Nucleophilic substitution of η5-pyrrolyl ligands in ruthenium(II) complexes

Article abstract of DOI:10.1021/om9700268

The reaction of RuCl₂(PPh₃)₃ with pyrrolyllithium results in the formation of the pyrrolyl complex (NC₄H₄)RuCl(PPh₃)₂, 1, which has been characterized by an X-ray diffraction study. The structure confirms the η⁵-bonding mode for the pyrrolyl ligand. Ligand substitution reactions with 1 have led to the facile synthesis of related η⁵-pyrrolyl ruthenium complexes with other suppporting ligands. Reactions of the PEt₃ derivatives (NC₄H₄)RuX(PEt₃)₂, X = Cl and I, with aryl- and alkyllithium reagents resulted in nucleophilic substitution of the pyrrolyl ligand accompanied by hydrogen transfer to the metal ion, forming (2-RNC₄H₃)RuH(PEt₃)₂. The hydride products could be converted to the corresponding chloride derivatives, in chlorinated solvents, and the complex (2-PhNC₄H₃)RuCl(PEt₃)₂ has been structurally characterized. A second nucleophilic substitution reaction on the coordinated pyrrolyl ligand has been characterized in some cases, and protonation of the substituted pyrrole complex led to isolation of the free substituted pyrrole with recycling of the ruthenium complex. The nucleophilic substitutions are sensitive to the electronic features of the supporting ligands in the complex and to the strength of the nucleophiles.

Full text of DOI:10.1021/om9700268

Organometallics 1997, 16, 2325-2334
2325
Nu cleop h ilic Su bstitu tion of η5-P yr r olyl Liga n d s in
Ru th en iu m (II) Com p lexes
M. Rakowski DuBois,* K. G. Parker, C. Ohman, and B. C. Noll
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309
Received J anuary 16, 1997X
The reaction of RuCl2(PPh3)3 with pyrrolyllithium results in the formation of the pyrrolyl
complex (NC4H4)RuCl(PPh3)2, 1, which has been characterized by an X-ray diffraction study.
The structure confirms the η5-bonding mode for the pyrrolyl ligand. Ligand substitution
reactions with 1 have led to the facile synthesis of related η5-pyrrolyl ruthenium complexes
with other suppporting ligands. Reactions of the PEt3 derivatives (NC4H4)RuX(PEt3)2, X )
Cl and I, with aryl- and alkyllithium reagents resulted in nucleophilic substitution of the
pyrrolyl ligand accompanied by hydrogen transfer to the metal ion, forming (2-RNC4H3)-
RuH(PEt3)2. The hydride products could be converted to the corresponding chloride
derivatives in chlorinated solvents, and the complex (2-PhNC4H3)RuCl(PEt3)2 has been
structurally characterized. A second nucleophilic substitution reaction on the coordinated
pyrrolyl ligand has been characterized in some cases, and protonation of the substituted
pyrrole complex led to isolation of the free substituted pyrrole with recycling of the ruthenium
complex. The nucleophilic substitutions are sensitive to the electronic features of the
supporting ligands in the complex and to the strength of the nucleophiles.
In tr od u ction
ate precursors.8 A notable exception is the η2-pyrrole
complex of osmium pentammine, which undergoes
selective electrophilic attack at the C3 position. The
metal-induced activation of the η2-ligand has led to facile
tautomerizations, Diels-Alder condensations, and fur-
ther synthetic elaborations to form highly substituted
indoles.9 Selective electrophilic substitution reactions
at the C3 position have also been observed for pyrro-
lylimido complexes of molybdenum and tungsten,10 and
electrophilic addition reactions to and rearrangements
of η1-N-bonded pyrrolyl complexes of CpRe(NO)(PPh3)
have been characterized.11
Free pyrrole is generally not susceptible to nucleo-
philic attack, but η5-coordination to a metal ion has the
potential for activating the ring toward reaction with
nucleophiles. In recent work, we have synthesized new
sandwich complexes of Ru(II) and Os(II) which contain
the tetramethylpyrrolyl and pentamethylpyrrole ligands,
[(cymene)M(η5-NC4Me4)]OTf and [(cymene)M(η5-MeNC4-
Me4)](OTf)2.12 Nucleophilic addition to the monocation
occurred at the cymene ligand to give η5-cyclohexadienyl
derivatives, but reactions of the dication with nucleo-
philes (H-, OR-) resulted in nucleophilic addition to the
R-carbon in the pentamethylpyrrole ligand, eq 1. The
resulting product of hydride addition, [(cymene)Ru(η4-
MeNC4(H)Me4)]OTf, contained a cyclic η4 ligand with
the substituted carbon of the ring bent out of the plane
Synthetic routes for the derivatization of indole rings
are of interest in the synthesis of natural products,1,2
and several η6-indole complexes, e.g., of Cr, Mn, and Ru,
have been developed that facilitate regioselective nu-
cleophilic addition or substitution reactions on the
carbocyclic ring.3-6 Substituted pyrrole heterocycles
also show important biological activity. For example,
various substituted pyrroles are known to act as anal-
gesics, anti-inflammatory agents, or to have antibacte-
rial properties.7 However, relatively few transition-
metal-pyrrole complexes have been found to be
synthetically useful in the preparation of substituted
pyrrole rings, and the syntheses of substituted pyrroles
have been largely limited to electrophilic additions to
the free ligand and to ring-closing reactions of appropri-
X Abstract published in Advance ACS Abstracts, May 1, 1997.
(1) Sundberg, R. J . Comprehensive Heterocyclic Chemistry; Katritz-
ky, A. R., Rees, C. W., Eds.; Pergamon Press: Oxford, 1984; Vol. 4, p
313.
(2) (a) Christophersen, C. Marine Indoles in Marine Natural Prod-
ucts: Chemical and Biological Perspectives; Scheuer, P. J ., Ed.;
Academic: New York, 1982; Vol. V, p 259. (b) Repke, D. B.; Ferguson,
W. J . J . Heterocycl. Chem. 1982, 19, 845.
(3) Lomenzo, S. A.; Nolan, S. P.; Trudell, M. L. Organometallics
1994, 13, 676.
(4) (a) Semmelhack, M. F.; Wolff, W.; Garcia, J . L. J . Organomet.
Chem. 1982, 240, C5. (b) Kozikowski, A. P.; Isobe, K. J . Chem. Soc.,
Chem. Commun. 1978, 1076. (c) Beswick, P. J .; Greenwood, C. S.;
Mowlem, T. J .; Nechvatal, G.; Widdowson, D. A. Tetrahedron 1988,
44, 7325. (d) Masters, N. F.; Mathews, N.; Nechvatal, G.; Widdowson,
D. A. Tetrahedron 1989, 45, 5955.
(5) Ryan, W. J .; Peterson, P. E.; Cao, Y.; Williard, P. G.; Sweigart,
D. A.; Baer, C. D.; Thompson, C. F.; Chung, Y. K.; Chung, T. M. Inorg.
Chim. Acta 1993, 211, 1.
(6) Moriarty, R. M.; Ku, Y. Y.; Gill, U. S. Organometallics 1988, 7,
660. (b) Gill, U. S.; Moriarty, R. M.; Ku, Y. Y.; Butler, I. R. J .
Organomet. Chem. 1991, 417, 313. (c) Moriarty, R. M.; Gill, U. S.; Ku,
Y. Y. J . Organomet. Chem. 1988, 350, 157.
(7) J ones, R. A.; Bean, G. P. The Chemistry of Pyrroles; Academic
Press: London, 1977; p 2. (b) Reference 1, p 374. (c) Pyrroles. The
Synthesis, Reactivity, and Physical Properties of Substituted Pyrroles;
J ones, R. A., Ed.; Wiley: New York, 1992. (d) Brogden, R. N.; Heel, R.
C.; Speight, T. M.; Avery, G. S. Drugs 1978, 15, 429.
(8) J ones, R. A. Comprehensive Heterocyclic Chemistry; Katritsky,
A. R., Rees, C. W., Eds.; Pergamon Press: Oxford, 1984; Vol. 4, p 201.
(9) (a) Cordone, R.; Harman, W. D.; Taube, H. J . Am. Chem. Soc.
1989, 111, 5969. (b) Myers, W. H.; Sabat, M.; Harman, W. D. J . Am.
Chem. Soc. 1991, 113, 6682. (c) Myers, W. H.; Koontz, J . I.; Harman,
W. D. J . Am. Chem. Soc. 1992, 114, 5684. (d) Hodges, L. M.; Moody,
M. W.; Harman, W. D. J . Am. Chem. Soc. 1994, 116, 7931. (e) Hodges,
L. M.; Spera, M. L.; Moody, M. W.; Harman, W. D. J . Am. Chem. Soc.
1996, 118, 7117.
(10) Seino, H.; Ishii, Y.; Sasagawa, T.; Hidai, M. J . Am. Chem. Soc.
1995, 117, 12181.
(11) J ohnson, T. J .; Arif, A. M.; Gladysz, J . A. Organometallics 1993,
12, 4728.
(12) Kvietok, F.; Allured, V.; Carperos, V.; Rakowski DuBois, M.
Organometallics 1994, 13, 60.
S0276-7333(97)00026-5 CCC: $14.00 © 1997 American Chemical Society

2326 Organometallics, Vol. 16, No. 11, 1997
Rakowski DuBois et al.
F igu r e 1. Perspective drawing and numbering scheme for
(η5-NC4H4)Ru(PPh3)2Cl, 1.
have the potential for synthetic utility in the synthesis
of a variety of substituted pyrroles.
by a dihedral angle of 32°. Reaction with acid led to
further ring reduction and elimination of a free cyclic
iminium ion.
In earlier work, Zakrzewski developed the chemistry
of pyrrolyl complexes of rhenium of the formula (η5-
NC4H4)Re(PR3)2(H)I.13 These complexes were found to
undergo nucleophilic substitution reactions at the R-car-
bon of the heterocycle, as shown in eq 2. The reactions
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of (NC4H4)Ru -
(P R3)2X Der iva tives. The reaction of (PPh3)3RuCl2
with pyrrolyllithium in refluxing toluene led to the
formation of a yellow crystalline product (NC4H4)-
Ru(PPh3)2Cl, 1, eq 3, which was isolated after chroma-
tography in 60-70% yield. The procedure is similar to
that reported for the synthesis of CpRu(PPh3)2Cl.15 In
the 1H NMR spectrum of 1, the resonances for the
pyrrolyl hydrogens are shifted upfield relative to the free
ligand to 5.61 and 4.24 ppm. The 31P NMR spectrum
shows a singlet for the equivalent phosphine ligands at
41.4 ppm. The upfield shifts in the proton spectrum
suggest an η5-coordination of the ring to the ruthenium
ion, and this bonding mode was confirmed by an X-ray
diffraction study. The complex crystallized in space
group P1h with two molecules per unit cell. A perspective
drawing of the molecule is shown in Figure 1, and
selected bond distances and angles are given in Table
1. The structure consists of discrete molecules in which
the ligands form a pseudotetrahedral coordination
geometry about the ruthenium ion. The Ru-C dis-
tances for the pyrrole ring are similar to those reported
for the η5-ligand in the analogous Cp complex,16 but the
Ru-Cl and Ru-P bonds in 1 are 0.01-0.03 Å shorter
than those for the Cp derivative. The P-Ru-P angle
in 1, 102.6(1)°, is also somewhat smaller than the same
angle in the Cp complex (103.99(4)°).
involve hydrogen transfer from the ring to the metal
ion. Similar nucleophilic substitutions of η5-cyclopen-
tadienyl ligands with hydrogen transfer to the metal ion
have been proposed.14
We report here new η5-pyrrolyl complexes of ruthe-
nium which promote nucleophilic substitutions at the
heterocycle by a similar pathway of hydrogen transfer
and metal hydride formation. The new pyrrole com-
plexes are easily synthesized and modified by coligand
substitution reactions, and the metal ion can be recycled
upon removal of the substituted pyrrole. The complexes
(13) (a) Felkin, H.; Zakrzewski, J . J . Am. Chem. Soc. 1985, 107,
3374. (b) Zakrzewski, J . Heterocycles 1990, 31, 383. (c) Zakrzewski, J .
J . Organomet. Chem. 1987, 326, C17; Ibid. 1987, 327, C41; Ibid. 1989,
362, C31.
(14) (a) Rigny, S.; Bakhmutov, V. I.; Nuber, B.; Leblanc, J . C.; Moise,
C. Inorg. Chem. 1996, 35, 3202. (b) Forschner, T. C.; Cooper, N. J . J .
Am. Chem. Soc. 1989, 111, 7420. (c) Green, M. L. H.; Lindsell, W. E.
J . Chem. Soc. A 1969, 2215.
(15) (a) Gilbert, J . D.; Wilkinson, G. J . Chem. Soc. A 1969, 1749.
(b) Bruce, M. I.; Windsor, N. J . Aust. J . Chem. 1977, 30, 1601.
(16) Bruce, M. I.; Wong, F. S.; Skelton, B. W.; White, A. H. J . Chem.
Soc., Dalton Trans. 1981, 1398.

Nucleophilic Substitution of η5-Pyrrolyl Ligands
Organometallics, Vol. 16, No. 11, 1997 2327
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for (p yr r )Ru Cl(P P h 3)2 (1)
Distances
Ru-N
2.239(3)
2.222(3)
2.161(3)
2.327(1)
1.393(6)
1.419(6)
1.382(5)
Ru-C(1)
Ru-C(3)
Ru-Cl(l)
Ru-P(2)
C(1)-C(2)
C(3)-C(4)
2.208(4)
2.187(3)
2.427(1)
2.304(1)
1.368(6)
1.404(6)
Ru-C(2)
Ru-C(4)
Ru-P(1)
N-C(1)
C(2)-C(3)
N-C(4)
Angles
88.7(1)
102.6(1)
Cl(1)-Ru-P(1)
P(1)-Ru-P(2)
Cl(1)-Ru-P(2)
90.7(1)
A similar reaction of RuH(Cl)(PPh3)3 with pyrrolyl-
lithium resulted in the formation of the hydride ana-
logue (η5-NC4H4)RuH(PPh3)2, 2, which has been isolated
and characterized by spectroscopic data. In particular,
the 1H NMR spectrum for 2 showed a characteristic
hydride resonance (triplet) in the NMR spectrum at
-13.79 ppm. Complete spectroscopic data are provided
in the Experimental Section. Despite the ease with
which the syntheses of 1 and 2 proceed, the attempted
reactions of the lithium salts of 2-acetylpyrrole, tetra-
methylpyrrole, and of 2,5-dimethylpyrrole with RuCl2-
(PPh3)3 under similar reaction conditions did not pro-
ceed in the first two cases and in the latter system gave
a mixture of products which were not readily separated.
Facile ligand substitution reactions have been char-
acterized for 1, which are similar to those reported for
CpRu(PPh3)2Cl.17 For example, reaction with KI in
ethanol leads to the synthesis of the iodide complex (η5-
NC4H4)Ru(PPh3)2I, 3, which has been isolated and
characterized by elemental analyses and spectroscopic
derivative. The product containing the nonlabile hy-
dride ligand did not undergo further nucleophilic sub-
stitution reactions.
The reactivity of the pyrrolyl ligand toward nucleo-
philes depends not only on the lability of the displaced
ligand, but also on the properties of the phosphine
ligand in the complex. For example, the triphenylphos-
phine derivative, (η5-NC4H4)Ru(PPh3)2Cl, did not react
with MeLi or PhLi under similar conditions, although
the reaction of MeLi did proceed with the iodide
analogue. Triethylphosphine has a somewhat smaller
cone angle than PPh3 (132° vs 145°, respectively) and
is a significantly stronger σ-donor ligand (for the
conjugate acid, pKa ) 8.69 vs 2.73 for PPh3).19 Elec-
tronic effects may account for the greater reactivity of
the triethylphosphine derivatives since greater electron
donation to the metal ion should enhance the lability
of the halide ligand. A similar labilizing effect has been
observed for the rate of Cl- exchange in CpRu(PR3)2Cl
as the donor ability of the phosphine ligand was
increased.20 When the reactions of (η5-NC4H4)Ru-
(PEt3)2I and (η5-NC4H4)Ru(PEt3)2Cl with an equivalent
of PhLi were monitored by NMR spectroscopy in sealed
tubes, both reactions were found to be complete within
the time of mixing at room temperature and we were
unable to compare relative rates as a function of the
leaving ligand under these conditions.
1
data. The chemical shifts for the H NMR resonances
for the pyrrolyl ligand in 3 at 5.64 and 4.46 ppm and
for the single resonance in the 31P NMR spectrum at
40.7 ppm are similar to those of the chloride derivative.
The reaction of 1 with excess triethylphosphine in
refluxing toluene led to the synthesis of the phosphine-
substituted product (η5-NC4H4)Ru(PEt3)2Cl, 4, and fur-
ther substitution with KI produced the iodide analogue,
(η5-NC4H4)Ru(PEt3)2I, 5. The cationic η5-pyrrolyl de-
rivatives [(η5-NC4H4)Ru(PEt3)3]PF6, [(η5-NC4H4)RuCO-
(PEt3)2]PF6, and (η5-NC4H4)Ru(PEt3)2(CH3CN)]BPh4 have
also been synthesized by procedures similar to those
reported for related cyclopentadienyl derivatives.16-18
Characterization data for all of the new complexes are
presented in the Experimental Section.
The spectroscopic data for the substituted pyrrolyl
complexes are distinctive. In the 1H NMR spectrum,
three new resonances are observed for the inequivalent
ring hydrogens and a high-field pseudotriplet near -14
ppm confirms the formation of the hydride product.
Spin-spin coupling between the pyrrole hydrogens is
not resolved, and the pyrrole resonances are observed
as singlets in the 400 MHz spectra. In the 31P NMR
spectrum, an AB pattern is observed, reflecting the loss
of Cs symmetry in the molecule. Although the hydride
products were identified spectroscopically, most of these
were converted to the chloride derivatives prior to
isolation. This was accomplished by quenching excess
Rea ction s w ith Nu cleop h iles. Although free pyr-
role is quite electron rich and does not undergo nucleo-
philic attack, coordination of the pyrrolyl ligand to the
ruthenium ion activates the ring toward nucleophilic
substitution. For example, the triethylphosphine de-
rivatives 4 and 5 react with strong nucleophiles, such
as alkyl- and aryllithium reagents, to produce Ru(II)-
hydride derivatives containing substituted pyrrolyl
ligands, as shown in eq 4. During this reaction, the ring
hydrogen was transferred to the metal ion displacing
the labile halide ligand. The reaction with the more
stabilized nucleophile CH(Me)CN- proceeded with the
iodide as a leaving group, but not with the chloride
(17) Bennett, M. A.; Bruce, M. I.; Matheson, T. W. Comprehensive
Organometallic Chemistry; Wilkinson, G., Stone, G. F. A., Abel, E. W.,
Eds.; Pergamon Press: Oxford, 1982; Vol. 4, p 783.
(18) Treichel, P. M.; Komar, D. A. Synth. React. Inorg. Met.-Org.
Chem. 1980, 10, 205.
(19) Rahman, M.; Liu, H. Y.; Eriks, K.; Prock, A.; Giering, W. P.
Organometallics 1989, 8, 1.
(20) Treichel, P. M.; Komar, D. A.; Vincenti, P. J . Inorg. Chim. Acta
1984, 88, 151.

2328 Organometallics, Vol. 16, No. 11, 1997
Rakowski DuBois et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for (2-P h NC4H3)Ru Cl(P Et3)2 (6b)
Distances
Ru-N
2.276(5)
2.296(5)
2.172(6)
2.288(2)
1.418(9)
1.462(10)
1.382(8)
Ru-C(1)
Ru-C(3)
Ru-Cl
Ru-P(2)
C(1)-C(2)
C(3)-C(4)
C(1)-C(5)
2.279(6)
2.238(6)
2.4246(14)
2.284(2)
1.417(9)
1.457(11)
1.462(8)
Ru-C(2)
Ru-C(4)
Ru-P(1)
N-C(1)
C(2)-C(3)
N-C(4)
Angles
P(1)-Ru-P(2)
Cl-Ru-P(1)
95.56(6)
89.44(6)
Cl-Ru-P(2)
89.22(5)
also appears to have slipped slightly away from the
phosphine ligands, as shown by the shorter distances
from the metal to C(3) and C(4)compared to those
between the metal and N, C(1), and C(2). The average
Ru-P distance of 2.286 (2) Å is significantly shorter for
this triethylphosphine derivative than that observed for
the triphenylphosphine complex 1.
F igu r e 2. Thermal ellipsoid drawing and numbering
scheme for (η5-2-PhNC4H3)Ru(PEt3)2Cl, 6b.
lithium reagent with tert-butyl chloride,21 if necessary,
and then placing the complex in a chloroform solution
for a few minutes or in dichloromethane for 15-20 h.22
Column chromatography was carried out to obtain the
pure chloride derivatives with substituted pyrrolyl
ligands. Isolated yields of the products at this stage
were rather low, 25-35%, even though the NMR studies
of the aryllithium substitutions indicated that those
reactions proceeded quantitatively. Some decomposi-
tion was observed during the hydride to chloride con-
version step in either solvent, even when the chlorinated
solvents were carefully distilled and protected from air
and light. A recent paper has reported that CH3Cl in
CH2Cl2 was a more effective reagent for the hydride/
chloride conversion of rhenium hydrides than the more
chlorinated solvents, and it was suggested that the
reaction may proceed by a more selective mechanism.23
However, in our systems, no hydride conversion was
observed using CH3Cl in THF and the yields of isolated
ruthenium chlorides using CH3Cl/CH2Cl2 were similar
to those for the other chlorinated solvents.
X-r a y Diffr a ct ion St u d y of (2-P h NC4H 3)R u -
(P Et3)2Cl. Single crystals of the phenyl-substituted
product (2-PhNC4H3)Ru(PEt3)2Cl, 6b, have been ob-
tained. An X-ray diffraction study was carried out in
order to verify the site of nucleophilic attack and to learn
more about the potential steric interactions between the
phosphine ligands and the ring substituent. A perspec-
tive drawing and numbering scheme of the structure
are given in Figure 2, and selected bond distances and
angles are presented in Table 2. The structure estab-
lishes that the η5-pyrrolyl ring contains a phenyl sub-
stituent on an R carbon of the ring. The plane of the
phenyl ring is rotated relative to that of the pyrrolyl
ligand; the angle between the normals to the two rings
is 20.9°. The orientation of the phenyl ring over the
chloride ligand appears to minimize steric repulsions
with the triethylphosphine ligands. The pyrrolyl ring
Rea ctivity of Nu cleop h iles. The range of nucleo-
philes which can be used successfully in these substitu-
tion reactions has been studied with the derivatives (η5-
NC4H4)Ru(PEt3)2X, X ) Cl, 4, and I, 5. Both alkyl- and
aryllithium reagents reacted readily to give the substi-
tuted products, but the substitutions were not always
successfully accomplished with Grignard reagents. For
example, while the reaction of MeMgCl with 4 resulted
in the formation of a product with a methylated pyrrole
ligand, the reaction of MeMgBr (in diethyl ether) led to
the formation of (η5-NC4H4)Ru(PEt3)2Br, which was
isolated by column chromatography in very low yield
and identified by NMR and mass spectroscopy. Similar
halogen-exchange products have been observed in the
reactions of CpRu(PPh3)2Cl with MeMgI and of Cp*Ru-
(PMe3)2Cl with RMgBr.24 The NMR spectrum of the
crude product from the MeMgBr reaction also showed
evidence for the formation of free pyrrole, but other
ruthenium containing products were not identified.
A series of other anionic nucleophiles have been
reacted with (η5-NC4H4)Ru(PEt3)2Cl, 4. The amide
derivative LiNMe2 reacted to form two products in about
equal amounts, which were tentatively identified as the
ring-substituted derivative, (η5-2-(NMe2)NC4H3)Ru-
(PEt3)2H, and the unsubstituted pyrrolyl product with
a hydride ligand, (η5-NC4H4)Ru(PEt3)2H, eq 5. These
products could form by a pathway of intermolecular
hydride transfer from the substituted pyrrole ligand, but
it seemed more likely that the products resulted from
competing reactions which involved nucleophilic attack
on the ring and on the metal ion. The latter Ru-
dimethylamide complex is proposed to undergo rapid
â-hydrogen elimination to form the observed hydride
product. The reaction of lithium dimethylamide with
RuCl2(PR3)4 has been reported to undergo a similar
rapid â-hydrogen elimination,25a while the reaction of
Cp*Ru(PMe3)2Cl with primary amides led to intractable
products.25b The identities of the products formed from
the reaction of 4 with LiN(CD3)2 were consistent with
the proposed mechanism. In this case, we observed in
(21) Protic reagents were not used to quench Li alkyl reactants
because protonation of the pyrrolyl ring led to complex decomposition.
t-BuCl reacted with the carbanion to form the hydrocarbon and
isobutene.
(22) Similar H/Cl exchanges have been observed for CpRu(PR3)2H
derivatives, see: Lemke, F. R.; Brammer, L. Organometallics 1995,
14, 3980.
(24) (a) Blackmore, T.; Bruce, M. I.; Stone, F. G. A. J . Chem. Soc. A
1971, 2376. (b) Bruce, M. I.; Gardner, R. C. F.; Stone, F. G. A. J . Chem.
Soc., Datlton Trans. 1979, 906. (c) Tilley, T. D.; Grubbs, R. H.; Bercaw,
J . E. Organometallics 1984, 3, 274.
(25) (a) Diamond, S. E.; Mares, F. J . Organomet. Chem. 1977, 142,
C55. (b) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 109, 1444.
(23) Heinekey, D. M.; Voges, M. H.; Barnhart, D. M. J . Am. Chem.
Soc. 1996, 118, 10792.

Nucleophilic Substitution of η5-Pyrrolyl Ligands
Organometallics, Vol. 16, No. 11, 1997 2329
ppm while a resonance for a Ru-D ligand was not
observed, eq 7. Although LiAlH4 has been used to
displace the halide ligand in CpRu(PR3)2Cl,24a,26 the
same reagent appears to lead to decomposition of the
(η5-NC4H4)Ru derivatives. Resonances for a coordinated
pyrrolyl ligand were not observed in the NMR spectrum
of the products of the latter reaction.
The reaction of 5 (but not 4) with the stabilized
carbanion LiCH(Me)CN appeared to form the pyrrole-
substituted product 2-(CN(Me)CH)NC4H3)Ru(PEt3)2H
in low yield. In the 1H NMR spectrum, resonances were
observed for the two diastereomers, e.g., A and B,
expected for the product. Unreacted starting material
1
2
the H and D NMR spectra resonances for the substi-
tuted pyrrole complex (2-N(CD3)2NC4H3)Ru(PEt3)2H
and a Ru-D complex with the unsubstituted hetero-
cycle, eq 6. Both hydride products were converted to
corresponding chlorides prior to isolation.
was also present, but addition of excess lithium reagent
to this reaction led to decomposition. Attempts to
convert the hydride product to the chloride derivative
with dichloromethane or chloroform were unsuccessful
in this case, and the substituted product has not been
successfully isolated. Nevertheless, this apparent re-
activity toward stabilized carbanions is significant
because it extends the range of nucleophilic pyrrole
substitutions to less basic reagents than have been
observed previously, and further work to optimize these
types of reactions is in progress.
Syn th eses of Com p lexes w ith Disu bstitu ted P yr -
r olyl Rin gs. The facile conversion of the nonlabile
hydride ligand to a labile chloride in the substituted
pyrrolyl products permits the repetition of the nucleo-
philic substitution reaction. For example, the reaction
of (2-PhNC4H3)Ru(PEt3)2Cl with an equivalent of PhLi
proceeded at room temperature to form the product with
a disubstituted pyrrolyl ligand, (2,5-Ph2NC4H2)Ru-
Other heteroatom-containing nucleophiles, such as
SR- or OR-, did not undergo nucleophilic attack on the
pyrrolyl ligand in 4. The reactions with NaSR (R ) Me,
t-Bu) appeared to form ruthenium-thiolate complexes
(η5-NC4H4)Ru(PEt3)2SR, which were tentatively identi-
fied by spectroscopic data. In contrast, no reaction at
all was observed between 4 and NaOMe or NaOtBu.
The reaction of Super-Hydride, LiEt3BH, with 4 at
room temperature proceeded to form the hydride com-
plex (η5-NC4H4)Ru(PEt3)2H, which was characterized by
spectroscopic data. The product appears to form by
hydride attack on the pyrrolyl ligand and hydrogen
transfer from the ring to the metal ion. When the
analogous reaction with Super-Deuteride was charac-
terized by 2H NMR spectroscopy, a resonance was
observed only for the deuterated pyrrolyl ligand at 5.87
1
(PEt3)2H, which was identified by H NMR data. The
hydride product was converted to the chloride derivative
(2,5-Ph2NC4H2)Ru(PEt3)2Cl, 7, which was further puri-
fied by chromatography and characterized spectroscopi-
cally. The 1H NMR spectrum of 7 showed a single
resonance for equivalent pyrrole hydrogens at 5.05 ppm,
and the 31P spectrum also showed a single resonance
at 35.4 ppm. Similar disubstituted pyrrolyl ligands
have been synthesized with the Re system described
above.13 In contrast, the reaction of (2-PhNC4-
(26) Davies, S. G.; Moon, S. D.; Simpson, S. J . J . Chem. Soc., Chem.
Commun. 1983, 1278.

2330 Organometallics, Vol. 16, No. 11, 1997
Rakowski DuBois et al.
H3)Ru(PEt3)2Cl with an equivalent of MeLi did not
proceed at room temperature to give a disubstituted
ring. The ease of the second substitution on the ring
may be dependent on the steric bulk of the substituent
group.
soluble complexes with triethylphosphine ligands; (η5-
NC4H4)Ru(PEt3)2Cl has been successfully isolated by
chromatography from the recycling reaction, but the
yields were very low.
The cationic derivatives of the formulas [(NC4H4)Ru-
(PR3)2L]+ and [(RNC4H4)Ru(PR3)2X]+ also have the
potential for promoting nucleophilic attack on the η5-
heterocyclic ligand, although mechanistic features and
competing reactions may vary. The characterizations
of the reactivities of these derivatives will be the subject
of future studies.
Con clu sion s. The new (η5-NC4H4)Ru(PR3)2X deriva-
tives reported here are synthesized in high yield from
readily available starting materials, and their electronic
properties can be modified and tuned by ligand substi-
tution reactions. The new complexes facilitate the
nucleophilic substitution of the η5-pyrrolyl ligand with
a range of nucleophiles, and both 2- and 2,5-substituted
pyrrolyl products have been isolated and characterized.
Protonation or alkylation of the substituted ligand
produces the free substituted pyrrole heterocycles. The
systems have potential for applications in the syntheses
of a wide range of substituted pyrrole molecules.
Rea ction s of (η5-NC4H3(R))Ru (P R3)2X Der iva -
tives w ith Electr op h iles. (η5-NC4H4)Ru(PPh3)2Cl
reacted with 1 equiv of triflic acid to form the product
with a protonated pyrrole nitrogen, [(η5-HNC4H4)-
Ru(PPh3)2Cl]OTf, 9. This complex was identified by 1H
NMR data, but it showed limited stability in solution
and was not successfully isolated in pure form. The
N-Me analogue, which was prepared by a reaction with
MeOTf, could be isolated, but it also tended to decom-
pose via loss of the neutral methylpyrrole ligand. Much
weaker acids, such as pyridinium chloride (1 equiv) or
excess ammonium chloride, also lead to the protonation
and dissociation of the η5-pyrrole ligand.
The lability of the neutral pyrrole ligands in these
complexes can be used in the isolation of free substituted
pyrrole heterocycles. For example, the reaction of (2-
PhNC4H3)Ru(PEt3)2Cl with gaseous HCl resulted in the
displacement of 2-phenylpyrrole, which was separated
from the ruthenium products by chromatography on an
alumina column, isolated in near quantitative yield, and
Exp er im en ta l Section
1
characterized by H NMR and mass spectroscopy. The
RuCl2(PPh3)3,27 RuHCl(PPh3)3,28 and tetramethylpyrrole29
were synthesized according to literature procedures. Pyrrole
was distilled from CaH2 and stored over Linde 4 Å molecular
sieves. Pyrrolyllithium salts were synthesized by combining
the appropriate reagent with 1 equiv of n-butyllithium in
hexane at room temperature. The insoluble product was
filtered and used immediately or stored at low temperature.
Diethyl ether, toluene, and benzene-d6 were distilled from
sodium benzophenone ketyl and stored over 4 Å molecular
sieves before use. Hexane, pentane, and deuterated chloro-
form were distilled from CaH2 and stored over 4 Å molecular
sieves before use. All reactions were carried out under a
nitrogen atmosphere using standard Schlenk techniques.
1H NMR spectra were recorded at 400.13 MHz, 13C NMR
spectra were recorded at 100.62 MHz, and 31P NMR were
recorded at 161.98 MHz on a Bruker AM-400 NMR spectrom-
eter. Chemical shifts were referenced to tetramethylsilane by
using the deuterated solvent signal as a secondary reference.
Mass spectra were obtained on a VG Analytical 7070 EQ-HF
mass spectrometer.
pyrrole could be further purified by sublimation, but this
reduced the yield to 45%. Ruthenium phosphine prod-
ucts were not successfully isolated from the chromatog-
raphy columns, but similar protonations of (R-pyrrolyl)-
Ru(PR3)2Cl derivatives coupled with further reactions
with pyrrolyllithium did allow us to regenerate the
starting reagent (η5-NC4H4)Ru(PR3)2Cl, eq 8. For ex-
Syn th esis of (NC4H4)Ru (P P h 3)2Cl, 1. RuCl2(PPh3)3 (1.0
g, 1.0 mmol) and pyrrolyllithium (0.090 g,1.2 mmol) were
combined in 100 mL of toluene, and the solution was stirred
at 40 °C under nitrogen for 3 h. The previously brown solution
changed to orange, and a white precipitate formed. The
solution was filtered through a bed of Celite, and the filtrate
was concentrated in vacuo. This solution was loaded onto an
alumina/toluene chromatography column, and 150 mL of
toluene were passed through to remove any triphenylphos-
phine. 1 was eluted as a yellow band with a 15:1 mixture of
toluene:acetonitrile and isolated by removal of solvent.
Yield: 0.50 g, 69%. Crystals suitable for X-ray diffraction were
grown by vapor diffusion of pentane into a concentrated
dichloromethane solution. 1H NMR (CDCl3): δ 7.36, 7.29, 7.20,
7.10 (m, PPh3), 5.61, 4.24 (2s, each 2H, pyrr). 31P NMR
(CDCl3): δ 41.4 (s, PPh3). 13C NMR (CDCl3): δ 137.2, 134.0,
127.6 (m, PPh3), 129.1 (s, PPh3), 108.4, 82.7 (2 s, pyrr). FAB+
MS (3-NOBA matrix): m/z 727 (M), 692 (M - Cl), 661 (M -
ample, addition of HCl to (2-BuNC4H3)Ru(PPh3)2Cl led
to the formation of free 2-Bupyrrole, which was ex-
tracted with multiple aliquots of ether and isolated in
65% yield. Addition of triphenylphosphine to the re-
maining ruthenium-containing residue led to the forma-
tion of Ru(PPh3)3Cl2, and this complex was converted
to the η5-pyrrolyl derivative in an overall yield of 33%
based on the initial substituted pyrrolyl complex. It
may be possible to improve these yields. However,
effective separation of the neutral substituted pyrrole
from the phosphine ruthenium products can be difficult,
and addition of pyrrolyllithium to the latter reaction
residue often leads to the formation of a mixture of
products. This was a particular problem for the highly
(27) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 237.
(28) Schunn, R. A.; Wonchoba, E. R. Inorg. Synth. 1971, 13, 131.
(29) J ohnson, A. W.; Markham, E.; Price, R.; Shaw, K. B. J . Chem.
Soc. 1958, 4254.

Nucleophilic Substitution of η5-Pyrrolyl Ligands
Organometallics, Vol. 16, No. 11, 1997 2331
Ta ble 3. Cr ysta l Da ta for Com p ou n d s 1 a n d 6b
mL of toluene, and the combined extracts were concentrated
in vacuo and chromatographed on an alumina/toluene column.
Complex 3 was eluted as an orange-red fraction with toluene.
An orange, air-stable, crystalline solid was obtained after
solvent removal. Yield: 0.18 g, 94%. 1H NMR (CDCl3): δ 7.34,
7.25, 7.14 (3m, PPh3), 5.64, 4.46 (2s, each 2H, pyrr). 13C NMR
(CDCl3): δ 137.7 (m, PPh3), 134.3, 127.5 (2m, PPh3), 129.2 (s,
PPh3), 107.4, 84.3 (2s, pyrr). 31P NMR (CDCl3): δ 40.7 (s,
PPh3). FAB+ MS (NOBA): m/z 819 (M), 753 (M - pyrr), 692
(M - I). Anal. Calcd for RuC16H34ClNP2: C, 43.78; H, 7.82;
N, 3.19. Found: C, 43.60; H, 7.68; N, 3.16.
Syn th esis of (NC4H4)Ru (P Et3)2Cl, 4. Triethylphosphine
(1.4 mL, 7.7 mmol) was added to a solution of 1 (0.70 g, 0.96
mmol) in 150 mL of toluene. This solution was refluxed with
stirring for 6 h. The solvent was removed from the resulting
yellow-green solution in vacuo. The green residue was dis-
solved in toluene and chromatographed on a neutral alumina/
toluene column. The major yellow fraction was eluted with a
10:1 mixture of toluene:acetone. Yield: 0.24 g, 57%. 1H NMR
(CDCl3): δ 5.85, 4.85 (2s, each 2H, pyrr), 2.06, 1.58 (2m, each
6H, PEt3), 1.09 (m, 18H, PEt3). 31P NMR (CDCl3): δ 37.8 (s,
PEt3). 13C NMR (CDCl3): δ 105.7, 75.4 (2s, pyrr), 20.7 (m,
PEt3), 8.2 (s, PEt3). EI+ MS: m/z 439 (M), 321 (M - PEt3).
Anal. Calcd for C16H34ClNP2Ru: C, 43.78; H, 7.81; N, 3.19.
Found: C, 43.43; H, 7.72; N, 2.87.
1
6b
formula
C41H36NP2Cl3Ru C22H38ClNP2Ru
fw
812.1
514.99
cryst syst
unit cell dimensions
a (Å)
b (Å)
c (Å)
triclinic
orthorhombic
9.924(2)
13.951(3)
14.370(3)
100.950(10)
105.370(10)
99.240(10)
1836.1(7)
P1h
22.1440(10)
39.726(3)
10.8680(7)
90
90
90
9560.5(10)
Fdd2
16
R (deg)
â (deg)
γ (deg)
volume, Å3
space group
Z
2
density, calcd, g/cm3
λ(Mo KR) (Å)
temp (K)
scan type
2θ range (deg)
1.274
0.710 73
298(1)
θ-2θ
3.0-50.0
1.431
0.710 73
123(2)
oscillation, 3.0°
2.05-25.18
3760
no. of independent reflns 7061
no. of reflns obsd
5306
0.754
3439
0.909
abs coeff (mm-1
)
Ra
0.0327
0.0536
Rw
GOF
0.0430b
1.00
0.1342c
1.063
largest peak in final
0.63 and -0.41
1.821 and -1.165
diff map e-/Å3
Syn th esis of (NC4H4)Ru (P Et3)2I, 5. Complex 4 (0.210 g,
0.478 mmol) and potassium iodide (0.159 g, 0.960 mmol) were
combined in 25 mL of degassed 95% ethanol. The mixture was
refluxed with stirring for 4 h, and the solvent was removed
from the resulting red solution on a rotary evaporator. The
red residue was extracted with 2 × 10 mL of toluene, and the
combined extracts were concentrated in vacuo and chromato-
graphed on a toluene/alumina column. Complex 5 was eluted
a
R ) R1 ) ∑|Fo| - |Fc|/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
c Rw ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
2
pyrr). Anal. Calcd for C40H34ClNP2Ru: C, 66.07; H, 4.68.
Found: C, 66.46; H, 4.49.
X-r a y Diffr a ction Stu d y of 1. The crystal was mounted
with epoxy cement on a glass fiber and placed into the four-
circle goniometer of a Nicolet P3/f automated diffractometer.
Cell dimensions were determined upon centering reflections
chosen from a 10 min φ rotation photograph and were refined
after centering 25 strong reflections chosen between 22° and
34° 2θ. Data collection through the range 3.0-50.0° 2θ
employed a variable speeed 2θ-θ scan. A hemisphere plus
one redundant layer was collected. Data were corrected for
Lorentz and polarization effects. All equivalent reflections
were merged, Rint ) 0.0193. Crystal data are given in Table
3.
The structure was solved by Patterson function, and ad-
ditional non-hydrogen atoms were located during subsequent
cycles of least-squares refinement followed by difference Fou-
rier synthesis. All non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms were placed
at calculated geometries and allowed to ride on the position
of the parent atom. Hydrogen thermal parameters were fixed
at 0.08 Å2. The asymmetric unit contains one molecule of
dichloromethane in addition to the ruthenium complex.
Syn th esis of (NC4H4)Ru H(P P h 3)2, 2. RuHCl(PPh3)3 (0.28
g, 0.30 mmol) and pyrrolyllithium (0.022 g, 0.30 mmol) were
combined in 25 mL of toluene. The solution was stirred and
refluxed under nitrogen for 14 h. The resulting orange
solution was filtered and concentrated in vacuo. This solution
was chromatographed on an alumina/toluene column, and 2
was eluted as a yellow band with a 15:1 mixture of toluene:
acetonitrile. Yield: 0.107 g, 52%. 1H NMR (C6D6): δ 7.56,
6.92 (2m, PPh3), 5.33, 5.03 (2s, each 2H, pyrr), -13.79 (t, J )
33 Hz, 1H, Ru-H). 13C NMR (C6D6): δ 140.3 (m, PPh3), 134.3,
127.5 (2m, PPh3), 129.3 (s, PPh3), 110.0, 82.0 (2s, pyrr). 31P
NMR (CDCl3): δ 66.1 (d, PPh3). CI+ MS: m/z 692 (M), 626
(M - pyrr). Anal. Calcd for C40H35NP2Ru: C, 69.38; H, 5.05.
Found: C, 69.17; H, 5.19.
as a red fraction with a 20:1 mixture of toluene:acetone.
A
red crystalline solid was obtained after solvent removal.
Yield: 0.198 g, 78%. 1H NMR (CDCl3): δ 5.96, 4.55 (2s, each
2H, pyrr), 1.95, 1.31 (2 m, each 6H, PEt3), 0.88 (m, 18 H, PEt3).
31P NMR (CDCl3): δ 34.70 (s, PEt3). FAB+ MS (NOBA): m/z
530 (M), 412 (M - PEt3).
Nu cleop h ilic Su bstitu tion Rea ction s. Syn th esis of (2-
P h NC4H3)Ru (P Et3)2H, 6a . Complex 4 (0.25 g, 0.57 mmol)
was dissolved in 20 mL of tetrahydrofuran, and 1.6 M
phenyllithium (0.36 mL, 0.57 mmol) was added dropwise. The
yellow-green solution turned orange within 5 min, and the
mixture was stirred for 16 h at room temperature. The solvent
was removed from the resultant orange solution, and the oily
residue was eluted on a toluene/alumina column. Complex
6a was eluted with toluene as an orange band and after solvent
removal was converted to the chloride (vide infra). 1H NMR
for 6a (C6D6): δ 8.04 (d, 2H, Ph), 7.17 (t, 2H, Ph), 7.03 (t, 1H,
Ph), 6.24, 5.46, 5.02 (3s, each 1H, pyrr), 1.30 (m, 12H, PEt3),
0.92 (m, 18H, PEt3), -14.22 (t, J ) 37 Hz, 1H, RuH). 31P NMR
(C6D6): δ 55.0 (m, PEt3). FAB+ MS (glycerol): m/z 480 (M -
H).
Syn th esis of (2-P h NC4H3)Ru (P Et3)2Cl, 6b. The oily,
orange residue of 6a was dissolved in dichloromethane. Pen-
tane was layered on top of the resultant green solution, and
the mixture was allowed to stand at room temperature for 1
week. Orange crystals of 6b, suitable for X-ray diffraction,
had formed at this point, and the nearly colorless mother liquor
was decanted from the crystals. Yield: 0.075 g, 27%. 1H NMR
(CDCl3): δ 7.70 (d, 2H, Ph), 7.33 (t, 2H, Ph), 7.31 (t, 1H, Ph),
5.64, 5.36, 4.71 (3s, each 1H, pyrr), 2.10 1.58 (2m, each 6H,
PEt3), 1.10 (m, 18H, PEt3). 31P NMR (CDCl3): δ 42.1, 36.5
(AB, J ) 47 Hz, PEt3). 13C NMR (C6D6): δ 128.7, 128.4, 128.1
(3s, Ph), 94.5, 75.3, 74.4 (3s, pyrr), 21.1 (m, PEt3), 9.1 (m, PEt3).
FAB+ MS (NOBA): m/z 515 (M), 480 (M - Cl). Anal. Calcd
for C22H38ClNP2Ru: C, 51.31; H, 7.41. Found: C, 51.69; H,
7.42.
Syn th esis of (NC4H4)Ru (P P h 3)2I, 3. Complex 1 (0.17 g,
0.24 mmol) and potassium iodide (0.81 g, 4.9 mmol) were
combined in 75 mL of degassed 95% ethanol. The solution
was refluxed with stirring for 20 h, and the solvent was
X-r a y Diffr a ct ion St u d y of (2-P h NC4H 3)R u (P E t 3)2Cl,
6b. The crystal used was selected from a sample under
Paratone oil and mounted on the drawn tip of a glass capillary
removed from the resulting orange solution on
a rotary
evaporator. The orange residue was extracted with 2 × 25

2332 Organometallics, Vol. 16, No. 11, 1997
Rakowski DuBois et al.
with a small quantity of silicone sealer. This assembly was
then placed in the 123 K nitrogen stream of a Rigaku R-Axis
II image plate diffractometer at Molecular Structure Corp.
Examination of the data frames from the image plate showed
the presence of satellite peaks neighboring each indexed
reflection. These satellites undoubtedly lead to the large
disagreement observed for refinement against all data as
collected on a Nicolet P3 instrument.
identified by NMR spectroscopy. 1H NMR (C6D6): δ 5.91, 5.14,
3.93 (3s, each 1H, pyrr), 2.53 (s, 6H, NMe2), 1.40 (m, 12H,
PEt3), 0.92 (m, 18H, PEt3), -12.61 (m, 1H, RuH). 31P NMR
(C6D6): δ 61.3, 53.9 (m, PEt3). EI+ MS: m/z 448 (M). Some
starting material and another compound, tentatively formu-
lated as (pyrr)RuH(PEt3)2, were also present in the crude
reaction mixture. However, NMR resonances were shifted
compared to those of the isolated hydride (see below). 1H NMR
(C6D6): δ 6.03, 5.02 (2s, each 2H, pyrr), 1.25 (m, 12H, PEt3),
0.98 (m, 18H, PEt3), -14.86 (t, J ) 35 Hz, 1H, RuH). 31P NMR
(C6D6): δ 55.82 (d, PEt3).
The crude mixture of hydride products was dissolved in 15
mL of chloroform and stirred for 5 min at room temperature.
The solvent was removed from the brown solution, and the
residue was chromatographed on an alumina/toluene column.
The first yellow fraction contained the desired product and was
eluted with a 20:1 mixture of toluene:acetone. Yield: 0.024
g, 22%. 1H NMR (C6D6): δ 5.22, 4.39, 4.09 (3s, each 1H, pyrr),
2.10 (s, 6H, NMe2), 2.00, 1.86, 1.46, 1.17 (4m, each 3H, PEt3),
1.05, 0.89 (2m, each 9H, PEt3). 31P NMR (C6D6): δ 45.7, 35.4
(AB pattern, J ) 45 Hz, PEt3). Anal. Calcd for C18H39ClN2P2-
Ru: C, 44.85; H, 8.09. Found: C, 44.48; H, 7.87.
Data reduction was performed on a Silicon Graphics Indy
workstation, and a solution obtained from a preliminary
dataset was applied to these structure factors. Final refine-
ment was performed on a Silicon Graphics Indigo2 workstation
using a â-release of SHELXTL version 5. The largest peaks
in the final difference map were located near the heavy atoms
and are likely to be absorption artifacts. All non-hydrogen
atoms were refined with anisotropic thermal parameters.
Hydrogen atoms were placed at calculated distances and
allowed to ride on the position of the parent atom. Values for
hydrogen thermal parameters were set to be 1.2 times the Ueq
of the corresponding carbon atom.
Syn th esis of (2,5-P h 2NC4H2)Ru Cl(P Et3)2, 7. Phenyl-
lithium (1.6 M, 0.37 mL, 0.59 mmol) was added to a solution
of 6b (0.305 g, 0.592 mmol) in 25 mL of tetrahydrofuran. The
reaction mixture was stirred for 2 h, and the solvent was
removed from the orange solution in vacuo. The Ru-H
product was dissolved in CHCl3 to form the chloride derivative.
After 5 min, the solvent was removed and the resulting product
was purified by chromatography on a toluene/alumina column.
Complex 7 was eluted as an orange band with a 10:1 mixture
of toluene:acetone. Yield: 0.085 g, 24%. 1H NMR (C6D6): δ
7.98 (d, 4H, Ph), 7.23 (t, 4H, Ph), 7.11 (t, 2H, Ph), 5.05 (s, 2H,
pyrr), 1.79 (m, 6H, PEt3), 1.31 (m, 6 H, PEt3), 0.90 (m, 18H,
PEt3). 31P NMR (C6D6): δ 35.4 (s, PEt3). FAB+ MS: m/e 591
(P), 556 (P - Cl), 473 (P - PEt3), 436 (P - PEt3, Cl). Anal.
Calcd for C28H42ClNP2Ru: C, 56.90; H, 7.11. Found: C, 56.97;
H, 7.10.
A second yellow fraction was eluted with a 10:1 mixture of
toluene:acetone and was identified as the starting reagent 4.
Yield: 29%.
Rea ction of 4 w ith LiBEt3H a n d LiBEt3D. Complex 4
(0.118 g, 0.269 mmol) was dissolved in 20 mL of tetrahydro-
furan. The hydride reagent (1 M in THF) (0.27 mL, 0.269
mmol) was added dropwise, and the solution was stirred at
room temperature under nitrogen for 8 h. The solvent was
removed from the resultant yellow solution in vacuo, yielding
a yellow oil, which was formulated as (η5-NC4H4)Ru(PEt3)2H.
1H NMR (C6D6): δ 5.84, 4.85 (2 s, each 2 H, pyrr), 1.34, 1.19
(2 m, each 6 H, PEt3), 0.81 (m, 18 H, PEt3), -16.58 (t, 1 H,
Ru-H). 31P NMR (C6D6): δ 48.93 (m, PEt3). FAB MS: m/e
404 (m). The same procedure was followed for the reaction of
4 with LiBEt3D to form (η5-NC4H3D)Ru(PEt3)2H. 1H NMR
(C6D6): same as above, but the resonance at δ 5.84 is reduced
in intensity. 2H NMR (CDCl3): δ 5.87 (s, pyrr). No resonance
observed in hydride region.
Syn th esis of (η5-2-CN(Me)CH)NC4H3)Ru (P Et3)2H. (η5-
NC4H4)Ru(PEt3)2I, 5, (0.342 g, 0.645 mmol) was dissolved in
25 mL of THF and cooled to -78 °C. A solution of LiCH(Me)-
CN in 10 mL of THF, prepared in situ at -78 °C (0.139 g,
2.26 mmol), was added dropwise. The mixture was allowed
to warm to room temperature and stirred for 14 h. The solvent
was removed from the resultant orange solution, and the 1H
NMR spectrum of the residue was recorded. The spectrum
showed resonances for unreacted 5 (60%) and for two new
products, which were tentatively identified as diasteromers
of 2-((CH(Me)CN)C4H3N)RuH(PEt3)2. Attempts to isolate
these products by chromatography on an alumina column led
to decomposition of the hydride derivatives. 1H NMR (both
isomers, C6D6): δ 6.00, 5.96, 5.18, 5.13, 4.73, 4.69 (6 s, each 1
H, pyrr), 3.84 (q, CHMeCN) (second quartet may be obscured
by THF (solvent) resonance), 1.66 (d, 6 H, Me), 1.41, 1.15 (2m,
each 18 H, PEt3), 0.92 (m, 36 H, PEt3), -12.94, -13.01 (2 t,
each 1 H, RuH). 31P NMR (C6D6): δ 54.32, 59.64 (2 m, PEt3).
Attempts to convert the hydride product to the chloride
derivative with chloroform or CH2Cl2 over a period of 1 day
were not successful.
Syn th eses of (2-MeNC4H3)Ru (P Et3)2H an d (2-MeNC4H3)-
Ru (P Et3)2Cl. Complex 4 (0.12 g, 0.27 mmol) was dissolved
in 15 mL of tetrahydrofuran, and the solution was cooled to 0
°C. MeLi (1.2 M, 0.22 mL, 0.27 mmol) was added dropwise
with stirring. The reaction mixture was stirred at room
temperature for 16 h, and the solvent was removed in vacuo
providing a brown residue. A concentrated toluene solution
of the residue was chromatographed on an alumina column.
A yellow fraction was eluted with 10:1 toluene:acetone and
was found to be (2-Mepyrr)RuH(PEt3)2, which was isolated as
an oily, yellow solid. Approximate yield: 0.035 g, 31%. 1H
NMR (C6D6): δ 5.92, 4.90, 4.59 (3s, each 1H, pyrr), 2.53 (s,
3H, pyrrMe), 1.98, 1.39 (2m, each 6H, PEt3), 1.02 (m, 18H,
PEt3), -13.45 (t, J ) 35 Hz, 1H, RuH). 31P NMR (C6D6): δ
59.5, 55.0 (2m, PEt3). FAB+ MS (NOBA): m/z 419 (M).
(2-MeNC4H3)RuH(PEt3)2 (0.035 g, 0.16 mmol) was dissolved
in 10 mL of chloroform. The brown solution was stirred for 5
min, and the solvent was removed in vacuo. A concentrated
toluene solution of the residue was chromatographed on a
toluene/alumina column, and a yellow band was eluted with
a 10:1 mixture of toluene:acetone. The product (2-MeNC4H3)-
RuCl(PEt3)2 was isolated as a yellow residue. Yield: 0.009 g,
24%. 1H NMR (CDCl3): δ 5.37, 4.74, 4.51 (3s, each 1H, pyrr),
2.12, 2.01, 1.61, 1.50 (4m, each 3H, PEt3), 1.98 (s, 3H, pyrrMe),
1.08 (m, 18H, PEt3). 31P NMR (CDCl3): δ 42.5, 35.0 (AB, J )
44 Hz, PEt3). 13C NMR (CDCl3): δ 90.9, 79.8, 76.9, 73.1 (4s,
pyrr), 20.8 (m, PEt3), 14.7 (s, pyrrMe), 8.3 (m, PEt3). EI+ MS:
m/z 453 (M), 335 (M - PEt3). Anal. Calcd for C17H36ClNP2-
Ru: C, 45.08; H, 7.45. Found: C, 45.14; H, 7.87.
Rea ction of (η5-C4H4N)Ru Cl(P Et3)2 w ith Na SMe. Com-
plex 4 (0.055 g, 0.125 mmol) and sodium methylthiolate (0.018
g, 0.257 mmol) were combined in 5 mL of tetrahydrofuran.
The mixture was stirred at 45 °C for 2 days, and the solvent
was removed from the resultant brown solution in vacuo. The
NMR spectrum showed the presence of starting material and
a small amount (ca. 20%) of a new product, which was
tentatively identified as (η5-C4H4N)Ru(SMe)(PEt3)2. There was
no evidence for nucleophilic attack at the pyrrolyl ring. 1H
NMR (C6D6): δ 5.95, 4.75 (2s, each 2H, pyrr), 2.65 (s, 3H, SMe),
Syn th esis of [2-(NMe2)NC4H3]Ru H(P Et3)2 an d [2-(NMe2)-
NC4H 3]R u Cl(P E t 3)2. Complex 4 (0.102 g, 0.23 mmol) and
lithium dimethylamide (0.012 g, 0.24 mmol) were combined
in 10 mL of tetrahydrofuran. The yellow solution was stirred
for 16 h, and the solvent was removed from the resultant
orange solution in vacuo. The resulting hydride product was

Nucleophilic Substitution of η5-Pyrrolyl Ligands
Organometallics, Vol. 16, No. 11, 1997 2333
2.10, 1.82 (2m, each 6H, PEt3), 0.91 (m, 18H, PEt3). 31P NMR
(C6D6): δ 39.1 (s, PEt3). FAB+ MS (glycerol): m/z 451 (M).
Reaction of (η5-C4H4N)Ru Cl(P Et3)2 with LiS-t-Bu . Com-
plex 6 (0.039 g, 0.089 mmol) and lithium tert-butylthiolate
(0.009 g, 0.09 mmol) were combined in 5 mL of tetrahydrofuran
and stirred at 45 °C for 2 days. The solvent was removed from
the resultant brown solution, and the residue was examined
via NMR spectroscopy. The major portion was unreacted 6
(ca. 50%), but a new product (ca. 30%) was present along with
unidentified impurities. 1H NMR for (η5-C4H4N)RuStBu(PEt3)2
(C6D6): δ 6.15, 4.79 (2s, each 2H, pyrr), 1.69 (s, 9H, StBu),
1.88, 1.28 (2m, each 6H, PEt3), 0.92 (m, 18H, PEt3). 31P NMR
(C6D6): δ 37.1 (s, PEt3). FAB+ MS (glycerol): m/z 493 (M).
Attem p ted Rea ction of 4 w ith Alk oxid es. Complex 4
(0.019 g, 0.043 mmol) and a molar excess of NaOR (R ) Me,
1.2 equiv, or R ) t-Bu, ca. 5 equiv) were combined in 5 mL of
tetrahydrofuran. The solution was heated at 45 °C in an oil
bath for 2 days. No evidence for a reaction was seen by NMR.
Nu cleop h ilic Su b st it u t ion s of Tr ip h en ylp h osp h in e
Der iva tives. Syn th esis of (2-MeNC4H3)Ru H(P P h 3)2 a n d
(2-MeNC4H3)Ru I(P P h 3)2. (η5-NC4H4)Ru(PPh3)2I, 3 (0.027 g,
0.033 mmol), was dissolved in 10 mL of tetrahydrofuran.
Methyllithium (1.2 M, 0.035 mL, 0.029 mmol) was added to
the orange solution. The reaction mixture slowly (ca. 30 min)
became yellow, and the reaction mixture continued to stir for
16 h. The solvent was removed in vacuo, providing a orange-
yellow, oily residue. 1H NMR (C6D6): δ 7.65, 7.53 (2m, each
6H, PPh3), 6.95 (m, 18H, PPh3), 5.19, 4.90, 4.87 (3s, each 1H,
pyrr), 2.10 (s, 3H, pyrrMe), -14.12 (t, J ) 34 Hz, 1H, RuH).
31P NMR (C6D6): δ 68.5, 66.7 (2m, PEt3). FAB+ MS (NOBA):
m/z 706 (M - H), 626 (M - H - Mepyrr), 444 (M - H - PPh3).
This product was converted to the iodide complex by the
following procedure. Iodine (0.036 g, 0.14 mmol) was added
to a slurry of the crude hydride product and potassium
carbonate (0.5 g) in dichloromethane. The solution im-
mediately became dark orange as the iodine dissolved and was
stirred for an hour. The solvent was removed in vacuo,
yielding a dark brown residue. 1H NMR (CDCl3): δ 7.40, 7.33,
7.21, 7.12 (4m, PPh3), 4.90, 4.54, 3.18 (3s, each 1H, pyrr), 2.25
(s, 3H, Me). 13C NMR (CDCl3): δ 137.6 (m, PPh3), 134.0 (m,
PPh3), 128.8 (m, PPh3), 126.9 (m, PPh3), 102.3, 76.8 (2s, pyrr),
84.7 (s, pyrr), 14.0 (s, Me). 31P NMR (C6D6): δ 45.2, 41.7 (2d,
J ) 44 Hz, PEt3). FAB+ MS (NOBA): m/z 834 (M + H), 754
(M - Mepyrr), 707 (M - I).
Syn th esis of (2-Bu NC4H3)Ru Cl(P P h 3)2. Complex 1 (2.00
g, 2.75 mmol) was dissolved in 25 mL of tetrahydrofuran.
n-Butyllithium (1.2 M, 2.29 mL, 2.75 mmol) was added
dropwise, and the solution was stirred at room temperature
for 4 h. The solvent was removed in vacuo, and the red oil
was dissolved in CHCl3 and stirred for 5 min to convert the
hydride product to the chloride. The solvent was removed, and
the oil was eluted as a red band on a toluene/alumina column
with a 10:1 mixture of toluene:acetone. Yield: 0.75 g, 35%.
1H NMR (CDCl3): δ 7.73, 7.64 (2m, each 6H, PPh3), 5.13, 4.59,
3.24 (3s, each 1H, pyrr), 2.92, 1.81, 1.41 (3m, 2H each, Bu),
0.90 (t, 3H, Bu). 31P NMR (CDCl3): δ 45.2, 43.2 (AB, PPh3).
No reaction of 1 was observed with PhLi or LiEt3BH at room
temperature or with MeLi at 60 °C.
Rea ction of (2-P h NC4H3)Ru H(P Et3)2, 6a , w ith HCl a n d
Isola tion of 2-P h en ylp yr r ole. Complex 6a (0.079 g, 0.15
mmol) was dissolved in 10 mL of tetrahydrofuran. Hydrogen
chloride gas was then passed through the solution for 1 min.
The orange solution immediately became red-brown, and the
solvent was removed after 5 min. The residue was redissolved
in toluene and loaded onto an alumina column. Toluene, 150
mL, followed by 150 mL of diethyl ether was passed through
the column to elute crude 2-phenylpyrrole as a tan solid in
near quantitative yield. The product was identified by 1H
NMR spectroscopy (see below). A yellow band, presumably
containing the ruthenium residue, remained behind on the
column. The 2-phenylpyrrole could be further purified by
sublimation; however, this reduced the yield to ca. 0.10 g, 45%.
1H NMR (CDCl3): δ 8.50 (br s, 1H, NH), 7.47 (d, 2H, Ph), 7.35
(t, 2H, Ph), 7.18 (t, 1H, Ph), 6.86, 6.51, 6.28 (3s, each 1H, pyrr).
EI+ MS: m/z 143 (M).
Rea ction of (2-Bu NC4H3)Ru (P P h 3)2Cl w ith HCl a n d
Regen er a tion of 1. (2-BuNC4H3)RuCl(PPh3)2Cl (0.242 g,
0.309 mmol) was dissolved in 20 mL of THF. Hydrogen
chloride was bubbled through the solution for 15 s, resulting
in a deep red solution. The solvent was evaporated in vacuo,
and the neutral pyrrole, 2-BuHNC4H3, was extracted from the
red residue with 5 × 5 mL of diethyl ether and identified by
NMR spectroscopy. Yield: 65%. 1H NMR (C6D6): δ 7.65 (br,
1 H, NH), 6.37, 6.29, 6.08 (br, 1 H each, pyrr), 2.3, 1.63, 0.72
(m, Bu).
PPh3 (0.154 g, 0.587 mmol) was added to the remaining
yellow residue, and the mixture was refluxed in methanol for
18 h. A red-brown precipitate formed, which was identified
by NMR spectroscopy as RuCl2(PPh3)3. Yield: 0.110 g, 37%.
After the product was washed with 2 × 5 mL of hexane,
pyrrolyllithium was added (0.018 g, 0.246 mmol) and the
mixture was dissolved in toluene. The solution was refluxed
for 3 h, then the solvent was removed and the product, 1, was
purified by chromatography as described above. Yield: 0.075
g, 33%.
Syn th esis of [(NC4H4)Ru (P Et3)3]P F 6. Complex 4 (0.497
g, 0.683 mmol) and LiPF6 (0.10 g, 0.69 mmol) were dissolved
in 125 mL of degassed 95% ethanol. Triethylphosphine (0.80
mL, 5.5 mmol) was added, and the solution refluxed while
stirring under nitrogen for 2 h. The initial orange solution
had become pale yellow. The solvent was removed in vacuo,
and a concentrated dichloromethane solution of the residue
was layered with pentane to precipitate the product as a light
gray solid. Yield: 0.565 g, 75%. 1H NMR (CDCl3): δ 6.15,
5.62 (2s, each 2H, pyrr), 1.82 (m, 18H, PEt3), 1.16 (m, 27H,
PEt3). 31P NMR (CDCl3): δ 30.0 (s, PEt3), -64.39 (PF6-).
FAB+ MS (NOBA): m/z 521 (M+), 404 (M+ - PEt3). Anal.
Calcd for C22H49NP2F6Ru: C, 39.66; H, 7.36. Found: C, 39.40;
H, 7.32.
Syn th esis of [(NC4H4)Ru (P Et3)2(CO)]P F 6. Complex 4
(0.125 g, 0.285 mmol) and LiPF6 (0.045 g, 0.296 mmol) were
dissolved in 15 mL of tetrahydrofuran, and the mixture was
warmed to 65 °C. Carbon monoxide gas was then bubbled
through the solution for 5 h in a fume hood. The initial orange
solution changed to pale yellow. The solvent was removed in
vacuo, and the residue was purified via recrystallization with
dichloromethane/diethyl ether to yield
a white powder.
Yield: 0.103 g, 63%. 1H NMR (DMSO): δ 6.90, 6.26 (2 s, each
2 H, pyrr), 1.98, 1.88 (2 m, each 6 H, PEt3), 1.05 (m, 18 H
PEt3). 31P NMR (DMSO): 41.5 (br, PEt3). FAB+ MS
(NOBA): m/e 421 (M+), 303 (M+ - CO). IR (KBr): 1968 cm-1
(νCO). Anal. Calcd for C17H34NOPF6Ru: C, 35.42; H, 5.89.
Found: C, 35.22; H, 5.66.
Syn th esis of [(η5-NC4H4)Ru (NCCH3)(P Et3)2]BP h 4. Com-
plex 4 (0.242 g, 0.551 mmol) and sodium tetraphenylborate
(0.375 g, 1.10 mmol) were dissolved in 15 mL of EtOH.
Acetonitrile (0.057 mL, 1.10 mmol) was syringed into the
solution, which was stirred for 14 h. The orange color changed
to green, and an off-white precipitate formed. The solid was
filtered and washed with 3 × 10 mL of EtOH. Yield: 0.247 g,
58%. 1H NMR (CDCl3): δ 7.33 (m, 8H, BPh4), 6.91 (t, 8 H,
BPh4), 6.76 (t, 4 H, BPh4), 6.24, 5.36 (2s, each 2 H, pyrr), 2.57
(s, 3 H, CH3CN), 2.03, 1.82 (2 m, each 6 H, PEt3), 1.13 (m, 18
H, PEt3). 31P NMR (CDCl3): δ 37.8 (PEt3). FAB+ MS
(NOBA): m/z 443 (M), 404 (M - CH3CN). Anal. Calcd for
C
42H57N2PBRu: C, 66.10; H, 7.47. Found: C, 65.85; H, 7.68.
Syn th esis of [(HNC4H4)Ru Cl(P P h 3)2]OTf. Complex 1
(0.100 g, 0.138 mmol) was dissolved in 10 mL of toluene.
Trifluoromethanesulfonic acid (0.012 mL, 0.14 mmol) was
added, and the solution stirred for 14 h. The solvent was
removed in vacuo. Yield: 0.102 g, 84%. Attempts at purifica-
tion via recrystallization with dichloromethane/pentane and
chromatography with a toluene/alumina column both led to
decomposition of the product via loss of pyrrole. 1H NMR

2334 Organometallics, Vol. 16, No. 11, 1997
Rakowski DuBois et al.
(CDCl3): δ 7.36-7.00 (br m, 30H, PPh3), 6.32, 4.62 (2s, each
2H, pyrr). 31P NMR (CDCl3): δ 37.9 (s, PPh3). FAB+ MS
(NOBA): m/z 728 (M - OTf), 727 (M - HOTf).
a
similar procedure, no reaction was observed with (2-
acetylpyrrolyl)lithium.
Syn th esis of [(1-Me-NC4H4)Ru Cl(P P h 3)2]OTf. Complex
1 (0.16 g, 0.22 mmol) was dissolved in 13 mL of toluene.
Methyl trifluoromethanesulfonate (0.026 mL, 0.22 mmol) was
added dropwise, and the solution stirred for 1 h. A pale
orange, crystalline precipitate formed, and the colorless solvent
was removed by cannula. Yield: 0.050 g, 26%. 1H NMR
(CDCl3): δ 7.33-7.20 (m, 30H, PPh3), 6.30, 4.75 (2s, each 2H,
pyrr), 2.21 (s, 3H, NMe). 31P NMR (CDCl3): δ 37.3 (s, PPh3).
At t em p t ed R ea ct ion s of R u Cl2(P P h 3)3 w it h (Tet r a -
m eth ylp yr r olyl)lith iu m a n d (2-Acetylp yr r olyl)lith iu m .
RuCl2(PPh3)3 (0.017 g, 0.018 mmol) and (tetramethylpyrrolyl)-
lithium (0.003 g, 0.023 mmol) were combined in 0.6 mL of C6D6
in an NMR tube. The tube was flame-sealed under vacuum
and placed in a 45 °C oil bath. NMR spectroscopy showed no
evidence of tetramethylpyrrole coordination after 3 days. In
Ack n ow led gm en t. This work was supported by a
grant from the Division of Chemical Sciences, Office of
Basic Energy Sciences, Office of Energy Research, U.S.
Department of Energy. Part of the structural determi-
nations were performed using equipment acquired
under National Science Foundation Grant No. CHE-
9505926.
Su p p or tin g In for m a tion Ava ila ble: Tables of data col-
lection and refinement details, atomic coordinates, bond
distances and angles, hydrogen atom coordinates, and thermal
parameters for 1 and 6b (23 pages). Ordering information is
given on any current masthead page.
OM9700268