Synthesis and reactivity of molybdenum(IV) olefin complexes supported by a chelating ancillary ligand

Article abstract of DOI:10.1021/om000758r

The reactivity of [Mo(NPh)Cl₂(o-(Me₃SiN)₂C₆ H₄·THF)] (1) with β-hydrogen-containing Grignard reagents was examined. Reaction of 1 with 2 equiv of RMgCl (R = CH₂CH₂Ph, CH₂CH₂CH₃, CH₂CH(CH₃)₂, CH₂CH₂CH₃, and CH(CH₃)CH₂CH₃) gave Mo(IV) olefin complexes of the type [Mo(NPh)(η²-olefin)(o-(Me³SiN)₂ C⁶H₄)] (olefin = styrene (2a), propene (2b), isobutene (2c), 1-butene (2d), and 2-butene (2e)). The crystal structure of 2a is reported. Reaction of 1 with 2 equiv of ethylmagnesium chloride afforded a mixture of metallacyclopentane [Mo(NPh)(CH₂CH₂CH₂CH₂) (o-(Me₃SiN)₂C₆H₄)] (3a) and an oligomeric molybdenum species having the empirical formula [Mo(NPh)(o-(Me₃SiN)₂C₆ H₄)]_x (3b). Pure 3a was obtained by reaction of 1 with 2 equiv of EtMgCl under an atmosphere of ethylene. Treatment of 3a with excess PMe₃ in benzene at 80°C afforded [Mo(NPh)(η²-ethylene)(o-(Me₃SiN)₂ C₆H₄)(PMe₃)₂] (3c). Compounds 2c and 2a react with acetone to yield the oxametalacyclopentanes [(Mo(NPh)(C(CH₃)₂CH₂C (CH₃)₂O)(o-(Me₃SiN)₂ C₆H₄))] (4a) and [(Mo(NPh)(C(H)PhCH₂C(CH₃)₂O) (o-(Me₃SiN)₂C₆H₄))] (4b), respectively. An X-ray crystallographic study on a single crystal of 4a was performed. Only one diasteriomer of 4b was formed and isolated. Its structure was assigned by NMR spectroscopy (ghmbc, ghmqc, and NOESY).

Full text of DOI:10.1021/om000758r

2032
Organometallics 2001, 20, 2032-2039
Syn th esis a n d Rea ctivity of Molybd en u m (IV) Olefin
Com p lexes Su p p or ted by a Ch ela tin g An cilla r y Liga n d
Thomas M. Cameron, Carlos G. Ortiz, Ion Ghiviriga, Khalil A. Abboud, and
J ames M. Boncella*
Department of Chemistry and Center for Catalysis, University of Florida,
Gainesville, Florida 32611-7200
Received August 31, 2000
The reactivity of [Mo(NPh)Cl2(o-(Me3SiN)2C6H4‚THF)] (1) with â-hydrogen-containing
Grignard reagents was examined. Reaction of 1 with 2 equiv of RMgCl (R ) CH2CH2Ph,
CH2CH2CH3, CH2CH(CH3)2, CH2CH2CH2CH3, and CH(CH3)CH2CH3) gave Mo(IV) olefin
complexes of the type [Mo(NPh)(η2-olefin)(o-(Me3SiN)2C6H4)] (olefin ) styrene (2a ), propene
(2b), isobutene (2c), 1-butene (2d ), and 2-butene (2e)). The crystal structure of 2a is reported.
Reaction of 1 with 2 equiv of ethylmagnesium chloride afforded a mixture of metallacyclo-
pentane [Mo(NPh)(CH2CH2CH2CH2)(o-(Me3SiN)2C6H4)] (3a ) and an oligomeric molybdenum
species having the empirical formula [Mo(NPh)(o-(Me3SiN)2C6H4)]x (3b). Pure 3a was
obtained by reaction of 1 with 2 equiv of EtMgCl under an atmosphere of ethylene. Treatment
of 3a with excess PMe3 in benzene at 80 °C afforded [Mo(NPh)(η2-ethylene)(o-(Me3SiN)2C6H4)-
(PMe3)2] (3c). Compounds 2c and 2a react with acetone to yield the oxametalacyclopentanes
[(Mo(NPh)(C(CH3)2CH2C(CH3)2O)(o-(Me3SiN)2C6H4)] (4a ) and [(Mo(NPh)(C(H)PhCH2C-
(CH3)2O)(o-(Me3SiN)2C6H4)] (4b), respectively. An X-ray crystallographic study on a single
crystal of 4a was performed. Only one diasteriomer of 4b was formed and isolated. Its
structure was assigned by NMR spectroscopy (ghmbc, ghmqc, and NOESY).
In tr od u ction
early transition metal organometallic chemistry,4 re-
searchers have also focused on the use of non-Cp colig-
ands in the study of chemical reactions performed by
high oxidation state early transition metal complexes.5-7
In recent years we have concentrated our efforts on
the study of W(IV) and W(VI) complexes that contain
the dianionic, diamide ligand [o-(Me3SiN)2C6H4]2-
((Me3Si)2-pda).8 This bidentate ligand has proven to be
â-Hydride transfer from transition metal centers is a
key step in many stoichiometric and catalytic reactions.
For example, â-hydride transfer is one important chain
termination step in transition metal-catalyzed olefin
polymerization and oligomerization.1 In addition, â-hy-
dride elimination is also the major decomposition path-
way for transition metal alkyls.2 This pathway often
gives transition metal olefin complexes, which have been
widely used in unusual organic transformations as well
as in the construction of complex organic molecules from
simple precursors.3 Although various cyclopentadienyl
(Cp) and derivative ring systems have overwhelmingly
dominated as the ancillary ligand of choice for most
(3) Millward, D. B.; Waymouth, R. M. Organometallics 1997, 16,
1153. (b) Takahashi, T.; Kotora, M.; Fischer, R.; Nishihara, Y.;
Nakajima, K. J . Am. Chem. Soc. 1995, 117, 11039. (c) Knight, K. S.;
Wang, D.; Waymouth, R. M.; Ziller, J . J . Am. Chem. Soc. 1994, 116,
1845. (d) Nugent, W. A.; Taber, D. F. J . Am. Chem. Soc. 1989, 111,
6435. (e) Taber, D. F.; Lovey, J . P.; Wang, Y.; Nugent, W. A.; Dixon,
D. A.; Harlow, R. L. J . Am. Chem. Soc. 1994, 116, 9457. (f) Dyer, D.
W.; Gibson, V. C.; Howard, J . A. K.; Whittle, B.; Wilson, C. J . Chem.
Soc., Chem. Commun. 1992, 1666. (g) Proulx, G.; Bergman, R. G. J .
Am. Chem. Soc. 1994, 116, 7953.
(4) Crowe, W. E.; Vu, A. T. J . Am. Chem. Soc. 1996, 118, 5508.
(5) Aoyagi, K.; Kalai, K.; Gantzel, P. K.; Tilley, T. D. Organometallics
1996, 15, 923. (b) Aoyagi, K.; Kalai, K.; Gantzel, P. K.; Tilley, T. D.
Polyhedron 1996, 15, 4299. (c) Pinado, G. J .; Thorton-Pett, M.;
Bochman, M. J . J . Chem. Soc., Dalton Trans. 1998, 393. (d) Lee, R.
A.; Lachicotte, R. J .; Bazan, G. C. J . Am. Chem. Soc. 1998, 120, 6037.
(e) Armistead, L. T.; White, D. S.; Gagne´, M. R. Organometallics 1998,
17, 216. (f) Shah, A. A.; Dorn, H.; Voigt, A.; Roesky, H. W.; Parisini,
E.; Schmidt, H. G.; Noltemeyer, M. Organometallics 1996, 15, 3176.
(g) Shah, A. A.; Dorn, H.; Roesky, H. W.; Parisini, E.; Schmidt, H. G.;
Noltemeyer, M. J . Chem. Soc., Dalton Trans. 1996, 4143. (h) Gue´rin,
F.; McConville, D. H.; Vittal, J . J .; Yap, G. A. P. Organometallics 1998,
17, 1290. (i) Gountchev, T.; Tilley, T. D. J . Am. Chem. Soc. 1997, 119,
12831. (j) Scollard, J . D.; McConville, D. H.; Rettig, S. J . Organome-
tallics 1997, 16, 1810. (k) Lee, C. H.; La, Y. H.; Park, S. J .; Park, J . W.
Organometallics 1998, 17, 3648. (l) J eon, Y. M.; Park, S. J .; Heo, J .;
Kim, K. Organometallics 1998, 17, 3161. (m) Gue´rin, F.; McConville,
D. H.; Vittal, J . J . Organometallics 1995, 14, 3154. (n) J ohnson, A. R.;
Davis, W. M.; Cummins, C. C. Organometallics 1996, 15, 3825. (o)
Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg, H.
Organometallics 1996, 15, 2672. (p) Dyer, P. W.; Gibson, V. C.; Howard,
J . A. K.; Wilson, C. J . Organomet. Chem. 1993, 462, C15. (q) Gue´rin,
F.; McConville, D. H.; Vittal, J . J . Organometallics 1997, 16, 1491.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, 1987. (b) Parshall, G. W.
Homogeneous Catalysis; J ohn Wiley & Sons: New York, 1980; Chapter
3. (c) Cross, R. J . The Chemistry of the Metal-Carbon Bond; Hartley,
F. R., Patai, S., Eds.; J ohn Wiley & Sons: New York, 1985; Vol. 2,
Chapter 8.
(2) Negishi, E.; Takahashi, T. Acc. Chem. Res. 1994, 21, 1277. (b)
Buchwald, S. L.; Nielsen, R. B. Chem. Rev. 1988, 88, 1047. (c) Dyer,
P. W.; Gibson, V. C.; Howard, J . A. K.; Whittle, B.; Wilson, C.
Polyhedron 1995, 14, 103. (d) Dyer, P. W.; Gibson, V. C.; Clegg, W. J .
Chem. Soc., Dalton Trans. 1995, 3313. (e) Grubbs, R. H.; Miyashita,
A. J . Am. Chem. Soc. 1978, 100, 1300. (f) Buchwald, S. L.; Watson, B.
T.; Huffman, J . C. J . Am. Chem. Soc. 1987, 109, 2544. (g) Buchwald,
S. L.; Kreutzer, K. A.; Fisher, R. A. J . Am. Chem. Soc. 1990, 112, 4600.
(h) Fernandez, F. J .; Gomez-Sal, P.; Manzanero, A.; Royo, P.; J acobsen,
H.; Berke, H. Organometallics 1997, 16, 1553. (i) Buijink, J . K. F.;
Kloestra, R.; Meetsma, A.; Teuben, J . H.; Smeets, W. J . J .; Spek, A. L.
Oranometallics 1996, 15, 2523. (j) Rietveld, M. H. P.; Teunisen, W.;
Hagen, H.; van der Water, L.; Grove, D. M.; van der Schaff, P. A.;
Mu¨hlebach, A.; Kooijman, H.; Smeets, W. J . J .; Veldman, N.; Spek, A.
L.; van Koten, G. Organometalics 1997, 16, 1674. (k) Kondakov, D.;
Negishi, E. J . Chem. Soc., Chem. Commun. 1996, 963. (l) Soleil, F.;
Choukroun, R. J . A. Chem. Soc. 1997, 119, 2938.
10.1021/om000758r CCC: $20.00 © 2001 American Chemical Society
Publication on Web 04/19/2001

Molybdenum(IV) Olefin Complexes
Organometallics, Vol. 20, No. 10, 2001 2033
very useful in the isolation of dialkyl and alkylidene
species of W(VI). It has also allowed us to convert some
of the â-hydrogen-containing dialkyls into olefin com-
plexes upon treatment with PMe3.9 These W(VI) â-hy-
drogen-containing dialkyls were otherwise stable to â-
hydrogen transfer reactions. Extension of this chemistry
to molybdenum has resulted in the synthesis of the
analogous non â-hydrogen containing Mo(VI) dialkyls.10
The â-hydrogen-containing Mo(VI) dialkyls, which are
not as stable as their tungsten counterparts, decompose
to afford the corresponding molybdenum olefin com-
plexes. The synthesis, structure, and initial reactivity
studies of these olefin complexes are reported herein.
Resu lts a n d Discu ssion
Syn th esis an d Ch ar acter ization of η2-Olefin Com -
p lexes a n d St r u ct u r e of [Mo(NP h )(η2-st yr en e)-
(o-(Me3SiN)2C6H4)]. The reaction of [Mo(NPh)Cl2(o-
(Me3SiN)2C6H4)‚THF] (1)10 in Et2O at -78 °C with 2
equiv of RMgCl (R ) CH2CH2Ph, n-Pr, and i-Bu) gave
bright red solutions that turned deep green when they
were warmed to 25 °C and stirred for several hours.
Upon workup, these reactions afforded the η2-olefin
complexes 2a -c as emerald green crystals or oils (eq
1). Complex 2a is stable in the solid state, while 2b and
2c decompose over the course of 1 day at room temper-
ature. Typically, 2b and 2c were generated and used
immediately for subsequent reaction chemistry.
F igu r e 1. Molecular structure of 2a (50% probability
thermal ellipsoids). Selected bond lengths (Å) and angles
(deg): Mo-N(1), 1.7366(17); Mo-N(2), 2.0098(16); Mo-
N(3), 2.0184(16); Mo-C(19), 2.145(2); Mo-C(20), 2.190(2);
C(19)-C(20), 1.452(3); C(19)-C(20)-C(21), 123.1(2).
Single crystals of 2a were grown from a concentrated
pentane solution at room temperature overnight. A
single-crystal X-ray diffraction experiment revealed that
2a is a pseudo-four-coordinate η2-styrene complex, this
particular isomer having the styrene phenyl ring ori-
ented anti with respect to the phenyl imido ligand
(Figure 1). The Mo-N(1) bond length of 1.7366(17) Å is
consistent with a molybdenum-nitrogen triple bond
interaction,2c,d,3f,11 while the Mo-N(2) and N(3) amide
bond lengths of 2.0098(16) and 2.0184(16) Å are with-
in the range expected for Mo-N single bonds.12 The
Mo-C(19) and Mo-C(20) bond distances are 2.145(2)
and 2.190(2) Å, respectively. The small difference in
these bond lengths is attributed to steric interactions
of the styrene phenyl ring with the phenyl ring of the
(Me3Si)2-pda functionality. The C(19)-C(20) bond length
of 1.452(3) Å is at the upper end of olefin bond lengths
in metal olefin complexes and supports a considerable
amount of metallacyclopropane character in 2a .13,14 The
crystal and refinement data for 2a are summarized in
Table 1.
NMR experiments revealed that the structure of 2a
in solution is consistent with that determined by X-ray
crystallography. There are, however, two isomers present
1
in solution in a 1:1 ratio. The H NMR spectrum of 2a
(6) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Organometallics
1992, 11, 1452. (b) Freundlich, J . S.; Schrock, R. R.; Davis, W. M.
Organometallics 1996, 15, 2777. (c) Cai, S.; Schrock, R. R. Inorg. Chem.
1991, 30, 4105. (d) Cummins, C. C.; Lee, J .; Schrock, R. R.; Davis, W.
D. Angew. Chem., Int. Ed. Engl. 1992, 31, 1501. (e) Schrock, R. R.;
Seidel, S. W.; Mo¨sch-Zanetti, N. C.; Dobbs, D. A.; Shih, K.-Y.; Davis,
W. M. Organometallics 1997, 16, 5195.
showed four singlets, corresponding to two sets of
(9) Wang, S.-Y. S.; Abboud, K. A.; Boncella, J . M. J . Am. Chem. Soc.
1997, 119, 11990. (b) Boncella, J . M.; Wang, S.-Y. S.; VanderLende,
D. D. J . Organomet. Chem. 1999, 591, 8.
(7) Hill, J . E.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1990,
9, 2211. (b) Kriley, C. E.; Kechener, J . L.; Fanwick, P. E.; Rothwell, I.
P. Organometallics 1993, 12, 2051. (c) Fanwick, P. E.; Rothwell, I. P.;
Kriley, C. E. Polyhedron 1996, 15, 2403. (d) Thorn, M. G.; Hill, J . E.;
Waratuke, S. A.; J ohnson, E. S.; Fanwick, P. E.; Rothwell, I. P. J . Am.
Chem. Soc. 1997, 119, 8630. (e) Vilardo, J . S.; Lockwood, M. A.; Hanson,
L. G.; Clark, J . R.; Parkin, B. C.; Fanwick, P. E.; Rothwell, I. P. J .
Chem. Soc., Dalton Trans. 1997, 3353.
(8) VanderLende, D. D.; Abboud, K. A.; Boncella, J . M. Polym. Prepr.
1994, 35, 691. (b) VanderLende, D. D.; Abboud, K. A.; Boncella, J . M.
Organometallics 1994, 13, 3378. (c) Boncella, J . M.; Wang, S.-Y. S.;
VanderLende, D. D.; Huff, R. L.; Vaughan, W. M.; Abboud, K. A. J .
Organomet. Chem. 1996, 530, 59. (d) Huff, R. L.; Wang, S.-Y. S.;
Abboud, K. A.; Boncella, J . M. Organometallics 1997, 16, 1779. (e)
Wang, S.-Y. S.; VanderLende, D. D.; Abboud, K. A.; Boncella, J . M.
Organometallics 1998, 17, 2628.
(10) Ortiz, C. G.; Abboud, K. A.; Boncella, J . M. Organometallics
1999, 18, 4253.
(11) Bryson, N.; Youinou, M. T.; Osborn, J . A. Organometallics 1991,
10, 3389.
(12) O’Donoghue, M. B.; Davis, W. M.; Schrock, R. R. Inorg. Chem.
1998, 37, 5149. (b) Duan, Z.; Verkade, J . G. Inorg. Chem. 1995, 34,
1576. (c) Mo¨sch-Zanetti, N. C.; Schrock, R. R.; Davis, W. M.; Wan-
ninger, K.; Siedel, S. W.; O’Donoghue, M. B. J . Am. Chem. Soc. 1997,
119, 11037.
(13) Burger, B. J .; Santarsiero, B. D.; Trimmer, M. S.; Bercaw, J .
E. J . Am. Chem. Soc. 1988, 110, 3134. (b) Clark, J . R.; Fanwick, I. P.;
Rothwell, I. P. J . Chem. Soc., Chem. Commun. 1995, 553.
(14) The average C-C bond length for metal-coordinated styrene
is 1.41(9) Å. A search of the October 1998 release of the Cambridge
Database. Allen, F. H.; Kenward, O. Chem. Des. Autom. News 1993,
8, 31.

2034 Organometallics, Vol. 20, No. 10, 2001
Cameron et al.
Ta ble 1. Cr ysta l Da ta , Da ta Collection , a n d
Str u ctu r e Refin em en t for 2a
ppm (6.4%) and a negative NOE at 3.38 ppm (1.7%).
This confirms the olefinic resonances of isomer A as
corresponding to the isomer shown in Figure 1.
We have also observed that the diasteriomers of 2a
do not interconvert on the NMR time scale up to 80 °C.
This large barrier for rotation of the olefin along the
metal-olefin axis is consistent with a large degree of
back-bonding from the d2 metal center to the styrene
fragment and is again consistent with the suggestion
that 2a has a considerable degree of metallacylopropane
character.16
empirical formula
fw
C26H35MoN3Si2
541.69
temperature
wavelength
cryst syst
173(2) K
0.71073 Å
monoclinic
space group
unit cell dimens
P2(1)/c
a ) 12.4996(1) Å,
R ) 90°
b ) 11.1300(1) Å,
â ) 91.25°
c ) 19.1658(2) Å,
γ ) 90°
Propene complex 2b also exists in two isomeric forms.
volume
2665.72(4) Å3
4
1
Although the H NMR spectrum of 2b showed only two
Z
singlets due to the trimethylsilyl groups, two doublets,
assigned to the propene-methyl groups were observed.
Six multiplets, corresponding to olefinic protons, were
also observed.
density (calcd)
abs coeff
1.350 Mg/m3
0.600 mm-1
F(000)
cryst size
θ range for data collection
limiting indices
1128
0.22 × 0.17 × 0.057 mm3
1.63-27.50°
-11 e h e 16, -13 e k e 14,
-24 e l e 23
18 247
1
The H NMR spectrum of the isobutene complex (2c)
displayed upfield resonances assigned to inequivalent
trimethylsilyl groups. In addition, two singlets assigned
to the isobutene-methyl groups were observed. However,
one of the doublets due to an olefinic proton was
obscured by the methyl resonance at 0.73 ppm. The
remaining olefinic proton was observed at 2.99 ppm
(1H). The isolation of 2c represents a rare example of
an early transition metal isobutene complex.2g,15a
Reaction of 1 with 2 equiv of n-BuMgCl, 2 equiv of
sec-BuMgCl, or 1 equiv of n-Bu2Mg afforded, after
appropriate workup, identical product mixtures, as
determined by 1H and 13C NMR spectroscopy. As a
no. of reflns collected
no. of indep reflns
completeness to θ ) 27.50°
abs corr
6091 [R(int) ) 0.0261]
99.4%
empirical (SADABS,
Blessing 1995)
0.949 and 0.824
full-matrix least-squares on F2
max. and min. transmn
refinement method
no. of data/restraints/params 6091/0/296
goodness-of-fit on F2
final R indices [I>2σ(I)]a
R indices (all data)
extinction coeff
largest diff peak and hole
1.051
R1 ) 0.0278, wR2 ) 0.0642 [5129]
R1 ) 0.0387, wR2 ) 0.0697
0.00005(15)
0.831 and -0.487 e Å-3
1
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|; wR2 ) [∑[w(Fo2 - Fc2)2]/∑[wFo22]]1/2
;
+
a
result of the complexity of the H NMR spectra of these
S ) [∑[w(Fo - Fc2)2]/(n - p)]1/2; w ) 1/[σ2(Fo2) + (0.0370p)2
0.31p]; p ) [max(Fo2,0) + 2Fc2]/3.
2
products, 13C (APT) spectroscopy was used to confirm
the identities of the complexes in this mixture as various
isomers of the η2-1-butene and η2-2-butene complexes
2d and 2e, respectively (eq 2). Five different resonances,
inequivalent trimethylsilyl groups. Other resonances,
due to the coordinated styrene, were observed in the
region spanning 1-5 ppm. Through a COSY 2D NMR
experiment two sets of olefinic resonances were identi-
fied for 2a . Isomer A had resonances at 1.16 ppm (m,
1H), 3.38 ppm (m, 1H), and 4.90 ppm (t, 1H). Isomer B
showed signals at 1.05 ppm (m, 1H), 2.22 ppm (t, 1H),
and 3.54 ppm (m, 1H). Furthermore, four resonances
due to coordinated styrene carbons were present in the
13C{1H} NMR spectrum.
We propose that the isomers differ only by the position
of the styrene phenyl group in relation to the imido
phenyl group. One isomer is depicted in Figure 1, and
in the other isomer (a diasteriomer) the styrene phenyl
group is syn to the imido phenyl group. This type of
isomerism for transition metal olefin complexes is well
precedented in the literature.2c,d,3f,15 It is possible to
assigned to dC(H) groups, were observed in this mix-
ture, supporting the existence of at least four different
olefin complexes. The 1-butene isomers were easily
identified in this mixture, because they have terminal
dCH2 olefin and methylene groups. We observed two
methylene resonances and two terminal dCH2 olefin
resonances, and these results support the existence of
two distinct 1-butene complexes. Of the five observed
dC(H) resonances, two must be attributed to the
internal olefin carbons of these 1-butene isomers. The
other three dC(H) resonances must be assigned to
2-butene isomers. These three dC(H) resonances can
be most easily explained by proposing the existence of
two 2-butene isomers: one cis and one trans. Unfortu-
nately, only three resonances corresponding to methyl
groups were observed. As five distinct methyl reso-
nances are expected, we can only assume that some of
1
assign each set of the above resonances in the H NMR
spectrum to their respective isomer in an NOE differ-
ence experiment. An ortho proton belonging to the
coordinated styrene fragment in the isomer of 2a shown
in Figure 1 is positioned directly over the phenyl ring
of the o-(Me3Si)2-pda functionality syn to it. These ortho
1
protons are shifted significantly upfield in the H NMR
spectrum as a result of the pda ring current and are
assigned to the resonance at 5.94 ppm (d, 2H). Irradia-
tion of these protons, in an NOE difference experiment,
produced positive NOES at 1.16 ppm (5.7%) and 4.90
(15) Clark, G. R.; Nielson, A. J .; Richard, C. E. F.; Ware, D. C. J .
Chem. Soc., Dalton Trans. 1995, 1907. (b) Clark, G. R.; Nielson, A. J .;
Richard, C. E. F. J . Chem. Soc., Dalton Trans. 1990, 1173.
(16) Su, F. M.; Cooper, C.; Geib, S. J .; Rheingold, A. L.; Mayer, J .
M. J . Am. Chem. Soc. 1986, 108, 3545.

Molybdenum(IV) Olefin Complexes
Organometallics, Vol. 20, No. 10, 2001 2035
Sch em e 1
the basal plane of 3a . A plane of symmetry that bisects
the N-Mo-N and CR-Mo-CR angles makes each R-
and â-carbon equivalent to the other. However, as
protons sitting above and below the plane are inequiva-
lent, each R-hydrogen couples to its geminal R-hydrogen
and to both vicinal â-hydrogens. Likewise, each â-hy-
drogen couples to its geminal â-hydrogen and to both
1
R-hydrogens. A single Me3Si resonance in the H NMR
spectrum of 3a was observed, as is consistent with the
proposed structure.
Metallacyclopentane 3a was also obtained after 1 was
allowed to react with 2 equiv of EtMgCl (Et2O, -78 °C)
and then warmed to room temperature (eq 4). The yield
of this reaction was much lower, as 1 equiv of “Mo” was
lost when two ethylene molecules coupled to make the
metallacycle. We propose that this material is best
described as an oligomeric molybdenum species having
the empirical formula [Mo(NPh)(o-(Me3SiN)2C6H4)]x
(3b). A high-yielding procedure for the generation of 3a
involved treatment of 1 with 2 equiv of EtMgCl (Et2O,
-78 °C) in the presence of excess dry ethylene (eq 5).
these signals overlap. The signals due to trimethylsilyl
groups are observed near 1.32 ppm.
As depicted in Scheme 1, we propose that 1-butene
and 2-butene complexes present in these mixtures result
from isomerization of the coordinated olefin through
allylic C-H activation. The reaction of 1 with sec-
BuMgCl should yield the di-sec-butyl complex 2g, which,
through â-hydride transfer, forms both 1-butene and
2-butene complexes 2d and 2e, respectively. However,
the di-n-butyl complex can only decompose to the
1-butene complex. At this point, allylic activation would
produce an allyl hydride intermediate (2h ), which can
reversibly be converted into a 2-butene complex by
insertion/migration into the opposite carbon. This allyl
mechanism is very common for transition metal-medi-
ated olefin isomerization.17-19
We propose that the formation of 3a occurs via the
pathway shown in Scheme 2. Upon addition of EtMgCl
to 1, the bright orange-red color of the dialkyl com-
plex appears. Upon warming, the solution darkens and
becomes the color of 3a . â-Hydride transfer from a
Mo(VI) diethyl complex would afford a Mo(IV) ethylene
complex. This ethylene complex could then dispropor-
tionate in the absence of excess ethylene to yield 3a and
three-coordinate [Mo(NPh)(o-(Me3SiN)2C6H4)]. This three-
coordinate, coordinatively unsaturated, and electron-
deficient intermediate then oligomerizes to generate 3b.
However, in the presence of excess ethylene coupling
of the coordinated ethylene molecule and a free ethylene
molecule gives 3a in essentially quantitative yield.
The oligomeric molybdenum species 3b can be syn-
thesized by treatment of a pentane solution of 2b with
excess lutidine. When 3b is synthesized in such a
manner it forms as a black precipitate that can be
isolated by filtration and purified by successive wash-
ings with pentane. Once pure, the solubility of 3b, in
conventional solvents (CHCl3, CH2Cl2, THF, Et2O,
F or m a tion of Mo(VI) Meta lla cyclop en ta n e [Mo-
(NP h )(CH2CH2CH2CH2)(o-(Me3SiN)2C6H4)] (3a ). The
reaction of 1 and 1 equiv of BrMgCH2CH2CH2CH2MgBr
in Et2O (-78 °C) resulted in the formation of red-orange
metallacyclopentane 3a (eq 3). We propose that 3a
adopts a square pyramidal geometry similar to the
tungsten analogue.8e Four multiplets are observed for
1
the metallacycle protons in the H NMR spectrum. The
o-(Me3Si)2-pda nitrogens and the two R-carbons occupy
(19) Although no hydride species are detected in solution, we have
isolated hydride complexes of a closely related tungsten system19b and
have spectroscopically observed a molybdenum P(Me)3-stabilized di-
hydride of this system (manuscript in preparation). (b) Boncella, J .
M.; Wang, S.-Y. S.; VanderLende, D. D. J . Organomet. Chem. 1999,
591, 8.
(17) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; J ohn Wiley and Sons: New York, 1984.
(18) Along these lines we have observed catalytic transformation of
allylanisole to trans-â-methylstyrene.

2036 Organometallics, Vol. 20, No. 10, 2001
Cameron et al.
Sch em e 2
Sch em e 3
butene and free H2-o-(Me3SiN)2-pda. The observation of
H2-o-(Me3Si)2-pda suggests that the butene formed was
more likely a result of the decomposition of 3a than from
the catalytic dimerization of ethylene.
F or m a tion of Mo(IV) Eth ylen e Com p lex [Mo-
(NP h )(η2-eth ylen e)(o-(Me3SiN)2C6H4)(P Me3)2] (3c).
When a small excess (2.2 equiv) of PMe3 was added to
a C6D6 solution of 3a and heated to 80 °C, formation of
[Mo(NPh)(η2-ethylene)(o-(Me3SiN)2C6H4)(PMe3)2] (3c)
was observed (eq 6). No 3c was produced under identical
conditions at room temperature. Alternatively, 3c was
prepared by reacting 2 equiv of EtMgCl with 1 (Et2O,
-78 °C) while in the presence of slightly more than 2
equiv of PMe3 (eq 7).
benzene, toluene, and CH3CN), decreases substantially,
making structural studies in solution difficult. All that
can be concluded by NMR spectroscopy is that the
formulation of 3b is supported by integration and
multiplicity of the aromatic proton resonances in the
1H NMR spectrum. If 3b is left under an inert atmo-
sphere at room temperature, it begins to decompose
1
within one month by H NMR, affording an intractable
mixture.
We came upon the synthesis of 3b via treatment with
lutidine by accident while we were exploring the chem-
istry of these olefin complexes with pyridine and pyri-
dine derivatives. Reaction of 2b with pyridine results
in the formation of a five-coordinate, square pyramidal,
bispyridine adduct, [Mo(NPh)(Py)2(o-(Me3SiN)2C6H4)].20
We attribute the difference in reactivity of 2b with
pyridine and lutidine to the different steric environ-
ments around the Lewis basic nitrogen atoms in both
molecules. Pyridine readily displaces propene from 2b
and remains bound to the metal center. Lutidine,
however, can displace olefin from 2b but is not involved
in adduct formation. Effective displacement of propene
from 2b, by lutidine, would generate the three-coordi-
nate, coordinatively unsaturated, and electron-deficient
[Mo(NPh)(o-(Me3SiN)2C6H4)], which then oligomerizes.
In general, we observe the formation of 3b whenever
reaction conditions permit loss of the olefin ligand
without replacement by another donor.
Significant interest has been shown in early transition
metal metallacyclopentane species due to their role in
the dimerization and trimerization of ethylene as a
means for catalytically preparing butene21 and hexene,22
respectively. We did not observe formation of metalla-
cycloheptane species nor the formation of hexene when
3a was exposed to excess ethylene. When a C6D6
solution of 3a was heated to 80 °C under ethylene
pressure (1-2 atm), the only identifiable products were
A broad singlet assigned to the trimethylsilyl protons
and a broadened singlet assigned to the trimethylphos-
phine methyl protons were observed in the 1H NMR
spectrum of 3c. Two broadened doublets were assigned
to the ethylene protons.23 The equilibrium between
metallacyclopentanes and bis-ethylene species has been
extensively studied in the past.3c,24 The need for heat
in the preparation of 3c from 3a suggests that 3a can
be better described as a metallacyclopentane than as a
bis-ethylene complex (Scheme 3). A bis-ethylene species
such as 3d could conceivably be part of an equilibrium
that lies toward 3a . Addition of PMe3, accompanied by
heat, could effectively trap 3d , ultimately resulting in
the formation of 3c.
Syn th esis of Oxa m eta lla cycles [(Mo(NP h )(C-
(CH3)2CH2C(CH3)2O)(o-(Me3SiN)2C6H4)] (4a ) a n d
[(Mo (N P h )(C (H )P h C H 2C (C H 3)2O )(o-(Me 3S iN )2-
C6H4)] (4b). Addition of acetone to a solution of 2c in
pentane resulted in the exclusive formation of 4a , as
determined by 1H and 13C NMR spectroscopy. A single-
crystal X-ray crystallographic study of 4a reveals the
square pyramidal geometry about molybdenum (Figure
2). The regioselectivity of this particular reaction, with
(20) The synthesis, structure, and reactivity studies of this pyridine
complex will be reported elsewhere (manuscript in preparation). We
include it here only to offer insight into the formation of 3b via
treatment of 2b with lutidine.
(21) McLain, S. J .; Schrock, R. R. J . Am. Chem. Soc. 1978, 100, 1315.
(b) McLain, S. J .; Sancho, J .; Schrock, R. R. J . Am. Chem. Soc. 1980,
102, 5610.
(22) Encrich, R.; Heinemann, O.; J olly, P. W.; Kru¨ger, C.; Verhounik,
G. P. J . Organometallics 1997, 16, 1511. (b) Meijboom, N.; Schaverien,
C. J .; Orpen, A. G. Organometallics 1990, 9, 774. (c) Briggs, J . R. J .
Chem. Soc., Chem. Comm. 1989, 674.
(23) We have previously isolated and characterized the correspond-
ing tungsten analogue of 3c.9
(24) Cohen, S. A.; Auburn, P. R.; Bercaw, J . E. J . Am. Chem. Soc.
1983, 105, 1136. (b) Erker, G.; Dorf, U.; Rheingold, A. L. Organome-
tallics 1988, 7, 138.

Molybdenum(IV) Olefin Complexes
Organometallics, Vol. 20, No. 10, 2001 2037
Ta ble 2. Cr ysta l Da ta , Da ta Collection , a n d
Str u ctu r e Refin em en t for 4a
empirical formula
fw
C25H41MoN3OSi2
551.73
temperature
wavelength
cryst syst
173(2) K
0.71073 Å
triclinic
space group
unit cell dimens
P1h
a ) 9.8841(7) Å,
R ) 101.370(1)°
b ) 11.2646(7) Å,
â ) 96.272(1)°
c ) 14.766(1) Å,
γ ) 115.921(1)°
1413.6(2) Å3
2
volume
Z
density (calcd)
abs coeff
1.296 Mg/m3
0.569 mm-1
F(000)
cryst size
θ range for data collection
limiting indices
580
0.27 × 0.25 × 0.16 mm3
1.44-27.50°
-12 e h e 10, -13 e k e 14,
-16 e l e 19
9474
no. of reflns collected
no. of indep reflns
completeness to θ ) 27.50°
abs corr
6236 [R(int) ) 0.0620]
96.0%
integration
F igu r e 2. Structure of 4a (50% probability thermal
ellipsoids). Selected bond lengths (Å) and angles (deg):
Mo-N(1), 1.7348(18); Mo-O(1), 1.9344(15); Mo-N(3),
2.0072(18); Mo-N(2), 2.0513(17); Mo-C(19), 2.209(2); O(1)-
C(21), 1.432(3); C(19)-C(20), 1.541(3); C(20)-C(21), 1.534-
(3); Mo-C(19)-C(20), 103.80(14); Mo-O(1)-C(21), 122.89-
(13); C(22)-C(19)-C(23), 109.7(2); C(24)-C(21)-C(25),
109.7(2); C(19)-C(20)-C(21), 111.91(18).
max. and min. transmn
refinement method
0.9639 and 0.8427
full-matrix least-squares on F2
no. of data/restraints/params 6236/0/300
goodness-of-fit on F2
final R indices [I>2σ(I)]a
R indices (all data)
1.066
R1 ) 0.0380, wR2 ) 0.1071 [6002]
R1 ) 0.0390, wR2 ) 0.1090
0.0002(10)
extinction coeff
largest diff peak and hole
0.481 and -0.789 e Å-3
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|; wR2 ) [∑[w(Fo2 - Fc2)2]/∑[wFo22]]1/2
;
+
a
respect to the formation of the metallacycle, became
quite clear upon examination of 4a . The methylene
carbon (C(20)) has taken up position between both
tertiary carbons, C(19) and C(21). The propensity for
molybdenum to form M-O bonds along with the mini-
mization of steric repulsion between the methyl groups
of acetone and the isobutene ligand in 2c during the
reaction explains the observed regioselectivity. The
Mo-N(1) distance of 1.7348(18) Å is consistent with a
metal-nitrogen triple bond,2c,d,3f,11 and the Mo-N(2)
and N(3) amide distances are within the range expected
for Mo-N single bonds.12 The Mo-O(1) distance of
1.9344(15) Å and the Mo-C(19) distance of 2.209(2) Å
are both consistent with metal-atom single bonds.25
The crystal and refinement data for 4a are summarized
in Table 2.
S ) [∑[w(Fo - Fc2)2]/(n - p)]1/2; w ) 1/[σ2(Fo2) + (0.0370p)2
0.31p], p ) [max(Fo2,0) + 2Fc2]/3.
2
When acetone was added to a dark green solution of
2a in pentane, the solution turned dark red in color.
Concentration of the pentane solution under reduced
1
pressure afforded a red solid. H NMR spectroscopy of
this product confirmed the existence of only one met-
allacycle-containing product. Pure 4b was obtained via
recrystallization from pentane at -30 °C, and the
stereochemistry of 4b was elucidated by 2-D NMR
(ghmqc, ghmbc, and NOESY). The proposed structure
for 4b is illustrated in Figure 3. Complex 4b adopts a
five-coordinate square pyramidal geometry very similar
to that of 4a . Of interest in 4b is the position of the
C(H)Ph fragment, once part of the coordinated styrene
in 2a . The carbon atom of this fragment is bound to the
molybdenum center, and the phenyl group occupies an
F igu r e 3. Proposed structure for 4b assigned via ghmbc,
ghmqc, and NOESY. Some of the observed NOES are
1
shown with arced lines. The observed H NMR resonances
are assigned to their corresponding protons.
equatorial position in reference to the metallacycle.
Steric constraints during the reaction of 2a with ace-
tone most likely dictate the ultimate configuration of
this metallacycle. Similar intramolecular coupling reac-
tions with in situ generated early metal metallocenes
(e.g., Cp2Ti, Cp2Zr, and Cp2Hf) have been extensively
(25) Cantrell, G. K.; Geib, S. J .; Meyer, T. Y. Organometallics 1999,
18, 4250. (b) Cantrell, G. K.; Geib, S. J .; Meyer, T. Y. Organometallics
2000, 19, 3562. (c) Schrock, R. R.; Luo, S.; Lee, J . C.; Zanetti, N. C.;
Davis, W. M. J . Am. Chem. Soc. 1996, 118, 3883.

2038 Organometallics, Vol. 20, No. 10, 2001
Cameron et al.
explored.2b,26 Recent developments in this field involve
the titanium-catalyzed cyclization of enones mediated
by silanes27 and titanium-based applications toward the
synthesis of γ-butyrolactones.28 We are currently in the
process of examining the reactivity of these olefin
complexes with various unsaturated organic substrates.
158.1, 158.8, (six peaks are obscured by overlap with C6D6 and
other aromatic resonances). HRMS calcd for [M + H]+:
544.1506. Found (LSIMS): 544.1569.
R ) CH2CH2CH3 (2b). The volume of the pentane extract
was reduced to 10 mL and then cooled to -78 °C for 2 h. Dark-
green microcrystals appeared, and after filtration, [Mo(NPh)-
(η2-propene)(o-(Me3SiN)2C6H4)] (2b ) was obtained as micro-
crystals (isolated yield 68%). 1H NMR (C6D6): δ 0.32 (27H,
NSiMe3), 0.36 (9H, NSiMe3), 0.45 (m, 1H, CH2CHCH3), 0.90
(ov, m, 4H, CH2CHCH3), 1.34 (m, 1H, CH2CHCH3), 2.40 (d,
3H, CH2CHCH3), 2.81 (m, 1H, CH2CHCH3), 3.32 (m, 1H,
CH2CHCH3), 4.01 (m, 1H, CH2CHCH3), 6.8-7.5 (aromatics).
13C NMR (C6D6): δ 1.5, 1.5, 1.6, 1.9, 20.0, 26.3, 56.8, 57.9, 64.2,
73.6, 123.7, 123.8, 124.2, 124.4, 124.6, 124.7, 124.8, 125.0,
125.2, 129.4, 129.5, 129.8, 130.9, 140.0, 158.3, 158.6 (four peaks
are obscured by overlap with C6D6 and other aromatic reso-
nances).
R ) CH2C(CH3)2 (2c). The pentane was removed from the
mixture under reduced pressure. This allowed [Mo(NPh)(η2-
isobutene)(o-(Me3SiN)2C6H4)] (2c) to be isolated as a thick,
dark-green oil. Further attempts to obtain 2c as a solid were
not successful (isolated yield 72%). 1H NMR (C6D6): δ 0.29
(9H, NSiMe3), 0.36 (9H, NSiMe3), 0.73 (ov, m, 4H, CH2C(CH3)2),
2.60 (s, 3H, CH2C(CH3)2), 2.99 (d, 1H, CH2C(CH3)2), 6.88 (t,
1H, N-Ph imido para proton), 7.00 (m, 2H, (Me3Si)2-pda
aromatic protons), 7.07 (t, 2H, N-Ph imido meta protons), 7.41
(m, 4H, (Me3Si)2-pda aromatic protons and N-Ph imido ortho
protons). 13C NMR (C6D6): δ 1.4, 2.0, 27.9, 33.8, 59.3, 81.3,
123.5, 123.9, 124.4, 124.7, 125.0, 125.3, 129.4, 132.2, 133.1,
158.2.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were conducted under a
dry argon atmosphere using standard Schlenk techniques, and
all compounds were handled in a nitrogen-filled drybox. All
solvents were distilled under nitrogen from sodium or sodium
benzophenone ketyl, stored over molecular sieves, and de-
gassed prior to use.
NMR spectra were obtained on a Varian Gemini 300, VXR
300, or Mercury 300 instrument with C6D6 or CDCl3 as
solvents, as noted, and referenced to residual solvent peaks.
An Inova 500 was used as indicated.
Compound 1, [Mo(NPh)Cl2(o-(Me3SiN)2C6H4)‚THF], was
synthesized following published procedures.10 Ethylene was
predried using 4 Å molecular sieves. All other reagents were
obtained from Aldrich Chemicals and stored over 4 Å molec-
ular sieves when necessary.
Complete Analysis Laboratories (Parsippany, NJ ) performed
elemental analyses. It was impossible to obtain satisfactory
elemental analyses on these compounds, and typically results
were ca. 1% lower than the theoretical values. Related
compounds are known to form carbides and nitrides upon
pyrolysis, and this may be responsible for the unsatisfactory
results. The 1H NMR spectra of 2a -c, 3a ,b, and 4a ,b are
included in the Supporting Information.
R ) CH2CH2CH2CH3, CH(CH3)CH2CH3, or (CH3CH2-
CH2CH2)2Mg (2d ,e). The pentane was removed from the
mixture under reduced pressure. This allowed a mixture of
[Mo(NPh)(η2-1-butene)(o-(Me3SiN)2C6H4)] (2d ) and [Mo(NPh)-
(η2-2-butene)(o-(Me3SiN)2C6H4)] (2e) to be isolated as a dark-
green oil. Further attempts to obtain either of these compounds
as solids and purify them were unsuccessful.
P r ep a r a tion of η2-Olefin Com p lexes. To an Et2O solution
of 1 (0.5 g, 0.86 mmol), cooled to -78 °C, was added dropwise
2 equiv of RMgCl (2.0 M in Et2O, 1.72 mmol, 0.86 mL) (R )
CH2CH2C6H5, CH2CH2CH3, CH2CH(CH3)2, CH2CH2CH2CH3,
CH(CH3)CH2CH3) or 1 equiv of Bu2Mg (1.0 M in heptane, 0.86
mmol, 0.86 mL), with stirring. The mixture quickly turned
from blue-purple to red. The reaction mixture was allowed to
stir at room temperature for about 2 h, during which time the
red solution changed to a forest-green-colored solution. After
this time, the diethyl ether was removed under reduced
pressure and the solids were dried for 1 h and then extracted
with pentane (3 × 25 mL).
P r ep a r a tion of [Mo(NP h )(CH2CH2CH2CH2)(o-(Me3-
SiN)2C6H4] (3a ). Meth od 1. One equivalent of BrMgCH2CH2-
CH2CH2MgBr (0.99 M in Et2O, 0.86 mmol, 0.87 mL) was added
to a diethyl ether solution of 1 (0.5 g, 0.86 mmol) cooled to
-78 °C. The blue solution quickly turned to a purple solution
upon addition of the alkylating agent. As the reaction mixture
was allowed to warm up to room temperature, the color of the
solution slowly turned red-orange. The red-orange solution was
stirred for 1 h and pumped to dryness (in vacuo). The
remaining solids were extracted with pentane and filtered. The
red-orange filtrate was pumped to dryness and dried overnight
R
) CH2CH2C6H5 (2a ). The volume of the combined
pentane extracts was reduced to 10 mL and then cooled to -78
°C for 2 h. Forest-green crystals appeared at the bottom of
the flask, after which the mixture was filtered to yield [Mo-
(NPh)(η2-styrene)(o-(Me3SiN)2C6H4)] (2a ) as a green crystalline
solid. Additional crops (usually two) can be crystallized from
the mother liquors, affording 2a in 77% isolated yield. Anal.
Calcd for C26H35N3Si2Mo‚0.32(CH3(CH2)3CH3): C, 58.49; H,
6.86; N, 7.42. Found: C, 57.46; H, 6.52; N, 8.05. 1H NMR
(C6D6): δ 0.09 (9H, NSiMe3), 0.29 (9H, NSiMe3), 0.36 (9H,
NSiMe3), 0.41 (9H, NSiMe3), 1.05 (m, 1H, CH2CHPh), 1.16
(m, 1H, CH2CHPh), 2.22 (t, 1H, CH2CHPh), 3.38 (m, 1H,
CH2CHPh), 3.54 (m, 1H, CH2CHPh), 4.90 (t, 1H, CH2CHPh),
5.94 (d, 2H, styrene ortho protons), 6.6-7.5 (aromatics). 13C
NMR (C6D6): δ 1.6, 1.6, 1.9, 2.0, 51.2, 53.1, 67.6, 74.5, 123.6,
123.8, 123.9, 124.0, 124.2, 124.3, 124.7, 125.1, 125.3 (ov), 125.5,
125.6, 125.8, 128.5, 129.0, 129.5, 130.8, 131.2, 144.5, 147.3,
1
(in vacuo). By H NMR spectroscopy, metallacyclopentane 3a
was obtained in low purity and yield.
Meth od 2. To a cooled (-78 °C) diethyl ether solution of 1
(0.5 g, 0.86 mmol), was added 2 equiv of EtMgCl (2.0 M in
Et2O, 1.7 mmol, 0.86 mL). Reaction workup, similar to that
described in method 1, provided both metallacyclopentane 3a
and oligomeric 3b in low purity.
Meth od 3. To a Schlenk tube containing a cooled (-78 °C)
diethyl ether solution of 1 (1.0 g, 0.86 mmol) was added
dropwise 2 equiv of EtMgCl (2.0 M in Et2O, 1.7 mmol, 0.86
mL). The solution quickly changed color from blue to purple.
This purple solution was frozen and the vessel evacuated.
Subsequently, the solution was allowed to thaw, while the neck
of the vessel was degassed for 5 min using dry ethylene.
Ethylene was added to the Schlenk tube (1-2 atm) and the
solution stirred for 1 h at room temperature. The resulting
red-orange solution was pumped to dryness (in vacuo), followed
by extraction with pentane. The volume of the filtrate was
reduced and the concentrated solution cooled to -78 °C. This
afforded dark-red crystals, which were isolated by filtration
(0.58 g) in 69% isolated yield. Further purification of 3a was
done by recrystallization from pentane at -78 °C. Anal. Calcd
for C22H35N3Si2Mo: C, 53.52; H, 7.14; N, 8.51. Found: C, 52.67;
(26) Reviews: (a) Broene, R. D.; Buchwald, S. L. Science 1993, 261,
1696. (b) Negishi, E. Chem. Scr. 1989, 29, 457. (c) Negishi, E.;
Takahashi, T. Acc. Chem. Res. 1994, 27, 124.
(27) Kablaoui, N. M.; Buchwald, S. L. J . Am. Chem. Soc. 1995, 117,
6785. (b) Kablaoui, N. M.; Buchwald, S. L. J . Am. Chem. Soc. 1996,
118, 3182. (c) Crowe, W. E.; Rachita, M. J . J . Am. Chem. Soc. 1995,
117, 6787.
(28) Kablaoui, N. M.; Hicks, F. A.; Buchwald, S. L. J . Am. Chem.
Soc. 1996, 118, 5818. (b) Crowe, W. E.; Vu, A. T. J . Am. Chem. Soc.
1996, 118, 1557.

Molybdenum(IV) Olefin Complexes
Organometallics, Vol. 20, No. 10, 2001 2039
1
H, 7.11; N, 8.44. H NMR (C6D6): δ 0.32 (18H, NSiMe3), 1.53
125.4, 125.5, 125.8, 128.7, 139.5, 145.7, 156.7. HRMS calcd
for [M + H]+: 554.1926 m/e. Found (LSIMS): 554.1948 m/e.
P r ep a r a t ion of [Mo(NP h )(C(H )P h CH 2C(CH 3)2O)(o-
(Me3SiN)2C6H4] (4b). Acetone (0.022 g, 0.38 mmol) was added
to a stirring green solution of 2a (0.20 g, 0.38 mmol) in 50 mL
of pentane at room temperature. The color of the reaction
mixture immediately changed from green to red. The resulting
pentane solution was concentrated in vacuo and cooled at -30
°C for 2 days, affording red microcrystals, which were isolated
by filtration and dried in vacuo. Additional crops can be
crystallized from the mother liquors, affording 4b in 78%
isolated yield. 1H NMR (C6D6; 500 MHz; from ghmbc and
ghmqc): δ -0.06 (9H, SiMe3), 0.38 (9H, SiMe3), 0.78 (Me), 1.47
(Me), 2.56 (m, 2H), 3.16 (“t”, 14.5 Hz, 1H), 6.85 (t of t, 7.5 Hz,
1.0 Hz, N-Ph imido para proton), 6.91 (t of t, 7.5 Hz, 1.0 Hz,
metallacycle phenyl para proton), 7.02 (d of d of d, 8 Hz, 7 Hz,
1.5 Hz, (Me3Si)2-pda aromatic proton), 7.09 (t, 8 Hz, N-Ph imido
meta protons), 7.10 (ov, (Me3Si)2-pda aromatic proton), 7.17
(t, 7.5 Hz, metallacycle phenyl meta protons), 7.30 (d of
d, 8 Hz, 1 Hz, metallacycle phenyl ortho protons), 7.32 (d of d,
8.5 Hz, 1.0 Hz, (Me3Si)2-pda aromatic proton), 7.40 (d of d,
(Me3Si)2-pda aromatic proton) 7.47 (d of d, 8.5 Hz, 1.0 Hz, N-Ph
imido ortho protons). 13C (C6D6; 500 MHz; from ghmbc and
ghmqc): δ -0.1, 1.0, 28.0, 32.4, 56.2, 76.7, 86.4, 121.2, 123.6,
123.7, 123.8, 124.3, 125.6, 127.6, 128.0, 128.2, 128.9, 133.2,
140.3, 154.0, 156.2. HRMS calcd for [M]+: 601.1844 m/e. Found
(LSIMS): 601.1869.
(m, 2H), 2.01 (m, 2H,), 2.64 (m, 2H), 3.13 (m, 2H), 6.90 (t, 1H,
N-Ph imido para proton), 7.05 (m, 2H, (Me3Si)2-pda aromatic
protons), 7.10 (t, 2H, N-Ph imido meta protons), 7.42 (m, 2H,
(Me3Si)2-pda aromatic protons), 7.50 (m, 2H, N-Ph imido ortho
protons). 13C NMR (C6D6): δ 1.0, 36.3, 57.3, 123.3, 124.5, 125.1,
125.6, 129.0, 133.4.
P r ep a r a tion of [Mo(NP h )(o-(Me3SiN)2C6H4)]x (3b). An
excess of lutidine (5 equiv) was added to a stirring green
pentane solution (20 mL) of 2b (0.5 g, 1.0 mmol). After 2 h of
stirring the solvents were removed under vacuum, affording
a black solid. This black solid was washed with cold pentane
and dried in vacuo (Isolated yield 68%). 1H NMR (C6D6): δ
0.85 (18H, NSiMe3), 6.30 (d, 2H), 7.60 (d, 2H), 7.99 (d, 2H),
8.12 (t, 1H), 8.43(d, 2H).
P r ep a r a tion of [Mo(NP h )(η2-eth ylen e)(o-(Me3SiN)2-
C6H4)(P Me3)2] (3c). A small excess of PMe3 (17 mg, 0.223
mmol) was added to a C6D6 solution of 3a (50 mgs, 0.101 mmol)
and heated to 80 °C, affording 3c in low purity and yield.
Alternatively, 3c was prepared in low purity and yield by
reacting 2 equiv of EtMgCl with 1 (Et2O, -78 °C) while in the
presence of slightly more than 2 equiv of PMe3. Evidence for
1
the formulation of 3c comes from comparison of the H NMR
spectrum with that of the tungsten analogue.9,23 Selected 1H
NMR (C6D6): δ 0.46 (br, 18H, SiMe3), 0.95 (br, 18H, PMe3),
2.22 (br, d, 2H), 2.66 (br, d, 2H).
P r ep a r a t ion of [Mo(NP h )(C(CH 3)2CH 2C(CH 3)2O)(o-
(Me3SiN)2C6H4] (4a ). Acetone (0.037 g, 0.65 mmol) was added
to a stirring green solution of 2c (0.32 g, 0.65 mmol) in 50 mL
of pentane at room temperature. The color of the reaction
mixture immediately changed from green to purple. The
resulting pentane solution was concentrated in vacuo and
cooled at -30 °C for 2 days, affording purple microcrystals,
which were isolated by filtration and dried in vacuo. Additional
crops can be crystallized from the mother liquors, affording
4a in 78% isolated yield. Anal. Calcd for C25H41N3Si2OMo: C,
Ack n ow led gm en t. We thank the National Science
Foundation (CHE 9523279) for funding of this work.
K.A.A. thanks the NSF and the University of Florida
for funding X-ray equipment purchases.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, anisotropic thermal parameters, and bond lengths
1
and angles for 2a and 4a as well as H NMR spectra of 2a -c,
1
54.42; H, 7.49; N, 7.62. Found: C, 53.27; H, 8.01; N, 7.96. H
3a ,b, and 4a ,b. The NOE difference spectrum associated with
2a . This material is available free of charge via the Internet
at http://pubs.acs.org.
NMR (CDCl3): δ 0.27 (9H, SiMe3), 0.28 (9H, SiMe3), 0.53 (Me),
0.95 (Me), 1.26 (Me), 1.86 (Me), 2.08 (d, 13 Hz, C(H)), 2.99 (d,
13 Hz, C(H)), 6.9-7.4 (aromatic protons, 9H). 13C NMR: δ 0.5,
3.3, 30.8, 31.4, 34.4, 39.5, 67.8, 78.0, 83.8, 119.7, 120.9, 122.0,
OM000758R