339
N[ Thirupathi et al[ : Polyhedron 07 "0888# 326Ð331
dinuclear complex B[ Thus\ the conformation of the P2N2
ring changes from chair "in L0# or twist "in L4# ð3Ł to a
sofa in 0 and A as a result of complexation[ The extent
of deviation from an ideal sofa conformation is higher
for molecules 0 and 1 of 0 which is\ however\ less than
that observed in the mononuclear complex A[ Signi_cant
variations in PÐN distances are not observed^ the average
2[0[ Synthesis of ðMo"CO#3"EtNP"OC5H3Br!3##2Ł 0
A solution of the l2!cyclotriphosphazane\ L0 "9[199 g\
9[160 mmol# and ðMo"CO#3"NBD#Ł ð7Ł "9[970 g\
9[160 mmol# in petrol "b[p[ 59!79>C\ 14 cm2# was heated
under re~ux for 3!4 h and cooled to 14>C[ Solvent was
removed under reduced pressure and the resulting oil was
dissolved in CH1Cl1!petrol "0]0# mixture and the solution
passed through a short silica gel column to remove any
decomposed material[ Removal of the solvent from the
eluent gave a colourless oily residue which was redis!
solved in 4 cm2 petrol[ Cooling the solution at 9>C for
13 h gave colourless transparent crystals of 0[ Yield]
9[032 g\ 44)[ M[p[ 019!014>C[ Analysis Calcd[ for
C17H16N2O6P2MoBr2] C\ 24[43^ H\ 1[76^ N\ 3[33[ Found]
C\ 24[31^ H\ 1[61^ N\ 3[51[ IR "nCO#] 1919 "s#\ 0822 "s# and
Ä
PÐN distance\ 0[58 A is comparable to that observed for
L0\ A and B[ The geometry of the nitrogen atoms deviate
from planarity and the extent of deviation is slightly
larger at N"0# than at N"1# or N"2#[ The average PÐO
distance involving phosphorus coordinated to the metal\
"Pc!O# is shorter than that involving uncoordinated phos!
phorus atom\ "Pu!O# as observed in the mononuclear
complex A[ These observations can be explained on the
basis of {{negative hyperconjugative|| interaction involv!
ing a nitrogen lone pair and a PÐO or PÐN sꢀ orbital[ As
noted earlier ð3Ł\ a X!N!P!Y "XꢁC or P^ YꢁO or N#
torsion angle of 89> would result in maximum {{negative
hyperconjugation|| while any departure from this value
would reduce this interaction[ Careful examination of C
"or P#ÐNÐPÐO torsion angles indicate that the PÐO bonds
involving coordinated phosphorus\ "Pc!O# are no longer
periplanar to the lone pair of electrons on N"0# as a result
of chelation[ Hence\ the nitrogen atom\ N"0# undergoes
pyramidalisation as observed in the mononuclear com!
plex A and ðMo"CO#3""EtN#4P3"O#n"OPh#1#Ł "nꢁ0 or 1#
ð1\4Ł[ The nitrogen atoms N"1# and N"2# also deviate
slightly from planarity unlike the mononuclear complex
A wherein these nitrogen atoms exhibit planar geometry[
This is due to the deviation of C"or P#!N!P!N torsion
angles from 89> in order to adopt an ideal sofa con!
formation "compare DCs values in Table 1#[ However\
the P2N2 ring in A undergoes distortion "DCs 7[9# in order
to maximise {{negative hyperconjugation||[ This di}er!
ence presumably arises due the bulkiness of the aryloxy
substituents in A[ It appears that the conformations of
the P!N ring are dictated by both {{negative hyp!
erconjugation|| as well as steric bulk of the substituents
on the phosphorus atoms[
0
0897 "br# cm−0[ H NMR] d 0[29 "t\ 2JHHꢁ6[09 Hz\ 5 H\
2
CH2#\ 0[39 "t\ JHHꢁ6[2 Hz\ 2 H\ CH2#\ 2[42 "br\ 5 H\
NCH1#\ 6[93!6[43 "m\ aromatic protons#[
2[1[ Synthesis of ðMo"CO#3"EtNP"OC5H3Br!1##2Ł 1
The reaction of l2!cyclotriphosphazane\ L1 with
ðMo"CO#3"NBD#Ł was carried out as described above to
give 1[ Recrystallisation of the reaction mixture from
CH1Cl1 gave 1 in near quantitative yield[ M[p[ 059!051>C[
FAB mass spectrum "87Mo\ 68Br#] m:z 834 "M¦#\ 806
"M¦! CO#\ 722 "M¦! 3 CO# with the expected mol!
ybdenum and bromine isotopic pattern[ IR "nCO#] 1916
"s#\ 0836 "s#\ 0892 "br# cm!0[ 0H NMR] d 0[31 "t\
2JHHꢁ5[8 Hz\ 5 H\ CH2#\ 0[34 "t\ 2JHHꢁ6[3 Hz\ 2 H\ CH2#\
2[68 "br m\ 3 H\ NCH1#\ 3[92 "br m\ 1 H\ NCH1#\ 6[99!
6[57 "m\ aromatic protons#[
2[2[ Other attempted reactions of l2!cyclotriphosphazanes
with `roup 5 metal tetracarbonyl precursors
A solution of the l2!cyclotriphosphazane\ L3 "9[199 g\
9[160 mmol# and ðMo"CO#3"NBD#Ł "9[970 g\ 9[160 mmol#
in petrol "14 cm2# was heated under re~ux as described
above for the synthesis of 0[ Solvent was removed under
reduced pressure and the resulting pasty mass was washed
with cold petrol "4 cm2# to remove any unreacted starting
materials[ The 20P NMR spectrum of the product showed
a doublet at 043[1 and 015[7 ppm "Jppꢁ13 Hz# and a
singlet at 011[7 ppm apart from the signals corresponding
to unreacted L3 and traces of other unidenti_ed species[
Several attempts to remove the unreacted L3 from the
reaction mixture were unsuccessful[ Hence\ the mixture
was used as such for further characterisation[ IR "nCO#]
0781 "s#\ 0809 "s#\ 0825 "s# and 1912 "s# cm!0[ FAB mass
spectrum "87Mo\ 68Br#] Molecular ion peak not observed[
m:z 806 ðMo"CO#2"EtNP"OC5H3Br##2Ł¦\ 750 ðMo
2[ Experimental
All reactions were carried out under an atmosphere of
dry nitrogen by using standard Schlenk!line techniques
ð5Ł[ Solvents were puri_ed by standard procedures and
freshly distilled prior to use ð6Ł[ The cyclotriphosphazanes
L0\ L1\ L3 and L4 were synthesised as reported previously
ð3Ł[ The IR spectra were recorded in nujol mull using
0
a Bio!Rad FTIR spectrometer[ The H "SiMe3!internal
standard# and 20P "74) H2PO3!external standard# NMR
spectra were recorded in CDCl2 employing a Bruker
AMX 399 or ACF!199 spectrometer[ Chemical shifts
down_eld from the standard were assigned positive
values[ The FAB mass spectrum was recorded with a
Finnigan MAT 7129 spectrometer[
"CO#"EtNP"OC5H3Br##2Ł¦\
722
ðMo"EtNP"OC5
H3Br##2Ł¦\ 707 ðMo"EtN#1"NCH1#P2"OC5H3Br#2Ł¦\ 663
ðMo"CO#3"EtN#2P2!"OC5H3Br#1Ł¦ and 624 "EtNP"O!
Thirupathi, Natesan
