Palladium (I) phosphido-bridged dinuclearderivatives with phosphite ligands

Article abstract of DOI:10.1016/S0277-5387(98)00089-8

New mono-phosphido-bridged cationic derivatives of dipalladium (I) have beenprepared by reacting [Pd₂(μ-PBu^t₂)(PPh₃) ₃]BF₄ (2) BF₄, with P (OR) ₃ (R=Me, Et, Ph) . Under a large excess of the entering phosphite, all the PPh₃ molecules terminally bonded to the central Pd₂(μ-PBu^t₂) core can be substituted, yielding [Pd₂(μ-PBu^t₂){P(OR)₃} ₄]BF₄, [ (4a) BF₄, R=Me; (4b) BF₄, R=Et and (4c) BF₄, R=Ph] . The intermediate mixed-ligand complex [Pd₂(μ-PBu^t₂)(PPh₃){P(OPh) ₃}₂]BF₄, (5) BF₄, was isolated in the reactionwith P (OPh) ₃. Moreover, the reactions of the new complexes with CO, isoprene andCS₂ were investigated and compared to the corresponding reactions of thephosphine-substituted complexes.

Full text of DOI:10.1016/S0277-5387(98)00089-8

Polyhedron Vol[ 06\ No[ 07\ pp[ 2034Ð2040\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166Ð4276"87#99978Ð7
Palladium"I# phosphido!bridged dinuclear
derivatives with phosphite ligands
Piero Leonia\b\ꢀ\ Stefano Papuccia and Marco Pasqualia
a Dipartimento di Chimica e Chimica Industriale\ Universita di Pisa\ I!45015 Pisa\ Italy
Á
b Scuola Normale Superiore\ Piazza dei Cavalieri\ I!45015 Pisa\ Italy
"Received 1 December 0886^ accepted 13 February 0887#
Abstract*New mono!phosphido!bridged cationic derivatives of dipalladium"I# have been prepared by react!
ing ðPd1"m−PBut1#"PPh2#2ŁBF3 "1#BF3\ with P"OR#2 "RꢁMe\ Et\ Ph#[ Under a large excess of the entering
phosphite\ all the PPh2 molecules terminally bonded to the central Pd1"m−PBut1# core can be substituted\
yielding ðPd1"m−PBut1#"P"OR#2#3ŁBF3\ ð"3a#BF3\ RꢁMe^ "3b#BF3\ RꢁEt and "3c#BF3\ RꢁPhŁ[ The inter!
mediate mixed!ligand complex ðPd1"m−PBu1t #"PPh2#"P"OPh#2#1ŁBF3\ "4#BF3\ was isolated in the reaction
with P"OPh#2[ Moreover\ the reactions of the new complexes with CO\ isoprene and CS1 were investigated and
compared to the corresponding reactions of the phosphine!substituted complexes[ Þ 0887 Elsevier Science
Ltd[ All rights reserved
Keywords] dinuclear ^ phosphido!bridges ^ palladium"I# ^ phosphite ^ cationic[
———————————————————————————————————————————————
The chemistry of phosphido!bridged palladium"I#
dinuclear derivatives was rather unexplored until a
few years ago ð0Ł[ Our group is involved in a syste!
matic study of this _eld ð1Ð6Ł\ and has shown that
the secondary phosphine!bridged ðPd1"m−PBut1#
"m−PBut1H#"PBu1t H#1ŁBF3\ "0#BF3 ð2Ł\ can be em!
ployed as the precursor of a series of mono!pho!
sphido!bridged cationic derivatives of general for!
mula ðPd1"m\PBu1t #"PR2#nŁBF3\ ð3Ł with n depending
on the steric demand of the phosphine ligand "nꢁ2\
RꢁPh ð"1#BF3Ł^ nꢁ3\ RꢁMe ð"2a#BF3Ł\ RꢁEt
ð"2b#BF3Ł or R2ꢁCy1H\ ð"2c#BF3Ł^ see Scheme 0#[
Both "0#BF3 and its derivatives with other phosphines
have shown an interesting reactivity^ they can be used
as a source of still rare examples of terminally bonded
Pd"I# carbonyls ð2b\ 4Ł or show cooperation of the two
metal centers in the coordination of polyunsaturated
molecules as isoprene ð4\ 5Ł or CS1 ð3b\ 6Ł[ We now
report the synthesis of new members of this family\
bearing phosphites terminally bonded to the central
EXPERIMENTAL
ðPd1"m−PBut1#Ł¦ core\ and compare their reactivity
with that given by their phosphine analogues[
General and instrumental
All reactions were performed under an atmosphere
of puri_ed nitrogen or carbon monoxide by using
ꢀ Address to whom correspondence should be addressed[
standard Schlenck techniques[ Solvents were dried by
2034

2035
P[ Leoni et al[
standard procedures and distilled under nitrogen prior H\ 3[55[ Found] C\ 46[5\ H\ 3[55[ 20P"0H# NMR
to use[ Deuterated solvents were used as purchased "CDCl2\ 187 K#] d "ppm# 259[9 "tt\ 1JPP ¼ 139\ 35 Hz\
1
and stored on molecular sieves under an inert atmo! m−PBut1#\ 007[9 "dm\ JPP ꢁ 139 Hz\ P"OPh#2 trans
sphere[ ðPd1"m−PBut1#"PPh2#2ŁBF3\ "1#BF3\ was pre! to m!P#\ 092 "m\ P"OPh#2 cis to m!P#[ 0H NMR
pared as previously described ð3bŁ[ IR spectra were "CDCl2\ 187 K#] d "ppm# 6[1 "m\ 59 H\ OC5H4#\ 0[2
2
recorded with a Perkin!Elmer FT!IR 0614X spec! "d\ JHPꢁ04 Hz\ 07 H\ PC"CH2#2#[ IR "Nujol\ KBr#]
trophotometer and NMR spectra with a Varian Gem! 0944 s\ br "nBF# cm−0
ini 199BB spectrometer\ frequencies were referenced
[
Preparation of ðPd1"m−PBut1#"PPh2#"P"OPh#2#1ŁBF3\
to the residual signal of the deuterated solvent "0H\ "4#BF3[ Triphenyl phosphite "3[96 mL\ 04[4 mmol#
02C# and to external 74) H2PO3 "20P#[ The progress was added to a red CH1Cl1 "09 mL# solution of "1#BF3
of the reactions was monitored by means of 20P"0H# "216 mg\ 9[15 mmol#[ The color of the solution turned
NMR spectroscopic analyses of small samples of a quickly orange^ after 04 min most of the solvent was
reaction mixture\ after adding a few drops of C5D5 evaporated and Et1O "29 mL# was added\ causing the
for the lock signal capture and the _eld homogeneity precipitation of an orange powder which was _ltered\
optimization operations[
washed with Et1O\ and vacuum dried "119 mg\ 53)
Preparation of ðPd1"m−PBut1#"P"OMe#2#3ŁBF3\ yield#[
"3a#BF3[ Trimethyl phosphite "9[05 mL\ 0[33 mmol#
Elem[ Anal[ Calcd for C51H52BF3O5P3Pd1] C\ 45[0\
was added to a red acetone "09 mL# solution of "1#BF3 H\ 3[67[ Found] C\ 47[4\ H\ 4[94[ 20P"0H# NMR "ace!
1
"068 mg\ 9[034 mmol#[ The solution turned quickly tone!d5\ 187 K#] d "ppm# 263[1 "ddd\ JPPꢁ084\ 091\
orange^ after 04 min most of the solvent was evap! 69 Hz\ m−PBut1#\ 013[1 "ddd\ JPPꢁ091\ 26 Hz\
1
orated and n!hexane "19 mL# was added\ causing the 2JPPꢁ252 Hz\ P"OPh#2#\ 002[5 "ddd\ JPPꢁ69\ 03 Hz\
1
precipitation of a yellow powder which was _ltered 2JPPꢁ252 Hz\ P"OPh#2#\ 15[7 "ddd\ 1JPPꢁ084\ 26 Hz\
o}\ washed with n!hexane\ and vacuum dried "84 mg\ 2JPPꢁ03 Hz#\ the spectrum shows other minor signals
69) yield#[
"see Results and Discussion# due to other compounds
Elem[ Anal[ Calcd for C19H43BF3P4Pd1] C\ 14[4\ which justify the low purity found in elemental analy!
H\ 4[67[ Found] C\ 14[5\ H\ 4[79)[ 20P"0H# NMR sis\ attempted puri_cation by column chro!
"CDCl2\ 187 K#] d "ppm# 234[4 "tm\ 1JPP ¼ 171\ 35 Hz\ matography led to decomposition[ 0H NMR "CDCl2\
1
m−PBut1#\ 025[1 "dm\ JPP ¼ 179 Hz\ P"OMe#2 trans 187 K#] d "ppm# 6[0 "m\ 34 H\ PC5H4¦OC5H4#\ 0[3
to m!P#\ 016[1 "m\ P"OMe#2 cis to m!P#[ 0H NMR "d\ 2JHPꢁ03[5 Hz\ 07 H\ PC"CH2#2#[ IR "Nujol\ KBr#]
"CDCl2\ 187 K#] d "ppm# 2[54 "m\ 25 H\ OCH2#\ 0[24 2939 "n1CH#\ 0477\ 0375 "nC1C#\ 0944 s\ br "nBF
"d\ 2JHPꢁ03[1 Hz\ 07 H\ PC"CH2#2#[ IR "Nujol\ KBr#] cm−0
0917 s\ br "nBF# cm−0
#
[
[
Reactions of "3a\b#BF3 with CS1 A 09!fold excess
Preparation of ðPd1"m−PBut1#"P"OEt#2#3ŁBF3\ of CS1 was added by syringe to a CDCl2 solution
"3b#BF3[ Triethyl phosphite "9[26 mL\ 1[05 mmol# was "9[4 mL# of "3a#BF3 "04 mg\ 9[9048 mmol# or "3b#BF3
added to a red acetone "04 mL# solution of "1#BF3 "07 mg\ 9[9051 mmol#[ The orange solutions turned
"155 mg\ 9[105 mmol#[ The solution turned quickly quickly yellow and were analyzed by 20P"0H# NMR
orange^ after 29 min most of the solvent was evap! spectroscopy "see Results and Discussion#[
orated after which n!hexane "14 mL# was added\ caus!
Reactions of "3a\b#BF3 with isoprene A 09!fold
ing the precipitation of a yellow powder[ The excess of isoprene was added by syringe to a CDCl2
suspension was left overnight at −29>C\ the solid solution "9[4 mL# of "3a#BF3 "05 mg\ 9[906 mmol# or
_ltered o}\ washed with n!hexane\ and vacuum dried "3b#BF3 "08 mg\ 9[9060 mmol#[ The orange solutions
"047 mg\ 55) yield#[
turned quickly yellow and were analyzed by 20P"0H#
Elem[ Anal[ Calcd for C21H67BF3O01P4Pd1] C\ 23[5\ NMR "see Results and Discussion#[
H\ 6[98[ Found] C\ 23[7\ H\ 5[88[ 20P"0H# NMR "Ace!
Reactions of "3a\b#BF3 with CO Carbon monoxide
tone!d5\ 187 K#] d "ppm# 234[5 "tm\ 1JPP ¼ 179\ 49 Hz\ was bubbled into orange CDCl2 solutions of complex
m−PBut1#\ 026[1 "dm\ 1JPP ¼ 179 Hz\ P"OEt#2 trans to "3a#BF3 or "3b#BF3 "ca 29 mg:mL#[ A faint bleaching
0
m!P#\ 012 "m\ P"OEt#2 cis to m!P#[ H NMR "CDCl2\ of the starting colour was observed and the solutions
187 K#] d "ppm# 2[8 "br s\ 13 H\ OCH1CH2#\ 0[2 "over! were analyzed by 20P"0H# NMR spectroscopy which
lapping m\ 43 H\ OCH1CH2¦PC"CH2#2#[ IR "Nujol\ exhibited only the resonances of the reagents[ The IR
KBr#] 0923 s\ br "nBF# cm−0
[
spectra of the solutions exhibited medium!weak nCO
Preparation of ðPd1"m−PBu1t #"P"OPh#2#3ŁBF3\ absorptions around 1969 cm−0
"3c#BF3[ Triphenyl phosphite "0[60 mL\ 5[41 mmol#
[
was added to a red CH1Cl1 "04 mL# solution of "1#BF3
"79 mg\ 9[954 mmol#[ The color of the solution turned
quickly orange^ after 04 min 1:2 of the solvent were
evaporated and Et1O "19 mL# was added\ causing the
precipitation of an orange powder which was _ltered\
RESULTS AND DISCUSSION
The unsaturated triphenylphosphine derivative
washed with Et1O\ and vacuum dried "77 mg\ 79) ðPd1"m−PBut1#"PPh2#2ŁBF3\ "1#BF3 ð3bŁ\ proved to be
yield#[
a
suitable precursor to phosphite substituted
Elem[ Anal[ Calcd for C79H67BF3O01P4Pd1] C\ 46[9\ complexes[ When acetone or methylene chloride solu!

Palladium"I# phosphido!bridged dinuclear derivatives with phosphite ligands
2036
tions of "1#BF3 were reacted at room temperature with the P!nuclei trans and cis to X\ the bridging phos!
an excess of the appropriate phosphite\ the cor! phorus[ Due to the magnetic non!equivalence of the
responding persubstituted derivatives "eq 0# were for! couples AA? and BB?\ the spectrum cannot be inter!
med and isolated as yellow microcrystalline solids in preted with simple _rst order approximations\ and
satisfactory to good yields "56Ð79)#[ The reactions can be quite complex[ In general\ the lines within
were fast and clean when at least a 09!fold excess of the multiplets are no longer directly correlated to the
1
1
1
the alkyl phosphite was employed^ in the case of values of JAX\ JBX and JAB\ but to combinations of
2
2
2
triphenyl phosphite a higher excess of the ligand these coupling constants and of JAA?\ JBB? and JAB?
[
was necessary[ The new complexes analyzed nicely When the di}erences "in Hertz# between the values of
for the composition ðPd1"m−PBut1#"P"OR#2#3ŁBF3\ dA\ dB and dX are much larger than coupling constants
ð"3a#BF3\ RꢁMe^ "3b#BF3\ RꢁEt and "3c#BF3\ values\ as in the case of the phosphine derivatives
RꢁPhŁ and\ as inferred by the analysis of 20P NMR ð3aŁ\ the spectrum is still relatively simple and easily
spectra "see below#\ retain the usual ð3aŁ structure simulated[ The large down_eld shift of dA and dB
exhibited by the analogous phosphine derivatives\ which occurs when phosphites are employed in place
with two palladium centers in a distorted square of the phosphines "around 099 ppm# approaches them
planar geometry sharing a bridging phosphido ligand to dX^ the spin system is better de_ned as AA?BB?C
and the metal!metal bond[
and give rise to an extreme complication of the spec!
**************************
**************************
The 20P"0H# NMR spectrum of "3b#BF3 is shown tra^ none of the nine independent variables of the spin
in Scheme 0\ with the numbering scheme[ system can be easily extracted from the spectrum[
This particular framework of phosphorus atoms Due to this di.culty only some spectral features were
"Pd1P4 planar core with C1v symmetry# constitutes an reproduced in the simulation with a satisfactory
AA?BB?X spin system where A and B are\ respectively\ approximation[ This is particularly true for the low
Fig[ 0[ 20P"0H# NMR spectrum "acetone!d5\ 182 K# of ðPd1"m−PBut1#"P"OEt#2#3ŁBF3 "3b#BF3\ with the numbering scheme[

2037
P[ Leoni et al[
_eld signal due to m!P\ which highly resembles the phosphorus "P1# of a PPh2 molecule"for its high _eld
signal given by the corresponding phosphorus ð3aŁ of position# trans to m!P "for the large JPPꢁ084# and at
ðPd1"m−PBut1#"PR2#3ŁBF3 "RꢁMe\ Et#\ and allows 013[1 "JPPꢁ252\ 26\ 091 Hz# and 002[5 "JPPꢁ252\ 69\
an approximate evaluation of dC\ 1JAC and 1JBC\ respec! 03 Hz#\ respectively assigned to P2 of the phosphite on
tively found at ca 234[4 ppm\ 171 and 35 Hz for the tricoordinated palladium center and to P3 of the
"3a#BF3\ ca 234[5 ppm\ 179 and 49 Hz for "3b#BF3 and phosphite cis to the phosphine molecule[
ca 259 ppm\ 139 and 35 Hz for "3c#BF3[ These values
con_rm the approximately planar disposition of the
Pd1"m!P#P3 core\ with two pseudo!trans and two
pseudo!cis "compared to m!P# phosphite ligands[
0H NMR spectra are easily interpreted and give the
expected integral ratio between the various types of
nuclei[
With lower P"OR#2:"1#BF3 ratios we observed the
formation of mixtures of products arising from the
progressive stepwise substitution of the three tri!
phenylphosphine molecules contained in "1#¦[ The
number of observed intermediates\ of general formula
ðPd1"m−PBut1#"PPh2#"2−n#"P"OPh#2#nŁBF3\ is gen!
erally high\ since di}erent geometrical isomers were
observed for a given value of n[ Therefore very
complex mixtures were formed in most cases but one[
The assignment of the latter two resonances has
In fact\ when "1#BF3 was reacted with a 09!fold excess been made by considering that the coupling to P0
of P"OPh#2 one of these intermediates can be isolated should be minor "69 Hz# when the angle PÐPdÐP0
su.ciently pure and readily identi_ed as approaches 89> "P3#\ and increase "091 Hz# when this
ðPd1"m−PBut1#"PPh2#"P"OPh#2#1ŁBF3\ "4#BF3[ Its angle becomes wider "P2#[ Larger values of JPP were
20P"0H# NMR spectrum is quite simple and shows a observed for phosphite!phosphite or phosphite!phos!
doublet of doublets of doublets "1JPPꢁ084\ 69\ phine couples with respect to the corresponding phos!
091 Hz# at 263[1 ppm for the bridging phosphide "P0#^ phine!phosphine couples of the structurally related
the remaining three P nuclei give resonances at cation "1#¦[ The exceedingly high value of
15[7 ppm "ddd\ JPPꢁ084\ 26\ 03 Hz#\ assigned to the 2JP2P3ꢁ252 Hz is probably due to a nearly linear dis!

Palladium"I# phosphido!bridged dinuclear derivatives with phosphite ligands
2038
position of the "PhO#2PÐPdÐPdÐP"OPh#2 fragment^ 20P"0H# NMR spectra of the solutions show that in
the corresponding constant was found at 024 Hz in both cases the same type of equilibrium given by the
"1#¦ ð3bŁ[
cations "0#¦ and "1#¦ has established\ yielding the CS1
The purity of the samples of "4#BF3 is not high "ca adducts "5a#BF3 and "5b#BF3 "eq 1#[ The spectra of
**************************
**************************
79)# and small amounts of other intermediates were these species are very simple\ as those given by the
observable in the spectrum but not identi_ed due to corresponding phosphine derivatives ð3bŁ\ and consist
severe overlapping of the weak signals[ Well separated of a high _eld triplet and a low _eld doublet coupled
1
signals were observed only in the phosphide region\ by a small JPP"cis#^ these parameters were found at
where two weak ddd appear at 258[7 "1JPPꢁ044\ 41\ 306[5\ 029[0 ppm and 16 Hz for "5a#BF3 and 243[1\
87 Hz# and 244[4 ppm "1JPPꢁ119\ 64\ 50 Hz# sug! 022[4 ppm and 13 Hz for "5b#BF3[
gesting for these derivatives the same type of skeleton
A signi_cant di}erence between the reactions given
by "3a#BF3 and "3b#BF3 concerns the position of the
assigned to "4#¦[
Reactivity of the cations "3a\b#¦[ The availability equilibrium[ In the former case this is shifted toward
of the new complexes allowed us to investigate the the reagents] with also larger amounts of CS1 the
in~uence of the substitution with phosphites on the resonances of the cation "3a#¦ are well visible in the
reactivity of this class of derivatives[ We decided to use spectrum\ although severely broadened by exchange
as tests the reactions with CS1\ isoprene and carbon processes[ On the contrary\ the reaction with "3b#BF3
monoxide\ which had previously been investigated for is shifted toward "5b#BF3 and\ with a 09!fold excess
the corresponding phosphine substituted derivatives of CS1\ the resonances assigned to "3b#¦ have nearly
ð2b\ 3Ð6Ł[
completely disappeared from the spectrum[
Reactions with CS1[ We knew that carbon disul_de
Reactions with isoprene[ Isoprene is another
reacts with the cations "0#¦!"2#¦ yielding the corres! potentially bidentate ligand which was shown to react
ponding adducts "see Scheme 1# ð3bŁ^ these exhibited with the phosphine cations "0#¦− "2#¦ yielding the
an unprecedented coordination mode of the CS1 mol! corresponding isoprene derivatives ðPd1"m−PBut1#
ecule\ with a central planar Pd1P2"CS1# core[ One or "m\h1\h1!isoprene#"PR2#1Ł¦\ as BF3 or tri~ate salts ð4\
two phosphine molecules are displaced from the star! 5Ł[ The cooperation between the two metal centers in
ting complex^ in one case "PMe2# this can behave as a the coordination of the bidentate ligand was demon!
nucleophile toward the metal bonded carbon disul_de strated also in these cases[ The diene molecule\ with
molecule ð7Ł[
the two double bonds in a trans con_guration\ was in
An orange CDCl2 solution of the alkyl phosphite fact shown to simultaneously coordinate to both met!
derivatives "3a#BF3 or "3b#BF3 turns immediately yel! als of the ðPd1"m−PBut1#"PR2#1Ł¦ fragment[ The same
low when reacted with a 09!fold excess of CS1[ The type of reaction is given by the phosphite cations "3a#¦

2049
P[ Leoni et al[
and "3b#¦ "eq[ 2#[ In fact\ after the addition of a 09]0 ligands have been prepared in good yields and purity[
molar excess of isoprene\ a CDCl2 solution of "3a#BF3 At least with the phosphites employed in this work\
"or "3b#BF3# exhibited in the 20P"0H# NMR spectrum electronically unsaturated derivatives bearing only
new resonances assigned to the diene derivatives three phosphite ligands proved to be too unstable to
"6a#BF3 and "6b#BF3\ together with the resonances be isolated or even observed as transient species[ The
of the starting complexes\ considerably broadened[ corresponding derivatives bearing phosphine ligands
Analogously to the reactions with CS1 described were shown to be isolable when the bulkier phosphines
above\ the equilibrium "eq[ 2# is greatly shifted to the ðas in complex "1#BF3Ł are employed\ or when at least
left when the phosphite is P"OMe#2 and to the right one of the phosphines is secondary\ and can saturate
when the phosphite is P"OEt#2[ As shown earlier for the electronic de_ciency of the tricoordinated pal!
the corresponding phosphine complexes\ the spectrum ladium center by donating the electrons of the P!H
of "6a#¦ "or "6b#¦# is due to an ABX spin system\ bond ðas in the phosphine!bridged "0#BF3Ł[ It was
where X is the bridging phosphorus and A and B are instead possible to isolate\ although not pure\ a stable
the similar\ but unequivalent\ phosphite P!nuclei "dA\ derivative with three mixed phosphine!phosphite ter!
dB\ dX and JAX ¼ JBX were respectively found at 023[1\ minal ligands\ complex "4#BF3[ This is probably stable
021[7\ 270[8 ppm and 42 Hz for "6a#BF3 and at 018[1\ due to the presence of a PPh2 molecule\ bulkier than
016[3\ 268[8 ppm and 40 Hz for "6b#BF3#[
P"OPh#2\ which was in fact found to be adjacent to
Reactions with CO Carbon monoxide was bubbled the unsaturated palladium center[
into orange solutions of complexes "3a\b#BF3[ An
The results observed by studying the reactivity of
immediate\ hardly perceptible\ bleaching of the solu! "3a\b#BF3 parallel those reported previously for their
tions\ together with the appearance of weak to phosphine analogues\ in fact both react with CO\ CS1
medium nCO absorptions around 1969 cm−0 in the IR and isoprene equilibrating\ respectively\ with the cor!
spectra\ was observed[ The 20P"0H# NMR spectra of responding derivatives "5Ð7a\b#BF3[
the solutions exhibited broad signals practically in the
As expected\ the reactivity of these systems is highly
same positions of those due to the starting materials[ dependent upon the dimensions of the ligands\ since
These results can be explained by the substitution of equilibria involving the trimethyl phosphite derivative
a
phosphite ligand by
a CO molecule\ giving "3a#BF3\ compared to those involving the triethyl
ðPd1"m−PBut1#"CO#"P"OR#2#2ŁBF3 ð"7a#BF3\ RꢁMe^ phosphite analogue "3b#BF3\ are much more shifted
"7b#BF3\ RꢁEtŁ\ as shown in eq[ 3[
towards the reactants[ Since solution NMR spectra
**************************
**************************
Equilibrium 3 should be far shifted to the left since showed that the reactivity of the phosphite complexes
the NMR resonances are not signi_cantly shifted with towards CO\ CS1 and isoprene does not di}er sig!
respect to those of "3a\b#BF3^ their severe broadening ni_cantly from that of the phosphine derivatives we
is assignable either to the rate of the direct and forward did not proceed further in the isolation of the products
reactions of eq[ 3 or to exchange equilibria between of these reactions[
coordinated and released P"OR#2 molecules[ An equi!
librium analogous to that shown in eq[ 3 was observed
when studying the reaction of the trimethylphosphine
Acknowled`ements*Financial support from the {Ministero
della Ricerca Scienti_ca e Tecnologica| "MURST# and the
derivative "2a#BF3 with carbon monoxide\ yielding
ðPd1"m−PBut1#"CO#"PMe2#2ŁBF3\ this equilibrium is
completely shifted to the right under 0 Atm of CO\
but is easily reverted by reducing PCO ð4Ł[
Consiglio Nazionale delle Ricerche "CNR\ Rome# is grate!
fully acknowledged[
REFERENCES
CONCLUSIONS
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Can[ J[ Chem[\ 0870\ 48\ 0077[ "c# Arif\ A[ M[\
The new complexes "3aÐc#BF3\ with a central
Pd1"m−PBut1# core binding four terminal phosphite

Palladium"I# phosphido!bridged dinuclear derivatives with phosphite ligands
2040
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