Strongly Polarized Iridiumδ--Aluminumδ+Pairs: Unconventional Reactivity Patterns including CO2Cooperative Reductive Cleavage

Reactivity Patterns Including CO Cooperative Reductive Cleavage

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δ−

δ+

Strongly Polarized Iridium −Aluminum Pairs: Unconventional

L é on Escomel, Iker Del Rosal, Laurent Maron, Erwann Jeanneau, Laurent Veyre, Chlo é Thieuleux,

and Cl é ment Camp*

Cite This: J. Am. Chem. Soc. 2021, 143, 4844 −4856

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sı Supporting Information

ABSTRACT: The iridium tetrahydride complex Cp*IrH reacts with

a range of isobutylaluminum derivatives of general formula

Al(iBu) (OAr) (x = 1, 2) to give the unusual iridium aluminum

3−x

species [Cp*IrH Al( Bu)(OAr)] (1) via a reductive elimination route.

The Lewis acidity of the Al atom in complex 1 is conﬁrmed by the

coordination of pyridine, leading to the adduct [Cp*IrH Al( Bu)-

OAr)(Py)] (2). Spectroscopic, crystallographic, and computational

(

data support the description of these heterobimetallic complexes 1

δ+

δ−

and 2 as featuring strongly polarized Al(III) −Ir(III) interactions.

Reactivity studies demonstrate that the binding of a Lewis base to Al

does not quench the reactivity of the Ir−Al motif and that both species 1 and 2 promote the cooperative reductive cleavage of a

range of heteroallenes. Speciﬁcally, complex 2 promotes the decarbonylation of CO and AdNCO, leading to CO (trapped as

Cp*IrH (CO)) and the alkylaluminum oxo ([(iBu)(OAr)Al(Py)] (μ-O) (3)) and ureate ({Al(OAr)( Bu)[κ -(N,O)AdNC(O)-

NHAd]} (4)) species, respectively. The bridged amidinate species Cp*IrH (μ-CyNC(H)NCy)Al( Bu)(OAr) (5) is formed in the

reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond

activation processes.

INTRODUCTION

methylaluminoxanes (MAOs) as cocatalysts with metallocene

■

complexes, which has revolutionized polyoleﬁn synthesis. In

contrast, in this contribution, we describe a very rare example

where alkylaluminum species promote umpolung at a d-block

metal, converting iridium half-metallocenes into nucleophiles

Alkylaluminum(III) reagents are classically used in organo-

metallic chemistry as catalysts activatorsdue to the

propensity of these strong Lewis acids to perform halide or

alkyl abstractionsleading to unsaturated, highly electrophilic

transition-metal (TM) cations paired with weakly coordinating

aluminate counteranions (Scheme 1, top). One of the most

seminal applications of this chemistry is the widespread use of

δ−

δ+

through the formation of polarized Ir −Al pairs (Scheme 1,

bottom).

The study of TM complexes bearing aluminum-based

metallo-ligands is still in its infancy. This is mostly due to

the synthetic challenges associated with the preparation of such

heterobimetallic species in a controlled way, which requires the

introduction of an Al center, the derivatives of most of which

are Lewis acidic, in the coordination sphere of a TM, classically

acting as a Lewis acids as well. Yet, such derivatives hold great

promises in terms of reactivity. In the case of late transition

metals, which feature higher electronegativities in comparison

to Al (1.61 on the Pauling scale), the binding of hard Al-based

ligands, acting as σ-acceptors, can reverse the classical ligand→

TM bonding situation and confer unique electronic properties

Scheme 1. Contrasting Reactivity of Alkylaluminum

Reagents with d-Block Metal Species

Received: February 12, 2021

Published: March 18, 2021

2021 American Chemical Society

J. Am. Chem. Soc. 2021, 143, 4844−4856

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to the resulting complexes, which opens up attractive

opportunities for cooperative reactivity. Although a range of

Scheme 3. Representative Reductive Alkane Elimination

Reactivity of Pentamethylcyclopentadienyl Iridium

Polyhydrides with Nucleophilic Metal−Alkyl Derivatives

−13

Z-type metal−alane L M−AlX Lewis adducts are known,

13,31

complexes featuring X-type metal−aluminum L M−AlX (L′ )

Reported in the Literature

(

m = 0, 1) covalent bonds are much more rare (Scheme 2) and

14−22

their reactivity remains almost unexplored.

Scheme 2. Representative Examples of Formally X Type

Aluminum Ligands Bound to Late Transition Metals and

Related Species of Relevance to the Current Study

reductive elimination approach (Scheme 3, bottom) and

demonstrated the ability of the resulting TaIr multiple-bond

motif to promote H/D isotope exchange reactions with

31−33

excellent catalytic performances.

Inspired by this exploratory work from Bergman and co-

workers, and in a continuation of our previous work, we

hypothesized that this alkane elimination chemistry could be

extended to the preparation of well-deﬁned iridium systems

bearing aluminum-based ligands. Such an approach could open

up unusual mechanistic pathways and help in an understanding

of more complex chemistry, such as the multifaceted role of

alkylaluminum reagents employed as cocatalysts in numerous

transition-metal-catalyzed processes. Accordingly, we inves-

tigated the reactivity of aluminum isobutyl derivatives toward

the iridium tetrahydride complex Cp*IrH₄, which led to the

formation of unusual bimetallic complexes featuring strongly

A groundbreaking achievement in this area was reported in

019 by Goicoechea, Aldridge, and colleagues, who described

δ+

δ−

polarized Al −Ir cores. These heterobimetallic complexes

were notably able to reductively cleave heteroallenes (CO ,

the transfer of polarity between gold(I) and a “naked” (NON)

δ+

δ−

isocyanates).

Al aluminyl(I) anion, leading to an Al −Au complex.

direct consequence of this umpolung is the unusual

nucleophilic reactivity at the gold center observed in the

RESULTS AND DISCUSSION

Preparation of Bimetallic Ir/Al Species. In view of

■

reductive insertion of CO . Very recently, Power reported the

preparation of an aluminum−copper metal−metal-bonded

preventing the formation of tetrametallic aggregates such as

Mes

Dip 23

species from Al(I), (BDI )CuAl(BDI ), and Arnold

those observed by Bergman (Scheme 3), we considered the

reported rare examples of An−Al dative interactions (An =

use of sterically hindered Al−alkyl sources. For that purpose,

we employed bulky isobutylaluminum aryloxy precursors and

4,25

U, Th),

described.

but the reactivity of these species was not

explored their reactivity toward Cp*IrH

It is important to note that all of the reported late-metal−

aluminum systems, shown in Scheme 2, rely on the use of

electronegative amido α-substituents to stabilize the Al center.

Although alkyl-substituted aluminyl anions and a monomeric

Treatment of diisobutyl(3,5-di-tert-butyl-4-hydroxytoluene)-

aluminum, denoted Al( Bu)

(OAr), with Cp*IrH

results in

Al-

the formation of the heterobimetallic complex [Cp*IrH

( Bu)(OAr)] (1) which is isolated in 72% yield after 24 h of

26−29

alanediyl species have been synthesized very recently,

reaction at room temperature (Scheme 4). One equivalent of

their coordination chemistry to late transition metals has yet to

be demonstrated. One notable exception is the unusual

ethylaluminum complex [Cp*(PMe )Ir(AlEt)] (Scheme 3,

Scheme 4. Synthesis of the Al−Ir Heterobimetallic Species 1

top), reported by Bergman and co-workers in 1998. This

compound was prepared without the requirement of isolating

challenging low-valent Al−alkyl species, via a simple double

deprotonation of a dihydride iridium(III) complex by the

commercially available triethylaluminum reagent. To our

surprise, no followup studies emerged from this preliminary

work to explore further the reactivity of this unconventional

molecular object featuring a low-valent Ir Al₂core. Very

recently, our group reported the preparation of heterobime-

tallic tantalum−iridium complexes using a similar alkane

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Journal of the American Chemical Society

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isobutane (quantiﬁed by H NMR, see Figure S1 ) is released

at room temperature. Upon heating at 110 °C for 1 week,

in the course of the reaction. The H NMR spectrum of 1,

compound 2 is obtained from Al( Bu)(OAr) and is isolated in

recorded in C D solution, shows isobutyl signals at δ 2.15,

18% yield from cold (−40 °C) recrystallization in a saturated

.08, and 0.31 ppm integrating respectively for 1H, 6H, and

H and indicating the presence of one isobutyl group per Al

pentane solution (Scheme 4). H NMR monitoring of this

reaction indicates the release of 2,6-di-tert-butyl-4-methylphe-

nol (see Figure S2 ). We attribute the preferential reductive

elimination of HOAr versus isobutane to the particularly high

steric hindrance of this phenoxy derivative. Note that complex

1 does not react with HOAr, even upon heating, while

treatment of 1 with 1 equiv of 2,6-diphenylphenol, which

features a lower steric proﬁle, results in the quick formation of

center as expected. The hydride resonance is observed as a

singlet at δ −16.80 ppm and integrates for 3H. This suggests

rapid exchange among the three hydrides on the NMR time

scale at room temperature, which is expected on the basis of

2,33,35,36

literature precedents for metal−polyhydride systems.

The IR spectrum of 1 exhibits two strong bands at σ 2144

−

−1

cm and 1973 cm assigned to metal−hydride stretches. The

most signiﬁcant feature of the crystallographic structure of 1,

shown in Figure 1 , is the Al −Ir distance of 2.406(2) Å, which

an intractable mixture of species, among which is Cp*IrH

(identiﬁed by H NMR), most likely due to the competition in

the protonolysis reactivities of the Al−C versus Al−Ir motifs

together with ligand redistribution phenomena.

The Lewis acidity of the Al atom in complex 1 is conﬁrmed

by the coordination of pyridine, leading to the adduct

[

Cp*IrH Al( Bu)(OAr)(Py)] (2), which is isolated in 68%

yield by cold crystallization in pentane (Scheme 5). The

Scheme 5. Reactivity of 1 with Pyridine

Figure 1. Solid-state molecular structure of 1. Displacement ellipsoids

are plotted at the 30% probability level. Hydrogen atoms have been

omitted for clarity. Selected bond distances (Å) and angles (deg):

Ir1−Al1 2.406(2), Al1−O1 1.695(4), Al1−C1 1.961(6), O1−Al1−

Ir1 120.60(18), O1−Al1−C1 115.4(3), C1−Al1−Ir1 124.0(2). Al1−

coordinated pyridine molecule can be dissociated from Al

upon treatment of 2 with B(C F ) , to restore complex 1

5 3

Ir1−Cp*

143.8(2).

centroid

(

Figure S11). The molecular structure of complex 2 is

underpinned by multinuclei NMR and IR spectroscopy,

elemental analysis, and X-ray diﬀraction analysis. The H

is the second shortest reported distance for a Ir species bearing

30,37−39

an Al atom in its coordination sphere.

The only species

NMR spectrum of 2 is for the most part similar to that of 1

with a typically shielded hydride signal integrating for 3H at δ

−17.26 ppm. Characteristic metal−hydride stretches around

featuring a shorter Al−Ir bond of 2.382(1) Å is the pincer

complex [PAlP]Ir(H) (Scheme 2) described by Yamashita

−1

and co-workers. The metal−metal separation in 1 is 0.10 Å

2100 cm are found in the DRIFT spectrum of 2.

shorter than the sum of the metallic radii of aluminum (1.248

The solid-state molecular structure of 2 (Figure 2) conﬁrms

Å) and iridium (1.260 Å), which translates into a formal

the N-coordination of the pyridine onto aluminum, with an

16,39

shortness ratio below unity (r = 0.959). Therefore, although

the close proximity between the Al and Ir centers in 1 is most

likely the result of the presence of bridging hydrides, a direct

metal−metal interaction cannot be excluded. Overall, this

Al1−N1 bond length (2.032(7) Å) in the expected range.

The Al cation adopts a pseudotetrahedral geometry with angles

lying in the 92.6(3)−119.9(2)° range. The pyridine donation

to Al results in an elongation of both the Al1−O1 bond

(1.695(4) Å in 1 vs 1.776(6) Å in 2) and the Al1···Ir1 distance

from 2.406(2) Å in 1 to 2.502(2) Å in 2. Note that the formal

result suggests a strong donation of the Cp*IrH iridate

fragment onto the cationic Al(III) site. The high electro-

philicity of the Al cation in 1 is also reﬂected in the short Al1−

shortness ratio for the Ir−Al parameter (r = 0.998) is at

O1 bond of 1.695(4) Å in comparison to similar Al−O

unity, indicating a strong interaction between the Cp*IrH and

42−44

parameters found in the literature.

Another characteristic

Al( Bu)(OAr)(Py) fragments. The acute bending of the Cp*

of the structure of 1 is the marked tilting of the Cp* ring with

ring with respect to the Ir−Al axis (Cp*

−Ir−Al angle of

centroid

respect to the Al−Ir axis (Al−Ir−Cp*

angle of 143.79°).

138.73° in 2 vs 143.79° in 1) suggests a terminal coordination

of at least one of the hydrides.

centroid

We propose that this geometrical arrangement is due to the

presence of a terminal hydride on the Ir center, as conﬁrmed

Structural Investigation via DFT. In order to get better

insights into the nature of the Ir−Al interaction in complexes 1

and 2 as well as to verify the position and role of the hydrides

in the bonding, DFT calculations (B3PW91) were carried out.

The bonding situations are very similar in 1 and 2 (see Figure

by computational data (see below).

In contrast to Al( Bu) (OAr), the more hindered species

isobutylbis(3,5-di-tert-butyl-4-hydroxytoluene)aluminum, de-

noted Al( Bu)(OAr) , does not react with IrCp*H in toluene

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J. Am. Chem. Soc. 2021, 143, 4844−4856

are found for 2 (Figure 3 ), so that a rapid exchange of the

Article

bonds as well from the Ir d lone pairs into the Al empty sp

orbital are observed, in line with the presence of three-center−

two-electron (3c-2e) Ir−H−Al bonds as well as some Ir−Al

interactions. The latter is corroborated by an analysis of the

Wiberg bond indexes (WBIs, Figure 3). The Ir−H WBIs are

around 0.7, in line with a mainly covalent interaction, whereas

the Al−H WBIs are close to 0.12−0.15, in line with electron

delocalization from the Ir−H bond onto an acceptor orbital on

Al. Interestingly, the Ir−Al WBI is around 0.3, in line with

some bonding interaction between Ir and Al. The NPA charge

on iridium is signiﬁcant in both cases, taking values of −1.033

and −0.882, respectively, while the eﬀective charges on the

aluminum centers are +1.932 and +1.874, respectively (Figure

). This analysis is consistent with the works of Crimmin and

Aldridge on related M−Al (M = Rh, Au) complexes. Indeed, a

substantial negative charge on the transition metal was

reported in these cases, as well as similar WBIs.

15,19

These

Figure 2. Solid-state molecular structure of 2. Displacement ellipsoids

are plotted at the 30% probability level. Hydrogen atoms have been

omitted for clarity. Selected bond distances (Å) and angles (deg):

Ir1−Al1 2.502(2), Al1−O1 1.776(6), Al1−C1 1.986(9), Al1−N1

data support the description of 1 and 2 as containing a strongly

polarized iridate(III) core, stabilized by Ir−H donation to the

[

Al( Bu)(OAr)Py ] (x = 0, 1) fragment. This formalism is

also consistent with the Pauling electronegativity gap between

iridium and aluminum (2.20 vs 1.61, respectively). The strong

.032(7), O1−Al1−Ir1 119.9(2), O1−Al1−N1 92.6(3), O1−Al1−

C1 113.2(3), N1−Al1−Ir1 113.2(2), C11−Al1−Ir1 114.4(3), C1−

Al1−N1 99.4(3), Al1−Ir1−Cp* 138.7(2).

δ−

δ+

polarity of these Ir −Al pairs results in a substantial

nucleophilic character of the Ir center, as conﬁrmed by the

reactivity studies described below.

centroid

S37 in the Supporting Information), and therefore hereafter

only the description of 2 is given. Two isoenergetic structures

Reactivity with Heteroallenes. Next, we probed the

δ+

δ−

reactivity of these Al −Ir derivatives toward electrophiles,

and we ﬁrst targeted carbon dioxide, given the importance of

45,46

CO activation by transition metals.

NMR monitoring of

the reaction of 1 with CO shows that a reaction occurs at

room temperature, yet a complex mixture of species is formed.

Among them, Cp*Ir(CO)H₂and Cp*IrH₄have been

unambiguously identiﬁed. Unstable aluminum−oxo copro-

ducts are most likely formed in the process and might explain

why this reaction aﬀords multiple products. Gratifyingly, the

coordination of the pyridine Lewis base to Al does not quench

the reactivity of the Ir−Al motif and helps stabilize the

resulting Al derivatives, leading to cleaner reactions that are

easier to decipher. Indeed, treatment of 2 with CO (0.8 atm,

0 equiv, rt) leads to the clean reductive cleavage of CO ,

aﬀording the iridium carbonyl species Cp *Ir(CO)H ,

together with Cp*IrH₄

(see Figure S13) and the

aluminum−oxo coproduct [(iBu)(OAr)Al(Py)] (μ-O) (3),

which is isolated in 86% yield (Scheme 6).

The solid-state structure of 3 is shown in Figure 4. The two

tetracoordinate Al atoms are connected by a bridging oxo

group in a nearly linear fashion (Al1−O1−Al2 angle of

Figure 3. Calculated structures, NPA charges, and Wiberg bond

indexes for the two conformers of complex 2.

74.4(1)°). The substituents at the tetrahedral Al sites adopt

hydrides in solution is expected, which is in agreement with the

H NMR data. The most stable structure exhibits two bridging

Scheme 6. Reactivity of 2 with CO₂

hydrides and one terminal Ir−H, whereas the three hydrogens

have a μ-coordination in the second isomer (+0.5 kcal/mol).

Interestingly, the presence of a terminal hydrogen has an eﬀect

on the geometry around the iridium center since the Al−Ir−X

(

X = Cp* centroid) angle is 136°, whereas this angle is 180° in

the second isomer. The former geometry and the computed

Ir−Al distance (2.51 Å computed vs 2.50 Å experimental) are

in line with the X-ray crystallographic structure. Natural

bonding orbital (NBO) analyses of the two isomers clearly

indicate the presence of three covalent Ir−H interactions (with

0−58% contribution from the Ir spd hybrid orbital). At the

second-order donor−acceptor level, donations from the Ir−H

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{

Al(OAr)( Bu)[κ -(N,O)AdNC(O)NHAd]} (4) (Scheme 7,

top). Note that when only 1 equiv of AdNCO is used, an

Scheme 7. Reactivity of 2 with Heteroallenes

Figure 4. Solid-state molecular structure of 3. Displacement ellipsoids

are plotted at the 30% probability level. Hydrogen atoms have been

omitted for clarity. Selected bond distances (Å) and angles (deg):

Al1−O1 1.697(2), Al1−O2 1.744(2), Al1−C1 1.971(3), Al1−N1

.006(2), Al2−O1 1.701(2), Al2−O3 1.750(2), Al2−C2 1.977(3),

Al2−N2 2.005(2), Al1−O1−Al2 174.4(1).

an eclipsed conformation, with the two isobutyl ligands

pointing in the same direction. The Al1−O1 and Al2−O1

bond distances (1.697(2) and 1.701(2) Å, respectively) are in

48,49

the expected range.

A DRIFT spectroscopy analysis of 3

shows the absence of O−H vibrations, in agreement with a

bridging oxo ligand (versus a bridging hydroxo). Note that, in

solution, complex 3 exists as a mixture of two rotamers in a

ratio of 93/7 which interconvert above 84 °C, as proved by a

equimolar mixture of 2 and 4 is obtained (Figure S21). The H

NMR spectrum for 4 displays a distinctive singlet at δ +4.40

ppm attributed to the NH proton from the ureate ligand. The

C resonance corresponding to the ureate central carbon

appears at a diagnostic chemical shift (δ +164.0 ppm) that is in

variable-temperature H NMR experiment (see Figure S15).

Despite the pivotal role of methylaluminoxane derivatives in

catalysis, very few well-deﬁned alkylaluminoxanes are known to

date. This can be attributed to the hydrolytic conditions

classically used to prepare such derivatives, which are

extremely diﬃcult to control, together with the propensity of

Al−O linkages to oligomerize to form insoluble amorphous

materials. Complex 3 thus adds to the handful of structurally

agreement with literature data. A typical ν(N−H) stretch is

−1

found at 3448 cm in the DRIFT spectrum of 4. The solid-

state molecular structure of 4 as determined by X-ray

diﬀraction is shown in Figure 5. The complex is four-

coordinate, with a κ -ureate ligand arranged to favor the

typical tetrahedral geometry around Al (O1−Al1−O2 =

109.36(8)°). The ureate ligand is bound to Al in a

nonsymmetrical fashion, where the Al1−O1 bond length

(1.863(2) Å) is shorter than the Al1−N1 length (1.911(2) Å),

48−54

characterized molecular aluminum oxide species.

Note

that examples of stoichiometric CO reduction by low-valent

63,64

Al species leading to C−O bond cleavage to yield CO + Al

as in previously characterized ureate complexes.

The

53−55

oxo/carbonate species have emerged only recently.

Here

planarity of the [OCN ] ureate core and the short O−C

the reaction mechanism is totally diﬀerent, since it does not

involve redox changes of the Al(III) center (see DFT

calculations below) but still allows the preparation of an

unconventional Al−oxo species without having to isolate the

low-valent Al derivative, which is remarkable. While insertion

(1.309(4) Å) and N−C (1.331(3) and 1.341(3) Å) distances

are consistent with electron delocalization and compare well

63,64

with reported values for metal-bound ureates.

By analogy with the reaction with CO and in agreement

with computational data (see below), we postulate that this

aluminum ureate complex arises from a transient Al−amido

species generated after CO extrusion. Complex 4 might thus

arise from isocyanate insertion into such an Al−NHAd

intermediate. Overall, this uncommon reaction adds to the

handful of examples of the metal-mediated decarbonylation of

9,56−58

of CO into polar metal−metal bonds

and main-group

9−61

Lewis pairs

has been reported, to our knowledge the

2−

reductive cleavage of CO₂leading to CO and O by

heterobimetallic systems has been described in only two

occurrences. Thomas described the oxidative addition of CO₂

onto a Zr−Co bond, aﬀording a (OC)Co(μ-O)Zr species, and

65−69

isocyanates and cyanates.

Mazzanti described the CO cleavage to CO gas and a U(V)

The reaction of 2 with dicyclohexylcarbodiimine does not

lead to the reductive cleavage of a CN bond but instead to

oxo species involving a bimetallic uranium−potassium

56,62

cooperative mechanism.

the formation of a bridged amidinate species, Cp*IrH (μ-

This bimetallic reductive cleavage of CO pushed us to

CyNC(H)NCy)Al( Bu)(OAr) (5) (Scheme 7, bottom),

explore further the reactivity of complex 2 toward other

heteroallenes. Treatment of 2 with 2 equiv of adamantyl

isocyanate results in the cleavage of the NC bond to

produce Cp*Ir(CO)H₂and the aluminum ureate species

arising from hydride transfer to the central carbon of the

heteroallene. The protonation of the central carbon of the

amidinate is conﬁrmed by NMR spectroscopy: the H NMR

spectrum for 5 displays a characteristic singlet at δ +6.99 ppm

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in η amidinates, but this value compares well with that

72,74

reported for μ-η ,η amidinates bridging heavy-metal ions.

The N1−Ir1 (2.088(4) Å) and N2−Al1 (1.905(4) Å) bond

lengths are comparable to those found in Al and Ir amidinate

20,75−77

complexes, respectively.

In order to better understand the reaction mechanisms

operating in these heteroallene activations by Ir−Al metal−

metal pairs, we carried out DFT calculations (B3PW91). The

reaction begins by the replacement of the pyridine by a CO₂

molecule that binds to Al and Ir (Figure 6). This substitution is

endothermic by 7.5 kcal/mol. From this adduct, the CO₂

undergoes a nucleophilic attack by the iridium center. Indeed,

at the transition state (TS), the CO molecule is bent in order

to overlap an empty orbital at the carbon of CO with a lone

pair of the iridium center (see the associated molecular orbital

in Figure S38 in the Supporting Information). The aluminum

center ensures an electrophilic assistance by binding to the

oxygen. The associated barrier is 18.9 kcal/mol, in line with a

kinetically accessible reaction. From the intrinsic reaction

coordinates, this yields a four-membered metallacyclic species

whose formation is slightly endothermic (+3.6 kcal/mol) with

respect to the reactants. Next, the small size of the CO₂

molecule allows a migratory insertion onto the Ir−Al bond.

This is easily achieved through a low-lying TS (barrier of 10.5

kcal/mol) and leads to the formation of a stable metal-

lacarboxylate complex (−11.5 kcal/mol) where the two

oxygens bind to Al while C is bound to Ir. This intermediate

is similar to the few examples where CO is reductively

19,58

inserted in polar metal−metal bonds.

The presence of three hydrides on the Ir center, in close

vicinity to the inserted CO , allows an easy hydrogen migration

from Ir to one of the oxygen atoms. This migration occurs

through a kinetically accessible TS (barrier of 25.8 kcal/mol),

which is followed by a C−O bond breaking TS to ultimately

yield the formation of an Al hydroxide molecule and

Cp*Ir(CO)H , whose formation is exothermic by 7.1 kcal/

mol with respect to the reactants (the hydrogen transfer + CO

bond breaking step being slightly endothermic by 4.4 kcal/mol

from the Ir(CO )Al carboxylate intermediate). The Al

hydroxide species can then react with a second equivalent of

complex 2. This reaction is kinetically facile with a barrier of

Figure 5. Solid-state molecular structures of 4 (top) and 5 (bottom).

Displacement ellipsoids are plotted at the 30% probability level.

Hydrogen atoms have been omitted for clarity. Selected bond

distances (Å) and angles (deg): for 4, Al1−O1 1.863(2), Al1−O2

3.4 kcal/mol and yields after pyridine recoordination the

experimentally observed compounds 3 and Cp*IrH . Other

pathways were investigated (see Figure S39 in the Supporting

Information) but the one reported here appears to be the most

.710(2), Al1−C2 1.961(3), Al1−N1 1.911(2), N1−C1 1.331(3),

N2−C1 1.341(3), O1−C1 1.309(4), N1−C1−O1 111.7(2), N1−

C1−N2 127.8(2), O1−Al1−N1 70.73(7), O1−Al1−O2 109.36(8);

for 5, Ir1−Al1 2.617(1), Al1−O1 1.766(4), Al1−C1 1.986(5), Al1−

N2 1.905(4), Ir1−N1 2.088(4), N1−C2 1.311(6), N2−C2 1.328(6),

N1−C2−N2 124.8(4), N2−Al1−Ir1 91.0(1), O1−Al1−C1 107.5(2),

favorable. This CO reduction mechanism is very diﬀerent

from that reported by Murray et al. for a diiron−hydride

complex, where the ﬁrst step is a hydrogen transfer to CO ,

or the reaction reported by Lu et al. using nickelate−group

13 complexes, where a CO disproportionation is observed.

N1−Ir1−Al1 81.2(1), Al1−Ir1−Cp*

144.85(1).

centroid

62,80−85

which correlates in the H− C HSQC NMR experiment to

the diagnostic C resonance found at δ +162.9 ppm.

The crystallographic structure of 5 is shown in Figure 5. The

bridging μ-η ,η amidinate ligand is located parallel to the

metal−metal axis, as is commonly found in metal−metal-

bonded dinuclear amidinate species.

70−72

This results in an

elongation of the Ir···Al distance to 2.617(1) Å (versus

.502(2) Å in 2). The ﬁve-membered Ir1−Al1−N2−C2−N1

ring is almost perfectly planar, and the N1−C2 and N2−C2

bond distances (1.311(6) and 1.328(6) Å, respectively) are in

72,73

the expected range for an amidinate motif.

N2 angle (124.8(4)°) is much larger than that classically found

The N1−C2−

849

J. Am. Chem. Soc. 2021, 143, 4844−4856

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Figure 6. Computed enthalpy proﬁle for the reaction of CO with 2 at room temperature.

sequence is quite similar to that reported for CO . In

steric bulk stops the reaction at the amidinate complex, as

observed experimentally.

particular, the replacement of pyridine by AdNCO is

endothermic by 9.7 kcal/mol. From this adduct, AdNCO

also undergoes a kinetically accessible (23.2 kcal/mol)

nucleophilic attack by the Ir center, yielding an unstable

four-membered metallacyclic intermediate (+7.2 kcal/mol).

CONCLUSION

■

In summary, the iridium tetrahydride complex Cp*IrH reacts

with isobutylaluminum aryloxy derivatives to give unusual

iridium aluminum species via a reductive elimination route.

Spectroscopic, crystallographic, and computational data

support the description of these heterobimetallic complexes

The next step is diﬀerent from that reported for CO and is

likely due to the steric bulk of the adamantyl group. Indeed,

AdNCO cannot easily insert between Ir and Al, so that the

hydrogen transfer from Ir to N occurs on the four-membered-

ring metallcycle with a barrier of 27.7 kcal/mol (hydride

transfer to the oxygen and AdNCO insertion followed by

hydrogen transfer were also computed and were found not to

be competitive; see Figures S40 and S41). This hydrogen

transfer is followed by a C−N bond breaking TS (barrier of 4.7

kcal/mol), which allows the formation of an Al amido complex

δ+

δ−

as featuring strongly polarized Al(III) −Ir(III) cores.

Reactivity studies demonstrate that the Al sites retain their

Lewis acidic character and that the binding of a Lewis base to

Al does not quench the reactivity of the Ir−Al motif. More

importantly, these Ir−Al species promote the cooperative

reductive cleavage of heteroallenes (CO , AdNCO). In these

processes, the Ir(III) center acts as a nucleophile. Although

and a molecule of Cp*Ir(CO)H (exothermic by 2.3 kcal/mol

88,105−109

some Ir(I) species are known to act as nucleophiles,

with respect to the reactants). The formed Al amide molecule

to the best of our knowledge such behavior is unusual for d

^d^o^e^sⁿ^o^t^r^e^a^c^t^wⁱ^t^h^a^m^o^l^e^c^u^l^e^o^f²⁽^a^s^o^b^s^e^r^v^e^d^wⁱ^t^h^C^O2⁾^,

presumably due to its steric bulk, but rather undergoes a [2 +

Ir(III) complexes and thus such a result opens up attractive

prospects for reactivity in catalysis. From the perspective of

aluminum, these complexes allow access to unconventional

motifs in molecular Al chemistry (e.g., oxos) without a change

in the formal oxidation state of the Al(III) center. This

] cycloaddition with another molecule of AdNCO (barrier of

.9 kcal/mol). This yields a stable cycloaddition product

(

−23.1 kcal/mol), which can rearrange to a more stable isomer

(−45.2 kcal/mol) through, for example, a 1,3-hydrogen shift.

contrasts with CO cleavage promoted by low-oxidation-state

3−55

While isocyanates are well-known to undergo catalytic

aluminum species,

which are notoriously diﬃcult to

97−101

polymerization or cyclotrimerization,

selective dimeriza-

isolate, and thus represents a major achievement. This work

also illustrates the multifaceted reactivity of transition metals

toward alkylaluminum reagents, which are employed as

cocatalysts in numerous processes. Future eﬀorts will be

devoted in our group to further explore the cooperative

heterobimetallic reactivity of these unconventional molecular

objects.

tion of isocyanates to substituted ureas after the elimination of

102−104

CO has been almost unexplored

and, to our knowledge,

this original cooperative decarbonylation mechanism of

AdNCO is unprecedented.

Calculations were also carried out on the reaction of 2 with

CyNCNCy (see Figure S42). In that case the increased

850

J. Am. Chem. Soc. 2021, 143, 4844−4856

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Figure 7. Computed enthalpy proﬁle for the reaction of AdNCO with 2 at room temperature.

EXPERIMENTAL SECTION

Elemental Analyses. Elemental analyses were performed under

an inert atmosphere at Mikroanalytisches Labor Pascher, Germany.

X-ray Structural Determinations. Experimental details regard-

ing single-crystal XRD measurements are provided in the Supporting

Information. CCDC 2059453−2059457 contain supplementary

crystallographic data for this paper. These data can be obtained free

of charge from The Cambridge Crystallographic Data Centre via

www.ccdc.cam.ac.uk/structures.

■

General Considerations. Unless otherwise noted, all reactions

were performed either using standard Schlenk line techniques or in an

MBraun glovebox under an atmosphere of puriﬁed argon (<1 ppm of

O /H O). Glassware and cannulas were stored in an oven at ∼100 °C

for at least 12 h prior to use. Toluene, n-pentane, octane, THF, and

diethyl ether were puriﬁed by passage through a column of activated

alumina, dried over Na/benzophenone, vacuum-transferred to a

storage ﬂask, and freeze−pump−thaw degassed prior to use.

Deuterated solvents (THF-d , toluene-d , and C D ) were dried

NMR Spectroscopy. Solution NMR spectra were recorded on

Bruker AV-300, AVQ-400, and AV-500 spectrometers. H and

chemical shifts were measured relative to residual solvent peaks, which

were assigned relative to an external TMS standard set at 0.00 ppm.

over Na/benzophenone, vacuum-transferred to a storage ﬂask, and

freeze−pump−thaw degassed prior to use. CO gas was dried over

freshly regenerated R311G BASF catalyst/molecular sieves (4 Å)

F chemical shifts are reported relative to BF ·OEt set at 0.00 ppm.

H and C NMR assignments were conﬁrmed by H− H COSY,

H− C HSQC, and HMBC experiments.

prior to use. The compounds Cp*IrH , Al( Bu)(OAr) , and

Synthesis of [Cp*IrH Al( Bu)(OAr)] (1). A 4 mL pentane

Al( Bu) (OAr) (Ar = 2,6-( Bu)-3-MeC H ) were prepared accord-

solution of IrCp*H (282.5 mg, 0.85 mmol, 1.0 equiv) was added

dropwise to a 8 mL colorless pentane solution of (2,6-di-tert-butyl-4-

methylphenoxy)diisobutylaluminum, Al( Bu) (OAr) (310.0 mg, 0.86

ing to the literature procedures. All other reagents were acquired from

commercial sources and used as received.

IR Spectroscopy. Samples were prepared in a glovebox (diluted in

dry KBr), sealed under argon in a DRIFT cell equipped with KBr

windows, and analyzed on a Nicolet 670 FT-IR spectrometer.

mmol, 1.0 equiv). The resulting solution was stirred at room

temperature for 20 h. Then, the volatiles were removed under

vacuum, yielding a white solid (550 mg of crude solid). This powder

851

J. Am. Chem. Soc. 2021, 143, 4844−4856

Journal of the American Chemical Society

Article

was dissolved in the minimum amount of pentane (ca. 7 mL), and the

H . The colorless crystals were extracted with 6.0 mL of toluene.

Then, the volatiles were removed under vacuum for 3 h, yielding the

solution was ﬁltered and stored at −40 °C for 16 h, yielding

compound 1 as white microcrystals (390.0 mg, 72% yield). H NMR

complex 3·C H as a white powder (92 mg, 86% yield). In solution,

(

500 MHz, C D , 293 K): δ 7.18 (s, 2H, CH ), 2.32 (s, 3H, CH -

two rotamers of complex 3 are in equilibrium at 293 K in a 7:93 ratio.

Ar), 2.15 (m, 1H, CH_i_B_u), 1.96 (s, 15H, CH₃_C_p_*), 1.65 (s, 18H,

CH₃_‑_t_B_u), 1.08 (d, J = 6.4 Hz, 6H, CH ), 0.31 (d, J = 7.1 Hz,

H NMR (500 MHz, C D , 293 K): δ rotamer #1 8.76 (m, 4H,

3‑iBu

CH_o_r_t_h_o_‑_P_y), 7.24 (s, 4H, CH ), 6.81 (m, 2H, CH_p_a_r_a_‑_P_y), 6.51 (m, 4H,

H, CH₂_‑_i_B_u), −16.80 (s, 3H, H−Ir). C{ H} NMR (125 MHz,

CH_m_e_t_a_‑_P_y), 2.40 (s, 6H, CH -Ar), 1.64 (m, 2H, CH ), 1.51 (s, 36H,

iBu

C D , 293 K): δ 155.46 (C ), 138.18 (C ), 126.41 (C ), 126.10

CH₃_‑_t_B_u), 0.97 (d, 6H, CH₃_‑_i_B_u), 0.82 (d, 6H, CH ), 0.69 (d, J =

5.8 Hz, 1H, CH₂_‑_i_B_u), 0.66 (d, J = 5.6 Hz, 1H, CH₂_‑_i_B_u), 0.60 (d,

3‑iBu

(

CH ), 94.64, (CCp*⁾^,³⁵^.⁰⁰⁽⁾^,³²^.⁸⁸⁽^C^H2‑iBu⁾^,³²^.¹⁸⁽⁾^,²⁸^.⁰⁴

^C^H3 ), 25.93 (CH ), 21.59 (ArCH ), 11.04 (CH3‑Cp*⁾^.^D^R^I^F^T^S

‑iBu

iBu

1H, CH₂_‑_i_B_u), 0.58 (d, 1H, CH₂_‑_i_B_u); δ rotamer #2 8.61 (m, 4H,

−

293 K, cm ) σ 2946 (s, νC−H⁾^,²⁹¹⁶⁽^s^,^νC−H⁾^,²⁸⁷⁷⁽^s^,^νC−H⁾^,²⁸⁵⁷

^s^,^νC−H⁾^,²¹⁴⁴⁽^s^,^νIr−H⁾^,¹⁹⁷³⁽^s^,^νIr−H), 1464 (s), 1425 (s), 1297

CH_o_r_t_h_o_‑_P_y), 7.24 (s, 4H, CH ), 6.77 (m, 2H, CH_p_a_r_a_‑_P_y), 6.36 (m, 4H,

CH_m_e_t_a_‑_P_y), 2.44 (s, 6H, CH -Ar), 1.88 (m, 2H, CH ), 1.42 (s, 36H,

iBu

s), 1286 (s), 1262 (s). Anal. Calcd for C H AlIrO: C, 54.95; H,

CH₃_‑_t_B_u), 1.34 (d, J = 6.4 Hz, 6H, CH₃_‑_i_B_u), 0.99 (d, J = 6.4 Hz,

HH HH

.95. Found: C, 54.96; H, 8.00.

H, CH₃_‑_i_B_u), 0.89 (d, J = 6.6 Hz, 1H, CH₂_‑_i_B_u), 0.86 (d, J = 6.4

HH HH

Synthesis of [Cp*IrH Al( Bu)(OAr)(Py)] (2). A 0.5 mL colorless

Hz, 1H, CH₂_‑_i_B_u), 0.61 (d, J = 6.7 Hz, 1H, CH₂_‑_i_B_u), 0.59 (d, J

HH HH

pentane solution of pyridine (15.6 mg, 0.20 mmol, 1.0 equiv) was

added dropwise to a 8.5 mL light yellow pentane solution of 1 (123.5

mg, 0.20 mmol, 1.0 equiv). The resulting pale yellow solution was

stirred at room temperature for 30 min. Then, the volatiles were

removed under vacuum, yielding a crude oﬀ-white oily material. This

crude material was dissolved in the minimum amount of pentane (ca.

6.6 Hz, 1H, CH₂_‑_i_B_u). C{ H} NMR (125 MHz, C D , 293 K): δ

6 6

rotamer #1 156.40 (C ), 149.38 (CH_o_r_t_h_o_‑_P_y), 140.48 (CH_p_a_r_a_‑_P_y),

39.12 (C ), 126.01 (CH ), 124.57 (C ), 124.46 (CH_m_e_t_a_‑_P_y), 34.96

Ar Ar Ar

(

C_t_B_u), 31.61 (CH₃_‑_t_B_u), 29.61 (CH₃_‑_i_B_u), 28.68 (CH₃_‑_i_B_u), 26.26

CH_i_B_u), 24.40 (CH₂_‑_i_B_u), 21.48 (CH₃_‑_A_r). DRIFTS (293 K, cm ): σ

−1

101 (m, ν_C₋_H), 3022 (m, ν_C₋_H), 2948 (s, ν_C₋_H), 2913 (s, ν_C₋_H),

855 (s, ν_C₋_H), 1616 (m), 1451 (s), 1423 (s), 1271 (s). Anal. Calcd

.5 mL), and the solution was ﬁltered and stored at −40 °C for 16 h,

yielding 2 as colorless needle crystals (94 mg, 68% yield). Colorless

block single crystals of 2 suitable for XRD studies were grown by slow

recrystallization of 2 in an octane/toluene (7/1) mixture at −40 °C

for C H Al N O ·C H : C, 75.65; H, 9.47; N, 3.21. Found: C,

5.42; H, 9.24; N, 3.24.

Synthesis of Compound 4. A 3 mL colorless toluene solution of

within 48 h. H NMR (500 MHz, C D , 293 K): δ 8.89 (d, 2H,

1-adamantyl isocyanate (82.5 mg, 0.47 mmol, 2.0 equiv) was added

dropwise to a 8 mL colorless pentane solution of 2 (167 mg, 0.23

mmol, 1.0 equiv). The reaction mixture was stirred at room

temperature for 24 h, yielding a brownish solution. Volatiles were

removed in vacuo, yielding a brownish solid containing an equimolar

^C^Hortho‑Py), 7.24 (s, 2H, CH ), 6.73 (t, 1H, CHpara‑Py⁾^,⁶^.⁴³⁽^t^,²^H^,

^C^Hmeta‑Py), 2.37 (s, 3H, CH -Ar), 2.03 (s, 15H, CH3Cp*⁾^,¹^.⁸⁶⁽^m^,¹^H^,

^C^HiBu), 1.61 (s, 18H, CH ), 1.06 (bs, 6H, CH ), 0.74 (d, 2H,

3‑tBu

3‑iBu

^C^H2 , J = 6.9 Hz), −17.26 (s, 3H, H−Ir). C{ H} NMR (125

MHz, C D , 293 K): δ 157.02 (C ), 149.63 (CHortho‑Py⁾^,¹³⁹^.¹⁵

‑iBu

mixture of Cp*IrH (CO) and complex 4 (ca. 240 mg). This solid was

(

^C^Hpara-Py), 126.31 (CH ), 124.61 (C ), 124.04 (CHmeta‑Py⁾^,⁹³^.⁵⁰

Ar Ar

dissolved in the minimum amount of pentane (ca. 8 mL), and the

solution was ﬁltered and stored at −40 °C for 3 weeks, yielding 4 as

colorless block crystals suitable for XRD analysis (110 mg, 76% yield).

C_C_p_*), 35.30 (C_t_B_u), 32.61 (CH₃_‑_t_B_u), 31.61 (CH₂_‑_i_B_u), 28.35

CH₃_‑_i_B_u), 26.58 (CH_i_B_u), 21.42 (CH₃_‑_A_r), 11.29 (CH₃_‑_C_p_*). DRIFTS

−

293 K, cm ): σ 2962 (s, ν_C₋_H), 2912 (s, ν_C₋_H), 2860 (s, ν_C₋_H),

128 (s, ν_I_r₋_H), 2109 (s, ν_I_r₋_H), 1611 (m), 1449 (m), 1265 (s). Anal.

Calcd for C H AlIrNO: C, 57.66; H, 8.16; N, 1.92. Found: C,

H NMR (500 MHz, C D , 293 K): δ 7.27 (s, 2H, CH ), 4.40 (s,

H, NH), 2.37 (s, 3H, CH -Ar), 2.19 (m, 1H, CH ), 1.88−1.98 (m,

iBu

8H, CH_A_dand CH₂_‑_A_d), 1.72 (s, 18H, CH₃_‑_t_B_u), 1.45−1.55 (m, 12H,

7.11; H, 7.78; N, 1.99.

Reaction of 2 with B(C F ) , Yielding Complex 1 and

CH₂_‑_A_d), 1.22 (dd, 6H, CH₃_‑_i_B_u), 0.59 (m, 2H, CH₂_‑_i_B_u). C{ H}

5 3

NMR (125 MHz, C D , 293 K): δ 163.96 (C_u_r_e_a_t_e) 154.47 (C_A_r),

(

Py)B(C F ) . A 0.4 mL colorless C D solution of tris-

6 5 3 6 6

38.59 (C ), 126.13 (CH ), 126.08 (C ), 53.11 (C ), 50.27 (C ),

Ar Ar Ar Ad Ad

(

pentaﬂuorophenyl)borane (8.2 mg, 16.0 μmol, 1.0 equiv) was

3.54 (CH₂_‑_A_d), 42.82 (CH₂_‑_A_d), 36.62 (CH₂_‑_A_d), 36.37 (CH₂_‑_A_d),

5.28 (C_t_B_u), 31.71 (CH₃_‑_t_B_u), 29.94 (CH ), 29.89 (CH ), 28.45

added to a 0.2 mL C D solution of complex 2 (11.7 mg, 16.0 μmol,

.0 equiv). The resulting light yellow solution was sealed under argon

(

CH₃_‑_i_B_u), 28.02 (CH₃_‑_i_B_u), 26.66 (CH_i_B_u), 21.81 (CH₂_‑_i_B_u), 21.58

in a J. Young NMR tube and was kept at room temperature for 24 h.

An analysis of the resulting reaction mixture by H NMR and

−1

(CH₃_‑_A_r). DRIFTS (293 K, cm ): σ 3448 (m, ν_N₋_H), 2944 (s, ν_C₋_H),

911 (s, ν_C₋_H), 2847 (s, ν_C₋_H), 1575 (s), 1451 (s), 1490 (m), 1429

m), 1278 (m). Anal. Calcd for C H AlN O : C, 76.15; H, 10.07;

(

NMR spectroscopy showed a quantitative formation of complex 1

together with the (Py)B(C F ) adduct. The NMR data for

5 3

N, 4.44. Found: C, 76.02; H, 10.12; N, 4.39.

(

Py)B(C F ) are in agreement with the previously reported

6 5 3

110

Synthesis of Compound 5. A 3 mL colorless pentane/toluene

(1/1) solution of N,N′-dicyclohexylcarbodiimide (44.5 mg, 0.22

mmol, 1.1 equiv) was added dropwise to a 6.5 mL colorless pentane

solution of 2 (144.5 mg, 0.20 mmol, 1.0 equiv). The resulting solution

was stirred and heated at T = 50 °C for 3 h, triggering a color change

from colorless to yellow. The crude reaction mixture was then cooled

to room temperature and stirred for 24 h. Volatiles were then

removed in vacuo, yielding a crude yellow powder (ca. 150 mg). This

solid was dissolved in the minimum amount of pentane (ca. 6 mL),

and the solution was ﬁltered and stored at −40 °C, yielding 5 as light

data.

Hz, 2H, CH

H NMR (300 MHz, C D , 293 K): δ 7.94 (d, J = 5.6

6 6 HH

), 6.57 (m, 1H, CH_p_a_r_a_‑_P_y), 6.23 (t, J = 7.2 Hz,

ortho‑Py

H, CH_m_e_t_a_‑_P_y). F NMR (282 MHz, C D , 293 K): δ −131.5 (d, J

20 Hz, 6F, CF_o_r_t_h_o), −155.4 (t, J = 21 Hz, 3F, CF ), −162.7 (m,

para

F, CF_m_e_t_a).

Reaction of 2 with CO , Yielding [(iBu)(OAr)Al(Py)] (μ-O) (3).

Complex 2 (174 mg, 0.24 mmol, 1.0 equiv) was dissolved in 20 mL of

pentane. The resulting solution was charged in one compartment of a

two-sided Schlenk reaction vessel featuring two isolated 74 cm

chambers. This double-Schlenk vessel was sealed under argon, the

pentane solution was frozen in liquid nitrogen, and then the whole

yellow block crystals suitable for XRD analysis (100 mg, 60% yield).

system was evacuated (10⁻mbar). The two compartments were

isolated from each other using a J. Young high-vacuum PTFE valve.

Afterward, dry CO₂(800 mbar, 2.43 mmol, 10.2 equiv) was

introduced in the ﬁrst compartment. Then, the J. Young valve was

H NMR (500 MHz, C D , 293 K): δ 7.24 (s, 2H, CH ), 6.99 (s,

6 6 Ar

^H^,^C^HAmidinate), 3.37 (m, 1H, CH ), 2.83 (m, 1H, CH ), 2.41 (s,

Cy Cy

H, CH -Ar), 2.35 (d, 1H, CH2‑Cy⁾^,²^.³²⁽^m^,¹^H^,^C^HiBu⁾^,²^.²³⁽^d^,

1H, CH2‑Cy), 1.80 (m, 2H, CH2‑Cy), 1.73 (s, 18H, CH3‑tBu), 1.66 (m,

2H, CH2‑Cy), 1.61 (s, 15H, CH3Cp*), 1.54 (m, 2H, CH2‑Cy), 1.45 (d,

opened for 15 min to let CO diﬀuse at room temperature from the

ﬁrst compartment into the pentane solution of 2 located in the second

compartment and the system was left in this conﬁguration for 5 days

without any stirring. This procedure triggered the nucleation of 2 as

colorless block-shaped crystals in a yellow solution. The yellow ﬁltrate

was removed from the ﬂask and analyzed by NMR spectroscopy,

HH = 6.7 Hz, 3H, CH3‑iBu), 1.41 (d, JHH = 6.6 Hz, 3H, CH3‑iBu),

0.95−1.39 (10H, m, CH2‑Cy), 0.93 (d, JHH = 6.6 Hz, 2H, CH2‑iBu),

−14.52 (s, 1H, H−Ir),), −14.99 (s, 1H, H−Ir). C{ H} NMR (125

MHz, C D , 293 K): δ 161.86 (CH ), 157.63 (C ), 139.62

Amidinate

(C ), 125.96 (CH ), 124.03 (C ), 92.05 (C_C_p_*), 69.61 (CH_C_y),

which showed the equimolar formation of Cp*IrH and Cp*Ir(CO)-

57.33 (CH ), 36.72 (CH₂_‑_C_y), 35.95 (CH₂_‑_C_y), 35.76 (C_t_B_u), 35.57

852

J. Am. Chem. Soc. 2021, 143, 4844−4856

Journal of the American Chemical Society

https://pubs.acs.org/doi/10.1021/jacs.1c01725.

Article

(

CH₂_‑_C_y), 35.24 (CH₂_‑_C_y), 34.46 (CH₂_‑_i_B_u), 32.63 (CH₃_‑_t_B_u), 29.13

^C^H3‑iBu⁾^,²⁸^.¹⁸⁽^C^H2‑Cy⁾^,²⁶^.⁹⁷⁽^C^H2‑Cy⁾^,²⁶^.⁷⁵⁽^C^H2‑Cy⁾²⁶^.⁷³

Funding

We gratefully acknowledge ﬁnancial support from the CNRS-

MOMENTUM program. CalMip is acknowledged for a

generous grant of computing time (CALMIP-EOS grant

^C^H²^‑^C^y⁾^,²⁶^.³⁶⁽^C^Hⁱ^B^u⁾^,²⁶^.³²⁽^C^H2‑Cy), 26.16 (CH2‑Cy⁾^,²¹^.⁴¹

−1

CH₃_‑_A_r), 10.48 (CH₃_‑_C_p_*). DRIFTS (293 K, cm ) σ 2949 (s, ν_C₋_H),

915 (s, ν_C₋_H), 2851 (s, ν_C₋_H), 2145 (w, ν_I_r₋_H), 2071 (w, ν_I_r₋_H), 1614

s, ν ), 1447 (m), 1421 (s), 1264 (s). Anal. Calcd for

0833).

(

CN

C H AlIrN O: C, 60.32; H, 8.95; N, 3.27. Found: C, 60.13; H,

Notes

.84; N, 3.28.

The authors declare no competing ﬁnancial interest.

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

ACKNOWLEDGMENTS

■

We thank Anne Baudouin, Christine Lucas, and Nesrine

Oueslati for their help with the NMR spectroscopic analyses.

We thank the anonymous reviewers for their very insightful

comments during the revision process of this manuscript.

NMR, IR, XRD and computational data (PDF)

Cartesian coordinates for the calculated structures

REFERENCES

■

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AUTHOR INFORMATION

■

(5) Lai, Q.; Cosio, M. N.; Ozerov, O. V. Ni Complexes of an Alane/

Tris(Phosphine) Ligand Built around a Strongly Lewis Acidic Tris(N-

Pyrrolyl)Aluminum. Chem. Commun. 2020, 56 (94), 14845−14848.

Corresponding Author

Clément Camp − Laboratory of Catalysis, Polymerization,

Processes and Materials, CP2M UMR 5128, Université de

Lyon, Institut de Chimie de Lyon, CNRS, Université Lyon 1,

F-69616 Villeurbanne, France; orcid.org/0000-0001-

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Processes and Materials, CP2M UMR 5128, Université de

Lyon, Institut de Chimie de Lyon, CNRS, Université Lyon 1,

F-69616 Villeurbanne, France; orcid.org/0000-0001-

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Iker Del Rosal − Université de Toulouse, CNRS, INSA, UPS,

UMR 5215, LPCNO, F-31077 Toulouse, France

Laurent Maron − Université de Toulouse, CNRS, INSA, UPS,

UMR 5215, LPCNO, F-31077 Toulouse, France;

orcid.org/0000-0003-2653-8557

Erwann Jeanneau − Université de Lyon, Centre de

Diﬀractométrie Henri Longchambon, 69100 Villeurbanne,

France

Laurent Veyre − Laboratory of Catalysis, Polymerization,

Processes and Materials, CP2M UMR 5128, Université de

Lyon, Institut de Chimie de Lyon, CNRS, Université Lyon 1,

F-69616 Villeurbanne, France

Chloé Thieuleux − Laboratory of Catalysis, Polymerization,

Processes and Materials, CP2M UMR 5128, Université de

Lyon, Institut de Chimie de Lyon, CNRS, Université Lyon 1,

F-69616 Villeurbanne, France; orcid.org/0000-0002-

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