Synthesis, fluxionality, and propene insertion reactions of zirconium boryldiene complexes with sterically undemanding Cp ligands

Article abstract of DOI:10.1021/om990859t

The reduction of Cp^RZrCl₃(dme) (Cp^R = Cp (a), C₅H₄SiMe₃ (b), C₅H₄Me (c), Ind (d)) with sodium amalgam in the presence of isoprene, followed by the addition of allylmagnesium chloride, gives the diene complexes Cp^RZr(η1-allyl)(η⁴-isoprene) (2a-d). The preparations are conveniently carried out as one-pot reactions. The reaction of 2a-d with B(C₆F₅)₃ in toluene solution at -78°C proceeds quantitatively to give the thermally unstable zwitterionic complexes Cp^RZr(η³-allyl){η¹:η ³-CH₂CMeCHCH₂B(C₆F₅) ₃} (3a-d), which on warming decompose under C-H activation and propene elimination to give Cp^RZr(C₆F₅){η⁴-CH ₂-CMeCHCHB(C₆F₅)₂} (4a-d). The complexes are stabilized by the coordination of one o-F atom of a boryl-C₆F₅ ring to the metal center. Compounds 4 are fluxional. The rotation of the Zr-C₆F₅ ligand is influenced by the steric demand of the Cp ligands (ΔG^≠ = 43-49 kJ mol^-1), while there is little variation in the rotational barriers of the B-C₆F₅ substituents (ΔG^≠ = ca. 47 kJ mol^-1). Recrystallization of 4a from diethyl ether affords the 16-electron complex 4a·OEt₂, in which fluorine coordination is replaced by an ether ligand. The structure of this complex has been determined; unlike its C₅Me₅ and C₅H₃(SiMe₃)₂ congeners, it shows the boryldiene moiety to occupy a prone (endo) conformation. Propene inserts into the CH₂ terminus of the boryldiene ligand under ambient conditions to give the metallacycles Cp^R-Zr(C₆F₅){η¹:η ³-CH₂CH(Me)-CH₂C(Me)CHCHB(C₆F ₅)₂} (5a-d), with complete regioselectivity and very high stereoselectivity. The insertion process is reversible; propene extrusion occurs via β-alkyl elimination from the major chair conformation isomer.

Full text of DOI:10.1021/om990859t

1150
Organometallics 2000, 19, 1150-1159
Syn th esis, F lu xion a lity, a n d P r op en e In ser tion Rea ction s
of Zir con iu m Bor yld ien e Com p lexes w ith Ster ica lly
Un d em a n d in g Cp Liga n d s
Marco M. Corradi, Gerardo J ime´nez Pindado, Mark J . Sarsfield,
Mark Thornton-Pett, and Manfred Bochmann*
School of Chemistry, University of Leeds, Leeds, U.K. LS2 9J T
Received October 26, 1999
The reduction of CpRZrCl3(dme) (CpR ) Cp (a ), C5H4SiMe3 (b), C5H4Me (c), Ind (d )) with
sodium amalgam in the presence of isoprene, followed by the addition of allylmagnesium
chloride, gives the diene complexes CpRZr(η3-allyl)(η4-isoprene) (2a -d ). The preparations
are conveniently carried out as one-pot reactions. The reaction of 2a -d with B(C6F5)3 in
toluene solution at -78 °C proceeds quantitatively to give the thermally unstable zwitterionic
complexes CpRZr(η3-allyl){η1:η3-CH2CMeCHCH2B(C6F5)3} (3a -d ), which on warming de-
compose under C-H activation and propene elimination to give CpRZr(C6F5){η4-CH2-
CMeCHCHB(C6F5)2} (4a -d ). The complexes are stabilized by the coordination of one o-F
atom of a boryl-C6F5 ring to the metal center. Compounds 4 are fluxional. The rotation of
the Zr-C6F5 ligand is influenced by the steric demand of the Cp ligands (∆Gq ) 43-49 kJ
mol-1), while there is little variation in the rotational barriers of the B-C6F5 substituents
(∆Gq ) ca. 47 kJ mol-1). Recrystallization of 4a from diethyl ether affords the 16-electron
complex 4a ‚OEt2, in which fluorine coordination is replaced by an ether ligand. The structure
of this complex has been determined; unlike its C5Me5 and C5H3(SiMe3)2 congeners, it shows
the boryldiene moiety to occupy a prone (endo) conformation. Propene inserts into the CH2
terminus of the boryldiene ligand under ambient conditions to give the metallacycles CpR-
Zr(C6F5){η1:η3-CH2CH(Me)-CH2C(Me)CHCHB(C6F5)2} (5a -d ), with complete regioselectivity
and very high stereoselectivity. The insertion process is reversible; propene extrusion occurs
via â-alkyl elimination from the major chair conformation isomer.
We have recently reported the reaction of diene half-
pentadienyl ligands (CpR ) C5H5 (Cp), C5H4SiMe3 (Cp′),
sandwich complexes of group 4 metals with B(C6F5)3 to
give zwitterionic bis(allylic) complexes of type A.1,2
These electron-deficient compounds may be regarded as
stabilized analogues of the 14-electron [CpZr(allyl)2]+
cation3 and show good activity for the polymerization
of ethene to high-molecular-weight polymers.1a,b With
bulky cyclopentadienyl ligands (e.g., Cp′′ ) 1,3-C5H3-
(SiMe3)2) and methyl substituents on the dienyl moiety,
the zwitterions A are readily isolable as crystalline
solids; they are, however, sufficiently reactive to un-
dergo well-defined decomposition reactions to boryldiene
complexes B and, subsequently, to borole complexes C
(Scheme 1).4 We now report the reactions of B(C6F5)3
with the analogous diene complexes CpRZr(η3-allyl)(η4-
diene),5,6 which have sterically less demanding cyclo-
C5H4Me (CpMe), indenyl (Ind)).
Resu lts a n d Discu ssion
Reduction of the trichloride complexes CpRZrCl3(dme)
(1; CpR ) Cp (a ), Cp′ (b), CpMe (c), Ind (d )) with sodium
amalgam in the presence of isoprene, followed by the
addition of allylmagnesium chloride, gives the diene
complexes CpRZr(η3-allyl)(η4-isoprene) (2a -d ) as dark
red to maroon crystalline solids (2a ,b,d ) or a maroon
oil (2c) in good yields. The preparations are conveniently
carried out as one-pot reactions. The reactions of 2a -d
with B(C6F5)3 in toluene solution at -78 °C proceed
quantitatively to give the thermally unstable zwitteri-
onic complexes CpRZr(η3-allyl){η1:η3-CH2CMeCHCH2B-
1
(C6F5)3} (3a -d ), which were characterized by H and
13C NMR spectroscopy (Scheme 2).7,8 In contrast to the
Cp′′ analogue reported earlier,1a the new compounds
2a -d are thermally very sensitive; they were generated
(1) (a) J ime´nez Pindado, G.; Thornton-Pett, M.; Bouwkamp, M.;
Meetsma, A.; Hessen, B.; Bochmann, M. Angew. Chem., Int. Ed. Engl.
1997, 36, 2358. (b) J ime´nez Pindado, G.; Thornton-Pett, M.; Bochmann,
M. J . Chem. Soc., Dalton Trans. 1997, 3115. (c) J ime´nez Pindado, G.;
Thornton-Pett, M.; Hursthouse, M. B.; Coles, S. J . J . Chem. Soc.,
Dalton Trans. 1999, 1663.
(2) Bochmann, M. Top. Catal. 1999, 7, 9.
(3) For related hafnium systems see: Hessen, B.; van der Heijden,
H. J . Organomet. Chem. 1997, 534, 237.
(4) J ime´nez Pindado, G.; Lancaster, S. J .; Thornton-Pett, M.; Boch-
mann, M. J . Am. Chem. Soc. 1998, 120, 6816.
(5) Erker, G.; Berg, K.; Benn, R.; Schroth, G. Chem. Ber. 1985, 118,
1383.
(6) Erker, G.; Kru¨ger, C.; Mu¨ller, G. Adv. Organomet. Chem. 1985,
24, 1.
(7) For related complexes see: (a) Temme, B.; Erker, G.; Karl, J .;
Luftmann, H.; Fro¨hlich, R.; Kotila, S. Angew. Chem. 1995, 107, 1867;
Angew. Chem., Int. Ed. Engl. 1995, 34, 1755. (b) Temme, B.; Karl, J .;
Erker, G. Eur. J . Chem. 1996, 2, 919. (c) Karl, J .; Erker, G.; Fro¨hlich,
R. J . Organomet. Chem. 1997, 535, 59. (d) Karl, J .; Erker, G. Chem.
Ber. 1997, 130, 1261. (e) Karl, J .; Erker, G.; Fro¨hlich, R.; Zippel, F.;
Bickelhaupt, F.; Schreuder Goedheijt, M.; Akkerman, O. S.; Binger,
P.; Stannek, J . Angew. Chem., Int. Ed. Engl. 1997, 36, 2771. (f) Karl,
J .; Dahlmann, M.; Erker, G.; Bergander, K. J . Am. Chem. Soc. 1998,
120, 5643.
10.1021/om990859t CCC: $19.00 © 2000 American Chemical Society
Publication on Web 02/24/2000

Zirconium Boryldiene Complexes with Cp Ligands
Organometallics, Vol. 19, No. 6, 2000 1151
Sch em e 1
Sch em e 2
4a ,b in toluene solution were followed by NMR spec-
troscopy under a number of reaction conditions, there
was no evidence for detectable amounts of borole
products.
Complexes 4a -d are highly fluxional in solution. Two
of the three C6F5 rings (structure D, rings 1 and 2) show
hindered rotation, and therefore the appearance of up
to 13 19F NMR resonances could be expected. At room
temperature, the 19F NMR spectrum of 4a exhibits 7
distinct 19F signals, whereas at -75 °C, this number
has increased to 11, 2 of which overlap and represent
two F atoms.
and handled in solution at temperatures below -50 °C
1
but could not be isolated. The H and 13C NMR spec-
troscopic data of all new compounds are collected in
Table 1.
When they are warmed to room temperature, 3a -d
undergo a clean decomposition reaction, consisting of
activation of a C-H bond of the B-CH2 moiety and
elimination of a molecule of propene, with the simulta-
neous migration of one of the B-C6F5 groups from boron
to the metal center, to give the complexes 4a -d as red
to maroon crystalline solids (Scheme 2).
These complexes are stable up to ca. 70 °C in solution.
We have reported earlier that boryldiene complexes with
Cp′′ ligands undergo a rearrangement to give borole
complexes of type C (Scheme 1). However, this reaction
appears to be restricted to bulky cyclopentadienyl
compounds;9 although the decomposition reactions of
The nature of the fluxionality exhibited by 4a is
conveniently elucidated by variable-temperature 19F
NMR spectroscopy. At -75 °C in toluene-d8, the o-F
atoms of the Zr-C6F5 ligand (ring 1, o(1)) are observed
at relatively high frequencies, δ -108.4 and -122.9. The
o(2) 19F resonances of ring 2 are also observed at this
temperature as two magnetically distinct environments
at δ -131.6 and -171.0. The high-field shift of δ -171.0
is consistent with the coordination of one o-F atom of
ring 2 to the metal center; rotation of this ring is
therefore highly hindered. Ring 3, by contrast, still
exchanges rapidly at -75 °C, as shown by the single
o(3)-F resonance at δ -130.2. Cooling to -90 °C is
required to slow the rotation of ring 3 about the B-C6F5
bond sufficiently to give two extremely broad, overlap-
ping o(3) 19F resonances at δ -130.2 and -131.7.
The observation of hindered rotation of the Zr-C6F5
unit (ring 1) may be explained as the result of steric
interaction between C6F5 and the Cp ligand. o-F coor-
dination, analogous to that of Zr‚‚‚Fo(2), seems unlikely
due to geometry constraints at the metal center, and
(8) For other examples of zwitterionic complexes of early transition
metals containing borato ligands see: (a) Braunschweig, H.; Wagner,
T. Chem. Ber. 1994, 127, 1613. (b) Bochmann, M.; Lancaster, S. L.;
Robinson, O. B. J . Chem. Soc., Chem. Commun. 1995, 2081. (c) Bohra,
R.; Hitchcock, P. B.; Lappert, M. F.; Au-Leung, S. F.; Leung, W. P. J .
Chem. Soc., Dalton Trans. 1995, 2999. (d) Ruwwe, J .; Erker, G.;
Fro¨hlich, R. Angew. Chem., Int. Ed. Engl. 1996, 35, 80. (e) Song, X.;
Bochmann, M. J . Organomet. Chem. 1997, 545-546, 597. (f) Sun, Y.;
Spence, R. E. v. H.; Piers, W. E.; Parvez, M.; Yap, G. P. A. J . Am.
Chem. Soc. 1997, 119, 5132. (g) Lancaster, S. J .; Thornton-Pett, M.;
Dawson, D. M.; Bochmann, M. Organometallics 1998, 17, 3829. (h)
Ahlers, W.; Erker, G.; Fro¨hlich, R. Eur. J . Inorg. Chem. 1998, 889. (i)
Piers, W. E. Chem. Eur. J . 1998, 4, 13, (j) Piers, W. E.; Sun, Y.; Lee,
L. W. M. Top. Catal. 1999, 7, 133, and references therein.
(9) C5Me5 derivatives are converted to borole complexes in a reaction
similar to the Cp′′ analogues: Hessen, B. Personal communication.

1152 Organometallics, Vol. 19, No. 6, 2000
Ta ble 1. 1H a n d 13C NMR Sp ectr oscop ic Da ta for New Zir con iu m Ha lf-Sa n d w ich Com p lexes
1H NMR 13C NMR
Corradi et al.
complex
δ
assgnt
δ
assgnt
Cp′Zr(η-C3H5)(η4-C4H5Me-2)
(2b) (C6D6)
-0.64 (d, 1H, J ) 7.4 Hz)
-0.57 (t, 1H, J ) 8.8 Hz)
0.26 (s, 9H)
1.28 (d, 1H, J ) 14.7 Hz)
1.59 (d, 1H, J ) 14.6 Hz)
1.60 (m, 1H)
dCH2 anti
dCH2 anti
SiMe3
0.4
26.4
46.1, 50.6
57.0, 59.3
110.1
111.9
116.6
117.4
123.5
SiMe3
diene Me
Zr-CH2
anti CH of C3H5
anti CH of C3H5
syn CH of C3H5
diene Me
syn CH of C3H5
2 dCH2 syn
diene CH
CH of C3H5 & 2,5 Cp H
3,4 Cp H
dCH2 anti
CH2 of C3H5
diene CH
C2,5 of C5H4
C3,4 of C5H4
C1 of C5H4
diene CMe
CH of C3H5
1.89 (s, 3H)
2.01 (m, 3H)
&
5.14 (t, 1H, J ) 9.9 Hz)
5.99 (m, 3H)
6.50 (m, 2H)
-0.67 (d, 1H, J ) 7.8 Hz)
-0.61 (d, 1H, J ) 8.8 Hz)
1.18 (d, 1H, J ) 14.7 Hz)
1.46 (d, 1H, J ) 14.7 Hz)
1.56 (d, 1H, J ) 9.1 Hz)
1.82 (s, 3H)
125.3
CpMeZr(η-C3H5)(η4-C4H5Me-2)
(2c) (C6D6)
15.6
26.1
46.0, 50.2
57.2, 59.4
108.0
108.7
109.8
110.7
123.8
Cp Me
diene Me
Zr-CH2
CH2 of C3H5
C2,5 of C5H4
C1 of C5H4
C3,4 of C5H4
diene CH
diene CMe
CH of C3H5
dCH2 anti
anti CH of C3H5
anti CH of C3H5
syn CH of C3H5
diene Me
dCH2 syn
Cp Me
syn CH of C3H5
diene CH
2,5 Cp H
1.86 (m, 2H)
1.96 (s, 3H)
2.00 (m, 1H)
5.07 (t, 1H, J ) 9.8 Hz)
5.88 (t, 2H, J ) 2.5 Hz)
5.91 (tt, 1H, J c,a ) 14.7,
J c,s ) 9.1 Hz)
125.5
CH of C3H5
6.04 (m, 2H)
3,4 Cp H
dCH2 anti
dCH2 anti
anti CH of C3H5
anti CH of C3H5
syn CH of C3H5
dCH2 syn
diene Me
syn CH of C3H5
diene CH
(Ind)Zr(η-C3H5)(η4-C4H5Me-2)
(2d ) (C6D6)
-0.42 (d, 1H, J ) 7.4 Hz)
-0.37 (d, 1H, J ) 7.4 Hz)
-0.03 (d, 1H, J ) 14.7 Hz)
0.39 (d, 1H, J ) 14.6 Hz)
1.66 (d, 1H, J ) 9.3 Hz)
1.77 (m, 2H)
26.1
diene Me
Zr-CH2
CH2 of C3H5
C2,4 of C5H3
diene CH
45.4, 49.2
62.5, 64.2
96.4, 96.7
109.7
115.8
C3 of C5H3
C6,9 of C6 ring
C1,5 of C6 ring
C7,8 of C6 ring
CH of C3H5
1.79 (s, 3H)
123.2, 123.3
123.6, 123.7
125.3, 125.4
126.2
2.13 (d, 1H, J ) 9.3 Hz)
4.98 (t, 1H, J ) 9.7 Hz)
5.90 (tt, 1H, J c,a ) 14.6,
J c,s ) 9.3 Hz)
6.67 (m, 2H), 6.78 (m, 1H)
6.87 (m, 2H)
CH of C3H5
Cp H
C6 ring
7.30 (m, 2H)
C6 ring
CpZr(η-C3H5){η3-CH2CMeCH-
CH2B(C6F5)3} (3a ) (C7D8, -50 °C)
-1.63 (d, 1H, J ) 13.8 Hz)
-1.33 (s, 1H)
0.79 (m, 1H)
0.95 (m, 2H)
1.08 (s, 3H)
B-CH2 anti
B-CH2 syn
Zr-CH2 anti
anti & syn CH2 of C3H5
diene Me
25.2
28.2 (br)
59.7
64.0, 70.5
103.7
112.2
diene Me
B-CH2
Zr-CH2
CH2 of C3H5
diene CH
Cp
2.30 (d, 1H, J ) 6.3 Hz)
Zr-CH2 syn
anti & syn CH2 of C3H5
diene CH
2.45 (m, 2H)
135.4
CH of C3H5
4.62 (d, 1H, J ) 14.4 Hz)
5.56 (s, 5H)
Cp
5.58 (m, 1H)
CH of C3H5
B-CH2 anti
B-CH2 syn
SiMe3
Zr-CH2 anti and anti &
syn CH2 of C3H5
diene Me
Cp′Zr(η-C3H5){η3-CH2CMeCH-
CH2B(C6F5)3} (3b) (C7D8, -50 °C)
-1.51 (d, 1H, J ) 14.3 Hz)
-0.94
24.1
27.7 (br)
60.1
64.0, 71.7
104.4
112.9, 116.6, 120.0
121.7
SiMe3
-1.35 (s, 1H)
diene Me
B-CH2
Zr-CH2
CH2 of C3H5
diene CH
Cp
-0.07 (s, 9H)
0.90 (m, 3H)
0.99 (s, 3H)
2.36 (d, 1H, J ) 6.9 Hz)
Zr-CH2 syn
anti & syn CH2 of C3H5
diene CH
2.55 (m, 2H)
4.62 (d, 1H, J ) 14.7 Hz)
5.42, 5.80, 6.04, 6.33 (m,
1H each)
135.5
CH of C3H5
Cp H
5.70 (m, 1H)
CH of C3H5
B-CH2 anti
B-CH2 syn
Zr-CH2 anti and anti &
syn CH2 of C3H5
diene Me
CpMeZr(η-C3H5){η3-CH2CMeCH-
CH2B(C6F5)3} (3c) (C7D8, -50 °C)
-1.55 (d, 1H, J ) 14.7 Hz)
-1.20 (s, 1H)
0.81 (m, 3H)
14.9
Cp Me
25.2
26.5 (br)
59.5
64.3, 71.2
103.8
111.2, 112.0,
112.7, 112.9
135.6
diene Me
B-CH2
Zr-CH2
CH2 of C3H5
diene CH
Cp
0.99 (s, 3H)
1.45 (s, 3H)
Cp Me
2.10 (d, 1H, J ) 6.6 Hz)
2.43 (d, 1H, J ) 15.0 Hz)
2.60 (d, 1H, J ) 8.1 Hz)
4.63 (d, 1H, J ) 14.7 Hz)
5.35 (m, 2H), 5.56 (m, 2H)
5.69 (m, 1H)
Zr-CH2 syn
anti CH2 of C3H5
syn CH2 of C3H5
diene CH
Cp H
CH of C3H5
CH of C3H5

Zirconium Boryldiene Complexes with Cp Ligands
Organometallics, Vol. 19, No. 6, 2000 1153
Ta ble 1. (Con tin u ed )
1H NMR
13C NMR
comp lex
δ
assgnt
δ
assgnt
(Ind)Zr(η-C3H5){η3-CH2CMeCH-
CH2B(C6F5)3} (3d ) (C7D8, -50 °C)
-1.14 (d, 1H, J ) 14.7 Hz)
-0.93 (s, 1H)
-0.13 (d, 1H, J ) 13.2 Hz)
0.12 (d, 1H, J ) 15.0 Hz)
0.92 (m, 1H)
B-CH2 anti
B-CH2 syn
anti CH2 of C3H5
anti CH2 of C3H5
Zr-CH2 anti
diene Me
syn CH2 of C3H5
Zr-CH2 syn
syn CH2 of C3H5
diene CH
CH of C3H5
H of C5 ring
H of C6 ring
H of C6 ring
Zr-CH2 anti
diene Me
22.5 (br)
25.1
58.0
70.5, 78.8
97.0, 99.2, 117.6
108.8
124.7, 124.9, 125.4,
125.8, 126.0, 126.9
137.7
B-CH2
diene Me
Zr-CH2
CH2 of C3H5
C of C5 ring
diene CMe
C of C6 ring
1.01 (s, 3H)
1.30 (m, 1H)
2.09 (d, 1H, J ) 6.6 Hz)
2.80 (d, 1H, J ) 8.1 Hz)
4.65 (d, 1H, J ) 14.7 Hz)
5.70 (m, 1H)
5.82, 6.14, 6.27 (s, 1H each)
6.61 (m, 3H)
7.42 (d, 1H, J ) 8.1 Hz)
0.06 (d, 1H, J ) 9.7 Hz)
1.37 (s, 3H)
2.13 (d, 1H, J ) 10.8 Hz)
2.90 (d, 1H, J ) 12.0 Hz)
5.89 (d, 1H, J ) 11.9 Hz)
6.09 (s, 5H)
diene CH
CpZr(C6F5){η4-CH2CMeCH-
CH2B(C6F5)2} (4a ) (C6D6)
26.4
72.8
98.4
114.0
115.2
121.6
-2.1
26.9
71.3
diene Me
Zr-CH2
B-CH
Zr-CH2 syn
B-CH
Cp
diene CH
Cp
diene CMe
diene CH
SiMe3
Cp′Zr(C6F5){η4-CH2CMeCH-
CH2B(C6F5)2} (4b) (C6D6)
-0.10 (s, 9H)
SiMe3
Zr-CH2 anti
diene Me
Zr-CH2 syn
B-CH
Cp H
diene CH
Cp H
Zr-CH2 anti
diene Me
Cp Me
Zr-CH2 syn
B-CH
diene CH & 2 Cp-H
Cp H
Zr-CH2 anti
diene Me
Zr-CH2 syn
Zr-CH
diene CH
C5 ring
C6 ring
C6 ring
C6 ring
C5 ring
0.28 (d, 1H, J ) 9.4 Hz)
diene Me
Zr-CH2
B-CH
1.36 (s, 3H)
2.13 (d, 1H, J ) 9.0 Hz)
3.03 (d, 1H, J ) 12.0 Hz)
5.65 (m, 1H)
5.89 (d, 1H, J ) 12.3 Hz)
6.43, 6.55, 7.23 (m, 1H each)
0.06 (d, 1H, J ) 10.5 Hz)
1.35 (s, 3H)
97.1
114.3, 116.3,
118.6, 121.8
120.2
Cp
diene CH
CpMeZr(C6F5){η4-CH2CMeCH-
CH2B(C6F5)2} (4c) (C6D6)
14.0
26.5
73.2
97.7
112.3, 112.5,
114.4, 115.2
120.8
26.6
76.8
Cp Me
diene Me
Zr-CH2
B-CH
Cp
1.56 (s, 3H)
2.12 (d, 1H, J ) 9.6 Hz)
2.96 (d, 1H, J ) 11.8 Hz)
5.84 (m, 3H)
6.04, 6.07, 6.25 (m, 1H each)
-0.62 (d, 1H, J ) 9.3 Hz)
1.12 (s, 3H)
1.43 (d, 1H, J ) 9.2 Hz)
3.23 (d, 1H, J ) 12.0 Hz)
5.53 (d, 1H, J ) 11.7 Hz)
5.98 (m, 1H), 6.20 (m, 1H)
6.41 (t, 1H, J ) 7.2 Hz)
6.59 (t, 1H, J ) 7.2 Hz)
6.88 (d, 1H, J ) 8.1 Hz)
7.07 (m, 1H)
diene CH
diene Me
Zr-CH2
Zr-CH
(Ind)Zr(C6F5){η4-CH2CMeCH-
CH2B(C6F5)2} (4d ) (C6D6)
94.1
97.2, 105.2
115.6, 118.8
120.9
121.8
124.8, 124.9
126.8, 128.5
C5 ring
C5-C6 bridge
diene CH
C5 ring
C6 ring
C6 ring
7.43 (d, 1H, 8.1)
C6 ring
no evidence for such an interaction has been found in
the crystallographically characterized 1,3-C5H3(SiMe3)2
and C5Me5 analogues.1a,b Further information regarding
the dynamic processes was obtained through a line-
shape analysis study. Warming a solution of 4a in
toluene-d8 from -75 to +60 °C results in the broaden-
ing, coalescence, and finally sharpening of both the o(1)
and o(2) 19F resonances. Thus, the two o(1) 19F signals
at δ -108.4 and -122.9 coalesce at -25 °C, and further
warming results in the formation of a single, sharp
resonance signal at δ -117.7. A similar, albeit slower,
process is observed for the o(2) resonances, which
coalesce at higher temperature (+10 °C) and at 60 °C
give a broad 19F signal at δ -148.1. This signal sharpens
on warming above 60 °C, although a large amount of
decomposition is also observed.
ment over the temperature range -75 to +60 °C. The
resulting thermodynamic parameters are shown in
Table 3.
The activation barriers in 4a -d for the rotation of
the B-C6F5 bonds, as derived from analysis of the
coalescence of the o(2) 19F resonance signals, are quite
similar to one another, with ∆Gq values of ca. 46 kJ
mol-1, and a corresponding similarity in the coalescence
temperatures, Tc (Table 3). From the o-fluoride inter-
change in the 18-electron bis-Cp system Cp2Zr{η3-CH2-
CHCHCH2B(C6F5)3}, Erker et al.10 have estimated the
strength of the Zr-F interaction to be in the region of
35 kJ mol-1. The higher interchange barrier found here
for 4 suggests rather stronger Zr-F coordination, in
agreement with the greater electron deficiency of these
16-electron complexes.
The rotational barriers of the Zr-C6F5 bonds vary to
a much greater extent. Given that the hindered rotation
about the Zr-C6F5 axis arises through steric interaction
between the cyclopentadienyl ring and the C6F5 moiety,
Compounds 4b-d exhibit behavior identical with that
of 4a . The 19F NMR chemical shifts for all four com-
plexes at both high and low temperatures are almost
identical (Table 2).
Rate constants for the fluxional processes in com-
(10) Karl, J .; Erker, G.; Fro¨hlich, R. J . Am. Chem. Soc. 1997, 119,
pounds 4a -d were measured by full line-shape treat-
11165.

1154 Organometallics, Vol. 19, No. 6, 2000
Corradi et al.
a higher activation barrier to rotation is observed for
complexes with more sterically demanding cyclopenta-
dienyl rings. Thus, for the least hindered compound 4a
the barrier to interconversion is ∆Gq(248 K) ) 43 kJ
mol-1, whereas compound 4b, with arguably the most
bulky ligand of the series (Cp′), has ∆Gq(273 K) ) 49
kJ mol-1
.
We found earlier that the Cp′′ derivative Cp′′Zr-
(C6F5){η4-CH2CMeCHCHB(C6F5)2} exists as a mixture
of two conformational isomers, resulting from prone
(endo) and supine (exo) orientation of the diene ligand
with respect to the cyclopentadienyl ring.1b The activa-
tion barrier for the prone/supine interchange has been
calculated as ∆Gq(233 K) ) 47 kJ mol-1. Analysis of the
19F NMR spectra of the Cp′ complex 4b affords evidence
that this compound also exists as a mixture of two such
isomers, with a coalescence temperature similar to that
of the Cp′′ derivative, although in this instance the
relative amount of the second isomer is small (1:50).
Recrystallization of 4a from diethyl ether afforded
crystals of CpZr(C6F5){η4-CH2CMeCHCHB(C6F5)2}-
(OEt2) (4a ‚OEt2) (eq 1).
The structure was solved by X-ray diffraction (Figure
1). In contrast to the analogous Cp′′ and C5Me5 com-
plexes, which do not bind ether, the less hindered
structure of 4a allows the entry of a diethyl ether ligand
into the coordination sphere of zirconium, to give a 16-
electron complex with a distorted-octahedral environ-
ment. In consequence, there is no coordination to an o-F
atom of one of the C6F5 substituents, as shown by the
long Zr‚‚‚o-F distances (Zr‚‚‚F(7) ) 3.700 Å, Zr‚‚‚F(11)
) 3.213 Å). The Zr-O bond of 2.3699(13) Å is signifi-
cantly longer than that in the related cationic hafnium
complex [Cp′′Hf(η4-C4H4Me2-2,3)(OEt2)]+ (2.148(2) Å).1c
Unlike Cp′′Zr(C6F5){η4-CH2CMeCHCHB(C6F5)2}, the
boryldiene unit in 4a ‚OEt2 adopts a prone (endo)
orientation (E). The diene conformations are most
probably a consequence of the steric requirements of the
cyclopentadienyl ligands; in previous crystal structures
of compounds of type 4 the supine conformation (F , for
Cp′′)1c and a diene orientation roughly perpendicular to
the cyclopentadienyl ligand (G, for C5Me5)1a had been
established.

Zirconium Boryldiene Complexes with Cp Ligands
Organometallics, Vol. 19, No. 6, 2000 1155
Ta ble 3. Th er m od yn a m ic Da ta for Zir con iu m
Bor yld ien e Com p lexes
a partial BdC double bond (H) to the bonding of the
metallacyclopentene unit (I).
∆Gq at Tc
∆Hq
∆Sq
Tc (°C)
(kJ mol-1
)
(kJ mol-1
)
(J K-1 mol-1
)
compd o(1) o(2) o(1) o(2) o(1) o(2)
o(1)
o(2)
4a
4b
4c
4d
-25
0
-15
-2
10
10
12
5
43
49
45
48
47
47
45
46
48
49
46
44
53
58
57
55
21
2
5
21
39
42
32
-12
P r op en e In ser tion Rea ction s. The reaction of
2a -d with B(C6F5)3 to give 4a -d generates 1 equiv of
propene as the byproduct. If the reaction proceeds in
vacuo, this propene is removed as it is liberated, and
complexes 4a -d are isolated in high yields. On the other
hand, if the propene is not removed, 4a -d are converted
slowly into new products, arising from the insertion of
propene into the least hindered CH2 terminus of the
boryldiene ligand, to afford the metallacyclic complexes
5a -d (Scheme 2).
The same complexes are also accessible from isolated
4a -d and propene. Treatment of a toluene solution of
CpZr(C6F5){η4-CH2CMeCHCHB(C6F5)2} (4a ) with ca. 1
equiv of propene at -30 °C, subsequent warming to
room temperature, and further stirring for 2 days
affords a pale yellow solution, containing the propene
insertion complex CpZr(C6F5){η1:η3-CH2CH(Me)CH2-
CMeCHCHB(C6F5)2} (5a ). Compound 5a was purified
by repeated recrystallizations as a pale yellow powder
which was characterized spectroscopically. Repeated
attempts to obtain crystalline material were unsuccess-
F igu r e 1. Molecular structure of CpZr(C6F5){η4-CH2-
CMeCHCHB(C6F5)2}(OEt2) (4a ‚OEt2), showing the atomic
numbering scheme. Ellipsoids are drawn at the 40%
probability level. Selected bond lengths (Å) and angles
(deg): Zr-C(6) ) 2.379(2), Zr-O(1) ) 2.3699(13), Zr-C(12)
) 2.344(2), Zr-C(13) ) 2.507(2), Zr-C(15) ) 2.466(2), Zr-
C(16) ) 2.425(2), C(12)-C(13) ) 1.421(3), C(13)-C(15) )
1.387(3), C(15)-C(16) ) 1.441(3), C(16)-B(1) ) 1.483(3),
B(1)-C(111) ) 1.591(3), B(1)-C(121) ) 1.602(3); O(1)-Zr-
C(6) ) 78.78(5), O(1)-Zr-C(12) ) 81.05(5), C(12)-Zr-C(6)
) 123.84(7), C(12)-Zr-C(16) ) 78.53(6), Zr-C(6)-C(7) )
131.36(14), Zr-C(6)-C(11) ) 115.79(13), C(12)-C(13)-
C(15) ) 122.3(2), C(13)-C(15)-C(16) ) 127.2(2), C(15)-
C(16)-B(1) ) 123.3(2), C(16)-B(1)-C(111) ) 122.9(2),
C(16)-B(1)-C(121) ) 122.4(2).
1
ful. The assignment of the H and 13C NMR resonances
(Table 4) was aided by the use of 13C-INEPT (1J (1H-
13C) couplings are listed in Table 4) and 1H-13C cor-
relation NMR experiments.
The room-temperature 19F NMR spectrum of 5a
exhibits nine resonance signals. The broad resonances
at δ -123.1 and -133.3 sharpened on warming the
sample from 24 to 54 °C. The former resonance was
assigned as the o-F of the Zr-C6F5 moiety (cf. ring 1 in
compound 4a ), while the latter is due to the o-F signal
of the B-C6F5 unit coordinated to the Zr center (cf. ring
2 in compound 4a ).
Yamamoto et al.11 pointed out that in the titanium
complexes Cp*TiCl(η4-diene) with a supine conformation
the TiC4 moieties are best described as σ2,π-metallacy-
clopentenes, while complexes with a prone conformation
have almost pure Ti(II) π-diene character. In contrast,
the bond length distribution within the boryldiene
ligand of the prone complex 4a ‚OEt2 is very similar to
that found in supine zirconium and hafnium com-
pounds, e.g. Cp′′Zr(C6F5){η4-CH2CMeCHCHB(C6F5)2},
and forms a σ2,π-metallacyclopentene.
The Zr-C6F5 and one of the B-C6F5 rings are parallel
to each other, in π-stacking fashion. The B-C(16) bond
of 1.483(3) Å is significantly shorter than the B-C6F5
bond distances of 1.591(3) and 1.602(3) Å and is short
also compared to other B-C(sp2) distances such as in
{C5H4-B(C6F5)2}TiCl3 (1.549(5) Å).12 As indicated
previously,1a this shortening may be explained by the
contribution of a zwitterionic resonance structure with
The insertion of propene to give 5a proceeds best on
a small scale, preferably as an NMR tube reaction; e.g.,
the reaction of 70 mg of 4a with propene in a 5 mm
NMR tube is complete after ca. 7 h to give a clean
sample of 5a . Reactions on a larger scale, however,
which require prolonged stirring under 1 bar of propene
to achieve complete conversion of 4a , were accompanied
by the formation of side products which proved difficult
to remove and required several recrystallization steps;
these were identified mainly as propene oligomers.
Thus, the reaction of a red solution of 4a with a
continuous stream of propene for ca. 3 h afforded a pale
yellow solution, the 13C{1H} NMR spectrum of which
exhibited numerous resonance signals, including those
of atactic polypropylene (δ 18-21, 29-30, 45-47). There
(13) For single propene insertion reactions with cationic Zr com-
plexes see: (a) Pellecchia, C.; Grassi, A.; Zambelli, A. J . Chem. Soc.,
Chem. Commun. 1993, 947. (b) Pellecchia, C.; Immirzi, A.; Zambelli,
A. J . Organomet. Chem. 1994, 479, C9. (c) Pellecchia, C.; Grassi, A.;
Zambelli, A. Organometallics 1994, 13, 298. (d) Thorn, M. G.; Etheridge,
Z. C.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1998, 17, 3636.
(e) Dahlmann, M.; Erker, G.; Nissinen, M.; Fro¨hlich, R. J . Am. Chem.
Soc. 1999, 121, 2820.
(11) Yamamoto, H.; Yasuda, H.; Tatsumi, K.; Lee, K.; Nakamura,
A.; Chen, J .; Kai, Y.; Kasai, N. Organometallics 1989, 8, 105.
(12) Duchateau, R.; Lancaster, S. J .; Thornton-Pett, M.; Bochmann,
M. Organometallics 1997, 16, 4995.

1156 Organometallics, Vol. 19, No. 6, 2000
Corradi et al.
Ta ble 4. 1H a n d 13C NMR Sp ectr oscop ic Da ta for Cp Zr (C6F 5){CH2CH(Me)CH2C(Me)CHCHB(C6F 5)2} (5a -A)
δ(1H)
assgnt
δ(13C)
assgnt
2
3
-0.58 (1H, dd, J ) 15.0, J ) 12.2 Hz)
Zr-CHaHbCH(Me)CH2-
26.1 (1J CH ) 126 Hz)
Zr-CHaHbCH(Me)CH2-;
Zr-CHB(C6F5)2-HC(Me)-
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHB(C6F5)2CHC(Me)-
C5H5
Zr-CHB(C6F5)2CHC(Me)-
Zr-CHB(C6F5)2; Zr-C6F5
Zr-CHB(C6F5)2CHC(Me)-
3
0.74 (3H, d, J ) 6.17 Hz)
Zr-CHaHb-CH(Me)CH2-
Zr-CHB(C6F5)2CHC(Me)-
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHB(C6F5)2CHC(Me)-
C5H5
30.8 (1J CH ) 130 Hz)
44.0 (1J CH ) 129 Hz)
87.9 (1J CH ) 122 Hz)
100.5 (1J CH ) 130 Hz)
113.5 (1J CH ) 175 Hz)
128.3 (1J CH ) 155 Hz)
134.0-152.2
1.53 (3H, s)
1.60 (1H, m, br)
1.71 (1H, m)
1.80 (2H, s)
3
3.30 (1H, d, J ) 16.8 Hz)
6.03 (5H, s)
3
6.18 (1H, d, J ) 16.8 Hz)
Zr-CHB(C6F5)2CHC(Me)-
152.8
Ta ble 5. 1H NMR Sp ectr oscop ic Da ta for th e P r op en e In ser tion Com p lexes 5a -d
δ(1H)
assgnt
5a
5b
5c
5d
2
2
2
2
Zr-CHaHbCH(Me)CH2-
-0.58 (dd, J ) 15.0,
-0.58 (dd, J ) 15.0,
-0.50 (dd, J ) 14.6,
-0.42 (dd, J ) 15.0,
3J ) 12.2 Hz)
3J ) 12.2 Hz)
3J ) 11.2 Hz)
3J ) 11.7 Hz)
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHaHbCH(Me)CH2-
Zr-CHB(C6F5)2CHC(Me)-
Zr-CHB(C6F5)2CHC(Me)-
Zr-CHB(C6F5)2CHC(Me)-
1.60
1.71
n/o
n/o
n/o
n/o
n/o
n/o
3
3
3
3
0.74 (d, J ) 6.2 Hz)
0.73 (d, J ) 5.7 Hz)
0.75 (d, J ) 6.2 Hz)
0.83 (d, J ) 6.2 Hz)
1.80
n/o
n/o
n/o
3
3
3
3
3.30 (d, J ) 16.8 Hz)
6.18 (d, J ) 16.8 Hz)
3.24 (d, J ) 16.6 Hz)
6.22 (d, J ) 16.6 Hz)
3.31 (d, J ) 16.3 Hz)
6.18 (d, J ) 16.3 Hz)
3.27 (d, J ) 16.5 Hz)
6.20 (d, J ) 16.5 Hz)
3
3
3
3
1.53
1.66 (s)
1.58 (s)
1.62 (s)
Sch em e 3
are a number of reports of stoichiometric propene
insertions into M-R bonds of cationic group 4 com-
plexes.10,13 It has also been shown that neutral Zr-alkyl
species, Cp*ZrR(diene), are capable of ethene oligomer-
ization;14 in this case, however, the insertion process
involves the Zr-alkyl bond and not the diene ligand.
On the other hand, ethene is capable of inserting into
the M-CH2 bonds of some titanium and zirconium diene
complexes, and the titanium-catalyzed coupling reac-
tions of dienes with 1-alkenes no doubt involve related
seven-membered metallacyclic intermediates.15
The formation of propene oligomerization byproducts
prevented the isolation of 5b-d . While a number of the
1H NMR resonances characteristic of 5a were also
observed in the 1H NMR spectra of 5b-d (Table 5),
isolation of pure samples of 5b-d was not possible, even
after several recrystallizations.
Surprisingly, the insertion of propene into the Zr-
diene bond of 4a proved to be reversible. The reaction
1
may be followed by monitoring the H NMR resonance
this instance a large amount of side products arising
from the thermal decomposition of 4a were also ob-
served.
of the Zr-CHa environment of 5a (δ -0.58) with respect
to the analogous position in the starting material 4a
(Hanti ) Hd′, δ 0.06). Both resonances were calibrated
against an internal standard (the residual protons in
the C6D6 solvent at δ 7.15) to ascertain the extent of
any decomposition (Scheme 3).
At 25 °C, despite the presence of an atmosphere of
propene gas, the signals for 5a were accompanied by a
small resonance assigned to the starting material, 4a .
Warming the NMR sample to 60 °C resulted in a change
in the 4a :5a ratio from 1:17 to 1:2, with little decom-
position or side reactions. Allowing the 1:2 mixture of
4a and 5a to stand for 24 h at room temperature under
a propene atmosphere resulted in the regeneration of
5a . The process is illustrated in Figure 2. A similar
series of 1H NMR experiments, performed under nitro-
gen upon complete removal of propene, further demon-
strated the reversible nature of the reaction, with the
appearance of distinct propene resonances, although in
The reaction of propene with compound 4a is strictly
regiospecific, affording exclusively the 1,2-insertion
product. Compounds of type 4 are chiral, and careful
baseline analysis in the region of the Ha proton environ-
ment at ca. δ -0.7 revealed that the propene insertion
is highly stereospecific, giving rise to major and minor
isomers, 5a -A and 5a -B, in a ratio of about 9:1. These
isomers arise from the addition of propene to the Zr-
CH2 bond with si and re stereochemistry, respectively
(Scheme 4).
The structure of the isomers may be determined from
consideration of the coupling constants to Ha. To mini-
mize steric interaction with the cyclopentadienyl ligand,
the methyl group of the inserted propene moiety will
be equatorial in a chair (5a -A) or boat (5a -B) conforma-
tion of the metallacycle. In the former (5a -A, major
isomer), the geminal (2J gem) and vicinal (3J vic) coupling
constants to Ha (2J (Ha-Hb) and 3J (Ha-Hc)) are suf-
ficiently similar (15.0 and 12.2 Hz, respectively), so that
(14) Hessen, B.; van der Heijden, H. J . Am. Chem. Soc. 1996, 118,
11670.

Zirconium Boryldiene Complexes with Cp Ligands
Organometallics, Vol. 19, No. 6, 2000 1157
1
F igu r e 2. Stacked plot of the H NMR spectra of 5a in the Ha region of the spectrum, in C6D6 under 1 bar of propene.
Heating from 25 to 60 °C leads to an increase of the Hanti signal of 4a due to propene extrusion from 5a -A, while the
intensity of the 5a -B signal remains unaffected (a -e). The original spectrum is restored on standing at 25 °C (f). Under
these conditions, conversion of 4a to 5a remains incomplete.
Sch em e 4
the resonance is observed as a pseudo-triplet, with
further fine structure due to long-range coupling to the
stereoisomers shifted slightly, with a notable decrease
in intensity of that associated with 5a -A and a corre-
sponding increase in the intensities of those proton
environments associated with the boryldiene complex
4a , as monitored by the increase in signal intensity for
the Hanti proton of 4a at δ 0.09. When the sample was
cooled to room temperature, the ratio Ha(5a -A):Ha(5a -
B) had changed from 9:1 to 5:1 (total experiment time
2.5 h), almost exclusively through elimination of pro-
pene from 5a -A. After a further 24 h under propene,
the ratio had returned to 7:1, exclusively through
regeneration of the 5a -A isomer (Figure 2). Over this
Me protons. In the case of 5a -B, a decrease in the Ha-
3
C-C-Hc dihedral angle results in a decrease in J vic
,
)
and a doublet of doublets is observed (2J gem and J vic
3
13.7 and 7.8 Hz, respectively). 2D H-1H NOESY and
1
1
1D H NOE NMR spectroscopic data corroborated the
chair conformation of 5a -A, with notable interactions
between the Ha, Hf, and Hd/d′ proton environments and
no interaction between Hf and Hb.
When the NMR sample of 5a was warmed to 60 °C
under 1 bar of propene, the Ha resonances for both

1158 Organometallics, Vol. 19, No. 6, 2000
Corradi et al.
degassed by several freeze-thaw cycles and stored over
activated 4 Å molecular sieves. The compounds CpZrCl3(dme)
and (Ind)ZrCl3(dme) (Ind ) η5-C9H7) were prepared according
to literature procedures.18,19 Unless stated otherwise, all
chemicals were used as purchased without further purification.
Isoprene was dried over Na and freshly distilled prior to use.
The NMR spectra were recorded on a Bruker DPX300 spec-
trometer. 1H NMR spectra (300.1 MHz) were referenced to the
residual solvent protons of the deuterated solvent used; 13C
NMR spectra (75.4 MHz) were referenced internally to the
D-coupled 13C resonances of the NMR solvent; 19F NMR spectra
(282.2 MHz) were referenced externally to CFCl3.
time period, only a very small amount of decomposition
was observed.
It is thus apparent that an equilibrium exists between
4a and 5a under the conditions of the NMR experiment.
Both stereoisomers, 5a -A and 5a -B, are formed in the
initial reaction of 4a with propene, and warming the
NMR sample causes propene extrusion preferentially
from 5a -A via â-alkyl elimination. The ratio 5a -A:5a -B
thus changes, but this is due solely to propene elimina-
tion from the A isomer, and not due to rearrangement
to isomer B. Related â-alkyl elimination reactions,
notably â-methyl eliminations, are rare in d0 systems
but have been observed as chain transfer reactions in
some cationic metallocene alkyl complexes and in olefin
polymerization systems.16
The deinsertion of propene has been proposed to
explain the isomerization of the propene insertion
products obtained from the reaction of rac-[C2H4(Ind)2-
Zr(η2-pyridyl)][MeB(C6F5)3] with propene.17 These sys-
tems exhibit â-alkyl elimination at 80 °C, whereupon
the kinetic products isomerize to give the thermody-
namic mixtures. In the system described here such
equilibration experiments were prevented by the ther-
mal instability of 4a above 70 °C.
P r ep a r a tion of Cp Zr Cl3‚d m e (1a ), Cp ′Zr Cl3‚d m e (1b),
Cp MeZr Cl3‚d m e (1c), a n d (In d )Zr Cl3‚d m e (1d ). These com-
plexes were prepared by following the procedure by Lund and
Livinghouse for the synthesis of CpZrCl3(dme).18 A typical
preparative route is given below for the synthesis of 1c. A
suspension of freshly sublimed ZrCl4 (22.0 g, 94 mmol) in CH2-
Cl2 (200 mL) was treated with SMe2 (12.0 g, 194 mmol) at 0
°C. After the mixture was warmed to room temperature, C5H4-
Me(SiMe3) (14.5 g, 95 mmol) was added dropwise and the
reaction mixture stirred for 16 h. The pale green suspension
was treated with dme (100 mL) until all the solid had
dissolved. The solvent was then removed in vacuo, and the
resulting white-green solid washed with dme (3 × 30 mL) and
dried to afford 1c as an off-white powder (28.2 g, 82%).
1
Cp ′Zr Cl3‚d m e (1b). H NMR (C6D6, 24 °C): δ 0.49 (s, 9H,
SiMe3), 3.28 (s, br, 10H, dme), 6.52 (t, 2H, J ) 2.5 Hz, Cp),
6.73 (t, 2H, J ) 2.5 Hz, Cp). 13C NMR (C6D6, 24 °C): δ 0.41
(SiMe3), 64.3 (OMe), 72.5 (OCH2), 122.0 (Cp), 126.1 (Cp). Anal.
Found (calcd) for C12H23O2Cl3SiZr: C, 33.8 (33.9); H, 5.3 (5.5).
Cp MeZr Cl3‚d m e (1c). 1H NMR (C6D6, 24 °C): δ 2.42 (s, 3H,
Me), 3.36 (s, br, 10H, dme), 6.26 (m, 4H, Cp). 13C NMR (C6D6,
24 °C): δ 16.6 (Me), 64.6 (OMe), 73.4 (OCH2), 118.2 (Cp), 120.5
(Cp). Anal. Found (calcd) for C10H17O2Cl3Zr: C, 32.2 (32.7);
H, 4.6 (4.7).
P r ep a r a tion of Cp Zr (η3-C3H5)(η4-C4H5Me-2) (2a ). This
compound was prepared by modification of a literature pro-
cedure.5 To a Schlenk tube charged with a freshly prepared
sodium amalgam (1% Na, 1.0 g, 43 mmol) and isoprene (1.45
g, 21 mmol) in thf (60 mL) at -78 °C was added a warm thf
solution (250 mL) of CpZrCl3‚dme (7.5 g, 21 mmol), with the
immediate formation of a pale yellow slurry. The reaction
mixture was warmed to room temperature and stirred for 12
h to afford a dark purple solution over pale gray solids. The
solution was filtered and cooled to -78 °C, and a solution of
MgCl(C3H5) in thf (2.0 M, 11.0 mL, 22 mmol) was added
dropwise. An immediate color change to dark brown was
observed. The reaction mixture was warmed to room temper-
ature and stirred for a further 3 h. The solvent was removed
in vacuo to yield a sticky brown solid, which was extracted
into light petroleum (3 × 50 mL). The resulting dark red
solution was concentrated to ca. 50 mL and cooled to -30 °C
to afford 2a as a red crystalline solid (3.4 g, 13 mmol, 61%).
Anal. Found (calcd) for C13H18Zr: C, 57.8 (58.8); H, 6.8 (6.8).
Con clu sion
The thermal stability of zwitterionic zirconium half-
sandwich complexes of type A (Scheme 1) is strongly
dependent on the steric requirements of the cyclopen-
tadienyl ligands. Derivatives with the less bulky Cp
ligands described here, CpR ) C5H5, Cp′, CpMe, Ind, are
themally labile and readily undergo C-H activation to
afford σ2,π-boryldiene complexes. The crystal structure
of the C5H5 complex shows that, unlike more bulky
congeners, the diene ligand adopts a prone conforma-
tion. In contrast to the 1,3-C5H3(SiMe3)2 analogues,
these complexes do not undergo a rearrangement to
borole complexes C. However, a highly regio- and
stereoselective propene insertion reaction is observed
to give new metallacycles. The insertion is reversible
and involves a â-alkyl elimination pathway, preferen-
tially from the stereoisomer with chair conformation.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under an atmosphere of dry nitrogen using standard Schlenk
line techniques. Solvents were distilled under nitrogen from
sodium (toluene, 1,2-dimethoxyethane (dme)), sodium-ben-
zophenone (thf), sodium-potassium alloy (light petroleum; bp
40-60 °C), or CaH2 (CH2Cl2). Deuterated solvents were
By the procedure for 2a , compounds 2b-d were prepared
similarly.
(15) (a) Hill, J . E.; Balaich, G. J .; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1991, 10, 3428. (b) Erker, G.; Engel, K.; Dorf, U.;
Atwood, J . L.; Hunter, W. E. Angew. Chem., Int. Ed. Engl. 1982, 21,
914. (c) Balaich, G. J .; Hill, J . E.; Waratuke, S. A.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1995, 14, 656.
(16) (a) Eshuis, J . J . W.; Tan, Y. Y.; Teuben, J . H.; Renkema, J . J .
Mol. Catal. 1990, 62, 277. (b) Eshuis, J . J . W.; Tan, Y. Y.; Meetsma,
A.; Teuben, J . H.; Renkema, J .; Evens, G. G. Organometallics 1992,
11, 362. (c) Resconi, L.; Piemontesi, F.; Franciscono, G.; Abis, L.;
Fiorani, T. J . Am. Chem. Soc. 1992, 114, 1025. (d) Mise, T.; Kageyama,
A.; Miya, S.; Yamazaki, H. Chem. Lett. 1991, 1525. (e) Kesti, M. R.;
Waymouth, R. M. J . Am. Chem. Soc. 1992, 114, 3565. (f) Yang, X.;
J ia, L.; Marks, T. J . J . Am. Chem. Soc. 1993, 115, 3392. (g) Horton, A.
D. Organometallics 1996, 15, 2675. (h) Resconi, L.; Camurati, I.;
Sudmeijer, O. Top. Catal. 1999, 7, 145 and references therein.
(17) Dagorne, S.; Rodewald, S.; J ordan, R. F. Organometallics 1997,
16, 5541.
Cp ′Zr (η-C3H5)(η4-C4H5Me-2) (2b): red crystalline solid (6.3
g, 75%). Anal. Found (calcd) for C16H26SiZr: C, 56.9 (56.9); H,
7.9 (7.8).
Cp MeZr (η-C3H5)(η4-C4H5Me-2) (2c): maroon oil (3.2 g,
76%). Anal. Found (calcd) for C14H20Zr: C, 57.3 (60.2); H, 7.1
(7.2).
(In d )Zr (η-C3H5)(η4-C4H5Me-2) (2d ); maroon microcrystal-
line solid (1.20 g, 25%). Anal. Found (calcd) for C17H20Zr: C,
64.5 (64.7); H, 6.3 (6.4).
(18) Lund, E. C.; Livinghouse, T. Organometallics 1990, 9, 2426.
(19) Shaw, S. L.; Morris, R. J .; Huffman, J . C. J . Organomet. Chem.
1995, 489, C4.

Zirconium Boryldiene Complexes with Cp Ligands
Organometallics, Vol. 19, No. 6, 2000 1159
P r ep a r a t ion of Cp R Zr (η-C3H 5){η4-CH 2CMeCH CH 2B-
(C6F 5)3} (Cp R ) Cp (3a ), Cp ′ (3b), Cp Me (3c), In d (3d )). A
typical preparative route is given below for the synthesis of
3a . To an NMR tube charged with 2a (20 mg, 75 µmol) in
toluene-d8 (0.3 mL) and cooled to -78 °C was carefully added
a toluene-d8 solution (0.3 mL) of B(C6F5)3 (38 mg, 75 µmol).
An immediate color change from red to clear orange was
observed. Compound 3a was identified as the sole reaction
product by low-temperature 1H and 13C{1H} NMR spectros-
copy.
at -30 °C afforded 5a as a pale yellow powder (0.12 g, 0.15
mmol, 38%). The compound retained small quantities of
propene oligomers (cf. Supporting Information, Figure S-1),
which prevented accurate elemental analyses. The compound
was identified by NMR spectroscopy. 19F NMR (282.2 MHz,
C6D6, 24 °C): δ -123.1 (s, br, Fo(1)), -129.0 (d, J ) 21 Hz, 2F,
F
o(3)), -133.3 (m, 2F, Fo(2)); p-F, -123.1 (t, J ) 21 Hz, 1F),
-152.9 (t, J ) 21 Hz, 1F), -153.3 (t, J ) 21 Hz, 1F); m-F,
-160.4 (2F), -161.2 (2F), -161.6 (2F).
Attem pted Syn th eses of Cp RZr (C6F5){η1:η3-CH2CH(Me)-
CH2C(Me)CH-CHB(C6F 5)2} (Cp R ) Cp ′ (5b), Cp Me (5c),
In d (5d )). A preparative route identical with that outlined
above for compound 5a was employed in the attempted
syntheses of compounds 5b-d . Similar color changes were
observed throughout. Pure samples of the desired products
were not isolated. The sticky powders obtained were charac-
terized as a mixture of compounds, containing the complexes
Compounds 3b-d were prepared similarly; in all cases, at
no point were the reaction vessels allowed to be above -50
°C. All attempts to isolate 3a -d resulted in propene evolution
and the formation of 4a -d .
P r ep a r a tion of Cp Zr (C6F 5){η4-CH2CMeCHCHB(C6F 5)2}
(4a ). To a Schlenk tube charged with a toluene solution (30
mL) of 2a (0.9 g, 3.40 mmol) cooled to -78 °C was added a
toluene solution (50 mL) of B(C6F5)3 (1.7 g, 3.33 mmol). An
immediate color change of red to yellow-brown was observed.
The reaction mixture was placed under reduced pressure,
warmed to room temperature, and stirred until all the volatiles
had been removed (ca. 2 h). The resulting red-brown solid was
extracted into light petroleum (3 × 50 mL). The dark red
solution obtained was concentrated to ca. 50 mL and cooled
to -30 °C to afford 4a as a red crystalline solid (1.7 g, 2.31
mmol, 68%). Anal. Found (calcd) for C28H12BF15Zr: C, 45.8
(45.7); H, 1.9 (1.6).
1
5b-d by H NMR spectroscopy.
NMR Tube Reaction of CpZr(C6F5){η4-CH2C(Me)CHCHB-
(C6F 5)2} w ith P r op en e. A 5 mm NMR tube fitted with a
PTFE valve and charged with 4a (70 mg, 95 µmol) in C6D6
(0.5 mL) was cooled to -78 °C, evacuated, and back-filled with
propene (2.8 mL, 116 µmol). The sample was warmed to room
temperature before the PTFE valve was closed.
X-r a y Cr ysta llogr a p h y. A crystal of 4a ‚OEt2 was coated
in an inert perfluoropolyether oil and mounted in a nitrogen
stream at 100(2) K on a Nonius Kappa CCD area-detector
diffractometer. Data collection was performed using Mo KR
radiation (λ ) 0.710 73 Å) with the CCD detector placed 30
mm from the sample via a mixture of 1° φ and ω scans at
different θ and κ settings using the program COLLECT.20 The
raw data were processed to produce conventional data using
the program DENZO-SMN.21 The data sets were corrected for
absorption using the program SORTAV.22 The structure was
solved by heavy-atom methods using SHELXS-9723 and refined
by full-matrix least-squares refinement (on F2) using SHELXL-
97.24 All non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were constrained
to idealized positions.
By following the procedure for 4a , compounds 4b-d were
prepared similarly. Cp ′Zr (C6F 5){η4-CH2CMeCHCHB(C6F 5)2}
(4b): maroon crystalline solid (2.4 g, 35%). Anal. Found (calcd)
for C31H20BF15SiZr: C, 46.5 (46.1); H, 2.7 (2.5).
Cp MeZr (C6F 5){η4-CH2CMeCHCHB(C6F 5)2} (4c): dark red
crystalline solid (2.5 g, 3.33 mmol, 58%). Anal. Found (calcd)
for C29H14BF15Zr: C, 47.1 (46.5); H, 2.3 (1.9).
(In d )Zr (C6F 5){η4-CH2CMeCHCHB(C6F 5)2} (4d ): dull ma-
roon solid (0.75 g, 0.96 mmol, 60%). Anal. Found (calcd) for
C
29H14BF15Zr: C, 47.0 (46.5); H, 2.3 (1.9).
P r epar ation of CpZr (C6F5){η1:η3-CH2CH(Me)CH2C(Me)-
CHCHB(C6F 5)2} (5a ). A Schlenk tube charged with a dark
red toluene solution (50 mL) of compound 4a (0.30 g, 0.41
mmol) was cooled to -30 °C, placed under vacuum for ca. 10
min, and back-filled with propene gas. The mixtures was
warmed to room temperature, sealed with 1 atm of propene
(ca. 80 mL, 3.33 mmol) above the toluene solution, and stirred
for 48 h to afford a pale yellow solution with dark brown oily
deposits. The solvent was removed in vacuo, and the resulting
orange powder was extracted into light petroleum (3 × 20 mL).
The solvent was removed in vacuo to afford a sticky pale yellow
powder, characterized as a mixture of compounds by 1H NMR
spectroscopy. Repeated recrystallization from light petroleum
Cr ysta l Da ta : C32H22BF15OZr, fw 809.53; crystal size 0.29
× 0.29 × 0.07 mm; monoclinic, space group P21/n, a ) 12.6710-
(2) Å, b ) 11.9740(1) Å, c ) 20.8219(3) Å; â ) 99.0930(8)°; V
) 3119.45(7) Å3; Z ) 4, Dcalcd ) 1.724 g cm-3; µ ) 0.470 mm-1
;
11 528 reflections collected, of which 6001 were unique (Rint
) 0.0115) and 5549 with I > 2σ(I) were observed; maximum
and minimum transmission 0.9679 and 0.8758, respectively;
final R1 (I > 2σ(I)) ) 0.0307, wR2 (all data) ) 0.0840;25
goodness of fit S ) 1.038 for 471 parameters.
Ack n ow led gm en t. This work was supported by the
Engineering and Physical Sciences Research Council.
We gratefully acknowledge fellowships by the Spanish
Ministry for Education and Culture (to G.J .P.) and by
BP-Amoco Chemicals Ltd. (to M.J .S.).
(20) Collect, Data Collection Software; Nonius BV, Delft, The
Netherlands, 1999.
(21) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter,
C. W., J r., Sweet, R. M., Eds.; Academic Press: New York, 1996; Vol.
276, pp 307-326.
(22) Blessing, R. H. Acta Crystollogr., Sect. A 1995, 51, 33.
(23) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(24) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany. 1997.
(25) R1 ) ∑(|Fo| - |Fc|)/∑|Fo|; wR2 ) [(∑w(Fo2 - Fc2)2/∑w(Fo2)2, with
w ) [σ2(Fo2) + (aP)2 + bP]-1, where a ) 0.0512, b ) 2.0350, and P )
Su p p or tin g In for m a tion Ava ila ble: Additional NMR
information and tables giving details of the X-ray structure
analysis of 4a ‚OEt2. This material is available free of charge
via the Internet at http://pubs.acs.org.
2
[2Fc + max(Fo2, 0)]/3.
OM990859T