The reactions of lithium trimethysilylmethyls with isocyanides; Structures and reactions of the derived lithium 1-azaallyls, β-diketiminates and a 1-azabuta-1,3-dienyl-3-amide

Article abstract of DOI:10.1039/b103553n

The reactions of lithium trimethysilymethyls with isocyanides were studied. These reactions provide a convenient source for synthesizing aldehydes, ketones, α-hydroxy-ketones, β-hydroxy-ketones, β-hydroxy-acids, α-keto-acids, and α-amino-acids. Each of the compounds 1-9 was fully characterized by multinuclear NMR spectroscopy, mass spectrometry, and microanalysis. X-ray diffraction data were also provided for the complexes 4, 6b and 8.

Full text of DOI:10.1039/b103553n

View Article Online / Journal Homepage / Table of Contents for this issue
The reactions of lithium trimethysilylmethyls with isocyanides;
structures and reactions of the derived lithium 1-azaallyls,
ꢀ-diketiminates and a 1-azabuta-1,3-dienyl-3-amide
Peter B. Hitchcock,a Michael F. Lappert*a and Marcus Layhb
a The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ
b Molecular Science Institute, School of Chemistry, University of the Witwatersrand,
Private Bag 3, Wits, 2050 Johannesburg, South Africa
Received 20th April 2001, Accepted 14th June 2001
First published as an Advance Article on the web 30th July 2001
The insertion of ArNC (Ar = 2,6-Me2C6H3) or ButNC into the Li–C bond of [Li{C(H)(R)RЈ}] (R = SiMe3, RЈ = R
or Ph) led to (i) the lithium 1-azaallyls [Li{N(RЉ)C(R)C(H)RЈ}(tmen)] (6a RЈ = R, RЉ = Ar; 6b RЈ = Ph, RЉ = Ar;
6c RЈ = Ph, RЉ = But), (ii) the lithium β-diketiminates [Li{N(But)C(R)C(H)C(R)NBut}][(LiCHR2)(CNBut)] 1,
Li{N(Ar)C(R)C(H)C(R)N(Ar)} 2 and [Li{N(Ar)C(R)C(H)C(Ph)N(R)}(tmen)] 7 (from 6a and PhCN), or (iii) the
lithium amide [Li{N(Ar)C(R)C[N(Ar)]᎐C(H)Ph}(tmen)] 8. Treatment of the lithium β-diketiminates 1 and 2 with
᎐
ZrCl4 yielded the complexes [ZrCl3{N(But)C(R)C(H)C(R)NBut}] 3 or [Zr{N(Ar)C(R)C(H)C(R)N(Ar)}Cl2(µ-Cl)2-
Li(OEt2)2] 4, while reaction of the lithium compounds 2 or 8 with MeOH gave in high yield the conjugate acids
of the corresponding anions [HN(Ar)C(R)C(H)C(R)NAr] 5 or [HN(Ar)C(R)C{N(Ar)}᎐C(H)Ph] 9. Each of the
᎐
compounds 1–9 was fully characterised by multinuclear NMR spectroscopy, mass spectrometry and microanalysis,
while X-ray diffraction data are also provided for the complexes 4, 6b and 8.
Reactions between a lithium alkyl LiRЈ and an isocyanide
RЉNC have been investigated in considerable detail. They
provide a convenient source for synthesising aldehydes,1,2
ketones,1,2 α-hydroxy-ketones,1–4 β-hydroxy-ketones,2 β-
hydroxy-acids,1 α-keto-acids,1,5 α-amino-acids6 or heterocycles
such as [R(RЈ)COC(H)᎐NC(H)(RЉ)]7 or [N᎐C(R)X{1,2-C H }]
᎐
᎐
6
4
(X = S, PPh, SiMe2, GeMe2, SnMe2).4 The lithio aldimine
LiC(RЈ)᎐NRЉ (a masked carbanion) was postulated to be an
᎐
intermediate, but has not been isolated.1,2,4–6,8
Our interest in this type of behaviour derives from (i) our
earlier studies on the reactions between a lithium trimethyl-
silylmethyl and an α-H-free nitrile to give lithium 1-azaallyls
(e.g. A), β-diketiminates (e.g. B or C) or 1,3-diazaallyls (e.g. D)
(R = SiMe3); and (ii) the observation that metal complexes con-
taining a bound isocyanide react with a halogenoalkane to give
C–C-coupled products. As for (i), examples include reactions
between LiCHR2 and PhCN affording A–D and C6H4-
[C(H)(R)Li(tmen)]2-1,2 E and ButNC yielding F.9 Regarding
(ii), illustrations are shown in eqns. (1)10 and (2).11
(1)
(2)
β-trimethylsilyl substituents. Thus treatment of isocyano-2,6-
dimethylbenzene (≡ ArNC) with [Li(SiR3)(thf )3] or PhNC with
LiNR2 gave the crystalline 4-aryl(lithio)amino-1-aza-2-sila-
cyclobut-3-ene G13 or the dimeric 1 : 1 adduct H,14 respectively.
Relevant to the present paper, we have previously shown that
A with isocyanobenzene yielded the 1,3-diazaallyllithium com-
pound DЈ.9 Moreover, in 1998 we briefly communicated our
As an extension of our research on nitriles, such as those of
(i) above, we turned our attention to isocyanide reactions with
lithium alkyls,12 silyls13 or amides14 containing one or more
DOI: 10.1039/b103553n
J. Chem. Soc., Dalton Trans., 2001, 2409–2416
This journal is © The Royal Society of Chemistry 2001
2409

View Article Online
Scheme 1
initial findings on the reactions of LiCHR2 with 2-isocyano-2-
methylpropane (affording 1) or ArNC (giving 2).12 This paper
provides full details of that report12 and provides significant
elaborations, encompassing the synthesis and characterisation
of eight additional new compounds 3–9 (Scheme 1). In the
interim, publications in 2000 by Leung and co-workers have
revealed reactions between the dilithium compound E15 and
ButNC, eqn. (3);16 both the crystalline lithium16a and the tin16b
complexes were X-ray-characterised.
unusual in being a heterobinuclear complex of a type more
frequently found in Group 3 and lanthanide chemistry,
originally in [Y{η5-C5H4(SiMe3)}2(µ-Cl)2Li(thf )2];17 although
examples in zirconium chemistry are shown in K,18a KЈ18b and
KЉ,18c for which, as for 4, the role of LiCl is presumed to be to
coordinatively saturate the zirconium environment of the
otherwise labile LiCl-free complex. Attempts to displace one or
more of the chloride ligands of 4 by treatment with methyl-
lithium led (v in Scheme 1) instead to the isolation of 2 and,
judged by its appearance, zirconium metal. Similarly, substi-
tution of a chloride ligand of 4 by a β-diketiminate did not
succeed; the only isolated product was (vi in Scheme 1) the
yellow β-diketimine 5. The latter was more rationally obtained
(vii in Scheme 1) by protonolysis of 2 using methanol.
(3)
Results and discussion
The reaction of LiCHR2 with ButNC or ArNC in diethyl ether
at low temperatures yielded (i or ii in Scheme 1) the lithium
β-diketiminate complexes: the yellow 1 and the orange 2 (see
also ref. 12). Although 1 is unusual in being a 1 : 1 : 1 adduct of
LiCHR2, Li{N(But)C(R)C(H)C(R)NBut} I and ButNC, con-
ceptually it has a skeletal precedent in the X-ray-characterised
complex J (obtained from LiCHR2 and PhCN in thf ).9,12 It is
noteworthy that 1 proved to be unreactive towards heat or
excess of ButNC (which might have been expected to yield the
free lithium β-diketiminate I). Reaction of 1 or 2 with an
equivalent portion of zirconium() chloride gave (iii or iv in
Scheme 1) in good yield the yellow, crystalline β-diketiminato-
zirconium() complexes 3 or 4, respectively. Complex 4 is
Whereas LiCHR2 with ArNC in the absence of a strong
neutral donor had yielded the 1 : 2 adduct, the lithium
β-diketiminate 2, introduction of tmen afforded (viii in Scheme
1) the 1 : 1 adduct, the red lithium 1-azaallyl 6a; similarly, the
yellow analogue 6b or 6c was obtained from [Li{CH(R)Ph}-
(tmen)] and ArNC or ButNC, respectively. The role of tmen (or
a similar strong neutral coligand) in the related LiCHR2–PhCN
reactions had previously been noted, the product having been A
or, in the absence of such a coligand, B.9 With ArNC or ButNC
complex 6a was converted (x or ix in Scheme 1) into the lithium
β-diketiminate 2 (in a slow reaction) or the orange 7, respec-
tively. While each of the above compounds 1–7, based on
2410
J. Chem. Soc., Dalton Trans., 2001, 2409–2416

View Article Online
Scheme 2
Li{CH(R)RЈ} (RЈ = R or Ph) as precursor, was a 1-azaallyl or
β-diketiminate derivative, a quite different outcome was
observed in deceptively similar system. Thus, when
a
[Li{CH(R)Ph}(tmen)] was treated with 2 ArNC at low tem-
perature in pentane the product (xi in Scheme 1) was the red,
crystalline 1-azabuta-1,3-dienyl-3-amido compound 8. The
formation of 8, rather than that of an isomeric lithium
β-diketiminate, may have been favoured by its extended conju-
gation; this feature was retained upon its protonolysis with
methanol to yield (xii in Scheme 1) the corresponding yellow
amine 9.
Each of the lithium 1-azaallyls or β-diketiminates 1, 2, 6a, 6b,
6c and 7 was both highly air-sensitive (hydrolysing readily) and
soluble in hydrocarbons, the phenyl-substituted derivatives
slightly less so than their trimethylsilyl analogues. The air-
sensitive lithium amide 8 and the zirconium β-diketiminates 3
and 4 were insoluble or only sparingly soluble in pentane, and
required diethyl ether or thf to dissolve significant amounts of
each.
Fig. 1 The molecular structure of the crystalline complex 4.
In our preliminary publication dealing with the synthesis of
the lithium β-diketiminates 1 and 2 from LiCHR2 and ButNC
or ArNC respectively, we noted that the C–C-bond-making
reactions also involved 1,2 shifts of a trimethylsilyl group and
that a 1-azaallyllithium compound was probably implicated in
the reaction pathway.12 Having now isolated not only examples
of the latter, 6a–6c, but also the azabutadienylamidolithium
compound 8, we now suggest a more comprehensive rational-
isation, illustrated in Scheme 2 for the case of [Li{CH(R)RЈ}-
(tmen)] and ArNC as reagents. The first step is envisaged to be
formation of the nitrile–lithium alkyl donor–acceptor adduct
L, which rearranged successively to the lithio-aldimine M and,
consequent upon a 1,2-Me3Si shift, the lithium 1-azaallyl 6.
When one of the three latter compounds, namely 6a, was sub-
jected to treatment with a further equivalent of ArNC, we pre-
sume that this proceeded via a further 1 : 1 adduct, analogous
to L (not shown in Scheme 2), which rearranged to the inter-
mediate N (related to M) and thence by a 1,2-Me3Si shift to the
lithium β-diketiminate 2. When the initial reaction was between
the lithium alkyl and 2 ArNC, we suggest that M rapidly
reacted with the second equivalent of ArNC to form the 1 : 1
adduct O, which was transformed into P (a process similar to
L→M). Thus, we envisage that the conversion of M into O is
faster than its isomerisation into 6. The successive rearrange-
ment O into P and thence by a 1,2-Me3Si shift into 8 completes
the reaction sequence.
Although isocyanohydrocarbon adducts of transition metal
complexes are well documented, analogues with main group
metals are rare, but H14 may be regarded as a model for L and
O. The lithioaldimine N, like its analogue P, corresponds to the
frequently postulated intermediate in C–C coupling reactions
of the type referred to in the first paragraph of the present
paper,1–8 while 1,2-Me3Si C→C shifts in appropriate carbanions
are well established.19
Crystal structures of complexes 4, 6b and 8
The molecular structures of complexes 4, 6b, and 8 with the
atom numbering schemes are shown in Figs. 1–3, respectively.
Selected bond distances and angles are listed in Tables 1–3.
The β-diketiminatozirconium() complex 4 (Fig. 1) was
crystallised from diethyl ether as a monomeric heterobinuclear
species in which the two metal atoms are bridged by the
chloride atoms Cl(3) and Cl(4). The zirconium atom is in
an approximately octahedral configuration, the two terminal
chloride atoms Cl(1) and Cl(2) occupy axial positions, Cl(1)–
Zr–Cl(2) 176.04(3)Њ, and the cisoid bond angles at zirconium
range from 82.02(9) to 96.74(4)Њ. The lithium atom is in a dis-
torted tetrahedral configuration, the bond angles at lithium
ranging from 92.2(2) [Cl(3)–Li–Cl(4)] to 120.2(3)Њ [O(2)–Li–
Cl(3)]. The Li–O and Li–Cl bond lengths and the angles
J. Chem. Soc., Dalton Trans., 2001, 2409–2416
2411

View Article Online
Table 1 Selected bond distances (Å) and angles (Њ) of complex 4
Table 2 Selected bond distances (Å) and angles (Њ) of complex 6b
Zr–N(1)
2.216(3)
2.421(1)
2.518(1)
1.919(6)
2.399(6)
1.941(3)
1.335(4)
1.455(4)
1.456(4)
Zr–N(2)
Zr–Cl(2)
Zr–Cl(4)
Li–O(2)
Li–Cl(4)
Si(2)–C(3)
N(2)–C(3)
C(1)–C(2)
2.209(2)
2.441(1)
2.528(1)
1.913(6)
2.415(6)
1.939(3)
1.340(4)
1.407(4)
Li–N(1)
Li–N(3)
Si–C(1)
N(1)–C(12)
C(2)–C(3)
C(3)–C(4)
C(5)–C(6)
C(7)–C(8)
1.946(10)
2.075(11)
1.909(5)
1.420(6)
1.457(6)
1.414(7)
1.390(7)
1.400(7)
Li–N(2)
2.119(10)
2.602(10)
1.363(6)
1.376(6)
1.398(7)
1.380(7)
1.369(7)
Zr–Cl(1)
Zr–Cl(3)
Li–O(1)
Li ؒ ؒ ؒ C(8)
N(1)–C(1)
C(1)–C(2)
C(3)–C(8)
C(4)–C(5)
C(6)–C(7)
Li–Cl(3)
Si(1)–C(1)
N(1)–C(1)
N(1)–C(4)
N(2)–C(12)
N(1)–Li–N(3)
N(3)–Li–N(2)
C(1)–N(1)–Li
N(1)–C(1)–C(2)
C(2)–C(1)–Si
133.9(5)
88.0(4)
115.0(4)
122.4(4)
113.9(4)
N(1)–Li–N(2)
C(1)–N(1)–C(12)
C(12)–N(1)–Li
N(1)–C(1)–Si
131.5(5)
117.8(4)
125.8(4)
123.0(3)
130.2(5)
N(2)–Zr–N(1)
N(1)–Zr–Cl(1)
N(1)–Zr–Cl(2)
N(2)–Zr–Cl(3)
Cl(1)–Zr–Cl(3)
N(2)–Zr–Cl(4)
Cl(1)–Zr–Cl(4)
Cl(3)–Zr–Cl(4)
O(2)–Li–Cl(3)
O(2)–Li–Cl(4)
Cl(3)–Li–Cl(4)
82.02(9)
95.77(7)
87.74(7)
176.33(7)
87.04(4)
96.74(7)
87.91(4)
86.91(3)
120.2(3)
109.9(3)
92.2(2)
N(2)–Zr–Cl(1)
N(2)–Zr–Cl(2)
Cl(1)–Zr–Cl(2)
N(1)–Zr–Cl(3)
Cl(2)–Zr–Cl(3)
N(1)–Zr–Cl(4)
Cl(2)–Zr–Cl(4)
O(2)–Li–O(1)
O(1)–Li–Cl(3)
O(1)–Li–Cl(4)
92.66(7)
89.64(7)
176.04(3)
94.37(7)
90.87(4)
176.16(7)
88.62(3)
114.3(3)
107.2(3)
110.8(3)
C(1)–C(2)–C(3)
Table 3 Selected bond distances (Å) and angles (Њ) of complex 8
Li–N(1)
Li–N(3)
Si–C(1)
N(1)–C(10)
N(2)–C(18)
C(2)–C(3)
C(4)–C(9)
C(5)–C(6)
C(7)–C(8)
2.130(6)
2.192(6)
1.945(4)
1.424(4)
1.398(4)
1.380(5)
1.391(5)
1.379(6)
1.387(6)
Li–N(2)
Li–N(4)
1.970(6)
2.214(6)
1.297(4)
1.355(4)
1.502(5)
1.454(5)
1.402(5)
1.375(6)
1.380(5)
N(1)–C(1)
N(2)–C(2)
C(1)–C(2)
C(3)–C(4)
C(4)–C(5)
C(6)–C(7)
C(8)–C(9)
N(2)–Li–N(1)
N(1)–Li–N(3)
N(1)–Li–N(4)
C(1)–N(1)–C(10)
C(10)–N(1)–Li
C(2)–N(2)–Li
N(1)–C(1)–C(2)
C(2)–C(1)–Si
80.2(2)
127.2(3)
118.2(3)
122.8(3)
124.0(3)
115.8(3)
115.2(3)
119.8(2)
115.7(3)
130.9(3)
N(2)–Li–N(3)
N(2)–Li–N(4)
N(3)–Li–N(4)
C(1)–N(1)–Li
C(2)–N(2)–C(18)
C(18)–N(2)–Li
N(1)–C(1)–Si
N(2)–C(2)–C(3)
C(3)–C(2)–C(1)
114.4(3)
140.9(3)
83.0(2)
113.0(3)
119.6(3)
120.8(3)
125.0(3)
128.6(3)
115.5(3)
N(2)–C(2)–C(1)
C(2)–C(3)–C(4)
2.703(2) Å in [ZrCl3{N(R)C(But)C(H)C(Ph)NR}] Q20 or
[Zr(η5-C9H7)Cl2{N(Ph)(CH)3NPh}],21 respectively, probably
because 4, unlike these, is coordinatively saturated at the
zirconium atom. For the latter compounds, the β-diketiminato
ligand has been described as having η5-character, and thus is
isoelectronic with an η5-cyclopentadienyl; consistent with this
view, the above trichloride with methylaluminoxane was shown
to be an efficient ethylene polymerisation catalyst.22 There is
effective electron delocalisation in 4, as evident from the simi-
larity in each pair of Zr–N and N–C average bond lengths:
2.213(8) and 1.338(8) Å, respectively. These distances may be
compared with the corresponding values in Q of 2.17(4) and
1.34(2) Å;20 the central C–C bond distance in each is also
similar, 1.407(4) and 1.42(1) Å in 4 and Q,20 respectively.
Fig. 2 The molecular structure of the crystalline complex 6b.
The crystalline 1-azaallyl compound 6b (Fig. 2) is mono-
meric. The sum of the angles subtended by the three nitrogen
atoms at the lithium atom is 354.2Њ. The deviation from
planarity may be due to a short (agostic) Li ؒ ؒ ؒ C contact of
2.60(1) Å involving an o-phenyl carbon atom, C(8); it may be
compared with 2.23(2) and 2.32(2) Å for the α- and β-Li–C
bonding distances, respectively in [Li{N(R)C(C6H4Br-4)CR2}-
(thf )].23 The nitrogen atom of the 1-azaallyl ligand, N(1), has
the shorter Li–N distance [1.946(10) Å] compared with those
of the chelating tmen: Li–N(2 or 3) = 2.097 0.022 Å. The
1-azaallyl ligand is bonded to the lithium atom as the eneamido
(rather than the η3-1-azaallyl) tautomer, as evident additionally
from the rather long N(1)–C(1) and short C(1)–C(2) distances
of 1.363(6) and 1.376(6) Å, appropriate for single and double
bonds, respectively, the wide N(1)–C(1)–C(2) angle of 122.4(4)Њ
and the long separation between the lithium atom and C(1)
and C(2) of 2.81(1) and 3.08(1) Å, respectively. The geometric
parameters of 6b are closely similar to those of R9 and of
Fig. 3 The molecular structure of the crystalline complex 8.
subtended at the lithium atom are very similar to those in the
complexes K,18a KЈ,18b and KЉ.18c As in K, the terminal Zr–Cl
bond lengths [mean 2.431(1) in 4 and 2.453 Å in K18a] are
shorter than the bridging [mean 2.523(6) (4) and 2.561(6) Å in
18a]. The six-membered metallacycle ZrN(1)C(2)C(3)N(2)
adopts a boat conformation, but the transannular Zr ؒ ؒ ؒ C(2)
distance of 3.425(5) Å is much longer than the 2.54(1) or
K
[Li{N(R)C(C H Br-4)᎐CR }(thf )],23 whereas the correspond-
᎐
6
4
2
ing distances of 2.571(8) and 2.724(8) Å in the binuclear
2412
J. Chem. Soc., Dalton Trans., 2001, 2409–2416

View Article Online
(4)
1-azaallyllithium compound of eqn. (3) and its Li–N bond
length of 1.957(8) Å are indicative of η3-bonding.16a The
arrangement about C(1)–C(2) in 6b is E; i.e. the Ph and SiMe3
groups are arranged in a transoid fashion.
The crystalline 1-azabuta-1,3-dienyl-3-amidolithium com-
plex 8 (Fig. 3) is a monomer, in which the four-coordinate lith-
ium atom is the spiro centre of a distorted tetrahedron, the two
endocyclic angles subtended at the lithium atom, being bite
angles, are inevitably acute, 80.2(2) and 83.0(2)Њ for N(1)–Li–
N(2) and N(3)–Li–N(4), respectively. The LiN(1)C(1)C(2)N(2)
metallacycle is planar, only C(2) deviating by 0.002 Å from the
mean plane. The dihedral angles between the two N,NЈ-aryl
planes and this plane are 85.7(1) and 64.2(1)Њ, the two aryl
substituents being mutually transoid. One short [Li–N(2),
1.970(6) Å] and three longer Li–N bond distances [2.130(6),
2.192(6) and 2.214(6) Å for Li–N(1, 3 and 4, respectively)], and
the alternating bond distances of the anionic ligand [1.297(4),
1.502(5), 1.355(4) and 1.380(5) Å, for N(1)–C(1), C(1)–C(2),
N(2)–C(2) and C(2)–C(3), respectively] indicate that the
negative charge is mainly localised at N(2). This is consistent
with the notion that complex 8 is a substituted lithium amide,
stabilised by a transannular Li–N(aryl) and chelating N,NЈ-
tmen dative bonds. We note that a typical Li–N(aryl) amide
bond length in a monomeric datively bound complex is close to
that for Li–N(2) in 8, namely 1.895(8) Å in [Li{N(H)Ph}-
(tmen)]24 or 2.00(1) Å in [Li{N(C10H7-1)Ph}(pmdien)].25 Com-
parison between some of the geometric parameters of 8 with
those of the binuclear complex S26 is also informative.
the enamido type of structure similar to that observed in the
solid state for 6b (cf. also refs. 9 and 27) with the Ph substituent
being trans to the SiMe3 group (cf. III). This was supported for
both compounds by 1H 6Li-NOE-difference spectra which
showed a close contact between the trans-butyl group (for 6c,
9% NOE enhancement) or the aryl methyl groups (for 6b, 8%
NOE enhancement), NMe (24 or 27% NOE enhancement,
respectively) and the ortho-H (11 or 19% NOE, respectively) of
the phenyl substituent but not to the olefinic hydrogen atom.
The major difference between the 1H NMR spectra of 6b and 6c
was that the signal for the two ortho-H atoms of the phenyl
substituent at δ 8.0 was much broader for complex 6c than for
6b indicating hindered rotation around the C–C(ipso) bond.
When a sample of 6c was cooled to 208 K (coalescence tem-
perature 223 K, corresponding to ∆G#223 K = 39.9 kJ molϪ1), the
o-1H signal split into two distinct doublets at δ 9.35 and 6.68.
This assignment for the two hydrogen atoms was also sup-
ported by a homonuclear NOE experiment at 193 K which
showed H(B) to be interacting strongly with PhCH but not
H(A). A weakening of the C–H(A) bond, indicated by a reduc-
tion of the CH(A) coupling constant (consistent with an agostic
Li–H–C interaction) was, however, not observed, 1J(13C–
1H) = 153 or 152 Hz for C–H(A) and C–H(B). When the tem-
perature was raised, the rate of rotation around the C–C(ipso)
bond was increased until at 323 K only a slightly broadened
singlet at δ 8.06 was observed. In the case of the sterically less
hindered complex 6b the rotation already at room temperature
was so fast that only one sharp doublet was noted; only when 6b
was cooled, the signal began to broaden until at 178 K it separ-
ated into two singlets at δ 9.03 and ca. δ 7.0 (obscured by other
signals in this region; coalescence temperature 193 K).
NMR spectra and solution behaviour
The 1H NMR spectrum of compound 6a in C7D8 or C6D6 solu-
tion at room temperature showed the presence of two sets of
signals indicating a mixture of two rotamers Ia,b and II in the
approximate ratio of 4 : 1, (eqn. 4), with a coalescence temper-
ature of 303 K. A second exchange process with a coalescence
temperature of 193 K was observed for the major isomer,
corresponding to the freezing of the rotation of the aryl group
around the N–C bond, thereby making the o-methyl groups A
and B at the aryl substituent magnetically different. The minor
isomer showed no signs of such behaviour above 177 K. As
delocalisation of π-electron density within the ligand may be
A hindered rotation around the N–C(ipso) bond, as found for
complex 6a (cf. rotamers Ia and Ib) was not observed for 6b
even at lower temperatures.
The NMR spectra of the other reported compounds showed
no unusual noteworthy features.
more efficient if the aryl group is remote from the C᎐C double
᎐
bond (rotamer Ia,b) and hence the N–C(aryl) bond for Ib
may have the higher double bond character, we suggest that the
rotation around this bond would be frozen out at a higher tem-
perature than in isomer II. Thus, it seems likely that rotamer
Ia,b is the major isomer.
Experimental
All manipulations were carried out under argon, using standard
Schlenk techniques. Solvents were distilled from drying agents
and degassed. The NMR spectra were recorded in C6D6 or
The 1H NMR spectra of solutions of complex 6b or 6c
in C7D8 at room temperature showed only signals of one
isomer for each. The chemical shift values for the PhCH
protons (δ 5.39 for 6b and δ 4.99 for 6c) indicate that each has
J. Chem. Soc., Dalton Trans., 2001, 2409–2416
2413

View Article Online
C7D8 at 298 K using the following Bruker instruments: DPX
[Zr{N(Ar)C(R)C(H)C(R)N(Ar)}Cl2(ꢁ-Cl)2Li(OEt2)2]
4.
ZrCl4 (0.37 g, 1.59 mmol) was added at Ϫ78 ЊC to a solution of
2 (0.68 g, 1.59 mmol) in Et2O (30 cm3). The reaction mixture
was allowed to warm to room temperature and was stirred for
14 h yielding an orange suspension, which was filtered to
remove a small amount of solid and cooled to give yellow
crystals of 4 (0.81 g, 63%). Another crop of 4 (0.30 g, 23.2%)
(Found: C, 47.9; H, 6.97; N, 3.89. C33H57Cl4LiN2O2Si2Zr
requires C, 48.9; H, 7.09; N, 3.45%) was obtained from the
mother liquor. Mass spectrum [m/z (%)]: 618 (20 [M Ϫ Li-
Cl(Et2O)2]ϩ), 603 (7 [M Ϫ LiCl(Et2O)2 Ϫ Me]ϩ), 583 (10
[M Ϫ LiCl(Et2O)2 Ϫ Cl]ϩ), 545 (25 [M Ϫ LiCl(Et2O)2 Ϫ
7
300 (1H, 300.1; 13C, 75.5; Li, 116.6 MHz) and AMX 500 (1H,
500.1; 13C, 125.7; 29Si, 99.4 MHz) and referenced internally to
residual solvent resonances (data in δ) in the case of 1H and 13
C
spectra. The Li and 29Si spectra were referenced externally to
LiCl and SiMe4, respectively. Unless otherwise stated, all NMR
spectra other than 1H were proton-decoupled. Electron impact
mass spectra were from solid samples using a Kratos MS 80 RF
instrument. Melting points were taken in sealed capillaries and
are uncorrected. Elemental analyses were determined by Medac
Ltd., Brunel University, Uxbridge, UK.
7
Preparations
SiMe3]ϩ), 509 (7 [M Ϫ LiCl(Et2O)2 Ϫ Ar]ϩ), 421 (73 [Ar]ϩ). H
1
NMR (C6D6): δ Ϫ0.05 (s, SiMe3, 18 H), 1.19 [t, CH3 (Et2O),
12 H, 3J(1H–1H) = 7.1], 2.34 (s, Me, 12 H), 3.62 [q, OCH2, 8H,
3J(1H–1H) = 7.1 Hz], 6.60 (s, CH, 1 H), 7.04 (s, broad, Ph, 6 H);
13C NMR (C6D6): δ 0.6 (s, SiMe3), 14.2 [s, Me (Et2O)], 20.4 (s,
Me), 66.4 (s, OCH2), 116.3 (s, CH), 122.9 (s, p-C), 128.6 (s,
m-C), 134.9 [s, ipso-C (Me)], 146.7 (s, ipso-C), 179.6 (s, CN).
[Li{N(But)C(R)C(H)C(R)N(But)}][LiC(H)R2](CNBut)
1.
ButNC (1.2 cm3, 10 mmol) was added to a solution of
LiCH(SiMe3)2 (1.17 g, 7.03 mmol) in Et2O at Ϫ40 ЊC. (The
chosen stoichiometry was optimal, based on several altern-
atives.) The reaction mixture was slowly warmed to room tem-
perature and then stirred for a further 15 h. The solvent was
removed in vacuo and “stripped” with pentane. The obtained
sticky, yellow residue was heated for 4 h at 60 ЊC in vacuo; then
extracted into pentane (80 cm3). The filtered extract was con-
centrated and cooled, yielding yellow crystals of 1 (0.68 g, 33%
based on Li) (Found: C, 59.0; H, 11.60; N, 7.20. C29H65Li2N3Si4
requires C, 59.0; H, 11.49; N, 7.37%), mp 137 ЊC (decomp.). 1H
NMR (C6D6): δ Ϫ1.69 (s, CHSi2, 1 H), 0.41 (s, SiMe3, 18 H),
0.52 (s, SiMe3, 18 H), 0.72 [s, But (CNBut), 9 H], 1.42 (s, But, 18
H), 5.40 (s, CH, 1 H); 7Li NMR (C6D6): δ 0.8; 13C NMR (C6D6):
δ 3.3 (s, CHSi2), 4.4 (s, SiMe3), 7.3 (s, SiMe3), 29.4 [s, C(CH3)3
(CNBut)], 32.8 (s, C(CH3)3), 54.7 (s, C(CH3)3), 55.9 [s, C(CH3)3
(CNBut)], 108.5 (s, CH), 142.3 [s, CN (CNBut)], 179.9 (s, CN).
The mass spectrum was not informative.
[HN(C6H3Me2-2,6)C(R)C(H)C(R)N(C6H3Me2-2,6)]
5.
Methanol (0.07 cm3, 1.61 mmol) was added to a solution of 2
(0.69 g, 1.61 mmol) in pentane (40 cm3). The colour changed
from red to yellow and a white precipitate was formed. The
mixture was stirred for 15 h at room temperature and then fil-
tered. Concentration of the filtrate and cooling gave yellow
needles of 5 (0.33 g, 48.5%). A second crop of crystals (0.22 g,
32.3%) (Found: C, 69.8; H, 8.81; N, 6.66. C25H38N2Si2 requires
C, 71.0; H, 9.06; N, 6.62%), mp 131 ЊC (decomp.) was isolated
from the mother liquor. Mass spectrum [m/z (%)]: 422 (60
[M]ϩ), 407 (35 [M Ϫ Me]ϩ), 349 (100 [M Ϫ SiMe3]ϩ), 317 (45
[M Ϫ Ar]ϩ). 1H NMR (C6D6): δ Ϫ0.01 (s, SiMe3, 18 H), 2.18 (s,
Me, 12 H), 5.71 (s, CH, 1H), 6.92 (s, broad, Ph, 12 H), 13.26 (s,
NH, 1 H); 13C NMR (C6D6): δ Ϫ0.1 (s, SiMe3), 18.9 (s, Me),
105.5 (s, CH), 125.0, 128.5 (s, m/p-C), 132.6 [s, ipso-C (Me)],
146.4 (s, ipso-C), 172.1 (s, CN).
[Li{N(C6H3Me2-2,6)C(R)C(H)C(R)N(C6H3Me2-2,6)}]
2.
Solid C6H3(Me2-2,6)NC (3.15 g, 2.4 mmol) was added to a
suspension of LiCH(SiMe3)2 (2.0 g, 1.2 mmol) in pentane (100
cm3) and Et2O (0.1 cm3) at Ϫ78 ЊC. The mixture was allowed to
warm to room temperature during a period of 15 h (in a plastic
bowl filled with acetone/dry ice). A dark red solution with a
small amount of white precipitate was obtained. After remov-
ing the solvent and extracting the residue into pentane (60 cm3),
the mixture was filtered and the filtrate concentrated and cooled
affording orange crystals of 2 which were contaminated by a
small amount of free isocyanide. The latter was sublimed off by
heating the sample for 1 h to 120 ЊC in vacuo leaving 2 (3.41 g,
66.3%) (Found: C, 69.9; H, 8.51; N, 6.67. C25H37LiN2Si2
requires C, 70.0; H, 8.70; N, 6.53%), mp 210 ЊC (decomp.).
Mass spectrum [m/z (%)]: 422 (6 [M Ϫ Li]ϩ), 407 (3 [M Ϫ Li Ϫ
Me]ϩ), 349 (19 [M Ϫ Li Ϫ SiMe3]ϩ). 1H NMR (C6D6): δ 0.05 (s,
SiMe3, 18 H), 2.03 (s, Me, 12 H), 5.48 (s, CH, 1 H), 6.90–6.92
[Li{N(C6H3Me2-2,6)C(R)C(H)R}(tmen)] 6a. LiCH(SiMe3)2
(0.44 g, 2.65 mmol) was dissolved in a mixture of pentane
(30 cm3) and tmen (0.40 cm3, 2.65 mmol). The mixture was
cooled to Ϫ90 ЊC and (C6H3Me2-2,6)NC (0.35 g, 2.65 mmol)
was added. After allowing the mixture to warm to room tem-
perature during a period of 3 h it was stirred for a further 12 h;
a dark green solution was obtained. After removing all volatiles
in vacuo and extracting the residue with pentane the red extract
was filtered. Upon cooling the filtrate dark red crystals of 6a
(0.73 g, 66.6%), mp 62 ЊC (decomp.) were obtained. Mass
spectrum [m/z (%)]: (LϪ = anionic ligand) 291 (55 [HL]ϩ), 276
(45 [HL Ϫ Me]ϩ), 218 (86 [HL Ϫ SiMe ]ϩ), 204 (80 [ArN᎐
᎐
3
1
CSiMe3]ϩ), 186 (53 [HL Ϫ Ar]ϩ), 116 (57 [tmen]ϩ). H NMR
7
(Ph, 4 H), 6.99–7.01 (Ph, 6 H); Li NMR (C6D6): δ 0.8; 13C
(C7D8) (values for rotamer II in brackets): δ 0.03 (0.30) [s,
CHSiMe3, 9 H], 0.20 (0.34) (s, SiMe3, 9 H), 1.42 (s, NCH2, 4 H),
1.51 (s, NMe, 12 H), 2.31 (2.24) (s, Me, 6 H), 3.8 (s, CH, 1 H),
6.80–7.15 (Ph, 3 H); 7Li NMR (C7D8): δ 0.51; 13C NMR (C7D8):
δ 0.6 (1.9) [s, SiMe3], 3.0 (4.6) [s, SiMe3], 20.3 (19.1) [s, Me], 45.3
[s, NMe], 56.5 [s, NCH2], 84.7 (83.7) [s, CH], 120.0 (120.5) [s,
p-C], 128.7 (128.1) [s, m-C], 129.2 (132.4) [s, ipso-C (Me)], 156.5
(154.7) [s, ipso-C], 172.2 and 169.8 [s, CN].
NMR (C6D6): δ 1.34 (s, SiMe3), 19.4 (s, Me), 104.6 (s, CH),
122.5 and 127.9 (s, m/p-C), 131.2 (s, o-C), 154.0 (s, ipso-C),
172.3 (s, CN).
[Zr{N(But)C(R)C(H)C(R)N(But)}Cl3] 3. ZrCl4 (0.27 g, 1.17
mmol) was added to a solution of 1 (0.68 g, 1.17 mmol) in Et2O
(20 cm3) at Ϫ30 ЊC. The reaction mixture was allowed to warm
to room temperature and was stirred for 14 h. The volatiles were
removed in vacuo. The residue was extracted into pentane (30
cm3) and the extract was filtered. Concentration of the filtrate
and cooling gave pale yellow crystals of 3 (0.26 g, 42.5%)
(Found: C, 37.9; H, 7.19; N, 5.05. C17H37Cl3N2Si2Zr requires C,
39.0; H, 7.13; N, 5.35%), mp > 120 ЊC (decomp.). Mass spec-
trum [m/z (%)]: 522 (38 [M]ϩ), 507 (45 [M Ϫ Me]ϩ), 487 (43
[M Ϫ Cl]ϩ), 465 (95 [M Ϫ CMe3]ϩ), 449 (18 [M Ϫ SiMe3]ϩ). 1H
NMR (C6D6): δ 0.26 (s, SiMe3, 18 H), 1.39 (s, But, 18 H), 6.42 (s,
CH, 1 H); 13C NMR (C6D6): δ 2.2 (s, SiMe3), 31.9 (s, C(CH3)3),
60.6 (s, C(CH3)3), 98.6 (s, CH), 162.0 (s, CN).
The signals of the two rotamers in solution were assigned by
1
NOE H NMR experiments involving the protons of the tri-
methylsilyl, aryl methyl, and olefinic CH groups.
[Li{N(Ar)C(R)C(H)Ph}(tmen)] 6b. C6H3(Me2-2,6)NC (2.24
g, 17 mmol) was added to a solution of [Li{CH(R)Ph}(tmen)]
(4.90 g, 17 mmol) in Et2O (150 cm3) at Ϫ60 ЊC. The reaction
mixture was allowed to warm to room temperature and was
stirred for 14 h to give a pale red suspension which was filtered.
Concentration and cooling of the filtrate gave 6b (5.00 g, 70%).
A second crop of crystals of 6b (0.86 g, 12%) (Found: C, 70.5;
2414
J. Chem. Soc., Dalton Trans., 2001, 2409–2416

View Article Online
H, 9.13; N, 9.62; C25H40LiN3Si3 requires C, 71.9; H, 9.65; N,
10.06%), mp 135 ЊC (decomp.) was isolated from the mother
liquor. Mass spectrum [m/z (%)]: 295 (20 [HL]ϩ), 280 (12
[HL Ϫ Me]ϩ), 222 (14 [HL Ϫ SiMe3]ϩ), 204 (100 [HL Ϫ
C7H7]ϩ). 1H NMR (C6D6): δ 0.22 (s, SiMe3, 9 H), 1.40 (s, NCH2,
4 H), 1.54 (s, NMe, 12 H), 5.39 (s, CH, 1 H), 6.69 (t, Ph, 1 H),
6.92 (t, Ph, 1 H, J = 7.35), 7.08 (d, Ph, J = 7.72, 2 H), 7.17 (d,
2.34 (s, Me, 12 H), 6.10 (s, CH, 1 H), 6.69 (t, Ph, 1 H), 6.70–7.08
(Ph, 10 H); 7Li NMR (C6D6): δ 1.44; 29Si NMR (C6D6): δ Ϫ8.5;
13C NMR (C6D6): δ 3.6 (s, SiMe3), 18.9, 20.8 (s, Me), 45.8 (s,
NMe), 57.3 (s, NCH2), 110.0 (s, CH), 117.7, 122.2, 123.2, 126.5,
126.9, 127.5, 128.0, 128.3, 128.7 (s, Ph), 140.1, 152.6, 153.1 [s,
ipso-C(Me)], 155.6 (s, C᎐CH), 195.4 (s, CN).
᎐
7
Ph, 2 H), 8.01 (d, Ph, J = 7.77 Hz, 2 H); Li NMR (C6D6):
[HN(C H Me -2,6)C(R)C{N(C H Me -2,6)}᎐C(H)Ph]
9.
᎐
6
3
2
6
3
2
δ 0.83; 13C NMR (C7D8): δ 1.9 (s, SiMe3), 20.3 (s, Me), 45.3 (s,
Methanol (0.05 cm3) was added to a suspension of 8 (0.66 g,
1.20 mmol) in pentane (30 cm3). An immediate colour change
from red to yellow and concomitant formation of a white pre-
cipitate were observed. After stirring for 10 min at room tem-
perature all volatiles were removed in vacuo; the residue was
extracted into pentane (30 cm3). The extract was filtered and the
filtrate concentrated and cooled to give yellow crystals of 9
(0.37 g, 79.4%) (Found: C, 78.8; H, 8.18; N, 6.50. C28H34N2Si
requires C, 78.8; H, 8.17; N, 6.58%). Mass spectrum [m/z (%)]:
1
1
NMe), 56.6 (s, NCH2), 99.4 [s, CH; H–coup., d, J(13C–1H)
151.6], 118.9 [s, p-C(Ph); 1H-coup., td, 1J(13C–1H) 159.3], 119.7
[s, p-C(Ar); H-coup., d, J(13C–1H) 156.5], 123.3 [s, o-C(Ph);
1
1
1H-coup., d, 1J(13C–1H) 154.0], 128.2 [s, m-C(Ph); 1H-coup., md,
1
1
1J(13C–1H) 153.4], 129.9 [s, m-C(Ar); H-coup., dd, J(13C–1H)
154.5, J(13C–1H) 8.0 Hz], 132.1 [s, ipso-C (ArMe)], 145.7 [s,
3
ipso-C(Ph)], 157.1 [s, ipso-C (Ar)], 167.1 (s, CN).
[Li{N(But)C(R)C(H)Ph}(tmen)] 6c. ButNC (0.39 cm3, 3.50
mmol) was added at Ϫ50 ЊC to a solution of [Li{CH(R)Ph}-
(tmen)] (1.0 g, 3.50 mmol) in Et2O (30 cm3). The yellow suspen-
sion was allowed to warm to room temperature; a clear solution
was obtained. This was stirred for 14 h, the solvent was
removed in vacuo and the residue was extracted into pentane
(30 cm3). Filtration of the extract and cooling of the filtrate to
Ϫ30 ЊC gave 6c (0.9 g, 69.6%) (Found: C, 67.6; H, 10.90; N,
11.42. C21H40LiN3Si requires C, 68.2; H, 10.91; N, 11.37%), mp
85 ЊC (decomp.). Mass spectrum [m/z (%)]: 369 (1 [M]ϩ); 247 (56
1
426 (37 [M]ϩ), 411 (8 [M Ϫ Me]ϩ), H NMR (C6D6, all signals
broad): δ 0.08 (s, SiMe3, 9 H), 2.03 and 2.12 (s, Me, 12 H), 6.30
(s, CH, 1 H), 6.74–6.96 (s, Ph, 11 H), 7.47 (s, NH, 1 H); 13C
NMR (C6D6): δ 1.5 (s, SiMe3), 18.5 and 19.3 (s, Me), 111.5 (s,
Me), 123.2, 124.3, 125.6, 127.1, 128.0, 128.3, 128.5 (s, Ph),
132.7, 135.9, 139.7, 140.5 (s, ipso-C), 150.6 (s, C᎐CH), 180.1 (s,
᎐
CN).
Crystal data and refinement details
1
[HL]ϩ). H NMR (C6D6): δ 0.48 (s, SiMe3, 9 H), 1.47 (s, But,
C33H57Cl4LiN2O2Si2Zr 4, M = 809.95, monoclinic, a =
14.838(3), b = 15.446(3), c = 19.174(4) Å, β = 105.05(2)Њ, U =
4244(2) Å3, T = 173(2) K, space group P21/n (no. 14), Z = 4,
Dc = 1.27 Mg mϪ3, µ(Mo-Kα) = 0.60 mmϪ1, 7750 reflections
measured, 7454 unique (Rint = 0.017), R1 = 0.040 for 5800
reflections with I > 2σ(I ), wR2 = 0.105 for all data.
9 H), 1.52 (s, NCH2, 4 H), 1.72 (s, NMe, 12 H), 4.99 (s, CH,
1 H), 6.63 (t, p-Ph, 1 H), 7.85 (t, m-Ph, 2 H), 8.06 (s, broad,
7
o-Ph, 2 H); Li NMR (C6D6): δ Ϫ0.54; 29Si NMR (C6D6): δ
Ϫ15.8; 13C NMR (C6D6): δ 4.3 (s, SiMe3), 34.5 (s, CMe3), 45.5
(s, NMe), 53.5 (s, CMe3), 56.3 (s, NCH2), 93.4 (s, CH), 117.3 (s,
p-C), 122.3 (s, broad, o-C), 129.1 (s, m-C), 143.7 (s, ipso-C),
166.4 (s, CN).
C25H40LiN3Si 6b, M = 417.6, monoclinic, a = 32.900(7),
b = 8.553(2), c = 19.852(5) Å, β = 113.77(2)Њ, U = 5112(2) Å3,
T = 173(2) K, space group C2/c (no. 15), Z = 8, Dc = 1.09 Mg
m
Ϫ3, µ(Mo-Kα) = 0.11 mmϪ1, 4567 reflections measured, 4494
[Li{N(C6H3Me2-2,6)C(R)C(H)C(Ph)N(R)}(tmen)] 7. PhCN
(0.10 cm3, 0.97 mmol) was added to a solution of 6a (0.4 g, 0.97
mmol) in pentane (30 cm3) at Ϫ40 ЊC. Upon warming up to
room temperature a clear orange solution was obtained which
was stirred for 15 h. Removing the volatiles in vacuo and
extracting with pentane (60 cm3) gave, upon concentrating and
cooling to Ϫ30 ЊC, orange crystals of 7 (0.32 g, 64%) (Found:
C, 64.2; H, 8.77; N, 8.98. C29H49LiN4Si2 requires C, 67.4; H,
9.56; N, 10.83%), mp 149 ЊC (decomp.). Mass spectrum [m/z
(%)]: 394 (55 [HLϩ), 379 (10 [HL Ϫ Me]ϩ), 321 (90 [HL Ϫ
SiMe3]ϩ), 289 (26 [HL Ϫ Ar]ϩ). 1H NMR (C6D6): δ 0.07 (s,
SiMe3, 9 H), 0.11 (s, SiMe3, 9 H), 1.81 (s, NCH2, 4 H), 1.91 (s,
NMe, 12 H), 2.31 (s, Me, 6 H), 5.57 (s, CH, 1 H), 6.82–7.27 (Ph,
6 H), 7.74 [d, o-Ph, 2 H, J(1H–1H) = 6.8 Hz]; 7Li NMR (C6D6):
δ 1.45; 13C NMR (C6D6): δ 1.0 (s, SiMe3), 4.2 (s, SiMe3), 19.4 (s,
Me), 46.4 (s, NMe), 57.3 (s, NCH2), 105.1 (s, CH), 122.3, 127.4,
127.8, 127.9, 128.8 (s, m/p-C), 130.3 [s, ipso-C(Me)], 150.8,
154.6 (s, ipso-C), 169.0, 177.9 (s, CN).
unique (Rint = 0.052), R1 = 0.088 for 2174 reflections with
I > 2σ(I ), wR2 = 0.222 for all data.
C34H49LiN4Si 8, M = 548.8, triclinic, a = 10.887(3), b =
11.272(2), c = 14.266(3) Å, α = 87.11(2), β = 76.64(2), γ =
84.46(2)Њ, U = 1695(1) Å3, T = 173(2) K, space group P1-
(no. 2), Z = 2, Dc = 1.08 Mg mϪ3, µ(Mo-Kα) = 0.10 mmϪ1, 4698
reflections measured, 4698 unique, R1 = 0.063 for 3066
reflections with I > 2σ(I ), wR2 = 0.178 for all data.
Data were collected on an Enraf-Nonius CAD4 diffract-
ometer using monochromatic Mo-Kα radiation (λ 0.71073 Å).
Crystals were enclosed in an oil drop and frozen in a stream of
cold nitrogen gas. Positions of non-hydrogen atoms were
derived by direct methods using SHELXS-8628 and refined on
F 2 with anisotropic thermal parameters for non-hydrogen
atoms and H atoms in riding mode, by full-matrix least-squares
using SHELXL-93.29
CCDC reference numbers 165562–165564.
See http://www.rsc.org/suppdata/dt/b1/b103553n/ for crystal-
lographic data in CIF or other electronic format.
[Li{N(C H Me -2,6)C(R)C[N(C H Me -2,6)]᎐C(H)Ph}-
᎐
6
3
2
6
3
2
(tmen)] 8. Solid (C6H3Me2-2,6)NC (1.95 g, 15 mmol) was added
to a suspension of [Li{CH(R)Ph}(tmen)] (2.13 g, 7.45 mmol) in
pentane (150 cm3) at Ϫ78 ЊC. The reaction mixture was allowed
to warm up slowly (in a Dewar vessel) to room temperature.
The red solution was stirred for 12 h, pentane (100 cm3) was
added and the mixture was filtered. The red precipitate was
found to be analytically pure 8 (1.32 g, 32%) (Found: C, 74.85;
H, 8.83; N, 11.65. C34H49LiN4Si requires C, 74.71; H, 9.00; N,
10.20%), mp 135 ЊC (decomp.). The filtrate was concentrated
and two more crops of crystals of 8 (0.66 and 0.52 g, 16% and
12.7%) were isolated after cooling to Ϫ30 ЊC. Mass spectrum
[m/z (%)]: 426 (60 [HL]ϩ), 411 (8 [HL Ϫ Me]ϩ). 1H NMR
(C6D6): δ 0.23 (s, SiMe3, 9 H), 1.53 (s, broad, tmen, 16 H), 2.04,
Acknowledgements
We are grateful to the EPSRC for providing a fellowship (to
M. L.) and other support. We also thank Dr A. G. Avent for
carrying out some of the NMR experiments and for helpful
discussions.
References
1 G. E. Niznik, W. H. Morrison and H. M. Walborsky, J. Org. Chem.,
1974, 39, 600.
2 H. M. Walborsky, W. H. Morrison and G. E. Niznik, J. Am. Chem.
Soc., 1970, 92, 6675.
J. Chem. Soc., Dalton Trans., 2001, 2409–2416
2415

View Article Online
3 M. J. Marks and H. M. Walborsky, J. Org. Chem., 1981, 46, 5404.
4 H. M. Walborsky and P. Ronman, J. Org. Chem., 1978, 43, 731.
5 H. M. Walborsky and G. E. Niznik, J. Am. Chem. Soc., 1969, 91,
7778.
6 N. Hirowatari and H. M. Walborsky, J. Org. Chem., 1974, 39, 604.
7 U. Schöllkopf and F. Gehrhart, Angew. Chem., Int. Ed. Engl., 1968,
7, 805.
8 M. P. Periasamy and H. M. Walborsky, J. Org. Chem., 1974, 74, 611.
9 P. B. Hitchcock, M. F. Lappert, M. Layh, D.-S. Liu, R. Sablong and
T. Shun, J. Chem. Soc., Dalton Trans., 2000, 2301 and refs. therein.
10 M. Murakami, H. Masuda, T. Kawano, H. Nakamura and Y. Ito,
J. Org. Chem., 1991, 56, 1.
17 J. L. Atwood, W. E. Hunter, R. D. Rogers, J. Holton, J. McMeeking,
R. Pearce and M. F. Lappert, J. Chem. Soc., Chem. Commun., 1978,
140.
18 (a) T. V. Lubben, P. T. Wolczanski and G. D. Van Duyne,
Organometallics, 1984, 3, 977; (b) H. Memmler, K. Walsh, L. H.
Gade and J. W. Lauher, Inorg. Chem., 1995, 34, 4062; (c) R. W.
Quan, G. C. Bazan, A. F. Kiely, W. P. Schaefer and J. E. Bercaw,
J. Am. Chem. Soc., 1994, 116, 4489.
19 cf., R. West, Adv. Organomet. Chem., 1977, 16, 1.
20 M. F. Lappert and D.-S. Liu, J. Organomet. Chem., 1995, 500, 203.
21 M. Rahim, N. J. Taylor, S. Xin and S. Collins, Organometallics, 1998,
17, 1315.
11 A. C. Filippou, C. Völkl and P. Kiprof, J. Organomet. Chem., 1991,
415, 375.
12 P. B. Hitchcock, M. F. Lappert and M. Layh, Chem. Commun., 1998,
201.
22 M. F. Lappert and D.-S. Liu, Neth. Pat. Appl., 1994, 9401515.
23 M. F. Lappert and M. Layh, Tetrahedron Lett., 1998, 39, 4745.
24 T. Fjeldberg, P. B. Hitchcock, M. F. Lappert and A. J. Thorne,
J. Chem. Soc., Chem. Commun., 1984, 822.
13 P. B. Hitchcock, M. F. Lappert and M. Layh, Angew. Chem., Int.
Ed., 1999, 38, 501.
14 C. F. Caro, P. B. Hitchcock, M. F. Lappert and M. Layh, Chem.
Commun., 1998, 1297.
15 M. F. Lappert, C. L. Raston, B. W. Skelton and A. H. White,
J. Chem. Soc., Chem Commun., 1982, 14.
16 (a) W.-P. Leung, H. Cheng, D.-S. Liu, Q.-G. Wang and T. C. W. Mak,
Organometallics, 2000, 19, 3001; (b) W.-P. Leung, H. Cheng, R.-B.
Huang, Q.-C. Yang and T. C. W. Mak, Chem. Commun., 2000, 451.
25 D. Barr, W. Clegg, R. E. Mulvey, R. Snaith and D. S. Wright,
J. Chem. Soc., Chem. Commun., 1987, 716.
26 M. G. Gardiner and C. L. Raston, Inorg. Chem., 1995, 34, 4206.
27 P. B. Hitchcock, M. F. Lappert and M. Layh, J. Chem. Soc., Dalton
Trans., 1998, 1619.
28 G. M. Sheldrick, SHELXS-86 Program for the Solution of Crystal
Structures, University of Göttingen, 1985.
29 G. M. Sheldrick SHELXL-93 Program for Crystal Structure
Refinement, University of Göttingen, 1993.
2416
J. Chem. Soc., Dalton Trans., 2001, 2409–2416