Flexible coordination of bulky amidinates and guanidinates towards rhodium(I): Conversion of kinetic to thermodymanic isomers

Article abstract of DOI:10.1039/b806542j

Reactions of the bulky amidinate and guanidinate salts K[(ArN) ₂CR] (R = Bu^t, NPrⁱ₂ or N(C ₆H₁₁)₂; Ar = 2,6-diisopropylphenyl) with [{RhCl(η⁴-COD)}₂] (COD =

Full text of DOI:10.1039/b806542j

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Flexible coordination of bulky amidinates and guanidinates towards
rhodium(I): conversion of kinetic to thermodymanic isomers†
Cameron Jones,*a David P. Millsa,b and Andreas Stascha
Received 17th April 2008, Accepted 2nd June 2008
First published as an Advance Article on the web 21st July 2008
DOI: 10.1039/b806542j
Reactions of the bulky amidinate and guanidinate salts K[(ArN)2CR] (R = But, NPri2 or N(C6H11)2;
4
Ar = 2,6-diisopropylphenyl) with [{RhCl(g -COD)}2] (COD = 1,5-cyclooctadiene) lead to KCl
5
elimination and the formation of the complexes, [Rh{(g -ArN)(ArN)CR}(COD)], in which the anionic
5
ligand coordinates the rhodium centre in an unprecedented g -cyclohexadienyl mode. The thermal
conversions of these complexes to their N,Nꢀ-chelated isomers, [Rh{j2-N,Nꢀ-(ArN)2CR}(COD)], were
carried out and the kinetics of these processes have been shown to be first order. The rates of the
isomerisations are inversely proportional to the size of the amidinate or guanidinate backbone
substituent. Analogies between the ligating properties of the bulky amidinates and guanidinates used in
the study, and those of b-diketiminates are discussed.
[Rh{(PhN)2CPh}(COD)]8 and [Rh{(CyN)2CFc}(CO)2]9; COD =
Introduction
1,5-cyclooctadiene, Cy = cyclohexyl, Fc = ferrocenyl) described
in the literature. Moreover, there are no crystallographically
elucidated guanidinate complexes of either metal in the +1
oxidation state.
The coordination of amidinates and guanidinates towards met-
als from all blocks of the periodic table has been extensively
examined.1 Throughout this work a variety of coordination modes
have been identified for these ligands, the complexes of which
have found many applications. In the past three years we have
extended the field to the use of very bulky guanidinates and
amidinates (e.g. [(ArN)2CR]−; R = N(C6H11)2 (Giso−), NPri2
(Priso−) or But (Piso−); Ar = 2,6-diisopropylphenyl) for the
stabilisation of novel low oxidation state s-, p-, d- and f-block
metal complexes. These include highly reactive group 2,2 13,3 144
and 155 metal(I) heterocycles, and the first examples of planar
4-coordinate lanthanide(II) complexes.6 Most recently, we have
employed the Piso− ligand to stabilise an unprecedented example
of a monomeric amidinato complex of a first row transition metal
Over the course of our studies with bulky amidinates and
guanidinates, it has become apparent that these ligands have
similar stabilising properties to those of sterically hindered b-
diketiminates, e.g. [(R1NCR2)2CH]− (R1 and R2 = alkyl or aryl).
These Nacnac− ligands, as they are sometimes known, have been
extensively used for the preparation of low oxidation state metal
complexes.10 These include an array of rhodium(I) and iridium(I)
examples in which the Nacnac− moiety acts as an N,Nꢀ-chelating
ligand, e.g. [M{(RNCMe)2CH}(COD)] (M = Rh, R = C6H3Me2-
2,611; M = Ir, R = Ar12). In this study analogies between the
Nacnac− ligand class and bulky amidinates and guanidinates are
further highlighted.
in the +1 oxidation state (viz. [Fe(j2-N,Nꢀ-Piso)(g -toluene)]).7 The
Fe(Piso) fragment of this compound has been shown to weakly
activate dinitrogen.
6
Although second and third row transition metal(I) amidinate
and guanidinate complexes have been previously reported,1 we
wished to examine the complexation of Piso−, Priso− and Giso−
with heavier transition metals, and compare the structural motifs
adopted by the formed complexes with those of less hindered
examples. The group 9 metals, rhodium and iridium, were seen
as being of particular interest because of the widespread use of
their complexes as, for example, catalysts for hydroformylation,
olefin hydrogenation and C–H activation processes. Despite
this, there are only two structurally characterised rhodium(I)
complexes incorporating an N,Nꢀ-chelating amidinate ligand (viz.
Results and discussion
Oro et al. previously prepared the rhodium(I) amidinate complex,
[Rh{j2-N,Nꢀ-(PhN)2CPh}(COD)], via a salt elimination reaction
between K[(PhN)2CPh] and [{RhCl(g -COD)}2].8 It was envis-
4
aged that a similar synthetic methodology would successfully give
N,Nꢀ-chelated complexes in this study. However, the treatment
4
of [{RhCl(g -COD)}2] with two equivalents of either [K(Piso)],
5
[K(Priso)] or [K(Giso)] in toluene led, instead, to the unusual g -
cyclohexadienyl complexes, 1–3, in low to good isolated yields
(Scheme 1). When the reactions were repeated in THF, 1–3 were
formed in similar yields. It is of note that a low yield (<2%) by-
4
product, [{Rh(g -COD)}4(l4-O2SiMe2)2], was isolated from the
aSchool of Chemistry, Monash University, PO Box 23, VIC, 3800, Australia
bSchool of Chemistry, Main Building, Cardiff University, Cardiff, UK CF10
3AT
reaction involving K[Giso] and subsequently crystallographically
characterised (see ESI†). Although the mechanism of formation
of this compound is unknown, it almost certainly originates from
contamination of the reaction mixture with a small amount of
silicone grease. No attempt was made to rationally synthesise the
compound in a higher yield, but it is worthy of mention that the
† Electronic supplementary information (ESI) available: Full crystallo-
4
graphic details for [{Rh(g -COD)}4(l4-O2SiMe2)2] and ORTEP diagrams
for 1, 2, 6 and 7. CCDC reference numbers 685416–685422. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b806542j
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Scheme 1 (i) K[Piso], K[Priso] or K[Giso], toluene, −KCl; (ii) toluene,
80 ◦C, 5 h.
Fig. 1 Molecular structure of 3 (25% thermal ellipsoids are shown,
hydrogen atoms are omitted for clarity).
abstraction of Me2SiO2 units from silicone grease in the presence
of organometallic reagents has been observed on a number of
previous occasions.13
from Rh(1) to the carbons of the coordinated aryl group, C(3)–
˚
˚
C(7), (1: 2.207(2)–2.508(2) A; 2: 2.185(3)–2.478(3) A; 3: 2.213(3)–
4
˚
Less success was had with the reactions of [{IrCl(g -COD)}2]
2.497(3) A) which are significantly shorter than the Rh(1)–C(2)
with two equivalents of either [K(Piso)], [K(Priso)] or [K(Giso)],
which in each case resulted in an intractable mixture of prod-
interactions. In addition, the C(2)–C(3) and C(2)–C(7) distances
are close to those expected for single bonded interactions. These
parameters are not dissimilar to those described for rhodium(I)
and iridium(I) cyclohexadienyl complexes in the literature.14 While
there appears to be some delocalisation over the anionic ligands
in the complexes, the geometric data strongly suggest a high
degree of double bond character to the N(1)–C(2) and C(1)–
N(2) attachments. There appears to be no significant inter- or
intramolecular interactions between any of the N-centres, or the
other aryl substituent, with the rhodium atoms of the complexes.
Although we have previously reported that the ligands used
in this study can act as localised imino–amides that N,arene-
chelate metal centres, e.g. Tl(I),3 we believe that there have been no
accounts of any amidinate or guanidinate coordinating a metal
2
ucts. Likewise, the treatment of [{RhCl(g -COE)2}2] (COE =
cyclooctene) with the amidinate or guanidinate salts resulted
in the formation of complex product mixtures. Oro et al. have
previously reported that treatment of the rhodium(I) amidinate
complex [Rh{(PhN)2CPh}(COD)] with CO affords the amidinate-
bridged rhodium carbonyl dimer, [Rh2{l-(PhN)2CPh}2(CO)4].8 In
contrast, exposure of toluene solutions of 1–3 to atmospheres of
CO led to the formation of rhodium metal and the free amidine
or guanidine, amongst other products. It is not known why these
differences occur, but the unusual “aryl only” coordination mode
of the amidinate or guanidinate ligands in 1–3 could be a factor
in the ease of reduction of these complexes.
5
Compounds 1–3 were crystallographically characterised and
found to have very similar structures in the solid state. As a
result, only the molecular structure of 3 is depicted in Fig. 1,
though relevant geometrical data for all complexes can be found
in Table 1. In each compound the amidinate or guanidinate
ligates the Rh(COD) fragment in what is best described as an
centre in an g -cyclohexadienyl fashion. Saying this, a recent
report12 on the coordination of N-aryl substituted b-diketiminates
to the Ir(COD) fragment has revealed that the very bulky
ligand in 4 (Fig. 2) coordinates the metal centre in a strikingly
similar fashion to the situation in 1–3. Interestingly, the less
bulky b-diketiminate ligands in 5 coordinate iridium in the more
conventional N,Nꢀ-fashion. There was no mention in the report
5
g -cyclohexadienyl fashion. Consistent with this are the distances
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 1–3
1
2
3
1
2
3
Rh(1)–C(3–7) centroid
Rh(1) · · · C(2)
Rh(1)–COD alkene centroid
C(2)–C(3)
C(2)–C(7)
C(2)–N(1)
1.876(3)
2.600(2)
2.024 (mean)
1.467(3)
1.472(3)
1.306(3)
1.367(3)
1.856(3)
2.662(2)
2.020 (mean)
1.483(4)
1.472(3)
1.300(3)
1.381(3)
1.865(3)
2.569(2)
2.014 (mean)
1.475(4)
1.467(4)
1.310(3)
1.373(3)
C(1)–N(2)
N(2)–C(14)
C(1)–N(3)
1.284(3)
1.413(3)
—
1.294(3)
1.408(3)
1.395(3)
1.300(3)
1.405(3)
1.390(3)
C(2)–N(1)–C(1)
N(1)–C(1)–N(2)
C(1)–N(2)–C(14)
136.8(2)
125.9(2)
122.2(2)
131.6(2)
123.6(2)
119.7(2)
133.5(2)
124.8(2)
122.8(2)
C(1)–N(1)
4800 | Dalton Trans., 2008, 4799–4804
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Finally, thermal isomerisations of the complexes were attempted
◦
by heating their toluene solutions at 80 C for 5 h. In each case,
the 1H NMR spectrum of the reaction mixture revealed that near
quantitative conversion to the 16-electron N,Nꢀ-chelated isomer
(6–8, Scheme 1) had occurred. The isolated crystalline yields of
the complexes were moderate to good. It is of note that the lowest
molecular weight complex, 1, can also be isomerised in high yield
when it is sublimed under reduced pressure (140 ◦C, 5 × 10−6 Torr).
These results suggest that complexes 1–3 are the kinetic products
in the original salt elimination reactions that gave them, and that
6–8 are their thermodynamically more stable isomeric forms.
The X-ray crystal structures of the three monomeric complexes
were obtained and found to be similar to each other and that of
[Rh{(PhN)2CPh}(COD)].8 As a result, only the molecular struc-
ture of 8 is depicted in Fig. 3, though relevant metrical parameters
for all complexes are given in Table 2. The rhodium centre in
each compound has a distorted square planar geometry with Rh–
C and Rh–N distances in the normal range.16 An examination
of the C–N distances within the amidinate or guanidinate ligand
backbones suggested a significant degree of delocalisation over
their CN2 or CN3 fragments. The NMR spectra of the complexes
are symmetrical and fully consistent with them retaining their solid
state structures in solution.
Fig. 2 Iridium b-diketiminate complexes related to the rhodium amidi-
nate and guanidinate complexes in this study (see ref. 12).
as to whether the b-diketiminate in 4 can change its coordination
mode when heated, for example. What is clear, however, is that the
structural similarities between 4 and 1–3 provide further support
for the aforementioned proposed analogies connecting bulky b-
diketiminate, amidinate and guanidinate ligands.
It is evident from the NMR spectra of 1–3 that they retain their
1
solid state structures in solution. Most telling in their H NMR
spectra are the high field positions of the signals corresponding to
the para- and meta-protons of the coordinated aryl substituent (e.g.
3.83 and 5.72 ppm respectively for 1). In addition, the chemical
shifts and 1JRhC couplings for the ortho-, meta- and para-carbons
1
of that substituent in the 13C{ H} NMR spectra of the complexes
1
1
(e.g. 115.5 ppm, JRhC = 2.3 Hz; 101.5 ppm, JRhC = 3.6 Hz;
74.5 ppm, 1JRhC = 5.2 Hz respectively for 1) are consistent with a
p-cyclohexadienyl coordination mode.
Considering the unusual amidinate or guanidinate coordination
mode in the 18-electron complexes, 1–3, it was proposed that
they might undergo isomerisation to more normal 16-electron
N,Nꢀ-chelated species, cf. [Rh{(PhN)2CPh}(COD)], under the
right conditions. A somewhat related isomerisation has been
recently observed when the 18-electron tris(arylamido)stannate
6
complex [Rh(COD){(g -ArꢀNSiMe2)Sn(ArꢀNSiMe2)2SiMe}] (Arꢀ
= 3,5-xylyl) was treated with a series of nucleophiles, e.g. PPh3.
6
This effected a shift in the Rh(COD) fragment from being g -
1
aryl coordinated to being g -coordinated by the tin lone pair
and the added nucleophile, e.g. as in the 16-electron compound
1
[Rh(COD)(PPh3){g -Sn(ArꢀNSiMe2)3SiMe}].15 In contrast, when
1–3 were treated with PPh3 in toluene, decomposition of the com-
plexes to unidentifiable mixtures rapidly occurred. Alternatively,
it was considered that the isomerisation of 1–3 might result from
their irradiation with UV light. However, when toluene solutions
of the complexes were irradiated (k = 254 nm) for 3 h, no
isomerisation was observed, as determined by NMR spectroscopy.
Fig. 3 Molecular structure of 8 (25% thermal ellipsoids are shown,
hydrogen atoms are omitted for clarity).
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 6–8
6
7
8
Rh(1)–N(1)
Rh(1)–N(2)
C(1)–N(1)
C(1)–N(2)
2.0926(18)
2.091(2)
2.087(2)
1.337(3)
1.353(3)
1.380(3)
2.002 (mean)
109.7(2)
63.54(8)
2.0889(13)
2.0939(13)
1.346(2)
1.350(2)
1.378(2)
2.001 (mean)
109.31(14)
63.46(5)
2.0836(17)
1.351(2)
1.332(3)
—
2.010 (mean)
108.76(17)
62.98(7)
C(1)–N(3)
Rh(1)–COD alkene centroid
N(1)–C(1)–N(2)
N(1)–Rh(1)–N(2)
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As the thermal isomerisations (at 80 ◦C) of toluene solutions
of 1–3 were effectively complete within 5 h, it was proposed
to examine the kinetics of these processes using 1H NMR
spectroscopy. It was believed this would shed light on the effect
the amidinate or guanidinate backbone substituent has on the
rates of the isomerisations. To achieve this, solutions of the same
concentration of 1–3 in C6D6 were prepared and an internal SiMe4
standard added to each. The 1H NMR spectra of the ◦samples were
proportional to the size of the amidinate or guanidinate backbone
substituent. This study has identified further analogies between
the ligating and stabilising properties of bulky amidinates and
guanidinates, and those of b-diketiminates. We are currently exam-
ining the coordination of these ligands to other low oxidation state
transition metal centres and will report on this work in due course.
Experimental section
1
obtained and they were subsequently heated to 80 C. Their H
NMR spectra were then taken at 15 min intervals. Monitoring the
integration of the meta-aryl (Rh coordinated) proton resonance,
relative to that of the internal standard, allowed a determination of
the change of absolute concentration of the complexes with time.
The conversion of 1 to 6 was found to be complete within 15 min
of heating, whilst the conversions of 2 to 7, and 3 to 8 took ca. 3
and 5 h respectively. Considering the rapid conversion of 1, only
the natural logarithm of the concentrations of 2 and 3 could be
accurately plotted against time (Fig. 4). Straight lines were fitted
to both sets of data with excellent correlations (R2 = 0.992 2, R2 =
0.972 3), thus demonstrating that the thermal isomerisations are
unimolecular processes following first order kinetics. The slopes
of the lines yielded rate constants for the isomerisations (2: k =
5.41 × 10−4 s−1, 3: k = 2.87 × 10−4 s−1) which, combined with
the rapid isomerisation of 1, indicate that there is an inverse
correlation between the rates of the conversions and the size of
the ligand backbone substituent. This is not surprising, as larger
backbone substituents would be expected to hinder the rotation
of the ligand ArN fragments about the C(1)–N bonds, and the
migration of the Rh(COD) fragment, both of which are required
for the isomerisations to occur.
Synthesis
General considerations. All manipulations were carried out
using standard Schlenk and glove box techniques under atmo-
spheres of high purity argon or dinitrogen. Hexane and toluene
were distilled over molten potassium metal. Melting points
were determined in sealed glass capillaries under argon and are
uncorrected. Mass spectra were recorded at the EPSRC National
Mass Spectrometric Service at Swansea University. Microanalyses
were obtained from the Campbell Microanalytical Laboratory,
University of Otago. IR spectra were recorded using a Nicolet 510
FT-IR spectrometer as Nujol mulls between NaCl plates. 1H and
1
13C{ H} NMR spectra were recorded on either Bruker DPX 300
or AV 200 spectrometers and were referenced to the resonances
of the solvent used. K[Piso], K[Priso], K[Giso]6 and [{RhCl(g -
4
COD)}2]17 were synthesised by variations of literature methods.
All other reagents were used as received.
Preparation of [Rh{(g5-ArN)(ArN)CBut}(COD)] 1. A suspen-
sion of [K(Piso)] (0.50 g, 1.09 mmol) in toluene (25 cm3) was
4
added to a solution of [{RhCl(g -COD)}2] (0.27 g, 0.55 mmol) in
toluene (15 cm3) at −78 ◦C over 10 min. The reaction mixture was
◦
warmed to 20 C over 2 h and stirred for a further hour to give
a yellow solution. Volatiles were then removed in vacuo and the
residue extracted into hexane (60 cm3) and filtered. The filtrate was
concentrated to ca. 20 cm3 and stored at −30 ◦C overnight to give
pale yellow blocks of 1. A second crop was obtained (0.19 g, 28%).
Mp 133–135 ◦C (decomp.); 1H NMR (200.13 MHz, C6D6, 298 K):
d 1.41 (2 × coincidental d, 3JHH = 6.6 Hz, 12 H, (CH3)2CH), 1.60
(d, 3JHH = 6.7 Hz, 6 H, (CH3)2CH), 1.61 (d, 3JHH = 6.9 Hz, 6 H,
(CH3)2CH), 1.64 (s, 9 H, (CH3)3C), 1.78 (m, 4 H, CH2CH), 2.07
(m, 4 H, CH2CH), 3.20 (sept, 3JHH = 6.8 Hz, 2 H, (CH3)2CH), 3.27
(br. m, 4 H, CH2CH), 3.65 (sept, 3JHH = 6.7 Hz, 2 H, (CH3)2CH),
3
5
3
3.85 (t, JHH = 5.8 Hz, 1 H, g -arene-p-Ar-H), 5.65 (d, JHH
=
5.8 Hz, 2 H, g -arene-m-Ar-H), 7.11 (t, 3JHH = 6.7 Hz, 1 H, p-Ar-
5
H), 7.30 (br. m, 2 H, m-Ar-H); 13C{ H} NMR (50.33 MHz, C6D6,
1
298 K): d 21.6 ((CH3)3C), 23.9, 24.8, 25.4, 26.7 ((CH3)2CH), 29.1,
29.8 ((CH3)2CH), 31.7 (CH2), 42.2 ((CH3)3C), 73.3 (br., CH2CH),
Fig. 4 Plot of ln [2] and ln [3] vs time for the thermal isomerisations of 2
and 3 in C6D6 at 80 ◦C.
74.5 (d, 1JRhC = 5.2 Hz, g -arene-p-Ar-C), 101.5 (d, 1JRhC = 3.6 Hz,
5
5
1
5
g -arene-m-Ar-C), 115.5 (d, JRhC = 2.3 Hz, g -arene-o-Ar-C),
121.4, 121.9, 138.8, 148.6 (Ar-C), 164.8 (CN2); MS (EI 70 eV) m/z
(%): 630 (MH+, 13), 573 (MH+ − But, 31), 522 (MH+ − COD, 29),
420 ({[N(Ar)2]CBut}H+, 17); IR m/cm−1 (Nujol): 1593 s, 1567 s,
1538 s, 1360 m, 1253 m, 1139 m, 910 m, 866 m, 842 m, 800 m; EI
acc. mass on M+: calc. for C37H55N2Rh 630.3415, found 630.3415;
C37H55N2Rh requires C 70.46, H 8.79, N 4.44%; found C 70.46, H
8.53, N 4.45%.
Conclusion
In summary, the reactions of a series of aryl-substituted amidi-
4
nate and guanidinate salts with [{RhCl(g -COD)}2] have yielded
complexes in which the ligand does not act as an N,Nꢀ-chelator,
but instead coordinates the rhodium centre solely through an aryl
5
substituent in an g -cyclohexadienyl mode. Thermal conversions
of these complexes to their N,Nꢀ-chelated isomers have been
carried out and the kinetics of these processes have been shown
to be first order. The rates of the isomerisations are inversely
Preparation of [Rh{(g5-ArN)(ArN)CNPri2}(COD)] 2. This
compound was prepared by a similar procedure to that used for
the synthesis of 1. Yellow blocks (yield 42%). Mp 164–166 ◦C
4802 | Dalton Trans., 2008, 4799–4804
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(decomp.); 1H NMR (200.13 MHz, C6D6, 298 K): d 1.50 (d, 3JHH
6.7 Hz, 12 H, (CH3)2CHN), 1.57–1.68 (overlapping d, JHH
=
=
(br. m, 4 H, CH2CH), 4.14 (sept, 3JHH = 6.8 Hz, 4 H, (CH3)2CH),
3
1
7.15–7.29 (m, 6 H, Ar-H); 13C{ H} NMR (50.33 MHz, C6D6,
ca. 6.8 Hz, 24 H, (CH3)2CH), 1.83 (m, 4 H, CH2), 2.12 (m, 4 H,
298K): d 24.0((CH3)3C), 25.9, 28.2((CH3)2CH), 30.2 ((CH3)2CH),
3
1
CH2), 3.40 (br. m, 4 H, CH2CH), 3.60 (sept, JHH = 6.9 Hz, 2
30.7 (CH2), 44.5 ((CH3)3C), 78.5 (d, JRhC = 13.7 Hz, CH2CH),
3
5
H, (CH3)2CHN), 3.83 (t, JHH = 5.8 Hz, 1 H, g -arene-p-Ar-H),
123.8, 124.5, 143.0, 143.9 (Ar-C), 186.8 (d, 2JRhC = 5.0 Hz, CN2C);
MS (EI 70 eV) m/z (%): 630 (MH+, 45), 573 (MH+ − But, 78),
522 (MH+ − COD, 92), 420 ({[N(Ar)2]CBut}H+, 21); IR m/cm−1
(Nujol): 1315 m, 1241 m, 1170 m, 1098 m, 949 m, 800 m, 761 m; EI
acc. mass on M+: calc. for C37H55N2Rh 630.3415, found 630.3418;
C37H55N2Rh requires C 70.46, H 8.79, N 4.44%; found C 70.19, H
8.91, N 4.45%.
3
3.94 (overlapping sept, JHH = ca. 6.9 Hz, 4 H, (CH3)2CH),
3
5
3
5.72 (d, JHH = 5.8 Hz, 2 H, g -arene-m-Ar-H), 7.11 (t, JHH
=
7.9 Hz, 1 H, p-Ar-H), 7.22–7.36 (m, 2 H, Ar-H); 13C{ H} NMR
(50.33 MHz, C6D6, 298 K): d 21.9 ((CH3)2CHN), 24.4, 24.8,
26.0, 26.4 ((CH3)2CH), 29.1 (b, 2 × (CH3)2CH), 31.7 (CH2),
1
1
47.0 ((CH3)2CHN), 72.1 (d, JRhC = 13.3 Hz, CH2CH), 74.6 (d,
1JRhC = 5.4 Hz, g -arene-p-Ar-C), 101.1 (d, JRhC = 3.5 Hz, g -
5
1
5
Preparation of [Rh{j2-N,Nꢀ-(ArN)2CNPri2}(COD)] 7. This
compound was prepared by a similar procedure to that used for the
synthesis of 6, except using◦2 as the starting material. Yellow blocks
(yield 56%). Mp 183–185 C (decomp.); 1H NMR (200.13 MHz,
arene-m-Ar-C), 116.5 (d, 1JRhC = 2.3 Hz, g -arene-o-Ar-C), 120.5,
5
122.2, 140.0, 142.4, 147.0 (Ar-C), 175.7 (CN3); MS (EI 70 eV)
m/z (%): 673 (MH+, 8), 630 (MH+ − Pri, 16), 573 (MH+
−
NPri2, 3), 565 (MH+ − COD, 4), 462 ({[N(Ar)]2CNPri2}H+, 3); IR
m/cm−1 (Nujol): 1555 s, 1537 s, 1366 m, 1311 m, 1279 m, 1260 m,
1218 m, 1134 m, 992 m, 848 m, 800 m; EI acc. mass on M+: calc.
for C39H60N3Rh 673.3837, found 673.3839; C39H60N3Rh requires
C 69.52, H 8.98, N 6.24%; found C 69.50, H 8.93, N 6.28%.
3
C6D6, 298 K): d 0.91 (d, JHH = 7.0 Hz, 12 H, (CH3)2CHN),
3
1.54 (d, JHH = 6.9 Hz, 12 H, (CH3)2CH), 1.61 (m, 4 H, CH2),
3
1.94 (d, JHH = 6.8 Hz, 12 H, (CH3)2CH), 2.42 (m, 4 H, CH2),
3
3.94 (br. m, 4 H, CH2CH), 4.11 (2 × overlapping sept, JHH
=
ca. 6.9 Hz, 6 H, (CH3)2CH), 7.18–7.34 (m, 6 H, Ar-H); 13C{ H}
NMR (50.33 MHz, C6D6, 298 K): d 23.5 ((CH3)2CHN), 26.1, 26.2
((CH3)2CH), 27.6 ((CH3)2CH), 30.9 (CH2), 49.0 ((CH3)2CHN),
76.2 (d, 1JRhC = 14.0 Hz, CH2CH), 123.8, 124.0, 143.8, 144.7 (Ar-
C), 174.5 (d, 2JRhC = 5.7 Hz, CN3); MS (EI 70 eV) m/z (%): 673
(MH+, 50), 630 (MH+ − Pri, 100), 573 (MH+ − NPri2, 13), 565
(MH+ − COD, 18), 462 ({[N(Ar)]2CNPri2}H+, 10); IR m/cm−1
(Nujol): 1434 s, 1407 s, 1316 m, 1275 m, 1245 m, 1176 m, 1124
m, 1109 m, 952 m, 932 m, 871 m, 799 s, 757 s, 658 m; EI acc.
mass on M+: calc. for C39H60N3Rh 673.3837, found 673.3834;
C39H60N3Rh requires C 69.52, H 8.98, N 6.24%; found C 69.82, H
9.00, N 6.35%.
1
Preparation of [Rh{(g5-ArN)(ArN)CN(C6H11)2}(COD)] 3.
This compound was prepared by a similar procedure to that used
for the synthesis of 1. Yellow blocks (yield 54%). Mp 169–171 ◦C
1
(decomp.); H NMR (200.13 MHz, C6D6, 298 K): d 1.45 (mc,
3
12 H, Cy-CH2), 1.54 (d, JHH = 7.0 Hz, 6 H, (CH3)2CH), 1.58
(d, 3JHH = 7.0 Hz, 6 H, (CH3)2CH), 1.62 (d, 3JHH = 6.6 Hz, 6 H,
(CH3)2CH), 1.70 (d, 3JHH = 6.7 Hz, 6 H, (CH3)2CH), 1.84 (br. m,
8 H, Cy-CH2), 2.12 (br. m, 8 H, COD-CH2), 3.46 (br. m, 4 H,
COD-CH), 3.57 (m, 2 H, Cy-CH), 3.59 (sept, 3JHH = 6.4 Hz, 2 H,
3
5
(CH3)2CH), 3.91 (t, 1 H, JHH = 5.8 Hz, g -arene-p-Ar-H), 3.94
3
3
(sept, JHH = 7.0 Hz, 2 H, (CH3)2CH), 5.74 (d, JHH = 5.8 Hz,
5
3
2 H, g -arene-m-Ar-H), 7.13 (t, JHH = 7.5 Hz, 1 H, p-Ar-H),
Preparation of [Rh{j2-N,Nꢀ-(ArN)2CN(C6H11)2}(COD)] 8.
This compound was prepared by a similar procedure to that used
for the synthesis of 6, except using 3 as the starting material.
Yellow blocks (yield 29%). Mp 164–166 ◦C (decomp.); 1H NMR
(300.13 MHz, C6D6, 298 K): d 0.91–1.08 (m, 8 H, Cy-CH2), 1.52
(mc, 12 H, Cy-CH2), 1.58 (d, 3JHH = 6.8 Hz, 12 H, (CH3)2CH), 1.59
7.34 (m, 2 H, m-Ar-H); 13C{ H} NMR (75.48 MHz, C6D6, 298
1
K): d 20.8, 23.5 (Cy-CH2), 25.0, 25.2, 26.1, 26.3 (br., (CH3)2CH),
28.1, 29.5 ((CH3)2CH), 30.7 (COD-CH2), 34.6 (Cy-CH2), 57.0
5
(CHN), 73.5 (d, 1JRhC = 5.2 Hz, g -arene-p-Ar-C), 75.4 (d, 1JRhC
=
1
5
13.0 Hz, COD-CH), 99.8 (d, JRhC = 3.6 Hz, g -arene-m-Ar-C),
119.1, 121.1, 122.6, 138.7, 144.0, 145.6 (br, Ar-C); MS (EI 70 eV)
m/z (%): 753 (MH+, 2), 710 (MH+ − Pri, 1), 670 (MH+ − Cy, 2),
645 (MH+ − COD, 1), 542 ({[N(Ar)]2CNCy2}H+, 12); IR m/cm−1
(Nujol): 1563 s, 1520 s, 1352 m, 1283 m, 1235 m, 1206 m, 1170 m,
1127 m, 1007 m, 970 m, 932 m, 891 m, 848 m, 802 m; EI
acc. mass on M+: calc. for C45H68N3Rh 753.4467, found 753.4463;
C45H68N3Rh requires C 71.69, H 9.09, N 5.57%; found C 70.21, H
9.15, N 5.31%.
3
(m, 4 H, COD-CH2), 1.93 (d, JHH = 6.8 Hz, 12 H, (CH3)2CH),
2.32 (m, 4 H, COD-CH2), 3.72 (m, 2 H, Cy-CH), 3.91 (br. m, 4 H,
3
COD-CH), 3.95 (sept, JHH = 6.8 Hz, 4 H, (CH3)2CH), 7.17
3
3
(tr, JHH = 6.4 Hz, 2 H, p-Ar-H), 7.26 (d, JHH = 6.8 Hz, 4 H,
m-Ar-H); 13C{ H} NMR (50.33 MHz, C6D6, 298 K): d 23.6 (Cy-
1
CH2), 26.1, 26.4 ((CH3)2CH), 26.9 (Cy-CH2), 27.6 ((CH3)2CH),
31.1 (COD-CH2), 35.8 (Cy-CH2), 58.6 (Cy-CHN), 76.7 (d, 1JRhC
=
4
13.0 Hz, COD-CH), 123.6, 123.8, 143.1, 145.1 (Ar-C), 174.1 (d,
2JRhC = 5.5 Hz, CN3); MS (EI 70 eV) m/z (%): 753 (MH+, 100),
710 (MH+ − Pri, 51), 670 (MH+ − Cy, 87), 645 (MH+ − COD,
39), 560 (MH+ − COD − Cy, 29), 542 ({[N(Ar)]2CNCy2}H+, 47);
IR m/cm−1 (Nujol): 1434 s, 1393 s, 1323 s, 1279 s, 1243 s, 1096
m, 1020 s, 896 m, 866 m, 825 m, 791 s, 772 m, 750 s, 660 m; EI
acc. mass on M+: calc. for C45H68N3Rh 753.4463, found 753.4463;
C45H68N3Rh requires C 71.69, H 9.09, N 5.57%; found C 71.88, H
9.36, N 5.67%.
N.B. a low yield (<2%) by-product, [{Rh(g -COD)}4(l4-
O2SiMe2)2], was isolated from the reaction mixture and crystal-
lographically characterised (see ESI†).
Preparation of [Rh{j2-N,Nꢀ-(ArN)2CBut}(COD)] 6. A solu-
tion of 1 (0.10 g, 0.16 mmol) in toluene (10 cm3) was heated at
80 ◦C for 5 h. Volatiles were removed from the resultant solution
in vacuo, the residue extracted into hexane (10 cm3) and filtered.
◦
The filtrate was concentrated to ca. 2 cm3 and stored at −30 C
overnight to give pale yellow blocks of 6. A second crop was
◦
1
obtained (0.06 g, 60%). Mp 133–135 C (decomp.); H NMR
(200.13 MHz, C6D6, 298 K): d 1.10 (s, 9 H, (CH3)3C), 1.58 (d,
3JHH = 6.8 Hz, 12 H, (CH3)2CH), 1.59 (br. m, 4 H, CH2), 1.76
(d, 3JHH = 6.7 Hz, 12 H, (CH3)2CH), 2.43 (br. m, 4 H, CH2), 3.83
X-Ray crystallography
4
Crystals of 1–3, 6, 7, 8·(hexane) and [{Rh(g -COD)}4(l4-
O2SiMe2)2] suitable for X-ray structural determination were
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The Royal Society of Chemistry 2008
Dalton Trans., 2008, 4799–4804 | 4803
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Table 3 Crystal data for compounds 1–3 and 6, 7 and 8·(hexane)
Compound
1
2
3
6
7
8·(hexane)
Empirical formula
FW
Temp./K
C37H55N2Rh
630.74
123(2)
C39H60N3Rh
673.81
123(2)
C45H68N3Rh
753.93
123(2)
C37H55N2Rh
630.74
123(2)
C39H60N3Rh
673.81
123(2)
C51H82N3Rh
840.11
123(2)
Cryst. syst.
Monoclinic
P21/n
Triclinic
P1
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
C2/c
Monoclinic
P21/n
¯
Space group
˚
a/A
12.178(2)
15.861(3)
16.978(3)
90
93.63(3)
90
3272.8(11)
4
1.280
10.163(2)
10.502(2)
19.025(4)
102.33(3)
109.60(1)
108.69(3)
6761(3)
2
11.3725(5)
17.6352(7)
20.1756(6)
90
94.264(1)
90
4035.1(3)
4
1.241
18.725(4)
16.203(3)
11.480(2)
90
106.75(3)
90
3335.3(11)
4
1.256
40.659(8)
11.960(2)
23.891(5)
90
108.90(3)
90
10 991(4)
12
1.222
12.1799(3)
23.6855(4)
16.3738(3)
90
101.444(1)
90
4629.72(16)
4
1.205
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
Vol./A
Z
Density (calcd)/Mg m−3
l(Mo-Ka)/mm−1
1.226
0.497
0.549
0.457
0.538
0.495
0.405
F(000)
1344
14 460
7487 (0.0232)
720
13 308
7394 (0.0208)
1616
55 950
11 843 (0.0650)
1344
15 377
8034 (0.0223)
4320
18 381
12 544 (0.0239)
1816
52 844
10 698 (0.0278)
No. of reflections collected
No. of independent reflns (Rint
)
Final R1 (I > 2r(I)) and wR2 0.0353 and 0.0967 0.0402 and 0.1063 0.0489 and 0.1225 0.0329 and 0.0841 0.0432 and 0.1129 0.0295 and 0.0766
indices (all data)
mounted in silicone oil. Crystallographic measurements were
made using either a Nonius Kappa CCD or a Bruker X8 CCD
diffractometer. The structures were solved by direct methods and
refined on F2 by full matrix least squares (SHELX-97)18 using all
unique data. Hydrogen atoms have been included in calculated
positions (riding model) for all structures. The crystal structure of
7 contains 1.5 crystallographically independent molecules in the
asymmetric unit. Only the metrical parameters of the full molecule
are discussed in the text. Crystal data, details of data collections
and refinement are given in Table 3.
3 (a) C. Jones, P. C. Junk, J. A. Platts and A. Stasch, J. Am. Chem. Soc.,
2006, 128, 2206; (b) C. Jones, P. C. Junk, J. A. Platts, D. Rathmann and
A. Stasch, Dalton Trans., 2005, 2497; (c) G. Jin, C. Jones, P. C. Junk,
A. Stasch and W. D. Woodul, New J. Chem., 2008, 32, 835.
4 S. P. Green, C. Jones, P. C. Junk, K.-A. Lippert and A. Stasch, Chem.
Commun., 2006, 3978.
5 S. P. Green, C. Jones, G. Jin and A. Stasch, Inorg. Chem., 2007, 46, 8.
6 D. Heitmann, C. Jones, P. C. Junk, K.-A. Lippert and A. Stasch, Dalton
Trans., 2007, 187.
7 R. P. Rose, C. Jones, C. Schulten, S. Aldridge and A. Stasch, Chem.–
Eur. J., in press.
8 F. L. Lahoz, A. Tiripicchio, M. T. Camellini, L. A. Oro and M. T.
Pinillos, J. Chem. Soc., Dalton Trans., 1985, 1487.
9 J. R. Hagadorn and J. Arnold, J. Organomet. Chem., 2001, 637–639,
521.
Acknowledgements
10 L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem. Rev., 2002,
102, 3031.
We thank the Australian Research Council (fellowships for CJ and
AS) and the EPSRC (studentship for DPM). The EPSRC Mass
Spectrometry Service at Swansea University is also thanked.
11 P. H. M. Budzelaar, N. N. P. Moonen, R. de Gelder, J. M. M. Smits and
A. W. Gal, Eur. J. Inorg. Chem., 2000, 753.
12 W. H. Bernskoetter, E. Lobkovsky and P. J. Chirik, Organometallics,
2005, 24, 6250.
13 I. Haiduc, Organometallics, 2004, 23, 3 and references therein.
14 See for example: (a) L. Dahlenburg and N. Hock, J. Organomet. Chem.,
1985, 284, 129; (b) M. Martin, E. Sola, S. Tejero, J. L. Andres and L. A.
Oro, Chem.–Eur. J., 2006, 12, 4043.
15 M. Kilian, H. Wadepohl and L. H. Gade, Organometallics, 2007, 26,
3076.
16 As determined by a survey of the Cambridge Crystallographic
Database, March 2008.
17 G. Giordano and R. H. Crabtree, Inorg. Synth., 1990, 28, 88.
18 G. M. Sheldrick, SHELX-97, University of Go¨ttingen, Germany, 1997.
References
1 For general references on the structure and reactivity of amidinate and
guanidinate complexes see: (a) J. Barker and M. Kilner, Coord. Chem.
Rev., 1994, 133, 219; (b) F. T. Edelmann, Coord. Chem. Rev., 1994, 137,
403; (c) P. J. Bailey and S. Price, Coord. Chem. Rev., 2001, 214, 91;
(d) M. P. Coles, Dalton Trans., 2006, 985 and references therein.
2 S. P. Green, C. Jones and A. Stasch, Science, 2007, 318, 1754.
4804 | Dalton Trans., 2008, 4799–4804
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The Royal Society of Chemistry 2008
©