The first silyl- and germylboryl complexes: Synthesis from novel (dichloro)silyl- and (dichloro)germylboranes, structure and reactivity

Article abstract of DOI:10.1039/b201100j

A series of silyl- and germyl(dichloro)boranes Cl₂B-ER₃ (5, ER₃ = Si(SiMe₃)₃; 6, ER₃ = Ge(SiMe₃)₃; 7, ER₃ = Si(SiMe₃)₂-Si(SiMe₃)₃; 8, ER₃ = SiPh₃) was obtained in good yields from the corresponding bis(dimethylamino)boranes (Me₂N)₂B-ER₃ (1, ER₃ = Si(SiMe₃)₃; 2, ER₃ = Ge(SiMe₃)₃; 3, ER₃ = Si(SiMe₃)₂-Si(SiMe₃)₃; 4, ER₃ = SiPh₃) upon reaction with BCl₃, and fully characterised in solution. These compounds proved to be versatile starting materials for the synthesis of the first silyl- and germylboryl complexes by salt elimination reactions starting from anionic transition metal complexes of the type Na[(η⁵-C₅R₅)Fe(CO)₂] and K[(η⁵-C₅R₅)-Mn(H)(CO)₂]. The novel iron and manganese boryl complexes [(η⁵-C₅R₄R′)(OC)₂Fe-B(Cl)S i(SiMe₃)₃] (9a, R = R′ = H; 9b, R = H, R′ = Me; 9c, R = R′ = Me), [(η⁵-C₅H₅)(OC)₂Fe-B(Cl)Ge(SiMe ₃)₃] (9d), [(η⁵-C₅H₅)(OC)₂-Fe-B(Cl)Si(SiMe ₃)₂Si(SiMe₃)₃] (9e), [(η⁵-C₅H₄Me)(OC)₂(H)Mn-B(Cl)Si(S iMe₃)₃] (10a) and [(η⁵-C₅H₄Me)(OC)₂-(H)Mn-B(Cl)Ge( SiMe₃)₃] (10b) were obtained in yields between 35 and 70%, fully characterised in solution and in the case of 9a, d, and 10a also in the crystalline state. They are all characterised by metal boron σ-bonds without indication of any metal-to-boron π-backdonation. There is, however, spectroscopical and structural evidence for the presence of a Mn-H-B bridge in the case of the manganese complexes 10a, b. The first transhalogenation of a metal coordinated boryl ligand was achieved by reaction of 9a with TlF affording the fluoroboryl complex [(η⁵-C₅H₅)(OC)₂Fe-B(F)Si(SiMe ₃)₃] (11), which was characterised in solution and in the solid state.

Full text of DOI:10.1039/b201100j

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The first silyl- and germylboryl complexes: synthesis from novel
(dichloro)silyl- and (dichloro)germylboranes, structure and
reactivity
H. Braunschweig,*a M. Colling,b C. Kollann†b and U. Englertb
a Department of Chemistry, Imperial College of Science, Technology, and Medicine,
South Kensington, London, UK SW7 2AY. E-mail: h.braunschweig@ic.ac.uk
b Institut für Anorganische Chemie, RWTH Aachen, Templergraben 55, 52056,
Aachen, Germany
Received 29th January 2002, Accepted 19th March 2002
First published as an Advance Article on the web 30th April 2002
A series of silyl- and germyl(dichloro)boranes Cl2B–ER3 (5, ER3 = Si(SiMe3)3; 6, ER3 = Ge(SiMe3)3;
7, ER3 = Si(SiMe3)2–Si(SiMe3)3; 8, ER3 = SiPh3) was obtained in good yields from the corresponding
bis(dimethylamino)boranes (Me2N)2B–ER3 (1, ER3 = Si(SiMe3)3; 2, ER3 = Ge(SiMe3)3; 3, ER3 = Si(SiMe3)2–
Si(SiMe3)3; 4, ER3 = SiPh3) upon reaction with BCl3, and fully characterised in solution. These compounds proved
to be versatile starting materials for the synthesis of the first silyl- and germylboryl complexes by salt elimination
reactions starting from anionic transition metal complexes of the type Na[(η5-C5R5)Fe(CO)2] and K[(η5-C5R5)-
Mn(H)(CO)2]. The novel iron and manganese boryl complexes [(η5-C5R4RЈ)(OC)2Fe–B(Cl)Si(SiMe3)3] (9a,
R = RЈ = H; 9b, R = H, RЈ = Me; 9c, R = RЈ = Me), [(η5-C5H5)(OC)2Fe–B(Cl)Ge(SiMe3)3] (9d), [(η5-C5H5)(OC)2-
Fe–B(Cl)Si(SiMe3)2Si(SiMe3)3] (9e), [(η5-C5H4Me)(OC)2(H)Mn–B(Cl)Si(SiMe3)3] (10a) and [(η5-C5H4Me)(OC)2-
(H)Mn–B(Cl)Ge(SiMe3)3] (10b) were obtained in yields between 35 and 70%, fully characterised in solution and in
the case of 9a, d, and 10a also in the crystalline state. They are all characterised by metal–boron σ-bonds without
indication of any metal-to-boron π-backdonation. There is, however, spectroscopical and structural evidence for
the presence of a Mn–H–B bridge in the case of the manganese complexes 10a, b. The first transhalogenation of
a metal coordinated boryl ligand was achieved by reaction of 9a with TlF affording the fluoroboryl complex
[(η5-C5H5)(OC)2Fe–B(F)Si(SiMe3)3] (11), which was characterised in solution and in the solid state.
centre is relieved by π-interaction with the boron bound O- or
Introduction
N-donors, thus competing with a possible π-backdonation
from the metal into the pz-orbital at boron. Boryl complexes
LxM–BR2 (R = alkyl, aryl) without ligand-to-boron π-
interaction are very rare, but have received significant interest
in studies, which addressed the nature of the metal–boron
linkage and the role of metal–boron π-interaction in par-
ticular.1,7 Due to the obvious difficulties accompanying the
synthesis of alkyl- and arylboryl complexes, corresponding
silyl- or germylboranes could provide a useful alternative.
With this in mind, we recently communicated on the use of
the bulky (dichloro)silylborane (Me3Si)3SiBCl2 for the synthesis
of the first coordinatively and electronically unsaturated ter-
Over the past decade transition metal complexes of boron have
become established as a novel class of compounds made up by
direct metal–boron interactions. In contrast to the other three
major groups in this area i.e. borides, metallaboranes, and
π-complexes with boron-containing ligands, transition metal
complexes of boron are characterised by electron-precise two-
centre two-electron bonds between boron and the metal centre.
According to this pattern of metal–boron interaction, a variety
of different coordination modes for boron-centred ligands was
realised, allowing for a systematic classification of those com-
pounds into borane, boryl, and borylene complexes.1 The par-
ticular interest in boryl complexes LxM–BR2 is due to their
importance for the functionalisation of hydrocarbons by metal-
catalysed hydroboration of olefins2 and photochemically
induced selective α-borylation of alkanes by C–H activation.3
The phenylene-1,2-dioxo or catechol group as a ligand to
boron has had a pivotal role in establishing these compounds,
and the vast majority of structurally authentic boryl complexes
derive from either catecholborane or dicatecholdiborane(4).1 In
the course of our investigations in this field we reported on a
series of boryl,4 diborane(4)yl,5 and η1-borazine complexes6
which were obtained via salt elimination reactions from anionic
transition metal complexes and amino(halo)boranes. In these
compounds and in the aforementioned catecholboryl com-
plexes, the electron deficiency at the three coordinate boron
minal borylene complex [(OC) Cr᎐B–Si(SiMe ) ].8 In the pres-
᎐
5
3 3
ent paper, we report on full experimental and spectroscopic
details for (Me3Si)3SiBCl2, a series of related new silyl- and
germylboranes, and their facile use as starting materials for the
preparation of the first silyl- and germylboryl complexes.
Experimental
General
All manipulations were carried out under an atmosphere of dry
nitrogen using standard Schlenk techniques, unless otherwise
stated. Solvents and reagents were dried by standard pro-
cedures, distilled and stored under nitrogen over molecular
sieves. (Me2N)2BSi(SiMe3)3,9 Li[Ge(SiMe3)3],10 ClB(NMe2)2,11
K[Si2(SiMe3)5],12 (Me2N)2BSiPh3,13 Na[(η5-C5H5)Fe(CO)2],14
Na[(η5-C5H4Me)Fe(CO)2],14 Na[(η5-C5Me5)Fe(CO)2],14 K[(η5-
C5H4Me)Mn(CO)2H]15 were synthesised according to literature
† Current address: Forschungszentrum Karlsruhe GmbH, Institut
für Technische Chemie, Chemisch-Phykalische Verfahren, D-76201
Karlsruhe, Germany.
DOI: 10.1039/b201100j
J. Chem. Soc., Dalton Trans., 2002, 2289–2296
This journal is © The Royal Society of Chemistry 2002
2289

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procedures. NMR: Varian Unity 500 at 499.834 MHz (1H,
standard TMS internal), 125.639 MHz (11B, standard BF3ؒOEt2
in C6D6 external), 125.639 MHz (13C{1H}, APT, standard TMS
internal), 99.263 MHz (29Si, standard TMS internal); all NMR
spectra were recorded in C6D6 as solvent, unless otherwise
stated. Elemental analyses were obtained from a Carlo-Erba
elemental analyser, model 1106 and IR spectra were recorded
on a Nicolet FT-IR AVATAR 360. Mass spectra were recorded
on a Finnigan MAT 95 (70 eV).
vacuum, the colourless oily residue was dried for 3 h at 50 ЊC
under vacuum. Pure 7 (5.40 g, 94%) was obtained as a colour-
less, air and moisture sensitive oil, which can be strored at
1
Ϫ30 ЊC. H-NMR (CDCl3): δ = 0.28 (s, 27 H, Si{Si(CH3)3}3),
0.33 (s, 18 H, Si{Si(CH3)3}2); 11B-NMR: δ = 79.7; 13C-NMR:
δ = 3.27 (Si{Si(CH3)3}2), 3.68 (Si{Si(CH3)3}3), 29Si-NMR:
δ = Ϫ9.04 (Si{Si(CH3)3}3), Ϫ9.59 (Si{Si(CH3)3}2), Ϫ104.76
(BSi{Si(CH3)3}2), Ϫ126.19 (Si{Si(CH3)3}3). C15H45BCl2Si7
(503.84): found C 35.36, H 8.72; requires C 35.76, H 9.00%.
Dichloro(triphenylsilyl)borane (8). As described for 5,
bis(dimethylamino)(triphenylsilyl)borane (4) (20.38 g, 51.75
mmol) was treated with BCl3 (18.19 g, 155.25 mmol, threefold
excess). After removing all volatiles under vacuum, the brown
oily residue was prepurified by condensation at 100 ЊC in high
vacuum into a cooled trap (Ϫ78 ЊC). The colourless crude
material, which is a 1 : 1 mixture of 8 and (Me2N)2BCl, is
distilled under vacuum affording pure 8 (8.41 g, 48%) at 54 ЊC/
14 mbar as a colourless, air and moisture sensitive liquid.
1H-NMR (CDCl3): δ = 7.50 (m, 6 H, m-C6H5), 7.68 (m, 3 H,
p-C6H5), 8.17 (m, 6 H, o-C6H5); 11B-NMR: δ = 55.5; 13C-NMR:
δ = 128.14 (m-C6H5), 135.07 (p-C6H5), 136.86 (o-C6H5).
C18H15BCl2Si (341.11): found C 63.36, H 4.23; requires C 63.38,
H 4.43%.
Syntheses
Bis(dimethylamino){tris(trimethylsilyl)germyl}borane
(2).
Li[Ge(SiMe3)3] (13.94 g, 27.00 mmol) was dissolved in 125 ml
of hexane at Ϫ78 ЊC. ClB(NMe2)2 (3.63 g, 27.00 mmol) was
added dropwise within 10 min. The white suspension was
allowed to come to ambient temperature within 2 h and stirred
overnight. The suspension was filtered and the colourless solid
rinsed twice with 30 ml of hexane. All volatiles of the bright
yellow filtrate were removed under vacuum and pure 2 (10.27 g,
97%) was obtained as a bright yellow, air and moisture sensitive
solid, which can be stored at Ϫ30 ЊC. 1H-NMR (CDCl3):
δ = 0.23 (s, 27 H, Ge{Si(CH3)3}3), 2.70 (s, 12 H, 2 N(CH3)2);
11B-NMR: δ = 39.3; 13C-NMR: δ = 3.28 (Ge{Si(CH3)3}3), 42.38
(N(CH3)2). C13H39BN2GeSi3 (391.13): found C 39.55, H 9.82,
N 6.85; requires C 39.92, H 10.05, N 7.16%.
[Chloro{tris(trimethylsilyl)silyl}boryl]dicarbonyl(ꢀ5-cyclo-
pentadienyl)iron (9a). Na[(η5-C5H5)Fe(CO)2] (1.15 g, 5.7 mmol)
was suspended in 30 ml of toluene at 0 ЊC. A solution of 3
(1.90 g, 5.77 mmol) in 10 ml of toluene was added dropwise
within 10 min. After stirring for another 5 min at 0 ЊC all
volatiles were removed under vacuum. The red–brown residue
was suspended in 30 ml of hexane and the mixture was centri-
fuged. The clear, red–brown solution was decanted from the
light solid, concentrated under vacuum to 10 ml and stored at
Ϫ80 ЊC. After 24 h pure 9a (1.87 g, 69%) was obtained as
yellow, air and moisture sensitive crystals, which have to be
Bis(dimethylamino){pentakis(trimethylsilyl)disilyl}borane (3).
As described for 2, K[Si2(SiMe3)5] (13.05 g, 21.59 mmol) was
treated with ClB(NMe2)2 (2.76 g, 20.54 mmol). After filtration,
the filtrate was concentrated under vacuum to 20 ml and stored
at Ϫ80 ЊC for 3 d. Pure 3 (5.93 g, 53%) was obtained as a
colourless, air and moisture sensitive solid, which can be stored
at Ϫ30 ЊC. 1H-NMR (CDCl3): δ = 0.23 (s, 27 H, Si{Si(CH3)3}3),
0.27 (s, 18 H, Si{Si(CH3)3}2), 2.67 (s, 12 H, 2 N(CH3)2);
11B-NMR: δ = 38.9; 13C-NMR: δ = 4.22 (Si{Si(CH3)3}3), 5.18
(Si{Si(CH3)3}2), 42.98 (N(CH3)2). C19H57BN2Si7 (521.09): found
C 43.11, H 10.41, N 5.29; requires C 43.79, H 11.03, N 5.38%.
1
stored at Ϫ30 ЊC. H-NMR: δ = 0.40 (s, 27 H, Si(CH3)3), 4.12
(s, 5 H, C5H5); 11B-NMR: δ = 141.2; 13C-NMR: δ = 3.18 (Si-
(CH3)3), 85.43 (C5H5), 213.69 (CO). IR (toluene): ν = 2009, 1956
cmϪ1 (CO). C16H32BClFeO2Si4 (470.88): found C 40.08, H
7.08; requires C 40.81, H 6.85%. MS m/z = 470 (Mϩ), 455
Dichloro{tris(trimethylsilyl)silyl}borane (5). Bis(dimethyl-
amino){tris(trimethylsilyl)silyl}borane (1) (5.80 g, 16.73 mmol)
was dissolved in 70 ml of hexane at Ϫ78 ЊC. A solution of BCl3
(3.92 g, 33.46 mmol) in 10 ml hexane was added dropwise
within 10 min. The white suspension was allowed to come
to ambient temperature within 2 h and was stirred over-
night. All volatiles of the bright yellow, clear solution were
removed under vacuum and the colourless residue was sub-
limed at 60 ЊC/0.001 Torr into a cold sublimation tube
(Ϫ78 ЊC). Pure 5 (4.93 g, 89.5%) was obtained as a colourless,
air and moisture sensitive solid, which can be stored at Ϫ30 ЊC.
1H-NMR (CDCl3): δ = 0.27 (s, 27 H, Si{Si(CH3)3}3); 11B-NMR:
δ = 79.2; 13C-NMR: δ = 1.9 (Ge{Si(CH3)3}3). C9H27BCl2Si4
(329.38): found C 32.43, H 8.67; requires C 32.82, H 8.26%.
(Mϩ Ϫ CH3), 442 (Mϩ Ϫ CO), 414 (Mϩ Ϫ 2CO), 427 (Mϩ
CH3 Ϫ CO), 73 (SiMe3).
Ϫ
[Chloro{tris(trimethylsilyl)silyl}boryl]dicarbonyl(ꢀ5-methyl-
cyclopentadienyl)iron (9b). As described for 9a, Na[(η5-C5H4-
Me)Fe(CO)2] (0.56 g, 2.62 mmol) was treated with 3 (0.86 g,
2.62 mmol). After decantation all volatiles were removed under
vacuum and almost pure 9b (0.64 g, 50%) was obtained as a
brown, air and moisture sensitive oil, which has to be stored at
1
Ϫ30 ЊC. H-NMR: δ = 0.41 (s, 27 H, Si(CH3)3), 1.49 (s, 3 H,
C5H4CH3), 4.09 (s, 4 H, C5H4CH3); 11B-NMR: δ = 140.1;
13C-NMR: δ = 3.26 (Si(CH3)3), 12.74 (C5H4CH3), 84.74, 86.01
(C5H4CH3), 103.06 (ipso-C, C5H4CH3), 214.15 (CO). IR
(toluene): ν = 2008, 1957 cmϪ1 (CO). C17H34BClFeO2Si4
(484.91): found C 43.78, H 6.98; requires C 42.11, H 7.07%.
Dichloro{tris(trimethylsilyl)germyl}borane (6). As described
for 5, bis(dimethylamino){tris(trimethylsilyl)germyl}borane (2)
(10.27 g, 26.26 mmol) was treated with BCl3 (6.77 g, 57.78
mmol, 10% excess). After removing all volatiles under vacuum
the bright yellow residue was dried for 3 h at ambient temper-
ature under vacuum. Pure 6 (9.52 g, 97%) was obtained as a
bright yellow, extremely air and moisture sensitive, pyrophoric
[Chloro{tris(trimethylsilyl)silyl}boryl]dicarbonyl(ꢀ5-penta-
methylcyclopentadienyl)iron (9c). As described for 9a, Na-
[(η5-C5Me5)Fe(CO)2] (0.50 g, 1.85 mmol) was treated with 3
(0.61 g, 1.85 mmol). Pure 9c (0.52 g, 52%) was obtained as
brown–yellow, air and moisture sensitive crystals, which have to
be stored at Ϫ30 ЊC. 1H-NMR: δ = 0.49 (s, 27 H, Si(CH3)3), 1.49
(s, 15 H, C5(CH3)5); 11B-NMR: δ = 138.9; 13C-NMR: δ = 3.59
(Si(CH3)3), 9.91 (C5(CH3)5), 97.18 (C5(CH3)5), 215.89 (CO).
IR (toluene): ν = 1990, 1939 cmϪ1 (CO). C21H42BClFeO2Si4
(541.02): found C 46.54, H 8.05; requires C 46.62, H 7.83%.
1
solid, which can be stored at Ϫ30 ЊC. H-NMR (CDCl3): δ =
0.30 (s, 27 H, Ge{Si(CH3)3}3); 11B-NMR: δ = 80.0; 13C-NMR:
δ = 2.46 (Ge{Si(CH3)3}3). C9H27BCl2GeSi3 (373.88): found
C 28.55, H 6.94; requires C 28.91, H 7.28%.
Dichloro{pentakis(trimethylsilyl)disilyl}borane (7). As des-
cribed for 5, bis(dimethylamino){pentakis(trimethylsilyl)disilyl}-
borane (3) (5.93 g, 11.40 mmol) was treated with BCl3 (2.94 g,
25.10 mmol, 10% excess). After removing all volatiles under
[Chloro{tris(trimethylsilyl)germyl}boryl]dicarbonyl(ꢀ5-cyclo-
pentadienyl)iron (9d). As described for 9a, Na[(η5-C5H5)-
Fe(CO)2] (0.49 g, 2.43 mmol) was treated with 4 (0.91 g,
2290
J. Chem. Soc., Dalton Trans., 2002, 2289–2296

View Article Online
2.43 mmol). Pure 9d (0.44 g, 35%) was obtained as brown–
yellow, extremely air and moisture sensitive crystals, which
have to be stored at Ϫ30 ЊC. 1H-NMR: δ = 0.42 (s, 27 H,
Ge{Si(CH3)3}3), 4.14 (s, 5 H, C5H5); 11B-NMR: δ = 139.0;
13C-NMR: δ = 3.73 (Ge{Si(CH3)3}3), 85.56 (C5H5), 213.65
(CO). IR (toluene): ν = 2009, 1956 cmϪ1(CO). C16H32BClFe-
GeO2Si3 (515.38): found C 37.08, H 6.12; requires C 37.29,
H 6.26%.
(CO). IR (toluene): ν = 2001, 1946 cmϪ1 (CO). MS m/z = 454
(Mϩ, 2%), 426 (Mϩ Ϫ CO, 26%), 398 (Mϩ Ϫ 2CO, <1%), 325
(Mϩ Ϫ SiMe3–CO, 8%), 277 (FBSi{SiMe3}3, 18%), 121 (CpFe,
38%), 73 (SiMe3, 71%). C16H32BFFeO2Si4 (454.43): found
C 42.01, H 6.90; requires C 42.29, H 7.10%.
X-Ray crystallography
Geometry and intensity data were collected on an ENRAF
Nonius CAD4 diffractometer using Mo-Kα radiation (λ =
0.7107 Å). Crystal data, data collection parameters, and con-
vergence results are compiled in Table 1. All crystals studied
were platelets sensitive to air and moisture and showed rel-
atively broad reflections. In the case of 9d crystal faces were
difficult to index and an empirical absorption correction16 was
applied. For the remaining crystals absorption corrections were
based on Gaussian integration.17 The structures were solved by
direct methods18 and refined on F 2 19 with hydrogen atoms in
calculated positions. For 10a only the Mn, Cl, and Si atoms
have been refined anisotropically. Displacement ellipsoid plots
were obtained with PLATON94.20
[Chloro{pentakis(trimethylsilyl)disilyl}boryl]dicarbonyl(ꢀ5-
cyclopentadienyl)iron (9e). As described for 9a, Na[(η5-C5H5)-
Fe(CO)2] (0.40 g, 2.00 mmol) was treated with 6 (1.00 g,
2.00 mmol). After decantation all volatiles were removed under
vacuum and almost pure 9e (0.42 g, 35%) was obtained as a
brown, extremely air and moisture sensitive oil, which has to be
stored at Ϫ30 ЊC for longer periods. 1H-NMR: δ = 0.38 (m, br,
45 H, Si(CH3)3), 4.18 (s, br, 5 H, C5H5); 11B-NMR: δ = 141.2;
13C-NMR: δ = 4.02 (Si{Si(CH3)3}2), 4.24 (Si{Si(CH3)3}3), 85.67
(C5H5), 214.25 (CO). IR (toluene): ν = 2007, 1956 cmϪ1 (CO).
C22H50BClFeO2Si7 (645.35): found C 39.88, H 7.12; requires
C 40.95, H 7.81%.
CCDC reference numbers 178620–178623.
See http://www.rsc.org/suppdata/dt/b2/b201100j/ for crystal-
lographic data in CIF or other electronic format.
[Chloro{tris(trimethylsilyl)silyl}boryl]dicarbonyl(ꢀ5-methyl-
cyclopentadienyl)hydrido-manganese (10a). K[(η5-C5H4Me)Mn-
(CO)2H] (0.86 g, 3.74 mmol) was suspended in 20 ml of toluene
at 0 ЊC. A solution of 3 (1.23 g, 3.74 mmol) in 5 ml of toluene
was added in one gush to the yellow suspension; after that the
colour changed spontaneously from yellow to dark red. After
stirring for 5 min at 0 ЊC all volatiles were removed under
vacuum, the red, oily residue was suspended in 25 ml of hexane
and centrifuged. The red solution was decanted from the lightly
yellow solid and concentrated under vacuum to 10 ml. After
storage at Ϫ80 ЊC for 7 d pure 10a (1.21 g, 67%) was obtained as
red, air and moisture sensitive crystals, which can be stored at
Ϫ30 ЊC. 1H-NMR: δ = Ϫ15.32 (br. s, 1 H, Mn-H), 0.48 (s, 27 H,
Si{Si(CH3)3}3), 1.37 (s, 3 H, C5H4CH3), 4.04–4.17 (m, 4 H,
C5H4CH3); 11B-NMR: δ = 105.2 (br. s); 13C-NMR: δ = 2.01
(Si{Si(CH3)3}3), 12.76 (C5H4CH3), 87.5–87.7 (C5H4CH3),
105.82 (ipso-C, C5H4CH3), 211.73 (CO). IR (toluene): ν = 1978,
1913 cmϪ1 (CO). C17H35BClMnO2Si4 (485.01): found C 40.97,
H 7.56; requires C 42.10, H 7.24%.
Results and discussion
(Dichloro)silyl- and -germylboranes
In view of the synthesis of boryl complexes via salt elimination
reactions from anionic transition metal complexes and halo-
boranes, the use of borane precursors of the type R3E-BCl2
(E = Si, Ge) appears to be advantageous. Silyl and germyl sub-
stituents do not compensate for the electron deficiency of the
boron atom, thus providing a strongly electrophilic centre for
the addition of an anionic transition metal species. Besides,
extremely bulky groups such as Si(SiMe3
)
3
and Ge(SiMe3)3
should provide sufficient sterical shielding to stabilise the target
boryl complexes.
As attempts to obtain the compounds R3
E-BCl (E = Si, Ge)
2
in useful yields and on a sufficient scale by direct reaction of
M[ER3] (M = Li, K) with BCl3 failed, we applied the stepwise
procedure outlined in Scheme 1.
[Chloro{tris(trimethylsilyl)germyl}boryl]dicarbonyl(ꢀ5-
methylcyclopentadienyl)hydrido-manganese (10b). As described
for 10a, K[(η5-C5H4Me)Mn(CO)2H] (0.35 g, 1.52 mmol) was
treated with 4 (0.57 g, 1.52 mmol). After storage at Ϫ80 ЊC for
2 d pure 10b (0.31 g, 38%) was obtained as red crystals, which
deliquesce above Ϫ30 ЊC into a red, extremely air and moisture
1
sensitive oil. H-NMR: δ = Ϫ15.03 (br. s, 1 H, Mn-H), 0.51 (s,
27 H, Ge{Si(CH3)3}3), 1.39 (s, 3 H, C5H4CH3), 4.05–4.16 (kB,
4 H, C5H4CH3); 11B-NMR: δ = 105.8 (br. s); 13C-NMR: δ = 3.37
(Ge{Si(CH3)3}3), 12.76 (C5H4CH3), 87.29–87.52 (C5H4CH3),
105.54 (ipso-C, C5H4CH3). IR (toluene): ν = 1975, 1914 cmϪ1
(CO). C17H35BClGeMnO2Si3 (529.51): found C 37.97, H 6.48;
requires C 38.56, H 6.66%.
[Fluoro{tris(trimethylsilyl)silyl}boryl]dicarbonyl(ꢀ5-cyclo-
pentadienyl)iron (11). 9a (1.87 g, 3.97 mmol) was dissolved in
30 ml of CH2Cl2 and TlF (1.33 g, 5.96 mmol, 50% excess) were
added at ambient temperature. The reaction mixture was stirred
for 24 h and all volatiles were removed under vacuum. The
brown–red residue was suspended in 30 ml of hexane, centri-
fuged and the brown–red solution was decanted from the light
brown solid. After reducing to 5 ml under vacuum 5 ml of
perfluorohexane were added and the two phase mixture was
stored at Ϫ80 ЊC for 4 d. 11 (0.83 g, 46%) was obtained as
yellow, extremely air and moisture sensitive crystals growing at
Scheme 1
Similar to the reported preparation of (Me2N)2B–Si(SiMe3)3
(1)9 and (Me2N)2B–SiPh3(3)13 the bis(dimethylamino) boranes
(Me2N)2B–Ge(SiMe3)3 (2) and (Me2N)2B–Si(SiMe3)2–Si(Si-
Me3)3 (4) were obtained from the reaction of M[ER3] with
(Me2N)2B–Cl. The boranes 1–4 were subsequently treated with
two equivalents of BCl3, thus affording the corresponding
dichloroboranes Cl2B–ER3 (5, ER3 = Si(SiMe3)3; 6, ER3 = Ge-
1
the interface of the two solvents. H-NMR: δ = 0.39 (s, 27 H,
1
Si(CH3)3), 4.15 (s, 5 H, C5H5); 11B-NMR: δ = 113.2 (d, JBF
=
232 Hz); 13C-NMR: δ = 2.93 (Si(CH3)3), 84.35 (C5H5), 214.19
J. Chem. Soc., Dalton Trans., 2002, 2289–2296
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Table 1 Crystal data for 9a, 9d, 10a and 11
9a
9d
10a
11
Empirical formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
C16H32BClFeO2Si4
C16H32BClFeGeO2Si3
515.39
C17H35BClMnO2Si4
485.01
Monoclinic
C2/c (15)
34.35(2)
9.268(9)
17.00(2)
90
C16H32BFFeO2Si4
454.43
Monoclinic
C2/c (15)
16.782(5)
9.611(3)
31.15(1)
90
470.89
Monoclinic
P21/c (14)
17.262(5)
9.403(2)
16.525(5)
90
Monoclinic
P21/c (14)
17.320(4)
9.425(2)
16.572(3)
90
β/Њ
106.72(2)
90
2569(1)
4
106.53(2)
90
2594(1)
4
100.94(5)
90
5312(9)
8
94.84(3)
90
5006(3)
8
γ/Њ
V/Å3
Z
µ/mmϪ1
0.882
1.950
0.765
0.803
Reflections measured
Independent reflections
Final R1 [I > 2σ(I )]
wR2 (all data)
GOF
14960
5031
0.0793
0.1649
0.905
12034
5105
0.0851
0.1925
11192
4687
0.1145
0.2245
0.894
10134
4894
0.0940
0.1981
1.134
0.969
(SiMe3)3; 7, ER3 = Si(SiMe3)2–Si(SiMe3)3; 8, ER3 = SiPh3) in
useful yields after removal of the accompanying two equiv-
alents of (Me2N)BCl2 under high vacuum.
carbons, are moderately air and moisture sensitive, and can be
stored at temperatures below Ϫ30 ЊC without significant
decomposition.
The new germyl borane (Me2N)2B–Ge(SiMe3)3 (2) was
obtained in almost quantitative yield (>97%) as a bright yellow
solid after filtration and evaporation of the reaction mixture. In
the case of (Me2N)2B–Si(SiMe3)2–Si(SiMe3)3 (4), however, the
crude solid material being obtained after removal of all volatile
materials under high vacuum, had to be recrystallised from
hexane at Ϫ80 ЊC giving 53% of the product as a colourless
solid.
Both compounds were characterised in solution by multi-
nuclear NMR spectroscopy and displayed the expected shifts
such as 11B NMR resonances at δ = 39.3 (2) and 38.9 (4).
The dichloroboranes 5 and 6 were obtained in high yields of
90–97% as colourless solids, while 7 was isolated as a colourless,
viscous oil in a similarly good yield of 94%. Due to its higher
volatility with respect to those of 5–7, the phenyl derivative
Cl2B–SiPh3 (8) had to be separated by fractionated distillation
at elevated temperatures from the accompanying (Me2N)BCl2,
thus accounting for a lower yield of 48%. All dichloroboranes,
and the triphenylsilyl derivative 8 in particular, proved to be
extremely sensitive towards air and moisture and thermally
rather labile, but can be stored neat or in solution at temper-
atures below Ϫ30 ЊC for prolonged periods of time without
decomposition.
A corresponding reaction of the anionic manganese complex
K[(η5-C5H4Me)Mn(CO)2H] with Cl2B–Si(SiMe3)3 (5) and
Cl2B–Ge(SiMe3)3 (6) in a 1 : 1 ratio at 0 ЊC in toluene afforded
the silyl- and germylboryl complexes [(η5-C5H4Me)(OC)2(H)-
Mn–B(Cl)Si(SiMe3)3] (10a) and [(η5-C5H4Me)(OC)2(H)Mn–
B(Cl)Ge(SiMe3)3] (10b) in yields of 67% and 38%, respectively,
according to Scheme 3.
The products 10a, b were obtained as dark red, air and mois-
ture sensitive crystals from hexane solutions at Ϫ30 ЊC, which
in the case of 10b melt into a red oil above this temperature.
Both complexes are stable under nitrogen and can be stored at
Ϫ30 ЊC without degradation. In the case of Cl2B–Si(SiMe3)2–
Si(SiMe3)3 (7) no reaction was observed with K[(η5-C5H4Me)-
Mn(CO)2H] – obviously due to the increased sterical shielding
of the borane and the decreased nucleophilicity of the man-
ganese complex with respect to its iron analogue. Attempts to
obtain the corresponding (triphenylsilyl)boryl complexes from
the reactions of Cl2B–SiPh3 (8) with Na[(η5-C5H5)Fe(CO)2] or
K[(η5-C5H4Me)Mn(CO)2H] under identical conditions resulted
in the formation of intractable, viscous liquids, which are
extremely sensitive towards air and moisture, and readily
decompose in hexane or toluene solution. The presence of
the target molecules [(η5-(C5H5)(OC)2Fe–B(Cl)SiPh3] (9f ) and
[(η5-C5H4Me)(OC)2(H)Mn–B(Cl)SiPh3] (10c), however, can be
deduced from characteristic spectroscopic data (vide infra) such
as the deshielded 11B NMR shifts at δ = 109.2 (9f ) and 81.3
The multinuclear NMR data of 5–8 in solution meet the
expectations, showing for example considerably deshielded 11B
NMR resonances with respect to those of the aminoborane
precursors at δ = 79.2 (5), 80.0 (6), 79.7 (7) and at δ = 55.5 (8).
The smaller boranes 5, 6, and 8 display single sets of signals for
1
(10c), and the shielded H NMR resonance for the manganese
bound hydrogen atom at δ = Ϫ15.9 in the case of the latter. The
enhanced sensitivity of Cl2B–SiPh3 (8) and the boryl complexes
9f and 10c with respect to all other compounds discussed here,
is supposed to be solely due to the lesser sterical shielding by the
phenyl groups. The presence of β-silyl groups in the boranes 1–
4, 5–8 and the complexes 9a–e, 10a, b could also account for
their increased stability with respect to that of the correspond-
ing phenyl derivatives 8, 9f, and 10c, as a β-silyl effect is well
known to stabilise electron deficient boron centres by formation
of non-classical three-centre two-electron bonds (hyperconjug-
ation) with adjacent silyl groups – there is, however, no
indication of the characteristic spectroscopical and structural
features of this effect (vide infra).21
1
the ER3-ligand in the H and 13C NMR spectra, thus proving
free rotation with respect to the B–E bond in solution. Cl2B–
Si(SiMe3)2–Si(SiMe3)3 (7) shows the expected two sets of signals
in a 2 : 3 ratio for the two different sets of SiMe3-ligands in the
1H, 13C, and 29Si NMR spectra.
Silyl- and germylboryl complexes of iron and manganese
Synthesis. A range of new iron boryl complexes was obtained
from the reaction of the boranes 5–7 with the strongly nucleo-
philic anionic iron complexes Na[(η5-C5R4RЈ)Fe(CO)2] (R, RЈ =
H, Me) in toluene at 0 ЊC according to Scheme 2 via salt elimin-
ation. The compounds [(η5-C5R4RЈ)(OC)2Fe–B(Cl)Si(SiMe3)3]
(9a, R = RЈ = H; 9b, R = H, RЈ = Me; 9c, R = RЈ = Me),
[(η5-C5H5)(OC)2Fe–B(Cl)Ge(SiMe3)3] (9d), and [(η5-C5H5)-
(OC)2Fe–B(Cl)Si(SiMe3)2–Si(SiMe3)3] (9e) were afforded in
yields between 35–69% as yellow or brown crystals in the case
of 9a, c, d or viscous liquids in the case of 9b, e. All complexes
readily dissolve in all common aliphatic and aromatic hydro-
Structure. Iron complexes. The structure of the boryl iron
complexes 9a–e in solution was derived from multinuclear
NMR and IR data (Table 2). All complexes show significantly
deshielded 11B NMR signals ranging from δ = 138.9 to 141.2.
The observed resonances are low-field shifted by approximately
2292
J. Chem. Soc., Dalton Trans., 2002, 2289–2296

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Table 2 Selected spectroscopic and structural data for 9a–e, 10a, b and 11
9a
9b
9c
9d
9e
10a
10b
11
δ11B
141.2
140.1
2008, 1957
—
138.9
1990, 1939
—
139.0
141.2
2007, 1956
—
105.2
105.8
1975, 1914
—
113.2
νCO/cmϪ1
dM–B/Å
dB–E/Å
2009, 1956
1.964(8)
2.030(8)
2009, 1956
1.985(11)
2.063(12)
1978, 1913
2.138(16)
2.052(16)
2001, 1946
1.983(9)
2.046(10)
Scheme 2
Scheme 3
20 ppm with respect to the diphenylboryl complex [(η5-
C5H5)(OC)2Fe–BPh2]22 and by even 80 ppm with respect to
aminoboryl complexes of the type [(η5-(C5H5)(OC)2Fe–B(X)-
NR2],4,5,6 thus being in the expected range for a metal coordin-
ated boryl ligand without π-donating substituents. The 1H- and
13C NMR spectra are unobtrusive and exhibit the expected sig-
nals for the SiMe3 groups and η5-C5R5 ligands. All complexes
show two CO stretching frequencies in the IR spectra, which
in the case of 9a, b, d, e were found at 2008–9 cmϪ1 and
1956–7 cmϪ1, thus being in the range of corresponding
The iron–boron distances were found to be 196.4(8) pm
(9a) and 198.5(11) pm (9d), thus being somewhat smaller than
in the amino boryl complex [(η5-C5Me5)(OC)2Fe–B(Cl)NMe2]
(202.7(5) pm),4 but still close to the sum of the covalent radii for
iron and boron.
A structural indication for the presence of a stabilising β-silyl
or hyperconjugative effect would be a significant distortion
i.e. reduction of the B–E–Si angles.21 In the case of 9a, d,
however, all corresponding angles range from 107 to 119Њ, and
the overall geometry of the E(SiMe3)3 moieties resembles that
aminoboryl (ν = 2000–2005, 1940–1946 cmϪ1
)
,
4,5,6 and alkyl iron
but red shifted
of the Si(SiMe ) ligand in [(OC) Cr᎐B–Si(SiMe ) ] for which
᎐
3
3
5
3 3
complexes (ν = 1999–2005, 1938–1944 cmϪ1 23
a hyperconjugation was ruled out on the basis of DFT
calculations.8
with respect to the related catecholboryl complex [(η5-C5H5)-
(OC)2FeBCat] (ν = 2024, 1971 cmϪ1), for which an albeit weak
iron–boron π-bond was established.22 The permethylated
cyclopentadienyl ligand in 9c causes the expected redshift with
respect to 9a, b, d, e and the CO stretching frequencies at ν =
1990 cmϪ1 and 1939 cmϪ1 match those of its amino counterpart
[η5-C5Me5(OC)2Fe–B(Cl)NMe2] (ν = 1988 cmϪ1, 1928 cmϪ1).4
These findings clearly indicate the absence of any iron–boron
π-backdonation in solution.1
Manganese complexes
The manganese boryl complexes [(η5-C5H4Me)(OC)2(H)Mn–
B(Cl)Si(SiMe3)3] (10a) and [(η5-C5H4Me)(OC)2(H)Mn–B(Cl)-
Ge(SiMe3)3] (10b) were characterised in solution by multinuclear
NMR and IR spectroscopy (Table 2). The CO stretching
frequencies at 1975–8 cmϪ1 and 1913–4 cmϪ1 match those of the
corresponding dihydride complex [(η5-C5H5)(OC)2Mn(H)2]
(1972, 1910 cmϪ1),24 thus indicating a manganese–boron
σ-bond without π-contribution. The SiMe3 groups and η5-C5R5
In the case of 9a and d suitable crystals for X-ray structure
analyses were obtained from hexane solutions at Ϫ30 ЊC within
several days. The compounds are isostructural, crystallise in
the monoclinic space group P21/c, and the molecules adopt
C1-symmetry in the solid state (Fig. 1). In both cases the plane
defined by Si(1)–B–Cl and Ge–B–Cl is almost orthogonal with
respect to the plane defined by Fe–B–Cpm (Cpm = centre point
of the cyclopentadienyl ring). This particular conformation in
the crystal has been already established for [(η5-(C5H5)(OC)2-
Fe–BPh2]22 andcomplexesofthetype[(η5-(C5H5)(OC)2Fe–B(X)-
NR2],4,5,6 and does not allow for π-backdonation from the
metal-like aЉ symmetrical HOMO into the vacant pz-orbital at
boron (Fig. 2).
1
ligands show the expected signals in the H- and 13C NMR
spectra, and for the metal coordinated boron centres deshielded
resonances at δ = 105.2 (10a) and 105.8 (10b) are detected in
the 11B NMR spectra. Although these signals are fairly low-
field shifted the effect of deshielding is less pronounced than in
the corresponding iron complexes 9a–e, thus indicating the
presence of a Mn–H–B bridge in solution and an increased
coordination number of the boron atoms. A corresponding
Mn–H–Si bridge is known for the corresponding silyl hydride
complexes [(η5-C5H5)(OC)2(H)MnSiR3].25 Similar interactions
J. Chem. Soc., Dalton Trans., 2002, 2289–2296
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Fig. 3 Mn–H resonance of 10a in boron coupled (1H-) and boron
decoupled (1H{11B}-) NMR spectra.
Fig. 4 X-Ray crystal structure of 10a with idealised position of the
manganese bound hydrogen atom. Selected bond lengths (Å): Mn–B
2.138(16), B–Si(1) 2.052(16).
Fig. 1 X-Ray crystal structure of 9a (left) and 9d (right). Selected
bond lengths (Å) and angles (Њ): 9a: Fe–B 1.964(8), B–Si(1) 2.030(8),
Si(1)–Si(2) 2.342(3), Si(1)–Si(3) 2.355(3), Si(1)–Si(4) 2.356(3), B–Si(1)–
Si(2) 118.6(2), B–Si(1)–Si(3) 107.2(2), B–Si(1)–Si(4) 107.7(2); 9d: Fe–B
1.985(11), B–Ge(1) 2.063(12), Ge(1)–Si(3) 2.389(3), Ge(1)–Si(2)
2.378(3), Ge–Si(4) 2.384(3), B–Ge(1)–Si(3) 106.9(3), B–Ge(1)–Si(2)
118.5(3), B–Ge(1)–Si(4) 107.8(3).
manganese–boron distance of 213.8(16) pm is considerably
greater than that of a related catecholboryl manganese complex
[(OC)5Mn–BCat]27 (210.8(6) pm) and those in the bridged
borylene complex [µ-B(NMe2){(η5-C5H4Me)Mn(CO)2}2]28
(203(1) pm), both of which are described as manganese–boron
σ-bonds.
The elongated metal–boron bond indicates the presence of
the Mn–H–B bridge in the crystal, too. However, due to broad,
particularly overlapping reflexes of the crystals, the quality of
the results and especially of the refinement is significantly
reduced, and hence, the exact position of the hydrogen atom
could not be determined from the X-ray structure analysis.
Fig. 2 Orbital mismatch in boryl iron complexes [(η5-C5H5)(OC)2Fe–
B(Cl)E(SiMe3)3] (E = Si, Ge) (9a, d): possible orbital interaction (left)
and schematic structure (right).
Reactivity. Both experimental and theoretical investigations
have shown that the strength of a metal–boron bond in boryl
complexes with respect to homolytic dissociation may well
exceed that of a metal–carbon bond in alkyl complexes.29 Des-
pite their thermodynamic stability, however, boryl complexes
tend to react with facile cleavage of the metal–boron bond, thus
giving evidence for their kinetic lability.1 As a consequence,
there is only limited information on substitution reactions at
boryl centres with retention of the metal–boron bond.30
The reaction of the silylboryl complex [(η5-C5H5)(OC)2-
Fe–B(Cl)Si(SiMe3)3] (9a) with a 50% excess of TlF in CH2Cl2
at ambient temperature afforded the fluorinated silylboryl
complex [(η5-C5H5)(OC)2Fe–B(F)Si(SiMe3)3] (11) according to
Scheme 4. As monitored by 11B NMR spectroscopy, the trans-
halogenation was completed after 24 h and not accompanied
by formation of any other boron-containing side products.
Complex 11 was isolated from a 1 : 1 mixture of hexane–
perfluorohexane at Ϫ80 ЊC as a yellow, crystalline material in
46% yield.
between boron and hydrogen co-ligands were reported for boryl
complexes of early transition metals such as [(η5-C5H5)2NbH2-
(BR2)] and are known to be more pronounced in cases of elec-
tron poor boron atoms i.e. boryl groups without π-donating
substituents.26 The presence of a Mn–H–B bridge in solution is
also indicated by the different line widths of the Mn–H reson-
ance at δ = Ϫ15.3 in the 1H- and 1H{11B}-NMR spectra (Fig. 3),
which were determined to be 15 and 5 Hz, respectively. In the
proton coupled 11B NMR spectra only broad singlets rather
than the expected doublets were observed, which is, however, in
accordance with earlier spectroscopic findings for related boryl
complexes.26
Suitable crystals of 10a for a X-ray structure analysis were
obtained after several days from hexane solution at Ϫ30 ЊC.
The complex crystallises in the monoclinic space group C2/c
and the molecule adopts C1-symmetry in the crystal (Fig. 4).
The two planes being defined by Si(1)–B–Cl and B–Mn–Cpm
slightly deviate by 9.2Њ from the coplanar arrangement. The
Neither the corresponding germylboryl complex 9d nor the
silylboryl manganese complex 10a displayed a comparable
2294
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Conclusion
The present study is concerned with a series of new silyl- and
germylboranes and provides insight into their reactivity
towards transition metal complexes of the type Na[(η5-C5R4RЈ)-
Fe(CO)2] (R, RЈ = H, Me) and K[(η5-C5H4Me)Mn(CO)2H].
The synthesis of [(η5-C5R4RЈ)(OC)2Fe–B(Cl)E(SiMe3)3] (E = Si,
Ge; 9a–d), [(η5-C5R4RЈ)(OC)2Fe–B(Cl)Si(SiMe3)2Si(SiMe3)3]
(9e) and [(η5-C5H4Me)(OC)2(H)Mn–B(Cl)E(SiMe3)3] (10a, b)
proves them to be versatile starting materials for the prepar-
ation of the first silyl- and germylboryl complexes via salt
elimination reactions. The silyl- and germylsubstituents do not
relieve the electron deficiency at the three coordinate boron
centre by π-interaction or hyperconjugation. However, the spec-
troscopic and structural findings for the iron complexes 9a–e
give no indication that this electron deficiency is compensated
for by metal–boron π-backdonation. In the case of the corre-
sponding manganese complexes 10a and b spectroscopic and
structural data prove a similar situation as far as the absence of
metal-to-boron π-donation is concerned. However, the electron
deficiency of the boron atom enables the formation of a Mn–
H–B bridge incorporating the manganese bound hydrogen
co-ligand. The first transhalogenation at a metal coordinated
boryl centre was carried out by reacting [(η5-C5R4RЈ)(OC)2-
Fe–B(Cl)Si(SiMe3)3] (9a) with TlF yielding the fluoro-
boryl complex [(η5-C5R4RЈ)(OC)2Fe–B(F)Si(SiMe3)3] (11),
which shows similar spectroscopic and structural features as its
precursor.
Scheme 4
reactivity towards TlF: 9d undergoes complete decomposition
within 2 h, while no reaction is observed in the case of 10d.
[(η5-C5H5)(OC)2Fe–B(F)Si(SiMe3)3] (11) was characterised in
solution and shows the expected IR and multinuclear NMR
data (Table 2). Introduction of the strong π-donor fluorine to
the boron centre results in a 11B NMR signal at δ = 113.2, which
is considerably high-field shifted with respect to that of the
starting material and shows the expected doublet splitting and a
1JB–F coupling of 232 Hz. The CO stretching frequencies in the
IR spectrum at 2001 and 1946 cmϪ1 closely resemble those of
9a–e, thus giving no evidence for an iron–boron π-backbonding
in solution.
Single crystals of 11 suitable for a X-ray structure analysis
were grown at Ϫ80 ЊC at the interface of a hexane–perfluoro-
hexane mixture. The complex crystallises in the monoclinic
space group C2/c and the molecule adopts C1-symmetry in the
crystal (Fig. 5).
Acknowledgements
We wish to thank EPSRC, RSoc, DFG and the Fonds der
Chemischen Industrie for financial support.
References
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10 D. Stalke and L. Lameyer, Organometallics, 1996, 15, 2839.
Fig. 5 X-Ray crystal structure of 11. Selected bond lengths (Å) and
angles (Њ): Fe–B 1.983(9), B–Si(1) 2.046(10), B–F 1.342(9), Si(1)–Si(2)
2.355(3), Si(1)–Si(3) 2.356(3), Si(1)–Si(4) 2.344(3), B–Si(1)–Si(2)
102.8(3), B–Si(1)–Si(3) 105.1(3), B–Si(1)–Si(4) 119.4(3).
The overall geometry of 11 in the crystal bears a close
resemblance to that of the corresponding chloro derivative
[(η5-C5H5)(OC)2Fe–B(Cl)Si(SiMe3)3] (9a). The dihedral angle
between the Si(1)–B–F and B–Fe–Cpm planes is 83.5Њ and the
iron–boron distance was found to be 198.3(9) pm, which again
provides no indication for a π-contribution to the metal–boron
bond. The boron–fluorine distance of 134.2(9) pm is consider-
ably smaller than the sum of the covalent radii of fluorine and
boron, thus reflecting the expected multiple bond character and
matching the corresponding distance in cis-[(Ph3P)2Pt(BF2)2],
which is the only other structurally authentic fluoroboryl
complex.31
J. Chem. Soc., Dalton Trans., 2002, 2289–2296
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