New approach to Ru(II) pincer ligand chemistry. Bis(tert-butylaminomethyl)pyridine coordinated to ruthenium(II)

Article abstract of DOI:10.1021/ic990737t

Reaction of 2,6-bis-((t)BuNHCH₂)₂NC₅H₃ ('N₂py') with RuCl₂(PPh₃)₃ gives two isomers of Ru(N₂py)Cl₂(PPh₃), 5, while reaction with RuCl<

Full text of DOI:10.1021/ic990737t

Inorg. Chem. 2000, 39, 1593-1597
1593
New Approach to Ru(II) Pincer Ligand Chemistry. Bis(tert-butylaminomethyl)pyridine
Coordinated to Ruthenium(II)
Christian Gemel, Kirsten Folting, and Kenneth G. Caulton*
Department of Chemistry, Indiana University, Bloomington, Indiana 47405
ReceiVed June 24, 1999
Reaction of 2,6-bis-(tBuNHCH2)2NC5H3 (“N2py”) with RuCl2(PPh3)3 gives two isomers of Ru(N2py)Cl2(PPh3),
5, while reaction with RuCl2(DMSO)4 (DMSO ) Me2SO) gives isomerically pure Ru(N2py)Cl2(DMSO), whose
structure is reported. The PPh3 of 5 can be replaced by CO, P(OPh)3, or pyridine. The chlorides in Ru(N2py)-
Cl2(CO) can both be replaced by F3CSO3-. Isomer structure preferences are discussed, and the reaction of Ru-
(N2py)Cl2(pyridine) with O2 gives apparent oxidation of N2py to give the diimine.
Introduction
Si-H reaction chemistry, including catalyzed dehydrogenation
of alkanes.9-16 Class 2 ligands support similar reactivity.
In many catalytic reactions, coordinatively unsaturated com-
plexes appear as reactive intermediates at some stage. Such
species initiate catalytic processes (catalyst precursor) and, of
course, are part of catalytic cycles themselves. Thus, investiga-
tions of the factors controlling and affecting the reactivity and
stability of unsaturated compounds are very important not only
for intrinsic reasons but for the understanding of virtually all
homogeneously catalyzed processes. In the case of many 16-
electron ruthenium complexes, one of the stabilizing factors is
the presence of π-stabilizing ligands such as alkoxides, thiolates,
and even halides.1-3
It is our purpose here to report progress on a related goal:
pincer ligand chemistry of Ru with a secondary amine donor at
sites E. We are interested in exploring systematically the
comparison of nitrogen and phosphorus donors beyond their
classical distinctions of nitrogen as a hard and pure σ-donor
and phosphorus soft and a potential π-acid. Moreover, we have
decided to make the donors E secondary (i.e., NHtBu) rather
than tertiary amines for the specific purpose of having a reactive
hydrogen accompanied by a bulky but 3-fold symmetric
substituent. This substitution pattern (ligand abbreviation N2py
when E′ ) N) will give rise to both mirror and C2 symmetric
isomers 3, which are not anticipated to interconvert on the
Recently, the pincer ligand class (1) has experienced a
renaissance4 from its earliest incarnations in monometal coor-
dination chemistry. Here, E is a nitrogen or phosphorus donor
and E′ can be either a pyridine nitrogen or a ring sp2 carbon.
This ligand is most often found as a meridional ligand (i.e., E′
and the two E will be approximately coplanar in the metal
coordination sphere).
synthetic time scale when the nitrogens are coordinated. Isomer
3(m) clearly has a crowded (“up”) and an uncrowded (“down”)
The Fryzuk ligand class (2) has some similar characteristics
but seems more flexible in that it can occasionally occupy three
facial sites on a metal.5-8 Ligands of class 1 have been very
productive, when bound to Rh and Ir, in supporting C-H and
(7) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Organometallics 1996,
15, 3329.
(8) Fryzuk, M. D. Can. J. Chem. 1992, 70, 2849.
(9) van der Zeijden, A. A. H.; van Koten, G.; Nordemann, R. A.; Kojic-
Prodic, B.; Spek, A L. Organometallics 1988, 7, 1957.
(10) van der Zeijden, A. A. H.; van Koten, G.; Luijk, R.; Nordemann, R.
A.; Spek, A. L. Organometallics 1988, 7, 1549.
(11) van der Zeijden, A. A. H.; van Koten, G.; Nordemann, R. A.; Luijk,
R. Organometallics 1988, 7, 1556.
(12) Rietveld, M. H. P.; Grove, D. M.; van Koten, G. New J. Chem. 1997,
21, 751.
(13) Wehman-Ooyevaar, I. C. M.; Luitwieler, I. F.; Vatter, K.; Grove, D.
M.; Smeets, W. J. J.; Horn, E.; Spek, A. L.; van Koten, G. Inorg.
Chim. Acta 1996, 252, 55.
* To whom correspondence should be addressed. E-mail: caulton@
indiana.edu.
(1) Johnson, T. J.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. Soc.
1992, 114, 2725.
(2) Bickford, C. C.; Johnson, T. J.; Davidson, E. R.; Caulton, K. G. Inorg.
Chem. 1994, 33, 1080.
(3) Johnson, T. J.; Folting, K.; Streib, W. E.; Martin, J. D.; Huffman, J.
C.; Jackson, S. A.; Eisenstein, O.; Caulton, K. C. Inorg. Chem. 1995,
34, 288.
(14) Van der Boom, M. E.; Liou, S. Y.; Bendavid, T.; Gozin, M.; Milstein,
D. J. Am. Chem. Soc. 1998, 120, 13415.
(15) Lee, D. W.; Kaska, W. C.; Jensen, C. M. Organometallics 1998, 17,
1.
(4) Canty, A. J.; van Koten, G. Acc. Chem. Res. 1995, 28, 406.
(5) Fryzuk, M. D.; Mylvaganam, M.; Zaworotko, M. J.; MacGillivray,
L. R. Polyhedron 1996, 15, 689.
(6) Fryzuk, M. D.; Gao, X.; Rettig, S. J. J. Am. Chem. Soc. 1995, 117,
3106.
(16) Rosini, G. P.; Wang, K.; Patel, B.; Goldman, A. S. Inorg. Chim. Acta
1998, 270, 537.
10.1021/ic990737t CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/04/2000

1594 Inorganic Chemistry, Vol. 39, No. 7, 2000
Gemel et al.
1
Chart 1
5 h all peaks in the H spectrum disappear with a comparable
rate for both isomers.
Interestingly, the same reaction as for the preparation of 5,
that is, heating RuCl2(PPh3)3 to reflux in benzene or toluene
for 12 h in the presence of 1,3-(bis-tert-butylaminomethyl)-
benzene (N2bzH) does not give the expected C-H attack
product RuH(N2bz) complex, but rather almost pure starting
materials were recovered.
This suggests that an important step in the reaction of RuCl2-
(PPh3)3 with N2py is coordination of the pyridine nitrogen atom
followed by loss of PPh3 ligands and coordination of the
secondary aliphatic nitrogens. Perhaps this means that the
secondary amine nitrogens are incompetent Lewis bases to
RuCl2(PPh3)3 unless the pyridine nitrogen can initiate binding
to Ru. These observations are consistent with other reports where
phenyl-based Ru(II) pincer ligand complexes cannot be made
by C-H oxidative addition;19,20 the aryllithium salt of the ligand
has to be used as the starting material rather than the free ligand
itself.21-23
sides, while in 3(C2) these are equivalent. The Ru(II)/Cl-,
NCMe, PPh3 chemistry of the related (but C2V symmetric) ligand
4 was recently reported, showing (a) a tendency for PPh3 to
occupy the coordination position in the plane of ligand 4 in
six-coordinate species and (b) PPh3 in the axial site of the
square-pyramidal cations (4)Ru(PPh3)X+ (X ) Cl or CF3SO3)
and (c) that in the absence of PPh3, the metal will avoid
unsaturation by binding N2 to form (4)Cl2Ru(µ-N2)RuCl2(4).17,18
Synthesis of Ru(N2py)Cl2(DMSO) (6). Reacting RuCl2-
(DMSO)4 with N2py in refluxing benzene for 15 h yields an
orange precipitate with the empirical formula Ru(N2py)Cl2-
(DMSO). The 1H NMR spectrum of this compound in CD2Cl2
shows an unsymmetrical surrounding of the metal (isomer A);
that is, the DMSO ligand is placed in an axial position and the
Results
Synthesis of Ru(N2py)Cl2(PPh3) (5). Reaction of RuCl2-
(PPh3)3 with 1 equiv of N2py in refluxing benzene for 5 h gives
compound 5 in a yield of 70% as orange microcrystals
crystallizing directly from the benzene solution. 5 is only soluble
in CH2Cl2, but not in benzene, toluene, THF, acetone, or
nitromethane. The red benzene filtrate contains neither of the
starting compounds nor the product, and also doubling the
amount of N2py has no effect on the yield. The 1H NMR
spectrum of 5 reveals two distinct isomers in a ratio of 1:4.
The major isomer shows three distinct chemical shifts for the
pyridine protons, four chemical shifts the benzylic CH2 protons,
two NH resonances (it should be noted that the NH proton shows
detectable coupling to the benzylic hydrogen in most of the
compounds reported here), and two separate singlets for the tBu
groups. That is, there is no molecular symmetry element. A
structure without any symmetry element (major isomer) is only
consistent with the tBu groups on each nitrogen being trans (anti)
to each other and the PPh3 ligand being in an axial position (A,
Chart 1). In contrast, the minor isomer shows only half of the
resonances, thus two chemical shifts for the pyridine protons,
two chemical shifts for the CH2 groups, only one singlet for
t
two Bu groups are mutually trans. The two methyl groups of
the DMSO ligand appear as two singlets at 3.60 and 2.85 ppm,
respectively. Suitable crystals of 6 could be obtained by slow
diffusion of Et2O into a CH2Cl2 solution of 6. The solid-state
structure determination (Figure 1 and Table 2) confirms the
meridional coordination of the N2py ligand, the cis stereochem-
istry of the chlorides, the inequivalence of the sulfoxide methyls,
and the trans (anti) relationship of the tBu groups. It also shows
that the DMSO is sulfur-bound. The two fused five-membered
rings each has an envelope conformation, and the bulk of the
tBu groups is accommodated by the occupying equatorial ring
positions. Because of this, our supposition (see Introduction)
t
that one conformation of the Bu groups crowds the cis axial
coordination sites is proven to be false. This makes the amine
hydrogens axial, which orients them so that intramolecular
hydrogen bonding is possible. In fact, H15 on N17 hydrogen-
bonds to the DMSO oxygen O5. The N-O distance is 2.79 Å,
and the angle N17-H15-O5 is 141.4°. H7 on N8 is 2.46 Å
from Cl2, but the angle at H7 is not so favorable for hydrogen
bonding. The unit cell incorporates CH2Cl2; H35 on its C26 is
2.60 Å from Cl2, and the angle C26-H35-Cl2 is 158.4°.
However, the two chemically inequivalent Ru-Cl distances are
essentially identical. The Ru-N(py) distance is over 0.2 Å
shorter than those to the secondary amines. While the angles
within the octahedron are 90 ( 12°, the constraints of the N2-
t
the Bu groups, and also only one NH resonance. Thus, we
conclude that the structure of the second isomer contains either
a mirror plane or a C2 axis and that four different structures are
t
possible: either the Bu being trans (anti) and the PPh3 ligand
in an equatorial position (B1) or the tBu being cis (syn) and the
PPh3 ligand being in either position (the two axial positions
are now not equivalent, thus three different structures are
possible, i.e., B2, B3, and B4 in Chart 1). Attempted isomer-
ization of 5 by heating to reflux in THF leads only to
decomposition of the complex. The instability of compound 5
in CD2Cl2 also prevented the recording of a 13C spectrum; within
(19) Weisman, A.; Gozin, M.; Kraatz, H.-B.; Milstein, D. Inorg. Chem.
1996, 35, 1792.
(20) Vigalok, A.; Uzan, O.; Shimon, L. J. W.; Ben-David, Y.; Martin, J.
M. L.; Milstein, D. J. Am. Chem. Soc. 1998, 120, 12539.
(21) Jia, G.; Lee, H. M.; Xia, H. P.; Williams, I. D. Organometallics 1996,
15, 5453.
(22) Lee, H. M.; Yao, J.; Jia, G. Organometallics 1997, 16, 3927.
(23) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten, G.
Organometallics 1996, 15, 5687.
(17) Abbenhuis, R. A. T. M.; del Rio, I.; Bergshoef, M. M.; Boersma, J.;
Spek, A. L.; van Koten, G. Inorg. Chem. 1998, 37, 1749.
(18) Del Rio, I.; Gossage, R. A.; Hannu, M. S.; Lutz, M.; Spek, A. L.; van
Koten, G. Organometallics 1999, 18, 1097.

Ru(II) Pincer Ligand Chemistry
Inorganic Chemistry, Vol. 39, No. 7, 2000 1595
Table 2. Selected Bond Distances(Å) and Angles (deg) for
RuCl2(DMSO)(N2py)
Distance
Ru(1)-Cl(2)
Ru(1)-Cl(3)
Ru(1)-S(4)
Ru(1)-N(8)
Ru(1)-N(15)
Ru(1)-N(17)
S(4)-O(5)
2.4521(6)
2.4574(6)
2.2090(6)
2.2204(20)
1.9855(20)
2.1970(21)
1.4980(18)
S(4)-C(6)
1.7843(27)
1.7969(26)
1.490(3)
1.526(3)
1.492(3)
1.524(3)
S(4)-C(7)
N(8)-C(9)
N(8)-C(18)
N(17)-C(16)
N(17)-C(22)
Angle
Cl(2)-Ru(1)-Cl(3)
Cl(2)-Ru(1)-S(4)
Cl(2)-Ru(1)-N(8)
Cl(2)-Ru(1)-N(15)
Cl(2)-Ru(1)-N(17)
Cl(3)-Ru(1)-S(4)
Cl(3)-Ru(1)-N(8)
Cl(3)-Ru(1)-N(15) 176.98(6)
Cl(3)-Ru(1)-N(17) 101.60(6)
S(4)-Ru(1)-N(8)
S(4)-Ru(1)-N(15)
S(4)-Ru(1)-N(17)
N(8)-Ru(1)-N(15)
91.973(22) O(5)-S(4)-C(6)
174.431(22) O(5)-S(4)-C(7)
104.45(12)
102.80(11)
97.84(12)
106.80(14)
130.33(15)
112.80(19)
79.82(6)
85.20(6)
90.72(6)
92.563(23) C(9)-N(8)-C(18)
99.96(6)
C(6)-S(4)-C(7)
Ru(1)-N(8)-C(9)
Ru(1)-N(8)-C(18)
Ru(1)-N(15)-C(10) 119.85(17)
Ru(1)-N(15)-C(14) 118.94(17)
C(10)-N(15)-C(14) 121.19(21)
Ru(1)-N(17)-C(16) 105.23(15)
Ru(1)-N(17)-C(22) 126.60(15)
C(16)-N(17)-C(22) 113.16(19)
102.55(6)
90.32(6)
85.20(6)
78.51(8)
N(8)-C(9)-C(10)
N(15)-C(10)-C(9)
111.21(20)
115.60(22)
Figure 1. ORTEP drawing of Ru(N2py)Cl2(DMSO), showing intramo-
lecular NH‚‚‚O hydrogen bonding.
N(8)-Ru(1)-N(17) 156.72(8)
N(15)-Ru(1)-N(17) 79.54(8)
N(15)-C(10)-C(11) 120.41(23)
N(15)-C(14)-C(13) 120.53(24)
N(15)-C(14)-C(16) 114.49(21)
Cl(27)-C(26)-Cl(28) 111.58(16)
Ru(1)-S(4)-O(5)
Ru(1)-S(4)-C(6)
Ru(1)-S(4)-C(7)
Ru(1)-N(8)-H(7)
C(9)-N(8)-H(7)
C(18)-N(8)-H(7)
113.99(7)
117.89(9)
117.47(9)
100.45(14)
100.51(19)
100.55(18)
Table 1. Crystallographic Data for RuCl2(DMSO)(N2py)CH2Cl2
formula
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
C18H35Cl4N3ORuS
13.353(2)
11.228(1)
17.536(2(5)
109.30(1)
2481.3(9)
4
space group
T, °C
P21/c
-163
0.710 69
1.565
11.61
0.0290
0.0319
λ, Å
F
calc, g/cm-3
µ(Mo KR), cm-1
Ru(1)-N(17)-H(15) 103.06(15)
C(16)-N(17)-H(15) 102.88(19)
C(22)-N(17)-H(15) 102.93(19)
R a
Rw
b
fw
584.44
Scheme 1
a R ) ||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc |)2/∑w|Fo| ]1/2 where
2
w ) 1/[σ2(|Fo|)].
py ligand are evident. The five-membered rings pull the two
aliphatic amine nitrogens away from Cl3 (and make N8-Ru-
N17 only 156.7°), and the envelope ring conformation pulls
N8 and N17 as much as 12° away from octahedral sites. The
constraints of the five-membered rings, which increase the cis
N-Ru-Cl3 angle, also serve to create additional room for the
disappeared and instead a new singlet with an integral area
assignable to two protons is detectable. This leads us to the
suggestion of a coordinated imine formed by an oxidation of
the benzylic CH2 and the NH groups (Scheme 1). Such
â-oxidation reactions are known to happen on coordinated
amines upon reaction with O2.24-27
t
tBu groups. The two Bu groups have the same conformation
arround the C-N(ring) bond, and this conformation maximizes
t
the distance between Cl3 and the Bu methyl group.
Other common Ru(II) starting materials, such as [Ru(η6-
cymene)Cl2]2, Ru(NH3)6Cl2, and RuCl2(COD), gave in all cases
complex mixtures of compounds on reaction with N2py, as
judged by the complexity of their NMR spectra.
Ru(N2py)(CF3SO3)2(CO) (10). Replacement of the chlorides
-
in 9 by CF3SO3 can be achieved by reaction with two moles
of AgCF3SO3 in CH2Cl2 within 30 min at 25 °C. The 1H NMR
data are consistent with a single product having a symmetric
structure B. However, the 19F spectrum shows two quartets
(J ) 3.1 Hz) separated by 0.23 ppm. This lack of symmetry in
Ru(N2py)Cl2(L). Reaction of 5 with ligands L (L ) CO or
two moles of P(OPh)3 or pyridine) leads to the substitution
products Ru(N2py)Cl2(L) (7-9). The reactions of 5 with CO
and P(OPh)3 take place at room temperature within a few
minutes, whereas the reaction with pyridine needs heating to
reflux in acetone for 2 h. In all cases free PPh3 could be detected
-
the 19F spectrum, however, rules out structure B1 (CF3SO3
trans, tBu trans) because only one 19F signal should be observed.
The relatively large F-F coupling between the two CF3 groups
(8J ) 3.1 Hz) can be due to a trans coordination of the CF3SO3
-
1
by 31P NMR. The H NMR in CD2Cl2 shows that Ru(N2py)-
ligands. Thus, the NMR features of this compound are consistent
with a structure with cis tBu groups and trans CF3SO3- ligands
(B2). This F-F coupling excludes an ionic formulation
[Ru(N2py)(CF3SO3)(CO)]+(CF3SO3)-.
Cl2(CO) (9) and Ru(N2py)Cl2(pyridine) (8) both give only one
isomer, which possesses an element of symmetry (structure B).
In contrast, Ru(N2py)Cl2(P(OPh)3) (7) shows two isomers in
the same ratio as the starting complex 5. However, heating this
mixture in acetone to reflux for 2 h leads to clean isomerization
of the minor isomer (A, no symmetry) into the major isomer
(B, 2-fold symmetry).
-
All attempts to abstract the weakly coordinating CF3SO3
ligand with reagents such as NaBPh4 or NaB(Ar′)4 (Ar′ ) 3,5-
(24) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. ReV. 1998, 98, 2599.
(25) Bailey, A. J.; James, B. R. J. Chem. Soc., Chem. Commun. 1996, 2343.
(26) Leising, R. A.; Ohman, J. S.; Acquaye, J. H.; Takeuchi, K. J. J. Chem.
Soc., Chem. Commun. 1989, 905.
Reaction with O2. Reaction of 8 with 1 equiv of O2 in CD2-
1
Cl2 gives a deep-purple solution. In the H NMR spectrum all
resonances of the CH2 groups and the NH protons have
(27) Thompson, M. S.; Meyer, T. J. J. Am. Chem. Soc. 1982, 104, 4106.

1596 Inorganic Chemistry, Vol. 39, No. 7, 2000
Gemel et al.
H3PO4. 19F NMR chemical shifts are externally referenced to CF3COOH
in benzene. Infrared spectra were recorded on a Nicolet 510P FT-IR
spectrometer.
bistrifluoromethylphenyl) failed and lead only to decomposition
of the complex, as judged by H NMR. Because the expected
product is +2 charged and contains acidic protons on the amine
ligand, the same reactions were repeated in the presence of an
acid trap (Na2CO3), in the hope of getting a single product, but
no clean reaction could be observed.
Dehydrohalogenation Reactions. In attempts to dehydro-
halogenate the HNRuCl unit in 9 to give Ru(N2py-2H)(CO),
compound 9 was reacted with a variety of bases, namely, 2,6-
lutidine, lithium 2,2,6,6-tetramethylpiperidide, MeLi, and BuLi.
All of these attempts failed in that they led only to intractable
materials. In a typical experiment, a slurry of Ru(N2py)Cl2(CO)
(9) in Et2O was cooled to -78 °C and reacted with 2 mol of
BuLi in Et2O to give an orange solution. However, warming
this solution led to a color change to dark-brown at room
temperature, and in 1H NMR no peaks assignable to N2py were
detectable. The orange solution obtained by reaction of 9 with
BuLi was also reacted with Cl2 at -78 °C, giving immediately
a yellow precipitate that was identified as the starting complex
9.
1
2,6-Pyridinedicarboxylic Acid Dimethyl Ester (C9H9NO4). 2,6-
Pyridinedicarboxylic acid (26.0 g, 155.7 mmol) and H2SO4(concentrated)
(0.2 mL) in methanol (200 mL) were heated to reflux for 100 h. After
evaporation of the solvent, the residue was redissolved in CH2Cl2 (200
mL) extracted twice with saturated aqueous solution of NaHCO3 (100
mL), followed by H2O (100 mL). The organic layer was dried over
Na2SO4, filtered and the solvent removed. The white product was dried
in vacuo. Yield: 25.0 g (82%). 1H NMR (25 °C, CDCl3): 8.33 (d, 2H,
J ) 7.8 Hz), 8.02 (t, 1H, J ) 7.8 Hz), 4.02 (s, 6H).
2,6-Pyridinedimethanol (C7H9NO2). To 2,6-pyridinedicarboxylic
acid dimethylester (20.9 g, 107.1 mmol) in MeOH (200 mL) was slowly
added NaBH4 (6.08 g, 160.7 mmol), whereupon the exothermic reaction
warmed the reaction mixture to reflux. The solution was then stirred
at room temperature for 12 h. After evaporation of the solvent, the
residue was dissolved in saturated aqueous NaHCO3 solution (200 mL)
and extracted with CHCl3 (300 mL) by continuous liquid-liquid
extraction for 15 h. After evaporation of the solvent, the product was
washed with Et2O and dried in vacuo. Yield: 10.7 g (72%). 1H NMR
(25 °C, CDCl3/DMSO-d6): δ 7.35 (t, 1H, J ) 7.8 Hz), 6.94 (d, 2H,
J ) 7.8 Hz), 4.34 (s, 4H), 3.64 (bs, 2H).
2,6-Bis(toluenesulfonylmethyl)pyridine (C21H21NO6S2). A solution
of 2,6-pyridinedimethanol (2.24 g, 16.1 mmol) and KOH (2.58 g, 46.0
mmol) in 50 mL of THF was cooled in an ice bath. and toluenesulfonyl
chloride (7.0 g, 36.7 mmol) in 150 mL of THF was added dropwise.
The temperature was not allowed to rise over 0 °C. The mixture was
stirred for 5 h at 0 °C and then for another 12 h at room temperature.
The white residue (KOH, KCl) was filtered off and washed twice with
THF (30 mL). The THF fractions were combined, and after evaporation
of the solvent, the product was dried in vacuo. Yield: 5.32 g (74%).
1H NMR (25 °C, CDCl3): δ 7.80 (m, 4H), 7.69 (m, 1H), 7.33 (m,
6H), 5.04 (s, 4H), 2.44 (s, 6H).
2,6-Bis(tert-butylaminomethyl)pyridine (C15H27N3). 2,6-Bis(tolu-
enesulfonylmethyl)pyridine (5.19 g, 11.6 mmol) and tert-butylamine
(36 mL, 350 mmol) were dissolved in benzene and heated to reflux
for 15 h. After evaporation of the solvent, the residue was redissolved
in CH2Cl2, extracted twice with saturated aqueous NaHCO3 (100 mL)
and H2O (100 mL), and dried over Na2SO4. The solvent was removed
and the product dried in vacuo. Yield: 2.66 g (92%). 1H NMR (25 °C,
CDCl3): δ 7.52 (t, 1H, J ) 8.0 Hz), 7.14 (d, 2H, J ) 8.0 Hz), 3.83 (s,
4H), 1.75 (bs, 2H), 1.34 (s, 18H).
Discussion
Because several isomers of Ru(N2py)Cl2L are observed, the
question of thermodynamic preference must be considered. The
situation with L ) P(OPh)3 is most clear because isomer A
transforms on heating to one symmetric isomer B. Conversion
from A to B3 involves only one inversion at the nitrogen. All
others require a change of the metal coordination sphere as well.
It is noteworthy that there is obviously considerable stereo-
chemical rigidity at the coordinated secondary amine. If there
were not, the A to B3 conversion would be fast. Moreover, the
degenerate rearrangement of A into its enantiomers (i.e.,
inversion at both of its nitrogens) could produce a time-averaged
mirror plane for isomer A. Therefore, the isomerization of Ru-
(N2py)Cl2(PPh3) was carried out in the presence of a base, i.e.,
1.5 equiv of 2,6-lutidine in CD2Cl2 solution, but no considerable
rate enhancement was observed.
Because only the DMSO complex clearly favors isomer A,
it may be that the intramolecular hydrogen bonding is the cause.
Moreover, given that putting both tBu in equatorial positions is
Ru(N2py)Cl2(PPh3) (5; C33H42Cl2N3PRu). A solution of RuCl2-
(PPh3)3 (1.14 g, 1.20 mmol) and 2,6-bis(tert-butylaminomethyl)pyridine
(0.3 g, 1.20 mmol) in benzene (50 mL) was heated to reflux for 5 h.
After the reaction mixture was cooled, the orange crystals formed were
collected on a glass frit, washed with Et2O several times, and dried in
vacuo. Yield: 0.56 g (68%). Anal. Calcd. for (C33H42Cl2N3PRu): C,
57.98; H, 6.19; N, 6.15. Found: C, 57.67; H, 6.34; N, 6.44. 1H NMR
(25 °C, CD2Cl2). For isomer I, δ 7.70 (m, 6H, PPh3), 7.44 (t, 1H, J )
8.1 Hz, N2py), 7.32 (m, 9H, PPh3), 6.85 (2H, d, J ) 8.1 Hz, N2py),
4.23 (dd, 2H, J1 ) 15.9 Hz, J2 ) 6.6 Hz, NH), 3.22 (dd, 2H, J1 ) 15.9
Hz, J2 ) 6.6 Hz, CH2), 2.80 (dd, J1 ) J2 ) 6.6 Hz, CH2), 1.121 (s,
t
clearly sterically favorable, it may be that only the anti Bu
stereochemistry is favored. The syn relationship puts the two
fused five-membered rings in conflict at their phenyl fusion. If
so, then structures A and B1 will be generally favored.
Experimental Section
General. All manipulations were carried out with standard Schlenk
and glovebox techniques under purified argon. Benzene, toluene, Et2O,
CH2Cl2, and pentane were dried using appropriate agents, distilled, and
stored in gastight solvent bulbs. Benzene-d6, CD2Cl2, and toluene-d8
were dried by appropriate methods and vacuum-distilled prior to use.
Pyridine and P(OPh)3 were purchased from Aldrich and used without
further purification. Gaseous reagents were purchased from Air Products
t
18H, Bu). For isomer II, δ 7.83 (dd, 1H, J1 ) J2 ) 8.1 Hz, N2py),
7.71 (m, 6H, PPh3), 7.31 (m, 9H, PPh3), 7.10 (d, 1H, J ) 8.1 Hz, N2-
py), 6.79 (d, 1H, J ) 8.1 Hz, N2py), 6.02 (dd, 1H, J1 ) 12.7 Hz, J2 )
5.0 Hz, NH), 4.02 (dd, 1H, J1 ) 15.9 Hz, J2 ) 5.0 Hz), 3.30 (m, 2H),
2.53 (dd, J1 ) J2 ) 5.0 Hz), 1.99 (dd, 1H, J1 ) 12.7 Hz, J2 ) 15.9
Hz), 1.16 (s, 9H), 1.09 (s, 9H). 31P{1H) NMR (CD2Cl2, 25 °C) for
isomer II: δ 56.0.
28
29
and used as received. RuCl2(PPh3)3 and RuCl2(DMSO)4 were
synthesized according to literature. 1H, 31P, 19F, and 13C NMR spectra
were recorded on a Varian Gemini 300 spectrometer (1H, 300 MHz;
31P, 122 MHz; 19F, 282 MHz; 13C, 75 MHz) or on a Varian INOVA
400 spectrometer (1H, 400 MHz; 31P, 161 MHz; 19F, 376 MHz; 13C,
100 MHz). 1H NMR chemical shifts are reported in ppm downfield of
tetramethylsilane with use of residual solvent resonances as internal
standards. 31P NMR chemical shifts are relative to an external 85%
Ru(N2py)Cl2(DMSO) (6; C17H33Cl2N3OSRu). A solution of RuCl2-
(DMSO)4 (226 mg, 0.466 mmol) and 2,6-bis(tert-butylaminomethyl)-
pyridine (120 mg, 0.481 mmol) in benzene (5 mL) was heated to reflux
for 15 h. After evaporation of the solvent, the precipitate was collected
on a glass frit, washed several times with small portions of Et2O, and
dried in vacuo. Yield: 189 mg (81%). Anal. Calcd for (C17H33Cl2N3-
OSRu): C, 40.88; H, 6.66; N, 8.41. Found: C, 40.94; H, 6.70; N, 8.55.
1H NMR (25 °C, CD2Cl2): δ 7.55 (dd, 1H, J1 ) J2 ) 8.0 Hz), 7.20 (d,
1H, J ) 8.0 Hz), 7.17 (d, 1H, J ) 8.0 Hz), 5.25 (d, 1H, J ) 8.4 Hz),
4.91 (d, 1H, 9.9 Hz), 4.40 (dd, 1H, J1 ) 15.9 Hz, J2 ) 12.3 Hz), 4.07
(28) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth. 1970,
12, 237.
(29) Evans, I. P.; Spencer, A.; Wilkinson, D. J. Chem. Soc., Dalton Trans.
1973, 204.

Ru(II) Pincer Ligand Chemistry
Inorganic Chemistry, Vol. 39, No. 7, 2000 1597
(dd, 1H, J1 ) 15.9 Hz, J2 ) 3.6 Hz), 3.85 (m, 2H), 3.60 (s, 3H, DMSO),
mL) was heated to reflux for 2 h. After evaporation of the solvent, the
precipitate was collected on a glass frit, washed several times with small
portions of Et2O, and dried in vacuo. Yield: 25.8 mg (57%). 1H NMR
(25 °C, CD2Cl2): δ 10.37 (dd, 2H, J1 ) 6.9 Hz, J2 ) 1.2 Hz, pyridine),
7.71 (t, 1H, J ) 6.9 Hz), 7.52 (t, 1H, J ) 8.1 Hz), 7.34 (m, 5H), 4.20
t
t
2.85 (s, 3H, DMSO), 1.15 (s, 9H, Bu), 1.10 (s, 9H, Bu).
Structure Determination of Ru(N2py)Cl2(DMSO)‚CH2Cl2. An
irregular triangular prism was attached to a glass fiber using silicone
grease and transferred to the goniostat where it was cooled to -163
°C for characterization and data collection. A preliminary search for
peaks and analysis using the programs DIRAX and TRACER revealed
a primitive monoclinic unit cell. Unit cell dimensions were obtained
by an unrestrained least-squares fit of the setting angles for 65 carefully
centered reflections having 2θ values between 19° and 21°. The upper
limit for the data collection was extended to 55° because of the strong
diffraction observed. Following the completed data collection, the
systematic extinction of 0k0 for k ) 2n + 1 and of h0l for l ) 2n +
1 uniquely identified the space group as P21/c. Four standards measured
every 300 reflections showed no significant trends. The limits for h, k,
and l were -17 to 17, 0 to -14, and -22 to 20, respectively. An
analytical absorption correction was carried out over the 0.685-0.810
transmission factor range. The structure was solved using DIRDIF-96.
The major part of the main molecule as well as the solvent molecule
was located in the initial run of the program. The remaining atoms
were located in the usual manner using least-squares refinement
followed by a difference Fourier calculation. Hydrogen atoms were
introduced in fixed, calculated positions with isotropic thermal param-
eters equal to 1.0 plus the isotropic equivalent of the parent atom. The
final full matrix least-squares refinement was carried out using
anisotropic thermal parameters on all nonhydrogen atoms. The total
number of parameters, including the scale factor and an overall isotropic
extinction parameter, was 254. The final difference map was featureless.
The largest peak was 0.31 e/Å3 located 1.2 Å from O(5), and the deepest
hole was -0.19 e/Å3.
t
(m, 6H), 0.91 (s, 18H, Bu).
Ru(N2py)Cl2(CO) (9; C16H27Cl2N3ORu). 5 (230 mg, 0.336 mmol)
in acetone (5 mL) was purged with CO for 2 min and stirred at room
temperature for 2 h. After evaporation of the solvent, the precipitate
was collected on a glass frit, washed with small portions of Et2O, and
dried in vacuo. Yield: 125 mg (83%). Anal. Calcd for (C16H27Cl2N3-
ORu): C, 42.76; H, 6.06; N, 9.35. Found: C, 42.53; H, 6.19; N, 9.62.
1H NMR (25 °C, CD2Cl2): δ 7.74 (t, 1H, J1 ) 8.1 Hz, N2py), 7.32 (d,
2H, J ) 8.1 Hz, N2py), 4.57 (dd, 2H, J1 ) 15.9 Hz, J2 ) 5.4 Hz,
CH2), 4.25 (m, 2H, NH), 4.05 (dd, 2H, J1 ) 15.9 Hz, J2 ) 8.1 Hz,
t
CH2), 1.37 (s, 18H, Bu). 13C{1H} NMR (CD2Cl2, 25 °C): δ 205.5
(CO), 161.4 (N2py), 137.4 (N2py), 119.5 (N2py), 59.6 (tBu-C), 57.3
(CH2), 28.1 (tBu-CH3). IR (CH2Cl2, 25 °C): 1935 cm-1 (νCO).
Ru(N2py)(CO)(CF3SO3)2 (10; C18H27F6N3S2O7Ru). A solution of
9 (49.8 mg, 0.111 mmol) and AgCF3SO3 (56.9 mg, 0.221 mmol) in
CH2Cl2 (5 mL) was stirred at room temperature for 30 min. The AgCl
formed was filtered off, the solvent was removed, and the residue was
collected on a glass frit, washed with small portions of Et2O, and dried
1
in vacuo. Yield: 42 mg (84%). H NMR (25 °C, CD2Cl2): δ 7.90 (t,
1H, J1 ) 7.8 Hz, N2py), 7.43 (d, 2H, J ) 7.8 Hz, N2py), 5.22 (m, 2H,
NH), 4.67 (dd, 2H, J1 ) 16.4 Hz, J2 ) 6 Hz, CH2), 4.25 (dd, 2H, J1 )
t
16.4 Hz, J2 ) 6 Hz, CH2), 1.37 (s, 18H, Bu). 19F{1H} NMR (25 °C,
CD2Cl2): δ -80.54 (q, J ) 3.1 Hz), -80.77 (q, J ) 3.1 Hz). IR (CH2-
Cl2, 25 °C): 1960 cm-1 (νCO).
Ru(py(CHNtBu)2)Cl2(pyridine) (11; C20H28Cl2N4Ru). 8 (50 mg,
0.12 mmol) was dissolved in CD2Cl2, and O2 (0.13 mmol) was added.
When the solution was stirred at room temperature, the color turned
Ru(N2py)Cl2(P(OPh)3) (7; C33H42Cl2N3O3PRu). A solution of 5
(101.3 mg, 0.148 mmol) and triphenyl phosphite (91.9 mg, 0.296 mmol)
in THF (5 mL) was heated to reflux for 15 h. After evaporation of the
solvent, the precipitate was collected on a glass frit, washed several
times with small portions of Et2O, and dried in vacuo. Yield: 88.2 mg
(81%). 1H NMR (25 °C, CD2Cl2). For isomer I: δ 7.64 (dd, 1H, J1 )
J2 ) 7.2 Hz, N2py), 7.6-6.8 (m, 17H, N2py, P(OPh)3), 5.95 (d, 2H,
J ) 13 Hz, NH), 4.17 (dd, 2H, J1 ) 15.6 Hz, J2 ) 3.6 Hz, CH2), 3.85
(dd, 2H, J1 ) 13 Hz, J2 ) 15.6 Hz, CH2), 1.33 (s, 18H). For isomer II:
δ 7.61 (dd, 1H, J1 ) J2 ) 7.2 Hz), 7.25 (d, 1H, J ) 7.2 Hz), 7.05 (m,
16H), 5.0 (d, 1H, J ) 11.2 Hz, NH), 4.53 (m, 2H), 4.08 (dd, 1H, J1 )
14.8 Hz, J2 ) 3.6 Hz, CH2), 3.37 (m, 2H, CH2), 1.48 (s, 9H, tBu), 1.20
1
from light-orange to deep-purple within 1 h. After 2 h, a H NMR
1
spectrum was recorded. H NMR (25 °C, CD2Cl2): δ 10.44 (d, 2H,
J ) 5.1 Hz, pyridine), 8.32 (s, 2H, CHdN), 7.92 (m, 1H), 7.75 (d, 2H,
t
J ) 8.1 Hz), 7.56 (m, 3H), 1.21 (s, 18H, Bu).
Acknowledgment. This work was supported by the U.S.
National Science Foundation and by the Austrian Science
Foundation FWF (Project J-1535) via a fellowship to C.G.
Supporting Information Available: One crystallographic file in
CIF format. This material is available free of charge via the Internet at
http://pubs.acs.org.
t
(s, 9H, Bu). 31P{1H) NMR (CD2Cl2, 25 °C). For isomer I: δ 124.3.
For isomer II: δ 122.9.
Ru(N2py)Cl2(pyridine) (8; C20H32Cl2N4Ru). A solution of 5 (61.7
mg, 0.0903 mmol) and pyridine (14.3 mg, 0.181 mmol) in acetone (5
IC990737T