Arylamine C-N bond oxidative addition to (silox)3Ta (silox = tBu3SiO)

Full text of DOI:10.1021/ja960092l

5132
J. Am. Chem. Soc. 1996, 118, 5132-5133
Communications to the Editor
tBu3SiO), oxidative addition of H2NC6H4X to (silox)3Ta (1)
deviated from the expected N-H cleavage.19 Oxidative addi-
tions of aryl C-N and related C-O bonds to 1 are reported
herein.
Arylamine C-N Bond Oxidative Addition to
t
(silox)3Ta (silox ) Bu3SiO)
Jeffrey B. Bonanno, Thomas P. Henry, David R. Neithamer,
Peter T. Wolczanski,* and Emil B. Lobkovsky
As Figure 1 illustrates, treatment of (silox)3Ta (1) with H2-
NC6H4X afforded N-H addition to provide (silox)3HTaNH-
(C6H4X) (2-X) and/or C-N activation to give (silox)3(H2N)-
Ta(C6H4-X) (3-X) depending on the substituent. For example,
Baker Laboratory, Department of Chemistry
Cornell UniVersity, Ithaca, New York 14853
1
the H NMR spectrum of 3-p-CF3 exhibited a broad singlet at
δ 5.27 attributed to the NH2, and its IR spectrum revealed telltale
3375- and 3460-cm-1 NH stretching vibrations.20 Related
thermally stable 3-X derivatives were similarly discerned, while
prototypical downfield TaH chemical shifts clearly distinguished
the 2-X species,21 which subsequently eliminated H2 to give
(silox)3TadN(C6H4X), as previously reported.19
ReceiVed January 11, 1996
Oxidative additions of carbon-nitrogen and -oxygen single
bonds may be critical in the hydrodenitrogenation (HDN)1,2 and
hydrodeoxygenation (HDO)3 of crude oil,4 yet few clear
examples are evident.5-11 In support of such pathways,
extensive investigations of transition metal-mediated C-N12-15
and C-O16-18 bond formationssthe microscopic reverseshave
recently been undertaken. While studying substituent effects
on 1,2-H2-elimination from (silox)3HTaN(H)(C6H4X) (silox )
A single-crystal X-ray structural study of (silox)3(H2N)Ta-
(C6H4-p-CF3) (3-p-CF3) revealed a slightly distorted square-
pyramidal geometry (Figure 1). Angles between the apical (O2)
and basal silox oxygens are 104.7(3)° ( O2-Ta-O1) and
102.9(2)° ( O2-Ta-O3), while related O2-Ta-N and O2-
Ta-C angles are 112.8(3)° and 108.1(3)°, respectively. The
geometry attenuates strong trans-influences of the C6H4-p-CF3,
NH2 ( N-Ta-C ) 139.1(4)°), and apical silox (d(Ta-Oap)
) 1.865(6) Å) groups, yet accommodates the steric demands
of the slightly flexed ( Ta-O-Si(ave) ) 168(5)°) silox
linkages ( O1-Ta-O3 ) 152.4(3)°). Remaining bond dis-
tances in 3-p-CF3 are normal, with d(Ta-C) ) 2.233(8) Å and
d(Ta-Oeq)ave ) 1.914(18) Å, but the amide bond length (d(Ta-
N) ) 1.998(8) Å) is somewhat long,22 probably because silox
O(pπ) f Ta(dπ) interactions are competitive with N(pπ) f
Ta(dπ) donation.
The propensity for C-N vs N-H activation may be cor-
related with substituent Hammett σ-parameters,23 as indicated
in Table 1. Since (silox)3Ta (1) reacts with various function-
alities and steric factors are critical, the substrate survey is
limited, but contrasting effects are revealed. Although the
correlation is moderate (F ) -0.69, R ) 0.93), substituents
that increase the basicity of aniline increase the relative rate of
NH activation, suggesting that nucleophilic attack by the amine
at an empty dxz/dyz orbital of 1 precedes oxidative addition. Use
of separate parameters indicates a slightly greater resonance (FR
) -0.95) than inductive (FI ) -0.65) contribution (F ) -1.6,
R ) 0.95),23,24 reminiscent of a recent correlation involving
arylthiolate reductive elimination.25 Substituent effects on CN
(1) (a) Ho, T. C. Catal. ReV.-Sci. Eng. 1988, 30, 117-160. (b) Ka¨tzer,
J. R.; Sivasubramanian, R. C. Catal. ReV.-Sci. Eng. 1979, 20, 155-208.
(c) Shah, Y. T.; Cronauer, D. C. Catal. ReV.-Sci. Eng. 1979, 20, 209-301.
(d) Laine, R. M. Catal. ReV.-Sci. Eng. 1983, 25, 459-474.
(2) Gray, S. D.; Weller, K. J.; Bruck, M. A.; Briggs, P. M.; Wigley, D.
E. J. Am. Chem. Soc. 1995, 117, 10678-10693 and references therein.
(3) Furimsky, E. Catal. ReV. Sci Eng. 1983, 25, 421-458.
(4) Gary, J. H.; Handwerk, G. E. Petroleum Refining: Technology and
Economics, 3rd ed.; Marcel Dekker, Inc.: New York, 1993. (b) Speight, J.
G. The Chemistry and Technology of Petroleum; Marcel Dekker: New York,
1983.
(5) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry, 2nd ed.;
University Science Books: Mill Valley, CA, 1987. (b) Bryndza, H. E.;
Tam, W. Chem. ReV. 1988, 88, 1163-1188.
(6) (a) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Leonelli, J.;
Marchant, N. S.; Smith, C. A.; Taylor, L. C. E. J. Am. Chem. Soc. 1985,
107, 3722-3724. (b) Hagadorn, J. R.; Arnold, J. Organometallics 1994,
131, 4670-4672.
(7) Atagi, A. M.; Over, D. E.; McAlister, D. R.; Mayer, J. M. J. Am.
Chem. Soc. 1991, 113, 870-874.
(8) (a) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Inorg. Chem.
1994, 33, 1448-1457. (b) Proulx, G.; Bergman, R. G. J. Am. Chem. Soc.
1994, 116, 7953-7954.
(9) (a) Wang, M. D.; Alper, H. J. Am. Chem. Soc. 1992, 114, 7018-
7024. (b) Calet, S.; Urso, F.; Alper, H. J. Am. Chem. Soc. 1989, 111, 931.
(c) Ikeda, S.-I.; Chatani, N.; Murai, S. Organometallics 1992, 11, 3494-
3495.
(10) Mayer, J. M. Polyhedron, 1995, 14, 3273-3292.
(11) CX (X ) N, O) multiple bond cleavage reactions are more common.
See: (a) Hall, K. A.; Mayer, J. M. J. Am. Chem. Soc. 1992, 114, 10402-
10411. (b) Su, F.-M.; Bryan, J. C.; Jang, S.; Mayer, J. M. Polyhedron 1989,
8, 1261-1277. (c) Miller, R. L.; Wolczanski, P. T.; Rheingold, A. L. J.
Am. Chem. Soc. 1993, 115, 10422-10423. (d) Meyer, K. E.; Walsh, P. J.;
Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 974-985. (e) Schrock, R.
R.; Listemann, M. L.; Sturgeoff, L. G. J. Am. Chem. Soc. 1982, 104, 4291-
4293.
(19) Bonanno, J. B.; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem.
Soc. 1994, 116, 11159-11160.
t
(20) 3-p-CF3: 1H NMR (THF-d8) δ 1.18 (s, Bu), 5.27 (s, NH2), 7.51
(12) (a) Kosugi, M.; Sano, H.; Kamehama, M.; Migita, T. Nippon Kagaku
Kaishi 1985, 3, 547-551. (b) Kosugi, M.; Kameyama, M.; Migita, T. Chem.
Lett. 1983, 927-928.
(d, J ) 8 Hz, 2 H, Ar), 8.20 (d, J ) 8 Hz, 2 H, Ar); 13C{1H} NMR δ 24.60
3
(SiC), 31.05 (C(CH3)3), 124.53 (q, Ar, JCF ) 4 Hz), 125.65 (q, CF3, JCF
2
) 272 Hz), 129.23 (q, Ar, JCF ) 32 Hz), 137.93 (Ar), 201.99 (TaC);19F
(13) (a) Louie, J.; Hartwig, J. F. J. Am. Chem. Soc. 1995, 117, 11598-
11599. (b) Louie, J.; Hartwig, J. F. Tetrahedron Lett. 1995, 36, 3609-
3612. (c) Driver, M. S.; Harwig, J. F. J. Am. Chem. Soc. 1995, 117, 4708-
4709. (d) Paul, F.; Patt, J.; Harwig, J. F. J. Am. Chem. Soc. 1994, 116,
5969-5970.
NMR δ -62.55. Anal. Calcd for TaSi3NF3O3C43H87: C, 52.26; H, 8.87;
N, 1.42. Found: C, 52.40; H, 8.81; N, 0.98. Crystal data: monoclinic, P21/
n, a ) 14.236(9) Å, b ) 26.209(8) Å, and c ) 15.068(4) Å, â ) 111.09(8)°,
V ) 5246(4) Å3, Z ) 4, Dcalcd ) 1.252 g/cm3, T ) 293(2) K, 6790
independent reflections, full matrix refinement on F 2 (Syntex P4, SHELX93),
R1(F) ) 7.58%, R2(wF 2) ) 14.25%, GOF(F 2) ) 0.943.
(14) (a) Guram, A. S.; Rennels, R. A.; Buchwald, S. L. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 1348-1350. (b) Guram, A. S.; Buchwald, S. L. J.
Am. Chem. Soc. 1994, 116, 7901-7902.
(21) 2-X, 1H NMR (C6D6) δ(TaH): X ) m-CF3, 21.63; m-F, 21.63; p-F,
21.42; H, 21.47; p-Ph, 21.54; p-Me, 21.38; p-OMe, 21.26; p-NMe2, 21.13.
(22) (a) Chisholm, M. H.; Tan, L.-S.; Huffman, J. C. J. Am. Chem. Soc.
1982, 104, 4879-4884. (b) Chisholm, M. H.; Huffman, J. C.; Tan, L.-S.
Inorg. Chem. 1981, 20, 1859-1866. (c) Chamberlain, L. R.; Steffey, B.
D.; Rothwell, I. P.; Huffman, J. C. Polyhedron 1989, 8, 341-349.
(23) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic
Chemistry, 2nd ed.; Harper and Row: New York, 1981.
(15) Villanueva, L. A.; Abboud, K. A.; Boncella, J. M. Orgaonmetallics
1994, 13, 3921-3931.
(16) Thompson, J. S.; Randall, S. L.; Atwood, J. D. Organometallics
1991, 10, 3906-3910.
(17) (a) Bernard, K. A.; Atwood, J. D. Organometallics 1989, 8, 795-
800. (b) Bernard, K. A.; Atwood, J. D. Organometallics 1988, 7, 235-
236. (c) Bernard, K. A.; Atwood, J. D. Organometallics 1987, 6, 1133-
1134.
(24) From σI and σR° values in ref 23, using methodology of: Wells, P.
R.; Ehrenson, S.; Taft, R. W. Prog. Phys. Org. Chem. 1968, 6, 147-322.
(25) Baran˜ano, D.; Harwig, J. F. J. Am. Chem. Soc. 1995, 117, 2937-
2938.
(18) Komiya, S.; Akai, Y.; Tanaka, K.; Yamamoto, T.; Yamamoto, A.
Organometallics 1985, 4, 1130-1136.
S0002-7863(96)00092-3 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 21, 1996 5133
The premise that an adjacent electrophilic site enables a
pathway for severing carbon-heteroatom bonds was probed
through additional substrates. Comparable oxidative additions
were not observed for p-CF3C6H4-CH3 (no reaction), p-CF3C6H4-
OH (O-H addition), and p-CF3-C6H4OCH3 (no reaction), but
1,2-dihydrofuran cleanly added to (silox)3Ta (1) to afford
(silox)3TaOCH2CH2CHdCH (4, 52%),30 indicative of nucleo-
philic attack at the LUMO of the vinyl ether, rather than the
saturated O-CH2 linkage (eq 1). Epoxides were cleanly
O
O
25 °C, 12 h
hexane
(silox)3Ta +
(silox)3Ta
(1)
(2)
1
4
O
O
25 °C, <5 min
hexane
(silox)3Ta +
(silox)3Ta
1
6
deoxygenated to give (silox)3TadO (5)31 and the corresponding
olefin in a process judged as concerted7 on the basis of
stereospecific (>95%) O-atom removal from cis- and trans-
decene oxide, but no intermediates were detected, even at -78
°C. In contrast, treatment of 1 with 3,3-dimethyloxetane cleanly
yielded (silox)3TaOCH2CMe2CH2 (6, 55%, eq 2),32 which was
thermally stable for weeks at 100 °C.
Figure 1. Selected bond distances (Å) and angles (deg) for (silox)3-
(H2N)Ta(C6H4-p-CF3) (3-p-CF3): see text and Ta-O1 ) 1.901(6), Ta-
O3 ) 1.927(5), Si-O(ave) ) 1.688(13); O1-Ta-N ) 83.6(3), O1-
Ta-C1 ) 87.1(3), O3-Ta-N ) 85.5(3), O3-Ta-C1 ) 84.8(3); Ta-
O1-Si1 ) 168.9(4), Ta-O2-Si2 ) 172.2(4), Ta-O3-Si3 ) 162.6(4).
The carbon-heteroatom cleavages can be accommodated by
mechanisms using both electrophilic and nucleophilic sites on
the metal center. Arylamine N-H vs C-N activation is a
consequence of energetically similar pathways; electrophilic
attack on the nitrogen lone pair is dominant in N-H scission,
and nucleophilic attack on the arene ring is most important to
Table 1. Relative Rates of NH- and CN-Bond Oxidative Addition
of Substituted Anilines to (silox)3Ta (1)a
2
C-N cleavage, yet the filled dz and empty dxz/dyz orbitals are
X
σ
m,p(X)b kNH(rel)c
kCN(rel)d
∆∆Gq (kcal/mol)a
necessary for both reactions. O-atom donation and electrophilic
attack by the R-positions of the oxygenated substrates are
integral features of oxidative additions leading to oxymetalla-
cycle formation and epoxide deoxygenation.7
3,5-(CF3)2
4-CF3
3-CF3
0.86e
0.54
0.43
0.30(7)
0.34
48(9)
21(4)
3.0(7)
-2.3(1)
-1.8(1)
-0.65(12)
0.71(12)
0.18(11)
0.28(11)
0.07(11)
0.0
-0.16(10)
0.04(12)
-0.11(10)
-0.38(6)
-0.54(4)
Lastly, in the the Satterfield mechanism1,33 regarding quino-
line hydrodenitrogenation, sp3 C-N bond cleavage is implicated
as the most significant. This study suggests that low-energy
arylamine C-N bond cleavage pathways are available to
heterogeneous surfaces of suitable nucleophilicity, such as the
relatively electron rich catalyts involved in hydrotreating, lending
credence to modification of the conventional mechanism as
proposed by Gioia and Lee.34
3-F
0.74(14)
0.63(12)
0.89(17)
1
4-F
aniline
4-Ph
0.06
0.00
-0.01
1.3(2)
0.93(17)
1.2(2)
1.9(2)
4-Me
4-OMe
4-NMe2
-0.17
-0.27
-0.83
2.5(2)
Acknowledgment. Support from the National Science Foundation
(CHE-9528914 and predoctoral fellowship for T.P.H.) and Cornell
University are gratefully acknowledged.
a Relative to NH addition of aniline at 25 °C; oxidative additions
were irreversible and determined via competition experiments under
pseudo-first-order conditions. b Use of σ+ (kNH) and σ- (kCN) did not
improve the correlations. c For NH oxidative addition: F ) -0.69, R
(corr coeff) ) 0.93. d For CN oxidative addition: F ) 2.1, R ) 0.84.
e Assuming σm(CF3) is additive.
Supporting Information Available: NMR data and procedures
pertaining to Table 1 and X-ray structural data for (silox)3(H2N)Ta-
(C6H4-p-CF3) (3-p-CF3): a summary of crystallographic parameters,
atomic coordinates, bond distances and angles, and anisotropic thermal
parameters (13 pages); structure factor tables (16 pages). Ordering
information is given on any current masthead page.
activation, while severely limited in scope, are opposite (F )
2.1, R ) 0.84) and approach those of electrophilic aromatic
substitution (F ∼ 3-9).26,27 Nucleophilic attack by the filled
JA960092L
dz orbital of 128 is expected to occur at the arylamine ipso
2
t
(30) 4: 1H NMR (C6D6) δ 1.32 (s, Bu), 2.17 (“q”, J ) 6 Hz, CH2),
carbon (LUMO+1) preceding C-N oxidative addition,29 hence
electron withdrawing substituents increase kCN(rel) while de-
creasing the relative rate of NH activation.
4.30 (t, J ) 6 Hz, OCH2), 7.32 (dt, J ) 13, 4 Hz, dCH-), 8.42 (d, J ) 13
Hz, TaCHd); 13C{1H} NMR δ 23.83 (SiC), 31.05 (C(CH3)3), 35.83 (CH2),
67.23 (OCH2), 144.17 (dCH-), 186.29 (TaCHd). Anal. Calcd for
TaSi3O4C40H87: C, 53.54; H, 9.77. Found: C, 53.74; H, 10.21.
(31) Neithamer, D. R.; LaPointe, R. E.; Wheeler, R. A.; Richeson, D.
S.; Van Duyne, G. D.; Wolczanski, P. T. J. Am. Chem. Soc. 1989, 111,
9056-9072.
(26) Wells, P. R. Chem. ReV. 1963, 63, 171-219.
(27) F ) 3.6, FR ) 1.5, FI ) 2.1, using specific σm,p inductive and
resonance values in: Ritchie, C. D.; Sager, W. F. Prog. Phys. Org. Chem.
1964, 2, 323-400. Interpretations based on this limited set of data are
extremely tentative, and use of other data sets (i.e., refs 22 and 23) gave
unrealistic fits.
(32) 6: 1H NMR (C6D6) δ 1.20 (s, Me2), 1.32 (s, tBu), 2.21 (s, TaCH2),
4.50 (s, OCH2); 13C{1H} NMR δ 24.00 (SiC), 30.73 (Me2), 31.15 (C(CH3)3),
47.81 (CMe2), 85.81 (OCH2), 86.50 (TaCH2). Anal. Calcd for
TaSi3O4C41H89: C, 54.03; H, 9.84. Found: C, 54.24; H, 9.90.
(33) Satterfield, C. N.; Smith, C. M.; Ingalls, M. Ind. Eng. Chem., Proc.
Des. DeV. 1985, 24, 1000-1004 and references therein.
(28) Covert, K. J.; Neithamer, D. R.; Zonnevylle, M. C.; LaPointe, R.
E.; Schaller, C. P.; Wolczanski, P. T. Inorg. Chem. 1991, 30, 2494-2508.
(29) For a related orbital argument relevant to C-S bond activation,
see: Myers, A. W.; Jones, W. D.; McClements, S. M. J. Am. Chem. Soc.
1995, 117, 11704-11709.
(34) Gioia, F.; Lee, V. Ind. Eng. Chem., Process Des. DeV. 1986, 25,
918-925.