Comparing structures and reactivity in analogous Fe and Ru complexes. (iPr-DAB)Fe(CO)2I2 and (iPr-DAB)FeI2: A perfectly reversible CO-carrier system. (R-DAB=N,N′-R2-1,4-diaza-1,3-butadiene)

Article abstract of DOI:10.1016/s0020-1693(99)00162-0

Fe(ⁱPr-DAB)(CO)₃ (1a) oxidatively adds I₂ to give (ⁱPr-DAB)Fe(CO)₂-trans-I₂ (2a). Photochemically or thermally, 2a readily dissociates both carbonyl ligands to give tetrahedral Fe(ⁱPr-DAB)I₂ (3a). Under an atmosphere of CO, complex 2a is quantitatively regenerated from 3a. The X-ray crystal structures of 2a and 3a have been determined. 2a: triclinic, space group P1?, a=8.7624(3), b=9.0550(4), c=10.6512(6) ?, α=95.429(4), β=105.245(4), γ=95.209(3)°, Z=2, R=0.0251. 3a: orthorhombic, space group Aba2, a=11.2693(10), b=15.933(2), c=7.5958(10) ?, Z=4, R=0.036. Contrasting the behaviour of 2a, the analogous ruthenium complexes (R-DAB)Ru(CO)₂trans-I₂ (4) are very stable, and the carbonyl ligands cannot be dissociated thermally. In the dichloro complexes, of which both the kinetic trans- (5) and the thermodynamic cis-compounds (6) have been isolated, both isomers undergo a photochemical CO mono-substitution to give for example the isolable trans-dichloro methanol complex (7).

Full text of DOI:10.1016/s0020-1693(99)00162-0

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 291 (1999) 438–447
Comparing structures and reactivity in analogous Fe and Ru
complexes. (iPr-DAB)Fe(CO)2I2 and (iPr-DAB)FeI2: a perfectly
reversible CO-carrier system.
(R-DAB=N,N%-R2-1,4-diaza-1,3-butadiene)
Joachim Breuer a,1, Hans-Werner Fru¨hauf b,*, Wilberth J.J. Smeets c,
Anthony L. Spek c,2
a Uni6ersita¨t GH Duisburg, FB 6, Organische Chemie, Lotharplatz 1, D-47048 Duisburg, Germany
b Uni6ersiteit 6an Amsterdam, Institute of Molecular Chemistry, Anorganische Chemie, Nieuwe Achtergracht 166,
NL-1018 WV Amsterdam, The Netherlands
c Bij6oet Center for Biomolecular Research, Vakgroep Kristal en Structuurchemie, Uni6ersiteit Utrecht, Padualaan 8,
NL-3548 CH Utrecht, The Netherlands
Received 25 March 1999
Abstract
Fe(iPr-DAB)(CO)3 (1a) oxidatively adds I2 to give (iPr-DAB)Fe(CO)2-trans-I2 (2a). Photochemically or thermally, 2a readily
dissociates both carbonyl ligands to give tetrahedral Fe(iPr-DAB)I2 (3a). Under an atmosphere of CO, complex 2a is
(
quantitatively regenerated from 3a. The X-ray crystal structures of 2a and 3a have been determined. 2a: triclinic, space group P1,
,
a=8.7624(3), b=9.0550(4), c=10.6512(6) A, h=95.429(4), i=105.245(4), k=95.209(3)°, Z=2, R=0.0251. 3a: orthorhombic,
,
space group Aba2, a=11.2693(10), b=15.933(2), c=7.5958(10) A, Z=4, R=0.036. Contrasting the behaviour of 2a, the
analogous ruthenium complexes (R-DAB)Ru(CO)2trans-I2 (4) are very stable, and the carbonyl ligands cannot be dissociated
thermally. In the dichloro complexes, of which both the kinetic trans- (5) and the thermodynamic cis-compounds (6) have been
isolated, both isomers undergo a photochemical CO mono-substitution to give for example the isolable trans-dichloro methanol
complex (7). © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Iron complexes; Ruthenium complexes; Diazadiene complexes; Carbonyl complexes
atmosphere of CO [7]. In this paper we demonstrate
that these relative stabilities of the metal–CO bonds are
reversed in the oxidation state +2. In order to com-
pare their structures and reactivities, we have prepared
some analogous complexes of iron(II) and ruth-
enium(II) of the composition (R-DAB)M(CO)2Hal2.
The most important and probably most general ac-
cess towards iron complexes of the type
L2Fe(CO)2Hal2, is by reaction of dihalogeno tetracar-
bonyliron, Fe(CO)4Hal2 [8], with two mono- or a
bidentate donor ligand [8–15]. A one-pot synthesis by
reacting FeCl2 with the ligand under a CO atmosphere
has also been described [16–18]. The chloride can then
be exchanged by metathesis with KBr or KI [18]. As
opposed to these reactions where the iron is already in
1. Introduction
It is well known that Fe(CO)5 is a stable compound
while Ru(CO)5 is not because it spontaneously looses
CO to give the stable Ru3(CO)12. Likewise, the zerova-
lent iron complexes (R-DAB)Fe(CO)3 (1) are isolable
[2–6], while the ruthenium counterparts (R-DAB)
Ru(CO)3 are not, because as with Ru(CO)5, they can
only be generated and handled in solution under an
* Corresponding author. Fax: +31-20-525 6458.
E-mail address: hwf@anorg.chem.uva.nl (H.-W. Fru¨hauf)
1 Present address: Deflize&Partner, Hoher Weg 2, 67067 Ludwigs-
hafen, Germany. This article contains unpublished results from the
Ph.D. Thesis of J. Breuer [1]
2 Also corresponding author.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00162-0

J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
439
the final oxidation state +2, there are only very few
examples where the halogen is oxidatively added to an
iron(0) complex L2Fe(CO)3. Two examples are the
syntheses of (PMe2Ph)2Fe(CO)2I2 [18] and (diars)Fe
(CO)2Hal2 [19] (diars=o-(Me2As)2C6H4; Hal=Br, I).
Complexes of the type L2Ru(CO)2Hal2 are most
conveniently prepared by reacting the polymeric
[L2Ru(CO)2Hal2]x [20–24] with appropriate ligands L
[23,25–30]. If the desired complex is not accessible via
this method it may be useful to first use labile ligands,
e.g. methanol or acetonitrile as coordinating solvents,
to break down the polymer, and then displace the
coordinated solvent molecules in a consecutive step by
the desired ligand. This method has been employed in
the present work (with methanol) and by tom Dieck et
(R1ꢀcyclo-C6H11, R2=H), and d (R1ꢀp-OCH3–C6H4,
R2=CH3).
2.1.1.1. Synthesis of [Ru(CO)2Cl2]n. In a modified pro-
cedure of Colton and Farthing [23], the polymeric
[Ru(CO)2Cl2]n is prepared by dissolving 10.52
g
RuCl3·nH2O in a mixture of 60 ml formic acid and 60
ml concentrated hydrochloric acid. The solution is
heated at 120°C for 15 h. Then the clear yellow solu-
tion is evaporated to dryness and the residue dried to
constant weight in vacuo (ca. 10−3 mbar) at 150°C. A
total of 6.87 g of [Ru(CO)2Cl2]n was obtained as a
yellow powder. IR (MeOH) wCO=2066 (s), 1993 (s)
cm−1
.
al. [31]. The interest in complexes with
a
2.1.1.2. Synthesis of [Ru(CO)2I2]n. After addition of
some hypophosphorous acid, hydroiodic acid (ca.
57%) is first distilled. Then 1.09 g RuCl3·nH2O is
suspended in 15 ml of the hydroiodic acid and in
vacuo evaporated to dryness three successive times.
The resulting black crystalline rutheniumtriiodide is
dissolved in a mixture of 20 ml formic acid and 20 ml
of the hydroiodic acid and heated at 130°C for 1.5 h.
The dark red solution is evaporated to dryness and the
residue is dried to constant weight in vacuo (ca. 10−3
mbar) at 100°C, yielding 1.45 g of [Ru(CO)2I2]n (3.53
Ru(CO)2Hal2-fragment has concentrated on the syn-
thesis of complete sets of all stereoisomers [25,32],
their isomerization reactions [33], analysis of their CO
stretching vibrations [34–36], and their catalytic prop-
erties [37–39]. In the present work, the respective
ruthenium complexes were made and used to compare
their properties with those of their homologous iron
counterparts.
2. Experimental
mmol Ru) as an orange powder. IR (MeOH) wCO
=
2120 (m), 2055 (s) cm−1
.
2.1. General information
Reactions were performed under an atmosphere of
dry argon or nitrogen using standard Schlenk tech-
niques. Solvents were carefully dried and distilled un-
der nitrogen. Elemental analyses were carried out by
Dornis und Kolbe, Mikroanalytisches Laboratorium,
Mu¨lheim a.d. Ruhr, Germany. The mass spectra in
FD mode (Varian MAT 311 A, 5 kV emitter, MeOH
or THF as solvents) were used with great advantage
to control the composition in particular the ruthenium
compounds. The dominant natural isotopes of chlorine
(2), iron (4), and ruthenium (7) gave rise to great
numbers of isotopomers such that the molecular peak
often stretches ten or more mass units. Its pattern is
characteristic of the sort of elements and number of
atoms present. The calculated [40] and observed pat-
terns were found to agree very well in the reported
compounds. Photolyses were carried out in a Pyrex
immersion well apparatus using a Philips HPK 125
high-pressure mercury lamp.
2.2. Formation of complexes (R-DAB)Fe(CO)2I2 (2)
2.2.1. (iPr-DAB)Fe(CO)2I2 (2a)
To a stirred solution of 1.60 g (5.70 mmol) (iPr-
DAB)Fe(CO)3 (1a) in 80 ml of THF was slowly added
at 0°C 1 equiv. of I2 (1.45 g, 5.69 mmol) in 20 ml of
THF. After 45 min the solvent was removed by evap-
oration. After crystallization from toluene/hexane (1:1)
under an atmosphere of CO, the product was obtained
as violet–black crystals in a yield of 78%. Anal. of 2a:
Found: C, 23.62; H, 3.26; N, 5.48, Fe, 11.18. Calc.: C,
23.74; H, 3.19; N, 5.54; Fe 11.04%. IR (toluene) wCO
:
1
2040 (s), 2000 (s) cm−1. H NMR (CDCl3, 300 K, 80
MHz) ppm: 8.59 (s, 2H, ꢀCH–N), 5.32 (sp, 2H, N–
3
3
CH(CH3)2, JH,H 6.4 Hz), 1.82 (d, 12H, JH,H 6.4 Hz).
2.2.2. (pAn-DAB; Me,Me)Fe(CO)2I2 (2d)
Analogous to the preparation of 2a from 0.40 g
(0.92 mmol) (pTol-DAB)Fe(CO)3 (1d) in 30 ml THF,
and 0.23 g (0.91 mmol) I2 in 10 ml THF. Yield (re-
crystallized twice from toluene/hexanes) 0.28 g (0.42
mmol, 46%) of black crystals of 2d. Anal. of 2d:
Found: C, 36.25; H, 3.10; N, 4.27; I, 38.40. Calc.: C,
2.1.1. Starting materials
The diazadiene ligands [41] and the complexes (R-
DAB)Fe(CO)3 (1) [4–6] have been prepared by known
procedures. The diazadiene ligands R1–NꢀCR2–
CR2ꢀN–R1 employed in this investigation are
a
36.28; H, 3.05; N, 4.23; I, 38.34%. IR (toluene) wCO
:
(R1ꢀCH(CH3)2, R2=H), b (R1ꢀC(CH3)3, R2=H), c
2047 (s), 2010 (s) cm−1. MS (FD): m/e=662 (M+).

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J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
2.3. Formation of complex (iPr-DAB)FeI2 (3a)
twice from acetone to give 0.20 g (0.36 mmol, 23%) of
dark orange crystals of 4a. Anal. of 4a: Found: C,
22.30; H, 3.01; N, 5.08. Calc.: C, 21.79; H, 2.93; N,
2.3.1. Photochemically
1
5.08%. IR (MeOH) wCO: 2052 (s), 1998 (m) cm−1. H
A solution of 740 mg (1.46 mmol) 2a in 100 ml of
toluene was irradiated for 15 min. After removal of the
solvent by evaporation, the crude product was crystal-
lized from a concentrated solution in toluene/hexane to
give 510 mg (78%) of complex 3a as black crystals.
Complex 2a can be completely regenerated by stirring a
toluene solution of 3a under an atmosphere of CO.
4
NMR (acetone-d6, ppm): 8.53 (d, 2H, JH,H 0.8 Hz,
3
4
ꢀCH–N), 4.60 (dsp, 2H, JH,H 6.5 Hz, JH,H 0.8 Hz,
3
CH(CH3)2), 1.63 (d, 12H, JH,H 6.5 Hz, CH3).
2.5.2. Thermal stability of 4a
In total 50 mg of 4a were dissolved in 0.6 ml of
acetone-d6. The red–orange solution was heated in a
sealed NMR tube in an oven at 180°C for 14 h. The
2.3.2. Thermally
A solution of 280 mg (0.55 mmol) 2a in 20 ml toluene
was stirred at 40–45°C for 7 h. The reaction proceeds
with evolution of CO and can be monitored by IR. The
intensely green solution is cooled to room temperature
(r.t.), and inversely filtered off the black precipitate,
which is washed with toluene. The combined toluene
solutions are concentrated in vacuo and cooled at −
20°C to give another crop of black crystals. Total yield
of 3a: 0.20 g (80%). Anal. of 3a: Found: C, 21.33; H,
3.63; N, 6.18; I, 56.50. Calc.: C, 21.36; H, 3.58; N, 6.23;
I, 56.42%. MS (FD): m/e=900 (4%, dimer [(iPr-
DAB)FeI2]2+), 450 (100%, [(iPr-DAB)FeI2]+).
1
subsequently measured H NMR spectrum showed in
addition to the bulk of unchanged 4a only two signals
of very low intensity at 8.07 ppm (s, ꢀCH–N) and 1.51
i
ppm (d, CH3) which have to be assigned to free Pr-
DAB, probably from beginning thermal decomposition.
There is no indication of a formation of the cis-diiodo
complex.
Table 1
Crystal data and details of the structure determinations
Compound
2a
3a
2.4. X-ray data collection, solution and refinement of
the structures of complexes 2a and 3a3
Crystal data
Empirical formula
Formula weight
Crystal system
Space group
C10H16FeI2N2O2
505.90
triclinic
C8H16FeI2N2
449.88
orthorhombic
Aba2 (no. 41)
11.2693(10)
15.933(2)
X-ray data were collected on an Enraf–Nonius
CAD4T (Rotating Anode) diffractometer at 150 K for
red (2a) and yellow–brown (3a) cut-to-size inert oil
covered crystals. Numerical details have been collected
in Table 1. Structures were solved by Patterson tech-
niques (DIRDIF [42]) (2a) or Direct Methods SHELXS 86
[43]) (3a) and refined on F2 with SHELXL96 [44] (2a)
and SHELXL93 [45] (3a). Correction for absorption was
done with a modified DIFABS [46] for 3a and analyti-
cally [47] for 2a. Hydrogen atoms were included at
calculated positions and refined riding on their carrier
atoms. A BASF/TWIN parameter [0.0(3)] was refined
to establish the absolute structure of 3a. Geometry
calculation and the ORTEP illustrations were done
with PLATON [48].
(
P1 (no. 2)
,
a (A)
8.7624(3)
9.0550(4)
10.6512(6)
95.429(4)
105.245(4)
95.209(3)
805.80(7)
2
,
b (A)
,
c (A)
7.5958(10)
h (°)
i (°)
k (°)
3
,
V (A )
1363.9(3)
4
2.191
840
Z
Dcalc (g cm−3
F(000)
)
2.085
476
4.8
v(Mo Ka) (mm−1
)
5.6
Crystal size (mm)
0.13×0.25×0.25
0.10×0.13×0.25
Data collection
Temperature (K)
Radiation Mo Ka (A)
q min., max. (°)
Dataset
150
0.71073
2.0, 27.5
150
0.71073
2.6, 25.0
,
−11:11; −11:11; −13:13; 0:18;
−13:13
7680
3679
0.080
2.5. Formation of complexes
(R-DAB)Ru(CO)2(trans-Hal)2
−9:0
1261
652
0.059
494
Total data
Unique data
Rint
2.5.1. Formation of (iPr-DAB)Ru(CO)2(trans-I)2 (4a)4
In total 0.64 g (1.6 mmol) 1/n[Ru(CO)2I2]n and 0.22 g
Observed data [I\2.0|(I)] 3040
i
Refinement
Nref, Npar
R, wR, S
(1.6 mmol) Pr-DAB were dissolved in 40 ml THF, and
3679, 166
0.0251, 0.0455,
1.06
652, 63
0.0362, 0.0677,
0.98
stirred in the dark for 1 day at r.t. The solvent was
removed in vacuo and the brown residue recrystallized
Max., average shift/error
0.00, 0.00
0.00, 0.00
−0.64, 0.66
Min., max. residual density −0.94, 0.83
−3
,
(e A
)
3 Full details may be obtained from the author A.L. Spek.
4 4a had at the same time been described by tom Dieck et al. [31].

J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
441
Table 2
Preparation and characterization of compounds (R-DAB)Ru(CO)2(trans-Cl)2 (5a–d)
Compound
(iPr-DAB)
(tBu-DAB)
(cHex-DAB) Ru(CO)2Cl2 (pAn-DAB;Me,Me)
Ru(CO)2Cl2 (5a)
Ru(CO)2Cl2 (5b)
(5c)
Ru(CO)2Cl2 (5d)
Starting materials
[Ru(CO)2Cl2]n (g, mmol Ru) 0.45, 1.97
0.94, 4.12
0.69, 4.10
18
light yellow crystals
0.24; 0.61; 15
391–401
1.31, 5.75
1.26, 5.72
24
dark yellow needles
0.57; 1.27; 22
442–551
0.66, 2.89
0.85, 2.87
1 (reflux)
light yellow crystals
0.38; 0.72; 25
R-DAB a–d (g, mmol)
Reaction time (h)
Appearance
0.26, 1.85
48
big orange crystals
0.11; 0.3; 16
362–373
Yield (gl, mmol %)
FD-MS: M+ (m/e)
IR(MeOH) wCO (cm−1
IR (KBr pellet), wRu–Cl
)
2063 (s), 2003 (m)
325
2061 (s), 1999 (m)
2061 (s), 2002 (m)
335
(cm−1
)
Formula
Mw
C10H16Cl2N2O2Ru
368.23
C12H20Cl2N2O2Ru
396.28
C16H24Cl2N2O2Ru
448.36
C20H20Cl2N2O4Ru
524.37
Anal. % Found (Calc.)
C
H
N
O
32.70 (32.62)
4.44 (4.38)
7.58 (7.61)
36.42 (36.37)
5.10 (5.09)
7.12 (7.07)
42.78 (42.86)
5.38 (5.40)
6.21 (6.25)
7.09 (7.14)
44.88 (45.81)
3.89 (3.84)
5.45 (5.34)
8.86 (8.07)
8.31 (8.07)
12.13 (12.20)
Cl
19.33 (19.26)
CHꢀN 8.62 (d)
4JH,H 0.8 Hz
CH(CH3)2 4.49 (dsp)
17.86 (17.89)
CHꢀN 8.61 (s)
CH3 1.64 (s)
1H NMR, l (ppm) (mult),
acetone-d6, 300 K,
5a–c: 80 MHz
5d: 300 MHz
CHꢀN 8.58 (d)
NꢀC–CH3 2.58 (s)
CH (Ph 2,3)
4JH,H 1.0 Hz
ꢀN–CH 3.92–7.34 (m)
CH2 (ring) 1.10–2.35
7.04–7.34 (m),
O–CH3 3.88 (s)
4
3JH,H 6.5 Hz, JH,H 0.8 Hz
CH(CH3)2 1.55 (d)
3JH,H 6.5 Hz
13C NMR, l (ppm), acetone- CO 197.47 CHꢀN 164.14
CO 197.83,
CO 197.76,
CHꢀN 164.13,
cHex–CH(1) 73.74
cHex-CH2(2) 34.11
cHex-CH2(3) 25.72
cHex-CH2(4) 26.00
CO 196.47
d6, 300 K,
1JC,H 180.7 Hz
CH(CH3)2 65.97
1JC,H 141.1 Hz
CH(CH3)2 23.06
1JC,H 128.0 Hz
CHꢀN 163.60
C(CH3)3 67.68
C(CH3)3 30.29
CHꢀN 177.37
C(CH3)ꢀN 20.71,
1JC,H 130.6 Hz,
CPh(1) 143.55,
CH Ph(2) 123.00,
1JC,H 164.5 Hz,
2JC,H 6.1 Hz,
5a–c: 20 MHz
5d: 75 MHz
CHPh(3) 115.36,
1JC,H 162.9 Hz
2JC,H 5.0 Hz
CPh(4) 160.13
O–CH3 55.90
2.5.3. General procedure for the formation of
(R-DAB)Ru(CO)2(trans-Cl)2 (5)
In the solid state: an orange crystal (10 mg) of 5a was
heated in an oil bath at 140°C for 3 h giving a light yellow
crystalline powder, which by IR and 1H NMR was
identified as pure 6a.
Polymeric [Ru(CO)2Cl2]n is stirred in methanol at r.t.
until a clear light yellow solution is obtained. After
additionofthediazadienesa–dthemixtureisstirredinthe
dark for the times specified in Table 2. The solvent is
consecutively removed in vacuo and the residue is
recrystallized twice from methanol.
MS (FD): m/e=367–373 (m/e=M+). Anal. of 6a:
Found: C, 32.71; H, 4.34; N, 7.62; O, 8.83; Cl, 19.33. Calc.:
C, 32.62;H, 4.38;N, 7.61;O, 8.69;Cl, 19.26%. IR(MeOH)
wCO: 2068 (s), 2007 (s) cm−1. 1H NMR (300 K, 80 MHz,
acetone-d6, ppm): 8.66, 8.57 (2×d, broad, CH–N), 4.94
2.6. Experiments towards the formation of complexes
all-cis-(R-DAB)Ru(CO)2Cl2 (6)
3
4
(dsp, JH,H 6.6 Hz, JH,H 1.2 Hz, CH(CH3)2), 4.29 (dsp,
3JH,H 6.5 Hz, 4JH,H 0.8 Hz, CH%(CH3)2), 1.51 (2×d, 6H,
3JH,H 6.6 Hz, CH3), 1.45 (2×d, 6H, 3JH,H 6.5 Hz, CH3).
13C NMR (300 K, 75 MHz, acetone-d6, ppm): 196.97,
189.87 (CO), 165.99 (ꢀCH–N; 1JC,H 120.9 Hz, nJC,H 13.0,
6.3 Hz), 164.40 (ꢀC%H–N; 1JC,H 122.5 Hz, nJC,H 13.0, 6.9
2.6.1. All-cis-(iPr-DAB)Ru(CO)2Cl2 (6a)
In solution: 0.44 g (1.19 mmol) 5a was dissolved in 20 ml
acetonitrile and refluxed in the dark. The isomerization
reaction can be monitored by IR or NMR, and is finished
after 5 h. The residue, after removal of the solvent in
vacuo, was recrystallized from methanol yielding 0.28 g
(0.76 mmol, 64%) of light yellow crystals of 6a.
1
Hz), 67.69 (CH(CH3)2; JC,H 145.6 Hz), 59.05
1
(C%H(CH3)2; JC,H 146.4 Hz), 23.26, 23.13 (CH(CH3)2;
1JC,H 127.7 Hz), 23.09, 22.33 (CH(C%H3)2; 1JC,H 145.6 Hz).

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J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
3
4
2.6.2. Equilibrium between (tBu-DAB)(CO)2Ru(trans-
Cl)2 (5b) and (tBu-DAB)(CO)2Ru(cis-Cl)2 (6b)
(dsp, 1H, JH,H 6.6 Hz, JH,H 1.2 Hz, CH(CH3)2),
3
4
4.34 (dsp, 1H, JH,H 6.6 Hz, JH,H 0.9 Hz,
CH%(CH3)2), 1.50, 1.38 (2×d, 6H, JH,H 6.6 Hz,
CH(CH3)2), 4.82 (s, 1H, OH), 3.29 (s, 3H, OCH3).
13C NMR (300 K, 20 MHz, methanol-d4) ppm:
203.74 (CO), 162.94, 160.07 (ꢀCH–N), 23.25, 23.01
(CH–(CH3)2).
3
A total of 50 mg of 5b were dissolved in 0.6 ml
acetone-d6, and the light yellow solution was heated
in an oven at 130°C in a sealed NMR tube. The
isomerization reaction was monitored by 1H NMR.
After 18 h a stable equilibrium composition between
5b and 6b of 43:57 was reached. The solvent was
evaporated and the light yellow residue was twice re-
crystallized from methanol, giving 10 mg of light yel-
2.7.2. Photolysis of (iPr-DAB)Ru(CO)2(cis-Cl)2 (6a)
Irradiation of a solution of 0.29 g (0.79 mmol) 6a
in 100 ml of methanol for 45 min and evaporation of
the solvent yielded 0.29 g (0.79 mmol) red–black
crystals of 7a, identical with the product starting
from 5a.
Stability of 7a: from solutions of 7a in methanol at
r.t. after several hours a light red precipitate of poly-
meric 8a [(iPr-DAB)Ru(CO)(Cl)2]n is formed (Anal. of
8a: Found: C, 31.63; H, 4.73; N, 7.82. Calc. C, 31.77;
H, 4.74; N, 8.24%, which on refluxing completely re-
dissolves under formation of 7a. 8a is also formed
when 7a is dissolved in THF or acetone, or when 7a
is irradiated in THF or benzene.
1
low crystals, which were identified by H NMR as a
30:70 mixture of 5b and 6b. This sample was again
heated at 130°C upon which (now from the other
side) a stable equilibrium composition between 5b and
1
6b again of 43:57 was reached. H NMR of 6b (300
K, 80 MHz, acetone-d6, ppm): 8.57, 8.51 (2×d,
3
ꢀCH–N, JH,H 1.2 Hz), 1.70, 1,57 (2×s, CH3).
2.6.3. Equilibrium between (cHex-DAB)(CO)2Ru(trans-
Cl)2 and (cHex-DAB)(CO)2(cis-Cl)2 (5c and 6c)
A total of 50 mg of 5c were dissolved in 0.6 ml
acetone-d6 and the light yellow solution was heated in
an oven at 130°C in a sealed NMR tube. After 10 h,
the reaction had apparently gone to completion,
showing only the signals of 6c. On cooling the sample
to r.t., most of 6c crystallized in pure form and was
isolated. In the supernatant mother liquor, however,
both 5c and 6c were still present in a ratio of 13:87
2.7.3. Photolysis of (pAn-DAB;Me,Me)Ru(CO)2(trans-
Cl)2 (5d)
Photolysis of 20 mg 5d in 8 ml of methanol in a
Pyrex cuvette was monitored by IR and proceeded to
completion after 45 min. After evaporation of the sol-
vent, a quantitative yield of red–black crystals of
(pAn-DAB;Me,Me)Ru(CO)(MeOH)(trans-Cl)2 (7d) was
1
1
as was indicated by H NMR. H NMR of 6c (300
K, 80 MHz, acetone-d6, ppm): 8.59, 8.53 (2×1H, s,
broad, ꢀCH–N), 4.57, 3.97 (2×1H, s, broad, N–
CH), 1.4–2.3 (m, 20H, ring-CH2).
obtained. IR (methanol) wCO: 1976 cm−1 1H NMR
.
(300 K, 300 MHz, methanol-d4) ppm: 7.22, 7.00 (2×
m, 4H, phenyl-H), 4.86 (s, 1H, CH3OH), 3.85, 3.84
(2×s, 3H, Ph–OCH3), 3.34 (s, 3H, CH3OH), 2.57,
2.40 (s, 3H, ꢀC(CH3)–N). 13C NMR (300 K, 75
MHz, methanol-d4) ppm: 201.44 (CO), 177.33, 173.94
(ꢀC(Me)–N), 160.44, 160.08 (phenyl, p-), 148.57,
140.86 (phenyl, ipso), 125.03, 122.62 (phenyl, o-),
115.32, 114.97 (phenyl, m-), 55.99 (OCH3), 21.10,
20.70 (CH3).
Stability of 7d: clear red solutions of 7d in various
solvents are stable. No formation of polymeric [(pAn-
DAB;Me,Me)Ru(CO)(trans-Cl)2]n analogous to 8a is
observed.
2.7. Photochemical substitution of CO in cis- and
trans-(R-DAB)Ru(CO)2Cl2
2.7.1. Photolysis of (iPr-DAB)Ru(CO)2(trans-Cl)2 (5a)
On irradiation of the light yellow solution of 0.44 g
(1.19 mmol) 5a in 80 ml methanol, CO is evolved
and the colour changes to deep red. The reaction was
monitored by IR and had gone to completion after
20 min. The solvent was removed in vacuo at r.t.
leaving a quantitative yield of almost black crystals
of (iPr-DAB)Ru(CO)(MeOH)(trans-Cl)2 (7a). The
product was spectroscopically pure and no further
purification was necessary. Anal. for 7a: Found: C,
32.24; H, 5.46; N, 7.58; O, 8.60; Cl, 18.97. Calc.: C,
32.27; H, 5.42; N, 7.53; O, 8.60; Cl, 19.05%. MS
(FD): m/e=677–682 [(iPr-DAB)Ru(CO)(Cl)2]2+. The
isotopic pattern of the molecular ion could not be
observed, only that of the dimer after loss of
2.8. Displacement of the coordinated methanol in 7a
and 7d by CO
When solutions of 7a and 7d in methanol are
stirred in an autoclave, under 70–80 bar of CO pres-
sure at r.t. for several hours, the coordinated
methanol is cleanly replaced by CO under formation
of 5a and 5d which have been identified by IR and
1H NMR.
methanol. IR (MeOH) wCO: 1967 cm−1, (THF) wCO
1955 cm−1 1H NMR (300 K, 300 MHz, methanol-
d4) ppm: 8.56, 8.11 (2×s broad, 1H, ꢀCH–N), 4.61
:
.

J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
443
3. Results
3.1. Complexes (R-DAB)Fe(CO)2I2 (2) and
(R-DAB)FeI2 (3)
Diazadiene-tricarbonyl-iron complexes (1a,b,d) react
in solution with iodine, already at low temperatures,
with liberation of CO to stereoselectively give diazadi-
ene-dicarbonyl-trans-diiodo-iron(II) (2) (Eq. (1)).
Fig. 1. Crystal structure of 2a. The thermal ellipsoids are drawn at the
50% probability level.
(1)
14e high-spin configuration. Therefore, an X-ray struc-
ture determination was undertaken.
The dark violet complexes 2 are very labile and very
readily react further, both thermally and photochemi-
cally, to give under CO-loss tetrahedral high spin com-
plexes 3. This reaction is perfectly reversible in the case
of 2a and 3a (Eq. (2)). When, e.g. the green toluene
solution of 3a is stirred under an atmosphere of CO at
r.t., the deep violet 2a is quantitatively reformed.
When the oxidative addition of iodine is done with
1b (R1=tert-butyl), the carbonyl ligands are further
labilized in 2b, which is therefore only observable by IR
as a short-lived intermediate, and the only isolable
product is 3b. This may be due to the greater steric bulk
of the tert-butyl groups.
3.1.1. Molecular structures of 2a and 3a
The crystal structures of complexes 2a and 3a are
shown in Figs. 1 and 2, together with the atomic
numbering. Tables 3 and 4 give selected bond lengths
and angles. 2a crystallizes with two molecules in a
general position in a triclinic unit cell and 3a with four
molecules (each located on a crystallographic two-fold
axes) in an orthorhombic unit cell. The structure of 3a
is non-centrosymmetric and polar. In 2a iron is coordi-
nated octahedrally with two trans-positioned I, two
cis-positioned CꢀO and two cis-coordinated N of the
iPr-DAB moiety. In 3a iron is coordinated tetrahedrally
(2)
1
In the H NMR spectrum of 2a, there is a single set
of resonances for the protons of both halves of the
iPr-DAB ligand and there is no diastereotopic splitting
of the doublet of the isopropyl methyl groups. Due to
the high quadrupole moment of the two iodo ligands
(nuclear spin 5/2), the resonance lines are clearly
broader than those in the starting tricarbonyl complex
1a. However, the hyperfine splitting of the isopropyl
resonances is clearly visible, and the coupling constants
i
with two I and two N of the Pr-DAB moiety. Bond
i
distances (Tables 2 and 3) in the Pr-DAB moiety are
1
are readily determined. This is not the case in the H
NMR spectrum of 3a, which only shows broad humps
without much fine structure at ca. 7.7 ppm (imine H),
4.6 ppm (methyne H), and a very broad doublet at 1.5
ppm (methyl). The FD mass spectrum of 3a shows two
peaks, a small one at m/e=900 of 4% relative intensity,
corresponding to a dimeric structure, [iPr-DAB)FeI2]2+
,
and a base peak (100% rel. int.) at m/e=450 (M+).
From this it was not clear whether the strong line
broadening in the NMR had to be ascribed to four
bridging iodines in a closed-shell dimeric structure with
an 18e configuration on both of the iron atoms, or to
the paramagnetism in a mononuclear complex with a
Fig. 2. Crystal structure of 3a. The thermal ellipsoids are drawn at the
50% probability level.

444
J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
Table 3
,
Selected bond distances (A) and angles (°) for 2a
,
Bond distances (A)
Fe1–I1
Fe1–I2
Fe1–N1
Fe1–N2
Fe1–C10
N2–C5
Fe1–C9
N1–C4
2.6173(4)
2.6147(4)
1.975(3)
1.980(3)
1.793(4)
1.283(5)
1.787(4)
1.285(5)
C4–C5
C9–O1
C10–O2
1.437(5)
1.130(5)
1.138(5)
Bond angles (°)
I1–Fe1–I2
N1–Fe1–N2
C9–Fe1–C10
177.64(2)
80.81(12)
88.58(18)
Scheme 1.
The reaction of polymeric [Ru(CO)2Cl2]n with diaza-
butadienes a–d in strongly coordinating solvents such
as methanol or acetonitrile leads, in a kinetically con-
trolled reaction, stereoselectively to the formation of the
trans-dichloro complexes 5a–d. No other conforma-
tional isomers can be detected. When a less strongly
coordinating solvent such as THF was used, a complex
mixture of isomers was obtained, which have not further
been analyzed. Contrasting the stability of 4a, which
cannot thermally be isomerized even under drastic con-
ditions (180°C for 14 h), complexes 5a–d isomerize on
warming in solution or in the solid state to the racemic
all-cis isomers 6, which are readily identified from their
NMR spectra. The two equivalent halves of the R-DAB
ligands in 5 become inequivalent in 6, giving rise to two
sets of resonances. In addition, due to the C1 symmetry
of 6 with the chiral ruthenium centre, the methyl groups
of the N-iPr groups in 6a are diastereotopically split.
The temperatures at which the isomerizations take place
is characteristic for each compound and seems to de-
pend on the steric properties of the R-DAB ligand.
While 5a is stable in refluxing methanol, it isomerizes
smoothly and quantitatively to 6a at ca. 80°C in reflux-
ing acetonitrile. In the solid state a higher temperature
of ca. 140°C is required. Complex 5b (R=tBu) isomer-
izes in solution at 130°C to give an equilibrium mixture
containing 5b and 6b in a ratio of 43:57 (determined by
NMR); this equilibrium composition can be established
from both sides. Complex 5c (R=cHex) isomerizes at
120°C to give 6c with a very low residual concentration
of 5c.
essentially the same for 2a and 3a. The major difference
involves the conformation of the Pr groups. The Fe–I
i
,
distances observed in 2a (2.6173(4) and 2.6147(4) A) are
,
significantly longer than those found for 3a (2.576(2) A).
A search in the Cambridge Crystallographic Database
[49] for other structures containing the FeNeI2 fragment
gave only one hit for a structure containing the tetrahe-
dral dinitrosyl-diiodo-iron species [50] with Fe–I dis-
,
tances 2.584 and 2.596 A.
3.2. Ruthenium complexes
3.2.1. Complexes (R-DAB)Ru(CO)2Hal2
Complexes 4–7 (cf. Eq. (2) and Scheme 1) have been
prepared in moderate yields in order to compare their
chemical properties with those of 2a. When the direct
homologue of 2a, i.e. the trans-diiodo ruthenium com-
plex 4a had been prepared, tom Dieck et al. [31]
reported on a series of such compounds, and only the
dichloro complexes were further investigated. The pub-
lished X-ray data of (pTol-DAB)Ru(CO)2-trans-I2 [31]
are used to compare its structural features with those of
2a (vide infra).
(3)
Table 4
,
Selected bond distances (A) and angles (°) for 3a
3.2.2. Formation and reacti6ity of complexes (R-DAB)
Ru(CO)(MeOH)(trans-Cl)2 (7)
,
Bond distances (A)
Fe–I1
Fe–N1
N1–C4
N1–C3
C4–C4a
2.576(2)
2.123(14)
1.23(2)
1.501(16)
1.467(18)
Photochemically, one of the two CO ligands in 5 and
6 can be dissociated in solution. Even in diffuse day-
light, dilute solutions of 5 and 6 are slowly photolyzed.
Photolysis with a high-pressure mercury lamp in
methanol or THF solution is complete within a few
minutes. With vigorous evolution of CO, the light
Bond angles (°)
I1–Fe–I1a
N1–Fe–N1a
110.96(12)
76.5(5)

J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
445
yellow solutions become dark red. The resulting
methanol complexes 7a,d, which are formed from either
5 (trans-Cl2) or 6 (cis-Cl2), are isolable, and have the
chloro ligands in trans-configuration and the coordi-
nated methanol in the plane of the R-DAB ligand (cf.
Scheme 1). The THF complex is too labile to be
isolable; on evaporation of the solvent, an inhomoge-
neous almost insoluble red solid is obtained. When a
methanol solution of 7a is left standing for several
hours, again a light red solid 8a precipitates, which can
be completely redissolved in boiling methanol regener-
ating 7a. The red solids appear to be solvent-free
polymeric [(R-DAB)Ru(CO)trans-Cl2]n. Contrasting
the lability of the methanol ligand in 7a, methanol
solutions of 7d appear indefinitely stable, but at r.t.
under a CO pressure of 90 bar, in both 7a and 7d, the
methanol ligand is cleanly substituted for CO, giving
complexes 5a,d.
bonds. Thermally, the Ru–CO bond in 4 and 5a–d
cannot be broken. A solution of 4 was heated in an
evacuated sealed NMR tube at 180°C for 14 h, and in
addition to the bulk of unchanged 4, only very minor
i
amounts of free Pr-DAB, indicating beginning disrup-
tion of the complex, could be observed. In complexes 5,
only one of the two CO ligands can be photochemically
dissociated (cf. Sections 2.7 and 3.2.2). In contrast,
both carbonyl ligands in 2a readily dissociate photo-
chemically and also thermally slightly above r.t. (Eq.
(2)) to give quantitative yields of the 14e-complex 3a. In
solution, 2a and 3a are in a perfectly reversible equi-
librium which can be shifted back and forth for any
number of times. Under 1 atm of CO pressure, the
equilibrium lies completely on the side of 2a at r.t.
Qualitative experiments indicated that the equilibrium
position depends on the CO partial pressure.
When solutions of the trans-dichloro complexes 5a–c
are heated in the dark, they isomerize to the obviously
thermodynamically more stable all-cis complexes 6a–c.
The trans-diiodo complex 4 does not isomerize even at
180°C (see above). This does not necessarily mean that
in this case this is the thermodynamically most stable
configuration, but the reason could also be that the
bulky iodines impose too high an activation barrier.
The isomerization of 5a–c proceeds in methanol, ace-
tone, or acetonitrile solutions at normal pressure or in
a sealed tube, and also in the solid state, i.e. there is no
influence of the reaction medium. During the isomeriza-
tion reaction there are no colour changes, and, with IR
or NMR monitoring, no intermediates can be observed.
The reaction is very clean, i.e. there are no side reac-
tions such as CO substitution or formation of dimers.
This is indicative of an intramolecular process. The
intramolecular isomerization of octahedral complexes
has been intensively studied [51], and the most likely
process here is a Bailar–twist [52] through a trigonal
prismatic transition state. The observed dependence of
the isomerization temperatures on the bulk of the nitro-
gen substituents in the R-DAB ligands (iPrBcHexB
tBu) is in agreement with such a process. The only
alternative that has to be considered is intermediate
dechelation k2“k1 of the diazadiene ligand, with con-
secutive Berry pseudorotation in the resulting five-coor-
dinate species, and rechelation. The fluxionality of
cationic (R-DAB)(allyl)Pd(II) complexes has been ex-
plained by such a dechelation–rechelation of the R-
DAB ligand [53–55], but we believe this is less likely in
the present case.
4. Discussion
4.1. Configuration and reacti6ity of complexes
(R-DAB)M(CO)2Hal2
The formation of complexes 2 by oxidative addition
of iodine to the tricarbonyl complexes 1 (Eq. (1)) can be
readily monitored by IR spectroscopy. The oxidation of
Fe(0) to Fe(II) results in a pronounced shift of the
carbonyl stretching bands toward higher frequencies by
about 70 and 30 cm−1. The resulting two CO bands
(A1 and B2) are of almost identical intensity, indicating
OC–Fe–CO angles close to 90°, i.e. relative cis-posi-
tions. In an all-cis configured octahedral complex (C1
symmetry), the two halves of the R-DAB ligand would
be inequivalent, having a carbonyl and an iodine in
trans-positions of the two nitrogens. The NMR spectra
of 2, however, show only one set of resonances for the
R-DAB ligands. Therefore, complexes 2 must have C2V
symmetry with trans-configured iodines, which is confi-
rmed by the X-ray structural analysis of 2a (see below).
Regardless of the halogen and the diazadiene ligand,
all ruthenium complexes 4 and 5a–d show two car-
bonyl stretching bands of comparable intensity; in the
low frequency region, only one strong absorption is
found and assigned to the Ru–Cl stretching vibration
(5a: 325 cm−1; 5c: 335 cm−1). A single set of NMR
resonances is observed for the R-DAB ligands, and
diastereotopic splitting for the N–iPr methyl groups is
absent. This again indicates C2V symmetry with trans-
configured iodines, and agrees with the spectroscopic
properties of known examples of this structural type
[30,31,36].
4.2. Comparison of the crystal and molecular structures
of 2a, 3a, and (pTol-DAB;Me,Me)Ru(CO)2I2 (4e)
The most striking difference in reactivity between 2a
and its direct homologue 4, or the analogous chloro
complexes 5a–d, concerns the stability of the M–CO
We expected that the enormous difference in the
stability of the M–CO bond in the two homologous Fe
and Ru complexes 2a and 4a would be clearly reflected

446
J. Breuer et al. / Inorganica Chimica Acta 291 (1999) 438–447
Table 5
monomeric 14e-configured Fe(II) complex. In solution
under an atmosphere of CO, 3a quantitatively takes up
two molecules of CO to form the isolable complex 2a
which in turn thermally, already slightly above r.t., or
photochemically, looses both carbonyl ligands to re-
form 3a. Complexes 4 and 5, ruthenium analogues of 2,
have been prepared and their thermal and photochemi-
cal reactivity has been investigated. Contrasting the
behaviour of 2, the carbonyl ligands in the trans-diiodo
complexes 4 and trans-dichloro complexes 5 are very
strongly bound and cannot be thermally dissociated.
The dichloro complexes 5 thermally only isomerize to
the thermodynamically more stable all-cis complexes 6.
Photochemically, only one of the two carbonyl ligands
can be exchanged for a molecule of donor solvent, THF
or methanol. The X-ray molecular structures of the
analogous trans-diiodo iron and ruthenium complexes
3 and 4 do not reflect, and do not provide any informa-
tion on the vastly different stability of their M–CO
bonds.
,
Bond lengths (A) in the NꢀC–CꢀN backbone of R-DAB ligands
Compound
2a
3a
Free c [56]
NꢀC
C–C
1.285(5)
1.437(5)
1.23(2)
1.467(18)
1.258(3)
1.457(3)
in the metal-to-carbon and/or carbon-to-oxygen bond
lengths. The structure of 4a has not been determined
because that of (pTol-DAB;Me,Me)Ru(CO)2I2 (4e) had
already been published by tom Dieck et al. [31]. The
bond lengths from the central metal to the coordinated
N, C, and I atoms in 2a and 4e are all approximately
,
0.1 A shorter for iron than for ruthenium, which
reflects the different radii of the two metals. So the
,
,
Fe–C9 (1.787(4) A) and Fe–C10 (1.793(4) A) bonds
are not exceptionally long and the C–O bonds of the
carbonyl ligands in 2a and 4e (2a: C9–O1 1.130(5) A,
C10–O2 1.138(5) A; 4e: C–O 1.139(7) A) are almost
identical. They show absolutely no indication of a
different amount of p-backdonation into the CꢁO p*-
orbitals, which might explain the different M–CO bond
strengths.
,
,
,
Acknowledgements
The structure determination of 4e had the additional
bonus that the complex molecules 4e cocrystallized with
one molecule of free, uncoordinated R-DAB ligand in
the lattice. This gave the additional information that
there is almost no p-backdonation from the Ru to the
This work was supported in part by the Fonds der
Chemischen Industrie, and by the Council for Chemical
Research of the Netherlands, Organisation for Scientific
Research (CW-NWO).
,
R-DAB ligand, because the CꢀN (1.28 A) and the
,
central C–C (1.50 A) bond lengths of the free and
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