Ruthenocene analogues with a novel C5B2 ligand: (η7-4-borataborepine)(η5-penta- methylcyclopentadienyl)ruthenium complexes

Article abstract of DOI:10.1002/anie.200461719

Away from the fold: Insertion of the terminal alkyne PhCH₂C ₂H (2) into the folded C₃B₂ heterocycle (R ² = CH₂SiMe₃, Me) of the formal 16-valence-electron complexes 1 gives the 18-valence-electron boron-containing ruthenocene analogues 3 with a 4-borataborepine as 6π-electron ligand. Side products 4 and C₆H₃(CH₂Ph)₃ are detected by mass spectrometry. Compound 4 is formed directly as the only product when 1 is treated with R₂C₂ (R = Et, p-tolyl).

Full text of DOI:10.1002/anie.200461719

Communications
Metallocenes
Herein we report the insertion of terminal alkynes into
the heterocycle of 1, which leads to the 18 VE complexes 4
with the novel h7-4-borataborepine as a six-electron (6e)
ligand, whereas with diorganylacetylenes the formation of
boratabenzene complexes 5 occurs.
Ruthenocene Analogues with a Novel C5B2
Ligand: (h7-4-Borataborepine)(h5-penta-
methylcyclopentadienyl)ruthenium Complexes**
Treatment of 1a with 3-phenyl-1-propyne (Scheme 1) in
hexane yields the yellow, relatively air-stable solid 4a, which
exhibits one broad signal at d = 29 ppm in the 11B NMR
Yong Nie, Hans Pritzkow, Chunhua Hu, Thomas Oeser,
Bettina Bach, Thomas Mꢀller, and Walter Siebert*
Dedicated to Professor Michael Veith
on the occasion of his 60th birthday
The violet, formally 16 valence electron (VE) sandwich
complexes 1[1] are folded along the B···B vector of the
heterocycle, as are the corresponding green iron complexes
(folding angle a = 41.38).[2] This effect causes a unique
reactivity leading to classic 18 VE complexes. Coordination
of the donor ligands DCO and DCN-R at the ruthenium center
yields yellow 2 with decreased folding angles (< 208).[1a] The
Scheme 1. Insertion of a terminal alkyne into 1 to give the 4-boratabor-
epine complexes 4; R2 =CH2SiMe3 (4a), R2 =Me (4b).
spectrum (downfield compared to that of 1a, d = 21.7 ppm).
The absence of a second 11B NMR signal in the upfield region
indicates that the uptake of the alkyne did not give a
ruthenacarborane with an apical boron atom, such as 3. In the
EI-MS spectra, a cutoff peak at m/z 630 [M+] shows that the
1:1 product does not lose the alkyne (which would occur an
adduct of 2). Aweak signal at m/z 532 [4aÀBCH2SiMe3]+ was
tentatively assigned to the complex [Cp*Ru(boratabenzene)]
(5a; Cp* = C5Me5). In addition, tribenzylbenzene was iden-
tified by MS as a side product. The structure of 4a (Figure 1),
established by a single-crystal X-ray diffraction,[3] demon-
strates the formation of a novel sandwich complex with the 4-
incorporation of boranediyl ([DBH] from BH3·THF) results in
the formation of ruthenacarboranes 3 and likewise the
incorporation of sulfur (from H2S) gives ruthenathiacarbor-
anes.
With phosphines, 1 forms donor–acceptor complexes 1-
PH2R (R = H, Ph), however, the triorganylphosphine adducts
1-PR3 (R = Me, Ph) are unstable. With tert-butylphosphaal-
ꢀ
borataborepine ligand, as a result of the insertion of the C C
[5]
À
À
unit of the alkyne into a B C bond of 1a. As the B1 C2 and
À
B3 C2 bonds in 1a are equivalent, both bonds react with the
alkyne yielding enantiomers, which are found in the crystal
ꢀ
kyne DP C-CMe3, no adduct but its incorporation into 1 is
structure.[3]
observed, however, it is not yet known which of the possible
isomers of the resulting ruthenaphosphacarborane is for-
med.[1b]
The seven-membered ring in 4a is less folded along the
À
B···B vector (a = 268), and the Ru B separations (2.527 and
2.542 ꢀ) are significantly elongated compared to those in
1a.[5] The Ru C bond lengths of the C5B2 ring vary between
À
À
À
2.203 (Ru C4) and 2.345 ꢀ (Ru C2). Because of the bonding
between the ruthenium center and the larger ring, the bonds
to the exocyclic a-atoms are tilted towards the ruthenium,
with the exception of those to C16 and C20, which are bound
to the boron atoms, which tilt in the opposite direction.
The influence of the bulky silyl groups in 4a is evident
when compared with 4b, obtained from the reaction of violet
1b and 3-phenyl-1-propyne in hexane (Scheme 1). The yellow
product was identified as a mixture of the expected 4-
borataborepine complex 4b and the boratabenzene com-
pound 5b by MS. While most of the bond lengths and angles
are similar to those in 4a, some differences arise in 4b
[*] Y. Nie, Dr. H. Pritzkow, Dr. B. Bach, Dr. T. Mꢀller, Prof. W. Siebert
Anorganisch-Chemisches Institut
Universitꢁt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
Fax: (+49)6221-545-609
E-mail: walter.siebert@urz.uni-heidelberg.de
Dr. C. Hu
Institut fꢀr Anorganische Chemie, RWTH Aachen
Professor Pirlet Strasse 1, 52056 Aachen (Germany)
Dr. T. Oeser
Organisch-Chemisches Institut
Universitꢁt Heidelberg
(Figure 1)[3] owing to the absence of the silyl groups: the Ru
B bond lengths of 2.429 and 2.443 ꢀ are significantly shorter
than those in 4a, and the folding along the B···B vector (a =
12.58) is only half the value of that in 4a. The seven-
À
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft.
We thank Prof. Dr. U. Englert (Aachen) for arranging the X-ray
analyses.
632
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200461719
Angew. Chem. Int. Ed. 2005, 44, 632 –634

Angewandte
Chemie
Scheme 2. Insertion of disubstituted alkynes into 1b to give the bora-
tabenzene complexes 5; R4 =Et (5c), R4 =p-tolyl (5d).
4c,d cause the complete elimination of one methylboranediyl
moiety [DB-Me] to give 5c,d directly, whereas 4a,b eliminate
[DB-R2] only slowly in solution (Scheme 2).
As with boratabenzenes,[7a] the 4-borataborepines in 4
function as 6e ligands, their 2e ene and the 4e allylic groups
are separated by two boron atoms, but are electronically
connected by their pz orbitals, as indicated by the short
boron–carbon bond lengths. The 4-borataborepine is formally
derived from the tropylium ion [C7H7]+ and the neutral
borepine C6H6BR[8a] (a 6e ligand in 6 with R = Cl[8b]) by
replacing two CH in [C7H7]+ by two BRÀ units and one CH in
C6H6BR by one BRÀ unit. Thus 4 is an isomer of 7[7b] and a
structural analogue of (h5-cyclopentadienyl)( h7-cyclohepta-
trienyl)chromium.[9]
Figure 1. Molecular structures of 4a (top) and 4b (bottom). Hydrogen
atoms are omitted for clarity. Selected bond lengths [ꢂ]: 4a: Ru-CCp*
2.172(3)–2.205(3), Ru-C1 2.287(3), Ru-C2 2.345(3), Ru-B2 2.542(3),
Ru-C3 2.311(3), Ru-C4 2.203(3), Ru-C5 2.303(3), Ru-B1 2.527(3), B1-C5
1.531(4), C5–C4 1.409(4), C4-C3 1.412(4), C3-B2 1.524(4), B2-C2
1.540(4), C2-C1 1.413(4), C1-B1 1.545(4). 4b: R–CCp* 2.178(3)-
2.201(3), Ru-C2 2.332(3), Ru-B2 2.443(3), Ru-C3 2.299(3), Ru-C4
2.234(3), Ru-C5 2.315(3), Ru-B1 2.429(4), Ru-C1 2.330(3), B2-C3
1.520(5), C3-C4 1.415(4), C4-C5 1.400(4), C5-B1 1.528(5), B1-C1
1.531(5), C1-C2 1.415(5), C2-B2 1.542(5).
The driving force for the alkyne insertion into the
electron-poor complex 1 is the formation of the 6p-electron
ligand 4-borataborepine in the 18 VE complexes 4. The first
insertion reactions of ethyne into one of the boratabenzene
rings of bis(boratabenzene)-zirconium and -titanium com-
plexes were reported by Ashe et al.[10] and Bazan et al.,[11] who
obtained complexes 8 and 9 containing 8aH-4-boratanaph-
thalene (R = Ph)[10] and boratacyclooctatetraene (R = Me)[11]
ligands, respectively.
In conclusion, we have demonstrated that the insertion of
terminal alkynes into the C3B2 heterocycle of the complexes 1
results in 18 VE boron-containing ruthenocene analogues 4,
which contain 4-borataborepine as a 6e ligand with classical
p bonding,[12] as the main products, together with the for-
mation (from 4) of boratabenzene complexes 5, which are
formed as the only products in the reactions of 1 with
disubstituted alkynes.
membered C5B2 ring is almost parallel to the Cp* ring, the
dihedral angle between the two best planes is 6.68.
To elucidate the unexpected formation of boratabenzene
complexes 5a,b, the stability of 4a in solution was monitored
by 11B NMR spectroscopy. Over several weeks a weak signal
at d = 16 ppm increased, which indicates that the borataben-
zene complex 5a was formed from 4a. In addition, the
reactions of 1b and 3-hexyne and di-p-tolylacetylene, respec-
tively, were carried out (Scheme 2), which led to the
boratabenzene complexes 5c,d, identified by MS and con-
firmed by an X-ray crystallographic study of 5c.[6] Clearly
steric requirements in the anticipated peralkylated complexes
Experimental Section
4a: 3-Phenyl-1-propyne (82 mg, 0.7 mmol) in hexane (5 mL) was
added to a violet solution of 1a[1a] (244 mg, 0.47 mmol) in hexane
Angew. Chem. Int. Ed. 2005, 44, 632 –634
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633

Communications
(10 mL) at À458C. After 30 min the cooling bath was removed and
refined anisotropically.[4] 1a: Monoclinic, space group P21/c,
C24H46B2RuSi2, a = 18.7559(8), b = 8.9859(4), c = 18.0098(8) ꢀ,
the reaction mixture warmed to room temperature, during which the
solution turned yellow. After filtration, the filtrate was dried in vacuo,
and the resultant oily residue purified by column chromatography on
silica gel. Eluting with hexane and then with hexane/CH2Cl2 (4:1)
gave a yellow elute, which was dried in vacuo and gave 4a as a yellow
solid (100 mg, 34%). Crystals suitable for X-ray analysis were grown
from a CH2Cl2 solution of 4a at room temperature, m.p. 1758C;
1H NMR (200 MHz, CDCl3): d = 7.39–7.17 (m, 5H; Ph), 5.41 (s, 1H;
CH), 3.86 (d, 1H; 2J(H,H) = 14.3 Hz, CH2Ph), 3.07 (d, 1H; 2J(H,H) =
b = 114.131(1)8, V= 2770.1(2) ꢀ3, Z = 4, 1calcd = 1.231 gcmÀ3
;
38020 reflections (qmax = 328) collected, 9545 independent
reflections [R(int) = 0.0539]. R1 = 0.0338 (I > 2s(I)), wR2 =
0.0823 (all data). 4a: Monoclinic, space group P21/n,
C33H54B2RuSi2,
a = 11.2417(7),
b = 19.6225(13),
c =
=
15.6347(10) ꢀ, b = 102.466(3)8, V= 3367.6(3) ꢀ3, Z = 4, 1calcd
1.242 gcmÀ3; 53110 reflections (qmax = 28.48) collected, 8451
unique reflections [R(int) = 0.0820]. R1 = 0.0477 (I > 2s(I)),
wR2 = 0.0956 (all data). 4b: Triclinic, space group P1,
¯
=
14.3 Hz, CH2Ph), 1.94 (s, 3H; BCCH3CH), 1.85 (s, 3H; CCH3), 1.80
=
(s, 3H; CCH3), 1.57 (s, 15H; C5(CH3)5), 0.15 (s, 18H; SiMe3), À0.28
C27H38B2Ru, a = 7.5443(6), b = 8.8867(7), c = 18.6554(15) ꢀ,
a = 87.062(4), b = 88.683(4), g = 69.228(4)8, V= 1167.88(16) ꢀ3,
Z = 2, 1calcd = 1.380 gcmÀ3; 18121 reflections (qmax = 28.38) col-
lected, 5778 unique reflections [R(int) = 0.0391]. R1 = 0.0401
(I > 2s(I)), wR2 = 0.0926 (all data). CCDC-244072 (1a), CCDC-
244073 (4a), CCDC-244074 (4b) contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB21EZ, UK; fax: (+ 44)1223-336-033; or
deposit@ccdc.cam.ac.uk).
(s, 2H; BCH2), À0.51 ppm (s, 2H; BCH2); 11B NMR (64 MHz,
CDCl3): d = 34 ppm (br.); 11B NMR (64 MHz, CD2Cl2): d = 29 ppm
(br.); 13C NMR (53 MHz, CDCl3): d = 143.3, 128.8, 128.0, 125.4 (Ph),
117.4 (allyl moiety, central carbon), 86.1 (C5(CH3)5), 47.7 (CH2Ph),
=
28.7 (BCCH3CH), 19.8, 18.3 (BC CCH3), 9.7 (C5(CH3)5), 1.02 ppm
(SiMe3). The signals for the boron-bound carbon atoms of the allyl
moiety, for BCH2SiMe3, and for the two = CMe moieties were not
observed; EI-MS: m/z (%) = 630 [M+] (57), 615 [M+ÀCH3] (11), 557
[M+ÀSiMe3]
(32),
532
[M+ÀSiMe3ÀBCH2]
(66),
446
[M+À2SiMe3ÀBCH2ÀCH] (100). HR-MS: m/z calcd for
12
C
33
1H5428Si211B2102Ru: 630.2993, found: 630.2996, D = 0.3 mmu.
[4] a) G. M. Sheldrick, SHELXS86, Univ. Gꢂttingen, 1986; b) G. M.
Sheldrick, SHELXL97, Univ. Gꢂttingen, 1997; c) G. M. Shel-
drick, SHELXTL, Version 5.1, Program Package for Structure
Solution and Refinement, Bruker Analytical X-ray Systems,
Inc., Madison, WI, 1998.
4b: obtained analogously to 4a. 3-phenyl-1-propyne (58 mg,
0.5 mmol) in hexane, 1b[1a] (140 mg, 0.38 mmol) in hexane (20 mL)
gave a yellow reaction mixture. After filtration a yellow residue was
obtained (40 mg), which is a mixture of 4b, 5b and tribenzlybenzene
(detected by MS). The filtrate resulted in a yellow solid (150 mg), a
mixture of 4b and 5b (detected by MS), which was recrystallized in
CH2Cl2 at room temperature to give 4b (81%), m.p. 203–2058C;
1H NMR (200 MHz, CDCl3): d = 7.09–7.36 (m, 5H; Ph), 5.54 (s, 1H;
CH), 3.97 (d, 1H; 2J(H,H) = 14.7 Hz, CH2Ph), 3.02 (d, 1H; 2J(H,H) =
[5] 1a,[1a] a dark violet oil, on cooling in hexane finally yielded
suitable crystals for an X-ray structural analysis,[3] which
confirms that the 1,3-diborolyl ring C3B2 is folded by 40.78
along the B···B vector, very similar to its green iron analogue.[2]
À
The Ru C2 bond length [2.029, cf. Fe-C 1.899 ꢀ] is markedly
=
À
14.7 Hz, CH2Ph), 1.97 (s, 3H; BCCH3CH), 1.92 (s, 3H; CCH3), 1.88
shorter than the other Ru C bond lengths of the heterocycle.
=
(s, 3H; CCH3),1.57 (s, 15H; C5(CH3)5), 0.68 (s, 3H; BCH3),
[6] Crystal data for 5c: data were collected on a Bruker Apex CCD
0.61 ppm (s, 3H; BCH3); 11B NMR (64 MHz, CDCl3): d = 26 ppm
(br.); 13C NMR (53 MHz, CDCl3): d = 142.9, 128.7, 127.9, 125.3 (Ph),
118.5, (allyl moiety, central carbon), 86.3 (C5(CH3)5), 46.5 (CH2Ph),
diffractometer at 200 K, triclinic, space group P1, C23H37BRu,
¯
a = 7.6562(9), b = 8.928(1), c = 16.051(2) ꢀ, a = 92.905(2), b =
93.060(2), g = 104.370(2)8, V= 1061.6(2) ꢀ3, Z = 2, 1calcd
=
27.9 (BCCH3CH), 22.2, 22.1 (BC CCH3), 9.5 ppm (C5(CH3)5). The
1.33 gcmÀ3; 6546 reflections (qmax = 26.48) collected, 4077 inde-
pendent reflections [R(int) = 0.0193]. R1 = 0.031 (I > 2s(I)),
=
signals for the boron-bound carbon atoms of the allyl moiety, for
BCH3, and for the two = CMe moieties were not observed. EI-MS:
wR2 = 0.0823. CCDC number: CCDC-256654. 5c: HR-MS: m/
12
m/z (%) = 486 [M+] (54), 444 [M+ÀBCH3ÀCH4] (41), [M+ÀCH2Ph]
z calcd. for
À0.8 mmu. 5d: HR-MS: m/z calcd. for
C
1H3711B102Ru: 426.2031, found: 426.2023, D =
23
12
12
(100). HR-MS: m/z calcd. for
486.2218, D = 1.5 mmu.
C
1H3811B2102Ru: 486.2203, found:
C
33
1H4111B102Ru:
27
550.2344, found: 550.2338, D = À0.7 mmu.
[7] a) G. E. Herberich, H. Ohst, Adv. Organomet. Chem. 1986, 25,
199 – 236; b) G. E. Herberich, H. J. Becker, K. Carsten, C.
Engelke, W. Koch, Chem. Ber. 1976, 109, 2382 – 2388.
[8] a) A. J. Ashe III, F. J. Drone, C. M. Kausch, J. Kroker, S. M. Al-
Taween, Pure Appl. Chem. 1990, 62, 513 – 517; b) A. J. Ashe III,
J. W. Kamp, W. Klein, R. Rousseau, Angew. Chem. 1993, 105,
1112; Angew. Chem. Int. Ed. Engl. 1993, 32, 1065 – 1066, and
references therein.
[9] E. O. Fischer, S. Breitschaft, Angew. Chem. 1963, 75, 94 – 95;
Angew. Chem. Int. Ed. Engl. 1963, 2, 44.
[10] A. J. Ashe III, S. Al-Ahmad, J. W. Kamp, V. G. Young, Jr.,
Angew. Chem. 1997, 109, 2104 – 2106; Angew. Chem. Int. Ed.
Engl. 1997, 36, 2014 – 2016.
Received: August 19, 2004
Published online: December 23, 2004
Keywords: boron · heterocycles · ring expansion · ruthenium ·
.
sandwich complexes
[1] a) T. Mꢁller, M. Kaschke, M. Strauch, A. Ginsberg, H. Pritzkow,
W. Siebert, Eur. J. Inorg. Chem. 1999, 1685 – 1692; b) B. Bach, Y.
Nie, H. Pritzkow, W. Siebert, J. Organomet. Chem. 2004, 689,
429 – 437.
[2] a) W. Siebert, R. Hettrich, H. Pritzkow, Angew. Chem. 1994, 106,
215 – 217; Angew. Chem. Int. Ed. Engl. 1994, 33, 203 – 204; b) R.
Hettrich, M. Kaschke, H. Wadepohl, W. Weinmann, M. Stephan,
H. Pritzkow, W. Siebert, I. Hyla-Kryspin, R. Gleiter, Chem. Eur.
J. 1996, 2, 487 – 494.
[11] X. Fang, D. Woodmansee, X. Bu, G. C. Bazan, Angew. Chem.
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[12] MO calculations for 1 and 4 are in progress (Dr. I. Hyla-Kryspin,
University of Mꢁnster, Germany).
[3] Crystal structure analyses for 1a, 4a, and 4b: intensity data for
1a were collected on a Bruker AXS SMART CCD diffractom-
eter at T= 103 (2) K, for 4a and 4b on a Bruker Apex CCD
diffractometer at T= 120(2) K. MoKa radiation, l = 0.71073 ꢀ,
graphite monochromator, w-scans. The structures were solved by
direct methods and refined by least-squares methods based on F2
with all measured reflections, all non-hydrogen atoms are
634
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2005, 44, 632 –634