Proton-transfer reactions to half-sandwich ruthenium trihydride complexes bearing hemilabile P,N ligands: Experimental and density functional theory studies

Inorg. Chem. 2010, 49, 6035–6057 6035

DOI: 10.1021/ic100710d

Proton-Transfer Reactions to Half-Sandwich Ruthenium Trihydride

Complexes Bearing Hemilabile P,N Ligands: Experimental and Density

Functional Theory Studies^†

ꢀ

Manuel Jimenez-Tenorio,* M. Carmen Puerta,* and Pedro Valerga

´

ꢀ

Departamento de Ciencia de Materiales e Ingenierıa Metaluꢀrgica y Quımica Inorganica, Facultad de Ciencias,

ꢀ

Universidad de Cadiz, 11510 Puerto Real, Cadiz, Spain

ꢀ

´

Salvador Moncho, Gregori Ujaque, and Agustı Lledos*

´

ꢁ

Departament de Quımica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

Received April 16, 2010

The trihydride complexes [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂X)] [X = pyridine (Py), 2a; quinoline (Quin), 2b] have been

prepared by reaction of the corresponding chloro derivatives [Cp*RuCl(κ²-P,N-ⁱPr₂PCH₂X)] [X=Py (1a), Quin (1b)]

with NaBH₄in methanol. Both 2a and 2b exhibit quantum-mechanical exchange coupling. The proton-transfer

reactions to 2a and 2b using strong as well as weak proton donors have been experimentally and computationally

studied. Density functional theory studies have been performed to analyze the stability of the proposed species, the

hydrogen exchange, and the protonation pathway. The reactions with weak donors such as PhCOOH, indole, or

salicylic acid in benzene or toluene result in the formation of hydrogen-bonded adducts between the proton donor and

the pendant pyridine or quinoline group. However, in a more polar solvent such as dichloromethane, there is spectral

evidence for the proton transfer to the hydride to yield a dihydrogen complex. The protonation with CF₃SO₃H in CD₂Cl₂

occurs in a stepwise manner. In a first step, the pendant pyridine or quinoline group is protonated to yield [Cp*RuH₃(κ¹-

P-ⁱPr₂PCH₂XH)]^þ[X = Py (4a) or Quin (4b)]. The NH proton is then transferred to the hydride and one molecule of

dihydrogen is released, furnishing the cationic mono(dihydrogen) complexes [Cp*Ru(H₂)(κ²-P,N-ⁱPr₂PCH₂X)]^þ[X=

Py (5a) or Quin (5b)]. These species are thermally stable and do not undergo irreversible rearrangement to their

dihydride isomers. In the presence of an excess of acid, a second protonation occurs at the hydride site and the

dicationic complexes [Cp*RuH₄(κ¹-P,N-ⁱPr₂PCH₂XH)]^2þ[X=Py (6a) or Quin (6b)] are generated. These species are

stable up to 273 K and consist of equilibrium mixtures between bis(dihydrogen) and dihydrido(dihydrogen) tautomeric

forms. Above this temperature, 6a and 6b are converted into the corresponding cationic mono(dihydrogen) complexes

5a/5b. The crystal structures of [Cp*RuCl(κ²-P,N-ⁱPr₂PCH₂Quin)] (1b), [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂Quin)] (2b), [Cp*-

RuH₃(κ¹-P-ⁱPr₂PCH₂Py

H

OOCC₆H₄OH)] (3a), [Cp*Ru(H₂)(κ²-P,N-ⁱPr₂PCH₂Quin)][BAr⁰₄] (5b), [Cp*Ru-

3 3 3 3 3 3₀

(N₂)(κ²-P,N-ⁱPr₂PCH₂Quin)][BAr ₄] (8b), and [Cp*Ru(O₂)(κ²-P,N-ⁱPr₂PCH₂Quin)][BAr⁰₄] (9b) are reported.

Introduction

features of this class of compounds is their propensity to

exhibit quantum-mechanical exchange coupling (QEC).^8,9

This behavior is related to high hydride mobility. In order

for such a phenomenon to be observed, a low energy barrier

Ruthenium trihydride complexes of the type [Cp*RuH₃-

(L)] (L = PR₃,^1-5AsPh₃,⁶SbPh₃,⁶N-heterocyclic carbene⁷)

are an important class of polyhydrides. One of the main

^†Dedicated to Prof. Serafin Bernal in recognition of his contribution to

inorganic chemistry, on the occasion of his retirement.

*To whom correspondence should be addressed. E-mail: manuel.tenorio@

uca.es (M.J.-T.), carmen.puerta@uca.es (M.C.P.), agusti@klingon.uab.es

(A.L.). Tel: þ34 956 016340 (M.J.-T.). Fax: þ34 956 016288 (M.J.-T.).

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r

2010 American Chemical Society

Published on Web 06/04/2010

pubs.acs.org/IC

ꢀ

Jimenez-Tenorio et al.

6036 Inorganic Chemistry, Vol. 49, No. 13, 2010

and a short path length are required for pairwise hydrogen

exchange. This has prompted detailed spectroscopic and

theoretical studies in order to account for the origin of the

QEC phenomenon and also the dynamic behavior of the

hydride ligands on these systems.^10-15QEC has proven to be

a hypersensitive indicator of weak interaction.¹⁶In this way,

QEC can be modulated through hydrogen bonding. Thus,

the addition of various proton donors such as methanol

(MeOH), indole, phenol, or hexafluoroisopropanol to [Cp*-

RuH₃(PCy₃)] leads to an increase of QEC between the

hydride sites.^17,18This has been interpreted in terms of a

hydrogen-bonding interaction¹⁹between [Cp*RuH₃(PCy₃)]

and the proton donors added. The protonation of [Cp*-

RuH₃(PR₃)] (PR₃= PPh₃, PCy₃) with a strong acid such as

(κ¹-P-ⁱPr₂PCH₂X)] leads to selectivity problems in the pro-

ton-transfer reaction, namely, protonation at the hydride site

and protonation at the metal or nitrogen atom of the pendant

pyridyl or quinolyl group.²²On the other hand, the nitrogen

atom in these groups may act as an internal base, which

assists proton transfer to the hydride ligands. This fact has

shown to be extremely important in reactions of hydride

complexes bearing PPh₂Py. Thus, the use of the phosphine

PPh₂Py instead of PPh₃in complexes of the type [Cp*-

RuH(P)₂] enormously alters the kinetic control of the pro-

ton-transfer reactions over this compound and its chemical

behavior.²³Thus, the reaction at low temperature of [Cp*-

RuH(PPh₂Py)₂] with 1 equiv of HBF₄yields the dihydride

[Cp*RuH₂(PPh₂Py)₂][BF₄], whereas a second protonation

HBF₄OEt₂led to extensive dihydrogen evolution and dehy-

leads to the dihydrogen-bonded complex [Cp*RuH{H

HPyPPh₂}(PPh₂Py)][BF₄]₂.

3

3 3 3

drogenation of one cyclohexyl ring of the PCy₃ligand.³At

variance with this, the trihydrides [Cp*RuH₃(EPh₃)] (E =

Inthis work, we describe thesynthesisand characterization

of Cp*Ru trihydride and related complexes containing the

As, Sb) were protonated by HBF₄OEt₂in CH₂Cl₂at 193 K,

3

i

furnishing the corresponding cationic bis(dihydrogen) com-

plexes [Cp*Ru(η²-H₂)₂(EPh₃)][BF₄], which were character-

ized in solution by T₁and ¹J_HDmeasurements.⁶These species

decompose at T > 273 K. [Cp*RuH₄(PCy₃)]^þwas identified

as the species resulting from protonation of the hydrogen-

hemilabile ligands Pr₂PCH₂Py or Pr₂PCH₂Quin and the

study by variable-temperature (VT) NMR spectroscopy of

their proton-transfer reactions with both weak and strong

protondonors. Density functionaltheory (DFT) studieshave

been performed to analyze the stability of the proposed

species, the hydrogen exchange, and the protonation pathway.

These studies suggest that the protonation reaction occurs in

two steps. First, the pendant nitrogen atom is protonated

and a dihydrogen-bonded hydride is formed. Then, the NH

proton is transferred to the hydride, releasing one molecule of

dihydrogen and furnishing the dihydrogen complex [Cp*-

Ru(H₂)(κ²-P,N-Me₂PCH₂Py)]^þ, which is more stable than its

ruthenium(IV) dihydride isomer. In the presence of an excess

of acid, a second protonation occurs, leading to the bis(di-

hydrogen) complex [Cp*Ru(η²-H₂)₂(κ¹-P-Me₂PCH₂PyH)]^2þ

as the most stable species. These results are fully consistent

with the experimental observations hereby presented.

bonded complex [Cp*RuH₃(PCy₃)] [HOR] [R = CH-

3 3 3

(CF₃)₂, C(CF₃)₃] by the corresponding ROH in a CDClF₂/

CDCF₃mixture at 200 K.¹⁸T₁measurements for [Cp*RuH₄-

(PCy₃)]^þwere consistent with a dihydrido(dihydrogen) struc-

ture [Cp*RuH₂(η²-H₂)(PCy₃)]^þ, although a bis(dihydrogen)

structure [Cp*Ru(η²-H₂)₂(PCy₃)]^þwas not ruled out.

We have now prepared Cp*Ru complexes bearing the

hemilabile ligands diisopropylphosphinomethylpyridine

(ⁱPr₂PCH₂Py) and diisopropylphosphinomethylquinoline

(ⁱPr₂PCH₂Quin). The trihydride complexes [Cp*RuH₃(κ¹-

P-ⁱPr₂PCH₂X)] [X = pyridine (Py), quinoline (Quin)], with

one dangling pyridine or quinoline group, have been synthe-

sized and characterized. P,N-donor ligands such as pyridyl-

phosphines PR₂Py and their relatives with CH₂groups as

spacers between the pyridine and the phosphorus atom have

a great interest because of their potential hemilabile character

because they can furnish complexes that behave as masked

16-electron coordinatively unsaturated species.^20,21The pre-

sence of several competing protonation sites in [Cp*RuH₃-

Results and Discussion

1. Preparation and Characterization of Halo- and Tri-

hydrido Complexes. The tetramer [{Cp*RuCl}₄] reacts

cleanly with either ⁱPr₂PCH₂Py or ⁱPr₂PCH₂Quin in petro-

leum ether, furnishing the corresponding chloro complex

[Cp*RuCl(κ²-P,N-ⁱPr₂PCH₂Py)] (1a) or [Cp*RuCl(κ²-

P,N-ⁱPr₂PCH₂Quin)] (1b) in good yield. 1a is a red-orange

compound that exhibits NMR features consistent with a

three-legged-piano-stool structure, involving a κ²-P,N

chelating phosphinomethylpyridine. In such a geometry,

the protons of the methylene group linking the phos-

phorus atoms and the pyridine are inequivalent and

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resonances that get sharper as the temperature increases,

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solution. Thus, the CH₂protons at 25 °C appear as two

broad signals, consistent with an unresolved ABX spin

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Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6037

Scheme 2

Figure 1. ORTEP drawing (50% thermal ellipsoids) of 1b. Hydrogen

atoms have been omitted. Selected bond lengths (A) and angles (deg) with

estimated standard deviations in parentheses: Ru1-P1 2.3135(7), Ru1-

N12.1712(19), Ru1-Cl1 2.4867(9), Ru1-C1 2.192(2), Ru1-C2 2.164(2),

Ru1-C3 2.192(2), Ru1-C4 2.211(2), Ru1-C5 2.181(2); P1-Ru1-N1

79.23(5), P1-Ru1-Cl1 95.42(2), N1-Ru1-Cl1 91.98(6).

comparable with values previously reported in the litera-

ture for related complexes, i.e., in [Cp*RuCl(dippe)],²⁴or

in [{η⁵-C₅H₄C(CH₃)₂CH(PPh₂)C₅H₄N}Ru(PPh₃)][PF₆].²⁵

1a and 1b react with an excess of NaBH₄in MeOH to

give the trihydride complexes [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂-

Py)] (2a) or [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂Quin)] (2b). The

reactions can be carried out at room temperature, but

because of the strong evolution of dihydrogen and the

observed exothermic effects, it is more convenient and

safe to perform the syntheses at 0 °C by using an ice bath.

Complexes 2a and 2b can also be prepared directly from

Scheme 1

i

[Cp*RuCl₂]_nby reaction with either Pr₂PCH₂Py or

ⁱPr₂PCH₂Quin and an excess of NaBH₄in MeOH, pre-

sumably through the intermediacy of the corresponding

ruthenium(III) derivative of the type [Cp*RuCl₂(ⁱPr₂-

PCH₂X)] (X=Py, Quin), which was not isolated (Scheme 2).

Both 2a and 2b are crystalline materials, very soluble in

both polar and nonpolar solvents, that exhibit medium-

explained in terms of dissociation of the quinoline group

from the ruthenium atom and recoordination on the other

side of the molecule upon rotation around the Ru-P bond.

This can be viewed as an effective racemization, which

involves the mutual exchange of the two CH₂protons

through the intermediacy of a 16-electron intermediate

containing one κ¹-P-phosphinomethylquinoline ligand,

as shown in Scheme 1.

Complexes of the type Cp*RuCl(P) are well-known.

They are usually blue or purple in color and in our system

constitute an obvious choice as intermediate species.

Interestingly, when recorded in CD₂Cl₂as the solvent,

very well-resolved NMR spectra were obtained for 1b, in

contrast with the behavior observed in a nonpolar solvent

such as C₆D₆. The observed differences in color between

compounds 1a and 1b, as well as the dynamic behavior of

1b in solution, prompted us to examine the solid-state

structure of 1b by X-ray analysis. An ORTEP view of

complex 1b is shown in Figure 1, together with the most

relevant bond distances and angles.

strong ν(Ru-H) bands in their IR spectra near 1989 cm^-1

.

The crystal structure of 2b was determined by means of

X-ray analysis. An ORTEP view of the complex 2b is

shown in Figure 2, together with the most relevant bond

distances and angles.

The structure of 2b consists of a packing of discrete

molecules of the trihydride complex. The nitrogen atom

of the quinoline group points away from the hydrides and

does not show any interaction either intra- or intermole-

cular with these ligands. The geometry around the ruthe-

nium atom in 2b can be described as a four-legged piano

stool, an arrangement very similar to that observed in the

structures of [Cp*RuH₃(PPh₃)],¹[Cp*RuH₃(P(pyrrolyl)₃)],²⁶

and [CpRuH₃(PPh₂Pr)].²⁷The hydride ligands H1 and

i

H3 adopt a mutually transoid disposition, whereas the

hydride H2 is transoid to the phosphorus atom. The

ruthenium-hydride separations between 1.51 and 1.54

A compare well with the Ru-H bond distances in the

Crystal structure analysis of the complex showed that

1b adopts standard three-legged-piano-stool geometry in

the solid state. The quinoline rings are planar, but the

five-membered ring formed by Ru1, P1, C20, C11, and

N1 is not planar. The plane defined by the quinoline

forms an angle of 37.8° with the plane defined by Ru1,

P1, and C20. All of the Ru-P, Ru-N, and Ru-Cl

separations, as well as the Ru-C bond distances, are

ꢀ

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Valerga, P. J. Chem. Soc., Dalton Trans. 1996, 377–381.

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Jimenez-Tenorio et al.

6038 Inorganic Chemistry, Vol. 49, No. 13, 2010

exchange between the central (H_A) and side hydride ligands

(H_Band H_C) has an energy barrier ΔG^qof 41.7 ( 0.8 kJ

mol^-1for 2a and 42.4 ( 0.7 kJ mol^-1for 2b (determined

by VT-NMR line-shape analysis). These values are inter-

mediate between 40 kJ mol^-1reported for the hydride-

exchange energy barrier in [CpRuH₃(PPh₃)]¹⁰and 46 kJ

mol^-1in the case of [Cp*RuH₃(PCy₃)].^2,8The QEC

constants in our systems also have values that are inter-

mediate between those reported for [Cp*RuH₃(PPh₃)]

(290 Hz at 190 K) and [Cp*RuH₃(PCy₃)] (60 Hz at

190 K).⁸This can be interpreted in terms of control of

the exchange coupling and the hydride-exchange barrier

as a function of the basicity of the ancillary ligands,

i

placing Pr₂PCH₂X (X = Py, Quin) between PPh₃and

PCy₃on this scale.

We have theoretically studied the hydrogen-exchange

process in the model complex [Cp*RuH₃(κ¹-P-Me₂-

PCH₂Py)] (2a_m). The optimized geometries of the mini-

mum and the transition state for the hydrogen exchange

are depicted in Figure 4.

Figure 2. ORTEP drawing (50% thermal ellipsoids) of 2b. Hydrogen

atoms except hydride have been omitted. Selected bond lengths (A) and

angles (deg) with estimated standard deviations in parentheses: Ru1-P1

2.2574(9), Ru1-H1 1.51(2), Ru1-H2 1.51(2), Ru1-H3 1.54(2),

Ru1-C1 2.2130(18), Ru1-C2 2.2291(18), Ru1-C3 2.2868(18), Ru1-C4

2.3133(17), Ru1-C5 2.2554(17), H1 H2 1.70, H2 H3 1.55; P1-

Two different conformations, both with a trihydride

nature but differing in the orientation of the pyridine ring,

were obtained as minima for the initial complex 2a_m. The

structure with the nitrogen atom of the pyridine pointing

away from the hydrides is 8.0 kJ mol^-1more stable than

the conformer with the nitrogen atom pointing toward

the hydrides. Indeed, this is the conformation found in the

X-ray structure of 2b (Figure 2). The transition state for

the exchange between central and lateral hydrides shows a

η²-H₂complex-like nature, as can be inferred from the

H-H distance and the H-Ru-H angle between the

exchanging atoms (0.872 A and 30.0°, respectively). As

found in previous theoretical studies of hydrogen ex-

change in trihydrides, this process entails approaching

and rotating the two exchanging hydrogen atoms.^12,13,28

3 3 3

Ru1-H2 94.9(8), P1-Ru1-H1 74.4(8), P1-Ru1-H3 70.5(7), H1-

Ru1-H2 68.5(10), H1-Ru1-H3 113.7(11), H2-Ru1-H3 60.9(10).

other discrete [(C₅R₅)RuH₃P] (R = H, Me) complexes

that have been structurally characterized (within the

uncertainty affecting the position of the hydride ligands

determined by X-ray crystallography).^1,26,27The values

determined for the Ru-H bond distances and their

arrangement around ruthenium lead to rather short

hydride-hydride separations, in the interval of 1.55-

1.70 A.

The calculated Gibbs energy of activation is 63 kJ mol^-1

,

2. Hydrogen Exchange in the Trihydrides. At room

temperature, the three hydrides in 2a/2b are equivalent

and appear as one doublet in the high-field region of the

¹H NMR spectra. These hydride resonances exhibit

minimum longitudinal relaxation times (T₁)_minof 189 ms

for 2a and 184 ms for 2b (400 MHz, CD₂Cl₂). These

values are consistent with the relatively short hydride-

hydride separations found by X-ray crystallography. In

contrast with 1a/1b, the CH₂protons of the phosphino-

methylpyridine or phosphinomethylquinoline ligands are

equivalent in the ¹H NMR spectra of 2a/2b, giving rise to

one doublet. This is characteristic of the κ¹-P-coordina-

tion mode for these ligands. As occurs in other Cp*RuH₃-

(P) [P = PⁱPr₃, PCy₃, P(pyrrolyl)₃] complexes, QEC has

also been observed for the hydride ligands in 2a and 2b. At

low temperature, the hydrides become inequivalent, giv-

slightly higher than the values determined for 2a and 2b

by VT-NMR line-shape analysis but in the range of the

theoretically calculated barriers for systems exhibiting

QEC.^12,13,28Calculations confirm that in these ruthenium

trihydrides exists a pathway with a low barrier and a short

path length for the hydrogen exchange, as required for

observation of QEC.

3. Reactions with Weak Proton Donors: Hydrogen and

Dihydrogen Bonding. The reactions of 2a/2bwith PhCOOH

or indole in the ratio 1:1 complex/proton donor in

CD₂Cl₂were monitored in the temperature range -80

to þ25 °C. Very slight changes in the chemical shifts

were observed in the ¹H and ³¹P{¹H} NMR spectra

compared to the values for 2a/2b in the absence of the

proton donor. The protic hydrogen of the donor appears in

the ¹H NMR spectra in all cases as a broad or very broad

low-field signal, at a chemical shift that varies considerably

withthe temperature. QEC and rapid hydride exchange are

maintained. As a general tendency, the values of the QEC

constants show a slight to moderate increase. The largest

1

ing rise to a complex multiplet in the H NMR spectra.

The VT ¹H NMR spectra of 2a/2b in the high-field region

(CD₂Cl₂) are shown in Figure 3.

1

The VT H NMR spectra were successfully simulated

assuming an ABCX spin system, where A-C are the

hydrides and X represents the phosphorus atom. At 193 K,

increase has been observed in the case of 2a upon the

addition of indole, in which

236 Hz (Table 1).

QEC

the QEC constants J(H_A,H_B) = J(H_A,H_C) =

J

QEC

HH

J

HH

changes from 176 to

derived by NMR line-shape analyses have values of

176 Hz for 2a and of 185 Hz for 2b. The values for these

constants are temperature-dependent, as is characteristic

in QEC, and at 213 K, their values increase to 273 and

311 Hz, respectively. The dynamic process of two-site

ꢀ

(28) Castillo, A.; Barea, G.; Esteruelas, M. A.; Lahoz, F. J.; Lledos, A.;

~

Maseras, F.; Modrego, J.; Onate, E.; Oro, L. A.; Ruiz, N.; Sola, E. Inorg.

Chem. 1999, 38, 1814–1824.

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6039

Figure 3. VT ¹H NMR spectra (hydride region, 600 MHz, CD₂Cl₂) of 2a (A) and 2b (B).

equilibrium involving the formation of dihydrogen-

bonded species [Cp*RuH₂(H HA)(κ¹-P-ⁱPr₂PCH₂X)]

3 3 3

(HA=PhCOOH, indole; X=Py, Quin) as well as species

containing one standard hydrogen bond between the

proton donor and the nitrogen atom of the pendant

pyridyl or quinolyl group in which the hydride ligands

do not participate in this interaction (Chart 1). Our data

suggest that the equilibrium is shifted toward the species

having hydrogen bonding with the nitrogen atom.

We have studied as well the interaction of 2a/2b with

salicylic acid (Table 1). The molecule of salicylic acid has

two protons of different acidity arranged in such a way

that the simultaneous interaction with both the nitrogen

atom of the pendant group and the hydride ligands might

be feasible. Upon the addition of 1 equiv of salicylic acid

QEC

Figure 4. Optimized geometries of the trihydride minimum and the

transition state for the hydrogenexchange in 2a_m. Hydrogen atoms except

hydrides have been omitted.

to 2b in dichloromethane (DCM),

J

HH

increased slightly

to a value of 202 Hz. (T₁)_minof the hydride resonance

changed also very slightly to a value of 200 ms. However,

the appearance of the VT H NMR spectra profile was

different from that obtained for the cases in which

PhCOOH or indole were added (Figure 5).

1

In contrast with this, it has been reported that the

addition of various proton donors to [Cp*RuH₃(PCy₃)]

leads to a significant increase of QEC between the hydride

sites, indicative of the formation of dihydrogen bonds

between the hydride ligands and the proton donor.^17,18In

our case, the values of (T₁)_minfor the hydride resonances

in the presence of the proton donor do not vary to a great

extent compared to the values measured in the absence of

With salicylic acid, as the temperature increases, the

second-order multiplet for the hydrides becomes a broad

resonance that does not resolve into one doublet, resulting

from rapid intramolecularhydride exchange. Furthermore,

at 298 K, the spectrum becomes featureless in the hydride

region (Figure 5B). The ³¹P{¹H} NMR at 193 K shows

one broad signal centered at 96.6 ppm, which is signifi-

cantly shifted from the position of the resonance for 2b at

the same temperature (88.4 ppm). As the temperature

increases, the phosphorus resonance becomes sharper.

An almost identical behavior was observed in the case of

compound 2a in the presence of 1 equiv of salicylic acid

(Figure 5A). However, at variance with 2b, (T₁)_minfor the

hydride resonance decreases to a value of 16 ms at 273 K.

This value is very short and consistent with the formation

PhCOOH or indole. However, the H H separations

3 3 3

expected in a dihydrogen bond should be in the range

1.61-2.10 A.^19,20This distance would be on the same

order as the hydride-hydride separations already present

in 2a/2b. Therefore, a significant shortening in (T₁)_minis

not expected even in the case of the formation of dihydro-

gen bonds. These data suggest that the interaction be-

tween the hydride ligands in 2a/2b and the proton of

either PhCOOH or indole is not very significant. We have

interpreted our data in terms of the occurrence of an

ꢀ

Jimenez-Tenorio et al.

6040 Inorganic Chemistry, Vol. 49, No. 13, 2010

Table 1. Values of ^QECJ_HHand (T₁)_minfor the Hydride Resonances and of δ for the Most Relevant ¹H and ³¹P{¹H} NMR Resonances of 2a/2b in the Presence of Weak

Proton Donors (400 MHz, CD₂Cl₂)

QEC

entry

complex

proton donor

J

HH

(Hz)^a

(T₁)_min(ms)

¹H δ (ppm):^bRuH₃, C₅(CH₃)₅

³¹P{¹H} δ (ppm)^b

1

2

3

4

5

6

7

8

2a

2b

176

184

236

225

185

195

202

189

175

192

16.7

184

189

186

200

-11.39, 1.92

-11.36, 1.95

-11.18, 2.00

-11.32, 1.93

-11.33, 1.93

-11.30, 1.92

-11.31, 1.93

-11.26, 1.92

86.8

89.6

87.4

94.3

88.4

89.8

87.5

96.6

PhCOOH

indole

salicylic acid

PhCOOH

indole

salicylic acid

^aAt 193 K. ^bAt 203 K.

Chart 1

for X-ray structure analysis, which showed this compound

to be the hydrogen-bonded supramolecular aggregate

[Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂Py

H

OOCC₆H₄OH)] (3a).

3 3 3 3 3 3

An ORTEP view of this compound is shown in Figure 6,

together with the most relevant bond distances and

angles.

The structure of compound 3a consists of molecules of

the trihydride complex 2a and of salicylic acid assembled

through a strong hydrogen bond between the hydrogen

atom of the carboxylic group and the nitrogen atom of the

pyridine substituent. The geometry and the dimensions of

the trihydride complex moiety do not differ much from

those found for 2b by X-ray crystallography. The nitro-

gen atom N1 of the pyridine and the oxygen atom O1 of

the salicylic acid are linked by a strong hydrogen bond

involving the atom H1b. This hydrogen atom is essen-

tially equidistant from O1 [1.25(3) A] and N1 [1.29(3) A].

The angle O1-H1b N1 of 176(2)° indicates that these

3 3 3

three atoms are colinear. There is another hydrogen bond

within the salicylic acid moiety involving the hydrogen

atom H3b and the oxygen atoms O1 and O2. However, in

this case, the hydrogen bond is unsymmetrical and the

H3b O2 separation is much longer [1.81(3) A]. There

3 3 3

are no intra- or intermolecular interactions with hydride

ligands. The Ru-H separations range from 1.48(2) to

1.55(2) A, being unexceptional. The supramolecular ar-

rangement of the trihydride complex and salicylic acid

strongly linked by a symmetrical hydrogen bond is similar

to that found by X-ray crystallography in the structure of

the adduct bis[1,2-bis(4⁰-pyridyl)ethene] (2R,3R)-tartaric

acid (2R,3R)-tartrate.²⁹

of species containing at least one dihydrogen ligand. We

have rationalized this behavior by considering the en-

hanced acidity of salicylic acid compared to other weak

proton donors due to the presence of a hydrogen-bond

donor near the carboxyl group. Thus, in a polar solvent

such as CD₂Cl₂, salicylic acid transfers one proton to the

nitrogen atom of the pendant groups in either 2a or 2b,

furnishing tightly hydrogen-bonded ion pairs (Chart 2).

In the case of 2a, a further equilibrium takes place in

which the proton on the nitrogen atom is transferred to

the hydrides, leading to a cationic dihydrogen complex

that may, in fact, contain up to two dihydrogen ligands,

given the short (T₁)_minvalue of 16.7 ms measured for this

system (Chart 3).

We carried out an attempt to isolate the product

resulting from the reaction of 2a with salicylic acid. Thus,

an orange crystalline material was obtained upon treat-

ment of a toluene solution of 2a with 1 equiv of salicylic

acid at room temperature. At variance with 2a, this pro-

duct was not soluble in petroleum ether. Its IR spectrum

showed a ν(Ru-H) band at 1979 cm^-1and one band

attributable to ν(CdO) at 1596 cm^-1. Recrystallization

from toluene/petroleum ether afforded crystals suitable

In this compound, a partial transfer of hydrogen

occurs, manifested in the almost centered O

H

N

H

3 3 3 3 3 3

interaction (bond distances: O H 1.277 A; N

3 3 3

(29) Farrell, D. M. M.; Ferguson, G.; Lough, A. J.; Glidewell, C. Acta

Crystallogr., Sect. B: Struct. Sci. 2002, 58, 272–288.

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6041

1.278 A). Likewise, in the case of 3a, a partial transfer of

the hydrogen atom from the salicylic acid to the nitrogen

atom of the pyridine has also occurred, furnishing an

aggregate that can be viewed as an intermediate situation

between an adduct of 2a with salicylic acid and an ion pair

of the cation [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂PyH)]^þwith one

salicylate anion.

Recent work has pointed out the profound effect that

the nature of the solvent can have on the outcome of the

protonation of neutral hydrides.³⁰Thus, the polarity of

the solvent plays a crucial role in determining the position

of the equilibrium in the proton-transfer reactions shown

in Charts 2 and 3. The NMR spectra of 3a in C₆D₆or

toluene-d₈differ considerably from those recorded in

CD₂Cl₂. At 298 K, one doublet is observed in the hydride

1

region of the H NMR spectrum, whereas in CD₂Cl₂at

the same temperature, the spectrum shows an extremely

broad resonance that almost merges with the baseline

(Figure 5A). T₁values measured at 298 K for the hydride

signal in CD₂Cl₂and in C₆D₆are 21 and 550 ms, re-

spectively. This observation is fully consistent with the

fact that equilibrium shifts in favor of ionic structures

because of the cooperative effect of hydrogen bonding

with polar neighbors as the solvent polarity increases.³¹

This has a remarkable effect on determining the position

of the proton-transfer equilibrium involving transition-

metal hydrides, as has recently been demonstrated in the

case of [RuH₂{P(CH₂CH₂PPh₂)₃].³²

4. Computational Study of Hydrogen Bonding with

Weak Acids. The formation of hydrogen-bonded adducts

was investigated with indole, using the model system 2a_m.

From previous computational studieson hydrogen-bonded

adducts between transition-metal trihydrides and weak

proton donors, it arises that 2a_mhas five potential hydro-

gen-bonding sites: the nitrogen atom of the ligand, the

three hydrides, and the metal.^33,34To account for all of

the possible hydrogen-bonded minima, we optimized the

adduct between indole and 2a_m, starting from different

regions around the metal and pyridine. In this way, three

stable hydrogen-bonded structures were obtained, as

shown in Figure 7 (top).

In the adduct 2a_mindole^NH, a normal hydrogen bond

3

occurs between the nitrogen of the pyridyl group and the

indole. The other two structures (2a_mindole^H1and

3

2a_mindole^H2) both exhibit a bifurcated dihydrogen bond

3

between the proton donor and two hydride ligands: the

central hydrogen atom and that on the side of the pyridyl

nitrogen atom (2a_mindole^H1) and the central atom and

3

(30) (a) Dub, P. A.; Baya, M.; Houghton, J.; Belkova, N. V.; Daran, J.-C.;

Poli, R.; Epstein, L. M.; Shubina, E. S. Eur. J. Inorg. 2007, 2813–2826.

(b) Dub, P. A.; Belkova, N. V.; Filippov, O. A.; Daran, J.-C.; Epstein, L. M.;

Figure 5. VT ¹H NMR spectra (hydride region, 400 MHz, CD₂Cl₂)

of samples made by the addition of 1 equiv of salicylic acid to 2a (A) or

2b (B).

ꢀ

Lledos, A.; Shubina, E. S.; Poli, R. Chem.—Eur. J. 2010, 16, 189–201.

(31) Sharif, S.; Denisov, G. S.; Toney, M. D.; Limbach, H.-H. J. Am.

that away from the pyridyl nitrogen atom (2a_mindole^H2).

3

Chem. Soc. 2006, 128, 3375–3387.

Recent studies have pointed out that in M-H HA

(32) Belkova, N. V.; Gribanova, T. N.; Gutsul, E. I.; Minyaev, R. M.;

Bianchini, C.; Peruzzini, M.; Zanobini, F.; Shubina, E. S.; Epstein, L. M.

J. Mol. Struct. 2007, 844-845, 115–131.

3 3 3

dihydrogen-bonded structures the proton could be inter-

acting with both the metal atom and the hydride ligand.³⁴

The relatively short Ru H(O) distances (2.841 A in

(33) Bakhmutova, E. V.; Bakhmutov, V. I.; Belkova, N. V.; Besora, M.;

ꢀ

ꢁ

Epstein, L. M.; Lledos, A.; Nikonov, G. I.; Shubina, E. S.; Tomas, J.;

3 3 3

2a_mindole^H1and 2.792 A in 2a_mindole^H2) and the almost

Vorontsov, E. V. Chem.—Eur. J. 2004, 10, 661–671.

(34) (a) Belkova, N. V.; Revin, P. O.; Besora, M.; Baya, M.; Epstein,

3

linear Ru H-O angles (169.5° in 2a_mindole^H1and

3 3 3

3

ꢀ

L. M.; Lledos, A.; Poli, R.; Shubina, E. S.; Vorontsov, E. V. Eur. J. Inorg.

174.0° in 2a_mindole^H2) suggest significant participation

3

2006, 2192–2209. (b) Belkova, N. V.; Besora, M.; Baya, M.; Dub, P. A.; Epstein,

of the metal atom to hydrogen bonding.³⁴The most stable

ꢀ

L. M.; Lledos, A.; Poli, R.; Revin, P. O.; Shubina, E. S. Chem.—Eur. J. 2008, 14,

9921–9934.

adduct in DCM is 2a_mindole^H1(ΔE_DCM= -28.8 kJ

3

ꢀ

Jimenez-Tenorio et al.

6042 Inorganic Chemistry, Vol. 49, No. 13, 2010

Chart 2

Figure 6. ORTEP drawing (50% thermal ellipsoids) of 3a. Hydrogen

atoms except hydride, H1b, and H3b have been omitted. Selected bond

lengths (A) and angles (deg) with estimated standard deviations in

parentheses: Ru1-P1 2.2519(7), Ru1-H1 1.55(2), Ru1-H2 1.53(2),

Ru1-H3 1.48(2), Ru1-C1 2.215(2), Ru1-C2 2.257(2), Ru1-C3

2.305(2), Ru1-C4 2.275(2), Ru1-C5 2.229(2), O1-H1b 1.25(3),

Chart 3

H1b N1 1.29(3), O3-H3b 0.82(3), O2 H3b 1.81(3), H1 H2

3 3 3

1.48, H1 H3 1.62; P1-Ru1-H2 76.0(9), P1-Ru1-H1 89.2(9),

3 3 3

P1-Ru1-H3 76.1(9), H1-Ru1-H2 57.5(12), H1-Ru1-H3 64.4(12),

H2-Ru1-H3 114.7(12), O1-H1b N1 176(2), O3-H3b O2 149(3).

3 3 3

mol^-1) than 2a_mindole^H1. Including entropic effects of

the solute, the relative stabilities of the three adducts get

3

closer: 2a_mindole^NHand 2a_mindole^H2are only 3.1 and

3

6.5 kJ mol^-1above 2a_mindole^H1when ΔG_DCMare com-

3

pared. Calculations indicate that the interaction of the

weak proton donor with the nitrogen atom of the P,N

ligand and with the hydride (in a bifurcated mode) should

be of similar strength, making the equilibrium schema-

tized in Chart 1 possible.

We have analyzed the influence of the hydrogen-bonding

interaction with indole in the H_lateral-H_centralexchange

responsible for QEC. The two most stable minima (2a_m

3

indole^NHand 2a_mindole^H1) have been taken as starting

3

points. The two transition states corresponding to the

hydrogen exchange with the trihydride interacting with

the indole are shown in Figure 7 (bottom). In both cases,

the presence of the indole leads to a decrease on the Gibbs

energy of activation for the hydrogen exchange, which is

reduced from 63 kJ mol^-1when the proton donor is

absent to 59.7 and 53.3 kJ mol^-1when it is placed in the

mol^-1relative to separated species), involving the bifurcated

interaction with the lateral hydride on the nitrogen-atom

side and the central hydride. The other dihydrogen-bonded

N-pyridyl side (TS_Hexchindole^NH) and the hydride side

3

(TS_Hexchindole^H1), respectively. This effect can be explai-

3

structure (2a_mindole^H2) is the less stable minimum

ned by reduction of the electronic density on the metal atom

induced by interaction with the proton donor. This reduc-

tion stabilizes the dihydrogen species (transition state for

the hydrogen exchange) and thus lowers the exchange

barrier. The same phenomenon has been experimentally

3

(ΔE_DCM= -15.1 kJ mol^-1). The species 2a_mindole^NH

3

containing a standard hydrogen bond between the proton

donor and the nitrogen atom of the pendant pyridyl

group is only marginally less stable (ΔE_DCM= -19.7 kJ

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6043

Figure 7. Optimized geometries ofthe hydrogen-bonded adductsof2a_mwithindole (top) andtransitionstatesfor hydrogenexchange (bottom). Hydrogen

atoms except hydrides, dihydrogen, and indole protons have been omitted.

observed and theoretically analyzed for QEC in adducts

of trihydride metallocenes with Lewis acids.³⁵The reduc-

tion of the electron density on ruthenium is more pro-

nounced when indole is interacting with hydride because

it is directly bonded to the metal. The lower the exchange

barrier the greater the exchange coupling should be in

agreement with the experimental results (Table 1). From

the lowering in ΔG^q_exchpointed out by the calculations, it

is not possible to discriminate between the two indole

adducts because both hydrogen bonding with the nitro-

gen atom and interaction with the hydride ligand should

increase the hydrogen-exchange coupling constants.

5. Reactions with CF₃SO₃H: Proton Transfer.

5.1. 1 equiv of Acid. Once we examined the interac-

tion of the trihydride complexes 2a/2b with weak proton

donors, we studied the proton-transfer reactions using the

strong acid CF₃SO₃H. As was done in the case of weak

proton donors, the reactions of 2a/2b with the 1:1 CF₃SO₃H

complex/acid ratio in CD₂Cl₂were monitored in the

temperature range -80 to þ25 °C (Figure 8).

centered at -11.2 ppm and exhibits (T₁)_minof 213 ms in

the case of 2a and 109 ms for 2b. The acidic proton

appears in the ¹H NMR spectra at 193 K as a very broad

low-field resonance near 14 ppm. As the temperature

rises, the hydride resonances get increasingly broad, until

the spectra become featureless in both the hydride and the

acidic proton regions at 243 K. The ³¹P{¹H} NMR spec-

tra at 183 K consist of one broad or very broad resonance

centeredat98.8ppm for2a(Δν_1/2=52 Hz) and at 98.6 ppm

for 2b (Δν_1/2= 440 Hz). These broad resonances become

sharper at higher temperatures, reaching respective half-

widths of 16 Hz (2a) and 64 Hz (2b) at 273 K. The process is

fully reversible. These spectral data suggest that the trihy-

drides 2a/2b are protonated by CF₃SO₃H at the nitrogen

atom of the pendant pyridine or quinoline group, furnish-

ing the cationic species [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂XH)]-

[CF₃SO₃] [X = Py (4a), Quin (4b)], which most likely

contain one dihydrogen bond between the NH and one

of the hydride ligands.

At temperatures above 243 K, a new rather broad

hydride resonance begins to appear in the ¹H NMR spec-

tra (Figure 8). Likewise, new signals also appear in the

³¹P{¹H} NMR spectra: one singlet at 84.5 ppm in the case

of 2a and one at 77.8 ppm in the case of 2b. (T₁)_minfor the

new hydride resonances are very short (10 and 11 ms, re-

spectively, in each case) and consistent with the presence

of a dihydrogen ligand. Furthermore, the acidic proton

resonances disappear at 298 K, and the doublet for the

CH₂group of the pendant pyridine or quinoline is

The ¹H NMR spectrum of 2a/2b upon the addition of

1 equiv of CF₃SO₃H showed at 193 K one rather broad

multiplet in the hydride region, which indicates the

occurrence of QEC in the system. The multiplet appears

~

ꢀ

(35) (a) Antinolo, A.; Carrillo, F.; Fernandez-Baeza, J.; Otero, A.;

Fajardo, M.; Chaudret, B. Inorg. Chem. 1992, 31, 5156–5157. (b) Camanyes,

ꢀ

S.; Maseras, F.; Moreno, M.; Lledos, A.; Lluch, J. M.; Bertran, J. Inorg. Chem.

1998, 37, 2334–2339.

ꢀ

Jimenez-Tenorio et al.

6044 Inorganic Chemistry, Vol. 49, No. 13, 2010

Chart 4

Figure 8. VT ¹H NMR (hydride region, 400 MHz) of samples made by

the addition of 1 equiv of CF₃SO₃H to a frozen CD₂Cl₂solution of 2a (A)

or 2b (B), followed by subsequent warming to the indicated temperatures.

replaced by two multiplets corresponding to the AB part

of an ABX spin system. The latter indicates a change in

the coordination mode of the PN ligand from κ¹-P to

chelating κ²-P,N. We have identified these products as the

cationic dihydrogen complexes [Cp*Ru(H₂)(κ²-P,N-ⁱPr₂-

PCH₂X)]^þ[X = Py (5a), Quin (5b)]. The coupling con-

stant ¹J_HDin these complexes was measured, having values

of 28.4 Hz for 5a and 28 Hz for 5b. Chart 4 summarizes the

species involved in the reaction of 2a/2b with 1 equiv of

CF₃SO₃H.

We have computationally studied the nature of the

product obtained by protonation with 1 equiv of a strong

acid. Optimization from different starting points by add-

ing one proton to 2a_mleads to three stable isomeric

structures for the cationic species 4a_m(Figure 9, top).

The most stable protonated product is 4a_m^NHwith the

N-pyridyl protonated. Protonation of the central hydride

gives structure 4a_m^2HH2with one central dihydrogen and

sition-metal hydrides.^22,37,38Thus, ion pairs of the three

4a_misomers with one triflate anion were optimized. The

three stable isomeric structures are kept in the presence

of the triflate counteranion (Figure 9, bottom). A

hydrogen bond between one triflate oxygen atom

and a protic hydrogen atom whether from the pyridyl

group (4a_m

NH

OTf) or from the dihydrogen ligand

OTf) also contributes to

3

2H2

2HH2

(4a_m

OTf and 4a_m

3

the ion-pair stability. The energy ordering found with-

out the counteranion is preserved when the triflate is

included, with the stability of the N-protonated isomer

being even increased with respect the hydride-proto-

nated species. 4a_m

NH

OTf is placed 32.7 and 32.2 kJ

_2HH3₂

mol^-1below 4a_m

tively. 4a_m

OTf and 4a_m

OTf is formed without a barrier when

OTf, respec-

2H2

3

NH

3

two lateral dihydride ligands. Protonation of both lateral

2H2

triflic acid is placed close to the nitrogen atom and it lies

55.5 kJ mol^-1below the separated reactants (2a_mand

HSO₃CF₃), in agreement with a fast and easy protonat-

ion with triflic acid. Indeed, calculations support the

initial protonation of the trihydride at the pendant pyr-

idine or quinoline group, furnishing the cationic species

4a and 4b.

hydrides gives the same bis(dihydrogen) product 4a_m

The stability of the two species arising from protonation

.

of the trihydride unit is very similar. 4a_m^NHis placed 20.6

2HH2

and 19.6 kJ mol^-1below 4a_m

and 4a_m^2H2, respec-

tively. Interestingly, in 4a_m^NH, the pyridyl group has

rotated in such a way that a strong dihydrogen bond is

formed between the N-proton and two hydrides. This

orientation could facilitate ulterior proton transfer to the

hydride site.

Protonation introduces a mobile hydrogen center in the

coordination sphere of the transition metal, allowing the

initial protonated intermediate to evolve in a variety of

ways.²²We have theoretically analyzed possible pathways

for proton transfer from the pyridyl nitrogen atom to

In a low-polar solvent, ion-pair formation between

the cationic protonation product and the triflate coun-

teranion (OTf) can be expected. Ion pairing can affect

both the thermodynamics of a reaction, by changing the

relative energies of the species involved, and its kinetics

and mechanisms, by providing alternative reaction

pathways.³⁶The ion-pair formation may become parti-

cularly important in proton-transfer reactions to tran-

ꢀ

(37) (a) Basallote, M. G.; Besora, M.; Duran, J.; Fernandez Trujillo,

ꢀ

ꢀ~

M. J.; Lledos, A.; Manez, M. A.; Maseras, F. J. Am. Chem. Soc. 2004, 126,

ꢀ

2320–2321. (b) Basallote, M. G.; Besora, M.; Castillo, C. E.; Fernandez Trujillo,

ꢀ~

ꢀ

M. J.; Lledos, A.; Maseras, F.; Manez, M. A. J. Am. Chem. Soc. 2007, 129, 6608–

ꢀ

6618. (c) Algarra, A. G.; Fernandez Trujillo, M. J.; Lledos, A.; Basallote, M. G.

Chem. Commun. 2009, 4563–4565.

ꢀ

(38) (a) Kovacs, G.; Ujaque, G.; Lledos, A. J. Am. Chem. Soc. 2008, 130,

853–864. (b) Xia, Y. Z.; Dudnik, A. S.; Gevorgyan, V; Li, Y. H. J. Am. Chem.

Soc. 2008, 130, 6940–6941.

(36) (a) Macchioni, A. Chem. Rev. 2005, 105, 2039–2073. (b) Clot, E. Eur.

J. Inorg. Chem. 2009, 2319–2328.

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6045

Figure 9. Optimized geometries of the isomers of the first protonation product (4a_m) without (top) and with (botton) the triflate counteranion. Hydrogen

atoms except hydrides, dihydrogen, or N-proton in the pyridyl have been omitted.

the trihydride unit. For the isolated cation, two transit-

ion states have been located for this process (Figure 10).

One [TS(NH-H_lat)] corresponds to proton transfer to the

lateral hydride and leads to the bis(dihydrogen) isomer

4a_m^2H2. The other one [TS(NH-H_cent)] describes proton-

ation of the central hydride and gives the dihydrido-

(dihydrogen) isomer 4a_m^2HH2. In both transition states,

the distance between the incoming proton and the closest

hydride is about 1 A, indicating that a dihydrogen unit has

already been formed at the transition state. ΔG^qbarriers of

47.0 and 45.2 kJ mol^-1are obtained for the formation of

4a_m^2H2and 4a_m^2HH2from 4a_m^NH, respectively.

when heating by proton transfer to the hydride site with

the formation of one or two dihydrogen ligands. The

triflate counteranion can assist the proton migration,

acting as a proton shuttle. Ulterior dihydrogen elimina-

tion could displace the protonation reaction toward the

dihydrogen complex formation.

5.2. Excess of Acid: Second Protonation. We have also

studied the proton-transfer reactions to 2a/2b in CD₂Cl₂

using an excess (3 equiv) of CF₃SO₃H in the temperature

range 193-298 K. Under these conditions, at 193 K, a

new broad resonance appears in the hydride region of

1

the H NMR spectrum at -8.1 ppm in the case of 2a

(Figure 11).

This new resonance has a (T₁)_minof 13.9 ms. The

It has been shown that triflate anions can behave as a

proton shuttle, facilitating proton transfer.³⁸Separated

2a_mand triflic acid are only 55.5 kJ mol^-1above the most

stable (4a_m, triflate) ion pair. Then the triflic acid can

³¹P{¹H} NMR spectrum at the same temperature displays

one singlet at 79.9 ppm. In analogous fashion, the H

1

protonate either a lateral or central hydride of the trihy-

dride, leading to the bis(dihydrogen) (4a_m

dihydrido(dihydrogen) (4a_m

NMR spectrum of 2b with an excess of CF₃SO₃H added

showed at 193 K one broad signal at -7.95 ppm having

a (T₁)_minof 12.4 ms (Figure 11B) and one singlet at

80.4 ppm in the ³¹P{¹H} NMR spectrum. At this tem-

perature, a small amount of the respective dihydrogen

complexes 5a/5b is already present as inferred from the ¹H

and ³¹P{¹H} NMR spectra. As the temperature increases,

the broad hydridic resonances near -8 ppm decrease their

intensity at the expense of the signals for the dihydrogen

ligand in 5a/5b. At 273 K, the dihydrogen complex 5a or

5b becomes predominant. The short (T₁)_minmeasured for

the new hydridic signals near -8 ppm indicates clearly the

2H2

OTf) and

OTf) ion pairs. The

3

2HH2

3

transition states for both proton transfers have been

located and are depicted in Figure 10 (bottom). The

transition state corresponding to the protonation of a

central hydride [TS(HOTf-H_cent)] lies only 5.2 kJ mol^-1

above 2a_mþ HOTf, being a bit lower than that of the

lateral hydride protonation [TS(HOTf-H_lat), 17.2 kJ

mol^-1above 2a_mþ HOTf].

Overall calculations agree with a very easy initial

protonation of the N-pyridyl by the triflic acid, followed

ꢀ

Jimenez-Tenorio et al.

6046 Inorganic Chemistry, Vol. 49, No. 13, 2010

Figure 10. Transition states of intramolecular proton transfer from the pyridyl nitrogen atom to the trihydride unit (top) and of trihydride protonation by

triflic acid (bottom). Hydrogen atoms except hydrides, dihydrogen, or N-proton in the pyridyl have been omitted.

ation of 4a/4b at the hydride site. These species can be

formulated either as bis(dihydrogen) complexes [Cp*

Ru(H₂)₂(κ¹-P-ⁱPr₂PCH₂XH)]^2þ(X=Py, Quin) or as dihy-

drido(dihydrogen) species [Cp*RuH₂(H₂)(κ¹-P-ⁱPr₂PCH₂-

XH)]^2þ. We have previously described the bis(dihydro-

gen) complexes [Cp*Ru(H₂)₂(EPh₃)]^þ(E = As, Sb),⁶

generated by protonation of the corresponding [Cp*RuH₃-

(EPh₃)] derivatives. These bis(dihydrogen) complexes

were stable up to 273 K and were characterized in solution

by T₁and ¹J_HDmeasurements. (T₁)_minmeasured for the

hydride resonances of the dicationic species [Cp*RuH₄-

(κ¹-P-ⁱPr₂PCH₂XH)]^2þ(13.9 ms for 6a and 12.4 ms for 6b)

are short and comparable to those of the dihydrogen

resonances in 5a/5b and in [Cp*Ru(H₂)₂(EPh₃)]^þ(E =

As, Sb).⁶A dihydrido(dihydrogen) structure has been

postulated for the related species [Cp*RuH₄(PCy₃)]^þ

[(T₁)_min=18 ms at 500 MHz], although a bis(dihydrogen)

structure was not ruled out in this case.¹⁸The two recently

reported bis(dihydrogen) osmium derivatives [TpOs(H₂)₂-

Figure 11. VT ¹H NMR (hydride region, 400 MHz) spectra of samples

made by the addition of an excess (3 equiv) of CF₃SO₃H to a frozen

CD₂Cl₂solution of 2a (A) or 2b (B), followed by subsequent warming to

the indicated temperatures.

(PⁱPr₃)][BF₄]³⁹and[Os(BAEA)(H₂)₂(PⁱPr₃)][BF₄]₂[BAEA=

bis(2-aminoethyl)amine]⁴⁰display (T₁)_minvalues of 12 and

ꢀ

(39) Castro-Rodrigo, R.; Esteruelas, M. A.; Lopez, A. M.; Olivan, M.;

presence of dihydrogen ligands. We attribute resonances to

the dicationic complexes [Cp*RuH₄(κ¹-P-ⁱPr₂PCH₂XH)]^2þ

[X=Py (6a), Quin (6b)], resulting from a second proton-

~

Onate, E. Organometallics 2007, 26, 4498–4509.

ꢀ

~

(40) Baya, M.; Esteruelas, M. A.; Olivan, M.; Onate, E. Inorg. Chem.

2009, 48, 2677–2686.

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6047

Chart 5

Figure 12. ³¹P{¹H} NMR spectra of samples made by the addition of

an excess of CF₃SO₃D (3 equiv) to a frozen CD₂Cl₂solution of 2a (A) or

2b (B), followed by subsequent warming to 233 K.

14 ms, respectively. On the other hand, the also related

half-sandwich dihydride(dihydrogen)osmium complex

[Cp*OsH₂(H₂)(PPh₃)][BF₄] (structure determined by neu-

tron diffraction) shows in its ¹H NMR spectrum a single

hydride resonance with a (T₁)_minof 79.2 ms at 400 MHz

(99 ms at 500 MHz) due to rapid scrambling between

dihydride and dihydrogen sites.⁴¹A comparison of all of

these data with ours suggests that 6a/6b can be better

formulated as the bis(dihydrogen) complexes [Cp*Ru-

(H₂)₂(κ¹-P-ⁱPr₂PCH₂XH)]^2þ(X = Py, Quin). In order to

confirm this, we attempted to measure ¹J_HDin any of the

possible isotopomers of [Cp*RuH_nD_4-n(κ¹-P-ⁱPr₂PCH₂-

XD)]^2þ(n = 1-3) by performing the reaction of 2a/2b

with an excess (3 equiv) of CF₃SO₃D. The hydride reson-

ances in the ¹H NMR spectra were broad and unresolved

and did not show any measurable H-D coupling. How-

ever, the ³¹P{¹H} NMR spectra did show coupling of

phosphorus-deuterium in the form of overlapping multi-

plets due to mixtures of isotopomers (Figure 12).

This is a feature more typical of terminal hydride (or

deuteride) ligands attached to ruthenium. Thus, whereas

the short (T₁)_minpoint to a bis(dihydrogen) structure, the

failure to observe ¹J_HDand the occurrence of phosphor-

us-deuterium couplings suggests that terminal hydride

ligands are also present in the system. We must therefore

assume that the dicationic species [Cp*RuH₄(κ¹-

P-ⁱPr₂PCH₂XH)]^2þexist in solution as equilibrium mix-

tures of both dihydride(dihydrogen) and bis(dihydrogen)

tautomers. Additionally, the rapid exchange of the NH

proton with the hydride and/or the hydrogen atoms of the

dihydrogen ligands also occurs in this system.

In the case of 2a plus an excess of CF₃SO₃H, apart from

the signal for the dihydrogen complex 5a, one hydridic

doublet resonance also appears at -5.55 ppm at 273 K

(Figure 11A). At 298 K, this doublet becomes one broad

unresolved signal. It corresponds to a species that displays

one singlet at 92.3 ppm in the ³¹P{¹H} NMR spectrum. A

new resonance also appears in the ¹⁹F NMR spectrum at

-78.6 ppm. We have rationalized these observations by

considering the formation of the ruthenium(IV) species

[Cp*RuH(CF₃SO₃)(κ²-P,N-ⁱPr₂PCH₂Py)][CF₃SO₃] (7a),

formally derived from the oxidative addition of a CF₃SO₃H

molecule to the coordinatively unsaturated complex

[Cp*Ru(κ²-P,N-ⁱPr₂PCH₂Py)]^þ(10a, vide infra).

Solutions of 7a for the NMR study were easily obtained

by treating 2a with 2 equiv of CF₃SO₃H in CD₂Cl₂under

argon. The resonance of the C5 ring for 7a appears at

103.26 ppm in the ¹³C{¹H} NMR spectrum, a value that is

consistent with the formulation as a formally seven-

coordinate ruthenium(IV) species.⁴²Attempts made to

isolate 7a as a solid were only partially successful. An

orange solid was obtained by the addition of petroleum

ether to acidic solutions of 7a in DCM. However, this

solid always converted to a sticky material when isolated

and washed. For this reason, it was not analyzed.

We have theoretically addressed the nature of the dipro-

tonated species. From the most stable monoprotonated

product 4a_m^NH, three protonation sites are available, cor-

responding to the three hydrides. Four different minima

have been found for the dicationic species 6a_m. Three of

them are dihydrogen-dihydride species, differing in the

relative position of the dihydrogen ligand, central in

6a_m^HH2Hand lateral in 6a_m^HHH2and 6a_m^H2HH. The fourth

has two dihydrogen ligands (6a_m^2H2; Figure 13).

6a and 6b are acidic and exist in equilibrium with the

corresponding monoprotonated species 4a/4b. As the

temperature increases, the equilibrium shifts to the mono-

protonated species, which undergo irreversible dihydrogen

elimination and transformation into the mono(dihydrogen)

complexes 5a/5b. At temperatures above 273 K, the dica-

tionic species disappear completely. The relationships

among the species involved in the protonation reactions

of 2a/2b with an excess of CF₃SO₃H are summarized in

Chart 5.

The four isomers have very similar stabilities. The most

stable complex is the bis(dihydrogen) structure 6a_m

2H2

,

ꢀ

(42) Aneetha, H.; Jimenez-Tenorio, M.; Puerta, M. C.; Valerga, P.;

Sapunov, V. N.; Schmid, R.; Kirchner, K.; Mereiter, K. Organometallics

2002, 21, 5334–5346.

(41) Gross, C. L.; Young, D. M.; Schultz, A. J.; Girolami, G. J. Chem.

Soc., Dalton Trans. 1997, 3081–3082.

ꢀ

Jimenez-Tenorio et al.

6048 Inorganic Chemistry, Vol. 49, No. 13, 2010

Figure 13. Optimized geometries of isomers of the product of the second protonation 6a_mwithout (top) and with (bottom) the triflate counteranion and

the transition state of the protonation. Hydrogen atoms except hydrides, dihydrogen, or N-proton in the pyridyl have been omitted.

HHH2

but 6a_m^HH2H, 6a_m^H2HH, and 6a_m

are only 9.6, 4.0,

the temperature, the protonated structures 4 can evolve

by eliminating dihydrogen, with a subsequent change in

the coordination mode of the P,N ligand from κ¹-P to

chelating κ²-P,N.

and 10.4 kJ mol^-1above the bis(dihydrogen) dication, re-

spectively. From these values and the proximity of the

hydrogen ligands, a fast interconversion between the bis-

(dihydrogen) and dihydride(dihydrogen) structures can

be envisaged.⁹The second protonation is less favored

than the first one. Formation of the most stable diproto-

nated isomer (6a_m^2H2) from the most stable monoproto-

nated compound (4a_m^NH) is an endergonic process, with

the diprotonated species being 6.8 kJ mol^-1less stable

than the monoprotonated one.

The dihydrogen elimination from the two isomers of

4a_mbearing dihydrogen ligands has been examined. Dihy-

drogen elimination from the bis(dihydrogen) 4a_m^2H2leads

to the dihydrogen complex 5a_mwith a Gibbs energy

barrier of 70.0 kJ mol^-1. The process from the dihydride-

2HH2

(dihydrogen) isomer 4a_m

leads to the dihydride

5a_m^2H, 19.6 kJ mol^-1less stable than the dihydrogen,

In the presence of triflate, two different ion pairs have

after crossing a Gibbs energy barrier of 81.1 kJ mol^-1

.

2H2

been found as minima: the bis(dihydrogen) 6a_m

and one dihydride(dihydrogen) with the dihydrogen li-

OTf

Kinetics and thermodynamics both lead to the dihydro-

gen 5a_m. The two located transition states are collected in

Figure 15. Their structures show that in addition to the

elimination of one dihydrogen unit the change of the

coordination mode of the P,N ligand from κ¹-P to chelat-

ing κ²-P,N is also taking place.

6. Isolation and Structure of 5a/5b and Related Com-

pounds. The dihydrogen complexes 5a and 5b were iso-

lated in the form of yellow crystalline materials by the

reaction of 1a or 1b with dihydrogen and NaBAr⁰₄[Ar⁰₄=

3,5-C₆H₃(CF₃)₂] in diethyl ether. These compounds are

stable both in the solid state and in solution under a

hydrogen atmosphere. Remarkably, these compounds do

not undergo irreversible isomerization to the correspond-

ing ruthenium(ΙV) dihydride complexes at 298 K. This

fact contrasts with the behavior commonly observed for

half-sandwich ruthenium dihydrogen derivatives.^43,44On

the other hand, the stability of the dihydrogen isomer

3

2HH2

gand at the central position (6a_m

OTf; Figure 13).

3

The bis(dihydrogen) remains as the most stable structure,

but only 5.9 kJ mol^-1below the dihydride(dihydrogen)

isomer. Kinetically, the second protonation is favored.

The transition state corresponding to the protonation of a

central hydride [TS2(HOTf-H_cent)] lies only 9.2 kJ mol^-1

NH

above 4a_mþ HOTf .

We have alsotheoretically addressed the feasibility of the

formation of ruthenium(IV) species [Cp*RuH(CF₃SO₃)-

(κ²-P,N-ⁱPr₂PCH₂Py)][CF₃SO₃] (7a;Chart6).7a_m(Figure14)

is a stable species, more stable than both the dihydrogen

complex 5a_m(13.1 kJ mol^-1below) and the unsaturated

complex 10a_m(53.2 kJ mol^-1below). Calculations do

support the formation of 7a.

5.3. Computational Study of Dihydrogen Elimination.

The experimental study shows that, upon an increase in

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6049

Chart 6

2H2

Figure 15. Transitionstatesfor the dihydrogeneliminationfrom4a_m

[TS(4a_m^2H2-5a_m), left] and from 4a_m

[TS(4a_m^2HH2-5a_m^2H), right].

Hydrogen atoms except hydrides or dihydrogen have been omitted.

2HH2

rally characterized is [Cp*Ru(H H)(dppm)][BF₄],^47,48

3 3 3

which contains an elongated dihydrogen ligand.⁴⁹The

dihydrogen ligand in this compound was not localized in

an initial X-ray crystallography structure analysis.⁴⁷

However, a subsequent neutron diffraction study re-

vealed the position and dimensions of the elongated

dihydrogen ligand.⁴⁸The complex cation [Cp*Ru(H₂)-

(κ²-P,N-ⁱPr₂PCH₂Py)]^þadopts a “three-legged-piano-

stool” structure. The conformation of the Ru1-P1-

C20-C11-N1 ring is similar to that found in the struc-

ture of 1b. The dihydrogen ligand was located and

refined. The Ru1-H1 and Ru1-H2 bond lengths have

values of 1.69(5) and 1.66(5) A, respectively, which

compare well with the values found in [TpRu(H₂)-

(ⁱPr₂PNHCH₂CH₂NHPⁱPr₂)][BAr⁰₄] by X-ray crystallo-

graphy [1.685(19) and 1.66(4) A]⁴⁶and in [Cp*Ru-

(H H)(dppm)][BF₄] by neutron diffraction [1.66(2)

3 3 3

and 1.67(2) A].⁴⁸The H1-H2 bond distance of 0.67(6)

A is also comparable to the value of 0.69(4) A reported for

[TpRu(H₂)(ⁱPr₂PNHCH₂CH₂NHPⁱPr₂)][BAr⁰₄]⁴⁶but much

shorter than the H1 H2 separation of 1.08(3) A in

3 3 3

Figure 14. Optimized geometry of the product 7a_m. Hydrogen atoms

except hydride have been omitted.

[Cp*Ru(H H)(dppm)][BF₄].⁴⁸Even considering the

3 3 3

experimental error in the determination of these struc-

tural parameters by X-ray crystallography, the results

are fully consistent with the presence of one dihydro-

gen molecule bound in a side-on manner to the ruthenium

atom.

versus the dihydride isomer for 5a and 5b resembles the

analogue properties of hydrotris(pyrazolyl)borate (Tp)

ruthenium dihydrogen complexes [TpRu(H₂)P₂]^þ[P₂=

1,2-bis(diisopropylphosphino)ethane,⁴⁵1,2-bis(diisopro-

pylphosphinoamino)ethane, 1,2-bis(diisopropylphosphi-

noamino)cyclohexane].⁴⁶

Single crystals of 5b were obtained by the slow diffusion

of petroleum ether through a diethyl ether solution of the

complex under dihydrogen. The resulting large yellow

crystals were subjected to X-ray structure analysis. An

ORTEP view of the complex cation [Cp*Ru(H₂)(κ²-

P,N-ⁱPr₂PCH₂Quin)]^þin5bis showninFigure16, together

with the most relevant bond distances and angles.

As far as we are aware, the only other half-sandwich

dihydrogen complex of ruthenium that has been structu-

Quantum-mechanical calculations have proven to be a

cost-effective high-quality technique for the precise loca-

tion of the positions of hydrogen atoms in transition-

metal complexes.⁹In order to refine the position of the

dihydrogen ligand in complex 5b, we fully optimized the

geometry of the real complex. The optimized structure is

depicted in Figure 17, together with that of the model

complex 5a_m, and a comparison of the calculated para-

meters with the X-ray determined and with those of 5a_m

can be found in the Supporting Information (Table 1S).

Bond distances and angles for the non-hydrogen atoms

are in excellent agreement with the X-ray structure.

The Ru-H₂unit presents a very similar arrangement in

the model complex 5a_mand in 5b, with Ru-H and H-H

(43) Morris, R. H. Coord. Chem. Rev. 2008, 252, 2381–2394.

(44) Jimenez-Tenorio, M.; Palacios, M. D.; Puerta, M. C.; Valerga, P.

Inorg. Chem. 2007, 46, 1001–1012.

ꢀ

(45) Jimenez-Tenorio, M. A.; Jimenez-Tenorio, M.; Puerta, M. C.;

(48) Klooster, W. T.; Koetzle, T. F.; Jia, G.; Fong, T. P.; Morris, R. H.;

Valerga, P. Inorg. Chim. Acta 1997, 259, 77–84.

ꢀ

(46) Jimenez-Tenorio, M.; Palacios, M. D.; Puerta, M. C.; Valerga, P.

Albinati, A. J. Am. Chem. Soc. 1994, 116, 7677–7681.

ꢀ

(49) (a) Gelabert, R.; Moreno, M.; Lluch, J. M.; Lledos, A. J. Am. Chem.

Organometallics 2005, 24, 3088–3098.

(47) Jia, G.; Lough, A. J.; Morris, R. H. Organometallics 1992, 11,

161–171.

ꢀ

Soc. 1997, 119, 9840–9847. (b) Heinekey, D. M.; Lledos, A.; Lluch, J. M. Chem.

Soc. Rev. 2004, 33, 175–182.

ꢀ

Jimenez-Tenorio et al.

6050 Inorganic Chemistry, Vol. 49, No. 13, 2010

Figure 16. ORTEP drawing (50% thermal ellipsoids) of the cation

[Cp*Ru(H₂)(κ²-N,P-ⁱPr₂PCH₂Quin)]^þin complex 5b. Hydrogen atoms

except dihydrogen have been omitted. Selected bond lengths (A) and

angles (deg) with estimated standard deviations in parentheses: Ru1-P1

2.2902(13), Ru1-N1 2.173(4), Ru1-H1 1.69(5), Ru1-H2 1.66(5),

Ru1-C1 2.231(5), Ru1-C2 2.183(4), Ru1-C3 2.203(4), Ru1-C4

2.185(5), Ru1-C5 2.232(5), H1-H2 0.67(6); P1-Ru1-N1 78.30(11),

H1-Ru1-H2 22.9(19).

Figure 17. Optimized geometries of the dihydrogen complexes 5b and

5a_mand the corresponding 16-electron species (10b and 10a_m).

distances of about 1.64 and 0.95 A, respectively. The

H-H distance indicates a somewhat activated dihydro-

gen ligand, although less than that in the elongated

drogen complex to a transoid square-based four-legged-

piano-stool dihydride. The optimized geometries of the

trans-dihydride 5a_mand the transition state for the

2H

dihydrogen ligand of [Cp*Ru(H H)(dppm)]^þ.^47-49

3 3 3

interconversion are shown in Figure 18.

The dihydrogen dissociation energies are also very similar

in both compounds (81.9 kJ mol^-1in 5a_mand 82.7 kJ

mol^-1in 5b). The apparent disagreement between the

calculated H-H separation in 5b and the distance ob-

tained by X-ray crystallography [0.67(6) A] can be attrib-

uted to the intrinsic limitations of this technique for the

accurate determination of bond distances involving hy-

drogen atoms, as well as the fact that the measurements

correspond to the solid state. We have determined the

H-H bond distances in a CD₂Cl₂solution based upon

(T₁)_min(eq 1) and ¹J_HDcoupling constants (eq 2).⁶

The transition state for the rearrangement [TS(H2-

HH)], depicted in Figure 18, has a dihydride nature (Ru-

H bond distances of 1.574 and 1.583 A), with no interac-

tion between the two hydrogen atoms (distance H-H of

2.408 A). The geometry around the ruthenium atom in

this transition state is similar to that reported for the

dihydrogen f trans-dihydride isomerization in related

half-sandwich complexes.⁵⁰In this system, the dihydride

is 19.6 kJ mol^-1less stable than the dihydrogen. More-

over, ΔG^qfor the isomerization (99.1 kJ mol^-1) is con-

siderably higher than that for the dihydrogen elimination

(40.1 kJ mol^-1). Both thermodynamics and kinetics favor

dihydrogen elimination from 5a_m, giving the unsaturated

complex 10a_m, in front of the oxidative addition that leads

to the dihydride 5a_m^2H. Indeed, this is the experimental

behavior observed in complexes 5a and 5b.

The dihydrogen ligand in 5a and 5b is extremely labile

and readily replaced by dinitrogen in DCM, furnishing the

dinitrogen complexes [Cp*Ru(N₂)(κ²-P,N-ⁱPr₂PCH₂X)]-

[BAr⁰₄] [X = Py (8a), Quin (8b)]. These compounds dis-

play strong ν(N₂) bands in their IR spectra at 2169 cm^-1

for 8a and at 2152 cm^-1for 8b. These values indicate little

degree of back-donation from the metal to the coordi-

nated dinitrogen and, hence, little activation of the NtN

bond, as has been typically observed in other half-sand-

wich Ru-N₂complexes.^46,51,52Exposure of 5b or 8b to air

in CD₂Cl₂led to the formation of the dioxygen complex

1=6

r_H_{3 3 3}¼ 5:815½ðT₁Þ_min=νꢀ

ð1Þ

H

1

r_H_{3 3 3}¼ 1:42 - 0:0167ð J_HD

Þ

ð2Þ

H

ν in eq 1 represents the NMR frequency of operation,

which in our case is 4 ꢁ 10⁸Hz. The resulting H-H bond

distances for 5b using eqs 1 and 2 are respectively 1.01 and

0.95 A. Both values are in much better agreement, with

the H-H separations derived from DFT calculations.

For compound 5a, the corresponding H-H bond dis-

tances obtained by the application of eqs 1 and 2 are 0.99

and 0.95 A, respectively.

In contrast with the behavior commonly found for the

half-sandwich ruthenium dihydrogen derivatives, isomer-

ization to the corresponding dihydride complexes has not

been observed for compounds 5a and 5b. In [(C₅R₅)-

RuL₂H₂]^þspecies systems, the only stable dihydride is

the trans-dihydride; thus, the dihydrogen-dihydride

interconversion implies an important stereochemical

change, passing from the three-legged-piano-stool dihy-

ꢀ

(50) (a) Baya, M.; Maresca, O.; Poli, R.; Coppel, Y.; Maseras, F.; Lledos,

A.; Belkova, N. V.; Dub, P. A.; Epstein, L. M.; Shubina, E. S. Inorg. Chem.

2006, 45, 10248–10262. (b) Rossin, A.; Gonsalvi, L.; Phillips, A. D.; Maresca, O.;

Lledos, A.; Peruzzini, M. Organometallics 2007, 26, 3289–3296.

ꢀ

(51) Aneetha, H.; Jimenez-Tenorio, M.; Puerta, M. C.; Valerga, P.;

Mereiter, K. Organometallics 2002, 21, 628–635.

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6051

2H

Figure 18. Optimized geometries of the trans-dihydride complex 5a_m

and the transition state for the dihydrogen-dihydride interconversion

[TS(H2-HH)].

[Cp*Ru(O₂)(κ²-P,N-ⁱPr₂PCH₂Quin)][BAr⁰₄] (9b). How-

ever, exposure of 5a or 8a to air led to the formation of

a mixture of uncharacterized species, which at this stage

were not further investigated. The X-ray crystal struc-

tures of 8b and 9b were determined. ORTEP views of the

complex cations [Cp*Ru(N₂)(κ²-P,N-ⁱPr₂PCH₂Quin)]^þ

in 8b and [Cp*Ru(O₂)(κ²-P,N-ⁱPr₂PCH₂Quin)]^þin 9b

are shown in Figures 19 and 20, respectively, together

with the most relevant bond distances and angles.

Figure 19. ORTEP drawing (50% thermal ellipsoids) of the cation

[Cp*Ru(N₂)(κ²-P,N-ⁱPr₂PCH₂Quin)]^þin complex 8b. Hydrogen atoms

have been omitted. Selected bond lengths (A) and angles (deg) with

estimated standard deviations in parentheses: Ru1-P1 2.3335(7),

Ru1-N1 1.9925(19), Ru1-N3 2.1730(19), Ru1-C1 2.209(2), Ru1-C2

2.177(2), Ru1-C3 2.219(2), Ru1-C4 2.238(2), Ru1-C5 2.204(2),

N1-N2 1.096(3); P1-Ru1-N1 95.35(5), P1-Ru1-N3 78.87(4),

N1-Ru1-N3 91.86(8), Ru1-N1-N2 172.06(19).

The complex cation in 8b shows a “three-legged-piano-

stool” structure, with the dinitrogen ligand bound in an

end-on manner. The Ru-N1-N2 angle of 172.06(19)°

indicates an almost linear Ru-N₂assembly, with a Ru-

N1 separation of 1.9925(19) A and a N1-N2 bond length

of 1.096(3) A. These bond distances compare well with

those reported for other half-sandwich Ru-N₂complexes

such as [CpRu(N₂)(dippe)][BAr⁰₄] [Ru-N1 1.961(3) A;

N1-N2 1.087(4) A]⁵¹or [Cp*Ru(N₂)(dppm)][BAr⁰₄]

[Ru-N1 1.975(2) A; N1-N2 1.083(4) A].⁵²As is usual in

terminal dinitrogen complexes, the N-N separation in 8b is

essentially identical with that corresponding to the free

dinitrogen molecule. The complex cation 9b also displays a

“three-legged-piano-stool” structure, with the dioxygen

ligand bound in a side-on manner, having an O1-O2 sepa-

ration of 1.398(4) A, which is very similar to that found in

[Cp*Ru(O₂)(L-L⁰)][BPh₄] [1.394(9) A; L-L⁰=1,3-(dioxan-

2-ylmethyl)diphenylphosphine],⁵³and also in [Cp*Ru(O₂)-

(dppe)][PF₆] [1.398(5) A].⁵⁴These distances are intermedi-

ate between those in the free dioxygen molecule and in the

ionic peroxide anion (1.49 A). The Ru-O bond lengths of

2.011(3) and 2.040(3) A suggest an essentially symmetrical

arrangement of the dioxygen ligand, very similar to that

found in related complexes.

Figure 20. ORTEP drawing (50% thermal ellipsoids) of the cation

[Cp*Ru(O₂)(κ²-P,N-ⁱPr₂PCH₂Quin)]^þin 9b. Hydrogen atoms have been

omitted. Selected bond lengths (A) and angles (deg) with estimated

standard deviations in parentheses: Ru1-P1 2 2.3079(10), Ru1-N1

2.165(3), Ru1-O1 2.011(3), Ru1-O2 2.040(3), Ru1-C1 2.259(4), Ru1-

C2 2.256(4), Ru1-C3 2.205(4), Ru1-C4 2.264(4), Ru1-C5 2.245(4),

O1-O2 1.398(4); P1-Ru1-N1 76.31(9), O1-Ru1-O2 40.36(11).

rated 16-electron species [Cp*Ru(κ²-P,N-ⁱPr₂PCH₂Py)]^þ

and [Cp*Ru(κ²-P,N-ⁱPr₂PCH₂Quin)]^þ. These extremely

air-sensitive species are homologues of the 16-electron

cationic complexes [Cp*Ru(PP)]^þ[PP=dippe, (PMeⁱPr₂)₂,

(PEt₃)₂]⁴²and [Cp*Ru(NN)]^þ[NN=Me₂NCH₂CH₂NR₂,

where R₂= Me₂, ⁱBu₂, (CH₂CH₂)₂O].^55,56We have been

able to isolate the blue complex [Cp*Ru(κ²-P,N-ⁱPr₂-

PCH₂Py)][BAr⁰₄] (10a) either by the reaction of 1a with

NaBAr⁰₄in fluorobenzene under argon or by pumping in

vacuo crystals of the dihydrogen complex 5a (Chart 7).

The dihydrogen complexes 5a and 5b release dihydro-

gen when they are dissolved in CD₂Cl₂under argon,

leading to bluish to greenish solutions. This tendency is

even greater for compound 5a, which loses dihydrogen in

the solid state under argon. This process involves a color

change from yellow to greenish blue. The blue color is

attributed to the formation of the coordinatively unsatu-

ꢀ

(52) Aneetha, H.; Jimenez-Tenorio, M.; Puerta, M. C.; Valerga, P.;

Mereiter, K. Organometallics 2003, 22, 1779–1782.

(53) Lindner, E.; Haustein, M.; Fawzi, R.; Steinmann, M.; Wegner, P.

Organometallics 1994, 13, 5021–5029.

(54) Kirchner, K.; Mauthner, K.; Mereiter, K.; Schmidt, R. J. Chem.

Soc., Chem. Commun. 1993, 892–893.

(55) Gemel, C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics

1997, 16, 5601–5603.

(56) Gemel, C.; Sapunov, V. N.; Mereiter, K.; Ferencic, M.; Schmid, R.;

Kirchner, K. Inorg. Chim. Acta 1999, 286, 114–120.

ꢀ

Jimenez-Tenorio et al.

6052 Inorganic Chemistry, Vol. 49, No. 13, 2010

Chart 7

Chart 8

Chart 9

It is important to mention that the C5-ring resonance

for 10a appears in the ¹³C{¹H} NMR spectrum as a broad

signal at 80.2 ppm. The position of the C5-ring resonance

allows one to distinguish between half-sandwich 16- and

18-electron complexes. This resonance appears in the

range 70-81 ppm in the case of 16-electron complexes

and between 81 and 100 ppm in the case of 18-electron

complexes.⁴²Hence, this spectral feature for 10a is fully

consistent with its formulation as a coordinatively un-

saturated species.

To structurally characterize the 16-electron com-

pounds, we have optimized the real complex 10b and

the model complex 10a_m. Their structures are depicted in

Figure 17. Both exhibit a pyramidalized geometry, with

values of the pyramidalization angle R of 153.8° and

160.8° for 10b and 5a_m, respectively. These values can

be compared with those of the corresponding 18-electron

dihydrogen complexes 5b and 5a_m(140.2° and 146.0°,

respectively). We have checked for the small complex

10a_mthe relative energy of the triplet state. The optimized

triplet is found 51.8 kJ mol^-1above the singlet, pointing

out the low-spin character of the ground state for this

unsaturated complex.

The 16-electron complex 10a is exceedingly reactive. It

turns brown in the solid state when stored for a few days.

It also decomposes in solution in most organic solvents. It

was characterized by NMR spectroscopy in fluoroben-

zene-d₅, where it appears to be more stable. The NMR

spectra at 298 K consist of broad features, which

become sharper at low temperatures. The ¹H NMR

spectrum at 238 K is consistent with the presence of a

κ²-P,N-ⁱPr₂PCH₂Py ligand. The hydrogen atoms of the

CH₂spacer group are inequivalent and appear shifted to

an unusually high field, i.e., from 2.87 ppm (H_ain 5a) to

1.00 (H_ain 10a). The H_a-H_bcorrelations as well as the

CH_a-H_bcorrelations were confirmed by means of

g-COSY and g-HSQC NMR spectra, respectively. If we

assume a “two-legged-piano-stool” structure for 10a,

analogous to that found for other 16-electron Cp*Ru-

(PP)^þand Cp*Ru(NN)^þcomplexes,^42,55,56we find that

the five-membered ring RuNCCP is relatively rigid but

not planar. Hence, the hydrogen atoms of the PCH₂

group can still adopt two inequivalent, mutually ex-

changeable positions through a hindered rotation around

the P-CH₂bond, as shown in Chart 8.

Conclusions

Alternatively, we might consider that the structure of

10a is bent or pyramidalized.^56-58DFT studies have

shown that variation of the ground-state energy of the

model compound [CpRu(PH₂CH₂CH₂PH₂)]^þreaches a

minimum with a value for the pyramidalization angle

R between 149° and 152°, whereas in the case of [CpRu-

(NH₂CH₂CH₂NH₂)]^þ, the minimum is reached for R

between 171° and 179° (structure not pyramidalized).^57,58

A pyramidalized structure should involve the dynamic

exchange between two possible configurations, in which

the atoms H_aand H_binterconvert each other as a result

(Chart 9).

The proton-transfer reactions to the trihydride complexes

2a and 2b using both weak and strong acids have been

experimentally studied and theoretically modeled by DFT

calculations. The reactions with weak donors result in the

formation of hydrogen-bonded adducts between the proton

donor and the pendant pyridine or quinoline group. This has

been unequivocally demonstrated by determination of the

X-ray crystal structure of the supramolecular aggregate 3a.

Proton transfer to the hydride ligands can be modulated by

solvent polarity. Protonation with CF₃SO₃H in CD₂Cl₂

occurs in a stepwise manner involving protonation at the

pendant nitrogen atom followed by hydrogen transfer to the

hydride, dihydrogen elimination, and formation of the dihy-

drogen complexes 5a/5b, which do not rearrange to their

dihydride isomers. With an excess of acid, a second proton-

ation occurs at the hydride site and the dicationic complexes

(57) Brunner, H.; Tsuno, T. Acc. Chem. Res. 2009, 42, 1501–1510.

(58) The pyramidalization angle R is defined as the angle formed by the

centroid of the Cp* ring, the ruthenium atom, and the centroid of the moiety

L-Ru-L (L=P, N).

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6053

6a or 6b are generated. Dihydrogen elimination from 5a/5b

generates highly reactive 16-electron complexes that exhibit

bent or pyramidalized structures, as inferred from spectral

and DFT calculations. These unsaturated complexes provide

binding sites for other small molecules such as dinitrogen or

dioxygen. The ability of the pendant pyridyl or quinoline

groups to interact with weak proton donors suggests the

possibility of using the hydride complexes 2a/2b as catalyst

precursors for a number of transformations in polar media

such asnitrile hydrationreactions. These studiesare currently

being carried out and will be reported in due course.

δ 10.95 [s, C₅(CH₃)₅], 17.83, 18.84, 19.57 [s, P(CH(CH₃)₂)₂],

25.30 [d, ¹J_CP=16.3 Hz, PCH(CH₃)₂], 25.82 [d, ¹J_CP=17.9 Hz,

PCH(CH₃)₂], 35.99 (d, J_CP= 16.3 Hz, PCH₂), 82.18 [s, C₅-

1

(CH₃)₅], 121.17, 121.57, 134.00, 154.78, 164.20 (C₅H₄N). Data

for 1b. Anal. Calcd for C₂₆H₃₇NClPRu: C, 58.8; H, 7.02; N, 2.6.

Found: C, 58.8; H, 6.91; N, 2.5. ¹H NMR (400 MHz, CD₂Cl₂,

298 K): δ 0.74 (m, 3 H), 1.10 (m, 3 H), 1.48 (m, 3 H), 1.58 (m, 3H)

[P(CH(CH₃)₂)₂], 1.37 [s, 15 H, C₅(CH₃)₅], 2.21, 2.63 [m, 1 H

each, P(CH(CH₃)₂)₂], 3.16 (dd, ²J_HH=16.4 Hz, ²J_HP=3.5 Hz,

2

1 H, PCH_aH_b), 3.57 (dd, ²J_HH= 16.4 Hz, J_HP= 10 Hz, 1 H,

PCH_aH_b), 7.40 (d), 7.49 (t), 7.71 (m), 7.73 (m), 7.90 (d), 9.67 (d)

(C₉H₆N). ³¹P{¹H} NMR (161.89 MHz, CD₂Cl₂, 298 K): δ 51.7

(s). ¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 298 K): δ 10.31 [s,

C₅(CH₃)₅], 18.86, 19.97, 20.13, 21.09 [s, P(CH(CH₃)₂)₂], 26.33

Experimental Section

1

[d, J_CP= 10.1 Hz, PCH(CH₃)₂], 28.36 [d, J_CP= 20.1 Hz,

PCH(CH₃)₂], 43.60 (d, J_CP= 18.9 Hz, PCH₂), 81.11 [s, C₅-

1

All synthetic operations were performed under a dry dini-

trogen or argon atmosphere following conventional Schlenk

techniques. Tetrahydrofuran, 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 other solvents were of

anhydrous quality and were used as received. All solvents

were deoxygenated immediately before use. The ligands

(CH₃)₅], 119.39, 126.67, 127.23, 128.42, 128.99, 134.82, 134.87,

151.46, 163.22 (C₉H₆N).

[Cp*RuH₃(K¹-P-ⁱPr₂PCH₂Py)] (2a) and [Cp*RuH₃(κ¹-P-ⁱPr₂-

PCH₂Quin)] (2b). To 1a or 1b (1 mmol) in MeOH (15 mL) at

0 °C (ice bath) was carefully added in small portions an excess of

solid NaBH₄(0.3 g). Caution! Strong dihydrogen evolution will

occur. Once the addition was finished, the ice bath was removed

and the mixture stirred for 10-15 min at room temperature.

Then, the solvent was removed in vacuo. The residue was

extracted with two portions of 10 mL of petroleum ether and

filtered through an anhydrous Na₂SO₄plug. The resulting

solution was concentrated to ca. 3 mL and cooled to -20 °C.

Colorless crystals were obtained that were filtered off and dried

in vacuo. 2a and 2b can also be obtained directly from

[{Cp*RuCl₂}_n] by reaction with the appropriate amount of the

i

ⁱPr₂PCH₂Py and Pr₂PCH₂Quin were respectively prepared

i

by the reaction of LiCH₂Py and LiCH₂Quin with Pr₂PCl,

following suitable adaptations of published procedures.⁵⁹

[{Cp*RuCl}₄]⁶⁰and NaBAr⁰₄⁶¹were prepared according to

literature methods. CF₃SO₃H, indole, benzoic acid, and

salicylic acid 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 Var-

ian Unity 400 MHz or Varian Inova 600 MHz equipment.

Chemical shifts are given in ppm from SiMe₄(¹H and ¹³C-

{¹H}), 85% H₃PO₄(³¹P{¹H}), or CFCl₃(¹⁹F). Longitudinal

relaxation time (T₁) measurements were made by the inver-

sion-recovery method. Activation parameters for fluxional

processes were obtained by a dynamic NMR line-shape

fitting simulation using the program DNMR3⁶²incorporated

into SpinWorks 2.4.⁶³Microanalysis was performed on ele-

mental analyzer model LECO CHNS-932 at the Servicio

i

corresponding phosphine Pr₂PCH₂Py or Pr₂PCH₂Quin and

an excess of solid NaBH₄in MeOH at 0 °C. Data for 2a. Yield:

0.27 g, 60%. Anal. Calcd for C₂₂H₃₈NPRu: C, 58.9; H, 8.54; N,

3.1. Found: C, 58.7; H, 8.61; N, 2.9. IR: ν(Ru-H) 1986 cm^-1. ¹H

2

NMR (400 MHz, toluene-d₈, 298 K): δ -10.92 (d, J_HP=

21.8 Hz, 3 H, RuH₃), 0.99 [m, 12 H, P(CH(CH₃)₂)₂], 1.87 [m,

=

2

2 H, P(CH(CH₃)₂)₂], 2.00 [s, 15 H, C₅(CH₃)₅], 3.06 (d, J_HP

9.2 Hz, PCH₂), 6.60 (t), 7.00 (t), 7.03 (d), 8.33 (d) (1 H each,

C₅H₄N ring). ³¹P{¹H} NMR (161.89 MHz, toluene-d₈, 298 K):

δ 88.7 (s). ¹³C{¹H} NMR (101 MHz, toluene-d₈, 298 K): δ 12.61

[C₅(CH₃)₅], 18.80, 19.38 [P(CH(CH₃)₂)₂], 27.80 [d, ¹J_PC=26 Hz,

ꢀ

Central de Ciencia y Tecnologıa, Universidad de Cadiz.

´

[Cp*RuCl(K²-P,N-ⁱPr₂PCH₂Py)] (1a) and [Cp*RuCl(κ²-

P,N-ⁱPr₂PCH₂Quin)] (1b). To[{Cp*RuCl}₄] (0.66 g, ca. 0.6 mmol)

in petroleum ether (20 mL) was added via syringe either

1

P(CH(CH₃)₂)₂], 42.55 (d, J_PC= 17.9 Hz, PCH₂), 94.94 [C₅-

i

ⁱPr₂PCH₂Py (0.65 mL, ca. 2.5 mmol) or Pr₂PCH₂Quin (0.75

(CH₃)₅], 120.72, 135.24, 137.47, 149.19, 159.06 (C₅H₄N ring).

Data for 2b. Yield: 0.33 g, 66%. Anal. Calcd for C₂₆H₄₀NPRu:

C, 62.6; H, 8.09; N, 2.8. Found: C, 62.7; H, 8.18; N, 2.6. IR:

ν(Ru-H) 1989 cm^-1. ¹H NMR (400 MHz, toluene-d₈, 298 K):

δ -10.82 (d, ²J_HP= 22 Hz, 3 H, RuH₃), 1.05 [m, 12 H, P(CH-

(CH₃)₂)₂], 1.90 [m, 2 H, P(CH(CH₃)₂)₂], 2.02 [s, 15 H, C₅(CH₃)₅],

3.25 (d, ²J_HP=9.2 Hz, PCH₂), 7.13, 7.23, 7.34, 7.36, 7.51, 8.05

(m, 1 H each, C₉H₆N ring). ³¹P{¹H} NMR (161.89 MHz, toluene-

d₈, 298 K): δ 89.1 (s). ¹³C{¹H} NMR (101 MHz, toluene-d₈, 298

K): δ 12.95 [C₅(CH₃)₅], 19.21, 19.68 [P(CH(CH₃)₂)₂], 28.52 [d,

¹J_PC=25 Hz, P(CH(CH₃)₂)₂], 43.56 (d, ¹J_PC= 16.9 Hz, PCH₂),

95.34 [C₅(CH₃)₅], 124.31, 126.00, 127.25, 128.02, 129.50, 129.94,

135.31, 148.91, 159.80 (C₉H₆N ring).

mL, ca. 2.5 mmol). The resulting red (for 1a) or black (for 1b)

suspension was stirred at room temperature for 30 min. Then,

the microcrystalline precipitate was filtered off, washed with

petroleum ether, and dried in vacuo. The resulting products

were pure enough for synthetic purposes. Both 1a and 1b could

be recrystallized from hot toluene/petroleum ether in the form

of red-orange or black crystals. Yield: 90% in both cases (65-

70% upon recrystallization). Data for 1a. Anal. Calcd for

C₂₂H₃₅NClPRu: C, 54.9; H, 7.33; N, 2.9. Found: C, 54.8; H,

7.01; N, 2.6. ¹H NMR (400 MHz, C₆D₆, 298 K): δ 0.67 (m, 3 H),

0.99 (m, 3 H), 1.27 (m, 6 H) [P(CH(CH₃)₂)₂], 1.66 [s, 15 H,

C₅(CH₃)₅], 2.07, 2.49 [m, 1 H each, P(CH(CH₃)₂)₂], 2.63 (dd,

[Cp*RuH₃(K¹-P-ⁱPr₂PCH₂Py)] C₆H₄(OH)COOH (3a). To a

²J_HH=15.6 Hz, ²J_HP=9.7 Hz, 1 H, PCH_aH_b), 3.47 (dd, ²J_HH

=

3

15.6 Hz, ²J_HP=8.2 Hz, 1 H, PCH_aH_b), 6.39 (t), 6.61 (d), 6.80 (t),

8.87 (d) (1 H each, C₅H₄N). ³¹P{¹H} NMR (161.89 MHz, C₆D₆,

298 K): δ 75.5 (s). ¹³C{¹H} NMR (101 MHz, C₆D₆, 298 K):

solution of 2a (0.23 g, ca. 0.5 mmol) in toluene was added

salicylic acid (0.07 g, ca. 0.5 mmol). The mixture was stirred at

room temperature for 2 h. Then, the solvent was removed in

vacuo and the orange residue washed with petroleum ether. The

product was dissolved in a minimum amount of toluene and the

solution filtered. The solution was layered with petroleum ether.

Slow diffusion of petroleum ether into the concentrated toluene

solution afforded well-formed orange crystals, suitable for

X-ray structure analysis. Yield: 0.16 g, 55%. Anal. Calcd for

C₂₉H₄₄NO₃PRu: C, 59.4; H, 7.56; N, 2.4. Found: C, 59.4; H,

7.48; N, 2.2. IR: ν(Ru-H) 1979 cm^-1, ν(CdO) 1596 cm^-1. ¹H

NMR (400 MHz, C₆D₆, 298 K): δ -10.84 (d, ²J_HP= 21.5 Hz,

(59) Jansen, A.; Pitter, S. Monatsch. Chem. 1999, 130, 783–794.

(60) (a) Fagan, P. J.; Ward, M. D.; Calabrese, J. C. J. Am. Chem. Soc.

1989, 111, 1698–1719. (b) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.;

Williams, I. D. Organometallics 1990, 9, 1843–1852.

(61) Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992, 11,

3920–3922.

(62) Kleier, D. A.; Binsch, G. J. Magn. Reson. 1970, 3, 146–160.

(63) Marat, K. SpinWorks 2.4; University of Manitoba: Winnipeg, Manitoba,

Canada, 2005.

ꢀ

Jimenez-Tenorio et al.

6054 Inorganic Chemistry, Vol. 49, No. 13, 2010

3 H, RuH₃), 0.97 [m, 12 H, P(CH(CH₃)₂)₂], 1.90 [m, 2 H,

P(CH(CH₃)₂)₂], 1.98 [s, 15 H, C₅(CH₃)₅], 3.12 (d, ²J_HP=9.3 Hz,

PCH₂), 6.53 (m), 6.95 (td), 7.21 (d), 8.42 (d) (1 H each, C₅H₄N

ring protons), 6.70 (t br), 7.05 (d), 7.11 (m), 8.21 (d br) (1 H each,

C₆H₄ring protons), 10.5 (br, 2 H, COOH þ OH). ³¹P{¹H} NMR

(161.89 MHz, C₆D₆, 298 K): δ 90.7 (s br). ¹³C{¹H} NMR

(101 MHz, C₆D₆, 298 K): δ 12.50 [C₅(CH₃)₅], 18.58, 19.22

and dried in a dinitrogen stream. Data for 8a. Yield: 0.43 g, 64%.

Calcd for C₅₄H₄₇N₃BF₂₄PRu: C, 48.5; H, 3.54; N, 3.1. Found:

C, 48.3; H, 3.61; N, 2.9. IR: ν(N₂) 2169 cm^-^{1 1}H NMR

.

(400 MHz, tetrahydrofuran-d₈, 298 K): δ 0.97 (m br, 6 H),

1.23 [m br, 6 H, P(CH(CH₃)₂)₂], 1.62 [s, 15 H, C₅(CH₃)₅], 2.45,

2.97 [m br, 1 H each, P(CH(CH₃)₂)₂], 3.32, 3.58 (br, 1 H each,

PCH₂), 7.27 (t), 7.39 (d), 7.72 (t), 9.09 (d) (1 H each, C₅H₄N).

³¹P{¹H} NMR (161.89 MHz, tetrahydrofuran-d₈, 298 K): δ 75.4

(s). ¹³C{¹H} NMR (101 MHz, tetrahydrofuran-d₈, 323 K):

δ 10.67 [s, C₅(CH₃)₅], 18.21, 19.29 [s, P(CH(CH₃)₂)₂], 25.49 [s

br, PCH(CH₃)₂], 33.97 (s br, PCH₂), 82.42 [s, C₅(CH₃)₅], 123.61,

137.73, 165.39 (C₅H₄N). Data for 8b. Yield: 0.53 g, 76%. Calcd

for C₅₈H₄₉N₃BF₂₄PRu: C, 50.2; H, 3.56; N, 3.0. Found: C, 50.0;

1

[P(CH(CH₃)₂)₂], 27.81 [d, J_PC= 24.3 Hz, P(CH(CH₃)₂)₂],

40.87 (d, ¹J_PC=17 Hz, PCH₂), 95.08 [C₅(CH₃)₅], 117.74, 118.75,

131.0, 135.12, 163.23 (C₆H₄ring), 121.31, 125.86, 136.54, 147.56,

157.90 (C₅H₄N ring), 174.11 (COOH). H NMR (400 MHz,

1

CD₂Cl₂, 298 K): δ -11.32 (br, RuH₃), 0.93 [m, 12 H, P(CH-

(CH₃)₂)₂], 1.90 [m, 2 H, P(CH(CH₃)₂)₂], 2.00 [s, 15 H, C₅(CH₃)₅],

3.16 (d, ²J_HP=9.2 Hz, PCH₂), 6.83 (t), 6.88 (d), 7.37 (t), 7.88 (d

br) (1 H each, C₆H₄ring protons), 7.26 (m), 7.49 (d), 7.73 (t),

8.59 (d) (1 H each, C₅H₄N ring protons), 9.90 (br, COOH þ

OH). ³¹P{¹H} NMR (161.89 MHz, CD₂Cl₂, 298 K): δ 91.1 (s br).

¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 298 K): δ 12.40 [C₅(CH₃)₅],

H, 3.48; N, 2.9. IR: ν(N₂) 2152 cm^{-1 1}H NMR (400 MHz,

.

CD₃NO₂, 298 K): δ 0.72 (m, 3 H), 1.02 (m, 3 H), 1.55 (m, 3 H),

1.60 (m, 3H) [P(CH(CH₃)₂)₂], 1.41 [s, 15 H, C₅(CH₃)₅], 2.68, 2.80

[m, 1 H each, P(CH(CH₃)₂)₂], 3.84 (dd, ²J_HH=18.4 Hz, ²J_HP

5.9 Hz, 1 H, PCH_aH_b), 4.15 (dd, J_HH= 18.4 Hz, J_HP

=

2

1

13.9 Hz, 1 H, PCH_aH_b), 7.81 (m), 7.83 (t), 8.06 (d), 8.08 (m), 8.54

(d), 8.69 (d) (C₉H₆N). ³¹P{¹H} NMR (161.89 MHz, CD₃NO₂,

298 K): δ 77.4 (s). ¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 298 K): δ

9.55 (s, C₅(CH₃)₅), 18.56, 18.89, 18.89, 20.10 [s, P(CH(CH₃)₂)₂],

26.00 [d, ¹J_CP=21.1 Hz, PCH(CH₃)₂], 29.25 [d, ¹J_CP=26 Hz,

18.50, 19.18 [P(CH(CH₃)₂)₂], 27.76 [d, J_PC= 25.1 Hz, P(CH-

(CH₃)₂)₂], 40.35 (d, J_PC= 17.9 Hz, PCH₂), 95.35 [C₅(CH₃)₅],

1

117.023, 118.52, 130.95, 134.32, 162.24 (C₆H₄ring), 121.97,

126.32, 137.67, 147.07, 157.73 (C₅H₄N ring).

[Cp*Ru(H₂)(K²-P,N-ⁱPr₂PCH₂Py)][BAr⁰₄] (5a) and [Cp*Ru(H₂)-

(κ²-P,N-ⁱPr₂PCH₂Quin)][BAr⁰₄] (5b). To an equimolar mixture

of 1a or 1b and NaBAr⁰₄(0.5 mmol) under dihydrogen was

added diethyl ether (20 mL). The mixture was stirred under

dihydrogen for 1 h. Then it was filtered through an anhydrous

Na₂SO₄plug. The solution was layered with petroleum ether in a

countercurrent of dihydrogen and left to stand at room tem-

perature in a dihydrogen atmosphere. Yellow crystals were

obtained that were filtered off and dried in an argon stream.

They were stored under dihydrogen. Otherwise, they lose dihy-

drogen gradually, much quicker in the case of 5a. NMR were

recorded under dihydrogen. Data for 5a. Yield: 0.39 g, 60%.

Anal. Calcd for C₅₄H₄₉NBF₂₄PRu: C, 49.5; H, 3.77; N, 1.1.

Found: C, 49.6; H, 3.61; N, 1.0. ¹H NMR (400 MHz, CD₂Cl₂,

298 K): δ -6.63 [br, 2 H, (T₁)_min=10 ms, Ru(H₂)], 0.73 (m, 3 H),

0.88 (m, 3 H), 1.12 (m, 3 H), 1.24 (m, 3 H) [P(CH(CH₃)₂)₂], 1.76

[s, 15 H, C₅(CH₃)₅], 2.27, 2.46 [m, 1 H each, P(CH(CH₃)₂)₂], 2.87

(dd, 1 H, ²J_HP=7.74 Hz, ²J_HaHb=17.4 Hz, PCH_aH_b), 3.32 (dd,

1 H, ²J_HP=10.5 Hz, ²J_HaHb=17.4 Hz, PCH_aH_b), 7.17 (t), 7.38

(d), 7.63 (t), 8.60 (d) (1 H each, C₅H₄N). ³¹P{¹H} NMR (161.89

MHz, CD₂Cl₂, 298 K): δ 84.5 (s). ¹³C{¹H} NMR (101 MHz,

CD₂Cl₂, 298 K): δ 10.92 [s, C₅(CH₃)₅], 18.34 [br, P(CH-

1

PCH(CH₃)₂], 40.00 (d, J_CP= 27.7 Hz, PCH₂), 95.34 [s, C₅-

(CH₃)₅], 108.60, 122.63, 129.66, 134.09, 136.92, 143.64 (C₉H₆N).

[Cp*Ru(O₂)(K²-P,N-ⁱPr₂PCH₂Quin)][BAr⁰₄] (9b). This com-

pound was obtained following an experimental procedure iden-

tical with that for 8a/8b but using air instead of dinitrogen.

Alternatively, it can be prepared quantitatively by stirring a

diethyl ether solution of 8b in the air for 1 h, followed by solvent

removal and washings with petroleum ether. Yield: essentially

quantitative. Calcd for C₅₈H₄₉NBF₂₄O₂PRu: C, 50.1; H, 3.55;

1

N, 1.0. Found: C, 50.0; H, 3.52; N, 0.9. H NMR (400 MHz,

CDCl₃, 298 K): δ 0.67 (m, 3 H), 0.98 (m, 3 H), 1.42 (m, 3 H), 1.57

(m, 3H) [P(CH(CH₃)₂)₂], 1.27 [s, 15 H, C₅(CH₃)₅], 2.51, 2.57 [m,

1 H each, P(CH(CH₃)₂)₂], 3.40 (dd, ²J_HH=17.4 Hz, ²J_HP=5.1

Hz, 1 H, PCH_aH_b), 3.73 (dd, ²J_HH= 17.4 Hz, ²J_HP= 13.6 Hz,

1 H, PCH_aH_b), 7.28 (d), 7.38 (m), 7.82 (d), 7.98 (t), 8.16 (d), 8.61

(d) (C₉H₆N). ³¹P{¹H} NMR (161.89 MHz, CDCl₃, 298 K): δ

75.3 (s). ¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 298 K): δ 9.36 [s,

C₅(CH₃)₅], 18.09, 18.69, 19.22, 19.68 [s, P(CH(CH₃)₂)₂], 24.94

1

[d, J_CP= 21.1 Hz, PCH(CH₃)₂], 28.49 [d, J_CP= 26 Hz,

PCH(CH₃)₂], 39.07 (d, J_CP= 24.4 Hz, PCH₂), 95.76 [s, C₅-

1

(CH₃)₅], 107.16, 120.78, 128.98, 133.60, 142.77, 148.82, 166.36

(C₉H₆N).

1

(CH₃)₂)₂], 24.37 [br, PCH(CH₃)₂], 36.90 (d, J_CP= 23.5 Hz,

[Cp*Ru(K²-P,N-ⁱPr₂PCH₂Py)][BAr⁰₄] (10a). To an equimolar

mixture of 1a and NaBAr⁰₄(0.5 mmol) under argon was added

thoroughly degassed fluorobenzene (20 mL). A blue color develo-

ped. The mixture was stirred under argon for 30 min. Then it was

filtered through an anhydrous Na₂SO₄plug. The solvent was

removed in vacuo, leaving a blue microcrystalline solid, which

was washed with one portion of petroleum ether and dried in

vacuo. The complex turned brown in a few days even when stored

under argon at -20 °C. Yield: essentially quantitative. Calcd for

C₅₄H₄₇NBF₂₄PRu: C, 49.6; H, 3.62; N, 1.1. Found: C, 49.5; H,

3.52; N, 1.0. ¹H NMR (600 MHz, fluorobenzene-d₅, 238 K): δ

0.18 (m, 3 H), 1.00 [m, 7 H, 6 H P(CH(CH₃)₂)₂þ 1 H PCH_aH_b],

1.13 (m, 3 H) [P(CH(CH₃)₂)₂], 1.63 [s, 15 H, C₅(CH₃)₅], 2.04,

PCH₂), 92.9 [s, C₅(CH₃)₅], 123.77, 138.43, 156.20, 163.22

(C₅H₄N). Data for 5b. Yield: 0.47 g, 69%. Anal. Calcd for

C₅₈H₅₁NBF₂₄PRu: C, 51.2; H, 3.78; N, 1.0. Found: C, 51.2; H,

3.60; N, 0.9. ¹H NMR (400 MHz, CD₂Cl₂, 298 K): δ -5.62 [br, 2

H, (T₁)_min=11 ms, Ru(H₂)], 0.18 (m, 3 H), 0.94 (m, 3 H), 1.46

(m, 6 H) [P(CH(CH₃)₂)₂], 1.58 [s, 15 H, C₅(CH₃)₅], 2.06, 2.69 [m,

1 H each, P(CH(CH₃)₂)₂], 3.74 (dd, 1 H, ²J_HP=5.5 Hz, ²J_HaHb

=

17.6 Hz, PCH_aH_b), 3.91 (dd, 1 H, ²J_HP=12.6 Hz, ²J_HaHb=17.6

Hz, PCH_aH_b), 7.70 (m, 2 H), 7.92 (m, 2 H), 8.27 (d, 1 H), 8.94 (d,

1 H) (C₉H₆N). ³¹P{¹H} NMR (161.89 MHz, CD₂Cl₂, 298 K): δ

77.8 (s). ¹³C(¹H) NMR (158.83 MHz, CD₂Cl₂, 253 K): δ 10.48 [s,

C₅(CH₃)₅], 17.71, 18.01, 18.24, 18.78 [s, P(CH(CH₃)₂)₂], 22.20

1

[d, J_CP= 23 Hz, PCH(CH₃)₂], 27.50 [d, J_CP= 23.2 Hz,

PCH(CH₃)₂], 43.72 (d, J_CP= 23 Hz, PCH₂), 92.56 [s, C₅-

1

2

2.18 [m, 1 H each, P(CH(CH₃)₂)₂], 2.79 (dd, J_HH= 15.5 Hz,

²J_HP=11.9 Hz, 1 H, PCH_aH_b), 7.11 (d), 7.26 (m), 7.50 (d), 7.98

(t), 8.57 (d) (C₅H₄N). ³¹P{¹H} NMR (242.84 MHz, fluoroben-

zene-d₅, 238 K): δ 78.3 (s). ¹³C{¹H} NMR (151.5 MHz, fluoro-

benzene-d₅, 238 K): δ 9.89 [s, C₅(CH₃)₅], 14.84, 17.13, 17.29, 18.65

[s, P(CH(CH₃)₂)₂], 21.50 [d, ¹J_CP=20.7 Hz, PCH(CH₃)₂], 25.39 [d,

¹J_CP= 24.5 Hz, PCH(CH₃)₂], 30.98 (d, ¹J_CP= 18.1 Hz, PCH₂),

80.2 [br, C₅(CH₃)₅], 124.10, 130.10, 138.98, 154.6 (C₅H₄N).

Solution NMR Study of the Protonation Reactions. Solutions

of the respective trihydride complexes 2a and 2b (0.1 mmol)

in CD₂Cl₂unless otherwise stated, prepared under an argon

(CH₃)₅], 120.68, 127.54, 128.94, 131.16, 132.19, 139.38, 148.95,

165.91 (C₉H₆N).

[Cp*Ru(N₂)(K²-P,N-ⁱPr₂PCH₂Py)][BAr⁰₄] (8a) and [Cp*Ru-

(N₂)(κ²-P,N-ⁱPr₂PCH₂Quin)][BAr⁰₄] (8b). To an equimolar mix-

ture of 1a or 1b and NaBAr⁰₄(0.5 mmol) under dinitrogen was

added diethyl ether (20 mL). The mixture was stirred under

dinitrogen for 1 h. Then it was filtered through an anhydrous

Na₂SO₄plug. The solution was concentrated by passing

through a dinitrogen stream. Layering the solution with petro-

leum ether afforded red-orange crystals, which were filtered off

Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6055

ꢀ

Jimenez-Tenorio et al.

6056 Inorganic Chemistry, Vol. 49, No. 13, 2010

atmosphere in NMR tubes, were frozen by immersion into

liquid nitrogen. The corresponding amount of proton donor

(0.1 mmol of either PhCOOH, indole, or salicylic acid) or

CF₃SO₃H (via micropipet: 0.1 mmol for 4a/4b; 0.3 mmol for

6a/6b; 0.2 mmol for 7a) was added. 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

193 K. Once shims were adjusted, the probe was warmed to

the desired temperature. The NMR temperature controller was

previously calibrated against a MeOH sample, with the repro-

ducibility being (0.5 °C.

PCH(CH₃)₂], 41.10 (br, PCH₂), 103.26 (s, C₅(CH₃)₅), 125.09,

126.35, 142.23, 154.16, 163.16 (C₅H₄N). ¹⁹F NMR (376.28 Hz,

CD₂Cl₂, 298 K) δ -78.6 (s).

DFT Calculations. DFT calculations were performed with the

Gaussian 03 package⁶⁴using the hybrid functional M05-2X.⁶⁵

The ruthenium atom was described with the Stuttgart pseudo-

potential SDD⁶⁶for the core electrons and its related basis set

for the outer ones, with an added set of f polarization functions

with exponent 1.235.⁶⁷Two different basis sets were used for the

other atoms: geometry optimizations and thermal corrections

(Gibbs energy) were calculated with a 6-31g(d,p) double-ζ basis

set including polarization functions in all atoms. Single-point

calculations in solvent were performed with the triple-ζ basis set

6-311þþG(2d,2p) with two sets of polarization functions and a

diffuse function in all atoms.⁶⁴

Selected Spectral Data for [Cp*RuH₃(K¹-P-ⁱPr₂PCH₂PyH)]-

[CF₃SO₃] (4a) and [Cp*RuH₃(κ¹-P-ⁱPr₂PCH₂QuinH)][CF₃SO₃]

(4b). Data for 4a. ¹H NMR (400 MHz, CD₂Cl₂, 203 K): δ

-11.36 [br, 3 H, (T₁)_min=213 ms, RuH₃]; 0.76 (m, 6 H), 0.95 (m,

6 H), 1.89 [s, 15 H, C₅(CH₃)₅], 1.90 [m, 2 H, P(CH(CH₃)₂)₂], 3.07

(d, 2 H, d, ²J_HP=7.8 Hz, PCH₂), 7.75 (t), 7.90 (d), 8.30 (t), 8.54

(d) (C₅H₄N), 13.84 (br, 1 H, NH). ³¹P{¹H} NMR (161.89 MHz,

CD₂Cl₂, 203 K): δ 98.9 (br).

Solvent calculations were carried out with the CPCM con-

tinuum model^68,69with default parameters for DCM as the

solvent (ε=8.93). If it is not stated otherwise, all of the energies

referred to in the text are Gibbs energies in the solvent. These

Gibbs energies in the solvent were calculated following the

equation G_solv=E_solv

þ (G_gas^BS1- E_gas^BS1).⁷⁰

BS2

X-ray Structure Determinations. Single crystals of com-

pounds 1b, 2b, 3a, 5b, 8b, and 9b were obtained and mounted

on a glass fiber to carry out the crystallographic study. Crystal

data and experimental details are given in Table 2. The X-ray

diffraction data collection was measured at 100 K on a Bruker

Smart APEX CCD three-circle diffractometer using a sealed

tube source with graphite-monochromated Mo KR radiation

Data for 4b. ¹H NMR (400 MHz, CD₂Cl₂, 203 K): δ -11.20

[br, 3 H, (T₁)_min=109 ms, RuH₃], 0.81 (m, 6 H), 0.96 (m, 6 H),

1.92 [s, 15 H, C₅(CH₃)₅], 1.95 [m, 2 H, P(CH(CH₃)₂)₂], 3.26 (d, 2

H, d, ²J_HP=9.2 Hz, PCH₂), 7.70 (t), 7.80 (m), 7.89 (t), 7.99 (d),

8.15 (d), 8.51 (br) (C₉H₆N), 13.50 (br, 1 H, NH). ³¹P{¹H} NMR

(161.89 MHz, CD₂Cl₂, 203 K): δ 97.9 (br).

Selected Spectral Data for [Cp*RuH₄(K¹-P-ⁱPr₂PCH₂PyH)]-

[CF₃SO₃]₂(6a) and [Cp*RuH₄(κ¹-P-ⁱPr₂PCH₂QuinH)][CF₃SO₃]₂

(6b). Data for 6a. ¹H NMR (400 MHz, CD₂Cl₂, 203 K): δ -8.09

[br, 4 H, (T₁)_min=13.9 ms, RuH₄], 0.90 (m, 12 H), 1.97 [s, 15 H,

(λ=0.710 73 A) at the Servicio Central de Ciencia y Tecnologıa

´

ꢀ

de la Universidad de Cadiz. In each case, four sets of frames were

recorded over a hemisphere of the reciprocal space by an ω scan

with δ(ω)=0.30° and an exposure of 10 s per frame. Correction

for absorption was applied by scans of equivalents using the

program SADABS.⁷¹An insignificant crystal decay correction

was also applied. The structure was solved by direct methods,

completed by subsequent difference Fourier syntheses and

refined on F²by full-matrix least-squares procedures using the

programs contained in the SHELXTL package.⁷²Non-hydro-

gen atoms were refined with anisotropic displacement para-

meters. The program ORTEP-3⁷³was used for plotting.

C₅(CH₃)₅], 2.31 [m, 2 H, P(CH(CH₃)₂)₂], 3.56 (d, 2 H, d, ²J_HP

=

4.6 Hz, PCH₂), 7.75 (d), 7.90 (t), 8.52 (t), 8.67 (br) (C₅H₄N),

14.80 (br, 1 H, NH). ³¹P{¹H} NMR (161.89 MHz, CD₂Cl₂, 203

K): δ 79.0 (br).

Data for 6b. ¹H NMR (400 MHz, CD₂Cl₂, 203 K): δ -7.96

[br, 4 H, (T₁)_min=12.4 ms, RuH₄], 0.92 (m, 6 H), 1.02 (m, 6 H),

1.96 [s, 15 H, C₅(CH₃)₅], 2.37 [m, 2 H, P(CH(CH₃)₂)₂], 3.52 (d,

2 H, d, ²J_HP=8.5 Hz, PCH₂), 7.51 (d), 7.95 (t), 8.15 (t), 8.21 (m),

8.23 (m), 8.93 (d) (C₉H₆N), 13.80 (br, 1 H, NH). ³¹P{¹H} NMR

(161.89 MHz, CD₂Cl₂, 203 K): δ 80.4 (br).

Acknowledgment. We thank the Spanish Ministerio de

ꢀ

Ciencia e Innovacion (DGICYT; Projects CTQ2007 60137/

BQU and CTQ2008-06866-C02-01/BQU and Consolider Inge-

Selected Spectral Data for [Cp*RuH(CF₃SO₃)(K²-P,N-ⁱPr₂-

PCH₂Py)][CF₃SO₃] (7a). ¹H NMR (400 MHz, CD₂Cl₂, 298 K):

δ -5.53 (br, 1 H, RuH); 0.84 (m, 3 H), 1.17 (m, 6 H), 1.49 (m,

3 H), 1.64 [P(CH(CH₃)₂)₂], 1.80 [s, 15 H, C₅(CH₃)₅], 2.30, 2.38 [m,

nio-2010 CSD2007-00006) and Junta de Andalucıa (Projects

´

PAI FQM188 and P08 FQM 03538) for financial support and

Johnson Matthey plc for generous loans of ruthenium trichlor-

ide. S.M. acknowledges a FPI fellowship from the Spanish

MICINN.

1 H each, P(CH(CH₃)₂)₂], 3.61 (1 H, dd, ²J_HH=17.1 Hz, ²J_HP

=

2

7.3 Hz, PCH_aH_b), 3.93 (dd, J_HH= 17.1 Hz, J_HP= 14.0 Hz,

1 H, PCH_aH_b), 7.67 (t), 7.85 (d), 8.12 (t), 8.47 (d) (C₅H₄N).

³¹P{¹H} NMR (161.89 MHz, CD₂Cl₂, 298 K): δ 92.3 (br).

¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 298 K): δ 10.49 [s, C₅-

(CH₃)₅], 17.99, 18.19, 19.12, 20.13 [s, P(CH(CH₃)₂)₂], 25.99

Supporting Information Available: Crystallographic data in

CIF format for complexes 1b, 2b, 3a, 5b, 8b, and 9b, tables of

1

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Article

Inorganic Chemistry, Vol. 49, No. 13, 2010 6057

Cartesian coordinates and total energies for all of the optimized

structures, and a comparison of computed and X-ray geometrical

parameters for 5b/5a. This material is available free of charge via

the Internet at http://pubs.acs.org. The crystal structures have also

been deposited with the Cambridge Crystallographic Data Centre

as CCDC 772200-772205. These coordinates can be obtained,

upon request, from the Director, Cambridge Crystallographic

Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.

Article Doi

Proton-transfer reactions to half-sandwich ruthenium trihydride complexes bearing hemilabile P,N ligands: Experimental and density functional theory studies

DOI: 10.1021/ic100710d

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