Crystalline (NN)C-M(NN) complexes: Synthesis, structure, bonding and lability [M = Si, Ge, Sn or Pb; (NN) = l, 2-(BuCH2N)2C6H4]

Article abstract of DOI:10.1039/b005216g

Each of the red-brown or red, isomorphous, crystalline adducts (NN)C-M(NN) [(NN) = l.l-CBu^tCH₂N₂C₆H₄ and M = Si, Ge, Sn or Pb] has been obtained from the carbene (NN)C and the appropriate silylene, ge

Full text of DOI:10.1039/b005216g

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Crystalline (NN)C–M(NN) complexes: synthesis, structure, bonding
and lability [M ؍ Si, Ge, Sn or Pb; (NN) ؍ 1,2-(ButCH2N)2C6H4]
Barbara Gehrhus, Peter B. Hitchcock and Michael F. Lappert
The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ
Received 29th June 2000, Accepted 28th July 2000
Published on the Web 23rd August 2000
Each of the red-brown or red, isomorphous, crystalline adducts (NN)C–M(NN) [(NN) = 1,2-(ButCH2N)2C6H4 and
M = Si, Ge, Sn or Pb] has been obtained from the carbene (NN)C and the appropriate silylene, germylene, stannylene
or plumbylene M(NN) in benzene and crystallisation from a hydrocarbon. They are monomeric, with the three-co-
ordinate Ccarb and M atoms in an almost planar (C) or pyramidal (M) environment. The C–M distances are more
than ca. 10% longer than for a typical MII–C bond in an MR2 molecule. Variable temperature 13C and xM NMR
spectra (xM = 29Si, 119Sn or 207Pb) in toluene-d8, as well as for the appropriate M(NN) and C(NN) precursors, have
been recorded. The Ccarb and M chemical shift data show that the compounds readily dissociate in solution, their
stability decreasing in the sequence Sn > Pb > Si > Ge. From the magnitude of the chemical shifts, their confor-
mation and C–M distances of the adducts, it is concluded that the C–M bond in each adduct is best formulated as
being electrostatic in nature, with the carbene moiety as electron donor and the M(NN) fragment as acceptor.
Introduction
Results and discussion
Interest in thermally stable carbenes was triggered by the
discovery about ten years ago of the first such compound,
This study has its origins in an attempt to synthesize a hetero-
leptic nickel(0) complex Ni{Si(NN)}n{C(NN)m} V, containing
both the silylene Si(NN) 1 and the then unknown isoleptic
carbene C(NN) 2 as ligands. It was prompted by our discovery
of the related nickel(0) complexes [Ni{Si(NN)}4] and [Ni-
(PPh3){Si(NN)}3], obtained from 1 and either [Ni(cod)2] or
[NiCl2(PPh3)2].14
the chelating bis(amino)carbene C[N(R)CHCHNR] (R =
adamantyl).1 A major theme of the numereous subsequent
publications has been their role as ligands in transition metal
chemistry. Examples are [Ni{CN(R)CHCHNR}2] (R = C6H2-
Me3-2,4,6)2 and [Pd{CN(Me)CHCHN)2CH2-cis}(NCMe)2]-
[BF4]2 (which catalyses the copolymerisation of C2H4 and
CO).3 Related carbenemetal complexes, in which the carbene
ring is saturated, are readily available from their dimers,
the enetetramines, including [C{N(CH2Ph)}2C6H4-1,2]2;4 an
Accordingly, the first task was to prepare the carbene 2, which
was achieved (steps i and ii of Scheme 1) by a two step syn-
example is [NiCl{CN(Me)CH2CH2NMe}3][BF4].5
The thermally stable carbenes have also featured as ligands
in main group element chemistry. Particularly relevant to the
present study are the complexes I,6 II,7 III,8 and IV,9 having
a Group 14 metal() complex as acceptor moiety.
Scheme 1 Synthesis of carbene–group 14 metal() adducts 8–11
We have been actively engaged in exploring the chemistry of
the thermally stable silylene Si[1,2-(ButCH2N)2C6H4] [≡ Si(NN)]
1. Recently we briefly communicated the synthesis, structure
and bonding of its 1:1 adduct with the then newly prepared
isoleptic carbene 2 (see Scheme 1).10 (Compound 2 had
independently been synthesised by Hahn et al., who also
described its crystal structure.11) We now provide full details of
this study and extensions to the synthesis and structure of 1:1
adducts of 2 with the heavier Group 14 element() congeners
M[1,2-(ButCH2N)2C6H4] (M = Ge 3,12 Sn 4,13 or Pb 512).
and compounds 2, 3–7 (R = CH2But). Reagents: i, Cl2C᎐S, 2 NEt3;
᎐
ii, C8K; iii, ¹ [Ni(cod)2]; iv, 7 ϩ 1; v, 2 ϩ 1, 3, 4 or 5; vi, (M = Ge) 2
¯
²
LiBun, then [GeCl2(diox)]; vii, M[N(SiMe3)2]2 (M = Sn or Pb).
thesis from C6H4[N(H)CH2But]2-1,2,13 using the methodology
pioneered by Kuhn and Kratz.15 In the thiourea reduction
step (step ii) we used potassium–graphite in thf; we found this
to be much more reactive than the sodium–potassium alloy
in toluene, used by Hahn et al.11 The carbene 2 (clearly a
monomer from the NMR spectroscopic data, as evident from
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This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b005216g

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Table 1 Selected geometric data (bond lengths in Å and angles in Њ) for
complexes 9–11
M = Ge
M = Sn
M = Pb
C(1)–M
2.339(3)
1.359(4)
1.360(4)
1.906(2)
1.889(3)
1.400(4)
1.397(4)
1.388(4)
1.398(4)
1.386(4)
1.424(4)
2.472(5)
1.349(6)
1.369(6)
2.104(5)
2.083(4)
1.401(6)
1.398(6)
1.385(7)
1.399(6)
1.387(6)
1.429(7)
2.586(7)
1.360(8)
1.364(8)
2.218(5)
2.167(5)
1.389(9)
1.391(9)
1.390(10)
1.386(9)
1.393(8)
1.419(9)
C(1)–N(1)
C(1)–N(2)
M–N(3)
M–N(4)
N(1)–C(3)
N(2)–C(2)
C(2)–C(3)
N(3)–C(18)
N(4)–C(19)
C(18)–C(19)
N(1)–C(1)–N(2)
N(1)–C(1)–M
N(2)–C(1)–M
N(3)–M–N(4)
N(3)–M–C(1)
105.7(2)
126.6(2)
115.4(2)
84.3(10)
101.26(10)
101.08(11)
124.4(2)
110.9(2)
124.6(2)
124.6(2)
124.5(2)
110.9(2)
113.30(2)
137.3(3)
108.9(3)
114.3(2)
123.62(2)
121.1(2)
105.4(4)
129.0(4)
117.0(3)
79.30(16)
98.41(17)
99.60(16)
123.8(4)
111.8(4)
124.3(4)
125.6(4)
123.9(4)
110.61(2)
113.5(3)
116.3(6)
126.5(6)
114.2(3)
124.7(3)
120.8(4)
104.7(6)
128.5(4)
117.1(4)
77.0(2)
97.1(2)
Fig. 1 Molecular structure of the adducts 9–11, illustrated for the
germanium compound 9.
N(4)–M–C(1)
100.9(2)
124.3(6)
112.4(6)
123.1(6)
125.1(6)
124.1(6)
110.8(6)
112.4(4)
132.1(5)
115.3(5)
114.3(4)
123.9(4)
120.7(6)
C(3)–N(1)–C(8)
C(1)–N(1)–C(2)
C(1)–N(1)–C(8)
C(13)–N(2)–C(1)
C(13)–N(2)–C(2)
C(1)–N(2)–C(2)
C(18)–N(3)–M
C(24)–N(3)–M
C(18)–N(3)–C(24)
C(19)–N(4)–M
C(29)–N(4)–M
C(19)–N(4)–C(29)
the X-ray analysis11) with [Ni(cod)2] yielded (step iii in Scheme
1) the new (carbene)nickel(0) complex [Ni{C(NN)}2] 7. An
attempt to use this as substrate for the target heteroleptic
nickel(0) complex V by treatment with Si(NN) 1 led instead
(step iv in Scheme 1) to the 1:1 carbene–silylene adduct 8.
Our initial rationalisation of this outcome was to consider that
V may have been a labile intermediate, the nickel atom thus
providing the template for an intramolecular ligand–ligand
coupling and elimination to yield 8. This remains a possibility;
however 8 was also obtained (step v of Scheme 1) directly, by
mixing 1 and 2 in benzene at ambient temperature. The related
(NN)C–M(NN) adducts (M = Ge 9, Sn 10 or Pb 11) were
obtained (step v of Scheme 1) from 2 and the germylene 3,
stannylene 4 or plumbylene 5, in a similar fashion.
The solid adducts (NN)C–M(NN) were dark red-brown
(M = Si 8), red (M = Ge 9), ruby dark red (M = Sn 10), or dark
red (M = Pb 11). X-Ray quality crystals were obtained from
pentane (8, 83%), hexane (9, 64%; or 11, 71%), or toluene
(10, 77%). Satisfactory microanalyses were recorded. Their EI-
mass spectra showed the parent molecular cation in substantial
(8 or 10) or low (11) intensity, or absent for 9.
Fig. 2 The presentation illustrating the fold angles Φ1 and Φ2.
The geometric parameters of the (NN)C moiety in com-
pounds 9–11 are closely similar to those in the parent carbene,11
the only significant feature being a slight widening by ca. 1.5Њ of
the N(1)–C–N(2) angle in the adducts from the 103.49(13) or
104.26(14)Њ in (NN)C; cf. 105.6(2)Њ in 8.10 However, the N(3)–
M–N(4) angles in 8 [87.5(2)Њ]10 or 10 [79.30(16)Њ] differ little
from those in their parent M(NN) molecules: 88.2(1) (M = Si)20
or 78.5(2)Њ (M = Sn).13 The fold angles at C1 (Φ1) and M (Φ2)
in the four (NN)C–M(NN) crystalline adducts 8–11 do not
show (Table 2) a monotonic trend as a function of M, being
29 2Њ for Φ1 and 77.5 2.5Њ for Φ2. There is a considerable
torsion between the closely planar C(1)N(1)N(2)C(2)C(3) and
MN(3)N(4)C(18)C(19) fragments, being 60.8(0.16) (8),10
56.71(0.26) (9), 56.89(0.19) (10) and 53.99(0.23)Њ (11).
The crystal structure of crystalline 8 was described in our
earlier communication;10 those of 9–11 are presented herein.
The four adducts 8–11 are isostructural and isomorphous. The
ORTEP16 diagrams are very similar; that for the germylene
adduct 9 is illustrated in Fig. 1. Selected geometric parameters
for the three adducts 9–11 are in Table 1; comparative values of
the C–M bond lengths and the fold angles Φ1 and Φ2 (Fig. 2)
at C and M, respectively, for 8–11 (also the N–C–M angles) and
I–IV are shown in Table 2.
Each of the crystalline adducts 9–11, like 8,10 is a monomer,
having an exceptionally long central bond between the three-
co-ordinate carbon [C(1)] and the M atoms. These C(1)–M
distances (Table 2) may be compared with those (av.) in the
Variable temperature (VT) 13C and xM NMR spectral
chemical shifts of each of the crystalline adducts (NN)C–M-
(NN) 8–11 (for M = Ge only 13C) in toluene-d8 revealed the
presence of the dissociative equilibrium (1), indicative of a labile
C–M bond. These data are illustrated graphically in Figs. 3
(xM = 29Si), 4 (xM = 119Sn) and 5 (xM = 207Pb); the reference com-
pounds, for which similar data are shown, are the free silylene 1
(Fig. 3), stannylene 4 (Fig. 4) and plumbylene 5 (Fig. 5). The
VT xM NMR chemical shifts for 1, 4 and 5 have not previously
been reported. The VT 13C NMR spectral chemical shifts for
each of the adducts 8–11 are compared in Fig. 6.
following MIIR2 compounds: SiC[C(SiMe3)2(CH2)2C(SiMe3)2]
[1.908(2) Å],17 [M{CH(SiMe3)2}2]2 [M = Ge, 2.016; M = Sn,
2.216(6) Å],18 and Pb[C6H(But-2)Me4-4,5,6]2 [2.357(4) Å].19
Thus, each C(1)–M distance in 8–11 is more than 10% longer
than in the appropriate divalent Group 14 element() hydro-
carbyl reference compound. The C(1)–M distances in 10 and 11
are closely similar to those in the corresponding (NЉNЉ)C–MR2
molecules II7 and IV.9 In 9–11, like 8,10 C(1) is in an almost
trigonal planar environment: the sum of the angles Σ at C(1) is
347.7 (9), 351.4 (10), or 350.3Њ (11) (cf.10 351.4Њ for 8). By con-
trast, M is in a pyramidal environment [Σ = 287.9 (9), 277.3
(10), or 274.5Њ (11); cf.10 291.6Њ for 8], attributed to the presence
on M of a stereochemically active lone pair of electrons.
(NN)C–M(NN)
C(NN) ϩ M(NN)
(1)
2
J. Chem. Soc., Dalton Trans., 2000, 3094–3099
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Table 2 Comparative C(1)–M bond lengths (Å) and angles (Њ) at C(1) and M
Complex
C(1)–M
N(1,2)–C(1)–M
Fold angle Φ1a
Fold angle Φ2a
Ref.
8 (NN)CSi(NN)
9 (NN)CGe(NN)
10 (NN)CSn(NN)
11 (NN)CPb(NN)
2.162(5)
2.339(3)
2.472(5)
2.586(7)
2.102(12)
2.379(5)
2.290(5)
2.540(6)
129.3(3), 116.5(3)
126.6(2), 115.40(19)
129.0(4), 117.0(3)
128.5(4), 117.1(4)
28
31
27
28
77
75
79
80
10
This work
This work
This work
6
7
8
9
b
I (NЈNЈ)CGeI2
II (NЉNЉ)CSn(C6H2Pri3-2,4,6)2
69
c
III (NЉNЉ)CPb(C6cH2Pri3-2,4,6)2
IV (NЉNЉ)CSnCl2
c
70.5
a Φ1 and Φ2 are defined in Fig. 2. b (NЈNЈ) ≡ [2,4,6-Me3C6H2NCH᎐] . c (NЉNЉ) ≡ [PriNCH᎐] .
᎐ 2
᎐ 2
Fig. 3 Temperature dependence of 29Si-NMR spectroscopic shifts
(δ) of the carbene–silylene adduct 8.
Fig. 6 Temperature dependence of 13C-NMR spectroscopic shifts
(δ) of the carbene 2 and the carbene–Group 14 metal() adducts 8–11.
carbene–transition metal complexes δ[13C] is at lower frequency
than for the free carbene, as illustrated in the present instance
by comparing this parameter for the bis(carbene)nickel(0)
complex Ni[C(NN)]2 7 of δ 208 with the δ 231.6 for the free
carbene 2, both at ambient temperature. On the other hand,
when a stannylene behaves as a ligand, δ[119Sn] is invariably at
higher frequency for the complex than the “free” ligand, as
shown (for example) for [Pt{Sn[N(SiMe3)2]2}3] (δ 885) and
Sn[N(SiMe3)2]2 (δ 775).21 We conclude that in each adduct the
carbene is the donor and the heavier homologue M(NN) is the
acceptor.
Fig. 4 Temperature dependence of 119Sn-NMR spectroscopic shifts
(δ) of the carbene–stannylene adduct 10.
We now turn to the nature of the C–M bond in each adduct
8–11. Both the crystallographic and the spectroscopic data
point to the same conclusion. First, that this bond is exceed-
ingly weak and progressively so for M = Sn > Pb > Si > Ge.
Secondly, that the attraction between C and M is electrostatic,
with C and M being the positive and negative ends of the CM
dipole, respectively. It is unprecedented for a divalent Group 14
element() bis(amide) to display acceptor properties and hence
the weak nature of the CM bond in 8–11 is unsurprising. That
the stannylene 4 is a better acceptor than the germylene 3 is
consistent with the observation that Sn[CH(SiMe3)2]2,22 unlike
its germanium analogue, forms a weak adduct with pyridine.
For the case of the silylene adduct 8 the above conclusions
have been placed on a more quantitative basis by molecular
orbital calculations on model compounds.10 In summary,
DFT calculations at the B3LYP/6-311ϩG** level on [(CH2)2-
(NH)2]C–Si[(NH)2(CH2)2] 12 or (H2N)2C–Si(NH2)2, or even
[(CH2)2(NH)2]C–SiH2, but not H2C–Si(NH2)2 or H2C–Si[(NH)2-
(CH2)2], showed good agreement with the experimentally
Fig. 5 Temperature dependence of 207Pb-NMR spectroscopic shifts
(δ) of the carbene–plumbylene adduct 11.
At 358 K it is evident (Fig. 6) that the stability of the adduct
with respect to dissociation decreases in the sequence Sn (10) >
Pb (11) > Ge (9) ≥ Si (8), the adduct 8 or 9 being essentially
absent. This trend is confirmed by the δ[29Si] (Fig. 3), δ[119Sn]
(Fig. 4) and δ[207Pb] (Fig. 5) data. At 198 K, on the other hand,
the presence of the largely undissociated adducts is indicated
for 8, 10 and 11 by the δ[xM] (Figs. 3–5) and δ[13C] (Fig. 6) data;
Fig. 6 also shows that the in the wider temperature range 8 is
more robust than 9. The overall conclusion is that stability of
the adducts in solution follows the sequence Sn > Pb > Si > Ge.
x
The 13C or M NMR (not 9) spectral chemical shift of each
adduct 8–11 is at lower frequency than that of the free carbene
(Fig. 6) or metallene M(NN) (Figs. 3–5). We note that for
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J. Chem. Soc., Dalton Trans., 2000, 3094–3099

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observed molecular symmetry, the C–Si bond length and the
weak C–Si bond. Thus, for the C1-symmetric model compound
12 the computed C–Si bond length was 2.024 Å, the C–Si dis-
sociation energy Ϫ13.4 kJ molϪ1, with a partial negative charge
on the silicon atom [Mulliken charge q[Si{(NH)2(CH2)2}]
Ϫ0.072] and a torsion barrier of only ca. 4 kJ molϪ1, there being
a significant twisted energy minimum. Related calculations on
suspension of C8K (prepared from K (6.4 g, 0.18 mol)) and
graphite (17.3 g, 1.44 mol)) in thf (600 cmϪ3) at 0 ЊC. The
mixture was stirred for 1 d at ambient temperature, then
filtered. The solvent was removed in vacuo from the filtrate. The
remaining residue was distilled to yield compound 2 (16.6 g,
81.6%) (Found: C, 78.9; H, 9.99; N, 10.94. C17H26N2 requires C,
79.0; H, 10.14; N, 10.84%) as a colourless, viscous liquid, bp
98–100 ЊC at 0.05 Torr, which subsequently solidified. 1H NMR
(300.13 MHz, CD3C6D5, 293 K): δ 0.9 (s, 18 H, CH3), 3.89
(s, 4 H, CH2) and 6.92–7.01 (m, 4 H, phenyl). 13C-{1H} NMR
(75.48 MHz, CD3C6H5, 293 K): δ 28.46 (CMe3), 33.83 (CMe3),
58.67 (CH2), 110.7, 120.71 and 136.33 (phenyl) and 231.63
(carbene C). MS: m/z 259 ([M ϩ 1]ϩ, 47%).
other H X᎐YH model compounds (X = Ge or Sn; Y = C, Si,
᎐
2
2
Ge or Sn) have been made.23
The present results regarding formation of the adducts 8–11
by the reverse of eqn. (1) may be contrasted with the following
observations. (i) The silylene M[N(But)(CH)2NBut] (M = Si)
failed to react with the corresponding carbene (M = C),
germylene (M = Ge) or CO.24 (ii) The silylene 1 was found to
react readily with the stannylene Sn(Ar)X [Ar = C6H3(NMe2)2-
2,6; X = Ar or N(SiMe)3],25 or M[N(SiMe3)2]2 (M = Ge, Sn or
Pb);26 although 1:1 adducts may have been transient inter-
mediates, the isolated crystalline products were Sn(Ar)[Si(N-
N)X],25 M[Si(NN)N(SiMe3)2]2 (M = Sn or Pb),26 or 13.26 (iii)
The labile adducts I,6 II,7 III8 and IV9 were formed from their
appropriate carbene and MX2 precursors, each of which has a
long and labile C–M bond (Table 2). (iv) Robust 1:1 adducts
〉C–M〈 (M = Ge or Sn) were obtained from the carbene
C[B(But)C(SiMe3)2BBut] and M[C6H(But-2)Me3-4,5,6]2, having
appreciably shorter C–M bonds than those listed in Table 2,
of 1.845(10) or 1.773(14) (M = Ge) or 2.032(2) Å (M = Sn),
respectively.27 As for (ii), the contrast between the above cited
insertion reactions25,26 and the present results involving in both
cases the silylene 1 is attributed to the fact that insertion is
inhibited when the MX2 (M = Ge, Sn or Pb) moiety has the
XϪ ligands joined as a chelate, as in M(NN). In support, we
note that each of the compounds MAr2 (M = Ge or Sn) forms
a 1:1 adduct with the chelated tin() amide SnЈ[1,8-(SiMe3N)2-
C10H6], derived from 1,8-diaminonaphthalene; the Sn–SnЈ
distance is exceptionally long [3.087(2) Å] and the pyramidal
tin atom SnЈ is the acceptor.28
Ni[C{1,2-(ButCH2N)2C6H4}]2 7. A solution of the carbene 2
(0.3 g, 1.16 mmol) in benzene (10 cm3) was added to a solution
of [Ni(cod)2] (0.16 g, 0.581 mmol) in benzene (10 cm3) at
ambient temperature. There was an immediate change to dark
violet. The mixture was stirred for 1 h, the solvent removed
and the residue recrystallised from hexane at Ϫ25 ЊC to afford
dark violet crystals of compound 7 (0.27 g, 82%) (Found: C,
70.4; H, 9.08; N, 9.62. C34H52N4Ni requires C, 71.0; H, 9.11;
N, 9.73%), mp 142–144 ЊC. 1H NMR (300.13 MHz, C6D6,
293 K): δ 0.89 (s, 18 H, CMe3), 4.42 (br s, 4 H, CH2) and 6.9–7.0
(m, 4H, phenyl). 13C-{1H} NMR (75.48 MHz, C6D6, 293 K):
δ 29.53 (CMe3), 34.61 (CMe3), 58.17 (CH2), 109.23, 119.54,
138.81 (phenyl) and 207.57 (carbene C). MS: m/z 574 (Mϩ,
8%).
S᎐C[1,2-(ButCH N) C H }] 6. A solution of thiophosgene
᎐
2
2
6
4
CSCl2 (7.8 cm3, 0.102 mol) in Et2O (50 cm3) was added to a
solution of C6H4[N(H)(CH2But)]2-1,2 (25.3 g, 0.102 mol) and
NEt3 (28.4 cm3, 0.204 mol) in Et2O (300 cm3) at Ϫ78 ЊC. The
mixture was stirred for 16 h at ambient temperature and fil-
tered. The solvent was removed in vacuo from the filtrate. The
residual solid was sublimed at ca. 140 ЊC at 10Ϫ5 Torr to yield
the colourless thiourea 6 (24.32 g, 83%), mp 92–93 ЊC. 1H NMR
(300.13 MHz, C6D6, 293 K): δ 0.98 (s, 18 H, CH3), 4.08 (br s,
4 H, CH2) and 6.94–6.77 (m, 4 H, phenyl). 13C NMR (75.48
MHz, C6D6, 293 K): δ 29.17 (CMe3), 35.47 (CMe3), 55.07
(CH ), 110.33, 121.95 and 133.84 (phenyl) and 175.09 (C᎐S).
᎐
2
MS: m/z 290 (Mϩ, 81%).
[C6H4(NCH2But)2-1,2]C–Si[1,2-(ButCH2N)2C6H4]
8
from
compounds 1 and 7. A solution of the silylene 1 (0.18 g,
0.66 mmol) in benzene (20 cm3) was slowly added to the
carbene–nickel complex 7 (0.19 g, 0.33 mmol) in benzene (20
cm3) at ambient temperature. There was a change from deep
violet to brown. The mixture was stirred for 3 h, the solvent
removed and the residue disolved in pentane and filtered. The
filtrate was concentrated and at Ϫ25 ЊC red-brown crystals of
8 (0.3 g, 85%) were obtained. For characterisation, see below.
Experimental
General procedures
All operations and manipulations were carried out under
purified argon, by conventional Schlenk techniques. Solvents
were dried and degassed before use. Microanalyses were carried
out by Medac Ltd. (Brunel University). The NMR spectra were
recorded using Bruker instruments: DPX 300 (1H and 13C)
and AMX 500 (29Si, 119Sn and 207Pb), and referenced internally
to residual solvent resonances (data in δ). Electron impact
mass spectra were taken from solid samples using a Kratos
MS 80 RF instrument. Melting points were obtained in sealed
capillaries and are uncorrected. The silylene 1 was synthesized
by a published procedure,20 germylene 3 was prepared from
C6H4[N(Li)CH2But]2-1,2 and [GeCl2(diox)] (diox = 1,4-
dioxane),12 while the stannylene 413 and plumbylene 512 were
prepared from C6H4[N(H)CH2But]2-1,2 and Sn[N(SiMe3)2]2 or
Pb[N(SiMe3)2]2, respectively.
General procedure for the synthesis of the adducts
[C6H4(NR)2-1,2]C–M[1,2-(RN)2C6H4] (M ؍ Si 8, Ge 9, Sn 10
or Pb 11; R ؍ CH2But). A solution of M[1,2-(ButCH2N)2C6H4]
(M = Si 1, Ge 3, Sn 4 or Pb 5) in benzene (20 cm3) was added to
a solution of the carbene C[1,2-(ButCH2N)2C6H4] 2 in benzene
(20 cm3). The mixture immediately turned red (Ge) or dark
red-brown (Si, Sn or Pb). It was stirred for 4 h at ambient
temperature; volatiles were removed in vacuo. The residue was
dissolved in an appropriate solvent and filtered. The filtrate was
concentrated to ca. 20 cm3 for crystallisation.
[C6H4(NCH2But)2-1,2]C–Si[1,2-(ButCH2N)2C6H4]
8.
Using the carbene 2 (0.65 g, 2.52 mmol) and silylene 1 (0.69 g,
2.52 mmol) and crystallisation from pentane at Ϫ25 ЊC yielded
dark red-brown crystals of compound 8 (1.11 g, 83%) (Found:
C, 74.5; H, 9.91; N, 10.47. C33H52N4Si requires C, 74.4; H, 9.84;
Syntheses
1
C[1,2-(ButCH2N)2C6H4] 2 (see also ref. 11). A solution of the
N, 10.51%), mp 92–94 ЊC (decomp.). H NMR (300.13 MHz,
thiourea 6 (22.87 g, 0.082 mol) in thf (100 cmϪ3) was added to a
CD3C6D5, 293 K): δ 0.82 and 0.9 (2 s, CH3, 36 H), 3.39 and 3.93
J. Chem. Soc., Dalton Trans., 2000, 3094–3099
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Table 3 Crystal data and refinement for complexes 9–11
9
10
11
Formula
M
C33H52GeN4
577.38
C33H52N4Sn
623.5
C33H52N4Pb
712.0
Crystal system
Space group
a/Å
b/Å
Monoclinic
P21/n (no. 14)
10.146(2)
16.243(9)
20.054(4)
101.85(2)
3234(2)
4
Monoclinic
P21/n (no.14)
10.396(3)
16.059(5)
20.198(36)
103.39(6)
3281(6)
4
Monoclinic
P21/n (no.14)
10.421(4)
16.015(4)
20.254(10)
102.61(4)
3299(2)
4
c/Å
β/Њ
U/Å3
Z
µ(Mo-Kα)/mm
T/K
Total reflections
Independent reflections
Reflections with I > 2σ(I)
R1 [I > 2σ(I)]
wR2 (all data)
0.97
173(2)
6018
5683
4370
0.042
0.104
0.81
173(2)
6096
5767
4063
0.047
0.108
5.14
173(2)
6112
5784
4274
0.041
0.086
(2 s, CH2, 8 H) and 6.87–6.94 (m, phenyl, 8 H). 13C-{1H} NMR
(CD3C6D5, 75.48 MHz, 293 K): δ 28.34 and 28.91 (CMe3),
55.08 and 57.53 (CMe3), 109.73, 111.3, 117.6, 124.75, 135.78
and 142.61 (phenyl) and 216.46 (carbene C). 29Si-{1H} NMR
(C6D6, 298 K): δ 77.14. MS: m/z 532 (Mϩ, 46%).
measured by an ω–2θ scan. Corrections were made for absorp-
tion using psi-scan measurements. The programs used for
structure solutions and refinement were SHELXS 8629 and
SHELXL 97,30 respectively. Further details are in Table 3.
CCDC reference number 186/2121.
[C6H4(NCH2But)2-1,2]C–Ge[1,2-(ButCH2N)2C6H4]
9.
See http://www.rsc.org/suppdata/dt/b0/b005216g/ for crystal-
lographic files in .cif format.
From the carbene 2 (0.43 g, 1.66 mmol) and the germylene
3 (0.53 g, 1.66 mmol), after crystallisation from hexane
first at room temperature and then at Ϫ25 ЊC, red crystals of
compound 9 (0.61 g, 63.5%) were obtained (Found: C, 68.4;
H, 8.77; N, 9.79. C33H52GeN4 requires C, 68.7; H, 9.08; N,
9.70%), mp 110–112 ЊC. 1H NMR (300.13 MHz, C6D6, 293 K):
δ 0.91 and 0.92 (2 s, 36 H, CH3), 3.68 and 3.96 (2 s, 8 H, CH2),
7.0 and 7.05 (2 m, 8 H, phenyl). 13C-{1H} NMR (C6D6, 75.48
MHz, 293 K): δ 28.4 and 28.7 (CMe3), 33.2 and 33.8 (CMe3),
56.8 and 58.2 (CH2), 110.0, 111.1, 117.4, 121.2, 136.1 and 143.7
(phenyl) and 224.9 (carbene C). MS m/z 320 ([M Ϫ carbene]ϩ,
23%).
Acknowledgements
We thank EPSRC for a fellowship for B. G. (who since 01.12.99
is an EPSRC Advanced Fellow) and for other support and
Dr A. G. Avent for assistance and advice with the NMR
spectroscopy.
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[C6H4(NCH2But)2-1,2]C–Sn[1,2-(ButCH2N)2C6H4]
10.
Using the carbene 2 (1.07 g, 4.147 mmol) and stannylene 4
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N, 9.11. C33H52N4Sn requires C, 63.6; H, 8.41; N, 8.98%), mp
168–170 ЊC. 1H NMR (300.13 MHz, C6D6, 293 K): δ 0.739 and
1.06 (2 s, 36 H, CH3), 3.57 and 3.89 (2 s, 8 H, CH2), 6.88 and
7.01 (2 m, 8 H, phenyl).13C-{1H} NMR (C6D6, 75.48 MHz,
293 K): δ 28.04 and 29.26 (CMe3), 33.82 and 34.29 (CMe3),
56.75 and 59.39 (CH2), 109.46, 112.26, 115.2, 122.84, 135.0
and 148.41 (phenyl) and 200.83 (carbene C). 119Sn-{1H} NMR
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[C6H4(NCH2But)2-1,2]C–Pb[1,2-(ButCH2N)2C6H4]
11.
From the carbene 2 (0.31 g, 1.2 mmol) and plumbylene 5
(0.54 g, 1.2 mmol) and crystallisation from hexane at room
temperature and then at Ϫ25 ЊC there were obtained dark red
crystals of compound 11 (0.85 g, 71%) (Found: C, 55.5: H, 7.30:
N, 7.77. C33H52N4Pb requires C, 55.7; H, 7.36; N, 7.87%),
1
mp > 60 ЊC (decomp.). H NMR (300.13 MHz, CD3C6D5, 293
K): δ 0.69 and 0.948 (2 s, 36 H, CH3), 3.67 and 4.13 (2 s, 8 H,
CH2), 6.75 and 6.85 (2 m, 8 H, phenyl).13C-{1H} NMR
(CD3C6D5, 293 K): δ 28.06 and 28.94 (CMe3), 33.8 and 34.54
(CMe3), 57.57 and 61.93 (CH2), 111.83, 112.29, 115.38, 122.31,
137.43 and 155.86 (phenyl) and 211.49 (carbene C). MS:
m/z 712 (Mϩ, 0.9%).
Crystal data and refinements details
Data were collected on an Enraf-Nonius CAD4 diffractometer
using monochromated Mo-Kα radiation, λ 0.71073 Å, with the
crystals under a stream of cold nitrogen gas. Intensities were
3098
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