The first bidentate phosphanylborohydride: Synthesis, structure, and reactivity towards [CpFe(CO)2I]

Article abstract of DOI:10.1016/j.jorganchem.2007.03.006

Deprotonation of the phosphane-borane adduct rac/meso-(HP(BH₃)(Ph)CH₂)₂ (2) with KH provides facile access to the bidentate phosphanylborohydride rac/meso-K₂[(P(BH₃)(Ph)CH₂)₂] (3

Full text of DOI:10.1016/j.jorganchem.2007.03.006

Journal of Organometallic Chemistry 692 (2007) 2949–2955
www.elsevier.com/locate/jorganchem
The first bidentate phosphanylborohydride: Synthesis, structure,
and reactivity towards [CpFe(CO)2I]
*
Franz Dornhaus, Michael Bolte, Hans-Wolfram Lerner, Matthias Wagner
Institut fu¨r Anorganische Chemie, J.W. Goethe-Universita¨t Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt (Main), Germany
Received 22 January 2007; received in revised form 21 February 2007; accepted 2 March 2007
Available online 12 March 2007
Abstract
Deprotonation of the phosphane-borane adduct rac/meso-(HP(BH3)(Ph)CH2)2 (2) with KH provides facile access to the bidentate
phosphanylborohydride rac/meso-K2[(P(BH3)(Ph)CH2)2] (3). Treatment of 3 with two equivalents of [CpFe(CO)2I] gives the dinuclear
complex rac/meso-[(CpFe(CO)2)2-l-(P(BH3)(Ph)CH2)2] (4). Single crystals of the pure diastereomers meso-2, meso-3(thf)4, and rac-4 have
been grown from toluene/pentane, diethyl ether/thf, and benzene/pentane, respectively. The molecular structures of all three compounds
have been determined by X-ray crystallography.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: P-ligands; Boron; Phosphanylborohydride; Ligand design; Isoelectronic analogs; Bidentate ligands
1. Introduction
The chemistry of phosphanylborohydrides B, in contrast,
is still largely undeveloped [1–3,10–15].
The ready availability of versatile toolboxes of ligands
with smoothly varying electron donor properties is a prere-
quisite for the rational design of novel homogeneous cata-
lysts. One such toolbox with highly promising potential for
development consists of the series of isoelectronic mole-
cules A–C (Fig. 1) [1–3]. In moving from the generic meth-
yldiorganyl phosphane A to the phosphanylborohydride B,
a BH3 moiety is substituted for the phosphane methyl
group. This leaves the central atom unchanged, but results
in a negatively charged ligand. In the corresponding silyl
compound C, the substitution pattern is conserved, but
the central phosphorus atom is replaced by silicon, again
introducing a negative charge.
Our group has recently assessed the relative Lewis basic-
ities of [P(BH3)Ph2]ꢀ and P(CH3)Ph2 with respect to the
main group Lewis acids H+, CH3þ and BH3. Based on
NMR spectroscopy, X-ray crystal structure analyses and
displacement experiments, we came to the conclusion that
the phosphanylborohydride [P(BH3)Ph2]ꢀ forms dative
bonds of higher p character, is thus better suited to direct
its electron lone pair towards the acceptor orbital of the
coordinated Lewis acid and consequently forms more sta-
ble r adducts than its neutral counterpart P(CH3)Ph2 [1].
A similar picture was obtained from a study of the chalco-
genated phosphanylborohydrides K[EP(BH3)R2] (E = O–
Te; R = Ph, tBu), for which a certain degree of E@P
multiple-bond character has to be assumed [2]. For example,
the tellurium derivative K[TeP(BH3)Ph2] is isolable in good
Phosphanes A have found extensive use as ligands in
coordination chemistry [4,5]. Silanides C, while not as
widespread as phosphanes, are also generating increasing
interest as ancillary ligands, because they are strongly elec-
tron-releasing and display a pronounced trans-effect [6–9].
yield whereas from a THF solution of P(CH3)Ph2 and Te
1
compound TeP(CH3)Ph2 forms only in trace amounts in a
dynamic equilibrium. Moreover, the reaction between
K[P(BH3)Ph2] and EP(CH3)Ph2 (E = S, Se) resulted in the
quantitative formation of K[EP(BH3)Ph2] and P(CH3)Ph2.
In a subsequent study [3], we have investigated the com-
plexes [CpFe(CO)2–P(CH3)Ph2]+, [CpFe(CO)2–P(BH3)Ph2],
*
Corresponding author. Fax: +49 69 798 29260.
E-mail address: Matthias.Wagner@chemie.uni-frankfurt.de (M.
Wagner).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.03.006

2950
F. Dornhaus et al. / Journal of Organometallic Chemistry 692 (2007) 2949–2955
-
-
Ph(H)P
P(H)Ph
C
C
P
P
Si
R
R
R
R
R
R
H2
H2
H3C
H3B
H3C
1
A
B
C
(i) + 2 BH3 thf
Fig. 1. A series of isoelectronic ligands: Phosphanes (A), phosphanyl-
borohydrides (B), and silanides (C).
BH3
Ph(H)P
BH3
and [CpFe(CO)2–Si(CH3)Ph2] in order to quantify the
ligand-to-metal charge transfer, using the 13C-NMR shifts
of the cyclopentadienyl rings and the carbonyl ligands as
well as the CO IR stretching frequencies as diagnostic
tools. Our results clearly show that phosphanes are the
weakest donors, silanides are the strongest donors and
the gap between them is nicely filled by the phosphanyl-
borohydrides.
P(H)Ph
C
C
H2
H2
2
(ii) + 2 KH
BH3
PhP
2K
BH3
PPh
Notwithstanding the encouraging perspectives, one has
to face the fact that silanide as well as phosphanylborohy-
dride complexes tend to be significantly less stable than
phosphane complexes. Possible decomposition pathways
include one-electron reduction processes ([SiR3]ꢀ) or
hydride transfer from boron to the metal atom
([P(BH3)R2]ꢀ) [3]. The unwanted cleavage of the metal–sil-
icon bond in silanide complexes has been suppressed by the
introduction of a chelatinꢀg ether into the ligand molecule
(e.g. ½R2Si–ðCH2Þn–ðPR20 ꢁ ; n = 1, 2) [9]. Corresponding
coordination compounds are readily accessible upon treat-
ment of appropriate metal complex fragments with
R2ðHÞSi–ðCH2Þn–PR02. The reaction occurs via binding of
the phosphane moiety and subsequent oxidative addition
of the Si–H bond.
C
C
H2
H2
3
(i) + 2 CpFe(CO)2I
CO
CO
OC
OC
Fe
Fe
Ph(H3B)P
P(BH3)Ph
C
C
H2
H2
4
Scheme 1. Synthesis of the phosphane-borane adduct 2, the correspond-
ing bidentate phosphanylborohydride 3, and the dinuclear iron complex 4.
(i) ꢀ78 ꢁC to rt, thf; (ii) 0 ꢁC to rt, thf.
We suggest adopting a similar strategy for the stabiliza-
tion of phosphanylborohydride complexes. To this end, we
require either (phosphꢀanoalkyl)phosphanylborohydrides
½RðH3BÞP–ðCH2Þn–PR02ꢁ or bidentate phosphanylborohy-
was isolated after repeated recrystallization of 2 from tolu-
ene/pentane in 26% yield. Compound
dride ligands [R(H3B)P–(CH2)n–P(BH3)R]2ꢀ
.
2 is readily
deprotonated by KH in thf to give the bidentate phospha-
nylborohydride K2[(P(BH3)(Ph)CH2)2] (3). Single crystals
grown by gas-phase diffusion of diethyl ether into a solu-
tion of 3 in thf consisted exclusively of the meso-diastereo-
mer meso-3(thf)4. The dinuclear iron complex 4 (Scheme 1)
is obtained by addition of a solution of 3 in thf to a solu-
tion of [CpFe(CO)2I] (2 equiv.) in thf at ꢀ78 ꢁC. Recrystal-
lization of 4 from benzene/pentane gave single crystals of
rac-4. Attempts to synthesize the corresponding mononu-
clear iron complex [CpFe(CO)-g2-(P(BH3)(Ph)CH2)2] with
a chelating phosphanylborohydride ligand from 1 equiv. of
[CpFe(CO)2I] and 1 equiv. of 3 under similar conditions
resulted in a complex mixture of various unidentifiable
boron- and phosphorus-containing products. Addition of
18-crown-6 to the reaction mixture and layering with
diethyl ether led to the deposition of a small number of
red crystals. An X-ray crystal structure analysis revealed
cations [{K(18-c-6)}2-l:g5-C5H5]+ together with [CpFe-
(CO)2]ꢀ anions [17]. It is important to note in this context
that chelate complexes [CpFe(CO)-g2-dppe]+ are well-
known for the neutral diphosphane ligand (P(Ph)2CH2)2
The purpose of this paper is to describe the prepara-
tion of the potentially bidentate donor molecule K2-
[(P(BH3)(Ph)CH2)2] (3)[16] (Scheme 1) along with the full
characterization of the phosphane-borane adduct (HP(BH3)-
(Ph)CH2)2 (2). The latter molecule not only serves as the
precursor of 3, but may also be employed directly for metal
complexation via the oxidative addition of its H–P bonds
[13]. Moreover, we will report the results of salt metathesis
reactions between 3 and the iron carbonyl complex [CpFe-
(CO)2I] (4; Scheme 1).
2. Results and discussion
2.1. Synthesis and spectroscopical characterization
Note: Pure diastereomers will be designated as rac or
meso whereas mixtures of diastereomers will not explicitly
be designated as rac/meso.
Treatment of (HP(Ph)CH2)2 (1) with a solution of
BH3 Æ thf in thf yields the borane adduct (HP(BH3)-
(Ph)CH2)2 (2; Scheme 1). The pure diastereomer meso-2

F. Dornhaus et al. / Journal of Organometallic Chemistry 692 (2007) 2949–2955
2951
(dppe) [18–27]. A special feature of our ligand 3 that could
be responsible for the fact that 3 does not readily adopt a
chelating coordination mode, is its reducing power [3].
Liu et al. have recently demonstrated that the reaction of
[CpFe(CO)2I] and dppe selectively leads to the bridged
complexes [(CpFe(CO)2)2-l-dppe]I2 when [Cp2Co] or
dilute MeLi are present as redox catalysts (17e–19e path-
way) [28]. Electron-transfer chain processes thus appear
to suppress the formation of the chelate complex
[CpFe(CO)-g2-dppe]I, and a similar effect may be operative
also in our case.
mization does not occur via borane transfer but rather
via pyramidal inversion [31]. In our special case, however,
borane transfer would be an intramolecular rather than an
intermolecular process making it a potentially competitive
racemization pathway that should not be excluded from
consideration. Iron complexation leads to a shift of the
31P resonance back to lower field (rac-4: d(31P) = 29.4).
This trend qualitatively agrees with the development of
the 31P chemical shifts along the series HP(BH3)Ph2,
K[P(BH3)Ph2], and [CpFe(CO)2–P(BH3)Ph2] (1.7 ppm [1],
ꢀ28.8 ppm [2], 34.3 ppm [3], respectively).
The 11B{1H} NMR spectrum of meso-2 is characterized
by a resonance at ꢀ41.6 ppm, testifying to the presence of
tetracoordinated boron nuclei [29]. Upon deprotonation,
the signal is shifted by 10.8 ppm to lower field (3: d
(11B) = ꢀ30.8). A similar effect has been observed in the
case of HP(BH3)Ph2 (d(11B) = ꢀ40.0) [1] as compared to
K[P(BH3)Ph2] (d(11B) = ꢀ30.1) [2]. No significant further
shift of the 11B resonance occurs upon formation of the
dinuclear iron complex rac-4 (d(11B) = ꢀ30.9; cf.
[CpFe(CO)2–P(BH3)Ph2]: d(11B) = ꢀ28.0 [3]).
None of the 11B/31P NMR signals is sufficiently well
1
resolved to determine the JBP coupling constants.
1
All H- and 13C NMR signals of meso-2, 3, and rac-4
appear in the expected regions. Importantly, the CO car-
bon nuclei of rac-4 give rise to two signals in the 13C
NMR spectrum (d(13C) = 213.2, 213.3). This is a result of
the presence of the chiral phosphanylborohydride ligand
which renders the two CO molecules of each CpFe(CO)2
fragment diastereotopic.
The IR spectrum of rac-4 is characterized by two car-
In contrast to the 11B nuclei, the 31P nuclei are less
shielded in meso-2 (d(31P) = ꢀ2.1) than in 3 (d(31P) =
ꢀ49.2; cf. PMe2Ph: d(31P) = ꢀ47.6[30]). The chemical shift
of ꢀ49.2 ppm represents the mean value of two signals at
ꢀ48.7 ppm and ꢀ49.7 ppm (intensity ratio 1:1) which arise
from rac- and meso-3. Interestingly, this 31P NMR spec-
trum is obtained irrespective of whether rac/meso-2 or
meso-2 are used in the deprotonation reaction. The fact
that enantiomerically pure phosphanylborohydrides can
racemize in solution already within 5 min at rt is well doc-
umented [31]. Imamoto et al. reported evidence that race-
bonyl stretching frequencies at m ¼ 2027, 1978 cm (cf.
ꢀ1
~
[CpFe(CO)2–P(BH3)Ph2]: ~m ¼ 2030, 1982 cmꢀ1 [3]).
2.2. X-ray crystal structure determinations
Details of the X-ray crystal structure analyses of meso-2,
meso-3(thf)4, and rac-4 are summarized in Table 1.
The borane adduct meso-2 (Fig. 2) possesses crystallo-
graphically imposed inversion symmetry. The P–B
˚
˚
(1.923(2) A) and P–C(phenyl) bond lengths (1.817(1) A)
of meso-2 are in good agreement with the corresponding
Table 1
Selected crystallographic data of meso-2, meso-3(thf)4, and rac-4
meso-2
meso-3(thf)4
rac-4
Formula
Fw
C
273.88
14H22B2P2
C30H52B2K2O4P2
638.48
C28H30B2Fe2O4P2 · C6H6
703.89
Color, shape
Temperature (K)
Crystal system
Space group
Colorless, plate
173(2)
Monoclinic
P21/c
8.7354(7)
9.8498(6)
9.7027(8)
90
95.606(7)
90
830.85(11)
2
1.095
292
0.243
Colorless, block
173(2)
Monoclinic
P21/n
15.154(2)
7.9144(13)
16.439(3)
90
111.232(11)
90
1837.8(5)
2
1.154
684
0.374
Yellow, rod
173(2)
Triclinic
Pꢀ1
˚
a (A)
9.4084(6)
14.4270(9)
14.6089(9)
106.626(5)
107.000(5)
97.300(5)
1768.32(19)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalcd. (g cmꢀ3
F(000)
)
1.322
728
0.945
l (mmꢀ1
)
Crystal size (mm)
0.50 · 0.46 · 0.26
16030
1829 (0.0474)
1829/0/87
1.091
0.0306, 0.0849
0.0315, 0.0858
0.245 and ꢀ0.251
0.12 · 0.08 · 0.06
11836
3351 (0.1418)
3351/0/183
0.893
0.0802, 0.1234
0.1982, 0.1588
0.295 and ꢀ0.432
0.24 · 0.11 · 0.10
27772
6602 (0.0377)
6602/18/491
1.034
0.0257, 0.0622
0.0308, 0.0643
0.243 and ꢀ0.271
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit on F2
R1, wR2 (I > 2r(I))
)
R1, wR2 (all data)
Largest difference in peak and hole (e A
ꢀ3
˚
)

2952
F. Dornhaus et al. / Journal of Organometallic Chemistry 692 (2007) 2949–2955
(meso-3(thf)4; Fig. 3). Moreover, each K+ ion establishes
short K–B distances to two adjacent anionic moieties
˚
˚
(K(1)–B(1)#1 = 3.058(7) A,
K(1)–B(1)#2 = 3.136(8) A).
Each BH3 group in turn binds to two K+ ions such that
a polymeric structure is formed in the solid state. Metal–
boron distances are a well-established measure of the den-
ticity of borohydride groups [33]. Addition of the ionic
radii of bidentate (1.6 0.1 A [33]) and tridentate borohy-
dride ligands (1.36 0.06 A [33]) to the ionic radius of K
(1.65 A [34]) results in K–B distances of 3.25 A and 3.01 A
for bi- and tridentate coordination modes, respectively. An
inspection of the crystal structure of meso-3(thf)4 leads to
the conclusion that the shorter K–B distance of
˚
+
˚
˚
˚
˚
3
˚
3.058(7) A indeed corresponds to an g bonded borohy-
dride ligand. Since the position of the K+ ion relative to
the second H3BPR2 ligand precludes an g3 coordination,
this interaction is best described as g2 (K–B = 3.136(8)
˚
˚
A). The P–B bonds (1.983(7) A) as well as the P–C bonds
˚
˚
(1.871(6) A, 1.843(6) A) in meso-3(thf)4 are significantly
longer and the corresponding bond angles smaller than in
the protonated derivative meso-2. This observation can eas-
ily be rationalized on the basis of fundamental orbital
hybridization arguments according to which atomic s char-
acter concentrates in orbitals representing an electron lone
pair [32]. As a consequence, the P–B and P–C bonds in
meso-3(thf)4 have a higher degree of p character than the
analogous bonds in meso-2.
Fig. 2. Molecular structure of meso-2 in the crystal. Selected bond lengths
˚
(A) and bond angles (ꢁ): P(1)–B(1) = 1.923(2), P(1)–C(1) = 1.817(1), P(1)–
C(7) = 1.832(1); B(1)–P(1)–C(1) = 115.0(1), B(1)–P(1)–C(7) = 114.9(1),
C(1)–P(1)–C(7) = 106.5(1). Symmetry transformation used to generate
equivalent atoms: ꢀx + 1, ꢀy + 1, ꢀz.
values in the related adduct K(18-crown-6)[(BH3)2PPh2]
The crystal structure analysis of rac-4 provides conclu-
sive evidence that the compound is indeed a dinuclear iron
complex with a bridging phosphanylborohydride ligand
rather than a mononuclear chelate complex (Fig. 4). The
˚
˚
˚
(P–B = 1.930(2) A/1.940(2) A; P–C(phenyl) = 1.829(2) A/
˚
1.831(2) A) [1]. In line with Bent’s rule, [32] the C–P–C
angle of 106.5(1)ꢁ in meso-2 is significantly smaller than
the two B–P–C bond angles (114.9(1)ꢁ, 115.0(1)ꢁ).
˚
˚
two Fe–P bond lengths of rac-4 (2.271(1) A, 2.275(1) A)
The phosphanylborohydride meso-3 crystallizes with
are identical to the Fe–P bond length of [CpFe(CO)2–
four thf ligands that are coordinated to its K+ ions
˚
P(BH3)Ph2] (2.271(1) A [3]). Even the conformations of
˚
Fig. 3. Molecular structure of meso-3(thf)4 in the crystal (only part of the polymeric structure is shown). Selected bond lengths (A), atom-atom distances
˚
(A), and bond angles (ꢁ): P(1)–B(1) = 1.983(7), P(1)–C(1) = 1.871(6), P(1)–C(11) = 1.843(6), K(1)–B(1)#1 = 3.058(7), K(1)–B(1)#2 = 3.136(8); B(1)–P(1)–
C(1) = 106.6(3), B(1)–P(1)–C(11) = 104.3(3), C(1)–P(1)–C(11) = 103.0(3), O(21)–K(1)–O(31) = 160.9(2). Symmetry transformations used to generate
equivalent atoms: #1: x, y + 1, z; #2: ꢀx + 3/2, y + 1/2, ꢀz + 3/2.

F. Dornhaus et al. / Journal of Organometallic Chemistry 692 (2007) 2949–2955
2953
˚
Fig. 4. Molecular structure of rac-4 in the crystal. Selected bond lengths (A), bond angles (deg), and torsion angles (deg): P(1)–Fe(1) = 2.275(1), P(2)–
Fe(2) = 2.271(1), P(1)–B(1) = 1.955(2), P(2)–B(2) = 1.948(2), P(1)–C(5) = 1.853(2), P(2)–C(6) = 1.851(2), P(1)–C(31) = 1.840(2), P(2)–C(41) = 1.838(2);
B(1)–P(1)–C(5) = 108.3(1), B(2)–P(2)–C(6) = 109.5(1), B(1)–P(1)–C(31) = 111.0(1), B(2)–P(2)–C(41) = 111.8(1), C(5)–P(1)–C(31) = 101.0(1), C(6)–P(2)–
C(41) = 102.8(1), B(1)–P(1)–Fe(1) = 114.2(1), B(2)–P(2)–Fe(2) = 114.1(1), C(5)–P(1)–Fe(1) = 111.6(1), C(31)–P(1)–Fe(1) = 109.9(1), C(41)–P(2)–
Fe(2) = 109.9(1); P(1)–C(5)–C(6)–P(2) = ꢀ166.9(1).
the [CpFe(CO)2–P(BH3)Ph] fragments are the same in both
complexes.
diethyl ether, toluene, C6D6) or Na/Pb alloy (pentane, hex-
ane) prior to use. NMR spectra were recorded on Bruker
AMX 250, AV 300 or AV 400 spectrometers. 1H- and
13C NMR shifts are reported relative to tetramethylsilane
and were referenced against residual solvent peaks
(C6D5H: d = 7.16; C6D6: d = 128.06; C4D7HO: d = 1.73,
3.58; C4D8O: d = 25.3, 67.4). 11B NMR spectra were refer-
enced against external BF3 Æ OEt2; 31P NMR spectra are
reported relative to external H3PO4 (85%). Abbreviations:
s = singlet, d = doublet, m = multiplet, br = broad,
n.r. = multiplet expected in the NMR spectrum but not
resolved, i = ipso, o = ortho, m = meta, p = para. Elemen-
tal analyses were performed by the microanalytical labora-
tory of the J.W. Goethe-Universita¨t Frankfurt, Germany.
3. Conclusion
The bidentate phosphanylborohydride K2[(P(BH3)-
(Ph)CH2)2] (3) forms upon deprotonation of the correspond-
ing phosphane-borane adduct (HP(BH3)(Ph)CH2)2 (2) with
KH in a clean and quantitative reaction. A 1:1 mixture of
rac- and meso-3 is obtained even when diasteriomerically
pure meso-2 is employed. This leads to the conclusion that
3 readily racemizes either via pyramidal inversion or via
reversible BH3 transfer between the two phosphorus donor
sites. Treatment of 3 with two equiv. of [CpFe(CO)2I] gives
the dinuclear complex [(CpFe(CO)2)2-l-(P(BH3)(Ph)CH2)2]
(4). Attempts at synthesising a corresponding mononuclear
compound with chelating phosphanylborohydride ligand
led to complex mixtures of decomposition products. One
possible solution of this problem would be to replace the
highly reactive dianionic ligand [(P(BH3)(Ph)CH2)2]2ꢀ by
the bidentate molecules Ph(H3B)(H)P–(CH2)2–PPh2 or
(HP(BH3)(Ph)CH2)2 (2) which could be introduced into
the coordination sphere of transition metal ions via an oxida-
tive P–H addition reaction.
4.2. Materials
Li metal, dppe, BH3 Æ thf solution (1 mol/L in thf) and
[CpFe(CO)2I] were purchased from Aldrich or Fluka and
used as received. KH was purchased from Aldrich as a dis-
persion in mineral oil; prior to use, the oil was washed off
with pentane on a Schlenk frit. (HP(Ph)CH2)2 (1) was
obtained by a modified literature procedure through reduc-
tive cleavage of dppe with Li powder in thf and subsequent
hydrolysis and distillation [35,36]. (HP(BH3)(Ph)CH2)2 (2)
has been published by Imamoto et al. [31] We have synthe-
sized 2 via a significantly different route (see below), which
we find more convenient.
4. Experimental
4.1. General considerations
All reactions and manipulations of air-sensitive com-
pounds were carried out under an atmosphere of dry nitro-
gen using standard Schlenk techniques. Solvents were
freshly distilled under argon from Na/benzophenone (thf,
4.3. Synthesis of (HP(BH3)(Ph)CH2)2 (2)
To a solution of (HP(Ph)CH2)2 (1; 3.22 g, 13.08 mmol)
in thf (40 mL) was added a calibrated solution of BH3 Æ thf

2954
F. Dornhaus et al. / Journal of Organometallic Chemistry 692 (2007) 2949–2955
in thf (1 mol/L; 26.2 mL, 26.2 mmol) at ꢀ78 ꢁC with stir-
ring. After the mixture had warmed to rt overnight, all vol-
atiles were removed in vacuo. The resulting oily residue
contained an impurity of HP(BH3)Ph2. The product was
purified by column chromatography (90 g silica-gel; eluent:
hexane/toluene 1:4, followed by neat toluene; Rf(2) = 0.31,
Rf(HP(BH3)Ph2) = 0.57). Evaporation of the eluate yielded
2 as a colorless crystalline solid. Yield: 2.36 g (66%). The
NMR signals of the two diastereomers of 2 overlap to such
an extent that a ratio rac:meso could not be determined.
Repeated recrystallization of 2 from toluene/pentane gave
the pure meso-diastereomer. Yield of meso-2: 0.95 g
(26%). X-ray quality crystals of meso-2 were obtained by
gas-phase diffusion of pentane into a toluene solution of
Yield: 0.184 g (62%). X-ray quality crystals of rac-4 were
obtained by gas-phase diffusion of pentane into a benzene
solution of 4. NMR-data of rac-4: 1H NMR (C6D6,
400.13 MHz): d = 2.00 (m, 6 H, BH3), 2.70 (m, 4 H,
CH2), 4.07 (s, 10 H, Cp), 7.00 – 7.21 (m, 6 H, H-m,p),
7.94 (m, 4 H, H-o). 13C{1H} NMR (C6D6, 75.45 MHz):
1
d = 28.4 (d, JPC = 11.5 Hz, CH2), 86.4 (n.r., Cp), 128.5
(m, C-m), 129.3 (m, C-p), 131.9 (m, C-o), 140.6 (d,
2
1JPC = 24.1 Hz, C-i), 213.2 (d, JPC = 17.9 Hz, CO),
2
213.3 (d, JPC = 19.0 Hz, CO). 11B NMR (C6D6,
128.38 MHz): d = ꢀ30.9 (n.r.). 31P{1H} NMR (C6D6,
~
161.98 MHz): d = 29.4 (n.r.). IR (CH3CN): m ¼ 2027,
1978 cmꢀ1
(CO).
Elemental
Anal.
Calcd.
for
C28H30B2Fe2O4P2 (625.78): C, 53.74; H, 4.83. Found: C,
53.74; H, 5.15%.
1
2. NMR data of meso-2: H NMR (C6D6, 300.03 MHz):
d = 1.3 (m, 6 H, BH3), 1.69 (n.r., 4 H, CH2) 4.78 (br d,
1JPH = 374 Hz, 2 H, PH), 6.96 (m, 6 H, H-m,p), 7.33 (m,
4 H, H-o).13C{1H} NMR (C6D6, 75.45 MHz): d = 17.9
4.6. X-ray structural characterization
1
(m, CH2), 124.0 (d, JPC = 54.0 Hz, C-i), 129.2 (m, C-m),
Data collections were performed on a Stoe IPDS-II two
circle diffractometer with graphite-monochromated Mo Ka
radiation. Empirical absorption corrections with the MUL-
ABS option [38] in the program PLATON [39] were per-
formed. Equivalent reflections were averaged. The
structures were solved by direct methods [40] and refined
with full-matrix least-squares on F2 using the program
SHELXL-97 [41]. Hydrogen atoms bonded to carbon and
boron were placed on ideal positions and refined with fixed
isotropic displacement parameters using a riding model. H-
atoms bonded to phosphorus were refined isotropically. In
the structure of rac-4, the phenyl ring bonded to P(2) is dis-
ordered over two positions with site occupancy factors of
0.649(7) and 0.351(7). The phenyl ring was refined with a
restraint to keep the six ring atoms in a common plane.
The compound rac-4 crystallizes with 1 equiv. of benzene.
Each benzene molecule is disordered over two positions
(occupancy factors: 0.61(2)/0.39(2)). Restraints were
applied to the benzene ring such that it has similar geomet-
ric parameters at both positions.
131.9 (m, C-p), 133.2 (m, C-o). 11B{1H} NMR (C6D6,
96.26 MHz): d = ꢀ41.6 (n.r.). 31P{1H} NMR (C6D6,
121.46 MHz): d = ꢀ2.1 (n.r.). Elemental Anal. Calcd. for
C14H22B2P2 (273.88): C, 61.39; H, 8.10. Found: C, 61.20;
H, 7.91%.
4.4. Synthesis of K2[(P(BH3)(Ph)CH2)2] (3)
Solid KH (0.076 g, 1.89 mmol) was added to a solution
of (HP(BH3)(Ph)CH2)2 (2; 0.241 g, 0.88 mmol) in thf
(10 mL) at 0 ꢁC with stirring. After the mixture had
warmed to rt overnight, all volatiles were removed in
vacuo. The resulting yellowish solid residue was washed
with pentane (1 · 10 mL) and thf (1 · 5 mL). The colorless
product was dried in vacuo. Yield: 0.288 g (93%) [37]. X-
ray quality crystals of meso-3(thf)4 were obtained by gas-
phase diffusion of diethyl ether into a thf solution of 3.
1H NMR (thf-D8, 400.13 MHz): d = 0.58 (m, 6 H, BH3),
1.26 (br, 4 H, CH2), 6.76 (m, 2 H, H-p), 6.93 (m, 4 H, H-
m), 7.44 (m, 4 H, H-o). 13C{1H} NMR (thf-D8, 100.62
MHz): d = 122 (n.r., C-p), 126 (n.r., C-m), 132 (n.r., C-o),
n.o. (CH2, C-i). Note: The solubility of 3 is very low even
in thf-D8; a decent 13C NMR spectrum was therefore not
obtained. 11B{1H} NMR (thf-D8, 128.38 MHz):
d = ꢀ30.8 (br). 31P{1H} NMR (thf-D8, 161.98 MHz):
d = ꢀ48.7, ꢀ49.7 (n.r.).
Acknowledgements
The authors are grateful to the ‘‘Deutsche Forschungs-
gemeinschaft’’ (DFG) and the ‘‘Fonds der Chemischen
Industrie’’ (FCI) for financial support.
Appendix A. Supplementary material
4.5. Synthesis of [(CpFe(CO)2)2-l-(P(BH3)(Ph)CH2)2]
(4)
CCDC 634049, 634048 and 634050 contain the supple-
mentary crystallographic data for meso-2, meso-3(thf)4
and rac-4. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supple-
mentary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2007.
03.006.
A solution of K2[(P(BH3)(Ph)CH2)2] (3; 0.165 g,
0.47 mmol) in thf (40 mL) was added to a solution of
[CpFe(CO)2I] (0.286 g, 0.94 mmol) in thf (10 mL) at
ꢀ78 ꢁC with stirring. After the mixture had warmed to
rt overnight, all volatiles were removed in vacuo. The
resulting brown solid residue was extracted into toluene
(10 mL) and the extract was filtered. Pentane (25 mL)
was added to the filtrate to precipitate a yellow solid.

F. Dornhaus et al. / Journal of Organometallic Chemistry 692 (2007) 2949–2955
[21] D. Sellmann, W. Weber, J. Organomet. Chem. 304 (1986) 195.
2955
References
[22] N.J. Coville, E.A. Darling, A.W. Hearn, P. Johnston, J. Organomet.
Chem. 328 (1987) 375.
[1] F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner, Eur. J. Inorg.
Chem. (2006) 1777.
[23] H. Schumann, J. Organomet. Chem. 320 (1987) 145.
[24] A.S. Goldman, D.R. Tyler, Inorg. Chem. 26 (1987) 253.
[25] A.R. Cutler, A.B. Todaro, Organometallics 7 (1988) 1782.
[26] M.P. Castellani, D.R. Tyler, Organometallics 8 (1989) 2113.
[27] T. Bach, D.N.A. Fox, M.T. Reetz, J. Chem. Soc., Chem. Commun.
(1992) 1634.
[2] F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner, Eur. J. Inorg.
Chem. (2006) 5138.
[3] T.I. Kuckmann, F. Dornhaus, M. Bolte, H.-W. Lerner, M.C.
¨
Holthausen, M. Wagner, Eur. J. Inorg. Chem., doi:10.1002/
ejic.200601207.
[28] J. Peng, L.-K. Liu, C.R. Chimie 5 (2002) 319.
[29] H. No¨th, B. Wrackmeyer, Nuclear Magnetic Resonance Spec-
troscopy of Boron Compounds, in: P. Diehl, E. Fluck, R.
Kosfeld (Eds.), NMR Basic Principles and Progress, Springer,
Berlin, 1978.
[30] B.E. Mann, J. Chem. Soc. Perkin Trans. II 1 (1972) 30.
[31] T. Imamoto, T. Oshiki, T. Onozawa, M. Matsuo, T. Hikosaka, M.
Yanagawa, Heteroatom Chem. 3 (1992) 563.
[4] L.D. Quin, A Guide to Organophosphorus Chemistry, John Wiley
Sons, Inc., New York, 2000.
[5] L.H. Gade, Koordinationschemie, Wiley-VCH, Weinheim, 1998.
[6] D.L. Lichtenberger, A. Rai-Chaudhuri, J. Am. Chem. Soc. 113 (1991)
2923.
[7] R.D. Brost, G.C. Bruce, F.L. Joslin, S.R. Stobart, Organometallics
16 (1997) 5669.
[8] H. Tobita, K. Hasegawa, J.J.G. Minglana, L.-S. Luh, M. Okazaki,
H. Ogino, Organometallics 18 (1999) 2058.
[9] M. Okazaki, S. Ohshitanai, M. Iwata, H. Tobita, H. Ogino, Coord.
Chem. Rev. 226 (2002) 167.
[10] W. Angerer, W.S. Sheldrick, W. Malisch, Chem. Ber. 118 (1985)
1261.
[11] D.A. Hoic, W.M. Davis, G.C. Fu, J. Am. Chem. Soc. 118 (1996)
8176.
[12] A.-C. Gaumont, M.B. Hursthouse, S.J. Coles, J.M. Brown, Chem.
Commun. (1999) 63.
[32] (a) H.A. Bent, Chem. Rev. 61 (1961) 275;
(b) J.E. Huheey, Inorg. Chem. 20 (1981) 4033;
(c) D.M. Root, C.R. Landis, T. Cleveland, J. Am. Chem. Soc. 115
(1993) 4201;
(d) M. Atanasov, D. Reinen, J. Phys. Chem. A 105 (2001) 5450.
[33] N. Edelstein, Inorg. Chem. 20 (1981) 297.
[34] R.D. Shannon, Acta Crystallogr. Sect. A. 32 (1976) 751.
[35] P. Brooks, M.J. Gallagher, A. Sarroff, Austr. J. Chem. 40 (1987)
1341.
[36] R.S. Dickson, P.S. Elmes, W.R. Jackson, Organometallics 18 (1999)
2912. We have performed the dppe cleavage in a solution that was
vigorously stirred overnight rather than irradiated in an ultrasonic
bath, and we have hydrolyzed the product mixture at ꢀ78 ꢁC instead
of 0 ꢁC. 31P NMR analysis showed ca. 5% HPPh2 impurity after
distillation.
[37] Most of the thf molecules that may be coordinated to the K+ ions will
be removed upon prolonged exposure of the microcrystalline material
to a vacuum. Our calculation of the yield of meso-3 is based on the
assumption that it contains no residual thf at all.
[38] R.H. Blessing, Acta Crystallogr. Sect. A. 51 (1995) 33.
[39] A.L. Spek, Acta Crystallogr. Sect. A. 46 (1990) C34.
[40] G.M. Sheldrick, Acta Crystallogr. Sect. A. 46 (1990) 467.
[41] G.M. Sheldrick, SHELXL-97. A Program for the Refinement of
Crystal Structures, Universita¨t Go¨ttingen, 1997.
[13] H. Dorn, C.A. Jaska, R.A. Singh, A.J. Lough, I. Manners, Chem.
Commun. (2000) 1041.
[14] G. Muller, J. Brand, Organometallics 22 (2003) 1463.
¨
[15] C.A. Jaska, A.J. Lough, I. Manners, Inorg. Chem. 43 (2004) 1090.
[16] (a) (The isoelectronic methyl derivative (P(CH3)(Ph)CH2)2 has been
described and is thus available for comparison) L. Horner, J.P. Bercz,
Tetrahedron Lett. 7 (1966) 5783;
(b) J.P. Bercz, L. Horner, Liebigs Ann. Chem. 703 (1967) 17;
(c) I. Kawada, Tetrahedron Lett. 10 (1969) 793.
[17] F. Dornhaus, Ph.D. thesis, J.W. Goethe-Universita¨t Frankfurt, 2007.
[18] P.M. Treichel, R.L. Shubkin, K.W. Barnett, D. Reichard, Inorg.
Chem. 5 (1966) 1177.
[19] R.J. Haines, A.L. du Preez, Inorg. Chem. 11 (1972) 330.
[20] M.L. Brown, J.L. Cramer, J.A. Ferguson, T.J. Meyer, N. Winterton,
J. Am. Chem. Soc. 94 (1972) 8707.