Reactivity of the bis(pentafluorophenyl)boranes CIB(C6F 5)2 and [HB(C6F5)2] n towards late transition metal reagents

Article abstract of DOI:10.1039/b414940h

The reactivities of the highly electrophilic boranes ClB(C ₆F₅)₂ (1) and [HB(C₆F ₅)₂]_n. (2) towards a range of organometallic reagents featuring metals from Groups 7-10 have been investigated. Salt elimination chemistry is observed between 1 and the nucleophilic anions [(η⁵-C₅R₅)Fe(CO)₂]- (R = H or Me) and [Mn(CO)₅]-, leading to the generation of the novel boryl complexes (η⁵-C₅R₅)Fe(CO) ₂B(C₆F₅)₂ [R = H (3) or Me (4)] and (OC)₅MnB(C₆F₅)₂ (5). Such systems are designed to probe the extent to which the strongly σ-donor boryl ligand can also act as a π-acceptor, a variety of spectroscopic, structural and computational probes imply that even with such strongly electron withdrawing boryl substituents, the π component of the metal-boron linkage is a relatively minor one. Similar reactivity is observed towards the hydridomanganese anion [η⁵-C₅H₄Me)Mn(CO) ₂H]^-, generating a thermally labile product identified spectroscopically as (η⁵-C₅H₄Me)Mn(CO) ₂(H)B(C₆F₅)₂ (6). Boranes 1 and 2 display different patterns of reactivity towards low-valent platinum and rhodium complexes than those demonstrated previously for less electrophilic reagents. Thus, reaction of 1 with (Ph₃)₂Pt(H₂C=CH ₂) ultimately generates EtB(C₆F₅)₂ (10) as the major boron-containing product, together with cis-(Ph ₃P)₂PtCl₂ and trans-(Ph₃P) ₂Pt(C₆F₅)Cl (9). The cationic platinum hydride [(Ph₃P)₃PtH]⁺ is identified as an intermediate in the reaction pathway. Reaction of 2 with [(Ph₃P) ₂Rh(μ-Cl)]₂, in toluene on the other hand, appears to proceed via ligand abstraction with both Ph₃P·HB(C ₆F₅)₂ (11) and the arene rhodium(I) cation [(Ph₃P)₂Rh(η-C₆H₅Me)] ⁺ (14) ultimately being formed.

Full text of DOI:10.1039/b414940h

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F U L L P A P E R
Reactivity of the bis(pentafluorophenyl)boranes ClB(C6F5)2 and
[HB(C6F5)2]n towards late transition metal reagents†
Amal Al-Fawaz,a Simon Aldridge,*a Deborah L. Coombs,a Anthony A. Dickinson,a
David J. Willock,a Li-ling Ooi,a Mark E. Light,b Simon J. Colesb and Michael B. Hursthouseb
a Centre for Fundamental and Applied Main Group Chemistry, School of Chemistry, Cardiff
University, PO Box 912, Park Place, Cardiff, UK CF10 3TB. E-mail: AldridgeS@cf.ac.uk;
Fax: (029) 20874030; Tel: (029) 20875495; Web: www.cf.ac.uk/chemy/cfamge
b EPSRC National Crystallography Service, Department of Chemistry, University of
Southampton, Highfield, Southampton, UK SO17 1BJ
Received 27th September 2004, Accepted 18th October 2004
First published as an Advance Article on the web 4th November 2004
The reactivities of the highly electrophilic boranes ClB(C6F5)2 (1) and [HB(C6F5)2]n (2) towards a range of
organometallic reagents featuring metals from Groups 7–10 have been investigated. Salt elimination chemistry is
5
observed between 1 and the nucleophilic anions [(g -C5R5)Fe(CO)2]− (R = H or Me) and [Mn(CO)5]−, leading to the
5
generation of the novel boryl complexes (g -C5R5)Fe(CO)2B(C6F5)2 [R = H (3) or Me (4)] and (OC)5MnB(C6F5)2 (5).
Such systems are designed to probe the extent to which the strongly r-donor boryl ligand can also act as a
p-acceptor; a variety of spectroscopic, structural and computational probes imply that even with such strongly
electron withdrawing boryl substituents, the p component of the metal–boron linkage is a relatively minor one.
5
Similar reactivity is observed towards the hydridomanganese anion [(g -C5H4Me)Mn(CO)2H]−, generating a
5
thermally labile product identified spectroscopically as (g -C5H4Me)Mn(CO)2(H)B(C6F5)2 (6). Boranes 1 and 2
display different patterns of reactivity towards low-valent platinum and rhodium complexes than those demonstrated
=
previously for less electrophilic reagents. Thus, reaction of 1 with (Ph3P)2Pt(H2C CH2) ultimately generates
EtB(C6F5)2 (10) as the major boron-containing product, together with cis-(Ph3P)2PtCl2 and trans-(Ph3P)2Pt(C6F5)Cl
(9). The cationic platinum hydride [(Ph3P)3PtH]+ is identified as an intermediate in the reaction pathway. Reaction of
2 with [(Ph3P)2Rh(l-Cl)]2, in toluene on the other hand, appears to proceed via ligand abstraction with both
6
Ph3P·HB(C6F5)2 (11) and the arene rhodium(I) cation [(Ph3P)2Rh(g -C6H5Me)]+ (14) ultimately being formed.
are much more scarce, despite the fact that complexes containing
the (g -C5Me5)Ir moiety have been reported to mediate the
1
Introduction
5
Transition metal boryl complexes (LnM–BX2) have been the
centre of intense recent research activity,1 partly because of
their involvement in the hydro- and diboration of multiple
bonds,2 but also because of their implication in highly selective
stoichiometric and catalytic functionalization of hydrocarbons.3
Such studies of reactivity have been complimented by a range
of structural investigations in which the nature of the metal–
boron bond has been probed by crystallographic, spectroscopic
and computational methods.1,4 One of the significant questions
investigated by such studies is the potential for the extremely
strongly r-donor boryl ligand also to act as a p acid by utilizing
the vacant boron-based orbital of p-symmetry. In the case of
complexes bearing p donor boryl substituents (e.g. X2 = cat,
ortho-O2C6H4) research to date implies a relatively minor role
for p back bonding;1 to what extent the nature of the M–B
bond can be altered by variation in the electronic properties of
X has been the subject of this and other studies.1,5 Ultimately a
better understanding of the nature of the M–B bond may help
to rationalize the unusual reactivity of such complexes.
activation of alkanes and arenes by [HB(C6F5)2]2.9 Within
this area we have been seeking to develop synthetic routes to
metal complexes containing the B(C6F5)2 ligand,5 since such
species would be expected to contain a highly Lewis acidic
boron centre and might therefore act as useful probes of the
potential for boryl ligands to act as p acids. The use of both
salt elimination and oxidative addition chemistries as routes
to M–B bonds have been widely demonstrated;1 hence, we have
sought to investigate the reactivity of ClB(C6F5)2 (1) towards
organometallic anions, and of 1 and [HB(C6F5)2]n (2) towards
low valent rhodium and platinum complexes. The results of these
studies, reported herein, reveal a combination of precedented
chemistry reminiscent of that observed for less electrophilic
boranes, and unusual reactivity stemming from the high Lewis
acidity of pentafluorophenyl substituted species.
2
Experimental
Pentafluorophenyl substituted boranes XB(C6F5)2 (X = aryl,
halogen, H) have received much recent attention due to the
robustness of their B–C bonds and the exploitation of their
high Lewis acidity in a variety of catalytic applications.6,7 The
reactivity of the borane [HB(C6F5)2]n,7 for example, towards
a range of early transition metal organometallic complexes
(chiefly from Groups 4–6) has been investigated in depth.8
Analogous studies involving later transition metal derivatives
General
All manipulations were carried out under a nitrogen or argon
atmosphere using standard Schlenk line or dry box tech-
niques. Solvents were pre-dried over sodium wire (hexanes,
toluene) or molecular sieves (dichloromethane) and purged
with nitrogen prior to distillation. Hexanes (potassium), toluene
(sodium), and dichloromethane (calcium hydride) were then
distilled from the appropriate drying agent before use. Benzene-
d6 and toluene-d8 (both Goss) were degassed and dried
† Electronic supplementary information (ESI) available: Crystal data
5
over potassium prior to use. Na[(g -C5R5)Fe(CO)2] (R =
for the monoclinic form of 3 and 8·3CHCl3; DFT parameters for
5
5
H and R = Me), Na[Mn(CO)5], K[(g -C5H4Me)Mn(CO)2H],
(g -C5H5)Fe(CO)2BX2 [X = C6F5, C6H5]. See http://www.rsc.org/
=
suppdata/dt/b4/b414940h/
(Ph3P)2Pt(H2C CH2), [(Ph3P)2Rh(l-Cl)]2, ClB(C6F5)2 (1) and
4 0 3 0
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
©

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[HB(C6F5)2]n (2) were prepared by minor modification of
literature methods.7,10–13
CCDC reference numbers 168238, 217993, 217994 and
249900–249902.
NMR spectra were measured on a Bruker AM-400 or Jeol
Eclipse 300 Plus FT-NMR spectrometer. Residual protons
of solvent were used for reference for 1H and 13C NMR,
while 11B and 19F NMR spectra were referenced with respect
to Et2O·BF3 and CFCl3, respectively. Infrared spectra were
measured for each compound either as a solution in hexanes
or pressed into a disk with an excess of dried KBr on a
Nicolet 500 FT-IR spectrometer. Mass spectra were measured
by the EPSRC National Mass Spectrometry Service Centre,
University of Wales Swansea and by the departmental service.
Perfluorotributylamine was used as the standard for high-
resolution EI mass spectra. Elemental analyses were carried
out both by the departmental analysis service and by Warwick
Analytical Service, University of Warwick.
See http://www.rsc.org/suppdata/dt/b4/b414940h/ for cry-
stallographic data in CIF or other electronic format.
Syntheses
(i) (g5-C5R5)Fe(CO)2B(C6F5)2 [R = H (3) and R = Me(4)].
Both complexes were prepared in a similar manner, exemplified
5
here for 3. To a suspension of (g -C5H5)Fe(CO)2Na (0.200 g,
1.05 mmol) in ca. 10 cm3 toluene at room temperature was added
one equivalent of ClB(C6F5)2 (1) (0.400 g, 1.05 mmol) in 12 cm3
toluene. The reaction mixture was stirred at room temperature
for 12 h, at which point examination of the supernatent by 11
B
NMR revealed complete conversion of 1 (dB 59.1) to a single
boron-containing species giving rise to a low-field resonance
(dB = 121.5, R = H; dB 121.3, R = Me). Filtration of the reaction
mixture, removal of volatiles in vacuo and recrystallization from
hexanes at −30 ◦C afforded golden yellow crystals of 3 or 4 in
Abbreviations: st = strong, md = medium, w = weak, sh =
shoulder, s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet, b = broad, fwhm = frequency width at half maximum.
yields of 30–45%. 3 and 4 have been characterized by 1H, 13C, 11
B
Crystallographic method
and 19F NMR, IR, mass spectrometry, elemental analysis and
1
Data were collected on an Enraf Nonius Kappa CCD diffrac-
single crystal X-ray diffraction. 3: H NMR (400 MHz, C6D6,
tometer equipped with a Mo-Ka radiation source (k =
21 ◦C), d 3.91 (s, C5H5). 13C NMR (76 MHz, C6D6, 21 ◦C), d 86.3
(C5H5), 137.3, 139.9, 140.7 (aromatic CF), 211.0 (CO). 11B NMR
(96 MHz, toluene, 21 ◦C), d 121.5. 19F NMR (283 MHz, toluene,
21 ◦C), d −132.9 (virtual dq, J = 21, 6 Hz), −153.7 (tt, para-CF,
J = 21, 6 Hz), −161.5 (m, meta-CF). IR (KBr disk, cm−1) m(CO)
2014 st, 1968 st. MS(EI): M+ = 522 (weak), isotopic pattern
corresponding to 1 B, 1 Fe atoms, strong fragment ion peaks
at m/z 494 [(M − CO)+, 60%] and 466 [(M − 2CO)+, 18%].
Elemental analysis: calculated for C19H5BF10FeO2, C 43.72%, H
0.97%; observed, C 43.55%, H 0.97%. No significant changes in
the 19F NMR spectrum were observed on cooling to −110 ◦C. 4:
1H NMR (400 MHz, C6D6, 21 ◦C), d 1.21 (s, C5Me5). 13C NMR
(76 MHz, C6D6, 21 ◦C), d 7.6 (C5Me5), 96.9 (C5Me5), 137.5,
138.0, 140.4 (aromatic CF), 212.3 (CO). 11B NMR (96 MHz,
toluene, 21 ◦C), d 121.3. 19F NMR (283 MHz, toluene, 21 ◦C),
d −133.1 (virtual dq, J = 21, 7 Hz, ortho-CF), −154.5 (t, J =
21 Hz, para-CF), −162.3 (m, meta-CF). IR (KBr disk, cm−1)
m(CO) 2004 st, 1954 st. MS(EI): M+ = 592 (weak), isotopic
pattern corresponding to 1 B, 1 Fe atoms, strong fragment
ion peak at m/z 564 [(M − CO)+, 60%]. Elemental analysis:
calculated for C24H15BF10FeO2, C 48.69%, H 2.55%; observed,
C 48.92%, H 2.71%.
˚
0.71073 A). Data collection and cell refinement were carried
out using DENZO,14 and structure solution and refinement
(by full-matrix least-squares) using SIR-92, DIRDIFF-99 and
SHELXL-97, respectively.15 In each case hydrogens were placed
in idealised positions and refined using a riding model with Uiso
set to 1.2 or 1.5 times the Ueq of the parent atom. Empirical
absorption corrections were carried out using SORTAV.15 Single
crystals of complex 3 could be grown from concentrated
solutions in hexanes or toluene. Crystals of the monoclinic
polymorph obtained from hexanes were found to give inferior
diffraction data to those of the triclinic polymorph obtained
from toluene. Given that the important structural parameters
5
for the (g -C5H5)Fe(CO)2B(C6F5)2 molecule vary minimally
between the two crystalline forms, only those for the latter
polymorph are reported here. Details of the data collection,
structure solution and refinement for 3 (triclinic polymorph), 4,
1
2
9 and 11· (C6H14) can be found in Table 1; relevant bond lengths
and angles are included in the figure captions. The structures of
the monoclinic form of 3 and of the solvate 8·3(CHCl3) (obtained
merely for verification of compound identity) are included solely
in the ESI.†
1
2
Table 1 Crystallographic data for 3 (triclinic polymorph), 4, 9 and 11· (C6H14)
1
2
3
4
9
11· (C6H14)
Empirical formula
Formula weight
T/K
C19H5BF10FeO2
521.89
120(2)
C24H15BF10FeO2
592.02
120(2)
Monoclinic
P21/c
10.6577(6)
14.1112(9)
15.9797(10)
90
103.113(4)
90
2340.6(2)
4, 1.680
0.745
C42H30ClF5P2Pt
922.14
120(2)
Orthorhombic
Pbca
11.9777(11)
23.238(2)
25.715(3)
90
90
90
C33H23BF10P
651.29
180(2)
Crystal system
Triclinic
Triclinic
¯
¯
Space group
P1
P1
˚
a/A
10.6895(2)
13.4060(2)
13.6885(2)
93.628(3)
93.588(3)
113.060(3)
1793.08(5)
4, 1.933
9.657(5)
˚
b/A
10.475(5)
14.595(5)
87.927(5)
88.553(5)
82.352(5)
1462.0(11)
2, 1.479
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
7157.6(12)
8, 1.711
4.142
Z, qcalc./Mg m−3
)
l/mm−1
0.959
0.181
F(000)
Reflections collected
1024
12458
1184
12031
3616
61611
662
22027
Independent reflections, Rint
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2r(I)]; R1, wR2
R indices (all data); R1, wR2
Largest diff. peak and hole/e A
6094 (0.0589)
6094/0/595
0.942
0.0431, 0.0741
0.0829, 0.0858
0.356, −0.431
4099 (0.1043)
4099/0/348
0.976
0.0513, 0.0841
0.1187, 0.1021
0.418, −0.466
8118 (0.0728)
8118/0/460
1.019
0.0337, 0.0679
0.0649, 0.0785
1.300, −1.642
6603 (0.0657)
6603/0/407
1.025
0.0521, 0.1005
0.0832, 0.1122
0.353, −0.311
−3
˚
)
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7
4 0 3 1

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(ii) (OC)5MnB(C6F5)2 (5). 5 was prepared in a manner
analogous to that described above for 3 and 4, using NaMn(CO)5
as the organometallic reagent. 5 was isolated as a pale yellow
microcrystalline material in yields of up to 42% after recrystalli-
sation from hexanes, and has been characterized by 13C, 11B and
19F NMR, IR, mass spectrometry and elemental analysis. 13C
crystals. Structure determination (see ESI†) served to confirm 8
as the second phosphorus-containing product (dP 15.1).19
=
(v) Reaction of 1 with (Ph3P)2Pt(H2C CH2): multinu-
clear NMR monitoring of the reaction. To a solution of
=
(Ph3P)2Pt(H2C CH2) (0.050g, 0.07 mmol) in toluene-d8 (ca.
1 cm3) at room temperature contained in a J. Young’s NMR
tube, was added a solution containing one equivalent of 1 in
toluene-d8 (ca. 1 cm3). After agitation, the reaction mixture was
monitored periodically (at 2 h intervals) over a period of 24 h.
The volatile boron-containing product giving rise to the signal
at dB 73.5 was confirmed as EtB(C6F5)2 (10),7 by comparison
of 1H, 13C, 11B and 19F NMR data with the literature values. In
addition to confirming the identities of the platinum phosphine
products 8 and 9, a number of intermediate species were also
identified, these being (sequentially) 13, [(Ph3P)3PtH]+ (12),20
and [HB(C6F5)2]n (2).7 NMR data for 13: 1H NMR (300 MHz,
C7D8, 21 ◦C), d 1.99 (b, m, PtCH2CH2B). 11B NMR (96 MHz,
C7D8, 21 ◦C), d 35.0. 19F NMR (283 MHz, C7D8, 21 ◦C), d
◦
NMR (76 MHz, C6D6, 21 C), d 124.0 (aromatic quaternary),
137.5, 139.7, 143.1 (aromatic CF), 208.0, 208.7 (CO). 11B NMR
(96 MHz, toluene, 21 ◦C), d 130.7. 19F NMR (283 MHz, toluene,
21 ◦C), d −132.7 (d, J = 21 Hz, ortho-CF), −151.0 (t, J = 21 Hz,
para-CF), −160.4 (m, meta-CF). IR (KBr disk, cm−1) m(CO)
2137 m, 2050 st, 2015 st sh, 1950 w. MS(EI): [M − CO]+
=
512 (10%), isotopic pattern corresponding to 1 B, 1 Mn atoms,
fragment ion peaks at m/z 484 [(M − 2CO)+, 5%], 456 [(M −
3CO)+, 10%], 428 [(M − 4CO)+, 16%], 456 [(M − 5CO)+, 100%],
corresponding to sequential loss of all five carbonyl ligands.
Elemental analysis: calculated for C17BF10MnO5, C 37.82%, H
0%; observed, C 38.05%, H 0.12%.
(iii) Reaction of 1 with K[(g5-C5H4Me)Mn(CO)2H]. To a
−131.2 (m, ortho-CF,), −159.5 (t, J = 21, para-F), −165.2 (m,
5
◦
meta-CF). 31P NMR (121 MHz, C7D8, 21 C) d 23.6 (1JPtP
=
suspension of K[(g -C5H4Me)Mn(CO)2H] (0.030 g, 0.13 mmol)
in toluene-d8 (ca. 1 cm3) at −50 ◦C contained in a J. Young’s
NMR tube, was added a solution containing one equivalent
of 1 in toluene-d8 (ca. 1 cm3). After agitation of the reaction
mixture and warming to −30 ◦C the solution became deep red in
5137 Hz, 2JPP = 12 Hz), 28.1 (1JPtP = 1769 Hz, 2JPP = 12 Hz).
=
(vi) Reaction of 2 with (Ph3P)2Pt(H2C CH2). To a solu-
tion of (Ph3P)2Pt(H2C CH2) (0.050 g, 0.07 mmol) in toluene
=
(5 cm3) at room temperature was added 10 cm3 of a toluene
solution containing 0.100 g of 2 {0.144 mmol of [HB(C6F5)2]2
dimer}. After stirring for 15 min, a colourless solution and a
finely divided black precipitate were formed. Comparison of
spectroscopic data with authentic samples showed the toluene
soluble products to be EtB(C6F5)2 (10)7 and Ph3P·HB(C6F5)2
(11) (vide infra).
5
colour, and spectroscopic data were measured at this point. (g -
1
C5H4Me)Mn(CO)2(H)B(C6F5)2, 6: H NMR (300 MHz, C7D8,
−30 ◦C), d −16.81 (b, 1H, MnHB), 1.11 (s, 3H, C5H4Me), 3.68
(s, 2H, C5H4Me), 3.85 (s, 2H, C5H4Me). 13C NMR (76 MHz,
C7D8, −30 ◦C), d 12.4 (C5H4Me), 87.1, 87.8 (CHs of C5H4Me),
225.8 (CO). 11B NMR (96 MHz, C7D8, −30 ◦C), d 84.2 (b,
fwhm ca. 940 Hz). 19F NMR (283 MHz, C7D8, −30 ◦C), d
−132.8 (b m, ortho-CF), −134.3 (b m, ortho-CF), −144.1 (b
m, para-CF), −149.9 (b m, para-CF), −161.6 (b m, meta-
CF), −163.3 (b m, meta-CF). IR (hexanes solution, cm−1) 1986
[m(CO), st], 1922 [m(CO), st], 1648 [m(MnH), md]. Subsequent
warming to room temperature led to a change in colour of
the solution to dark brown, to the disappearance of the 11B
resonance due to 6 and to the appearance of a number of
11B signals, predominant among these being a doublet at dB
−25.6 (1JB–H = 80 Hz). IR monitoring of the decomposition
process reveals rapid loss in intensity of the carbonyl bands
associated with 6 (1986, 1922 cm−1) with concomitant growth of
a number of new features, including major bands at 2022 and
(vii) Reaction of 2 with [(Ph3P)2Rh(l-Cl)]2. To a suspension
of [(Ph3P)2Rh(l-Cl)]2 (0.060 g, 0.05 mmol of dimer) in toluene
(5 cm3) at room temperature was added 5 cm3 of a toluene
solution containing 0.100g of 2 {0.144 mmol of [HB(C6F5)2]2
dimer}. The reaction mixture was stirred for 72 h, during which
time the pale red [(Ph3P)2Rh(l-Cl)]2 dissolved generating a
red-brown solution. Examination of the reaction mixture by
31P NMR at this point revealed two signals, a sharp doublet
1
(dP 44.7, JRhP = 208 Hz) and a broader resonance (dP 12.0,
fwhm = ca. 140 Hz), whereas the corresponding 11B spectrum
displayed signals at dB −23.9 (broad doublet, 1JBH = 48 Hz) and
−2.5. Removal of volatiles in vacuo, extraction with hexanes
(ca. 10 cm3) and cooling to −50 ◦C for 1 week led to the
isolation of Ph3P·HB(C6F5)2 (11) as a colourless crystalline solid
5
1941 cm−1 characteristic of (g -C5H4Me)Mn(CO)3.16 Attempts
to recrystallize 6, even at −50 ◦C invariably led to the isolation of
decomposition products. Trapping experiments with HSiPh2Me
were carried out in a J. Young’s NMR tube as detailed above,
with the formation of 6 being established by multinuclear
NMR at −30 ◦C prior to the addition of excess silane by
syringe (0.050 g, 0.25 mmol). Subsequent photolysis for 12 h
at −30 ◦C led to complete conversion to the known compound
1
(yield ca. 45%). 11 has been characterized by H, 13C, 11B, 19F
and 31P NMR, IR, mass spectrometry and single crystal X-ray
diffraction, and was shown to give identical spectroscopic data
to samples prepared independently from 2 and PPh3. 1H NMR
(300 MHz, C6D6, 21 ◦C), d 4.64 (b, fwhm ca. 150 Hz, 1H, BH),
6.88–7.02 and 7.32–7.44 (m, 15H, PPh3). 13C NMR (76 MHz,
C6D6, 21 ◦C), d 127.6, 131.4, 133.2 (aromatic CH), 138.9, 141.7,
150.2 (aromatic CF). 11B NMR (96 MHz, C6D6, 21 ◦C), d −23.9
5
(g -C5H4Me)Mn(CO)2(H)SiPh2Me (7).11,17
=
(iv) Reaction of 1 with (Ph3P)2Pt(H2C CH2): isolation
(b d, JBH = 47 Hz). 19F NMR (283 MHz, C6D6, 21 ◦C), d
1
of platinum phosphine products. To a solution of (Ph3P)2
3
=
Pt(H2C CH2) (0.100 g, 0.13 mmol) in toluene (15 cm ) at room
−127.4 (d, J = 21 Hz, ortho-F), −157.6 (t, J = 21 Hz, para-
CF), −163.8 (m, meta-CF). 31P NMR (121 MHz, C6D6, 21 ◦C)
dP 12.0 (b, fwhm ca. 140 Hz). IR (KBr disk, cm−1) m(BH) 2610
md. MS(EI): M+ = 608 (100%), isotopic pattern corresponding
to 1 B atom. Reliable elemental analysis was precluded by
the air-sensitivity of 11. The residual hexane insoluble red-
brown oily solid was shown by comparison of spectroscopic
data with those reported previously,21 to be the known cation
temperature was added 10 cm3 of a toluene solution containing
one equivalent of 1. After stirring for 12 h, the reaction
mixture was examined by 11B and 31P NMR, revealing complete
consumption of the starting materials, and the appearance of
resonances at dB 73.5 and at dP 24.3 (1JPt–P = 3169 Hz) and 15.1
(1JPt–P = 3680 Hz). Removal of volatiles in vacuo, re-extraction
◦
into toluenes and cooling to −30 C for ca. 1 week led to the
6
isolation of trans-(Ph3P)2Pt(C6F5)Cl (9) as colourless crystals
suitable for X-ray diffraction (yield ca. 33%). Spectroscopic
data are in agreement with those reported previously,18 and
confirm 9 as the phosphorus-containing species giving rise
to the resonance at dP 24.3. Recrystallization of the toluene-
insoluble material from chloroform led to the isolation of cis-
[(Ph3P)2Rh(g -C6H5Me)]+ (dP 44.7, 1JRhP = 208 Hz), present as
the [ClB(C6F5)3]− salt (dB −2.5).21 The same compound was
identified as the product from the reaction of [(Ph3P)2Rh(l-
Cl)]2 with ClB(C6F5)2, 1, and the cationic component is identical
to that isolated from the reaction of [(Ph3P)2Rh(l-Cl)]2 with
Na{B[C6H3(CF3)2-3,5]4} in a mixed dichloromethane/toluene
solvent system.22
•
(Ph3P)2PtCl2 3(CHCl3), 8·3(CHCl3) as colourless X-ray quality
4 0 3 2
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7

View Article Online
spectively) and which has been ascribed to partial quaternization
of the boron centre by interaction with the manganese-bound
hydride ligand.23 This structural inference is given further
credence in the case of 6 by the substantial narrowing of the
hydride resonance on 11B decoupling.
3
Results and discussion
Synthetic and reaction chemistry
(i) Reactivity towards organometallic anions. The reac-
5
tions of ClB(C6F5)2, 1, with the organometallic anions [(g -
C5R5)Fe(CO)2]− (R = H or Me) and [Mn(CO)5]− proceed via the
salt elimination chemistry outlined in Scheme 1 to generate the
novel bis(pentafluorophenyl)-boryl complexes LnMB(C6F5)2,
Attempts to isolate 6 as a pure compound were frustrated
by its thermal frailty. Warming to room temperature resulted
in a rapid red to brown colour change, in the disappearance
of the resonance at dB 84.3, and in the appearance of a
number of high-field 11B NMR signals, prominent among these
being a doublet at dB −25.6 (1JBH = 80 Hz). This thermal
5
5
[LnM = (g -C5H5)Fe(CO)2 (3), (g -C5Me5)Fe(CO)2 (4), Mn(CO)5
(5)] in moderate yields (35–45%). These complexes have been
characterized by multinuclear NMR, IR, mass spectrometry,
elemental analysis and, in the cases of 3 and 4, by single
crystal X-ray diffraction. Particularly characteristic are the
very low field 11B NMR shifts (dB 121.5, 121.3 and 130.7
for 3, 4 and 5, respectively) which are characteristic of bo-
ryl complexes featuring weakly p donor substituents [cf. dB
5
frailty mirrors that reported by Schlecht and Hartwig for (g -
C5H4Me)Mn(CO)2(H)BX2 (X = Me, Cy).17 Although it is diffi-
cult to plot the course of the thermal decomposition of 6 with any
5
certainty, complexes of the type (g -C5H4Me)Mn(CO)2(H)BX2
are known to react via loss of the borane HBX2,17 and this,
together with the similarity in chemical shift and coupling
constant for the predominant boron-containing decomposition
5
141.2, 121.0 and 106.2 for (g -C5H5)Fe(CO)2B(Cl)Si(SiMe3)3,
(g -C5H5)Fe(CO)2B(C6H5)2 and fac-(Me3P)3Ir(H)2(9-BBN), re-
5
1d
product with those reported for [HB(C6F5)3]− (dB −25.5, 1JBH
=
spectively (9-BBN = 9-borabicyclononane, BC8H14)]. Mass
80 Hz),24 implies that initial loss of the HB(C6F5)2 fragment may
feature in the mechanistic pathway. Additionally, IR monitoring
spectrometry and IR data are also consistent with the proposed
formulations for 3–5, in particular displaying the fragmenta-
tion patterns and carbonyl stretching frequencies, respectively,
consistent with complexes containing the B(C6F5)2 ligand.
5
of the decomposition process reveals that (g -C5H4Me)Mn(CO)3
is a major carbonyl containing product [m(CO) 2022 and
1941 cm−1].16
5
Previously reported complexes of the type (g -C5H4Me)
Mn(CO)2(H)BX2 have been shown to react photolytically with
5
the silane HSiPh2Me to give (g -C5H4Me)Mn(CO)2(H)SiPh2Me
(7).17 Consequently, the reaction of HSiPh2Me with 6 at
−30 ◦C was examined and identification of 7 as the manganese-
containing product therefore provides additional indirect ev-
5
idence for the identification of 6 as (g -C5H4Me)Mn(CO)2-
(H)B(C6F5)2.
(ii) Reactivity towards low-valent platinum and rhodium com-
plexes. The reactivity of 1 towards anionic organometallic
reagents therefore mirrors that of related diaryl, dialkyl and
bis(heteroatom) stabilised boranes [e.g. Ph2BCl, (9-BBN)Br
and ClBcat] in generating complexes containing metal–boron
bonds.1 Given that another precedented route to complexes con-
taining such linkages is the oxidative addition of B–H or B–Cl
bonds,1 we sought to probe the reactivity of 1 and [HB(C6F5)2]n
(2) towards low-valent rhodium and platinum complexes. Initial
=
studies focussed on the reaction of 1 with (Ph3P)2Pt(H2C CH2)
as this reagent has previously been employed to great effect in
the synthesis of boryl species of types cis-(Ph3P)2Pt(BX2)2 and
trans-(Ph3P)2Pt(Y)BX2 by oxidative addition of B–B or B–Y
bonds (Y = Cl or Br).1,25 In the case of 1, however, reaction
Scheme 1 Generation of metal–boron bonds by the reaction of
organometallic anions with ClB(C6F5)2, 1. Trapping of the ther-
5
mally labile complex (g -C5H4Me)Mn(CO)2(H)B(C6F5)2, 6, with
diphenylmethylsilane.
=
with (Ph3P)2Pt(H2C CH2) does not proceed to the isolation
The reactivity of 1 towards the hydrido-manganese anion
of a platinum boryl complex, but rather to the formation of
two main platinum-containing species, cis-(Ph3P)2PtCl2 (8) and
trans-(Ph3P)2Pt(C6F5)Cl (9). The formation of both 9 (originally
reported by Rosevear and Stone in 196518) and of 8 was implied
by spectroscopic data obtained for the crude (pumped down) re-
action mixture and subsequently confirmed crystallographically
in both cases. No boron-containing products were detected by
11B NMR analysis of the same (pumped down) reaction mixture.
In order to determine the nature of the boron-containing
product(s) and in an attempt to shed light on the mechanism
for the formation of 8 and 9, the reaction was repeated in
toluene-d8 with periodic monitoring by multinuclear (1H, 11B, 19F
and 31P) NMR. 11B NMR measurements revealed predominant
conversion of 1 to a single boron-containing compound giving
rise to a signal at dB 73.5, which was subsequently shown by
further comparison of spectroscopic data with the literature
values reported by Piers and co-workers, to be the volatile borane
EtB(C6F5)2 (10).7 Conversion of 1 to 10 was accomplished over
a period of ca. 24 h and presumably results from the formal
5
[(g -C5H4Me)Mn(CO)2H]− in toluene has also been examined.
In this case a very rapid reaction was observed at −30 ◦C,
leading to the generation of a red solution and a pale precip-
itate. Spectroscopic data obtained at this point reveal clean
conversion of 1 to a single boron-containing species giving
rise to a very broad resonance (fwhm ca. 940 Hz) at dB 84.2
(cf. 59.1 for 1). 1H, 13C and 19F NMR spectra display the
5
appropriate resonances associated with g -C5H4Me, CO and
C6F5 substituents and, in addition, a broad high-field resonance
1
is observed in the H spectrum (dH −16.81) which sharpens
markedly on 11B decoupling. Furthermore, the IR spectrum
displays features at 1986, 1922 and 1648 cm−1 which are similar
to those associated with the m(CO) and m(MnH) stretches of
5
(g -C5H4Me)Mn(CO)2(H)BX2 (e.g. 1975, 1910, 1592 and 1967,
1901, 1597 cm−1 for X = Me and Cy, respectively).17 The available
spectroscopic data are therefore consistent with a formulation as
5
(g -C5H4Me)Mn(CO)2(H)B(C6F5)2 (6). Notably, the 11B NMR
shifts for 6 and 3 (dB 121.5 and 84.3) reveal that the extent of
deshielding is less marked in the case of 6, a phenomenon pre-
=
hydroboration of the ethylene ligand of (Ph3P)2Pt(H2C CH2)
5
viously observed for (g -C5H4Me)Mn(CO)2(H)B(Cl)Si(SiMe3)3
by [HB(C6F5)2]n (2). Indeed NMR monitoring of the course
of the reaction reveals that [HB(C6F5)2]2 (dB 17.0, dH 4.2, dF
5
and (g -C5H5)Fe(CO)2B(Cl)Si(SiMe3)3 (dB 141.2 and 105.2, re-
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7
4 0 3 3

View Article Online
−134.5, −149.1, −161.4) is in fact an intermediate present in
relatively low concentrations at t = ca. 90 min. The concentration
of [HB(C6F5)2]2 subsequently falls, such that there is no trace
detectable by NMR once the reaction reaches completion. The
feasibility of the proposed hydroboration reaction is amply
justified by literature precedent,7 and readily demonstrated by
final product mixture,‡ but none of these has the spectroscopic
properties associated with a vinylplatinum complex.30 It is of
course conceivable that further hydroboration of vinyl groups
by 2 to give saturated products could occur.
At first inspection the reaction of the borane [HB(C6F5)2]n (2)
with [(Ph3P)2Rh(l-Cl)]2 (B : Rh 3 : 1) in toluene also appears to
diverge from the oxidative addition based chemistry delineated
for other boranes of the type HBX2.1 The 31P and 11B NMR
spectra of the crude (pumped down) reaction mixture each
=
independent reaction of (Ph3P)2Pt(H2C CH2) with excess 2,
which under these conditions rapidly generates EtB(C6F5)2 [to-
gether with Ph3P·HB(C6F5)2 (11) and insoluble platinum black].
Regarding the origins of the borane 2, one possibility with
significant literature precedent is chloride/hydride exchange
between 1 and a hydride containing species.26 Consistent with
display two signals, the former showing a sharp doublet (1JRhP
=
208 Hz) at dP 44.7 and a broad resonance at dP 12.0 (fwhm =
ca. 140 Hz), the latter signals at dB −2.5 and dB −23.9 (broad
doublet, 1JBH = 47 Hz). Recrystallization from hexanes yields a
colourless crystalline solid subsequently shown by spectroscopic
and crystallographic analysis (and by comparison with a sample
prepared independently from 2 and PPh3) to be Ph3P·HB(C6F5)2,
11 (dP 12.0, dB −23.9). The rhodium/phosphine containing
component of the residual (hexane insoluble) red-brown oily
solid was shown, by comparison of multinuclear NMR data
this hypothesis is the observation in the reaction mixture of 31
P
(dP 23.2, 1JPtP = 2810 Hz, 2JPP = 18 Hz; dP 23.7, 1JPtP = 2290 Hz,
1
1
2JPP = 18 Hz) and H NMR resonances (dH −5.69, JPtH
=
2
2
776 Hz, JPH,trans = 160 Hz, JPH,cis = 13 Hz) associated with
the known hydride [(Ph3P)3PtH]+ (12).20 The concentration time
1
profile for 12, determined by H and 31P NMR data, indicates
that it reaches detectable concentrations at short reaction times
(t < 90 min), and that it too is an intermediate in the reaction
sequence.
6
with those reported previously, to be the cation [(Ph3P)2Rh(g -
C6H5Me)]+ (14), present as the [ClB(C6F5)3]− salt.21 The same
compound is identified as the product from the reaction of
[(Ph3P)2Rh(l-Cl)]2 with ClB(C6F5)2, 1.§
Given the known chemistry of complexes of the types
(R3P)2Pt(Y)(CH2CH2X) and (R3P)2Pt(Y)(H),27 it is plausible
that the Pt–H linkage in 12 is formed by a b-hydride elimination
process, originating from a complex such as 13 (Fig. 1), itself
produced by insertion of ethylene into the Pt–B bond of an
initially formed platinum boryl complex (Ph3P)2Pt(Cl)B(C6F5)2.
Although such a premise is necessarily speculative, both the
initial B–Cl oxidative addition step and the subsequent alkene
insertion into the M–B bond are well precedented in the
literature.1,25,28 Furthermore, 11B and 31P NMR resonances
consistent with an intermediate similar to 13 are detected
at very short reaction times (t = ca. 30 min.) prior to the
appearance of signals associated with 12 or 2. The 11B resonance
(dB 35) is shifted markedly up-field compared to that expected
for a three-coordinate (alkyl)B(C6F5)2 derivative [e.g. Dd ≈
40 ppm compared to EtB(C6F5)2, 10, (dB 73.5)7] consistent
with partial quaternization of the boron centre. Similar upfield
shifts (Dd ≈ 50 ppm) have been observed by Bochmann and
co-workers for intramolecular coordination of a metal-bound
chloride ligand to a B(C6F5)2 containing Lewis acid {e.g. dB
Superficially, therefore the ultimate products of the reaction
of 2 with [(Ph3P)2Rh(l-Cl)]2 (Scheme 2) appear to be derived
from abstraction of either the rhodium-bound chloride or
triphenylphosphine ligands by the strongly Lewis acidic bo-
rane (with the anion [ClB(C6F5)3]− presumably resulting from
subsequent exchange of aryl substituents with the excess of 2
used¶). Previous studies have examined the reactivity of four-
coordinate Rh(I) phosphine- and halide-containing complexes
with a variety of Lewis acids. On the basis of spectroscopic
data, possible interactions of BX3 with the metal itself, or with
the phosphine or chloride ligands were postulated, although
31a
no definitive structural data were reported. More recently,
abstraction of phosphine ligands from low valent late tran-
sition metal complexes by Lewis acidic boranes has received
31b,c
literature precedent (e.g. for ruthenium and iridium),
while
chloride abstraction from [(Ph3P)2Rh(l-Cl)]2 to give cationic
bis(phosphine) rhodium species is known to occur upon reaction
with salts of weakly coordinating carborane or tetraarylborate
anions.21,22
5
5
59.8 and 4.5, respectively, for [g -C5H4B(C6F5)2]TiCl3 and (g -
C5H5)[g -C5H4B(C6F5)2](l-Cl)TiCl}.29 The presence of a similar
5
intramolecular Cl→B interaction in 13 would also explain the
observed cis geometry of the intermediate indicated by its 31P
NMR spectrum (dP 23.6, 1JPtP = 5137 Hz, 2JPP = 12 Hz; dP 28.1,
1JPtP = 1769 Hz, 2JPP = 12 Hz) and the very high Pt–P coupling
constant for the PPh3 ligand trans to the Pt–Cl · · · B linkage.
Scheme
2 Ligand abstraction from [(Ph3P)2Rh(l-Cl)]2 by [HB
(C6F5)2]n, 2; generation of Ph3P·HB(C6F5)2, 11 and [(Ph3P)2Rh
6
(g -C5H4Me)]+, 14.
Fig. 1 Proposed structure for the first detectable intermediate in the
=
reaction of 1 with (Ph3P)2Pt(H2C CH2).
Closer examination of the course of the reaction of 2 with
[(Ph3P)2Rh(l-Cl)]2 in toluene-d8 was attempted by multinuclear
NMR and reveals the presence of a Rh(III) species present in low
From the spectroscopically identified platinum hydride in-
termediate [(Ph3P)3PtH]+ (12), therefore, the proposed chlo-
ride/hydride exchange step, followed by phosphine loss would
generate one of the final products, in cis-(Ph3P)2PtCl2 (8), with
subsequent chloride/aryl exchange between boron and platinum
accounting for the formation of trans-(Ph3P)2Pt(C6F5)Cl (9).
Finally, implicit in the proposal of a b-hydride elimination
step for the formation of 12, is the generation of a vinyl-
containing co-product. Although we were able to detect weak
1H resonances associated with a vinyl group (dH 5.92, 6.25, 6.72;
JHH = 3, 12, 19 Hz) early in the reaction, the ultimate fate
of this unit is unclear. Small amounts of platinum/phosphine
containing species (other than 8 or 9) are observed in the
concentrations at t > 30 min. This species is characterized by 31
P
(dP 38.4, 1JRhP = 116 Hz), 11B (dB 71.0) and 1H NMR resonances
1
2
(dH −16.38, JRhH = 27 Hz, JPH = 12 Hz) characteristic of
‡ In addition these platinum-contining products also do not appear to fit
the spectroscopic profiles of products derived from the decomposition
=
of (Ph3P)2Pt(H2C CH2) in aromatic solvents (see reference 25b and
references therein).
§ Note added in proof: The structure of 14 has subsequently been
confirmed crystallographically.22
¶ For a related example of C6F5 transfer between boron centres see
reference 46.
4 0 3 4
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7

View Article Online
a trigonal bipyramidal hydrido-rhodium boryl complex, trans-
(Ph3P)2RhH(Cl)BX2, [cf. dP 39.9, 1JRhP = 117 Hz and dH −14.96,
1
2
4a,32
JRhH = 27 Hz, JPH = 14 Hz for (Ph3P)2RhH(Cl)Bcat ] and
is tentatively assigned as (Ph3P)2RhH(Cl)B(C6F5)2. Although
this compound is never present in concentrations approaching
that of 14, its formation does imply that at least to a minor
degree, B–H oxidative addition chemistry competes with ligand
abstraction processes in this system.
Structure and bonding
1
2
The structures of compounds 3, 4, 9 and 11· (C6H14) have
been determined by single crystal X-ray diffraction. The asym-
metric unit of iron boryl complex 3 (triclinic polymorph,
Fig. 2 and Table 1) consists of two very similar but crys-
tallographically independent molecules, each displaying the
expected half sandwich geometry at iron, with the coordi-
nation sphere being completed by two carbonyl and one
bis(pentafluorophenyl)boryl ligands. Of interest is the Fe–B
5
Fig. 3 Molecular structure of (g -C5Me5)Fe(CO)2B(C6F5)2, 4. Rel-
evant bond lengths (A) and angles (◦): Fe(1)–B(1) 1.968(5),
˚
˚
distance [1.964(4), 1.965(5) A], which is among the shortest
reported for three-coordinate boryl ligands coordinated to
Fe(1)–centroid 1.735(4), Fe(1)–C(11) 1.750(5), Fe(1)–C(12) 1.749(5),
B(1)–C(13) 1.599(6), B(1)–C(19) 1.588(6); C(11)–Fe(1)–C(12) 94.7(2),
centroid–Fe(1)–B(1)–C(13) 41.3(3), Fe(1)–B(1)–C(13)–C(14) 65.0(3),
Fe(1)–B(1)–C(19)–C(24) 74.1 (3). Hydrogen atoms omitted for clarity.
5
˚
1d,33
the (g -C5R5)Fe(CO)2 fragment [1.942(3)–2.090(3) A]
and
significantly (3.4%) shorter than the corresponding bond in
34
˚
the related B(C6H5)2 complex [2.034(3) A]. Perfluorination
of the boryl substituent backbone also appears to result in
a significantly different orientation of the ligand with respect
cyclopentadien◦yl ligand and a less bulky boryl substituent are
43.1(3) and 7.9 .34
Although the Fe–B bond lengths for 3 and 4 [1.968(5) A] imply
5
to the (g -C5R5)Fe(CO)2 fragment. Thus centroid–Fe–B–Cipso
torsion angles (ϑ) of 28.4(3) and 27.9(3)◦ are measured for 3,
˚
compared to 75◦ for (g -C5H5)Fe(CO)2B(C6H5)2,34 despite the
5
an enhanced Fe→B p interaction, and FT-Raman measured
Fe–B stretching frequencies are significantly higher than for
alkoxoboryl analogues (e.g. 577 cm−1 for 3 vs. 520–530 cm−1),36
analysis of the carbonyl stretching frequencies of 3 and 4 is not
so clear-cut. Thus, for example, the measured values for 3 and
larger steric demands of the B(C6F5)2 ligand and its increasing
5
proximity to the ancillary (g -C5H5) ligand as ϑ falls from 90
to 0◦. Hoffmann and co-workers have determined for related
carbene systems that the most favourable metal to ligand back-
bonding is attained at a torsion angle of 0◦.35 Hence, both the
markedly reduced torsion angle and appreciably shorter Fe–B
distance for 2 imply an increased back-bonding component for
the B(C6F5)2 ligand compared to B(C6H5)2. Presumably the steric
demands of B(C6F5)2 prevent the attainment of the ideal (ϑ =
0◦) ligand orientation. Consistent with this, the corresponding
5
5
(g -C5H5)Fe(CO)2B(C6H5)2 and (g -C5H5)Fe(CO)2Bcat are 2014
and 1968; 2021 and 1951; 2024 and 1971 cm−1,34 despite the fact
that the B(C6F5)2 ligand, for example, would be expected to be
both a poorer r donor and stronger p acceptor than B(C6H5)2.
In order to examine more rigorously the nature of the metal–
ligand bonding in 3 and related boryl complexes, a series of
DFT calculations was carried out using a recently precedented
5
angles in (g -C5Me5)Fe(CO)2B(C6F5)2 (4, Fig. 3 and Table 1) and
5
method.37
in (g -C5H5)Fe(CO)2Bcat which feature, respectively, a bulkier
5
Calculated structural parameters for
3
and (g -
C5H5)Fe(CO)2B(C6H5)2 (see ESI†) are in good agreement
with the geometries determined for the molecules in the solid
state by X-ray diffraction. Central to the analysis of the
Fe–B bonds in these two compounds and the related species
5
(g -C5H5)Fe(CO)2BX2 (X = H, F, Cl) are (i) the r : p covalent
ratios determined from partitioning of the bonding density;37
(ii) the bond dissociation energies (BDEs, Do); and (iii) the
relative contributions (attractive electrostatic and orbital,
repulsive Pauli) to the overall metal–ligand interaction energy.38
Salient parameters are collected in Table 2. Analysis of this data
reveals that the Fe–B bond in 3 is indeed stronger and possesses
5
a greater p component than that in (g -C5H5)Fe(CO)2B(C6H5)2.
Furthermore, consideration of the various components of DEint
also reveals a significantly enhanced electrostatic contribution
for 3, which might superficially be ascribed to a greater
bond polarity Fed−–Bd+ in the perfluorinated compound.
However, putting these results in a wider context, comparison
5
of the complexes (g -C5H5)Fe(CO)2BX2 (X = C6F5, C6H5,
H, F, Cl) reveals that although the p contribution in 3 is
among the largest determined, even with this most favourable
choice of boryl substituents, p back-bonding accounts for no
more than 20% of the overall covalent interaction. Such an
observation is consistent with an energy mismatch between the
appropriate p symmetry donor and acceptor orbitals in the
Fig.
2 Molecular structure of one of the two independent
molecules in the asymmetric unit of the triclinic polymorph of
5
˚
(g -C5H5)Fe(CO)2B(C6F5)2, 3. Relevant bond lengths (A) and an-
gles (◦): Fe(1)–B(1) 1.964(4), Fe(1)–centroid 1.729(4), Fe(1)–C(6)
1.760(4), Fe(1)–C(7) 1.749(4), B(1)–C(8) 1.589(5), B(1)–C(14)
1.600(5); C(6)–Fe(1)–C(7) 94.0(2), centroid–Fe(1)–B(1)–C(14) 27.9(3),
Fe(1)–B(1)–C(14)–C(19) 65.8(3), Fe(1)–B(1)–C(8)-C(9) 73.8(3). Hydro-
gen atoms omitted for clarity.
5
[(g -C5H5)Fe(CO)2]+ and [BX2]− fragments, respectively.37
The structures of (Ph3P)2Pt(C6F5)Cl (9) and Ph3P·HB(C6F5)2
(11, as the hexane hemi-solvate) have also been determined
and are shown in Figs. 4 and 5, respectively. The former
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7
4 0 3 5

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5
Table 2 DFT analysis of bonding in complexes (g -C5H5)Fe(CO)2BX2 (X = C6F5, C6H5, H, F, Cl)
Breakdown of orbital
contribution to bond (%)
a
bc
bc
bc
c
BDE (Do)bc
DEelstat
DEorb
DEPauli
DEelstat/DEorb
˚
X
Calculated d(Fe–B) /A
r
p
C6F5 (3)
C6H5
H
F
Cl
2.006 (1.965d)
2.107 (2.03434)
1.988
81.9
90.4
84.1
94.0
82.1
18.0
9.5
15.8
6.0
53.6
45.5
66.8
65.9
58.1
−112.9
−60.8
−194.2
−322.4
−239.6
−224.5
−226.8
228.0
107.5
285.6
244.1
250.3
0.58
0.19
0.57
0.49
0.51
−136.2
−110.4
−116.3
2.010
2.008 (1.94233)
17.8
a Crystallographically determined distances in parentheses; a 2–3% over-estimate in similar distances has previously been observed using generalized
gradient approximation (GGA) methods. b All values in kcal mol−1 c DEelstat, DEorb and DEPauli are respectively the contributions to the instantaneous
.
interaction energy (between metal and boryl fragments) due to electrostatic attraction, orbital interaction and Pauli repulsion (DEint = DEelstat
+
DEorb + DEPauli). The instantaneous interaction energy, DEint, differs from the BDE (Do) in that it does not take into account the geometric and
electronic relaxation that takes place in the isolated components following bond breakage. This relaxation is associated with the energy term DEprep
38
such that −Do = DEint + DEprep
.
d Mean of two crystallographically independent values obtained for the triclinic polymorph.
Fig.
5
Molecular structure of Ph3P·HB(C6F5)2, 11. Relevant
˚
Fig. 4 Molecular structure of trans-(Ph3P)2Pt(C6F5)Cl, 9. Relevant
bond lengths (A) and angles (◦): P(1)–B(1) 1.986(2), B(1)–C(1)
1.625(3), B(1)–C(7) 1.627(3), B(1)–H(1) 1.00; P(1)–B(1)–C(1) 118.1(1),
P(1)–B(1)–C(7) 110.3(2), P(1)–B(1)–H(1) 105.8. Hydrogen atoms, except
that attached to B(1), and half molecule of hexane in the asymmetric unit
omitted for clarity.
◦
˚
bond lengths (A) and angles ( ): Pt(1)–P(1) 2.307(1), Pt(1)–P(2)
2.302(1), Pt(1)–Cl(1) 2.370(1), Pt(1)–C(19) 2.017(4); P(1)–Pt(1)–P(2)
176.6(1), Cl(1)–Pt(1)–C(19) 179.5(1), P(1)–Pt(1)–Cl(1) 87.8(1),
P(1)–Pt(1)–C(19) 91.7(1), P(2)–Pt(1)–Cl(1) 88.9(1), P(2)–Pt(1)–C(19)
91.6(1), P(1)–Pt(1)–C(19)–C(24) 71.8(2). Hydrogen atoms omitted for
clarity.
4
Conclusions
confirms the trans square planar geometry implied by 31P NMR
The reactivity of the strongly Lewis acidic chloroborane
ClB(C6F5)2, 1, towards anionic organometallic reagents mirrors
that of other monohaloboranes in providing access to transition
metal complexes containing M–B bonds via salt elimination.
The resulting metal–boron complexes contain, in B(C6F5)2, one
of the most strongly p acidic boryl ligands reported to date. How-
measurements and which is also found in (Ph3P)2Pt(C6H5)Cl,
[Ph2P(CH2)nPPh2]Pt(C6F5)Cl (n
=
10, 14, 18, 20) and
{PhP[(CH2)14]2PPh}Pt(C6F5)Cl;39,40 the alternative cis geometry
prevails in (Et3P)2Pt(C6F5)Cl and [Ph2P(CH2)nPPh2]Pt(C6F5)Cl
(n = 1).41,42 Important structural parameters defining the Pt–Cipso
bond length and the orientation of the aryl ligand with respect
to the P2PtCl plane are in close agreement with those found for
5
ever, even in complexes of the type (g -C5R5)Fe(CO)2B(C6F5)2,
◦
˚
the role of p back bonding in the M–B linkage is found to
be a relatively minor one, presumably reflecting the relatively
high energy of the boron-centred acceptor orbital. Attempts to
generate similar bonds from 1 or [HB(C6F5)2]n, 2, via B–Cl or
B–H oxidative addition illustrate how the chemistries of these
boranes diverge from less electrophilic systems such as XBcat
related compounds [i.e. 2.071(4) A and 72.0 (mean) for the Pt–
Cipso bond length and◦P–Pt–Cipso–Cortho torsion angle, compared
39
˚
to 2.00(2) A and 72.8 (mean) for (Ph3P)2Pt(C6H5)Cl].
To our knowledge the borane phosphine adduct 11 represents
the first structurally characterized neutral donor adduct of this
borane, L·HB(C6F5)2 (although 1 : 1 adducts with thf and PMe3,
for example, have been spectroscopically characterized).7 The
overall geometry displays the staggered orientation of boron-
and phosphorus-bound substituents expected on steric grounds
(mean Cipso–P–B–Cipso torsion angle = 61.6◦) and also found
=
(X = Cl, H). Thus the reaction of 1 with (Ph3P)2Pt(H2C CH2)
ultimately generates EtB(C6F5)2 and chloro-platinum(II) species,
whereas the reaction of 2 with [(Ph3P)2Rh(l-Cl)]2 generates
products resulting from ligand abstraction from rhodium by
the highly electrophilic borane.
in Ph3P·B(C6F5)3.43 The P–B distance in 11 [1.986(2) A] is
˚
significantly shorter than that found in the B(C6F5)3 complex
˚
[2.180(6) A], again presumably on steric grounds, being more
Acknowledgements
˚
consistent with that found in Me2PhP·HB(CN)(ipc) [1.958(4) A,
ipc = isopinocamphenyl, C10H17] and significantly longer than
S. A. would like to thank the EPSRC (for grant GR/S07667
and for a studentship for D. L. C.). We would also like to
44,45
˚
that found in Ph3P·BH3 (mean 1.917 A).
4 0 3 6
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7

View Article Online
acknowledge the EPSRC for support of the National Crystallog-
raphy Service. All calculations were carried out using the Helix
computing facility at Cardiff University. We would also like to
thank Prof. T. B. Marder (Durham) for helpful comments.
22 O. Buttler, D. L. Coombs and S. Aldridge, unpublished results.
23 H. Braunschweig, M. Colling, C. Kollann and U. Englert, J. Chem.
Soc., Dalton Trans., 2002, 2289.
24 X. Chen, F.-C. Liu, C. E. Plecnik, S. Liu, B. Du, E. A. Meyers and
S. G. Shore, Organometallics, 2004, 23, 2100.
25 For representative examples see: (a) T. Ishiyama, N. Matsuda, M.
Murata, F. Ozawa, A. Suzuki and N. Miyaura, Organometallics, 1996,
15, 713; (b) G. Lesley, P. Nguyen, N. J. Taylor, T. B. Marder, A. J.
Scott, W. Clegg and N. C. Norman, Organometallics, 1996, 15, 5137;
(c) C. N. Iverson and M. R. Smith III, Organometallics, 1996, 15,
5155; (d) W. Clegg, F. J. Lawlor, G. Lesley, T. B. Marder, N. C.
Norman, A. G. Orpen, M. J. Quayle, C. R. Ricem, A. J. Scott and
F. E. S. Souza, J. Organomet. Chem., 1998, 550, 183; (e) D. Curtis,
M. J. G. Lesley, N. C. Norman, A. G. Orpen and J. Starbuck, J. Chem.
Soc., Dalton Trans., 1999, 1687.
References and notes
1 For recent reviews see: (a) G. J. Irvine, M. J. G. Lesley, T. B. Marder,
N. C. Norman, C. R. Rice, E. G. Robins, W. R. Roper, G. Whittell
and L. J. Wright, Chem. Rev., 1998, 98, 2685; (b) H. Braunschweig,
Angew. Chem., Int. Ed., 1998, 37, 1786; (c) M. R. Smith III, Prog.
Inorg. Chem., 1999, 48, 505; (d) H. Braunschweig and M. Colling,
Coord. Chem. Rev., 2001, 223, 1; (e) S. Aldridge and D. L. Coombs,
Coord. Chem. Rev., 2004, 248, 535.
2 See, for example: (a) K. Burgess and M. J. Ohlmeyer, Chem. Rev.,
1991, 91, 1179; (b) I. Beletskaya and A. Pelter, Tetrahedron, 1997,
53, 4957; (c) T. B. Marder and N. C. Norman, Top. Catal., 1998, 5,
63; (d) T. Ishiyama and N. Miyaura, J. Organomet. Chem., 2000, 611,
392.
26 Chloride/hydride exchange converting 1 to 2 using a silane reagent is
one of the established routes to 2 (ref. 7). In addition, analogous
5
exchange reactions using metal hydrides {e.g. stannanes or [(g -
C5H5)2Zr(Cl)H]n} have also been reported (ref. 6a).
27 See, for example: R. Romeo, G. Alibrandi and L. M. Scolaro, Inorg.
Chem., 1993, 32, 4688.
3 T. Ishiyama and N. Miyaura, J. Organomet. Chem., 2003, 680, 3 and
references therein.
28 See, for example: (a) R. T. Baker, J. C. Calabrese, S. A. Westcott,
P. Nguyen and T. B. Marder, J. Am. Chem. Soc., 1993, 115, 4367;
(b) R. T. Baker, J. C. Calabrese, S. A. Westcott and T. B. Marder,
J. Am. Chem. Soc., 1995, 117, 8777; (c) Q. Cui, D. G. Musaev and K.
Morokuma, Organometallics, 1997, 16, 1355. For related insertion
reactions of alkynes into M–B bonds see, for example, references
25a,b and c; (d) G. R. Clark, G. J. Irvine, W. R. Roper and L. J.
Wright, Organometallics, 1997, 16, 5499.
29 S. J. Lancaster, S. Al-Benna, M. Thornton-Pett and M. Bochmann,
Organometallics, 2000, 19, 1599.
30 (a) C. J. Cardin, D. J. Cardin and M. F. Lappert, J. Chem. Soc., Dalton
Trans., 1977, 767; (b) A. Ohtaka, H. Kuniyasu, M. Kinomoto and
H. Kurosawa, J. Am. Chem. Soc., 2002, 124, 14324.
31 (a) D. D. Lehman and D. F. Shriver, Inorg. Chem., 1974, 13, 2203;
(b) R. T. Baker, D. W. Ovenall, J. C. Calabrese, S. A. Westcott, N. J.
Taylor, I. D. Williams and T. B. Marder, J. Am. Chem. Soc., 1990,
112, 9399; (c) K. Essalah, J.-C. Barthelat, V. Montiel, S. Lachaize, B.
Donnadieu, B. Chaudret and S. Sabo-Etienne, J. Organomet. Chem.,
2003, 680, 182.
32 K. Burgess, W. A. van der Donk, S. A. Westcott, T. B. Marder, R. T.
Baker and J. C. Calabrese, J. Am. Chem. Soc., 1992, 114, 9350.
33 H. Braunschweig, K. Radacki, F. Seller and G. Whittell,
Organometallics, 2004, 23, 4178.
34 J. F. Hartwig and S. Huber, J. Am. Chem. Soc., 1993, 115, 4908.
35 B. E. R. Schilling, R. Hoffmann and D. Lichtenberger, J. Am. Chem.
Soc., 1979, 101, 585.
36 S. Aldridge, R. J. Calder, A. Rossin, A. A. Dickinson, D. J. Willock,
C. Jones, D. J. Evans, J. W. Steed, M. E. Light and M. B. Hursthouse,
J. Chem. Soc., Dalton Trans., 2002, 2020.
4 (a) W. H. Lam, S. Shimada, A. S. Batsanov, Z. Lin, T. B. Marder,
J. Cowan, J. A. K. Howard, S. A. Mason and G. J. McIntyre,
Organometallics, 2003, 22, 4557; (b) K. C. Lam, W. H. Lam, Z. Lin,
T. B. Marder and N. C. Norman, Inorg. Chem., 2004, 43, 2541 and
references therein.
5 For a preliminary communication of parts of this work see: S.
Aldridge, A. Al-Fawaz, R. J. Calder, A. A. Dickinson, D. J. Willock,
M. E. Light and M. B. Hursthouse, Chem. Commun., 2001, 1846.
6 For recent reviews see: (a) W. E. Piers and T. Chivers, Chem. Soc.
Rev., 1997, 345; (b) T. Chivers, J. Fluorine Chem., 2002, 115, 1.
7 (a) D. J. Parks, R. E. v. H Spence and W. E. Piers, Angew. Chem., Int.
Ed. Engl., 1995, 34, 809; (b) D. J. Parks, W. E. Piers and G. P. A. Yap,
Organometallics, 1998, 17, 5492.
8 For recent examples see: (a) M. Hill, G. Kehr, G. Erker, O. Kataeva
and R. Fro¨hlich, Chem Commun., 2004, 1020; (b) E. F. Van der
Eide, W. E. Piers, P. E. Romero, M. Parvez and R. McDonald,
Organometallics, 2004, 23, 314.
9 C. N. Iverson and M. R. Smith III, J. Am. Chem. Soc., 1999, 121,
7696.
10 (a) R. B. King and M. B. Bisnette, J. Organomet. Chem., 1967, 8, 287;
(b) R. B. King, Acc. Chem. Res., 1970, 3, 417.
11 H. Braunschweig and B. Gante, J. Organomet. Chem., 1997, 545, 163.
12 M. Camalli, F. Caruso, S. Chaloukpa, E. M. Leber, H. Rimml and
L. M. Venanzi, Helv. Chim. Acta, 1990, 73, 2263.
13 J. A. Osborn, F. H. Jardine, J. F. Young and G. Wilkinson, J. Chem.
Soc. A, 1966, 1711.
14 Denzo: Z. Otwinowski and W. Minor, in Methods in Enzymology,
eds. C. W. Carter and R. M. Sweet, Academic Press, New York, 1996,
vol. 276, p. 307.
15 Sir-97: (a) A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano,
C. Giocavazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and
R. Spagna, J. Appl. Crystallogr., 1999, 32, 115; (b) Dirdiff-99: P. T.
Beurskens, G. Peurskens, W. P. Bosman, R. de Gelder, S. Garcia-
Granda, R.O. Gould, R. Israel and J. M. M. Smits, University of
Nijmegen, Netherlands, 1996; (c) G. M. Sheldrick, Acta Crystallogr.,
Sect. A, 1990, 46, 467; (d) Sortav: R. H. Blessing, Acta Crystallogr.,
Sect. A, 1995, 51, 33.
16 T. E. Bitterwolf, K. A. Lott, A. J. Rest and J. Mascetti, J. Organomet.
Chem., 1991, 419, 113.
17 S. Schlecht and J. F. Hartwig, J. Am. Chem. Soc., 2000, 122, 9435.
18 (a) D. T. Rosevear and F. G. A. Stone, J. Chem. Soc., 1965, 5275;
(b) A. J. Mukhedkar, M. Green and F. G. A. Stone, J. Chem. Soc. A,
1970, 947.
37 (a) A. A. Dickinson, D. J. Willock, R. J. Calder and S. Aldridge,
Organometallics, 2002, 21, 1146; (b) S. Aldridge, A. Rossin, D. L.
Coombs and D. J. Willock, Dalton Trans., 2004, 2649.
38 J. Uddin and G. Frenking, J. Am. Chem. Soc., 2001, 123, 1683.
39 W. Conzelmann, J. D. Koola, U. Kunze and J. Stra¨hle, Inorg. Chim.
Acta, 1984, 89, 147.
40 (a) E. B. Bauer, J. Ruwwe, J. M. Mart´ın-Alvarez, T. B. Peters, J. C.
Bohling, F. A. Hampel, S. Szafert, T. Lis and J. A. Gladysz, Chem.
Commun., 2000, 261; (b) E. B. Bauer, F. Hampel and J. A. Gladysz,
Organometallics, 2003, 22, 5567.
41 N. Bresciani-Pahor, M. Plazzotta, L. Randaccio, G. Bruno, V.
Ricevuto, R. Romeo and U. Belluco, Inorg. Chim. Acta, 1978, 31,
171.
42 G. B. Deacon, K. T. Nelson and E. R. T. Tiekink, Acta Crystallogr.,
Sect. C, 1991, 47, 955.
43 H. Jacobsen, H. Berke, S. Do¨ring, G. Kehr, G. Erker, R. Fro¨hlich
and O. Meyer, Organometallics, 1999, 18, 1724.
44 P. Vedrenne, V. Le Guen, L. Toupet, T. Le Gall and C. Mioskowski,
J. Am. Chem. Soc., 1999, 121, 1090.
45 J. C. Huffman, W. A. Skupinski and K. G. Caulton, Cryst. Struct.
Commun., 1982, 11, 1435.
46 V. C. Williams, W. E. Piers, C. Dai, Z. Li, S. Collins, W. Clegg, M. R. J.
Elsegood and T. B. Marder, Angew. Chem., Int. Ed., 1999, 38, 3695.
19 O. J. Scherer, H. Jungmann and K. Hussong, J. Organomet. Chem.,
1983, 247, C1.
20 (a) K. Thomas, J. T. Dumler, B. W. Renoe, C. J. Nyman and D. M.
Roundhill, Inorg. Chem., 1972, 11, 1795; (b) R. G. Goel and R. C.
Srivastava, J. Organomet. Chem., 1983, 244, 303.
21 (a) S. Courtenay and D. W. Stephan, Organometallics, 2001, 20,
1442; (b) A. Rifat, N. J. Patmore, M. F. Mahon and A. S. Weller,
Organometallics, 2002, 21, 2856.
D a l t o n T r a n s . , 2 0 0 4 , 4 0 3 0 – 4 0 3 7
4 0 3 7