Rhodium (I) complexes of the dppn ligand, 3,6-bis (2′-pyridyl) pyridazine and X-ray structure of [Rh (CO) (dppn) (PPh3) ] (PF6)

Article abstract of DOI:10.1016/S0277-5387(98)00073-4

The reaction of the 3,6-bis (2′-pyridyl) pyridazine (dppn) ligand, with one and two equivalents of [Rh (CO) ₂S_n] (PF₆) , (s = THF) , yields respectively the mononuclear complex [Rh (CO) ₂ (dppn) ] (PF₆) 1 and the binuclear complex [Rh₂ (CO) ₄ (dppn) ] (PF₆) ₂ 3. Furthermore, the reaction of 1 with PPh₃ results in a substitution reaction to give [Rh (CO) (dppn) (PPh₃) ₂] (PF₆) 2. The unsaturated complex 3 reacts with the monodentate phosphine PPh₃ to yield a mixture of the known compound [Rh (CO) ₂ (PPh₃) ₂] (PF₆) and of the mononuclear [Rh (CO) (dppn) (PPh₃) ] (PF₆) 4, the crystal structure of which was established by X-ray diffraction. Moreover, 3 reacts with the bis (diphenylphosphino) methane (dppm) ligand in a 1 : 2 ratio to form the binuclear A-frame complex [Rh₂ (CO) ₂ (dppn) (μ-dppm) ₂] (PF₆) ₂ 5. However, the reaction of 3 with excess dppm (1 : 4 ratio) gives the known complex [Rh (CO) (dppm) ₂] (PF₆) 6.

Full text of DOI:10.1016/S0277-5387(98)00073-4

Polyhedron Vol[ 06\ No[ 07\ pp[ 2972Ð2977\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII ] S9166Ð4276"87#99962Ð3
Rhodium"I# complexes of the dppn ligand\ 2\5!
bis"1?!pyridyl#pyridazine and X!ray structure
of ðRh"CO#"dppn#"PPh2#Ł"PF5#
Noureddine Rahmouni\a\c Ali A[ Bahsoun\a Marie!Therese Youinou\a
ꢀ Á
John A[ Osborn\aꢁ Jean Fischerb and Aziz Ezzamartyc
a Laboratoire de Chimie des Metaux de Transition et de Catalyse
ꢀ
b Laboratoire de Cristallochimie et Chimie Structurale\ URA 313 C[N[R[S[\ Institut Le Bel\
Universite Louis Pasteur\ 3 rue Blaise Pascal\ 56999 Strasbourg\ France
ꢀ
c Laboratoire de Catalyse\ Universite Hassan II\ Faculte des Sciences Ain Chok\ B[P[ 4255\ Maarif\
ꢀ
ꢀ
¼
Casablanca\ Maroc
"Received 08 September 0886 ] accepted 01 February 0887#
Abstract*The reaction of the 2\5!bis"1?!pyridyl#pyridazine"dppn# ligand\ with one and two equivalents of
ðRh"CO#1SnŁ"PF5#\ "s ꢂ THF#\ yields respectively the mononuclear complex ðRh"CO#1"dppn#Ł"PF5# 0 and the
binuclear complex ðRh1"CO#3"dppn#Ł"PF5#1 2[ Furthermore\ the reaction of 0 with PPh2 results in a substitution
reaction to give ðRh"CO#"dppn#"PPh2#1Ł"PF5# 1[ The unsaturated complex 2 reacts with the monodentate
phosphine PPh2 to yield a mixture of the known compound ðRh"CO#1"PPh2#1Ł"PF5# and of the mononuclear
ðRh"CO#"dppn#"PPh2#Ł"PF5# 3\ the crystal structure of which was established by X!ray di}raction[ Moreover\
2 reacts with the bis"diphenylphosphino#methane"dppm# ligand in a 0 ] 1 ratio to form the binuclear A!frame
complex ðRh1"CO#1"dppn#"m!dppm#1Ł"PF5#1 4[ However\ the reaction of 2 with excess dppm "0 ] 3 ratio# gives
the known complex ðRh"CO#"dppm#1Ł"PF5# 5[ Þ 0887 Elsevier Science Ltd[ All rights reserved
Keywords] 2\5!bis"1?!pyridyl#pyridazine ^ bis"diphenylphosphino#methane ^ triphenylphosphine ^ carbonyl ^
rhodium ^ X!ray structure[
———————————————————————————————————————————————
The heterocyclic 2\5!bis"1?!pyridyl#pyridazine ligand\ binuclear units joined through bromide ligands is
hereafter dppn\ is interesting in that it provides two found ^ "iii# certain heterobinuclear complexes using
adjacent chelating sites which are able to coordinate two separate steps with a sequential addition of one
equivalent of each of metal complexes ð2Ł ^ "iv# a
transition metals at an internuclear distance of
approximately 2[4 A[ This can allow the two metals
tetranuclear Cu"I# grid!like complex\ ðCu3"dppn#3Ł3¦
[
Ä
It was seen that when one tetrahedral metal ion is
incorporated into the dppn ligand\ self!assembly of
the monometallic units is possible to yield a complex
in which the four copper atoms are coplanar and
spanned by four dppn ligands[ The X!ray structure
determination shows that pairs of the quasi!planar
dppn ligands align in parallel above and below the
rhombic array of Cu3 ð3Ł[ This principle has sub!
sequently been expanded to the synthesis of a variety
of fascinating self!assembled structures ð4Ł[
to interact via ligand bridges or electronically across
the dppn planar framework[ Such properties have
been exploited in several ways to synthesise\ for exam!
ple ] "i# a binuclear Ni"II# complex ð0Ł in which the
magnetic properties denote the presence of an exch!
ange interaction between the two metal centres ^ "ii#
several binuclear Cu"II# complexes ð1Ł such as ðCu1"m!
OH#Cl2"H1O#"dppn#Ł\ for which structural studies
show that the hydroxy ligand bridges the two metal
Ä
centres with a Cu"II# to Cu"II# separation of 2[265 A[
The presence of two metals held in close proximity
is conceptually of great interest in homogeneous cata!
lysts for several reasons[ For example\ a substrate may
be activated by a simultaneous interaction with both
In ðCu1"m!OH#Br2"dppn#Łn\ a polymeric stacking of
ꢁ Author to whom correspondence should be addressed[
2972

2973
N[ Rahmouni et al[
metal centres[ Alternatively\ the two metals could THF "1 cm2# and CH1Cl1"1 cm2#"Yield ] 74)#[ IR
serve to activate selectively di}erent substrates\ but "Nujol mull\ cm−0# nCO 1099 "s#\ 1949 "s# ^ nPÐF 739
their proximity would allow further interactions "br\ s#\ 459 "s# ^ n"CꢂC or CꢂN# 0599 "mw#\ 0489 "w#[
between the activated molecules[ Heterobimetallic Anal ] Calcd for C05H09N3O1F5PRh ] C\ 24[60 ^ H\
systems may be of particular interest for this type of 0[76 ^ N\ 09[33 ^ Rh\ 08[01[ Found ] C\ 25[43 ^ H\ 0[41 ^
reactivity[
N\ 8[47 ^ Rh\ 07[02[
In this paper we present the synthesis and charac!
terisation of mononuclear and binuclear cationic
Rh"I# complexes of the dppn ligand[ Further reactions
of the dirhodium complex of dppn with PPh2 and
CH1"PPh1#1 were also studied[ The single crystal X!
ray structure of a monomeric dppn derivative of Rh"I#
is also described[
Preparation of ðRh"CO#"dppn#"PPh2#1Ł"PF5# 1
Complex 0 "9[099 g\ 9[074 mmol# in acetone "4 cm2#
was added to an acetone solution "4 cm2# of PPh2
"9[986 g\ 9[269 mmol#[ The light brown precipitate
was _ltered\ washed several times with Et1O "2×4
cm2# and dried under vacuum "Yield ] 74)#[ IR
"Nujol mull\ cm−0
#
nCO 0839[ 20P"0H# NMR\
0
""CD2#1CO\ dppm#\ 30 "d\ I ꢂ 1\ JRhÐP ꢂ 002 Hz\
PPh2#\ −032 "hept\ I ꢂ 0\ PF5−#[ Anal ] Calcd for
C40H39N3OF5P2Rh ] C\ 48[19 ^ H\ 2[89 ^ N\ 4[30[
Found ] C\ 47[04 ^ H\ 2[82 ^ N\ 4[30[
Preparation of ðRh1"CO#3"dppn#Ł"PF5#1 2
A solution of dppn "9[099 g\ 9[314 mmol# in benzene
"4 cm2# was added to
a yellow solution of
EXPERIMENTAL
ðRh"CO#1SnŁ"PF5#"9[749 mmol# in THF "4 cm2#[ The
compound 2 precipitated out as an orange micro!
crystalline compound which was _ltered and washed
with THF "1 cm2# and then CH1Cl1 "1 cm2#"Yield ]
89)#[ IR "Nujol mull\ cm−0# nCO 1099 "s#\ 1949 "s# ^
General
All reactions were carried out under an atmosphere
of prepuri_ed nitrogen or argon using standard Sch!
lenk techniques or performed in a Vacuum Atmo!
spheres Corporation glove box[ Solvents such as Et1O\
THF and hydrocarbons were distilled from sodium
and benzophenone and CH1Cl1 from CaH1 under
nitrogen[ The 2\5!bis"1?!pyridyl#pyridazine"dppn#ð5Ł
and bis"diphenylphosphino#methane"dppm# ligands
ð6Ł as well as ðRh"CO#1ClŁ1 ð7Ł were prepared accord!
ing to literature procedures[ RhCl2 = 2H1O\ AgPF5 and
PPh2 were respectively purchased from Johnson
Matthey and Strem Chemicals and used as supplied[
IR spectra were recorded on a PerkinÐElmer 486
instrument[ NMR spectra were run on a Bruker SY
199 spectrometer[ Solvent peaks "0H\ 02C NMR#
served as internal references with the data _tted rela!
tively to TMS[ 20P"0H# NMR spectra were referenced
to external 74) H2PO3 with down_eld chemical shifts
reported as positive[ Attempts to record the mass spec!
tra of these compounds by spectroscopic methods
were unsuccessful[
0
nPÐF 739 "br\ s#\ 459 "s# ^ n"CꢂC or CꢂN# 0599 "mw#[ H
NMR ""CD2#1CO\ dppm# H arom ] 8[24 "s\ 1H#\ 8[11
"d\ 1H#\ 7[78 "d\ 1H#\ 7[56 "t\ 1H#\ 7[05 "t\ 1H#[ Anal ]
Calcd for C07H09N3O3F01P1Rh1 ] C\ 14[57 ^ H\ 0[19 ^ N\
5[54 ^ P\ 6[25 ^ Rh\ 13[33[ Found ] C\ 15[24 ^ H\ 0[17 ^
N\ 5[14 ^ P\ 6[14 ^ Rh\ 12[15[
Preparation of ðRh"CO#"dppn#PPh2#Ł"PF5# 3
A solution of PPh2 "9[982 g\ 9[245 mmol# in
CH1Cl1 "4 cm2# was added dropwise to a slurry of the
dimer 2 "9[099 g\ 9[008 mmol# in CH1Cl1 "4 cm2#
under vigorous stirring for 0 h[ The deep red solution
was _ltered over celite and evaporated to dryness[
After recrystallisation from CH1Cl1:hexane\ a mix!
ture of yellow crystals of the known complex
ðRh"CO#1"PPh2#1Ł"PF5# ð8Ł and of red crystals of
ðRh"CO#"dppn#"PPh2#Ł"PF5# 3 was obtained[ For
3 ] IR "Nujol mull\ cm−0# nCO 1999 "s# ^ 20P"0H#
NMR ""CD2#1CO:CH1Cl1\ dppm#\ 31[13 "d\ I ꢂ 0\
JRh!P ꢂ 049 Hz\ PPh2#\ −031 "hept\ I ꢂ 0\ PF5−#[
X!ray quality crystals of 3 = "CH2#1CO were obtained
from a 0 ] 0 mixture of acetone:ethanol[
Preparation of ðRh"CO#1"dppn#Ł"PF5# 0
A solution of ðRh"CO#1SnŁ"PF5#"S ꢂ THF# pre!
pared from a 1 ] 0 reaction mixture of AgPF5"9[104
mg\ 9[749 mmol# and ðRh"CO#1ClŁ1 "9[054 mg\ 9[314 Preparation of ðRh1"CO#1"dppn#"m!dppm#1Ł"PF5#1 4
mmol# in THF "09 cm2# was added dropwise to a
solution of dppn "9[199 g\ 9[749 mmol# in benzene
To a suspension of 2 "9[099 g\ 9[008 mmol# in
"09 cm2#[ The yellow!green precipitate which formed CH1Cl1 "4 cm2# was added dropwise a solution of
rapidly was separated and washed successively with dppm "9[980 g\ 9[126 mmol# in CH1Cl1 "4 cm2#[ The

Rhodium"I# complexes of the 2\5!bis"1?!pyridyl#pyridazine ligand
Table 0[ X!ray experimental data for 3 = acetone
2974
reaction mixture was allowed to stir for 1 h during
which a deep green colour developed[ The green
precipitate which formed after addition of Et1O "39
cm2# was _ltered o}\ washed successively with C5H5
and Et1O and dried under vacuum "Yield ] 89)#[
IR "Nujol mull\ cm−0#\ besides speci_c absorptions
due to dppn and PF5−\ nCO 1999 "vs#[ 20P"0H# NMR
"CD1Cl1\ dppm#\ 13[4 "m\ I ꢂ 3# and −032 "hept\
I ꢂ 1#[ H NMR "CD1Cl1\ dppm#\ 8[3Ð7 and 6[5Ð5[7
"m\ H arom#\ 3[92 "m\ 0CH1#[ Anal ] Calcd for a ">#
C55H43N3O1F01P5Rh1 ] C\ 49[88 ^ H\ 2[49 ^ N\ 2[59 ^ P\
00[86 ^ Rh\ 02[13[ Found ] C\ 38[49 ^ H\ 2[54 ^ N\ 2[69 ^
P\ 01[03 ^ Rh\ 01[79[
Formula
C22H14N3OPRh
= PF5 = OC"CH2#1
729[4
red
triclinic
02[210"3#
02[394"3#
09[592"2#
86[61"1#
000[15"1#
73[64"1#
0635[5
Molecular weight
Colour
Crystal system
a "_#
b "_#
c "_#
0
b ">#
g ">#
V "_2#
Z
1
Dcalc "g cm−2
#
0[468
Wavelength "_#
9[6096
5[285
P!0
Nonius CAD3!F
9[12×9[17×9[24
182
MoÐKa graphite mono!
chromated
u:1u
variable
0[99¦9[23×tg"u#
2h2k¦0
1:12
3774
2055
359
9[62:0[98
9[932
Reaction of 2 with an excess of dppn to `ive
ðRh"CO#"dppm#1Ł"PF5# 5
m "cm−0
#
Space group
Di}ractometer
Crystal size "mm#
T "K#
A solution of dppm "9[071 g\ 9[362 mmol# in CH1Cl1
"4 cm2# was added to a slurry of the dimer 2 "9[099 g\
9[008 mmol# in CH1Cl1 "4 cm2#[ The mixture was
stirred for 1 h at room temperature and the solvent
evaporated to dryness under vacuum[ A yellow prod!
uct 5 was extracted with ether "Yield ] 89)#[ IR
"Nujol mull\ cm−0# nCO 0834 "s#[ 20P"0H# NMR
"CD1Cl1\ dppm# −08[4 "d\ I ꢂ 3\ JRh−P ꢂ 092 Hz\
dppm#\ and −032 "hept\ I ꢂ 0\ PF−5 #[ 0H NMR
""CD2#1CO\ dppm# 6[1Ð6[4 "m\ H arom[#\ 3[4 ppm "m\
0CH1#[ Anal ] Calcd for C40H33OF5P4Rh ] C\ 47[51 ^
H\ 3[10 ^ P\ 03[74 ^ Rh\ 8[75[ Found ] C\ 47[13 ^ H\
3[97 ^ P\ 03[02 ^ Rh\ 8[73[
Radiation
Mode
Scan speed
Scan width ">#
Octants
u min:max ">#
Number of data colleted
Number of data with I × 2s"I#
Number of variables
Abs min:max
R"F#
Rw"F#
9[945
p
9[97
9[09
0[984
X!ray
crystal
structure
analysis
of
Largest peak in _nal di}[ "e A−2
GOF
#
ðRh"CO#"dppn#"PPh2#Ł"PF5# = acetone\ 3 = acetone
Suitable red single crystals for 3 = acetone were
obtained by recrystallisation from an acetone!ethanol
mixture at room temperature[ One single crystal was
cut out from a cluster of deep red crystals and mounted
on a rotation!free goniometer head[ A systematic
search in reciprocal space using a Enraf!Nonius
CAD3ÐF automatic di}ractometer showed that crys!
tals of 3 = acetone belong to the triclinic system[ Quan!
titative data were obtained at room temperature[ All
experimental parameters used are given in Table 0[
The resulting data set was transferred to a VAX com!
puter\ and for all subsequent calculations the Enraf!
Nonius Molen package was used ð09Ł[ Three standard
re~ections were measured every hour during the entire
such as B"H# ꢂ 0[2 Beqv"C# _1 but not re_ned[ Full
least squares re_nements ] s1"F1# ꢂ s1 counts ¦"pI#1[
A _nal di}erence map revealed no signi_cant maxima[
The scattering factor coe.cients and anomalous dis!
persion coe.cients come respectively from ð00Ł[ Table
0 lists experimental details and _nal results[
RESULTS AND DISCUSSION
The deep yellow!green compound\ ðRh"CO#1
data period showed no signi_cant trend[ The raw data "dppn#Ł"PF5# 0\ was obtained in high yield by the
were converted to intensities and corrected for Lor! reaction of equimolar amounts of ðRh"CO#1
entz and polarisation factors[ Absorption corrections "THF#nŁ"PF5# and dppn ð5Ł[ The IR spectrum of 0
derived from the F scans of 3 re~ections were applied[ displays two strong absorptions at 1099 and 1949
The structure was solved using the heavy atom cm−0\ typical of terminal cis carbonyl ligands and
method[ After re_nement of the heavy atoms\ a similar to those reported for the analogous 1\1?!bipyri!
di}erence!Fourier map revealed maxima of residual dine of o!phenenthroline carbonyl complexes of
electronic density close to the positions expected for Rh"I#ð01\02Ł[ Hence one chelating site of the dppn
hydrogen atoms ^ they were introduced in structure ligand is coordinated to the Rh"I# centre completing
factor calculations by their computed coordinates the square planar con_guration for 0[ The reaction of
"C0H ꢂ 9[84 _# and isotropic temperature factors 0 with PPh2 "0 ] 1 mol ratio# gives a brick red complex

2975
N[ Rahmouni et al[
which analyses as ðRh"CO#"dppn#"PPh2#1Ł"PF5# 1[ Rh0N distances "Rh0N0 ꢂ 1[989 "4# _# and
The 20P"0H# NMR spectrum shows a doublet at 30 Rh0N01 ꢂ 1[985 "4# _ and the Rh0CO of 0[722 "6#
ppm ð0J"Rh0P# ꢂ 002 HzŁ which suggests a trigonal _ as well as the Rh0P of 1[156 "1# _ are within the
bipyramid con_guration for the pentacoordinated range of expected bond lengths for this type of Rh"I#
Rh"I# derivative ð02Ł with two axial PPh2 ligands and cation[ Selected bond distances and angles are given
an equatorial CO ligand which is also revealed by the in Table 1[ The unexpected feature of this structure is
presence of a strong absorption band at 0839 cm−0 in the coordination of PPh2 to Rh"I# in a trans position
the IR spectrum[
to N01 of the pyridyl arm and cis to the N!pyridazine\
When two equivalents of ðRh"CO#1"THF#nŁ"PF5# whereas simple steric considerations might have
are added to one equivalent of dppn in a THF:C5H5 placed the PPh2 cis to N01[ The result is that the
mixture\ an orange dimeric complex 2\ corresponding phenyl groups of the phosphine block the free chel!
to ðRh1"CO#3"dppn#Ł"PF5#1\ is obtained[ Its 0H NMR ating site of dppn which may be responsible for the
spectrum shows _ve aromatic resonances of equal loss of Rh"I# from this site[ We therefore sought to
intensity as one singlet\ two doublets and two triplets stabilise the bimetallic unit in 2 by use of the bis"di!
indicating that both coordination sites of the dppn phenylphosphino#methane ligand "dppm#\ which is
ligand are occupied by Rh"I# ions[ Also\ the IR spec! well known to form binuclear A!Frame structures
trum in the carbonyl region shows only two terminal "Scheme 1#[
nCO absorptions at 1099 and 1949 cm−0[ Hence we can
propose the symmetric binuclear structure shown in in CH1Cl1 "0 ] 1 molar ratio# gives a deep green com!
Scheme 0[ pound isolated in reasonable yield\ which analyses as
Treatment of the unsaturated dimer 2 with dppm
However\ one Rh"I# in 2 can be relatively easily ðRh1"CO#1"dppn#"dppm#1Ł"PF5#1 4[ Its IR spectrum
removed by ligands such as phosphines "Scheme 0#[ in Nujol mull displays a very strong absorption nCO at
Treatment of 2 with PPh2 gives ðRh"CO#1"PPh2#1Ł"PF5# 1999 cm−0#\ characteristic of terminal carbonyls\ as
ð8Ł and ðRh"CO#"dppn#"PPh2#Ł"PF5# 3\ the formation well as absorption bands due to the coordinated
of which can be followed by 20P NMR[ We have struc! ligands dppn and dppm and to the PF5 − anion[ The
turally characterised 3 = "CH2#1CO by X!ray di}rac! 20P"0H# NMR spectrum shows one signal due to coor!
tion "Fig[ 0#\ which enables us in part to understand dinated dppm at d ꢂ 13[4 ppm"m#\ indicating that 4
the instability of the binuclear unit[ The distorted possesses only equivalent phosphorus environments\
square planar Rh"I# cation is quasi!symmetrically while the 0H NMR spectrum reveals the presence of a
coordinated to the two nitrogen atoms "N0 and N01# symmetrically coordinated dppn[ Therefore the spec!
by one chelating site of the dppn ligand[ The two troscopic features indicate the formation of a classical
Scheme 0[

Rhodium"I# complexes of the 2\5!bis"1?!pyridyl#pyridazine ligand
2976
Fig[ 0[ Ortep plot of one molecule of 3 = acetone showing the numbering scheme used[ Ellipsoids are scaled to enclose 49)
of the electronic density[ Hydrogen and solvate atoms are omitted for clarity[
Table 1[ Selected bond lengths "_# and angles "># for
ðRh"CO#"dppn#"PPh2#Ł"PF5# = acetone
geometry "TBP# based on the CO ligand and a chel!
ating site of the dppn ligand in the equatorial plane[
However we cannot exclude two other structural
possibilities where only either the central pyridazine
or the two pyridine end groups are coordinated to
rhodium\ as in 4b and 4c respectively ^ both Rh"I#
atoms would then possess a 05e− con_guration[ Such
structures gain support from preliminary studies
which show that this complex reacts rapidly with CO
and H1\ more typical of an unsaturated Rh"I# centre[
Further studies of this compound and its reactivity
are in progress[
Rh0C0
Rh0N0
Rh0N01
Rh0P0
C00O0
N00N1
N00C5
N10C2
C20C3
C20C02
C30C4
C40C5
C50C6
C60C7
0[722"6#
1[989"4#
1[985"4#
1[156"1#
0[030"6#
0[235"6#
0[233"6#
0[214"7#
0[398"8#
0[380"8#
0[235"8#
0[391"7#
0[357"7#
0[271"7#
C70C8
0[276"8#
0[242"6#
0[256"8#
0[266"8#
0[230"7#
0[264"8#
0[227"7#
0[284"8#
0[25"0#
C60N01
C80C09
C090C00
C000N01
C020C03
C020N07
C030C04
C040C05
C050C06
C060N07
P00C08
P00C14
P00C20
0[27"0#
0[229"8#
0[730"6#
0[712"5#
0[721"5#
Finally\ we found that the reaction of four equi!
valents of dppm with complex 2 in CH1Cl1 occurs with
the total displacement of the dppn ligand\ yielding a
complex 5 having an analogous formulation to that
already
synthesised
by
another
route
C00Rh0N0
C00Rh0N01
C00Rh0P0
N00Rh0N01 66[4"1#
N00Rh0P0 84[8"0#
063[4"1#
86[9"1#
78[5"1#
N010Rh0P0 061[6"0#
ðRh"CO#"dppm#1Ł¦ð03Ł[ Its spectroscopic features\
including the IR spectrum "nCO at 0834 cm−0# and the
20P"0H# NMR data in CD1Cl1 "d ꢂ −08[4 ppm "d#\
Rh0C00O0
N00C50C6
066[3"5#
004[4"4#
C50C60N01 004[0"4#
0
with JRh−P ꢂ 092 Hz#\ are closely similar to those
previously reported[
CONCLUSION
A!frame type structure as in 4a with two bridging
The 2\5!bis"1?!pyridyl#pyridazine ligand\ which
dppm units occupying mutually trans positions at the possesses two contiguous binding sites for metal ions\
two Rh"I# centres and with the tetradentate dppn has been found to form both mononuclear and
ligand as third bridge[ Each Rh"I# would then possess binuclear complexes with Rh"I#[ However\ the
a 07e− con_guration with a trigonal bipyramidal binuclear compounds were found to be relatively lab!

2977
N[ Rahmouni et al[
support and the Moroccan Government for a research leave
accorded to Noureddine Rahmouni[
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7[ McCleverty\ J[ A[ and Wilkinson\ G[\ Inor`[
Synth[\ 0855\ VIII\ 100[
8[ Hieber\ W[ and Frey\ V[\ Chem[ Ber[\ 0855\ 88\
1503[
09[ Fair\ C[ F[ In MolEN ] An Interactive Intelli`ent
System for Structure Analysis\ Nonius\ Delf\ The
Netherlands\ 0889[
00[ Cromer\ D[ T[ and Waber\ J[ T[\ International
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Kynoch Press\ Birmingham\ England\ 0863\
Table 1[1b ^ Table 1[2[0[
Scheme 1[
01[ Reddy\ G[ K[ N[ and Susheelamma\ C[ H[\ J[
Chem[ Soc[\ Chem[ Commun[\ 0869\ 43[
02[ Cocevar\ C[\ Mestroni\ G[ and Camus\ A[\ J[
Or`anomet[ Chem[\ 0861\ 24\ 278[
ile but their stability could be increased\ in part\ by
the binding of further bridging ligands such as dppm[
03[ Pignolet\ L[ H[\ Doughty\ D[ H[\ Nowicki\ S[ C[
and Casalnuovo\ A[ L[\ Inor`[ Chem[\ 0879\ 08\
1061[
Acknowled`ements*We thank Dr Rafael Sablong and Regis
Gauvin for helpful discussions\ the C[N[R[S[ for _nancial
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