Amide derivatives of tantalum and a niobium-promoted ring opening of 3,5-lutidine

Article abstract of DOI:10.1016/S0020-1693(02)01308-7

Various tantalum amide compounds were prepared in an attempt to observe C-N bond activation. Addition of lithium amides to THF solutions of (silox)₂TaCl₃ (3) in the presence of trace amounts of the corresponding amine afforded (silox)₂TaCl₂NR₂ (NR₂=NMe₂, 4-NMe₂; N(CH₂)₃CH₂, 4-pyrr; N(CH₂)₄CH₂, 4-pip). Treatment of 4-pyrr with EtMgCl and 4-pip with MeMgBr provided (silox)₂TaEt₂(N(CH₂)₃CH ₂) (5-pyrr-Et₂) and (silox)₂TaMe₂(N(CH₂)₄CH ₂) (5-pip-Me₂). Thermolysis of 5-pip-Me₂ generated CH₄ and η²-imine complex (silox)₂Ta(CH₃)(η²-NC₅H ₉) (6). In contrast, 5-pyrr-Et₂ thermally degraded to the ethylene adduct, (silox)₂(C₄H₈N)Ta(η²-C ₂H₄) (7-pyrr) and C₂H₆. Na/Hg reductions of 4-pyrr and 4-pip in the presence of 1 equiv. C₂H₄ generated 7-pyrr and (^tBu₃SiO)₂(C₅H₁₀N) Ta(η²-C₂H₄) (7-pip); under an excess of C₂H₄, tantallacyclopentane (silox)₂(C₄H₈N)TaCH₂(CH ₂)₂CH₂ (8-pyrr) was prepared. With pyridine present, Na/Hg reduction of 4-pyrr and 4-pip provided η²-pyridine complexes (silox)₂(C₄H₈N)Ta(η²-(N,C)- NC₅H₅) (9-pyrr) and (silox)₂(C₅H₁₀N)Ta(η²-(N,C)- NC₅H₅) (9-pip). Treatment of 9-pyrr and 9-pip with 1 equiv. CH₃NH₂ in C₆D₆ revealed the formation of tantalum imido derivatives (silox)₂(C₄H₈N)Ta=NMe (10-pyrr) and (silox)₂(C₅H₁₀N)Ta=NMe (10-pip), respectively, via the α-pyridyl-methylimido complex, (silox)₂Ta(NMe)(NC₅H₄) (11). Na/Hg reduction of (silox)₃NbCl₂ (13) in the presence of excess 3,5-lutidine afforded (silox)₃Nb(η²-3,5-Me₂-NC₅H ₃) (2-3,5-Lut), which was heated for 4 days at 120°C to give (silox)₂NbN-cis-CH=CMe-cis-CH=CMe-trans-CH=CHCMe₂Si ^tBu₂O (14), whose structure was confirmed by X-ray crystallography. The direct participation of a silox group in the ring opening is a rare occurrence for this typically ancillary ligand, and provides another pathway for C-N bond activation relevant to hydrodenitrogenation (HDN).

Full text of DOI:10.1016/S0020-1693(02)01308-7

Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
www.elsevier.com/locate/ica
Amide derivatives of tantalum and a niobium-promoted
ring opening of 3,5-lutidine
Jeffrey B. Bonanno, Adam S. Veige, Peter T. Wolczanski *, Emil B. Lobkovsky
Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
Received 3 June 2002
Dedicated to our friend and colleague Professor Richard R. Schrock, whose pioneering work in early transition metal chemistry has been
inspirational to our endeavors.
Abstract
Various tantalum amide compounds were prepared in an attempt to observe Cꢀ
/
N bond activation. Addition of lithium amides to
THF solutions of (silox)2TaCl3 (3) in the presence of trace amounts of the corresponding amine afforded (silox)2TaCl2NR2 (NR2ꢀ
/
ꢁ
ꢃ
ꢁ
ꢃ
/
NMe2, 4-NMe2; N(CH2)3C
/
H2, 4-pyrr; N(CH2)4C
H2) (5-pyrrꢀ
and h2-imine complex (silox)2Ta(CH3)(h2-NC5H9) (6). In contrast, 5-pyrrꢀ
(silox)2(C4H8N)Ta(h2-C2H4) (7-pyrr) and C2H6. Na/Hg reductions of 4-pyrr and 4-pip in the presence of 1 equiv. C2H4 generated 7-
H2, 4-pip). Treatment of 4-pyrr with EtMgCl and 4-pip with MeMgBr provided
ꢁ
ꢃ
ꢁ
ꢃ
(silox)2TaEt2(/N(CH2)3C
/
/
Et2) and (silox)2TaMe2(/N(CH2)4C
/
H2) (5-pipꢀ
/
Me2). Thermolysis of 5-pipꢀ/Me2 generated CH4
/
Et2 thermally degraded to the ethylene adduct,
ꢁ
ꢃ
/
pyrr and (tBu3SiO)2(C5H10N)Ta(h2-C2H4) (7-pip); under an excess of C2H4, tantallacyclopentane (silox)2(C4H8N)
H2 (8-pyrr) was prepared. With pyridine present, Na/Hg reduction of 4-pyrr and 4-pip provided h2-pyridine complexes
(silox)2(C4H8N)Ta(h2-(N,C)ꢀNC5H5) (9-pyrr) and (silox)2(C5H10N)Ta(h2-(N,C)ꢀ
NC5H5) (9-pip). Treatment of 9-pyrr and 9-pip
with 1 equiv. CH3NH2 in C6D6 revealed the formation of tantalum imido derivatives (silox)2(C4H8N)TaꢄNMe (10-pyrr) and
(silox)2(C5H10N)TaꢄNMe (10-pip), respectively, via the a-pyridylꢁmethylimido complex, (silox)2Ta(NMe)(NC5H4) (11). Na/Hg
reduction of (silox)3NbCl2 (13) in the presence of excess 3,5-lutidine afforded (silox)3Nb(h2-3,5-Me2ꢀ
/
TaCH2(CH2)2C
/
/
/
/
/
/
NC5H3) (2-3,5-Lut), which
ꢁ
ꢃ
was heated for 4 days at 120 8C to give (silox)
/
2NbN-cis-CHꢄCMe-cis-CHꢄCMe-trans-CHꢄCHCMe2SitBu2O (14), whose structure
was confirmed by X-ray crystallography. The direct participation of a silox group in the ring opening is a rare occurrence for this
typically ancillary ligand, and provides another pathway for CꢀN bond activation relevant to hydrodenitrogenation (HDN).
# 2002 Elsevier Science B.V. All rights reserved.
/
Keywords: Amide derivatives; Tantalum; 3,5-Lutidine; Niobium; Pyridine; Ring-opening; Siloxide; Metallacycle
1. Introduction
The scission of carbonꢁ
cornerstone of crude oil purification that enables its
use as fuel or as the raw material for commodity
chemicals. Hydrodesulfurization (HDS) is imperative,
and removal of additional nitrogenous and oxygenated
functionalities is increasing in importance as the need to
utilize coal derivatives and lower quality heavy crude
oils becomes crucial to the world’s energy concerns.
Hydrodenitrogenation (HDN) requires the breaking of
carbonꢀnitrogen bonds during the course of hydro-
treatment, and two general classes of nitrogen contain-
ing species are targeted: amines (RxNH3ꢂx (xꢀ1ꢁ3))
and aromatics (pyridines, quinolines, etc) [1,2]. Aro-
matics represent the more difficult case as they may first
require hydrogenation, which is costly in energy and
/
heteroatom bonds is the
/
/
/
dihydrogen [1ꢁ
schemes for HDN that include binding events, hydro-
gen/alkyl transfer processes, CꢀN cleavage steps, and
substrate elimination have been proposed [1ꢁ8].
HDN typically occurs simultaneously with HDS on
sulfided Co/Mo/Al2O3 or Ni/Mo/Al2O3 at ꢀ400 8C
/
3]. A variety of conventional mechanistic
/
/
* Corresponding author. Tel.:ꢃ
4137.
E-mail address: ptw2@cornell.edu (P.T. Wolczanski).
/1-607-255 7220; fax: ꢃ1-607-255
/
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 3 0 8 - 7

174
J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
?
2.1.2. (silox)2TaR2NR2 and thermolyses
and 70 atm [1]. The presence of reduced metal sites
operating in concert with a Lewis acidic support may
promote the formation of nucleophilic hydrides or
adsorbed hydrocarbyl species critical to catalysis [7,8].
Binding could occur at acidic sites through nitrogen lone
pairs or at reduced metal sites through p-bonding/
ꢁ
ꢃ
/
Treatment of (silox)2TaCl2(/N(CH2)3C
H2) (4-pyrr)
ꢁ
ꢃ
and (silox)2TaCl2(/N(CH2)4C/H2) (4-pip) with EtMgCl
and MeMgBr in Et2O afforded the pyrrolidide and
ꢁ
ꢃ
piperidyl alkyls, (silox)2TaEt2(/N(CH2)3C
ꢁ
/
H2) (5-pyrrꢀ
/
backbonding [9ꢁ
the CꢀN bond of a bound species through attack at the
a-carbon [1ꢁ8], reduced metal sites could oxidatively
N bonds [12ꢁ17], and organic fragments may be
/11]. Surface nucleophiles could cleave
ꢃ
/
Et2) and (silox)2TaMe2(/N(CH2)4C/
H2) (5-pipꢀMe2), re-
/
1
/
spectively (Eq. (2)). Like the amide chlorides, H NMR
spectra exhibited resonances consistent with a single
type of siloxide, and symmetric
add Cꢀ
/
/
liberated via hydrogenation.
In order to model HDN transformations, the chem-
istry of (silox)3M (Mꢀ
SiO) and various nitrogen-containing substrates has
been examined. The oxidative addition of NꢀH and
ArꢀNH2 bonds to (silox)3Ta (1) has been observed [12],
and examples of the latter CꢀN bond cleavage reveal an
alternative to current HDN mechanistic postulations
[1ꢁ
8]. In addition, thermolyses of (silox)3Nb(h2-N,Cꢀ
/
Ta (1), NbL (2-L), siloxꢀt
Bu3-
/
/
/
ð2Þ
/
amide and alkyl groups (Table 1) [28,29]. Carbonꢁ
hydrogen coupling constants were normal (5-pyrrꢀEt2:
121
/
/
/
/
1JCHaꢀ
Hz), hence agostic interactions [30] were ruled out.
Thermolyses of the amide alkyls were undertaken in
an attempt to observe CꢀN bond cleavage, but the
degradations did not occur smoothly. Piperidide (si-
lox)2(C5H10N)TaMe2 (5-pipꢀMe2) decomposed comple-
/
123, 1JCHbꢀ
/
127 Hz; 5-pipꢀ/Me2: JCH
ꢀ
/
1
py) and related compounds [13,18,19] promote the ring-
opening of the bound heterocycles. Herein are reported
various amide derivatives [20,21] that display b-activa-
/
tions [22ꢁ25], and an unusual lutidine ring opening
/
germane to HDN.
/
tely to a mixture of products after thermolysis in C6D6
for 12 days at 130 8C. Production of methane was
evident from a signal at d 0.15 in the 1H NMR
2. Results and discussion
spectrum, and the major organometallic product (ꢀ
/
50%) was tentatively assigned as the h2-imine complex
(silox)2Ta(CH3)(h2-NC5H9) (6, Eq. (3)) [25]. A pair of
inequivalent siloxide resonances (d 1.17, 1.15) were
observed among a number of smaller resonances in the
1H NMR spectrum. Two
2.1. Amide derivatives
2.1.1. (silox)2TaCl2NR2
Slow addition of secondary lithium amides to THF
solutions of (silox)2TaCl3 (3) [26] in the presence of
catalytic quantities (ꢀ/0.1%) of the corresponding
amine (HNMe2, pyrrolidine, piperidine) generated
ð3Þ
LiCl and the metal amides (silox)2TaCl2NR2 (NR2ꢀ
/
ꢁ
ꢃ
ꢁ
ꢃ
/
NMe2, 4-NMe2; N(CH2)3C
/
H2, 4-pyrr; N(CH2)4C
H2, 4-
pip) in moderate to excellent yields (Eq (1)). These
reactions proceeded without added amine but gave
multiplets (d 4.12, ‘t’d; 4.24, ‘t’d), each integrating as
one proton, were assigned to the a-methylene of the
imine ligand. The coupling pattern may be explained as
a combination of one small vicinal coupling (3JHH
ꢀ3
/
Hz) and a large vicinal coupling on the same order as the
geminal coupling (3JHHꢀ2
/
JHH 12 Hz). A resonance
ꢀ
/
observed at d 3.01 (dd, 1H) was assigned to the imine
CH. Unfortunately, the complexity of the spectrum
prevented further assignments, and attempts to purify
the compound by crystallization and sublimation failed.
Of various mechanisms, b-abstraction of an amide a-
hydrogen by one of the methyls to directly give methane
and 6 seems most likely.
ð1Þ
1
lower yields [27]. The H and 13C{1H} NMR spectra of
these species revealed equivalent siloxides and amide
substituents (Table 1), consistent with a trigonal-bipyr-
amidal geometry with axial siloxides, or a square-
pyramidal configuration with an apical amide. Given
the dynamics intrinsic to five-coordinate d0 species,
fluxional processes leading to the symmetrization evi-
dent in the spectra are also plausible; variable tempera-
ture NMR spectral measurements were not undertaken.
In contrast to the reactivity of piperidide 5-pipꢀ
thermal decomposition of pyrrolidide (silox)2(C4H8N)-
TaEt2 (5-pyrrꢀEt2) proceeded more rapidly (ꢀ60%
after 2.5 h at
/Me2,
/
/

Table 1
1H and 13C{1H} NMR spectral data (d, assignment, mult, J (Hz)) for the complexes in C6D6 unless otherwise noted
Compound
1H NMR (d, mult, assignment, J (Hz))
13C{1H} NMR (d, assignment, J (Hz))
((H3C)3C)3 Other
C(CH3)3
C(CH3)3
Other
(tBu3SiO)2TaCl2(NMe2) (4-Me2)
1.32
1.35
3.60, s, NMe2
1.19, m, (CH2)2; 4.64, m, N(CH2)2
30.42
30.40
24.35
24.34
47.64, N(CH3)2
26.63, (CH2)2; 59.24, N(CH2)2
ꢁ
ꢃ
(tBu3SiO)2TaCl2(/N(CH2)3CH2) (4-pyrr)
ꢁ
ꢃ/
(tBu3SiO)2TaCl2(/N(CH2)4CH2) (4-pip)
1.34
1.27
1.04, m, CH2; 1.45, m, (CH2)2; 4.17, m, N(CH2)2
1.48, m, (CH2)2; 1.82, m, Et2; 3.77, m, N(CH2)2
30.46
30.80
24.33
23.79
23.32, (CH2); 25.57, (CH2)2; 56.86, N(CH2)2
ꢁ
ꢃ/
(tBu3SiO)2TaEt2(/N(CH2)3C
/
H2) (5-pyrrꢀEt2)
/
10.84, CH2CH3, JCH
49.53, N(CH2)2, JCH
TaCH2Me, JCH 123
24.86, (CH2); 26.90, (CH2)2; 47.33, N(CH2)2,
JCH 136; 57.60, TaMe2, JCH 121
27.25, (CH2)2; 54.26, H2CꢄCH2, JCH
55.68, N(CH2)2
25.77, CH2; 29.02, (CH2)2; 55.08,
H2CꢀCH2, JCH 147; 56.07, N(CH2)2
26.93, NCH2CH2; 35.41, TaCH2CH2,
ꢀ/127; 26.75, (CH2)2;
ꢀ/
138; 63.38,
ꢀ/
ꢁ
ꢃ
/
(tBu3SiO)2TaMe2(/N(CH2)4C
H2)
(5-pipꢀMe2)
/
a,b
1.30
1.13
1.15
1.21
1.16, s, TaMe2; 3.40, m, N(CH2)2
30.77
23.85
23.24
23.32
23.64
ꢀ/
ꢀ/
(tBu3SiO)2Ta(h2-C2H4)(NC4H8) (7-pyrr)
1.64, m, (CH2)2; 1.84, s, H2Cꢄ/CH2; 4.12, m, NCH2CH2 29.92
/
ꢀ/147;
(tBu3SiO)2Ta(h2-C2H4)(NC5H10
)
(7-pip)
1.53, m, (CH2)2; 1.80, s, H2Cꢄ/CH2; 4.03, m, N(CH2)2
29.99
30.92
b
/
ꢀ/
ꢁ
ꢃ
(tBu3SiO)2(H8C4N)
/
TaCH2(CH2)2C/
1.56, m (CH2)2; 2.26, m, TaCH2; 2.89, m, TaCH2CH2;
c
H2 (8-pyrr)
3.90, m, N(CH2)2
JCH
JCH
ꢀ
ꢀ/
/
126; 53.27, N(CH2)2; 76.99, TaCH2,
116
ꢁ
ꢃ
/
(tBu3SiO)2(/CH(CH2)3N)
Ta(h2-NC5H5) (9-pyrr)
1.15, 1.19 1.55, m, NCH2CH2; 3.69, d, TaCH, 3Jꢀ
N(CH2)2; 5.36, t, TaNCHCH, Jꢀ6; 5.83, ddt,
TaNCHCHCH, Jꢀ6, 9, 1; 6.41, dm, TaCHCH, Jꢀ
7.55, dm, TaNCH, Jꢀ
1.17, 1.24 1.35ꢁ1.60, m, NCH2CH2CH2; 3.74, m, N(CH2)2; 3.90, d, 29.98, 30.18 23.07, 23.53 25.01, CH2; 28.59, (CH2)2; 54.03, N(CH2)2;
TaCH, 3Jꢀ
TaNCHCHCH, Jꢀ
7.54, dm, TaNCH, Jꢀ
/
1.3; 4.08, m,
29.92, 30.02 23.18, 23.39 27.07, (CH2)2; 54.66, N(CH2)2; 76.03, TaCH;
/
109.01, TaNCHCH; 120.51, TaCHCHCH;
/
/
9;
128.29, TaCHCH; 144.75, TaNCH
/
6
ꢁ
ꢃ
/
(tBu3SiO)2(/CH2(CH2)4N)
Ta(h2-NC5H5) (9-pip)
/
/
1.3; 5.43, t, TaNCHCH, Jꢀ
/
6; 5.87, ddt,
77.21, TaCH; 109.16, TaNCHCH; 121.46,
TaCHCHCH; 126.94, TaCHCH; 145.19,
TaNCH
/
6, 9, 1; 6.39, dm, TaCHCH, J ꢀ9;
/
/
6
ꢁ
ꢃ
ꢃ
(tBu3SiO)2(/CH2(CH2)3N)
/
Taꢄ
/
NMe (10-pyrr)
b
NMe (10-pip)
1.25
1.28
1.49, m, (CH2)2; 3.85, m, N(CH2)2; 3.94, s, NCH3
1.48, m, (CH2)2; 3.75, m, N(CH)2)2; 3.88, s, NCH3
29.94
23.20
26.35, (CH2)2; 30.49, NCH3; 48.49, N(CH2)2
ꢁ
(tBu3SiO)2(/CH2(CH2)4N)
/Taꢀ
/
(tBu3SiO)2Ta(NMe)(NC5H4) (11)
1.41
3.93, s, NCH3; 6.48, ddd, TaNCHCH, Jꢀ
7.01, td, TaCCHCH, Jꢀ7.5, 1.2; 7.74, dt, TaCCH,
Jꢀ7.4, 1.3; 8.32, dt, TaNCH, Jꢀ5.1, 1.3
/
7.6, 5.1, 1.1; 30.67
23.75
48.12, NCH3, JCH
JCH
162; 130.22, ꢄ
136.67, ꢄCHꢀ, JCH
JCH 178; 238.87, TaC
ꢀ
/
/
134; 122.33, ꢄ
CHꢀ, JCH 165;
158; 144.33, ꢄCHꢀ,
/
CHꢀ
/
,
/
ꢀ
/
/
ꢀ/
/
/
/
/
ꢀ
/
/
/
ꢀ/
(tBu3SiO)2Taꢄ
(silox)3Nb(h2-3,5-Me2ꢀ
/
NMe(NHMe) (12)
1.27
1.23
3.47, d, HNCH3, Jꢀ
1.84, s, (CH3)2; 5.02, s, CH; 5.54, bs, N(CH)2
/
7; 3.98, s, ꢄNCH3; 4.58, br q, NH
/
/
NC5H3) (2-3,5-Lut)
31.45
24.35
20.86, CH3; 120.71, N(CH)2, n1/2
126.78, NCHCMe; 127.19, NCHCMeCH
ꢀ142 Hz;
/
t
1.24, s, Bu; 1.43, s, C(CH3)2; 1.66, s, C(CH3); 2.01, s,
(silox)2/
ꢁ
1.27
30.94, 31.58 23.62, 24.12 21.10, CH3; 21.95, CH3; 26.73, (CH3)2; 32.96,
C(CH3)2; 121.64, C(CH3); 127.09, CH;
130.63, CH; 134.32, C(CH3); 139.64, CH;
141.84, b, NC
t
t
ꢃ
C(CH3); 5.54, s, CH; 6.12, d, CH, Jꢀ16; 6.86, d, CH,
/
NbNCHꢄCMeCHꢄCMeCHꢄCHCMe2SitBu2O
(14)
Jꢀ/16; 7.03, s, NCH
a
b
c
(H2)2 in 1H NMR spectrum. CH2 obscured in 1H NMR spectrum. Assigned via homonuclear 1H NMR decoupling, selective 13C{1H} decoupling experiments, and comparison to related
compounds.

176
J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
in the formation of tantallacyclopentane (si-
ꢁ
ꢃ
lox)2(C4H8N)/TaCH2(CH2)2C/H2 (8-pyrr, Eq. (6)). Only
a minor quantity of the analogous product was observed
in the piperidide system. A combination of homonuclear
ð4Þ
115 8C), and afforded the ethylene adduct,
(silox)2(C4H8N)Ta(h2-C2H4) (7-pyrr,
ꢀ80%) and
/
C2H6 (Eq. (4)) as the major products. A 13C{1H}
NMR spectrum of 7-pyrr revealed normal resonances
for the siloxide and amide and a broad resonance
ð6Þ
assigned to the h2-ethylene carbons at
(1JCH
observed for (silox)3Ta(h2-C2H4) (e.g. JCH
[31], which is considered to possess metallacyclopropane
character. Perhaps 7-pyrr is generated via a b-abstrac-
tion path similar to that of the pyrrolidide dimethyl
derivative of Eq. (3).
d
54.26
1H NMR decoupling experiments, selective 13C{1H}
heteronuclear decoupling experiments, and comparisons
with related compounds permitted the spectral assign-
ments for 8-pyrr shown in Table 1. Note that 8-pyrr is
also likely to be fluxional since the metallacycle exhibits
only two types of methylene resonances.
ꢀ
/
147 Hz). Related spectral features have been
1
ꢀ143 Hz)
/
ꢁ
ꢃ
Thermolysis of (silox)2(C4H8N)
pyrr) in sealed NMR tubes led to elimination of
ethylene, yielding 7-pyrr (115 8C, 1 h, ꢀ40% com-
/
TaCH2(CH2)2CH2 (8-
/
2.1.3. Reductions of (silox)2TaCl2NR2
In an attempt to generate Ta(III) centers [12,15,32]
/
plete). These reactions were reversible and reverted to
the coupled product upon standing at room tempera-
ture. Heating 8-pyrr in refluxing toluene with flowing
nitrogen atmosphere allowed isolation of 7-pyrr,
although the product contained a substantial amount
of unidentified impurities.
capable of oxidatively adding a Cꢀ
/
N bond, the chlor-
ides were subjected to reductions. When treated with
sodium amalgam in various solvents (THF, DME,
toluene), or with cesium in benzene, the amides
ꢁ
ꢃ
(silox)2TaCl2NR2 (NR2ꢀ
/
NMe2, 4-Me2; N(CH2)3C/H2,
ꢁ
ꢃ
/
With 1 equiv. or excess pyridine, Na/Hg reduction of
ꢃ
4-pyrr; N(CH2)4C
H2, 4-pip) generated complex mix-
ꢁ
tures, and all attempts at purification and isolation were
unsuccessful. Reductions with Na/Hg in the presence of
H2, PMe3, or CO as trapping agents were similarly
(silox)2TaCl2(/N(CH2)3CH2) (4-pyrr) and (silox)2TaCl2
ꢁ
ꢃ
(
/
N(CH2)4CH2
(silox)2(C4H8N)Ta(h2-(N,C)ꢀ
and (silox)2(C5H10N)Ta(h2-(N,C)ꢀ
/
) (4-pip) generated h2-pyridine complexes
NC5H5) (9-pyrr, 81%)
NC5H5) (9-pip,
/
ꢁ
ꢃ
abortive. Treatment of (silox)2TaCl2(/N(CH2)3C/H2) (4-
ꢁ
/
ꢃ
82%; Eq. (7)). The NMR spectra of these compounds
pyrr) and (silox)2TaCl2(/N(CH2)4C/H2) (4-pip) with ex-
bear striking resemblance to the static, crystallographi-
NC5H5) com-
cess Na/Hg in the presence of 1 equiv. of ethylene
generated 7-pyrr and (tBu3SiO)2(C5H10N)Ta(h2-C2H4)
(7-pip), respectively (Eq. (5)). NMR spectra of 7-pip
showed characteristic signals for the siloxide and
piperidide ligands in addition to the resonance of the
coordinated ethylene at d 1.80. Carbons signals at d
cally characterized (silox)3Ta(h2-(N,C)ꢀ
plex [31]. Thermolysis
/
55.08 (1JCH
ꢀ
/
147 Hz) and d 56.06 (1JCH
ꢀ135 Hz) were
/
ð7Þ
assigned to the ethylene ligand and the amido a-
methylene, respectively,
of 9-pyrr and 9-pip in C6D6 (130 8C, weeks) proceeded
with loss of pyridine (1H NMR) and generation of
intractable mixtures of unidentified siloxide containing
species.
ð5Þ
based on selective heteronuclear 13C{1H} decoupling
experiments. Thermolysis studies suggested that the
ethylene ligands of these compounds are tightly bound.
For example, thermolysis of a sample of 7-pyrr at 80 8C
for 2 days and 115 8C for 17 h showed little change; free
C2H4 was not observed (1H NMR).
2.1.4. Degradation of h2-py complexes with methylamine
In HDN, nucleophilic attack has been proposed as
one path toward Cꢀ
/
N bond cleavage [1ꢁ8], hence
/
degradation in the presence of a reasonably relevant
nucleophile, MeNH2, was undertaken. Treatment of
ꢁ
ꢃ
Reduction of (silox)2TaCl2(/N(CH2)3C/H2) (4-pyrr)
under excess C2H4 or exposure of (silox)2-
(C4H8N)Ta(h2-C2H4) (7-pyrr) to excess C2H4 resulted
(silox)2(C4H8N)Ta(h2-(N,C)ꢀ
/
NC5H5) (9-pyrr) and
(silox)2(C5H10N)Ta(h2-(N,C)ꢀ
/NC5H5) (9-pip)

J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ
/184
177
1, several paths may account for this phenomenon.
Initial transamination leads to a methylamidopyridine
species that can undergo a-activation of the py. Proton
incorporation can be subsequently effected via 1,2-
elimination to give an imido-hydride or the product
via an intermediate that has reincorporated pyrrolidine.
Since (silox)2Ta(NMe)(NC5D4) (11-d4) is observed, its
formation via H2 loss from the amidohydride a-pyridyl
species provides yet another means of H/D exchange. 1H
NMR spectral analysis of 11-d4 shows little H incor-
ð8Þ
with 1 equiv. CH3NH2 in C6D6 revealed the formation
of tantalum imido derivatives (silox)2(C4H8N)Taꢄ
/
NMe
(10-pyrr) and (silox)2(C5H10N)TaꢄNMe (10-pip, Eq.
/
1
(8)), respectively. H NMR spectra of these compounds
revealed standard shifts for all the ligands, and a
13C{1H} NMR spectrum of 10-pyrr corroborated its
formulation.
poration into the TaNCH position (d 8.32, ꢀ3% H). It
/
is perhaps more puzzling that deuterium remains in a-
positions of the product, perhaps suggesting that there
exists a more direct path from 9-pyrr to 10-pyrr that
does not involve a-pyridine activation.
The reactions with methyl amine proceeded with an
initial release of secondary amine (piperidine or pyrro-
lidine) and H2, as shown in Scheme 1. One intermediate
was cleanly observed during the course of the transfor-
mation, and 1H and 13C{1H} NMR spectra permitted its
2.2. A 3,5-lutidine adduct
2.2.1. Synthesis of (silox)3Nb(h2-3,5-Me2ꢀ
3,5-Lut)
/
NC5H3) (2-
tentative identification as the a-pyridylꢁ
/
methylimido
complex, (silox)2Ta(NMe)(NC5H4) (11), based in part on
comparison with other a-pyridyl compounds [33]. The
relative rates of 9-pyrr and 9-pip were slightly different;
95% of the pyrrolidide is consumed after 1 week (23 8C)
while only 66% of the piperidide is converted during the
same time span, and a greater amount of 11 is detected in
the former, presumably due to its greater rate of
formation. Anoher product detected (1H NMR) in the
While the above derivatives were prepared in the hope
of observing model denitrogenation steps, no discrete
Cꢀ
/
N bond cleavage events could be identified. In
contrast, the pyridine ring opening of (silox)3Nb(h2-
py) (2-py) and various related picoline derivatives has
been observed [13,18,19], and it was noted that increas-
ing steric bulk on the heterocycle apparently hampers a
critical bimolecular step in the overall process. Seeking a
labile source of (silox)3Nb (2), 3,5-lutidine was
9-pip reaction was tentatively assigned as (silox)2Taꢄ
/
NMe(NHMe) (12), which may result from reaction of
residual MeNH2 with product 10-pip.
Treatment of (silox)2(C4H8N)Ta(h2-(N,C)ꢀ
/
NC5D5)
(9-pyrr-d5), generated by Na/Hg reduction of (si-
ð9Þ
ꢁ
ꢃ
/
lox)2TaCl2(/N(CH2)3C
with methylamine yielded (silox)2(C4H8N)Taꢄ
(10-pyrr), H2 (d 4.46), HD (d 4.42, t, JHD 43 Hz),
H2) (4-pyrr) under pyridine-d5,
/NMe
ꢀ
/
explored as a ‘masking ligand’ [19]. Treatment of
(silox)3NbCl2 (13) with sodium amalgam in the presence
of excess 3,5-lutidine afforded (silox)3Nb(h2-3,5-Me2ꢀ
NC5H3) (2-3,5-Lut) in 57% yield (Eq. (9)). A singlet
was observed for the 3,5-dimethyl substituents, and a
1
and partially a-protio pyridine. Integration of the H
NMR showed a total of 38% H (50% for complete
exchange in one site) in the a-positions of the free
pyridine (0.76 H in one a-position). As shown in Scheme
/
Scheme 1.

178
J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
broad singlet was attributed to the a-hydrogens, sig-
nifying rapid shuttling between both N,C-bound forms,
eliminate, reinsert and undergo a retro 2ꢃ
afford the imido cyclometallated product.
/
2 reaction to
as was observed for the (silox)3Nb(h2-N,Cꢀ
various picoline derivatives [13,18].
/NC5H5) and
2.2.3. X-ray crystal structure of (silox)2/
ꢁ
2.2.2. Thermolysis of (silox)3Nb(h2-3,5-Me2ꢀ
(2-3,5-Lut)
Thermolysis of (silox)3Nb(h2-3,5-Me2ꢀ
/
NC5H3)
NbN-cis-CHꢄCMe-cis-CHꢄCMe-trans-
/
ꢃ
/
CHꢄCHCMe2SitBu2O (14)
Table 2 provides the crystallographic data for (silox)2
/
NC5H3) (2-
/
ꢁ
3,5-Lut) for 4 days at 120 8C led to an unusual Cꢀ
/
N
NbN-cis-CHꢄCMe-cis-CHꢄCMe-trans-CHꢄCHCMe2
/
ꢁ
ꢃ
bond activation product, (silox)
/
2NbN-cis-CHꢄCMe-
/
/
SitBu2O (14), while Table 3 lists pertinent bond dis-
tances and angles. Fig. 1. shows that 3,5-lutidine ring-
ꢃ
/
cis-CHꢄCMe-trans-CHꢄCHCMe2SitBu2O (14), invol-
ving CH-bond activation of the tBu3SiO ligand, as
shown in Eq. (10). Dihydrogen is a
opened product 14 is pseudo-tetrahedral, with Oꢀ
and NꢀNbꢀO angles that average 110.7 (18) and 108.2
(11)8, respectively. The nearly linear (ꢅNbꢀN1ꢀC1ꢀ
171.6 (4)8) niobium imido functionality possesses a
/
Nbꢀ
/
O
/
/
/
/
/
/
˚
typical distance of 1.773 (5) A [35], the niobium siloxide
˚
bond lengths (1.903 (10) A (ave)) are normal, and the
˚
˚
alternating single (d(N1ꢀ
/
C1)ꢀ
C6)ꢀ
1.532 (8) A) and double (d(cis-C1ꢀ
/
1.396 (7) A, d(C2ꢀ
/
˚
C4)ꢀ
/
1.458 (9) A, d(C5ꢀ
/
/
1.453 (13) A, d(C9ꢀ
C2)ꢀ1.359
1.303 (11) A, d(trans-C6ꢀC9)ꢀ
1.269 (10) A) bonds of the metallacycle are readily
discerned. The siloxide containing the metallacycle (ꢅ
NbꢀO1ꢀSi1ꢀ167.5 (2)8) cannot be distinguished from
the remaining silox ligands (ꢅNbꢀO2ꢀSi2ꢀ166.1 (2)8,
NbꢀO3ꢀSi3ꢀ167.1 (2)8) aside from its periphery.
/
˚
C8)ꢀ
(7) A, d(cis-C4ꢀ
/
/
/
˚
˚
/
C5)ꢀ
/
/
/
ð10Þ
presumed byproduct in the reaction, although Toepler
pump measurements detected only 0.20 equiv. H2 per
˚
/
/
/
/
mol of 14 formed. The reaction is remarkably clean (ꢁ
/
/
/
/
/
90%) according to monitoring by 1H NMR spectro-
scopy, but 14 could only be isolated in 27% yield from
hexanes due to its extreme solubility.
ꢅ
/
/
/
/
A mechanism for the complicated conversion of 2-3,5-
Lut to 14 is given in Scheme 2, and some of its features
show a commonality to aforementioned results. a-
Pyridyl formation [33] precedes cyclometallation
[31,34] concomitant with loss of H2. A migratory
insertion of the ‘tucked-in’ cyclometallated Bu group
leads to a substituted metallaziridine [15] that can b-H-
3. Conclusions
Efforts to demonstrate carbonꢀ
tion via the thermolysis of Ta(V) amidoalkyl derivatives
/
nitrogen bond activa-
t
failed, as did attempts to observe oxidative addition of
amide Cꢀ/N bonds via putative Ta(III) species. Instead,
Scheme 2.

J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ
/184
179
Table 2
Crystal
served for Nb, but in this instance the Cꢀ
/
N bond
data
and
structure
refinement
ꢃ
for
(silox)2/
scission in 3,5-lutidine involved a cyclometallation of a
silox ligand [31,34], rather than the dinuclear path
evident in the ring openings of less hindered pyridine
and picolines. The involvement of the silox ligand in the
bond cleavage process sets a precedent for its involve-
ꢁ
NbNCHꢄCMeCHꢄCMeCHꢄCHCMe2SitBu2O (14)
Empirical formula
Formula weight
Temperature (K)
C43H88NO3Si3Nb
844.32
173(2)
˚
l (A)
0.71073
monoclinic
P21/c
ment in (silox)3M(olefin)0
/(silox)3M(alkylidene) rear-
Crystal system
Space group
rangements [36].
˚
a (A)
18.8098 (15)
11.7518 (10)
22.7705 (19)
100.672 (4)
4946.3 (7)
4
˚
b (A)
˚
c (A)
4. Experimental
b (8)
3
V (A )
˚
Z
4.1. General considerations
Density (calc) (Mg mꢂ3
)
1.134
0.350
Absorption coefficient (mmꢂ1
Crystal size (mm3)
Indices
)
All manipulations were performed using either glove-
box or high vacuum line techniques. All glassware was
oven dried. THF and ether were distilled under nitrogen
from purple sodium benzophenone ketyl and vacuum
transferred from the same prior to use. Hydrocarbon
solvents were treated in the same manner with the
0.40ꢄ
185
225
1.10ꢁ20.89
/
0.20ꢄ
h 518, ꢂ
l 522
/
0.10
ꢂ
ꢂ/
/
/
/
/115
/
k 510,
/
/
/
uRange (8)
Reflections
/
23 649
Independent reflections
Data/restraints/parameters
5185 (Rint
5185/0/488
ꢀ0.0725)
/
addition of 1ꢁ
2 ml lꢂ1 tetraglyme. Benzene-d6 was dried
/
a
GOF
1.009
b
R [I ꢁ
R (all indices)
Largest difference peak and hole
/
2s(I)]
R1ꢀ
R1ꢀ
0.348 and ꢂ
/
0.0484, wR2ꢀ
0.0830, wR2ꢀ
0.278
/
0.1030
0.1169
˚
over sodium and activated 4 A molecular sieves, vacuum
transferred, and stored under nitrogen. Pyridine and
˚
pyridine-d5 were dried over activated 4 A molecular
b
/
/
/
ꢂ3
˚
(e A
)
sieves and vacuum transferred before use. THF-d8 was
dried over sodium and vacuum transferred from sodium
benzophenone ketyl prior to use. Ethylene (Matheson)
a
GOFꢀ
/
[a w(jFojꢂ
/
jFcj)2/(nꢂ
/
p)]1/2; n, number of independent
reflections; p, number of parameters.
was passed through a trap at ꢂ
/
78 8C before use.
Primary and secondary amines were purchased from
˚
amides were generated from the amine and nBuLi
(Aldrich) and crystallized prior to use. Grignard solu-
tions were purchased from Aldrich. (silox)2TaCl3 (3)
evidence of b-H-abstractions in the former, and the
preparation of olefin, metallacyclic and h2-N-hetero-
cyclic compounds in the latter instances proved to be the
rule. An N-heterocyclic ring opening was again ob-
Aldrich and dried over activated 4 A sieves. Lithium
Table 3
Selected interatomic distances (A) and angles (8) for (silox)
ꢁ
ꢃ
a
2NbNCHꢄCMeCHꢄCMeCHꢄCHCMe2SitBu2O (14)
˚
/
Bond lengths
Nbꢀ
Nbꢀ
Nbꢀ
Nbꢀ
Si1ꢀ
Si2ꢀ
Si3ꢀ
Cꢀ
/
N
1.773 (5)
1.912 (3)
1.892 (3)
1.906 (4)
1.665 (4)
1.658 (3)
1.653 (4)
1.540 (12)
Nꢀ
C1ꢀ
C2ꢀ
C2ꢀ
C4ꢀ
C4ꢀ
C5ꢀ
/
C1
1.396 (7)
1.359 (8)
C5ꢀ
C6ꢀ
C5Aꢀ
C5Aꢀ
C6Aꢀ
C9ꢀ
SiꢀC(ave)
/
C6
1.453 (13)
1.269 (10)
1.51 (2)
/
O1
O2
O3
/C2
/C9
/
/C3
1.501 (8)
1.458 (9)
1.303 (11)
1.26 (2)
/
C6A
C7A
C33
/
/C4
/
1.55 (2)
/
O1
O2
O3
/C5
/
1.640 (18)
1.532 (8)
1.915 (10)
/
/C5A
/C8
/
/C7
1.523 (13)
/
/
C(ave)
Bond angles
Nꢀ
Nꢀ
Nꢀ
Nbꢀ
NꢀC1ꢀ
C1ꢀC2ꢀ
C5ꢀC6ꢀ
C4ꢀC5Aꢀ
OꢀSiꢀC(ave)
CꢀCꢀC(ave)
/
Nbꢀ
Nbꢀ
Nbꢀ
Nꢀ
/
O1
O2
O3
C1
109.14 (18)
106.96 (17)
108.48 (19)
171.6 (4)
O1ꢀ
O1ꢀ
O2ꢀ
C1ꢀ
C3ꢀ
C2ꢀ
C6ꢀ
C6Aꢀ
CꢀSiꢀ
/
Nbꢀ
Nbꢀ
Nbꢀ
C2ꢀ
C2ꢀ
C4ꢀ
C9ꢀ
/
O2
O3
O3
109.52 (14)
112.73 (15)
109.84 (14)
127.0 (10)
115.6 (6)
Nbꢀ
Nbꢀ
Nbꢀ
C4ꢀC5ꢀ
C4ꢀC5ꢀ
C6ꢀC5ꢀ
C4ꢀ
C5Aꢀ
SiꢀCꢀ
/
O1ꢀ
O2ꢀ
O3ꢀ
/
Si1
Si2
Si3
167.5 (2)
166.1 (2)
167.1 (2)
122.6 (9)
120.1 (9)
117.2 (10)
121.3 (15)
116.2 (14)
111.3 (16)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
C4
C4
C5
C8
/
/
C6
C7
C7
/
/
C2
C3
C9
C7A
128.6 (6)
117.5 (6)
133.4 (9)
/
/
/
/
/
/
/
/
128.6 (7)
/
/
/
/
/
/
128.2 (7)
116.0 (18)
112.4 (9)
/
C5Aꢀ
C6Aꢀ
C(ave)
/C6A
/
/
122.1 (16)
106.3 (11)
107.5 (12)
/
C5Aꢀ
/
C7A
/
/
C33
/
/
/
/C(ave)
/
/
/
/
a
Disorder as described in experimental; both models included.

180
J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
ꢁ
ꢃ
Fig. 1. Molecular view of (silox)2
NbNCHꢄCMeCHꢄCMeCHꢄCHCMe2SitBu2O (14).
/
and (silox)3NbCl2 (13) were prepared following pub-
lished procedures [26].
1H and 13C{1H} NMR spectra were obtained on
Varian XL-200 and XL-400 spectrometers. Chemical
shifts are reported relative to benzene-d6 (1H, d 7.15;
13C{1H}, d 128.00. IR spectra were recorded on a
hexane. The solution was filtered, concentrated, and
cooled causing a white solid to precipitate. Recrystalliza-
tion from hexane netted 241 mg 4-Me2 (48%). IR (Nujol,
cmꢂ1) 1465 (s), 1375 (s), 1265 (m), 1180 (w), 1135 (m),
1050 (m), 1010 (m), 930 (s), 860 (br, s), 815 (s), 625 (s).
Anal. Calc. for TaSi2NCl2O2C26H60: C, 42.97; H, 8.32;
N, 1.93. Found: C, 42.97; H, 8.12; N, 1.91%.
Mattson FT IR, PerkinꢁElmer 299B grating IR, or PE
/
377 grating IR. Combustion analyses were performed by
Oneida Research Services (Whitesboro, NY), Robertson
Microlit Laboratories (Madison, NJ), or Texas Analy-
tical (Houston, TX).
ꢁ
ꢃ
/
4.2.2. (silox)2TaCl2(N(CH2)3CH2) (4-pyrr)
/
A 250 ml flask was charged with 3 (1.705 g, 2.374
mmol) and fitted with a solid addition tube containing
lithium pyrrolidide (0.185 g, 2.401 mmol). The flask was
attached to a 1808 needle valve and evacuated. A
4.2. Synthesis
catalytic quantity of pyrrolidine (ꢀ
/
0.1 equiv.) was
4.2.1. (silox)2TaCl2NMe2 (4-Me2)
condensed into the flask at ꢂ78 8C followed by THF
/
A 100 ml flask was charged with (silox)2TaCl3 (3, 0.500
g, 0.696 mmol) and fitted with a sidearm containing
lithium dimethylamide (0.035 g, 0.686 mmol). THF (60
(70 ml). Warming to 23 8C resulted in an orange/yellow
solution. The lithium pyrrolidide was added slowly to
the stirred solution, which became bright yellow. After
stirring for 4 h, the volatiles were removed and the solids
were triturated twice with hexane. The solids were
extracted with hexane, the solution was filtered and
the salts were washed repeatedly until the washings were
colorless. The hexane solution was concentrated to 5 ml
ml) and a catalytic amount of dimethylamine (ꢀ
equiv.) were added to the flask in vacuo at
78 8C. The solution was warmed to 23 8C and stirred.
/
0.05
ꢂ
/
Slow addition of the lithium amide generated a yellow
color in the solution. After stirring for 24 h, the volatiles
were removed and the solid residue was extracted with
and cooled to ꢂ78 8C, yielding 1.556 g of 4-pyrr (87%)
/

J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ
/184
181
as pale yellow crystals. IR (Nujol, cmꢂ1) 1475 (s), 1375
(m), 1340 (m), 1180 (w), 1045 (m), 1010 (w), 940 (s), 865
(br, s), 820 (s), 625 (s). Anal. Calc. for TaCl2Si2-
NO2C28H62: C, 44.67; H, 8.30; N, 1.86. Found: C,
44.85; H, 8.48; N, 1.67%.
syringe. A white precipitate was observed after 1 h and
stirring continued for 24 h. The volatiles were removed
in vacuo and the solid residue was triturated with
hexane. Extraction of the residue with hexane and
filtration gave a solution which was cooled to ꢂ
/
78 8C
to afford 0.584 g colorless microcrystals of 5-pipꢀ
/
Me2.
ꢁ
ꢃ
/
4.2.3. (silox)2TaCl2(
/
N(CH2)4C
H2) (4-pip)
A second crop was obtained (0.092 g, 88% total). IR
(Nujol, cmꢂ1) 1465 (s), 1375 (s), 1315 (w), 1280 (w),
1190 (w), 1150 (m), 1090 (m), 1050 (w), 1040 (m), 1025
Into a 250 ml flask was placed 3 (1.968 g, 2.740
mmol). A solid addition tube containing lithium piper-
idide (0.250 g, 2.745 mmol) was attached to the flask.
(w), 1010 (w), 955 (w), 920 (s), 930ꢁ800 (br, s), 720 (m),
/
THF (90 ml) and a small amount of piperidine (ꢀ
/
0.1
620 (s). Anal. Calc. for TaSi2NO2C31H70: C, 51.29; H,
9.72; N, 1.93. Found: C, 50.90; H, 10.10; N, 1.78%.
equiv.) were added via vacuum transfer at ꢂ78 8C. The
/
flask was warmed to 23 8C and the lithium amide was
added to the solution over 30 min generating a bright
yellow color. After stirring for 6 h the volatiles were
removed. Hexane was added and the solid residue was
extracted repeatedly until no yellow color remained in
the salts. The hexane solution was concentrated to 8 ml
4.2.6. (silox)2(C4H8N)Ta(h2-C2H4) (7-pyrr)
4.2.6.1. From 4-pyrr. Into a 100 ml flask were placed 4-
pyrr (1.589 g, 2.111 mmol) and Na/Hg (0.194 g Na,
21.36 g Hg, 8.438 mmol, 4 equiv.). The flask was
attached to a gas bulb and evacuated. DME (50 ml)
and cooled to ꢂ78 8C, yielding a copious mass of pale
/
yellow crystals that were collected by filtration and
washed once with cold hexane (1.694 g). A second crop
of 4-pip was obtained (0.215 g, 91% total). IR (Nujol,
cmꢂ1) 1475 (s), 1375 (m), 1270 (w), 1190 (m), 1145 (m),
was added at ꢂ78 8C. The solution was warmed and
/
exposed to ethylene (137 Torr in 287.8 ml, 2.151 mmol,
1.02 equiv.). The purple color that formed initially faded
to brown then yellow over 5 h, and the solution was
stirred for an additional 2 h. The volatiles were removed,
and the amalgam was decanted from the solid. The
solids were extracted with hexane and filtered. Removal
1085 (m), 1050 (m), 1035 (w), 1010 (m), 955 (s), 920ꢁ800
/
(br, s), 625 (s). Anal. Calc. for TaSi2NCl2O2C29H64: C,
45.42; H, 8.41; N, 1.83. Found: C, 45.40; H, 8.44; N,
1.53%.
of the hexane in vacuo gave a yellow crystalline material
1
95% pure by H NMR spectral assay.
that was ꢁ
/
4.2.4. (silox)2(C4H8N)TaEt2 (5-pyrrꢀ
/
Et2)
A 100 ml flask was charged with 4-pyrr (0.813 g, 1.080
4.2.6.2. Synthesis from 5-pyrrꢀ
/
Et2. A 100 ml flask was
mmol) and attached to a 1808 needle valve. The flask
was evacuated and Et2O (50 ml) was added at ꢂ
charged with 5-pyrrꢀEt2 (0.501 g, 0.677 mmol) and
/
/
78 8C
attached to a reflux condenser on a 1808 needle valve.
The apparatus was evacuated and toluene (30 ml) was
added via vacuum transfer. Argon was admitted and the
solution was refluxed for a total of 15 h. The solution
was cooled and the volatiles were removed. The solid
was extracted into hexane, and the solution was filtered
in vacuo. Against a counterflow of argon, EtMgCl (1.18
ml, 2.0 M in Et2O, 2.36 mmol, 2.2 equiv.) was added via
syringe to the cold solution. The solution was degassed,
warmed, and stirred. The initial pale yellow color faded
over 1 h as the solution became turbid, and stirring was
maintained for an additional 15 h. The volatiles were
removed and the resulting white solid was extracted into
hexane and filtered. The salts were washed several times
with hexane. The hexane solution was concentrated and
and concentrated to 5 ml, affording 246 mg of yellow
1
95% pure by H
microcrystalline 5-pyrrꢀ
/
Et2 (51%, ꢁ
/
NMR assay) upon cooling to ꢂ
/
78 8C. Analytically
pure samples were obtained upon recrystallization. IR
(Nujol, cmꢂ1) 1475 (m), 1375 (m), 1345 (w), 1115 (w),
1065 (w), 1035 (w), 990 (m), 955 (m), 915 (br, s), 820 (s),
670 (w), 625 (s). Anal. Calc. for TaSi2NO2C30H66: C,
50.75; H, 9.37; N, 1.97. Found: C, 50.69; H, 9.48; N,
1.67%.
cooled to ꢂ
microcrystals of 5-pyrrꢀ
/
78 8C, affording 0.637 g (80%) colorless
/
Et2. IR (Nujol, cmꢂ1) 1470 (s),
1375 (s), 1335 (m), 1290 (w), 1250 (br, w), 1200 (br, w),
1180 (br, w), 1165 (br, w), 1105 (w), 1070 (m), 1045 (m),
1010 (w), 990 (m), 920 (br, s), 860 (br, s), 820 (s), 620 (s).
Anal. Calc. for TaSi2NO2C32H72: C, 51.94; H, 9.81; N,
1.89. Found: C, 52.31; H, 10.38; N, 1.82%.
4.2.7. (silox)2(C5H10N)Ta(h2-C2H4) (7-pip)
A 50 ml flask was charged with 4-pip (1.028 g, 1.341
mmol) and Na/Hg (0.125 g Na, 13.52 g Hg, 5.437 mmol,
4.2.5. (silox)2(C5H10N)TaMe2 (5-pipꢀ
/
Me2)
A 250 ml flask was charged with 4-pip (0.808 g, 1.054
4 equiv.). DME (20 ml) was added at ꢂ78 8C followed
/
mmol) and fitted with a septum. The flask was
by an excess of ethylene (ꢀ700 Torr). The solution was
/
evacuated and Et2O (100 ml) was added at ꢂ
/
78 8C.
warmed to 23 8C and stirred. The initial purple color
faded to yellow within 1 h and the solution was stirred
for an additional 1.5 h. The volatiles were removed, and
the solid was extracted into hexane and filtered. The
The solution was warmed to 23 8C while stirred. Argon
was admitted to the assembly and MeMgBr (0.77 ml, 3.0
M in Et2O, 2.31 mmol, 2.2 equiv.) was added via

182
J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
hexane was removed and Et2O was added. Concentra-
tion and cooling of the solution produced yellow
crystals of 7-pip, which were isolated by filtration
(0.422 g, 44%). IR (Nujol, cmꢂ1) 1475 (m), 1375 (m),
1305 (w), 1270 (w), 1255 (w), 1205 (m), 1150 (m), 1110
(m), 1060 (m), 1030 (m), 1010 (w), 975 (s), 910 (br, s),
875 (m), 855 (m), 820 (s), 670 (w), 630 (s). Anal. Calc. for
TaSi2NO2C31H68: C, 51.43; H, 9.47; N, 1.93. Found: C,
51.24; H, 9.57; N, 1.65%.
for TaSi2N2O2C33H67: C, 52.08; H, 8.87; N, 3.68.
Found: C, 51.87; H, 8.96; N, 3.63%.
4.2.10. (silox)2(C5H10N)Ta(h2-(N,C)ꢀ
pip)
/
NC5H5) (9-
Into a 25 ml flask were placed 4-pip (0.611 g, 0.797
mmol) and a portion of Na/Hg (0.077 g Na, 8.05 g Hg,
3.349 mmol, 4.2 equiv.). DME (15 ml) and excess
pyridine were added via vacuum transfer at ꢂ78 8C.
/
ꢁ
ꢃ
/
The solution was warmed and stirred for 18 h. After
removal of the volatiles, the solids were triturated twice
with hexane. Extraction of the solid residue and filtra-
tion gave an amber solution that was concentrated and
4.2.8. (silox)2(C4H8N)TaCH2(CH2)2CH2 (8-pyrr)
/
A 100 ml flask was charged with 4-pyrr (0.498 g, 0.661
mmol) and Na/Hg (0.061 g Na, 9.69 g Hg, 2.653 mmol,
4 equiv.). DME (50 ml) was added at ꢂ78 8C and 570
/
cooled (ꢂ78 8C) to afford yellow crystals (0.192 g).
/
Torr of ethylene was admitted. The solution turned deep
purple as it was warmed to 23 8C over 5 min. The
purple faded and was replaced by a bright yellow color
within 1 h. After the solution was stirred for a total of 24
h, the volatiles were removed and the residue was
triturated once with hexane. The solid was extracted
into hexane and filtered. The salts were washed twice
and the hexane solution was concentrated to 3 ml.
Two additional crops were acquired in the same manner
(0.316 g, 82% total). IR (Nujol, cmꢂ1) 1500 (w), 1475
(s), 1375 (m), 1310 (w), 1235 (s), 1195 (w), 1150 (w), 1130
(w), 1095 (w), 1030 (w), 1025 (m), 1005 (m), 970ꢁ860
/
(br, s), 855 (w), 820 (s), 715 (s), 625 (s). Anal. Calc. for
TaSi2N2O2C34H69: C, 52.69; H, 8.97; N, 3.61. Found: C,
51.80; H, 9.01; N, 3.31%.
Cooling to ꢂ
powder (0.303 g). H NMR showed the solid consisted
of ꢀ
/
78 8C and filtration yielded an off white
1
4.2.11. (silox)3Nb(h2-3,5-Me2ꢀ
/
NC5H3) (2-3,5-Lut)
/
15% (silox)2Ta(h2-C2H4)(NC4H8). Prolonged ex-
A 50 ml flask charged with (silox)3NbCl2 (13, 500 mg,
0.617 mmol) and 2.5 equiv. Na/Hg (3.74 g, 0.95% Na).
The system was evacuated and 3,5-lutidene (3 ml) was
condensed from a measuring finger, followed by 30 ml
of THF. Upon warming, the solution turned purple, and
after stirring for 12 h it became brown. The volatiles
were stripped and the residue was triturated with
posure of this material to an atmosphere of C2H4 in
hexane solution followed by recrystallization gave 8-
1
95% purity according to H NMR spectro-
pyrr in ꢁ
/
scopy. IR (Nujol, cmꢂ1) 1465 (s), 1375 (s), 1330 (m),
1310 (w), 1285 (w), 1240 (w), 1185 (br, w), 1105 (m),
1080 (w), 1065 (w), 1030 (m), 1010 (m), 980ꢁ850 (br, s),
/
815 (s), 720 (m), 620 (s). Anal. Calc. for TaSi2-
NO2C32H70: C, 52.08; H, 9.56; N, 1.90. Found: C,
52.66; H, 9.76; N, 1.64%.
hexanes (3ꢄ
hexanes and filtered. The hexanes were removed and the
solid was dissolved in ether and cooled to ꢂ78 8C,
/
10 ml). The residue was taken up in
/
affording 290 mg (57%) of 2-3,5-Lut as burgundy
microcrystals. Anal. Calc. for NbSi3O3NC43H90: C,
61.02; H, 10.72; N, 1.65. Found: C, 60.70; H, 10.57;
N, 1.38%.
4.2.9. (silox)2(C4H8N)Ta(h2-(N,C)ꢀ
pyrr)
A 100 ml flask was charged with 4-pyrr (0.945 g, 1.255
mmol) and Na/Hg (0.125 g Na, 14.33 g Hg, 5.437 mmol,
4.3 equiv.). The flask was evacuated and DME (50 ml)
/
NC5H5) (9-
4.2.12. (silox)2/
was added via vacuum transfer at ꢂ78 8C. An argon
/
ꢁ
ꢃ
atmosphere was admitted to the apparatus and pyridine
(1.01 ml, 12.54 mmol, 10 equiv.) was syringed into the
cold solution. As the solution was warmed a dark green
color was observed. This color faded over 5 h as the
solution took on a yellow/orange hue. The volatiles were
then removed, the amalgam was decanted from the flask
and the remaining solids were slurried with hexane. The
solution was filtered and the salts were washed with
hexane until the washings were colorless. The amber
hexane solution was concentrated and cooled to
NbNCHꢄCMeCHꢄCMeCHꢄCHCMe2SitBu2O (14)
A 50 ml bomb reactor was charged with 2-3,5-Lut
(272 mg, 0.321 mmol) and 10 ml cyclohexane, then
evacuated. The vessel was heated at 120 8C for 2.5 days.
Toepler pump analysis of the system revealed 0.057
mmol of a combustible gas, presumed to be H2. This was
20% of the expected amount based on a 72% conversion
to 14 according to 1H NMR analysis. The bomb reactor
was again charged with cyclohexane and the reaction
mixture was heated at 120 8C for an additional 1.5
days. All volatiles were removed, leaving a brown oil
ꢂ78 8C, and yellow crystals were collected by filtration
/
(0.770 g, 81%). IR (Nujol, cmꢂ1) 1590 (w), 1510 (w),
1475 (s), 1420 (w), 1375 (m), 1330 (m), 1290 (w), 1240
(s), 1135 (m), 1105 (w), 1080 (w), 1035 (m), 1000 (w), 985
that was triturated with pentane (3ꢄ 5 ml). The residue
/
was then taken up in hexanes (2 ml) and after slow
evaporation in a small vial, 75 mg of yellow, micro-
crystalline 14 was obtained (27%). Anal. Calc. for
(s), 960ꢁ880 (br, s),820 (s), 710 (s), 625 (s). Anal. Calc.
/

J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ
/184
183
NbSi3O3NC43H88: C, 59.75; H, 10.51. Found: C, 59.77;
H, 10.76%.
4.5. Physical studies
4.5.1. X-ray crystal structure determination of (silox)2
/
ꢁ
ꢃ
NbN-CHꢄCMeCHꢄCMeCHꢄCHCMe2SitBu2O (14)
4.3. NMR tube reactions
Yellow crystals of 14 were grown from a slow
evaporation of a concentrated solution in pentane. The
crystals were isolated and covered in isobutylene. A
suitable crystal was placed under a 173 8C N2 stream on
the goniometer head of a Siemens SMART CCD Area
Detector system equipped with fine-focus molybdenum
X-ray tube (Table 2). The crystal system was monoclinic
and the space group was P21/c. An empirical correction
for absorption (SADABS) was applied to the data. The
structure was solved by direct methods (SHELXS), and
the refinement was by full-matrix least-squares on F2.
All non-hydrogen atoms were anisotropically refined
and hydrogen atoms were treated as idealized contribu-
tions. Atoms C5, C6 and C7 are disordered. Switching
to space group P21 did not relieve the disorder hence it
was presumed to be intrinsic to the compound. The arm
of the N-containing fragment can be attached between
C4 and C9 (C5, C6 and C7) or between C4 and C33
(C5A, C6A and C7A). The occupancies are 60% for the
former and 40% for the latter.
4.3.1. 9-Pyrr and MeNH2
A sample of 9-pyrr (0.014 g, 0.018 mmol) was placed
in an NMR tube sealed to a 14/20 joint. The tube was
attached to a gas bulb and evacuated. C6D6 (0.6 ml) was
added in vacuo at 77 K followed by MeNH2 (27.5 Torr
in 12.3 ml, 0.018 mmol). The tube was flame sealed
under dynamic vacuum and warmed to 25 8C. After
ꢀ
12 h the 1H NMR of the solution revealed pyridine (d
/
6.65, 6.97, 8.52), pyrrolidine (d 2.64, NCH2; d 1.38,
NCH2CH2), H2 (d 4.46), 9-pyrr (ꢀ30%), intermediate
48%), and
/
a-pyridyl (silox)2Ta(NMe)(NC5H4) (11) (ꢀ
/
methyl imido pyrrolidide 10-pyrr (22%). By 1 week, the
starting material was almost completely consumed
(ꢀ/5% remaining). The conversion to 10-pyrr was
ꢀ/90% complete after 16 days.
4.4. 9-Pip and MeNH2
Acknowledgements
An NMR tube attached to a 14/20 joint was charged
with 9-pip (0.014 g, 0.018 mmol) and attached to a gas
bulb. The tube was evacuated and C6D6 (0.6 ml)
followed by MeNH2 (27.0 Torr in 12.3 ml, 0.018
mmol) were added in vacuo at 77 K. The tube was
flame sealed and warmed to 25 8C. After 5 days, the
reaction mixture was comprised of pyridine, piperidine,
The National Science Foundation (CHE-9816134)
and Cornell University are gratefully acknowledged.
References
H2, starting material (ꢀ
/
41%), intermediate 11 (ꢀ
/
9%),
[1] R. Prins, Adv. Catalysis 46 (2002) 399.
product 10-pip (ꢀ34%), and a product tentatively
/
[2] (a) T.C. Ho, Catal. Rev. Sci. Eng. 30 (1988) 117;
(b) C.N. Satterfield, Heterogenous Catalysis in Industrial Prac-
tice, McGraw-Hill, New York, 1991;
assigned as methyl imido methyl amido (silox)2Taꢄ
NMe(NH(Me) (12, 16%).
/
(c) J.R. Katzer, R. Sivasubramanian, Catal. Rev. Sci. Eng. 20
(1979) 155.
[3] C. Bianchini, A. Meli, F. Vizza, Eur. J. Inorg. Chem. 1 (2001) 43.
[4] R. Prins, M. Jian, M. Flechsenhar, Polyhedron 16 (1997) 3235.
[5] K.J. Weller, P.A. Fox, S.D. Gray, D.E. Wigley, Polyhedron 16
(1997) 3139.
4.4.1. 9-Pyrr-d5 and MeNH2
A 10 ml flask was charged with 4-pyrr (0.035 g, 0.046
mmol) and sodium amalgam (0.005 g Na, 0.217 mmol, 5
[6] R.J. Angelici, Polyhedron 16 (1997) 3073.
[7] R.M. Laine, Catal. Rev. Sci. Eng. 25 (1983) 459.
[8] (a) V. Schwartz, V.T. da Silva, S.T. Oyama, J. Mol. Catal., A
Chem. 163 (2000) 251;
equiv.). DME was added at ꢂ78 8C followed by excess
/
pyridine-d5. The solution was warmed and stirred for 6
h. After removal of the volatiles, the residue was
triturated three times with hexane and filtered. Removal
(b) J.A. Marzari, S. Rajagopal, R. Miranda, J. Catal. 156 (1995)
255.
[9] For h2-pyridines, see: (a) K.J. Covert, D.R. Neithamer, M.
Zonnevylle, R.E. LaPointe, C.P. Schaller, P.T. Wolczanski, Inorg.
Chem. 30 (1991) 2494;
of the volatiles yielded a yellow crystalline material (ꢁ
/
1
95% pure by H NMR). This material (0.016 g, 0.021
mmol) was taken up in C6D6 (0.6 ml) and transferred to
an NMR tube attached to a 14/20 joint. The tube was
attached to a gas bulb and the solution was freeze/pump/
thaw degassed three times. MeNH2 (31.1 Torr in 12.3
ml, 0.021 mmol) was added at 77 K and the tube was
sealed with a torch. The solution was warmed and
(b) D.P. Smith, J.R. Strickler, S.D. Gray, M.A. Bruck, R.S.
Holmes, D.E. Wigley, Organometallics 11 (1992) 1275;
(c) J.R. Strickler, M.A. Bruck, D.E. Wigley, J. Am. Chem. Soc.
112 (1990) 2814.
[10] For h6-pyridines, see: (a) S.G. Davies, M.R. Shipton, J. Chem.
Soc., Chem. Commun. (1989) 995;
(b) B. Chaudret, F.A. Jalon, J. Chem. Soc., Chem. Commun.
allowed to stand for ꢀ/3 weeks.

184
J.B. Bonanno et al. / Inorganica Chimica Acta 345 (2003) 173ꢁ184
/
(1988) 711;
[25] E. Rosenberg, S.E. Kabir, K.I. Hardcastle, M. Day, E. Wolf,
Organometallics 9 (1990) 2214 (and references therein).
[26] R.E. LaPointe, P.T. Wolczanski, G.E. Van Duyne, Organome-
tallics 4 (1985) 1810.
(c) E.J. Wucherer, E.L. Muetterties, Organometallics 6 (1987)
1691;
(d) K. Dimroth, R. Thamm, H. Kaletsch, Z. Naturforsch., B:
Anorg. Chem., Org. Chem., 39B (1984) 207;
(e) R.E. Schmidt, W. Massa, Z. Naturforsch., B: Anorg. Chem.,
Org. Chem., 39B (1984) 213.
[27] Caution: related procedures (cf. Ta(NMe2)5; D.C. Bradley, I.M.
Thomas, Can. J. Chem. 40 (1962) 1355) without amine present
have resulted in a highly explosive powder (presumably unreacted
LiNR2) upon work-up.
[11] K.D. Allen, M.A. Bruck, S.D. Gray, R.P. Kingsborough, D.P.
Smith, K.J. Weller, D.E. Wigley, Polyhedron 14 (1995) 3315.
[12] J.B. Bonanno, T.P. Henry, D.R. Neithamer, P.T. Wolczanski,
E.B. Lobkovsky, J. Am. Chem. Soc. 118 (1996) 5132.
[13] T.S. Kleckley, J.L. Bennett, P.T. Wolczanski, E.B. Lobkovsky, J.
Am. Chem. Soc. 119 (1997) 247.
[28] S.A. Strazisar, P.T. Wolczanski, J. Am. Chem. Soc. 124 (2001)
4728.
[29] S.W. Schweiger, M.M. Salberg, A.L. Pulvirenti, E.E. Freeman,
P.E. Fanwick, I.P. Rothwell, J. Chem. Soc., Dalton Trans. (2001)
2020.
[30] M. Brookhart, M.L.H. Green, L. Wong, Prog. Inorg. Chem. 36
(1988) 1.
[14] (a) M.H. Chisholm, K. Folting, J.C. Huffman, J. Leonelli, N.S.
Marchant, C.A. Smith, L.C.E. Taylor, J. Am. Chem. Soc. 107
(1985) 3722;
[31] (a) K.J. Covert, D.R. Neithamer, M.C. Zonnevylle, R.E. La-
Pointe, C.P. Schaller, P.T. Wolczanski, Inorg. Chem. 30 (1991)
2494;
(b) K.J. Ahmed, M.H. Chisholm, K. Folting, J.C. Huffman, J.
Chem. Soc., Chem. Commun. (1985) 152.
(b) D.R. Neithamer, L. Pa´rka´nyi, J.F. Mitchell, P.T. Wolczanski,
J. Am. Chem. Soc. 110 (1988) 4421.
[15] (a) S.D. Gray, K.J. Weller, M.A. Bruck, P.M. Briggs, D.E.
Wigley, J. Am. Chem. Soc. 117 (1995) 10678;
[32] D.S.J. Arney, P.A. Fox, M.A. Bruck, D.E. Wigley, Organome-
tallics 16 (1997) 3421.
(b) K.J. Weller, S.D. Gray, P.M. Briggs, D.E. Wigley, Organo-
metallics 14 (1995) 5588;
[33] For examples of a-pyridyl complexes, see: (a) S. Dagorne, S.
Rodewald, R.F. Jordan, Organometallics 16 (1997) 5541;
(b) R. Duchateau, E.A.C. Brussee, A. Meetsma, J.H. Teuben,
Organometallics 16 (1997) 5506;
(c) K.J. Weller, I. Filippov, P.M. Briggs, D.E. Wigley, J.
Organomet. Chem. 528 (1997) 225.
[16] (a) M. Tayebani, S. Gambarotta, G.P.A. Yap, Ang. Chem., Int.
Ed. Engl. 37 (1998) 3002;
(c) B.-J. Deelman, W.M. Stevels, M.T. Lakin, A.L. Spek, J.H.
Teuben, Organometallics 13 (1994) 3881;
(b) M. Tayebani, H. Feghali, S. Gambarotta, C. Bensimon,
Organometallics 16 (1997) 5084.
(d) A.S. Guram, R.F. Jordan, Organometallics 10 (1991) 3470;
(e) R.F. Jordan, A.S. Guram, Organometallics 9 (1990) 2116;
(f) R.F. Jordan, D.F. Taylor, N.C. Baenziger, Organometallics 9
(1990) 1546;
[17] M. Gandelman, D. Milstein, J. Chem. Soc., Chem. Commun.
(2000) 1603.
[18] T.S. Kleckley, Ph.D. thesis, Cornell University, 1998.
[19] A.S. Veige, T.S. Kleckley, R.L.M. Chamberlin, D.R. Neithamer,
C.E. Lee, P.T. Wolczanski, E.B. Lobkovsky, W.V. Glassey, J.
Organomet. Chem. 591 (1999) 194.
(g) W.J. Evans, L.R. Chamberlain, T.A. Ulibarri, J.W. Ziller, J.
Am. Chem. Soc. 110 (1988) 6423;
(h) K.H. den Haan, Y. Wielstra, J.H. Teuben, Organometallics 6
(1987) 2053;
[20] S.W. Schweiger, D.L. Tillison, M.G. Thorn, P.E. Fanwick, I.P.
Rothwell, J. Chem. Soc., Dalton Trans. (2001) 2401.
[21] (a) P.A. Fox, S.D. Gray, M.A. Bruck, D.E. Wigley, Inorg. Chem.
35 (1996) 6027;
(i) M.E. Thompson, S.M. Baxter, A.R. Bulls, B.J. Burger, M.C.
Nolan, B.D. Santarsiero, W.P. Schafer, J.E. Bercaw, J. Am.
Chem. Soc. 109 (1987) 203;
(b) P.A. Fox, M.A. Bruck, S.D. Gray, N.E. Gruhn, C. Grittini,
D.E. Wigley, Organometallics 17 (1998) 2720.
(j) P.L. Watson, J. Chem. Soc., Chem. Commun. (1983) 276;
(k) E. Klei, J.H. Reuben, J. Organomet. Chem. 214 (1981) 53.
[34] R.L. Miller, R. Toreki, R.E. LaPointe, P.T. Wolczanski, G.D.
Van Duyne, D.C. Roe, J. Am. Chem. Soc. 115 (1993) 5570.
[22] (a) M. Egorova, Y. Zhao, P. Kukula, R. Prins, J. Catal. 206
(2002) 263;
(b) F. Rota, V.S. Ranade, R. Prins, J. Catal. 200 (2001) 389.
[23] D.A. Vicic, W.D. Jones, Organometallics 18 (1999) 134.
[24] S.E. Kabir, D.S. Kolwaite, E. Rosenberg, Organometallics 15
(1996) 1979.
[35] W.A. Nugent, J.M. Mayer, Metalꢁ
/
Ligand Multiple Bonds,
Wiley, New York, 1988.
[36] A.S. Veige, P.T. Wolczanski, E.B. Lobkovsky, Angew. Chem. Int.
Ed. 40 (2001) 3629.