New tantalum compounds supported by 3,3′-disubstituted-l,l′-bi-2naphthoxide ligation

Article abstract of DOI:10.1039/b005681m

Several tantalum compounds supported by 3,3′-disubstituted-1,1′-bi-2-naphthol derived ligands have been prepared and initial aspects of their reactivity studied. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b005681m

View Article Online / Journal Homepage / Table of Contents for this issue
New tantalum compounds supported by 3,3Ј-disubstituted-1,1Ј-bi-2-
naphthoxide ligation†
Matthew G. Thorn, John E. Moses, Phillip E. Fanwick and Ian P. Rothwell*
Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette,
IN 47907-1393, USA. E-mail: rothwell@purdue.edu
Received 7th June 2000, Accepted 14th July 2000
Published on the Web 28th July 2000
Several tantalum compounds supported by 3,3Ј-disub-
stituted-1,1Ј-bi-2-naphthol derived ligands have been
prepared and initial aspects of their reactivity studied.
The use of ortho-substituted phenoxide ligands (ArO) to sup-
port organometallics at niobium and tantalum metal centers
has proven very successful.1 However, to date few examples of
asymmetric versions of this [(ArO)2M] (M = Nb, Ta) based
chemistry have been reported although we2 and others3 have
recently reported on the use of chiral ortho-(1-naphthyl)-
phenoxides as ancillary ligands. However, while the important
chiral auxiliary 1,1Ј-bi-2-naphthol has found applications in
many areas of asymmetric transition metal chemistry,4 the
niobium and tantalum chemistry of this ligand appears to be
underdeveloped. We report here, some of our initial results on
the chemistry of 3,3Ј-disubstituted derivatives of this ligand
system with tantalum.
We have prepared a number of parent 3,3Ј-disubstituted
ligands 1–3 (Scheme 1) via straightforward literature methods
Fig. 1 Molecular structure of (S)-4 showing the atomic numbering
scheme. Selected interatomic distances (Å) and angles (Њ): Ta–O(1)
2.036(4), Ta–O(2) 2.039(3), Ta–N(3) 2.006(5), Ta–N(4) 2.009(5), Ta–
N(5) 2.000(5), Ta–N(6) 2.465(5); O(1)–Ta–O(2) 84.9(2), O(1)–Ta–N(3)
175.1(2), O(1)–Ta–N(4) 89.2(2), O(1)–Ta–N(5) 94.9(2), O(1)–Ta–N(6)
91.9(2), O(2)–Ta–N(3) 94.1(2), O(2)–Ta–N(4) 164.7(2), O(2)–Ta–N(5)
91.5(2), O(2)–Ta–N(6) 79.2(2), N(3)–Ta–N(4) 90.5(3), N(3)–Ta–N(5)
89.9(3), N(3)–Ta–N(6) 93.2(2), N(4)–Ta–N(5) 103.1(2), N(4)–Ta–N(6)
86.0(2), N(5)–Ta–N(6) 170.3(2), Ta–O(1)–C(11) 130.3(4), Ta–O(2)–
C(21) 132.5(3).
Scheme 1
insensitive to the bulk of the 3,3Ј-substituents in these com-
pounds. The solid state structures of (S)-4 (Fig. 1), (R)-6 and
(R,S)-7,§ confirm the presence of coordinated Me2NH. All
three compounds possess a pseudo-octahedral geometry about
the metal center with the amine group cis to both aryloxide
oxygen atoms. The structural parameters are essentially identi-
cal for all three compounds although the solid-state structure
of (R)-6 contained a disorder of the Ta atom along the amide–
amine axis.
using either resolved or racemic versions of 2,2Ј-dihydroxy-
1,1Ј-binaphthol.5 Reaction of [Ta2Cl10] with 1–3 or their
dilithium or dipotassium salts lead to an as yet unidentified
mixture (NMR) of products. However, reaction of [Ta-
(NMe2)5]6 with 1–3 afforded compounds 4–7 as yellow solids
in high yields (Scheme 2).‡ The solution NMR spectroscopic
properties of 4–7 indicate the presence of coordinated Me2NH,
formed from the protonolysis reaction between 1–3 and
[Ta(NMe2)5], as well as a single resonance for the three Ta–
NMe2 groups. The coordination of the amine appears to be
Addition of SiCl4 to a hydrocarbon solution of (S)-4 leads
to the formation of a mixture of (S)-9 and (S)-10 (Scheme 3,
Fig. 2).§ The formation of (S)-10 appears to result from (S)-9
reacting with excess HCl that is generated in the Me2NH-
catalyzed amide/chloride replacement reaction. It has proven
difficult to physically separate and characterize (S)-9 and
(S)-10, although a few crystals of (S)-10 were obtained from
benzene–pentane solutions. Both compounds also have essen-
tially the same NMR spectroscopic properties. Treatment of a
C6D6 solution of the (S)-9, (S)-10 mixture with Bu3SnH in
the presence of PMe3 leads to a species which we formulate
1
as the monohydride (S)-11 (Scheme 3). The H NMR spec-
trum of (S)-11 contains a Ta–H resonance as a doublet of
doublets at δ 22.0 (2JH–P = 92 and 95 Hz). Two SiMe3 reson-
ances for the binaphthoxide ligand are also present. The 31P
NMR spectrum of (S)-11 also shows non-equivalent phos-
phine ligands. Previous work with monodentate aryloxide
Scheme 2
† Electronic supplementary information (ESI) available: preparation
and spectroscopic data for compounds 4–11. See http://www.rsc.org/
suppdata/dt/b0/b005681m/
DOI: 10.1039/b005681m
J. Chem. Soc., Dalton Trans., 2000, 2659–2660
This journal is © The Royal Society of Chemistry 2000
2659

View Article Online
Scheme 3
2
2.07 (br, NMe2); 0.77 (s, SiMe3). (S)-11: δ 22.0 (dd, JH–P = 92, 95 Hz,
Ta–H); 8.24 (s), 6.67–8.41; 1.74 (br, NMe2); 1.36 (d), 1.00 (d, 2JH–P = 9.2
Hz, PMe3); 0.81 (s), 0.39 (s, SiMe3). 13C: (S)-4: δ 164.9 (Ta–O–C); 46.7
(NMe2); 40.5 (NHMe2); Ϫ0.1 (SiMe3). (R)-5: δ 165.0 (Ta–O–C); 47.1
(NMe2); 39.6 (NHMe2); Ϫ0.8, Ϫ1.4 (SiMe2Ph). (R)-6: δ 165.8 (Ta–O–
C); 46.9 (NMe2); 40.9 (NHMe2); Ϫ2.1 (SiMePh2). (R,S)-7: δ 165.7 (Ta–
O–C); 46.1 (NMe2); 40.0 (NHMe2). (S)-8: δ 164.9 (Ta–O–C); 45.6
(NMe2); Ϫ0.1 (SiMe3). (S)-9 and (S)-10: δ 163.0 (Ta–O–C); 35.8
2
(NMe2); 0.4 (SiMe3). 31P 11: δ 10.9 (d, JPP = 42.0 Hz, PMe3); 3.7 (d,
2JPP = 42 Hz, PMe3).
§ Crystal data: For (S)-4 at 193 K: TaN4O2Si2C34H53, M = 786.95,
space group P212121 (no. 19), a = 11.0515(3), b = 15.2435(4),
c = 21.8989(5) Å, V = 3689.2(3) Å3, Dc = 1.417 g cmϪ3, Z = 4. Of the
8380 unique reflections collected (8.00 р 2θ р 55.00Њ) with Mo-Kα
2
radiation (λ = 0.71073 Å), the 8380 with Fo2 > 2σ(Fo ) were used in
the final least-squares refinement to yield R(Fo) = 0.045 and
2
Rw(Fo ) = 0.088. For (R)-6 at 173 K: TaN4O2Si2C72H79, M = 1269.58,
space group C2221 (no. 20), a = 11.4866(2), b = 20.5325(4),
c = 26.7517(5) Å, V = 6309.4(4) Å3, Dc = 1.336 g cmϪ3, Z = 4. Of
the 7930 unique reflections collected (8.00 р 2θ р 57.42Њ) with
Fig. 2 Molecular structure of (S)-10 showing the atomic numbering
scheme. Selected interatomic distances (Å) and angles (Њ): Ta–O(1)
1.889(6), Ta–O(2) 1.893(7), Ta–Cl(3) 2.420(3), Ta–Cl(4) 2.431(3), Ta–
Cl(5) 2.362(2), Ta–Cl(6) 2.379(2); O(1)–Ta–O(2) 89.8(3), O(1)–Ta–Cl(3)
89.8(2), O(1)–Ta–Cl(4) 173.4(2), O(1)–Ta–Cl(5) 96.0(2), O(1)–Ta–Cl(6)
90.0(2), O(2)–Ta–Cl(3) 176.3(2), O(2)–Ta–Cl(4) 93.2(2), O(2)–Ta–Cl(5)
89.5(2), O(2)–Ta–Cl(6) 93.0(2), Cl(3)–Ta–Cl(4) 87.6(1), Cl(3)–Ta–Cl(5)
86.9(1), Cl(3)–Ta–Cl(6) 90.7(1), Cl(4)–Ta–Cl(5) 89.9(1), Cl(4)–Ta–Cl(6)
84.0(1), Cl(5)–Ta–Cl(6) 173.5(1), Ta–O(1)–C(21) 135.7(6), Ta–O(2)–
C(11) 134.7(6).
2
Mo-Kα radiation (λ = 0.71073 Å), the 7930 with Fo2 > 2σ(Fo )
were used in the final least-squares refinement to yield R(Fo) = 0.040
2
and Rw(Fo ) = 0.073. For (R,S)-7 at 173 K: TaN4O2Si2C70H71, M =
1237.49, space group P21/c (no. 14), a = 11.6987(2), b = 18.2575(4),
c = 28.1025(5) Å, β = 94.759(1)Њ, V = 5981.7(4) Å3, Dc = 1.374 g cmϪ3
,
Z = 4. Of the 14457 unique reflections collected (8.00 р 2θ р 55.70Њ)
2
with Mo-Kα radiation (λ = 0.71073 Å), the 14457 with Fo2 > 2σ(Fo )
were used in the final least-squares refinement to yield R(Fo) = 0.048
2
and Rw(Fo ) = 0.077. For (S)-10 at 173 K: TaCl4NO2Si2C31H39,
M = 836.59, space group C2 (no. 5), a = 27.604(2), b = 12.7559(7),
c = 11.549(1) Å, β = 100.591(3)Њ, V = 3997.4(9) Å3, Dc = 1.390 g cmϪ3
,
ligands has shown that seven-coordinate mono-, di- and tri-
hydrides adopt a pentagonal bipyramidal structure with
trans-axial aryloxide oxygen atoms. The assigned structure for
(S)-11 (axial O and Cl) is, therefore, based upon these previ-
ous results and the spectroscopic data.
Z = 4. Of the 8683 unique reflections collected (8.00 р 2θ р 55.85Њ)
2
with Mo-Kα radiation (λ = 0.71073 Å), the 8683 with Fo2 > 2σ(Fo )
were used in the final least-squares refinement to yield R(Fo) = 0.054
2
and Rw(Fo ) = 0.130. CCDC reference number 186/2089.
In an attempt to avoid the formation of (S)-10, solid (S)-4
was gently heated under vacuum to remove Me2NH leading to
the amine-free (S)-8. Unfortunately treatment of (S)-8 with
SiCl4 generated a complex mixture resulting from incomplete
amide replacement. Apparently for (S)-8 the lack of coordin-
ated Me2NH leads to poor catalysis of the chloride replacement
reaction.
1 I. P. Rothwell, Chem. Commun., 1997, 1331; I. P. Rothwell, Acc.
Chem. Res., 1988, 21, 153; J. S. Vilardo, M. A. Lockwood, L. G.
Hanson, J. R. Clark, B. C. Parkin and I. P. Rothwell, J. Chem. Soc.,
Dalton Trans., 1997, 3353; B. C. Parkin, J. R. Clark, V. M. Visciglio,
P. E. Fanwick and I. P. Rothwell, Organometallics, 1995, 14, 3002.
2 J. S. Vilardo, M. G. Thorn, P. E. Fanwick and I. P. Rothwell, Chem.
Commun., 1998, 2425; M. G. Thorn, J. S. Vilardo, P. E. Fanwick and
I. P. Rothwell, Chem. Commun., 1998, 2427; P. N. Riley, M. G. Thorn,
J. S. Vilardo, M. A. Lockwood, P. E. Fanwick and I. P. Rothwell,
Organometallics, 1999, 18, 3016.
Acknowledgements
We thank the National Science Foundation for financial
support of this research.
3 S. Saito, T. Kano, H. Muto, M. Nakadai and H. Yamamoto, J. Am.
Chem. Soc., 1999, 121, 8943; S. Saito, T. Kano, K. Hatanaka and
H. Yamamoto, J. Org. Chem., 1997, 62, 5651.
4 R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley,
New York, 1994; S. S. Zhu, D. R. Cefalo, D. S. La, J. Y. Jamieson,
W. M. Davis, A. H. Hoveyda and R. R. Schrock, J. Am. Chem. Soc.,
1999, 121, 8251; K. M. Totland, T. J. Boyd, G. G. Lavoie, W. M. Davis
and R. R. Schrock, Macromolecules, 1996, 29, 6114; T. J. Boyle, N. W.
Eilerts, J. A. Heppert and F. Takusagawa, Organometallics, 1992, 11,
1112; N. M. Brunkan, P. S. White and M. R. Gagne, Angew. Chem.,
Int. Ed., 1998, 37, 1579.
5 P. J. Cox, W. Wang and V. Snieckus, Tetrahedron Lett., 1992, 33, 2253
and references therein.
6 P. N. Riley, J. R. Parker, P. E. Fanwick and I. P. Rothwell, Organo-
metallics, 1999, 18, 3579.
Notes and references
‡ Selected spectroscopic data: NMR (C6D6, 30 ЊC) aromatic signals
unless indicated: 1H: (S)-4: δ 8.12 (s), 7.77 (d), 6.82–7.20; 3.19 (s,
NMe2); 1.87 (br, NHMe2); 0.47 (s, SiMe3). 5: δ 8.09 (s), 7.63–7.76 (m),
6.86–7.25; 3.14 (s, NMe2); 1.98 (s, NHMe2); 0.70 (s), 0.69 (s, SiMe2Ph).
(R)-6: δ 7.88 (s), 7.72 (m), 7.40 (d), 6.81–7.30; 2.89 (s, NMe2); 1.81 (s,
NHMe2); 1.00 (s, SiMePh2). (R,S)-7: δ 8.12 (s), 7.85–8.12 (m), 7.44 (d),
7.29 (d), 7.10–7.16 (m), 6.86–6.97; 2.70 (s, NMe2); 1.79 (s, NHMe2). (R)-
8: δ 8.14 (s), 7.78 (d), 7.28 (d), 7.08 (t), 6.89 (t); 3.07 (s, NMe2); 0.48 (s,
SiMe3). (S)-9 and (S)-10: δ 8.23 (s), 7.65 (d), 6.65–7.16; 6.77 (br, NH);
2660
J. Chem. Soc., Dalton Trans., 2000, 2659–2660