A new route to metallacycloalkanes

Article abstract of DOI:10.1039/b504747a

Reaction of the bis-alkenyl complex cis-[Pt(PPh₃) ₂-(CH₂CH₂CH=CH₂)₂] with Grubbs 1st generation catalyst gives, in high yield, the metallacycloalkene cis-[Pt(PPh₃)₂(CH

Full text of DOI:10.1039/b504747a

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A new route to metallacycloalkanes
Katja Dralle, Nastassia L. Jaffa, Tanya le Roex, John R. Moss,* Susan Travis, Nicholas D. Watermeyer and
Akella Sivaramakrishna
Received (in Cambridge, UK) 6th April 2005, Accepted 26th May 2005
First published as an Advance Article on the web 16th June 2005
DOI: 10.1039/b504747a
and m 5 2,3)12 and Cp*2HfH(CH2)mCHLCH2 (m 5 4 or 5) have
Reaction of the bis-alkenyl complex cis-[Pt(PPh3)2-
been described.13
(CH2CH2CHLCH2)2] with Grubbs 1st generation catalyst
We now find that reaction of Pt(COD)Cl2 with the Grignard
reagent BrMgCH2CH2CHLCH2, followed by PPh3 leads to the
bis-alkenyl compound cis-[Pt(PPh3)2(CH2CH2CHLCH2)2] 1 in
good yield (see Scheme 1).
gives, in high yield, the metallacycloalkene cis-
[Pt(PPh3)2(CH2CH2CHLCHCH2CH2)], which can be hydro-
genated to the metallacycloalkane cis-[Pt(PPh3)2(CH2)6].
Metallacycloalkane compounds are well known1 and many have
been prepared by the following two routes:2–4
This compound was fully characterised by analytical and
spectroscopic methods.{ Crystals of 1 suitable for X-ray were
grown from CH2Cl2–hexane and the structure with two pendant
alkene groups was confirmed (see Fig. 1).{
LM22 + Y(CH2)nY A LM(CH2)n + 2Y2 (Y 5 triflate)
(1)
Reaction of
1
with Grubbs 1st generation catalyst,
LMX2 + M1(CH2)nM1 A LM(CH2)n + 2M1X
RuCl2(PCy3)2(LCHPh), (5 mol%) results in ring closing metathesis
(RCM) to yield the metallacycloheptene in high yield (see
Scheme 1). This reaction can readily be followed by observation
(M1 5 Li or MgBr, X 5 halogen)
(2)
1
Metallacycles are of particular importance since they are key
intermediates in important catalytic reactions for example
metallacyclobutanes in alkene metathesis.5
of the disappearance of the LCH2 signal of 1 in the H NMR
spectrum and the appearance of a new LCH signal. Thus it is seen
that the RCM is about 90% complete in the first 15 minutes. The
organometallic product of this reaction, 2, was isolated as
colourless crystals in high yield and its composition was
determined by analytical and spectroscopic methods.{
Confirmation that the RCM had taken place to yield a
metallacycloheptene was obtained from the X-ray crystal structure
of 2 (see Fig. 2).{
Although small metallacycles (with four- to six-membered rings)
can be relatively easily prepared, medium ring compounds with
seven to eleven members are difficult to make.1 It is just these
medium ring metallacycles that have been implicated6 and
recently shown7 to occur as intermediates in catalytic trimerisation
reactions of ethylene to give 1-hexene. More recently a process for
tetramerisation of ethylene has been reported8,9 to give 1-octene,
which might be expected to occur via a metallacyclononane.9
Lindner and co-workers made a systematic study of the
synthesis of metallacycles by the reaction of Na2Os(CO)4 with
Y(CH2)nY (Y 5 triflate).2 They found that, whereas the 5-, 6- and
7-membered ring compounds (CO)4Os(CH2)n (n 5 4–6) could be
synthesised, the yields of the 8-, 9-, and 10-membered ring analogs
dropped to zero, and di- and trimetallacycles became the favoured
and isolated products.2
This structure appears to be the first example of a structurally
characterised metallacycloheptene. The ring shows a twist-boat
conformation.
Reaction of 2 with hydrogen in the presence of Pd/C (10%)
results in saturation of the CLC double bond to yield the
metallacycloheptane, 3, in quantitative yield. This complex has
been reported previously by Whitesides and co-workers, who
prepared it using the dilithium route, but isolated it in only 3%
yield.
The use of Grubbs catalysts for constructing medium and large
rings in organic chemistry has found wide application and led to
the efficient preparation of organic ring compounds that are
otherwise very difficult to make.10
The methodology described here can also be applied to
metallacycles of larger size. Thus we have spectroscopic evidence
Recently the elegant synthesis of ‘‘molecular gyroscopes’’ was
described by Gladysz et al. using Grubbs catalysts for ring closing
metathesis (RCM) of alkene groups bonded to phosphorus.11
We envisaged that new C–C bonds could be formed from
complexes bearing pendant alkene groups, i.e. from metal alkenyl
compounds containing the functionality M–(CH2)mCHLCH2. Few
compounds of this class have been prepared although the
compounds (g5-C5R5)Fe(CO)2(CH2)mCHLCH2 (R 5 H or Me
Department of Chemistry, University of Cape Town, Rondebosch, 7701,
South Africa. E-mail: jrm@science.uct.ac.za; Fax: +27 21 689-7499;
Tel: +27 21 650-2535
Scheme 1 (i) Et2O, 278 uC; (ii) PPh3; (iii) Grubbs catalyst generation 1,
CH2Cl2, reflux 1 h; (iv) Pd/C, H2, MeOH–CH2Cl2.
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In addition, we are also exploring the application of this route to
other metal and ligand systems in order to prepare a range of
previously unknown metallacycles with medium to large rings and
thence to explore their chemistry.14
Notes and references
{ Spectroscopic data. Compound 1 (all at 298 K, CDCl3): d 1H: 0.84–1.96
(m, 8H, CH2), 4.38–4.68 (m, 4H, LCH2), 5.35–5.55 m, 2H, LCH), 7.08–7.83
(m, 30H, Ph). d 31P{1H}: 27.01 (s) (1JPtP 1765). Yield 5 67%; mp 105–
1
120 uC (dec.). Compound 2: d H: 1.24–1.69 (m, 4H, CH2), 2.23–2.55 (t,
4H, CH2CHL), 5.67–5.74 (t, 2H, LCH), 7.07–7.52 (m, 30H, Ph). d31P{1H}:
27.4 (s) (1JPtP 1765). Yield 5 80%; mp 167–169 uC (dec.). Compound 3: d
1H: 0.83–1.74 (m, 12H, CH2), 7.11–7.80 (m, 30H, Ph). d 31P{1H}: 28.6 (s)
(1JPtP 3028). Yield 5 98%; mp 138–146 uC (dec.). Compound 4: d 1H: 0.80–
1.92 (m, 16H, CH2), 6.7–7.94 (m, 30H, Ph). d 31P{1H}: 29.3 (s) (1JPtP 2894).
Yield 5 62%; mp 140–141 uC (dec.).
{ Crystallographic data. Intensity data were collected at 113 K on a Nonius
Kappa CCD diffractometer using graphite-monochromated Mo-Ka
radiation (l 5 0.71069 s). 1: C44H44P2Pt?0.5C6H14, M 5 872.95,
monoclinic, P21/n, a 5 17.2027(2), b 5 10.3525(1), c 5 23.4504(3) s,
a 5 90.00, b 5 108.608(1), c 5 90.00u, V 5 3957.98(8) s3, Z 5 4, m 5
3.654 mm21, unique reflections 5 9486 [Rint 5 0.0471], R1 5 0.0243,
wR2 5 0.0466 [I . 2s(I)]. Atom C7 in one of the butenyl ligands was found
to be disordered over two positions with site occupancy factors of 0.81
(C7A) and 0.19 (C7B). This disorder was treated by forcing the
temperature factors of the two partial atoms to refine to the same value,
then fixing this value and allowing the site occupancy factors to refine to
give a total site occupancy of one. The refined site occupancy factors were
then fixed and the isotropic temperature factors of the two partial atoms
were allowed to refine independently. Hydrogen atoms were not placed on
the two partial atoms. All non-hydrogen atoms were refined anisotropi-
cally, with the exception of the disordered atom C7 which was refined
Fig. 1 Molecular structure of the major component of compound 1.
Selected bond lengths (s): Pt(1)–P(1) 2.300; Pt(1)–P(2) 2.304; Pt(1)–C(1)
2.127(2); Pt(1)–C(5) 2.095(3); C(3)–C(4) 1.304(4); C(1)–C(2) 1.535(4);
C(7)–C(8) 1.247(6); C(5)–C(6) 1.533(4). Selected bond angles (u): P(1)–
Pt(1)–P(2) 99.65(2); C(1)–Pt(1)–C(5) 83.07(2).
¯
isotropically 2: C42H40P2Pt, M 5 801.81, triclinic, P1, a 5 10.1405(1),
b 5 10.3988(2), c 5 17.2796(3) s, a 5 94.001(1), b 5 106.261(1),
c 5 103.161(1)u, V 5 1685.81(5) s3, Z 5 2, m 5 4.286 mm21, unique
reflections 5 8024 [Rint 5 0.0612], R1 5 0.0301, wR2 5 0.0573 [I . 2s(I)].
CCDC 270701–270702. See http://dx.doi.org/10.1039/b504747a for crystal-
lographic data in CIF or other electronic format.
1 B. Blom, H. Clayton, M. Kilkenny and J. R. Moss, Adv. Organomet.
Chem., 2005, accepted for publication.
2 E. Lindner, R.-M. Jansen and H. A. Mayer, Angew Chem., Int. Ed.
Engl., 1986, 25, 1008; E. Lindner, R.-M. Jansen, W. Hiller and R. Fawzi,
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M. Steinman, Chem. Ber., 1996, 129, 945.
3 J. X. McDermott, J. F. White and G. M. Whitesides, J. Am. Chem.
Soc., 1976, 98, 6521.
4 N. W. Alcock, K. H. Bryars and P. G. Pringle, J. Organomet. Chem.,
1990, 386, 399.
5 R. H. Grubbs, Tetrahedron, 2004, 60, 7177 and references therein.
6 D. S. McGuiness, P. Wasserscheid, W. Keim, J. T. Dixon, J. J.
C. Grove, C. Hu and U. Englert, Chem. Commun., 2003, 334 and
references therein.
7 T. Agapie, S. J. Schofer, J. A. Labinger and J. E. Bercaw, J. Am. Chem.
Soc., 2004, 126, 1304.
8 A. Bollmann, K. Blann, J. T. Dixon, F. M. Hess, E. Killian,
H. Maumela, D. S. McGuiness, D. H. Morgan, A. Neveling, S. Otto,
M. Overett, A. M. Z. Slawin, P. Wasserscheid and S. Kuhlmann, J. Am.
Chem. Soc., 2004, 126, 14712.
9 M. Overett, K. Blann, A. Bollmann, J. T. Dixon, F. M. Hess, E. Killian,
H. Maumela, D. H. Morgan, A. Neveling and S. Otto, Chem.
Commun., 2005, 622.
10 M. P. Sibi and T. Subramian, Synlett, 2004, 1211 and references therein.
11 T. Shima, F. Hampel and J. A. Gladysz, Angew. Chem. Int. Ed., 2004,
43, 2.
Fig. 2 Molecular structure of compound 2. Selected bond lengths (s):
Pt(1)–P(1) 2.290; Pt(1)–P(2) 2.317; Pt(1)–C(1) 2.136(3); Pt(1)–C(6)
2.115(3); C(2)–C(3) 1.507(5); C(3)–C(4) 1.328 (6); C(4)–C(5) 1.497 (6).
Selected bond angles (u): P(1)–Pt(1)–P(2) 97.34(3); C(1)–Pt(1)–C(6)
87.15(14).
12 L. Hermans and S. F. Mapolie, Polyhedron, 1997, 16, 869 and references
therein; G. Joorst, R. Karlie and S. F. Mapolie, S. Afr. J. Chem., 1998,
51, 132.
13 J. E. Bercaw and J. R. Moss, Organometallics, 1992, 11, 639.
14 B. Blom, N. L. Jaffa, A. Sivaramakrishna, J. R. Moss, T. Mahamo,
E. Hager, T. le Roex, H. Clayton and G. Smith, unpublished results.
to show for example that the bis-pentenyl complex, cis-
[Pt(PPh3)2(CH2CH2CH2CHLCH2)2], also undergoes RCM to
give, after hydrogenation, the corresponding platinacyclononane
4 in high yield and under mild conditions.14
3866 | Chem. Commun., 2005, 3865–3866
This journal is ß The Royal Society of Chemistry 2005