Ansa-metallocenes with B-N and B-P linkages: The importance of N-H?F-C hydrogen bonding in pentafluorophenyl boron compounds

Article abstract of DOI:10.1016/S0022-328X(03)00346-2

The reaction of Cp′(Cp^B)ZrCl₂ [Cp^B=η⁵-C₅H₄ B(C₆F₅)₂] with LiNHCMe₃ gave Cp′(Cp^B)(μ-NHCMe₃)ZrCl, with a constrained-geometry type Cp-B-N chelate ligand. The ¹⁹ F-NMR spectrum of the zirconium complexes, as well as that of the titanium analogue, reveals C-F?H-N hydrogen bonding to one of the ortho-F atoms of a C₆F₅ ring, strong enough to persist in solution at room temperature. The reaction of Cp′ (Cp^B)TiCl₂ with LiPPh₂ affords the Cp-B-P chelate complex Cp′(Cp^B)(μ-PPh₂) TiCl, the first example of a crystallographically characterised Ti(IV) phosphido compound. A ¹⁹F-NMR study of a number of adducts of B(C₆F₅)₃ with prim- and sec-amines demonstrates the importance of intramolecular hydrogen bonding to C₆F₅ in this class of compounds, while there are no such interactions in B(C₆F₅)₃ (PHR₂) (R=Cy, Ph). The crystal structures of Cp′ (Cp^B)(μ-PPh₂)TiCl, B(C₆F₅) ₃(NHMe₂) and B(C₆F₅) ₃(PHCy₂) are reported.

Full text of DOI:10.1016/S0022-328X(03)00346-2

Journal of Organometallic Chemistry 680 (2003) 193Á205
/
www.elsevier.com/locate/jorganchem
Ansa-metallocenes with Bꢀ
/
N and Bꢀ
/
P linkages: the importance of
Nꢀ
/
H
/
ꢀ ꢀ ꢀ
/
Fꢀ
/
C hydrogen bonding in pentafluorophenyl boron
compounds
Simon J. Lancaster *, Andrew J. Mountford, David L. Hughes, Mark Schormann,
Manfred Bochmann *
Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK
Received 19 March 2003; received in revised form 23 April 2003; accepted 23 April 2003
Dedicated to Professor M.F. Hawthorne on the occasion of his 75th birthday
Abstract
The reaction of Cp?(CpB)ZrCl2 [CpBꢀ
geometry type CpꢀBꢀ
N chelate ligand. The 19F-NMR spectrum of the zirconium complexes, as well as that of the titanium
analogue, reveals Cꢀ ꢀ ꢀ ꢀHꢀN hydrogen bonding to one of the ortho-F atoms of a C6F5 ring, strong enough to persist in solution at
/
h5-C5H4B(C6F5)2] with LiNHCMe3 gave Cp?(CpB)(m-NHCMe3)ZrCl, with a constrained-
/
/
/
F/
/
/
room temperature. The reaction of Cp?(CpB)TiCl2 with LiPPh2 affords the Cpꢀ
/
Bꢀ
P chelate complex Cp?(CpB)(m-PPh2)TiCl, the
/
first example of a crystallographically characterised Ti(IV) phosphido compound. A 19F-NMR study of a number of adducts of
B(C6F5)3 with prim- and sec-amines demonstrates the importance of intramolecular hydrogen bonding to C6F5 in this class of
compounds, while there are no such interactions in B(C6F5)3(PHR2) (Rꢀ
Cy, Ph). The crystal structures of Cp?(CpB)(m-PPh2)TiCl,
B(C6F5)3(NHMe2) and B(C6F5)3(PHCy2) are reported.
/
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Ansa-metallocenes; Boron; Hydrogen bonding; Heteroatom bridges; Amido complexes; Phosphido complexes
1. Introduction
(CpB)TiCl3 with LiCp? [4]. This route has recently
been extended to zirconocenes [5].
We recently reported the synthesis of Group 4
cyclopentadienyl complexes bearing Lewis acidic
bis(pentafluorophenyl)boryl substituents and their be-
haviour as self-activating alkene polymerisation cata-
lysts [1]. In titanium complexes the boryl substituents
were found to activate chloro ligands, depending on the
The bonding in this type of complexes is a fine
balance of steric factors. For example, whereas
(CpB)(Ind)TiCl2 has a crystallographically characterised
Cpꢀ
/
Bꢀ
/
Clꢀ
/
Ti linkage, there is no such Bꢀ
/
Cl interaction
C5H5
in the zirconium analogues Cp?(CpB)ZrCl2 (Cp?ꢀ
/
and C9H7), which, unlike the titanocenes, readily form
adducts between weak bases such as Me2S and boron
(III) [5]. The steric relief in going from titanium to
CpBꢀ
/
Tiꢀ/Cl angle [2]. Reetz reported the preparation of
the first boryl zirconocenes through the dehalosilylation
reaction between ZrCl4 or CpZrCl3 and C5H4(Si-
zirconium means that the Cpꢀ
/
Bꢀ
/
Clꢀ
/
Zr interaction is
Me3)BX2 (Xꢀ
Titanocenes with boryl-cyclopentadienyl ligands,
Cp?(CpB)TiCl2 (CpBꢀh5-C5H4B(C6F5)2, Cp?ꢀ
C5H5
(II), C9H7, C5H4SiMe3), are accessible by reacting
/Me, Et, OEt and C6F5 (I, Chart 1)) [3].
not favoured.
Our initial studies on the interaction of titanium
complexes with boryl-Cp ligands demonstrated that
/
/
the Cpꢀ
ClꢀTi. Here we report several complexes of the type
Cp(CpB)M(Cl)(m-NHR) (Mꢀ
Ti, Zr) which display
CpꢀBꢀN ‘constrained geometry’ bonding, as well as
examples of related compounds with CpꢀBꢀP linkages.
/
Bꢀ
/
Nꢀ
/
Ti linkage was preferred over Cpꢀ
/
Bꢀ
/
/
/
* Corresponding authors. Tel./fax: ꢁ
E-mail addresses: s.lancaster@uea.ac.uk (S.J. Lancaster),
m.bochmann@uea.ac.uk (M. Bochmann).
/
44-1603-59-2009.
/
/
/
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00346-2

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S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á205
/
Plate 1.
A more detailed structural investigation revealed the
importance of Nꢀ FꢀC hydrogen bonding, a feature
that has also been found to be prominent in adducts of
B(C6F5)3 with amines. Dunitz and Taylor, in their
statistical analysis of crystallographic data, have pointed
out that ‘organic fluorine hardly ever accepts hydrogen
resonances, one of which, at d ꢂ142.6, shows a
/
/
H
/
ꢀ ꢀ ꢀ
/
/
significant high-field shift from the normal o-F region.
Prompted by this observation, we recorded the 19F-
NMR spectrum of the titanium complex 1, which
proved to be very similar. The explanation for this
unusual 19F signal was apparent on re-examination of
the solid-state structure of 1 which showed a previously
bonds’ [6]. Nevertheless, in biological chemistry OH
/
ꢀ ꢀ ꢀ
/
FꢀC and NH FꢀC interactions are considered im-
/
/
ꢀ ꢀ ꢀ
/
/
unrecognised Nꢀ
/
H
˚
/
ꢀ ꢀ ꢀ
/
F interaction, with a short H
distance of 2.11 A and a wide NꢀHꢀF angle of 1478.
High-field o-F shifts have been reported for compounds
with Zr F contacts [9,10], as well as for the anion
ꢀ ꢀ ꢀ
[NH2{B(C6F5)3}2]ꢂ which provided crystallographic
evidence for a range of Nꢀ ꢀ ꢀ ꢀF interactions [11].
Dunitz et al. have laid down criteria for such
interactions, i.e. the H FꢀC interaction should be
ꢀ ꢀ ꢀ
significantly shorter than the sum of the van der Waals
/
ꢀ ꢀ ꢀ
/
F
portant for the binding of fluorinated substrates to
enzymes [7], even if this notion has been somewhat
controversial [8]. A number of complexes of perfluor-
oaryl boranes with amines and phosphines have there-
fore been included in this study.
/
/
/
/
/
H
/
/
/
/
/
2. Results and discussion
˚
radii (ca. 2.55 A) and preferably be no longer than ca.
˚
2.2Á
/
2.3 A, with obtuse Hꢀ
/
Fꢀ
/
C angles [6]. The NH
diborate
/
ꢀ ꢀ ꢀ
/
F
Following the procedure we developed for the pre-
paration of Cp(CpB)TiCl(NHCMe3) (1), the reaction of
interactions
in
the
m-NH2
anion
[NH2{B(C6F5)3}2]ꢂ range from 1.90 to 2.43 A (Fig. 2)
Cp(CpB)ZrCl2(SMe2)
LiNHCMe3 resulted in the analogous zirconium com-
with
one
equivalent
of
˚
[11]. This was reflected in its solution behaviour where
1
plex 2 (Scheme 1). The H- and 11B-NMR resonances
at ꢂ90 8C only one of the six C6F5 substituents was
/
found to rotate freely, although there was no evidence
for hindered rotation on the NMR timescale at room
temperature. Complexes 1 and 2 have similar intramo-
were almost identical to those of 1 (Table 1). The room
temperature 19F-NMR spectrum of 2 (Fig. 1) was more
complex than anticipated, with a separate resonance for
each of the ten fluorine nuclei in the molecule. Evidently
lecular Nꢀ
cases they prevent free rotation in solution even at room
temperature. Indeed, the Nꢀ ꢀ ꢀ ꢀFꢀC bonding in 2 is
/
H
/
ꢀ ꢀ ꢀ
/
Fꢀ
/
C hydrogen bonds; however, in these
rotation of the two chemically inequivalent Bꢀ
/
C6F5
moieties is strongly hindered. There are four o-F
/
H/
/
/
Scheme 1.

S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á
/205
195
Table 1
Multinuclear NMR data of pentafluorophenyl boron compounds

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S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á205
/
Table 1 (Continued)

S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á
/205
197
Table 1 (Continued)

198
S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á205
/
Table 1 (Continued)
Fig. 1. 19F-NMR spectrum of the zirconium complex 2 at 25 8C. The high-field o-F signal at d ꢂ
/
142.6 is indicative of hydrogen bonding to NꢀH.
/

S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á
/205
199
Having successfully prepared examples with ‘con-
strained geometry’ ansa-cyclopentadienyl-amido Cpꢀ
BꢀNꢀM bonding we wished to determine whether the
analogous phosphido complexes would adopt a similar
CpꢀBꢀPꢀM structure. Ansa-cyclopentadienyl phos-
/
/
/
/
/
/
phido complexes with a bridging carbon or silicon
atom have recently been prepared by Erker and co-
workers [12]. The first fully characterised mononuclear
metallocene(IV) diphosphides, Cp2M(PR2)2 (Mꢀ
Hf; RꢀPh, Cy, Et) were reported in 1983 [13,14].
However, the reaction of Cp2TiCl2 with LiPR2 (RꢀEt,
/
Zr,
/
/
Ph) yielded the diamagnetic Ti(III) dimers [Cp2Ti(m-
PR2)]2 [15], evidently due to reduction of Ti(IV) by
LiPR2.
The reaction between Cp(CpB)TiCl2 and one equiva-
lent LiPPh2 in toluene did not give rise to a dramatic
colour change but was accompanied by the precipitation
of LiCl (Scheme 3). The product, Cp(CpB)Ti(PPh2)Cl
(4), was isolated by crystallisation from toluene solution.
The red colour indicated that titanium had not been
reduced, and indeed 4 is diamagnetic. The presence of a
single resonance in the 31P-NMR spectrum and the
expected chlorine analysis suggest that 4 is a monomeric
titanocene(IV) phosphido chloride. The 11B resonances
Fig. 2. Structure of the anion [NH2{B(C6F5)3}2]ꢂ, illustrating the Cꢀ
ꢀ ꢀ ꢀ
/
F/
/HN hydrogen-bonding pattern [11].
sufficiently rigid to show Nꢀ
/
H
/
ꢀ ꢀ ꢀ
/
F fluorine coupling in
the 1H-NMR spectrum at 25 8C (d 3.13, JHF
ꢀ
/
22.3 Hz).
N
Efforts were made to extend the synthesis of CpꢀBꢀ
/
/
constrained geometry-type systems to the parent NH2
linkage. Because of the low solubility of NaNH2, the
reaction with CpBCpTiCl2 required the use of tetrahy-
drofuran as the solvent and extended reaction times.
Over 36 h the sodium amide dissolved and a bright red
solution of Cp(CpB)Ti(NH2)Cl (3) was formed (Scheme
2). Attempts to grow crystals suitable for X-ray diffrac-
tion were not successful; however, the structure repre-
sented in Scheme 2 is consistent with the elemental
analysis and spectroscopic data. The 1H-NMR spectrum
shows signals for four inequivalent protons of the
C5H4B ring. The NH2 group is diastereotopic, although
the coupling is obscured by line-broadening. In addi-
at d ꢂ
and together with the broadened 31P-NMR signal this
leads us to propose a CpꢀBꢀPꢀTi chelate formation.
/8.9 indicate a tetrahedral environment at boron,
/
/
/
Apparently, the interaction of the phosphide ligand with
boron prevents reduction of the metal centre and
facilitates the isolation of the first titanocene(IV)
phosphide.
The structure of 4 was determined by X-ray diffrac-
tion. There are two independent molecules in the unit
cell; one is well resolved and is shown in Fig. 3, the other
shows disorder with alternative sites for the Cl and Cp
ligands with 50% occupancy at each site. The metal
centre has a distorted tetrahedral geometry. The struc-
tion, the 11B-NMR resonance, d ꢂ
tetrahedral coordination environment. The data suggest
CpꢀBꢀNꢀTi bonding, as in 1. The case for a Nꢀ ꢀ ꢀ ꢀ
FꢀC hydrogen bonding interaction in this complex is
/
6.3, indicates a
/
/
/
/
H
/
/
ture confirms the presence of a Cpꢀ
ring, with CpB(centroid)ꢀ
TiꢀP angles for the two
molecules of 92.78 and 93.98. In comparison, the
CpB(centroid)ꢀ
TiꢀCl angle is wider, 108.48. The Bꢀ
/
Bꢀ
/
Pꢀ/Ti chelate
/
/
/
less clear-cut since, although the two C6F5 groups are
inequivalent at room temperature, no high field o-F
resonance is observed. Poor solubility precluded a low-
temperature study.
/
/
/P
˚
distances of 2.054(4) and 2.066(4) A are slightly longer
than the corresponding bond in (C6F5)3B(PH2CMe3)
˚
(2.015(3) and 2.034(3) A for two independent molecules)
[23]. The Tiꢀ
/
Cl bond length is as expected for titanocene
Scheme 2.
Scheme 3.

200
S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á205
/
also play a role in neutral compounds, we have
examined the complexes of B(C6F5)3 with NH2CMe3
and NHMe2, to form primary (5) and secondary (6)
amine adducts (Scheme 4). Complexation was con-
firmed by the 11B-NMR resonances at d ꢂ
1.4 (6), which are typical for four-coordinate neutral
adducts.
/5.2 (5) and
ꢂ
/
Comparison of 5 with complex 1 suggests a more
complex hydrogen bonding arrangement in the former,
due to the presence of the third C6F5 substituent. The
variable-temperature 19F-NMR spectra of 5 are shown
in Fig. 4. One broad o-F resonance (d ꢂ
observed at room temperature. Cooling to ꢂ
results in decoalescence into three o-F peaks with an
integral ratio of 2:2:2. The o-F signal at d ꢂ136.7 is
high-field shifted due to an interaction with an Nꢀ
hydrogen atom. Cooling below ꢂ60 8C sees a further
/
134.6) is
/
40 8C
/
/H
/
Fig. 3. Molecular structure of Cp(CpB)(m-PPh2)TiCl (4). Thermal
ellipsoids are drawn at 50% probability. The asymmetric unit consists
splitting of the high-field o-F peak. This is consistent
with the structure in Scheme 4 which has two o-Fs
of two molecules; the fully ordered one of these is shown selected bond
˚
P 2.6522(13), BꢀP
lengths (A) and angles (8): Tiꢀ
/
Cl 2.320(2), Tiꢀ
/
/
B
˚
˚
2.054(4), Tiꢀ
BꢀC(11) 1.635(5), Bꢀ
92.90(13), CpB(centroid)ꢀ
/
Cp (centroid) 2.051 A, Tiꢀ
C(31) 1.647(6), Clꢀ
TiꢀP 92.78.
/
Cp(centroid) 2.074(4) A,
/
/
/
TiꢀP 100.20(5), TiꢀPꢀB
/
/
/
/
/
˚
chlorides, 2.320(2) A. The Tiꢀ
/
P bond lengths of
˚
2.6522(13) and 2.6563(13) A compare well with the
corresponding bonds in Cp2Ti(PPh2)(PMe3) (2.681(3)
ꢂ
˚
A) and [Cp2Ti(PPh2)2] (2.67(1) and 2.71(1) A) [15].
˚
The structure is consistent with a Tiꢀ
P0B donor interaction, while the bond length distribu-
tion in related titanium complexes with BꢀN, BꢀCl and
BꢀO linkages was slightly in favour of a B-heteroatom
s-bond, with dative bonding to the metal [2]. The
C(11)ꢀTiꢀP angle of 62.24(9)8 is slightly more acute
/
P s-bond and a
/
/
/
/
/
/
than the corresponding angles in II and its m-OH
analogue [2,4].
The existence of persistent NH
/
ꢀ ꢀ ꢀ
/
F hydrogen bonding
in complexes 1Á3 led us to look for similar, possibly
/
unrecognised cases. A great number of Lewis base
adducts of B(C6F5)3 have been reported [16,17]. The
contribution of Cꢀ
/
F
/
ꢀ ꢀ ꢀ
/
HN bonding to the structure of
the anion [NH2{B(C6F5)3}2]ꢂ has been discussed above.
In order to determine whether hydrogen bonding would
Fig. 4. Temperature dependence of the 19F VT-NMR spectrum of 5,
OꢀF.
/
Scheme 4.

S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á
/205
201
Scheme 5.
interacting with a single Nꢀ
/
H, which renders the
nitrogen chiral and the two C6F5 groups diastereotopic.
capable of hydrogen bonding, shows no sign of hindered
rotation even on cooling to ꢂ60 8C.
This situation may be compared with Oꢀ
hydrogen bonding in pentafluorophenyl Group 13
compounds. OH F hydrogen-bonding is found in the
ꢀ ꢀ ꢀ
hydrate B(C6F5)3(OH2) [19], in the anion
/
The 19F-NMR spectrum of 6 at room temperature
/
H
/
ꢀ ꢀ ꢀ
/
Fꢀ/C
closely resembles that of 5 at ꢂ40 8C, i.e. hydrogen-
bonding in 6 is even stronger. This is indicated by
/
/
/
hindered rotation and a high-field shift for two o-F
atoms at 20 8C of d ꢂ
/
142.2.
[(C6F5)3B(H3O2)B(C6F5)3]ꢂ [20] and in (C6F5)3Al(OH2)
[21], but is absent in [(C6F5)3B(OH)B(C6F5)3]ꢂ [22],
(CpB)CpTi(m-OH)Cl [4], or in the adducts
Some time ago we reported the t-butylamine com-
and
plexes
(Flu)B(C6F5)2(NH2CMe3)
(7)
[1]
[(CpBNH2CMe3)Ti(m-Cl)(m-NCMe3)]2 (8) [4] (Chart 2).
A reinvestigation of the crystal structures showed that in
B(C6F5)3(OH2)×
MeOH [17]. The latter is closely related to the amine
adducts 5 and 6, and the absence of F H interactions
ꢀ ꢀ ꢀ
in this compounds is therefore somewhat surprising.
In view of the strong tendency for Nꢀ Fꢀ
/OHCMe3
and
B(C6F5)3(MeOH)×
/
both cases at least one short Nꢀ
/
H
/
ꢀ ꢀ ꢀ
/
Fꢀ
/
C interaction
/
/
was present, with Nꢀ
/
Hꢀ
/
F angles of about 1308. The
19F-NMR data for 7 and 8, as well as those for the
indenylborane analogue (Ind)B(C6F5)2(NH2CMe3) (9)
[1], show broad o-F resonances at room temperature,
/
H
/
ꢀ ꢀ ꢀ
/
/C
interactions in amine complexes of B(C6F5)2X, the
question arose whether hydrogen bonding was also
while cooling to ꢂ
/
40 8C leads to complex spectra with
relevant for Pꢀ
/
H bonds. Bradley has reported a number
characteristic high-field o-F shifts (Table 1). The
structure of 8 is also noteworthy because the second
of PH3 and H2PCMe3 adducts of fluorinated tris(phe-
nyl)boranes, including the crystal structure of
(C6F5)3B(PH2CMe3). In those examples both inter-
and intra-molecular hydrogen-bonding interactions
Nꢀ
/
H engages in intramolecular hydrogen-bonding to
the chloride ligand, with a short NHꢀ
/Cl distance of 2.29
˚
A. Similar NH
/
ꢀ ꢀ ꢀ
/
Cl hydrogen-bonding interactions have
were observed, although the intramolecular H
/
ꢀ ꢀ ꢀ
/
F
˚
2.35 A place them at the borderline
been reported, for example, for the sec-amine titanium
complexes Ti(NR)Cl2(NHMe2)2 (Rꢀi
Pr, C6H5) [18].
The overriding picture that emerges is that in amine
distance of 2.33Á
/
/
of the Dunitz criteria [23]. The crystal structure of
(C6F5)3B(PH2Ph) was published very recently but, by
adducts of pentafluoroaryl boranes, borates and boryl-
contrast, no Pꢀ
/
H
/
ꢀ ꢀ ꢀ
/
Fꢀ
/
C interaction was described [24].
Cp complexes, hydrogen bonding between Cꢀ
/
F bonds
Our analysis of the data indicates that the shortest Pꢀ
/
H
/
˚
F distance is long, 2.40 A, and is associated with an
and amine-hydrogen atoms significantly contributes to
bonding and provides the reason for strongly hindered
aryl rotation which, in some cases, persists even at room
temperature. In these cases, at least, organic fluorine
does form strong hydrogen bonds. This point is
reinforced by the observation that the tert-amine adduct
B(C6F5)3(MeNEt2), which is bulkier than 6 but not
ꢀ ꢀ ꢀ
/
acute Pꢀ
/
HꢀF angle of 998; therefore, it should not be
/
regarded as a significant interaction.
The reactions between B(C6F5)3 and the secondary
phosphines PHCy2 and PHPh2 gave the colourless
crystalline adducts, (C6F5)3B(PHCy2) (10) and
(C6F5)3B(PHPh2) (11) (Scheme 5). The Pꢀ
/
H signals in
Plate 2.

202
S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á205
/
˚
and 2.46 A, both intramolecular. H(46a)
/
ꢀ ꢀ ꢀ
/
F(35?) is the
˚
shortest intermolecular contact at 2.55 A, i.e. at a typical
van der Waals distance.
The principal packing feature between molecules is
the strong interaction of F(23) with the C(11Á
a neighbouring molecule; the six F C distances are in
ꢀ ꢀ ꢀ
3.374(2) A. There are no over-
/16) ring of
/
/
˚
the range of 3.143(2)Á
/
lapping aromatic rings.
3. Conclusion
The interaction of Lewis acidic borylcyclopentadienyl
ligands with donor anions Eꢂ leads to intramolecular
Cpꢀ
plexes do not show this structural feature if Eꢀ
contrast to their Ti analogues, now it could be shown
that stable complexes with an ansa-CpꢀBꢀEꢀZr ar-
rangement are formed if EꢀNHCMe3. By the same
route complexes with CpꢀBꢀPR2 ligands are also
/
Bꢀ
/
E chelate formation. Whereas zirconium com-
Fig. 5. Structure of B(C6F5)3(NHMe2) (6), showing the atomic
numbering scheme. Ellipsoids are drawn at 50% probability. Selected
/
Cl, in
˚
bond lengths (A) and angles (8) for one of the two essentially identical
molecules: Bꢀ
C(31) 1.658(5), Nꢀ
F(32) 2.10, N F(32) 2.751(4), C(11)ꢀ
ꢀ ꢀ ꢀ
C(31) 115.3(3), C(11)ꢀBꢀN 103.9(2), C(21)ꢀ
F(22) 123, NꢀHꢀF(32) 128.
/
N 1.653(4), Bꢀ
/
C(11) 1.647(5), Bꢀ
F(22) 2.15, N F(22) 2.755(3), Hꢀ
ꢀ ꢀ ꢀ
BꢀC(21) 113.4(3), C(11)ꢀBꢀ
BꢀC(31) 105.7(3), NꢀHꢀ
/
C(21) 1.655(4), Bꢀ
/
/
/
/
/
H 0.91, Hꢀ
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
accessible, as shown here in the first structurally
/
/
characterised example of a Ti(IV) phosphido complex.
1
Hydrogen-bonding between Nꢀ/H and o-F atoms of
the H-NMR spectra of the free phosphines are shifted
by d 2.34 (10) and 1.49 (11) on coordination to
B(C6F5)3. Adduct formation is also indicated by the
C6F5 groups is a frequent feature, both in amido-
bridged ansa-metallocene complexes and in amine
adducts of B(C6F5)3. In some cases these intramolecular
interactions are sufficiently strong to persist in solution
11B chemical shifts of d ꢂ
The 19F-NMR spectra presented no evidence for solu-
tion-phase Pꢀ FꢀC interactions.
The crystal structures of 6 and 10 are shown in Figs. 5
and 6, respectively. The bonding description based on
the spectroscopic parameters is supported by the solid-
state structure of 6. There are two independent mole-
cules in the crystal; they have essentially identical
molecular conformations but lie in different orientations
/
9.4 and ꢂ13.5, respectively.
/
even at room temperature and may allow H/
coupling to be observed. Hydrogen-bonding has a
ꢀ ꢀ ꢀ
/
F
/
H
/
ꢀ ꢀ ꢀ
/
/
˚
in the cell. The amino-hydrogen is ca. 2.1 A from two o-
F atoms and is involved in a bifurcated, intramolecular
F
/
ꢀ ꢀ ꢀ
some short H
and F atoms of neighbouring molecules, although none
/
H
/
ꢀ ꢀ ꢀ
/
F hydrogen bonding system. There are also
/
ꢀ ꢀ ꢀF contacts between the methyl H-atoms
/
˚
are shorter than 2.42 A. The most significant packing
arrangements involve the ring of C(31Á36). Firstly, this
ring lies approximately parallel to, and overlapping
with, the ring of C(71Á76) of the second molecule, at a
distance of 3.43 A. Secondly, F(34) points directly into
the centre of the C(61Á66) ring of the same neighbour-
ing molecule. The perpendicular distance of F(34) from
/
/
˚
/
˚
the ring plane is 2.993(3) A, while the six F(34)
/
ꢀ ꢀ ꢀ
/
C
˚
distances are in the range 3.191(4)Á3.390(4) A.
/
In 10, the boron atom is tetrahedrally coordinated as
Fig. 6. Molecular structure of B(C6F5)3(PHCy2) (10), showing the
atomic numbering scheme. Hydrogen atoms of the cyclohexyl groups
have been omitted for clarity. Ellipsoids are drawn at 50% probability.
expected. There is no indication for PHꢀ ꢀ ꢀF close
contacts. The PꢀH and BꢀP bond lengths refine to
1.273(15) and 2.0270(14) A, respectively; the latter is
/
/
/
/
˚
Selected bond lengths (A) and angles (8): Bꢀ
/
P 2.0270(14), Bꢀ
C(31) 1.6490(18), PꢀH 1.273(15),
C(51) 1.8441(13), C(11)ꢀBꢀC(21) 115.79(10),
C(31) 103.91(10), C(11)ꢀBꢀP 111.24(8), C(21)ꢀBꢀC(31)
111.81(10), C(21)ꢀBꢀP 102.40(8), BꢀPꢀH 112.7(7).
/
C(11)
˚
1.6533(18), Bꢀ
PꢀC(41) 1.8460(13), Pꢀ
C(11)ꢀBꢀ
/
C(21) 1.6484(18), Bꢀ
/
/
˚
rather shorter than the Bꢀ
There are no very short H
ꢀ ꢀ ꢀ
the shortest are H(1) F(12) and H(1)
ꢀ ꢀ ꢀ
/
P distance in 4 of 2.054(4) A.
F contacts in this structure;
ꢀ ꢀ ꢀF(36) at 2.40
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/

S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á
/205
203
formative influence on molecular geometry and dy-
namics and is particularly strong where two fluorines
temperature for 36 h. The solvent was removed and
the product extracted with 10 cm3 toluene. Cooling to ꢂ
/
connect to a single Nꢀ
/
H functionality, to give a Cꢀ
/
F
/
ꢀ ꢀ ꢀ
/
25 8C overnight gave red crystals, which retained ca.
0.33 equivalents of toluene even after drying under
vacuum (0.7 g, 1.16 mmol, 60%). Anal. Found: C, 47.86;
H, 2.06; N, 2.05%; Calc. for C24.31H13.64BClF10NTi: C,
48.35; H, 2.28; N, 2.32%.
H
/
ꢀ ꢀ ꢀ
/
FꢀC arrangement as in 6. Although weak hydrogen
/
bonding to prim-phosphines has been reported, the sec-
phosphine-B(C6F5)3 adducts studied here do not show
any such interaction.
4. Experimental
4.4. {C5H4B(C6F5)2}CpTi(Cl)(m-PPh2) (4)
4.1. General procedures
A solution of {C5H4B(C6F5)2}CpTiCl2 (1.44 g, 2.43
mmol) in toluene (50 ml) was cooled to ꢂ78 8C and
/
All manipulations were performed under a dinitrogen
atmosphere using standard Schlenk techniques. Solvents
were distilled under N2 over sodium (toluene), sodium/
benzophenone (diethyl ether, tetrahydrofuran), Na/K
solid LiPPh2 (0.47 g, 2.43 mmol) was added. Slow
warming to room temperature and stirring for 30 min
gave a deep red solution and a small amount of fine
precipitate. Stirring was continued for a further 2 h
before the solid was allowed to settle and separated by
filtration. Removal of the solvent under reduced pres-
sure gave a red solid which was recrystallised from
dichloromethane and light petroleum affording red
crystals suitable for X-ray crystallography, yield 1.01
g, 1.45 mmol, 56%. Anal. Found: C, 54.17; H, 2.69; Cl,
5.75%. Calc. for C34H19BClF10P: C, 54.99; H, 2.58; Cl,
4.77%.
alloy (light petroleum (bp 40Á
/
60 8C)) or CaH2 (dichlor-
omethane). NMR solvents (C6D6, CD2Cl2, CDCl3 and
˚
C6D5CD3) were dried over 4 A molecular sieves and
degassed by several freeze-thaw cycles. NMR spectra
were recorded on a Bruker Avance DPX300 spectro-
meter. Chemical shifts are reported in ppm and refer-
enced to residual solvent resonances (1H, 13C) or
external BF3×
/
OEt2 (11B) and CFCl3 (19F). PPh2H,
PCy2H (Strem) and NMe2H (Fluka) were used as
˚
supplied, H2NCMe3 was dried over activated 4 A
molecular sieves. The complexes
Cp{C5H4B(C6F5)2}TiCl2
Cp{C5H4B(C6F5)2×
SMe2}ZrCl2 were prepared according to literature
procedures [4]. The syntheses of 1 [4], 7 [4], 8 [4], and
9 [1] have been reported previously.
4.5. (C6F5)3B(NH2CMe3) (5)
and
/
The compound was prepared by mixing a solution of
B(C6F5)3 (2.65 g, 5.2 mmol) in 30 ml toluene with
NH2CMe3 (20.7 ml of a 0.25 M solution in toluene) and
isolated as colourless crystals (2.56 g, 82.6%). Anal.
Found: C, 45.52; H, 1.86; N, 2.40%. Calc. for
C20H7BF15N: C, 45.16; H, 1.90; N, 2.39%.
4.2. {C5H4B(C6F5)2}CpZr(Cl)(m-NHCMe3) (2)
A solution of {C5H4B(C6F5)2×
/
SMe2}CpZrCl2 (0.75 g,
1.07 mmol) in toluene (10 cm3) was cooled to ꢂ
/
78 8C
and solid LiNCMe3H (0.084 g, 1.07 mmol) was added.
Warming to room temperature and stirring for 30 min
gave a pale yellow solution and a small amount of fine
precipitate. Stirring was continued for a further 2 h
before the solids were allowed to settle and separated by
filtration. The product was isolated by concentrating the
solution to 3 ml and adding 10 ml light petroleum to
precipitate a fine off-white solid (0.6 g, 0.89 mmol, 83%).
Anal. Found: C, 47.00; H, 2.97; N, 2.02; Cl, 4.90%;
Calc. for C26H19BClNF10Zr: C, 46.41; H, 2.85; N, 2.08;
Cl, 5.27%.
4.6. (C6F5)3B(NHMe2) (6)
This compound was made from B(C6F5)3 (3.74 g, 7.3
mmol) and NMe2H (7.3 mmol, 3.03 ml of a 2.41 M
solution in toluene) and isolated as colourless crystals
after recrystallisation from a light petroleum/dichloro-
methane mixture (3.21 g, 79%). Anal. Found: C, 43.08;
H, 1.11; N, 2.55%. Calc. for C20H7BF15N: C, 43.12; H,
1.27; N, 2.51%.
4.7. (C6F5)3B(PHCy2) (10)
4.3. {C5H4B(C6F5)2}CpTi(Cl)(m-NH2)×
/
0.33(C7H8)
(3)
In a similar procedure to 5, from B(C6F5)3 (0.76 g, 1.5
mmol) and PCy2H (0.30 ml, 1.6 mmol) and isolated as
colourless crystals after recrystallisation from a light
petroleum/dichloromethane mixture (0.91 g, 85%).
Anal. Found: C, 51.34; H, 3.54%. Calc. for
C30H23BF15P: C, 50.73; H, 3.26%.
To a solution of {C5H4B(C6F5)2}CpTiCl2 (1.15 g,
1.94 mmol) in tetrahydrofuran (20 ml) NaNH2 (0.076 g,
1.94 mmol) was added. The reaction was followed by
1H-NMR and was complete after stirring at room

204
S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á205
/
Table 2
Crystal data for compounds 4, 6 and 10
Compound
4
6
10
Empirical formula
fw
C34H19BClF10PTi
742.6
triclinic
C20H7BF15
557.1
N
C30H23BF15
710.3
monoclinic
P
Crystal system
Space group
monoclinic
Cc (No. 9)
14.910(3)
15.423(3)
19.373(4)
90
¯
1 (No. 2)
P/
P21/n (equiv. to no. 14)
˚
a (A)
10.073(2)
12.807(3)
23.750(5)
78.75(3)
86.57(3)
87.93(3)
2998.7(10)
4
11.666(1)
12.077(1)
20.562(1)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
112.50(3)
90
96.052(3)
90
g (8)
V, (A
ꢂ3
˚
)
4116.1(14)
8
1.798
2880.8(4)
4
1.638
Z
Dcalc (g cmꢂ3
m, mmꢂ1
F(0 0 0)
)
1.645
0.517
1488
0.201
2192
0.215
1432
u Range (8)
Index range
1.65
115
l 528
/
u 5
/
25.4
2.05
175
235l 5
/
u 5
h 5
23
/
25.4
1.95
145
l 525
/
u 5
/
26.4
ꢂ
/
/
h 5
/11, ꢂ
/
145
/
k 5
/
15, ꢂ
/
285
/
ꢂ
/
/
/17, ꢂ
/
175
/
k 5
/
18, ꢂ
/
ꢂ
/
/
h 5
/14, 05
/
k 5
/
15, 05
/
/
/
/
/
No. of reflections collected/unique/ 15 085/9399/5199 (Rint
observed
ꢀ/
0.059)
11 941/7013/5649 (Rint
ꢀ/
0.072)
32 362/5887/5426 (Rint
ꢀ/0.023)
Data/restraints/parameters
Goodness of fit on F2, S
9399/0/914
0.860
7013/2/667
0.959
5887/0/428
1.032
R1 [I ꢀ
/
2s(I)]
wR2 (all data)
0.043
0.093
0.038
0.091
0.032
0.086
Weighting parameters a, b
0.0102, 0
0.0313, 0
0.0469, 1.14
Largest difference peak and hole
ꢂ3
0.30 and ꢂ
/
0.34
0.20 and ꢂ
/
0.18
0.34 and ꢂ0.23
/
˚
e A
Definitions: Rint
ꢀ
/
/
(SjF2oꢂ
/
F2c (mean)j/SF2o); Sꢀ
/
[(Sw(F2oꢂ
/
F2c)2)/(nꢂ
/
p)]1/2; wR2ꢀ
/
[Sw(F2oꢂ
/
Fc2)2/Sw(Fo2)2]1/2; R1ꢀ
/
(SjjFojꢂjFcjj/SjFoj); weighting
/
scheme wꢀ
/
[s2(F2o)ꢁ(aP)2ꢁ
/
bP]ꢂ1, where Pꢀ
/
[2F2cꢁ
/
max(F2o, 0)]/3.
4.8. (C6F5)3B(PHPh2) (11)
mined by the direct methods routines in the SHELXS
program [28] and refined by full-matrix least-squares
methods, on F2s, in SHELXL [28]. In general, the non-
hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atoms were included in idealised
positions and their Uiso values were set to ride on the Ueq
values of the parent nitrogen and carbon atoms.
Scattering factors for neutral atoms were taken from
Ref.[29]. Computer programs used in these analyses
were run on a Silicon Graphics Indy at the University of
East Anglia, or a DEC-Alpha Station 200 4/100 in the
Biological Chemistry Department, John Innes Centre.
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre, CCDC No.
To a solution of B(C6F5)3 (1.24 g, 2.4 mmol) in
toluene (50 ml) was added PPh2H (0.45 ml, 2.4 mmol).
The solution was stirred for 1 h before removal of the
solvent in vacuo. The crude product was recrystallised
from a light petroleum/dichloromethane mixture at ꢂ
/
25 8C affording colourless, needle-shaped crystals (1.31
g, 84%). Anal. Found: C, 50.85; H, 1.41%. Calc. for
C30H13BF15P: C, 51.61; H, 1.59%.
4.9. X-ray crystallography
The analytical procedures were similar for the three
samples. Crystal and refinement data are collated in
Table 2. For each, a crystal was mounted in oil on a
glass fibre and fixed in the cold nitrogen stream.
Intensity data for complexes 4 and 6 were measured
on a Rigaku R-Axis IIc image plate diffractometer
210664Á210666 for compounds 4, 6 and 10.
/
Acknowledgements
equipped with a rotating anode X-ray source (MoÁ
radiation) and graphite monochromator; the data were
processed with the DENZO SCALEPACK programs [25].
Complex 10 was measured on a Bruker Smart APEX
CCD instrument and processed using the SAINT [26]
programs and corrected with SADABS [27]. All data were
measured at 140 K. The structure of each was deter-
/
Ka
This work was supported by the Engineering and
Physical Sciences Research Council and the University
of East Anglia. We are grateful to Dr T. Wagner of
Bruker AXS for measurement of the data for compound
10.
/

S.J. Lancaster et al. / Journal of Organometallic Chemistry 680 (2003) 193Á
/205
205
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