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Second Sphere Coordination of Cationic Rhodium Complexes by Dibenzo[3n]crown-n Ethers.

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Table 3. Anodic oxidation of ,R-trimethylsilylcarboxylicacids in acetonitnl&/
ethanol (5 : 1) [a].
Acid
T ["C]
Product
Yield [b] [%I
4a, b
5a, b
11
12
13
14
15
20
20
20
60
20
20
20
2,5-norbornadiene
I-methyl-l,4-cyclohexadiene[c]
bicyclo[4.4.0]deca- 1,4-diene
2-norbornene
4-methyl-1-cyclohexene
4,5-dimethyl-l-cyclohexene
Cphenyl- 1-cyclohexene
76
67
83 [dl
60
73
89
91 Id1
[a] See Table 2 for electrolysis conditions. [b] Determined by gas chromatography. [c] Including 10% toluene. [d] Isolated yield.
and
the
cationic
rhodium(1)
complexes['],
[fi(~od)(NH,),]~and [Rh(nbd)(NH&]@, and discovered
that in the case of DB24C8 and DB30C10 the 1,5-cyclooctadiene (cod) and norbornadiene (nbd) ligands also prefer
to occupy positions in which they are sandwiched between
the two benzene rings of the receptors. In addition to presenting 'H-NMR spectroscopic evidence for this adduct
stereochemistry in solution, X-ray structuresr3]of the crystalline adducts['] [Rh(cod)(NH&. DB30C10][PF6] 1,
[Rh(cod)(NH3),.DB24C8][PF6]
2, and [Rh(nbd)(NH,),.
DB24C8][PF6]3 provide conclusive proof of a remarkable
receptor geometry, clearly much more general in its occurrence than believed previously"'.
when the 15% yield of 2,5-norbornadiene from 5-norbornene-2,3-dicarboxylic acidfzb1
is compared with the 76% obtained starting from 4 .
Received: November 21, 1983;
revised: December 21, 1983 [Z 627 IE]
German version: Angew. Chem. 96 (1984) 238
CAS Registry numbers:
1, 88946-47-8; 2, 5683-31-8; 3, 88946-48-9; 4a, 88946-49-0; 4b, 88946-50-3;
5a, 88946-51-4; 5b, 88946-52-5; 6, 88946-53-6; 7a, 88946-54-7; 7b, 88946-558; 8, 88946-56-9;9, 88946-57-0; 10a, 88946-58-1; lob, 89015-36-1; 11, 8894659-2; 12 (isomer I), 88946-66-1; 12 (isomer 2), 88946-65-0; 13, 88946-60-5;
14, 88946-61-6; 15, 88946-62-7; 16a, 88946-63-8; 16b, 88946-64-9; 17, 7628769-9; 18, 498-66-8; 2,5-norbornadiene, 121-46-0; l-methyl-l,4-cyclohexadiene, 4313-57-9; bicyclo[4.4.0]deca-l,4-diene,62690-61-3: 4-methyl-I-cyclo4300-00-9; 4-phenyl-I-cyclohexene, 591-47-9; 4,5-dimethyl-l-cyclohexene,
hexene, 4994-16-5.
[I] L. A. Paquette, R. V. Williams, Tetrahedron Lett. 22 (1981) 4643.
[2] a) P. Radlick, R. Klem, S. Spurlock, J. J. Sims, E. E. van Tamelen, T. Whitesides, Tetrahedron Lett. 1968, 5117; b) H. H. Westberg, H. J. Dauben,
Jr., ibid. 1968, 5123; c) J. H. P. Utley in N. L. Weinberg: Technique of
Electroorganic Synthesis, Part I, Wiley, New York 1974, p. 873.
[3] T. Sbono, H. Ohmizu, N. Kise, Chem. Lett. 1980, 1571.
Second Sphere Coordination of Cationic Rhodium
Complexes by Dibenzo[L]crown-n Ethers**
By Howard M. Colquhoun, Simon M . Doughty,
J . Fraser Stoddart*, and David J. Williams
Dibenzo-crown ethers of the general type DB3nCn
(n = 6-12) form"] stable adducts with [Pt(bpy)(NH,),]'@
in which the 2,2'-bipyridyl ligand (bpy) participates as a nacceptor in charge transfer interactions with the benzene
rings (n-donors). We have now investigated the structures
of 1 : 1 adducts formed between these DB3nCn receptors[21
[*I Dr. J. F. Stoddart, S. M. Doughty
Department of Chemistry, The University
Sheffield S3 7HF (UK)
Dr. H. M. Colquhoun
New Science Group, Imperial Chemical Industries PLC
The Heath, Runcorn WA7 4QE (UK)
Dr. D. J. Williams
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
London SW7 2AY (UK)
[**I The work was supported by the Science and Engineering Research
Council in the United Kingdom.
Angew. Chem. Int. Ed. Engl. 23 (1984) No. 3
Fig. 1. Structure of the cation of [Rh(cod)(NH3)z.DB30C10][PF6]
in the crystal. Torsion angles ["I (0-C-C-0
and C-C-0-C)
associated with the 30membered ring are given. Four shortest hydrogen bond distances [A]
[ N . . .O], [ H . . '01, angles ["I between COC planes and HO vectors, and
[N-H...O]
angles ["I: "(1). . .0(22)]H,, 3.19, 2.30, 3, 154;
"(1). ..0(28)]Hb, 3.16, 2.37, 45, 139; [N(1)...O(7)]Hc, 2.96, 2.06, 42, 155;
"(2). . .0(19)]H., 3.18,2.29,40, 155. Separation [A] between mean planes of
the benzo rings and cod hydrogen atoms: [ring (29130). . .HI, Ho (40), 2.61;
H,(41),2.98;H.(42),3.33;[ring(14/15)...H]Ho(44),3.13;
He(45),2.87;H,
(46), 3.19.
The solid-state structures (Figs. 1 and 2) of 1-3 reveal
several surprising features: (a) the preference of the cisNH3 ligands, without exception, to straddle the side of one
of the polyether chains, cf. the solid state structures of
[Pt(bpy)(NH,),. DB3nCn][PF6], (n = 8, lo)['] which also exhibit this characteristic; (b) the tendency of both NH3 ligands to underutilize their hydrogen bonding potential towards the polyether chains (only two [N-H . . .O] distances of less than 3 A are present in all of the structures),
of transition-metal ammine
cf. the solid-state
adducts with 18C6 and DB18C6 where [N-H.. .O] distances are considerably shorter; and (c) the invariably
close juxtaposition of the organic ligands cod and nbd
with the benzene rings of DB30C10 and DB24C8, despite
the lack of any obvious stabilizing interactions, cf. the
charge transfer in [Pt(bpy)(NH,), .DB3nCn][PF6]z['1.The
distances quoted in Figure 1, together with the three shortest [N-H-. .O] distances of 3.03, 3.13, and 3.34 A, and of
2.95, 3.01, and 3.27 A for 2 and 3, respectively, suggest
that the additive effect of a substantial number of very
weak hydrogen bonds and electrostatic interactions confers stability upon the adducts. In both DB24C8 adducts 2
and 3 one of the four phenolic oxymethylene units in the
receptor is distorted from its customary ~oplanarity".~'
with the benzene ring in order that the 0 atom can form a
hydrogen bond to one of the NH3 ligands with an approximately trigonal approach to the oxygen atom. It is unclear
0 Verlag Chemie GmbH, 0-6940 Weinheim, 1984
0570-0833/84/0303-0235 $ 02.50/0
235
whether adduct stability is enhanced by any attractive interactiod6]between either the cod or the nbd ligands in
the complexes and the benzene rings in either DB30C10 or
DB24C8 since certain nonbonded atoms only just approach the sum of their van der Waals' radii.
2 6= 1.41. These intra- and intermolecular nuclear Overhauser effects also confirm the signal assignments in Figure 3.
I
n
Fig. 3. Partial
'H-NMR
line spectra for the complexes
[Rh(cod)(NH,), .DB3nCn][PF6]and [Rh(nbd)(NH3)z.DB3nCn][PF6]. The ligand protons are designated in Fig. 2 and the signals (singlets) for the benzoprotons refer to [Rh(cod)(NH,),. I)B3nCn][PF6].
Received: November 22, 1983 [Z 629 IE]
German version: Angew. Chern. 96 (1984) 232
CAS Registry numbers:
[Rh(cOd)(NHp)z.DB30ClO][PF6], 88995-94-2; [Rh(cod)(NH,)z.DB24C8][PF,], 88995-95-3: [Rh(nbd)(NH&. DB24C81[PF6],88995-98-6.
Fig. 2. Computer sketches [(a) and (b)] of space-filling representations of a)
[Rh(cod)(NH3)2.DB24C8]"and b) [Rh(nbd)(NH&, DB24C81".
The principal structural features characteristic of the
solid state are found to prevail in solution, as judged by
the anisotropic diamagnetic shielding effect of the benzene
rings upon the chemical shifts of the 'H-NMR signals of
cod or nbd ligands. Comparison of the 'H-NMR spectra
of [Rh(L)(NH3),.DB3nCn][PF,]
(L=cod, nbd; n=6-12)
with those of the corresponding 1 : 1 adduct with 18C6 in
CD2C12reveals substantial upfield shifts for all protons of
the cod and nbd ligands (Fig. 3). The shifts assume their
greatest magnitude for Hein the cod ligand and for Hb in
the nbd ligand when the receptor is DB24C8. They are accompanied by modest shifts to lower field for the aromatic
C6H4protons relative to the singlets observed at 6 = 6.876.90 for these protons in the free crown ethers. Significantly, this shift also attains its maximum in both series of adducts when the receptor is DB24C8.
Qualitative analysis of nuclear Overhauser effects from
difference spectra recorded at 400 MHz confirm that the
structure of 2 in CDzC12solution is similar to that in the
solid state (Fig. 2a). When the signals at 6= 1.62 and 3.54
were irradiated in separate experiments, enhancements of
the signal intensities for the C6H4 protons at 6=7.03, as
well as for the other cod protons, were observed in both
cases. Irradiation of the aromatic protons produced the expected reciprocal effect in the signals at 6=1.62 and
6=3.54, but no enhancement in the intensity of the signal
236
0 Verlag Chernie GrnbH, 0-6940 Weinheirn, 1984
[I] H. M. Colquhoun, J. F. Stoddart, D. J. Williams, J. B. Wolstenholme, R.
Zarzycki, Angew. Chern. 93 (1981) 1093; Angew. Chem. Int. Ed. Engl. 20
(1981) 1051; H. M. Colquhoun, S . M. Doughty, J. M. Maud, J. F. Stoddart, D. I. Williams, J. B. Wolstenholme, Israel J . Chem., in press.
[2] Experimental: The crown ethers DB18C6 and DB24C8 were obtained
from Aldrich; DB21C7, DB27C9, DB30C10, DB33Cl1, and DB36C12
were synthesized by a stepwise procedure (cf. Ill). [R~(CO~)(NH,)~I[PF~],
m.p. 209-215", and [Rh(nbd)(NH,),][PF,], m.p. 159--164", were prepared from [Rh(cod)CI], (R. B. King, Organornetallic Synthesis 1 (1965)
132) and [Rh(nbd)Cl], (E. W. Abel, M. A. Bennett, G. Wilkinson, J. Chern.
SOC.1959, 3178), respectively, by treatment of these chloride dimers with
NH, @=0.88) and then with NH,PF6. The crystalline adducts 1, m.p.
95-loo", 2, m.p. 135--145", and 3, m.p. 118-129", were obtained by
layering Et20 on top of either CH2CI2or (CH2C1), solutions (1 :1 stoichiometries). All new crown ethers, complexes, and crystalline adducts
gave satisfactory elemental analyses and spectroscopic data.
[3] Crystal data 1: monoclinic, a =9.268(2), 6=34.335(7), c = 13.421(3)
,9-93.92(2)", Y=4261
space group P l , / c . Z=4, p,=1.45 g cm'. 2 :
monoclinic, a=9.195(3), b=29.380(9), c = 13.900(6)
,9=93.04(3)",
V=3750 A', space group I??,/<. Z = 4 , p C =1.49 g cm-'. 3: orthorhombic,
V=7360 A', space group
a=15.427(3), b = 18.739(3), c=25.458(5)
Pbca, Z=8,p,= 1.49 g cm-'. Data were measured on a Nicolet R3m diffractometer using the w-scan routine with graphite-monochromated CuKa
radiation. Structures were solved by the heavy-atom method and refined
anisotropically to give R values of 0.034, 0.043, and 0.047, respectively,
for 3915, 3401, and 2984 independent observed reflections [8 6 5 0 " ,
lFol> 3 o(IF,l)]. Further details of the crystal structure investigations can
be obtained from the Director of Cambridge Crystallographic Data Centre, University Chemical Laboratory, Lensfield Road, Cambridge CB2
IEW. Any request should be accompanied by the full literature citation
for this communication.
[4] H. M. Colquhoun, D. F. Lewis, J. F. Stoddart, D. J. Williams, J . Chern.
SOC.Dalton Trans. 1983, 607.
[5] H. M. Colquhoun, E. P. Goodings, J. M. Maud, J. F. Stoddart, D. J. Williams, J . B. Wolstenholme, J . Chern. SOC.Chern. Cornrnun. 1983, 1140.
[6] S. Zushi, Y. Kodama, Y. Fukuda, K. Nishihata, M. Nishio, M. Hirota, J.
Uzawa, BUN. Chern. SOC.Japan 54 (1981) 2113.
0570-0833/84/0303-0236 $ 02.50/0
A,
AS,
A,
A,
Angew. Chern. l n t . Ed. Engl. 23 (1984) No. 3
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