High nuclearity iridium clusters derived from the transformation of [Ir4(CO)11(PPh2Cl)] on silica gel and the thermolysis of [HIr4(CO)10(μ-PPh2)]

Article abstract of DOI:10.1016/s0277-5387(98)00031-x

The monosubstituted compound [Ir₄(CO)₁₁(PPh₂Cl)] reacts on silica gel to give [HIr₄(CO)₁₀(μ-PPh₂)] and the novel compounds [Ir₄(CO)₁₁(PPh₂OH)] and [Ir₆(μ-CO)(CO)₁₂(μ-PPh₂)₂] whose relative yields (up to 75, 10 and 40%, respectively) depend on cluster loading and the polarity of the eluent. The molecular structure of the hexanuclear compound was established by an X-ray analysis and consists of an octahedron of iridium atoms with two diphenylphosphido groups symmetrically bridging two non consecutive edges. Thermolysis of [HIr₄(CO)₁₀(μ-PPh₂)] in THF results in the formation of the same hexanuclear compound (up to 40%), together with [Ir₇(μ-CO)(CO)₁₃(μ-PPh₂)(μ ₃-PPhC₆H₄)] (10%) and [Ir₈(μ-CO)₂(CO)₁₄(η ¹-Ph)(μ-PPh₂)(μ₄-PPh)] (40%), depending on the reaction conditions; their molecular structures were determined by X-ray analyses. The heptanuclear compound exhibits a capped octahedral metal frame with a diphenyl-phosphido and a phenyl orthometallated phosphido ligands bridging two opposite equatorial edges of the octahedron; the octanuclear cluster exhibits a fused octahedron-square based pyramid metal atom arrangement with the phosphinedene ligand bonded to the square face of the pyramid and the phosphido group to one of the edges of the octahedron. Possible mechanisms for the formation of these high nuclearity clusters are discussed.

Full text of DOI:10.1016/s0277-5387(98)00031-x

Polyhedron Vol[ 06\ No[ 06\ pp[ 1754Ð1764\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII ] S9166Ð4276"87#99920ÐX
High nuclearity iridium clusters derived from the
transformation of ðIr3"CO#00"PPh1Cl#Ł on silica gel
and the thermolysis of ðHIr3"CO#09"m!PPh1#Ł ^
synthesis and characterization of ðIr5"m!CO#
"CO#01"m!PPh1#1Ł\ ðIr6"m!CO#"CO#02"m!PPh1#
"m2!PPhC5H3#Ł and ðIr7"m!CO#1
"CO#03"h0!Ph#"m!PPh1#"m3!PPh#Ł$
Maria Helena de Araujo\a Maria D[ Vargas\aꢀ Dario Bragab and
Fabrizia Grepionib
a Instituto de Qu(mica\ Universidade Estadual de Campinas\ CP 5043\ Campinas\ 02972!869\ SP\ Brazil
ꢁ
b Dipartimento di Chimica {{G[ Ciamician||\ Universita degli Studi di Bologna\ Via Selmi 1\ 39015\
ꢁ
Bologna\ Italy
"Received 09 October 0886 ^ accepted 29 December 0886#
Abstract*The monosubstituted compound ðIr3"CO#00"PPh1Cl#Ł reacts on silica gel to give ðHIr3"CO#09"m!
PPh1#Ł and the novel compounds ðIr3"CO#00"PPh1OH#Ł and ðIr5"m!CO#"CO#01"m!PPh1#1Ł whose relative yields
"up to 64\ 09 and 39)\ respectively# depend on cluster loading and the polarity of the eluent[ The molecular
structure of the hexanuclear compound was established by an X!ray analysis and consists of an octahedron
of iridium atoms with two diphenylphosphido groups symmetrically bridging two non consecutive edges[
Thermolysis of ðHIr3"CO#09"m!PPh1#Ł in THF results in the formation of the same hexanuclear compound
"up to 39)#\ together with ðIr6"m!CO#"CO#02"m!PPh1#"m2!PPhC5H3#Ł "09)# and ðIr7"m!CO#1"CO#03"h0!Ph#"m!
PPh1#"m3!PPh#Ł "39)#\ depending on the reaction conditions ^ their molecular structures were determined by
X!ray analyses[ The heptanuclear compound exhibits a capped octahedral metal frame with a diphenyl!
phosphido and a phenyl orthometallated phosphido ligands bridging two opposite equatorial edges of the
octahedron ^ the octanuclear cluster exhibits a fused octahedron!square based pyramid metal atom arrangement
with the phosphinedene ligand bonded to the square face of the pyramid and the phosphido group to one of
the edges of the octahedron[ Possible mechanisms for the formation of these high nuclearity clusters are
discussed[ Þ 0887 Elsevier Science Ltd[ All rights reserved
Keywords] high nuclearity clusters ^ iridium ^ synthesis ^ thermolysis[
———————————————————————————————————————————————
Surface mediated cluster synthesis has emerged in choice of the inorganic oxide that plays the role of the
recent years as an extremely e.cient and selective
alternative to the established synthetic routes ð0Ł
involving vacuum pyrolysis\ thermolysis and
reduction of preformed carbonyls ð1Ł[ The selectivity
of surface mediated syntheses is controlled by the
solvent in conventional syntheses[ A number of high
nuclearity iridium clusters\ which were previously
obtained from the reduction of ðIr3"CO#01Ł\ e[g[
ðIr5"CO#04Ł1− ð2\3Ł\ ðIr7"CO11Ł1− ð4Ł\ have been pro!
duced by reductive carbonylation of ðIr3"CO#01Ł
adsorbed on MgO surfaces ð5\6Ł[ Similarly\ neutral
carbonyl Ir\ Rh\ Os and Ru clusters have been syn!
thesized from the reductive carbonylation of sup!
ported halide precursors on SiO1 ð0Ł[
ꢀ Author to whom correspondence should be addressed[
$ Dedicated to Prof[ the Lord Lewis for his outstanding
contribution to chemistry and for his enthusiastic support to
the younger generation[
Transformations of cluster compounds on silica gel
1754

1755
M[ H[ de Araujo et al[
or alumina during puri_cation have been described the substitution\ not only of a CO\ but also of a PPh1Cl
ð7Ł and are certainly much more common than sug! ligand\ according to the following equations ]
gested by literature reports[ To our knowledge\
ðIr3 "CO#00 "PPh1Cl#Ł\2a¦X−
:
however\ not a single case involving cluster build!up
has been reported so far[ This report describes our
studies involving the synthesis and transformation of
ðIr3"CO#00"PPh1Cl#Ł on silica gel plates to give the
novel compound ðIr5"m!CO#"CO#01"m!PPh1#1Ł\ and an
alternative route to this compound and to ðIr6"m!
CO#"CO#02"m!PPh1#"m2!PPhC5H3#Ł "09)# and ðIr7"m!
CO#1"CO#03"h0!Ph#"m!PPh1#!"m3!PPh#Ł "up to 39)#\
via thermolysis of ðHIr3"CO#09"m!PPh1#Ł[
{{ðIr3 "CO#09 "PPh1Cl#XŁ−||¦CO
ðIr3 "CO#00 "PPh1Cl#Ł\ 2a¦X−
:
{{ðIr3 "CO#00XŁ−||¦PPh1Cl
{{ðIr3 "CO#09 "PPh1Cl#XŁ−||¦PPh1Cl :
ðIr3 "CO#09 "PPh1Cl#1Ł\ 3¦X−
{{ðIr3 "CO#00XŁ−||¦CO : ðIr3 "CO#01Ł\0¦X−
X ꢂ Br− or Cl−
RESULTS AND DISCUSSION
The process is driven by the precipitation of 0 and
occurs\ most probably\ as a result of the high lability
of the PPh1Cl ligand[ By comparison\ reaction of the
analogous compound ðIr3"CO#00"PPh1Me#Ł with
PPNCl occurs only under much harsher conditions
Synthesis and characterisation of ðIr3"CO#00"PPh1Cl#Ł\
2a
The cluster compound ðIr3"CO#01Ł\ 0\ reacts with
equivalent amounts of Bu3NBr and PPNCl in re~ux!
ing THF to yield Bu3NðIr3"CO#00BrŁ\ 1a\ and PPNðIr3
"CO#00ClŁ\ 1b\ respectively\ in quantitative yields ð8Ł[
The reactions of 1a and 1b with 0 equivalent of PPh1Cl
in CH1Cl1 or acetone at room temperature lead to an
immediate colour change from orange to yellow\ and
formation of ðIr3"CO#00"PPh1Cl#Ł\ 2a\ as evidenced by
IR and 20P NMR spectroscopies[ If these reaction
"THF\ re~ux\
2
h#\ to yield PPNðIr3"CO#09
"PPh1Me#ClŁ\ and is readily reversed in the presence
of CO\ without formation of 0 ð00Ł[ In fact\ lab!
ilization of ligands other than CO in the presence
of halides has not yet been observed in tetranuclear
iridium systems[
mixtures are left stirring\ however\ precipitation of 0 Study of the behaviour of 2a on TLC plates
starts to occur\ after 09 min[ These reactions were
monitored by 20P"0H# NMR spectroscopy in
Puri_cation of 2a by TLC was only possible if per!
CH1Cl1:CDCl2\ for 3 h under atmospheres of Ar and formed under speci_c conditions\ such as very low
CO[ The spectra of the mixtures under Ar\ just after cluster loading\ quick elution of the compound and
the addition of PPh1Cl to 1a and 1b\ showed only a extraction from the plates\ as soon as it separates
very strong peak at d 24[1 "s# attributed to 2a and a out from the base line[ Under the chromatographic
weak broad peak at
d −22[2\ attributed to conditions normally employed for the puri_cation of
ðIr3"CO#09"PPh1Cl#1Ł\ 3[ A decrease in the con! the PR2\ PR1H and PRH1 derivatives of 0 ð01aŁ
centration of 2a\ concomitant with an increase in that "½19 mg of the compound per plate\ CH1Cl1 ] hexane
of 3\ was noted during the _rst hour\ but no sub! 0 ] 3 as eluent#\ the mixture reacted on the silica gel to
stantial change was evidenced during the next 2 h[ give three products\ which separated out\ and whose
Furthermore\ no additional peaks were observed in yields "based on 0# were extremely sensitive to cluster
the spectra of the supernatants of either reaction mix! loading and to the polarity of the eluent[ Low cluster
tures[ Under an atmosphere of CO\ the process loading "09 mg:plate# and solvent polarity
occurred more rapidly\ and the 20P"0H# NMR spectra "CH1Cl1:hexane 0[4 ] 7[4# yielded the novel yellow
of the supernatants of both reaction mixtures showed compound ðIr3"CO#00"PPh1OH#Ł\ 2b "09)# and the
only the presence of 3\ after 29 min[ Further pre! known orange species ðHIr3"CO#09"m!PPh1#Ł ð01bŁ\ 4
cipitation of 0 and darkening of the solutions were in high yields "64)#[ This compound was previously
observed after longer periods of time\ in the absence obtained from ðIr3"CO#09"PPh1H#Ł\ 2c\ upon depro!
of CO\ due to the decomposition of 3 into unidenti_ed tonation and protonation of the resulting anion
species[
ðIr3"CO#09"m!PPh1#Ł−\ in 74) yield\ based on 0[ High
In order to investigate whether the presence of cluster loading "39 mg:plate# and solvent polarity
PPNCl or Bu3NBr was necessary for the formation "CH1Cl1:hexane 2 ] 6#\ however\ resulted in the dark!
of 0 and 3\ pure samples of 2a were left stirring in ening of the reaction mixture on the plates and sep!
CH1Cl1:CDCl2 under Ar and under CO for 3 h\ during aration of 4 "09)#\ 2b "09)# and of the dark brown
which time precipitation of 0 was not noted and the species ðIr5"m!CO#"CO#01"m!PPh1#1Ł\ 5 "39)#\ see
20P"0H# NMR spectrum of 2b stayed unchanged[ It is Scheme 0[
well known that PPNCl catalyses CO substitution by
Interestingly\ compounds 2b\ 4 and 5 were formed
nucleophiles in ruthenium carbonyl clusters ð09Ł[ In in small amounts\ when an excess silica gel for TLC
our case\ however\ the halide seems to be catalysing was added to solutions of 2a in CH1Cl1:CDCl2\ both

High nuclearity iridium clusters from ðIr3"CO#00"PPh1Cl#Ł on silica gel
1756
Scheme 0[
in the presence and in the absence of PPNCl or ðIr3"CO#00"PPh1OSi2#Ł species[ Also\ oxidative
Bu3NBr\ and the mixtures were left stirring under Ar addition of surface silanol groups at an Ir0Ir bond\
or in air for 0 h\ as shown by 20P NMR spectroscopy[ as with ðM2"CO#01Ł "M ꢂ Ru and Os#\ from which
Quantitative formation of 2b was shown to occur\ ð"m!H#M2"CO#09OSi2Ł are formed on silica surface
by 20P NMR spectroscopy\ upon addition of degassed ð03Ł\ would result in species such as ð"m!H#Ir3
water to a solution of 2a in CH1Cl1:CDCl2[ Further! "CO#09"OSi2#"PPh1Cl#Ł[ Both reactions are favoured
more\ this compound is stable on TLC plates\ and on highly hydroxilated surfaces[ In addition\ oxi!
therefore\ it must result from the reaction of 2a with dation of these species and of 2a "and possibly 3# may
the silica gel surface water[ This process is related to also occur\ with the generation of reactive fragments\
the previously reported hydrolysis of the ami! whose combination would be favoured by the high
nophosphinidene ligand of ðRu3"CO#01"m2!P"NPri1#1#Ł cluster concentration on the plates\ to generate the
absorbed onto silica that yields ðPri1NH1Ł hexanuclear cluster 5[
ðRu3"CO#01"m2!P1O#Ł\ possibly via formation of the
hydroxyphosphinidene cluster ðRu3"CO#01"m2!POH#Ł
ð02Ł[
The transformation of 2a into 4 and 5 has not been
investigated under conditions that would discount the
Characterisation of ðIr3"CO#00"PPh1OH#Ł\ 2b
The formulation of compound 2b was based on
importance of the water and oxygen in their forma! spectroscopic and analytical data "see Table 0#\ as
tion\ so we can only speculate about the possible reac! crystals suitable for an X!ray analysis could not be
tions of 2a on the silica gel surface that might be obtained[ The hydroxil proton of 2b appears at d 2[0\
involved in the formation of these species[ Thus\ elec! JPÐH ꢂ 02 Hz in the 0H NMR spectrum\ at 122 K[ The
trophilic attack of the silanol group at the P0Cl bond 20P"0H# NMR spectrum of 2b in CD1Cl1\ at 184 K\
of the PPh1Cl coordinated ligand in 2a and elim! consists of a broad singlet at d 61[2[ On cooling to 122
ination of HCl would result in the formation of the K\ two signals are resolved at d 57[7 and 54[4 in the

1757
M[ H[ de Araujo et al[
Table 0[ 0H and 20P"0H# NMR spectra of compounds 2b and 5Ð7
Compounds
20P "0H#
0H
ðIr3"CO#00"PPh1OH#Ł 2ba
ðIr5"m!CO#"CO#01"m!PPh1#1Ł 5b
57[7\ 54[1 "s\ 0 ] 9[92#
2[0 "d\ JPÐH 02#
6[5Ð6[4 "Ph\ m#
6[5Ð6[1 "Ph\ m#
6[5Ð5[6 "Ph\ m#
6[6Ð5[8 "Ph\ m#
016[6 s
ðIr6"m!CO#"CO#02"m!PPh1#"m2!PPhC5H3#Ł 6c
ðIr7"m!CO#1"CO#03"h0!Ph#"m!PPh1#"m3!PPh#Ł 7c
041[6 d\ 142[5 d\ 2JPÐP
3
080[0 d\ 36[9 d\ 2JPÐP 52
Chemical shifts in ppm\ coupling constants in Hz[
a −39>C in CD1Cl1\
b 14 to −89>C in CD1Cl1\
c 14>C in CDCl2[
intensity ratio 0 ] 9[92[ These data indicate that 2b ray crystallography were obtained from CH1Cl1:hex!
exists in solution in the form of two inter!converting ane[ A perspective view of 5 is shown in Fig[ 0\ tog!
isomers which\ by analogy with the ðIr3"CO#00LŁ ether with the labeling scheme[ Selected bond
"L ꢂ PPh2\ PPh1Me\ PMe2#\ compounds\ are the distances and angles of 5 are listed in Table 1[ The
C2vaxial and C2vradial isomers ð04Ł[
molecule contains an Ir5 octahedral core\ with eleven
Although to our knowledge this is the _rst report Ir0Ir bond distances falling in a fairly narrow range
of a phosphinous acid derivative R1POH stabilized ðfrom 1[618"0# to 1[680"0# _Ł[ Two diphenyl!
by a carbonyl cluster\ PH1OH itself and some of its phosphido ligands symmetrically bridge two non!con!
derivatives have been stabilized previously by P!com! secutive edges belonging to two di}erent equators of
plexation to {{W"CO#4|| ð05Ł[
the octahedral frame[ P0Ir bond distances average to
1[183"3# and 1[170"3# _ for the P"0#Ph1 and P"1#Ph1
ligands\ respectively[ Interestingly\ the Ir0Ir edge\
X!ray molecular structure of ðIr5"m!CO#"CO#01"m! which is bridged by the closest PPh1 group also shows
PPh1#1Ł\ 5
the shortest metal!metal bond distance in the octa!
hedron frame[ Twelve CO ligands are terminally
Compound 5 was characterized by analytical and bound\ two on each metal vertex\ while the thirteenth
spectroscopic methods "see Table 0 and Experimental# CO group symmetrically bridges one edge of the octa!
and by an X!ray analysis[ Crystals of 5 suitable for X! hedron equator not substituted by the PPh1 ligands[
Fig[ 0[ Molecular structure of ðIr5"m!CO#"CO#01"m!PPh1#1Ł\ 5[

High nuclearity iridium clusters from ðIr3"CO#00"PPh1Cl#Ł on silica gel
1758
Table 1[ Relevant bond lengths ð_Ł for 5\ 6 and 7
5
6
7
Ir"0#0Ir"1#
Ir"0#0Ir"2#
Ir"0#0Ir"3#
Ir"0#0Ir"5#
Ir"1#0Ir"3#
Ir"1#0Ir"4#
Ir"1#0Ir"5#
Ir"2#0Ir"3#
Ir"2#0Ir"4#
Ir"2#0Ir"5#
Ir"3#0Ir"4#
Ir"4#0Ir"5#
1[625"0#
1[645"0#
1[681"0#
1[670"0#
1[640"0#
1[728"0#
1[680"0#
1[664"0#
1[667"0#
1[671"0#
1[651"0#
1[618"0#
Ir"0#0Ir"3#
Ir"0#0Ir"2#
Ir"0#0Ir"6#
Ir"0#0Ir"5#
Ir"0#0Ir"1#
Ir"1#0Ir"6#
Ir"1#0Ir"4#
Ir"1#0Ir"2#
Ir"1#0Ir"3#
Ir"2#0Ir"6#
Ir"2#0Ir"4#
Ir"2#0Ir"5#
Ir"3#0Ir"5#
Ir"3#0Ir"4#
Ir"4#0Ir"5#
1[617"3#
1[677"3#
1[681"4#
1[700"4#
1[739"3#
1[601"4#
1[636"4#
1[706"3#
1[717"3#
1[521"4#
1[610"4#
1[618"4#
1[647"3#
1[755"3#
1[630"3#
Ir"0#0Ir"1#
Ir"0#0Ir"2#
Ir"0#0Ir"3#
Ir"0#0Ir"4#
Ir"0#0Ir"6#
Ir"0#0Ir"7#
Ir"1#0Ir"2#
Ir"1#0Ir"4#
Ir"2#0Ir"3#
Ir"3#0Ir"4#
Ir"3#0Ir"5#
Ir"3#0Ir"6#
Ir"4#0Ir"5#
Ir"4#0Ir"7#
Ir"5#0Ir"6#
Ir"5#0Ir"7#
Ir"6#0Ir"7#
1[644"1#
1[734"1#
1[686"1#
1[624"1#
1[669"1#
1[719"1#
1[688"1#
1[635"1#
1[676"1#
1[709"1#
1[600"1#
1[641"1#
1[641"1#
1[632"1#
1[706"1#
1[641"1#
1[652"1#
Ir"0#0P"0#
Ir"2#0P"0#
Ir"4#0P"1#
Ir"5#0P"1#
1[180"3#
1[186"3#
1[171"3#
1[168"3#
Ir"1#0P"0#
Ir"4#0P"0#
Ir"0#0P"1#
Ir"5#0P"1#
Ir"3#0C"006#
1[16"1#
1[17"1#
1[22"1#
1[15"1#
1[06"2#
P"0#0C"69#
P"0#0C"65#
P"1#0C"71#
P"1#0C"77#
0[700"8#
0[729"8#
0[727"8#
0[707"09#
Ir"1#0P"0#
Ir"2#0P"0#
Ir"3#0P"0#
Ir"4#0P"0#
Ir"5#0P"1#
Ir"7#0P"1#
Ir"2#0C"89#
1[399"8#
1[397"8#
1[150"09#
1[235"8#
1[166"8#
1[155"8#
1[95"3#
P"0#0C"099#
P"0#0C"095#
P"1#0C"001#
P"1#0C"007#
0[79"3#
0[79"3#
0[65"2#
0[68"3#
mean Ir0C"t#
mean Ir0C"b#
mean C0O
0[75"1#
1[95"1#
0[02"1#
P"0#0C"85#
P"1#0C"091#
P"1#0C"097#
C"89#0C"84#
C"89#0C"80#
C"80#0C"81#
C"81#0C"82#
C"82#0C"83#
C"83#0C"84#
mean Ir0C"b#
mean Ir0C"t#
mean C0O
0[79"1#
0[79"1#
0[71"1#
0[30"4#
0[33"4#
0[17"5#
0[49"5#
0[20"5#
0[26"5#
1[92"2#
0[76"2#
0[02"3#
mean Ir0C"t#
mean Ir0C"b#
mean C0O
0[73"3#
0[88"09#
0[07"3#
Cluster 5 possesses 75 valence electrons\ and exhibits 1[665"0#\ 1[665"0# and 1[662"0# _\ respectivelyŁ and
a remarkably similar molecular geometry to those of so do the metal!carbon bond lengths ðav[ Ir0C"COt#
the dianionic ðIr5"m!CO#2"CO#01Ł1− ð06Ł and the 0[75"1#\ 0[76"1# and 0[75"1# ^ Ir0C"COb# 1[95"1#\
monoanionic ðIr5"m!CO#1"CO#1"m!PPh1#Ł− ð07Ł clus! 1[94"1# and 1[93"1#\ respectivelyŁ[
ters[ The latter compound was recently obtained from
In spite of the lack of symmetry of compound 5 in
the oxidation of ðIr5"m!CO#2"CO#01Ł1− with ðFeCp1Ł¦ the solid state\ the 20P "0H# NMR spectrum showed a
in the presence of PPh1H\ followed by deprotonation singlet at d 016[6 from 184 to 072 K which indicates
of the coordinated phosphine[ Two of the three bridg! that it is ~uxional at those temperatures[
ing CO ligands in the dianionic compound are for!
mally replaced by two 2!electron donor PPh1 groups
in 5\ whilst ðIr5"m!CO#1"CO#01"m!PPh1#Ł− results\ for! Thermolysis of ðHIr3"CO#09"m!PPh1#Ł\ 4
mally\ from the replacement of one m!CO in the
dianion by a m!PPh1 fragment[ The steric arrangement
In order to _nd out whether compound 5 would also
of the remaining twelve CO ligands does not di}er be formed under thermolytic conditions\ compound 4
substantially in the three species[ Average Ir0Ir bond was heated in THF under re~ux[ After 01 h\ three
distances compare well in 5\ ðIr5"m!CO#1"CO#01"m! compounds were isolated in su.cient yields to be fully
PPh1#Ł− and ðIr5"m!CO#2"CO#01Ł1− ðav[ Ir0Ir characterized by analytical and spectroscopic data

1769
M[ H[ de Araujo et al[
Formation of high nuclearity clusters from other
and by X!ray analyses ] compound 5 "39)#\ ðIr6"m!
CO#1"CO#01"m!PPh1#"m2!PPhC5H3#Ł\ "09)# and phosphido compounds\ such as ðHRu2"CO#09"m!
6
ðIr7"m!CO#"CO#04"h0!Ph#"m!PPh1#"m3!PPh#Ł 7\ "07)#\
in addition to starting material 4 "07)#[ Heating com!
pound 4 for an additional 01 h period did not lead to
the formation of other products\ but resulted in an
increase in the yield of the octanuclear cluster 7 "39)#
and a decrease in that of the hexanuclear compound
5 "03)#\ whilst that of 6 "09)# remained unchanged ^
some starting material 4 "8)# was also recovered
under these conditions[ Furthermore\ thermolysis of
4 in THF for longer periods of time\ or in re~uxing
toluene for 01 h led to larger amounts of decompo!
sition material on the base line of the TLC plates[
Formation of 5 might be rationalized in terms of
condensation of 4 with a reactive unsaturated hyd!
rido!phosphido fragment with loss of H1 and CO "See
Scheme 1#[ Considering that heating compound 5
under re~ux in THF for 01 h does not lead to cluster
build up\ it is possible that compounds 6 and 7 might
result from further condensation of a monomeric and
a dimeric unsaturated fragments\ respectively\ with 5\
PPh1#Ł\ ðHRu2"CO#8"m!PPh1#Ł ð08\19Ł\ ðH1Ru2
"CO#7"m!PPh1#1Ł ð19Ł and ðH2Ru2"CO#6"m!PPh1#2Ł
ð19Ł\ has been shown to occur previously[ Also in
these cases\ products resulting from the activation of
P0CPh and orthometallation were isolated[ It is inter!
esting\ however\ that heating ðHM2"CO#09"m!PPh1#Ł
"M ꢂ Ru ð19Ł and Os ð10Ł# under mild conditions
leads to the formation of the unsaturated compound
ðHRu2"CO#8"m!PPh1#Ł and of the orthometallated
product ðH1Os2"CO#8"m!PPhC5H3#Ł\ respectively\
whilst even under mild conditions\ compound 4 under!
goes cluster build up[
X!ray molecular structure of ðIr6"m!CO#"CO#02"m!
PPh1#"m2!PPhC5H3#Ł\ 6
The molecular structure of 6 is shown in Fig[ 1[
Selected bond distances are listed in Table 1[ The
molecule possesses 87 valence electrons\ and exhibits
accompanied by orthometallation and cleavage of a a capped octahedron arrangement of iridium atoms\
P0CPh bond\ respectively[ with _fteen Ir0Ir bond distances falling in the range
Scheme 1[

High nuclearity iridium clusters from ðIr3"CO#00"PPh1Cl#Ł on silica gel
1760
Fig[ 1[ Molecular structure of ðIr6"m!CO#"CO#02"m!PPh1#"m2!PPhC5H3#Ł\ 6[
from 1[521"4# to 1[755"3# _[ A diphenylphophido and Ir00Ir4# sharing a triangular face[ Ir0Ir bond dis!
a phenyl orthometallated phosphido ligands bridge tances range from 1[600"1# to 1[734"1# _[ The m!PPh1
two opposite equatorial edges of the octahedron[ Thir! ligand symmetrically bridges one of the edges of the
teen CO ligands are terminally bound\ two on six octahedron[ A second PPh1 ligand has undergone
metal vertex and one on the seventh metal atom\ while P0C bond cleavage ^ the two resulting fragments\ viz
the fourteenth CO group symmetrically bridges the the phenyl ligand and the phenyl phosphinedene\ bind
edge formed by the capping iridium atom and the in h0!fashion to one of the basal atoms and in m3!
iridium atom bearing only one terminal CO[ The only fashion the four basal atoms of the square based pyra!
other known heptanuclear iridium cluster\ ðIr6"m! mid\ respectively[ A similar kind of m3!coordination
CO#"CO#00"C7H01#"C7H00#"C7H09#Ł\
which
was of a PPh ligand\ which donates four electrons to the
obtained from the reaction of 0 with 0\4!cyclo! metal frame\ has previously been observed in the pen!
octadiene in re~uxing chorobenzene ð11Ł\ exhibits a tanuclear iridium compounds ðIr4"m!CO#1"CO#6L"h4!
similar metal framework arrangement[ The steric C4Me4#"m3!PPh#Ł "L ꢂ CO\ PPh2# ð12Ł[ Fourteen car!
arrangement of the thirteen CO ligands does not di}er bonyls are terminally bound to the iridium atoms\
substantially in the two species[ Average Ir0Ir bond while the remaining two CO ligands symmetrically
distances compare well in 6 and ðIr6"m!CO#"CO#00 bridge one of the basal square pyramids and one of
"C7H01#"C7H00#"C7H09#Ł ðav[ Ir0Ir 1[656"4#\ and the octahedron edges[ The only two other octanuclear
1[652"0# _\ respectivelyŁ and the same can be said for iridium clusters whose structures have been deter!
the metal!carbon bond lengths ðav[ Ir0C"COt# 0[73"3# mined to date are ðIr7"CO#11Ł− ð13Ł and ðIr7Au1
and 0[75"4# ^ Ir0C"COb# 0[88"09# and 1[93"3#\ respec! "CO#19"PhPPPh#"PEt2#Ł ð14Ł\ which exhibit bis!tetra!
tivelyŁ[
nuclear frameworks linked by an Ir0Ir bond and by
the PhPPPh ligand\ respectively[
X!ray molecular structure of ðIr7"m!CO#1"CO#03"h0!
Ph#"m!PPh1#"m3!PPh#Ł\ 7
EXPERIMENTAL
Compound 7 was formulated on the basis of ana! General procedures and materials
lytical and spectroscopic data "see Table 0 and Exper!
imental# but an X!ray analysis experiment was
Iridium trichloride "Johnson and Matthey#\ PPNCl
necessary to establish its structure unambiguously[ and Bu3NBr "Aldrich#\ diphenyl phosphine and chlo!
The molecular structure of 7 is shown in Fig[ 2\ tog! rodiphenyl phosphine "Strem Chemicals# were used
ether with the labeling scheme[ Selected bond dis! as purchased[ The compounds ðIr3"CO#01Ł 0 ð15Ł\
tances are listed in Table 1[ The metal arrangement ðIr3"CO#00"PPh1H#Ł 2c\ ðHIr3"CO#09"m!PPh1#Ł 4 ð01Ł\
can be described as a fused polyhedron\ formed by Bu3NðIr3"CO#00BrŁ 1a and PPNðIr3"CO#00ClŁ 1b ð8Ł
an octahedron and a square based pyramid "atoms were prepared by literature methods[ Manipulations

1761
M[ H[ de Araujo et al[
Fig[ 2[ Molecular structure of ðIr7"m!CO#1"CO#03"h0!Ph#"m!PPh1#"m3!PPh#Ł\ 7[
were performed in Schlenk tubes\ under an atmo! m\ cm−0[ Use of Bu3NðIr3"CO#00BrŁ 1a\ instead of 1b\
sphere of dry Ar\ unless otherwise speci_ed[ Solvents gave similar yields of 2a\ under the same conditions[
were dried as previously described ð01Ł and freshly
distilled under Ar and degassed before use[ Pre!
Investi`ation of the stability of 2a in the presence of
parative TLC was carried out in air by using ca 1
PPNCl or Bu3NBr
mm thick glass!backed silica gel plates "19×19 cm#
prepared from silica GF143 Type 59\ Fluka\ and the
An orange solution of PPNðIr3"CO#00ClŁ 1b "037[4
compounds extracted from the silica with dichlo!
mg\ 9[98 mmol# in CH1Cl1 "4 cm2# was cooled to
romethane[ All substituted Ir3 cluster compounds
−29>C and treated with PPh1Cl "05[5 ml\ 9[98 mmol#[
were stored under an inert atmosphere for they were
Quick warming of the reaction mixture to 19>C was
found to be slightly air sensitive in the solid state[
followed by addition of 9[4 cm2 of CDCl2[ A 20P "0H#
FAB!MS were obtained on a VG AutoSpec using p!
NMR spectrum was recorded immediately\ and every
nitrobenzyl alcohol as a matrix at the University of
29 min thereafter[ After 09 min stirring at room tem!
Sussex\ U[K[ IR spectra on a JASCO IR 699 between
perature 0 started to precipitate\ and was decanted\
1199 and 0599 cm−0 using CaF1 cells[ 0H and 20P
before each sampling[ Same procedure was followed
"0H# NMR data were obtained on a Bruker AC 299
in the reaction of Bu3NðIr3"CO#00BrŁ\ 1a with PPh1Cl[
instrument\ using deuterated solvents as lock and ref!
erence ð0H SiMe3 ^ 20P 74) H2PO3 "external#Ł[ Mic!
Investi`ation of the stability of 2a in the absence of
PPNCl or Bu3NBr
roanalyses were performed at the Instituto de
Quꢁ(mica\ UNICAMP\ Brazil[
Solutions of pure 2a "19 mg\ 9[905 mmol# in
CH1Cl1 ] CDCl2 "9[7 cm2 ] 9[4 cm2# were left stirring
under Ar and under CO for 3 h[ No precipitation of
0 was observed and the 20P "0H# NMR spectra of both
solutions showed only the presence of 2a[
Preparation of ðIr3"CO#00"PPh1Cl#Ł\ 2a
An orange solution of PPNðIr3"CO#00ClŁ 1b "26[0
mg\ 9[912 mmol# in CH1Cl1 "1 cm2# was cooled to
−29>C and treated with PPh1Cl "3[0 ml\ 9[912 mmol#[
The yellow reaction mixture was warmed to 14>C[
Quick puri_cation of the reaction mixture by TLC\ Reaction of ðIr3"CO#00"PPh1Cl#Ł 2a on TLC plates
using CH1Cl1:hexane "2 ] 6# as eluent\ taking care to
load each plate with a maximum of 2 mg of 2a\ and
Method 0 ] Low cluster loading "09 mg:plate#\
extracting the yellow compound from the plates\ just CH1Cl1:hexane "0[4 ] 7[4#\ yielded the orange species
after it had separated out from the base line\ gave 4 "72[4 mg\ 64)#\ the yellow compound ðIr3"CO#00
pure 2a "06[2 mg\ 59)#\ IR "nCO hexane# ] 1973 s\ 1941 "PPh1OH#Ł 2b "00[4 mg\ 09)# ^ Rf 9[68\ IR "nCO
vs\ 1939 vs\ 1929 vs\ 0844 m\ 0774 w\ 0734 m and 0713 hexane# ] 1973 s\ 1941 vs\ 1903 vs\ 0863 vs\ 0779 w\

High nuclearity iridium clusters from ðIr3"CO#00"PPh1Cl#Ł on silica gel
1762
0734 m and 0712 m cm−0 and the brown compound "PPh1OH#Ł 2b\ con_rmed by 20P "0H# NMR spectro!
ðIr5"m!CO#"CO#01"m!PPh1#1Ł 5 "7[4 mg\ 4)# Rf 9[53\ scopy[
IR "nCO hexane# ] 1967 s\ 1949 vs\ 1939 vs\ 1919 wsh\
1909 s\ 0882 s\ 0846 w and 0731 s cm−0[ Found ] C\
Thermolysis of 4
12[1 ^ H\ 9[7[ Calc[ for C26H19O02P1Ir5 ] C\ 12[4 ^ H\
0[9)[ Method 1 ] High cluster loading "39 mg:plate#\
CH1Cl1:hexane "2 ] 6#\ resulted in the separation of
compounds 4 "00 mg\ 09)#\ 2b "00[4 mg\ 09)# and
5 "57 mg\ 39)#[
A solution of compound 4 "099 mg\ 9[97 mmol# in
THF "19 cm2# was heated under re~ux for 01 h[ The
solvent was evaporated\ the mixture was dissolved in
CH1Cl1 "1 cm2# and puri_ed by TLC with CH1Cl1:hex!
ane "0 ] 4# as eluent\ to yield ] compounds 5 "Rf 9[40\ 59
mg\ 39)# ^ ðIr6"m!CO#1CO#01"m!PPh1#"m2!PPhC5H3#Ł 6
"Rf 9[47\ 06 mg\ 09)#\ IR "nCO hexane# ] 1963 m\ 1935
Reactions of 2a with silica `el
The following reactions were monitored by 20P "0H#
NMR spectroscopy\ after stirring for 0 h at 14>C
under "a# Ar and "b# air[ Addition of silica gel for
TLC "excess\ approximately 49 mg# to three solutions
containing 2a "19 mg\ 9[905 mmol# and PPNCl "0
equiv[#\ 2a and Bu3NBr "0 equiv[# or pure 2a in
CH1Cl1 ] CDCl2 "1 cm2 ] 0 cm2# led to the formation of
compounds 2b\ 4 and 5 in trace amounts[
s\ 1939 vs\ 1911 m\ 1995 w\ 0882 w and 0749 w\ cm−0
^
and ðIr7"m!CO#"CO#04"h0!Ph#"m!PPh1#"m3!PPh#Ł 7 "Rf
9[39\ 17 mg\ 04)# ] IR "nCO hexane# ] 1965 s\ 1937 vs\
1927 vs\ 1997 m\ 0880 m\ 0844 m and 0739 s\ cm−0
^
Found ] C\ 19[1 ^ H\ 9[5[ Calc[ for C39H19O05P1Ir7 ]
C\ 19[3 ^ H\ 9[7)[ FAB!MS m:z ꢂ 1251 "ꢂM# ðM!
n"CO#Ł "n ꢂ 0Ð05# ^ three brown species "Rf 9[13\ 9[18\
9[51# in minute amounts and unreacted 4 "07 mg\
07)#[
Reaction of 2a with H1O
The thermolysis of compound 4 was repeated "a#
under the same conditions but for 13 h\ and gave the
Addition of H1O "49 ml\ 1[74 mmol# to a solution same three products\ 5 "09 mg\ 03)#\ 6 "7 mg\ 09)#
of 2a "09 mg\ 9[997 mmol# in CH1Cl1 ] CDCl2 "3 cm2 ] and 7 "26 mg\ 39)#\ and unreacted 4 "3 mg\ 8)# ^ "b#
0 cm2# led to quantitative formation of ðIr3"CO#00 in toluene under re~ux for 01 h\ and produced the
Table 2[ Crystal data and details of measurements for compounds 5\ 6 and 7
Compound
5
6
7
Formula
Formula weight
Crystal system
Space group
a "_#
b "_#
c "_#
a ">#
b ">#
C26H19Ir5O02P1
0764[56
Triclinic
P!0
02[989 "1#
04[696 "2#
09[554 "2#
092[41 "1#
81[08 "1#
66[319 "09#
1979[5 "7#
182 "1#
C27H08Ir6O03P1
1981[76
Triclinic
P!0
8[763 "7#
00[236 "3#
08[221 "5#
82[77 "2#
81[55 "3#
89[09 "3#
1048 "1#
182 "1#
C39H19Ir7O05P1
1239[09
Monoclinic
P10:c
08[283 "6#
02[316 "4#
19[570 "8#
89
006[95 "2#
89
3685 "2#
182 "1#
2[130
g ">#
V "_2#
T "K#
Dcalcd "mg m−2
Z
#
1[883
1
2[119
1
3
F "999#
0565
0745
3025
l "MoÐKa#\ _
9[60958
07[48
9[60958
19[77
9[60958
10[36
Absorption coe.cient "mm−0
Psi!scan correction
#
min[Ðmax[ transmission
u range ">#
9[50*0[99
2Ð14
9[37Ð0[99
2Ð14
9[45Ð0[99
2Ð14
Re~ections collected
Independent re~ections
Independent re~ections
with I × 1s"I#
5811
5189
3328
6656
6414
2035
6824
6562
3436
No[ of re_ned parameters
R0 "on F\ I × 1s"I##
wR1 "on F1\ all data#
245
R0 ꢂ 9[9348
wR1 ꢂ 9[0363
204
R0 ꢂ 9[0084
wR1 ꢂ 9[2693
259
R0 ꢂ 9[9692
wR1 ꢂ 9[1153

1763
M[ H[ de Araujo et al[
4[ Angoletta\ M[\ Malatesta\ L[ and Caglio\ G[\ J[
Or`anomet[ Chem[\ 0864\ 86\ 88[
5[ Maloney\ S[ D[\ Kelley\ M[ J[\ Koningsberger\ D[
C[ and Gates\ B[ C[\ J[ Phys[ Chem[\ 0880\ 84\
8395[
6[ Maloney\ S[ D[\ Kelley\ M[ J[ and Gates\ B[ C[\
J[ Or`anomet[ Chem[\ 0881\ 324\ 266[
7[ "a# Lu\ K[!L[\ Chen\ C[!J[\ Lin\ Y[!W[\ Gau\ H[!
M[\ Hong\ F[!E[ and Wen\ Y[!S[\ Or`an!
ometallics\ 0882\ 01\ 1077 ^ "b# Gervasio\ G[ and
Sappa\ E[\ J[ Or`anomet[ Chem[\ 0884\ 387\ 62
and references therein ^ "c# Gervasio\ G[\ Mara!
bello\ D[ and Sappa\ E[\ J[ Chem[ Soc[\ Dalton
Trans[\ 0886\ 0740 and references therein[
8[ Ciani\ G[\ Chini\ P[\ Martinengo\ S[\ Manassero\
M[\ Sironi\ A[ and Canziani\ F[\ J[ Or`anomet[
Chem[\ 0867\ 041\ C24[
same products 5 "12 mg\ 29)#\ 6 "4 mg\ 5)# and 7
"16 mg\ 21)#\ and unreacted 4 "3 mg\ 8)#[
Thermolysis of ðIr5"m!CO#"CO#01"m!PPh1#1Ł\ 5[ A
solution of compound 5 "19 mg\ 9[90 mmol# in THF
"09 cm2# was heated under re~ux for 01 h[ The reaction
was monitored by IR spectroscopy\ which showed no
changes in the nCO region[ The solvent was evaporated\
the mixture was dissolved in CH1Cl1 "0 cm2# and pur!
i_ed by TLC with CH1Cl1:hexane "0[4 ] 7[4# as eluent[
Only compound 5 "05 mg\ 73)# was recovered from
the plates\ which showed also some decomposition
material on the base line[
Crystal structure determination[ Crystal data and
details of measurements for compounds 5\ 6 and 7 are
summarized in Table 2[ Di}raction intensities were
collected at room temperature on an Enraf!Nonius
CAD!3 di}ractometer equipped with a graphite
monochromator "MoÐKa\ l ꢂ 9[60958 _#[ Intensity
data were reduced to F1o [ Crystals were obtained from
CH1Cl1:hexane by slow evaporation[ The structures
were solved by direct methods\ followed by least!squa!
res re_nements[ For all calculations the crys!
tallographic programs SHELX75 ð16aŁ and
SHELXL82 ð16bŁ were used[ Empirical absorption
correction was applied for the three compounds by
azimuthal scanning of re~ections with x × 79>[ Ir and
P atoms and CO groups in 5\ Ir\ P and O atoms in 6
and 7 were re_ned anisotropically[ All phenyl rings
"except for the orthometallated ring in 7# were re_ned
as rigid groups[ Due to the scarce quality of data\
constraints were applied for compound 6 on re_ning
Ir0CCO and C0O distances[ The hydrogen atoms
were added in calculated positions "C1sp0H 9[82 _#
and re_ned {{riding|| on the corresponding C atoms[
For graphical representations the program
SCHAKAL81 ð16cŁ was used[
09[ Rivomanana\ S[\ Lavigne\ G[\ Lugan\ N[ and
Bonnet\ J[!J[\ Or`anometallics\ 0880\ 09\ 1174[
00[ Vargas\ M[ D[\ unpublished results[
01[ "a# Mann\ B[ E[\ Vargas\ M[ D[\ Khattar\ R[\
J[ Chem[ Soc[\ Dalton Trans[\ 0881\ 0614 ^ "b#
Livotto\ F[ S[\ Raithby\ P[ and Vargas\ M[ D[\
J[ Chem[ Soc[\ Dalton Trans[\ 0882\ 0686[
02[ "a# Corrigan\ J[ F[\ Doherty\ S[\ Taylor\ J[ and
Carty\ A[ J[\ J[ Am[ Chem[ Soc[\ 0883\ 005\ 8688 ^
"b# Wang\ W[\ Corrigan\ J[ F[\ Doherty\ S[\
Enright\ G[ D[\ Taylor\ J[ N[ and Carty\ A[ J[\
Or`anometallics\ 0885\ 04\ 1669[
03[ Basset\ J[ M[ and Choplin\ A[\ J[ Mol[ Catal[\
0882\ 10\ 84[
04[ Ros\ R[\ Scrivanti\ A[\ Albano\ V[ G[ and Gar!
laschelli\ L[\ J[ Chem[ Soc[\ Dalton Trans[\ 0875\
1300[
05[ "a# Mercier\ F[ and Matthey\ F[\ J[ Chem[ Soc[\
Chem[ Commun[\ 0873\ 671 ^ "b# Mercier\ F[\ Mat!
they\ F[\ A_ong!Akpan\ C[ and Nixon\ J[ F[\ J[
Or`anomet[ Chem[\ 0877\ 237\ 250[
06[ Demartin\ F[\ Manassero\ M[\ Sansoni\ M[\ Gar!
laschelli\ L[ and Martinengo\ S[\ J[ Chem[ Soc[\
Chem[ Commun[\ 0879\ 892[
07[ Della Pergola\ R[\ Brivio\ E[\ Garlaschelli\ L[\
Masciocchi\ N[ and Manassero\ M[\ J[ Cluster
Sci[\ 0883\ 4\ 252[
Acknowled`ements*We thank FAPESP\ PADCT and
CNPq of Brazil "M[H[A[ and M[D[V[# and the Ministero
della Universita e della Ricerca Scienti_ca e Tecnologica
ꢁ
of Italy "D[B[ and F[G[# for research grants\ Johnson and
Matthey plc for their generous loan of IrCl2 and Prof[ J[ F[
Nixon for the FAB!MS at the University of Sussex[
08[ "a# MacLaughlin\ S[ A[\ Taylor\ N[ J[ and Carty\
A[ J[\ Or`anometallics\ 0873\ 2\ 281 ^ "b# ibid\ Can[
J[ Chem[\ 0871\ 59\ 76 ^ "c# ibid\ Inor`[ Chem[\
0872\ 11\ 0398 ^ "d# van Gastel\ F[\ Taylor\ N[ J[
and Carty\ A[ J[\ J[ Chem[ Soc[\ Chem[ Commun[\
0876\ 0938 ^ "e# ibid\ Inor`[ Chem[\ 0878\ 17\ 74[
a19[ Field\ J[ S[\ Haines\ J[ and Mulla\ F[\ J[
Or`anomet[ Chem[\ 0889\ 278\ 116[
Supplementary material available*Complete listings of frac!
tional atomic coordinates\ anisotropic thermal parameters
and bond lengths and angles[
10[ Colbran\ S[ B[\ Irele\ P[ T[\ Johnson\ B[ F[ G[\
Lahoz\ F[ J[\ Lewis\ J[ and Raithby\ P[ R[\ J[
Chem[ Soc[\ Dalton Trans[\ 0873\ 1612[
11[ "a# Pierpont\ C[ G[\ Inor`[ Chem[\ 0868\ 07\ 1861 ^
"b# Pierpont\ C[ G[\ Stuntz\ G[ F[ and Shapley\ J[
R[\ J[ Am[ Chem[ Soc[\ 0867\ 099\ 505[
12[ Khattar\ R[\ Naylor\ S[\ Vargas\ M[ D[\ Braga\
D[ and Grepioni\ F[\ Or`anometallics\ 0889\ 8\
534[
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High nuclearity iridium clusters from ðIr3"CO#00"PPh1Cl#Ł on silica gel
1764
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