When Applying the Mercury Poisoning Test to Palladacycle-Catalyzed Reactions, One Should Not Consider the Common Misconception of Mercury(0) Selectivity

This is an open access article published under an ACS AuthorChoice License, which permits

copying and redistribution of the article or any adaptations for non-commercial purposes.

Article

Cite This: Organometallics XXXX, XXX, XXX −XXX

When Applying the Mercury Poisoning Test to Palladacycle-

Catalyzed Reactions, One Should Not Consider the Common

Misconception of Mercury(0) Selectivity

Olga N. Gorunova,^†Ivan M. Novitskiy,^‡Yuri K. Grishin,^‡Igor P. Gloriozov,^‡

Vitaly A. Roznyatovsky,^‡Victor N. Khrustalev,^§,∥Konstantin A. Kochetkov,^†and Valery V. Dunina*^,‡

^†A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciencies, Vavilova St. 28, 119991 Moscow,

Russian Federation

^‡Department of Chemistry, M. V. Lomonosov Moscow State University, Lenin Hills, 119991 Moscow, Russian Federation

^§Inorganic Chemistry Department, Peoples’ Friendship University of Russia, Miklukho-Maklay Street 6, 117198 Moscow, Russian

Federation

^∥National Research Center, Kurchatov Institute, Acad. Kurchatov Sq. 1, Moscow 123182, Russian Federation

S

* Supporting Information

ABSTRACT: The aim of this study was to demonstrate the

absolute necessity of control experiments for a correct interpreta-

tion of mercury drop test results when applied to mechanistic

studies of palladacycle-catalyzed reactions. It was shown that the

interaction of diverse azapalladacycles with metallic mercury leads

to the formation of organomercuric chlorides during the redox-

transmetalation process. The structure of these organomercurials

1

was conﬁrmed by elemental analysis, H, ¹³C{¹H}, and ¹⁹⁹Hg{¹H}

NMR spectra, X-ray diﬀraction analysis, and DFT calculations. The

behavior and properties of C,N-mercuracycles bearing the weak and

labile N···Hg bond are discussed on the basis of the temperature

dependence of the NMR spectra and calculated thermodynamic

parameters of the dechelation process.

or supported), whereas an observation that Hg(0) quenches the

activity may be consistent with a Pd(0) intermediate”.^1cIn

support of this idea, it is useful to mention that there are several

known examples of mercury(0) interaction with soluble

molecular complexes of zero-valent metals, such as palladium,

platinum, and rhodium.⁸Of course, the interaction of metallic

mercury with metal complexes in elevated formal oxidation

states bound by protective ligands usually is considered

impossible.^1c,7,9

Mechanistic studies are particularly important in the case of

cross-coupling catalysis with cyclopalladated complexes

(CPCs), palladacycles, or pincer palladabicycles, which have

remained a subject of debate until now. In contrast to the widely

accepted classic Pd(II)/Pd(0) pathway for these processes,¹⁰

recent experimental¹¹and theoretical investigations of these

processes,¹²along with signiﬁcant progress in the chemistry of

cyclometalated palladium(IV) complexes,¹³have provided

evidence in favor of alternative Pd(II)/Pd(IV) catalytic cycle

viability. The most valuable and quite convincing experimental

conﬁrmation of the Pd(II)/Pd(IV) pathway for the intra-

INTRODUCTION

■

The success of catalytic system development is dependent on a

clear understanding of the reaction mechanism and the nature of

the true catalyst. Among a rather rich collection of diagnostic

tools proposed to explore this issue,^1,2the mercury poisoning

test is the most popular due to its easy procedures. This method,

known for almost a century,³was ﬁrst based on the ability of

mercury(0) to amalgamate zero-valent metals or to adsorb on

the metal surface.⁴The interpretation of mercury poisoning

results has signiﬁcantly changed over time. Initially, this test was

considered a way to distinguish between homogeneous and

heterogeneous catalysts; the suppression of the reaction by

excess metallic mercury served as evidence for heterogeneous

catalysis.⁵Later, Schwartz suggested using more mechanistically

oriented terms: “homotopic and heterotopic” catalysis, depend-

ing on the nature of the catalytic sites, not on the phases

involved.⁶However, this reasonable terminology is still almost

never used. The next step in the interpretation of mercury(0)

poisoning results was made by Jones,^1c,7who suggested relating

the results of the test for palladium-catalyzed cross-coupling

reactions with the type of catalytic cycle as follows: “the

observation that Hg(0) does not aﬀect the catalysis can conﬁrm

a mechanism that does not involve unprotected Pd(0) (soluble

Received: May 28, 2018

A

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

molecular version of the Heck cross-coupling reaction has been

provided by Vicente’s recent research.¹⁴

without any visible evidence of palladium black formation,

providing good yields and a rather high enantioselectivity of the

binaphthyl product. In addition, the catalyst was almost

quantitatively recovered after the reaction completion, and the

kinetic curve for this reaction did not reveal any induction

period. However, we discovered an unexpected contradiction

between these properties of the catalytic system and a positive

mercury drop test. The control experiment showed that the

reason for the catalysis suppression is the redox-transmetalation

of the cyclopalladated (pre)catalyst.^29bHerein we report an

evaluation of the limits of the mercury poisoning test

applicability to CPC-catalyzed reactions.

As one would expect, the mercury poisoning test has been

widely used to estimate the mechanism of cross-coupling

processes, but the results have often been contradictory. In

accordance with Jones’s suggestion,^1cthe observations that

mercury(0) has no eﬀect on the Heck, Suzuki and related

reactions catalyzed by C,N-,^11d,15and C,P-palladacycles¹⁶or

N,C,N′-,¹⁷C,N,O-,^14c,dC,N,S-,^11aC,N,Se-,¹⁸P,C,P-,¹⁹and S,C,S-

pincer complexes^11fallow the exclusion of any catalytic cycles via

the unprotected palladium(0) intermediates. However, in only a

few studies, a logical homogeneous Pd(II)/Pd(IV) catalytic

cycle^11a,d,f,19bor homogeneous catalysis via molecular

palladium(II) species^17,19awas suggested. In Vicente’s re-

search,^14c,dthis conclusion was unambiguously conﬁrmed by a

rich set of additional testing experiments and ESI-MS detection

of two palladium(IV) intermediates in the catalytic process. The

opposite assumption about the homogeneous Pd(II)/Pd(0)

pathway has been made in other reports^15,16after a negative

mercury drop test was obtained, despite the lack of an induction

period in the kinetic curve¹⁶and the opportunity to regenerate

and reuse the catalyst.^16a,bAlthough the formation of strongly

protected soluble palladium(0) species was not proven, it may

be assumed in systems with C,P- or P,C,P-CPCs used as a

(pre)catalyst. The rare exception is the research of Singh’s team,

who not only conﬁrmed C,N(S)-palladacycle thermal decom-

position under catalysis conditions and isolated and charac-

terized in detail the nanoparticles (NPs) formed with Pd₇S

stoichiometry but also established their homogeneous catalytic

activity provided by palladium(0) atom leaching.¹⁵

RESULTS AND DISCUSSION

■

In this research, we worked to solve the following two main

problems: to assess the limits of mercury poisoning test

applicability for other CPC-catalyzed cross-coupling reactions

and to estimate the inﬂuence of the control test conditions on

the result.

Mercury(0) Testing of Diverse Azapalladacycles. The

ﬁrst problem arose from the fact that the sole known report on

palladacycle reactions with mercury(0) was devoted to imine-

derived CPCs and aimed at the preparative synthesis of planar

chiral ferrocenylmercuric chlorides.³⁰Under these circum-

stances, it was reasonable to assume that the similar anomalous

reactivity of high-valent palladium complex 1a with metallic

mercury to provide arylmercuric chloride 1b (L¹HgCl) as the

redox-transmetalation product^29bis due to the speciﬁc proper-

ties of the iminate ligand (Scheme 1).

More serious problems arise in the case of a positive mercury

test. It was shown that mercury(0) suppresses (completely or

partially)²⁰the catalytic activity in cross-coupling reactions of

palladium(II) cyclometalated C,N-,^20c,21C,P-,²²and C,S-

complexes²³and P,C,P-,^{2b,7b,20a,b,24}S,C,S-,^7a,9b,25Se,C,Se-,²⁶

and C,N,E (E = S, Se, Te)-pincers.²⁷This result was considered

by the authors as evidence of homogeneous catalysis with

molecular palladium(0) species or colloidal palladiu-

m(0),^{7a,b,9b,21e,f,22,24a}heterogeneous catalysis with palladium(0)

nanoparticles (NPs),^{2b,21a−d,23,24b,26}or a “cocktail” of homoge-

neous and heterogeneous pathways.^27,28According to the Jones

concept,^1ca positive mercury test may be consistent with a

catalytic cycle involving a palladium(0) intermediate. However,

such a conclusion in some studies was not convincing enough

because of an absence of any additional mechanistic

tests,^20c,24a,26discrepancy in the various test results,^2b,20b,21c,d

and a lack of the expected induction period in the kinetic

curve.^{9b,20,21a,b,d}The more serious drawback of most of the

above-mentioned mechanistic studies (excluding some re-

ports)^9b,24is the absence of the absolutely necessary control

experiments, including the mercury(0) reactions with the

starting (pre)catalyst and other catalysis participants; in these

circumstances, the mercury drop test interpretation must be

recognized as incorrect.^1a,d

Scheme 1. Redox-Transmetallation of the Catalyst rac-1a

To estimate the scope of this unusual reactivity, we performed

the main control experiment (required for the classic mercury

drop test)^1a,dfor a series of azapalladacycles derived from diverse

N-donor ligands (Chart 1). This set of potential (pre)catalysts

included complexes bearing a tertiary amino-group as an (sp³)

Chart 1. Structures of the Cyclopalladated Dimers Used in

the Present Research

We have proposed that if the alternative Pd(II)/Pd(IV)

catalytic cycle for cross-coupling is possible in principle then it

may operate either alone or in combination with the classic

Pd(II)/Pd(0) route. Previously, we developed a catalytic system

with the maximum contribution of the palladacycle-retaining

pathway of the Suzuki reaction that is necessary for the eﬃcient

chirality transfer in an asymmetric version of this process.²⁹The

following properties of this system satisﬁed this condition: The

catalyst can operate in air at room and reduced temperatures

B

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

N-donor on an arylene framework (2a, 3a) or a ferrocenylene

backbone (4a), and two more structures with (sp²)N-donors of

oxazolinyl (5a) or pyridyl (6a) heterocyclic rings in addition to

the nonmetallocenic planar chiral iminate C,N-dimers (R_pl)- and

rac-1a. To make the results of such a screening most compelling,

all control experiments were conducted on a preparative level,

aﬀording the possibility of spectral and structural character-

ization of the reaction products and mercury(0) of the highest

purity (99.999%) was used.

Inﬂuence of the Structure and Conditions on the

Control Experiment Result. This series of control experi-

ments showed that all C,N-palladacycles interact with metallic

mercury, aﬀording arylmercuric chlorides (Chart 2), although

duration compared to its highly soluble enantiopure form (R_pl)-

1a under the same conditions (entries 2 and 3, respectively).

The cross-coupling reactions are usually carried out either

under inert gas or in air; therefore, mechanistic testing and

diverse control experiments should be conducted strictly in the

same atmosphere. As far as we know, estimates of the inﬂuence

of this factor are extremely rare. They are limited by the mercury

poisoning test performance for the phosphite C,P-palladacycle-

catalyzed Suzuki−Miyaura cross-coupling reaction both in air

and under argon with no diﬀerence in the results of the ﬁrst run

(90−100% yield of the product)^16a,bbut with controversial

results for the second cycle.^16aTherefore, it was necessary to

assess the impact of these conditions on the results of our control

experiments. We did not ﬁnd signiﬁcant diﬀerences in the

reactions of C,N-dimer (S_C)-5a with metallic mercury

performed under argon and air: in both conditions redox-

transmetalation product (S_C)-5b was isolated in almost identical

yields (93 and 90%; entries 11 and 12, respectively).

Chart 2. Structures of Isolated Organomercuric Chlorides

1b−6b

There is one more important factor that determines the rate of

the redox-transmetalation process, namely, the mercury(0)-to-

palladium(II) ratio. As an illustration of its eﬃciency, we can

compare the results of decreasing the mercury(0) excess from

the standard 330 equiv to only 20 equiv in the redox-

transmetalation of dimer 5a at the same temperature: Even

after an 8-fold increase in the reaction duration, the yield of

arylmercuric chloride 5b was noticeably reduced (93 and 79%;

entries 13 and 11, respectively). It should be noted that in the

application of the mercury drop test, this parameter has varied

over a very broad range starting from less than 100 equiv of

mercury(0)^7b,22,24ato 4000−20 000 equiv,^{14d,19a,21b,d}without

any explanation regarding the choice of the value. To emphasize

the importance of this factor, we can mention a rare example of

its estimation. A drastic dependence of the mercury poisoning

eﬀect on the Hg/Pd ratio was reported in Suzuki and Heck

reactions (at 110 and 130 °C, respectively) catalyzed by ylide

C,P-palladacycles: the yield of the cross-coupling product

decreased from 73 to 85% in the presence of 100 mercury(0)

equivalents down to trace quantities at 300 equiv.²²From this

example, it becomes obvious that the lowering of the

mercury(0) excess in the control experiment compared with

that used in the mercury poisoning of the catalytic process leads

to incorrect conclusions from this kind of mechanistic testing.

Metallic Mercury Reactivity. At ﬁrst glance, our results

from the control experiments may seem anomalous from the

standpoint of the widely accepted view on the interaction of

metallic mercury with only zero-valent metals^1c,7,9or (much

more rarely) with their molecular complexes.⁸However, there is

series of reports (mainly dated in the previous century) that may

raise doubts as to the validity of this widespread opinion.

The most powerful argument against this common mis-

conception is provided by the preparative synthesis of a series of

cyclomercurated compounds via redox-transmetalation by

metallic mercury of chiral azapalladacycles derived from

ferrocenylimines under very mild conditions at room temper-

ature. These cyclomercurated compounds were isolated in very

high yields (92−98%), exceeding the eﬃciency of direct

cyclomercuration of imine ligands by the standard method.

Their structure was convincingly conﬁrmed by elemental

analysis, optical rotation values, IR spectral data, and selected

¹H NMR spectral data, as well as X-ray crystal structure data and

circular dichroism spectral data for one of 12 compounds.^30a

This report by Wu from 1999 remained the sole example of the

implementation of the redox-transmetalation of CPCs with

the eﬃciency of their redox-transmetalation is strongly depend-

ent on the CPC structure and solubility and on the testing

conditions (Table 1). All cyclopalladated C,N-dimers 1a−6a

reacted with metallic mercury in toluene even at room

temperature. Under these conditions, the diﬀerence in their

reactivity was especially pronounced: The yields of isolated

arylmercuric chlorides varied from ∼8% after 144 h for 2b to

71% at 96 h for 5b (entries 4 and 10, respectively). This process

could be considerably accelerated by the introduction of a base:

For example, in the presence of potassium ﬂuoride arylmercuric

chloride 5b was isolated after 9 h in a yield of 94% compared to a

yield of 71% after 96 h in the absence of base (entries 12 and 10,

respectively). The redox-active ferrocenylene backbone of

starting dimer 4a also makes a signiﬁcant contribution to the

acceleration of the transmetalation: After reaction at room

temperature for 3.5 h, mercurial 4b was isolated in a yield of

81%, the yield of its analogue 2b with a naphthylene backbone

and identical side chain was only 8% after 144 h, and starting

dimer 2a was recovered in an intact state in a yield of 61%

(entries 8 and 4, respectively).

At increased temperature (up to 70−90 °C), the trans-

formation of C,N-CPCs into arylmercuric chlorides was also

considerably accelerated. For example, arylmercurials rac-1b,

(S_C)-5b, and 6b were isolated after 1−3 h of heating in yields of

more than 90% (entries 2, 11, and 15, respectively), while the

same reactions of dimers rac-1a, (S_C)-5a, and 6a performed at

room temperature required 48−96 h (entries 1, 10, and 14,

respectively). As one might expect, the low solubility of the

starting μ-chloride cyclopalladated dimers makes some con-

tribution to the slowdown of the reaction. For example, the

redox-transmetalation of dimer rac-1a, which is practically

insoluble in toluene, required a 3-fold increase in the reaction

C

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

a

Table 1. Mercury(0) Poisoning of Diverse Palladacycles (Control Experiments)

a

Typical reaction conditions: mixture of the cyclopalladated dimer (∼0.05 mmol) and metallic mercury excess (∼33 mmol, 330 equiv) was

b

c

intensively stirred in toluene (∼15 mL) under air (if not stated otherwise). Isolated yield is presented. Experiments were conducted with a

racemic cyclopalladated dimer of extremely low solubility. The enantiopure dimer (R_pl)-1a was completely soluble in toluene, in contrast to the

d

e

f

g

insoluble racemic form. Starting cyclopalladated dimer was recovered in a yield of 61%. The reaction was performed under argon. Yield of pure

complex 4b (TLC and ¹H NMR data) isolated as red-brown oil; after multistage crystallization, one of its racemic diastereomers was separated in a

h

yield of 53% in the crystal state. The reaction was conducted in the presence of KF (10 equiv/Pd).

mercury(0) published before the beginning of our own

research.^29bBefore the report by Wu, the similar Pd^II/Hg⁰

redox-exchange was realized with a nontypical analogue of

CPCs, [{(η²,η¹C,C,C-L)Pd(μ-Cl)}₂] (L⁻= acetoxynorbornen-

yl), aﬀording the alkylmercuric chloride [(η¹C-L)HgCl] in a

yield of 30%.³¹In addition, we can mention the related redox-

transmetalation processes, namely, interaction of planar chiral

cyclopalladated ferrocenylimines (as μ-chloride dimers) with

zero-valent tin to aﬀord cyclometalated Sn(IV) derivatives

(S_pl,S_pl)-[(κ²C,N-L)₂SnCl₂].³²

tigation of mercury(0) reactions with diverse π-allyl palladium-

(II) complexes.³³It was shown that these reactions provide

allylmercuric halides or bis(allyl)mercurials (along with metallic

palladium) in high yields under mild conditions. As a rare

exception to this high reactivity, we can mention that the

triphenylphosphine derivative [(η³-All)PdCl(PPh₃)] of the

allylic μ-chloride dimer was found not to react with metallic

mercury.^33cThe authors proposed a mechanism for this

reaction, including the cleavage of the μ-halide bridges in the

π−AllPdCl molecule, π−σ-rearrangement of the π-allyl ligand,

causing cis-migration of the σ-bonded allyl group from

palladium to the mercury atom, and ﬁnal internal redox reaction

producing palladium(0) and alkylmercury chloride.^33c

As another valuable contribution to disproving the common

misconceptions regarding limited mercury(0) reactivity, we can

mention the Nesmeyanov’s research devoted to the inves-

D

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Moreover, eﬃcient mercury(0) interactions with palladium-

(II) compounds have even found analytical applications.³⁴

Several examples from platinum(II) chemistry may also be

mentioned. First, it was shown that high-temperature

thermolysis of organometallic platinum(II) complex R₂Pt(cod)

tertiary amino groups,^21b−fpyridine,^21aor an oxazoline N-

donor,^20cwith our CPCs 2a−6a tested in the control

experiments (Table 1) allows us to assume a similar reactivity

of these palladacycles with mercury(0). Second, the high

temperature regime used for the mercury drop test in Suzuki−

Miyaura and Mizoroki−Heck reactions (from 80 to 140 °C)

should signiﬁcantly speed up the redox-transmetalation process.

Third, inhibition of catalysis at the introduction of mercury(0)

at the starting point of the reaction^21a−ccan serve as evidence for

the interaction of Hg(0) with the (pre)catalyst and not with the

product of its activation. Fourth, the lack of the expected

induction period in the kinetic curve^20c,21a,b,dand some

contradictions between the mercury poisoning and other testing

results^21c,dare also important evidence of the alternative

interpretation of the positive mercury test. Finally, all these

facts indicate that the most likely reason for the positive

mercury(0) poisoning test may be the redox-transmetalation of

the palladium(II)-containing C,N-metallacyclic (pre)catalyst,

not the suppression of catalysis via Pd(0)/Hg(0) interaction.

The authors can conﬁrm or refute the alternative explanation of

this test result with a simple control experiment.

Conﬁrmation of the Structure of the Redox-Trans-

metalation Products. The next task of our research was to

provide the most convincing evidence of the structure of

organomercuric chlorides 1b−6b because (i) they were isolated

under unusual circumstances and (ii) they are mainly new

compounds. Among mercurials 1b−6b, (S_C)-3b,³⁹and rac-4b⁴⁰

were previously prepared by classic routes based on the

interaction of mercury(II) chloride with the corresponding

metalated ligand: (S_C)-L³Cu,^39b(S_C)-L³Li,^39aor rac-L⁴Li.⁴⁰To

solve our structural problem, we used ¹H, ¹³C{¹H}, and

¹⁹⁹Hg{¹H} NMR spectroscopy, X-ray diﬀraction analysis of

four mercurials, and density functional theory (DFT)

calculations.

Crystal Structure of Mercurials. The X-ray diﬀraction

study of arylmercurial rac-1b was reported previously without a

discussion of its structure;^29bin this work we performed a

crystallographic study of other organomercuric chlorides (R_C)-

2b, (R_CS_pl)*-4b, (S_C)-5b, and 6b (Table 2, Figures S41−S44)

isolated in our control experiments. Among these complexes,

only a derivative of the tertiary α-methylbenzylamine, (S_C)-3b,

had been previously crystallographically characterized.^39aWith

the exception of the arylmercuric chloride (R_C)-2b, all

remaining complexes have only one or no close enough

analogues in the rich collection of related mercurials (Tables

S1−S6); therefore, for their structure discussion we were forced

to use more distant analogues (Chart 3).

The interpretation of the X-ray diﬀraction data obtained in the

previous century sometimes needs to be signiﬁcantly adjusted by

taking into account the modern revision of the van der Waals

radii (R_vdW): Instead of the previously widely accepted Bondi

value of 1.55 Å for the mercury atom,⁴¹the recently

recommended values are 1.73−2.00 Å⁴²(corresponding to the

ab initio-calculated R_vdWvalue equal to 1.75 Å)⁴³or 2.1−2.2 Å.⁴⁴

Taking into account the recommended crystallographic van der

Waals radii of mercury and nitrogen (2.00 and 1.6 Å,

respectively),^44awe can see that the Hg−N distances observed

in the structures of isolated organomercurials 1b, 2b, 4b, and 5b

(2.59−2.82 Å) are essentially shortened in comparison with the

sum of their van der Waals radii (3.6 Å), even after their

correction based on packing eﬀects (∼0.2 Å).⁴⁵These

parameters allow us to propose the formation of optimal ﬁve-

membered mercuracycles in the crystals of 1b, 2b, 4b, and 5b.

t

(R = BuCH₂, cod = cycloocta-1,5-diene) in the presence of

mercury(0) results in the formation of dialkyl mercurial HgR₂in

high yield.³⁵Second, complete poisoning of high-valent

platinum catalysts, (cod)Pt^IICI₂and even H₂Pt^IVCl₆(Speier’s

catalyst), was observed after their long treatment with

mercury(0) before introduction of the other reaction partic-

ipants.^8a,36Among the other redox processes on a mercury(0)

surface we can also mention the formation of R₂Hg mercurials

(R = aryl, alkyl) from thallium(III) organometallic compounds,

TlR₃or R₂TlHlg.³⁷

Consequences for Catalysis Studies. Therefore, mer-

cury(0) reactions with homogeneous molecular metal com-

plexes in elevated formal oxidation states cannot be considered

exotic precedents. Thus, in the case of a positive mercury drop

test it is absolutely necessary to perform additional control

experiments to ensure that the (pre)catalyst does not react with

mercury(0) under the catalysis conditions.^1a,b,38However, to

the best of our knowledge, among the many dozens of

publications on the use of the mercury poisoning test for

mechanistic elucidation of CPC-catalyzed reactions, only three

examples of such control experiment performance are known.

All these probes were made for catalytic systems with pincer

(pre)catalysts and using only NMR control.^9b,24Thus, it was

shown that phosphinite P,C,P-pincer palladium(II) complexes

do not react with mercury(0) alone but undergo oxidation and

probably hydrolysis in the presence of a mercury(0) and

Cs₂CO₃mixture. This assumption was based on the observed

similarity of the ³¹P{¹H} NMR chemical shifts with those for

known phosphine oxide ⁱPr₂PhP(O) and phosphinate ⁱPr₂P-

(O)OPh.²⁴

The third version of the reported control experiment^9bseems

rather inconclusive. First, it was performed in the presence of too

low of a mercury(0) excess, namely, with only 20 equiv

compared with the 300−500 equiv used in this work for the

mercury poisoning of catalysis. Second (and most importantly),

the assumption of the intact state of the neutral [(κ³S,C,S-

L)PdCl] pincer (pre)catalyst in the presence of mercury(0) was

based on ¹H NMR spectral data conﬁrming the retention of the

pyridine (Py) coordination with palladium in the case of the

cationic derivative [(κ³S,C,S-L)Pd(Py)]BF₄, which was not used

either in the Heck coupling catalysis or in the mercury(0)

poisoning test. This probe cannot be recognized as a correct

control experiment, taking into account the known drastic

diﬀerence between the behavior in catalysis of the neutral pincer

(pre)catalyst [(κ³C,N,O-L′)PdI(κ²CO-L″)] and its cationic

dehalogenated derivative and the opposite results obtained

from the mercury(0) poisoning test for these species.^14c,d

A positive mercury poisoning test was reported for almost all

cross-coupling reactions catalyzed by C,N-palladacycles.^21a−f

This result was used as the basis for the assumption of the

leading role of palladium(0) NPs, colloidal or low-ligated

palladium(0) species in the catalytic processes. Since these

studies did not include any control experiments excluding the

possibility of (pre)catalyst deactivation due to its reaction with

mercury(0), an alternative explanation for the positive mercury

poisoning test must be discussed. Several arguments can be

made in favor of possible (pre)catalyst killing by mercury(0).

First, the close structural similarity of azapalladacycles bearing

E

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Table 2. Comparison of the Structural and Stereochemical Characteristics of Isolated Mercurials 1b−6b with Those of Their

a

Analogues

a

b

The ranges of the same parameters for related compounds are presented in round brackets (see the Supporting Information). Intramolecular

c

d

e

distance Hg···N. Intermolecular distance Hg···N′. Data only for known related arylmercuric chlorides (Table S3). Analogues are unknown.

f

g

Intermolecular Hg−Cl′ contacts in the plane approximately orthogonal to the mercuracycle. The organomercury chloride crystallizes in the form

of an inﬁnite chain of mutually orthogonal dimers connected by stronger chloride bridges in the axial position and weaker equatorial bridges.

h

i

Intermolecular Hg−Cl′ contacts nearly in the plane of the mercuracycle. The interplanar angle {HgNC^α}/{HgC¹C²C^α} denoted as ω_envwas used

j

k

for characterizing the mercuracycle envelope-shaped bending. Data for all known related arylmercuric halides (Table S3). Mercuracycle twisting,

ϖ_av, is calculated as the average of the absolute values of all intrachelate torsion angles.

In general, all structures of these isolated organomercuric

chlorides may be considered typical representatives of the

corresponding organomercurials.^45,46In accordance with the

preferable sp-hybridization of mercury(II), they contain an

almost linear C−Hg−Cl segment, with the corresponding angles

varying over a rather narrow range 171.8−179.1° (Table 2).

Their other geometric characteristics, such as the Hg−C, Hg−

N, and Hg−Cl bond lengths, and valent angles either fall into the

intervals of the values for their known analogues or lie close to

the boundaries of these intervals (Tables S1−S6). The

geometric parameters of all ﬁve-membered mercuracycles are

similar to those of their nearest analogues. In derivatives of

tertiary amines (2b, 4b), mercuracycles are highly puckered in

the envelope-like conformation, with the parameter ϖ_av

(average of the absolute values of all intrachelate torsion angles)

equal to 29.0−30.7° and an interplanar angle {HgNC^α}/

{HgC¹C²C^α} (ω_env) of 42.4−43.2° (Table 2). In contrast, the

mercurials with (sp²)-hybridized N-donors (1b, 5b) contain an

almost ﬂat mercuracycle, with ϖ_avand ω_envvalues varying in the

ranges 1.6−6.9 and 2.4−9.9°, respectively. It should be noted

that there are a few main distinctive structural and stereo-

chemical features of our new mercurials.

Surprising, among the extensive collection of mercurated

arylimines in the Cambridge Crystallographic Data Centre

(CCDC), we have not found close enough analogues (not only

stereochemical but also structural analogues) to the non-

metallocenic planar chiral organomercuric chloride rac-1b. As a

result, for its geometric parameters analysis, we were forced to

use the simplest achiral analogues, namely, the bromide⁴⁷and

azides⁴⁸of mercurated N-arylbenzaldimines (A) and related

planar chiral organomercuric chlorides derived from N-

arylferrocenylaldimines or -ketimines (B)⁴⁹(Table S2). In the

complex rac-1b, the Hg−C and Hg−Cl bonds are somewhat

elongated in comparison with models A and B, while the Hg−N

F

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Chart 3. Generalized Structures of Models A−F

Figure 2. Molecular structures of the organomercuric chloride (R_C)-2b.

Hydrogen atoms are omitted for clarity, and only selected atoms are

labeled. Thermal ellipsoids are given at 50% probability level.

similar to that reported for the corresponding C,N-pallada-

cycles.⁵¹As an additional peculiarity of the mercurial (R_C)-2b,

we can note that it exists in the crystal as a monomer, in contrast

to the extensive systems of intermolecular Hg···Cl secondary

interactions typical for its analogues of type C (Chart 3).

The most amazing feature of ferrocenylmercuric chloride 4b

is its chelated structure with an intramolecular Hg−N bond of

2.82 Å (Table 2, Figure 3a), which is closer to the sum of the

bond in compound 1b is noticeably stronger than that in

analogues A and B. Racemic mercurial 1b exists in the crystal as a

chloride-bridged dimer containing both (R_pl)- and (S_pl)-

enantiomers, with the central four-membered core {Hg(μ-

Cl)₂Hg} oriented nearly orthogonally between two approx-

imately parallel mercuracycles with an interplanar angle

{Hg₂Cl₂}{C¹C²C^αNHg} equal to 82.45° (Figure 1). It should

Figure 3. Molecular structure of the organomercuric chloride

(R_C,S_pl)*-4b (a). Formation of an anti-dimeric structure in the crystal

for ferrocenylethylamine mercurial (R_C,S_pl)*-4b via the weak

intermolecular interactions Hg···Cl (b). Hydrogen atoms are omitted

for clarity, and only selected atoms are labeled. Thermal ellipsoids are

given at 50% probability level.

covalent radii of these atoms⁵²than to the sum of their van der

Waals radii (2.34 and 3.65 Å, respectively). In contrast,

mercuracycles were not detected among the related derivatives

of α-nonsubstituted tertiary ferrocenylmethyl amines (type D),

in which the intramolecular Hg···N distances are larger than 4.0

Å⁵³(Table S4). According to the negative or positive signs of the

C¹C²C^αN torsion angle in the isolated racemic mixture of

(R_CS_pl)- and (S_CR_pl)-diastereomers of mercurial 4b (−50.22 or

50.22°, respectively), the mercuracycle conformation in them

must be described as λ(R_C) or δ(S_C), respectively, with an

equatorial position of the α-methyl group in both diastereomers,

which is evident from the torsion angle C¹C²C^αC(Me) equal to

−179.1°. These conformational peculiarities most likely deﬁne

the dimerization of organomercuric chloride (R_CS_pl)*-4b via

two chloride bridges, with a central four-membered fragment

{Hg(μ-Cl)₂Hg} oriented nearly orthogonally between two

approximately parallel mean coordination planes (Figure 3b).

For comparison, similar α-nonsubstituted ferrocenylmethyl-

amines in known mercurials D prefer to function mainly as C,N-

bridging ligands at rather short intermolecular Hg···N′ distances

(2.77−2.93 Å). In addition, the metal participates in the

secondary intermolecular Hg···Cl′ interactions oriented inter-

mediately between the axial and equatorial positions with

torsion angles ∠Cl′HgC¹C²reduced by 32−45° compared to

180° (Table S4).

Figure 1. Fragment of the crystal packing of mercurial rac-1b showing

the dimerization via two intermolecular Hg···Cl′ bridges in the

approximately axial position.

be noted that intermolecular Hg···Hlg′ interactions are not

found in model bromide A (Ar = Ph, X = Br) and chlorides of

type B. In the dimer rac-1b, the N-aryl ring is rotated relative to

the mercuracycle to 73.3°, while the corresponding angles vary

widely from 2.4 to 88.1° in model structures A and B.

The C,N-mercuracycle in compound (R_C)-2b with a

naphthylene-1,2 backbone is ﬁxed in the crystal in the δ(R_C)

conformation with an axial position of the Me group at the α-

carbon stereocenter, which is evident from the torsion angle

C¹C²C^αC(Me) equal to −82.7° (Figure 2). In contrast, the

known analogues of type C with phenylene^39aor naphthylene-

2,3⁵⁰backbones contain the similar mercuracycle in the λ(R_C)

or δ(S_C) conformation with an equatorial orientation of the α-

methyl group, which is evident from the variation of the absolute

value of the same angle C¹C²C^αC(Me) varied in the range

166.2−174.2° (Table S3). This contrasting stereochemistry is

We can note two diﬀerences of mercurial (S_C)-5b bearing a

chiral oxazolinyl N-donor from its closest achiral analogue

(E¹)⁵⁴and from the less similar organomercuric chloride

derived from the 2-ferrocenylnaphthoxazole (E²)⁵⁵(Chart 3,

G

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Table S5). First, our complex (S_C)-5b crystallizes as inﬁnite

double-folded tapes consisting of mutually orthogonal dimers

connected by stronger chloride bridges in the axial position and

weaker equatorial chloride bridges at Hg···Cl′ and Hg′···Cl

distances equal to 3.187 and 3.535 Å, respectively (Figure 4).

which prefer Hg···N′ intermolecular interactions rather than

C,N-chelation if the latter leads to the formation of a six-

membered metallacycle. It should be noted that the CCDC does

not contain any data for organomercurials with six-membered

C,N-mercuracycles. However, coordination compounds with

six-membered N,N-chelate rings formed by diamine⁵⁶or

diimine ligands⁵⁷are known. In contrast to the T-shaped

functionalized organomercuric chlorides, they contain the (sp³)-

hybridized mercury(II) atom in a distorted tetrahedral

coordination environment with a rather strong Hg−N bonds

(2.246−2.475 Å) inside the chair-shaped chelate ring. In

contrast to T-shaped functionalized organomercuric chlorides,

these chelates contain the (sp³)-hybridized mercury(II) atom in

a distorted tetrahedral coordination environment with rather

strong Hg−N bonds (2.246−2.475 Å) inside the chair-shaped

chelate ring.

DFT Calculations of Organomercurials. To estimate the

possibility of formation of six-membered C,N-mercuracycles

and to exclude the eﬀect of crystal packing, we performed DFT

calculations and geometry optimization for arylmercury(II)

chloride 6b and its chelated model with a ﬁve-membered

mercuracycle (κ²C,N-F¹) in the gas phase. The two most

important diﬀerences between the experimental and calculated

structures should be noted (Figure 6, Table S12): the rotation of

Figure 4. Molecular structure of organomercuric chloride (S_C)-5b (a).

Fragment of the crystal packing of mercurial (S_C)-5b illustrating the

formation of inﬁnite double folded tapes via intermolecular chloride

bridges between the mutually orthogonal dimers with stronger Hg···Cl′

interactions in the axial position than in the equatorial position at

distances equal to 3.187 and 3.535 Å, respectively (b). Hydrogen atoms

are omitted for clarity, and only selected atoms are labeled. Thermal

ellipsoids are given at 50% probability level.

Conversely, intermolecular secondary interactions of this kind

were not found in the crystal of its achiral analogue E¹, and only

one axial chloride bridge between two nonequivalent organo-

mercuric chlorides at a distance of 3.245 Å was observed in the

case of 2-ferrocenylnaphthoxazole derivative E². Second, the

mercuracycle of complex (S_C)-5b possesses puckering similar to

that found for its naphthoxazole analogue E², in contrast with

the ideally planar metallacycle in oxazoline analogue E¹with ϖ_av

values equal to 6.9, 7.5−5.2, and 0.0, respectively, despite the

comparable Hg−N bond lengths in the ﬁrst two compounds.

The only exception in our series of mercurated compounds is

arylmercurial 6b with an intramolecular Hg···N distance

elongated up to 3.27 Å but containing a shorter intermolecular

Hg···N′ contact of 3.004 Å (Figure 5, Table S1). Its structure is

Figure 6. Energy proﬁle of the rotation of mercurial 6b about the

(Py)C²′−O bond.

the pyridyl ring from the nearly coplanar position in the crystal

ca. 20° of the optimized structure (rot³) with torsion angles

C²OC²′N equal to 4.0 and −19.67°, respectively, and a

shortening of the intramolecular Hg···N distance from 3.253 Å

in the crystal to 2.915 Å in the gas phase. The last value is close to

the upper limits of the characteristic ranges typical for ﬁve-

membered C,N-mercuracycles bearing (sp²)-hybridized nitro-

gen donors: 2.69−2.90 Å for iminoaryl derivatives (Table S2) or

2.60−2.80 Å for pyridyl-donor analogues (Table S6). The

observed evidence of weak intramolecular Hg···N interactions

calculated for the gas phase structure of mercurial 6b may be

explained by excluding under these conditions any competing

intermolecular interactions such as Hg···N′ and Hg···Cl′, which

were detected in the crystal state.

Figure 5. Molecular structure of the organomercuric chloride 6b (a). A

fragment of the crystal packing of the arylmercury chloride 6b showing

rather short intermolecular contacts Hg···N between the chains of

nearly parallel dimers formed due to intermolecular Hg···Cl bridges in

the mean coordination plane (b). Hydrogen atoms are omitted for

clarity, and only selected atoms are labeled. Thermal ellipsoids are given

at 50% probability level.

composed of chloride-bridged dimers formed due to the

intermolecular Hg···Cl′ contacts at a distance of 3.292 Å,

which is less than the sum of the van der Waals radii of these

atoms (3.85 Å).^44aAn unusual property of this structure is the

anomalous, almost coplanar disposition of the central four-

membered core {Hg(μ-Cl)₂Hg} relative to the phenylmercuric

fragment, with the interplanar {Hg₂Cl₂}{PhHgCl} angle equal

to 8.77° (Figure 5). The pyridine rings of these dimers are

rotated relative to the phenylmercuric chloride mean plane by

60.98° to connect the adjacent parallel columns of dimers via

intermolecular Hg···N′ contacts at a distance of 3.004 Å. Thus,

arylmercurial 6b structure is typical of mercury(II) compounds,

The rotation of the pyridine ring about the C²′−O bond of the

2-phenoxy-pyridine ligand of mercurial 6b revealed three

possible rotamers (rot¹−rot³) formed via transition states TS1

and TS2 with barriers of 3.5 and 6.0 kcal/mol respectively

(Figure 6). The parameters of rotamer rot³correspond to its

chelated form with a very weak intramolecular Hg···N

interaction (bond order, 0.14). However, despite intermediate

H

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

rotamer rot²having higher energy (ΔG 1.7 kcal/mol) than

rotamer rot³, the most stable form was dechelated rotamer rot¹

with an energy of only 0.2 kcal/mol lower than that of the C,N-

chelated mercurial.

The nature of the secondary Hg···N intramolecular

interaction in the mercurial 6b was estimated using Bader’s

atoms-in-molecule (AIM) theory.⁵⁸The topological analysis of

electron density at the Hg···N bond (Figure 7a) revealed the

To estimate the inﬂuence of the chelate ring size on the

mercurial stability, we also performed similar DFT calculations

for the known analogue F¹(L′HgCl) derived from 2-

phenylpyridine (HL′) and bearing a ﬁve-membered mercura-

cycle.⁵⁹Its optimized structure (Table S13) contains a stronger

Hg−N bond (2.661 Å) of higher order (0.23). The rotation of

the pyridyl ring about the single C²−C^2′bond reveals the higher

stability of the C,N-chelated form rot^1′compared to dechelated

rotamers rot^2′and rot^3′(5.4 kcal/mol) with rotation barriers of

9.0−9.5 kcal/mol (Figure S40). The enantiomeric nature of

these helical rotamers is evident from the opposite signs of the

torsion angle NC^2′C²C¹, equal to −139.02 and +139.09° in rot^2′

and rot^3′, respectively. The topological analysis of the optimized

F¹structure (Figure 7b) provides the following parameters for

the Hg−N bcp: slightly higher total electron density ρ(r_c) at the

bcp (0.03 au), increased values of the Laplacian ∇²ρ(r_c) (0.11

au), and a |λ₁\λ₃| ratio of 0.18. These parameter values indicate a

slightly higher stability of the Hg−N bond in the ﬁve-membered

mercuracycle of the model mercurial F¹compared to its six-

membered counterpart 6b.

Figure 7. Bond (red) and cycle (yellow) critical points for the six-

membered mercuracycle 6b (a) and its ﬁve-membered analogue F¹(b)

according to topological analysis in AIM theory.

Unfortunately, DFT calculations of mercurated nitrogen

donors are very limited,^47,48,60and only two reports were

devoted to the mercurials bearing (sp²)-hybridized nitrogen

donors.^47,48It was shown that the secondary Hg···N intra-

molecular interaction energy of the mercurated benzaldimine

bromides L′HgBr (A¹) is on the order of 2.5−3 kcal/mol.⁴⁷An

energy diﬀerence of 6.4 kcal/mol was found between the

chelated and dechelated rotamers of azidomercurated benzaldi-

mine L′HgN₃. The topological parameters ρ(r_c) and Laplacian

bond critical point (bcp) with the following parameters: a low

total electron density ρ(r_c) at the bcp (0.02 au), low positive

value of Laplacian ∇²ρ(r_c) (0.06 au), and ratio of the

perpendicular contractions of ρ to its parallel expansion,

|λ₁\λ₃| (0.16). These topological properties indicate the

formation of an extremely weak noncovalent bond or closed-

shell interaction.

a

Table 3. ¹⁹⁹Hg{¹H}, ¹H and ¹³C{¹H} NMR Spectral Parameters of Organomercuric Chlorides 1b−6b

a

Numbering scheme for complexes 3b−6b: The carbon directly connected to mercury is ﬁrst, with increasing carbon numbers in the direction of a

substituent. However, for mercurials (R_pl)-1b and (R_C)-2b possessing ligands with established numbering conventions, such conventions were

maintained. The minor diastereomer parameters were extracted from the spectra of a mixture of both diastereomers.

b

I

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

∇²ρ(r_c) of the iminate ﬁve-membered mercuracycle were equal

contribution from the spin−spin coupling via Hg ← NC^α−H

bonds (³J_HHgconstant) inside the mercuracycle cannot be

excluded since, in the crystal of 1b, the shortest Hg−N bond

distance was 2.586 Å, compared to 2.620−2.824 Å for

mercurials 2b−5b (Table 2). The ¹³C{¹H} NMR spectra of all

mercurials 1b−5b reveal the interaction of the α-carbon atom

with mercury(II) with ³J_CHgconstant values ranging from 118 to

26 Hz. We propose that such variations can be mainly explained

by the known dihedral angle dependence of the J_CHgconstant

values,^46dalthough in the case of mercurial 1b, an additional

contribution from Hg−N−^αC spin−spin coupling (²J_CHg

constant) cannot be excluded.

In principle, the most reliable information regarding the

retention of nitrogen-to-mercury coordination in solution could

be obtained from the ¹⁹⁹Hg-¹³C coupling constants for exocyclic

N-substituents. However, only in the ¹³C{¹H} NMR spectra of

mercurial 5b bearing an oxazolinyl N-donor were satellites

detected for a very distant asymmetric carbon atom (C⁹), with a

formal ⁵J_CHgconstant equal to 14 Hz. This can be explained by a

more eﬃcient spin−spin coupling through the chain Hg−C¹

C²−C^αN−C⁹of double bonds (⁵J_CHgconstant), with a

possible contribution from Hg−N−C⁹spin−spin coupling

(²J_CHgconstant). Thus, only mercurials with (sp²) nitrogen

donors showed weak indications of possible chelation of such

ligands. The absence of any signs of the ¹⁹⁹Hg−¹³C interaction

with the NMe₂carbons of 2b−4b, with the ipso-carbon of the N-

aryl substituent in 1b or with C¹¹carbon of the pyridine ring in

6b points to a predominantly dechelated state of mercurials 2b−

4b and 6b in solution at ambient temperature.

to 0.026 au and 0.027 au, respectively.⁴⁸

Structure of the Organomercuric Chlorides in Sol-

ution. The structure and stereochemistry of arylmercuric

chlorides 1b−6b isolated in our control experiments were

conﬁrmed by ¹H, ¹³C{¹H}, and ¹⁹⁹Hg{¹H} NMR spectroscopy,

with signal assignments based on the gCOSY, gHMQC, and

gHMBC techniques. It should be noted that the NMR spectral

studies were reported only for mercurial (S_C)-3b,³⁹while its

ferrocenyl analogue rac-4b was characterized only by elemental

analysis.⁴⁰We succeeded in the isolation of one of its two

racemic diastereomers, namely, the major one, (R_CS_pl)*-4b; the

relative conﬁgurations of the α-carbon center and planar

chirality were established by X-ray diﬀraction analysis of this

predominant diastereomer (vide supra).

The spectral data for organomercuric chlorides 1b−6b are in

agreement with the recognized trends in the NMR character-

istics of this class of mercurials,^46d,61which conﬁrms their

structure. The ¹⁹⁹Hg NMR chemical shifts for arylmercuric

chlorides 1b−3b, 5b, and 6b were observed from −905 to

−1115 ppm, while a highﬁeld shift to −685 or −734 ppm was

found for diastereomeric ferrocenylmercuric chloride 4b (Table

3). These values are close to the previously reported values for

related organomercury chlorides (Tables S7−S11).

The spin−spin coupling of the ¹⁹⁹Hg nucleus with the proton

and carbon nuclei of the organomercurials provides the most

important characteristics of their ¹H and ¹³C{¹H} NMR spectra,

which can serve as convenient tools for detecting the redox-

transmetalation products formed during the mercury drop test

or corresponding control experiments. In the ¹H NMR spectra

of arylmercuric chlorides, the most useful characteristic may be

Dynamic NMR of the Organomercuric Chlorides.

Dynamic NMR of the organomercuric chlorides was undertaken

to clarify the possibility of retaining Hg···N interactions in

solution and to estimate the quantitative aspects of this process.

For this goal, mercurated tertiary amines (R_C)-2b and (R_C,S_pl)*-

4b bearing two diastereotopic NMe groups were used as

examples. Previously, the dynamic behavior was studied at a

qualitative level only for arylmercuric chlorides (S_C)-3b³⁹and

(R_C)-C⁵⁰and for their α-unsubstituted ferrocenyl analogue of

type D where R = Me (rac-D¹, Chart 3).^53,53b

3

the J_HHgconstants based on the eﬃcient ¹⁹⁹Hg nucleus

interaction with the ortho-proton of the metalated aromatic

ring, possessing rather large values: For example, ³J_HHgconstants

equal to 187−223 Hz were found for mercurials 2b, 3b, 5b, and

6b (Table 3). The characteristic satellites due to the interaction

of mercury with the meta- and para-protons of the same

aromatic ring have much lower spin−spin coupling constants:

4

5

42−78 Hz for J_HHgand 17 Hz for J_HHg. Moreover, mercury

satellite detection is often problematic due to strong overlapping

signals in the ¹H NMR spectra of compounds with complicated

hydrocarbon skeletons.

The temperature dependence of the ¹H NMR spectra of the

mercurial (R_C)-2b in CDCl₃solution was studied in the range

from −45 to 55 °C. It is important that even at ambient

temperature, the spectrum indicated the nonequivalence of the

diastereotopic N-methyl groups: two broadened signals were

observed for their protons at δ_H2.15 and 2.46 ppm, with their

half width equal to 120 Hz (Figures S36 and S38). The slow

exchange limit was achieved at −15 °C, when two narrow

anisochronous signals (Δν_1/23.6 Hz) were observed for N-

methyl protons at 2.05 and 2.65 ppm. The simulated ¹H NMR

spectra of (R_C)-2b and the exchange rate constants are

presented in Figure S36. The following activation parameters

of the dynamic process for mercurial (R_C)-2b were found:

Therefore, in a practical sense, the ¹³C{¹H} NMR spectra are

more useful for organomercurial detection in solutions. The

signals of the mercury-bonded carbon of the metalated aromatic

ring in the ¹³C{¹H} NMR spectra of arylmercuric chlorides 2b,

3b, 5b, and 6b are ﬂanked by satellites arising from ¹³C−¹⁹⁹Hg

1

spin−spin coupling, with very high J_CHgconstant values of

2378−2567 Hz. The remaining ¹⁹⁹Hg−¹³C coupling constants

for the metalated aromatic ring in the spectra of 1b−3b, 5b, and

6b decrease from 214 to 19 Hz in accordance with the standard

regularity^61ain the sequence J_CHg≫ J_CHg> J_CHg> J_CHg

(Table 3).

1

3

2

4

ΔG₂₉₈^⧧= 13.7 0.2 kcal/mol, ΔH₂₉₈^⧧= 16.0 0.1 kcal/mol,

⧧

The spectral characteristics of the side chain are primarily of

interest to clarify the fate of the mercuracycle after organo-

mercuric chloride dissolution. The ¹H NMR spectra of

mercurials 1b−6b are not suitable to solve this problem, since

only in the case of arylimine-derived mercurial 1b was the ¹⁹⁹Hg

coupling with the α-methine proton detected with a long-range

⁴J_HHgconstant equal to 10 Hz. The main reason for a rather

eﬀective ¹⁹⁹Hg−¹H interaction in this case lies in the sp²-

hybridization of the α-carbon atom providing the ideal planarity

of the Hg−C⁴C⁵−C^α−H chain. However, an additional

and ΔS₂₉₈= 7.6

0.2 cal/mol/deg (the Eyring plot is

presented on the Figure S37).

For comparison, it should be noted that only one resonance

1

was observed for the NMe₂group in the H NMR spectra of

analogues (S_C)-3b³⁹and (R_C)-C⁵⁰measured at room temper-

ature, while two anisochronous resonances for this group were

observed only at temperatures below −70 or −60 °C,

respectively. Such dynamic behavior is explained by the

retention of Hg−N coordination, resulting in a blocked

inversion at the nitrogen on the NMR time scale at low

J

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

temperatures, while this bond cleavage at ambient temperature

oﬀers an opportunity for fast pyramidal inversion at the nitrogen.

However, signiﬁcant diﬀerences in the dynamic behavior of

mercurial (R_C)-2b and its analogues (S_C)-3b and (R_C)-C allow

us to assume a considerable inﬂuence of steric eﬀects on the

lability extent of the related organomercuric chlorides. The

equilibrium between species bearing a monodentate aryl ligand

or a bidentate weakly κ²C,N-bonded amine may be signiﬁcantly

shifted toward the latter for the (R_C)-2b complex derived from

naphth-1-ylethylamine to avoid the steric hindrance between

C(8) hydrogen of the naphthalene ring and the α-Me or Me₂N

groups of the free-rotating N-decoordinated arylalkylamine

ligand (L²)⁻.

In contrast to α-naphthylethylamine derivative (R_C)-2b, the

¹H NMR spectrum of its ferrocenyl analogue (R_C,S_pl)*-4b in

CD₂Cl₂contains only one rather narrow singlet of NMe₂group

protons (Figure S39). Its broadening was observed at temper-

atures below −30 °C, and only at −85 °C did this signal shape

become close to that expected for the moment of coalescence.

Although we were unable to measure the exact diﬀerence

between the chemical shifts of the diastereotopic NMe₂group

signals at the slow exchange limit, the upper limit of the

magnitude of the dynamic process barrier was estimated as

ΔG₂₃₃^⧧< 9 1 kcal/mol.

For comparison, it should be noted that in the case of α-

unsubstituted analogue rac-D¹(Chart 3), dimethylamino group

protons remain isochronous even at −80 °C; the authors

propose that such ﬂuxional behavior means that the intra-

molecular Hg···N interaction is not preserved in solution.^53b

The diﬀerence in the degree of dynamic mobility of mercurials

(R_C)-2b and (R_C,S_pl)*-4b may be partly attributed to the

geometric requirements of their arylene frameworks, which are

six- or ﬁve-membered, respectively. In reality, the sum of the

angles Hg−C¹−C²and C¹−C²−C^αincreases from 236.8° for

(R_C)-2b in crystalline form (240° is expected for an ideal

hexagon) to 240.5° for (R_C,S_pl)*-4b and to an average value of

253° for a series of α-unsubstituted analogues rac-D (Chart 3,

Tables S3 and S4), which is close to the value of 252° expected

for an ideal pentagon.

The most important consequence of these geometry changes

is the increasing Hg···C^αdistance from 3.149 Å in (R_C)-2b to

3.320 Å in (R_C,S_pl)*-4b and 3.571 Å in α-unsubstituted

analogues rac-D. This should lead to the removal of the nitrogen

atom from mercury and reduce the ability of the N-donor to

interact with the metal.

with the conditions required for the control experiments and

mercury drop test conditions.

The structure of the isolated organomercurials was convinc-

ingly conﬁrmed by ¹H, ¹³C{¹H}, and ¹⁹⁹Hg{¹H} NMR

spectroscopy and crystallography. The behavior of the C,N-

mercuracycles bearing a rather weak and labile N···Hg bond was

discussed on the basis of the temperature dependence of the

NMR spectra and the thermodynamic parameters of the

dechelation process, calculated by the DFT method. The set

of the presented spectral data for the isolated organomercurials,

especially the ¹⁹⁹Hg-¹³C spin−spin coupling constant values, can

serve as a convenient tool for detecting the related redox-

transmetalation products formed during the mercury drop test

or corresponding control experiments. After ensuring that all the

necessary conditions are met, the ubiquitous mercury poisoning

test ceases to be the simplest possible test, but these conditions

are an important way to avoid erroneous mechanistic

conclusions from its application.

Since the rich (but unfortunately forgotten) mercury(0)

chemistry⁶²is not limited to the considered reactions (vide

supra), and the library of cyclopalladated (pre)catalysts is not

limited to the azapalladacycles, it is also necessary to determine

all the possible transformations of other C,E-palladacycles and

other participants in the catalytic system (including substrates,

reagents, and bases) occurring during the mercury poisoning

test. This research is now in progress by our group.

EXPERIMENTAL SECTION

■

General Information. The ¹H (400.0 MHz), ¹³C{¹H} (100.6

MHz), and ¹¹⁹Hg{¹H} (71.5 MHz) NMR spectra were recorded on the

Agilent 400-MR spectrometer. The measurements were carried out at

ambient temperature (unless otherwise speciﬁed) in CDCl₃solutions.

The chemical shifts are reported in δ-scale in parts per million relative to

residual CHCl₃(δ 7.26 ppm for ¹H or δ 77.16 ppm for ¹³C{¹H} NMR)

and relative to (CH₃)₂Hg as an external reference for the ¹¹⁹Hg{¹H}

NMR; constant J values are presented in Hz. The signal assignment was

based on the gCOSY, gHMQC, and gHMBC experiments. Dynamic

NMR study was performed using line-shape analysis of the spectra

acquired at diﬀerent temperatures. The exchange rate constant for each

temperature was determined using simulation algorithm DNMR3

program SPINWORKS 4.1.⁶³The activation parameters for the

exchange process were calculated using Eyring equation. Optical

rotations were measured with a A. Kruss Optronic P8000 polarimeter in

̈

a 0.25 dm cell at 20 °C. The melting points were measured on an

Electrothermal IA 9000 series device. The TLC on Silufol UV-254 was

used to follow the course of reactions. Compound puriﬁcation was

performed using short dry column⁶⁴or ﬂash-chromatography on silica

gel (60, Fluka).

CONCLUSION

■

Toluene was dried over CaCl₂, reﬂuxed over Na and then distilled

under argon. Hexane and light petroleum ether (40−70 °C) were

distilled from Na under argon. Anhydrous MeOH was prepared by

distillation from MeONa. Diethyl ether was dried over KOH, then

reﬂuxed and distilled from Na/benzophenone under argon. Chloro-

form and dichloromethane were passed through a short Al₂O₃column

(L 40/250, Fluka 60) and distilled from P₂O₅under argon. CDCl₃

(from Aldrich) was distilled from CaH₂under argon just before using.

KF (from Acrus) and metallic mercury of >99.999% purity (from Abcr)

were used as received.

Dimeric cyclopalladated complexes (R_pl)- and rac-di-μ-chloro-bis{4-

(N-2,6-dimethylphenyl)iminomethyl[2.2]paracyclophane-5-yl-C,N}-

dipalladium(II), (R_pl)-1a and rac-1a;⁶⁵(R_C)-di-μ-chloro-bis{1-(1′-

(N,N-dimethylamino)ethyl)naphthyl-2C,N}dipalladium(II), (R_C)-

2a;⁶⁶(S_C)-di-μ-chloro-bis{2-(1′-(N,N-dimethylamino)ethyl)phenyl-

C,N}dipalladium(II), (S_C)-3a;⁶⁷di-μ-chloro-bis[2-{1′-

(dimethylamino)ethyl}ferrocenyl-C,N]-dipalladium(II), rac-4a;⁴⁰

(S_C)-di-μ-chlorobis-{2-[(4′-tert-butyl)oxazolin-2′-yl]phenyl-C,N}-

The main goal of the presented research was to dispel the myth

of narrow mercury(0) selectivity and emphasize the absolute

necessity of control experiments that exclude the possibility of

cyclopalladated (pre)catalyst killing by metallic mercury as the

reason for a positive mercury poisoning test. The almost

complete disregard for this mandatory requirement^1a,b,d,38bis

based on the widespread misconception that completely rejects

the possibility of mercury(0) interaction with homogeneous

molecular complexes containing d⁸metals in high oxidation

states.^1c,7,9Contrary to these assumptions, our investigation of

the interaction of mercury(0) with diverse C,N-palladacycles has

shown the formation of organomercuric chlorides as a result of

their redox-transmetalation. We have established a signiﬁcant

dependence of this process’s eﬀectiveness on the palladacycle

structure, reaction conditions, mercury/palladium ratio and

base presence. These circumstances require strict compliance

K

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

dipalladium(II), (S_C)-5a;⁶⁸and di-μ-chloro-bis{2-(pyridinyl-2′-oxy)-

phenyl-C,N}dipalladium(II), 6a,⁶⁹were prepared by known methods.

Caution: Despite the arylmercury(II) compounds being generally quite

stable, the toxicity of organomercury(II) compounds is well-documented

and appropriate precautions should be taken in the handling of all

organomercury(II) compounds.

as almost colorless crystalline powder. The almost colorless needle-like

crystals of complex (R_C)-2b suitable for X-ray diﬀraction studies were

obtained by slow crystallization from a solvent mixture dichlorome-

tane/diethyl ether/petroleum ether. Data for (R_C)-2b: mp 159−161

°C. R_f= 0.59 (light petroleum ether/diethyl ether 4:1). [α]²_D²− 40° (c

0.25, CH₂Cl₂). Anal. Calcd for C₁₄H₁₆NClHg requires: C 38.72; H

1

Redox-Transmetalation Reactions of C,N-Palladacycles with

Mercury(0). (R_pl)-{4-(N-2,6-Dimethylphenyl)iminomethyl[2.2]-

paracyclophane-5-yl-C,N}mercury(II) chloride, (R_pl)-1b. A mixture

of enantiopure dimer (R_pl)-1a (0.0151 g, 0.0157 mmol) and metallic

mercury excess (1.8917 g, 9.4307 mmol, 277 equiv) in toluene (15 mL)

was intensively stirred at 90 °C for 1 h in air. At this stage the

palladacycle was completely reacted (TLC data). After removing the

metallic mercury, the light-yellow solution was evaporated in a vacuum

to dryness. The crude product was puriﬁed using short dry column

chromatography on silica (h = 4 cm, d = 2 cm; eluents: petroleum ether,

petroleum ether/diethyl ether 10:1, 7:1 and 5:1) to aﬀord arylmercuric

chloride (R_pl)-1b (0.0162 g, 0.0282 mmol, 90% yield) as light-yellow

amorphous powder. Data for (R_pl)-1b: mp 236−239 °C. R_f= 0.28

(petroleum ether/dichloromethane 3:2); 0.27 (toluene). [α]²_D²+507.6°

(c 0.11, dichloromethane). Anal. Calcd for C₂₅H₂₄NClHg requires: C

52.27; H 4.21. Found: C 52.67; H 4.32. ¹H NMR (CDCl₃): Aromatic

protons of the [2.2]paracyclophane moiety: δ 6.43 (dd, 1H, ³J_HH7.8,

⁴J_HH1.9, H¹³), 6.56 (dd, 1H, ³J_HH7.8, ⁴J_HH1.9, H¹²), 6.57 (d, 1H, ³J_HH

3.71; N 3.22. Found: C 38.68; H 3.60; N 3.16. H NMR (CDCl₃):

Protons of the aromatic moiety: δ_H7.48 (ddd, 1H, ³J_HH8.1, ³J_HH6.9,

³J_HH6.9, ⁴J_HH1.4, H⁶), 7.53 (ddd, 1H, ³J_HH8.3, ⁴J_HH1.8, H⁷), 7.56 (dd,

1H, ³J_HH8.1, ³J_HHg187, H³), 7.72 (dd, 1H, ³J_HH8.1, ³J_HHg54, H⁴), 7.87

(dd, 1H, ³J_HH8.1, ⁴J_HH1.8, H⁵), 8.05 (br.d, 1H, ³J_HH8.3, H⁸); side chain

protons: 1.42 (d, 3H, ³J_HH6.7, α-Me), 2.16 (br. s, Δν_1/2≥ 120 Hz, 3H,

NMe), 2.56 (br. s, Δν_1/2≥ 120 Hz, 3H, NMe), 4.48 (q, 1H, ³J_HH6.7, α-

CH). ¹³C{¹H} NMR (CDCl₃): Carbons of the aromatic moiety: δ_C

129.04 (J_CHg9, C⁵), 121.83 (J_CHg20, C⁸), 125.89 (J_CHg6, C⁶), 126.32

(J_CHg18, C⁷), 126.93 (J_CHg208, C⁴), 131.56 (J_CHg194, C⁹), 133.69

(J_CHg134, C³), 133.78 (C¹⁰), 145.01 (J_CHg2495, C²), 147.09 (J_CHg51,

C¹); side chain carbons: 23.45 (α-Me), 42.3 (br. s, NMe₂), 44.2 (br. s,

NMe₂), 60.97 (J_CHg106, α-CH). ¹⁹⁹Hg{¹H} NMR (CDCl₃): δ_Hg

−905.3 ppm (s).

(S_C)-{2-(1′-(N,N-Dimethylamino)ethyl)phenyl-C,N}mercury(II)

Chloride, (S_C)-3b. A mixture of dimer (S_C)-3a (0.0400 g, 0.0689 mmol)

and metallic mercury excess (9.127 g, 45.50 mmol, 330 equiv) in

toluene (15 mL) was intensively stirred at 70 °C for 8 h in air. After

removing the metallic mercury, the solution was evaporated in a

vacuum to dryness. The crude product was puriﬁed using short dry

column chromatography on silica (h = 4 cm, d = 2.5 cm; eluents light

petroleum ether and light petroleum ether/diethyl ether 2:1 mixture) to

aﬀord transmetalation product (S_C)-3b (0.0412 g, 0.1072 mmol, 78%)

as almost colorless amorphous powder. Data for (S_C)-3b: mp 75−78

°C. R_f= 0.36 (light petroleum ether/diethyl ether 4:1). [α]²_D²+ 51° (c

0.25, CH₂Cl₂). Anal. Calcd for C₁₀H₁₄NClHg requires: C 31.26; H

7.7, H⁷), 6.59 (dd, 1H, ³J_HH7.8, ⁴J_HH1.9, H¹⁶), 6.63 (dd, 1H, ³J_HH7.8,

3

4

⁴J_HH1.9, H¹⁵), 6.83 (dd, 1H, J_HH7.7, J_HHg78.0, H⁸); methylene

protons of the [2.2]paracyclophane moiety: 2.89 (ddd, 1H, ²J_HH13.3,

³J_HH6.6, ³J_HH10.3, H^10s), 3.06 (ddd, 1H, ²J_HH14.0, ³J_HH6.6, ³J_HH10.4,

H^9a), 3.17 (ddd, 1H, ²J_HH13.5, ³J_HH4.0, ³J_HH10.9, H^2s), 3.24 (ddd, 1H,

²J_HH13.5, ³J_HH4.0, ³J_HH10.8, H^1a), 3.27 (ddd, 1H, ²J_HH13.5, ³J_HH3.7,

³J_HH10.9, H^1s), 3.29 (ddd, 1H, ²J_HH13.3, ³J_HH2.1, ³J_HH10.4, H^10a), 3.39

(ddd, 1H, ²J_HH13.5, ³J_HH3.7, ³J_HH10.8, H^2a), 3.59 (ddd, 1H, ²J_HH14.0,

³J_HH2.1, ³J_HH10.3, H^9s); side chain protons: 2.30 (s, 6H, 2Me), 7.01−

1

3.67; N 3.64. Found: C 31.41; H 3.80; N 3.48. H NMR (CDCl₃):

protons of the aromatic moiety: δ_H7.22 (m, 2H, H³, H⁵), 7.23 (m, 1H,

H⁴), 7.41 (m, 1H, ³J_HHg223, H⁶); side chain protons: 1.31 (d, 3H, ³J_HH

6.7, α-Me), 2.27 (s, 6H, NMe₂), 3.51 (q, 1H, ³J_HH6.7, ³J_HHg24, α-CH).

¹³C{¹H} NMR (CDCl₃): carbons of the aromatic moiety: δ_C128.50

(J_CHg169, C³), 128.81 (J_CHg31, C⁴), 132.21 (J_CHg214, C⁵), 127.32

(J_CHg140, C⁶), 147.04 (J_CHg2464, C¹), 150.73 (J_CHg49, C²); side chain

carbons: 21.77 (α-Me), 42.52 (NMe₂), 66.05 (J_CHg93, α-CH).

¹⁹⁹Hg{¹H} NMR (CDCl₃): δ_Hg−933.4 ppm (s).

7.05 (m, 1H, A part of AB₂system, J_AB7.5, para-H of C₆H₃), 7.13 (ps. d,

2H, B part of AB₂system, J_AB7.5, meta-H, C₆H₃), 8.63 (s, 1H, J_HHg10.4,

CHN). ¹³C{¹H} NMR (CDCl₃): Aromatic carbons of the

[2.2]paracyclophane moiety: δ 131.69 (C¹²), 133.01 (C¹⁵), 133.16

(C¹⁶), 133.66 (C¹³), 135.93 (J_CHg202, C⁸), 136.11 (J_CHg30, C⁷),

138.85 (C¹¹), 138.11 (J_CHg48, C⁵), 139.10 (C¹⁴), 144.04 (J_CHg164,

C⁶), 153.80 (C⁴), 146.36 (J_CHg91, C³); methylene carbons of the

[2.2]paracyclophane moiety: 33.54 (J_CHg23, C⁹), 35.79 (C¹), 36.17

(C¹⁰), 41.31 (J_CHg125, C²); side chain carbons: 19.04 (Me), 124.73 (p-

C), 128.30 (o-C), 128.44 (m-C), 149.42 (i-C), 161.96 (J_CHg118, CH

N). ¹⁹⁹Hg{¹H} NMR (CDCl₃): δ_Hg−977.6 ppm (s).

rac-{4-(N-2, 6-Dimethylphenyl)iminomethyl[2. 2]-

paracyclophane-5-yl-C,N}mercury(II) Chloride, rac-1b. A suspension

of dimer rac-1a (0.0300 g, 0.0312 mmol) and metallic mercury excess

(4.134 g, 20.61 mmol, 330 equiv) was intensively stirred for 3 h in

boiling toluene (15 mL) in air, which was accompanied by color

changing from yellow to light-yellow. After removing the metallic

mercury, the light-yellow solution was evaporated in a vacuum to

dryness. The crude product was puriﬁed using short dry column

chromatography on silica (h = 4 cm, d = 2.5 cm; petroleum ether,

petroleum ether/dichloromethane 2:1, 1:1) to aﬀord individual

transmetalation product rac-1b (0.0322 g, 0.0560 mmol, 90%) as a

yellow amorphous powder. Crystalline complex rac-1b suitable for X-

ray diﬀraction studies was obtained by slow evaporation of its solution

in a solvent mixture toluene/petroleum ether/chloroform. Data for rac-

1b: mp (decomp.) 239−241 °C. R_f= 0.27 (toluene); 0.28 (petroleum

ether/dichloromethane 3:2).

rac-[2-{1′-(Dimethylamino)ethyl}ferrocenyl-C,N]mercury(II)

Chloride, rac-4b. A mixture of dimer rac-4a (0.180 g, 0.2261 mmol)

and metallic mercury excess (27.00 g, 134.6 mmol, 298 equiv) in

toluene (20 mL) was intensively stirred at room temperature for 3.5 h

under argon. After 50 min after start of the reaction the precipitate of

the cyclopalladated dimer is completely dissolved. After removal of

metallic mercury and its washing with toluene (3 × 5 mL), the solutions

were evaporated in a vacuum to dryness. The chromatographic

puriﬁcation of the crude product using short dry column chromatog-

raphy on silica (h = 3 cm, d = 1.5 cm; eluents toluene/ethyl acetate 5:1,

ethyl acetate, methanol) aﬀords individual cyclomercurated complex

rac-4b (0.180 g, 0.3657 mmol, 81%) as red-brown oil. After multistage

crystallization from methanol major diastereomeric racemate (R_CS_pl)*-

7b was isolated as orange crystals (118 mg, 0.2397 mmol, 53%) with mp

115 °C. Anal. Calcd for C₁₄H₁₈ClFeHgN requires: C 34.16; H 3.69.

Found: C 34.19; H 3.81.

Spectral Data for Isolated (R_CS_pl)* Diastereomer. ¹H NMR

(CDCl₃): δ_H1.12 (d, 3H, ³J_HH6.8, α-Me), 2.12 (s, 6H, NMe₂), 3.92

(q, 1H, ³J_HH6.8, α-CH), 4.06 (dd, 1H, J_HHg51, ³J_HH2.3, ⁴J_HH1.1, H⁵),

4.08 (s, 5H, Cp), 4.22 (dd, 1H, J_HHg42, ³J_HH2.5, ³J_HH2.3, H⁴), 4.35 (br.

dd, 1H, J_HHg31, ³J_HH2.5, ⁴J_HH1.1, H³). ¹³C{¹H} NMR (CDCl₃): δ_C

9.08 (α-Me), 39.19 (NMe₂), 59.81 (J_CHg34, α-CH), 67.86 (²J_CHg156,

C⁵), 69.07 (³J_CHg206, C⁴), 69.38 (Cp), 72.27 (³J_CHg253, C³), 87.14

(C¹), 95.14 (²J_CHg131, C²). ¹⁹⁹Hg{¹H} NMR (CDCl₃): δ_Hg−733.9

ppm (s).

(R_C)-{1-(1′-(N,N-Dimethylamino)ethyl)naphthyl-2C,N}mercury(II)

Chloride, (R_C)-2b. A mixture of dimer (R_C)-2a (0.0400 g, 0.0588

mmol) and metallic mercury excess (7.780 g, 38.79 mmol, 330 equiv) in

toluene (15 mL) was intensively stirred at 70 °C for 9 h under argon,

accompanied by color changing from bright yellow to almost colorless.

After removing the metallic mercury, the solution was evaporated in a

vacuum to dryness. The crude product was puriﬁed using short dry

column chromatography on silica (h = 4 cm, d = 2.5 cm; eluents light

petroleum ether and light petroleum ether/diethyl ether 3:1 mixture) to

aﬀord transmetalation product (R_C)-2b (0.0411 g, 0.0946 mmol, 81%)

Spectral Data for Diastereomer Mixture. ¹H NMR (CDCl₃): δ_Hof

major diastereomer: 1.12 (d, ³J_HH6.8, 3H, α-Me), 2.12 (s, 6H, NMe₂),

3.93 (q, ³J_HH6.6, 1H, α-H), 4.06 (dd, ³J_HH2.3, ⁴J_HH1.1, 1H, H⁵), 4.08

(s, Cp), 4.23 (dd, ³J_HH2.4, ³J_HH2.4, 1H, H⁴), 4.36 (ddd, ³J_HH2.4, ⁴J_HH

L

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

1.1, ⁴J_HH0.4, 1H, H³); δ_Hof minor diastereomer: 1.31 (d, ³J_HH6.8, 3H,

α-Me), 2.37 (s, 6H, NMe₂), 3.26 (q, ³J_HH6.7, 1H, α-H), 4.12 (m, 2H,

H3, H5), 4.17 (s, Cp), 4.33 (dd, ³J_HH2.4, ³J_HH2.4, 1H, H⁴). ¹³C{¹H}

NMR (CDCl₃): δ_Cof major diastereomer: 9.19 (α-Me), 39.14 (NMe₂),

59.93 (³J_CHg33, α-CH), 67.88 (²J_CHg156, C⁵), 69.21 (³J_CHg206, C⁴),

69.41 (Cp), 72.53 (³J_CHg248, C³), 87.08 (C¹), 94.57 (C²); δ_Cof minor

diastereomer: 12.34 (α-Me), 41.21 (NMe₂), 56.00 (³J_CHg26, α-CH),

66.17 (²J_CHg160, C⁵), 68.94 (Cp), 70.13 (³J_CHg208, C⁴), 71.62 (³J_CHg

260, C³), 81.92 (C¹), 98.40 (C²). ¹⁹⁹Hg{¹H} NMR (CDCl₃): δ_Hg

−732.8 (major diastereomer), −684.8 (minor diastereomer).

(S_C)-{2-[2′-(4-tert-Butyl)oxazolinyl]phenyl-C,N}mercury(II) Chlor-

ide, (S_C)-5b. A mixture of dimer (S_C)-5a (0.0400 g, 0.0581 mmol) and

metallic mercury excess (7.70 g, 38.4 mmol, 330 equiv) in toluene (15

mL) was intensively stirred at room temperature for 4 days under argon.

After removing the metallic mercury, the solution was evaporated in a

vacuum to dryness. The crude product was puriﬁed using short dry

column chromatography on silica (h = 4 cm, d = 2.5 cm; eluents light

petroleum ether and light petroleum ether/diethyl ether 2:1 mixture) to

aﬀord transmetalation product (S_C)-5b (0.0362 g, 0.08259 mmol, 71%)

as almost colorless crystalline powder. Data for (S_C)-5b: mp 150−151

°C. [α]²_D²+ 22° (c 0.25, CH₂Cl₂). R_f= 0.64 (light petroleum ether/

diethyl ether 4:1). Anal. Calcd for C₁₃H₁₆NClOHg requires: C 35.62;

H 3.68; N 3.20. Found: C 35.36; H 3.71; N 3.15. ¹H NMR (CDCl₃):

Protons of the aromatic moiety: δ_H7.51 (ddd, 1H, J_HHg49, ³J_HH7.4,

³J_HH7.4, ⁴J_HH1.4, H⁵), 7.41 (ddd, 1H, J_HHg206, ³J_HH7.4, ⁴J_HH1.4, ⁵J_HH

Reaction paths were found by the intrinsic reaction coordinate (IRC)

method.⁷³All calculations were performed using the MBC100k cluster

at the Joint Supercomputer Center (JSCC) (Moscow, Russia) with the

use of the PRIRODA04 program written by Laikov.⁷⁴

X-ray Diﬀraction Study of Mercurials. X-ray diﬀraction data

were collected at the “Belok” beamline of the Kurchatov Synchrotron

Radiation Source (National Research Center “Kurchatov Institute”,

Moscow, Russian Federation) using a Rayonix SX165 CCD detector at

λ = 0.96990 Å (for (R_C)-2b), 0.96260 Å (for (R_C,S_pl)*-4b), and

0.80246 Å (for (S_C)-5b and 6b). All data sets were collected at 100 K. In

total, 480−720 frames were collected with an oscillation range of 1.0° in

the φ scanning mode using two diﬀerent orientations for each crystal.

The semiempirical correction for absorption was applied using the Scala

program.⁷⁵The data were indexed and integrated using the utility

iMOSFLM from the CCP4 software suite.⁷⁶For details, see Table S14.

The structures were solved by intrinsic phasing modiﬁcation of direct

methods⁷⁷and reﬁned by a full-matrix least-squares technique on F²

with anisotropic displacement parameters for all non-hydrogen atoms.

All hydrogen atoms were placed in calculated positions and reﬁned

within the riding model with ﬁxed isotropic displacement parameters

[U_iso(H) = 1.5U_eq(C) for the methyl groups and 1.2U_eq(C) for the

other groups]. All calculations were carried out using the SHELXTL

program.⁷⁸

ASSOCIATED CONTENT

0.6, H⁶), 7.35 (ddd, 1H, J_HHg17, ³J_HH7.4, ³J_HH7.8, ⁴J_HH1.4, H⁴), 7.88

(ddd, 1H, J_HHg62, ³J_HH7.8, ⁴J_HH1.4, ⁵J_HH0.6, H³); side chain protons:

0.96 (s, 9H, ^tBu), 4.01 (dd, 1H, ³J_HH8.8, ³J_HH10.2, J_HHg3, α-C⁹H), 4.28

(dd, 1H, ²J_HH8.7, ³J_HH8.8, C⁸H₂), 4.46 (dd, 1H, ²J_HH8.7, ³J_HH10.2,

C⁸H₂). ¹³C{¹H} NMR (CDCl₃): Carbons of the aromatic moiety: δ_C

128.54 (³J_CHg145, C³), 128.54 (⁴J_CHg29, C⁴), 132.14 (J_CHg40, C⁷),

132.21 (³J_CHg209, C⁵), 136.96 (²J_CHg132, C⁶), 150.62 (¹J_CHg2567, C¹),

167.76 (²J_CHg105, C²); side chain carbons: 26.05 (Me₃C), 33.77

(CMe₃), 70.43 (C⁸H₂), 75.54 (J_CHg14, α-C⁹H). ¹⁹⁹Hg{¹H} NMR

(CDCl₃): δ_Hg−1056.6 ppm (s).

■

S

* Supporting Information

The Supporting Information is available free of charge on the

ACS Publications website at DOI: 10.1021/acs.organo-

met.8b00363.

Cartesian coordinates of calculated complexes reported in

this study (XYZ)

Additional experimental details; bond lengths and angles,

ﬁgures and tables giving ¹H, ¹³C, and ¹⁹⁹Hg NMR spectra,

gCOSY, gHMQC and gHMBC NMR; VT NMR spectra

and DFT data; tables of X-ray diﬀraction and NMR data

for known analogues (PDF)

{2-(Pyridinyl-2′-oxy)phenyl-C,N}mercury(II) Chloride, 6b. A mix-

ture of dimer 6a (0.0400 g, 0.0641 mmol) and metallic mercury excess

(8.49 g, 42.3 mmol, 330 equiv) in toluene (15 mL) was intensively

stirred at 70 °C for 1 h in air. After removing the metallic mercury, the

solution was evaporated in a vacuum to dryness. The crude product was

puriﬁed using short dry column chromatography on silica (h = 4 cm, d =

2.5 cm; eluents: light petroleum ether and light petroleum ether/diethyl

ether 1:1 and 1:3 mixtures) to aﬀord individual transmetalation product

6b (0.0481 g, 0.1184 mmol, 92%) as almost colorless amorphous

powder. After slow recrystallization from DCM/Et₂O/petroleum ether,

complex 6b was isolated (0.0363 g, 0.0894 mmol, 70%) as almost

colorless thin needle-like crystals. Data for 6b: mp 158−161 °C. R_f=

0.24 (light petroleum ether/diethyl ether 1:1). Anal. Calcd for

C₁₁H₈NOClHg requires: C 32.52; H 1.98. Found: C 32.30; H 2.09.

Accession Codes

CCDC 1843928−1843931 contain the supplementary crystallo-

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

charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-

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

bridge Crystallographic Data Centre, 12 Union Road, Cam-

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

3

¹H NMR (CDCl₃): δ_H6.94 (br.d, 1H, J_HH8.2, H⁸), 7.04 (ddd, 1H,

AUTHOR INFORMATION

³J_HH5.0, ³J_HH7.2, ⁴J_HH0.9, H¹⁰), 7.15 (d, 1H, ³J_HH8.0, H³), 7.23 (m,

1H, H⁵), 7.35 (m, 1H, ³J_HHg208, H⁶), 7.36 (m, 1H, H⁴), 7.71 (ddd, 1H,

³J_HH8.2, ³J_HH7.2, ⁴J_HH2.0, H⁹), 8.19 (ddd, 1H, ³J_HH5.0, ⁴J_HH2.0, ⁵J_HH

0.6, H¹¹). ¹³C{¹H} NMR (CDCl₃): δ_C112.57 (C⁸), 119.47 (C¹⁰),

121.50 (³J_CHg104, C³), 125.38 (³J_CHg193, C⁵), 130.48 (⁴J_CHg19, C⁴),

136.65 (²J_CHg78, C⁶), 140.06 (C⁹), 142.59 (¹J_CHg2378, C¹), 147.56

(C¹¹), 157.06 (²J_CHg30, C²), 163.07, C⁷). ¹⁹⁹Hg{¹H} NMR (CDCl₃):

δ_Hg−1115.0 ppm (s).

■

Corresponding Author

*E-mail: dunina@org.chem.msu.ru. Fax: +7 (495) 932 8846.

Tel.: +7(495) 939 5376.

ORCID

Olga N. Gorunova: 0000-0001-6947-4763

Ivan M. Novitskiy: 0000-0002-2675-3348

Victor N. Khrustalev: 0000-0001-8806-2975

Valery V. Dunina: 0000-0003-4289-0294

Computational Details. The geometries of molecules, transition

states, and intermediates were fully optimized by means of density

functional theory (DFT) calculations. The PBE functional⁷⁰and scalar-

relativistic theory were used, the latter employing the four-component

spin-free Hamiltonian derived by Dyall⁷¹and applied variationally. The

full electron double size basis set was used. The numbers of contracted

and primitive functions used respectively {2,1}/{6,2} for H, {3,2,1}/

{10,7,3} for C, N, and O, {4,3,1}/{15,11,3} for Cl, {8,7,5,2}/

{30,29,20,14} for Hg.⁷²Stationary points on the potential energy

surface (PES) were identiﬁed by analyzing Hessians. The thermody-

namic functions (Gibbs energies, G) at 298.15 K were calculated using

an approximation of restricted rotator and harmonic oscillator.

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

We thank the Russian Foundation of Basic Researches (grant no.

18-03-01026a). The NMR part of this work was supported by

M. V. Lomonosov Moscow State University “Program of

Development” (Y.K.G., V.A.R.).

M

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

R. B. Palladacyclic Pre-Catalysts for Suzuki Coupling, Buchwald−

Hartwig Amination and Related Reactions. In Palladacycles. Synthesis,

Characterization and Applications; Dupont, J., Pfeffer, M., Eds.; Wiley-

VCH: Weinheim, 2008; pp 209−225. (c) Dupont, J.; Consorti, C. S.;

Spencer, J. The Potential of Palladacycles: More Than Just Precatalysts.

Chem. Rev. 2005, 105, 2527−2571. (d) Beletskaya, I. P.; Cheprakov, A.

V. Palladacycles in Catalysis − a Critical Survey. J. Organomet. Chem.

2004, 689, 4055−4082. (e) Beletskaya, I. P.; Cheprakov, A. V. The

Heck Reaction as a Sharpening Stone of Palladium Catalysis. Chem. Rev.

2000, 100, 3009−3066.

REFERENCES

■

(1) (a) Crabtree, R. H. Resolving Heterogeneity Problems and

Impurity Artifacts in Operationally Homogeneous Transition Metal

Catalysts. Chem. Rev. 2012, 112, 1536−1554. (b) Schmidt, A. F.;

Kurokhtina, A. A. Distinguishing between the Homogeneous and

Heterogeneous Mechanisms of Catalysis in the Mizoroki−Heck and

Suzuki−Miyaura Reactions: Problems and Prospects. Kinet. Catal.

2012, 53, 714−730. (c) Phan, N. T. S.; van der Sluys, M.; Jones, C. W.

On the Nature of the Active Species in Palladium Catalyzed Mizoroki−

Heck and Suzuki−Miyaura Couplings − Homogeneous or Heteroge-

neous Catalysis, A Critical Review. Adv. Synth. Catal. 2006, 348, 609−

679. (d) Widegren, J. A.; Finke, R. G. A Review of the Problem of

Distinguishing True Homogeneous Catalysis from Soluble or other

Metal-Particle Heterogeneous Catalysis under Reducing Conditions. J.

Mol. Catal. A: Chem. 2003, 198, 317−341.

́

(11) (a) Ramírez-Rave, S.; Morales-Morales, D.; Grevy, J.-M.

Microwave Assisted Suzuki-Miyaura and Mizoroki-Heck Cross-

couplings Catalyzed by non-Symmetric Pd(II) CNS Pincers Supported

by Iminophosphorane Ligands. Inorg. Chim. Acta 2017, 462, 249−255.

(b) Das, U.; Pattanayak, P.; Patra, D.; Brandao, P.; Felix, V.;

̃

Chattopadhyay, S. Design, Synthesis and Properties of Orthopalladated

Complexes: Proheterogeneous Catalyst. Polyhedron 2016, 110, 165−

171. (c) Zhang, H.; Lei, A. Palladium(IV) Chemistry Supported by

Pincer Type Ligands. Dalton Trans 2011, 40, 8745−8754. (d) Avila-

(2) (a) Drost, R. M.; Rosar, V.; Marta, S. D.; Lutz, M.; Demitri, N.;

Milani, B.; de Bruin, B.; Elsevier, C. J. Pd-Catalyzed Z-Selective

Semihydrogenation of Alkynes: Determining the Type of Active

Species. ChemCatChem 2015, 7, 2095−2107. (b) Bolliger, J. L.;

Blacque, O.; Frech, C. M. Rationally Designed Pincer-Type Heck

Catalysts Bearing Aminophosphine Substituents: Pd^IVIntermediates

and Palladium Nanoparticles. Chem. - Eur. J. 2008, 14, 7969−7977.

́

Sorrosa, A.; Estudiante-Negrete, F.; Hernandez-Ortega, S.; Toscano, R.

A.; Morales-Morales, D. Buchwald−Hartwig C−N Cross Coupling

Reactions Catalyzed by a Pseudo-Pincer Pd(II) Compound. Inorg.

Chim. Acta 2010, 363, 1262−1268. (e) Gerber, R.; Blacque, O.; Frech,

C. M. Suzuki Cross-Coupling Reactions Catalyzed by an Aliphatic

Phosphine-Based Pincer Complex of Palladium: Evidence for a

Molecular Mechanism. ChemCatChem 2009, 1, 393−400. (f) Hossain,

Md.A.; Lucarini, S.; Powell, D.; Bowman-James, K. Ditopic Double

Pincer Palladacycle Catalyst for C-C Coupling. Inorg. Chem. 2004, 43,

̈

(3) Paal, C.; Hartmann, W. Uber den Einfluß von Fremdstoffen auf die

̈

Aktivitat der Katalysatoren. IV. Versuche mit Palladiumhydrosol in

Qegenwart von Queksilber und Quecksilberoxyd. Ber. Deutsch. Ber.

Dtsch. Chem. Ges. 1918, 51, 711−737.

(4) (a) Steckel, J. A. Density Functional Theory Study of Mercury

Adsorption on Metal Surfaces. Phys. Rev. B: Condens. Matter Mater.

Phys. 2008, 77, 115412. (b) Campbell, K. C.; Hislop, J. S. Mercury

Adsorption, Catalyst Poisoning, and Reactivation Phenomena on Metal

Catalysts. J. Catal. 1969, 13, 12−19.

̈

7275−7277. (g) Sjovall, S.; Wendt, O. F.; Andersson, C. Synthesis,

Characterisation and Catalytic Investigation of a New Type of PC(sp³)

P Pincer Pd(II) Complex. J. Chem. Soc., Dalton Trans. 2002, 1396−

́

1400. (h) Morales-Morales, D.; Redon, R.; Yung, C.; Jensen, C. M.

(5) (a) Anton, D. R.; Crabtree, R. H. Dibenzo[a,e]cyclooctatetraene

in a Proposed Test for Heterogeneity in Catalysts Formed from Soluble

Platinum Group Metal Complexes. Organometallics 1983, 2, 855−859.

(b) Foley, P.; DiCosimo, R.; Whitesides, G. M. Mechanism of Thermal

Decomposition of Dineopentylbis(triethylphosphine)platinum(II):

Formation of Bis(triethy1phosphine)-3,3-dimethy1p1atinacyc1obu-

tane. J. Am. Chem. Soc. 1980, 102, 6713−6725.

High Yield Olefination of a Wide Scope of Aryl Chlorides Catalyzed by

The Phosphinito Palladium PCP Pincer Complex: [PdCl-

{C₆H₃(OPPrⁱ₂)₂-2,6}]. Chem. Commun. 2000, 1619−1620. (i) Ohff,

M.; Ohff, A.; van der Boom, M. E.; Milstein, D. Highly Active Pd(II)

PCP-Type Catalysts for the Heck Reaction. J. Am. Chem. Soc. 1997,

119, 11687−1688.

(12) (a) Lucio-Martínez, F.; Adrio, L. A.; Polo-Ces, P.; Ortigueira, J.

(6) Schwartz, J. Alkane Activation by Oxide-Bound Organorhodium

Complexes. Acc. Chem. Res. 1985, 18, 302−308.

́

M.; Fernandez, J. J.; Adams, H.; Pereira, M. T.; Vila, J. M. Palladacycle

Catalysis: an Innovation to the Suzuki−Miyaura Cross-Coupling

Reaction. Dalton Trans. 2016, 45, 17598−17601. (b) Gerber, R.;

Blacque, O.; Frech, C. M. Negishi Cross-Coupling Reaction Catalyzed

by an Aliphatic, Phosphine Based Pincer Complex of Palladium. Biaryl

Formation via Cationic Pincer-Type Pd^ivIntermediates. Dalton Trans.

2011, 40, 8996−9003. (c) Blacque, O.; Frech, C. M. Pincer-Type Heck

Catalysts and Mechanisms Based on Pd^IVIntermediates: A Computa-

tional Study. Chem. - Eur. J. 2010, 16, 1521−1531. (d) Sundermann, A.;

Uzan, O.; Martin, J. M. L. Computational Study of a New Heck

Reaction Mechanism Catalyzed by Palladium(II/IV) Species. Chem. -

Eur. J. 2001, 7, 1703−1711.

(7) (a) Yu, K.; Sommer, W.; Weck, M.; Jones, C. W. Silica and

Polymer-tethered Pd−SCS-pincer Complexes: Evidence for Precatalyst

Decomposition to Form Soluble Catalytic Species in Mizoroki−Heck

Chemistry. J. Catal. 2004, 226, 101−110. (b) Sommer, W. J.; Yu, K.;

Sears, J. S.; Ji, Y.; Zheng, X.; Davis, R. J.; Sherrill, C. D.; Jones, C. W.;

Weck, M. Investigations into the Stability of Tethered Palladium(II)

Pincer Complexes during Heck Catalysis. Organometallics 2005, 24,

4351−4361.

(8) (a) Stein, J.; Lewis, L. N.; Gao, Y.; Scott, R. A. In situ

Determination of the Active Catalyst in Hydrosilylation Reactions

Using Highly Reactive Pt(0) Catalyst Precursors. J. Am. Chem. Soc.

1999, 121, 3693−3703. (b) van Asselt, R.; Elsevier, C. J. Homogeneous

Catalytic Hydrogenation of Alkenes by Zero-valent Palladium

Complexes of cis-Fixed Dinitrogen Ligands. J. Mol. Catal. 1991, 65,

L13−L19. (c) Jones, R. A.; Real, F. M.; Wilkinson, G.; Galas, A. M. R.;

Hursthouse, M. B. Further Chemistry of Trimethylphosphine

Complexes of Rhodium(I): X-Ray Crystal Structures of Dodeca-

(trimethy1phosphine)tetrarhodiumhexamercury, Hg₆Rh₄(PMe₃)₁₂,

and trans-Chlorobis(trimethy1phosphine)(triphenylphosphine)-

rhodium(I). J. Chem. Soc., Dalton Trans. 1981, 126−131.

(13) (a) Camasso, N. M.; Canty, A. J.; Ariafard, A.; Sanford, M. S.

Experimental and Computational Studies of High-Valent Nickel and

Palladium Complexes. Organometallics 2017, 36, 4382−4393. (b) Xu,

L.-M.; Li, B.-J.; Yang, Z.; Shi, Z.-J. Organopalladium(IV) chemistry.

Chem. Soc. Rev. 2010, 39, 712−733. (c) Albrecht, M.; van Koten, G.

Platinum Group Organometallics Based on ^aPincer° Complexes:

Sensors, Switches, and Catalysts. Angew. Chem., Int. Ed. 2001, 40,

3750−3781.

́

(14) (a) Vicente-Hernandez, I.; Chicote, M.-T.; Vicente, J.; Bautista,

D. A New Type of Oxidative Addition of an Iodoarene to a Pd(II)

Complex. Chem. Commun. 2016, 52, 594−596. (b) Martínez-Martínez,

A.-J.; Chicote, M.-T.; Bautista, D.; Vicente, J. Synthesis of Palladium-

(II), -(III), and -(IV) Complexes with Acyclic Diaminocarbene

(9) (a) Shiels, R. A.; Jones, C. W. A Convergence of Homogeneous

and Heterogeneous Catalysis: Immobilized Organometallic Catalysts.

Model Systems in Catalysis 2010, 20, 441−455. (b) Yu, K.; Sommer, W.;

Richardson, J. M.; Weck, M.; Jones, C. W. Evidence that SCS Pincer

Pd(II) Complexes are only Precatalysts in Heck Catalysis and the

Implications for Catalyst Recovery and Reuse. Adv. Synth. Catal. 2005,

347, 161−171.

́

Ligands. Organometallics 2012, 31, 3711−3719. (c) Julia-Hernandez,

F.; Arcas, A.; Vicente, J. Providing Support in Favor of the Existence of a

Pd^II/Pd^IVCatalytic Cycle in a Heck-Type Reaction. Chem. - Eur. J.

́

(10) (a) Beletskaya, I. P.; Cheprakov, A. V.; Colacot, T. J. Modern

Heck Reactions. New Catalysis Series 2014, 21, 355−478. (b) Bedford,

2012, 18, 7780−7786. (d) Vicente, J.; Arcas, A.; Julia-Hernandez, F.;

Bautista, D. Synthesis of a Palladium(IV) Complex by Oxidative

N

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Addition of an Aryl Halide to Palladium(II) and Its Use as Precatalyst in

a C−C Coupling Reaction. Angew. Chem., Int. Ed. 2011, 50, 6896−

6899.

(15) Joshi, H.; Prakash, O.; Sharma, A. K.; Sharma, K. N.; Singh, A. K.

Suzuki Coupling Reactions Catalyzed with Palladacycles and

Palladium(II) Complexes of 2-Thiophenemethylamine-Based Schiff

Bases: Examples of Divergent Pathways for the Same Ligand. Eur. J.

Inorg. Chem. 2015, 1542−1552.

(16) (a) Błaszczyk, I.; Gniewek, A.; Trzeciak, A. M. Orthometallated

Palladium Trimers in C−C Coupling Reactions. J. Organomet. Chem.

2012, 710, 44−52. (b) Błaszczyk, I.; Gniewek, A.; Trzeciak, A. M.

Monomeric Triphenylphosphite Palladacycles with N-Imidazole

Ligands as Catalysts of Suzuki-Miyaura and Sonogashira Reactions. J.

Organomet. Chem. 2011, 696, 3601−3607. (c) Peris, E.; Loch, J. A.;

Mata, J.; Crabtree, R. H. A Pd Complex of a Tridentate Pincer CNC

Bis-Carbene Ligand as a Robust Homogenous Heck Catalyst. Chem.

Commun. 2001, 201−202.

(17) (a) Singh, M. P.; Saleem, F.; Pal, R. S.; Singh, A. K. Palladacycles

Having Normal and Spiro Chelate Rings Designed from Bi- and

Tridentate Ligands with an Indole Core: Structure, Synthesis and

Applications as Catalysts. New J. Chem. 2017, 41, 11342−11352.

Facilitate Suzuki and Heck Coupling Reactions. J. Mol. Catal. A: Chem.

2014, 383-384, 249−259.

(23) Zim, D.; Nobre, S. M.; Monteiro, A. L. Suzuki Cross-Coupling

Reaction Catalyzed by Sulfur-Containing Palladacycles: Formation of

Palladium Active Species. J. Mol. Catal. A: Chem. 2008, 287, 16−23.

(24) (a) Lipke, M. C.; Woloszynek, R. A.; Ma, L.; Protasiewicz, J. D.

m-Terphenyl Anchored Palladium Diphosphinite PCP-Pincer Com-

plexes That Promote the Suzuki-Miyaura Reaction Under Mild

Conditions. Organometallics 2009, 28, 188−196. (b) Eberhard, M. R.

Insights into the Heck Reaction with PCP Pincer Palladium(II)

Complexes. Org. Lett. 2004, 6, 2125−2128.

(25) Bergbreiter, D. E.; Osburn, P. L.; Frels, J. D. Mechanistic Studies

of SCS-Pd Complexes Used in Heck Catalysis. Adv. Synth. Catal. 2005,

347, 172−184.

(26) Sigeev, A. S.; Peregudov, A. S.; Cheprakov, A. V.; Beletskaya, I. P.

The Palladium Slow-Release Pre-Catalysts and Nanoparticles in the

“Phosphine-Free” Mizoroki−Heck and Suzuki−Miyaura Reactions.

Adv. Synth. Catal. 2015, 357, 417−429.

(27) (a) Bhaskar, R.; Sharma, A. K.; Yadav, M. K.; Singh, A. K.

Sonogashira (Cu and Amine Free) and Suzuki Coupling in Air

Catalyzed via Nanoparticles Formed in situ from Pd(II) Complexes of

Chalcogenated Schiff Bases of 1-Naphthaldehyde and their Reduced

Forms. Dalton Trans. 2017, 46, 15235−15248. (b) Rao, G. K.; Kumar,

A.; Singh, M. P.; Singh, A. K. Palladium(II) Complex of an

Organotellurium Ligand as a Catalyst for Suzuki Miyaura Coupling:

Generation and Role of Nano-Sized Pd₃Te₂. J. Organomet. Chem. 2014,

749, 1−6. (c) Rao, G. K.; Kumar, A.; Kumar, S.; Dupare, U. B.; Singh, A.

K. Palladacycles of Thioethers Catalyzing Suzuki−Miyaura C−C

Coupling: Generation and Catalytic Activity of Nanoparticles.

Organometallics 2013, 32, 2452−2458.

́

(b) Avila-Sorrosa, A.; Jimenez-Vazquez, H. A.; Reyes-Arellano, A.;

́

Pioquinto-Mendoza, J. R.; Toscano, R. A.; Gonzalez-Sebastian, L.;

Morales-Morales, D. Novel Synthesis of a Non-Symmetric N¹CN²-

Pd(II) Pincer Complex by a Tandem Reaction Using a Meta-

Hydroxylated Imine Ligand. J. Organomet. Chem. 2016, 819, 69−75.

(18) Sharma, A. K.; Joshi, H.; Bhaskar, R.; Kumar, S.; Singh, A. K.

Palladacycles of Sulfated and Selenated Schiff Bases of Ferrocene-

Carboxaldehyde as Catalysts for O-Arylation and Suzuki−Miyaura

Coupling. Dalton Trans. 2017, 46, 2485−2496.

(28) Ananikov, V. P.; Beletskaya, I. P. Toward the Ideal Catalyst:

From Atomic Centers to a “Cocktail” of Catalysts. Organometallics

2012, 31, 1595−1604.

(19) (a) Olsson, D.; Wendt, O. F. Suzuki Reaction Catalysed by a

Pc_sp3P Pincer Pd(II) Complex: Evidence for a Mechanism Involving

Molecular Species. J. Organomet. Chem. 2009, 694, 3112−3115.

(b) Bolliger, J. L.; Blacque, O.; Frech, C. M. Short, Facile, and High-

Yielding Synthesis of Extremely Efficient Pincer-Type Suzuki Catalysts

Bearing Aminophosphine Substituents. Angew. Chem., Int. Ed. 2007, 46,

6514−6517.

(20) (a) Olsson, D.; Nilsson, P.; El Masnaouy, M.; Wendt, O. F. A

Catalytic and Mechanistic Investigation of a PCP Pincer Palladium

Complex in the Stille Reaction. J. Chem. Soc., Dalton Trans. 2005,

1924−1929. (b) Nilsson, P.; Wendt, O. F. Kinetic Investigation of a

PC(sp³)P Pincer Palladium (II) Complex in the Heck Reaction. J.

Organomet. Chem. 2005, 690, 4197−4202. (c) Rosol, M.; Moyano, A.

1′-Carbopalladated-4-ferrocenyl-1,3-oxazolines as Catalysts for Heck

Reactions: Further Evidence in Support of the Pd(0)/Pd(II)

Mechanism. J. Organomet. Chem. 2005, 690, 2291−2296.

(29) (a) Gorunova, O. N.; Grishin, Yu. K.; Ilyin, M. M., Jr.;

́

Kochetkov, K. A.; Churakov, A. V.; Kuzmina, L. G.; Dunina, V. V.

Enantioselective Catalysis of Suzuki reaction with Planar-Chiral CN-

Palladacycles: Competition of two Catalytic Cycles. Russ. Chem. Bull.

2017, 66, 282−292. (b) Gorunova, O. N.; Livantsov, M. V.; Grishin, Y.

K.; Ilyin, M. M., Jr.; Kochetkov, K. A.; Churakov, A. V.; Kuz’mina, L. G.;

Khrustalev, V. N.; Dunina, V. V. Evidence on Palladacycle-Retaining

Pathway for Suzuki Coupling. Inapplicability of Hg-drop Test for

Palladacycle Catalysed Reactions. J. Organomet. Chem. 2013, 737, 59−

63.

(30) (a) Wu, Y.; Huo, Sh.; Gong, J.; Cui, X.; Ding, L.; Ding, K.; Du,

Ch.; Liu, Y.; Song, M. Studies on the Cyclometallation of

Ferrocenylimines. J. Organomet. Chem. 2001, 637-639, 27−46.

(b) Cui, X. L.; Wu, Y. J.; Du, Ch. X.; Yang, L. R.; Zhu, Y.

Transmetallation Reactions of Planar Chiral Cyclopalladated Ferroce-

nylimines with Metallic Mercury. Tetrahedron: Asymmetry 1999, 10,

1255−1262.

(31) Vedejs, E.; Salomon, M. F. Preparation, Stereochemistry, and

Rearrangement of Mercurials in the Norbornenyl-Nortricyclyl System.

J. Org. Chem. 1972, 37, 2075−2079.

(32) Wu, Y. J.; Cui, X. L.; Hou, J. J.; Yang, L. R.; Wang, M.; Du, C. X.;

Zhu, Y. Transmetallation Reactions of Planar Chiral Cyclopalladated

and Cyclomercurated Ferrocenylimines with Metallic Tin. Acta Chim.

Sin. 2000, 58, 871−875.

(33) (a) Nesmeyanov, A. N.; Blinova, V. A.; Shchirina-Eingorn, I. V.;

Kritskaya, I. I. Synthesis of Some Difficulty Accessible Allylic

Organomercury Compounds. Bull. Acad. Sci. USSR, Div. Chem. Sci.

1977, 26, 2178−2180. (b) Rubezhov, A. Z.; Voronchikhina, L. I.;

Gubin, S. P. Synthesis of m- and p-Fluorophenylallyl Mercury

Chlorides. Bull. Acad. Sci. USSR, Div. Chem. Sci. 1972, 21, 2060−

2062. (c) Nesmeyanov, A. N.; Rubezhov, A. Z.; Leites, V.; Gubin, S. P.

The Reactions of Metallic Mercury with π-Allyl Compounds of Ni, Pd

and Pt. J. Organomet. Chem. 1968, 12, 187−198. (d) Gubin, S. P.;

Rubezhov, A. Z.; Denisovich, L. I.; Nesmeyanov, A. N. Reaction of

Metallic Mercury with π-Allyl Compounds of Palladium. Bull. Acad. Sci.

USSR, Div. Chem. Sci. 1966, 15, 1630.

(21) (a) Baier, H.; Kelling, A.; Schilde, U.; Holdt, H.-J. Investigation of

the Catalytic Activity of a 2-Phenylidenepyridine Palladium(II)

Complex Bearing 4,5-Dicyano-1,3-bis(mesityl)imidazol-2-ylidene in

the Mizoroki-Heck Reaction. Z. Anorg. Allg. Chem. 2016, 642, 140−

147. (b) Baier, H.; Kelling, A.; Holdt, H.-J. PEPPSI-Effect on Suzuki−

Miyaura Reactions Using 4,5-Dicyano-1,3-dimesitylimidazol-2-yli-

dene-Palladium Complexes: A Comparison between trans-Ligands.

Eur. J. Inorg. Chem. 2015, 1950−1957. (c) Baier, H.; Metzner, Ph.;

̈

Korzdorfer, Th.; Kelling, A.; Holdt, H.-J. Efficient Palladium(II)

Precatalysts Bearing 4,5-Dicyanoimidazol-2-ylidene for the Mizoroki−

Heck Reaction. Eur. J. Inorg. Chem. 2014, 2952−2960. (d) Poulain, A.;

Neels, A.; Albrecht, M. Palladium Complexes Containing Potentially

Chelating Pyridylidene-Type Carbene Ligands. Eur. J. Inorg. Chem.

2009, 1871−1881. (e) Consorti, C. S.; Flores, F. R.; Dupont, J. Kinetics

and Mechanistic Aspects of the Heck Reaction Promoted by a CN-

Palladacycle. J. Am. Chem. Soc. 2005, 127, 12054−12065. (f) Consorti,

C. S.; Zanini, M. L.; Leal, S.; Ebeling, G.; Dupont, J. Chloropalladated

Propargyl Amine: A Highly Efficient Phosphine-Free Catalyst

Precursor for the Heck Reaction. Org. Lett. 2003, 5, 983−986.

(22) Sabounchei, S. J.; Ahmadi, M.; Panahimehr, M.; Bagherjeri, F. A.;

Nasri, Z. Phosphine Mono- and bis-Ylide Palladacycles as Homoge-

neous Molecular Precatalysts: Simple and Efficient Protocol Greatly

O

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

(34) (a) Costa, R. D.; Cossich, E. S.; Tavares, C. R. G. Influence of the

Temperature, Volume and Type of Solution in the Mercury

Vaporization of Dental Amalgam Residue. Sci. Total Environ. 2008,

407, 1−6. (b) Palaniappan, R. Indirect Spectrophotometric Determi-

nation of Palladium(II). Pak. J. Sci. Ind. Res. 1989, 32 (2), 79−81.

(35) Whitesides, G. M.; Hackett, M.; Brainard, R. L.; Lavalleye, J.-P. P.

M.; Sowinski, A. F.; Izumi, A. N.; Moore, S. S.; Brown, D. W.; Staudt, E.

M. Suppression of Unwanted Heterogeneous Platinum(0)-Catalyzed

Reactions by Poisoning with Mercury(0) in Systems Involving

Competing Homogeneous Reactions of Soluble Organoplatinum

Compounds: Thermal Decomposition of Bis(triethylphosphine)-

3,3,4,4-tetramet hylplatinacyclopentane. Organometallics 1985, 4,

1819−1830.

Rev. 1999, 193-195, 283−359. (c) Holloway, C. E.; Melník, M. Mercury

Organometallic Compounds. Classification and Analysis of Crystallo-

graphic and Structural Data. J. Organomet. Chem. 1995, 495, 1−31.

(d) Wardell, J. L. Mercury. In Comprehensive Organometallic Chemistry;

Wilkinson, G.; Stone, F. G. A.; Abel, E. W., Eds.; Pergamon: Oxford,

́

1982; Vol. 2, pp 863−978. (e) Grdenic, D. The Structural Chemistry of

Mercury. Quart. Rev., Chem. Soc. 1965, 19, 303−328.

(47) Baligar, R. S.; Sharma, S.; Singh, H. B.; Butcher, R. J. Synthesis

and Structure of New Schiff Base Derivatives Obtained from 2-

(Formylphenyl)mercury Bromide. J. Organomet. Chem. 2011, 696,

3015−3022.

(48) Das, Sh.; Singh, H. B.; Butcher, R. J. Isolation of Organomercury-

(II) Azides Stabilized by Intramolecular Coordination. J. Organomet.

Chem. 2015, 799−800, 184−194.

(36) Lewis, L. N.; Lewis, N. Platinum-Catalyzed Hydrosilylation -

Colloid Formation as the Essential Step. J. Am. Chem. Soc. 1986, 108,

7228−7231.

(49) (a) Wu, Y. J.; Huo, S. Q.; Zhu, Y.; Yang, L. Cyclometallation of

Ferrocenylimines. Part II. Studies on the Cyclomercuration of [l-

(Arylimino)ethyl]ferrocenes and Related Structure-Reactivity Rela-

tionships. J. Organomet. Chem. 1994, 481, 235−242. (b) Shou, Q. H.;

Yang, J. W.; Ying, Z.; Li, Y. ortho-Mercuration of Ferrocenylimines. J.

Organomet. Chem. 1994, 470, 17−22.

(37) (a) Butin, K. P.; Gunkin, I. F.; Petri, R.; Beletskaya, I. P.; Reutov,

O. A. Exchange of Organometallic Compounds with Mercury Metal.

VII. Interaction of Di-p-Anisylthallium Chloride with Mercury in

Pyridine, Ethylenediamine and Dimethylsulfoxide; Prevaling Role of

Homogeneous Reaction. J. Organomet. Chem. 1976, 114, 239−250.

(b) Reutov, O. A.; Butin, K. P. “Organic Calomels” and Other

Organometallic Compounds as Intermediates in Transmetallation

Reactions of Organometallic Compounds with Mercury Metal. J.

Organomet. Chem. 1975, 99, 171−184. (c) Butin, K. P.; Strelets, V. V.;

Gunkin, I. F.; Beletskaya, I. P.; Reutov, O. A. Exchange of

Organometallic Compounds with Mercury Metal. VI. Substituted

Diarylthallium Cations; Evidence for Intermediate Ar−Tl⁺−Hg−Ar

Species. J. Organomet. Chem. 1975, 85, 123−130. (d) Butin, K. P.;

Strelets, V. V.; Beletskaya, I. P.; Reutov, O. A. Exchange of

Organometallic Compounds with Mercury Metal. V. The Interaction

of Diethyltallium Chloride with Mercury. J. Organomet. Chem. 1974, 64,

189−191. (e) Gilman, H.; Jones, R. G. Relative Reactivities of

Organometallic Compounds. XXVII. Triphenylthallium. J. Am. Chem.

Soc. 1939, 61, 1513−1515.

(38) (a) Crabtree, R. H. Deactivation in Homogeneous Transition

Metal Catalysis: Causes, Avoidance, and Cure. Chem. Rev. 2015, 115,

127−150. (b) Dyson, P. J. Arene Hydrogenation by Homogeneous

Catalysts: Fact or Fiction? Dalton Trans. 2003, 2964−2974.

(39) (a) Attar, S.; Nelson, J. H.; Fischer, J. Crystal Structures of Chiral

Halo{2[ l-(S)-(dimethylamino)ethyl]phenyl-C¹,N}mercury(II) Com-

plexes. Organometallics 1995, 14, 4776−4780. (b) van der Ploeg, A. F.

M. J.; van der Kolk, C. E. M.; van Koten, G. Arylmercury(II)

Compounds Involving Intramolecular Coordination via 2-Me₂NCH₂-

and Chiral (S)-2-Me₂NCHMe-ring Substituents. J. Organomet. Chem.

1981, 212, 283−290.

(50) Gul, N.; Nelson, J. H. Synthesis and Structures of Chiral

̈

Halo[N,N-dimethyl-α-(2-naphthyl)ethylamine-3,C,N]mercury(II)

complexes. J. Mol. Struct. 1999, 475, 121−130.

(51) (a) Dunina, V. V. Chiral Cyclopalladated Compounds: New

Structures, Methodologies and Applications. A Personal Account. Curr.

Org. Chem. 2011, 15, 3415−3440. (b) Alcock, N. W.; Hulmes, D. I.;

Brown, J. M. Contrasting Behaviour of Related Palladium Complex-

derived Resolving Agents. 8-H Conformational Locking of the 1-

Naphthyl Side-chain. J. Chem. Soc., Chem. Commun. 1995, 395−397.

́

(52) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, V.;

́

Echeverría, J.; Cremades, E.; Barragan, F.; Alvarez, S. Covalent Radii

Revisited. Dalton Trans. 2008, 2832−2838.

(53) (a) Wang, H.-X.; Li, Y.-J.; Wu, H.-F.; Gao, R.-Q.; Geng, F.-Y.;

Yang, X.-L.; Wan, L.; Jin, R.; Cui, X.-L.; Wu, Y.-J. Ortho-Mercurated

[({N-Methyl-N-arylamino}methyl)ferrocenes] and their Transpalla-

dation. Crystal Structures of [(η⁵-C₅H₅)Fe{η⁵-C₅H₃(HgCl)CH₂N-

(CH₃)C₆H₄OCH₃-4}]₂, [(η⁵-C₅H₅)Fe{η⁵-C₅H₃(HgCl)CH₂N(CH₃)-

C₆H₄Cl-3}] and [(η⁵-C₅H₄HgCl)Fe{η⁵-C₅H₄CH₂N(CH₃)C₆H₄Cl-

4}]. Polyhedron 2006, 25, 3305−3311. (b) Seidel, N.; Jacob, K.;

Fischer, A. K.; Merzweiler, K.; Wagner, C.; Fontani, M.; Zanello, P. [2-

(N,N-Dimethylaminomethyl)ferrocenyl] as a Ligand towards Mercury.

J. Organomet. Chem. 2001, 630, 149−156. (c) Kuz’mina, L. G.;

Struchkov, Yu. T.; Troitskaya, L. L.; Sokolov, V. I. X-ray Diffraction

Structural Study of Nonbonding Interactions and Coordination in

Heteroorganic Compounds. Part XXVI. X-ray Diffraction Structural

Study of 1-Chloromercuri-2-dimethylaminomethylferrocene. J. Struct.

Chem. 1985, 26, 428−432.

(40) Sokolov, V. I.; Troitskaya, L. L.; Reutov, O. A. Asymmetric

Induction in the Course of Internal Palladation of Enantiomeric 1-

Dimethylaminomethylferrocene. J. Organomet. Chem. 1977, 133, C28−

C30.

(54) Apte, S. D.; Zade, S. S.; Singh, H. B.; Butcher, R. Contrasting

Behavior of Bis[2-(4,4-dimethyl-2-oxazolinyl)phenyl] Chalcogenides

(Se/Te) toward Mercuric Chloride: Facile Cleavage of the Te-C Bond.

Organometallics 2003, 22, 5473−5477.

(55) Li, H.; Wei, K.; Du, Ch.; Zhu, Y.; Xu, Ch.; Wu, Y. Synthesis,

Characterization and Crystal Structures of a New 2-Ferrocenylnaph-

thoxazole and its Mercurated Derivatives. J. Organomet. Chem. 2007,

692, 1033−1038.

(41) Bondi, A. van der Waals Volumes and Radii. J. Phys. Chem. 1964,

68, 441−451.

(42) Canty, A. J.; Deacon, G. B. The van der Waals Radius of Mercury.

Inorg. Chim. Acta 1980, 45, L225−L227.

̈

(43) Pyykko, P.; Straka, M. Ab initio Studies of the Dimers (HgH₂)₂

and (HgMe₂)₂. Metallophilic Attraction and the van der Waals Radii of

Mercury. Phys. Chem. Chem. Phys. 2000, 2, 2489−2493.

(56) (a) Hamid, G.; Somaieh, Y.; Yunes, A.; Michal, D.; Vaclav, E.;

Majid, R.; Neslihan, O. Complexation of 1,3-Dimorpholinopropane

with Hg(II) and Zn(II) Salts: Syntheses, Crystal Structures and

Antibacterial Studies. Chin. J. Inorg. Chem. 2015, 31, 1076−1084.

(44) (a) Batsanov, S. S. Van der Waals Radii of Elements. Inorg. Mater.

2001, 37, 871−885. (b) Batsanov, S. S. On the Additivity of van der

Waals Radii. J. Chem. Soc., Dalton Trans. 1998, 1541−1546.

̈

(b) Neuba, A.; Herres-Pawlis, S.; Seewald, O.; Borner, J.; Heuwing, A.

(45) Kuz’mina, L. G.; Bokii, N. G.; Struchkov, Y. T. The Structural

Chemistry of Organic Compounds of Mercury and Its Analogues (Zinc

and Cadmium). Russ. Chem. Rev. 1975, 44, 73−85.

̈

J.; Florke, U.; Henkel, G. A Systematic Study on the Coordination

Properties of the Guanidine Ligand Bis(tetramethylguanidino)propane

with the Metals Manganese, Cobalt, Nickel, Zinc, Cadmium, Mercury,

and Silver. Z. Anorg. Allg. Chem. 2010, 636, 2641−2649. (c) Tang, X.-

Y.; Yuan, R.-X.; Ren, Zh-G.; Li, H.-X.; Zhang, Y.; Lang, J.-P.

Interactions of a Cationic Mercury(II) Thiolate Complex [Hg(Tab)₂]-

(PF₆)₂with N-Donor Ligands. Inorg. Chem. 2009, 48, 2639−2651.

(d) Choi, S.-N.; Kim, S.-Yu.; Ryu, H.-W.; Lee, Y.-M. Dichloro-

(46) (a) Gabbaï, F. P.; Burress, C. N.; Melaimi, M.-A.; Taylor, T. J.

Mercury and Cadmium Organometallics. In Comprehensive Organo-

metallic Chemistry III; Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier:

Oxford, 2007; Vol. 2, pp 419−462. (b) Casas, J. S.; García-Tasende, M.

S.; Sordo, J. Structural Aspects of the Coordination Chemistry of

Organothallium(III) and Organomercury(II) derivatives. Coord. Chem.

P

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

[(6R,7S,8S,14S)-(−)-sparteine-κ²N,N′]mercury(II). Acta Crystallogr.,

Sect. C: Cryst. Struct. Commun. 2005, 61, m504−m506.

Cyclopalladated Complexes of (S)-4-tert-Butyl-2-phenyl-2-oxazoline.

X-ray Study of (S,S)-di-μ-Chloro-bis-{2-[2-(4-tert-butyl)oxazolinyl]-

phenyl-C,N}dipalladium(II). J. Organomet. Chem. 2002, 654, 66−73.

(69) de Geest, D. J.; O'Keefe, B. J.; Steel, P. J. Cyclometallated

Compounds. XIII. Cyclopalladation of 2-Phenoxypyridine and

Structurally-related Compounds. J. Organomet. Chem. 1999, 579, 97−

105.

(70) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient

Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868.

(71) Dyall, K. G. An Exact Separation of the Spin-free and Spin-

dependent Terms of the Dirac-Coulomb-Breit Hamiltonian. J. Chem.

Phys. 1994, 100, 2118−2127.

(72) Laikov, D. N. A. New Class of Atomic Basis Functions for

Accurate Electronic Structure Calculations of Molecules. Chem. Phys.

Lett. 2005, 416, 116−120.

(57) Musavi, S. A.; Montazerozohori, M.; Masoudiasl, A.; Naghiha, R.;

Joohari, S.; Assoud, A. Crystal Structure, DNA Interaction and Thermal

Analysis Data of Two New Antimicrobial Active Binuclear Cadmium

and Mercury Complexes. J. Mol. Struct. 2017, 1145, 65−75.

(58) (a) Bader, R. F. W. A. Quantum Theory of Molecular Structure

and Its Applications. Chem. Rev. 1991, 91, 893−928. (b) Bader, R. F. W.

Atoms in Molecules: A Quantum Theory; Oxford University Press: New

York, 1990.

(59) (a) Constable, E. C.; Cargill Thompson, A. M. W.; Leese, T. A.;

Reese, D. G. F.; Tocher, D. A. Cyclometallation Reactions of 2-

Phenylpyridine; Crystal and Molecular Structure of (2-{2-Pyridyl}-

phenyl)palladium(II) Tetramer and (2-{2-Pyridyl}phenyl)mercury-

(II) Tetramer. Inorg. Chim. Acta 1991, 182, 93−100. (b) Constable, E.

C.; Leese, T. A.; Tocher, D. A. Polynuclear Intermediates in the

Synthesis of Cyclometallated Complexes; the Crystal and Molecular

Structure of (2-PyridylphenyI)mercury(II) Chloride Tetramer. J.

Chem. Soc., Chem. Commun. 1989, 570−571.

(73) Gonzalez, C.; Schlegel, H. B. Reaction Path Following in Mass-

Weighted Internal Coordinates. J. Phys. Chem. 1990, 94, 5523−5527.

(74) Laikov, D. N.; Ustynyuk, Yu. A PRIRODA-04: a Quantum-

Chemical Program Suite. New Possibilities in the Study of Molecular

Systems with the Application of Parallel Computing. Russ. Chem. Bull.

2005, 54, 820−826.

̈

(60) Beleaga, A.; Bojan, V. R.; Pollnitz, A.; Rat,̧ C. I.; Silvestru, C.

Organomercury(II) and Tellurium(II) Compounds with the “Pincer”

Ligand 2,6-[O(CH₂CH₂)₂NCH₂]₂C₆H₃− Stabilization of an Unusual

Organotellurium(II) Cationic Species. Dalton Trans. 2011, 40, 8830−

8838.

(75) Evans, P. Scaling and Assessment of Data Quality. Acta

Crystallogr., Sect. D: Biol. Crystallogr. 2006, 62, 72−82.

(76) (a) Battye, T. G. G.; Kontogiannis, L.; Johnson, O.; Powell, H. R.;

Leslie, A. G. W. iMOSFLM: a New Graphical Interface for Diffraction-

Image Processing with MOSFLM. Acta Crystallogr., Sect. D: Biol.

Crystallogr. 2011, 67, 271−281. (b) Winn, M. D.; Ballard, C. C.;

Cowtan, K. D.; Dodson, E. J.; Emsley, P.; Evans, P. R.; Keegan, R. M.;

Krissinel, E. B.; Leslie, A. G. W.; McCoy, A.; McNicholas, S. J.;

Murshudov, G. N.; Pannu, N. S.; Potterton, E. A.; Powell, H. R.; Read,

R. J.; Vagin, A.; Wilson, K. S. Overview of the CCP4 Suite and Current

Developments. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2011, D67,

235−242.

(61) (a) Rowland, K. E.; Thomas, R. D. Carbon-13 and Mercury-199

NMR Data for Methyl-Substituted Bisaryl Mercury Compounds. Magn.

Reson. Chem. 1985, 23, 916−919. (b) Wells, P. R.; Hawker, D. W.

Mercury-199 NMR Chemical Shifts in Substituted Diphenylmercury

and Phenylmercuric Chloride. Org. Magn. Reson. 1981, 17, 26−27.

(c) Chisholm, M. H.; Godleski, S. Applications of Carbon-13 NMR in

Inorganic Chemistry. Prog. Inorg. Chem. 2007, 20, 299−436.

(d) Petrosyan, V. S.; Reutov, O. A. NMR Spectra and Structure of

Organomercury Compounds. J. Organomet. Chem. 1974, 76, 123−169.

(62) (a) Crabtree, R. H. The Organometallic Chemistry of Alkanes.

Chem. Rev. 1985, 85, 245−269. (b) Larock, R. C. Organomercurials in

Organic Synthesis. Tetrahedron 1982, 38, 1713−1754. (c) Larock, R. C.

Organomercury Compounds in Organic Synthesis. Angew. Chem., Int.

Ed. Engl. 1978, 17, 27−37. (d) Zeller, K. P.; Straub, H. Organo-

quecksilber-Verbindungen; In Houben−Weyl’s Methoden der Organ-

ischen Chemie, 4th ed.; Straub, H., Zeller, K. P., Leditschke, H., Eds.;

Thieme Verlag: Stuttgart, 1974; Band 13/2b, pp 96−100.

(77) Sheldrick, G. M. SHELXT − Integrated Space-Group and

Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv.

2015, 71, 3−8.

(78) (a) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,

Sect. A: Found. Crystallogr. 2008, 64, 112−122. (b) Sheldrick, G. M.

Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C:

Struct. Chem. 2015, 71, 3−8.

(63) Marat, K. SPINWORKS 4 Software; University of Manitoba:

Winnipeg MB, Canada. https://home.cc.umanitoba.ca/~wolowiec/

spinworks/.

(64) Sharp, J. T.; Gosney, I.; Rowley, A. G. Practical Organic Chemistry

− A Student Handbook of Techniques; Chapman and Hall: London,

1989; Chapter 4.2.2d.

(65) Dunina, V. V.; Turubanova, E. I.; Livantsov, M. V.; Lyssenko, K.

A.; Vorontsova, N. V.; Antonov, D.; Grishin, Y. K. Yu.; Grishin, Y. K.

First enantiopure imine CN-palladacycle of non-metallocenic planar

chirality with the [2.2]paracyclophane backbone. Tetrahedron:

Asymmetry 2009, 20, 1661−1671.

(66) Allen, D. G.; McLaughlin, G. M.; Robertson, G. B.; Steffen, W. L.;

Salem, G.; Wild, S. B. Resolutions Involving Metal Complexation.

Preparation and Resolution of (R,S)-Methylphenyl(8-quinoly1)-

phosphine and Its Arsenic Analogue. Crystal and Molecular Structure

of (+)₅₈₉-[(R)-Dimethyl(1-ethyl-α-naphthyl)aminato-C²,N]-[(S)-met

hylphenyl(8-quinolyl)phosphine]palladium(II) Hexafluorophosphate.

Inorg. Chem. 1982, 21, 1007−1014.

(67) Tani, K.; Brown, L. D.; Ahmed, J.; Ibers, J. A.; Yokota, M.;

Nakamura, A.; Otsuka, S. Chiral Metal Complexes. 4. Resolution of

Racemic Tertiary Phosphines with Chiral Palladium(II) Complexes.

The Chemistry of Diastereomeric Phosphine Pd(II) Species in

Solution, and the Absolute Configuration of [(S)-Isopropyl-tert-

butylphenylphosphine]-[(R)-N,N-dimethyl-α-(2-naphthyl)-ethyl-

amine-3C,N]chloropalladium(II) Determined by X-Ray Diffraction. J.

Am. Chem. Soc. 1977, 99, 7876−7886.

(68) Peterson, D. L.; Keuseman, K. J.; Kataeva, N. A.; Kuz’mina, L. G.;

Howard, J. A. K.; Dunina, V. V.; Smoliakova, I. P. Homochiral

Q

DOI: 10.1021/acs.organomet.8b00363

Organometallics XXXX, XXX, XXX−XXX

Article Doi

When Applying the Mercury Poisoning Test to Palladacycle-Catalyzed Reactions, One Should Not Consider the Common Misconception of Mercury(0) Selectivity

DOI: 10.1021/acs.organomet.8b00363

Source and publish data:

Authors:

Article abstract of DOI:10.1021/acs.organomet.8b00363

Full text of DOI:10.1021/acs.organomet.8b00363

Products guided by the article

R&D Labs maybe for 1437789-79-1

Relevant to this article

Hot Product