K[ Maitra\ J[H[ Nelson : Polyhedron 07 "0888# 192Ð109
194
The infrared\ 0H and 20P"0H# NMR spectral data for
the two "dppe#M"CO#3 complexes are in accord with
those reported previously ð8Ł[ The X!ray crystal structures
also agree with those reported previously0[ The 02C"0H#
NMR spectra are second order ð01Ł and the values of 1J
"PP# "Cr\ 00[2 Hz^ Mo\ 2[6 Hz# are lower than might be
expected ð02Ł "15Ð67 Hz for Cr and 01Ð44 Hz for Mo#[
This is because the two coupling pathways for PÐP coup!
ling\ through the metal "1J# and via the ligand backbone
"2J# often have similar magnitudes and opposite signs
ð03Ł[
"DPVP#M"CO#4³cis!"DPVP#1M"CO#3³trans!"DPVP#1
M"CO#3 for the same reason[ The MoÐP bond lengths
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for "dppe#Mo"CO#3 "1[4919"00# A# lie between the values
for cis! and trans!"DPVP#1Mo"CO#3 but the 20P chemical
shifts for "dppe#M"CO#3 are considerably down_eld of
those for cis!"DPVP#1M"CO#3\ as a result of a large down!
_eld contribution to the chemical shift on forming a _ve!
membered chelate ring ð14Ł[
2[ Experimental section
The infrared spectrum of fac!"dppe#"DPVP#Mo"CO#2
shows two CO vibrations ð04\05Ł and the 20P"0H# NMR
2[0[ Reagents and physical measurements
spectrum
contains
a
doublet
and
triplet
"1J"PP#ꢀ13[9 Hz# in a 1]0 integrated intensity ratio con!
Commercially available\ reagent grade chemicals were
used as received[ Tetrahydrofuran was distilled under
nitrogen from sodium benzophenone ketyl[ Silica gel for
column chromatography "grade 01\ 17Ð199 mesh# was
obtained from Aldrich[ Melting points were determined
on a Mel!Temp apparatus and are uncorrected[ Elemen!
tal analyses were performed by Galbraith Laboratories\
Knoxville\ TN[ Solution infrared spectra were obtained
on a PerkinÐElmer Paragon 0999 PC FT spectrometer in
sealed CaF1 cells[ 20P"0H#\ 02C"0H# and 0H NMR spec!
tra were recorded at 010[55 "191[24#\ 64[9 "014[69# and
299[05 "388[75# MHz\ respectively\ on either a General
Electric GN!299 or Varian Unity Plus!499 spectrometer[
Proton and carbon chemical shifts are relative to internal
Me3Si[ Phosphorus chemical shifts are relative to external
PPh2 "d 20Pꢀ−5[9 ppm#^ all shifts to low _eld "high
frequency# are positive[
0
sistent with the proposed facial geometry[ The H and
02C"0H# NMR spectra are also consistent with the pro!
posed structure[ In particular two CO resonances are
observed in the latter with PÐC coupling constants in the
range expected for CO|s cis to phosphorus ð06\07Ł[
The 0H and 02C"0H# NMR spectra of the cis! and
trans!"DPVP#1M"CO#3 complexes are very similar to
those of cis! and trans!"DPVP#1PdCl1 and assignments
were made in the same manner as for these compounds
ð08Ł[ The 02C chemical shifts of the carbonyl carbons
trans to DPVP are always down_eld of those cis to DPVP\
re~ecting greater metal COp!back!bonding for the trans
CO|s[ The magnitudes of 1J"PMC# to the trans CO|s are
always larger than those to the cis CO|s\ except for
"DPVP#Cr"CO#4[ This seemingly anomalous behavior
has been observed for several other "R2P#Cr"CO#4 com!
plexes ð07\19Ð11Ł[ The larger magnitude of the trans coup!
ling has been attributed ð11Ł to the larger mutual
polarizability when a phosphine is trans to CO[ The signs
of 1J"PWC# in tungsten carbonyl complexes of phos!
phines are positive for trans couplings and negative for
cis couplings ð12Ł\ and such is probably the case for cis!
"DPVP#1M"CO#3 and "dppe#M"CO#3 as well[
2[1[ Reaction of DPVP with Mo"CO#5
A solution containing 1[49 g "8[36 mmol# of Mo"CO#5
and 3[91 g "07[83 mmol# of diphenylvinylphosphine in
499 ml of dry tetrahydrofuran was placed in a quartz
vessel\ purged with dry nitrogen and photolyzed for 03 h
"Hg lamps\ 124 nm# at about 9 to 2>C in a Rayonet
photochemical reactor[ The solvent was removed on a
rotary evaporator and the yellowÐgreen oily residue was
chromatographed on silica gel using 09) benzene in
hexanes as eluant[ Several fractions of 049Ð064 ml each
were collected and monitored by 20P"0H# NMR spec!
troscopy[ The _rst few fractions contained
"DPVP#Mo"CO#4 and diphenylvinylphosphine oxide[
These fractions were combined\ the solvent was removed
on a rotary evaporator and the colorless oily residue was
crystallized from hot hexane to yield 9[94 g "0[1)# of
"DPVP#Mo"CO#4[ The intermediate fractions\ which
contained a mixture of cis! and trans!"DPVP#1Mo"CO#3\
were combined\ reduced in volume to about 49 ml and
placed in a freezer at −19>C for 01 h[ The pale yellow
crystals that formed were isolated by _ltration and dried
under vacuum to yield 3[9 g "55[7)# of a mixture of cis!
and trans!"DPVP#1Mo"CO#3[ Repeated fractional crys!
The structures of the cis! and trans!"DPVP#1Mo"CO#3
complexes were con_rmed by X!ray crystallography and
are shown in Figs 0 and 1\ respectively[ Selected bond
distances and angles are given in Table 1[ Both complexes
exist as discrete molecules with no abnormal inter!
molecular contacts[ The cis!isomer has no symmetry
while the trans!isomer has Ci symmetry[ The MoÐP bond
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lengths for the cis!isomer "1[4498"09# A\ ave[# are longer
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than those for the trans!isomer "1[3602"6# A# due to the
greater trans!in~uence of CO than R2P ð13Ł[ The relative
20P chemical shifts for the complexes follow the order
0
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MꢀCr] Bennett et al[ ð09Ł report] aꢀ05[62"5# A\ bꢀ03[45"3# A\
Ä
cꢀ11[21"5# A\ Pbca\ Zꢀ7\ Rꢀ9[955[ We _nd] aꢀ05[577"2# A\
bꢀ03[458"0# A\ cꢀ11[240"1# A\ Pbca\ Zꢀ7\ Rꢀ9[9451[ MꢀMo]
Bernal et al[ ð00Ł report] aꢀ11[599"7# A\ bꢀ05[688"3# A\
cꢀ03[476"3# A\ Pbca\ Zꢀ7\ Rꢀ9[933[ We _nd] aꢀ05[721"1# A\
Ä
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bꢀ03[529"2# A\ cꢀ11[574"2# A\ Pbca\ Zꢀ7\ Rꢀ9[9283[
Maitra, Kalyani
