Mono(NCN-pincer palladium)-metalloporphyrin catalysts: Evidence for supramolecular bimetallic catalysis

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Mono(NCN-pincer palladium)-metalloporphyrin catalysts: evidence for

supramolecular bimetallic catalysis†

Bart M. J. M. Suijkerbuijk,^aDanie¨l J. Schamhart,^aHuub Kooijman,^bAnthony L. Spek,^bGerard van Koten^aand

Robertus J. M. Klein Gebbink*^a

Received 30th November 2009, Accepted 27th April 2010

First published as an Advance Article on the web 2nd June 2010

DOI: 10.1039/b925236n

The synthesis and catalytic properties of ditopic mono-pincer-mono-porphyrin complexes were

investigated. The statistical Adler condensation reaction of 3,5-bis(methoxymethyl)-

4-bromo-benzaldehyde, p-tolylaldehyde, and pyrrole, furnished an AB₃-type tetraphenylporphyrin,

containing three meso-p-tolyl groups and one meso-3,5-bis(methoxymethyl)-4-bromophenyl group. This

material was converted into the ditopic ligand [2H(Br)], which comprises one porphyrin site and an

NCN-pincer type ligand moiety. In order to metalate this compound in a stepwise, site-selective

manner, two distinct synthetic routes were followed. Route A relies on the introduction of a metal in the

porphyrin cavity followed by pincer metalation and a reversal of this order is employed for route B. For

the hetero-bimetallic pincer-porphyrin target compounds, route A invariably proved to be the highest

yielding alternative, giving pincer-porphyrin hybrids of general formula [M¹(M²X)] (M¹= 2H, Mg, Co,

Ni, Zn; M²= Pd, Br; X = Cl, Br). ¹⁹⁵Pt NMR spectroscopy revealed that the porphyrin metal has a

modest inﬂuence on the electron density on the NCN-pincer Pt site. When the analogous cationic Pd

complexes were used as Lewis acid catalysts for the double Michael addition between methyl vinyl

ketone and ethyl a-cyanoacetate, it was noted that the catalytic activity did not depend on the central

metal for M¹= 2H, Ni, and Zn. However, when Mg occupied the porphyrin cavity, the rate of the

reaction increased by a factor of six. Although a rate enhancement was observed when catalysis was

conducted with a mixture of the two constituents of [Mg(PdOH₂)]BF₄(i.e. MgTTP and

[PdOH₂(NCN)]BF₄) this could not fully account for the rate enhancement. We believe that the

rationale for this behaviour is dual, consisting of “cooperative dual catalysis” and supramolecular

aggregation of two or more catalyst-substrate complexes.

Introduction

ECE-pincer metal complexes have found extensive application as

catalysts in many organic transformations.^1–11Their widespread

use has been prompted by the ease of alteration of several key pa-

rameters of the pincer system. Chart 1 shows the general formula

of such an organometallic pincer complex. It comprises an M–

C_aryls-bond that is kinetically stabilised by two ﬂanking electron-

donating groups E, forming a robust organometallic complex.

Depending on the chelated metal, a number of additional ligands

(L) will occupy the remainder of the available coordination sites.

By selecting speciﬁc combinations of M, E, and L_n, metallopincer

complexes can be obtained with potential applications in research

areas ranging from materials science^12–18and catalysis^1–11,19to

sensing^20,21and bio-marking.^22,23As changes in these combinations

Chart 1

greatly alter the properties of the ECE-pincer metal complexes, we

have previously also investigated strategies to electronically tune

the properties of a given ECE-organometallic moiety. The pincer

para-substituent Z proved key in this respect: Van de Kuil²⁴and

Slagt^25,26found that in both NCN-pincer Ni and Pt complexes,

the electron density on the metal centre is proportional to the

electron-withdrawing or -donating character of Z, as indexed

by its Hammett parameter s_p. Variation of the para-substituent

on ECE-pincer metal complexes is therefore a powerful tool in

the development of catalysts and materials with well-deﬁned and

ﬁne-tuned properties.^27–30The para-substituent has also been used

extensively to graft and anchor pincer-metal complexes to a variety

^aChemical Biology & Organic Chemistry, Debye Institute for Nanomaterials

Science, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH

Utrecht, The Netherlands. E-mail: r.j.m.kleingebbink@uu.nl; Fax: +31-30-

2523615; Tel: +31-30-2531889

^bCrystal and Structural Chemistry, Bijvoet Center for Biomolecular Re-

search, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH

Utrecht, The Netherlands.

† Electronic supplementary information (ESI) available: Synthesis and

analytical data for MgTTP, NiTPP and ZnTTP. CCDC reference number

755788. For ESI and crystallographic data in CIF or other electronic

format see DOI: 10.1039/b925236n

of materials and supports.^{13,17,18,31–49}Alternatively, h -coordination

6

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of [RuC₅R₅]⁺fragments to the pincer phenyl ring can signiﬁcantly

change the properties of the pincer-born metal centre.^50–52

Although some substituents can be directly introduced at

the para-position of the NCN-pincer metal moiety through

electrophilic aromatic substitution, most of these direct methods

employ rather harsh reaction conditions.^25,53,54In the majority of

cases the introduction of a new para-substituent therefore involves

considerable synthetic efforts. For this reason we set out to develop

a modular way of changing the electronic properties of the pincer

para-substituent using mild techniques and requiring a minimal

number of synthetic steps. A modular strategy for the variation

of substituents may, furthermore, be a research tool of general

interest, e.g., in catalyst optimization.

It has long been known that the electronic properties of a

metalloporphyrin depend on the metal that is situated in its

core.^55–57This is for instance manifested in the electrochemical

and photophysical properties of metalloporphyrins. During the

course of a few decades, a “periodic table of metalloporphyrins”

has been virtually completed and essentially any metal can be

successfully introduced in the porphyrin framework.⁵⁸Whereas in

the beginning some porphyrin metalation reactions still employed

rather forcing conditions, milder ways have gradually been de-

veloped to introduce particular metals with very mild methods.

These beneﬁcial aspects of porphyrin chemistry encouraged us

to synthesise ECE-pincer-porphyrin hybrids and to evaluate the

potential of the metalloporphyrin to act as a modular pincer

para-substituent. In order to prevent a possible dilution of the

effect of the porphyrin on the metallopincer, as might be

the case when multiple metallopincer groups are attached (cf. the

[M¹(M²X)₄] systems studied recently),^59,60we set out to investi-

gate meso-mono(NCN-pincer metal)-(metallo)porphyrin hybrids,

[M¹(M²X)] (see Chart 2).

Chart 2

Synthesis and characterisation

Synthesis of the ditopic ligand

For the synthesis of the targeted mono(NCN-pincer)-porphyrin

hybrid ligand [2H(Br)] an Adler-type condensation reaction⁶¹

was employed, since Lindsey-type procedures were found to

be less suitable in related cases.^59,62A synthetic strategy sim-

ilar to that utilised for the synthesis of the tetrakis(NCN-

pincer)-porphyrin hybrids discussed in two previous papers^59,62

was used, in which a benzaldehyde with two benzylic methox-

ide groups at its 3- and 5-positions was employed in

the porphyrin synthesis step (Scheme 1). To arrive at the

desired 5-(NCN-pincer ligand)-10,15,20-tris(p-tolyl)-substituted

porphyrin framework, a statistical condensation reaction was

employed. The previously described 3,5-bis(methoxymethyl)-4-

bromobenzaldehyde 1⁵⁹and p-tolualdehyde were reacted in a

1 : 5.8 molar ratio with pyrrole (6.8 equivalents) in reﬂuxing

propionic acid to give a mixture of meso-[3,5-bis(methoxymethyl)-

4-bromophenyl]_n-(p-tolyl)_4-nporphyrins (n = 0–4). After oxida-

tion with DDQ in CH₂Cl₂to remove chlorin impurities, the

mixture was subjected to column chromatography on silica

Here, the synthesis of the ditopic pincer-porphyrin hybrid

ligand system is described along with the stepwise and orthogonal

metalation of each of the ligand sites. The effect of the metallopor-

phyrin para-substituent on the electron density of the NCN-pincer

metal moiety and the resulting behaviour of these compounds as

homogeneous catalysts is discussed.

Scheme 1 Synthetic route toward [2H(Br)]: (i) a. pyrrole, propionic acid, reﬂux; b. DDQ, CH₂Cl₂; (ii) 33% HBr/HOAc, CH₂Cl₂; (iii) HNMe₂, CH₂Cl₂.

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Fig. 1 ¹H NMR spectrum of 2 in CDCl₃at 25 ^◦C.

gel. The polarity difference of the 3,5-bis(methoxymethyl)-4-

Ligand metalation

bromophenyl- and p-tolyl-substituents allowed for the sepa-

ration of each of the porphyrin components of the mixture

to give the desired 5-[3,5-bis(methoxymethyl)-4-bromophenyl]-

10,15,20-tris(p-tolyl)porphyrin (2) in 7.4% yield. The by-

products 5,15-bis[3,5-bis(methoxymethyl)-4-bromophenyl]-10,20-

bis(p-tolyl)-porphyrin and meso-tetrakis(p-tolyl)porphyrin (TTP)

were also isolated in 1.0% and 13% yield, respectively.

In order to be able to introduce electronically diverse metals into

the porphyrin skeleton that do not interfere with subsequent reac-

tions at the pincer unit, e.g., halide abstraction with AgBF₄(vide

infra), several metals were considered. It was decided to introduce

relatively electronegative Co(II), electron richer Ni(II) and Zn(II),

and electropositive Mg(II) in the porphyrin moiety of [2H(Br)].

For subsequent catalytic studies, the NCN-pincer Pd compounds

are of interest, whereas the corresponding platinum compounds

were also targeted in order to determine the electronic effects

of the metalloporphyrin on the NCN-pincer metal group. To

obtain the mono(NCN-metallopincer)-metalloporphyrin hybrids,

two different routes can be followed, each of which consists of a

two-step protocol in which ﬁrst one coordination site is metalated

followed by the second one. Porphyrin metalation followed by

pincer metalation will be referred to as Route A, while the strategy

in which the pincer site is metalated prior to porphyrin metalation

is named Route B (Scheme 2). Route A proved to be superior

for all targeted [M¹(M²X)] compounds. Whereas the ﬁnal yields

for Route A were approximately 80% over two steps, Route B

only furnished around 60% of the desired ﬁnal product (Table 1,

vide infra). The lower yields obtained via Route B are in most

cases ascribed to the second step, i.e. porphyrin metalation in the

presence of an already metalated NCN-pincer unit.

The AB₃substitution pattern of 2 was readily apparent from its

¹H NMR spectrum (300 MHz), which showed three types of b-H

signals (see Fig. 1). The magnetic non-equivalence of the protons

at the 2- and 8-positions (Fig. 1(i)) with respect to those at the

3- and 7-positions (j) on the porphyrin ring leads to an AB-pattern

at d = 8.87 and 8.81 ppm (³J_HH= 4.8 Hz). On the other hand,

the two sets of b-protons situated in between the two different

p-tolyl groups (d and e) give rise to an apparent singlet at d =

8.86 ppm. The integral ratio of the peaks corresponding to the

pincer aryl-protons and the p-tolyl aryl-protons (2 : 12) provided

further evidence for the expected one-to-three ratio and thus for

the desired structure. The symmetry of the molecule was further

corroborated by ¹³C NMR spectroscopy, which typically showed

three signals with approximate intensities of 1 : 2 : 1 in the C_meso

region (d ª 120 ppm).⁶³

The effective method of HBr/HOAc treatment^62,64was sub-

sequently applied to convert 2 into 5-[3,5-bis(bromomethyl)-4-

bromophenyl]-10,15,20-tris(p-tolyl)porphyrin (3) in 82% isolated

yield (Scheme 1). When HBr/HOAc solutions containing traces

of Br₂impurity were used, b-bromination occurred to a small

In all cases, the introduction of a metal in the porphyrin

cavity of [2H(Br)] proceeded selectively and in high yields.

Lindsey’s procedure⁶⁵to introduce Mg(II) by means of treatment

with MgBr₂·OEt₂in CH₂Cl₂in the presence of Et₃N gave

[Mg(Br)] in 96% yield. Zinc was also routinely introduced using

1

extent (≤6% by H NMR). The desired ditopic ligand [2H(Br)]

was obtained from the reaction of 3 with HNMe₂in 97% yield. All

66

1

compounds were fully characterised by means of ¹H and ¹³C{ H}

Zn(OAc)₂·2H₂O in a mixed solvent system of MeOH and CH₂Cl₂

to yield 89% of [Zn(Br)]. If the latter two compounds are precipi-

NMR spectroscopy, UV-vis spectroscopy, MALDI-TOF MS, and

elemental analysis (see Experimental).

tated from CH₂Cl₂with hexanes, they form solid materials, which

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Scheme 2 Synthetic route toward bimetallic mono(NCN-pincer metal)-metalloporphyrin hybrids [M¹(M²X)]: (i) for M¹= Mg: MgBr₂·OEt₂, i-Pr₂NEt,

CH₂Cl₂; for M¹= Co: Co(OAc)₂·4H₂O, MeOH–CH₂Cl₂, reﬂux; for M¹= Ni: Ni(acac)₂, toluene, reﬂux, or Ni(OAc)₂·2H₂O, MeOH–CH₂Cl₂; for M¹=

Zn: Zn(OAc)₂·2H₂O, MeOH–CH₂Cl₂; (ii) for M²X = PdBr: [Pd₂dba₃]·CHCl₃, benzene; for M²X = PdCl: (i) a. [Pd₂dba₃]·CHCl₃, benzene; b. NaCl,

H₂O–CH₂Cl₂; for M²X = PtCl: (i) a. [Pt₂dipdba₃], benzene, reﬂux; b. AgBF₄, Et₃N, CH₂Cl₂; c. NaCl, H₂O–CH₂Cl₂.

Table 1 The dependence of overall yields (%) of [M¹(M²X)] on the

porphyrins).¹¹⁵Addition of coordinating solvents such as pyridine

or THF, however, leads to rapid dissolution of [Mg(Br)] and

[Zn(Br)] in CH₂Cl₂and benzene, and hexanes to a lesser extent.

In order to obtain ﬁnal proof for the structure of [Mg(Br)]

its bis(THF)-adduct {[Mg(Br)](THF)₂} was analysed by X-ray

crystallography. Dark red crystals were grown from a mixed

solvent system of CH₂Cl₂/hexanes/THF (40 : 20 : 1, v/v/v) by

slow concentration through evaporation of the solvents. The

molecular structure shows a central Mg atom that is surrounded

by six ligands in a distorted octahedral ligand arrangement

(Fig. 2). Four pyrrolic nitrogen atoms provided by the porphyrin

dianion occupy the meridional positions with Mg–N distances of

synthetic route

Route A

Route B

[Co(PdBr)]

[Mg(PdCl)]

[Ni(PdBr)]

[Zn(PdBr)]

[Mg(PtCl)]

[Ni(PtCl)]

[Zn(PtCl)]

84

89

82

88

86

78

N/A

66

76

61

57

61

hardly re-dissolve in non-coordinating solvents. The relatively

strong interaction of magnesium^67,68and zinc porphyrins⁶⁹with

nitrogenous bases could induce the formation of supramolecular

˚

2.074(4)–2.077(4) A. The two apical position are occupied by THF

molecules, the oxygen atoms of which reside at 2.220(4) (O1) and

complexes consisting of two or more [M¹(Br)] units (M¹

Mg or Zn) with inherent solubility problems (see a previous

=

˚

2.224(4) A (O2) from the magnesium atom. The latter values are

common for bis(oxygen) coordinated magnesium porphyrins⁷⁰and

signiﬁcantly shorter than those found in the magnesium porphyrin

publication for related meso-tetrakis(NCN-pincer ligand) zinc(II)

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which is particularly important when the starting material is in its

free-base form.

Thus, pincer palladation of all [M¹(Br)] compounds (M¹

=

2H, Mg, Co, Ni, Zn) proceeded smoothly with [Pd₂dba₃]·CHCl₃

in benzene at room temperature to furnish the corresponding

[M¹(PdBr)] complexes in good yields (see Table 1). During

palladation of [Mg(Br)], halide exchange (Br/Cl) at Pd was found

to be substantial. Most probably, the chloride ions originate from

residual chloroform in the starting material, which can react with

pincer metal complexes to give the corresponding ECE-pincer

metal chloride complexes. Hence, the [Mg(PdX)] product mixture

(X = Br, Cl) was converted into the analogous chloridopalladio(II)

compound [Mg(PdCl)] using NaCl as the chloride source in a

biphasic system of H₂O and CH₂Cl₂.

Introduction of platinum proceeded similarly facile using 0.55

equivalents of [Pt₂dipdba₃] in benzene at reﬂux temperature to

give the corresponding [M¹(PtBr)] complexes (M¹= 2H, Mg,

Ni, Zn). Unlike their tetrakis(pincer) substituted analogs,⁵⁹these

complexes are sufﬁciently soluble in (combinations of) non-

chlorinated solvents to allow for their isolation as the bromide

complexes. To allow a direct comparison to the tetrapincer por-

phyrin complexes described previously⁵⁹the chloride complexes

seemed more relevant. Halide abstraction with AgBF₄followed by

treatment with brine proved to be the most effective and least time-

consuming way to obtain the chloridoplatino(II) complexes. Since

traces of moisture had rendered the used AgBF₄acidic, the halide

abstraction reactions were carried out in the presence of a base to

prevent de-metalation of the metalloporphyrin. Accordingly, the

desired [M¹(PtCl)] compounds were obtained in yields ranging

from 88 to 95%.

Fig. 2 Molecular structure of {[Mg(Br)](THF)₂} with displacement

ellipsoids at the 50% probability level. Hydrogen atoms and disordered

non-coordinated solvent molecules have been omitted for clarity. Only

one conformation of the orientationally disordered p-tolyl substituents is

shown. Residual electron density in the proximity of C2, C3, and C12,

C13, which is ascribed to partial bromination, has been left out as well.

71

˚

bis-adducts of nitrogenous bases such as pyridine [2.369(2) A]

72

˚

and N-methylimidazole (2.297 A).

The porphyrin macrocycle adopts a wave-type non-planar

deformation mode,⁷³with the N3- and N1-pyrrole rings tilted from

planarity. The dihedral angles of the three meso-tolyl groups with

respect to the central tetrapyrrolic macrocycle are between 61.0(2)^◦

and 62.1(2)^◦, with the meso-3,5-bis[(dimethylamino)methyl]-4-

bromophenyl group at 66.4(2)^◦. The crystallographic data fur-

thermore show residual electron density at the positions close to

C2, C3, C12, and C13. This is ascribed to a minor, partially b-

brominated contamination in the starting material, which appar-

ently co-crystallises with the major product. Besides conﬁrming

the proposed structure of [Mg(Br)], this structure furthermore

substantiates the AB₃skeletal substitution pattern on the parent

[2H(Br)] ligand and thus on all of its derivatives discussed in this

paper.

Nickel(II) porphyrin [Ni(Br)] was synthesised in 94% by nick-

elation of [2H(Br)] with Ni(acac)₂in boiling toluene. Cobalt(II)

was introduced via treatment of [2H(Br)] with Co(OAc)₂·4H₂O⁶⁶

in a yield of 96%. The resulting [Co(Br)] was obtained as a highly

air- and light-sensitive solid due to the dual presence of a Co(II)

centre and tertiary amine ligands within one molecule. In none of

the cases, evidence was found for a competing metalation of the

NCN-pincer ligand site during porphyrin metalation.

Porphyrin metalation after pincer metalation

Notwithstanding the successful and high-yielding application of

route A for the synthesis of the hetero-bimetallic compounds, it

is noteworthy that for a number of compounds route B proved

to be a valuable alternative. We set out to synthesise compounds

[M¹(PdBr)] (M¹= Ni, Zn) and [M¹(PtCl)] (M¹= Mg, Ni, Zn) by

porphyrin metalation of the corresponding free-base porphyrin

precursors [2H(PdBr)] and [2H(PtCl)]. Ni(acac)₂could not be

used as a nickelating agent, since the solubility of the free-base

porphyrins in toluene is too low. The use of Ni(OAc)₂·4H₂O in a

mixed solvent system (MeOH–CH₂Cl₂)⁶⁶led to the formation of

the desired compounds, [Ni(PdBr)] and [Ni(PtCl)], in satisfactory

yields. Substantial amounts of unidentiﬁed by-product were

observed in the ¹H NMR spectra of the crude products, but fortu-

nately these could be readily removed by column chromatography

on silica gel. Similarly, zinc(II) could be introduced using the same

procedure as for [Zn(Br)]. [Zn(PdBr)] and [Zn(PtCl)] were thus

obtained in 86 and 72% yield, respectively. Though the synthesis

of [Mg(PdCl)] was not attempted via Route B, [Mg(PtCl)] was

obtained by metalation of [2H(PtCl)] using Lindsey’s conditions.⁶⁵

All porphyrin metalation reactions were followed by UV-vis

spectroscopy. As soon as the lowest energy absorption band of

the free-base porphyrin (~645 nm) had disappeared, indicating

complete consumption of the starting material, the work-up was

immediately performed in order to prevent product losses due to

the formation of undesired by-products.

Pincer metalation

In order to metalate the pincer ligand of [M¹(Br)] oxidative

addition of the aryl bromide moiety to M(0) precursors was chosen

as the metalation method. As we observed earlier, this mild method

is very selective,⁵⁹and therefore ensures site-speciﬁc metalation,

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Table 2 ¹⁹⁵Pt NMR chemical shifts obtained from [M¹(PtCl)]

Characterisation of hetero-bimetallic compounds

d_Pt/ppm^a

s_p

All bimetallic complexes were fully characterised by a com-

1

bination of ¹H and ¹³C{ H} NMR spectroscopy, and UV-vis

[2H(PtCl)]

[Ni(PtCl)]

[Zn(PtCl)]

[Mg(PtCl)]

[PtCl(NCN)]

-3181

-3183

-3189

-3196

-3147

-0.25

-0.27

-0.30

-0.34

0.00

spectroscopy. In addition, they were analysed by MALDI-TOF

mass spectrometry and elemental analysis. In every case, the

1

¹H and ¹³C{ H} NMR spectra corroborated the AB₃skeleton

1

of the porphyrin. ¹³C{ H} NMR spectroscopy, for example,

^aChemical shifts were referenced to an external standard (1 M Na₂[PtCl₆]

in D₂O) before each run.

showed four peaks in the C_aand C_bregions⁵⁷around d =

150 and 131 ppm, respectively. Although not all peaks were

resolved in each case, this clearly conﬁrmed the presence of four

magnetically unique C_aand C_bnuclei, which is as expected for

an AB₃porphyrin. At larger distances from the porphyrin core,

these differences fade, which is illustrated by the fact that the

methyl-C atoms of the two non-equivalent p-tolyl groups resonate

at almost identical frequencies. UV-vis spectroscopy revealed

that metalation of the NCN-pincer ligand moiety causes small

perturbations of the electronic spectra. While metalloporphyrins

[M¹(Br)] exhibit spectra that are virtually identical to their TTP

analogues, peripheral palladation and platination bring about

small bathochromic shifts of the Soret band amounting to ~1 and

~3 nm, respectively. MALDI-TOF spectra invariably showed

a number of peaks corresponding to the [M]⁺, [M–X]⁺, and

[M–M²X]⁺ions. The successful incorporation of palladium and

platinum was illustrated by ¹H NMR spectroscopy, which showed

downﬁeld shifts for the benzylic- and dimethylamino protons

upon coordination of the NMe₂groupings to the metal centre.

Equally indicative were the substantial upﬁeld shifts of the pincer

aryl-protons by approximately 0.6 ppm after metalation of the

NCN-pincer ligand unit. A further notable observation was that

the solubility of [Mg(M²X)] and [Zn(M²X)] in non-coordinating

solvents such as benzene and CH₂Cl₂is dramatically enhanced in

comparison with the parent metalloporphyrins. ¹H NMR analyses

conﬁrmed that the parent [Mg(Br)] and [Zn(Br)] compounds exist

as higher order aggregates in solution due to intermolecular M–N

(M = Mg or Zn) interactions, while the introduction of a metal

in the pincer fragment leads to intramolecular coordination of the

tertiary amines to palladium or platinum.

electron density.^57,75,76The fact that the ¹⁹⁵Pt NMR resonance

frequencies of a number of para-substituted NCN-pincer PtCl

([PtCl(NCN-Z)], Z = para-substituent) are known, allowed us

to deduce Hammett substituent constants for the [5,10,15-tris(p-

tolyl)porphyrinato]M¹(II) group as a whole. To this end, we used

Slagt’s formula (eqn (1)):⁷⁷

d(¹⁹⁵Pt) = 170.8s_p- 3137.8

(1)

The results are summarised in Table 2. A comparison of the val-

ues found for the classical para-substituted systems and the current

para-metalloporphyrin substituted systems leads to the conclusion

that, with direct C_meso–C_parabonding, the electronic inﬂuence ex-

erted by a [5,10,15-tris(p-tolyl)porphyrinato]magnesium(II) group

quite closely matches that of a phenolic OH group (viz. s_p=-0.34

and -0.37, respectively).⁷⁸On the other end of the spectrum, the

free-base 5,10,15-tris(p-tolyl)porphyrin para-substituent comes

electronically closer to a tert-butyl substituent.

Catalysis

NCN-pincer metal complexes have been used extensively as

homogeneous catalysts for C–C coupling reactions. In this respect,

the Lewis acid catalysed Michael addition of a-cyano carboxylates

to alkyl vinyl ketones has been the subject of speciﬁc focus.^{30,34,79–84}

The relationship between the catalytic activities of several para-

substituted NCN-pincer palladium aqua complexes [Pd(NCN-

Z)OH₂]BF₄(Z = para-substituent) in this reaction and the nature

of the para-substituent was recently investigated by Van Koten

et al.⁸¹They found that there is an effect of the para-substituent on

the catalytic performance of the nearby palladium(II) centre. While

the reaction is relatively slow when either an electron-donating

or -withdrawing substituent is present at the para-position, there

seems to be an optimum in the catalytic activity of the NCN-

pincer palladium system when the Hammett parameter of its

para-substituent approaches 0. Likewise, Richards found that

the introduction of a para-nitro substituent in similar Phebox-

platinum complexes led to a tenfold decrease of its activity in

the same Michael addition compared to the para-H analog.³⁰

These ﬁndings prompted us to investigate the [M¹(M²X)] hybrids

complexes in the same Michael reaction.

The platinum-containing [M¹(PtCl)] compounds (M¹= 2H,

Mg, Ni, Zn) were furthermore analysed by ¹⁹⁵Pt NMR spec-

troscopy, since it has been previously shown to be an invaluable

tool for the analysis of the platinum-centred electron density

in NCN-pincer platinum complexes.^25,74Samples were measured

at 2–10 mM concentrations in CDCl₃. It was found that for

each compound the deviation of d_Ptwas less than 1 ppm within

this concentration range. In comparison with the range of d_Pt

achievable by classical para-substitution of NCN-pincer platinum

complexes (between -3236 and -2992 ppm),²⁵the current span

is modest (Table 2). However, these values are detectable and

reproducible and, therefore, indicate a difference in the electron

density at Pt as a direct consequence of a change of the porphyrin

metal.

Compared to the parent [PtCl(NCN)] system, all para-

porphyrin groups are electron donating. The obtained chemical

shifts show that the electron density at Pt increases in the

order M¹= 2H < Ni < Zn < Mg. Interestingly, this order

parallels the order of increasing energy of the HOMO of the re-

spective metal complex of the corresponding tetraphenylporphyrin

(TPP) complexes, i.e. the order of increasing ability to donate

Cationic palladium complexes

In order to use them as catalysts in the double Michael ad-

dition reaction the neutral complexes [2H(PdBr)], [Mg(PdCl)],

[Co(PdBr)], [Ni(PdBr)], and [Zn(PdBr)] were converted into

the corresponding cationic complexes [M¹(PdOH₂)]BF₄. To this

end, these compounds were reacted with an excess of AgBF₄

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Scheme 3 Synthesis of cationic aqua complexes [M¹(PdOH₂)]BF₄: (i) AgBF₄, i-Pr₂NEt, CH₂Cl₂, H₂O.

(1.4–1.9 equiv.) in CH₂Cl₂in the presence of an excess of the

base i-Pr₂NEt (~30 equiv.) (Scheme 3).

signals corresponding to the halidopalladio(II) compound were

completely absent, indicating a full conversion to the cationic

complex. These aqua complexes were not stored prior to use, but

synthesised and immediately used in the catalysis experiments.

Use of the latter was imperative since, in our case, AgBF₄always

seemed to contain traces of acid, which readily led to partial

demetalation of the magnesium(II) and zinc(II) porphyrins. Its

non-nucleophilic character further ensured that the corresponding

cationic complexes could be obtained in their aqua-form. After

completion of the halide abstraction, the product mixtures were

ﬁltered over Celite to remove AgX and non-dissolved AgBF₄.

After evaporation, the ﬁltrates were thoroughly washed with

H₂O, which removed i-Pr₂NEt·HX and residual silver salts, and

with hexanes, which eliminated any remaining i-Pr₂NEt. Final

puriﬁcation was achieved by precipitation of the desired cationic

complexes from a solution in acetone/MeOH with hexanes or

Et₂O. For the synthesis of [2H(PdOH₂)]BF₄a slightly modiﬁed

procedure without base was used, because it was envisaged that

it might accelerate the introduction of silver into the porphyrin

moiety. Thus, addition of AgBF₄led to quick formation of a

greenish reaction mixture, which, after removal of silver salts,

Catalytic double Michael addition

The catalysts (0.5% Pd) were accurately weighed into a reaction

ﬂask and CH₂Cl₂was added, leading to a suspension. Upon

subsequent addition of ethyl a-cyanoacetate (CN, 1 equiv.) all

solids dissolved. Methyl vinyl ketone (MVK, 3 equiv.) was added

and the double Michael addition (reaction 1) was initiated by

addition of Hu¨nig’s base (i-Pr₂NEt, 0.1 equiv.), and the reaction

progress was followed by ¹H NMR spectroscopy.^81,86

The catalytic results are summarised in Fig. 3 and in Table 3.

The data show that the catalytic activities of [2H(PdOH₂)]BF₄,

[Ni(PdOH₂)]BF₄, and [Zn(PdOH₂)]BF₄are remarkably sim-

ilar to that of the non-porphyrin substituted compound

[Pd(NCN)OH₂]BF₄.⁸⁷Apparently, the intramolecular inﬂuence

of the (metallo)porphyrin on the palladium(II) centre is too

small to cause signiﬁcant differences. A remarkable effect, how-

ever, was observed for the magnesium(II) porphyrin-containing

[Mg(PdOH₂)]BF₄, whose k_obsis more than six-fold higher than that

of [Pd(NCN)OH₂]BF₄. Plotting -ln([Q]/[Q]₀) vs. time revealed

that the reaction is ﬁrst order in both Q = CN and Q = MVK for

all catalysts.

1

turned red again upon addition of base. H NMR spectroscopy

conﬁrmed the free-base identity of the porphyrin part as the signals

corresponding to the pyrrolic protons at d = -2.81 ppm integrated

for two with respect to the benzylic signals. Unfortunately,

attempts to dehalogenate [Co(PdBr)] failed due to its tendency

to (partially) oxidise to the corresponding Co(III) species and the

synthesis of [Co(PdOH₂)]BF₄was therefore abandoned.

¹H and ¹⁹F NMR spectroscopy, and TLC analyses⁸⁵substanti-

ated the successful syntheses of the cationic complexes. MALDI-

TOF mass spectrometry was particularly diagnostic. With

9-nitroanthracene (9NA) as matrix, the parent halidopalladio(II)

complexes [M¹(PdX)] exhibited a strong molecular ion peak

in every case (vide supra), in addition to the [M–X]⁺peak.

In the cationic aqua complexes [M¹(PdOH₂)]BF₄, however, the

We anticipated that a fair comparison of the performances of

the pincer-porphyrin hybrids would require a determination of the

catalytic activities of their (metallo)porphyrin constituents MTTP

(M = 2H, Mg, Ni, Zn) (Chart 3). 2HTTP, NiTTP,⁸⁸and ZnTTP⁸⁹

were prepared according to literature procedures and MgTTP was

prepared following Lindsey’s procedure for the preparation of

magnesium(II) porphyrins.⁶⁵It was found that TTP and NiTTP

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Table 3 Catalytic results of the catalysts (1.60 mM) used for the double

Michael addition

Table 4 Observed

rate

constants

for

different

ratios

of

[Pd(NCN)OH₂]BF₄and MgTTP

Catalyst

k_obs(¥ 10^-6s^-1)^a

t

_1/2/min^b

[[Pd(NCN)OH₂]BF₄]/mM [MgTTP]/mM k_obs(¥ 10^-6s^-1)

[Pd(NCN)OH₂]BF₄

[2H(PdOH₂)]BF₄

[Mg(PdOH₂)]BF₄

[Ni(PdOH₂)]BF₄

[Zn(PdOH₂)]BF₄

2HTTP

MgTTP

NiTTP

ZnTTP

300

280

1919

305

298

6

26

6

7

39

41

6

38

Entry 1 1.60

Entry 2 0.00

Entry 3 0.80

Entry 4 0.40

Entry 5 0.20

Entry 6 1.60

Entry 7 0.80

Entry 8 0.80

Entry 9 0.40

0.00

1.60

0.00

1.60

0.40

0.80

300

26

130

55

39

24

1925

444

1925

1650

1925

657

180

294

136

AgX (X = Br, BF₄)

[PdBr(NCN)]

Blank

6

only increases from 6 to 7 ¥ 10^-6s^-1(background reaction vs.

ZnTTP-catalysed reaction), the catalytic activity of MgTTP is

higher with a k_obsof 26 ¥ 10^-6s^-1.

^aDetermined by ¹H NMR spectroscopy. The rate constant k_obswas

determined by plotting -ln([CN]/[CN]₀) vs. time in seconds. t_1/2

ln2/(k ¥ 60)

b

=

In order to investigate intermolecular effects in the Michael

addition, several experiments involving the constituents of the

pincer-porphyrin hybrids, [Pd(NCN)OH₂]BF₄and the appropriate

MTTP, were conducted. It was found that the addition of

stoichiometric amounts of either 2HTTP, NiTTP, or ZnTTP to

catalytic runs of [Pd(NCN)OH₂]BF₄did not lead to appreciable

effects on the rate of the reaction. However, a dramatic increase

in the rate was observed when one equivalent of MgTTP was

used in combination with [Pd(NCN)OH₂]BF₄: whereas k_obsfor

[Pd(NCN)OH₂]BF₄was found to be 300 ¥ 10^-6s^-1, addition of

an equimolar amount of MgTTP (with respect to Pd) virtually

doubled the reaction rate to k_obs= 657 ¥ 10^-6s^-1(Table 4).

Interestingly, this value is still a factor of three lower than that of

[Mg(PdOH₂)]BF₄itself, which indicates that its increased catalytic

activity is not solely due to the arbitrary combination of the two

constituents.

Next, the reaction was performed at different concentrations

of [Pd(NCN)OH₂]BF₄and MgTTP and combinations thereof.

Entries 1, 3, 4 and 5 of Table 4 show that a doubling of

the concentration of [Pd(NCN)OH₂]BF₄leads to an increase

in reaction rate by a factor of ~2.3, which makes the order in

[Pd(NCN)OH₂]BF₄for this reaction amounting to 1.15 in the

absence of MgTTP. When MgTTP is added to the catalytic system,

it functions as a co-catalyst. The addition of an equimolar amount

of MgTTP leads to a 2.2 times faster reaction (cf. entries 1

and 6), while MgTTP itself is only a moderate catalyst (entry

2). Entries 1, 2, 7, 8 and 9 show that the overall effect of

[Pd(NCN)OH₂]BF₄on the catalytic rate is larger than that

of MgTTP. With respect to entry 8, the use of half the amount

of [Pd(NCN)OH₂]BF₄leads to a rate decrease of 54% (entry 9),

whereas the use of a [Pd(NCN)OH₂]BF₄/MgTTP ratio of 2/1

leads to a drop in activity of only 39% (entry 7). This is in accord

with the fact that [Pd(NCN)OH₂]BF₄itself is a better catalyst than

MgTTP. However, it is clear that the rate enhancement cannot be

attributed to the mere sum of the catalytic activities of the two

components.

Fig. 3 Plots of 1000{-ln([CN]/[CN]₀)} vs. time for cationic NCN-pincer

palladium complexes.

On the other hand, when the two co-catalysts are merged

within one molecule, as in [Mg(PdOH₂]BF₄, the situation changes

dramatically. At the same total concentration of NCN-pincer

palladium(II) aqua complex and magnesium(II) porphyrin, the

rate of [Mg(PdOH₂]BF₄exceeds that of a 1 : 1 combination of

MgTTP and [Pd(NCN)OH₂]BF₄by a factor of three (Table 5). For

example, at a concentration of 1.60 mM the rate is 1919 ¥ 10^-6s^-1

Chart 3

did not show any activity when compared to the blank reaction.

However, ZnTTP showed some activity (36% conversion after 18 h

compared to 28% for the blank). This is ascribed to the potential

of the nitrile group of CN to coordinate to zinc(II), which also

inductively renders its a-CH₂protons more acidic. Whereas k_obs

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Table 5 Comparison of the catalytic activities of [Mg(PdOH₂)]BF₄and

substitution of the porphyrin core does not lead to an enhanced

effect of the metalloporphyrin on the NCN-pincer metal centre of

the mono-systems compared to those of the tetrakis-systems. In

fact, the d_Ptrange obtained for the tetra-pincer-porphyrin hybrids

[M¹(PtCl)₄] seems to exceed that of the corresponding mono-

pincer-porphyrin hybrids [M¹(PtCl)] (for M¹= 2H, Ni, Zn), viz.

14 ppm for the former compared to 8 ppm for the latter. This

might originate from a difference in electron-donating ability of

the (metallo)porphyrin parts of these molecules.

combinations of its components

[[Mg(PdOH₂)]BF₄]/mM

Entry 1 1.60

Entry 2 0.80

Entry 3 0.40

k_obs(¥ 10^-6s^-1)

1919

897

411

[[Pd(NCN)OH₂]BF₄] (mM)

[MgTTP] (mM)

The current research was initially aimed at intramolecularly

inﬂuencing the catalytic properties of the NCN-pincer palladium

centres by changing the electronic characteristics of their metal-

loporphyrin para-substituents through metalation with electroni-

cally diverse metals. When taking into account the small electronic

effects exerted by the (metallo)porphyrin on the metallopincer

moiety, as demonstrated by the rather small differences between

the ¹⁹⁵Pt NMR chemical shifts of different [M¹(PtCl)] molecules,

it is not surprising that the catalytic activities of [2H(PdOH₂)]BF₄,

[Ni(PdOH₂)]BF₄, and [Zn(PdOH₂)]BF₄are remarkably simi-

lar and virtually identical to that of [Pd(NCN)OH₂]BF₄. The

signiﬁcant exception to this observation is [Mg(PdOH₂)]BF₄,

which shows a six-fold higher catalytic activity compared to

the other NCN-pincer Pd complexes. The ¹⁹⁵Pt chemical shift

of the related [Mg(PtCl)] strongly suggests that the exceedingly

high activity of [Mg(PdOH₂)]BF₄cannot be ascribed to in-

tramolecular electronic effects broughtabout by the magnesium(II)

porphyrin. The rate increase in the two-catalyst-systems consisting

of [Pd(NCN)OH₂]BF₄and MgTTP showed that, indeed, an

intermolecular mechanism needs to be invoked, as the effect of

MgTTP on the activity of [Pd(NCN)OH₂]BF₄by far exceeds the

expected increase in case these two metal–ligand moieties would

only operate as independent catalysts.

Entry 4

Entry 5

1.60

0.80

1.60

0.80

657

294

for [Mg(PdOH₂]BF₄and 657 ¥ 10^-6s^-1for the 1 : 1 combination

of MgTTP and [Pd(NCN)OH₂]BF₄(entry 1 vs. 4). At 0.80 mM,

these rates have been reduced by a factor of approximately two

to 897 and 294 ¥ 10^-6s^-1, respectively (entry 2 vs. 5). A further

reduction of the concentration of [Mg(PdOH₂]BF₄to 0.4 mM

ﬁnally leads to a k_obsof 411 ¥ 10^-6s^-1(entry 3). Consequently, it

seems that for the three investigated concentrations, a doubling

of the concentration brings about an approximate doubling in the

activity. To a good approximation the reaction rate is ﬁrst order

in [Mg(PdOH₂)]BF₄, and also ﬁrst order in the combination of

MgTTP and [Pd(NCN)OH₂]BF₄.

After the catalytic runs, the pincer-porphyrin hybrid catalysts

could be efﬁciently precipitated from the reaction mixtures. The

addition of hexanes to the (complete) catalytic runs brought about

a greater than 99.9% precipitation of the catalysts (as judged

from UV-vis spectra of the hexane layer), which were isolated as

their complexes with the reaction product. The re-application of

these complexes as catalysts in the same double Michael addition

reaction led to identical activities for at least two consecutive runs.

Bimetallic catalysis

Discussion

In their work on NCN-pincer M-catalysed (M = Pd, Pt) double

Michael additions between a-cyano acetates and methyl vinyl

ketone, Richards and co-workers showed that the catalytic mech-

anism of these reactions operates by virtue of coordination of

the nitrogen atom of the cyano group of the substrate to the

palladium atom at the position trans with respect to the C–M

s-bond.^79,80This coordination event inductively lowers the pK_a

of the CH₂protons adjacent to the cyano group, leading to an

enhanced deprotonation and reaction (Scheme 4).

During the course of the research reported here, it was found

that the reaction rate of the [Pd(NCN)OH₂]BF₄-catalysed double

Michael addition is ﬁrst order in [CN], ﬁrst order in [MVK] and

approximately ﬁrst order in [catalyst]. These ﬁndings indicate a

transition state in which all three components are present, which

is in accordance with the nucleophilic attack of the transient

palladium-coordinated cyano enolate on the a,b-unsaturated

ketone MVK (Scheme 4, TS 1). The order in [Pd(NCN)OH₂]BF₄

deviates somewhat from 1 (~1.15), which shows that more than

one catalytic mechanism is operative. This might indicate that, in

addition to activating the cyano substrate, the palladium catalyst

is also capable of activating the MVK towards nucleophilic attack

(vide infra), albeit to a smaller extent. It was also found that

MgTTP catalyses the double Michael addition reaction, albeit

with a rather low reaction rate (cf. k_obsis 26 ¥ 10^-6s^-1compared

Intramolecular electronic interaction

The mono(NCN-pincer metal)-metalloporphyrin hybrid com-

plexes described here are best compared to the tetrakis(NCN-

pincer metal)-metalloporphyrin hybrid complexes described

earlier,⁵⁹regarding their physical properties and, consequently,

regarding the interactions between the metal sites within these

complexes. The metalation of the meso-NCN-pincer ligands of

a tetrakis(NCN-pincer)-metalloporphyrin causes a substantial

bathochromic shift of the Soret band in the electronic spectra of the

molecule (Dl_maxª4 nm for palladation and 12 nm for platination).⁵⁹

This was ascribed to an electronic interaction between the

porphyrin and the meso-phenyl groups, caused by peripheral

palladation or platination. Given the smaller changes of the Soret

band of the present mono(NCN-pincer)-metalloporphyrin hybrids

upon metalation of the pincer sites (Dl_maxª1 nm for palladation

and 3 nm for platination), it seems that this effect is in fact

cumulative. From preliminary ¹⁹⁵Pt NMR studies it was concluded

that in the tetra-substituted systems the electronic properties of

the porphyrin are passed on to the peripheral metal centres.⁵⁹In

light of the cumulative effect of the metallopincer moieties on the

porphyrin core, we anticipated a potential dilution of the effects of

the porphyrin on multiple NCN-pincer metal centres. As it turns

out, ¹⁹⁵Pt NMR spectroscopy on these systems shows that mono-

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Scheme 4 Proposed mechanisms and transition states for the catalysed Michael addition reaction (R = H or CH₂CH₂C(O)CH₃). The porphyrin

substituents have been omitted for clarity.

to 300 ¥ 10^-6s^-1for [Pd(NCN)OH₂]BF₄). The catalytic effect

of MgTTP is probably caused by coordination of either of the

substrates to the magnesium centre.

as “cooperative dual catalysis”, they used a combination of a

(salen)Al m-oxo dimer and a (pybox)YbCl₃complex to greatly

increase the rate and enantioselectivity of the reaction with

respect to the rates achieved by either of the two catalysts

independently. Recently, Peters et al. described the elegant use

of a bis(palladium complex) ferrocene as a bimetallic catalyst

for highly enantioselective Michael additions between a-cyano-

aryl-acetates and methyl vinyl ketone.⁹³They attribute activation

The observed rate increase upon combining MgTTP and

[Pd(NCN)OH₂]BF₄in a co-catalytic mixture might be explained

by the well-known ability of Lewis acids to catalyse Michael

additions via coordination to, and concomitant activation of,

Michael acceptor systems.⁹⁰For the co-catalytic set-up, we propose

that MgTTP enhances the rate of reaction through activation of

MVK toward nucleophilic attack by coordination to its carbonyl

oxygen atom through its hard magnesium atom (Scheme 4, TS

2). It should be noted, however, that due to the substantial

catalytic activity of [Pd(NCN)OH₂]BF₄both the palladium-

catalysed reaction and the co-catalytic reaction are likely operating

simultaneously and each contribute to the overall reaction rate.

Similar co-catalytic behaviour has been observed before, for

instance by Ito and co-workers. They showed that nitriles, which

are activated by coordination to rhodium, can be alkylated by

using the ability of a co-catalytic palladium complex to generate

=

of methyl vinyl ketone to coordination of its C C bond to the

soft Pd.

The one-to-one merger of MgTTP and [Pd(NCN)OH₂]BF₄into

one molecule, i.e. into [Mg(PdOH₂)]BF₄, leads to a three-fold in-

crease of its catalytic activity compared to that found for a 1 : 1 mix-

ture of its constituents. Molecular modelling studies showed that

the enhanced performance cannot be explained by the classical

effect of bimetallic catalysis, i.e. wherein two intramolecular metal

sites cooperate directly.^93–96The distance between a palladium-

coordinated CN carbanion and a magnesium-coordinated MVK

reactant within the same pincer-porphyrin unit would be simply

too large for a direct reaction to occur. Since the two substrates

cannot react with each other intramolecularly, a rationale for the

rate enhancement has to be based on intermolecular arguments.

3

electrophilic h -allyl species from allylic carbonates.⁹¹A related

effect was exploited by Jacobsen et al. in an enantioselective

conjugate cyanation of unsatured imides.⁹²In what was coined

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With an initial 200-fold excess of CN and a 600-fold excess

of MVK it is plausible to assume that the pincer-porphyrin

hybrids exist as fully substrate-coordinated species. The CN nitrile

is coordinated to palladium while the magnesium(II) ions are

coordinated to the MVK carbonyl atom. When the C_aposition

of the coordinated CN group is deprotonated, each catalyst-

substrate complex contains two activated substrate species. The

moment two such perligated molecules approach each other,

the ﬁrst Michael addition is intermolecular. The occurrence of

this reaction at the same time interconnects the two pincer-

porphyrin hybrids via two coordination bonds (Mg–O and Pd–N

bonds), making the second Michael addition on the opposite

site of the complex an intramolecular reaction, which would

lead to a rate enhancement. Several such mechanisms can be

proposed. However, more experimental evidence will be needed

to formulate a deﬁnitive model explaining the observed catalytic

rate enhancement.

Surprisingly, however, the magnesium-palladium hybrid

[Mg(PdOH₂)]BF₄catalysed the double Michael reaction six times

faster than all other hybrids. Control experiments showed that this

observation could partially be attributed to the activating effect of

the magnesium(II) porphyrin moiety on MVK, which leads to a

cooperative dual catalysis mechanism in which the CN-substrate

is activated by the pincer-Pd fragment while the magnesium

porphyrin activates the MVK substrate. To fully account for the

enhanced activity of [Mg(PdOH₂)]BF₄, though, a supramolecular

mechanism has been proposed. To the best of our knowledge, this

is one of the ﬁrst examples in which such supramolecular catalysis

behaviour is operative. It shows the promising application of the

conceptof “cooperative dualcatalysis” butalsounderlines the pos-

sibility of enhancing the catalytic properties of these systems even

further by merging or interconnecting the collaborating catalysts.

Experimental

Finally, it is worthwhile to discuss the differences between the

similar zinc(II) and magnesium(II) porphyrins, since, unlike their

magnesium(II) relatives, none of the catalyst(-mixtures) containing

ZnTTP or [Zn(PdOH₂)]BF₄showed a signiﬁcant increase in

activity. While their sizes are similar, zinc(II) is considered to be a

“softer” metal than magnesium(II).^97,98In a number of cases, this

has led to intricate differences between their reactivities in identical

ligand systems.^99,100Being a hard ion, magnesium(II) prefers to

bind to hard oxygen-containing ligands such as carbonyls,^101,102

while the interaction of zinc(II) porphyrins with ketones is known

to be extremely weak.¹⁰³For the current situation, these ﬁndings

lead to the much stronger coordination of MVK to magnesium

compared to zinc,¹⁰⁴which would lead to a more efﬁcient activation

of MVK. Based on the hard–soft acid–based (HSAB) concept, it is

expected that MVK is activated by coordination of its oxygen atom

General

Unless stated otherwise, all reactions were performed under a

dry, oxygen-free, nitrogen atmosphere using standard Schlenk

techniques and were shielded from ambient light using aluminium

foil. Et₂O and THF were carefully dried and distilled from

sodium/benzophenone prior to use, while CH₂Cl₂, Et₃N, and i-

Pr₂NEt were distilled from CaH₂. Pyrrole was dis_◦tilled from CaH₂

and stored under a nitrogen atmosphere at -30 C. Methyl vinyl

ketone and ethyl a-cyanoacetate were each distilled three times

prior to use. All solvents and liquid reagents were thoroughly

deoxygenated with a steady stream of nitrogen for at least

20 min before storage or use. 3,5-Bis(methoxymethyl)-4-bromo-

benzaldehyde (1),⁵⁹[Pd₂dba₃]·CHCl₃,¹⁰⁸and [Pt₂dipdba₃]¹⁰⁹were

synthesised according to literature procedures. The syntheses of

MgTTP, NiTTP and ZnTTP are described in the electronic sup-

plementary information. Column chromatography was performed

using ACROS silica gel for column chromatography, 0.060–

0.200 mm, pore diameter ca. 6 nm or Merck Aluminium oxide 90,

=

to magnesium rather than by its C C double bond to Pd, which

is the rationale put forward by Peters et al. for their systems.⁹³

active basic (0.063–0.200 mm). ¹H and ¹³C{ H} NMR spectra were

1

Conclusions

recorded at 300 MHz and 75 MHz, respectively, on a Varian 300

spectrometer operating at 298 K, and were referenced to residual

solvent signal. J values are given in Hz. The ¹³C NMR signals for

the free-base porphyrin a- and b-carbon atoms were not resolved

due to extreme line-broadening.¹¹⁰UV-vis spectra were recorded

on a Cary 50 scan UV-visible spectrophotometer. MALDI-

TOF measurements were performed on an Applied Biosys-

tems Voyager-DE PRO biospectrometry workstation with either

9-nitroanthracene (9NA) or 2,5-dihydroxybenzoic acid (DHB)

as the matrix, or without matrix (LDI); ESI-MS measurements

were performed at the Biomolecular Mass Spectrometry Group,

Bijvoet Centre for Biomolecular Research, Utrecht University,

the Netherlands. Elemental microanalyses were performed by

Dornis und Kolbe, Mikroanalytisches Laboratorium, Mu¨llheim

a/d Ruhr, Germany.

A series of hetero-bimetallic mono-pincer-porphyrin hybrids have

been synthesised in excellent yields. Two routes were employed to

arrive at these compounds, namely route A, in which the porphyrin

is metalated prior to pincer metalation and route B, in which the

latter precedes the former. In all cases, route A proved to be the

highest yielding, although it sacriﬁces the modular approach of

the synthesis route to a certain extent. In accordance with ¹⁹⁵Pt

NMR measurements on [M¹(PtCl)] (M¹= 2H, Mg, Ni, Zn),

which did not show a strong inﬂuence of the metalloporphyrin

pincer-para substituent on the electron density at the Pt centre,

the catalytic activities of the corresponding cationic palladium

complexes [M¹(PdOH₂)]BF₄(M¹= 2H, Ni, Zn) in the double

Michael reaction of ethyl a-cyanoacetate with methyl vinyl ketone

turned out to be very similar and comparable to the value found

for [Pd(NCN)OH₂]BF₄. To genuinely promote a through-bond

inﬂuence of the porphyrin on the pincer, several times greater

than the ones we observe in the current systems, it is advisable

to introduce a spacer in between the two constituents that allows

for co-planarity of the two attached p-systems. In this respect,

the ethyn-diyl spacer has proven to be highly promising in related

systems.^105–107

5-[3,5-Bis(methoxymethyl)-4-bromophenyl]-10,15,20-tris(p-

tolyl)porphyrin (2)

Freshly distilled pyrrole (14.1 mL, 203 mmol) was added

during 1 min to a colourless, reﬂuxing solution of 3,5-

bis(methoxymethyl)-4-bromobenzaldehyde 1 (7.91 g, 29.0 mmol)

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and p-tolualdehyde (20.6 mL, 174 mmol) in propionic acid

(200 mL). The solution immediately darkened, eventually turning

black, and reﬂux was maintained for a further 35 min under air.

The solution was allowed to cool down to room temperature

overnight, after which the purple microcrystalline precipitate was

ﬁltered off and washed with MeOH until the washings were colour-

less. The residue was dissolved in CH₂Cl₂(1.1 L), treated with

DDQ (300 mg, 1.32 mmol) and the resulting orange mixture was

stirred at ambient temperature for 30 min. The mixture was loaded

onto a silica gel column, which was prepared with hexanes/CH₂Cl₂

(1 : 1, v/v). The ﬁrst band was eluted with hexanes/CH₂Cl₂(1 : 1 →

1 : 5, v/v) and the volatiles were evaporated to give TTP (3.71 g,

13%) as a purple, crystalline solid. LDI-TOF MS: m/z 671.61 ([M

+ H]⁺), calcd for C₄₈H₃₉N₄: 671.32. The second band containing

2 was eluted with hexanes/CH₂Cl₂(1 : 5, v/v) and CH₂Cl₂–THF

(19 : 1, v/v). The volatiles were concentrated to 10 mL and MeOH

(80 mL) was added at once to induce precipitation of 2 as a purple,

ﬂuffy solid (1.78 g, 7.4%), which was collected by centrifugation.

Found: C 74.24, H 5.20, N 6.71. Calcd for C₅₁H₄₃BrN₄O₂: C 74.36,

H 5.26, N 6.80%; l_max(CH₂Cl₂)/nm 419 (log e 5.72), 516 (4.30),

553 (4.04), 594 (3.77), 646 (3.77); d_H(CDCl₃) 8.87 (6 H, m, b-H),

8.81 (2 H, d, J 4.8, b-H), 8.25 (2 H, s, ArH_pincer), 8.09 (6 H, d, J

7.8, ArH_p-tol), 7.56 (6 H, d, J 7.8, ArH_p-tol), 4.85 (4 H, s, CH₂O),

3.54 (6 H, s, OCH₃), 2.71 (9 H, s, ArCH₃), -2.78 (2 H, s, NH);

d_C(CDCl₃) 141.6, 139.5, 139.4, 137.6, 136.5, 134.7, 134.2, 127.6,

123.1, 120.7, 120.5, 118.6, 74.6, 59.0, 21.7; ESI-MS: m/z 825.11

([M + H]⁺. C₅₁H₄₄BrN₄O₂requires 825.26).

organic layer was dried (MgSO₄), ﬁltered and concentrated with

MeOH (100 mL) to 40 mL. The product was isolated as a purple

solid. Yield: 258 mg (97%). Found: C 74.83, H 5.75, N 9.80. Calcd

for C₅₃H₄₉BrN₆: C 74.90, H 5.81, N 9.89%; l_max(CH₂Cl₂)/nm 419

(log e 5.88), 517 (4.49), 552 (4.19), 592 (3.99), 648 (3.89); d_H(CDCl₃)

8.88 (6 H, m, b-H), 8.81 (2 H, d, J 4.8, b-H), 8.19 (2 H, s, ArH_pincer),

8.10 (6 H, d, J 7.8, ArH_p-tol), 7.56 (6 H, d, J 7.8, ArH_p-tol), 3.84

(4 H, s, CH₂N), 2.71 (9 H, s, ArCH₃), 2.43 (12 H, s, N(CH₃)₂),

-2.77 (2 H, s, NH); d_C(CDCl₃) 140.9, 139.4, 139.4, 137.5, 137.3,

135.6, 134.6, 127.6, 127.2, 120.5, 120.4, 118.8, 64.4, 46.0, 21.7;

MALDI-TOF MS (DHB): m/z 849.86 ([M + H]⁺. C₅₃H₄₉BrN₆

requires 825.26).

5-(3,5-Bis[(dimethylamino)methyl]-4-bromidopalladio(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrin ([2H(PdBr)])

[2H(Br)] (37 mg, 44 mmol) was dissolved in dry benzene (10 mL),

[Pd₂dba₃]·CHCl₃(25 mg, 24 mmol) was added, and the dark red

solution stirred at ambient temperature for 16 h. MeOH (0.2 mL)

and Et₂NH (0.2 mL) were then added and after three hours,

the mixture was ﬁltered over Celite and the residue was washed

with benzene/acetone (1 : 1, v/v, 20 mL). The red ﬁltrate was

concentrated to 5 mL and hexanes (80 mL) were added to

precipitate the product [2H(PdBr)] as a purple solid, which was

isolated by centrifugation. Possible dba contamination can be

washed away with hexanes. Yield: 38 mg (90%). Found: C 66.48,

H 5.04, N 8.71. Calcd for C₅₃H₄₉BrN₆Pd: C 66.56, H 5.16, N

8.79%; l_max(CH₂Cl₂)/nm 421 (log e 5.79), 517 (4.37), 554 (4.13),

595 (3.83), 651 (3.78); d_H(CDCl₃) 8.85 (8 H, m, b-H), 8.09 (6 H, d,

J 7.8, ArH_p-tol), 7.59 (2 H, s, ArH_pincer), 7.54 (6 H, d, J 7.8, ArH_p-tol),

4.24 (4 H, s, CH₂N), 3.17 (12 H, s, N(CH₃)₂), 2.71 (9 H, s, ArCH₃),

-2.77 (2 H, s, NH); d_C(CDCl₃) 157.0, 143.3, 139.3, 139.0, 137.5,

137.5, 134.6, 131.2 (br), 127.6, 126.3, 120.4, 120.3, 120.1, 74.8,

54.0, 31.1; MALDI-TOF MS (DHB): m/z 957.09 ([M + H]⁺.

C₅₃H₅₀BrN₆Pd requires 956.34), 874.97 ([M - Br]⁺. C₅₃H₄₉N₆Pd

requires 875.31), 769.77 ([M - PdBr]⁺. C₅₃H₅₀N₆requires 769.40).

5-[3,5-Bis(bromomethyl)-4-bromophenyl]-10,15,20-tris(p-

tolyl)porphyrin (3)

A suspension of 2 (483 mg, 586 mmol) in CH₂Cl₂(43 mL) was

treated with HBr/HOAc (185 mL) and the resulting green solution

was stirred for 4.5 h at room temperature. Ice water was added

and after 10 min, the layers were separated. The organic layer

was washed with H₂O (100 mL) and 4 M K₂CO₃(2 ¥ 100 mL)

(the organic layer now turned red), dried (MgSO₄), ﬁltered, and

concentrated to 40 mL. The red solution was loaded onto a silica

gel column, and the desired product was eluted as the ﬁrst red

band with CH₂Cl₂–hexane (1 : 1, v/v). This band was collected,

evaporated to 20 mL and hexane was added to induce precipitation

of the title compound as a purple solid. Yield: 439 mg (82%).

Found: C 63.74, H 4.12, N 5.96. Calcd for C₄₉H₃₇Br₃N₄: C 63.86,

H 4.06, N 6.08%; l_max(CH₂Cl₂)/nm 420 (log e 5.71), 516 (4.32),

553 (4.00), 592 (3.82), 647 (3.74); d_H(CDCl₃) 8.92 (2 H, d, J 4.8,

b-H), 8.87 (4 H, s, b-H), 8.80 (2 H, d, J 4.8, b-H), 8.28 (2 H, s,

ArH_pincer), 8.09 (6 H, d, J 7.8, ArH_p-tol), 7.56 (6 H, d, J 7.8, ArH_p-tol),

4.92 (4 H, s, CH₂Br), 2.71 (9 H, s, ArCH₃), -2.79 (2 H, s, NH);

d_C(CDCl₃) 142.6, 139.3, 139.2, 137.6, 137.5, 137.1, 137.0, 134.6,

127.6, 126.4, 121.0, 120.7, 116.5, 34.1, 21.7; MALDI-TOF MS

(DHB): m/z 923.01 ([M + H]⁺. C₄₉H₃₈Br₃N₄requires 923.05).

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromophenyl)-10,15,20-

tris(p-tolyl)porphyrinato]-magnesium(II) ([Mg(Br)])

Magnesium was introduced by stirring a solution of [2H(Br)]

(102 mg, 120 mmol) in a mixture of CH₂Cl₂(10 mL) and Et₃N

(1 mL) with MgBr₂·OEt₂(668mg, 2.59mmol) at room temperature

for 15 min. All volatiles were subsequently evaporated and the

residue was suspended in CH₂Cl₂and loaded onto an alumina col-

umn. Elution with Et₃N/CH₂Cl₂(1 : 200, v/v) gave residual start-

ing material, whereas the desired product was eluted with THF–

CH₂Cl₂(1 : 10, v/v). The product-containing band was evaporated

to dryness, toluene was added and the mixture was evaporated to

dryness once again. The remaining solid was taken up in CH₂Cl₂

(40 mL) and washed with H₂O (2 ¥ 60 mL), K₂CO₃(0.5 M, 2 ¥

60 mL), and brine (50 mL). The organic layer was dried (MgSO₄),

ﬁltered and concentrated to 5 mL. Hexanes (50 mL) were added,

the mixture was concentrated to 30 mL) and the precipitated

blue/greenish solid was collected by centrifugation and dried in

vacuo. Yield: 100 mg (96%). Found: C 66.90, H 6.85, N 6.87. Calcd

for C₆₇H₈₃BrCl₂MgN₆O₃(C₅₃H₄₇BrMgN₆·CH₂Cl₂·3H₂O·2C₆H₁₄):

C 67.31, H 7.00, N 7.03%; l_max(CH₂Cl₂)/nm 427 (log e 5.84), 565

(4.33), 605 (4.11); d_H(CDCl₃/1% pyridine-d₅) 8.87 (6 H, m, b-H),

5-(3,5-Bis[(dimethylamino)methyl]-4-bromophenyl)-10,15,20-

tris(p-tolyl)porphyrin ([2H(Br)])

A dark red solution of 3 (288 mg, 312 mmol) in CH₂Cl₂(40 mL)

was treated with Me₂NH (0.5 mL, excess) at room temperature and

the solution was stirred for 3 h. Degassed H₂O (40 mL) was added

and after 3 h of vigorous stirring, the layers were separated and the

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8.81 (2 H, d, J 4.4, b-H), 8.15 (2 H, s, ArH_pincer), 8.07 (6 H, d, J 7.6,

ArH_p-tol), 7.51 (6 H, d, J 7.6, ArH_p-tol), 3.81 (4 H, s, CH₂N), 2.69

(9 H, s, ArCH₃), 2.41 (12 H, s, N(CH₃)₂; d_C(CDCl₃/1% pyridine-

d₅) 150.3, 150.3, 150.0, 142.6, 141.1, 136.8, 136.7, 136.0, 134.8,

134.8, 132.2, 132.0, 132.0, 131.5, 127.2, 126.8, 122.1, 121.9, 120.3,

64.5, 46.0, 21.7; LDI-TOF MS: m/z 872.31 (M⁺. C₅₃H₄₇BrMgN₆

requires 872.29).

Et₂NH (2 drops) after 2 h. After a further 3 h, all volatiles were

evaporated in vacuo and the red residue was redissolved in benzene

(20 mL) and ﬁltered through Celite. The ﬁltrate was concentrated

to dryness and the resulting solid was washed with pentane (3 ¥

50 mL) to give a red solid. Yield: 55.2 mg (81%). l_max(CH₂Cl₂)/nm

413 (relative intensity 1.000), 530 (0.060); d_H(CDCl₃) 15.91 (8 H,

br, b-H), 13.06 (6 H, br, ArH_p-tol), 12.57 (2 H, br, ArH_pincer), 9.74

(6 H, br, ArH_p-tol), 5.47 (4 H, s, CH₂N), 4.16 (6 H, s, ArCH₃),

4.13 (3 H, s, ArCH₃), 4.07 (12 H, s, N(CH₃)₂); due to extreme

line broadening a ¹³C spectrum could not be recorded; MALDI-

TOF MS (9NA): m/z 1013.73 ([M]⁺. C₅₃H₄₇BrCoN₆Pd requires

1013.14), 932.51 ([M - Br]⁺. C₅₃H₄₇CoN₆Pd requires 932.23),

[5-(3,5-Bis[(dimethylamino)methyl]-4-chloridopalladio(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]magnesium(II) ([Mg(PdCl)])

[Pd₂dba₃]·CHCl₃(48 mg, 46 mmol) and [Mg(Br)] (60 mg, 69 mmol)

were weighed into a ﬂame-dried Schlenk and dry benzene (30 mL)

was added, yielding a reddish suspension. Dry THF (2 mL) was

added whereupon all solids dissolved, and the solution was stirred

for 3 h at room temperature. Et₂NH (100 mL) and MeOH (100 mL)

were then added and after an additional 2 h of stirring, the mixture

was ﬁltered over Celite and the residue was washed with acetone.

All volatiles were evaporated and the resulting purple solid was

stirred overnight in a mixture of CH₂Cl₂(10 mL) and brine

(10 mL). The organic layer was isolated, dried (MgSO₄), ﬁltered,

and concentrated to 5 mL. Upon addition of hexanes (80 mL) the

desired product precipitated as a greenish solid, which was isolated

by centrifugation and dried in vacuo. Yield: 59 mg (88%). Found:

C 67.93, H 5.05, N 8.78. Calcd for C₅₃H₄₇ClMgN₆Pd: C 68.14, H

5.07, N 9.00%; l_max(CH₂Cl₂)/nm 426 (log e 5.84), 566 (4.39), 606

(4.20); d_H(CDCl₃/1% pyridine-d₅) 8.87 (8 H, m, b-H), 8.06 (6 H,

m, ArH_p-tol), 7.58 (2 H, s, ArH_pincer), 7.50 (6 H, m, ArH_p-tol), 4.20

(4 H, s, CH₂N), 3.11 (12 H, s, N(CH₃)₂), 2.69 (6 H, s, ArCH₃), 2.67

(3 H, s, ArCH₃); d_C(CDCl₃/1% pyridine-d₅) 155.4, 150.4, 150.3,

150.2, 150.1, 142.8, 141.1, 140.7, 136.8, 134.8, 132.0, 131.9, 131.7,

127.2, 126.6, 121.9, 121.8, 121.7, 75.1, 53.5, 21.7; MALDI-TOF

MS (9NA): m/z 934.63 ([M]⁺. C₅₃H₄₇ClMgN₆Pd requires 934.25),

897.53 ([M - Cl]⁺. C₅₃H₄₇MgN₆Pd requires 897.54), 791.29 ([M -

PdCl]⁺. C₅₃H₄₇MgN₆requires 791.37).

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromophenyl)-10,15,20-

tris(p-tolyl)porphyrinato]nickel(II) ([Ni(Br)])

[2H(Br)] (23 mg, 27 mmol) and Ni(acac)₂(0.16 g, 623 mmol) were

suspended in dry toluene and the mixture was heated to reﬂux

for 2 h. All volatiles were subsequently evaporated in vacuo and

the remaining orange solid was dissolved in CH₂Cl₂(20 mL)

and washed with 5% K₂CO₃(4 ¥ 40 mL). The organic layer

was isolated, dried (MgSO₄) and ﬁltered over basic Al₂O₃with

THF–CH₂Cl₂(1 : 49, v/v). The orange ﬁltrate was concentrated

to 3 mL, MeOH (50 mL) was added and the orange mixture

was concentrated to 20 mL. After 1 h, the orange solid was

isolated by centrifugation and dried in vacuo. Yield: 23 mg (94%).

l

_max(CH₂Cl₂)/nm 416 (log e 5.73), 528 (4.59); d_H(CDCl₃) 8.77 (6 H,

m, b-H), 8.71 (2H, d, J 5.1, b-H), 7.99 (2 H, s, ArH_pincer), 7.89

(6 H, d, J 7.5, ArH_p-tol), 7.48 (6 H, d, J 7.5, ArH_p-tol), 3.78 (4 H, s,

CH₂N), 2.65 (6 H, s, ArCH₃), 2.39 (12 H, s, N(CH₃)₂); d_C(CDCl₃)

143.0, 143.0, 142.9, 142.6, 139.6, 138.1, 137.5, 137.5, 134.8, 133.8,

133.7, 132.5, 132.3, 132.2, 131.8, 127.7, 127.1, 119.3, 119.2, 117.8,

64.4, 45.9, 21.6; MALDI-TOF MS (DHB): m/z 906.40 ([M + H]⁺.

C₅₃H₄₈BrN₆Ni requires 906.24).

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromophenyl)-10,15,20-

tris(p-tolyl)porphyrinato]cobalt(II) ([Co(Br)])

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromidopalladio(II)-phenyl)-

A dark red solution of [2H(Br)] (60.2 mg, 70.8 mmol) in CH₂Cl₂

(30 mL) was stirred at room temperature and a dark red solution

of Co(OAc)₂·4H₂O (600 mg, 2.41 mmol) in hot MeOH (10 mL)

was added. The solution was subsequently heated to reﬂux for

2 h and then stirred at ambient temperature for 12 h. The red

suspension was washed with NaHCO₃(5% in H₂O, 3 ¥ 50 mL),

H₂O (3 ¥ 50 mL), brine (50 mL), dried (MgSO₄), and ﬁltered. The

clear, red ﬁltrate was concentrated to dryness and stored in vacuo

to give the title complex as a bright red solid. Yield: 61.8 mg (96%).

Because of its instability, this compound was immediately used in

the following step. l_max(CH₂Cl₂)/nm 412 (relative intensity 1.000),

529 (0.058); MALDI-TOF MS (DHB): m/z 907.43 ([M + H]⁺.

C₅₃H₄₈BrN₆Co requires 907.24).

10,15,20-tris(p-tolyl)porphyrinato]nickel(II) ([Ni(PdBr)])

Route A: [Ni(Br)] (54.0 mg, 59.6 mmol) and [Pd₂dba₃]·CHCl₃

(32 mg, 30.9 mmol) were dissolved in benzene (20 mL) and the dark

red mixture was stirred at ambient temperature for 16 h. HNEt₂

(5 drops) and MeOH (1 mL) were then added and after 3 h, the

mixture was ﬁltered over Celite and the residue was washed with

benzene (20 mL). The dark red ﬁltrate was concentrated to 10 mL,

hexanes (40 mL) were added and the solution was concentrated to

approximately 30 mL and stored for 2 h at -30 ^◦C. The formed dark

orange precipitate was collected by centrifugation and sonicated

with hexanes (40 mL) for 30 min and centrifuged again. The

resulting orange solid was dried in vacuo. Yield: 56.0 mg (95%).

Route B: [2H(PdBr)] (36.8 mg, 38.5 mmol) was dissolved in

CH₂Cl₂(10 mL) and a saturated solution of Ni(OAc)₂·4H₂O

in MeOH (2 mL) was added under stirring. After 24 h at

reﬂux temperature, the mixture was cooled to room temperature,

extracted with H₂O (4 ¥ 10 mL), and the organic layer was dried

(MgSO₄), ﬁltered, and concentrated to 5 mL. Addition of hexanes

(30 mL) led to the full precipitation of the title compound as

an orange solid. Yield: 29.7 mg (74%). Found: C 63.06, H 4.75,

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromidopalladio(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]-cobalt(II) ([Co(PdBr)])

[Co(Br)] (60.8 mg, 67.2 mmol) was dissolved in benzene (20 mL)

followed by [Pd₂dba₃]·CHCl₃(40.0 mg, 38.6 mmol) and the

resulting dark solution was stirred during 48 h at ambient

temperature. THF (3 mL) was subsequently added, followed by

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N 8.21. Calcd for C₅₃H₄₇BrN₆NiPd: C 62.84, H 4.68, N 8.30%;

_max(CH₂Cl₂)/nm 418 (log e 5.74), 530 (4.62); d_H(CDCl₃) 8.72

and concentrated to 3 mL. Addition of hexanes (30 mL) led

to the full precipitation of the title compound as a red solid.

Yield: 32.8 mg (84%). Found: C 62.29, H 4.74, N 8.18. Calcd for

C₅₃H₄₇BrN₆PdZn: C 62.43, H 4.65, N 8.24%; l_max(CH₂Cl₂)/nm

422 (log e 5.78), 549 (4.36), 590 (3.89); d_H(CDCl₃/1% pyridine-d₅)

l

(8 H, m, b-H), 7.88 (6 H, m, ArH_p-tol), 7.44 (6 H, m, ArH_p-tol), 7.33

(2 H, s, ArH_pincer), 4.10 (4 H, s, CH₂N), 3.06 (12 H, s, N(CH₃)₂),

2.62 (6 H, s, ArCH₃), 2.60 (3 H, s, ArCH₃); d_C(CDCl₃) 157.1,

143.6, 143.0, 143.0, 143.0, 142.9, 138.2, 137.7, 133.9, 133.8, 132.4,

132.3, 132.1, 127.8, 125.5, 119.3, 119.1, 74.8, 54.1, 21.7; MALDI-

TOF MS (9NA): m/z 1011.66 ([M]⁺. C₅₃H₄₇BrN₆NiPd requires

1011.15), 933.48 ([M - Br]⁺. C₅₃H₄₇N₆NiPd requires 933.23).

8.89 (8 H, m, b-H), 8.07 (6 H, m, ArH_p-tol), 7.50 (8 H, m, ArH_p-tol

+

ArH_pincer), 4.10 (4 H, s, CH₂N), 3.08 (12 H, s, N(CH₃)₂), 2.69 (6 H,

s, ArCH₃), 2.67 (3 H, s, ArCH₃); d_C(CDCl₃/1% pyridine-d₅) 156.4,

150.4, 150.4, 150.3, 150.2, 142.9, 140.8, 140.4, 136.9, 134.7, 131.8,

131.7, 131.5, 127.3, 126.5, 120.9, 120.8, 120.6, 74.8, 54.1, 21.7;

MALDI-TOF MS (9NA): m/z 1021.09 ([M]⁺. C₅₃H₄₇BrN₆PdZn

requires 1020.14).

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromophenyl)-10,15,20-

tris(p-tolyl)porphyrinato]zinc(II) ([Zn(Br)])

[2H(Br)] (76.0 mg, 89.4 mmol) was dissolved in dry CH₂Cl₂and

stirred at room temperature. Subsequently, a saturated solution

of Zn(OAc)₂·2H₂O in degassed MeOH (2 mL, excess) was added

and stirring was continued. After 30 min, degassed H₂O (40 mL),

CH₂Cl₂(20 mL), and K₂CO₃(6 M, 2 mL) were added and the

phases were separated. The organic layer was washed with brine

(30 mL), dried (MgSO₄), ﬁltered and loaded onto a silica gel

column. Some contamination was eluted with CH₂Cl₂/hexanes

(1 : 1, v/v) and the product with CH₂Cl₂/hexanes/THF (1 : 1 : 3,

v/v/v) as a pink band. The volatiles were evaporated in vacuo

and the purple residue was redissolved in CH₂Cl₂(20 mL),

hexanes (60 mL) were added and the solution was concentrated to

20 mL. The precipitated pink solid was collected by centrifugation

and dried in vacuo to give the very insoluble title compound.

Yield: 71 mg (89%). Found: C 68.70, H 5.75, N 8.36. Calcd

for C₅₃H₄₉BrN₆OZn (C₅₃H₄₇BrN₆Zn·H₂O): C 68.35, H 5.30, N

9.02%; l_max(CH₂Cl₂)/nm 424 (log e 5.76), 553 (4.34), 597 (3.84);

d_H(CDCl₃/1% pyridine-d₅) 8.86 (6 H, m, b-H), 8.80 (2 H, d, J 4.8,

b-H), 8.16 (2 H, s, ArH_pincer), 8.06 (6 H, d, J 6.9, ArH_p-tol), 7.50

(6 H, d, J 6.9, ArH_p-tol), 3.84 (4 H, s, CH₂N), 2.68 (9 H, s, ArCH₃),

2.42 (12 H, s, N(CH₃)₂; d_C(CDCl₃/1% pyridine-d₅) 150.4, 150.3,

150.0, 142.4, 140.8, 136.9, 136.7, 135.9, 134.7, 132.0, 131.8, 131.7,

131.3, 127.2, 126.9, 121.0, 120.8, 119.2. 64.5, 46.0, 21.7; LDI-TOF

MS: m/z 912.35 (M⁺. C₅₃H₄₇BrN₆Zn requires 912.23).

5-(4-Aquapalladio(II)-3,5-bis[(dimethylamino)methyl]phenyl)-

10,15,20-tris(p-tolyl)porphyrin ([2H(PdOH₂)]BF₄)

[2H(PdBr)] (27 mg, 28 mmol) was dissolved in dry CH₂Cl₂(30 mL)

and the dark red solution was stirred at ambient temperature while

shielded from light. Upon addition of AgBF₄(8 mg, 41 mmol)

the mixture quickly turned green and after 5 min H₂O (1 drop)

was added and the mixture was ﬁltered over Celite. The residue

was washed with acetone (20 mL) to give a green ﬁltrate. All

volatiles were evaporated and the remaining dark residue was

washed extensively with H₂O (6 ¥ 10 mL) on a plug of cotton. The

latter was then extracted with acetone (10 mL) and the product

mixture was precipitated with Et₂O (40 mL). The solid was re-

dissolved in acetone (30 mL), ﬁltered over Celite and i-Pr₂NEt

(200 mL) was added, which restored the dark red colour of the free-

base porphyrin. All volatiles were evaporated and the red solid was

washed with hexanes (3 ¥ 50 mL) and sonicated with demi H₂O

(90 mL) for 1 h. The mixture was then again ﬁltered over Celite

and the residue was thoroughly washed with H₂O (3 ¥ 50 mL).

The desired complex was then washed off with acetone/MeOH

(2 : 1, v/v, 3 ¥ 50 mL) to give a pink ﬁltrate, which was evaporated

to dryness. Acetone (20 mL) was added and the resulting mixture

was treated with hexanes to yield the title compound as a red

solid, which was isolated by centrifugation and thoroughly dried

in vacuo. Yield: 22 mg (79%). d_H(CD₂Cl₂/10% pyridine-d₅) 8.91

(4 H, s, b-H), 8.89 (4 H, s, b-H), 8.11 (6 H, m, ArH_p-tol), 7.74 (2 H, s,

ArH_pincer), 7.60 (6 H, m, ArH_p-tol), 4.41 (4 H, s, CH₂N), 2.89 (12 H,

s, N(CH₃)₂), 2.72 (6 H, s, ArCH₃), 2.67 (3 H, s, ArCH₃), -2.81

(2 H, s, NH); d_F(CD₂Cl₂/10% pyridine-d₅) -153; MALDI-TOF

MS (9NA): m/z 876.00 ([M - H₂O - BF₄]⁺. C₅₃H₄₉N₆Pd requires

875.31).

[5-(3,5-Bis[(dimethylamino)methyl]-4-bromidopalladio(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]zinc(II) ([Zn(PdBr)])

Route A: [Zn(Br)] (66.0 mg, 72.3 mmol) was dissolved in a mixture

of benzene (20 mL) and THF (10 mL) and stirred at ambient tem-

perature. [Pd₂dba₃]·CHCl₃(43 mg, 41.5 mmol) was subsequently

added and the dark red solution was subsequently stirred for 28 h.

HNEt₂(1 mL) and MeOH (1 mL) were then added and after 1 h,

the mixture was ﬁltered over Celite and the residue was washed

with acetone/benzene (1 : 1, v/v, 30 mL). The dark pink ﬁltrate

was concentrated to 10 mL, hexanes (40 mL) were added and the

solution was concentrated to approximately 30 mL. The formed

purple precipitate was collected by centrifugation and sonicated

with hexanes (40 mL) for 30 min and centrifuged again. The

resulting purple solid was dried in vacuo. Yield: 67.8 mg (92%).

Route B: [2H(PdBr)] (36.6 mg, 38.3 mmol) was dissolved in

CH₂Cl₂(8 mL) and a saturated solution of Zn(OAc)₂·2H₂O in

MeOH (2 mL) was added under stirring. After 2 h at ambient

temperature, the mixture was extracted with H₂O (4 ¥ 10 mL),

dried (MgSO₄) and ﬁltered. The pink solution was ﬁltered over

silica gel with THF–CH₂Cl₂(1 : 2, v/v), the ﬁrst band was collected

[5-(4-Aquapalladio(II)-3,5-bis[(dimethylamino)methyl]phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]-magnesium(II)

([Mg(PdOH₂)]BF₄)

[Mg(PdCl)] (28 mg, 29 mmol) was dissolved in dry CH₂Cl₂(25 mL),

i-Pr₂NEt (700 mL) was added and the pink solution was stirred at

ambient temperature while shielded from light. AgBF₄(10 mg,

51 mmol) was subsequently added and after 5 min the mixture

was ﬁltered over Celite and the residue was washed with acetone

(20 mL). The ﬁltrate was evaporated to dryness and the remaining

dark residue was washed with hexanes (3 ¥ 50 mL) and sonicated

with demi H₂O (90 mL) for 1 h. The mixture was then again

ﬁltered over Celite and the residue was thoroughly washed with

demi H₂O (3 ¥ 50 mL). The desired complex was then washed

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off with acetone/MeOH (2 : 1, v/v, 3 ¥ 50 mL) to give a pink

ﬁltrate, which was evaporated to dryness. Acetone (20 mL) was

added and the resulting mixture was treated with hexanes to

yield the title compound as a pink solid, which was isolated by

centrifugation and thoroughly dried in vacuo. Yield: 22 mg (79%).

d_H(CD₂Cl₂/10% pyridine-d₅) 8.90 (8 H, m, b-H), 8.08 (6 H, m,

ArH_p-tol), 7.73 (2 H, s, ArH_pincer), 7.57 (6 H, m, ArH_p-tol), 4.39 (4 H,

s, CH₂N), 2.88 (12 H, s, N(CH₃)₂), 2.72 (6 H, s, ArCH₃), 2.71 (3 H,

s, ArCH₃); d_F(CD₂Cl₂/10% pyridine-d₅) -150; MALDI-TOF MS

(9NA): m/z 896.43 ([M - H₂O - BF₄]⁺. C₅₃H₄₇N₆MgPd requires

897.28).

5-(3,5-Bis[(dimethylamino)methyl]-4-chloridoplatino(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrin ([2H(PtCl)])

[Pt₂dipdba₃] (374 mg, 278 mmol) was added to a degassed, dark

red solution of 3 (438 mg, 515 mmol) in dry benzene (30 mL) and

the dark purple solution was heated to reﬂux and stirred. The

progress of the reaction was monitored by TLC (hexanes/THF,

1 : 1, v/v). After 5 h all Pt₂(dipdba)₃had reacted but a bit of 3

was still visible. Another 35 mg of Pt₂(dipdba)₃were added, the

mixture was heated for another 60 min to reﬂux after which time

the black solution was cooled RT and evaporated to dryness in

vacuo. THF (30 mL) was added and the dark solution was stirred

overnight and ﬁltered over Celite to give a dark red solution. After

concentration of the ﬁltrate to 5 mL hexanes (60 mL) were added

and _◦the precipitate was collected by centrifugation after 16 h at

-30 C (514 mg). The compound was subsequently dissolved in

CH₂Cl₂(40 mL) and evaporated onto silica gel (20 g). The silica gel

was poured on top of a silica gel column (prepared with 1% MeOH

in CH₂Cl₂) and [2H(PtBr)] was eluted as the third band using a

gradient of 1% MeOH to 3% MeOH. Yield: 480 mg (89%). Found:

C 60.78, H 4.66, N 7.86. Calcd for C₅₃H₄₉BrN₆Pt: C 60.92, H 4.73,

N 8.04%; l_max(CH₂Cl₂)/nm 423 (log e 5.76), 517 (4.42), 555 (4.14),

594 (3.97), 650 (3.84); d_H(CDCl₃) 8.86 (8 H, m, b-H), 8.08 (6 H, d,

J 7.8, ArH_p-tol), 7.60 (2 H, s, ArH_pincer), 7.54 (6 H, d, J 7.8, ArH_p-tol),

4.24 (4 H, s, CH₂N), 3.29 (12 H, s, N(CH₃)₂), 2.71 (6 H, s, ArCH₃),

2.70 (6 H, s, ArCH₃), -2.75 (2 H, s, NH); d_C(CDCl₃) 145.9,

141.8, 139.4, 137.7, 137.5, 134.7, 134.6, 131.1 (b), 127.6, 126.2,

121.1, 120.3, 120.2, 77.7, 55.5, 21.7; d_Pt(CDCl₃) -3196; MALDI-

TOF MS (DHB): m/z 1044.00 ([M + H]⁺. C₅₃H₅₀BrN₆Pt requires

1044.29). This material was dissolved in dry CH₂Cl₂(30 mL) and

the dark red solution was stirred at ambient temperature while

shielded from light. Upon addition of AgBF₄(97.3 mg, 500 mmol)

the mixture quickly turned green. After 5 min, brine (50 mL) was

added and the mixture was vigorously stirred for 2 h. The layers

were separated and the organic layer was dried (MgSO₄), ﬁltered

and concentrated to 20 mL. Addition of hexanes (60 mL) led to the

precipitation of the title compound as a purple solid. Yield: 437 mg

(95%). l_max(CH₂Cl₂)/nm 423 (log e 5.76), 517 (4.42), 555 (4.14),

594 (3.97), 650 (3.84); d_H(CDCl₃) 8.86 (8 H, m, b-H), 8.08 (6 H, d,

J 7.8, ArH_p-tol), 7.60 (2 H, s, ArH_pincer), 7.55 (6 H, d, J 7.8, ArH_p-tol),

4.25 (4 H, s, CH₂N), 3.26 (12 H, s, N(CH₃)₂), 2.71 (6 H, s, ArCH₃),

2.70 (6 H, s, ArCH₃), -2.75 (2 H, s, NH); d_C(CDCl₃) 144.8, 141.8,

139.4, 137.6, 137.5, 134.7, 134.6, 131.1 (b), 127.6, 126.2, 121.1,

120.2 (2 ¥), 78.0, 54.8, 21.7; d_Pt(CDCl₃) -3181; MALDI-TOF MS

(DHB): m/z 1001.23 ([M+H]⁺. C₅₃H₅₀ClN₆Pt requires 1000.55).

[5-(4-Aquapalladio(II)-3,5-bis[(dimethylamino)methyl]phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]-nickel(II) ([Ni(PdOH₂)]BF₄)

[Ni(PdBr)] (28.0 mg, 27.6 mmol) was dissolved in a mixture of

CH₂Cl₂(30 mL) and i-Pr₂NEt (500 mL) and the resulting orange

solution was stirred at room temperature. AgBF₄(11 mg, 56 mmol)

was subsequently added followed by H₂O (2 drops) after 15 min.

The mixture was subsequently ﬁltered over Celite and the residue

was washed with MeOH/acetone (1 : 1, v/v, 20 mL). The orange

ﬁltrate was evaporated to dryness and sonicated for 40 min with

demi H₂O (40 mL). The mixture was ﬁltered over a glass frit and the

residue was thoroughly washed with H₂O (4 ¥ 50 mL). The residue

was subsequently extracted with acetone/MeOH (3 : 1, v/v, 2 ¥

30 mL) and all volatiles were evaporated in vacuo. The residue was

solubilized in hot acetone (30 mL), hexanes (40 mL) were added,

and the mixture was concentrated to 20 mL. The resulting red

precipitate was collected by centrifugation and thoroughly dried

in vacuo. Yield: 28 mg (98%). d_H(CD₂Cl₂/10% pyridine-d₅) 8.85

(8 H, m, b-H), 7.92 (6 H, m, ArH_p-tol), 7.55 (2 H, s, ArH_pincer), 7.54

(6 H, m, ArH_p-tol), 4.36 (4 H, s, CH₂N), 2.85 (12 H, s, N(CH₃)₂),

2.67 (9 H, s, ArCH₃); d_F(CD₂Cl₂/10% pyridine-d₅) -151; MALDI-

TOF MS (9NA): m/z 933.64 ([M - H₂O - BF₄]⁺. C₅₃H₄₇N₆NiPd

requires 933.23).

[5-(4-Aquapalladio(II)-3,5-bis[(dimethylamino)methyl]phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]-zinc(II) ([Zn(PdOH₂)]BF₄)

[Zn(PdBr)] (62 mg, 61 mmol) was dissolved in a mixture of CH₂Cl₂

(25 mL) and i-Pr₂NEt (1 mL) and the resulting pink solution

was stirred at room temperature. AgBF₄(20 mg, 102 mmol) was

subsequently added followed by H₂O (2 drops) after 15 min. The

mixture was subsequently ﬁltered over Celite and the residue was

washed with MeOH/acetone (1 : 1, v/v, 40 mL). The purple ﬁltrate

was evaporated to dryness and sonicated for 40 min with demi

H₂O (40 mL). The mixture was ﬁltered over a glass frit and the

residue was thoroughly washed with H₂O (4 ¥ 50 mL). The residue

was subsequently extracted with acetone/MeOH (3 : 1, v/v, 3 ¥

50 mL) and all volatiles were evaporated in vacuo. The residue was

solubilised in hot acetone (30 mL), hexanes (40 mL) were added,

and the mixture was concentrated to 20 mL. The resulting red

precipitate was collected by centrifugation and thoroughly dried in

vacuo. Yield: 55 mg (86%). d_H(CD₂Cl₂/10% pyridine-d₅) 8.87 (8 H,

m, b-H), 8.09 (6 H, m, ArH_p-tol), 7.73 (2 H, s, ArH_pincer), 7.60 (6 H,

m, ArH_p-tol), 4.52 (4 H, s, CH₂N), 2.97 (12 H, s, N(CH₃)₂), 2.70

(6 H, s, ArCH₃), 2.69 (3 H, s, ArCH₃); d_F(CD₂Cl₂/10% pyridine-

d₅) -152; MALDI-TOF MS (9NA): m/z 939.43 ([M - H₂O -

BF₄]⁺. C₅₃H₄₇N₆PdZn requires 939.22).

[5-(3,5-Bis[(dimethylamino)methyl]-4-chloridoplatino(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]-magnesium(II) ([Mg(PtCl)])

Route A: a suspension of [Mg(Br)] (42 mg, 48 mmol) and

[Pt₂dipdba₃] (32 mg, 24 mmol) in dry benzene (10 mL) was treated

with THF (3 mL) to give a clear solution. The dark solution was

heated to reﬂux and stirring was continued for 3 h. The solution

was allowed to cool down to ambient temperature, ﬁltered over

Celite and the ﬁltrate was evaporated to dryness. The resulting

greenish solid was sonicated with hexanes (70 mL) and isolated by

centrifugation. It was re-dissolved in a mixture of CH₂Cl₂(30 mL)

and i-Pr₂NEt (1 mL), and subsequently treated with AgBF₄

(10 mg, 51 mmol). After 5 min of stirring at room temperature, the

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mixture was diluted with brine (30 mL) and vigorously stirred for

an additional 2 h. The layers were separated and the organic layer

was dried (MgSO₄), ﬁltered, and concentrated to 5 mL. Addition

of hexanes (40 mL) followed by concentration of the mixture to

20 mL led to the precipitation of the title compound as a greenish

solid, which was dried in vacuo. Yield: 45 mg (92%).

Route B: a solution of [2H(PtCl)] (30 mg, 30 mmol) in

dry CH₂Cl₂(30 mL) was treated with i-Pr₂NEt (1 mL) and

MgBr₂·OEt₂(500 mg, 1.94 mmol) and the mixture was stirred

overnight at ambient temperature. The resulting pink solution

was washed with 5% NaHCO₃(3 ¥ 50 mL) and brine (2 ¥ 50 mL)

and loaded onto a column with alumina. The desired product

was eluted with MeOH–CH₂Cl₂(1 : 9, v/v). The volatiles were

evaporated and the resulting solid was re-dissolved in CH₂Cl₂

(10 mL). Hexanes (60 mL) were added and the mixture was

concentrated to 30 mL and the resulting greenish solid was isolated

by means of centrifugation. Yield: 22 mg (72%).

to give an orange solid, which was isolated by centrifugation.

Yield: 16 mg (67%). Found: C 59.95, H 5.00, N 6.65. Calcd

for C₆₀H₆₅Cl₃MgN₆OPt (C₅₃H₄₇ClMgN₆Pt·CH₂Cl₂·H₂O·C₆H₁₄):

C 59.46, H 5.41, N 6.93%; l_max(CH₂Cl₂)/nm 430 (log e 5.80),

566 (4.38), 608 (4.26); d_H(CDCl₃) 8.80 (2 H, d, J 5.2, b-H),

8.76 (6 H, m, b-H), 7.89 (6 H, d, J 8.0, ArH_p-tol), 7.46 (6 H,

d, J 8.0, ArH_p-tol), 7.39 (2 H, s, ArH_pincer), 4.21 (4 H, s, CH₂N),

3.23 (12 H, s, N(CH₃)₂), 2.64 (6 H, s, ArCH₃), 2.63 (3 H, s,

ArCH₃); d_C(CDCl₃) 153.4, 150.3, 150.2, 150.2, 150.1, 142.0, 141.2,

138.6, 136.8, 134.6, 134.6, 132.5, 131.6, 131.6, 131.4, 127.2, 126.0,

121.5, 121.3, 76.3, 54.0, 20.8; d_Pt(CDCl₃) -3183; MALDI-TOF

MS (DHB): m/z 1056.27 (M⁺. C₅₃H₄₇ClN₆NiPt requires 1056.26),

1021.27 ([M - Cl]⁺. C₅₃H₄₇N₆NiPt requires 1021.29), 825.30 ([M -

PtCl]⁺. C₅₃H₄₇N₆Ni requires 825.32).

[5-(3,5-Bis[(dimethylamino)methyl]-4-chloridoplatino(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]-zinc(II) ([Zn(PtCl)])

Found: C 59.95, H 5.00, N 6.65. Calcd for C₆₀H₆₅Cl₃MgN₆OPt

(C₅₃H₄₇ClMgN₆Pt·CH₂Cl₂·H₂O·C₆H₁₄): C 59.46, H 5.41, N 6.93%;

Route A: [Zn(Br)] (40 mg, 44 mmol) was dissolved in dry benzene

(5 mL), [Pt₂dipdba₃] (32 mg, 24 mmol) was added, and the dark red

solution was heated to reﬂux for 16 h. After cooling to ambient

temperature, the mixture was ﬁltered over Celite and the residue

was washed with benzene/acetone (1 : 1, v/v, 20 mL). The red

ﬁltrate was concentrated to 5 mL and hexanes (20 mL) were

subsequently added to precipitate the crude product [Zn(PtX)]

(X = Br, Cl) as a purple/green solid. The solid was dissolved in

dry CH₂Cl₂(30 mL) and i-Pr₂NEt (1 mL, excess) was added to

give a pink solution, which was stirred at ambient temperature.

AgBF₄(10 mg, 52 mmol) was subsequently added followed after

5 min by brine (30 mL) and the mixture was vigorously stirred for

1 h. The organic layer was isolated, dried (MgSO₄), ﬁltered and

loaded onto a silica gel column (CH₂Cl₂). The desired product

was eluted with MeOH–CH₂Cl₂(1 : 9, v/v) as a pink band, which

was concentrated to 5 mL and diluted with hexanes (80 mL) to

give the product as a green/purple solid, which was isolated by

centrifugation. Yield: 41 mg (88%).

Route B: [2H(PtCl)] (30 mg, 30 mmol) was dissolved in degassed

CHCl₃(10 mL) and the dark red solution was treated with a

saturated solution of Zn(OAc)₂·2H₂O in MeOH (1 mL) and the

resulting mixture was stirred at room temperature for 20 min. The

pink mixture was extracted with H₂O (2 ¥ 20 mL) and washed with

brine (20 mL). The organic layer was dried (MgSO₄), loaded onto a

silica gel column and the product was eluted with MeOH–CH₂Cl₂

(1 : 19, v/v) as a pink band, which was concentrated to 5 mL and

diluted with hexanes (80 mL) to give an purple/greenish solid,

which was isolated by centrifugation. Yield: 23 mg (72%). Found:

C 59.95, H 5.00, N 6.65. Calcd for C₆₀H₆₅Cl₃MgN₆OPt: C 59.46, H

5.41, N 6.93%; l_max(CH₂Cl₂)/nm 430 (log e 5.80), 566 (4.38), 608

(4.26); d_H(CDCl₃) 9.01 (2 H, d, J 4.4, b-H), 8.96 (6 H, m, b-H), 8.09

(6 H, d, J 7.6, ArH_p-tol), 7.63 (2 H, s, ArH_pincer), 7.55 (6 H, d, J 7.6,

ArH_p-tol), 4.28 (4 H, s, CH₂N), 3.28 (12 H, s, N(CH₃)₂), 2.71 (6 H,

s, ArCH₃), 2.70 (3 H, s, ArCH₃); d_C(CDCl₃) 150.6, 150.5, 150.5,

150.4, 144.5, 141.6, 140.5, 138.2, 137.3, 134.5, 132.1, 131.9, 127.4,

126.0, 122.2, 121.3, 121.2, 78.1, 54.9, 21.7; d_Pt(CDCl₃) -3189;

MALDI-TOF MS (DHB): m/z 1062.58 (M⁺. C₅₃H₄₇ClN₆PtZn

requires 1062.25), 1027.29 ([M - Cl]⁺. C₅₃H₄₇N₆PtZn requires

1027.28), 831.38 ([M - PtCl]⁺. C₅₃H₄₇N₆Zn requires 831.32).

l

_max(CH₂Cl₂)/nm 430 (log e 5.80), 566 (4.38), 608 (4.26);

d_H(CDCl₃/1% pyridine-d₅) 8.91 (2 H, d, J 4.0, b-H), 8.80 (6 H,

m, b-H), 8.06 (6 H, d, J 7.6, ArH_p-tol), 7.56 (8 H, m, ArH_pincer

+

ArH_p-tol), 4.28 (4 H, s, CH₂N), 3.17 (12 H, s, N(CH₃)₂), 2.67 (9 H,

s, ArCH₃); d_C(CDCl₃/1% pyridine-d₅) 153.4, 150.3, 150.2, 150.2,

150.1, 142.0, 141.2, 138.6, 136.8, 134.6, 134.6, 132.5, 131.6, 131.6,

131.4, 127.2, 126.0, 121.5, 121.3, 76.3, 54.0, 20.8; d_Pt(CDCl₃/1%

pyridine-d₅) -3195; MALDI-TOF MS (9NA): m/z 1021.93 ([M]⁺.

C₅₃H₄₇ClMgN₆Pt requires 1022.30).

[5-(3,5-Bis[(dimethylamino)methyl]-4-chloridoplatino(II)-phenyl)-

10,15,20-tris(p-tolyl)porphyrinato]nickel(II) ([Ni(PtCl)])

Route A: [Ni(Br)] (22 mg, 24 mmol) was dissolved in dry benzene

(5 mL), [Pt₂dipdba₃] (16.1 mg, 12 mmol) was added, and the

dark red solution was heated to reﬂux for 12 h. After cooling

to ambient temperature, the mixture was ﬁltered over Celite and

the residue was washed with benzene/acetone (1 : 1, 20 mL). The

orange ﬁltrate was concentrated to 5 mL and hexanes (20 mL) were

subsequently added to precipitate the crude product [Ni(PtX)]

(X = Br, Cl) as an orange solid. The solid was dissolved in dry

CH₂Cl₂(30 mL) and i-Pr₂NEt (1 mL, excess) was added to give

an orange solution, which was stirred at ambient temperature.

AgBF₄(5 mg, 26 mmol) was subsequently added followed after

5 min by brine (30 mL) and the mixture was vigorously stirred for

1 h. The organic layer was isolated, dried (MgSO₄), ﬁltered and

loaded onto a silica gel column (CH₂Cl₂). The desired product was

eluted with MeOH–CH₂Cl₂(1 : 19, v/v) as an orange band, which

was concentrated to 5 mL and diluted with hexanes (80 mL) to

give an orange solid, which was isolated by centrifugation. Yield:

23 mg (91%).

Route B: [2H(PtCl)] (23 mg, 23 mmol) was dissolved in degassed

CHCl₃(6 mL) and the dark red solution was treated with a

saturated solution of Ni(OAc)₂·4H₂O in MeOH (1 mL) and the

resulting mixture was heated to reﬂux overnight. After cooling to

room temperature, the orange mixture was extracted with H₂O

(4 ¥ 20 mL) and washed with brine (20 mL). The organic layer was

dried (MgSO₄), loaded onto a silica gel column and the product

was eluted with MeOH–CH₂Cl₂(1 : 19, v/v) as an orange band,

which was concentrated to 5 mL and diluted with hexanes (80 mL)

Double Michael addition. A ﬂame-dried vial was charged with

the appropriate Pd catalyst (8.0 mmol) and dry CH₂Cl₂(5.0 mL)

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was added. After 15 min of stirring at 20 ^◦C, ethyl a-cyanoacetate

(170 mL, 1.60 mmol) was added which led to quick dissolution

of all solids. Methyl vinyl ketone (390 mL, 4.80 mmol) was

subsequently added, followed by i-Pr₂NEt (28 mL, 0.16 mmol) and

the reaction mixture was stirred in the dark. Samples (100 mL) were

taken at appropriate time intervals, and the CH₂Cl₂and methyl

vinyl ketone were quickly removed with a gentle stream of nitrogen

(approximately 20 s). The samples were subsequently analysed by

¹H NMR spectroscopy and the conversions were determined by

comparison of the signal intensities of the ethyl CH₂protons (d =

4.28 ppm) with the CH₂protons of ethyl a-cyanoacetate (d =

3.45 ppm).

2 J. Kjellgren, H. Sunde´n and K. J. Szabo´, J. Am. Chem. Soc., 2004, 126,

474–475.

3 V. J. Olsson, S. Sebelius, N. Selander and K. J. Szabo´, J. Am. Chem.

Soc., 2006, 128, 4588–4589.

4 S. Sebelius, V. J. Olsson, O. A. Wallner and K. J. Szabo, J. Am. Chem.

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X-Ray crystal structure determination of compound

{[Mg(Br)](THF)₂}

C₆₁H_62.82Br_1.18MgN₆O₂+ disordered solvent, FW = 1030.99‡,

3

¯

purple plate, 0.30 ¥ 0.12 ¥ 0.03 mm , triclinic, P1 (no. 2), a =

˚

9.6539(12), b = 10.7179(12), c = 28.370(4) A, a = 92.826(12),

◦

3

˚

b = 99.512(11), g = 90.753(17) , V = 2890.9(6) A , Z = 2, D_x=

1.184 g cm^-3‡, m = 0.90 mm^-1‡. 35 693 reﬂections were measured

on a Nonius Kappa CCD diffractometer with rotating anode

˚

(graphite monochromator, l = 0.71073 A) at a temperature of

-1

˚

150 K up to a resolution of (sin q/l)_max=0.59 A . Intensities were

integrated with HKL2000.¹¹¹The reﬂections were corrected for

absorption on the basis of multiple measured reﬂections using

the MULABS routine of the program PLATON¹¹²(0.78–0.97

correction range). 9890 Reﬂections were unique (R_int=0.0732).

The structure was solved with the program SHELXS-86¹¹³using

3

˚

Direct Methods. The crystal structure contains voids (248 A

per unit cell) ﬁlled with disordered solvent molecules. Their

contribution to the structure factors was secured by back-Fourier

transformation using the routine SQUEEZE of the program

PLATON,¹¹²resulting in 55 electrons/unit cell. Residual electron

density indicated the presence of the bromine substituted starting

material, which was included in the reﬁnement with partial

occupancy. The structure was reﬁned with SHELXL-97¹¹⁴against

F²of all reﬂections. Most non-hydrogen atoms were reﬁned

with anisotropic displacement parameters. Hydrogen atoms were

introduced in calculated positions and reﬁned with a riding model.

One tolyl and one THF moiety were reﬁned with disorder models,

respectively. 637 Parameters were reﬁned with 51 restraints.

R1/wR2 [I > 2s(I)]: 0.0842/0.2145. R₁/wR₂[all reﬂections]:

0.1335/0.2381. S = 1.039. Residual electron density between -0.48

28 I. Go¨ttker-Schnetmann, P. White and M. Brookhart, J. Am. Chem.

Soc., 2004, 126, 1804–1811.

29 J. Aydin, N. Selander and Szabo´, Tetrahedron Lett., 2006, 47, 8999–

9001.

3

˚

and 0.72 e/A . Geometry calculations and checking for higher

symmetry was performed with the PLATON program.¹¹²

30 J. S. Fossey and C. J. Richards, Organometallics, 2004, 23, 367–

373.

Acknowledgements

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M. Lutz, A. L. Spek, A. J. Canty and G. van Koten, Organometallics,

2001, 20, 3159–3168.

We thank The Netherlands Organisation for Scientiﬁc Research

for a Jonge Chemici scholarship (B. M. J. M. S. and R. J. M. K. G.).

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‡ The derived parameters do not contain the contribution of the disordered

solvent.

6214 | Dalton Trans., 2010, 39, 6198–6216

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The Royal Society of Chemistry 2010

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Article Doi

Mono(NCN-pincer palladium)-metalloporphyrin catalysts: Evidence for supramolecular bimetallic catalysis

DOI: 10.1039/b925236n

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