Hydridorhodathiaboranes: Synthesis, characterization, and reactivity

Article

pubs.acs.org/Organometallics

Hydridorhodathiaboranes: Synthesis, Characterization, and

Reactivity

†

,†

†

†,‡

́

Alvaro Alvarez, Beatriz Calvo, Ramon Macıas,* Fernando J. Lahoz, and Luis A. Oro

́

†

́

Instituto de Sıntesis Quımica y Catal

́

isis Homogen

́

ea (ISQCH), Universidad de Zaragoza-Consejo Superior de Investigaciones

Cientíﬁcas, 50009-Zaragoza, Spain

^‡Center of Research Excellence in Petroleum Reﬁning and Petrochemicals, King Fahd University of Petroleum and Minerals

(KFUPM), Dhahran 31261, Saudi Arabia

S

* Supporting Information

ABSTRACT: The reaction between pyridine and [8,8-

(PPh₃)₂-nido-8,7-RhSB₉H₁₀] (1) has given the opportunity

to synthesize a new family of 11-vertex hydridorhodathiabor-

anes that feature boron-bound N-heterocyclic ligands. To

explore the scope of this reaction, 1 has been treated with the

methylpyridine isomers (picolines) 2-Me-NC₅H₄, 3-Me-

NC₅H₄, and 4-Me-NC₅H₄, aﬀording the picoline ligated

clusters [8,8,8-(H)(PPh₃)₂-9-(L)-nido-8,7-RhSB₉H₉], where L

= 2-Me-NC₅H₄(3), 3-Me-NC₅H₄(4), 4-Me-NC₅H₄(5).

Thermal treatment of these nido clusters leads to dehydrogenation and the formation of isonido/closo-[1,1-(PPh₃)₂-3-(L)-1,2-

RhSB₉H₈] (9−11). Compounds 3−5 react with ethylene to form [1,1-(η²-C₂H₄)(PPh₃)-3-(L)-1,2-RhSB₉H₈] (13−15).

Similarly, treatment of 3−5 with carbon monoxide produces [1,1-(CO)(PPh₃)-3-(L)-1,2-RhSB₉H₈] (17−19). These series of η²-

C₂H₄and CO ligated 11-vertex isonido/closo-rhodathiaboranes result from the substitution of one PPh₃ligand by ethylene or CO

together with H₂loss and a concomitant nido to closo/isonido cluster structural transformation. The reactivity of 3−5 with

propene, 1-hexene, and cyclohexene under a hydrogen atmosphere is also reported and compared with the reactivity of the

pyridine ligated analogue [8,8,8-(H)(PPh₃)₂-9-(NC₅H₅)-nido-8,7-RhSB₉H₉] (2). Low-temperature NMR studies have allowed

the characterization of intermediates which undergo inter- and intramolecular exchange processes, depending on the nature of

the N-heterocyclic ligand. The CO ligand enhances the nonrigidity of the cluster, opening mechanisms of H₂loss.

PPh₃ligands and the addition of a third phosphine at the metal

center, [8,8,8-(PR₃)₃-nido-8,7-RhSB₉H₁₀] (Scheme 1).⁵

Alternatively, the treatment of 1 with pyridine aﬀords a

hydridorhodathiaborane, [8,8,8-(H)(PPh₃)₂-9-(NC₅H₅)-nido-

8,7-RhSB₉H₉] (2), in which the pyridine ligand binds to

boron-9 adjacent to the metal on the pentagonal face (Scheme

1).⁶

The bis-PPh₃ligated 11-vertex nido-rhodathiaborane 1 also

undergoes substitution reactions with 1,3-dimethylimidazol-2-

ylidene (IMe), giving a mixture that contains the products of

monosubstitution and disubstitution, [8,8-(PPh₃)(IMe)-nido-

8,7-RhSB₉H₁₀] and [8,8-(IMe)₂-nido-8,7-RhSB₉H₁₀] (Scheme

1).⁷The treatment of the monosubstituted carbene ligated

nido-rhodathiaborane with pyridine aﬀords a new isonido

cluster, [1,1-(IMe)(PPh₃)-3-(NC₅H₅)-isonido-8,7-RhSB₉H₈],

formed by pyridine-cage substitution and dihydrogen loss.

Interestingly, the bis-carbene ligated analogue does not react

with pyridine.

INTRODUCTION

■

The reactivity of metallacarboranes with organic molecules to

give polyhedral clusters that feature metal−carbon bonds has

been well studied.¹In contrast, the organometallic chemistry of

metallaboranes and metallaheteroboranes (containing p-block

elements other than carbon in the cluster framework) has been

less well developed.²There is a great potential for novel

chemistry in this area that may be developed by a combination

of the (oxidative and coordinative) ﬂexibility of transition-metal

centers together with the capability of boron-based clusters to

exhibit redox ﬂexibility in their classical closo−nido−arachno−

hypho structural transformation.³In other words, the synergic

cooperation between a metal center and a (hetero)borane

fragment can open new opportunities for bond activation and

catalysis.

In the context of organometallic chemistry and catalysis

based on metallaheteroboranes, we have focused our work on

the 11-vertex rhodathiaborane [8,8-(PPh₃)₂-nido-8,7-

RhSB₉H₁₀] (1).⁴This polyhedral compound exhibits two

principal points of reactivity: the metal center and an adjacent

B−H unit on the pentagonal face (Scheme 1). Reactions with

monodentate phosphines led to the formation of metal−ligand

substitution products, [8,8-(PR₃)(PPh₃)-nido-8,7-RhSB₉H₁₀],

as well as compounds resulting from the substitution of the

These results demonstrate that compounds 1 and 2 are

versatile clusters that can be easily prepared and systematically

modiﬁed at the rhodium center by substitutional chemistry.

Received: April 9, 2014

A

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Scheme 1. Reactivity of Compounds 1 and 2 with Lewis Bases: Systematic Cluster Tailoring

The fact that the exopolyhedral ligands play a crucial role in the

reactivity of these clusters is clearly demonstrated by the

diﬀerent outcomes of the reactions with pyridine.

8,7-RhSB₉H₉] (3) and [1,1-(PPh₃)₂-3-(2-Me-NC₅H₄)-isonido-

1,2-RhSB₉H₈]. The latter compound is the result of 2-picoline-

cage substitution and dihydrogen loss (vide infra), aﬀording a

cluster with a closo/isonido electron count.

Recently, we have reported that the treatment of nido-

hydridorhodathiaboranes [8,8,8-(H)(PR₃)₂-9-(NC₅H₅)-8,7-

RhSB₉H₉] and closo/isonido clusters [1,1-(PR₃)₂-3-(NC₅H₅)-

1,2-RhSB₉H₈] with triﬂic acid yield the corresponding cationic

rhodathiaboranes [8,8,8-(H)(PR₃)₂-9-(NC₅H₅)-nido-8,7-

RhSB₉H₁₀]⁺and [1,1-(PR₃)₂-3-(NC₅H₅)-isonido-1,2-

RhSB₉H₉]⁺.⁸These polyhedral cations show a remarkable

stereochemical nonrigidity that is the key to their reactivity.

Overall, this family of neutral and cationic 11-vertex

rhodathiaboranes has revealed a rich chemistry that embraces

(i) nido to closo dehydrogenations,⁹(ii) dihydrogen-promoted

closo to nido transformations,^6b,7(iii) oxidative addition of sp

C−H bonds,¹⁰(iv) proton-assisted H₂activation,¹¹and (v)

catalysis of hydrogenation and isomerization of oleﬁns.^6b

In these reactions, the clusters exhibit metal−borane

collaboration through structural transformations that lead to

metal−ligand hapticity changes. In other words, these NC₅H₅

ligated rhodathiaboranes combine the ﬂexibility of the {Rh-

(PPh₃)₂} center with the capability of the 11-vertex {RhSB₉}

cage to exhibit redox ﬂexibility through closo−nido structural

transformations. This metal/borane synergy has resulted in the

development of new stoichiometric cycles.^6,12

On the basis of the results summarized above, we logically

aimed to change the pyridine substituent at the boron vertices.

Herein, we report the reactions of the parent rhodathiaborane 1

with the methylpyridine isomers (picolines) 2-Me-NC₅H₄, 3-

Me-NC₅H₄, and 4-Me-NC₅H₄. The new picoline ligated

clusters are compared with their pyridine counterparts, in

order to ﬁnd trends and diﬀerences within this unique series of

polyhedral clusters. In addition, the reactivity of these

rhodathiaboranes has been studied with a focus on hydrogen

loss and on their reactions with ethylene and CO.

Under the same conditions, the reaction of 1 with 3- or 4-

picoline aﬀorded good yields of air-stable red solids that were

characterized as the hydridorhodathiaboranes [8,8,8-(H)-

(PPh₃)₂-9-(3-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (4) and [8,8,8-

(H)(PPh₃)₂-9-(4-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (5), mirror-

ing the results previously obtained with pyridine (Scheme 2).⁶

Scheme 2. Synthesis of Hydridorhodathiaboranes

The three new hydridorhodathiaboranes 3−5 have been

characterized by multielement NMR spectroscopy. In addition,

the molecular structures of the 3- and 4-picoline ligated

compounds have been determined by X-ray diﬀraction analysis.

The structures are based on an 11-vertex nido-{RhSB₉}

skeleton that can be formally derived from an icosahedron by

the removal of a vertex. The pentagonal face is made up by a

{Rh(H)(PPh₃)} group, a sulfur vertex, two BH units, and a

boron vertex substituted by an N-heterocyclic ligand (Figure

1). In addition, there is a bridging hydrogen atom along the

B(9)−B(10) edge. The same structural motifs are found in the

pyridine ligated analogues [8,8,8-(H)(PR₃)₂-9-(NC₅H₅)-nido-

8,7-RhSB₉H₉], where PR₃= PPh₃(2), PMePh₂(6) (Table

1).^5,6,9Compounds 2−6 are 13-skeletal-electron-pair clusters

(sep) that conform to Wade’s rules.^3aThis fact is in contrast

with the precursor 1, which has 12 sep, typical of a closo/isonido

cage, but exhibits an 11-vertex nido structure. This discrepancy

RESULTS AND DISCUSSION

■

Synthesis and Characterization of Picoline-Ligated

11-Vertex Rhodathiaboranes. Reaction of compound 1

with excess 2-picoline aﬀorded a mixture containing the

rhodathiaboranes [8,8,8-(H)(PPh₃)₂-9-(2-Me-NC₅H₄)-nido-

B

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suggesting a stronger structural trans inﬂuence in comparison

to the B(3)−B(4) edge to which the other phosphine, P(2),

lies trans. The shorter Rh−P distances found in the bis-PMePh₂

derivative 6 agree well with the fact that methyldiphenylphos-

phine is a better σ-donor ligand than PPh₃.

It is well-known that the boron vertices of metal-face-bound

carborane ligands have a larger trans inﬂuence than the cage

carbon atoms.¹⁴This fact is important because it implies that

the most stable metal-to-carborane exopolyhedral ligand

orientation is that in which the strongest structural trans eﬀect

ligands on the metal lie eﬀectively trans to the carbon atoms.

This may be extended to metallathiaboranes where the metal-

bound sulfur atoms also have a lower trans inﬂuence than the

boron atoms in the face of the metal-to-thiborane linkage.

Thus, in the hydridorhodathiaboranes 2−6, the hydride ligand

lies trans to the sulfur vertex. The same kind of exopolyhedral

ligand control has been observed in other metallathiaboranes

that bear hydride ligands.¹⁵Moreover, in some 11-vertex nido-

rhodathiaboranes, it has been calculated that a metal−

thiaborane interaction change from a sulfur−metal−hydride

trans arrangement to a boron−metal−hydride trans conﬁg-

uration can have an energy cost as high as 12 kcal/mol.^12,16

Figure 1. Molecular structure of 4. Only the ipso carbon atoms on the

phenyl groups are included to aid clarity. Ellipsoids are shown at the

50% probability level.

1

¹¹B and H NMR data for compounds 3−5 are given in

Table 2; and Figure 2 compares the ¹¹B spectra of the 2- and 3-

picoline ligated clusters 3 and 4 with those of the previously

reported pyridine analogues 2 and [8,8,8-(H)(PMe₃)(PPh₃)-9-

(NC₅H₅)-nido-8,7-RhSB₉H₉] (7). These nido-hydridorhoda-

thiaboranes show nine resonances in the interval between δ_B

+15 and −30 ppm, in agreement with an asymmetric molecular

structure in solution. The spectra among the clusters are

remarkably similar, with the only noticeable deviation

corresponding to the B(10) resonance of the 2-picoline

derivative, which is deshielded by about 4 ppm from the

general trend (Figure 2).

between skeletal electron pairs and structure has been dealt

with previously in detail.¹³

Table 1 gathers selected distances and angles for compounds

2 and 4−6. Overall, there are no substantial diﬀerences among

intramolecular distances and angles in these series of

hydridorhodathiaboranes. It is noteworthy, however, that the

3-picoline derivative 4 exhibits the longest Rh−P distance at

2.3752(8) Å, perhaps due to steric interactions between the

methyl group at position 3 in the N-heterocyclic ring and the

bulky PPh₃ligands. In all of the clusters except for 5, the

longest Rh−P distance corresponds to the phosphine ligand

that is trans to boron-9, substituted with the pyridinic ligand,

The ¹H{¹¹B} NMR spectra of 3−5 show a broad singlet and

an apparent quartet in the high-ﬁeld region, assigned to the

Table 1. Selected Interatomic Distances (Å) and Angles (deg) between Interatomic Vectors with Standard Uncertainties (su) in

Parentheses for [8,8,8-(H)(PPh₃)₂-9-(NC₅H₄)-nido-8,7-RhSB₉H₉] (2), [8,8,8-(H)(PPh₃)₂-9-(3-Me-NC₅H₄)-nido-8,7-RhSB₉H₉]

(4), [8,8,8-(H)(PPh₃)₂-9-(4-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (5), and [8,8,8-(H)(PMePh₂)₂-9-(NC₅H₄)-nido-8,7-RhSB₉H₉] (6)

2^6a

4

5

6⁹

Rh(8)−S(7)

Rh(8)−P(1)

Rh(8)−P(2)

Rh(8)−B(3)

Rh(8)−B(4)

Rh(8)−B(9)

S(7)−B(2)

S(7)−B(3)

2.431(2)

2.354(2)

2.341(2)

2.201(10)

2.217(11)

2.220(9)

1.980(9)

2.059(11)

1.953(9)

1.547(11)

1.727(14)

1.906(14)

1.856(14)

100.27(7)

96.38(7)

102.05(8)

120.6(5)

87.1(3)

2.4132(8)

2.3752(8)

2.3383(7)

2.235(3)

2.236(3)

2.208(3)

1.991(3)

2.085(3)

1.909(3)

1.569(3)

1.738(4)

1.902(4)

1.868(4)

101.68(3)

103.16(3)

97.63(3)

120.81(16)

88.17(7)

157.80(8)

95.54(8)

2.4373(14)

2.3488(14)

2.3560(14)

2.239(6)

2.216(5)

2.210(6)

1.984(6)

2.041(6)

1.943(6)

1.555(7)

1.741(8)

1.915(9)

1.870(8)

101.77(5)

96.81(5)

101.03(5)

121.6(4)

88.02(15)

159.02(15)

97.28(15)

2.4270(5)

2.3224(6)

2.3091(6)

2.230(2)

2.209(2)

2.214(2)

1.996(3)

2.060(3)

1.928(3)

1.556(3)

1.748(4)

1.913(4)

1.874(3)

98.10(2)

97.82(2)

105.080(19)

119.30(15)

87.79(6)

163.22(6)

95.66(6)

S(7)−B(11)

N(1)−B(9)

B(6)−B(11) (shortest)

B(2)−B(3) (longest)

B(9)−B(10)

P(1)−Rh(8)−P(2)

S(7)−Rh(8)−P(1)

S(7)−Rh(8)−P(2)

Rh(8)−B(9)−N(1)

S(7)−Rh(8)−B(9)

P(1)−Rh(8)−B(9)

P(2)−Rh(8)−B(9)

162.4(3)

95.8(3)

C

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1

Table 2. ¹¹B and H NMR Data for [8,8,8-(H)(PPh₃)₂-9-(2-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (3), [8,8,8-(H)(PPh₃)₂-9-(3-Me-

NC₅H₄)-nido-8,7-RhSB₉H₉] (4), and [8,8,8-(H)(PPh₃)₂-9-(4-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (5) in CD₂Cl₂Compared to the

Corresponding DFT/GIAO-Calculated ¹¹B Nuclear Shielding Values Calculated for the PH₃Models (in Brackets)

3

4

5

a

b

assignt

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

c

9

+11.1 [+18.8]

2-Me-NC₅H₄

+3.42

+12.1 [+17.9]

+8.1 [+8.9]

+3.9 [+7.5]

+0.6 [+2.2]

−3.7 [−0.1]

3-Me-NC₅H₄

+3.51

+11.8 [+17.6]

4-Me-NC₅H₄

+3.53

d

e

3

+6.1 [+8.5]

+7.8 [+9.4]

6

+4.0 [+5.5]

+1.5 [+2.1]

−3.9 [+1.9]

+3.03

+2.60

+3.3 [+7.4]

+2.63

f

11

4

+3.58

+4.13

+0.2 [+2.2]

+4.13

+3.26

+2.85

−3.8 [−0.1]

+2.85

g

h

i

5

−12.1 [−14.0]

+1.93

−10.0 [−11.1]

+1.83

−10.2 [−10.7]

+1.81

10

1

−14.4 [−19.2]

−25.0 [−23.8]

−27.2 [−27.9]

+1.06

−17.9 [−22.7]

−25.6 [−25.4]

−29.1 [−28.5]

+0.92

−17.9 [−23.0]

−25.7 [−25.1]

−28.5 [−28.4]

+0.88

j

+1.49

+1.50

+1.49

2

+1.21

+1.11

+1.09

μ(9, 10)

−0.95

−12.49

−1.38

−12.47

−1.42

−12.43

k

l

m

Rh(8)-H

a

b

Assignments based on H{¹¹B} selective experiments and DFT calculations. Proton chemical shifts corresponding to boron-bound hydrogen

1

c

d

e

f

g

atoms. Picoline-substituted vertex. ¹J(¹¹B−¹H) = 132 Hz. ¹J(¹¹B−¹H) = 112 Hz. ¹J(¹¹B−¹H) = 127 Hz. ¹J(¹¹B−¹H) = 142 Hz. ¹J(¹¹B−¹H) =

h

i

j

k

140 Hz. ¹J(¹¹B−¹H) = 137 Hz. ¹J(¹¹B−¹H) = 146 Hz. ¹J(¹¹B−¹H) = 150 Hz. Apparent quartet: ¹J(¹⁰³Rh−¹H) + ²J(³¹P_A−¹H) + ²J(³¹P_B−¹H) ≈ 17

l

m

Hz. Apparent quartet: ¹J(¹⁰³Rh−¹H) + ²J(³¹P_A−¹H) + ²J(³¹P_B−¹H) ≈ 17 Hz. Apparent quartet: ¹J(¹⁰³Rh−¹H) + ²J(³¹P_A−¹H) + ²J(³¹P_B−¹H) ≈ 20

1

Hz; H{³¹P} δ −12.43 (d, J(¹⁰³Rh−¹H) = 19.7 Hz, H).

Figure 2. Representation of the ¹¹B NMR spectra of 2−4 and 7. Hatched lines connect equivalent positions. Assignments made on the basis of DFT

calculations.

B(9)−B(10) bridging hydrogen atom and to the Rh−H

hydride ligand, respectively. Thus, these spectroscopic data

can be taken as diagnostic for the formation of these 11-vertex

nido-hydridorhodathiaboranes. In this regard, it is interesting to

note that the B(9)−H−B(10) bridging proton resonance of the

2-picoline derivative (δ_H−0.95 ppm) features a signiﬁcant shift

toward low frequency from the mean value of δ_H−1.28 ppm

that has been found in the series of picoline ligated nido clusters

reported here, as well as the previously reported hydrido-

rhodathiaborane counterparts of general formulation [8,8,8-

(H)(PR₃)₂-9-(NC₅H₅)-nido-8,7-RhSB₉H₉], where PR₃= PPh₃

(2), PMePh₂(6), PPh₃and PMe₃(7), PPhMe₂, or PPh₃and

PMe₂Ph.⁹

being signiﬁcantly broader. This latter resonance broadens and

shifts to low frequency as the temperature increases, whereas

the low-frequency signal moves slightly to higher frequency.

This variable-temperature NMR behavior is illustrated in Figure

S1 for compound 5: from low to high temperatures, the two

resonances broaden and cross each other. Similar changes were

ﬁrst reported for the pyridine analogue 2.^6a

It has been proposed that the temperature-dependent

broadening in the ³¹P{¹H} spectra of pyridine ligated

hydridorhothiaboranes [8,8,8-(H)(PR₃)₂-9-(NC₅H₅)-nido-

RhSB₉H₉] may arise mainly from the eﬀects of “thermal

decoupling” on the boron nuclei,¹⁷together with the

dissociation of the phosphine ligand trans to B(9).^6b,9On

this rationale, the broader peak at high frequency in this new

family of 11-vertex hydrido ligated clusters may be assigned to

the phosphine ligand that is trans to the picoline-substituted

boron vertex at the 9-position.

The lower conformational freedom of the 2-picoline

substituent around the B(3)−N bond in comparison to

pyridine and 3- and 4-picolines may be the cause of the shift

to higher frequency of the B(9)−H−B(10) bridging proton

resonance.

Studies of Reactivity. Thermal and Chemical Cluster

Dehydrogenations. The hydridorhodathiaboranes 3−5 are

stable in solution at room temperature. However, heating at

The ³¹P{¹H} NMR spectra of 3−5 exhibit two doublets of

doublets at low temperature, the signal at the highest frequency

D

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Scheme 3. Reactivity of 2−5: Thermal Dehydrogenation and Reactions with C₂H₄

Scheme 4. Reactions of 2−5 with Carbon Monoxide

reﬂux temperature in dichloromethane results in the loss of H₂,

yielding the corresponding closo/isonido clusters [1,1-(PPh₃)₂-

3-(L)-1,2-RhSB₉H₈], where L = 2-Me-NC₅H₄(9), 3-Me-

NC₅H₄(10), 4-Me-NC₅H₄(11) (Scheme 3).

a mixture composed of 1-hexene (63%), 2-hexene (34%), and

1-hexane (3%). Moreover, 3 reacted with cyclohexene to give

2% of cyclohexane after 1 day. These results demonstrate that

the 2-picoline derivative 3 is more reactive with alkenes than

the pyridine analogue 2 and that the reaction products are the

result of the hydrogenation and isomerization of the double

bonds (in the case of 1-hexene).

In a fashion similar to the reactions with ethylene, the

treatment of these pyridine- and picoline ligated hydrido-

rhodathiaboranes 2−5 with carbon monoxide aﬀords the

products of hydrogen loss and PPh₃substitution, [1,1-

(CO)(PPh₃)-3-(L)-1,2-RhSB₉H₈], (17−19) (Scheme 4).^6a

It should be noted that the reactivity of the picoline ligated

hydridorhodathiaboranes 3−5 with carbon monoxide and with

ethylene, reported here, reproduces the results previously

reported for the pyridine ligated analogue 2.^6b

As we can see, thermal dehydrogenation and reactions with

CO and C₂H₄are convenient routes to the synthesis of 11-

vertex rhodathiaboranes with closo/isonido cluster geometries,

which bear diﬀerent exopolyhedral ligands at either the metal

center or the boron-3 vertex. Thus, these reactions broaden the

scope of the substitution chemistry in this system, allowing a

systematic tuning of their reactivity.

The picoline ligated rhodathiaboranes 2−5 react with

ethylene to give the corresponding closo/isonido clusters, [1,1-

(η²-C₂H₄)(PPh₃)-3-(L)-1,2-RhSB₉H₈] (13−15). In these re-

actions, we have also observed formation of ethane.

The η²-C₂H₄ligand in these 11-vertex closo/isonido clusters is

labile, and it can be substituted by PPh₃to give the

corresponding bis-PPh₃ligated derivatives (Scheme 3). In

fact, this route is more appropriate for the synthesis of the

closo/isonido compounds 8−11 than the thermal dehydrogen-

ation of the hydride nido clusters 2−5.

The reactivity of compounds 2 and 3 has been also explored

with other alkenes. Thus, the pyridine ligated cluster 2 reacts

slowly with propylene at room temperature, and after 4 days of

stirring the result is a mixture that contains propane together

with the starting reagent 2 (35%) and its dehydrogenation

product 8 (65%). The reaction with 1-hexene, after 3 days,

aﬀorded 1-hexene (75%), 2-hexene (17%), 3-hexene (7%), and

1-hexane (1%). Under the same conditions, compound 2 did

not react with cyclohexene.

In the case of the 2-picoline analogue 3 after 1 h the reaction

with propylene aﬀords the bis-PPh₃closo derivative 9 and

formation of propane. Reaction with 1-hexene, after 1 day, gave

All of the new 11-vertex isonido clusters 9−11, 13−15, and

17−19 have been characterized by NMR spectroscopy, and the

data are gathered in Tables 3−5. A comparison of the ¹¹B NMR

E

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Table 3. ¹¹B and ¹H NMR Data for [1,1-(PPh₃)₂-3-(NC₅H₅)-isonido-1,2-RhSB₉H₉] (8), [1,1-(PPh₃)₂-3-(2-Me-NC₅H₄)-closo-1,2-

RhSB₉H₈] (9), [1,1-(PPh₃)₂-3-(3-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (10), and [1,1-(PPh₃)₂-3-(4-Me-NC₅H₄)-closo-1,2-RhSB₉H₈]

(11) in CD₂Cl₂Compared to the Corresponding DFT/GIAO-Calculated ¹¹B Nuclear Shielding Values (in Brackets)

8^6b

9

10

11

a

b

assignt

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

c

3

+54.6 [+58.4]

NC₅H₅

+53.3 [+57.8]

2-Me-

+54.8 [+59.0]

3-Me-

+54.9 [+59.5]

4-Me-

NC₅H₄

+4.09

+1.29

(2H)

d

e

9

+27.3 [+30.1]

+4.09

+1.27

+25.4 [+29.7]

+4.32

+27.5 [+30.2]

+4.24

+27.3 [+29.6]

4, 5

−0.5 [+6.7, +5.4]

−0.6 [+10.8, +3.1]

+1.27

+2.40

+0.5 [+7.9, +4.1]

+1.28

+2.37

−0.7 [+8.4, +3.4]

8

−15.2 [−12.2]

+2.16

−14.2 [−13.1]

−21.9 [−15.4, −23.0]

−14.3 [−12.6]

−23.8 [−14.8, −22.4]

−15.5 [−12.9]

−24.6 [−14.1, −22.0]

+2.17

f

6, 7

−24.2 [−18.1, −21.8]

−0.22

(2H)

−0.10

(2H)

+0.05

(4H)

−0.23

(4H)

g

10, 11

−34.4 [−29.3, −29.6]

−0.27

(2H)

−29.8 [−26.5, −31.1]

−29.9 [−28.8, −29.5]

−0.29

(2H)

−30.7 [−28.0, −29.7]

a

b

1

Assignments based on H{¹¹B} selective experiments and DFT calculations. Proton chemical shifts corresponding to boron-bound hydrogen

c

d

e

f

g

atoms. Picoline-substituted vertex. ¹J(¹¹B−¹H) = 144 Hz. ¹J(¹¹B−¹H) = 137 Hz. ¹J(¹¹B−¹H) = 129 Hz. ¹J(¹¹B−¹H) = 139 Hz.

1

Table 4. ¹¹B and H NMR Data for [1,1-(PPh₃)(η²-C₂H₄)-3-(NC₅H₅)-isonido-1,2-RhSB₉H₈] (12), [1,1-(PPh₃)(η²-C₂H₄)-3-(2-

Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (13), [1,1-(PPh₃)(η²-C₂H₄)-3-(3-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (14), and [1,1-(PPh₃)(η²-

C₂H₄)-3-(4-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (15) in CD₂Cl₂Compared to the Corresponding DFT/GIAO-Calculated ¹¹B

Nuclear Shielding Values (in Brackets)

12^6a

13

14

15

a

b

assignt

δ(¹¹B)

δ(¹H)

NC₅H₅

δ(¹¹B)

+54.9

δ(¹H)

δ(¹¹B)

+56.3

δ(¹H)

δ(¹¹B)

δ(¹H)

c

3

+55.7 [+58.5]

2-Me-NC₅H₄

+4.27

3-Me-NC₅H₄

+4.22

+55.3

4-Me-NC₅H₄

+4.33

d

e

f

g

9

5

4

8

7

6

+26.4 [+28.5]

+4.36

+1.80

+2.06

+2.46

+0.54

−0.17

+24.9

+4.0

+26.2

+1.4

+26.2

+0.8 [+9.0]

+2.01

+1.93

+0.1

+2.05

−0.1 [+4.2]

−1.1

+1.58

−0.1

−14.6

−22.6

−24.6

+1.65

−0.7

+1.72

−14.5 [−13.3]

−22.2 [−16.8]

−24.6 [−22.0]

−14.1

−20.4

−25.4

+2.53

+2.30

−15.3

−22.5

−25.1

−30.0

+2.45

+0.87

+0.37

+0.39

h

−0.54

−0.23

10, 11

−30.3 [−27.4, −27.0]

+0.42, −0.01

−29.1, −29.8

+0.23, −0.10

−30.0, −30.7

+0.19, −0.21

+0.53, −0.01

a

b

Assignments based on H{¹¹B} selective experiments and DFT calculations. Proton chemical shifts corresponding to boron-bound hydrogen

1

c

d

e

f

g

h

atoms. Picoline-substituted vertex. ¹J(¹¹B−¹H) = 124 Hz. ¹J(¹¹B−¹H) = 127 Hz. ¹J(¹¹B−¹H) = 124 Hz. ¹J(¹¹B−¹H) = 127 Hz. ¹J(¹¹B−¹H) =

134 Hz.

Table 5. ¹¹B and ¹H NMR Data for [1,1-(PPh₃)(CO)-9-(NC₅H₅)-closo-1,2-RhSB₉H₉] (16), [1,1-(PPh₃)(CO)-3-(2-Me-NC₅H₄)-

closo-1,2-RhSB₉H₈] (17), [1,1-(PPh₃)(CO)-3-(3-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (18), and [1,1-(PPh₃)(CO)-3-(4-Me-NC₅H₄)-

closo-1,2-RhSB₉H₈] (19) in CD₂Cl₂Compared to the Corresponding DFT/GIAO-Calculated ¹¹B Nuclear Shielding Values (in

Brackets)

16^6b

17

18

19

a

b

assignt

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

δ(¹¹B)

δ(¹H)

c

3

+55.4 [+59.5] NC₅H₅

+53.8 [+57.7]

2-Me-

+55.7 [+59.7]

3-Me-

+55.3 [+58.7]

4-Me-

NC₅H₅

+4.34

NC₅H₅

+4.33

NC₅H₅

+4.44

d

e

f

9

5

+28.1

+4.34

+2.39

+1.08

+27.4 [+29.2]

+28.2 [+30.1]

+28.2 [+29.7]

+1.5 [+12.2]

[+30.4]

+1.1 [+8.9]

+0.97 (2B) [+14.2,

+0.8]

+2.40

+1.2 [+8.8]

+2.40

+2.50

4

8

6

7

−0.7 [+4.2]

−14.4 [−13.4] +2.37

−24.4 [−17.1] +0.66

+1.33

+2.40

+0.73

−0.7 [+4.2]

+1.12

−0.5 [+1.3]

−14.4 [−14.4]

−24.5 [−17.3]

+1.21

−13.6 [−14.3]

−22.9 [−17.2]

−14.7 [−13.6]

−24.9 [−17.1]

−26.1 [−21.6]

+2.40

+2.50

+0.65

+0.68

−26.1 [−21.8] −0.08

−24.9 [−22.9]

+0.03

−25.9 [−24.1]

+0.22

g

h

i

+0.01 (3H)

10, 11 −31.9

+0.07, 0.00 −31.8 [−24.0, −30.6]

−32.0 [−26.8,

−0.01 (2H)

−31.9 [−25.9,−29.7 ]

+0.15 (2H)

−29.3]

a

b

Assignments based on H{¹¹B} selective experiments and DFT calculations. Proton chemical shifts corresponding to boron-bound hydrogen

1

c

d

e

f

g

h

atoms. Picoline-substituted vertex. ¹J(¹¹B−¹H) = 118 Hz. ¹J(¹¹B−¹H) = 129 Hz. ¹J(¹¹B−¹H) = 133 Hz. ¹J(¹¹B−¹H) = 127 Hz. ¹J(¹¹B−¹H) =

i

j

138 Hz. ¹J(¹¹B−¹H) = 142 Hz. ¹J(¹¹B−¹H) = 138 Hz.

spectra corresponding to the pyridine derivative 8 and the 2-

picoline derivatives 9, 13, and 17 is depicted in Figure 3. The

patterns are very similar within this series of 11-vertex closo/

isonido clusters, suggesting that changes between the

exopolyhedral ligands, either at the metal or at the boron

vertex, do not substantially aﬀect the overall shielding of the

boron cage nuclei.

F

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Figure 3. Diagram that represents the chemical shifts in the ¹¹B NMR spectra of 8, 9, 13, and 17. Hatched lines connect equivalent positions.

Assignments are based on DFT GIAO calculations.

The ³¹P{¹H} NMR spectra of the closo/isonido derivatives 8−

19 show doublets at room temperature. It is of interest to note

that, as the temperature decreases, the broad doublet of the 2-

picoline derivative 9 broadens further and splits into two broad

doublets. This variable-temperature behavior demonstrates that

the cluster is undergoing a ﬂuxional process. A plausible

mechanism that could rationalize this intramolecular rearrange-

ment is a hindered rotation of the 2-picoline ligand around the

N−B(3) bond, rendering the exopolyhedral PPh₃ligands at the

rhodium center nonequivalent (Scheme 5). The free energy of

activation, ΔG^⧧₂₇₃, measured at the coalescence temperature is

12 kcal/mol.

the N-heterocyclic ligands studied herein does not lead to a

signiﬁcant charge diﬀerence at the metal center.

The 2-picoline ligated cluster 9 has been characterized by X-

ray crystallography (Figure 4). Table 7 gives selected distances

Scheme 5. Hindered Rotation of the 2-Picoline Ligand

around the B(3)−N Bond in Compound 9

Figure 4. Molecular structure of [1,1-(PPh₃)₂-3-(2-Me-NC₅H₄)-closo-

1,2-RhSB₉H₈] (9). Only the ipso carbon atoms on the phenyl groups

are included to aid clarity. Ellipsoids are shown at the 50% probability

level.

Table 6 gathers the IR CO stretching frequencies of the CO

ligated closo/isonido clusters 16−19. The frequencies are similar

and angles for this derivative and, to help in comparison, for the

pyridine ligated analogues [1,1-(PR₃)-3-(NC₅H₅)-1,2-

RhSB₉H₈], where PR₃= PPh₃(8), PMe₃and PPh₃(20), or

PMe₂Ph (21). At ﬁrst sight, the structures all look like 11-vertex

closo clusters based on an octadecahedron. It should be noted

that the clusters exhibit long Rh(1)−B(5) distances close to 2.5

Å, which is the upper limit normally considered as bonding. In

the case of compound 8, the distance 2.562(6) Å is outside this

limit. This elongation results in the formation of a pseudo-

square open face that is a structural feature common in closo 11-

vertex clusters,¹⁹which represent intermediates along the

structural continuum from closo to nido.^16,20

Reactions with CO at Low Temperatures. In the previous

section, it was mentioned that the reaction of 11-vertex

rhodathiaboranes with carbon monoxide aﬀords the products of

dihydrogen loss and the substitution of one of the PPh₃ligands

by CO. These reactions are quantitative when carried out at

room temperature for periods on the order of hours. However,

short reaction times and low-temperature NMR studies have

allowed the characterization of intermediates that provide new

Table 6. Measured and Calculated IR Stretching Frequencies

ν_CO(cm⁻¹

)

a

compd

exptl

calcd

[1,1-(CO)(PPh₃)-3-(NC₅H₅)-1,2-RhSB₉H₈] (16)

[1,1-(CO)(PPh₃)-3-(2-Me-NC₅H₄)-1,2-RhSB₉H₈] (17)

[1,1-(CO)(PPh₃)-3-(3-Me-NC₅H₄)-1,2-RhSB₉H₈] (18)

[1,1-(CO)(PPh₃)-3-(4-Me-NC₅H₄)-1,2-RhSB₉H₈] (19)

1980

1982

1974

1985

1903

1905

1898

1911

a

The computed carbonyl frequencies were scaled with a 0.9613

factor.¹⁸

within the series, with the smallest value corresponding to the

3-picoline derivative. The DFT-calculated values are around 76

cm⁻¹smaller than the measured data, and they follow the

experimental trend. Decreasing CO frequency is an accepted

measure of increasing negative charge buildup on the metal

center. Hence, it appears that the substitution of boron-3 with

G

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Table 7. Selected Interatomic Distances (Å) and Angles (deg) between Interatomic Vectors with Standard Uncertainties (su) in

Parentheses for [1,1-(PPh₃)₂-3-(NC₅H₅)-isonido-8,7-RhSB₉H₉] (8), [1,1-(PPh₃)₂-3-(2-Me-NC₅H₄)-closo-8,7-RhSB₉H₈] (9),

[1,1-(PPh₃)(PMe₃)-3-(NC₅H₅)-closo-8,7-RhSB₉H₈] (20), and [1,1-(PMe₂Ph)₂-3-(NC₅H₅)-closo-8,7-RhSB₉H₈] (21)

8¹⁰

9

20

2.3841(9)

21

Rh(1)−S(2)

Rh(1)−P(1)

Rh(1)−P(2)

Rh(1)−B(3)

2.3997(14)

2.3278(13)

2.3012(12)

2.085(6)

2.400(6)

2.562(6)

2.344(6)

2.387(6)

1.918(6)

1.956(6)

1.989(6)

1.532(8)

1.709(8)

1.893(9)

96.97(4)

102.32(5)

110.83(5)

112.65(17)

112.42(16)

119.02(16)

2.3885(14)

2.3276(15)

2.3243(15)

2.119(7)

2.435(7)

2.485(7)

2.364(7)

2.372(7)

1.934(8)

1.921(7)

2.001(7)

1.556(7)

1.716(10)

1.905(10)

97.86(5

2.3826(11)

2.2821(11)

2.2741(11)

2.067(4)

2.362(5)

2.487(5)

2.333(4)

2.409(5)

1.932(5)

1.969(5)

1.989(5)

1.541(5)

1.712(6)

1.916(7)

96.27(4)

103.77(4)

112.02(4)

116.40(12)

104.50(13)

121.22(12)

2.2889(10) [PMe₃]

2.2710(9) [PPh₃]

2.087(4)

Rh(1)-B4)

2.401(4)

Rh(1)−B(5)

Rh(1)−B(6)

Rh(1)−B(7)

S(2)−B(4)

S(2)−B(5)

S(2)−B(8)

N−B(3)

B(3)−B(7) (shortest)

B(4)−B(8) (longest)

P(1)−Rh(1)−P(2)

P(1)−Rh(1)−S(2)

P(2)−Rh(1)−S(2)

P(1)−Rh(1)−B(3)

P(2)−Rh(1)−B(3)

B(3)−Rh(1)−S(2)

2.471(4)

2.380(4)

2.354(4)

1.953(4)

1.937(4)

1.999(5)

1.546(5)

1.705(5)

1.917(6)

96.68(4)

107.75(5)

103.80(5)

112.83(19)

112.3(2)

119.79(18)

103.17(4)

110.92(3)

114.79(11)

108.42(11)

120.32(11)

Figure 5. [¹H−¹H]-NOESY at 273 K in CD₂Cl₂of the reaction mixture formed after the treatment of 3 with CO. The oﬀ-diagonal peaks are of the

same phase as the diagonal peaks, indicating chemical exchange.

insights dealing with the mechanism of hydrogen loss from

these clusters. These results are, therefore, relevant to the

reverse reaction: the addition of H₂to some 11-vertex isonido-

rhodathiaboranes.^6a,7The following paragraphs describe these

results.

Carbon monoxide was bubbled for 2 min through a CD₂Cl₂

solution of the 2-picoline ligated hydridorhodathiaborane 3 in a

5 mm NMR tube at room temperature, and the resulting

reaction mixture was then studied by variable-temperature

(VT) multielement NMR spectroscopy, starting at low

temperatures. At −50 °C, the ³¹P{¹H} spectrum shows a

sharp doublet at δ_P+35.0 ppm and a very broad peak at δ_P

+33.8 ppm, together with free PPh₃and small amounts of O

PPh₃. Interestingly, at 0 °C, the broad signal sharpens and shifts

toward higher frequency to became a doublet that overlaps the

highest intensity doublet (Figure S2 (Supporting Informa-

H

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Figure 6. ³¹P{¹H} NMR spectrum in CD₂Cl₂of compound 5 after treatment with CO at 223 K.

Figure 7. VT ¹H{¹¹B} NMR spectra at diﬀerent temperatures of 5 after treatment with CO. The peaks labeled with blue squares correspond to the

starting reactant 5.

1

tion)). The H{¹¹B} NMR spectra at −70 and −50 °C show

three peaks in the negative region. The two broad signals at δ_H

−2.93 and −4.67 ppm can be assigned to B−H−B bridging

hydrogen atoms, which typically occupy positions at B−B edges

on the nontriangulated open faces of boron-based clusters. The

sharp doublet at δ_H−11.33 ppm corresponds to a Rh−H

B proton signal at −2.93 ppm and the Rh−H hydride

resonance (Figure 5).

Similarly, the reaction mixtures resulting from the bubbling

of CO for several minutes through CD₂Cl₂solutions of the

hydridorhodathiaboranes 2, 4, and 5, at room temperature,

were studied by VT NMR spectroscopy starting at low

temperature. For the three systems, the ³¹P{¹H} NMR spectra

at −50 °C exhibit three doublets at around +36.5, +34.5, and

+29.2 ppm. In the three samples studied, the highest intensity

signal corresponds to the peak close to +34 ppm, whereas the

doublet at highest ﬁeld exhibits the lowest intensity (Figure 6).

The ³¹P{¹H} spectra showed free PPh₃and OPPh₃, together

1

hydride ligand. The H NMR hydride resonance broadens

considerably as the temperature rises, indicating that the

hydride ligand is undergoing site exchange (Figure S3

(Supporting Information)). This is conﬁrmed by a [¹H−¹H]-

NOESY experiment at 0 °C that shows oﬀ-diagonal peaks of

the same phase as the diagonal peak between the broad B−H−

I

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Figure 8. [³¹P−¹H]-HMBC experiment at 223 K of 5 after treatment with CO.

with diﬀerent amounts of the products of H₂loss 8, 10, and 11

and the products of H₂loss and CO binding 16, 18, and 19.

Interestingly, at higher temperatures these ³¹P{¹H} reso-

nances (purple, red, and green squares in Figure 6 and Figures

S7−S10 (Supporting Information)) broaden and shift,

suggesting that the species are undergoing processes of

interconversion in solution.

involves the hydride ligand and one of the B−H−B hydrogen

atoms (Figure 5 and Figure S3 (Supporting Information)).

For the 2-picoline system, a [³¹P−¹H]-HMBC experiment at

223 K showed a correlation between the broad ³¹P doublet of

lower intensity and the hydride resonance (Figure S4

(Supporting Information)). Similarly, the mixtures formed

from the reactions of 2, 4, and 5 with CO exhibited [³¹P−¹H]-

HMBC spectra with correlations between the highest intensity

1

The H{¹¹B} NMR spectra of the pyridine and 3- and 4-

1

³¹P and H doublets and between the lowest intensity ³¹P and

picoline ligated systems with CO each show two broad singlets

¹H signals (Figure 8).

at δ_Hca. −3.0 and −4.5 ppm and a sharp doublet at ca. −11.5

1

ppm (Figure 7). This pattern resembles the H{¹¹B} spectra

Stereochemical Nonrigidity. The observations described

above permit us to conclude that the reactions with CO lead to

the formation of the substitution products [8,8,8-(CO)(H)-

(PPh₃)-9-(L)-nido-8,7-RhSB₉H₉], where L = NC₅H₅, 2-Me-

NC₅H₄, 3-Me-NC₅H₄, 4-Me-NC₅H₄, which, according to the

¹H{¹¹B} and ¹¹B{¹H} NMR data (Figures S12 and S13

(Supporting Information)), maintain the 11-vertex nido cage of

their bis-PPh₃ligated precursors 2−5.

The data demonstrate the formation of two new species in

the 2-picoline reaction system upon treatment with CO,

whereas for the pyridine and 3- and 4-picoline containing

clusters, there are clearly three new compounds. These species

are stable at low temperatures, but at room and higher

temperatures they undergo hydrogen loss and a consequent

nido to closo (or isonido) cluster structural transformation. The

VT NMR data show that the intermediates interconvert. More

speciﬁcally, it may be proposed that these labile rhodathiabor-

anes are isomers that exhibit diﬀerent {Rh(CO)(H)(PPh₃)} to

{η⁴-SB₉H₉(L)} conﬁgurations (L = pyridine, 2-, 3-, or 4-

picoline). In other words, the substitution of a PPh₃ligand by

discussed above for the 2-picoline system (Figure S3

(Supporting Information)), and, following the same rationale,

the broad resonances can therefore be assigned to B−H−B

bridging hydrogen atoms and the low-frequency doublet to a

Rh−H hydride ligand.

It should be noted that, in the ¹H{¹¹B} spectra of the

pyridine and 3- and 4-picoline ligated species, there are two

new low-intensity peaks: one at around δ_H−1.7 ppm and the

other at around −11.0 ppm (green squares in Figures 7 and 8

and Figures S5 and S6 (Supporting Information)). These

signals may be attributed to a B−H−B bridging hydrogen atom

and a hydride ligand of a new isomer that is not observed in the

reaction with the 2-picoline ligated derivative 3.

For the three systems formed upon treatment of 2, 4, and 5

with CO, the small-intensity peaks (green squares) disappear as

the temperature increases, whereas the two resonances at

around δ_H−3.0 and −4.5 ppm broaden and coalesce into a

broad peak (Figure 7). This VT NMR behavior clearly

contrasts with that of the 2-picoline derivative described earlier

where, as the temperature increases, the rearrangement process

J

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Figure 9. Energy comparisons for DFT optimized metal to thiaborane conﬁgurational isomers of the pyridine ligated model 2a and of the 2-picoline

ligated counterpart 3a.

CO appears to enhance the stereochemical nonrigidity of the

metal−thiaborane linkage, favoring isomerization processes.

The NMR data show that two of the three isomers detected

in the reactions of CO with 2, 4, and 5 are very similar to the

two species detected in the system with the 2-picoline

counterpart 3 (Figure S3 (Supporting Information) and Figure

7). However, the interconversions between the species appear

to be diﬀerent.

A priori, these ﬁndings may be rationalized in terms of the

diﬀerent steric requirements of the 2-picoline substituent in

comparison to pyridine, 3-picoline, and 4-picoline, resulting in

diﬀerent energy barriers for the transition states of the

structural rearrangement processes together with stabilization

of the products.

DFT Study. In order to attain more insight into the ﬂuxional

and exchange processes involved in the compounds reported

here, we carried out density functional theory (DFT)

calculations on model structures. The PPh₃ligands were

replaced by PH₃to reduce calculation time.

Thus, DFT calculations on [8,8,8-(CO)(H)(PH₃)-9-

(NC₅H₅)-nido-8,7-RhSB₉H₉] (2a) and [8,8,8-(CO)(H)(PH₃)-

9-(2-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (3a) demonstrate that, of

the six possible spatial combinations of the ligands around the

metal center, the most stable is that in which the hydride lies

trans to the sulfur vertex, the CO ligand lies trans to the B(3)−

B(4) edge, and the PH₃group occupies a position trans to the

B(9) vertex (Figure 9). The pyridine and 2-picoline isomers

2a_1−2a_6 and 3a_1−3a_6 follow the same relative energy

trend.

as large as 5.5 kcal/mol (see Figure S14 (Supporting

Information)).

It has been previously demonstrated that substitution

reactions of 2 with monodentate phosphines follow dissociative

mechanisms, the dissociation of the PPh₃ligand trans to the

B(9) vertex being more favored.⁹It is reasonable to expect,

therefore, that the treatment of 2 and 3 with CO under the

conditions described above (short reaction times and low

temperatures) is more likely to result in the substitution of the

PPh₃trans to the B(9) vertex. Under this assumption, the PH₃

models 2a_2 and 3a_2 would correspond to the kinetic

reaction products, whereas the isomers 2a_1 and 3a_1 would

be the thermodynamic products (Figure 9).

Following this analysis, we can conclude that the major

intermediate (red square signals in Figures 5−8) is more likely

to be the isomer with a metal to thiaborane conﬁguration which

resembles that in 2a_2 and 3a_2 (Figure 9). A pseudorotation

of the {Rh(H)(CO)(PPh₃)} group relative to the η⁴-

{SB₉H₉(L)} moiety can aﬀord diﬀerent metal to thiaborane

conﬁgurations that can account for the intermediates that are

observed by NMR at low temperatures.

A clockwise {Rh(H)(CO)(PH₃)} to η⁴-{SB₉H₉(L)} rotation

in the isomers 2a_1, 2a_2, 3a_1, and 3a_2 results in the

formation of the corresponding isomers, 2a_6, 2a_5, 3a_6, and

3a_5. These intermediates (Rh−H hydride trans to boron

vertices) exhibit higher energies than the parent isomers (Rh−

H hydride trans to S(7)). However, this type of metal−

thiaborane pseudorotation draws the B(9)−B(10) bridging

hydrogen atom closer to the hydride ligand, facilitating its

chemical exchange. Thus, intermediates 3a_5 and 3a_6 can

account for the VT NMR behavior observed in the 2-picoline

system (Figure 5 and Figure S3 (Supporting Information)).

Regarding the second major intermediate (purple squares in

Figures 5−8), this species does not feature a Rh−H hydride

ligand and therefore the DFT-calculated isomers depicted in

It is interesting to note that, for the 2-picoline ligated

isomers, the conformers in which the methyl group is adjacent

to the pentagonal open face of the cluster are more stable than

those in which this substituent is oriented toward the B(1)

vertex. In some of the 2-picoline ligated isomers, a conforma-

tional change around the N−B(9) bond has an energy penalty

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Figure 10. DFT-calculated rotational isomers for the PH₃ligated models 2a and 3a with two hydrogen atoms on the pentagonal open face along the

B(10)−B(11) and B(9)−Rh(8) edges.

Scheme 6. Proposed Tautomerization Processes in CO-Ligated Rhodathiaboranes Preceding H₂Loss

Figure 9 do not provide reasonable models that could account

for the structure of this second derivative. Consequently, in the

search for other plausible intermediates, we carried out DFT

calculations using as starting points isomers with bridging

hydrogen atoms along the Rh(8)−B(9) and B(10)−B(11)

edges of the pentagonal face. The optimizations gave the

isomers 2a_7, 2a_8, 3a_7, and 3a_8, of lower energy than the

hydride ligated clusters (Figures 9 and 10). In these calculated

PH₃models, one hydrogen atom occupies a position along the

Rh(8)−B(9) edge in a clearly asymmetric fashion almost 2.0 Å

from the metal center, whereas the other hydrogen atom

bridges the B(10)−B(11) edge (Figure 10). In this new

conﬁguration, these two hydrogen atoms are 2.06 Å apart, this

allowing a facile chemical exchange between the two nuclear

positions on the pentagonal open face. This ﬂuxional process

would lead to a single proton resonance in the negative region

1

of the H{¹¹B} NMR spectra. Following this discussion, it is

reasonable to propose that the second major isomer is a cluster

that exhibits a nuclear conﬁguration similar to that of the

models 2a_7, 2a_8, 3a_7, and 3a_8 and that the two hydrogen

atoms on the pentagonal face undergo fast exchange at both

low and high temperatures, rendering both protons indis-

tinguishable on the NMR time scale (purple squares in Figures

5−8). Related to this process is, for example, the low-energy

barrier tautomerism of the endo/bridging H atoms in

[B₁₁H₁₄]⁻.²¹

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In view of these DFT results, it may be proposed that the

hydride ligated isomers found in the pyridine and 3- and 4-

picoline systems, model 2a_2, interconvert with the second

major isomers, model 2a_7, at higher temperatures (Scheme

6). Under the same conditions, the 2-picoline ligated analogues

do not undergo signiﬁcant interconversion. However, as

indicated above, the hydride ligated species, represented by

3a_2, undergo intramolecular exchange between the Rh−H

hydride ligand and the B−H−B bridging hydrogen atom, most

probably through metal−thiaborane pseudorotations that bring

the two hydrogen atoms closer, as suggested in the isomer

3a_5.

The diﬀerent behavior in the interconversion of the CO

ligated pyridine and 3- and 4-picoline isomers versus the CO

ligated 2-picoline counterparts suggests that the rearrangement

processes involved in the proposed 2a_2 ↔ 2a_5 ↔ 2a_7

tautomerizations (Scheme 6) have lower energy barriers for the

pyridine and 3- and 4-picoline ligated clusters than for the 2-

picoline analogues. However, the exchange of the hydride

ligand and the B−H−B bridging hydrogen atom, which should

involve cluster rearrangements of the type 2a_2 ↔ 2a_5 and

3a_2 ↔ 3a_5, is favored in the 2-picoline ligated isomers,

probably because the energy barrier between the hydride

species 3a_5 and the other isomer 3a_7 is higher than that in

the pyridine and 3- and 4-picoline derivatives (Scheme 6).

It should be noted that a related mechanism of hydrogen M−

H/B−H−M exchange, involving key M−(η²-H₂) intermediates,

has been reported for exo-nido-osmacarboranes that exhibit

{Os(H)₂(PPh₃)₂} fragments exopolyhedrically linked to 11-

vertex nido-carborane ligands, [7-R-7,9-C₂B₉H₉]²⁻, via two B−

H−Os bonds.²²

The reactions of picoline ligated hydridorhodathiaboranes

3−5 with C₂H₄and CO in this report resemble those found for

the pyridine analogue 2, giving products of ligand substitution

and cluster dehydrogenation 12−19. These reactions nicely

illustrate the structural ﬂexibility and chemical tunability of

these 11-vertex clusters and demonstrate that the parent

rhodathiaborane [8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀] (1), ﬁrst

reported in 1990,⁴is actually a rich source of organometallic

chemistry.

The study of the reactions between the hydridorhodathia-

boranes and CO at low temperatures has allowed the

identiﬁcation of intermediates that have provided new insights

into the loss of hydrogen from the clusters. Upon the

substitution of one of the PPh₃ligands by CO, the clusters

become more reactive, undergoing, at low temperature,

intramolecular as well as intermolecular exchange processes

that are a consequence of the increased cluster nonrigidity. The

dynamic behavior observed for the 2-picoline system is diﬀerent

to that of the pyridine and 3- and 4-picoline systems, with DFT

calculations supporting the proposition that the diﬀerence in

cluster ﬂuxionality may be attributed to the steric eﬀect of the

methyl group of the 2-methyl-pyridine substituent. The

intramolecular exchange between the hydride ligand and the

B−H−B bridging hydrogen atom found at low temperatures

for the 2-picoline system is also relevant here because it should

involve a transition state in which the two hydrogen atoms

reach a close proximity in the cluster, representing therefore a

crucial step toward hydrogen loss. Although the detailed

mechanism is unclear, the formation of Rh−(η²-H₂)

intermediates could facilitate the exchange of the hydrogen

atoms at low temperatures. In this regard, we have recently

reported that dihydrogen activation on a carbene ligated

rhodathiaborane takes place through structural transformations

of the cluster, involving the formation of dihydrogen ligated

intermediates.⁷For the carbonyl intermediates, the ﬁnal release

could occur similarly via H₂coordination to the rhodium

center.

It is worth mentioning that the {Rh(H)(CO)(L)} to η⁴-

{SB₉H₉(L)} pseudorotations described earlier are related to the

well-known rotational twisting of exopolyhedral metal-contain-

ing fragments bound through (BH)_n−M interactions to nido-

carboranes.²³In addition, the ﬂexibility of heteroboranes as

face-bound ligands is well documented in, for example,

metallacarboranes and metallathiaboranes.²⁴In the case of 11-

vertex rhodathiaboranes, the parent cluster 1 undergoes an

interesting ﬂuxional process that involves a hindered rotation

with respect to the {SB₉H₁₀} fragment.⁴Recently, we have

proved that the introduction of carbenes as exopolyhedral

ligands or protonation of the clusters results in an enhancement

of the nonrigidity in the metal-to-thiaborane linkage, opening

new ways of ﬂuxional and exchange processes.^7,8,11The CO

ligand appears to induce an analogous lability in the metal−

thiaborane connection.

EXPERIMENTAL SECTION

■

General Considerations. All reactions were carried out under an

argon atmosphere using standard Schlenk-line techniques. Solvents

were obtained from an Innovative Technology Solvent Puriﬁcation

System. All commercial reagents were used as received without further

puriﬁcation. The rhodathiaborane [8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀]

(1) was prepared by published methods.⁴

¹H and ¹¹B NMR data, focused on cluster B−H units, are gathered

1

in Tables 3−5. Additional H NMR data are given below.

NMR spectra were recorded on Bruker Avance 300 MHz, AV 400

MHz, and AV 500 MHz spectrometers, using ¹¹B, ¹¹B{¹H}, ¹H,

¹H{¹¹B}, ¹H{¹¹B(selective)},²⁵³¹P{¹H}, [¹H−¹H]-NOESY, and

[¹H−³¹P]-HMBC techniques.²⁶¹H chemical shifts were measured

relative to partially deuterated solvent peaks but are reported in ppm

relative to tetramethylsilane. ¹¹B chemical shifts were measured relative

to BF₃·OEt₂. ³¹P chemical shifts were measured relative to H₃PO₄

(85%). Mass spectrometry data were recorded on a VG Autospec

double-focusing mass spectrometer, on a Microﬂex MALDI-TOF

instrument, and on a ESQUIRE 3000+ API-TRAP instrument,

operating in either positive or negative mode. In each case there

was an excellent correspondence between the calculated and measured

isotopomer envelopes. A well-matched isotope pattern may be taken

as a good criterion of identity.²⁷

CONCLUSIONS

■

It has been shown that the previously reported reaction

between the rhodathiaborane [8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀]

(1) and pyridine to give the hydridorhodathiaborane [8,8,8-

(H)(PPh₃)₂-9-(NC₅H₅)-nido-8,7-RhSB₉H₉] (2) can extended

to the 2-, 3-, and 4-methylpyridine isomers, aﬀording in good

yields the corresponding picoline ligated hydridorhodathiabor-

anes 3−5. These results illustrate the scope of this reaction that,

in principle, can be carried out with a vast number of N-

heterocyclic ligands.

The 3- and 4-picoline ligated hydrides (4 and 5) exhibit a

thermal stability toward dehydrogenation and nido−closo

structural transformation that is similar to that of the pyridine

counterpart 2. However, the 2-picoline analogue loses hydro-

gen signiﬁcantly faster.

GC analyses were performed on either a Hewlett-Packard HP 5890

Series II gas chromatograph equipped with a ﬂame ionization detector

and a 25 m (0.32 mm inner diameter, 0.17 mm ﬁlm thickness) HP-

Ultra-1 column or on an Agilent 6890 Series GC system equipped

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with an Agilent 5973 mass-selective detector and a 30 m (0.25 mm i.d.,

0.25 mm f.t.) HP-5MS column.

[M − (PPh₃) − 2H]⁺. Isotope envelopes match those calculated from

the known isotopic abundances of the constituent elements.

[8,8,8-H(PPh₃)₂-9-(4-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (5). In a

Schlenk tube, a solution of 1 (300 mg, 0.393 mmol) in 15 mL of

CH₂Cl₂was treated with 381 μL (363 mg; 3.90 mmol) of 4-

methylpyridine. The reaction mixture was stirred at room temperature

under an atmosphere of argon for 4 h, the solvent was evaporated to

dryness, and the residue was washed three times with hexane to isolate

5. Yield: 255 mg, 0.296 mmol, 75%. Anal. Calcd for C₄₂H₄₇B₉NP₂RhS·

CH₂Cl₂: C, 54.65; H, 5.23; N, 1.48; S, 3.39. Found: C, 54.18; H, 5.48;

N, 1.46; S, 3.41. IR (ATR, cm⁻¹): ν 2520 vs (BH), 2465 vs (BH),

2033 m (RhH). ¹H NMR (300 MHz, CD₂Cl₂, 300 K): δ 7.70 (d, 2H;

4-CH₃-NC₅H₄), 7.36 (t, 2H; 4-CH₃-NC₅H₄), 7.26−6.85 (30H,

2PPh₃), 2.27 (m, 3H, 4-CH₃-NC₅H₄). ³¹P{¹H} NMR (121 MHz,

X-ray Structure Analysis of Crystals of 4, 5, and 9. Crystals

were grown by slow diﬀusion of hexane into dichloromethane

solutions. In all cases, the crystals were coated with perﬂuoropolyether,

mounted on a glass ﬁber, and ﬁxed in a cold nitrogen stream (T =

100(2) K) to the goniometer head. Data collections were performed

on a Bruker Kappa APEX DUO CCD area detector diﬀractometer

with monochromatic radiation λ(Mo Kα) = 0.7107073 Å, using

narrow frames (0.3° in ω). The data were reduced (SAINT)²⁸and

corrected for absorption eﬀects by multiscan methods (SADABS).²⁹

The structure was solved using the SHELXS-86 program³⁰and reﬁned

against all F²data by full-matrix least-squares techniques (SHELXL-

97).³¹All non-hydrogen atoms were reﬁned with anisotropic

displacement parameters. Hydrogen atoms were included in calculated

positions and reﬁned with a positional and thermal riding model.

Calculations. All DFT calculations were performed using the

Gaussian 09 package.³²Structures were initially optimized using

standard methods with the STO-3G* basis-sets for C, B, P, S, and H

with the LANL2DZ basis set for the rhodium atom. The ﬁnal

optimizations, including frequency analyses to conﬁrm the true

minima, were performed using B3LYP methodology, with the 6-

31G* and LANL2DZ basis sets. The GIAO nuclear shielding

calculations were performed on the ﬁnal optimized geometries, and

computed ¹¹B shielding values were related to chemical shifts by

comparison with the computed value for B₂H₆, which was taken to be

δ(¹¹B) +16.6 ppm relative to the BF₃·OEt₂0.0 ppm standard.

Synthesis of Picoline-Ligated 11-Vertex Hydridorohodathia-

boranes 3−5. [8,8,8-H(PPh₃)₂-9-(2-Me-NC₅H₄)-nido-8,7-RhSB₉H₉]

(3). In a Schlenk tube, 100 mg (0.130 mmol) of 1 was dissolved in

10 mL of CH₂Cl₂, resulting in a bright red solution. A 190 μL portion

(182 mg, 1.95 mmol) of 2-methylpyridine was syringed into the

solution, and the reaction mixture was stirred at room temperature for

4 h to give a 1:1 mixture of 3 and its dehydrogenation product [1,1-

(PPh₃)₂-3-(2-Me-Py)-closo-1,2-RhSB₉H₈]. This mixture was cooled to

liquid nitrogen temperature, and the vessel was evacuated and then

exposed to a hydrogen-ﬁlled balloon. The resulting system was stirred

at room temperature for 4 h. After this time, the solvent was

evaporated to dryness and the residue washed three times with

CH₂Cl₂/hexane, to obtain 3. Yield: 97.0 mg, 0.112 mmol, 87%. Anal.

Calcd for C₄₂H₄₇B₉NP₂RhS: C, 58.65; H, 5.51; N, 1.63; S, 3.73.

Found: C, 58.23; H, 5.41; N, 1.25; S, 3.98. IR (ATR, cm⁻¹): ν 2502 vs

1

CD₂Cl₂, 300 K): δ 33.0 [d, J (Rh, P) = 121 Hz; 2PPh₃]. ³¹P{¹H}

2

NMR (121 MHz, CD₂Cl₂, 203 K) δ 37.0 [br dd, ¹J_RhP= 107 Hz; J_PP

1

not resolved due to the broadness of the peak], 30.0 [dd, J_RhP= 128

Hz; ²J_PP= 18 Hz]. LRMS (MALDI⁺): m/z 596 [M − (PPh₃) − 2H]⁺.

Isotope envelopes match those calculated from the known isotopic

abundances of the constituent elements.

Preparation of Bis-PPh₃-Ligated closo-Rhodathiaboranes 9−

11. As a general procedure, a 10-fold excess of PPh₃was added to a

solution of the corresponding ethylene ligated rhodathiaboranes 13−

15, which were dissolved in 10 mL of CH₂Cl₂. The orange-red

solution was stirred at room temperature for several hours to give a red

solution. The solvent was evaporated to dryness and the residue

washed three times with hexane. The ﬁnal solids were recrystallized

from CH₂Cl₂/hexane to give the bis-PPh₃ligated rhodathiaboranes

[1,1-(PPh₃)₂-3-(L)-closo-1,2-RhSB₉H₈], where L = 2-Me-NC₅H₄(9),

3-Me-NC₅H₄(10), 4-Me-NC₅H₄(11).

[1,1-(PPh₃)₂-3-(2-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (9). The reaction

was carried out with 120 mg (0.458 mmol) of PPh₃and 30 mg (0.048

mmol) of [1,1-(PPh₃)(η²-C₂H₄)-3-(2-Me-NC₅H₄)-closo-1,2-RhSB₉H₈]

(13), with stirring for 6 h. Yield: 35 mg, 0.0408 mmol, 85%. Anal.

Calcd for C₄₂H₄₅B₉NP₂RhS·CH₂Cl₂: C, 54.77; H, 5.02; N, 1.49; S,

3.40. Found: C, 54.42; H, 4.91; N, 1.17; S, 3.44%. IR (ATR, cm⁻¹): ν

2568 vs (BH), 2492 vs (BH), 2456 vs (BH), 1259 m (BH), 1079 s,

1001 s, 797 m, 690 vs ¹H NMR (300 MHz, CD₂Cl₂, 300 K): δ 8.89 (d,

2H, 2-CH₃-NC₅H₄), 8.07 (m, 1H, 2-CH₃-NC₅H₄), 7.72 (m, 2H, 2-

CH₃-NC₅H₄), 7.50−7.00 (30H, 2PPh₃), 3.04 (s, 3H, 2-CH₃-NC₅H₄).

1

³¹P{¹H} NMR (161 Hz, CD₂Cl₂, 183 K): +41.4 (1P, dd, J_P-Rh= 145

1

²J_P-P= 22), +34.3 (1P, dd, J_P-Rh= 152). ³¹P{¹H} NMR (121 MHz,

1

CD₂Cl₂, 300 K): δ +38.7 [d, J_RhP= 149 Hz; 2PPh₃]. LRMS

(BH), 2042 m (RhH). H NMR (300 MHz, CD₂Cl₂, 300 K): δ 8.97

(MALDI⁺/DCTB): m/z 596 [M − (PPh₃)]⁺. Isotope envelopes

match those calculated from the known isotopic abundances of the

constituent elements.

(d, 2H, 2-CH₃-NC₅H₄), 8.02 (m, 1H, 2-CH₃-NC₅H₄), 7.69 (m, 1H, 2-

CH₃-Py), 7.23−7.00 (30H, 2PPh₃), 3.10 (s, 3H, 2-CH₃-Py). ³¹P{¹H}

1

NMR (121 MHz, CD₂Cl₂, 300 K): δ +34.5 [br dd, J_RhP= 97.66 Hz,

[1,1-(PPh₃)₂-3-(3-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (10). The reac-

tion was carried out with 126 mg (0.480 mmol) of PPh₃and 30 mg

(0.048 mmol) of [1,1-(PPh₃)(η²-C₂H₄)-3-(3-Me-NC₅H₄)-closo-1,2-

RhSB₉H₈] (14), with stirring for 12 h. Yield: 33 mg, 0.0385 mmol,

80%. Anal. Calcd for C₄₂H₄₅B₉NP₂RhS·CH₂Cl₂: C, 54.77; H, 5.02; N,

1.49; S, 3.40. Found: C, 54.33; H, 4.94; N, 1.37; S, 3.34. IR (ATR,

cm⁻¹): ν 2569 vs (BH), 2490 vs (BH), 2459 vs (BH), 1258 m (BH),

1081 s, 1003 s, 796 m, 691 vs ¹H NMR (300 MHz, CD₂Cl₂, 300 K): δ

8.92 (d, 2H, 3-CH₃-NC₅H₄), 8.01 (m, 1H, 3-CH₃-NC₅H₄), 7.54 (m,

1H, 3-CH₃-NC₅H₄), 7.26−7.00 (30H, 2PPh₃), 2.48 (s, 3H, 3-CH₃-

1

²J_PPno resolved due to the broadness of the peak], +32.6 [dd, J_RhP

=

129 Hz, ²J_PP= 18.3 Hz]. ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 243 K): δ

+36.6 [br dd, ¹J_RhP= 106 Hz, ²J_PPnot resolved due to the broadness of

1

2

the peak], +32.3 [dd, J_RhP= 125 Hz, J_PP= 19 Hz]. LRMS

(MALDI⁺): m/z 596 [M − (PPh₃) − 2H]⁺. Isotope envelopes match

those calculated from the known isotopic abundances of the

constituent elements.

[8,8,8-H(PPh₃)₂-9-(3-Me-NC₅H₄)-nido-8,7-RhSB₉H₉] (4). To a

bright yellow solution of 100 mg (0.131 mmol) of 1 in 10 mL of

CH₂Cl₂was added 127 μL (121 mg; 1.30 mmol) of 3-methylpyridine.

After 4 h of stirring at room temperature under an atmosphere of

argon, the solvent was evaporated to dryness and the solid residue

washed three times with hexane. The ﬁnal product was characterized

as compound 4. Yield: 91.0 mg, 0.106 mmol, 81%. Anal. Calcd for

C₄₂H₄₇B₉NP₂RhS·2CH₂Cl₂: C, 51.31; H, 4.99; N, 1.36; S, 3.11.

Found: C, 50.82; H, 5.03; N, 1.31; S, 2.35. IR (ATR, cm⁻¹): ν 2529 vs

NC₅H₄). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): δ 40.2 [d, ¹J_RhP

=

147 Hz; 2PPh₃]. LRMS (MALDI⁺/DCTB): m/z 596 [M − (PPh₃)]⁺.

Isotope envelopes match those calculated from the known isotopic

abundances of the constituent elements.

[1,1-(PPh₃)₂-3-(4-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (11). The reac-

tion was carried out with 105 mg (0.40 mmol) of PPh₃and 25 mg

(0.040 mmol) of [1,1-(PPh₃)(η²-C₂H₄)-3-(4-Me-NC₅H₄)-closo-1,2-

RhSB₉H₈] (15), with stirring for 16 h. Yield: 26 mg, 0.030 mmol, 75%.

Anal. Calcd for C₄₂H₄₅B₉NP₂RhS·2CH₂Cl₂: C, 51.41; H, 4.80; N,

1.36; S, 3.12%. Found: C, 50.91; H, 4.35; N, 0.88; S, 2.64. IR (ATR,

cm⁻¹): ν 2502 vs (BH), 2453 vs (BH), 1264 m (BH), 1085 s, 1004 s,

1

(BH), 2040 m (RhH). H NMR (300 MHz, CD₂Cl₂, 300 K): δ 7.96

(m, 2H; 3-CH₃-NC₅H₄), 7.68 (m, 1H; 3-CH₃-NC₅H₄), 7.33 (t, 1H; 3-

CH₃-NC₅H₄), 7.31−7.04 (30H, 2PPh₃), 2.20 (s, 3H, 3-CH₃-NC₅H₄).

³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): +32.7 [d, ¹J_RhP= 120 Hz;

2PPh₃]. ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 243 K) δ +35.7 [br dd,

1

693 vs. H NMR (300 MHz, CD₂Cl₂, 300 K): δ 8.75 (d, 2H, 4-CH₃-

2

¹J_RhP= 103 Hz; J_PPnot resolved due to the broadness of the peak],

NC₅H₄), 7.51 (m, 2H, 4-CH₃-NC₅H₄), 7.25−7.03 (30H, 2PPh₃), 2.73

+30.7 [dd, ¹J_RhP= 128 Hz; ²J_PP= 19 Hz]. LRMS (MALDI⁺): m/z 596

(s, 3H, 4-CH₃-NC₅H₄). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): δ

N

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1

39.6 [d, J_RhP= 153 Hz; 2PPh₃]. LRMS (MALDI⁺/DCTB): m/z 595

cm⁻¹): ν 2567 vs (BH), 2520 vs (BH), 2493 vs (BH), 2466 vs (BH),

1982 vs (CO), 1632 m, 1479 m, 1434 m, 1262 m, 1161 m, 1092 m,

1006 m, 935 m, 935 m, 877 m, 829 m, 800 m, 746 m, 692 vs, 577 w,

[M − (PPh₃) − H]⁺. Isotope envelopes match those calculated from

the known isotopic abundances of the constituent elements.

1

Synthesis of Ethylene-Ligated closo-Rhodathioboranes 13−

15. As a general procedure, 100 mg of the corresponding

hydridorhodathiaborane [8,8,8-(PPh₃)₂H-9-(L)-nido-8,7-RhSB₉H₉],

where L= 2-Me-NC₅H₄(3), 3- Me-NC₅H₄(4), 4-Me-NC₅H₄(5),

was dissolved in 20 mL of CH₂Cl₂in a Schlenk tube. After three

freeze−thaw cycles, a balloon containing ethylene was attached to the

Schlenk tube, and the rhodathiaborane solution was exposed to the

gas. The system was stirred at room temperature. After a variable

length of time, the reaction mixture was concentrated by solvent

evaporation under vacuum, and hexane was added to produce an

orange-red precipitate, which was washed several times with hexane.

The solid was crystallized from CH₂Cl₂/hexane to isolate the

respective ethylene ligated clusters [1,1-(η²-C₂H₄)(PPh₃)-3-(L)-closo-

1,2-RhSB₉H₈].

525 vs. H NMR (300 MHz, CD₂Cl₂, 300 K): δ 9.41 (d, 1H, 2-CH₃-

NC₅H₄), 8.04 (d, 1H, 2-CH₃-NC₅H₄), 7.62 (t, 2H, 2-CH₃-NC₅H₄),

7.50−7.05 (15H, PPh₃), 3.02 (m, 3H, 2-CH₃-NC₅H₄). ³¹P{¹H} NMR

(121 MHz, CD₂Cl₂, 300 K): δ 37.7 (d, ¹J_RhP= 133 Hz; PPh₃). LRMS

(MALDI⁺/DCTB): m/z 596 [M − (CO)]⁺. Isotope envelopes match

those calculated from the known isotopic abundances of the

constituent elements.

[1,1-(PPh₃)(CO)-3-(3-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (18). The re-

action was carried out with 150 mg (0.174 mmol) of 4, and stirring

under an atmosphere of CO was maintained for 2 h. Yield: 97.0 mg,

0.156 mmol, 90%. Anal. Calcd for C₂₅H₃₀B₉NOPRhS·CH₂Cl₂: C,

44.06; H, 4.55; N, 1.98; S, 4.52. Found: C, 44.41; H, 4.42; N, 1.76; S,

4.32. IR (ATR, cm⁻¹): ν 2563 vs (BH), 2519 vs (BH), 2494 vs (BH),

2464 vs (BH), 1974 vs (CO), 1619 m, 1478 m, 1433 m, 1180 m, 1093

m, 1005 m, 939 m, 742 m, 684 vs, 524 v. ¹H NMR (300 MHz,

CD₂Cl₂, 300 K): δ 8.90 (d, 2H, 3-CH₃-NC₅H₄), 8.01 (d, 1H, 3-CH₃-

NC₅H₄), 7.58 (t, 1H, 3-CH₃-NC₅H₄), 7.34−7.28 (15H, PPh₃), 2.40

(m, 3H, 3-CH₃-NC₅H₄). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K):

δ 37.9 (d, ¹J _RhP= 136 Hz; PPh₃). LRMS (MALDI⁺/DCTB): m/z 596

[M − (CO)]⁺. Isotope envelopes match those calculated from the

known isotopic abundances of the constituent elements.

[1,1-(PPh₃)(η²-C₂H₄)-3-(2-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (13). The

reaction was carried out with 100 mg (0.116 mmol) of 3, and the

solution was exposed to an ethylene atmosphere for 2 h. Yield: 62 mg,

0.099 mmol, 86%. Anal. Calcd for C₂₆H₃₄B₉NPRhS: C, 50.06; H, 5.49;

N, 2.5; S, 5.14. Found: C, 50.26; H, 5.63; N, 2.32; S, 5.01. IR (ATR,

cm⁻¹): ν 2528 vs (BH), 2507 vs (BH), 2497 vs (BH), 2472 vs (BH),

2452 vs (BH), 1618 w, 1476 s, 1451 w, 1430 s, 1260 m, 1151 m, 1087

s, 1010 m, 946 m, 748 m, 692 s, 526 s, 492 m, 456 m (Rh-C₂H₄), 418

m (Rh-C₂H₄), 325 w (RhP). ¹H NMR (300 MHz, CD₂Cl₂, 300 K): δ

9.45 (m, 2H, 2-CH₃-NC₅H₅), 8.07 (m, 2H, 2-Me-NC₅H₅), 7.70−7.01

(15H, PPh₃), 3.05 (s, 3H, 2-CH₃-NC₅H₅), 2.16 (m, 2H, C₂H₄), 1.99

(m, 2H, C₂H₄). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): δ 34.19

[1,1-(PPh₃)(CO)-3-(4-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (19). The re-

action was carried out with 30 mg (0.035 mmol) of 5, and stirring

under an atmosphere of CO was maintained for 8 h. Yield: 20.0 mg,

0.032 mmol, 91%. Anal. Calcd for C₂₅H₃₀B₉NOPRhS·CH₂Cl₂: C,

44.06; H, 4.55; N, 1.98; S, 4.52. Found: C, 44.51; H, 4.43; N, 1.73; S,

4.02. IR (ATR, cm⁻¹): ν 2567 vs (BH), 2523 vs (BH), 2501 vs (BH),

2465 vs (BH), 1993 vs (CO), 1978 vs (CO), 1632 m, 1479 m, 1452 w,

[d, J_RhP= 134 Hz, PPh₃]. LRMS (MALDI⁺/DCTB): m/z 595 [M −

1

(C₂H₄) − H]⁺. Isotope envelopes match those calculated from the

known isotopic abundances of the constituent elements.

1

1434 m, 1163 m, 1092 s, 1006 m, 935 m, 746 s, 692 vs, 525 vs H

[1,1-(PPh₃)(η²-C₂H₄)-3-(3-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (14). The

reaction was carried out with 100 mg (0.116 mmol) of 4, and the

solution was exposed to an ethylene atmosphere for 4 h. Yield: 60 mg,

0.096 mmol, 83%. Anal. Calcd for C₂₆H₃₄B₉NPRhS: C, 50.06; H, 5.49;

N, 2.5; S, 5.14. Found: C, 50.46; H, 5.66; N, 2.30; S, 5.08.IR (ATR,

cm⁻¹): ν 2529 vs (BH), 2505 vs (BH), 2499 vs (BH), 2476 vs (BH),

2453 vs (BH), 1616 w, 1479 s, 1450 w, 1432 s, 1261 m, 1152 m, 1089

s, 1010 m, 947 m, 747 m, 692 s, 525 s, 491 m, 455 m (Rh-C₂H₄), 417

m (Rh-C₂H₄), 326 w (RhP). ¹H NMR (300 MHz, CD₂Cl₂, 300 K): δ

9.14 (m, 2H, 3-CH₃-NC₅H₄), 8.44 (m, 1H, 3-CH₃-NC₅H₄), 8.10 (m,

1H, 3-CH₃-NC₅H₄), 7.70−7.03 (15H, PPh₃), 2.52 (s, 3H, 3-CH₃-

NC₅H₄), 2.28 (m, 2H,C₂H₄), 2.05 (m, 2H, C₂H₄). ³¹P{¹H} NMR

(121 MHz, CD₂Cl₂, 300 K): δ 40.3 [d, ¹J_RhP= 137 Hz, PPh₃]. LRMS

(MALDI⁺/DCTB): m/z 595 [M − (C₂H₄) − H]⁺. Isotope envelopes

match those calculated from the known isotopic abundances of the

constituent elements.

NMR (300 MHz, CD₂Cl₂, 300 K): δ 8.97 (m, 2H, 4-CH₃-NC₅H₄),

7.46 (m, 2H, 4-CH₃-NC₅H₄), 7.36−7.27 (15H, PPh₃), 2.65 (s, 3H, 4-

CH₃-NC₅H₄). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): δ 37.9 (d,

¹J

= 132 Hz; PPh₃). LRMS (MALDI⁺/DCTB): m/z 596 [M −

RhP

(CO)]⁺. Isotope envelopes match those calculated from the known

isotopic abundances of the constituent elements.

Reactions with Carbon Monoxide: Characterization of

Intermediates. Carbon monoxide was bubbled for several minutes

(3−9 min) through a CD₂Cl₂solution of the corresponding nido-

hydridorhodathiaborane 2−5 in a 5 mm NMR tube at room

temperature. The sample was subsequently cooled to −50 °C in an

isopropyl alcohol bath and transferred to an NMR spectrometer in

which the temperature of the probe was set to −50 °C. The system

was studied at diﬀerent temperatures, allowing the identiﬁcation of the

diﬀerent intermediates that form before hydrogen loss occurs to yield

the CO ligated closo clusters 16−19 described above. The following

are the NMR data for the reaction mixtures that contain the labile new

species. Spectra can be seen in the main text as well the Supporting

Information of this paper.

[1,1-(PPh₃)(η²-C₂H₄)-3-(4-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (15). The

reaction was carried out with 100 mg (0.116 mmol) of 5, and the

solution was exposed to an ethylene atmosphere for 12 h. Yield: 54

mg, 0.087 mmol, 75%. Anal. Calcd for C₂₆H₃₄B₉NPRhS·CH₂Cl₂: C,

45.76; H, 5.12; N, 1.98; S, 4.52. Found: C, 45.91; H, 4.98; N, 1.69; S,

4.07. IR (ATR, cm⁻¹): ν 2549 vs (BH), 2517 vs (BH), 2482 vs (BH),

2470 vs (BH), 1630 s, 1478 m, 1451 w, 1433 s, 1256 w, 1161 m, 1090

s, 1005 s, 936 m, 743 s, 693 vs, 525 vs, 491 s, 457 m (Rh-C₂H₄), 424 m

1

Reaction of 2 with CO. Nine minutes of CO bubbling. H{¹¹B}

NMR (500 MHz, CD₂Cl₂, 223 K): δ +9.27 to +7.06 (aromatics,

NC₅H₅, PPh₃), +3.92 (s, BH), +3.41 (s, BH), +1.86 (s, BH), +0.28 (s,

BH), −1.66 (low intensity br s, BH), −2.93 (s, BHB), −4.56 (s, BHB),

1

−10.96 (low intensity apparent t, J_RhH= 20.4 Hz, RhH), −11.25 (d,

¹J_RhH= 22.1 Hz, 1H). There are also resonances corresponding to 2,

which is in solution as a minor species. ³¹P{¹H} NMR (202 MHz,

CD₂Cl₂, 203 K): δ +38.9 (d, ¹J_RhP= 131 Hz, compound 16), +36.6 (d,

1

(Rh-C₂H₄), 339 w (RhP). H NMR (300 MHz, CD₂Cl₂, 300 K): δ

9.14 (m, 2H, 4-CH₃-NC₅H₄), 7.53 (m, 2H, 4-CH₃-NC₅H₄), 7.70−7.01

(15H, PPh₃), 2.71 (s, 3H, 4-CH₃-NC₅H₄), 2.26 (m, 2H, C₂H₄), 2.06

(m, 2H, C₂H₄). ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): δ 40.3 [d,

¹J_RhP= 137 Hz, PPh₃]. LRMS (MALDI⁺/DCTB): m/z 596 [M −

(C₂H₄)]⁺. Isotope envelopes match those calculated from the known

isotopic abundances of the constituent elements.

CO-Ligated closo-Rhodathiaboranes 17−19. The procedure

was the same as that for ethylene, but using a CO-ﬁlled balloon.

[1,1-(PPh₃)(CO)-3-(2-Me-NC₅H₄)-closo-1,2-RhSB₉H₈] (17). The re-

action was carried out with 60 mg (0.070 mmol) of 3 with stirring

under an atmosphere of CO for 2 h. Yield: 37.6 mg, 0.0604 mmol,

87%. Anal. Calcd for C₂₅H₃₀B₉NOPRhS·CH₂Cl₂: C, 44.06; H, 4.55; N,

1.98; S, 4.52. Found: C, 44.09; H, 4.53; N, 1.83; S, 4.27. IR (ATR,

1

¹J_RhP= 125.2 Hz), +35.2 (d, J_RhP= 99.4 Hz), +29.5 (d, J_RhP= 121.9

Hz), +28.6 (OPPh₃), −7.9 (PPh₃); the resonances exhibit a

1:2.94:11.30:1.60:0.77:14.04 relative intensity ratio, respectively.

[¹H−³¹P]-HMBC (500 MHz, CD₂Cl₂, 203 K) {ordered as (δ_H, δ_P)

correlation}: (−10.96, +29.5), (−11.35, +35.2); as expected, all the ³¹P

resonances exhibit correlations with aromatic signals.

Reaction of 3 with CO. Three minutes of CO bubbling. ¹¹B-{¹H}

NMR (160 MHz; CD₂Cl₂, 273 K): δ +12.8 (s, minor species) +8.2 (d,

¹J_BH= 118 Hz, major species), +5.8 (minor species), +3.6 (d, ¹J_BH= 72

Hz, major), −2.1 (minor species), −4.4 (minor species), −9.2 (d, ¹J_BH

= 137 Hz, minor species), −13.5 (major species), −12.5 (minor

O

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species), −13.5 (major species), −18.5 (minor species), −19.6 (d, ¹J_BH

2 and a 20-fold excess of cyclohexane were stirred for 7 days with no

sign of reaction.

[8,8,8-H(PPh₃)₂-9-(NC₅H₅)-nido-8,7-RHSB₉H₉] (2) with 1-Hexene.

In a 5 mm NMR tube, 2 mg (0.0025 mmol) of 2 was dissolved in 0.6

mL of CH₂Cl₂together with a 20-fold excess of 1-hexene. GC after 1

day of reaction showed a mixture of 1-hexene (75%), 2-hexene (17%),

3-hexene (7%), and hexane (1%).

[8,8,8-H(PPh₃)₂-9-(NC₅H₅)-nido-8,7-RHSB₉H₉] (2) with Propylene.

In a 5 mm NMR tube, 16 mg (0.018 mmol) of 2 was dissolved in 0.6

mL of CD₂Cl₂in a NMR tube and propylene was bubbled through the

solution for 5 min. After 4 days of stirring, the composition of the

reaction mixture contained propylene, some propane, closo derivative 8

(65%), and starting material 2 (35%).

[8,8,8-H(PPh₃)₂-9-(2-Me-NC₅H₄)-nido-8,7-RHSB₉H₉] (3) with Cy-

clohexene. In a 5 mm NMR tube, 12.5 mg (0.014 mmol) of 3 in 0.6

mL of CD₂Cl₂and a 20-fold excess of cyclohexene were dissolved.

After 5 days, there was formation of cyclohexane (2%) and the closo-

rhodathiaborane 9.

[8,8,8-H(PPh₃)₂-9-(2-Me-NC₅H₄)-nido-8,7-RHSB₉H₉] (3) with 1-

Hexene. In a Schlenk tube, 12.5 mg (0.014 mmol) of 3 was dissolved

in 0.6 mL of CH₂Cl₂with a 20-fold excess of 1-hexene. The solution

was stirred at room temperature under an atmosphere of argon. The

reaction was monitored by GC, and after 1 day the composition of the

mixture was 34% of 2-hexene, 63% of 1-hexene, and 3% of hexane.

Compound 3 aﬀorded the closo derivative 9.

[8,8,8-H(PPh₃)₂-9-(2-Me-NC₅H₄)-nido-8,7-RHSB₉H₉] (3) with Pro-

pylene. In an NMR tube, 14 mg (0.016 mmol) of 3 was dissolved in

0.6 mL of CD₂Cl₂and propylene gas was bubbled through the solution

for 5 min. In 1 h, the hydridorhodathiaborane underwent trans-

formation to the closo cluster 9, with concomitant formation of

propane.

1

= 127 Hz, major species), −22.3 (d, J_BH= 146 Hz, major species),

−24.6 (major species), −26.0 (d, ¹J_BH= 146 Hz, major species), −28.3

1

(d, J_BH= 145 Hz, minor species), −32.1 (minor species). H{¹¹B}

NMR (400 MHz, CD₂Cl₂, 223 K): δ +9.21 (d, 5.2 Hz, o-2-Me-

NC₅H₄, minor species), +9.15 (d, 5.5 Hz, o-2-Me-NC₅H₄, major

species), +7.98 (pseudo-t, 7.5 Hz, 2-Me-NC₅H₄, major species), +7.92

(pseudo-t, 7.5 Hz, 2-Me-NC₅H₄, minor species), +7.57 to +7.16

(aromatics, 2-Me-NC₅H₄, PPh₃), +4.04 (BH, minor species), +3.37

(BH, major species), +3.03 (BH, major), +2.92 (s, CH₃; minor

species), +2.60 (BH, minor species), +2.35 (BH, major species), +2.26

(s, CH₃; major species), +2.18 (BH, major species), +2.04 (BH, minor

species), +1.87 (BH, major species), +1.32 (2BH, major species),

+0.90 (BH, minor species), +0.15 (BH, major species), −2.88 (s,

1

BHB), −4.63 (s, BHB), −11.33 (d, J_RhH= 22.3 Hz, RhH). H{¹¹B}

NMR (400 MHz, CD₂Cl₂, 273 K): selected resonances, −2.81 (s,

1

BHB), −4.59 (s, BHB), −11.42 (d, J_RhH= 17.8 Hz, RhH), relative

intensity ratio 1:1:0.27. ³¹P{¹H} NMR (162 MHz, CD₂Cl₂, 223 K): δ

+35.5 (d, ¹J_RhP= 127 Hz), +35.0 (br. d, ¹J_RhP= 91 Hz; this broad signal

overlaps partially with the previous resonance), +28.4 (OPPh₃),

−7.4 (PPh₃): the resonances exhibit a 2.0:0.7:0.4:2.3 relative intensity

ratio, respectively. [¹H−³¹P]-HMBC (500 MHz, CD₂Cl₂, 203 K)

{ordered as (δ_H, δ_P) correlation}: [−11.28, +35.7 (br peak)].

[¹H−¹H]-NOESY (500 MHz, CD₂Cl₂, 273 K): (−2.75, −11.31);

this oﬀ-diagonal peak is of the same phase as the diagonal peaks,

demonstrating that the correlation is due to chemical exchange

between the Rh−H hydride ligand and the B−H−B bridging hydrogen

atom of one of the intermediates.

Reaction of 4 with CO. ¹H{¹¹B} NMR (400 MHz, CD₂Cl₂, 223 K):

δ +8.97 (m, 3-Me-NC₅H₄, minor), +8.88 (m, 3-Me-NC₅H₄, major),

+8.75 (s, 3-Me-NC₅H₄, major), +8.65 (s, 3-Me-NC₅H₄, major), +7.65

to +6.71 (aromatics, 4-Me-NC₅H₄and PPh₃), +3.95 (s, BH, major),

+3.50 (s, BH, major), +2.99 (s, BH, minor), +2.11 (s, CH₃), +1.99 (s,

BH, major), +1.39 (s, BH, major), +1.29 (s, BH), +1.05 (s, BH), +0.89

(s, BH), +0.24 (s, BH), −1.60 (BH, minor species), −2.99 (s, BHB),

−4.55 (s, BHB), −10.88 (low intensity apparent t, J = 10.88 Hz,

ASSOCIATED CONTENT

* Supporting Information

■

S

Figures, tables, and CIF ﬁles giving 1D and 2D NMR spectra,

DFT-calculated coordinates and energies, and crystallographic

data for 4, 5, and 9. This material is available free of charge via

the Internet at http://pubs.acs.org.

1

RhH), −11.86 (d, J_RhH= 22.6 Hz, RhH).

Reaction of 5 with CO. ¹¹B{¹H} NMR (160 MHz; CD₂Cl₂, 273

K): δ +55.2 (compound 19), +27.9 (compound 19), +15.9, +8.17,

+7.0, +5.0 (¹J_BH= 119 Hz), +1.2, −3.1, −9.8 (¹J_BH= 145 Hz), −13.5,

−19.3, −20.3, −22.8 (compound 19), −25.2 (¹J_BH= 132 Hz), −28.2

AUTHOR INFORMATION

Corresponding Author

*E-mail for R.M.: rmacias@unizar.es.

■

1

(¹J_BH= 145 Hz), −32.5 (compound 19). H{¹¹B} NMR (500 MHz,

CD₂Cl₂, 223 K): δ +8.84 (br. m, 4-Me-NC₅H₄), +8.67 (d, J = 6.0 Hz,

4-Me-NC₅H₄), +7.65 to +6.71 (aromatics, 4-Me-NC₅H₄and PPh₃),

+3.90 (s,BH), +3.39 (s, BH), +2.57 (s, BH), +2.11 (s, CH₃), +1.96 (s,

BH), +1.37 (s, BH), +1.29 (s, BH), +1.05 (s, BH), +0.89 (s, BH),

+0.24 (s, BH), −1.64 (BH, minor species), −2.99 (s, BHB), −4.55 (s,

BHB), −10.95 (low intensity apparent t, J = 19.9 Hz, RhH), −11.26

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

1

(d, J_RhH= 22.6 Hz, RhH). H{¹¹B} NMR (500 MHz, CD₂Cl₂, 300

K): δ +9.18 to +6.38 (aromatics, 4-Me-NC₅H₄and PPh₃), +3.82

(BH), +3.40 (BH), +3.04 (BH), +2.65 (BH), +2.51 (s, CH₃; major

component), +2.30 (BH), +2.24 (BH), +2.11 (s, CH₃; minor

component), +1.45 (BH), +1.28 (BH), +1.02 (BH), +0.21 (BH),

−2.92 (v broad, BHB), −4.51 (v. broad, BHB), −10.96 (apparent

We acknowledge the Spanish Ministry of Science and

Innovation (CTQ2009-10132, CONSOLIDER INGENIO,

CSD2009-00050, MULTICAT and CSD2006-0015, Crystal-

lization Factory) for support of this work. B.C. thanks the

́ ́

“Diputacion General de Aragon” for a predoctoral scholarship.

We also thank Dr. J. Bould for useful discussions.

1

triplet, J_RhH= 22.9 Hz, minor species), −11.35 (d, J_RhH= 21.3 Hz,

RhH); there are also resonances corresponding to 19, which is in

solution as a minor species. ³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 223

K): δ +38.6 (d, ¹J_RhP= 131 Hz, compound 19), +36.6 (d, ¹J_RhP= 125

Hz), +34.5 (d, ¹J_RhP= 103 Hz), +29.8 (d, ¹J_RhP= 122 Hz), +28.4 (O

REFERENCES

■

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PPh₃), −7.4 (free PPh₃): the resonances exhibit

a

1.00:1.90:9.86:0.76:0.28:11.50 relative intensity ratio, respectively.

1

³¹P{¹H} NMR (121 MHz, CD₂Cl₂, 300 K): δ +37.8 (d, J_RhP= 126

Hz, compound 19) +35.8 (very broad, PPh₃), +32.8 (very broad,

PPh₃), +27.2 (OPPh₃), −5.3 (free PPh₃): the resonances exhibit a

1.00:0.24:0.33:0.04:1.02 relative intensity ratio, respectively. [¹H−³¹P]-

HMBC (500 MHz, CD₂Cl₂, 223 K) {ordered as (δ_H, δ_P) correlation}:

(−10.95, +29.8), (−11.35, +34.5), (+2.65, +34.5); as expected, all the

³¹P resonances correlate with aromatic signals.

Reactions with Alkenes. [8,8,8-H(PPh₃)₂-9-(NC₅H₅)-nido-8,7-

RHSB₉H₉] (2) with Cyclohexene. Two milligrams (0.0025 mmol) of

P

dx.doi.org/10.1021/om500374g | Organometallics XXXX, XXX, XXX−XXX

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Hydridorhodathiaboranes: Synthesis, characterization, and reactivity

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