Bridging and terminal half-sandwich ruthenium dinitrogen complexes and related derivatives: A structural study

Article abstract of DOI:10.1021/om010730v

The reaction of [CpRuCl(P)₂] [(P)₂ = dippe (1,2-bis(diisopropylphosphino)ethane; (PEt₃)₂; (PMeⁱPr₂)₂] with Na[BAr′₄] (Ar′₄ = 3,5-bis(trifluoromethyl)phenyl) in fluorobenzene under argon generates the corresponding cationic 16-electron species [CpRu(P)₂]⁺, which reacts with trace amounts of dinitrogen present even in high-purity argon furnishing the dinitrogen-bridged complexes [{CpRu(P)₂}₂(μ-N₂)][BAr′₄] ₂ [(P)₂ = dippe 1a; (PEt₃)₂ 1b; (PMeⁱPr₂)₂ 1c]. If the reaction is performed under dinitrogen, the terminal dinitrogen complexes [CpRu-(N₂)(P)₂][BAr′₄] [(P)₂ = dippe 2a; (PMeⁱPr₂)₂ 2c] are obtained. Compound 1b was obtained irrespectively of the atmosphere used, and no terminal dinitrogen complex has been detected. The crystal structures of 1a, 1b, and 2a have been determined. During one attempt to isolate the 16-electron complex [CpRu(PMeⁱPr₂)₂][BAr′₄], the 18-electron tris(phosphine) derivative [CpRu(PMeⁱPr₂)₃][BAr′₄], 3, was obtained instead, and it was structurally characterized. Halide abstraction from [CpRuCl(PMeⁱPr₂)(PPh₃)] under dinitrogen using Na[BAr′₄] yielded [CpRu(N₂)(PMeⁱPr₂)(PPh₃)] [BAr′₄], 2d, but under argon the complex [CpRu(PMeⁱPr₂)(PPh₃)]-[BAr′₄], 4, which contains a rare η³-coordinated PPh₃ ligand as shown by X-ray crystallography, was isolated.

Full text of DOI:10.1021/om010730v

628
Organometallics 2002, 21, 628-635
Br id gin g a n d Ter m in a l Ha lf-Sa n d w ich Ru th en iu m
Din itr ogen Com p lexes a n d Rela ted Der iva tives:
A Str u ctu r a l Stu d y
Halikhedkar Aneetha, Manuel J ime´nez-Tenorio, M. Carmen Puerta, and
Pedro Valerga*
Departamento de Ciencia de Materiales e Ingenier´ıa Metalu´rgica y Quı´mica Inorga´nica,
Facultad de Ciencias, Universidad de Ca´diz, 11510 Puerto Real, Ca´diz, Spain
Kurt Mereiter
Institute of Mineralogy, Crystallography, and Structural Chemistry, Vienna University of
Technology, Getreidemarkt 9, A-1060 Vienna, Austria
Received August 9, 2001
The reaction of [CpRuCl(P)2] [(P)2 ) dippe (1,2-bis(diisopropylphosphino)ethane; (PEt3)2;
(PMeiPr2)2] with Na[BAr′4] (Ar′4 ) 3,5-bis(trifluoromethyl)phenyl) in fluorobenzene under
argon generates the corresponding cationic 16-electron species [CpRu(P)2]+, which reacts
with trace amounts of dinitrogen present even in high-purity argon furnishing the dinitrogen-
bridged complexes [{CpRu(P)2}2(µ-N2)][BAr′4]2 [(P)2 ) dippe 1a ; (PEt3)2 1b; (PMeiPr2)2 1c].
If the reaction is performed under dinitrogen, the terminal dinitrogen complexes [CpRu-
(N2)(P)2][BAr′4] [(P)2 ) dippe 2a ; (PMeiPr2)2 2c] are obtained. Compound 1b was obtained
irrespectively of the atmosphere used, and no terminal dinitrogen complex has been detected.
The crystal structures of 1a , 1b, and 2a have been determined. During one attempt to isolate
the 16-electron complex [CpRu(PMeiPr2)2][BAr′4], the 18-electron tris(phosphine) derivative
[CpRu(PMeiPr2)3][BAr′4], 3, was obtained instead, and it was structurally characterized.
Halide abstraction from [CpRuCl(PMeiPr2)(PPh3)] under dinitrogen using Na[BAr′4] yielded
[CpRu(N2)(PMeiPr2)(PPh3)][BAr′4], 2d , but under argon the complex [CpRu(PMeiPr2)(PPh3)]-
[BAr′4], 4, which contains a rare η3-coordinated PPh3 ligand as shown by X-ray crystal-
lography, was isolated.
In tr od u ction
electron derivatives[CpRu(CF3SO3)(dcpe)] or [Cp*Ru(CF3-
SO3)(dppe)], respectively. Under these conditions, we
have shown that dinitrogen becomes a good ligand,
furnishing half-sandwich ruthenium dinitrogen com-
plexes of the type [(C5R5)Ru(N2)(P)2]+ [R ) H or Me,
(P)2 ) 1,2-bis(diisopropylphosphino)ethane (dippe); R )
Me, (P)2 ) (PEt3)2].4,5 At variance with their hydrotris-
(pyrazolyl)borate counterparts [TpRu(N2)(P)2]+ [(P)2 )
dippe; (PEt3)2],6,7 the complexes [(C5R5)Ru(N2)(P)2]+ are
extremely labile, and all attempts to purify these
materials by recrystallization led to dinitrogen loss and
formation of different species ranging from dioxygen
complexes [Cp*Ru(O2)(P2)]+8 to the sandwich derivative
[CpRu(η6-C6H5BPh3)].4 The introduction of the bulky,
noncoordinating anion [BAr′4]- 9 and its use as halide
scavenger in combination with fluorobenzene as solvent
opens new possibilities for the generation and stabiliza-
Cationic 16-electron species of the type [(C5R5)Ru-
(P)2]+ (R ) H, Me) have been postulated as intermedi-
ates in many reactions involving the well-known half-
sandwich halo complexes [(C5R5)RuX(P)2].1 These coor-
dinatively unsaturated species can be generated by
halide abstraction from the latter by using a suitable
halide scavenger reagent, most often Ag+ or Tl+ salts.
However, the [(C5R5)Ru(P)2]+ cations generated in situ
are extremely reactive species, which usually react with
any suitable donor molecule in the reaction mixture,
furnishing 18-electron complexes. The donor can be a
solvent molecule, particularly if it is coordinating, i.e.,
MeCN, acetone, THF, etc. The counterion may also act
as a ligand. Even poorly coordinating anions such as
[CF3SO3]-, [BF4]-, or even [BPh4]- are known to bind
to a metal center. Thus, reports claiming the isolation
of 16-electron complexes such as [CpRu(dcpe)][CF3SO3]
(4) de los R´ıos, I.; J ime´nez-Tenorio, M.; Padilla, J .; Puerta, M. C.;
Valerga, P. Organometallics 1996, 15, 4565.
(5) Tenorio, M. J .; Puerta, M. C.; Valerga, P. J . Organomet. Chem.
2000, 609, 161.
(6) J ime´nez-Tenorio, M. A.; Tenorio, M. J .; Puerta, M. C.; Valerga,
P. Inorg. Chim. Acta 1997, 259, 77.
(dcpe
)
1,2-bis(dicyclohexylphosphino)ethane)2 or
[Cp*Ru(dppe)][CF3SO3] (dppe ) 1,2-bis(diphenylphos-
phino)ethane)3 might actually correspond to the 18-
(1) Davies, S. G.; McNally, J . P.; Smallridge, A. J . Adv. Organomet.
Chem. 1990, 30, 1, and references therein.
(2) J oslin, F. L.; J ohnson, M. P.; Mague, J . T.; Roundhill, D. M.
Organometallics 1997, 16, 5601.
(3) Kirchner, K.; Mauthner, K.; Mereiter, K.; Schmid, R. J . Chem.
Soc., Chem. Commun. 1993, 892.
(7) J ime´nez-Tenorio, M. A.; Tenorio, M. A.; Puerta, M. C.; Valerga,
P. J . Chem. Soc., Dalton Trans. 1998, 3601.
(8) de los R´ıos, I.; J ime´nez-Tenorio, M.; Padilla, J .; Puerta, M. C.;
Valerga, P. J . Chem. Soc., Dalton Trans. 1996, 377.
(9) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920.
10.1021/om010730v CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/22/2002

Half-Sandwich Ru Dinitrogen Complexes
Organometallics, Vol. 21, No. 4, 2002 629
[Cp Ru Cl(P MeiP r 2)2]. A solution of RuCl3 was made by
boiling hydrated ruthenium trichloride (0.5 g, ca. 1.9 mmol)
in ethanol (5 mL). The insoluble matter, if any, was separated
from the liquor by decantation. The solution was cooled, and
freshly cracked cyclopentadiene (1 mL, excess) was added. This
mixture was added dropwise to a refluxing solution containing
PMeiPr2 (1.2 mL, 7.9 mmol) and cyclopentadiene (1 mL, excess)
in EtOH (80 mL). Once the addition was completed, the
reaction mixture was heated under reflux for another 2 h.
During this time, the color changed from dark green to orange-
red. After this time, the solvent was removed in vacuo, and
the residue extracted with petroleum ether (50 mL). Concen-
tration (to ca. 10 mL) and cooling to -20 °C gave bright orange-
red needle-shaped crystals, which were filtered off and dried
in vacuo. Yield: 0.6 g, 67%. The spectral properties of this
compound were coincident with those previously reported.5
[{Cp Ru (P )2}2(µ-N2)][BAr ′4]2 [(P )2 ) d ip p e 1a ; (P Et3)2 1b;
(P MeiP r 2)2 1c]. To a solution of the corresponding derivative
[CpRuCl(P)2] [(P)2 ) dippe for 1a , (PEt3)2 for 1b, or (PMeiPr2)2
for 1c] (0.5 mmol) in fluorobenzene (10 mL) under argon was
added solid NaBAr′4 (0.44 g, 0.5 mmol). Dinitrogen (6 mL, ca.
0.25 mmol) was injected through the reaction mixture using
a gas-tight syringe. The mixture was stirred for 15 min at room
temperature. Sodium chloride was removed by filtration
through Celite. The resulting solution was layered with
petroleum ether and left standing undisturbed at room tem-
perature. Well-formed yellow crystals were obtained by slow
diffusion of the petroleum ether into the fluorobenzene solu-
tion. These crystals were isolated by cannulating off the
supernatant liquor and dried under an argon stream. Yield:
60-70%. 1a : Anal. Calcd for C102H97N2B2F48P4Ru2: C, 46.9;
H, 3.72; N, 1.07. Found: C, 46.7; H, 3.82; N, 0.90. Raman:
tion of highly electrophilic cationic complexes. Thus,
following the recent isolation of remarkably stable
coordinatively unsaturated complexes [(C5R5)Ru(N-N)]-
[BAr′4] (R ) Me, N-N ) Me2NCH2CH2NMe2, Me2NCH2-
CH2NiBu2; R ) H, N-N ) Me2NCH2CH2NMe2),10,11 we
have been able to synthesize the first genuine cationic
16-electron half-sandwich ruthenium phosphine com-
plexes [Cp*Ru(P)2][BAr′4] [(P)2 ) dippe, (PMeiPr2)2].12
These compounds are extremely reactive deep blue
materials, which have been unequivocally characterized
by X-ray structure analysis. We have now carried out
the halide abstraction reactions from a series of cyclo-
pentadienyl phosphine complexes [CpRuCl(P)2] using
Na[BAr′4] in fluorobenzene, with the aim of isolating
the corresponding 16-electron complexes [CpRu(P)2]-
[BAr′4]. Indeed, these species are generated, but they
have shown to have an enormous avidity for dinitrogen.
Hence, they react even with trace amounts of N2 present
in high-purity argon, furnishing the dinitrogen-bridged
complexes [{CpRu(P)2}2(µ-N2)][BAr′4]2 [(P)2 ) dippe 1a ;
(PEt3)2 1b; (PMeiPr2)2 1c]. Only when aromatic substit-
uents were present on one of the phosphine ligands was
a compound of formula [CpRu(PPh3)(PMeiPr2)][BAr′4]
isolated, but it turned out to be an 18-electron species,
in which one CdC bond from one of the aromatic rings
fills the vacant coordination site, leading to a rare η3-
coordination mode for the PPh3 ligand. The synthesis,
structure, and spectral properties of all these com-
pounds and of related species are described in detail in
the present work.
ν(NtN) 2050 cm-1 1H NMR (400 MHz, CD2Cl2): δ 1.21 (m,
.
P(CH(CH3)2)2), 1.87 (m, PCH2), 2.25 (double multiplet, P(CH-
(CH3)2)2), 5.08 (s, RuC5H5). 31P{1H} NMR (161.89 MHz, CD2-
Cl2): δ 92.2 (s). 1b: Anal. Calcd for C98H94N2B2F48P4Ru2: C,
46.0; H, 3.67; N, 1.09. Found: C, 46.2; H, 3.62; N, 0.50.
Exp er im en ta l Section
All synthetic operations were performed under a dry dini-
trogen or argon atmosphere by following conventional Schlenk
techniques. Tetrahydrofuran, diethyl ether, and petroleum
ether (boiling point range 40-60 °C) were distilled from the
appropriate drying agents. Solvents were deoxygenated by
three freeze/pump/thaw cycles and stored under argon. [CpRu-
Cl(dippe)],8 [CpRuCl(PEt3)2],13 and [CpRuCl(PMeiPr2)(PPh3)]13
were prepared according to reported procedures. A new, more
efficient synthetic procedure has been developed for the
preparation of [CpRuCl(PMeiPr2)2], and details are given. IR
spectra were recorded in Nujol mulls on a Perkin-Elmer FTIR
Spectrum 1000 spectrophotometer. Raman spectra were re-
corded at the Serveis Cientifico-Te`cnics, Universitat de Bar-
celona, using a J obin-Yvon T64000 dispersive spectrometer
equipped with a Coherent Innova 306 argon laser as excitation
source (λ ) 514 nm). NMR spectra were taken on a Varian
Unity 400 MHz or Varian Gemini 200 MHz equipment.
Chemical shifts are given in parts per million from SiMe4 (1H
and 13C{1H}) or 85% H3PO4 (31P{1H}). Microanalysis was
performed by the Serveis Cient´ıfico-Te`cnics, Universitat de
Barcelona. The nitrogen content was found to be low or even
very low in several cases, due to the lability of the N2 ligand
in these compounds. Therefore, the found and calculated
percentage figures do not match for nitrogen content in these
cases, whereas carbon and hydrogen microanalysis is accept-
able.
1
Raman: ν(NtN) 2064 cm-1. H NMR (400 MHz, CD2Cl2): δ
1.12 (m, P(CH2CH3)3), 1.80 (double multiplet, P(CH2CH3)3),
5.01 (s, RuC5H5). 31P{1H} NMR (161.89 MHz, CD2Cl2): δ 30.9
(s). 1c: Anal. Calcd for C102H102N2B2F48P4Ru2: C, 46.8; H, 3.90;
N, 1.07. Found: C, 46.7; H, 3.91; N, 0.44. Raman: ν(NtN)
1
not observed due to decomposition. H NMR (400 MHz, CD2-
Cl2): δ 1.19 (m, P(CH(CH3)2)2), 1.36 (m, PCH3), 2.15 (double
multiplet, P(CH(CH3)2)2), 5.09 (s, RuC5H5). 31P{1H} NMR
(161.89 MHz, CD2Cl2): δ 37.5 (s).
[Cp Ru (N2)(P )2][BAr ′4] [(P )2 ) d ip p e 2a ; (P MeiP r 2)2 2c;
(P MeiP r 2)(P P h 3) 2d ]. These compounds were obtained in a
fashion analogous to that for the dinitrogen-bridged derivatives
1a -1c, starting from [CpRuCl(P)2] [(P)2 ) dippe for 2a ,
(PMeiPr2)2 for 2c, or (PMeiPr2)(PPh3) for 2d ] (0.25 mmol) and
NaBAr′4 (0.22 g, 0.25 mmol) in fluorobenzene under a dini-
trogen atmosphere. Yield: ca. 80% in all cases. 2a : Anal. Calcd
for C51H49N2BF24P2Ru: C, 46.4; H, 3.72; N, 2.12. Found: C,
1
46.1; H, 3.69; N, 1.87. IR: ν(NtN) 2158 cm-1. H NMR (400
MHz, CD2Cl2): δ 1.21 (m, P(CH(CH3)2)2), 1.87 (m, PCH2), 2.25
(double multiplet, P(CH(CH3)2)2), 5.16 (s, RuC5H5). 31P{1H}
NMR (161.89 MHz, CD2Cl2): δ 92.2 (s). 2c: Anal. Calcd for
C
51H51N2BF24P2Ru: C, 46.3; H, 3.86; N, 2.12. Found: C, 46.5;
1
H, 3.67; N, 1.70. IR: ν(NtN) 2164 cm-1. H NMR (400 MHz,
CD2Cl2): δ 1.20 (m, P(CH(CH3)2)2), 1.36 (m, PCH3), 2.20
(double multiplet, P(CH(CH3)2)2), 5.08 (s, RuC5H5). 31P{1H}
NMR (161.89 MHz, CD2Cl2): δ 37.5 (s). 2d : Anal. Calcd for
(10) (a) Gemel, C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organo-
metallics 1997, 16, 5601. (b) Gemel, C.; Sapunov, V. N.; Mereiter, K.;
Ferencic, M.; Schmid, R.; Kirchner, K. Inorg. Chim. Acta 1999, 286,
114.
(11) Gemel, C.; Huffman, J . C.; Caulton, K. G.; Mauthner, K.;
Kirchner, K.; J . Organomet. Chem. 2000, 593-594, 342.
(12) Tenorio, M. J .; Puerta, M. C.; Valerga, P.; Mereiter, K. J . Am.
Chem. Soc. 2000, 122, 11230.
C
62H49N2BF24P2Ru: C, 51.3; H, 3.38; N, 1.93. Found: C, 51.1;
1
H, 3.38; N, 0.43. IR: ν(NtN) 2177 cm-1. H NMR (400 MHz,
CD2Cl2, 243 K): δ 0.51 (m, PCH3), 0.80-1.20 (m, P(CH-
(CH3)2)2), (double multiplet, P(CH(CH3)2)2), 4.87 (s, RuC5H5).
31P{1H} NMR (161.89 MHz, CD2Cl2, 243 K): δ 43.9 (d, J PP
)
2
31.5 Hz, PMeiPr2), 37.3 (d, J PP ) 31.5 Hz, PPh3).
2
[Cp Ru (P MeiP r 2)3][BAr ′4], 3. A solution of [CpRuCl(P-
(13) Coto, A.; Tenorio, M. J .; Puerta, M. C.; Valerga, P. Organo-
metallics 1998, 17, 4392.
MeiPr2)2)] (0.12 g, 0.25 mmol) in fluorobenzene (6 mL) was

630 Organometallics, Vol. 21, No. 4, 2002
Aneetha et al.
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for Com p ou n d s 1a , 1b, 2a , 3, a n d 4
1a (with FPh) 1b (with 2 FPh) 2a
108H103B2F49N2P4Ru2 C110H104B2F50N2P4Ru2 C51H49BF24N2P2Ru C58H68BF24P3Ru
3
4 (with 2FPh)
formula
fw
T (K)
C
C75H59BF26P2Ru
1616.03
213(2)
2707.56
2751.60
1319.74
1425.91
223(2)
223(2)
213(2)
223(2)
cryst size (mm)
cryst syst
space group
cell params
0.80 × 0.60 × 0.32
0.8 × 0.7 × 0.4
0.46 × 0.42 × 0.38
0.72 × 0.68 × 0.40 0.7 × 0.4 × 0.3
triclinic
triclinic
monoclinic
monoclinic
monoclinic
P1 (no. 2)
a ) 13.986(4) Å
b ) 14.321(4) Å
c ) 15.273(5) Å
R ) 83.25(1)°
â ) 69.96(1)°
γ ) 85.60(1)°
2852(2)
P1 (no. 2)
a ) 13.310(3) Å
b ) 13.702(3) Å
c ) 17.120(3) Å
R ) 83.76(1)°
â ) 73.03(1)°
γ ) 81.54(1)°
2947(1)
P21/n (no. 14)
a ) 12.391(4) Å
b ) 35.677(12) Å
c ) 12.885(4) Å
Cc (no. 9)
P21/c (no. 14)
a ) 21.264(9) Å
b ) 15.092(6) Å
c ) 20.992(9) Å
a ) 23.172(12) Å
b ) 12.868(7) Å
c ) 25.179(13) Å
â ) 90.01(1)°
â ) 106.06(1)°
â ) 105.85(3)°
volume (Å3)
5696(3)
4
1.539
4.47
2656
6474(5)
4
7222(7)
4
Z
F
1
1
calc (g cm-3
)
1.577
4.49
1364
1.551
4.37
2772
1.463
4.22
1.486
3.71
µ(Mo KR) (cm-1
F(000)
)
2904
3264
max. and min.
0.83-0.74
1.000-0.906
0.894-0.756
0.86-0.80
1.000-0.912
transmn factors
θ range for data
collection (deg)
1.92 to 30.00
1.25 to 30.00
1.74 to 30.00
1.68 to 27.50
1.68 to 27.50
no. of reflns collected
no. of unique reflns
52 172
16 347
43 201
16 821
82 786
16 486
39 811
14 831
130 804
16 564
(Rint)0.017)
(Rint)0.020)
(Rint)0.039)
(Rint)0.019)
(Rint)0.057)
no. of obsd reflns
(I > 2σI)
no. of params
14 834
13 390
13 778
12 962
12 147
758
816
773
886
970
final R1, wR2
values (I > 2σI)
final R1, wR2
values (all data)
residual electron
density peaks (e Å-3
0.0364, 0.0963
0.0648, 0.1614
0.0639, 0.1513
0.0469, 0.1193
0.0452, 0.1076
0.0409, 0.1020
0.0809, 0.1796
0.0754, 0.1607
0.0561, 0.1311
0.0707, 0.1240
+0.924/-0.64
+1.624/-1.074
+0.77/-0.72
+0.47/-0.86
+0.694/-0.564
)
treated with a slight excess over the stoichiometric amount of
PMeiPr2. Upon stirring for a few minutes at room temperature,
NaBAr′4 (0.22 g, 0.25 mmol) was added. A color change to
yellow was observed. The mixture was stirred for 15 min.
Sodium chloride was removed by filtration through Celite. The
filtrate was layered with petroleum ether and left undisturbed
at room temperature. Yellow crystals were obtained by slow
diffusion of petroleum ether into the fluorobenzene, which were
separated from the supernatant liquor and dried in an argon
stream. Yield: 0.21 g, 60%. Anal. Calcd for C58H68BF24P3Ru:
X-r a y Str u ctu r e Deter m in a tion s. Crystals of 1a , 1b, 2a ,
3, and 4 were obtained by slow diffusion of petroleum ether
into fluorobenzene solutions. Crystal data and experimental
details are given in Table 1. X-ray data were collected on a
Bruker Smart CCD area detector diffractometer (graphite-
monochromated Mo KR radiation, λ ) 0.71073 Å, 0.3° ω-scan
frames covering complete spheres of the reciprocal space).
Corrections for Lorentz and polarization effects, for crystal
decay, and for absorption were applied. All structures were
solved by direct methods using the program SHELXS97.14
Structure refinement on F2 was carried out with program
SHELXL97.15 All non-hydrogen atoms were refined anisotro-
pically. Hydrogen atoms were inserted in idealized positions
and were refined riding with the atoms to which they were
bonded. In four of the five compounds the CF3 groups showed
high rotatory motion about the C-CF3 bond axes or a corre-
sponding orientation disorder. Where necessary, this was
taken into account by refining CF3 groups split into two
orientations, of which the predominanting was calculated with
anisotropic temperature factors and the subordinate one with
isotropic temperature factors. Salient crystallographic data are
summarized in Table 1; further details are given in the
Supporting Information.
1
C, 48.8; H, 4.77. Found: C, 49.0; H, 4.79. H NMR (400 MHz,
CD2Cl2): δ 1.21 (m, P(CH(CH3)2)2), 1.35 (m, PCH3), 2.09
(double multiplet, P(CH(CH3)2)2), 4.94 (s, RuC5H5). 31P{1H}
NMR (161.89 MHz, CD2Cl2): δ 32.2 (s).
[Cp Ru (P MeiP r 2)(η3-P P h 3)][BAr ′4], 4. To a solution of
[CpRuCl(PMeiPr2)(PPh3)] (0.5 g, 0.84 mmol) in fluorobenzene
(10 mL) under argon was added solid NaBAr′4 (0.74 g, 0.84
mmol). The mixture was stirred for 15 min at room temper-
ature. Sodium chloride was removed by filtration through
Celite. The resulting solution was layered with petroleum
ether and left standing undisturbed at room temperature.
Well-formed red crystals were obtained by slow diffusion of
the petroleum ether into the fluorobenzene solution. These
crystals were isolated by cannulating off the supernatant
liquor and dried under an argon stream. The crystals lose
fluorobenzene of crystallization (they contain 2 fluorobenzene
molecules per complex cation) almost immediately and usually
Resu lts a n d Discu ssion
In an attempt to obtain the cationic coordinatively
unsaturated derivatives [CpRu(P)2][BAr′4] [(P)2 ) dippe,
(PEt3)2, (PMeiPr2)2], we carried out the reaction of the
corresponding complexes [CpRuCl(P)2] with Na[BAr′4]
in fluorobenzene under an argon atmosphere. We had
previously noticed during the reaction of the related
systems [Cp*RuCl(P)2] with Na[BAr′4] in fluorobenzene
crumble when dried. Yield: 0.89 g, 75%. Anal. Calcd for C62H49
-
BF24P2Ru: C, 52.3; H, 3.44. Found: C, 51.9; H, 3.34. 1H NMR
(400 MHz, CD2Cl2, 243 K): δ 0.50-1.30 (m br, PCH3, P(CH-
(CH3)2)2), 2.10 (m, P(CH(CH3)2)2), 4.38 (RuC5H5), 6.17, 6.26 (m,
η3-P(C6H5), 7.46 t, 7,29 m, 7.65 m (P(C6H5)). 31P{1H} NMR
2
(161.89 MHz, CD2Cl2, 243 K): δ 36.8 (d, J PP ) 39.1 Hz), 48.9
2
(d, J PP ) 39.1 Hz). 13C{1H} NMR (100.58 MHz, CD2Cl2, 298
K): δ 6.6 (d, J CP ) 61.5 Hz, PCH3), 14.4, 14.5, 15.2 (s, P(CH-
(CH3)2)2), 24.9 (d, J CP ) 66.8 Hz, P(CH(CH3)2)2), 82.1 (RuC5H5),
85.4 (d, J CP ) 7.7 Hz, η3-P(C6H5)), 87.6 (d, J CP ) 9.4 Hz, η3-
P(C6H5)), 128.6 d, 129.3 d, 131.7 t, 132.2 s, 133.7 d (P(C6H5)).
(14) Sheldrick, G. M. SHELXS97, Program for Crystal Structure
Solution; University of Go¨ttingen, 1990.
(15) Sheldrick, G. M. SHELXL97, Program for Crystal Structure
Refinement; University of Go¨ttingen, 1997.

Half-Sandwich Ru Dinitrogen Complexes
Organometallics, Vol. 21, No. 4, 2002 631
F igu r e 1. ORTEP drawing (50% thermal ellipsoids) of the
cation [{CpRu(dippe)}2(µ-N2)]2+ in complex 1a . Hydrogen
atoms have been omitted. Selected bond lengths (Å) and
angles (deg) with estimated standard deviations in paren-
theses: Ru-C(1) 2.199(2); Ru-C(2) 2.233(2); Ru-C(3)
2.243(2); Ru-C(4) 2.250(2); Ru-C(5) 2.231(2); Ru-P(1)
2.3306(8); Ru-P(2) 2.3361(7); Ru-N 1.980(1); N-N#1
1.118(3); P(1)-Ru-P(2) 82.60(2); Ru-N1-N#1 170.7(2).
F igu r e 2. ORTEP drawing (50% thermal ellipsoids) of the
cation [{CpRu(PEt3)2}2(µ-N2)]2+ in complex 1b. Hydrogen
atoms have been omitted. Selected bond lengths (Å) and
angles (deg) with estimated standard deviations in paren-
theses: Ru-C(1) 2.208(5); Ru-C(2) 2.222(5); Ru-C(3)
2.223(5); Ru-C(4) 2.171(5); Ru-C(5) 2.190(5); Ru-P(1)
2.334(1); Ru-P(2) 2.351(1); Ru-N 1.977(3); N-N#1 1.114-
(5); P(1)-Ru-P(2) 95.42(4); Ru-N1-N#1 172.3(3).
under argon the immediate development of a deep blue
color, indicative of the formation of the 16-electron
cationic complexes [Cp*Ru(P)2][BAr′4] in the reaction
mixture.12 However, no blue color was observed during
the reaction of the cyclopentadienyl derivatives. Instead,
clear yellow or yellow-orange solutions were obtained
upon removal of sodium chloride from the mother liquor
by filtration through Celite. Yellow crystals were ob-
tained by slow diffusion of petroleum ether into these
solutions under an argon atmosphere. Microanalysis
indicated the presence of small but significant amounts
of nitrogen in these materials (less than 1%). However,
no band in the IR spectra attributable to ν(N2) in a
terminal dinitrogen complex was detected. Rather un-
expectedly, X-ray structure analysis for the dippe and
PEt3 derivatives showed them to be binuclear dinitro-
gen-bridged complexes, namely, [{CpRu(dippe)}2(µ-N2)]-
[BAr′4]2, 1a , and [{CpRu(PEt3)2}2(µ-N2)][BAr′4]2, 1b.
Likewise, a formulation as [{CpRu(PMeiPr2)}2(µ-N2)]-
[BAr′4]2, 1c, can be proposed for the PMeiPr2 derivative.
ORTEP16 diagrams of the complex cations [{CpRu-
(dippe)}2(µ-N2)]2+ and [{CpRu(PEt3)2}2(µ-N2)]2+ are shown
in Figures 1 and 2, respectively. Both dinitrogen com-
plexes crystallized as fluorobenzene solvates, in the form
of 1a ‚FPh and 1b‚2 FPh. The structure of the complex
cations can be described as a centrosymmetrical ar-
rangement of {[CpRu(P)2]+} moieties linked through a
dinitrogen molecule. The crystallographic center of
symmetry lies in the midpoint of the N-N bond, making
equivalent the two ruthenium sites. Each ruthenium
adopts the typical three-legged piano stool geometry
found for other complexes that contain the cyclopenta-
dienyl bis(phospine) auxiliary fragments.1-4,8 The dini-
trogen ligand is linearly assembled to the two ruthe-
nium atoms, as indicated by the value of the angle Ru-
N1-N# of 170.7(2)° for 1a and 172.3(3)° for 1b. The two
nitrogen atoms and the two ruthenium atoms are
contained in the same plane, as a result of the center of
symmetry. The Ru-N bond distances are ca. 1.98 Å for
both compounds, whereas the N1-N# separations are
1.118(3) Å in the case of 1a and 1.114(5) Å for 1b. These
values compare well with the N-N bond distances
recently reported for the dinitrogen-bridged complexes
[{mer,trans-RuCl2(NN′N)}2(µ-N2)] (N-N 1.110(3) Å;
NN′N ) 2,6-bis[(dimethylamino)methyl]pyridine)17 and
[{RuH2(N2)(PiPr3)2}2(µ-N2)] (bridging N-N 1.113(2) Å;
terminal N-N 1.105(2) Å).18 In the complex [{Ru-
(NH3)5}2(µ-N2)][BF4]2 the N-N separation was found to
be 1.124 Å.19 In all cases, the N-N separation is slightly
longer than the bond length of 1.0977 Å found for the
free N2 molecule.20 The main difference between the
structures of 1a and 1b lies in the value of the P1-
Ru-P2 angle (82.60(2)° versus 95.42(4)°), which is
smaller in the case of the dippe derivative due to the
“bite angle” imposed for the chelating nature of the
phosphine ligand. All other bond distances and angles
in the two complexes are in the expected range, being
unexceptional. Consistently with the centrosymmetrical
nature of the binuclear dinitrogen complex cations, the
ν(N2) band is inactive in the IR, but active in Raman.
Thus, the Raman spectrum of complexes 1a and 1b
shows medium-strong bands at 2050 and 2064 cm-1
,
respectively. Complex 1c seems to be more labile and
was destroyed by the action of the laser, so its Raman
spectrum could not be recorded. It appears that, at
variance with their Cp*Ru counterparts, the 16-electron
complexes [CpRu(P)2]+ [(P)2 ) dippe, (PEt3)2, (PMeiPr2)2]
are exceedingly reactive, having an enormous avidity
(17) Abbenhuis, R. A. T. M.; del R´ıo, I.; Bergshoef, M. M.; Boersma,
J .; Veldman, N.; Spek, A. L.; van Koten, G. Inorg. Chem. 1998, 37,
1749.
(18) Abdur-Rashid, K.; Gusev, D. G.; Lough, A. J .; Morris, R. H.
Organometallics 2000, 19, 1652.
(19) Ondrechen, M. J .; Ratner, M. A.; Ellis, D. E. J . Am. Chem. Soc.
1981, 103, 1656.
(16) J ohnson, C. K. ORTEP, A Thermal Ellipsoid Plotting Program;
Oak Ridge National Laboratory: Oak Ridge, TN, 1965.
(20) Handbook of Chemistry and Physics, 76th ed.; Lide, R. D., Ed.;
CRC Press: New York, 1995; Section 9, p 20.

632 Organometallics, Vol. 21, No. 4, 2002
Aneetha et al.
for dinitrogen. Thus, upon generation by halide abstrac-
tion, the coordinatively unsaturated complex cations
react immediately with the small amount of N2 present
in the argon used as protective atmosphere (ca. 2 ppm).
The dinitrogen-bridged complexes 1a -1c were isolated
in a reproducible manner as the only species resulting
from the reaction, in ca. 50% yield under these condi-
tions. The reaction of highly reactive coordinatively
unsaturated complexes with trace amounts of N2 present
in high-purity argon or even helium to give dinitrogen
complexes has been reported by other authors. Thus,
photolysis of [RuH2(PP3)] (PP3 ) P(CH2CH2PPh2)3)21 in
THF under argon atmospheres (BOC Pureshield Argon,
99.995%) yielded the terminal Ru0 dinitrogen complex
[Ru(N2)(PP3)], albeit in small quantities.22 This was
attributed to the efficient scavenging of N2 by the
cyclometalated complex of formula [Ru(PP3)] formed
upon irradiation of the dihydride:22
F igu r e 3. ORTEP drawing (50% thermal ellipsoids) of the
cation [CpRu(N2)(dippe)]+ in complex 2a . Hydrogen atoms
have been omitted. Selected bond lengths (Å) and angles
(deg) with estimated standard deviations in parentheses:
Ru-C(1) 2.216(4); Ru-C(2) 2.228(5); Ru-C(3) 2.220(4);
Ru-C(4) 2.202(4); Ru-C(5) 2.224(4); Ru-P(1) 2.327(1);
Ru-P(2) 2.326(1); Ru-N(1) 1.961(3); N(1)-N(2) 1.087(4);
P(1)-Ru-P(2) 83.86(3); Ru-N(1)-N(2) 175.8(4).
The complex [Mo(CO)(depe)2] (depe ) 1,2-bis(dieth-
ylphosphino)ethane)23 is stabilized by an agostic inter-
action with one of the CH3 groups of the depe ligand.
This compound is so reactive toward dinitrogen that
both in solution and in the solid state it can scavenge
traces of dinitrogen inside a glovebox operated under a
helium atmosphere to give the bridging dinitrogen
complex [{Mo(CO)(depe)2}2(µ-N2)].23 It therefore appears
that the moieties {[CpRu(P)2]+} possess N2-scavenging
abilities similar to those of [Ru(PP3)] and [Mo(CO)-
(depe)2]. The procedure for the synthesis of the N2-
bridged complexes 1a -1c can be standarized by intro-
ducing the stoichiometric amount of N2 into the reaction
mixture via syringe, resulting in 60-70% yield of
isolated product.
the terminal dinitrogen complexes 2a and 2c are es-
sentially identical. This seems logical, given the fact that
the chemical environment around each ruthenium atom
remains the same, irrespectively of being a bridging or
a terminal dinitrogen complex. Compounds 1a and 2a
react slowly with dichloromethane, furnishing blue
solutions. These blue solutions display broad features
1
in its H NMR spectrum, indicative of the presence of
paramagnetic species. No attempt was made to identify
these species. The X-ray crystal structure of 2a was
determined, to compare with the structure of its dini-
trogen-bridged counterpart. An ORTEP view of the
complex cation is shown in Figure 3. It shows a “three-
legged piano stool” structure, with the dinitrogen ligand
bound in the end-on manner, resembling very much the
structure of the homologous iron complex cation [CpFe-
(N2)(dippe)]+.24 All structural parameters within the
complex [CpRu(N2)(dippe)]+, with the exception of those
involving the N2-ligand, are essentially identical to those
found for the bridging dinitrogen derivative 1a . Thus,
the Ru-N1-N2 angle of 175.8(4)° indicates an almost
perfectly linear Ru-N2 assembly, with a Ru-N1 sepa-
ration of 1.961(3) Å and a N1-N2 bond length of 1.087-
(4) Å. These bond distances compare well with those
reported for other terminal Ru-N2 complexes such as
[TpRu(N2)(PEt3)2][BPh4] (Tp ) hydrotris(pyrazolyl)-
borate(1-); Ru-N1 1.910(2) Å, N1-N2 1.010(2) Å)7 or
[TpRu(N2)(PN)][CF3SO3] (PN ) Ph2PCH2CH2NMe2;
Ru-N1 1.943(4) Å, N1-N2 1.097(5) Å).25 Whereas in
terminal dinitrogen complexes the N-N separation is
essentially identical to that corresponding to the free
N2 molecule,26 in the bridging N2 complexes it is slightly
longer (ca. 0.1 Å). It has been shown by EHMO calcula-
We have previously reported the preparation of some
labile terminal dinitrogen half-sandwich ruthenium
complexes of the type [(C5R5)Ru(P2)][BPh4] [R ) H, Me,
P2 ) dippe; R ) Me, P2 ) (PEt3)2]. Attempts made to
purify these complexes led to dinitrogen loss in all cases.
However, the use of Na[BAr′4] as halide scavenger and
anion for crystallization has made possible the standa-
rization of the procedure for the synthesis of cationic
dinitrogen complexes of ruthenium. Thus, the reaction
of [CpRuCl(P)2] with Na[BAr′4] in fluorobenzene under
N2 yielded the terminal dinitrogen complexes [CpRu-
(N2)(P)2][BAr′4] [(P)2 ) dippe 2a, (PMeiPr2)2 2c, (PMeiPr2)-
(PPh3) 2d ]. The reaction of [CpRuCl(PEt3)2] with Na-
[BAr′4] under dinitrogen failed to give [CpRu(N2)-
(PEt3)2][BAr′4], and the dinitrogen-bridged complex 1b
was obtained instead. As expected, all terminal dini-
trogen complexes display one strong ν(N2) band in their
IR spectra, in the range 2150-2180 cm-1. It is interest-
1
ing to note that the H and 31P{1H} NMR spectra of the
bridging dinitrogen complexes 1a and 1c and those of
(21) Bianchini, C.; Perez, P. J .; Peruzzini, M.; Zanobini, F.; Vacca,
A. Inorg. Chem. 1991, 30, 279.
(22) Osman, R.; Pattison, D. L.; Perutz, R. N.; Bianchini, C.; Casares,
J . A.; Peruzzini, M. J . Am. Chem. Soc. 1997, 119, 8459.
(23) Luo, X.-L.; Kubas, G. J .; Burns, C. J .; Butcher, R. J .; Bryan, J .
C. Inorg. Chem. 1995, 34, 6538.
(24) de la J ara Leal, A.; Tenorio, M. J .; Puerta, M. C.; Valerga, P.
Organometallics 1995, 14, 3839.
(25) Gemel, C.; Wiede, P.; Mereiter, K.; Sapunov, V. N.; Schmid,
R.; Kirchner, K. J . Chem. Soc., Dalton Trans. 1996, 4071.

Half-Sandwich Ru Dinitrogen Complexes
Organometallics, Vol. 21, No. 4, 2002 633
tions that upon binding to ruthenium, there is a
reinforcement of the σ-bonding and a weakening of the
π-bonding in the N2 ligand.25 These opposite effects lead
to almost no change in the N-N bond distance upon
coordination. However, when the dinitrogen ligand acts
as a bridge between two ruthenium centers, there is an
overall weakening effect, which leads to a small elonga-
tion of the N-N bond, consistent with back-donation of
electron density from RuII to N2.
Despite the great affinity of the {[CpRu(P)2]+} moi-
eties for N2, we kept searching for coordinatively
unsaturated species. In one of our earlier attempts to
prepare the 16-electron complex [CpRu(PMeiPr2)2]-
[BAr′4] by reaction of [CpRuCl(PMeiPr2)2] with Na-
[BAr′4] in fluorobenzene under argon, we isolated a
yellow crystalline material, which was identified as the
tris(phosphine) derivative [CpRu(PMeiPr2)3][BAr′4], 3.
This material was formed in the reaction mixture due
possibly to the presence of free PMeiPr2 accompanying
the starting material [CpRuCl(PMeiPr2)2], since it had
been obtained following our previously published
method: thermal substitution of PPh3 in [CpRuCl-
(PPh3)(PMeiPr2)] by PMeiPr2 followed by column chro-
matography.5 We have now modified the procedure for
the synthesis of [CpRuCl(PMeiPr2)2], which is conve-
niently prepared by direct reaction of hydrated ruthe-
nium trichloride with cyclopentadiene and PMeiPr2 in
boiling ethanol, being isolated as a crystalline material
void of free phosphine impurities. Hence, 3 can be
synthesized in good yield by reaction of [CpRuCl-
(PMeiPr2)2] with 1 equiv of PMeiPr2 and Na[BAr′4] in
fluorobenzene. It is rather surprising the fact that three
bulky phosphine ligands such as PMeiPr2 can bind
simultaneously to the same ruthenium atom, adopting
a fac-stereochemistry. Furthermore, we have been
unable to generate the analogous tris(phosphine) com-
plex [Cp*Ru(PMeiPr2)3][BAr′4] by reaction of the genu-
ine 16-electron complex [Cp*Ru(PMeiPr2)2][BAr′4]12 with
an excess of PMeiPr2. Although Cp* is more sterically
demanding than Cp, it seems that the stabilization of
the coordinatively unsaturated Cp*Ru species is due to
electronic rather than steric reasons. We recently
reached a similar conclusion concerning the stabilization
of the neutral 16-electron complex [Cp*RuCl(PMeiPr2)]
versus the 18-electron derivative [Cp*RuCl(PMeiPr2)2].5
The X-ray crystal structure of 3 was determined. An
ORTEP view of the complex cation is shown in Figure
4. Again, the complex cation adopts a “three-legged
piano stool structure”, with the three phosphine ligands
in a fac-disposition around ruthenium. The Ru-P
separations are in the range expected, being unexcep-
tional, whereas the P-Ru-P angles are all close to 95°.
To minimize the steric pressure, the substituent groups
of each phosphine adopt a particular orientation: the
methyl groups of each of the PMeiPr2 ligands are all
pointing down in the same direction, away from the
ruthenium. The isopropyl substituents also point away
from the ruthenium, but toward the Cp plane. The
result is a quite symmetrical arrangement of the phos-
F igu r e 4. ORTEP drawing (50% thermal ellipsoids) of the
cation [CpRu(PMeiPr2)3]+ in complex 3. Hydrogen atoms
have been omitted. Selected bond lengths (Å) and angles
(deg) with estimated standard deviations in parentheses:
Ru-C(1) 2.245(5); Ru-C(2) 2.241(5); Ru-C(3) 2.222(5);
Ru-C(4) 2.246(6); Ru-P(3) 2.366(2); Ru-C(5) 2.240(5);
Ru-P(1) 2.368(2); Ru-P(2) 2.356(1); P(1)-Ru-P(2) 95.12-
(4); P(2)-Ru-P(3) 94.85(4); P(1)-Ru-P(3) 94.47(6).
phines around the metal, which is consistent with a
“perfect fit” of the three ligands despite the bulk of the
substituents on the phosphorus atoms.
Although the terminal dinitrogen complex [CpRu-
(N2)(PPh3)(PMeiPr2)][BAr′4] has been prepared in this
work, the reaction of [CpRuCl(PPh3)(PMeiPr2)] with Na-
[BAr′4] and the stoichiometric amount of N2 in fluo-
robenzene under argon did not produce the dinitrogen-
bridged complex [{CpRu(PPh3)(PMeiPr2)}2(µ-N2)][BAr′4]2.
Instead, a red crystalline compound of formula [CpRu-
1
(PPh3)(PMeiPr2)][BAr′4], 4, was obtained. The H NMR
spectrum of this material in CD2Cl2 under Ar displayed
two multiplet resonances at 6.17 and 6.26 ppm, apart
from signals due to Cp, PMeiPr2, and the aromatic
protons of PPh3. The 31P{1H} consisted of broad fea-
tures, being temperature-dependent. At 243 K, two
rather broad doublets were observed in the 31P{1H}
NMR spectrum, whereas the 1H spectrum remains
essentially identical to that recorded at 298 K. The 31P-
{1H} NMR spectrum becomes featureless at 363 K
(using C2D2Cl4 as solvent). However, even at this
1
temperature the H NMR spectrum is essentially iden-
tical to that recorded at 298 K. Some of these resonances
had been previously observed in the 1H and 31P{1H}
NMR spectra of the terminal dinitrogen complex 2d .
1
The H NMR resonances around 6.2 ppm were initially
attributed to an agostic interaction of the metal with
ortho-hydrogens of the phenyl groups of the PPh3 ligand,
as it is known to occur in [RuCl2(PPh3)3].27 However,
an X-ray structure analysis performed on the fluoroben-
zene solvate 4‚2 FPh proved this structural assignment
to be incorrect. Instead, a very rare η3-coordination
mode for the PPh3 ligand was found. An ORTEP view
of the complex cation [CpRu(η3-PPh3)(PMeiPr2)]+ is
shown in Figure 5. The structure can be described as a
bent “two-legged piano stool” in which the vacant
coordination position is occupied by one of the CdC
(26) For X-ray structures of terminal Ru-N2 complexes see: Schlaf,
M.; Lough, A. J .; Morris, R. H. Organometallics 1997, 16, 1253. J ia,
G.; Meek, D. W.; Gallucci, J . C. Inorg. Chem. 1991, 30, 403. Chaudret,
B.; Devillers, J .; Poilblanc, R. Organometallics 1985, 4, 1727. Camen-
zind, M. J .; J ames, B. R.; Dolphin, D.; Sparapany, J . W.; Ibers, J . A.
Inorg. Chem. 1988, 27, 3054.
(27) La Placa, S. J .; Ibers, J . A. Inorg. Chem. 1965, 4, 778.

634 Organometallics, Vol. 21, No. 4, 2002
Aneetha et al.
Sch em e 1. Ru th en iu m Com p lexes Con ta in in g
Ch ela tin g P h osp h in e Liga n d s Actin g a s
Six-Electr on Don or via Coor d in a tion of On e of th e
Bia r yl Dou ble Bon d s (Refs 29-31)
F igu r e 5. ORTEP drawing (50% thermal ellipsoids) of the
cation [CpRu(η3-PPh3)(PMeiPr2)]+ in complex 4. Hydrogen
atoms have been omitted. Selected bond lengths (Å) and
angles (deg) with estimated standard deviations in paren-
theses: Ru-C(1) 2.201(3); Ru-C(2) 2.193(3); Ru-C(3)
2.214(3); Ru-C(4) 2.195(3); Ru-C(5) 2.191(3); Ru-P(1)
2.2951(11); Ru-P(2) 2.3717(12); Ru-C(6) 2.371(3); Ru-
C(7) 2.459(3); P(1)-C(6) 1.799(3); C(6)-C(7) 1.420(4); C(6)-
C(11) 1.427(4); C(7)-C(8) 1.414(4); C(8)-C(9) 1.366(5);
C(9)-C(10) 1.406(5); C(10)-C(11) 1.362(4); P(1)-Ru-P(2)
96.81(4); P(1)-C(6)-C(3) 116.9(2); Ru-P(1)-C(6) 69.6(1);
Ru-P(1)-C(12) 124.1(1); Ru-P(1)-C(18) 130.4(1).
the η3-interaction with the metal. As a result, all ortho-
protons in the PPh3 ligand should have a contribution
derived from the interaction with the metal in their
chemical shifts, leading to a low-frequency position in
1
the H NMR spectrum. In any case, the NMR spectra
of 4 and the dynamic process responsible for their
temperature dependence are rather complicated and not
straightforward to figure out. Hence, our interpretation
must be considered only as tentative. In ruthenium
chemistry, the systems shown in Scheme 1 display a
behavior closely related to that of 4.29-31 All these
systems, which have been subjected to very detailed
NMR studies29,30 as well as to X-ray structure analysis
in several instances, attain the 18-electron configuration
by coordination of one of the biaryl double bonds to
ruthenium. They also exhibit a dynamic behavior in
solution involving double bond dissociation, and these
processes have been studied by 2D-NMR exchange
spectroscopy.29,30 Thus, the coordination of the CdC
bond to the metal is weak and therefore can be displaced
by ligands such as N2. In fact, it appears to occur an
equilibrium between the dinitrogen complex 2d and 4
in dichloromethane solution under dinitrogen:
bonds of a phenyl substituent of the PPh3 ligand. In this
way the system attains the 18-electron configuration.
Thus, the PPh3 ligand is acting as a chelating ligand,
which binds to the metal through the phosphorus atom
and simultaneously through a π-interaction involving
two carbon atoms of one of the phenyl rings, in a fashion
which resembles the coordination of π-allyls. The ru-
thenium atom is located out of the plane of the phenyl
ring, and unsymmetrically bonded to the carbon atoms
C(6) (Ru-C(6) 2.371(3) Å) and C(7) (Ru-C(7) 2.459(3)
Å). This type of η3-coordination greatly distorts the PPh3
ligand, as suggested by the value of 69.56(10)° for the
angle Ru-P(1)-C(6) in comparison with the values of
124.1(1)° and 130.4(1)° found respectively for the angles
Ru-P(1)-C(12) and Ru-P(1)-C(18). The dihedral angle
formed by the plane defined by the atoms Ru-C(6)-
C(7) and the plane of the phenyl ring is 58.2°. These
structural features match very well those reported very
recently for the complex [CpMo(CO)2(η3-PPh3)][BAr′4],28
which constitutes the first structurally characterized
example of a complex containing a four-electron donor
chelating η3-PPh3 ligand. By considering the molecular
structure of 4, we might attribute to the protons
attached to the η3-phenyl ring the mutiplet signals
observed around 6.2 ppm in the 1H NMR spectrum.
However, and at variance with the complex [CpMo(CO)2-
(η3-PPh3)]+,28 two multiplets are observed in our case.
These multiplets at 6.17 and 6.26 ppm correlate with
two doublet resonances at 85.4 and 87.6 ppm in the 13C-
{1H} NMR spectrum, as shown by a 2D-HETCOR NMR
experiment. It is likely that rapid phenyl ring scram-
bling takes place in solution. This means that all of the
phenyl rings should be exchanging and participating in
[CpRu(N2)(PPh3)(PMeiPr2)]+
a
2d
+ + N2
[CpRu(η3 - PPh3)(PMeiPr2)]
4
At low temperature, the equilibrium is shifted to the
dinitrogen complex, whereas higher temperatures favor
N2 dissociation, in analogy with what happens in the
system [CpFe(N2)(dippe)]+.24
We can conclude that if there are aromatic substitu-
ents present in a phosphine ligand, either monodentate
as PPh3 or bidentate as BINAP or related ligands,29-31
the stabilization of coordinatively unsaturated species
by coordination of double bonds of the arene substitu-
ents becomes feasible. One of these systems is the often-
invoked 16-electron {[CpRu(PPh3)2]+} fragment,1 which
(29) Feiken, N.; Pregosin, P. S.; Trabesinger, G.; Scalone, M.
Organometallics 1997, 16, 537.
(30) Feiken, N.; Pregosin, P. S.; Trabesinger, G.; Albinati, A.; Evoli,
G. L. Organometallics 1997, 16, 5756.
(28) Cheng, T.-Y.; Szalda, D. J .; Bullock, R. M. J . Chem. Soc., Chem.
Commun. 1999, 1629.
(31) Pathak, D. D.; Adams, H.; Bailey, N. A.; King, P. J .; White, C.
J . Organomet. Chem. 1994, 479, 237.

Half-Sandwich Ru Dinitrogen Complexes
Organometallics, Vol. 21, No. 4, 2002 635
is involved in many catalytic transformations,32 and it
is a binding site for many small molecules. We have
actually isolated a yellow glassy solid from the reaction
of [CpRuCl(PPh3)2] with NaBAr′4 in fluorobenzene
under argon. All attempts to obtain a crystalline mate-
rial have been so far unsuccessful. However, the NMR
of the crude product shows two multiplet signals at 6.16
and 6.23 ppm, very much like those displayed by
compound 4. Likewise, two doublets were observed in
the 13C{1H} NMR spectrum at 85.4 and 87.6 ppm in
connection with the mentioned proton resonances. The
31P{1H} NMR consists of one very broad feature at room
temperature, which apparently splits into two broad
resonances at -85 °C. Although the material was not
obtained in pure form, these data support the existence
of the fragment {[CpRu(PPh3)2]+} in the form of a
complex containing CdC bonds coordinated to ruthe-
nium in the same fashion as in compound 4, and hence
it should be formulated as [CpRu(η3-PPh3)(η1-PPh3)]+.
in some instances. In most cases, the direct reaction of
[CpRu(P)2]+ with N2 leads to the corresponding terminal
dinitrogen complexes [CpRu(N2)(P)2]+. From the struc-
tural point of view, both bridging and terminal N2
complexes have similar features, with slight differences
in the N-N bond distance, which is longer in the case
of a bridging dinitrogen ligand. Stabilization of 16-
electron species [CpRu(P)2]+ is feasible when aromatic
substituent groups are present in any of the phosphine
ligands, by coordination of one of the CdC bonds of the
arene substituents to the metal, as it has been observed
for [CpRu(PMeiPr2)(η3-PPh3)][BAr′4]. This unusual co-
ordination mode is apparently preferred over the sta-
bilization by agostic interaction for attaining the 18-
electron configuration in these complexes.
Ack n ow led gm en t. We thank the Ministerio de
Educacio´n y Cultura of Spain (DGICYT, Project PB97-
1357, Accion Integrada HU-1998-0026, PN99-EXT) for
financial support, J ohnson Matthey plc for generous
loans of ruthenium trichloride, and the Royal Society
of Chemistry for the award of a grant for international
authors (to M.J .T.).
Con clu sion s
At variance with their Cp* counterparts, the cationic
16-electron complexes [CpRu(P)2]+ display an enormous
avidity for dinitrogen, being capable of scavenging it
from high-purity argon, resulting in the formation of
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
structural data, including data collection parameters, posi-
tional and thermal parameters, and bond distances and angles
for complexes 1a , 1b, 2a , 3, and 4. This material is available
free of charge via the Internet at http://pubs.acs.org.
dinitrogen-bridged complexes [{CpRu(P)2}2(µ-N2)]2+
,
which have been isolated and structurally characterized
(32) Naota, T.; Takaya, H.; Murahashi, S. Chem. Rev. 1998, 98,
2599.
OM010730V