The solution dynamics of adduct formation and electronic communication between ligand and metal core in electron deficient quinoline triosmium clusters

Article abstract of DOI:10.1016/S0277-5387(98)00100-4

The coordination of ammonia and of aliphatic amines (RNH₂(R = Et, n-Bu, S-Bu, t-Bu, cyclohexyl) and Et₂NH) to the electron deficient clusters Os₃(CO)₉(μ₃-η²-C ₉H₆N) (μ-H) (1) and Os₃(CO)₉(μ₃-η²-XC ₉H₅N)(μ-H) (X = 5-NH₂, 4; 3-NH₂, 5; 6-NH₂, 6; 5-Br, 7; 5-CH₃, 8) has been studied. The initially formed adducts of the amines with 1 gradually isomerize to give a mixture of two isomers whose ratio varies with the cluster, the solvent and the amine. Studies of the variation of the isomer ratio with temperature yield ΔH° and ΔS° values for the isomer equilibrium. The primary cause of the change in the isomer ratio is the variation in ΔS° which is rationalized as being due to solvation effects. The overall structure of the two isomers is assigned on the basis of NMR measurements to one where the amine occupies an axial position on the cluster and where the hydride and quinoline ring bridge different edges of the cluster. The equilibrium constant for amine complex formation is primarily determined by the steric bulk of the amine. The amine substituted complex 4 shows absolutely no tendency to coordinate amines and this is ascribed to relief of the electron deficiency at the metal core by the mesomeric effects of the para-amino group. The isomeric 5 and 6, however, do undergo coordination of amines at the metal core. The 5-methyl substituted complex 8 does not complex amine either. Compounds 1,4-8 all undergo simple protonation with both coordinating (CF₃CO₂H) and non-coordinating acids (HBF₄) to give cationic dihydrido complexes whose solution structures are elucidated by NMR techniques. The chemistry of these electron deficient clusters is compared with related μ₃-η² imidoyl complexes and can be understood in terms of the Hammett equation, at least for protonation.

Full text of DOI:10.1016/S0277-5387(98)00100-4

Polyhedron Vol[ 06\ No[ 06\ pp[ 1864Ð1873\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166Ð4276"87#99099Ð3
The solution dynamics of adduct formation and
electronic communication between ligand and metal
core in electron de_cient quinoline triosmium
clusters%
Avi Bar Dina\ Brian Bergmana\ Edward Rosenberga\ ꢀ\ Ryan Smitha\
Walter Dastru|b\ Roberto Gobettob\ Luciano Miloneb and Alessandra Vialeb
aDepartment of Chemistry\ The University of Montana\ Missoula\ MT 48701\ U[S[A[
bDipartimento di Chimica IFM\ Universita di Torino\ 09014 Torino\ Italy
ꢁ
"Received 20 October 0886^ accepted 03 March 0887#
Abstract*The coordination of ammonia and of aliphatic amines "RNH1"RꢂEt\ n!Bu\ s!Bu\ t!Bu\ cyclohexyl#
and Et1NH# to the electron de_cient clusters Os2"CO#8"m2!h1!C8H5N#"m!H# "0# and Os2"CO#8"m2!h1!XC8H4N#"m!
H# "Xꢂ4!NH1\ 3^ 2!NH1\ 4^ 5!NH1\ 5^ 4!Br\ 6^ 4!CH2\ 7# has been studied[ The initially formed adducts of the
amines with 0 gradually isomerize to give a mixture of two isomers whose ratio varies with the cluster\ the
solvent and the amine[ Studies of the variation of the isomer ratio with temperature yield DH> and DS> values
for the isomer equilibrium[ The primary cause of the change in the isomer ratio is the variation in DS> which
is rationalized as being due to solvation e}ects[ The overall structure of the two isomers is assigned on the
basis of NMR measurements to one where the amine occupies an axial position on the cluster and where the
hydride and quinoline ring bridge di}erent edges of the cluster[ The equilibrium constant for amine complex
formation is primarily determined by the steric bulk of the amine[ The amine substituted complex 3 shows
absolutely no tendency to coordinate amines and this is ascribed to relief of the electron de_ciency at the metal
core by the mesomeric e}ects of the para!amino group[ The isomeric 4 and 5\ however\ do undergo coordination
of amines at the metal core[ The 4!methyl substituted complex 7 does not complex amine either[ Compounds
0\3Ð7 all undergo simple protonation with both coordinating "CF2CO1H# and non!coordinating acids "HBF3#
to give cationic dihydrido complexes whose solution structures are elucidated by NMR techniques[ The
chemistry of these electron de_cient clusters is compared with related m2!h1 imidoyl complexes and can be
understood in terms of the Hammett equation\ at least for protonation[ Þ 0887 Elsevier Science Ltd[ All
rights reserved
Keywords] Amines ^ clusters ^ Osmium ^ Quinolines[
———————————————————————————————————————————————
INTRODUCTION
be synthesized in good yield with a wide range of
substituents in the quinoline ring ð0\ 3Ł[
We recently reported the synthesis and reactivity of
a novel class of electron de_cient triosmium clusters
Os2"CO#8"m2!h ð1Ł!C8H5N#"m!H# "0# from the reaction
of quinoline with Os2"CO#09"CH2CN#1 followed by
thermolysis or photolysis of the initially formed deca!
carbonyl eq[ "0# ð0Ð2Ł[ This type of compound can
The reaction of these complexes with soft nucle!
ophiles such as phosphines results in ligand addition
at the metal core along with rearrangement eq[ "1# ð0\
2Ł[ On the other hand\ reaction with hydride ð0Ł or
carbanions ð3Ł results in nucleophilic attack at the 4!
position of the quinoline ring[ Subsequent pro!
tonation leads to a nucleophilic addition product eq[
"2# ð3Ł and hydride abstraction from the intermediate
anion e}ects overall nucleophilic substitution eq[ "3#
ð3Ł[ In light of this diverse reactivity\ we thought it
would be useful to study the reactivity of 0 with amines
ꢀ Author to whom correspondence should be addressed[
% Dedicated\ with respect and admiration to Professor Jack
Lewis on the occasion of his 69th birthday[
1864

1865
A[ Bar Din et al[
and carboxylic acids which are intermediate in nucle! 1?# was observed eq[ "4# ð4Ł[ The neutral adduct
ophilicity relative to phosphines and carbanions[
Os2"CO#8"m!h1!C1N"!CH1!#2"m!H#1"CF2CO1# "2#\ was
We recently completed detailed studies of the reac! the main product of the reaction of tri~uoroacetic acid
tion of these ligands with the electron precise\ but with the m2!imidoyl complexes but a small amount
quite reactive m2 imidoyl complexes of the type\ of a monoprotonated species was observed to be in
Os2"CO#8"m2!h1!C1N"!CH1!#2"m!H#\ where coor! equilibrium with the adduct eq[ "5#[ In the case of non!
dination was highly selective for primary amines and coordinating anions such as BF−3 \ only simple pro!
where the formation of two axially coordinated tonation was observed ð5\ 6Ł[
isomers\ Os2"CO#8"m!h1!C1N"!CH1!#2"m!H#L "1 and
We report here the results of studies on the coor!

The solution dynamics of adduct formation and electronic communication
1866
dination chemistry of ammonia\ aliphatic amines\ and sample of 0 treated with excess ammonia shows two
protic acids with 0\ in an attempt to de_ne the ster! sets of nine carbonyls "I] 076[2\ 074[4\ 074[5\ 079[3\
068[7\ 067[7 "1J02C!0Hꢂ03 Hz#\ 066[2"1J02C!0Hꢂ8
eodynamics of its coordination sites and how these
di}er from those observed in 1 and 2 "eqs[ "4Ð5##[ One
of our research goals in developing the chemistry of
complexes such as 0 was to understand the degree of
electronic communication between the quinoline ring
and the metal core[ Our initial e}orts in this area have
resulted in the synthesis of the compounds
Os2"CO#8"m2!h1!XC8H4N#"m!H# "Xꢂ4!NH1\ 3^ 2!NH1\
4^ 5!NH1\ 5^ 4!Br\ 6^ 4!CH2\ 7#[ We report here our
initial results on the synthesis of these compounds
according to the methods outlined in eqs[ "0Ð3#[ Stud!
ies of their reactivity reveal the extraordinary impact
of the electron de_cient bonding mode of the cluster
on the substituent in the 4!position and vice versa[
Hz#\ 065[6\ 065[1 ppm^ II] 076[2\ 075[6\ 073[5\ 071[9\
079[7\ 066[7"1J02C!0Hꢂ01[4 Hz#\ 066[4 "1J02C!
0Hꢂ8[5 Hz#\ 065[7\ 065[1 ppm#[ Signi_cantly\ the
spectrum shows no resonances with 02C satellites that\
if present are indicative of a large trans!carbonyl coup!
ling associated with the presence of an Os"CO#3 group
ð4Ł[ The previously reported amine complexes of trios!
mium clusters\ 1 and 1?\ invariably have the amine "or
ammonia# in an axial position eq[ "4# ð4Ł[ Based on
these facts alone\ we can propose two alternative
structures for the set of isomers formed from the inter!
action of amines with 0 eq[ "6#[ One set has the hydride
and the quinoline ring sharing a common edge while
the amine occupies either axial site on the third\
unbridged osmium atom "structures A\ A?\ eq[ "6##[
This structure is directly analogous to that observed
related to m2 imidoyl complexes\ 1 and 1?\ for which
solid state structures are available eq[ "4# ð4Ł[
RESULTS AND DISCUSSION
Reactions with amines
On the other hand\ coordination of the amine at
the electron de_cient osmium edge of 0 could lead to
a structure where the quinoline ring and the hydride
are on di}erent edges with the amine occupying an
axial position on the osmium atom bridged by the
hydride but not by the quinoline ring structures B\ B?\
eq[ "6##[ This type of structure has been observed in
the case of one imidoyl complex bearing ethyl and
propyl groups on the imidoyl carbon and nitrogen
atoms respectively eq[ "7# ð7Ł[ We have also obtained
indirect evidence for this structural type as a short!
The addition of a large excess "49 fold# of ammonia
and various aliphatic amines to 0 results in an instant
color change from green to orange and in the appear!
ance of two new hydride peaks in the 0H NMR in the
range of −01 to −03 ppm "Table 0#[ The resonance at
higher _eld "isomer I# is invariably in greater intensity
"except in the case of NH2# and the lower _eld res!
onance "isomer II# gradually increases in intensity
until a _nal ratio "I:II#\ in the range of 9[4 to 3[7\ is
reached which does not change further "Table 0#[
The 02C NMR "CDCl2\ −59>C# of a 02CO enriched lived intermediate from the selective incorporation of

1867
A[ Bar Din et al[
Table 0[ Chemical Shifts "ppm# and Isomer Ratios for Amine Adducts of Os2"CO#8"m2!h1!
C8H5N#"m!H#\ 0[0
Isomer 0
Isomer II
Solvent
Temperature
I:II
NH2
−02[54 ppm
−02[39
−02[55
−02[32
−02[79
−03[01
−02[48:
−02[51
−02[28
−02[50
−02[35
−02[94
−01[69
−02[95
−01[66
*
−02[45
−01[86:
−02[99
−01[65
−02[92
−01[70
CDCl2
acetone
CDCl2
acetone
CDCl2
CDCl2
CDCl2
RT
RT
RT
−39>C
RT
−39>C
−39>C
9[4
0[2
0[2
2[7
*
6[3
2[2
EtNH1
Et1NHa
t!BuNH1
s!BuNH1
b
n!BuNH1
CyNH1
CDCl2
CDCl2
acetone
RT
RT
RT
1[7
2[0
3[7
a only one isomer observed
b four hydride resonances observed
carbon monoxide into 0 ð2Ł[ In the case of phosphines protons can be used to qualitatively assess the distance
reacting with 0\ such an intermediate is probably the between these two types of hydrogens ð8Ł[ Thus\ for
initial product as well but goes on to rearrange as Os2"CO#09"m!h1!C8H5N#"m!H# "8# the T0 of the hydride
shown above eq[ "1# ð0\ 2Ł[
is 6[9 s while for 0 it is 3[9 s "Figure 0#[ We can attribute
The initial formation of one isomer followed by the the shorter relaxation time in 0 to the proximity of
gradual appearance of a second has been shown to be the hydrogen of C"6# to the m!hydride[ If the amine
an intermolecular process for the related m2!imidoyl adducts of 0 have a structure identical to their m2!
complexes ð4Ł[ It would appear that this is also the case imidoyl analogs then the T0 of the m!hydride would
for 0 reacting with amines since the overall behavior of be expected to have a relaxation time similar to 8[ In
0 towards amines is so similar ð4Ł[ The question of the fact\ the T0 of the ammonia adduct of 0 is 0[3 s which
structure of the amine adducts of 0 "A or B# still is consistent with a structure where the ammonia pro!
remains unanswered in the absence of a solid state tons are proximal to the hydride^ i[e[\ the structure
structure[
resulting from addition of the ligand to the carbon
The change in longitudinal relaxation time "T0# of bridged edge of the cluster without further rearrange!
hydrides in metal clusters induced by proximal ligand ment "structure B\ eq[ "6##[

The solution dynamics of adduct formation and electronic communication
1868
Scheme 0[
This suggested structure is further supported by the
In our previous study of the imidoyl amine adducts\
0H NMR data obtained for the s!butyl adduct 0[ Here\ the initially formed isomer has the amine on the same
four hydride resonances are observed[ This is face of the osmium triangle as the pyrrolidine ring
undoubtedly due to the presence of diastereomers "i[e[\ syn!# ð4Ł[ This isomer is more favored for the
induced by the presence of the chiral center on the s! bulkier amines and this also appears to be the trend
butyl amine[ In the structure proposed based on the for the amine complexes of 0 Table 0[ In fact\ for
T0 measurements "structure B\ eq[ "6##\ the environ! the secondary amine Et1NH only one isomer with a
ment on the osmium atom bound to the amine is hydride chemical shift similar to the proposed syn!
quite asymmetric owing to the presence of the bridging isomer is observed Table 0[ Our initial thought for
hydride on one of the two edges of the triangle associ! the imidoyl series was that the strictly sigma!bond
ated with the amine coordinated osmium atom[ In the framework of the pyrrolidine ring was less bulky than
case of the structure adopted by the m2!imidoyl amine the carbonyl ligands which have p!electrons ð4Ł[ In
adducts "1 and 1? eq[ "4##\ the localized environment light of the isomer ratios observed for the amine com!
on the amine bound nitrogen is more symmetric and plexes of 0\ this cannot be the case since the quinoline
indeed only two hydride resonances are observed for ring also has p!electron density[ Yet\ the syn!isomer
the s!butyl complex ð4Ł[
is still favored for bulkier ligands and the anti!isomer
Finally\ the structure proposed is most consistent for the least bulky "ammonia#[ In order to further
with a reversible amine coordination based on the investigate this point\ we measured the e}ect of tem!
principle of least motion since only the motion of the perature and solvent on the isomer ratio for three
C"7# carbon pivoting on the coordinated nitrogen is amine adducts of 0[ There are two obvious trends
required to reform 0 from its corresponding amine in the data "Table 1#[ First\ it can be seen that the
adduct[ This motion is related to the reversible coor! population of the syn!isomer is enhanced in the more
dination of the C1N bond observed in the m2! to m! polar solvent acetone Table 1[ This\ of course\ is sens!
to m2!imidoyl interconversions ð4Ł[
ible in light of the expected greater polarity of the OsÐ

1879
A[ Bar Din et al[
Table 1[ DH> "kJ:mol# and DS> "J:mol K# for Amine Adducts of Os2"CO#8"m2!h1!C8H5N#"m!H#\ 0a1
k"I:II# 162 K
k"I:II# 187 K
DH> kJ:mol
DS> J:mol K
solvent
NH2
NH2
NH1Et
NH1Et
CycNH1
CycNH1
9[41
0[44
0[11
3[9
2[34
4[01
9[38
0[22
0[23
2[74
2[96
3[70 "extr[#
−9[7429[08
−1[0429[64
2[2429[37
1[1929[63
−9[8429[43
−0[3329[16
−7[3329[66
−3[2721[8
02[820[7
08[621[8
5[6521[1
CDCl2
Acetone
CDCl2
Acetone
CDCl2
7[1020[0
Acetone
a Values and errors obtained by taking the least squares _t to the function ln I:IIꢂDH>−TDS> for at least
ten temperatures between 122 and 187 K[
N bonds with the quinoline and amine relative to the even in the presence of a 099!fold excess of n!BuNH1[
OsÐCO bonds[ Overall\ the DH> values hover around This can be attributed to the electron donating ability
zero\ ranging from −2 to ¦1 kJ:mole[ The most sig! of the amino group which funnels electron density
ni_cant di}erences between compounds and between down to the electron de_cient C"7#ÐOs1 bonding
solvents are in the DS> Table 1[ Signi_cantly\ the framework by conventional benzenoid resonance[
ammonia complex is the only one with a negative DS>[
The 2! and 5!amino derivatives 4 and 5 do coor!
This indicates that solvation\ not steric e}ects\ can dinate n!BuNH1\ as 0[ The formation constants are of
account for the observed di}erences in the isomer the same order of magnitude as for 0\ with 5 showing
ratios[ Apparently\ the more polar syn! isomers lead a signi_cantly larger formation constant than 4 or 0
to more disordered soluteÐsolvent interactions and "Table 2#[ As for 0\ isomer I\ presumably the more
this e}ect is enhanced by the presence of non!polar polar isomer is favored with the equilibrium ratios of
substituents on the amine[ That the larger cyclohexyl I:II being two to three times larger than for 0 Table
group shows a less positive DS> than the ethyl group 2[ One might have expected the Kf for 5 to be less than
is di.cult to rationalize but may relate to the mobility that of 4 since the electron donating amino group is
of this ligand in the adduct[
on the carbocyclic ring\ albeit in the meta position[
The trends in the equilibrium constants for the for! Clearly\ the magnitude of Kf and the I:II ratio depend
mation of amine complexes with 0 follow the trends on a subtle combination of factors which cannot be
observed for the related m2 imidoyl species\ n!Bu×s! delineated at this time[ The one _rm conclusion that
Bu×t!Bu[ The absolute values for the equilibrium can be drawn from these studies is the profound in~u!
constants for 0 however\ are much greater being 33[3\ ence that substitution at the 4!position of the quino!
1[6\ and 9[28^ and 0[14\ 9[26\ and 9[994 for 0 and the line ring has on the electron density at the metal core[
m2!imidoyls respectively ð4Ł[ This undoubtedly re~ects This is born out by our studies of the Os2"CO#8"m2!h1!
the greater electron de_ciency for the 35e− cluster "4!Br#C8H4N#"m!H# ð3Ł "6# where the electron with!
relative to the reactive but electron!precise m2!imido! drawing bromine in the 4!position gives the largest Kf
yls[
of all the derivatives of 0 investigated so far[ In the
In order to assess the impact of an electron donating case of Os2"CO#8"m2!h1!"4!CH2#C8H4N#"m!H# ð3Ł "7#\
group on the coordination chemistry observed for 0\ where there is only a weakly electron donating group
we undertook the synthesis of the 2!\ 4! and 5!amino in the 4!position amine complex formation was also
analogs of 0[ The synthesis of these complexes pro! not observed even in the presence of a large excess of
ceeded in a straightforward manner[ Signi_cantly\ the n!BuNH1[
4!amino derivative\ Os2"CO#8"m2!h1!4!NH1C8H4#"m!H#
"3# formed directly\ at ambient temperatures\ without
requiring thermal or photochemical decarbonylation Reactions with protic acids
eq[ "8# ð0Ð2Ł[ This undoubtedly re~ects the impact of
the strong p!electron donor in a position para! to the
In order to further probe the electron distribution
incipient three center\ two electron band[ The 2! and in 0 and 3Ð7 we investigated their reactions with
5!amino derivatives 4 and 5 did require the usual CF2CO1H and HBF3[ Addition of a six!fold excess of
decarbonylation procedure "eqs[ "09Ð00##[ In all of CF2CO1H to a CD1Cl1 solution of 0 results in com!
these reactions "eqs[ "8Ð00## no detectable competition plete conversion to a deep orange solution which exhi!
for coordination of the quinoline nitrogen by the ani! bits two hydride resonances at −02[55 and
line amino groups is seen but the yields of 4 and 5 −00[50 ppm in a 0]0 ratio[ The aromatic resonances
were signi_cantly lower than for 3 and 0[
are all shifted down_eld with respect to 0[ An equi!
The reaction of 3 with n!BuNH1 in both CD1Cl1 librium constant for protonation was calculated from
and CD2OD showed no sign of complex formation a titration of 0 with CF2CO1H "Table 3#[ The 02C!

The solution dynamics of adduct formation and electronic communication
1870
Table 2[ Equilibrium Constants and Isomer Ratios for n!BuNH1 Complexes
of Electron De_cient Quinoline Clustersa2
Compound
KFORM
I:II
d hydride I"II#
Solvent
0
4
5
6
33[3
1[7
−02[28"−01[65#
−02[31"−01[70#
−02[31"−01[68#
−02[36"−01[89#
CDCl2
CD1Cl1
CD1Cl1
CDCl2
42[8
55[6
83[4
6[2
3[5
0[1
a 209) at 11>C
NMR "CD1Cl1# of a 02CO sample of 0 in the presence and 061[34 ppm appear as doublets "1J02C!0Hꢂ8[04
of the same excess gives a 02C NMR in the carbonyl and 6[52 Hz#[ Protonation with the non!coordinating
0
region showing nine resonances at 079[54\ 064[19\ acid\ HBF3 yields the virtually identical H Table 3
061[49\ 061[34\ 060[90\ 056[82\ 055[41\ 048[73\ and and 02C NMR "CD1Cl1# data "079[50\ 064[67\ 061[81\
048[88 ppm[ The two resonances at 048[73 and 061[25\ 060[32\ 057[02\ 055[60\ 048[83\ 047[74 ppm
047[88 ppm appear as doublets of doublets in the pro! with an identical coupling pattern#[ These data are
ton coupled spectrum "1J02C!0Hꢂ02[63\ 3[47 and consistent with simple protonation to give a dihydride
02[62\ 5[09 Hz respectively# while the two at 079[54 cation eq[ "01# as opposed to acid adduct formation

1871
A[ Bar Din et al[
Table 3[ Protonation Equilibria for Electron De_cient Quinoline Trios!
mium Clustersa3
Compound
Keq
Acid
d hydrides
Solvent
CDCl2
CDCl2
CDCl2
CDCl2
CDCl2
CDCl2
CDCl2
0
0
3
4
5
6
7
9[01
CF2CO1H
HBF3
−02[55
−00[50
−02[69
−00[54
−03[24
−01[59
−02[70
−00[62
−02[61
−00[69
−02[67
−00[49
−03[99
−01[04
01[1
19[7
9[61
CF2CO1H
CF2CO1H
CF2CO1H
CF2CO1H
CF2CO1H
0[77
9[94
0[08
a Measured by 0H NMR 209) at ¦11>C
eq[ "5#[ The equilibrium constant for formation of the that the partially averaged acid:amine resonance is
cation is considerably larger for the stronger acid\ found between 4 and 5 ppm\ suggesting a higher
HBF3 Table 3[ The observation of well resolved car! degree of amine protonation[ The protonation equi!
bonylÐhydride couplings indicates that the protonated librium values "Table 3# obtained from these experi!
species is rigid on the NMR time scale while the ments are consistent with 3 having the greatest
hydrides in the related cationic m2!imidoyl species are in~uence on the electron density at the metal core[ A
~uxional at ambient temperatures[
Hammett plot of the equilibrium data using standard
The protonation of 3 with aliquots of CF2CO1H values of s09 yields a reasonably good straight line
reveals that the 4!amino derivative is considerably with a correlation coe.cient of 9[82 and r value of
more basic at the metal core than 0 Table 3[ After the −9[02 "Figure 0#[
_rst aliquot "slightly in excess of 0 equivalent# is
added\ 3 is completely converted to the dihydride cat!
ion and the resonance at 4[59 ppm attributable to the
amino resonance is no longer observed[ Instead\ a
broad resonance at 6[71 ppm is observed which is
CONCLUSIONS
The electron de_cient m2!h1!quinoline triosmium
attributable to a partially averaged signal of the clusters exhibit behavior towards amines similar to
CF2CO1H and the amino group of 3[ The CF2CO1H the related m2!h1 pyrrolidine triosmium clusters ð4Ł[
proton resonance is observed at 7[99 ppm in the pres! Both show initial formation of a single isomer which
ence of 0[ As more CF2CO1H is added to the solution then equilibrates to a mixture of two complexes[ The
of 3\ the acid amine resonance shifts to lower _elds and equilibrium constants in both series depend on the
sharpens somewhat indicating more rapid exchange steric bulk of the amine with the overall magnitudes
between the amine and the acid[ Signi_cantly\ the being much greater for the quinoline series[ Based on
amine resonances for 4 and 5 are found at con! the NMR evidence accumulated to date\ the actual
siderably higher _elds than for 3 at 3[03 and 3[68 ppm structure of the amineÐquinoline adducts is di}erent
respectively[ On treatment with CF2CO1H\ the same from that of the imidoyls[ However\ de_nitive con!
overall behavior as for 3 is observed for 4 and 5 except clusions about the actual structures must await solid

The solution dynamics of adduct formation and electronic communication
1872
Fig[ 0[ Hammett\ s:r Plot of the Protonation Equilibria for Compounds 0\ 3Ð7 reacting with CF2CO1H "error bars for the
s values are from reference ð09Ł and are 209) for the Keq values#[
state structural determinations which have been were purchased from Aldrich in single sample ampules
di.cult to obtain owing to the instability of the and used as received[ Chloroform!d0 was dried over
adducts as crystalline solids[
molecular sieves before use[ NMR spectra were rec!
orded on Jeol EX!399 or Varian Unity Plus 399 NMR
spectrometers[ Samples for T0 measurement were pre!
viously degassed by three freeze thaw cycles[ The non
selective inversion recovery pulse sequence was used
to obtain T0 values[ Infrared spectra were recorded
on a PerkinÐElmer 0599 spectrometer and elemental
analyses were performed by Schwarzkopf Micro!
analytical Laboratories\ Woodside\ New York[
In sharp contrast to the m2!h1!imidoyl clusters\ the
m2!h1!quinoline clusters do not form acid adducts but
simply undergo protonation in the presence of
CF2CO1H[
The most interesting aspect of these studies is the
profound in~uence that substituents in the 4!position
have on the electronic properties of the metal core[
That the simple free energy relationship normally
applied to organic reactions can be used to rationalize
the relationship between substitution on the carbo!
cyclic ring and protonation at the metal core is
reassuring in that it says that the relatively complex
interactions "from an orbital point of view# between
an organic moiety and two metal atoms can be under!
stood in terms of a traditional physical organic chem!
istry model[ The isomer I and II populations and the
somewhat higher value of Kf for the 5!amino quino!
line derivative\ are less well understood\ but seem to
be dominated by solvation e}ects\ at least from the
data gathered so far[
Preparation of Os2"CO#8"m2!h1!"4!NH1#C8 H4N#"m!
H# 3[ Os2"CO#09"MeCN#1 "9[149 g\ 9[157 mmol# was
dissolved in CH1Cl1 "049 mL# and 4!amino quinoline
"9[979 g\ 9[4 mmol# was added[ The reaction mixture
was stirred for 05 h at room temperature[ The resulting
deep green solution was separated and _ltered through
a 03ý silica gel column eluted with hexane:CH1Cl1
"69]29#\ giving two bands[ The _rst yellow band was
a
mixture of the isomers Os2"CO#09"m!h1!"4!
NH1#C8H4N#"m!H# "less than 09)#[ The second frac!
tion yielded "9[112 g\ 9[108 mmol\ 71[0) overall from
Os2"CO#09"CH2CN#1# of the green major product\ 3\
Os2"CO#8"m2!h1!"4!NH1#C8H4N#"m!H# which gave
green crystals from hexane:CH1Cl1 at −19C[
EXPERIMENTAL
Analytical and spectroscopic data for ðOs2"CO#8"m2!
h1!"4!NH1#C8H4N#"m!H#Ł 3[ Anal[ calcd for
C07H7N1O8Os2] C\ 11[27\ H\ 9[67^ N\ 1[65[ Found] C\
11[26^ H\ 9[64^ N\ 1[72[ IR "n"CO# in hexane#] 1979w\
1958m\ 1939s\ 1902s\ 0870s\ 0856w cm−0[ 0H!NMR at
399 MHz in CDCl2] d 8[14 "dd\ H"1##\ 6[96 "t\ H"2##\
General] Compounds 0 ð0Ł\ 6 ð00Ł 7 ð3Ł\ and 4!amino
quinoline ð00Ł and 4!bromo quinoline ð00Ł were syn!
thesized by known literature procedures[ 2!Amino
quinoline and 5!amino quinoline were purchased from
Aldrich Chemical Co[ and used as received[ Methylene
chloride was distilled from calcium hydride before use[ 7[99 "dd\ H"3##\ 7[05 "dd\ H"5#\ 5[32 "d\ H"6##\ 4[59
Acetone!d5\ methylene chloride!d1\ and methanol!d3 "broad singlet\ NH1#\ −02[90 "s\ hydride#[

1873
A[ Bar Din et al[
Synthesis of Os2"CO#8"m2!h1!"n!X#C8H4N#"m!H#\ 4 integration of the appropriate resonances[ For for!
"nꢀ2\ XꢀNH1#\ 5 "nꢀ5\ XꢀNH1#\ 6 "nꢀ4\ XꢀBr#[ mation constants\ the equilibrium expression was]
Os2"CO#09"CH2CN#1 "9[149Ð9[499 g\ 9[16Ð9[43 mmol#
ðcluster−amine adductŁ
was dissolved in 049Ð199 mL CH1Cl1 and a two!fold
molar excess of the substituted quinoline was added
by syringe[ The solution was stirred for 05Ð19 h and
then _ltered through a small silica gel column to
remove excess ligand and a small amount of brown
decomposition product[ The yellow methylene chlor!
ide solution was then photolyzed using a Rayonet
photochemical reaction chamber equipped with
299 nm lamps for 1Ð3 h or until the infrared spectrum
showed essentially complete conversion to the green
nonacarbonyl derivative[ The green methylene solu!
tion was then concentrated and puri_ed by thin layer
chromatography using 0]0 hexane:methylene chloride
"for 4 and 5# or 6]2 hexane:methylene chloride "for 6#[
Yields for 4 and 5 ranged from 49Ð59) while those
for 6 were 79Ð74)[
Kf"L:mol#ꢂ
ðclusterŁðamineŁ
in most cases the equilibrium constant was evaluated
at several concentrations of added amine and an aver!
age value is reported in Table 2[ For the protonation
equilibrium\ the expression used was]
ðclusterH¦ŁðX−Ł
Kpꢂ
ðclusterŁðHXŁ
Again\ the value of the equilibrium constant was
evaluated at several acid concentrations in most cases[
Acknowled`ements[ We gratefully acknowledge the National
Science Foundation CHE 8514256 "E[ Rosenberg#\ the Con!
siglio Nazionale Ricerche "CNR\ L[ Milone#\ the Ministry
of Education "L[ Milone#\ the University of Montana "E[
Rosenberg#\ and the University of Turin "E[ Rosenberg and
L[ Milone# and the CNR Programma di Scambi Intern!
azionali "E[ Rosenberg#[
Analytical and spectroscopic data for Os2"CO#8"m2!
h1"2!NH1#C8H4N#"m!H#
4[
Calculated
for
C07H7N1O8Os2] C\ 11[27^ H\ 9[67^ N\ 1[65[ Found] C\
11[01^ H\ 0[91^ N\ 1[73[ IR"n"CO# in CH1Cl1#] 1965w\
1949s\ 1906s\ 0878m\ br cm−0[ 0H NMR at 399 MHz
in Acetone!d5] d 8[20"d\ 0H#\ 7[57"dd\ 0H#\ 7[50"dd\
0H#\ 6[30"d\ 0H#\ 6[29"dd\ 0H#\ 3[03"s\ br\ 1H#\
−01[12"s\ 0H#[
REFERENCES
0[ Rosenberg\ E[\ Kabir\ S[ E[\ Kolwaite\ D[ S[\
Hardcastle\ K[ I[\ Cresswell\ W[ and Grindsta}\
J[\ Or`anometallics\ 0884\ 03\ 2500[
Analytical and spectroscopic data for Os2"CO#8"m2!
1[ Rosenberg\ E[\ Kolwaite\ D[ S[\ Kabir\ S[ E[\
Hardcastle\ K[ I[\ McPhillips\ T[ and Duque\ R[\
Day\ M[\ Or`anometallics\ 0885\ 04\ 0868[
2[ Rosenberg\ E[\ Kolwaite\ D[S[\ Arcia\ E[\ Hard!
castle\ K[I[\ Ciurash\ J[\ Duque\ R[\ Gobetto\ R[\
Milone\ L[\ Osella\ D[\ Botta\ M[\ Dastru{\ W[\
Viale\ A[\ Fiedler\ J[\ Or`anometallics\ 0887\ 06\
304[
h1!"5!NH1#C8H4N#"m!H#
5[
Calculated
for
C07H7N1O8Os2] C\ 11[27^ H\ 9[67^ N\ 1[65[ Found] C\
11[38\ H\ 9[75^ N\ 1[60[ IR "n"CO# in CH1Cl1#] 1965w\
0
1930s\ 1907s\ 0877m\ br\ 0862w\ br cm−0[ H NMR
at 399 MHz in CDCl2] d 7[81"dd\ 0H#\ 6[72"d\ 0H#\
6[68"dd\ 0H#\ 6[25"d\ 0H#\ 5[86"dd\ 0H#\ 3[68"s\ br
1H#\ −01[12"s\ 0H#[
3[ Rosenberg\ E[\ Bergman\ B[\ Hardcastle\ K[I[\
Visi\ Mondana\ Ciurash\ Joana\ 0887 "submitted#[
4[ Rosenberg\ E[\ Kabir\ S[ E[\ Day\ M[\ Wolf\ E[\
McPhillips\ T[ and Hardcastle\ K[ I[\ Or`an!
ometallics\ 0884\ 03\ 610[
5[ Rosenberg\ E[\ Hardcastle\ K[ I[\ Kabir\ S[ E[\
Milone\ L[\ Gobetto\ R[\ Botta\ M[\ Nishimura\
N[ and Yin\ M[\ Or`anometallics\ 0884\ 03\ 2957[
6[ Rosenberg\ E[\ Day\ M[\ Espitia\ D[\ Kabir\ S[ E[\
Day\ M[\ Hardcastle\ K[ I[ and Irving\ M[\ J[
Cluster Sci[\ 0883\ 4\ 37l[
7[ Rosenberg\ E[\ Hardcastle\ K[ I[\ Kabir\ S[ E[\
Gobetto\ R[\ Milone\ L[ and Osella\ D[\ Or`an!
ometallics\ 0880\ 09\ 2449[
8[ Aime\ S[\ Gobetto\ R[ "to be published#[
09[ Hammett\ L[ P[\ Physical Or`anic Chemistry\ 1nd
edn[ McGrawÐHill\ New York\ 0869[
Spectroscopic and analytical data for Os2"CO#8"m2!
h1!"4!Br#C8H4N# 6[ Calculated for C07H5NO8BrOs2]
C\ 19[86^ H\ 9[37\ N\ 0[25[ Found] C\ 19[73^ H\ 9[27^
N\ 0[26^ IR"n"CO# in CH1Cl1#] 1966m\ 1949s\ 1919s\
0
0889s\ 0866w\ 0841w cm−0[ H NMR at 399 MHz in
CDCl2] d 8[21"dd\ 0H#\ 7[38"dd\ 0H#\ 7[28"d\ 0H#\
6[35"d\ 0H#\ 6[08"dd\ 0H#\ −01[96"s\ 0H#[
Evaluation of isomer ratios and equilibrium
constants[ Compounds 0 or 3Ð7\ were weighed directly
into ~ame dried NMR tubes in 8Ð00 mg samples
"½9[90 mmol#[ 9[59 mL of the NMR solvent was then
added by syringe\ followed by syringe addition of 1Ð
19 mL of the amine or acid[ The NMR tube was then
capped and shaken and the proton or 02C NMR moni!
tored for at least 13 h after which time no further
changes in the spectra were observed[ The isomer
ratios and equilibrium constants were evaluated by
00[ Bradford\ L[\ Elliot\ T[ J[ and Rowe\ F[ M[\ J[
Amer[ Chem[ Soc[\ 0836\ 58\ 326[