Synthesis of some very bulky N,N′-disubstituted amidines and initial studies of their coordination chemistry

Article abstract of DOI:10.1039/a805548c

N,N′-Bis(2,6-diisopropylphenyl)-4-toluamidine, -4-anisylamidine and -acetamidine have been prepared for the first time from 2,6-diisopropylaniline and the acid chlorides via the corresponding imidoyl chlorides. The crystal structures of all three amidines were determined, indicating that the first is a disordered mixture of Z-anti and E-syn tautomeric forms, the second Z-anti, and the third E-anti in the solid state. Despite these differences, all three form identical coordination complexes with Mo(CO)₃ in which the ligand is in the Z-anti geometry, and the metal is π-coordinated to the imino 2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards metal. The coordination mode was confirmed by single-crystal X-ray structure determination of the toluamidine and methylamidine complexes with Mo(CO)₃. In the case only of the methylamidine, an isolable intermediate is first formed in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)₅ unit. The crystal structure of this complex shows that the ligand is in the E-anti geometry, with the imino nitrogen coordinated to Mo, d(Mo-N) = 2.352(2) A. The structures are closely related in that the initial Mo(CO)₅ N-coordination sets up the metal for conversion to the more thermodynamically stable π-coordinated Mo(CO)₃ complex. The high steric bulk of these superamidine ligands is seen in the failure of any of them to form the metal-metal bonded Mo₂(amidinate)₄ complexes typically prepared using common, less bulky, amidines.

Full text of DOI:10.1039/a805548c

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Synthesis of some very bulky N,NЈ-disubstituted amidines and
initial studies of their coordination chemistry†
René T. Boeré,a Vicki Klassena and Gotthelf Wolmershäuserb
a Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge,
Alberta T1K 3M4, Canada. E-mail: boere@uleth.ca
b Fachbereich Chemie der Universität Kaiserslautern, Erwin-Schrödinger-Straße,
D-67663 Kaiserslautern, Germany
Received 17th July 1998, Accepted 21st October 1998
N,NЈ-Bis(2,6-diisopropylphenyl)-4-toluamidine, -4-anisylamidine and -acetamidine have been prepared for the first
time from 2,6-diisopropylaniline and the acid chlorides via the corresponding imidoyl chlorides. The crystal structures
of all three amidines were determined, indicating that the first is a disordered mixture of Z-anti and E-syn tautomeric
forms, the second Z-anti, and the third E-anti in the solid state. Despite these differences, all three form identical
coordination complexes with Mo(CO)3 in which the ligand is in the Z-anti geometry, and the metal is π-coordinated
to the imino 2,6-diisopropylphenyl ring, and the amino N–H unit is directed towards metal. The coordination mode
was confirmed by single-crystal X-ray structure determination of the toluamidine and methylamidine complexes with
Mo(CO)3. In the case only of the methylamidine, an isolable intermediate is first formed in which the neutral amidine
is coordinated in a monodentate fashion to an Mo(CO)5 unit. The crystal structure of this complex shows that the
ligand is in the E-anti geometry, with the imino nitrogen coordinated to Mo, d(Mo–N) = 2.352(2) Å. The structures
are closely related in that the initial Mo(CO)5 N-coordination sets up the metal for conversion to the more thermo-
dynamically stable π-coordinated Mo(CO)3 complex. The high steric bulk of these superamidine ligands is seen in the
failure of any of them to form the metal–metal bonded Mo2(amidinate)4 complexes typically prepared using
common, less bulky, amidines.
Mo(CO)6 differs significantly from that previously found for
Introduction
analogous non-bulky amidines, such as N,NЈ-diphenylbenz-
So-called “super-bulky” substituents were originally developed
amidine, which was investigated many years ago by Cotton and
in order to stabilize low-coordinate main-group elements of the
Kilner.6 In particular, whereas heating diphenylbenzamidine
3rd period and beyond, allowing, to name one famous example,
together with Mo(CO)6 produced the quadruply-bonded
Yoshifuji to isolate the first compound containing a P᎐P double
᎐
dimolybdenum complex 3, albeit in poor yield, we find that
analogous reactions of the bulky superamidines produced
two kinds of products, an N-coordinated LMo(CO)5 complex
and/or a half-sandwich LMo(CO)3 complex in which one of
the aryl rings of the ligand is π-complexed to Mo(CO)3. The
Cotton reaction is completely blocked, and there is no evi-
dence of any metal complex in a higher oxidation state than
Mo(0).
bond.1 Such substituents have since found extensive application
in many areas of main-group chemistry, including some of the
2nd period elements, e.g. boron.2 Chemists who incorporate
these substituents have always been aware that their large bulk
may have created some perturbation of the bonds they were
investigating, but in any case had no choice; lowering the
bulk only slightly could lead to decomposition of the thermo-
dynamically stable, but kinetically unstable bond, usually via a
polymerization reaction. In view of these facts, it is surprising
that more attention has not been given to making analogous
compounds using these substituents with the elements that do
not intrinsically need them for kinetic stabilization, e.g. the
second-period elements such as C, N and O. Here direct
comparison between analogous crowded and non-crowded
molecules ought to be possible, and the influence of the steric
bulk should be evident, and indeed often quantifiable.
It is our contention that the use of super-bulky substituents
on these elements will also lead to unique patterns of reactivity,
and in this work we report on the application of one such
group, the 2,6-diisopropylphenyl (Dip) substituent3 1, to N,NЈ-
disubstituted amidine ligands 2. Somewhat less bulky substitu-
ents (trimethylsilyl,4 cyclohexyl5) have already found extensive
application in amidinate metal complexes. We demonstrate that
the super-bulky substituent does not prevent the synthesis of
the ligands themselves, which have been prepared by fairly
straightforward modifications of classical amidine synthetic
procedures, nor do they fail to react with transition elements.
Nevertheless, the course of the reactions with, in this case,
Complexes of neutral monodentate amidines are rare.7
Recently Bailey has reported Agϩ and Co2ϩ complexes of
triphenylguanidine (which can act as an amidine in mono-
dentate or bidentate coordination modes),8 and Cotton has
reported several complexes of N,NЈ-diphenylformamidine with
Agϩ and divalent Mn, Co and Ni ions.9 The only zero-valent
Group 6 metal complex of a neutral amidine that we are
aware of before this work is Raubenheimer’s (OC)5W–
NH᎐C(NMe )Ph.10 This complex is produced, via an imidate
complex, by NH insertion into a metal–carbene bond, rather
than through thermal reaction with the metal carbonyl, and in
contrast to our LMo(CO)5 complex, is found in solution in two
isomeric forms.
᎐
2
† Part of this work was presented at the 31st International Conference
on Coordination Chemistry, Vancouver, Canada, August 18–23, 1996.
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Table 1 Crystal data and structure refinement
Compound
7a
7b
7c
8a
8c
9c
Formula
M
C32H42N2
454.68
C32H42N2O
470.68
C26H38N2
378.58
C35H42MoN2O3 C29H38MoN2O3 C31H38MoN2O5
634.65
558.55
614.57
T/K
λ(Mo-Kα)/Å
Scan mode
Crystal system
293(2)
0.71073
ω scans
Monoclinic
P21/c
293(2)
0.71073
φ oscillation
Monoclinic
P21/c
293(2)
0.71073
φ oscillation
Orthorhombic
C2221
293(2)
293(2)
0.71073
φ oscillation
Monoclinic
P21/n
293(2)
0.71073
φ rotation
Monoclinic
P21/c
0.71073
φ rotation
Triclinic
¯
P1
Space group
a/Å
b/Å
c/Å
α/Њ
18.409(2)
9.9850(10)
17.6590(10)
18.269(2)
10.1220(10)
17.899(2)
14.9260(10)
20.1330(10)
16.671(2)
9.7485(12)
10.5118(13)
18.577(3)
73.567(11)
80.949(11)
64.730(10)
1649.7(4)
2
10.8448(11)
19.285(2)
14.3146(14)
10.9975(10)
21.7750(18)
14.5403(13)
β/Њ
117.130(10)
117.717(9)
101.993(8)
111.524(7)
γ/Њ
V/Å3
2888.8(5)
4
1.045
2930.1(5)
4
1.067
5009.7(7)
8
1.004
2928.5(5)
4
1.267
3239.2(5)
4
1.260
Z
Dc/Mg mϪ3
1.278
0.432
µ/mmϪ1
0.060
0.064
0.058
0.477
0.442
F(000)
Crystal
Reflections collected
Independent reflections
Rint
Final R indices [I > 2σ(I)]
R1, wR2
992
1024
Colourless block
20572
5646
0.0393
1664
Colourless block
22132
5435
0.0466
664
Yellow plate
17169
6303
0.0686
1168
Yellow plate
61104
8322
0.0655
0.0420, 0.1093
1280
Yellow prism
25416
6135
0.0526
0.0370, 0.1001
Colourless block
6226
5026
0.0275
0.0580, 0.1262
0.0561, 0.1570
0.0466, 0.1186
0.0418, 0.1029
R indices (all data) R1, wR2
0.1395, 0.1524
0.0769, 0.1728
0.0802, 0.1385
0.0627, 0.1120
0.0683, 0.1240
0.0512, 0.1086
characterized by elemental analysis, mass spectrometry as well
Results and discussion
Ligand synthesis
1
as H and 13C NMR spectroscopy. The details are given in the
Experimental section. Using these procedures, superamidines
can readily be prepared at low cost and in high yield on a
reasonable scale for their further use as ligands in coordination
chemistry.
Our synthesis follows a classical route for the synthesis of N,NЈ-
disubstituted amidines,11 but each step of the procedure
required extensive changes and optimization. The procedure is
outlined in Scheme 1, and the particulars of each step are
Isomers and tautomers. Both isomers and tautomers are
expected for N,NЈ-disubstituted amidines,12 and it was immedi-
1
ately obvious from the H NMR spectra of all three amidines
that more than one isomer was present in solution. (In each
case, the minor isomer is also undergoing a dynamic process in
solution at room temperature; for simplicity, the NMR para-
meters of the major solution species only are reported in the
Experimental section.) The possible isomers and their tauto-
meric forms are outlined in Scheme 2. The tautomers for the
Scheme 1
detailed in the Experimental section. The major modifications
that were required reflected the high solubility of all diiso-
propylphenyl-containing compounds in non-polar solvents
and/or their extreme insolubility in water. Commercially avail-
able 2,6-diisopropylaniline 4, was converted to the corre-
sponding amides of acetic 5c, 4-methylbenzoic 5a, or
4-methoxybenzoic acid 5b, via the corresponding acid chlor-
ides. Dehydration and chlorination produced the imidoyl-
chlorides 6, which for the aryl acids could be isolated, but for
the acetic acid derivative was prepared in situ. The imidoyl-
chlorides reacted directly with a second equivalent of 4 to pro-
duce the acid chloride salts of the desired amidine, which were
readily converted to the free amidines 7, using 25% aqueous
ammonia. All of these compounds are new, and have been fully
Scheme 2
E-anti and Z-syn isomers are degenerate, while the Z-anti and
E-syn isomers are related by tautomerism. It was not obvious
from the spectroscopic information which isomers or tautomers
we were dealing with. We therefore elected to measure the crys-
tal structures of all three. The details of the crystallographic
structure determinations are compiled in Tables 1 and 2. Ball-
and-stick perspective diagrams of the amidines and the metal
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Table 2 Selected interatomic distances (Å) and angles (Њ)
7a
N(1)–C(1)
1.344(3)
1.317(3)
0.027(6)
1.422(3)
1.429(3)
1.483(3)
C(1)–N(1)–C(9)
C(1)–N(2)–C(21)
N(2)–C(1)–N(1)
N(2)–C(1)–C(2)
N(1)–C(1)–C(2)
129.9(2)
119.40(18)
120.4(2)
116.43(19)
123.1(2)
N(2)–C(1)
a
∆
CN
N(1)–C(9)
N(2)–C(21)
C(1)–C(2)
7b
N(1)–C(1)
1.3633(17)
1.3066(17)
0.057(3)
1.4294(17)
1.4262(17)
1.4890(18)
0.92(2)
C(1)–N(1)–C(9)
C(1)–N(2)–C(21)
N(2)–C(1)–N(1)
N(2)–C(1)–C(2)
N(1)–C(1)–C(2)
131.14(12)
119.49(11)
121.38(12)
117.04(11)
121.53(11)
N(2)–C(1)
a
∆
CN
N(1)–C(9)
N(2)–C(21)
C(1)–C(2)
N(1)–H(1)
7c
N(1)–C(1)
1.324(2)
1.330(2)
0.006(4)
1.427(2)
1.425(2)
1.493(3)
0.97(2)
C(1)–N(1)–C(9)
C(1)–N(2)–C(21)
N(2)–C(1)–N(1)
N(2)–C(1)–C(2)
N(1)–C(1)–C(2)
N(2)–H(1)–N(1Ј)
121.9(1)
122.9(1)
117.4(1)
121.2(2)
121.4(2)
171(5)
N(2)–C(1)
a
∆
CN
N(1)–C(9)
N(2)–C(21)
C(1)–C(2)
N(2)–H(3)
N(1Ј)–H(3)
2.00(2)
8a
C(1)–N(2)
C(1)–N(1)
1.297(4)
1.355(4)
0.058(8)
1.490(4)
1.440(4)
1.394(4)
0.89(1)
1.953(4)
1.948(4)
1.952(4)
2.91(2)
N(2)–C(1)–N(1)
N(2)–C(1)–C(2)
N(1)–C(1)–C(2)
123.3(2)
116.4(2)
120.3(2)
130.4(2)
126.7(2)
84.43(16)
83.09(15)
87.37(16)
152(2)
a
∆
CC(1N)–C(2)
C(1)–N(1)–C(9)
C(9)–N(1)
C(21)–N(2)
N(1)–H(1)
Mo(1)–C(43)
Mo(1)–C(41)
Mo(1)–C(42)
Mo(1)–H(1)
C(1)–N(2)–C(21)
C(43)–Mo(1)–C(41)
C(43)–Mo(1)–C(42)
C(41)–Mo(1)–C(42)
Mo(1)–H(1)–N(1)
8c
N(1)–C(1)
1.358(3)
1.288(3)
0.070(6)
1.453(3)
1.395(3)
1.511(4)
0.88(3)
1.952(3)
1.955(3)
1.959(4)
2.98(3)
C(1)–N(1)–C(9)
125.6(2)
126.8(2)
124.6(2)
117.4(2)
118.0(2)
83.72(12)
86.34(14)
87.0(2)
N(2)–C(1)
C(1)–N(2)–C(21)
N(2)–C(1)–N(1)
N(2)–C(1)–C(2)
a
∆
CN
N(1)–C(9)
N(2)–C(21)
C(1)–C(2)
N(1)–C(1)–C(2)
C(35)–Mo(1)–C(34)
C(35)–Mo(1)–C(33)
C(34)–Mo(1)–C(33)
Mo(1)–H(1)–N(1)
N(1)–H(1)
Mo(1)–C(35)
Mo(1)–C(34)
Mo(1)–C(33)
Mo(1)–H(1)
155.34(8)
9c
N(1)–C(1)
1.302(3)
1.351(3)
0.049(6)
1.455(3)
1.439(3)
1.500(3)
0.890(7)
2.3519(19)
1.962(3)
2.016(4)
2.049(4)
2.062(4)
2.095(4)
2.88(2)
C(1)–N(1)–C(9)
115.80(19)
128.28(15)
115.83(14)
125.2(2)
120.0(2)
124.4(2)
N(2)–C(1)
C(1)–N(1)–Mo(1)
C(9)–N(1)–Mo(1)
C(1)–N(2)–C(21)
N(1)–C(1)–N(2)
N(1)–C(1)–C(2)
a
∆
CN
N(1)–C(9)
N(2)–C(21)
C(1)–C(2)
Fig. 1 PLUTO diagrams, showing the atom numbering schemes, of
(a) 7a {tautomers: H(1) occupancy 72%; H(2), 28%}, (b) 7b {single
tautomer}, and (c) 8a.
N(2)–H(3)
N(2)–C(1)–C(2)
115.6(2)
Mo(1)–N(1)
Mo(1)–C(41)
Mo(1)–C(45)
Mo(1)–C(44)
Mo(1)–C(42)
Mo(1)–C(43)
Mo(1)–H(3)
C(41)–Mo(1)–N(1)
C(45)–Mo(1)–N(1)
C(44)–Mo(1)–N(1)
C(42)–Mo(1)–N(1)
C(43)–Mo(1)–N(1)
Mo(1)–H(3)–N(2)
173.10(13)
102.99(10)
96.77(10)
92.82(10)
86.93(10)
128(2)
Z-anti (72% refined occupancy) and E-syn (28% refined occu-
pancy). On the other hand, 7c (Fig. 2a) is found to be E-anti
in the solid state in a strongly H-bonded dimeric structure, and
consistently 7c is much less soluble in non-polar solvents than
7a,b.
Häfelinger and Kuske have compiled an up-to-date review
of structural data on amidines. They define the parameter
a
∆
CN = d(C–N) Ϫ d(C᎐N).
᎐
∆
= d(C–N) Ϫ d(C᎐N) for the central N–C–N linkage found
᎐
CN
complexes they form are presented in Fig. 1 and 2. Comparison
with Scheme 2 indicates that no less than three of the four
structural possibilities are present in the solid-state structures!
Thus 7b (Fig. 1b) is found in the solid state to be entirely Z-anti
while 7a (Fig. 1a) is disordered between the two tautomers
in all amidines.12 This parameter ranges from 0 [e.g. in an E-anti
hydrogen-bonded dimer of di(para-bromophenyl)formamidine]
to 0.178 Å in an amidine where conjugation is minimized due to
bulky substituents on nitrogen and carbon [d(C–N) = 1.441(5);
d(C᎐N) = 1.263(5) Å]. This parameter is included in Table 2 for
᎐
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the two molecules. Whether this serves to maximize H-bonding
between the pyramidalized amino and planar imino nitrogen
atoms, or whether it is a response to the high steric bulk of the
diisopropylphenyl groups is unclear.
∆
is much larger for 7b which does not interact in the
CN
crystal with neighbouring molecules and shows no evidence
of H-bonding. The value 0.057 Å is identical to the average of
two values from independent molecules of N,NЈ-diphenylbenz-
amidine, which also crystallizes in the Z-anti structure.12 How-
ever, 7a, which is almost isostructural to 7b, has the very low
∆
CN value of 0.027 Å. This observation caused us to look care-
fully at the electron-density map around the nitrogen atoms,
and we were able to refine a disorder model in which about ¼ of
the molecules have the hydrogen on N(2), and ¾ on N(1). This
means that both tautomers, Z-anti and E-syn, co-exist in a sin-
gle crystal of 7a. In order to verify this unprecedented result, we
have determined this structure from two data sets collected on
different crystals, and find virtually the same ratios of the two
tautomers from both structure determinations. As mentioned
above, NMR spectra show conclusively that 7 exists in solution
in two isomeric forms, irrespective of which isomer they crystal-
lize in. The relative proportions of the isomers seem to be
independent of sample origin, so that an equilibrium seems to
exist. At this time, we are unable to make a definitive correlation
between the solid state and solution structures. However, we
note that two of the ligand geometries (Z-anti and E-anti) are
found in the metal complexes discussed below, but that each
metal complex is isomerically pure in solution by NMR! Thus
metal coordination influences the geometry of the ligands in a
very definite way.
Reaction with Mo(CO)6. Amidines 7a–c were heated with
Mo(CO)6 in refluxing n-heptane under an atmosphere of N2
(Scheme 3). The course of the reaction was easily monitored by
Scheme 3
solution infrared spectroscopy and we observed that 7a,b
reacted slowly, with little evidence of any intermediate, to give
the final products, bright yellow crystalline solids which were
produced in 54 (8a) and 65% (8b) yield. The structure of both
compounds was indicated by 1H NMR and IR spectroscopy to
be a half-sandwich “piano-stool” complex of Mo(CO)3, rather
1
than a nitrogen coordination complex. In the H NMR spec-
trum, the signals due to the aromatic hydrogen atoms of one of
the diisopropylaniline groups is shifted over 2 ppm upfield,
while the other signals changed little. The solution IR (Table 3)
consisted of three bands in the carbonyl stretching region, a
very strong singlet at about 1966 cmϪ1, and a slightly less
intense doublet at about 1885 cmϪ1. This is the pattern expected
for a fac-octahedral tricarbonyl metal complex with highly
asymmetric co-ligands.13
On the other hand, when 7c reacted with Mo(CO)6 under
identical conditions, solution IR spectroscopy showed the ini-
tial formation of a different set of signals, which grew in rapidly
at the reflux temperature, and reached a maximum after ca. 1 h.
Fig. 2 PLUTO diagrams, showing the atom numbering schemes, of
(a) 7c, (b) 9c and (c) 8c. The hydrogen-bonded dimer of 7c is shown by
including a second molecule, located at Ϫx, y, ¹ Ϫ z, related to the first
¯
²
by a two-fold axis approximately perpendicular to the page.
the structures we have determined. As expected, ∆CN is very
small for the hydrogen-bonded dimer structure observed for 7c,
[in fact, at 0.006(4) Å the difference is statistically insignifi-
cant].13 The pair of amidine molecules are related to each other
by a two-fold axis approximately perpendicular to the N–C–N
planes, but there is a considerable twist between the planes in
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Table 3 Solution IR dataa
respect to the C(1)᎐N(2) bond, the metal complex also has Z
᎐
symmetry. The N–H of the amino group corresponds to the
ν(N–C–N)/
“catcher’s thumb”, and there is a close contact of 2.91(2) Å
between H(1) and Mo, less than a reasonable guess at the sum
of their van der Waals’ radii. Further evidence for a perturb-
ation of the metal coordination environment by the N(1)–H(1)
unit is that the V-shaped side of the (CO)3 piano-stool is twisted
towards, and bisected by, this unit. The C(41)–Mo–C(42) angle
is significantly larger than the other angles involving the carb-
onyl ligands. Indeed, the metal could just as well have coordin-
ated to the opposite face of the same ring, with significantly less
steric hindrance, but prefers the inner coordination pocket. The
balance of the evidence suggests a secondary coordination
effect by the amino unit, the “thumb” of the “catcher”. The
structure of 9c is shown in Fig. 2b. The Mo(CO)5 group is
coordinated by a single nitrogen atom, the imino-N, which is the
more basic atom in the amidine ligand.7 The ligand is in the
E-anti configuration (i.e. the same isomer as found in the
hydrogen-bonded dimer structure of 7c) but the metal complex
Ϫ1
ν(N–H)/cmϪ1
cmϪ1
ν(C᎐O)/cm
᎐
Compound
᎐
7a
7b
7c
3431, 3366
3431, 3366
3391, 3378,
3366, 3350
3216b
1620
1620
1643
—
—
—
8a
8b
8c
9c
1615
1614
1640
1603, 1582
1966, 1896, 1879
1965, 1896, 1879
1966, 1896, 1876
2072, 1989, 1942,
1931, 1908
3216b
3193b
3312b
a n-Heptane solution in 0.2 mm NaCl solution cell, unless otherwise
noted. b CHCl3 solution in 0.2 mm NaCl solution cell; these weak bands
are not observed in n-heptane because of limited solubility of the
complexes.
If heating was continued these signals gradually disappeared to
be replaced by a final set of peaks similar to those of the piano
stool complexes 8a,b. The intermediate thus is consumed more
rapidly than Mo(CO)6 itself. All the peaks were identified by
comparison with spectra of the purified products and those of
the starting materials. When the reaction was quenched after
1.5 h at reflux, we were able to crystallize mixtures of Mo(CO)6,
8c and the intermediate product. The Mo(CO)6 could be sub-
limed out of the mixture, and recrystallization from n-heptane
by cooling saturated solutions to Ϫ30 ЊC without heating,
affording pale yellow crystals of the intermediate, 9c, in 47%
yield. The carbonyl stretching frequencies in the IR spectrum
are consistent with a LMo(CO)5 complex, in which L is an
has Z symmetry with respect to the C(1)᎐N(1) bond. That the
᎐
hydrogen bonds are now broken is evident in the large change in
the two C–N bond distances, which are now clearly differenti-
ated for the single and the double bond (∆CN = 0.049 Å). The 1H
NMR shows that only one isomer is present in solution, which
we presume to be the same as in the crystal. This is in contrast
to (OC) W–NH᎐C(NMe )Ph, for which non-inter-converting
᎐
5
2
“E” and “Z” isomers are formed in solution in a 3:1 ratio.10
structure has been obtained for the E isomer, and interestingly
= 0.05(1) Å, statistically identical to that in 9c.7 The ν(C᎐N)
A
∆
᎐
CN
values of 9c and this tungsten complex are also very similar.
However, the Mo–N bond length in 9c is significantly longer at
2.352(2) vs. 2.243(5) Å for the W–N bond; a difference accentu-
ated by the (slightly) greater radius of W over Mo. It is certainly
possible that the great steric bulk of the superamidine is signifi-
cantly weakening the Mo–N bond, but we hesitate to draw
premature conclusions. Preliminary evidence suggests that the
W(CO)5 complex of 7c has significantly greater thermal stabil-
ity than 9c, so that a difference exists between these two metals
that cannot be ignored.
1
asymmetrical ligand,14 and the H NMR shows the absence
of the upfield shift in the aromatic region indicative of
π-coordination. Further indication that this species is nitrogen-
coordinated was provided by the solution IR data in the C᎐N
᎐
region. In the free ligand, an asymmetrical doublet is observed
at 1643 cmϪ1. This peak is found, essentially unchanged, at 1640
cmϪ1 in 8c (Table 3). However, in 9c we find instead two well-
separated bands at 1603 and 1582 cmϪ1, indicating that in the
complex the energies of the N–C–N bonds have been affected.
Final confirmation of the bonding mode came from a single-
crystal structure.
In a separate experiment, a heptane solution of 9c was heated
and monitored by solution IR spectroscopy. This resulted in
direct conversion to 8c, along with some decomposition, indi-
cating that 9c is a genuine intermediate on the way to 8c. In
another experiment, we heated 9c in heptane under one atmos-
phere of carbon monoxide. Not only did the CO inhibit the
formation of 8c, it also displaced the ligand from 9c, so that
slowly Mo(CO)6 and the free amidine formed in solution.
The biggest surprise in our structure determinations,
unanticipated from the NMR data, was that of 8c, which
strongly resembles that of 8a, the “Catcher’s mitt” type, in
which the ligand has isomerized to the Z-anti geometry (Fig.
2c). In retrospect, the distinct differences in the NMR spectra
of 8c compared to 8a,b are probably due to ring-current shield-
ing effects perpendicular to the CH3C6H4 and CH3OC6H4- rings
on the amidinyl C atom. The structures of 8c and 9c provide
an appealing visual mechanism for the reaction, in which an
Mo(CO)5 unit held by the imino nitrogen close to an electron-
rich benzene ring (activated by two C3H7 substituents) loses two
further CO ligands and slides over to the tripodal ligand
environment of the aryl ring. All the spectroscopic evidence
suggests that only one isomeric form exists in solution for each
of these metal complexes, and since we have confirmed that
purified 9c converts smoothly to 8c, the change from η1-N
to η6-C coordination evidently induces E-anti to Z-anti
ligand isomerization. The structural studies also suggest
one possible reason why the methylamidine 7c alone forms the
N-coordinated complex 9c, since this is the one ligand which
crystallizes preferentially in the E-anti form. This hydrogen-
bonded dimer is appreciably less soluble than the other amidine
ligands, and it is possible that complexation of the E-anti
geometry occurs before isomerization of the ligand in heptane
solution, and that this leads to the formation of the metastable
9c in the case of ligand 7c alone.
Crystal structures of the metal complexes
For 8, IR and NMR evidence indicated the presence of an
Mo(CO)3 group on one of the diisopropylaniline rings. How-
ever, there was no clear indication of which of the two, the
amino or the imino ring, was involved, no information on the
geometry of the amidine, nor the choice of face of the ring
occupied by the Mo(CO)3 group. What was clear from the
NMR was that each metal complex contained only one amidine
configuration, but differences in spectral features between the
ligands with aryl- and alkyl-substituents on the amidinyl C
atom were too large to allow us to make any definitive assign-
ments of ligand conformation in a given complex, except that
8a and 8b have the same configuration. For 9c, we also needed
proof of the coordination mode. We have therefore determined
the single-crystal structures of 8a,8c and 9c.
The structure of 8a is presented in Fig. 1c. The structure
resembles a “baseball catcher’s mitt”, in which the amidine
ligand, itself in the Z-anti tautomer, has caught the Mo(CO)3
fragment with the inside face of the imino-bearing ring. With
Comparison to previous results
In 1975, Cotton, Kilner et al. reported the results of reacting
Mo(CO)6 in refluxing light petroleum (bp 100–120 ЊC) with
J. Chem. Soc., Dalton Trans., 1998, 4147–4154
4151

View Article Online
N,NЈ-diphenylbenzamidine.6 The only product which could be
isolated was a red compound, which precipitated from the hot
solution in 16% yield. X-Ray crystallography confirmed this
material to be a quadruply-bonded Mo2(amidine)4 species. In
the same paper they reported, however, that under similar reac-
tion conditions Cr(CO)6 produced an insoluble red compound
which did not appear to retain any carbonyl groups as well as a
soluble yellow product with two intense IR signals at 1964 and
1883 (br) cmϪ1 and a mass spectrum which fitted for LCr(CO)3.6
The structure of this compound was not further investigated,
but it may well be similar to that of 8. We could not detect any
evidence of a Mo2(amidine)4 species using ligands 7, and we
attribute this to the much greater steric requirements of the
superamidines. Prolonged heating of solutions of 8 lead to the
slow formation of a black tar from which no recognizable com-
pounds could be isolated. Increasing the ratio of amidine to
Mo(CO)6 up to the 2:1 ratio required for Mo2(amidine)4 has no
effect on product distribution, but complicates the work-up due
to the presence of unreacted amidine.
USA and by the analytical services of the Fachbereich Chemie,
Universität Kaiserslautern.
Preparation of 4-CH3C6H4C(O)NH(2,6-iPr2C6H3) 5a
To 2,6-diisopropylaniline (20.0 g, 113 mmol) in 70 mL of dry
CH2Cl2 was added 8.7 g (56.3 mmol) para-toluoyl chloride in 45
mL CH2Cl2 with stirring. A precipitate formed. The mixture
was heated at reflux for 20 h. After cooling a white solid was
filtered off and washed with ice-cold CH2Cl2 and dried in vacuo
to give 12.5 g (42.3 mmol, 75% yield) of 5a which was pure by
NMR. An analytical sample was obtained by recrystallization
from toluene, mp 218 ЊC (decomp.) (Calc. for C20H25NO: C,
81.3; H, 8.53; N, 4.7. Found: C, 81.1; H, 8.4; N, 4.7%). IR:
1
ν(N–H) 3341, ν(C᎐O) 1644 cmϪ1. H NMR: δ 7.85–7.82 (m,
᎐
2 H), 7.4 (s, 1 H, concentration dependent), 7.37–7.20 (m, 5 H),
3.14 (hept, 6.8, 2 H), 2.45 (s, 3 H), 1.22 (d, 6.8 Hz, 12 H). 13C
NMR: δ 167.02, 146.63, 142.29, 131.796, 131.63, 129.53,
128.51, 127.42, 123.64, 29.04, 23.79, 21.66. MS: m/z 295 (Mϩ,
i
100); 252 (M Ϫ iPrϩ, 32); 176 (C6H3 Pr2NHϩ, 38); 119
(CH3C6H4COϩ, 14%).
Conclusions
Preparation of 4-CH3OC6H4C(O)NH(2,6-iPr2C6H3) 5b
In this work we have demonstrated that superamidines bearing
very bulky substituents are accessible using highly-modified
standard organic synthetic routes. The amidines exist in a
variety of isomeric forms, which seem to be interchangeable.
Secondly, in thermal reactions with Mo(CO)6, these super-
amidines behave very differently from N,NЈ-diphenylbenz-
amidine, the closest non-bulky model ligand. Thus we observe
for the superamidines two coordination modes, (1) monoden-
tate imine-N coordination and (2) π-aryl coordination, which
are not observed for diphenylbenzamidine. The metal–ligand
interaction is very specific, such that consistently only one
ligand geometry is found in each type of metal complex. Con-
versely, the superamidines did not undergo the redox reaction
with the metal that the N,NЈ-diphenyl ligand undergoes to form
M–M quadruply-bonded species. The competition experiments
with CO indicate that 7c is a weak monodentate ligand.
We are continuing our studies on thermal reactions with the
other Group 6 hexacarbonyls. Initial indications are that simi-
lar products form, although the reactions proceed markedly
slower and the products are more difficult to purify. We expect
to see other consequences of steric bulk in our continued
exploration of the coordination chemistry of superamidines,
including superamidinate anions.
Prepared in the same way as 5a in 78% yield, mp 273–274 ЊC
(decomp.) (Calc. for C20H25NO2: C, 77.14; H, 8.09; N, 4.50.
Found: C, 77.23; H, 8.09; N, 4.46%). IR: ν(N–H) 3328, ν(C᎐O)
᎐
1640 cmϪ1. 1H NMR: δ 7.85 (d, 8.9, 2 H) 7.43 (s, 1 H, concen-
tration dependent), 7.36–7.18 (m, 3 H), 6.93 (d, 8.9, 2 H), 3.87
(s, 3 H), 3.12 (hept, 6.9, 2 H), 1.19 (d, 6.9, 12 H). 13C NMR:
δ 166.41, 162.42, 146.5, 131.51, 129.08, 128.33, 126.77, 123.50,
113.95, 55.49, 28.89, 23.65. MS: m/z 311.18839 (Mϩ, 58); 268
i
(M Ϫ iPrϩ, 35); 176 (C6H3 Pr2NHϩ, 70); 134 (CH3OC6H4COϩ,
100%).
Preparation of CH3C(O)NH(2,6-iPrC6H3) 5c
Neat acetyl chloride (8.03 mL, 113 mmol) was carefully pipet-
ted into a solution of 2,6-diisopropylaniline (20.0 g, 113 mmol)
in 200 mL of dry pyridine (CAUTION: vigorous reaction, use
cooling), whereupon the mixture was refluxed for 3 h. The sol-
vent was removed, and the residues taken up in 200 mL CH2Cl2
and washed twice with 200 mL water. After drying and removal
of solvent, the crude product was recrystallized from 100 mL
toluene to give 16.7 g of colourless crystals (76.1 mmol, 68%
yield), mp 192–196 ЊC (Calc. for C14H21NO: C, 76.67; H, 9.65; N,
6.39. Found: C, 76.58; H, 9.45; N, 6.45%). IR: ν(N–H) 3249,
ν(C᎐O) 1647 cmϪ1. 1H NMR: δ 7.36–7.14 (m, 3 H), 7.05 (s, 1 H,
᎐
Experimental
General
concentration dependent), 3.18 (32%, hept, 6.9, 2 H), 3.07
(68%, hept, 6.9, 2 H), 2.15 (68%, s, 3 H), 1.72 (32%, s, 3 H), 1.24
(32%, d, 6.9, 6 H), 1.18 (68%, d, 6.9, 12 H), 1.16 (32%, d, 6.9 Hz,
6 H). 13C NMR: 32% isomer δ 173.87, 146.63, 132.17, 128.92,
123.78, 28.33, 22.9, 22.63, 19.99; 68% isomer δ 169.77, 146.19,
131.3, 128.16, 123.25, 28.61, 24.29, 23.51. MS: m/z 219.16244
2,6-Diisopropylaniline (Accros, Aldrich), para-toluoyl chloride
(Accros, Aldrich), para-anisoyl chloride (Aldrich), acetyl chlor-
ide (Aldrich) and molybdenum carbonyl (Strem) were com-
mercial products, and used as received, except that the aniline
was vacuum distilled and stored under nitrogen before use.
Solvents were reagent grade, and distilled from sodium wire
(toluene), P2O5 (CH2Cl2) or LiAlH4 (n-heptane). Pyridine was
dried over molecular sieves. Reactions involving metal carbonyl
derivatives were performed under an atmosphere of purified N2
using a dry-box, Schlenk ware and vacuum-line techniques; all
other procedures were performed in vessels open to the atmos-
phere but protected by CaCl2 drying tubes. Infrared spectra
were recorded on a BOMEM MB102 Fourier transform spec-
trometer, and are KBr pellets unless otherwise specified. NMR
spectra were acquired at 250.13 (1H) and 62.90 (13C) MHz
on a Bruker AC250-F spectrometer, and are in CDCl3 unless
otherwise specified. Mass spectra were recorded by the Mass
Spectrometry Center, University of Alberta, Canada and in the
Fachbereich Chemie, Universität Kaiserslautern. Elemental
analyses were performed by MHW Laboratories, Phoenix, AZ,
(Mϩ, 91); 204 (M Ϫ CH3ϩ, 63); 176 (C6H3 Pr2NHϩ, 100); 162
i
(C11H16Nϩ, 70); 134 (C9H12Nϩ, 28%).
Preparation of 4-CH3C6H4C(Cl)N(2,6-iPr2C6H3) 6a
Complex 2a (12.4 g, 42.9 mmol) was refluxed in 9 mL of SOCl2
(excess) for 1.5 h (oil bath at 80–90 ЊC), after which the bath
temperature was raised to 140 ЊC and the remaining SOCl2 was
distilled off. The residues were vacuum distilled (air condenser,
CAUTION: solid product may block narrow take-off
adapters), bp 135–140 ЊC at 1 × 10Ϫ2 Torr. On cooling a bright
yellow solid was obtained which was analytically pure 6a (12.6
g, 40.1 mmol, 96% yield) , mp 61–63 ЊC (Calc. for C20H24ClN: C,
76.5; H, 7.7; N, 4.5. Found: C, 76.5; H, 7.7; N, 4.5%). 1H NMR:
δ 8.10 (d, 8.3, 2 H), 7.31 (d, 8.3, 2 H), 7.18 (s, 3 H), 2.81 (hept,
6.9, 2 H), 2.45 (s, 3 H), 1.21 (d, 6.9, 6 H), 1.15 (d, 6.9 Hz, 6 H).
13C NMR: δ 143.92, 143.44, 142.77, 136.82, 132.38, 129.44,
4152
J. Chem. Soc., Dalton Trans., 1998, 4147–4154

View Article Online
124.77, 123.05, 28.67, 23.30, 22.88, 21.47. MS: m/z 313 (Mϩ on
35Cl, 14); 278 (M Ϫ Clϩ, 100%).
22.52, 19.64. MS: m/z 378.30313 (Mϩ, 18); 335 (M Ϫ iPrϩ, 28);
202 (M Ϫ C6H3 Pr2NHϩ, 100); 177 (C6H3 Pr2NH2ϩ, 8%).
i
i
i
Preparation of 4-CH3OC6H4C(Cl)N(2,6-iPr2C6H3) 6b
Preparation of ç6-[4-CH3C6H4C(NC6H3 Pr2-2,6)NH(2,6-iPr2-
C6H3)]Mo(CO)3 8a
Prepared by the same method as 6a, yellow solid, bp 160–
170 ЊC at 1 × 10Ϫ2 Torr (97% yield), mp 104–105 ЊC (Calc. for
C20H24ClNO: C, 72.82; H, 7.33; N, 4.25. Found: C, 72.80; H,
7.46; N, 4.32%). 1H NMR: δ 8.17 (d, 9.9, 2 H), 7.17 (s, 3 H), 6.97
(d, 9.9, 2 H), 3.85 (s, 3 H), 2.84 (hept, 6.9, 2 H), 1.22 (d, 6.9,
6 H), 1.16 (d, 6.9 Hz, 6 H). 13C NMR: δ 163.00, 143.99, 143.15,
137.12, 131.42, 127.55, 124.89, 123.14, 113.96, 55.59, 28.79,
23.41, 23.01. MS: m/z 329.15447 (Mϩ on 35Cl, 14); 294
(M Ϫ Clϩ, 100); 121 (C8H9Oϩ, 15%).
500 mg (1.1 mmol) of 7a and 290 mg (1.1 mmol) of Mo(CO)6
were loaded under N2 into a Schlenk tube. 27 mL of dry
n-heptane was then added, and the mixture heated to reflux.
Progress of the reaction was monitored by solution IR, and
heating discontinued after 28 h. Collection of the green-tinged
yellow crystals provided 380 mg of 8a [0.60 mmol, 54%
yield, mp 130 ЊC (decomp.)]. Recrystallization from 12 mL of
n-heptane provided bright yellow analytically pure crystals
(Calc. for C35H42MoN2O3: C, 66.24; H, 6.67; N, 4.41. Found: C,
Preparation of 4-CH3C6H4C(NC6H3iPr2-2,6)NH(2,6-iPr2C6H3)
7a
66.46; H, 6.77; N, 4.26%). IR: ν(N–H) 3426, 3194, ν(C᎐O) 1952,
᎐
1871, ν(N–C–N) 1613 cmϪ1. 1H NMR: δ 8.20 (s, 1 H), 7.29–6.96
(m, 7 H), 5.79–5.66 (m, 3 H), 3.17 (hept, 6.8, 2 H), 2.85 (hept,
6.9, 2 H), 2.27 (s, 3 H), 1.28 (d, 6.9, 6 H), 1.27 (d, 6.9, 6 H), 1.20
(d, 6.8, 6 H), 0.86 (d, 6.8 Hz, 6 H). 13C NMR spectrum not
obtained due to sample instability. MS: m/z 636.22411 (Mϩ
based on 98Mo, 0.05); 454 (Lϩ, 51%); 411 (L Ϫ iPrϩ, 54); 278
To 9.00 g (28.7 mmol) 6a in 70 mL dry toluene was added 5.08 g
(28.7 mmol) 2,6-diisopropylaniline, and the mixture was
refluxed for 20 h. Removal of the solvent and drying the resi-
dues in vacuo gave a quantitative yield of 7aؒHCl. This material
was dissolved in 100 mL 95% ethanol and treated with six 15
mL portions of 25% aqueous NH3. The beige solid was filtered
off and air dried for 20 h. Recrystallization from 65 mL 95%
ethanol produced off-white crystals of 7a (8.72 g, 19.2 mmol,
67% yield). An analytical sample was obtained after a second
recrystallization, mp 139–140 ЊC (Calc. for C32H42N2: C, 84.5;
H, 9.3; N, 6.2. Found: C, 84.6; H, 9.2; N, 6.1%). IR: ν(N–H)
i
i
(L Ϫ C6H3 Pr2NHϩ, 100); 177 (C6H3 Pr2NH2ϩ, 24); 162 (C6H3-
iPr2ϩ, 14).
i
Preparation of ç6-[4-CH3OC6H4C(NC6H3 Pr2-2,6)NH(2,6-iPr2-
C6H3)]Mo(CO)3 8b
Prepared from 500 mg of 7b in a similar manner to 8a. Yield
447 mg (0.69 mmol, 65%) of bright yellow crystals, mp 130–
135 ЊC (decomp.) (Calc. for C35H42MoN2O4: C, 64.61; H, 6.51;
N, 4.31. Found: C, 64.76; H, 6.64; N, 4.11%). IR: ν(N–H) 3436,
1
3428, 3366, ν(N–C–N) 1613 cmϪ1. H NMR: δ 7.29–6.97 (m,
10H), 5.67 (s, 1 H), 3.30–3.31 (m, 4 H), 2.27 (s, 3 H), 1.34 (d,
7.0, 6 H), 1.23 (d, 6.7, 6 H), 0.98 (d, 6.7, 6 H), 0.88 (d, 6.8 Hz,
6 H). 13C NMR: δ 153.39, 145.14, 143.89, 139.29, 139.08,
134.12, 132.13, 128.68, 128.31, 127.36, 123.30, 123.17, 28.51,
28.32, 25.11, 24.37, 22.47, 22.37, 21.23. MS: m/z 454 (Mϩ, 67);
3219, ν(C᎐O) 1950, 1871, ν(N–C–N) 1613 cmϪ1 1H NMR:
.
᎐
δ 8.18 (s, 1 H), 7.26 (d, 9, 2 H), 7.29–7.06 (m, 3 H), 6.69 (d, 9, 2
H), 5.79–5.66 (m, 3 H), 3.74 (s, 3 H), 3.17 (hept, 6.8, 2 H), 2.84
(hept, 6.9, 2 H), 1.28 (d, 6.9, 6 H), 1.27 (d, 6.7, 6 H), 1.20 (d, 6.8,
6 H), 0.88 (d, 6.8 Hz, 6 H). 13C NMR spectrum not obtained
due to sample instability. MS: m/z 652.22032 (Mϩ based on
98Mo, 1); 568 (Mϩ Ϫ 3CO, 6); 470 (Lϩ, 13); 454 (L Ϫ CH4ϩ, 11);
427 (L Ϫ iPrϩ, 18); 411 (L Ϫ iPr Ϫ CH4ϩ, 16); 294 (L Ϫ C6H3-
i
411 (M Ϫ iPrϩ, 28); 278 (M Ϫ C6H3 Pr2NHϩ, 100); 177 (C6H3-
i
iPr2NH2ϩ, 86); 162 (C6H3 Pr2ϩ, 14%).
Preparation of 4-CH3OC6H4C(NC6H3iPr2-2,6)NH(2,6-iPr2-
C6H3) 7b
iPr2NHϩ, 100); 278 (L Ϫ C6H3 Pr2NH Ϫ CH4ϩ, 72); 177 (C6H3-
i
Produced from 6b as for 7a, off-white crystals (64% yield), mp
164–165 ЊC (Calc. for C32H42N2O: C, 81.66; H, 8.99; N, 5.95.
Found: C, 81.80; H, 8.83; N, 6.00%). IR: ν(N–H) 3426, 3368,
ν(N–C–N) 1615 cmϪ1. 1H NMR: δ 7.35–6.70 (m, 10H), 5.66 (s,
1 H), 3.74 (s, 3 H), 3.28–3.11 (m, 4 H), 1.34 (d, 6.9, 6 H), 1.23 (d,
6.7, 6 H), 0.99 (d, 6.8, 6 H), 0.90 (d, 6.8 Hz, 6 H). 13C NMR:
δ 160.23, 152.89, 145.11, 143.94, 139.30, 134.18, 130.27, 127.49,
127.35, 123.62, 123.25, 123.15, 112.99, 28.50, 28.33, 25.07,
24.37, 22.44. MS: m/z 470.3301 (Mϩ, 24); 427 (M Ϫ iPrϩ, 30);
iPr2NH2ϩ, 13%).
Preparation of ç6-[CH3C(NC6H3 Pr2-2,6)NH(2,6-iPr2C6H3)]-
Mo(CO)3 8c
i
Prepared from 500 mg of 7c in a similar manner to 8a. Reaction
stopped after 20 h, after IR indicated that all the intermediate
was consumed. On cooling, a black solid was filtered off, and
the filtrate cooled to Ϫ30 ЊC. Slightly green-tinted yellow crys-
tals formed, which were filtered and dried under vacuum, yield
571 mg (1.0 mmol, 77%). Recrystallization from 13 mL of
n-heptane with some Celite (hot-filtered) provided an analytical
sample as bright yellow crystals, mp 95 ЊC (decomp.) (Calc. for
C29H38MoN2O3: C, 62.36; H, 6.86; N, 5.02. Found: C, 62.50; H,
i
i
294 (M Ϫ C6H3 Pr2NHϩ, 100); 177 (C6H3 Pr2NH2ϩ, 8); 121
(C8H9Oϩ, 19%).
Preparation of CH3C(NC6H3iPr2-2,6)NH(2,6-iPr2C6H3) 7c
11.45 g PCl5 (55.0 mmol) was dissolved in 50 mL dry benzene
with heating under N2. To the cooled solution was added 10.9 g
5c (50.0 mmol), and the mixture was refluxed for 30 min, until
gas evolution ceased. To the cooled, N2-flushed, solution was
added 8.86 g 2,6-diisopropylaniline in 50 mL of dry benzene,
whereupon the mixture was again refluxed, for 20 h. On cool-
ing, an off-white precipitate of 7cؒHCl formed, which was fil-
tered off and washed with hexanes. The free base was liberated
as before, and recrystallization from 900 mL 95% ethanol pro-
duced white crystals of 7c (14.3 g, 37.8 mmol, 75% yield). An
analytical sample was obtained after a second recrystallization,
mp 227–230 ЊC (Calc. for C26H38N2: C, 82.48; H, 10.12; N, 7.40.
Found: C, 82.60; H, 9.96; N, 7.53%). IR: ν(N–H) 3622–3116,
ν(N–C–N) 1641 cmϪ1. 1H NMR: δ 7.29–7.04 (m, 6H), 5.40 (s, 1
H), 3.31–3.10 (m, 4 H), 1.88 (s, 3 H), 1.40–1.01 (m, 24 H). 13C
NMR: δ 153.81, 147.04, 143.05, 139.77, 133.38, 128.37, 125.30,
123.63, 123.19, 28.25, 28.05, 24.69, 24.60, 23.55, 23.40, 23.23,
6.92; N, 4.83%). IR: ν(N–H) 3426, 3239, ν(C᎐O) 1952, 1871,
᎐
1
ν(N–C–N) 1640 cmϪ1. H NMR: δ 7.98 (s, 1 H), 7.35–7.17 (m,
3 H), 5.82–5.58 (m, 3 H), 3.19 (hept, 6.9, 2 H), 2.81 (hept, 6.9,
2 H), 1.79 (s, 3 H), 1.29 (d, 6.9, 6 H), 1.25 (d, 6.9, 6 H), 1.24 (d,
6.9, 6 H), 1.22 (d, 6.9 Hz, 6 H). 13C NMR spectrum not
obtained due to sample instability. MS: m/z 560.19365 (Mϩ
based on 98Mo, 5); 474 (M Ϫ 3CO, Hϩ, 29); 378 (Lϩ, 20); 335
i
i
(L Ϫ iPrϩ, 20); 202 (L Ϫ C6H3 Pr2NHϩ, 100); 177 (C6H3 Pr2-
NH2ϩ, 32%).
i
Preparation of ç1-[CH3C(NC6H3 Pr2-2,6)NH(2,6-iPr2C6H3)]-
Mo(CO)5 9c
500 mg (1.3 mmol) of 7c and 350 mg (1.3 mmol) of Mo(CO)6
were loaded under N2 into a Schlenk tube; 27 mL of dry
n-heptane was then added, and the mixture heated to reflux.
Progress of the reaction was monitored by solution IR, and
J. Chem. Soc., Dalton Trans., 1998, 4147–4154
4153

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heating discontinued after 1.5 h. At room temperature, colour-
less crystals formed (unreacted 7c), which were filtered off and
discarded. Cooling the filtrate to Ϫ30 ЊC produced 380 mg of
green-tinted yellow crystals [0.62 mol, 47% yield, mp 125–130 ЊC
(decomp.)]. An analytical sample of pale yellow crystals was
obtained by dissolving this material at room temperature in 23
mL of n-heptane, and cooling to Ϫ30 ЊC (Calc. for C31H38-
MoN2O5: C, 60.58; H, 6.23; N, 4.56. Found: C, 60.99; H, 6.27;
Engineering Research Council of Canada, the University of
Lethbridge research fund and the Alexander von Humboldt-
Foundation. R. T. B. wishes to thank Professor Dr. O. J. Scherer
and Dr. G. Wolmershauser for their hospitality during a sabbat-
ical leave at Kaiserslautern and acknowledges the access given
to the facilities of the Fachbereich Chemie of the University.
References
N, 4.40%). IR: ν(N–H) 3341, ν(C᎐O) 2071, 2000, 1930, ν(N–C–
᎐
N) 1640, 1600, 1579 cmϪ1. 1H NMR: δ 7.37 (s, 1 H), 7.40–7.16
(m, 6 H), 3.16 (hept, 6.9, 2 H), 3.15 (hept, 6.8, 2 H), 1.42 (s,
3 H), 1.40 (d, 6.9, 6 H), 1.30 (d, 6.8, 6 H), 1.27 (d, 6.9, 6 H), 1.11
(d, 6.8 Hz, 6 H). 13C NMR spectrum not obtained due to
sample instability. MS: m/z 560.19517 (M Ϫ 2COϩ, 5); 474
(M Ϫ 5CO, Hϩ, 29); 378 (Lϩ, 17); 335 (L Ϫ iPrϩ, 19); 202
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Details of data collection, crystal parameters, solution and
refinement are presented in Table 1. Refinement was on F2
against all reflections. The weighted R-factor wR and goodness
of fit S are based on F2, conventional R-factors R are based on
F, with F set to zero for negative F2. The threshold expression
of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
The hydrogen atoms were refined freely with isotropic thermal
parameters; all other atoms were refined anisotropically. For 7a,
a disorder model was refined with a 72:28 ratio for the H atoms
attached to N(1) and N(2), for which atoms the distances d(N–
H) were constrained to 0.93 Å. For 7c, which crystallizes in a
chiral space group, no reliable determination of the absolute
structure was possible. Selected interatomic distances and
angles, including H-bonding, are given in Table 2. PLUTO
diagrams were prepared using the version incorporated into
NRCVAX.15
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CCDC reference number 186/1209.
See http://www.rsc.org/suppdata/dt/1998/4147/ for crystallo-
graphic files in .cif format.
Acknowledgements
This work was supported by the Natural Sciences and
Paper 8/05548C
4154
J. Chem. Soc., Dalton Trans., 1998, 4147–4154