Spectroscopic and electrochemical studies of group 6 and 8 transition metal carbonyl derivatives of tris{(diphenylphosphinomethyl)dimethylsilyl}methane

Article abstract of DOI:10.1080/15533174.2012.756900

A new series of transition metal carbonyl complexes of tris{(diphenylphosphinomethyl)dimethylsilyl}methane are described in this work. Treatment of M(CO)₆ (M = Cr, W, Mo) and Fe₂(CO) ₉ with [(Ph₂PCH₂Me₂Si) ₃CH] in tetrahydrofuran at elevated temperature resulted in the isolation of [M(CO)₃{(Ph₂PCH₂Me ₂Si)₃CH}] (M = Cr(1), Mo(2), W(3), Fe(4)) in good yield. These complexes have been characterized by elemental analysis, conductivity measurements, mass spectrometry, with IR, electronic, ¹H and ³¹P NMR spectroscopy, and cyclic voltammetry. The data suggest that complexes 1, 2, 3, and 4 have octahedral geometry around the metal atom with tridentate coordination of the ligand. Electrochemical studies of 1, 2, 3, and 4 using cyclic voltammetry indicate quasireversible metal centered oxidation (E°^/ -1.217 V(1), -1.218 V(2), -1.166 V(3), and -1.258 V(4) versus Ag/Ag⁺) and ligand reductions (0.292 V, 0.170 V, -0.331 V, and 0.338 V versus Ag/Ag⁺). Copyright Taylor & Francis Group, LLC.

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Spectroscopic and Electrochemical Studies of Group
6 and 8 Transition Metal Carbonyl Derivatives of
tris{(diphenylphosphinomethyl)dimethylsilyl}methane
Sushil K. Gupta a & Siddhi Nigam a
a School of Studies in Chemistry, Jiwaji University , Gwalior , India
Accepted author version posted online: 17 Apr 2013.Published online: 14 May 2013.
To cite this article: Sushil K. Gupta & Siddhi Nigam (2013) Spectroscopic and Electrochemical Studies of Group 6 and 8
Transition Metal Carbonyl Derivatives of tris{(diphenylphosphinomethyl)dimethylsilyl}methane, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:9, 1175-1180, DOI: 10.1080/15533174.2012.756900
To link to this article: http://dx.doi.org/10.1080/15533174.2012.756900
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:1175–1180, 2013
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.756900
Spectroscopic and Electrochemical Studies of Group 6
and 8 Transition Metal Carbonyl Derivatives of
tris{(diphenylphosphinomethyl)dimethylsilyl}methane
Sushil K. Gupta and Siddhi Nigam
School of Studies in Chemistry, Jiwaji University, Gwalior, India
of the precursor (Ph2PMe2Si)3CH has discrete planar carban-
ions and no Li−P coordination.[4,5] However, the lithium com-
pound with a [LiC(SiMe2CH2PPh2)3] precursor has an un-
usual tricyclic structure with lithium bound to a carbanionic
center and three phosphorus atoms.[6] Carbonyl complexes
have received less attention[7,8] and reports are currently lim-
ited to our studies of [M(CO)3{(Ph2PMe2Si)3CH}][9] where
M = Cr and W and cis-[Mo(CO)4{(Ph2PMe2Si)3CH}][4] and
[MCl2{(Ph2PMe2Si)3CH}][10] (M = Mn(II) and Fe(II)). The
tripodal ligand is bidentate toward molybdenum and triden-
tate toward chromium, tungsten, manganese, and iron. In the
present study, we describe the ligating behavior of the tripodal
ligand, (Ph2PCH2Me2Si)3CH with M(CO)6 (M = Cr, W, Mo)
and Fe2(CO)9. We also report our findings on the electrochem-
ical behavior of these carbonyl complexes.
A
new series of transition metal carbonyl complexes
of tris{(diphenylphosphinomethyl)dimethylsilyl}methane are de-
scribed in this work. Treatment of M(CO)6 (M = Cr, W,
Mo) and Fe2(CO)9 with [(Ph2PCH2Me2Si)3CH] in tetrahydro-
furan at elevated temperature resulted in the isolation of
[M(CO)3{(Ph2PCH2Me2Si)3CH}] (M = Cr(1), Mo(2), W(3), Fe(4))
in good yield. These complexes have been characterized by elemen-
tal analysis, conductivity measurements, mass spectrometry, with
IR, electronic, H and 31P NMR spectroscopy, and cyclic voltam-
1
metry. The data suggest that complexes 1, 2, 3, and 4 have octa-
hedral geometry around the metal atom with tridentate coordina-
tion of the ligand. Electrochemical studies of 1, 2, 3, and 4 using
cyclic voltammetry indicate quasireversible metal centered oxida-
tion (E◦/ −1.217 V(1), −1.218 V(2), −1.166 V(3), and −1.258 V(4)
versus Ag/Ag+) and ligand reductions (0.292 V, 0.170 V, −0.331 V,
and 0.338 V versus Ag/Ag+).
Keywords cyclic voltammetry, M(0)-carbonyl (M = Cr, Mo, W, Fe),
NMR, tris{(diphenylphosphinomethyl}-dimethylsilyl)
methane
EXPERIMENTAL
All reactions were conducted under an argon atmosphere
by the use of standard Schlenk techniques on a double mani-
fold vacuum line.[11,12] All the chemicals were of reagent grade
and were used as received. Chromium, molybdenum and tung-
sten hexacarbonyls and Fe2(CO)9 were obtained from Aldrich
(India). The ligand, (Ph2PCH2Me2Si)3CH, was synthesized fol-
lowing the reported method.[6] Solvents were purified by stan-
dard methods.[13]
INTRODUCTION
Polydentate phosphine ligands have received attention be-
cause of their rich coordination chemistry and the catalytic
application of their metal complexes.[1–3] We have been ex-
ploring the chemistry of sterically hindered tripodal phosphine
ligands of the type (Ph2PMe2Si)3CH and (Ph2PCH2Me2Si)3CH
with main group and transition metals. The lithium com-
pound, [Li(tmen)2][C(SiMe2PPh2)3], obtained by metallation
Physical Measurements
Melting points were recorded in capillary tubes and
are uncorrected. Elemental analyses were obtained with a
Carlo-Erba model DP 200 instrument (United Kingdom).
Molar conductances in 10–4 mol dm–3 MeCN solution were
measured using a Global DCM-900 digital conductivity
meter (Global Electronics, India). The IR spectra were
obtained in KBr pellets on a Shimadzu Prestise-21 FT IR
Received 2 September 2012; accepted 4 December 2012.
The authors are grateful to the University Grants Commis-
sion (UGC), New Delhi for financial assistance (grant number:
F.12–132/2001 (SR-I)) and for the award of a fellowship to S.N. They
thank SAIF, CDRI, Lucknow, for recording mass spectra and BHU, spectrometer (Japan). The FAB mass spectra were recorded
Varanasi, for NMR spectra as well as Dr. J. D. Smith, University of
Sussex, England, for discussion. The authors also thank the reviewers
for their constructive suggestions.
Address correspondence to Sushil K. Gupta, School of Studies
in Chemistry, Jiwaji University, Gwalior 474011, India. E-mail:
skggwr@gmail.com
in the positive mode on a JEOL SX-102 mass spectrometer
(Japan) using 3-nitrophenyl methanol (m-nitrobenzyl alcohol,
1
m-NBA) as the matrix: m/z values are given for H, 12C, 16O,
28Si, 31P, 52Cr, 98Mo, and 184W. The samples dissolved in
(CHCl3/MeOH/EtOH) were introduced into the FAB source.
1175

1176
S. K. GUPTA AND S. NIGAM
Yield: 0.267 g (59%), m.p. 224◦C (dec.). Anal. Calc. for
C49H55P3Si3O3Mo (%): C, 60.8; H, 5.7; P, 9.6. Found: C, 61.2;
H, 5.8; P, 10.0. MS (FAB+) (m/z): 966 [M+]. ꢁM (10−4 M,
CH3CN, 298 K): 30 S cm2mol−1. IR (KBr, ν (cm−1)):1938,
1815 [ν(CO)], 1261 [δ(C – H)], 1022, 864, 756 [ρ(H3C)Si], 694
[νas(Si –C)], 610 [νs(Si –C)]. UV-Vis (CH3CN, λ (nm)): 273,
324. 1H NMR (CDCl3, δ (ppm)): –0.10 (s, CH), 0.06 (s, SiMe2),
The electronic spectra in 10−4 mol dm−3 C6H6 solution
were obtained by use of a Shimadzu UV-160A recording
1
spectrophotometer (Japan). The 1H and 31P{ H} NMR spectra
were recorded on a 300 MHz JEOL AL 300 FT NMR instru-
ment (Japan) at 300.4 (1H) and 121.5 MHz (31P) and chemical
shifts are relative to SiMe4 for H and H3PO4 (85%) for P.
1
Electrochemical Measurements
1.25 (s, CH2), 7.25–7.77 (m, Ph). 31P{ H} NMR (CDCl3, δ
(ppm)): 3.8 (s, PPh2). CV data: E◦/(1) –1.218 V; E◦/(2) 0.170 V.
Cyclic voltammetric measurements were carried out with
an Advanced Electrochemical System, the PARSTAT 2253
instrument (Princeton Applied Research, USA) equipped
with a three-electrode system. The microcell model KO264
consisted of a glassy carbon working electrode with Pt wire as
an auxiliary electrode and a nonaqueous Ag/AgNO3 reference
electrode with 0.1 M AgNO3 in acetonitrile as a filling solution.
Tetrabutylammonium perchlorate (TBAP) (0.1 M solution
in CH3CN) was used as the supporting electrolyte. Cyclic
voltammograms with scan speeds of 100–500 mV s–1 were run
in 10−4 M CH3CN solution under a nitrogen atmosphere. The
potentials measured against an Ag/Ag+ reference electrode
were compared to those for the ferrocene-ferrocenium couple,
Synthesis of Tricarbonyl[tris{(diphenylphosphinomethyl)
dimethylsilyl}methane] tungsten(0)
[W(CO)3{(Ph2PCH2Me2Si)3CH}] (3)
A solution of [W(CO)6] (0.278 g, 0.789 mmol) and
(Ph2PCH2Me2Si)3CH (0.619 g, 0.789 mmol) in THF (100 mL)
was slowly heated to reflux for 22 h. After cooling, a dark yel-
low precipitate of [W(CO)3{(Ph2PCH2Me2Si)3CH}] was fil-
tered off, washed with light petroleum (40 – 60◦C) and dried in
vacuo. Yield: 0.415 g (90%), m.p. 248◦C (dec.). Anal. Calcd.
for C49H55P3Si3O3W (%): C, 55.8; H, 5.2; P, 8.8. Found: C,
56.2; H, 5.4; P, 9.3. MS (FAB+) (m/z): 1052 [M+]. ꢁM (10−4 M,
CH3CN, 298 K): 10 S cm2mol−1. IR (KBr, ν (cm−1)):1919, 1815
[ν (CO)], 1261 [δ (C – H)], 1024, 868, 748 [ρ (H3C)Si], 694 [νas
(Si –C)], 610 [νs (Si –C)]. UV-Vis (CH3CN, λ (nm)): 273, 311.
1H NMR (CDCl3, δ (ppm)): –0.10 (s, CH), 0.00 (s, SiMe2), 1.22
which under the same experimental conditions gave E1/2
0.5(Epa + Epc) = 0.048V and ꢀEp = (Epa − Epc) = 80 mV.
=
Synthesis of Tricarbonyl[tris{(diphenylphosphinomethyl)
dimethylsilyl}methane] chromium(0)
1
(s, CH2), 7.19–7.66 (m, Ph). 31P{ H} NMR (CDCl3, δ (ppm)):
4.1 (s, PPh2). CV data: E◦/(1) –1.166 V; E◦/(2) –0.331 V.
[Cr(CO)3{(Ph2PCH2Me2Si)3CH}] (1)
To a solution of Cr(CO)6 (0.149 g, 0.677 mmol) in THF
(50 mL) was added dropwise a solution of (Ph2PCH2Me2Si)3CH
(0.531 g, 0.677 mmol) in THF (50 mL) at room tem-
perature and the mixture was slowly heated to reflux
for 72 h. After cooling, a greenish yellow precipitate of
[Cr(CO)3{(Ph2PCH2Me2Si)3CH}] was filtered off, washed
with light petroleum (40–60◦C), and dried in vacuo. Yield:
0.396 g (64%), m.p. 206◦C (dec.). Anal. Calcd. for
C49H55P3Si3O3Cr (%): C, 63.9; H, 5.9; P, 10.1. Found: C, 63.6;
H, 6.2; P, 10.7. MS (FAB+) (m/z): 920 [M+]. ꢁM (10−4 M,
CH3CN, 298 K): 50 S cm2mol−1. IR (KBr, ν (cm−1)):1925,
1815 [ν(CO)], 1261 [δ(C – H)], 1022, 866, 748 [ρ(H3C)Si], 663
[νas(Si –C)], 610 [νs(Si –C)]. UV-Vis (CH3CN, λ (nm)): 270,
305. 1H NMR (CDCl3, δ (ppm)): –0.11 (s, CH), 0.07 (s, SiMe2),
Synthesis of Tricarbonyl[tris{(diphenylphosphinomethyl)
dimethylsilyl}methane] iron(0)
[Fe(CO)3{(Ph2PCH2Me2Si)3CH}] (4)
A solution of [Fe2(CO)9] (0.225 g, 0.618 mmol) and,
(Ph2PCH2Me2Si)3CH (0.485 g, 0.618 mmol) in THF (100 cm3)
was slowly heated to reflux for 43 h. After cooling a red-
dish brown solid of [Fe(CO)3{(Ph2PCH2Me2Si)3CH}] was fil-
tered off, washed with light petroleum (40–60◦C), and dried in
vacuo. Yield: 0.289 g (72%), m.p. 304◦C (dec.). Anal. Calcd.
for C49H55P3Si3O3Fe (%): C, 63.6; H, 5.9; P, 10.1. Found: C,
64.1; H, 6.2; P, 10.8. MS (FAB+) (m/z): 924 [M+]. ꢁM (10−4 M,
CH3CN, 298 K): 60 S cm2mol−1. IR (KBr, ν (cm−1)):1937, 1815
[ν (CO)], 1261 [δ (C – H)], 1022, 869, 748 [ρ (H3C)Si], 694 [νas
(Si –C)], 610 [νs (Si –C)]. UV-Vis (CH3CN, λ (nm)): 273, 330.
1H NMR (CDCl3, δ (ppm)): –0.10 (s, CH), 0.00 (s, SiMe2), 1.18
1
1.25 (s, CH2), 7.25–7.73 (m, Ph). 31P{ H} NMR (CDCl3, δ
(ppm)): 0.6 (s, PPh2). CV data: E◦/(1) –1.217 V; E◦/(2) 0.292 V.
1
(s, CH2), 7.19–7.66 (m, Ph). 31P{ H} NMR (CDCl3, δ (ppm)):
12.6 (s, PPh2). CV data: E◦/(1) –1.258 V; E◦/(2) 0.338 V.
Synthesis of Tricarbonyl[tris{(diphenylphosphinomethyl)
dimethylsilyl}methane] molybdenum(0)
[Mo(CO)3{(Ph2PCH2Me2Si)3CH}] (2)
RESULTS AND DISCUSSION
A solution of Mo(CO)6 (0.155 g, 0.587 mmol) in
THF (45 mL) was added dropwise to a solution of
(Ph2PCH2Me2Si)3CH (0.460 g, 0.587 mmol) in THF (45 mL)
Synthesis and Properties
The reactivity of tris{(diphenylphosphinomethyl)dimethyl
at room temperature and the mixture was slowly heated silyl}methane, [(Ph2PCH2Me2Si)3CH], a sterically hindered
to reflux for 48 h. After cooling, a pale yellow precipi- tripodal ligand, toward transition metal carbonyl complexes
tate of [Mo(CO)3{(Ph2PCH2Me2Si)3CH}] was filtered off, has been examined. Greenish yellow chromium, pale yellow
washed with light petroleum (40–60◦C), and dried in vacuo. molybdenum, dark yellow tungsten, and reddish brown iron

SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES
1177
(Scheme 1) that appear from analytical data and from the spec-
troscopic results described subsequently with a composition of
[M(CO)3{(Ph2PCH2Me2Si)3CH}] [M = Cr(1); Mo(2); W(3);
Fe(4)] have been obtained in good yield. All the complexes
are stable at room temperature, soluble in benzene, chloroform,
DMSO and DMF and melt with decomposition in the temper-
ature range 206–304◦C. The molar conductance in acetonitrile
is low compared to values reported[14] for 1:1 electrolytes (ꢁM
120–160 S cm2mol–1) suggesting that these are nonelectrolytes.
Elemental analyses agreed well with the previous formulations.
related compounds, [M(CO)3{(Ph2PMe2Si)3CH}] (M = Cr,
W),[9] [{(Ph2PCH2CH2)2PPh}M(CO)3] (M = Cr,[25] W[24]),
[CH(CH2PPh2)2]2Cr(CO)3,[26]
[W(CO)3{cyclo-(Me3SiCH2
PC3H6)3}],[27] [{CH(Ph2P)2CH2PPh2}W(CO)3],[8,28] [W(CO)3
L3] (L3 = MeC(CH2SMe)3),[29] and [Fe(CO)3(TPM)] (TPM =
tris(diphenylphosphino)methane.[7]
Electronic Spectra
The electronic spectra of complexes 1, 2, 3, and 4 show two
characteristic bands, one at lower wavelength ca. 270 nm for
an intraligand charge transfer (ILCT) transition and an intense
broad band appearing at >300 nm. This longer wavelength tran-
sition is assigned to a MLCT band (d(M(0) → π∗ (ligand)). The
energy of the MLCT transition state of the compounds follows
the order Cr > W > Mo > Fe, which is similar to those of reported
carbonyl octahedral complexes.[30]
1H NMR Spectra
The 1H NMR spectra of complexes 1, 2, 3, and 4 have been
assigned by comparison with those of the free ligand. An impor-
tant observation is the downfield shift of the diphenylphosphine
protons by 0.2–0.3 ppm. This may be ascribed to the coordi-
nation of diphenylphosphine-P to the metal center. The SiMe2
protons experience a small perturbation and the chemical shift
data are similar to those of the free ligand data. The CH2 proton
appears as a singlet at ca.1.2 ppm lower frequency to that of the
free ligand (1.4 ppm). The presence of singlet peak and absence
of phosphorus-hydrogen coupling clearly indicates that all the
SiMe2CH2PPh2 groups lie in the same chemical environment.
SCH. 1.
Mass Spectra
The FAB mass spectrum of complex 1 exhibits a weak
molecular ion peak with correct isotope pattern at m/z 920
which fits the molecular formula [C49H55P3Si3O3Cr]. Peaks
at m/z 892, 864, and 836 are due to successive loss of three
carbonyl groups, as expected for a complex containing the
[Cr(CO)3] moiety.[15] Other important peaks at m/z 712, 654,
572, 555, 498, 281, and 223 have a similar fragmentation
pattern as observed in the ligand.
Complexes 2, 3, and 4 show molecular ion peaks at m/z 966,
1052, and 924, respectively, in their mass spectra. They also
show successive loss of three CO groups at m/z 938, 910, 882
(2), 1024, 996, 968 (3), and 896, 868 and 840 (4), respectively.
The isotopic pattern of each peak in 2, 3, and 4 confirms the
presence of molybdenum, tungsten, and iron.
1
31P{ H} NMR Spectra
1
The 31P{ H} NMR spectra of complexes 1, 2, 3 and 4 at
room temperature display sharp singlets at δ 0.6, 3.8, 4.1, and
12.5 ppm, respectively, indicating that the three phosphorus
atoms are equivalent.[31] The observed chemical shifts are typi-
cal for coordinated phosphorus of this type.[24] The shifts upon
coordination are 18.0, 21.2, 21.5, and 30.0 ppm for 1, 2, 3, and 4
respectively (δ P for ligand is –17.4 ppm). Thus, 31P NMR spec-
tra confirm the tridentate monometallic bonding of the tripodal
phosphine ligand.
IR Spectra
The IR spectra of complexes 1, 2, 3, and 4 in the finger-print
region (1200–700 cm−1) are similar to that for the free ligand
which confirms the presence of the ligand HC(SiMe2CH2PPh2)3
in these complexes. A medium intensity band at 1261 cm−1
is observed in all the complexes which is assigned to bending
Cyclic Voltammetry
The electrochemical properties of the complexes 1, 2, 3,
methyl vibrations, δ(CH3). The bands at 1022–1024, 864–869, and 4 were investigated by cyclic voltammetry (CV) in 0.1 M
and 748–756 cm−1 are assigned to methyl-silicon rocking [NBu4][ClO4] or CH3CN solution with 100–500 mV/s scan
modes, ρ(CH3)(Si). The silicon-carbon (tertiary) asymmetric rates. All CV data were collected under a nitrogen atmosphere
and symmetric stretching vibrations νas(SiC) and νs(SiC) and potentials were reported with reference to Ag/0.1MAgNO3.
are observed at 663–694 and 610 cm−1, respectively. These All of the complexes show one oxidation (E◦/ −1.217 (1),
assignments are in good agreement with related bulky silyl- –1.218 (2), −1.166 (3), and −1.258 (4) V) and one reduction
substituted compounds.[16–18] All the complexes show two (E◦/ .292 (1), 0.170 (2), −0.331 (3), and 0.338 (4) V), both
terminal C – O stretching vibrations consistent with A1 and quasireversible in nature (Table 1, Figure 1). By analogy with
E modes expected for a pseudo C3v, X3MY3 coordination similar carbonyl complexes we suggest that the oxidation is
structure.[19–23] The pattern is characteristic of a complex primarily a metal-centered electron extraction.[32–34] In every
in which the [M(CO)3] moiety is attached to a triphosphine case one quasireversible oxidation (M0 → M+) is observed. The
ligand.[3,7,24] The ν(CO) bands are similar to those reported for peak separation, ꢀEp, varies as a function of scan rates which

1178
S. K. GUPTA AND S. NIGAM
TABLE 1
Cyclic Voltammetric dataa of a 0.1 mM solution of [M(CO)3{(Ph2PCH2Me2Si)3CH}] (1-4) in CH3CN/0.1 M NBu4ClO4 at a
glassy carbon electrode vs Ag/0.1 M AgNO3 at different scan rates
Scan
Rate
Epa V(1)
(ipa)/μA
Epc V(1)
(ipc)/μA
Eº/(1)
V
ꢀEp
mV
Epa/ V(2) Epc/ V(2)
ꢀEp/
mV
Complex
(ipa)/μA
(ipc)/μA
Eº/(2)/V
1
100
200
300
400
500
–1.064
(0.839)
–1.008
(1.208)
–0.984
(2.138)
–0.952
(2.638)
–920
–1.408
(–4.056)
–1.424
(–5.812)
–1.464
(–7.141)
–1.456
(–8.392)
1.496
–1.236
–1.216
–1.224
–1.204
–1.208
344
416
480
504
576
0.736
(2.356)
0.748
(4.125)
0.856
(6.155)
1.248
(9.115)
1.224
–0.384
(–1.684)
–0.408
(–3.045)
–0.280
(–4.372)
–0.384
(–5.004)
–0.432
0.176
1120
1156
1136
1632
1656
0.170
0.288
0.432
0.396
(3.535)
(–9.683)
(11.620)
(–6.215)
2
3
4
100
200
300
400
500
–1.072
(1.210)
–1.024
(1.503)
–0.984
(2.515)
–0.928
(3.430)
–0.920
(3.980)
–1.408
(–3.578)
–1.424
(–4.292)
–1.472
(–6.063)
–1.480
(–7.124)
1.472
–1.240
–1.224
–1.228
–1.204
–1.196
336
400
488
552
552
0.672
(1.592)
0.656
(2.347)
0.736
(4.256)
0.848
(6.190)
0.728
–0.336
(–1.348)
–0.312
(–2.029)
–0.376
(–3.713)
–0.472
(–4.734)
–0.448
0.168
0.172
0.180
0.188
0.140
1008
968
1112
1320
1176
(–8.065)
(6.747)
(–5.267)
100
200
300
400
500
–1.088
(0.151)
–1.088
(0.548)
–1.120
(0.913)
–1.096
(1.493)
–1.072
(2.255)
–1.232
(–4.912)
–1.224
(–8.519)
–1.232
(–11.180)
–1.280
(–13.460)
1.232
–1.160
–1.156
–1.176
–1.188
–1.152
144
136
112
184
160
–0.104
(3.987)
–0.296
(5.671)
–0.248
(8.044)
–0.224
(10.140) (–11.340)
–0.232 –0.416
(12.260) (–12.860)
–0.424
(–4.233)
–0.456
(–7.750)
–0.480
–0.264
–0.376
–0.364
–0.328
–0.324
320
160
232
208
184
(–9.904)
–0.432
(–15.780)
100
200
300
400
500
–1.048
(0.559)
–1.064
(1.370)
–1.048)
(1.676)
–1.072
(2.085)
–1.072
(2.464)
–1.432
(–3.988)
–1.456
(–5.639)
–1.472
(–6.768)
–1.456
(–8.364)
– 1.464
(–9.615)
–1.240
–1.260
–1.260
–1.264
–1.268
384
392
424
384
392
0.824
(3.448)
0.896
(5.223)
1.032
(7.615)
1.072
(10.09)
1.312
–0.322
(–1.658)
–0.360
(–3.115)
–0.384
(–3.995)
–0.352
(–5.123)
–0.336
0.251
0.268
0.324
0.360
0.488
–1146
–1256
–1416
–1424
–1648
(12.60)
(–5.629)
1
2
aEo/
=
(Epa + Epc); ꢀEp = (Epa − Epc).
further shows a quasi-reversible nature of the electrode process. quasi-reversible in nature and the peak separation varies as a
The reduction reflects electron accommodation in the π∗ MO function of scan rates. A linear plot of the cathodic peak current
of the chelated ligand. The reduction appears at a more positive (ipc) versus the square root of the scan rate (ν1/2) passes close
potential than that of the free ligand, reflecting the stabilization to the origin, indicating that the electrode process is mainly
of the π∗ MO upon coordination. The ligand reduction is also diffusion controlled.

SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES
1179
FIG. 1. Cyclic Voltammograms of a 0.1 mM solution of complex 1(a), 2(b), 3(c), and 4(d) in CH3CN/0.1 M NBu4ClO4 at a glassy carbon electrode versus
Ag/0.1 M AgNO3 at 100 mV/s scan rate.
Efforts to grow single crystals did not succeed, and this pre-
cluded a single-crystal X-ray determination.
Proposed Structure of the Complex
The previous analytical evidence suggests an octahedral
geometry around the metal with tridentate coordination of
the phosphorus ligand. The proposed structure is shown
in Figure 2. The carbon, silicon, and phosphorus atoms
of the ligand HC(SiMe2CH2PPh2)3 retain their tetrahedral
configuration in the complex. Similar structures have been
proposed for [M(CO)3{Ph2PMe2Si)3CH}] (M = Cr, W),[9]
[Mo(CO)3(CyPH2)3],[35] and [Fe(CO)3(TPM)].[7]
CONCLUSION
In the present study we have demonstrated the use of
tris{(diphenylphosphinomethyl)dimethylsilyl}methane for the
synthesis of novel complexes of the type [[M(CO)3
{(Ph2PCH2Me2Si)3CH}] (M = Cr(0)(1), Mo(0)(2), W(0)(3),
and Fe(0)(4). These complexes have been synthesized and
FIG. 2. Proposed structure of [M(CO)3{(Ph2PCH2Me2Si)3CH}] (M = Cr,
Mo, W, Fe).
characterized by different spectroscopic tools. The mass

1180
S. K. GUPTA AND S. NIGAM
fragmentation pattern shows successive removal of CO, which 14. Geary, W.J. Coord. Chem. Rev. 1971, 7, 81–122.
15. Ellis, J.E. J. Organomet Chem. 1975, 86, 1–56.
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Compounds, 6th edn.; Wiley, Chichester, England, 2004.
is a characteristic pattern of this type of compound. All the
complexes show two terminal C – O stretching vibrations
consistent with the A1 and E modes expected for a pseudo
1
C3v, X3MY3 coordination structure. H and 31P NMR spectra
also confirm tridentate monometallic bonding of the tripodal 18. Uhl, W.; Pohlmann, M.; Wartchow, R. Angew. Chem. Int. Ed. Engl. 1988,
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phosphine ligand. Cyclic voltammogram results show quasire-
19. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination
Compounds, 5th edn.; Wiley, New York, 1997.
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versible metal centered oxidation, M+/M0 (E◦/ −1.217 V(1),
−1.218 V(2), −1.166 V(3), and −1.258 V(4) vs Ag/Ag+) and
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0.338 V vs. Ag/Ag+).
21. Abel, E.W.; Bennett, M.A.; Wilkinson, G. J. Chem. Soc. 1959, 2323–
2327.
22. Chalmers, A.A.; Lewis, J.; Whyman, R. J. Chem. Soc. 1967, 1817–
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