Synthesis, structural characterization, and preliminary reactivity profile of a series of monocyclopentadienyl, monoacetamidinate titanium(III) alkyl complexes bearing β-hydrogens

Article abstract of DOI:10.1021/om100877d

Alkylation of Cp*TiCl₂[N(i-Pr)C(Me)N(i-Pr)] (Cp* = η⁵-C₅Me₅) (1) with two equivalents of an alkyllithium reagent provided high yields of the thermally stable, crystalline, paramagnetic titanium(III) alkyl complexes of general structure Cp*Ti(R)[N(i-Pr)C(Me)N(i-Pr)] where R = Et (2), n-Bu (3), i-Bu (4), neopentyl (5), and n-hexyl (6). Solid-state structural characterization of compounds 2-5 by single-crystal X-ray analysis revealed the absence of α- or β-hydrogen agostic interactions between the metal center and the alkyl group R. Isocyanides (R′NC) undergo quantitative 1,1-insertion into the titanium-carbon bond of the alkyl group of 2-6 to provide high yields of the corresponding series of crystalline, paramagnetic Ti(III) η²- iminoacyl derivatives, Cp*Ti[η²-N(R′)=CR)][N(i-Pr) C(Me)N(i-Pr)] (7-11, respectively), which were also structurally characterized by X-ray crystallography for compounds 7 and 9-11. Finally, compounds 3-5 were oxidized with PbCl₂ in diethyl ether to cleanly generate the respective Ti(IV) monochloro, monoalkyl complexes Cp*Ti(R)(Cl)[N(i-Pr) C(Me)N(i-Pr)] (12-14, respectively), the solid-state structures of which were also determined by single-crystal X-ray analyses.

Full text of DOI:10.1021/om100877d

Organometallics 2010, 29, 6587–6593 6587
DOI: 10.1021/om100877d
Synthesis, Structural Characterization, and Preliminary Reactivity
Profile of a Series of Monocyclopentadienyl, Monoacetamidinate
Titanium(III) Alkyl Complexes Bearing β-Hydrogens
Emily F. Trunkely, Albert Epshteyn, Peter Y. Zavalij, and Lawrence R. Sita*
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742,
United States
Received September 9, 2010
Alkylation of Cp*TiCl2[N(i-Pr)C(Me)N(i-Pr)] (Cp*=η5-C5Me5) (1) with two equivalents of an alkyl-
lithium reagent provided high yields of the thermally stable, crystalline, paramagnetic titanium(III) alkyl
complexes of general structure Cp*Ti(R)[N(i-Pr)C(Me)N(i-Pr)] where R=Et (2), n-Bu (3), i-Bu (4), neo-
pentyl (5), and n-hexyl (6). Solid-state structural characterization of compounds 2-5 by single-crystal
X-ray analysis revealed the absence of R- or β-hydrogen agostic interactions between the metal center and
the alkyl group R. Isocyanides (R0NC) undergo quantitative 1,1-insertion into the titanium-carbon
bond of the alkyl group of 2-6 to provide high yields of the corresponding series of crystalline, para-
magnetic Ti(III) η2-iminoacyl derivatives, Cp*Ti[η2-N(R0)dCR)][N(i-Pr)C(Me)N(i-Pr)] (7-11, re-
spectively), which were also structurally characterized by X-ray crystallography for compounds 7 and
9-11. Finally, compounds 3-5 were oxidized with PbCl2 in diethyl ether to cleanly generate the respec-
tive Ti(IV) monochloro, monoalkyl complexes Cp*Ti(R)(Cl)[N(i-Pr)C(Me)N(i-Pr)] (12-14, respec-
tively), the solid-state structures of which were also determined by single-crystal X-ray analyses.
Introduction
ever since the seminal contributions made by Teuben and co-
workers4 over 20 years ago first introduced the bis(η5-penta-
methylcyclopentadienyl), monoalkyl complexes, Cp*2TiR
(Cp*=η5-C5Me5), where R=Me (Ia), Et (Ib), n-Pr (Ic),
CH2Ph (Id), and Np (Np=CH2CMe3) (Ie). Unfortunately,
due to the low thermal stabilities displayed in solution for Ib
and Ic at ambient temperature as the result of a low activation
barrier for rapid and reversible β-hydrogen transfer from the R
group to the metal, the only solid-state structural information
The organometallic chemistry of group 4 metal {M=Ti, Zr,
and Hf} complexes incorporating formal M(III, d1) centers
with open-shell electronic configurations is, at present, still
ꢀ
farlessdevelopedvis-a-vis the wealth of information now avail-
able regarding the structures, stabilities, and chemical reactiv-
ity associated with the corresponding M(II, d2) and M(IV, d0)
formal oxidation states.1-3 As the demand for new metal-
catalyzed organic transformations that can be conducted with
high efficiency and selectivity remains unabated, it is essential
that this gap in knowledge be significantly narrowed. In this
regard, the scientific record has remained largely silent on
the synthesis, structural characterization, and chemical reactiv-
ity of molecularly discrete organometallic Ti(III) complexes
(3) Although Ti(IV, d0) centers are widely considered to be respon-
sible for the chain-growth propagation of polyolefins, experimental
evidence appears to suggest that a Ti(III, d1,) oxidation state is required
for the (stereoselective) coordination polymerization of styrene; see, for
instance: (a) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143–1170. (b)
Guram, A. S.; Jordan, R. F. Compr. Organomet. Chem. 1995, 4, 589–625. (c)
McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587–2598. (d)
Tomotsu, N.; Ishihara, N.; Newman, T. H.; Malanga, M. T. J. Mol. Catal. A:
Chem. 1998, 128, 167–190. (e) Pellecchia, C.; Grassi, A. Top. Catal. 1999, 7,
125–132. (f) Rodrigues, A. S.; Kirillov, E.; Carpentier, J. F. Coord. Chem. Rev.
2008, 252, 2115–2136. (g) Nifant'ev, I. E.; Ustynyuk, L. Y.; Besedin, D. V.
Organometallics 2003, 22, 2619–2629. (h) Pastorino, R.; Capacchione, C.;
Ferro, R.; Milione, S.; Grassi, A. Macromolecules 2009, 42, 2480–2487. (i)
Mahanthappa, M. K.; Waymouth, R. M. J. Am. Chem. Soc. 2001, 123, 12093–
12094. (j) Michiue, K.; Jordan, R. F. Macromolecules 2003, 36, 9707–9709.
(4) (a) Pattiasina, J. W.; Hissink, C. E.; de Boer, J. L.; Meetsma, A.;
Teuben, J. H.; Spek, A. L. J. Am. Chem. Soc. 1985, 107, 7758–7759.
(b) Luinstra, G. A.; Teuben, J. H. J. Chem. Soc., Chem. Commun. 1990,
1470–1471. (c) Luinstra, G. A.; Ten Cate, L. C.; Heeres, H. J.; Pattiasina,
J. W.; Meetsma, A.; Teuben, J. H. Organometallics 1991, 10, 3227–3237.
(d) Luinstra, G. A.; Teuben, J. H. J. Organomet. Chem. 1991, 420, 337–344.
(e) Luinstra, G. A.; Vogelzang, J.; Teuben, J. H. Organometallics 1992, 11,
2273–2281. (f) Luinstra, G. A.; Teuben, J. H. J. Am. Chem. Soc. 1992, 114,
3361–3367. Also see: (g) Walter, M. D.; Sofield, C. D.; Andersen, R. A.
Organometallics 2008, 27, 2959–2970 for related work with Cp02TiX (Cp0 =
η5-[1,3-(t-Bu)2C5H3]; X = Cl, Me).
*To whom correspondence should be addressed. E-mail: lsita@
umd.edu.
(1) For general discussions and applications of group 4 organome-
tallic chemistry, see: (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.;
Finke, R. G. Principles and Applications of Organotransition Metal
Chemistry; University Science Books: Mill Valley, CA, 1987. (b) Marek,
I., Ed. Titanium and Zirconium in Organic Synthesis; Wiley-VCH:
New York, 2002.
(2) For investigations of Ti(II) and Zr(II) chemistry, see, for instance:
(a) Cohen, S. A.; Auburn, P. R.; Bercaw, J. E. J. Am. Chem. Soc. 1983,
105, 1136–1143. (b) Buchwald, S. L.; Nielsen, R. B. Chem. Rev. 1988, 88,
1047–1058. (c) Negishi, E.; Takahashi, T. Acc. Chem. Res. 1994, 27, 124–
130. (d) Thorn, M. G.; Hill, J. E.; Waratuke, S. A.; Johnson, E. S.; Fanwick,
P. E.; Rothwell, I. P. J. Am. Chem. Soc. 1997, 119, 8630–8641. (e) Waratuke,
S. A.; Thorn, M. G.; Fanwick, P. E.; Rothwell, A. P.; Rothwell, I. P. J. Am.
Chem. Soc. 1999, 121, 9111–9119. (f) Negishi, E. Dalton Trans. 2005, 827–
848. (g) Huynh, K.; Vignolle, J.; Tilley, T. D. Angew. Chem., Int. Ed. 2009,
48, 2835–2837. (h) Miller, A. D.; Tannaci, J. F.; Johnson, S. A.; Hyuk, L.;
McBee, J. L.; Tilley, T. D. J. Am. Chem. Soc. 2009, 131, 4917–4927, and
references therein.
r
2010 American Chemical Society
Published on Web 11/12/2010
pubs.acs.org/Organometallics

6588 Organometallics, Vol. 29, No. 23, 2010
Trunkely et al.
for this series of compounds that has been reported to date
is for the derivative Ie, in which no β-hydrogens are pre-
sent.4b Indeed, to the best of our knowledge, to date, only two
structurally characterized Ti(III) alkyl complexes bearing
β-hydrogens have been reported in the literature, and in each
case, the compound represented a single isolated example.5 In
addition, while the Teuben group briefly explored the chemi-
cal reactivity of Ia and Ib, structural identification of the pro-
ducts of these reactions rested on vibrational spectroscopy and
elemental analyses and not on solid-state molecular structures
and geometric parameters acquired through single-crystal
X-ray crystallography.
Over the past decade, we have established and documented
the unique ability of the η5-cyclopentadienyl/η2-amidinate
(CpAm) ligand environment to support the synthesis and
structural characterization of neutral and cationic, mid- to
high-valent, second- and third-row group 4 {Zr and Hf} and
group 5 {Ta} metal complexes bearing alkyl substituents that
are (kinetically) stable toward both β-hydrogen and β-alkyl
group transfer processes.6-8 Regarding first-row group 4 metal
congeners, Mountford and co-workers9 have established the
solid-state structures and solution chemistry of the mono-
nuclear CpAm Ti(IV) imido complexes of general formula
Cp*Ti(dNR)[N(R1)C(R2)N(R3)]. Hagadorn and co-workers10
further developed two novel classes of geometrically con-
strained bisamidinate ligands and employed these for investi-
gating the syntheses and structures of dinuclear CpAm Ti(IV)
and Ti(III) complexes. Finally, we have previously reported the
syntheses and structural characterization of several derivatives
of CpAm Ti(IV) dimethyl complexes of general formula (η5-
C5R5)Ti(Me)2[N(R1)C(Me)N(R2)] (R=H and Me) that are
conveniently prepared in high yield via carbodiimide insertion
into a Ti-Me bond of preformed (η5-C5R5)Ti(Me)3.11 Herein,
we now report the results of investigations that serve to extend
the utility of the CpAm ligand set for accessing a new family
of structurally characterized Ti(III) alkyl complexes bearing
β-hydrogens of general structure Cp*Ti(R)[N(i-Pr)C(Me)N-
(i-Pr)] that further includes a preliminary screening of chemical
reactivity involving insertions of isocyanides, R0NC, into the
titanium-carbon bond to form the corresponding series of
Ti(III) η2-iminoacyl derivatives, Cp*Ti[η2-CRdNR0][N(i-Pr)-
C(Me)N(i-Pr)], as well as PbCl2-mediated chemical oxidation
to provide the corresponding Ti(IV) chloro, alkyl complexes,
Cp*Ti(R)(Cl)[N(i-Pr)C(Me)N(i-Pr)], in high yield. These
findings serve as a complement to those reported by Teuben
and co-workers for similar reactions involving Ia-Ie. In addi-
tion, since the solution chemistry of the new series of CpAm
Ti(III) monoalkyl complexes appears to be completely devoid
of β-hydrogen transfer processes, this report should prove
useful in the further development of Ti(III)-based organome-
tallic chemistry, including the design of molecularly discrete
Ti(III) catalysts for the (stereoselective) coordination poly-
merization of styrene and R-olefins.3,8
(5) (a) Bailey, B. C.; Basuli, F.; Huffman, J. C.; Mindiola, D. J.
Organometallics 2006, 25, 3963–3968. (b) Bai, G.; Wei, P.; Stephan, D. W.
Organometallics 2006, 25, 2649–2655.
(6) For CpAm group 4 Zr(II), Zr(IV), and Hf(IV) β-hydrogen-bearing
alkyl complexes, see: (a) Keaton, R. J.; Koterwas, L. A.; Fettinger, J. C.;
Sita, L. R. J. Am. Chem. Soc. 2002, 124, 5932–5933. (b) Keaton, R. J.; Sita,
L. R. Organometallics 2002, 21, 4315–4317. (c) Keaton, R. J.; Sita, L. R.
Organometallics 2002, 21, 4315–4317. (d) Zhang, Y.; Keaton, R. J.; Sita, L. R.
J. Am. Chem. Soc. 2003, 125, 8749–8747. (e)Kissounko, D. A.; Epshteyn, A.;
Fettinger, J. C.; Sita, L. R. Organometallics 2006, 25, 1076–1078. (f) Harney,
M. B.; Keaton, R. J.; Fettinger, J. C.; Sita, L. R. J. Am. Chem. Soc. 2006, 128,
3420–3432. (g) Fontaine, P. P.; Epshteyn, A.; Zavalij, P. Y.; Sita, L. R.
J. Organomet. Chem. 2007, 692, 4683–4689. (h) Epshteyn, A.; Trunkely,
E. F.; Kissounko, D. A.; Fettinger, J. C.; Sita, L R. Organometallics 2009, 28,
2520–2526.
Results and Discussion
A. Synthesis and Structural Characterization of Cp*Ti(R)-
[N(i-Pr)C(Me)N(i-Pr). Scheme 1 summarizes synthetic meth-
odology that was employed in the present work.12 Succinctly,
reaction of the CpAm Ti(IV) dichloride precursor Cp*Ti(Cl)2-
[N(i-Pr)C(Me)N(i-Pr)] (1)13 with 2 equiv of an alkyllithium
(RLi) reagent in diethyl ether (Et2O) at ambient temperature
provided the paramagnetic, dark purple products 2-6, which,
except for the oily material obtained in the case of 6 where R =
Hex, could be obtained in analytically pure form in high yield
through recrystallization from pentane at -30 °C. Elemental
(C, H, and N) analyses obtained for 2-5 proved to be fully
consistent with the CpAm Ti(III) monoalkyl formulation that
is depicted for these compounds in Scheme 1, and fortunately,
in the case of 6, a crystalline product could be subsequently
obtained from its reaction with 2,6-dimethylphenylisocyanide,
the structural characterization of which also served to unequi-
vocally establish the identity of this CpAm Ti(III) alkyl deriv-
ative (vide infra).
(7) For CpAm group 5 Ta(IV, d1) and Ta(V, d0) β-hydrogen-bearing
alkyl complexes, see: Epshteyn, A.; Zavalij, P. Y.; Sita, L. R. J. Am.
Chem. Soc. 2006, 128, 16052–16053.
(8) For cationic CpAm Zr(IV) and Hf(IV) β-hydrogen-bearing alkyl
complexes that are active for the living (stereoselective) coordination
polymerization of ethene, propene, R-olefins, and R,ω-nonconjugated
dienes, see: (a) Jayaratne, K. C.; Sita, L. R. J. Am. Chem. Soc. 2000, 122,
958–959. (b) Jayaratne, K. C.; Sita, L. R. J. Am. Chem. Soc. 2001, 123, 10754–
10755. (c) Keaton, R. J.; Jayaratne, K. C.; Henningsen, D. A.; Koterwas, L. A.;
Sita, L. R. J. Am. Chem. Soc. 2001, 123, 6197–6198. (d) Keaton, R. J.; Sita,
L. R. J. Am. Chem. Soc. 2002, 124, 9070–9071. (e) Zhang, Y.; Keaton, R. J.;
Sita, L. R. J. Am. Chem. Soc. 2003, 125, 9062–9069. (f) Harney, M. B.;
Keaton, R. J.; Sita, L. R. J. Am. Chem. Soc. 2004, 126, 4536–4537. (g) Zhang,
Y.; Reeder, E. K.; Keaton, R. J.; Sita, L. R. Organometallics 2004, 23, 3512–
3520. (h) Kissounko, D. A.; Zhang, Y.; Harney, M. B. Adv. Synth. Catal. 2005,
347, 426–432. (i) Harney, M. B.; Zhang, Y.; Sita, L. R. Angew. Chem., Int. Ed.
2006, 45, 2400–2404. (j) Harney, M. B.; Zhang, Y.; Sita, L. R. Angew. Chem.,
Int. Ed. 2006, 45, 6140–6144. (k) Zhang, W.; Sita, L. R. J. Am. Chem. Soc.
2008, 130, 442–443. (l) Zhang, W.; Sita, L. R. Adv. Synth. Catal. 2008, 350,
439–447. (m) Zhang, W.; Wei, J.; Sita, L. R. Macromolecules 2008, 41, 7829–
7833. (n) Sita, L. R. Angew. Chem., Int. Ed. 2009, 48, 2464–2472. (o) Wei,
J.; Zhang, W.; Sita, L. R. Angew. Chem., Int. Ed. 2010, 49, 1768–1772.
(p) Wei, J.; Zhang, W.; Wickham, R.; Sita, L. R. Angew. Chem., Int. Ed. 2010,
49, in press.
(9) (a) Stewart, P. J.; Blake, A. J.; Mountford, P. J. Organomet.
Chem. 1998, 564, 209–214. (b) Stewart, P. J.; Blake, A. J.; Mountford, P.
Organometallics 1998, 17, 3271–3281. (c) Guiducci, A. E.; Cowley, A. R.;
Skinner, M. E. G.; Mountford, P. J. Chem. Soc., Dalton Trans. 2001, 1392–
1394. (d) Boyd, C. L.; Clot, E.; Guiducci, A. E.; Mountford, P. Organome-
tallics 2005, 24, 2347–2367. (e) Guiducci, A. E.; Boyd, C. L.; Mountford, P.
Organometallics 2006, 25, 1167–1187. (f) Guiducci, A. E.; Boyd, C. L.;
Clot, E.; Mountford, P. J. Chem. Soc., Dalton Trans. 2009, 5960–5979.
(10) (a) Hagadorn, J. R.; McNevin, M. J. Organometallics 2003,
22, 609–611. (b) McNevin, M. J.; Hagadorn, J. R. Inorg. Chem. 2004, 43,
8547–8554.
1
Given the paramagnetic nature of 2-6, H NMR spec-
troscopy could not be used to establish with certainty the mo-
lecular structures of this series of compounds. Fortunately,
however, this task could be accomplished through single-
crystal X-ray analyses of 2-5, which yielded the solid-state
molecular structures and selected geometric parameters that
are presented in Figure 1 and Table 1, respectively.12 From
(11) (a) Sita, L. R.; Babcock, J. R. Organometallics 1998, 17, 5228–
5230. (b) Koterwas, L. A.; Fettinger, J. C.; Sita, L. R. Organometallics 1999,
18, 4183–4190. (c) Babcock, J. R.; Incarvito, C.; Rheingold, A. L.; Fettinger,
J. C.; Sita, L. R. Organometallics 1999, 18, 5729–5732.
(12) Details provided in the Supporting Information.
(13) Fontaine, P. P.; Yonke, B. L.; Zavalij, P. Y.; Sita, L. R. J. Am.
Chem. Soc. 2010, 132, 12273–12285.

Article
Organometallics, Vol. 29, No. 23, 2010 6589
Scheme 1
degree of thermal stability is in keeping with that reported
by Stephen and co-workers5b for the half-sandwich, β-diketi-
minato Ti(III) n-butyl derivative (η5-C5H5)Ti(n-Bu)[HC-
(CMeNC6H3(i-Pr)2)2], as well as our own prior observations
of significantly high barriers for β-hydrogen transfer (abstrac-
tion) processes within analogous neutral second- and third-
row group 4 and 5 CpAm metal alkyl complexes.6,7 Finally, of
potential interest with respect to possible mechanisms for
1-hexene production via early transition-metal-catalyzed se-
lective ethene trimerization,15 no qualitative difference could
be discerned between the thermal stability displayed by the
n-butyl derivative 3 vs that of the n-hexyl analogue 6, thereby
suggesting the absence of any unique intra- or intermolecular
pathways involving abstraction of more remote γ-, δ-, or ε-
hydrogen atoms within the longer n-alkyl chain of the latter.
C. Chemical Reactivity of Cp*Ti(R)[N(i-Pr)C(Me)N(i-Pr)].
i. 1,1-Migratory Insertion of R0NC. We have previously shown
that cationic CpAm group 4 Zr(IV) and Hf(IV) alkyl com-
plexes are highly active initiators for the living coordination
polymerization of ethene, R-olefins, and R,ω-nonconjugated
dienes.8 In contrast, compounds 2-6 were all found to be
completely inert in solution toward 1,2- (or 2,1-) migratory
insertion of alkenes and dienes into the titanium-carbon bond,
including ethene, propene, 1,3-butadiene, 1,5-hexadiene, cyclo-
pentene, norbornene, and styrene. On the other hand, with
isocyanides R0NC (R0 =t-Bu or 2,6-Me2C6H3), 1,1-migratory
insertion proceeded quantitatively overnight in pentane solu-
tion at room temperature to provide the corresponding para-
magnetic, dark blue or dark purple crystalline CpAm Ti(III) η2-
iminoacyl derivatives 7-11 in excellent yields according to
Scheme 1.16 Similar 1,1-insertion of an isocyanide into the
titanium-carbon bond of Ib was previously established by the
Teuben group; however, no validating solid-state molecular
structure for the product of this reaction was ever reported.4 In
the present study, single-crystal X-ray analyses were performed
for compounds 7 and 9-11, and the data presented in Figure 2
and Table 2 for the solid-state molecular structures and selected
geometric parameters, respectively, for these compounds con-
firm a bidentate η2-iminoacyl coordination mode, as depicted
in Scheme 1.12,16 As Table 2 reveals, the geometrical parameters
about the Ti(III) metal center and the η2-iminoacyl CdN bond
length remain fairly constant for this series of complexes in spite
of variations in the nature of the migrating R group and of the
R0 group of the isocyanide involved in the 1,1-insertion process.
However, the influence of varying magnitudes of nonbonded
these data, it can be seen that all four compounds share a similar
idealized Cs-symmetric piano-stool molecular geometry for the
CpAmTiR ligand environment. Importantly, none of the solid-
state structures show any evidence to support the existence of
R- or β-hydrogen agostic interactions between the alkyl sub-
stituent and the metal center.14 The data in Table 1 also reveal
that while most of the selected geometric parameters remain
essentially invariant for the series of compounds, the Ti1-
C19-C20 bond angle dramatically increases as the steric bulk
of the alkyl substituent increases [cf. 116.73(19)° for 2, 119.2(6)°
for 3, 120.15(10)° for 4, and 128.91(10)° for 5]. On the basis of
this simple inspection, it can be concluded that the CpAm
ligand environment about the metal is uniquely set up to
position much of the steric bulk of the alkyl substituent
“underneath” the η2-amidinate fragment, and an increase in
nonbonded steric interactions that occurs between the alkyl
substituent and the CpAm fragment is most readily accom-
modated through a single bond-angle distortion about the
alkyl group R-carbon. Similar observations have been pre-
viously documented by us for neutral and cationic CpAm
Zr(IV) and CpAm Hf(IV) complexes with large β-hydrogen-
bearing alkyl substituents, including t-Bu groups.6a,f In
the case of the isobutyl derivative 4, a small distortion away
from an idealized tetrahedral geometry is observed for the
β-carbon, as revealed by the sum of the bond angles C19-
C20-C21, C19-C20-C22, and C21-C19-C22, which is
∼333°, and this value can be compared to 327° expected for a
tetravalent, tetracoordinate geometry vs 360° for trigonal-
coplanar carbon. However, it can be reasonably concluded
that the origin of this distortion is most likely the result of
steric strain rather than being the manifestation of a second-
ary β-hydrogen agostic interaction.6f
(15) (a) Hessen, B. J. Mol. Catal. A: Chem. 2004, 213, 129–135. (b)
Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Organometallics 2002, 21, 5122–
5135. (c) Deckers, P. J. W.; Hessen, B.; Teuben, J. H. Angew. Chem., Int. Ed.
2001, 40, 2516–2519. (d) You, Y.; Girolami, G. S. Organometallics 2008, 27,
3172–3180. (e) Andes, C.; Harkins, S. B.; Murtuza, S.; Oyler, K.; Sen, A.
J. Am. Chem. Soc. 2001, 123, 7423–7424. (f) Briggs, J. R. J. Chem. Soc.,
Chem. Commun. 1989, 674–675. (g) Dixon, J. T.; Green, M. J.; Hess, F. M.;
Morgan, D. H. J. Organomet. Chem. 2004, 689, 3641–3668. (h) Wass, D. F.
Dalton Trans. 2007, 816-819 (review).
B. ThermalStabilityofofCp*Ti(R)[N(i-Pr)C(Me)N(i-Pr)].
In the solid-state and hydrocarbon (pentane, benzene, and
toluene) solutions, compounds 2-6 proved to be indefinitely
stable at room temperature under an inert atmosphere of dinitro-
gen. Thesesolutions were also shownto bethermally robust at
elevated temperature for extended periods of time (e.g., 50 °C,
72 h), with no evidence for decomposition involving release of
1-alkenes being obtained by1H NMR spectroscopy. This high
(16) For structures of other early transition metal η2-iminoacyl
complexes obtained through 1,1-insertion of isocyanides into metal-carbon
bonds, see, for instance: (a) Chamberlain, L. R.; Durfee, L. D.; Fanwick,
P.E.;Kobriger,L.;Latesky,S.L.;McMullen, A.K.;Rothwell,I.P.;Folting,
K.; Huffman, J. C. J. Am. Chem. Soc. 1987, 109, 390–402. (b) Durfee, L. D.;
Rothwell, I. P. Chem. Rev. 1988, 88, 1059–1079. (c) Giannini, L.; Caselli, A.;
Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N.; Sgamellotti, A. J. Am.
Chem. Soc. 1997, 119, 9198–9210. (d) Thorn, M. G.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1999, 18, 4442–4447. (e) Thorn, M. G.; Lee, J.; Fanwick,
P. E.; Rothwell, I. P. J. Chem. Soc., Dalton Trans. 2002, 3398–3405. (f)
Sebastian, A.; Royo, P.; Gomez-Sal, P.; de Arellano, C. R. Eur. J. Inorg. Chem.
2004, 3814–3821. (g) Spencer, L. P.; Fryzuk, M. D. J. Organomet. Chem. 2005,
690, 5788–5803. (h) Thomson, R. K.; Schafer, L. L. Organometallics 2010, 29,
3546–3555.
(14) (a) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg.
Chem. 1988, 36, 1–124. (b) Scherer, W.; McGrady, G. S. Angew. Chem., Int.
Ed. 2004, 43, 1782–1806. (c) Brookhart, M.; Green, M. L. H.; Parkin, G.
Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 6908–6914.

6590 Organometallics, Vol. 29, No. 23, 2010
Trunkely et al.
Figure 1. Molecular structures (30% thermal ellipsoids) of compounds 2, 3, 4, and 5. Hydrogen atoms have been removed for the sake of
clarity except for those located on the Et, n-Bu, i-Bu, and Np groups, respectively, which are represented by small spheres of arbitrary size.
˚
Table 1. Selected Bond Lengths (A) and Bond Angles (deg) for
increasingly more obtuse [cf. 164.54(13)° for 9 vs 168.02(19)°
Compounds 2, 3, 4, and 5
for 10 (see Table 2)].
ii. Chemical Oxidation. It was serendipitously discovered
that upon introduction of a small quantity of dichlorome-
thane (CH2Cl2) to a hydrocarbon solution of 3, instantaneous
and quantitative oxidation of the metal center occurred with
concomitant chloride atom abstraction to cleanly provide the
diamagnetic, orange-red CpAm Ti(IV) n-butyl, chloride deriv-
ative Cp*Ti(n-Bu)(Cl)[N(i-Pr)C(Me)N(i-Pr)] (12).3c A some-
what less convenient route to 12 involves chemical oxidation
of 3 using PbCl2 in Et2O in the manner previously reported
by Teuben and co-workers,4 and in this way, chemical oxida-
tions of 4 and 5 were also carried out to provide the corres-
ponding derivatives Cp*Ti(R)(Cl)[N(i-Pr)C(Me)N(i-Pr)],
where R=i-Bu (13) and Np (14), which were also isolated as
diamagnetic orange-red crystalline materials according to
Scheme 1. Here, it is interesting to note that all attempts to
prepare compounds 12-14 through direct reaction of the
CpAm Ti(IV) dichloride precursor 1 with one equivalent of
the respective organometallic reagents, RLi or RMgCl, were
unsuccessful since metal-centered, one-electron reduction to
Ti(III) was always the preferred reaction pathway. Thus, it
would now appear that the best synthetic route to these and
parameter
2
3
4
5
Ti1-C19
2.149(3)
2.078(2)
2.084(2)
1.537(4)
64.55(8)
2.119(12)
2.1587(14) 2.1708(14)
Ti1-N1
2.0739(12) 2.0794(10) 2.0857(11)
2.0872(12) 2.0867(10) 2.0898(11)
1.565(13)
64.22(5)
Ti1-N2
C19-C20
1.5373(19) 1.5354(19)
64.34(4) 64.13(4)
120.15(10) 128.91(10)
112.60(12) 110.22(15)
110.36(13) 109.94(14)
111.51(12)
N1-Ti1-N2
Ti1-C19-C20
C19-C20-C21
C19-C20-C22
C19-C20-C23
C21-C20-C22
116.73(19) 119.2(6)
117.3(5)
109.92(13) 109.82(19)
steric interactions that arise with different combinations of
R and R0 do emerge for at least two key structural parameters
that are listed in Table 2. More specifically, the increased
steric bulk when R0 = t-Bu vs the case for R0=2,6-Me2C6H3
appears to manifest in an increase in the parameter Φ, which
is defined as the angle between the mean planes determined
by N1-Ti1-N2 and N3-Ti1-C19 [cf. 103.5° in 7 vs 74.2-
76.3° for 9-11]. In addition, for R0 =2,6-Me2C6H3, as the
steric bulk of themigrating R group increases, theTi-CR-Cβ
angle of the iminoacyl carbon atom responds by becoming

Article
Organometallics, Vol. 29, No. 23, 2010 6591
Figure 2. Molecular structures (30% thermal ellipsoids) of compounds 7, 9, 10, and 11. Hydrogen atoms have been removed for the
sake of clarity.
˚
Table 2. Selected Bond Lengths (A) and Bond Angles (deg) for Compounds 7, 9, 10, and 11
parameter
7
9
10
11
Ti1-C19
2.093(2)
2.162(19)
2.109(2)
2.0706(19)
1.287(3)
36.01(8)
71.04(13)
72.95(13)
161.8(2)
153.08(16)
103.5
2.0976(17)
2.1857(14)
2.1086(14)
2.0623(14)
1.289(2)
36.10(6)
70.46(9)
73.44(10)
164.54(13)
156.43(11)
75.7
2.1191(15)
2.2053(12)
2.1076(13)
2.0554(12)
1.2919(19)
36.02(5)
69.30(8)
74.68(9)
168.02(19)
155.88(10)
74.3
2.0912(15)
2.1971(12)
2.1138(13)
2.0617(11)
1.2886(19)
36.14(5)
70.68(8)
73.17(8)
167.47(12)
158.13(10)
76.3
Ti1-N1
Ti1-N2
Ti1-N3
C19-N3
C19-Ti1-N3
Ti1-C19-N3
Ti1-N3-C19
Ti1-C19-C20
Ti1-N3-CR(N3)
Θ(N1-Ti1-N2, N3-Ti1-C19)
other Cp*Ti(R)(Cl)[N(R1)C(R2)N(R3)] derivatives is via the
overall two-step reduction/oxidation pathway that is detailed
in Scheme 1 (e.g., 1 f 3 f 12).
Since compounds 12-14 also now represent a new series
of CpAm Ti(IV) alkyl, chloride complexes, single-crystal
X-ray analyses were conducted, and Figure 3 presents the
solid-state molecular structures that were obtained from
these studies.12 Once again, these structures are distinguished
by the notable lack of any evidence for the existence of either
R- or β-hydrogen agostic interactions between the metal
center and the R group. This structural feature is in keeping
with the high degree of thermal stability that is displayed by
these compounds in the solid-state and toluene solutions up
to temperatures of at least 90 °C, as supported by 1H NMR

6592 Organometallics, Vol. 29, No. 23, 2010
Trunkely et al.
Figure 3. Molecular structures (30% thermal ellipsoids) of compounds 12, 13, and 14. Hydrogen atoms have been removed for the sake
of clarity.
Scheme 2
Conclusion
In summary, the present report serves to establish the CpAm
ligand environment as a versatile new experimental platform
for expanding our knowledge of the fundamental organome-
tallic chemistry of Ti(III) and, in particular, for molecularly
discrete metal complexes that incorporate alkyl substituents
bearing β-hydrogens. On the basis of our prior experience with
the CpAm ligand set that has successfully supported a wide
variety of studies concerning the organometallic chemistry of
mid- to high-valent early transition metals,6-8,11,13,20 it is
possible that through strategic engineering of nonbonded
steric interactions, the newly established class of CpAm Ti(III)
alkyl complexes, (η5-C5R05)Ti(R)[N(R1)C(R2)N(R3)], could
provide access to a wide variety of desirable reaction paths
leading to novel Ti(III)-mediated organic transformations.
Efforts toward achieving this goal are currently in progress.
spectroscopy. A notable apparent departure from stability,
however, was discovered for compound 14. More specifi-
cally, whereas combustion-based elemental analyses (C, H,
and N) for compounds 12 and 13 were fully consistent with
the Cp*Ti(n-R)(Cl)[N(i-Pr)C(Me)N(i-Pr)] molecular com-
position where R = n-Bu and i-Bu, respectively, elemental
analyses of crystalline 14, which was determined to be
analytically pure on the basis of 1H NMR spectroscopy,12
consistently yielded, for five separate analyses, C, H, and N
percentages that matched an empirical composition for 14
less a CMe4 fragment. As Scheme 2 reveals, this observation
most likely originates with facile hydrogen-atom abstrac-
tion from the Cp* ligand by the R-carbon of the Np group
to form the “tuck-in” complex 15. There is now consider-
able precedent in the literature for this type of hydrogen
abstraction process, and with respect to Cp* group 4 metal
derivatives in particular, the previously introduced Ti(III)
alkyl derivatives of Cp*2Ti-R (I) are known to eliminate
RH with formation of the tuck-in complex Cp*Ti{η5:η1-
C5Me4(CH2)}4a,c,17 and the Ti(IV) dimethyl complex, Cp*2-
Ti(Me)2, thermally eliminates CH4 to provide Cp*Ti(Me)-
{ η5:η1-C5Me4(CH2)} in high yield.17,18 Finally, Teuben and
co-workers19 have reported that Cp*2Zr(Cl)(Np) under-
goes clean thermal decomposition to provide the tuck-in
complex, Cp*Zr(Cl){ η5:η1-C5Me4(CH2)}, in a syntheti-
cally useful process.
Experimental Section
General Considerations. All manipulations were carried out
under an atmosphere of dinitrogen using standard glovebox tech-
niques. Solvents were dried (Na/benzophenone for Et2O and pen-
tane; Na for toluene) and distilled under argon prior to use. C6D6
for NMR spectroscopy was purchased from Cambridge Isotope
Laboratories, dried over Na/K, degassed, and vacuum trans-
ferred prior to use. Celite was oven-dried (150 °C for several
days) prior to use. NpLi and 1 were prepared according to the
literaturemethods. Allother alkyllithium reagents were obtained
from commercial sources and titrated prior to use. Elemental
analyses were performed by Midwest Microlab, LLC. 1H NMR
spectra were recorded at 400 MHz at 25 °C.
Cp*Ti(Et)[N(i-Pr)C(Me)N(i-Pr)] (2). To a solution of 1
(0.545 g, 1.38 mmol) in Et2O (70 mL) was added EtLi (0.50 M
in benzene/cyclohexane, 90:10, 1.4 mL, 2.8 mmol) at ambient
temperature. The reaction was stirred for 16 h, during which time
the solution changed in color from burgundy to brown. The
volatiles were removed in vacuo. The resulting crude product was
taken upina minimalamountofpentane, the mixture was filtered
through a small pad of Celite in a glass frit, and the filtrate was
(17) (a) Bercaw, J. E.; Brintzinger, H. H. J. Am. Chem. Soc. 1971, 93,
2045–2046. (b) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H.
J. Am. Chem. Soc. 1972, 94, 1219–1238.
(18) McDade, C.; Green, J. C.; Bercaw, J. E. Organometallics 1982, 1,
1629–1634.
(19) Fandos, R.; Meetsma, A.; Teuben, J. H. Organometallics 1991,
10, 2665–2671.
(20) (a) Hirotsu, M.; Fontaine, P. P.; Epshteyn, A.; Zavalij, P. Y.;
Sita, L. R. J. Am. Chem. Soc. 2007, 129, 9284–9285. (b) Hirotsu, M.;
Fontaine, P. P.; Zavalij, P. Y.; Sita, L. R. J. Am. Chem. Soc. 2007, 129,
12690–12692.

Article
Organometallics, Vol. 29, No. 23, 2010 6593
concentrated in vacuo. Upon cooling to -35 °C, compound 2 was
isolated as a purple crystalline material, which was then recrys-
tallized from pentane at -35 °C to provide analytically pure
material. Yield of 2: 0.331 g (0.938 mmol, 68%). Anal. Calcd for
TiC20H37N2: C, 67.98; H, 10.55; N, 7.93. Found: C, 68.18; H,
10.27; N, 8.08.
added 2,6-dimethylphenylisocyanide (0.024 g, 0.182 mmol) in
pentane (3 mL). The reaction mixture was then stirred for 18 h
and then cooled to -30 °C, whereupon the desired product was
obtained as a paramagnetic dark purple crystalline material. Yield
of 10: 0.049 g (0.093 mmol, 61%). Anal. Calcd for TiC32H52N3: C,
72.98; H, 9.95; N, 7.98. Found: C, 72.72; H, 9.92; N, 8.03.
Cp*Ti[η2-C(n-Hex)dN(2,6-Me2C6H3)][N(i-Pr)C(Me)N(i-Pr)]
(11). The crude product obtained for 6 was taken up in pentane
(4 mL), and to the solution was added 2,6-dimethylphenylisocya-
nide (0.064 g, 0.488 mmol) in pentane (3 mL) at ambient tem-
perature. The reaction mixture was then stirred for 18 h and then
cooled to -30 °C, whereupon the desired product was obtained
as a paramagnetic dark purple crystalline material. Yield of 11:
0.104 g (0.192 mmol, 47%). Anal. Calcd for TiC33H54N3: C,
73.31; H, 10.07; N, 7.77. Found: C, 73.42; H, 9.97; N, 7.75.
Cp*Ti(n-Bu)(Cl)[N(i-Pr)C(Me)N(i-Pr)] (12). To a solution of
3 (0.133 g, 0.349 mmol) in Et2O (10 mL) was added PbCl2 (0.048 g,
0.173 mmol) all at once. The reaction was stirred for 2 h at amb-
ient temperature, during which time the solution changed in color
from purple to orange. After the general workup procedure, the
desired product was isolated and recrystallized from pentane to
provide a diamagnetic orange-red crystalline material. Yield of
12: 0.094 g (0.225 mmol, 61%). 1H NMR (C6D6): δ 3.65 (m, 1H,
CH(CH3)2), 3.28 (m, 1H, CH(CH3)2), 2.25 (m, 1H, TiCH2), 1.98
(s, 15H, C5Me5), 1.74 (s, 3H, CH3), 1.37 (d, 3H, CH(CH3)2, 1.33
(d, 3H, CH(CH3)2, 1.32-1.19 (m, 4H, CH2CH2CH2CH3), 1.09
(d, 3H, CH(CH3)2, 1.05 (d, 3H, CH(CH3)2, 0.97 (t, 3H, CH3),
0.69 (t, 1H, TiCH2). Anal. Calcd for TiC22H41N2Cl: C, 63.38; H,
9.91; N, 6.72. Found: C, 63.49; H, 9.71; N, 6.60.
Cp*Ti(i-Bu)(Cl)[N(i-Pr)C(Me)N(i-Pr)] (13). To a solution of
4 (0.181 g, 0.474 mmol) in Et2O (10 mL) was added PbCl2
(0.066 g, 0.237 mmol) at ambient temperature. The reaction was
stirred for 2 h at ambient temperature, during which time the
solutionchangedincolorfrompurpletoorange. After the general
workup procedure, the desired product was isolated and recrys-
tallized from pentane to provide a diamagnetic orange-red crys-
talline material. Yield of 13: 0.083g (0.199 mmol, 42%). 1H NMR
(C6D6): δ 3.70 (m, 1H, CH(CH3)2), 3.34(m, 1H, CH(CH3)2), 2.28
(m, 1H, CH2CH(CH3)2), 1.97 (s, 15H, C5Me5), 1.72 (s, 3H, CH3),
1.37 (d, 3H, CH(CH3)2), 1.23 (d, 3H, CH(CH3)2), 1.22 (d, 6H,
CH2CH(CH3)2), 1.15 (t, 1H, TiCH2), 1.13 (d, 3H, CH(CH3)2),
1.07 (d, 3H, CH(CH3)2), 0.88 (m, 1H, TiCH2). Anal. Calcd for
TiC22H41N2Cl: C, 63.38; H, 9.91; N, 6.72. Found: C, 63.03; H,
10.06; N, 6.75.
Cp*Ti(n-Bu)[N(i-Pr)C(Me)N(i-Pr)] (3). To a solution of 1
(0.511 g, 1.29 mmol) in Et2O (75 mL) was added n-BuLi (1.6 M
in hexanes, 1.6 mL, 2.6 mmol) at ambient temperature, and the
mixture was stirred for 16 h, during which time the solution
changed in color from burgundy to purple. The desired product
was isolated according to the general workup procedure. Yield of
3: 0.367 g (0.962 mmol, 75%). Anal. Calcd for TiC22H41N2: C,
69.27; H, 10.83; N, 7.35. Found: C, 68.94; H, 10.58; N, 7.30.
Cp*Ti(i-Bu)[N(i-Pr)C(Me)N(i-Pr)] (4). To a solution of 1
(0.489 g, 1.27 mmol) in Et2O (75 mL) was added i-BuLi (1.7 M
in heptane, 1.5 mL, 2.6 mmol) at ambient temperature. The reac-
tion was stirred for 16 h, during which time the solution changed
in color from burgundy to purple. The desired product was iso-
lated according to the general workup procedure. Yield of 4:
0.400 g (1.05 mmol, 83%). Anal. Calcd for TiC22H41N2: C, 69.27;
H, 10.83; N, 7.35. Found: C, 69.36; H, 10.80; N, 7.34.
Cp*Ti(Np)[N(i-Pr)C(Me)N(i-Pr)] (5). To a solution of 1
(0.128 g, 0.324 mmol) in Et2O (75 mL) was added NpLi (0.25 M
in hexanes, 2.6 mL, 0.65 mmol) at ambient temperature. The reac-
tion was stirred for 16 h, during which time the solution changed in
color from burgundy to purple. The desired product was isolated
according to the general workup procedure. Yield of 5: 0.126 g
(0.319 mmol, 98%). Anal. Calcd for TiC23H43N2: C, 69.85; H,
10.96; N, 7.08. Found: C, 69.57; H, 10.52; N, 7.04.
Cp*Ti(n-Hex)[N(i-Pr)C(Me)N(i-Pr)] (6). To a solution of 1
(0.161 g, 0.407 mmol) in Et2O (75 mL) was added n-hexyllithium
(2.5 M in n-hexane, 0.33 mL, 0.81 mmol) at ambient tempera-
ture. The reaction was stirred for 16 h, during which time the
solution changed in color from burgundy to bright purple. The
desired product was isolated as a purple oil according to the
general workup procedure. Yield of 6: 0.199 g. While the purity
of this crude product was not sufficient for obtaining a satisfac-
tory elemental analysis, it is of sufficient purity to be used in
subsequent chemical reactions (vide infra).
Cp*Ti[η2-C(Et)dN(t-Bu)][N(i-Pr)C(Me)N(i-Pr)] (7). To a
solution of 2 (0.107 g, 0.303 mmol) in pentane (4 mL) was added
t-BuNC (0.040 g, 0.481 mmol). The reaction mixture was then
stirred for 18 h and then cooled to -30 °C, whereupon the desired
product was obtained as a paramagnetic dark blue crystalline
material. Yield of 7: 0.127 g (0.291 mmol, 96%). Anal. Calcd for
TiC25H46N3: C, 68.79; H, 10.62; N, 9.63. Found: C, 69.01; H,
10.59; N, 9.87.
Cp*Ti(Np)(Cl)[N(i-Pr)C(Me)N(i-Pr)] (14). To a solution of 5
(0.196 g, 0.496 mmol) in Et2O (10 mL) was added PbCl2 (0.069 g,
0.248 mmol). The reaction was stirred for 2 h at ambient tem-
perature, during which time the solution changed in color from
purpletoorange. After the general workupprocedure, the desired
product was isolated and recrystallized from pentane to provide a
diamagnetic orange-red crystalline material. Yield of 14: 0.085 g
(0.197mmol, 40%). 1H NMR(C6D6): δ 3.72 (m, 1H, CH(CH3)2),
3.45 (m, 1H, CH(CH3)2), 1.96 (s, 15H, C5Me5), 1.70 (s, 3H, CH3),
1.37 (d, 3H, CH(CH3)2), 1.36 (s, 9H, CH2C(CH3)3), 1.23 (d, 3H,
CH(CH3)2), 1.16 (d, 3H, CH(CH3)2), 1.11 (d, 3H, CH(CH3)2),
0.89 (s, 1H, TiCH2), 0.10 (d, 1H, TiCH2). Anal. Calcd for
TiC23H43N2Cl: C, 64.09; H, 10.06; N, 6.50. Found: C, 60.78; H,
8.75; N, 7.14.
Cp*Ti[η2-C(n-Bu)dN(2,6-Me2C6H3)][N(i-Pr)C(Me)N(i-Pr)]
(8). To a solution of 3 (0.084 g, 0.220 mmol) in pentane (2 mL)
was added 2,6-dimethylphenylisocyanide (0.035 g, 0.264 mmol)
in pentane (2 mL) at ambient temperature. The reaction was
stirred for 18 h and then cooled to -30 °C, whereupon the
desired product was obtained as a paramagnetic dark purple
crystalline material. Yield of 8: 0.062 g (0.121 mmol, 55%).
Anal. Calcd for TiC31H50N3: C, 72.63; H, 9.83; N, 8.20. Found:
C, 72.64; H, 9.74; N, 8.26.
Cp*Ti[η2-C(i-Bu)dN(2,6-Me2C6H3)][N(i-Pr)C(Me)N(i-Pr)] (9).
To a solution of 4 (0.122 g, 0.320 mmol) in pentane (2 mL) was
added 2,6-dimethylphenylisocyanide (0.050 g, 0.384 mmol) in pen-
tane (3 mL) at ambient temperature, and the solution immediately
darkened. The reaction mixture was then stirred for 18 h and then
cooled to -30 °C, whereupon the desired product was obtained as a
paramagnetic dark purple crystalline material. Yield of 9: 0.100 g
(0.195 mmol, 61%). Anal. Calcd for TiC31H50N3: C, 72.63; H, 9.83;
N, 8.20. Found: C, 72.76; H, 9.93; N, 8.08.
Acknowledgment. Funding for this work was provided
by the NSF (CHE-0848293), for which we are grateful.
Supporting Information Available: Details of single-crystal
X-ray analyses, including tables of bond lengths, angles, and
anisotropic displacement parameters for the solid-state struc-
tures and complete X-ray crystallographic data (CIF) for com-
pounds 2-5, 7, and 9-12. This material is available free of
charge via the Internet at http://pubs.acs.org.
Cp*Ti[η2-C(Np)dN(2,6-Me2C6H3)][N(i-Pr)C(Me)N(i-Pr)] (10).
To a solution of 5 (0.060 g, 0.152 mmol) in pentane (2 mL) was