Intermolecular C-H activations of hydrocarbons initiated by Cp*M(NO)(CH2CMe3)(η3-CH 2CHCHPh) complexes (M = Mo, W)

Article

pubs.acs.org/Organometallics

Intermolecular C−H Activations of Hydrocarbons Initiated by

Cp*M(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) Complexes (M = Mo, W)

Rhett A. Baillie,^†Renee W. Y. Man,^†Monica V. Shree,^†Catherine Chow,^†Michelle E. Thibault,^†

W. Stephen McNeil,*^,‡and Peter Legzdins*^,†

^†Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1

^‡Department of Chemistry, The University of British Columbia Okanagan, Kelowna, British Columbia, Canada V1V 1V7

S

* Supporting Information

ABSTRACT: Thermolysis of Cp*W(NO)(CH₂CMe₃)(η³-

CH₂CHCHPh) (1) at 55 °C leads to the loss of neopentane

and the formation of the 16e η²-allene intermediate complex

Cp*W(NO)(η ²-CH₂CCHPh) (A), which has been

isolated as its 18e PMe₃adduct (2). Further support for the

existence of the allene intermediate A is provided by the

thermolysis of 1 in cyclohexene, which affords Cp*W(NO)-

(H)(η³-CH₂C(3-cyclohexenyl)CHPh) (3) as the principal

organometallic product. In the presence of n-heptane, n-

octane, or n-pentane, A effects C−H activations of the

hydrocarbons exclusively at their terminal carbons and forms

18e Cp*W(NO)(n-alkyl)(η³-CH₂CHCHPh) complexes (4−

6). Similarly, treatments of 1 with mesitylene, methylcyclohex-

ane, and ethylcyclohexane all lead to the corresponding primary sp³C−H activation products (7−9). Complex mixtures of

organometallic products result when 1 is thermolyzed in p-xylene and toluene, reflecting the occurrence of both aryl and benzylic

C−H activations. Interestingly, the aryl C−H activations do not afford the expected Cp*W(NO)(aryl)(η ³-CH₂CHCHPh)

products but rather their Cp*W(NO)(H)[η ³-CH(aryl)CHCHPh] isomers resulting from aryl−H exchange. The thermal

chemistry of the molybdenum analogue of 1, namely Cp*Mo(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) (14), has also been

investigated, and it turns out to be much more limited in scope. When 14 is heated at 35 °C in neat mesitylene for 22 h, it results

in conversion to the mesitylene-activated product Cp*Mo(NO)(CH₂C₆H₃-3,5-Me₂)(η³-CH₂CHCHPh) (15) in low yield, but

thermolyses of 14 in other hydrocarbons do not produce tractable organometallic materials. The results of DFT calculations on

the model reaction of CpW(NO)(η²-CH₂CCHMe) with propane confirm that the rate-determining step is the cleavage of

a propane C−H bond and that the lower energy anti conformers favor terminal activation by 11.5 kJ/mol. All new complexes

have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of

them have been established by X-ray crystallographic analyses.

exclusively at their terminal carbon atoms and forms Cp*W-

(NO)(n-alkyl)(η³-CH₂CHCHMe) complexes.²

INTRODUCTION

■

In recent years we have been exploring the C−H activation

chemistry of the family of 18e Cp*W(NO)(alkyl)(η ³-allyl)

compounds (Cp* = η⁵-C₅Me₅). Two particularly interesting

members of this family are the dimethylallyl complex

Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCMe₂) and the monome-

thylallyl complex Cp*W(NO)(CH ₂CMe₃)(η ³-

CH₂CHCHMe). The dimethylallyl compound loses neo-

pentane at 50 °C and forms two reactive 16e intermediate

species. One intermediate is an η²-allene complex, and the

other is an η²-diene complex; both effect a variety of C−H

bond activations, some of which are unique to these

complexes.¹The monomethylallyl compound, on the other

hand, loses neopentane at ambient temperatures and forms

only the η ²-diene intermediate Cp*W(NO)(η ²-CH₂

CHCHCH₂). In the presence of linear alkanes this

intermediate effects C−H activations of the hydrocarbons

While extending our investigations of the thermal chemistry

of these two allyl complexes to encompass various heteroatom-

containing organic substrates, we subsequently discovered that

they can also effect concurrent N−H and α-C−H activations of

cyclic amines at room temperature without losing neopentane.³

The detailed exploration of this latter chemistry led us to

synthesize other Cp*W(NO)(alkyl)(η ³-allyl) complexes, one

of which was Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) (1).

We soon discovered that, in addition to being able to react with

cyclic amines at 20 °C, complex 1 also possesses a thermal

reaction pathway. Thus, at temperatures above 55 °C it begins

to lose neopentane and generates only the 16e intermediate

allene complex Cp*W(NO)(η²-CH₂CCHPh) (A), which

Received: August 4, 2011

Published: October 28, 2011

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Scheme 1

Scheme 2

effects selective C−H activations of certain hydrocarbons. We

therefore decided to explore this thermal chemistry more fully

in order to establish the scope and mechanisms of these

conversions so that they could be meaningfully compared with

those previously reported for Cp*W(NO)(CH₂CMe₃)(η³-

CH₂CHCMe₂) and Cp*W(NO)(CH₂CMe₃)(η ³-

CH₂CHCHMe). We have also extended our studies to

encompass the molybdenum analogue of 1, namely Cp*Mo-

(NO)(CH₂CMe₃)(η³-CH₂CHCHPh), to see how the C−H

activation chemistry is affected when the metal is changed. This

article reports the results of these investigations.

cm⁻¹, thereby indicating that the isomers 2a,b have virtually

identical electron densities at their tungsten centers. The

isolation of complex 2 establishes that it is the 16e η²-allene

intermediate Cp*W(NO)(η²-CH₂CCHPh) (A in Scheme

2), formed by loss of neopentane from 1, which is responsible

for the subsequent C−H activation chemistry.

The solid-state molecular structure of 2a has been established

by a single-crystal X-ray crystallographic analysis and is shown

in Figure 1. The most notable feature of this structure, which

RESULTS AND DISCUSSION

■

Synthesis and Properties of Cp*W(NO)(CH₂CMe₃)(η³-

CH₂CHCHPh) (1). Complex 1 can be synthesized via

sequential metatheses with magnesium reagents from Cp*W-

(NO)Cl₂(Scheme 1), and it is isolable in moderate yields as an

orange powder.⁴It is soluble in most organic solvents such as

Et₂O, THF, and benzene, but it is only sparingly soluble in

pentane. As a solid, the compound is thermally stable at room

temperature for months and in solutions at the same

temperature it is stable for a few weeks. However, in solutions

at temperatures above 55 °C it begins to react.

In the solid state 1 exhibits a piano-stool molecular geometry

with the allyl ligand in an endo,syn conformation pointing away

from the Cp* ring.³Most importantly, it exists as only one

isomer in which the phenyl substituent of the allyl ligand is

situated proximal to the nitrosyl ligand in the least sterically

demanding orientation (as depicted in Scheme 1).

Figure 1. Solid-state molecular structure of Cp*W(NO)(η ²-CH₂

CCHPh)(PMe₃) (2a) with 30% probability thermal ellipsoids

shown. Selected interatomic distances (Å) and angles (deg): C(11)−

C(12) = 1.433(7), C(12)−C(13) = 1.342(6), C(11)−H(11A) =

1.04(6), C(11)−H(11B) = 1.06(5), W(1)−N(1) = 1.777(4), N(1)−

O(1) = 1.233(5), W(1)−P(1) = 2.4410(15); W(1)−N(1)−O(1) =

173.9(3), C(11)−C(12)−C(13) = 136.8(5).

Reactive Intermediates: Trapping and Labeling

Studies with 1. The thermal reaction of 1 in neat PMe₃at

55 °C for 3 days affords the base-stabilized adduct of the η²-

allene complex, namely Cp*W(NO)(η ²-CH₂CCHPh)-

(PMe₃) (2) (Scheme 2). The adduct has been isolated in 64%

yield after chromatography of the final reaction mixture on

silica with Et₂O as eluant. NMR spectroscopic data indicate that

2 exists in C₆D₆as a mixture of isomers, 2a,b, in an

closely resembles that exhibited by Cp*W(NO)(η ²-H₂C

CCMe₂)(PMe₃),¹is the nonlinear allene ligand framework.

The C(11)−C(12)−C(13) angle of 136.8(5)° is a manifes-

tation of the considerable back-donation of electron density

from the metal center to the η²-allene π* orbitals that also

results in the lengthening of the C(11)−C(12) bond to

1.433(7) Å. This elongation suggests a decrease in the C(11)−

C(12) bond order from formally 2 to about 1.5. This view is

1

approximate ratio of 4:1. The H and ¹³C{¹H} NMR spectra

exhibited by 2a,b in C₆D₆are consistent with the isomers

differing in their orientations of the allene ligand, the major

isomer having the phenyl substituent on the same side as the

PMe₃group as shown in Scheme 2. The IR spectrum of

complex 2 as a Nujol mull exhibits a single ν_NOband at 1526

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further supported by the ¹³C{¹H} and ¹H NMR spectra of 2a,b

in C₆D₆, which exhibit large upfield shifts for the methylene

carbon and hydrogen signals, thereby indicating that the

terminal carbons have considerable sp³character.¹

Further support for the existence of the allene intermediate A

is provided by the thermolysis of 1 in cyclohexene, which

affords Cp*W(NO)(H)(η ³-CH₂C(3-cyclohexenyl)CHPh) (3)

as the principal organometallic product. Complex 3 is

completely analogous to the product obtained from the

reaction between cyclohexene and Cp*W(NO)(η ²-CH₂

CCMe₂), the allene intermediate arising from the

thermolysis of Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCMe₂) at

50 °C.¹Consistently, the proposed mechanism for the

formation of 3 shown in Scheme 3 thus involves the

Scheme 3

Figure 2. Solid-state molecular structure of Cp*W(NO)(H)(η ³-

CH₂C(3-cyclohexenyl)CHPh) (3) with 30% probability thermal

ellipsoids shown. Selected interatomic distances (Å) and angles

(deg): W(1)−C(1) = 2.262(3), W(1)−C(2) = 2.328(2), W(1)−C(3)

= 2.360(2), W(1)−N(1) = 1.763(2), N(1)−O(1) = 1.216(3), C(1)−

C(2) = 1.403(3), C(2)−C(3) = 1.403(3), C(3)−C(4) = 1.492(3),

C(2)−C(10) = 1.521(3), C(10)−C(11) = 1.492(3), C(11)−C(12) =

1.317(4); C(1)−C(2)−C(3) = 119.0(2), C(2)−C(3)−C(4) =

125.6(2), C(1)−C(2)−C(10) = 122.9(2), C(2)−C(10)−C(11) =

114.8(2), C(10)−C(11)−C(12) = 123.4(2), W(1)−N(1)−O(1) =

169.5(2).

Scheme 4

coordination of cyclohexene to the tungsten center, coupling

of the two coordinated olefin ligands, β-H elimination of the

cyclohexyl ring in the newly formed metallacycle, and

isomerization to the final product. A single-crystal X-ray

analysis confirms the solid-state molecular structure of 3

(Figure 2). The intramolecular metrical parameters of this

structure are fully consistent with the bonding representation

shown for this complex in Scheme 3.

Scheme 5

Thermolyses of 1 in n-Alkanes. Thermolysis of 1 at 55

°C in n-heptane, n-octane, or n-pentane leads to the selective

activation of the terminal sp³C−H bonds of the alkanes,

affording only the product Cp*W(NO)(n-C₇H₁₅)(η ³-

CH₂CHCHPh) (4), Cp*W(NO)(n-C ₈H_{1 7})(η ³-

CH₂CHCHPh) (5), or Cp*W(NO)(n-C₅H₁₁)(η ³-

CH₂CHCHPh) (6), respectively, as shown in Scheme 4. Not

surprisingly, the physical properties of complexes 4−6 generally

resemble those of reactant 1. Since the results for each of these

alkane reactions are identical, only the n-heptane reaction

leading to 4 is discussed in detail below.

The formation of 4 via the intermediate allene complex A

may be viewed as occurring in the manner depicted in Scheme

5, in which [W]* = the Cp*W(NO) fragment and R =

(CH₂)₅Me. Complex 4 is an 18-electron species and is stable

with respect to β-H elimination at 55 °C, confirmed by the fact

that it is isolated in high yields as the only organometallic

product. It is likely that at higher temperatures the n-heptyl

ligand does undergo such a transformation, since our original

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Figure 3. ¹³C APT NMR spectrum of 4 in C₆D₆.

attempts to activate linear alkanes with 1 were carried out at 75

°C and resulted in an “indecipherable” product mixture.⁵

The selectivity of the reaction involving n-heptane has been

confirmed by ¹³C{¹H} APT NMR spectroscopy. The presence

of the n-heptyl ligand is indicated in the ¹³C{¹H} APT NMR

spectrum of 4 (Figure 3) by the seven peaks from 14.8 to 38.3

ppm. There are six methylene C atoms and only a single methyl

C atom, indicative of the terminal activation of a primary sp³

C−H bond at one of the two methyl groups. Nonterminal

single C−H bond activation would have been indicated by four

methylene signals pointing up along with three signals pointing

down for the two methyl C atoms and one methine C from

activation of a secondary sp³C−H bond. The other peaks in

the spectrum of 4 can be assigned as shown in Figure 3.

The solid-state molecular structure of 4 is shown in Figure 4.

Even though there is a 1:1 disorder at the end of the n-heptyl

ligand, the other metrical parameters of this complex are similar

to those extant in other Cp*W(NO)(alkyl)(η ³-allyl) com-

plexes.^1,2

In contrast to our initial expectations, the thermal reactivity

of 1 in n-heptane via an intermediate η²-allene complex is

analogous to that of the monomethylallyl compound Cp*W-

(NO)(CH₂CMe₃)(η³-CH₂CHCHMe), which also initiates a

single activation of the terminal sp³C−H bond but via an

intermediate η²-diene complex.²We had originally anticipated

that the C−H activation chemistry of 1 would more closely

resemble that of the dimethylallyl compound Cp*W(NO)-

(CH₂CMe₃)(η³-CH₂CHCMe₂), which effects multiple C−H

bond activations of linear alkanes and loses the 1,1-

dimethylallyl ligand to form tungsten hydride complexes via

both η²-allene and η²-diene intermediate species.¹

Figure 4. Solid-state molecular structure of Cp*W(NO)(n-

C₇H₁₅)(η ³-CH₂CHCHPh) (4) with 30% probability thermal

ellipsoids and 1:1 disorder in the alkyl chain being shown. Selected

interatomic distances (Å) and angles (deg): W(1)−C(11) = 2.350(2),

W(1)−C(12) = 2.3194(19), W(1)−C(13) = 2.3080(18), W(1)−

C(20) = 2.2408(19), W(1)−N(1) = 1.7740(16), N(1)−O(1) =

1.223(2), C(11)−C(12) = 1.387(3), C(12)−C(13) = 1.426(3),

C(13)−C(14) = 1.479(3); C(11)−C(12)−C(13) = 117.51(19),

C(12)−C(13)−C(14) = 121.62(18), W(1)−C(20)−C(21) =

115.20(13), W(1)−N(1)−O(1) = 170.12(15).

Scheme 6

Thermolysis of 1 in Mesitylene. Treatment of complex 1

with mesitylene at 75 °C yields exclusively the benzylic sp³C−

H activated product Cp*W(NO)(CH₂C₆H₃-3,5-Me₂)(η³-

CH₂CHCHPh) (7) (Scheme 6). The selective reactivity of

the sp³-hybridized C−H bonds is identical with that exhibited

by a number of other Cp*W(NO)-containing complexes⁶and

is attributable to the steric bulk of the mesitylene methyl

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substituents hindering access of the tungsten center to the aryl

C−H bonds. A single-crystal X-ray crystallographic analysis of

an orange prism of 7 reveals that its solid-state molecular

structure (Figure 5) closely resembles those of related

Figure 6. Solid-state molecular structure of Cp*W(NO)(CH₂C₆H₁₁)-

(η³-CH₂CHCHPh) (8) with 30% probability thermal ellipsoids

shown. Selected interatomic distances (Å) and angles (deg): W(1)−

C(11) = 2.222(5), W(1)−C(12) = 2.369(5), W(1)−C(13) =

2.557(5), W(1)−C(20) = 2.226(5), W(1)−N(1) = 1.780(4),

N(1)−O(1) = 1.222(5), C(11)−C(12) = 1.448(7), C(12)−C(13) =

1.361(7), C(13)−C(14) = 1.466(7); C(11)−C(12)−C(13) =

117.8(5), C(12)−C(13)−C(14) = 126.4(5), W(1)−C(20)−C(21) =

119.4(3), W(1)−N(1)−O(1) = 169.2(4).

Figure 5. Solid-state molecular structure of Cp*W(NO)(CH₂C₆H₃-

3,5-Me₂)(η ³-CH₂CHCHPh) (7) with 30% probability thermal

ellipsoids shown. Selected interatomic distances (Å) and angles

(deg): W(1)−C(1) = 2.254(3), W(1)−C(10) = 2.347(3), W(1)−

C(11) = 2.311(3), W(1)−C(12) = 2.309(3), W(1)−N(1) = 1.782(3),

N(1)−O(1) = 1.209(3), C(10)−C(11) = 1.379(4), C(11)−C(12) =

1.419(4); C(10)−C(11)−C(12) = 118.3(3), C(11)−C(12)−C(13) =

123.9(3), O(1)−N(1)−W(1) = 171.1(2).

other phenylallyl-containing complexes. Another unusual

feature of complex 8 is that its Nujol mull infrared nitrosyl

stretching frequency of 1562 cm⁻¹is distinctly lower in energy

than those exhibited by other Cp*W(NO)(alkyl)(η ³-

CH₂CHCHPh) complexes (e.g., alkyl = neopentyl (ν _NO1588

cm⁻¹), linear alkyl (ν_ΝO1598 cm⁻¹), mesitylene (ν_ΝO1604

cm⁻¹)). In other words, complex 8 possesses a more electron-

rich metal center than do the other Cp*W(NO)(alkyl)(η ³-

CH₂CHCHPh) complexes.

Thermolysis of 1 in Ethylcyclohexane. Thermolysis of 1

in ethylcyclohexane at 55 °C for 2 days results in the loss of

neopentane and the formation of the new organometallic

complex Cp*W(NO)(CH₂CH₂C₆H₁₁)(η³-CH₂CHCHPh) (9)

(Scheme 8), which can be isolated by chromatography on

Cp*W(NO)(alkyl)(η ³-allyl) complexes.^1,2The ¹H NMR

spectrum of 7 in C₆D₆indicates that it maintains this structure

in solution.

Thermolysis of 1 in Methylcyclohexane. Thermolysis

of 1 in methylcyclohexane at 55 °C for 2 days affords a single

organometallic complex, namely dark orange Cp*W(NO)-

(CH₂C₆H₁₁)(η³-CH₂CHCHPh) (8) (Scheme 7), as well as

some unreacted starting material. The solid-state molecular

structure of complex 8 is shown in Figure 6.

Scheme 7

Scheme 8

Activation of the primary sp³C−H bond of the

methylcyclohexane was indicated initially by the ¹³C APT

NMR spectrum of 8 and then confirmed by the crystallographic

analysis. Bond lengths of the allyl ligand in 8 display the

expected σ−π distortion characteristic of Cp*W(NO)(alkyl)-

(η³-allyl) complexes^1,2with a longer C(11)−C(12) bond

distance of 1.448(7) Å and a shorter C(12)−C(13) bond of

1.361(7) Å. An unusual feature of the solid-state molecular

structure of 8 is that the phenyl substituent of the allyl ligand is

positioned adjacent to the more sterically demanding alkyl

ligand. Such an arrangement does not usually occur for the

alumina followed by recrystallization from pentane at −30 °C.

Evidence for the selective terminal C−H bond activation of the

ethylcyclohexane is again provided by the ¹³C APT NMR

spectrum of 9 (Figure 7). The signals due to the newly formed

cyclohexylethyl ligand are those from 15.1 to 44.8 ppm, and all

of them are attributable to methylene C atoms except for that at

44.8 ppm, which is due to the methine C of the cyclohexyl. The

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Cp* peaks at 1.63 and 1.65 ppm, with two broad W−H signals

at −0.17 and 0.00 ppm. As with the other C−H activations

discussed previously, the broad meso-hydrogen peak of 1 is no

longer evident, but two new meso-hydrogen signals appear as

two sets of doublets of doublets located near 5.7 and 6.0 ppm,

respectively, with nearly identical coupling constants (12.6, 9.9

Hz and 12.4, 10.1 Hz). Furthermore, a duplicate of every peak

in the spectrum is evident. The two sets of signals are also

relatively close in chemical shifts, but a COSY experiment has

identified their respective correlations. Finally, the two pairs of

singlets found between 2.0 and 2.5 ppm, with each singlet

integrating to give a 3:15 ratio against the sharp Cp* signal, are

assigned to the inequivalent methyl groups on the aryl ring on

each product. On the basis of the current evidence we

formulate 10a,b as shown in Scheme 9, with the least sterically

crowded 10a being the main product. Crystals of 10a suitable

for an X-ray crystallographic analysis were eventually grown

from a pentane solution of 10 maintained at −30 °C, and the

subsequently determined solid-state molecular structure of the

complex is shown in Figure 8.

Figure 7. ¹³C APT NMR spectrum of 9 in C₆D₆.

absence of other methine or methyl signals indicates that the

C−H bond of the terminal methyl group of ethylcyclohexane

has been activated.

In closing this section, it should be noted that the

thermolysis of 1 at 55 °C in cyclohexane, a substrate containing

only secondary C−H bonds, does not result in the formation of

any Cp*W(NO)-containing organometallic products, and 1 is

recovered unchanged.

Thermolysis of 1 in p-Xylene. Treatment of complex 1

with p-xylene at 55 °C for 3 days produces a mixture of three

organometallic complexes, as indicated by the presence of three

1

Cp* peaks in the H NMR spectrum of the final reaction

mixture at 1.41, 1.63, and 1.65 ppm with relative intensities

2:5:4, respectively (Scheme 9). Attempts to grow crystals of

these products have afforded two differently colored solids that

have been characterized by ¹H NMR spectroscopy. The

benzylic sp³C−H activated product Cp*W(NO)(CH₂C₆H₄-

4-Me)(η³-CH₂CHCHPh) (11) has been manually separated as

Figure 8. Solid-state molecular structure of Cp*W(NO)(H)(η ³-

CHPhCHCH(C₆H₃-2,5-Me₂)) (10a) with 30% probability thermal

ellipsoids shown. Selected interatomic distances (Å) and angles (deg):

W(1)−C(11) = 2.421(3), W(1)−C(12) = 2.321(3), W(1)−C(13) =

2.281(3), W(1)−N(1) = 1.775(3), N(1)−O(1) = 1.224(4), C(11)−

C(12) = 1.394(5), C(12)−C(13) = 1.425(5), C(11)−C(20) =

1.475(5), C(13)−C(14) = 1.488(5); C(11)−C(12)−C(13) =

119.7(3), C(12)−C(13)−C(14) = 120.7(3), C(12)−C(11)−C(20)

= 123.2(3), W(1)−N(1)−O(1) = 166.9(3). As shown, the asymmetric

unit also contains a molecule of pentane disordered about an inversion

center.

1

an orange solid, and its clean H and ¹³C NMR spectra are

comparable to those exhibited by complex 7, since the two

compounds are essentially isostructural. As a solid and in

solution complex 11 may be stored at −30 °C for at least 1

month without the occurrence of any noticeable decom-

position.

The residual yellow powder contains trace amounts of

product 11 as well as the isomeric complexes Cp*W(NO)-

(H)(η³-CHPhCHCH(C₆H₃-2,5-Me₂)) (10a,b), whose ¹H

NMR spectrum in C₆D₆reveals slightly more downfield shifted

Scheme 9

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Scheme 10

Figure 9. 600 MHz ¹H NMR spectrum of the mixture of products resulting from the thermolysis of 1 in toluene with signals attributable to isomers

12 being identified.

As shown in Scheme 9, the hydrido complexes 10a,b

probably result from isomerization of the aryl compound

initially formed by activation of an aromatic sp²C−H bond of

p-xylene by intermediate A. We have recently documented a

similar isomerization for Cp*W(NO)(Ph)(η ³-

CH₂CHCHMe).⁷In any event, the distribution of products

in Scheme 9 indicates a proclivity of intermediate A to

preferentially activate aromatic C−H bonds over benzylic

bonds, a trend commonly seen with many C−H activating

complexes.⁸Indeed, the approximate 4:1 ratio in favor of the

aryl products in this system is comparable to that found for the

similar reaction of Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCMe₂)

with p-xylene.¹

those observed with p-xylene. The thermal reaction yields a

dark orange oil that consists of an inseparable mixture of sp²

and sp³C−H activated products (Scheme 10). These products

1

were characterized as a mixture by H NMR spectroscopy, and

thus many of the resonances expected for each individual

compound were not discernible due to overlapping signals. The

600 MHz ¹H NMR spectrum of a C₆D₆solution of the orange

oil is shown in Figure 9. A meso-hydrogen signal is evident as a

doublet of doublets of doublets at 5.08 ppm. Along with a Cp*

resonance at 1.41 ppm, this part of the spectrum is consistent

with the occurrence of alkyl C−H activation, but only in a 4:15

ratio with respect to the mixture of aryl C−H activation

products, which again have isomerized to their corresponding

hydrido complexes.⁹

Thermolysis of 1 in Toluene. The thermolysis of 1 in

toluene at 55 °C for 3 days results in transformations similar to

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A special feature of the ¹H NMR spectrum shown in Figure 9

is the presence of multiple hydride peaks at about −0.14 ppm.

It is likely that each hydride peak corresponds to the various

isomers of 12 resulting from initial formation of o-, m-, and p-

toluene activated species, since there are only minimal

structural differences between the various isomers. Such an

inference is supported by the broad Cp* signal and the

superimposed doublet of doublets at 5.94 ppm.

Consequently, it can be concluded that both aryl and

benzylic C−H activations occur when 1 is thermolyzed in p-

xylene or toluene. Given the larger amounts of migration

products as compared to the alkyl activation products, a greater

preference for the activation of aryl C−H bonds is evident in

these systems. Furthermore, the unique formation of C−C

bonds by migration is most likely driven by the extended π-

conjugation of the allyl ligands in the final products.

Molybdenum Analogue of Complex 1. Synthesis and

Thermal Chemistry of Cp*Mo(NO)(CH₂CMe₃)(η ³-

CH₂CHCHPh) (14). Complex 14 can be isolated from the

reaction of Cp*Mo(NO)Cl₂with the appropriate binary

magnesium reagents (cf. Scheme 1) as a brown solid in 28%

yield. Its ¹H NMR spectrum in C₆D₆displays the typical signals

characteristic of piano-stool Cp*Mo(NO)(alkyl)(η ³-allyl)

complexes.¹⁰The resonances due to the protons on the allyl

ligand appear clearly as doublets at 1.62 and 2.30 ppm

(corresponding to CH₂), a doublet at 3.84 ppm (corresponding

to CHPh), and a distinctive doublet of doublets of doublets at

5.50 ppm (corresponding to the meso proton). The

molybdenum compound appears to be moderately unstable

at room temperature in solution, undergoing some decom-

position in a benzene solution after overnight storage. For

comparison, it may be noted that the tungsten analogue of 14,

i.e. 1, requires a temperature of 55 °C in order to initiate its

thermal chemistry (vide supra).

Figure 10. Solid-state molecular structure of Cp*Mo(NO)(CH₂C₆H₃-

3,5-Me₂)(η³-CH₂CHCHPh) (15) with 30% probability thermal

ellipsoids shown. Selected interatomic distances (Å) and angles

(deg): Mo(1)−C(10) = 2.275(2), Mo(1)−C(1) = 2.364(2), Mo(1)−

C(2) = 2.319(2), Mo(1)−C(3) = 2.327(2), Mo(1)−N(1) = 1.778(2),

N(1)−O(1) = 1.207(3), C(1)−C(2) = 1.374(4), C(2)−C(3) =

1.413(3), C(3)−C(4) = 1.479(3); C(1)−C(2)−C(3) = 119.7(2),

C(2)−C(3)−C(4) = 124.6(2), O(1)−N(1)−Mo(1) = 170.41(18).

Regrettably, thermolyses of 14 in other hydrocarbons do not

produce tractable organometallic materials.

Computational Investigations. In an effort to better

understand the observed selectivity of these C−H activation

processes, a model reaction was examined by DFT calculations,

in which the Cp* and the phenyl allene moiety of A were

modeled by Cp and methylallene, respectively. The reaction

profile chosen for investigation was that of this modified allene

complex A′ and propane, which can be activated at either a

primary C−H bond to yield an n-propyl allyl complex or at a

secondary C−H bond to afford an isopropyl allyl. A similar

reaction profile has been previously investigated theoretically by

Fan and Hall:¹¹namely, the initial decomposition pathway of

CpW(NO)(CH₃)(η³-Me₂CCHCH₂) to afford CH₄and the

CpW(NO)(η²-Me₂CCCH₂) congener of phenylallene complex

A. Their results showed a preferred pathway involving a

tungsten-assisted transfer of the hydrogen atom from the

dimethylallyl methine carbon to the alkyl ligand, affording an

alkane σ complex that can then lose CH₄to form the allene

intermediate. The reverse of this pathway thus represents the

mechanism for C−H activation of a new hydrocarbon molecule

by the tungsten allene intermediate. Our results mirror this

preferred pathway for alkane C−H activation, yielding the

reaction in Scheme 12 for the transformation of CpW(NO)-

When complex 14 is heated at 35 °C in neat mesitylene for

22 h, it undergoes conversion to a single identifiable

organometallic complex, which is the mesitylene-activated

product Cp*Mo(NO)(CH₂C₆H₃-3,5-Me₂)(η³-CH₂CHCHPh)

1

(15) (Scheme 11). The H NMR spectrum of 15 in C₆D₆

Scheme 11

displays signals characteristic of the PhCHCHCH₂ligand as

well as new resonances corresponding to the CH₂and methyl

groups on the mesityl ligand. This behavior is consistent with

that of the W congener 1, which activates mesitylene upon

heating at 70 °C for 18 h (vide supra). This conversion

underlines again the more reactive nature of the molybdenum

systems; i.e., heating at a lower temperature for a similar period

of time is sufficient to induce the same transformation. The

solid-state molecular structure of 15 has been established by a

single-crystal X-ray crystallographic analysis and is shown in

Figure 10; it is essentially isostructural with its tungsten

analogue 7 (Figure 5).

Scheme 12

(η ²-CH₃CHCCH₂) (A′) to CpW(NO)(C₃H₇)(η ³-

CH₃CHCHCH₂) (C) with endo,anti configurations being

shown for each organometallic complex.

With the removal of one methyl group from the allyl ligand,

these reaction pathways are somewhat complicated by the

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availability of a greater number of allyl conformations in the

alkyl allyl compounds C, with the allyl group being either endo

or exo, the CH₃substituent on the allyl being either anti or syn,

and the CH₃group being either proximal to or distal from the

alkyl ligand. An investigation of the reaction profile for terminal

C−H activation of propane using the distal endo conformations

(both anti and syn) shows the transition state to lie at a

calculated free energy of at least 17.5 kJ/mol above the lowest-

energy pathway (as described in the Supporting Information),

and so we have discounted further investigation of the distal

species. In addition, our previous examination of these

methylallyl complexes¹⁰has shown the endo conformations

to be slightly favored over exo, and so we have limited our

investigation of the reaction profile shown in Scheme 12 to the

proximal endo arrangements. Although most solid-state

molecular structures of various Cp*W(NO)(η ³-alkylallyl)(R)

complexes exhibit a distal methyl group, with the nitrosyl ligand

situated between the allyl CH₃and the alkyl ligand,^3,10the

various conformations of η³-allyl moieties in cyclopentadienyl

metal complexes have been shown computationally to have low

interconversion barriers.¹²Furthermore, we have observed

rapid interconversion of allyl group conformations at room

temperature for certain complexes, suggesting that conformers

for which the required H-atom transfer reaction would be

nonviable can rapidly rearrange in solution as needed to form

reactive allyl/allene ligand orientations.⁷Also, Fan and Hall’s

investigation¹¹suggests that both endo and exo allyl con-

formers are related by a single structure that lies on the Scheme

12 reaction pathway (between TS and C), so that conclusions

regarding the reaction mechanism from A′ to endo-C will also

apply to a pathway ending with exo-C.

Table 1. DFT Calculated Relative Enthalpies and Free

Energies (in kJ/mol) for Proximal Conformations of

Compounds A′, B, TS, and C

metal−allene linkage exhibits a high degree of metallocyclo-

propane character, as exhibited by dramatically elongated (∼14

pm) C1−C2 bond lengths relative to the C2−C3 distances

(149 and 135 pm, respectively), and by the 136° C1−C2−C3

angles. The allene binding is asymmetric, with the W−C2

distances being ∼10−11 pm shorter than the W−C1 bond

length.

The reaction mechanism begins from allene intermediate A′

with the coordination of the alkane molecule to form σ

complex B. An agostic interaction has H1 bridging between W

and C5, with a corresponding elongation of the C5−H1 bond

relative to the other C5−H bonds by about 3.5 pm and as

much as 4.3 pm for the i-Pr2 configurations. The new W−H1

interaction leads to an overall weakening of the tungsten−

allene bond, with consequent increases to W−C1 and W−C2

distances and a decrease to the C1−C2 distance, resulting from

reduced W→allene π back-bonding. The asymmetry of the

allene binding is slightly diminished, but the W−C2 bonds

(average 210 pm) are still significantly shorter than the W−C1

bond (average 219 pm). The formation of the σ-alkane

complex is enthalpically favored by between 18.5 (syn i-Pr1)

and 29 kJ/mol (anti i-Pr2), with the proximity of the allyl CH₃

group to the propane moiety accounting for the relatively lower

enthalpic stability (by ∼6 kJ/mol) of the syn configurations.

The binding of the propane is entropically disfavored, and so B

lies in a free energy well above A′ and propane in all cases:

∼17−19 kJ/mol uphill for the anti configurations and ∼24−30

kJ/mol uphill for the syn species.

The transition state for the C−H activation process results

from an increased interaction of the transferred H1 with both

W and C2 of the allene and a related decreased interaction

between H1 and the C5 α-carbon of the nascent alkyl group.

The transition state is relatively early, as expected for an

exergonic process, with the breaking C5−H1 bond still being

considerably shorter than the C2−H1 bond being formed

(averages of 148 vs 168 pm). There is a strong interaction

between the transferring H and the tungsten center in the

transition state, as evidenced by a W−H1 distance of ∼178 pm,

so that the metal is clearly assisting with the C−H activation

process, despite the absence of a discrete tungsten hydride

In addition to potential variations in the allyl group,

conformational differences exist in the alkane entity, in that

different possible orientations are available for an approaching

propane molecule, leading to different configurations of the

resulting n-propyl or isopropyl ligands. Certain orientations will

be clearly disfavored: namely, those with large groups in

greatest steric proximity to the Cp ligand. Accordingly, we have

examined the reaction pathway A′ → B → TS → C with one n-

propyl conformation and two isopropyl arrangements (Scheme

Scheme 13

13), using both the endo,syn and endo,anti conformations for

the allyl moiety and the methyl group proximal to the incoming

alkane. The n-propyl pathway was also examined using

endo,syn and endo,anti conformations and a distal methyl

group. The calculated relative enthalpies and free energies for

all species are given in Tables 1 and 2, with the values of

proximal endo,anti-n-PrB taken as 0.0 kJ/mol, and the free

energy reaction profiles for these reaction pathways are shown

in Figure 11. Representative calculated structures are shown in

Figure 12, illustrating the proximal endo,anti pathway leading

to the n-propyl product.

The calculated structures for allene complexes A′ reproduce

the key features of the solid-state molecular structure of

phosphine-trapped allene complex 2a. The η²-allene ligand has

the C1−C2 vector roughly orthogonal to the W−NO axis. The

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Table 2. Calculated Bond Lengths (pm) of the Compounds in Scheme 12

B

TS

C

A′

n-Pr

i-Pr1

i-Pr2

n-Pr

i-Pr1

i-Pr2

n-Pr

i-Pr1

i-Pr2

Endo,Anti

219.6

221.0

344.8

238.3

178.8

145.4

134.9

154.9

145.4

Endo, Syn

219.0

221.7

347.8

237.8

178.9

145.6

135.0

159.8

146.0

W−C1

W−C2

W−C3

W−C5

W−H1

C1−C2

C2−C3

C2−H1

C5−H1

217.2

206.6

331.0

219.4

210.6

332.6

284.2

207.7

145.9

134.8

235.1

113.1

219.5

209.3

331.4

314.4

206.4

146.4

134.9

269.2

113.3

219.4

210.3

332.2

292.2

205.5

146.0

134.8

241.9

113.7

220.3

220.4

343.3

246.6

176.9

145.1

134.9

157.3

150.0

218.8

222.2

348.2

240.5

178.0

145.6

134.9

154.2

149.4

226.6

236.9

255.3

223.8

291.4

145.0

140.3

108.7

365.2

226.8

236.6

256.6

228.2

290.1

145.0

140.4

108.7

356.3

227.1

236.5

253.9

227.3

291.4

144.8

140.4

108.7

369.8

148.7

135.0

W−C1

W−C2

W−C3

W−C5

W−H1

C1−C2

C2−C3

C2−H1

C5−H1

217.1

206.8

331.1

218.6

211.3

336.1

286.8

208.2

146.4

134.9

249.3

113.2

218.5

210.0

334.7

317.0

210.3

146.7

135.0

283.2

113.3

218.3

210.9

335.7

294.2

209.4

146.6

134.9

260.5

113.8

220.1

220.9

345.4

246.2

177.0

145.2

135.0

162.8

146.8

222.2

243.5

269.7

222.6

304.9

146.4

138.8

108.8

370.8

222.3

245.0

272.2

226.0

306.6

146.5

138.8

108.8

364.2

218.9

252.4

299.2

223.6

309.5

147.4

137.7

108.9

3.842

148.7

134.8

Figure 12. Calculated structures of the compounds in Scheme 12, as

proximal endo,anti conformers with activation of a C−H bond leading

to the n-propyl product.

which H1 has now wholly transferred to C2 but maintains an

agostic interaction to the tungsten and in which all four allene

carbon atoms, H1, and the tungsten center are coplanar and

still roughly orthogonal to the W−NO vector. Attempts to

optimize this second agostic structure as either a discrete

intermediate or a second transition state did not result in a

converged structure; instead, optimization proceeded smoothly

to the final η³-allyl product endo,syn-n-Pr-C. However, because

such a transformation requires a rotation of the allyl carbon

plane by approximately 90°, rotation in the opposite direction

would presumably afford the exo conformer with equal ease.

Figure 11. Reaction profiles for the mechanism shown in Scheme 12.

intermediate. An intrinsic reaction coordinate (IRC) calcu-

lation¹³on syn-n-Pr-B confirms that this transition state links A′

and a structure perhaps best described as a dialkyl species, in

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Calculated η³-allyl molecular structures C reproduce the key

features of the solid-state structures of similar compounds, such

as phenylallyl complex 8, including the observed σ−π distortion

in which C1 is bound more strongly to the metal than C3,

especially in the syn conformers (W−C1 average 234 pm vs

anti W−C3 average 255 pm and syn W−C3 average 280 pm).

Similarly, the C1−C2 bonds (average 146 pm) are consistently

longer than the C2−C3 bonds (average 139 pm).

group in the isopropyl path is either directed toward (i-Pr1) or

away from (i-Pr2) the nitrosyl ligand. In the i-Pr1 arrangement,

this CH₃is in close proximity to the cyclopentadienyl group,

while in i-Pr2 it lies in proximity to both the cyclopentadienyl

and the allene/allyl moiety, especially for the syn conformers.

Examination of the W−C bond lengths shows a consistently

greater W−C5 distance along the isopropyl pathways (Table

2), reflective of a steric destabilization. These steric effects

would presumably be exacerbated in the experimentally

investigated complexes, which employ bulkier alkanes and a

Cp* ligand, further promoting the selectivity for primary CH

bonds. Electronically this selectivity is favored by the fact that

the incipient metal−carbon bond is sufficiently strong to

compensate for the breaking of a strong CH bond.

Comparison of the calculated reaction profiles for the various

conformers offers a rationale for the observed preference of

allene intermediate A for the activation of terminal over internal

sp³C−H bonds as well as some insight as into the most

reactive conformation. The syn arrangements lead to higher-

energy structures than do the anti arrangements, both for σ

complexes B and for C−H activation transition states TS. For

complexes B, the syn arrangement directs the allene methyl

group toward the incoming alkane, leading to a steric

destabilization that reduces the effectiveness of alkane binding,

as evidenced by higher free energies ranging from 7.4 to 10.4

kJ/mol and by longer W−H1 distances: an elongation of 0.5

pm for n-Pr and 3.9 pm for both i-Pr conformations. In the

transition states, the syn arrangements lead to a greater

destabilization, with syn-TS lying 10.2 kJ/mol above the anti

species for n-Pr and 9.3 kJ/mol above for i-Pr1. For the i-Pr2

case, which places the alkane methyl groups in closest proximity

to the allene CH₃, no stable transition-state geometry could be

optimized, suggesting that there exists no viable reaction

pathway for secondary C−H bond activation in this

conformation. These higher energies for the syn arrangement

are not reflected in the calculated transition-state W−H

distances but appear to be structurally manifested most clearly

in the nature of the C2−H1 bond being formed: the greater

steric demands of the syn allene methyl result in a longer C−H

contact at the transition state (i.e., 154.9 vs 159.8 pm for n-Pr

and 157.3 vs 162.8 pm for i-Pr1), suggesting that it is harder to

form the new allyl C−H bond in this conformation.

Of greater interest are the differences that emerge when

comparing the various alkane conformations, which lead to

either the n-propyl or isopropyl allyl products. There are

minimal energy differences and thus little expected discrim-

ination among alkane binding modes in σ complexes B. For the

more-favored anti allene conformation, the three alkane binding

conformations are separated by only 2.3 kJ/mol. However,

larger energy differences are manifested in the transition states.

n-Pr-TS lies at an energy of 50.0 kJ/mol above n-Pr-B,

representing the energy barrier to the reaction from the

enthalpically favored σ complex. The i-Pr2- and i-Pr1-TS

structures are 10.7 and 19.0 kJ/mol higher in energy,

respectively, leading to energy barriers from B to TS of 61.5

and 77.5 kJ/mol. Thus, the anti conformers favor primary C−H

activation by 11.5 kJ/mol. Assuming kinetic control of these

reactions, such a barrier would predict a ratio in favor of the n-

propyl product of 68:1 at 55 °C, consistent with the essentially

quantitative selectivity for primary C−H bonds that is

experimentally observed at this temperature. For the less stable

syn conformers, the differences are even larger, with the i-Pr1

barrier being 25.5 kJ/mol higher than the n-Pr barrier.

EPILOGUE

■

At the outset of this work, it was our working hypothesis that

the nature of the 16e intermediate formed by thermolysis of the

Cp*W(NO)(alkyl)(η³-allyl) precursor complex determines the

types of C−H activations initiated by that complex. Thus, the

η²-allene intermediate effects multiple C−H bond activations

of alkanes, whereas the η²-diene intermediate effects only single

C−H bond activations at the terminal carbons of the alkanes.

Similarly, the η²-allene intermediate effects only single C−H

bond activations of benzene to cleanly form Cp*W(NO)(Ph)-

(η³-allyl) products, whereas the η²-diene intermediate reacts

with benzene to produce several isomeric products. This

hypothesis is consistent with the thermal chemistry exhibited

by the dimethylallyl complex Cp*W(NO)(CH₂CMe₃)(η³-

CH₂CHCMe₂), which generates both η²-allene and η²-diene

intermediates,¹and the monomethylallyl complex Cp*W(NO)-

(CH₂CMe₃)(η³-CH₂CHCHMe), which generates only a η²-

diene intermediate.²Consequently, we initially expected that

the thermal chemistry of Cp*W(NO)(CH₂CMe₃)(η ³-

CH₂CHCHPh) (1) would more resemble that of Cp*W-

(NO)(CH₂CMe₃)(η³-CH₂CHCMe₂), since 1 forms only a η²-

allene intermediate complex upon thermolysis at 55 °C.

However, this work has established that 1 initiates the selective

single activation of primary sp³C−H bonds and forms several

isomeric products during its reactions with p-xylene and

toluene. In other words, the thermal chemistry of 1 via a η²-

allene intermediate more resembles that of Cp*W(NO)-

(CH₂CMe₃)(η³-CH₂CHCHMe) via a η²-diene intermediate,

and so it cannot simply be the nature of the reactive

intermediate alone that determines the outcomes of the various

C−H activation processes.

The other intriguing question that remains to be answered is

why some of the organometallic complexes formed by these

C−H activation processes are stable under the experimental

conditions employed while others exhibit further reactivity such

as multiple C−H bond activations of the organic substrates or

isomerizations of the type shown in Schemes 9 and 10 that

result in the formation of tungsten hydrido complexes. It is also

not clear at present why aryl complexes exhibit a particular

proclivity to isomerize in such a manner. Experiments designed

to provide answers to these and other questions are currently in

progress, and the results of these investigations will be reported

in due course.

We attribute these energy differences primarily to the

additional steric strain required by the activation of a secondary

C−H bond. On the isopropyl pathways, the alkyl fragment is

attached such that one methyl group is oriented down and away

from the rest of the complex, which is the same position as the

−CH₂CH₃group on the n-propyl pathway. The second methyl

EXPERIMENTAL SECTION

General Methods. All reactions and subsequent manipulations

involving organometallic reagents were performed under anaerobic

and anhydrous conditions either under high vacuum or an inert

■

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atmosphere of prepurified dinitrogen. Purification of inert gases was

achieved by passing them first through a column containing MnO and

then a column of activated 4 Å molecular sieves. Conventional

glovebox and vacuum-line Schlenk techniques were utilized through-

out. The gloveboxes used were Innovative Technologies LabMaster

100 and MS-130 BG dual-station models equipped with freezers

maintained at −30 °C. All glassware was heated in an oven to 275 °C

to remove any moisture and then cooled to room temperature under

vacuum. Most reactions were performed in thick-walled glass vessels

possessing Kontes greaseless stopcocks and side arm inlets for

vacuum-line attachment. Small-scale reactions and NMR spectroscopic

analyses were conducted in J. Young NMR tubes which were also

equipped with Kontes greaseless stopcocks. All solvents were dried

with appropriate drying agents under a dinitrogen atmosphere and

were distilled prior to use or they were transferred directly under

vacuum from the appropriate drying agent. Hydrocarbon solvents,

diethyl ether, and tetrahydrofuran were dried and distilled from

sodium benzophenone ketyl. The syntheses of (CH₂CHCHPh)MgCl

and (Me₃CCH₂)MgCl from cinnamyl chloride and neopentyl

chloride, respectively, and magnesium (Strem) were performed in a

manner similar to that described previously for the preparation of

other allyl- and alkylmagnesium reagents, and they were transformed

into the corresponding bis(allyl)- and bis(alkyl)magnesium reagents in

the usual manner.⁶Cp*W(NO)Cl₂was prepared according to the

published procedure,¹⁴and all other chemicals were ordered from

commercial suppliers and used as received. The progress of most

reactions was monitored by NMR spectroscopy, but the isolated yields

of all new complexes have not been optimized.

mmol) was dissolved in PMe₃(3 mL) to give an orange solution, and

the mixture was heated at 55 °C for 3 days to produce a dark orange-

brown solution. The solvent was removed in vacuo from the final

mixture to give an oily residue. The residue was dissolved in pentane,

and the solution was transferred to the top of a silica column (0.5 × 5

cm). Elution of the column with Et₂O developed a dark yellow band

that was eluted and collected. Removal of solvent from the eluate

afforded 2 as a light orange solid (30 mg, 64% yield). The NMR

spectroscopic properties of this solid indicated that it consisted of two

isomers of Cp*W(NO)(PMe₃)(η²-CH₂CCHPh), with the major

isomer 2a constituting 78% of the mixture and the minor isomer 2b

being 22%. Orange crystals of 2a suitable for a crystallographic analysis

were grown by slow evaporation of a Et₂O solution at ambient

temperatures.

Characterization Data for 2a: IR (cm⁻¹) 1526 (s, ν_NO); ¹H NMR

(400 MHz, C₆D₆) δ 0.96 (d, ²J_HH= 9.9, 1H, allene CH₂), 1.27 (d, ²J_HP

= 9.1, 9H, PMe₃), 1.66 (s, 15H, C₅Me₅), 2.47 (d, ²J_HH= 9.9, 1H, allene

CH₂), 6.94 (m, 1H, allene PhCH), 7.12 (m, 1H, aryl H), 7.36 (m, 2H,

aryl H), 7.99 (m, 2H, aryl H); ¹³C APT NMR (100 MHz, C₆D₆) δ 9.4

1

(allene CH₂), 10.8 (C₅Me₅), 17.0 (d, J_CP= 31.4, PMe₃), 105.3

2

(C₅Me₅), 125.9 (aryl C), 127.4 (d, J_CP= 7.7, allene PhCH), 127.7

(aryl C), 129.0 (aryl C), 142.7 (d, ²J_CP= 3.1, ipso C), 177.4 (d, ²J_CP

=

1

20.7 allene C); ³¹P{¹H} NMR (121 MHz, C₆D₆) δ −11.8 (s, J_PW

348, PMe₃); MS (LREI, m/z, probe temperature 150 °C) 541 [M⁺].

Characterization Data for 2b: ¹H NMR (400 MHz, C₆D₆) δ 0.39

2

(m, 1H, allene CH₂), 1.07 (d, J_HP= 8.5, 9H, PMe₃), 1.53 (obscured,

1H, allene CH₂), 1.68 (s, 15H, C₅Me₅), 7.14 (obscured, 1H, aryl H),

7.23 (m, 1H, allene PhCH), 7.42 (m, 2H, aryl H), 8.02 (m, 2H, aryl

All IR samples were prepared as Nujol mulls sandwiched between

NaCl plates, and their spectra were recorded on a Thermo Nicolet

Model 4700 FT-IR spectrometer. NMR spectra were recorded at room

temperature on Bruker AV-300, AV-400, and AV-600 spectrometers.

All chemical shifts are reported in ppm, and all coupling constants are

reported in Hz. ¹H NMR spectra are referenced to the residual protio

isotopomer present in C₆D₆(7.16 ppm), and ¹³C APT NMR spectra

are referenced to the natural-abundance carbon signal of C₆D₆₁(128.39

H); ¹³C APT NMR (100 MHz, C₆D₆) δ 10.8 (C₅Me₅), 11.7 (d, ²J_CP

=

1

14.6, allene CH₂), 16.0 (d, J_CP= 33.0, PMe₃), 105.1 (C₅Me₅), 125.3

(aryl C), 125.9 (d, ²J_CP= 3.1, allene PhCH), 127.3 (aryl C), 129.0 (aryl

2

C), 142.9 (ipso C), 173.4 (d, J_CP= 14.6, allene C); ³¹P{¹H} NMR

1

(121 MHz, C₆D₆) δ −10.4 (s, J_PW=340, PMe₃).

Thermolysis of 1 in Cyclohexene: Preparation of Cp*W-

(NO)(H)(η ³-CH₂C(3-cyclohexenyl)CHPh) (3). Complex 3 was

synthesized by the thermolysis of 1 (53.7 mg, 0.100 mmol) in

cyclohexene (2 mL) at 75 °C for 1 day. The volatiles were removed in

vacuo from the final reaction mixture, and the yellow-brown residue

was redissolved in pentane. The pentane solution was transferred to

the top of an alumina column (6 × 0.5 cm) supported on glass wool in

a Pasteur pipet. A yellow band was eluted with 1:1 Et₂O/pentane as

eluant and was collected. The eluate was taken to dryness under

reduced pressure, and the residue was recrystallized from pentane to

give complex 3 as yellow-orange rods (33 mg, 66% yield).

1

ppm). When necessary, H−¹H COSY, H−¹³C HMBC, and H−¹³C

1

HSQC experiments were carried out to correlate and assign H and

¹³C NMR signals. Low-resolution mass spectra (EI, 70 eV) were

recorded by the staff of the UBC mass spectrometry facility using a

Kratos MS-50 spectrometer. Elemental analyses were performed by

Mr. David Wong of the UBC microanalytical facility.

Preparation of Cp*W(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) (1).

This complex was prepared by employing a slightly modified version

of the published procedure.³In a glovebox, a Schlenk flask was charged

w i t h C p * W ( N O ) C l ₂( 2 . 0 0 g , 4 . 7 6 m m o l ) ,

(CH₂CMe₃)₂Mg·x(dioxane) (0.810 g, 476 mmol, 170 g/mol titer),

and a magnetic stir bar. On a Schlenk line, the solid reactants were

frozen to −196 °C using a liquid N₂bath, and THF (ca. 30 mL) was

cannulated into the flask. The mixture was warmed to room

temperature while being stirred for 1 h to produce a dark purple

solution. The THF was removed from the final reaction mixture in

vacuo to give a purple solid that was redissolved in Et₂O (ca. 15 mL),

and the resulting solution was cooled to −78 °C in a dry ice/acetone

bath. In a glovebox, a second Schlenk flask was charged with

(CH₂CHCHPh)₂Mg·x(dioxane) (1.36 g, 5.48 mmol, 248 g/mol titer)

which was further diluted with Et₂O (ca. 30 mL). The allyl Grignard

solution was cannulated dropwise into the cold purple Cp*W(NO)-

(CH₂CMe₃)Cl solution over 30 min. When it was warmed to room

temperature, the reaction mixture turned brown. The solvent was

removed under reduced pressure, and the brown solid remaining was

redissolved in 1:1 pentane/Et₂O and chromatographed on an alumina

column (2 × 10 cm). An orange-brown band was eluted with Et₂O to

give a dark orange eluate. Solvent was removed from the eluate in

vacuo, and the resulting solid was recrystallized from pentane (−30

°C) to give orange crystals of 1 (801 mg, 31% yield). The identity of 1

was confirmed by its spectroscopic properties, which agreed with those

reported previously.³

1

Characterization Data for 3: IR (cm⁻¹) 1560 (s, ν_NO); H NMR

1

(400 MHz, C₆D₆) δ 0.20 (s, J_WH= 126, 1H, WH), 1.61 (s, 15H,

C₅Me₅), 2.00 (br s, 1H, allyl CH₂), 3.10 (m, 1H, cyclohexenyl tertiary

CH), 3.50 (m, 1H, allyl CH₂), 5.86 (m, 1H, cyclohexenyl CH), 6.14

(br s, 1H, allyl CHPh), 6.16 (m, 1H, cyclohexenyl CH), 6.70 (t,

³J_HH= 8.0, 1H, para CH), 6.91 (t, ³J_HH= 8.0, 2H, meta CH), 7.01 (d,

³J_HH= 7.6, 2H, ortho CH); ¹³C APT NMR (100 MHz, C₆D₆) δ 9.9

(C₅Me₅), 21.3, 25.8 (cyclohexenyl CH₂), 33.5 (cyclohexenyl

CH₂CH), 44.9 (cyclohexenyl CHCH), 51.4 (allyl CH₂), 73.0

(allyl CHPh), 105.5 (C₅Me₅), 124.9 (para C), 125.4 (allyl C), 128.2

(meta C), 129.5 (cyclohexenyl CH), 129.6 (ortho C), 130.1

(cyclohexenyl CH), 139.7 (phenyl ipso C); MS (LREI, m/z, probe

temperature 100 °C) 547 [M⁺]. Anal. Calcd for C₂₅H₃₃NOW: C,

54.86; H, 6.08; N, 2.56. Found: C, 55.01; H, 6.10; N, 2.47.

Thermolysis of 1 in n-Heptane: Preparation of Cp*W(NO)(n-

C₇H₁₅)(η³-CH₂CHCHPh) (4). In a glovebox, a reaction flask equipped

with a Kontes greaseless stopcock was charged with 1 (92 mg, 0.171

mmol) and n-heptane (ca. 15 mL) to give a yellow mixture. The

stirred mixture was heated in a water/ethylene glycol bath at 55 °C for

3 days to produce a yellow-orange solution. The solvent was removed

from the final solution under reduced pressure to give a brown oily

residue. The oil was then dissolved in pentane, the solution was

transferred to the top of an alumina column (0.5 × 4 cm), and the

column was developed with pentane. The dark yellow band that

developed was eluted with a 2:1 mixture of pentane and Et₂O. The

solvents were removed from the eluate under vacuum, and the orange

Thermolysis of 1 in PMe₃: Preparation of Cp*W(NO)(PMe₃)-

(η²-CH₂CCHPh) (2). In a glovebox, compound 1 (51 mg, 0.095

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oil remaining was crystallized from pentane at −30 °C overnight to

give yellow-orange cluster crystals of 4 (84 mg, 87% yield).

Characterization Data for 4: IR (cm⁻¹) 1598 (s, ν_NO); MS

CH), 143.1 (ipso C). Anal. Calcd for C₂₄H₃₅NOW: C, 53.64; H, 6.56;

N, 2.61. Found: C, 53.46; H, 6.53, N, 2.76.

Thermolysis of 1 in Mesitylene: Preparation of Cp*W(NO)-

(CH₂C₆H₃-3,5-Me₂)(η³-CH₂CHCHPh) (7). In a glovebox, a sample of

1 (33 mg, 0.061 mmol) was dissolved in mesitylene (1 mL) in a 30 mL

reaction flask sealed with a Kontes greaseless stopcock to give an

orange solution. The solution was heated at 75 °C for 18 h,

whereupon it became golden orange. Removal of the volatile

components from the final reaction mixture in vacuo afforded a dark

1

(LREI, m/z, probe temperature 150 °C) 565 [M⁺]; H NMR (400

3

MHz, C₆D₆) δ 0.94 (t, J_HH= 7.0, 3H, n-heptyl Me), 1.11 (m, 2H, n-

heptyl CH₂), 1.26 (m, 2H, n-heptyl CH₂), 1.32 (br s, 2H, n-heptyl

CH₂), 1.40 (obscured, 2H, n-heptyl CH₂), 1.43 (s, 15H, C₅Me₅), 1.56

(br s, 4H, n-heptyl CH₂), 1.64 (d, ³J_HH= 13.3, 1H, allyl CH₂), 2.15 (d,

2

³J_HH= 9.8, 1H, allyl CHPh), 3.25 (d, J_HH= 6.7, 1H, allyl CH₂), 5.51

1

(ddd, ³J_HH= 13.3, 9.8, 7.0, 1H, meso CH), 7.05−7.36 (m, 5H, aryl H);

orange oil whose H NMR spectrum confirmed the formation of 7.

¹³C APT NMR (100 MHz, C₆D₆) δ 9.8 (C₅Me₅), 14.8 (n-heptyl Me),

Storage of a pentane solution of 7 at −30 °C overnight resulted in the

deposition of 7 as fine orange crystals (23 mg, 64% yield).

18.4 (n-heptyl CH₂), 23.7 (n-heptyl CH₂), 30.2 (n-heptyl CH₂), 33.1

(n-heptyl CH₂), 34.6(n- heptyl CH₂), 38.3 (n-heptyl CH₂), 63.2 (allyl

CHPh), 73.1 (allyl CH₂), 106.2 (C₅Me₅), 107.4 (meso CH), 125.7−

128.7 (aryl CH); HRMS-EI (m/z) [M⁺] calcd for ¹⁸⁶WC₂₆H₃₉NO

567.257 53, found 567.257 54.

Characterization Data for 7: IR (cm⁻¹): 1604 (s, ν_NO); ¹H NMR

3

(400 MHz, C₆D₆) δ 1.43 (s, 15H, C₅Me₅), 1.75 (d, J_HH= 13.4, 1H,

2

3

allyl CH₂), 1.99 (d, J_HH= 9.1, 1H, CH₂Ar), 2.27 (d, J_HH= 9.9, 1H,

allyl CH₂), 2.34 (s, 6H, ArCH₃), 2.75 (d, ²J_HH= 9.1, 1H, CH₂Ar), 3.59

3

(d, J_HH= 7.0, 1H, allyl CHPh), 5.15 (ddd, J_HH= 13.3, 9.9, 7.2, 1H,

meso CH), 6.69 (s, 1H, aryl CH), 6.92 - 7.00 (m, 1H, aryl CH), 7.17 -

7.30 (m, 6H, aryl CH); ¹³C APT NMR (100 MHz, C₆D₆): δ 9.8

(C₅Me₅), 22.3 (CH₂Ar), 22.3 (ArCH₃), 64.9 (allyl CHPh), 75.8 (allyl

CH₂), 106.7 (C₅Me₅), 107.5 (meso CH), 125.7 (aryl C), 125.9 (aryl

C), 127.3 (aryl C), 127.4 (aryl C), 128.5 (aryl C), 137.0 (ipso C),

142.3 (ipso C), 153.3 (ipso C); MS (LREI, m/z, probe temperature

150 °C): 557 [M⁺]. Anal. Calcd for C₂₈H₃₅NOW: C, 57.45; H, 6.03;

N, 2.39. Found: C, 57.33; H, 5.85; N, 2.42.

Thermolysis of 1 in n-Octane: Preparation of Cp*W(NO)(n-

C₈H₁₇)(η³-CH₂CHCHPh) (5). In a glovebox, a glass reaction flask

equipped with a Kontes greaseless stopcock was charged with 1 (90

mg, 0.166 mmol) and n-octane (ca. 15 mL) to give a yellow mixture.

The mixture was heated at 55 °C for 3 days, whereupon it became

dark orange. The solvent was removed from the final mixture under

reduced pressure, the remaining brown oil was dissolved in a minimum

of pentane, and this solution was transferred to the top of an alumina

column (0.5 × 4 cm). Elution of the column with 4:1 pentane/Et₂O

afforded a dark yellow eluate. The solvents were removed from the

eluate in vacuo to give a yellow oil that was crystallized from pentane

at −30 °C overnight to produce 5 as a fine yellow solid (54 mg, 56%

yield).

Thermolysis of 1 in Methylcyclohexane: Preparation of

Cp*W(NO)(CH₂C₆H₁₁)(η³-CH₂CHCHPh) (8). In a glovebox, 1 (66

mg, 0.123 mmol) was dissolved in methylcyclohexane (ca. 5 mL) in a

glass reaction flask equipped with a Kontes greaseless stopcock. The

reaction mixture was placed in a water/ethylene glycol bath and was

heated at 55 °C for 2 days to give a dark orange-red solution. The

solvent was then removed under reduced pressure, the resulting

residue was dissolved in pentane, and the solution was transferred to

the top of an alumina column (0.5 × 4 cm). A yellow band was eluted

from the column with a 2:1 mixture of pentane and Et₂O. The eluate

was reduced under vacuum to give a yellow oil which was crystallized

from pentane at −30 °C to obtain dark orange, X-ray-quality crystals

of 8 (28 mg, 41% yield).

1

Characterization Data for 5: IR (cm⁻¹) 1599 (s, ν_NO); H NMR

(400 MHz, C₆D₆) δ 0.92 (t, ³J_HH= 7.0, 3H, n-octyl Me), 1.11 (m, 2H,

n-octyl CH₂), 1.26 (m, 2H, n-octyl CH₂), 1.36 (m, 4H, n-octyl CH₂),

1.44 (s, 15H, C₅Me₅), 1.58 (m, 2H, n-octyl CH₂), 1.63 (m, 2H, n-octyl

CH₂), 1.69 (obscured, 1H, allyl CH₂), 1.77 (m, 2H, n-octyl CH₂), 2.17

3

(d, J_HH= 9.8, 1H, allyl CHPh), 3.27 (d, J_HH= 7.0, 1H, allyl CH₂),

5.52 (ddd, ³J_HH= 13.3, 9.8, 7.0, 1H, meso CH), 7.05 (m, 1H, aryl H),

7.28 (m, 2H, aryl H), 7.37 (m, 2H, aryl H); ¹³C APT NMR (100

MHz, C₆D₆) δ 9.8 (C₅Me₅), 14.8 (n-octyl Me), 18.4 (n-octyl CH₂),

23.6 (n-octyl CH₂), 30.5 (n-octyl CH₂), 30.6 (n-octyl CH₂), 32.9 (n-

octyl CH₂), 34.6 (n-octyl CH₂), 38.3 (n-octyl CH₂), 63.1 (allyl CHPh),

73.2 (allyl CH₂), 106.2 (C₅Me₅), 107.4 (meso CH), 125.6 (aryl CH),

127.5 (aryl CH), 128.7 (aryl CH), 143.1 (ipso C); HRMS-EI (m/z)

[M⁺] calcd for ¹⁸⁴WC₂₇H₄₁NO 579.269 75, found 579.269 77. Anal.

Calcd for C₂₇H₄₁NOW: C, 55.96; H, 7.13; N, 2.42. Found: C, 55.19;

H, 7.01; N, 2.50.

1

Characterization Data for 8: IR (cm⁻¹) 1562 (s, ν_NO); H NMR

(400 MHz, C₆D₆) δ 1.12 (m, 2H, cyclic CH₂), 1.25 (m, 2H, cyclic

CH₂), 1.36 (obscured, 1H, WCH₂C₆H₁₁), 1.35 (m, 4H, cyclic CH₂),

3

1.41 (s, 15H, C₅Me₅), 1.67 (d, J_HH= 13.2, 1H, allyl CH₂), 1.72 (m,

3

1H, cyclic CH), 1.91 (m, 2H, cyclic CH₂), 2.20 (d, J_HH= 9.7, 1 H,

allyl CHPh), 2.66 (br d, ³J_HH= 11.8, 1H, WCH₂C₆H₁₁), 3.43 (d, ³J_HH

= 7.0, 1H, allyl CH₂), 5.56 (ddd, ³J_HH= 13.2, 9.7, 7.0, 1H, meso CH),

7.05 (m, 1H, aryl H), 7.27 (m, 2H, aryl H), 7.38 (m, 2H, aryl H); ¹³

C

Thermolysis of 1 in n-Pentane: Preparation of Cp*W(NO)(n-

C₅H₁₁)(η³-CH₂CHCHPh) (6). In a glovebox, a sample of 1 (41 mg,

0.076 mmol) was suspended in n-pentane (ca. 10 mL). The orange

suspension was transferred to a reaction flask equipped with a Kontes

greaseless stopcock and was heated at 55 °C for 3 days. Removal of

solvent from the final orange solution in vacuo afforded an oily

residue. The oil was redissolved in a minimum amount of pentane, and

this solution was transferred to the top of an alumina column (0.5 × 4

cm). A yellow band was developed and eluted from the column with a

3:1 mixture of pentane and Et₂O. The solvents were removed from the

eluate under reduced pressure, and complex 5 was obtained as a light

orange solid by recrystallization of the residue from pentane at −30 °C

overnight (31 mg, 76% yield).

APT NMR (100 MHz, C₆D₆) δ 9.7 (C₅Me₅), 25.9 (cyclic CH₂), 27.7

(cyclic CH₂), 28.0 (cyclic CH₂), 37.8 (cyclic CH₂), 42.4

(WCH₂C₆H₁₁), 45.2 (cyclic CH), 63.7 (allyl CHPh), 72.4 (allyl

CH₂), 106.4 (C₅Me₅), 108.4 (meso CH), 125.7 (aryl CH), 127.7 (aryl

CH), 128.7 (aryl CH), 143.6 (ipso C); HRMS-EI (m/z) [M⁺] calcd

for ¹⁸⁴WC₂₆H₃₇NO 563.238 45, found 563.238 47.

Thermolysis of 1 in Ethylcyclohexane: Preparation of

Cp*W(NO)(CH₂CH₂C₆H₁₁)(η³-CH₂CHCHPh) (9). In a glovebox, a

glass reaction flask equipped with a Kontes greaseless stopcock was

charged with 1 (70 mg, 0.130 mmol) and ethylcyclohexane (ca. 10

mL) to produce an orange solution. The reaction mixture was heated

at 55 °C for 2 days, whereupon it became dark orange-brown. The

solvent was removed from the final mixture under reduced pressure,

and the remaining oily residue was redissolved in pentane and

transferred to the top of an alumina column (0.5 × 3 cm). A yellow

band was eluted from the column with a 1:1 mixture of pentan and

Et₂O to give a dark yellow eluate. The solvents were removed from the

eluate in vacuo, and orange crystals of 9 were obtained by

recrystallization of the residue from pentane at −30 °C overnight

(32 mg, 46% yield).

Characterization Data for 6: IR (cm⁻¹) 1598 (s, ν_NO); MS

1

(LREI, m/z, probe temperature 150 °C) 537 [P⁺, ¹⁸⁴W]; H NMR

3

(400 MHz, C₆D₆) δ 0.86 (t, J_HH= 7.0, 3H, n-pentyl Me), 1.05 (m,

2H, n-pentyl CH₂), 1.11 (m, 2H, n-pentyl CH₂), 1.26 (m, 2H, n-pentyl

CH₂), 1.33 (br s, 2H, n-pentyl CH₂), 1.43 (s, 15H, C₅Me₅), 1.63

3

(obscured, 1H, allyl CH₂), 2.16 (d, J_HH= 9.8, 1H, allyl CHPh), 3.27

3

(m, 1H, allyl CH₂), 5.51 (ddd, J_HH= 13.3, 9.8, 7.0, 1H, meso CH),

7.05 − 7.36 (m, 5H, aryl H); ¹³C APT NMR (100 MHz, C₆D₆) δ 9.8

(C₅Me₅), 14.6 (n-pentyl Me), 18.3 (n-pentyl CH₂), 23.4 (n-pentyl

CH₂), 34.1 (n-pentyl CH₂), 40.5 (n-pentyl CH₂), 63.2 (allyl CHPh),

73.1 (allyl CH₂), 106.2 (C₅Me₅), 107.4 (meso CH), 125.6−128.7 (aryl

1

Characterization Data for 9: IR (cm⁻¹) 1562 (s, ν_NO); H NMR

(400 MHz, C₆D₆) δ 1.12 (m, 2H, WCH₂CH₂C₆H₁₁), 1.24 (m, 2H,

cyclic CH₂), 1.26 (m, 2H, cyclic CH₂), 1.31 (obscured, 1H,

WCH₂CH₂C₆H₁₁), 1.35 (m, 4H, cyclic CH₂), 1.44 (s, 15H, C₅Me₅),

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1.67 (d, ³J_HH= 13.3, 1H, allyl CH₂), 1.73 (m, 1H, cyclic CH), 1.84 (m,

2H, cyclic CH₂), 2.11 (obscured, 1H, WCH₂CH₂C₆H₁₁), 2.16 (d, ³J_HH

= 9.8, 1H, allyl CHPh), 3.27 (d, ³J_HH= 7.4, 1H, allyl CH₂), 5.54 (ddd,

³J_HH= 13.3, 9.8, 7.4, 1H, meso CH), 7.05 (m, 1H, aryl H), 7.28 (m,

2H, aryl H), 7.36 (m, 2H, aryl H); ¹³C APT NMR (100 MHz, C₆D₆)

δ 9.8 (C₅Me₅), 15.1 (WCH₂CH₂C₆H₁₁), 27.7 (cyclic CH₂), 27.9

(cyclic CH₂), 34.2 (cyclic CH₂), 34.3 (cyclic CH₂), 42.2

(WCH₂CH₂C₆H₁₁), 44.8 (cyclic CH), 63.1 (allyl CHPh), 72.4 (allyl

CH₂), 106.2 (C₅Me₅), 107.4 (meso CH), 125.6 (aryl CH), 127.5 (aryl

CH), 128.7 (aryl CH), 143.1 (ipso C); HRMS-EI (m/z) [M⁺] calcd

for ¹⁸⁴WC₂₇H₃₉NO 577.254 10, found 577.254 12. Anal. Calcd for

C₂₇H₃₉NOW: C, 56.16; H, 6.81; N, 2.43. Found: C, 54.93; H, 6.74; N,

2.43. Elemental analysis for carbon content was consistently lower

than the calculated value. This may be due to incomplete combustion

of the solid.

pentane at −30 °C produced complexes 12 and 13 as a yellow solid

(55 mg, 18%). The complexes were characterized as a mixture.

Characterization Data for Isomers 12: IR (cm⁻¹) 1596 (s, ν_NO);

¹H NMR (600 MHz, C₆D₆, selected signals, mixture of isomers) δ

1

−0.17 (s, J_WH= 123.2, 1H, WH), −0.13 (s, J_WH= 123.2, 1H, WH),

−0.10 (s, ¹J_WH= 122.7, 1H, WH), 1.63 (s, 15H, C₅Me₅), 2.00 (d, ³J_HH

3

= 10.0, 1H, allyl CH), 2.04 (d, J_HH= 10.0, 1H, allyl CH), 2.063 (d,

3

³J_HH= 10.0, 1H, allyl CH), 2.064 (d, J_HH= 10.0, 1H, allyl CH), 2.11

(s, 3H, ArCH₃), 2.17 (s, 3H, ArCH₃), 2.21 (s, 3H, ArCH₃), 2.35 (s,

3H, ArCH₃), 2.71 (d, ³J_HH₃= 12.9, 1H, allyl CH), 2.74 (d, ³J_HH= 12.9,

3

1H, allyl CH), 2.78 (d, J_HH= 12.3, 1H, allyl CH), 2.80 (d, J_HH

=

3

12.3, 1H, allyl CH), 5.91 (dd, J_HH= 12.9, 10.0, 1H, meso CH), 5.92

(dd, ³J_HH= 12.3, 10.0, 1H, meso CH), 5.94 (dd, ³J_HH= 12.3, 10.0, 1H,

meso CH), 5.95 (dd, ³J_HH= 12.9, 10.0, 1H, meso CH), 6.84−7.56 (m,

36H, aryl H); ¹³C APT NMR (100 MHz, C₆D₆) δ 10.6 (C₅Me₅), 21.4

(ArCH₃), 21.5 (ArCH₃), 21.9 (ArCH₃), 22.3 (ArCH₃), 62.7 (allyl

CH), 63.0 (allyl CH), 63.2 (allyl CH), 63.3 (allyl CH), 75.6 (allyl CH),

75.9 (allyl CH), 76.4 (allyl CH), 76.7 (allyl CH), 103.6 (meso CH),

104.0 (meso CH), 104.2 (meso CH), 104.2 (meso CH), 105.3

(C₅Me₅), 124.2−129.8 (aryl CH), 135.0−143.5 (ipso C); HRMS-EI

(m/z) [M⁺] calcd for ¹⁸⁴WC₂₆H₃₁NO 557.191 52, found 557.191 23.

Anal. Calcd for C₂₆H₃₁NOW: C, 56.03; H, 5.61; N, 2.51. Found: C,

56.61; H, 5.82; N, 2.41.

Thermolysis of 1 in p-Xylene. In a glovebox, a sample of 1 (88

mg, 0.16 mmol) was dissolved in an excess of p-xylene (8.5 mL) to

give an orange solution which was transferred into a glass reaction flask

that was subsequently sealed with a Kontes greaseless stopper.

Thermolysis of the mixture at 55 °C for 3 days produced a deep yellow

solution. The solvent was then removed in vacuo to give a dark orange

oil, which was dissolved in pentane and transferred to the top of a

silica column (0.5 × 5 cm). Elution of the column with Et₂O

developed an orange band that was eluted and collected. Removal of

solvent from the eluate in vacuo afforded an orange oil, which was

redissolved in pentane and cooled at −30 °C overnight to induce the

precipitation of a yellow powder (consisting primarily of 10a,b) and an

orange powder (11) (75 mg, 80%). X-ray-quality crystals of 10a were

obtained by recrystallization of the yellow powder from pentane at

−30 °C for 5 days.

Characterization Data for 13: (selected signals, mixture of

1

isomers) H NMR (600 MHz, C₆D₆) δ 1.41 (s, 15H, C₅Me₅), 1.71

3

(d, J_HH= 13.5, 1H, allyl CH₂), 2.28 (d, J_HH= 10.0, 1H, allyl CH),

3

3.49 (d, J_HH= 7.0, 1H, allyl CH₂), 5.08 (ddd, J_HH= 13.5, 10.0, 7.0,

1H, meso CH); ¹³C APT NMR (150 MHz, C₆D₆) δ 10.0 (C₅Me₅),

64.8 (allyl CH), 75.8 (allyl CH₂), 106.8 (C₅Me₅), 107.2 (meso CH).

Preparation of Cp*Mo(NO)(CH₂CMe₃)(η³-CH₂CHCHPh) (14).

Cp*Mo(NO)Cl₂(0.758 g, 2.3 mmol) was dissolved in THF (40 mL)

to give an orange solution. A separate Schlenk flask was charged with

(CH₂CMe₃)₂Mg·x(dioxane) in THF solution (0.72 mL, titer 301 mL/

mol of CH₂CMe₃) and additional THF (5 mL). The latter solution

was frozen at −196 °C under a flow of dinitrogen, and the orange

solution was cannulated dropwise onto the colorless solution over 30

min. The resulting mixture was warmed to room temperature over 1 h

while being stirred. Volatiles were removed from the final brown

solution in vacuo, and the brown residue was redissolved in Et₂O (10

mL) to give a brown solution. A separate Schlenk flask was charged

with (CH₂CHCHPh)₂Mg·x(dioxane) (4.3 mL, titer 2340 mL/mol of

CH₂CHCHPh) and Et₂O (5 mL) to give an orange solution. The

latter solution was frozen at −196 °C under a flow of dinitrogen, and

the brown solution was cannulated dropwise onto the frozen orange

solid over a period of 30 min. The resulting mixture became red-brown

after being warmed to room temperature while being stirred over 1 h.

The volatiles were then removed in vacuo, the resulting brown solid

was redissolved in cold (- 70 °C) 4:1 pentane/Et₂O, and this solution

was transferred onto a silica column. Elution of the column with cold

4:1 pentane/Et₂O developed a red band that was eluted and collected.

Removal of solvent from the eluate in vacuo left an oily red-brown

residue which was recrystallized from cold pentane to give 14 as a

brown solid (0.155 g, 28% yield).

Characterization Data for 10a: IR (cm⁻¹) 1581 (s, ν_NO) 1728

1

(m, ν_WH); H NMR (300 MHz, C₆D₆) δ 0.00 (s, J_WH= 122.3, 1H,

WH), 1.63 (s, 15H, C₅Me₅), 2.03 (d, ³J_HH= 9.6, 1H, allyl CH), 2.07 (s,

3H, ArCH₃), 2.27 (s, 3H, ArCH₃), 3.04 (d, J_HH= 12.6 Hz, 1H, allyl

3

CH), 6.01 (dd, J_HH= 12.6, 9.9, 1H, meso CH), 6.75−7.95 (m, 8H,

aryl CH); ¹³C APT NMR (100 MHz, C₆D₆) δ 10.6 (C₅Me₅), 20.1

(ArCH₃), 21.6 (ArCH₃), 63.4 (allyl CH), 72.6 (allyl CH), 105.1 (meso

CH), 105.4 (C₅Me₅), 125.8 (aryl C), 126.7 (aryl C), 127.6 (aryl C),

127.8 (aryl C), 129.0 (aryl C), 130.5 (ipso C), 130.5 (aryl C), 136.6

(ipso C), 143.2 (ipso C); MS (LREI, m/z, probe temperature 180 °C)

571 [M⁺]. Anal. Calcd for C₂₇H₃₃NOW: C, 56.75; H, 5.82; N, 2.45.

Found: C, 55.20; H, 5.85; N, 2.48.

Selected Signals for 10b: ¹H NMR (300 MHz, C₆D₆) δ −0.17 (s,

¹J_WH= 123.2, 1H, WH), 1.65 (s, 15H, C₅Me₅), 2.35 (s, 3H, ArCH₃),

2.40 (d, ³J_HH= 4.7, 1H, allyl CH), 2.43 (s, 3H, ArCH₃), 2.82 (d, ³J_HH

=

12.6, 1H, allyl CH), 5.72 (dd, ³J_HH= 12.4, 10.1, 1H, meso CH), 6.75−

7.95 (m, 8H, aryl CH); MS (LREI, m/z, probe temperature 150 °C)

571 [M⁺].

Characterization Data for 11: ¹H NMR (300 MHz, C₆D₆) δ 1.41

3

2

(s, 15H, C₅Me₅), 1.72 (d, J_HH= 13.2, 1H, allyl CH₂), 1.99 (d, J_HH

=

9.4, 1H, alkyl CH₂), 2.24 (s, 3H, ArCH₃), 2.28 (d, ³J_HH= 9.9 Hz, 1H,

allyl CH₂), 2.76 (d, ²J_HH= 9.4, 1H, alkyl CH₂), 3.51 (d, ³J_HH= 7.0, 1H,

3

allyl CHPh), 5.11 (ddd, J_HH= 13.4, 9.9, 7.2, 1H, meso CH), 6.84 -

7.61 (m, 8H, aryl CH); ¹³C APT NMR (100 MHz, C₆D₆) δ 9.7

(C₅Me₅), 22.1 (CH₂Ar), 21.4 (ArCH₃), 64.7 (allyl CHPh), 76.0 (allyl

CH₂), 106.6 (C₅Me₅), 107.3 (meso CH), 125.7 (aryl C), 127.3 (aryl

C), 128.5 (aryl C), 129.0 (aryl C), 129.1 (aryl C), 132.6 (ipso C),

142.3 (ipso C), 150.3 (ipso C); MS (LREI, m/z, probe temperature

150 °C): 571 [M⁺].

Characterization Data for 14: IR (cm⁻¹) 1611 (s, ν_NO); ¹H NMR

(300 MHz, C₆D₆) δ 1.05 (d, ²J_HH= 11.0, 1H, CH₂CMe₃), 1.35 (s, 9H,

CH₂CMe₃), 1.37 (s, 15H, C₅Me₅), 1.62 (d, ³J_HH= 15.2, 1H, allyl CH₂),

2

3

1.73 (d, J_HH= 11.0, 1H, CH₂CMe₃), 2.30 (d, J_HH= 10.6, 1H, allyl

3

CH₂), 3.87 (d, J_HH= 7.6, 1H, allyl CHPh), 5.50 (ddd, J_HH= 14.0,

3

10.6, 7.6, 1H, meso CH), 7.06 (m, 1H, para CH), 7.25 (t, J_HH= 7.8,

2H, meta CH), 7.36 (d, J_HH= 7.9, 2H, ortho CH); ¹³C APT NMR

3

Thermolysis of 1 in Toluene. In a glovebox, a reaction flask with

a Kontes greaseless stopper was charged with complex 1 (287 mg,

0.534 mmol) and excess toluene (10 mL) to give a yellow-orange

solution. The solution was heated at 55 °C for 3 days, during which

time the yellow solution changed to a deep orange. A dark orange

residue was then obtained by removing the volatile components from

the final reaction mixture in vacuo. The residue was dissolved in 4:1

pentane/Et₂O and added to the top of a silica column (0.5 × 5 cm).

An orange band was eluted from the column with Et₂O to give a light

orange eluate. Removal of solvents from the eluate under reduced

pressure afforded an orange oil. Recrystallization of this oil from

(100 MHz, C₆D₆) δ 10.0 (C₅Me₅), 35.2 (CH₂CMe₃), 37.0

(CH₂CMe₃), 39.4 (CH₂CMe₃), 67.7 (allyl CHPh), 77.6 (allyl CH₂),

108.1 (C₅Me₅), 112.9 (meso CH), 125.9 (aryl C), 127.8 (aryl C),

128.6 (aryl C), 141.9 (ipso C); MS (LREI, m/z, probe temperature

120 °C) 451 [M⁺]. Anal. Calcd for C₂₄H₃₅MoNO: C, 64.13; H, 7.85;

N, 3.12. Found: C, 62.32; H, 7.54; N, 3.12. Elemental analysis for

carbon content was consistently lower than the calculated value. This

may be due to incomplete combustion of the solid.

Thermolysis of 14 in Mesitylene: Preparation of Cp*Mo-

(NO)(η³- CH₂CHCHPh)(CH₂-3,5-(CH₃)₂C₆H₃) (15). In a glovebox,

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Table 3. X-ray Crystallographic Data for Complexes 2a, 3, 4, 7, 8, 10a, and 15

2a

3

4

Crystal Data

empirical formula

cryst habit, color

cryst size (mm)

C₂₂H₃₂NOPW

plate, yellow

C₂₅H₃₃NOW

prism, orange

C₂₆H₃₉NOW

block, orange

0.08 × 0.08 ×

0.03

0.60 × 0.60 ×

0.35

0.50 × 0.25 ×

0.20

cryst syst

space group

V (Å³)

a (Å)

orthorhombic

P2₁2₁2₁

2174.5(8)

7.8753(17)

9.070(2)

30.441(7)

90

triclinic

monoclinic

C2/c

P1

̅

1066.2(3)

9.4452(15)

11.0514(17)

11.6303(16)

71.176(7)

86.420(8)

68.403(8)

2

4828.3(4)

22.6699(11)

14.4074(7)

15.4067(8)

90

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

Z

90

106.360(2)

90

4

8

calcd density (Mg/

1.653

1.705

1.556

m³)

abs coeff (mm⁻¹

)

5.396

1072

5.432

544

4.810

2272

F₀₀₀

Data Collection and Refinement

no. of measd rflns:

total

35 888

31 022

6219

31 615

8682

no. of measd rflns:

unique

6351

a

final R indices

R1 = 0.0309,

wR2 = 0.0564

R1 = 0.0204,

wR2 = 0.0484

R1 = 0.0202,

wR2 = 0.0475

goodness of fit on

1.118

1.105

1.034

b

F²

largest diff peak

1.546 and

−3.314

0.859 and

−1.352

4.296 and

−0.840

and hole (e⁻

Å⁻³

)

7

8

10a

15

Crystal Data

empirical formula

cryst habit, color

cryst size (mm)

cryst syst

C₂₈H₃₅NOW

C₂₆H₃₇NOW

C_29.5H_38.5NOW

plate, yellow

0.16 × 0.07 × 0.05

monoclinic

P2₁/n

C₂₈H₃₅MoNO

square, orange

0.50 × 0.40 × 0.20

monoclinic

P2₁/n

plate, orange

0.40 × 0.20 × 0.20

triclinic

rectangle, yellow

0.35 × 0.25 × 0.20

monoclinic

P2₁/n

space group

V (Å³)

P1

̅

2463.29(13)

8.5682(3)

13.0558(4)

22.2189(6)

90

1130.56(13)

2576.5(4)

8.5854(7)

14.6515(13)

20.5856(17)

90

2472.3(18)

8.569(5)

13.070(5)

22.268(5)

90

a (Å)

8.7144(6)

b (Å)

9.5092(6)

c (Å)

14.0254(10)

α (deg)

91.032(3)

β (deg)

97.6680(10)

90

103.061(3)

95.737(2)

90

97.560(5)

90

γ (deg)

92.570(4)

Z

4

2

4

calcd density (Mg/m³)

1.579

1.655

1.565

1.337

abs coeff (mm⁻¹

)

4.708

5.126

4.505

0.549

F₀₀₀

1168

564

1218

1040

Data Collection and Refinement

no. of measd rflns: total

no. of measd rflns: unique

26 848

5708

18 513

5197

29 643

7547

28 641

5685

a

final R indices

R1 = 0.0209, wR2 = 0.0466 R1 = 0.0324, wR2 = 0.0826 R1 = 0.0312, wR2 = 0.0727 R1 = 0.0314, wR2 = 0.0763

b

goodness of fit on F²

1.042

1.196

1.053

1.036

largest diff peak and hole (e⁻Å⁻³

)

1.447 and −0.968

3.615 and −1.618

3.687 and −1.649

b

0.836 and −0.556

a

R1 on F = ∑(|F_o| − |F_c|)|/∑|F_o|; wR2 = [(∑(F_o²− F_c²)²)/∑w(F_o)²]^1/2; w = [σ²F_o]⁻¹. GOF = [∑(w(|F_o| − |F_c|)²)/(degrees of freedom)]^1/2

.

2

complex 14 (93 mg, 0.22 mmol) was dissolved in mesitylene, and the

orange-brown solution was heated for 24 h at 35 °C. The mixture was

then taken to dryness in vacuo, the remaining black residue was

redissolved in pentane, and the solution was transferred onto an

alumina column (1.5 × 5 cm). Elution of the column with a 4:1

mixture of pentane and Et₂O produced a peach-colored band, which

was collected. Solvent was removed from the eluate in vacuo, and the

residual yellow-orange solid was recrystallized from Et₂O at −30 °C to

give 15 as orange crystals (12 mg, 11% yield).

Characterization Data for 15: IR (cm⁻¹) 1616 (s, ν_NO); ¹H NMR

(300 MHz, C₆D₆) δ 1.37 (s, 15H, C₅Me₅), 1.83 (dd, ³J_HH= 13.7, ²J_HH

2

= 1.17, 1H, allyl CH₂), 2.02 (d, J_HH= 8.2, 1H, CH₂Ar), 2.32 (s, 6H,

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ArCH₃), 2.42 (d, ³J_HH= 10.5, 1H, allyl CH₂), 2.78 (d, ²J_HH= 7.9, 1H,

CH₂Ar), 3.60 (d, ³J_HH= 7.3, 1H, allyl CHPh), 5.09 (ddd, ³J_HH= 13.8,

10.5, 7.3, 1H, meso CH), 6.67 (s, 1H, aryl CH), 7.13 − 7.23 (m, 7H,

aryl CH); ¹³C APT NMR (100 MHz, C₆D₆) δ 9.8 (C₅Me₅), 22.3

(ArCH₃), 29.6 (CH₂Ar), 71.2 (allyl CHPh), 81.4 (allyl CH₂), 108.1

(C₅Me₅), 108.1 (meso CH), 125.7 (aryl CH), 126.8 (aryl CH), 127.2

(aryl CH), 128.7 (aryl CH), 137.1 (ipso C), 142.0 (ipso C), 153.6

(ipso C); MS (LREI, m/z, probe temperature 120 °C) 499 [M⁺]; MS

(HREI, m/z, ¹⁰⁰Mo) calcd 501.179 34, found 501.178 46. Anal. Calcd

for C₂₈H₃₅MoNO: C, 67.59; H, 7.09; N, 2.82. Found: C, 67.66; H,

7.10; N, 3.31.

X-ray Crystallography. Data collection was carried out at −100

°C on a Rigaku AFC7/ADSC CCD diffractometer or at −170 ± 2 °C

on a Bruker X8 or DUO APEX diffractometer, using graphite-

monochromated Mo Kα radiation.

Data for 2a were collected to a maximum 2θ value of 60.1° in 0.5°

oscillations. The structure was solved by direct methods¹⁵and

expanded using Fourier techniques. The structure was a two-

component twin. All non-hydrogen atoms were refined anisotropically.

Hydrogens H11A, H11B, and H13 were refined isotropically. All other

hydrogen atoms were included in fixed positions. The final cycle of

full-matrix least-squares analysis was based on 6351 observed

reflections and 256 variable parameters.

F_c;¹⁷the values for Δf′ and Δf″ were those of Creagh and McAuley.¹⁸

The values for mass attenuation coefficients are those of Creagh and

Hubbell.¹⁹All calculations were performed using SHELXL-97²⁰via the

WinGX interface.²¹X-ray crystallographic data for all seven structures

are presented in Table 3, and full details of all crystallographic analyses

are provided in the Supporting Information.

Computational Methods. All theoretical calculations were

performed using Gaussian03W²²utilizing a DFT²³method using the

three-parameter exchange functional of Becke²⁴and the correlation

functional of Lee, Yang, and Parr (B3LYP).²⁵Geometry optimizations

were carried out using the LANL2DZ basis set, which includes both

Dunning and Hay’s D95 sets for H, C, N, and O²⁶and the relativistic

electron core potential (ECP) sets of Hay and Wadt for W.²⁷

Frequency calculations on optimized geometries established that

transition states possessed one and only one imaginary frequency

whose atomic displacement vectors were consistent with the expected

reaction pathway and that intermediates possessed either no imaginary

frequencies or frequencies of negligible energy (<50i cm⁻¹).

Thermodynamic enthalpies and free energies are reported in kJ/mol,

as calculated at standard states (298.15 K and 1 atm).

ASSOCIATED CONTENT

* Supporting Information

■

S

Data for 3 were collected to a maximum 2θ value of 60.6° in 0.5°

oscillations. The structure was solved by direct methods¹⁵and

expanded using Fourier techniques. All non-hydrogen atoms were

refined anisotropically. Hydrogens H01, H1A, H1B, H3, H10, H11,

and H12 were refined isotropically. All other hydrogen atoms were

included in fixed positions. The final cycle of full-matrix least-squares

analysis was based on 6219 observed reflections and 286 variable

parameters.

Tables giving optimized structure and final thermochemical

parameters of the various CpW(NO)(R)(η ³-allyl) complexes

subjected to DFT calculations, a figure giving reaction profiles

for the mechanism given in Scheme 1, and CIF files providing

full details of the crystallographic analyses of complexes 2a, 3, 4,

7, 8, 10a, and 15. This material is available free of charge via the

Internet at http://pubs.acs.org.

Data for 4 were collected to a maximum 2θ value of 65.3° in 0.5°

oscillations. The structure was solved by direct methods¹⁵and

expanded using Fourier techniques. The C25−C26 fragment was

disordered in two orientations, each with 50% occupancy. All non-

hydrogen atoms were refined anisotropically, and all hydrogen atoms

were included in fixed positions. The final cycle of full-matrix least-

squares analysis was based on 8682 observed reflections and 286

variable parameters.

AUTHOR INFORMATION

Corresponding Author

*E-mail: stephen.mcneil@ubc.ca (W.S.M.); legzdins@chem.

ubc.ca (P.L.).

■

ACKNOWLEDGMENTS

■

Data for 7 were collected to a maximum 2θ value of 55.4° in 0.5°

oscillations. The structure was solved by direct methods¹⁵and

expanded using Fourier techniques. All non-hydrogen atoms were

refined anisotropically, and all hydrogen atoms were included in fixed

positions. The final cycle of full-matrix least-squares analysis was based

on 5708 observed reflections and 287 variable parameters.

Data for 8 were collected to a maximum 2θ value of 55.2° in 0.5°

oscillations. The structure was solved by direct methods¹⁵and

expanded using Fourier techniques. All non-hydrogen atoms were

refined anisotropically, and all hydrogen atoms were included in fixed

positions. The final cycle of full-matrix least-squares analysis was based

on 5197 observed reflections and 271 variable parameters.

Data for 10a were collected to a maximum 2θ value of 60.2° in 0.5°

oscillations. The structure was solved by direct methods¹⁵and

expanded using Fourier techniques. The asymmetric unit also

contained a molecule of pentane disordered about an inversion

center. All non-hydrogen atoms were refined anisotropically. Hydro-

gen H1 was refined isotropically. All other hydrogen atoms were

included in fixed positions. The final cycle of full-matrix least-squares

analysis was based on 7547 observed reflections and 309 variable

parameters.

We are grateful to The Dow Chemical Co. for continuing

support of this work, and we thank Drs. David Graf, Bill Tenn,

Pete Nickias, and Brandon Rodriguez for assistance and helpful

discussions. We also acknowledge Drs. Maria Ezhova and Jason

Traer of the UBC High-Resolution NMR Facility for their

1

assistance in obtaining the 600 MHz H NMR spectra of

complexes 12 and 13 as well as Dr. Brian Patrick, Dr. Miriam

Buschhaus, and Mr. Scott Semproni for their assistance with the

X-ray crystallography. C.C. thanks NSERC Canada for the

award of a CGS M Postgraduate Scholarship.

REFERENCES

■

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dx.doi.org/10.1021/om200731s|Organometallics 2011, 30, 6201−6217

Article Doi

Intermolecular C-H activations of hydrocarbons initiated by Cp*M(NO)(CH2CMe3)(η3-CH 2CHCHPh) complexes (M = Mo, W)

DOI: 10.1021/om200731s

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Article abstract of DOI:10.1021/om200731s

Full text of DOI:10.1021/om200731s

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