The synthesis and structural characterization of linear and macrocyclic bis(dinitrosyliron) complexes supported by bis(phosphine) bridging ligands

Article abstract of DOI:10.1139/v03-040

Reactions involving Fe(NO)₂(CO)₂ and the bis(phosphine) ligands bis(diphenylphosphino)methane (DPPM), bis(diphenylphosphino)acetylene (DPPA), 1,6-bis(diphenylphosphino)hexane (DPPH), and 1,4-bis(diphenylphosphino)-benzene (DPPB) have been examined. From these reactions, the mononuclear complex, Fe(κ¹-DPPM)(NO) ₂(CO) 3, linear dinuclear species of the type Fe₂(μ -L)(NO)₄(CO)₂ (L = Ph₂PCH₂PPh ₂ 4, Ph₂PC≡CPPh₂ 5, Ph ₂PCH₂(CH₃)₄CH₂PPh ₂ 6, and Ph₂P(p-C₆H₄)PPh ₂ 7), and macrocyclic dinuclear species of the type Fe ₂(μ-L)₂(NO)₄ (L = Ph₂PCH ₂PPh₂ 8 and Ph₂PC≡CPPh₂ 9) were isolated and spectroscopically characterized. For 4, 5, 8, and 9, the solid-state molecular structures of the products were determined by use of single-crystal X-ray diffraction techniques.

Full text of DOI:10.1139/v03-040

468
The synthesis and structural characterization of
linear and macrocyclic bis(dinitrosyliron)
complexes supported by bis(phosphine)
bridging ligands
Lijuan Li, Nada Reginato, Michael Urschey, Mark Stradiotto, and
John D. Liarakos
Abstract: Reactions involving Fe(NO)2(CO)2 and the bis(phosphine) ligands bis(diphenylphosphino)methane (DPPM),
bis(diphenylphosphino)acetylene (DPPA), 1,6-bis(diphenylphosphino)hexane (DPPH), and 1,4-bis(diphenylphosphino)-
benzene (DPPB) have been examined. From these reactions, the mononuclear complex, Fe(κ1-DPPM)(NO)2(CO) 3, lin-
ear dinuclear species of the type Fe2(µ-L)(NO)4(CO)2 (L = Ph2PCH2PPh2 4, Ph2PCϵCPPh2 5, Ph2PCH2(CH3)4CH2PPh2
6, and Ph2P(p-C6H4)PPh2 7), and macrocyclic dinuclear species of the type Fe2(µ-L)2(NO)4 (L = Ph2PCH2PPh2 8 and
Ph2PCϵCPPh2 9) were isolated and spectroscopically characterized. For 4, 5, 8, and 9, the solid-state molecular struc-
tures of the products were determined by use of single-crystal X-ray diffraction techniques.
Key words: dinitrosyliron, iron nitrosyls, dinuclear macrocycles, bis(phosphine) complexes.
Résumé : On a étudié des réactions impliquant le Fe(NO)2(CO)2 et les ligands bis(phosphines), bis(diphénylphos-
phino)méthane (DPPM), bis(diphénylphosphino)acétylène (DPPA), 1,6-bis(diphénylphosphino)hexane (DPPH), et 1,4-
bis(diphénylphosphino)benzène (DPPB). À partir de ces réactions on a isolé le complexe mononucléaire Fe(κ1-DPPM)-
(NO)2(CO) (3), les espèces dinucléaires linéaires du type Fe2(µ-L)(NO)4(CO)2 (L = Ph2PCH2PPh2 (4); Ph2PCϵCPPh2
(5); Ph2PCH2(CH3)4CH2PPh2 (6) et Ph2P(p-C6H4)PPh2 (7)) et les espèces dinucléaires macrocycliques de type Fe2(µ-
L)2(NO)4 (L = Ph2PCH2PPh2 (8); Ph2PCϵCPPh2 (9)) et on les a caractérisés par spectroscopie. Les structures molécu-
laires à l’état solide des produits 4, 5, 8 et 9 ont été déterminées par la technique de diffraction des rayons X par un
cristal unique.
Mots clés : dinitrosylfer, nitrosyles de fer, macrocycles dinucléaires, complexes de bis(phosphine).
[Traduit par la Rédaction] Li et al. 475
Introduction
after the biosynthetic evolution of NO in vitro and from the
addition of NO to iron-centered proteins (7). As part of our
ongoing study of this class of chemically and biologically
important complexes, we reported on the synthesis, struc-
tural characterization, and electrochemical behavior of com-
pounds such as 1 that are derived from the reaction of
Fe(NO)2(CO)(PR3) with tetracyanoethylene (8–10). These
molecules represent the first crystallographically character-
ized examples of dinitrosyliron-based complexes containing
π-bound olefinic ligands. Subsequently, we have prepared
and studied the non-heme iron complex, 2, which comprises
imidazole and nitrosyl ligands (Scheme 1) (11, 12).
Dinitrosyliron-based compounds are known to participate
in a variety of important chemical processes ranging from
the transfer of molecular oxygen to alkenes or phosphines
(1, 2) to the polymerization of olefins (3–6). Some non-
heme iron nitrosyl complexes have also been identified as
nitric oxide storage substances within biological systems;
these have been detected by EPR studies, both as products
Received 10 February 2003. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 17 April 2003.
We dedicate this article to Professor Don Arnold, in
recognition of his remarkable contributions to chemical
research in Canada.
Building upon this research, we have recently turned our
focus to the preparation of both linear and macrocyclic bis-
(dinitrosyliron) complexes bridged by either one or two bis-
(phosphine) ligands, respectively, in the anticipation that these
dinuclear species may exhibit interesting and unusual proper-
ties related to the proximal nature of the two metal fragments
(13). The pioneering work of Cowie and co-workers (14),
Puddephatt and co-workers (15), and others demonstrates the
reactivity advantages that can be brought about by connecting
late metal fragments with bridging bis(phosphine) ligands such
as DPPM (DPPM = bis(diphenylphosphino)methane). More-
over, Hong and co-workers have shown that dinuclear Group
L. Li1 and J.D. Liarakos. Department of Chemistry and
Biochemistry, California State University, Long Beach, CA
90840, U.S.A.
N. Reginato and M. Urschey. Department of Chemistry,
McMaster University, Hamilton, ON L8S 4M1, Canada.
M. Stradiotto.2 Department of Chemistry, Dalhousie
University, Halifax, NS B3H 4J3, Canada.
1Corresponding author (e-mail: lli@csulb.edu).
2Corresponding author (e-mail: mark.stradiotto@dal.ca).
Can. J. Chem. 81: 468–475 (2003)
doi: 10.1139/V03-040
© 2003 NRC Canada

Li et al.
469
Scheme 1. Substitution reactions of Fe(NO)2(CO)2, yielding 1
and 2.
Scheme 2. Generalized synthetic pathway to compounds 3–7.
10 complexes of the type cyclo[M(κ 2-DPPM)]2(µ-DPPA)2
(DPPA = bis(diphenylphosphino)acetylene) exhibit interesting
photoluminescent behavior (16). Despite the well-established
history of dinuclear bis(phosphine) complexes in the field of
inorganic chemistry, bis(dinitrosyliron) derivatives of this class
are still rare, and their reactivity properties remain essentially
unexplored (17).
Herein we report the synthesis and structural characteriza-
tion of bis(dinitrosyliron) complexes spanned by a structur-
ally diverse series of bis(phosphine) ligands, including:
(a) DPPM; (b) DPPH (DPPH = 1,6-bis(diphenylphos-
phino)hexane); (c) DPPA; and (d) DPPB (DPPB = 1,4-bis-
(diphenylphosphino)benzene). Depending on the reaction
conditions employed, either linear diiron constructs con-
nected by one bis(phosphine) linker, (NO)2FeP~PFe(NO)2
(A), or macrocyclic species spanned by two bridging lig-
ands, [(NO)2Fe]2(P~P)2 (B), are obtained.
Scheme 3. Preparation of compounds 8 and 9.
bonyl and the two nitrosyl ligands in 3–7 relative to
Fe(NO)2(CO)2 is characteristic of phosphine-substituted di-
nitrosyliron complexes (9). In turn, the nitrosyl stretching
frequencies observed for both 8 and 9 appear at an even
lower wavenumber. The macrocyclic DPPM-supported com-
plex, 8, exhibits four distinct IR absorptions (1733, 1721,
1687, and 1668 cm–1) in the solid and in solution (spectra
obtained from samples dissolved in CH2Cl2 match previ-
ously reported values (19)), possibly arising from the inter-
action of the Fe(NO)2 centers, as has been observed in other
cyclic systems (19, 20). This phenomenon appears to depend
on ring size, as the related ten-membered ring compound, 9,
displays only two nitrosyl stretching signals (1723 and
1679 cm–1) in both the solid and liquid states. Based on the
observed IR frequencies, the nitrosyl groups are best de-
scribed as linear, donating NO+ fragments (vide infra) (21,
22). The formation of 3–9 was also followed by use of NMR
spectroscopy, and each of the dinuclear compounds (4–9)
exhibit a single 31P NMR resonance in the range of 33–
57 ppm, consistent with a disubstituted bis(phosphine)
complex.
Results and discussion
The mononuclear complex, 3, and the linear diiron spe-
cies, 4–7, were readily prepared from Fe(NO)2(CO)2 via ad-
dition of the desired bis(phosphine), as depicted in
Scheme 2. For compounds 3–5, these could then be con-
verted into the corresponding cyclic compounds 8 (from ei-
ther 3 or 4) and 9 (from 5) (Scheme 3). Compounds 3–9
are air sensitive and undergo complete decomposition after
several hours. Decomposition also occurs (albeit more
slowly) when these complexes are stored either in degassed
solvents or as pure solids under dinitrogen at ambient tem-
perature. Interestingly, Braunstein et al. have previously
observed the formation of both 3 and 8 as side products in
the process of preparing Pt–Fe clusters (18), while
Atkinson et al., in examining the reaction between [Fe2(µ-
I)2(NO)4] and DPPM, were able to isolate compound 8 as
the corresponding tetrahydrofuran-solvated complex (19).
However, in both cases no X-ray crystallographic structural
data were provided.
In an attempt to evaluate how altering the characteristics
of the bridging bis(phosphine) ligand impacts the structural
topology of these linear and macrocyclic bis(dinitrosyliron)
complexes, an X-ray crystallographic study of compounds 4,
5, 8, and 9 was conducted. Crystallographic collection and
refinement parameters and selected metrical parameters ap-
The conversion of Fe(NO)2(CO)2 into compounds 3–7 and
subsequently into 8 or 9 is readily monitored by use of infra-
red spectroscopy; selected FT-IR data are listed in Table 1.
The decrease in stretching frequencies observed for the car-
© 2003 NRC Canada

470
Can. J. Chem. Vol. 81, 2003
Table 1. Nitrosyl and carbonyl IR stretching frequencies for 3–9 (KBr pellet).
Compounds
νCO (cm–1)
νNO (cm–1)
[Fe(DPPM)(NO)2(CO)], 3
[Fe2(µ-DPPM)(NO)4(CO)2], 4
[Fe2(µ-DPPA)(NO)4(CO)2], 5
[Fe2(µ-DPPH)(NO)4(CO)2], 6
[Fe2(µ-DPPB)(NO)4(CO)2], 7
[Fe2(µ-DPPM)2(NO)4], 8
2014, 1994; 2005a
2005; 2004a
2020, 2005
1999
2009, 1999
—
1763, 1720 (s), 1700; 1761,a 1718a
1760, 1719 (s), 1702; 1764,a 1718a
1767, 1716
1755, 1701
1760, 1707
1733, 1721, 1687, 1668
1723, 1679
[Fe2(µ-DPPA)2(NO)4], 9
—
aMeasured in THF solution.
Table 2. Crystallographic collection and refinement parameters for 4, 5, 8, and 9·CH2Cl2.
4
5
8
9·CH2Cl2
Empirical formula
Molecular weight
Description
Size (mm3)
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C27H22P2N4Fe2O6
672.13
Red needle
0.42 × 0.09 × 0.03
213(2)
C28H20P2N4Fe2O6
682.12
Dark red plate
0.3 × 0.16 × 0.08
213(2)
C50H44P4N4Fe2O4
1000.47
Dark red prism
0.25 × 0.15 × 0.14
213(2)
Monoclinic
P21/c
21.2512(1)
12.3414(1)
22.2870(2)
90.000
112.49(1)
90.000
5400.69(7)
4
1.230
ω-scans
C53H42P4N4Fe2O4Cl2
1105.39
Dark red prism
0.28 × 0.25 × 0.12
213(2)
Monoclinic
P21/c
21.3908(2)
13.8839(1)
17.8203(2)
90.000
101.463(1)
90.000
5186.84(8)
4
1.416
ω-scans
Triclinic
P1
Triclinic
P1
8.3037(1)
10.9324(3)
17.6037(2)
78.43(2)
77.318(1)
82.198(2)
1520.35(5)
2
1.468
ω-scans
684
1.105
1.20 to 22.50
–10 ≤ h ≤ 10
–13 ≤ k ≤13
–21 ≤ l ≤ 21
11 146
3892
3851/0/370
1.011
8.714(23)
9.539(28)
9.959(25)
114.52(8)
96.13(16)
97.76(12)
734.1(34)
1
1.543
ω-scans
346
1.145
2.29 to 27.34
–11 ≤ h ≤ 11
–12 ≤ k ≤ 12
–12 ≤ l ≤ 12
5231
2673
2673/0/190
0.938
γ (°)
Volume (Å3)
Z
Dcalcd (g cm–3)
Scan mode
F(000)
2064
0.698
2264
0.834
Absorption coefficient (mm–1)
θ-range (°)
Index ranges
1.04 to 22.50
–27 ≤ h ≤ 27
–16 ≤ k ≤ 16
–28 ≤ l ≤ 20
31 207
6976
6922/0/577
1.120
0.97 to 22.50
–27 ≤ h ≤ 27
–17 ≤ k ≤ 17
–22 ≤ l ≤ 22
28 244
6769
6763/12/656
1.017
Reflections collected
Independent reflections
Data/restraints/parameters
GoF on F2 (all)
Final R (I > 2σ(I))
R1 = 0.0658;
wR2 = 0.1162
R1 = 0.1384;
wR2 = 0.1466
0.9098, 0.7914
0.338
R1 = 0.0772;
wR2 = 0.1810
R1 = 0.1462;
wR2 = 0.2146
0.8722, 0.1802
0.971
R1 = 0.0885;
wR2 = 0.2818
R1 = 0.1201
wR2 = 0.3163
0.8944, 0.6976
2.932
R1 = 0.1134;
wR2 = 0.2865
R1 = 0.1451
wR2 = 0.3264
0.8577, 0.2080
2.605
R indices (all data)
Transmittance (max., min.)
Largest diff. peak (e Å–3)
Largest diff. hole (e Å–3)
–0.302
–0.405
–0.444
–1.606
pear in Tables 2 and 3, respectively. Thermal ellipsoid plots
of the refined molecular structures of the DPPM compounds,
4 and 8, and the DPPA compounds, 5 and 9, appear in
Figs. 1 to 4, respectively.
The iron centers in all four of the crystallographically
characterized compounds possess distorted tetrahedral ge-
ometries, a structural feature that is common to dinitro-
syliron complexes (12, 22). The iron—iron distances in both
the linear (4, ~5.2 Å; 5, ~7.6 Å) and macrocyclic (8, ~4.4 Å;
9, ~7.0 Å) compounds are all significantly longer than the
related distances found in other structurally characterized
bis(dinitrosyliron) species described as possessing a metal—
metal bond (23). The crystallographically determined struc-
tures of the linear species, 4 and 5, can be compared with
that of [Fe(NO)2Cl]2(µ-DPPE) (DPPE = 1,2-bis(diphenyl-
phosphino)ethane), where DPPE stands as a single bridge
joining the two metal centers (17).
Despite the range in N-Fe-N angles (115.6(4)° to
126.5(4)°), all eight of the Fe(NO)2 units in compounds 4, 5,
8, and 9 exhibit “attracto” conformations (N-Fe-N > O-Fe-
© 2003 NRC Canada

Li et al.
471
Table 3. Selected bond lengths (Å) and angles (°) for 4, 5, 8, and 9·CH2Cl2.
4
5
8
9·CH2Cl2
Bond lengths (Å)
Fe—Fe
5.21
7.60
4.35
7.01
Fe(1)—N(1)
Fe(1)—N(2)
Fe(2)—N(3)
Fe(2)—N(4)
N(1)—O
N(2)—O
N(3)—O
N(4)—O
1.693(8)
1.654(6)
1.675(8)
1.705(8)
1.171(8)
1.175(6)
1.182(8)
1.163(8)
1.680(7)
1.73(1)
—
1.643(9)
1.644(8)
1.668(9)
1.644(9)
1.19(1)
1.20(1)
1.18(1)
1.19(1)
1.66(1)
1.65(1)
1.67(1)
1.646(9)
1.19(1)
1.19(1)
1.16(1)
1.20(1)
—
1.169(7)
1.164(9)
—
—
Bond angles (°)
Fe(1)-N(1)-O
Fe(1)-N(2)-O
Fe(2)-N(3)-O
Fe(2)-N(4)-O
N(1)-Fe(1)-N(2)
N(3)-Fe(2)-N(4)
*O-Fe(1)-O*
*O-Fe(2)-O*
177.8(7)
174.8(7)
175.0(7)
177.1(8)
122.1(8)
118.1(9)
119.9
175.9(6)
178.1(7)
—
—
115.6(4)
—
174(1)
176.2(8)
172.9(7)
174.5(9)
179.6(8)
120.5(4)
126.5(4)
116.4
168.9(8)
166.6(8)
177.1(9)
117.0(4)
116.8(4)
109.6
114.1
—
116.2
110.3
124.3
*Nitrosyl oxygen atoms.
O) (24–26). The observation of contracted Fe—N distances
(~1.64 to ~1.73 Å) and lengthened N—O bonds (~1.16 to
~1.20 Å) in these complexes indicates significant iron–
nitrosyl multiple bond character, arising owing to apprecia-
ble back-donation from the iron fragment into the π*-orbital
on the nitrosyl ligand (22). By comparison, Ray et al. re-
ported crystallographic data for a series of trigonal bipyra-
midal iron nitrosyl complexes, in which the Fe—N(O) and
N—O distances are in the range of ~1.73–1.75 Å and ~1.12–
1.15 Å, respectively (27). These X-ray structural data, in ad-
dition to the observation of nearly linear Fe-N-O linkages,
corroborate the IR spectroscopic results and suggest that the
NO units in 4, 5, 8, and 9 function as three-electron donors.
Compounds 5 and 9 represent the first examples of crys-
tallographically characterized species containing the Fe-
(NO)2(µ-DPPA) fragment, and as such are worthy of further
commentary. The “anti” orientation of the Fe(NO)2 groups,
coupled with the presence of a crystallographic inversion
center, results in an interesting solid-state molecular geome-
try for the linear bis(dinitrosyliron) species, 5, in which ten
of the non-hydrogen atoms (O(1), N(2), Fe(1), P(1), C(1),
C(1A), P(1A), Fe(1A), N(2A), and O(1A)) are essentially
coplanar (mean deviation from the plane ~0.32 Å). The non-
linear nature of the P-CϵC fragment in 5 (P(1)-C(1)-C(1A)
172.9(8)°) parallels other crystallographically characterized
compounds of the type LnM-DPPA-MLn (28–34) and pre-
sumably arises because of steric congestion in the vicinity of
the triple bond. Interestingly, such steric demands do not re-
sult in a lengthening of the alkyne bonds in either 5
structure found for PdPtCl4(µ-DPPA)2 (37). The puckering
of the ring framework in 9 gives rise to a “bow-tie” orienta-
tion of the alkyne units, in which these fragments are twisted
by approximately 49° with respect to one another (Fig. 5).
As was observed for 5, the two P-CϵC-P units in 9 exhibit
concave bowing; however, one P-CϵC-P fragment is only
slightly bent (P(3)-C(3)-C(4) 173.9(9)°; P(4)-C(4)-C(3)
175.5(9)°), while the other exhibits more pronounced asym-
metric bending (P(1)-C(1)-C(2) 170.8(9)°; P(2)-C(2)-C(1)
165.8(9)°). Upon viewing the structure of 9 down the Fe–Fe
vector, it is evident that the DPPA ligands can be loosely
classified as “staggered” (P(1)-C(1)-C(2)-P(2)) and “eclipsed”
(P(3)-C(3)-C(4)-P(4)), with the former experiencing greater
strain and subsequently more pronounced deviation from lin-
earity than the latter. It is interesting to note that although
Mo2(µ-DPPA)2(CO)8 possesses similarly “staggered” and
“eclipsed” DPPA ligands (36), a correlation between the de-
gree of nonlinearity of the DPPA ligands and their relative
orientation does not exist in this Mo-based system.
Experimental
General
All manipulations were carried out in an atmosphere of
dry dinitrogen using freshly distilled and degassed solvents.
Unless otherwise stated, all chemicals, including
bis(diphenylphosphino)methane (DPPM, Aldrich), 1,6-bis-
(diphenylphosphino)hexane (DPPH, Aldrich), bis(diphenyl-
phosphino)acetylene (DPPA, Strem Chemicals), and 1,4-
bis(diphenylphosphino)benzene (DPPB, Organometallics
Inc.) were used as supplied. Fe(NO)2(CO)2 was prepared
(1.21(1) Å) or
9 (C(1)-C(2) 1.198(4) Å; C(3)-C(4)
1.20(1) Å), which remain essentially unchanged relative to
free DPPA (35).
1
following a published procedure (38). The H, 13C, and 31P
The overall molecular structure of the macrocyclic DPPA
compound, 9, can be described as a severely twisted ten-
membered ring, a geometry that is similar to Mo2(µ-
DPPA)2(CO)8 (36), but different from the nearly planar
NMR spectral data were acquired using either a Bruker
AC-200 or AC-300 spectrometer in deuterated chloroform,
unless otherwise stated. All 13C and 31P NMR spectra were
recorded in proton-decoupled mode with phosphorus chem-
© 2003 NRC Canada

472
Can. J. Chem. Vol. 81, 2003
Fig. 1. The X-ray structure of 4, showing the atomic numbering
scheme. Anisotropic thermal displacement ellipsoids are shown
at the 30% probability level.
Fig. 3. The X-ray structure of 5, showing the atomic numbering
scheme. Anisotropic thermal displacement ellipsoids are shown
at the 30% probability level.
X-Ray crystallography
Fig. 2. The X-ray structure of 8, showing the atomic numbering
scheme. Anisotropic thermal displacement ellipsoids are shown
at the 30% probability level.
Crystallographic data for 4, 5, 8, and 9·CH2Cl2 were col-
lected from suitable samples mounted on glass fibers. The
instrument used for the collection of diffraction data was a
Siemens P4 diffractometer equipped with
a Siemens
SMART 1K CCD Area Detector (using the program
SMART) and a rotating anode using graphite-mono-
chromated Mo Kα radiation (λ = 0.71073 Å). Data process-
ing was carried out by use of the program SAINT, while the
program SADABS was utilized for the scaling of diffraction
data, the application of a decay correction, and an empirical
absorption correction based on redundant reflections. Struc-
tures were solved by using the direct methods procedure in
the Siemens SHELXTL program library and refined by full-
matrix least squares methods on F2. All non-hydrogen at-
oms, with the exception of the disordered atoms in
9·CH2Cl2, were refined using anisotropic thermal parame-
ters. Hydrogen atoms were added as fixed contributors at
calculated positions, with isotropic thermal parameters based
on the bonded carbon atom. Compound 5 crystallizes in the
space group P1 with half a molecule per asymmetric unit;
the other half of the molecule may be generated by a crystal-
lographic inversion center, resulting in the observation of
only one molecule per unit cell (Z = 1). Combustion analy-
sis, previously obtained by others (39), for compound 8
(similarly prepared in tetrahydrofuran) suggested the pres-
ence of one solvated tetrahydrofuran per molecule of 8 in
the crystalline lattice. However, despite the fact that the data
readily allow for a complete anisotropic refinement of the
target molecule, attempts to resolve atomic positions for the
disordered solvate were unsuccessful, leading to rather high
values for the residual electron density and the refinement
statistics. In the case of 9·CH2Cl2, the final refined structure
involved a disordered model in which the phenyl rings con-
taining C(20)–C(25) and C(50)–C(55) could exist in either
of two orientations resulting from rotation about the P—
C(ipso) bond. Based on the observed thermal displacement
ical shifts externally referenced relative to 85% H3PO4 in
D2O. Melting and decomposition points were measured us-
ing differential scanning calorimetry performed on a DSC
2910 instrument (TA instruments). IR spectra were re-
corded on a Bio-Rad FTS-40 single-beam spectrometer us-
ing KBr pellets, unless otherwise stated. Mass spectra were
recorded on a Micromass Quattro LC instrument using pos-
itive electrospray ionization (ESI+). Despite repeated at-
tempts, satisfactory elemental analysis data for the
compounds reported herein could not be obtained.
© 2003 NRC Canada

Li et al.
473
Fig. 5. Views of the crystallographically determined structure of
9·CH2Cl2: (a) highlighting the “bow-tie” orientation of the
alkyne units and (b) down the Fe(1)–Fe(2) vector (selected atoms
omitted for clarity).
Fig. 4. The X-ray structure of 9·CH2Cl2, with thermal displace-
ment ellipsoids shown at the 30% probability level. For clarity,
hydrogen atoms and the dichloromethane solvate have been omit-
ted, and only the most highly populated components of the dis-
ordered phenyl rings are shown.
ellipsoids, it was assumed that only these carbon atoms were
significantly affected by this disorder process. The occupan-
cies for each of the two orientations were each allowed to be
refined as a free variable (final ratio of approximately 55:45
for both of the phenyl units). Moreover, during the refine-
ment of 9·CH2Cl2, a disordered molecule of dichloro-
methane was located in the asymmetric unit. Given the
magnitude, location, and number of electron density differ-
ence peaks observed in the region of the solvate, the final re-
fined structure was based on a disordered model that
involved two possible orientations generated by rotation
about a fixed and non-disordered (fully occupied) central
methylene carbon. The occupancies for each of the two ori-
entations were each allowed to be refined as a free variable
(final ratio of approximately 90:10). Hydrogen atoms for
each unique component of the disordered phenyl and di-
chloromethane units were added at calculated positions with
occupancy factors equal to the occupancy factor of the asso-
ciated carbon atom. The hydrogen atoms were refined using
a riding model with isotropic displacement parameters equal
to 1.2 times the equivalent isotropic displacement parameter
of the attached carbon (40–43).3
phosphine ligand in THF was added Fe(NO)2(CO)2 at room
temperature. After stirring the solution for 18 h, the solvent
was removed under reduced pressure and the remaining
solid washed with pentane.
General preparation of compounds 3–7
General preparation of compounds 8 and 9
Method (c): A solution of the reactants was filtered into a
sealable tube, degassed by use of freeze-pump-thaw proce-
dures, flame-sealed under vacuum, and subsequently heated
to 75°C.
Method (a): To an Erlenmeyer flask containing Fe(NO)2-
(CO)2 was added a suspension of the phosphine ligand in
pentane at room temperature. After stirring the solution for
18 h, the precipitate generated was filtered and washed with
pentane. Method (b): To an Erlenmeyer flask containing the
3 Supplementary data may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC
205068 (4), 205069 (5), 205070 (8), and 205071 (9·CH2Cl2) contain the supplementary data for this paper. These data can be obtained, free
of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge, U.K.; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2003 NRC Canada

474
Can. J. Chem. Vol. 81, 2003
[Fe(κ1-DPPM)(NO)2(CO)] 3
[Fe2(µ-DPPB)(NO)4(CO)2] 7
Method (b): DPPB (500 mg, 1.1 mmol), Fe(NO)2(CO)2
(0.27 mL, 2.5 mmol), and THF (25 mL) yielded 7 (760 mg,
94%); m.p. 301°C (with decomposition). IR (KBr pellet)
Method (a): Fe(NO)2(CO)2 (0.1 mL, 0.9 mmol) and
DPPM (170 mg, 0.44 mmol) in pentane (8 mL) produced 3
as bright orange-red powder (70 mg, 30%). Method (b):
DPPM (170 mg, 0.44 mmol), Fe(NO)2(CO)2 (0.05 mL,
0.45 mmol), and THF (6 mL) produced 3 (160 mg,
69%), m.p. 119°C (with decomposition). IR (KBr) (cm–1) ν:
2014 (CO), 1994 (CO), 1763 (NO), 1720 (shoulder) (NO),
1700 (NO). IR (THF-solution) (cm–1) ν: 2005 (CO), 1761
(NO), 1718 (NO). 1H NMR (200 MHz) δ: 3.21 (d, 2H,
2JHP = 8.7 Hz, CH2), 7.27–7.49 (m, 20H, Ph). 13C NMR
(50 MHz) δ: 31.7 (m, CH2), 127.9–137.6 (Ph), 221.3 (s,
(cm–1) ν: 2009 (CO), 1999 (CO), 1760 (NO), 1707 (NO). H
1
NMR (200 MHz) δ: 7.34–7.42 (m, Ph). 13C NMR (50 MHz)
δ: 129.0 (d, JCP = 10.8 Hz, Co or Cm and o-C6H4), 130.8 (s,
Cp), 132.3 (d, JCP = 24.6 Hz, i-C6H4), 133.2 (d, JCP
=
13.6 Hz, Cm or Co), 136.9 (d, JCP = 38.2 Hz, Ci), 221.0 (s,
CO). 31P NMR (121 MHz) δ: 57.1 (s).
[Fe2(µ-DPPM)2(NO)4] 8
CO). 31P NMR (121 MHz) δ: –25.0 (d, 1P, JPP = 105.6 Hz),
2
Method (c): After stirring DPPM (72 mg, 0.19 mmol) and
4 (125 mg, 0.19 mmol) in THF (6 mL) for 18 h, the solution
gradually turned black. After 24 h a red crystalline product
(8) was isolated by filtration (45 mg, 24%); these crystals
were used for X-ray diffraction studies. Alternative route us-
ing method (c): 3 (150 mg, 0.28 mmol) in THF (5 mL)
(35 mg, 13%); m.p. 167°C. IR (KBr) (cm–1) ν: 1733 (NO),
1721 (NO), 1687 (NO), 1668 (NO); the spectrum run in
2
48.0 (d, 1P, JPP = 105.6 Hz, P-Fe).
[Fe2(µ-DPPM)(NO)4(CO)2] 4
Method (a): Fe(NO)2(CO)2 (0.34 mL, 3.1 mmol) was
added to a suspension of DPPM (120 mg, 0.31 mmol) in
pentane (10 mL). During the course of the reaction the
DPPM dissolved, and a dark red - brown powder precipi-
tated, which was filtered and washed with pentane (190 mg,
92%). Method (b): DPPM (500 mg, 1.3 mmol), Fe(NO)2-
(CO)2 (0.3 mL, 2.7 mmol), and THF (10 mL) produced 4
(690 mg, 79%), m.p. 144°C (with decomposition). IR (KBr)
(cm–1) ν: 2005 (CO), 1760 (NO), 1719 (shoulder) (NO),
1702 (NO). IR (THF-solution) (cm–1) ν: 2004 (CO), 1764
1
CH2Cl2 matches previously reported values (19). H NMR
2
(200 MHz) δ: 3.7 (t, JHP = 6.5 Hz, 2 × CH2), 7.5–7.3 (m,
Ph, 40H). 31P NMR (121 MHz) δ: 43.5 (s). MS-MS (90:10
CH2Cl2/MeOH, m/z, (%)): 1000 ([M]+, 100), 970 ([M –
NO]+, 2), 500 ([M/2]+, 45).
[Fe2(µ-DPPA)2(NO)4] 9
1
Method (c): After stirring 5 (100 mg, 1.5 mmol) and
DPPA (58 mg, 1.5 mmol) in THF (5 mL) for 18 h, the solu-
tion gradually turned black. After 72 h the tube was opened,
the solvent removed under reduced pressure, and the remain-
ing brown solid (9) washed with pentane (90 mg, 64%). Sin-
gle crystals suitable for X-ray analysis were grown from
CH2Cl2 by slow evaporation of the solvent under an atmo-
sphere of dinitrogen. IR (KBr) (cm–1) ν: 1723 (NO), 1679
(NO), 1718 (NO). H NMR (300 MHz, CD2Cl2) δ: 3.76 (t,
2
2H, JHP = 9.7 Hz, CH2), 7.41–7.44 (m, 20H, Ph). 13C NMR
1
(75 MHz) δ: 32.6 (t, JCP = 11.4 Hz, CH2), 129.3 (t, JCP
=
5.2 Hz, Co or Cm), 131.1 (s, Cp), 132.6 (t, JCP = 6.5 Hz, Cm
or Co), 134.3 (t, JCP = 22.2 Hz, Ci), 221.1 (s, CO). 31P NMR
(121 MHz) δ: 45.6 (s). Single crystals suitable for X-ray dif-
fraction studies were grown from pentane by slow evapora-
tion under an atmosphere of dinitrogen.
1
(NO). H NMR (200 MHz) δ: 7.51–7.09 (m, Ph, 40H). 31P
NMR (121 MHz) δ: 38.6 (s).
[Fe2(µ-DPPA)(NO)4(CO)2] 5
Method (b): DPPA (300 mg, 0.76 mmol), Fe(NO)2(CO)2
(0.18 mL, 1.6 mmol), and THF (6 mL) yielded 5 (370 mg,
71%). IR (KBr) (cm–1) ν: 2020 (CO), 2005 (CO), 1716
Summary
The results described herein demonstrate that both linear
and macrocyclic organometallic complexes containing a pair
of dinitrosyliron fragments spanned by either one or two
bis(phosphine) ligands can be selectively prepared from
Fe(NO)2(CO)2. The X-ray crystallographic characterization
of four members of this series reveals that the choice of
bridging bis(phosphine) ligand used in these syntheses has a
profound influence on the molecular structure of the result-
ing diiron framework. This preliminary synthetic and struc-
tural investigation provides the groundwork for exploring the
chemical, physical, and reactivity properties of this class of
molecules. These studies are underway and will be the focus
of future reports.
1
(NO), 1767 (NO). H NMR (300 MHz) δ: 7.43–7.64 (m,
20H, Ph). 13C NMR (50 MHz) δ: 129.1 (d, JCP = 11.5 Hz, Co
or Cm), 131.1 (s, Cp), 131.8 (d, JCP = 14.4 Hz, Cm or Co),
132.0 (d, JCP = 47.9 Hz, Ci), 218.7 (s, CϵO). 13P NMR
(121 MHz) δ: 33.1 (s). Single crystals suitable for X-ray dif-
fraction studies were grown from pentane by slow evapora-
tion under an atmosphere of dinitrogen.
[Fe2(µ-DPPH)(NO)4(CO)2] 6
Method (b): DPPH (500 mg, 1.2 mmol), Fe(NO)2(CO)2
(0.3 mL, 2.8 mmol), and THF (15 mL) produced 6 (500 mg,
56%). IR (KBr) (cm–1) ν: 1999 (CO), 1755 (NO), 1701
1
(NO). H NMR (200 MHz) δ: 1.0–1.4 (m, 8H, PCH2(CH2)4-
Acknowledgments
CH2P), 2.29 (m, 4H, PCH2(CH2)4CH2P), 7.40–7.42 (m, 20H,
Ph). 13C NMR (50 MHz) δ: 24.1 (s, 2 × CH2), 30.0 (d,
Support of this work by the Natural Sciences and Engi-
neering Research Council of Canada (NSERC), Research
Corporation (CC5392), and the Petroleum Research Fund
administered by the American Chemical Society (37034-
GB3) is gratefully acknowledged. We would also like to
1JCP = 8.4 Hz, 2 × PCH2), 30.5 (s, 2 × CH2), 128.7 (d, JCP
=
9.5 Hz, Co or Cm), 130.0 (s, Cp), 131.8 (d, JCP = 11.8 Hz, Cm
or Co), 134.0 (d, JCP = 39.6 Hz, Ci), 222.0 (s, CO). 31P NMR
(121 MHz) δ: 49.2 (s).
© 2003 NRC Canada

Li et al.
475
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© 2003 NRC Canada