; Shimon, L. J. W.; Ben-David, Y.;
Milstein, D. Organometallics 1999, 18, 895-905.
(71) Hoover, J. F.; Stryker, J. M. J. Am. Chem. Soc. 1990, 112, 464-465.
(72) Bergamini, P.; Costa, E.; Cramer, P.; Hogg, J.; Orpen, A. G.; Pringle,
P. G. Organometallics 1994, 13, 1058-1060.
(73) Trace, R. L.; Sanchez, J.; Yang, J.; Yin, J.; Jones, W. M. Organo-
metallics 1992, 11, 1440-1442.
(74) Tan, K. L.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2002,
124, 3202-3203.
(64) Jordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.; Willett,
R. J. Am. Chem. Soc. 1987, 109, 4111-4113.
(65) Mintz, E. A.; Moloy, K. G.; Marks, T. J.; Day, V. W. J. Am. Chem.
Soc. 1982, 104, 4692-4695.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8385

Zhang et al.
Scheme 3. Proposed Reaction Pathway of
[(PCP)Ru(CO)(η1-ClCH2Cl)]+ (3) with PhCHN2 To Form
[(PCP-CHPh)Ru(CO)]+ (7)
Figure 6. ORTEP diagram (30% probability) of [(PCP-CCHPh)Ru(CO)]-
[BAr′4] (8) (hydrogen atoms, except the “C(Ph)H” hydrogen, and the BAr′4
counterion have been omitted for clarity). Selected bond length (Å) and
bond angles (deg): Ru1-C2, 2.352(2); Ru1-C10, 1.980(2); C2-C10,
1.466(5); C10-C11, 1.316(4); C2-C3, 1.420(4); C2-C7, 1.420(4); C3-
C4, 1.355(4); C4-C5, 1.379(5); C5-C6, 1.409(5); C6-C7, 1.344(4); C2-
C10-C11, 134.7(3); C10-C11-C12, 127.1(3); C2-Ru1-C10, 38.3(1);
C2-Ru1-C1, 144.5(1); P1-Ru1-P2, 166.1(1).
that this reaction is exothermic by more than 30 kcal/mol;
other computational studies relevant to this transformation
are given below. In an effort to experimentally observe
reaction intermediates for the conversion of 3 to 7, we
monitored the reaction of 3 and PhCHN2 using variable
(N2)]+ (2249 cm-1). It is also feasible to consider that the
preferred square planar geometry of four-coordinate Rh(I)
inhibits the C-C bond formation step.
1
temperature H NMR spectroscopy in CD2Cl2. Complex 3
and PhCHN2 were dissolved in CD2Cl2 at -70 °C and
transferred to an NMR probe precooled to this temperature.
At -70 °C, there was no observation of a downfield
resonance that would be diagnostic of the formation of a
benzylidene complex; however, complex 3 was converted
to a new complex that is likely a ruthenium diazophenyl-
methane complex. The temperature of the NMR probe was
incrementally increased to room temperature. At -40 °C, a
decrease in the intensity of resonances due to 3 is observed,
and the formation of a resonance at 26.0 ppm (1H NMR)
occurs. This downfield resonance most likely indicates the
formation of the benzylidene complex [(PCP)(CO)Rud
CHPh][BAr′4]. At 10 °C, the resonance due to the putative
carbene complex disappears and the quantitative formation
of complex 7 is observed. These results suggest that 7 is
formed from an intermediate carbene complex rather than
direct attack of N2CHPh on the Ru-aryl moiety. Rhodium
benzylidene complexes with a pincer ligand have been
synthesized from the reaction of phenyldiazomethane with
rhodium dinitrogen precursors, although no carbene inser-
tion reaction has been reported for the Rh benzylidene
complex.53,56,75 For example, the benzylidene complex
(PCPMe2)RhdCHPh is isolable (PCPMe2 ) 2,6-(CH2PtBu2)2-
3,5-Me2-C6H1). The difference in reactivity with phenyl-
diazomethane between the PCP-Ru system reported herein
and the Rh systems may be derived from the ability of the
Rh(I) complexes to stabilize (kinetically and/or thermody-
namically) the benzylidene moiety through metal-to-ligand
π-back-bonding. Evidence of increased π-back-bonding
ability for the Rh systems versus the Ru fragment discussed
herein is apparent from the relative νNN of the dinitrogen
complexes (PCPMe2)Rh(N2) (2120 cm-1) and [(PCP)Ru(CO)-
Reaction of 3 with PhCtCH. The formation of vinyl-
idene ligands from reaction of transition metal systems
with terminal acetylenes is known.76 To determine if the
vinylidene-Cipso coupling reaction occurs as observed for
the formation of 7, the reaction of 3 with phenylacetylene
in CD2Cl2 was monitored by NMR spectroscopy. The
combination of 3 and PhCtCH results in an immediate color
change from orange to green and the formation of a new
complex, as indicated by two new virtual triplets at 1.62 and
1
1.10 ppm in the H NMR spectrum and a singlet at 31.5
ppm in 31P NMR spectrum. In addition, a triplet at 6.55 ppm
1
with a coupling constant of J ) 3 Hz is observed by H
NMR spectroscopy. This complex undergoes slow transfor-
mation to a new product with complete conversion observed
by NMR spectroscopy after 3-4 days at room temperature.
Two new virtual triplets at 1.43 and 1.20 ppm and a broad
singlet at 5.87 ppm are present in the 1H NMR spectrum of
the final product, and a new singlet at 37.4 ppm is observed
in the 31P NMR spectrum. This ultimate product is likely a
result of a vinylidene-Cipso coupling to yield [(PCPsCd
CHPh)Ru(CO)][BAr′4] (PCPsCdCHPh ) κ4-P,P,C,C-1-
(CdCHPh)-2,6-(CH2PtBu2)2sC6H3) (8). The structure of 8
is similar to that of 7 (Figure 6). However, the phenyl ring
of the {CdCHPh} fragment resides in a plane of mirror
symmetry that renders the two phosphine groups symmetry
equivalent. In contrast, the CHPh group is in a perpendicular
orientation for complex 7, which results in two symmetry
unique phosphines. Thus, four tert-butyl groups are observed
as four doublets for 7, while only two virtual triplets were
1
observed for 8 by H NMR spectroscopy. Likewise, two
resonances are observed for 7 and a single resonance is
observed for 8 by 31P NMR spectroscopy.
(75) Cohen, R.; Rybtchinski, B.; Gandelman, M.; Rozenberg, H.; Martin,
J. M. L.; Milstein, D. J. Am. Chem. Soc. 2003, 125, 6532-6546.
(76) Bruce, M. I. Chem. ReV. 1991, 91, 197-257.
8386 Inorganic Chemistry, Vol. 44, No. 23, 2005

Synthesis of FiWe-Coordinate Ru(II) Complexes
Jia et al. and Gusev et al. have reported similar coupling
reactions of terminal acetylenes with ruthenium pincer
complexes.77-79 However, reaction of terminal acetylenes
with osmium derivatives resulted in isolable vinylidene
complexes.79,80 For the reaction of (PCP-Ph)Ru(PPh3)(Cl)
(PCP-Ph ) 2,6-(CH2PPh2)2C6H3) with PhCtCH, Jia et al.
discussed the mechanism as proceeding via alkyne coordina-
tion, transformation to a vinylidene complex followed by
the C-C coupling step to form the product. Neither the
proposed alkyne-coordinated intermediate nor the vinylidene
complex has been observed.77,78 In contrast, an intermediate
Ru complex is observed for the reaction of 3 with PhCtCH
to form 8, and likely identities of this system are the η2-
alkyne complex [(PCP)Ru(CO)(η2-PhCCH)][BAr′4] or the
vinylidene complex [(PCP)(CO)RudCdCHPh][BAr′4]. The
observed intermediate is unlikely a Ru hydride-alkynyl
complex, since the anticipated upfield resonance due to a
hydrido ligand is not observed. No resonance downfield of
200 ppm, except a triplet at 208.5 ppm due to CO, is
observed in the 13C NMR spectrum, which provides evidence
against the presence of a vinylidene intermediate; however,
due to likely C-P coupling and relaxation, the intensity of
this resonance is anticipated to be weak and difficult to
observe. Thus, the absence of an assignable vinylidene
carbon resonance is not sufficient evidence to conclusively
assign the identity of the intermediate. On the basis of DFT
calculations (see below), we suggest that the intermediate is
the vinylidene complex [(PCP)(CO)RudCdCHPh][BAr′4];
however, the inability to cleanly isolate and grow crystals
of this system precludes a definitive conclusion based solely
on experimental data.
The reactions of phenylacetylene with five-coordinate
complexes 1 or 6 were studied to determine if the weakly
bound CH2Cl2 of 3 is necessary to observe the formation of
8. Reaction of triflate complex 6 with PhCtCH yields
similar results as observed for complex 3, including the
formation of an intermediate and the eventual conversion to
the final coupling product, 8, albeit the total reaction time is
∼10 days at room temperature compared to ∼3 days starting
from complex 3. In contrast, there is no observable reaction
between chloride complex 1 and PhCtCH at room temper-
ature after 7 days.
DFT Calculations on the Formation of Complexes 7
and 8. The formation of complexes 7 and 8 was probed using
similar computational methodologies to those described
above. Given the difficulties in isolating appropriate transition
states for carbene (and vinylidene) insertion, the correspond-
ing DFT calculations on truncated PCP′ models (vide supra)
were also performed. Calculations support the experimental
inference about the intermediacy of terminal [(PCP)(CO)-
Rud(C)0,1dCHPh]+ complexes, as both species are found
to be stable minima. Furthermore, the insertion reactions are
Figure 7. Calculated ONIOM reaction energies in kcal/mol.
Figure 8. Calculated structure of the product from insertion of the alkyne
into the PCP ligand starting from [(PCP)(CO)Ru(η2-HCtCPh)]+. Some
atoms of the PCP ligand are shown in wire frame for clarity.
found to be thermodynamically feasible: ∆E ) -8 kcal/
mol for dC(H)Ph insertion to form 7 and -27 kcal/mol for
dCdC(H)Ph insertion to form 8 (Figure 7). The correspond-
ing enthalpy values for truncated PCP′ models are -17 kcal/
mol (carbene insertion) and -22 kcal/mol (vinylidene
insertion). These QM energetics on small models, combined
with the analysis of the QM portion of the QM/MM
extrapolated energies, suggest that the difference in the
energetics of carbene and vinylidene has both electronic and
steric components. Interestingly, the carbene insertion is
retarded (∼4-5 kcal/mol) by steric factors, while the
vinylidene insertion is facilitated by a comparable amount
by steric factors. Presumably, this is a reflection of the extra
carbon atom of the vinylidene minimizing steric hindrance
between the phenyl substituent and the phosphine tert-butyl
groups of complex 8 as compared with complex 7.
A terminal alkyne complex as a possible intermediate in
the formation of 8 was probed through QM/MM calculations.
Construction of [(PCP)(CO)Ru(η2-HCtCPh)]+ (alkyne in
the equatorial plane) followed by geometry optimization
yielded a high energy intermediate (ca. 13 kcal/mol above
8) corresponding to the insertion of the alkyne triple bond
into the Ru-Cipso of the PCP ligand (Figure 8). Model
calculations on [(PCP′)(CO)Ru(η2-HCtCH)]+ yielded a
stationary point, but this species was a transition state with
the imaginary frequency corresponding to the rotation of the
acetylene ligand to a conformation with the CtC bond
perpendicular to the equatorial plane, which is 23 kcal/mol
(77) Lee, H. M.; Yao, J.; Jia, G. Organometallics 1997, 16, 3927.
(78) Jia, G.; Lee, H. M.; Xia, H. P.; Williams, I. D. Organometallics 1996,
15, 5453.
(79) Gusev, D. G.; Maxwell, T.; Dolgushin, F. M.; Lyssenko, M.; Lough,
A. J. Organometallics 2002, 21, 1095-1100.
(80) Wen, T. B.; Cheung, Y. K.; Yao, J.; Wong, W.-T.; Zhou, Z. Y.; Jia,
G. Organometallics 2000, 19, 3803-3809.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8387

Zhang et al.
Scheme 4. Reaction of [(PCP)Ru(CO)(η1-ClCH2Cl)]+ (3) with
PhCtCH To Yield the Coupling Product via an Observable
Intermediate Proposed To Be the Vinylidene Complex
[(PCP)(CO)RudCdCHPh]+
19F spectra were recorded on a Varian Mercury instrument operating
at a frequency of 376.5 MHz with CF3CO2H (-78.5 ppm) as the
external standard. IR spectra were acquired of solutions in KBr
solvent cells using a Mattson Genesis II FT-IR instrument.
Elemental analyses were conducted by Atlantic Microlab, Inc.
(PCP)Ru(CO)(Cl) (1), (PCP)Ru(CO)(OTf) (6), phenyldiazomethane,
and NaBAr′4 were synthesized as previously reported.25,27,81,82
Phenylacetylene was purchased from a commercial source and used
without further purification.
[{(PCP)Ru(CO)}2(µ-Cl)][BAr′4] (2). (PCP)Ru(CO)(Cl) (1)
(0.225 g, 0.403 mmol) was dissolved in approximately 20 mL of
CH2Cl2, and 0.5 equiv of NaBAr′4 (0.200 g, 0.220 mmol) was
added. After stirring for 30 min, the color changed from brown to
dark red and the CO absorption changed from 1920 to 1939 cm-1
,
as monitored by IR spectroscopy. After vacuum filtration through
a fine porosity frit, the filtrate was concentrated to 1-2 mL and
10 mL of hexanes was added to yield an orange solid. The solid
was collected with a fine porosity frit, washed with hexanes, and
dried in vacuo (0.310 g, 0.160 mmol, 80%). Crystals suitable for
an X-ray diffraction study were obtained by slow diffusion of
pentane into a CH2Cl2 solution of 2 at -20 °C. IR (CH2Cl2
solution): νCO ) 1939 cm-1. 1H NMR (CDCl3, δ): 7.71 (8H, br s,
BAr′4 phenyl), 7.52 (4H, br s, BAr′4 phenyl), 7.16 (4H, m, PCP
phenyl), 7.02 (2H, m, PCP phenyl), 3.45 (8H, m, PCP CH2), 1.74-
0.85 (∼72H, overlapping multiplets, PCP CH3). 31P{1H} NMR
(CDCl3, δ): 74.1 (d, JPP ) 228 Hz), 68.9 (d, JPP ) 228 Hz). 19F
NMR (CDCl3, δ): -63.0. Anal. Calc for C82H98BClF24O2P4Ru2:
C, 50.67; H, 5.08. Found: C, 50.16; H, 4.85.
higher in energy than the vinylidene model [(PCP′)(CO)-
RudCdCH2]+. Such a perpendicular conformation for the
experimental [(PCP)(CO)Ru(η2-HCtCPh)]+ seems even less
plausible on steric grounds, given the expected steric
repulsion between the Ph and the tert-butyl groups. (See
Table 1 for crystallographic data and parameters for com-
plexes 2, 3, 4, 7, and 8.)
Summary
[(PCP)Ru(CO)(η1-ClCH2Cl)][BAr′4] (3). (PCP)Ru(CO)(OTf)
(6) (0.100 g, 0.149 mmol) was dissolved in 10 mL of CH2Cl2, and
approximately 1 equiv of NaBAr′4 (0.140 g, 0.158 mmol) was
added. After stirring for 30 min, the color changed from brown to
The 14-electron fragment [(PCP)Ru(CO)]+ appears to bind
weakly coordinating ligands such as dinitrogen, methylene
chloride, and fluorobenzene in preference to formation of
agostic interactions. This suggestion is supported by both
experimental observations and calculations. The reaction of
[(PCP)Ru(CO)(η1-ClCH2Cl)][BAr′4] (3) with N2CHPh or
phenylacetylene results in transformations involving the C-C
bond formation of the PCP phenyl ring. Experimental studies
suggest that the reaction with N2CHPh proceeds via the
formation of a Ru benzylidene complex and that an
intermediate vinylidene complex may be central to the
reaction with phenylacetylene. The QM/MM calculations on
[(PCP)(CO)Rud(C)0,1dCHPh]+ and the DFT calculations
on [(PCP′)(CO)Rud(C)0,1dCH2]+ provide support for the
thermodynamic feasibility of the experimental mechanisms
leading to 7 (Scheme 3) and 8 (Scheme 4).
orange and the CO absorption changed from 1941 to 1964 cm-1
,
as monitored by IR spectroscopy. The solution was filtered through
a fine porosity frit, and the filtrate was concentrated to 1 mL under
reduced pressure. Approximately 10 mL of pentane was added, and
the formation of an orange precipitate was noted. Upon filtration
through a fine porosity frit, the solid was washed with pentane and
dried in vacuo (0.180 g, 0.122 mmol, 82%). Crystals suitable for
an X-ray diffraction study were obtained by slow diffusion of
pentane into a CH2Cl2 solution of 3 at -20 °C. IR (CH2Cl2
1
solution): νCO ) 1964 cm-1. H NMR (CD2Cl2, δ): 7.74 (8H, br
s, BAr′4 phenyl), 7.58 (4H, br s, BAr′4 phenyl), 7.23 (2H, d, JHH
)
8 Hz, phenyl), 7.02 (1H, t, JHH ) 8 Hz, PCP phenyl), 5.35 (2H, s,
free CH2Cl2), 3.50 (4H, m, PCP CH2), 1.50 (18H, vt, N ) 15 Hz,
PCP CH3), 1.11 (18H, vt, N ) 15 Hz, PCP CH3). 31P{1H} NMR
(CD2Cl2, δ): 71.0 (br s). 19F NMR (CD2Cl2, δ): -63.0. This
compound is extremely air and moisture sensitive. Thus, elemental
analysis was not obtained.
Experimental Section
General Methods. Unless otherwise noted, all procedures were
performed under an atmosphere of dinitrogen in a glovebox or using
standard Schlenk techniques. Oxygen levels were <15 ppm for all
glovebox manipulations. Pentane and fluorobenzene were distilled
from P2O5. Methylene chloride was purchased as an OptiDry solvent
(<50 ppm H2O), passed through two columns of activated alumina,
and then distilled over CaH2 prior to use. CD2Cl2 and CDCl3 were
degassed via three freeze-pump-thaw cycles and stored over 4
[(PCP)Ru(CO)(η1-N2)][BAr′4] (4). In a 25 mL round-bottom
flask, (PCP)Ru(CO)(OTf) (6) (0.030 g, 0.045 mmol) was dissolved
in 5-10 mL of fluorobenzene. Approximately 1 equiv of NaBAr′4
was added, and the reaction progress was monitored by IR
spectroscopy. After 30 min, the CO absorption (1944 cm-1) due
to the starting material had disappeared, and a major absorption at
1987 cm-1 was accompanied by a small side peak at 1953 cm-1
.
1
In addition, an absorption at 2249 cm-1 was observed. The solution
was stirred for approximately 3 h, during which time the IR
spectrum did not change significantly. The solution was filtered
Å molecular sieves. H and 13C NMR measurements were per-
formed on a Varian Mercury 300 or 400 MHz spectrometer and
referenced to tetramethylsilane (TMS) using resonances due to
residual protons in the deuterated solvents or the 13C resonances
of the deuterated solvents. All 31P NMR spectra were recorded on
a Varian Mercury instrument operating at a frequency of 161 MHz
with 85% phosphoric acid (0 ppm) as the external standard. All
(81) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992,
11, 3920-3922.
(82) Creary, X. Organic Synthesis; Wiley: New York, 1990; Collect. Vol.
No. VII, p 438.
8388 Inorganic Chemistry, Vol. 44, No. 23, 2005

Synthesis of FiWe-Coordinate Ru(II) Complexes
through a fine porosity frit, and the filtrate was transferred to a
glass tube. After dilution with fluorobenzene, pentane was layered
on top of the solution. Slow diffusion at -20 °C yielded orange
needle crystals. A single crystal was selected for X-ray diffraction
analysis.
[(PCP-CCHPh)Ru(CO)][BAr′4] (8). (A) Method A. [(PCP)-
Ru(CO)(η1-CH2Cl2)][BAr′4] (3) (0.100 g, 0.068 mmol) was dis-
solved in 10 mL of CH2Cl2. Excess phenylacetylene (0.030 mL,
0.27 mmol) was added with an immediate color change from orange
to green. The solution was stirred for 4 days with no further color
change noted. As monitored by IR spectroscopy, upon addition of
the phenylacetylene, the CO absorption changed from 1964 to 1943
cm-1. The solution was concentrated to approximately 5 mL under
reduced pressure, and pentane was added to yield a green
precipitate. Upon filtration, the collected green solid was washed
with pentane and dried in vacuo (0.080 g, 0.054 mmol, 80%).
[(PCP)Ru(CO)(FC6H5)][BAr′4] (5). The preparation procedure
was similar to that for complex 4. After addition of NaBAr′4 and
upon observation of equilibrium by IR spectroscopy, the solution
was purged with argon for 10 min. The peaks at 1987 cm-1 due to
one CO absorption and at 2249 cm-1 due to N2 absorption
disappeared, and only one CO frequency at 1953 cm-1 was
observed. The solution was purged with dinitrogen, and the
absorptions at 1987 and 2249 cm-1 appeared with the side peak at
1953 cm-1. The solution was then filtered through a fine porosity
frit, and the filtrate was transferred to a glass tube and diluted with
fluorobenzene. Repeated attempts to grow crystals resulted in
decomposition upon removal of crystals from the solvent.
[(PCP-CHPh)Ru(CO)][BAr′4] (7). [(PCP)Ru(CO)( η1-CH2Cl2)]-
[BAr′4] (3) (0.150 g, 0.102 mmol) was dissolved in 15 mL of
CH2Cl2. A red solution of excess PhCHN2 in pentane was added.
The resulting solution was stirred for 30 min, during which time
the color changed from orange to pink. The solution was concen-
trated to approximately 5 mL under reduced pressure, and 10 mL
of pentane was added to yield a pink precipitate. The solid was
collected by vacuum filtration, washed with pentane, and dried in
vacuo (0.120 g, 0.081 mmol, 80%). Crystals suitable for an X-ray
diffraction study were obtained by slow diffusion of pentane into
(B) Method B. [(PCP)Ru(CO)(η1-CH2Cl2)][BAr′4] (3) (0.150 g,
0.10 mmol) was dissolved in 15 mL of CH2Cl2. Excess phenyl-
acetylene was added, and the color of the solution changed to green.
A new CO absorption was observed at 1943 cm-1 by IR
spectroscopy. The volatiles were evaporated under reduced pressure.
The resulting green residue was dissolved in 20 mL of tetrahydro-
furan (THF) and heated to reflux for 3 h. After cooling to room
temperature, the solution was concentrated to approximately 5 mL
under reduced pressure, and 10 mL of pentane was added to yield
a green precipitate. Upon filtration, the collected green solid was
washed with pentane and dried in vacuo (0.130 g, 0.088 mmol,
86%). Crystals suitable for an X-ray diffraction study were obtained
by slow diffusion of pentane into a CH2Cl2 solution of 8 at -20
1
°C. IR (CH2Cl2 solution): νCO ) 1943 cm-1. H NMR (CD2Cl2,
δ): 7.79 (1H, t, JHH ) 8 Hz), 7.73 (8H, br s, BAr′4 phenyl), 7.57
(4H, br s, BAr′4 phenyl), 7.34 (2H, d, JHH ) 8 Hz, phenyl), 7.10
(3H, overlapping multiplet, phenyl), 6.54 (2H, d, JHH ) 8 Hz,
phenyl), 5.87 (1H, br s, PhCH), 3.40 (2H, m, PCP CH2), 2.99 (2H,
m, PCP CH2), 1.43 (18H, vt, N ) 15 Hz, PCP CH3), 1.20 (18H,
vt, N ) 13 Hz, PCP CH3). 13C{1H} NMR (CDCl3, δ): 201.6 (t,
JPC ) 12 Hz, CO), 162.0 (m, JBC ) 50 Hz, BsCipso), 155.2 (br s,
RusCddCHPh), 148.1-117.7 (multiple resonances due to aromatic
carbons, olefin carbon, and CF3), 39.6 (vt, N ) 14 Hz, PCP CH2),
37.3 (vt, N ) 16 Hz, PCP CMe3), 31.1, 28.8 (each a vt, N ) 5 Hz,
PCP CH3). 31P{1H} NMR (CD2Cl2, δ): 37.4. 19F NMR (CD2Cl2,
δ): -63.2. Anal. Calc for C65H61BF24OP2Ru: C, 52.47; H, 4.13.
Found: C, 52.42; H, 4.14.
a CH2Cl2 solution of 7 at -20 °C. IR (CH2Cl2 solution): νCO
)
1931 cm-1. 1H NMR (CD2Cl2, δ): 8.65 (1H, s, PhCH), 7.88 (2H,
t, JHH ) 7 Hz), 7.73 (8H, br s, BAr′4 phenyl), 7.57 (4H, br s, BAr′4
phenyl), 7.50-7.12 (∼5H, overlapping multiplets, phenyl), 6.38
(1H, t, JHH ) 8 Hz, phenyl), 3.90 (1H, m, PCP CH2), 3.68 (1H, m,
PCP CH2), 3.23 (1H, m, PCP CH2), 2.98 (1H, m, PCP CH2), 1.55
(9H, d, JPH ) 14 Hz, PCP CH3), 1.18 (9H, d, JPH ) 14 Hz, PCP
CH3), 0.90 (9H, d, JPH ) 14 Hz, PCP CH3), 0.86 (9H, d, JPH ) 14
Hz, PCP CH3). 13C{1H} NMR (CDCl3, δ): 202.8 (t, JPC ) 12 Hz,
CO), 162.0 (m, JBC ) 50 Hz, B-Cipso), 147.2-117.7 (multiple
resonances due to aromatic carbons and CF3), 44.4, 35.5 (each a d,
JPC ) 15 Hz, PCP CH2), 41.7 (br s, Ru-CHPh), 37.1 (m, PCP
CMe3), 30.8, 29.3, 29.1, 28.2 (each a d, JPC ) 4 Hz, PCP CH3).
NMR Study of Complex 3 with PhCtCH in CD2Cl2. A screw
cap NMR tube was charged with [(PCP)Ru(CO)(η1-CH2Cl2)][BAr′4]
(3) (0.020 g, 0.014 mmol) in 0.6 mL of CD2Cl2. Phenylacetylene
(∼5 µL, 0.04 mmol) was added, and an immediate color change
from brown to green was observed. The reaction was monitored
by 1H and 31P NMR spectroscopy. During the initial time, a single
31P{1H} NMR (CD2Cl2, δ): 46.2 (d, JPP ) 218 Hz), 23.6 (d, JPP
)
218 Hz). 19F NMR (CD2Cl2, δ): -63.2. Anal. Calc for C64H61-
BF24OP2Ru: C, 52.08; H, 4.17. Found: C, 52.67; H, 4.07.
1
Variable Temperature H NMR Study of the Reaction of
[(PCP)Ru(CO)(η1-ClCH2Cl)][BAr′4] (3) with PhCHN2. An NMR
tube was charged with approximately 20 mg of [(PCP)Ru(CO)-
(η1-CH2Cl2)][BAr′4] (3) in 0.7 mL of CD2Cl2 and cooled to -70
°C in an acetone/dry ice bath. Approximately 3 equiv of PhCHN2
was added via syringe with an immediate color change from brown
to red. The reaction mixture was transferred to an NMR probe
cooled to -70 °C and was monitored by 1H NMR spectroscopy as
the temperature was incrementally increased to 25 °C. At -70 °C,
there was no observation of a downfield resonance that would be
diagnostic of the formation of a benzylidene complex; however,
complex 3 was converted to a new complex that is likely a
ruthenium diazophenylmethane complex. At -40 °C, a broad
resonance was observed at 26.0 ppm (1H NMR) that is consistent
with the formation of [(PCP)(CO)RudCHPh][BAr′4]. At 10 °C,
the carbene resonance disappears and complete conversion to
complex 7 is observed. The NMR resonances other than that
assigned as being due to the putative ruthenium carbene hy-
drogen have not been assigned due to the complication of NMR
spectra.
PCP-Ru species was observed with the following data. H NMR
1
(δ): 7.9-7.2 (overlapping aromatic rings), 6.54 (2H, d, JHH ) 8
Hz, phenyl), 6.55 (1H, t, J ) 3 Hz), 3.90 (2H, m, PCP CH2), 3.02
(4H, m, PCP CH2), 1.62 (18H, vt, N ) 15 Hz, PCP CH3), 1.10
(18H, vt, N ) 13 Hz, PCP CH3). 31P{1H} NMR (δ): 31.5. The
excess PhCtCH was observed as a singlet at 3.15 ppm. During
1
the reaction time, a new product appeared, as observed in H and
31P NMR spectroscopy. Features of the new product include a broad
singlet at 5.87 ppm and two virtual triplets at 1.42 (N ) 15 Hz)
and 1.16 ppm (N ) 13 Hz) in the 1H NMR spectrum and a singlet
at 37.4 ppm in the 31P NMR spectrum. This is consistent with the
formation of complex 8. Over the reaction time, the decrease of
the intensities due to the first product resonances was accompanied
by an increase of the intensities of the resonances of complex 8,
and the resonance at 3.15 ppm due to the free PhCtCH was not
changed. After 4 days, complete conversion to complex 8 was
achieved, as observed by both 1H and 31P NMR spectroscopy.
Complex 8 was stable with excess PhCtCH in CD2Cl2 for at least
48 h.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8389

Zhang et al.
Computational Methods. Density functional and hybrid quan-
tum mechanics/molecular mechanics (QM/MM) calculations were
performed on truncated and full experimental models, respectively.
The QM/MM approach was employed according to the ONIOM
methodology.83 For analysis of ligand (i.e., N2, CH2Cl2, PhF)
binding, the MM region contained three out of the four tert-butyl
groups attached to the phosphorus atoms in each model; the tert-
butyl group with an agostic interaction was chosen for QM
modeling. The MM-modeled tert-butyl groups were described with
the universal force field (UFF).84 The QM region included the
remainder of the molecule. Density functional theory (DFT),85 using
the B3LYP hybrid functional,86-89 was employed for the QM core
and in DFT calculations on truncated experimental models (tert-
butyl groups were replaced by hydrogen; the phenyl substituent
on the carbene and vinylidene ligands was replaced by hydrogen).
Ruthenium and the main group elements were described with the
Stevens (CEP-31G) relativistic effective core potentials (ECPs) and
valence basis sets (VBSs).90,91 The valence basis sets of the main
group elements (carbon, nitrogen, oxygen, chlorine, and fluorine)
were augmented as needed with a d polarization function with an
exponent (êd ) 0.80), and a d polarization function with an exponent
(êd ) 0.55) was used on phosphorus. For Ru complexes, the
geometry was optimized for singlet cations, and all the geometries
were fully optimized without any symmetry constraints. The
Opt)NoMicro option was used to aid the convergence of ONIOM
geometry optimizations. All calculations were performed using the
Gaussian suite of programs.92 When available, crystal structures
for Ru complexes were used to initiate the geometry optimization
calculations.
Acknowledgment. T.B.G. acknowledges the National
Science Foundation (CAREER Award; CHE 0238167) and
the Alfred P. Sloan Foundation (Research Fellowship) for
support of this research and the research group of Professor
Bruce Eaton for use of their argon-filled glovebox. T.R.C.
wishes to acknowledge support by the Office of Basic Energy
Sciences, United States Department of Energy, through Grant
DOE-FG02-97ER14811. Calculations employed the UNT
computational chemistry resource, for which K.A.B. and
T.R.C. acknowledge the NSF for support through Grant
CHE-0342824.
Supporting Information Available: Files (cif) for structures
of complexes 2, 3, 4, 7, and 8 and all structures calculated by DFT,
optimized structures for computed ruthenium complexes, and
discussion of the X-ray structure of complex 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
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8390 Inorganic Chemistry, Vol. 44, No. 23, 2005