Coordinatively and electronically unsaturated tris(trimethylsilyl)silyl complexes of manganese and iron

Article abstract of DOI:10.1016/S0020-1693(02)01182-9

The neutral, bis(silyl) complexes M[Si(SiMe₃)₃]₂(THF)_n (3, M=Mn, n=2; 4, M=Fe, n=1) represent reactive, useful starting materials for the synthesis of various silyl derivatives of Mn and Fe. The reaction of 3 with dmpe (dmpe=Me₂PCH₂CH₂PMe₂) produced the yellow-orange complex Mn[Si(SiMe₃)₃]₂(dmpe), which was characterized by X-ray crystallography as possessing Mn-Si distances of 2.643(4) and 2.642(3) ?. A related benzophenone complex, Mn[Si(SiMe₃)₃]₂(OCPh₂) ₂, is dark blue in color but possesses neutral ketone ligands (by IR spectroscopy and X-ray crystallography). The reaction of [NEt₄]{Fe[Si(SiMe₃)₃]₂Cl} with CO gave [NEt₄]{Fe(CO)₃[Si(SiMe₃)₃] ₂Cl}, and the reaction of 3 with CNXyl (Xyl=2,6-Me₂-C₆H₃) produced Mn[Si(SiMe₃)₃]₂(CNXyl)(THF) and the reduced manganese complex (XylNC)₅MnSi(SiMe₃)₃.

Full text of DOI:10.1016/S0020-1693(02)01182-9

Inorganica Chimica Acta 341 (2002) 91Á98
/
www.elsevier.com/locate/ica
Coordinatively and electronically unsaturated tris(trimethylsilyl)silyl
complexes of manganese and iron
Richard H. Heyn, T. Don Tilley *
Department of Chemistry, University of California, Berkeley, CA 94720-1460, USA
Received 2 May 2002; accepted 8 July 2002
This paper is dedicated to Ken Raymond, a great friend and colleague, on the occasion of his 60th birthday.
Abstract
The neutral, bis(silyl) complexes M[Si(SiMe3)3]2(THF)n (3, Mꢀ
materials for the synthesis of various silyl derivatives of Mn and Fe. The reaction of 3 with dmpe (dmpeꢀ
produced the yellowÁorange complex Mn[Si(SiMe3)3]2(dmpe), which was characterized by X-ray crystallography as possessing
MnÃSi distances of 2.643(4) and 2.642(3) A. A related benzophenone complex, Mn[Si(SiMe3)3]2(OCPh2)2, is dark blue in color but
possesses neutral ketone ligands (by IR spectroscopy and X-ray crystallography). The reaction of [NEt4]{Fe[Si(SiMe3)3]2Cl} with
CO gave [NEt4]{Fe(CO)3[Si(SiMe3)3]2Cl}, and the reaction of 3 with CNXyl (Xylꢀ C6H3) produced Mn[Si(SiMe3)3]2(CN-
/
Mn, nꢀ
/
2; 4, Mꢀ
/
Fe, nꢀ/1) represent reactive, useful starting
/
Me2PCH2CH2PMe2)
/
˚
/
/
2,6-Me2Ã
/
Xyl)(THF) and the reduced manganese complex (XylNC)5MnSi(SiMe3)3.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Silyl complexes; Manganese complexes; Iron complexes; Coordinatively unsaturated
1. Introduction
coordinate silyl complexes of Cr, Mn and Fe. These
complexes were prepared by reactions of (THF)3Li-
Si(SiMe3)3 with metal dihalides, which allowed isolation
In recent years, transition-metal silicon chemistry has
received increased attention as new stoichiometric and
of complexes of the types {M[Si(SiMe3)3]2Cl}ꢁ (Mꢀ
/
Cr, Mn, Fe; DMEꢀ
Si)3Si]2M(DME) (Mꢀ
/
1,2-dimethoxyethane), [(Me3-
catalytic processes based on metalÁsilicon bonded
/
/Mn, Fe) and [(Me3-
species have been developed [1]. The discovery of new
reactivity patterns for transition-metal silyl complexes
will rely to some degree on development of new classes
of compounds characterized by high reactivity. To date,
most transition-metal silyl derivatives are based on
‘traditional’ coordination spheres featuring coordinative
unsaturation supported by cyclopentadienyl, phosphine,
or p-acid ligands. With the expectation that coordinative
unsaturation and hitherto unexplored coordination
geometries might lead to new types of reactions for
Si)3Si]2Fe(OEt2) [2]. To characterize the chemical
behavior of these complexes, we have studied their
reactions with small molecules that coordinate to the
metal and expand the coordination spheres. Here we
describe new reactions of manganese and iron bis(silyl)
complexes, and the molecular structures of two four-
coordinate Mn silyl complexes.
metalÁ/silicon bonded compounds, we have explored
2. Experimental
routes to electron-deficient silyl complexes with exceed-
ingly low coordination numbers. In a previous report,
we described the synthesis of high-spin three- and four-
All manipulations were performed under an inert
atmosphere of N2 or Ar, using either a high-vacuum
swivel-frit apparatus, standard Schlenk techniques, or a
Vacuum Atmospheres glove-box. Dry, oxygen-free
solvents were employed throughout. Elemental analyses
were performed by Mikroanalytiches Labor Pascher
* Corresponding author. Fax: ꢂ
/
1-510-642 8940
E-mail address: tdtilley@socrates.berkeley.edu (T.D. Tilley).
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 1 8 2 - 9

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R.H. Heyn, T.D. Tilley / Inorganica Chimica Acta 341 (2002) 91Á98
/
(Germany) or Schwarzkopf Microanalytical Labora-
tories. Infrared spectra were recorded on a PerkinÁ
Elmer 1330 spectrometer. Electronic spectra were re-
corded on an IBM 9420 UVÁVis spectrophotometer.
NMR spectra were obtained with a GE-QE 300 instru-
ment at 300 or 75.5 MHz (1H or 13C, respectively) or on
1
a Varian EM 390 (90 MHz, H). Benzophenone was
recrystallized from ethanol and dried under vacuum
before use. Li(THF)3Si(SiMe3)3 was prepared according
to a published procedure [3].
total yield of 90%. The amount of THF in the product
varies somewhat with drying time. Recrystallization
from pentane with a small amount of added THF
allowed isolation of microcrystals of analytically pure
3. Anal. Calc. for C26H70MnO2Si8: C, 45.0; H, 10.2.
Found: C, 44.2; H, 10.1%. Melting point (m.p.) (dec.):
/
/
140Á142 8C. Evans’ moment: 5.7 BM. IR (CsI, Nujol,
/
cmꢁ1): 1292w, 1252w sh, 1237m, 1072w, 1029m, 857m
sh, 834br s, 742w, 731w, 676m, 621m.
2.3. Fe[Si(SiMe3)3]2(THF) (4)
2.1. Li(THF)3{Mn[Si(SiMe3)3]2Cl} (1)
The procedure was analogous to that for 3, starting
with Li(THF)3{FeCl[Si(SiMe3)3]2} (0.91 g, 1.20 mmol),
Me3SiOSO2CF3 (0.5 ml, 2.6 mmol), and Et2O (35 ml).
Both MnCl2 (1.30 g, 10.3 mmol) and Li(THF)3Si-
(SiMe3)3 (10.1 g, 20.6 mmol) were combined in a 100 ml
flask. The solids were cooled to ꢁ
/
78 8C and Et2O (50
The blueÁpurple solution was stirred at r.t. for 2 h. Two
/
ml) was condensed onto the solids. The mixture was
warmed to room temperature (r.t.) and the heteroge-
neous dark yellow mixture was stirred for 2.5 h. The
mixture was filtered, and the insoluble material was
crops of dark green crystals totaling 0.47 g (0.75 mmol,
62%) were obtained from cooled pentane solutions.
Analysis of the hydrolytic degradation products, as
described for 1, established the stoichiometry of 4. IR
(CsI, Nujol, cmꢁ1): 1255w sh, 1240m, 1037w sh, 1018m,
832br s, 743w, 732w, 680m, 621m, 431w, 394w.
washed with Et2O (2ꢃ
solutions were concentrated to 15 ml and then cooled to
78 8C. Addition of pentane (35 ml) precipitated a
yellow solid, which was isolated by filtration at ꢁ78 8C
/15 ml). The combined ether
ꢁ
/
/
2.4. Mn[Si(SiMe3)3]2(dmpe) (5)
to give 7.52 g (9.37 mmol, 91%) of product. The amount
of THF present can vary with the length of drying time
after isolation of the product. The compound was
shown to contain lithium by a flame test. As reported
previously, compounds of this type sometimes exhibit
consistently low and variable carbon analyses (possibly
due to the formation of stable carbides during the
combustion analysis) [2], and this was observed for
compound 1. Thus, the composition of the complex was
confirmed by an analysis of its hydrolytic degradation
products. To a benzene-d6 solution of the product and a
weighed amount of ferrocene standard was added an
A
25 ml flask was charged with Mn[Si(Si-
Me3)3]2(THF)2 (0.39 g, 0.56 mmol) and cooled to
78 8C. Pentane (20 ml) was condensed into the flask,
ꢁ
/
followed by the addition of dmpe (0.1 ml, 0.60 mmol)
via syringe. Immediately the reaction became bright
yellow. The mixture was warmed to r.t. and after 3 h, the
volatile material was removed under vacuum. The
yellow residue was extracted with Et2O (15 ml) to
remove a small amount of black solid. After removal
of the Et2O, crystallization from pentane provided two
crops of yellowÁ
mmol, 84%). Anal. Calc. for C24H70MnP2Si8: C, 41.2;
H, 10.1. Found: C, 40.9; H, 10.1%. M.p. (dec.): 196Á
/orange crystals totalling 0.33 g (0.47
1
excess of water. A H NMR spectrum of the resulting
solution revealed complete hydrolysis, and integration
of the resonances for HSi(SiMe3)3 and THF against that
of the standard established the stoichiometry of 1.
/
199 8C. Evans’ Moment: 6.1 BM. IR (CsI, Nujol,
cmꢁ1): 1409w, 1302w, 1288w, 1250w, 1236s, 947w,
934w, 830vs, 737w, 704w, 671m, 620m, 419w, 385w.
2.2. Mn[Si(SiMe3)3]2(THF)2 (3)
2.5. Mn[Si(SiMe3)3]2(OCPh2)2 (6)
A 100 ml flask was charged with Li(THF)3{MnCl-
[Si(SiMe3)3]2} (8.05 g, 10.3 mmol) and Me3SiOSO2CF3
A
50 ml flask was charged with Mn[Si(Si-
Me3)3]2(THF)2 (1.44 g, 2.1 mmol) and Ph2CO (0.75 g,
4.1 mmol). The solids were cooled to ꢁ78 8C, and
(3.0 ml, 15.5 mmol). The mixture was cooled to ꢁ78 8C
/
and Et2O (75 ml) was condensed into the flask. The
reaction mixture was allowed to warm to r.t., and the
resulting yellow solution was stirred for 3 h. The volatile
material was removed, and pentane (75 ml) was added.
The insoluble material was removed by filtration and
/
pentane (40 ml) was condensed into the flask. The
purple mixture was warmed to r.t. and stirred for 1.25 h.
After the volatiles were removed in vacuo, the purple
residue was extracted with pentane (3ꢃ40 ml). Cooling
/
washed with pentane (3ꢃ
30 ml, the yellow solution was cooled to ꢁ
filtration afforded 3.28 g (4.84 mmol) of pale yellow
microcrystals. Repeating the isolation procedure gave
2.80 g (4.35 mmol) of crystals in a second crop, for a
/
20 ml). After concentration to
and concentrating the resulting purple solution resulted
in isolation of three crops of product in a combined
yield of 1.75 g (1.9 mmol, 92%). Anal. Calc. for
C44H74MnO2Si8: C, 57.8; H, 8.15. Found: C, 57.7; H,
/
78 8C, and
8.19%. M.p.: 118Á122 8C. Evans’ Moment: 5.7 BM.
/

R.H. Heyn, T.D. Tilley / Inorganica Chimica Acta 341 (2002) 91Á
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93
UVÁ
/
Vis (pentane, nm): 640 (1000), 619 (1300), 451
optimized. For the red product (8), hydrolytic degrada-
tion with a standard provided a stoichiometry consistent
with Mn[Si(SiMe3)3]2(CNXyl)(THF). IR (CsI, Nujol,
cmꢁ1): 2160m, 2018w, 1981w, 1295w, 1249m sh, 1235m,
1167w, 1030w, 970w, 855s sh, 832vs, 775m, 742m, 731w,
678m, 621m, 434w, 395w. The air-stable yellow product
(9) was characterized by NMR spectroscopy and mass
(800), 376 (1100), 313 (2700), 248 (60 000), 220 (28 000).
IR (CsI, Nujol, cmꢁ1): 1623m, 1611m, 1594m, 1571m,
1450m, 1317m, 1327m, 1317m, 1290m, 1251m sh,
1237m, 1180w, 1159w, 1076w, 1030w, 1001w, 946w,
926w, 831s, 762m, 731w, 701s, 678m, 638m, 621m,
424w.
spectrometry.
Mass
spectroscopy:
Calc.
C54H72MnN5Si4: 957.4254. Found: 957.4221%. M.p.
for
2.6. [NEt4]{Fe(CO)3[Si(SiMe3)3]2Cl} (7)
1
(dec.): 221Á231 8C. H NMR (benzene-d6, 300 MHz,
/
A
60 ml Schlenk flask was charged with
24 8C): d 0.66 (s, 27H, SiCH3), 2.09 (s, 6H, o-CH3),
2.51 (s, 24H, o-CH3), 6.61 (m, 3H, C6H3), 6.75 (s, 12H,
C6H3). IR (CsI, Nujol, cmꢁ1): 2118s, 1998br vs, 1589m,
1231m, 1188w, 1162w, 1092w, 1030w, 919w, 859m, 831s,
769s, 675m sh, 663s, 621w, 600m, 592m, 552w, 505m,
492m sh, 399w.
[NEt4]{FeCl[Si(SiMe3)3]2} (1.25 g, 1.74 mmol) and
Et2O (40 ml). The resulting purple mixture was then
transferred to a FischerÁ
60 psi of CO. After stirring for 4 h, the excess CO was
removed, and the orangeÁred mixture was transferred
to a Schlenk flask. The volatiles were removed, and the
resulting orangeÁred residue was extracted with CH3CN
(40 ml). After filtration, the solution was cooled to ꢁ
35 8C, which subsequently provided two crops of
orangeÁred crystals, totaling 1.09 g (1.36 mmol, 78%).
Anal. Calc. for C29H74ClFeNO3Si8: C, 43.5; H, 9.31; Cl,
4.43; N, 1.75. Found: C, 43.1; H, 9.31; Cl, 4.08; N,
1.81%. M.p. (dec.): 147Á
d3, 90 MHz, 30 8C): d 0.26 (s, 54H, SiCH3), 1.21 (m,
12H, NCCH3), 3.18 (q, JHH
13C{1H} NMR (acetonitrile-d3, 75.5 MHz, 24 8C): d
4.90 (SiCH3), 8.43 (NCCH3), 53.6 (NCH2), 216.9 (CO),
227.5 (CO). IR (CsI, Nujol, cmꢁ1): 1953s, 1921s,
1833m, 1259m, 1239m, 1169w, 860m sh, 839br s,
800m, 677m, 640w, 620m, 599m, 592m sh.
/
Porter bottle and pressurized to
/
/
2.8. Structure determination of 5
/
Crystallographic data are summarized in Table 1. A
/
yellowÁ
random orientation in a glass capillary and flame-sealed.
Centering of 24 randomly selected reflections with 155
2u 5308 provided unit cell data. The selection of the
/
orange crystal was mounted under N2 in a
/
/
149 8C. 1H NMR (acetonitrile-
/
monoclinic cell was confirmed by axial photographs.
The data were corrected for Lorentz and polarization
effects, and for a decay in the intensity of three check
reflections of 2.5%. A semi-empirical absorption correc-
tion based on the C-scan method was employed.
Systematic absences uniquely determined the space
group as P21/c. The structure was solved via a Patterson
map and refined by full-matrix least-squares methods.
Due to a lack of data, only the Mn, P, and Si atoms were
3
ꢀ7 Hz, 8H, NCH2).
/
2.7. Reaction of Mn[Si(SiMe3)3]2(THF)2 with
CN(2,6-Me2C6H3); synthesis of
Mn[Si(SiMe3)3]2[CN(2,6-Me2C6H3)](THF) (8) and
Mn[Si(SiMe3)3][CN(2,6-Me2C6H3)]5 (9)
Table 1
Crystallographic data for Mn[Si(SiMe3)3]2(OCPh2)2 (5)
Chemical formula
Formula weight
T (8C)
C24H70Si8P2Mn
700.4
20
A
50 ml flask was charged with Mn[Si(Si-
Me3)3]2(THF)1.6 (0.45 g, 0.67 mmol). The solid was
cooled to ꢁ78 8C, and pentane (20 ml) was condensed
/
Space group
˚
P21/c
into the flask. In a separate flask, CN(2,6-Me2C6H3)
(CNXyl; 0.26 g, 2.00 mmol) was dissolved in pentane (20
ml), and the clear solution was transferred via cannula
to the cooled suspension. The reaction mixture imme-
a (A)
˚
13.125 (3)
18.191 (5)
19.486 (5)
104.80(2)
4498 (2)
4
b (A)
˚
c (A)
b (8)
3
V (A )
˚
diately became red and was stirred at ꢁ78 8C for 1 h.
/
Z
rcalc (g cmꢁ1
)
1.034
0.574
The reaction was then warmed to r.t. and the now
homogeneous dark red solution was stirred for 1.5 h.
After 0.5 h, an orange precipitate began to form. The
reaction mixture was concentrated to 5 ml, and the
precipitate was removed by filtration and then washed
with pentane (2ꢃ
solid. Cooling the filtrate to ꢁ
provided 0.17 g of red powder. Neither product gave
consistent results by combustion analysis. Use of greater
amounts of CNXyl in the synthesis increased the yield of
the yellow product, but the yield of this species was not
m (mmꢁ1
)
˚
l (Mo Ka) (A)
0.71073
12.2
Data/parameters
Weighting scheme
Scan type
w
ꢁ1ꢀs2(F)ꢂ0.0006F2
Wycoff
Scan speed (8 minꢁ1 in v)
5.00Á29.00
/
/
5 ml), which provided 0.17 g of yellow
78 8C subsequently
a
RF (%)
RwF (%)
Goodness-of-fit
6.34
7.01
1.56
/
b
a
RFꢀajjFojꢁjFcjj/ajFoj.
b
2 1/2
RwFꢀ[a w(jFojꢁjFcj)2/a wjFoj ]
.

94
R.H. Heyn, T.D. Tilley / Inorganica Chimica Acta 341 (2002) 91Á98
/
refined anisotropically. The hydrogen atoms were
placed in idealized, calculated positions (d(CÃH)ꢀ
0.96 A), with a fixed thermal parameter approximately
equal to 1.2 times the isotropic thermal of the attached
carbon atom.
3. Results and discussion
/
/
˚
In general, reactions of (THF)3LiSi(SiMe3)3 with
MnCl2 or FeCl2 in an ethereal solvent produce anionic
complexes of the type [Li(ether)x]{M[Si(SiMe3)3]2Cl}.
We previously described the DME derivatives [Li(D-
ME)2]{M[Si(SiMe3)3]2Cl} (Mꢀ
gous reactions in THF give the corresponding adducts
[Li(THF)3]{M[Si(SiMe3)3]2Cl} (1, MꢀMn; 2, MꢀFe).
These anionic species may be converted to the neutral
complexes M[Si(SiMe3)3]2(DME) (MꢀMn, Fe) and
/
Mn, Fe) [2], and analo-
2.9. Structure determination of 6
/
/
Crystallographic data are summarized in Table 2. A
deep purple crystal was mounted under N2 in a random
orientation in a glass capillary and flame-sealed. Cen-
/
Fe[Si(SiMe3)3]2(OEt2) [2], but we have found the THF
adducts 3 and 4 to be more synthetically useful. These
compounds were prepared by reactions of 1 and 2 with
tering of 25 randomly selected reflections with 155
/
Me3SiOTf (OTfꢁ ꢀ
triflate), as shown in Eq. (1).
/
2u 5308 provided unit cell data. The selection of the
/
tetragonal cell was confirmed by axial photographs. The
data were corrected for Lorentz and polarization effects,
and for a decay in the intensity of three check reflections
of 1.5%. A profile fitting procedure was applied to the
data to enhance the quality of weak reflections. A semi-
empirical absorption correction based on the C-scan
method was employed. Systematic absences uniquely
determined the space group as I41cd The structure was
solved via direct methods and refined by full-matrix
least-squares methods. One reflection with large D/s
was removed from the final refinement. Due to a lack of
data, only the Mn, Si(1), and Si(5) atoms were refined
Complexes 3 and 4, which were isolated in 90 and 62%
yields, respectively, are paramagnetic and, therefore,
little information can be obtained by NMR spectro-
scopy. Furthermore, our experience has shown that
combustion analyses of these compounds often provide
low and variable values for carbon, presumably due to
the formation of carbides which do not burn completely
during the analysis. Therefore, in some cases, an
alternative and reliable method of analysis was em-
ployed involving destructive hydrolysis of the complexes
to liberate the coordinated base and the silyl ligand as
HSi(SiMe3)3. Integration of the resonances for the
hydrolysis products against an internal standard
(usually ferrocene) provided the stoichiometry of the
compound. Further characterization was based on
infrared spectroscopy, which revealed absorptions due
to the ligands present. Particularly diagnostic are three
characteristic absorptions between 600 and 900 cmꢁ1
due to the -Si(SiMe3)3 groups. For example, for 3 these
anisotropically. The hydrogen atoms were placed in
˚
H)ꢀ0.96 A), with
idealized, calculated positions (d(CÃ
/
/
a fixed thermal parameter approximately equal to 1.2
times the isotropic thermal of the attached carbon atom.
All calculations employed the Siemens SHELXTL-PLUS
computing package (Siemens Analytical X-ray Instru-
ments, Inc., Madison, WI).
absorptions appear at 834, 676 and 621 cmꢁ1
.
Table 2
Crystallographic data for Mn[Si(SiMe3)3]2(dmpe) (6)
ð1Þ
Chemical formula
Formula weight
T (8C)
C44H74MnO2Si8
914.7
22
Space group
˚
I41cd
a (A)
˚
28.562 (4)
27.792 (7)
22672 (9)
16
3.1. Reactions of Mn[Si(SiMe3)3]2(THF)2 (3) with
phosphines
c (A)
3
V (A )
˚
Z
rcalc (g cmꢁ1
)
1.072
0.418
Addition of monodentate phosphines (53 equiv. of
/
m (mmꢁ1
)
PMe3 or P(OMe)3) to 3 produced materials that possess
the stoichiometry Mn[Si(SiMe3)3]2(PR3)x(THF)1ꢁx (by
NMR analysis of the hydrolysis products). It is difficult
to rigorously characterize the products of these reactions
as single compounds or as mixtures of 3 and Mn[Si(Si-
Me3)3]2(PR3)x, and we were not able to obtain X-ray
quality crystals. We, therefore, more closely examined
˚
l (Mo Ka) (A)
0.71073
8.3
Data/parameters
Weighting scheme
Scan type
w
ꢁ1ꢀs2(F)ꢂ0.0024F2
Wycoff
Scan speed (8 minꢁ1 in v)
2.00Á14.65
/
a
RF (%)
RwF (%)
Goodness-of-fit
6.67
8.79
1.37
b
the reaction of
Me2PCH2CH2PMe2 (dmpe), which provided good
yields of the yellowÁorange complex 5 (Eq. (2)). This
3 with the bidentate phosphine
a
RFꢀajjFojꢁjFcjj/ajFoj.
b
2 1/2
RwFꢀ[a w(jFojꢁjFcj)2/a wjFoj ]
.
/

R.H. Heyn, T.D. Tilley / Inorganica Chimica Acta 341 (2002) 91Á
/98
95
compound may also be prepared from the reaction of 1
with dmpe, albeit in lower yields.
Table 3
˚
Selected bond distances (A) and angles (8) for 5
Bond distances
Mn(1)ÃP(1)
Mn(1)ÃP(2)
Si(1)ÃSi(2)
Si(1)ÃSi(3)
Si(1)ÃSi(4)
2.675(3) Mn(1)ÃSi(1)
2.647(4) Mn(1)ÃSi(5)
2.334(6) Si(5)ÃSi(6)
2.351(5) Si(5)ÃSi(7)
2.367(5) Si(5)ÃSi(8)
2.643(4)
2.642(3)
2.345(5)
2.361(5)
2.339(5)
ð2Þ
Complex 5 has a meff value of 6.1 BM (determined by
the Evans method [4]), which is nearly the same as the
value observed for 3 (5.7 BM) and consistent with a
high-spin configuration. Infrared absorptions attributed
to the silyl ligands in 5 appeared at 830, 671 and 620
Bond angles
P(1)ÃMn(1)ÃP(2)
P(2)ÃMn(1)ÃSi(1)
P(2)ÃMn(1)ÃSi(5)
Mn(1)ÃSi(1)ÃSi(2)
Si(2)ÃSi(1)ÃSi(3)
Si(2)ÃSi(1)ÃSi(4)
Mn(1)ÃSi(5)ÃSi(6)
Si(6)ÃSi(5)ÃSi(7)
Si(6)ÃSi(5)ÃSi(8)
78.1(1) P(1)ÃMn(1)ÃSi(1)
106.0(1) P(1)ÃMn(1)ÃSi(5)
107.3(1) Si(1)ÃMn(1)ÃSi(5)
110.5(2) Mn(1)ÃSi(1)ÃSi(3)
104.6(2) Mn(1)ÃSi(1)ÃSi(4)
102.0(2) Si(3)ÃSi(1)ÃSi(4)
117.5(2) Mn(1)ÃSi(5)ÃSi(7)
103.5(2) Mn(1)ÃSi(5)ÃSi(8)
101.4(2) Si(67)ÃSi(5)ÃSi(8)
108.0(1)
109.5(1)
133.8(1)
112.4(1)
121.6(2)
104.1(2)
114.3(2)
112.8(1)
106.0(2)
cmꢁ1
.
3.2. Structure of Mn[Si(SiMe3)3]2(dmpe) (5)
An ORTEP diagram of the molecular structure of 5 is
given in Fig. 1, and bond distances and angles appear in
Table 3. The high-spin nature of 5 is reflected in the
these distortions are not as severe as those observed in
[NEt4]{Fe[Si(SiMe3)3]2Cl}, despite the fact that biden-
˚
Si distances of 2.643(4) and 2.642(3) A, which are
MnÃ
/
tate dmpe is more sterically demanding than a chloride
˚
Si distances in 5 (2.33Á2.35 A)
considerably longer than the longest previously reported
˚
ligand. However, the SiÃ
/
/
MnÃ
/
Si distance (2.564 (6) A for the six-coordinate and
Si dis-
˚
are about 0.02 A longer than those found in
[NEt4]{Fe[Si(SiMe3)3]2Cl}.
low-spin (CO)5MnSi(SiMe3)3 [5]). Other MnÃ
/
˚
tances range from 2.31 to 2.50 A [1a,1b]. Compound 5
has a distorted tetrahedral coordination geometry, with
a SiÃ
/
MnÃ
/
Si angle (133.8(1)8) which is undoubtedly due
P distances
average to 2.66 A, and are similar to MnÃP bond
lengths found in other high-spin Mn(II) complexes. For
example, the MnÃP distance in MnBr2(dmpe)2 is
2.655(4) A [6] and in Mn[TeSi(SiMe3)3]2(dmpe) it is
3.3. Reactions of Mn[Si(SiMe3)3]2(THF)2 (3) with
ketones
to the steric bulk of the silyl ligand. The MnÃ
/
˚
/
A few reports have described the insertion of organic
/
carbonyl compounds into MÃ/Si bonds. Whereas low-
˚
valent manganese and iron silyl complexes are known to
insert organic carbonyls to give a-siloxy alkyl derivatives
˚
2.600(3) A [7]. For Mn[CH(SiMe3)2]2(dmpe) this dis-
˚
[9], (h5-C5Me5)Cl3TaSiMe3 adds to CÄ
/O double bonds
tance is even longer at 2.775(4) A [8]. The PÃ
angle in 5 of 78.1(1) is also comparable with the
corresponding angles reported for the above two com-
/
MnÃ/P
via nucleophilic transfer of the silyl group to the
carbonyl carbon atom [10]. Given the unique properties
of 3 as a coordinatively unsaturated, high-spin silyl
complex, we were interested in examining possible
insertion reactions with ketones and aldehydes.
plexes. The PÃ
/
MnÃ/Si angles show less distortion and
are near the tetrahedral value (average 107.7(1)8).
As in [NEt4]{Fe[Si(SiMe3)3]2Cl} [2], the -Si(SiMe3)3
ligands of 5 exhibit a distorted tetrahedral environment
Reactions of 3 with 1 equiv. of acetone or acetophe-
none at various stoichiometries did not yield crystalline
materials that could be identified as pure products. With
1:1 ratios of reactants, powders were isolated which
exhibited the stoichiometry Mn[Si(SiMe3)3]2(THF)(ke-
about the donor Si atoms. The MnÃ
/
Si(1)Ã
/
Si angles are
Si(5)ÃSi
˚
110.5(2), 112.4(1) and 121.6(2) A and the MnÃ
/
/
angles are 112.8(1), 114.3(2) and 117.5(2)8. Therefore,
tone) (ketoneꢀMe2CO, PhMeCO), as determined by
/
destructive hydrolysis. In these hydrolysis reactions, the
corresponding ketone was released. Interestingly, while
complexes of acetone are yellow, complexes of aceto-
phenone are considerably darker and were isolated as
deep purple powders.
The reaction of 3 with 2 equiv. of benzophenone
provided a pure compound that was characterized as the
adduct Mn[Si(SiMe3)3]2(OCPh2)2 (6), isolated in 92%
yield as dark blue crystals from pentane (Eq. (3)). The
magnetic moment (5.7 BM) indicates that the complex
has an electronic structure similar to those of the other
Fig. 1. ORTEP view of Mn[Si(SiMe3)3]2(dmpe) (5).

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R.H. Heyn, T.D. Tilley / Inorganica Chimica Acta 341 (2002) 91Á98
/
Mn[Si(SiMe3)3]2 derivatives. The infrared spectrum of 6
contains absorbances at 1623 and 1611 cmꢁ1 which are
Table 4
˚
Selected bond distances (A) and angles (8) for 6
assigned to the CÄ
/
O stretches of the coordinated
benzophenone ligands. These values may be compared
Bond distances
Mn(1)ÃSi(1)
Mn(1)ÃO(1)
Si(1)ÃSi(2)
Si(1)ÃSi(4)
Si(5)ÃSi(6)
O(1)ÃC(1)
C(1)ÃC(2)
C(1)ÃC(8)
2.642(6) Mn(1)ÃSi(5)
2.13(1)
Mn(1)ÃO(2)
2.354(8) Si(1)ÃSi(3)
2.354(8) Si(5)ÃSi(7)
2.337(8) Si(5)ÃSi(8)
2.662(6)
2.14(1)
2.366(8)
2.355(7)
2.355(9)
1.29(2)
1.43(2)
1.44(2)
with the CÄ
/
O stretching frequencies for free benzophe-
none (1659 cmꢁ1) and for the orthometallated complex
(CO)4MnOCPh(C6H4) (1519 cmꢁ1) [11]. These data
indicate that the CÄ/O bonds in 6 possess a high degree
1.24(2)
1.51(2)
1.45(3)
O(2)ÃC(101)
C(101)ÃC(102)
C(101)ÃC(108)
of double bond character, as might be expected for a
coordination complex of the electron-deficient Mn(II)
center.
Bond angles
Si(1)ÃMn(1)ÃSi(5)
Si(5)ÃMn(1)ÃO(1)
Si(5)ÃMn(1)ÃO(2)
Mn(1)ÃSi(1)ÃSi(2)
Mn(1)ÃSi(1)ÃSi(4)
Si(2)ÃSi(1)ÃSi(4)
Mn(1)ÃSi(5)ÃSi(6)
Si(6)ÃSi(5)ÃSi(7)
Si(6)ÃSi(5)ÃSi(8)
Mn(1)ÃO(1)ÃC(1)
133.3(2) Si(1)ÃMn(1)ÃO(1)
106.9(4) Si(1)ÃMn(1)ÃO(2)
104.7(4) O(2)ÃMn(1)ÃO(2)
108.4(2) Mn(1)ÃSi(1)ÃSi(3)
112.3(3) Si(2)ÃSi(1)ÃSi(3)
104.8(3) Si(3)ÃSi(1)ÃSi(4)
111.0(3) Mn(1)ÃSi(5)ÃSi(7)
104.3(3) Mn(1)ÃSi(5)ÃSi(8)
104.8(3) Si(7)ÃSi(5)ÃSi(8)
170.0(1) Mn(1)ÃO(2)ÃC(101)
102.1(4)
111.1(4)
90.3(5)
122.1(2)
102.4(3)
105.1(3)
122.1(3)
110.6(3)
102.5(3)
165.0(1)
ð3Þ
The deep blue color of 6 is very similar to that of the
benzophenone ketyl radical. The UVÁ
contains bands at 640 nm (oꢀ
1000 Mꢁ1 cmꢁ1) and 313
nm (oꢀ
2700 Mꢁ1 cmꢁ1), which are close in energy to
bands reported for the benzophenone radical anion in
aqueous solution, at 615 nm (oꢀ
6100 Mꢁ1 cmꢁ1) and
339 nm (oꢀ
20 000 Mꢁ1 cmꢁ1) [12]. Additionally, the
carbon-centered radical (tBu3SiO)3TiOPh2C+ exhibits
an absorption at 646 nm (oꢀ
1800 Mꢁ1 cmꢁ1) [13],
/
Vis spectrum of 6
/
/
˚
bond distances, 2.642(6) and 2.662(6) A, are comparable
with those observed in 5.
/
/
˚
The MnÃ
significantly longer than the MnÃ
for (CO)5Mn(OCPhEt) (2.064(3) A) and (CO)4-
/O distances in 6, 2.13(1) and 2.14(1) A, are
/O distances reported
/
˚
and the benzophenone ketyl complex Ca(OCPh2)2-
(HMPA)3 exhibits an absorption at 635 nm [14]. Based
on these comparisons, it seems possible that at least
some of the unpaired electron density in high-spin 6 is
delocalized into the p-system of the coordinated benzo-
phenone.
˚
(Ph3As)Mn(OCPh2) (average 2.04 A) [15]. More rele-
vant is a comparison to the MnÃO distances in the four-
/
coordinate, Mn(II) aryloxide Mn[O(2,4,6-tBu3Ã
C6H2)]2(NCMe)2, which are 1.910(6) A [16]. The latter
comparison is most consistent with the characterization
of the MnÃO bonds in 6 as dative, rather than normal
covalent bonds. The MnÃOÃC angles are rather large,
at 165(1) and 170(1)8. The inequivalent CÄO distances
of 1.24(2) and 1.29(2) A are nearly the same as the
analogous distance in free benzophenone (1.23 A) [17],
but are significantly shorter than the CÃO distance
observed for the ketyl complex Ca(OCPh2)2(HMPA)3
˚
(1.31(2) A) [14]. The dihedral angles associated with
both pairs of phenyl rings, 54.4 and 52.88, are also
similar to the corresponding parameter found in free
/
˚
/
/
/
/
˚
3.4. Structure of Mn[Si(SiMe3)3]2(OCPh2) (6)
˚
/
An ORTEP view of the molecular structure of 6 is given
in Fig. 2, and bond distances and angles are listed in
Table 4. The complex exhibits a tetrahedral coordina-
tion geometry, which is distorted by the steric demands
of the bulky silyl groups. Thus the SiÃ
133.3(2)8, whereas the OÃMnÃO angle is only 90.3(5)8
and the OÃMnÃSi angles average to 1068. The MnÃSi
/
MnÃ/Si angle is
benzophenone (568) [17]. The measured CÃ
in the phenyl rings vary considerably between 1.30(4)
˚
and 1.48(4) A, but in an apparently random manner.
/C distances
/
/
/
/
/
Thus, the metrical parameters for 6 are highly consistent
with a Mn(II) center complexed by two benzophenone
ligands which have not been significantly reduced by
electron transfer.
3.5. Reactions of [NEt4]{FeCl[Si(SiMe3)3]2} and
Mn[Si(SiMe3)3]2(THF)2 (3) with p-acids
Coordinatively unsaturated silyl complexes of man-
ganese and iron are in general reactive toward p-acids
Fig. 2. ORTEP view of Mn[Si(SiMe3)3]2(OCPh2)2 (6).
such as CO and CNXyl (Xylꢀ
/
2,6-Me2Ã/C6H3). A pure

R.H. Heyn, T.D. Tilley / Inorganica Chimica Acta 341 (2002) 91Á
/98
97
product
[NEt4]{FeCl[Si(SiMe3)3]2} [2] with carbon monoxide
7
was isolated from the reaction of
phenone ligands in 6 are not significantly reduced.
Presumably, the dark blue color of 6 results from a
metal-to-ligand charge transfer transition. Reactions of
coordinatively unsaturated, bis(silyl) complexes of Mn
and Fe with the p-acids CNXyl and CO have been
observed to give diamagnetic, coordinatively saturated
complexes. For the reaction of CNXyl with 3, a novel
redox process occurs to produce a reduced iron center.
Overall, the results reported here indicate that highly
unsaturated compounds of the first row metals sup-
ported by the bulky silyl ligand -Si(SiMe3)3 exhibit a rich
reaction chemistry. Future efforts will focus on exploi-
tation of this chemistry in search of new chemical
transformations.
(Eq. (4)). Both H and 13C{1H} NMR spectra reveal
1
the presence of equivalent -Si(SiMe3)3 ligands, which is
consistent with two possible geometries for a six-
coordinate Fe center. One possible isomer has cis-
Si(SiMe3)3 ligands and a fac arrangement of the CO
ligands, while the other one has trans silyl groups with a
mer grouping of the CO groups. The available spectro-
scopic data do not allow us to distinguish between these
two possibilities, but we prefer the isomer with trans
silyl groups based on steric considerations.
ð4Þ
Reactions of 3 with one or 2 equiv. of CNXyl
produced light orange to red paramagnetic powders
which analyzed (by hydrolytic degradation) as Mn[Si(Si-
Me3)3]2(CNXyl)(THF) (8). This reaction also produced
an air-stable, yellow, diamagnetic complex that did not
cleanly degrade by hydrolysis in benzene-d6. However,
this product was characterized as (XylNC)5Mn-
Si(SiMe3)3 (9) by NMR spectroscopy and mass spectro-
metry (Eq. (5)). As expected, the yield of this product
increased with use of more CNXyl in the synthesis, but
the yield of this reaction was not optimized. The
formation of this product represents an interesting
reduction of Mn(II) to Mn(I), but attempts to identify
other redox products in the reaction, or other silicon-
based products, were not successful. Complex 9 is
similar to the stannyl derivative (XylNC)5MnSnPh3,
reported by Cooper and coworkers [18].
Acknowledgements
We acknowledge the National Science Foundation for
their generous support of this work. We also thank Greg
Mitchell for experimental assistance.
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/
absorption spectrum that is similar to that for the
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