N-H activation by Rh(I) via metal-ligand cooperation

Article

pubs.acs.org/Organometallics

N−H Activation by Rh(I) via Metal−Ligand Cooperation

Moran Feller,^†Yael Diskin-Posner,^‡Linda J. W. Shimon,^‡Eyal Ben-Ari,^†and David Milstein*^,†

‡

^†Department of Organic Chemistry and Department of Chemical Research Support, The Weizmann Institute of Science, Rehovot,

76100, Israel

S

* Supporting Information

ABSTRACT: In continuation of our studies on bond

activation and catalysis by pincer complexes, based on

metal−ligand cooperation, we present here a rare example of

amine N−H activation by Rh(I) complexes. The novel

dearomatized pincer complexes [(PNN*)RhL′] (PNN = 2-

(CH₂-P^tBu₂)-6-(CH₂-NEt₂)C₅H₃N, PNN* = deprotonated

PNN, L′ = N₂(5), C₂H₄(6)) and [(ⁱPrPNP*)RhL′] (ⁱPrPNP

i

= 2,6-(CH₂-PⁱPr₂)₂C₅H₃N, PrPNP* = deprotonated PrPNP,

L′ = C₂H₄(7), cyclooctene (9)) were prepared and fully characterized by NMR and X-ray analysis. Complexes 5−7 and 9

undergo facile N−H activation of anilines involving aromatization of the pincer ligand without a change in the formal oxidation

state of the metal center to form stable anilide complexes [(PNN)Rh(NHAr)] and [(ⁱPrPNP)Rh(NHAr)] (Ar = C₆H₅, o-Br-

C₆H₄, m-Cl-p-Cl-C₆H₃, p-NO₂-C₆H₄). Anilines possessing electron-withdrawing groups accelerate the N−H activation and yield

more stable anilide complexes. The pincer and the ancillary ligands also aﬀect the activation rate, which supports an associative

mechanism. Spin saturation transfer experiments show chemical exchange between the pyridylic arm of the pincer ligand and the

NH− protons of anilines prior to and after the N−H activation. The reverse N−H formation by metal−ligand cooperation from

the anilide complexes was observed to give free anilines and dearomatized Rh(I) complexes upon addition of CO or PEt₃.

Deprotonation of complexes [(PNL)Rh(p-NO₂-NH₂C₆H₄)] (13, P = P^tBu₂, L = NEt₂; 15, P = L = PⁱPr₂) yields the

dearomatized anionic complexes [(PNL*)Rh(p-NO₂-NH₂C₆H₄)]. An associative mechanism, involving N−H activation of an

apically coordinated aniline in a pentacoordinated Rh(I) complex, is suggested.

and alcohols,^3a(g) dehydrogenative acylation of alcohols with

INTRODUCTION

■

esters,^2e(h) dehydrogenative amidation of esters with amines,^2f

(i) hydrogenation of organic carbonates, carbamates, and

formate esters, indicating a mild, two-step hydrogenation of

CO₂to methanol,^2g(j) hydrogenation of urea derivatives to

form methanol and amines,^3b(k) selective formation of primary

amines from alcohols and ammonia, with liberation of water,^5c

(l) dehydrogenative coupling of primary alcohols to form

acetals,^5b(m) coupling of β-amino alcohols to form peptides by

PNN-Ru, or pyrazines by PNP-Ru, with H₂liberation,⁹(n) Fe-

catalyzed hydrogenation of ketones at low pressure and

ambient temperature,^6a,c(o) Fe-catalyzed hydrogenation of

CO₂to formate salts at low pressure^6band (p) direct synthesis

of imines from alcohols and amines with liberation of H₂and

water.^4bPolymerization of diols to form polyesters with H₂

liberation catalyzed by the PNN-Ru complex was also

reported.¹⁰Several computational studies (DFT) of these

catalytic reactions have appeared.¹¹

Our group has discovered a new mode of metal−ligand

cooperation, involving aromatization−dearomatization of pyr-

idine-based ^RPNP and PNN (R = Bu; Pr) pincer ligands

(Scheme 1), as well as bipyridine-based PNN pincer ligands.

Metal−ligand cooperation based on acridine pincer complexes

has also been demonstrated.¹

t

i

Scheme 1

Metal−ligand cooperation by aromatization−dearomatiza-

tion is involved in several new, environmentally benign

reactions developed by us, catalyzed by pincer-type PNN-

Ru,^2,3PNP-Ru,^2a,h,4acridine-PNP-Ru,⁵and PNP-Fe⁶com-

plexes, including (a) dehydrogenative coupling of primary

alcohols to form esters,^2a,d,h,4a(b) dehydrogenation of

secondary alcohols to ketones,^2b,h,4a(c) hydrogenation of

esters to alcohols^2c,h,7and cyclic diesters to diols,^3c(d) coupling

of alcohols with amines to form amides with liberation of H₂,^2d

(e) formation of polyamides by dehydrogenative coupling of

diamines and diols,^2i,8(f) hydrogenation of amides to amines

Other examples of bond activation and catalysis that involve

(or may involve) metal ligand cooperation by aromatization−

dearomatization of pyridine-based pincer complexes were

recently reported.¹²

The activation of X−H (X = H, C, O, N) bonds via metal−

ligand cooperation by aromatization−dearomatization of the

Received: May 7, 2012

Published: May 18, 2012

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ligand formally involves proton transfer from a substrate to the

dearomatized ligand, which leads to H−X cleavage with

concomitant aromatization and no change in the oxidation

state of the metal center. The activation of Csp²−H and Csp³−

H bonds was demonstrated by the dearomatized pincer

complex [(^tBuPNP*)Ir(COE)], which reacts with benzene^13a

and acetone^13bto give the aromatic complexes [(^tBuPNP)Ir-

(R)] (R = C₆H₅and CH₂COCH₃, respectively), with no

overall change in the formal metal oxidation state (Scheme 2).

amido-bridged iridium hydride dimers, was reported by our

group.³⁰Hartwig and Goldman reported ammonia oxidative

addition by the pincer complex [^tBu₂P(CH₂)₂CH-

(CH₂)₂P^tBu₂]Ir(I), to form a monomeric amido iridium

hydride.³¹Hartwig also reported the double N−H cleavage of

hydrazines by pincer Ir complexes.³²Turculet reported the N−

H oxidative addition of ammonia and anilines by an iridium

silyl pincer complex to give stable anilido hydride complexes

[(Cy-PSⁱP)Ir(H)(NHR)] (Cy-PSⁱP = MeSi(o-C₆H₄PCy₂)₂).³³

The corresponding Rh silyl complex reacts with anilines and

ammonia to give only adduct complexes. Activation of

ammonia by a dimeric Pd pincer complex via a binuclear

oxidative addition to give amido and hydrido Pd monomers was

described by Ozerov and co-workers.³⁴Very recently, Oro has

reported formation of M-NH₂(M = Rh, Ir) by reaction of

ammonia with {M(μ-OMe)(tetraﬂuorobenzobarrelene)}₂.³⁵

Recently, we have reported N−H activation of amines

promoted by the nonaromatic complex [(^tBuPNP*)RuH-

(CO)] via metal−ligand cooperation.³⁶The reaction of this

complex with electron-rich amines, such as ammonia, leads to

reversible activation, while with electron-poor substrates, such

as p-nitroaniline, stable N−H activation products are obtained

(Scheme 3). N−H activation of amides (rather than amines) by

metal−ligand cooperation was very recently reported by

Muniz.³⁷

Scheme 2

The latter complexes react with H₂to give exclusively the trans-

dihydride complexes, and upon reaction with D₂, the trans-

hydride−deuteride complexes [(^tBuPNP)Ir(H)(D)(R)], with

one deuterium atom incorporated into a benzylic position, are

obtained (Scheme 2).¹³The complex that activates H₂was

found to be an Ir(III) intermediate [(^tBuPNP*)Ir(H)(R)],

which is in equilibrium with the Ir(I) complex [(^tBuPNP)Ir-

(R)].^13,14The anionic dearomatized pincer complex

[(^tBuPNP*)RhCl][K] activates benzene and hydrogen by

metal−ligand cooperation to yield the corresponding aromat-

ized phenyl and hydrido complexes, respectively.¹⁵

Scheme 3

The complex [(PNN*)RuH(CO)], bearing a dearomatized

pincer ligand, activates O−H bonds of alcohols²and water.¹⁶

The reaction with water yields the aromatized trans-hydrido−

hydroxo complex [(PNN)Ru(H)(CO)(OH)]. The latter

promotes water splitting to H₂and O₂in a stoichiometric

cycle involving consecutive heat- and light-induced steps, using

no sacriﬁcial reagents.¹⁶Here, we focus on the activation of N−

H bonds of amines by pincer complexes based on metal−ligand

cooperation.

Amines are an important class of compounds with a wide

range of uses in the chemical, pharmaceutical, and agrochemical

industries, as intermediates, surfactants, dyes, polymers,

plasticizing agents, and ﬁne chemicals.¹⁷N−H bond activation

and N−H elimination of amines mediated by metal complexes

could be fundamental steps in the catalytic formation and

functionalization of amines, although examples of such

processes are rare and far less explored than the activation of

C−H and O−H bonds. Investigation of N−H bond activation

and formation can also shed light on important metal-catalyzed

transformations, which involve amines and ammonia,¹⁸such as

hydroamination,¹⁹hydroaminomethylation,²⁰aryl halides ami-

nation,²¹reductive aminations,²²and reduction of nitriles.²³

The ﬁrst example of catalytic oleﬁn amination based on N−

H activation was demonstrated by our group using an Ir(I)

complex.²⁴

Here, we report on a rare case of N−H activation via metal−

i

ligand cooperation by novel dearomatized PrPNP- and PNN-

based Rh(I) complexes. The obtained anilido complexes react

with ancillary ligands, such as CO, to eliminate anilines via

metal−ligand cooperation, regaining dearomatization. Mecha-

nistic issues of this unusual N−H activation process are

discussed.

RESULTS AND DISCUSSION

Synthesis and Characterization of PNN and PrPNP

■

i

Rh(I) Complexes. Addition of the PNN ligand (PNN = 2-

(CH₂-P^tBu₂)-6-(CH₂-NEt₂)C₅H₃N) to a THF solution of the

cationic precursor [Rh(COE)₂(THF)₂][BF₄] (COE = cyclo-

octene) under nitrogen resulted in the formation of a yellow

precipitate that was isolated and characterized as the cationic

dinitrogen complex [(PNN)RhN₂][BF₄] (1) (Scheme 4). The

³¹P{¹H} NMR spectrum of 1 exhibits a sharp doublet at 93.31

ppm (¹J_RhP= 161.6 Hz) both in acetone and in methylene

chloride.³⁸The ¹⁹F NMR spectrum of complex 1 in acetone

exhibits a sharp signal at −152 ppm, typical of a free BF₄

counteranion, while the ¹⁹F NMR spectrum recorded in

methylene chloride³⁹exhibits a very broad signal at −151.5

ppm, which becomes narrower at lower temperatures.^40,41

Thus, in the noncoordinating methylene chloride solvent, a

weak interaction of the metal center with the counterion is

observed at ambient temperature.^41a,42This weak metal−

counteranion interaction probably stabilizes the complex,

whereas in acetone, stabilization is gained by solvent

coordination.

The few reported direct observations of N−H oxidative

addition of amines by late transition metals include the early

example of aniline activation by Ru₃(CO)₁₂,²⁵N−H oxidative

addition of indoles by [Ir(COD)(PMe₃)₃][Cl],²⁶and aniline

oxidative addition by (PCP)Ir²⁷and (POCOP)Ir²⁸complexes

(PCP = 2,6-(CH₂-P^tBu₂)₂C₆H₃, POCOP = 2,6-

(OP^tBu₂)₂C₆H₃) to give anilido hydride complexes.²⁹Direct

observation of oxidative addition of ammonia to Ir(I), to form

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by 0.03 Å than in free dinitrogen, as expected for a bridging N−

N bond.⁴³

Scheme 4

Addition of the PNN ligand to an acetone solution of the

cationic precursor [Rh(COE)₂(acetone)₂][BF₄] under argon

resulted in the formation of the cationic complex 2 (Scheme

4).⁴⁴The ³¹P{¹H}NMR spectrum of 2 reveals a sharp doublet

at 86.85 ppm (¹J_RhP= 193.4 Hz). The X-ray crystal structure of

2 (Figure 2, Table 2) exhibits a distorted square-planar

geometry with N(1)−Rh(1)−P(1) and N(2)−Rh(1)−O(1)

bond angles of 163.9° and 176.1°, respectively. The bond angle

Rh(1)−O(1)−C(20) of 132.1° indicates that the acetone

ligand is coordinated through one of the oxygen electron lone

pairs. The ¹⁹F NMR of 2 reveals a broad signal at 151.5 ppm,

implying a weak interaction of the counteranion with the metal

center in the solution.⁴²When complex 2 was exposed to a

nitrogen atmosphere, the dinitrogen complex 1 was formed.

Complexes 3 and 4 were obtained by addition of the ligands

PNN and ⁱPrPNP (ⁱPrPNP = 2,6-(CH₂-PⁱPr₂)₂C₅H₃N),

respectively, to an acetone solution of [Rh(C₂H₄)₂(acetone)₂]-

[BF₄] under nitrogen. The ³¹P{¹H} NMR spectra of 3 and 4

exhibit sharp doublets at 81.65 ppm (¹J_RhP= 168.9 Hz) and

53.90 (¹J_RhP= 122.4 Hz), respectively. The ethylene ligands of

As mentioned above, complex 1 was characterized as a

mononuclear “end-on” N₂complex under nitrogen; however,

when a concentrated acetone solution of 1 was layered with

pentane, crystals of the N₂-bridged dimeric complex [(PNN)-

Rh]₂(N₂-μ)[2BF₄] (1a) were obtained (Figure 1, Table 1). The

1

3 and 4 give rise to a signal at 3.50 ppm in the H NMR

spectrum, as in the case of the analogous complex [(^tBuPNP)-

Rh(C₂H₄)][OTf],⁴⁵and about 2 ppm upﬁeld from the

chemical shift of free ethylene. The ethylene ligand of 3

appears as a broad singlet,⁴⁶whereas that of 4 exhibits a sharp

triplet of doublets signal (³J_PH= 3.3 Hz, ²J_RhH= 2.2 Hz). In the

¹³C{¹H} NMR spectrum, the ethylene ligands of 3 and 4

appear as a doublet at 59.72 ppm (¹J_CRh= 12.7 Hz) and as a

2

doublets of triplet at 52.34 (¹J_RhC= 10.7 Hz, J_PC= 1.7 Hz),

respectively, about 60−65 ppm upﬁeld from the free ethylene

signal. The X-ray structures of 3 and 4 reveal distorted square-

planar geometries around the metal center (Figure 2, Table

3)⁴⁷with ethylene bonds (C(20)−C(21)) slightly elongated as

compared with free ethylene.⁴⁸

Synthesis and Characterization of Dearomatized

(PNN) and (ⁱPrPNP) Rh(I) Complexes. Upon reaction of

complex 1 with an equivalent of base (^tBuOK) in THF, a

mixture of the neutral, dearomatized dinitrogen mononuclear

and dinuclear complexes 5 and 5a, respectively, was obtained

(Scheme 5). According to the ³¹P{¹H} NMR spectrum at 297

K, the mononuclear form is the dominant one, with a molar

ratio of 5:5a = 3:1, whereas at 215 K, the ratio is 5:5a = 2:1.

Complexes 3, 4, and the previously reported complex

[(ⁱPrPNP)Rh(COE)][BF₄]⁴⁹(8) also aﬀorded the dearomat-

ized complexes 6, 7, and 9, respectively, by deprotonation in

quantitative yields (Scheme 5). The ³¹P{¹H} NMR spectra of 5,

5a, and 6 give rise to sharp doublets at 84.76 (¹J_RhP= 173.7

Hz), 83.51 (¹J_RhP= 170.1 Hz), and 70.71 (²J_RhP= 177.4 Hz)

ppm, respectively, shifted about 10 ppm upﬁeld as compared

with the cationic analogues. In addition, the Rh−P coupling

constants are increased by about 8 Hz, which may imply a

stronger Rh−P σ bond in the dearomatized complexes. The ¹H

NMR spectra of 5 and 6 give rise to a signal at 3.4 ppm

corresponding to one proton, which give a ¹J C−H correlation

with a CH doublet signal at 62.7 ppm (¹J_PC= 57.1 Hz) and

67.39 ppm (¹J_PC= 55.2 Hz), respectively, indicating that

deprotonation at the benzylic phosphine “arm” took place.

Moreover, the benzylic amine “arm” gives rise to a two-proton

Figure 1. X-ray crystal structure of 1a at the 50% probability level.

Hydrogen atoms and counteranions are omitted for clarity.

Table 1. Selected Bond Lengths (Å) and Bond Angles (deg)

of 1a

Rh(1)−N(1)

Rh(1)−N(2)

Rh(1)−N(5)

Rh(1)−P(1)

Rh(2)−N(3)

Rh(2)−N(4)

Rh(2)−N(6)

Rh(2)−P(2)

N(5)−N(6)

2.168(2)

2.007(2)

1.913(2)

2.2342(7)

2.175(2)

2.008(2)

1.922(2)

2.2412(7)

1.124(3)

N(2)−Rh(1)−N(5)

N(1)−Rh(1)−P(1)

Rh(1)−N(5)−N(6)

N(4)−Rh(2)−N(6)

N(3)−Rh(2)−P(2)

Rh(2)−N(6)−N(5)

174.86(9)

164.98(6)

176.8(2)

176.75(9)

165.67(6)

175.5(2)

X-ray structure of 1a reveals a binuclear complex with a

distorted square-planar geometry around the metal centers. The

planes of the two pyridine rings are almost perpendicular, with

a dihedral angle of 79°. The N(5)−N(6) bond length is longer

1

singlet in the H NMR spectrum at 3.13 and 2.89 ppm for

complexes 5 and 6, respectively, about 1.5 ppm upﬁeld shifted

in comparison with the cationic complexes 1 and 3. These

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Figure 2. X-ray crystal structure of 2 (left) and 3 (right) at the 50% probability level. Hydrogen atoms and counteranions are omitted for clarity.

Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)

of 2

We assume that the ﬂuxionality of complex 9 is due to weak

coordination of the bulky COE ligand. Indeed, when an excess

of ethylene was introduced to a benzene solution of complex 9,

the ethylene complex 7 was obtained. On the other hand,

complex 7 did not react with a large excess of COE.

Rh(1)−N(1)

Rh(1)−N(2)

Rh(1)−P(1)

Rh(1)−O(1)

O(1)−C(20)

2.1906(14)

1.9660(13)

2.2167(4)

2.0839(12)

1.235(2)

N(1)−Rh(1)−P(1)

N(2)−Rh(1)−O(1)

N(1)−Rh(1)−N(2)

P(1)−Rh(1)−N(2)

N(1)−Rh(1)−O(1)

P(1)−Rh(1)−O(1)

Rh(1)−O(1)−C(20)

163.90(4)

176.13(5)

80.56(5)

84.54(4)

95.65(5)

99.15(4)

132.07(12)

The N−N IR band of complex 5 (2110 cm⁻¹) is slightly red

shifted from one of the two N−N stretching frequencies of 1

(2157 cm⁻¹). A similar shift was observed for the [(^tBuPNP*)-

RhN₂] complex.⁵¹The ethylene ligands in complexes 6 and 7

1

exhibit an upﬁeld shift of 0.64 and 0.30 ppm in the H NMR

spectra and 16.29 and 7.83 ppm in the ¹³C{¹H} NMR spectra,

respectively, as compared with their cationic analogous 3 and 4,

suggesting an enhancement of the π-back-donation due to

deprotonation.

Table 3. Selected Bond Lengths (Å) and Bond Angles (deg)

of 3 and 4

[(PNN)Rh(C₂H₄)]

[(ⁱPrPNP)Rh(C₂H₄)]

[BF₄] (3)

[BF₄] (4)

Deprotonation of complex 2 under argon was not selective

and resulted in a mixture of four unidentiﬁed complexes.

N−H Activation of Anilines by Dearomatized (PNN)

and (ⁱPrPNP) Rh(I) Complexes. Synthesis and Character-

ization of the Resulting Anilide Complexes. Interestingly,

Rh(1)−N(1)

Rh(1)−N(2)

Rh(1)−P(1)

2.2205(17)

2.0504(17)

2.2385(5)

2.101(2)

2.2872(7)

2.2831(7)

2.123(3)

2.131(3)

1.334(6)

Rh(1)−P(2)

Rh(1)−C(20)

Rh(1)−C(21)

C(20)−C(21)

N(1)−Rh(1)−P(1)

N(1)−Rh(1)−N(2)

P(1)−Rh(1)−N(2)

N(2)−Rh(1)−C(20)

N(2)−Rh(1)−C(21)

P(2)−Rh(1)−N(2)

P(1)−Rh(1)−P(2)

2.150(2)

2.139(2)

1.376(4)

163.72(5)

81.03(7)

83.13(5)

164.69(9)

157.41(9)

i

upon reaction of the dearomatized PNN and PrPNP Rh(I)

complexes 5⁵²−7 and 9 with an equivalent of aniline or

substituted aniline at 60 °C, N−H activation took place,

resulting in aromatization of the pincer ligand and formation of

stable Rh(I) anilide complexes (Scheme 6). The ³¹P{¹H}NMR

spectra of the PNN anilide complexes 10−13 feature a sharp

83.68(6)

161.74(16)

161.73(15)

84.30(6)

1

doublet at 87 ppm with a J_RhPcoupling constant of 206−220

Hz, which is larger than that observed for the Rh(I) cationic or

dearomatized complexes 1−3 and 5−6 (¹J_RhP= 160−180 Hz).

167.95(2)

i

The ³¹P{¹H}NMR spectra of the PrPNP anilide complexes 14

and 15 reveal only one doublet signal at about 45 ppm,

indicating equivalent phosphines. The J_RhPcoupling constants

1

signals give a J C−H correlation with a CH₂doublet signal at

63 ppm⁵⁰(d, J = 1.8 Hz) and 64.07 ppm (d, J = 1.5 Hz),

respectively, about the same chemical shift as in the starting

cationic complexes.

of complexes 14 and 15 are also larger than in the case of

complexes 4 and 7−9. The ¹H NMR spectra of the PNN-based

anilide complexes 10−13 exhibit two proton signals for the two

benzylic “arms”, and in complexes 14 and 15, the phosphine

benzylic “arms” give rise to a 4-proton virtual triplet signal. The

NH-C anilide carbon is shifted to lower ﬁeld by 10−15 ppm

relative to the corresponding free aniline. However, the Rh−

Complex 7 exhibits an AB splitting pattern, indicating two

nonequivalent phosphine atoms. The deprotonated “arm” of 7

gives rise to a doublet signal at 3.35 ppm (²J_PH= 4.0 Hz) in the

¹H NMR spectrum, corresponding to one proton, and a CH

doublet signal at 63.36 (¹J_PC= 50.8 Hz) in the ¹³C{¹H} DEPT

spectra. The ³¹P{¹H} NMR spectrum of complex 9 exhibits

very broad signals at ambient temperature, and a sharp AB

1

NHAr H signals are shifted to higher ﬁeld. For example, the

Rh−NH signal in complexes 10 and 14 is shifted by 0.88 and

1.88 ppm, respectively, as compared with that in free aniline.

Crystallographic characterization of 12 conﬁrmed the

formation of an aromatic anilide complex and revealed a

system at 223 K centered at 32.63 (dd, ¹J_RhP= 136.2 Hz, ²J_PP

=

1

2

312.8 Hz) and 45.55 (dd, J_RhP= 130.4 Hz, J_PP= 312.8 Hz).

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Scheme 5

While the anilide ligand in complexes 10 and 14 retains its

Scheme 6

symmetry and exhibits only three CH signals in the ¹H and ¹³

C

NMR spectra, the p-nitroanilide ligand in complexes 13 and 15

gives rise to four signals. The inequivalence of the two sides of

the ring in complexes 13 and 15 indicates that the p-

nitroanilide ligand is not rotating on the NMR time scale.

However, the retained symmetry in the case of the anilide

complexes 10 and 14 is probably not due to facile rotation, but

rather to fast dissociation−association of aniline. Spin

saturation transfer (SST) experiments⁵⁴preformed with

complexes 10, 13, 14, and 15 support this assumption.

Selective spin saturation of the Py−CH₂−P signal in complex

10 indicates a chemical exchange between the benzylic

phosphine “arm” and the N−H anilide proton (Figure 4).

Upon selective irradiation of the Py−CH₂−N signal, only

negligible exchange between the benzylic amine “arm” and the

N−H anilide proton was observed. Addition of an excess of

aniline to a benzene solution of 10 and selective irradiation of

the Py−CH₂−P signal revealed chemical exchange with the free

aniline. SST experiments with complex 14 also demonstrated

fast chemical exchange between the “benzylic arm” protons and

the anilide ligand, both in the presence or in the absence of free

aniline. In the presence of free aniline, exchange with the NH₂

group is also observed. In the case of the p-nitroanilide

complexes 13 and 15, no SST eﬀect was observed, indicating

that the N−H activation in this case is irreversible.

slightly distorted square-planar geometry (P(1)−Rh(1)−N(2)

= 165.05(11)^o) with an amide ligand positioned trans to an

aromatic pyridine moiety (Figure 3, Table 4). The anilide aryl

Complexes 10 and 14 can be obtained indirectly by

deprotonation of the cationic aniline complexes 16 and 17,

respectively. Addition of excess aniline to THF suspensions of

complexes 1 and 8 resulted in the cationic aniline complexes in

high yield after heating to 60 °C for 2 and 4 h respectively.

Complexes 16 and 17 were further reacted with ^tBuOK to give

the anilide complexes 10 and 14 in 83% and 89% yields,

respectively (Scheme 7). By contrast, addition of the less basic

p-nitroaniline to the cationic complexes 1 and 8 did not yield

Figure 3. X-ray crystal structure of 12 at the 50% probability level.

Hydrogen atoms (besides N(1)-H) are omitted for clarity.

Table 4. Selected Bond Lengths (Å) and Bond Angles (deg)

a

of 12

Rh(1)−N(1)

Rh(1)−N(2)

Rh(1)−N(11)

Rh(1)−P(1)

N(1)−C(1)

2.063(3)

2.243(4)

1.982(3)

2.1816(8)

1.353(4)

P(1)−Rh(1)−N(2)

N(1)−Rh(1)−N(11)

N(11)−Rh(1)−N(2)

P(1)−Rh(1)−N(11)

N(1)−Rh(1)−N(2)

N(1)−Rh(1)−P(1)

Rh(1)−N(1)−C(1)

165.05(11)

175.30(12)

82.69(14)

84.34(9)

i

the corresponding p-nitroaniline cationic PNN and PrPNP

complexes. Complexes 16 and 17 exhibit sharp doublet signals

in the ³¹P{¹H} NMR at 82.99 (¹J_RhP= 197.1 Hz) and 49.29

(¹J_RhP= 135.7 Hz), respectively. While the chemical shifts of

the cationic aniline complexes 16 and 17 are only slightly

shifted (by about 4 ppm) upﬁeld as compared to their anilide

92.60(14)

100.33(8)

129.1(3)

a

Another conformer with a diﬀerent position at N(2) was also

detected.

1

analogues 10 and 14, respectively, the J_RhPcoupling constants

are dramatically decreased, by 23 and 21 Hz, respectively, and

are in the range of cationic Rh(I) PNN and ⁱPrPNP complexes.

Complex 17 is a stable, isolable complex, in contrast to complex

16, which was stable in solution only in the presence of an

excess of aniline. This may be due to the steric hindrance

imposed by the P^tBu₂group. The NMR spectrum of complex

and the pyridine planes are almost perpendicular with a

dihedral angle of 83.9°. The Rh(1)−N(1) bond distance

(2.063(3) Å) in 12 is comparable to that of other anilide late

transition-metal complexes.^{27,28,29a,33,53}

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Figure 4. Spin saturation transfer experiments with complex 10. Top view: ¹H NMR spectrum of 10 in benzene. (1 and 2): Spin saturation of signals

b and a,⁵⁵respectively, in the absence of free aniline. (3): Spin saturation of signal b in the presence of free aniline. (The multiplets at 2.6 and 3.0

ppm are assigned to N(CH₂CH₃).)

Scheme 7

Figure 5. X-ray crystal structure of 16 (left) and 17 (right) at the 50% probability level. Hydrogen atoms (besides N(3)-H in 16 and N(2)-H in 17)

and counteranions are omitted for clarity.

16 exhibits separate signals of the bound and the free added

aniline. The NH−C carbons of the aniline ligand are slightly

shifted upﬁeld in complexes 16 and 17 (by 4.7 and 1.1 ppm,

respectively) relative to free aniline, and by about 16 ppm

relative to the anilide ligand in complexes 10 and 14. The Rh−

NH signals of complexes 16 and 17 are shifted upﬁeld by 0.57

and 0.91 ppm, respectively, as compared with the amino group

of free aniline, in an opposite trend to the anilide complexes 10

and 14. Single-crystal X-ray structures of 16 and 17 (Figure 5,

Tables 5 and 6 respectively) reveal a slightly distorted square-

planar geometry. The aniline and the pyridine planes are almost

perpendicular with a dihedral angle of about 89° and 80° for 16

and 17, respectively, as in complex 12. The Rh−N(aniline)

bond lengths in 16 and 17 are longer by about 0.085 and 0.07

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equilibrium was observed. DFT studies show that the formation

of electron-poor anilides is thermodynamically favorable by

10−15 kcal/mol. Brookhart and co-workers also observed a

similar trend of reactivity with N−H oxidative addition to a 14-

electron Ir(I) pincer complex.²⁸

Table 5. Selected Bond Lengths (Å) and Bond Angles (deg)

of 16

a

Rh(1)−P(1)

Rh(1)−N(1)

Rh(1)−N(2)

Rh(1)−N(3)

N(3)−C(20)

2.2125(9)

1.998(3)

2.215(3)

2.143(3)

1.455(5)

P(1)−Rh(1)−N(2)

N(1)−Rh(1)−N(3)

N(1)−Rh(1)−P(1)

N(1)−Rh(1)−N(2)

N(3)−Rh(1)−P(1)

N(3)−Rh(1)−N(2)

Rh(1)−N(3)−C(20)

163.32(9)

176.91(12)

83.39(9)

We have also examined the reactivity of the PNP complex

[(^tBuPNP*)RhN₂]⁵¹toward N−H activation and have found

that the reactions were rather slow and nonselective. We

believe that this is a result of steric hindrance of the bulkier

PNP complex as compared with PNN complexes. In line with

steric hindrance retardation of N−H activation, the reaction of

complex 5 with the bulky 2,4,6-tribromoaniiline was non-

selective and gave a mixture of four unidentiﬁed products.

The N−H activation rate was found to be aﬀected by the

aniline substituents, the pincer ligand, and the ancillary ligands.

Follow-up of the progress of reactions of complexes 5−7 and 9

with an equivalent of p-nitroaniline using the same concen-

trations and temperatures⁵⁶reveals that the rate of N−H

activation follows the trend 7 > 9 > 5 > 6. Thus, reaction of p-

nitroaniline with complexes 5, 7, and 9 at 60 °C reached

completion after 5 h, less than 5 and 25 min, respectively,

whereas complex 6 reached 66% conversion after 24 h.

Signiﬁcantly, the reaction rate of complex 9 was accelerated

in the presence of an excess (60 equiv) of COE, and the

reaction reached completion after 5 min at ambient temper-

ature instead of 5 h at the same conditions in the absence of

added COE.

Follow-up of the progress of reactions of complexes 5−7 and

9 with an equivalent of aniline using the same concentrations

and temperatures reveals that the rate of N−H activation

follows the order 9 > 5 > 6 > 7.⁵⁷Thus, the reaction of

complexes 5−7 and 9 with aniline under the same conditions

and temperatures led to full conversion of complexes 9 and 5

after 6 and 7 h, respectively, whereas only 60% and 10%

conversions were observed for complexes 6 and 7, respectively,

after 20 h. In addition, performing the reaction of complex 7

with the same concentration of aniline and temperature under a

constant ﬂow of argon (which could remove free ethylene) did

81.00(12)

98.69(9)

97.15(12)

117.8(2)

a

The X-ray structure of 16 contains two molecules of the complex in

the asymmetric unit.

Table 6. Selected Bond Lengths (Å) and Bond Angles (deg)

of 17

Rh(1)−P(1)

Rh(1)−P(2)

Rh(1)−N(1)

Rh(1)−N(2)

N(2)−C(20)

2.2691(5)

2.2943(5)

2.0618(15)

2.1299(16)

1.438(3)

P(1)−Rh(1)−P(2)

N(1)−Rh(1)−N(2)

N(1)−Rh(1)−P(1)

N(1)−Rh(1)−P(2)

N(2)−Rh(1)−P(1)

N(2)−Rh(1)−P(2)

Rh(1)−N(2)−C(20)

165.717(18)

176.99(6)

83.99(4)

83.14(4)

93.19(5)

99.54(5)

118.93(12)

Å, respectively, as compared with the corresponding bond of

the anilide complex 12.

Trends in Reactivity. The N−H activation process was faster

with electron-poor anilines, such as p-nitroaniline, than with

more basic anilines, such as aniline itself. For example, the

reactions of the PNN complex 5 with an equivalent of aniline

and p-nitroaniline at 60 °C reached completion after 9 and 5 h,

respectively. Moreover, the reactions of complexes 5−7 and 9

with p-tert-butylaniline were sluggish and not selective. A

similar trend was observed in the N−H activation of anilines by

the complex [(PNN*)RuH(CO)], both experimentally and by

DFT calculations.³⁶The PNN* Ru complex gave stable anilide

complexes only with the electron-poor anilines p-nitroaniline

and o-chloro-p-nitroaniline, whereas with the halide-substituted

anilines o-bromoaniline and m-chloro-p-chloroaniline, an

Scheme 8

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Scheme 9

Scheme 10

not inﬂuence the reaction rate. Performing the reactions of

complexes 5−7 and 9 with 4 equiv of aniline did not inﬂuence

the reaction rates.

the SST experiments exhibit only signals of the starting

complexes. Upon selective saturation of the deprotonated

benzylic arms of complexes 5−7 and 9, an SST eﬀect was

observed for the free aniline signal, indicating fast chemical

exchange between the free aniline and the benzylic arm.

N−H Bond Formation; Elimination of Anilines. Fast

elimination of anilines from complexes 10−15 was observed

upon reaction with CO at ambient temperature. Along with the

Follow-up of the reaction of complexes 5 and 5a by ³¹P{¹H}

NMR with anilines reveals that the mononuclear 5 reacts faster

than the binuclear 5a and it is the ﬁrst to be fully consumed.

The reaction rates were similar in toluene, benzene, or THF

under the same conditions.

1

The reaction of complexes 5−7 and 9 with aniline and p-

free anilines, which were detected both by H NMR and by

1

nitroaniline were followed by ³¹P{¹H} and H NMR spectros-

GC-MS, the deprotonated carbonyl complexes 18 and 19 were

isolated (Scheme 8). Complexes 18 and 19 can be obtained

also by addition of CO to the dearomatized complexes 5−7 and

9 or by deprotonation of the cationic carbonyl complexes

[(PNN)Rh(CO)][BF₄] (20) and [(ⁱPrPNP)Rh(CO)][BF₄]

(21) (Scheme 9). The ³¹P{¹H} NMR spectrum of the reaction

copy also at low temperatures (in the range of 283−200 K);

however, no intermediates were detected.

SST experiments were preformed with complexes 5−7 and 9

at 283 K in the presence of an excess of aniline. ³¹P{¹H} NMR

spectra of the reaction mixtures preformed prior to and after

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mixture of complex 15 and CO at 195 K exhibits signals of

complexes 15 and 19 exclusively. An SST experiment

performed with the deprotonated carbonyl complex 18 in the

presence of an excess of aniline exhibits proton exchange

between the deprotonated benzylic arm and the free aniline,

although no aniline addition product was observed.

When complexes 10, 13, 14, and 15 were exposed to a large

excess of triethylphosphine at ambient temperature, no reaction

took place.⁵⁸However, upon heating the reaction mixtures of

complexes 14 and 15 at 60 °C for 12 h, full conversion to form

the dearomatized complex [(ⁱPrPNP*)Rh(PEt₃)] (22) along

with the corresponding free anilines were observed (Scheme 8).

Complex 22 can be synthesized independently by addition of

the free phosphine to complexes 4 or 8, followed by

deprotonation or by addition of triethylphosphine to the

dearomatized complex 7 or 9 (Scheme 9). Upon heating

complexes 10 and 13 with an excess of triethylphosphine at 60

°C for 12 h, 90% of complex 10 and 33% of complex 13 reacted

to give a mixture of unidentiﬁed complexes.⁵⁹

case of intermediates I−III, also intermediates V−VII were not

detected.

The existence of an associative pathway A is supported by the

following experimental evidence: (a) The N−H activation rate

of p-nitroaniline was found to be faster with the ethylene

complex 7, in which ethylene is more tightly bound and less

bulky than the COE complex 9.⁶²(b) N−H activation by

complex 9 was signiﬁcantly accelerated in the presence of

COE.⁶³(c) N−H activation of aniline by complex 7 was not

accelerated when preformed in an open system. (d) The

existence of fast exchange between the benzylic arm protons

and the NH−anilide proton, as well as the proton exchange

between free aniline and the benzylic arm prior to the N−H

activation, as observed in the SST experiments also supports

pathway A. (e) The fact that the N−H activation and

elimination reactions are eﬀected by steric factors is also in

accordance with pathway A.

Deprotonation of the Anilide Complexes to Give Anionic

Rh(I) Complexes. Recently, our group has reported several

anionic dearomatized pincer complexes; the complex

[(^tBuPNP*)RhCl][K], which was obtained by deprotonation

of the complex [(^tBuPNP)RhCl] under argon,¹⁵the complex

[(PNN*)Pt^II(Cl)(R)][Li] (R = CH₃, C₆H₅) with a decoordi-

nated hemilabile amine arm,^64aand the anionic doubly

deprotonated complexes [(^tBuPNP**)M^II(X)]Y (^tBuPNP**

= doubly deprotonated PNP; M = Pd, Pt; X = Cl, Me; Y = Li,

K).^64bThese complexes constitute uncommon examples of

anionic transition-metal complexes lacking strong π-acceptor

ligands (capable of lowering the electron density at the metal

center), such as CO, oleﬁns, or electron-withdrawing

phosphines.⁶⁴

The addition of 1 equiv of p-nitroaniline to the anilide

complexes 10 and 14 aﬀords the p-nitroanilide complexes 13

and 15, respectively, and free aniline, which was detected by

¹H{³¹P}NMR spectroscopy and GC-MS (Scheme 8).⁶⁰

Possible Mechanisms of N−H Activation and Elimination.

Possible mechanisms for the N−H bond activation process and

its microscopic reverse N−H bond formation by the PNN−

i

and PrPNP−Rh(I) dearomatized complexes are described in

Scheme 10. Pathway A represents an associative mechanism, in

which preliminary coordination of the aniline derivative leads to

proton transfer from the aniline to the deprotonated benzylic

arm. The aniline can coordinate to the metal center at the

apical position (complex I) or add in a concerted fashion

(complex II), involving direct protonation of the benzylic arm

by the aniline.⁶¹Mechanism A is similar to the postulated

mechanism for N−H activation by [(^tBuPNP*)Ru(CO)H].³⁶

The activation of ND₃by [(^tBuPNP*)Ru(CO)H] was highly

stereospeciﬁc and occurred only on one face of the ligand,

which supports an intramolecular mechanism with one

coordinated molecule of ND₃. Since, in the case of complexes

5−7 and 9, two empty apical positions are available for

precoordination, such selectivity is not expected. It is worth

mentioning that, upon follow-up of the reactions of complexes

5−7 and 9 with anilines at various temperatures (190−313 K)

by ³¹P{¹H} NMR spectroscopy, the potential intermediates I−

III were not detected.

Here, we report on the anionic complexes [(PNN*)Rh(p-

NO₂-NHC₆H₄)][K] (24) and [(ⁱPrPNP*)Rh(p-NO₂-

NHC₆H₄)][K] (25), which were obtained by deprotonation

of complexes 13 and 15, respectively, by various bases (^tBuOK,

KN(SiMe₃)₃, and KH) (Scheme 11). The electron-withdrawing

Scheme 11

Pathway B is a dissociative mechanism, in which a

tricoordinate dearomatized intermediate IV is formed and

binds aniline to give the square-planar V. Intermediate V can

activate the N−H bond either by oxidative addition (complex

VI) or by a concerted mechanism (complex VII), followed by

proton migration to the side arm with concomitant

aromatization to form the aromatic anilide complex. Such a

mechanism was observed for C−H activation by the complexes

[(^tBuPNP*)RhCl][K]¹⁵and [(^tBuPNP*)Ir(COE)].¹³In the

case of the latter, DFT calculations suggest that one or two

molecules of water may serve as a “proton shuttle” for the

proton transfer from the metal center to the benzylic arm. The

transition state of the proton transfer was found to be lower by

9.4 and 15.2 kcal mol⁻¹for one or two molecules of water

involved, respectively, than the direct proton transfer.¹⁴In the

case of pathway B, water may play a role in a proton transfer

from the relatively remote aniline to the benzylic arm. As in the

p-nitroanilide plays an important role in the stabilization of the

anionic complexes, since the deprotonation of complexes 10

and 14 did not yield anionic complexes. Complexes 24 and 25

are stable in solution; however, under vacuum, partial

decomposition took place, probably due to traces of water.

Complexes 24 and 25 were fully characterized by NMR. The

³¹P{¹H} NMR spectrum of 24 exhibits a sharp doublet at 80.09

ppm (¹J_RhP= 206.9 Hz). The dearomatized phosphine arm of

complex 24 gives rise to a one-proton signal at 3.10 ppm and a

1

CH signal at 63.54 ppm in the H and ¹³C{¹H} NMR spectra,

respectively. The amine benzylic arm of complex 24 gives rise

to a two-proton signal at 3.46 ppm and a CH₂signal at 64.89

ppm. Complex 25 exhibits a characteristic AB pattern of

1

2

doublets at 46.07 (dd, J_RhP= 150.5 Hz, J_PP= 314.2 Hz) and

1

2

39.65 (dd, J_RhP= 148.7 Hz, J_PP= 314.2 Hz), indicating

nonequivalent phosphorus atoms. The deprotonated benzylic

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NMR chemical shifts are reported in parts per million (ppm)

downﬁeld from tetramethylsilane. In ¹H NMR, the chemical shifts

were referenced to the residual hydrogen signal of the deuterated

solvents. In ¹³C{¹H} NMR measurements, the signals of deuterated

solvents were used as a reference. ³¹P NMR chemical shifts are

reported in parts per million downﬁeld from H₃PO₄and referenced to

an external 85% solution of phosphoric acid in D₂O. Abbreviations

used in the description of NMR data are as follows: br, broad; s,

singlet; d, doublet; t, triplet; q, quartet; m, multiplet; v, virtual.

Temperature calibration of the spectrometer was performed using

CH₃OH/CD₃OD. IR spectra were measured with a Nicolet-6700 FT-

IR spectrometer. Elemental analyses were performed by the Unit of

Chemical Research Support, Weizmann Institute of Science.

[(PNN)RhN₂][BF₄] (1). [Rh(COE)₂Cl]₂(118.0 mg, 0.165 mmol)

and AgBF₄(64.2 mg, 0.330 mmol) were suspended in THF (5 mL)

under nitrogen, and the suspension was stirred in the dark for 1 h,

resulting in precipitation of a light gray solid (AgCl), which was

ﬁltered oﬀ through a 0.2 μm Teﬂon ﬁlter. A THF solution (3 mL) of

the PNN ligand (106.4 mg, 0.330 mmol) was immediately added to

the ﬁltrate. The reaction was stirred for 24 h, during which a yellow

precipitate was formed. The precipitate was collected by vacuum

ﬁltration, washed with THF (7 mL), and dried under vacuum. Yield:

102.6 mg (57%). Crystals suitable for X-ray analysis of 1a were

obtained by layering a concentrated acetone solution of 1a with

arm gives rise to a one-proton signal at 3.24 ppm and a CH

signal at 59.4 ppm, while the second benzylic arm gives rise to a

two-proton signal at 2.90 ppm and a CH₂signal at 36.15 ppm.

SUMMARY

■

It is evident that metal−ligand cooperation by pincer

complexes, based on aromatization−dearomatization of the

pincer ligand, can play an important role in bond activation and

in the development of new homogeneously catalyzed reactions.

Several X−H bonds (X = H, C, O, N) have been activated in

this fashion. This study demonstrates a rare case of N−H

activation by metal−ligand cooperation, as well as a rare

example of N−H activation by Rh. The reverse reaction, N−H

bond formation by metal−ligand cooperation, is also

demonstrated. Thus, the new dearomatized complexes

[(PNN*)RhL′] (5, L′ = N₂; 6, L′ = C₂H₄) and [(ⁱPrPNP*)-

RhL′] (7, L′ = C₂H₄; 9, L′ = COE) react with anilines to give

aromatized stable anilide complexes [(PNL)Rh(NHAr)] (PNL

i

= PNN, PrPNP; Ar = C₆H₅, o-Br-C₆H₄, m-Cl-p-Cl-C₆H₃, p-

NO₂-C₆H₄). N−H formation to give free anilines and

dearomatized Rh(I) complexes takes place upon reaction of

the anilide complexes with CO or PEt₃. Spin saturation transfer

experiments with the anilide complexes indicate proton

exchange between the NH−anilide and the benzylic arm of

the pincer ligand prior to and subsequent to the N−H

activation; however, for p-nitroanilide complexes, such a

chemical exchange was not observed. The N−H activation

process is aﬀected by electronic and steric factors. Anilines

possessing electron-withdrawing groups accelerate the N−H

activation and yield more stable anilide complexes, whereas

bulky anilines and bulky pincer ligands retard the activation.

Our studies suggest that the N−H activation and elimination

occurs via an associative mechanism. In addition, deprotonation

of complexes [(PNL)Rh(p-NO₂-NH₂C₆H₄)] (13, P = P^tBu₂, L

= NEt₂; 15, P = L = PⁱPr₂) yields the dearomatized anionic

complexes [(PNL*)Rh(p-NO₂-NH₂C₆H₄)].

pentane.

1

³¹P{¹H} NMR (121 MHz, acetone-d₆, 293 K): 93.31 (d, J_RhP

=

1

161.6 Hz). H NMR (500 MHz, acetone-d₆, 293 K): 1.47 (d, 18H,

³J_HP= 14.0 Hz, (CH₃)₃CP), 1.52−1.79 (br m, 6H, CH₃CH₂N), 3.14−

3.26 (m, 2H, CH₃CH₂N), 3.27−3.37 (m, 2H, CH₃CH₂N), 3.77 (d,

2

2H, J_HP= 9.5 Hz, CH₂P), 4.55 (br m, 2H, Py-CH₂N), 7.45 (d, 1H,

³J_HH= 7.8 Hz, Py-CH), 7.56 (d, 1H, J_HH= 7.8 Hz, Py-CH), 7.95 (t,

3

1H, ³J_HH= 7.8 Hz, Py-CH). ¹H NMR (500 MHz, acetone-d₆, 253 K):

1.45 (d, 9H, ³J_HP= 14.0 Hz, (CH₃)₃CP), 1.46 (d, 9H, ³J_HP= 14.0 Hz,

(CH₃)₃CP), 1.52 (t, 3H, ³J_HH= 7.0 Hz, CH₃CH₂N), 1.72 (t, 3H, ³J_HH

= 7.0 Hz, CH₃CH₂N), 3.11−3.24 (m, 2H, CH₃CH₂N), 3.24−3.37 (m,

2

2H, CH₃CH₂N), 3.80 (d, 2H, J_HP= 9.4 Hz, CH₂P), AB system

centered at 4.49 (d, J_HH= 17.0 Hz, Py-CH₂N) and 4.75 (d, J_HH

2

=

17.0 Hz, Py-CH₂N), 7.45 (d, 1H, ³J_HH₃= 7.8 Hz, Py-CH), 7.56 (d, 1H,

³J_HH= 7.8 Hz, Py-CH), 7.95 (t, 1H, J_HH= 7.8 Hz, Py-CH). ¹³C{¹H}

NMR (75 MHz, acetone-d₆, 293 K): 12.60 (s, CH₃CH₂N), 29.46 (d,

²J_CP= 4.5 Hz, (CH₃)₃CP), 35.02 (d, ¹J_CP= 24.1 Hz, CH₂P), 35.76 (br

d, ¹J_CP= 16 Hz, (CH₃)₃CP), 56.3 (br m, CH₃CH₂₃N), 63.49 (d, J = 2.0

Hz, Py-CH₂N), 119.77 (s, Py-CH), 120.20 (d, J_CP= 10.6 Hz, Py-

CH), 139.34 (s, Py-CH), 164.12−164.28 (m, Py-C2 and Py-C5).

IR(ν_NN) = 2069, 2157 cm⁻¹. Anal. for C₃₈H₇₀B₂F₈N₆P₂Rh₂: Calcd C,

43.37; H, 6.70. Found: C, 43.37; H, 6.75.

Further experimental and theoretical investigations on

metal−ligand cooperation via aromatization−dearomatization,

and its implications for catalytic design, are in progress. While

the reported cases so far involve bonds to hydrogen, and mostly

late transition-metal complexes, we believe that the scope of

this approach can be even wider.

X-ray structural analysis of 1a. Crystal data: C₃₈H₇₀N₆P₂Rh₂

+

C₃H₆O + 2BF₄, orange chunk, 0.20 × 0.10 × 0.10 mm³, monoclinic,

P2₁/c, a = 18.5320(4) Å, b = 15.3840(4) Å, c = 18.8970(4) Å, β =

109.264 (1)°, from 10 687 reﬂections, T = 120(2) K, V = 5085.8(2)

Å³, Z = 4, F_w= 1110.46, D_c= 1.450 Mg/m⁻³, μ = 0.778 mm⁻¹.

Data collection and processing: Nonius KappaCCD diﬀractometer,

Mo Kα (λ = 0.71073 Å), graphite monochromator, −24 ≤ h ≤ 21,

−19 ≤ k ≤ 19, −22 ≤ l ≤ 24, 2θ_max= 55.06, frame scan width = 1.0°,

scan speed = 1.0° per 150 s, typical peak mosaicity 1.421°, 56 613

reﬂections collected, 11 652 independent reﬂections (R_int= 0.068).

The data were processed with HKL2000.

EXPERIMENTAL SECTION

■

General Procedures. All experiments with metal complexes and

phosphine ligands were carried out under an atmosphere of puriﬁed

nitrogen in a Vacuum Atmospheres glovebox equipped with a MO 40-

2 inert gas puriﬁer or using standard Schlenk techniques. All solvents

were reagent grade or better. All nondeuterated solvents, except

methylene chloride and acetone, were reﬂuxed over sodium/

benzophenone ketyl and distilled under an argon atmosphere.

Methylene chloride and acetone were used as received and dried

over 4 Å molecular sieves and calcium sulfate, respectively. Deuterated

solvents were used as received. All the solvents were degassed with

argon and kept in the glovebox over 4 Å molecular sieves (acetone was

kept over calcium sulfate). Other commercially available reagents were

used as received.

Solution and reﬁnement: Structure solved by direct methods with

SIR-97. Full-matrix least-squares reﬁnement based on F²with

SHELXL-97. 565 parameters with no restraints, ﬁnal R₁= 0.0392

(based on F²) for data with I > 2σ(I), R₁= 0.0740 on 11 652

reﬂections, goodness-of-ﬁt on F²= 1.081, largest electron density peak

= 1.090 e Å⁻³, and largest hole = −0.719 e Å⁻³.

[(PNN)Rh(acetone)][BF₄] (2). [Rh(COE)₂Cl]₂(72.4 mg, 0.101

mmol) and AgBF₄(39.3 mg, 0.202 mmol) were suspended in acetone

(5 mL) under argon, and the suspension was stirred in the dark for 1

h, resulting in the precipitation of a light gray solid (AgCl). The

precipitate was ﬁltered oﬀ through a 0.2 μm Teﬂon ﬁlter. An acetone

solution (3 mL) of the PNN ligand (65.2 mg, 0.202 mmol) was

The ⁱPrPNP⁶⁵and PNN^2aligands, [Rh(COE)₂Cl]₂,⁶⁶[Rh-

(C₂H₄)₂(Cl-μ)]₂,⁶⁷and [(ⁱPrPNP)Rh(COE)][BF₄]⁴⁹(8) were

prepared according to literature procedures. The previously reported

complex [(^tBuPNP)Rh(N₂)][BF₄]^15,51was prepared by the procedure

described below for the synthesis of complex 1. ¹H, ¹³C, and ³¹P NMR

spectra were recorded using Bruker DPX-250, Bruker Avance-400

NMR, and Bruker Avance 500 NMR spectrometers. All spectra were

recorded at 23 °C unless otherwise noted. H NMR and ¹³C{¹H}

1

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immediately added to the ﬁltrate, and the reaction mixture was stirred

for 10 min. The solvent was removed under vacuum to give an orange

oil, which was washed with pentane (15 mL) and dried under vacuum.

Yield: 84% (96.8 mg). Crystals suitable for X-ray analysis were

obtained by layering a concentrated acetone solution of 2 with

pentane.

74.2262(10)°, γ = 85.5839(6)° from 10° of data, T = 120(2) K, V =

1199.92(3) Å³, Z = 2, F_w= 540.23, D_c= 1.495 Mg/m⁻³, μ = 0.820

mm⁻¹.

Data collection and processing: Nonius KappaCCD diﬀractometer,

Mo Kα (λ = 0.71073 Å), graphite monochromator, 0≤ h ≤ 10, −15 ≤

k ≤ 15, −16 ≤ l ≤ 18, 2θ_max= 54.96, frame scan width = 1.0°, scan

speed = 1.0° per 30 s, typical peak mosaicity 0.69°, 23 846 reﬂections

collected, 5500 independent reﬂections (R_int= 0.027). The data were

processed with HKL-scalepack software.

³¹P{¹H} NMR (121 MHz, acetone-d₆): 86.85 (d, ¹J_RhP= 193.4 Hz).

3

¹H NMR (500 MHz, acetone-d₆): 1.36 (d, 18H, J_HP= 13.1 Hz,

3

(CH₃)₃CP), 1.46 (t, 6H, J_HH= 7.2 Hz, CH₃CH₂N), 2.86−2.77 (m,

2

Solution and reﬁnement: Structure solved by direct methods with

SHELXS. Full-matrix least-squares reﬁnement based on F²with

SHELXL-97. 295 parameters with no restraints, ﬁnal R₁= 0.0305

(based on F²) for data with I > 2σ(I), R₁= 0.0334 on 5500 reﬂections,

goodness-of-ﬁt on F²= 1.099, largest electron density peak = 1.390 e

Å⁻³, and largest hole = −0.868 e Å⁻³.

2H, CH₃CH₂N), 2.91−3.00 (m, 2H, CH₃CH₂N), 3.19 (d, 2H, J_HP

=

8.9 Hz, CH₂P), 4.20 (br s, 2H, Py-CH₂N), 7.17 (d, 1H, ³J_HH= 7.9 Hz,

3

Py-CH), 7.26 (d, 1H, J_HH= 7.9 Hz, Py-CH), 7.70 (t, 1H, J_HH= 7.9

Hz, Py-CH). ¹³C{¹H} NMR (101 MHz, acetone-d₆): 10.81 (s,

CH₃CH₂N), 29.24 (d, J_CP= 5.6 Hz, (CH₃)₃CP), 35.02 (dd, J_CP

16.1 Hz, ²J_CRh= 1.5 Hz, (CH₃)₃CP), 35.56 (dd, ¹J_CP= 22.1 Hz, ²J_CRh

2

1

=

[(ⁱPrPNP)Rh(C₂H₄)][BF₄] (4). [Rh(C₂H₄)₂Cl]₂(42.0 mg, 0.108

mmol) and AgBF₄(42.0 mg, 0.216 mmol) were suspended in acetone

(5 mL) under nitrogen, and the suspension was stirred in the dark for

1 h, resulting in the precipitation of a light gray solid (AgCl). The

precipitate was ﬁltered oﬀ through a 0.2 μm Teﬂon ﬁlter. An acetone

2.1 Hz, CH₂P), 52.47 (d, J = 1.6 Hz, CH₃CH₂N), 64.42 (d, J = 2.2 Hz,

Py-CH₂N), 119.80 (s, Py-CH), 121.71 (dd, ³J_CP= 11.0 Hz, ³J_CRh= 1.5

Hz, Py-CH), 133.72 (s, Py-CH), 161.60 (br d, J = 1.6 Hz, Py-C),

2

163.67 (dd, J_CP= 22.1 Hz, J_CRh= 2.1 Hz, Py-C), 223.28 (s,

(CH₃)₂CO). Acceptable elemental analysis results for 2 could not be

obtained. The NMR spectrum of 2 appears in the Supporting

Information.

i

solution (3 mL) of PrPNP (73.2 mg, 0.216 mmol) was immediately

added to the ﬁltrate, and the reaction mixture was stirred for 10 min to

give a clear brown solution. The solvent was removed under vacuum,

and the brown solid was washed with pentane (15 mL) and dried

under vacuum. Yield: 96% (115.4 mg). Crystals suitable for X-ray

analysis were obtained by layering a concentrated acetone solution of 4

with pentane.

X-ray structural analysis of 2. Crystal data: C₂₂H₄₁N₂OPRh + BF₄,

orange plates, 0.20 × 0.10 × 0.10 mm³, monoclinic, P2₁/c, a =

11.1560(1) Å, b = 14.3340(2) Å, c = 16.5290(3) Å, β = 90.1630(6)°,

from 11 771 reﬂections, T = 120(2) K, V = 2643.14(6) Å³, Z = 4, F_w=

570.26, D_c= 1.433 Mg/m⁻³, μ = 0.751 mm⁻¹.

Data collection and processing: Nonius KappaCCD diﬀractometer,

Mo Kα (λ = 0.71073 Å), graphite monochromator, −16 ≤ h ≤ 16,

−16 ≤ k ≤ 21, −24 ≤ l ≤ 23, 2θ_max= 64.06, frame scan width = 1.0°,

scan speed = 1.0° per 20 s, typical peak mosaicity 0.467°, 40 760

reﬂections collected, 16 760 independent reﬂections (R_int= 0.053).

The data were processed with HKL2000 software.

Solution and reﬁnement: Structure solved by direct methods with

SIR-97. Full-matrix least-squares reﬁnement based on F²with

SHELXL-97. 299 parameters with no restraints, ﬁnal R₁= 0.0322

(based on F²) for data with I > 2σ(I), R₁= 0.0432 on 8992 reﬂections,

goodness-of-ﬁt on F²= 1.030, largest electron density peak = 1.215 e

Å⁻³, and largest hole = −0.645 e Å⁻³.

[(PNN)Rh(C₂H₄)][BF₄] (3). [Rh(C₂H₄)₂Cl]₂(60.0 mg, 0.154

mmol) and AgBF₄(60.0 mg, 0.308 mmol) were suspended in acetone

(5 mL) under nitrogen, and the reaction was stirred in the dark for 1 h,

resulting in the precipitation of a light gray solid (AgCl). The

precipitate was ﬁltered oﬀ through a 0.2 μm Teﬂon ﬁlter. An acetone

solution (3 mL) of the PNN ligand (99.3 mg, 0.308 mmol) was

immediately added to the ﬁltrate, and the reaction mixture was stirred

for 10 min. The solvent was removed under vacuum, and the yellow

solid was washed with pentane (15 mL) and dried under vacuum.

Yield: 95% (158.1 mg)

³¹P{¹H} NMR (121 MHz, acetone-d₆): 53.90 (d, ¹J_RhP= 122.4 Hz).

¹H NMR (500 MHz, acetone-d₆): 1.17 (dd, 12 H, ³J_PH= 7.0 Hz, ³J_HH

3

= 7.3 Hz, (CH₃)₂CH), 1.26 (dd, 12H, J_PH= 8.7 Hz, J_HH= 7.3 Hz,

3

(CH₃)₂CH), 2.40−2.51 (m, 4H, (CH₃)₂CH), 3.51 (dt, 4H, J_PH= 3.3

Hz, ²J_RhH= 2.2 Hz (coupling constant were detriment also by ¹H{³¹P}

NMR), CH₂CH₂), 3.80 (vt, 4H, J_PH₃= 4.1 Hz, CH₂P), 7.69 (d, 1H,

³J_HH= 7.7 Hz, Py-CH), 8.00 (t, 2H, J_HH= 7.7 Hz, Py-CH). ¹³C{¹H}

NMR (126 MHz, acetone-d₆): 19.02 (s, (CH₃)₂CH), 19.80 (vt, J_PC

=

2

2.3 Hz, (CH₃)₂CH), 25.82 (d vt, J_RhC= 1.5 Hz, J_PC= 11.7 Hz,

1

(CH₃)₂CH), 36.98 (vt, J_PC= 9.8 Hz, CH₂P), 52.34 (dt, J_RhC= 10.7

Hz, ²J_PC= 1.7 Hz, CH₂CH₂), 122.36 (d vt, ³J_RhC= 0.7 Hz, J_PC= 5.4

Hz, Py-CH), 141.62 (s, Py-CH), 166.51 (d vt, ²J_RhC= 1.6 Hz, J_PC= 5.3

Hz, Py-C). Anal. for C₂₁H₃₉BF₄NP₂Rh: Calcd C, 45.27; H, 7.05.

Found: C, 45.92; H, 7.23.

X-ray structural analysis of 4. Crystal data: C₂₁H₃₉NP₂Rh + BF₄,

orange needles, 0.50 × 0.05 × 0.05 mm³, monoclinic, P2₁/n, a =

11.6467(5) Å, b = 16.1779(8) Å, c = 13.9470(8) Å, β = 104.855(3)°,

from 21 485 reﬂections, T = 120(2) K, V = 2540.1(2) Å³, Z = 4, F_w=

557.19, D_c= 1.457 Mg/m⁻³, μ = 0.836 mm⁻¹.

Data collection and processing: Bruker KappaApexII CCD

diﬀractometer, Mo Kα (λ = 0.71073 Å), graphite monochromator,

−16 ≤ h ≤ 17, −24 ≤ k ≤ 15, −18 ≤ l ≤ 20, 2θ_max= 66.44, frame scan

width = 0.5°, scan speed = 1.0° per 40 s, typical peak mosaicity 0.71°,

Crystals suitable for X-ray analysis were obtained by layering a

concentrated acetone solution of 3 with pentane.

21 113 reﬂections collected, 9862 independent reﬂections (R_int

=

³¹P{¹H} NMR (121 MHz, acetone-d₆): 81.65 (d, ¹J_RhP= 168.9 Hz).

0.0504). The data were processed with APEX2.

3

¹H NMR (500 MHz, acetone-d₆): 1.35 (d, 18H, J_HP= 13.3 Hz,

Solution and reﬁnement: Structure solved by direct methods with

Bruker AutoStructure. Full-matrix least-squares reﬁnement based on F²

with SHELXL-97. 283 parameters with no restraints, ﬁnal R₁= 0.0468

(based on F²) for data with I > 2σ(I), R₁= 0.0843 on 9570 reﬂections,

goodness-of-ﬁt on F²= 0.958, largest electron density peak = 1.457 e

Å⁻³, and largest hole = −1.211 e Å⁻³.

[(PNN*)RhN₂] (5) and [((PNN*)Rh)₂)(N₂-μ)] (5a). To a

suspension of [(PNN)RhN₂][BF₄] (1) (54.1 mg, 0.10 mmol) in

THF (5 mL) under nitrogen was added a THF (5 mL) solution of

^tBuOK (12.3 mg, 0.11 mmol), and the reaction mixture turned red.

The solution was stirred vigorously at ambient temperature overnight

(or until the entire yellow solid (starting complex) disappeared), and

the solvent was removed under vacuum. The residue was extracted

with benzene, and the extracts were combined and ﬁltered through a

0.2 μm Teﬂon ﬁlter. The solvent was removed under vacuum to give a

mixture of complexes 5 and 5a as a red solid (75.5 mg) in 78% yield.

The assignment of the signals of complexes 5 and 5a was done based

on the mixture.

3

(CH₃)₃CP), 1.40 (t, 6H, J_HH= 7.1 Hz, CH₃CH₂N), 2.69−2.78 (m,

2H, CH₃CH₂N), 2.92−2.99 (m, 2H, CH₃CH₂N), 3.52 (br s, 4H,

2

CH₂CH₂), 3.77 (d, 2H, J_HP= 9.3 Hz, CH₂P), 4.39 (s, 2H, Py-

CH₂N), 7.57 (d, 1H, ³J_HH= 7.7 Hz, Py-H), 7.74 (d, 1H, ³J_HH= 7.8 Hz,

3

Py-H), 8.07 (t, 1H, J_HH= 7.8 Hz, Py-H). ¹³C{¹H} NMR (125 MHz,

2

acetone-d₆): 12.61 (s, CH₃CH₂N), 29.75 (d, J_CP= 3.8 Hz,

1

2

(CH₃)₃CP), 36.85 (dd, J_CP= 13.6 Hz, J_CRh= 1.8 Hz, (CH₃)₃CP,

2

overlapping with the doublet signal at 37.08 ppm), 37.08 (d, J_CP

=

23.8 Hz, CH₂P, overlapping with the doublet of doublet signal at 36.85

1

ppm), 54.00 (br s, CH₃CH₂N), 59.72 (d, J_RhP= 12.7 Hz, CH₂

CH₂), 65.15 (d, J = 1.8 Hz, Py-CH₂N), 119.66 (s, Py-CH), 122.04 (d,

³J_CP= 10.2 Hz, Py-CH), 141.39 (s, Py-CH), 163.48 (br s, Py-C),

163.56 (m, Py-C). Anal. for C₂₁H₃₉BF₄N₂PRh: Calcd C, 46.69; H,

7.28. Found: C, 46.80; H, 7.27.

X-ray structural analysis of 3. Crystal data: C₂₁H₃₉N₂PRh + BF₄,

orange prisms, 0.25 × 0.22 × 0.18 mm³, triclinic, P1, a = 7.8170(1) Å,

̅

b = 11.8504(2) Å, c = 13.9795(2) Å, α = 74.3341(10)°, β =

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³¹P{¹H} NMR (121 MHz, toluene-d₆, 293 K): 84.76 (d, 1P, ¹J_RhP

=

[(ⁱPrPNP*)Rh(COE)] (9). Complex 9 was synthesized in the same

manner as complex 5 from [(ⁱPrPNP)Rh(COE)][BF₄] (8) (74.9 mg,

0.117 mmol) and BuOK (13.1 mg, 0.117 mmol), and the reaction

1

173.7 Hz) (complex 5, 75% by integration) and 83.51 (d, 2P, J_RhP

1

t

170.1 Hz) (complex 5a, 25% by integration). H NMR (300 MHz,

toluene-d₆): 1.22 (t, ³J_HH= 7.2 Hz, CH₃CH₂N 5a), 1.34 (t, ³J_HH= 7.2

mixture was stirred at ambient temperature for 30 min. Complex 9 was

obtained as a red solid in 96% (61.9 mg) yield. The NMR

characterization of complex 9 was performed at 223 K since, at

ambient temperature, only very broad signals were observed.

3

Hz, CH₃CH₂N 5), 1.47 (d, J_HP= 13.0 Hz, (CH₃)₃CP 5a), 1.49 (d,

³J_HP= 12.8 Hz, (CH₃)₃CP 5), 2.32−2.46 (m, CH₃CH₂N 5a), 2.62−

2.78 (m, CH₃CH₂N 5), 2.78−2.95 (m, CH₃CH₂N 5), 3.01 (br s, Py-

CH₂N 5a), 3.14 (br s, Py-CH₂N 5), 3.38 (q, ¹J_HP= ²J_HRh= 1.6 Hz, in

³¹P{¹H} NMR (202 MHz, toluene-d_8,223 K): AB system centered

at 32.63 (dd, ¹J_RhP= 136.2 Hz, ²J_PP= 312.8 Hz) and 45.55 (dd, ¹J_RhP

=

1

¹H{³¹P} appears as a d, J_HP= 1.6 Hz, CHP 5a), 3.42 (dd, J_HP= 1.5

Hz, ²J_HRh= 1.1 Hz, in ¹H{³¹P} appears as a d, ¹J_HP= 1.5 Hz, CHP 5),

5.13−5.19 (m, Py-CH 5 + 5a), 6.11 (br d, ³J_HH= 8.7 Hz, Py-CH 5 +

5a), 6.34−6.42 (m, Py-CH 5 + 5a). ¹³C{¹H} NMR (100 MHz,

2

1

130.4 Hz, J_PP= 312.8 Hz). H NMR (500 MHz, toluene-d₈, 223 K):

0.74 (dd, 6H, J = 7.3, 10.9 Hz, CH(CH₃)₂), 1.1 (br s, 6H, CH(CH₃)₂),

1.17 (dd overlapping with a broad signal at 1.2, 6H, J = 7.4, 12.7 Hz,

CH(CH₃)₂), 1.2 (br s, 6H, CH(CH₃)₂), 1.42 (br s) and 1.54 (br s)

and 1.74 (br m) (total 14H, overlapping signals of COE, CH₂and

CH(CH₃)₂according to C−H correlation and COSY), 2.25 (d, 2H,

²J_PH= 7.2 Hz, CH₂P), 2.46 (br m, 2H, COE,CH₂), 3.23 (br s, 1H,

CHP), 3.85 (very br s, 2H, COE, CHCH), 5.39 (br m, 1H, Py-CH),

6.47−6.54 (m, 2H, Py-CH). ¹³C{¹H} NMR (126 MHz, toluene-d_8,

223 K): 17.34 (br s, CH(CH₃)₂), 17.91 (br s, CH(CH₃)₂), 18.64 (br s,

2

toluene-d₈): 11.94 (s, CH₃CH₂N 5 + 5a), 29.83 (d, J_CP= 5.2 Hz,

(CH₃)₃CP 5a), 30.29 (d, ²J_CP= 5.5 Hz, (CH₃)₃CP 5), 36.07 (d, ¹J_CP

=

1

22.0 Hz, (CH₃)₃CP 5), 36.43 (br d, J_CP= 24.4 Hz, (CH₃)₃CP 5a,

53.09 (d, J = 1.7 Hz, CH₃CH₂N 5a), 54.42 (br s, CH₃CH₂N 5), 62.70

(dd, J_RhC= 1.1 Hz, J_PC= 57.1 Hz, CH-P 5 or 5a), 63.04 (d, J = 1.8

Hz, Py-CH₂N 5 or 5a overlapping with another CH-P signal that

could not be identiﬁed both in DEPT and in ¹³C{¹H} NMR), 63.47

(d, J = 1.8 Hz, Py-CH₂N 5 or 5a), 95.17 (s, Py-CH 5), 96.02 (s, P-CH

5a), 112.25 (d, J_CP= 18.3 Hz, Py-CH 5), 112.84 (d, J_CP= 19.2 Hz,

Py-CH 5a), 131.14 (s, Py-CH 5), 131.45 (s, Py-CH 5a), 157.63 (d, J_CP

= 1.4 Hz, Py-C 5a), 158.78 (d, J_CP= 1.3 Hz, Py-C 5), 169.90−170.19

(m, Py-C 5 + 5a). IR(ν_NN) = 2110 cm⁻¹. Anal. for C₁₉H₃₄N₂PRh:

Calcd C, 50.45; H, 7.58. Found: C, 50.50; H, 8.07.

2

1

CH(CH₃)₂), 20.07 (br s, CH(CH₃)₂), 25.5 (very br m, CH(CH₃)₂),

2

3

27.03 (br s, COE, CH₂), 32.26 (br s, COE, CH₂), 35.5 (br d, J_PC

=

18.2 Hz, CH₂P and COE-CH₂according to C−H correlation), 62.22

1

(br d, J_PC= 57 Hz, CHP), 63.6 (br s, COE, CHCH), 96.5 (br m,

3

Py-CH), 114.28 (br d, J_PC= 18 Hz, Py-CH), 132.3 (br s, Py-CH),

158.6 (br m, Py-C), 173.5 (br m, Py-C). Acceptable elemental analysis

results for 9 could not be obtained. The NMR spectrum of 9 appears

in the Supporting Information.

[(PNN)Rh(NHC₆H₅)] (10). Method A: [(PNN*)RhN₂] (5) (15.0

mg, 0.033 mmol) was placed in an NMR tube, and a benzene-d₆(or

THF) solution (0.5 mL) of aniline (3 μL, 0.033 mmol) was added.

The NMR tube was heated in an oil bath at 60 °C overnight, during

which the color changed from red to brown, and complex 10 was

obtained in quantitative yield according to a ³¹P{¹H} NMR

spectrum.⁵⁷

[(PNN*)Rh(C₂H₄)] (6). Complex 6 was synthesized in the same

manner as complex 5 from [(PNN)Rh(C₂H₄)][BF₄] (3) (64.9 mg,

t

0.120 mmol) and BuOK (13.4 mg, 0.120 mmol), and the reaction

mixture was stirred at ambient temperature for 30 min. Complex 6 was

obtained as a red solid in 92% (50.0 mg) yield.

³¹P{¹H} NMR (121 MHz, benzene-d₆): 70.71 (d, ¹J_RhP= 177.4 Hz).

3

¹H NMR (300 MHz, benzene-d₆): 1.01 (t, 6H, J_HH= 7.1 Hz,

CH₃CH₂N), 1.38 (d, 18H, ³J_PH= 12.3 Hz, (CH₃)₃CP), 1.86−1.94 (m,

2H, CH₃CH₂N), 2.08−2.20 (m, 2H, CH₃CH₂N), 2.86 (s, overlapping

with the signal at 2.89, total integration 6H, assignment according to

HSQC, CH₂CH₂), 2.89 (s, overlapping with the signal at 2.86, total

integration 6H, assignment according to HSQC, Py-CH₂N), 3.42 (br

Method B: To a THF (5 mL) suspension of complex 17 (39.7 mg,

t

0.065 mmol) was added BuOK (7.3 mg, 0.065 mmol) in THF (5

mL), and a clear dark brown solution was immediately obtained. The

reaction mixture was stirred at ambient temperature for 2 h, after

which the solvent was removed by vacuum. The residue was extracted

with benzene. The extracts were combined and ﬁltered through a 0.2

μm Teﬂon ﬁlter, and the solvent was removed under vacuum to give

complex 10 as a brown solid in 83% (28.1 mg) yield.

3

s, 1H, CH-P), 6.35 (d, 1H, J_HH= 8.7 Hz, Py-H), 6.44−6.48 (m, 2H,

Py-H). ¹³C{¹H} NMR (101 MHz, benzene-d₆): 11.65 (s, CH₃CH₂N),

30.02 (d, ²J_CP= 4.4 Hz, (CH₃)₃CP), 36.14 (dd, ¹J_CP= 20.4 Hz, ²J_CRh

=

1.9 Hz, (CH₃)₃CP), 48.86 (dd, ¹J_CRh= 13.2 Hz, ²J_CP= 1.7 Hz, CH₂

CH₂), 52.19 (br s, CH₃CH₂N), 64.07 (d, J = 1.5 Hz, Py-CH₂N), 67.39

³¹P{¹H} NMR (121 MHz, benzene-d₆): 87.23 (d, ¹J_RhP= 220.4 Hz).

1

3

(d, J_CP= 55.2 Hz, CH-P), 93.52 (s, Py-CH), 113.60 (d, J_CP= 18.0

Hz, Py-CH), 132.28 (s, Py-CH), 158.23 (s, Py-C), 168.33−168.67 (m,

Py-C). Acceptable elemental analysis results for 6 could not be

obtained. The NMR spectrum of 6 appears in the Supporting

Information.

3

¹H NMR (300 MHz, benzene-d₆): 1.19 (t, 6H, J_HH= 7.1 Hz,

CH₃CH₂N), 1.31 (d, 18H, ³J_HP= 12.5 Hz, (CH₃)₃CP), 2.07 (br s, 1H,

2

Rh-NH), 2.28 (d, 2H, J_HP= 8.3 Hz, CH₂P), 2.56−2.68 (m, 2H,

CH₃CH₂N), 3.01 (m, 2H, CH₃CH₂N), 3.10 (s, 2H, Py-CH₂N), 6.01

3

[(ⁱPrPNP*)Rh(C₂H₄)] (7). Complex 7 was synthesized in the same

(d, 1H, J_HH= 7.6 Hz, Py-CH), 6.31 (d, 1H, J_HH= 7.7 Hz, Py-CH),

3

manner as complex 5 from [(ⁱPrPNP)Rh(C₂H₄)][BF₄] (4) (81.3 mg,

6.46 (t, 1H, J_HH= 7.0 Hz, anil-CH), 6.95 (t, 1H, J_HH= 7.6 Hz, Py-

CH), 7.01 (d, 2H, ³J_HH= 7.7 Hz, anil-CH), 7.28 (t, 2H, ³J_HH= 7.6 Hz,

anil-CH). ¹³C{¹H} NMR (125) MHz, benzene-d₆): 11.34 (s,

t

0.146 mmol) and BuOK (16.3 mg, 0.146 mmol), and the reaction

mixture was stirred at ambient temperature for 30 min. Complex 7 was

obtained as a red solid in 86% (59.0 mg) yield.

2

1

CH₃CH₂N), 29.41 (d, J_CP= 5.8 Hz, (CH₃)₃CP), 34.63 (dd, J_CP

=

2

1

³¹P{¹H} NMR (121 MHz, benzene-d₆): AB system centered at

13.0, J_CRh= 2.5 Hz, (CH₃)₃CP), 36.48 (d, J_CP= 17.0 Hz, CH₂P),

52.87 (br d or two overlapping singlets, in case of a doublet J = 1.7 Hz,

CH₃CH₂N), 63.53 (d, J = 2.1 Hz, Py-CH₂N), 107.22 (s, anil-CH),

116.13 (s, anil-CH), 117.47 (s, Py-CH), 119.82 (d, ³J_CP= 9.3 Hz, Py-

CH), 127.39 (s, Py-CH), 128.86 (s, anil-CH), 160.50 (s, anil-C or Py-

C), 160.55−160.62 (m, Py-C), 163.21 (s, anil-C or Py-C). Acceptable

elemental analysis results for 10 could not be obtained. The NMR

spectrum of 10 appears in the Supporting Information

1

2

1

45.15 and 40.38 (dd, J_RhP= 127.2 Hz, J_PP= 322.5 Hz). H NMR

(500 MHz, benzene-d₆): 0.77−0.81 (m, 12H, (CH₃)₂CH), 0.86−0.91

(m, 6H, (CH₃)₂CH), 1.15−1.23 (m, 6H, (CH₃)₂CH), 1.44−1.52 (m,

2

2H, (CH₃)₂CH), 1.83−1.91 (m, 2H, (CH₃)₂CH), 2.44 (d, 2H, J_PH

=

9.2 Hz, CH₂-P), 3.20 (dt, 4H, ³J_PH= 3.7 Hz, ²J_RhH= 1.9 Hz (coupling

constants were detriment also by H{³¹P} NMR), CH₂CH₂), 3.35

1

2

(d, 1H, J_PH= 4.0 Hz, CHP), 5.38 (br d, 1H, J = 5.5 Hz, Py-CH),

6.46−6.50 (m, 2H, Py-CH). ¹³C{¹H} NMR (126 MHz, benzene-d₆):

[(PNN)Rh(o-Br-NHC₆H₄)] (11). Complex 11 was synthesized in

the same manner as complex 10 by method A with complex 5 (15.0

mg, 0.033 mmol) and o-bromoaniline (4 μL, 0.035 mmol). The

reaction mixture was heated overnight at 60 °C, during which the

color changed from red to brown, and complex 11 was obtained in

quantitative yield according to ³¹P{¹H} NMR.

2

17.77 (br d, J_PC= 11 Hz, (CH₃)₂CH), 18.59 (d, J_PC= 5.2 Hz,

(CH₃)₂CH), 18.74 (d, ²J_PC= 5.4 Hz, (CH₃)₂CH), 23.73 (ddd, J = 1.5,

3.4, 16.0 Hz, (CH₃)₂CH), 24.90 (ddd, J = 1.5, 3.5, 23.7 Hz,

1

(CH₃)₂CH), 34.91 (d, J_PC= 18.7 Hz, CH₂P), 44.51 (dt, J_RhC= 11.7

Hz, ²J_PC= 1.7 Hz, CH₂CH₂), 63.36 (d, ¹J_PC= 50.8 Hz, CHP), 96.75

(dd, J = 0.5, 11.4 Hz, Py-CH), 114.75 (d, J_PC= 18.4 Hz, Py-CH),

132.12 (br s, Py-CH), 173.87 (dd, J = 2.4, 3.5 Hz, Py-C), 174.03 (dd, J

= 2.5, 3.8 Hz, Py-C). Anal. for C₂₁H₃₈NP₂Rh: Calcd C, 53.74; H, 8.16.

Found: C, 53.68; H, 8.27.

³¹P{¹H} NMR (121 MHz, benzene-d₆): 87.33 (d, ¹J_RhP= 208.8 Hz).

3

¹H NMR (400 MHz, benzene-d₆): 1.18 (br t, 6H, J_HH= 7.0 Hz,

CH₃CH₂N), 1.30 (18H, ³J_HP= 12.6 Hz, (CH₃)₃CP), 2.28 (d, 2H, ²J_HP

= 8.4 Hz, CH₂P), 2.44−2.60 (br m, 2H, CH₃CH₂N), 2.82−2.96 (br m,

4094

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Article

1

2H, CH₃CH₂N), 2.99 (br s, 1H, RhNH), 3.07 (s, 2H, Py-CH₂N), 6.01

³¹P{¹H} NMR (121 MHz, THF-d₈): 87.44 (d, J_RhP= 216.4 Hz).

3

(br d, 1H, J_HH= 7.6 Hz, Py-CH), 6.15 (ddd, 1H, J_HH= 6.8, 7.7 Hz,

⁴J_HH= 1.7, anil-CH), 6.30 (br d, 1H, ³J_HH= 7.6 Hz, Py-CH), 6.93 (br

dt, 1H, ³J_HH= 7.6 Hz, ⁵J_PH= 0.8 Hz, Py-CH), 7.23 (m, 1H, anil-CH),

¹H NMR (400 MHz, THF-d₈): 1.30 (d, 18H, J_HP= 12.8 Hz,

(CH₃)₃CP), 1.38 (t, 6H, J_HH= 6.7 Hz, CH₃CH₂N), 2.73−2.83 (m,

2H, CH₃CH₂N), 2.92 (d, 2H, J_HP= 8.5 Hz, CH₂P, overlapping with

the signal at 2.89−3.03), 2.89−3.03 (m, 2H, CH₃CH₂N), 3.95 (s, 2H,

Py-CH₂N), 4.25 (s, 1H, RhNH), 5.91 (dd, 1H, J_HH= 9.4 Hz, J_HH

3

2

7.50 (dd, 1H, ³J_HH= 8.2 Hz, ⁴J_HH= 1.7, anil-CH), 7.56 (dd, 1H, ³J_HH

=

3

4

7.7 Hz, ⁴J_HH= 1.6, anil-CH). ¹³C{¹H} NMR (101 MHz, benzene-d₆):

=

3

4

2

2.5 Hz, anil-CH), 6.80 (dd, 1H, J_HH= 9.5 Hz, J_HH= 2.5 Hz, anil-

11.37 (br s, CH₃CH₂N), 29.40 (d, J_CP= 5.7 Hz, (CH₃)₃CP), 34.64

CH), 6.93 (d, 1H, ³J_HH= 7.7 Hz, Py-CH), 7.07 (d, 1H, ³J_HH= 7.7 Hz,

(dd, ¹J_CP= 13.2 Hz, ²J_CRh= 2.4 Hz, (CH₃)₃CP), 36.40 (d, ¹J_CP= 17.3

Hz, CH₂P), 52.86 (br s, CH₃CH₂N), 63.50 (br d, J = 2.0 Hz, Py-

CH₂N), 107.27 (s, anil-CH), 113.67 (br s, anil-CBr), 116.73 (s, anil-

3

4

Py-CH), 7.37 (dd, 2H, J_HH= 9.5 Hz, J_HH= 2.5 Hz, anil-CH), 7.54

(dd, 1H, J_HH= 7.7 Hz, J_PH= 0.8 Hz, Py-CH), 7.64 (dd, 2H, J_HH

3

5

3

=

4

3

4

3

9.3 Hz, J_HH= 2.6 Hz, anil-CH), 8.51 (dd, 2H, J_HH= 9.5 Hz, J_HH

CH), 117.50 (s, Py-CH), 119.87 (d, J_CP= 10.4 Hz, Py-CH), 127.83

2.6 Hz, anil-CH). ¹³C{¹H} NMR (101) MHz, THF-d₈): 11.60 (s,

(s, Py-CH), 127.93 (s, anil-CH), 131.87 (s, anil-CH), 158.11 (s, anil-

CNH), 160.46 (s, Py-C), 160.72 (dd, J = 3.4, 6.3 Hz, Py-C).

Acceptable elemental analysis results for 11 could not be obtained.

The NMR spectrum of 11 appears in the Supporting Information.

[(PNN)Rh(m-Cl-p-Cl-NHC₆H₃)] (12). Complex 12 was synthesized

in the same manner as complex 10 by method A with complex 5 (15.0

mg, 0.033 mmol) and m,p-dichloroaniline (5.3 mg, 0.033 mmol). The

reaction mixture was heated for 3 h at 60 °C, during which the color

changed from red to brown, and complex 12 was obtained in 97%

yield by integration according to ³¹P{¹H} NMR (another signal at

89.25 ppm (¹J_RhP= 198.3 Hz) could be PNNRhCl). Crystals suitable

for X-ray analysis were obtained from a concentrated solution of 12 in

benzene by slow evaporation.

2

1

CH₃CH₂N), 29.80 (d, J_CP= 5.6 Hz, (CH₃)₃CP), 35.46 (dd, J_CP

=

14.1 Hz, ²J_CRh= 2.2 Hz, (CH₃)₃CP), 36.85 (d, ¹J_CP= 19.3 Hz, CH₂P),

53.98 (br s, CH₃CH₂N), 64.48 (br d, J = 1.8 Hz, Py-CH₂N), 116.21 (s,

anil-CH), 116.56 (s, anil-CH), 119.98 (s, Py-CH), 121.24 (d, J_CP

3

=

10.8 Hz, Py-CH), 125.84 (s, anil-CH), 127.76 (s, anil-CH), 130.26 (s,

anil-C), 132.01 (s, Py-CH), 161.89 (s, anil-C or Py-C), 162.44 (br dd,

J = 3.6, 6.2 Hz, Py-C), 168.20 (s, anil-C or Py-C). Anal. for

C₂₅H₄₀N₄O₂PRh: Calcd C, 53.38; H, 7.17. Found: C, 53.10; H, 7.13.

[(ⁱPrPNP)Rh(NHC₆H₅)] (14). Method A: [(ⁱPrPNP*)Rh(COE)]

(9) (15.0 mg, 0.027 mmol) was placed in an NMR tube, and a

benzene-d₆(or THF) solution (0.5 mL) of aniline (9 μL, 0.099 mmol)

was added. The NMR tube was heated in an oil bath at 60 °C

overnight, during which the color changed from red to brown, and

complex 14 was obtained in quantitative yield according to ³¹P{¹H}

NMR. The reaction of complex 7 with 1.2 equiv of aniline under the

same conditions was sluggish, and for full conversion, a large excess of

aniline is required.

³¹P{¹H} NMR (121 MHz, benzene-d₆): 87.31 (d, ¹J_RhP= 216.7 Hz).

3

¹H NMR (500 MHz, benzene-d₆): 1.13 (t, 6H, J_HH= 7.3 Hz,

CH₃CH₂N), 1.23 (d, 18H, ³J_HP= 12.5 Hz, (CH₃)₃CP), 2.17 (br s, Rh-

2

NH-An), 2.26 (d, 2H, J_HP= 8.5 Hz, CH₂P), 2.44−2.57 (m, 2H,

CH₃CH₂N), 2.77−2.90 (m, 2H, CH₃CH₂N), 3.02 (s, 2H, Py-CH₂N),

Method B: To a THF (5 mL) suspension of complex 17 (23.7 mg,

0.038 mmol) was added BuOK (4.2 mg, 0.038 mmol) in THF (5

5.80 (dd, 1H, ³J_HP= 8.5 Hz, ⁴J_HP= 2.5 Hz, An-CH), 6.01 (d, 1H, ³J_HP

t

4

= 8.0 Hz, Py-CH), 6.25 (d, 1H, J_HP= 2.5 Hz, An-CH), 6.30 (d, 1H,

mL), and a clear dark brown solution was immediately obtained. The

reaction mixture was stirred at ambient temperature for 2 h, after

which the solvent was removed by vacuum. The residue was extracted

with benzene. The extracts were combined and ﬁltered through a 0.2

μm Teﬂon ﬁlter, and the solvent was removed under vacuum to give

complex 14 as a brown solid in 89% (18.2 mg) yield.

³J_HP= 7.5 Hz, Py-CH), 6.89 (m, overlapping with a signal at 6.91,

according to a C−H correlation and COSY, the signal was attributed

to An-CH), 6.91 (m, overlapping with a signal at 6.91, according to a

C−H correlation and COSY, the signal was attributed to Py-CH).

¹³C{¹H} NMR (126 MHz, benzene-d₆): 11.30 (s, CH₃CH₂N), 29.29

2

1

2

³¹P{¹H} NMR (121 MHz, benzene-d₆): 45.35 (d, ¹J_RhP= 156.7 Hz).

¹H NMR (500 MHz, benzene-d₆): 1.02 (q, 12 H, ³J_PH= ³J_HH= 6.7 Hz,

(CH₃)₂CH), 1.23 (dd, 12H, ³J_PH= 8.0 Hz, ³J_HH= 7.4 Hz, (CH₃)₂CH),

1.85−1.97 (m, 4H, (CH₃)₂CH), 1.87 (overlapping with (CH₃)₂CH

signal, appears as a broad singlet in the SST experiment upon

irradiation of CH₂P signal, Rh-NH), 2.47 (vt, 4H, J_PH= 3.4 Hz,

CH₂P), 6.31 (d, 2H, ³J_HH= 7.6 Hz, Py-CH), 6.46 (br t, 1H, ³J_HH= 6.9

Hz, anil-CH), 6.86 (m, (overlapping with asignal at 6.88), 2H, anil-

CH), 6.88 (m, (overlapping with a signal at 6.86), 1H, Py-CH), 7.26

(dd, 2H, J_HH= 1.0, 7.1 Hz, anil-CH). ¹³C{¹H} NMR (126 MHz,

benzene-d₆): 18.04 (s, (CH₃)₂CH), 19.02 (vt, J_PC= 3.7 Hz,

(d, J_CP= 5.8 Hz, (CH₃)₃CP), 34.55 (dd, J_CP= 13.8 Hz, J_CRh= 2.5

2

Hz (CH₃)₃CP), 36.27 (d, J_CP= 17.6 Hz, CH₂P), 52.92 (br s,

3

CH₃CH₂N), 63.41 (d, J_CP= 2.0 Hz, Py-CH₂N), 114.36 (s, An-CH),

116.23 (s, An-CH), 117.51 (s, Py-CH), 119.82 (d, ³J_CP= 10.2 Hz, Py-

CH), 128.40 (s, Py-CH), 160.54 (br s, Py-C), 160.78 (dd, J = 2.5, 3.8

Hz, Py-C). Anal. for C₂₅H₃₉Cl₂N₃PRh: Calcd C, 51.21; H, 6.70.

Found: C, 52.1; H, 6.75.

X-ray structural analysis of 12. Crystal data: C₂₅H₃₉Cl₂N₃PRh, red

prisms, 0.53 × 0.11 × 0.06 mm³, orthorhombic, P2₁2₁2₁, a =

14.1476(5) Å, b = 24.9498(9) Å, c = 7.5796(3) Å, from 26 018

reﬂections, T = 120(2) K, V = 2675.45(17) Å³, Z = 4, F_w= 586.37, D_c

= 1.456 Mg/m⁻³, μ = 0.916 mm⁻¹.

2

(CH₃)₂CH), 24.94 (d vt, J_RhC= 1.6 Hz, J_PC= 8.8 Hz, (CH₃)₂CH),

Data collection and processing: Bruker KappaApexII CCD

diﬀractometer, Mo Kα (λ = 0.71073 Å), graphite monochromator,

−18 ≤ h ≤ 17, −33 ≤ k ≤ 33, −7 ≤ l ≤ 10, 2θ_max= 56.78, frame scan

width = 0.5°, scan speed = 1.0° per 120 s, typical peak mosaicity 0.69°,

35.67 (vt, J_PC= 6.4 Hz, CH₂P), 107.46 (s, anil-CH), 116.47 (s, anil-

CH), 119.49 (t, J_PC= 4.8 Hz, Py-CH), 128.44 (s, anil-CH), 129.47 (s,

Py-CH), 163.60 (d vt, ²J_RhC= 0.7 Hz, J_PC= 6.0 Hz, Py-C), 164.71 (br

s, anil-C). Acceptable elemental analysis results for 14 could not be

obtained. The NMR spectrum of 14 appears in the Supporting

Information.

25 465 reﬂections collected, 7167 independent reﬂections (R_int

=

0.0518). The data were processed with APEX2.

Solution and reﬁnement: Structure solved by direct methods with

Bruker AutoStructure. Full-matrix least-squares reﬁnement based on F²

with SHELXL-97. 330 parameters with no restraints, ﬁnal R₁= 0.0377

(based on F²) for data with I > 2σ(I), R₁= 0.0429 on 6691 reﬂections,

goodness-of-ﬁt on F²= 1.034, largest electron density peak = 1.280 e

Å⁻³, and largest hole = −0.877 eÅ³

[(PNN)Rh(p-NO₂−NHC₆H₄)] (13). Complex 13 was synthesized in

the same manner as complex 10 by method A with complex 5 (30.4

mg, 0.067 mmol) and p-nitroaniline (9.2 mg, 0.067 mmol). The

reaction mixture was heated for 3 h at 60 °C in THF, during which the

color changed from red to deep brown. The solvent was removed

under vacuum to give complex 13 as a dark brown solid in quantitative

yield. Complex 13 has medium solubility in benzene and good

solubility in THF.

[(ⁱPrPNP)Rh(p-NO₂−NHC₆H₄)] (15). Complex 15 was synthesized

in the same manner as complex 10 by method A with complex 7 (15

mg, 0.032 mmol) and p-nitroaniline (4.4 mg, 0.032 mmol). The

reaction mixture was heated for 1 h at 60 °C, during which the color

changed from red to deep purple. The solvent was removed by

vacuum to give a dark brown solid as complex 15 in quantitative yield.

Complex 15 has medium solubility in benzene and good solubility in

THF.

³¹P{¹H} NMR (121 MHz, benzene-d₆): 46.87 (d, ¹J_RhP= 149.6 Hz).

¹H NMR (400 MHz, THF-d₈): 1.14−1.20 (m, 24 H, (according to

3

¹H{³¹P}: 1.17 (d, 12H, J_HH= 6.9 Hz), 1.18 (d, 12H, J_HH= 7.1 Hz),

(CH₃)₂CH)), 2.09 (br quin. 4H, according to H{³¹P}: sept. J_HH

=

1

3

7.0 Hz (CH₃)₂CH), 3.19 (vt, 4H, J_PH= 3.7 Hz, CH₂P), 4.47 (br s, 1H,

3

Rh-NH), 5.86 (dd, 1H, J_HH= 2.5, 9.4, anil-CH), 7.09 (d, 2H, J_HH

=

4095

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7.7 Hz, Py-CH), 7.33 (dd, 1H, J_HH= 2.6, 9.4, anil-CH), 7.50 (t, 1H,

³J_HH= 7.7 Hz, Py-CH), 6.56 (dd, 1H, J_HH= 2.5, 9.4, anil-CH), 7.64 (br

dd, 1H, J_HH= 2.6, 9.4 Hz, anil-CH). ¹³C{¹H} NMR (100 MHz, THF-

d₈): 18.53 (br s, (CH₃)₂CH), 19.52 (vt, J_PC= 3.5 Hz, (CH₃)₂CH),

= 2800.39(8) Å³, Z = 4, F_w= 605.31, D_c= 1.436 Mg/m⁻³, μ = 0.712

mm⁻¹.

Data collection and processing: Nonius KappaCCD diﬀractometer,

Mo Kα (λ = 0.71073 Å), graphite monochromator; −13 ≤ h ≤ 13,

−19 ≤ k ≤ 19, −24 ≤ l ≤ 24, frame scan width = 1.0°, scan speed =

1.0° per 20 s, typical peak mosaicity 0.768°, 69895 reﬂections

collected, 12 844 independent reﬂections (R_int= 0.1109). The data

were processed with HKL2000.

Solution and reﬁnement: Structure solved by direct methods with

SIR-92. Full-matrix least-squares reﬁnement based on F²with

SHELXL-97. 663 parameters with no restraints, ﬁnal R₁= 0.0526

(based on F²) for data with I > 2σ(I), R₁= 0.0769 on 12 838

reﬂections, goodness-of-ﬁt on F²= 1.104, largest electron density peak

= 2.632 e Å⁻³, and hole = −1.725 e Å⁻³.

25.78 (d vt, J_PC= 9.4 Hz, ²J_RhC= 1.4 Hz, (CH₃)₂CH), 36.02 (vt, J_PC

=

7.6 Hz, CH₂P), 115.85 (s, anil-CH), 117.48 (s, anil-CH), 121.18 (vt,

J_PC= 5.4 Hz, Py-CH), 125.49 (s, anil-CH), 127.73 (s, anil-CH),

130.15 (s, anil-C), 133.90 (s, Py-CH), 165.32 (br vt, J_PC= 5.4 Hz, Py-

C), 168.36 (s, anil-C). Anal. for C₂₅H₄₀N₃O₂PRh: Calcd C, 51.82; H,

6.96. Found: C, 51.65; H, 6.90.

Spin Saturation Transfer (SST) Experiments. Spin saturation

transfer experiments were performed on the anilide complexes 10 and

14 in benzene-d₆and on the p-nitroanilide complexes 13 and 15 in

THF-d₈(0.02 M) and on the mixture of the anilide complexes with

about a 5-fold excess of the corresponding free aniline. Each

experiment involved selective spin saturation at the hydrogen atoms

of the methylene benzylic arm (Py−CH₂−P). The response of the

NH−anilide or NH₂−aniline signal was detected by comparison

(diﬀerence spectrum) with a control experiment in which the sample

was irradiated oﬀ-resonance under the same conditions. Using the SST

technique, exchange between the benzylic protons Py−CH₂−P and

the NH−anilide and between the benzylic protons Py−CH₂−P and

NH₂−aniline was observed for complexes 10 and 14 only.

SST experiments were also preformed on complexes 5−7 and 9

(0.02 M) at 283 K in the presence of a 5-fold excess of aniline in

toluene-d₈. ³¹P{¹H} NMR spectra of the reaction mixtures performed

prior to and after the SST experiments exhibits only signals of the

starting complexes. Using the SST technique, exchange between the

dearomatized benzylic arm Py−CH−P and the NH₂−aniline was

observed.

[(ⁱPrPNP)Rh(NH₂C₆H₅)][BF₄] (17). To a suspension of [(ⁱPrPNP)-

Rh(COE)][BF₄] (8) (31.0 mg, 0.048 mmol) in THF (7 mL) in a

Schlenk tube was added aniline (100 μL, 1.10 mmol), and the reaction

was heated at 60 °C for 4 h. A clear orange solution was obtained, and

the THF volume was reduced to 1 mL by vacuum. Pentane was added

to the THF solution, and a precipitate was formed. The precipitate was

left overnight with the pentane to allow easy decantation. After

decantation, the light brown solid was washed with pentane (20 mL)

and the solid was dried under vacuum to give the complex

[(ⁱPrPNP)Rh(NH₂C₆H₅)][BF₄] (17) in 96% yield (28.3 mg). Crystals

suitable for X-ray analysis were obtained by layering a concentrated

THF solution of 17 with pentane.

1

³¹P{¹H} NMR (162 MHz, THF-d₈): 49.29 (d, J_RhP= 135.7 Hz).

3

¹H NMR (400 MHz, THF-d₈): 1.09 (q, 12 H, J_HH= J_PH= 6.9 Hz,

3

(CH₃)₂CH), 1.24 (dd apears as q, 12H, J_HH= 7.2 Hz, J_PH= 8.9 Hz,

(CH₃)₂CH), 1.98−2.09 (m, 4H, according to ¹H{³¹P}: sept. ³J_HH= 7.0

Hz, (CH₃)₂CH), 3.29 (vt, 4H, J_PH= 3.9 Hz, CH₂P), 5.27 (br s, 2H,

Rh-NH₂), 7.17 (t, 1H, ³J_HH= 7.7 Hz, Py-CH), 7.20 (d, 2H, ³J_HH= 7.7

Hz, Py-CH), 7.30 (br d, 1H, ³J_HH= 8 Hz, anil-CH), 6.99 (tt, 1H, ³J_HH

= 7.4 Hz, ⁴J_HH= 1.1 Hz, anil-CH), 7.53 (br t, 1H, ³J_HH= 7.7 Hz, anil-

CH). ¹³C{¹H} NMR (101 MHz, THF-d₈): 17.94 (s, (CH₃)₂CH),

19.31 (vt, J_PC= 3.5 Hz, (CH₃)₂CH), 24.66 (vt, J_PC= 10.2 Hz,

(CH₃)₂CH), 35.14 (vt, J_PC= 8.9 Hz, CH₂P), 121.18 (vt, J_PC= 5.2 Hz,

Py-CH), 123.91 (s, anil-CH), 125.17 (s, anil-CH), 129.17 (s, Py-CH),

135.19 (s, anil-CH), 148.24 (s, anil-C), 165.32 (br vt, J_PC= 5.4 Hz, Py-

C). Anal. for C₂₅H₄₂BF₄N₂P₂Rh: Calcd C, 48.25; H, 6.80. Found: C,

48.38; H, 6.84.

[(PNN)Rh(NH₂C₆H₆)][BF₄] (16). To a suspension of [(PNN)-

RhN₂][BF₄] (1) (41.6 mg, 0.077 mmol) in THF (7 mL) in a Schlenk

tube was added aniline (100 μL, 1.10 mmol), and the suspension was

heated at 60 °C for 2 h. A clear orange solution was obtained, and the

solvent volume was reduced to 1 mL by vacuum. Pentane was added

to the THF solution, forming a precipitate, which was left standing

overnight to allow easy decantation. After decantation, the light brown

solid was washed with pentane (20 mL) and the solid was dried under

vacuum to give the complex [(PNN)Rh(NH₂C₆H₅)][BF₄] (16) in

84% yield (39.7 mg). Complex 16 has medium solubility in THF at

ambient temperature, and it reacts readily with methylene chloride. It

was found to be unstable in solution without a slight excess of aniline.

The excess of aniline also improves the complex solubility in THF.

When a solution of complex 16 was exposed to air, an unidentiﬁed

green complex was obtained. Crystals suitable for X-ray analysis were

obtained by addition of aniline (one drop) to a concentrated THF

solution of 16 and layering with pentane.

X-ray structural analysis of 17. Crystal data: C₂₅H₄₂N₂P₂Rh + BF₄,

orange needle, 0.16 × 0.01 × 0.01 mm³, monoclinic, P2₁/n, a =

11.5987(4) Å, b = 21.1484(7) Å, c = 11.7603(4) Å, β = 102.226(1)^o

from 18° of data, T = 120(2) K, V = 2819.30(17) Å³, Z = 4, F_w

=

622.27, D_c= 1.466 Mg/m⁻³, μ = 0.763 mm⁻¹.

Data collection and processing: Bruker KappaApexII CCD

diﬀractometer, Mo Kα (λ = 0.71073 Å), graphite monochromator;

Miracol optics, −16 ≤ h ≤ 14, −29 ≤ k ≤ 26, −16 ≤ l ≤ 16, 2θ max =

60.50°, frame scan width = 0.5°, scan speed = 1.0° per 160 s, typical

peak mosaicity 0.79°, 30 707 reﬂections collected, 8359 independent

reﬂections (R_int= 0.034). The data were processed with the

BrukerApex2 package.

Solution and reﬁnement: Structure solved by direct methods with

Bruker AutoStructure. Full-matrix least-squares reﬁnement based on F²

with SHELXL-97. 330 parameters with no restraints, ﬁnal R₁= 0.0288

(based on F²) for data with I > 2σ(I), R₁= 0.0454 on 8359 reﬂections,

goodness-of-ﬁt on F²= 1.015, largest electron density peak = 0.869 e

Å⁻³, and hole = −0.332 e Å⁻³.

Treatment of Complexes 10 and 14 with p-Nitroaniline. A

7.0 mg (0.017 mmol) portion of 10 was placed in an NMR tube and

dissolved in a 0.5 mL THF solution of p-nitroaniline (0.034 M, 0.017

mmol). The NMR tube was shaken to give a clear solution and placed

in an oil bath and heated to 60 °C for 20 h. The same procedure was

performed with complex 14 (9.3 mg, 0.017 mmol). The progress of

the reactions was monitored by ³¹P{¹H} NMR after 1, 4, and 18 h,

which revealed for both 10 and 14 45% conversion to complexes 13

and 15, respectively, after 1 h, 80% conversion after 4 h, and full

conversion after 18 h. Free aniline in the reactions mixture was

detected by GCMS.

1

³¹P{¹H} NMR (162 MHz, THF-d₈): 82.99 (d, J_RhP= 197.1 Hz).

3

¹H NMR (400 MHz, THF-d₈): 1.35 (d, 18H, J_HP= 12.8 Hz,

(CH₃)₃CP), 1.43 (t, 6H, ³J_HH= 7.1 Hz, CH₃CH₂N), 2.50 (dq (appears

as q in ¹H{³¹P} NMR), 4H, ³J_HH= 7.1 Hz, ⁴J_PH= 1.8 Hz, CH₃CH₂N),

3.06 (d, 2H, ²J_HP= 9.0 Hz, CH₂P), 3.94 (s, 2H, Py-CH₂N), 4.93 (br s,

2H, Rh-NH₂), 6.98 (overlapping with free aniline signal, 1H, Py-CH),

7.11 (m, overlapping with signal at 7.13, 1H, anil-CH), 7.13 (m,

overlapping with signal at 7.11, 1H, Py-CH), 7.25 (br t, 2H, ³J_HH= 7.5

Hz, anil-CH), 7.55 (t, 2H, ³J_HH= 7.7 Hz, Py-CH), 7.65 (d, 2H, ³J_HH

=

7.5 Hz, anil-CH). ¹³C{¹H} NMR (101) MHz, THF-d₈): 12.20 (s,

CH₃CH₂N), 29.52 (d, ²J_CP= 5.4 Hz, (CH₃)₃CP), 35.29 (d, ¹J_CP= 15.1

1

Hz, (CH₃)₃CP), 36.61 (d, J_CP= 22.1 Hz, CH₂P), 54.58 (br s,

CH₃CH₂N), 64.36 (d, J = 1.6 Hz, Py-CH₂N), 118.64 (s, Py-CH),

3

120.87 (d, J_CP= 10.7 Hz, Py-CH), 125.04 (s, anil-CH), 125.85 (s,

anil-CH), 129.25 (s, anil-CH), 133.86 (s, Py-CH), 144.65 (s, anil-C),

162.84 (s, Py-C), 162.8 (m, Py-C). Acceptable elemental analysis

results for 16 could not be obtained. The NMR spectrum of 16

appears in the Supporting Information.

X-ray structural analysis of 16. Crystal data: C₂₅H₄₂N₃PRh + BF₄,

orange plate, 0.15 × 0.15 × 0.05 mm³, triclinic, P-1, a = 10.6386(2) Å,

b = 15.1960(2) Å, c = 18.7985(3) Å, α = 74.9166(7)^o, β =

84.3107(7)^o, γ = 72.6717(6)^ofrom 12 761 reﬂections, T = 120(2) K, V

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1

Treatment of Complexes 10 and 13−15 with CO. A benzene-

d₆solution of 10 (10.0 mg, 0.019 mmol) was placed in a J. Young

NMR tube and cooled to −196 °C, and the nitrogen atmosphere was

replaced by CO. The reaction mixture was slowly warmed to room

temperature, and the solution color changed from brown to red.

(CH₃)₂CH), 34.78 (d, J_PC= 18.6 Hz, CH₂P), 61.48 (dd, J = 2.0 Hz,

¹J_PC= 51.8 Hz, CHP), 97.87 (d, J_PC= 11.7 Hz, Py-CH), 114.43 (d,

3

³J_PC= 19.0 Hz, Py-CH), 132.54 (vt, J = 1.5 Hz, Py-CH), 159.35 (ddd,

J = 1.8, 3.7 Hz, ²J_PC= 8.5 Hz, Py-C), 174.10 (ddd, J = 2.4, 4.7 Hz, ²J_PC

1

2

= 20.7 Hz, Py-C), 197.90 (dt, J_RhC= 65.7 Hz, J_PC= 13.3 Hz, CO).

IR(ν_CO) = 1954.2 cm⁻¹. Anal. for C₂₀H₃₄NOP₂Rh: Calcd C, 51.18; H,

7.30. Found: C, 50.41; H, 7.33.

[(PNN)Rh(CO)][BF₄] (20). An acetone solution (7 mL) of complex

1 (15 mg, 0.028 mmol) in a Schlenk tube was cooled to −196 °C, and

the nitrogen atmosphere was replaced by CO. The reaction mixture

was slowly warmed to room temperature to give a bright yellow

solution. The solvent was removed under vacuum, and the obtained

solid was washed with pentane (10 mL) and dried again under vacuum

to give complex 20 as a yellow solid in quantitative yield. ³¹P{¹H}

1

According to ³¹P{¹H} NMR, H NMR, and GCMS, complex 18 and

the corresponding aniline were obtained in quantitative yield.

Complexes 13, 14, and 15 were reacted in the same maner as 10 to

give complexes 18 and 19, respectively, along with the corresponding

free aniline.

Treatment of Complexes 14 and 15 with PEt₃. A benzene-d₆

solution of 14 (7.6 mg, 0.014 mmol) was placed in a J. Young NMR

tube, and 0.05 mL of PEt3 (0.339 mmol) was added. The NMR tube

was placed in an oil bath and heated to 60 °C for 12 h, during which

the color turned from brown to red, and complex 22 was obtained in

quantitative yield along with free aniline according to ³¹P{¹H} NMR,

¹H NMR, and GCMS. Complex 15 (8.5 mg, 0.015 mmol) was reacted

in the same manner as 14 in THF with PEt₃(0.05 mL, 0.339 mmol) to

give complex 22 and p-nitroaniline in quantitative yield.

1

NMR (121 MHz, acetone-d₆): 98.18 (d, J_RhP= 149.4 Hz). H NMR

(400 MHz, acetone-d₆): 1.42 (d, 18H, J_PH= 14.8 Hz, (CH₃)₃CP),

3

1.60 (t, 6H, J_HH= 7.1 Hz, CH₃CH₂N), 3.10−3.19 (m, 2H,

2

CH₃CH₂N), 3.31−3.40 (m, 2H, CH₃CH₂N), 4.07 (d, J_PH= 9.6 Hz,

2H, CH₂P), 4.57 (br s, 2H, Py-CH₂N), 7.59 (d, 1H, ³J_HH= 7.9 Hz, Py-

H), 6.27 (d, 1H, ³J_HH= 7.9 Hz, Py-H), 8.05 (dt, J = 0.9, ³J_HH= 7.9 Hz,

2H, Py-H). ¹³C{¹H} NMR (101 MHz, acetone-d₆): 13.29 (s,

[(PNN*)Rh(CO)] (18). Method A: A benzene solution (7 mL) of

[(PNN*)RhN₂] (5) (15 mg, 0.033 mmol) in a Schlenk tube was

cooled to −196 °C, and the nitrogen atmosphere was replaced by CO.

The reaction mixture was slowly warmed to room temperature, and

the solution color changed from dark red to red (minor change). The

solvent was removed under vacuum to give complex 18 as a red solid

in quantitative yield. Method B: To a THF (3 mL) suspension of

[(PNN)Rh(CO)][BF₄] (20) (21.0 mg, 0.04 mmol) was added a THF

2

1

CH₃CH₂N), 28.90 (d, J_CP= 4.3 Hz, (CH₃)₃CP), 36.09 (d, J_CP

=

1

2

23.2 Hz, CH₂P), 36.30 (dd, J_CP= 21.8 Hz, J_CRh= 1.8 Hz,

(CH₃)₃CP), 56.84 (br d, J = 1.9 Hz, CH₃CH₂N), 54.68 (br d, J = 1.4

Hz, Py-CH₂N), 120.61 (s, Py-CH), 122.58 (d, J_CP= 10.7 Hz, Py-

3

CH), 141.39 (s, Py-CH), 162.98 (br d, J = 1.9 Hz, Py-C), 163.26−

1

2

163.34 (m, Py-C), 193.15 (dd, J_RhC= 73.7 Hz, J_CP= 16.8 Hz, CO).

IR(ν_CO) = 1965.8 cm⁻¹. Anal. for C₂₀H₃₅BF₄N₂OPRh: Calcd C, 44.47;

H, 6.53. Found: C, 44.62; H, 6.61.

t

(3 mL) solution of BuOK (4.5 mg, 0.04 mmol), and the reaction

mixture turned to a clear red solution. The solution was stirred at

ambient temperature for 2 h (or until most of the yellow solid

(complex 20) disappeared), and the solvent was removed under

vacuum. The residue was extracted with benzene. The extracts were

combined and ﬁltered through a 0.2 μm Teﬂon ﬁlter, and the solvent

was removed under vacuum, resulting in complex 18 as a red solid in

90% (16.3 mg) yield.

[(ⁱPrPNP)Rh(CO)][BF₄] (21). Complex 21 was synthesized in the

same manner as complex 20 from [(ⁱPrPNP)Rh(COE)][BF₄] (8) or

[(ⁱPrPNP)Rh(C₂H₄)][BF₄] (4). When complex 8 was used, further

washing of the obtained solid with pentane (20 mL) was required in

order to remove free COE. Complex 21 was obtained as a yellow solid

in quantitative yield.

³¹P{¹H} NMR (162 MHz, benzene-d₆): 90.88 (d, ¹J_RhP= 156.6 Hz).

Complex 21 dissolves well in acetone and methylene chloride and is

stable in methylene chloride, whereas in acetone-d₆, fast H−D

exchange with the benzylic arms was observed. Because of the H−D

exchange in acetone-d₆, the CH₂−P signal was observed as a very

broad multiplet in the ¹H NMR and was not observed in the

¹³C{¹H}NMR. The ³¹P{¹H} NMR of the complex in acetone-d₆

appears as a doublet of multiplets.

3

¹H NMR (400 MHz, benzene-d₆): 1.16 (t, 6H, J_HH= 7.1 Hz,

CH₃CH₂N), 1.45 (d, 18H, ³J_PH= 13.5 Hz, (CH₃)₃CP), 2.28−3.39 (m,

2H, CH₃CH₂N), 2.40−2.51 (m, 2H, CH₃CH₂N), 2.94 (br s, 2H, Py-

CH₂N), 3.44 (br s, 1H, CHP), 5.14 (d, 1H, ³J_HH= 6.6 Hz, Py-H), 6.27

3

(d, 1H, J_HH= 8.6 Hz, Py-H), 6.39−6.46 (m, 2H, Py-H). ¹³C{¹H}

2

NMR 101 MHz, benzene-d₆): 12.69 (s, CH₃CH₂N), 29.74 (br d, J_CP

³¹P{¹H} NMR (121 MHz, acetone-d₆): 65.93 (d of multiplet, J_RhP

1

= 3.2 Hz, (CH₃)₃CP), 36.50 (d, ¹J_CP= 26.7 Hz, (CH₃)₃CP), 54.85 (s,

1

= 119.4 Hz). ³¹P{¹H} NMR (202 MHz, methylene chloride-d₂): 64.73

CH₃CH₂N), 63.12 (d, J_CP= 56.0 Hz, CHP), 64.11 (s, Py-CH₂N),

1

(d, J_RhP= 119.4 Hz). H NMR (300 MHz, acetone-d₆): 1.23 (dd, 12

3

95.85 (s, Py-CH), 113.43 (d, J_CP= 23.2 Hz, Py-CH), 132.56 (s, Py-

3

H, J_PH= 8.5 Hz, J_HH= 7.0 Hz, (CH₃)₂CH), 1.34 (dd, 12H, J_PH

=

CH), 119.82 (d, ³J_CP= 9.3 Hz, Py-CH), 127.39 (s, Py-CH), 157.66 (br

10.8 Hz, J_HH= 7.0 Hz, (CH₃)₂CH), 2.47−2.60 (m, 4H, in H{³¹P}

3

1

s, Py-C), 168.71−169.04 (m, Py-C), 195.57−196.56 (br d, J_RhC= 57

3

NMR appears as hep. J_HH= 7.0 Hz, (CH₃)₂CH), 4.03−4.11 (br m,

Hz, CO). IR(ν_CO) = 1939.0 cm⁻¹. Anal. for C₂₀H₃₄N₂OPRh: Calcd C,

53.10; H, 7.58. Found: C, 52.64; H, 7.64.

CHD-P), 7.72 (d, 2H, ³J_HH= 7.8 Hz, Py-CH), 8.04 (t, 1H, ³J_HH= 7.8

1

Hz, Py-CH). H NMR (500 MHz, methylene chloride-d₂): 1.19 (dd,

[(ⁱPrPNP*)Rh(CO)] (19). Complex 19 was synthesized in the same

manner as complex 18. Method A: Reaction of [(ⁱPrPNP*)Rh(C₂H₄)]

(7) (15 mg, 0.032 mmol) resulted in quantitative yield of complex 19

as a red solid. Method B: Reaction of [(ⁱPrPNP)Rh(CO)][BF₄] (21)

12H, ³J_PH= 8.5 Hz, ³J_HH= 7.0 Hz, (CH₃)₂CH), 1.30 (dd, 12H, ³J_PH

=

10.5 Hz, J_HH= 7.0 Hz, (CH₃)₂CH), 2.37−2.46 (m, 4H, in H{³¹P}

3

1

3

NMR appears as hep. J_HH= 7.0 Hz, (CH₃)₂CH), 3.76 (vt, 4H, J_PH

=

4.0 Hz, CH₂P), 7.59 (d, 2H, ³J_HH= 7.7 Hz, Py-CH), 7.90 (t, 1H, ³J_HH

= 7.7 Hz, Py-CH). ¹³C{¹H} NMR (101 MHz, acetone-d₆): 18.42 (s,

(CH₃)₂CH), 19.49 (br s, (CH₃)₂CH), 25.73 (m, (CH₃)₂CH), 122.92

(vt, J_PC= 5.6 Hz, Py-CH), 141.62 (s, Py-CH), 165.69 (br s, Py-C),

194.69 (dt, ¹J_RhC= 69.0, ²J_PC= 14.0 Hz, RhCO). ¹³C{¹H} NMR (125

t

with BuOK resulted in complex 19 in quantitative yield.

³¹P{¹H} NMR (202 MHz, benzene-d₆): AB system centered at

1

2

1

61.41 (dd, J_RhP= 123.5 Hz, J_PP= 249.0 Hz) and 58.30 (dd, J_RhP

=

2

1

123.5 Hz, J_PP= 249.0 Hz). H NMR (500 MHz, benzene-d₆): 0.81

3

(dd, 6H, J_PH= 13.5 Hz, J_HH= 7.0 Hz, (CH₃)₂CH), 1.00 (dd, 6H,

MHz, methylene chloride-d₂): 18.33 (s, (CH₃)₂CH), 19.33 (vt, J_PC

=

³J_PH= 16.2 Hz, ³J_HH= 7.1 Hz, (CH₃)₂CH), 1.22 (dd, 6H, ³J_PH= 14.0

2

2.6 Hz (CH₃)₂CH), 25.56 (d vt, J_RhC= 1.7 Hz, J_PC= 13.1 Hz,

(CH₃)₂CH), 35.69 (vt, J_PC= 9.8 Hz, CH₂P), 122.50 (vt, J_PC= 5.6 Hz,

Py-CH), 141.11 (s, Py-CH), 164.50 (d vt, ²J_RhC= 1.6 Hz, J_PC= 5.7 Hz,

Py-C), 193.40 (dt, ¹J_RhC= 69.0, ²J_PC= 14.0 Hz, CO). IR(ν_CO) = 1976

cm⁻¹. Anal. for C₂₀H₃₅BF₄NOP₂Rh: Calcd C, 43.11; H, 6.33. Found:

C, 43.98; H, 6.53.

3

Hz, J_HH= 6.8 Hz, (CH₃)₂CH), 1.35 (dd, 6H, J_PH= 16.3 Hz, J_HH

=

7.0 Hz, (CH₃)₂CH), 1.60 (m, 2H, in H{³¹P} NMR appears as hep.

³J_HH= 7.0 Hz, (CH₃)₂CH), 2.06 (d hep., 2H, in ¹H{³¹P} NMR

appears as hep. ³J_HH= 7.0 Hz, J_PH= 2.6 Hz, (CH₃)₂CH), 2.53 (d, 2H,

²J_PH= 9.5 Hz, CH₂P), 3.45 (d, 1H, ²J_PH= 4.4 Hz, CHP), 5.35 (d, 1H,

³J_HH= 6.0 Hz, Py-CH), 6.39−6.45 (m, 2H, Py-CH). ¹³C{¹H} NMR

(125 MHz, benzene-d₆): 18.10 (s, (CH₃)₂CH), 18.28 (s, (CH₃)₂CH),

1

[(ⁱPrPNP*)Rh(PEt₃)] (22). To a suspension of [(ⁱPrPNP)Rh-

(COE)][BF₄] 8 (22.5 mg, 0.035 mmol) in THF (3 mL) was added

a drop of PEt₃(about 15 mg, 0.13 mmol), and the reaction was stirred

at ambient temperature for 30 min, during which a clear yellow

solution was obtained. Pentane (17 mL) was added, and a yellow

2

19.27 (d, J_PC= 5.5 Hz, (CH₃)₂CH), 19.99 (d, J_PC= 5.6 Hz,

2

1

(CH₃)₂CH), 25.02 (d vt, J_RhC

(CH₃)₂CH), 26.46 (d vt, J_RhC

=

³J_PC= 2.1 Hz, J_PC= 21.3 Hz,

³J_PC= 2.2 Hz, J_PC= 29.3 Hz,

2

1

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Article

precipitate was obtained, which was separated by decantation and

washed with 20 mL of pentane. The yellow solid was dried under

vacuum to give the complex [(ⁱPrPNP)Rh(PEt₃)][BF₄] (23) in 94%

yield. To a THF solution (3 mL) of 23 (21.1 mg, 0.033 mmol) was

added ^tBuOK (3.7 mg, 0.033 mmol) in THF (3 mL), and the solution

color changed immediately from yellow to red. The reaction nixture

was stirred at ambient temperature for 30 min, after which the solvent

was removed under vacuum. The residue was extracted with benzene.

The extracts were combined and ﬁltered through a (0.2 μm) Teﬂon

ﬁlter, and the solvent was removed under vacuum, resulting in

complex 22 as a red solid in 91% (16.9 mg) yield.

9.7 Hz, anil-CH), 6.10 (br t, 1H, ³J_HH= 7.0 Hz, Py-H), 7.18 (br d, ³J_HH

3

= 9.8 Hz, anil-CH), 7.25 (br d, J_HH= 9.9 Hz, anil-CH), 7.60 (br d,

³J_HH= 9.7 Hz, anil-CH). ¹³C{¹H} NMR (101 MHz, THF-d₈): 11.28

(s, CH₃CH₂N), 30.62 (d, ²J_CP= 4.4 Hz, (CH₃)₃CP), 35.88 (dd, ¹J_CP

=

2

18.1 Hz, J_CRh= 1.7 Hz, (CH₃)₃CP), 52.78 (br s, CH₃CH₂N), 63.54

1

(d, J_CP= 55.0 Hz, CHP), 64.89 (s, Py-CH₂N), 94.12 (s, Py-CH),

3

109.18 (d, J_CP= 18.0 Hz, Py-CH), 120.43 (s, anil-CH), 122.62 (s,

anil-CH), 123.46 (s, anil-CH), 126.29 (s, anil-CH), 128.06 (s, anil-C),

128.90 (s, Py-CH), 158.09 (br d, J = 1.2 Hz, C), 167.70 (s, C), 169.53

(m, Py-C). Acceptable elemental analysis results for 24 could not be

obtained. The NMR spectrum of 24 appears in the Supporting

Information.

³¹P{¹H} NMR (202 MHz, benzene-d₆): ABX system centered at

50.18 (ddd, 1P, ¹J_RhP= 136.2 Hz, ²J_PPtrans= 269.7 Hz, ²J_PPcis= 37.7 Hz)

and 43.95 (ddd, 1P, ¹J_RhP= 135.8 Hz, ²J_PPtrans= 269.7 Hz, ²J_PPcis= 40.2

Hz), 28.68 (br dt, 1P, ¹J_RhP= 155.9 Hz, ²J_PPcis= 39 Hz). ¹H NMR (500

[(ⁱPrPNP*)Rh(p-NO₂−NHC₆H₄)][K] (25). Complex 25 was pre-

pared in the same manner as complex 24 from complex [(ⁱPrPNP)-

Rh(p-NO₂−NHC₆H₄)] (15) (10 mg, 0.017 mmol). According to the

³¹P{¹H} spectrum, complex 15 was fully converted to complex 25.

³¹P{¹H} NMR (202 MHz, THF-d₈): AB system centered at 46.07

3

MHz, benzene-d₆): 0.95 (dd, 3H, J_HH= 6.9 Hz, J_PH= 5.1 Hz,

P(CH₂CH₃)₃), 0.99−1.07 (m, overlapping with an impurity signal,

should give a 6H signal, real intgration gives 14H signal,

1

2

1

(dd, J_RhP= 150.5 Hz, J_PP= 314.2 Hz) and 39.65 (dd, J_RhP= 148.7

3

2

1

P(CH₂CH₃)₃), 1.28 (dd, 6H, J_HH= 6.7 Hz, J_PH= 5.1 Hz,

Hz, J_PP= 314.2 Hz). H NMR (500 MHz, THF-d₈): 1.20−1.29 (m,

3

overlapping with ^tBuOH signal, (CH₃)₂CH), 1.77 (m, 2H,

(CH₃)₂CH), 1.39 (dd, 6H, J_HH= 7.1 Hz, J_PH= 8.3 Hz,

2

3

1

(CH₃)₂CH), 1.53 (quin. 6H, J_PH= J_HH= 7.3 Hz, P(CH₂CH₃)₃),

(CH₃)₂CH), 1.94 (m, 2H, (CH₃)₂CH), 2.73 (d, 2H, J_PH= 8.4 Hz,

1.64 (m, appeaprs as hept. in H{³¹P} NMR, J_HH= 6.9 Hz, 2H,

1

3

CH₂P), 3.08 (d, ¹J_PH= 3.3 Hz, CHP), 5.18 (d, 1H, ³J_HH= 6.5 Hz, Py-

(CH₃)₂CH), 1.95 (m, appeaprs as hept. in H{³¹P} NMR, J_HH= 6.9

Hz, 2H, (CH₃)₂CH), 2.61 (d, 2H, ²J_PH= 9.0 Hz, CH₂P), 3.51 (d, 1H,

²J_PH= 3.2 Hz, CHP), 5.54 (d, 1H, ³J_HH= 6.2 Hz, Py-CH), 6.54 (br d,

1

3

CH), 5.78 (d, 1H, ³J_HH= 8.5 Hz, Py-CH), 5.91 (dd, 1H, J_HH= 2.0, 9.7

3

Hz, anil-CH), 6.08 (br t, 1H, J_HH= 7.5 Hz, Py-CH), 6.98 (dd, 1H,

J_HH= 2.0, 9.9, anil-CH), 7.24 (dd, 1H, J_HH= 2.0, 9.7, anil-CH). The

Rh−NH signal was not detected. ¹³C{¹H} NMR (126 MHz, THF-d₈):

1H, J_HH= 8.6 Hz, Py-CH), 6.60 (m, 1H, Py-CH). ¹³C{¹H} NMR

3

2

18.51 (s, (CH₃)₂CH), 18.72 (s, (CH₃)₂CH), 19.68 (d, J_PC= 7.4 Hz,

(126 MHz, benzene-d₆): 18.23 (s, P(CH₂CH₃)₃), 18.64 (s, P-

2

1

2

(CH₃)₂CH), 20.06 (d, J_PC= 7.6 Hz, (CH₃)₂CH), 25.75 (d, J_PC

=

(CH₂CH₃)₃), 19.50 (d, J_PC= 6.2 Hz, (CH₃)₂CH), 21.04 (d, J_PC

=

1

7.0 Hz, (CH₃)₂CH), 21.96 (br d, ¹J_PC= 23.7 Hz, P(CH₂CH₃)₃), 26.29

14.9 Hz, (CH₃)₂CH), 26.67 (d, J_PC= 21.33 Hz, (CH₃)₂CH), 36.15

1

(d, ¹J_PC= 16.6 Hz, (CH₃)₂CH), 28.17 (d, ¹J_PC= 22.7 Hz, (CH₃)₂CH),

(d, J_PC= 17.7 Hz, CH₂P), 59.94 (d, J_PC= 50.6 Hz, CHP), 96.77 (d,

³J_PC= 11.2 Hz, Py-CH), 110.65 (d, ³J_PC= 17.9 Hz, Py-CH), 119.50 (s,

anil-CH), 123.24 (s, anil-CH), 123.46 (s, anil-CH), 126.20 (s, anil-

1

37.27 (dd, J = 3.5 Hz, J_PC= 19.8 Hz, CH₂P), 61.93 (dd, J = 2.4 Hz,

¹J_PC= 51.8 Hz, CHP), 96.55 (d, J_PC= 10.6 Hz, Py-CH), 112.58 (d,

3

³J_PC= 18.1 Hz, Py-CH), 131.56 (br s, Py-CH), 158.35 (br d, J_PC= 7

2

CH), 127.66 (s, anil-C), 129.41 (s, Py-CH), 160.92 (br d, J_PC= 11.4

Hz, Py-C), 172.31 (d m, ²J_PC= 21 Hz, Py-C). Anal. for C₂₅H₄₉NP₃Rh:

Calcd C, 53.67; H, 8.83. Found: C, 53.43; H, 8.93.

Hz, Py-C), 166.9 (br s, Py-C), 169.11 (s, anil-C). Acceptable elemental

analysis results for 25 could not be obtained. A copy of the NMR

spectrum of 25 appears in the Supporting Information.

[(ⁱPrPNP)Rh(PEt₃)][BF₄] (23). The synthesis of complex 23 is

described above, under description of the synthesis of complex 22.

³¹P{¹H} NMR (202 MHz, acetone-d₆): 56.44 (dd, 2P, J_PP= 39.3

2

ASSOCIATED CONTENT

* Supporting Information

■

Hz, ¹J_PRh= 134.9 Hz), 30.04 (dt, 1P, ²J_PP= 39.3 Hz, ¹J_PRh= 155.6 Hz).

S

¹H NMR (500 MHz, acetone-d₆): 1.23 (dd appears as q, 12 H, ³J_PH

=

Crystallographic data (CIF); ﬁgure of X-ray structure of 4; and

ﬁgures of ¹H and ³¹P{¹H} spectra of the complexes 2, 6, 9, 10,

14, 16, 24, and 25. This material is available free of charge via

the Internet at http://pubs.acs.org.

³J_HH= 6.8 Hz, (CH₃)₂CH), 1.19 (dt, 9H, J_HH= 7.5 Hz, J_PH= 15.4

3

Hz, P(CH₂CH₃)₃), 1.34 (dd appears as q, 12H, J_PH₃= 8.5 Hz, J_HH

=

3

7.2 Hz, (CH₃)₂CH), 1.81 (br quin., 6H, J_PH= J_HH= 7.5 Hz, in

¹H{³¹P} appears as a dq with J_RhH= 0.9 Hz, P(CH₂CH₃)₃), 2.33 (m,

3

4H, in ¹H{³¹P} NMR appears as hep. ³J_HH= 7.0 Hz, (CH₃)₂CH), 3.65

AUTHOR INFORMATION

Corresponding Author

*E-mail: david.milstein@weizmann.ac.il.

3

■

(vt, 4H, J_PH= 3.7 Hz, P-CH₂), 7.57 (d, 2H, J_HH= 7.7 Hz, Py-CH),

7.90 (t, 1H, J_HH= 7.7 Hz, Py-CH). ¹³C{¹H} NMR (125 MHz,

3

acetone-d₆): 9.63 (s, P(CH₂CH₃)₃), 18.51 (s, (CH₃)₂CH), 19.53 (vt,

J_PC= 2.6 Hz, (CH₃)₂CH), 21.69 (d of m, ¹J_PC= 28 Hz, P(CH₂CH₃)₃),

26.52 (d vt, ³J_PCor ²J_RhC= 2.1 Hz, J_PC= 10.9 Hz (CH₃)₂CH), 36.89 (d

vt, J_PC= 9.8 Hz, ³J_PCor ²J_RhC= 2.4 Hz, CH₂P), 121.50 (d vt, J_PC= 4.5

Notes

The authors declare no competing ﬁnancial interest.

3

Hz, J_RhC= 1.1 Hz, Py-CH), 139.02 (s, Py-CH), 163.11 (vt, J_PC= 4.3

Biographies

Hz, Py-C). Anal. for C₂₅H₅₀BF₄NP₃Rh: Calcd C, 46.39; H, 7.79.

David Milstein received his Ph.D. degree at the Hebrew University of

Jerusalem in 1976 with Prof. Blum. He carried out postdoctoral studies

at Colorado State University, where together with his advisor, John

Stille, he discovered the Stille reaction. In 1979 he joined the DuPont

Company in Wilmington, DE, where he became a Group Leader in the

homogeneous catalysis area. In 1987 he accepted a professorial

appointment at the Weizmann Institute of Science, where he was Head

of the Department of Organic Chemistry in 1996−2005. In 2000 he

became Head of the Kimmel Center for Molecular Design. He has

been the Israel Matz Professor of Organic Chemistry since 1996. His

research interests focus on the development of fundamental

organometallic chemistry and its application to the design of new

sustainable processes catalyzed by transition-metal complexes. He has

served on several editorial boards, and he is a member of the German

National Academy of Sciences. Awards received include the Kolthoﬀ

Found: C, 46.78; H, 7.74.

[(PNN*)Rh(p-NO₂-NHC₆H₄)][K] (24). To a THF solution (5 mL)

of [(PNN)Rh(p-NO₂-NHC₆H₄)] 13 (10 mg, 0.018 mmol) was added

^tBuOK (2.0 mg, 0.018 mmol) in THF (5 mL), and the reaction color

turned immediately from deep red to purple. According to the

³¹P{¹H} spectrum, complex 13 was fully converted to complex 24.

Since complex 24 was not stable under vacuum, it was fully

charcterized in situ by NMR. For charcterization, complex 13 was

t

placed in an NMR tube and dissolved in a solution of BuOK (2 mg,

0.018 mmol) in 0.5 mL of THF-d₈and the NMR tube was shaken a

few times.

³¹P{¹H} NMR (121 MHz, THF-d₈): 80.09 (d, J_RhP= 206.9 Hz).

1

¹H NMR (500 MHz, THF-d₈): 1.21 (d, J_PH= 11.7 Hz, (CH₃)₃CP),

3

1.32 (t, ³J_HH= 7.1 Hz, CH₃CH₂N), 2.66−2.83 (br m, 4H, CH₃CH₂N),

3.10 (br s, 1H, CHP), 3.46 (br s, 2H, Py-CH₂N), 5.00 (d, 1H, ³J_HH

=

3

6.5 Hz, Py-H), 5.68 (d, 1H, J_HH= 8.7 Hz, Py-H), 5.89 (br d, J_HH

4098

dx.doi.org/10.1021/om300248r | Organometallics 2012, 31, 4083−4101

Organometallics

Article

Chem. Soc. 2011, 133, 1682. (g) Balaraman, E.; Gunanathan, C.;

Zhang, J.; Shimon, L. J. W.; Milstein, D. Nat. Chem. 2011, 3, 609.

(h) Zhang, J.; Balaraman, E.; Leitus, G.; Milstein, D. Organometallics

2011, 30, 5716. (i) Gnanaprakasam, B.; Balaraman, E.; Gunanathan,

C.; Milstein, D. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 1755.

(3) For bipyridyl-based PNN complexes, see refs 2g and 2i and also:

(a) Balaraman, E.; Gnanaprakasam, B.; Shimon, L. J. W.; Milstein, D. J.

Am. Chem. Soc. 2010, 132, 16756. (b) Balaraman, E.; Ben-David, Y.;

Milstein, D. Angew. Chem., Int. Ed. 2011, 50, 11702. (c) Balaraman, E.;

Fogler, E.; Milstein, D. Chem. Commun. 2012, 48, 1111.

(4) (a) Zhang, J.; Gandelman, M.; Shimon, L. J. W.; Rozenberg, H.;

Milstein, D. Organometallics 2004, 23, 4026. (b) Gnanaprakasam, B.;

Zhang, J.; Milstein, D. Angew. Chem., Int. Ed. 2010, 49, 1468.

(5) (a) Gunanathan, C.; Gnanaprakasam, B.; Iron, M. A.; Shimon, L.

J. W.; Milstein, D. J. Am. Chem. Soc. 2010, 132, 14763. (b) Gunanathan,

C.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2009, 131, 3146.

(c) Gunanathan, C.; Milstein, D. Angew. Chem., Int. Ed. 2008, 47,

8661.

(6) (a) Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew.

Chem., Int. Ed. 2011, 50, 2120. (b) Langer, R.; Diskin-Posner, Y.;

Leitus, G.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D. Angew. Chem.,

Int. Ed. 2011, 50, 9948. (c) Langer, R.; Iron, M. A.; Konstantinovski,

L.; Diskin-Posner, Y.; Leitus, G.; Ben-David, Y.; Milstein, D. Chem.

Eur. J. 2012. DOI: 10.1002/chem.201200159.

(7) Fogler, E.; Balaraman, E.; Ben-David, Y.; Leitus, G.; Shimon, L. J.

W.; Milstein, D. Organometallics 2011, 30, 3826.

(8) Zeng, H.; Guan, Z. J. Am. Chem. Soc. 2011, 133, 1159.

(9) Gnanaprakasam, B.; Balaraman, E.; Ben-David, Y.; Milstein, D.

Angew. Chem., Int. Ed. 2011, 50, 12240.

Prize, the Israel Chemical Society Prize, the ACS Award in

Organometallic Chemistry, the RSC Sir Geoﬀrey Wilkinson Award,

and the Meitner-Humboldt Award; in 2012 he received the Israel Prize

(Israel’s highest honor).

Moran Feller received her M.S. degree for her work with Prof. Yoel

Kashman in the ﬁeld of natural product isolation and structural

elucidation. In 2004 Moran joined the Milstein group, where she

investigated the synthesis and reactivity of phosphino-pyridine pincer

complexes of late transition metals. After graduating with a Ph.D.

degree in 2008, Moran remained in the group as a postdoctoral fellow

and in 2011 became an assistant staﬀ scientist. Moran’s research

focuses on the activation of N−H and O−H bonds by phosphino-

pyridine pincer complexes of late transition metals, primarily

employing metal−ligand cooperation.

Yael Diskin-Posner did her M.Sc. degree with Prof. Uri Shmueli from

the Tel-Aviv University. After a few years in the biotechnology

industry, she returned to do a Ph.D. in crystallography at the Tel-Aviv

University with Prof. Israel Goldberg, which she ﬁnished in 2003. She

carried out her postdoctoral studies at the Weizmann Institute under

the supervision of Prof. Zippora Shakked, working on p53-DNA

binding domain structures. Since 2007 she has been a staﬀ scientist in

the chemical research support department in the Weizmann Institute

of Science. She received the Levine-Jortner prize from the Israel

Chemical Society in 2002.

Linda Shimon received her Ph.D. degree at the Weizmann Institute in

1988 in the department of structural chemistry. She carried out her

postdoctoral studies at Harvard University, in the group of Prof.

Stephen Harrison, where she worked on the crystallographic studies of

protein/DNA complexes. In 1993 she returned to the Weizmann

Institute to the X-ray crystallography laboratory. Since 1997 she has

headed the X-ray laboratory and the Kimmelman Laboratory for

Macromolecular Crystallography. She has received several awards,

including the Schmidt Prize and the Maxine Singer Prize from the

Weizmann Institute, and serves on the referee board for Acta

Crystallographica.

(10) Hunsicker, D. M.; Dauphinais, B. C.; McIlrath, S. P.; Robertson,

N. J. Macromol. Rapid Commun. 2012, 33, 232.

(11) (a) Zeng, G.; Li, S. Inorg. Chem. 2011, 50, 10572. (b) Li, H.;

Wang, X.; Huang, F.; Lu, G.; Jiang, J.; Wang, Z.-X. Organometallics

2011, 30, 5233. (c) Sandhya, K. S.; Suresh, C. H. Organometallics

2011, 30, 3888. (d) Cantillo, D. Eur. J. Inorg. Chem. 2011, 19, 3008.

(e) Yang, X. Inorg. Chem. 2011, 50, 12836.

(12) (a) Rigoli, J. W.; Moyer, S. A.; Pearce, S. D.; Schomaker, J. M.

Org. Biomol. Chem. 2012, 10, 1746. (b) He, L.-P.; Chen, T.; Xue, D.-

X.; Eddaoudi, M.; Huang, K.-W. J. Organomet. Chem. 2012, 700, 202.

(c) Huﬀ, C. A.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 18122.

(d) Sun, Y.; Koehler, C.; Tan, R.; Annibale, V. T.; Song, D. Chem.

Commun. 2011, 47, 8349. (e) del Pozo, C.; Iglesias, M.; Sanchez, F.

Organometallics 2011, 30, 2180. (f) Staubitz, A.; Sloan, M. E.;

Robertson, A. P. M.; Friedrich, A.; Schneider, S.; Gates, P. J.; Schmedt

auf der Gunne, J.; Manners, I. J. Am. Chem. Soc. 2010, 132, 13332.

(g) van der Vlugt, J. I.; Lutz, M.; Pidko, E. A.; Vogt, D.; Spek, A. L.

Dalton Trans. 2009, 6, 1016. (h) Tanaka, R.; Yamashita, M.; Nozaki, K.

J. Am. Chem. Soc. 2009, 131, 14168.

(13) (a) Ben Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.

Chem. Soc. 2006, 128, 15390. (b) Schwartsburd, L.; Iron, M. A.;

Konstantinovski, L.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J. W.;

Milstein, D. Organometallics 2010, 29, 3817.

(14) (a) Iron, M. A.; Ben-Ari, E.; Cohen, R.; Milstein, D. Dalton

Trans. 2009, 9433. (b) Zeng, G.; Guo, Y.; Li, S. Inorg. Chem. 2009, 48,

10257.

Eyal Ben-Ari received his B.Sc. in chemistry in 1999 at Tel-Aviv

University. Between the years 2000 and 2007 he conducted his M.Sc.

and Ph.D. research with Prof. David Milstein, at the Weizmann

Institute of Science. His research dealt with cleavage of strong C−H

bonds by iridium and rhodium PNP pincer complexes. Currently he is

a team leader at Agan Aroma and Fine Chemicals Co.

ACKNOWLEDGMENTS

■

This research was supported by the European Research Council

under the FP7 framework, (ERC No. 246837), by the Israel

Science Foundation, by the MINERVA Foundation, and by the

Kimmel Center for Molecular Design. D.M. holds the Israel

Matz Professorial Chair of Organic Chemistry.

(15) Schwartsburd, L.; Iron, M. A.; Konstantinovski, L.; Ben-Ari, E.;

Milstein, D. Organometallics 2011, 30, 2721.

(16) Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstantinovski, L.;

Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein, D. Science 2009,

324, 74.

(17) (a) Lawrence, S. A. Amines: Synthesis, Properties and Applications;

Cambridge University Press: Cambridge, U.K., 2004. (b) Roundhill, D.

M. Chem. Rev. 1992, 92, 1.

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Angew. Chem., Int. Ed. 2011, 50, 86. (b) van der Vlugt, J. I. Chem. Soc.

Rev. 2010, 39, 2302. (c) Enthaler, S. ChemSusChem 2010, 3, 1024.

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(39) Complex 1 reacts slowly with methylene chloride at ambient

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activation product (δ³¹P{¹H} NMR (DCM-d₂): 65.51 (d, ¹J_RhP= 127.1

Hz)).

(40) See the Supporting Information.

(41) We have observed previously that a weak interaction of the

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1

(46) The ethylene signals in the H and ¹³C{¹H} NMR spectra are

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Information.

(48) (a)

The CC bond length in free gaseous ethylene is

estimated to be 1.3305(10) Å. Craig, N. C.; Groner, P.; McKean, D.

C. J. Phys. Chem. A 2006, 110, 7461. (b) The CC bond length

from X-ray data is 1.313 Å. Van Nes, G. J. H.; Vos, A. Acta Crystallogr.,

Sect. B 1979, 35, 2593.

(49) Feller, M.; Iron, A. M.; Shimon, L. J. W.; Diskin-Posner, Y.;

Leitus, G.; Milstein, D. J. Am. Chem. Soc. 2008, 130, 14374.

(50) The ¹³C{¹H} NMR of a mixture of complexes 5 and 5a gives

rise to two signals at 63.04 (d, J = 1.8 Hz) and 63.47 (d, J = 1.8 Hz)

assigned to the Py−CH₂−N functionality. See the Experimental

Section.

(51) (a) Hanson, S. K.; Heinekey, D. M.; Goldberg, K. I. Angew.

Chem., Int. Ed. 2007, 46, 4736. (b) Hanson, S. K.; Heinekey, D. M.;

Goldberg, K. I. Organometallics 2008, 27, 1454.

(52) Complex 5 stands for the mixture of the monomer and the

dimer complexes 5 and 5a, respectively.

(53) (a) Tejel, C.; Ciriano, M. A.; Bordonaba, M.; Lop

Lahoz, F. J.; Oro, L. A. Inorg. Chem. 2002, 41, 2348. (b) Tejel, C.;

Ciriano, M. A.; Bordonaba, M.; Lopez, J. A.; Lahoz, F. J.; Oro, L. A.

́

ez, J. A.;

́

Chem.Eur. J. 2002, 8, 3128. (c) Fandos, R.; Martínez-Ripoll, M.;

Otero, A.; Ruiz, M. J.; Rodríguez, A.; Terreros, P. Organometallics

1998, 17, 1465.

(54) For a concise illustration of the SST technique, see: (a) Jarek,

R. L.; Flesher, R. J.; Shin, S. K. J. Chem. Educ. 1997, 74, 978. For

previous examples of the use of spin saturation transfer in studies of

chemical exchange, see: (b) Portnoy, M.; Milstein, D. Organometallics

1993, 12, 1665. (c) Vigalok, A.; Kraatz, H.-B.; Konstantinovski, L.;

Milstein, D. Chem.Eur. J. 1997, 3, 253. (d) Rybtchinski, B.;

Konstantinovski, L.; Shimon, L. J. W.; Vigalok, A.; Milstein, D.

Chem.Eur. J. 2000, 6, 3287. (e) Montag, M.; Schwartsburd, L.;

4100

dx.doi.org/10.1021/om300248r | Organometallics 2012, 31, 4083−4101

Organometallics

Article

Cohen, R.; Leitus, G.; Ben-David, Y.; Martin, J. M. L.; Milstein, D.

Angew. Chem., Int. Ed. 2007, 46, 1901.

(55) Upon saturation of signal a, only the adjacent signal was aﬀected

due to the proximity to the saturated signal and not as a result of

chemical exchange.

(56) All reactions were performed under the same conditions: 0.011

mmol of the complex and the aniline in 0.5 mL of THF were placed in

a J. Young NMR tube, and the reactions were followed by ³¹P{¹H}

NMR at ambient temperature or 60 °C.

(57) The reaction of complexes 5−7 and 9 with an equivalent of

aniline may be sluggish, due to lower stability of the anilide complexes

10 and 14, as compared with the more electron-poor anilide

complexes. Complexes 10 and 14 can be obtained selectively by

addition of an excess of aniline, or by deprotonation of complexes 16

and 17, respectively.

(58) In the case of the reaction of complexes 9−15 and

triethylphosphine, after 4 days at ambient temperature, traces of new

unidentiﬁed complexes were obtained according to ³¹P{¹H} NMR.

(59) The ³¹P{¹H} NMR spectrum of the reaction mixtures is similar

to the spectrum that was obtained by addition of an excess of

triethylphosphine to complex 5. According to the signal pattern of the

spectrum, it is likely that the reaction mixture includes complexes with

two and three PEt₃ligands.

(60) Complexes 10, 13, 14, and 15 were also reacted with an excess

of ethylene. In the case of complexes 10 and 13, the reaction with

ethylene was found to be nonselective and led to partial

decomposition of the complexes and to the formation of unidentiﬁed

precipitate. The reaction of complex 14 with ethylene led to the

formation of free aniline and complex 7. The reaction of complex 15

with ethylene resulted in the formation of a new major complex,

according to the ³¹P{¹H} NMR of the reaction mixture, which gives

rise to a signal at 42.84 ppm (d, ¹J_RhP= 100.4 Hz, 90% by integration).

We assume that the product is an ethylene adduct complex of 15;

however, due to its ﬂuxionality, we could not detect the ethylene

ligand. The reaction of complex 15 and ethylene was found to be

reversible, and upon heating the reaction mixture to 60 °C, only

complex 15 was obtained.

(61) Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001,

66, 7931.

(62) The fact that aniline N−H activation was faster with the COE

complex 9 than with the ethylene complex 7 is probably due to the

lack of stability of the anilide complexes 10 and 14 as compared with

the less electron-rich p-nitroanilide complexes 13 and 15. Thus, the

equilibrium described in pathway A is further shifted towards the

anilide complexes in the case of the more loosely bound COE complex

9 than in the case of the ethylene complex 7.

(63) The COE ligand in complex 9 is weakly bound; thus, if complex

9 in the presence of aniline is in an equilibrium of coordination/

dissociation of COE/aniline, an excess of COE will push the

equilibrium toward the COE-bound complex, which is the reactive

species in the associative mechanism. However, such an equilibrium

was not observable.

(64) (a) Vuzman, D.; Poverenov, E.; Shimon, L. J. W.; Diskin-

Posner, Y.; Milstein, D. Organometallics 2008, 27, 2627. (b) Feller, M.;

Ben-Ari, E.; Iron, M. A.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J.

W.; Konstantinovski, L.; Milstein, D. Inorg. Chem. 2010, 49, 1615 and

references therein.

(65) Jansen, A.; Pitter, S. Monatsh. Chem. 1999, 130, 783.

(66) van der Ent, A.; Onderdelinden, A. L. Inorg. Synth. 1990, 28, 90.

(67) Cramer, R. Inorg. Synth. 1990, 28, 86.

NOTE ADDED AFTER ASAP PUBLICATION

■

In the version of this paper published on May 18, 2012, some

biographical information was inadvertently left out. The version

that appears as of May 24, 2012, contains this information.

4101

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N-H activation by Rh(I) via metal-ligand cooperation

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