Synthesis and reactivity of the octahedral d6 parent amido complexes TpRu(L)(L′)(NH2) (Tp = hydridotris(pyrazolyl)borate; L = L′ = PMe3, P(OMe)3; L = CO, L′ = PPh3) and [TpRu(PPh3)(NH2)2][Li]

Article abstract of DOI:10.1021/om010739x

A series of octahedral ruthenium(II) parent amido complexes of the type TpRu(L)(L′)(NH₂) (L/L′ = neutral and two-electron-donor ligands) and [TpRu(PPh₃)(NH₂)₂][Li] (Tp = hydridotris(pyrazolyl)borate) have been prepared. Preliminary reactivity studies indicate that the amido moieties are highly basic: for example, TpRu(L)(L′)(NH₂) complexes deprotonate phenylacetylene at room temperature to form [TpRu(L)(L′)(NH₃)][PhC₂] ion pairs, as determined by ¹H NMR spectroscopy.

Full text of DOI:10.1021/om010739x

5254
Organometallics 2001, 20, 5254-5256
Syn th esis a n d Rea ctivity of th e Octa h ed r a l d 6 P a r en t
Am id o Com p lexes Tp Ru (L)(L′)(NH2) (Tp )
Hyd r id otr is(p yr a zolyl)bor a te; L ) L′ ) P Me3, P (OMe)3; L
) CO, L′ ) P P h 3) a n d [Tp Ru (P P h 3)(NH2)2][Li]
K. N. J ayaprakash, David Conner, and T. Brent Gunnoe*
Department of Chemistry, North Carolina State University,
Raleigh, North Carolina 27695-8204
Received August 13, 2001
Summary: A series of octahedral ruthenium(II) parent
amido complexes of the type TpRu(L)(L′)(NH2) (L/ L′ )
neutral and two-electron-donor ligands) and [TpRu-
(PPh3)(NH2)2][Li] (Tp ) hydridotris(pyrazolyl)borate)
have been prepared. Preliminary reactivity studies in-
dicate that the amido moieties are highly basic: for
example, TpRu(L)(L′)(NH2) complexes deprotonate phen-
ylacetylene at room temperature to form [TpRu(L)(L′)-
(NH3)][PhC2] ion pairs, as determined by 1H NMR
spectroscopy.
ability to deprotonate several C-H bonds. Such extraor-
dinary basicity and reactivity raises several questions,
including the following: (1) is the enhanced basicity a
general feature of such complexes and (2) what features
control the amido reactivity? To begin to answer these
questions, complexes with variable ancillary ligands
must be accessed. We now report the synthesis and
preliminary reactivity of the first example (to our
knowledge) of a series of octahedral and d6 parent amido
complexes in which the ancillary ligands are systemati-
cally varied. Particularly germane here are CpRuII (Cp
) cyclopentadienyl) phosphine complexes with amido
ligands reported by Roundhill et al.12
{TpRu(L)(L′)} complexes have received significant
recent attention.13 These fragments offer the significant
synthetic advantage of being able to systematically
control the steric and electronic features of the metal
coordination sphere via variation of L and L′. Reflux of
the known complex TpRu(PPh3)2(Cl)14 with excess tri-
methylphosphine or trimethyl phosphite in toluene
yields TpRu(PMe3)2(Cl) (1) and TpRu{P(OMe)3}2(Cl) (2)
in high yields (95% and 87%, respectively) after workup.
Reactions of 1, 2, TpRu(CO)(PPh3)(Cl),15 and TpRu-
(PPh3)2(Cl) with AgOTf yield the corresponding triflate
complexes TpRu(PMe3)2(OTf) (3), TpRu{P(OMe)3}2(OTf)
(4), TpRu(CO)(PPh3)(OTf) (5), and TpRu(PPh3)2(OTf)
(6). Complexes 3-5 can be isolated cleanly, while the
triphenylphosphine complex 6 has eluded isolation and
is generated in situ. Reactions of complexes 3-6 in
different solvents at variable temperatures with metal
amides (e.g., NaNH2 or LiNH2) or metal amides in
combination with ammonia result in no reaction, isola-
tion of the corresponding ammine complexes, or decom-
position.
The synthesis and reactivity of late-metal complexes
with heteroatomic π-donating ligands have received
significant recent attention.1-6 Efforts in this area have
been prompted in part due to the expectation that the
combination of “soft” late metals with “hard” donor
ligands (e.g., oxygen- and nitrogen-based ligands) can
result in weak bonds and reactive ligand moieties;
however, thermochemical studies of metal-heteroatom
bond strengths suggest that homolytic bond strengths
between late metals and heteroatom ligands are not
inherently weak.7,8 Additionally, it has been suggested
that the scarcity of late-metal systems with π-donating
ligands is due to the presence of π-conflict between filled
metal dπ orbitals and lone electron pairs residing on
the π-donating ligands.1,9 Recently, application of Dra-
go’s E-C bonding theory to understanding the bonding
and reactivity of such complexes has been reported and
raises questions as to the importance of π-π repulsion
in such systems.3
Bergman et al.'s recent reports of the synthesis and
reactivity of the Ru(II) complex trans-(DMPE)2Ru(H)-
(NH2) (DMPE ) 1,2-bis(dimethylphosphinoethane)) pro-
vide a striking example of a highly reactive ruthenium
amido moiety.10,11 The parent amido ligand of this
complex exhibits remarkable reactivity, including the
Reaction of 3-6 with excess NH3 in THF yields the
cationic ammine complexes [TpRu(PMe3)2(NH3)][OTf]
(7), [TpRu{P(OMe)3}2(NH3)][OTf] (8), [TpRu(CO)(PPh3)-
(NH3)][OTf] (9), and [TpRu(PPh3)(NH3)2][OTf] (10) in
high yields (74-95% yield) (Scheme 1).16 Attempts to
suppress PPh3/NH3 ligand exchange for complex 10 to
allow the isolation of [TpRu(PPh3)2(NH3)][OTf] have
(1) Mayer, J . M. Comments Inorg. Chem. 1988, 8, 125-135.
(2) Bergman, R. G. Polyhedron 1995, 14, 3227-3237.
(3) Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments Inorg.
Chem. 1999, 21, 115-129.
(4) Cundari, T. R. Chem. Rev. 2000, 100, 807-818.
(5) Sharp, P. R. Comments Inorg. Chem. 1999, 21, 85-114.
(6) Sharp, P. R. J . Chem. Soc., Dalton Trans. 2000, 2647-2657.
(7) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw, J .
E. J . Am. Chem. Soc. 1987, 109, 1444-1456.
(12) J oslin, F. L.; J ohnson, M. P.; Mague, J . T.; Roundhill, D. M.
Organometallics 1991, 10, 2781-2794.
(13) Slugovc, C.; Schmid, R.; Kirchner, K. Coord. Chem. Rev. 1999,
185-186, 109-126.
(14) Buriez, B.; Burns, I. D.; Hill, A. F.; White, A. J . P.; Williams,
D. J .; Wilton-Ely, J . D. E. T. Organometallics 1999, 18, 1504-1516.
(15) Sun, N.-Y.; Simpson, S. J . J . Organomet. Chem. 1992, 434, 341-
349.
(8) Hartwig, J . F.; Andersen, R. A.; Bergman, R. G. Organometallics
1991, 10, 1875-1887.
(9) Caulton, K. G. New J . Chem. 1994, 18, 25-41.
(10) Kaplan, A. W.; Ritter, J . C. M.; Bergman, R. G. J . Am. Chem.
Soc. 1998, 120, 6828-6829.
(11) Fulton, J . R.; Bouwkamp, M. W.; Bergman, R. G. J . Am. Chem.
Soc. 2000, 122, 8799-8800.
10.1021/om010739x CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/10/2001

Communications
Organometallics, Vol. 20, No. 25, 2001 5255
Ta ble 1. 1H a n d 31P NMR Ch em ica l Sh ifts (p p m )
Sch em e 1. P r ep a r a tion of Am m in e Com p lexes
7-10 a n d Am id o Com p lexes 11-14a
for Com p lexes 11-14
NH2 resonance
complex
(1H NMR)
31P NMRa
TpRu(PMe3)2(NH2) (11)
-2.20
-1.91
-1.79
-2.60
17.5
-11.3
48.7
TpRu{P(OMe)3}2(NH2) (12)
TpRu(CO)(PPh3)(NH2) (13)
[TpRu(PPh3)(NH2)2][Li] (14)
-3.5
a
Referenced to external 85% phosphoric acid.
the amido complexes are only persistent for a few days.
Thus, attempts at recrystallization and clean elemental
analysis were not successful. Complexes 11-14 display
upfield chemical shifts (1H NMR) for the amido protons,
and the relative chemical shifts of 11-13 are consistent
with the donating ability of L and L′ (Table 1). That is,
the more donating L and L′ are, the more upfield the
chemical shift for the NH2 resonances. Given the highly
reactive nature of the neutral monoamido complexes
11-13, we anticipate that the amido ligands of 14 are
electronically stabilized by direct interaction with the
lithium cation. The 1H NMR of 14 shows equivalent NH2
ligands (broad singlet at -2.60 ppm integrated for 4H),
and variable-temperature NMR reveals that this singlet
decoalesces into two broad singlets (each 2H) at low
temperature. The variable-temperature NMR studies
are consistent with rapid exchange of the lithium cation
between the two amido ligands.
a
Note that complex 14 is anionic with a lithium counterion.
Combination of the amido complex 11 with ap-
proximately 1 equiv of phenylacetylene in an NMR tube
reaction (THF-d8) results in reaction during the time
thus far failed. For example, reaction of 6 with a THF
solution of NH3 at -78 °C results in the isolation of a
solid whose 1H NMR spectrum is consistent with an
approximately 1:1 ratio of [TpRu(PPh3)(NH3)2][OTf] (10)
and [TpRu(PPh3)2(NH3)][OTf].
1
between sample preparation and H NMR acquisition.
1
In the H NMR spectrum of the reaction mixture, the
upfield resonance due to the amido ligand is absent, as
is the characteristic acetylene proton of phenylacetylene,
and a broad singlet at 2.23 ppm (3H) is observed. These
observations are consistent with rapid deprotonation of
phenylacetylene (pKa ≈ 23) by the amido ligand of 11
to yield a cationic amine complex with phenylacetylide
anion as the counterion (Scheme 2).20 The aromatic
protons for the acetylide moiety are observed as mul-
tiplets at 7.25 and 7.38 ppm. Heating the reaction
mixture at 80 °C for approximately 21 h results in the
formation of several new intractable Tp-containing
complexes. Although the rate of reaction varies, analo-
gous results for 12 and 13 are observed. Complexes 15-
17 are highly reactive, and all attempts at isolation have
thus far failed. For the reaction of TpRu(CO)(PPh3)-
(NH2) (13) with phenylacetylene, more than 24 h is
Examples of octahedral and d6 parent amido com-
plexes are scant compared with amido complexes with
lower d-electron counts.7,8,10-12,17,18 Reaction of the cat-
ionic ammine complexes 7-10 with methyllithium
results in formation of the corresponding parent amido
complexes TpRu(PMe3)2(NH2) (11; 95%), TpRu{P(O-
Me)3}2(NH2) (12; 57%), TpRu(CO)(PPh3)(NH2) (13; 91%),
and [TpRu(PPh3)(NH2)2][Li] (14; 95%) (Scheme 1).19
Complexes 11-13 have been characterized by 1H NMR,
13C NMR, 31P NMR, and IR spectroscopy as well as mass
spectrometry. Under inert atmosphere in the solid state,
(16) The following is a representative procedure. [TpRu{P(OMe)3}2-
(NH3)][OTf] (8). To a solution of TpRu{P(OMe)3}2Cl (2; 1.2549 g, 2.102
mmol) in approximately 50 mL of THF was added a solution of AgOTf
(0.5413 g, 2.108 mmol, 15 mL of THF). The solution was refluxed for
20 h, cooled to room temperature, and vacuum-filtered through a fine-
porosity frit. To the yellow filtrate was added a solution of ammonia
in THF. The mixture was stirred for 24 h at room temperature, during
which time a color change to pale pink was observed. The reaction
solution was concentrated to approximately 40 mL in vacuo, and
hexanes (approximately 40 mL) were added to precipitate the product.
The resulting solid was collected via vacuum filtration through a fine-
porosity frit and washed with hexanes (3 × 10 mL) to give a white
(19) The following is a representative procedure. TpRu(PMe3)2(NH2)
(11). A solution of [TpRu(PMe3)2(NH3)][OTf] (7; 0.2423 g, 0.383 mmol)
was dissolved in THF (∼15 mL) and cooled to -78 °C. MeLi (0.30 mL,
1.4 M solution in diethyl ether, 0.42 mmol) was added dropwise via a
microsyringe. The solution turned immediately turned pale yellow, and
stirring was continued for another 5 min at -78 °C. The slush bath
was removed, and the reaction mixture was warmed to room temper-
ature. The solvent was removed under reduced pressure to give a
yellow-brown solid. The solid was dissolved in toluene (20 mL) and
filtered through a fine-porosity frit. Removal of solvent from the filtrate
in vacuo gave the desired product in 95% yield (0.175 g). IR (THF):
solid (1.134 g, 74% yield). IR (thin film on KBr plate): νNH ) 3359
-1
cm
.
1H NMR (CD2Cl2, δ): 7.79 (4H, overlapping m, Tp CH-3 or -5),
7.75, 7.63 (each 1H, each a d, Tp CH-3 or -5), 6.32 (2H, t, Tp CH-4),
6.17 (1H, t, Tp CH-4), 3.37 (18H, vt, J PH ) 10 Hz, P(OCH3)3), 2.09
(3H, bs, NH3). 13C{1H} NMR (CD3CN, δ): 148.7, 144.6, 138.2, 137.3
(each a s, Tp CH-3 or -5), 107.6, 107.5 (each a s, Tp CH-4), 53.2 (s,
P(OCH3)3). 31P{1H} NMR (CD3CN, δ): -21.0 (s, P(OCH3)3). CV (CH3-
CN, TBAH, 100 mV/s): E1/2 ) 1.40 V (Ru(III/II)). Anal. Calcd for C16H31
BF3N7O9P2RuS: C, 26.39; H, 4.29; N, 13.46; Found: C, 26.22; H, 4.23;
N, 13.23.
νBH ) 2463 cm-1, νNH ) 3115, 3230 cm-1 1H NMR (C6D6, δ): 7.87,
.
7.55, 7.48, 7.15 (6H, 2:1:2:1 integration, each a d, Tp CH-3 or -5
position), 6.00, 5.88 (3H, 2:1 integration, each a t, Tp CH-4 position),
1.07 (18H, vt, J PH ) 10 Hz, P(CH3)3), -2.20 (2H, bs, NH2). 13C{1H}
NMR (C6D6, δ): 145.4, 142.8, 13.9, 135.3 (Tp 3- or 5-position), 105.8,
105.4 (Tp 4-position), 18.6 (t, J PC ) 12 Hz, P(CH3)3). 31P{1H} NMR
(C6D6, δ): 17.5 (PMe3). FAB MS (m/z): 483.1 [TpRu(PMe3)2(NH2)]+,
467.1 [TpRu(PMe3)2]+.
-
(17) Macgregor, S. A.; MacQueen, D. Inorg. Chem. 1999, 38, 4868-
4876.
(18) Dewey, M. A.; Knight, D. A.; Arif, A.; Gladysz, J . A. Chem. Ber.
1992, 125, 815-824.
(20) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in
Organic Chemistry, 3rd ed.; Harper Collins: New York, 1987.

5256 Organometallics, Vol. 20, No. 25, 2001
Communications
Sch em e 2. Rea ction of Am id o Com p lexes 11-13
ammonia dissociation (regardless of mechanistic details)
may be kinetically more inert for the TpRu complexes
reported herein. In addition, the presence of nonchelat-
ing phosphine ligands for 11-13 could afford alternative
reaction pathways not readily available for trans-
(DMPE)2Ru(H)(NH2). Preliminary results indicate that
analogous reactions with TpRu(L)(L′)(NHtBu) (L ) L′
) PMe3, P(OMe)3; L ) CO, L′ ) PPh3) proceed more
cleanly than for the parent amido systems, and consis-
tent with this observation is the more labile nature of
tBuNH2 ligands compared with NH3 for the TpRu
complexes discussed herein.21 In addition, the phenyl
amido complex TpRu(CO)(PPh3)(NHPh) does not depro-
tonate phenylacetylene at room temperature, indicating
that the phenyl substituent mitigates the basicity of the
amido moiety.22 This is consistent with the fact that
ammonia is more basic than aniline; however, more
thorough studies will be required to quantitatively
compare the basicity differences.
w ith P h en yla cetylen e
The first examples of octahedral and d6 amido com-
plexes with variable ancillary ligands have been re-
ported, along with initial reactivity studies. These
systems exhibit a highly basic amido ligand, indicating
that such reactivity could be a general feature of this
class of amido complexes. A highlight of our preliminary
efforts is the qualitative demonstration that the ancil-
lary ligands impact the kinetics of amido reactivity with
phenylacetylene as well as play an important role in
ultimate reaction pathways.
required to fully deprotonate phenylacetylene. The
reaction of complex 12 with phenylacetylene occurs
before acquisition of the 1H NMR spectrum can be
completed. Consistent with the case for complex 15,
heating THF-d8 solutions of 16 and 17 results in the
formation of multiple and intractable products. The
qualitative kinetic trend for the deprotonation of the
acetylene C-H bond corresponds to the donating abili-
ties of the ancillary ligands (11 ≈ 12 > 13); however,
contributions from steric factors could also be important.
The complicated reactivity product mixtures resulting
from the reaction of 11-13 with phenylacetylene with
heating contrasts with that reported for trans-
(DMPE)2Ru(H)(NH2), and two features likely contribute
to the observed differences in reactivity. First, while
deprotonation reactions by the amido ligands appear to
be relatively facile, subsequent cleavage of the Ru-NH3
bonds may be more difficult for the TpRu systems. Thus,
while [(DMPE)2Ru(H)(NH3)][X] undergoes relatively
clean ligand exchange to form trans-(DMPE)2Ru(H)(X)
(X ) phenylacetylide, enolate) complexes, analogous
Ack n ow led gm en t is made to the donors of the
Petroleum Research Fund (administered by the Ameri-
can Chemical Society) and to North Carolina State
University for support of this research. We thank
Professor George Dubay (Duke University) for as-
sistance with mass spectral analysis and Professor
Robert Bergman (UCsBerkeley) for useful comments.
Su p p or tin g In for m a tion Ava ila ble: Text giving com-
plete synthetic and characterization details for complexes
1
1-17 and figures giving H NMR spectra for complexes 11-
14. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM010739X
(21) Conner, D.; J ayaprakash, K. N.; Gunnoe, T. B. Manuscript in
preparation.
(22) (a) J ayaprakash, K. N.; Gunnoe, T. B. Inorg. Chem., in press.
(b) TpRu(CO)(PPh3)(NHPh) does react with phenylacetylene at el-
evated temperatures. This reaction will be detailed in
publication.
a future