Cyclohydroamination of aminoalkenes catalyzed by disilazide alkaline-earth metal complexes: Reactivity patterns and deactivation pathways

FULL PAPER

DOI: 10.1002/chem.201203562

Cyclohydroamination of Aminoalkenes Catalyzed by Disilazide Alkaline-

Earth Metal Complexes: Reactivity Patterns and Deactivation Pathways

Bo Liu,^[a]Thierry Roisnel,^[b]Jean-FranÅois Carpentier,*^[a]and Yann Sarazin*^[a]

Abstract: The behavior of the first ami-

nophenolate catalysts of the large alka-

line earth metals (Ae) [(LOⁱ)AeN-

class their congeners containing the N-

(SiMe₂H)₂amide owing to the lower

the synthesis of Ae heteroleptic com-

plexes able to resist deleterious

ꢀ

Schlenk-type equilibria, the use of the

ꢀ

A

N

Ba; R=H, Me; x=0–2) for the cyclo-

hydroamination of terminal aminoal-

kenes is discussed. The complexes

activity in the case of catalyzed trans-

formations that involve reactive amine

(and potentially other) substrates.

Mechanistic and kinetic investigations

further illustrate the interplay between

the catalytic activity, operative mecha-

nism, and identity of the metal, ancil-

lary ligand, and amido group. These

studies suggest that the widely accept-

ed mechanism for cyclohydroamination

reactions cannot be extended systemat-

ically to all alkaline-earth catalysts.

suffer from irreversible deactivation

through the dehydrogenative coupling

of amine and hydrosilane moieties.

This deactivation process takes place at

258C in the case of [(LOⁱ)AeN-

[(BDI)AeN

Sr, Ba,

H₂C[C(Me)N-2,6-(iPr)₂C₆H₃]₂))

[(BDI)CaN(SiMe₃)₂A(thf)] supported by

A

(thf)_x] (Ae=Ca,

(BDI)H=

and

A

U

A

₂ACHTUNGRTEN(NUNG thf)_x] phenolate complexes

the b-diketiminate (BDI)^ꢀligand have

also been employed for comparative

and mechanistic considerations. The

catalytic performances decrease in the

order Ca>Sr@Ba, which is the oppo-

site trend to that previously observed

during the intermolecular hydroamina-

tion of activated alkenes catalyzed by

the same alkaline-earth metal com-

plexes. Catalyst efficacy increases when

the chelating and donating ability of

the aminophenolate ligands decreases.

For given metals and ancillary scaf-

A

CHTUNGTRENNUNG

albeit under conditions harsher than

those required for effective cyclohy-

droamination catalysis. A mechanistic

scenario for cyclohydroamination cata-

The [(BDI)CaNACHTUGTNRENNUG(SiMe₂H)₂ACHTUGNTERN{NUGN H₂NCH₂C-

lyzed by [(LX)AeN

G

ACHTUNGTRENNUNG

complexes ((LX)^ꢀ=(LOⁱ)^ꢀor (BDI)^ꢀ)

first Ca–aminoalkene adduct structural-

ly characterized, was prepared quanti-

tatively and essentially behaves like

is proposed. Although beneficial for

[(BDI)CaNACTHNUGTRNENUG(SiMe₂H)ACHTUNGTREN(NUNG thf)], thus serv-

Keywords: alkaline-earth metals ·

ing as a model compound for mecha-

nistic studies, as illustrated during stoi-

chiometric reactions monitored by

¹H NMR spectroscopy.

alkenes

·

amido complexes

·

cyclohydroamination ·

reaction mechanisms

folds, disilazide catalysts that incorpo-

ꢀ

rate the N

N

pounds^[1]by addition of an N H bond across unsaturated

carbon–carbon linkages, have become something of a hot

topic.^[2]Following the seminal work of Marks and co-work-

ers with rare-earth metal complexes,^[2b,3]catalysts based on

metals spanning across almost the entire Periodic Table

have been reported to mediate these very slightly exother-

mic but otherwise entropically unfavorable reactions.^[2]

Late-transition metals have shown characteristic robustness

and functional group tolerance and can promote the regiose-

lective, and sometimes stereoselective, Markovnikov addi-

tion of amines to nonactivated alkenes.^[2c,d]On the other

hand, catalysts based on oxophilic metals typically display

high reaction rates.^{[2a–c,3–5]}Perhaps more strikingly, rare-

earth metal complexes generate linear products through re-

gioselective anti-Markovnikov addition of amines to activat-

ed olefins. Nearly two decades have elapsed since this reac-

tion was identified as one of the “Ten Challenges in Cataly-

sis” by Haggin,^[6]and yet the breakthroughs required to

ꢀ

Introduction

Atom-efficient catalyzed hydroamination reactions, which

afford the formation of valuable nitrogen-containing com-

[a] Dr. B. Liu, Prof. Dr. J.-F. Carpentier, Dr. Y. Sarazin

Organometallics: Materials and Catalysis

Institut des Sciences Chimiques de Rennes

UMR 6226 CNRS, Universitꢀ de Rennes 1

Campus de Beaulieu, Rennes, 35042 Cedex (France)

Fax : (+33) (0)2 23 23 69 39

E-mail: jean-francois.carpentier@univ-rennes1.fr

yann.sarazin@univ-rennes1.fr

[b] Dr. T. Roisnel

Centre de Diffractomꢀtrie X

Institut des Sciences Chimiques de Rennes

UMR 6226 CNRS, Universitꢀ de Rennes 1

Campus de Beaulieu, Rennes, 35042 Cedex (France)

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.201203562.

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broaden the substrate scope, minimize catalyst loading, and

optimize reaction rates have remained elusive.

In 2005, Hill, Barrett, and co-workers revealed that the

As part of a program to implement new catalyst systems

for atom-efficient reactions, we became interested in devel-

oping ways to stabilize electron-deficient alkaline-earth spe-

ꢀ

ubiquitous

[(BDI)CaN

b-diketiminate

amido/calcium

((BDI)H=H₂C{C(Me)N-2,6-

complex

cies. We found that Ae···H Si b-agostic interactions in

charge-neutral heteroleptic alkaline-earth metal complexes

G

(iPr)₂C₆H₃]₂) constitutes a very competent catalyst for the

cyclohydroamination of aminoalkenes.^[8]In a series of re-

markable contributions, they further elaborated on their ini-

tial success to demonstrate that the large alkaline-earth

metals (Ae=Ca, Sr, and Ba) are particularly suited to the

catalysis of a range of hydroelementation reactions,^[9,10]and

they provided useful insight into the mechanisms that oper-

ate with complexes of these metals.^[9g]In a similar manner

to their next-of-kin the rare-earth and alkali metals, the co-

ordination chemistry of the large (ionic radii for coordina-

of the type [(LX)AeNACTHNGUTERNNUG

(SiMe₂H)₂] (Ae=Ca, Sr, Ba; (LX)^ꢀ=

monoanionic ancillary aminophenolate, iminoanilide, or b-

diketiminate ligand) constitute an effective way to prevent

solution ligand redistribution reactions that are too fre-

quently observed with their [(LX)AeNACHTUNRTGENUNG(SiMe₃)₂] congeners

and that these complexes are potent catalysts for ring-open-

ing polymerization,^[22k,n]hydrophosphonylation,^[23]or inter-

molecular hydroamination and hydrophosphination reac-

tions.^[24]We were surprised to observe that reaction rates in-

creased linearly with the size of the metal center in these

catalyzed reactions, whereas the selectivity was main-

tained.^[25]In contrast with the earlier predictions of Hill and

co-workers based on DFT computations and observations

tion number (CN)=6: 1.00, 1.18, and 1.35 ꢂ for Ca²⁺, Sr²⁺

,

and Ba²⁺, respectively),^[11]electropositive, and highly polar-

izable Ca–Ba elements is largely governed by electrostatic

and steric factors; consequently, bonding is essentially non-

directional and highly ionic. The authors showed that Ca

catalysts frequently, but not systematically, exhibited better

catalytic performances than their (Mg) Sr and Ba analogues

for hydroamination reactions. However, one notable excep-

tion was the intermolecular hydroamination of activated al-

kenes, in which Sr catalysts outclassed Ca catalysts.^[9e,g–h]No

clear pattern for reactivity versus metal size could therefore

be established, even if it appeared that the Mg and Ba cata-

lysts were always rather mediocre. In analogy with the rare-

earth systems developed by Marks and co-workers, the alka-

line-earth catalysts developed by Hill and co-workers fol-

lowed the rules developed by Baldwin for ring-closure

during cyclohydroamination reactions and also promoted

the anti-Markovnikov intermolecular hydroamination of vi-

nylarenes and dienes.^[9]

made with [Ae{NACTHUNTRGENN(UG SiMe₃)₂}₂ACHTUTGNREN(NGUN thf)_x] (Ae=Ca, Sr, Ba; x=0,

2),^[9e,h]we noticed that this trend was particularly pro-

nounced in intermolecular hydroamination reactions. The

Ba catalysts performed systematically better than Sr and, to

a greater extent, Ca catalysts in three complete families of

stable [(LX)AeNACHTNUTRGNE(UNG SiMe₃)₂] complexes supported by various

ligand scaffolds, thus yielding linear products after the regio-

specific anti-Markovnikov addition of the amine group to

the C=C unsaturation.^[24]

Herein, we report that Ca, Sr, and Ba heteroleptic

[(LX)AeNACTHUNGTRNNEUG(SiMe₂R)₂ACHTUTGNREN(NGUN thf)_x] (R=H, Me) complexes bearing

aminophenolate ligands are active catalysts in the cyclohy-

droamination of aminoalkenes and show that reaction rates

decrease regularly on moving from Ca to Ba in this intramo-

lecular version of hydroamination reactions. The behavior of

these catalysts is compared to that of their b-diketiminate

analogues, the roles of the supporting ligand and of the

NR₂moiety are questioned, and a mechanistic scenario

that highlights a specific catalyst deactivation pathway is

proposed.

In the wake of the promising accounts of Hill and Barrett,

several research groups have become involved in the devel-

opment of large Ae (Ca, Sr, Ba)^[12]catalysts supported by ni-

trogen-containing ancillaries for hydroamination reactions.

Roesky and co-workers reported that Ca catalysts outper-

formed their Sr analogues in cyclohydroamination reactions

catalyzed by heteroleptic aminotroponiminate^[13]or 2,5-bis-

ꢀ

Results and Discussion

[N-ACHTUNGTRENNUNG

(aryl)iminomethyl]pyrrolyl^[14]complexes. Moderate enan-

tioselectivity (i.e., 12–26% ee) was observed by Wixey and

Ward in the cyclohydroamination of aminoalkenes with Ca

catalysts bearing chiral 1,2-diamine^[15]or bisimidazoline^[16]li-

gands,^[17]but their kinetic stability was somewhat limited, an

issue often encountered in Ae coordination chemistry, in

which deleterious Schlenk-type equilibria are trouble-

some.^[18]To our knowledge, Ca–Ba phenolate complexes

have never been employed for cyclohydroamination reac-

tions, although Hultzsch and co-workers recently achieved

highly enantioselective reactions with a chiral Mg parent.^[12d]

Beyond catalytic hydroamination, Ca–Ba catalysts have also

displayed notable efficacy in hydrosilylation,^[19]alkene hy-

drogenation,^[20]or styrene^[21]and cyclic esters^[7,18a,22]polymer-

ization reactions in the past decade or so, which is a testimo-

ny to the growing importance of this field.

Catalyst selection and syntheses: Four proligands (LOⁱ)H

were selected for the preparation of alkaline-earth metal

catalysts on account of their varying chelating abilities and

stereoelectronic properties (Figure 1). Because it is the

benchmark proACTHNUTRGNENGUliACHUTGTNRENgUNG and in this area, (BDI)H was also used for

comparative purposes. As they revealed high efficiency in

the intermolecular hydroamination of activated alkenes,^[24]

the complexes [(LO⁴)AeN

ACHTNUGTRENNGU(SiMe₃)₂ACHUTNGTREN(NUGN thf)_x] (Ae=Ca, x=0

(1); Sr, x=1 (2); Ba, x=0 (3)) containing the tetradentate

phenolate (LO⁴)^ꢀwere picked as our catalysts of choice for

initial screening. To assess the importance of the identity of

the amide group attached to the metal center, the complexes

[(LO⁴)CaN

[{(LO⁴)AeN

also selected. Although it shows some signs of decomposi-

A

E

(4)

and

the

dimeric

AHCTUNGTRENNUNG

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Cyclohydroamination of Aminoalkenes

FULL PAPER

seem pertinent to proceed at

this stage with the syntheses of

Sr and Ba complexes bearing

(LO¹)^ꢀor (LO²)^ꢀligands. In-

stead, the complexes 1–3 and

[(BDI)AeNACHTUNGTRENNG(U SiMe₂H)₂ACHTUNTGERN(NUGN thf)_x]

(Ae=Ca, x=1 (11); Sr, x=2

(12); Ba, x=2 (13)) were com-

pared. The latter species sup-

ported by the b-diketiminate

ligand had previously proved to

be substantially more active

than phenolate or iminoanilide

derivatives in the intermolecu-

lar version of hydroamination

reactions.^[24]For comparative

purposes, we also studied

(thf)],^[7]the

[(BDI)CaNACTHNUTRGENNUG(SiMe₃)₂ACHTUTGNRENNUGN

benchmark catalyst for intra-

molecular hydroamination with

alkaline-earth-metal catalysis.^[9]

The panel of catalysts employed

in this study is displayed in

Figure 1.

Figure 1. Proligands and related complexes employed in this study for cyclohydroamination catalysis.

The [{(LO⁴)SrN

((5)₂) complex is a centrosym-

ACHTUGNERTN(NUNG SiMe₂H)₂}₂]

tion through Schlenk-type equilibria after periods of several

days in solution, we found that the Ba complex 3 was suffi-

ciently stable for catalytic reactions. In contrast, we have

shown that the complete stability of its derivative 6 is war-

ranted by a pattern of internal Ba···H-Si b-agostic interac-

tions.^[22m]The Ca complex 4, which contains an additional

coordinated molecule of THF is stable, although Ca···H-Si

agostic bonding was not established.^[22n]The new Sr complex

(5)₂was prepared in 73% yield by means of one-pot reac-

metric dimer in the solid state (Figure 2), with a central

{Sr₂O₂} planar core in which the two metal centers are bridg-

ed by the O_phenoxideatoms. There is some disorder in one of

the {SiMe₂H} fragments (only the main component is depict-

tion of [Sr{NACHTUNGTRENNUNG(SiMe₃)₂}₂ACHTUNRGTENNGNU ACTHUNGTREN(NUGN SiMe₂H)₂. It

(thf)₂], (LO⁴)H, and HN

is very sparingly soluble in aromatic solvents. NMR spectro-

scopic data recorded in [D₈]THF show that the dimer splits

partly in this coordinating solvent;^[26]furthermore, Vanꢃt

1

Hoff analysis of the H NMR spectroscopic data recorded in

the temperature range 253–333 K gave values of

7.29 kJmol^ꢀ1and 5.5 Jmol^ꢀ1K^ꢀ1for the dissociation enthal-

py and entropy, respectively, with splitting of the dimer oc-

curring spontaneously at elevated temperature.^[26]

The syntheses of the calcium complexes [{(LO¹)CaN-

ACHTUNGTRENNUNG ACHTUNGTRENNUGN

(SiMe₂H)₂}₂] ((7)₂), [(LO²)CaN(SiMe₂H)₂] (8), [(LO³)CaN-

ACHTUNGTRENNUNG ACHUTNGTREN(NUGN SiMe₂H)₂}₂] ((10)₂) have

(SiMe₂H)₂] (9), and [{(LO¹)CaN

been described previously.^[22i,k,n]Pulse-gradient spin-echo

NMR spectroscopic data indicated that these Ca species, di-

meric in the solid state, split into monomeric species in aro-

matic solvents;^[22n]therefore, we made the assumption that

this would be also the case under catalytic conditions. The

Figure 2. ORTEP diagram of the solid-state structure of [(LO⁴)SrN-

AHCTNUGTRENN(GUN SiMe₂H)₂]₂((5)₂). The noninteracting solvent molecule and hydrogen

atoms are omitted for clarity. Ellipsoids are drawn at the 50% probability

level; only the main components of disordered groups are depicted. Se-

lected bond lengths [ꢂ] and angles [8]: Sr1–O25#1 2.509(2), Sr1–O25

2.528(2), Sr1–N30 2.536(3), Sr1–O(4) 2.616(2), Sr1–O8 2.695(2), Sr1–N1

2.748(2), Sr1–Si3A 3.621(1), Sr1–N30 2.536(3); O25#1-Sr1-N30 105.01(8),

O25-Sr1-O(4) 136.96(6), N30-Sr1-O8 93.60(8), O25#1-Sr1-N1 98.33(6),

O8-Sr1-N1 62.98(6), Si2-N30-Sr1 117.2(2), Si3B-N30-Sr2 117.1(2).

complexes [(LO³)SrN(SiMe₂H)₂] and [(LO³)BaN

ACHTNUTRGENNUG AHCUTNGTREN(NUGN SiMe₂H)₂]

were also already available,^[22k]but they eventually proved

to be totally inert toward aminoalkenes. Besides, considering

the activity versus ligand and activity versus metal trends

observed during preliminary tests (see below), it did not

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J.-F. Carpentier and Y. Sarazin et al.

ed in Figure 2). Each Sr atom is six-coordinate, as the ligand

is bonded in a m²:k¹,k⁴-N,O,O,O fashion to the metal center.

ꢀ

The Sr O_phenoxidedistance of 2.53 ꢂ is shorter than those to

the O atoms of the side-arm ether groups (2.61–2.69 ꢂ). The

ꢀ

Sr1 N30 distance of 2.54 ꢂ is far smaller than Sr1 N1

(2.75 ꢂ). There is no clear evidence for the presence of

[27]

ꢀ

Sr···H Si agostic interactions in (5)₂,

and Si3A-N30-Sr1 angles of 117.2(2)8 and 117.1(2)8 are

as the Sr1-N30-Si2

equivalent. The two Sr-N-Si-H cores are coplanar, which

ꢀ

could be seen as consistent with the presence of Sr···H Si

bonding involving both {SiMe₂H} moieties,^[27]but could also

be the adventitious result of the minimization of steric fac-

tors.

The solid-state structure of the previously synthesized^[24]

b-diketiminate Sr complex 12 was also solved (Figure 3).

Figure 3. ORTEP diagram of the solid-state structure of [(BDI)SrN-

ACHUTNGTREN(NUG SiMe₂H)₂ACHTUNGTERN(NUGN thf)₂] (12). The noninteracting solvent molecule, isopropyl

ꢀ

Factors that corroborate the presence of Si···H Si agostic

groups on the BDI phenyl groups, and hydrogen atoms are omitted for

clarity. Ellipsoids are drawn at the 50% probability level. Selected bond

lengths [ꢂ] and angles [8]: Sr1–N1 2.473(2), Sr1–N31 2.542(2), Sr1–N51

2.556(2), Sr1–O21 2.597(2), Sr1–O11 2.613(2), Sr1–H1 2.82(3); N1-Sr1-

N31 104.32(6), N1-Sr1-N51 109.08(6), N1-Sr1-O21 119.80(7), N1-Sr1-O11

111.07(6), Si1-N1-Sr1 104.80(9), Si2-N1-Sr1 127.5(1).

bonding include a marked discrepancy between the two

{SiMe₂H} groups (Si1-N1-Sr1: 104.88, Si2-N1-Sr1: 127.48;

ꢀ

Sr1 Si1: 3.32 ꢂ, Sr1 Si2: 3.74 ꢂ) and the near coplanarity

of the H-Si1-N1-Sr1 fragment (torsion angles: H-Si1-N1-Sr1

ꢀ9.88; H-Si2-N1-Sr1 ꢀ31.98).

Catalytic activity during cyclohydroamination: In a prelimi-

nary set of qualitative experiments, the catalytic ability of 1–

13 in the cyclohydroamination of 1-amino-2,2-diphenyl-4-

pentene (A) and 1-amino-2,2-dimethyl-4-pentene (B), two

well-known substrates for which comparison with existing

catalysts is possible, was investigated (Scheme 1). The reac-

tions were carried out at 60 or 808C in [D₆]benzene with 1.7

or 8.3 mol% catalyst loading, and the conversion was moni-

1

tored by H NMR spectroscopy (Table 1).^[28]The initial as-

Scheme 1. Cyclohydroamination of 1-amino-2,2-diphenyl-4-pentene (A)

and 1-amino-2,2-dimethyl-4-pentene (B) with catalysts 1–13.

sumption was that catalysts 1–13 would operate according to

the commonly accepted mechanism depicted in Scheme 2.^[29]

The conversion of substrate B

catalyzed by 1–3 is slower than

Table 1. Cyclohydroamination reactions catalyzed by 1–13.

that of A, as expected on ac-

count of the Thorpe–Ingold

effect that favors cyclization for

bulkier geminal substituents. In

both cases, ring-closure pro-

ceeds according to the guide-

lines developed by Baldwin (5-

exo-trig).

The cyclohydroamination of

A catalyzed by Ca complex 1 at

808C was complete within less

than 30 min (Table 1, entry 1),

thus leading selectively to the

formation of 2-methyl-4,4-di-

phenylpyrrolidine. By compari-

son, full conversion required

one hour with the Sr analogue

Entry

Catalyst

Substrate

[Substrate]₀T^re[8C]

/[Ae]₀

t

Conv.^[a]

[%]

[h]

1^[b]

2^[b]

3^[b]

4^[b]

G

1

2

3

(6)₂

60

80

0.5

1

100

99

10

6

E

N

C

E

R

E

1

5^[c]

R

(SiMe₃)

N

60

12

60

80

60

80

5 min

1.5

5

1.5

25

5

3 min

12 min

1.5

36

29

45 min

3

8

>99

96

99

31

3

70

61

18

99

98

0

6^[b]

N

1

2

3

4

7^[b]

G

E

8^[b]

N

9^[b]

N

C

10^[b]

11^[b]

12^[b]

13^[c]

14^[c]

15^[c]

16^[c]

17^[c]

18^[c]

19^[c]

20^[c]

R

G

4

N

(5)₂

(6)₂

(10)₂

(7)₂

8

9

4

11

12

G

R

N

E

N

ACHTUNGTRENNUNG

R

G

N

92

93

91

89

2

(Table 1, entry 2), whereas

only 10% conversion was ach-

ieved with Ba complex

(Table 1, entry 3) in that time.

The activity trend was therefore 20 mmol, [D₆]benzene=0.4 mL.

N

E

N

T

E

CHTUNGTRENNUNG

3

G

C

[a] Conversion determined by ¹H NMR spectroscopy. [b] Ae=40 mmol, [D₆]benzene=0.4 mL. [c] Ae=

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Cyclohydroamination of Aminoalkenes

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The Ca complex 4 was less effi-

cient than its Sr analogue (5)₂

(Table 1, entries 10 and 11), but

this seemingly contradictive

result was later explained when

a specific and preponderant de-

composition pathway was iden-

tified for catalyst 4 (see below).

To remove any potential ambi-

guity, the b-diketiminate com-

plexes 11–13 were also tested,

with catalytic performances de-

creasing steadily according to

Ca>Sr>Ba

(Table 1,

en-

tries 18–20).

Although it does not affect

the overall Ca>Sr@Ba trend,

the nature of the amide group

on the metal center bears a

strong influence on the out-

come of catalytic reactions. In-

Scheme 2. Common insertion mechanism for cyclohydroamination reactions.^[2]

Ca>Sr@Ba; that is, it was the exact opposite of that ob-

served during intermolecular hydroamination and hydro-

phosphination reactions catalyzed by these three com-

plexes.^[24]The low catalytic activity exhibited by 3 toward

the reactive substrate A under the chosen experimental con-

ditions was in agreement with another experiment that uti-

lized (6)₂(Table 1, entry 4) as the catalytic precursor, which

gave a comparable result. Note that Hill and co-workers re-

ported failed attempts to catalyze the cyclohydroamination

dependently of the nature of the metal center and ancillary

ꢀ

ligand, slower rates were observed with the N

group bound to the metal center than with the NACHTNUGTRNE(UNG SiMe₃)₂

G

group. In the case of the Ca catalysts, this was particularly

obvious upon comparison of entries 6 and 9, entries 13 and

14 (taking place at 60 and 808C, respectively), or even en-

tries 5 and 18 in Table 1. The superiority of the Ae–N-

AHCTUNTGRENGUN(N SiMe₃)₂species in terms of activity was also evidenced for

Sr (Table 1, entries 7 and 11) and Ba complexes (Table 1,

entries 8 and 12). These findings could be easily rationalized

of

[Ba{CH

A

with [Ba{N

ACHTUNGTRENNUNG(SiMe₃)₂}₂], [Ba{NACHTNUREGT(NGNUN SiMe₃)₂}₂ACHTNUGTERNUN(GN thf)₂], or

G

on the basis of the relative acidity of the HN

HN

(SiMe₃)₂moieties (pK_a=22.6 and 25.8, respectively).^[31]

Indeed, Hill and co-workers have elegantly demonstrated

the reversibility of the protonolysis of [(BDI)CaN(SiMe₃)₂-

(thf)] with benzylamine,^[32]and have shown that a similar

equilibrium constituted a serious impediment to fast catalyt-

ic turnovers in the case of HN(SiMe₃)₂released upon the

addition of an excess of substrate B to [(BDI)CaN(SiMe₃)₂-

(thf)]. In contrast, the cyclohydroamination of B catalyzed

by [(BDI)MgMe(thf)] was not hindered by the formation of

CH₄.^[9c,g]Hence, the initial equilibrium between the catalyst

[(LX)AeN(SiMe₂R)₂A(thf)_x] and the active species

(Scheme 2) lies much more toward the side of the reactants

with the relatively acidic HN(SiMe₂H)₂moiety (R=H) than

it does for the HN(SiMe₃)₂species (R=Me), thus resulting

in lower catalytic turnover rates. The higher catalytic initia-

ACHTUNGTRNEN(UNG SiMe₂H)₂and

The reaction rates were somewhat lower in the case of B,

which allowed a more accurate screening of the catalyst effi-

ciency, and we therefore focused more closely on this sub-

strate. The purity of B was regularly checked by employing

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

[(BDI)CaNACHTUNGTRENNUNG(SiMe₃)₂ACHTUNGTRENNUNG(thf)], for which the reaction rates at

608C were too fast to be determined accurately (Table 1,

entry 5). Hill and co-workers reported full conversion of B

(and A) within 15 min with this catalyst ([Ca]₀/[substrate]₀=

1:10) at room temperature,^[8]and similar results were ob-

tained in our hands. Full conversion required 1.5 and 5 h, re-

spectively, with the Ca and Sr catalysts 1 and 2 (Table 1, en-

tries 6 and 7), thus affording 2,4,4-trimethylpyrrolidine selec-

tively. Again, the Ba catalyst 3 was much less efficient

(Table 1, entry 8). Besides, the conversion of 12 equivalents

of B versus the catalyst 1–3 was monitored by ¹H NMR

spectroscopy.^[30]Complete conversion was achieved in 20

and 60 min with 1 and 2, respectively; in contrast, only 28%

of B was converted after 60 min when 3 was employed. This

outcome further corroborated the activity trend Ca>Sr>

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

A

CHTUNGTRENNUNG

AHCTUNGTRENNUNG

tion efficiency of Group 3 metal–NACTHNUTRGEN(UNG SiMe₃)₂complexes over

ꢀ

their

N

(SiHMe₂)₂analogues in cyclohydroamination has

been reported also by OꢃShaughnessy and Scott^[33]and

Hultzsch and Hampel.^[34]Besides, a deactivation pathway

Ba for these alkaline-earth metal catalysts incorporating N-

(SiMe₃)₂moieties. The fact that this trend depends on the

specific to [(LX)AeNACTHNUGTRENNU(G SiMe₂H)₂ACHTGNUTREN(UNGN thf)_x] complexes was dis-

covered, with ensuing limited turnover numbers and lower

reaction rates (see below).

The influence of the ligand scaffold was interrogated by

utilizing Ca complexes only. Comparative tests performed

under rigorously identical conditions revealed that for the

ꢀ

nature of the metal and not amide group was demonstrated

ꢀ

when catalysts bearing the N

N

The Sr catalyst (5)₂proved noticeably more efficient than its

Ba derivative (6)₂(compare entries 11 and 12 in Table 1).

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J.-F. Carpentier and Y. Sarazin et al.

complete family of [(LOⁱ)CaN

ACHTNUGTRENNG(U SiMe₂H)₂ACHTUNGTREN(NUGN thf)_x] catalysts (i=

1–4)^[35,36]the activity varied according to 9<4<8<(7)₂

(Table 1, entries 14–17); that is, the activity essentially de-

creased when the number of donor atoms increased in the

supporting ligand. Decreasing hydroamination activity with

increasing electron-donating and chelating ability of the an-

cillary ligand had been postulated before,^[12a]but to the best

of our knowledge it has been demonstrated here for the first

time with a family of directly comparable Ca catalysts that

differ only in the nature of the phenolate ligand. However,

note that Hill and co-workers reported that the unsolvated

complexes [Ae{N

ACHTUNGTRENNUNG

than their THF-bound analogues [Ae{N

G

CHTUNGTRENNUNG

Figure 4. Semilogarithmic plot of substrate conversion versus reaction

(Ae=Mg, Ca, Sr). Our interpretation of these and our re-

sults is that low coordination number and chelating ability

are intrinsically beneficial to catalytic activity provided it

does not come at the expense of catalyst stability. Interest-

ingly, the four-coordinated Ca complex 11 was slightly less

active than (7)₂(Table 1, entries 14 and 18), thus indicating

that extrapolation of these preliminary conclusions across

different families of ligands may be premature. The limited

time for the cyclohydroamination of B (12 equiv vs. Ae, 20 mmol of Ae)

4

catalyzed by [(LO⁴)CaN

G

;

), [(LO )SrN-

^

4

A

U

ACHTUGNRETN(NUGN SiMe₃)₂] (3, k_obs=

~

;

), and [(LO )CaN

(SiMe₂H)₂A ;

(thf)] (4, k_obs=0.1ꢄ10^ꢀ4s^ꢀ1

k_obsfor the Ca, Sr, and Ba (1–3) aminophenolate catalysts

were 24.0ꢄ10^ꢀ4, 7.4ꢄ10^ꢀ4, and 1.0ꢄ10^ꢀ4s^ꢀ1, respectively. It

is not clear whether the role of the coordinated molecule of

THF in 2 is neutral or prejudicial to the activity of the cata-

lyst; however, this possibility could not be assessed because,

synthetic availability of [(LOⁱ)CaN

(stable only for i=1 and 4) did not allow the analogous

comparison with [(BDI)CaN(SiMe₃)₂A(thf)].

On the whole, the cyclization of A and B is substantially

slower with 1–3 than with [(BDI)CaN(SiMe₃)₂A

(thf)].^[9]

ACHTUNGTRENUN(G SiMe₃)₂ACHUTNGTREN(NUGN thf)_x] catalysts

A

CHTUNGTRENNUNG

A

CHTUNGTRENNUNG

Nonetheless, reaction rates for Ca–phenolate systems, in

particular (10)₂and (7)₂(Table 1, entries 13 and 14), com-

pare favorably with those reported by Roesky and co-work-

ers for aminotroponiminate^[13]and 2,5-bis[N-

ACHTNUTRGNEUNG(aryl)iminome-

thyl]pyrrolyl^[14]Ca and Sr catalysts. The Ca complexes devel-

oped by Wixey and Ward supported by chiral 1,2-dia-

mines^[15]or bisimidazoline^[16]ligands are even less active, al-

though they afford the formation of the cyclic products with

some degree of enantioselectivity (i.e., 5–26% ee).

Kinetic studies: The conversion of 12 equivalents of B cata-

lyzed by the aminophenolate complexes 1–3 and the b-dike-

timinate complexes 11–13 was monitored by H NMR spec-

troscopy to gain further information on the influence of the

metal center (Table 2).^[30]The semilogarithmic plots of sub-

strate conversion versus reaction gave straight lines in all

cases, thus indicating first-order dependence upon monomer

concentration (Figures 4 and 5). The observed rate constants

Figure 5. Semilogarithmic plot of substrate conversion versus reaction

time for the cyclohydroamination of B (12 equiv vs. Ae, 20 mmol of Ae)

1

catalyzed by [(BDI)CaN

[(BDI)SrN(SiMe₂H)₂A

(thf)₂] (12, k_obs=2.6ꢄ10^ꢀ4s^ꢀ1

(SiMe₂H)₂A

(thf)₂] (13, k_obs=0.9ꢄ10^ꢀ4s^ꢀ1

808C.

(SiMe₂H)

E

k

_obs=10.3ꢄ10^ꢀ4s^ꢀ1

;

),

^

&

G

;

), and [(BDI)BaN-

) in [D₆]benzene (0.4 mL) at

N

G

despite our repeated synthetic efforts, this single THF mole-

cule could not be removed from the metal center. The reac-

tions proceeded more slowly with the catalysts 11–13 con-

taining the b-diketiminate scaffold (k_obs=10.3ꢄ10^ꢀ4, 2.6ꢄ

10^ꢀ4, and 0.9ꢄ10^ꢀ4s^ꢀ1, respectively; Table 2). Comparison

across the two families are ill advised as both the ligand and

amide groups differ from one to the other family; yet, for

both families, these data fully agree with the trend Ca>Sr@

Ba observed earlier. Although the cyclization of only

12 equivalents of B with 3 or 13 is relatively slow, these con-

stitute the first examples of Ba catalysts for cyclohydroami-

Table 2. Cyclohydroamination of aminoalkene B catalyzed by 1–4 and

11–13.^[a]

Entry

Catalyst

t

Conv.^[b]

[%]

k_obs

[10^ꢀ4s^ꢀ1

]

[h]

U

1

2

3

4

5

6

7

N

G

1

2

3

0.3

1

0.75 93

3

8

95

93

28

24.0

7.4

1.0

10.3

2.6

0.9

G

N

G

(thf) ] 11

R

12

4

91

89

92

E

(thf)₂] 13

29

0.1

nation. Catalyst 4, with its N

exhibited a partial kinetic order of one in substrate concen-

(SiMe₂H)^ꢀamide group, also

ACHTUNGTRENNUNG

[a] Ae=20 mmol, 808C, [D₆]benzene=0.4 mL. [b] Conversion determined

1

by H NMR spectroscopy.

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Cyclohydroamination of Aminoalkenes

FULL PAPER

tration, but as expected on the basis of the preliminary test

it unveiled very low catalytic efficiency in comparison with 1

(Table 2, entries 1 and 7), with a k_obsvalue of 0.1ꢄ10^ꢀ4s^ꢀ1

only.

The situation was different with (7)₂and 8, that is, the cat-

alysts that had displayed the best performances in the series

[(LOⁱ)AeN (thf)_x] during the qualitative tests.^[37]

ACHTUNGTRENNUNG(SiMe₂H)₂ACHTUGNTRENNUGN

The situation of (7)₂was envisaged in the light of previous

studies by pulse-gradient spin echo NMR spectroscopy,^[22n]

which showed that (7)₂fully dissociates in [D₆]benzene. It

seemed pertinent to consider that this would also be the

case in the additional presence of 12 equivalents of substrate

(versus Ca), and therefore we consider that the cyclohydroa-

mination catalyst in this case is the monomeric 7.^[35]After,

respectively, a short or rather long (ca. 2 or 40 min) induc-

tion period, the cyclization of B increased linearly with reac-

tion time for both 7 and 8, thus indicating a zero-order de-

pendence upon [B]₀.^[26]Further studies were undertaken

with 7, the most efficient of these two catalysts, to keep re-

Figure 7. Plot of k_obsvalues versus [B]₀for the cyclohydroamination of B

catalyzed by [(LO¹)CaN

ACHTNUGTRNENUG(SiMe₂H)₂] (7) at 808C with [7]₀=50.0 mm and

[B]₀=0.5–4.0m.

8.7ꢄ10^ꢀ4mols^ꢀ1for [B]₀=4.0m (Figure 7). These results

were diagnostic of catalyst inhibition by the substrate; a sim-

ilar phenomenon has already been documented by Hultzsch

and co-workers for the cyclohydroamination of 1-amino-4-

pentene catalyzed by chiral binaphtolate lanthanide cata-

lysts.^[4p]

The rate dependence upon catalyst concentration was ex-

amined by varying the initial concentration of 7 in the range

4.30–52.9 mm while keeping [B]₀constant (0.60m). The

values of k_obsextracted from the linear regime (substrate

conversion in the range 30–90%) of the plot of conversion

versus reaction time for each catalyst concentration from

1.5ꢄ10^ꢀ4to 21.2ꢄ10^ꢀ4molL^ꢀ1s^ꢀ1. The plot of k_obsvalue

versus the initial concentration of the catalyst was a straight

1

action times reasonably short and compatible with H NMR

spectroscopic monitoring. The reactions were performed at

808C by maintaining the concentration in

7 constant

(50.0 mm), but with varying substrate concentration in the

range 0.5–4.0m (Figure 6). In all cases, an initial curvature

line (Figure 8), and the corresponding plot of lnACHTUNRGTNEUNG(k_obs) versus

ln([7]₀) was a line with the slope of 1.06 (R²=0.9969).^[26]

Both of these findings were diagnostic of a first-order de-

pendence upon catalyst concentration, thus confirming that

(7)₂did not preserve its dimeric nature under catalytic con-

ditions, as otherwise a noninteger kinetic order of 0.5 in cat-

alyst concentration typical of dimeric precatalysts would

have been expected.^[38]Under the assumption that (7)₂fully

dissociates in solution, the cyclization of B catalyzed by 7

Figure 6. Plot of substrate conversion versus reaction time for the cyclo-

hydroamination of B catalyzed by [(LO¹)CaN

ACHTNUTRGENG(UN SiMe₂H)₂] (7) at 808C

with constant initial concentration of 7 (50.0 mm) and [B]₀=0.5m (k_obs

=

21.1ꢄ10^ꢀ4mos^ꢀ1

18.6ꢄ10^ꢀ4mols^ꢀ1

;

), 1.0m (k_obs=20.7ꢄ10^ꢀ4mols^ꢀ1

;

), 2.0m (k_obs

), and 4.0m (k_obs

~

^

), 3.0m (k_obs=14.1ꢄ10^ꢀ4mols^ꢀ1

;

&

*

;

8.7ꢄ10^ꢀ4mols^ꢀ1

;

*

).

indicative of rate acceleration was observed and became

more pronounced with increasing substrate concentration.

Moreover, after this induction period, the formation of 2-

methyl-4,4-diphenylpyrrolidine increased linearly with reac-

tion time up to approximately 90–95% conversion (i.e.,

until inhibition by reversible coordination of the product),

thus confirming a 0th order in [B]₀. This outcome is compat-

ible with the generally accepted mechanism for the cyclohy-

droamination reaction, in which the rate-determining step

consists of the insertion of the polarized coordinated olefin

ꢀ

into the Ae N bond (Scheme 2). Finally, the k_obsvalue de-

creased markedly with increasing initial substrate concentra-

Figure 8. Plot of k_obsvalues versus initial catalyst concentration for the cy-

clohydroamination of

[D₆]benzene at 808C with [B]₀=0.6m.

B ACHTNUGTNRUEGN(SiMe₂H)₂] (7) in

catalyzed by [(LO¹)CaN

tion, from k_obs=21.2ꢄ10^ꢀ4mols^ꢀ1for [B]₀=0.50m down to

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J.-F. Carpentier and Y. Sarazin et al.

therefore obeyed the empirically determined rate law given

in Equation (1):

ꢀd½Bꢁ=dt ¼ k½7ꢁ₀

ð1Þ

The activation energy for the cyclohydroamination of B

catalyzed by 7 was E_a=97.6 kJmol^ꢀ1according to Arrhenius

analysis of values of k_obsdetermined in the temperature

range 313–353 K.^[26]The corresponding activation enthalpy

(DH^ꢀ=94.9

ꢀ29.7

ACHTUNGTRENNUNG

(3.0) kJmol^ꢀ1) and activation entropy (DS^ꢀ=

ACHTUNGTRENNUNG

(8.9) Jmol^ꢀ1K^ꢀ1) were determined by using Eyring

analysis. These values differ largely from those reported by

Hill and co-workers for the cyclization of (1-allylcyclohex-

yl)amine (a substrate considerably easier to cyclize than B)

Figure 9. Plots of substrate conversion versus reaction time for the cyclo-

hydroamination of B catalyzed by [(LO¹)CaN

ACHTNUGTRNEG(UN SiMe₃)₂(10) ([(10)₂]=

(thf)] (DH^ꢀ=63.1 kJmol^ꢀ1and

with [(BDI)CaNACHTUNGTRENNUNG(SiMe₃)₂ACHTUTGNRENNUGN

10 mmol; 12 equiv of B versus Ca; [D₆]benzene=0.4 mL) at 296, 313, 318,

323, and 333 K.

DS^ꢀ=ꢀ77.7 Jmol^ꢀ1K^ꢀ1).^[9g]

The initial qualitative screening suggested that

[{(LO¹)CaN

G

obvious change in the resonance signals characteristic of the

Ca complex were noted upon addition of one, or even four,

ACHTUNGTRENNUNG

tries 13 and 14). The behavior of (10)₂toward substrate B

was investigated in more detail (12 equiv of B vs. Ca). The

cyclization occurred at 808C with zero-order dependence

upon [B]₀, but without an induction period and no sign of

inhibition by the substrate or product (Figure 9). The activa-

tion energy (E_a=85.0 kJmol^ꢀ1) and activation enthalpy and

equivalents of B to [(BDI)CaNACHTGUNTRENNU(G SiMe₃)₂ACHTUNGTREN(NUGN thf)]; in both cases,

B was fully cyclized within 10 minutes at room tempera-

ture.^[26]Whether with this complex or with 1, the presence

of a resonance at very high field (typically between d=

ꢀ

ꢀ0.30 and ꢀ1.90 ppm), indicative of Ca NHR, moieties was

never discovered. Besides, signs for the presence of other

entropy

(DH^ꢀ=82.4

N

and

DS^ꢀ=ꢀ41.3

short-lived species, such as those that result from the inser-

(13.1) Jmol^ꢀ1K^ꢀ1) deduced from analyses of the Arrhenius

and Eyring (R²=0.9926 and 0.9920, respectively) plots^[26]

were markedly lower than those determined for (7)₂.

tion of the polarized C=C unsaturation into the (LO )Ca

4

ꢀ

NHR bond, were not detectable on the NMR timescale.

These observations suggest that the reaction between 1 and

B is an acid–base equilibrium with a strong preference for

the side of the reactants [Eq. (2)] and that [(LO⁴)CaN-

Stoichiometric and model reactions: In an effort to gain in-

sight into the mechanisms that operate with our Ae–pheno-

late cyclohydroamination catalysts, the stoichiometric reac-

AHCTUNTGREGN(NNU SiMe₃)₂] probably constitutes the main catalyst resting state

in the catalytic cycle associated with 1.

tion of [(LO⁴)CaN

(SiMe₃)₂] (1) and aminoalkene B in

To enhance our understanding of the behavior of com-

1

ꢀ

plexes that contain the N

G

tion of [(LO⁴)CaN

G

(thf)] (4) with one equivalent

of 2,4,4-trimethylpyrrolidine at

408C was detected, and only

59% of the substrate had been

converted after 90 minutes. For-

mation of the cyclic amine

product was concomitant with

the disappearance of B (Figure 10), and the associated semi-

logarithmic plot of the consumption of B versus the reaction

time was linear, consistent with first-order dependence on

[B]₀.

During the course of 90 min, only incremental amounts of

free HNACHTUNGTRENNUNG(SiMe₃)₂(no more than 2% with respect to Ca or

of B in [D₆]benzene was monitored in the same fashion by

variable-temperature (VT) spectroscopy

¹H NMR

(Figure 11). The system was essentially inert below 608C, as

no evolution was noted over 1–2 h. New resonance signals

were detected at 608C, notably at d=4.47 and 2.74 ppm;

yet, their intensities were rather low, and these signals did

not match those expected for 2,4,4-trimethylpyrrolidine. The

cyclization of B took place slowly at 808C and several sets

of signals were detected, which clearly identified as corre-

sponding to the expected cyclic amine product (thus indicat-

ing less than 10% conversion of the substrate after 50 mi-

nutes at 808C). Signals of the aforementioned species at d=

4.47 and 2.74 ppm, for which the intensities had substantially

enhanced, were also detected. Besides, these signals were

B) were detected at any given time, and in particular the

quantity of free amine was far below that expected from

ꢀ

aminolysis of the Ca N

(SiMe₃)₂bond by H₂NCH₂C-

(CH₃)₂CH₂CH=CH₂. Moreover, no resonance signals for the

phenoxy species other than those for starting 1 were detect-

ed. Similar observations have been made previously by Hill

and co-workers with [(BDI)CaN

ACHUTGTNERN(GUN SiMe₃)₂ACHUTNGTREN(NUGN thf)], and indeed

we have checked that under our experimental protocol no

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Cyclohydroamination of Aminoalkenes

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Figure 10. VT ¹H NMR (500.1 MHz, [D₆]benzene) monitoring of the reaction of [(LO⁴)CaN

ACHTUNTRGENUNG(SiMe₃)₂] (1) and one equivalent of B (1=40 mmol,

[D₆]benzene=0.4 mL). Top: d=4.9–7.8 ppm; bottom: d=ꢀ0.9–3.2 ppm. Resonance signals that belong to the catalyst, substrate, and cyclized product

are identified by 1, B, and P, respectively. Note the formation of a small amount of HN(SiMe₃)₂in the spectrum of complex 1 by itself. The integration of

this background amine was subtracted for calculations of HN(SiMe₃)₂released upon reaction of 1 with B.

AHCTUNGTRENNUNG

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J.-F. Carpentier and Y. Sarazin et al.

Figure 11. VT ¹H NMR (500.1 MHz, [D₆]benzene) monitoring of the reaction of [(LO⁴)CaN

ACTHNUTRGNEN(UG SiMe₂H)₂ACHTUGNTREN(NUNG thf)] (4) and one equivalent of aminoalkene B

(4=40 mmol, [D₆]benzene=0.4 mL). Resonance signals that belong to 4, substrate, cyclic product, dihydrogen, and the unidentified byproducts are iden-

tified by 4, B, P, H₂, and U, respectively.

accompanied by new signals of strong intensities at d=7.48,

6.90, and 0.90 ppm, whereas another signal characteristic of

the Me₂SiH moiety was identified at d=5.02 ppm (and over-

lapped partly with the vinylic resonance of B). These obser-

vations unambiguously suggested that 4 did not remain

intact during the reaction, but a new metallic species (U)

formed in large proportions. Attempts to identify these by-

products at this stage were hampered by the reactivity of B

toward 4, and also potentially toward this new metallic spe-

cies, and by the complexity of the ¹H NMR data in the

region d=0.0–4.0 ppm.

did not afford either of the potentially expected complexes,

but yielded instead (SiMe₂H)(SiMe₂NH-

[(LO⁴)CaN

AHCTUNGTRENNUNG

CH₂CH₂OCH₃)] (14) as a crystalline colorless solid (the

nonoptimized yield was 31%) following fractionated recrys-

tallization (Scheme 3).

1

The H NMR spectrum of 14 is characterized by two dou-

blets at d=7.57 and 7.02 ppm that correspond to the aro-

matic hydrogen atoms (⁴J_H_ꢀ_H=2.8 Hz), a multiplet at d=

5.09 ppm assigned to SiH (¹J_Si_ꢀ_H=172 Hz); the resonance

The stoichiometric reaction of 4 and 2-methoxyethyla-

mine, carried out on a preparative scale and also monitored

by ¹H NMR spectroscopy, was most informative. Hill and

co-workers had previously shown that the reaction of

[(BDI)CaN

the dimeric [((BDI)Ca

yields,^[39]whereas with its Sr parent the amine adduct

ACHTUNGTRENNUNG(SiMe₃)₂ACHTUNGTRENNUNG(thf)] and 2-methoxyethylamine yielded

A

ACHTUNGTRENNUNG

[(BDI)SrNACHTUNGTRENNUNG(SiMe₃)₂ACHTUNGTRENNUNG{H₂NCAHTNUGTRENUN(NG CH₂)₂OMe}] was obtained prepon-

derantly.^[9g]To our surprise, we found that the equimolar re-

action of 4 and 2-methoxyethylamine at room temperature

Scheme 3. Reaction of 4 and 2-methoxyethylamine to yield 14.

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Cyclohydroamination of Aminoalkenes

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1

The key H NMR data for 14 were fully consistent with

the new species U formed (along with H₂) during the reac-

tion of the Ca–aminophenolate 4 and one equivalent of B

(see above; Figure 11). We therefore concluded that a com-

plex of the type [(LO⁴)CaN

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

tion (i.e., U) detected during the cyclohydroamination of B.

No information regarding the catalytic ability toward the cy-

clohydroamination of such a complex was directly gathered.

However, we verified that 14 was itself totally inert toward

B, even at 808C. One can therefore postulate that

[(LO⁴)CaN

ACTHNUTRGENNU(G SiMe₂H){SiMe₂NHCH₂CACHTUTGNERN(NUGN CH₃)₂CH₂CH=CH₂}]

(U) is catalytically inactive and that its rapid formation

under catalytic conditions results in lower reactions rates

and turnover numbers.

The reaction of [(BDI)CaNACHTNUGTRENN(UG SiMe₂H)₂ACHTUGNTREN(NNGU thf)] (11) with B in

Figure 12. Solid-state structure of [(LO⁴)CaN

ACHTUNGTRENUNG(SiMe₂H)(SiMe₂NHCH₂-

1

[D₆]benzene monitored by VT H NMR spectroscopy dem-

onstrated that the deactivation pathway identified in the

case of 4 does not necessarily occur with all [(LX)CaN-

CH₂OMe)] (14). The noninteracting solvent molecule and hydrogen

atoms (except those on N and Si atoms) are omitted for clarity. Ellipsoids

are drawn at the 50% probability level. Selected bond lengths [ꢂ] and

angles [8]: N1–Ca1 2.389(2), N21–Ca1 2.692(2), O24–Ca1 2.504(2), O32–

Ca1 2.466(2), N35–Ca1 2.565(2), O38–Ca1 2.463(2), O41–Ca1 2.241(1),

N1–Si:2 1.677(2), N21–Si2 1.758(2); N1-Si2-N21 105.74(9), Si2-N1-Si1

130.4(1).

ACHUNTGRENUN(G SiMe₂H)₂ACHUTGNTREN(NUGN thf)_x], at least at the temperatures at which these

compounds are catalytically active for cyclohydroamination.

Whether with 1 or 12 equivalents of B versus 11, the forma-

tion of 2,4,4-trimethylpyrrolidine proceeded extremely

slowly at room temperature (16% conversion of one equiva-

lent of B after 60 minutes), whereas clean cyclization with-

out the formation of byproducts occurred more rapidly at

608C (22% conversion of 12 equivalents of B after 75 min).

The formation of H₂and species of the type

signals for the NSiACHTUNGTRENNUNG(CH₃)₂NH and NSiCAHTUNGTRNE(NUGN CH₃)₂H moieties are

found as a doublet and singlet at d=0.38 (³J_H_ꢀ_H=2.8 Hz)

1

and 0.33 ppm, respectively.^[26]By combining the H, {¹H}¹³C,

and HMBC NMR spectroscopic data, and by analogy with

“

ACHTUNGTRENNUNG

G

CAHUTGTNRENN(GU SiMe₂H){SiMe₂NHCH₂CACHTUTGNERN(NUGN CH₃)₂CH₂CH=CH₂}-

1

related reported examples,^[40]a triplet in the H NMR spec-

trum at d=0.92 ppm with integration for 1H was assigned

to the amine SiNHCH₂. The {¹H}²⁹Si NMR spectrum of 14

exhibited two singlets at d=ꢀ13.25 and ꢀ30.06 ppm, indica-

tive of two nonequivalent silylamido groups. The solid-state

structure of 14 was determined by X-ray diffraction studies

of crystals obtained from a solution in pentane (Figure 12).

tures (20–608C). These observations led to the clean and

quantitative preparations of the model compounds

[(BDI)AeN

G

N

ACHTUNGTRENNUNG

(16)) and [(BDI)AeN

N

ACHTUNGTRENNUNG

CH₂}] (Ae=Ca (17), Sr (18)) by treatment of 11 or 12 with

the appropriate amine, 2-methoxyethylamine, or B in pen-

tane at room temperature (Scheme 4).

However, although complexes 15 and 16 were perfectly

stable in solution up to 608C according to VT ¹H NMR

spectroscopy, they evolved at 808C over two hours to give

ꢀ

The Ca atom is seven-coordinated. The Ca1 N21 bond

ꢀ

length (2.69 ꢂ) is longer than for Ca1 N1 (2.39 ꢂ) and Ca1-

N35 (2.56 ꢂ), which are nearly equivalent to those found in

[(LO⁶)CaN

ACHTUNGTRENNUNG(SiMe₂H)₂ACHTUNGTRENN(UGN thf)] (4). The Si2-N21 bond length of

ꢀ

1.76 ꢂ is markedly longer than for Si2 N1 (1.68 ꢂ). The

Si2-N1-Si1 angle of 130.38 in 14 is a little wider than in its

parent compound 4 (125.18).^[22n]

the complexes [(BDI)AeNAHCTUNERTGG(NUNN SiMe₂H)ACHTNURGTEG{NNUN SiMe₂HNACHTNGUTRENUN(NG CH₂)₂OMe}]

(Ae=Ca (19), Sr (20)) almost quantitatively with the re-

lease of H₂. The Sr complex 16 was similar to its [(BDI)SrN-

The formation for 14 is reminiscent of the cross-dehydro-

coupling of organosilanes with amines mediated by a tris(ox-

azolinyl)boratomagnesium amide precatalyst reported re-

cently by Sadow and co-workers.^[41]Indeed, the ¹H NMR

spectroscopic monitoring of the equimolar reaction of 4 and

2-methoxyethylamine in [D₆]benzene at room temperature

indicated gradual, but eventually the near-complete (after

12 h) consumption of 4 to give predominately 14 with the re-

lease of large amounts of H₂(singlet at d=4.47 ppm), small

ACHTUNGNERTU(GNN SiMe₃)₂ACHNUTTRGEG{NUNN H₂NACTHNUGTREN(UNGN CH₂)₂OMe}] analogue already described by

1

Hill and co-workers.^[9g]In particular, the H NMR spectrum

of 16 exhibited a triplet at d=0.04 ppm assigned to the hy-

drogen atoms of the coordinated chelating amine H₂N-

AHCTUNGTRENNUNG

A

CHTUNGTRENNUNG

AHCTUNGTRENNUNG

temperature combined with the inability of 11 and 12 to me-

diate the cyclization of B below 60–808C prompted us to

synthesize model compounds by reaction of 11 or 12 with B

on a preparative scale. Reactions in pentane at 258C afford-

contamination with [(LO⁴)₂Ca], negligible amounts of free

3

HN

N

ꢀ

tiplet at d=4.71 ppm), and an unidentified [(LX)Ca NHR]

species (broad singlet at d=ꢀ0.72 ppm) were also dis-

cerned.^[26]

ed [(BDI)AeN

ACTHGNURTEN(NUGN SiMe₂H)₂AHCTUNRTEG{GNNNU H₂NCH₂CCATHUNGTRENN(NGU CH₃)₂CH₂CH=CH₂}₂]

(Ae=Ca (17), Sr (18)) as pale yellow solids in excellent

Chem. Eur. J. 2013, 00, 0 – 0

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Scheme 4. Preparation of the model compounds 15–22.

yields (Scheme 4). The identities of these compounds were

confirmed by NMR and FTIR spectroscopy, and their puri-

ties were attested by combustion analysis. Notably, in the

¹H NMR spectra recorded in [D₆]benzene, the broad reso-

nance for the H₂NR protons normally found at d=0.42 ppm

for the free aminoalkene appears as a well-resolved triplet

at lower field for 17 and 18 (d=0.72 and 0.85 ppm). X-ray

crystals of 17 suitable for diffraction studies were grown

from a concentrated solution in pentane, and its solid-state

structure was determined (Figure 13). To our knowledge, 17

represents the very first example of the structural characteri-

zation of a Ca–aminoalkene adduct. The Ca center is five-

coordinate and sits in a geometry that averages as distorted-

square-pyramidal and trigonal-bipyramidal environments

(t=0.53).^[43]The Si2-N60-Si3 angle of 126.58 resembles

ꢀ

closely that found in 12. The Ca N bond lengths to the N

atoms in the coordinated amine (2.54–2.56 ꢂ) are much

longer than those to the N atoms from the b-diketiminate

ꢀ

core (2.39–2.40 ꢂ), whereas the Ca N60 bond length is

even shorter (2.33 ꢂ). Unsurprisingly, the C=C double

bonds of the aminoalkenes are not coordinated to the metal

center.

Upon heating solutions of complexes 17 and 18 in

[D₆]benzene to 808C, the gradual but quantitative formation

of 2,4,4-trimethylpyrrolidine was observed by using

¹H NMR spectroscopy (Scheme 4; complexes 21 and 22).

Attempts to crystallize a metallic complex from these mix-

tures failed, but coordination of the cyclic amine moiety

onto the metal center was established by means of NMR

spectroscopy. Moreover, it proved impossible to remove the

cyclic product by extraction with pentane and application of

dynamic vacuum, even upon gentle heating. The relative

ease of the cyclization of the aminoalkene in these com-

plexes and their excellent solubility in aromatic solvents en-

couraged us to interrogate their reactivity, and our efforts

focused on the more reactive 17. The evolution of a solution

1

of 17 in [D₆]benzene was monitored by VT H NMR spec-

troscopy at several temperatures in the range 50–808C. We

found that in all cases cyclization of the two equivalents of

the aminoalkene versus Ca occurred without an induction

period and with first-order dependence upon the concentra-

tion in 17.^[26]The activation energy value of 103.1 kJmol^ꢀ1

was extracted from the Arrhenius plot (Figure 14); further-

more, the use of Eyring analysis disclosed a high activation

Figure 13. Solid-state structure of [(BDI)AeN

ACHTUNGTRENNUNG

ACHTUTNGRENG(NU SiMe₂H)₂ACHTUNTGERN{NUNG H₂NCH₂C-

is represented. The noninteracting solvent molecule, isopropyl groups,

and hydrogen atoms are omitted for clarity. Ellipsoids are drawn at the

50% probability level. Selected bond lengths [ꢂ] and angles [8]: Ca1–

N60 2.333(2), Ca1–N21 2.394(2), Ca1–N1 2.403(2), Ca1–N41 2.545(2),

Ca1–N51 2.560(2); N60-Ca1-N21 113.94(7), N60-Ca1-N1 116.94(7), N60-

Ca1-N41 91.30(8), N60-Ca1-N51 119.86(8), Si2-N60-Ca1 114.6(1), Si3-

N60-Ca1 118.9(1), Si2-N60-Si3 126.5(1).

ACTHNUTRGNEUNG

enthalpy (DH^ꢀ=102.4(6.7) kJmol^ꢀ1) and a rather low acti-

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Cyclohydroamination of Aminoalkenes

FULL PAPER

vation entropy (DS^ꢀ=ꢀ21.9

(3.2) Jmol^ꢀ1K^ꢀ1), with a corre-

ACHTUNGTRENNUNG

sponding activation Gibbs energy of DG^ꢀ=108.9 kJmol^ꢀ1at

298 K.

The ¹H NMR spectroscopic monitoring at 808C of the

cyclization of the two molecules of B coordinated onto the

metal center in 17 gave an initial k_obs,17¹value of 5.5ꢄ10^ꢀ4s^ꢀ1

(Figure 15).^[44]There was no evidence for the presence of

Figure 16. Sequential semilogarithmic plots for the conversion of the two

1

equivalents of aminoalkene B in [(BDI)CaN

(SiMe₂H)

E

=

4.2ꢄ10^ꢀ4s^ꢀ1

;

), followed by conversion of two additional batches of two

^

equivalents of B versus Ca (k_obs,11²=3.7ꢄ10 and k_obs,11³=3.4ꢄ10^ꢀ4s^ꢀ1

;

&

~

and ) using 20 mmol of 11 in [D₆]benzene (0.4 mL) at 808C.

sive batches of two equivalents of B (Figure 16), with the

corresponding values k_obs,11¹=4.2ꢄ10^ꢀ4s^ꢀ1, k_obs,11²=3.7ꢄ

10^ꢀ4s^ꢀ1, and k_obs,11³=3.4ꢄ10^ꢀ4s^ꢀ1, respectively. Again, the

values of k_obswere constant (within experimental error), and

they were commensurate with those values determined for

17 and with the value determined during the cyclization of

12 equivalents of B versus 11 (Figure 5; k_obs=10.3ꢄ10^ꢀ4s^ꢀ1).

Figure 14. Arrhenius plot for the cyclization of the coordinated aminoal-

kene B in the complex [(BDI)CaNCATHUNGNERTN(NUG SiMe₂H)₂AHCTUNREGT{GNUNN H₂NCH₂CACTHNGUTREN(NUNG CH₃)₂CH₂CH=

CH₂}₂] (17) upon heating a solution of 17 (20 mmol) in [D₆]benzene

(0.4 mL).

1

uncoordinated B during this reaction; besides, the H NMR

data recorded after full conversion were consistent with co-

ordination of both molecules of 2,4,4-trimethylpyrrolidine

onto the Ca center (i.e., 21). After complete conversion of

the aminoalkene had been ensured, a second batch of B

(2 equiv) was introduced into the reaction mixture, and the

measured observed rate constant for this second batch of

substrate was k_obs,17²=5.7ꢄ10^ꢀ4s^ꢀ1. A third batch of two

equivalents of B was fully converted with k_obs,17³=5.4ꢄ

10^ꢀ4s^ꢀ1. The near-identical values of k_obsdetermined during

the conversion of three consecutive batches of two equiva-

lents of B versus Ca confirmed the excellent reproducibility

of the measurements and indicated that the catalytically

active species associated to 17 did not suffer from product

inhibition nor catalyst decay. In a similar set of experiments,

the THF adduct 11 was employed to convert three succes-

Conclusion

The complexes of the large alkaline-earth metals

[(LOⁱ)AeN

ACHTUNGTRNENUG(SiMe₂R)₂ACHTUNGTNER(NUGN thf)_x] (i=1–4; Ae=Ca, Sr, Ba; R=H,

Me; x=0–2) constitute the first examples of competent Ae–

aminophenolate catalysts for the cyclohydroamination of

two types of terminal aminoalkene. Cyclization occurred in

all cases according to the guidelines developed by Baldwin,

and the expected Thorpe–Ingold effect was observed. The

complexes [(BDI)AeN

A

₂A

x=1–2) and [(BDI)CaN

N

CHTUNGTRENNUNG

ubiquitous b-diketiminate (BDI)^ꢀligand were also utilized.

This last complex, reported by Hill and co-workers, dis-

played the greatest efficacy of all the tested catalysts by a

long margin. General trends were established, which are

given as follows:

1) For a given ligand, the catalytic activity decreases in

the order Ca>Sr@Ba, that is, the smaller the metal center,

the more effective the catalyst. This trend is the same as

that observed and largely documented by Hill and co-work-

ers for intramolecular cyclohydroamination reactions cata-

lyzed by a variety of alkaline-earth complexes.^[9]Yet, it is

the exact opposite of the trend previously observed during

intermolecular hydroamination and hydrophosphination re-

actions of activated alkenes catalyzed by three complete

families of charge-neutral heteroleptic alkaline-earth metal

complexes.^[24]It is not clear at this stage why the activity

trends are reversed on moving from inter- to intramolecular

hydroamination reactions, and DFT calculations have so far

not been conclusive. Hill and co-workers reported the in-

ability of Ba complexes to catalyze the cyclohydroamination

of B and argued that this behavior was probably a conse-

Figure 15. Sequential semilogarithmic plots for the conversion of the ami-

noalkene

B

in [(BDI)CaNCATHGNURTNENGNU(SiMe₂H)₂ACHUTNRGTENUNNG{H₂NCH₂CCATHNUGTREN(NGUN CH₃)₂CH₂CH=CH₂}₂]

(17; k_obs,17¹=5.5ꢄ10^ꢀ4s^ꢀ1

;

), followed by conversion of two additional

^

batches of two equivalents of B versus Ca (k_obs,17²=5.7ꢄ10 and k_obs,17

=

3

5.4ꢄ10^ꢀ4s^ꢀ1

;

and ) using 20 mmol of 17 in [D₆]benzene (0.4 mL) at

~

&

808C.

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J.-F. Carpentier and Y. Sarazin et al.

quence of the inability of the large Ba centers to sufficiently

find two explanations. First, the lower basicity of the N-

ACHTUNGTRENNUG(SiMe₂H)₂ion in comparison with the NAHCUTNTGERN(NUGN SiMe₃)₂ion, thus

ꢀ

polarize the C=C double bond to enable its insertion into

[9g]

ꢀ

the Ba N bond. Yet, the excellent catalytic behavior of

resulting in a less favorable shift of the aminoalkene/amide

exchange equilibrium [Eq. (2)]. Secondly, in the case of the

Ba complexes during intermolecular hydroamination reac-

tions^[24]along with the moderate activity displayed by 3, (6)₂

and 13 toward aminoalkenes A and B suggest this might be

too simplistic an interpretation. By considering the large

variation of the ionic radius between Ca, Sr, and Ba togeth-

er with the different nature of intramolecular (cyclization of

a single molecule) and intermolecular (coupling of two sub-

strates) reactions, it may be pertinent to consider that en-

tropic factors in fundamentally highly congested transition

states are of utmost significance.

[(LOⁱ)AeN

ACHTNUGTRENNG(U SiMe₂H)₂ACHTUNGTRENN(UGN thf)_x] phenolate complexes, a case of

catalyst deactivation through dehydrogenative coupling of

the amine and hydrosilane was identified, thus readily lead-

ing, even at room temperature, to the formation of a catalyt-

ically inert alkaline-earth complex. This decomposition path-

way was not necessarily specific to catalysts supported by

ꢀ

aminophenolate ligands because similar N Si dehydrogena-

tive coupling was evidenced between [(BDI)AeN

A

AHCTUNGRTEG(NNUN thf)_x] (Ae=Ca, Sr) and 2-methoxyethylamine, albeit under

2) For a given metal center (Ca was used for conven-

ience), catalyst performance increases when the chelating

and donating ability of the aminophenolate ligand decreases.

This finding can be interpreted both in terms of steric con-

gestion, the availability of coordination sites on the central

atom for the incoming substrate, and electronic considera-

tions because the more electron-rich the metal center, the

lower its ability to polarize the alkene and favor its insertion

slightly more forcing conditions than those required for ef-

fective hydroamination catalysis. This finding led us to pro-

pose the extended mechanistic scenario depicted in

Scheme 5 for cyclohydroamination catalyzed by [(LX)AeN-

(thf)_x] complexes ((LX)^ꢀ=(LOⁱ}^ꢀor (BDI)^ꢀ). We

ACHUTNGREN(NUG SiMe₂H)₂ACHTUGNTRENNUGN

conclude that, although beneficial for the synthesis of stable

alkaline-earth complexes owing to stabilization by internal

ꢀ

Ae···H-Si agostic interactions, the use of the NACTHNUGTRNEUNG(SiMe₂H)₂

ꢀ

into the Ae N bond.

3) For a given ligand framework and metal center, com-

ion may be prejudicial to catalytic activity in the case of cat-

alyzed reactions involving reactive amine substrates (and

ꢀ

plexes that incorporate the N

(SiMe₃)₂amido group are cat-

possibly other Z H active substrates).

alytically far superior to their analogues that contain the N-

Kinetic studies hinted at other subtleties. In the cases of

catalysts bearing the ligands (BDI)^ꢀor (LO⁴}^ꢀ, first-order

dependence upon initial substrate concentration was deter-

ꢀ

(SiMe₂H)₂amide. This outcome is in striking contrast with

other catalytic processes^{[22k,n,23,24]}and this observation could

Scheme 5. Mechanisms for cyclohydroamination catalyzed by [(LX)AeNACHTNUTRGENNG(U SiMe₂H)₂ACHTUNTGERN(NUGN thf)_x].

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Cyclohydroamination of Aminoalkenes

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Sr, x=2 (12); Ba, x=2 (13)),^[24]and the proligands (LOⁱ)H (i=1–4)^[47]

mined. On the other hand, consumption of the substrate

and (BDI)H^[48]were all prepared as described elsewhere.

with [(LO¹)CaN(SiMe₂H)₂] and [(LO¹)CaN

ACHTUNGTRENNUNG CAHUTGNTREN(NUGN SiMe₃)₂] was in-

G

R

A mixture of [Sr{NACHTUNGTERGNN(UN SiMe₃)₂}₂ACHTUNGTRENNUNG(thf)₂]

dependent from the substrate concentration; furthermore,

the former complex exhibited inhibition by the substrate

and product, whereas no evidence of these inhibitions were

detected for the latter. These cases are further illustrations

of the fine interplay between catalytic activity (and opera-

tive mechanisms) and the nature of the metal center, ligand

scaffold, and amido groups. It is apparent from these results

that the excessively simplistic mechanism given in Scheme 5

cannot be generalized for all alkaline-earth metal hydroami-

nation catalysts and that further studies are required. The

AHCTUNGTRENNUNG

in Et₂O (10 mL) overnight at room temperature. After addition of a solu-

tion of (LO⁴)H (0.26 g, 0.74 mmol) in Et₂O (5 mL), a white precipitate

formed slowly upon stirring at room temperature. The suspension was

stirred for a further 6 h, and the precipitate was isolated by filtration. Fol-

lowing drying to constant weight, (5)₂was obtained as a colorless powder

(0.31 g, 73%). Recrystallization from a concentrated solution of (5)₂in

benzene afforded X-ray quality single crystals. The dimeric complex

showed very poor solubility in aromatic solvents and highly dynamic be-

havior in [D₈]THF, which is indicative of significant dissociation in this

solvent (assignments for both the monomeric and dimeric complexes are

given).

isolation of [(BDI)CaNCATHUNGNERTN(NUG SiMe₂H)₂AHCTUNREGT{GNUNN H₂NCH₂CACTHNGUTREN(UNNG CH₃)₂CH₂CH=

For the monomer: ¹H NMR ([D₈]THF, 298 K, 400.1 MHz): d=7.32 (d,

⁴J_HH=2.6 Hz, 1H; m-H), 6.99 (d, ⁴J_HH=2.6 Hz, 1H; m-H), 4.98 (m,

¹J_SiH=164 Hz, 2H; SiH), 3.94 (br, 2H; ArCH₂N), 3.84 (brs, 4H; CH₂O),

CH₂}₂] (17), the first example of a Ca–aminoalkene adduct

structurally characterized, is a first step in this direction.

This unique complex essentially behaves like the more

3.76 (s, 6H; OCH₃), 2.91 (d, ⁴J_HH=2.6 Hz, 4H; NCH₂CH₂), 1.68 (s, 9H;

3

o-C

(CH₃)₃), 1.48 (s, 9H; p-C

E

standard [(BDI)CaNACTHNUTRGENNUG(SiMe₂H)ACHTUNTGREN(NUNG thf)] complex (11). NMR

AHCTUNGTRENNUNG

(CH₃)₂H); (¹H}¹³C NMR ([D₈]THF, 298 K, 100.6 MHz): d=166.7 (i-C),

spectroscopic monitoring experiments indicate that both

aminoalkene molecules remain coordinated to the Ca center

under catalytic conditions and that after complete cycliza-

tion the final product is also tightly bound to the metal

center. We are now investigating the use of this and related

alkaline-earth complexes for the cyclohydroamination of a

broad range of substrates.

136.4 (o-C), 131.4 (p-C), 126.7 (o-C), 123.8 (m-C), 123.4 (m-C), 71.2

(CH₂O), 62.2 (ArCH₂N), 60.5 (OCH₃), 54.4 (NCH₂CH₂), 36.1 (o-C-

A

ACHTGNUERTN(NUGN CH₃)₃), 32.8 (p-CAHCUTNTRGEN(GNUN CH₃)₃), 30.7 (o-CCAHTNUGTREN(NUGN CH₃)₃), 5.3 ppm

AHCTUNGTRENNUNG

1

For the dimer: H NMR ([D₈]THF, 298 K, 400.1 MHz): d=7.28 (d, J_HH

2.6 Hz, 2H; m-H), 6.94 (d, ⁴J_HH=2.6 Hz, 2H; m-H), 4.91 (m, J_SiH

162 Hz, 4H; SiH), 3.90 (br, 4H; ArCH₂N), 3.82 (br s, 8H; CH₂O), 3.72

(s, 12H; OCH₃), 1.99 (br s, 8H; NCH₂CH₂), 1.68 (s, 18H; o-C(CH₃)₃),

(CH₃)₂H);

(CH₃)₃), 0.26 ppm (d, ³J_HH=2.8 Hz, 24H; Si

1.48 (s, 18H; p-CACTHNUGRTENNUNG ACHTUNGTRENNUNG

{¹H}¹³C NMR ([D₈]THF, 298 K, 100.6 MHz): d=167.9 (i-C), 135.8 (o-C),

129.7 (p-C), 126.8 (o-C), 123.4 (m-C), 122.7 (m-C), 69.9 (CH₂O), 60.4

Experimental Section

(OCH₃), 60.1 (ArCH₂N), 53.4 (NCH₂CH₂), 36.0 (o-C

ACHTUNGTRENNUNG

General procedures: All manipulations were performed in an inert at-

mosphere by using standard Schlenk techniques or in a Jacomex glove

box (O₂<1 ppm, H₂O<5 ppm) for catalyst loading. NMR spectra were

A

E

N

{¹H}²⁹Si NMR ([D₈]THF, 298 K, 79.5 MHz): d=ꢀ26.90 ppm; FTIR (nujol

in KBr plates): n˜ =2005 (s), 1971 (s), 1917 (s), 1771 (w), 1602 cm^ꢀ1(s); el-

emental analysis (%) calcd for C₅₀H₁₀₀N₄O₆Si₄Sr₂(1140.92 gmol^ꢀ1): C

52.64, H 8.83, N 4.91; found: C 52.46, H 8.75, N 4.79.

1

recorded on Bruker AC-300, AC-400, and AM-500 spectrometers. H and

¹³C chemicals shifts were determined by using the residual signals of the

deuterated solvents and were calibrated versus SiMe₄. Assignment of the

signals was carried out using 1D (¹H, ¹³C{¹H}) and 2D (COSY, HMBC

HMQC) NMR experiments. ¹⁹F{¹H} chemical shifts were determined by

an external reference to an aqueous solution of NaBF₄. ²⁹Si chemical

shifts are reported relative to SiMe₄. Elemental analyses were performed

on a Carlo Erba 1108 Elemental Analyzer instrument at the London

Metropolitan University by Stephen Boyer and were the average of a

minimum of two independent measurements. FTIR spectra were record-

ed at room temperature as nujol mulls in KBr plates on a Shimadzu Af-

finity-IR spectrometer. CaI₂, SrI₂, and BaI₂(anhydrous beads; 99.995%)

were purchased from Aldrich and used as received. Reagents HN-

ACHUTNERGNNUG ACHTUNTGERN(NUNG SiMe₂H)(SiMe₂NHCH₂CH₂OCH₃)] (14): 2-Methoxyethyla-

[(LO⁴)CaN

mine (32 mL, 0.37 mmol) was added slowly to a solution of 4 (200 mg,

0.34 mmol) in toluene (3 mL) at room temperature. After 3 h, the reac-

tion solution was concentrated to 0.5 mL and diluted by the addition of

pentane (1.5 mL). Fractionated crystallization at ꢀ308C over the course

of several days afforded 14 as colorless crystals (60 mg, 31%) suitable for

X-ray diffraction studies. ¹H NMR ([D₆]benzene, 298 K, 400.1 MHz): d=

7.57 (d, ⁴J_HH=2.8 Hz, 1H; m-H), 7.02 (d, ⁴J_HH=2.8 Hz, 1H; m-H), 5.09

1

3

(m, J_SiH=172 Hz, 1H; SiMe₂H), 3.35 (t, J_HH=4.8 Hz, 2H; CH₂CH₂NH),

3.28 (br s, 2H; ArCH₂N), 3.13 (s, 6H; CH₂NCH₂CH₂OCH₃), 3.07 (s, 3H;

CH₃OCH₂CH₂NH), 2.97 (m, 4H; CH₂NCH₂CH₂), 2.76 (m, 2H;

ACHTUNGTRENNUNG(SiMe₃)₂(Acros), HNACHTUNGTRENNUNG(SiMe₂H)₂(ABCR), and 2-methoxyethylamine

CH₂CH₂NH), 2.18 (m, 4H; CH₂NCH₂CH₂), 1.78 (s, 9H; o-C

(s, 9H; p-C

(CH₃)₃), 0.92 (t, ³J_HH=7.8 Hz, 1H; CH₂CH₂NH), 0.38 (d,

³J_HH=2.8 Hz, 6H; NSi

ACTHNGUERTN(NGNU CH₃)₂H), 0.33 ppm (s, 6H; NSiACHTNGUTRENNU(G CH₃)₂NH);

ACHTUGNTRNEN(UNG CH₃)₃), 1.51

(Acros) were dried over activated 3 ꢂ molecular sieves and distilled

under reduced pressure prior to use. The substrates 1-amino-2,2-diphen-

yl-4-pentene (A) and 1-amino-2,2-dimethyl-4-pentene (B) were synthe-

sized according to a reported procedure.^[45]Toluene was distilled under

argon from melted sodium prior to use. THF was first predried over

sodium hydroxide and distilled under argon over CaH₂, and then freshly

distilled a second time under argon from Na/benzophenone prior to use.

Et₂O, dichloromethane, and pentane were distilled under argon from Na/

benzophenone, CaH₂, and Na/benzophenone/tetraglyme, respectively. All

the deuterated solvents (Eurisotop, Saclay, France) were stored in sealed

ampoules over activated 3 ꢂ molecular sieves and were degassed by sev-

AHCTUNGTRENNUNG

{¹H}¹³C NMR ([D₆]benzene, 298 K, 100.6 MHz): d=165.9 (i-C), 135.3 (o-

C), 131.3 (p-C), 125.5 (o-C), 123.4 (m-C), 122.9 (m-C), 74.9

(CH₂CH₂NH),

(CH₃OCH₂CH₂NCH₂), 58.6 (CH₃OCH₂CH₂NH), 54.3 (CH₂NCH₂CH₂O),

41.7 (CH₂CH₂NH), 35.3 (o-C(CH₃)₃), 33.7 (p-C(CH₃)₃), 32.2 (p-C(CH₃)₃),

(CH₃)₂NH);

(CH₃)₂NH),

69.4

(CH₂NCH₂CH₂O),

62.5

(ArCH₂N),

59.4

A

U

ACHTUNGTRENNUNG

29.9 (o-CACHTGNURTEN(UGNN CH₃)₃), 4.75 (SiACHTUTGNENRNGU(CH₃)₂H), 3.67 ppm (SiACTUHNGTRENNUGN

{¹H}²⁹Si NMR ([D₆]benzene, 298 K, 79.5 MHz): d=ꢀ13.25 (Si

ACHTUNGTRENNUNG

ꢀ30.06 ppm (Si

ACHTUGNERTN(NUNG CH₃)₂H); elemental analysis (%) calcd for

C₂₈H₅₇CaN₃Si₂O₄(596.02 gmol^ꢀ1): C 56.42, H 9.64, N 7.05; found: C

56.50, H 9.58, N 6.98.

eral freeze–thaw cycles. The precursors [Ae{N

Sr, Ba)^[22e,46]and [Ae{N (thf)_x] (Ae=Ca, x=1; Sr, x=²/₃; Ba,

(SiMe₂H)₂}₂A

x=0),^[22k]the complexes [(LO⁴}CaN(SiMe₃)₂] (1),^[22l][(LO⁴}SrN

(SiMe₃)₂-

(thf)] (2),^[24][(LO⁴}BaN (thf)] (3),^[22m][(LO⁴)CaN

(SiMe₃)₂A (SiMe₂H)₂A(thf)]

(4),^[22n][(LO⁴)BaN (thf)] (6),^[22m][(LO¹)CaN(SiMe₂H)₂] (7),^[22n]

(SiMe₂H)₂A

[(LO²)CaN(SiMe₂H)₂] (8),^[22n][(LO³)CaN(SiMe₂H)₂] (9),^[22l][(LO¹)CaN-

(SiMe₃)₂] (10),^[22i]and [(BDI)AeN

(SiMe₂H)₂A(thf)_x] (Ae=Ca, x=1 (11);

ACHTUTGNERNNUG(SiMe₃)₂}₂HCATUNGTREN(NGUN thf)₂], (Ae=Ca,

A

CHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

A

ACHTUNGTRENNUNG

a

A

R

G

N

CHTUNGTRENNUNG

A

E

U

0.32 mmol) in pentane (3 mL) at room temperature. A white precipitate

gradually appeared. After 3 h, this solid was isolated by cannula filtration

and dried under vacuum. The solution was kept at ꢀ308C to afford two

A

ACHTUNGTRENNUNG

A

R

CHTUNGTRENNUNG

Chem. Eur. J. 2013, 00, 0 – 0

ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

&

15

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ÞÞ

These are not the final page numbers!

J.-F. Carpentier and Y. Sarazin et al.

crops of 15 as colorless crystals after crystallization (180 mg, 85%).

¹H NMR ([D₆]benzene, 298 K, 400.1 MHz): d=7.09 (m, 6H; arom-H),

4.93 (s, 1H; MeCCHCMe), 4.89 (m, ¹J_SiH=159 Hz, 2H; SiH), 3.62 (m,

([D₆]benzene, 298 K, 125.8 MHz): d=165.1 (C(Me)=N), 149.7 (i-C),

142.3 (o-C), 135.1 (CH₂=CHCH₂), 124.7 (p-C), 124.1 (m-C), 118.3 (CH₂=

CHCH₂), 94.9 (MeCCHCMe), 53.3 (CH₂NH₂), 44.7 (CH₂=CHCH₂), 35.4

2H; CH

MeOCH₂), 2.19 (s, 3H; CH₃O), 1.80 (br, 2H; CH₂NH₂), 1.72 (s, 6H;

(CH₃)₂), 2.47 (t, ³J_HH=4.5 Hz, 2H;

ACHTUNGTRENNUNG(CH₃)₂), 3.31 (m, 2H; CHAHCTUNGTRENNGUN

(C

(CH₃)₂), 28.5 (CH

E

G

ACHTUGNTRENN(UNG CH₃)₂), 25.2 (CH-

A

R

ACHTUNGTRENNUNG

3

(CH₃)CCHCACHTUNGTRENNUNG(CH₃)), 1.46–1.15 (m, 24H; CHAHCTUGNTREN(NGNU CH₃)₂), 0.48 (d, J_HH=

([D₆]benzene, 298 K, 79.5 MHz): d=ꢀ26.85 ppm; FTIR (nujol in KBr

2.9 Hz, 12H; SiMe₂H), 0.31 ppm (brm, 2H; CH₂NH₂); {¹H}¹³C NMR

([D₆]benzene, 298 K, 100.6 MHz): d=166.0 (C(Me)=N), 149.7 (i-C),

143.3 (o-C), 124.5 (p-C), 124.1 (m-C), 95.9 (MeCCHCMe), 73.1

plates): n˜ =2017 (s), 1924 (w), 1960 (sh), 1624 (w), 1585 (m), 1543 (s),

1512 (s) cm^ꢀ1

;

elemental analysis (%) calcd for C₄₇H₈₅SrN₅Si₂

(864.00 gmol^ꢀ1): C 65.34, H 9.92, N 8.11; found: C 64.92, H 9.87, N 8.72.

¹H NMR data for [(BDI)CaN

(SiMe₂H)₂(2,4,4-trimethylpyrrolidine)₂]

(MeOCH₂), 59.0 (CH₃O), 40.8 (CH₂NH₂), 29.1 (CH

ACHTUGNTRENN(UNG CH₃)₂), 25.6 (CH-

AHCTUNGTRENNUNG

A

R

ACHTUNGTRENNUNG

(21) generated in situ: ([D₆]benzene, 353 K, 500.13 MHz): d=7.13 (dd,

([D₆]benzene, 298 K, 79.5 MHz): d = ꢀ25.52 ppm; satisfactory elemental

³J_HH=7.5, ⁴J_HH=1.3 Hz, 4H; m-H), 7.07 (t, ³J_HH=7.6 Hz, 2H; p-H),

analysis for this compound could not be obtained reliably.

4.90(m, 2H; SiH; 1H; MeCCHCMe), 3.31 (hept, ³J_HH=6.8 Hz, 4H; CH-

3

ACHTUNGTRENNUNG[(BDI)SrNACHTUNGTRENNUNG(SiMe₂H)₂(NH₂CH₂CH₂OCH₃)] (16): Following an identical

G

N

=

(CH₃)₂), 2.32 (dd, ²J_HH=10.8, ³J_HH=6.5 Hz, 2H;

(CH₃)), 1.50 (br, 2H;

protocol to that described for 15, the reaction of 2-methoxyethylamine

(31 mL, 0.35 mmol) and 12 (250 mg, 0.32 mmol) afforded 16 as colorless

crystals (200 mg, 88%). ¹H NMR ([D₆]benzene, 298 K, 500.1 MHz): d=

7.11 (d, ³J_HH=7.2 Hz, 4H; m-H), 7.04 (t, ³J_HH=7.2 Hz, 2H; p-H), 4.92

(m, ¹J_SiH=184 Hz, 2H; SiH), 4.89 (s, 1H; MeCCHCMe), 3.43 (m, 4H;

N

AHCTUNGTRENNUNG

3

N

ACHTUNGNRET(NGNU CH₃)₂), 1.27 (d, J_HH=

AHCTUNGTRENNUNG

CH

(brm, 8H; (CH₃)CCHC

CH

(CH₃)₂), 0.47 (d, ³J_HH=3.0 Hz, 12H; Si

ACHTUNGTRENNUNG

G

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

0.84 (s, 6H; NHCH_aH_bC

0.29 ppm (d, J_HH=2.9 Hz, 12H; Si

G

ACHTUNGTRENNUNG

3

A

E

N

2H; CH₂NH₂); {¹H}¹³C NMR ([D₆]benzene, 298 K, 125.8 MHz): d=164.9

(C(Me)=N), 149.2 (i-C), 142.6 (o-C), 124.3 (p-C), 124.1 (m-C), 94.9

(MeCCHCMe), 73.5 (MeOCH₂), 58.6 (CH₃-O), 41.4 (CH₂NH₂), 28.6

X-ray diffraction crystallography: Suitable crystals for X-ray diffraction

analysis of (5)₂, 12, 14, 16, and 17 were obtained by recrystallization of

the purified products. Diffraction data were collected at 150 K using a

Bruker APEX CCD diffractometer with graphite-monochromated Mo_Ka

radiation (l=0.71073 ꢂ). A combination of w and F scans was carried

out to obtain at least a unique data set. The crystal structures were

solved by direct methods, the remaining atoms were located from differ-

ence Fourier synthesis followed by full-matrix least-squares refinement

based on F2 (programs SIR97 and SHELXL-97).^[49]Many hydrogen

atoms could be found from the Fourier-difference analysis. Carbon- and

oxygen-bound hydrogen atoms were placed at calculated positions and

forced to ride on the attached atom. The hydrogen-atom contributions

were calculated but not refined. All non-hydrogen atoms were refined

with anisotropic displacement parameters. The locations of the largest

peaks in the final-difference Fourier-map calculation and the magnitude

of the residual electron densities were of no chemical significance. The

relevant collection and refinement data are summarized in Table 3.

CCDC-900840 ((5)₂), CCDC-900841 (12), CCDC-900842 (14), CCDC-

900843 (16), and CCDC-900844 (17) contain the supplementary crystallo-

graphic data for this paper. These data can be obtained free of charge

from The Cambridge Crystallographic Data Centre via www.ccdc.cam.

ac.uk/data_request/cif.

(CH

ACHTUNGTRENNUNG

ACHTUNGTRENNUNG(CH₃)₂), 25.3 (CHACHTUNGTRENNUNG(CH₃)₂), 25.3 ((CH₃)CCHCACHTUNGTREN(NUGN CH₃)), 5.2 ppm (Si-

(CH₃)₂H); {¹H}²⁹Si NMR ([D₆]benzene, 298 K, 79.5 MHz): d=

ꢀ27.57 ppm; FTIR (nujol in KBr plates): n˜ =1992 (sh), 1986 (s), 1925

(m), 1550 cm^ꢀ1(s); elemental analysis (%) calcd for C₃₆H₆₄SrN₄OSi₂

(712.71 gmol^ꢀ1): C 60.67, H 9.05, N 7.86; found: C 60.58, H 9.09, N 7.73.

ACHTUNGTRENNUNG[(BDI)CaNACHTUNGTRENNUNG(SiMe₂H)₂ACHTUNGTRENNUNG{NH₂CH₂C(Me)₂CH₂CH=CH₂}₂] (17): 1-Amino-

2,2-dimethyl-4-pentene (70 mg, 0.62 mmol) was added slowly to a solu-

tion of 11 (0.19 g, 0.28 mmol) in pentane (5 mL) at room temperature.

After 3 h, removal of the solvent under vacuum yielded a light yellow

solid, which was purified by washing with pentane (4 mL) and dried in

vacuo. This procedure was repeated three times to give 17 quantitatively

after drying to a constant weight (220 mg, 95%). X-ray quality crystals

were grown from a solution of 17 in pentane stored at ꢀ308C with very

slow evaporation of the solvent. ¹H NMR ([D₆]benzene, 298 K,

500.1 MHz): d=7.09 (d, ³J_HH=7.2 Hz, 4H; m-H), 7.02 (t, ³J_HH=7.2 Hz,

2H; p-H), 5.61 (m, 2H; CH₂=CHCH₂), 5.02–4.99 (m, 4H; CH₂=CHCH₂),

4.96(m, 2H; SiH), 4.88 (s, 1H; MeCCHCMe), 3.46 (m, 4H; CHACHTUNGTRENNUNG

2.07 (t, ³J_HH=3.6 Hz, 4H; CH₂NH₂), 1.72 (s, 6H; (CH₃)CCHC

ACHTUNGTRENNUNG

1.67 (d, ³J_HH=3.6 Hz, 4H; CH₂=CHCH₂), 1.36 (d, ³J_HH=7.0 Hz, 12H;

CH

8.5 Hz, 4H; CH₂NH₂), 0.56 (s, 12H; CH₂C

³J_HH=3.0 Hz, 12H; Si(CH₃)₂H); {¹H}¹³C NMR ([D₆]benzene, 298 K,

A

Protocol for NMR-scale cyclohydroamination reactions: Catalyzed cyclo-

hydroamination reactions monitored by means of ¹H NMR spectroscopy

were carried out by using the following procedure: In a glove-box, the

catalyst was loaded into an NMR tube. By using Schlenk techniques, the

substrate and [D₆]benzene (0.4 mL) were added into the NMR tube. The

tube was sealed, vigorously shaken, and immerged into an oil bath preset

at the desired temperature. After the required amount of time, the NMR

ACHTUNGTRENNUNG

125.8 MHz): d=166.4 (C(Me)=N), 149.4 (i-C), 142.4 (o-C),135.0 (CH₂=

CCHCH₂), 124.8 (p-C), 124.1 (m-C), 118.3 (CH₂=CHCH₂), 95.2

(MeCCHCMe), 53.5 (CH₂NH₂), 44.9 (CH₂=CHCH₂), 35.3 (C

28.6 (CH(CH₃)₂), 26.0 (C(CH₃)₂), 25.7 (CH(CH₃)₂), 25.3 (CH

25.0 ((CH₃)CCHC(CH₃)), 5.4 ppm (Si(CH₃)₂H);

{¹H}²⁹Si NMR

A

U

G

1

tube was removed from the oil bath and the H NMR spectrum of the re-

([D₆]benzene, 298 K, 79.5 MHz): d=ꢀ24.64 ppm; FTIR (nujol in KBr

plates): n˜ =2025 (s), 1924 (w), 1624 (w), 1581 (m), 1539 (s), 1516 cm^ꢀ1

(s); elemental analysis (%) calcd for C₄₇H₈₅CaN₅Si₂(816.46 gmol^ꢀ1): C

69.14, H 10.49, N 8.58; found: C 69.04, H 10.53, N 8.62.

action mixture was recorded. The conversion was calculated by compar-

ing the relative intensities of resonance signals characteristic of the sub-

strate and product.

NMR spectroscopic monitoring of cyclohydroamination reactions: Cata-

lyzed cyclohydroamination reactions monitored by H NMR spectroscopy

ACHTUNGTRENNUNG[(BDI)SrNACHTUNGTRENNUNG(SiMe₂H)₂ACHTUNGTRENNUNG{NH₂CH₂C(Me)₂CH₂CH=CH₂}₂] (18): Following an

identical procedure to that described for 17, the reaction of 1-amino-2,2-

dimethyl-4-pentene (90 mg, 0.79 mmol) and 12 (280 mg, 0.35 mmol) af-

1

were carried out by using the following procedure: In a glove-box, the

catalyst was loaded into an NMR tube. By using Schlenk techniques, the

substrate and [D₆]benzene (0.4 mL) were added into the NMR tube. The

tube was sealed, vigorously shaken, and inserted into the probe of a

Bruker AM 500 NMR spectrometer preheated to the required tempera-

ture. The reaction kinetics were monitored (using the multi_zgvd com-

mand; D1=0.2 s; DS=0; NS=8, or more) over the course of three or

more half-lives on the basis of amine consumption by comparing the rela-

tive intensities of resonance signals characteristic of the substrate and

product.

forded 18 as

a

pale yellow powder (290 mg, 96%). ¹H NMR

([D₆]benzene, 298 K, 500.1 MHz): d=7.12 (d, ³J_HH=7.2 Hz, 4H; m-H),

7.05 (t, ³J_HH=7.2 Hz, 2H; p-H), 5.61 (m, 2H; CH₂=CHCH₂), 5.01–4.96

(m, 4H; CH₂=CHCH₂), 4.94 (m, 2H; SiH), 4.90 (s, 1H; MeCCHCMe),

3.44 (m, 4H; CH

6H; (CH₃)CCHC

(CH₃)), 1.64 (d, ³J_HH=3.6 Hz, 4H; CH₂=CHCH₂), 1.36

(d, ³J_HH=7.0 Hz, 12H; CH(CH₃)₂), 1.26 (d, ³J_HH=7.0 Hz, 12H; CH-

(CH₃)₂), 0.85 (t, ³J_HH=8.5 Hz, 4H; CH₂NH₂), 0.54 (s, 12H; CH₂C-

(CH₃)₂CH₂), 0.40 ppm (d, ³J_HH=3.0 Hz, 12H; Si(CH₃)₂H); {¹H}¹³C NMR

ACHTUNGTRENNUNG

(CH₃)₂), 2.07 (t, ³J_HH=3.6 Hz, 4H; CH₂NH₂), 1.69 (s,

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

ACHTUNGTRENNUNG

G

ACHTUNGTRENNUNG

&

16

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www.chemeurj.org

ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 0000, 00, 0 – 0

ÝÝ

These are not the final page numbers!

Cyclohydroamination of Aminoalkenes

FULL PAPER

Table 3. Summary of crystallographic data for compounds (5)₂, 12, 14, 16, and 17.

(5)₂

12

14

16

17

empirical formula

CCDC number

formula weight

crystal system

space group

a [ꢂ]

b [ꢂ]

c [ꢂ]

a [8]

b [8]

C₅₀H₁₀₀N₄O₆Si₄Sr₂

900844

1140.94

C₄₁H₇₁N₃O₂Si₂Sr

900840

787.81

C₂₈H₅₇CaN₃O₄Si₂

900841

596.03

monoclinic

P2₁/n

9.4997(4)

26.2765(11)

14.0987(5)

90

96.991(2)

90

3493.1(2)

4

1.133

0.281

C₃₆H₆₄N₄OSi₂Sr

900842

712.71

monoclinic

Cc

12.6035(9)

19.5047(13)

17.6446(12)

90

108.845(3)

90

4105.0(5)

4

1.153

1.402

C₄₇H₈₅CaN₅Si₂

900843

816.46

monoclinic

P2₁/n

11.7644(5)

22.7348(10)

19.1741(8)

90

91.284(2)

90

5127.0(4)

4

1.058

0.203

triclinic

¯

P1

11.1741(2)

12.4674(3)

12.4791(3)

63.1060(10)

88.9700(10)

80.7940(10)

1527.57(6)

2

10.9482(9)

11.6660(9)

20.2339(18)

85.017(3)

11.6660(9)

67.047(3)

2360.6(3)

2

g [8]

volume [ꢂ³]

Z

1 [gcm^ꢀ3

]

1.240

1.869

608

1.100

1.225

840

m [mm^ꢀ1

(000)

]

F

A

1304

1528

1800

crystal size [mm]

q range [8]

limiting indices

0.40ꢄ0.28ꢄ0.20

1.83–27.45

ꢀ14<h<12

ꢀ16<k<11

ꢀ16<l<16

0.0339

0.57ꢄ0.46ꢄ0.23

2.35–27.08

ꢀ14<h<14

ꢀ11<k<15

ꢀ26<l<26

0.0384

0.54ꢄ0.16ꢄ0.09

2.91–27.47

ꢀ10<h<10

ꢀ32<k<34

ꢀ18<l<18

0.0524

0.54ꢄ0.37ꢄ0.23

3.42–27.47

ꢀ16<h<16

ꢀ25<k<25

ꢀ22<l<22

0.0327

0.55ꢄ0.53ꢄ0.18

1.39–27.50

ꢀ15<h<15

ꢀ29<k<29

ꢀ20<l<24

0.0731

R_int

refl. collected

24433

27002

28920

30427

45915

refl. unique [I>2s(I)]

data/restraints/parameters

goodness-of-fit on F²

R₁[I>2s (I)] (all data)

wR₂[I>2s (I)] (all data)

6937

6937/0/325

1.174

0.0377

0.0502AHCNUTGTRENNUNG

1.693 and ꢀ0.813

10581

10581/0/462

1.034

0.0426 (0.0634)

0.1059 (0.1128)

0.763 and ꢀ0.391

7957

7957/0/362

0.954

0.0499 (0.1227)

0.0755 (0.1372)

0.368 and ꢀ0.395

8867

8867/2/402

1.036

0.0293 (0.0700)

0.0340 (0.0714)

0.483 and ꢀ0.415

68699

11681/0/522

1.063

0.0564 (0.1508)

0.0952 (0.1798)

0.737 and ꢀ0.406

G

largest difference [eA^ꢀ3

]

Details of the kinetic measurements with corresponding plots; Vanꢃt Hoff

analysis and the FTIR spectrum of (5)₂; ¹H NMR spectroscopic monitor-

ing of the reaction of 1 and 1-amino-2,2-dimethyl-4-pentene (B) in

[D₆]benzene; crystallographic data of (5)₂, 12, 14, 16, and 17 (as CIF

files); and representation of the solid-state structure of 16 are given in

the Supporting Information

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Chem. Commun. 2003 , 3048; m) P. D. Knight, I. Munslow, P. N.

OꢃShaughnessy, P. Scott, Chem. Commun. 2004 , 894; n) D. V. Grib-

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Acknowledgements

Financial support from the European Research Council (Marie Curie

FP7-PEOPLE-2010-IIF fellowship to B.L. ChemCatSusDe), the CNRS

(Y.S.), and the Institut Universitaire de France (J.F.C.) is gratefully ac-

knowledged. We thank Stephen Boyer (London Metropolitan University)

for his assistance with elemental analyses.

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[26] See the Supporting Information for details.

[27] Yet, solution ¹H NMR (¹J_SiH=162 Hz in

a 4:1 mixture of

[D₆]benzene and 1,2-C₆H₄F₂) and solid-state FTIR (v˜_s(SiH)=2005,

1971, 1917 cm^ꢀ1) spectroscopic data were both compatible with the

presence of stabilizing Sr···H-Si interactions.

[28] The present study focuses solely on the intrinsic reactivity of the al-

kaline-earth complexes, and for this reason only, two of the most

standard substrates were examined; therefore, the full extent of sub-

strate scope was not explored and will be reported elsewhere.

[29] Note that although commonly presented, the mechanism depicted in

Scheme 2 is somewhat excessively simplistic, and the groups of Hill

and Sadow have proposed alternative or more sophisticated mecha-

nisms; for example, see references [9g] and [12b]. Note also that

recent computational studies by Tobisch^[12c]have suggested that the

Mg-catalyzed hydroamination proceeds through reversible olefin in-

sertion and rate-determining protonolysis.

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¹H NMR spectroscopic kinetic monitoring was not performed for

[(LO³)CaN

ACTHNUTRGEN(UGN SiMe₂H)₂] (9) nor for the Sr and Ba analogues.

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Cyclohydroamination of Aminoalkenes

FULL PAPER

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only the amine adduct 15 was obtained by using 11 as the starting

material. Besides, heating 15 to 808C quantitatively afforded the

ꢀ

product of dehydrogenative N Si coupling, that is, [(BDI)CaN-

A

R

U

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T=808C.

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crystallography, and it very closely resembled [(BDI)SrN

{H₂N

(CH₂)₂OMe}],^[9g]with a five-coordinated Sr center bearing a

chelating H₂N(CH₂)₂OMe bidentate ligand instead of the two THF

molecules found in 12. The Si-N-Si angle 136.08 in 16 was noticeably

wider than in [(BDI)SrN(SiMe₃)₂A{H₂N(CH₂)₂OMe}] (123.58) or in

12 (127.48); whereas [(BDI)SrN(SiMe₃)₂A{H₂N(CH₂)₂OMe}] was in

75:25 equilibrium with [(BDI)Sr{HN(CH₂)₂OMe}] through amine/

amide exchange,^[9g]there was no spectroscopic evidence for such an

equilibrium involving 16 and [(BDI)Sr{HN(CH₂)₂OMe}]. We attrib-

uted the specific behavior of 16 to the low basicity of the N-

ACHTUNGTRNE(NUNG SiMe₃)₂-

A

U

ACHTUNGTRENNUNG

A

N

ACHTUNGTRENNUNG

A

N

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

ꢀ

N

ACHTUNGTREN(UNNG SiMe₃)₂and MeO-

ACHTUNGTRENNUNG

A

CHTUNGTRENNUNG

AHCTUNGTRENNUNG

A

Received: October 5, 2012

Published online: && &&, 0000

ment of [(BDI)CaN

(SiMe₃)

G

Chem. Eur. J. 2013, 00, 0 – 0

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J.-F. Carpentier and Y. Sarazin et al.

Homogeneous Catalysis

B. Liu, T. Roisnel, J.-F. Carpentier,*

Y. Sarazin* ....................... &&& — &&&

Cyclohydroamination of Aminoal-

kenes Catalyzed by Disilazide Alka-

line-Earth Metal Complexes: Reac-

tivity Patterns and Deactivation Path-

ways

Playing a role: Phenolate and b-diketi-

minate disilazide complexes of the

large alkaline-earth metals (Ca, Sr,

and Ba) have been employed as com-

petent catalysts for the cyclohydroami-

nation of terminal aminoalkenes (see

scheme). Trends regarding the catalytic

activity of these complexes have been

established and allow the discrimina-

tion between metal, ligand framework,

and amido groups. A specific deactiva-

tion pathway has been identified, and

several model compounds have been

used for stoichiometric investigations.

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Article Doi

Cyclohydroamination of aminoalkenes catalyzed by disilazide alkaline-earth metal complexes: Reactivity patterns and deactivation pathways

DOI: 10.1002/chem.201203562

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Full text of DOI:10.1002/chem.201203562

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