Dennett et al.
863
moiety from the putative [Fe(CO)3(PPh3)(η2-BTMSA)] ini-
tial product via addition of the second PPh3 ligand.
To test this hypothesis, the reaction of 1 with the sterically
less-demanding PMe3 was investigated and we report here
that the substitution reaction does indeed proceed by step-
wise loss of CO to yield [Fe(CO)3(PMe3)(η2-BTMSA)] (2)
and [Fe(CO)2(PMe3)2(η2-BTMSA)] (3), respectively.
orange crystals of [Fe(CO)2(PMe3)2(η2-BTMSA)] (3, 31.5 mg,
41.6%) were formed, which proved suitable for an X-ray
crystallographic study.
Method 2
Trimethylphosphine (3.4 µL, 0.033 mmol) was added to a
hexane solution (5 mL) of [Fe(CO)3(PMe3)(η2-BTMSA)] (2,
12.5 mg, 0.0324 mmol) at r.t. and the solution stirred for
2 h. The solvent was removed in vacuo at r.t. The residue
was dissolved in pentane and the solution filtered, concen-
trated, and cooled to –80 °C. Yellow-orange crystals of
[Fe(CO)2(PMe3)2(η2-BTMSA)] (3, 5.0 mg) were obtained in
35% yield.
Experimental section
All reactions were carried out using standard Schlenk
techniques under a dry and oxygen-free nitrogen atmo-
sphere. Hydrocarbon solvents were dried over CaH2 and dis-
tilled under nitrogen using normal procedures prior to use.
[Fe(CO)4(η2-BTMSA)] (1) was prepared as described in the
literature (5). Carbon-13 carbon monoxide (Isotec, Inc.) and
trimethylphosphine (Aldrich) were used as supplied. IR so-
lution spectra (KBr cell) were recorded on a Bomem MB-
100 FT IR spectrometer. NMR samples were prepared under
a nitrogen atmosphere. NMR spectra were recorded on a
Bruker AM-400 MHz operating at 400 MHz for 1H,
161.9 MHz for 31P, and 100.6 MHz for 13C NMR nuclei.
Elemental analyses were performed by the Microanalytical
Laboratory, Department of Chemistry, University of Alberta.
Electron impact (EI) mass spectra were recorded on a
AEI/Kratos MS 50 spectrometer.
Method 3
Excess trimethylphosphine (50.0 µL, 0.483 mmol) was
added to a hexane solution (10 mL) of [Fe(CO)4(η2-
BTMSA)] (1, 39.0 mg, 0.115 mmol) at r.t. and the solution
stirred for 3 h. The solvent was removed in vacuo at r.t. The
yellow residue was dissolved in pentane and the solution fil-
tered, concentrated, and cooled to –80 °C. Yellow-orange
crystals of [Fe(CO)2(PMe3)2(η2-BTMSA)] (3, 30.0 mg) were
obtained in 59.9% yield. IR (n-pentane, cm–1): υCO 1930
(m), 1868 (s); υCϵC 1774 (w). 1H NMR (CD2Cl2, r.t.) δ: 1.05
(vt, apparent JPH = 3.7 Hz, 18H, P(CH3)3), 0.28 (s/br, 18H,
Si(CH3)3). 13C{1H} NMR (CD2Cl2, r.t.) δ: 225.0 (s/br, CO),
116.3 (s, CSiMe3), 18.6 (vt, apparent JPC = 12.5 Hz,
P(CH3)), 1.7 (s, Si(CH3)). 31P{1H} NMR (CD2Cl2, r.t.) δ:
26.6 (s). MS (EI, 16 eV) m/z: 434 (M+), 302 (M+ – 2CO –
PMe3). Anal. calcd. for C16H36FeO2P2Si2 (%): C 44.24, H
8.35; found: C 44.25, H 8.41.
Preparation of [Fe(CO)3(PMe3)(2-BTMSA)] (2)
Trimethylphosphine (24.6 µL, 0.238 mmol) was added to
a hexane solution (25 mL) of [Fe(CO)4(η2-BTMSA)] (1,
64.0 mg, 0.189 mmol) at 10 °C and the solution stirred for
5 h. The solvent was removed in vacuo at –20 °C. The yel-
low residue was dissolved in pentane and the solution fil-
tered, concentrated, and cooled to –80 °C. Yellow crystals of
[Fe(CO)3(PMe3)(η2-BTMSA)] (2, 56.0 mg) were obtained in
76.6% yield. IR (n-pentane, cm–1): υCO 2018 (s), 1949 (s),
[Fe(13CO)2(PMe3)2(η2-BTMSA)] (3*)
[Fe(13CO)2(PMe3)2(η2-BTMSA)] (3*) was prepared by
method 1 using [Fe(13CO)4(η2-BTMSA)] (1*) as the starting
material. IR (n-pentane, cm–1): υCO 1888 (m), 1824 (s);
1
1920 (s); υCϵC 1823 (w/br). H NMR (CD2Cl2, –70 °C) δ:
2
1.01 (d, JPH = 8 Hz, 9H, P(CH3)3), 0.22 (s/br, 18H,
1
Si(CH3)3). 13C{1H} NMR (CD2Cl2, –70 °C) δ: 220.9 (d,
υCϵC 1771 (w). H NMR (CD2Cl2, –80 °C) δ: 0.95 (vt, ap-
2
2JCP = 35 Hz, 2COeq), 214.6 (d, J = 59 Hz, COax), 99.5
parent JPH = 3.7 Hz, 18H, P(CH3)3), 0.18 (s, 18H, Si(CH3)3).
(s, CSiMe3), 16.5 (d, JCP = 28CPHz, P(CH3)), –0.3 (s,
13C{1H} NMR (CD2Cl2, –80 °C) δ: 224.7 (t, JCP = 31 Hz,
1
2
Si(CH3)). 31P{1H} NMR (CD2Cl2, room temperature (r.t.)) δ:
22.4 (s). MS (EI, 16 eV) m/z: 386 (M+), 302 (M+ – 3CO).
Anal. calcd. for C14H27FeO3P1Si2 (%): C 43.52, H 7.00;
found: C 43.23, H 7.09.
CO), 114.0 (s, CSiMe3), 17.8 (vt, apparent JPC = 12.5 Hz,
P(CH3)), 1.0 (s, Si(CH3)). 31P{1H} NMR (CD2Cl2, –80 °C) δ:
2
29.2 (t, JCP = 31 Hz). MS (EI, 16 eV) m/z: 436 (M+); esti-
mated ratios: [Fe(13CO)2(PMe3)2(η2-BTMSA)] 75%,
[Fe(13CO)(12CO)(PMe3)2(η2-BTMSA)] 25%.
[Fe(13CO)3(PMe3)(η2-BTMSA)] (2*)
[Fe(13CO)3(PMe3)(η2-BTMSA)] (2*) was prepared by the
same procedure using [Fe(13CO)4(η2-BTMSA)] (1*) as the
starting material. IR (n-pentane, cm–1): υCO 1971 (s), 1902
(s), 1875 (s); υCϵC 1822 (w/br).
Preparation of [Fe(13CO)4(η2-BTMSA)] (1*)
[Fe(13CO)4(η2-BTMSA)] (1*) was prepared by stirring a
hexane (20 mL) solution of [Fe(CO)4(η2-BTMSA)] (1,
191.5 mg, 0.567 mmol) in a 100 mL round-bottomed flask,
under an atmosphere of 13CO (approx. 3.23 mmol) for
2 days. The solvent was removed in vacuo at –20 °C. The
yellow residue was dissolved in pentane and the solution fil-
tered, concentrated, and cooled to –80 °C. Yellow crystals of
[Fe(13CO)4(η2-BTMSA)] (1*, 125.5 mg) were obtained in
64.8% yield. IR (n-pentane, cm–1): υCO 2029 (w), 1958 (vs),
1924 (s); υCϵC 1873 (w) (for comparison, 1: IR (n-
pentane, cm–1): υCO 2077 (w), 2001 (vs), 1968 (s); υCϵC
1874 (w)).
Preparations of [Fe(CO)2(PMe3)2(η2-BTMSA)] (3)
Method 1
Trimethylphosphine (2 equiv., 36.0 µL, 0.348 mmol) was
added to a hexane solution (25 mL) of [Fe(CO)4(η2-
BTMSA)] (1, 59.0 mg, 0.175 mmol) at r.t. and the solution
stirred for 2 h. The solvent was removed in vacuo at 0 °C.
The yellow residue was dissolved in pentane and the solu-
tion filtered, concentrated, and cooled to –80 °C. Yellow-
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