Electron density manipulation in rhodium(I) phosphine complexes: Structure of acetylacetonatocarbonylferrocenyl- diphenylphosphinerhodium(I)

Article abstract of DOI:10.1016/S0277-5387(98)00049-7

The title complex [Rh(acac)(CO)(PPh₂Fc)] (acac = acetylacetonato, PPh₂Fc = ferrocenyldiphenylphosphine), was obtained in acetone by reaction of the tertiary phosphine with [Rh(acac)(CO)₂] and was characterised by IR spectroscopy, ¹H and ³¹P NMR and single crystal X-ray crystallography. This is a rare example illustrating the incorporation of the ferrocenyl moiety in a monodentate tertiary phosphine complex of rhodium(I). It crystallises in the triclinic space group P1 with two independent molecules in the asymmetric unit and refined to R=2.40% from 5215 reflections. The independent molecules, showing the usual square planar geometry, differ mainly in the rotation mode of the asymmetric phosphine around the Rh-P bond and a slight deviation in the Rh-CO bond from linearity, which was correlated with IR data.

Full text of DOI:10.1016/S0277-5387(98)00049-7

Polyhedron Vol[ 06\ No[ 04\ pp[ 1336Ð1342\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166Ð4276"87#99938Ð6
Electron density manipulation in rhodium"I#
phosphine complexes] structure of
acetylacetonatocarbonylferrocenyl!
diphenylphosphinerhodium"I#
Stefanus Otto\ Andreas Roodt\ꢀ Johannes J[ C[ Erasmus and Jannie C[ Swarts
Department of Chemistry\ University of the Free State\ Bloemfontein\ 8299 South Africa
"Received 08 November 0886^ accepted 16 January 0887#
Abstract*The title complex ðRh"acac#"CO#"PPh1Fc#Ł "acac
ꢁ acetylacetonato\ PPh1Fc ꢁ fer!
rocenyldiphenylphosphine#\ was obtained in acetone by reaction of the tertiary phosphine with ðRh"acac#"CO#1Ł
and was characterised by IR spectroscopy\ 0H and 20P NMR and single crystal X!ray crystallography[ This is
a rare example illustrating the incorporation of the ferrocenyl moiety in a monodentate tertiary phosphine
complex of rhodium"I#[ It crystallises in the triclinic space group P with two independent molecules in the
¹
0
asymmetric unit and re_ned to Rꢁ1[39) from 4104 re~ections[ The independent molecules\ showing the
usual square planar geometry\ di}er mainly in the rotation mode of the asymmetric phosphine around the Rh!
P bond and a slight deviation in the Rh!CO bond from linearity\ which was correlated with IR data[ Þ 0887
Elsevier Science Ltd[ All rights reserved
Keywords] structure^ characterisation^ rhodium^ ferrocene^ phosphine
———————————————————————————————————————————————
The structure of the title compound was determined methods\ the electronic characteristics of Rh"I# or
in the wider context of research done by our group on Rh"III# compounds[ Current research has revealed a
ðRh"b!dik#"CO#"PR2#Ł complexes ð0Ł "b!dikꢁb!dike! direct correlation between the Lewis basicity of the
tone^ PR2ꢁtertiary phosphine ligands#[ These com! central rhodium atom and the oxidation potential of
plexes are especially well known for the oxidative the ferrocenyl unit attached to the b!diketone in com!
addition studies performed on them ð1Ł[ Investigations plexes of the type ðRh"b!dik#"P"OPh#2#1Ł and ðRh"b!
on symmetrical and unsymmetrical bidentate ligands\
the e}ect of di}erent bidentate ligand donor atoms
bonded to the metal centre as well as di}erent phos!
phine and phosphite ligands and solvent e}ects were
some of the studies performed by our group[ Fur!
thermore it was shown that Rh!P coupling constants
obtained from 20P NMR studies can give some more
valuable information about the character of the Rh!
P bond and correlations between bond lengths\ bite
angle of the bidentate ligand and reactivity were made
ð2Ł[
dik#"COD#Ł where b!dik ꢁ ferrocenylacetonato\ ferro!
cenyltri~uoroacetonato and diferrocenylacetonato
and COD ꢁ cis!0\4!cyclooctadiene ð3Ł[
In this paper we report the crystal and molecular
structure of acetylacetonatocarbonylferrocenyl!
diphenylphosphinerhodium"I#\ which has been deter!
mined to gain additional information on the bonding
mode and steric demand of this very crystalline
unsymmetrical phosphine ligand\ PPh1Fc[ This forms
part of a programme to investigate the e}ect thereof
on selected aspects of organometallic platinum group
metal complexes[ A common platinum"II# compound
containing this phosphine ligand\ trans!dichloro!
bis"ferrocenyldiphenylphosphine#platinum"II#\ was
also prepared as part of this platinum group metal
project and the structure was already published ð4Ł[
For the tuning of the reactivity of organometallic com!
plexes a thorough understanding of the characteristics
The ferrocenyl group is a convenient moiety to
introduce as part of the ligand system "very good s!
donor# of these Rh"I# complexes since it provides a
convenient tool to study\ especially by electrochemical
ꢀAuthor to whom correspondence should be addressed[
1336

1337
S[ Otto et al[
of the di}erent ligands employed in the system is of at a temperature of 182"1# K[ The unit cell was deter!
crucial importance[ The structural information mined and re_ned from 14 re~ections in the u range
obtained from this study is compared with that of 2[13Ð12[76>[ Crystal data for ðRh"acac#"CO#
related complexes and correlated with its NMR and "PPh1Fc#Ł] C45H41O5P1Fe1Rh1\ triclinic\ space group
Ä
IR parameters[
P \ aꢁ01[359"1#\ bꢁ03[941"2#\ cꢁ05[214"2# A\ aꢁ
¹
0
094[85"2#\ bꢁ009[41"2#\ gꢁ84[04"2#>\ Vꢁ1407[1"7#
A\ Zꢁ1\ Dcꢁ0[472 g cm−2\ Dmꢁ0[436 g cm−2 "aque!
Ä
EXPERIMENTAL
ous NaI#\ m"Mo!Ka#ꢁ0[212 mm−0\ F"999#ꢁ0105\ hkl
ranges −02²h²03\ −04²k²05\ −07²l²9[ The
4113 independent re~ections collected of 4307 mea!
sured re~ections were corrected for Lorentz and polar!
isation e}ects and empirical absorption corrections
were done on the faced crystal[ A correction was also
applied for decay "9[2)# which was determined by
monitoring of three standards every 099 re~ections[
Data reduction was done by Pro_t ð6Ł[ The structure
was solved by the heavy atom method and re_ned by
full!matrix least!squares calculations respectively using
the SHELXS75 and SHELXL82 series of programmes
ð7Ł[ Re_nement converged to a _nal Rꢁ9[9139 "for
4104 with Fo×3s"Fo#\ wR1ꢁ5[19\ for all unique 4112
data\ 0 suppressed\ 515 parameters#\ with allowance
for thermal anisotropy for all non!hydrogen atoms[
The positions of the methine protons were determined
from a di}erence Fourier map and re_ned isotropically[
Other hydrogen atoms were calculated in the idealised
positions riding on the adjacent carbon atom and
re_ned with an overall isotropic thermal parameter[
Physical measurements
IR spectra were recorded on a Hitachi 169Ð49 spec!
trometer in KBr pellets in the region 3999Ð149 cm−0
or as a 9[9941 M solution in CHCl2 in the region 1199Ð
0549 cm−0
[
NMR ð0H "299 MHz#\ 20P"0H#
"010[386 MHz#\ 14>CŁ spectra were recorded on a
Bruker 299 MHz spectrometer in CDCl2 and chemical
shifts are reported relative to the residual CHCl2 peak
0
"6[13 ppm# for the H spectra and relative to 74)
H2PO3 "9 ppm# for the 20P spectra "positive shifts
down_eld#[
Preparation
PPh1Fc[ Prepared according to literature pro!
cedures ð5Ł and puri_ed by column chromatography
0
"Hexane]Benzene\ 8]0#[ NMR\ d "ppm#] H] 3[95 "s\
4H#^ 3[98 "q\ 1H#^ 3[25 "t\ 1H#^ 6[2Ð6[3 "m\ 09H#^ 20P]
−05[07 "s#[
A
weighting scheme wꢁ0:ðs1"Fo1#¦"9[9183ꢀP#1
¦2[28ꢀPŁ\ where Pꢁ"F1o¦1ꢀFc1#:2\ was used in the
latter stages of the re_nement[ The maximum and mini!
mum peaks on the _nal di}erence Fourier map\ and
ðRh"acac#"CO#1Ł[ To a stirred solution of ðRh"m!
Cl#"CO#1Ł1 "40 mg^ 9[020 mmol# in freshly distilled
DMF "1 ml# was added acetylacetone "17 mg^
9[164 mmol# and stirring was continued for a further
1 min before the reaction mixture was quenched with
ca 79 ml of distilled water[ The strawberry red pre!
cipitate obtained was isolated by centrifugation and
recrystallised from hot acetone as _ne dark green
needles "37 mg^ yield ꢁ 79)#[ NMR\ d "ppm#] 0H]
1[98 "s\ 5H#^ 4[52 "s\ 0H#[
goodness!of!_t
Ä
corresponded
to
9[305
and
−9[283 eA−2\ and 0[955 respectively[ The graphics
were done with ORTEP II ð8Ł[ A summary of selected
bond lengths\ angles and torsion angles for molecules
0 and 1 is given in Table 0[
ðRh"acac#"CO#"PPh1Fc#Ł[ Prepared by the slow
treatment of a stirred acetone solution "3 ml# of the
freshly prepared ðRh"acac#"CO#1Ł "37 mg^ 9[08 mmol#
with solid PPh1Fc "66 mg^ 9[197 mmol# resulting in
the product as a _ne orange precipitate in reasonable
yields "ca 69)#[ Bright orange medium quality crys!
tals\ suitable for X!ray analysis\ were obtained by the
slow evaporation of a concentrated acetone solution[
NMR \ d "ppm#] 0H] 0[56 "s\ 2H#^ 1[03 "s\ 2H#^ 3[15 "s\
4H#^ 3[32 "m\ 1H#^ 3[36 "m\ 1H#^ 4[35 "s\ 0H#^ 6[2Ð6[6
"m\ 09H#^ 20P] 31[2 "d#\ 0JRh!Pꢁ066[2 Hz[
RESULTS AND DISCUSSION
Description of the structure of ðRh"acac#"CO#"PPh1Fc#Ł
Both molecules crystallise with slightly distorted
square planar geometry around the central Rh atoms\
see Fig[ 0[ The closest contact between di}erent Rh
Ä
centres of the two Rh entities is 5[6 A\ suggesting no
signi_cant intermolecular Rh!Rh interactions[ The
di}erence in the trans in~uence of the phosphine and
carbonyl groups is obvious from the di}erence in the
Ä
Ä
Rh!O bond distances of 9[934 A and 9[929 A for mol!
ecules 0 and 1 respectively\ the longer bond cor!
responding to the one trans to the PPh1Fc ligand[
The phosphorus atoms are tetrahedrally surrounded
Crystal structure
An orange cube of the title compound with dimen!
sions of 9[19×9[14×9[14 mm was mounted on an by the two phenyl rings\ the ferrocenyl ligand and the
Enraf Nonius CAD 3 four circle di}ractometer[ Rh atom with the C!P!Rh bonds all larger than the
Graphite
monochromated
Mo!Ka
radiation ideal 098[4>\ ca 009Ð006>\ while all C!P!C angles are
Ä
"lꢁ9[60962 A# and a u!1u scan type were used to smaller than average\ at ca 091Ð095>[ The deviation
measure the intensity data in the range 0[60²u²14[94 from normal tetrahedral angles towards smaller values

Electron density manipulation in rhodium"I# phosphine complexes
1338
Ä
Table 0[ Bond lengths "A#\ angles "># and tortion angles "># for molecule 0 and 1 with e[s[d[|s
in parentheses
Molecule 0
0[688"3#
Molecule 1
Rh"0#!C"05#
Rh"0#!O"00#
Rh"0#!O"01#
Rh"0#!P"0#
Rh"1#!C"15#
Rh"1#!O"10#
Rh"1#!O"11#
Rh"1#!P"1#
0[799"3#
1[927"2#
1[957"2#
1[1264"02#
0[713"3#
0[717"3#
0[794"3#
0[154"4#
0[150"4#
0[035"4#
0[493"5#
0[267"6#
0[279"6#
0[409"6#
1[916"2#
1[961"2#
1[1220"00#
0[729"3#
0[713"3#
0[797"3#
0[169"4#
0[168"4#
0[033"4#
0[384"5#
0[272"6#
0[272"6#
0[386"5#
P"0#!C"000#
P"0#!C"010#
P"0#!C"020#
O"00#!C"01#
O"01#!C"03#
O"02#!C"05#
C"00#!C"01#
C"01#!C"02#
C"02#!C"03#
C"03#!C"04#
P"1#!C"100#
P"1#!C"110#
P"1#!C"120#
O"10#!C"11#
O"11#!C"13#
O"12#!C"15#
C"10#!C"11#
C"11#!C"12#
C"12#!C"13#
C"13#!C"14#
O"00#!Rh"0#!O"01#
O"00#!Rh"0#!P"0#
O"01#!Rh"0#!P"0#
C"05#!Rh"0#!O"00#
C"05#!Rh"0#!O"01#
C"05#!Rh"0#!P"0#
O"02#!C"05#!Rh
C"1+3#!O"0+1#!Rh"0#avg
"C!P!Rh#avg
"C!P!C#avg
O"00#!C"01#!C"02#
O"00#!C"01#!C"00#
O"01#!C"03#!C"02#
O"01#!C"03#!C"04#
C"01#!C"02#!C"03#
C"02#!C"01#!C"00#
C"02#!C"03#!C"04#
77[98"01#
77[62"8#
063[46"8#
065[9"1#
82[5"1#
78[75"02#
066[2"3#
016[2"2#
003[21"02#
093[0"1#
014[2"3#
003[4"3#
014[7"3#
003[8"3#
015[1"3#
019[0"3#
008[2"3#
O"10#!Rh"1#!O"11#
O"10#!Rh"1#!P"1#
O"11#!Rh"1#!P"1#
C"15#!Rh"1#!O"10#
C"15#!Rh"1#!O"11#
C"15#!Rh"1#!P"1#
O"12#!C"15#!Rh"1#
C"1+3#!O"0+1#!Rh"1#avg
"C!P!Rh#avg
77[93"01#
89[47"8#
067[43"8#
065[2"1#
80[6"1#
78[57"03#
064[1"3#
016[1"2#
003[4"1#
092[8"1#
013[7"3#
004[9"3#
014[1"4#
004[0"3#
016[2"4#
019[1"3#
008[5"4#
"C!P!C#avg
O"10#!C"11#!C"12#
O"10#!C"11#!C"10#
O"11#!C"13#!C"12#
O"11#!C"13#!C"14#
C"11#!C"12#!C"13#
C"12#!C"11#!C"10#
C"12#!C"13#!C"14#
C021!C020!C030!C031
C022!C021!C031!C032
C023!C022!C032!C033
C024!C023!C033!C034
C020!C024!C034!C030
O00!Rh0!P0!C000
O00!Rh0!P0!C010
O00!Rh0!P0!C020
C021!C020!P0!Rh0
C030!C020!P0!C000
!3[5"3#
!4[1"3#
!3[3"3#
!4[8"4#
!6[0"3#
!097[4"1#
09[6"1#
015[1"1#
0[1"3#
C121!C120!C130!C131
C122!C121!C131!C132
C123!C122!C132!C133
C124!C123!C133!C134
C120!C124!C134!C130
O10!Rh1!P1!C100
O10!Rh1!P1!C110
O10!Rh1!P1!C120
C121!C120!P1!Rh1
C130!C120!P1!C100
!4[2"3#
!4[9"4#
!4[8"3#
!4[8"4#
!5[1"3#
!000[1"1#
6[4"1#
012[2"1#
!09[8"3#
!35[4"1#
!26[2"1#
for the C!P!C angles in phosphine ligands can be explai!
The P!C bond distances to the phenyl rings are
ned on the basis of the valence!shell electron!pair repul! within normal limits for this type of bond\ while the P!
sion theory where the phosphorous lone pair will repel C bond for the ferrocenyl moiety is appreciably shorter
Ä
the bonding pair electrons to a greater extent than they by 9[921"7# A[ The same tendency was also previously
will repel each other[ Greater deviation from normal observed in structural studies containing the PPh1Fc
tetrahedral angles towards smaller values are then nor! ligand ð4Ł[ This observation can be attributed to the
mally an indication of more lone pair character on the better electron donating capability of the ferrocenyl
phosphorous atom[ Upon coordination the lone pair moiety compared to phenyl\ giving rise to a shorter P!
becomes a bonding pair\ resulting in weakened repul! C bond[
sion and the angles become closer to the expected value[
The Fe!C bond lengths are all within normal ranges
Ä
This observation also holds true in the current study for ferrocene compounds\ averaging 1[926"4# A for
where coordination gives rise to an average increase of both the substituted and unsubstituted rings in
2[9"1#> in the C!P!C angles compared with those in the molecules 0 and 1[ Selected torsion angles are given
uncoordinated phosphine ð09Ł[
in Table 1 and show the cyclopentadienyl rings for

1349
S[ Otto et al[
Fig[ 0[ An ORTEP II drawing of molecule 0 of the coordination compound showing the numbering scheme[ The _rst digit
refers to molecule 0 or 1 and the second to the number of the atom in the molecule[ Displacement ellipsoids correspond to
29) probability level[ Hydrogen atoms are omitted for clarity[
Table 1[ Comparisons of Rh"b!Dik#"CO#"PR2# complexes with e[s[d[|s in parentheses
Rh"acac#"CO#"PPh1Fc#a
Rh"acac#"CO#"PPh2#
Rh"2!Bz!acac#"CO#"PPh2#
Rh!C"5#
Rh!O"0#
Rh!O"1#
Rh!P"0#
0[799"3#
1[922"2#
1[969"2#
1[1242"01#
0[157"4#
0[169"4#
0[034"4#
77[96"01#
78[55"8#
81[6"1#
0[790"7#
1[918"4#
1[976"3#
1[133"1#
0[163"6#
0[164"4#
0[042"00#
76[8"1#
81[9"0#
81[3"1#
76[7"1#
065[7"8#
0[790"4#
1[937"2#
1[969"2#
1[121"0#
0[155"4#
0[153"4#
0[036"4#
77[5"0#
74[8"0#
81[8"1#
81[6"0#
067[0"3#
O"0#!C"1#
O"1#!C"3#
O"2#!C"5#
O"0#!Rh!O"1#
O"0#!Rh!P
C"5#!Rh!O"1#
C"5#!Rh!P
O"2#!C"5#!Rh
n"CO# "cm!0#
KBr
78[55"03#
066[2"3#\ 064[1"3#
0863\ 0847
0879
0872
0873
0848
0871
CHCl2
20P"0H#
d"P#:ppm
31[2
066[2
37[88
062[9
38[33
064[9
0JRh!P:Hz
a Average for molecule 0 and 1[
both molecules to be in almost an eclipsed confor! almost 09> is observed[ A di}erence in rotation around
mation[
the Rh!P bond for the di}erent molecules of almost 2>
An important di}erence between the independent enhances this e}ect "Fig[ 2#[
molecules lies in the rotation of the ferrocenyl moiety
The Rh!P bond distance in the title compound com!
relative to the coordination plane where a di}erence of pared with the analogous ðRh"acac#"CO#"PPh2#Ł ð00Ł

Electron density manipulation in rhodium"I# phosphine complexes
1340
complex is slightly shorter\ indicating stronger Lewis observed for either of the molecules[ This is however
basicity\ as one would expect the larger steric demand to be expected given the usual accuracy by which the
of the PPh1Fc ligand to give rise to an increase in the
Rh!P bond[ It is however about the same length as the
Rh!P bond found in the ðRh"2!Bz!acac#"CO#
"PPh2#Ł ð01Ł "2!Bz!acac ꢁ 2!benzyl!acetylacetonato#
complex[
individual atoms in a carbonyl group can be deter!
mined by X!ray crystallography at ambient tempera!
ture[ The observed di}erence in n"CO# therefore
originates from electronic factors induced by packing
e}ects[ These packing forces induces a bent mode in
the Rh"1#!C"15#!"O12# bond "064[1"3#> molecule 1#
compared to the Rh"0#!C"05#!O"02# bond "066[2"3#>
molecule 0#\ also see Fig[ 2[ This gives rise to a decrease
in sp character in the carbonyl moiety in molecule 1\
which in turn is re~ected in the corresponding decrease
in the n"CO# value of 0847 cm−0 compared to the n"CO#
value of 0863 cm−0 for molecules 1 and 0 respectively[
Motivation for this assignment comes from a previous
solid state IR and X!ray crystallographic investigation
ð02Ł of the Rh analogue of Vaska|s complex\
ðRh"PPh2#1"CO#"Cl#Ł\ wherein the Rh!CO moiety "as
determined from two di}erent polymorphs# exhibited
angles of 066[1"3#> and 053"3#> respectively\ with cor!
IR and NMR Spectra
The results of the IR and NMR investigations are
summarised in Table 1[ Certainly the most important
aspect to note from the IR spectra for the title com!
pound is the presence of two carbonyl stretching fre!
quencies at 0863 and 0847 cm−0 "KBr discs#
respectively for the two independent molecules[ The
presence of these two peaks in the solid state was one
of the interesting discoveries made upon isolation of the
crystalline title compound since ðRh"b!dik#"CO#"PR2#Ł
complexes are usually characterised by a single car!
bonyl stretching frequency[ Thus\ additional charac!
terisation beyond that of normal IR spectroscopy was
responding n"CO# values of 0872 cm−0 and 0854 cm−0
[
However\ in the case of the ðRh"2!Bz!acac#""CO#PPh2#Ł
complex there is not as good a correlation as in the
above mentioned examples "Rh!CO angle of 066[7"3#
and n"CO# 0848 cm−0#[ A more detailed investigation
to these e}ects is currently being undertaken on a broad
spectrum of metal carbonyl complexes[
deemed
necessary[
Solution
IR
"single
n"CO#ꢁ0879 cm−0 in CHCl2# and NMR results
showed only the expected compound and suggested
two {packing isomers| to be present in the crystalline
solid state[ "Fig[ 1#[
Upon comparison of the respective n"CO# values
obtained in solution "although they only di}er slightly#
Upon solution of the molecular structure by X!ray
crystallography this was indeed revealed and a sig!
ni_cant di}erence of 1[0"3#> was observed in the Rh!
C!O angles for the two independent molecules giving
rise to the di}erence of 05 cm−0 in the n"CO# values[
No signi_cant di}erence in either the Rh!C nor the C!
for
the
title
compound\
ðRh"2!Bz!acac#
"CO#"PPh2#Ł and ðRh"acac#"CO#"PPh2#Ł of 0879 cm−0
\
0871 cm−0 and 0873 cm−0 respectively "listed in Table
1# suggests that the metal atom with the highest electron
O bond lengths in the Rh!CO moieties\ indicating a density to be that of the title compound\ secondly the
di}erence in Rh!C or C!O bond strength\ could be 2!Bz!acac:PPh2 complex and thirdly the acac:PPh2
Fig[ 1[ Packing diagram of the unit cell showing the relative orientation of the two independent molecules in the unit cell[
Hydrogen atoms are omitted for clarity[ Displacement ellipsoids are at arbitrary size[

1341
S[ Otto et al[
Fig[ 2[ Molecules 0 and 1 superimposed on each other showing the subtule di}erences due to packing e}ects[ Hydrogen
atoms are omitted for clarity[ Displacement ellipsoids are at arbitrary size[ The solid bonds correspond to molecule 0 and
the open bonds to molecule 1[
complex[ This conclusion is also con_rmed by the The e}ect of the PPh1Fc ligand in corresponding reac!
NMR results obtained[ The 20P chemical shifts for the tivity studies of Rh"I#\ Pt"II# and Pd"II# complexes will
acac:PPh2 and 2!Bz!acac:PPh2 complexes are within be investigated in future[
9[3 ppm\ suggesting almost equal electronic environ!
ments for the respective P atoms\ the 2!Bz!acac:PPh2
complex being the more shielded of the two "up_eld FRD and the Research Fund of the University of the Free
State is gratefully acknowledged[
Acknowled`ements*Financial assistance of the South African
shift#[ One would expect an increase in electron density
on the Rh centre established by the better electron
donating capability of the 2!Bz!acac ligand compared
to acac[ The 20P chemical shift for the acac:PPh1Fc
complex is 6 ppm further up_eld\ indicating a sub!
stantial increase in the electronic shielding on the P
atom of the PPh1Fc ligand in comparison with the PPh2
ligand in the other two mentioned complexes[ First
order coupling between the Rh and P atoms arising
from orbital interactions between the respective nuclei
suggests the most e}ective interaction to be that of the
PPh1Fc ligand "066[2 Hz#\ the 2!Bz!acac:PPh2 complex
second "064[9 Hz# and the acac:PPh2 complex the least
e}ective "062[9 Hz#[ The magnitude of coupling con!
stants can to a great extent be correlated successfully
with the bond lengths obtained in similar systems ð2Ł[
This is also re~ected in the present case where the
Rh!P bond distances for the acac:PPh1Fc and 2!Bz!
acac:PPh2 complexes are the same in length and that
of the acac:PPh2 complex is a bit longer\ resulting in
the smaller coupling constant thereof[
REFERENCES
0[ Botha\ L[ J[\ Basson\ S[ S[ and Leipoldt\ J[ G[\
Inor`[ Chim[ Acta\ 0876\ 015\ 14[ Graham\ D[ E[\
Lamprecht\ G[ J[\ Potgieter\ I[ M[\ Roodt\ A[ and
Leipoldt\ J[ G[\ Transition Met[ Chem[\ 0880\ 082[
1[ Steyn\ G[ J[ J[\ Roodt\ A[ and Leipoldt\ J[ G[\
Inor`[ Chem[\ 0881\ 20\ 2366 "and references
within#[
2[ Steyn\ G[ J[ J[\ Roodt\ A[\ Poletaeva\ I[ and Var!
shavsky\ Y[\ J[ Or`anomet[ Chem[\ 0886\ 425:6\
086[
3[ Du Plessis\ W[ C[\ Roodt\ A[\ Vosloo\ T[ and
Swarts\ J[ C[\ Submitted to J[C[S[ Dalton Trans[
4[ Otto\ S[ and Roodt\ A[\ Acta Cryst[\ 0886\ C42\
0303[
5[ Sollott\ G[ P[\ Mertwoy\ H[ E[\ Portnoy\ S[ and
Snead\ J[ L[\ J[ Or`[ Chem[\ 0852\ 17\ 0989[
6[ Streltsov\ V[ A[ and Zavodnik\ V[ E[\ Kri!
stallo`raphia\0878\ 23"5#\ 0258[
This study enabled a well de_ned characterisation of
the title compound\ showing several interesting aspects[
7[ Sheldrick\ G[ M[\ Acta Cryst[\ 0889\ A35\ 356[ Shel!
drick\ G[ M[\ SHELXL82\ Program for Crystal

Electron density manipulation in rhodium"I# phosphine complexes
1342
Structure Re_nement\ University of Gottingen\ 00[ Leiplodt\ J[ G[\ Basson\ S[ S[\ Bok\ L[ D[ C[ and
Ã
Germany\ 0882[
Gerber\ T[ I[ A[\ Inor`[ Chim[ Acta\ 0867\ 15\ L24[
01[ Roodt\ A[\ Leipoldt\ J[ G[\ Swarts\ J[ C[ and Steyn\
G[ J[ J[\ Acta Cryst[\ 0881\ C37\ 436[
02[ Kemp\ G[\ Roodt\ A[ and Purcell\ W[\ Rhodium
Express\ 0884\ 01\ 10[
8[ Johnson\ C[ K[\ ORTEPII\ Report ORNL!4027\
Oak Ridge National Laboratory\ Tennessee\ USA\
0865[
09[ Adeleke\ J[ A[ and Liu\ L[\ Acta Cryst[\ 0882\ C38\
579[