An Unsymmetric Imino-Phosphanamidinate Ligand and its Y(III) Complex: Synthesis, Characterization, and Catalytic Hydroboration of Carbonyl Compounds

Srinivas Anga, Joydev Acharya, and Vadapalli Chandrasekhar*

Article

An Unsymmetric Imino−Phosphanamidinate Ligand and its Y(III)

Complex: Synthesis, Characterization, and Catalytic Hydroboration

of Carbonyl Compounds

Cite This: https://dx.doi.org/10.1021/acs.joc.0c02383

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sı Supporting Information

ABSTRACT: An imino-phosphanamide ligand, [NHIⁱ^P^r²^M^e²P(Ph)NH-2,6- Pr C H ]

(

LH), containing two diﬀerent N-substituents was prepared by the direct reaction of

the lithium salt of N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropyl-

phenyl phosphanamine, PhP(Cl)NH-2,6- Pr -C H . Reaction of LH with Y(N-

(

SiMe ) ) aﬀorded the heteroleptic complex, [{L}Y(N(SiMe ) ) ] (1), by

3 2 3 3 2 2

elimination of HN(SiMe ) . Compound 1 was characterized by multinuclear NMR

and X-ray crystallography. In the complex, the Y(III) center was found to be

tetracoordinate in a distorted tetrahedral geometry. The ligand, imino-phosphanami-

−

dinate, [L] , functions in a chelating manner, and its coordination to Y(III) results in

a distorted 4-membered YPN ring. As a proof of principle of its activity, 1 was used as

a precatalyst for the hydroboration of various aldehydes and ketones using HBpin as

the hydrogen source. The hydroboration reaction was rapid and clean even with low

catalyst loadings (0.01−0.1 mol %). In addition, a very good functional group

tolerance was observed in these reactions.

INTRODUCTION

■

A principal strategy in inorganic and organometallic chemistry

is the design of speciﬁc ligand systems to prepare metal

complexes of particular nuclearity, coordination number,

geometry, and reactivity. The primary function of these

ligands is to provide stereoelectronic modulation that allows

harnessing of speciﬁc properties from the metal complex, for

example, catalytic speciﬁcity and eﬃciency. Ligands such as

phosphines and more recently N-heterocyclic carbenes and

their larger extended family have been playing a very crucial

role in organometallic complexes and catalysis. Similarly,

cyclopentadienyl ligands have been ubiquitous in their

applications in organometallic complexes and catalysis by

Figure 1. Diﬀerent types of N-ligands (I−IV) and diﬀerent types of

coordination modes of amidinate and guanidinate ligands (where R =

alkyl or aryl or NR ) (A−C).

such complexes. Simultaneously, there have been eﬀorts in

developing new families of ligands that can increase the

repertoire of the organometallic complexes. Thus, there have

been eﬀorts on nitrogen-based electron rich ligands such as

possibility of substituent variation in their backbone as well as

6,9

amidinate, guanidinate, iminophosphonamide, and bora-

on the nitrogen atoms, thus allowing a ﬁne-tuning of their

amidinate ligands (Figure 1). Some of these have already

5,6,9

steric and electronic properties.

These properties of the

found wide applications in the formation of a range of metal

complexes including in the use for stabilization of unusual

ligands allow them to display versatile coordination behavior.

oxidation states of main-group elements (Figure S82 ). Among

Special Issue: The New Golden Age of Organo-

phosphorus Chemistry

these ligands, the amidinate and guanidinate ligands have

,6,9

received signiﬁcant attention by many research groups.

These ligands are considered as pseudoallyl ligands and can

Received: October 8, 2020

commonly act as bidentate (η ) or bridging monodentate

(

μ−η :η ) or four-electron donors through metal−nitrogen σ-

bonds (Figure 1). In addition, these ligands have the

XXXX American Chemical Society

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Scheme 1. Diﬀerent Types of NPN Ligands and Their Synthesis (eqs 1 and 2). Our Synthetic Approach for the New NPN

Ligand (eq 3)

The versatility of the amidinate and the guanidinate ligands

has spurred interest in modifying these ligands by the

replacement of the central carbon with another main-group

RESULTS AND DISCUSSION

Synthesis of the LH and the Y(III) Complex 1. The

ligand LH was readily synthesized in good yield by a salt

elimination involving a reaction between PhP(Cl)NHDipp

(Dipp = 2,6-diisopropylphenyl) with the lithium salt of N-

■

element such as boron or phosphorus. While a large number

of P−N−P, P−C−P, and N−P−N (monoanionic with

P(V)) ligands are well-known, N−P−N (monoanionic with

P(III)) ligands that can be considered as equivalent to the

amidinate N−C−N ligands discussed above are sparse. The

known synthetic strategies for preparing these ligands are

shown in Scheme 1. While eq 1 aﬀords a ligand that would be

dianionic where the oxidation of state of phosphorus would be

heterocyclic imine (NHI) in Et O (see the Experimental

Section) (Scheme 2). This compound was fully characterized

Scheme 2. Synthesis of the LH

3, eq 2 would aﬀord a monoanionic ligand, but the oxidation

state of phosphorus would be +5.

We wished to develop a ligand where the phosphorus center

would be in an oxidation state of +3 and would be a potential

amidinate ligand bearing a unit negative charge. In search of

such a system, we developed an N-heterocyclic imine (NHI)-

by multinuclear NMR spectroscopy. In the H NMR spectrum,

iPr2Me2

LH displayed two sets of doublets for the methyl groups, two

septets for the isopropyl groups and one singlet for the

backbone methyl groups. The characteristic signal for the

amine NH appears at δ = 4.69 ppm as a doublet due to

coupling with the phosphorus nucleus. In the P{ H} NMR

spectrum, the ligand displays a sharp singlet at 76.3 ppm which

is in a range similar to that of the family of ligands that contain

based imino-phosphanamide ligand, [NHI

P(Ph)NH-

,6- PrC H ], LH (Scheme 1, eq 3). Upon metalation, the

6 3

ligand is expected to lose a proton and bind in a monoanionic

fashion similar to that of the amidinate ligands. Apart from

being an unsymmetrical ligand where the two nitrogenous

substituents on phosphorus are completely diﬀerent, it is to be

noted that this system is amenable to stereoelectronic

modulation through substitution at the phosphorus as well as

the NPN motifs DippN(H)P(Ph)N( Bu)C(n-Bu)N Bu

(

74.1 ppm), DippN(H)P(Ph)N(Cy)C( Bu)NCy (69.1

the nitrogen centers. LH has two possible coordination sites,

ppm), and DippN(H)P(Ph)N(Cy)C(n-Bu)NCy (72.3

the primary coordination sites being the two nitrogen centers

ppm) reported in the literature (where Dipp = 2,6-

(

in a chelating fashion) while a potential additional

diisopropylphenyl; n-Bu = n-Butyl; Bu = tert-Butyl; Cy =

Cyclohexyl).

coordination site is the neutral phosphorus(III) site. To

demonstrate the coordination capability of this ligand we chose

complexation with Y(III) as a representative example,

particularly since such complexes can be utilized in catalytic

LH, which contains the reactive NH, reacts readily with

Y(N(SiMe ) ) (in toluene at 60 °C) to aﬀord the

corresponding heteroleptic Y(III) complex 1 in 76% yield

Scheme 3). The reaction proceeds by the elimination of

HN(SiMe ) . In the process, the ligand assumes an anionic

amidinate character by the loss of a proton. Compound 1 was

fully characterized by multinuclear NMR as well as single-

crystal X-ray diﬀraction analysis. In its H NMR spectrum, 1

revealed the presence of two distinct signals for two

−N(SiMe ) groups due to their diﬀerent chemical surround-

2 3

(

reactions. Herein, we report the synthesis and character-

ization of LH and its metalation behavior with Y(III) aﬀording

the complex [{L}Y(N(SiMe ) ) ], 1 (see Scheme 3). In

2 2

addition to the complete characterization of 1 we also report

its utility, as a proof of principle, for the hydroboration of a

wide range of ketones and aldehydes.

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Scheme 3. Synthesis of Complex 1

Figure 2. (a) Molecular structure of the complex 1; (b) topology around the Y(III) considering immediate coordination; (c) representation of the

perpendicular planes containing the coordinating N atoms, the central Y(III) ion and P(III) center of the ligand. (All hydrogen atoms (except C35

and C41 methyl hydrogens) were omitted for clarity.)

ings within the complex. Similarly, all the isopropyl groups are

also distinguished because of the diﬀerence in the nature of the

substituents on the phosphorus center (see the Experimental

hydrogen atoms (H35b and H41a) of the −N(SiMe ) groups

(see Table S2 ). This feature is indicative of the Lewis acidity of

the Y(III) center and has been observed in some silylamido

Section). The P{ H} NMR spectrum of 1 reveals a singlet at

03.02 ppm which is considerably deshielded with respect to

rare earth metal complexes. The distorted tetrahedral

geometry around the Y(III) is indicated by the N−Y−N

bond angles which are deviated from the ideal value. The

highest deviation is seen for the N1−Y1−N3 bond angle

(123.82(8)°). However, the N1−Y1−N4 (108.85(8)°) and

N2−Y1−N3 (106.21(8)°) bond angles are almost close to the

ideal value (see Table S2). Further, the molecular structure of

1 reveals that the two planes containing the Y P N motifs are

what was observed for the parent ligand, LH.

X-ray Crystallography. X-ray-quality crystals of 1 were

grown from a saturated solution of n-hexane at −35 °C.

SCXRD study reveals that the complex crystallizes in the

monoclinic system (P2 /c). The neutral complex contains a

four-coordinated Y(III) and the immediate chemical environ-

ment around Y(III) (4N) is generated by the chelating

coordination action of the bidentate mono anionic ligand (L)

and two negatively charged −N(SiMe ) groups (Figure 2a).

nearly orthogonal to each other (72.0°) (Figure 2c).

A close observation of the P1 center of the ligand reveals

that it is trigonal pyramidal (Figure 3), similar to what is found

in phosphine ligands and, therefore, should be amenable to

binding to soft metal centers. This aspect would merit a future

investigation.

Although the coordination geometry around Y(III) can be

described as distorted tetrahedral, an exact geometry

calculation through continuous SHAPE measurement reveals

it to be of the type, vacant trigonal dipyramidal (see Figure 2b

and Table S3 ).

An examination of the Y(III)−N bond lengths reveals the

following. Understandably, the strongest Y(III)−N bond is

associated with N2 [Y1−N2, 2.254(2) Å] in view of the

expected negative charge on this nitrogen as a result of

deprotonation during complex formation. Also, the two Y−N

distances involving the −N(SiMe ) groups are comparable

while being slightly longer than Y1−N2 (see Table S2). On the

other hand, the Y1−N1 bond distance (2.323(2) Å) is the

longest. Notably, the central Y(III) ion is found to be involved

in a weak agostic C−H···M interaction involving the two

Figure 3. Pyramidal nature of the P atom in the complex 1. (Only

selected atoms in 1 are shown for the sake of clarity.)

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It is of interest to compare the coordination action of the

that are sterically encumbered) has been further carried out.

These results are summarized in Table 2.

ligand, L with analogous ligands containing the N−B−N and

8d,17a

N−C−N motifs (Table 1).

It may be seen that the ligands

Benzophenone, cyclohexyl phenyl ketone, isobutyrophe-

none, and acetophenone were reduced rapidly to the respective

boronate esters within 10 min (entries 1−5). The catalyst

showed good functional group tolerance toward −Br, −OMe,

Table 1. Comparison of N−B−N, N−C−N, and N−P−N

Ligands

and −NO groups (entries 6−7) by achieving complete

reduction. At the same time, electronically deactivated

triﬂuoroacetophenone was also readily reduced within a

short period. Note that mono and diacetyl ferrocene were

also tested for the reduction, and the reaction was smooth

(

entries 11 and 12). We further tested the reduction of the

naturally occurring sterically hindered cyclic ketone, camphor,

with the same catalyst loading (entry 13). Further hydro-

boration of 1,4-diacetylbenzene also proceeded eﬃciently.

As can be seen from Table 3 a variety of aldehydes could

also be easily reduced. These include simple benzaldehyde to

those containing electron-withdrawing, electron-donating, or

diﬀerent functional groups. Benzaldehyde and 4-

(

dimethylamino)benzaldehyde were smoothly reduced to

their corresponding boronic esters (entries 1 and 2). Aliphatic

aldehydes such as 2-phenylpropanal and 2,2-diphenylacetalde-

hyde also reacted very well (entries 3 and 4). We have

observed no reactivity change in the case of 2-napthaldehyde

and cyclohexanecarbaldehyde, which could be converted to the

targeted products (entries 5 and 6) in a short period.

Substrates with electron-withdrawing groups also gave reduced

products in high yields (entries 7 and 8). Further, the catalyst

showed substrate tolerance to those that contained −NO and

containing the N−B−N motif tend to be dianionic while the

ligands containing the N−C−N and N−P−N motifs are mono

anionic. However, the bite angles found in the complexes

formed from the N−B−N and N−C−N ligands are almost

−

Br groups. Dialdehydes and α−β unsaturated aldehydes are

also seen to be reduced spontaneously in the presence of 1

(

entries 9 and 10). In entry 10, the reduction of the CO

d,17a

same.

On the other hand, the bite angle is the smallest in

group occurred exclusively over the reduction of the CC

bond. It is worth noting that the reduction of 2-formylpyridine

proceeded chemoselectively with the reduction of the CO

group over the competitive pyridine hydroboration reaction.

The latter is the common reaction path with lanthanide

N−P−N ligands owing to longer P−N bond lengths, which in

turn are the result of the larger size of the phosphorus center.

Hydroboration of Carbonyl Compounds. Hydrobora-

tion of carbonyl compounds has emerged as an atom-

economical and selective synthetic route for the synthesis of

various borate esters, which are intermediates of valuable

functionalized alcohols. There has been signiﬁcant develop-

ment in the carbonyl hydroboration reactions catalyzed by the

catalysts such as [Cp*

LaH]

However, in this case the

reaction rate is slightly slower than that observed for the

reduction of the other aldehydes (Table 3, entry 11). This is

possibly due to the coordination of pyridine to Y(III) during

the catalytic cycle.

complexes of s-block, main group, and transition metal ions.

In addition, catalyst-free hydroboration reactions have also

In addition to the common substrate scope to probe the

general suitability including scalability and solvent-free

conditions for the greener processes, preparative-scale

reactions were further investigated. Large-scale reactions (1

g) were performed using benzaldehyde and acetophenone as

liquid substrates in neat conditions. The reaction is exothermic

in the case of benzaldehyde and is completed within 30 min.

We also tested the hydroboration reaction using 4-

(dimethylamino)benzaldehyde and benzophenone as solid

substrates in neat conditions where HBpin acted as the

solvent. In a similar fashion to the liquid substrates, the

reaction was found to be complete within 30 min and the

catalyst showed similar reactivity toward ketone and aldehydes.

In both cases, we have used 0.01 mol % of catalyst loading and

isolated the reduced products in >90% isolated yields (see the

Experimental Section).

been documented. Homoleptic lanthanide complexes such as

La(N(SiMe ) ) , (Cp) La (Cp = cyclopentadienyl) and

(

MeCp) La (MeCp = methylcyclopentadienyl) also are

known as catalysts for the hydroboration of aldehydes and

ketones. In view of this, it was of interest to examine the

catalytic behavior of 1. A promising aspect of the latter is its

high lipophilicity being readily soluble in common organic

hydrocarbon solvents including n-pentane and n-hexane. As a

proof of principle, in order to examine the catalytic activity of

, we have performed the catalytic hydroboration of ketones

and aldehydes which are described below.

Initial screening of the catalyst was carried out by using

benzophenone as the reactant, HBpin as the reducing agent,

and 1 as the catalyst (using 0.01 mol %). The reaction

proceeded smoothly at room temperature and was complete

within 10 min. It is noted that the precursor Y(N(SiMe) )

Further, we have studied a competitive intermolecular

hydroboration reaction involving a 1:1 mixture of aldehyde

and ketone (Scheme 4). These studies showed that the

aldehyde was chemoselectively reduced with 92% conversion,

indicating aldehydes are more reactive than ketones toward the

itself acts as a catalyst for the hydroboration reaction.

However, the reaction rate is slightly diminished as compared

with 1. Reduction of wide variety ketones (possessing both

electron-withdrawing and donating groups, as well as those

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Table 2. Scope of Hydroboration of Ketone Catalyzed by 1.

Reaction conditions: ketone (0.25 mmol), HBpin (0.30 mmol, 1.2 equiv), catalyst (0.01 or 0.1 mol %). The reaction was carried out in C D at 25

°C and monitored by H and B NMR.

hydroboration reaction. We have tried another reaction

involving a mixture of an activated ketone, 4-methoxyaceto-

phenone, and benzaldehyde. Even in this case, the reduction of

benzaldehyde was dominant pathway with a selectivity of 99%

aldehyde hydroboration at room temperature in 10 min. This

chemoselectivity is similar to that reported earlier for

SUMMARY

■

We have developed a new unsymmetrical imino-phosphaami-

dinate (NPN) ligand [L] which is similar in its coordination

−

capability to the well-known amidinate/guanidinate ligands.

The 1:1 reaction of the parent compound LH with

Y(N(SiMe ) ) proceeds smoothly with the elimination of 1

2 3

La(N(TMS) ) , Cp La, and (MeCp) La.

equiv of HN(SiMe₃)₂aﬀording the complex [{L}Y(N-

We propose a plausible reaction mechanism for the

hydroboration reaction based on literature precedents

(

[

SiMe ) ) ] (1). As anticipated, the monoanionic ligand

3 2 2

−

L] functions in a chelating manner and enforces a distorted

(Scheme 5). Thus, we suggest that the metal amide initially

tetrahedral geometry around the four-coordinate Y(III) center.

The complex 1, which is highly soluble in common organic

solvents, including n-pentane/n-hexane was found to be a very

good catalyst for the hydroboration of a wide range of ketones

and aldehydes. The newly developed ligand also has a potential

P(III) donor which would allow synthesis of heterometallic

complexes with varied reactivity. Further, the stereoelectronic

modulation of the ligand is possible through substitution both

at the nitrogen as well as at the phosphorus centers. These

aspects are being currently investigated in our laboratory.

reacts with HBpin with the elimination HN(SiMe₃)₂to

generate a metal hydride (I) as the catalytically active species.

This kind of metal hydride formation has been commonly

suggested in the case of reactions involving complexes of

alkaline earth metal ions. The next step involves the

nucleophilic attack of the hydride on the electrophilic C

center of the carbonyl compound furnishing the intermediate

II, which further undergoes product elimination upon reaction

with another HBpin molecule to regenerate the metal hydride

species I.

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Article

hexane, n-pentane, and toluene were dried using standard methods.

Table 3. Scope of Aldehyde−Hydroboration Using 1 as the

H, C{ H} P{ H}, B{ H}, and F{ H} NMR spectra were

Catalyst

recorded on a Bruker Nano Bay 300 MHz NMR spectrometer. H

and C{ H} NMR spectra were referenced to the peaks of residual

protons of the deuterated solvent ( H) or the deuterated solvent itself.

F { H}, P{ H}, and B{ H} NMR spectra were referenced to

CFCl , H PO , and BF ·Et O, respectively. H− H COSY,

H− C{ H} HMQC, and H− C{ H} HMBC methods were used

to conﬁrm the NMR peaks assignments for the new compounds.

High-resolution mass spectra (HRMS) were recorded with a

microTOF-QII mass spectrometer. The yttrium amide Y(N-

(

SiMe ) ) was prepared using a procedure similar to that reported

3 2 3

in the literature for Nd, Sm, and Eu and puriﬁed by sublimation.

PhP(Cl)NHDipp, imidazolin-2-imine, and the corresponding

lithium salt were prepared according to literature procedures. All

of the ketones and aldehydes were purchased at the highest

commercial quality. Solid compounds were used without further

puriﬁcation, while liquid compounds were distilled prior to use.

Synthesis of LH. A diethyl ether solution (20 mL) of

PhP(Cl)NHDipp (Dipp = 2,6-diiso propylphenyl) (320 mg, 1.00

mmol) was added dropwise to a lithium salt of N-heterocyclic imine

(NHI) 201 mg (1.00 mmol) in diethyl ether (20 mL) at −78 °C. The

reaction mixture was stirred for 2 h and warmed to room temperature.

Diethyl ether was removed completely under vacuum, and the title

compound was extracted in n-hexane. After n-hexane was evaporated

under vacuum, the LH obtained as a light-yellow jelly compound.

Several attempts to obtain the ligand as a solid by the crystallization

did not succeed. Yield: 410 mg (85%). H NMR (C D , 300 MHz, 25

C): δ = 8.27 (t, J_H_H= 6.2, 2H, Ar-H), 7.40 (t, J_H_H= 6.2, 2H, Ar-H),

.25−7.16 (m, mixed with C D , 2H, Ar-H), 7.06 (t, J = 6.2, 2H,

Ar-H), 5.02 (sept, 2H, NHI- Pr-CH), 4.69 (d, J

Hz, 6H, 2 × Pr-CH ), 1.25 (d, J = 7 Hz, 6H, 2 × Pr-CH ), 1.06

(

= 6.2, 1H, NH),

H−H

.09 (sept, 2H, Dipp- Pr-CH), 1.61 (s, 6H, 2 × CH ), 1.30 (d, J = 7

3 HH

i i

mixed d, J_H_H= 7 Hz, 12 H, 4 × Pr-CH ). P{ H} NMR (C D ,

3 6 6

13 1

21.5 MHz, 25 °C): δ = 76.3. C{ H} NMR (C D , 75 MHz, 25

6 6

C): δ = 150.4 (d, CN), 142.1 (d, ArC-NH), 141.2 (d, ArC-P),

30.4 (d, ArC), 128.2 (d, ArC), 123.7 (ArC), 122.8 (ArC), 115.9

CC), 46.5 (d, N-CH(CH ) ), 28.5 (ArC-CH(CH ) ), 24.1 (ArC-

(

3 2

CH(CH ) , 21.6 (d, N-CH(CH ) ), 10.0 (H C-CC-CH ). HRMS

(

ESI-TOF) m/z: [M + K] calcd for C H N PK 517.2862; found

29 43 4

17.2857.

Synthesis of the Complex 1. The ligand LH, 50 mg (0.104

mmol) and Y(N(SiMe) ) (60 mg, 0.104 mmol) were mixed together

in toluene (5 mL), and the reaction mixture was stirred in a preheated

oil bath at 60 °C for 2 h. After this time, toluene was removed in

vacuo to give a white solid, which was recrystallized from n-hexane at

−

35 °C. After 2 days, colorless single crystals of complex 1 suitable for

XRD analysis were isolated. Yield: 70 mg (76%; with respect to

metal). H NMR (C D , 300 MHz, 25 °C): δ = 7.92 (t, J = 6.8, 2H,

Ar-H), 7.28 (dd, J_H₋_H= 6.8, 1H, Ar-H), 7.21 (t, J_H_H= 9.0, 2H, Ar-

CH), 7.07 (t, J_H_H= 7.7, 3H, Ar-H), 5.36 (sept, 1H, NHI- Pr-CH),

.93 (sept, 1H, NHI- Pr-CH), 3.89 (sept, 1H, Dipp- Pr-CH), 3.77

(sept, 1H, Dipp- Pr-CH), 1.67 (d, J

= 6.9 Hz, 3H, Pr-CH ), 1.61

H−H 3

(

d, J_H_H= 6.5 Hz, 3H, Pr-CH )1.48 (s, 6H, 2 × CH ), 1.37 (d, J

.7 Hz, 6 H, 2 × Pr-CH ), 1.26 (br s, 12 H, 4 × Pr-CH ), 0.56 (s,

3 3

31 1

8H, 2 × SiMe ), 0.37 (s, 18H, 2 × SiMe ). P{ H} NMR (C D ,

21.5 MHz, 25 °C): δ = 103.0. C{ H} NMR (C D , 75 MHz, 25

C): δ = 152.5 (d, CN), 151.7 (ArC-N), 147.6 (ArC-P), 146.0 (d,

ArC), 144.5, (ArC), 131.5 (d, ArC), 129.5 (ArC), 124.4 (ArC), 123.8

ArC), 122.7 (CC), 47.4 (N-CH(CH ) ), 31.9 (ArC-CH(CH ) ),

29.5 (ArC-CH(CH ) ), 29.3(ArC-CH(CH ) ), 27.8(ArC-CH-

3 2 3 2

Reaction conditions: Aldehyde (0.25 mmol), HBpin (0.30 mmol, 1.1

(

3 2

equiv), catalyst (0.01 mol %). The reaction was carried out in C D at

5 °C and monitored by H NMR spectroscopy.

(

CH ) ), 26.5(ArC-CH(CH ) ), 24.6 (d, N-CH(CH ) ), 23.0 (d,

3 2 3 2 3 2

N-CH(CH ) ), 14.3 (H C-CC-CH ), 9.9 (Si(CH ) ), 6.2 (Si-

3 3

(

CH ) ).

3 3

EXPERIMENTAL SECTION

■

Typical Procedure for Hydroboration Reactions. Hydro-

General Methods. All manipulations of air- and moisture-

sensitive materials were performed under an inert atmosphere in

oven-dried Schlenk-type glassware, either on a dual manifold Schlenk

line interfaced with a high vacuum (10⁻Torr) line or in an argon-/

nitrogen-ﬁlled M. Braun glovebox. Tetrahydrofuran, diethyl ether, n-

boration reactions were performed by using the following standard

protocol. In a glovebox, the ketone/aldehyde (0.25 mmol) was loaded

into an NMR tube. This was followed by addition of HBpin (0.30

mmol 1.2 equiv) and then by an appropriate loading of 1 (0.01 or 0.1

mol %). The NMR tube was sealed with rubber septum and shaken

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Scheme 4. Competitive Intermolecular Aldehyde vs Ketone Hydroboration Selectivity Study

Characterization of the Products. The data for the compounds

a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i,

Scheme 5. Plausible Mechanism for the Hydroboration of

Carbonyl Compounds Catalyzed by 1 ([L-Y-N(SiMe ) ] =

and 3k is already described in the literature, and the presented data

[

L-Y(N(SiMe ) ) ]). In the following catalytic cycle one

3 2 2

agrees (Supporting Information ) with literature reports. Complete

remaining N(SiMe ) group on Y(III) is not shown for

characterization data for the new compounds 2k, 2l, 2m, and 3j is

clarity.

presented below.

-(Diphenylmethoxy)pinacolborane (2a). H NMR (C D , 300

MHz, 25 °C): δ = 7.43 (d, J_H_H= 7.5 Hz, 4H, Ar-H), 7.09 (t, J_H_H= 7.5

Hz, 4H, Ar-H), 7.01 (t, J_H_H= 7.4 Hz, 2H, Ar-H), 6.41 (s, 1H, O-CH),

.98 (s, 12H, 2 × C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25

3 2 6 6

13 1

(

C): δ = 22.7. C{ H} NMR (C D ,75 MHz, 25 °C): δ = 143.8

ArC), 128.5 (ArC), 127.5 (ArC), 126.9 (ArC), 82.8 (C(CH ) ), 78.5

6 6

O-CH), 24.1 (C(CH ) ).

-(Cyclohexylphenylmethoxy)pinacolborane (2b). ¹H NMR

C D , 300 MHz, 25 °C): δ = 7.39 (d, J = 7.4 Hz, 2H, Ar-H),

.18 (t, J_H_H= 7.4 Hz, 2H, Ar-H), 7.10 (t, J_H_H= 7.3 Hz, 1H, Ar-H),

.07 (d, J_H_H= 6.8 Hz, 1H, O-CH), 2.01 (d, J_H_H= 12 Hz, 1H, Cy-

(

CH), 1.70−1.56 (m, 6H, Cy-CH ), 1.26−1.07 (m, 4H, CyCH ), 1.05

(

s, 6H, C(CH ) ), 1.02 (s, 6H, C(CH ) ). B{ H} NMR (C D , 96.3

3 2 3 2 6 6

MHz, 25 °C): δ = 22.5. C{ H} NMR (C D , 75 MHz, 25 °C): δ =

43.1 (ArC), 128.2 (ArC), 127.3 (ArC), 127.0 (ArC), 82.4

(

C(CH ) ), 81.4 (O-CH), 45.4 (Cy-C), 29.6 (Cy-C), 28.6 (Cy-C),

6.7 (Cy-C), 26.4 (Cy-C), 26.3 (Cy-C), 24.6 (C(CH ) ).

3 2

-(Isopropylphenylmethoxy)pinacolborane(2c). H NMR (C D ,

6 6

00 MHz, 25 °C): δ = 7.53 (d, J_H_H= 7.3 Hz, 2H, Ar-H), 7.16 (t, J_H_H

well, and the reaction was monitored by ¹H and ¹¹B NMR

spectroscopy by comparing relative intensities of resonances

characteristic of the substrates and products.

Typical Procedure for Scale Up Reactions. In a glass vial, solid

ketone (benzophenone, 1 g, 5.48 mmol) or aldehyde (4-

= 7.6 Hz, 2H, Ar-H), 7.08 (t, JHH = 7.0 Hz, 1H, Ar-H), 5.03 (d, JHH

6.1 Hz, 1H, O-CH), 1.99 (m, 1H, CH(CH ), 1.04 (s, 6H,

C(CH ), 1.00 (s, 6H, C(CH ), 0.99 (d, JHH = 7.8 Hz, 3H,

CH(CH ), 0.86 (d, JHH = 8.0 Hz, 3H, CH(CH

(C , 96.3 MHz, 25 °C): δ = 22.6. C{ H} NMR (C

25 °C): δ = 143.1 (ArC), 128.2 (ArC), 127.3 (ArC), 126.8 (ArC),

)

3 2

)

3 2

)

). B{ H} NMR

, 75 MHz,

6 6

(

dimethylamino)benzaldehyde, 1 g, 6.70 mmol) and HBpin (0.71

mL, 5.60 mmol for benzophenone and 0.87 mL, 6.80 mmol for 4-

dimethylamino)benzaldehyde) were taken. To this 0.01 mol % of

catalyst was added (neat condition), and the reaction mixture was

82.4 (C(CH

19.1 (CH(CH

)

), 81.8 (O-CH), 35.8 (CH(CH

), 17.8 (CH(CH ).

)

), 24.6 (C(CH

) ),

3 2

(

)

3 2

2-(1-Phenylethoxy)pinacolborane (2d). ¹H NMR (C

, 300

monitored by H and B NMR spectroscopy. After 30 min, excess

HBpin was removed in vacuum to give products as white solids

MHz, 25 °C): δ = 7.35 (d, JHH = 7.4 Hz, 2H, Ar-H,), 7.13 (t, JHH

7.7 Hz, 2H, Ar-H), 7.04 (t, JHH = 7.3 Hz, 1H, Ar-H), 5.40 (q, JHH

(

yields: 1.62 g (95%) for benzophenone and 1.75 g (94%) for 4-

dimethylamino) benzaldehyde). In the case of liquid substrates

acetophenone (1g, 8.32 mmol) or benzaldehyde (1g, 9.42 mmol)),

6.4 Hz, 1H, O-CH), 1.44 (d, JHH = 6.5 Hz, 3H, CH-CH

), 1.02 (s,

). B{ H} NMR (C , 96.3

MHz, 25 °C): δ = 22.5. C{ H} NMR (C , 75 MHz, 25 °C): δ =

145.3 (ArC), 128.5 (ArC), 127.3 (ArC), 125.6 (ArC), 82.5

(C(CH ), 72.9 (O-CH), 25.7 (C(CH ), 24.6 (CH ).

2-(1-(p-Tolyl)ethoxy)pinacolborane (2e). H NMR (C

MHz, 25 °C): δ = 7.30 (d, JHH = 7.9 Hz, 2H, Ar-H), 6.97 (d, JHH

7.8 Hz, 2H, Ar-H), 5.41 (q, JHH = 6.5 Hz, 1H, O-CH), 2.08 (s, 3H, p-

6H, C(CH

)

), 0.99 (s, 6H, C(CH

)

6 6

no solvent was used and the reaction was performed in neat

conditions using HBpin (1.07 g, 8.40 mmol for acetophenone and

)

.21 g, 9.50 mmol for benzaldehyde) and 0.01 mol % of catalyst. The

D , 300

6 6

reaction was exothermic in the case of benzaldehyde, and after

completion of the reaction products were isolated as white sticky

solids (yields: 1.87 g (90.5%) for acetophenone and 2.11 g (95%) for

benzaldehyde).

), 1.47 (d, JHH = 6.4 Hz, 3H, CHCH

), 1.03 (s, 6H, C(CH

, 96.3 MHz, 25 °C): δ =

, 75 MHz, 25 °C): δ = 142.5 (ArC), 136.6

(ArC), 129.2 (ArC), 125.7(ArC), 82.4 (C(CH ) ), 72.8 (O-CH), 25.8

) ),

3 2

1.00 (s, 6H, C(CH

)

). B{ H} NMR (C

6 6

Competing Procedure for Selective Hydroboration of

Ketone vs Aldehyde. In a glass vial acetophenone (120.1 mg, 1

mmol), benzaldehyde (106.1 mg, 1 mmol) and HBpin (128.0 mg, 1

mmol) were added, and to this a solution containing an appropriate

loading of catalyst (0.01 mol %) in C D was then added sequentially.

22.5. C{ H} NMR (C

(CH-CH ), 24.6 (C(CH ) ), 21.0 (p-CH ).

2-(1-(4-Methoxyphenyl)ethoxy)pinacolborane (2f). ¹H NMR

(C D , 300 MHz, 25 °C): δ = 7.29 (d, J = 8.5 Hz, 2H, Ar-H),

The reaction was monitored by H and B NMR spectroscopy (see

the Supporting Information ).

6.75 (d, J_H_H= 8.7 Hz, 2H, Ar-H), 5.40 (q, J_H_H= 6.4 Hz, 1H, O-CH),

3.30 (s, 3H, OCH ), 1.48 (d, J = 6.4 Hz, 3H, CH-CH ), 1.03 (s,

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

H, C(CH ) ), 1.01(s, 6H, C(CH ) ). B{ H} NMR (C D , 96.3

2-(Benzyloxy)pinacolborane (3a). H NMR (C D , 300 MHz, 25

6 6

MHz, 25 °C): δ = 22.5. C{ H} NMR (C D , 75 MHz, 25 °C): δ =

59.3 (ArC-OCH ), 137.4 (ArC), 126.9 (ArC), 114.0 (ArC), 82.4

C(CH ) ), 72.6 (O-CH), 54.7 (OCH ), 25.7 (CH-CH ), 24.7

°C): δ = 7.30 (d, J_H_H= 7.3 Hz, 2H, Ar-H), 7.13 (t, J_H_H= 7.8 Hz2H,

Ar-H), 7.06 (t, J_H_H= 7.2 Hz, 1H, Ar-H), 4.93 (s, 2H, O-CH ), 1.04 (s,

(

12H, 2 × C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ =

3 2 6 6

13 1

C(CH ) ), 24.6(C(CH ) ).

22.7. C{ H} NMR (C D , 125 MHz, 25 °C): δ = 140.0 (ArC),

6 6

-(1-(4-Bromophenyl)ethoxy)pinacolborane (2g). ¹H NMR

C D , 300 MHz, 25 °C): δ = 7.22 (d, J = 8.9 Hz, 2H, Ar-H),

.99 (d, J_H_H= 8.7 Hz, 2H, Ar-H), 5.21 (q, J_H_H= 6.1 Hz, 1H, O-CH),

.32 (d, J_H_H= 6.2 Hz, 3H, CH-CH ), 1.01 (s, 6H, C(CH ) ), 0.99(s,

H, C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.4.

C{ H} NMR (C D , 75 MHz, 25 °C): δ = 144.2 (ArC), 131.6

ArC), 127.4 (ArC), 121.2(ArC-Br), 82.6 (C(CH ) ), 72.2 (O-CH),

5.4 (CH-CH ), 24.7 (C(CH ) ), 24.6 (C(CH ) ).

-(1-(4-Nitrophenyl)ethoxy)pinacolborane (2h). H NMR (C D ,

00 MHz, 25 °C): δ = 7.81 (d, J_H_H= 8.4 Hz, 2H, Ar-H), 7.00 (d, J_H_H

8.3 Hz, 2H, Ar-H), 5.18 (q, J_H_H= 6.4 Hz, 1H, O-CH), 1.25 (d, J_H_H

6.4 Hz, 3H, CH-CH ), 1.03 (s, 6H, (C(CH ) ), 1.00 (s, 6H,

C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.5.

C{ H} NMR (C D , 75 MHz, 25 °C): δ = 151.7 (ArC), 147.4

ArC), 126.0 (ArC), 123.6 (ArC), 82.9 (C(CH ) ), 71.9 (O-CH),

128.5 (ArC), 127.5 (ArC), 127.0 (ArC), 82.7 (C(CH ) ), 66.9 (CH -

3 2 2

(

O), 24.7 (C(CH ) ).

3 2

2-(4-N,N′-Dimethylaminobenzyloxy)pinacolborane (3b). ¹H

NMR (C D , 300 MHz, 25 °C): δ = 7.33 (d, J = 8.5 Hz, 2H,

Ar-H) 6.55 (d, J_H_H= 7.6 Hz, 2H, Ar-H), 4.99 (s, 2H, O-CH ), 2.50 (s,

6H, N(CH ) ), 1.06 (s, 12H, 2 × C(CH ) ). B{ H} NMR (C D ,

3 2 3 2 6 6

13 1

(

96.3 MHz, 25 °C): δ = 22.8. C{ H} NMR (C D , 125 MHz, 25

6 6

°C): δ = 150.5 (ArC-NMe ), 128.9 (ArC), 112.8 (ArC), 82.5

(C(CH ) ), 67.2 (CH -O), 40.3 (N(CH ) ), 24.7 (C(CH ) ). HRMS

3 2

(ESI-TOF) m/z: [M + H] calcd for C H BNO 278.1927, found

278.1925.

2-(2-Phenylpropoxy)pinacolborane (3c). ¹H NMR (C D , 300

15 25 3

(

MHz, 25 °C): δ = 7.21−7.07 (m, 5H, Ar-H) 4.13−4.08 (m, 1H, O-

CH ), 4.01−3.95 (m, 1H, O-CH ), 3.01−2.89 (m, 1H, CH), 1.24 (d,

(

3H, CH ), 1.06 (s, 12H, 2 × C(CH ) ). B{ H} NMR (C D , 96.3

3 3 2 6 6

13 1

5.3 (CH-CH ), 24.6 (C(CH ) ).

MHz, 25 °C): δ = 22.4. C{ H} NMR (C D , 125 MHz, 25 °C): δ =

6 6

-(2,2,2-Triﬂuoro-1-phenylethoxy)pinacolborane(2i). ¹H NMR

144.1 (ArC), 128.5 (ArC), 127.9 (ArC), 126.6 (ArC), 82.4

(C(CH ) ), 70.6 (CH -O), 41.8 (CH-CH ), 24.7 (C(CH ) ), 24.6

(

C D , 300 MHz, 25 °C): δ = 7.38 (d, J = 4.0 Hz, 2H, Ar-H),

6 6 HH

3 2

.01 (t, J_H_H= 3.4 Hz, 3H, Ar-H), 5.57 (q, J_H_H= 6.4 Hz, 1H, O-CH-

(C(CH ) ), 17.7 (CH-CH ).

3 2 3

CF ), 0.97 (s, 6H, (C(CH ) ), 0.93 (s, 6H, (C(CH ) ). B{ H}

2-(2,2-Diphenylethoxy)pinacolborane (3d): H NMR (C D , 300

6 6

NMR (C D , 96.3 MHz, 25 °C): δ = 22.8. F{ H} NMR (C D ,

MHz, 25 °C): δ = 7.17 (d, J_H_H= 7.6 Hz, 4H, Ar-H), 7.08 (t, J_H_H= 7.5

Hz, 4H, Ar-H), 7.00 (t, J_H_H= 7.1 Hz, 2H, Ar-H), 4.48 (d, 2H, J_H_H

.0 Hz O-CH ,), 4.21 (t, J = 7.0 Hz, 1H, CH), 0.97 (s, 12H, 2 ×

82.4 MHz, 25 °C): δ = −78.14. C{ H} NMR (C D , 75 MHz, 25

(

C): δ = 133.9 (ArC), 129.5 (ArC), 128.6 (ArC), 127.9 (ArC), 126.5

CF ), 122.7 (ArC), 83.7 (C(CH ) ), 74.9 (O-CH), 24.4 (C(CH ) ),

C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.3.

3 2 6 6

13 1

4.3 (C(CH ) ).

C{ H} NMR (C D , 125 MHz, 25 °C): δ = 142.3 (ArC), 128.9

6 6

-(1-Ferrocenylethoxy)pinacolborane (2j). H NMR (C D , 300

^M^H^z^,²⁵^°^C⁾^:^δ⁼⁵^.²⁸⁽^q^,^JHH = 6.4 Hz, 1H, O-CH), 4.34 (s, 1H, Cp-

6 6

(ArC), 128.6 (ArC), 126.6 (ArC), 82.5 (C(CH ) ), 78.2 (CH -O),

53.0 (CH-CH ), 24.6 (C(CH ) ). HRMS (ESI-TOF) m/z: [M +

3 2 2

3 2

H), 4.06 (s, 6H, Cp-H), 3.96 (s, 2H, Cp-H) 1.48 (d, J = 6.0 Hz,

Na] calcd for C H ONa 221.0942, found 221.0937.

14 14

H, CH ), 1.08 (s, 12H, 2 × C(CH ) ). B{ H} NMR (C D , 96.3

-(Naphthalen-2-ylmethoxy)pinacolborane (3e). 1_H_N_M_R

C D , 300 MHz, 25 °C): δ = 7.77 (br s, 1H, nap-H), 7.61−

MHz, 25 °C): δ = 22.5. C{ H} NMR (C D , 75 MHz, 25 °C): δ =

(

2.5 (Cp-C), 82.4 (C(CH ) ), 69.2 (O-CH), 68.9 (Cp-C), 67.9 (Cp-

3 2

.57(m, 3H, nap-H), 7.39 (d, 1H, nap-H), 7.23 (t, J = 4.6 Hz, 2H,

C), 66.1 (Cp-CH), 24.8 (C(CH ) ), 24.7 (C(CH ) ), 24.0 (CH-

CH ). HRMS (ESI-TOF) m/z: [M + H] calcd for C H F O

3 2

nap-H), 5.10 (s, 2H, O-CH ), 1.05 (s, 12H, 2 × C(CH ) ). B{ H}

NMR (C D , 96.3 MHz, 25 °C): δ = 22.8 ppm C{ H} NMR (C D ,

25 MHz, 25 °C): δ = 137.5 (nap-C), 133.9 (nap-C), 133.4 (nap-C),

28.3 (nap-C), 126.2 (nap-C), 125.9 (nap-C), 125.7 (nap-C), 125.2

3 2

12 14 e

30.0394, found 230.0390.

(

,2-(1,1-Diferrocenylethoxy)dipinacolborane (2k). Isolated as a

red-brown solid. Yield: 115 mg (87%). H NMR (C D , 300 MHz, 25

C): δ = 5.29 (q, J_H_H= 6.4 Hz, 2H, O-CH), 4.36 (s, 2H, Cp-H), 4.11

s, 2H, Cp-H), 4.04 (s, 4H, Cp-H) 1.50 (d, J = 6.0 Hz, 6H, 2CH₃)

nap-C), 82.8 (C(CH ) ), 67.0 (CH -O), 24.7 (C(CH ) ).

3 2 2 3 2

(

-(Cyclohexylmethoxy)pinacolborane (3f). H NMR (C D , 300

6 6

^M^H^z^,²⁵^°^C⁾^:^δ⁼³^.⁷⁵⁽^d^,^JHH = 6.4 Hz, 2H, O-CH ), 1.72−1.68 (m,

.09, 1.08 (s, 24H, 4 × C(CH ) ). B{ H} NMR (C D , 96.3 MHz,

H, CH ), 1.62−1.46 (m, 4H, CH ), 1.28−18 (m, 1H, CH), 1.15−

₅_°_C₎_:_δ₌₂₂_.₂_.1 C{ H} NMR (C D , 75 MHz, 25 °C): δ = 92.7

.07 (m, 2H, CH ), 1.07 (s, 12H, 2 × C(CH ) ), 0.96−0.83 (m, 2H,

3 2

d, Cp-C), 82.4 (C(CH ) ), 69.2 (Cp-C), 68.9 (Cp-C), 68.1 (Cp-C),

3 2

CH ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.5 ppm

6.8 (CH-CH ), 24.8 (C(CH ) ), 24.7 (C(CH ) ), 24.0 (CH-CH ).

3 3 2 3 2 3

C{ H} NMR (C D , 125 MHz, 25 °C): δ = 82.3 C(CH ) , 70.5 (O-

HRMS (ESI-TOF) m/z: [M + Na] calcd for C H FeO Na

CH ), 39.8 (CH), 29.7 (CH ), 26.8 (CH ), 26.1 (CH ), 24.7

97.0554; found 297.0548.

,7,7-Trimethylbicyclo[2.2.1]heptan-2-yl)oxy)dipinacolborane-

2l). Isolated as a white-crystalline solid. Yield: 65 mg (93%). H

C(CH ) .

2-((4-Nitrobenzyl)oxy)pinacolborane (3g). H NMR (C D , 300

^M^H^z^,²⁵^°^C⁾^:^δ⁼⁷^.⁷⁹⁽^d^,^JHH ⁼⁸^.²^H^z^,²^H^,^A^r^-^H⁾⁶^.⁹²⁽^d^,^JHH = 8.3

Hz, 2H, Ar-H), 4.69 (s, 2H, O-CH ), 1.04 (s, 12H, 2H, 2 ×

C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.7.

C{ H} NMR (C D , 125 MHz, 25 °C): δ = 147.6 (ArC-NO ),

146.6 (ArC), 126.8 (ArC), 123.5 (ArC), 83.1 C(CH

CH ), 24.6 C(CH ) .

(

6 6

NMR (C D , 300 MHz, 25 °C): δ = 4.25−4.21 (dd, 1H, O-CH),

.97.1.89 (m, 1H, CH ), 1.75−1.66 (m, 1H, CH ), 1.57−1.48 (m,

H, CH ), 1.44.-1.32(m, 1H, CH ), 1.61 (s, 3H, CH ), 1.06 (s, 12H),

.02 (s, 3H, CH ), 0.96−0.85(m, 2H, CH ), 0.74 (s, 3H, CH ).

B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.2. C{ H} NMR

C D , 75 MHz, 25 °C): δ = 82.2 (BpinC(CH ) ), 81.8 (O-CH), 49.3

CH C(CH )CH), 46.8 (C(CH ) ), 45.4 (CH CCH ), 40.8 (CH ),

3.9 (CH ), 27.5 (CH ), 24.7 (BpinC(CH ) ), 24.6 (BpinC(CH ) ),

0.5 (C(CH ) ), 20.4 (C(CH ) ), 11.7 (C-CH ). HRMS (ESI-TOF)

m/z: [M + Na] calcd for C H ONa 177.1255, found 177.1249.

)

, 65.6 (O-

(

3 2

-((4-Bromobenzyl)oxy) pinacolborane (3h). H NMR (C D ,

6 6

2‑

300 MHz, 25 °C): δ = 7.21 (d, JHH = 7.2 Hz, 2H, Ar-H) 6.92 (d, JHH

= 7.6 Hz, 2H, Ar-H), 4.73 (s, 2H, O-CH ), 1.03 (s, 12H, 2 ×

, 96.3 MHz, 25 °C): δ = 22.7.

, 125 MHz, 25 °C): δ = 138.9 (ArC), 131.6

(ArC), 128.7(ArC), 121.5 (ArC-Br), 82.8 (C(CH ) ), 66.1 (O-CH ),

3 2

C(CH

C{ H} NMR (C

)

). B{ H} NMR (C

6 6

,4-(Diethoxy)dipinacolboranebenzene (2m). Isolated as a white-

crystalline solid. Yield: 94 mg (90%). H NMR (C D , 300 MHz, 25

6 6

C): δ = 7.29 (s, 4H, Ar-H), 5.35 (q, J_H_H= 6.4 Hz, 2H, 2 × O-CH,),

24.6 (C(CH ) ).

1,4-(Dimethoxy)dipinacolboranebenzene (3i). H NMR (C D ,

6 6

3 2

.41 (d, J_H_H= 6.4 Hz, 6H, 2 × CH ), 1.02, and 1.00 (s, 24H, 4 ×

C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.4.

300 MHz, 25 °C): δ = 7.24 (s, 4H, Ar-H), 4.89 (s, 4H, 2 × O-CH ),

11 1

C{ H} NMR (C D , 75 MHz, 25 °C): δ = 144.1 (ArC), 125.6

1.03 (s, 24H, 4 × C(CH ) ). B{ H} NMR (C D , 96.3 MHz, 25

3 2 6 6

13 1

(

ArC), 82.5 (C(CH ) ), 72.7 (CH−CH ), 25.7 (CH-CH ), 24.7

°C): δ = 22.7. C{ H} NMR (C D , 125 MHz, 25 °C): δ = 139.1

6 6

C(CH ) , 24.6 C(CH ) . HRMS (ESI-TOF) m/z: [M + H] calcd for

(ArC-CH -O), 127.1 (ArC), 82.7 (C(CH ) ), 66.7 (O-CH ), 24.7

C H O 167.1072, found 167.1067.

(C(CH ) ).

3 2

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

b) Elsevier, C. J.; Reedijk, J.; Walton, P. H.; Ward, M. D. Ligand

Article

-(4-N,N′-Dimethylaminocinnamylmethoxy)pinacolborane (3j).

DEDICATION

■

Isolated as a yellow-crystalline solid. Yield: 70 mg (92%). H NMR

This article is dedicated to Prof. S.S. Krishnamurthy on his

0th birthday.

(

C D , 300 MHz, 25 °C): δ = 7.23 (d, J = 8.7 Hz, 2H, Ar-H), 6.64

6 6 HH

d, J_H_H= 15.8 Hz, 1H, CH), 6.48 (d, J_H_H= 8.6 Hz, 2H, Ar-H), 6.18

td, J_H_H= 15.8 Hz; J_H_H= 5.8 Hz,1H, CH), 4.62 (d, J_H_H= 5.6 Hz, 2H,

O-CH ), 2.49 (s, 6H, N(CH ) ), 1.07 (s, 12H, 2 × (C(CH ) ).

REFERENCES

■

B{ H} NMR (C D , 96.3 MHz, 25 °C): δ = 22.7. C{ H} NMR

(

1) (a) Stradiotto, M.; Lundgren, R. J. Ligand design in metal

chemistry: reactivity and catalysis; John Willey & Sons Ltd., 2016.

design in coordination chemistry: approaches to new catalysts, new

materials, and a more sustainable environment. Dalton Trans. 2003 ,

869 −1880. (c) Gavrilova, A. L.; Bosnich, B. Principles of

Mononucleating and Binucleating Ligand Design. Chem. Rev. 2004,

(

C D , 125 MHz, 25 °C): δ = 150.4 (ArC-NMe ), 131.9 (Ar-CC),

27.9 (ArC), 122.9(ArC), 112.7 (CC-O), 82.5 (C(CH ) ), 66.1

and antimony ligands ; MacMillan: London, 1973. (c) Tolman, C. A.

(CH -O), 40.1 (N(CH ) ), 24.7 (CH ). HRMS (ESI-TOF) m/z: [M

2 3 2 3

H] calcd for C H BNO 304.2084, found 304.2082.

17 26 3

-(Methoxypyridine)pinacolborane (3k). H NMR (C D , 300

6 6

MHz, 25 °C): δ = 8.39 (d, J_H_H= 4.8 Hz, 1H, Py-H), 7.26 (d, J_H_H

.8 Hz, 1H, Py-H), 7.11 (dt, 1H, Py-H), 6.65−6.61 (m, 1H, Py-H),

11 1

104, 349−383.

(

.18 (s, 2H, O-CH ), 1.07 (s, 12H, 2 × C(CH ) ). B{ H} NMR

3 2

(2) (a) Hartwig, J. F. Organotransition Metal Chemistry: from Bonding

to Catalysis; University Science Books: Sausalito, CA, 2010.

C D , 96.3 MHz, 25 °C): δ = 22.1. C{ H} NMR (C D , 125 MHz,

5 °C): δ = 159.9 (PyC), 148.6 (PyC), 136.5 (PyC), 122.1 (PyC),

19.9 (PyC), 82.6 (C(CH ) ), 67.8 (O-CH ), 24.8 (C(CH ) ).

(

b) MacAuliﬀe, C. A. Transition metal complexes of phosphorus, arsenic

3 2

Steric effects of Phosphorus Ligands in Organometallic Chemistry

and Homogeneous Catalysis. Chem. Rev. 1977, 77, 313−348.

HRMS (ESI-TOF) m/z: [M + H] calcd for C H BNO 236.1458,

found 236.1455.

(

d) Crabtree, R. H. Carbonyls, Phosphine Complexes, and Ligand

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.joc.0c02383.

■

Substitution Reactions; John Wiley & Sons, Inc.: 2005; pp 87−124.

e) Pignolet, L. M. Homogeneous Catalysis with Metal Phosphine

Complexes; Springer: New York, 2013.

(3) (a) de Fremont, P.; Marion, N.; Nolan, S. P. Carbenes:

Synthesis, properties, and organometallic chemistry. Coord. Chem. Rev.

009, 253, 862 −892. (b) Hopkinson, M. N.; Richter, C.; Schedler,

(

NMR plots of all compounds and details of X-ray

diﬀraction studies (PDF)

M.; Glorius, F. An overview of N -Heterocyclic carbenes. Nature 2014,

510, 485−496. (c) Nolan, S. P. N-Heterocyclic carbenes effective tools

for organometallic synthesis; Wiley-VCH, 2014. (d) Glorius, F. N-

Heterocyclic carbenes in transition metal catalysis; Springer-Verlag:

Berlin, 2007. (e) Huynh, H. V. The Organometallic Chemistry of N-

Heterocyclic Carbenes; John Wiley & Sons, Ltd.: Chichester, UK, 2017.

f) Nesterov, V.; Reiter, D.; Bag, P.; Frisch, P.; Holzner, R.; Porzelt,

A.; Inoue, S. NHCs in Main Group Chemistry. Chem. Rev. 2018 , 118 ,

678 −9842. (g) Doddi, A.; Peters, M.; Tamm, M. N -Heterocyclic

Accession Codes

CCDC 2018159 contains the supplementary crystallographic

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

via www.ccdc.cam.ac.uk/data_request/cif, or by emailing

data_request@ccdc.cam.ac.uk, or by contacting The Cam-

bridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

(

Carbene Adducts of Main Group Elements and Their Use as Ligands

in Transition Metal Chemistry. Chem. Rev. 2019, 119, 6994−7112.

(4) (a) Togni, A.; Halterman, R. L. Metallocenes: synthesis, reactivity,

applications; Wiley-VCH Verlag, 2008. (b) Kaminsky, W. Metallocene

Catalysts. In Kirk-Othmer Encyclopedia of Chemical Technology; John

Wiley & Sons, Inc., 2015; pp 1 −25. (c) Jutzi, P.; Burford, N.

Structurally Diverse π -Cyclopentadienyl Complexes of the Main

Group Elements. Chem. Rev. 1999 , 99 , 969 −990. (d) Siemeling, U.

Chelate Complexes of Cyclopentadienyl Ligands Bearing Pendant O-

Donors. Chem. Rev. 2000, 100, 1495−1526. (e) Kresinski, R. A.

Lanthanides: Cyclopentadienyl Compounds. In Encyclopedia of

Inorganic and Bioinorganic Chemistry ; John Wiley & Sons, Ltd.,

AUTHOR INFORMATION

Corresponding Author

Vadapalli Chandrasekhar − Tata Institute of Fundamental

Research Hyderabad, 500046 Hyderabad, India;

Department of Chemistry, IIT Kanpur, Kanpur 208016,

India; orcid.org/0000-0003-1968-2980 ; Phone: +91 40

■

0203101; Email: vc@tifrh.res.in, vc@iitk.ac.in

Authors

Srinivas Anga − Tata Institute of Fundamental Research

Hyderabad, 500046 Hyderabad, India

Joydev Acharya − Tata Institute of Fundamental Research

Hyderabad, 500046 Hyderabad, India; Department of

Chemistry, IIT Kanpur, Kanpur 208016, India;

orcid.org/0000-0002-9480-4725

012. (f) Arndt, S.; Okuda, J. Mono(cyclopentadienyl) Complexes of

the Rare-Earth Metals. Chem. Rev. 2002, 102, 1953−1976. (g) Butler,

I. R. Transition metal complexes of cyclopentadienyl ligands. In

Organometallic Chemistry; Green, M., Ed.; The Royal Society of

Chemistry, 2001; Vol. 29, pp 442−478.

5) (a) Junk, P. C.; Cole, M. L. Alkali-metal bis(aryl)-

formamidinates: a study of coordinative versatility. Chem. Commun.

007 , 1579 −1590. (b) Edelmann, F. T. Lanthanide amidinates and

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.joc.0c02383

guanidinates: from laboratory curiosities to efficient homogeneous

catalysts and precursors for rare-earth oxide thin films. Chem. Soc. Rev.

2009 , 38 , 2253 −2268. (c) Edelmann, F. T. Lanthanide amidinates

and guanidinates in catalysis and materials science: a continuing

success story. Chem. Soc. Rev. 2012, 41, 7657−7672. (d) Edelmann, F.

T. Homogeneous Catalysis Using Lanthanide Amidinates and

Guanidinates. In Molecular Catalysis of Rare-Earth Elements; Roesky,

P. W., Ed. Springer: Berlin, 2010; pp 109 −163. (e) Schmidt, J. A. R.;

Arnold, J. First-row transition metal complexes of sterically-hindered

amidinates. J. Chem. Soc., Dalton Trans. 2002, 3454−3461. (f) Nijhuis,

C. A.; Jellema, E.; Sciarone, T. J. J.; Meetsma, A.; Budzelaar, P. H. M.;

Hessen, B. First-Row Transition Metal Bis(amidinate) Complexes;

Planar Four-Coordination of Fe(II) Enforced by Sterically Demand-

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

V.C. is thankful to the Department of Science and Technology,

New Delhi, India, for a National J. C. Bose Fellowship. S.A. is

thankful to Tata Institute of Fundamental Research, Hyder-

abad, for a postdoctoral fellowship, and J.A. is thankful to Tata

Institute of Fundamental Research, Hyderabad, for ﬁnancial

assistance. We thank Prof. V. Krishnan, NISER Bhubaneswar,

for HRMS measurements.

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Herbst-Irmer, R. RGe(I)Ge(I)R Compound (R = PhC(N Bu) ) with

Article

ing Aryl Substituents. Eur. J. Inorg. Chem. 2005, 2005, 2089−2099.

S.; Sen, S. S.; Roesky, H. W.; Koley, D.; Grubmu

ller, H.; Pal, A.;

g) Kissounko, D. A.; Zabalov, M. V.; Brusova, G. P.; Lemenovskii, D.

A. Principal trends in the chemistry of amidinate complexes of main-

a Ge −Ge Single Bond and a Comparison with the Gauche

Conformation of Hydrazine. Organometallics 2008 , 27 , 5459 −5463.

(e) Jones, C. Bulky guanidinates for the stabilization of low oxidation

state metallacycles. Coord. Chem. Rev. 2010, 254, 1273−1289.

(f) Green, S. P.; Jones, C.; Junk, P. C.; Lippert, K. A.; Stasch, A.

Synthetic, structural and theoretical studies of amidinate and

guanidinate stabilized germanium(i) dimers. Chem. Commun. 2006,

3978−3980. (g) Bisai, M. K.; Swamy, V. S. V. S. N.; Das, T.; Vanka,

V.; Gonnade, R. G.; Sen, S. S. Synthesis and Reactivity of a

Hypersilylsilylene. Inorg. Chem. 2019, 58, 10536−10542. (h) Swamy,

V. S. V. S. N.; Raj, K. V.; Vanka, K.; Sen, S. S.; Roesky, H. W. Silylene

induced cooperative B −H bond activation and unprecedented

aldehyde C −H bond splitting with amidinate ring expansion. Chem.

Commun. 2019, 55, 3536−3539. (i) Pahar, S.; Karak, S.; Pait, M.; Raj,

K. V.; Vanka, K.; Sen, S. S. Access to Silicon(II)- and Germanium(II)-

Indium Compounds. Organometallics 2018, 37 , 1206 −1213.

(10) (a) Bhattacharyya, P.; Woollins, J. D. Bis(diphenylphosphino)-

amine and related chemistry. Polyhedron 1995, 14, 3367−3388.

(b) Balakrishna, M. S.; Reddy, S. V.; Krishnamurthy, S. S.; Nixon, J.

F.; Burckett St. Laurent, J. C. T. R. Coordination chemistry of

diphosphinoamine and cyclodiphosphazane ligands. Coord. Chem. Rev.

1994 , 129 , 1 −90. (c) Fliedel, C.; Ghisolfi, A.; Braunstein, P.

Functional Short-Bite Ligands: Synthesis, Coordination Chemistry,

and Applications of N-Functionalized Bis(diaryl/dialkylphosphino)-

amine-type Ligands. Chem. Rev. 2016 , 116 , 9237 −9304. (d) Fei, Z.;

Dyson, P. J. The chemistry of phosphinoamides and related

compounds. Coord. Chem. Rev. 2005 , 249 , 2056 −2074. (e) Witt,

M.; Roesky, H. W. Transition and Main Group Metals in Cyclic

Phosphazanes and Phosphazenes. Chem. Rev. 1994 , 94 , 1163 −1181.

(11) (a) Puddephatt, R. J. Chemistry of Bis(dipheny1phosphino)-

methane. Chem. Soc. Rev. 1983 , 12 , 99 −127. (b) Chaudret, B.;

Delavaux, B.; Poilblanc, R. Bisdiphenylphosphinomethane in

dinuclear complexes. Coord. Chem. Rev. 1988 , 86 , 191 −243.

group and transition elements. Russ. Chem. Rev. 2006 , 75 , 351 −374.

6) (a) Bailey, P. J.; Pace, S. The coordination chemistry of

guanidines and guanidinates. Coord. Chem. Rev. 2001 , 214 , 91 −141.

b) Trifonov, A. A. Guanidinate and amidopyridinate rare-earth

complexes: Towards highly reactive alkyl and hydrido species. Coord.

Chem. Rev. 2010 , 254 , 1327 −1347. (c) Barry, S. T. Amidinates,

guanidinates and iminopyrrolidinates: Understanding precursor

thermolysis to design a better ligand. Coord. Chem. Rev. 2013, 257,

(

192−3201.

7) (a) Vollmerhaus, R.; Tomaszewski, R.; Shao, P.; Taylor, N. J.;

Wiacek, K. J.; Lewis, S. P.; Al-Humydi, A.; Collins, S. Synthesis and

Structure of Group 4 iminophosphonamide Complexes. Organo-

metallics 2005, 24, 494−507. (b) Nekoueishahraki, B.; Roesky, H. W.;

Schwab, G.; Stern, D.; Stalke, D. Synthesis and Structural Character-

ization of Aluminum Iminophosphonamide Complexes. Inorg. Chem.

009, 48, 9174−9179. (c) Nebra, N.; Lescot, C.; Dauban, P.; Mallet-

Ladeira, S.; Martin-Vaca, B.; Bourissou, D. Intermolecular Alkene

Aziridination: An Original and Efficient CuI ···CuI Dinuclear Catalyst

Deriving from a Phospha-Amidinate Ligand. Eur. J. Org. Chem. 2013 ,

013 , 984 −990. (d) Stasch, A. Synthesis of a Dimeric Magnesium (I)

Compound by an MgI/MgII Redox Reaction. Angew. Chem., Int. Ed.

014 , 53 , 10200 −10203. (e) Prashanth, B.; Singh, S. A new bulky

iminophosphonamide as an N , N ′-chelating ligand: synthesis and

structural characterization of heteroleptic group 13 element

complexes. Dalton Trans. 2014 , 43 , 16880 −16888. (f) Hawley, A.

L.; Stasch, A. Structural Diversity in Sterically Demanding

Diiminophosphinato Alkali Metal Complexes. Eur. J. Inorg. Chem.

015 , 2015 , 258 −270. (g) Rufanov, K. A.; Pruss, N. K.; Sundermeyer,

J. Simple entry into N -tert -butyl-iminophosphonamide rare-earth

metal alkyl and chlorido complexes. Dalton Trans. 2016 , 45 , 1525 −

538. (h) Stasch, A. Synthesis, Structure, and Reactivity of a Dimeric

Zinc(I) Compound Stabilized by a Sterically Demanding Diimino-

phosphinate Ligand. Chem. - Eur. J. 2012, 18, 15105−15112.

(12) (a) Wu, X.; Tamm, M. Transition metal complexes supported

by highly basicimidazolin-2-iminato and imidazolin-2-imine N-donor

ligands. Coord. Chem. Rev. 2014 , 260 , 116 −138. (b) Ochiai, T.; Franz,

D.; Inoue, S. Applications of N-heterocyclic imines in main group

chemistry. Chem. Soc. Rev. 2016, 45, 6327−6344. See also references

cited therein.

(

I) Feuerstein, T. J.; Goswami, B.; Rauthe, P.; Koppe, R.; Lebedkin,

S.; Kappes, M. M.; Roesky, P. W. Alkali metal complexes of an

enantiopure iminophosphonamide ligand with bright delayed

fluorescence. Chem. Sci. 2019, 10, 4742−4749. See also references

cited therein.

chemistry of boraamidinate ligands. Coord. Chem. Rev. 2007 , 251 ,

8) (a) Fedorchuk, C.; Copsey, M.; Chivers, T. The coordination

97 −924. (b) Corrente, A. M.; Chivers, T. Lanthanide Complexes of

Boraamidinate Ligands: Synthesis and X-ray Structures of {[Li-

(13) (a) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H.

Synthesis and Structural Chemistry of Non-Cyclopentadienyl

Organolanthanide Complexes. Chem. Rev. 2002, 102, 1851 −1896.

(b) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Cationic

Organometallic Complexes of Scandium, Yttrium, and the Lantha-

noids. Chem. Rev. 2006 , 106 , 2404 −2433. (c) Trifonov, A. A. Non-

metallocene rare-earth organometallic derivatives: synthesis, structure,

and application in the catalysis of transformations of unsaturated

substrates. Russ. Chem. Rev. 2007, 76, 1122 −1144. (d) Kaneko, H.;

Nagae, H.; Tsurugi, H.; Mashima, K. End Functionalized Polymer-

ization of 2-Vinylpyridine through Initial C −H Bond Activation of N-

heteroaromatics and Internal Alkynes by Yttrium Ene −Diamido

Complexes. J. Am. Chem. Soc. 2011, 133, 19626 −19629. (e) Mills, D.

P.; Lewis, W.; Blake, A. J.; Liddle, S. T. Reactivity Studies of a T-

Shaped Yttrium Carbene: C −F and C −O Bond Activation and C C

−

THF) ][bamLnCl (THF)]} (bam = [PhB(NDipp) ] ; Ln = Y, Pr,

Nd, Sm, Ho, Er, Yb) and {bamLnCl(THF) } (Ln = Y, Sm). Inorg.

Chem. 2010 , 49 , 2457 −2463. (c) Harder, S.; Naglav, D. Bora-

Amidinate Complexes of Lanthanide (II) Metals. Eur. J. Inorg. Chem.

4 2 2 2 2

010 , 2836 −2840. (d) Harder, S. Syntheses and structures of bora-

amidinate lanthanide (III) complexes. Dalton Trans. 2010, 39, 6677−

681. (e) Harder, S.; Freitag, B.; Stegner, P.; Pahl, J.; Naglav, D.

Strontium Chemistry with Silicone Grease. Z. Anorg. Allg. Chem.

015, 641, 2129−2134. (f) Chivers, T.; Eisler, D. J.; Fedorchuk, C.;

Schatte, G.; Tuononen, H. M.; Boere, R. T. Syntheses and Structures

of Magnesium and Zinc Boraamidinates: EPR and DFT Investigations

of Li, Mg, Zn, B, and In Complexes of the [PhB(N Bu) ] Anion

•‑

Bond Formation Promoted by [Y(BIPM)(I)(THF) ] (BIPM =

Radical. Inorg. Chem. 2006, 45, 2119−2131. (g) Chivers, T.; Eisler, D.

J.; Fedorchuk, C.; Schatte, G.; Tuononen, H. M.; Boere, R. T. Stable

spirocyclic neutral radicals: aluminium and gallium Boraamidinates.

Chem. Commun. 2005, 3930−3932.

C(PPh NSiMe ) ). Organometallics 2013, 32, 1239−1250. (f) Ortu,

3 2

F.; Gregson, M.; Wooles, A. J.; Mills, D. P.; Liddle, S. T. Yttrium

methanide and methanediide bis(silyl)amide complexes. Organo-

metallics 2017, 36, 4584−4590. (g) Ye, P.; Shao, Y.; Ye, X.; Zhang, F.;

Li, R.; Sun, J.; Xu, B.; Chen, J. Homoleptic Bis(trimethylsilyl)amides

of Yttrium Complexes Catalyzed Hydroboration Reduction of Amides

to Amines. Org. Lett. 2020, 22, 1306−1310. (h) Huang, Z.; Wang, S.;

Zhu, X.; Yuan, Q.; Wei, Y.; Zhou, S.; Mu, X. Well-Defined Amidate-

Functionalized N -Heterocyclic Carbene-Supported Rare-Earth Metal

Complexes as Catalysts for Efficient Hydroboration of Unactivated

Imines and Nitriles. Inorg. Chem. 2018, 57, 15069−15078. See also

references cited therein.

b) Bonyhady, S. J.; Collis, D.; Frenking, G.; Holzmann, N.; Jones, C.;

9) (a) Green, S. P.; Jones, C.; Stasch, A. Stable Magnesium (I)

Compounds with Mg-Mg Bonds. Science 2007, 318, 1754−1757.

Stasch, A. Synthesis of a stable adduct of dialane(4) (Al H ) via

(

hydrogenation of a magnesium(I) dimer. Nat. Chem. 2010, 2, 865 −

69. (c) Sen, S. S.; Jana, A.; Roesky, H. W.; Schulzke, C. A

Remarkable Base-Stabilized Bis(silylene) with a Silicon(I)−Silicon(I)

Bond. Angew. Chem., Int. Ed. 2009, 48, 8536−8538. (d) Nagendran,

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

14) Chivers, T.; Copsey, M. C.; Fedorchuk, C.; Parvez, M.; Stubbs,

lanthanide Complexes as Catalysts for Hydroboration Reaction

toward Aldehydes and Ketones. Org. Lett. 2017, 19, 3382−3385.

Highly efficient hydroboration of carbonyl compounds catalyzed by

tris (methylcyclopentadienyl)lanthanide complexes. Org. Biomol.

Chem. 2018, 16, 2787−2791. (d) Wang, W.; Shen, X.; Zhao, F.;

Jiang, H.; Yao, W.; Pullarkat, S. A.; Xu, L.; Ma, M. Ytterbium-

Catalyzed Hydroboration of Aldehydes and Ketones. J. Org. Chem.

2018, 83, 69−74.

(21) Dudnik, A. S.; Weidner, V. L.; Motta, A.; Delferro, M.; Marks,

T. J. Atom-efficient regioselective 1,2-dearomatization of function-

alized pyridines by an earth-abundant organolanthanide catalyst. Nat.

Chem. 2014, 6, 1100−1107.

M. Synthesis of Acyclic NPNCN Systems and Metalation Reactions

with Organolithium, -magnesium, and -aluminum Reagents. Organo-

metallics 2005, 24, 1919−1928.

15) (a) Hargittai, I.; Rouvray, D. H. Book Review: Fuzzy

Definitions: Concepts in Chemistry −A Contemporary Challenge.

Angew. Chem., Int. Ed. Engl. 1997 , 36 , 2525 −2525. (b) Zabrodsky, H.;

Peleg, S.; Avnir, D. Continuous symmetry measures. J. Am. Chem. Soc.

16) (a) Den Haan, K. H.; de Boer, J. L.; Teuben, J. H. Synthesis of

992, 114, 7843−7851.

monomeric permethylyttrocene derivatives. The crystal structures of

Cp *YN(SiMe ) and Cp *YCH(SiMe ) . Organometallics 1986, 5,

3 2

726−1733. (b) Klooster, W. T.; Brammer, L.; Schaverien, C. J.;

Budzelaar, H. M. C-H Bonds Are Not Elongated by Coordination to

(22) (a) Arrowsmith, M.; Hadlington, T. J.; Hill, M. S.; Kociok-

Kohn, G. Magnesium-catalyzed Hydroboration of Aldehydes and

Ketones. Chem. Commun. 2012, 48, 4567−4569. (b) Brand, S.;

Causero, A.; Elsen, H.; Pahl, J.; Langer, J.; Harder, S. Ligand Effects in

Calcium Catalyzed Ketone Hydroboration. Eur. J. Inorg. Chem. 2020,

Lanthanide Metals: Single-Crystal Neutron Diffraction Structures of

C Me )Y(OC H Bu )CH(SiMe ) at 20 K and (C Me )La{CH-

SiMe ) } at 15 K. J. Am. Chem. Soc. 1999, 121, 1381−1382.

c) Fryzuk, M. D.; Jafarpour, L.; Kerton, F. M.; Love, J. B.; Patrick, B.

tetracoordinate lanthanide amides [(Me Si) N] Ln(μ -Cl)Li(THF)

2 2

(

020, 1728−1735.

23) Zhou, S. L.; Wang, S. W.; Yang, G. S.; Liu, X.; Sheng, E.; Zhang,

K.; Cheng, L.; Huang, Z. Synthesis, structure, and catalytic activity of

O.; Rettig, S. J. Carbon −Carbon Bond Formation Using Yttrium(III)

and the Lanthanide Elements. Organometallics 2001 , 20 , 1387 −1396.

d) Matsuo, Y.; Mashima, K.; Tani, K. Selective Formation of

Homoleptic and Heteroleptic 2,5-Bis(N-aryliminomethyl)pyrrolyl

Yttrium Complexes and Their Performance as Initiators of ε -

Caprolactone Polymerization. Organometallics 2001, 20 , 3510 −3518.

e) Kim, Y. K.; Livinghouse, T.; Horino, Y. Chelating Bis-

thiophosphinic amidate)s as Versatile Supporting Ligands for the

Jones, P. G.; Grunenberg, J. Structural and theoretical investigation of

Ln Nd, Sm, Eu). Polyhedron 2003, 22, 1019−1024.

24) Tamm, M.; Petrovic, D.; Randoll, S.; Beer, S.; Bannenberg, T.;

(

-iminoimidazolines − carbene analogues of iminophosphoranes. Org.

Biomol. Chem. 2007, 5, 523−530.

Group 3 Metals. An Application to the Synthesis of Highly Active

Catalysts for Intramolecular Alkene Hydroamination. J. Am. Chem.

Soc. 2003, 125 , 9560 −9561. (f) Arnold, P. L.; Mungur, S. A.; Blake, A.

J.; Wilson, C. Anionic Amido N-Heterocyclic Carbenes: Synthesis of

Covalently Tethered Lanthanide −Carbene Complexes. Angew. Chem.,

Int. Ed. 2003 , 42 , 5981 −5984. (g) Arnold, P. L.; Liddle, S. T.

Deprotonation of N-Heterocyclic Carbenes to Afford Heterobime-

tallic Organolanthanide Complexes. Organometallics 2006, 25, 1485−

NOTE ADDED AFTER ASAP PUBLICATION

Published ASAP on December 2, 2020; Supporting Informa-

tion revised on December 8, 2020.

■

491. (h) Edworthy, I. S.; Blake, A. J.; Wilson, C.; Arnold, P. L.

Synthesis and NHC Lability of d Lithium, Yttrium, Titanium, and

Zirconium Amido Bis(N-heterocyclic carbene) Complexes. Organo-

metallics 2007, 26, 3684−3689. (i) Trambitas, A. G.; Panda, T. K.;

Jenter, J.; Roesky, P. W.; Daniliuc, C.; Hrib, C. G.; Jones, P. G.;

Tamm, M. Rare-Earth Metal Alkyl, Amido, and Cyclopentadienyl

Complexes Supported by Imidazolin-2-iminato Ligands: Synthesis,

Structural Characterization, and Catalytic Application. Inorg. Chem.

17) (a) Luo, Y.; Fan, S.; Yang, J.; Fang, J.; Xu, P. Rare earth metal

010, 49, 2435−2446.

bis(amide) complexes bearing amidinate ancillary ligands: Synthesis,

characterization, and performance as catalyst precursors for cis -1,4

selective polymerization of isoprene. Dalton Trans. 2011, 40, 3053−

059. (b) Kazeminejad, N.; Munzfeld, L.; Gamer, M. T.; Roesky, P.

W. Mono- and bimetallic amidinate samarium complexes − synthesis,

structure, and hydroamination catalysis. Dalton Trans. 2019, 48,

153−8160.

18) (a) Shegavi, M. L.; Bose, S. K. Recent advances in the catalytic

hydroboration of carbonyl compounds. Catal. Sci. Technol. 2019 , 9 ,

307 −3336. (b) Chong, C. C.; Kinjo, R. Catalytic Hydroboration of

Carbonyl Derivatives, Imines, and Carbon Dioxide. ACS Catal. 2015 ,

ki, k.; Hreczycho, G. Hydrosilylation and

hydroboration in a sustainable manner: from Earth-abundant catalysts

, 3238 −3259. (c) Kucins

to catalyst-free solutions. Green Chem. 2020, 22, 5210−5224.

19) (a) Stachowiak, H.; Kazmierczak, J.; Kucinski, K.; Hreczycho,

G. Catalyst-Free and Solvent-Free Hydroboration of Aldehydes. Green

Chem. 2018, 20, 1738−1742. (b) Wang, W.; Man, L.; Weiwei, Y.;

Mengtao, M.; Sumod, A. P.; Li, X.; Pak-Hing, L. Catalyst-free and

solvent-free hydroboration of ketones. New J. Chem. 2019, 43,

(

0744−10749. See also references cited therein.

20) (a) Weidner, V. L.; Barger, C. J.; Delferro, M.; Lohr, T. L.;

Marks, T. J. Rapid, Mild, and Selective Ketone and Aldehyde

Hydroboration/Reduction Mediated by a Simple Lanthanide

Catalyst. ACS Catal. 2017, 7, 1244−1247. (b) Chen, S.; Yan, D.;

Xue, M.; Hong, Y.; Yao, Y.; Shen, Q. Tris(cyclopentadienyl)-