Synthesis and characterization of highly fluorinated tungsten(II) metallacyclopropene complexes. Kinetics and mechanism of an unprecedented η2-vinyl isomerization

Organometallics 1996, 15, 1545-1564

1545

Syn th esis a n d Ch a r a cter iza tion of High ly F lu or in a ted

Tu n gsten (II) Meta lla cyclop r op en e Com p lexes. Kin etics

2

a n d Mech a n ism of a n Un p r eced en ted η -Vin yl

Isom er iza tion

†

,†

†

J aqueline L. Kiplinger, Thomas G. Richmond,* Atta M. Arif,

‡

,‡

Carlos D u¨ cker-Benfer, and Rudi van Eldik*

Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, and Institute for

Inorganic Chemistry, University of Erlangen-N u¨ rnberg, 91058 Erlangen, Germany

Received December 5, 1995^X

This report describes a novel migratory insertion reaction which leads to the formation of

2

highly fluorinated η -vinyl complexes at a tungsten(II) metal center. Insight into the nature

of this transformation was obtained by isolation and crystallographic characterization of a

kinetic intermediate in the insertion process. Ambient-temperature photolysis of a toluene

solution of the tungsten(II) tetrafluoroaryl metallacycle 2 and perfluoro-2-butyne accesses

2

the kinetic η -vinyl complex 3 in which the fluoride is trans to the inserted acetylene and

cis to both carbonyl ligands. The solid-state structure of 3 has been determined. Upon

2

heating, 3 is converted to the thermodynamic η -vinyl product 4 in which the fluoride ligands

is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand.

Detailed kinetic studies are reported for this isomerization reaction using both infrared

spectroscopy and UV-visible spectroscopy. In the absence of added ligand, this transforma-

q

tion displays first-order disappearance of 3 with ∆H ) 124((2) kJ /mol, ∆S ) +48((5)

q

3

J /(mol‚K) and ∆V ) +15.6((0.4) cm /mol. This is in accord with a limiting dissociative

mechanism. Carbon monoxide enhances the rate of isomerization and shows first-order

q

dependence in p(CO) with ∆H ) 98((3) kJ /mol, ∆S ) -5((9) J /(mol‚K), and ∆V ) +3.9-

3

q

(

)

(0.2) cm /mol. The P(OMe)

3

-promoted isomerization displays saturation behavior with ∆H

q

3

77((2) kJ /mol, ∆S ) -46((6) J /(mol‚K), and ∆V ) +5.5((0.4) cm /mol at 2.2 M P(OMe)

3

.

The negative entropy and positive volume of activation indicate that congestion is developed

in the transition state. The kinetic data for the ligand-promoted transformations are in

agreement with a mechanism involving a rapid pre-equilibrium (K) during which the adduct

species [3‚P(OMe)

this process, kobs ) Kk[P(OMe)

adduct species [3‚P(OMe) ] has been obtained. Nonlinear least-squares analysis of the kobs

versus [P(OMe)

] plot determined a K ) 1.4 ( 0.1 M and a k ) (89 ( 13) × 10

3

] is formed, followed by a rate-determining step (k) to produce 5. For

3

]/(1 + k[P(OMe) ]). Visible spectroscopic evidence for the

3

-

1

-5 -1

3

s

, such

-

3

-1 -1

that kK ) 1.2 × 10

M

s

for the adduct formation. It is unlikely that an actual 20-

2

electron species is generated since the η -vinyl ligand can conceivably change its hapticity

and function in an η mode.

1

In tr od u ction

The chemical modification and ultimate functional-

ization of fluorocarbons continues to provide a challenge

for synthetic chemists.¹Recently, we discovered a new

method for facile transformation of strong C-F bonds

into C-C bonds within the coordination sphere of a

tungsten(II) metal center by sequential C-F activation

and alkyne insertion (eq 1).²In our ongoing quest to

develop metal-based reagents for the functionalization

3

2

of fluorocarbons we uncovered an unusual η -vinyl

isomerization process.²Ambient-temperature photoly-

sis of a toluene solution of 2 and perfluoro-2-butyne

2

†

accesses the kinetic η -vinyl complex 3 in which the

fluoride is trans to the inserted acetylene and cis to both

University of Utah.

University of Erlangen-N u¨ rnberg.

Abstract published in Advance ACS Abstracts, February 15, 1996.

‡

X

2

carbonyl ligands. Upon heating, the kinetic η -vinyl

isomer 3 is smoothly converted to the thermodynamic

η -vinyl product 4 in which the fluoride ligands is now

cis to the inserted alkyne and trans to one CO and cis

(

1) Kiplinger, J . L.; Richmond, T. G.; Osterberg, C. E. Chem. Rev.

994, 94, 373-431.

2) Kiplinger, J . L.; King, M. A.; Arif, A. M.; Richmond, T. G.

Organometallics 1993, 12, 3382-3384.

3) Kiplinger, J . L.; Richmond, T. G. J . Am. Chem. Soc. 1996, 118,

805-1806.

1

(

2

(

4

1

to the second CO ligand (eq 2). To our knowledge this

0

1

546 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

indirect routes. For instance, addition of an anionic

dithiocarbamate ligand to the cationic butadienyl com-

4

+

plex [(S2CNMe2)2W(η -C4Ph4H)] results in dechelation

2

of the vinyl tail to form a neutral tungsten(IV) d vinyl-

substituted η -vinyl complex of the type (S2CNMe2)2W-

η -CPhdCPhCPhdCHPh) (eq 8). In another unusual

2

13

(

system provided the first well-defined examples of

alkyne insertion into a perfluoro aromatic carbon-metal

bond and offered a rare opportunity to examine the

2

kinetics of an η -vinyl rearrangement.

example, protonation of the carbyne complex Tp′-

In contrast to the present work, nearly all examples

t

2

(CO) MotCN(Me)(Bu ) in the presence of phenylacety-

of η -vinyl complexes are prepared by external nucleo-

2

5

lene yields the cationic η -vinyliminium complex [Tp′-

philic attack on coordinated alkyne ligands. Repre-

2

t

+

6

-8

(CO) Mo(η -C(Ph)dC(H)C(H)dN(Me)(Bu ))] which reacts

sentative complexes prepared by Templeton (eqs 3-4),

2

9

,10

11

12

with LiEt BH to form the neutral η -vinylamine com-

plex Tp′(CO)2Mo(η -C(Ph)dC(H)C(H)dN(Me)(Bu )) (eq

Green (eq 5),

Reger (eq 6), and Davidson (eq 7)

3

2

t

are shown in Scheme 1. If a metal is electronically

1

4

9

).

Sch em e 1

It is surprising that there have been no kinetic studies

2

concerning η -vinyl processes given the postulated role

of vinyl-stabilized intermediates in a variety of catalytic

1

5

2

chemical transformations and the prevalence of η -

1

6

vinyl complexes in organometallic chemistry.

Al-

2

though group VI η -vinyl systems have been the subject

of a number of dynamic nuclear magnetic resonance

studies (e.g. the classic windshield-wiper pro-

6

,9c,12c,d,14,17,18

cess),

herein we report the first detailed

(9) (a) Allen, S. R.; Green, M.; Orpen, A. G.; Williams, I. D. J . Chem.

Soc., Chem. Commun. 1982, 826-828. (b) Green, M.; Norman, N. C.;

Orpen, A. G. J . Am. Chem. Soc. 1981, 103, 1267-1269. (c) Allen, S.

R.; Beevor, R. G.; Green, M.; Norman, N. C.; Orpen, A. G.; Williams,

I. D. J . Chem. Soc., Dalton Trans. 1985, 435-450. (d) Beevor, R. G.;

Green, M.; Orpen, A.; Williams, I. D. J . Chem. Soc., Chem. Commun.

1

saturated, only the η -vinyl complex is formed.

Templeton and co-workers have elegantly demon-

strated that η -vinyl complexes can also be formed using

2

1

983, 673-675.

10) Allen, S. R.; Green, M.; Norman, N. C.; Paddick, K. E.; Orpen,

A. G. J . Chem. Soc., Chem. Commun. 1983, 1625-1633.

11) (a) Reger, D. L.; Belmore, K. A.; Mintz, E.; McElligot, P. J .

(

4) Throughout the remainder of the manuscript, for convenience,

L will refer to the ligand chelate fragment

(

Organometallics 1984, 3, 134-140. (b) Reger, D. L.; McElligot, P. J .

J . Am. Chem. Soc. 1990, 102, 5923-5924. (c) Reger, D. L. Acc. Chem.

Res. 1988, 21, 229-235.

(12) (a) Davidson, J . L.; Vasapollo, G.; Manojlovi c´ -Muir, L.; Muir,

K. W. J . Chem. Soc., Chem. Commun. 1982, 1025-1027. (b) Davidson,

J . L.; Vasapollo, G.; Manojlovi c´ -Muir, L.; Muir, K. W. J . Chem. Soc.,

Chem. Commun. 1982, 1025-1027. (c) Agh-Atabay, N. M.; Canoira,

L. J .; Carlton, L.; Davidson, J . L. J . Chem. Soc., Dalton Trans. 1991,

cis and trans describe the stereochemistry between the inserted alkyne

2

(

η -vinyl fragment) and the fluoride ligand. F

4

-Pia refers to the ligand

chelate fragment

1

175-1182. (d) Carlton, L.; Davidson, J . L. J . Chem. Soc., Dalton

Trans. 1987, 895-905.

13) Feng, S. G.; Gamble, A. S.; Templeton, J . L. Organometallics

989, 8, 2024-2031.

14) Gamble, A. S.; White, P. S.; Templeton, J . L. Organometallics

(

1

(

991, 10, 693-702.

4

(

5) For an excellent review concerning d alkyne complexes and their

(15) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;

related chemistry see: Templeton, J . L. Adv. Organomet. Chem. 1989,

Wiley: New York, 1992.

2

1

9, 1-100.

6) Feng, S. G.; Templeton, J . L. Organometallics 1992, 11, 2168-

175.

(16) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.

Principles and Applications of Organotransition Metal Chemistry, 2nd

ed.; University Science Books: Mill Valley, CA, 1987.

(17) Carlton, L.; Davidson, J . L.; Miller, J . C.; Muir, K. W. J . Chem.

Soc., Chem. Commun. 1984, 11-13.

(18) Davidson, J . L.; Wilson, W. F.; Manojlovi c´ -Muir, L.; Muir, K.

W. J . Organomet. Chem. 1983, 254, C6-C10.

(

(7) Morrow, J . R.; Tonker, T. L.; Templeton, J . L. J . Am. Chem. Soc.

985, 107, 6956-6963.

(8) Feng, S. G.; White, P. S.; Templeton, J . L. J . Am. Chem. Soc.

992, 114, 2951-2960.

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1547

2

kinetic investigation of an η -vinyl isomerization at a

(CD

CdNCH

NCH 3.04 d, 3H; NCH

(δ): NdCH 158.9 s; NCH

Hz); NCH 65.61 s; NCH 61.58 d ( J CF ) 6 Hz). C{ F} NMR

CD Cl ) (δ): CO 215.24 d ( J CF ) 13 Hz, J CW ) 136 Hz); CO

14.97 d ( J CF ) 20 Hz, J CW ) 184 Hz); WdC

2

Cl

2

) (δ): NdCH 8.83 s, 1H; CdNCH

3.95 m, 1H; NCH 3.13 m, 1H; NCH

2.55 s, 3H. C{ H} NMR (CD

2

5.05 m, 1H;

3.09 m, 1H;

Cl

3 3

53.37 s; NCH 52.48 d ( J CF ) 4

pseudo-six-coordinate tungsten(II) metal center. A por-

tion of this work has been the subject of a preliminary

2

1

3

1

3

2

)

3

_c_o_m_m_u_n_i_c_a_t_i_o_n_.2

3

13

19

2

1

(

2

(

2

Exp er im en ta l Section

2

1

R

CF

3

196.79 dq

CF ) 40 Hz, ²J CF ) 34 Hz); C

J CF 131.63 dq ( J CF ) 271 Hz,

R 3

1

2

1

Gen er a l P r oced u r es. All manipulations involving air-

sensitive reagents were performed under an atmosphere of

prepurified nitrogen using standard Schlenk techniques or a

Vacuum Atmosphere glovebox. Solvents were purified as

4

J

CF ) 29 Hz); C

â 3

â

CF

3

130.89 dq ( J CF ) 278 Hz, J CF ) 37 Hz);

2

WC

coupling, aryl carbon resonances could not be resolved.

NMR (CD Cl ) (δ): C -CF -58.32 d, 3F; C CF -59.35 d, 3F;

CF 32.4 dq ( J CF ) not resolved). Due to extensive C-F

1

9

F

2

â

3

R

3

2

follows: Tetrahydrofuran (THF) was predried with CaH and

ortho C-F -131.84 br, 1F; C-F -140.17 m, 1F; C-F -144.68

m, 1F; C-F -156.05 m, 1F; W-F -172.26 s, 1F.

P r ep a r a tion of cis-{(L)W(CO) (F )} (4). Under a nitrogen

2

distilled under nitrogen from sodium benzophenone ketyl

radical. Diethyl ether and hexanes were predried with 4 Å

molecular sieves and distilled under nitrogen from sodium

benzophenone ketyl radical. Methylene chloride was predried

atmosphere, a 100 mL glass bomb sealed with a Teflon valve

and equipped with a magnetic stir bar was cooled to -196 °C

and charged with perfluoro-2-butyne (1.38 g, 8.52 mmol). In

a separate Schlenk flask, a slurry of 2 (1.00 g, 1.87 mmol) (νCO

2 5

and distilled under nitrogen from P O . Toluene was distilled

under nitrogen from sodium metal. Trimethyl phosphite was

obtained from Aldrich, distilled from sodium metal, and stored

under nitrogen. Carbon monoxide and tert-butyl isonitrile

were obtained from commercial sources and used without

-1

2

020, 1934, 1900 cm ) in freshly distilled toluene (30 mL) was

prepared and degassed and transferred under nitrogen by

syringe to the glass bomb. The resulting bright orange

solution was degassed by three freeze-pump-thaw cycles and

warmed to room temperature. The reaction mixture was

heated to 80 °C for 7 h in an oil bath. Initial color change to

a red-orange color was observed within 30 min, and within 7

h the solution turned a maroon color. An IR spectrum of the

crude product solution confirmed the reaction was complete

1

3

further purification.

CO was obtained from Cambridge

Isotopes and used without further purification.

1

H, C{ H}, P{ H}, and 19_F_N_M_R_s_p_e_c_t_r_a_w_e_r_e_o_b_t_a_i_n_e_d

13

1

31

1

on Varian XL-300 spectrometers at 300, 75, 121, and 281 MHz,

respectively. All chemical shifts are reported in δ (ppm) units

with the following abbreviations: d ) doublet, m ) multiplet,

q ) quartet, s ) singlet, t ) triplet, and apr ) apparent.

Deuterated acetone and methylene chloride H spectra were

assigned to δ 2.04 and 5.32 ppm, and C{ H} spectra were

-1

1

(νCO 2019, 1915 cm ). Crystallization was achieved by slowly

cooling the reaction mixture to room temperature over 12 h.

The solid was collected by filtration and washed with two 20

mL portions of toluene. Isolation gave 0.89 g (1.3 mmol, 67%

yield) of an army-green powder 4: Mp 138-140 °C; IR νCO

1

3

1

9

assigned to δ 29.8 and 53.8 ppm, respectively. For F and

1

3

19

C{ F} NMR spectra, CFCl

3

was used as the external

3

1

reference at δ 0.00 ppm. For P{ H} NMR spectra 85% H

PO was used as the external reference at δ 0.00 ppm. Melting

points were obtained in open capillary tubes and reported in

C. Mass spectra were obtained by Dr. Elliot Rachlin of the

University of Utah on a Finnigan MAT 95 double-focusing

high-resolution mass spectrometer operating with ionization

by SIMS using a 20 keV Cesium gun. Elemental analyses

were performed by Atlantic Microlab, Norcross, GA, and Desert

Analytics, Tucson, AZ.

P r ep a r a tion of tr a n s-{(L)W(CO)

2

(F )} (3). Under a ni-

trogen atmosphere, a 100 mL glass bomb sealed with a Teflon

valve and equipped with a magnetic stir bar was cooled to

196 °C and charged with perfluoro-2-butyne (0.39 g, 2.4

mmol). In a separate Schlenk flask, a slurry of previously

3

-

1

(

11 2 2 11

Nujol) 2026, 1925 cm . Anal. Calcd for WC17H N O F ‚

4

1

/

2

C

7

H

8

(714.19 g/mol): C, 34.48; H, 2.12; N, 3.92; F, 29.26.

Found: C, 33.76; H, 2.02; N, 3.80; F, 28.54. Note: toluene

°

was observed in the ¹H NMR spectrum. H NMR (CD

δ): NdCH 8.82 s, 1H; CdNCH 4.77 m, 1H; CdNCH

m, 1H; NCH 2.91 m, 1H; NCH 2.61 m, 1H; NCH 3.23 s, 3H;

NCH 2.95 d, 3H. C{ H} NMR (CD Cl ) (δ): NdCH 157.2 d

CF ) 6 Hz); NCH 55.9 s; NCH 50.5 d ( J CF ) 15 Hz); NCH

2.45 s; NCH 61.08 d ( J CF ) 3 Hz). C{ F} NMR (CD

1

Cl

3.96

)

2

(

2

3

1

3

1

3

2

3

(

J

3

2

3

13

19

6

(

2

Cl

2

)

2

1

δ): CO 221.82 d ( J CF ) 5 Hz, J CW ) 142 Hz); CO 221.79

2

1

2

(

J

CF ) 55 Hz, J CW ) 150 Hz); WdC

R

CF

3

202.8 dq ( J CF ) 41

127.9 q ( J CF ) 278

CF 31.5 dq ( J CF ) not resolved). Due to extensive

1

Hz); C

Hz); WC

R

CF

3

131.2 q ( J CF ) 273 Hz); C

â

3

-

2

â

3

C-F coupling, aryl carbon resonances could not be resolved.

1

9

-1

reported 2 (0.51 g, 0.95 mmol) (νCO 2020, 1934, 1900 cm

)

1

9

F NMR (CD

apr d, 3F; ortho C-F -130.19 br, 1F; W-F -138.27 s, 1F; C-F

141.10 m, 1F; C-F -143.46 m, 1F; C-F -155.02 m, 1F.

P r ep a r a tion of cis-{(L)W(CO)(F )(P (OCH )} (5). A 100

mL Schlenk flask was charged with 3 (0.0497 g, 0.0744 mmol)

2 2 â 3 R 3

Cl ) (δ): C CF -58.88 apr t, 3F; C CF -60.80

in freshly distilled toluene (30 mL) was prepared and degassed

and transferred under nitrogen by syringe to the glass bomb.

The resulting bright orange solution was degassed by three

freeze-pump-thaw cycles and warmed to room temperature.

The reaction mixture was irradiated with a Hanovia 450 W

medium-pressure Hg lamp filtered through a Pyrex cell at a

distance of ca. 10 cm for 160 min. Initial color change to a

red-orange color was observed within 30 min, and within 160

min the solution turned a dark golden yellow color. An IR

spectrum of the crude product solution confirmed the reaction

-

3 3

)

-

1

(ν

CO 2046, 1965 cm ) and freshly distilled toluene (20 mL).

The resulting yellow solution was thoroughly degassed, and

P(OMe) (0.040 mL, 0.34 mmol) was added via syringe. Within

h at ambient temperature the solution turned an intense

magenta color. IR monitoring confirmed the reaction was

complete in 15 h (νCO 1953 cm ). The reaction solution was

filtered through Celite, and the black insoluble matter was

discarded. The toluene solvent was then removed in vacuo to

afford a gooey residue. The residue was dissolved in 20 mL

3

5

-

1

-1

was complete (νCO 2046, 1965 cm ). (Further irradiation leads

-

1

to the generation of 4 (νCO 2020, 1915 cm ) as well as

photochemical decomposition of 2.) The dark golden yellow

solution was evaporated to dryness, redissolved in CH

loaded onto a 3 in. Florisil column. A yellow band was

collected with approximately 1 L of CH Cl . Reduction of the

volume CH Cl to 15 mL and addition of hexanes and cooling

2 2

Cl , and

of CH

sequence repeated three times) to eventually afford a crystal-

line magenta solid. The crude product was then recrystallized

from Et O (5 mL)/hexanes (25 mL) at -10 °C resulting in

magenta microcrystalline 5 (0.0353 g, 59% yield): Mp 138-

2 2

Cl , and then the solvent was removed in vacuo

(

2

to -10 °C affords orange crystalline 3 in 50% yield (0.32 g,

_.₄₇_m_m_o_l₎_:_M_p₁₃₈_-₁₄₀_°_C_;_I_R_ν_C_O₍_N_u_j_o_l₎₂₀₃₆_,₁₉₅₉_c_m_-1

0

.

-

1

41 °C; IR νCO (Nujol) 1956, 1943 (sh) cm . Anal. Calcd for

Anal. Calcd for WC17

1

11 2 2

H N O F11 (668.12 g/mol): C, 30.56; H,

.66; N, 4.19. Found: C, 30.64; H, 1.67; N, 4.13. H NMR

1

5, WC19

.62; N, 3.47. Found: C, 29.02; H, 2.54; N, 3.58. H NMR

CDCl ) (δ): NdCH 8.82 s, 1H; CdNCH 5.08 m, 1H; CdNCH

.82 m, 1H; NCH 3.13 m, 1H; NCH 2.93 m, 1H; NCH 2.98

2.56 s, 3H; P(OCH 3.34, d ( J PH ) 11 Hz), 9H.

H

20

F

11

N

2

O

4

P‚ /

2 2 2

CH Cl (806.62 g/mol): C, 29.04; H,

1

2

(

3

2

(

19) (a) Osterberg, C. E.; King, M. A.; Arif, A. M.; Richmond, T. G.

Angew. Chem., Int. Ed. Engl. 1990, 29, 888-890. (b) Richmond, T. G.

Coord. Chem. Rev. 1990, 105, 221-250.

2

3

d, 3H; NCH

3

3 3

)

1

548 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

1

3

1

) (δ): CO 235.60 pair of d (²J CF ) 12

67.15

53.05 s;

3

C{ H} NMR (acetone-d

6

and the highest peak in the final map was 1.499 e/Å (about

1.05 Å from the W atom).

2

1

Hz, J CP ) 7 Hz, J CW ) 146 Hz); NdCH 160.17 s; NCH

s; NCH

P(OCH

2

3

2

62.30 d ( J CF ) 7 Hz); NCH

3

53.32 s; NCH

3

X-r a y Str u ctu r e of cis-{(L)W(CO) (F )} (4). A dark red

2

)

52.61 apr q; P(OCH

3

)

3

52.19 dd (²J CP ) 7 Hz, J CF

4

)

prism was obtained by slow crystallization from a toluene

solution of 4 at room temperature. Data were collected at

ambient temperature on an Enraf-Nonius CAD-4 diffractome-

ter with Mo KR radiation, using the ω-2θ scan technique

(4.00° < 2θ < 50.00°) for a crystal of dimensions 0.32 mm ×

0.25 mm × 0.15 mm, mounted on a glass fiber.

3

1

2

3

Hz). P{ H} NMR (acetone-d

PF ) 8 Hz, J PW ) 621 Hz). F NMR (acetone-d

-51.14 dd ( J PF ) 8 Hz, J FF ) 27 Hz), 3F; C

6

) (δ): 146.25 dd ( J PF ) 81 Hz,

4

1

19

J

6

) (δ): C

R

-

4

6

CF

3

â

CF -55.93

3

6

s, 3F; ortho C-F -131.35 m ( J FF ) 27 Hz), 1F; C-F -142.89

apr pair of d, 1F; C-F -149.70 apr t, 1F; C-F -159.04 apr t,

1

2

13

19

F; W-F -177.49 d ( J PF ) 81 Hz), 1F. C{ F} NMR (CDCl

δ): WdC

3

)

Cell constants were obtained from 25 reflections with 10°

< 2θ < 25°. The space group (P 1h , No. 2) was determined from

least-squares refinement. Standard reflections showed no

decay during data collection. Lorentz, polarization, and

empirical absorption (ψ scans) corrections were applied.

Of 4384 reflections collected at ambient temperature, 4068

were unique; 3700 of these had I > 3σ(I) and were used in the

solution and refinement as detailed above. Final refinement

included all non-hydrogen atoms as anisotropic contributions

and hydrogens as fixed isotropic contributions. All the hy-

drogen atoms were located and their positions refined. For

(

R

CF

3

189.45 m (due to extensive C-P and C-F

multiplets could not be resolved); C CF 131.46

CF 31.28 m (due to extensive C-P

and C-F coupling the C multiplets could not be resolved);

133.20 q ( J CF ) 277 Hz) (due to extensive C-F coupling

phenyl carbon resonances could not be resolved); P(OCH

coupling the C

R

3

1

q ( J CF ) 270 Hz); WC

â

3

â

1

â 3

C CF

3 3

)

1

5

2.61 qm ( J CH ) 139 Hz, due to extensive C-P and C-F

couplings the methyl carbon multiplets could not be resolved);

P(OCH ) 52.19 qdd ( J CH ) 146 Hz, J CP ) 7 Hz, J CF ) 3

3 3

Hz).

1

2

4

P r ep a r a tion of (F

bomb sealed with a Teflon valve was charged with (F

F)(CO) (2) (1.51 g, 2.82 mmol) and 30 mL of freshly distilled

THF. The resulting orange slurry was degassed, placed under

4

-P ia )W(F )(¹³CO)

3

(6). A 100 mL glass

385 parameters, R ) 0.0207, R

w

) 0.0266, and the highest

3

4

-Pia)W-

peak in the final map was 0.477 e/Å .

(

3

Sp ectr a l Stu d ies. Infrared spectra were recorded in 1.0

mm or 0.1 mm CaF₂cells on a BioRad Model FTS-40 FTIR

spectrometer operating with a resolution of 2.0 cm . Visible

spectra were recorded on a Hewlett Packard Model 8452A

diode array spectrophotometer in a 1.00 cm Pyrex glass cell

modified for work with air-sensitive compounds and gases.

Variable-temperature kinetic runs were performed employing

a thermostated cell holder using a VWR Scientific Model 1166

1

3

-1

reduced pressure, and cooled to -196 °C. CO (1.12 mmol)

was condensed into the reaction vessel. The mixture was then

heated in an oil bath at 70 °C for 22 h. An IR spectrum

revealed that the CO enrichment was not complete. The now

dark orange solution was charged with ¹³CO (0.93 mmol) and

heated in an oil bath at 70 °C. IR monitoring confirmed that

the CO-substituted reaction was complete in 18 h (νCO 2019,

2

The THF solvent was then removed in vacuo, and the resulting

orange solid was collected by filtration, washed twice with 15

mL hexanes, and dried in vacuo to afford 6 in essentially

quantitative yield. Mass spectrometry determined an ap-

1

3

1

3

thermostated bath (P(OMe) studies) and a VWR Scientific

3

011, 1999, 1989, 1973, 1932, 1925, 1904, 1868, 1831 cm^-¹).

Model 1110 thermostated bath (isomerization and CO studies)

for temperature regulation. The temperature of the thermo-

stated baths and the temperature of the solutions in the Pyrex

cell were verified using an electronic thermocouple.

Kin etic Meth od s. All isomerization reactions were carried

out under either first-order (spontaneous) or pseudo-first-order

1

3

1

proximate 30% isotopic enrichment of 6.

(

2

C{ H} NMR

2

1

CDCl

3

) (δ): CO 232.55 ( J CF ) 41 Hz, J CW ) 116 Hz); CO

(CO- or P(OMe) -promoted) conditions with the concentration

3

2

1

2

21.58 ( J CF ) 14 Hz, J CW ) 132 Hz); CO 218.76 ( J CF ) 6

of the nucleophile at least 1 order of magnitude greater than

that of the kinetic isomer 3. Isomerization was monitored by

FTIR and visible spectroscopy, and excellent agreement was

obtained between the two methods.

1

Hz, J CW ) 122 Hz).

Cr ystallogr aph y. X-r ay Str u ctu r e of tr a n s-{(L)W(CO)

2

-

(

F )} (3). An orange prism was obtained by layering a CH

2

Cl

2

solution of 3 with hexanes and cooling to -10 °C. Data were

collected at ambient temperature on an Enraf-Nonius CAD-4

diffractometer with Mo KR radiation, using the ω-2θ scan

technique (4.00° < 2θ < 50.00°) for a crystal of dimensions

In the FTIR studies, the spontaneous and CO-promoted

reactions were initiated by immersing a Schlenk flask (equipped

with a septum-covered valve) charged with a toluene solution

of 3 (or 3 and added CO) into a thermostated circulating water

bath. Aliquots of the reaction mixture were obtained using a

gastight syringe and immediately cooled to 0 °C to quench the

reaction. FTIR spectra were then obtained using a 1.0-mm

0

.42 mm × 0.39 mm × 0.19 mm, mounted on a glass fiber.

Cell constants were obtained from 25 reflections with 10°

<

2θ < 25°. The space group (Pbca, No. 61) was determined

CaF

2

septum-fitted solution IR cell. The change in absorbance

from systematic absences (0kl, k ) 2n + 1; n0l, l ) 2n + 1;

hk0, h ) 2n + 1) and subsequent least-squares refinement.

Standard reflections showed no decay during data collection.

Lorentz, polarization, and empirical absorption (ψ scans)

-1

at an appropriate wavelength (2100-1900 cm ) was recorded

as a function of time. The change in absorbance (disappear-

-

1

ance) of highest energy band of 3 (2046 cm ) was monitored

-

1

since the low-energy band (1965 cm ) was obscured due to

solvent subtraction problems incurred using the 1.0-mm

solution IR cell. However, good agreement was also obtained

when the change in absorbance (appearance) of highest energy

corrections were applied. The structure was solved by the

_s_t_a_n_d_a_r_d_h_e_a_v_y_-_a_t_o_m_t_e_c_h_n_i_q_u_e_s_w_i_t_h_S_P_D_/_V_A_X_p_a_c_k_a_g_e_.₂0

Of 2410 reflections collected at ambient temperature, 2409

of these had I > 3σ(I) and were used in the solution and

refinement (SDP PLUS software). Final refinement included

all non-hydrogen atoms as anisotropic contributions and

hydrogens as fixed isotropic contributions. The hydrogen

atoms on C10, C11, and C12 were located but were not refined.

Scattering factors, and ∆f ′ and ∆f ′′ values, were taken from

-1

band of 4 (2019 cm ) was monitored. An isosbestic point was

-

1

maintained at 2037 cm throughout the course of the trans-

formation. The room-temperature P(OMe) -promoted isomer-

ization reactions were initiated by injecting a septum-fitted

Schlenk flask containing a toluene solution of 3 with P(OMe)

3

2

1

using a gastight syringe. Aliquots of the reaction mixture were

obtained using a gastight syringe, and then FTIR spectra were

the literature. For 299 parameters, R ) 0.0378, R

w

) 0.0411,

2

obtained using a 1.0-mm CaF septum-fitted solution IR cell.

Again, the change in absorbance (disappearance) of highest

energy band of 3 was monitored.

In the UV-vis studies, the spontaneous, CO- and P(OMe) -

3

promoted reactions were initiated by immersing a 1.0-cm glass

cell charged with a toluene solution of 3 (or 3 and added CO

(

20) Frenz, B. A. The Enraf-Nonius CAD 4 SPD-A Real-Time System

for Concurrent X-ray Data Collection and Crystal Structure Determi-

nation. In Computing and Crystallography; Schenk, H., Olthof-

Hazelkamp, R., van Konigveld, H., Bassi, G. C., Eds.; Delft University

Press: Delft, Holland, 1978; pp 64-71.

(21) Comer, D. T.; Waber, J . T. In International Tables for X-ray

Crystallography; Ibers, J . A., Hamilton, W. C., Eds.; Kynoch: Bir-

mingham, England, 1974; Vol. IV, Tables 2.2B and 2.3.1, pp 72-98,

49-150.

or P(OMe)

3

) into a thermostated ((0.5 °C) cell compartment

1

of the spectrometer. (The components within the cell were

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1549

thoroughly mixed by shaking.) The temperature of the cell

was allowed to equilibrate for 5 min before spectra were

obtained. The change in absorbance at an appropriate wave-

length (580 nm for spontaneous and CO-promoted; 500 nm for

P(OMe) -promoted) was recorded as a function of time. Isos-

3

bestic points were observed at 345, 415, and 492 nm for the

spontaneous and CO-promoted reactions and at 360 and 452

alkyne to the fluoride. Irradiation at the W-F reso-

nance also results in the collapse of the pair of doublets

to a pair of singlets for the carbonyl ligands demon-

strating coupling to W-F. Irradiation at the CF3(Câ)

1

9

F NMR resonance (Figure 1d) results in the appear-

ance of a singlet at δ 32.4 ppm indicating coupling of

the CF3 to Câ. Again, a partial collapse of the CR doublet

nm for the P(OMe)

3

reaction.

2

of quartets at δ 196.8 ppm to a doublet with J CF ) 40

Plots of ln(A ) and ln(A

t

∞

- A ) vs time were linear for more

t

Hz was observed due to the proximity of the CF3(CR)

than 3 half-lives, and kobsd was determined from the slope of

this line by least-squares analysis. Rate constants were

reproducible within (5% in independent runs.

1

9

and CF3(Câ) F NMR resonances.

The carbenoid character of C is reflected by the large

R

2

Volu m e of Activa tion Mea su r em en ts. All measure-

downfield chemical shift, whereas the four-coordinate

ments were made with freshly prepared solutions in which the

23

carbon, Câ, has a significant upfield chemical shift.

-

4

complex 3 concentration was 2 × 10 M. The temperature

was set to 60.1 °C for both the CO-independent and CO-

dependent isomerization reactions. The CO-independent and

CO-dependent isomerization reactions were followed spectro-

photometrically at λ ) 580 nm by a modified (double beam)

Zeiss PMQ II and a Cary 1.3 UV-vis spectrophotometer

equipped with a homemade, thermostated ((0.1 °C) high-

Importantly, for 3 the fluoride was determined to be cis

2

to both CO ligands (δ 214.9 ppm, J CF ) 20 Hz, and δ

2

15.2 ppm, J CF ) 12 Hz), leaving the inserted acetylene

trans to the fluoride. The structure of 3 was verified

crystallographically (Figure 2a).

The ¹H NMR for 3 displays four different highly

coupled multiplet resonances (δ 5.05, 3.95, 3.13, and

3.09 ppm) for the methylene protons on the ethylene

backbone; each intergrate to one proton. This non-

equivalence illustrates not only the chirality of the

seven-coordinate tungsten(II) metal center but also the

retained coordination of the ligand in solution. Each

N-methyl group integrates to three protons; one appears

pressure cell. The k

and the k value was measured in CO-saturated toluene. For

the P(OMe) -promoted isomerization reactions, the tempera-

1

value was measured in CO-free toluene,

2

3

ture was set to 25 °C, and the reactions were followed

spectrophotometrically at λ ) 500 nm. The CO was of pa

quality (Messer-Griesheim), and the P(OMe)

distilled prior to use.

3

(Fluka) was

4

as a doublet at δ 3.04 ppm ( J HF ) 4.62 Hz) and the

Resu lts

other as a singlet at δ 2.55 ppm. The imine proton is a

singlet at 8.83 ppm.

Syn th esis a n d Ch a r a cter iza tion of tr a n s-{(L)W-

CO)2(F )} (3) a n d cis-{(L)W(CO)2(F )} (4). As de-

picted in eq 1, ambient-temperature visible-light pho-

The ¹⁹F NMR spectrum for 3 shows seven resonances

as expected with appropriate integrations. The trifluo-

romethyl groups are displayed as apparent doublets (δ

(

tolysis of a toluene solution of 2 (νCO 2020, 1934, 1900

2

-

1

-58.32 and -59.35 ppm). The fluoride ortho to the η -

cm ) in the presence of perfluorobutyne generates a

vinyl moiety is easily recognized and appears as a

distinctive broad resonance at δ -131.84 ppm. The

remaining aromatic fluorides are not exceptional and

are observed as highly coupled multiplet resonances at

δ -140.17, -144.68, and -156.05 ppm. The W-F

resonance is located farthest upfield as a singlet at δ

-172.26 ppm.

dark yellow solution with 3 as the major species (νCO

-

1

2

5

046, 1965 cm ). Orange crystalline 3 is isolated in

0% yield following chromatography. Due to the ex-

1

3

1

tensive carbon-fluorine coupling in the C{ H} spec-

trum (Figure 1a), the identification of 3 as an η -vinyl

2

or metallacyclopropenyl complex was ascertained by a

_s_e_r_i_e_s_o_f1 C{ F} NMR experiments (Figure 1b-d).

3

19

2

_B_r_o_a_d_-_b_a_n_d1 C{ F} decoupling was not possible due

3

19

The kinetic η -vinyl complex 3 is smoothly converted

2

to the thermodynamic η -vinyl product 4 at 60 °C,

to the large frequency range (approximately 200 ppm)

1

9

indicating that 3 is indeed an intermediate in the

formation of 4 (eq 2). The transformation is accompa-

in the F region for 3. Thus, several single-frequency

1

3

19

C{ F} decoupling experiments were performed.

-

1

_I_n_t_h_e1 C{ H} spectrum (Figure 1a), CR appears as a

3

1

nied by a marked shift (∼50 cm ) to lower energy in

the CO stretching frequencies. Alternatively, 4 is more

conveniently synthesized in a direct manner by treat-

ment of 2 with perfluoro-2-butyne in toluene at 80 °C

2

doublet of quartets at δ 196.8 ppm with J CF ) 40 Hz

2

from the CF3 group and J CF ) 34 Hz from the fluoride;

the CO resonances appear as a pair of doublets at δ

-

1

2

to give a maroon solution of 4 (νCO 2019, 1915 cm ),

2

14.9 ppm ( J CF ) 20 Hz) and δ 215.2 ppm ( J CF ) 13

1

3

1

which crystallizes as an air-stable green solid product

Hz). The Câ resonance was not visible in the C{ H}

1

3

_s_p_e_c_t_r_u_m_._A_s_i_l_l_u_s_t_r_a_t_e_d_i_n_F_i_g_u_r_e₁_,1 C{ F} NMR

3

19

in 68% isolated yield. As with compound 3, the C-

1

9

{ H} NMR spectrum for 4 was complex due to extensive

spectra were obtained while irradiating at specific

F

1

3

19

carbon-fluorine coupling and C{ F} identical to those

NMR resonances corresponding to the CF3(Câ) (δ -58.3

detailed above were performed. It was determined that

ppm), CF3(CR) (δ -59.4 ppm), and W-F (δ -172.26

2

13

19

_p_p_m₎_m_o_i_e_t_i_e_s_._I_r_r_a_d_i_a_t_i_o_n_a_t_t_h_e_C_F₃₍_C_R₎₁9F resonance

complex 4 possesses the requisite η -vinyl C{ F} NMR

chemical shifts at δ 202.8 and 40.8 ppm coinciding with

(

Figure 1b) results in the collapse of doublet of quartets

1

3

1

2

CR and Câ, respectively. In the C{ H} NMR spectrum,

to a doublet with J CF ) 34 Hz indicating coupling of

the CF3 group to CR. Due to the proximity of the CF3-

2

CR appears as a quartet with J CF ) 40.8 Hz from the

_C_â₎_a_n_d_C_F₃₍_C_R₎1 F NMR resonances, appearance of a

9

CF3 group with no discernible coupling from the W-F

in accord with a cis arrangement of the W-F and the

(

singlet at δ 32.4 ppm corresponding to Câ was also

2

_o_b_s_e_r_v_e_d_._L_i_k_e_w_i_s_e_,_i_r_r_a_d_i_a_t_i_o_n_a_t_t_h_e_W_-_F19F NMR

inserted alkyne. Notable is the increased J CF coupling

resonance (Figure 1c) results in the collapse of doublet

2

(22) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;

of quartets to a quartet with J CF ) 40 Hz indicating

Wiley: New York, 1988.

coupling of the W-F to CR and providing strong spec-

troscopic evidence for a trans orientation of the inserted

23) Mann, B. E.; Taylor, B. F. 13_C_N_M_R_D_a_t_a_f_o_r_O_r_g_a_n_o_m_e_t_a_l_l_i_c

(

Compounds; Academic Press: New York, 1981.

1

550 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

1

3

1

13

19

F igu r e 1. (a) C{ H} spectrum of 3. (b) C{ F} spectrum of 3 from irradiation of the CF

3

(C

R

) resonance at δ -59.4

ppm. (c) ¹³C{ F} spectrum of 3 from irradiation of the W-F resonance at δ -172.26 ppm. (d) C{ F} spectrum of 3

19

13

19

1

3

19

from irradiation of the CF

experiments.

3 â

(C ) resonance at δ -58.3 ppm. The arrows indicate the fluorines irradiated in the C{ F}

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1551

Ta ble 1. Cr ysta llogr a p h ic Da ta for

2 2

tr a n s-(L)W(CO) (F ) (3) a n d cis-(L)W(CO) (F )

1

(

2 7 8

4‚ / C H )

3

4

molecular formula

WF11O2N2C17H11

WF11O2N2C17H11‚

1

/

2C7H8

mol weight, g mol^-

space group

cryst system

1

668.122

714.195

P 1h (No. 2)

triclinic

a ) 8.100(1) Å

b ) 12.111(3) Å

c ) 12.944(4) Å

R ) 100.69(2)°

â ) 97.92(3)°

γ ) 107.97(2)°

1160.79

Pbca (No. 61)

orthorhombic

a ) 12.902(3) Å

b ) 16.185(2) Å

c ) 19.089(3) Å

cell constants

V, Å³

Z

3985.98

8.0

2.227

2.0

2.043

-

3

calcd density, g cm

3

cryst dimens, mm

abs coeff (µ), cm

0.42 × 0.39 × 0.19 0.32 × 0.25 × 0.15

-

1

60.363

51.819

0.709 30

4384

radiation, λ(Mo KR), Å 0.709 30

no. of reflcns measd

θ range, deg

2410

2

4.00-50.00

θ/2θ scan

0.8000 +

4.00-50.00

θ/2θ scan

0.8000 +

0.3400(tan θ)

bisecting, ω ) 0

anisotropic

empirical

46.4511

scan technique:

scan width, deg

0

.3400(tan θ)

data collcn posn

decay corr appl

abs corr

min % transm

max % transm

av % transm

highest peak in diff

Fourier map, e Å

max ∆F value in diff

Fourier map, e Å

ignorance factor, p

no. of observns,

I > 3.00σ(I)

no. of variables

data to param ratio

shift to error ratio

error in an observn

of unit weight

R

bisecting, ω ) 0

none

empirical

40.6145

99.7504

76.2845

1.499

99.9931

79.3357

0.477

-

3

2987.965

565.267

-

0.04

2409

0.04

3700

299

385

8.057

0.003

0.9683

9.610

0.021

0.8023

0.0378

0.0411

0.0207

0.0266

Rw

F igu r e 2. (a) ORTEP representation of 3. (b) ORTEP

representation of 4.

a

Relevant expressions are as follows, where Fo and Fc represent

respectively the observed and calculated structure factor ampli-

2

tudes. R(Fo) ) ∑(|Fo| - |Fc|/∑|Fo|). Rw(Fo) ) [∑(|Fo| - |Fc|) /

constant for one of the carbonyl ligands at δ 221.79 ppm

2

1/2

∑

w|Fo| ]

.

2

(

J CF ) 55 Hz) which clearly demonstrates that the

2

4

ligand is trans to the fluoride.

ligand at δ 221.82 ppm is cis to the fluoride with J CF

The other carbonyl

substituents are roughly orthogonal to the MCRCâ plane.

(2) There are short M-CR distances (1.92-1.96 Å) in

the metal-carbon double bond range. (3) The M-Câ

distances (2.19-2.30 Å) are in the metal-carbon single-

bond range. (4) CR-Câ bond distances are suggestive

of double-bond character. For both compounds 3 and

4, comparable crystallographic data were obtained sup-

porting their formulation as η -vinyl complexes. In

2

)

5 Hz.²⁴The structure of 4 was confirmed by X-ray

2

crystallography (Figure 2b).

The ¹H NMR and the ¹⁹F NMR spectra for 4 are

essentially identical to those of 3. One notable pecu-

liarity in the ¹⁹F NMR for 4 is that the W-F resonance

was located unusually downfield as a singlet at δ

5

2

-

138.27 ppm. Its identity of the W-F resonance was

compounds 3 and 4, the plane defined by the two Câ

substituents labeled C5 and C17 is roughly orthogonal

to the WCRCâ (W-C3-C4) plane as shown by the RR-

ascertained by noting an upfield shift to δ -140.24 ppm

upon addition of D2O to the sample.¹⁹

2

X-r a y Cr ysta llogr a p h ic An a lyses of tr a n s-{(L)W-

CR-Câ-Râ torsional angles in both the kinetic η -vinyl

(

CO)2(F )} (3) a n d cis-{(L)W(CO)2(F )} (4). The struc-

complex 3 (C16-C3-C4-C5 ) -69.9° and C16-C3-

2

tures of both η -vinyl complexes were confirmed by

X-ray crystallography. Data collection information,

positional parameters, selected bond distances, and

bond angles for 3 and 4 are presented in Tables 1-4.

There exist several prominent structural features for

C4-C17 ) 74.1°) and the thermodynamic η -vinyl

complex 4 (C16-C3-C4-C5 ) 72.4° and C16-C3-C4-

3

C17 ) -75.0°). In addition, the sp hybridization of the

Câ carbon is elucidated upon examination of the C-C-R

and R-C-R bond angles at the four-coordinate carbon

center in 3 (C5-C4-C17 ) 110.1°, C3-C4-C5 )

2

η -vinyl complexes: (1) The orientations of the two Câ

1

22.0°, C3-C4-C17 ) 119.0°, and C3-C4-W ) 60.4°)

(24) (a) Blake, A. J .; Cockman, R. W.; Ebsworth, E. A. V.; Holloway,

and 4 (C5-C4-C17 ) 111.2°, C3-C4-C5 ) 121.8°,

C3-C4-C17 ) 119.6°, and C3-C4-W ) 60.2°). Thus,

the approximate tetrahedral angles at Câ in both

J . H. J . Chem. Soc., Chem. Commun. 1988, 529-530. (b) Darensbourg,

D. J .; Klausmeyer, K. K.; Reibenspies, J . H. Inorg. Chem. 1995, 34,

4

933-4934.

1

552 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

Ta ble 2. Atom ic Coor d in a tes a n d Equ iva len t

Ta ble 3. Atom ic Coor d in a tes a n d Equ iva len t

2

Isotr op ic Th er m a l P a r a m eter s (Å ) for

1

tr a n s-(L)W(CO)

2

(F ) (3)

cis-(L)W(CO)

2

(F ) (4‚ /

2

C

7

H

8

)

a

2

a

2

atom

x

y

z

B (Å )

atom

x

y

z

B (Å )

W

F1

F2

F3

F4

F5

F6

F7

0.22744(3)

0.1314(5)

0.2849(7)

0.1353(8)

-0.0493(7)

-0.0823(6)

0.3343(7)

0.4262(6)

0.4658(6)

0.4342(5)

0.3005(6)

0.3566(6)

0.3723(7)

0.1138(8)

0.1135(6)

0.2754(6)

0.3176(9)

0.156(1)

0.00666(2)

-0.0742(4)

0.1828(5)

0.2642(6)

0.2944(5)

0.2316(5)

0.0254(7)

-0.0531(5)

0.0768(6)

0.1627(5)

0.2239(4)

0.2536(5)

-0.1477(5)

-0.0522(6)

0.0928(5)

0.0219(5)

-0.0928(6)

-0.0298(8)

0.0490(7)

0.1236(6)

0.1611(6)

0.1904(8)

0.2337(8)

0.2473(8)

0.2167(7)

0.1734(6)

0.1505(6)

0.0823(7)

0.0861(7)

0.0531(9)

-0.0570(8)

0.0263(9)

0.1891(7)

0.05482(2)

2.957(7)

4.3(1)

8.0(2)

10.5(3)

9.5(2)

7.3(2)

9.6(3)

7.4(2)

8.2(2)

6.4(2)

5.6(2)

7.2(2)

7.4(3)

7.8(3)

3.3(2)

4.0(2)

4.9(3)

5.2(3)

3.5(2)

3.4(2)

3.6(2)

5.7(3)

7.0(3)

6.3(3)

5.2(3)

3.7(2)

4.1(3)

4.7(3)

4.4(3)

5.7(3)

5.6(3)

5.2(3)

4.4(3)

W

F1

F2

F3

F4

F5

F6

F7

F8

F9

F10

F11

O1

0.90123(2)

0.8542(4)

0.5061(4)

0.5993(5)

0.8952(5)

1.1052(4)

0.5880(5)

0.5732(5)

0.3907(4)

0.6453(4)

0.5079(4)

0.4301(4)

1.0481(6)

0.7715(6)

1.0581(5)

1.1716(5)

0.9976(7)

0.8171(7)

0.6868(6)

0.7004(6)

0.7628(6)

0.6597(7)

0.7047(8)

0.8540(8)

0.9595(7)

0.9186(6)

1.0462(6)

1.2005(6)

1.2966(7)

1.1512(8)

1.2550(9)

0.5611(7)

0.5740(6)

1.000(2)

0.770(3)

0.865(3)

0.720(4)

0.896(2)

1.144(3)

1.140(9)

0.873(9)

1.275(9)

1.347(9)

1.429(9)

1.267(9)

0.915(9)

1.057(9)

1.396(9)

1.271(9)

0.91343(2)

0.9492(2)

0.5373(3)

0.3479(3)

0.3281(3)

0.5056(3)

0.7427(3)

0.9133(3)

0.5749(3)

0.6777(3)

0.7878(3)

0.6027(3)

0.8828(4)

1.1210(3)

0.8249(3)

1.0685(4)

0.8953(5)

1.0459(4)

0.8180(4)

0.7334(4)

0.6303(4)

0.5368(4)

0.4365(5)

0.4270(4)

0.5179(5)

0.6211(4)

0.7147(4)

0.9111(4)

1.0126(5)

1.1579(4)

1.1361(6)

0.8076(5)

0.7020(4)

0.4079(8)

0.463(2)

0.72005(1)

0.5767(2)

0.7425(3)

0.7547(3)

0.6905(4)

0.6218(3)

0.8994(2)

0.8901(3)

0.7763(3)

0.4765(2)

0.5469(3)

0.5493(3)

0.9466(3)

0.8242(4)

0.6357(3)

0.7431(3)

0.8640(4)

0.7892(4)

0.7562(4)

0.6656(4)

0.6802(4)

0.7145(4)

0.7211(5)

0.6878(5)

0.6535(5)

0.6493(4)

0.6152(4)

0.6021(4)

0.7003(5)

0.6805(5)

0.8564(5)

0.8293(4)

0.5615(4)

2.0174(8)

2.048(2)

2.375(3)

3.43(6)

4.63(8)

5.98(9)

7.1(1)

5.83(9)

4.93(8)

5.43(8)

5.30(9)

4.15(7)

4.66(8)

4.74(8)

5.6(1)

2.89(8)

3.31(9)

3.6(1)

2.8(1)

2.65(9)

2.8(1)

3.4(1)

4.1(1)

4.5(1)

4.0(1)

3.0(1)

3.2(1)

3.7(1)

4.2(1)

4.1(1)

5.3(2)

3.6(1)

3.2(1)

9.9(3)

10.4(7)

8.9(6)

14.(1)

7.2(5)

18.4(8)

5.0

0.0100(4)

0.2468(4)

0.3119(4)

0.2457(5)

0.1178(5)

0.2478(4)

0.1830(4)

0.1966(5)

0.0576(5)

0.0188(4)

0.1186(4)

0.0638(6)

0.1899(6)

0.0124(5)

-0.0599(5)

0.0651(8)

0.1401(7)

0.1272(5)

0.1062(6)

0.1451(6)

0.2116(7)

0.2464(8)

0.2139(7)

0.1496(7)

0.1152(6)

0.0420(7)

-0.0625(7)

-0.0952(6)

-0.0715(7)

-0.1004(7)

0.1889(6)

0.0764(6)

F8

F9

F10

F11

O1

O2

N1

N2

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

O2

N1

N2

C1

C2

C3

C4

C5

C6

C7

0.3196(8)

0.2727(8)

0.1834(9)

0.196(1)

0.119(1)

0.025(1)

C8

C9

0.010(1)

0.0875(8)

0.0659(8)

0.0972(8)

0.2074(9)

0.3846(9)

0.265(1)

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

H1

H2

H3

H4

H5

H6

H7

H8

H9

H10

0.3862(9)

0.3387(9)

a

B values for anisotropically refined atoms are given in the form

of the isotropic equivalent displacement parameter defined as (4/

)[a â11 + b â22 + c â33 + ab(cos γ)â12 + ac(cos â)â13 + bc(cos R)â23].

0.390(2)

0.517(2)

0.506(1)

0.427(2)

0.695(6)

1.068(6)

0.876(6)

0.972(6)

1.081(6)

1.216(6)

0.888(6)

1.192(6)

1.182(6)

1.068(6)

2.044(2)

2.041(2)

2.018(1)

1.997(2)

0.565(6)

0.471(6)

0.566(6)

0.747(6)

0.682(6)

0.408(6)

0.700(6)

0.860(6)

0.901(6)

2

3

1

compounds are inconsistent with an η -vinyl structure

where M, CR, Câ, and the two Câ constituents would lie

in a plane. In the kinetic η -vinyl complex 3, W-CR

W-C3) has a bond distance of 1.95(1) Å, W-Câ (W-

5.0

2

5

2

(

C4) has a bond distance of 2.21(1) Å, and CR-Câ (C3-

C4) definitely has double-bond character with a bond

distance of 1.41(1) Å. Similarly, for the thermodynamic

2

η -vinyl complex 4, W-CR (W-C3) has a bond distance

of 1.938(5) Å, W-Câ (W-C4) has a bond distance of

5.0

2

(

.196(5) Å, and the double-bond character of CR-Câ

a

B values for anisotropically refined atoms are given in the form

C3-C4) is reflected in the bond distance of 1.448(7) Å.

of the isotropic equivalent displacement parameter defined as (4/

2

Also noteworthy is that in both 3 and 4 the sum of the

angles around CR(C3) adds up to 360° as expected for

3)[a â11 + b â22 + c â33 + ab(cos γ)â12 + ac(cos â)â13 + bc(cos R)â23].

All hydrogen atoms were located and refined except for those of

the toluene.

2

an sp center with no pyramidalization.

The geometry around the tungsten(II) metal center

in both compounds can be described as roughly octahe-

dral if one considers that the η -vinyl ligand occupies a

C4 ) 92.7(2)°, and C3-W-C4 ) 40.4(2)°) and one

carbonyl ligand (F1-W-C2 ) 91.0(2)°) and trans to the

second carbonyl ligand (F1-W-C1 ) 168.8(2)°). These

structural variations not only seem to produce marked

differences in reactivities of 3 and 4 but also appear to

affect the solid-state packing of the molecules.

A survey of the packing in the unit cell shows that

the complex 4 crystallizes as infinite chains of head-to-

tail dimers linked by an C12-H‚‚‚F1-W interaction

2

single coordination site. The key structural difference

2

between the kinetic η -vinyl complex 3 and the ther-

2

modynamic η -vinyl complex 4 is the relative orientation

of the inserted alkyne to the other ligands around the

tungsten(II) metal center. In 3, the alkyne is roughly

trans to the fluoride (F1-W-C3 ) 156.1(3)° and F1-

W-C4 ) 156.4(4)°) and cis to the two carbonyl ligands

(

3

Supporting Information). The C12‚‚‚F1 separation of

(

F1-W-C1 ) 82.8(4)°, F1-W-C2 ) 82.8(4)° and C3-

W-C4 ) 38.9(5)°). In contrast, the inserted alkyne in

is cis to the fluoride (F1-W-C3 ) 112.3(2)°, F1-W-

.17 Å with a C12-H-F1 angle of 145° is consistent

2

6

with weak intermolecular hydrogen bonding.

The

4

(

26) (a) Green, R. D. Hydrogen Bonding by C-H Groups; Wiley: New

(

25) Allen, S. R.; Baker, P. K.; Barnes, S. G.; Bottrill, M.; Green,

M.; Orpen, A. G.; Welch, A. J . J . Chem. Soc., Dalton Trans. 1983, 927-

39.

York, 1974; Chapter 5. (b) Desiraju, G. R. J . Chem. Soc., Chem.

Commun. 1990, 454-455. (c) Desiraju, G. R. Acc. Chem. Res. 1991,

24, 290-296.

9

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1553

cm^-¹) and the ¹³CO-labeled thermodynamic η -vinyl

2

Ta ble 4. Selected Dista n ces (Å) a n d An gles (d eg)

a

for tr a n s-(L)W(CO)

2

(F ) (3) a n d cis-(L)W(CO)

2

(F ) (4)

-1

complex 8 (νCO 2021, 1992, 1976, 1921, 1909, 1883 cm

were prepared. Incorporation of CO into both carbonyl

positions in 7 and 8 was confirmed by C{ H} NMR

spectroscopy which revealed equally intense CO en-

)

1

3

4

1

3

1

W-F1

W-N1

W-N2

W-C1

W-C2

W-C3

W-C4

C3-C4

1.994(6)

2.182(9)

2.29(1)

2.00(1)

1.96(1)

1.95(1)

2.21(1)

1.41(1)

1.996(3)

2.178(4)

2.342(5)

1.996(6)

2.037(6)

1.938(5)

2.196(5)

1.448(7)

1

3

2

hanced carbonyl signals at δ 214.9 ppm ( J CF ) 20 Hz,

1

2

1

J CW ) 184 Hz) and 215.2 ppm ( J CF ) 13 Hz, J CW )

2

1

36 Hz) and δ 221.79 ppm ( J CF ) 55 Hz, J CW ) 150

2

1

Hz) and 221.82 ppm ( J CF ) 5 Hz, J CW ) 142 Hz),

respectively.

Syn th esis a n d Ch a r a cter iza tion of cis-{(L)W-

(CO)(F )(P (OCH3)3)} (5). Treatment of a toluene solu-

tion of 3 with 5 equiv of P(OMe)3 at ambient tempera-

ture for 15 h affords a magenta solution of 5 (νCO 1953

F1-W-C1

82.8(4)

168.8(2)

160.1(2)

158.2(2)

159.1(2)

40.4(2)

119.6(5)

132.3(5)

121.8(5)

116.5(3)

118.8(4)

148.2(4)

111.2(5)

84.5(2)

94.6(2)

92.7(2)

112.3(2)

91.0(2)

91.3(3)

80.2(2)

60.2(3)

78.9(2)

N1-W-C2

100.7(4)

118.4(4)

105.1(4)

38.9(5)

119.(1)

133.(1)

N2-W-C3

N2-W-C4

C3-W-C4

-1

cm ) which was isolated as a magenta microcrystalline

solid in 59% yield from Et2O/hexanes. NMR spectros-

copy provided a wealth of structural information for the

C3-C4-C17

C4-C3-C16

C3-C4-C5

122.(1)

W-C4-C5

111.3(6)

126.7(9)

144.9(9)

110.1(9)

162.5(5)

160.8(4)

156.4(4)

156.1(3)

82.4(5)

87.0(6)

78.6(5)

60.4(5)

81.9(6)

-69.93(1.60)

74.05(1.57)

-50.69(1.15)

-0.18(1.53)

28.36(1.56)

4.42(1.50)

-39.82(0.92)

55.36(0.69)

2

isotopically enriched P(OMe)3-substituted η -vinyl com-

W-C4-C17

W-C3-C16

C5-C4-C17

N2-W-C2

1

19

plex which contains four different spin /2 nuclei ( F,

3

1

13

183

31

1

P, C, W) in close proximity. The P{ H} spectrum

reveals a doublet of quartets for the coordinated P(OMe)3

N1-W-C1

2

1

at δ 146.25 ppm with J PF ) 81 Hz and J PW ) 621 Hz.

F1-W-C4

19

Likewise, the F NMR shows a doublet for W-F at δ

F1-W-C3

2

-

177.49 ppm with J PF ) 81 Hz. P(OMe)3 is also

F1-W-C2

C1-W-C2

coupled to the trifluoromethyl group attached to the

4

C2-W-C3

alkylidene carbon with a J PF ) 8 Hz. This long-range

interaction is also evident in the F NMR spectrum of

C3-C4-W

19

C1-W-C3

5

since the trifluoromethyl resonance appears as a

C16-C3-C4-C5

C16-C3-C4-C17

W-C4-C5-C10

C4-C5-C10-C11

C5-C10-C11-N1

C10-C11-N1-W

C11-N1-W-C4

N1-W-C4-C5

72.36(0.73)

-74.99(0.70)

47.44(0.55)

-8.82(0.74)

-19.27(0.80)

1.58(0.75)

25.87(0.44)

-45.45(0.33)

4

doublet of doublets with J PF ) 8 Hz from the trimethyl

phosphite ligand and a remarkable J FF ) 27 Hz from

6

the ortho fluorine on the aromatic ring. The latter

coupling is probably a “through-space” interaction which

is not uncommon in other highly fluorinated systems.²⁸

In fact, previous work from this group has demonstrated

that the fluorine ortho to the tungsten center in struc-

turally related complexes readily engages in long-range

interactions with other nuclei in the metallacycle.²⁹

The large ²J _P_Fcoupling constant suggests a trans

orientation between the fluoride and the phosphite

a

Numbers in parentheses are estimated standard deviations

in the least significant digits.

C12-N‚‚‚F1 interaction has a distance of 2.15 Å which

is shorter than the H‚‚‚F van der Waals contact separa-

tion of 2.6 Å.²⁷The basicity of the fluoride was further

confirmed by the F NMR signal at δ -138.27 ppm

which is slightly solvent dependent and shifts to δ

13

ligands around the tungsten metal center. In the C-

1

9

1

{ H} spectrum, the CO resonance appears as a pair of

2

doublets at δ 235.60 ppm with J

CF

) 12 Hz, J

CP

) 7

1

-

140.24 ppm upon addition of D2O to the sample

suggesting hydrogen bonding to the fluoride.

Hz, and J _C_W) 146 Hz. The carbonyl coupling con-

stants were unambiguously ascertained upon selective

1

9

In

1

9

contrast, 3 does not exhibit hydrogen bonding in the

solid state or in solution. This could be a result of the

steric environment about the fluoride in 3 which is

essentially encased by the ethylene ligand backbone (see

Figure 2a), but the fluoride in 4 is accessible for

intermolecular hydrogen bonding (see Figure 2b).

Isotop ic En r ich m en t of tr a n s-{(L)W(CO)2(F )} (3)

a n d cis-{(L)W(CO)2(F )} (4). ¹³CO-labeled compounds

irradiation at the W-F

F NMR resonance at δ

-177.49 ppm which results in the collapse of the CO

2

doublets to one doublet with J

CP

) 7 Hz. The small

2

J _C_Fcarbonyl coupling constant indicates a cis orienta-

tion between the carbonyl and fluoride ligands. The

carbon resonances belonging to the η -vinyl fragment

were not visible in the C{ H} NMR spectrum due to

2

4

2

1

3

1

19

the extensive coupling. Irradiation at the CF (C )

3

R

F

2

were prepared in an effort to learn more about the η -

NMR resonance at δ -51.14 ppm results in the collapse

of the quartet to a singlet at δ 131.46 ppm and the

appearance of the C_Rresonance as a pair of doublets

centered at δ 189.45 ppm. Likewise, irradiation at the

vinyl systems as well as corroborate the ¹³C{ F} NMR

experiments. Isotopic exchange at 70 °C gave equal

incorporation of ¹CO into all three carbonyl positions

in 6 and was confirmed by ¹³C{ H} NMR spectroscopy

19

3

1

19

CF (C ) F NMR resonance at δ -55.93 ppm results in

3

â

1

3

which revealed equally intense CO enhanced carbonyl

the collapse of the quartet to a singlet at δ 133.20 ppm

2

1

signals at δ 232.55 ppm ( J CF ) 41 Hz, J CW ) 116 Hz),

for the trifluoromethyl group and the appearance of the

C resonance as a doublet centered at δ 31.28 ppm. The

â

2

1

2

21.58 ppm ( J CF ) 14 Hz, J CW ) 132 Hz), and 218.76

2

1

ppm ( J CF ) 6 Hz, J CW ) 122 Hz).

Using the same methods as those listed above for the

(28) (a) Servis, K. L.; Fang, K. N. J . Am. Chem. Soc. 1968, 90, 6712-

6717. (b) Servis, K. L.; J erome, F. R. J . Am. Chem. Soc. 1971, 93,

1

3

2

preparation of 3 and 4, the CO-enriched kinetic η -

vinyl complex 7 (νCO 2047, 2021, 2001, 1966, 1946, 1928

1

535-1537. (c) Mallory, F. B.; Mallory, C. W.; Ricker, W. M. J . Org.

Chem. 1985, 50, 457-461.

29) Benn, R.; Rufi n´ ska, A.; King, M. A.; Osterberg, C. E.; Richmond,

T. G. J . Organomet. Chem. 1989, 376, 359-366.

(

(27) Bondi, A. J . Phys. Chem. 1964, 68, 441-451.

1

554 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

source of the additional couplings to CR and Câ could

not be unequivocally ascertained.

Modeling studies³⁰suggest that a trans orientation

of the fluoride and P(OCH3)3 ligands is sterically favored

1

3

relative to the cis orientation. Furthermore, the C-

1

9

{

F} NMR studies suggest that the trifluoromethyl

moiety attached to the alkylidene carbon and the methyl

groups on the trimethyl phosphite ligand are in close

proximity. The ¹³C{ H} NMR spectrum displays the

P(OCH3)3 ligand methyl resonances as an apparent

quartet at δ 52.61 ppm and a doublet of doublets at δ

1

2

4

5

2.19 ppm with J CP ) 7 Hz and J CF ) 3 Hz. Thus,

the methyl groups on the trimethyl phosphite ligand are

not chemically equivalent. The different chemical shifts

and coupling pattern reflect some sort of steric conges-

tion preventing free rotation of the P(OCH3)3 ligand. The

1

3

19

C{ F} NMR spectra are quite illustrative and present

a more enigmatic coupling pattern for the δ 52.19 ppm

doublet of doublets which when fully coupled appears

1

as a complex quartet ( J CH ) 146 Hz) of doublet of

doublets resulting from coupling of the methyl moiety

to the phosphorus atom and the tungsten fluoride

ligand. Similarly, the apparent quartet at δ 52.19 ppm

becomes quite intricate and emerges as a quartet of

1

multiplets ( J CH ) 139 Hz) resulting from coupling of

the methyl fragment to not only the phosphorus atom

and the tungsten fluoride but also the trifluoromethyl

2

groups on the η -vinyl fragment as confirmed by numer-

ous decoupling experiments.

1

The H NMR spectrum for 5 is analogous to those

F igu r e 3. (a) Infrared spectral changes as a function of

displayed by 3 and 4. It is interesting that the imine

proton is not affected by the increase in electron density

at the tungsten center and emerges as a singlet at 8.82

2

-3

time for the η -vinyl isomerization of 2.55 × 10 M 3 in

toluene at 70 °C. (b) Visible spectral changes as a function

-4

of time (∆t ) 600 s) for the reaction between 2 × 10 M 3

2

19

ppm. Unlike the other η -vinyl complexes, the F NMR

spectrum for 5 is quite interesting due to the presence

of the trimethyl phosphite ligand on the tungsten metal.

The resonances for the trifluoromethyl groups emerge

as a singlet at δ -55.93 ppm and as a doublet of

3

and 0.21 M P(OMe) at 25 °C and 100 atm.

4

6

doublets at δ -51.14 ppm ( J PF ) 8 Hz and J FF ) 27

Hz) which integrate to three fluorines each. The

couplings due to the trimethyl phosphite and ortho

fluorine (δ -131.35 ppm) on the tetrafluoroaryl group

were determined from the aforementioned decoupling

experiments. The aromatic fluorines appear as highly

coupled multiplet resonances at δ -142.89, -149.70,

and -159.04 ppm, and the W-F resonance is located

2

farthest upfield as a doublet at δ -177.49 ppm ( J PF )

8

1 Hz) due to coupling from the trans P(OMe)3.

F igu r e 4. Plot of kobs (s^-¹) versus CO concentration (M)

2

for the η -vinyl isomerization of 3 in toluene solution at 80

Isom er ization Kin etic Stu dies. The η -vinyl isomer-

°

C.

ization shown in eq 2 proceeds readily at or above 60

C in toluene solution. Photolysis of a toluene solution

°

term rate law described in eq 10. The observed rate

of 3 results in decomposition of the complex rather than

isomerization. The IR spectral changes as a function

of time for eq 2 at 70 °C are illustrated in Figure 3a.

Isosbestic points are maintained at 2037, 2000, and

-

1

936 cm . Both the disappearance of 3 as well as the

2

constants for the spontaneous and CO-promoted η -vinyl

appearance of 4 gave identical rate constants within

isomerizations as a function of temperature and exter-

experimental error.

Interestingly, the η -vinyl isomerization of 3 exhibits

nal pressure (0-100 MPa) are collected in Tables 5 and

2

6

, respectively. Figure 5 illustrates the pressure de-

a 20-30% rate enhancement in the presence of CO

pendence of the isomerization in the absence and

presence of CO.

-

3

31

(

[CO] ∼ 9 × 10 M). As shown in Figure 4, the rate

increases linearly with p(CO) which suggests the two-

q

The activation parameters, ∆H ) +124((2) kJ /mol,

q

3

∆

S ) +48((5) J /(mol‚K), and ∆V ) +15.6((0.4) cm /

(

30) CAChe Worksystem 3.0 (CAChe Scientific, Beaverton, OR).

1

-

mol, were determined for the ligand-independent pro-

cess (see Tables 5 and 6). The ligand-dependent process

(31) Henry’s law constant (221.47 L‚atm‚mol ) obtained from:

L u¨ hring, P.; Schumpe, A. J . Chem. Eng. Data 1989, 34, 250-252.

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1555

Ta ble 5. Obser ved Ra te Con sta n ts, Activa tion

En th a lp ies, a n d Activa tion En tr op ies for th e

Sp on ta n eou s, CO-P r om oted , a n d

2

P (OMe)

3

-P r om oted η -Vin yl Isom er iza tion a s a

F u n ction of Tem p er a tu r e

H^q,

kJ mol

∆S ,

q

∆

[ligand], M

T, °C

rate const^a

-1

J mol K^-¹

-1

no CO

k1, s^-

1

-

4

6

7

8

9

0

0.868 × 10

124 ( 2

98 ( 3

90 ( 7

77 ( 2

+48 ( 5

-5 ( 9

4

3.106 × 10

-

4

11.200 × 10

37.700 × 10

2

-1 -1

CO, 0.009

10 k2, M

s

-

2

6

7

8

9

0

0.182 × 10

0.461 × 10

1.330 × 10

3.610 × 10

2

F igu r e 5. Pressure dependence of the η -vinyl isomeriza-

-4

tion for a 2 × 10 M toluene solution of 3 at 60.1 °C in the

absence of CO (9) and in the presence of 0.009 M CO (b).

-

1

-1

P(OMe)3, 0.20

P(OMe)3, 1.98

kK, M

s

-

4

kinetic isomer 3 is substitution labile as determined by

2

3

4

0

6.608 × 10

+1 ( 24

-46 ( 6

4

4.5 9.145 × 10

both IR and NMR spectroscopic techniques. Specifical-

-

4

13

0

19.117 × 10

70.505 × 10

ly, treatment of a toluene solution of CO-labeled 3 with

12

2

atm of CO at ambient temperature results in loss of

-

1

k, s

1

3

-

4

the CO label and uptake of CO by 3 upon conversion

to 4. Importantly, treatment of a toluene-d8 solution

of 3 with 1 atm of CO at 80 °C for 10 min results in

1

2

3

4

0

1.281 × 10

4.012 × 10

4 b

13

4.5 6.398 × 10

-

4

0

11.510 × 10

approximately 50% isomerization (with incorporation of

33.575 × 10

1

3

13

CO upon conversion to 4) and uptake of the CO label

a

Determined by IR spectroscopy. ^bDetermined by UV-vis

by 3 in accord with a dissociative process. Treatment

spectroscopy.

2

of 3 with tert-butyl isonitrile does not promote the η -

vinyl isomerization but instead leads to degradation of

3 presumably due to attack of the imine functionality

of 3 by the nucleophilic isonitrile. The substitution inert

4 does not react with tert-butyl isonitrile, CO, or

P(OMe)3.

Ta ble 6. Obser ved Ra te Con sta n ts a n d Activa tion

Volu m es for th e Sp on ta n eou s, CO-P r om oted , a n d

2

P (OMe)

3

-P r om oted η -Vin yl Isom er iza tion s

_∆_Vq_,

P,

MPa

-1

[ligand], M

rate const^a

cm³mol

2

_n_o_C_Ob

4

-1

The η -vinyl isomerization is, however, promoted by

10 k1, s

5

2.40 ( 0.34

2.11 ( 0.24

1.82 ( 0.10

1.60 ( 0.13

1.40 ( 0.13

+15.6 ( 0.4

+3.9 ( 0.2

P(OMe)3, and the kinetics of this process were investi-

gated. As depicted in eq 11, treatment of a toluene

2

5

7

5

0

5

1

00

CO, 0.009^b

10 k2, M s^-¹

0.216 ( 0.037

0.210 ( 0.026

0.202 ( 0.011

0.197 ( 0.014

0.188 ( 0.015

2

-1

5

2

5

7

5

0

5

00

P(OMe)3, 0.21^c

P(OMe)3, 2.22^c

4

-1

10 kobs, s

1

5

00

50

0

1.87 ( 0.01

1.40 ( 0.02

1.04 ( 0.07

0.76 ( 0.02

+15.7 ( 0.6

+5.5 ( 0.4

solution of 3 with P(OMe)3 at or above room tempera-

ture affords 5 in which the P(OMe)3 is trans to the

fluoride and the inserted acetylene is cis to the fluoride.

The isomerization reaction was monitored by observing

changes in the visible spectra as a function of time as

illustrated in Figure 3b. Again, excellent agreement

was obtained with rates determined by infrared spec-

troscopy. The yellow color of the starting material is

replaced by the intense magenta color of the P(OMe)3-

substituted product, and isosbestic points (360 and 452

nm) are maintained throughout the course of the

transformation. Upon extended reaction times and high

1

4

-1

10 kobs, s

1

5

00

50

0

6.8 ( 0.2

6.0 ( 0.2

5.47 ( 0.04

4.9 ( 0.2

1

a

Rate constants are the mean values of at least three kinetic

runs. ^bKinetic runs performed at 60 °C. Kinetic runs performed

at 25 °C.

c

appears to be first order in added CO with activation

parameters ∆H^q) +98((3) kJ /mol, ∆S ) -5((9)

q

[P(OMe) ], a small amount of secondary reactivity of this

3

q

3

J /(mol‚K), and ∆V ) +3.9((0.2) cm /mol (Tables 5 and

complex is observed and results in some formation of

6

). A complete listing of observed rate constants as a

the disubstituted phosphite complex as well as decom-

position products. The formation of the bis(phosphite)

function of ligand concentration is available as Sup-

porting Information.

Solutions of both 3 and 4 are indefinitely stable in

the dark at ambient temperature under a nitrogen

atmosphere. The thermodynamic isomer 4 is substitu-

tion inert and thermally robust. Treatment of a toluene

1

9

complex was ascertained by the diagnostic F NMR

2

doublet of doublet resonance at δ -186.68 ppm ( J PF )

2

73 Hz and J PP ) 43 Hz). The repetitive scan spectra

recorded under these conditions also have some devia-

tions from that reported in Figure 3b.

1

3

12

solution of CO-labeled 4 with 2 atm of CO at 60 °C

The rate of eq 11 varies with the P(OMe)3 concentra-

tion as well as with temperature and pressure. The

does not result in loss of the ¹³CO label. However, the

1

556 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

3

F igu r e 7. Repetitive scan spectra for the P(OMe) -

2

promoted η -vinyl isomerization in toluene at 25 °C.

-

4

Conditions: [3] ) 2 × 10 M; [P(OMe)

3

] ) 2.20 M; first

spectrum recorded before mixing using a tandem cuvette;

subsequent spectra recorded at 100 s intervals.

F igu r e 6. Plot of kobs (s^-¹) versus P(OMe)

concentration

3

2

-4

(

M) for the η -vinyl isomerization of 2 × 10 M 3 in toluene

solution at 25 °C.

Sch em e 2

reaction is first-order in the tungsten complex 3. The

η -vinyl isomerization process (eq 11) displays satura-

2

F igu r e 8. Pressure dependence of the η -vinyl isomeriza-

-

4

tion kinetics, in which the reactivity tends toward a

limiting value with increasing concentration of P(OMe)3.

Figure 6 illustrates this saturation behavior and shows

kobs as a function of [P(OMe)3] at 25 °C. This behavior

is typical of a mechanism involving the formation of an

tion for a 2 × 10 M toluene solution of 3 at 25 °C in the

3

presence of 0.21 M P(OMe)

M P(OMe) (b).

(9) and in the presence of 2.22

3

at ca. 460 nm and an absorbance increase at ca. 400

nm, on mixing 3 and P(OMe)3. Importantly, the extent

of the spectral changes correlates directly with the

P(OMe)3 concentration employed. It follows that this

spectral change must be due to the rapid formation of

the adduct on mixing the two components. The complex

possesses λmax at 400 nm and at 460 nm. The subse-

quent conversion to 5 is a clean process which exhibits

a single isosbestic at λ ) 420 nm as illustrated in the

repetitive scan spectrum in Figure 7. Unfortunately,

attempts to observe the adduct formation using vari-

able-temperature NMR spectroscopy proved unsuccess-

ful.

The observed rate constants for the P(OMe) -pro-

moted η -vinyl isomerization as a function of tempera-

ture and pressure are reported in Tables 5 and 6.

Figure 8 displays the pressure dependence of the

isomerization in the presence of P(OMe)3. At low

trimethyl phosphite concentrations, the activation pa-

3

2

adduct as shown in Scheme 2 and described by eq 12.

The concentration dependence of the reaction at low

P(OMe)3] (ca. 0.2 M) shows linear behavior and k2 )

[

kK. For high [P(OMe)3] (ca. 2 M), the limiting kobs value

is in fact the rate constant k. The solid line in Figure

6

represents the least-squares fit of the data and gives

-

1

-5 -1

K ) 1.4 ( 0.1 M and k ) (89 ( 13) × 10

s , such

-

3

-1 -1 33

that kK ) 1.2 × 10 The initial slope of the

M

s .

-

3

-1 -1

plot at low [P(OMe)3] has a value of 1.1 × 10

M

s

3

2

which must represent kK and is indeed close to that

calculated from the values of k and K above. An error

due to a change in the reaction medium upon mixing

solutions of 3 and P(OMe)3 can be excluded, since

apparent association constants from medium effects are

q

-1

rameters ∆H ) +90((7) kJ /mol, ∆S ) +1((24)

q

on the order of e0.1 M , which is significantly less than

3

_t_h_e_K_v_a_l_u_e_o_b_t_a_i_n_e_d_i_n_t_h_e_p_r_e_s_e_n_t_s_t_u_d_y_.₃4

J /(mol‚K), and ∆V ) +15.7((0.6) cm /mol were deter-

mined for kK (Tables 5 and 6). The activation param-

Spectra of solutions of 3 and P(OMe)3 were recorded

before and immediately after mixing in the tandem

cuvette in an attempt to obtain evidence for the adduct

q

eters, ∆H ) +77((2) kJ /mol, ∆S ) -46((6) J /(mol‚K),

and ∆V ) +5.5((0.4) cm /mol, were determined at high

P(OMe)3] for k (Tables 5 and 6). A complete listing of

observed rate constants as a function of ligand concen-

tration is available as Supporting Information.

q

3

[

3‚P(OMe)3]. As shown in Figure 7, there is an instan-

taneous change in the spectrum, an absorbance decrease

(

32) (a) Bassetti, M.; Mannina, L.; Monti, D. Organometallics 1994,

1

3, 3293-3299. (b) Wax, M. J .; Bergman, R. G. J . Am. Chem. Soc.

981, 103, 7028-7030. (c) Monti, D.; Bassetti, M. J . Am. Chem. Soc.

993, 115, 4658-4664.

Discu ssion

(

33) Sigma Plot Version 1.02, Windows 3.10 Enhanced (J andel

2

For m ation of η -Vin yl Com plexes. Although metal-

mediated couplings of perfluoroalkenes and -alkynes are

well precedented, simple insertion reactions in which

Scientific, Corte Madera, CA).

34) Beck, M. T. Chemistry of Complex Equilibria; Van Nostrand

Reinhold: London, 1970; p 86.

(

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1557

Sch em e 3

the migrating group is highly fluorinated are quite rare,

presumably due to the increased strength and reduced

nucleophilicity of the metal-carbon bond compared to

those of hydrocarbon analogues.³⁵The slightly shorter

3

6

metal-CAryl bond in 2 (2.207(4) Å) compared to 10

3

7

(

2.226(5) Å) is consistent with this trend.

Thus, an attractive mechanistic rationale for the

chemistry presented in this work involves initial CO loss

from 2 followed by coordination of the acetylene to

Indeed, it is remarkable that migration of the highly

fluorinated metallacycle is facile at room temperature

when a coordination site is made available by photolysis.

Davidson and co-workers reported several examples of

intramolecular nucleophilic attack on coordinated per-

4

generate the d alkyne complex 13. As depicted in

Scheme 3, this transient complex is an 18-electron

system in which the hexafluoro-2-butyne serves as a

two-electron donor ligand. Subsequent migration of the

pendant tetrafluoroaryl group at the coordinated alkyne

2

fluoro-2-butyne to form novel η -vinyl complexes as

1

2d,17

depicted in eq 13.

These reactions involve attack

by lone pairs of coordinated ligands rather than the

migratory insertion pathway discovered in the present

2

would then yield the kinetic η -vinyl complex 3. It

seems likely that the slow step in the thermal reaction

sequence is loss of CO. This is substantiated by the

important observation that isotopic incorporation of

3

8

work.

(35) (a) Alb e´ niz, A. C.; Espinet, P.; J eannin, Y.; Philoche-Levisalles,

1

3

CO into the parent compound 2 requires temperatures

M.; Mann, B. E. J . Am. Chem. Soc. 1990, 112, 6594-6600. (b) Alb e´ niz,

A. C.; Espinet, P.; Foces-Foces, C.; Cano, F. H. Organometallics 1990,

of at least 60 °C, which is the same temperature

required for thermal production of 4. The fast step

appears to be the aryl migration since all spectroscopic

attempts to detect complex 13 have proven unsuccessful.

The migration is certainly promoted by the electron-

poor perfluorinated alkyne ligand since the CF3 groups

increase the electrophilicity of the alkyne carbons.

Additionally, due to its inherent electron deficiency,

hexafluoro-2-butyne resists functioning in a four-

9

1

, 1079-1085. (c) Alb e´ niz, A. C.; Espinet, P. Organometallics 1991,

0, 2987-2988. (d) Gipson, S. L.; Kneten, K. Inorg. Chim. Acta 1989,

57, 143-145.

(

36) Osterberg, C. E. Ph.D. Thesis, University of Utah, 1990.

37) Kiplinger, J . L. Unpublished results (data to appear in an

upcoming paper).

5 4

38) For a related reaction involving TlSC H N see: (a) Davidson,

(

J . L.; Murray, I. E. P.; Preston, P. N.; Russo, M. V.; Manojlovi c´ -Muir,

L.; Muir, K. W. J . Chem. Soc., Chem. Commun. 1981, 1059-1061. (b)

Davidson, J . L.; Murray, I. E. P.; Preston, P. N.; Russo, M. V. J . Chem.

Soc., Dalton Trans. 1983, 1783-1787.

1

558 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

electron donor capacity; it prefers to act as a two-

electron donor.⁵In fact, Davidson and co-workers have

observed similar intermolecular reactivity trends for bis-

ing frequencies (∼50 cm^-¹) which suggests the presence

of greater electron density at the metal center for the

2

thermodynamic η -vinyl product 4. Due to steric prob-

3

(

perfluoro-2-butyne) complexes with heteroatom nucleo-

lems associated with forcing the rigid tridentate η -

1

2b-d,17,38b

philes.

The perfluorinated alkyne ligands not

[C,N,N′] imine ligand to assume a facial coordination

2

only act as “nucleophile magnets” but the resulting η -

vinyl product showcases the second hexafluoro-2-butyne

ligand residing as a two-electron donor.

mode, the kinetic η -vinyl complex 3 shows a greater

distortion from octahedral geometry than does the

2

thermodynamic η -vinyl isomer 4 (vide infra). Thus, the

An alternative mechanism would entail the hetero-

lytic cleavage of the W-CAryl bond to generate the

species 14 in which the metal fragment is an 18-electron

tungsten(II) cationic complex with hexafluoro-2-butyne

serving as a four-electron donor ligand. As depicted in

Scheme 3, this process can be considered as the in-

tramolecular counterpart to the existing intermolecular

nucleophilic additions reported for cationic d⁴alkyne

complexes. The pendant tetrafluoroaryl group exists as

a stabilized carbanion³⁹and could then attack the

alkyne carbons in an intramolecular fashion to yield 3.

In this capacity, hexafluoro-2-butyne encourages the

conversion of the alkyne to its more electron-rich

isolobal η -vinyl cousin. However, it seems unlikely

that the electron-deficient perfluorinated alkyne would

serve as a four-electron donor ligand or even allow the

formation of the cationic tungsten(II) complex 14.

As illustrated in Scheme 3, a third possibility could

involve the concomitant dechelation of the NMe2 ap-

pendage with CO loss upon coordination of the alkyne

to afford the dicarbonyl complex 15 in which hexafluoro-

shift to lower stretching frequency simply could reflect

an increase in the F pπ to metal dπ to CO π* back-

bonding as a result of better orbital overlap between

the metal and ligands upon isomerization.

The average CO stretching frequencies of 3 and 4 are

greater than that of the tricarbonyl starting material 2

2

and suggest that the highly fluorinated η -vinyl ligand

is a strong π-acceptor. It has been shown that hexaflu-

oro-2-butyne is capable of acting as a more effective

12b

double-faced π-acid than carbon monoxide.

Further-

2

more, it is also known that η -vinyl ligands are isolobal

to four-electron donor acetylenes and use essentially the

40

same orbitals in their interactions with metal centers.

2

40

2

Hence, it follows that the perfluorinated η -vinyl frag-

ment generated in these complexes is also an effective

π acid.

As has been demonstrated through hydrogen bonding

studies of related tungsten(II) fluoride carbonyl com-

19

plexes, the F NMR resonance of the fluoride bound to

19

tungsten is quite sensitive to electronic effects. Im-

portantly, a decrease in the basicity of the fluoride

ligand accompanies the isomerization as evidenced by

a dramatic shift in the W-F resonance from δ -172.26

ppm for 3 to δ -138.27 ppm for 4 and a reduction in

2

-butyne serves as a four-electron donor ligand. Aryl

migration followed by reattachment of the NMe2 arm

would then produce 3. In fact, this sort of anchimeric

assistance has recently been reported for ligand sub-

stitution reactions in square-planar iridium(I) and rho-

dium(I) complexes that incorporate the potentially

terdentate monoanionic saturated [C,N,N′] ligand sys-

tem C6H4CH2N(Me)CH2CH2NMe2-2.⁴¹

the tendency of W-F to engage in hydrogen bonding.

19

This trend is strengthened by 2 which displays a

F

NMR resonance at δ -223.38 ppm (CDCl3) for W-F and

also exhibits significant hydrogen bonding in both the

19

solid state and solution.

At a first glance, one notices an apparent difficulty

associated with the first mechanism in that a two-

electron donor alkyne ligand is not isolobal with a three-

The ¹³C{ H} NMR spectra are also a decisive tool for

identifying η -vinyl ligands. The carbenoid character

1

2

of CR in these complexes is reflected in large downfield

2

electron donor η -vinyl ligand. However, since the

2

chemical shifts.

Indeed, compounds 3-5 possess

nucleophile source (and extra electrons) is derived from

the metal-CAryl bond upon migration it does accurately

account for the observed reaction chemistry. Thus, we

favor mechanism I although transient dissociation of the

NMe2 group (“arm-off-arm-on” process) is difficult to

4

2

spectroscopic parameters compatible with other d η -

vinyl monomeric complexes as shown in Table 7. The

1

3

19

use of C{ F} decoupling experiments in conjunction

1

3

with the preparation of CO-labeled complexes eluci-

dated several coupling interactions involving the per-

4

2

rule out.

2

fluorinated η -vinyl moiety. Presumably a consequence

Photolysis appears to access the early portion of the

of a strong F(pπ)-W(dπ)-CR(pπ) orbital interaction in

compound 3, the alkylidene carbon unveiled a rather

reaction coordinate for the thermal reaction of 2 with

2

hexafluoro-2-butyne, since the kinetic η -vinyl complex

2

significant coupling of J CF ) 34 Hz to the trans fluoride.

2

3

is easily converted to the thermodynamic η -vinyl

The presence of this interaction indicates that both the

complex 4 at or above 60 °C. This provides strong

evidence that 3 is indeed an intermediate in the forma-

tion of 4. The isomerization is accompanied by a

significant shift to lower energy in the carbonyl stretch-

2

fluoride as well as the η -vinyl fragment retain coordi-

nation to the metal center in solution. The coupling of

the Câ carbon to the tungsten fluoride could not be

resolved. Two carbonyl resonances were displayed at

2

1

δ 215.24 ppm with J CF ) 13 Hz and J CW ) 136 Hz

(

39) Cohen, S. C.; Massey, A. Adv. Fluorine Chem. 1970, 6, 83-

85.

40) Brower, D. C.; Birdwhistell, K. R.; Templeton, J . L. Organo-

metallics 1986, 5, 94-98.

41) Wehman-Ooyevaar, I. C. M.; Kapteijn, G. M.; Grove, D. M.;

2

1

and at δ 214.97 ppm with J CF ) 20 Hz and J CW ) 184

Hz for the carbonyls cis to the fluoride. The tungsten

bound fluoride also coupled to one methyl and one

methylene carbon producing doublets with 4 and 6 Hz

couplings, respectively.

2

(

Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Chem. Soc., Dalton

Trans. 1994, 703-711.

(42) A similar process has been reported for five-coordinate chiral

tin complexes that contain a bidentate C,N ligand: (a) van Koten, G.;

J astrzebski, J . T. B. H.; Noltes, J . G.; Pontenagel, W. M. G. F.; Kroon,

J .; Spek, A. L. J . Am. Chem. Soc. 1978, 100, 5021-5028. (b)

J astrzebski, J . T. B. H.; Boersma, J .; van Koten, G. J . Organomet.

Chem. 1991, 413, 43-53.

For complex 4, the coupling of CR and Câ could not be

determined in accordance with a cis relationship with

the metal fluoride. The two carbonyl resonances emerged

2

1

at δ 221.82 ppm with J CF ) 5 Hz and J CW ) 142 Hz

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1559

Ta ble 7. Releva n t Str u ctu r a l a n d Sp ectr oscop ic P a r a m eter s for Molybd en u m (II) a n d Tu n gsten (II)

2

a

η -Vin yl Com p lexes

complex

MdCR, Å

M-Câ, Å

CR-Câ, Å

δ(CR), ppm

δ(Câ), ppm

ref

9b,c

9c

9a,c

18

38a

14

60

12a

17

12a

13

this work

2

CpMo[P(OMe)3]2(η -CPhCHPh)

1.95

1.94

1.96

1.92

1.91

1.97

1.96

1.91

1.89

1.94

1.95

1.94

N/A

2.30

2.29

2.25

2.26

2.29

2.32

2.12

2.28

2.19

2.33

2.18

2.30

2.32

2.21

2.196

N/A

1.43

1.44

1.46

1.44

1.43

1.42

1.39

1.45

1.44

1.45

1.42

1.41

1.43

1.41

1.45

N/A

255.5

286.5

237.4

276.5

N/A

242.6

N/A

260.6

196.8

202.8

189.5

26.8

29.9

35.7

23.9

N/A

40.7

N/A

62.1

32.4

40.8

31.3

2

t

CpMo[P(OMe)3]2(η -CBu CHPh)

2

CpMo[P(OMe)3]2(η -CMeCPh2)

5

2

(

η -C9H7)Mo[P(OMe)3]2(η -CSiMe3CH2)

2

CpMoCl(CF3CtCCF3)[η -CF3CC(CF3)(PEt3)]

2

CpMoCl(CF3CtCF3)[η -CF3CC(CF3)(PEt3)]

3

CpMo(CF3CtCCF3)[η -CF3CC(CF3)(NC5H4S)]

2

t

[

(Tp′)(CO)2Mo(η -CPhdCHCHdN(Me)(Bu )][BF4]

2

CpW(CO)2[η -CF3CC(CF3)(-C(dO)SMe)]

2

CpW(SC6H4CH3)(CF3CtCCF3)[η -CF3CC(CF3)(PEt3)]

3

i

CpW(CF3CtCCF3)[η -CF3CC(CF3)(SPr )]

2

t

CpWCl(CF3CtCCF3)[η -CF3CC(CF3)(CNBu )]

2

(

dtc)3W(η -CPhdCPhCPhdCHPh)

trans-(L)W(CO)2(F) (3)

cis-(L)W(CO)2(F) (4)

cis-(L)W(CO)(F)(P(OMe)3) (5)

a

N/A ) data not available.

Sch em e 4

for the carbonyl cis to the fluoride and at δ 221.79 ppm

2

1

with J CF ) 55 Hz and J CW ) 150 Hz for the carbonyl

trans to the fluoride. The carbonyl trans to the fluoride

showed the largest coupling constant. The tungsten

bound fluoride also coupled to one methyl and one

methylene carbon producing doublets with 15 and 3 Hz

couplings, respectively.

Due to the presence of P(OMe)3 in compound 5, the

2

J CF and J CP couplings to the η -vinyl ligand could not

be resolved. However, the sole carbonyl ligand was

below, complex 4 is remarkably robust and exhibits no

measurable fluxional processes up to 90 °C.

2

observed at δ 235.60 ppm with J CF ) 12 Hz, J CP ) 7

A single trifluoromethyl resonance would be antici-

1

Hz, and J CW ) 146 Hz. The small couplings constants

2

pated for a dynamic η -vinyl process occurring in these

complexes since rotation of the η -vinyl fragment would

for these interactions provide compelling evidence for

a cis orientation of the carbonyl ligand with the P(OMe)3

and fluoride ligands.⁴³Further evidence for the geom-

etry about the tungsten(II) metal center is gleaned from

2

necessarily make the two CF3 groups equivalent. In-

19

stead, two CF3 resonances are observed in the F NMR

2

spectra for the η -vinyl complexes 3-5. Note that

1

9

31

1

the F NMR and P{ H} NMR spectra which reveal a

9c

12c-d,17,18

14

Green, Davidson,

and Templeton have ob-

2

large J PF coupling constant of 81 Hz which strongly

2

served a plethora of fluxional processes in their η -vinyl

suggests a trans relationship between the fluoride

systems. Typically, some sort of windshield wiper type

4

3

ligand and the P(OMe)3 ligand. One point of interest

2

motion (less than or equal 90° rotation) of the η -vinyl

1

3

19

is that the C{ F} NMR data how that the trimethyl

phosphite ligand appears to have restricted rotation as

evidenced by the appearance of two methyl resonances

fragment is invoked to explain the dynamic behavior

in these systems as illustrated in Scheme 4. Thus, it is

noteworthy that Green reported the isolation of two

1

at δ 52.61 ppm as an apparent quartet with J CH ) 139

2

distinct η -vinyl isomers for the complex [CpMo-

Hz (due to extensive C-P and C-F couplings the

2

[

P(OMe)3]2(η -C(CH2Ph)CHPh)] which only differ in the

methyl carbon multiplets could not be resolved) and at

2

9c

orientation of the η -vinyl moiety. Presumably, the

1

2

4

δ 52.19 ppm with J CH ) 146 Hz, J CP ) 7 Hz, and J CF

3 Hz. The restricted freedom of rotation of the

inherent steric constraints imposed by the rigid triden-

)

3

tate η -[C,N,N′] chelate ligand system prevent this

trimethyl phosphite ligand was qualitatively confirmed

through modeling studies.

classical windshield wiper motion from occurring (rota-

2

tion of the η -vinyl ligand). Any dynamic process would

2

The W-CR coupling for the coordinated η -vinyl ligand

require a disconnection/reconnection between Câ and the

aromatic carbon, which is highly unlikely. Hence,

complexes 3-5 are static on the NMR time scale as

expected for a six-coordinate complex.

which is frequently observed in tungsten(II) alkylidene

8

,13,23

complexes

was not discernible, presumably due to

extensive fluorination in complexes 3-5. The rigid

2

structure of the η -vinyl products at room temperature

In contrast to structurally similar later transition

1

3

is also illustrated by the C NMR data. Formation of

2

metal complexes, the η -vinyl complexes reported in this

2

η -vinyl ligands with two different Câ substituents

work are chemically robust toward multiple alkyne

insertions into the W-Caryl bond. The later transition

metal complexes readily undergo multiple insertion

reactions with activated acetylenes to form large met-

allacycle complexes as well as heterocyclic ring systems

creates diastereotopic carbonyl ligands due to chirality

at the Câ carbon and the metal center. Because of the

low symmetry of the molecule, the carbonyl carbons are

going to be inequivalent regardless of the time scale of

2

the η -vinyl rotation. Indeed, only one isomer is ob-

44

upon metal extrusion.

In fact, a mechanism for

served for compounds 3 and 4. Although heating 3

generates 4 via the isomerization process discussed

2

Ziegler-Natta type alkyne polymerization based on η -

vinyl intermediates has been proposed. Thus, these

tungsten(II) η -vinyl complexes could actually resemble

45

2

(

43) (a) Doherty, N. M.; Hoffman, N. W. Chem. Rev. 1991, 91, 553-

a snapshot along the reaction path for alkyne insertion

into a M-C bond.

5

7

73. (b) Simpson, R. D.; Bergman, R. G. Organometallics 1993, 12,

81-796.

1

560 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

2

The highly fluorinated η -vinyl complexes presented

carbonyl bond lengths comparable to values reported for

related tungsten(II) fluoride carbonyl complexes.¹

Interestingly, the W-F bond distance is essentially

identical in both complexes 3 (1.994 Å) and 4 (1.996 Å)

and does not appear to be strongly affected by the ligand

trans to it. However, in both six-coordinate complexes

the W-F bond is somewhat shorter than the 2.037(2)

9,49

in this work are unique. Importantly, this work il-

lustrates the distinctive reaction chemistry associated

with metal fluoride compounds since the η -vinyl de-

2

rivatives are not accessible from known tungsten(II)

chloride complexes.⁴⁶

2

Solid -Sta te Str u ctu r es of th e η -Vin yl P r od u cts.

Single-crystal X-ray studies unambiguously confirmed

the molecular structures of the η -vinyl complexes 3 and

Close examination revealed the structures to be

remarkably similar (Table 4). Due to the relatively

small C4-W-C3 bite angle of the η -vinyl moiety in

Å reported for the precursor seven-coordinate tungsten-

2

36

(II) fluoride complex 2.

This is most likely a conse-

2

4

.

quence of the highly fluorinated η -vinyl ligand which

is electron-withdrawing and makes the metal center

rather electron poor in comparison to complex 2. In

regards to σ bonding, the fluoride ligand would be

expected to have a stronger bonding interaction with a

less basic metal center, thus shortening the W-F bond

distance. Furthermore, the amount of fluoride pπ to

metal dπ donation would be expected to increase with

a decrease in metal basicity and this in turn would

result in a shortening of the metal-fluoride bond. Thus,

in these tungsten(II) fluoride complexes the highly

2

compounds 3 (38.9(5)°) and 4 (40.4(2)°), the ligand can

be considered as occupying a single coordination site

such that the tungsten metal center adopts a pseudooc-

tahedral geometry in these systems. Both complexes

possess structural parameters in accord with the pro-

posed metallacyclopropene framework (Table 7). Com-

pound 3 has a short W-C3 bond distance of 1.95(1) Å

4

7

which is consistent with a WdC double bond.

The

2

W-C4 bond distance of 2.21(1) Å is in the range of a

W-C single bond.⁴⁷Furthermore, the C3-C4 bond

clearly exhibits partial double-bond character with a

bond length of 1.41(1) Å, justifying the proposed η -vinyl

structure. The kinetic η -vinyl complex exhibits similar

fluorinated η -vinyl, or cyclic alkylidene, fragment ap-

pears electrophilic enough to invoke π donation from the

fluoride ligand. This reduced electron density on the

fluoride ligand could also justify the dramatic downfield

2

19

shift observed for the W-F resonance in the F NMR

structural parameters with a W-C3 bond length of

spectra for 3 (δ -172.26 ppm) and 4 (δ -138.27 ppm)

versus that reported for 2 (δ -214.60 ppm, acetone-d6).

1

.938(5) Å, a W-C4 bond length of 2.196(5) Å, and a

C3-C4 bond distance of 1.448(7) Å.

In both the structures of 3 and 4 the length of the

W-N1 bond in the five-membered metallacycle is

significantly shorter than the W-N2 bond (Table 4).

This can also be readily explained using the metal-

ligand π overlap argument. An increase in the metal-

ligand π interaction results in an increase in bond order

and a decrease in the metal-ligand bond length. Thus,

Molecular orbital studies regarding the CpM(CO)2

fragment have shown that the preferred orientation for

2

the π-acid η -vinyl fragment is perpendicular to the

double-faced-π-acid carbonyl ligands. That is, the op-

timal orientation is such that the empty p orbital on

the alkylidene carbon fragment will align itself anti-

symmetric with respect to the mirror plane which

bisects the carbonyl ligands.⁴⁸The three π-acids are

roughly orthogonal to each other in both structures.

However, upon isomerization the tungsten metal center

better attains an octahedral geometry as shown by

comparing the bond angles around tungsten in 3 (C1-

W-C2 ) 87.0(6)°; C2-W-C3 ) 78.6(5)°; Cl-W-C3 )

2

the imine N1 atom with sp hybridization (sum of angles

around N1 in both complexes is 360°) is expected to have

a greater bonding interaction and shorter bond lengths

3

than the sp -hybridized N2 atom. It is noteworthy to

mention that the W-N1 bond in 4 (2.342(5) Å) which

2

is trans to the η -vinyl fragment is significantly longer

than the W-N1 bond in 3 (2.29(1) Å) which is trans to

a carbonyl ligand. This implies a stronger trans influ-

8

1.9(6)°; C2-W-F ) 82.4(5)°; C1-W-F ) 82.8(4)°; C3-

W-F ) 156.1(3)°) with those in complex 4 (C1-W-C2

91.3(3)°; C2-W-C3 ) 80.2(2)°; C1-W-C3 ) 78.9-

2

ence for the perfluorinated η -vinyl ligand relative to a

)

(

carbonyl ligand. The strong trans influence for alky-

2)°; C2-W-F ) 91.0(2)°; C1-W-F ) 168.8(2)°; C3-

50

lidene ligands has been noted by others.

W-F ) 112.3(2)°). Thus, the geometry around tungsten

Thus, it would appear that a cummulative effect of

many subtle differences in sterics and electronics be-

tween the two structures perhaps best rationalizes why

the isomerization occurs. The insertion of the hexafluoro-

2

for the thermodynamic η -vinyl complex is slightly more

2

octahedral than for the kinetic η -vinyl complex. This

would be expected so as to maximize overlap for bonding

and hence minimize competition for metal dπ electron

density. This is in agreement with the spectroscopic

observations (vide supra).

The W-C1 and W-C2 bonds in 3 (2.00(1) and 1.96-

1) Å) and 4 (1.996(6) and 2.037(6) Å) have typical W-C

2

-butyne into the W-CAryl bond generates a six-

membered tungstenacycle which is not planar in either

complex. This is in contrast with five-membered met-

allacycles, such as that contained within the tungsten-

(

(II) complex 2, which are planar presumably due to

extensive delocalization of π electron density throughout

(

44) (a) Maassarani, F.; Pfeffer, M.; Le Borgne, G. Organometallics

5

1

metallacycle.

Examination of the torsional angles

1

987, 6, 2029-2043. (b) Wu, G.; Rheingold, A. L.; Heck, R. F.

Organometallics 1986, 5, 1922-1924. (c) Bahsoun, A.; Dehand, J .;

Pfeffer, M.; Zinsius, M.; Bouaoud, S. E.; Le Borgne, G. J . Chem. Soc.,

Dalton Trans. 1979, 547-556. (d) Arlen, C.; Pfeffer, M.; Fischer, J .;

Mitschler, A. J . Chem. Soc., Chem. Commun. 1983, 928-929.

within and surrounding the six-membered metallacycle

(49) Kiplinger, J . L.; Arif, A. M.; Richmond, T. G. Inorg. Chem. 1995,

34, 399-401.

(

45) Carlton, L.; Davidson, J . L.; Ewing, P.; Manojlovi c´ -Muir, L.;

Muir, K. J . Chem. Soc., Chem. Commun. 1985, 1474-1476.

46) (a) Richmond, T. G.; King, M. A.; Kelson, E. P.; Arif, A. M.

(50) (a) Birdwhistell, K. R.; Nieter Burgmayer, S. J .; Templeton, J .

L. J . Am. Chem. Soc. 1983, 105, 7789-7790. (b) Appleton, T. G.; Clark,

H. C.; Manzer, L. E. Coord. Chem. Rev. 1973, 10, 335-422. (c)

Shustorovich, E. M.; Porai-Koshits, M. A.; Buslaev, Y. A. Coord. Chem.

Rev. 1975, 17, 1-98.

(

Organometallics 1987, 6, 1995-1996. (b) Poss, M. J .; Arif, A. M.;

Richmond, T. G. Organometallics 1988, 7, 1669-1670.

(

47) Churchill, M. R.; Youngs, W. J . Inorg. Chem. 1979, 18, 2454-

2

458.

48) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D. L. J . Am.

Chem. Soc. 1979, 101, 585-591.

(51) (a) Bruce, M. I. Angew. Chem., Int. Ed. Engl. 1977, 16, 73-86.

(b) Richmond, T. G.; Osterberg, C. E.; Arif, A. M. J . Am. Chem. Soc.

1987, 109, 8091-8092.

(

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1561

Sch em e 5

in each structure shows a larger deviation from planar-

ity for the tungstenacycle in 3 (W-C4-C5-C10, -50.7°;

C4-C5-C10-C11, -0.2°; C5-C10-C11-N1, 28.4°;

C1-C11-N1-W, 4.4°; C11-N1-W-C4, -39.8°; N1-

W-C4-C5, 55.4°) than in 4 (W-C4-C5-C10, 47.4°;

C4-C5-C10-C11, -8.8°; C5-C10-C11-N1, -19.3°;

C1-C11-N1-W, 1.6°; C11-N1-W-C4, 25.9°; N1-W-

C4-C5, -45.5°). The greater distortion from planarity

in 3 most likely stems from the fact that the monoan-

of acetone to the imine of 16 to afford 17 in which the

3

tridentate monoanionic η -[C,N,N′] ligand is coordinated

to the metal center in a facial manner (eq 14).⁵³

3

ionic η -[C,N,N′] chelate ligand fragment (defined earlier

as L) is forced into an unfavorable facial arrangement

in 3 whereas the tridentate chelate binds to the tung-

sten center in a meridional manner in 4. These two

distinct bonding arrangements for the tridentate ligand

can be gleaned from the N2-W-C4-C5 torsional angle

of 127.2°, the N2-W-C4 bond angle of 105.1°, and the

N2-W-C3 bond angle of 118.4° in 3 versus a N2-W-

C4-C5 torsional angle of -47.0°, a N2-W-C4 bond

angle of 159.1°, and a N2-W-C3 angle of 158.2° in 4.

In seven-coordinate tungsten(II) complexes with a

capped octahedral geometry, the phenyl carbon of the

2

Kin etics a n d Mech a n ism of th e η -Vin yl Isom er -

iza tion . The kinetics and mechanisms of ligand sub-

stitution reactions of octahedral metal carbonyl com-

plexes comprises a vast body of research and has been

the subject of several reviews. The η -vinyl isomer-

ization process follows the two-term rate law given in

eq 10. This suggests that a competitive dual pathway

mechanism is operative as is illustrated in Scheme 5.

3

monoanionic η -[C,N,N′] chelating imine ligand caps an

5

4

2

octahedral face rather than binds in a strictly meridi-

onal or facial manner.¹

9,46,49

In contrast, recent reports

have demonstrated that the saturated tridentate mono-

3

anionic η -[C,N,N′] amine ligand, which can be consid-

ered as the more flexible cousin of the unsaturated

imine ligand, can readily attain and typically favors a

facial binding array in stereochemically similar tung-

The k term is a first-order process with respect to

1

the disappearance of the tungsten complex 3. The large

3

-1

positive volume of activation (+15.6 cm mol ) and

5

2

-1

sten(II) carbonyl complexes.

The intense strain in-

entropy of activation (+48 J mol

K ) suggest that a

3

flicted upon the rigid η -[C,N,N′] imine ligand in con-

fining the ligand to coordination in a strictly meridional

fashion is perhaps best illustrated by the facile addition

(53) (a) Anderson, C. M.; Puddephatt, R. J .; Ferguson, G.; Lough,

A. J . J . Chem. Soc., Chem. Commun. 1989, 1297-1298. (b) Anderson,

C. M.; Crespo, M.; Ferguson, G.; Lough, A. J . Organometallics 1992,

1

1, 1177-1181.

(

52) (a) Buffin, B. P.; Arif, A. M.; Richmond, T. G. J . Chem. Soc.,

(54) (a) Basolo, F. Polyhedron 1990, 9, 1503-1535. (b) Darensbourg,

Chem. Commun. 1993, 1432-1434. (b) Buffin, B. P.; Poss, M. J .; Arif,

A. M.; Richmond, T. G. Inorg. Chem. 1993, 32, 3805-3806.

D. J . Adv. Organomet. Chem. 1982, 21, 113-150. (c) Howell, J . A. S.;

Burkinshaw, P. M. Chem. Rev. 1983, 83, 557-599.

1

562 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

limiting dissociative mechanism is operative. Dissocia-

tion of CO is the rate-determining step, followed by

rapid isomerization and recombination with CO. An

informative comparison is provided by the CO substitu-

tion reaction of Cr(CO)4(phen) (phen ) 1,10-phenan-

throline) with P(OMe)3 as the attacking nucleophile. It

was determined that the reaction proceeds via a dis-

sociative mechanism characterized by a large volume

Sch em e 6

3

-1

of activation (+13.8 ( 0.5 cm mol ) which is compa-

rable to the value obtained for k1.⁵⁵Large positive

The dissociative pathway via a 16-electron intermedi-

ate is consistent with the 16/18-electron rule; the

associative pathway involving a 20-electron intermedi-

ate is incongruous with this formalism. However, it has

3

volumes of activation in the range from 16 to 24 cm

-1

mol have also been reported for the dissociation of CO

from ruthenium cluster compounds of the type [Ru3-

-

56

2

(

CO)10/11] .

Similarly, a dissociative mechanism was

previously been suggested that the η -vinyl ligand can

2

1

reported for the ring closure reaction of Cr(CO)5(dab)

change its hapticity from η -to η as depicted in Scheme

q

38a,45,60

2

(

)

dab ) 1,4-diisopropyl-1,4-diazabutadiene) with a ∆V

6.

In such a manner, the η -vinyl ligand could

+17.2 ( 1.0 cm³mol

-1 57

.

Also consistent with a

dissociative process is the enthalpy of activation (124

conceivably accept a pair of electrons and the complex

would then maintain an 18-electron count at the metal

center during the associative pathway and thus avoid

a 20-electron transition state. The well-known rate-

enhancing ability of variable hapticity ligands (e.g

-

1

kJ mol ) which is somewhat smaller than the M-CO

bond dissociation values for other group VI metal

carbonyl complexes.⁵⁸In conjunction with the unusu-

ally high CO stretching frequencies of complex 3 (vide

supra), the reduced W-CO bond energy could similarly

be a consequence of the great π-acceptor ability of the

6

1

54a

indenyl, nitrosyl ) to dramatically enhance the rate

of ligand substitution reactions suggests that this is a

reasonable explanation. It is noteworthy that, unlike

the static six-coordinate systems, both five-coordinate

and seven-coordinate complexes are known to readily

undergo nonrigid processes at the metal center.⁶²Thus,

the rearrangements depicted in Scheme 5 could ratio-

2

perfluorinated η -vinyl ligand. The presence of the

highly fluorinated η -vinyl ligand withdraws electron

2

density from the metal center, reduces back-bonding,

and weakens the W-CO bond, thus promoting a dis-

sociative mechanism. cis-Labilization by fluoride may

also promote CO loss.⁵⁹

2

nalize the observed η -vinyl isomerization.

The tendency toward saturation is typical of a process

that entails the formation of a kinetically detectable

intermediate. Wax and Bergman observed saturation

kinetics for the migratory CO insertion reaction of

CpMo(CO) (CH ) in a series of methyl-substituted THF

solvents which provided compelling evidence for solvent-

assisted alkyl migration although they did not actually

The k2 term is a second-order process, with a small

negative entropy of activation (-5 J mol^-

1

K

-1

) and a

32b

3

-1

small positive volume of activation (+3.9 cm mol ).

Importantly, the enthalpy of activation for the k2 term

98 kJ mol ) is significantly less than that for the k1

3

-

1

(

process which is in accord with less bond breaking and

more bond formation in the transition state. A direct

observe the solvent-coordinated intermediate. Recently,

q

32a,c

comparison of the ∆S values for the k1 and k2 terms is

Monti and Bassetti

reported the detection of a weak

not possible due to the different units of k1 and k2 that

will affect the ∆S value. The CO-assisted isomerization

molecular iron-phosphine complex in the phosphine-

q

5

induced migratory insertion reaction of (η -C H )Fe-

9

7

reaction is clearly an intramolecular process. The near

2 3

(CO) (CH ) which also exhibits saturation kinetics.

q

5

zero values for ∆S and ∆V imply that the reaction is

intramolecular during which bond formation and break-

age practically cancel each other in terms of volume and

entropy changes. The first-order dependence of the rate

on the CO concentration provides compelling evidence

that an association of 3 with CO occurs to assist the

isomerization process. This association can be visual-

ized in terms of an interchange mechanism I during

which bond formation and bond breakage contributions

cancel each other in terms of volume and entropy effects.

This would mean that attack by free CO and the

subsequent release of coordinated CO occur in a con-

certed manner. Thus, an interchange (I) mechanism

Importantly, slippage of the indenyl ligand from η to

3

an η mode was not invoked to allow for the association

of the phosphine.

The greatest limitation imposed by CO-promoted

kinetics was the inability to attain high enough solution

63

concentrations to observe saturation.

As such, we

2

chose to examine the kinetics of the η -vinyl isomeriza-

tion reaction using the sterically similar trimethyl

phosphite to achieve higher nucleophile concentrations.

2

The reaction of the kinetic η -vinyl complex 3 with

trimethyl phosphite clearly exhibits saturation kinetics

as shown in Figure 6. The observed saturation kinetics

is interpreted in terms of a rapid pre-equilibrium (K)

during which the adduct species [3‚P(OMe)3] is formed,

followed by a rate-determining step (k) to produce 5,

thus, providing compelling evidence for the existence

of the mechanism proposed in Scheme 2. Direct evi-

dence for the formation of the adduct was reported above

2

best rationalizes the CO-promoted η -vinyl isomeriza-

tion process (eq 2).

(

55) Schneider, K. J .; van Eldik, R. Organometallics 1990, 9, 1235-

1

6

1

6

240.

(56) Taube, D. J .; van Eldik, R.; Ford, P. C. Organometallics 1987,

, 125-129.

(

421.

(

(see Figure 7), and the treatment of the kinetic data

57) Reddy, K. B.; van Eldik, R. Organometallics 1990, 9, 1418-

58) Sim o˜ es, J . A. M.; Beauchamp, J . L. Chem. Rev. 1990, 90, 629-

(60) Davidson, J . L.; Shiralian, M.; Manojlovi c´ -Muir, L.; Muir, K.

W. J . Chem. Soc., Dalton Trans. 1984, 2167-2176.

(61) O’Connor, J . M.; Casey, C. P. Chem. Rev. 1987, 87, 307-318.

(62) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transi-

tion Metal Complexes, 2nd ed.; VCH Publishers: New York, 1991.

(63) Wilhelm, E.; Battino, R. Chem. Rev. 1973, 73, 1-9.

88.

(

59) (a) Atwood, J . D.; Brown, T. L. J . Am. Chem. Soc. 1976, 98,

3

1

160-3166. (b) Lichtenberger, D. L.; Brown, T. L. J . Am. Chem. Soc.

978, 100, 366-373. (c) Hoffman, N. W.; Prokopuk, N.; Robbins, M.

J .; J ones, C. M.; Doherty, N. M. Inorg. Chem. 1991, 30, 4177-4181.

Tungsten(II) Metallacyclopropene Complexes

Organometallics, Vol. 15, No. 6, 1996 1563

suggested a formation constant of 1.4 ( 0.1 M^-¹. This

value is such that relatively high nucleophile concentra-

tions have to be employed to achieve saturation. Natu-

rally, this would not have been seen for the CO-assisted

reaction at the low CO concentrations (e0.009 M) used.

Furthermore, the large difference in nucleophilicity

between CO and P(OMe)3 will strongly affect the value

of K, which accounts for the large difference in the

observed reactivities (k2[CO] , kK[P(OMe)3]). The

steric congestion would occur in the transition state if

2

1

the η -vinyl moiety is reluctant to slip into the η mode.

Such a slippage process would also add to an overall

volume increase in the transition state. A large nega-

-

1

-1

tive entropy of activation (-40.2 J mol

small positive volume of activation (+6.2 cm mol

have also been reported for chelate ring closure in (o-

K ) and a

3

-1

)

6

5

phenanthroline)Cr(CO)5.

This ring closure process

involves a highly structured transition state (negative

-

3

-1 -1

q

value of kK ()1.1 × 10

M

s

) was taken from the

∆S ) in which Cr-N bond formation is outweighed by

initial slope at low [P(OMe)3] in Figure 6. The molec-

ular nature of the precursor adduct [3‚P(OMe)3] could

not be determined due to the interference of the

subsequent reaction to produce 5. The observed spectral

changes during formation of the adduct suggest that

P(OMe)3 enters the coordination sphere of the complex

Cr-CO bond breakage in terms of volume changes

q

(small positive ∆V ). Small positive ∆V values and

q

large negative ∆S values were also reported for the

3

+

q

3

-1

racemization of both Cr(phen)3 (∆V ) +3.3 cm mol

,

q

-1

3+

q

∆S ) -56 J mol

K ) and Cr(bipy)3 (∆V ) +3.4

3

-1

q

-1

cm mol , ∆S ) -63 J mol

interpreted in terms of an intramolecular twist rear-

rangement mechanism without bond rupture.

K ) which were

3

or at least binds to a coordinated ligand. By way of

3

2a

66

comparison, Basetti and co-workers

librium constants ranging from K ) 0.94 to 8.0 M for

the formation of [(η -C9H7)Fe(CO)2(CH3), phosphine]

observed equi-

-

1

The large positive volume of activation found at low

5

phosphite concentration (i.e. for kK) is a composite value

q

and proposed that the adduct consists of “electron

donor-acceptor complex”. The equilibrium constant in

the present study is in close agreement with the above

values.

given by ∆V ) ∆V (k) + ∆V(K). The contributions

represent the volume of activation for the rate-deter-

mining step and the reaction volume for the precursor

q

3

-1

formation, respectively. Since ∆V (k) ) +5.5 cm mol

,

it follows that ∆V(K) ) 15.7 - 5.5 ) +10.2 cm mol^-¹.

Thus, precursor formation is accompanied by a volume

increase of 10 cm mol ! This can only mean that the

3

At low phosphite concentration, where kobs ) kK-

[

P(OMe)3], the reaction is characterized by a large

3

-1

3

-1

positive volume of activation (+15.7 cm mol ) and

binding of P(OMe)3 to 3 during this step must involve a

almost zero entropy of activation and an enthalpy of

2

-1

major rearrangement of the kinetic η -vinyl complex.

activation of 90 kJ mol . In contrast, at high phosphite

concentration (rate essentially zero order with respect

to [P(OMe)3]), where kobs ) k, the reaction is described

by a small positive volume of activation (+5.5 cm

mol ), a large negative entropy of activation (-46 J

This reorganization could partially reflect the actual

2

isomerization process, for instance involving an η to

1

3

η slippage (see Scheme 6). Alternatively, desolvation

-

1

of P(OMe) during the formation of the precursor adduct

3

-1

could also contribute toward the observed overall vol-

mol

K ), and an enthalpy of activation of 77 kJ mol .

ume increase. In general, it is difficult to account in

an absolute manner for the volume changes associated

with the precursor formation. Interestingly, the ∆V^q

value for kK is very close to that determined for the

spontaneous isomerization reaction (k1) and emphasizes

the overall volume expansion associated with both the

spontaneous and phosphite-induced isomerization reac-

tions.

The apparently disparate activation parameters are in

accord with the precursor formation mechanism shown

in Scheme 2. The negative entropy of activation for the

rate-determining step reflects that there is significantly

greater steric congestion in the transition state relative

to the ground state which would be expected for a

system involving a seven-coordinate presursor complex.

3

2a

By way of comparison, Bassetti and co-workers

q

-1

q

Thus, the observed kinetic behavior and the P(OMe) -

reported ∆S ) -84.1 J mol

K

and ∆H ) 78.7 kJ

3

2

-

1

assisted η -vinyl isomerization can be accurately de-

mol

for the alkyl migration within the precursor

species [(η -C9H7)Fe(CO)2(CH3),PPh3] to afford (η -C9H7)-

5

scribed by a slight modification of the mechanism

depicted in Scheme 5. This revised mechanistic ratio-

nale is shown in Scheme 7. Instead of an interchange

pathway, the second-order dependence describes a

process in which a molecular complex is formed in a

rapid pre-equilibrium (K) with added P(OMe)3 and the

Fe(CO)(PPh3)(COCH3). It is also noteworthy that Berg-

_m_a_n_a_n_d_W_a_x32b observed a trend (k(2,5-Me2THF) < k(2-

MeTHF) < k(3-MeTHF) < k(THF)) in rate constants for

the tetrahydrofuran solvent-assisted CpMo(CO)3(CH3)

migratory insertion reaction which was consistent with

steric inhibition of the entering group upon associative

activation.

2

kinetic η -vinyl complex 3. The phosphite activates the

system toward rearrangement with concomitant extru-

2

sion of CO (k) to afford the thermodynamic η -vinyl

The small positive volume of activation associated

with the rate-determining step (k) indicates some

volume expansion on going from the ground state to the

transition state. The value is very typical for a dis-

sociative interchange (Id) ligand substitution mecha-

complex 5 (see Scheme 2). Note that since the CO

kinetics were measured at the low end of the saturation

curve, it is reasonable to assume that a similar pathway

2

also explains the CO-promoted η -vinyl isomerization.

6

4

nism. This presumably arises from steric congestion

Con clu sion

around the metal atom as a consequence of more W-CO

3

bond lengthening than W-P shortening as the rigid η -

We have demonstrated that under mild conditions

intramolecular attack by highly fluorinated pendant

2

[

C,N,N′] imine chelate ligand and the η -vinyl group

rearranges in the transition state. Furthermore, greater

(65) Zhang, S.; Zang, V.; Dobson, G. R.; van Eldik, R. Inorg. Chem.

1

991, 30, 355-356.

(66) (a) Lawrence, G. A.; Suvachittanont, S. Inorg. Chim. Acta 1979,

(64) (a) van Eldik, R.; Merbach, A. E. Comments Inorg. Chem. 1992,

1

2, 341-378. (b) van Eldik, R.; Asano, T.; le Noble, W. J . Chem. Rev.

989, 89, 549-688.

32, L13-L15. (b) Lawrance, G. A.; Stranks, D. R. Inorg. Chem. 1977,

16, 929-935.

1

564 Organometallics, Vol. 15, No. 6, 1996

Kiplinger et al.

Sch em e 7

aryl nucleophiles at two-electron donor alkyne ligands

affords η -vinyl complexes. Coupled with our carbon-

fluorine bond activation chemistry, this allows for net

and reactivity directed toward catalytic activation and

functionalization of carbon-fluorine bonds.

2

replacement of a carbon-fluorine bond by a carbon-

Ack n ow led gm en t. An AAUW American Fellowship

to J .L.K. is gratefully acknowledged. The mass spec-

trometer was purchased with funds from the NSF

2

carbon bond. The kinetic η -vinyl complex, trans-(L)W-

(CO)2(F) (3), in which the fluoride is trans to the inserted

acetylene and cis to both carbonyl ligands, is accessible

(Grant CHE-9002690) and the University of Utah

2

through photochemistry. Upon heating, the kinetic η -

Institutional Funds Committee. This research was

supported in part by the Alfred P. Sloan Foundation in

the form of a Research Fellowship awarded to T.G.R.

2

vinyl complex is converted to a thermodynamic η -vinyl

complex, cis-(L)W(CO)2(F) (4), in which the fluoride is

cis to the inserted acetylene and trans to one CO cis to

the other carbonyl ligand. In addition to a ligand-

independent pathway, kinetic measurements reveal

that the isomerization is promoted by added ligand (CO

or P(OMe)3). The kinetic measurements and spectro-

scopic data are in agreement with the rapid and

reversible formation of a weak complex between the

(1991-1995). R.v.E. gratefully acknowledges financial

support from the Deutsche Forschungsgemeinschaft and

the Volkswagen-Stiftung. We also thank the Reviewers

for useful comments.

Su p p or tin g In for m a tion Ava ila ble: Tables of observed

rate constants as a function of ligand concentration and

temperature for all reactions studied, tables giving full crystal-

lographic data for 3, including bond distances, bond angles,

torsion angles, final positional and thermal parameters, and

least-squares planes, and a crystal packing diagram for 4 (20

pages). This material is contained in many libraries on

microfiche, immediately follows this article in the microfilm

version of the journal, can be ordered from the ACS, and can

be downloaded from the Internet; see any current masthead

page for ordering information and Internet access instructions.

2

P(OMe)3 and the kinetic η -vinyl complex, followed by

rate-determining rearrangement at the metal center

with formation of P(OMe)3-substituted thermodynamic

product cis-(L)W(CO)(P(OMe)3)(F) (5). Importantly,

details concerning the intimate nature of the reaction

steps were readily obtained from the volumes, energies,

and entropies of activation.

Although these ligand-based systems are limited with

respect to catalytic chemistry, they clearly serve as

model compounds for the systematic studies of structure

OM9509251

Article Doi

Synthesis and characterization of highly fluorinated tungsten(II) metallacyclopropene complexes. Kinetics and mechanism of an unprecedented η2-vinyl isomerization

DOI: 10.1021/om9509251

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Article abstract of DOI:10.1021/om9509251

Full text of DOI:10.1021/om9509251

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