Synthesis, structure, and reactivity of ruthenium(II) terminal imido complexes

Article abstract of DOI:10.1021/om9609473

The reactions of [(η⁶-cymene)RuCl₂]₂ and [(η⁶-C₆Me₆)RuCl₆]₂ with LiNH-R (R = 2,6-diisopropylphenyl (Ar), 2,6-dimethylphenyl (Ar′), 2,4,6-tri-tert-butylphenyl (Ar*)) lead to a number of different products depending on the nature of ligands employed. The addition of 2 equiv of LiNHAr to [(η⁶-C₆Me₆)RuCl₂]₂ gives the amido complex (η⁶-C₆Me₆)RuCl(NHAr). Reaction of 4 equiv of the lithium amides with the ruthenium complex [(η⁶-cymene)RuCl₂]₂ or [(η⁶-C₆Me₆)RuCl₂]₂ yields imido complexes. The steric bulk of the substituents on either the η⁶-arene or nitrogen influence the structure of the final product. Large ligands such as the η⁶-C₆Me₆ or the Ar* group prevent the formation of bridged complexes, while combinations of ligands which have smaller steric requirements give dimeric compounds. The structures of (η⁶-cymene)RuCl₂(NH₂Ar), (η⁶-C₆Me₆)RuCl(NHAr), and [(η⁶-cymene)Os(NAr)]₂ are presented and discussed in relation to the previously reported structures of [(η⁶-cymene)Ru(NAr)]₂ and (η⁶-cymene)Ru(≡NAr*).

Full text of DOI:10.1021/om9609473

Organometallics 1997, 16, 1203-1208
1203
Syn th esis, Str u ctu r e, a n d Rea ctivity of Ru th en iu m (II)
Ter m in a l Im id o Com p lexes
Anthony K. Burrell* and Andrew J . Steedman
Department of Chemistry, Massey University, Private Bag 11222,
Palmerston North, New Zealand
Received November 7, 1996X
The reactions of [(η6-cymene)RuCl2]2 and [(η6-C6Me6)RuCl2]2 with LiNH-R (R ) 2,6-
diisopropylphenyl (Ar), 2,6-dimethylphenyl (Ar′), 2,4,6-tri-tert-butylphenyl (Ar*)) lead to a
number of different products depending on the nature of ligands employed. The addition of
2 equiv of LiNHAr to [(η6-C6Me6)RuCl2]2 gives the amido complex (η6-C6Me6)RuCl(NHAr).
Reaction of 4 equiv of the lithium amides with the ruthenium complex [(η6-cymene)RuCl2]2
or [(η6-C6Me6)RuCl2]2 yields imido complexes. The steric bulk of the substituents on either
the η6-arene or nitrogen influence the structure of the final product. Large ligands such as
the η6-C6Me6 or the Ar* group prevent the formation of bridged complexes, while combinations
of ligands which have smaller steric requirements give dimeric compounds. The structures
of (η6-cymene)RuCl2(NH2Ar), (η6-C6Me6)RuCl(NHAr), and [(η6-cymene)Os(NAr)]2 are pre-
sented and discussed in relation to the previously reported structures of [(η6-cymene)Ru-
(NAr)]2 and (η6-cymene)Ru(tNAr*).
In tr od u ction
Previous work has shown that the preference for
bridged or monomeric imido complexes can be controlled
by adjusting the steric requirements of the ancillary
ligands or the organic group on the imido ligand.8 Using
a more sterically demanding imido ligand, it is possible
to isolate complexes that contain monomeric imidos.7
Here we report the synthesis and structures of d6
ruthenium imido complexes. Portions of this work have
been communicated previously.5
The number of transition metal imido complexes has
grown dramatically in recent years1,2 with one notable
exception, low-valent terminal imido compounds. Tran-
sition metal complexes that contain terminal imido
ligands with d-electron counts other than d0-4 are
represented by only a few examples.3 Complexes of this
type tend to be reactive, displaying nucleophillic behav-
ior at the imido carbon. Thus, many of the d6 imido
complexes react with small molecules that contain
multiple bonds. In particular the reaction of Cp*Ir(tN-
t-Bu) with MeO2CCtCCO2Me in which the IrtN bond
is cleaved to form an η4-pyrrole is intriguing.
It is possible reactions of this type could be extended
to other substrates by varying the transition metal or
the nature of the imido and ancillary ligands. Extend-
ing the chemistry of these complexes in this fashion has
proved difficult. The second-row analogues of the
known complexes have not been reported. Terminal
imido complexes of rhodium are poorly characterized,4
and until recently5 only a single well-characterized
example of a d4 ruthenium terminal imido complex was
known.6 The ruthenium analogue of the d6 osmium
complexes appeared to form bridged complexes.7
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Unless otherwise noted all
reactions and manipulations were performed under an inert
atmosphere in a Innovative Technologies drybox. Nuclear
magnetic resonance spectroscopy was performed at 6.34 T on
a J EOL GX270W spectrometer operating at 270 MHz for 1H.
1H NMR spectra were referenced to benzene at 7.15 ppm, and
13C NMR were referenced to benzene at 128 ppm. Elemental
analysis was carried out at the microanalytical laboratory of
the University of Otago, Dunedin, New Zealand. Infrared
spectra were recorded on a BIO-RAD FTS-40 spectrophotom-
eter as a thin film of Nujol mull between KBr disks. Benzene,
toluene, and THF were distilled from sodium/benzophenone.
Pentane, hexane, and hexamethyldisiloxane were distilled
from sodium/potassium alloy, and deuterated benzene was
distilled from sodium/benzophenone. Lithium amides were
prepared from the freshly distilled anilines by treatment with
n-butyllithium in benzene. [(η6-C6Me6)RuCl2]2, [(η6-cymene)-
RuCl2]2,9 and 2,4,6-tri-tert-butylaniline10 were prepared from
literature methods. Unless otherwise noted, all other reagents
were used as received from commercial suppliers.
X Abstract published in Advance ACS Abstracts, February 1, 1997.
(1) Wigley, D. E. Prog. Inorg. Chem 1994, 42, 239-482.
(2) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds; J ohn
Wiley: New York, 1988.
(3) (a) Glueck, D. S.; Green, J . C.; Michelman, R. I.; Wright, I. N.
Organometallics 1992, 11, 4221-5. (b) Michelman, R. I.; Andersen, R.
A.; Bergman, R. G. J . Am. Chem. Soc. 1991, 113, 5100-2. (c)
Michelman, R. I.; Bergman, R. G.; Andersen, R. A. Organometallics
1993, 12, 2741-51. (d) Michelman, R. I. Ph.D. Thesis, UC Berkeley,
1993. (e) Michelman, R. I.; Ball, G. E.; Bergman, R. G.; Andersen, R.
A. Organometallics 1994, 13, 869-81. (f) Baranger, A. M.; Hollander,
F. J .; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 7890-1. (g) Dobbs,
D. A.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 3836-7. (h) Glueck,
D. S.; Wu, J .; Hollander, F. J .; Bergman, R. G. J . Am. Chem. Soc. 1991,
113, 2041-54. (i) Glueck, D. S.; Hollander, F. J .; Bergman, R. G. J .
Am. Chem. Soc. 1989, 111, 2719-21.
(6) Danopoulos, A. A.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse,
M. B. Polyhedron 1992, 11, 2961-4.
(7) Kee, T. P.; Park, L. Y.; Robbins, J .; Schrock, R. R. J . Chem. Soc.,
Chem. Commun. 1991, 121-2.
(8) Burrell, A. K.; Bryan, J . C. Angew. Chem. 1993, 105, 85-86;
Burrell, A. K.; Clark, D. L.; Gordon, P. L.; Sattelberger, A. P.; Bryan,
J . C. J . Am. Chem. Soc. 1994, 116, 3813-3821 and references therein.
(9) (a) Blake, R. E.; Heyn, R. H.; Tilly, T. D. Polyhedron 1992, 11,
709. (b) Bennett, M. A.; Huang, T.-N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1982, 21, 74.
(10) (a) Cillinane, N. M.; Leyshon, D. M. J . Chem. Soc. 1954, 2942.
(b) Barlett, D. B.; Roha, M.; Stiles, M. R. J . Am. Chem. Soc. 1954, 76,
2349.
(4) McGlinchey, M. J .; Stone, F. G. A. J . Chem. Soc., Chem.
Commun. 1970, 1265.
(5) Burrell, A. K.; Steedman, A. J . J . Chem. Soc., Chem. Commun.
1995, 2109-10.
S0276-7333(96)00947-8 CCC: $14.00 © 1997 American Chemical Society

1204 Organometallics, Vol. 16, No. 6, 1997
Burrell and Steedman
[(η6-C6Me6)Ru (µ-NAr ′)]2. A solution of LiNHAr′ (75 mg,
0.6 mmol) in THF (5 mL) was added to a THF (10 mL)
suspension of [(η6-C6Me6)RuCl2]2 (100 mg, 0.150 mmol). This
mixture was stirred at room temperature for 12 h after which
it was black color. The THF was removed in vacuo and the
dark solid extracted with benzene and filtered through Celite.
Evaporation of the benzene gave 33 mg of a brown product in
29% yield. The product can be recrystallized from pentane at
-35 °C. Anal. Calcd: C, 62.80; H, 7.11; N, 3.66. Found: C,
62.11; H, 7.62; N, 3.73. 1H NMR (C6D6): δ 7.30 (d, J ) 7.3,
2H, Me2C6H3), 7.17 (t, J ) 7.3, 1H, Me2C6H3), 2.45 (s, 6H,
Me2C6H3)), 2.11 (s, 18H, C6Me6). 13C NMR: δ 166.4 (Me2C6H3),
125.7 (Me2C6H3), 124.0 (Me2C6H3), 121.1 (Me2C6H3), 89.6 (C6-
Me6), 19.6 (Me2C6H3), 18.2 (C6Me6).
through Celite. Evaporation of the benzene gave 76 mg of a
green product in 47% yield. The product can be recrystallized
from pentane at -35 °C. Anal. Calcd: C, 67.98; H, 8.76; N,
2.83. Found: C, 67.38; H, 8.66; N, 2.70. 1H NMR: δ (s, 2H,
(CMe3)3C6H2), 5.11 (d, J ) 6.2, 2H, MeC6H4CHMe2), 5.03 (d, J
) 6.2, 2H, MeC6H4CHMe2), 2.65 (sept, J ) 6.8, 1H, MeC6-
H4CHMe2), 2.01 (s, 3H, MeC6H4CHMe2), 1.87 (s, 18H, (CMe3)2-
C6H2CMe3), 1.26 (s, 9H, (CMe3)2C6H2CMe3), 1.19 (d, J ) 6.9,
6H, MeC6H4CHMe2). 13C NMR: δ 157.9 (CMe3C6H2(CMe3)2),
148.1 (CMe3C6H2(CMe3)2), 145.6 (CMe3C6H2(CMe3)2), 121.7
(CMe3C6H2(CMe3)2), 102.4 (MeC6H4CHMe2), 90.3 (MeC6H4-
CHMe2), 79.4 (MeC6H4CHMe2), 77.4 (MeC6H4CHMe2), 38.0
(CMe3C6H2(CMe3)2), 35.5 (CMe3C6H2(CMe3)2), 32.9 (MeC6H4-
CHMe2), 31.5 (CMe3C6H2(CMe3)2), 31.2 (CMe3C6H2(CMe3)2),
23.9 (MeC6H4CHMe2), 20.8 (MeC6H4CHMe2).
(η6-C6Me6)Ru tNAr *. A solution of LiNHAr* (165 mg,
0.617 mmol) in THF (5 mL) was added to a THF (10 mL)
suspension of [(η6-C6Me6)RuCl2]2 (100 mg, 0.150 mmol). This
mixture was stirred at room temperature for 12 h after which
it was a deep-green color. The THF was removed in vacuo
and the black-green solid extracted with benzene and filtered
through Celite. Evaporation of the benzene gave 63 mg of a
deep green product in 40% yield. The product can be recrys-
tallized from pentane at -35 °C. Anal. Calcd: C, 68.93; H,
9.06; N, 2.68. Found: C, 68.48; H, 9.79; N, 3.39. 1H NMR: δ
7.20 (s, 2H, (CMe3)3C6H2), 2.11 (s, 18H, C6Me6), 1.81 (s, 18H,
CMe3C6H2(CMe3)2), 1.27 (s, 9H, CMe3C6H2(CMe3)2). 13C
NMR: δ 146.9 (CMe3C6H2(CMe3)2), 128.7 (CMe3C6H2(CMe3)2),
128.4 (CMe3C6H2(CMe3)2), 121.6 (CMe3C6H2(CMe3)2), 89.2 (C6-
Me6), 38.2 (CMe3C6H2(CMe3)2), 31.3 (CMe3C6H2(CMe3)2), 30.9
(CMe3C6H2(CMe3)2), 30.6 (CMe3C6H2(CMe3)2), 18.2 (C6Me6).
(η6-C6Me6)Ru Cl(NHAr ). A solution of LiNHAr (54 mg,
0.28 mmol) in THF (5 mL) was added to a THF (10 mL)
suspension of [(η6-C6Me6)RuCl2]2 (100 mg, 0.150 mmol). This
mixture was stirred at room temperature for 12 h after which
it was a dark red color. The THF was removed in vacuo and
the dark red solid then extracted with toluene and filtered
through Celite. Removal of the toluene to a minimal volume
and cooling to -35 °C gave 93 mg of a red crystalline solid in
65% yield. Anal. Calcd: C, 60.67; H, 7.64; N, 2.95. Found:
C, 60.07; H, 7.81; N, 3.06. 1H NMR: δ 10.18 (s, 1H, NH), 7.26
(d, J ) 7.0, 2H, (Me2CH)2C6H3), 7.18 (t, J ) 7.0, 1H, (Me2-
CH)2C6H3), 3.63 (sept, J ) 6.6, 2H, (Me2CH)2C6H3), 1.69 (s,
18H, e, C6Me6), 1.16 (d, J ) 7.0, 12H, (Me2CH)2C6H3). 13C
NMR: δ 152.5 ((Me2CH)2C6H3), 142.6 ((Me2CH)2C6H3), 124.7
((Me2CH)2C6H3), 122.2 ((Me2CH)2C6H3), 88.0 (C6Me6), 28.3
((Me2CH)2C6H3), 28.1 ((Me2CH)2C6H3), 15.8 (C6Me6).
(η6-cym en e)Ru Cl2(NH2Ar ). A solution of NH2Ar (73 mg,
0.412 mmol) in toluene (5 mL) was added to a toluene (10 mL)
suspension of [(η6-cymene)RuCl2]2 (250 mg, 0.204 mmol). This
mixture was stirred at room temperature for 12 h. The toluene
was then removed in vacuo leaving 150 mg of a yellow product
in 76% yield. The product can be recrystallized from a
toluene-pentane soultion at -35 °C. Anal. Calcd: C, 54.65;
H, 6.88; N, 2.90. Found: C, 54.38; H, 6.61; N, 2.97. IR
(KBr): 3300 (w), 3252 (w), 1605 (w), 1580 (w), 1169 (w), 1029
(m), 877 (w), 800 (m), 760 (w), 719 (w) cm-1
.
1H NMR: δ (d,
J
) 0.8, 2H, (Me2CH)2C6H3), 7.27 (t, J ) 0.8, 1H, (Me2-
CH)2C6H3), 4.96 (d, J ) 6.2, 2H, MeC6H4CHMe2), 4.82 (d, J )
6.2, 2H, MeC6H4CHMe2), 4.76 (br s, 2H, NH2), 3.44 (sept, J )
6.7, 2H, (Me2CH)2C6H3), 2.91 (sept, J ) 7.0, 1H, MeC6H4-
CHMe2), 2.09 (s, 3H, MeC6H4CHMe2), 1.32 (d, J ) 6.9, 12H,
(Me2CH)2C6H3), 1.28 (d, J ) 7.0, 6H, MeC6H4CHMe2). 13C
NMR: δ 139.0 ((Me2CH)2C6H3), 123.5 ((Me2CH)2C6H3), 123.4
((Me2CH)2C6H3), 105.3 ((Me2CH)2C6H3), 94.3 (MeC6H4CHMe2),
82.8 (MeC6H4CHMe2), 77.0 (MeC6H4CHMe2), 31.0 (MeC6H4-
CHMe2), 27.7 ((Me2CH)2C6H3), 22.4 ((Me2CH)2C6H3), 22.1
(MeC6H4CHMe2), 17.7 (MeC6H4CHMe2).
[(η6-cym en e)Ru (µ-NAr )]2. Meth od a . A solution of LiN-
HAr (122 mg, 0.666 mmol) in THF (5 mL) was added to a THF
(10 mL) suspension of [(η6-cymene)RuCl2]2 (100 mg, 0.163
mmol). This mixture was stirred at room temperature for 12
h after which it was a deep-green color. The THF was removed
in vacuo and the green-black solid extracted with benzene and
filtered through Celite. Evaporation of the benzene gave 50
mg of a green-black product in 37% yield. The product can be
recrystallized from pentane at -35 °C. Anal. Calcd: C, 64.36;
H, 7.61; N, 3.41. Found: C, 64.53; H, 7.82; N, 3.54. 1H NMR:
(C6D6): δ 7.33 (d, J ) 1.8, 2H, (Me2CH)2C6H3), 7.20 (t, J )
0.9, 1H, (Me2CH)2C6H3), 4.74 (d, J ) 5.9, 2H, MeC6H4CHMe2),
4.55 (d, J ) 5.9, 2H, MeC6H4CHMe2), 3.61 (br s, -, 2H,
(Me2CH)2C6H3), 2.52 (sept, J ) 6.8, 1H, MeC6H4CHMe2), 1.76
(s, 3H, MeC6H4CHMe2), 1.43 (d, J ) 6.6, 12H, (Me2CH)2C6H3),
1.03 (d, J ) 6.6, 6H, MeC6H4CHMe2). 13C NMR: (C6D6): δ
167.7 ((Me2CH)2C6H3), 128.7 ((Me2CH)2C6H3), 123.3 ((Me2-
CH)2C6H3), 122.9 ((Me2CH)2C6H3), 102.1 (MeC6H4CHMe2), 90.8
(MeC6H4CHMe2), 77.7 (MeC6H4CHMe2), 77.6 (MeC6H4CHMe2),
30.8 (MeC6H4CHMe2), 26.7 ((Me2CH)2C6H3), 26.5 ((Me2-
CH)2C6H3), 24.0 (MeC6H4CHMe2), 19.1 (MeC6H4CHMe2).
(η6-C6Me6)Ru N(P h )C(O)N(Ar ). A solution of (η6-C6Me6)-
RuCl(NHAr) (100 mg, 0.210 mmol) in benzene (10 mL) was
added to a solution of phenyl isocyanate (26 mg, 0.218 mmol)
in benzene (5 mL). This mixture was stirred at room temper-
ature for 12 h after which it was a yellow color. The benzene
was removed in vacuo, and the yellow solid was extracted with
toluene and filtered through Celite. Reduction in volume of
the toluene gave 67 mg of a yellow product in 57% yield. The
product can be recrystallized from a toluene pentane soultion
at -35 °C. IR (KBr): 2965 (m), 2925 (m), 2292 (m), 1777 (s),
1718 (s), 1596 (s), 1500 (s), 1443 (s), 1385 (m), 932 (w), 768
(m) cm-1
. Anal. Calcd: C, 66.75; H, 7.23; N, 5.02. Found:
C, 66.14; H, 7.42; N, 5.13. 1H NMR: δ 7.30 (m, 5H, Ph), 7.18
(t, J ) 7.7, 1H, (Me2CH)2C6H3), 7.07 (d, J ) 8.1, 2H, (Me2-
CH)2C6H3), 3.13 (br s, 2H, (Me2CH)2C6H3), 2.08 (s, 18H, C6Me6),
1.17 (d, J ) 6.2, 12H, (Me2CH)2C6H3). 13C NMR: δ 170.4 (CO).
152.4 ((Me2CH)2C6H3), 140.2 (C6H5), 129.0 (C6H5), 127.4 ((Me2-
CH)2C6H3), 127.2 ((Me2CH)2C6H3), 125.6 (C6H5), 123.9 (C6H5),
120.8 ((Me2CH)2C6H3), 89.4 (C6Me6), 25.9 ((Me2CH)2C6H3), 25.1
((Me2CH)2C6H3), 18.0 (C6Me6).
(η6-cym en e)Ru tNAr *. A solution of LiNHAr* (179 mg,
0.669 mmol) in THF (5 mL) was added to a THF (10 mL)
suspension of [(η6-cymene)RuCl2]2 (100 mg, 0.163 mmol). This
mixture was stirred at room temperature for 12 h after which
it was a deep-green color. The THF was removed in vacuo,
and the green solid was extracted with benzene and filtered
Meth od b. A solution of potassium bis(trimethylsilyl)amide
(83 mg, 0.416 mmol) in benzene (5 mL) was added to a benzene
(10 mL) suspension of (η6-cymene)RuCl2(NH2Ar) (100 mg,
0.207 mmol). This mixture was stirred at room temperature
for 12 h after which to give deep-green color. The benzene
was removed in vacuo, and the green-black solid was extracted
with toluene and filtered through Celite. Evaporation of the
toluene and recrystallization from pentane at -35 °C gave 58
mg of a green-black product (in 68% yield) that had spectro-
scopic properties identical to those of the compound isolated
in method a.
[(η6-cym en e)Ru (µ-NAr ′)]2. A solution of LiNHAr′ (85 mg,
0.669 mmol) in THF (5 mL) was added to a THF (10 mL)
suspension of [(η6-cymene)RuCl2]2 (100 mg, 0.163 mmol). This

Ru(II) Terminal Imido Complexes
Organometallics, Vol. 16, No. 6, 1997 1205
Ta ble 1. Cr ysta l Da ta for (η6-cym en e)Ru Cl2(NH2Ar ), (η6-C6Me6)Ru Cl(NHAr ), a n d [(η6-cym en e)Os(NAr )]2
identification code
empirical formula
(η6-cymene)RuCl2(NH2Ar)
(η6-C6Me6)RuCl(NHAr)
C24H35ClNRu
[(η6-cymene)Os(NAr)]2
C44H62N2Os2
C22H33Cl2NRu
fw
483.46
474.05
999.36
temp, K
291(2)
168(2)
183(2)
wavelength, Å
cryst system
space group
a, Å
0.710 73
monoclinic
Cc (No. 9)
19.865(4)
0.710 73
monoclinic
P21/c (No. 14)
9.699(7)
0.710 73
monoclinic
P21/c (No. 14)
19.733(7)
b, Å
6.930(4)
14.095(14)
10.254(2)
c, Å
33.57(2)
16.758(10)
19.378(4)
R, deg
90
98.47(3)
90
4571(4)
90
90
99.38(3)
90
3869(2)
â, deg
100.82(8)
90
2250(3)
γ, deg
V, Å3
Z
8
4
4
D(calcd), Mg/m
abs coeff, mm-1
F(000)
1.405
0.926
2000
1.399
0.824
988
1.716
6.595
1968
cryst size, mm
θ range for data collcn, deg
index ranges
0.70 × 0.70 × 0.50
0.64 × 0.20 × 0.06
0.41 × 0.45 × 0.11
1.23-24.99
2.14-18.00
1.05-24.98
0 e h e 23, 0 e k e 8,
-39 e l e 39
4149
-10 e h e 0, 0 e k e 15,
-17 e l e 17
1665
-23 e h e 23, -12 e k e 0,
0 e l e 23
7012
no. of collcd reflns
indepdt reflns
refinment method
4149 (Rint ) 0.0000)
full-matrix least squares of F2
4144/2/481
1547 (Rint ) 0.1763)
full-matrix least squares of F2
1539/132/239
6786 (Rint ) 0.0837)
full-matrix least squares of F2
6786/0/433
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.061
1.059
1.032
R1 ) 0.0262, wR2 ) 0.0842
R1 ) 0.0371, wR2 ) 0.0977
0.503 and -0.413
R1 ) 0.0825, wR2 ) 0.1584
R1 ) 0.1579, wR2 ) 0.1945
0.764 and -0.669
R1 ) 0.0374, wR2 ) 0.1006
R1 ) 0.0524, wR2 ) 0.1091
1.936 and -1.931
largest diff peak and hole, e‚Å-3
mixture was stirred at room temperature for 12 h after which
it was a brown color. The THF was removed in vacuo, and
the brown solid was extracted with toluene and filtered
through Celite. Removal of the toluene to minimal volume
and cooling to -35 °C gave 44 mg of a brown crystalline
product in 38% yield. Anal. Calcd: C, 60.99; H, 6.54; N, 3.95.
Found: C, 60.43; H, 6.51; N, 4.14. 1H NMR: (C6D6): δ 7.33
(d, J ) 7.3, 2H, Me2C6H3), 7.17 (t, J ) 7.3, 1H, Me2C6H3), 4.37
(d, 6.0, 2H, MeC6H4CHMe2), 4.26 (d, J ) 5.9, 2H, MeC6H4-
CHMe2), 2.35 (s, 6H, Me2C6H3) 2.20 (sept, J ) 6.9, 1H,
MeC6H4CHMe2), 1.73 (s, 3H, MeC6H4CHMe2), 0.97 (d, J ) 7.0,
6H, MeC6H4CHMe2). 13C NMR: δ 169.7 (Me2C6H3), 127.7
(Me2C6H3), 126.0 (Me2C6H3), 121.6 (Me2C6H3), 100.6 (MeC6H4-
CHMe2), 89.2 (MeC6H4CHMe2), 81.8 (MeC6H4CHMe2), 79.2
(MeC6H4CHMe2), 31.7 (MeC6H4CHMe2), 23.7 (MeC6H4CHMe2),
19.6 (Me2C6H3),19.1 (MeC6H4CHMe2).
showed crystal decay of 35%, and a linear correction was
applied. No correction for extinction was applied.
Single crystals of (η6-cymene)RuCl2(NH2Ar) were grown by
the evaporation of a benzene solution. A orange cubic shaped
crystal was secured to the end of a glass fiber with epoxide.
Crystallographic data are summarized in Table 1, and all other
relevant data are available as Supporting Information. In-
tensity data were collected using an Enraf-Nonius CAD-4
diffractometer. The data were corrected for Lorentz, polariza-
tion, and X-ray absorption effects, the last by an empirical
method based on azimuthal scan data (Tmax:Tmin ) 0.9754:
0.5636). No correction for extinction was applied.
Single crystals of [(η6-cymene)Os(µ-NAr)]2 were grown by
the evaporation of a benzene solution. A dark purple hexagonal-
shaped crystal was secured to the end of a glass fiber with
silicone grease and then placed in a cold stream of nitrogen.
Crystallographic data are summarized in Table 1, and all other
relevant data are available as Supporting Information. In-
tensity data were collected using an Enraf-Nonius CAD-4
diffractometer. The data were corrected for Lorentz, polariza-
tion, and X-ray absorption effects, the last by an empirical
method based on azimuthal scan data (Tmax:Tmin ) 0.9357:
0.6366). No correction for extinction was applied.
X-r a y Exp er im en ta l Section
Gen er a l Meth od s. Crystallographic data are summarized
in Table 1, and all other relevant data are available as
Supporting Information. Scattering factors are included in
SHELX-93. The positions of the Ru or Os atoms were
determined from a Patterson synthesis. Calculations were
carried out using a IBM-compatible 486 computer and SHELX-
93.11 The remaining non-hydrogen atoms were located by
application of a series of alternating least-squares cycles and
difference Fourier maps. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Hydrogen atoms
were included in the structure factor calculations at idealized
positions but were not subsequently refined.
Resu lts
The general route for the synthesis of d6 imido
complexes is given in eqs 1 and 2.
[Cp*IrCl2]2 + 4LiNHR f
Single crystals of (η6-C6Me6)RuCl(NHAr) were grown by the
evaporation of a benzene solution. A red plate was secured to
the end of a glass fiber with silicone grease and then placed
in a cold stream of nitrogen. Some difficulties were encoun-
tered with mounting as significant crystal deterioration was
noted before the crystal was placed in the cold stream.
Intensity data were collected using a Siemens P4 diffracto-
meter. The data were corrected for Lorentz and polarization
effects. Systematic monitoring of three check reflections
2Cp*IrdNR + 2H2N-R + 4LiCl (1)
[η6C6Me6OsCl2]2 + 4LiNHR f
2η6-C6Me6OsdNR + 2H2NR + 4LiCl (2)
This procedure has been shown to be useful in the
synthesis of ruthenium compounds, but the yields are
somewhat lower and the products from initial studies
were clearly dimeric.7 The ability to influence the
preference for imido ligand bridging has been demon-
(11) Sheldrick, G. M. SHELXL-93, Institut fu¨r Anorganische Chemie
der Universita¨t Go¨ttingen, Germany, 1993.

1206 Organometallics, Vol. 16, No. 6, 1997
Burrell and Steedman
strated a number of times and appears to be strongly
dependent upon the steric requirements of the groups
on the imido.8 In the synthesis of d6 terminal imido
complexes of ruthenium both the size of the η6-arene
and the organic group on the imido can be changed to
adjust the steric pressure at the metal center. It should
be noted that all of the X-ray structures of the mono-
meric d6 terminal imido complexes presently known
have either η5-Cp* or η6-C6Me6 as the ancillary ligand.
The analogous ruthenium complex contained only an
η6-benzene ligand and was dimeric. It is reasonable to
consider that if the η6-C6Me6 ligand was employed in
the synthesis of ruthenium imidos, monomeric species
would be much more likely.
The reaction of [(η6-C6Me6)RuCl2]2 with 4 equiv of
LiNHAr′ gives a black solution which upon workup
yields a very reactive dark powder which analyses
correctly for (η6-C6Me6)RutNAr′. Although, the struc-
ture cannot be easily determined, it is most likely to be
dimeric, due to the relatively small size of the 2,6-
dimethylphenyl group.
F igu r e 1. Structure of (η6-C6Me6)RuCl(NHAr) with ther-
mal ellipsoids drawn at the 50% probability level. Selected
bond lengths (Å): Ru-N, 1.94, Ru-Cl, 2.383(7).
The use of larger anilines should reduce the possibility
of forming dimeric species. Thus, the reaction of [(η6-
C6Me6)RuCl2]2 with 4 equiv of LiNHAr over a period of
12 h gives a very dark green solution that decomposes
to an unidentifiable mixture. Any attempt at workup
accelerates the decomposition preventing characteriza-
tion. However, if the reaction is halted after only 1 h,
a small amount of a red crystalline compound can be
as a signal at 170.4 ppm. This is a reasonable indication
of the presence of a terminal imido complex such as (η6-
C6Me6)Ru(tNAr).
If a larger imido ligand is employed, a more stable
complex can be obtained. This compound analyses for
(η6-C6Me6)Ru(tNAr*), and due to the bulky nature of
the ligands we believe it to be a monomeric complex
shown in Scheme 3. It was not possible to obtain
crystals of (η6-C6Me6)Ru(tNAr*) suitable for X-ray
diffraction. Treatment with proton sources such as
alcohols or water results in decomposition and the
isolation of only H2NAr*. While this combination of
ligands enables the isolation of a relatively stable
complex, the steric constraints they impose limit the
reactivity of the imido ligand. The η6-cymene ligand is
less sterically demanding than hexamethylbenzene, but
previous work7a,b indicated that it should provide enough
protection to enable the isolation of monomeric com-
plexes. Therefore, the use of cymene as an ancillary
ligand was investigated.
1
isolated. The H NMR of this compound indicates the
presence of both the η6-C6Me6 ligand and the 2,6-
diisopropylphenyl group, in a 1:1 ratio. The only other
resonance present is a 1 proton signal that appears at
10.18 ppm. These data combined with the elemental
analysis provide a formulation of (η6-C6Me6)RuCl-
(NHAr). This compound can be obtained in better yield
by reacting 1.8 equ of LiAr with [(η6-C6Me6)RuCl2]2.
This amido complex is highly reactive and decomposes
slowly even under argon at low temperature. However,
on one occasion single crystals suitable for X-ray dif-
fraction were obtained. These crystals were extremely
unstable, but a rapid collection of X-ray data was carried
out and the structure determined (Table 1).
The structure (Figure 1) shows the coordination about
the ruthenium as a two-legged piano-stool. The aryl
group of the amido ligand occupies a geometry which
places the aromatic ring almost parallel to the η6-C6-
Me6 ring. The mean planes of each of the rings are
tilted at an angle of 5(1)° to each other. The isopropyl
groups are bent away to minimize any steric interac-
tions with the methyl’s of the η6-arene.
This complex is effectively an imido precursor as
treatment with base removes HCl to afford the putative
imido complex (η6-C6Me6)Ru(tNAr). Thus, treatment
of a solution of (η6-C6Me6)RuCl(NHAr) with either NEt3
or KN(TMS)2 causes an immediate color change from
red to green black. Once again it is not possible to
isolate any compounds from the resulting solution.
However, if the reaction with base is carried out in the
presence of a species that can react with a coordinated
imido ligand, such as PhNCO, a stable complex is
obtained. The yellow crystalline solid obtained analyses
correctly for (η6-C6Me6)Ru(NArCONPh). The carbonyl
group produces a very strong absorption in the IR
spectrum at 1718 cm-1 and is apparent in the 13C NMR
The reaction of [(η6-cymene)RuCl2]2 with 4 equiv of
LiNHAr′ gives a green solution which gives a dark green
solid upon workup. As with the hexamethylbenzene
analogue, it is not possible to determine the precise
structure of the complex (η6-cymene)RutNAr′. How-
ever the structure is most likely dimeric as shown in
Scheme 1. The reaction of [(η6-cymene)RuCl2]2 with 4
equiv of LiNHAr also gives a dark green solid in 37%
yield that correctly analyses for (η6-cymene)RutNAr.
An alternative synthesis of (η6-cymene)RutNAr proved
to be higher yielding (51% overall). Treatment of [(η6-
cymene)RuCl2]2 with 2,6-diisopropylanaline gives (η6-
cymene)RuCl2(NH2Ar) in 76% yield. This complex
crystallized as small yellow cubes suitable for X-ray
diffraction.
The structure of (η6-cymene)RuCl2(NH2Ar) shown in
Figure 2 (Table 2) has similarities to (η6-C6Me6)RuCl-
(NHAr) in that the orientation of the 2,6-diisopropyl-
phenyl group is effectively parallel to the plane of the
η6-arene. The mean planes of each of the rings are tilted
at an angle of 18.4(3)° to each other. The N-Ru

Ru(II) Terminal Imido Complexes
Organometallics, Vol. 16, No. 6, 1997 1207
Ta ble 2. Su m m a r y of Ru -N Bon d Len gth s
compd
Ru-N (Å)
ref
compd
Ru-N (Å)
ref
(η6-cymene)RuCl2(NH2Ar)
(η6-C6Me6)RuCl(NHAr)
[(η6-cymene)Ru(NAr)]2
2.18(1)
1.94(2)
1.974(8)
[(η6-C6H6)Ru(NAr)]2
1.974(8)
1.753(3)
7
5
(η6-cymene)Ru(tNAr*)
5
F igu r e 3. Structure of [(η6-cymene)Ru(NAr)]2. The hy-
drogen atoms have been omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)-N(1), 1.959(8), Ru-
(1)-N(2), 1.977(7), Ru(2)-N(1), 1.985(8), Ru(2)-N(2), 1.976-
(8), Ru(1)-Ru(2), 2.7515(12); Ru(1)-N(1)-Ru(2), 88.5(3),
Ru(1)-N(2)-Ru(2), 88.2(3), N(1)-Ru(1)-N(2), 78.5(3), N(1)-
Ru(2)-N(2), 77.9(3).
Figu r e 2. Structure of molecule 2 of (η6-cymene)RuCl2(NH2-
Ar) with thermal ellipsoids drawn at the 50% probability
level. Selected bond lengths (Å): Ru(2)-N(2), 2.15(1), Ru-
(2)-Cl(21), 2.429(4), Ru(2)-Cl(22), 2.418(5).
Sch em e 1
distance at 2.188(12) Å is significantly longer than the
Ru-N distance of 1.94(2) Å observed in the structure of
(η6-C6Me6)RuCl(NHAr).
F igu r e 4. Structure of [(η6-cymene)Os(NAr)]2. The hydro-
gen atoms have been omitted, from the top view, for clarity.
Selected bond lengths (Å) and angles (deg): Os(1)-N(1),
1.978(6), Os(1)-N(2), 1.986(6), Os(2)-N(1), 1.980(6), Os-
(2)-N(2), 1.970(6), Os(1)-Os(2), 2.8142(7); Os(1)-N(1)-
Os(2), 90.6(2), Os(1)-N(2)-Os(2), 90.7(2), N(1)-Os(1)-
N(2), 77.2(2), N(1)-Os(2)-N(2), 77.5(2).
Treatment of (η6-cymene)RuCl2(NH2Ar) with base
yields (η6-cymene)RutNAr in 68% yield. The structure5
is shown in Figure 3 and confirms that in the solid state
the complex exists as the dimeric species [(η6-cymene)-
Ru(µ2-NAr)]2. The structure is very similar to that of
the previously reported complex [(η6-C6H6)Ru(µ2-NAr)]2,8
in that there is a distinct deformation of the ruthenium-
nitrogen plane. The nitrogen atoms are bent some
1.132(7) Å above an ideal “flat” ruthenium-nitrogen
plane. Also the ruthenium-ruthenium distance, 2.814-
(1) Å, is short and falls within the range of known Ru-
Ru bonds. This is more likely due to the geometry
imposed by the bridging imido ligands than the presence
of a Ru-Ru bond. This is supported by the appearance
of only one signal for the isopropyl groups on the µ-NAr
ligands, indicating rapid inversion of the butterfly
structure in solution.
The dimeric nature of complex made us curious as to
why the analogous osmium complex, (η6-cymene)-
OstNAr, is monomeric. To answer this we prepared
(η6-cymene)OstNAr using the published procedure,3c
and crystals were grown from benzene solution. The
X-ray diffraction study (Table 1, Figure 4) proved that
the ruthenium and osmium complexes are effectively
isostructural. The structure of imido [(η6-cymene)Os-

1208 Organometallics, Vol. 16, No. 6, 1997
Burrell and Steedman
Sch em e 2
F igu r e 5. Structure of (η6-cymene)Ru(tNAr*), molecule
one. Selected bond lengths (Å) and angles (deg): Ru(1)-
N(1), 1.751(14), N(1)-C(121), 1.39(2); Ru(1)-N(1)-C(121),
178.5(12).
similar to that observed in the related osmium complex
(η6-C6Me6)OstN-t-Bu at 1.737(3) Å.3 Table 2 lists all
the Ru-N bonds for the structures presented and shows
a clear progression as the type of bond changes from
simple coordination in (η6-cymene)RuCl2(NH2Ar) through
to the imido bond in (η6-cymene)RutNAr*.12
Sch em e 3
Con clu sion
Sch em e 4
We have shown that it is possible to isolate d6
terminal imido complexes of ruthenium. Steric factors
can be used to dominate the propensity for these
complexes to dimerize and allow the isolation of a
monomeric compound. Complexes with combinations
of the less sterically demanding ligands such as [(η6-
C6H6)Ru(NAr)]2,7 [(η6-C6Me6)Ru(NAr′)]2, [(η6-cymene)-
5
Ru(NAr′)]2, and [(η6-cymene)Ru(NAr)]2 form dimeric
species. The use of more sterically demanding ligands
enables the isolation of terminal imido complexes such
as (η6-C6Me6)Ru(NAr*) and (η6-cymene)Ru(NAr*).5 Un-
fortunately, the need to provide steric protection to the
terminal imido also limits their reactivity. A compro-
mise between the need for protection and the desire for
reactivity can be reached if the correct combination of
ligands is employed. Such an example is found with
the complexes (η6-C6Me6)Ru(NAr) and (η6-cymene)Ru-
(NAr*), which are both monomeric and reactive toward
small molecules.12 We are continuing to explore differ-
ent combinations of ligands in an attempt to find the
correct balance of complex stability and imido ligand
reactivity.
(µ2-NAr)]2 is very similar to the imido complex [(η6-
cymene)Ru(µ2-NAr)]2. There is a deformation of the
osmium-nitrogen plane, and there is a short osmium-
osmium distance, 2.7515(12) Å. In the solid state these
complexes are clearly dimeric. For these compounds to
crystallize as dimers they must exist as dimeric com-
plexes in solution; however this does not rule out the
possibility of a monomer-dimer equilibrium. A variable
temperture NMR study3c has been previously carried
out on [(η6-cymene)Os(µ2-NAr)]2, and the low-tempera-
ture NMR data reported are consistent with the X-ray
structure. However, more work is required to precisely
determine the nature of the solution species.
While -NAr is generally considered a sterically
demanding ligand, -NAr* is more demanding still. The
reaction of 4 equiv of LiNHAr* with [(η6-cymene)RuCl2]2
in THF once again yields a deep-green colored solution
and a complex that has the formulation (η6-cymene)-
RutNAr* (Scheme 2). The only conclusive method for
determining the structure of this compound was single-
crystal X-ray analysis.5 The molecular geometry, shown
in Figure 5, clearly indicates that (η6-cymene)RutNAr*
is a monomeric complex containing a terminal imido
ligand. The averaged Ru-N-C angle is approximately
linear at 177.8(4)°. The averaged Ru-N distance, at
1.753(3) Å, is consistent with the multiple-bond char-
acter expected of a terminal imido ligand1,2 and com-
pares well with the only other structurally characterized
terminal imido complex of ruthenium, Ru(tNAr)2-
(PMe3)2, at 1.785(6) Å.6 The Ru-N distance is also
Ack n ow led gm en t. We are grateful for support of
this work from the Massey University Research Fund
and the New Zealand Lottery Grants Board.
Su p p or tin g In for m a tion Ava ila ble: For compounds (η6-
cymene)RuCl2(NH2Ar), (η6-C6Me6)RuCl(NHAr), and [(η6-cy-
mene)Os(NAr)]2, tables of crystal data, fractional atomic
coordinates and U values, bond distances and angles, aniso-
tropic thermal parameters, and hydrogen atom coordinates
and U values (24 pages). Ordering information is given on
any current masthead page.
OM9609473
(12) The cycloaddition chemistry of (η6-cymene)RutNAr* has re-
cently been reported: Danopoulos, A. A.; Wilkinson, G.; Sweet, T. K.
N.; Hursthouse, M. B. J Chem. Soc., Dalton Trans. 1996, 19, 3771-
3778.