Synthesis, structure and reactivity of an (η6-naphthalene)iron(0) complex having a 1,2-bis(dicyclohexylphosphino)ethane ligand

Article abstract of DOI:10.1016/S0022-328X(97)00770-5

A zerovalent iron complex having an η⁶-naphthalene ligand, Fe(η⁶-C₁₀H₈)(dcype) (3) [dcype=1,2-bis(dicyclohexylphosphino)ethane] has been prepared by the reduction of high spin 14 electron dichloroiron(II) complex, FeCl₂(dcype) (1) with sodium-naphthalene. In refluxing benzene solution of 3, the coordinated naphthalene can be replaced by benzene giving Fe(η⁶-C₆H₆)(dcype) (4). Exposure of 3 to CO results in the formation of Fe(CO)₃(dcype) (5). Protonation of 3 with HBF₄ yields cationic complex, [FeH(η⁶-C₁₀H₈)(dcype)][BF₄] (6), which can be deprotonated by lithium diisopropylamide.

Full text of DOI:10.1016/S0022-328X(97)00770-5

Journal of Organometallic Chemistry 556 (1998) 89–95
Synthesis, structure and reactivity of an (p6-naphthalene)iron(0)
complex having a 1,2-bis(dicyclohexylphosphino)ethane ligand
Hiroaki Kubo, Masafumi Hirano, Sanshiro Komiya *
Department of Applied Chemistry, Faculty of Technology, Tokyo Uni6ersity of Agriculture and Technology, 2-24-16 Nakacho, Koganei,
Tokyo 184-8588, Japan
Received 1 September 1997; received in revised form 26 November 1997
Abstract
A zerovalent iron complex having an p6-naphthalene ligand, Fe(p6-C10H8)(dcype) (3) [dcype=1,2-bis(dicyclohexylphos-
phino)ethane] has been prepared by the reduction of high spin 14 electron dichloroiron(II) complex, FeCl2(dcype) (1) with
sodium-naphthalene. In refluxing benzene solution of 3, the coordinated naphthalene can be replaced by benzene giving
Fe(p6-C6H6)(dcype) (4). Exposure of 3 to CO results in the formation of Fe(CO)3(dcype) (5). Protonation of 3 with HBF4 yields
cationic complex, [FeH(p6-C10H8)(dcype)][BF4] (6), which can be deprotonated by lithium diisopropylamide. © 1998 Elsevier
Science S.A. All rights reserved.
Keywords: Iron(0) complex; Naphthalene complex; Sodium-naphthalene; Reduction of 14e complex; Crystal structure
1. Introduction
Fe(N2)(depe)2 [depe=1,2-bis(diethylphosphino)ethane]
by the reduction of FeCl2(depe)2 with sodium-naph-
thalene under a nitrogen atmosphere [3], while the
reduction under argon led to the facile in¸tr¹am¹o¹l¹ecºular
Synthesis and reactivity of iron(0) complexes have
been the subject of intense study relevant to the activa-
tion of C–H bonds and small molecules during the past
decades. The preparation methods for iron(0) com-
plexes are generally divided into the synthesis using
atomic metal [1] or the chemical reduction of iron(II)
[2]. In addition, ligand exchange reaction of zerovalent
iron complexes such as Fe(CO)5 is also a convenient
method for preparation. Among them, much effort has
been made to prepare iron(0) complexes by the chemi-
cal reduction since Chatt et al. demonstrated the reduc-
tion of MCl2(diphosphine)2 by sodium-naphthalene [2].
A number of reductions of FeCl2(diphosphine)2 have
been carried out by this system, where most of these
attempts gave divalent hydridoiron complexes such as
FeH(C10H7)(diphosphine)2 ([2]f–i). We have recently
C–H
bond
activation
giving
FeH(MeCH-
PEtC2H4PEt2)(depe) ([3]c). Such chemical reductions of
these coordinatively saturated dichloroiron(II) com-
plexes leading to the formation of iron(0) are still
limited so far and those of coordinatively unsaturated
iron(II) are rare. Followings are the examples; Muetter-
ties et al. reported reductions of 16e FeCl2[P(OMe)3]3
and 14e FeCl2(PMe3¸)2¹w¹¹ithº sodium amalgam giving
Fe[P(OMe)3]5 and FeH[P(CH2)Me2](PMe3)3, respec-
tively [4]. Hoberg et al. reported the first example of a
coordinatively
unsaturated
iron(0)
complex,
Fe(C2H4)2(PEt3)2 by the reduction of FeCl2 with mag-
nesium in the presence of ethylene and PEt3 and they
determined its crystal structure [5]. Quite recently, Jolly
reported isolation of
a zerovalent iron complex
et al. showed
a
series of reductions of 14e
FeCl2(diphosphine) and FeCl2(PEt3)2 with activated
magnesium in the presence of dienes giving (di-
ene)iron(0) or hydrido(dienyl)iron(II) complexes [6].
* Corresponding author. Tel.: +81 423 877500; fax: +81 423
877500; e-mail: komiya@cc.tuat.ac.jp
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00770-5

90
H. Kubo et al. / Journal of Organometallic Chemistry 556 (1998) 89–95
Girolami et al. produced zerovalent Fe(p6-C6H4Me2-
1,4)(dippe) [dippe=1,2-bis(diisopropyl-phosphino)-
ethane] by the hydrogenation of Fe(CH2C6H4Me-
4)2(dippe) [7]. However, in most of these reductions,
intramolecular C–H bond activation of ancillary phos-
phine or added diene, or formation of a coordinatively
saturated homoleptic complex are observed. In this
paper, we wish to report the reduction of 14e
dichloroiron(II) complex having a bulky diphosphine
FeCl2(dcype) (1) [dcype=1,2-bis(dicyclohexylphos-
phino)ethane] with sodium-naphthalene giving zerova-
lent Fe(p6-C10H8)(dcype) (3), the structure and the
chemical reactivities of 3 are also described.
Complex 2a contained a small amount of its stereo
isomer, trans,cis,cis-FeCl2(CO)2−(dcype) (2b) (B4%)
which could not be separated by the recrystallization.
31P{1H}-NMR spectrum of 2a in C6D6 shows two
doublets at 60.59 and 90.20 ppm, indicating that two
phosphorus nuclei of dcype are inequivalent, whereas
2b shows only one singlet at 70.02 ppm. In the IR
spectrum of 2a, two absorption bands due to terminal
CO are observed at 2034 and 1975 cm−1 with equal
intensity, suggesting that two CO ligands are locating in
the mutually cis configuration. These spectroscopic
data support cis,cis,cis-FeCl2(CO)2(dcype) structure of
2a. Complex 2 easily and completely released the CO
ligands with discoloration to give the starting com-
pound 1 at r.t. under reduced pressure. Thus, coordina-
tion of CO to 1 is weak and is a reversible process.
2. Results and discussion
2.1. Preparation of FeCl2(dcype) (1)
Although Jolly et al. has reported in situ reaction of
FeCl2 · 1.5THF, dcype, and a diene in THF in the
presence of active Mg [6]b, no isolation and characteri-
zation of FeCl2(dcype) (1) have been performed. Since
the coordinatively unsaturated iron complexes formu-
lated as FeCl2L2 tend to be stabilized in benzene [8], we
thus employed benzene as solvent for the preparation
of 1. Reaction of anhydrous FeCl2 with dcype in ben-
zene at 70°C quantitatively yielded light purple powder
of 1. Recrystallization of 1 from benzene gave light
purple needles [Eq. (1)].
2.2. Reduction of FeCl2(dcype) (1) with sodium-
naphthalene
Reduction of 1 with a few times excess of sodium-
naphthalene in THF under argon resulted in the forma-
tion of a dark brown suspension in a day at r.t. From
the reaction mixture, dark green prisms of the zerova-
lent iron complex having an p6-naphthalene ligand,
Fe(p6-C10H8)(dcype) (3) were isolated in 30% yield [Eq.
(3)].
However, complete spectroscopic characterization of 1
was unsuccessful due to its paramagnetism. Magnetic
susceptibility (veff) of 1 measured by Gouy method is
4.99 B.M. which corresponds to four unpaired electrons
(4.90 B.M.), suggesting a high spin state of 1. No strong
evidence for the monomeric structure of 1 was given.
However, from the known molecular structure of the
analogous FeCl2(dippe), 1 is considered to have tetrahe-
dral structure [9]. Similar 14e complex FeCl2(PPh3)2 is
also reported as a tetrahedral structure [10]. They all
have mononuclear high spin configurations (FeCl2−
(dippe): 4.9–5.0 B.M. [9], FeCl2(PPh3)2: 4.88 B.M. [11],
5.07 B.M. [12]).
Because 1 is expected to be a coordinatively unsatu-
rated 14e complex having a sterically congested and
electron donating dcype ligand, 1 would be susceptible
to addition of the compact and electron withdrawing
ligand. Exposure of 1 to a CO atmosphere (1 atm) in a
minimum amount of THF at room temperature (r.t.)
immediately gave an orange solution, from which or-
ange diamagnetic dicarbonyl complex, cis,cis,cis-
FeCl2(CO)2(dcype) (2a) precipitated on cooling at
−20°C for 2 days under CO in 79% yield [Eq. (2)].
The molecular structure of 3 was unambiguously
determined by X-ray crystallography. Two independent
molecules in the unit cell were found and have essen-
tially the same structure. Thus, the following discussion
will refer to the molecule A. The ORTEP drawing of the
molecule A is depicted in Fig. 1 and the crystallo-
graphic data and selected bond distances and angles are
shown in Tables 1 and 2, respectively.
The bond distances between Fe(1) and aromatic car-
bons are good criteria for characterization of the hap-
ticity of the naphthalene ligand. The six bond distances
˚
˚
˚
˚
of Fe(1)–C(1) [2.105(4) A], Fe(1)–C(2) [2.099(4) A],
˚
Fe(1)–C(3) [2.097(4) A], Fe(1)–C(4) [2.105(4) A],
Fe(1)–C(5) [2.202(4) A], and Fe(1)–C(10) [2.193(4) A]
˚

H. Kubo et al. / Journal of Organometallic Chemistry 556 (1998) 89–95
91
Table 2
Selected bond distances (A) and angles (°) for 3
˚
Molecule A
Distances
Fe(1)–P(1)
2.173(1) Fe(1)–P(2)
2.105(4) Fe(1)–C(2)
2.097(4) Fe(1)–C(4)
2.202(4) Fe(1)–C(10)
1.403(6) C(2)–C(3)
1.405(6) C(4)–C(5)
1.441(6) C(5)–C(10)
1.375(7) C(7)–C(8)
1.364(7) C(9)–C(10)
2.182(1)
Fe(1)–C(1)
Fe(1)–C(3)
Fe(1)–C(5)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(6)–C(7)
C(8)–C(9)
2.099(4)
2.105(4)
2.193(4)
1.402(6)
1.429(6)
1.434(6)
1.398(8)
1.435(6)
Angles
P(1)–Fe(1)–P(2)
C(1)–C(2)–C(3)
C(3)–C(4)–C(5)
C(4)–C(5)–C(10)
C(5)–C(6)–C(7)
C(7)–C(8)–C(9)
86.06(4) C(2)–C(1)–C(10)
123.7(4)
119.1(4)
123.1(4)
118.3(4)
120.2(5)
120.7(5)
C(2)–C(3)–C(4)
C(4)–C(5)–C(6)
C(6)–C(5)–C(10)
C(6)–C(7)–C(8)
C(7)–C(9)–C(10)
118.7(4)
122.7(4)
119.0(4)
120.8(5)
121.6(5)
Fig. 1. ORTEP drawing of one of two independent Fe(p6-
C10H8)(dcype) (3) molecules (molecule A) with selected atomic num-
bers. Hydrogen atoms are omitted for clarity.
Molecule B
Distances
are basically within the Fe–C bond distances and re-
sembles the values reported in zerovalent (p6-arene)iron
Fe(2)–P(3)
2.175(1) Fe(2)–P(4)
2.184(1)
6
˚
complexes, Fe(p -toluene)(bpy) [2.087–2.112 A] [1]d,
Fe(2)–C(37)
Fe(2)–C(39)
Fe(2)–C(41)
C(37)–C(38)
C(39)–C(40)
C(41)–C(42)
C(42)–C(43)
C(44)–C(45)
2.112(4) Fe(2)–C(38)
2.078(4) Fe(2)–C(40)
2.206(3) Fe(2)–C(46)
1.419(7) C(38)–C(39)
1.403(6) C(40)–C(41)
1.421(6) C(41)–C(46)
1.348(8) C(43)–C(44)
1.367(8) C(45)–C(46)
2.088(4)
2.107(4)
2.211(4)
1.383(7)
1.410(6)
1.413(6)
1.401(9)
1.420(6)
6
6
˚
Fe(p -toluene)(C2H4)2 [2.08–2.16 A] [1]f or Fe(p -ben-
zene)(p5-thiadiborolene) [2.058–2.090 A] [13]. The
˚
˚
bond distances of Fe(1)–C(5) [2.202(4) A] and Fe(1)–
˚
C(10) [2.193(4) A] are slightly longer than those of
other Fe–C bonds. The C–C bond distances among
C(1), C(2), C(3), C(4), C(5) and C(10) appear in the
˚
range 1.403–1.434 A, while clear bond alternation is
Angles
P(3)–Fe(2)–P(4)
found in the uncoordinated aromatic ring C(5)–C(10)
85.94(4) C(38)–C(37)–C(46) 121.2(4)
˚
[1.364–1.441 A]. The bond distances of C(5)–C(6)
C(37)–C(38)–C(39) 119.7(4)
C(39)–C(40)–C(41) 121.7(4)
C(40)–C(41)–C(46) 119.2(4)
C(42)–C(43)–C(44) 121.6(5)
C(44)–C(45)–C(46) 120.2(5)
C(38)–C(39)–C(40) 119.5(4)
C(40)–C(41)–C(42) 122.1(4)
C(42)–C(41)–C(46) 118.7(4)
C(43)–C(44)–C(45) 120.0(5)
C(37)–C(46)–C(45) 122.1(5)
Table 1
Crystallographic
(3 · 0.5C6H14
data
of
Fe(p6-C10H8)(dcype) · 0.5C6H14
)
Empirical formula
Formula weight
C39H63FeP2
649.81
˚
˚
˚
˚
[1.441(6) A], C(7)–C(8) [1.398(8) A], and C(9)–C(10)
Crystal dimensions (mm3)
Crystal system
0.67×0.43×0.17
Monoclinic
P21/a(c14)
16.821(2)
22.143(8)
19.537(4)
97.34(2)
7217(2)
8
5.61
3 984.00
1.196
[1.435(6) A] are slightly longer than those of C(6)–C(7)
˚
[1.375(7) A] and C(8)–C(9) [1.364(7) A]. This indicates
that the resonance structure of naphthalene is not
extended to the uncoordinated benzo-ring. Thus, hap-
ticity of the naphthalene ligand is p6 in the solid state,
although it slightly tilts against the benzo-ring. 1H-
NMR spectrum of 3 shows two broad singlets at 4.20
and 5.69 ppm assignable to the coordinated naph-
thalene ring, and multiplets at 7.09 and 7.41 ppm
assignable to the uncoordinated moiety. The 13C{1H}-
NMR spectrum shows three singlets at 59.99, 79.46 and
97.62 ppm assignable to the coordinated naphthalene
ring and two singlets at 121.07 and 126.89 ppm due to
the uncoordinated naphthalene ring. 31P{1H}-NMR
spectrum of 3 shows a singlet at 94.60 ppm, suggesting
that two phosphorus nuclei of dcype are magnetically
equivalent. These NMR data are consistent with the
symmetrical p6 coordination of naphthalene to the iron.
Space group
˚
a (A)
˚
b (A)
˚
c (A)
i (°)
V (A )
3
˚
Z
v (cm−1
F000
)
Dcalc. (g cm−3
Radiation
)
Mo–Kh
293
16 341
Temp (K)
Unique reflections
Used reflections for refinement
10 343 (ꢀFoꢀ\3|ꢀFoꢀ)
Ra
0.054
Rwb
0.071
1.51
Direct methods [22]
S
Method of phase determination
a R=S(ꢁFoꢀ−ꢀFcꢁ)/SꢀFoꢀ.
b Rw=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwꢀFoꢀ ]
.
2 0.5

92
H. Kubo et al. / Journal of Organometallic Chemistry 556 (1998) 89–95
Table 3
Atomic coordinates of Fe(p6-C10H8)(dcype)·0.5C6H14
C58
C59
C60
C61
C62
C63
0.1622(3)
0.2186(3)
0.1837(3)
0.0709(2)
0.0565(2)
0.0419(3)
−0.0198(2)
0.0316(2)
0.0717(2)
0.2714(2)
0.2371(2)
0.2801(2)
0.3219(2)
0.3557(2)
0.3128(2)
0.2731(2)
0.3289(2)
0.3698(2)
0.3357(2)
0.2810(2)
0.2399(2)
0.0275(8)
0.068(1)
1.0410(3)
1.0295(2)
0.9697(2)
0.7396(2)
0.6708(2)
0.6086(2)
0.6157(2)
0.6838(3)
0.7454(2)
0.8881(2)
0.8842(2)
0.9468(2)
1.0139(2)
1.0199(2)
0.9565(2)
0.7446(8)
0.741(1)
0.075(2)
0.067(1)
0.054(1)
0.0411(10)
0.054(1)
0.068(2)
0.067(2)
0.058(1)
0.049(1)
0.041(1)
0.049(1)
0.059(1)
0.062(1)
0.057(1)
0.051(1)
0.265(8)
0.38(1)
x
y
z
Uij
Fe1
Fe2
P1
P2
P3
P4
C1
C2
C3
C4
C5
C6
C7
C8
C9
0.47821(3)
0.20624(3)
0.56495(5)
0.57524(5)
0.12880(6)
0.10206(5)
0.3784(2)
0.4057(2)
0.4153(2)
0.3964(2)
0.3664(2)
0.3454(3)
0.3181(3)
0.3099(3)
0.3300(2)
0.3585(2)
0.6676(2)
0.6651(2)
0.5806(2)
0.6024(3)
0.6075(3)
0.6661(3)
0.6459(3)
0.6410(3)
0.5561(2)
0.4855(2)
0.4812(3)
0.4777(3)
0.5472(3)
0.5510(3)
0.5535(2)
0.6185(3)
0.5923(3)
0.5667(3)
0.5026(3)
0.5296(2)
0.6225(2)
0.6579(3)
0.7017(3)
0.6486(3)
0.6125(3)
0.5676(3)
0.2854(2)
0.2640(2)
0.2735(3)
0.3057(2)
0.3304(2)
0.3643(3)
0.3865(3)
0.3780(3)
0.3455(3)
0.3201(2)
0.0297(2)
0.0092(2)
0.0972(2)
0.0598(2)
0.0296(3)
0.0949(3)
0.1307(3)
0.1628(2)
0.1628(2)
0.1051(3)
0.1404(3)
0.19163(3)
0.16246(3)
0.12044(5)
0.25439(5)
0.08777(5)
0.22004(5)
0.1351(2)
0.1574(2)
0.2198(2)
0.2581(2)
0.2365(2)
0.2763(2)
0.2529(3)
0.1906(4)
0.1515(3)
0.1726(2)
0.1503(2)
0.2156(2)
0.0643(2)
0.0952(2)
0.0504(2)
−0.0007(3)
−0.0314(2)
0.0132(2)
0.0690(2)
0.0251(2)
−0.0173(2)
0.0182(2)
0.0627(2)
0.1044(2)
0.3114(2)
0.3588(2)
0.4033(2)
0.3722(2)
0.3252(2)
0.2797(2)
0.3033(2)
0.2675(2)
0.3084(3)
0.3592(2)
0.3944(2)
0.3526(2)
0.2329(2)
0.1982(3)
0.1361(3)
0.1084(2)
0.1424(2)
0.1149(3)
0.1489(4)
0.2118(4)
0.2400(3)
0.2057(2)
0.1133(2)
0.1756(2)
0.0319(2)
0.0642(2)
0.0205(2)
−0.0225(2)
−0.0551(2)
−0.0113(2)
0.0361(2)
−0.0158(2)
−0.0558(2)
0.32867(3)
0.80758(3)
0.31875(5)
0.31591(5)
0.82823(5)
0.81403(5)
0.3334(3)
0.3995(2)
0.4090(2)
0.3519(2)
0.2846(2)
0.2267(3)
0.1628(3)
0.1529(3)
0.2063(2)
0.2745(2)
0.3166(2)
0.2917(2)
0.3916(2)
0.4609(2)
0.5203(2)
0.5115(2)
0.4435(2)
0.3838(2)
0.2409(2)
0.2383(2)
0.1762(2)
0.1101(2)
0.1117(2)
0.1740(2)
0.2450(2)
0.2375(2)
0.1804(2)
0.1124(2)
0.1193(2)
0.1754(2)
0.3883(2)
0.4507(2)
0.5067(2)
0.5266(2)
0.4642(2)
0.4105(2)
0.7889(2)
0.7282(2)
0.7305(3)
0.7925(2)
0.8525(2)
0.9153(3)
0.9717(3)
0.9703(3)
0.9111(3)
0.8508(2)
0.8498(2)
0.8191(2)
0.7582(2)
0.6920(2)
0.6342(2)
0.6189(2)
0.6830(3)
0.7413(2)
0.9022(2)
0.9140(2)
0.9746(3)
0.0375(1)
0.0387(1)
0.0409(3)
0.0377(3)
0.0399(3)
0.0368(2)
0.053(1)
0.055(1)
0.053(1)
0.052(1)
0.051(1)
0.070(2)
0.077(2)
0.083(2)
0.070(2)
0.051(1)
0.049(1)
0.048(1)
0.048(1)
0.057(1)
0.070(2)
0.078(2)
0.070(2)
0.062(1)
0.047(1)
0.053(1)
0.063(1)
0.071(2)
0.065(1)
0.057(1)
0.0413(10)
0.056(1)
0.064(1)
0.066(2)
0.059(1)
0.046(1)
0.046(1)
0.061(1)
0.076(2)
0.073(2)
0.066(2)
0.055(1)
0.059(1)
0.064(2)
0.066(2)
0.060(1)
0.050(1)
0.072(2)
0.093(2)
0.093(2)
0.074(2)
0.051(1)
0.046(1)
0.044(1)
0.047(1)
0.055(1)
0.066(1)
0.068(2)
0.060(1)
0.059(1)
0.047(1)
0.060(1)
0.072(2)
C64 −0.0282(3)
C65 −0.0164(3)
C66 −0.0015(2)
C67
C68
C69
C70
C71
C72
C73
C74
C75
C76
C77
C78
0.0993(2)
0.1523(2)
0.1502(3)
0.1777(3)
0.1253(3)
0.1230(2)
0.739(1)
0.789(1)
0.7894(9)
0.8211(8)
0.8228(8)
0.8568(7)
0.1035(7)
0.1191(7)
0.1579(7)
0.1489(6)
0.6879(9)
0.6352(8)
0.5772(8)
0.5246(6)
0.275(6)
0.215(5)
0.237(6)
0.187(4)
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
C37
C38
C39
C40
C41
C42
C43
C44
C45
C46
C47
C48
C49
C50
C51
C52
C53
C54
C55
C56
C57
The present result is in sharp contrast to the previous
report on similar reduction of FeCl2(dmpe)2 [dmpe=
1,2-bis(dimethylphosphino)ethane], where hydrido(n-
aphthyl)-iron(II) and homoleptic dimer Fe2(dmpe)5
have been yielded ([2]g). The formation of zerovalent
18e complex 3 would arise from the reduction of 14e
complex 1 with sodium-naphthalene followed by the
coordination of naphthalene. Such formation of p6-
naphthalene complex having a tertiary phosphine lig-
and is rare, although those complexes having benzene
or functionalized benzene are prepared by the metal
vapor synthesis [1], hydrogenation of Fe(CH2C6H4Me-
4)2(dippe) [7], or reaction of Fe(N2)(depe)2 with styrene
[14]. Only Ru(p6-C10H8)(cod) (cod=cycloocta-1,5-di-
ene) was obtained by the reduction of Ru(acac)2(cod)
(acac=acetylacetonate) with sodium-naphthalene [15]
or by hydrogenation of Ru(cod)(cot) (cot=cycloocta-
1,3,5-triene) in the presence of naphthalene [16].
Scheme 1. Ligand exchange reaction of naphthalene in 3 with benzene
under reflux giving Fe(p6-C6H6)(dcype) (4).

H. Kubo et al. / Journal of Organometallic Chemistry 556 (1998) 89–95
93
2.3. Chemical reactions of Fe(p6-C10H8)(dcype) (3)
gen or argon using standard Schlenk and vacuum-line
techniques. Benzene, hexane, tetrahydrofuran and di-
ethyl ether were dried and distilled under N2 from
sodium benzophenone ketyl and dichloromethane was
dried and distilled over anhydrous CaSO4. Dcype [1,2-
bis(dicyclohexylphosphino)ethane] and its precursor
1,2-bis(dichlorophosphino)ethane were prepared ac-
cording to the literature method [20]. Anhydrous FeCl2
was purchased from Koso and dried at 120°C for 12 h
under vacuum before use. Naphthalene was purchased
from Kanto and used as received. HBF4 · OEt2 (85%)
Since an p6-naphthalene ligand is one of the most
labile arene ligand [16], the chemical reactivities of 3 are
topic of interest. Ligand exchange reaction of naph-
thalene in 3 with benzene smoothly took place under
reflux conditions giving Fe(p6-C6H6)(dcype) (4)
(Scheme 1). It is interesting to note that neither of arene
ligand in analogous iron(0), Fe(p6-toluene)(bpy)
(bpy=2,2%-bipyridine) ([1]d) nor Fe(p6-C6H4Me2-
1,4)(dippe) [7] can be replaced by the external arenes
1
1
even at elevated temperature. H-NMR spectrum of 4
was purchased from Aldrich and used as received. H-
shows a broad singlet at 4.91 ppm assignable to the
coordinated benzene ring and the 31P{1H}-NMR spec-
trum showed a singlet peak at 102.15 ppm. It is worth
noting that the chemical shift of the p6-benzene in the
1H-NMR spectrum is 0.23 ppm upfield from that of
isomorphous ruthenium analogue, Ru(p6-C6H6)(dcype)
(5.14 ppm) [17].
Complex 3 could be quantitatively transformed to
known Fe(CO)3(dcype) (5) [18] by exposure to excess
CO (1 atm). IR spectrum of 5 shows stretching bands
of terminal CO absorption at 1968, 1890, 1873 cm−1 in
CH2Cl2, which are identical with those reported by
Angelici et al. [18].
Protonation of 3 was easily carried out by HBF4 in
Et2O to give an orange powder of a cationic hydride
complex, [FeH(p6-C10H8)(dcype)]BF4 (6). 1H-NMR
spectrum of 6 in CD2Cl2 shows a triplet signal at
−19.00 ppm due to the hydride. Coordinated and
uncoordinated ring protons appear at 5.94 and 6.32
ppm as broad singlets, and at 7.65 and 7.74 ppm as
multiplets, respectively. These values are slightly
downfield from those of 3, probably due to decrease in
electron density at iron. The 31P{1H}-NMR spectrum
shows a singlet at 103.51 ppm, suggesting symmetrical
environment of the dcype ligand. These spectroscopic
data support the structure of 6. It is worthwhile to note
that the protonation of zerovalent M(arene)(diene)
(M=Fe, Ru) does not give a hydridometal(II) but an
allylmetal(II) complex [M(arene)(allyl)]+ [18].
and 13C{1H}-NMR spectra were recorded on a JEOL
1
LA-300 spectrometer (300 MHz for H, 75.4 MHz for
13C) and chemical shifts were reported in ppm from
TMS. 31P{1H}-NMR spectra were recorded on a JEOL
LA-300 (122 MHz) and chemical shifts were reported in
ppm downfield from external 85% H3PO4 in D2O. IR
spectra were recorded on a JASCO FT/IR-5M spec-
trometer. Melting points were measured under nitrogen
with Yazawa MP-21 capillary melting apparatus and
the values are uncorrected. Elemental analyses were
performed with Perkin Elmer 2400 series II CHN ana-
lyzer. Magnetic Susceptibility was measured by Sher-
wood Scientific MSB-MKI magnetic susceptibility
balance.
3.2. Synthesis of FeCl2(dcype) (1)
A benzene (49 ml) solution of anhydrous FeCl2
(0.680 g, 5.37 mmol), dcype (2.44 g, 5.78 mmol) was
heated at 70°C and stirred for 24 h. Then, this mixture
was filtered through a filter paper and set aside at r.t.
Light purple needles of FeCl2(dcype) (1) containing one
molecule of benzene per 1 was obtained from the
reaction mixture in a day (3.23 g, 5.15 mmol, 96%).
Anal. Found: C, 61.25; H, 8.65. Calc. for
C32H54Cl2FeP2: C, 61.25; H, 8.67%. veff=4.99 B.M.
Deprotonation of 6 was achieved by treatment with
lithium diisopropylamide (LDA) in THF at 0°C to give
3. However, neither of other bases such as Na2CO3 nor
Et3N remained unreacted with 6. This fact implies that
6 is far less acidic than other protonated Group 8 arene
complexes [15,19]. The weak acidity of 6 would be
arisen from the ancillary dcype ligand as a strong
electron donor.
3.3. Reaction of FeCl2(dcype) with CO
A solution of FeCl2(dcype) (0.1598 g, 0.255 mmol) in
a minimum amount of THF (1 ml) was exposed to CO
atmosphere at r.t. for 8 h during which the mixture
immediately turned to an orange solution. The reddish
orange precipitate was obtained in 2 days at −20°C.
The resulting precipitate was separated from the solu-
tion by using cannula, washed with Et2O (6 ml) and
then dried under flush of CO stream (0.140 g, 0.23
mmol, 91%). 2a: 31P{1H}-NMR (C6D6): l 60.59 (d,
J=35.2 Hz, 1P), 90.20 (d, J=35.2 Hz, 1P). IR (KBr):
2034(s), 1975(s) cm−1 (wCO). 2b: 31P{1H}-NMR: l
70.02(s).
3. Experimental section
3.1. General
All manipulations were performed under dry nitro-

94
H. Kubo et al. / Journal of Organometallic Chemistry 556 (1998) 89–95
3.4. Synthesis of Fe(p6-naphthalene)(dcype) (3)
excess amount of HBF4 (85% in Et2O, 50 drops) at 0°C.
The mixture allowed to warm at r.t. and stirred for 24
h. The supernatant solution was removed by using
cannula, and the resulting insoluble materials were
washed with Et2O (20 ml) and dried under reduced
pressure to give [FeH(p6-naphthalene)(dcype)][BF4] (6)
as an orange powder (0.103 g, 0.148 mmol, 72%).
1H-NMR (CD2Cl2): l −19.00 (t, 1H, J=84 Hz, Fe-
H), 5.96, 6.32 (br, 4H, coord. ring, C10H8), 7.65, 7.74
(m, 4H, uncoord. ring, C10H8). 31P{1H}-NMR
(CD2Cl2): l 103.51 (s).
To a THF solution (22 ml) of FeCl2(dcype) (1) (2.03
g, 3.24 mmol) was added dropwise in THF solution of
sodium naphthalene (55 ml, 15.0 mmol) at r.t. under
Ar. After the reaction at r.t. for 23 h, the solvent was
evaporated to dryness. The resulting dark green tar was
extracted with hexane (140 ml). Volatile matters were
removed in vacuo and finally by using oil diffusion
pump. Recrystallization of the resulting solid from cold
hexane (70 ml) gave dark green crystals of Fe(p6-naph-
thalene)(dcype) · 0.5C6H14 (3 · 0.5C6H14) (0.593 g,
0.977 mmol, 30%). m.p. 166–167°C (decomp.). Anal.
Found: C, 71.67; H, 9.33. Calc. for C78H126Fe2P4: C,
3.8. Deprotonation of [FeH(p6-naphthalene)-
(dcype)][BF4] with an excess amount of LDA
1
72.10; H, 9.77%. H-NMR (C6D6): l 4.20, 5.69 (br, 4H,
coord. ring, C10H8), 7.09, 7.41 (m, 4H, uncoord. ring,
C10H8). 13C{1H}-NMR (C6D6): l 59.99, 79.46 (s, coord.
ring, C10H8), 97.62 (s, ring junction, C10H8), 121.07,
126.89 (s, uncoord. ring, C10H8). 31P{1H}-NMR
(C6D6): l 94.60 (s).
To a
THF solution (7 ml) of [FeH(p6-naph-
thalene)(dcype)][BF4] (6) (0.0248 g, 0.0357 mmol) was
added an excess amount of lithium diisopropylamide
solution (ca. 0.8 mmol in THF) at 0°C. The mixture
allowed to warm to r.t. and stirred for 24 h. The solvent
was removed under reduced pressure and the resulting
solid was extracted with hexane (10 ml). All volatile
matters were removed in vacuo and the resulting dark
green powder was finally dried using oil diffusion pump
to give Fe(p6-naphthalene)(dcype) (3) as a dark green
powder (0.0186 g, 0.0306 mmol, 86%). All 1H-,
31P{1H}-NMR and IR spectra were identical to those
of 3.
3.5. Preparation of Fe(p6-benzene)(dcype) (4)
A
benzene solution (5 ml) of Fe(p6-naph-
thalene)(dcype) (0.0139 g, 0.0229 mmol) was refluxed
and stirred for 4 h. The dark green reaction mixture
turned to dark brown during course of the reaction.
The solvent was removed to dryness, and the resultant
brown solid was extracted with hexane (8 ml). The
filtrate was evaporated to dryness under reduced pres-
sure to give Fe(p6-benzene)(dcype) (4) as dark brown
solid (0.0100 g, 0.0180 mmol, 79%). Recrystallization of
the resulting solid from hexane (0.5 mL) gave brown
hexagonal crystals of 4. m.p. 127°C (decomp.). Anal.
Found: C, 69.03; H, 9.80. Calc. for C32H54FeP2: C,
69.06; H, 9.78%. 1H-NMR (C6D6): l 4.91 (br, 6H,
C6H6). 31P{1H}-NMR (C6D6): l 102.15 (s).
3.9. Crystallographic analyses for 3
Dark green crystals were grown from saturated solu-
tion of 3 in hexane. A crystal of suitable size was
selected and mounted in a glass capillary tube (GLAS,
0.7 mmƒ). The data were collected at 20°C using
TEXSAN automatic data collection series [21] on a
Rigaku R-AXIS II imaging plate system using Mo–Kh
˚
radiation (u=0.71070 A). Using the criteria ꢀFoꢀ\
3.6. Reaction of Fe(p6-naphthalene)(dcype) with CO
3.0|ꢀFoꢀ, 10343 out of 16341 reflections were used and
the structure was solved by the direct methods. Absorp-
tion and decay corrections were not applied for 3. The
crystal system was monoclinic and the space group was
P21/a (c14). Two independent molecules of 3 were
observed in a unit cell and the ORTEP drawing of one of
them is illustrated in Fig. 1. Both independent
molecules have comparable bond distances and angles
as shown in Table 2. From the difference Fourier map,
incorporation of a hexane molecule was found and
refined isotropically. All non-hydrogen atoms of 3 were
refined anisotropically. The hydrogens were located on
the ideal positions and were not refined. The refine-
ments were carried out by using full-matrix least
squares techniques on F, minimizing the function
w(ꢀFoꢀ−ꢀFcꢀ)2, where the weight w is defined as 4F2o/
[|2(F2o)]. [|2(Fo2)=(S2(C+R2B)+(pFo2)2/L2p, where
Fo=observed structure factor amplitude, S=scan rate,
A THF solution (6 ml) of Fe(p6-naphthalene)(dcype)
(0.0492 g, 0.0811 mmol) was exposed to CO atmo-
sphere (1 atm). The mixture was stirred at r.t. for 42 h,
during which the dark green solution turned to dark
brown. The solvent was removed to dryness, and the
resulting solid was extracted with hexane (14 ml). The
filtrate was evaporated to dryness under reduced pres-
sure to give a known orange powder of Fe(CO)3(dcype)
(5) (0.0425 g, 0.0756 mmol, 93%) [18]. IR (CH2Cl2):
1968(s), 1890(sh), 1873(s) cm−1 (wCO).
3.7. Protonation of Fe(p6-naphthalene)(dcype) with
excess amount of HBF4
A
Et2O solution (10 ml) of Fe(p6-naph-
thalene)(dcype) (0.124 g, 0.205 mmol) was added to an

H. Kubo et al. / Journal of Organometallic Chemistry 556 (1998) 89–95
95
Jesson, J. Am. Chem. Soc. 101 (1979) 1742. (j) M.V. Baker, L.D.
Field, Organometallics 5 (1986) 821.
C=total integrated peak count, R=ratio of scan time
to background counting time, B=total background
count, Lp=Lorentz-polarization factor, p=p-factor].
We used a p factor (0.050) to downweight the intense
reflections and then a goodness of fit of 1.51 was
obtained. The final R (Rw) value was 0.054 (0.071).
Plots of Sw(ꢀFoꢀ−ꢀFcꢀ)2 versus ꢀFoꢀ, reflection order in
data collection, (sin q)/u and various classes of indices
showed no unusual trends. Crystallographic data are
summarized in Table 1. The atomic coordinates are
listed in Table 3.
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Acknowledgements
We thank Dr M. Oshima and Prof. H. Suzuki of
Tokyo Institute of Technology for collection of X-ray
diffraction data of 3. This work was financially sup-
ported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Science, Sports and Culture,
Japan.
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