Synthesis and structure of a five-coordinate organochromium(III) thiolate complex from a chromium(II) alkyl precursor

Article abstract of DOI:10.1021/om970574l

The reaction of the Cr(II) methyl complex, CrMe[N(SiMe₂CH₂PPh₂)₂], with diphenyl disulfide (Ph-SSPh) leads to the formation of the five-coordinate, paramagnetic complex CrMe(SPh)[N(SiMe₂CH₂PPh₂)₂] by an overall one-electron oxidation. The complex is unusual in that the phenyl thiolate moiety is terminal and does not engage in bridging to generate a dinuclear system having octahedral Cr(III) centers. The complex was characterized both in solution and in the solid state.

Full text of DOI:10.1021/om970574l

5116
Organometallics 1997, 16, 5116-5119
Syn th esis a n d Str u ctu r e of a F ive-Coor d in a te
Or ga n och r om iu m (III) Th iola te Com p lex fr om a
Ch r om iu m (II) Alk yl P r ecu r sor
Michael D. Fryzuk,* Daniel B. Leznoff, and Steven J . Rettig†
Department of Chemistry, University of British Columbia, 2036 Main Mall,
Vancouver, British Columbia, Canada V6T 1Z1
Received J uly 8, 1997X
Summary: The reaction of the Cr(II) methyl complex,
CrMe[N(SiMe2CH2PPh2)2], with diphenyl disulfide (Ph-
SSPh) leads to the formation of the five-coordinate,
paramagnetic complex CrMe(SPh)[N(SiMe2CH2PPh2)2]
by an overall one-electron oxidation. The complex is
unusual in that the phenyl thiolate moiety is terminal
and does not engage in bridging to generate a dinuclear
system having octahedral Cr(III) centers. The complex
was characterized both in solution and in the solid state.
(II) center on the disulfide; in the same paper, PhSSPh
was shown to react with cobaltocene, Cp2Co, via an
outer-sphere electron-transfer mechanism.12 The other
example is the one-electron oxidation of [Cr(H2O)6]2+ by
PhSSPh,13,14 analogous to studies of similar transforma-
tions using alkyl halides.3,15-19 This paper reports the
reaction of PhSSPh with a paramagnetic, square-planar
organometallic chromium(II) complex20,21 to give an
unusual five-coordinate chromium(III) complex via one-
electron oxidative addition.
In tr od u ction
Resu lts a n d Discu ssion
Oxidative addition is considered to be one of the
fundamental processes in organometallic chemistry.1,2
In this reaction, a substrate interacts with a transition
metal complex in an overall two-electron redox process
in which the formal oxidation state of the metal center
is increased by two. One-electron oxidation processes,
on the other hand, have been less-studied in an orga-
nometallic context.3 However, divalent first-row transi-
tion metals, in particular Cr, Fe, and Co, generally
undergo one-electron redox processes to yield M(III)
systems and not M(IV) complexes.1,4
Addition of 0.5 equiv of PhSSPh to a brown solution
of CrMe[N(SiMe2CH2PPh2)2] (1)21 at 0 °C resulted in a
rapid color change to purple; reaction at room temper-
ature yielded a dark brown solution from which no
product could be isolated. After workup, a solid with
the empirical formula {CrMe(SPh)[N(SiMe2CH2PPh2)2]}x
(2) was obtained (eq 1). The chromium(III) thiolate
One type of reagent that easily undergoes both one-
and two-electron oxidation reactions with transition
metals are diaryl disulfides, ArSSAr.4 The S-S bond
in diphenyl disulfide in particular is known to be easily
cleaved, resulting in the formation of PhS• radicals.5
Complexes which undergo this formal one-electron
oxidation with PhSSPh include [CpM(CO)3]2 (M ) Cr,6,7
Mo,6 W8,9), [Cp*Cr(CO)3]2,10 and W(iPr3P)2(CO)3.11 The
one-electron oxidative addition of disulfides to a formally
divalent first-row transition metal seems to be restricted
to two studies; the dinuclear complex Cp2Ta(µ-CH2)2-
CoCp was shown to react via initial attack of the cobalt-
complex 2 was expected to be dinuclear, in part due to
the overwhelming preference of chromium(III) to ac-
quire an octahedral geometry4 and also due to the high
propensity of thiolates, in particular phenylthiolates, to
bridge metal centers.22 Examples of bridging chromium
thiolates include [CpCr(CO)2(SPh)]2 and [CpCr(SPh)]2S,7
Cp2Cr2(µ-SPh)(µ3-S)2FeCp and CpCr(µ-SPh)3Fe(µ-SPh)3-
CrCp,23 and Cp2W(µ-SPh)Cr(CO)4.24 However, the solu-
tion magnetic moment of 2 (Evans’ method25,26) of 3.8
† Professional Officer: UBC Crystallographic Service.
X Abstract published in Advance ACS Abstracts, October 15, 1997.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
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metallics 1992, 11, 1711.
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679.
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Chem. 1987, 26, 1064.
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G. J . Am. Chem. Soc. 1994, 116, 7917.
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Baird, M. C. J . Chem. Soc., Chem. Commun. 1991, 798-799.
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(20) Fryzuk, M. D.; Leznoff, D. B.; Rettig, S. J .; Thompson, R. C.
Inorg. Chem. 1994, 33, 5528.
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1995, 14, 5193.
(22) Koschmieder, S. U.; Wilkinson, G. Polyhedron 1991, 10, 135.
S0276-7333(97)00574-8 CCC: $14.00 © 1997 American Chemical Society

Notes
Organometallics, Vol. 16, No. 23, 1997 5117
Ta ble 1. Cr ysta llogr a p h ic Da ta for
Cr Me(SP h )[N(SiMe2CH2P P h 2)2] (2)a
formula
fw
C37H44CrNP2Si2S
704.94
color, habit
cryst size, mm
cryst system
space group
a, Å
purple, prism
0.20 × 0.25 × 0.35
monoclinic
P21/c (No. 14)
9.931(2)
20.573(4)
18.397(3)
94.31(2)
3748(1)
b, Å
c, Å
â, deg
V, Å3
Z
F
4
calcd, g/cm3
1.249
1484
5.36
0.89-1.00
w-2q
F(000)
µ(Mo KR), cm-1
transmission factors
scan type
scan range, deg in ω
scan speed, deg/min
data collected
2θmax, deg
cryst decay, %
total no. of reflns
no. of unique reflns
Rmerge
1.26 + 0.35 tan θ
16 (up to 8 rescans)
+h, +k, (l
50
negligible
7221
6789
0.077
no. of reflns with I g 3σ(I)
no. of variables
R
Rw
gof
2926
398
0.045
0.042
1.98
0.001
-0.28, +0.27
F igu r e 1. Molecular structure (ORTEP) and numbering
scheme for CrMe(SPh)[N(SiMe2CH2PPh2)2] (2), 33% prob-
ability ellipsoids.
max ∆/σ (last cycle)
residual density, e/Å3
µB was consistent with a mononuclear high-spin Cr(III)
complex; this value remained unchanged as the tem-
perature was reduced to -78 °C. The mass spectrum
a
Temperature 294 K, Rigaku AFC6S diffractometer, Mo KR
radiation (λ ) 0.710 69 Å), graphite monochromator, takeoff angle
6.0°, aperture 6.0 × 6.0 mm at a distance of 285 mm from the
crystal, stationary background counts at each end of the scan (scan/
background time ratio 2:1), σ2(F2) ) [S2(C + 4B)]/Lp2 (S ) scan
rate, C ) scan count, B ) normalized background count), function
minimized ∑w(|Fo| - |Fc|)2, where w ) 4Fo2/σ2(Fo2), R ) ∑||Fo| -
indicated only a monomer fragment at m/ e 689 (M+
-
1
Me), and the H NMR spectrum consisted of a series of
very broad, paramagnetically shifted resonances from
which no structural information could be ascertained.
An X-ray crystal structure of thiolate 2 was obtained
in order to determine the nuclearity of the system.
The solid state molecular structure, shown in Figure
1, revealed that thiolate 2 was a five-coordinate chro-
mium(III) complex with a terminal phenylthiolate ligand.
The geometry of the complex could be considered as a
distorted square pyramid, in which the methyl group,
C(37), occupies the apical position. The trans angles of
the square base are then described by P(1)-Cr-P(2) and
S(1)-Cr-N(1), which are 166.30(6)° and 150.0(1)°,
respectively (Table 2). Although less satisfactory, a
distorted trigonal-bipyramidal geometry can be consid-
ered, in which the phosphines are axial and the equato-
rial angles are defined by S(1)-Cr-C(37), S(1)-Cr-
N(1), and C(37)-Cr-N(1). These angles are 92.8(2)°,
150.0(1)°, and 117.2(2)°, respectively, two of which are
obviously substantially distorted from the ideal 120° for
trigonal-bipyramidal coordination.
|Fc||/∑|Fo|, Rw ) (∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2, and gof ) [∑w(|Fo| -
2
|Fc|)2/(m - n)]1/2. Values given for R, Rw, and gof are based on those
reflections with I g 3σ(I).
annulene), and recently, two-legged piano-stool [η5-
Me4C5SiMe2-η1-NtBu]CrCH2SiMe3.30
Other
non-
octahedral complexes of chromium(III) include trigonal
31
32
Cr(NiPr2)3 and Cr[N(SiMe3)2]3 and trigonal-monopy-
ramidal Cr[(tBuMe2Si)NCH2CH2]3N].33
The Cr-P bond lengths of 2.449(2) and 2.479(2) Å
(Table 2) are typical of high-spin Cr(III)-P bonds.
Other examples include Cr-P bonds ranging from
2.429(1) to 2.444(1) Å in [CrCl{N(CH2CH2PMe2)2}2],34
2.414(2) Å in [CpCrCl2](dppe)35 (dppe ) Ph2PCH2CH2-
PPh2), and 2.426(2) Å in Cp*CrMe2(PMe3).36 The Cr-N
bond length of 2.017(4) Å in thiolate 2 is relatively long
compared to other Cr(III)-amide bond lengths, ex-
amples including 1.996(2) and 2.017(2) Å in [CrCl-
{N(CH2CH2PMe2)2}2],34 1.932(3) and 1.931(3) Å in Cp*Cr-
The few structurally characterized examples of five-
coordinate chromium(III) complexes are trigonal-bi-
pyramidal CrCl3(NMe3)2,27,28 distorted trigonal-bipyra-
midal Na2CrPh5‚3Et2O‚THF,29 square-pyramidal Cr-
(tmtaa)Cl (tmtaa ) tetramethyl-dibenzotetraaza[14]-
(29) Mu¨ller, E.; Krause, J .; Schmiedeknecht, K. J . Organomet. Chem.
1972, 44, 127.
(30) Liang, Y.; Yap, G. P. A.; Rheingold, A. L.; Theopold, K. H.
Organometallics 1996, 15, 5284.
(31) Bradley, D. C.; Hursthouse, M. B.; Newing, C. W. Chem.
Commun. 1971, 411.
(32) Bradley, D. C.; Hursthouse, M. B.; Rodesiler, D. F. Chem.
Commun. 1969, 14.
(23) Nefedov, S. E.; Pasynskii, A. A.; Eremenko, I. L.; Gasanov, G.
S.; Ellert, O. G.; Novotortsev, V. M.; Yanovsky, A. I.; Struchkov, Y. T.
J . Organomet. Chem. 1993, 443, 101.
(33) Cummins, C. C.; Lee, J .; Schrock, R. R.; Davis, W. D. Angew.
Chem., Int. Ed. Engl. 1992, 31, 1501.
(24) Prout, K.; Rees, G. V. Acta. Crystallogr., Sect. B 1974, B30, 2717.
(25) Evans, D. F. J . Chem. Soc. 1959, 2003.
(26) Sur, S. K. J . Magn. Reson. 1989, 82, 169.
(27) Fowles, G. W. A.; Greene, P. T. Chem. Commun. 1966, 784.
(28) Greene, P. T.; Russ, B. J .; Wood, J . S. J . Chem. Soc. A 1971,
3636.
(34) Al-Soudani, A. R. H.; Batsanov, A. S.; Edwards, P. G.; Howard,
J . A. K. J . Chem. Soc., Dalton Trans. 1994, 987.
(35) Fettinger, J . C.; Mattamana, S. P.; Poli, R.; Rogers, R. D.
Organometallics 1996, 15, 4211.
(36) Grohmann, A.; Ko¨hler, F. H.; Mu¨ller, G.; Zeh, H. Chem. Ber.
1989, 122, 897.

5118 Organometallics, Vol. 16, No. 23, 1997
Notes
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Cr Me(SP h )[N(SiMe2CH2P P h 2)2] (2)
bond length of 2.300(15) Å in Li3CrMe6‚3C4H8O2 can be
attributed to the trianionic nature of the complex.45 The
only other comparable Cr(III)-C bond length can be
found in the cationic complex [Cp*CrMe(THF)2]BPh4,
with a Cr-C bond length of 2.056(8) Å;46 it was noted
that this was the shortest Cr-CMe bond length observed
in a series of complexes prepared in the Theopold
laboratory.47 The pentacoordinate nature of thiolate 2
could be a factor in rationalizing this short bond length,
although how is not clear.
Cr(1)-S(1)
Cr(1)-P(2)
Cr(1)-C(37)
P(1)-C(1)
P(1)-C(13)
P(2)-C(19)
Si(1)-N(1)
Si(1)-C(3)
Si(2)-N(1)
Si(2)-C(5)
2.371(2)
2.479(2)
2.054(5)
1.826(6)
1.829(6)
1.826(6)
1.732(4)
1.876(7)
1.731(4)
1.860(6)
Cr(1)-P(1)
Cr(1)-N(1)
S(1)-C(31)
P(1)-C(7)
P(2)-C(2)
P(2)-C(25)
Si(1)-C(1)
Si(1)-C(4)
Si(2)-C(2)
Si(2)-C(6)
2.449(2)
2.017(4)
1.771(7)
1.818(6)
1.829(5)
1.834(6)
1.862(6)
1.880(6)
1.897(5)
1.864(7)
S(1)-Cr(1)-P(1)
S(1)-Cr(1)-N(1)
P(1)-Cr(1)-P(2)
P(1)-Cr(1)-C(37)
P(2)-Cr(1)-C(37)
93.90(7) S(1)-Cr(1)-P(2)
150.0(1) S(1)-Cr(1)-C(37)
99.76(6)
92.8(2)
85.6(1)
83.1(1)
Exp er im en ta l Section
166.30(6) P(1)-Cr(1)-N(1)
All manipulations were performed under an atmosphere of
dry, oxygen-free dinitrogen or argon by means of standard
Schlenk or glovebox techniques. The glovebox used was a
Vacuum Atmospheres HE-553-2 workstation equipped with a
MO-40-2H purification system and a -40 °C freezer. 1H NMR
spectroscopy was performed on a Varian XL-300 or a Bruker
AC-200 instrument operating at 300 and 200 MHz, respec-
tively, and were referenced to internal C6D5H (7.15 ppm).
Magnetic moments were measured by a modification of Evans’
method25,26 (C6D5H or Cp2Fe as a reference peak) on the NMR
spectrometers listed above at room temperature and down to
-78 °C. Microanalyses (C, H, N) were performed by Mr. P.
Borda of this department.
The chromium(II) complex CrMe[N(SiMe2CH2PPh2)2] was
prepared as previously described.20 Diphenyl disulfide was
sublimed prior to use. All other reagents were obtained from
commercial sources and used as received. Hexanes, toluene,
and THF were heated to reflux over CaH2 prior to a final
distillation from either sodium metal or sodium benzophenone
ketyl under an Ar atmosphere. Deuterated solvents were dried
by activated 3 Å molecular sieves; oxygen was removed by
trap-to-trap distillation and three freeze-pump-thaw cycles.
Syn th esis of Cr Me(SP h )[N(SiMe2CH2P P h 2)2] (2). To a
red-brown solution of CrMe[N(SiMe2CH2PPh2)2] (1) (0.16 g,
0.27 mmol) in toluene (10 mL) cooled to 0 °C was added a
solution of PhSSPh (0.03 g, 0.14 mmol) in toluene (5 mL).
Immediately, the solution changed to a dark purple color. After
the mixture was stirred for 1 h at 0 °C, the solution was
warmed to room temperature and the solvent removed almost
to dryness. The residue was quickly dissolved in 1 mL of
hexanes and filtered through Celite, and the solvent was
removed in vacuo. Recrystallization from hexanes/toluene (1
mL: 3 drops) in a -40 °C freezer yielded a thick oil, which
upon agitation gave CrMe(SPh)[N(SiMe2CH2PPh2)2] (2) as
purple crystals. Yield: 0.12 g (66%). Anal. Calcd for
88.4(2)
89.9(2)
P(2)-Cr(1)-N(1)
N(1)-Cr(1)-C(37) 117.2(2)
Cr(1)-P(1)-C(1) 100.4(2)
Cr(1)-S(1)-C(31) 101.9(2)
Cr(1)-P(1)-C(7)
C(1)-P(1)-C(7)
C(7)-P(1)-C(13)
Cr(1)-P(2)-C(19) 112.6(2)
C(2)-P(2)-C(19) 103.9(3)
C(19)-P(2)-C(25) 102.2(3)
117.0(2)
104.6(2)
104.2(3)
Cr(1)-P(1)-C(13) 121.5(2)
C(1)-P(1)-C(13)
Cr(1)-P(2)-C(2)
107.6(3)
104.5(2)
Cr(1)-P(2)-C(25) 124.6(2)
C(2)-P(2)-C(25)
N(1)-Si(1)-C(1)
N(1)-Si(1)-C(4)
C(1)-Si(1)-C(4)
N(1)-Si(2)-C(2)
N(1)-Si(2)-C(6)
C(2)-Si(2)-C(6)
Cr(1)-N(1)-Si(1)
Si(1)-N(1)-Si(2)
P(2)-C(2)-Si(2)
107.4(3)
107.0(2)
113.5(3)
108.4(3)
106.8(2)
114.0(2)
107.5(3)
120.7(2)
118.6(2)
109.3(3)
N(1)-Si(1)-C(3)
C(1)-Si(1)-C(3)
C(3)-Si(1)-C(4)
N(1)-Si(2)-C(5)
C(2)-Si(2)-C(5)
C(5)-Si(2)-C(6)
Cr(1)-N(1)-Si(2)
P(1)-C(1)-Si(1)
115.0(3)
105.7(3)
106.8(3)
113.6(3)
107.7(3)
106.8(3)
120.5(2)
108.0(3)
S(1)-C(31)-C(32) 122.6(6)
S(1)-C(31)-C(36) 119.3(6)
(quinolinediamide),37 and a very short 1.87 Å in
Cr(NiPr2)3.31 Note that the change in coordination
number and geometry does not affect these bond lengths
to any great extent. The Cr-S bond length of 2.371(2)
Å is unremarkable and can be compared with terminal
Cr(III)-S bonds of 2.389(5) Å in [(en)Cr(SCH2CH2NH2)2]-
ClO4,38 2.364(5) Å (average) in (PPh4)Na[Cr3(SCH2-
CH2O)6],39 and 2.396(2) Å (average) in Cr(CS2NEt2)3.40
Interestingly, the Cr(III)-S bond lengths in bridging
phenylthiolates are not that different. The Cr-S bond
lengths in Cp2Cr2(µ-SPh)(µ3-S)2FeCp and CpCr(µ-SPh)3-
Fe(µ-SPh)3CrCp23 range from 2.336(3) to 2.383(8) Å, and
in [CpCr(µ-SPh)]2S the range is from 2.365(1) to
2.383(1) Å.7 Note that the Cr-S(1)-C(31) bond angle
of 101.9(2)° in 2 implies that the second lone pair on
the thiolate is not interacting with the metal; a bond
angle of closer to 180° would be expected in that
situation. A Cr(II) phosphine thiolate, namely trans-
Cr(SH)2(dmpe)2, has been reported.41
C
37H44CrNP2SSi2‚C7H8: C, 63.04; H, 6.29; N, 1.99. Found: C,
62.95; H, 6.36; N, 2.13. 1H NMR (C6D6): δ 13.0, 10.6, 10.0,
6.0, 4.7, all very broad. MS: m/ e 689 (M+ - Me), 580 (M+
Me - SPh). µeff ) 3.8 µB.
-
The Cr(III)-C(37) bond length of 2.054(5) Å in 2 is
quite short and can be compared to Cr(III)-Me bond
lengths of 2.09(2) and 2.14(2) Å in octahedral, neutral
CrMe3[tBuSi(CH2PMe2)3],42 2.067(5) Å in Cp*CrMe2-
X-r a y Cr ysta llogr a p h ic An a lysis of Cr Me(SP h )[N(Si-
Me2CH2P P h 2)2] (2). Crystallographic data appear in Table
1. The final unit-cell parameters were obtained by least-
squares on the setting angles for 25 reflections with 2θ ) 21.0-
28.9°. The intensities of three standard reflections, measured
every 200 reflections throughout the data collection, showed
only small random fluctuations. The data were processed48
and corrected for Lorentz and polarization effects and absorp-
tion (empirical, based on azimuthal scans).
(PMe3),36 2.073(3)
Å
in [CpCrMe]2(µ-Cl)2,43 and
2.087(2) Å in [Cp*CrMe]2(µ-Cl)2.44 A very long Cr-C
(37) Danopoulos, A. A.; Wilkinson, G.; Sweet, T. K. N.; Hursthouse,
M. B. J . Chem. Soc., Dalton Trans. 1996, 271.
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(41) Arif, A. M.; Hefner, J . G.; J ones, R. A.; Koschmieder, S. U. J .
Coord. Chem. 1991, 23, 13.
The structure was solved by direct methods. All non-
hydrogen atoms were refined with anisotropic thermal pa-
rameters. The hydrogen atoms were fixed in calculated
positions with C-H ) 0.99 Å and BH ) 1.2Bbonded
. A
atom
(42) Gardner, T. G.; Girolami, G. S. J . Chem. Soc., Chem. Commun.
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(48) teXsan, Structure Analysis Package; Molecular Structure
Corp.: The Woodlands, TX, 1995.

Notes
Organometallics, Vol. 16, No. 23, 1997 5119
secondary extinction correction was applied (Zachariasen type,
isotropic), and the final value of the extinction coefficient was
3.4(6) × 10-7. Neutral-atom scattering factors and anomalous
dispersion corrections were taken from the International
Tables for X-ray Crystallography.49
Ack n ow led gm en t. This work was supported by
NSERC in the form of a grant to M.D.F. and a 1967
Science and Engineering Postgraduate Scholarship to
D.B.L.
Selected bond lengths and bond angles appear in Table 2.
Tables of final atomic coordinates and equivalent isotropic
thermal parameters, anisotropic thermal parameters, complete
bond lengths and angles, torsion angles, intermolecular con-
tacts, and least-squares planes are included as Supporting
Information.
Su p p or tin g In for m a tion Ava ila ble: Tables of final
atomic coordinates and equivalent isotropic thermal param-
eters, anisotropic thermal parameters, complete bond lengths
and angles, torsion angles, intermolecular contacts, and least-
squares planes (25 pages). Ordering information is given on
any current masthead page.
(49) (a) International Tables for X-ray Crystallography; Kynoch
Press: Birmingham, U.K. (present distributor Kluwer Academic
Publishers: Boston, MA), 1974; Vol. IV, pp 99-102. (b) International
Tables for Crystallography; Kluwer Academic Publishers: Boston, MA,
1992; Vol. C, pp 200-206.
OM970574L