Dimanganese bridging borylene complexes and their reactions with unsaturated palladium(0) complexes - Syntheses, structures and calculated properties

Article abstract of DOI:10.1002/zaac.200800252

The dimanganese bridging borylene complex [μ-BMes {(η⁵- C₅H₄Me)Mn(CO)₂}₂] was synthesized from Mes(Cl)BB(Cl)Mes and K[(η⁵-C₅H ₄Me)Mn(CO)₂H] at low temperature, providing a small sample after manual separation of crystals, allowing a perfunctory spectroscopic analysis, but affording conclusive X-ray crystallographic structural data. The trimetallic bridging borylene complex [(μ³-BCl) {{(η⁵-C₅H₄Me)Mn(CO)₂} {Pd(PCy₃)}₂}] was prepared by the addition of [Pd(PCy ₃)₂] to a solution of [μ-BCl{(η⁵-C ₅H₄Me)Mn(CO)₂}₂], affording pure crystals that were fully characterised including X-ray crystallographic analysis. The structure is reconciled with detailed theoretical analysis for related model complexes, [(μ³-BX){{(η⁵-C ₅H₅)Mn(CO)₂}{Pd(PMe₃)}₂}] (X = Me, Cl).

Full text of DOI:10.1002/zaac.200800252

DOI: 10.1002/zaac.200800252
Dimanganese Bridging Borylene Complexes and their Reactions with
Unsaturated Palladium(0) Complexes ؊ Syntheses, Structures and Calculated
Properties
Holger Braunschweig*, Michael Burzler, Rian D. Dewhurst, Krzysztof Radacki, and Fabian Seeler
Würzburg, Institut für Anorganische Chemie der Bayerische Julius-Maximilians-Universität Würzburg
th
Received June 10 , 2008.
th
Dedicated to Professor Heinrich Nöth on the Occasion of his 80 Birthday
5
Abstract. The dimanganese bridging borylene complex
solution of [μ-BCl{(η -C
5
H
4
Me)Mn(CO)
2
}
2
], affording pure
5
[
μ-BMes {(η -C
5
H
4
Me)Mn(CO)
2
}
2
]
was synthesized from
Me)Mn(CO) H] at low
crystals that were fully characterised including X-ray crystallo-
graphic analysis. The structure is reconciled with detailed
5
Mes(Cl)BB(Cl)Mes and K[(η -C
5
H
4
2
temperature, providing a small sample after manual separation of
crystals, allowing a perfunctory spectroscopic analysis, but afford-
ing conclusive X-ray crystallographic structural data. The trimetal-
theoretical
[(μ -BX){{(η -C
analysis
for
related model
complexes,
3
5
5
H
5
)Mn(CO)
2
}{Pd(PMe )} }] (X ϭ Me, Cl).
3 2
3
5
lic bridging borylene complex [(μ -BCl){{(η -C
5
H
4
Me)Mn(CO)
2
}
Keywords: Boron; Borylene complexes; Manganese; Palladium;
{
Pd(PCy )} }] was prepared by the addition of [Pd(PCy
3
2
3
)
2
] to a
Phosphines
Introduction
rivative of the family of complexes of type 1, and a μ3-
bridging trimetallic chloroborylene with a MnPd B core.
2
The
dimanganese
bridging
borylene
complexes
Their molecular structures are determined from X-ray crys-
tallographic analysis, and the structure of the latter is rec-
onciled with detailed theoretical analysis for a related
model complex.
[
{L(OC) Mn} BX] (L ϭ Cp, CpЈ; X ϭ amino, alkyl, alkoxy,
2
2
halide) (1), when first reported in 1995 [1], were the first to
be described as borylene complexes, a class of complex that
is now numerous, including examples from transition met-
als from groups six to ten, and forms the basis of rich
further chemistry [2, 3], Adding to their interest, complexes
1
were surprisingly thermally stable and convenient to
Results and Discussion
handle, many also in ambient conditions. This stability,
however, seemed not to restrict their controlled reaction
with various substrates, and from the stable “Mn B” scaf-
fold blossomed a wealth of new boron-containing architec-
tures, including reaction of the BϪX bond (with water, pro-
tic acids, alcohols, or amines) [1b, 1d], or one or both of
Given the aforementioned difficulty of the syntheses of
complexes of type 1, expanding the field of Mn BX com-
plexes to include aryl derivatives has remained a challenge;
simple nucleophilic attack by aryllithium species of
2
2
[
{L(CO) Mn} BCl] (L ϭ Cp, CpЈ) was found to be
2 2
the BϪMn bonds (with SbF , transition metal bases or
PCy ) [2f, 2h, 3g].
3
unsuccessful, and success thus hinges on the non-trivial
synthesis of the corresponding diaryldiborane(4) species
Ar(X)BB(X)Ar (X ϭ halide). From the reaction of a
sample of the known species Mes(Cl)BB(Cl)Mes [4], and
3
Whereas dimanganese borylene complexes of the form 1
have been at the core of a number of important advances
in boron ligand chemistry, their lengthy synthetic route has
hampered attempts to proliferate the complexes and exploit
their unique chemistry. Herein we present the synthesis of
a dimanganese mesitylborylene complex, the first aryl de-
5
the anionic hydrido species K[(η -C H Me)Mn(CO) H] at
5
4
2
low temperature, we were however able to manually separ-
ate a small sample of the desired compound 1a as orange
crystals (Scheme 1).
*
Prof. Dr. H. Braunschweig
Institut für Anorganische Chemie,
Bayerische Julius-Maximilians-Universität Würzburg,
Am Hubland
D-97074 Würzburg.
Fax : (ϩ 49) 931-888-4623.
E-mail: h.braunschweig@mail.uni-wuerzburg.de
Scheme 1 Synthesis of 1a.
Z. Anorg. Allg. Chem. 2008, 634, 1875Ϫ1879
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1875

H. Braunschweig, M. Burzler, R. D. Dewhurst, K. Radacki, F. Seeler
From this we were able to conduct an X-ray crystallo-
graphic analysis, but sadly only a perfunctory spectroscopic
1
1
study. The B NMR resonance of 1a was found at
65 ppm, to much lower field than those of amino
100Ϫ103 ppm) and chloro (1c: 133 ppm; scheme 3) deriva-
1
(
tives, but very close to that of the only published alkyl-
substituted example (1b: 170 ppm; scheme 3) [1e].
Scheme 2 Addition of group 10 metal complexes to metal-
borylene bonds.
Figure 1 Molecular structure of 1a. Ellipsoids shown at 50 %
probability.
˚
Selected distances/A and angles/°: Mn1ϪMn1Ј 2.8363(8), Mn1ϪB1 2.035(3),
B1ϪC21 1.578(5); B1ϪMn1ϪMn1Ј 45.83(9), Mn1ϪB1ϪMn1Ј 88.33(17),
C21ϪB1ϪMn1 135.83(9), C2ϪMn1ϪC1 91.43(12), C1ϪMn1ϪB1
113.07(11), C2ϪMn1ϪB1 78.61(10).
The complex 1a in the crystal was found to be essentially
isostructural to its structurally determined amino, alkoxy,
halo and alkyl counterparts [1a, 1b, 1e, 2h]. The BϪX (X ϭ
˚
Mes) distance of 1.578(5) A places 1a between the substitu-
ents with double bonds to boron such as alkoxy- (X ϭ OEt)
and aminoborylene (X ϭ NMe , 4-hydropyridinyl) com-
2
˚
plexes (1.34Ϫ1.42 A) and those with single bonds to boron,
the alkyl (X ϭ Bu, 1b) and halide (X ϭ Cl, 1c) examples
1.61Ϫ1.77 A). The Mn-Mn (2.8363(8) A) and MnϪB
2.035(3) A) distances all lie near the upper regions of the
t
˚
˚
(
(
˚
range of corresponding lengths of previously described
˚
˚
complexes (2.79Ϫ2.82 A and 1.98Ϫ2.04 A, respectively),
leading to a significantly dilated Mn B core. The plane of
B’ species. a) see ref. [2h].
Scheme 3 Synthesis of ‘MnPd
2
2
the mesityl group sits near to orthogonal to the Mn B plane
2
(torsion angle MnϪBϪCϪC 83.01(12)°), tilted slightly
away from each respective proximal CO ligand, however the
structure is otherwise largely unremarkable.
similar dinuclear core bridged by both the borylene ligand
and one CO [3g]. The [M(PCy ) ] (M ϭ Pd, Pt) metal bases
3
2
Transition metal bases such as [M(PCy ) ] (M ϭ Pd, Pt)
insert also into bridging ‘M BX’ moieties, such as the Fe,Pt
3
2
2
demonstrate a willingness to attach themselves to metal-
borylene fragments, whether terminal [3g, 5] or bridging
system shown in Scheme 2, giving a highly unusual trimet-
3
2
2
allic species with a μ -B atom and μ -Br and μ -CO ligands.
t
5
(Scheme 2) [2h, 6]. In 2005, our group reported the inser-
In the case of the dimanganese complex [μ-B Bu{(η -
C H Me) Mn(CO) } ] (1b), the addition of two equivalents
tion of a single ‘Pd(PCy )’ fragment into the MϭB bond of
3
5
4
2 2
the terminal borylene complexes [(OC) MЈϭBϭN(SiMe ) ]
of [Pd(PCy ) ] results in complete displacement of one of
5
3 2
3 2
(MЈ ϭ Cr, W) to yield a bridging borylene complex sup-
the ‘MnL ’ fragments and double insertion of ‘Pd(PCy )’
n
3
ported by a semi-bridging CO ligand [5a], and this was ex-
tended the next year to include Pt-based examples [5b], In
into the remaining MϭB bond (Scheme 3).
In accordance with the results with 1b, two equivalents
2
007, a similar monoinsertion of “M(PCy )” (M ϭ Pd, Pt)
of the metal base [Pd(PCy ) ] were added to the chloro de-
3
3 2
rivative 1c; monitoring the reaction by 11B and P NMR
31
fragments was noted into the MϭB bond of the terminal
alkyl borylene complex [Cp(OC) MnϭB Bu], giving a very
t
spectroscopy revealed a similar degradation of the starting
2
1876
www.zaac.wiley-vch.de
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 1875Ϫ1879

Dimanganese Bridging Borylene Complexes
material and new signals growing corresponding to the ex-
appears to be inserted more closely into the void between
the two palladium atoms, or in other words, there is an
apparent splaying of the two Pd-containing ‘wings’ of the
pected dipalladated complex 2c and the phosphino-manga-
5
nese by-product [(η -C H Me)Mn(CO) (PCy )] [2h]. In
5
4
2
3
this case, the conversion was apparently faster than that of
b, needing only five days to arrive at completion. Like the
earlier reaction, the 1c/2c conversion yields a large upfield
MnBPd butterfly. Additionally, as the two Pd atoms gain
2
1
more interaction from the borylene fragment, they appar-
ently augment their interaction with the bridging carbonyls,
further bending the MnϪCϪO axes (2b: 158.9(5),
160.1(5)°; 2c: 164.2(3), 165.5(3)°).
To elucidate the bonding situation in compounds of type
2, SCF calculations at the DFT/B3LYP level of theory were
1
1
shift of the B NMR signal, from 134 to 104 ppm. Thus,
the synthesis of 2c reinforces the spectroscopic rift between
t
the Bu- and chloro-substituted borylene complexes, with
1
1
surprisingly different positions of the B (2b: 150 ppm; 2c:
3
1
1
04 ppm) and P NMR (2b: 27.1 ppm; 2c: 33.2 ppm) sig-
performed. The C -symmetrical geometries of model com-
s
*
*
nals for such intrinsically similar complexes.
pounds 2b and 2c were optimized with the Turbomole
package and the wave function was then analyzed with the
NBO 5 and the TopMod programs [7]. Electronically, both
*
*
structures show strong similarities. In both 2b and 2c the
Wieberg Bond Index (WBI) has a slightly higher value for
*
*
MnϪB than PdϪB interactions (2b : 0.72 vs. 0.52; 2c : 0.71
vs. 0.58, respectively). The Electron Localization Function
(ELF) topology in 2 suggests a localized bonding picture
with two 3c2e-bonds. The interaction between boron and
metal atoms is described by adjacent trisynaptic valence
basins BMnPd (Fig. 3). The ELF basins around the core of
both molecules have similar populations. The lower popu-
lation of the BϪCl basin in comparison to BϪC (0.71 vs.
2.0) can be attributed to the lower covalent character of
the boron-halogen bond. This results in a slightly higher
*
*
population of both BPdMn basins in 2c (2b : 1.8 e¯ ;
*
2
c : 2.0 e¯ ).
Figure 2 Molecular structure of 2c. Ellipsoids shown at 50 %
probability.
˚
Selected distances/A and angles/°: Pd1ϪMn1 2.6482(6), Pd2ϪMn1
2
.6560(5), Pd1ϪPd2 2.9625(4), Mn1ϪB1 2.024(4), Pd1ϪB1 2.029(4),
Pd2ϪB1 2.031(4), Cl1ϪB1 1.799(4), Pd1ϪC1 2.121(3), Pd2ϪC2 2.148(4),
Mn1ϪC1 1.806(4), Mn1ϪC2 1.809(4), Pd1ϪP1 2.3119(9); Pd2ϪP2
2
1
9
.3421(9), Cl1ϪB1ϪMn1 139.4(2), Cl1ϪB1ϪPd1 123.7(2), Cl1ϪB1ϪPd2
22.3(2), Mn1ϪB1ϪPd1 81.60(14), Mn1ϪB1ϪPd2 81.82(14), Pd1ϪB1ϪPd2
3.72(15),
Mn1ϪC1ϪPd1
84.40(14),
Mn1ϪC2ϪPd2
83.85(14),
O1ϪC1ϪMn1 164.2(3), O2ϪC2ϪMn1 165.5(3).
The dramatic contrast in the spectral properties between
the alkyl-substituted 2b and chloro-substituted 2c is re-
flected also in the X-ray crystallographic data of the two
complexes. While the two structures are essentially isostruc-
tural, there are significant differences in the geometry of the
Figure 3 Isosurface of the ELF ϭ 0.65 surface of 2c*. The
envelopes of core and valence basins in remote parts of molecule
are omitted for clarity.
MnPd B core. The most significant changes are observed
2
in the lengthening of the PdϪPd distance in the chloro
˚
derivative (approximately 4 %; 2b: 2.8423(7) A; 2c:
2
In the previous paragraphs are outlined the extensions
we have made to the chemistry of manganese borylene com-
plexes. The synthesis of the first aryl derivative of a di-
manganese bridging borylene complex (1a) was hampered
by separation issues but this and related complexes remain
a target of synthetic efforts in our group. The addition of
˚
.9625(4) A), an axis predicted theoretically to contain no
bonding interaction and thus not inherently constrained
2h], and the contraction of the BϪPd distances (approxi-
mately 5 % based on the average lengths; 2b: 2.144(7),
[
˚
˚
2
.128(8) A; 2c: 2.031(4), 2.029(4) A). At the same time, the
two MnϪPd distances are essentially held static (2b:
[Pt(PCy )] fragments to chloro-derivative 1c gave the second
3
˚
˚
2.6426(10), 2.6458(10) A; 2c: 2.6560(5), 2.6482(6) A), and
example of a bridging borylene complex with a MnPt B
2
the MnϪB distance relaxes a small, albeit significant,
core, which is structurally distorted from the earlier ex-
ample 1b, an effect that cannot be accounted for theoreti-
cally and presumably results from the vastly different steric
˚
amount in the chloro complex (2b: 1.987(7) A; 2c:
˚
2
.024(4) A). The overall result is that the boron atom of 2c
Z. Anorg. Allg. Chem. 2008, 1875Ϫ1879
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1877

H. Braunschweig, M. Burzler, R. D. Dewhurst, K. Radacki, F. Seeler
t
Crystal data for 2c: C44H73BClMnO P Pd , M ϭ 1009.96, 0.15 ϫ 0.09 ϫ
2
2
2
r
requirements of the BϪCl vs. BϪ Bu fragments. This syn-
0
1
.07 mm, orthorhombic, space group Pbca,
8.1416(13), c ϭ 25.4347(18) A, Z ϭ 8, ρcalcd ϭ 1.495 g·cm , λ ϭ 0.71073 A,
a
ϭ
19.4535(14),
b
ϭ
thetic result reinforces also the idea that chloro (1a) and
alkyl (1b) derivatives are akin in terms of their reactivity, in
contrast to the stubbornly unreactive amino derivatives.
˚
3
˚
F(000) ϭ 4176, T ϭ 173(2) K, R(all data): R
1
4
1
ϭ 0.0501, wR
.73 < θ < 26.18, 63839/8932 reflections collected/unique, Rint ϭ 0.0515,
78 parameters.
2
ϭ 0.0814,
Crystallographic data for the structures have been deposited with
the Cambridge Crystallographic Data Centre, 1a CCDC 676538,
Experimental Section
2
c CCDC 676537. Copies of the data can be obtained free of
General considerations
charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK(Fax: int.code(1223)336-033; e-mail for
inquiry: fileserv@ccdc.cam.ac.uk).
All manipulations were conducted in an atmosphere of dry argon
by employing either standard Schlenk techniques or a glovebox.
Solvents were distilled over appropriate drying agents. The crystal
data for 1a and 2c were collected on a Bruker D8 Apex I dif-
fractometer with a CCD area detector and graphite monochrom-
ated MoKα radiation. The structures were solved using direct meth-
ods, refined with the SHELX software package [8] and expanded
using Fourier techniques. All non-hydrogen atoms were refined an-
isotropically. Hydrogen atoms were assigned idealized positions
and were included in structure factor calculations.
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. R.D.D. thanks the
Alexander von Humboldt Foundation for a postdoctoral fellow-
ship.
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Synthesis of [μ-BMes{(η -C H Me)Mn(CO) } ] (1a)
5
4
2 2
5
A suspension of K[(η -C
5
H
4
Me)Mn(CO)
2
H] (1.40 g, 6.09 mmol) in
2
5 mL toluene was cooled to Ϫ20 °C and a solution of B
2 2 2
Mes Cl
(1.0 g, 3.02 mmol) in 20 mL toluene was added. This mixture
was stirred at Ϫ20 °C for one hour, then warmed to room
temperature. At this point a 11B NMR spectrum of the mixture
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showed three signals at 165 ppm (1a), 144 ppm (presumably
5
[
(η -C
5
H
4
Me)Mn(CO)
2
BMes]) and 24 ppm (MesBH
2
). After fil-
tration, the volatiles were removed under high vacuum, and the
residue extracted with 10 mL hexanes. A black solid was obtained
by cooling to Ϫ35 °C, from which red crystals of 1a were manually
separated for X-ray crystallographic analysis.
1H NMR (200 MHz): δ ϭ 6.75 (s, 2H, Mes), 4.24 (m, 2H, C
5
H
4
Me), 4.14
Me)
(
m, 2H, C
5
H
4
Me), 2.35 (s, 6H, Me), 2.16 (s, 3H, Me), 1.72 (s, 6H, C
5 4
H
1
1
ppm. B NMR (64 MHz): δ ϭ 165 (s, br) ppm.
4
5, 4352Ϫ4355.
Crystal data for 1a: C25
2 4 r
H25BMn O , M ϭ 510.14, 0.30 ϫ 0.17 ϫ 0.09 mm,
[
3] (a) D. Vidovic, M. Findlater, G. Reeske, A. H. Cowley, Chem.
orthorhombic, space group Pbcn, a ϭ 13.7372(12), b ϭ 12.5303(11), c ϭ
˚
3
˚
´
1
2.6327(11) A, Z ϭ 4, ρcalcd ϭ 1.558 g·cm , λ ϭ 0.71073 A, F(000) ϭ 1048,
T ϭ 173(2) K, R(all data): R ϭ 0.0498, wR ϭ 0.1025, 2.20 < θ < 26.40,
1772/2231 reflections collected/unique, Rint ϭ 0.0441, 150 parameters.
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1
2
4
Synthesis of
3
5
[
(μ -BCl){{(η -C H Me)Mn(CO) }{Pd(PCy )} }] (2c)
5 4 2 3 2
In an NMR tube a mixture of 1c (0.030 g, 0.071 mmol) and
Pd(PCy ] (0.104 g, 0.155 mmol) was dissolved in 0.6 mL C
After one day a B NMR spectrum of the mixture showed two
[
3
)
2
6 6
D .
11
31
signals at 131 ppm (1c) and 104 ppm (2c). A P NMR spectrum
showed signals at 92 ppm ([(η -C
5
5
H
4
Me)Mn(CO)
2 3
PCy ]), 39 ppm
(
[Pd(PCy ]), 33 ppm (2c) and 10 ppm (PCy
3
)
2
3
). After five days the
7
785Ϫ7787; (h) H. Braunschweig, M. Burzler, K. Radacki, F.
reaction was complete and the solution was placed into a vial in a
glovebox and layered with 4 mL hexanes. 2c precipitated as orange
crystals, suitable for X-ray crystallographic analysis. Yield: 0.019 g
Seeler, Angew. Chem. Int. Ed. 2007, 46, 8071Ϫ8073; (i) H. H.
Braunschweig, K. Radacki, D. Rais, F. Seeler, K. Radacki, D.
Rais, A. Schneider, F. Seeler, J. Am. Chem. Soc. 2007, 129,
(27 %).
1
0350Ϫ10351; (j) H. Braunschweig, I. Fernandez, G. Frenk-
1H NMR (500 MHz): δ ϭ 4.55 (m, 2H, C
.97 (s, 3H, C Me), 2.18Ϫ1.15 ppm (m, 66H, Cy). C{ H} NMR
126 MHz): δ ϭ 98.9 (ipso-C, C Me), 84.7, 83.4 (C Me), 34.1 (d,
CP ϭ 12.7 Hz, C , Cy), 32.4, 31.4, 28.6, 28.5 (s, br, Cy), 27.1 (s, Cy), 14.7
s, C Me) ppm; the signal for the semi-bridging CO was not observed.
5
4 5 4
H Me), 4.43 (m, 2H, C H Me),
13 1
ing, K. Radacki, F. Seeler, Angew. Chem. Int. Ed. 2007, 46,
5215Ϫ5218; (k) H. Braunschweig, K. Radacki, K. Uttinger,
Angew. Chem. Int. Ed. 2007, 46, 1Ϫ5; (l) H. Braunschweig, M.
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1
5 4
H
(
5
H
4
5 4
H
1
1
J
(
5 4
H
1
1
31
B NMR (160 MHz): δ ϭ 104 ppm. P NMR (202 MHz): δ ϭ 33.2 (s) ppm.
Ϫ1
IR (benzene): ν ϭ 1829, 1783 cm . EA calcd for C44
2.32; H: 7.28; found C: 51.65; H: 7.08 %.
2 2 2
H73BClMnO P Pd : C:
5
1878
www.zaac.wiley-vch.de
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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atory which is part of the Pacific Northwest Laboratory, P.O.
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[
[
[
[
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www.zaac.wiley-vch.de
1879