Amidinato- and triazenido-bridged binuclear complexes of palladium and platinum

Article abstract of DOI:10.1016/S0277-5387(98)00142-9

The reaction of [M₂Cl₂(μ-Cl)₂(PR₃)₂] (M=Pd or Pt; PR₃=PEt₃, PBu₃, PMe₂Ph, PMePh₂) with lithium amidinate or sodium triazenide gave binuclear comp

Full text of DOI:10.1016/S0277-5387(98)00142-9

Polyhedron Vol[ 06\ No[ 19\ pp[ 2420Ð2439\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166!4276"87#99031!8
Amidinato! and triazenido!bridged binuclear
complexes of palladium and platinum
Anshu Singhala\ Vimal K[ Jainaꢀ\ Munirathinam Nethajib\ Ashoka G[
Samuelsonb\ D[ Jayaprakashb and Ray J[ Butcherc
aChemistry Division\ Bhabha Atomic Research Centre\ Mumbai\ 399 974\ India
bDepartment of Inorganic and Physical Chemistry Indian Institute of Science\ Bangalore\ 459901\ India
cDepartment of Chemistry\ Howard University\ Washington\ DC 19948\ U[S[A
"Received 1 December 0886^ accepted 5 April 0887#
Abstract*The reaction of ðM1Cl1"m!Cl#1"PR2#1Ł "MꢁPd or Pt^ PR2ꢁPEt2\ PBu2\ PMe1Ph\ PMePh1# with
lithium amidinate or sodium triazenide gave binuclear complexes containing amidinato! or triazenido!bridges\
ðM1Cl1"m!ArNENAr#1"PR2#1Ł "EꢁCH\ CMe or N#[ These complexes were characterized by elemental analysis
and NMR "0H\ 20P or 084Pt# data[ The structures of two complexes\ ðPd1Cl1"m!PhNC"Me#NPh#1"PMe1Ph#1Ł
"09# and ðPt1Cl1"m!PhNNNPh#1"PEt2#1Ł "00# were established by single crystal X!ray structural analyses[ The
084Pt NMR data show coupling between two metal centers in the cis triazenido!bridged complex[ The corres!
ponding amidinate bridged complex does not show coupling[ The role of the bridging ligand in mediating
interaction between the metal centers is probed through Extended Huckel Theory "EHT# calculations[ It is
suggested that MÐM interactions are primarily a}ected by the bridging ligands[ Þ 0887 Elsevier Science Ltd[
All rights reserved[
Keywords] palladium^ platinum^ amidine^ triazene^ X!ray structure^ Extended Huckel Theory
———————————————————————————————————————————————
INTRODUCTION
the amidinate ion ð6\ 7Ł[ Electronic and steric proper!
ties of an amidine ligand can be modi_ed by varying
the organic substituents on the nitrogen atoms and
the central carbon atom[ For example\ formamidinate
ligands are known to favour unusual structural fea!
tures in metal complexes ð8\ 09Ł[
Recently we have synthesised and characterised a
series of binuclear palladium and platinum complexes
ð0Ð4Ł of the type ðM1X1"m!Y#1L1#Ł "I and II#[ In particu!
lar\ molecules with anionic bidentate three!atom
bridging ligands showed unusual properties[ For
example\ complexes containing bridging carboxylate
ð1Ł and triazenido ð2Ł groups exhibited unusually
strong MÐM interactions with a formal bond order of
zero\ whereas such interactions were vanishingly small
for the corresponding acetamidinato ð3Ł! and 1! hyd!
roxypyridinato ð4Ł!bridged complexes[ This has
motivated us to initiate a systematic study on pal!
ladium and platinum complexes with anionic three!
atom ligands[ Amidines are one of the members of "where MꢁPd or Pt^ Xꢁhalide\ alkyl or aryl groups\
this class of ligands[ They are known to stabilize Yꢁanionic one!atom bridging ligand such as halide\
metal!metal bonds ð5Ł[ Amidines coordinate either in SR etc[\ two!atom bridging ligand such as pyrazolate
the neutral form "via amine!N or imine!N atom# or as ion or three!atom bridging ligands such as AcO\
RNNNR!\ RNCR?NR−\ etc[#
Herein we report\ as part of our ongoing inves!
tigation\ synthesis and characterisation of palladium
ꢀ Author to whom correspondence should be addressed[
Fax] 80!911!445!9649^ Tel] 80!911!440!0465[
2420

2421
A[ Singha et all
and platinum complexes with amidinate ligands[ For ðPt1Cl1"m!tolNCHNtol#1"PMe1Ph#1Ł is comparable to
comparison\ X!ray structure and 084Pt NMR data for the corresponding acetamidinato! and triazenido!
a triazenido!bridged platinum complex\ ðPt1Cl1"m! bridged ð2\ 3Ł platinum complexes[ The 0H NMR spec!
PhNNNPh#1"PEt2#1Ł "00# are also included[
tra of these complexes showed two singlets of equal
integration each for methyl and methoxy protons of
aryl groups attached to the nitrogen atoms[ One can
be assigned to the NAr group trans to the phosphine
and other trans to the terminal chloride[ The sym trans
con_guration is further substantiated by the presence
of one NCHN resonance for the formamidinate
group\ however in the platinum complex two closely
spaced singlets were observed[ The complexes con!
taining PMe1Ph ligands displayed two doublets due
to J"20PÐ0H# couplings for methyl protons indicating
non!equivalence of the methyl groups[ The 084Pt NMR
spectrum of ðPt1Cl1"m!tolNC"H#Ntol##1"PMe1Ph#1#Ł
RESULTS AND DISCUSSION
Amidinato!bridged binuclear palladium and plati!
num complexes\ ðM1Cl1"m!ArN1CHÐNAr#1 "PR2#1Ł
"MꢁPd or Pt^ Arꢁtol\ MeOC5H3# can readily be
obtained by the reaction of ðM1Cl1"m!Cl#1"PR2#1Ł
"MꢁPd or Pt^ PR2ꢁPEt2\ PBu2\ PMe1Ph or PMePh1#
with the lithium salt of formamidine in 0]1 molar
ratio[ The treatment of ðM1Cl1"m!Cl#1"PR2#1Ł with
formamidines a}ords mononuclear complexes con!
taining neutral formamidine[ These complexes are
yellow to orange coloured crystalline solids\ soluble
in common organic solvents[
0
exhibited a doublet at d!2134 ppm with J"084PtÐ20P#
2444 Hz[ The 084Pt NMR spectrum of ðPt1Cl1"m!
PhNNNPh#1"PEt2#1Ł "00# showed a doublet at d!
The 20P"0H# NMR spectra "Table 0# of these com!
plexes exhibited a single resonance for tertiary phos!
0
2083 ppm with J"084PtÐ20P# 2431 Hz "Fig[ 0#[ Unlike
phines indicating the formation of only one isomeric the amidinato bridged complex 09\ the spectrum of 00
form exclusively[ The magnitude of J"PtÐP# for the also showed nJ"PtÐPt# coupling of 0424 Hz in the 084Pt
0
Table 0[ 0H and 20P"0H# NMR data for the palladium and platinum complexes with amidimes
Complex
d20P
0H NMR data
ðPtCl1"dtfH#"PBu2#Ł "0#
−6[9a
9[85"t\ 6[1 Hz\ PCCCMe#^ 0[35Ð0[54 "m\ PCH1CH1−#^0[76 "m\ PCH1#^ 1[21 "s\
tol!Me\ 5 H#^ 5[84"d\ 7[3 Hz\ 1 H#^ 6[03"d\ 6[5 Hz\ 3 H#^ 6[31"d\ 7[2 Hz\ 1 H#
ðC5H3Ł^7[07"d\d\ 09[6 Hz\ NCHN#^ 7[86 "d\ 01 Hz\ NH!#
ðPt1Cl1"m!dtf#1"PMe1Ph#1Ł "1#
ðPd1Cl1"m!dtf#1"PEt2#1Ł "2#
−15[1b 0[62\ 0[84 "each d\ 00[5 Hz\ PMe1#^ 1[02 "s#\ 1[15 "s# "each 5 H\ tol!Me#^ 5[59"d#
5[63 "d#\ 5[86 "d#\ 6[04 "d# "each 5[1 Hz\ C5H3#^ 6[20!6[30 "m#\ 6[69!6[65 "m#
ðPhŁ^ 6[46\ 6[50 "each s\ NCHN#
10[7
11[9
04[6
04[7
0[9
0[92 "d\t\ 6[6 Hz "t#\ 05 Hz"d#\ PCH1Me#^ 0[51 "m#\ 0[75"m# "PCH1−#^ 1[07"s#\
1[23"s# "tol!Me#^ 5[60 "s#ꢀ^ 6[96 "d#\ 6[26 "d# "each 7[1 Hz\ C5H3#^ 6[23 "s\
NCHN#
0[95 "d\t\ 6[6 Hz"t#\ 05 Hz"d#\ PCH1Me#^ 0[45Ð0[50 "m#\ 0[79Ð0[78 "m#
"PCH1−#^ 2[58"s#^ 2[79"s# "OMe#^ 5[37"d#\ 5[62"d#\ 5[72"d#\ 6[30 "d# "each
7[7 Hz\ C5H3#^ 6[17 "s#\ 6[23 "s# "NCHN#
9[89 "t\ 6[1 Hz\ PCCCMe#^ 0[21 "m\ PCCH1CH1#^ 0[35Ð0[75 "m\ PCH1−#^ 1[07
"s#\ 1[23 "s# "tol!Me#^ 5[57 "d\#ꢀꢀ^ 6[95"d#\ 6[39 "d# "each 7[1 Hz\ C5H3#^ 6[24"s\
NCHN#
9[80"t\ 6[1 Hz\ PCCCMe#^ 0[13Ð0[35 "m\ PCCH1CH1−#^ 0[76 "m\ PCH1−#^
2[57"s#\ 2[70 "s# "OMe#^ 5[36 "d#\ 5[58 "d#\ 5[72"d#\ 6[33 "d# "each 7[7 Hz\ C5H3#^
6[18 "s#\ 6[22 "s#^ 6[24 "s# "NCHN#
ðPd1Cl1"m!bpmpf#1"PEt2#1Ł "3#
ðPd1Cl1"m!dtf#1"PBu2#1Ł "4#
ðPd1Cl1"m!bpmpf#1"PBu2#1Ł "5#
ðPd1Cl1"m!dtf#1"PMe1Ph#1Ł "6#
0[61 "d#\ 0[84 "d# "each 01[1 Hz\ PMe1#^ 1[00 "s#\ 1[15 "s# "tol!Me#^ 5[40 "d#\
5[59"d#\ 5[87 "d# "each 7[1 Hz\ C5H3\ 5 H#^ 6[10!6[39 "m#\ 6[59!6[54 "m\
Ph¦C5H3 "1 H#¦NCHN#
ðPd1Cl1"m!bpmpf#1"PMe1Ph#1Ł "7# 0[0
0[61 "d#\ 0[81 "d# "each 01[1 Hz\ PMe1#^ 2[51 "s#\ 2[64 "s# "OMe#^ 5[13 "d# 5[47
"d#\ 5[63 "d# "each 7[7 Hz\ C5H3\ 5 H#^ 6[13!6[47 "m\ Ph¦C5H3 "1 H#¦NCHN#
1[14 "d\ 01[9 Hz\ PMe#^ 1[94 "s#\ 1[22 "s# "tol!Me#^ 5[24 "d#\ 5[31 "d# "C5H3\ 3 H#^
6[94 "m#\ 6[33 "m#\ 7[92 "m# "Ph¦C5H3¦NCHN#
0[67 "s\ CMe#^ 0[73 "d# 1[97 "d# "each 01[3 Hz PMe1#^ 5[06Ð6[07 "m#\ 7[95 "m#
ðPhŁ
ðPd1Cl1"m!dtf#1"PMePh1#1Ł "8#
ðPd1Cl1"m!dpa#1"PMe1Ph#1Ł "09#
ðPt1Cl1"m!dpt#1"PEt2#1Ł "00#
02[7
1[8
−01[1c 0[95 "m\ 07 H\ PCMe#^ 0[58 "m\ 5 H#\ 0[80"m\ 5 H# "PCH1−#^ 5[88 "m# 6[59 "t\
6[2 Hz#\ 6[21 "t\ 6[7 Hz# 6[59 "d\ 6[8 Hz# ð19 H\ PhŁ
dtfHꢁtolN1C"H#NHtol^ dtfꢁðtolNC"H#NtolŁ−^ bpmpfꢁðMeOC5H3NC"H#NC5H3OMeŁ− dpaꢁðPhNC"Me#NPhŁ−
dptꢁðPhNNNPhŁ− "a#0J"PtÐP#ꢁ2240 Hz "b#0J"PtÐP#ꢁ2469 Hz "c#0J"PtÐP#ꢁ2385 Hz ꢀ integrated to 3 H protons
ꢀꢀAB quartet\ integrated to 3 H protons[

Amidinato! and triazenido!bridged binuclear complexes of palladium and platinum
2422
Fig[ 0[ 084Pt"0H#NMR spectrum of ðPt1Cl1"m!PhNNNPh#1"PEt2#1Ł in CDC02[
NMR spectrum indicating signi_cant platinum dinato!bridged complexes ð00Ð02Ł[ There are distinctly
platinum interaction as reported earlier by us ð2Ł[
two types of PdÐN distances "Table 1#[ One with chlor!
A few reactions of formamidinato!bridged pal! ide trans to nitrogen is shorter than the other one
ladium complexes were also investigated[ The complex
ðPd1Cl1"m!tolNCHNtol#1"PBu2#1Ł on treatment with
an ethereal solution of HCl a}orded a mononuclear
complex\ ðPdCl1"tolN1CHÐNHtol#"PBu2#Ł "d 20P
15[0 ppm# formed by protonation of the bridging
ligand eq[ "0#[ A similar species "d 20P 15[0 ppm# was
formed when ðPd1Cl1"m!Cl#1"PBu2#1Ł was treated with
di!p!tolylformamidine[ It is interesting to note that
the triazenido!bridged complexes react reversibly with
HCl ð2Ł[ Addition of triphenylphosphine to a CDCl2
solution of ðPd1Cl1"m!tolNCHNtol#1"PBu2#1Ł has no
e}ect on its 20P NMR spectra indicating non!lability
of the formamidinato!bridges with neutral donor
ligands[
where phosphine is trans to nitrogen\ owing to the
stronger trans in~uence of the phosphine[ The two PdÐ
N distances lie in the range 0[75 and 1[04 A reported in
several palladium complexes ð5\ 00\ 03Ð05Ł[ The two
PdÐP and PdÐCl distances are essentially identical and
compare well with the reported values ð06\ 07Ł[ The
Ä
Ä
PdÐPd separation ð1[803"1# AŁ is shorter than the
2
Ä
ðPd1"m!NHCPhNH#1"h !C2H4#1Ł ð2[107"0# AŁ\ however
it is comparable to ðPt1"m!PhNCHNPh#1"h1!PhN!
Ä
CHNPh#1Ł"1[807"8# A# ð02Ł[ The two palladium atoms
lie within the distances reported for binuclear com!
plexes containing anionic three!atom bridging ligands
"Table 2# ð08Ð14Ł[
The complex 00 has two platinum atoms at a sep!
Ä
aration of 1[8291"7# A "Table 3#[ This distance is com!
ðPd1Cl1"m−tolNC"H#Ntol#1"PBu2#1Ł¦1HCl
:1ðPdCl1"tolNHC"H#Ntol#"PBu2#Ł[[[[ "0#
parable with other binuclear complexes containing
anionic three atom bridging ligands "Table 2#[ The
two NÐN bonds are nearly equivalent and the NÐNÐ
N angle is 005[5"5#> indicating pronounced p!electron
deloclization ð19Ł[ The PtÐN bond distance trans to
the phosphine ligand is longer than the PtÐN bond
trans to the chloride[ The bridging PhNNNPh ligands
are cis with respect to each other[ Unlike complex
09\ complex 00 has a crystallographically imposed C1
symmetry[
The face to face juxtaposition of two square planar
d7 metal centres is expected to result in antibonding
interactions between the metal centres on the basis
of qualitative molecular orbital theory[ However\ the
frequent occurrence of short contacts in such units
has caused much debate ð15Ł regarding the possible
ways by which these metalÐmetal interactions could
become favorable[ Recent work in this area has sug!
gested several factors which make the metalÐmetal
interaction in these systems less antibonding ð16Ł[ In
the present work\ it was possible to observe PtÐPt
coupling in the 084Pt NMR spectra of the triazenido!
bridged complexes\ whereas in the corresponding ace!
tamidinato!bridged platinum derivatives no coupling
between the metal centres could be observed[ The
metalÐmetal distance in the complex 09 should be
The molecular structures of acetamidinato! and tri!
azenido!bridged complexes\ ðPd1Cl1"m!PhNC"Me#N!
Ph#1"PMe1Ph#1Ł
"09#
and
ðPt1Cl1"m!
PhNNNPh#1"PEt2#1Ł "00# were established by X!ray
di}raction[ The structures of 09 and 00 comprise of
four molecules per unit cell separated by normal van
der Waals distances[ Molecular structures together
with the crystallographic numbering scheme are
shown in ORTEP drawings "Figs 1 and 2#[ Each
molecule consists of two distorted square planar metal
"Pd or Pt# atoms bridged together by ðPhNC"Me#N!
PhŁ! or ðPhNNNPhŁ− groups[ The bridging ligands in
both molecules are cis with respect to each other\
whereas the ancillary ligands Cl and PR2 are trans
related[
In 09 the CÐN bond distances ðN"0A#ÐC"00A#\
N"0B#ÐC"00A#\ N"0C#ÐC"00B#\ N"0D#ÐC"00B# ðav[
Ä
0[215 AŁ are intermediate between the typical CÐN
Ä
Ä
"0[37 A# and C1N "0[13 A# covalent bond distances\
indicating p!electron delocalozation in the NCN skel!
eton[ This is further substantiated by the sum of inter
bond angles around carbon "248[8># and nitrogen "av[
248[6"4#># atoms of the NCN skeleton[ The NCN bite
angles ð010[6"5#\ 011[5"5#>Ł and bite distances ð"N"0A#Ð
Ä
Ä
N"0B# 1[210 A and N"0C#ÐN"0D# 1[213 AŁ are of the comparable to that of complex 00 since MÐM dis!
same magnitude as reported for other bridging ami! tances are primarily controlled by the ligand ð17Ł[ It is

2423
A[ Singha et all
Fig[ 1[ Molecular structure with crystallographic numbering scheme for ðPd1Cl1"m!PhNC"Me#NPh#1"PMe1Ph#1Ł "09# "phenyl
groups are omitted for clarity#[
Fig[ 2[ ORTEP view with crystallographic numbering scheme for ðPt1Cl1"m!PhNNNPh#1"PEt2#1Ł "00# "phenyl groups are
omitted for clarity#[

Amidinato! and triazenido!bridged binuclear complexes of palladium and platinum
2424
Ä
Table 1[Selected bond lengths "A# and angles "># for ðPd1Cl1"m!PhNC"Me#NPh#1"PMe1Ph#1Ł
"09#
Pd"0#ÐN"0A#
Pd"0#ÐN"0D#
Pd"0#ÐP"0#
Pd"0#ÐCl"0#
P"0#ÐC"00#
P"0#ÐC"01#
P"0#ÐC"000#
N"0A#ÐC"0A#
1[986"4#
1[948"4#
1[151"1#
1[200"1#
0[706"6#
0[688"6#
0[720"7#
0[339"7#
0[210"7#
0[327"7#
0[221"7#
1[803"1#
77[4"1#
065[4"1#
80[0"1#
82[1"1#
064[1"1#
75[81"7#
013[9"4#
013[6"4#
010[6"5#
007[7"5#
008[3"5#
Pd"1#ÐN"0C#
Pd"1#ÐN"0B#
Pd"1#ÐP"1#
Pd"1#ÐCl"1#
P"1#ÐC"10#
1[001"4#
1[951"4#
1[151"1#
1[203"1#
0[709"6#
0[795"6#
0[798"7#
0[320"8#
0[186"8#
0[311"7#
0[243"7#
P"1#ÐC"11#
P"1#ÐC"100#
N"0C#ÐC"0C#
N"0C#ÐC"00B#
N"0D#ÐC"0D#
N"0D#ÐC"00B#
N"0A#ÐC"00A#
N"0B#ÐC"0B#
N"0B#ÐC"00A#
Pd"0#ÐPd"1#
N"0D#ÐPd"0#ÐN"0A#
N"0A#ÐPd"0#ÐP"0#
N"0A#ÐPd"0#ÐCl"0#
N"0D#ÐPd"0#ÐP"0#
N"0D#ÐPd"0#ÐCl"0#
P"0#ÐPd"0#ÐCl"0#
C"00A#ÐN"0A#ÐPd"0#
C"00B#ÐN"0D#ÐPd"0#
N"0A#ÐC"00A#ÐN"0B#
N"0A#ÐC"00A#ÐC"01A#
N"0B#ÐC"00A#ÐC"01A#
N"0B#ÐPd"1#ÐNÐ"0C#
N"0C#ÐPd"1#ÐP"1#
N"0C#ÐPd"1#ÐCl"1#
N"0B#ÐPd"1#ÐP"1#
N"0B#ÐPd"1#ÐCl"1#
P"1#ÐPd"1#ÐCl"1#
C"00A#ÐN"0B#ÐPd"1#
C"00B#ÐN"0C#ÐPd"1#
N"0C#ÐC"00B#ÐN"0D#
N"0C#ÐC"00B#ÐC"01B#
N"0D#ÐC"00B#ÐC"01B#
78[9"1#
065[1"1#
89[3"1#
82[9"1#
063[4"1#
76[20"7#
015[5"4#
013[4"4#
011[5"5#
007[6"6#
007[5"5#
Table 2[ PdÐPd distance in some binuclear palladium complexes
Complex
PdÐPd distance
"A#
Reference
Ä
ðPd1"m!MeNNNMe#1"h2!C3H6#1Ł
ðPd1"m!tolNNNtol#1"h2!C3H6#1Ł
ðPd1"m!OAc#1"h2!C2H4#1Ł
1[86
1[75
1[83
2[017"0#
2[359
1[835"1#
1[831"1#
1[810"1#
1[871"2#
08
19
10
00
11
12
13
14
14
ðPd1"m!NHCPhNH#1"h2!C2H4#1Ł
ðPd1"m!Cl#1"h2!C2H4#1Ł
ðPd1Cl1"m!OAc#1"PMe1Ph#1Ł
ðPd1Cl1"m!Spy#1"PMe2#1Ł
ðPd1Cl1"m!Spy#1"PMe1Ph#1Ł
ðPd1Cl1"m!Spy#1"PMePh1#1Ł
SpyꢁSC4H3N "1!mercaptopyridinate ion#[
possible that the ligand controls\ not only the distance structed based on observed metal!ligand geometries of
but the interaction between the two metal centres in a related d7 complexes[ The reduced overlap population
signi_cant fashion[ In order to probe the role of the "ROP# computed by EHT\ gives a measure of the
ligand in mediating metalÐmetal interactions\ we have relative interaction between the metal centres in vari!
carried out Extended Huckel Theory "EHT# cal! ous complexes studied[ Being fully aware of the limi!
culations on model systems[ Our results suggest that tations of EHT to reliably quantify interaction
in addition to the factors identi_ed earlier\ the nature energies\ we merely interpret trends in the computed
of bridging ligands and their relative disposition "Sch! ROP as done by Aullon and Alvarez ð29Ł[ The com!
eme 0# in the metal complex could play a signi_cant puted ROPs along with the MÐM distances and the
role in determining the metalÐmetal interactions[
nature of the bridge are given in Table 4 together with
Calculations were carried out using the program the ROP computed in the absence of the bridging
CACAO ð18Ł\ on model complexes constructed using ligand[ In general the bridging ligand has greater
the crystallographic coordinates for the heavy atoms in~uence on metalÐmetal interactions in these systems
wherever available[ In other cases\ models were con! compared to the ancillary ligands Cl and PH2[ While

2425
A[ Singha et all
Ä
Table 3[ Selected bond lengths "A# and angles "># for ðPt1CI1"m!PhNNNPh#1 "PEt2#1Ł "00#
Pt"0A#ÐPt"0#
Pt"0#ÐCI"0#
Pt"0#ÐP"0#
Pt"0#ÐN"0A#
Pt"0A#ÐN"0C#
P"0#ÐC"0#
P"0#ÐPt"0#ÐN"0A#
C0"0#ÐPt"0#ÐP"0#
C0"0#ÐPt"0#ÐN"0A#
Pt"0#ÐN"0A#ÐN"0B#
Pt"0A#ÐN"0CA#ÐN"0B#
Pt"0A#ÐN"0CA#ÐC"0BA#
1[8291"7#
1[212"1#
1[146"1#
1[903"5#
1[009"5#
0[68"1#
P"0#ÐC"2#
P"0#ÐC"4#
N"0A#ÐN"0B#
N"0B#ÐN"0C#
N"0C#ÐC"0B#
N"0A#ÐC"0A#
Pt"0#ÐN"0A#ÐC"0A#
N"0A#ÐN"0B#ÐN"0CA#
N"0BA#ÐN"0C#ÐC"0B#
N"0B#ÐN"0A#ÐC"0A#
Pt"0#ÐP"0#ÐC"0#
Pt"0#ÐP"0#ÐC"2#
Pt"0#ÐP"0#ÐC"4#
0[62"1#
0[798"8#
0[208"8#
0[185"7#
0[359"8#
0[342"7#
011[4"4#
005[5"5#
098[5"5#
098[3"5#
013[0"5#
002[6"6#
002[5"2#
82[8"1#
78[01"6#
064[3"1#
016[5"3#
004[7"3#
023[3"4#
Scheme 0[ X!Y!XꢁO1C"Me#ÐO or HN1NÐNH or HN1C"H#ÐNH
Table 4[ Reduced Overlap Populations computed by EHT
Geometry
PtÐPt
ROP "×092#
With bridge Without bridge Ref[
Distance
"Aý#
Coupling
constant "Hz#
Complex
Bridge Cl and PH2
ðPt1"NNN#1Cl1"PH2#1Ł
cis
trans
cis
trans
cis
trans
cis
trans
cis
trans
trans
cis
1[829
1[832
1[801
0476
0037
48
49
48
35
31
15
30
15
25
14
23
14
43
42
41
49
45
46
2
cis
ðPt1"OAc#1Cl1"PH2#1Ł
ðPt1"NCN#1C01"PH2#1Ł
trans
trans
cis
1
cis
trans
trans
cis
02
3
trans
cis
trans
Not observed
cis
Bridging ligands] NNN1HNNNH^ OAcꢁOC"CH2#O^ NCN1HNC"H#NH[

Amidinato! and triazenido!bridged binuclear complexes of palladium and platinum
2426
the s donor and p− acceptor capabilities of the not been addressed\ the e}ect of p acidic ligands in
ligand\ PH2 "with no d orbitals on the P# would be modulating the ROP of the interacting metal centres
di}erent from that of PPh2\ we expect the trends would has been studied[ They have noted an increase in the
be similar even if PPh2 were to be used in the calcu! ROP with increase in the number of p acid!ligands
lations[ The bridging ligand reduces the observed surrounding the metal atom[ Where structures are
ROP except in the case of triazenide ligand where the available\ the corresponding MÐM distances observed
ROP is increased marginally[ It is also important to in such complexes are also smaller[ The X!ray crystallo!
note that the relative orientation of the supporting graphic database analysis done by them demonstrates
ligands Cl and PH2\ do not change the ROP to a the generality of the phenomenon[ Similarly\ p donor
signi_cant degree[ However\ the cis or trans nature of ligands were shown to increase the antibonding e}ect
the bridging ligand changes the ROP between the between the metal atoms[
metal centres by approximately 9[90 units which is
On the basis of the results obtained above\ it is clear
19) of the computed ROP[ This suggests that the how the nature and relative disposition of the bridge
metalÐmetal interaction is signi_cantly a}ected by the determines whether one observes PtÐPt coupling in
nature and relative orientation of the bridging ligand[ the 084Pt NMR[ There are two three!atom bridged
The ROP in these three cases are not very di}erent[ complexes for which PtÐPt coupling have been
However\ it is important to note the relative changes observed and one\ the amidinato!bridged complex
the ligands bring about in the computed ROP[ For where there is no PtÐPt coupling[ In the case of the
the amidinato complex and the acetato complex\ the amidinato complex some of us had studied earlier ð3Ł\
ROP is decreased by 25) and 08) respectively on the geometry of the bridging ligands are trans and no
adding the bridging ligands[ In the case of amidinato PtÐPt coupling was observed[ This is readily explained
complex\ the reduction in the ROP is even greater by the large reduction in ROP "44)# with amidinato
"44)# when the bridging ligands are trans[ A sig! ligands in the trans geometry[ In cases where the bridg!
ni_cant change is observed in the case of the triazenido ing ligands are cis to each other\ the reduction in ROP
complex where a small increase "0)# in the computed is less\ especially in the case of triazenido! and acetato!
ROP is observed[ To understand how the amidinato bridged complexes[ Hence it is possible to observe the
complex enhances the antibonding interaction PtÐPt coupling in the 084Pt NMR spectra of the latter
between the metal centres\ and the triazenido ligand systems[
decreases the antibonding interaction\ a fragment
molecular orbital analysis was carried out[ The results
of this analysis suggest that the bridging ligand pri!
EXPERIMENTAL
marily interacts through its non bonding s donor
orbitals and the empty pꢀ orbitals[ Apart from
donation of electrons to the empty metal orbitals\ the
s orbitals interact with the metalÐmetal s "cis or trans
geometry# and p "trans geometry only# orbitals[ The
empty pꢀ orbitals on the other hand have the appro!
priate symmetry to interact with the metalÐmetal d
type orbitals[ The former interaction results in the
interaction of the _lled shells and reduces the ROP
and the latter is responsible for a marginal increase in
ROP[ In the trans geometry\ there is a greater
reduction in the MÐM ROP due to destabilisation of
the p type MÐM bonding orbitals[ The metalÐmetal
interaction is signi_cantly decreased on adding the
amidinato bridging ligands\ because of the larger over!
lap of the the nonbonding electrons in the ligand with
the _lled metalÐmetal s orbital[ In addition\ the ami!
dinato ligand is a poor p acceptor because the pꢀ levels
lie much higher in energy and have smaller con!
Formamidines "ArN1CHÐNHAr#^ Arꢁ3!MeC5H3
"tol#\ 3!MeOC5H3# ð20Ł and ðM1Cl1"m!Cl#1"PR2#1Ł
"MꢁPd or Pt# ð21Ł and ðPt1Cl1"m!PhNNNPh#1"PEt2#1Ł2
were prepared according to the literature methods[
All the reactions were carried out in dried and distilled
analytical grade solvents under a nitrogen atmosphere[
0
The H\ 20P"0H# and 084Pt "0H# NMR spectra were
recorded on a Bruker DPX!299 spectrometer in freshly
prepared CDCl2 solutions[ Chemical shifts are
referred to internal chloroform peak "d CHCl2
0
6[15 ppm# for H\ external 74) H2PO3 for 20P and
external Na1PtCl5 solution in D1O for 084Pt[ Elemental
analyses were carried out by the Analytical Chemistry
Division of this research centre[
tributions on the interacting atoms compared to the Preparation of ðPtCl1"tolNCH!NHtol#"PBu2#Ł
p acceptor orbitals of the triazenido ligand[ On the
other hand the triazenido ligand has suitable pꢀ
To a
dichloromethane "09 cm2# solution of
orbitals of low energy which stabilize the MÐM d ðPt1Cl1"m!Cl#1"PBu2#1Ł "008 mg\ 9[016 mmol# was
bond[ As a result the triazenido ligand increases the added a dichloromethane "4 cm2# solution of N\N? !
MÐM ROP\ albeit\ to a small extent[
di!p!tolylformamidine "53 mg\ 9[173 mmol# and the
Our results are in complete agreement with a recent reaction mixture was stirred for 0 h at room tempera!
study carried out on the interaction between d7 metal ture[ The solvent was stripped o} in vacuo and the
centres stacked in a face to face fashion by Aullon and residue was recrystallised from hexane as a pale yellow
Alvarez ð17Ł[ While the nature of bridging ligands has colored solid "69 mg\ 39) yield#[

2427
A[ Singha et all
Table 5[Physical and analytical data for palladium and platinum complexes with amidine ligands
Recry[solvent
") yield#
melting point
">C#
) analyses found "calcd[#
Complex
C
H
N
ðPtCl1"dtfH#"PBu2#Ł "0#
hexane "39#
013Ð015
149Ð144 "d#
084Ð088 "d#
083Ð088 "d#
069Ð061
36[1 "35[7#
36[1 "35[6#
38[5 "41[1#
37[9 "37[8#
44[5 "46[0#
42[4 "43[0#
43[5 "43[8#
40[6"40[5#
47[6 "48[4#
42[2 "43[9#
28[6 "28[4#
5[1 "5[2# 2[8 "3[9#
3[0 "3[3# 3[6 "3[6#
5[3 "5[2# 4[5 "4[7#
4[2 "4[7# 4[2 "4[3#
6[0 "6[4# 3[5 "3[8#
5[6 "6[9# 3[7 "3[6#
4[5 "4[1# 4[4 "4[5#
3[9 "3[8# 4[4 "4[1#
3[8 "4[9# 3[8 "3[8#
4[0 "3[8# 4[7 "4[6#
3[4 "3[5# 6[4 "6[6#
ðPt1Cl1"m!dtf#1"PMe1Ph#1Ł "1#
ðPd1Cl1"m!dtf#1"PEt2#1Ł "2#
ðPd1Cl1"m!bpmpf#1#"PEt2#1Ł "3#
ðPd1Cl1"m!dtf#1"PBu2#1Ł "4#
ðPd1Cl1"m!bpmpf#1"PBu2#1Ł "5#
ðPd1Cl1"m!dtf#1"PMe1Ph#1Ł "6#
benzene!hexane "59#
benzene!hexane "37#
benzene!hexane "51#
hexane "51#
benzene!hexane "51#
benzene!hexane "47#
079Ð071
087Ð192 "d#
081Ð085 "d#
195Ð109 "d#
075Ð089 "d#
063Ð067 "d#
ðPd1Cl1"m!bpmpf#1"PMe1Ph#1Ł "7# benzene!hexane "48#
ðPd1Cl1"m!dtf#1"PMePh#1#1Ł "8#
ðPd1Cl1"m!dpa#1"PMe1Ph#1Ł "09#
ðPt1Cl1"m!dpt#1"PEt2#1Ł "00#
benzene!hexane "48#
benzene!hexane "48#
CH1C01!benzene!
hexane "54#
dtfHꢁtolNꢁCHÐNHtol^ dtfꢁðtolNC"H#NtolŁ−^ bpmpfꢁ ðMeOC5H3NC"H#NC5H3OMeŁ− dpaꢁðPhNC"Me#NPhŁ−^
dptꢁðPhNNNPhŁ−[
Preparation of ðPd1Cl1"m!tolNC"H#Ntol#1"PMe1Ph#1#Ł Crystallo`raphy
To a lithioformamidinate suspension\ prepared by
All measurements for ðPd1Cl1"m!PhNC"Me#N!
neutralizing a THF solution of N\N?!di!p!tolyl! Ph#1"PMe1Ph#1Ł "09# were made at 1921>C on a
formamidine "87 mg\ 9[325 mmol# with a hexane solu! Rigaku AFC 5S di}ractometer using graphite mono!
tion of n!butyllithium "9[34 N\ 0 cm2\ 9[34 mmol#\ chromated MoÐKa radiation "l ꢁ9[60962 A#[ The
Ä
solid ðPd1Cl1"m!Cl#1"PMe1Ph#1#Ł "017 mg\ 9[192 mmol# crystallographic data together with data collection
was added[ The resulting solution was stirred for two and structure re_nement details are given in Table 6[
days at room temperature under a nitrogen atmo! The numbering scheme employed is shown in Fig[ 1
sphere[ The solvents were removed in vacuo and the drawn with the ORTEP program ð22Ł[ All the data
residue was extracted with benzene "2×2 cm2# and were corrected for Lorentz and polarization e}ects[
_ltered[ The _lterate was concentrated in vacuo and The structure was solved by a combination of the
the residue was recrystallised from benzene!hexane Patterson method and direct methods ð23Ł and re_ned
mixture in 47) "008 mg# yield as an orange crystalline by full!matrix least!squares on F1[ Neutral atom scat!
solid[ Similarly all other complexes were prepared[ tering factors were taken from Cromer and Waber
Pertinent data are given in Table 5[
ð24Ł[ Anamolous dispersion e}ects were included in
Fcalc ð25Ł[ The values of Df? and Dfý were those of
Cromer ð26Ł[ All calculations were performed using
the TEXSAN ð27Ł crystallographic software package
of the Molecular Structure Corporation[
Reaction between ðPd1Cl1"m!tolNC"H#Ntol#1"PBu2#1Ł
and PPh2
The crystal data for the complex ðPt1Cl1"m!
PhNNNPh#1"PEt2#1Ł "00# were collected on an Enraf
Nonius CAD!3 with monochromated MoKa[ Three
check re~ections were measured for every 099 re~ec!
tions^ these showed no decay in intensity during the
period of data collection[ The structure was solved by
Patterson and full matrix least squares re_nement on
Fo using SHELX −65 ð28Ł[ The re_nement was car!
ried out _rst with isotropic thermal parameters and
subsequently with anisotropic thermal parameters for
all non!hydrogen atoms[ The scattering factors for
Pt were taken from International tables for X!ray
crystallography ð24Ł and the absorption corrections
were made using Psi data ð39Ł[
To a CDCl2 solution of ðPd1Cl1"m!tolNC"H#Ntol#1
"PBu2#1Ł "13[4 mg\ 9[911 mmol# in a 4 mm NMR tube
was added solid triphenylphosphine "00[4 mg\
9[933 mmol#[ The resulting solution was studied by
20P NMR spectroscopy[
Reaction between ðPd1Cl1"m!tolNC"H#Ntol#1"PBu2#1Ł
and HCl
To a dichloromethane "4 cm2# solution of ðPd1Cl1"m!
tolNC"H#Ntol#1"PBu2#1Ł "15[6 mg\ 9[913 mmol# was
added an ethereal solution of HCl "9[91 cm2\ 1[33 N\
9[937 mmol#[ After stirring for 29 min\ the solvent was
stripped o} and the residue was dissolved in CDCl2[
The resulting solution was studied by 20P NMR spec!
troscopy[
Acknowled`ements*We thank Drs[ J[P[ Mittal and C[ Gop!
inathan for encouragement of this work[ We are grateful to

Amidinato! and triazenido!bridged binuclear complexes of palladium and platinum
2428
Table 6[ Crystal data and structure re_nement details for ðPd1Cl1"m!PhNC"Me#NPh#1
"PMe1Ph#1Ł "09# and ðPt1Cl1"m!PhNNNPh#1"PEt2#1Ł "00#
09
00
Empirical Formula
Formula Weight
Temperature
C33H37Cl1N3P1Pd1
867[49
C25H49Cl1N5P1Pt1
0978[76
182"1# K
182 K
Ä
Ä
Wavelength
9[60962 A
9[6096 A
Crystal System
Space group
Unit cell dimensions
Monoclinic
P10:c
a ꢁ01[047"5# A
bꢁ08[389"6# A
c ꢁ08[189"7# A
Monoclinic
C1:c
Ä
Ä
Ä
Ä
a ꢁ12[917"0# A
Ä
bꢁ8[723"2# A
c ꢁ08[955"0# A
Ä
b ꢁ89[38"1#>
3460"2# A
b ꢁ098[21"2#>
3963"0# A
2
2
Ä
Ä
Volume
Z
3
3
Density
Absorption coe.cient
F"999#
0[311 Mg:m2
0[996 mm−0
0873
0[6656 g:cm2
60[62 cm−0
1001
Crystal Size
u range for data collection
Index ranges
9[36×9[21×9[06 mm
1[98 to 16[499
9¾h¾04\
9¾k¾14\−14¾l¾14
09801
9[3×9[2×9[14 mm
1¾1u¾49>
9¾h¾13\ 9¾k¾09\
−19¾0¾19
3014
Re~ections collected
Independent re~ections
09316
2471 "Rintꢁ9[931#
"Rintꢁ9[9226#
SHELXA
9[816 and 9[272
Full!matrix least!squares on
F1
Absorption correction
Max[ and min[ transmission
Re_nement method
Empirical
0[166 and 9[788
Full!matrix least squa!
res on=F9=
Data:restraints:parameters
Goodness!of!_t on F1
09308:9:383
0[907
1888:9:052
0[1091
Final R indices ðI ×1s"I#Ł
R0ꢁ9[9541\ wR1ꢁ9[9645
R0ꢁ9[9235\
wR1ꢁ9[9288
*
R indices "all data#
R0ꢁ9[0533\ wR1ꢁ9[1885
Extinction coe.cient
Largest di}[ peak and hole
9[99908"4#
9[553 and −9[545 eA
*
−2
−2
Ä
Ä
0[1 and −0[0 eA
the Head of the Analytical Chemistry Division BARC\ for
providing microanalyses for the complexes[
2[ Singhal\ A[ and Jain\ V[ K[\ Polyhedron\ 0884\ 03\
174[
3[ Singhal\ A[ and Jain\ V[ K[\ Can[ J[ Chem[\ 0885\
63\ 1907[
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