Synthesis and structures of 1,3,1′,3′-tetrabenzyl-2,2′-biimidazolidinylidenes (electron-rich alkenes), their aminal intermediates and their degradation products

Article abstract of DOI:10.1039/a802123f

Benzyl (R) substituted enetetramines 9 and 3 have been studied. From HNR(CH₂)₂NRH and CH(NMe)₂OBu^t or CH(OMe)₂NMe₂, two new intermediates along the pathway to 9, namely the orthoamide 11 an

Full text of DOI:10.1039/a802123f

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Synthesis and structures of 1,3,1Ј,3Ј-tetrabenzyl-2,2Ј-
biimidazolidinylidenes (electron-rich alkenes), their aminal
intermediates and their degradation products
Bekir Çetinkaya,a Engin Çetinkaya,a José A. Chamizo,b Peter B. Hitchcock,b
Hatam A. Jasim,b Hasan Küçükbaya and Michael F. Lappert*,†,b
a Chemistry Department, Faculty of Arts and Sciences, Inönü University, 44069 Malatya,
Turkey
b The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ
Benzyl (R) substituted enetetramines 9 and 3 have been studied. From HNR(CH2)2NRH and
CH(NMe2)2OBut or CH(OMe)2NMe2, two new intermediates along the pathway to 9, namely the
orthoamide 11 and the bis(orthoamide) 12 were isolated. Each of 11 and 12 was converted into 9 by
refluxing in toluene. Photolysis of 9 yielded the isomer 10, while thermolysis of 9 gave the di(debenzylated)
product 1,1Ј-dibenzyl-2,2Ј-biimidazoline 13. A route to 3 (R ؍ RЈ ؍ CH2Ph) similar to those used for
9, involving the condensation of 1,2-C6H4[N(R)H]2 with CH(OMe)2NMe2, or the reaction between
1,3-dibenzylbenzimidazolium chloride 8 (X ؍ Cl) and NaH, did not give the expected enetetramine 3
(the dibenzo-analogue of 9), the bis(debenzylated) product 15 being obtained instead. Heating the
orthoamide 1,2-RNC6H4N(R)C(H)NMe2, prepared from CH(NMe2)2OBut and 1,2-C6H4[N(H)R]2, also
gave 15. The reactions of S8, PhNCS or KOH with a mixture of 8 (X ؍ Cl) and NaH gave 17, 18 or 19,
respectively, consistent with the transient formation in each reaction of the tetrabenzylenetetramine 3
(R ؍ RЈ ؍ CH2Ph). The molecular structure of each of the crystalline compounds 10, 11, 12 and 13 was
established by X-ray diffraction.
For some years we have used enetetramines (electron-rich
continuous removal by distillation of MeOH and Me2NH.
olefins) such as 1, 2 and 3 as (i) sources of carbenetransition
The reaction has been extended to (i) six-membered bicyclic
analogues of 1,11 (ii) compounds 212 and 3,3 (iii) optically
active compounds 4–6,13 (iv) the macrocycle 7,14 (v) functional-
R
N
R′
(CH2)n
N
N
N
(H2C)m
(CH2)m
C
C
C
C
Me
N
R
N
Me
N
N
N
R
N
N
R
R′
R′
C
C
C
H
1
2
N
N
N
H
R
N
R′
R′′
Me
R′
2
2
2
N
4
5
6
C
C
N
N
R
N
N
N
R′
C
C
3
N
metal complexes,1–3 (ii) powerful reducing agents, especially
chlorine atom-abstractors,2,4,5 or (iii) benzoin catalysts.6 The
compounds have an extensive organic chemistry.7 They do not
dissociate into imidazolidinylidenes (electron-rich carbenes),
although scrambling reactions between two different com-
pounds 1 (e.g. R = RЈ = Ph with R = RЈ = p-MeC6H4) were
shown to occur in the presence of RhI catalysts;8 carbene-
rhodium() complexes were isolable intermediates in the
catalytic cycle; this was the first example of model experiments
implicating carbenemetal complexes in olefin metathesis. Ther-
7
ised analogues of 1 [R = (CH ) CH᎐CH ,15 CH CH᎐CHMe15
᎐
᎐
2
2
2
2
and (CH2)3PPh2 16] and (vi) unsymmetrical analogues of 1
(R ≠ RЈ).12 Symmetrical tetraarylenetetramines (1, R = an
unhindered aryl group, e.g. R = Ph) have been prepared by
a similar procedure (EtOH elimination) from the orthoester
CH(OEt)3 and HN(R)(CH2)2N(R)H,17a or by heating
PhN(CH2)2N(Ph)C(H)CCl3 (CHCl3 elimination).17b
We have described a useful alternative method for preparing
compounds 1 and 2, from sodium hydride and either a 4,5-
dihydroimidazolium halide, eqn. (2) [e.g. for 1 or 2, n = m = 2,
mally stable electron-rich carbenes such as CNRCH᎐CHNR
᎐
(R = adamantyl) have recently gained prominence.9
The general route to compounds 1 involves interaction of
the appropriate N,NЈ-disubstituted 1,2-diaminoethane, HNR-
(CH2)2NRH (R = a primary alkyl or an unhindered aryl group)
with the dimethyl acetal of N,N-dimethylformamide in an inert
atmosphere, eqn. (1).10 The equilibrium is driven to the right by
R
N
2
X–
+
2NaH
1
+
H2
+
2NaX
(2)
N
2HN(R)(CH2)2N(R)H ϩ 2CH(NMe2)(OMe)2
1 (R = RЈ) ϩ 2Me2NH ϩ 4MeOH (1)
R′
R = CH2Ph] or a bis(tetrahydropyridinium) salt [e.g. for 2,
n = 2, m = 3, R = CH2Ph].12 This procedure was adopted for
† E-Mail: M.F.Lappert@sussex.ac.uk
J. Chem. Soc., Perkin Trans. 1, 1998
2047

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the synthesis of the enetetramine 3 (R = RЈ = Me) from 1,3-
dimethylbenzimidazolium iodide 8 (X = I) and NaH;3 it has the
R
R
N
H
NH
i or vi
R
NH
R
N
NMe2
N
R
X–
11
ii (ref. 11)
v or vi
N
iv iii
R′
R
N
R
N
R
N
R
R
N
R
N
8
N
H
N
H
N
vii
x
viii
advantages that it requires extremely mild conditions, affords
the products in high yield and is particularly suitable for
unsymmetrical enetetramines, e.g. 1 and 2 (R ≠ RЈ).
The biimidazolidinylidene 1 (R = RЈ = allyl) was not access-
ible using the procedure of eqn. (1) and, if formed, spon-
taneously rearranged to the isomer 1Ј (R = RЈ = allyl).15 This
C
C
C
C
N
R
N
R
N
R
N
R
N
N
R
R
R
R
12
9 (ref. 11)
10
ix
R
vii
R
N
R
N
R′
N
N
R
R
+
C
C
2
+ R
R
N
N
R
N
N
C
C
N
N
R
R′
13
14
Scheme 1 Routes to enetetramine 9 and its thermal or photochemical
degradation or aminolysis (R = CH2Ph). Reagents and conditions: i,
CH(NMe2)3, C5H12, 36 ЊC, 2 h; ii, CH(NMe2)(OMe)2, MeC6H11, 110 ЊC
(distn), 3 h; iii, C6H12, 80 ЊC, 1.5 h; iv, 4 Me2NH, THF, 20 ЊC, 18 h; v,
CH(NMe2)(OMe)2, C6H12, 80 ЊC, 3 h; vi, CH(NMe2)2(OBut), ca. 25 ЊC,
2 h; vii, PhMe, 110 ЊC, 3 h; viii, hν, Et2O, 20 ЊC, 18 h; ix, Me2C6H4,
140 ЊC, 6 h; x, RN(H)(CH2)2NHR, THF, 20 ЊC, 40 h.
1′
thermal amino-Claisen rearrangement was believed to be [3,3]-
sigmatropic, because the corresponding thermal transform-
ation of the tetracrotyl analogue 1 (R = RЈ = CH CH᎐CHMe)
regiospecifically yielded 1Ј [R = CH CH᎐CHMe, RЈ = CH(Me)-
᎐
2
᎐
2
CH᎐CH ], while its photochemical isomerisation gave not only
᎐
2
the latter but also the isomer 1Ј (R = RЈ = crotyl). In a prelimin-
ary publication we noted that a similar 1 → 1Ј isomerisation
(9 → 10, viii in Scheme 1) occurred for the case of
R = CH2Ph and outline X-ray data were also shown for 10;15
full details are now provided.
Tetrakis(N-piperidyl)ethene [together with bis(N-piperidyl)-
carbene] has been obtained by deprotonation of the amidinium
salt [(C5H12N)2CH][BF4] with LiNPri2.18a Reduction of oxalic
amidines with metallic lithium and addition of an electrophile
yielded enetetramines; e.g. [Me(Ph)N][Me(4-MeC H )N]C᎐C-
᎐
6
4
[N(4-MeC H )][N(Ph)Me] from [Me(Ph)N][4-MeC H N]C᎐C-
᎐
6
4
6
4
[N(4-MeC6H4)][Me(Ph)N] and successively Li and MeI.18b
Fig. 1 X-Ray crystal structure of 11
Treatment of the thiourea RN(CH2)2NRCS with potassium
yielded the carbene (R = But) or its dimer 1 (R = RЈ = Me, Et or
Pri).18c
or 1,2-bis(benzylamino)ethane was converted into 11 or 12,
respectively (iv and x in Scheme 1). Photolysis of 9 yielded the
isomer 10 (viii in Scheme 1). Thermolysis of 9 or 10 afforded
dibenzyl and the debenzylated products, the bis(dihydroimid-
azole) 13 or dihydroimidazole 14 (ix and vii in Scheme 1).
Ethyl and allyl analogues of the orthoamide 11 (R = Et 11a
The objectives of the present study were to (i) identify aminal
intermediates in the reaction of eqn. (1); (ii) study the thermal
and photochemical degradation reactions of the enetetramine 9
(1, R = RЈ = CH2Ph); and (iii) attempt to obtain the tetrabenzyl
compound 3 (R = RЈ = CH2Ph) and study its reactivity. In the
event, the latter compound proved to be elusive, but trapping
and decomposition reactions support the notion that it has a
transient existence.
and R = CH CH᎐CH 11b) were obtained from the appropriate
᎐
2
2
diamine and CH(NMe2)2OBut; upon heating, the former gave
an enetetramine (9, R = Et),7 and the latter an isomer (10,
R = CH CH᎐CH ).15
᎐
2
2
Characterisation of the new compounds 10, 11, 11a, 11b, 12
and 13 is shown in Tables 1 (colours, mps and analytical data), 2
(1H NMR spectral data), 3 (13C NMR spectral data) and 4
(selected IR spectral and MS data). The molecular structures of
the crystalline orthoamide 11 (Fig. 1), the bis(orthoamide) 12
(Fig. 2), the rearrangement product 10 (Fig. 3) of the enetetra-
mine 9 and the biimidazoline 13 (Fig. 4) have been determined
from single crystal X-ray diffraction data.‡ Selected bond
lengths and angles are listed in Tables 5 (11), 6 (12), 7 (10) and 8
(13).
Results and discussion
The tetrabenzylenetetramine 9 has previously been described,
having been prepared from the diamine HN(CH2Ph)-
(CH2)2N(CH2Ph)H and the aminal CH(NMe2)(OMe)2 (ii in
Scheme 1);11 its X-ray structure has also been reported.12 It has
been suggested that in similar reactions, an orthoamide such as
11 (R = CH2Ph) might be an intermediate.10 We now show that,
from equimolar portions of the diamine and the orthoamide
CH(NMe2)3 or CH(NMe2)2OBut, the monocyclic ortho-
amide 11 was formed (i or vi in Scheme 1) [an analogue of 11
(R = Me) had previously been made similarly19]; while using the
Bredereck reagent CH(NMe2)2OBut, or under more forcing
conditions CH(NMe2)(OMe)2, and the diamine in appropriate
stoichiometry, gave the bicyclic orthoamide 12 (v or vi in
Scheme 1). Each of 11 and 12 upon heating gave 9 (iii and vii in
Scheme 1), and the latter in turn upon treatment with Me2NH
‡ Full crystallographic details, excluding structure factor tables, have
been deposited at the Cambridge Crystallographic Data Centre
(CCDC). For details of the deposition scheme, see ‘Instructions for
Authors’, J. Chem. Soc., Perkin Trans. 1, available via the RSC Web
page (http://www.rsc.org/authors). Any request to the CCDC for this
material should quote the full literature citation and the reference
number 207/221.
2048
J. Chem. Soc., Perkin Trans. 1, 1998

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Table 1 Colours, yields, mps and analytical data for the new compounds
Found (required) (%)
Compound no.
Colour
Mp (ЊC)
Yield (%)
C
H
N
10
White
White
White
White
White
White
Cream
Yellow
White
Cream
White
Yellow
White
98–99
oil
49–50
oil
92
58
83b
56c
87
56
70
58
80d
14
65
52
76
81.0 (81.6)
72.2 (72.0)
77.0 (77.3)
63.3 (63.2)
67.3 (67.7)
81.4 (81.6)
76.0 (75.5)
79.1 (80.4)
80.6 (81.1)
83.7 (84.6)
75.1 (76.4)
77.6 (77.6)
79.7 (79.7)
7.0 (7.2)
11.0 (11.2)
18.6 (18.7)
14.0 (14.2)
24.8 (24.6)
19.9 (21.5)
11.4 (11.2)
17.2 (17.6)
11.9 (12.2)
13.3 (13.5)
9.2 (9.4)
10a (10, R = CH2CHCH2)
9.4 (9.3)
8.1 (8.5)
12.1 (12.3)
10.2 (10.8)
7.2 (7.2)
7.3 (6.9)
6.9 (7.2)
5.3 (5.3)
6.1 (6.4)
5.3 (5.4)
5.3 (5.3)
6.2 (6.4)
11
11a (11, R = Et)
11b (11, R = CH2CHCH2)
12
13
16
15
20
17
18
19
65–70a
105–106
70–71
215–217
143–145
190–191
203–205
114–115
8.4 (8.5)
9.6 (9.7)
8.9 (8.9)
a The compound first melted then resolidified. b 50% based on i in Scheme 1. c 50% based on vi and 47% based on x in Scheme 1. d The yield
calculated from the acetal method.
Table 2 1H NMR spectroscopic chemical shift (δ) data, with assignments for the new compounds;a J values in Hz
Compound no.
Ring CH2
CH2 Ph
Aromatics
Others
11b
2.33 (m), 2.83 (m, AAЈBBЈ)
3.68 (q, AB)
7.23 (m, C6H5)
2.48 (s, Me2N)
4.12 (s, H-C2)
11a
11b
12b
2.37 (NMe2), 3.58 (2-CH)
2.19 (NMe2), 3.47 (2-CH)
4.37 (s, CH)
2.20–2.30 (m, AAЈBBЈ)d
f
7.00–7.50 (m, C6H5)
7.00–7.60 (m, C6H5)
3.10 (s)e
13b
16c
15c
20c
17c
2.90 (t, CH2N᎐)g
4.80 (s)
4.10 (s)
6.25 (s)
4.27 (s), 5.19 (s)
5.66 (s)
᎐
3.70 (t, CH2NR)
—
6.30–6.70 (m)
7.14 (s)
7.15–7.34 (m)
7.88 (m)
6.94–7.26 (m)
7.83 (d)
7.09–7.32 (m)
7.42 (m)
2.12 (s, NMe2)
5.48 (s, CH)
—
—
—
18c
19c
—
—
5.81 (s)
7.10–7.63 (m)
6.79–6.82 (m)
7.26–7.31 (m)
4.18 (d),h 4.81 (s)
4.10 (t, NH)i
8.21 (s, CHO)
a Chemical shifts (δ) relative to SiMe4; abbreviations: s = singlet, d = doublet, t = triplet, m = multiplet. b Spectra recorded in C6D6. c Spectra recorded
in CDCl3. d CH2’s of the orthoamide rings. e CH2’s of the ethylenediamine bridge. f The other signals (singlets) at δ 3.10, 3.30, 3.70, 4.10 and 4.20 are
not assigned. g J = 10. h J = 6. i J = 6.
Table 3 13C NMR spectroscopic chemical shift (δ) data, with assignments, for the new compoundsa
Compound
no.
Ring CH2
CH2Ph
Aromatics
Other
11b
11a
49.6
49.5
58.4
—
128.1, 128.6, 129.3, 140.8
—
101.2 (C-2)
102.2 (C-2), 38.8 [N(CH3)2], 14.5 (CH2CH3), 48.4
(CH2CH3)
11b
49.7
—
—
38.8 [N(CH3)2], 101.2 (C-2), 115.8 (CH᎐CH2),
137.3 (CH2᎐᎐CH)
100.4 (C-2)
99.5 (C-bridging)
37.3, 112.8
᎐
12b
13b
16c
15c
48.6,d 50.7
50.0, 52.5
—
54.7, 57.5f
54.6
51.0
126.4, 126.6, 126.9, 127.3
128.0, 128.3, 128.5, 128.6, 128.7
118.7, 127.1, 127.4, 128.7, 139.2, 140.5
110.8, 120.5, 122.9, 124.1, 126.8, 127.4, 128.6,
135.5, 136.9, 142.6, 142.8
109.6, 119.5, 122.5, 126.1, 127.4, 128.6, 135.5,
136.6, 142.6, 153.3
110.1, 123.5, 127.9, 128.3, 129.2, 136.1
113.3, 122.4, 122.9, 123.9, 126.2, 128.4, 128.5,
128.8, 129.1, 130.4, 133.4
111.7, 117.0, 127.1, 128.5, 126.6, 129.2, 129.8,
129.9, 136.7, 138.4, 144.9
—
48.5
20c
—
34.5, 47.0
17c
18c
—
—
49.0
50.1
132.5
165.7, 150.7
19c
e
47.6, 48.6
163.8
a Chemical shifts (δ) relative to SiMe4 = 0. b Spectra recorded in C6D6. c Spectra recorded in CDCl3. d C of the orthoamide. e 15N = Ϫ249.1 (N CHO),
Ϫ323.0 (N H). f Attached to ring N.
The conformations of the five-membered rings in the ortho-
amide 11 and the bicyclic orthoamide 12 have an envelope-like
shape. The methine carbon [C(1)] in 11 is ca. 0.56 Å below the
N(1)᎐C(3)᎐C(2)᎐N(2) plane; the three substituent atoms C(4),
C(5) and N(3) [attached to N(1), N(2) and C(1), respectively]
are equatorial to this plane, with C(4) and C(5) ca. 0.6 Å out of
this plane. In 12, by contrast, one of the ring carbons [C(3)] is
ca. 0.6 Å above the N(1)᎐C(1)᎐N(2)᎐C(4) plane; the C(5) sub-
J. Chem. Soc., Perkin Trans. 1, 1998
2049

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Table 4 Selected IRa and mass spectral data for the new compounds
Compound no.
ν(C᎐N)/cmϪ1
m/z (rel. intensity, %; assignment; Mϩ = parent molecular ion)
᎐
11
12
13
—
—
1522
b
b
318 (13, Mϩ), 227 (43, [M Ϫ 91]ϩ), 186 (15, [M Ϫ 132]ϩ), 159 (5, [Mϩ/2]), 132 (15, [M Ϫ 18]ϩ),
91 (100, [M Ϫ 227]ϩ)
16
15
20
17
18
19
—
343 (15, Mϩ), 299 (100, [M Ϫ 44]ϩ)
1603
1610
1612
1601
c
414 (55, Mϩ), 323 (100, [M Ϫ 91]ϩ)
298 (50, Mϩ), 207 (100, [M Ϫ 91]ϩ), 91 (100, [M Ϫ 207]ϩ)
330 (100, Mϩ), 297 (20, [M Ϫ 33]ϩ), 239 (80, [M Ϫ 91]ϩ)
434 (80, [M ϩ 1]ϩ), 402 (18, [M Ϫ 32]ϩ), 310 (75, [M Ϫ 123]ϩ), 298 (30, [M Ϫ 135]ϩ)
316 (18, Mϩ), 299 (25, [M Ϫ 17]ϩ), 197 (20, [M Ϫ 119]ϩ), 91 (100, [M Ϫ 225]ϩ)
a Spectra recorded as Nujol mulls. b Parent ion was not observed; fragmentation similar to that of 1, with different intensities. c νCO = 1657 cmϪ1
.
Table 5 Selected bond lengths (Å) and angles (Њ) for the ortho-
amide 11
N(1)–C(1)
N(1)–C(4)
N(2)–C(2)
N(3)–C(1)
N(3)–C(19)
1.457(6)
1.461(6)
1.465(7)
1.432(6)
1.453(7)
N(1)–C(3)
N(2)–C(1)
N(2)–C(5)
N(3)–C(18)
C(2)–C(3)
1.450(6)
1.458(6)
1.455(6)
1.451(7)
1.489(7)
C(1)–N(1)–C(3)
C(3)–N(1)–C(4)
C(1)–N(2)–C(5)
C(1)–N(3)–C(18)
C(18)–N(3)–C(19)
N(1)–C(1)–N(3)
106.0(3)
113.6(4)
114.7(4)
115.0(4)
114.0(4)
110.0(4)
C(1)–N(1)–C(4)
C(1)–N(2)–C(2)
C(2)–N(2)–C(5)
C(1)–N(3)–C(19)
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
113.4(4)
106.9(4)
113.8(4)
117.2(4)
101.0(4)
116.5(4)
Table 6 Selected bond lengths (Å) and angles (Њ) for the bicyclic
orthoamide 12
N(1)–C(1)
N(1)–C(5)
N(2)–C(4)
N(3)–C(1)
N(3)–C(25)
1.446(6)
1.451(6)
1.486(7)
1.461(6)
1.459(7)
N(1)–C(3)
N(2)–C(1)
N(2)–C(24)
N(3)–C(2)
C(3)–C(4)
1.454(6)
1.468(6)
1.474(7)
1.460(6)
1.509(8)
Fig. 2 X-Ray crystal structure of 12
C(1)–N(1)–C(3)
C(3)–N(1)–C(5)
C(1)–N(2)–C(24)
C(1)–N(3)–C(2)
C(2)–N(3)–C(25)
N(1)–C(1)–N(3)
106.2(4)
112.7(4)
114.5(4)
112.0(4)
113.2(4)
109.7(4)
C(1)–N(1)–C(5)
C(1)–N(2)–C(4)
C(4)–N(2)–C(24)
C(1)–N(3)–C(25)
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
114.6(4)
105.9(3)
111.3(4)
111.5(4)
106.1(4)
115.6(4)
Table 7 Selected bond lengths (Å) and angles (Њ) for the isomer 10
of the enetetramine 9
N(1)–C(1)
N(1)–C(7)
N(2)–C(3)
N(3)–C(2)
N(3)–C(8)
N(4)–C(6)
C(1)–C(10)
C(5)–C(6)
1.466(4)
1.456(4)
1.453(4)
1.392(2)
1.447(3)
1.469(4)
1.556(3)
1.506(3)
N(1)–C(4)
N(2)–C(1)
N(2)–C(9)
N(3)–C(5)
N(4)–C(2)
C(1)–C(2)
C(3)–C(4)
1.456(4)
1.475(4)
1.451(4)
1.460(4)
1.276(3)
1.536(4)
1.508(5)
Fig. 3 X-Ray crystal structure of 10
C(1)–N(1)–C(4)
C(4)–N(1)–C(7)
C(1)–N(2)–C(9)
C(2)–N(3)–C(5)
C(5)–N(3)–C(8)
N(1)–C(1)–N(2)
N(1)–C(1)–C(10)
N(2)–C(1)–C(10)
N(3)–C(2)–N(4)
N(4)–C(2)–C(1)
110.8(2)
117.5(2)
118.2(2)
106.3(2)
116.8(2)
102.1(2)
108.1(2)
115.8(2)
115.2(2)
120.6(2)
C(1)–N(1)–C(7)
C(1)–N(2)–C(3)
C(3)–N(2)–C(9)
C(2)–N(3)–C(8)
C(2)–N(4)–C(6)
N(1)–C(1)–C(2)
N(2)–C(1)–C(2)
C(2)–C(1)–C(10)
N(3)–C(2)–C(1)
N(2)–C(3)–C(4)
118.4(2)
108.4(2)
117.7(2)
127.5(2)
107.0(2)
115.3(2)
107.8(2)
107.9(2)
124.2(2)
101.6(2)
stituent at N(1) is in an equatorial site and ca. 0.6 Å above this
plane, while the other two substituents [C(24) and N(3)] are on
opposite sides of the ring with both ca. 1.0 Å out of the plane.
Each nitrogen atom in 11 or 12 is in a distorted pyramidal
Fig. 4 X-Ray crystal structure of 13
2050
J. Chem. Soc., Perkin Trans. 1, 1998

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Table 8 Selected bond lengths (Å) and angles (Њ) for the 1,1Ј-
dibenzyl-2,2Ј-biimidazoline 13
R
N
R
N
R
N
R
N
–R•
–R•
C
C
C
C
C
C
C
N(1)–C(1)
N(1)–C(8)
N(2)–C(4)
N(3)–C(5)
N(4)–C(6)
C(1)–C(2)
C(5)–C(6)
1.369(5)
1.453(4)
1.485(6)
1.481(6)
1.469(6)
1.480(6)
1.506(6)
N(1)–C(3)
N(2)–C(1)
N(3)–C(2)
N(4)–C(2)
N(4)–C(7)
C(3)–C(4)
1.468(6)
1.281(5)
1.276(5)
1.366(5)
1.449(5)
1.524(5)
N
R
N
R
N
•
N
R
R•
9
R
N
R
N
R
N
N
C
N
N
R
N
N
R
R
C(1)–N(1)–C(3)
C(3)–N(1)–C(8)
C(2)–N(3)–C(5)
C(2)–N(4)–C(7)
N(1)–C(1)–N(2)
N(2)–C(1)–C(2)
N(3)–C(2)–C(1)
107.7(3)
120.2(3)
105.4(3)
127.6(3)
117.1(4)
121.6(3)
121.9(3)
C(1)–N(1)–C(8)
C(1)–N(2)–C(4)
C(2)–N(4)–C(6)
C(6)–N(4)–C(7)
N(1)–C(1)–C(2)
N(3)–C(2)–N(4)
N(4)–C(2)–C(1)
126.8(3)
105.6(3)
106.2(3)
119.6(3)
121.3(3)
117.4(3)
120.5(3)
13
10
–R•
1/2 1
1/2 2
etc.
R
R
R
R
R
N
N
N
–R•
RH
CH
C• + 1/2
C
N
N
N
R
14
environment, implying that there is a stereochemically active
lone pair of electrons. The sum of the C᎐N᎐C angles at N(1)
and N(2) in 11 and 12 is closely similar, but at N(3) is 9.5Њ
greater in 11 than in 12, presumably because of the greater
steric strain in the latter. The N(2)᎐C(1)᎐N(3) bond angles are
greater than N(1)᎐C(1)᎐N(3) for both 11 and 12. The N᎐C
bond length mean values of 1.45(1) Å in 11 and 1.46(1) in 12
are unexceptional.
Scheme 2 Proposed mechanism for the debenzylation 9 → 13 and
10 → 14 and the isomerisation 9 → 10 (R = CH2Ph)
R
R
N
NH
C
S
N
R
17
The conformations of the five-membered rings in the isomer
10 of the enetetramine 9 differ. The saturated ring is envelope-
like, in which C(3) is ca. 0.52 Å below the N(2)᎐C(1)᎐N(1)᎐
C(4) plane and the substituent atoms on the two nitrogens are
equatorial and trans to one another, with C(7) ca. 0.78 Å above
and C(9) ca. 0.44 Å below the plane. The unsaturated ring in 10,
like both in the biimidazoline 13, is almost planar. The sum of
the angles at N(1), N(2) and N(3) in 10 and N(1) and N(4) in 13,
each bearing a benzyl group, shows that each of these nitrogen
atoms is closer to being trigonal planar than pyramidal. The
NH
R
iv + v
R
R
NPh
S–
N
+
N
+
iv + vi
X–
C
N
N
R
18
R
iv + vii
i
iii
8 (X = Cl)
R
NH
C᎐N and C(sp2)᎐N bond lengths in 10 and 13 have similar
iv
᎐
NCHO
values of 1.276(3) and a mean of 1.279(5) and 1.392(2) and a
mean of 1.367(4) Å, respectively.
R
19
The amino-Claisen rearrangement of 9 → 10 has prece-
R
R
N
R
dents in (i) the transformations of eqn. (3),20 (ii) 1 → 1Ј
H
N
C
N
N
N
ii
C
R
N
R
N
R
N
NMe2
CH2Ph
N
CH2Ph
N
S
S
viii
C
C
C
C
(3)
16
15
20
N
S
N
S
PhCH2
Scheme 3 Routes to derivatives of the transient enetetramine 3
(R = RЈ = CH2Ph). Reagents and conditions: i, CH(NMe2)2(OBut),
75 ЊC, 2 h; ii, PhMe, 110 ЊC, 3 h; iii, CH(NMe2)(OMe)2, PhMe, 110 ЊC,
2 h; iv, NaH, THF, 20 ЊC, 8 h; v, S8; vi, PhNCS; vii, KOH, H2O–EtOH,
75–80 ЊC, 2 h; viii, Me2C6H4, 140 ЊC, 2 h.
CH2Ph
(R = CH CH᎐CH ),15 and (iii) 2 (n = 2 or 3, m = 2 or 3,
᎐
2
2
R = CH2Ph) to the isomer 2Ј.21 The mechanism of the photo-
chemical isomerisation for case (ii) was considered to be at least
in part intermolecular because of the nature of 1Ј when
R = crotyl.15 The debenzylation reactions 9 → 13 and
10 → 14, likewise, are almost certainly free radical in char-
acter, as evident from the concomitant formation of bibenzyl in
each case.
Bredereck’s reagent, and then 16 was heated (i and ii in Scheme
3) also afforded 15. Evidence was therefore sought for at least
the transient formation of the tetrabenzylenetetramine 3
(R = RЈ = CH2Ph) from 8 (X = Cl) and NaH, by trapping reac-
tions, using S8, PhNCS or KOH, which yielded the thiourea 17,
the zwitterion 18 and N,NЈ-bisbenzyl-N-formyl-1,2-diamino-
benzene 19 (v, vi and vii in Scheme 3). The benzylbenzimidazole
20, upon heating, underwent debenzylation and C᎐C coupling
to give 15 (viii in Scheme 3), presumably by a radical coupling
mechanism. Related bis(benzimidazoles) are known.22
The thermal instability of the tetrabenzylenetetramine 3
(R = RЈ = CH2Ph) is attributed to steric effects, as may be
judged by examining X-ray crystallographic data on 912 and 3
(R = RЈ = Me),3 both being stable in toluene up to ca. 100 ЊC.
The latter has each fused bicyclic moiety coplanar, with the
methyl groups bent out of the plane on opposite sides of the
fused rings, the two ends of the molecules twisted with respect
Suggested mechanisms for the isomerisation 9 → 10 and
the debenzylations 9 → 13 and 10 → 14 (viii, ix and vii,
respectively in Scheme 1) are shown in Scheme 2.
Attempts to prepare the tetrabenzylenetetramine 3 (R = RЈ =
CH2Ph), using either 1,2-bis(dibenzylamino)benzene and the
acetal CH(NMe2)(OMe)2, or the corresponding 1,2-N,NЈ-
dibenzylbenzimidazolium chloride 8 (X = Cl) and NaH (iii and
iv in Scheme 3) proved to be unsuccessful, the bis(debenzylated)
product 15 being obtained instead. This is surprising, because
both methods had been effective in the preparation of the
analogous tetramethylenetetramine 3 (R = RЈ = Me).3 Further-
more, an alternative strategy whereby 1,2-bis(dibenzyl-
amino)benzene was converted into the orthoamide 16, using
to one another by ca. 21Њ about the central C᎐C bond, thus
᎐
J. Chem. Soc., Perkin Trans. 1, 1998
2051

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reducing the steric strain between adjacent methyl groups.3 The
molecular structure of 9 showed that the conformation of the
five-membered rings was such that the central NCNЈ planes are
amine and methanol to escape. From the resultant product,
unreacted starting materials were eliminated in vacuo. Pentane
was added to the yellow residual oil and the mixture was filtered
through Celite. After elimination of volatiles from the filtrate
in vacuo, 10a (2.55 g, 58%) was obtained. δH(C6D6) 2.4 and 2.7
(AB system, dq, 4H, saturated ring-H), 2.8 and 3.3 (AB system,
dt, 4H, unsaturated ring-H), 2.8 (m, 4H, NCH2, saturated ring),
3.0 and 3.2 (AB system, m, 2H, NCH2, rearranged group), 3.9
twisted by ca. 17Њ with respect to one another about the C᎐C
᎐
bond, and the other two endocyclic carbon atoms are out of the
NCNЈ plane: above for one ring and below for the other.12 The
sum of angles at the four nitrogens is ca. 331Њ in 912 and ca. 342Њ
in 3 (R = RЈ = Me).3
(d, 2H, NCH , unsaturated ring), 4.9 (m, 8H, ᎐CH ), 5.6 (m,
᎐
2
2
3H, ᎐CH᎐, rearranged and attached saturated ring), 5.9 (m, 1H,
᎐
Experimental
᎐CH᎐, attached unsaturated ring). δ (C D ) 39.41 (NCH ,
᎐
C
6
6
2
rearranged group), 48.93 (saturated ring), 51.96, 52.39
(unsaturated ring), 52.08 (NCH2, attached saturated ring),
52.51 (NCH2, attached unsaturated ring), 81.93 (C-2, saturated
ring), 165.72 (C-2, unsaturated ring).
General procedures and starting materials
All experiments were performed under argon or dinitrogen
1
using freshly distilled dry solvents. H and 13C NMR spectra
were recorded using a Bruker WM360 or a Bruker AMX-500
spectrometer. J Values are given in Hz. IR and mass spectra
were obtained on a Perkin-Elmer 597 and a Kratos MS902
instrument, respectively. Melting points were recorded using an
electrothermal melting point apparatus and are uncorrected.
The starting compounds, not available commercially, were
prepared according to the procedures described in the
literature. But the procedure for N,NЈ-dibenzyl-o-phenylene-
diamine, involving the reaction of the 1,3-dibenzylbenzimid-
azolium chloride and aqueous KOH gave in our hands N-
formyl-N,NЈ-dibenzyl-o-phenylenediamine 19. Therefore, we
adopted another method (cf. ref. 23) which has not been
described in the literature.
Preparation of 2-dimethylamino-1,3-dibenzylimidazolidine 11
Cooled (Ϫ30 ЊC) dimethylamine (1.5 cm3, 22.6 mmol) was
added to a solution of the enetetramine 9 (2.85 g, 5.7 mmol) in
THF (20 cm3). The mixture was stirred at ca. 20 ЊC for 18 h.
Volatiles were removed under reduced pressure to leave a yellow
oil, which was dissolved in n-hexane (10 cm3) and cooled to
Ϫ78 ЊC. The white precipitate of 11 (2.80 g, 83%) was recrystal-
lised from Et2O (10 cm3) and n-hexane (10 cm3) at Ϫ78 ЊC.
Preparation of 2-dimethylamino-1,3-diethylimidazolidine 11a
(11, R ؍ Et)
A mixture of 1,2-bis(ethylamino)ethane (3.24 g, 28 mmol) and
tert-butoxybis(dimethylamino)methane (5.04 g, 29 mmol) was
stirred at ca. 20 ЊC for 100 min. Volatile unreacted starting
materials were eliminated in vacuo. n-Hexane was added to the
yellow residual oil and the mixture was filtered through Celite.
After hexane elimination in vacuo from the filtrate, 11a (2.7 g,
56%) was obtained as a dense yellow oil.
Preparation of 1,2-bis(benzylamino)benzene
Benzoyl chloride (23 cm3, 194.4 mmol) was added dropwise to
a solution of 1,2-diaminobenzene (10 g, 92.59 mmol) and
pyridine (15 cm3) in THF (50 cm3). The precipitate, 1,2-
C6H4(NHCOPh)2 (28.9 g, 99%) was filtered off, washed with
diethyl ether (2 × 25 cm3) and dried at 100 ЊC. A portion of the
latter (10 g, 31.64 mmol) in THF (150 cm3) was added dropwise
to a stirred suspension of LiAlH4 (6 g, 163 mmol). The mixture
was heated under reflux for 3 h, then cooled in an ice-bath and
the remaining hydride was carefully quenched by dropwise add-
ition of water and then 15% aqueous NaOH (10 cm3). The
white precipitate was filtered off and thoroughly washed with
diethyl ether. The combined filtrate and washings were washed
with water, and dried (Na2SO4). Volatiles were evaporated in
vacuo and the residue was recrystallised from ethanol to yield
yellow crystals of the title amine (7.38 g, 81%).
Preparation of 2-dimethylamino-1,3-diallylimidazolidine 11b
(11, R ؍ CH CH᎐CH )
᎐
2
2
A mixture of 1,2-bis(allylamino)ethane (1.5 g, 10.71 mmol) and
tris(dimethylamino)methane (1.6 g, 11.03 mmol) was refluxed in
hexane for 2 h under distillation conditions; ca. half of the sol-
vent was eliminated and the mixture cooled to Ϫ30 ЊC to afford,
after filtration and washing with cold hexane, 11b (1.82 g, 87%).
Isolation of the bis(orthoamide) 12
A mixture of 1,2-bis(benzylamino)ethane (10 cm3, 41.6 mmol)
and dimethylformamide dimethyl acetal (5.7 cm3, 43 mmol) in
cyclohexane (20 cm3) was heated, keeping the bath temperature
below 100 ЊC and allowing the formed MeOH and Me2NH to
be distilled off. In order to complete the reaction, a small
portion of the cyclohexane (ca. 5 cm3) was also distilled off.
Volatiles were removed at ca. 25 ЊC/10Ϫ2 Torr. The residue was
extracted into toluene (2 cm3) and n-hexane (10 cm3) and the
extract was filtered. Upon cooling, the filtrate yielded white
needles of the bis(orthoamide) 12 (5.85 g).
Preparation of the rearranged product 10 from the enetetramine 9
(R ؍ CH2Ph)
A suspension of the enetetramine 9 (1.84 g, 3.68 mmol)11 in
diethyl ether (60 cm3) was irradiated using a medium pressure
mercury UV-lamp at ca. 20 ЊC for 8 h. Volatiles were removed in
vacuo, and the residue was dissolved in warm n-hexane (10
cm3). On cooling to ca. 20 ЊC, cubic crystals of 10 (1.76 g, 96%)
were obtained. δH(C6D6) 2.51 and 2.75 (AB system, dq, 4H,
saturated ring-H, JHAHB 8.35), 2.93 and 3.68 (A2X2 system, dt,
4H, unsaturated ring-H, JHAHX 9.6), 3.69 and 4.10 (AB system,
dd, 4H, CH2Ph attached to saturated ring nitrogens, JHAHB 13.4),
3.74 (s, 2H, CH2Ph attached to C), 4.68 (s, 2H, CH2Ph attached
to unsaturated ring nitrogen), 7.12–7.75 (m, 20H, aromatic
protons). δC(C6D6) 39.67 (CH2Ph attached to C), 47.97 (C of
saturated ring), 51.97, 52.39 (C of unsaturated ring), 53.30
(NCH2Ph of saturated ring), 53.72 (NCH2Ph of unsaturated
ring), 83.59 (C-2 of saturated ring), 166.35 (C-2 of unsaturated
ring).
Preparation of the enetetramine 9 (cf. ref. 11)
The reaction described above for 12 was carried out in methyl-
cyclohexane (100 cm3), using the diamine (40.9 g, 170.6 mmol)
and the acetal (24 cm3, 180.9 mmol) at a higher temperature (oil
bath at 90 ЊC for 3 h and then 120 ЊC for 1 h). Cream crystals of
9 (13.5 g, 31.7%) were obtained upon cooling to ca. 20 ЊC. The
filtrate was evaporated in vacuo to give an oily residue which,
upon crystallisation from n-hexane (30 cm3), yielded further
crystals of 9 (12.0 g).
Preparation of 10a (10, R ؍ CH CH᎐CH )
᎐
2
2
A stirred solution of N,N-dimethylformamide dimethyl acetal
(4.9 g, 40 mmol) and 1,2-bis(allylamino)ethane (4.37 g, 30
mmol) was heated under reflux for 3 h at 90 ЊC under an argon
atmosphere. The reaction mixture was then heated at 120 ЊC
under distillation conditions, allowing the produced dimethyl-
Conversion of 12 into 9
A solution of 12 (1.8 g, 3.6 mmol) in toluene (30 cm3) was
heated under reflux for 3 h. The solution was cooled to 20 ЊC,
the volume was reduced to ca. 10 cm3 and n-hexane (10 cm3)
was added yielding crystals of 9 (1.71 g, 95%).
2052
J. Chem. Soc., Perkin Trans. 1, 1998

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Table 9 Crystal data and final refinement parameters for compounds 11, 12, 10 and 13
Compound
Molecular formula
M
Crystal size/mm
Crystal system
Space group
11
12
C50H56N6
741.04
0.4 × 0.1 × 0.25
Triclinic
¯
P1
10
C34H36N4
500.69
0.4 × 0.25 × 0.20
Triclinic
¯
P1
13
C20H22N4
318.42
0.17 × 0.15 × 0.10
Triclinic
¯
P1
C19H25N3
295.45
0.4 × 0.5 × 0.45
Monoclinic
P21/n
a/Å
b/Å
c/Å
α/Њ
11.663(1)
5.958(2)
25.268(3)
—
98.72(1)
—
1735.5
4
1.13
6.153(3)
12.178(2)
14.251(2)
89.04(1)
83.84(2)
81.89(3)
1051.2
1
10.939(3)
12.107(2)
12.456(1)
115.27(1)
106.47(2)
94.11(1)
1394.8
2
6.865(4)
9.018(3)
14.560(3)
88.44(2)
88.67(3)
71.59(4)
854.8
2
1.29
340
0.73
β/Њ
γ/Њ
U/Å3
Z
Dc/g cmϪ3
F(000)
1.17
398
0.64
1.19
536
0.66
640
0.63
µ (cmϪ1
)
θ range/Њ
Observed reflections with
0–22
959
0–25
1926
0–25
2446
0–25
1304
I > σ(I)
R1
0.051
0.060
0.2
0.066
0.082
0.2
0.044
0.051
0.2
0.045
0.044
0.5
wR
∆ρmax/e ÅϪ3
¹
2
2
a R1 = (Σ||Fo| Ϫ |Fc||)/(Σ|Fo|). b wR = {[Σw(|Fo| Ϫ |Fc|) ]/(Σw|Fo| )} .
²
Conversion of 11 into 9
the debenzylation, but only 15 was obtained, rather than the
enetetramine 3 (R = RЈ = CH2Ph).
2-Dimethylamino-1,3-dibenzylimidazolidine 11 (0.25 g, 0.85
mmol) in cyclohexane (3 cm3) was refluxed for 90 min. The
formerly colourless solution became yellow. Upon cooling to
ca. 20 ЊC, pale yellow crystals of 9 (0.2 g, 95.2%) were
deposited.
Preparation of the orthoamide 16
A mixture of 1,2-bis(benzylamino)benzene (2 g, 6.94 mmol)
and tert-butoxybis(dimethylamino)methane (2.2 cm3, 7.94
mmol) was stirred at ca. 20 ЊC for 2 h, then heated at 75 ЊC for
2 h. Volatiles were eliminated in vacuo. n-Hexane (30 cm3) was
added to the residue and the mixture was filtered. The filtrate
was concentrated to ca. half of the original volume. Upon
cooling, cream crystals of compound 16 (1.38 g, 58%) were
obtained.
Reaction of the enetetramine 9 with 1,2-bis(benzylamino)ethane
A mixture of 9 (1.27 g, 2.54 mmol) and the diamine (0.65 g, 27
mmol) in THF (10 cm3) was stirred at ca. 20 ЊC for 4 h. Volatiles
were removed in vacuo. n-Hexane (20 cm3) was added with
shaking to the cream residue. The cream precipitate was separ-
ated by filtration and identified as 12 (0.6 g, 47.2%). After 2 d at
ca. 20 ЊC, the filtrate yielded white crystals of 9 (0.49 g, 33%).
Conversion of the orthoamide 16 into 15
A solution of compound 16 (1 g, 2.92 mmol) in toluene (10
cm3) was refluxed for 3 h. The volume of the solution was then
concentrated to ca. half of the initial volume and n-hexane
(3 cm3) was added. Upon cooling (Ϫ30 ЊC), white crystals of
15 (0.5 g, 85%) were obtained.
Debenzylation of the enetetramine 9
A solution of 9 (0.9 g, 1.8 mmol) in xylene (10 cm3) was heated
under reflux for 6 h. The volume of the solution was reduced to
ca. 4 cm3 and n-hexane (6 cm3) was added. Upon cooling to
Ϫ30 ЊC, cream crystals of 1,1Ј-dibenzyl-2,2Ј-biimidazoline 13
(0.4 g, 70%) were obtained. Gas chromatographic analysis of
the filtrate showed it to comprise a mixture of 13, toluene and
bibenzyl.
Preparations of compounds 17 and 18
In order to trap 3 (R = RЈ = CH2Ph) during the formation of
15, elemental sulfur (0.16 g, 0.63 mmol) was added to a mixture
of 8 (X = Cl) (1.7 g, 5.14 mmol) and NaH (0.13 g, 5.42 mmol).
After stirring for 2 h at ca. 20 ЊC and then at 80 ЊC for 1 h,
volatiles were removed in vacuo and the residue was extracted
with toluene. Addition of n-hexane and cooling to Ϫ30 ЊC
yielded white crystals of the thiourea 17 (1.08 g, 65%).
Similar to the above procedure, but in place of sulfur, PhNCS
(0.6 cm3, 5.03 mmol) was added to a mixture of 8 (X = Cl)
(1.7 g, 5.14 mmol) and NaH (0.13 g, 5.42 mmol). Stirring for 2 h
at ca. 20 ЊC and similar work-up afforded compound 18 (1.13 g,
52%).
Preparation of 15 and 20 from 8 (X ؍ Cl)
To a suspension of 8 (X = Cl) (5 g, 16.95 mmol) in THF (60
cm3) was added NaH (0.4 g, 16.66 mmol). The mixture was
stirred for 8 h at ca. 20 ЊC. The solvent was removed in vacuo,
toluene (100 cm3) was added and the suspension was filtered.
The resultant bright yellow filtrate was concentrated to ca. 20
cm3 and n-hexane (10 cm3) was added. Upon cooling, white
crystals of the bis(benzimidazole) 15 (3.8 g, 56%) were
obtained. Upon further cooling of the mother liquor, 1,2-
dibenzylbenzimidazole 20 (0.6 g, 14%) was obtained.
Preparation of 19
Preparation of 15 from 1,2-bis(benzylamino)benzene
Compound 19 (1.8 g, 76%) was isolated when 8 (X = Cl) (2.5 g,
7.47 mmol) and KOH (1.5 g, 26.78 mmol) in technical alcohol
(IMS) (25 cm3) were heated under reflux for 2 h.
A stirred solution of the diaminobenzene (5 g, 17.36 mmol) and
N,N-dimethylformamide dimethyl acetal (2.5 cm3, 19.13 mmol)
in toluene (15 cm3) was heated at 90 ЊC for 2 h and then at 145–
150 ЊC under distillation conditions for 30 min in an argon
atmosphere, allowing the produced dimethylamine and meth-
anol to distil off. The volatiles were removed in vacuo. The oily
residue in a toluene–n-hexane (2:1) mixture was cooled to
Ϫ30 ЊC, yielding 15 (5.7 g, 80%). This reaction was repeated
using a water bath at 90 ЊC for 4 h, in an attempt to avoid
X-Ray crystallography
In each case, a crystal was sealed in a Lindemann glass capillary
under argon and data collected on an Enraf-Nonius CAD4 dif-
fractometer at ambient temperature using monochromated
Mo-Kα radiation (λ = 0.710 69 Å). Cell dimensions were calcu-
lated from setting angles for 25 reflections with 7 < θ < 10Њ.
J. Chem. Soc., Perkin Trans. 1, 1998
2053

View Online
Recl., 1997, 365, and refs. cited therein; (b) W. A. Herrmann and
C. Köcher, Angew. Chem., Int. Ed. Engl., 1997, 36, 2163.
10 H. E. Winberg, J. E. Carnahan, D. D. Coffman and M. Brown,
J. Am. Chem. Soc., 1965, 87, 2055.
Intensities were measured by ω Ϫ 2θ scans and corrected
for Lorentz and polarisation effects but not for absorption.
Structure solution was by direct methods using MULTAN;24
and refinement, using the Enraf-Nonius MOLEN25 programs
was by full-matrix least-squares on F using reflections with
I > σ(I) and weighting scheme of w = 1/σ2( F ). Non-H atoms
were refined anisotropically. For 10 and 12 the H atoms were
refined isotropically, while for 11 and 13 the H atoms were fixed
at calculated positions with Biso = 6.0 Å2. Crystal data are in
Table 9.
11 P. B. Hitchcock, M. F. Lappert and P. L. Pye, J. Chem. Soc., Dalton
Trans., 1977, 2160.
12 E. Çetinkaya, P. B. Hitchcock, H. A. Jasim, M. F. Lappert and
K. Spyropoulos, J. Chem. Soc., Perkin Trans. 1, 1992, 561.
13 A. W. Coleman, P. B. Hitchcock, M. F. Lappert, R. K. Maskell and
J. H. Müller, J. Organomet. Chem., 1985, 296, 173.
14 P. B. Hitchcock, M. F. Lappert, P. Terreros and K. P. Wainwright,
J. Chem. Soc., Chem. Commun., 1980, 1180.
15 J. A. Chamizo and M. F. Lappert, J. Org. Chem., 1989, 54, 4684.
16 J. A. Chamizo, P. B. Hitchcock, H. A. Jasim and M. F. Lappert,
J. Organomet. Chem., 1993, 451, 89.
Acknowledgements
17 (a) H.-W. Wanzlick, F. Esser and H.-J. Kleiner, Chem. Ber., 1963, 96,
1208; (b) H.-W. Wanzlick and E. Schikora, Angew. Chem., 1960, 72,
494.
18 (a) R. W. Alder and M. E. Blake, Chem. Commun., 1997, 1513; (b)
M. Wenzel, D. Lindauer, R. Beckert, R. Boese and E. Anders, Chem.
Ber., 1996, 129, 39; (c) M. K. Denk, A. Thadani, K. Hatano and
A. J. Lough, Angew. Chem., Int. Ed. Engl., 1997, 36, 2607.
19 J. Daub, A. Hasenhündl, K. P. Krenkler and J. Schmetzer, Liebigs
Ann. Chem., 1980, 997.
20 J. E. Baldwin, S. E. Branz and J. A. Walker, J. Org. Chem., 1977, 42,
4142; J. E. Baldwin and J. A. Walker, J. Am. Chem. Soc., 1974, 96,
596.
21 K. Spyropoulos, D.Phil. Thesis, University of Sussex, 1985.
22 K. H. Taffs, L. V. Prosser, F. B. Wigton and M. M. Joullié, J. Org.
Chem., 1961, 26, 462.
23 S. Miyano, M. Nawa, A. Mori and H. Hashimoto, Bull. Chem. Soc.
Jpn., 1984, 57, 2171.
24 C. K. Fair, MOLEN—a Structure Determination System, Enraf-
Nonius, Delft, 1990.
25 P. Main, G. Germain and M. Woolfson, MULTAN—a Program
for Automatic Solution of Crystal Structures, University of York,
1984.
We thank Universidad Nacional Autonoma de Mexico for a
grant to J. A. C. and the Government of Iraq for a grant to
H. A. J. and the EPSRC for other support.
References
1 B. Çetinkaya, P. B. Hitchcock, M. F. Lappert, D. B. Shaw,
K. Spyropoulos and N. J. W. Warhurst, J. Organomet. Chem., 1993,
459, 311.
2 M. F. Lappert, J. Organomet. Chem., 1988, 358, 185.
3 E. Çetinkaya, P. B. Hitchcock, H. Küçükbay, M. F. Lappert and
S. Al-Juaid, J. Organomet. Chem., 1994, 481, 89.
4 H. Goldwhite, J. Kaminski, G. Millhauser, J. Ortiz, M. Vargas,
L. Vertal, M. F. Lappert and S. J. Smith, J. Organomet. Chem., 1986,
310, 21.
5 B. Çetinkaya, G. H. King, S. S. Krishnamurthy, M. F. Lappert and
J. B. Pedley, J. Chem. Soc., Chem. Commun., 1971, 1370.
6 M. F. Lappert and R. K. Maskell, J. Chem. Soc., Chem. Commun.,
1982, 580.
7 R. W. Hoffmann, Angew. Chem., Int. Ed. Engl., 1968, 11, 754;
J. Hocker and R. Merten, Angew. Chem., Int. Ed. Engl., 1972, 11,
964; F. Roeterdink, J. W. Scheeren and W. H. Laarhoven,
Tetrahedron Lett., 1983, 24, 2307.
8 D. J. Cardin, M. J. Doyle and M. F. Lappert, J. Chem. Soc., Chem.
Commun., 1972, 927.
Paper 8/02123F
Received 17th March 1998
Accepted 8th May 1998
9 (a) A. J. Arduengo, J. R. Goerlich and W. F. Marshall, Liebigs Ann.
2054
J. Chem. Soc., Perkin Trans. 1, 1998