Versatile reactivity of a rhodium(i) boryl complex towards ketones and imines

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Versatile reactivity of a rhodium(I) boryl complex

towards ketones and imines†

Cite this: Dalton Trans., 2014, 43,

6786

Sabrina I. Kalläne, Thomas Braun,* Beatrice Braun and Stefan Mebs

The rhodium(I) boryl complex [Rh(Bpin)(PEt₃)₃] (1) reacts with the ketones α,α,α-triﬂuoroacetophenone

and 9-ﬂuorenone by insertion of the CvO bond to give [Rh{η³-C(CF₃)(OBpin)C₆H₅}(PEt₃)₂] (4) and

[Rh{η⁵-C₁₃H₈(OBpin)}(PEt₃)₂] (6), whereas the reaction with acetophenone leads to the formation of

[Rh(H)(PEt₃)₃] (2), [Rh(OBpin)(PEt₃)₃] (3) and (E)-(Ph)CHvCHBpin. Treatment of 1 with ketimines generates

[Rh{η³-C₆H₅vC(Ph)N(Ph)(Bpin)}(PEt₃)₂] (7), [Rh{(η³-C₁₂H₈)N(Ph)(Bpin)}(PEt₃)₂] (8) or [Rh{CPh₂N(H)(Bpin)}-

(PEt₃)₂] (9). The insertion of aldimines into the Rh–B bond gives access to [Rh[η³-CH{N(C₆H₁₃)Bpin}-

C₆H₅](PEt₃)₂] (11) or [Rh[η³-CH{N(Ph)Bpin}C₆H₅](PEt₃)₂] (12). The latter is converted into the C–H

activation product [Rh{(C₆H₄)-o-N(Bpin)(CH₂Ph)}(PEt₃)₃] (13). Complex 13 reacts with B₂pin₂to yield the

boryl complex 1 and the amine PhCH₂N(Bpin)(C₆H₄-o-Bpin).

Received 9th January 2014,

Accepted 17th February 2014

DOI: 10.1039/c4dt00080c

www.rsc.org/dalton

α-amino boronates with [Pt(cod)(Cl)₂] (cod = 1,5-cycloocta-

Introduction

diene) as a catalyst.⁴³The synthetic potential is limited by the

Transition metal boryl complexes^1–6have received consider- substrates: good results were only obtained by treatment of

able attention due to their role as key intermediates in metal- aldimines of the type ArCHvNR bearing a sterically bulky

catalyzed borylation reactions to generate borylated N-aryl group (R) or ortho directing groups at the C-aryl substitu-

derivatives.^7–12Rhodium boryl complexes¹³are known to ents (Ar) and by using B₂cat₂. The authors observed no reac-

enable catalytic processes such as the hydroboration and de- tion by using the same catalyst, but B₂pin₂(pin = pinacolato)

hydrogenative borylation of olefins,^14–22the diboration of as a diborane. Furthermore, the addition of phosphine to the

alkenes and alkynes^23,24or the functionalization of hydro- platinum catalyst reduced its activity. Rhodium phosphine

carbons via C–H activation reactions.^{10,12,25–31}

complexes were proposed to be ineﬀective catalysts for the aldi-

Many examples of the metal-catalyzed diboration of alkenes mine diboration. Wilkinson’s catalyst [Rh(Cl)(PPh₃)₃] provides

and alkynes using diboranes have been reported,⁸particularly large amounts of the hydroboration product ArCH₂N(Bcat)R

employing Rh (for the alkenes)^32–35and Pt complexes (in both with respect to the diboration product.^37,43It was proposed

cases). In certain circumstances the reaction also proceeds in that the reason for the unselective reactivity is the poor regio-

the presence of Lewis-bases³⁶or without a catalyst. Methods control of the CvN insertion step into a metal–boron bond. In

for the 1,2-diboration of carbon–heteroatom double bonds are the case of aldimines the formation of M–C and B–N bonds leads

rare, although such a conversion would for instance represent to diboration, whereas the formation of M–N and B–C bonds can

a direct pathway to a variety of α-functionalized boronate cause β-hydrogen elimination reactions providing hydroboranes,

esters,^37,38which are useful building blocks^39,40and some of which can then undergo hydroboration reactions.³⁷

which have pharmaceutical applications.^40,41In most of the

Baker and Westcott also investigated the rhodium-catalyzed

cases the reaction of diboranes with heteroatom-containing, borylation of ketimines with diboranes.⁴⁴The use of acetophe-

unsaturated organics are not selective and give a variety of none-derived imines PhC(CH₂R)vN(Ar) and B₂cat′₂(cat′ =

products.

4-^tBu-1,2-O₂-C₆H₃) resulted in the formation of N-(boryl)enam-

Baker and Westcott have reported the rhodium-catalyzed ines and N-borylamines. Combined DFT and ONIOM studies

diboration of a thioketone by selective addition of B₂cat₂(cat = gave an insight into the mechanism.⁴⁵An oxidative addition of

catecholato) to thiocamphor.^37,42In 2000, Baker et al. also the diborane at [Rh(Cl)(PH₃)₃] and imine coordination is fol-

achieved the catalytic diboration of CvN bonds to synthesize lowed by a regioselective insertion of the imine into the M–B

bond by N–B bond formation. Then two possible steps can

occur: either carbon–boron bond formation yields the desired

diboration product or β-hydrogen elimination takes place to

give the N-(boryl)enamines and HBcat′, which subsequently

Humboldt-Universität zu Berlin, Department of Chemistry, Brook-Taylor-Straße 2,

D-12489 Berlin, Germany. E-mail: thomas.braun@chemie.hu-berlin.de

†CCDC 977662–977667. For crystallographic data in CIF or other electronic

can add to the unreacted imine.

format see DOI: 10.1039/c4dt00080c

6786 | Dalton Trans., 2014, 43, 6786–6801

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Concerning the diboration of CvO double bonds, Sadighi

et al. succeeded in the catalytic diboration of aldehydes using

a unique copper(^I) boryl complex, [(IPr)Cu(Bpin)] (IPr = 1,3-bis-

(2,6-diisopropylphenyl)imidazol-2-ylidene), as a catalyst to give

RCH(OBpin)Bpin.⁴⁶A stoichiometric reaction of the complex

with mesitylaldehyde generates [(IPr)Cu{CH(Ar)(OBpin)}], by

the insertion of the carbonyl group into a metal–boron bond,

which accompanied by a metal–carbon σ-bond formation. No

evidence for the formation of the alternative regioisomer was

found and an attempt to synthesize it using the appropriate

alcohol failed giving the same product as for the insertion

reaction of the aldehyde.¹¹The catalytic diboration also pro-

ceeds using [(IPr)Cu{CH(Ar)(OBpin)}] as a catalyst or [(ICy)Cu-

(O^tBu)] (ICy = 1,3-cyclohexylimidazol-2-ylidene) as a precatalyst.

The activity of these {(IPr)Cu} complexes in the catalytic

diboration of ketones has also been demonstrated.^47–49

Recently the synthesis of the 16-electron rhodium boryl

complex [Rh(Bpin)(PEt₃)₃] (1)⁵⁰was reported. This complex is

capable of both, stoichiometric C–H and catalytic C–F or N–H

bond activation reactions.^50,51In this contribution we report

on the reactivity of

1 towards ketones, ketimines and

aldimines. The synthesis of rhodium complexes by insertion

of CvO and CvN bond containing compounds into the Rh–B

bond is described. Reactivity studies of these complexes

bearing

a Rh–C–O–B or a Rh–C–N–B linkage are also

presented.

Scheme 1 Reactivity of complex

1

towards acetophenone (a) and

styrene (b) and the proposed mechanism for the formation of (E)-(Ph)-

CHvCHBpin (c).

Results and discussion

Reactivity of complex 1 towards ketones

of 0.5 equivalent alkene with 2 resulted in the formation of

PhCHvC(Bpin)₂.

Adding 0.5 equivalent of acetophenone to the boryl complex

[Rh(Bpin)(PEt₃)₃] (1) resulted in the formation of [Rh(H)-

(PEt₃)₃] (2) and [Rh(OBpin)(PEt₃)₃] (3) (Scheme 1a). Complex 3

was synthesized before and identified by comparison of the

NMR data with an authentic sample. Moreover, the vinylboro-

nate ester (E)-(Ph)CHvCHBpin was identified by ¹H and

¹³C NMR spectroscopy. In addition traces of PhCHvC(Bpin)₂

could be detected by GC-MS analysis. The alkene PhC-

(OBpin)vCH₂, which would be the result of a β-hydrogen

elimination after insertion of the ketone into the Rh–B bond

and O–B formation in 1,⁴⁴was not found.

Mechanistically we assume an initial insertion of the aceto-

phenone into the Rh–B bond to produce complex A, which

bears an oxygen–boron linkage (Scheme 1c). A β-hydrogen

elimination step leads then to the formation of the hydrido

complex 2 and PhC(OBpin)vCH₂. The latter might reinsert

into the Rh–H bond to form complex B. Then, a migration of

the borate ester entity to the metal results in the formation of

3 and the release of styrene. This alkene might react with

additional boryl complex 1 by dehydrogenative borylation to

give (E)-(Ph)CHvCHBpin^52–54and 2. Independent reactions

support these suggestions. Treatment of 1 with stoichiometric

amounts of styrene led selectively to 2 and (E)-(Ph)CHv

CHBpin, as is depicted in Scheme 1b. Furthermore, a reaction

Apparently, the treatment of the boryl complex 1 with

acetophenone leads to an insertion reaction, but the presence

of a β-hydrogen atom at a ketone induces further reaction

steps. To avoid the β-hydrogen elimination, we investigated the

reactivity of the boryl complex 1 towards α,α,α-trifluoroaceto-

phenone which bears fluorine instead of hydrogen atoms at

the α-position. Adding α,α,α-trifluoroacetophenone to 1 gave

instantaneously the rhodium η³-benzyl complex [Rh{η³-C(CF₃)-

(OBpin)C₆H₅}(PEt₃)₂] (4) and one equivalent of phosphine, by

insertion of the CvO double bond into the metal–boron bond

(Scheme 2). Product 4 was characterized by NMR spectroscopy

and liquid injection field desorption ionization mass spectro-

metry (LIFDI MS). LIFDI data revealed a peak at m/z 460 which

can be assigned to the molecular ion [M]⁺. The ³¹P{¹H} NMR

spectrum of 4 reveals two signals at δ 28.1 and 21.8 ppm due

to the inequivalent phosphine ligands. The phosphorus–

phosphorus coupling constant of 36 Hz is in the typical range

for cis-phosphines.^55–57The phosphorus–rhodium coupling

constants of 257 Hz and 160 Hz are fairly large and indicate

the presence of a rhodium(^I) species.^55–57The signal at δ

28.1 ppm with the larger phosphorus–rhodium coupling con-

stant is caused by the phosphorus atom in the trans position

to the ring according to extended Hückel MO calculations.^58,59

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Table 1 Selected bond lengths (Å) and angles (°) for 4 with estimated

standard deviations in parentheses

Bond

Length

Bond

Angle

Rh1–C1

Rh1–C10

Rh1–C11

R1–P1

Rh1–P2

C1–O1

C1–C10

C1–C2

B1–O1

C10–C11

C10–C15

C11–C12

C12–C13

C13–C14

C14–C15

2.1248(14)

2.1929(14)

2.3833(15)

2.2850(4)

2.2274(4)

1.4244(17)

1.454(2)

1.504(2)

1.359(2)

1.422(2)

1.430(2)

1.415(2)

1.363(3)

1.408(3)

1.368(2)

C1–Rh1–P2

C1–Rh1–P1

C10–Rh1–P1

P2–Rh1–P1

P2–Rh1–C11

P1–Rh1–C11

O1–C1–C10

O1–C1–C2

C10–C1–C2

C10–C1–Rh1

C11–C10–C15

C11–C10–C1

C15–C10–C1

C10–C11–Rh

99.37(4)

164.60(4)

127.20(4)

95.936(14)

166.06(4)

97.61(4)

116.19(13)

107.33(12)

121.37(13)

72.86(8)

117.03(14)

120.51(14)

121.34(13)

164.73(8)

are summarized in Table 1. The structure reveals an approxi-

mately square planar coordination geometry with P1, P2, C1

Scheme 2 Syntheses of complexes 4 and 6 and reactivity of complex 4 and C11 occupying the four coordination sites. The distance

towards CO.

between the plane defined by these atoms and Rh1 is 0.04 Å.

The dihedral angle between this plane and the plane defined

by the benzyl group is 80.6° (for comparison 75.4° in [Rh-

(η³-CH₂C₆H₅)(PiPr₃)₂]).⁵⁹The rhodium–carbon distances are

2.125(1) Å for Rh1–C1, 2.193(1) Å for Rh1–C10 and 2.383(2) Å

for Rh1–C11 and are comparable to those found for [Rh-

(η³-CH₂C₆H₅)(PiPr₃)₂] (2.125(9), 2.23(1), 2.41(1) Å)⁵⁹or [Rh-

(η³-CH₂C₆H₅)(dippp)] (2.141(4), 2.197(3), 2.362(3) Å).⁶⁴As a

result of the coordination at the rhodium center the delocali-

zation in the aromatic ring is repealed which is evidenced

by short carbon–carbon distances for C12–C13 (1.363(3) Å) and

C14–C15 (1.368(2) Å). The other ring carbon–carbon distances

range between 1.408(3) and 1.430(2) Å.

Treatment of the rhodium(^I) benzyl complex 4 with CO led

to the insertion of CO into the rhodium–carbon bond as well

as to CO coordination (Scheme 2). The generation of trans-

[Rh{C(O)C(CF₃)(Ph)OBpin}(CO)(PEt₃)₂] (5) can be observed by a

color change from dark red to yellow and the precipitation of a

hardly soluble solid. The formation of 5 is in sharp contrast to

Fig. 1 An ORTEP diagram of 4. The ellipsoids are drawn at the 50%

probability level. The hydrogen atoms are omitted for clarity.

a report by Werner et al., who treated [Rh(η³-CH₂C₆H₅)-

(PiPr₃)₂] with CO, which gave [Rh(η¹-CH₂C₆H₅)(CO)(PiPr₃)₂].⁵⁹

In 5 an intramolecular B–O interaction between the Lewis-

The signal at δ 21.8 ppm exhibits an additional coupling of acidic boron atom and the oxygen atom of the CvO unit

seems to favor the CO insertion and leads to a five membered

8 Hz to the fluorine atoms and can be assigned to the phos-

phine which is located in the trans position to the carbon

ring formation. The ³¹P{¹H} NMR spectrum of 5 displays a

atom bearing the CF₃group. The presence of the latter moiety doublet of doublets at δ 25.6 ppm and a doublet of doublet of

is also revealed in the ¹⁹F NMR spectrum by a signal at δ

quartets at δ 22.7 ppm. The resonances reveal a phosphorus–

phosphorus coupling of 210 Hz for the phosphorus atoms,

−57.4 ppm. For the boron atom a resonance at δ 22.5 ppm can

be detected in the ¹¹B NMR spectrum. The chemical shift is which are oriented in a mutual trans position. The phos-

typical of a pinacol borate ester.^60–63Complex 4 is not very

phorus–rhodium coupling constants of both signals are

141 Hz and comparable to that in trans-[Rh(Me)(CO)(PEt₃)₂]

at room temperature according to the NMR spectra. In the (J_RhP= 140 Hz).⁶⁵A quartet splitting is caused by a fluorine–

stable in solution and decomposition starts within a few hours

phosphorus coupling of 4 Hz. The same coupling constant is

presence of free phosphine its stability rises to one day.

found in the ¹⁹F{¹H} NMR spectrum for a signal at δ

The molecular structure of 4 was confirmed by single-

crystal X-ray analysis (Fig. 1). Selected bond lengths and angles −71.8 ppm. For the boron atom a resonance is detected at δ

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Table 2 Selected bond lengths (Å) and angles (°) in 5 with estimated

standard deviations in parentheses

Bond

Length

Bond

Angle

Rh1–C13

Rh1–C14

Rh1–P1

Rh1–P2

O1–C13

O2–C14

O2–B1

O3–C16

O3–B1

O4–B1

1.878(4)

2.016(4)

2.3100(9)

2.3333(10)

1.147(5)

1.266(4)

1.616(4)

1.401(4)

1.450(5)

1.427(5)

1.423(4)

1.580(5)

C13–Rh1–C14

C13–Rh1–P1

C14–Rh1–P1

C13–Rh1–P2

C14–Rh1–P2

P1–Rh1–P2

C14–O2–B1

C16–O3–B1

O1–C13–Rh1

O2–C14–C16

O5–B1–O4

175.04(15)

91.12(11)

91.59(10)

88.62(12

90.71(11)

154.61(4)

114.2(3)

114.3(3)

177.5(3)

107.1(3)

108.4(3)

118.2(3)

108.8(3)

98.7(3)

O5–B1

C14–C16

O5–B1–O3

O4–B1–O2

O3–B1–O2

O3–C16–C14

105.5(3)

Fig. 2 An ORTEP diagram of 5. The ellipsoids are drawn at the 50%

probability level. The hydrogen atoms are omitted for clarity.

interaction between the Lewis-acid boronic ester and the car-

bonyl group. A similar result was found for N-(2-(4,4,5,5-tetra-

15.3 ppm in the ¹¹B NMR spectrum. This resonance is shifted methyl-1,3,2-dioxaboronlan-2-yl)phenyl)acetamide, where an

to higher field when compared to the signal of 4 or to other interaction between the boron atom and the oxygen atom of

pinacol esters of boric acids, and to lower field when compared the acetamide group leads to a B–O distance of 1.598(3) Å.⁷¹

to the resonance for borate anions ([B(pin)₂]⁻: δ 8 ppm).⁶⁶The This interaction eﬀects the ring formation and an elongation

IR spectrum of 5 reveals absorption bands at 1952 cm⁻¹and of the C14–O2 bond to be 1.266(4) Å. The comparable distance

1478 cm⁻¹which are characteristic for a rhodium(I) carbonyl in [Rh(I)(COMe)(4-C₅NF₄)(PEt₃)₂] is 1.202(2) Å.⁶⁷

ligand and for the acyl moiety, respectively.^67,68Note that the

Treatment of the rhodium(I) boryl complex 1 with 9-fluore-

rhodium acyl complex [Rh{C(O)CH₂Ph}(CO)₂(κ²-iPr₂PCH₂- none yielded the CvO insertion product [Rh{η⁵-C₁₃H₈(OBpin)}-

PiPr₂)] exhibits an absorption band at 1714 cm⁻¹in the IR (PEt₃)₂] (6) as well as free phosphine within one hour

spectrum.⁶⁹The isotopologue of 5, trans-[Rh{¹³C(O)C(CF₃)(Ph)- (Scheme 2). The formally negative charge at the metal bound

OBpin}(¹³CO)(PEt₃)₂] (5a), was obtained on treatment of 4 with fluorene is likely to be delocalized in the five-membered ring,

¹³CO. The ¹³C NMR spectrum shows one doublet of doublet of which is consistent with an η⁵-coordination of the fluorenyl

triplets at δ 198.7 ppm which can be assigned to the carbonyl ligand at the rhodium atom in 6. Complex 6 was characterized

ligand and one at δ 296.1 ppm indicating the presence of the by NMR spectroscopy and elemental analysis. The ³¹P{¹H}

acyl moiety. The carbon–rhodium and the carbon–phosphorus NMR spectrum of 6 displays two doublet of doublets at δ 40.7

coupling constants have characteristic values of 52 Hz (CuO), and 19.8 ppm. The phosphorus–rhodium coupling constants

42 Hz (CvO) and 16 Hz (CuO), 12 Hz (CvO).⁶⁷The carbon– are 254 Hz and 204 Hz and the phosphorus–phosphorus coup-

carbon coupling is 34 Hz. The signals of 5a in the ³¹P{¹H} ling constant is 43 Hz. This pattern confirms again the pres-

NMR spectrum exhibit two additional carbon–phosphorus ence of a rhodium(^I) species with a cis alignment of the two

couplings in comparison to 5.

phosphine ligands. The presence of the borate ester moiety is

The molecular structure of 5 was confirmed by single- revealed in the ¹¹B NMR spectrum by a signal at δ 22.7 ppm.

crystal X-ray analysis (Fig. 2). Selected bond lengths and angles The ¹H and ¹³C NMR spectra of 6 exhibit signals in the aro-

are summarized in Table 2. The rhodium atom is coordinated matic region caused by the fluorenyl group. Compound 6 exhi-

by a CO ligand, an acyl unit and two phosphine ligands. The bits a pronounced sensitivity towards air and moisture as solid

square-planar geometry is strongly distorted as evidenced by a as well as in solution. The solubility in hexamethyldisilane,

P1–Rh1–P2 angle of 154.61(4)° and a C13–Rh1–C14 angle of hexane or benzene is very low.

175.04(15)°. The metal–carbon bond length to the carbonyl

The identity of 6 was further confirmed by single-crystal

ligand of 1.878(4) Å is comparable to that in trans-[Rh(4-C₅NF₄)- X-ray analysis. An ORTEP drawing is presented in Fig. 3,

(CO)(PEt₃)₂] (1.8494(16) Å).⁶⁷The rhodium–carbon distance whereas selected bond distances and angles are reported in

Rh1–C14 of 2.016(4) Å is relatively short, but comparable with Table 3. The rhodium atom is coordinated by two phosphorus

the bond in other rhodium(^III) acyl complexes like [RhI(COMe)- atoms with a P1–Rh–P2 angle of 97.51(3)° and one fluorenyl

(4-C₅NF₄)(PEt₃)₂] (2.0018(19) Å).^67,70The short distance ligand with a rhodium–centroid distance of 1.9847(12) Å. The

between the boron atom and the oxygen atom in the acyl P1–Rh–P2 plane is nearly perpendicular to the plane defined

moiety of 1.616(4) Å (for comparison the B–O bond lengths in by the fluorenyl system (dihedral angle: 88.54(12)°). There are

the borate ester moiety are 1.423(4) to 1.450(5) Å) and the five short (Rh1–C1 2.217(3) Å, Rh1–C2 2.355(3) Å, Rh1–C5

nearly tetrahedral geometry at the boron atom indicate an 2.355(3) Å, Rh1–C3 2.360(3) Å, Rh1–C4 2.365(3) Å) rhodium–

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Scheme 3 Syntheses of complexes 7 and 8.

Complexes 7 and 8 could be isolated and were characterized

by NMR spectroscopy. The ³¹P{¹H} NMR spectrum at 293 K of

7 reveals two broad doublets at δ 31.8 and 30.5 ppm in a 5 : 1

ratio, which can be assigned to two isomeric structures. The

phosphorus–rhodium coupling constant for each signal is

212 Hz, indicating the presence of rhodium(^I) complexes.

NMR analysis of a solution of 7 at higher temperature shows

that the two resonances are coalesced at 333 K and the

rhodium–phosphorus coupling constant is retained (Fig. 4).

For compound 8, a single resonance at δ 34.2 ppm can be

detected in the ³¹P{¹H} NMR spectrum, which exhibits a

phosphorus–rhodium coupling constant of 215 Hz. Variable-

temperature NMR analysis of a solution of 8 shows that the

resonance splits into two signals at low temperature. The ratio

of the signals is temperature-dependent (1 : 0.55 at 243 K),

which also suggests an equilibration between two isomers. We

assume that the presence of two isomers of 7 and 8 is caused

by a restricted rotation about the C–N bond. In addition the

variable-temperature ³¹P{¹H} NMR analysis of a solution of 7

indicates a dynamic behavior, which presumably involves an

additional intramolecular exchange of the phosphine ligands

in the isomers. Thus, the NMR spectrum at 253 K exhibits a

very broad signal for the major isomer, which splits into two

signals at 223 K. At 203 K the expected pattern of a doublet of

doublets at δ 35.5 ppm and a doublet of doublets at δ

29.5 ppm with coupling constants of 210 and 213 Hz (J_RhP) as

well as of 46 Hz (J_PP) was observed. At 223 K the signal for the

minor isomer starts to decoalesce (Fig. 4). For the boron atoms

in complexes 7 and 8 resonances can be detected in the ¹¹B

NMR spectrum at δ 25.2 (7) and 24.8 ppm (8), respectively.

They appear in the typical range for aminoborate esters.^51,72,73

The molecular structures of 7 and 8 were confirmed by single-

crystal X-ray analysis (Fig. 5 and 6). Selected bond lengths and

angles are summarized in Tables 4 and 5. The asymmetric

unit of 7 includes two crystallographically independent mole-

cules, which show only minor diﬀerences in the bond length

and angles. Therefore, only one of the two crystallographically

independent molecules is shown and discussed. In the struc-

ture of 7 the central rhodium atom is coordinated by two

Fig. 3 An ORTEP diagram of 6. The ellipsoids are drawn at the 50%

probability level. The hydrogen atoms are omitted for clarity.

Table 3 Selected bond lengths (Å) and angles (°) for 6 with estimated

standard deviations in parentheses

Bond

Length

Bond

Angle

Rh1–P1

Rh1–P2

Rh1–C1

Rh1–C2

Rh1–C5

Rh1–C3

Rh1–C4

O1–B1

O1–C1

C1–C5

C1–C2

C2–C3

C3–C4

C4–C5

2.2573(8)

2.2040(9)

2.217(3)

2.355(3)

2.360(3)

2.365(3)

1.371(4)

1.392(4)

1.432(4)

1.433(4)

1.467(4)

1.429(5)

P2–Rh1–C1

P2–Rh1–P1

C1–Rh1–P1

P1–Rh1–C2

P1–Rh1–C5

P1–Rh1–C3

P1–Rh1–C4

B1–O1–C1

O1–C1–C5

O1–C1–C2

C5–C1–C2

C3–C2–C1

C2–C3–C4

C5–C4–C3

C4–C5–C1

96.30(8)

97.51(3)

165.35(8)

130.67(9)

139.29(8)

104.94(8)

109.23(8)

122.4(3)

125.5(3)

123.5(3)

109.5(3)

107.2(3)

107.3(3)

108.2(3)

106.9(3)

carbon bond lengths, indicating a η⁵coordination. The geo-

metry at the carbon atom C1 is nearly trigonal-planar with an

angular sum of 358.5(3)°.

Reactivity of complex 1 towards imines

The boryl complex [Rh(Bpin)(PEt₃)₃] (1) also reacted with

the ketimines, N-(diphenylmethylene)aniline or N-(fluoren-

9-ylidene)aniline (Scheme 3). Adding the latter compounds to

a solution of 1 in Me₆Si₂resulted in the formation of a red or

purple solid within one day or half an hour, respectively. In a

comparable way to the insertion reactions of ketones, the com-

plexes [Rh{η³-C₆H₅vC(Ph)N(Ph)(Bpin)}(PEt₃)₂] (7) and [Rh{(η³-

C₁₂H₈)N(Ph)(Bpin)}(PEt₃)₂] (8) were furnished by insertion of

the C–N double bond into the rhodium–boron bond, and N–B

bonds are generated. However, in each case the rhodium atom

is coordinated in a remote position at an aromatic ring, which

results in an enamine structure.

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Fig. 6 An ORTEP diagram of 8. The ellipsoids are drawn at the 50%

probability level. The hydrogen atoms are omitted for clarity.

Table 4 Selected bond lengths (Å) and angles (°) for 7 with estimated

standard deviations in parentheses (the data for the second crystallogra-

phically independent molecules are comparable and are therefore not

shown)

Bond

Length

Bond

Angle

Rh1–C13

Rh1–C14

Rh1–P2

2.201(2)

2.212(2)

2.2299(6)

2.2477(6)

2.312(2)

2.793(2)

2.695(2)

2.437(2)

1.424(3)

1.423(3)

1.452(2)

1.411(3)

1.432(4)

1.401(3)

1.463(3)

1.370(3)

1.461(3)

1.373(3)

C13–Rh1–P2

C13–Rh1–P1

P2–Rh1–P1

P2–Rh1–C15

P1–Rh1–C15

C18–N1–B1

99.44(7)

161.64(7)

98.87(2)

159.83(6)

97.12(6)

124.70(17)

116.60(17)

117.74(18)

118.2(2)

118.6(2)

123.07(19)

125.3(2)

121.61(18)

113.1(2)

118.11(19)

121.1(2)

Rh1–P1

Rh1–C15

Rh1–C16

Rh1–C36

Rh1–C37

N1–C18

N1–B1

N1–C17

C13–C14

C13–C37

C14–C15

C15–C16

C16–C17

C16–C36

C36–C37

C18–N1–C17

B1–N1–C17

C14–C13–C37

C15–C14–C13

C14–C15–C16

C17–C16–C36

C17–C16–C15

C36–C16–C15

C16–C17–N1

C37–C36–C16

C36–C37–C13

Fig. 4 Variable temperature ³¹P{¹H} NMR spectra (121.5 MHz,

[D₈]toluene) of 7.

122.8(2)

phosphine ligands with a P1–Rh–P2 angle of 99.44(7)° and an

allylic moiety. Three short rhodium–carbon bond lengths

(Rh1–C13 2.201(2) Å, Rh1–C14 2.212(2) Å, Rh1–C15 2.312(2) Å)

indicate η³coordination. The distance between the rhodium

atom and the plane defined by the carbon atoms C13, C14,

C15, C16, C36 and C37 is 1.92836(17) Å. This plane is perpen-

dicular to the P1–Rh1–P2 plane with a dihedral angle of

89.14(9)°. The Bpin group is arranged on the same side as the

metal atom with regard to the PhCN moiety. The geometry at

the carbon atom C17 is nearly trigonal-planar which is indi-

cated by an angular sum of 359.72(10)°. The C16–C17 bond

distance of 1.370(3) Å is significantly shorter than the C17–C30

bond length (1.464(3) Å) and can be assigned to a carbon–

carbon double bond⁷⁴which verifies the formation of an

enamine. The carbon–carbon bond distance C36–C37 (1.373(3) Å)

is also very short, whereas the other C–C bond lengths in the

Fig. 5 An ORTEP diagram of 7. The ellipsoids are drawn at the 50%

probability level. The hydrogen atoms are omitted for clarity. The asym-

metric unit cell contains two crystallographically independent mole-

cules; only one of them is shown.

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Table 5 Selected bond lengths (Å) and angles (°) for 8 with estimated

standard deviations in parentheses

Bond

Length

Bond

Angle

Rh1–C14

Rh1–P1

Rh1–C13

Rh1–P2

Rh1–C18

Rh1–C15

Rh1–C16

Rh1–C17

N1–B1

2.206(3)

2.2245(7)

2.235(3)

2.2377(8)

2.347(3)

2.409(3)

2.682(3)

2.706(3)

1.421(4)

1.437(3)

1.408(4)

1.417(4)

1.431(4)

1.385(4)

1.459(4)

1.452(4)

1.386(4)

1.439(4)

1.433(4)

1.429(4)

C14–Rh1–P1

C14–Rh1–P2

P1–Rh1–P2

P1–Rh1–C18

P2–Rh1–C18

B1–N1–C19

C18–C13–C14

C13–C14–C15

C16–C15–C14

C15–C16–C17

C19–C17–C18

C19–C17–C16

C18–C17–C16

C13–C18–C17

C16–C17–C19

C19–C32–C33

98.55(8)

162.27(7)

95.03(3)

159.72(7)

99.46(7)

118.9(2)

119.5(2)

119.7(3)

120.8(2)

120.1(2)

132.8(2)

109.6(2)

117.6(2)

120.4(2)

109.6(2)

109.3(2)

N1–C19

C13–C18

C13–C14

C14–C15

C15–C16

C16–C17

C16–C33

C17–C19

C17–C18

C19–C32

C32–C33

Scheme 4 Syntheses of complexes 9, 9’ and 11–13.

metal bound ring are in the range of 1.401(3) to 1.463(3) Å (for

the η³-allyl entity: 1.401(3) and 1.411(3) Å). The C17–N1 bond

length (1.452(2) Å) is long for a CvC–NR₂bond,⁷⁵which is

probably caused in part by the presence of the boryl moiety

with the empty orbital at the boron atom. However it is com-

parable with the corresponding bond lengths of 1.424(3) Å in

7, 1.437(3) Å in 8 as well as 1.442(3) Å and 1.458(3) Å in 13.

The bonding situation in 8 is comparable to the one in 7.

The rhodium atom is coordinated by two phosphines with a

P1–Rh–P2 angle of 98.55(8)° and in a η³-fashion by the fluore-

nyl ligand. The distance of the plane defined by the carbon

atoms C13, C14, C15, C16, C17 and C18 to the metal atom is

1.9264(2) Å and in a similar range as it was found for complex

7. Again, this plane is nearly perpendicular to the P1–Rh–P2

plane (dihedral angle: 84.25(9)°) and the aminoborate ester

moiety is arranged on the same side as the rhodium atom with

respect to the plane defined by the fluorenyl ligand. The

crystal data reveal three short (Rh1–C14 2.206(3) Å, Rh1–C13

2.235(3) Å, Rh1–C18 2.347(3) Å) and one medium (Rh1–C15

2.409(3) Å) rhodium–carbon bond lengths. The geometry at

the carbon atom C19 is nearly trigonal-planar with an angular

sum of 359.7(2)°. A distance of the C17–C19 bond of 1.386(4) Å

confirms the presence of a double bond.

In addition, we investigated the reactivity of the boryl

complex 1 towards a ketimine which does not carry any further

substituent at the nitrogen atom. Adding benzophenone imine

to a solution of 1 led to the insertion of the imine into the

rhodium–boron bond. A complete conversion was observed

within seconds to give the complex [Rh{CPh₂N(H)(Bpin)}-

(PEt₃)₂] (9, Scheme 4) and free phosphine. Note that the

formation of [Rh{NvCPh₂}(PEt₃)₃] (10)⁷⁶and HBpin was

observed when the reaction solution was highly concentrated

or when the organic substrate was added rapidly to 1.

complex 9 is only stable for a few hours at room temperature.

Therefore complex 9 was identified by NMR spectroscopy and

LIFDI MS only. The latter reveals a peak at m/z 647 which can

be assigned to the molecular ion [M]⁺. The ³¹P{¹H} NMR spec-

trum of 9 at room temperature shows two doublet of doublets

at δ 22.3 and 18.7 ppm with phosphorus–rhodium coupling

constants of 163 Hz and 262 Hz as well as a phosphorus–phos-

phorus coupling constant of 32 Hz. The coupling constants

are in accordance with the presence of a Rh(^I) complex and

comparable to those found for 4, 11 and 12 (see below).

Complex 9 exhibits a signal at δ 24.6 ppm in the ¹¹B NMR

spectrum which indicates the presence of the aminoborate

ester moiety. The ¹H NMR spectrum of 9 displays only three

resonances in the aromatic region in a ratio of 4 : 4 : 2, and the

¹³C NMR spectrum shows three resonances for CH carbon

atoms in the aromatic region. This suggests the presence of a

complex which is fluxional on the NMR time scale rendering

some of the CH units to be equivalent. The formation of an

intermediate η³-benzyl complex might result in equivalent

hydrogen and carbon atoms by a rotation of the phenyl

groups.

Variable temperature ³¹P{¹H} NMR spectra of a solution of

9 and free phosphine show at low temperature (<273 K) the

presence of 9 and of a second complex 9′ for which we suggest

the structure to be [Rh{η¹-CPh₂N(H)(Bpin)}(PEt₃)₃] (Fig. 7). The

broadness of the signals of 9′ and of PEt₃might possibly be

attributed to an intermolecular exchange with free phosphine.

The exchange would have to be associative, because the reson-

ances for 9 remain sharp at 273 K, implying that 9′ does not

get converted into 9. However, we were not able to identify

a signal for 9′ at higher temperatures, because of a rapid

decomposition. However, at 253 K the signal for PEt₃sharpens

whereas a broad doublet at δ 13.8 ppm with a phosphorus–

rhodium coupling constants of 145 Hz for 9′ can be observed.

The broadening indicates an intramolecular exchange process

Without the presence of free phosphine complex 9 decom-

poses very fast, and even in the presence of free phosphine

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Fig. 7 (a) Variable temperature ³¹P{¹H} NMR spectra (121.5 MHz, [D₈]toluene) of a solution of 9 and 9’. (b) Magniﬁcation of the ³¹P{¹H} NMR spec-

trum (121.5 MHz, [D₈]toluene) at 273 K (*: traces of 10).

of the phosphine ligands at 9′. Further decrease of the temp-

Initially, the reaction of 1 with N-benzylideneaniline pro-

erature to 188 K leads to a splitting into two signals at δ 23.7 ceeded in a similar way and the benzyl complex [Rh[η³-CH-

and 13.1 ppm in a ratio of 1 : 2, which suggests the presence of {N(Ph)Bpin}C₆H₅](PEt₃)₂] (12) was obtained. But within

a square planar rhodium complex bearing three PEt₃ligands. 10 minutes the reaction solution changed its color and NMR

The phosphorus–rhodium coupling constants of 119 Hz spectroscopic studies revealed the formation of [Rh{(C₆H₄)-

and 155 Hz indicate the presence of a Rh(^I) species and o-N(Bpin)(CH₂Ph)}(PEt₃)₃] (13) and the decrease of the amount

the phosphorus–phosphorus coupling constant of 37 Hz of 12 and of free phosphine (Scheme 4). Complex 13 is gener-

is in a typical range for phosphine ligands in a mutual ated by C–H activation at the N-bound phenyl ring and a con-

cis-position.^{50,51,55–57,77}We suggest 9′ to be the σ-complex comitant C–H bond formation at the benzyl moiety. Complex

1

[Rh{η¹-CPh₂N(H)(Bpin)}(PEt₃)₃] with the anionic ligand bound 12 was only characterized in solution by H and ³¹P{¹H} NMR

to rhodium via the CPh₂carbon atom due to the similarity of spectroscopy. The spectra resemble those of 11. The ³¹P{¹H}

the ³¹P{¹H} NMR data for organorhodium(I) complexes [Rh(R)- NMR spectrum of 13 shows two signals in a ratio of 1 : 2. The

(PEt₃)₃].^56,76The presence of three phosphine ligands argues chemical shift and the phosphorus–rhodium and phos-

against an η³-benzylic structure.^55,59,78,79

phorus–phosphorus coupling constants are in agreement

Whereas benzaldehyde does not react with 1 in a selective with those found for other aryl complexes.⁸⁰A resonance at

way, a selective insertion reaction at 1 with aldimines was δ 24.8 ppm in the ¹¹B NMR spectrum indicates the presence of

observed. Treatment with N-benzylidenehexan-1-amine gener- the N–Bpin bond.

ated free phosphine and complex 11, for which we suggest a

The molecular structure in the solid-state of 13 was deter-

benzylic structure [Rh[η³-CH{N(C₆H₁₃)Bpin}C₆H₅](PEt₃)₂] (11) mined by single-crystal X-ray diﬀraction. An ORTEP drawing is

(Scheme 4). Complex 11 was characterized by NMR spec- presented in Fig. 8, whereas selected bond distances and

troscopy and LIFDI MS. The LIFDI data reveal a peak at m/z angles are reported in Table 6. The rhodium atom is co-

460 which can be assigned to the molecular ion [M]⁺. The ordinated by the aryl ligand and three phosphine ligands in an

³¹P{¹H} NMR spectrum of 11 exhibits two doublets of doublets approximately square planar geometry. The aryl plane is

at δ 25.8 and 21.7 ppm. The phosphorus–rhodium coupling arranged in an orthogonal position to the plane defined by the

constant of 270 Hz or 168 Hz is comparable to those which atoms P1, P2, P3, C19 and Rh1 (dihedral angle: 82.96(15)°).

were determined for 4 and 9 and again confirm the oxidation The Rh–C19 distance of 2.077(3) Å and the Rh–P distances

state of Rh(^I).^55–57The phosphorus–phosphorus coupling con- agree well with the corresponding distances found for

1

stant of 26 Hz is relatively small. Analogous to 4 the H NMR [Rh(C₆H₄-o-OMe)(PEt₃)₃].⁵⁶

spectrum displays three broad signals in the aromatic region.

Furthermore, a signal at δ 4.15 ppm with a phosphorus–hydro-

gen coupling of 5 Hz can be assigned to the benzylic proton.

Consecutive reactions

These NMR spectroscopic data indicate the presence of an

With regard to a diboration reaction we also investigated the

reactivity of the insertion reaction products towards B₂pin₂.

η³-benzyl complex.

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others.^37,43Comparable observations have been reported with

Pt and Cu catalysts.^81–84However, in the latter cases water or

protic solvent was used for the reaction work-up.

Treatment of 4 with B₂pin₂also did not lead to any dibora-

tion. Instead the generation of the boryl complex 1 and of

PhCH(OBpin)CF₃was observed. In addition, [Rh{C(vCF₂)Ph}-

(PEt₃)₃] (14), FBpin as well as pinBOBpin were identified

(Scheme 5). The ³¹P{¹H} NMR spectrum of 14 displays a reson-

ance for the phosphine in the trans position to the vinyl ligand

at δ 20.1 ppm. It appears as a doublet of triplet of doublet of

doublets due to couplings to the rhodium, phosphorus and

the fluorine atoms. The coupling pattern of the resonance at δ

11.6 ppm, which can be assigned to the phosphine ligands in

a mutual cis position, appears as a doublet of doublet of doub-

lets and exhibits couplings to rhodium, phosphorus and one

of the fluorine atoms. The ¹⁹F NMR spectrum shows signals

at δ −75.1 and −69.3 ppm. The formation of 14 can tentatively

be explained by initial generation of the carbene complex

Fig. 8 An ORTEP diagram of 13. The ellipsoids are drawn at the 50%

probability level. The hydrogen atoms are omitted for clarity.

[Rh(Bpin)₂(OBpin)(vCPhCF₃)(PEt₃)₂] from

4 by oxidative

addition of B₂pin₂and OBpin migration to the metal center.

Elimination of pinBOBpin might yield the rhodium boryl

complex [Rh(Bpin)(vCPhCF₃)(PEt₃)₂].^50,51A subsequent β-F-

elimination step and FBpin formation by reductive elimination

gives the fluorovinyl ligand and complex 14.^85–87As an alterna-

tive, the fluorine atom can be transferred directly to the metal-

bound boryl moiety. There are some precedents for boryl-

assisted and other comparable ligand-assisted C–F activation

Table 6 Selected bond lengths (Å) and angles (°) for 13 with estimated

standard deviations in parentheses

Bond

Length

Bond

Angle

Rh1–C19

Rh1–P1

Rh1–P2

Rh1–P3

N1–B1

N1–C20

N1–C21

C19–C37

C19–C20

C20–C34

C34–C35

C35–C36

C36–C37

2.077(3)

2.3094(7)

2.3245(8)

2.3364(8)

1.404(4)

1.442(3)

1.458(3)

1.413(4)

1.422(4)

1.400(4)

1.386(4)

1.381(4)

1.385(4)

C19–Rh1–P1

C19–Rh1–P2

P1–Rh1–P2

C19–Rh1–P3

P1–Rh1–P3

83.60(7)

177.39(8)

94.23(3)

81.78(8) reactions in the literature.^{22,50,85,88–95}

161.99(3)

The aryl complex 13 successfully reacted with B₂pin₂within

P2–Rh1–P3

100.61(3)

124.1(2)

115.7(2)

120.1(2)

115.2(3)

118.7(2)

126.1(2)

121.0(2)

16 h at 50 °C to yield the boryl complex 1 and the diborylated

amine PhCH₂N(Bpin)(C₆H₄-o-Bpin) (Scheme 5). The latter was

characterized by NMR spectroscopy and GC-MS analysis. In

the ¹¹B NMR spectrum a resonance at δ 28.9 ppm for the boro-

nate ester moiety and a resonance at δ 24.6 ppm for the amino-

borate ester group were detected. Catalytic investigations by

treatment of N-benzylideneaniline with B₂pin₂in the presence

of 1 led to a product mixture.

B1–N1–C20

B1–N1–C21

C20–N1–C21

C37–C19–C20

C37–C19–Rh1

C20–C19–Rh1

C34–C20–C19

Unfortunately, in most of the cases either no reaction occurred

or only reaction mixtures were generated, for which none of

the products could be identified apart from complex 1.

However, complex 9 reacted at room temperature with B₂pin₂

in the presence of phosphine in cyclohexane within a few

hours to yield 1 (Scheme 5). The formation of 1 was confirmed

by ³¹P{¹H} NMR spectroscopy. The ¹H NMR and ¹³C NMR

spectra revealed the generation of Ph₂CHN(H)Bpin as the only

organic product. Only minor amounts of the diboration

product Ph₂C(Bpin)N(H)Bpin were formed according to GC-MS

analysis. In principle Ph₂CHN(H)Bpin could be generated by

hydrolysis, but the presence of adventitious water is not very

likely, because in the presence of water 1 would be converted

into [Rh(H)(PEt₃)₃] (2). In addition, the N–Bpin bond is labile

and aminoborate esters like Ph₂CHN(H)Bpin have a high reac-

tivity towards water or even alcohols.^73,81At present, the source

of the NH hydrogen atom in Ph₂CHN(H)Bpin is unclear. Note

that the [Rh(Cl)(PPh₃)₃] catalyzed reaction of aldimines with

diboranes also led to hydroboration products amongst

Conclusions

We have reported on the reactivity of a rhodium boryl complex

towards carbon–heteroatom double bonds. Complex [Rh(Bpin)-

(PEt₃)₃] (1) reacts with ketones, aldimines and ketimines by

insertion of the CvO or the CvN entities into the Rh–B bond

to give a boron–oxygen or a boron–nitrogen bond. In the pres-

ence of an aromatic system, stabilization of the products

occurs by η³or η⁵coordination, and a variety of bonding

modes was observed. The presence of β-hydrogen atoms can

lead to β-H-elimination. Although the insertion of carbon–

heteroatom double bonds into metal–boron bonds was

suggested before in metal-catalyzed hydroboration and dibora-

tion reactions, this important key step was never observed in a

model reaction. The insertion products of ketones are the first

examples of such a type of compounds and their formation

supports the proposed mechanisms.⁴⁷Moreover, the insertion

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were measured on an Agilent 6890N gas-phase chromatograph

(Agilent 19091S-433 Hewlett-Packard) and an Agilent 5973

Network mass selective detector at 70 eV. The microanalyses

were obtained using a Euro EA HEKAtech elemental analyzer.

Treatment of [Rh(Bpin)(PEt₃)₃] (1) with acetophenone

A solution of [Rh(Bpin)(PEt₃)₃] (1) (39.5 mg, 68 μmol) in hexa-

methyldisilane (0.3 mL) in a PFA tube was treated with aceto-

phenone (3.9 mg, 34 μmol). After 15 min the ³¹P{¹H} NMR

spectroscopic data of the reaction solution revealed the com-

plete conversion of 1 and the formation of [Rh(H)(PEt₃)₃] (2) as

1

well as of [Rh(OBpin)(PEt₃)₃] (3) in a ratio of 1 : 1. The H and

¹³C{¹H} NMR spectroscopic data indicated the presence of (E)-

(Ph)CHvCHBpin as the main product. The latter was identi-

fied by comparison with literature NMR data.⁵³Analytical data

for 3: (Found: C, 48.07; H, 9.60. C₂₄H₅₇BO₃P₃Rh requires C,

1

48.02; H, 9.57%); H NMR (300.1 MHz, Me₆Si₂): δ = 2.06 (12H,

m, CH₂), 1.83 (6H, m, CH₂), 1.61–1.45 (39H, m, CH₃) ppm. ¹¹

B

NMR (96.3 MHz, Me₆Si₂): δ = 22.8 (Δν_1/2≈ 150 Hz) ppm.

¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = 78.5 (CMe₂), 25.7 (CH₃),

21.3 (d, J_PC= 25 Hz, CH₂), 16.9 (t, J = 10 Hz, CH₂), 9.2 (CH₃)

Scheme 5 Reactivity of complexes 9, 4 and 13 towards B₂pin₂.

ppm. ³¹P{¹H} NMR (121.5 MHz, Me₆Si₂): δ = 40.2 (1P, dt, J_RhP

=

products of an imine⁹⁶in a metal–boron single⁹⁷bond are

unprecedented. The reactions also confirm that a Rh–C and a

N–B bond formation is favored over a Rh–N and a C–B bond

formation. Overall, the results demonstrate that the insertion

reactions into a Rh–B bond can lead to diverse products, and

consecutive reactions such as C–H or C–F activation or CO

insertion steps were also observed. Although no catalytic pro-

cedure reaction has been developed so far, the transformations

might be of certain interest for the development of new boryla-

tion reactions in the future.

172 Hz, J_PP= 43 Hz), 21.4 (2P, dd, J_RhP= 142 Hz, J_PP= 43 Hz,

J_FP= 8 Hz) ppm. MS (LIFDI, Me₆Si₂), m/z: 600 [M]⁺.

Treatment of [Rh(Bpin)(PEt₃)₃] (1) with styrene

(a) A solution of [Rh(Bpin)(PEt₃)₃] (1) (43.7 mg, 75 μmol) in

hexamethyldisilane (0.3 mL) in a PFA tube was treated with

styrene (8.6 μL, 75 μmol). After 15 min the NMR spectroscopic

data of the reaction solution revealed a quantitative conversion

and the formation of [Rh(H)(PEt₃)₃] (2) as well as the formation

of (E)-(Ph)CHvCHBpin. The latter was identified by compari-

son with literature NMR data.⁵³

(b) A solution of [Rh(Bpin)(PEt₃)₃] (1) (28.6 mg, 49 μmol) in

hexamethyldisilane (0.2 mL) in a PFA tube was treated with

styrene (2.8 μL, 25 μmol). After 1 h the NMR spectroscopic

Experimental

[D₆]benzene, [D₈]toluene, [D₁₂]cyclohexane, cyclohexane, data of the reaction solution revealed quantitative conversion

hexane, and hexamethyldisilane were dried by stirring over and the formation of [Rh(H)(PEt₃)₃] (2) as well as the formation

Na/K and then distilled. Complex [Rh(Bpin)(PEt₃)₃] (1) was pre- of (E)-(Ph)CHvC(Bpin)₂. The latter was identified by compari-

pared according to the literature.⁵¹The imines N-(diphenyl- son with literature NMR data.⁵⁴

methylene)aniline,⁹⁸N-(fluoren-9-ylidene)aniline,⁹⁹and N-

Synthesis of [Rh{η³-C(CF₃)(OBpin)C₆H₅}(PEt₃)₂] (4)

benzylidenehexan-1-amine¹⁰⁰were prepared according to the

literature. The NMR spectra were recorded at 300 K (if not A solution of [Rh(Bpin)(PEt₃)₃] (1) (71.8 mg, 123 μmol) in hexa-

stated otherwise) on a Bruker Avance 400, a Bruker DPX 300 or methyldisilane (0.3 mL) in a PFA tube was treated with

a Bruker Avance III 300 NMR spectrometer. The ¹H NMR α,α,α-trifluoroacetophenone (21.4 mg, 123 μmol). After 5 min

chemical shifts were referenced to residual C₆D₅H at δ at room temperature the volatiles were removed under vacuum

7.16 ppm, [D₇]toluene at δ 2.09 ppm or [D₁₁]cyclohexane at δ to give a dark red oil. Yield 80.6 mg. ¹H NMR (300.1 MHz,

1.43 ppm. The ¹¹B{¹H} NMR spectra were referenced to exter- Me₆Si₂): δ = 7.62 (2H, br s, CH_ar), 7.24 (1H, t, J_HH= 7 Hz, CH_ar),

nal BF₃·OEt₂at δ 0.0 ppm, the ¹⁹F NMR spectra to external 7.10 (1H, br s, CH_ar), 6.34 (1H, br s, CH_ar), 2.28 (3H, m, CH₂),

CFCl₃at δ 0.0 ppm, and the ³¹P{¹H} NMR spectra to external 2.10 (3H, m, CH₂), 1.70 (6H, m, CH₂), 1.60 (6H, s, CH₃), 1.58

2

H₃PO₄at δ 0.0 ppm. In order to get a H lock signal, C₆D₆was (6H, s, CH₃), 1.49 (9H, dt, J_RhH= 15 Hz, J_PH= 8 Hz, CH₃), 0.94

introduced in the space between the glass NMR tubes and the (9H, dt, J_RhH= 15 Hz, J_PH= 7 Hz, CH₃) ppm. ¹¹B NMR

PFA inliners, which contained the reaction mixture with hexa- (96.3 MHz, Me₆Si₂): δ = 22.5 (Δν_1/2≈ 60 Hz) ppm. ¹³C{¹H}

methyldisilane or cyclohexane as a solvent. Mass spectra were NMR (75.5 MHz, Me₆Si₂): δ = 123.8 (CH_ar), 109.2 (q, J_FC= 276

measured on a Micromass Q-Tof-2 instrument equipped with a Hz, CF₃), 82.4 (CMe₂), 65.3 (q, J_FC= 36 Hz, CCF₃), 25.1 (CH₃),

Linden LIFDI source (Linden CMS GmbH). GC-MS spectra 19.6 (d, J_PC= 23 Hz, CH₂), 18.2 (d, J_PC= 19 Hz, CH₂), 9.2 (CH₃),

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1

9.1 (CH₃) ppm. The signals for the other aromatic carbon J_CP= 16 Hz, J_CP= 13 Hz) ppm. The H, ¹¹B and ¹⁹F NMR data

atoms were not observed. The resonances for the CF₃and are identical to those for 6.

CCF₃carbon atoms were confirmed by a ¹³C–¹⁹F-HMQC spec-

Synthesis of [Rh{η⁵-C₁₃H₈(OBpin)}(PEt₃)₂] (6)

9 Hz) ppm. ³¹P{¹H} NMR (121.5 MHz, Me₆Si₂): δ = 28.1 (dd, A solution of [Rh(Bpin)(PEt₃)₃] (1) (78.5 mg, 134 μmol) in hexa-

trum. ¹⁹F{¹H} NMR (75.3 MHz, Me₆Si₂): δ = −57.4 (d, J_PF

=

J_RhP= 257 Hz, J_PP= 36 Hz), 21.8 (ddq, J_RhP= 160 Hz, J_PPmethyldisilane (0.6 mL) in a PFA tube was treated with

=

36 Hz, J_FP= 8 Hz) ppm. MS (LIFDI, Me₆Si₂), m/z: 640 [M]⁺. The fluoren-9-one (24.2 mg, 134 μmol). After stirring for 1 h at

reaction solution always contained small amounts (5–10%) of room temperature, the volatiles were removed under vacuum.

PhCH(OBpin)CF₃, which was identified by comparison of the The residue was extracted with hexane (3 × 1 mL). The extract

NMR data with data of an independently synthesized sample was dried under vacuum to give a very air sensitive orange red

by treatment of α,α,α-trifluoroacetophenone with HBpin in C₆D₆powder. Yield 80.6 mg (93%). (Found: C, 57.36; H, 7.89.

at room temperature (50% conversion after 9 d). Analytical C₃₁H₅₀BO₃P₂Rh requires C, 57.60; H, 7.80%); ¹H NMR

data for PhCH(OBpin)CF₃: ¹H NMR (300.1 MHz, C₆D₆): δ = (300.1 MHz, C₆D₆): δ = 7.61 (2H, d, J_HH= 8 Hz, CH_ar), 7.50 (2H,

7.38 (2H, m, CH_ar), 7.02 (3H, m, CH_ar), 5.58 (1H, q, J_FH= 7 Hz, d, J_HH= 8 Hz, CH_ar), 7.13 (2H, t, J_HH= 7 Hz, CH_ar), 6.99 (2H, t,

1

CH), 0.98 (6H, s, CH₃), 0.93 (6H, s, CH₃) ppm. ¹³C{¹H} NMR J_HH= 7 Hz, CH_ar), 1.59 (6H, m, q in the H{³¹P} spectrum, J_HH

(75.5 MHz, Me₆Si₂): δ = 134.7 (C_ar), 129.6 (CH_ar), 128.7 (CH_ar), = 7 Hz, CH₂), 1.27 (6H, m, q in the ¹H{³¹P} spectrum, J_HH

=

128.3 (CH_ar), 124.4 (q, J_FC= 280 Hz, CF₃), 83.6 (CMe₂), 75.0 (q, 7 Hz, CH₂), 0.94 (12H, s, CH₃), 0.84 (9H, m, t in the ¹H{³¹P}

1

J_FC= 33 Hz, CCF₃), 25.1 (CH₃), 25.0 (CH₃) ppm. ¹⁹F{¹H} NMR spectrum, J_HH= 8 Hz, CH₃), 0.63 (9H, m, t in the H{³¹P} spec-

(75.3 MHz, C₆D₆): δ = −78.4 (s) ppm. GC-MS, m/z: 302 [M], 287 trum, J_HH= 7 Hz, CH₃) ppm. ¹¹B NMR (96.3 MHz, C₆D₆): δ =

[M − CH₃].

22.7 (Δν_1/2≈ 200 Hz) ppm.¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ =

120.7 (CH_ar), 119.6 (d, J = 2 Hz, CH_ar), 118.1(d, J = 3 Hz, CH_ar),

113.9 (CH_ar), 111.1 (br, C_ar), 102.3 (dm, J = 24 Hz, CO), 97.7 (q,

Synthesis of trans-[Rh{C(O)C(CF₃)(Ph)OBpin}(CO)(PEt₃)₂] (5)

A solution of [Rh(Bpin)(PEt₃)₃] (1) (113.9 mg, 195 μmol) in J = 2 Hz, C_ar), 83.2 (CMe₂), 24.4 (CH₃), 20.2 (d, J_PC= 21 Hz,

hexamethyldisilane (1.0 mL) in a PFA tube was treated with CH₂), 19.1 (d, J_PC= 23 Hz, CH₂), 8.2 (CH₃), 8.0 (CH₃)

α,α,α-trifluoroacetophenone (34.0 mg, 195 μmol). After stirring ppm.³¹P{¹H} NMR (121.5 MHz, Me₆Si₂): δ = 40.7 (dd, J_RhP

=

for 30 min at room temperature, the volatiles were removed 254 Hz, J_PP= 43 Hz), 19.8 (dd, J_RhP= 204 Hz, J_PP= 44 Hz) ppm.

under vacuum. The residue was dissolved in hexamethyldisi-

lane (0.7 mL) and the solution was filtered. After the filtrate

Synthesis of [Rh{η³-C₆H₅vC(Ph)N(Ph)(Bpin)}(PEt₃)₂] (7)

was cooled to 77 K and degassed, the vessel was purged with A solution of [Rh(Bpin)(PEt₃)₃] (1) (86.7 mg, 149 μmol) in hexa-

CO. The dark red reaction mixture was then allowed to warm methyldisilane (0.7 mL) in a PFA tube was treated with N-

to room temperature. A yellow solid precipitated within 2 h, (diphenylmethylene)aniline (38.2 mg, 149 μmol) to give a dark

which was separated and washed with hexamethyldisilane (2 × red solution. After stirring for 1 d a dark red solid precipitated

0.25 mL), hexane (2 × 0.25 mL) and dried in vacuo. Yield at room temperature, which was separated and washed with

81.0 mg (60%). (Found: C, 48.37; H, 6.88. C₂₈H₄₇BF₃O₅P₂Rh hexamethyldisilane (0.2 mL) and dried in vacuo. Yield 87.0 mg

requires C, 48.30; H, 6.80%); ν (ATR, diamond) 1952 (CuO), (81%). (Found: C, 61.76; H, 8.03; N, 1.75. C₃₇H₅₇BNO₂P₂Rh

¯

1478 (CvO), 903 cm⁻^{1 1}H NMR (300.1 MHz, C₆D₆): δ = 8.59 requires C, 61.42; H, 7.94; N, 1.94%); ¹H NMR (300.1 MHz,

.

(2H, d, J_HH= 8 Hz, CH_ar), 7.09 (2H, td, J_HH= 7 Hz, J = 1 Hz, C₆D₆, major isomer): δ = 7.74 (2H, d, J_HH= 7 Hz, CH_ar), 7.67

CH_ar), 6.97 (1H, tt, J_HH= 7 Hz, J = 1 Hz, CH_ar), 1.55 (18H, m, (2H, d, J_HH= 7 Hz, CH_ar), 7.34–7.14 (4H, m, CH_ar), 6.98 (1H, br

CH₂, CH₃), 1.24 (3H, m, CH₂), 0.94 (9H, m, CH₃), 0.76 (9H, m, t, CH_ar), 6.89 (1H, t, J_HH= 7 Hz, CH_ar), 6.45 (1H, d, J = 8 Hz,

CH₃), 0.63 (3H, m, CH₂) ppm. ¹¹B NMR (96.3 MHz, C₆D₆): δ = CH_ring), 5.84 (1H, br m, CH_ring), 5.52 (1H, br t, CH_ring), 5.20

15.3 (Δν_1/2≈ 200 Hz) ppm. ¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = (1H, d, J = 6 Hz, CH_ring), 4.09 (1H, m, CH_ring), 1.54–0.82 (42H,

296.1 (d, J_RhC= 42 Hz, CvO), 198.7 (d, J_RhC= 53 Hz, CuO), m, CH₂, CH₃) ppm. ¹H NMR (300.1 MHz, C₆D₆, minor isomer):

137.0 (C_ar), 128.8 (CH_ar), 128.3 (CH_ar), 128.3 (CH_ar), 124.4 (q, δ = 7.89 (2H, d, J_HH= 8 Hz, CH_ar), 7.82 (2H, d, J_HH= 7 Hz,

J_FC= 286 Hz, CF₃), 100.1 (q, J_FC= 23 Hz, CCF₃), 80.1 (CMe₂), CH_ar), 5.97 (1H, m, J = 6 Hz, CH_ring), 5.79 (1H, br t, CH_ring),

26.1 (CH₃), 26.0 (CH₃), 18.7 (d, J_PC= 24 Hz, CH₂), 17.9 (d, J_PC

=

5.66 (1H, d, J = 8 Hz, CH_ring), 4.28 (1H, m, CH_ring) ppm. The

24 Hz, CH₂), 8.4 (CH₃) ppm. ¹⁹F{¹H} NMR (75.3 MHz, C₆D₆): δ signals for the other hydrogen atoms are obscured by signals

= −71.8 (d, J_PF= 4 Hz) ppm. ³¹P{¹H} NMR (121.5 MHz, C₆D₆): δ of the major isomer. ¹¹B NMR (96.3 MHz, Me₆Si₂): δ = 25.2

= 21.8 (ddq, J_PP= 210 Hz, J_RhP= 141 Hz, J_FP= 4 Hz), 19.8 (dd, (Δν_1/2≈ 250 Hz) ppm. ¹³C{¹H} NMR (75.5 MHz, C₆D₆, major

J_PP= 210 Hz, J_RhP= 141 Hz) ppm. Complex 5a was prepared in isomer): δ = 148.4 (C_ar), 143.6 (C_ar), 134.1 (t, J = 7 Hz, CvC),

a similar manner using ¹³CO. Analytical data for 5a: ν (ATR, 129.0 (CH_ar), 128.1 (CH_ar), 127.9 (CH_ar), 124.2 (CH_ar), 121.5

¯

diamond) 1906 (CuO), 1445 (CvO), 885 cm⁻¹

;

¹³C{¹H} NMR (CH_ar), 121.5 (CH_ar), 112.6 (br s, CH_ring), 103.1 (br s, CH_ring),

(75.5 MHz, [D₈]toluene): δ = 296.1 (ddt, J_RhC= 42 Hz, J_CC

=

99.6 (br s, CH_ring), 82.1 (CMe₂), 80.7 (br s, CH_ring), 66.2 (td, J_PC

34 Hz, J_PC= 12 Hz, CvO), 198.7 (ddt, J_RhC= 52 Hz, J_CC= 34 Hz, = 7 Hz, J_Rh,C= 5 Hz, CH_ring), 25.0 (CH₃), 23.9 (CH₂), 21.1 (t, J =

J_PC= 16 Hz, CuO) ppm. The other data are similar to those for 11 Hz, CH₂), 8.9 (CH₃) ppm. The signal for one quaternary

5. ³¹P{¹H} NMR (121.5 MHz, [D₈]toluene): δ = 20.6 (ddm, J_PP

=

carbon atom of the enamine was not found. ³¹P{¹H} NMR

210 Hz, J_RhP= 141 Hz), 17.9 (dddd, J_PP= 210 Hz, J_RhP= 141 Hz, (121.5 MHz, Me₆Si₂, 300 K): δ = 31.8 (1P, d, J_RhP= 212 Hz,

6796 | Dalton Trans., 2014, 43, 6786–6801

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Paper

major isomer), 30.5 (0.2P, d, J_RhP= 212 Hz, minor isomer) 135.1 (br s, C_ar), 129.0 (CH_ar), 123.6 (CH_ar), 118.1 (br s, CH_ar),

ppm. ³¹P{¹H} NMR (121.5 MHz, [D₈]toluene, 273 K): δ = 31.8 81.3 (CMe₂), 68.7 (dm, J_RhC= 42 Hz, CN), 25.0 (CH₃), 19.7 (d,

(1P, d, J_RhP= 210 Hz, major product), 30.4 (0.3P, d, J_RhP= 209 J_PC= 21 Hz, CH₂), 18.0 (d, J_PC= 17 Hz, CH₂), 9.3 (CH₃) ppm.

Hz, minor isomer) ppm. ³¹P{¹H} NMR (121.5 MHz, [D₈] ³¹P{¹H} NMR (121.5 MHz, Me₆Si₂, 300 K): δ = 22.3 (dd, J_RhP

=

toluene, 253 K): δ = ∼32.0 (1P, br d, ∼200 Hz, major isomer), 163 Hz, J_PP= 32 Hz), 18.7 (dd, J_RhP= 262 Hz, J_PP= 32 Hz) ppm.

30.5 (0.3P, d, J_RhP= 209 Hz, minor isomer) ppm. ³¹P{¹H} NMR MS (LIFDI, Me₆Si₂), m/z: 647 [M]⁺. Analytical data for 9′:

(121.5 MHz, [D₈]toluene, 223 K): δ = 34.9 (br d, J_RhP∼ 210 Hz, ³¹P{¹H} NMR (121.5 MHz, [D₈]toluene, 253 K): δ = 13.8 (br d,

major isomer), 30.6 (d, J_RhP= 208 Hz, minor isomer), 29.7 (br J = 145 Hz) ppm. ³¹P{¹H} NMR (121.5 MHz, [D₈]toluene,

d, J_RhP

(121.5 MHz, [D₈]toluene, 203 K): δ = 35.5 (dd, J_RhP= 210 Hz, J_PPdd, J_RhP= 155 Hz, J_PP= 37 Hz) ppm.

∼

210 Hz, major isomer) ppm. ³¹P{¹H} NMR 188 K): δ = 23.7 (1P, dt, J_RhP= 119 Hz, J_PP= 37 Hz), 13.1 (2P,

= 46 Hz, major isomer), 29.5 (dd, J_RhP= 213 Hz, J_PP= 46 Hz,

(b) A solution of [Rh(Bpin)(PEt₃)₃] (1) (39.7 mg, 68 μmol) in

major isomer) ppm. ³¹P{¹H} NMR (121.5 MHz, [D₈]toluene, hexamethyldisilane (0.2 mL) in a PFA tube was treated with

333 K): δ = 26.1 (d, J_RhP= 212 Hz) ppm.

benzophenone imine (12.2 mg, 68 μmol) without stirring.

After 5 min at room temperature the volatiles were removed

under vacuum and the dark red oil was redissolved in hexa-

Synthesis of [Rh{(η³-C₁₂H₈)N(Ph)(Bpin)}(PEt₃)₂] (8)

A solution of [Rh(Bpin)(PEt₃)₃] (1) (92.8 mg, 159 μmol) in hexa- methyldisilane. The NMR spectroscopic data revealed a quanti-

methyldisilane (0.7 mL) in a PFA tube was treated with N- tative conversion of and the formation of and

1

9

(fluoren-9-ylidene)aniline (40.5 mg, 159 μmol). After 30 min [Rh{NvCPh₂}(PEt₃)₃] (10) in a ratio of 100 : 6. Complex 10 was

the volatiles were removed under vacuum. The purple residue identified by its NMR data.⁷⁶

was washed with hexamethyldisilane (2 × 0.3 mL) and hexane

(c) A solution of [Rh(Bpin)(PEt₃)₃] (1) (11.7 mg, 20 μmol) in

(2 × 0.3 mL) and then dried in vacuo to give a purple solid. hexamethyldisilane (0.4 mL) in a PFA tube was treated slowly

Yield 83.1 mg (80%). (Found: C, 61.71; H, 7.84; N, 1.72. with benzophenone imine (3.6 mg, 20 μmol). The NMR spec-

C₃₇H₅₅BNO₂P₂Rh requires C, 61.59; H, 7.68; N, 1.94%); ¹H troscopic data of the reaction solution revealed a quantitative

NMR (300.1 MHz, [D₈]toluene): δ = 8.01 (1H, br d, J_HH= 8, formation of 9 after 5 min at room temperature and the for-

CH), 7.68 (1H, br s, CH), 7.47–6.95 (7H, m, CH), 6.89 (1H, br s, mation of 9 and [Rh{NvCPh₂}(PEt₃)₃] (10) in a ratio of 10 : 1

CH), 6.78 (1H, t, J_HH= 7 Hz, CH), 6.22 (1H, br s, CH), 5.98 (1H, after 4 h. Complex 10 was identified by its NMR data.⁷⁶

br s, CH_fluorene), 1.29–1.02 (24H, m, CH₂, CH₃), 0.74 (18H, m,

Synthesis of [Rh[η³-CH{N(C₆H₁₃)Bpin}C₆H₅](PEt₃)₂] (11)

CH₃) ppm. ¹¹B NMR (96.3 MHz, C₆D₆): δ = 24.8 (Δν_1/2≈ 500

Hz) ppm.¹³C{¹H} NMR (75.5 MHz, [D₈]toluene): δ = 149.1 (C_ar), A solution of [Rh(Bpin)(PEt₃)₃] (1) (74.8 mg, 128 μmol) in hexa-

139.8 (NC_fluorene), 131.9 (d, J = 7 Hz, CH_fluorene), 129.6 (CH), methyldisilane (0.4 mL) in a PFA tube was treated with N-ben-

128.5 (CH), 123.7 (CH), 122.5 (CH), 121.3 (CH), 118.9 (CH), zylidenehexan-1-amine (24.2 mg, 128 μmol). After 5 min at

117.3 (CH), 116.9 (CH), 109.9 (C_fluorene), 98.6 (br s, CH_fluorene), room temperature the volatiles were removed under vacuum to

97.8 (br s, C_fluorene), 87.0 (br s, C_fluorene), 82.3 (CMe₂), 70.6 (br give a red oil. Yield 85.1 mg of crude product, which contains

1

s, CH_fluorene), 25.4 (CH₃), 24.3 (CH₃), 20.1 (d, J_PC= 11 Hz, CH₂), 2% impurities. H NMR (300.1 MHz, Me₆Si₂): δ = 7.45 (2H, br

8.2 (CH₃) ppm. The signal for one quarternary carbon atom s, CH_ar), 6.99 (1H, t, J_HH= 7 Hz, CH_ar), 6.34 (2H, br s, CH_ar),

was not found. ³¹P{¹H} NMR (121.5 MHz, C₆D₆, 300 K): δ = 4.15 (1H, t, J_PH= 5 Hz, NCH), 3.66 (1H, dt, J_HH= 13 Hz, J_HH

=

34.2 (br d, J_RhP= 215 Hz) ppm. ³¹P{¹H} NMR (121.5 MHz, 7 Hz, NCH₂), 3.37 (1H, dt, J_HH= 13 Hz, J_HH= 6 Hz, NCH₂), 2.09

1

[D₈]toluene, 243 K): δ = 35.0 (1P, d, J_RhP= 213 Hz, major (6H, m, t in the H{³¹P} spectrum, J_HH= 7 Hz, CH₂), 2.09 (6H,

isomer), 33.2 (0.55P, d, J_RhP= 210 Hz, minor isomer) ppm. m, CH₂), 1.90–1.28 (23H, m, CH₂, CH₃), 1.50 (12H, s, CH₂),

³¹P{¹H} NMR (121.5 MHz, [D₈]toluene, 203 K): δ = 35.0 (1P, d, 1.20 (9H, m, CH₃) ppm. ¹¹B NMR (96.3 MHz, Me₆Si₂): δ = 24.5

J_RhP= 213 Hz, major isomer), 33.2 (0.85P, d, J_RhP= 210 Hz, (Δν_1/2≈ 400 Hz) ppm. ¹³C{¹H} NMR (75.5 MHz, Me₆Si₂): δ =

minor isomer) ppm.

121.7 (CH_ar), 81.6 (CMe₂), 65.5 (dd, J_RhC= 42 Hz, J_PC= 12 Hz,

CHN), 52.8 (NCH₂), 32.5 (CH₂), 30.6 (CH₂), 27.1 (CH₂), 25.7

(CH₃), 23.5 (CH₂), 21.6 (d, J_P,C= 20 Hz, CH₂), 19.0 (d, J_PC= 16

Synthesis of [Rh{CPh₂N(H)(Bpin)}(PEt₃)₂] (9) and 9′

(a) A solution of [Rh(Bpin)(PEt₃)₃] (1) (67.2 mg, 115 μmol) in Hz, CH₂), 14.7 (CH₃), 9.2 (CH₃) ppm. The signals for the other

hexamethyldisilane (0.6 mL) in a PFA tube was treated slowly aromatic carbon atoms were not observed. ³¹P{¹H} NMR

with benzophenone imine (20.8 mg, 115 μmol) while stirring. (121.5 MHz, Me₆Si₂): δ = 25.8 (dd, J_RhP= 270 Hz, J_PP= 26 Hz),

After 5 min at room temperature the NMR spectroscopic data 21.7 (dd, J_RhP= 168 Hz, J_PP= 26 Hz) ppm. MS (LIFDI, Me₆Si₂),

of the reaction solution revealed a quantitative conversion of 1 m/z: 655 [M]⁺.

and the formation of 9 and 9′ in a ratio of 3 : 1 (according to

1

Synthesis of [Rh{(C₆H₄)-o-N(Bpin)(CH₂Ph)}(PEt₃)₃] (13)

the ³¹P{¹H} NMR at 188 K) and PEt₃. Analytical data for 9: H

NMR (300.1 MHz, Me₆Si₂): δ = 7.66 (4H, d, J_HH= 8 Hz, 4H, A solution of [Rh(Bpin)(PEt₃)₃] (1) (91.9 mg, 157 μmol) in hexa-

CH_ar), 7.49 (4H, t, J_HH= 8 Hz, CH_ar), 7.25 (2H, t, J_HH= 7 Hz, methyldisilane (0.6 mL) in a PFA tube was treated with N-ben-

CH_ar), 3.08 (1H, d, J_PH= 7, NH), 1.67 (12H, m, CH₂), 1.57–1.21 zylideneaniline (28.5 mg, 157 μmol). The solution turned red

(30H, m, CH₃) ppm. ¹¹B NMR (96.3 MHz, Me₆Si₂): δ = 24.6 immediately. The NMR spectroscopy data revealed the for-

(Δν_1/2≈ 400 Hz) ppm. ¹³C{¹H} NMR (75.5 MHz, C₆D₆): δ = mation of 12. After 10 min the solution turned orange. After

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Dalton Transactions

1 h the volatiles were removed under vacuum. The residue was reaction solution revealed the complete conversion of 4 and

washed with cold hexane (0.2 mL) and dried in vacuo to give 13 the formation of [Rh(Bpin)(PEt₃)₃] (1) and [Rh{C(vCF₂)Ph}-

as a very air sensitive yellow solid. Yield 111.0 mg (92%). (PEt₃)₃] (14) in a ratio of approximately 1 : 1. The ¹⁹F{¹H} NMR

Analytical data for 13: (Found: C, 58.39; H, 8.96; N, 1.63. spectrum shows the resonances of 14, FBpin, PhCH(OBpin)-

C₃₇H₆₈BNO₂P₃Rh requires C, 58.05; H, 8.95; N, 1.83%); ¹H CF₃and an unknown product at δ −66.5 ppm in a ratio of

NMR (300.1 MHz, C₆D₆): δ = 8.03 (1H, dd, J_HH= J_PH= 7 Hz, 1 : 1.5 : 0.5 : 1. Furthermore, PhCH(OBpin)CF₃as well as pin-

CH_ar), 7.67 (1H, d, J_HH= 8 Hz, CH_ar), 7.57 (2H, d, J_HH= 8 Hz, BOBpin were identified by GC-MS measurements. Analytical

CH_ar), 7.15 (2H, m, CH_ar), 7.09 (1H, m, CH_ar), 6.96 (1H, t, J_HH

=

data for 14: ¹⁹F{¹H} NMR (75.3 MHz, Me₆Si₂): δ = −75.1 (dm,

7 Hz, CH_ar), 6.86 (1H, t, J_HH= 7 Hz, CH_ar), 6.30 (2H, s, NCH₂), J_FF= 73 Hz), −69.3 (ddq, J_FF= 73 Hz, J_PF= 24 Hz, J_PF= J_RhF

=

1

1.38 (6H, m, q in the H{³¹P} spectrum, J_HH= 7 Hz, CH₂), 1.27 4 Hz,) ppm. ³¹P{¹H} NMR (121.5 MHz, Me₆Si₂): δ = 20.1

(12H, m, q in the ¹H{³¹P} spectrum, J_HH= 8 Hz, CH₂), 1.00 (1P, dtdd, J_RhP= 128 Hz, J_PP= 37 Hz, J_FP= 24 Hz, J_FP= 6 Hz),

1

(12H, s, CH₃), 0.96 (9H, m, t in the H{³¹P} spectrum, J_HH= 8 11.6 (2P, ddt, J_RhP= 148 Hz, J_PP= 37 Hz, J_FP= 5 Hz) ppm. The

1

Hz, CH₃), 0.86 (18H, m, t in the H{³¹P} spectrum, J_HH= 8 Hz, signals of 14 in the ¹H NMR spectrum are obscured by the

CH₃) ppm. ¹¹B NMR (96.3 MHz, Me₆Si₂): δ = 24.8 (Δν_1/2≈ 250 signals of 1. MS (LIFDI, cyclohexane), m/z: 478 [M − PEt₃]⁺.

Hz) ppm.¹³C{¹H} NMR (75.5 MHz, cyclohexane): δ = 164.8 (ddt,

J_RhC= 77 Hz, J_PC= 27 Hz, J_PC= 17 Hz, RhC_ar), 153.1 (m, C_ar),

146.8 (C_ar), 141.7 (CH_ar), 141.4 (t, J_PC= 4 Hz, CH_ar), 127.6

(CH_ar), 126.9 (CH_ar), 126.2 (m, CH_ar), 125.0 (CH_ar), 120.3 (d, t,

J_PC= 4 Hz, CH_ar), 81.7 (CMe₂), 53.4 (NCH₂), 25.8 (CH₃), 19.9 (d,

J_PC= 15 Hz, CH₂), 18.9 (d, J_PC= 10 Hz, CH₂), 8.8 (CH₃), 8.7

(CH₃) ppm. ³¹P{¹H} NMR (121.5 MHz, Me₆Si₂): δ = 14.7 (1P, dt,

J_RhP= 115 Hz, J_PP= 34 Hz), 8.8 (2P, dd, J_RhP= 159 Hz, J_PP= 34

Treatment of [Rh{(C₆H₄)-o-N(Bpin)(CH₂Ph)}(PEt₃)₃] (13) with

B₂pin₂

A

mixture of [Rh{(C₆H₄)-o-N(Bpin)(CH₂C₆H₅)}(PEt₃)₃] (13)

(18.2 mg, 24 μmol) and B₂pin₂(9.0 mg, 36 μmol) in [D₁₂]cyclo-

hexane (0.2 mL) in a PFA tube was heated to 50 °C for 16 h.

The NMR spectroscopic data of the reaction solution revealed

the quantitative consumption of 13 and the formation of

[Rh(Bpin)(PEt₃)₃] (1) and PhCH₂N(Bpin)(C₆H₄-o-Bpin). Analytical

data for PhCH₂N(Bpin)(C₆H₄-o-Bpin): ¹H NMR (300.1 MHz,

[D₁₂]cyclohexane): δ = 7.97 (1H, dd, J_HH= 7 Hz, J_HH= 2 Hz,

CH_ar), 7.36–7.17 (6H, m, CH_ar), 7.13 (1H, t, J_HH= 7 Hz, CH_ar),

6.87 (1H, d, J_HH= 8 Hz, CH_ar), 4.62 (2H, s, CH₂), 1.34 (12H, s,

CH₃), 1.32 (12H, m, CH₃) ppm. ¹¹B NMR (96.3 MHz, [D₁₂]cyclo-

1

Hz) ppm. Analytical data for 12: H NMR (300.1 MHz, Me₆Si₂):

δ = 8.39 (d, J_HH= 8 Hz, 2H, CH_ar), 7.62–7.39 (m, 4H, CH_ar),

7.21 (m, 1H, CH_ar), 7.13 (m, 1H, CH_ar), 6.44 (m, 2H, CH_ar),

4.87 (dd, J_PH= 7 Hz, J = 3 Hz, 1H, NCH) ppm. The signals for

the ethyl and methyl groups are obscured by signals of 1 and

13. ³¹P{¹H} NMR (121.5 MHz, Me₆Si₂): δ = 24.2 (dd, J_RhP

=

275 Hz, J_PP= 27 Hz), 22.8 (dd, J_RhP= 170 Hz, J_PP= 27 Hz) ppm.

hexane):

δ =

28.9 (CB), 24.6 (NB) ppm. ¹³C{¹H} NMR

(75.5 MHz, [D₁₂]cyclohexane): δ = 152.3 (C_ar), 141.8 (C_ar), 137.4

(CH_ar), 131.2 (CH_ar), 129.9 (CH_ar), 129.1 (CH_ar), 128.1 (CH_ar),

126.6 (CH_ar), 124.7 (CH_ar), 83.1 (CMe₂), 82.7 (CMe₂), 56.3

(CH₂), 25.0–27.0 (CH₃) ppm. The signal for the boron-bound

carbon atom was not observed.

Treatment of [Rh{CPh₂N(H)(Bpin)}(PEt₃)₂] (9) and 9′ with

B₂pin₂

B₂pin₂(15.8 mg, 62 μmol) was added in a PFA tube to a solu-

tion of complex 9 in cyclohexane (0.3 mL), which was prepared

in situ from [Rh(Bpin)(PEt₃)₃] (1) (33.0 mg, 57 μmol) and ben-

zophenone imine (10.3 mg, 57 μmol). After 4 h at room temp-

erature the NMR spectroscopic data of the reaction solution

Structure determination of complexes 4, 5, 6, 7, 8, and 13

revealed the complete consumption of 9 and the quantitative Purple crystals of 4, red crystals of 6, dark red crystals of 7,

formation of [Rh(Bpin)(PEt₃)₃] (1) as well as the formation of deep purple crystals of 8, and orange crystals of 12 precipitated

Ph₂CHN(H)Bpin as the main product. Analytical data for from hexane solutions at −30 °C. Yellow crystals of 6 were

Ph₂CHN(H)Bpin: ¹H NMR (300.1 MHz, [D₁₂]cyclohexane): δ = obtained by crystallization from a low concentrated reaction

7.61 (4H, d, J_HH= 8 Hz, CH_ar), 7.49–7.34 (6H, m, CH_ar), 6.26 solution of hexamethyldisilane. The diﬀraction data were col-

(1H, s, CH), 1.30 (12H, s, CH₃) ppm. The signal for N-bound lected on a STOE IPDS 2θ diﬀractometer at 100 K, except for

hydrogen was not observed. ¹¹B NMR (96.3 MHz, [D₁₂]cyclo- complex 5 for which the data were collected at 90 K. Crystallo-

hexane): δ = 26.2 (Δν_1/2≈ 550 Hz) ppm. ¹³C{¹H} NMR graphic data are depicted in Table 7. The structures were

(75.5 MHz, cyclohexane): δ = 144.5 (C_ar), 129.3 (CH_ar), 127.6 solved by direct methods (SHELXS-97¹⁰¹and SIR97¹⁰³) and

(CH_ar), 126.3 (CH_ar), 82.0 (CMe₂), 61.6 (NCH), 24.6 (CH₃) ppm. were refined with the full-matrix least-squares method on F²

GC-MS, m/z: 309 [M], 294 [M − CH₃].

(SHELX-97 and SHELXL-2013).^101,102Complex 6 shows dis-

order of one ethyl group. The orientational disorder was

treated using rigid bond restraints (DELU) and a linear

restraint (ISOR) for the ethyl group. A SQUEEZE refinement

Treatment of [Rh{η³-C(CF₃)(OBpin)C₆H₅}(PEt₃)₂] (4) with

B₂pin₂

B₂pin₂(19.6 mg, 77 μmol) was added in a PFA tube to a solu- was applied for complex 13 for which the remaining electron

tion of complex 4 in cyclohexane (0.3 mL), which was prepared density (ca. 2 electrons) did not allow an appropriate dis-

in situ from [Rh(Bpin)(PEt₃)₃] (1) (40.9 mg, 70 μmol) and ordered model.

α,α,α-trifluoroacetophenone (12.2 mg, 70 μmol). After 3 d at

The hydrogen atoms were placed at the calculated positions

room temperature the ³¹P{¹H} NMR spectroscopic data of the and were refined by using a riding model.

6798 | Dalton Trans., 2014, 43, 6786–6801

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Paper

Table 7 Crystallographic data

Compound

4

5

6

7

8

13

Empirical formula

Formula weight

C

₂₆H₄₇BF₃O₃P₂Rh C₂₈H₄₇BF₃O₅P₂Rh C₃₁H₅₀BO₃P₂Rh

C₃₇H₅₇BNO₂P₂Rh C₃₇H₅₅BNO₂P₂Rh C₃₇H₆₈BNO₂P₃Rh

723.50 721.48 765.55

0.36 × 0.12 × 0.03 0.20 × 0.14 × 0.06 0.48 × 0.29 × 0.19

640.30

696.32 646.37

Crystal size (mm³)

0.33 × 0.30 × 0.28 0.40 × 0.28 × 0.10 0.26 × 0.13 ×

0.11

Wavelength (Å)

Crystal system

Space group

0.71073

Monoclinic

P2₁/c

0.71073

Monoclinic

P2₁/c

0.71073

Orthorhombic

Pna2₁

0.71073

Monoclinic

P2₁/c

0.71073

Monoclinic

P2₁/n

0.71073

Monoclinic

C2/c

a (Å)

b (Å)

c (Å)

16.1641(4)

10.6262(2)

19.1733(4)

112.801(2)

3035.91(12)

4

10.4240(5)

29.0136(13)

13.0004(6)

124.428(3)

3243.1(3)

4

24.5391(5)

10.0402(2)

13.0353(3)

19.0638(3)

20.0967(4)

20.5505(4)

107.6360(10)

7503.3(2)

8

15.1541(5)

13.2907(5)

18.0052(6)

95.441(2)

3610.1(2)

4

42.3611(15)

10.5311(2)

23.6156(8)

120.338(3)

9092.5(5)

8

β (°)

V (Å³)

3211.60(12)

4

Z

Calculated density

1.401

1.426

1.337

1.281

1.327

1.118

(Mg m⁻³

)

μ (Mo-Kα) (mm⁻¹

θ range (°)

)

0.711

2.10–29.50

51 321

8454

0.0399

0.838

99.9%

0.0301, 0.0471

0.0211, 0.0464

6623

0.677

2.36–26.76

23 758

6630

0.0872

1.017

97.1%

0.0679, 0.1089

0.0479, 0.1021

5171

0.660

2.03–28.32

29 371

7952

0.0681

0.836

99.5%

0.0424, 0.0630

0.0307, 0.0611

6246

0.572

4.63–26.85

91 569

15 810

0.0527

1.039

98.0%

0.0501, 0.0850

0.0352, 0.0808

12 772

0.594

3.27–29.23

35 936

9707

0.0961

0.943

98.9%

0.0840, 0.0777

0.0462, 0.0700

6766

0.508

4.67–26.00

46 376

8863

0.0983

1.040

99.4%

0.0515, 0.1145

0.0406, 0.1089

7377

Reflections collected

Independent reflections

R_int

Goodness-of-fit on F ²

Completeness to max. θ

R₁, ωR₂on all data

R₁, ωR₂[I₀> 2σ(I₀)]

Reflect. with [I₀> 2σ(I₀)]

Largest diﬀ. peak, hole

0.506/−0.802

0.864/−1.556

0.564/−0.843

0.798/−1.178

0.716/−0.684

0.831/−1.116

(e A⁻³

CCDC

)

977662

977663

977664

977665

977666

977667

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Article Doi

Versatile reactivity of a rhodium(i) boryl complex towards ketones and imines

DOI: 10.1039/c4dt00080c

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Article abstract of DOI:10.1039/c4dt00080c

Full text of DOI:10.1039/c4dt00080c

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