Ruthenium, rhodium, and iridium bis(σ-B-H) diisopropylaminoborane complexes

Article abstract of DOI:10.1021/om1004995

The coordination chemistry of diisopropylaminoborane H₂B-N ⁱPr₂ with valence isoelectronic metal fragments to form, essentially isostructural, [MH₂(η²:η²- H₂B-NⁱPr₂)(PCy₃)₂] ⁿ⁺ (M = Ru, n = 0; Rh and Ir, n = 1) has been explored by a combination of X-ray crystallography, NMR spectroscopy, and computational techniques. In the solid state and solution the aminoborane interacts with the metal centers through one four-center four-electron interaction, forming bis(σ-B-H) complexes. The structural data point to tighter interactions between both the Ru and Ir congeners compared to the Rh with significantly shorter M...B distances in the first two. These tighter interactions are mirrored in the spectroscopic data, with the Ru and Ir complexes showing more deshielded ¹¹B chemical shifts and ¹H M-H-B resonances that are more shielded than observed for the rhodium complex. Analysis of the bonding between metal and borane using the NBO approach is in very good agreement with the variations in the geometrical and spectroscopic parameters. There is overall a stronger interaction between the borane and the metal fragment for neutral Ru compared to cationic Rh, with cationic Ir in an intermediate situation.

Full text of DOI:10.1021/om1004995

Organometallics 2010, 29, 5591–5595 5591
DOI: 10.1021/om1004995
Ruthenium, Rhodium, and Iridium Bis(σ-B-H) Diisopropylaminoborane
Complexes†
Gilles Alcaraz,*,‡ Adrian B. Chaplin,§ Charlotte J. Stevens,§ Eric Clot,^ Laure Vendier,‡
Andrew S. Weller,*,§ and Sylviane Sabo-Etienne*,‡
‡CNRS, LCC (Laboratoire de Chimie de Coordination), 205 Route de Narbonne, 31077 Toulouse, France,
§
and Universite de Toulouse, UPS, INPT 31077 Toulouse, France, Department of Chemistry, Inorganic
ꢀ
Laboratories, University of Oxford, OX1 3QR, United Kingdom, and ^Institut Charles Gerhardt, Universiteꢀ
ꢁ
de Montpellier 2, CNRS 5253, cc 1501, Place Eugene Bataillon, 34095 Montpellier, France
Received May 21, 2010
The coordination chemistry of diisopropylaminoborane H2B-NiPr2 with valence isoelectronic metal
fragments to form, essentially isostructural, [MH2(η2:η2-H2B-NiPr2)(PCy3)2]nþ (M = Ru, n = 0; Rh and
Ir, n = 1) has been explored by a combination of X-ray crystallography, NMR spectroscopy, and
computational techniques. In the solid state and solution the aminoborane interacts with the metal centers
through one four-center four-electron interaction, forming bis(σ-B-H) complexes. The structural data
point to tighter interactions between both the Ru and Ir congeners compared to the Rh with significantly
shorter M B distances in the first two. These tighter interactions are mirrored in the spectroscopic data,
3 3 3
with the Ru and Ir complexes showing more deshielded 11B chemical shifts and 1H M-H-B resonances
that are more shielded than observed for the rhodium complex. Analysis of the bonding between metal and
borane using the NBO approach is in very good agreement with the variations in the geometrical and
spectroscopic parameters. There is overall a stronger interaction between the borane and the metal
fragment for neutral Ru compared to cationic Rh, with cationic Ir in an intermediate situation.
Introduction
1,3,5-Me3C6H2) being the first example6 of a new family7 of
stable complexes (Scheme 1) in which mesitylborane coordi-
nates to the metal through two geminal σ-B-H bonds, leading
to a four-center four-electron bonding mode. This compound
was synthesized in high yield by addition of H2BMes to
[RuH2(η2-H2)2(PCy3)2].
Organometallic compounds involving two identical σ-E-H
(E = H, Si, B, C) bonds coordinated to one metal center are
scarce.1 For bis(σ-dihydrogen) complexes, [RuH2(η2-H2)2-
(PCy3)2] (1, Scheme 1) is the complex that has so far been
shown to exhibit the most versatile properties,2 and isoelectronic
cationic Rh and Ir analogues also exist, although their chemistry
is less well developed.3 With regard to boranes (R2BH),4 bis(σ-
borane) complexes have, until recently, been limited to titanium,
as illustrated by the isolation of Cp2Ti(η2-H-BCat)2 2 reported
by Hartwig et al in 1996 (Cat = 1,2-O2C6H4).5 Recently, some
of us have reported compounds of general formulation [Ln-
Ru(H2BR)], with [RuH2(η2:η2-H2B-Mes)(PCy3)2] 3 (Mes =
Related complexes incorporating aminoboranes, H2B-NR2,
have very recently been reported. While studying the metal-
induced dehydrogenation of amine-borane adducts, such as
H3B-NHMe2, Alcaraz and Sabo-Etienne have reported the
synthesis of the bis(σ-B-H) monomeric aminoborane ruthe-
nium complexes [RuH2(η2:η2-H2B-NHnMe2-n)(PCy3)2] (4)
(n = 0-2) by reaction of complex 1 with H3B-NHnMe3-n
(n = 1-3) under stoichiometric conditions.8 Independently,
Weller and co-workers have reported Shimoi-type9 amine-bor-
ane complexes of rhodium by reaction of H3B-NHMe2 with
† Part of the Dietmar Seyferth Festschrift. In honor of Prof. Dr. h.c. mult.
Dietmar Seyferth for his outstanding contribution as Editor of Organome-
tallics.
[Rh(PiBu3)2][BArF ], with the bis(σ-B-H) dimethylaminobor-
4
ane rhodium complex [RhH2(η2:η2:H2B-NMe2)(PiBu3)2]-
[BArF ] {ArF=C6H3(CF3)2}, isoelectronic to 4, spectroscopi-
*To whom correspondence should be addressed. E-mail: sylviane.sabo@
4
lcc-toulouse.fr.
cally characterized as the final organometallic product from the
catalytic dehydrogenation of H3B-NHMe2 using these sys-
tems.10 Replacing phosphines by N-heterocyclic carbenes,
(1) (a) Kubas, G. J. Metal Dihydrogen and sigma-Bond Complexes;
Kluwer Academic/Plenum Publishers: New York, 2001. (b) Perutz, R. N.;
Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007, 46, 2578–2592.
(2) (a) Sabo-Etienne, S.; Chaudret, B. Coord. Chem. Rev. 1998,
178-180, 381–407. (b) Alcaraz, G.; Grellier, M.; Sabo-Etienne, S. Acc.
Chem. Res. 2009, 42, 1640–1649.
(3) (a) Ingleson, M. J.; Brayshaw, S. K.; Mahon, M. F.; Ruggiero,
G. D.; Weller, A. S. Inorg. Chem. 2005, 44, 3162–3171. (b) Crabtree, R. H.;
Lavin, M.; Bonneviot, L. J. Am. Chem. Soc. 1986, 108, 4032–4037.
(4) Alcaraz, G.; Sabo-Etienne, S. Coord. Chem. Rev. 2008, 252, 2395–
2409.
(7) (a) Hesp, K. D.; Rankin, M. A.; McDonald, R.; Stradiotto, M.
Inorg. Chem. 2008, 47, 7471–7473. (b) Gloaguen, Y.; Alcaraz, G.; Vendier,
L.; Sabo-Etienne, S. J. Organomet. Chem. 2009, 694, 2839–2841.
(8) Alcaraz, G.; Vendier, L.; Clot, E.; Sabo-Etienne, S. Angew.
Chem., Int. Ed. 2010, 49, 918–920.
(9) Shimoi, M.; Nagai, S.-i.; Ichikawa, M.; Kawano, Y.; Katoh, K.;
Uruichi, M.; Ogino, H. J. Am. Chem. Soc. 1999, 121, 11704–11712.
(10) (a) Douglas, T. M.; Chaplin, A. B.; Weller, A. S. J. Am. Chem.
Soc. 2008, 130, 14432–14433. (b) Chaplin, A. B.; Weller, A. S. Inorg. Chem.
2010, 49, 1111–1121.
(5) Hartwig, J. F.; Muhoro, C. N.; He, X.; Eisenstein, O.; Bosque, R.;
Maseras, F. J. Am. Chem. Soc. 1996, 118, 10936–10937.
(6) Alcaraz, G.; Clot, E.; Helmstedt, U.; Vendier, L.; Sabo-Etienne,
S. J. Am. Chem. Soc. 2007, 129, 8704–8705.
r
2010 American Chemical Society
Published on Web 08/05/2010
pubs.acs.org/Organometallics

5592 Organometallics, Vol. 29, No. 21, 2010
Alcaraz et al.
Scheme 1. Representative Bis(σ-dihydrogen) and Bis(σ-borane)
Metal Complexes
more shielded, resonance (a triplet for 7: δ -12.37; an apparent
doublet of doublets of triplets for 8: δ -15.40; an apparent
quartet for 9: δ -15.5) in a 2:2 relative integration ratio. For all
compounds, the lower-field signal sharpens upon 11B decoupling.
For 8 and 9 selective decoupling of the M-H-B resonance
collapses the corresponding hydride signal to a doublet of triplets
for 8(JHRh =22,JHP =11Hz) andatripletfor9(JHP =14Hz),
demonstrating coupling (presumably trans) between M-H and
M-H-B. The 1H{31P} spectra reveal the remaining coupling for
8 (JHH = 15 Hz) and 9 (JHH=11 Hz). In the 11B{1H} spectra of
7-9, a broad signal is observed slightly downfield shifted or
similar to free diisopropylaminoborane (δ 35): 7, δ 45; 8, δ 34
(very broad); 9, δ 46.
Scheme 2. Syntheses of [RuH2(η2:η2-H2B-NiPr2)(PCy3)2] (7) and
[MH2(η2:η2-H2B-NiPr2)(PCy3)2][BArF ] (M = Rh (8), Ir (9))
4
The solid-state structures of the new complexes are shown in
Figure 1 (Table 1). In the three complexes 7-9, the metal atom is
in a pseudo-octahedral environment, with the tricyclohexylpho-
sphines in axial positions and the hydrides mutually cis. The
X-ray structure of 7 was determined at 110 K, and the quality of
the data enables the secure location of the hydrogen atoms (the
hydrides H0a and H0b and the boron-attached hydrogen atoms
H1a and H1b) in the equatorial plane around the ruthenium. For
the rhodium, 8, and iridium, 9, complexes the diisopropylami-
noborane is disordered over two closely related sites (distri-
buted 71.9%/28.1% for 8and 77.5%/22.5% for 9). This disorder
is slight canting of the H2B-NiPr2 ligand, i.e., M-B-N
174.9(8)ꢀ (major) and 171(3)ꢀ for 9, albeit with a rather large
error associated with the minor component. Nevertheless the hy-
dride ligands (M-H) in 8 and 9 were located in the final diffe-
rence maps and freely refined, although the M-H-B hydrogen
atoms were placed in calculated positions. In solution a C2v-sym-
metric structure is indicated for all three complexes. The M-B
Aldridge and co-workers have isolated the corresponding
bis(σ-B-H) diisopropylaminoborane cationic rhodium and
iridium complexes [MH2(η2:η2-H2B-NiPr2)(IMes)2][BArF
]
4
(M=Rh, Ir, IMes=2,5-Mes2-N2C3H2) upon dehydrogena-
tion of diisopropylamine-borane.11
In this paper, we now present a straightforward route to
bis(σ-B-H) diisopropylaminoborane complexes of Ru, Rh,
and Ir tricyclohexylphosphine dihydrides, by addition of
preformed H2B-NiPr2 to precursor bis(dihydrogen) com-
plexes. This leads to a unique set of isoelectronic complexes
that differ only in the nature of the metal center and charge.
This presents a valuable opportunity to evaluate the impact
of the metal on the B-H bond coordination and activation,
which we do by a combination of spectroscopic, solid-state,
and computational techniques. Such studies on isoelectronic
and isostructural systems involving boranes are rare.12
distance (see Table 1) is shorter than the sum of the covalent radii
P
in 7but rather similar in the case of 8and 9(
A (Ru), 2.10 A (Ir), and 2.09 A (Rh)).13 Similar M B separa-
rcov(M-B) = 2.12
˚
˚
˚
3 3 3
tions have been recently reported for [MH2(η2:η2-H2B-NiPr2)-
(IMes)2][BArF ] (M=Rh, Ir).11 There is a correlation between
4
the M-BH2 distances and the observed 11B and 1H M-H-B
chemical shifts in solution. The shortest distances (Ru, 7, and Ir,
9) are associated with the most deshielded 11B resonances com-
pared to free ligand and highest-field bridging hydride chemical
shifts in the 1H NMR spectra, suggesting stronger interactions
between metal and borane, while complex 8has the longest M-B
distance and a 11B chemical shift that is very similar to free ligand
and a corresponding lower-field Rh-H-B resonance.
Results and Discussion
Complexes [RuH2(η2:η2-H2B-NiPr2)(PCy3)2] (7), [RhH2-
(η2:η2-H2B-NiPr2)(PCy3)2][BArF ] (8), and [IrH2(η2:η2-H2B-
4
In order to gain more information on the borane coordina-
tion, DFT(B3PW91) geometry optimizations were carried out
on the actual experimental systems, yielding 7a, 8a, and 9a for
Ru, Rh, and Ir, respectively. Selected geometrical parameters are
given in Table 1, and the agreement with the experimental values
is very good. The calculations allow more secure location of the
two hydrides H0a and H0b and of the two bridging hydrogen
atoms H1a and H1b. From the calculated bond distances, there
is a clear trend in the interaction between the borane H2B-NiPr2
and the transition metal fragment MH2(PCy3)2 (M = Ru, Rhþ,
Irþ). The M-B, M H1a, and M H1b bond distances
NiPr2)(PCy3)2][BArF ] (9) were synthesized by reaction of a
4
slight excess of H2B-NiPr2 with the corresponding bis(dihy-
drogen) metal complexes 1, [RhH2(η2-H2)2(PCy3)2][BArF ] (5),
4
and [IrH2(η2-H2)2(PCy3)2][BArF ] (6). The latter group 9
4
complexes were generated in situ under dihydrogen pressure
(Scheme 2).3a The resulting bis(σ-B-H) diisopropylaminobor-
ane complexes were fully characterized by NMR spectroscopy
and X-ray diffraction crystallography. The NMR spectroscopic
properties of the new complexes are similar to the data reported
for [RuH2(η2:η2-H2B-NR1R2)(PCy3)2] (R1, R2 = H, Me),8
3 3 3
3 3 3
[MH2(η2:η2-H2B-NiPr2)(IMes)2][BArF ] (M = Rh, Ir),11 and
4
increase along the series Ru<Ir<Rh and, concomitantly, the
B-H1a and B-H1b bond distances decrease. This would tend
to indicate that there is overall a stronger interaction between the
borane and the metal fragment for neutral Ru compared to
cationic Rh, with cationic Ir in an intermediate situation.
[RhH2(η2:η2:H2B-NMe2)(PiBu3)2][BArF ].10 The 1H NMR
4
spectra demonstrate a M-H-B interaction by the observation
of a quadrupolar broadened relative integral 2 H signal (7: δ
-6.91; 8: δ -2.30; 9: δ -6.58), and the dihydride by a sharper,
(11) Tang, C. Y.; Thompson, A. L.; Aldridge, S. Angew. Chem., Int.
Ed. 2010, 49, 921–925.
(12) Weller, A. S.; Fehlner, T. P. Organometallics 1999, 18, 447–450.
(13) Lin, Z. In Contemporary Metal Boron Chemitry I: Borylenes, Boryls,
Borane σ-Complexes and Borohydrides, Structure and Bonding; Marder, T. B.,
Lin, Z., Eds.; Springer Verlag: Berlin, 2008; Vol. 130, pp 123-149.

Article
Organometallics, Vol. 29, No. 21, 2010 5593
Figure 1. X-ray structure of [RuH2(η2:η2:H2B-NiPr2)(PCy3)2] (7) and [MH2(η2:η2:H2B-NiPr2)(PCy3)2][BArF4] (M = Rh (8), Ir (9)). The
hydrogen atoms not associated with the metal center, the [BArF - anions, and minor disordered components are omitted for clarity.
]
4
Table 1. Selected Geometrical Parameters for the Experimental (7-9) and Calculated Structures (7a-9a) and the Computed Structure of
iPr2NBH2
Ru
Rha
Ira
7
7a
8
8a
9
9a
iPr2NBH2
M-B
1.980(3)
2.3051(5)
2.3141(5)
1.393(3)
1.72(2)
1.68(3)
1.54(2)
1.53(2)
1.22(2)
2.003
2.351
2.337
1.412
1.820
1.805
1.601
1.607
1.298
1.306
152.1
178.8
2.140(13), [2.10(4)]b
2.3335(8)
2.3285(7)
2.159
2.389
2.378
1.383
1.895
1.874
1.528
1.532
1.252
1.258
155.5
178.2
2.022(14), [2.10(5)]c
2.3380(9)
2.3316(8)
2.088
2.398
2.388
1.384
1.848
1.832
1.571
1.576
1.289
1.296
156.3
178.3
M-P1
M-P2
B-N
1.357(13), [1.40(4)]b
1.380(14), [1.34(5)]c
1.393
d
d
M-H1b
M-H1a
M-H0a
M-H0b
B-H1b
B-H1a
P1-M-P2
M-B-N
d
d
1.46(3)
1.48(3)
1.47(3)
1.44(3)
d
d
1.195
1.195
d
d
1.25(3)
152.71(2)
177.83(19)
156.24(3)
173.9(7), [170(3)]b
156.54(3)
174.9(8), [171(3)]c
a Numbers in brackets are for the disordered component. b 28.1%. c 22.5%. d Hydrogens not located.
In the framework of the Dewar-Chatt-Duncanson
model, the bonding of borane to a d6 transition metal
fragment can be described as the result of the synergistic σ-
donation from the σ(B-H) density to the metal and π-back-
donation from an occupied nonbonding d orbital on the
metal into an accepting orbital on borane. A generic molec-
ular orbital (MO) diagram for the interaction between the
pseudo-C2v d6 fragment M(H)2(PR3)2 (M = Ru, Rhþ, Irþ)
and the borane H2BR is shown in Figure 2. The σ-donation
from the B-H bonds is operative from the two highest
occupied MOs of the borane ligand. In the particular case
of borane, back-donation from the metal is mostly effective
through donation from the dxz lone pair on Ru to the vacant
p AO on boron; the latter is the LUMO of the borane ligand
(see Figure 2). In the present systems with aminoboranes,
this scheme can be modified by considering that the empty p
orbital on boron is now stabilized by donation from the
nitrogen lone pair. This provides an associated higher-lying
BN π* orbital that can accept electron density from an
appropriate, filled, metal orbital.
To shed more light on the electronic structure of the
complexes 7a, 8a, and 9a, a NBO analysis was carried out.
In the Lewis-like description of the electronic structure used
in the NBO analysis, the electronic transfers introduced in
Figure 2. Schematic MO diagram of the interaction between
the d6 fragment M(H)2(PR3)2 (M = Ru, Rhþ, Irþ) and the
borane H2BR. The phosphine ligands pointing along the z axis
have been omitted for clarity.
the above MO diagram are best described as departure from
a strictly localized picture.14 The σ-donation from the B-H
bond to the metal is effective through an interaction between
the occupied σ(B-H) bond and the vacant σ*(M-H) bond
in trans position. The magnitude of the interaction is best
(14) Weinhold, F.; Landis, C. R. Valency and Bonding: A Natural
Bond Orbital Donor-Acceptor Perspective; Cambridge University Press:
Cambridge, 2005.

5594 Organometallics, Vol. 29, No. 21, 2010
Alcaraz et al.
Table 2. Composition of the NLMO σnlmo(B-H) and LPnlmo(M) Resulting from the Delocalization of the Parent NBO (σ(BH) and
LP(M)) into the Accepting NBO σ*(MH) and π*(BN), Respectively
7a: M = Ru
8a: M = Rhþ
9a: M = Irþ
σnlmo(B-H)
LPnlmo(M)
0.934 σ(BH) þ 0.319 σ*(MH)
0.938 LP(M) þ 0.297 π*(BN)
0.955 σ(BH) þ 0.266 σ*(MH)
0.976 LP(M) þ 0.176 π*(BN)
0.937 σ(BH) þ 0.318 σ*(MH)
0.964 LP(M) þ 0.223 π*(BN)
˚
procedures and stored under argon over 4 A molecular sieves or over
illustrated by the relative weight of the two components in
the resulting natural localized molecular orbital (NLMO,
Table 2). Due to the cationic nature of the rhodium complex
8a, the valence orbitals of the MH2(PCy3)2 fragment are
lower in energy for M = Rhþ than for M = Ru. Conse-
quently larger σ-donation from the borane should have been
observed, contrary to the results presented in Table 2, where
the composition of the σ(BH) NLMO clearly indicates that
σ-donation is larger with Ru. However the orbitals of the
cationic rhodium complex are also more contracted than
those of the neutral ruthenium complex, and this is detri-
mental to an effective overlap between the interacting orbi-
tals in the σ-donation process. A third-row transition metal
such as iridium has more diffuse valence orbitals, and the
composition of the σ(BH) NLMO is very similar to that of
the neutral ruthenium analogue.
The Lewis structure for the three complexes 7a, 8a, and 9a
features a BdN π-bond as the result of the interaction of the
nitrogen lone pair with the empty p AO on boron. Nevertheless,
back-donation in the π*(BN) orbital from the metal nonbond-
ing dxz AO, acting as a lone pair (LP), is still possible. Table 2
gives the expression of the corresponding NLMO, and it is clear
that back-donation varies according to Ru > Irþ > Rhþ. The
lower energy of the valence orbitals for the cationic fragment
results in less efficient interaction with the vacant π*(BN)
orbital. This reduced interaction is partly compensated for by
the more diffuse character of the orbital in the case of iridium,
yielding a situation intermediate between Ru and Rh. In the
case of Rh, both factors, lower energy and more contracted
orbitals, do not favor efficient back-donation.
potassium for d8-THF. C6H5F and 1,2-C6H4F2 were dried over
˚
CaH2, vacuum distilled, and stored over 3 A molecular sieves.
H2BNiPr2,15 [RuH2(η2-H2)2(PCy3)2],16 [RhH2(η2-H2)2(PCy3)2]-
[BArF ],3a and [IrH2(η2-H2)2(PCy3)2][BArF ] (see Supporting In-
4
4
formation) were prepared by literature methods. NMR spectra were
recorded on a Bruker 400 MHz Avance, a Bruker 300 MHz Avance,
or a Varian Unity Plus 500 MHz spectrometer at room temperature,
unless otherwise stated. Chemical shifts are quoted in ppm and
coupling constants in Hz. Microanalyses were performed at the
Laboratoire de Chimie de Coordination (7) or at the London
Metropolitan University (8, 9).
Synthesis of [RuH2(η2:η2-H2BNiPr2)(PCy3)2] (7). At room
temperature, H2BNiPr2 (74 μL) was added to a toluene solution
(1 mL) of RuH2(η2-H2)2(PCy3)2 (0.0315 g, 0.0471 mmol) and the
solution stirred for 15 h. Evaporation of the solvent and washing of
the resulting solid with cold pentane afforded pure complex 7 as a
beige solid (0.024 g, 66%). Crystals suitable for X-ray analysis were
grown from a saturated pentane solution held at -37 ꢀC. 31P{1H}
1
NMR (C6D6, 121.49 MHz): 77.8 (s). H NMR (C6D6, 300.13
MHz): 3.55 (sept, 2H, 3JHH=6.6 Hz, 2H,CH iPr), 1.16-2.38 (m,
66H, Cy), 1.35 (d, 3JHH=6.6 Hz, 12H, CH3 iPr), -6.91 (br, 2H,
RuH2B), -12.37 (t, 2JHP=25.0 Hz, RuH2). 13C{1H} NMR (C6D6,
100.61 MHz): 47.70 (s, CH iPr), 38.97, 30.79, 28.14, and 17.14 (Cy),
23.86, (s, CH3 iPr). 11B{1H} NMR (C6D6, 128.38 MHz): 45 (br).
Anal. Calcd for C42H84BNP2Ru (776.952 g mol-1): C, 64.93; H,
3
10.90; N, 1.80. Found: C, 65.20; H, 10.88; N, 1.61.
Synthesis of [RhH2(η2:η2-H2BNiPr2)(PCy3)2][BArF4] (8). A
yellow solution of [RhH2(η2-H2)2(PCy3)2][BArF4] (0.093 mmol) in
1,2-C6H4F2 (2 mL) was prepared in situ by hydrogenation (4 atm,
20 min) of [Rh(C7H8)(PCy3)2][BArF4] (0.150 g, 0.093 mmol), as
previously described.3a This solution was placed under an Ar
atmosphere, and H2BNiPr2 (50 μL) was added. The resulting pale
yellow solution was layered with pentane and held at 5 ꢀC to afford
the product as colorless crystals. Yield: 0.085 g (56%). 1H NMR
(C6H5F, 500 MHz): 8.37 (br, 8H, [BArF4]-), 7.68(s, 4H, [BArF4]-),
3.45 (sept, 3JHH = 6.7 Hz, 2H, CH iPr), 1.11-1.91 (m, 66H, Cy),
The results from the NBO analysis are in very good agree-
ment with the variations in the geometrical parameters observed
for the calculated structures. The close values for the B-H bond
distances in 7a and 9a (Table 1) agree with the description of the
σ-donation as being of the same magnitude in the two com-
plexes. The significantly lower values for 8a indicate a less
efficient σ-donation from borane. Nevertheless there is transfer
of electron density from B-H in all three cases, as illustrated by
the lengthening of the B-H bond with respect to the value for
the free borane. The trends in metal to borane back-donation
discussed above are nicely illustrated by the variation of the
i
1.20 (d, 3JHH = 6.6 Hz, 12H, CH3 Pr), -2.30 (br, RhH2B), -15.40
(apparent ddt, 2H, RhH2, 1JHRh = 22, 2JHH = 15, 2JHP = 11 Hz,
from selective decoupling experiments). 13C{1H} NMR (d8-THF,
1
126 MHz): 163.0 (q, JBC = 49, [BArF4]-), 135.8 (s, [BArF4]-),
=
130.2 (qq, 2JFC=32 Hz, 3JBC=3 Hz, [BArF4]-), 125.7 (q, 1JFC
272 Hz, [BArF4]-), 118.3 (br, [BArF4]-), 52.4 (s, CH iPr), 37.6, 31.5,
i
28.2, and 27.2 (Cy), 24.7 (s, CH3 Pr). 11B{1H} NMR (C6H5F, 160
MHz): 34 (vbr, 1B, RhH2B), -5.8 (s, 1B, [BArF4]-).31P{1H} NMR
(C6H5F, 202 MHz): 59.5 (d, JRhP = 103 Hz). Anal. Calcd for
1
˚
˚
M-B bond distance: Ru-B = 2.003 A, Ir-B = 2.088 A, and
C74H96B2F24NP2Rh (1642.0 g mol-1): C, 54.13; H, 5.89; N, 0.85.
˚
Rh-B = 2.159 A. This analysis also correlates with the
3
Found: C, 54.22; H, 5.95; N, 0.83. ESI-MS (1,2-C6H4F2, 60 ꢀC, 4.5
observed NMR data: less efficient σ-donation from the B-H
bond to the metal σ*(ΜH) orbital in 8 results in a lower-field
M-H-B chemical shift, whereas the M-H-B chemical shifts
in 7 and 9 are essentially the same and at higher field. Likewise
the 11B chemical shift for the three isoelectronic complexes
generally tracks the involvement of the π*(ΒΝ) orbital in
kV) positive ion: m/z 778.50 [M]þ (calcd 778.52).
Synthesis of [IrH2(η2:η2-H2BNiPr2)(PCy3)2][BArF
]
4
(9).
Complex 9 was produced in a similar manner to 8 starting from
[IrH2(η2-H2)2(PCy3)2][BArF4], which was generated in situ from
addition of H2 to [IrH{P(η2-C6H9)(C6H11)2}{P(η3-C6H8)-
(C6H11)2}][BArF4] (0.030 g, 0.020 mmol) (see Supporting In-
formation for synthesis and solid-state structure). 1H NMR (500
MHz, C6H5F): 8.35 (br, 8H, [BArF4]-), 7.67 (s, 4H, [BArF4]-),
3.46 (sept, 3JHH = 7 Hz, 2H, CH iPr), 2.05-0.95 (m, Cy), 1.21
(d, 3JHH = 7 Hz, CH3 iPr), -6.58 (br, 2H, IrH2B), -15.15 (dt,
M
chemical shift change from free aminoborane.
B bonding: a smaller contribution leads to a smaller
3 3 3
Experimental Section
General Procedures. Manipulations were done using standard
Schlenk and glovebox techniques (O2 level<1ppm;Arasinertgas).
Solvents were dried using an MBraun solvent purification system.
Deuterated solvents were prepared through freeze-pump-thaw
(15) Euzenat, L.; Horhant, D.; Ribourdouille, Y.; Duriez, C.; Alcaraz,
G.; Vaultier, M. Chem. Commun. 2003, 2280–2281.
(16) Borowski, A. F.; Sabo-Etienne, S.; Christ, M. L.; Donnadieu, B.;
Chaudret, B. Organometallics 1996, 15, 1427–1434.

Article
Organometallics, Vol. 29, No. 21, 2010 5595
2H, IrH2, 2JHP=14 Hz, 2JHH=11 Hz, from selective decoupling
experiments). 11B{1H} NMR (160 MHz, C6H5F): 46.3 (br,
BH2), -5.9 (s, [BArF4]-). 31P{1H} NMR (202 MHz, C6H5F):
34.20 (s). Yield: 0.021 g (65%). Anal. Calcd for C74H96B2F24-
hydrogen atoms were placed in calculated positions using the
riding model. Disorder of the aminoborane ligand was treated
by modeling it over two sites and restraining the geometry of the
alkyl substituents. Disorder of the phosphine ligands was trea-
ted by modeling the appropriate substituents over two sites and
restraining their geometry. Rotational disorder of the CF3
groups of the anion in 8 and 9 was treated by modeling the
fluorine atoms over two sites and restraining their geometry.
Restraints to thermal parameters were applied where necessary
in order to maintain sensible values. Graphical representations
of the structures were made using ORTEP3.21
NP2Ir (1731.3 g mol-1): C, 51.3; H, 5.59; N, 0.81. Found: C,
3
51.4; H, 5.75; N, 0.83. ESI-MS (C6H5F, 60 ꢀC, 4.5 kV) positive
ion: m/z 868.62 [M]þ (calcd 868.58).
X-ray Structural Analysis for 7. Data were collected at low
temperature (110 K) on an Xcalibur Oxford Diffraction dif-
fractometer using graphite-monochromated Mo KR radiation
˚
(λ = 0.71073 A) and equipped with an Oxford Instruments
cooler device. The final unit cell parameters were obtained by
means of a least-squares refinement. The structure was solved by
direct methods using SIR9217 and refined by means of least-
squares procedures on F2 with the aid of the program SHEL-
XL9718 included in the software package WinGX version 1.63.19
The atomic scattering factors were taken from International
Tables for X-ray Crystallography.20 All hydrogen atoms were
geometrically placed, except for the atoms H0a, H0b, H1a, and
H1b, which were located by Fourier differences and refined by
using a riding model. All non-hydrogen atoms were anisotropi-
cally refined, and in the last cycles of refinement a weighting
Computational Details. All the calculations have been per-
formed with the Gaussian03 package26 at the B3PW91 level.27
The ruthenium, rhodium, and iridium atoms were represented
by the relativistic effective core potential (RECP) from the
Stuttgart group (16 valence electrons) and the associated basis
set,28 augmented by an f polarization function.29 The phos-
phorus atom was represented by RECP from the Stuttgart
group and the associated basis set,30 augmented by a d polar-
ization function (R = 0.387).31 The remaining atoms (C, H, B,
N) were represented by a 6-31G(d,p) basis set.32 Full optimiza-
tions of geometry without any constraint were performed,
followed by analytical computation of the Hessian matrix to
confirm the nature of the located extrema as minima on the
potential energy surface. Natural bonding orbital analysis33 was
performed with NBO version 5.0 implemented in Gaussian03.
scheme was used, where weights are calculated from the follow-
2
ing formula: w = 1/[σ2(Fo2) þ (aP)2 þ bP] where P = (Fo
þ
2
2Fc )/3. Drawing of the molecule was performed with the
program ORTEP3221 with 30% probability displacement ellip-
soids for non-hydrogen atoms.
X-ray Structural Analysis for 8 and 9. Data were collected on
an Enraf Nonius Kappa CCD diffractometer using graphite-
monochromated Mo KR radiation (λ = 0.71073 A) and a low-
Acknowledgment. We thank the CNRS, the ANR
(ANR-09-BLAN-0184-01 HyBoCat) for support (G.A.,
˚
temperature device [150(2) K];22 data were collected using
COLLECT; and reduction and cell refinement was performed
using DENZO/SCALEPACK.23 The structures were solved by
direct methods using SIR200424 and refined with full-matrix
least-squares on F2 using SHELXL-97.25 All non-hydrogen
atoms were refined anisotropically. The hydride ligands H0A
and H0A were located on the Fourier difference map and freely
refined; their isotropic displacement parameters were fixed to
ride on the parent atoms. H1a and H1b were placed in calculated
positions, with the B-H distance free to refine (AFIX 94, the
restraint with identical B-H distances was applied) despite the
presence of geometrically sensible Fourier peaks. All other
ꢀ
L.V., E.C., S.S.E.), the Universite de Toulouse (UPS,
Aide Ponctuelle a la Cooperation) for a grant (G.A.),
ꢁ
ꢀ
University of Oxford, and the EPRSC.
Supporting Information Available: Tables, text, and CIF files
giving addition structural information for 7, 8, and 9. Synthesis,
characterization data, and solid-state structure of [IrH{P(η2-C6H9)-
(C6H11)2}{P(η3-C6H8)(C6H11)2}][BArF4], a full citation for ref 26,
and coordinates for the calculated structures. This material is
available free of charge via the Internet at http://pubs/acs/org.
(26) Frisch, M. J.; et al. Gaussian 03, Revision C.02; Gaussian Inc.:
Wallingford, CT, 2004.
(17) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.
J. Appl. Crystallogr. 1993, 26, 343–350.
(18) Sheldrick, G. M. SHELXL97; Instit€ut f€ur Anorganische Chemie
(27) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (b) Perdew,
J. P.; Wang, Y. Phys. Rev. B 1992, 45, 13244–13249.
(28) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
€
€
€
der Universitat: Gottingen, Germany, 1998.
Theor. Chim. Acta 1990, 77, 123–141.
(19) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
(20) International Tables for X-Ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV.
(21) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565–565.
(22) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105–107.
(23) Otwinowski, Z.; Minor, W. Methods in Enzymology; Macromo-
lecular Crystallography, Part A; Carter Jr., C. W., Sweets, R. M., Eds;
Academic Press: New York, 1997; Vol. 276.
€
(29) Ehlers, A. W.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth,
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 208, 111–114.
(30) Bergner, A.; Dolg, M.; Kuchle, W.; Stoll, H.; Preuss, H. Mol.
€
€
Phys. 1993, 80, 1431–1441.
€
(31) Hollwarth, A.; Bohme, H.; Dapprich, S.; Ehlers, A. W.; Gobbi,
A.; Jonas, V.; Kohler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
€
€
Chem. Phys. Lett. 1993, 208, 237–240.
(24) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.;
Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 2005, 38, 381–388.
(32) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213–
222.
(33) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899–926.
(25) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.