Syntheses, properties and M?ssbauer studies of cyanamide and cyanoguanidine complexes of iron(II). Crystal structures of trans-[FeH(NCNH2)(Ph2PCH2CH2PPh 2)2][BF4] and trans-[Fe(N

Article abstract of DOI:10.1016/s0020-1693(99)00021-3

The complexes trans-[FeH(NCR)(dppe)₂][BF₄] (1) (R=NH₂, NMe₂, NEt₂ or NC(NH₂)₂; dppe=Ph₂PCH₂CH₂PPh₂) and trans-[FeL(NCR)(depe)₂

Full text of DOI:10.1016/s0020-1693(99)00021-3

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 291 (1999) 39–48
Syntheses, properties and Mo¨ssbauer studies of cyanamide and
cyanoguanidine complexes of iron(II). Crystal structures of
trans-[FeH(NCNH2)(Ph2PCH2CH2PPh2)2][BF4] and
trans-[Fe(NCNEt2)2(Et2PCH2CH2PEt2)2][BF4]2
Lu´ısa M.D.R.S. Martins a, Joa˜o J.R. Frau´sto da Silva a, Armando J.L. Pombeiro a,*,
Richard A. Henderson b, David J. Evans b, Franco Benetollo c, Gabriella Bombieri d,
Rino A. Michelin e
a Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, A6. Ro6isco Pais, 1096 Lisbon codex, Portugal
b Nitrogen Fixation Laboratory, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
c Istituto di Chimica e Tecnologia dei Radioelementi del CNR, Corso Stati Uniti 4, 35020 Padua, Italy
d Istituto di Chimica Farmaceutica, Uni6ersita` di Milano, 6iale Abruzzi 42, 20131 Milan, Italy
e Dipartimento di Processi Chimini dell’Ingegneria, Uni6ersita´ di Pado6a, Via F. Marzolo 9, 35131 Padua, Italy
Received 4 September 1998; accepted 14 December 1998
Abstract
The complexes trans-[FeH(NCR)(dppe)2][BF4] (1) (R=NH2, NMe2, NEt2 or NC(NH2)2; dppe=Ph2PCH2CH2PPh2) and
trans-[FeL(NCR)(depe)2]Yn (R=NH2, NMe2, NEt2 or NC(NH2)2; depe=Et2PCH2CH2PEt2; Y=BF4 or BPh4; (2), L=Br,
n=1; (3), L=NCR, n=2) have been prepared by treatment of trans-[FeHCl(dppe)2] (in THF and in the presence of Tl[BF4]) or
trans-[FeBr2(depe)2] (in MeOH and in the presence of [NBu4][BF4] or Na[BPh4]), respectively, with the appropriate cyanamide.
NMR and Mo¨ssbauer spectral, as well as FAB mass spectrometric data are reported. Mo¨ssbauer partial isomer shift (PIS) and
partial quadrupole splitting (PQS) parameters have been estimated for the cyanamide and dppe ligands and rationalised, with the
overall IS and QS, in terms of p- and s-electronic effects, the cyanamides behaving as more effective s-donors and weaker
p-acceptors than organonitriles. FAB MS fragmentation patterns are also proposed. The crystal structures of 1 (R=NH2) and
3 (R=NEt2, Y=BF4) are reported. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Mo¨ssbauer study; Crystal structures; Iron complexes; Cyanamide complexes; Cyanoguanidine complexes
1. Introduction
to dinitrogen-binding iron(II) phosphinic centres the
investigation of the reactions of NCNH2 and its
organo-derivatives NꢀCNMe2 and NꢀCNEt2, as well as
its dimeric form, cyanoguanidine, NꢀCNꢁNC(NH2)2.
Therefore, we have prepared three series of cyanamide
and cyanoguanidine complexes of the types trans-
[FeH(NCR)(dppe)2][BF4] (1) (dppe=Ph2PCH2CH2-
Cyanamide (NꢀCNH2) is a recognised substrate of
nitrogenase [1] whose coordination chemistry still re-
mains underdeveloped. In pursuit of our interest [2] on
the study of its activation, as well as of its derivatives,
by a variety of transition metal centres, and in view of
the discovery [3] of an alternative nitrogenase contain-
ing iron as the only transition metal, we have extended
PPh2),
trans-[FeBr(NCR)(depe)2]Y
(2)
(depe=
Et2PCH2CH2PEt2; Y=BF4 or BPh4) and trans-
[Fe(NCR)2(depe)2]Y2 (3). Because the bonding
properties of such ligands have not yet been fully
elucidated, we have applied Mo¨ssbauer spectroscopy
(which has been successfully used [4] for other low-spin
octahedral iron(II) phosphinic complexes) to investigate
* Corresponding author. Tel.: +351-1-841 9237; fax: +351-1-846
4455.
E-mail address: pombeiro@alfa.ist.utl.pt (A.J.L. Pombeiro)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00021-3

40
L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
This preparative method involves replacement of the
chloride ligand by the cyanamide (NCR), assisted by
the thallium salt, and is analogous to that followed [5]
for the synthesis of the related isocyanide complexes
trans-[FeH(CNR)(dppe)2]+ (R=alkyl or aryl).
The reaction of trans-[FeBr2(depe)2] in a methanolic
solution with a stoichiometric amount of the appropri-
ate cyanamide (NCR), under an inert atmosphere, for
ca. 1 h, leads to the formation of the monocyanamide
complexes trans-[FeBr(NCR)(depe)2]+ ((2); R=NH2
(2a), NMe2 (2b), NEt2 (2c) or NC(NH2)2 (2d)) which
were isolated as their BF4− or BPh4− salts (usually red
in colour) upon addition of [NBu4][BF4] or Na[BPh4]
(Eq. (i), Scheme 1, X=NBu4 or Na, Y=BF4 or BPh4,
respectively). However, if a 2-fold molar amount of the
cyanamide is used, the dicyanamide species trans-
[Fe(NCR)2(depe)2]2+ ((3); R=NH2 (3a), NMe2 (3b),
NEt2 (3c) or NC(NH2)2 (3d)) are obtained (Eq. (ii),
Scheme 1), isolated as the BF4− or BPh4− salts (red in
colour). Complexes 3 can also be obtained by the
reaction of the monocyanamide compounds with the
corresponding cyanamide (Eq. (iii), Scheme 1).
These reactions are comparable with those reported
[6] for trans-[FeBr2(depe)2] with organonitriles occur-
ring [7] via the stepwise displacement of the bromide
ligands.
Complexes 1, 2 and 3 were characterised by IR
(Table 1), multinuclear (1H, 31P and 13C) NMR (Tables
2 and 3) and Mo¨ssbauer (Table 4) spectroscopies, ele-
mental analysis (Table 1), FAB mass spectrometry, as
well as, for 1 (R=NH2) or 3 (R=NEt2, Y=BF4), by
single-crystal X-ray structural analyses.
Scheme 1.
their electron donor/acceptor abilities (in particular
partial isomer shifts and quadrupole splittings for these
still uncommon ligands were derived), and we have
determined the X-ray crystal and molecular structures
of two such complexes.
2. Results and discussion
2.1. Syntheses
Treatment of a THF solution of trans-[FeHCl-
(dppe)2] with Tl[BF4] followed by addition of the ap-
propriate cyanamide NCR (R=NH2, NMe2, NEt2 or
NC(NH2)2 (cyanoguanidine)) (in
a
stoichiometric
amount), under an inert atmosphere, for ca. 1 h, leads
to the formation of trans-[FeH(NCR)(dppe)2][BF4] ((1);
R=NH2 (1a), NMe2 (1b), NEt2 (1c) or NC(NH2)2 (1d))
which have been isolated as orange solids (Eq. (1)).
trans-[FeHCl(dppe)2]+NCR+Tl[BF4]
THF
“ trans-[FeH(NCR)(dppe)2][BF4]+TlCl
(1)
1
Table 1
Physical and analytical data for trans-[FeH(NCR)(dppe)2][BF4] (1), trans-[FeBr(NCR)(depe)2]Ya (2) and trans-[Fe(NCR)2(depe)2]Y2 (3)
a
R
Colour
w(NꢀC)b
w(Fe–H)b
Analysis (%)c
C
H
N
d
1a
1b
1c
1d
NH2
orange
orange
orange
orange
2270 m
2225 s
2215 m
2215 s
1850 w,br
1870 w,br
1885 w,br
1880 w,br
64.4(64.8)
65.4(65.4)
66.0(65.9)
63.4(63.3)
4.9(5.2)
5.5(5.5)
5.9(5.7)
5.6(5.2)
2.8(2.8)
NMe2
NEt2
NC(NH2)2
2.4(2.8)
2.4(2.7)
5.3(5.5)
e
e
e
d
2a
2b
2c
2d
NH2
red
red
orange
red
2210 s
2230 s
2220 s
2210 s
37.0(37.2)
39.4(39.2)
60.9(61.0)
36.5(36.7)
6.9(7.4)
7.7(7.7)
8.3(8.1)
7.0(7.3)
3.7(4.1)
4.4(4.0)
2.8(2.9)
7.7(7.8)
NMe2
f
NEt2
NC(NH2)2
d,f
3a
3b
3c
3d
NH2
red
red
red
red
2240 s
2240 s
2225 s
2220 s
69.7(70.6)
39.8(39.9)
43.3(43.0)
35.8(35.6)
7.9(7.8)
7.7(7.7)
8.2(8.2)
7.0(7.0)
4.7(4.7)
7.2(7.2)
6.6(6.7)
NMe2
NEt2
NC(NH2)2
13.6(13.8)
a Y=BF4 unless stated otherwise.
b In KBr pellets; values in cm−192.5; s, strong; m, medium; w, weak; br, broad.
c Required values in parentheses.
d w(N–H)=3300–3160 cm−1
.
e w(N–H)=3460–3280 cm−1
f Y=BPh4.
.

L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
41
Table 2
Proton and 31P{1H} NMR data for trans-[FeH(NCR)(dppe)2][BF4] (1), trans-[FeBr(NCR)(depe)2]Ya (2) and trans-[Fe(NCR)2(depe)2]Y2 (3)
a
R
Complex
l (1H)b
Assignment
J (Hz)
l (31P)c
−56.18
NH2
1a
7.32–7.13 (m, 40H)
6.18 (s, 2H)
C6H5 (dppe)
NCNH2
2.80–2.60 (m,br, 4H)
2.45g (m,br, 4H)
−22.52 (qt, 1H)
1/2Ph2PCH2CH2PPh2
1/2Ph2PCH2CH2PPh2
hydride
2JHP=47.8
NMe2
1b
1c
7.72–7.20 (m, 40H)
3.00–2.82 (m,br, 4H)
2.66 (s, 3H)
2.65 (s, 3H)
2.42–2.26 (m,br, 4H)
−22.08 (qt, 1H)
C6H5 (dppe)
−54.60
1/2Ph2PCH2CH2PPh2
1/2NCN(CH3)2
1/2NCN(CH3)2
1/2Ph2PCH2CH2PPh2
hydride
2JHP=47.5
3JHH=7.1
NEt2
7.65–7.10 (m, 40H)
2.94 (q, 4H)
C6H5 (dppe)
−55.40e
NCN(CH2CH3)2
1/2Ph2PCH2CH2PPh2
1/2Ph2PCH2CH2PPh2
NCN(CH2CH3)2
hydride
2.80h (m,br, 4H)
2.44–2.30 (m,br, 4H)
0.94 (t, 6H)
3JHH=7.2
2JHP=47.8
−22.34 (qt, 1H)
NC(NH2)2
NH2
1d
2a
7.70–7.02 (m, 40H)
3.00–2.80 (m,br, 4H)
2.50g (m,br, 4H)
C6H5 (dppe)
−54.28
−70.47
1/2Ph2PCH2CH2PPh2
1/2Ph2PCH2CH2PPh2
hydride
−22.91 (qt, 1H)
2JHP=47.3
6.49 (s, 2H)
NCNH2
2.41 (m, 8H)i
2.26 (dq, 8H)
2.07 (dq, 8H)
1.46 (m, 24H)
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=7.8, 2JHP=15.6
3JHH=7.8, 2JHP=15.6
NMe2
2b
2c
2.98 (s, 6H)
NCN(CH3)2
−74.63
−74.63
2.48 (m, 8H)i
2.33 (dq, 8H)
2.12 (dq, 8H)
1.51 (m, 24H)
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=7.8, 2JHP=15.6
3JHH=7.6, 2JHP=15.2
d,e
NEt2
7.49 (m, 8H)
7.28 (t, 8H)
7.17 (t, 4H)
3.10 (q, 4H)
2.19 (m, 8H)i
2.03 (dq, 8H)
1.87 (dq, 8H)
1.27 (m, 24H)
0.90 (t, 6H)
Ho (BPh4−
Hm (BPh4−
Hp (BPh4−
)
)
)
3JHH=7.0
3JHH=7.1
3JHH=7.2
NCN(CH2CH3)2
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=7.8, 2JHP=15.6
3JHH=7.6, 2JHP=15.2
NCN(CH2CH3)2
3JHH=7.2
NC(NH2)2
2d
3a
3.13 (s, 4H)
NCN(NH2)2
−74.06
−71.31
2.12 (m, 8H)i
2.07 (dq, 8H)
1.86 (dq, 8H)
1.32 (m, 24H)
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=7.5, 2JHP=15.0
3JHH=7.6, 2JHP=15.2
d
NH2
7.48 (m, 16H)
7.08 (t, 16H)
6.93 (t, 8H)
Ho (BPh4−
)
Hm (BPh4−
)
3JHH=7.2
3JHH=6.9
Hp (BPh4−
NCNH2
)
6.78 (s, 2H)j
2.39 (m, 8H)i
2.23 (dq, 8H)
2.07 (dq, 8H)
1.44 (m, 24H)
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=8.1, 2JHP=16.2
3JHH=7.6, 2JHP=15.2
NMe2
3b
2.97 (s, 12H)
2.47 (m, 8H)i
2.30 (dq, 8H)
2.12 (dq, 8H)
1.51 (m, 24H)
NCN(CH3)2
−72.77
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=7.5, 2JHP=15.0
3JHH=7.7, 2JHP=15.4
(continued)

42
L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
Table 2 (continued)
R
Complex
l (1H)b
Assignment
J (Hz)
l (31P)c
−75.28
f
NEt2
3c
3.06 (q, 8H)
NCN(CH2CH3)2
Et2PCH2CH2PEt2CH2
CH2 (Et, depe)
CH3 (depe)
3JHH=7.1
2.24 (m, 8H)i
1.88 (m, 16H)k
1.39 (m, 24H)
1.90 (t, 12H)
3JHH=8.0, 2JHP=16.0
3JHH=7.4
NCN(CH2CH3)2
NC(NH2)2
3d
3.47 (s, 8H)
NCN(NH2)2
−71.42
2.20 (m, 8H)i
1.97 (dq, 8H)
1.82 (dq, 8H)
1.29 (m, 24H)
Et2PCH2CH2PEt2
1/2CH2 (Et, depe)
1/2CH2 (Et, depe)
CH3 (depe)
3JHH=7.4, 2JHP=14.8
3JHH=7.2, 2JHP=14.4
a Y=BF4 unless otherwise stated.
b In (CD3)2CO unless otherwise stated; l in ppm relative to internal SiMe4; s, singlet; t, triplet; q, quartet; qt, quintet; dq, doublet of quartets;
m, multiplet; br, broad resonance; subscripts o, m, and p denote the o-, m- and p-protons of the phenyl ring, respectively.
c In (CD3)2CO unless otherwise stated; l (singlet resonance) in ppm relative to external P(OMe)3.
d Y=BPh4.
e In CD2Cl2.
f In CDCl3.
g Partial overlapping with the solvent resonance.
h Partial overlapping with the NCN(CH2CH3)2 quartet.
i Filled-in doublet, not resolved.
j Lower intensity than expected due to proton exchanging with the solvent water.
k Multiplet resulting from two doublets of partially overlaped quartets.
doublet centred at l 2.48–2.12, corresponding to the
AA% part of an A2XX%A2% (A,A%=1H; X,X%=31P) spin
system as found [6] in the 1H NMR spectra of the
analogous organonitrile complexes. For complexes 2 or
2.2. Spectroscopic data
The solid-state IR spectra (KBr pellets) of complexes
1, 2 and 3 exhibit strong w(NC) bands (Table 1) in the
range of 2270–2210 cm−1, at slightly higher wavenum-
bers (by ca. 25–10 cm−1) than those observed for the
corresponding free cyanamides, in agreement with the
h1-coordination through the cyano group acting mainly
as an electron-donor to the metal. The cyanamides
appear to behave as weaker p-electron acceptors than
organonitriles since w(NC) for the latter species under-
goes a shift to lower frequencies upon coordination [6],
at the related complexes trans-[FeL(NCR)(depe)2]Yn
(R=alkyl or aryl; Y=BF4 or BPh4; L=Br, n=1;
L=NCR, n=2). Additional IR broad and strong in-
tensity bands in the range of 3300–3160 cm−1
(NCNH2) and 3460–3280 cm−1 [NCNC(NH2)2] are
assigned to w(NH), whereas other strong bands at
1630–1550 cm−1 (NCNH2) or 1650–1560 cm−1
[NCNC(NH2)2] are due to l(NH) and/or w(NꢁC). The
trans configuration is assigned to all complexes on the
basis of a singlet in their 31P{1H} NMR spectra (Table
2).
3 the MeCH2– protons appear as two doublets (2JHP
=
14.4–16.2 Hz) of quartets (3JHH=7.2–8.1 Hz) at l
2.33–1.97 and 2.12–1.39, each of them arising from
CH2 coupling to one 31P nucleus (doublet) and to the
three protons of the methyl group (quartet). For 3c
these resonances partially overlap to give a 1:3:4:4:3:1
sextet at l 1.88.
In the 13C NMR spectra (both 1H decoupled and
coupled) of complexes 1 (Table 3) the cyano-carbon
(NCR) resonance is observed as a singlet at l ca. 125
ppm which corresponds to a slight downfield shift (by
ca. 7 ppm) upon coordination. For the cyanoguanidine
complex 1d, the imine carbon NCNC(NH2)2 resonance
occurs at l 160.38 ppm. The resonances of the different
types of carbons at the aromatic rings of the dppe have
also been identified (Table 3). Moreover, in the 13C{1H}
NMR spectra, the resonance of the –CH2CH2– group
bridging the phosphorus atoms is a quintet (ca. 12 Hz)
at l ca. 32 ppm, arising from coupling to the four
31P nuclei. These resonances split into triplets (1JCH ca.
133 Hz) of those quintets in the 13C–1H coupled
spectra.
Consistent with the trans geometry for complexes 1, a
quintet resonance is observed in the H NMR spectra
1
(in (CD3)2CO) (Table 2) at ca. l −22 (2JHP ca. 47 Hz)
attributable to Fe–H. The resonances of the methylene
protons of dppe in 1 occur as two broad multiplets at l
ca. 2–3 thus suggesting two non-equivalent sets of CH2
groups, whereas the resonances of the –CH2CH2–
group of depe (complexes 2 or 3) appear as a filled-in
2.3. Mo¨ssbauer data
Mo¨ssbauer spectra at 77 K were obtained for com-
plexes 1 (R=NH2 (1a), NMe2 (1b), NEt2 (1c) or

L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
43
Table 3
13C{1H} and 13C NMR dataa for trans-[FeH(NCR)(dppe)2][BF4] (1)
R
d
13C{1H}
JCP (Hz)
13C
1JCH (Hz)
Assignment
1a NH2
133.47
130.86
128.06
126.02
124.61
31.46
s,br
d
d
d
s
s,br
dd
dd
dd
s
Ci (dppe)
Cm (dppe)
Cp (dppe)
Co (dppe)
NCR
17.6 [3J]
10.1 [4J]
50.7 [2J]
160.6
158.4
161.3
qt
12.1
tqt
133.1
Ph2PCH2CH2PPh2
1b NMe2
133.80
131.02
127.98
126.16
125.81
38.83
d
d
d
d
s
51.5 [1J]
25.6 [3J]
11.0 [4J]
41.2 [2J]
d
dd
dd
Ci (dppe)
Cm (dppe)
Cp (dppe)
Co (dppe)
NCN(CH3)2
NCN(CH3)2
Ph2PCH2CH2PPh2
160.7
156.7
160.7
dd
c
s
qt
q
tqt
118.1
133.2
30.73
12.3b
1c NEt2
135.87
132.99
129.95
128.21
126.05
45.25
dm
d
d
d
s
s
qt
s
62.0 [1J]
16.4 [3J]
10.9 [4J]
49.5 [2J]
d
Ci (dppe)
Cm (dppe)
Cp (dppe)
Co (dppe)
NCN(CH2CH3)2
NCN(CH2CH3)2
Ph2PCH2CH2PPh2
NCN(CH2CH3)2
dd
dd
dd
s
t
tqt
q
161.9
161.3
178.0
139.6
133.0
127.6
32.72
13.51
12.1b
1d NC(NH2)2
160.38
134.37
131.08
127.80
126.17
124.33
30.83
s
s
NCNC(NH2)2
Ci (dppe)
Cm (dppe)
Cp (dppe)
Co (dppe)
s,br
s
d
d
s
s,br
d
dd
160.7
159.4
161.4
17.4 [4J]
62.2 [2J]
dd
c
NCNC(NH2)2
Ph2PCH2CH2PPh2
qt
12.2b
tqt
132.7
a In CD2Cl2; l in ppm relative to SiMe4; s, singlet; d, doublet; t, triplet; q, quartet; qt, quintet; br, broad; dm, doublet of multiplets; tqt, triplet
of quintets; subscripts i, o, m and p denote the ipso-, ortho-, meta- and para-carbons, respectively, of the phenyl rings.
b Owing to virtual coupling to the four equivalent phosphorus nuclei.
c Partial overlapping with the phenyl ring resonance.
than those quoted (0.47 and 1.45 mm s−1 [4a,8] and
NC(NH2)2 (1d)), 2 (R=NH2 (2a) or NEt2 (2c)) and 3
(R=NH2 (3a), NMe2 (3b), NEt2 (3c) or NC(NH2)2
0.47 and 1.51 mm s−1 [9]) for trans-[FeBr2(depe)2],
indicating that the cyanamide ligands act as more effec-
tive s-electron donors than bromide, in agreement with
the observed lability, towards displacement reactions,
of the latter ligand at the {FeII(depe)2} centre.
(3d)) and the data are presented in Table 4. A typical
spectrum is shown in Fig. 1 (for 1d).
Complexes 2 and 3 present IS (e.g. IS=0.24−0.28
mm s−1 for trans-[Fe(NCR)2(depe)2]2+ (R=alkyl or
aryl)) and QS values (QS=1.16−1.23 mm s−1 for
trans-[FeBr(NCR)(depe)2]+) [6] higher and lower, re-
spectively, than those of the analogous mono- and
di-organonitrile complexes. Since the isomer shift of a
complex decreases [4e] with an increase of both the
s-electron donor and the p-electron acceptor character
of the ligands, IS= −constant×(s+p), and the QS
decreases with a decrease of the p-electron acceptance
and with an increase of the s-donor ability of the
ligands, QS=constant×(p−s), these results indicate
a weaker p-electron acceptor ability of the cyanamide
ligands compared with the organonitriles, consistent
with the IR results discussed above. Moreover, all our
cyanamide complexes present lower IS and QS values
The Mo¨ssbauer spectral data were also analysed in
terms of the point-charge model [4e], and partial isomer
shifts (PIS) and partial quadrupole splittings (PQS)
were derived (Table 4). In this model the observed IS is
the sum of the PIS of the individual ligands (Eq. (2)),
whereas the QS is given by a difference of partial values
for the ligands, according to expressions dependent
upon the composition and structure, i.e. Eqs. (3) and
(4) for the general types trans-[FeACB4] and trans-
[FeA2B4], which include our complexes 1, 2 and 3
(A=NCR, B=dppe/2 (1) or depe/2 (2 or 3), C=H (1)
or Br (2)), respectively.
IS=S PIS
(2)

44
L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
QS=2PQS(A)+2PQS(C)−4PQS(B)
QS=4PQS(A)−4PQS(B)
(3)
(4)
By application of these equations to our data for
complexes 2 and 3 (and considering that PIS= −0.02
(B) and 0.26 (C) mm s−1, PQS(B)=0.45 or −0.63 mm
s−1 (with reference to PQS(H)=0.00 or to PQS(Cl)=
−0.27 mm s−1, respectively), and PQS(C)=0.82 or
−0.27 mm s−1 (with reference to PQS(H)=0.00 or to
PQS(Cl)= −0.27 mm s−1, respectively) [4a], we have
estimated the PIS and PQS values for the cyanamide
Table 4
Mo¨ssbauer isomer shift (IS) and quadrupole splitting (QS)
parametersa
for
trans-[FeH(NCR)(dppe)2][BF4]
(1),
trans-
b
[FeBr(NCR)(depe)2][BF4] (2) and trans-[Fe(NCR)2(depe)2]Y2 (3),
and estimated partial isomer shifts (PIS) and partial quadrupole
splittings (PQS) for the cyanamide ligands
R
IS
QS
Y1/2
Fig. 1. Mo¨ssbauer spectrum of trans-[FeH(NCNC(NH2)2)(dppe)2]-
[BF4] (1d) at 77 K and referenced against iron foil at 298 K.
Experimental
1a NH2
1b NMe2
1c NEt2
0.29
0.28
0.27
0.26
0.33
0.35
0.33
0.31
0.32
0.34
0.80
0.90
0.94
1.02
1.03
0.99
1.13
1.08
1.05
1.01
0.21
0.16
0.15
0.14
0.34
0.21
0.21
0.12
0.18
0.16
ligands (Table 4). The application of Eqs. (2) and (3) to
complexes 1, leads us to estimate the PIS and PQS
values for the dppe ligand.
1d NC(NH2)2
2a NH2
e
2c NEt2
3a NH2
e
In comparison with the related organonitriles or N2
ligands, the cyanamides present slightly higher PIS
values (0.18–0.21 versus 0.15–0.19 [6] or 0.09 [4a] mm
3b NMe2
3c NEt2
3d NC(NH2)2
s
−1) but PQS values (0.65–0.72 mm s−1) are in the
Calculated
NCR
lower limit of the range for those exhibited by the other
ligands (0.69–0.74 [6] or 0.78 [4a] mm s−1, respec-
tively). Hence, the cyanamide ligands present weaker
summed s-donor and p-acceptor contributions (higher
PIS), in particular behaving as more effective s-donors
but weaker p-acceptors (lower PQS) than organonitriles
or dinitrogen.
d
PISc
PQS
PQS(H)=
PQS(Cl)=
−0.27 mm s−1
0.00 mm s−1
f
NH2
0.18
0.20
0.19
0.21
0.67
0.72
0.65
0.70
−0.41
NMe2
−0.36
−0.43
−0.38
f
NEt2
NC(NH2)2
2.4. FAB MS
dppe/2
0.00
0.11
−0.98
The FAB mass spectra of the complexes trans-[FeL-
a Values in mm s−190.01, recorded at 77 K and referenced against
iron foil at 298 K; Y1/2=half width at half height.
(NCR)(depe)2]Yn
(R=NH2,
NMe2,
NEt2
or
NC(NH2)2; Y=BF4 or BPh4; (2), L=Br, n=1; (3),
L=NCR, n=2) were run in 3-nitrobenzyl alcohol
(NBA) matrices and the corresponding molecular ions
were clearly detected (with the expected bromine iso-
topic pattern for complexes 2).
b Y=BF4 unless stated otherwise.
c Values calculated by using the expression PIS(NCR)=IS−0.18
or PIS(NCR)=0.5 IS+0.04 derived from application of Eq. (2) to
complexes 2 or 3, respectively, or the expression PIS(dppe/2)=0.25
IS−0.25 PIS(NCR)−0.018 derived from application of Eq. (2) to
complexes 1.
For the dicyanamide complexes 3b, 3c or 3d the peak
detected at the highest m/z is due to the monocationic
aggregate [Fe(NCR)2(depe)2 · BF4]+ in accord with the
behaviour observed [6,10] for some [MLn2+][Y−]2 type
salts, but such a species is not detected for the [BPh4]−
salt 3a. The fluoro-ions [FeF(depe)2]+ (m/z 847) and
[FeF(NCR)(depe)]+ are also detected for the [BF4]−
salts and can be considered to be formed by fluorina-
d Values calculated, ignoring lattice contributions, by using the
expression PQS(NCR)=0.5 QS+x (x=0.08 for PQS(H)=0.00 mm
s−1 or x=−0.99 for PQS(Cl)=−0.27 mm s−1) or PQS(NCR)=
0.25 QS+y (y=0.45 for PQS(H)=0.00 mm s−1 or y=−0.63 for
PQS(Cl)=−0.27 mm s−1) derived from application of Eqs. (3) or
(4) to complexes 2 or 3, respectively, or the expression PQS(dppe/
2)=0.5 PQS(NCR)−0.25 QS−z (z=0.00 for PQS(H)=0.00 mm
s−1 or z=0.55 for PQS(Cl)=−0.27 mm s−1) derived from applica-
tion of Eq. (3) to complexes 1.
+
+
’
’
(m/z 468) or [Fe(NCR)(depe)]
e Y=BPh4.
tion of [Fe(depe)2]
under FAB MS conditions.
f Average values for the mono- and di-cyanamide complexes.

L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
45
Scheme 2. Proposed general fragmentation pattern for complexes trans-[FeBr(NCR)(dppe2)][BF4] (2) and trans-[Fe(NCR)2(dppe2)]Y2 (3) under
FAB conditions.
The fragmentation pathways can be initiated by the
elimination of the monodentate ligands from the molec-
2.4.1. Crystal structures of trans-[FeH(NCNH2)(dppe)2]-
[BF4] and trans-[Fe(NCNEt2)2(depe)2][BF4]2
ular ion—see the general proposed fragmentation pat-
The molecular structures of trans-[FeH(NCNH2)-
(dppe)2][BF4] (1a) and trans-[Fe(NCEt2)2(depe)2][BF4]2
(3c) have been determined by X-ray diffraction studies.
They are shown in Fig. 2 and selected bond lengths and
angles are listed in Table 5. For 1a, the iron atom is
octahedrally coordinated and displaced out of the equa-
+
’
tern depicted in Scheme 2—to give [Fe(depe)2]
(m/z
468) which undergoes similar fragmentation patterns
for all the mono- and di-cyanamide complexes, as
observed for the related organonitrile complexes [6].
This indicates the possible generation of a low oxida-
tion state iron–diphosphine centre by reduction of a
parent complex.
,
torial plane (−0.103(2) A) of the four P atoms towards
the coordinated nitrogen atom of the cyanamide. The
,
For complexes 2, elimination of a diphosphine ligand
occurs only after the loss of the cyanamide ligand, as
observed in complexes 1 [11], in accord with the
Fe–H separation, 1.59(9) A, is comparable to the value
,
of 1.53(9) A [12] found in [FeH(N2)(Ph2PC2H4PPhC2-
H4PPhC2H4PPh2)]Br · EtOH and agrees with the value
,
stronger coordination of the chelating diphosphine. The
of 1.53 A estimated [13] as the sum of the iron and
hydrogen covalent radii. The Fe–P bond distances
+
’
molecular ion of the liberated diphosphine, depe
,
,
follows a fragmentation pathway analogous to that
exhibited by a genuine sample of depe. In contrast to
the behaviour observed [6] for the organonitrile com-
plexes, in the cyanamide complexes the diphosphine
ligand itself cannot undergo partial fragmentation.
(2.244(4) A, averaged value) are shorter than in trans-
,
[Fe(NCMe)2(dppe)2][BF4]2 · CH2Cl2 (2.331(3) A, aver-
aged value) [14] in agreement with the greater electron
donor character of the hydride and cyanamide ligands
than that of acetonitrile, and are comparable to those
+
of [FeH(N2)(depe)2]+ (2.240(2) A) [15]. The Fe–N
’
,
In addition, the dibromide ion [FeBr2(depe)2]
was
,
detected at m/z 626 with the expected bromine isotopic
bond distance of 1a has a value, 1.95(1) A, comparable
to that of trans-[Fe(NCMe)2(dppe)2][BF4]2 · CH2Cl2
pattern. It conceivably results from the reaction of
[FeBr(depe)2]+ with Br under FAB MS conditions,
(1.913(6) A) [14] and [FeH(N2)(depe)2] (1.825(7) A)
[15]. While the [Fe(NCMe)2(dppe)2]2+ complex cation
is centrosymmetric and as a consequence the P atoms
of each dppe ligand are perfectly trans to each other, in
our complex 1a the trans angles for P(1)–Fe–P(2) and
P(3)–Fe–P(4) are 176.2(2) and 173.3(2)°, respectively.
The dppe ligands have an about gauche conformation
+
’
,
,
and not from contamination with trans-[FeBr2(depe)2]
since the presence of this complex was not detected (e.g.
by NMR or elemental analysis) in any of the
cyanamide complexes. Loss of depe generates a frag-
ment ion at m/z 420 with the same bromine isotopic
+
’
pattern, assigned to [FeBr2(depe)]
.

46
L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
Table 5
of the ethylenic chain with P(1)–C(14)–C(15)–P(3) and
P(2)–C(40)–C(41)–P(4) torsion angles of −44(1) and
34(1)°, respectively, consistent with the NMR results
discussed above.
,
Selected bond distances (A) and angles (°) for trans-[FeH(NCNH2)-
(dppe)2][BF4] (1a) or trans-[Fe(NCNEt2)2(depe)2][BF4]2 (3c)
1a
3c
For trans-[Fe(NCNEt2)2(depe)2][BF4]2 (3c), the iron
atom lies on a crystallographic inversion center with the
two depe ligands in the equatorial plane and the two
cyanamide ligands mutually trans in an octahedral co-
ordination geometry. The depe ligands have a cis con-
formation of the ethylenic chain with a P–C–C–P
torsional angle of 0°, in agreement with the NMR
results. The same conformation of the bridging ethylene
has been found in trans-[FeCl2(dmpe)2] [16], but not in
About the Fe atom
Fe–P(1)
Fe–P(2)
Fe–P(3)
Fe–P(4)
Fe–N(1)
Fe–H
P–Caliph. av.
P–Cphen. av.
P–Cethylen. av.
2.261(4)
2.249(4)
2.229(4)
2.238(4)
1.95(1)
1.59(9)
1.85(1)
1.84(1)
1.50(2)
2.282(2)
2.276(3)
–
–
1.908(8)
–
1.84(2)
–
–
P(1)–Fe–N(1)
P(2)–Fe–N(1)
P(3)–Fe–N(1)
P(4)–Fe–N(1)
P(1)–Fe–P(2)
P(1)–Fe–P(3)
P(2)–Fe–P(4)
H(1)–Fe–N(1)
86.9(3)
93.8(3)
96.9(3)
92.9(3)
83.6(1)
176.2(2)
173.3(2)
171(5)
89.6(2)
88.7(2)
–
–
85.5(1)
–
–
–
In the cyanamide ligands
N(1)–C
N(2)–C
N(2)–C(12)
N(2)–C(14)
1.15(2) C(1)
1.34(2) C(1)
–
–
1.14(1) C(11)
1.36(1) C(11)
1.58(3)
1.50(2)
Fe–N(1)–C
174(1) C(1)
–
–
176(1) C(11)
113(1)
119(1)
C(11)–N(2)–C(12)
C(11)–N(2)–C(14)
N(1)–C–N(2)
177(2) C(1)
178(1) C(11)
trans-[FeI2(depe)2] which was gauche with a P–C–C–P
torsional angle of 50.0(2)° [17].
The Fe–P bond distances of 2.277(3) A (Fe–P(1))
,
,
and 2.285(2) A (Fe–P(2)) (Table 5) are slightly shorter
,
than those in [FeI2(depe)2] (2.295(1) and 2.323(1) A)
[17], but comparable to the values of 2.260(2) and
,
2.268(3) A found in [FeCl2(depe)2] [18]. These com-
plexes exhibit different conformations of the bridging
ethylene in the diphosphine ligands, and the isomeriza-
tion process due to the conformational changes which
could be related either to the hindrance of the sub-
stituent at the phosphorus atoms, or to that of the
ligands in the axial positions.
,
The Fe–N bond distance of 1.919(7) A (Table 5) is
,
comparable to the value of 1.913(6) A [14] reported for
trans-[Fe(NCMe)2(dppe)2][BF4]2 · CH2Cl2 and to that of
,
1.894(4) A [17] in [Fe(NCMe)2(opdp)2]I2. The N-amine
atom of the diethylcyanamide ligand has a planar geo-
metry (the sum of the angles around N(2) is 359(1)°)
rather than pyramidal as observed in mer-
[ReCl2(NCNEt2)(PMePh2)3] [2f] and in the free ligands
dimethylcyanamide (NCNMe2) [19] and cyanamide
(NCNH2) [20,21].
The linear NC–NEt2 ligand (the N–C–N angle is
Fig. 2. Molecular structures of (a) trans-[FeH(NCNH2)(dppe)2][BF4]
(1a) and (b) trans-[Fe(NCNEt2)2(depe)2][BF4]2 (3c).
,
178(1)°) has a C(11)–N(2) bond distance of 1.32(1) A

L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
47
which is shorter than the analogous distance in mer-
pound (1a, R=NH2). Tl[BF4] (72.8 mg, 0.25 mmol)
was added to a solution of trans-[FeHCl(dppe)2] (0.20
g, 0.22 mmol) in THF (60 cm3) and the suspension was
stirred for ca. 10 min at room temperature (r.t.). The
colour changed to pale pink and powdered cyanamide
(9.4 mg, 0.22 mmol) was then added slowly immedi-
ately giving an orange suspension. The precipitate of
TlCl was filtered off and the filtrate concentrated in
vacuo. Cooling to ca. −18°C led to the precipitation of
1a as an orange solid which was filtered off, washed
with a THF/Et2O (1:5) mixture and recrystallized from
CH2Cl2/Et2O and dried in vacuo (ca. 80% yield).
,
[ReCl2(NCNEt2)(PMePh2)3] (1.34(1) A) [2f] and in free
,
NCNMe2 and NCNH2 (1.351 [19] and 1.346 A [20],
microwave results). Therefore, the lone pair of the
amine N atom is delocalized into the p-bonding of the
cyano group, with resulting shortening of the Et2N–
CN bond and enhancement of the electron donor abil-
ity of the diethylcyanamide ligand towards the cationic
Fe(II) metal centre, in agreement with the IR and
Mo¨ssbauer results discussed above. Similar behaviour is
found in trans-[Pt(CF3)(NCNEt2)(PPh3)2][BF4] [2d],
and in trans-[Cr(NCNEt2)(CO)5] [22]. Hence, the
canonical form (a) presents a significant contribution in
the VB representation of the cyanamide ligand.
3.1.2. trans-[FeBr(NCR)(depe)2]Y (2; R=NH2 (2a),
NMe2 (2b), NEt2 (2c) or NC(NH2)2 (2d); Y=BF4 or
BPh4) and trans-[Fe(NCR)2(depe)2]Y2 (3; R=NH2
(3a), NMe2 (3b), NEt2 (3c) or NC(NH2)2 (3d);
Y=BF4 or BPh4)
The general procedure followed in the syntheses of
complexes 2 and 3 involved the addition of the appro-
priate cyanamide in a stoichiometric (2) or 2-fold (3)
molar ratio to a solution of trans-[FeBr2(depe)2] in
MeOH (50 cm3). The solution was left to stir overnight
at r.t. and [NBu4][BF4] or Na[BPh4] in methanol was
then added (in a 1:1 (2) or 2:1 (3) molar ratio, relative
to the starting complex). Cooling to ca. −18°C led to
the precipitation of the mono- or di-cyanamide com-
plex usually as a red solid which was filtered-off,
washed with MeOH/Et2O (1:4) and dried in vacuo (ca.
70% average yield).
3. Experimental
3.1. Syntheses
All manipulations were routinely performed under an
atmosphere of dinitrogen using standard vacuum and
inert-gas flow techniques. Solvents were purified by
standard procedures and freshly distilled immediately
prior to use. The complexes trans-[FeHCl(dppe)2] and
trans-[FeBr2(depe)2] were prepared by literature meth-
ods [9,23]. The cyanamides were used as purchased
from Aldrich.
IR measurements were carried out on a Perkin-Elmer
683 spectrophotometer and 1H, 31P and 13C NMR
spectra were recorded on a Varian Unity 300 spectrom-
eter, at the Centro de Qu´ımica Estrutural. Mo¨ssbauer
spectra were determined at the Nitrogen Fixation Lab-
oratory on an E.S. Technology MS-105 Mo¨ssbauer
spectrometer with a 25 mCi 57Co source in a rhodium
matrix, recorded at 77 K and referenced against iron
foil at 298 K. The FAB mass spectrometric measure-
ments were performed on a Trio 2000 spectrometer at
the Centro de Qu´ımica Estrutural. Positive-ion FAB
mass spectra were obtained by bombarding NBA ma-
trices of the samples with 8 keV (ca. 1.28×1015 J) Xe
atoms. Nominal molecular masses were calculated us-
ing the most abundant isotopes, i.e. 56Fe (92%), 79Br
(50.7%) and the expected natural abundance isotope
cluster patterns were observed for the various ion clus-
ters. However, further complexity due to addition (from
the matrix) or loss of hydrogen was usually not taken
into account. Mass calibration for data system acquisi-
tion was achieved using CsI.
3.2. Crystallography
X-ray data were collected on a Philips PW1100 (Febo
system) diffractometer, using graphite-monochromated
radiation, u(Mo Ka)=0.71069 A, at r.t. Data collec-
,
tion parameters are summarized in Table 6. The orien-
tation matrix and cell dimensions were determined by
least-squares refinement of the angular positions of 30
reflections. Three standard reflections were monitored
every 180 reflections. There were no significant fluctua-
tions of intensities other than those expected from
Poisson statistics. The intensity data were corrected for
LP and for absorption as described by North et al. [24].
No correction was made for extinction.
The positions of the heavy atoms were found from
Patterson syntheses [25]. All non-H atoms were located
in the subsequent Fourier maps. The structures were
refined by full-matrix least-squares. Anisotropic tem-
perature factors for the non-hydrogen atoms, except
those of the phenyls, refined isotropically, were applied
in 1a. The H-atoms were placed in calculated positions
with fixed, isotropic thermal parameters (1.2 Ueq of the
parent carbon atom). The hydride atom was found in a
final difference Fourier and refined isotropically. The
non-hydrogen atoms in 3c were refined anisotropically.
3.1.1. trans-[FeH(NCR)(dppe)2][BF4] (1; R=NH2 (1a),
NMe2 (1b), NEt2 (1c) or NC(NH2)2 (1d))
Complexes 1 were prepared by a common method,
and a typical procedure is given below for the com-

48
L.M.D.R.S. Martins et al. / Inorganica Chimica Acta 291 (1999) 39–48
Table 6
Richards, J. Organomet. Chem. 469 (1993) 179. (d) M.F.C. Guedes
da Silva, E.M.P.R.P. Branco, Y. Wang, J.J.R. Frau´sto da Silva,
A.J.L. Pombeiro, R. Bertani, R.A. Michelin, M. Mozzon, F.
Benetollo, G. Bombieri, J. Organomet. Chem. 490 (1995) 89. (e)
M.F.C. Guedes da Silva, C.M.P. Ferreira, E.M.P.R.P. Branco,
J.J.R. Frau´sto da Silva, A.J.L. Pombeiro, R.A. Michelin, U.
Belluco, R. Bertani, M. Mozzon, G. Bombieri, F. Benetollo, V.Yu.
Kukushkin, Inorg. Chim. Acta 265 (1997) 267. (f) M.T.A.R.S.
Costa, J.J.R. Frau´sto da Silva, A.J.L. Pombeiro, R.A. Michelin,
G. Bombieri, F. Benetollo, Inorg. Chim. Acta 280 (1998) 308.
[3] See, e.g. R.R. Eady, Adv. Inorg. Chem. 36 (1991) 77.
[4] (a) D.J. Evans, M. Jimenez-Tenorio, G.J. Leigh, J. Chem. Soc.,
Dalton Trans. (1991) 1785. (b) J.E. Barclay, G.J. Leigh, A.
Houlton, J. Silver, J. Chem. Soc., Dalton Trans. (1988) 2865. (c)
J. Silver, Inorg. Chim. Acta 184 (1991) 235. (d) R.V.D. Parish, B.E.
Riley, J. Chem. Soc., Dalton Trans. (1979) 482. (e) G.M. Bancroft,
Coord. Chem. Rev. 11 (1973) 247, and Refs. therein. (f) J.M.
Bellerby, M.J. Mays, J. Chem. Soc., Dalton Trans. (1975) 1281.
(g) G.M. Bancroft, R.E.B. Garrod, A.G. Maddock, M.J. Mays,
B.E. Prater, J. Am. Chem. Soc. 94 (1972) 647. (h) G.M. Bancroft,
M.J. Mays, B.E. Prater, F.P. Stefanini, J. Chem. Soc. A (1970)
2146.
Crystal data and details of refinement for trans-[FeH(NCNH2)-
(dppe)2][BF4] (1a) and trans-[Fe(NCNEt2)2(depe)2][BF4]2 (3c)
Compound
1a
3c
Empirical formula
Formula weight
Temperature (°C)
Crystal size (mm)
Crystal system
Space group
C53H51BF4FeN2P4 C30H68B2F8FeN4P4
982.6
23
0.28×0.21×0.30
monoclinic
P21/n
838.3
23
0.36×0.32×0.40
orthorhombic
Pbca
Z
4
4
,
a (A)
21.573(4)
16.556(3)
13.471(3)
90.04(3)
4811(2)
1.35
3–26
2040
5.01
3125
16.446(3)
18.203(3)
14.617(3)
–
4376(1)
1.27
3–26
1766
5.31
4289
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Dcalc (g cm−3
q Range (°)
F(000)
)
v(Mo Ka) (mm−1
)
[5] M.B. Baptista, M.A.N.D.A. Lemos, J.J.R. Frau´sto da Silva, A.J.L.
Pombeiro, J. Organomet. Chem. 424 (1992) 49.
[6] L.M.D.R.S. Martins, M.T. Duarte, A.M. Galva˜o, C. Resende,
A.J.L. Pombeiro, R.A. Henderson, D.J. Evans, J. Chem. Soc.,
Dalton Trans. (1998) 3311.
Reflections collected
Observed reflections
[I]3|(I)]
2964
1805
GOF
1.09
1.16
0.073
R=S[ꢀFoꢀ−ꢀFcꢀ]/SꢀFoꢀ 0.062
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Acknowledgements
This work has been partially supported by the
JNICT and the Institute for the International Scientific
and Technological Co-operation (ICCTI) (Portugal)/
The British Council (UK) and the JNICT or ICCTI/
CNR (Italy) protocols of collaboration, the PRAXIS
XXI Programme and the Foundation for Science and
Technology (FCT) (Portugal), and the BBSRC (UK).
We also thank Mr Indale´cio Marques (Centro de
Qu´ımica Estrutural) for running the FAB mass spectra.
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