Half-sandwich hydride complexes of ruthenium with bidentate phosphinoamine ligands: Proton-transfer reactions to [(C5R5)RuH(L)] [R = H, Me; L = dippae, (R,R)-dippach]

Article abstract of DOI:10.1021/ic061745u

The complexes [(C₅R₅) RuH(dippae)] [R = H (1a), Me (2a); dippae = 1,2-bis(diisopropylphosphinoamino)ethane] and [(C ₅R₅)RuH((R,R)-dippach)] [R = H (1b), Me (2b); (R,R)-dippach - (R,R)-1,2-bis(diisopropylphosphinoamino)-cyclohexane] have been prepared and characterized. The cationic ruthenium(IV) dihydride derivatives [(C₅R₅)RuH₂-(dippae)][BPh₄] [R = H (3a), Me (4a)] and [(C₅R₅)RuH₂((R,R)-dippach)] [BPh₄] [R = H (3b), Me (4b)] are also reported. No significant intramolecular interaction between the amino protons and the hydrogen atoms bound to the metal has been observed in any of these compounds. The X-ray crystal structure of 4a was determined. The proton-transfer processes over the monohydrides 2a and 2b with HBF₄·OEt₂ have been studied by NMR spectroscopy. Dicationic dihydride complexes [CpRuH ₂(LH)]²⁺ [LH = dippaeH⁺ (5a), (R,R)-dippachH⁺ (5b)] and [Cp*RuH₂(LH)]²⁺ [LH = dippaeH⁺ (6a), (H,H)-dippachH⁺ (6b)] result respectively from the protonation of either the monohydrides 1a,b or 2a,b or the dihydrides 3a,b or 4a,b at one of the NH groups of the phosphinoamine ligands by an excess of HBF₄. These dicationic derivatives exhibit fluxional behavior in solution. In the course of the protonation of 1a with HBF ₄·OEt₂, a cationic dihydrogen complex and a dihydrogen-bonded derivative have been identified as intermediates by NMR spectroscopy. Another dihydrogen species, namely, [CpRu(H...HOOCPh)((R,R)- dippach)], was also identified in the course of the reaction of 1b with benzole acid in toluene-d₈. The reaction of 1a with 0.5 equiv of 1,1,1,3,3,3-hexafluoroisopropanol generates a hydride species having a very short (T₁)_min of 6.5 ms at 400 MHz, an experimental fact for which no satisfactory explanation has yet been found.

Full text of DOI:10.1021/ic061745u

Inorg. Chem. 2007, 46, 1001−1012
Half-Sandwich Hydride Complexes of Ruthenium with Bidentate
Phosphinoamine Ligands: Proton-Transfer Reactions to [(C5R5)RuH(L)]
[R H, Me; L dippae, (R,R)-dippach]
)
)
Manuel Jime´nez-Tenorio, M. Dolores Palacios, M. Carmen Puerta, and Pedro Valerga*
Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y Qu´ımica Inorga´nica, Facultad
de Ciencias, UniVersidad de Ca´diz, 11510 Puerto Real, Ca´diz, Spain
Received September 14, 2006
The complexes [(C5R5)RuH(dippae)] [R
)
H (1a), Me (2a); dippae
)
1,2-bis(diisopropylphosphinoamino)ethane]
and [(C5R5)RuH((R,R)-dippach)] [R H (1b), Me (2b); (R,R)-dippach
)
) (R,R)-1,2-bis(diisopropylphosphinoamino)-
cyclohexane] have been prepared and characterized. The cationic ruthenium(IV) dihydride derivatives [(C5R5)RuH2-
(dippae)][BPh4] [R H (3a), Me (4a)] and [(C5R5)RuH2((R,R)-dippach)][BPh4] [R H (3b), Me (4b)] are also
)
)
reported. No significant intramolecular interaction between the amino protons and the hydrogen atoms bound to
the metal has been observed in any of these compounds. The X-ray crystal structure of 4a was determined. The
proton-transfer processes over the monohydrides 2a and 2b with HBF4
‚
OEt2 have been studied by NMR spectroscopy.
+
+
Dicationic dihydride complexes [CpRuH2(LH)]2 [LH
)
dippaeH+ (5a), (R,R)-dippachH+ (5b)] and [Cp*RuH2(LH)]2
[LH
)
dippaeH+ (6a), (R,R)-dippachH+ (6b)] result respectively from the protonation of either the monohydrides
1a,b or 2a,b or the dihydrides 3a,b or 4a,b at one of the NH groups of the phosphinoamine ligands by an excess
of HBF4. These dicationic derivatives exhibit fluxional behavior in solution. In the course of the protonation of 1a
with HBF4‚OEt2, a cationic dihydrogen complex and a dihydrogen-bonded derivative have been identified as
intermediates by NMR spectroscopy. Another dihydrogen species, namely, [CpRu(H‚‚‚HOOCPh)((R,R)-dippach)],
was also identified in the course of the reaction of 1b with benzoic acid in toluene-d8. The reaction of 1a with 0.5
equiv of 1,1,1,3,3,3-hexafluoroisopropanol generates a hydride species having a very short (T1)min of 6.5 ms at 400
MHz, an experimental fact for which no satisfactory explanation has yet been found.
Introduction
to establish the stepwise nature of this process and the
identification of several intermediate species. Thus, the
proton-transfer reaction from a donor HX to a hydride HMLn
is preceded by the formation of a dihydrogen-bonded
complex XH‚‚‚HMLn.6,9,10 This species is converted to a
dihydrogen complex forming a contact ion pair stabilized
by hydrogen bonding with the anion LnM(H2)+‚‚‚X-, prior
to the formation of the free [LnM(H2)]+ and X- ions as
The protonation reactions of half-sandwich ruthenium
hydride systems of the type [(C5R5)RuHLL′] (R ) H or Me;
L, L′ ) tertiary phosphine or CO) have been the subject of
many thorough synthetic, as well as mechanistic, and
theoretical studies.1-8 From these studies, it has been possible
* To whom correspondence should be addressed. E-mail: pedro.valerga@
uca.es. Tel: +34 956 016340. Fax: +34 956 016288.
(1) Papish, E. T.; Magee, M. P.; Norton, J. R. In Recent AdVances in
Hydride Chemistry; Peruzzini, M., Poli, R., Eds.; Elsevier: Amsterdam,
The Netherlands, 2001; Chapter 2, pp 39-74 and references cited
therein.
(2) Belkova, N. V.; Ionidis, A. V.; Epstein, L. M.; Shubina, E. S.;
Gruendemann, S.; Golubev, N. S.; Limbach, H.-H. Eur. J. Inorg.
Chem. 2001, 1753-1761.
(3) Jia, G.; Lau, C.-P. Coord. Chem. ReV. 1999, 190-192, 83-108.
(4) Ontko, A. C.; Houlis, J. F.; Schnabel, R. C.; Roddick, D. M.; Fong,
T. P.; Lough, A. J.; Morris, R. H. Organometallics 1998, 17, 5467-
5476.
(5) de los R´ıos, I.; Jime´nez-Tenorio, M.; Padilla, J.; Puerta, M. C.; Valerga,
P. Organometallics 1996, 15, 4565-4575.
(6) Epstein, L. M.; Belkova, N. V.; Shubina, E. S. In Recent AdVances in
Hydride Chemistry; Peruzzini, M., Poli, R., Eds.; Elsevier: Amsterdam,
The Netherlands, 2001; Chapter 14, pp 391-418 and references cited
therein.
(7) Belkova, N. V.; Besora, M.; Epstein, L. M.; Lledo´s, A.; Maseras, F.;
Shubina, E. S. J. Am. Chem. Soc. 2003, 125, 7715-7725.
(8) Lam, Y.-F.; Yin, C.; Yeung, C.-H.; Ng, S.-M.; Jia, G.; Lau, C.-P.
Organometallics 2002, 21, 1898-1902.
(9) Crabtree, R. H.; Siegbahn, P. E. M.; Eisenstein, O.; Rheingold, A. L.;
Koetzle, T. F. Acc. Chem. Res. 1996, 29, 348-354.
(10) Lough, A. J.; Park, S.; Ramachandran, S.; Morris, R. H. J. Am. Chem.
Soc. 1994, 116, 8356-8357.
10.1021/ic061745u CCC: $37.00
Published on Web 01/06/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 3, 2007 1001

Jime´nez-Tenorio et al.
reaction products. In most cases, the dihydrogen complex
undergoes isomerization to a ruthenium(IV) dihydride com-
plex.1,3,5
characterization of a series of CpRu and Cp*Ru hydride and
related complexes containing either the phosphinoamine
ligand dippae or the enantiopure (R,R)-dippach and the study
by variable-temperature (VT)-NMR spectroscopy of their
proton-transfer reactions.
Experimental Section
All synthetic operations were performed under a dry dinitrogen
or argon atmosphere following conventional Schlenk techniques.
Tetrahydrofuran (THF), diethyl ether, and petroleum ether (boiling
point range 40-60 °C) were obtained oxygen- and water-free from
an Innovative Technology, Inc., solvent purification apparatus.
Toluene and fluorobenzene were of anhydrous quality and were
used as received. All solvents were deoxygenated immediately
before use. The ligands (R,R)-dippach and dippae were prepared
following suitable adaptations of published procedures.15-19 The
complexes [CpRuCl(L)] [L ) (R,R)-dippach, dippae] were obtained
by suitable adaptation of the procedures previously reported by us
for the preparation of [CpRuCl(dippe)] and [Cp*RuCl(dippe)]
[dippe ) 1,2-bis(diisopropylphosphino)ethane].20 HBF4, benzoic
acid, and 1,1,1,3,3,3-hexafluoroisopropanol (HFIPOH) were used
as supplied by Aldrich. IR spectra were taken in Nujol mulls on a
Perkin-Elmer SPECTRUM 1000 FTIR spectrophotometer. NMR
spectra were taken on a Varian Unity 400 MHz or a Varian Gemini
300 MHz equipment. Chemical shifts are given in ppm from SiMe4
(1H and 13C{1H}), 85% H3PO4 (31P{1H}), or CFCl3 (19F). Longi-
tudinal relaxation time (T1) measurements were made by the
inversion-recovery method. Activation parameters for fluxional
processes were obtained by a dynamic NMR line-shape fitting
simulation using the program DNMR321 incorporated into Spin-
Works 2.2.22 Microanalysis was performed on a elemental analyzer
model LECO CHNS-932 at the Servicio Central de Ciencia y
Tecnolog´ıa, Universidad de Ca´diz, Ca´diz, Spain.
In a recent work, we described the preparation and
characterization of hydride complexes of the type [TpRuH-
(L)] and [TpRu(H2)(L)][BAr′4] [Tp ) hydrotris(pyrazolyl)-
borate; Ar′4 ) 3,5-C6H3(CF3)2] bearing the phosphinoamine
ligands L ) dippae [1,2-bis(diisopropylphosphinoamino)-
ethane] or L ) (R,R)-dippach [(R,R)-bis(diisopropylphos-
phinoamino)cyclohexane].11 We remarked upon the fact that
the TpRu dihydrogen complexes are stable species that do
not rearrange to their dihydride tautomers at variance with
CpRu or Cp*Ru related systems12,13 and that this allowed
the study of the proton-transfer reactions without the interfer-
ence of such an isomerization process. We were able to detect
by NMR spectroscopy dihydrogen-bonded intermediates, as
well as dicationic dihydrogen complexes resulting from
protonation at one of the lone pairs of the NH groups of the
phosphinoamine ligand. All of the intermediate species
identified in these systems were consistent with those recently
proposed in the literature for proton-transfer reactions.1,2,6
We also identified in the course of the protonation of
[TpRuH(dippae)] with 0.5 equiv of HBF4‚OEt2 a remarkable
hydride species having an extremely short (T1)min of 0.5 ms
at -62 °C and 400 MHz. In some other rare case, a very
short relaxation time of 1.4 ms at -40 °C and 400 MHz for
the hydride NMR signal of [{C5H4CH(CH2CH2)2NHMe}-
RuH(PPh3)2][BF4] had been previously reported.14 The causes
for these fast relaxation phenomena are still unknown.
We have now completed the study of the proton-transfer
reaction on ruthenium hydrides bearing phosphinoamine
ligands extending the work to the corresponding cyclopen-
tadienyl and pentamethylcyclopentadienyl derivatives. At
variance with the TpRu complexes, the driving force of these
reactions is the formation of ruthenium(IV) dihydride
complexes. This fact complicates the detection of intermedi-
ate species in the process but at the same time affords the
opportunity to study new complexes that have no parallel in
TpRu chemistry. In this work, we describe the synthesis and
[CpRuH(L)] [L ) dippae (1a), (R,R)-dippach (1b)]. To a
solution of either [CpRuCl(dippae)] (0.5 g, 1.2 mmol) or [CpRuCl-
((R,R)-dippach))] (0.5 g, 1 mmol) in ethanol (10 mL) was added
an excess of solid NaBH4 (0.1 g). The mixture was heated under
reflux for 1 h. Upon cooling, an off-white precipitate was formed.
The solids were filtered off, washed with ethanol (2 mL) and
petroleum ether (5 mL), and dried in vacuo. Data for 1a. Yield:
0.4 g, 72%. Anal. Calcd for C19H40N2P2Ru: C, 49.7; H, 8.77; N,
6.1. Found: C, 49.3; H, 8.50, N, 6.3. IR: ν(RuH) 1986, ν(NH)
1
2
3365 cm-1. H NMR (400 MHz, C6D6, 298 K): δ -13.6 (t, JHP
) 37 Hz, 1 H, RuH), 0.76 (m, 2 H, NH), 0.90, 0.97, 1.14, and
1.23 (m, 24 H, PCH(CH3)2), 1.57 (m, 4 H, PCH(CH3)2), 2.60 and
3.00 (m, 4 H, (CH2)2), 4.73 (s, 5 H, C5H5). 31P{1H} NMR (161.89
MHz, C6D6, 298 K): δ 132.2 (s). 13C{1H} NMR (75.4 MHz, C6D6,
298 K): δ 17.1, 18.3, 18.8, and 20.4 (s, PCH(CH3)2), 32.2 and
34.8 (m, PCH(CH3)2), 44.8 (s, (CH2)2), 78.1 (s, C5H5). Data for
1b. Yield: 0.25 g, 70%. Anal. Calcd for C23H46N2P2Ru: C, 53.8;
H, 9.03; N, 5.5. Found: C, 54.0; H, 9.15; N, 5.6. IR: ν(RuH) 2016,
(15) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics 2001,
20, 1047-1049.
(16) Wiegrabe, W.; Bock, H. Chem. Ber. 1968, 101, 1414-1427.
(17) Balakrishna, M. S.; Abhyankar, R. M.; Mague, J. T. J. Chem. Soc.,
Dalton Trans. 1999, 1407-1412.
(11) Jime´nez-Tenorio, M.; Palacios, M. D.; Puerta, M. C.; Valerga, P.
Organometallics 2005, 24, 3088-3098.
(18) Zubiri, M. R. I.; Milton, H. L.; Cole-Hamilton, D. J.; Slawin, A. M.
Z.; Woollins, J. D. Polyhedron 2004, 23, 693-699.
(12) Jime´nez-Tenorio, M.; Jime´nez-Tenorio, M. A.; Puerta, M. C.; Valerga,
P. J. Chem. Soc., Dalton Trans. 1998, 3601-3607.
(19) Miyano, S.; Nawa, M.; Hashimoto, H. Chem. Lett. 1980, 729-730.
(20) de los R´ıos, I.; Jime´nez-Tenorio, M.; Padilla, J.; Puerta. M. C.; Valerga,
P. J. Chem. Soc., Dalton Trans. 1996, 277-381.
(13) Chan, W.-C.; Lau, C.-P.; Chen, Y.-Z.; Fang, Y.-Q.; Ng, S.-M.; Jia,
G. Organometallics 1997, 16, 34-44.
(14) Castellanos, A.; Ayllo´n, J. A.; Sabo-EÄ ttienne, S.; Donnadieu, B.;
Chaudret, B.; Yao, W.; Kavallieratos, K.; Crabtree, R. H. C. R. Acad.
Sci. Paris, Ser. IIc 1999, 2, 359-368.
(21) Kleier, D. A.; Binsch, G. J. Magn. Reson. 1970, 3, 146-160.
(22) Marat, K. SpinWorks 2.2; University of Manitoba: Winnipeg, Mani-
toba, Canada, 2003.
1002 Inorganic Chemistry, Vol. 46, No. 3, 2007

Half-Sandwich Hydride Complexes of Ruthenium
1
ν(NH) 3374 cm-1. H NMR (400 MHz, C6D6, 298 K): δ -13.6
C, 66.4; H, 7.78, N, 3.8. IR: ν(RuH) 1967, ν(NH) 3343 cm-1. 1H
NMR (400 MHz, CD3COCD3, 298 K): δ -8.75 (t, JHP ) 21.1
(dd, 2JHP ) 37 Hz, 2JHP′ ) 35.6 Hz, 1 H, RuH), 0.99, 1.18 (m, 24
H, PCH(CH3)2), 1.31 (m, 4 H, (CH2)2), 1.52 (m, 2 H, NH), 1.66
(m, 4 H, PCH(CH3)2), 2.87 (m, 2 H, CHCH), 4.67 (s, 5 H, C5H5).
31P{1H} NMR (161.89 MHz, C6D6, 298 K): δ 127.6 (d, Jpp) 42
Hz), 130.1 (d, Jpp) 42 Hz). 13C{1H} NMR (75.4 MHz, C6D6, 298
K): δ 17.2, 17.3, 18.6, 18.4, 18.7, 18.9, 19.3, and 20.4 (s, PCH-
(CH3)2), 25.5, 25.6, 27.1, and 28.2 (s, (CH2)4), 35.4, 36.6, 36.8,
and 37.5 (m, PCH(CH3)2), 56.8 and 59.2 (s, CHCH), 78.1 (s, C5H5).
These compounds are also accessible by deprotonation of the
corresponding dihydride complexes [CpRuH2(dippae)][BPh4] (3a)
or [CpRuH2(dippach)][BPh4] (3b) (vide infra): To a solution of
the respective dihydride complex 3a or 3b (0.5 mmol) in THF (5
mL) was added solid KOBut (0.1 g, excess). The mixture was stirred
for 10 min at room temperature. Then the solvent was removed in
vacuo, the residue extracted with toluene (4 mL), and the resulting
solution filtered off. Concentration of the solution, followed by the
addition of petroleum ether and cooling to -20 °C, afforded
microcrystals, which were filtered off and dried in vacuo. Yield:
60-65% in both cases.
[Cp*RuH(L)] [L ) dippae (2a), (R,R)-dippach (2b)]. To a
solution of either [Cp*RuCl(dippae)] (0.6 g, 1.2 mmol) or [Cp*RuCl-
((R,R)-dippach)] (0.6 g, 1 mmol) in methanol (10 mL) was added
an excess of solid NaOH (1 pellet, ca. 0.2 g). The mixture was
stirred at room temperature for 10 min. The resulting white
precipitate was filtered off, washed with ethanol (2 mL) and
petroleum ether (5 mL), and dried in vacuo. Data for 2a. Yield:
0.5 g, 78%. Anal. Calcd for C24H50N2P2Ru: C, 54.4; H, 9.51; N,
5.3. Found: C, 54.6; H, 9.39, N, 5.3. IR: ν(RuH) 1984, ν(NH)
2
Hz, 2 H, RuH2), 1.24 (m, 24 H, PCH(CH3)2), 2.09 (m, 4 H,
PCH(CH3)2), 2.81 and 3.15 (m, 6 H, (CH2)2 overlapping with NH),
5.52 (s, 5 H, C5H5). 31P{1H} NMR (161.89 MHz, CD3COCD3, 298
K): δ 125.7 (s). 13C{1H} NMR (75.4 MHz, CD3COCD3, 298 K):
δ 17.2 and 18.1 (s, PCH(CH3)2), 33.1 and 33.5 (m, PCH(CH3)2),
43.1 (s, (CH2)2), 78.7 (s, C5H5). Data for 3b. Yield: 0.51 g, 60%.
Anal. Calcd for C47H67N2BP2Ru: C, 67.7; H, 8.10; N, 3.4. Found:
C, 67.6; H, 8.25; N, 3.4. IR: ν(RuH) 2064, ν(NH) 3326, 3342
1
cm-1. H NMR (400 MHz, CD3COCD3, 298 K): δ -8.76 (dd,
2JHP ) 22.4 Hz, 2JHP′ ) 18.5 Hz, 2 H, RuH2), 1.22 (m, 32 H, PCH-
(CH3)2 overlapping with (CH2)2), 1.64 (m, 2 H, NH), 1.92 and 2.04
(m, 4 H, PCH(CH3)2), 3.08 (m, 2 H, CHCH), 5.50 (s, 5 H, C5H5).
31P{1H} NMR (161.89 MHz, CD3COCD3, 298 K): δ 120.6 (s).
13C{1H} NMR (75.4 MHz, CD3COCD3, 298 K): δ 17.9 and 18.9
(s, PCH(CH3)2), 25.9 (s, (CH2)4), 33.6 and 36.9 (m, PCH(CH3)2),
58.4 (s, CHCH), 86.7 (s, C5H5).
[Cp*RuH2(L)][BPh4] [L ) dippae (4a), (R,R)-dippach (4b)].
These compounds were prepared in a fashion analogous to that
reported above for 3a and 3b, starting from either [Cp*RuCl-
(dippae)] or [Cp*RuCl((R,R)-dippach)]. Data for 4a. Yield: 0.42
g, 50%. Anal. Calcd for C48H71N2BP2Ru: C, 67.8; H, 8.42; N, 3.3.
Found: C, 67.6; H, 8.39, N, 3.5. IR: ν(RuH) 1989, ν(NH) 3307
cm-1. 1H NMR (400 MHz, CD3COCD3, 298 K): δ -8.43 (t, 2JHP
) 24 Hz, 2 H, RuH2), 1.28 (m, 24 H, PCH(CH3)2), 1.72 (m, 2 H,
NH), 1.97 (s, 15 H, C5(CH3)5), 2.82 (m, 4 H, PCH(CH3)2), 3.05
(m, 4 H, (CH2)2). 31P{1H} NMR (161.89 MHz, CD3COCD3, 298
K): δ 122.8 (s). 13C{1H} NMR (75.4 MHz, CD3COCD3, 298 K):
δ 11.7 (s, C5(CH3)5), 18.1 and 19.8 (s, PCH(CH3)2), 32.6 (m, PCH-
(CH3)2), 43.6 (s, (CH2)2), 99.8 (s, C5(CH3)5). Data for 4b. Yield:
0.45 g, 50%. Anal. Calcd for C52H77N2BP2Ru: C, 69.1; H, 8.59;
N, 3.1. Found: C, 68.9; H, 8.25; N, 3.3. IR: ν(RuH) 2010, 2071,
3358 cm-1. H NMR (400 MHz, C6D6, 298 K): δ -14.2 (t, JHP
) 36 Hz, 1 H, RuH), 0.79 (m, 2 H, NH), 1.12, 1.29 (m, 24 H,
PCH(CH3)2), 1.91 (s, 15 H, C5(CH3)5), 2.71 (m, 4 H, PCH(CH3)2),
2.89 and 3.02 (m, 4 H, (CH2)2). 31P{1H} NMR (161.89 MHz, C6D6,
298 K): δ 123.7 (s). 13C{1H} NMR (75.4 MHz, C6D6, 298 K): δ
12.9 (s, C5(CH3)5), 16.2, 17.3, 19.5, and 21.3 (s, PCH(CH3)2), 31.5
and 33.4 (m, PCH(CH3)2), 44.7 (s, (CH2)2), 90.4 (s, C5(CH3)5). Data
for 2b. Yield: 0.32 g, 70%. Anal. Calcd for C28H56N2P2Ru: C,
57.6; H, 9.67; N, 4.8. Found: C, 58.3; H, 9.65; N, 5.0. IR: ν(RuH)
1
2
1
ν(NH) 3350 cm-1. H NMR (400 MHz, CD3COCD3, 298 K): δ
-8.54 (dd, 2JHP ) 26.4 Hz, 2JHP′ ) 23.1 Hz, 2 H, RuH2), 1.15 (m,
32 H, PCH(CH3)2 overlapping with (CH2)2), 1.52 (m, 2 H, NH),
1.85 (s, 15 H, C5(CH3)5), 2.16 (m, 4 H, PCH(CH3)2), 2.81 (m, 2 H,
CHCH). 31P{1H} NMR (161.89 MHz, CD3COCD3, 298 K): δ
123.6 (s). 13C{1H} NMR (75.4 MHz, CD3COCD3, 298 K): δ 11.8
(s, C5(CH3)5), 17.5, 19.0, 19.3, and 19.9 (s, PCH(CH3)2), 32.6 and
33.8 (s, (CH2)4), 36.3 (m, PCH(CH3)2), 58.4 (s, CHCH), 99.6 (s,
C5(CH3)5).
1980, ν(NH) 3385 cm-1. H NMR (400 MHz, C6D6, 298 K): δ
1
-14.1 (dd, 2JHP ) 34.9 Hz, 2JHP′ ) 33.6 Hz, 1 H, RuH), 1.22 (m,
32 H, PCH(CH3)2 overlapping with (CH2)4), 1.46 (m, 2 H, NH),
1.95 (s, 15 H, C5(CH3)5), 2.35 (m, 4 H, PCH(CH3)2), 3.25 (m, 2 H,
CHCH). 31P{1H} NMR (161.89 MHz, C6D6, 298 K): δ 121.3 (d,
Jpp) 45 Hz), 126.3 (d, Jpp) 45 Hz). 13C{1H} NMR (75.4 MHz,
C6D6, 298 K): δ 12.8 (s, C5(CH3)5), 17.5, 18.1, 18.5, 19.1, 20.2,
20.4, and 20.8 (s, PCH(CH3)2), 21.3, 31.4, 31.6, and 33.2 (s, (CH2)4),
33.4, 33.5, 36.2, and 36.7 (m, PCH(CH3)2), 55.8 and 61.8 (s,
CHCH), 90.5 (s, C5(CH3)5).
NMR Study of Proton-Transfer Reactions. Solutions of the
respective monohydride complexes 1a,b or 2a,b in CD2Cl2 unless
otherwise stated, prepared under an argon atmosphere in NMR
tubes, were frozen by immersion into liquid nitrogen. The corre-
sponding amount of HBF4 or of other acid was added via syringe
or micropipette. The solvent was allowed to melt. Then, the tubes
were shaken, to mix the reagents, and stored in an ethanol/liquid
nitrogen bath. The samples prepared in this way were studied by
NMR at low temperatures. The sample was removed from the bath
and inserted into the precooled probe of the Varian UNITY-400
spectrometer at 185 K. Once shims were adjusted, the probe was
warmed to the desired temperature. The NMR temperature control-
ler was previously calibrated against a methanol sample, with the
reproducibility being (0.5 °C.
X-ray Structure Determinations. Crystal data and experimental
details are given in Table 1. X-ray diffraction data were collected
on a Bruker SMART APEX 3-circle diffractometer (graphite-
monochromated Mo KR radiation, λ ) 0.710 73 Å) with a CCD
area detector at the Servicio Central de Ciencia y Tecnolog´ıa de la
Universidad de Ca´diz. Hemispheres of the reciprocal space were
measured by ω scan frames with δ(ω) ) 0.30°. Corrections for
As occurs with 1a and 1b, the monohydrides 2a and 2b are also
accessible by deprotonation of the corresponding dihydride com-
plexes [Cp*RuH2(dippae)][BPh4] (4a) or [Cp*RuH2(dippach)]-
[BPh4] (4b) (vide infra) using KOBut in THF. The procedure is
entirely analogous to that outlined above for a compounds 1a and
1b, starting now from either 4a or 4b. Yield: 60-65% in both
cases.
[CpRuH2(L)][BPh4] [L ) dippae (3a), (R,R)-dippach (3b)].
Hydrogen gas was bubbled through a solution of either [CpRuCl-
(dippae)] or [CpRuCl(R,R-dippach)] (1 mmol) in methanol (15 mL).
An excess of solid NaBPh4 (0.4 g) was added. An off-white
precipitate was gradually formed. It was filtered off, washed with
ethanol and petroleum ether, and dried in vacuo. The products were
recrystallized from acetone/ethanol. Data for 3a. Yield: 0.4 g, 50%.
Anal. Calcd for C43H61N2BP2Ru: C, 66.2; H, 7.88; N, 3.6. Found:
Inorganic Chemistry, Vol. 46, No. 3, 2007 1003

Jime´nez-Tenorio et al.
Table 1. Summary of Crystallographic Data for 4a
Table 2. 1H NMR Chemical Shifts and (T1)min Values for the Hydride
Protons in Monohydride and Dihydride Complexes
compound
formula
fw
4a
C48H71N2BP2Ru
849.89
293(2)
compound
δ RuH (ppm)
Monohydridesb
(T1)min (ms)a
T (K)
[CpRuH(dippae)] (1a)
[CpRuH((R,R)-dippach)] (1b)
[Cp*RuH(dippae)] (2a)
-13.6
-13.6
-14.2
-14.1
398
430
370
425
cryst size (mm)
cryst syst
space group
cell param
0.23 × 0.32 × 0.34
monoclinic
P21/c (No. 14)
a ) 11.9028(6) Å
b ) 20.125(1) Å
c ) 19.618(1) Å
â ) 97.640(1)°
4657.7(4)
[Cp*RuH((R,R)-dippach)] (2b)
Dihydridesc
[CpRuH2(dippae)][BPh4] (3a)
[CpRuH2((R,R)-dippach)][BPh4] (3b)
[Cp*RuH2(dippae)][BPh4] (4a)
-8.75
-8.82
-8.43
-8.77
306
373
281
297
V (Å3)
[Cp*RuH2((R,R)-dippach)][BPh4] (4b)
Z
F
4
calc (g cm-3
)
1.212
Mo KR/0.710 73
4.38
a At 400 MHz. b In toluene-d8. c In acetone-d6.
radiation/λ (Å)
µ(Mo KR) (cm-1
F(000)
)
coligand, namely, 1a and 2a, whereas their 31P{1H} NMR
spectra display one sharp singlet. The free chiral and
enantiomerically pure phosphinoamine (R,R)-dippach has C2
symmetry. However, when bound to ruthenium in complexes
1b and 2b, the phosphorus atoms become inequivalent, and
hence two doublets of an AM spin system are observed in
their respective 31P{1H} NMR spectra. Consistent with this,
the signal for the hydride ligand in these complexes appears
1808
max, min transm factors
θ range for data collection
reflns collcd
unique reflns
no. of obsd reflns [I > 2σ(I)]
no. of param
final R, wR values [I > 2σ(I)]
final R, wR values (all data)
GOF
1.000, 0.876
1.5 < θ < 25.1
34 883
8191 (Rint ) 0.040)
7145
508
0.0537, 0.1176
0.0667, 0.1245
1.059
2
weighting scheme
1/[σ2(Fo ) + (0.0536P)2 + 5.9715P]
1
where P ) (Fo2 + 2Fc )/3]
2
in the H NMR spectra as a high-field doublet of doublets
max, ave shift/error
0.01, 0.00
-0.41, 0.87
(X part of an AMX spin system). In any case, the values
residual electron density
2
2
found for the coupling constants JHP and JHP′ are very
similar (i.e., 37 and 35.6 Hz for 1b). These NMR patterns
have been previously observed by us for the recently reported
monohydride complex [TpRuH((R,R)-dippach)].11 As we did
also with TpRuH derivatives, we wanted to determine the
occurrence or absence of weak NH‚‚‚HRu interactions. NMR
NOESY and ROESY experiments failed to show any
significant NH‚‚‚HRu contact in these cases, just as happens
also with the TpRu hydrides bearing dippae and (R,R)-
dippach. The minimum longitudinal relaxation times (T1)min
of the hydride protons were measured by the inversion-
recovery method. These are listed in Table 2.
peaks (e Å-3
)
absorption and crystal decay (insignificant) were applied by the
semiempirical method from equivalents using the program SAD-
ABS.23 The structures were solved by direct methods, completed
by subsequent difference Fourier synthesis, and refined on F 2 by
full-matrix least-squares procedures using the program SHELXTL.24
The two hydrogen atoms bonded to the metal were localized in a
regular difference Fourier map and isotropically refined with
restricted Ru-H bond lengths. The program ORTEP-325 was used
for plotting.
Results and Discussion
For the monohydride complexes, the values of (T1)min are
in between 370 and 430 ms. These values are somewhat
shorter than those reported for other half-sandwich mono-
hydride complexes of ruthenium (i.e., 520 ms for [{C5H4-
CH(CH2CH2)2NMe}RuH(PPh3)2]14 or 480 ms for [CpRuH-
(PPh3)2]26) but of the same order of magnitude as those
measured for the TpRu monohydride derivatives [TpRuH-
(dippae)] (397 ms) and [TpRuH((R,R)-dippach)] (373 ms).11
As has been proposed for these TpRuH complexes, in here
the cause for the relatively short (T1)min values measured
should also be the sum of interactions of the hydride with
all other neighboring nuclei within the molecule. Again, the
contributions of the interactions of the hydride with the phos-
phinoamine protons NH‚‚‚HRu, in particular, do not appear to
be of particular relevance in the overall relaxation processes.
The dihydride complexes [CpRuH2(L)][BPh4] [L ) dippae
(3a), (R,R)-dippach (3b)] and [Cp*RuH2(L)][BPh4] [L )
dippae (4a), (R,R)-dippach (4b)] were prepared by reaction
of the corresponding chloro complex [CpRuCl(L)] or
[Cp*RuCl(L)] with H2 and NaBPh4 in methanol in the form
Preparation and Characterization of Hydride Com-
plexes 1-4. The monohydride complexes [CpRuH(L)] [L
) dippae (1a), (R,R)-dippach (1b)] were prepared by reaction
of the corresponding chloro complex [CpRuCl(L)] with
NaBH4 in refluxing ethanol. The pentamethylcyclopentadi-
enyl homologous derivatives [Cp*RuH(L)] [L ) dippae (2a),
(R,R)-dippach (2b)] were better prepared by reaction of the
chloro complexes [Cp*RuCl(L)] with an excess of NaOH
in methanol at room temperature. All of these neutral
monohydride complexes are also accessible by the depro-
tonation reaction of the corresponding cationic dihydride
complex [(C5R5)RuH(L)] (R ) H, Me; L ) dippae, (R,R)-
dippach] (vide infra) using KOBut in THF. Complexes 1a,b
and 2a,b are very air-sensitive white microcrystalline solids
that gradually darken even when stored under argon at -20
°C. The hydride ligand appears as one high-field triplet in
the 1H NMR spectra of complexes containing dippae as the
(23) Sheldrick, G. M. SADABS, University of Go¨ttingen: Go¨ttingen,
Germany, 2001.
(24) Sheldrick, G. M. SHELXTL, version 6.10; Crystal Structure Analysis
Package; Bruker AXS: Madison, WI, 2000.
(25) Farruggia, L. J. ORTEP-3 for Windows, version 1.076. J. Appl.
Crystallogr. 1997, 30, 565.
(26) Desrosiers, P. J.; Cai, L.; Richards, R.; Halpern, J. J. Am. Chem. Soc.
1991, 113, 4173-4184.
1004 Inorganic Chemistry, Vol. 46, No. 3, 2007

Half-Sandwich Hydride Complexes of Ruthenium
Figure 2. VT 1H (400 MHz, hydride region) and 31P{1H} (161.89 MHz)
NMR spectra in acetone-d6 of 3b.
Figure 1. ORTEP drawing (30% thermal ellipsoids) of the cation
[Cp*RuH2(dippae)]+ in complex 4a. Hydrogen atoms, except hydride
ligands, have been omitted. Selected bond lengths (Å) and angles (deg)
with estimated standard deviations in parentheses: bond lengths Ru(1)-
P(1) 2.3215(10); Ru(1)-P(2) 2.3099(10); Ru(1)-H(1) 1.53(3); Ru(1)-H(2)
1.55(3); P(1)-N(1) 1.697(4); P(2)-N(2) 1.672(4); bond angles P(1)-Ru-
(1)-P(2) 98.41(4); P(1)-Ru(1)-H(1) 67.4(14); P(1)-Ru(1)-H(2) 72.6-
(14); P(2)-Ru(1)-H(1) 71.6(18); P(2)-Ru(1)-H(2) 69.0(13); H(1)-
Ru(1)-H(2) 117(2); torsion angles P(1)-N(1)-C(17)-C(18) 55.4(5);
P(2)-N(2)-C(18)-C(17) -99.8(4); N(1)-C(17)-C(18)-N(2) 48.7(5).
of off-white microcrystalline solids. The crystal structure of
4a was determined. An ORTEP view of the complex cation
[Cp*RuH2(dippae)]+ is shown in Figure 1, together with a
listing of selected bond lengths and angles.
The cation exhibits a four-legged piano-stool structure,
with hydride ligands arranged in a transoid disposition with
an angle H(1)-Ru(1)-H(2) of 123(2)°. This angle is similar
to the value found by neutron diffraction for the dihydride
complex [CpRuH2(PMe3)2][BF4] [118.8(4)°]27 and by X-ray
diffraction for [Cp*RuH2(PPhiPr2)2][BAr′4] [124.5(17)°].28
The Ru-H separations of 1.53(3) and 1.55(3) Å are
consistent with those found in other half-sandwich ruthenium
dihydride complexes, i.e., 1.50(3) and 1.53(3) Å in [Cp*RuH2-
(PPhiPr2)2][BAr′4]28 or 1.599(8) and 1.604(9) Å for [Cp*RuH2-
(PMe3)2][BF4] (neutron diffraction).27 The ruthenium atom
and the dippae ligand are part of a seven-membered ring.
The P(1)-Ru(1)-P(2) angle has a value of 98.41(4)°, which
is intermediate between 87.53(7)° in [Cp*RuH2(dippe)]-
[BPh4]5 and 107.96(2)° in [Cp*RuH2(PPhiPr2)2][BAr′4]28 and
is larger than the value of 93.88(4)° found for [TpRu(H2)-
(dippae)][BAr′4],11 in which the Tp ligand imposes a cis
arrangement of the phosphorus atoms. Hence, the seven-
membered ring, in combination with the transoid stereo-
chemistry, increases the value of the P(1)-Ru(1)-P(2) angle,
placing complex 4a structurally in between transoid dihydride
complexes with bidentate phosphines and those bearing
monodentate phosphines.
Figure 3. VT 1H (400 MHz, hydride region) and 31P{1H} (161.89 MHz)
NMR spectra in acetone-d6 of 4b.
and one singlet in the 31P{1H} NMR spectra, as is expected
for systems having pseudo-C2V symmetry in solution. The
simplicity of the 13C{1H} NMR spectra for these complexes
is also consistent with this. However, for complexes 3b and
4b, which bear the chiral phosphinoamine (R,R)-dippae, the
situation is different. The hydride protons give rise to a
1
doublet of doublets in their room temperature H NMR
spectra, whereas the 31P{1H} NMR spectra consist of one
apparent singlet. The NMR spectra for both 3b and 4b are
temperature-dependent and exhibit a somewhat different
behavior as a function of the presence of either Cp (3b) or
1
Cp* (4b) as the coligand. The VT H (hydride region) and
31P{1H} NMR spectra of 3b and 4b are respectively shown
in Figures 2 and 3.
At variance with this, the resonances in the 1H and 31P{1H}
NMR spectra of 3a and 4a undergo broadening at low
temperature, but no decoalescence occurs. When the tem-
perature is lowered in the case of compound 3b, decoales-
cence of the 1H NMR hydride resonance to two broad signals
at -88 °C is observed, whereas the room temperature
31P{1H} NMR resonance decoalesces to two broad singlets
The 1H NMR spectra of complexes 3a and 4a display one
high-field triplet resonance for the equivalent hydride ligands
(27) Brammer, L.; Klooster, W. T.; Lemke, F. R. Organometallics 1996,
15, 1721-1727.
(28) Aneetha, H.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.; Sapunov,
V. N.; Schmid, R.; Kirchner, K.; Mereiter, K. Organometallics 2002,
21, 5334-5346.
Inorganic Chemistry, Vol. 46, No. 3, 2007 1005

Jime´nez-Tenorio et al.
(Figure 2). Likewise, for compound 4b, the hydride reso-
nance splits into three broad signals in the intensity ratio
2:1:1 at -88 °C. At this temperature, the 31P{1H} NMR
spectrum consists of four separate singlet resonances (Figure
3), so the P-P coupling is not resolved. For both 3b and
observed differences between the VT-NMR spectra of 3b
and 4b are then most likely due to the existence of a rotation
barrier around the Ru-Cp* bond in the case of 4b, which
generates two diastereomers depending on the orientation
of the methyl groups of the Cp* ring relative to the
ruthenium-phosphinoamine fragment, as shown.
1
4b, the H NMR signals corresponding to the protons of
either Cp or Cp* remain as singlets in the temperature range
studied. The fact that the hydride resonances appear as
doublet of doublets at room temperature indicates the
magnetic inequivalence of the phosphorus atoms. The
presence of one singlet in the 31P{1H} NMR spectra indicates
averaging of the chemical shifts of rapidly exchanging
phosphorus atoms. The dynamic process responsible for this
behavior has been interpreted in terms of freezing of the
equilibrium between rapidly exchanging conformers in
solution resulting from the restricted rotation around the
Ru-P bond, which causes a flipping motion of the diami-
nocyclohexane fragment. A similar phenomenon has been
invoked as an explanation for the dynamic behavior of [Ru-
(OAc)2((R,R)-dppach)] [dppach ) 1,2-bis(diphenylphosphi-
noamino)ethane].29
Each of the diastereomers gives rise to two resonances in
the slow-exchange 31P{1H} NMR spectrum corresponding
to an AM spin system and to two separate hydride resonances
in the 1H NMR spectrum. The rotation barrier of around Ru-
Cp in 3b must be lower in energy than that in 4b because of
the lower steric hindrance of the hydrogen substituents
compared to the methyl groups in Cp*. Hence, a decoales-
cence similar to that observed in the NMR spectra of 4b
should be expected but only at temperatures well below
-88 °C.
The values of (T1)min for 3a,b and 4a,b were also
determined and appear listed in Table 2. Values range from
281 to 397 ms, which are short for “classical” dihydride
complexes but of the same order of magnitude as those found
for the monohydride complexes 1a,b and 2a,b. Again, no
significant NH‚‚‚HRu interactions were found by ROESY
experiments. Taking into consideration the values of (T1)min
for the monohydrides as a reference, we can estimate the
H‚‚‚H separation in the dihydride complexes in a manner
similar to that used for the derivatives [TpRu(H2)(L)][BAr′4]
[L ) (R,R)-dippach, dippae] using the expression26,30,31
1
1
1
)
+
(1)
T1(H2)obs T1(H2)true T1(H)obs
The term 1/T1(H)obs in eq 1 corresponds to the value of
(T1)min measured for the hydride resonance of either 1a,b or
2a,b, considering that the contribution to the relaxation of
the hydride ligand in these complexes comes mainly from
dipole-dipole interactions with the metal and through space
with all of the remaining atoms. The resulting corrected
values for (T1)min of the hydride protons can be used for the
calculation of the H‚‚‚H separation using the equation
Values of 37-39 kJ mol-1 have been estimated by means
of NMR line-shape fitting for the free energy of activation
∆Gq of these processes. Conformers A and B are related
298
by a 180° rotation around the Ru-Cp or Ru-Cp* axis but
only assuming free rotation of the Cp or Cp* groups. At
low temperature, the two hydride ligands are inequivalent
and each of them gives rise to separate resonances. The
rH···H ) 5.815[(T1)min/ν]1/6
(2)
(30) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155-284.
(31) Cayuela, E.; Jalo´n, F.; Manzano, B. R.; Espino, G.; Weissensteiner,
W.; Mereiter, K. J. Am. Chem. Soc. 2004, 126, 7049-7062.
(29) Kuznetsov, V. F.; Jefferson, G. R.; Yap, G. P. A.; Alper, H.
Organometallics 2002, 21, 4241-4248.
1006 Inorganic Chemistry, Vol. 46, No. 3, 2007

Half-Sandwich Hydride Complexes of Ruthenium
Table 3. Observed and Corrected (T1)min Valuesa and Calculated H‚‚‚H
Separations in Dihydride Complexes
obsd (T1)min
(T1)min for RuH in corrected (T1)min rH‚‚‚H
compd for RuH2 (ms)b monohydride (ms)c
for RuH2 (ms)
(Å)
3a
3b
4a
4b
306
373
281
297
398
430
370
425
1323
2814
1168
986
2.24
2.55
2.20
2.14
a At 400 MHz. b In acetone-d6. c In toluene-d8.
In this equation, ν represents the NMR frequency of
operation, which in our case is 4 × 108 Hz. All of the results
are summarized in Table 3.
It is clear that the extra hydridic proton in all of these
dihydride complexes contributes very little to the overall
dipole-dipole relaxation, leading to H‚‚‚H separations longer
than 2.1 Å in all cases, consistent with their formulation as
ruthenium(IV) dihydrides. Furthermore, the value of 2.20 Å
calculated for the H‚‚‚H separation in 4a can be compared
to the value of 2.631 Å found in the solid state by X-ray
diffraction.
In all cases, the hydride signals exhibit long (T1)min values
(greater than 300 ms at 400 MHz), consistent with their
formulation as “classical” dihydrides. Complexes 5a and 6a
containing dippae as the coligand display one singlet
resonance in their 31P{1H} NMR spectra at room temperature.
These resonances are shifted ca. 30 ppm downfield with
respect to the position of the signal of the corresponding
dihydride complex. One high-field triplet is observed in the
1H NMR spectra for the hydride ligands. When the temper-
Study of Proton-Transfer Reactions. We have studied
1
by VT H and 31P{1H} NMR spectroscopy the protonation
1
ature is lowered, the 31P{1H} and the H NMR hydride
reactions of 1a,b and 2a,b with HBF4‚OEt2. We have also
performed some experiments in selected cases using other
acids of different strength in order to get an insight into the
processes of proton transfer to hydride complexes.
The monohydride complexes 1a,b and 2a,b react with an
excess of HBF4‚OEt2 in CD2Cl2, furnishing dicationic
dihydrides [CpRuH2(LH)]2+ [LH ) dippaeH+ (5a), (R,R)-
dippachH+ (5b)] and [Cp*RuH2(LH)]2+ [LH ) dippaeH+
(6a), (R,R)-dippachH+ (6b)], respectively, in which one of
the NH groups of the phosphinoamine ligands has been
protonated. The same species were obtained by treatment
of the monocationic dihydrides 3a,b or 4a,b with HBF4‚OEt2
in CD2Cl2 or acetone-d6.
We had previously observed the protonation of the NH
groups of the phosphinoamine ligands in the course of the
proton-transfer reactions over the complexes [TpRuH(L)] [L
) dippae, (R,R)-dippach], leading to dicationic species of
the type [TpRu(H2)(LH)]2+, which in some instances undergo
tautomerization to [TpRuH(LH2)]2+.11 These dicationic hy-
dride complexes are characterized by a downfield shift of
the relevant 31P{1H} NMR resonances and the occurrence
of fast proton-exchange equilibria. In the case of CpRu and
Cp*Ru derivatives, this has also been observed. In Table 4
are summarized selected 1H and 31P{1H} NMR data for the
dicationic derivatives 5a,b and 6a,b.
resonances get gradually broader, but no decoalescence is
observed. At variance with this, the VT-NMR spectra of
complexes with (R,R)-dippach, 5b and 6b, show different
profiles. For reference, the VT H (hydride region) and
31P{1H} NMR spectra of 6b are shown in Figure 4.
1
For both 5b and 6b, two separate resonances are observed
in the 31P{1H} NMR spectra at low temperatures. These
resonances are ca. 70 ppm apart from each other. The signals
at very low field are attributed to the phosphorus atoms next
to the protonated NH groups. At these low temperatures, the
hydride ligands are inequivalent and give rise to two separate
resonances in the 1H NMR spectra, which couple separately
to each of the phosphorus atoms. As the temperature is raised,
1
the resonances in the H and 31P{1H} NMR spectra get
progressively broader. At 25 °C, the 31P{1H} NMR spectra
are featureless whereas the hydride resonances have become
one triplet. The activation parameters for the dynamic process
responsible for this behavior were determined by means of
NMR line-shape fitting. For 5b, values of 19.1 ( 0.8 kJ
mol-1 and -110 ( 4 J K-1 mol-1 were obtained for ∆Hq
and ∆Sq, respectively, whereas for 6b, ∆Hq was 23 ( 1 kJ
mol-1 and ∆S* -85 ( 6 J K-1 mol-1. These parameters led
to the free energy of activation ∆Gq values of 52 ( 2 kJ
298
mol-1 for 5b and of 49 ( 3 kJ mol-1 for 6b. The largely
negative values obtained for ∆Sq are consistent with a process
1
Table 4. Selected H and 31P{1H} NMR Data for Dicationic Dihydride Complexes in CD2Cl2 at the Indicated Temperatures
compound
1H NMR
31P{1H} NMR
[CpRuH2(dippaeH)]2+ (5a)
at 25 °C: δ -8.79 (t, 2JHP ) 22.4 Hz, RuH2), 5.30 (s, C5H5)
at 25 °C: δ -8.40 (t, 2JHP ) 22.4 Hz, RuH2), 5.82 (s, C5H5)
at -88 °C: δ -8.37 (dd, 2JHP ) 28 Hz, 2JHP′ ) 14 Hz),
-8.73 (t, 2JHP ) 22 Hz) (RuH2), 6.02 (s, C5H5)
at 25 °C: δ 158.5
[CpRuH2((R,R)-dippachH)]2+ (5b)a
at 25 °C: featureless
at -88 °C: δ 187.8 (br), 115.8 (br)
[Cp*RuH2(dippaeH)]2+ (6a)a
at 25 °C: δ -7.98 (t, 2JHP ) 25 Hz, RuH2), 2.07 (s, C5(CH3)5)
at 35 °C: δ -8.04 (t, 2JHP ) 25.3 Hz, RuH2), 2.01 (s, C5(CH3)5)
at -88 °C: δ -8.04 (dd, 2JHP ) 28 Hz, 2JHP′ ) 15 Hz),
-8.68 (t, 2JHP ) 26 Hz) (RuH2), 1.91 (s, C5(CH3)5)
at 25 °C: δ 155.0
at 35 °C: 161 (very broad)
at -88 °C: δ 192.4 (s), 119.7 (s)
[Cp*RuH2((R,R)-dippachH)]2+ (6b)
a In acetone-d6.
Inorganic Chemistry, Vol. 46, No. 3, 2007 1007

Jime´nez-Tenorio et al.
1
Figure 4. VT H NMR (left, hydride region, 400 MHz) and VT 31P{1H} NMR (right, 161.89 MHz) of [Cp*RuH2((R,R)-dippachH)]2+ (6b) in CD2Cl2.
in which the controlling step is associative in character. We
have interpreted this in terms of an intermolecular rather than
intramolecular base-assisted proton exchange between the
two NH sites, as shown.
dihydride complexes 3a,b or 4a,b (in the form of [BF4]-
salts in solution) as the final thermodynamic products of the
proton-transfer processes. In the course of the protonation
of 1a, it was possible to detect at low temperature the
presence of the dihydrogen complex [CpRu(H2)(dippae)]+
as a metastable intermediate in the formation of the dihydride
derivative 3a.
The dihydrogen adduct is characterized by the presence
of one broad resonance at -9.55 ppm with a short (T1)min of
1
20 ms in the low-temperature H NMR spectra and one
singlet at 113.3 ppm in the 31P{1H} spectrum. The value of
1
the coupling constant JHD of 26 Hz measured for the
isotopomer [CpRu(HD)(dippae)]+ is also consistent with the
presence of a η2-H2 ligand. In the course of the protonation
of 1b with a stoichiometric amount of HBF4 at -88 °C, a
broad resonance with a short T1 of ca. 20 ms attributable to
an intermediate dihydrogen complex was also observed in
Several species may act as the base in this process: the
BF4 ion, diethyl ether, or even the solvent (CD2Cl2 or
-
acetone-d6). As the temperature is raised, the rapid exchange
between NH and NH2 protons renders the phosphorus atoms
equivalent in the NMR time scale, accounting for the
averaged spectra at room temperature. All attempts made to
isolate the dicationic dihydrides as solids failed. Presumably,
they are exceedingly acidic species that are only stable in
solution, as was also pointed out for the derivatives [TpRu-
(H2)(dippaeH)]2+ and [TpRu(H2)(dippachH)]2+.11
1
the H NMR spectrum, but only for a brief period of time.
This signal disappears when the temperature is raised to -74
°C, suggesting that the dihydrogen complex [CpRu(H2)-
((R,R)-dippach)]+ is kinetically much less stable than its
counterpart containing dippae. This fact also made impossible
the measurement of the corresponding 1JHD coupling constant.
No signals attributable to metastable intermediate dihydrogen
complexes were observed when the protonation reactions of
the Cp* monohydrides 2a,b with HBF4 in CD2Cl2 were
monitored by NMR spectroscopy in an analogous fashion.
Going back to the proton-transfer reaction to 1a, at -88 °C
both the 1H and 31P{1H} NMR spectra show the presence of
the dihydrogen derivative [CpRu(H2)(dippae)]+, plus small
amounts of the dihydride 3a (Figure 5).
In the absence of an excess of HBF4, i.e., using stoichio-
metric amounts of HBF4 in CD2Cl2, all of the monohydride
complexes 1a,b and 2a,b react, yielding the corresponding
1
The triplet resonance near -14 ppm present in the H
NMR spectrum and the broad signal at 133 ppm in the
31P{1H} NMR spectrum were, in principle, attributed to the
nonprotonated monohydride complex 1a. When the temper-
1008 Inorganic Chemistry, Vol. 46, No. 3, 2007

Half-Sandwich Hydride Complexes of Ruthenium
Figure 5. VT 1H NMR (left, hydride region, 400 MHz) and VT 31P{1H}
NMR (right, 161.89 MHz) of a sample made up by the addition of HBF4
to a frozen CD2Cl2 solution of 1a below -90 °C, followed by subsequent
warming to the indicated temperatures.
Figure 6. VT 1H NMR (left, hydride region, 400 MHz) and VT 31P{1H}
NMR (right, 161.89 MHz) of a sample made up by the addition of less
than 0.5 equiv of HBF4
to a CD2Cl2 solution of 1a.
of the monohydride 1a, which remains in excess, as expected.
The observed increase in (T1)min for the resonance at -14
ppm with respect to the values measured in the experiment
in which a stoichiometric amount of acid was used (T1 e
190 ms) seems reasonable, given the fact that an averaging
of the observed T1 for the hydridic protons of 1a and the
dihydrogen-bonded species should be expected when the
protonation is carried out with a less than 1 equiv of HBF4.
It is very important to note that dihydrogen-bonded inter-
mediates have usually been observed when proton-transfer
reactions are performed with relatively weak proton do-
nors.2,6,7 In this case and also in our previous report on the
proton-transfer reactions to [TpRuH(L)] complexes,11 dihy-
drogen-bonded intermediates have been detected by NMR
spectroscopy when a strong acid such as HBF4 is used. In
these cases, a remarkable shortening in the value of (T1)min
was observed, which was explained in terms of the efficient
contribution of the fluorine atoms to the relaxation of
dihydrogen-bonded species of the type [TpRu(H‚‚‚HBF4)-
(L)] in equilibrium with contact ion pairs of the type
1
ature is raised, the dihydrogen resonance in the H NMR
spectrum and the associated signal in the 31P{1H} NMR
spectrum disappear as [CpRu(H2)(dippae)]+ irreversibly
rearranges to the dihydride derivative 3a. At -49 °C, a
significant broadening of the H and 31P{1H} NMR reso-
1
nances initially ascribed to the starting monohydride complex
1a is observed. At this temperature, the measured T1 for the
hydride resonance at -14.15 ppm was 190 ms, a value
significantly shorter than the 398 ms measured for the
hydride ligand in 1a (400 MHz, toluene-d8). These data are
consistent with the formation of an intermediate dihydrogen-
bonded species prior to the proton transfer to yield the
dihydrogen complex [CpRu(H2)(dippae)]+. Proton-hydride
exchange in an extremely short dihydrogen bond has been
reported to cause a very significant reduction in the measured
30
(T1)min
.
An alternative explanation for the increase in the
relaxation rate could be a fast equilibrium between the
monohydride and dihydrogen complexes. If this were the
case, an averaging of the T1 values for both the monohydride
and dihydrogen resonances would be expected.32 In our
system, because the measured T1 for the dihydrogen protons
at this temperature is 23 ms and the 31P{1H} NMR signal
for [CpRu(H2)(dippae)]+ remains sharp, this alternative seems
less likely than the well-precedented hypothesis in favor of
the formation of a dihydrogen-bonded intermediate.2,6-10 An
experiment of protonation of 1a performed with less than
0.5 equiv of HBF4 showed more clearly the formation of
the dihydrogen-bonded intermediate in the temperature range
-88 to -25 °C (Figure 6).
In this experiment, a (T1)min of 240 ms was measured for
the broad triplet resonance at ca. 14 ppm. Above -25 °C,
the formation of the dihydride complex 3a is quantitative,
indicating the consumption of all of the HBF4 added, whereas
the resonance at ca. -14 ppm sharpens and increases the
value of its T1, as is indicative of the presence in the mixture
- 11
Ru(H2)+‚‚‚BF4 . In the case of the protonation of 1a, the
shortest T1 measured for the signal attributed to the dihy-
drogen-bonded species was 190 ms, a value that is not
particularly short. If we apply eq 1 for the determination of
T1 due solely to the H‚‚‚H interaction, the result is 363 ms,
which by application of eq 2 leads to a H‚‚‚H separation of
1.81 Å, fully consistent with the formation of a standard
dihydrogen bond between the hydride ligand and a proton
donor.6,9 Ruling out close contacts with the [BF4]- ion in
this case, we can propose the formulation as [CpRu(H‚‚‚
HOEt2)(dippae)][BF4] for the observed dihydrogen-bonded
species in this system.
(32) Bakhmutov, V. I. Practical NMR Relaxation for Chemists; Wiley:
Chichester, U.K., 2004. Bakhmutov, V. I. Eur. J. Inorg. Chem. 2005,
245-255.
Inorganic Chemistry, Vol. 46, No. 3, 2007 1009

Jime´nez-Tenorio et al.
It is interesting to note that, in these systems containing
phosphinoamine ligands, metastable intermediate dihydrogen
complexes of the type [(C5R5)Ru(H2)(L)]+ are difficult to
detect and undergo rapid rearrangement to the corresponding
dihydride complexes. In comparison, related systems bearing
either monodentate or bidentate phosphine ligands furnish
dihydrogen intermediate complexes that are kinetically more
stable than those with phosphinoamine ligands.5,29,33 One
possible explanation to this observation is that the NH groups
play an active role in the process of isomerization from
dihydrogen to dihydride. For instance, the NH group might
eventually act as an internal base deprotonating the acidic
dihydrogen ligand to yield a cationic monohydride. A direct
proton transfer from the NH2 to the metal would yield the
thermodynamically more stable cationic dihydride complex.
Figure 7. VT 1H NMR (left, hydride region, 400 MHz) and VT 31P{1H}
NMR (right, 161.89 MHz) of a sample made up by the addition of an excess
of PhCOOH to a toluene-d8 solution of 1a.
although not the involvement, of a dihydrogen-bonded
complex in the observed process.
The VT 31P{1H} NMR spectra show one rather broad
signal at 127.9 ppm, which gets sharper as the temperature
is raised. The position of this signal falls close to that reported
for the cationic dihydride complex 2a in acetone-d6. At -25
°C, one broad resonance resembling two overlapping singlets
arises at 129.4 ppm and one broad resonance is visible at
138.2 ppm. At 0 °C, four signals are observed, whereas at
25 °C, only three rather broad features of approximately the
same intensity are present. We have interpreted these
observations in terms of a protonation-deprotonation equi-
librium involving strongly associated species given the low
polarity of the solvent used in this case:
Although we have no formal proof for this isomerization
pathway, we have previously observed the deprotonation of
dihydrogen ligands by NH acting as an internal base in the
systems [TpRu(H2)(L)]+ and [TpRu(H2)(LH)]2+, leading to
monohydrides of the type [TpRuH(LH)]+ and [TpRuH-
(LH2)]2+, respectively.11 On the other hand, density functional
theory studies performed on the model system [{C5H4CH2-
CH2NH2}RuH(PH3)2] suggest an active role of pendent
amino groups in several alternative pathways for the proton-
transfer reactions in this system.34 Therefore, the involvement
of amino groups in the mechanism of dihydrogen to
dihydride isomerization appears feasible and cannot be ruled
out as one possible reason for the observed kinetic instability
of dihydrogen complexes with phosphinoamine ligands.
We have also carried out a survey on proton-transfer
reactions in some of the complexes using weak acids such
as benzoic acid or the acidic alcohol HFIPOH, in order to
compare with the results obtained with the strong acid HBF4‚
OEt2.
The VT 1H NMR spectra of a sample of 1a in toluene-d8
upon the addition of an excess of PhCOOH (usually more
than 2 equiv) display two high-field resonances: one minor
triplet at -13.8 ppm and a major triplet at -9.5 ppm in the
entire range of temperatures studied (Figure 7). One broad
resonance overlapping with the triplet at -9.5 ppm is also
visible in between -25 and 0 °C. At 25 °C, only two broad
features are observed. The (T1)min’s for all of these signals,
including the broad overlapping resonance, are similar in
value to those measured for the monohydride 1a and the
dihydride 3a, which, in principle, rules out the detection,
[CpRuH(dippae)] + HOOCPh /
[CpRuH2(dippae)][PhCOO]
The equilibrium is shifted to the dihydride at low tem-
peratures, whereas the spectra are dominated by signals
attributed mainly to the dihydride in benzoate form, most
likely forming a tight ion pair. As the temperature is raised,
the equilibrium shifts to the left, which can be interpreted
as the attack of the benzoate ion onto the dihydride, that is,
a proton transfer back from the dihydride to the benzoate.
The possibility exists that the broad resonance visible in the
temperature range -25 to 0 °C in the 1H NMR spectra might
correspond to an intermediate of the type [CpRu(H)(H‚‚‚
OOCPh)(dippae)] rather than to a dihydrogen-bonded spe-
cies, given the relatively long (T1)min value measured for this
resonance (400 ms), but, of course, any other possibility
cannot be ruled out.
The reaction of the chiral compound 1b with an excess of
PhCOOH shows similarities but also differences with that
of 1a (Figure 8).
As also happens in the previous case, signals attributable
to 1b and also to [CpRuH2((R,R)-dippach)][PhCOO] are
observed in the 1H and 31P{1H} NMR spectra at low
temperatures. The values of T1 measured for the hydridic
(33) Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J. Organomet. Chem.
2000, 609, 161-168.
(34) Ayllo´n, J. A.; Sayers, S. F.; Sabo-Ettienne, S.; Donnadieu, B.;
Chaudret, B.; Clot, E. Organometallics 1999, 18, 3981-3990.
1010 Inorganic Chemistry, Vol. 46, No. 3, 2007

Half-Sandwich Hydride Complexes of Ruthenium
Figure 8. VT 1H NMR (left, hydride region, 400 MHz) and VT 31P{1H}
NMR (right, 161.89 MHz) of a sample made up by the addition of 5 equiv
of PhCOOH to a toluene-d8 solution of 1b.
Figure 9. Plot of the variation of T1 with temperature for the resonance
at ca. -14 ppm observed in the reaction of 1b with an excess of PhCOOH.
resonances in the temperature range -88 to 0 °C are
consistent with this formulation. However, at 0 °C, an abrupt
shortening in the longitudinal relaxation times of both
resonances occurs, falling from 560 ms at 0 °C to a common
value of 150 ms at 25 °C. At higher temperatures, the signals
1
in the H and 31P{1H} NMR spectra get broader. At 70 °C,
only one broad resonance is observed in each of the spectra,
and the T1’s for the hydridic resonances increase their values
smoothly, as shown in Figure 9.
In this case, a protonation-deprotonation equilibrium
involving tight ion pairs seems to occur also at low
temperatures as for 1a. However, above 0 °C, differences
do appear. The drop of the T1’s for both hydridic resonances
to a common value of 150 ms is consistent with a rapid
exchange involving the formation at this temperature of a
long-lived dihydrogen-bonded species with a short H‚‚‚H
contact:
Figure 10. VT 1H NMR (left, hydride region, 400 MHz) and VT 31P-
{1H} NMR (right, 161.89 MHz) of a sample made up by the addition of
0.5 equiv of HFIPOH to a CD2Cl2 solution of 1a.
amounts of HBF4‚OEt2. It is particularly interesting to note
here the formation of the dihydrogen complex [CpRu(H2)-
(dippae)]+, most likely forming a tight ion pair with the
1
[(CF3)2CHO]- anion. This species is responsible for the H
NMR signal at -9.53 ppm and the 31P{1H} NMR resonance
at 113.3 ppm. The (T1)min value of 22 ms is also consistent
with this formulation. At the temperature of -49 °C, the
formation of the tight ion-paired dihydride species [CpRuH2-
(dippae)][(CF3)2CHO] begins, increasing its amount at the
expense of the dihydrogen complex as the temperature is
raised. In the entire temperature range, a resonance is present
at ca. -14 ppm, attributable, in principle, to the monohydride
1a. This resonance is a triplet at low temperature, becomes
broader as the temperature is raised, and then becomes a
sharp triplet again at 25 °C. The species responsible for this
signal gives a broad resonance centered at 137 ppm in the
31P{1H} NMR spectrum at -88 °C, which gets sharper as
the temperature is raised and shifts to a singlet at 132.7 ppm
at 25 °C. The latter position is consistent with that of 1a.
Apart from the broadening of these NMR resonances, the
signal at -14 ppm displays an unusually short (T1)min value
Using eq 1 for estimation of the contribution of the H‚‚‚H
dipole-dipole interaction to relaxation and eq 2 for deter-
mination of the distance, the result is a H‚‚‚H separation of
1.68 Å, fully consistent with the formation of a dihydrogen
bond between benzoic acid and 1b. The homologous species
[TpRu(H‚‚‚HOOCPh)((R,R)-dippach)] containing Tp as the
coligand, having a H‚‚‚H separation of 1.75 Å, has been
recently reported by us.11
Finally, we have studied the proton-transfer reactions using
less than 1 equiv of the acidic alcohol HFIPOH. Figure 10
shows the VT NMR spectra of a sample made up by the
addition of 0.5 equiv of HFIPOH to 1a in CD2Cl2.
These spectra bear a great resemblance to those depicted
in Figure 5, corresponding to protonation with stoichiometric
Inorganic Chemistry, Vol. 46, No. 3, 2007 1011

Jime´nez-Tenorio et al.
in this case the hypothesis that close H‚‚‚F contacts between
the hydride and the fluorine atoms of HFIPOH might be
responsible for the anomalous fast relaxation of the hydride
proton in 1a. With these data in our hands, whatever
explanation might be suggested at this moment for this fast
relaxation phenomenon, it would be merely speculative, and
further research is needed. It is important to mention that
this phenomenon has only been observed when 1a reacted
with less than 1 equiV of HFIPOH. The reaction with a
stoichiometric amount or with an excess of HFIPOH only
revealed the presence of the dihydrogen complex [CpRu-
(H2)(dippae)]+, which irreversibly rearranges to the dihydride
species as the temperature is raised, with no traces of hydridic
species having extra short longitudinal relaxation times.
Figure 11. 1H NMR (hydride region, CD2Cl2, 400 MHz, -20 °C) profile
of 1a + 0.5 equiv of HFIPOH recorded at variable delay times in a typical
inversion-recovery experiment for T1 determination, showing the faster
relaxation of the resonance at higher field compared to that at -9.5 ppm
attributed to a dihydrogen complex.
Conclusions
A series of neutral and cationic CpRu and Cp*Ru hydride
complexes bearing chelating phosphinoamine ligands have
been prepared and characterized in which no significant
interactions between the hydrogen atoms bound to the metal
and the NH groups of the phosphinoamine ligands have been
detected. Protonation of the monohydride complexes 1a,b
or 2a,b or of the dihydrides 3a,b or 4a,b with an excess of
HBF4 leads to dicationic dihydride complexes 5a,b or 6a,b
resulting from protonation of one of the NH groups of the
phosphinoamine ligand. In the course of the protonation of
1a with HBF4, the metastable dihydrogen complex [CpRu-
(H2)(dippae)]+ was detected as an intermediate. Spectral
evidence for the formation of a dihydrogen-bonded species
of the type [CpRu(H‚‚‚HOEt2)(dippae)]+ prior to the proton-
transfer process has also been obtained. When a weak acid
such as PhCOOH was used in a solvent of low polarity such
as toluene-d8, a protonation-deprotonation equilibrium most
likely involving the formation of tight ion pairs occurs. In
the case of the reaction of 1b, the dihydrogen-bonded
complex [CpRu(H‚‚‚HOOCPh)((R,R)-dippach)] has been
identified. A remarkable shortening in the (T1)min value of
the hydride signal of the monohydrides 1a to 6.5 ms (i.e.,
shorter than that for the dihydrogen complex [CpRu(H2)-
(dippae)]+) has been observed upon the addition of 0.5 equiv
of HFIPOH in CD2Cl2. Paramagnetic contributions to
relaxation have been ruled out. Although everything seems
to point to the formation of a dihydrogen-bonded species
between 1a and HFIPOH, this is another example of a system
having an anomalously short (T1)min, and the reasons for this
fast relaxation phenomenon remain as yet unknown.
of 6.5 ms. Figure 11 shows clearly the rapid relaxation of
the signal at -14 ppm at -20 °C, which has already passed
through the null intensity point at a delay of 10 ms, whereas
the signal corresponding to the dihydrogen protons at ca.
-9.5 ppm is still inverted.
This behavior resembles very much the phenomenon
previously observed by us11 and by other researchers14
involving species having very short (T1)min’s. We can also
rule out here the contributions to relaxation coming from
paramagnetic species, so the phenomenon shown in Figure
11 is clearly not an artifact. The reasons why this phenom-
enon occurs are yet unknown. In here, a minimum longitu-
dinal relaxation time of 6.5 ms is far shorter than that
observed for the dihydrogen complex and would involve an
unrealistically short H-H distance of 0.74 Å. Everything
would suggest that the species responsible for this signal is
a dihydrogen-bonded species of the type [CpRu(H‚‚‚HOCH-
(CF3)2)(dippae)], except for the anomalously short (T1)min
.
As a tentative explanation in this particular case, we could
eventually propose a multiple simultaneous interaction of the
hydride with the hydrogen atom of the alcohol and the
fluorine atoms of the CF3 substituents, maybe favored by
additional hydrogen bonding between the HFIPOH molecule
and the NH groups of the phosphinoamine ligand. Given
the NMR properties of the 19F nucleus compared to those of
1H, an efficient contribution to relaxation would be expected
from H‚‚‚F dipole-dipole interactions. We have carried out
1
a 2D HOESY H-19F NMR experiment in order to gather
information about this possibility. Only one signal is present
in the 19F NMR spectrum of the mixture resulting from the
addition of 0.5 equiv of HFIPOH to 1a in CD2Cl2. No H‚‚
‚F interactions were observed other than the expected
coupling with the isopropyl proton of HFIPOH. Furthermore,
no anomalous shortening of T1 of the 19F NMR resonance
of HFIPOH in the mixture was observed, when compared
to the value measured for T1 of the 19F NMR resonance of
pure HFIPOH in a CD2Cl2 solution. If indeed fluorine atoms
were causing fast relaxation on the hydride proton due to
dipole-dipole interactions, a reduction in T1 of the fluorine
atoms should also be expected. Hence, these results rule out
Acknowledgment. We thank the Ministerio de Educacio´n
y Ciencia (DGI, Project CTQ2004-00776/BQU, and Grant
BES2002-1422 to M.D.P.) and Junta de Andaluc´ıa (Grant
PAI FQM188) for financial support and Johnson Matthey
plc for generous loans of ruthenium trichloride.
Supporting Information Available: Tables of X-ray structural
data in CIF format, including data collection parameters, positional
and thermal parameters, and bond distances and angles for complex
4a. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC061745U
1012 Inorganic Chemistry, Vol. 46, No. 3, 2007