Synthetic and structural experiments on yttrium, cerium and magnesium trimethylsilylmethyls and their reaction products with nitriles; with a note on two cerium β-diketiminates

Article abstract of DOI:10.1039/b316695n

The yttrium, cerium and magnesium bis(trimethylsilyl)methyls [Ln{CH(SiMe₃)₂}₃] [Ln = Y (1), Ce (2)], and the known compound Mg[CH(SiMe₃)₂]₂ (C) and [Mg(μ-Br){CH(SiMe₃)₂}(OEt₂)]₂ (D) formed the crystalline nitrile adducts [l(NCBu^t)₂] (5), [2(NCPh)] (6), [C(NCR)₂] [R = Bu_t (8), Ph (9), C ₆H₃Me₂-2,6 (10)] and [Mg(μ-Br){CH(SiMe ₃)₂}(NCR)]₂ [R = Bu_t (11), Ph (12), C₆H₃Me₂-2,6 (13)], rather than β-diketiminato-metal insertion products. The β-diketiminato-cerium complex [Ce{(N(SiMe₃)C(C₆H₄Bu _t-4))₂CH}{N(SiMe₃)₂}₂] (16) was obtained from [Ce{N(SiMe₃)₂}₃] and the β-diketimine H[{N(SiMe₃)C(C₆H₄Bu _t-4)}₂CH]]. The cerium alkyl 2 and [Ln{CH(SiMe ₃)(SiMe₂OMe)}₃] [Ln = Y (3), Ce (4)] were obtained from the appropriate lithium alkyl precursor and [Ce(OC ₆H₂Bu_t2-2,6-Me-4)₃] or LnCl ₃, respectively. Heating complex 3 with benzonitrile in toluene afforded 2,2-dimethyl-4,6-diphenyl-5-trimethylsilyl-1,3-diaza-2-silahexa-1,3- diene (7), a member of a new class of heterocycles. The X-ray structures of the crystalline compounds 1-7, D, [Mg{CH(SiMe₃)₂} ₂(OEt₂)₂], the known [Ce(Cl){(N(SiMe ₃)C(Ph))₂CH}₂] (E) and 16 are reported. The cerium alkyl 2 (like 1) has one close Ce ... C contact for each ligand, attributed to a γ-C-Ce agostic interaction. The Ln alkyls 3 and 4 have a trigonal prismatic arrangement of the chelating ligands (each of the same chirality at C_α) around the metal. In an arene solution at 313 K 3 exists as two isomers, as evident from detailed NMR spectroscopic experiments.

Full text of DOI:10.1039/b316695n

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Synthetic and structural experiments on yttrium, cerium and
magnesium trimethylsilylmethyls and their reaction products with
nitriles; with a note on two cerium ꢀ-diketiminates
Anthony G. Avent,a Catherine. F. Caro,a Peter B. Hitchcock,a Michael F. Lappert,*a
Zhengning Lia and Xue-Hong Weia,b
a The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ.
E-mail: m.f.lappert@sussex.ac.uk
b The School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006,
P. R. China
Received 19th December 2003, Accepted 19th March 2004
First published as an Advance Article on the web 21st April 2004
The yttrium, cerium and magnesium bis(trimethylsilyl)methyls [Ln{CH(SiMe3)2}3] [Ln = Y (1), Ce (2)], and the
known compound Mg[CH(SiMe3)2]2 (C) and [Mg(µ-Br){CH(SiMe3)2}(OEt2)]2 (D) formed the crystalline nitrile
adducts [1(NCBut)2] (5), [2(NCPh)] (6), [C(NCR)2] [R = But (8), Ph (9), C6H3Me2-2,6 (10)] and [Mg(µ-Br)-
{CH(SiMe3)2}(NCR)]2 [R = But (11), Ph (12), C6H3Me2-2,6 (13)], rather than β-diketiminato–metal insertion
products. The β-diketiminato–cerium complex [Ce{(N(SiMe3)C(C6H4But-4))2CH}{N(SiMe3)2}2] (16) was
obtained from [Ce{N(SiMe3)2}3] and the β-diketimine H[{N(SiMe3)C(C6H4But-4)}2CH]]. The cerium alkyl 2 and
[Ln{CH(SiMe3)(SiMe2OMe)}3] [Ln = Y (3), Ce (4)] were obtained from the appropriate lithium alkyl precursor
and [Ce(OC6H2But2-2,6-Me-4)3] or LnCl3, respectively. Heating complex 3 with benzonitrile in toluene afforded
2,2-dimethyl-4,6-diphenyl-5-trimethylsilyl-1,3-diaza-2-silahexa-1,3-diene (7), a member of a new class of
heterocycles. The X-ray structures of the crystalline compounds 1–7, D, [Mg{CH(SiMe3)2}2(OEt2)2], the known
[Ce(Cl){(N(SiMe3)C(Ph))2CH}2] (E) and 16 are reported. The cerium alkyl 2 (like 1) has one close Ce ؒ ؒ ؒ C
contact for each ligand, attributed to a γ-C–Ce agostic interaction. The Ln alkyls 3 and 4 have a trigonal prismatic
arrangement of the chelating ligands (each of the same chirality at Cα) around the metal. In an arene solution at
313 K 3 exists as two isomers, as evident from detailed NMR spectroscopic experiments.
observed when Yb{CH(SiMe3)2}2(OEt2) was treated with benzo-
Introduction
nitrile12 or 2-cyano-2-methylpropane,13 Scheme 2; structures
of the crystalline Yb() 1-azaallyl13 and of two β-diketim-
inates12,14 were determined.
Our interest in group 3 and lanthanoid metal (collective
abbreviated as Ln) trimethylsilylmethyls began in the early
1970s, with the preparation of the first momonuclear Ln alkyls
1
2
Ln(CH2SiMe3)3(thf )2 and Ln[CH(SiMe3)2]3(thf )2 (Ln = Sc,
Y), Sc[CH2(SiMe2C6H4OMe-2)]3 and Y[CH(SiMe3)2]3.2 The
1
3
compounds Eu(CH2SiMe3)3(thf )3 and Ln(CH2SiMe2Ph)3-
(thf )2 ( Ln = Sc, Y)4a were reported later. The X-ray structures
of [Y(CH2SiMe3)3(thf )3]4b and [Sc(CH2SiMe2Ph)3(thf )2]4a have
been described. The Sc and Y trimethylsilylmethyls Ln(CH2-
SiMe3)3(thf )2 (Ln = Sc, Y)4b,5 and phenyldimethylsilylmethyls4a
have been used as convenient substrates for reactions with vari-
ous protic compounds, yielding novel Ln derivatives. Very
recently, a series of lanthanide metal trimethylsilylmethyls
Ln(CH2SiMe3)3(12-crown-4), (Ln = Sc, Y, Sm, Gd, Tb, Dy, Ho,
Er, Tm, Yb, Lu) was reported.5h The lutetium alkyl [Lu(CH2-
SiMe3)3(thf )2] was used to prepare a novel lutetium dialkyl
cationic complex.6 The first homoleptic, neutral, crystalline
bis(trimethylsilyl)methyls [Ln{CH(SiMe3)2}3] (Ln = La, Sm)
Scheme 1 Formation of a lithium 1-azaallyl, β-diketiminate and
1,3-diazaallyl from [Li{CH(SiMe3)2}]∞ (A) and PhCN.11
were described in 1988 and were structurally characterised.7a
A
novel feature was the first use of a bulky aryloxide as a
leaving group; [Ln(OC6H3But2-2,6)3] was the precursor.7a From
LnCl3 and the lithium alkyl [LiCH(SiMe3)2], the product
was [Li(thf )4][LnCl{CH(SiMe3)2}3],7b [La{CH(SiMe3)2}3(µ-Cl)-
Li(pmdeta)] (pmdeta = MeN(CH2CH2NMe2)2),7c or [Y{CH-
(SiMe3)2}3(µ-Cl)Li(OEt2)3].7d The structure of [Y{CH-
(SiMe3)2}3]ؒ1/6C6H6 was published in 1998;8 it and the lutetium
analogue8 were used as a precursor for reactions with protic
compounds.7d,8 The synthesis and structures of the crystalline
lithium alkyls [Li{CH(SiMe3)2}]∞ A9 and [Li{CH(SiMe3)-
(SiMe2OMe)}]8 B,10 used in the present work, are in the
literature.
Scheme 2 Formation of a Yb() 1-azaallyl,13 and of two Yb()
β-diketiminates.12,14
The reactions of alkali metal (M) bis(trimethylsilyl)methyls
with α-H-free nitriles were shown to give the corresponding
metal 1-azaallyl, β-diketiminate or 1,3-diazaallyl, as illustrated
for M = Li in Scheme 1.11 Similar insertion reactions were
Lithium 1-azaallyls or a 1,3-diazaallyl were obtained from
the lithium alkyl B and ButCN,15 PhCN,15 1-adamantane-
carbonitrile (AdCN),16 or 2,5-Me2C6H3CN,15 Scheme 3; various
β-diketiminates are also accessible.17
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
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Scheme
3
Formation of lithium 1-azaallyls and
a
1,3-diazaallyl from [Li{CH(SiMe3)(SiMe2OMe)]8 (B) and ButCN,15 PhCN,15
1-adamantanecarbonitrile (AdCN),16 or 2,5-Me2C6H3CN.15
An objective of the present work was to explore the reactions
of various Ln() bis(trimethylsilyl)methyls with ButCN and
PhCN. A possible outcome might have been to discover new
routes to Ln() 1-azaallyls and β-diketiminates. A selection of
such compounds, including [Ln(Cl)L2(thf )] (Ln = Ce, Nd),13
[Ln(I)L2(thf )] (Ln = Sm, Yb),13 [Ln(Cl)LЈ2] (Ln = Ce (E), Nd),12
and [Tm(I)LЈ2]12 have been prepared from LnX3 (X = Cl, I)
and NaL or KLЈ [L = N(SiMe3)C(But){CH(SiMe3)}, LЈ =
{N(SiMe3)C(Ph)}2CH]; from [Ce(Cl)LЈ2] and A the product
was the X-ray-characterised compound [Ce{CH(SiMe3)}2LЈ].12
Other β-diketiminato–lanthanide metal() halides to have been
prepared and characterised are [GdBr2{(N(Ph)C(Me))2CH}-
Yttrium and cerium alkyls
Synthesis and structures. Treatment of the yttrium or
cerium() aryloxide [Ln(OC6H2But2-2,6-Me-4)3] (Ln = Y, Ce)
with three equivalents of bis(trimethylsilyl)methyllithium (A) in
hexane at ambient temperature gave the homoleptic, crystalline
bis(trimethylsilyl)methyl–yttrium() (1) or –cerium() (2) in
good yield, eqn. (1). Both 1 and 2 have been well characterised
by 1H, 13C and 29Si NMR spectroscopy and single crystal X-ray
diffraction. An objective in repreparing 1 (cf. ref. 2) had been to
obtain X-ray quality crystals.
(thf )2],18a [LnBr{(N(Pri)C(Me))2CH}2] (Ln
[Yb(Cl)2LЉ(thf )2],18c–f [Yb(Cl)LЉ(OC6H2But2-2,6-Me-4)-
(thf )],18d,f [{YbLЉ(thf )}2(µ-Cl)3],15 [Yb(Cl)LЉ(η-C5H4Me)],18c,e,g
[Yb(Cl)LЉ(η5-C9H7)],18d,e,g [YbLٞ(η-C5H5)(µ-Cl)2Li(thf )2],18e
=
Sm, Gd),18b
(1)
and [Yb(LЉ)(η-5C5Me5)(µ-Cl)2]]18e [LЉ
=
{N(C6H3Pri2-2,6)-
C(Me)}2CH; Lٞ = {N(C6H3Pri2-2,6)C(Me)C(H)C(Me)NC6H4-
Me-4}].
From the anhydrous LnCl3 (Ln = Y, Ce) and the methoxy
analogue B of A, in similar proportions to eqn. (1), the prod-
ucts were the homoleptic Y (3) and Ce (4) alkyls, likewise
obtained in good yields, eqn. (2). Whereas LnCl3 with 3
Li[CH(SiMe3)2] had yielded LiCl-containing Ln() trialkyl
products,7b,c it is interesting that this proved not to be the case
when employing 3Li[CH(SiMe3)(SiMe2OMe); this is attributed
to the intramolecular dative interaction.
A further aim was to examine the reactions of bis(trimethyl-
silyl)methylmagnesium reagents with α-hydrogen-free nitriles.
Previously we had shown that neither Mg[CH(SiMe3)2]2 (C)19
nor [Mg(µ-Br){CH(SiMe3)2}(OEt2)]2 (D)20 underwent insertion
reactions with isonitriles, but gave donor–acceptor adducts
[Mg{CH(SiMe3)2}2(CNRЈ)2] or [Mg(µ-Br){CH(SiMe3)2}-
(CNRЈ)]2 (RЈ = But or C6H3Me2-2,6), respectively;20 this was
in contrast to the behaviour of Li[CH(SiMe3)2], which gave
1-azaallyls or 1,3-diazaallyls.11 A magnesium 1-azaallyl and a
β-diketiminate [Mg{N(SiMe3)C(But)CH(SiMe3)}2] and [Mg-
{(N(SiMe3)C(Ph))2CH}2] were readily prepared from MgBr2
and [Li{N(SiMe3)C(But)CH(SiMe3)}]2 or [Li{(N(SiMe3)-
C(Ph))2CH}]2, respectively.21
(2)
The yttrium alkyl 1 had been mentioned in a preliminary
communication, alongside some well characterised d-block
analogues such as [Cr{CH(SiMe3)2}3].2 Its identity, however,
needed confirmation, since its method of preparation from
YCl3 left an element of uncertainly in the light of the later
disclosure that YCl3 with 3LiCH(SiMe3)2 in diethyl ether gave
[Y{CH(SiMe3)2}3(µ-Cl)Li(OEt2)3].7d It is noteworthy that, by
contrast, LnCl3 proved to be a viable source of the homoleptic
Y and Ce alkyls of eqn. (2), which is attributed to the chelating
nature of the ligand in 3 and 4.
Results and discussion
There are two aspects of earlier recent publications which acted
as a trigger for the present study, which focuses on yttrium,
cerium and magnesium trimethylsilylmethyls and Ce() β-di-
ketiminates. The first relates to the widespread prior use4–6 of
related alkyls as precursors to a wider range of compounds; for
this reason the range of well characterised compounds is herein
extended to the new crystalline Y and Ce() alkyls 1–4. The
second concerns the known ability of alkali metal alkyls, such
as M[CH(SiMe3)2] (M = Li, K) or an Yb() analogue, to
undergo insertion reactions with α-H-free nitriles (Schemes 1
and 2);11–14 hence we now report on the behaviour of 1–3 and of
the magnesium bis(trimethylsilyl)methyls C and D with ButCN,
PhCN and 2,6-Me2C6H3CN.
Each of the colourless (1–3) or pale yellow (4) homoleptic
Y and Ce alkyls was obtained in X-ray quality crystalline
form. Each achieves coordination saturation by forming three
covalent/ionic Ln–C bonds, with three additional close
Ln ؒ ؒ ؒ CH3 (1, 2) or Ln
OMe (3, 4) contacts.
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
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Table 1 Selected bond lengths (Å) and angles (Њ) for 1
Table 4 Selected bond lengths (Å) and angles (Њ) for 4
Y–C(1)
C(1)–Si(1)
2.353(5)
1.850(5)
Y ؒ ؒ ؒ C(2)
C(1)–Si(2)
2.963(6)
1.853(6)
Ce–C(1)
2.598(4)
Ce–O
2.519(3)
O–Ce–OЈ
82.28(12)
106.34(11)
110.09(9)
100.33(13)
121.0(2)
O–Ce–C(1)
63.57(12)
142.56(12)
100.10(16)
95.33(15)
C(1)–Y–C(1)Ј 108.63(1)
Si(2)–C(1)–Y 126.3(3)
Si(1)–C(1)–Y 102.1(2)
OЈ-Ce–C(1)
C(1)–Ce–C(1Ј)
Si(1)–O–Ce
Si(2)–C(1)–Ce
OЉ–Ce–C(1)
O-Si(1)–C(1)
Si(1)–C(1)–Ce
Symmetry transformations used to generate equivalent atoms: ЈϪy ϩ 1,
x Ϫ y ϩ 1, z.
Symmetry transformations used to generate equivalent atoms: ЈϪy ϩ 1,
x Ϫy ϩ 1, z and ЉϪx ϩ y, Ϫx ϩ 1, z.
Table 2 Selected bond lengths (Å) and angles (Њ) for 2
Ce–C(1)
C(1)–Si(1)
2.475(7)
1.829(8)
Ce ؒ ؒ ؒ C(2)
C(1)–Si(2)
3.068(70
1.852(7)
C(1)–Ce–C(1)Ј
Si(2)–C(1)–Ce
110.08(16)
122.3(4)
Si(1)–C(1)–Ce
102.8(3)
Symmetry transformations used to generate equivalent atoms: ЈϪy ϩ 1,
x Ϫ y ϩ 1, z.
Table 3 Selected bond lengths (Å) and angles (Њ) for 3
Y–C(1)
Y–C(15)
Y–O(2)
2.476(3)
2.485(3)
2.379(2)
Y–C(8)
Y–O(1)
Y–O(3)
2.468(3)
2.366(2)
2.370(2)
O(1)–Y–O(3)
O(3)–Y–O(2)
O(3)–Y–C(8)
O(1)–Y–C(1)
O(2)–Y–C(1)
O(1)–Y–C(15)
O(2)–Y–C(15)
C(1)–Y–C(15)
O(2)–Si(3)–C(8)
Si(1)–O(1)–Y
85.06(7)
82.50(7)
106.96(9)
66.92(9)
105.68(10)
106.19(10)
146.98(9)
106.88(11)
99.16(13)
99.08(9)
O(1)–Y–O(2)
O(1)–Y–C(8)
O(2)–Y–C(8)
O(3)–Y–C(1)
C(8)–Y–C(1)
O(3)–Y–C(15)
C(8)–Y–C(15)
O(1)–Si(1)–C(1)
O(3)–Si(5)–C(15)
Si(1)–C(1)–Y
81.70(8)
144.11(9)
67.08(9)
148.75(9)
103.94(11)
66.73(9)
109.63(11)
98.79(13)
98.79(13)
92.98(13)
Fig. 2 ORTEP (20% probability level) of 3 (hydrogen atoms are
omitted).
The crystalline alkyls 1 and 2 are isomorphous with one an-
other and7a with the La and Sm analogues; their structures are
illustrated (for the Ce complex 2) in Fig. 1; selected geometrical
parameters are listed in Tables 1 (1) and 2 (2). The data of Table
1 are similar to those published for the benzene solvate.7d As has
recently been discussed in the context of [La{CH(SiMe3)2}3]
using DFT calculations, the most likely explanation for the
observation that each complex has one short Ln ؒ ؒ ؒ CH3 bond
and one narrow Ln–C–Si angle for each ligand is that there are
agostic Si ؒ ؒ ؒ Cβ rather than γ-C ؒ ؒ ؒ H ؒ ؒ ؒ Ln interactions.22
Fig. 3 ORTEP (20% probability level) of 4 (hydrogen atoms are
omitted).
eclipsed by the three methoxy oxygen atoms. Each ligand is
C,O-bound to the metal atom in a chelating mode,Ln–C–Si–O,
with the C–Ln–O bite angle of 66.9 0.2Њ (3) or 63.57(12)Њ (4);
the other endocyclic angles subtended at the remaining three
atoms are ca. 93, 99 and 99Њ for 3, and 95.33(15), 101.10(16) and
100.33(13)Њ for 4, at C, Si and O, respectively. The difference in
the Ln–C and the shorter Ln–O bond lengths is ca. 0.10 (3) and
0.08 Å (4); but the pairs of endocyclic C–Si and O–Si distances
are closely similar for 3 and 4. The difference in the Ln–C
bond lengths as between the yttrium alkyls 1 and 3, or the Ce
analogues 2 and 4, is ca. 0.12 Å for both pairs (3 and 4 being the
longer).
Fig. 1 ORTEP (20% probability level) of 2 (hydrogen atoms are
omitted).
The isostructural, but not isomorphous, metal alkyl mole-
cules 3 and 4 are illustrated in Figs. 2 (3) and 3 (4); selected
geometrical parameters are listed in Tables 3 (3) and 4 (4). Each
of the distorted trigonal prismatic molecules has approximate
(3), or well defined (4), three-fold symmetry. The three methine
carbon atoms (each having the same chirality) are almost
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
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A 1H-detected 2D 89Y–1H shift correlation experiment on 3 in
C6D6 at 313 K in C6D6 showed the presence of two 89Y peaks at
δ 797 and δ 755. The 2D spectrum showed that the former
signal correlated with the CH doublet observed at δ Ϫ0.53 in
Table 5 Selected bond lengths (Å) and angles (Њ) for 5
Y–N(1)
2.450(6)
2.422(4)
1.138(8)
1.496(11)
Y–N(2)
N(1)–C(1)
C(1)–C(2)
2.449(7)
1.129(8)
1.485(10)
Y–C(7)
N(2)–C(4)
C(4)–C(5)
1
the H NMR spectrum, while the δ 755 signal correlated with
both the CH doublets at δ Ϫ0.70 and δ Ϫ1.06. This shows that
in solution 3 exists as two isomers; the first, 3Ј, is the more
symmetric and gave only one CH and one OCH3 signal, while
the second 3Љ gave two CH and two OCH3 signals in the ratio
2 : 1. The ratio of 3Ј : 3Љ was ca. 7 : 6.
Spin saturation transfer experiments on 3 performed at
313 K (at this temperature, the signals were sharpest) in tolu-
ene-d8 showed that all three CH doublets are in mutual chemi-
cal exchange. Furthermore, an experiment in which only the
upfield peak of the δ 0.70 doublet was irradiated showed
exchange to the upfield peaks of the other two doublets only;
this shows that the exchange process is intramolecular with all
CHs remaining on the same yttrium atom.
N(2)–Y–C(7)
N(2)–Y–N(1)
C(7)–Y–N(2)
94.81(9)
180.0
94.87(9)
C(7)–Y–C(7)
C(7)–Y–N(1)
119.31(3)
85.19(9)
Symmetry transformations used to generate equivalent atoms: ЈϪy,
x Ϫy, z, ЉϪx ϩ y, Ϫx, z, and ٞ;Ϫy ϩ 1, x Ϫ y, z.
The symmetric isomer 3Ј is consistent with the structure
revealed by X-ray crystallography, with a distorted trigonal
prismatic coordination about the central yttrium atom and with
each of the chiral methine carbon atoms having the same hand-
edness. Isomer 3Љ is assigned to have a distorted square pyram-
idal structure about the five-coordinate yttrium atom. There is
an equilibrium between 3Ј and 3Љ, as indicated schematically
in Scheme 4. Thus, it is suggested that from 3Ј one of the
Y–O bonds opens to provide a distorted square pyramidal
short-lived intermediate leaving the two remaining chelating
ligands with cis-OMe groups, which rapidly isomerises to the
trans 3Љ.
Fig. 4 ORTEP (20% probability level) of 5 (hydrogen atoms are
omitted).
There are two independent molecules of 6 with closely simi-
lar geometries, shown for one of them in Fig. 5 with selected
Scheme 4 Schematic representation of the proposed mechanism for
the exchange between the isomers 3Ј and 3Љ.
The reactions of the yttrium (1, 3) or cerium (2, 4) alkyls with
an ꢁ-hydrogen-free nitrile. Treatment of the yttrium alkyl 1 with
2-cyano-2-methylpropane in hexane at ambient temperature
gave the 1 : 2 adduct product 5 (eqn. (3)); the related 1 : 1 adduct
compound 6 was obtained from the cerium alkyl 2 and
benzonitrile, eqn. (4). Even when heated in toluene, neither 5
nor 6 showed any indication of an insertion of the nitrile into
the Ln–C bond. We presume that the transition state for inser-
tion is too sterically demanding for such a reaction to occur.
(3)
(4)
Fig. 5 ORTEP (20% probability level) of 6 (hydrogen atoms are
omitted).
geometrical data in Table 6. The cerium atom is the centre of a
distorted tetrahedron. The Ce–N–C22–C23 moiety deviates
from linearity at N. The Ce–C bond lengths are only very
slightly longer in 6 than in 2.
Surprisingly, the novel, crystalline organic compound 7
resulted from the reaction of the yttrium alkyl 3 with benzo-
nitrile in refluxing toluene (ca. 40 min), eqn. (5). The proposed
reaction pathway is shown in Scheme 5. Thus, it is suggested
that the first step is the usual formation of the 1 : 1 adduct F, its
rearrangement to the metal 1-azaallyl G, which with further
There is a slightly distorted trigonal bipyramidal molecule of
5, lying on a three-fold axis, shown in Fig. 4, with selected data
in Table 5. The C–C᎐N–Y–N–CЈ᎐CЈ atoms are arranged in a
linear array. Each of the methine carbon atoms is tilted slightly
more to one of the nitriles than the other: cf., the C7–Y–N1
and C7–Y–N2 angles in Table 5. The Y–C bond lengths are
ca. 0.09 Å longer in 5 than in 1 and the C–Y–C angles are much
wider in 5 than in 1, being close to sp2 (5) and sp3 (1) values.
᎐
᎐
᎐
᎐
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
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Table 6 Selected bond lengths (Å) and angles (Њ) for 6
Table 7 Selected bond lengths (Å) and angles (Њ) for 7
Ce–C(1)
Ce–C(3)
N–C(22)
2.497(4)
2.491(4)
1.147(6)
Ce–C(2)
Ce–N
C(22)–C(23)
2.486(5)
2.607(4)
1.410(5)
Si(1)–N(1)
N(1)–C(1)
C(2)–C(3)
1.7367(18)
1.281(3)
1.521(3)
Si(1)–N(2)
N(2)–C(3)
C(1)–C(2)
1.7429(18)
1.280(3)
1.516(3)
C(2)–Ce–C(3)
C(3)–Ce–C(1)
N–C(22)–C(23)
C(3)–Ce–N
108.90(15)
103.93(13)
179.4(5)
C(2)–Ce–C(1)
C(22)–N–Ce
C(2)–Ce–N
C(1)–Ce–N
117.31(13)
170.6(4)
119.27(14)
95.80(14)
N(1)–Si(1)–N(2)
N(1)–C(1)–C(2)
C(1)–N(1)–Si(1)
107.44(9)
124.72(18)
121.02(14)
C(1)–C(2)–C(3)
N(2)–C(3)–C(2)
N(3)–N(2)–Si(1)
115.71(17)
125.39(19)
120.20(15)
110.18(13)
six-membered N1Si1N2C3C2C1 ring has a flattened boat con-
formation, with C2 and Si1 out of the C1N1N2C3 plane, with
which the phenyl groups are almost coplanar and hence conju-
gated. The endocyclic bond angles are widest at C1 and C3 and
narrowest at Si and C2. The CN, endocyclic CC, exocyclic CC,
2
3
and C2–Si3 distances are appropriate for CN double, Csp –Csp
,
3
3
3
Csp –Csp and Csp –Si [1.944(2) Å] bond lengths, respectively.
Magnesium alkyls and their reactions with nitriles
Each of the known bis(trimethylsilyl)methylmagnesium com-
19
pounds [Mg{CH(SiMe3)2}2]∞ (the monomer abbreviated as
C) and [Mg(µ-Br){CH(SiMe3)2}(OEt2)]2 (D)20 was treated at
ambient temperature in turn with each of three α-H-free
nitriles. As shown in eqns. (6) and (7), this led to the adducts
C(NCR)2 [R = But (8), Ph (9), C6H3Me2-2,6 (10)] and [Mg-
(µ-Br){CH(SiMe3)2}(NCR)]2 [R = But (11), Ph (12), C6H3Me2-
2,6 (13)].
Scheme 5 Proposed pathway to 7, shown for the transformation of
one of the three CH(SiMe3)(SiMe2OMe) (= L) ligand
(6)
(5)
PhCN affords the β-diketiminato–yttrium complex H, followed
by the methoxyyttrium-elimination/cyclisation to give 7. The
dialkylyttrium methoxide I is assumed eventually to afford a
polymeric homoleptic yttrium methoxide.
As 7 is the first member of the new heterocyclic system – the
1,3-diaza-2-silacyclohexa-1,3-dienes, it seemed appropriate to
determine its molecular structure. This is illustrated in Fig. 6,
with selected geometrical parameters shown in Table 7. The
(7)
Each of 8–13 was obtained in good yield as a colourless solid
and was characterised by microanalysis and multinuclear NMR
and IR spectra. The latter showed that the CN stretching band
had shifted to higher wavenumber by 25–45 cmϪ1 compared
with that of the precursor nitrile. Attempts to promote inser-
tion of the nitrile into the Mg–C bond, by using more forcing
conditions [refluxing each of 8–13 for several hours in toluene,
or employing ButCN (for 8 or 11) or PhCN (for 9 or 12) as
solvent] proved to be unsuccessful. A further unsuccessful strat-
egy was to treat D with PhCN in presence of 2 tmen; this gave
14, eqn. (8). The notion had been that a monomeric magnesium
substrate 14 might have been more amenable to undergo inser-
tion than the dimeric D. Complex 14, obtained in good yield,
was identified by microanalysis and multinuclear NMR spectra
(8)
.
During the course of these studies X-ray quality crystals of D
and of [Mg{CH(SiMe3)2}2(OEt2)] 15 [eqn. (9)] became avail-
able. It did not seem to be necessary to collect crystallographic
Fig. 6 ORTEP (20% probability level) of 7.
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
1571

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Table 8 Selected bond lengths (Å) and angles (Њ) for D
Table 9 Selected bond lengths (Å) and angles (Њ) for 15
Br(1)–Mg(1)
Br(2)–Mg(1)
Si(1)–C(1)
2.582(2)
2.579(2)
1.846(7)
1.838(7)
1.837(7)
1.838(7)
2.024(5)
2.020(5)
Br(1)–Mg(2)
Br(2)–Mg(2)
Si(1)–C(2)
2..580(2)
2.587(2)
1.873(2)
1.870(8)
1.862(9)
1.876(8)
2.114(7)
2.125(6)
Mg–O
2.044(2)
1.844(2)
1.876(2)
1.841(2)
1.883(2)
1.451(2)
Mg–C(1)
2.141(2)
1.872(2)
1.887(2)
1.872(2)
1.885(2)
1.498(3)
Si(1)–C(1)
Si(1)–C(3)
Si(2)–C(1)
Si(2)–C(7)
O–C(8)
Si(1)–C(2)
Si(1)–C(4)
Si(2)–C(5)
Si(2)–C(6)
C(8)–C(9)
Si(2)–C(1)
Si(2)–C(5)
Si(3)–C(12)
Si(4)–C(12)
Mg(1)–O(1)
Mg(2)–O(2)
Si(3)–C(13)
Si(4)–C(16)
Mg(1)–C(1)
Mg(2)–C(12)
O–Mg–C(1)
105.78(5)
110.36(10)
108.14(11)
105.27(11)
111.49(10)
107.59(12)
108.74(11)
113.6(2)
C(1)–Mg–C(1)Ј
C(1)–Si(1)–C(3)
C(1)–Si(1)–C(4)
C(3)–Si(1)–C(4)
C(1)–Si(2)–C(7)
C(1)–Si(2)–C(6)
C(7)–Si(2)–C(6)
C(8)–O–Mg
148.45(10)
113.39(9)
114.06(9)
105.10(12)
114.43(9)
109.72(10)
104.53(11)
123.19(11)
106.72(8)
112.1(2)
C(1)–Si(1)–C(2)
C(2)–Si(1)–C(3)
C(2)–Si(1)–C(4)
C(1)–Si(2)–C(5)
C(5)–Si(2)–C(7)
C(5)–Si(2)–C(6)
C(8)–O–C(8)Ј
Mg(2)–Br(1)–Mg(1)
C(1)–Si(1)–C(2)
C(2)–Si(1)–C(3)
C(2)–Si(1)–C(4)
C(1)–Si(2)–C(5)
C(5)–Si(2)–C(7)
C(5)–Si(2)–C(6)
C(12)–Si(3)–C(14)
O(1)–Mg(1)–C(1)
O(2)–Mg(2)–C(12)
C(1)–Mg(1)–Br(2)
C(1)–Mg(1)–Br(1)
C(12)–Mg(2)–Br(1)
C(12)–Mg(2)–Br(2)
89.79(7)
114.0(3)
105.5(4)
106.6(4)
109.4(4)
105.4(4)
107.7(4)
112.0(4)
109.2(2)
110.2(2)
125.3(2)
123.5(2)
122.9(2)
124.7(2)
Mg(1)–Br(2)–Mg(2)
C(1)–Si(1)–C(3)
C(1)–Si(1)–C(4)
C(3)–Si(1)–C(4)
C(1)–Si(2)–C(7)
C(1)–Si(2)–C(6)
C(7)–Si(2)–C(6)
C(12)–Si(4)–C(16)
O(1)–Mg(1)–Br(2)
O(2)–Mg(2)–Br(1)
O(1)–Mg(1)–Br(1)
Br(2)–Mg(1)–Br(1)
O(2)–Mg(2)–Br(2)
Br(1)–Mg(2)–Br(2)
89.69(7)
110.0(3)
112.0(3)
108.4(4)
114.5(3)
111.4(3)
108.0(4)
111.6(4)
100.8(2)
103.4(2)
103.8(2)
90.24(7)
101.6(2)
90.11(7)
Si(2)–C(1)–Si(1)
Si(1)–C(1)–Mg
118.58(10)
120.05(9)
Si(2)–C(1)–Mg
O–C(8)–C(9)
Symmetry transformations used to generate equivalent atoms: x, Ϫy,
Ϫ z
(9)
data either on the nitrile analogues 11–13 of D, or on 8–10
because (unlike for 15) they have the usual four-coordinate
magnesium atom environment.
The X-ray structure of the crystalline complex D is illustrated
in Fig. 7, with selected geometrical parameters in Table 8. The
structure is unexceptional, the skeletal parameters being similar
to those reported for [Mg(µ-Br)Et(OEt2)]2.24 By contrast crys-
20
talline [Mg(µ-Br){CH(SiMe3)2}(CNBut)]2 is a loosely bound
dimer, having very unequal Mg–Br distances of 2.561(5) and
2.927(5) Å.25 The two-fold symmetric molecule 15 is illustrated
3
in Fig. 8, with selected data in Table 9. The Mg–Csp bond dis-
tance is very similar to that in [Mg{CH(SiMe3)2}2(CNC6H4Me-
2)2]20 or [Mg{CH(SiMe3)2}2]∞.19 The much wider C–Mg–CЈ
angle than the C(CЈ)–Mg–O bond angles is noteworthy.
Fig. 8 ORTEP (20% probability level) of 15 (hydrogen atoms are
omitted).
eqn. (10).12 Another complex, [Ce(LЉ){N(SiMe3)2}2] (16),
obtained in moderate yield as X-ray quality dark-red crystals, is
shown in eqn. (11).
(10)
(11)
Fig. 7 ORTEP (20% probability level) of D (hydrogen atoms are
The molecular structure of the distorted trigonal pyramidal
bis(β-diketiminate) [Ce(Cl)LЈ2] (E) is illustrated in Fig. 9, with
selected geometrical parameters in Table 10. It is isomorphous
with the neodymium analogue,12 the structure of which is
shown schematically in J. The cerium atom is ca. 1.83 Å out of
each of the NC1C3N and NC22C24N planes, compared with
ca. 2.25 Å in J. The latter has Nd-Cα and Nd–Cβ contacts of
ca. 2.93 and 2.95 Å.12
omitted).
Cerium ꢀ-diketiminates
At the outset of this investigation it had been expected [by
analogy with the Yb() system12] that the cerium alkyl 2 would
react with PhCN to give a cerium β-diketiminate, contain-
ing the ligand [{N(SiMe3)C(Ph)}2CH]Ϫ (᎐ LЈ). In the event
᎐
᎐
this prediction proved to be unfounded, eqn. (2). It seemed
The distorted trigonal bipyramidal molecule [Ce(LЉ)-
{N(SiMe3)2}2] (16) is illustrated in Fig. 10, and selected geo-
metrical parameters are shown in Table 11. Its structure may
be compared with that of [Ce(LЈ){CH(SiMe3)2}3];12 selected
desirable to establish structures of cerium β-diketiminates,
albeit prepared by different routes. The chloro–cerium()
bis(β-diketiminate) [Ce(Cl)LЈ2] (E) had previously been made,
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
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Table 10 Selected bond lengths (Å) and angles (Њ) for E
Ce–N(1)
Ce–N(4)
Ce–Cl
Ce ؒ ؒ ؒ C(2)
Ce ؒ ؒ ؒ C(22)
Ce ؒ ؒ ؒ C(24)
N(2)–C(3)
N(4)–C(24)
C(2)–C(3)
2.423(6)
2.483(5)
2.6973(16)
2.960(6)
2.972(7)
2.947(6)
1.334(7)
1.334(7)
1.427(8)
Ce–N(3)
Ce–N(2)
2.425(6)
2.487(5)
2.940(6)
2.968(6)
2.994(6)
1.331(8)
1.325(8)
1.413(10)
Ce ؒ ؒ ؒ C(1)
Ce ؒ ؒ ؒ C(3)
Ce ؒ ؒ ؒ C(23)
N(1)–C(1)
N(3)–C(22)
C(1)–C(2)
N(1)–Ce–N(3)
N(3)–Ce–N(4)
N(3)–Ce–N(2)
N(1)–Ce–Cl
124.27(17)
75.82(18)
105.53(18)
122.14(14)
113.57(12)
N(1)–Ce–N(4)
N(1)–Ce–N(2)
N(4)–Ce–N(2)
N(2)–Ce–Cl
101.79(18)
76.33(18)
178.1(2)
90.41(11)
90.29(12)
N(3)–Ce–Cl
N(4)–Ce–Cl
Table 11 Selected bond lengths (Å) and angles (Њ) for 16
Ce–N(1)
Ce–N(3)
Ce–Cl
Ce ؒ ؒ ؒ C(2)
C(2)–C(3)
N(4)–C(3)
2.400(5)
2.479(5)
2.6973(16)
2.981(6)
1.386(8)
1.368(7)
Ce–N(2)
Ce–N(4)
Ce ؒ ؒ ؒ C(1)
C(1)–C(2)
N(3)–C(1)
2.370(5)
2.455(5)
2.940(6)
1.442(8)
1.325(7)
Fig. 10 ORTEP (20% probability level) of 16 (hydrogen atoms are
omitted).
N(2)–Ce–N(1)
N(1)–Ce–N(4)
N(1)–Ce–N(3)
108.37(16)
135.75(15)
105.25(15)
N(2)–Ce–N(4)
N(2)–Ce–N(3)
N(4)–Ce–N(3)
104.88(16)
124.05(16)
78.21(16)
Conclusions
The synthesis of the crystalline Y and Ce alkyls [Ln{CH-
(SiMe3)2}3] (1, 2) and [Ln{CH(SiMe3)(SiMe2OMe)}3] (3, 4) is
reported. Each achieves coordination saturation by forming
three Ln–C bonds, with three additional close Ln ؒ ؒ ؒ CH3 (1,
2) or Ln OMe (3, 4) contacts to the distorted trigonally pris-
matic six-coordinate metal. Crystalline 3, in C6D6 or C6D5CD3
solution at 313 K exists as two isomers 3Ј (identical to 3)
and the square pyramidal 3Љ. The bis(trimethylsilyl)methyls 1
and 2, like Mg[CH(SiMe3)2]2 or [Mg(µ-Br){CH(SiMe3)2}-
(OEt2)]2, merely formed adducts (5, 6 and 8–13, respectively)
with α-H-free nitriles, and not (β-diketiminato) insertion prod-
ucts. By contrast, reaction of the Y alkyl 3 with benzonitrile
afforded the first 1,3-diaza-2-silahexa-1,3-diene 7. Two crystal-
line cerium β-diketiminates were made from CeCl3 or [Ce{N-
(SiMe3)2}3]: the known [Ce(Cl)LЈ2] (E) and the new [Ce(LЉ)-
{N(SiMe3)2}2] (16), which are shown to have the ligand LЈ or LЉ
bound to the metal in an η5-fashion; LЈ = [{N(SiMe3)-
C(Ph)}2CH] and LЉ = [{N(SiMe3)C(C6H4But-4)}2CH]. The
X-ray structures of eleven compounds, including the new
three-coordinate magnesium alkyl [Mg{CH(SiMe3)2}2(OEt2)]
(15) and the known [Mg(µ-Br){CH(SiMe3)2}(OEt2)]2 (D), are
reported.
Fig. 9 ORTEP (20% probability level) of E (hydrogen atoms are
omitted).
Experimental
geometrical data for its Ce(LЈ) fragment, sketched in K, are
similar to those for Ce(LЉ) moiety of 16. In 16, the cerium atom
is ca. 1.79 Å out of the N3C1C3N4 plane. The Ce–NSi2 bond
distance (Ce–N1) is significantly longer than in [Ce{N-
(SiMe3)2}3], 2.320(3) Å.26
All manipulations were performed under argon using standard
Schlenk techniques. Toluene was dried using sodium. Benzene,
hexane and pentane were dried using sodium–potassium
alloy. Diethyl ether and thf were dried and distilled from
sodium–benzophenone and stored over a sodium mirror under
argon. The NMR spectra were recorded on a Bruker DPX
300 (300.1 MHz for 1H, 75.5 MHz for 13C) or AMX 500
The bonding in each Ce–LЈ (E) or the Ce–LЉ (16) fragment
may be described as η5-ligation, as for J and K.12
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
1573

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(99.36 MHz for 29Si) instruments and referenced externally
(29Si, using SiMe4) or internally to the residual solvent reson-
ances (chemical shift data in δ). All NMR spectra (1H,13C) were
obtained from a 1H detected 2D 89Y–1H shift correlation
experiment): δ 797 (3Ј), 755 (3Љ) (δ measured relative to aqueous
YCl3).
1
measured in C6D6 at 298 K and other than H were proton-
decoupled. Electron impact mass spectra were taken 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.
The compounds [Li{µ-CH(SiMe3)2}]∞ (A),9 [Li{µ-CH(SiMe3)-
(SiMe2OMe)}]8 (B),10 Mg[CH(SiMe3)2] (C),19 [Mg(µ-Br){CH-
(SiMe3)2}(OEt2)]2 (D),20 Ce(Cl){(N(SiMe3)C(Ph)2)2CH}2] (E),12
and [Ln(OC6H2But2-2,6-Me-4)3] (M = Y or Ce)23 were prepared
by published procedures.
[Ce{CH(SiMe3)(SiMe2OMe)}3] 4. Cerium() chloride
(0.15 g, 0.60 mmol) was added in small portions to a solution of
the lithium alkyl B (0.32 g, 3 equivalents) in Et2O (40 cm3) at
Ϫ30 ЊC. The resulting mixture was slowly warmed to room
temperature and stirred for 24 h. The volatiles were removed
in vacuo and the residue was extracted with hexane; the extract
was filtered. The filtrate was concentrated and stored at Ϫ25 ЊC,
yielding pale yellow crystals of compound 4 (0.26 g, 67%)
(Found: C, 35.4; H, 7.85. C21H57CeO3Si6, requires C, 37.8; H,
8.62%), mp 154 ЊC (decomp.).
Preparations
[Y{CH(SiMe3)2}3(NCBut)2] 5. 2-Cyano-2-methylpropane
(0.39 cm3, 3.52 mmol) was added to a stirred solution of the
yttrium alkyl 1 (0.67 g, 1.18 mmol) in hexane (10 cm3) at 0 ЊC.
The mixture was stirred for 10 min at 0 ЊC and then for 3 h at
room temperature. The mixture was filtered; the filtrate was
concentrated in vacuo to ca. 5 cm3 and cooled (Ϫ27 ЊC), afford-
ing colourless cubic crystals of compound 5 (0.72 g, 88%) mp
[Y{CH(SiMe3)2}3] 1. The lithium alkyl A (1.81 g, 3 equiv-
alents) was added to a stirred mixture of [Y(OC6H2But2-2,6-
Me-4)3] (2.76 g, 3.70 mmol) in hexane (50 cm3) at ca. 25 ЊC. The
lithium alkyl gradually dissolved; after ca. 4 h the colourless
precipitate was removed by filtration. The filtrate was concen-
trated to ca. 40 cm3 and cooled (Ϫ27 ЊC), providing colourless
crystals of compound 1 (0.97 g), which were filtered off. The
filtrate was concentrated further, yielding a second crop of 1
(0.74 g; overall yield, 83%), mp 105–106 ЊC. 1H NMR: δ 0.26 (s,
54 H), Ϫ0.62 (d, 2J(1H–89Y) = 1.2 Hz, 3 H); 13C NMR: δ 50.0 (d,
1
88 ЊC (decomp.). H NMR: δ 0.88 (s, 18 H), 0.43 (s, 54 H),
Ϫ0.96 (s, br, 3 H); 13C NMR: δ 127.07, 48.02 (d, 1J = 30.0 Hz),
26.82, 25.59, 5.96; 29Si NMR: δ Ϫ7.92.
2
7J(13C–89Y) = 30.2 Hz); 29Si NMR: δ Ϫ10.3 (d, J(29Si–89Y) =
[Ce{CH(SiMe3)2}3(NCPh)] 6. Benzonitrile (18.5 cm3 of a
0.0101 g cm3 solution in hexane, 1.81 mmol) was added to a
yellow solution of 2 (0.55 g, 0.89 mmol) in hexane (10 cm3) at
room temperature resulting in a red solution. The latter was
concentrated in vacuo to ca. 5 cm3 and upon cooling (Ϫ27 ЊC)
afforded orange cubic crystals of compound 6 (0.12 g, 19%)
(Found: C, 47.7; H, 8.50, N 1.98. C28H62CeNSi6 requires C,
0.8 Hz). EI-MS (m/z, assignment, %): 552 ([M Ϫ CH2]ϩ, 19),
407 ([M Ϫ CHR2]ϩ, 74), 247 ([M Ϫ (CHR2)2]ϩ, 14), 146 (100),
73 (83, [SiMe3]ϩ).
[Ce{CH(SiMe3)2}3] 2. A solution of [Ce(OC6H2But-2,6-
Me-4)3] (6.01 g, 7.53 mmol) in hexane (100 cm3) was added to
a suspension of the lithium alkyl A (3.80 g, 3 equivalents) in
hexane (30 cm3) at ca. 25 ЊC. A golden–yellow solution and a
colourless precipitate were gradually formed. The mixture was
stirred for 2 h, then filtered; The precipitate was washed with
hexane (100 cm3). The combined filtrate and washings were
concentrated to ca. 30 cm3 and cooled (Ϫ27 ЊC), affording a
yellow powder, which was separated by filtration, dissolved in
hexane (150 cm3) and refiltered. The filtrate was concentrated to
ca. 30 cm3 and cooled (Ϫ27 ЊC), yielding yellow needles of
1
46.6; H, 8.66, N 1.94%). H NMR: δ 1.85 (br, 2 H), 1.24 (br,
1 H), Ϫ0.98 (s, 54 H); 13C NMR: δ 132.122, 128.319, 123.426,
8.739.
Me2Si{NC(Ph)CH(SiMe3)C(Ph)N 7. Benzonitrile (0.18 cm3,
1.74 mmol) was added by syringe to a stirred solution of
[Y{κ2-CH(SiMe3)(SiMe2OMe)}3] 3 (0.18 g, 0.29 mmol) in
toluene (ca. 25 cm3) at room temperature. The resulting solu-
tion was heated to 110 ЊC and stirred for 40 min; it became
orange. The volatiles were removed in vacuo and the residue was
“stripped” twice with pentane, then extracted with hexane
(30 cm3) and the extract was filtered. The filtrate was concen-
trated to ca. 10 cm3 and stored at Ϫ25 ЊC for 12 h, yielding pale
yellow crystals of compound 7 (0.21 g, 68%) (Found: C, 66.8;
H, 7.28; N, 7.92. C20H26N2Si2 requires C, 68.5; H, 7.47; N,
7.99%), mp, 153–155 ЊC (decomp.). 1H NMR: δ Ϫ0.18 (s, 9 H,
SiMe3), 0.58, (s, 3 H, SiMe2), 0.65, (s, 3 H, SiMe2), 5.57 (s, 1 H,
CH ), 7.20 (m, 6 H, Ph), 8.06 (d, 4 H, Ph); 13C NMR: δ Ϫ0.74,
Ϫ0.44, 0.86, 44.5, 130.6, 142.4, 176.6; 29Si NMR: δ Ϫ6.23
(SiMe2), 2.01 (SiMe3). EI-MS (m/z, %, assignment): 350 (76%,
[M]ϩ), 247 (100%, [YCH(SiMe3)2]ϩ), 129 (95%, [C(SiMe3-
SiMe]ϩ), 73(40%, [SiMe3]ϩ), 43 (9%, [SiMe]ϩ).
1
compound 2 (3.84 g, 83%). H NMR: δ Ϫ2.20 (s, 54 H), 0.87
(s, 3 H); 13C NMR: δ 10.83, 1.40; 29Si NMR: δ Ϫ6.24.
[Y{CH(SiMe3)(SiMe2OMe)}3] 3. Yttrium() chloride
(0.11 g, 0.56 mmol) was added in small portions to a solution of
the lithium alkyl B (0.32 g, 3 equivalents) in Et2O (40 cm3) at
Ϫ30 ЊC. The resulting mixture was slowly warmed to room
temperature and stirred for 24 h. The volatiles were removed
in vacuo and the residue was extracted with hexane; the extract
was filtered. The filtrate was concentrated and stored at Ϫ25 ЊC,
yielding colourless needles of compound 3 (0.28 g, 82%)
(Found: C, 38.8; H, 9.27. C21H57O3Si6Y requires C, 41.0; H,
9.34%), mp 164–166 ЊC. X-Ray-suitable crystals were obtained
by recrystallisation from Et2O. In solution there are two isomers
3Ј and 3Љ in the ration of 7 : 6; 3Ј, the more symmetric species,
revealed one CH and one OCH3 1H NMR spectral signal, while
3Љ gave two CH and two OCH3 signals in the ratio of 2 : 1.
[Mg{CH(SiMe3)2}2(NCBut)]2 8. 2-Cyano-2-methylpropane
(0.44 cm3, 4 mmol) was added to a solution of Mg[CH-
(SiMe3)2]2 (C) (0.68 g, 2 mmol) in hexane (50 cm3) at Ϫ40 ЊC.
The reaction mixture was allowed to warm up slowly to
room temperature and stirred overnight. Removal of volatiles
in vacuo afforded the white solid 8 (0.83 g, 90%) (Found: C,
56.0; H, 10.5; N, 5.42. C24H56MgN2Si4 requires C, 56.6; H, 11.0;
2
1H NMR (C6D6, 298 K): δ Ϫ1.06 [d, J(1H–89Y) 1.4, 1 H,
CH (3Љ)], Ϫ0.70 [d, 2J(1H–89Y) 2, 2 H, CH (3Љ)], Ϫ0.53 [d,
2J(1H–89Y) 2, 3 H, CH (3Ј)], 0.0–0.4 (45 H, SiMe2 and SiMe3),
3.08 [9 H, OCH3 (3Ј)], 3.23 [6 H, OCH3 (3Љ)], 3.28 [3 H, OCH3
(3Љ)]; 13C NMR (C6D6, 298 K): δ Ϫ1–6 (SiMe2 and SiMe3), 34.4
1
N, 5.51%). H NMR: δ Ϫ1.39 (s, 1 H, CH), 0.44 (s, 18 H,
1
1
[d, J(13C–89Y) 20, CH (3Ј)], 31.3 [d, J(13C–89Y) 22, CH (3Љ,
major)], 34.8 [d, 1J(13C–89Y) 21 Hz, CH (3Љ, minor)], 51.4
(OCH3, 3Ј), 52.1 and 52.0 (OCH3, 3Љ, major and minor, respect-
ively); 29Si NMR (C6D6, 298 K): δ 25.8 [d, 2J(29Si–89Y) 2, SiOMe
(3Љ, minor)], 23.8 [d, 2J(29Si–89Y) 2, SiOMe (3Љ, major)], 24.0 [d,
2J(29Si–89Y) 2 Hz, SiOMe (3Ј)]; 89Y NMR (313 K, C6D6,
SiMe3), 0.75 (s, 9 H, CMe3); 13C NMR: δ Ϫ0.5 (CH), 5.8
(SiMe3), 26.8 (CMe3), 27.9 (CMe3), 126.4 (CN); 29Si NMR:
δ 3.7 (SiMe3). IR νCN: 2261 cmϪ1
.
[Mg{CH(SiMe3)2}2(NCPh)2] 9. Benzonitrile (0.17 cm3,
1.7 mmol) was added to a solution of C (0.27 g, 0.8 mmol) in
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
1574

View Article Online
hexane (40 cm3) at Ϫ40 ЊC. The yellow solution was allowed to
warm up slowly to room temperature and stirred overnight.
Removal of volatiles in vacuo afforded the yellow crystalline
solid 9 (0.45 g, 96%) (Found: C, 60.5; H, 8.59; N, 5.10.
C28H48MgN2Si4 requires C, 61.3; H, 8.76; N, 5.11%). 1H NMR:
δ Ϫ1.26 (s, 1 H, CH), 0.49 (s, 18 H, SiMe3), 6.51 (t, 2 H, 3J = 7.7,
Ar–H), 6.68 (t, 1 H, 3J = 7.7, Ar–H), 7.13 (d, 2 H, 3J = 7.2 Hz,
Ar–H); 13C NMR: δ 1.5 (CH), 5.9 (SiMe3), 112.6, 119.2, 128.6,
132.9 (Ar), 133.4 (CN); 29Si NMR: δ 3.5 (SiMe3). IR νCN: 2262
tion of D (0.4 g, 0.59 mmol) in diethyl ether (50 cm3) at Ϫ40 ЊC.
The reaction mixture was allowed to warm up to room temper-
ature overnight with stirring. Volatiles were removed in vacuo
and the white product was dissolved in toluene (10 cm3).
Refrigeration at Ϫ10 ЊC afforded white crystals of 13 (0.4 g,
85%) (Found: C, 46.9; H, 7.28; N, 3.61. C16H38BrMgNSi2
requires C, 48.7; H, 7.11; N, 3.55%). 1H NMR: δ Ϫ1.11 (s, 1 H,
CH), 0.51 (s, 18 H, SiMe3), 2.13 (s, 6 H, Me), 6.41 (d, 2 H,
3
3J = 7.6, Ar–H), 6.72 (t, 1 H, J = 7.7 Hz, Ar–H); 13C NMR:
cmϪ1
.
δ 1.4 (CH), 5.5 (SiMe3), 113.9, 117.5, 127.6, 131.8 (Ar), 143.1
(CN); 29Si NMR: δ Ϫ 3.2 (SiMe3). IR νCN: 2252 cmϪ1
.
[Mg{CH(SiMe3)2}2(NCC6H3Me2-2,6)] 10. 2,6-Dimethyl-
(cyano)benzene (0.13 g, 1 mmol) was added to a solution of C
(0.17 g, 0.5 mmol) in diethyl ether (40 cm3) at Ϫ40 ЊC; a white
precipitate and turquoise solution developed immediately.
Upon warming to room temperature the precipitate redissolved
and a pale yellow clear solution formed. The reaction mixture
was stirred overnight. Volatiles were removed in vacuo and the
yellow solid was dissolved in pentane (20 cm3). The solution
was concentrated to approximately 5 cm3 and refrigeration
at Ϫ10 ЊC afforded pale yellow crystals of 10 (0.28 g, 90%)
(Found: C, 63.2; H, 9.14; N, 4.52. C32H56MgN2Si4 requires C,
63.6; H, 9.27; N, 4.64%). 1H NMR: δ Ϫ1.20 (s, 1 H, CH), 0.51
(s, 18 H, SiMe3), 2.21 (s, 6 H, Me), 6.45 (d, 2 H, 3J = 7.7, Ar–H),
MgBr{CH(SiMe3)}2(tmen) 14. A solution of tmen (0.24 cm3,
1.63 mmol) and benzonitrile (0.17 cm3, 1.63 mmol) in diethyl
ether (20 cm3) was added dropwise to a solution of D (0.55 g,
0.82 mmol) in diethyl ether (30 cm3) at Ϫ40 ЊC. The reaction
mixture was allowed to warm slowly to room temperature over-
night with constant stirring to give a cloudy solution. Volatiles
were removed in vacuo and the pale yellow solid was washed
with pentane (10 cm3) affording the white solid 14 (0.55 g, 89%)
(Found: C, 39.7; H, 9.20; N, 7.36. C13H35BrMgN3Si2 requires C,
41.2; H, 9.20; N, 7.39%). 1H NMR: δ Ϫ1.60 (s, 1 H, CH), 0.44
(s, 18 H, SiMe3); 13C NMR: δ 1.4 (CH), 6.0 (SiMe3); 29Si NMR:
δ Ϫ3.1 (SiMe3).
3
6.75 (t, 1 H, J = 7.7 Hz, Ar–H); 13C NMR: δ 1.4 (CH), 6.0
[Ce(Cl){(N(SiMe3)C(Ph))2CH}2] E. This compound was pre-
pared by a literature procedure.13 Single crystals of E, suitable
for X-ray analysis, were obtained by crystallisation from
tetrahydrofuran.
(SiMe3), 20.6 (CH3), 112.1, 118.0, 127.3, 131.5 (Ar), 143.3
(CN); 29Si NMR: δ 3.6 (SiMe3). IR νCN: 2243 cmϪ1
.
[Mg{(ꢂ-Br){CH(SiMe3)2}(OEt2)}2 D.20. A solution of CH-
(Br)(SiMe3)2 (3.88 g, 16 mmol) in diethyl ether (50 cm3) was
added dropwise to a stirred suspension of a 10% excess of mag-
nesium turnings (0.42 g, 17.6 mmol) in diethyl ether (100 cm3).
The reaction mixture was refluxed for 2 h, then filtered. Volat-
iles were removed from the filtrate in vacuo to yield a white solid
which was then dissolved in hot hexane (100 cm3). The solution
was concentrated and refrigeration at Ϫ10 ЊC afforded colour-
less single crystals of D (4.65 g, 86%) (Found: C, 38.4; H, 8.62.
C11H29BrMgOSi2 requires C, 39.2; H, 8.61%). 1H NMR:
δ Ϫ1.51 (s, 1 H, CH), 0.41 (s, 18 H, SiMe3), 0.89 [t, 6 H,
O(CH2CH3)2], 3.50 [q, 4 H, O(CH2CH3)2]; 13C NMR: δ 1.2
(CH), 5.4 (SiMe3), 13.8 [O(CH2CH3)2], 65.6 [O(CH2CH3)2]; 29Si
NMR: δ Ϫ2.9 (SiMe3).
[Ce{(N(SiMe3)C(C6H4But-4))2CH}{N(SiMe3)2}2] 16. A solu-
tion of the β-diketimine H[{N(SiMe3)C(C6H4But-4)}2CH]]
(0.54 g, 0.87 mmol) in hexane (20 cm3) was added to a solution
of [Ce{N(SiMe3)2}3] (0.41 g, 0.866 mmol) in hexane (11 cm3).
The mixture was refluxed for 22 h resulting in a brown solution.
The volatiles were removed in vacuo. The residue was extracted
into hexane; the extract was filtered. The filtrate was evaporated
to ca. 5 cm3 and cooled (Ϫ27 ЊC). Dark red prismatic single
crystals of compound 16 (0.44 g, 54%), mp 150–153 ЊC, were
formed after a few days. 1H NMR: δ 6.01 (s, 4 H), 6.21 (s, 4 H),
0.98 (s, 18 H), 0.93 (s, br, 18 H), Ϫ6.76 (s, br, 36 H); 13C NMR:
δ 183.6, 154.1, 152.1, 130. 7, 125.3, 103.0, 36.7, 31.0, 6.11,
Ϫ1.95; 29Si NMR: δ 5.03, Ϫ1.95; 14N NMR: δ Ϫ359.3 (∆w1/2
ca. 100 Hz, N(SiMe3)2; δ rel. to MeNO2); IR νmax: 1607 cmϪ1
.
[Mg(ꢂ-Br){CH(SiMe3)2}(NCBut)]2 11. 2-Cyano-2-methyl-
propane (0.67 cm3, 6.1 mmol) was added to a solution of D
(2.02 g, 3 mmol) in diethyl ether (50 cm3) at Ϫ40 ЊC. The reac-
tion mixture was allowed to warm up to room temperature and
stirred overnight. Volatiles were removed in vacuo to afford 11
(1.56 g, 75%) (Found: C, 41.0; H, 5.95; N, 4.01. C12H28BrM-
Crystal data and refinement details for 1–7, D, E and 15–16
Diffraction data were collected on a Nonius Kappa CCD dif-
fractometer or a NoniusCAD4 diffractometer for D and 15
using monochromated Mo-Kα radiation, λ 0.71073 Å at
173(2) K. Crystals were coated in oil and then directly mounted
on the diffractometer under a stream of cold nitrogen gas. The
structures were refined on all F 2 using SHELXL-9727a or
SHELXL-9327b for D and 15. For 2, the hydrogen on C1 was
located on a difference map and refined; there was unresolved
residual density along the three-fold axis through the origin
which is presumed to be very disordered hexane solvate. For 5,
there are two independent molecules both lying on three-fold
axes; there was also a poorly defined molecule of cyclohexane
solvate lying on a three-fold axis. For 6, there are two independ-
ent molecules; the phenyl groups were included as rigid bodies.
Further details are found in Table 12.
1
gNSi2 requires C, 41.6; H, 8.09; N, 4.05%). H NMR: δ Ϫ1.25
(s, 1 H, CH), 0.45 (s, 18 H, SiMe3), 0.80 (s, 9 H, CMe3); 13C
NMR: δ Ϫ0.6 (CH), 5.8 (SiMe3), 26.9 (CMe3), 28.0 (CMe3),
126.5 (CN); 29Si NMR: δ Ϫ3.4 (SiMe3). IR νCN: 2279 cmϪ1
.
[Mg(ꢂ-Br){CH(SiMe3)2}(NCPh)]2 12. Benzonitrile (0.39 cm3,
3.8 mmol) was added to a solution of D (1.28 g, 1.9 mmol) in
diethyl ether (50 cm3) at Ϫ40 ЊC. The resulting yellow solution
was allowed to warm up to room temperature with constant
stirring. Volatiles were removed in vacuo and the resulting solid
was dissolved in pentane (20 cm3). Refrigeration of the solution
at Ϫ10 ЊC overnight afforded pale yellow crystals of 12 (1.09 g,
78%) (Found: C, 45.1; H, 6.49; N, 3.81. C14H24BrMgNSi2
requires C, 45.9; H, 6.56; N, 3.83%). 1H NMR: δ Ϫ1.13 (s, 1 H,
CH), 0.34 (s, 18 H, SiMe3), 6.72 (t, 2 H, 3J = 6.2, Ar–H), 6.88 (t,
2 H, 3J = 4, Ar–H), 7.02 (d, 1 H, 3J = 6 Hz, Ar–H); 13C NMR:
δ Ϫ0.1 (CH), 5.6 (SiMe3), 112.8, 118.8, 128.9, 131.9 (Ar), 132.4
CCDC reference numbers 229450–229460.
See http://www.rsc.org/suppdata/dt/b3/b316695n/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
(CN); 29Si NMR: δ Ϫ3.2 (SiMe3). IR νCN: 2261 cmϪ1
.
We thank the EPSRC and F.M.C.Ltd. for a CASE studentship
for C. F. C. and the Royal Society for a K. C. Wong Fellowship
for Z. L and a Sino–British Fellowship for X.-H. W.
[Mg(ꢂ-Br){CH(SiMe3)2}(NCC6H3Me2-2,6)]2 13. 2,6-Di-
methyl(cyano)benzene (0.15 g, 1.18 mmol) was added to a solu-
D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
1575

D
Table 12 Crystal and refinement data for 1–7, D, E and 15–16
Compound
1
2
3
4
5
6
Formula
M
C21H57Si6Y
567.12
C21H57CeSi6
618.33
C21H57O3Si6YؒC4H10O
689.24
C21H57CeO3Si6
666.33
C31H75N2Si6Yؒ½C6H12
775.46
C28H62CeNSi6
721.45
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
Trigonal
P31c (no. 159)
16.2345(10)
16.2345(10)
8.6294(3)
90
90
120
1969.7(2)
2
1.67
Trigonal
P31c (no. 159)
16.3636(8)
16.3636(8)
8.5950(8)
90
90
120
1993.1(2)
2
1.33
Monoclinic
P21/n (no. 14)
11.8736(2)
18.9420(3)
19.0835(3)
90
106.618(1)
90
4112.8(1)
4
Trigonal
P31c (no. 9)
15.9563(3)
15.9563(3)
9.6101(2)
90
90
120
2118.96(7)
2
1.26
Rhombohedral
R3c (no. 167)
12.4967(4)
12.4967(4)
108.85(4)
90
90
120
14722(5)
12
1.36
Triclinic
P1 (no. 2)
¯
¯
12.1618(4)
12.8020(4)
27.1173(9)
79.606(2)
84.609(2)
80.598(2)
4087.9(2)
4
γ/Њ
U/Å3
Z
µ/mmϪ1
1.62
1.31
Unique reflections, Rint
Reflections with I > 2σ(I )
Final R indices [I > 2σ(I )] R1, wR2
R indices (all data) R1, wR2
2180, 0.067
1927
0.048, 0.114
0.058, 0.119
2213, 0.061
2004
0.044, 0.114
0.051, 0.119
6852, 0.073
5362
0.043, 0.077
0.066, 0.084
3227, 0.041
3003
0.029, 0.086
0.033, 0.089
2187, 0.095
1684
0.042, 0.088
0.063, 0.094
18393, 0.061
13040
0.050, 0.114
0.082, 0.128
Compound
7
D
15
E
16
Formula
M
C20H26N2Si2
350.61
C22H58Br2Mg2O2Si4
675.5
C18H48MgOSi4
417.2
C42H58CeClN4Si4
906.85
C41H81CeN4Si6
938.76
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
Monoclinic
P21/c (no. 14)
10.4609(3)
9.9181(3)
19.2816(6)
90
93.388(1)
90
1997.0(1)
4
Monoclinic
P21/n (no. 14)
16.184(2)
9.244(2)
25.873(4)
90
107.910(10)
90
3683.2(5)
4
Orthorhombic
C2221 (no. 20)
9.676(4)
16.620(8)
17.173(3)
90
90
90
2762(2)
4
0.24
Triclinic
P1 (no. 2)
Monoclinic
P21/c (no. 14)
12.6286(6)
18.6283(11)
22.8848(11)
90
93.537(3))
90
5373.4(5)
4
¯
11.9825(9)
12.4284(10)
15.9086(15)
94.607(4)
94.084(5)
90.114(4)
2355.4(3)
2
γ/Њ
U/Å3
Z
µ/mmϪ1
0.18
2.38
1.16
1.01
Unique reflections, Rint
Reflections with I > 2σ(I )
Final R indices [I > 2σ(I )] R1, wR2
R indices (all data) R1, wR2
3304, 0.0514
2777
0.044, 0.097
0.056, 0.103
6462, 0.0318
4335
0.074, 0.176
0.115, 0.205
2447, 0.0555
2354
0.035, 0.089
0.038, 0.090
8244, 0.092
5313
0.069, 0.107
0.125, 0.127
7374, 0.119
5325
0.054, 0.110
0.088, 0.122

View Article Online
12 P. B. Hitchcock, M. F. Lappert and S. Tian, J. Chem. Soc.,
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D a l t o n T r a n s . , 2 0 0 4 , 1 5 6 7 – 1 5 7 7
1577