Reactions of permethylmetallocene alkyne complexes of titanium and zirconium with tris(perfluorophenyl)borane

Article abstract of DOI:10.1039/a908591b

Functionalization of the pentamethylcyclopentadienyl ligands by an electrophilic substitution of hydrogen atoms by [B(C₆F₅)₃] is observed at the Cp* ligands of the alkyne complexes [Cp*₂M(η²-PhC₂

Full text of DOI:10.1039/a908591b

Reactions of permethylmetallocene alkyne complexes of titanium and
zirconium with tris(perfluorophenyl)borane
Vladimir V. Burlakov,a Paul-Michael Pellny,b Perdita Arndt,b Wolfgang Baumann,b Anke Spannenberg,b
Vladimir B. Shur*a and Uwe Rosenthal*b
a A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov St. 28, 117813,
Moscow, Russia
b Institut für Organische Katalyseforschung an der Universität Rostock, Buchbinderstr. 5 - 6, D-18055 Rostock,
Germany
Received (in Cambridge, UK) 20th October 1999, Accepted 11th January 2000
Functionalization of the pentamethylcyclopentadienyl
ligands by an electrophilic substitution of hydrogen atoms
by [B(C6F5)3] is observed at the Cp* ligands of the alkyne
2
complexes [Cp*2M(h -PhC2SiMe3], connnected with (M =
Ti, formation of 1) or without (M = Zr, formation of 2) loss
of the alkyne and molecular hydrogen.
Recently we have published the reaction of the bis(trimethylsi-
2
lyl)acetylene complex of titanocene [Cp2Ti(h -Me3SiC2-
SiMe3)]1 with [HNMe3][BPh4] giving cationic complexes of
the type [Cp2TiL2][BPh4] with L = THF and pyridine.2 More
2
recently we have found that in the interaction of [Cp2Ti(h -
Me3SiC2SiMe3)] with [B(C6F5)3] an electrophilic substitution
5
of a hydrogen atom in one of the h -C5H5 rings takes place, and
5
the paramagnetic zwitterionic titanium complex [(h -
5
C5H5)Ti{h -C5H4B(C6F5)3}] is formed together with liberation
of dihydrogen.3 In this complex the ortho-fluorine atoms of two
perfluorphenyl groups coordinate at the titanium centre.
Such an interaction but with only one perfluorphenyl group
was described previously in the reaction product of the
zirconacyclopentadiene [Cp2Zr(C4Me4)] with [B(C6F5)3] giv-
Fig. 1 Crystal structure of 1 at the 30% probability level for thermal
5
5
ing
[(h -C5H5)Zr{s-C(Me)NC(Me)–C(Me)NCHMe}{h -
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond lengths
(Å) and angles (°): Ti–F15 2.406(3), C30–F15 1.391(5), C7–C13 1.514(5),
C13–B 1.649(6); B–C13–C7 124.8(3).
C5H4B(C6F5)3}].4 Starting from the alkyne complex
2
[Cp2Zr(PMe3)(h -EtC2Et)] and [HB(C6F5)2] the alkenyl com-
5
5
plex [(h -C5H5)Zr{s-C(Et)NCHEt}{h -C5H4BH(C6F5)2}] was
obtained in which the hydrogen of the B–H groups coordinate at
the Zr centre.5
fluorphenyl groups coordinates at the titanium centre [Ti–
5
5
F152.406(3) Å]. This is longer than found in [(h -C5H5)Ti{h -
Also, the so-called ‘tuck in’ permethylmetallocene com-
plexes5 were obtained with [B(C6F5)3] and [HB(C6F5)2]. Some
aspects of these compounds were reviewed by Piers in 1998.5
Here, we report the different reactions of the perme-
C5H4B(C6F5)3}]3 (2.248, 2.223 Å).
5
The alkenyl compound [(h -C5Me5)Zr{C(Ph)NCH(Si-
5
Me3)}{h -C5Me4CH2B(C6F5)3}] 2 is formed also by an
electrophilic substitution of a hydrogen atom in one methyl
group of the Cp* ligand but without dissociation of the alkyne
and liberation of dihydrogen (Scheme 2).¶
2
thylmetallocene alkyne complexes [Cp* M(h -PhC2SiMe3)]
2
(M = Ti6 and Zr7) with [B(C6F5)3], leading to functionalization
of the pentamethylcyclopentadienyl ligand.
The composition of the diamagnetic complex 2 was verified
by elemental analysis and crystallography. For solubility
reasons, NMR investigations had to be carried out in THF-d8,
but some undefined changes prevented a full analysis of the
spectra.∑ However, the borane attack at one methyl group is
5
5
The compound [(h -C5Me5)Ti{h -C5Me4CH2B(C6F5)3}] 1
is formed by dissociation of the alkyne and an electrophilic
substitution of a hydrogen atom in one methyl group of the Cp*
ligand together with liberation of dihydrogen (Scheme 1).†
The composition of the Ti(III) complex 1 was verified by
elemental analysis‡ and crystallography.
1
evident from a strong line broadening of both the H and 13C
methylene signals (diastereotopic protons at 2.65 and 2.81
ppm). The chemical shifts for the vinyl group, a strong
deshielding for the a carbon atom (228.9 ppm) and an upfield
The X-ray crystal structure analysis of 1§ (Fig. 1) revealed a
bent permethyltitanocene which consists of one unsubstituted
and one substituted pentamethylcyclopentadienyl ligand. In this
complex the ortho-fluorine atom of only one of the per-
Scheme 1
Scheme 2
Chem. Commun., 2000, 241–242
This journal is © The Royal Society of Chemistry 2000
241

‡ Data for 1: elemental analysis for C38H29TiBF15 (M = 829.31). Calc.: C,
55.04; H, 3.52. Found: C, 55.02; H, 3.59%. NMR: As expected for Ti(III),3
no NMR signals (1H and 13C) could be obtained from solutions of 1 in
THF.
§ X-Ray structure analysis of 1 and 2: STOE-IPDS diffractometer, graphite
monochromated Mo-Ka radiation, solution of structures by direct methods
(SHELXS-86: G. M. Sheldrick, Acta. Crystallogr., Sect. A, 1990, 46, 467),
refinement with full matrix least square techniques against F2 (SHELXL-
93: G. M. Sheldrick, University of Göttingen, Germany, 1993).
1: monoclinic, space group C2/c, a = 37.705(8), b = 10.990(2), c =
18.178(4) Å; b = 106.48(3)°; V = 7223(3) Å3, Z = 8, Dc = 1.525 g cm23
;
10465 reflections measured, 5758 were symmetry independent and 2868
were observed [I > 2s(I)], R = 0.052, wR2 (all data) = 0.116, 496
parameters.
2: monoclinic, space group P21/c; a = 12.827(3), b = 18.862(4), c =
19.499(4) Å, b = 94.26(3)°; V = 4704.6(18) Å3, Z = 4, Dc = 1.480 g
cm23; 13886 reflections measured, 7099 were symmetry independent and
3131 were observed [I > 2s(I)], R = 0.045, wR2 (all data) = 0.074, 608
parameters. CCDC 182/1520. See http://www.rsc.org/suppdata/cc/a9/
a908591b/ for crystallographic files in .cif format.
¶ General procedure for the preparation of complex 2: 0.368 g (0.719
mmol) of [B(C6F5)3] was dissolved in 15 mL of toluene and added to 0.370
g (0.690 mmol) of [Cp*2Zr(h -PhC2SiMe3)].7 The green solution was
2
Fig. 2 Crystal structure of 2 at the 30% probability level for thermal
ellipsoids. Hydrogen atoms except H1 are omitted for clarity. Selected bond
lengths (Å) and angles (°): Zr–C1 2.518(6), Zr–C2 2.238(5), C9–C10
1.487(6), C10–B 1.694(6), Zr–H1 2.250, Zr–F15 4.744, C39–F15 1.369(5);
C1–C2–Zr 86.5(4), B–C10–C9 121.6(4).
filtered. After standing for one day at room temperature red crystals
deposited which were separated from the mother liquor, washed with cooled
toluene and dried in vacuo to give 0.684 g (94.6%) of 2;. mp 176–178 °C
(decomp.).
∑ Data for 2: elemental analysis for C49H44SiBZrF15 (M = 1047.98). Calc.:
C, 56.16; H, 4.23. Found : C, 55.99; H, 4.24%. 1H NMR (THF-d8, 297 K):
d 0.07 (s, 9H, SiMe3); 1.30, 1.51, 1.64, 1.80 (4 s, 3H each, Cp-Me); 1.95 (s,
15H, Cp*); 2.65, 2.81 (br, 1H each, BCH2); 4.49 (s, 1H, CH); 7.14 (2H, o-
Ph); 7.19 (1H, p-Ph); 7.34 (2H, m-Ph). 13C NMR (THF-d8, 297 K, not all
signals unambiguously identified): d 1.2 (SiMe3); 12.2, 12.4, 12.6, 12.7
(Cp-Me); 12.7 (Cp*); 22.9 (br, BCH2); 104.9 (CH); 123.7 (Cp*); 126.6 (o-
Ph); 126.8 (p-Ph); 128.7 (m-Ph); 228.9 (Zr–C).
shift with a small coupling constant 1JCH (104.9 ppm, 111 Hz)
for the b position, are characteristic for a ‘b-CH agostic’
structure8 although the deshielding of the proton is not as
pronounced for complex 2 as was found for other zirconium
cyclopentadienyl compounds with this structural fea-
ture.8,10b,12
1 (a) V. V. Burlakov, U. Rosenthal, P. V. Petrowsky, V. B. Shur and M. E.
Vol’pin, Metalloorg. Khim., 1988, 1, 953; Organomet. Chem. USSR,
1988, 1, 526; (b)V. V. Burlakov, A. V. Polyakov, A. I. Yanovsky, Yu. T.
Struchkov, V. B. Shur, M. E. Vol’pin, U. Rosenthal and H. Görls,
J. Organomet. Chem., 1994, 476, 197.
2 (a) A. Ohff, R. Kempe, W. Baumann and U. Rosenthal, J. Organomet.
Chem., 1996, 520, 241; (b) W. Ahlers, B. Temme, G. Erker, R. Fröhlich
and F. Zippel, Organometallics, 1997, 16, 1440.
3 (a) V. V. Burlakov, S. I. Troyanov, A. V. Letov, E. I. Mysov, G. G. Furin
and V. B. Shur, Izv. Akad. Nauk, Ser. Khim., 1999, 1022; Russ. Chem.
Bull., 1999, 48, 1012, (Engl. Transl.); (b) V. V. Burlakov, S. I.
Troyanov, L. I. Strunkina, M. Kh. Minacheva, A. V. Letov, G. G. Furin,
U. Rosenthal and V. B. Shur, J. Organomet. Chem., 2000, in press.
4 J. Ruwwe, G. Erker and R. Fröhlich, Angew. Chem., 1996, 108, 108;
Angew. Chem., Int. Ed. Engl., 1996, 35, 80.
5 W. E. Piers, Chem. Eur. J., 1998, 4, 13; and references therein.
6 (a) V. V. Burlakov, U. Rosenthal, R. Beckhaus, A. W. Polyakov, Yu. T.
Struchkov, G. Oehme, V. B. Shur and M. E. Vol’pin, Metalloorg.
Khim., 1990, 3, 476; Organomet. Chem. USSR, 1990, 3, 237; (b) U.
Rosenthal, H. Görls, V. V. Burlakov, V. B. Shur and M. E. Vol’pin,
J. Organomet. Chem., 1992, 426, 53.
7 (a) A. K. List, K. Koo, A. L. Rheingold and G. L. Hillhouse, Inorg.
Chim Acta, 1998, 270, 399; (b) P.-M. Pellny, V. V. Burlakov, W.
Baumann, A. Spannenberg and U. Rosenthal, Z. Anorg. Allg. Chem.,
1999, 625, 910.
8 I. Hyla-Kryspin, R. Gleiter, C. Krüger, R. Zwettler and G. Erker,
Organometallics, 1990, 9, 517 and references therein.
9 J. Hiller, U. Thewalt, M. Polasek, L. Petrusova, V. Varga, P. Sedmera
and K. Mach, Organometallics, 1996, 15, 3752.
10 (a) C. Lefeber, A. Ohff, A. Tillack, W. Baumann, R. Kempe, V. V.
Burlakov, U. Rosenthal and H. Görls, J. Organomet. Chem., 1995, 501,
179; (b) P. Arndt, C. Lefeber, R. Kempe, A. Tillack and U. Rosenthal,
Chem. Ber., 1996, 129, 1281.
The X-ray crystal structure analysis of 2§ (Fig. 2) revealed,
similarly as found also for complex 1, a bent perme-
thylmetallocene which consists also of one unsubstituted and
one substituted pentamethylcyclopentadienyl ligand, but no
fluorine atom coordinates at the zirconium centre [shortest
distance Zr–F15 4.744 Å]. Additionally an alkenyl group is s-
bonded with an agostic interaction8 to the zirconium atom
presenting the typical small angle Zr–C2–C1 of 86.5° for such
a type of bonding. In complexes 1 and 2 an identically
5
functionalized Cp* ligand [h -C5Me4CH2B(C6F5)3] is shown.
Owing to the additional interaction in 1 the angle B–C13–C7 of
124.8(3)° is larger compared to the corresponding angle B–
C10–C9 of 121.6(4)° in 2.
The reactions of the corresponding complexes of bis-
2
(trimethylsilyl) acetylene [Cp* M(h -Me3SiC2SiMe3)] (M =
2
Ti6 and Zr9) gave with [B(C6F5)3] only oils or such solids which
could not be purified by crystallisation.
The novelty of the reactions in this work is, in contrast to
former observed intermolecular reactions for titanium7b,10 and
zirconium7b,11 an intramolecular course via C–H activation for
the formation of 1 and 2. In the inter- and the intramolecular
reactions the higher stability of the Ti(III) oxidation state as well
as the larger zirconium atom can give an explanation for the
different types of reaction: elimination or addition of the
reacting substrate or group.
The work was supported by the Max-Planck-Gesellschaft, the
Fonds der Chemischen Industrie and the Russian Foundation for
Basic Research (Project code 99-03-33008).
Notes and references
† General procedure for the preparation of complex 1: 0.507 g (0.990
11 C. Lefeber, A. Ohff, A. Tillack, W. Baumann, R. Kempe, V. V.
Burlakov and U. Rosenthal, J. Organomet. Chem., 1995, 501, 189.
12 (a) U. Rosenthal, A. Ohff, M. Michalik, H. Görls, V. V. Burlakov and
V. B. Shur, Angew. Chem., 1993, 105, 1228; (b) D. Thomas, N.
Peulecke, V. V. Burlakov, B. Heller, W. Baumann, A. Spannenberg, R.
Kempe, U. Rosenthal and R. Beckhaus, Z. Anorg. Allg. Chem., 1998,
624, 919.
mmol) of [B(C6F5)3] was dissolved in 10 mL of toluene and added to 0.474
2
g (0.962 mmol) of [Cp*2Ti(h -PhC2SiMe3)].6 The yellow–brown solution
was filtered. After standing for 2 days at room temperature 0.123 g (15.4%)
of yellow–brown crystals of 1 were formed which were separated from the
mother-liquor, washed with cooled toluene and dried in vacuo; mp 141–143
°C (decomp.).
Communication a908591b
242
Chem. Commun., 2000, 241–242