Reactivity of [Cp2Ti(CO)2] and B(C6F5)3: Formation of the acylborane complexes [Cp2Ti(CO)(η2-OCB(C6 F5)3)] and [Cp2Ti(THF)(η2- OCB(C6F5)3)]

Article abstract of DOI:10.1021/om030185t

The reaction of [Cp₂Ti(CO)₂] with B(C₆F₅)₃ leads, surprisingly, as revealed by X-ray structure determination to the unexpected titana acylborane [Cp₂-Ti(L)(η²-OCB(C₆ F₅)₃)] (1, L = CO, O-outside configuration; 2, L = THF, O-inside configuration) with the tris(perfluorophenyl)borane, as a Lewis acid, attached to the carbonyl carbon atom. The acylborane picture is strengthened by a theoretical calculation (ELF).

Full text of DOI:10.1021/om030185t

Organometallics 2003, 22, 1995-1997
1995
Rea ctivity of [Cp Ti(CO) ] a n d B(C F ) : F or m a tion of
2
2
6
5 3
2
th e Acylbor a n e Com p lexes [Cp Ti(CO)(η -OCB(C F ) )]
2
6
5 3
2
a n d [Cp Ti(THF )(η -OCB(C F ) )]
2
6
5 3
Robert Choukroun,* Christian Lorber, Christine Lepetit, and Bruno Donnadieu
Laboratoire de Chimie de Coordination du CNRS, 205 Route de Narbonne,
F-31077 Toulouse Cedex 4, France
Received March 11, 2003
Summary: The reaction of [Cp2Ti(CO)2] with B(C6F5)3
leads, surprisingly, as revealed by X-ray structure de-
termination to the unexpected titana acylborane [Cp2-
Sch em e 1
2
Ti(L)(η -OCB(C6F5)3)] (1, L ) CO, “O-outside” configu-
ration; 2, L ) THF, “O-inside” configuration) with the
tris(perfluorophenyl)borane, as a Lewis acid, attached
to the carbonyl carbon atom. The acylborane picture is
strengthened by a theoretical calculation (ELF).
report, a new aspect of this chemistry is observed
between L and Cp2Ti(CO)2 where neither the formation
of an adduct of L on the metal nor interaction with the
oxygen atom of the carbonyl moiety occurred.
The field of Lewis acid chemistry has given rise to a
large organic and organometallic chemistry. From a
significant amount of literature, it appears that the
Lewis acid borane L ) B(C6F5)3 is especially suitable
for the formation of cationic active species in Ziegler-
Indeed, the reaction in pentane solution of Cp2Ti(CO)2
and L leads to the unexpected formation of the acyl-
2
borane [Cp2Ti(CO)(η -OCB(C6F5)3)] (1) (Scheme 1) with
1
Natta catalysts for olefin polymerization. Recent works
a rare O-outside structure (Figure 1).
have been devoted to its Lewis acid properties toward
organic substrates and organometallic complexes.
The main feature of this structure is the attach-
ment of the borane to the carbon of the carbonyl moiety.
The Ti-C(1), Ti-O(1), and C(1)-O(1) bond lengths
of the TiCO acyl fragment (2.187(4), 2.108(3), and
2
-7
We continue our investigations into the reactivity of
L with other organometallic complexes, and another
approach is its reactivity with early-transition-metal
complexes containing carbonyl CtO ligands. Several
adducts of Lewis-type acids with different transition
metals have been described in which the borane (or the
Lewis acid) is either coordinated to the metal or
1
.219(4) Å, respectively) are different from those ob-
1
2
served in the acyl [Cp2TiCl(COMe)] (A) and the
1
3
zwitterionic [Cp2Ti(CO-i-Pr)NCBPh3] (B) complexes
A, 2.07(2), 2.194(14), 1.18(2) Å; B, 2.04(2), 2.17(1),
.23(2) Å, respectively). There is a shortening of the
(
1
interacts with the carbonyl oxygen atom.8
-11
Ti-O distance which could reflect a σ Ti-O bond (Ti-O
distances for the Ti-µ-O(i-Pr)-Ti bridge are in the
In this
1
4
*
To whom correspondence should be addressed. E-mail: choukrou@
lcc-toulouse.fr.
1) For leading recent reviews: (a) Coates, G. W.; Hustad, P. D.;
range of 1.96 to 2.10 Å ). The Ti-C(1) bond is elongated
2
and could reflect a C(sp ) character (similar distances
(
15
are observed in a Ti(II) diene complex ). As a conse-
Reiinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236-2257. (b) You-
Xian Chen, E.; Marks, T. J . Chem. Rev. 2000, 100, 1391-1434. (c)
Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed.
quence, the Ti-O-C angle is less acute in 1 (77.1(2)°)
than in A and B (68.3(7) and 67.5(10)°, respectively).
The Ti-C(2) and C(2)-O(2) bond lengths and Ti-C-O
angle (2.081(5) and 1.134(5) Å, 177.3(4)°) of the Ti-CO
1
999, 38, 428-447.
2) (a) Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345-354.
b) Parks, D. J .; Piers, M.; Parvez, W. E.; Atencio, R.; Zaworotko, M.
(
(
Organometallics 1998, 17, 1369-1377. (c) Parks, D. J .; Blackwell, J .
M.; Piers, W. E. J . Org. Chem. 2000, 3090-3098. (d) Parks, D. J .;
Spence, R. E. v. H.; Piers, W. E. Angew. Chem., Int. Ed. Engl. 1995,
16
unit are nearly similar to those of [Cp2Ti(CO)2]
(2.030(11) and 1.15(1) Å, 179.4°), and the C(2)-O(2)
3
4, 809-810. (e) Blackwell, J . M.; Piers, W. E.; Parvez, M.; McDonald,
R. Organometallics 2002, 21, 1400-1407.
3) (a) J acobsen, H.; Berke, H.; D o¨ ring, S.; Kehr, G.; Erker, G.;
distance is similar tothat observed in free CO (1.128 22(7)
1
7
Å) and H3B-CO (1.13(2) Å ). Atoms Ti, C(1), O(1), C(2),
(
Fr o¨ hlich, R.; Meyer, O. Organometallics 1999, 18, 1724-1735. (b)
Vagedes, D.; Kehr, G.; K o¨ nig, D.; Wedeking, K.; Fr o¨ lich, R.; Erker, G.;
M u¨ ck-Lichtenfeld, C.; Grimme, S. Eur. J . Inorg. Chem. 2002, 2015-
(10) Churchill, M. R.; Wasserman, H.; Holmes, S. J .; Schrock, R. R.
Organometallics 1982, 1, 766-768.
2
021.
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1272-1273.
(
4) Klosin, J .; Roof, G. R.; Chen, E. Y. X. Organometallics 2000, 19,
4
684-4686.
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Dalton Trans. 1977, 2297-2300.
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1996, 516, 11-16.
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D. H. J . Chem. Soc., Dalton Trans. 1996, 3931-3936.
(6) (a) Green, M. L. H.; Haggitt, J .; Mehnert, C. P. J . Chem. Soc.,
Chem. Commun. 1995, 1853-1854. (b) Antinolo, A.; Carillo-Hermosilla,
F.; del Hierro, I.; Otero, A.; Fajardo, M.; Mugnier, Y. Organometallics
(14) (a) Boyle, T. J .; Schwartz, R. W.; Doedens, R. J .; Ziller, J . W.,
Inorg. Chem. 1995, 34, 1110-1120 and references therein. (b) Siedle,
A. R.; Huffman, J . C. Inorg. Chem. 1990, 29, 3131-3133.
(15) Devore, F. D. D.; Timmers, J .; Hasha, D. L.; Rosen, R. K.;
Marks, T. J .; Deck, P. A.; Stern, C. L. Organometallics 1995, 14, 3132-
3134 (usual Ti-C single bonds lie within the range of 2.16-2.27 Å).
(16) Atwood, J . L.; Stone, K. E.; Alt, H. G.; Hrncir, D. C.; Rausch,
M. D. J . Organomet. Chem. 1975, 96, C4-C6.
1
997, 16, 4161-4166.
7) (a) Choukroun, R.; Lorber, C.; Donnadieu, B. Chem. Eur. J . 2002,
, 2700-2704. (b) Wolff, F.; Choukroun, R.; Lorber, C.; Donnadieu, B.
(
8
Eur. J . Inorg. Chem. 2003, 628-632.
(
8) Schriver, D. F. Acc. Chem. Res. 1970, 3, 231-238.
(
9) Braunschweig, H.; Colling, M. Coord. Chem. Rev. 2001, 223,
1
-51.
(17) Gordy, W.; Ring, H.; Burg A. B. Phys. Rev. 1950, 78, 512-514.
1
0.1021/om030185t CCC: $25.00 © 2003 American Chemical Society
Publication on Web 04/05/2003

1
996 Organometallics, Vol. 22, No. 10, 2003
Communications
F igu r e 2. Molecular structure of 2. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles
(
deg): Ti(1)-C(1) ) 2.129 (3), Ti(1)-O(1) ) 2.109(2), Ti(1)-
F igu r e 1. Molecular structure of 1. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles
O(2) ) 2.266(2), C(1)-B(1) ) 1.672(5), C(1)-O(1) ) 1.226(3),
Cp1-Ti ) 2.075, Cp2-Ti ) 2.073; Ti(1)-C(1)-O(1) )
7
(
deg): Ti(1)-C(2) ) 2.081(5), Ti(1)-C(1) ) 2.187(4), Ti(1)-
2.30(17), Ti(1)-O(1)-C(1) ) 74.06(17), Ti(1)-C(1)-B(1)
162.0(2), Cp1-Ti-Cp2 ) 134.47.
O(1) ) 2.108(3), C(1)-B(1) ) 1.650(6), C(1)-O(1) ) 1.219(4),
Cp1-Ti ) 2.057, Cp2-Ti ) 2.051; Ti(1)-C(2)-O(2) )
1
7
)
77.3(4), Ti(1)-O(1)-C(1) ) 77.1(2), Ti(1)-C(1)-O(1) )
0.0(2), Ti(1)-C(1)-B(1) ) 161.6(3), Cp1-Ti-Cp2 ) 132.99.
that labile THF is easily displaced by donor molecules.18
All atoms Ti, C(1), O(1), and B(1) are contained in the
same plane, as well as the coordinated THF.
Sch em e 2
The problem of the O-outside/O-inside configuration
in early transition metals by insertion of CO into a
metal-carbon bond has been extensively studied by
1
9
synthetic, mechanistic, and theoretical points of view
and well described by J ordan and co-workers20 on the
first isolable terminal carbonyl acyl cationic complex,
(C5Me5)2Zr(CO)(η -COCH3)] . Here the solid-state trans-
2
+
[
formation of the O-outside complex 1 suspended in
pentane or toluene leading to the thermodynamically
more stable structure, O-inside complex 2, is in relation
to the formation of a Ti-O π bonding upon CO substitu-
tion.
and O(2) are contained in the same plane, whereas the
boron atom is 0.287 Å out of the plane. This complex is
insoluble in benzene and toluene, which precludes any
spectroscopic NMR studies, and decomposes in CH2Cl2
1
to give Cp2TiCl2 as a red solid (controlled by H NMR).
Compounds 1 and 2 can be viewed either as the Ti(IV)
The IR spectrum of 1 (KBr) shows two ν(CO) bands at
+
2
borato-acyl species [Cp2Ti (CO){η -C(dO)-R}] or as
Ti(II) side-bound OC-B(C6F5)3 analogous to [Cp2Ti(CO)-
2
072 and 1608 cm-1, attributed to the terminal carbonyl
CO and the acyl group, respectively. The ν(CO) band at
{
olefin}]. To propose a coherent bonding picture, we
-
1
2
072 cm observed in 1 is higher than those observed
analyzed the specroscopic (IR) and structural data,
together with ELF studies, and compare them to those
-
1
in Cp2Ti(CO)2 (1977 and 1899 cm
in hexane), in
agreement with the structural parameters of the Ti-
CO moiety discussed above and consistent with a Ti(IV)
species.
2
12
for the known η -acyl complex [Cp2TiCl(COMe)] (A)
1
21
and η -acyl complex [Cp TiCl(-C(dO)(CH ) O-)] (C).
The ELF analysis, the geometrical parameters (vide
2
2 3
-
1
infra), and the IR data for 1 (ν(CO) 1608 cm ) and A
When a slurry of 1 in toluene is treated with THF,
-
1
(
ν(CO) 1620 cm ) are therefore very similar and in
CO evolution occurred. The resulting yellow solution
2
agreement with η -acyl complexes including a dative
Ti-O bond, with data very different from those of the
2
gives, after workup, crystalline [Cp2Ti(THF)(η -OCB-
(C6F5)3)] (2) (Scheme 2), which was fully characterized
by an X-ray structure determination (Figure 2). The
structural data are nearly the same for the [Cp2Ti(η -
(18) Bochmann, M.; J aggar, A. J .; Wilson, L. M.; Hursthouse, M.
2
B.; Motevalli, M. Polyhedron 1989, 8, 1838-1843.
(19) (a) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.,
OCB(C6F5)3)] moiety as in 1, except that 2 is a CO
O-inside complex. The Ti-C(1) distance is ca. 0.06 Å
shorter than the corresponding distance in 1 (the Ti-
O(1)-C(1) angle is reduced to 72.30(17)°). The Ti-O(2)
distance (2.266(2) Å) is 0.11 Å longer than the Ti-O
Hoffmann, R. J . Am. Chem. Soc. 1985, 107, 4440-4451 and references
therein. (b) de Angelis, F.; Sgamellotti, A.; Re, N. Organometallics
2
000, 19, 4904-4911. (c) Lupinetti, A. J .; Strauss, S. H.; Frenking, G.
Prog. Inorg. Chem. 2001, 49, 1-112.
(20) Guo, Z.; Swenson, D. C.; Guram, A. S.; J ordan, R. F. Organo-
metallics 1994, 13, 766-773.
(21) Crowe, W. E.; Vu, A. T. J . Am. Chem. Soc. 1996, 118, 1557-
+
distance in [(C5Me5)2TiMe(THF)] , in which it was found
1558.

Communications
Organometallics, Vol. 22, No. 10, 2003 1997
η1-acyl complex C (Ti-O ) 3.116(4) Å, Ti-C ) 2.218(3)
Å, C-O ) 1.211(3) Å).
via the titanocene, of the elusive carbonylborane OCB-
3
a,23
(C6F5)3.
With regard to this last aspect, 1 and 2
One question remains unclear: why does the borane
not simply attack at the more nucleophilic site, which
is the O atom of the carbonyl ligand (as expected from
the atomic charges (AIM or Mulliken) or the molecular
would then be regarded as models, as intermediate
species, in the carbonylation reactions of organoboranes,
2
4
well-known organic reactions. Exploration of the
2
5
reactivity of 1 and 2 toward nitrile, isonitrile, and
2
2
electrostatic potential )? The attack of B(C6F5)3 at the
oxygen atom of CO has been investigated at the B3PW91/
phosphine is in progress.
Ack n ow led gm en t. We thank the CALMIP (Calcul
Intensif en Midi-Pyr e´ n e´ es, Toulouse, France) for com-
puting facilities and Professor Bernard Silvi for helpful
discussions.
6
-31G* level using BF3 as a model. The pyramidal BF3
moiety initially located at 1.350 Å from the oxygen atom
of CO (the boron atom being aligned with the C and O
atoms) is pushed away side-on at 2.461 Å from the
oxygen atom of CO at the end of the geometry optimiza-
tion, and a planar BF3 moiety is recovered. This sug-
gests that the coordination of BF3 to the oxygen of CO
would be very unfavorable. Although we have no
explanation to assess this point, we could only state that
the surprising electrophilic attack at the carbonyl
carbon is possible in terms of frontier molecular orbital
overlap, namely between the LUMO of B(C6F5)3 and the
HOMO of Cp2Ti(CO)2.
Su p p or tin g In for m a tion Ava ila ble: Full experimental
details, theoretical studies, and crystallographic data for
compounds 1 and 2, including ORTEP diagrams and tables of
crystal data and data collection parameters, atomic coordi-
nates, anisotropic displacement parameters, and all bond
lengths and bond angles. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM030185T
By taking these results into account, we can consider
that 1 is the first example of an O-outside acylborane
titanium complex and that 1 and 2 are trapped forms,
(23) A few CO-borane adducts have been isolated: J effery, J . C.;
Norman, N. C.; Pardoe, J . A. J .; Timms, P. L. Chem. Commun. 2000,
2
367-2368 and references therein.
(24) (a) Kabalka, G. W.; Gotsick, J . T.; Pace, R. D.; Li, N.-S.
Organometallics 1994, 13, 5163-5165 and references therein. (b)
(22) Gadre, S. R. In Computational Chemistry: Reviews of Current
Brown, H. C. Acc. Chem. Res. 1969, 2, 65-72.
Trends; Lesczynski, J ., Ed.; World Scientific: Singapore, 1999; Vol. 4,
pp 1-53, and references therein.
(25) Preliminary results show the formation of a titana(IV)azirine
7
a
complex.