or phenyl ligand. This results in the formation of a new C–C bond
with concomitant C–N bond cleavage to give the observed ring-
opened oximate complexes (eqn. 2). For 2 this sequence occurs
twice. This supposition is supported by the observation that
addition of one equiv. of pyNO to 2 produces complex 5, along
with the single ring-opened compound (C5Me5)2Th(Ph)[g2-
(O,N)-ONLCH–(CHLCH)2–Ph] and unreacted 2. This pathway
differs from the chemistry observed for 1 and is consistent with the
greater migratory aptitude of a phenyl moiety compared to a
benzyl group.15
(2)
As noted by Wigley and co-workers, intramolecular 1,2-
migration of hydride, alkyl, and aryl ligands in the tantalum
t
complexes [g2-(N,C)-2,4,6-NC5 Bu3H2]Ta(OAr)2R effects C–N
bond cleavage in the coordinated g2-(N,C) pyridine ligand.3a,3c
For other pyridine complexes, presumably N-bound intramole-
cular alkylation results in a disruption of the aromatic p-system,
but without C–N bond cleavage.16 For example, Erker and co-
workers reported that the reaction of (C5Me5)2Th(butadiene) with
pyridine affords an g3-allyl thorium metallacycle that results from
C–C coupling of the diene to the a-carbon of the pyridine ring;
however, no intermediate pyridine complex was detected.16b
In conclusion, we have found that thorium(IV) alkyl and aryl
complexes mediate the facile ring-opening and dearomatization of
the pyridine ring of pyNO under ambient conditions to afford the
first thorium g2-(O,N)-oximate complexes. These unique chemical
transformations represent a new entry in the reactivity of pyNO.
Extension of this chemistry to other N-heterocyclic compounds is
currently under investigation in our laboratory.
Fig. 1 The molecular structure of complex 5?pyNO with thermal
ellipsoids at the 25% probability level. The methyl substituents on the
pentamethylcyclopentadienyl ligands have been omitted for clarity.
Selected bond distances (s) and angles (u): Th(1)–O(2) 5 2.332(3),
Th(1)–N(2) 5 2.577(4), Th(1)–O(3) 5 2.334(4), Th(1)–N(3) 5 2.519(5),
O(2)–N(2) 5 1.372(5), O(3)–N(3) 5 1.365(5), N(2)–C(26) 5 1.280(6),
C(26)–C(27) 5 1.431(7), C(27)–C(28) 5 1.341(8), C(28)–C(29) 5 1.444(8),
C(29)–C(30) 5 1.332(7), C(30)–C(31) 5 1.463(8), N(3)–C(37) 5 1.280(7),
C(37)–C(38) 5 1.445(8), C(38)–C(39) 5 1.346(8), C(39)–C(40) 5 1.431(8),
C(40)–C(41)
5
1.344(8), C(41)–C(42)
5
1.471(8); N(2)–Th(1)–
O(2) 5 31.98(12), N(3)–Th(1)–O(3) 5 32.39(12).
ring-opening and dearomatization of two pyNO molecules. As is
evident from the geometric parameters, the oximate ligands
possess alternating NLC double, C–C single, and CLC double
bonds with trans–cis–trans orientations respectively. Both oximate
ligands are bound to the thorium(IV) metal center in an g2-(O,N)
fashion with a Th–O s-bond and a Th–N dative interaction:
Th(1)–O(2) 5 2.332(3), Th(1)–N(2) 5 2.577(4) s and N(2)–Th(1)–
O(2) 5 31.98(12)u. Th(1)–O(3) 5 2.334(4), Th(1)–N(3) 5
2.519(5) s and N(3)–Th(1)–O(3) 5 32.39(12)u. The thorium–
oxygen interactions are longer than those reported for thorium
alkoxide complexes,8 but substantially shorter (yca. 0.2 s) than
For financial support we acknowledge LANL (Director’s
Postdoctoral Fellowship to J.A.P.), the Division of Chemical
Sciences, Office of Basic Energy Sciences and the Los Alamos
National Laboratory LDRD Program.
Jaime A. Pool, Brian L. Scott and Jaqueline L. Kiplinger*
Chemistry Division, Los Alamos National Laboratory, Los Alamos,
NM 87545, USA. E-mail: kiplinger@lanl.gov; Fax: (505)667-9905;
Tel: (505)665-9553
expected for
a
dative interaction.9 The thorium–nitrogen
Notes and references
dative interactions are substantially longer (yca. 0.3 s) than
{ Crystal structure data for 5?pyNO: C57H79N3O3Th, M 5 1086.278,
triclinic, a 5 13.700(3), b 5 14.541(3), c 5 15.156(3) s, a 5 103.102(3),
b 5 110.879(3), c 5 95.230(3)u, U 5 2698.1(9) s3, T 5 203(2) K, space
those observed for thorium amides.10 Interestingly, the
oximate O–N bond distances (O(2)–N(2)
5 1.372(5) and
group P1, Z 5 2, m(Mo–Ka) 5 2.806 mm21, l 5 0.71073 s, 14366
¯
O(3)–N(3) 5 1.365(5) s) are significantly shorter than those
reported for structurally related transition metal oximate com-
reflections measured, 7170 unique (Rint 5 0.0160) which were used in all
calculations. Final wR(F2) 5 0.0843 (all data). CCDC 263799. See http://
other electronic format.
plexes
Ta(ONMe2)[OSi(SiMe3)3](NMe2)3
(1.466(13)),11
MoO2(ONEt2)2 (1.427(3)),12 and Ti(ONEt2)4 (1.402(7) s)12.
Combined, these geometrical data suggest electronic delocalization
throughout the three-membered Th–O–N metallacycle, as pre-
viously noted for transition metal oximate compounds.11–14
The cleavage of the C–N bond in these aromatic N-heterocyclic
systems is most likely facilitated by the neighboring electron-
withdrawing oxygen atom. Thus, a plausible mechanism involves
initial O-coordination of the pyNO ligand to the oxophilic
thorium(IV) metal center, followed by 1,4-migration of the benzyl
1 K. J. Weller, P. A. Fox, S. D. Gray and D. E. Wigley, Polyhedron, 1997,
16, 3139–3163 and references cited therein.
2 For examples, see: (a) P. L. Watson, J. Chem. Soc., Chem. Commun.,
1983, 276–277; (b) A. Dormond, A. A. El Bouadili and C. Mo¨ıse,
J. Chem. Soc., Chem. Commun., 1985, 914–916; (c) M. E. Thompson,
S. M. Baxter, A. R. Bulls, B. J. Burger, M. C. Nolan, B. D. Santasiero,
W. P. Schaefer and J. E. Bercaw, J. Am. Chem. Soc., 1987, 109,
203–219; (d) R. F. Jordan, D. F. Taylor and N. C. Baenziger,
Organometallics, 1990, 9, 1546–1557; (e) R. Boaretto, P. Roussel,
2592 | Chem. Commun., 2005, 2591–2593
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