Chelating N-pyrrolylphosphino-N′-arylaldimine ligands: Synthesis, ligand behaviour and applications in catalysis

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Chelating N-pyrrolylphosphino-N^ꢀ-arylaldimine ligands: synthesis, ligand

behaviour and applications in catalysis

Carly E. Anderson,†^aAndrei S. Batsanov,^bPhilip W. Dyer,*‡^aJohn Fawcett^aand Judith A. K. Howard^b

Received 14th August 2006, Accepted 19th September 2006

First published as an Advance Article on the web 2nd October 2006

DOI: 10.1039/b611652c

Two families of variously-substituted N-pyrrolylphosphino-N^ꢀ-arylaldimine ligands,

i

=

2-(aryl–N CH)C₄H₃N–PR₂{3a–d R = Ph; 4a–d R = Pr ₂N}, have been prepared from the

corresponding pyrrolylaldimines 2. The donor characteristics/basicity of P–N-chelating 3 and 4 have

been assessed using a combination of ³¹P{ H} NMR and IR spectroscopies through study of the

1

magnitudes of ¹J_SePfor the phosphorus(V) selenides 7 and 8, and measurement of m_COfor the complexes

[RhCl(CO)(3,4-j²-P,N)] (5, 6), respectively. The synthesis of the palladium(II) complexes

[PdCl₂(3,4-j²-P,N)] (9, 10) was readily achieved from reaction of 3 or 4 with [PdCl₂(MeCN)₂] in

CH₂Cl₂. X-Ray crystallographic studies of 13d and 14b conﬁrm the chelating nature of the P–N

ligands, which adopt a distorted ‘envelope’ conformation, and highlight the potentially signiﬁcant steric

demands of these metal scaffolds. Reaction of equimolar quantities of 3 with [NiBr₂(DME)] in MeCN

afforded [NiBr₂(3-j²-P,N)] (15), while the same reaction undertaken in CH₂Cl₂with 3c gave rise to the

=

homoleptic bis(pyrrolatoimine) derivative [Ni{2-(mes–N CH)C₄H₃N}₂] (16) in 45% yield, following

P–N bond cleavage. Complex 16c was characterised in the solid-state by X-ray crystallography. No

identiﬁable metal-containing complexes could be obtained on reaction of 4 with a variety of sources of

Ni(II). The palladium dichloride complexes 13 and 14 proved inactive in combination with MAO or

EtAlCl₂for ethylene polymerisation, and with methanesulfonic acid for CO/ethylene

co-polymerisation. Contrastingly, the nickel complexes 15 in combination with 4.5 eq. EtAlCl₂

catalysed the formation of butenes and hexenes with moderate activity from ethylene at 1 bar.

amino-functionalised tertiary phosphines synthesised in this way

Introduction

make attractive ligand targets in their own right, as variation

in the nature of the substituents at nitrogen can be used to

considerably alter the steric and electronic character of the P-

donor moieties.^20–23This kind of strategy has been exploited in a

number of recent studies, which demonstrate the utility of pyrrole-

derived building blocks for the preparation of a range of bidentate

P-containing ligands.^9,24–30These pyrrolyl-substituted phosphine

centres are strongly p-acidic, a feature that is of particular interest

in catalysis involving both mono- and bi-dentate ligands.

Building on these reports and our previous work on P–N-

chelating scaffolds,^10,31,32we describe here the synthesis, prelimi-

nary coordination chemistry, and donor/basicity characteristics

of a number of sterically demanding N-pyrrolylphosphino-N^ꢀ-

arylaldimine ligands, which combine electron-rich aldimine and

tuneable phosphine donor moieties.²⁵The application of these

metal scaffolds in oleﬁn oligomerisation is outlined.

Ease and ﬂexibility of synthesis are important considerations

for ligand systems designed for applications in catalysis, fa-

cilitating study of the important correlation between catalyst

structure, properties and performance. Bidentate P–N ligands

have been particularly successful in this regard,^1,2and have been

exploited in a wide variety of metal-catalysed processes, in-

cluding transfer hydrogenation,³asymmetric hydroformylation,⁴

oleﬁn oligomerisation/polymerisation,^5–8co-polymerisation,^9,10

and coupling reactions.^11,12The heteroditopic nature of such

ligands has been used to engender both control and selectivity

in reactions occurring at metal centres; the signiﬁcant electronic

asymmetry that is possible having a considerable impact.^13–16

The formation of direct phosphorus–heteroatom bonds (e.g.

from reaction of halophosphines with bifunctional nitrogen

derivatives) is a versatile methodology for the preparation of

chelating ligands, with the simplicity and considerable scope

of P–N bond formation being especially valuable.^17–19Indeed,

Results and discussion

^aDepartment of Chemistry, University of Leicester, University Road, Leices-

ter, UK LE1 7RH

N-Pyrrolylphosphino-N^ꢀ-arylaldimine ligand syntheses

^bDepartment of Chemistry, Durham University, South Road, Durham, UK

DH1 3LE

The desired heteroditopic ligands were prepared in a two-step

process. Firstly, a range of variously-substituted 2-pyrrole-N^ꢀ-

arylaldimines 2a–d were prepared from 2-pyrrolecarbaldehyde (1)

via condensation (ca. 18 h) under Dean and Stark conditions

in the presence of a catalytic quantity of para-toluenesulfonic

acid (p-TSA) (Scheme 1). The resulting aldimines were obtained

† Current address: Department of Chemistry, Durham University, South

Road, Durham, UK, DH1 3LE. Fax: 0191 384 4737; Tel: 0191 334 2150;

E-mail: p.w.dyer@durham.ac.uk

‡ Current address: Department of Chemistry, Durham University, South

Road, Durham, UK, DH1 3LE. Fax: 0191 384 4737; Tel: 0191 334 2150;

E-mail: p.w.dyer@durham.ac.uk

5362 | Dalton Trans., 2006, 5362–5378

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as crystalline solids in moderate to good isolated yields (53–

73%). It was found necessary to store all four derivatives under

a nitrogen atmosphere to avoid degradation. Spectroscopic data

for compounds 2 were consistent with their proposed structures,

with the aldimine carbons giving rise to resonances at ca. 150 ppm

with the exception of 3b, which despite repeated attempts could

only be obtained cleanly in ca. 30% yield. Ligands 3 were obtained

as viscous brown oils or waxy solids, while their counterparts 4

were obtained as beige crystalline solids following puriﬁcation.

The use of BuⁿLi, as described above, proved essential since

organic bases such as NEt₃or DBU were found not to deprotonate

the pyrrole nitrogen of 2 (even at elevated temperatures). This dif-

ﬁculty, relative to the comparative ease of reaction of Ph₂PCl with

pyrrole, 2-pyrrole-N^ꢀ-alkylaldimines or oxazoline-functionalised

derivatives that require only NEt₃,^25,26,33has tentatively been

attributed to the presence of strong hydrogen bonding interactions

of the pyrrole proton and the aldimine nitrogen centre.

1

by ¹³C{ H} NMR spectroscopy and both NH (∼3200 cm⁻¹) and

characteristic imine (∼1585 cm⁻¹) absorption bands visible by IR

spectroscopy.³³

Notably, although a number of attempts were made to prepare

the N^ꢀ-arylketimine analogues of 2 from 2-acetylpyrrole and the

desired aniline using a range of differing methodologies, only a

trace of the desired product could be detected in each case. The

comparatively unreactive nature of the acetyl precursor relative to

its aldehyde counterpart is presumed to result from a combination

of additional steric constraints imposed by the methyl group and

enhanced mesomeric deactivation of the carbonyl fragment by the

ring nitrogen.³⁵

Each of the phosphorus-donor ligands 3 and 4 exhibited a single

1

Scheme 1 Reagents and conditions: (i) toluene, p-TSA (cat.), reﬂux, Dean

and Stark, 16–20 h; (ii) BuⁿLi, DME, −78 ^◦C to RT, 1 h; (iii) Ph₂PCl (neat)

or (Prⁱ₂N)₂PCl, DME, 1 h. (Pyrrolyl numbering scheme included.)

resonance by ³¹P{ H} NMR spectroscopy (Table 1). As would

be expected, the signals for the tris(amino)phosphines 4 (ca. +80

ppm) were observed at higher frequencies than those for 3 (ca. +48

ppm), a direct consequence of the presence of two additional elec-

tronegative amino substituents at phosphorus for 4.²⁰These data

are comparable to those observed for related 7-aza-N-indolyl- and

(keto-functionalised)-N-pyrrolylphosphines.^9,28,29,36Within each of

The P-donor components were introduced by initial deproto-

nation of 2 by BuⁿLi in 1,2-dimethoxyethane (DME), followed by

addition of the desired chlorophosphine (Scheme 1). This method-

ology was used to prepare two families of P–N ligands bearing

either phenyl (3a–d) or diisopropylamino (4a–d) substituents at

phosphorus, each being isolated in high yields (typically >80%),

the two series of ligands 3 and 4, the ³¹P{ H} NMR chemical shifts

1

were largely independent of the nature of the aldimine substituent.

1

The ¹H and ¹³C{ H} NMR spectra for all the ligands 3 and

Table 1 Selected spectroscopic data for compounds 2–4 and complexes 13, 14, 15a and 16

=

N

CH

Compound

d(³¹P)^a/ppm

d(¹H)^b/ppm (⁴J_PH/Hz)

d(¹³C)^c/ppm (³J_PC/Hz)

m_CN^d/cm⁻¹

2a

—

8.32

8.25

7.96

8.05

150.5

149.9

153.7

153.0

1583

1585

1587

1585

1589^h

1585^h

1582^h

1588^h

1589^h

1584^h

1588^h

1585^h

1596

1597

1590

1597

1601

1600

1605

1599

1596

1592

2b

2c

2d

3a

47.5

47.9

48.4^e

49.1

84.4

83.2

82.8

82.7

66.5

65.8^f

64.4

65.5

81.3

81.6

81.4^e

80.9

—

8.68 (1.2)

8.51 (2.4)

8.35 (3.0)

8.31 (1.8)

8.99 (5.7)

8.96 (5.6)

8.67 (5.6)

8.79 (5.7)^g

8.23 (3.2)

7.96 (2.9)

7.79 (3.0)

7.78 (3.3)

8.01 (3.0)

8.04 (3.0)

7.76 (3.8)

7.83 (4.1)

—

149.9 (9.8)

149.5 (10.3)ⁱ

156.6 (7.9)

152.3 (6.8)

152.0 (24.9)

151.7 (24.4)

154.5 (25.6)

152.9 (25.9)ⁱ

154.5 (7.2)

153.7 (7.0)

156.7 (7.7)

155.6 (7.9)

154.9 (7.5)

154.8 (7.6)

156.4 (7.3)

155.4 (8.8)ⁱ

—

3b

3c

3d

4a

4b

4c

4d

13a

13b

13c

13d

14a

14b

14c

14d

15a

16

—

7.17

162.4

^a121.5 MHz, CDCl₃. ^b300.1 MHz. ^c75.5 MHz, CDCl₃. ^dNeat, ATR. ^e162.0 MHz, CDCl₃. ^f101.3 MHz, CDCl₃. ^g400.1 MHz, CDCl₃. ^hKBr, CH₂Cl₂.

ⁱ100.1 MHz, CDCl₃.

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4

4 were similar and comparable to those of 2. A J_PHcoupling

1

31

constant of ca. 6 Hz (conﬁrmed by H{ P} NMR) is observed

for 4 to the aldimine protons and lies at the upper end of the

normally quoted scale (1–4 Hz). The aldimine carbons exhibit

³J_PCcoupling of ca. 9 Hz for 3 and ca. 24 Hz for 4, a difference

that is presumed to reﬂect the greater s-character at phosphorus

for the tris(aminophosphines) 4 compared with that for 3 (vide

infra).²⁰The IR spectra of 3 and 4 exhibit a C N stretch in

=

the range 1584 to 1589 cm⁻¹, comparable with the parent com-

pounds 2.

Synthesis of rhodium(I) chloride carbonyl complexes of

N-pyrrolylphosphino-N^ꢀ-arylaldimines

Reaction of two equivalents of ligands 3 or 4 with [Rh(l-

Cl)(CO)₂]₂in CDCl₃under an atmosphere of CO (necessary to

prevent gradual decomposition in solution) was undertaken in a

manner analogous to that reported previously (Scheme 2).^20,37This

afforded two series of complexes 5 and 6, which were characterised

in situ by NMR (¹H, ¹³C, ³¹P) and IR spectroscopy. The complexes

were assigned a P–N-chelating structure, cis-[RhCl(CO)(3,4-j²-

P,N)], in which the P-donor lies cis to the carbonyl, on the basis

of the spectroscopic data and in accordance with trans-inﬂuence

Scheme 2 Reagents and conditions: (i) 0.5 [RhCl(CO)₂]₂, CDCl₃, CO

(1 atm), RT; (ii) Se, 80 ^◦C, CDCl₃,

[PdCl₂(MeCN)₂], CH₂Cl₂.

1 h; (iii) [PdCl₂(COD)] or

1

effects. The relatively large magnitudes of the J_RhP(ca. 180–230

the magnitude of the ¹J_RhPcoupling constant varies according to

1

Hz) and J_RhC(ca. 50–80 Hz) coupling constants (Table 2) are

the nature of the substituents at phosphorus, with average values

1

consistent with the proposed regiochemistry and those determined

for related, structurally characterised complexes.^9,16,38There was

no spectroscopic evidence to suggest the formation of the trans-

[RhCl(CO)(3,4-j¹-P,N)₂] bis(phosphine) derivatives or the pres-

ence of unreacted [Rh(l-Cl)(CO)₂]₂.

being ca. d +90 ppm, J_RhP185 Hz (5; Ph₂P) and d +117 ppm,

¹J_RhP235 Hz (6; {Prⁱ₂N}₂P). In both series Dd [= d(complex) −

1

d(ligand)] is positive. Although the magnitudes of J_RhPare

sometimes not particularly diagnostic,²⁰the complexes bearing

the tris(aminophosphine)-based ligands 6, present the greater

magnitudes, consistent with the greater s-character associated with

the P-donor component of 4 vs. that of 3.^9,20

Each set of rhodium complexes 5 and 6 presents a doublet

1

by ³¹P{ H} NMR spectroscopy, for which the chemical shift and

Table 2 Selected spectroscopic data for [RhCl(CO)(3,4-j²-P,N)] (5, 6), phosphinopyrrolylaldimine selenides 7, 8, selenide derivatives 10, 12 and related

=

R₃P Se derivatives

Compound

d(³¹P)^a/ppm

¹J_MP/Hz

d(¹³C)^bCO/ppm (¹J_RhC/Hz)

m_CO^e/cm⁻¹

5a

5b

5c

5d

6a

6b

6c

6d

7a

7b

7c

7d

8a

8b

8c

8d

10

12

92.9

92.7

90.9

90.7

117.9

117.7

117.8

117.5

56.7

56.0

55.9

58.2

59.9

60.4

58.4

60.4

8.0

185^c

186^c

185^c

183^c

233^c

236^c

235^c

820^d

821^d

820^d

823^d

846^d

848^d

860^d

850^d

812^d

842^d

684^d

736^d

744^d

759^d

784^d

862^d

867^d

186.9 (65.2)

187.5 (67.4)

188.2 (70.0)

188.2 (61.7)

188.9 (79.6)

189.1 (69.0)

189.0 (69.1)

189.1 (73.0)

—

2017

2013

2018

2014

2005

2000

2002

2005

—

39

SePMe₃

39

SePPh₃

34.1

59.7

70.2

81.2

60.9

74.9

SeP(NPrⁱ)Ph₂

20

SeP(NPrⁱ)₂Ph²⁰

—

40

SeP(NMe₂)₃

SeP(NEt₂)₂(NC₄H₄)⁴¹

SeP(NMe₂)₂(NC₄H₄)⁴¹

^a121.5 MHz, CDCl₃. ^b100.6 MHz, CDCl₃. ^cM = Rh. ^dM = Se. ^eKBr, CDCl₃, CO.

5364 | Dalton Trans., 2006, 5362–5378

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The carbonyl stretching frequencies determined for complexes

of the type [RhCl(CO)(PR₃)₂] have routinely been used to assess

the electronic characteristics of monodentate phosphines,^15,20,37,42

and to a lesser extent bidentate diphosphine ligands.⁴³Although

this approach has been previously employed for evaluating

heteroditopic cis-chelating P–E ligands (E = N, O),^15,16,28these

types of system potentially present a problem as a result of their

asymmetry with respect to the ‘reporter’ CO unit, a situation that

may give an inaccurate picture of the electronic character of the

P–N entity as a whole and must therefore be used with caution.

The two series of IR data (5a–d and 6a–d) are both entirely

self-consistent with little alteration observed on changing the

arylaldimine substituent (Table 2). As expected from previous

analyses of the donor behaviour of aminophosphines,^20,21the

magnitude of m_COfor the mono-aminophosphine series 5 (ca.

2015 cm⁻¹) is greater than that of the corresponding tris-amino

set 6 (ca. 2003 cm⁻¹), as a result of lone pair donation from the

diisopropylamino substituents to phosphorus in the latter series.

However, the values of m_COfor both 5 and 6 are considerably

higher than those observed for the corresponding complexes

of either Ph₂(pyrrolyl)P (9) {1992 cm⁻¹}, the related P–N-

chelating aza-N-indolyldiphenylphosphine (1992 cm⁻¹), or the P–

O-chelating 2-keto-functionalised N-pyrrolyldiphenylphosphine

(1989 cm⁻¹).^9,24,28These discrepancies suggest that the signiﬁcantly

greater steric demands imposed by the N-arylimine component

combined with the greater r-donor character of an imine vs. either

an azaindole or a ketone noticeably inﬂuence the CO stretching

frequency. Moreover, the inference concerning the donor character

that can be made from the IR data for5 and 6 are at odds with those

Scheme 3 Reagents and conditions: (i) Ph₂PCl, NEt₃, toluene, 100 ^◦C,

12 h; (ii) KH, THF, −78 ^◦C to RT, 3 h; (iii) (Prⁱ₂N)₂PCl, THF, RT, 12 h;

(iv) Se, 80 ^◦C, CDCl₃, 1 h.

ent pyrrolylphosphine selenides, 10 (¹J_SeP= 812 Hz) and 12 (¹J_SeP

=

842 Hz), and the previously reported systems SeP(pyrrolyl)(NR₂)₂

{R = Me, Et} (¹J_SeP= ca. 865 Hz).⁴¹Furthermore the data from 7

and 8 indicate that addition of a pendant imine in the 2-position of

the pyrrolyl rings has little impact on the basicity of the P-donor

component of 3 and 4.

Together, the ¹J_SePdata for 7 and 8 clearly conﬁrm the expected

trend in basicity, namely that the phosphine fragments of 3 are

somewhat better donors than those of 4, although both are

comparatively poor donors (relative to alkyl or aryl phosphines),

as a result of the presence of the electron-accepting pyrrolyl

fragment. Furthermore, these data highlight an attenuation in

basicity on introducing two diisopropylamino groups (−I effect)

at P,^20,24consistent with the lower r-basicity of 4.

Thus, it would appear that the relative donor ability of unsym-

metrical scaffolds 3 and 4 as an ensemble is not accurately reﬂected

by the carbonyl stretching frequencies of the rhodium complexes

5 and 6 and that the donor character of the P-component of these

systems is akin to that of parent pyrrolyl phosphines 9 and 11.

1

made upon the basis of the magnitudes of J_RhP, which indicate

a reversed ligand basicity. Thus, in order to further probe these

apparent discrepancies in net donor character in greater depth, an

alternative approach was sought.

Reactions of N-pyrrolylphosphino-N^ꢀ-arylaldimines with Se

Palladium dichloride complexes of N-pyrrolylphosphino-N^ꢀ-

arylaldimine ligands 3 and 4

An inverse relationship exists between the r-basicity of a phos-

phine and the magnitude of the ⁷⁷Se–³¹P coupling constant that

arises from the corresponding selenide derivative. This can be used

to estimate the Lewis basicity of the parent P(III) compound.^20,44,45

Hence, in order to examine the donor behaviour of the P-

component of ligands 3 and 4, their corresponding phosphorus

selenides, 7a–d and 8a–d, respectively, were prepared. These were

synthesised cleanly by reaction of 3 and 4 with excess grey

selenium in CDCl₃at 80 ^◦C (Scheme 2). For comparison, the

corresponding unfunctionalised pyrrolylphosphine selenides 10

and 12 were prepared from pyrrole via the P(III) derivatives 9²⁴

and 11, respectively (Scheme 3). In contrast to the preparation

of 9,³⁴more forcing conditions were required for the formation

of 11, namely the sequential reaction of pyrrole with KH and

(Prⁱ₂N)₂PCl; no reaction was obtained using NEt₃in toluene at

reﬂux. A hydride base proved essential since deprotonation with

BuⁿLi followed by trapping with chlorophosphine afforded an

intractable mixture of regioisomers, in accordance with related

observations appearing in the literature.³⁵

The synthesis of the PdCl₂complexes 13 and 14 of these two

new families of P–N ligands was undertaken with a view to

screening their utility as proinitiators in oleﬁn polymerisation.

The desired cis-dichloride complexes were obtained in good to

excellent yields (>70%) from reaction of one equivalent of 3 and 4

with [PdCl₂(COD)] or the more labile [PdCl₂(MeCN)₂], in either

chloroform or dichloromethane; satisfactory mass spectrometric

and elemental analyses were obtained in all cases. These new

complexes are stable indeﬁnitely in the solid state under air, but

degrade slowly (days) in solution unless anaerobic conditions

are ensured. The enhanced stability evident for the P–N bonds

of the various metal-bound ligands, compared to that of the

free pyrrolylaldimines, is in line with previous observations for

coordinated aminophosphines.^20,29,31

Each of the j²-P,N palladium(II) complexes displays a single

1

resonance by ³¹P{ H} NMR spectroscopy at ca. +65 ppm

for complexes of 3 and ca. +81 ppm for those of ligands 4

(Table 1). The diphenylphosphinopyrrolylaldimines 3 exhibit a

signiﬁcant coordination chemical shift upon complexation, Dd

ca. +17 ppm, to higher frequency. In contrast, the corresponding

tris(aminophosphine) series of ligands 4 showed a much smaller

and negative value of Dd, ca. −2 ppm.

As expected, the P-diphenyl selenides 7 exhibited the lower

magnitudes of ¹J_SeP(ca. 820 Hz), while the tris(aminophosphine)

derivatives 8 showed values in the range 846–860 Hz (Table 2).

Both sets of data are in reasonable agreement with those of the par-

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◦

˚

Table 3 Selected bond distances (A) and angles ( ) for 13d and 14b

13d

14b

Pd(1)–Cl(1)

Pd(1)–Cl(2)

Pd(1)–P(2)

Pd(1)–N(1)

P(1)–N(2)

C(2)–C(3)

C(3)–C(4)

C(4)–C(5)

N(1)–C(1)

2.2855(5)

2.3487(5)

2.1959(5)

2.0593(15)

1.7121(16)

1.377(3)

1.401(3)

1.354(3)

1.292(2)

Pd(1)–Cl(1)

Pd(1)–Cl(2)

Pd(1)–P(1)

Pd(1)–N(2)

P(1)–N(1)

P(1)–N(3)

P(1)–N(4)

C(1)–C(2)

C(2)–C(3)

C(3)–C(4)

N(2)–C(5)

2.2776(11)

2.3499(10)

2.2081(11)

2.037(3)

1.717(3)

1.658(3)

1.631(3)

1.359(6)

1.388(6)

1.358(5)

1.277(5)

P(2)–Pd(1)–N(1)

N(1)–Pd(1)–Cl(2)

Cl(2)–Pd(1)–Cl(1)

Cl(1)–Pd(1)–P(2)

P(2)–N(2)–C(5)

C(5)–N(2)–C(2)

C(2)–N(2)–P(2)

92.34(4)

91.47(4)

90.998(18) Cl(2)–Pd(1)–Cl(1)

85.402(19) Cl(1)–Pd(1)–P(1)

127.31(13)

107.10(15)

124.39(13)

P(1)–Pd(1)–N(2)

N(2)–Pd(1)–Cl(2)

91.33(9)

90.15(9)

89.42(4)

89.44(4)

127.3(3)

106.9(3)

124.9(3)

Fig. 2 Molecular structure of [PdCl₂(4b-j²-P,N)] (14b) with the thermal

ellipsoids set at the 50% probability level (two solvent molecules omitted

for clarity).

P(1)–N(1)–C(1)

C(1)–N(1)–C(4)

C(4)–N(1)–P(1)

the two Pd–Cl bond distances of each complex, the bond trans

to phosphorus being the longer, as expected.⁴⁶The Pd–P bond

distances for complex 13d bearing the diphenylpyrrolylaldimine

Few appreciable differences are observed between the ¹H NMR

spectral data of the free and of the bound ligands. The most

signiﬁcant feature is a shift to lower frequency (Dd ca. −0.4 to

−1.2 ppm) for the aldimine proton resonances (Table 1), which

was accompanied by a reduction in the magnitudes of the coupling

of these protons to phosphorus for all the complexes except 13c,d.

An analogous attenuation in the aldimine carbon coupling to

phosphorus was also noted, although there was no discernible

trend associated with the changes in the chemical shift for this

˚

[2.1959(5) A] is marginally shorter than that determined for the

˚

bis(diisopropyl)amino-functionalised ligand of14b [2.2081(11)A].

In 13d, the plane of the N-aryl ring lies at an angle of 72^◦to the

Pd(1) coordination plane, while in 14b the arylimine ring plane is

near-perpendicular, 83^◦, to the coordination plane of palladium.

The crystallographically-determined P–N bite angles at palla-

dium [13d: 92.34(4)^◦; 14b: 91.33(9)^◦] are comparable, whilst the

˚

=

aldimine C N bond distance for 13d {1.292(2) A} differs slightly

1

carbon atom by ¹³C{ H} NMR spectroscopy.

˚

from that of 14b {1.277(5) A}. In gross terms, however, both these

The molecular structures of complexes 13d and 14b were

investigated by X-ray crystallography, with crystals being grown

by slow evaporation from CH₂Cl₂solutions (Figs. 1, 2 and Table 3).

The gross molecular structures of both complexes are comparable,

the palladium centres adopting near-square planar geometries

with the anticipated j²-P,N-coordination of ligands 3 and 4 (in

accordance with the spectroscopic data obtained).

sets of metric parameters are comparable to those observed in

related phosphine-imine ligands, but lie towards the higher end of

the ranges previously observed.^6,10,47–49

Nickel dibromide complexes of N-pyrrolylphosphino-N^ꢀ-

arylaldimine ligands 3a–d

There is considerable literature precedent indicating that polymeri-

sation initiators based on Ni(II) are considerably more active than

their heavier Group 10 congeners.^50–52Hence, the corresponding

P–N-chelated nickel dibromide complexes [NiBr₂(3-j²-P,N)] (15)

were prepared by reaction of equimolar quantities of ligands 3

with [NiBr₂(DME)] in MeCN, and isolated as green/brown solids

in moderate yields (47–70%).

Each complex gave rise to an ion corresponding to [NiBr(3)]⁺

by mass spectrometry and was found to be paramagnetic in

solution. Despite numerous attempts, crystals of 15 suitable for

study by X-ray diffraction could not be obtained. An alternative

synthetic strategy involving displacement of triphenylphosphine

from [NiBr₂(PPh₃)₂] proved successful for the preparation of 15b,

which was isolated in 71% yield following reaction of 3b with the

diphosphine complex in MeCN using a modiﬁcation of a related

literature procedure (Scheme 4).⁵³Despite repeated attempts

using a range of Ni(II) starting materials, reactions involving the

tris(aminophosphine)aldimines 4 afford signiﬁcant quantities of

Prⁱ₂NH₂Br as the only identiﬁable product in each case, irrespective

of the solvent employed. Notably, the reaction between equimolar

quantities of 3c and [NiBr₂(DME)] performed in CH₂Cl₂under

rigorously anaerobic and anhydrous conditions gives rise to the

Fig. 1 Molecular structure of [PdCl₂(3d-j²-P,N)] (13d) with the thermal

ellipsoids set at the 50% probability level.

In both 13d and 14b the six-membered metallacyclic ring is

puckered, with the P–N ligand backbone adopting a distorted

‘envelope’ conformation. The differing trans-inﬂuences of the N-

and P-donor units are clearly reﬂected by the inequivalence of

5366 | Dalton Trans., 2006, 5362–5378

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◦

˚

homoleptic bis(pyrrolatoimine) Ni(II) complex trans-[Ni{2-(Mes–

Table 4 Selected bond distances (A) and angles ( ) for 16

2

=

N CH)C₄H₃N-j -N,N}₂] (16) in near-quantitative isolated yield

Molecule A

Molecule B

(45%) as a red/brown, air stable solid (Scheme 4).

Ni(1)–N(1)

Ni(1)–N(2)

Ni(1)–N(3)

Ni(1)–N(4)

N(1)–C(1)

N(1)–N(3)

N(2)–C(2)

C(2)–C(3)

C(3)–C(4)

C(4)–C(5)

N(2)–C(5)

N(4)–C(7)

C(7)–C(8)

C(8)–C(9)

C(9)–C(10)

C(10)–N(4)

1.9221(15)

1.9061(15)

1.9262(15)

1.8983(15)

1.307(2)

1.403(3)

1.388(2)

1.400(3)

1.387(3)

1.399(3)

1.352(2)

1.382(2)

1.399(3)

1.390(3)

1.394(3)

1.350(2)

Ni(2)–N(5)

Ni(2)–N(6)

C(1)–N(1)

N(6)–C(32)

C(32)–C(33)

C(33)–C(34)

C(34)–C(35)

C(35)–N(6)

1.9392(15)

1.9148(15)

1.303(2)

1.395(3)

1.380(2)

1.398(3)

1.388(3)

1.395(3)

N(2)–Ni(1)–N(1)

N(1)–Ni(1)–N(4)

N(4)–Ni(1)–N(3)

N(2)–Ni(1)–N(3)

C(1)–N(1)–Ni(1)

Ni(1)–N(1)–C(11)

C(1)–N(1)–C(11)

C(21)–N(3)–Ni(1)

C(21)–N(3)–C(6)

C(6)–N(3)–Ni(1)

83.80(6)

96.56(6)

83.80(7)

N(5)–Ni(2)–N(6)

N(5)–Ni(2)–N(6)^ꢀ

C(31)–N(5)–C(41)

Ni(2)–N(5)–C(31)

Ni(2)–N(5)–C(41)

83.68(6)

96.32(6)

115.99(15)

112.12(12)

131.19(12)

Scheme 4 Reagents and conditions: (i) [NiBr₂(DME)], MeCN, RT, 3 h;

(ii) [NiBr₂(DME)], CH₂Cl₂, RT, 3 h.

97.74(6)

113.03(13)

128.14(12)

118.83(15)

128.07(12)

119.00(16)

112.92(12)

The observed solvent dependency of the reactions of 3 has been

attributed to moderation of the reactivity of the Ni(II) species

by the in situ formation of [NiBr₂(MeCN)₂]. In contrast to the

behaviour of 3c, which undergoes clean P–N bond cleavage and

results in the formation of Ni(II) pyrrolato complexes, identical

reactions between [NiBr₂(DME)] and 3a,b,d in CH₂Cl₂did not

afford any tractable products.

Clearly the formation of 16 from 3c must involve P–N bond

cleavage, however both the mechanism for this process and the

origins of its substrate speciﬁcity to 3c remain elusive. Although

attempts were made to probe the fate of the Ph₂P moiety by

³¹P NMR spectroscopy, neither the formation of Ph₂PBr nor

other P-containing products could be observed. A small number

of examples of P–N bond cleavage of aminophosphines in the

presence of Group 10 metal complexes have been observed

previously.^20,54However, in these reports P–N bond rupture was

induced by either the deliberate addition of acids (e.g. HCl, ROH)

or the presence of adventitious water. Although the reactions of

3 and 4 with [NiBr₂(DME)] were carried out under scrupulously

dry conditions, the presence of trace quantities of protic impurities

cannot be ruled out. Hence no deﬁnitive mechanism for the P–N

bond rupture observed here can be presented.

The molecular structure of 16 was conﬁrmed by X-ray diffrac-

tion (Fig. 3, Table 4). The asymmetric unit of 16 (Fig. 3) comprises

one molecule (A) in a general position and a half of another

molecule (B) whose Ni(2) atom lies at an inversion centre. The four-

fold coordination of nickel in molecule B is thus rigorously square

planar (trans), whereas molecule A experiences a slight distortion

intermediate between tetrahedral and pyramidal. Thus, deviations

of the four nitrogen atoms from their mean plane are: N(1) and

˚

N(3) −0.18, N(2) and N(4) 0.18 A, whilst Ni(1) deviates from

˚

the same plane by 0.04 A. The N(1)Ni(1)N(2) and N(3)Ni(1)N(4)

planes form a dihedral angle of 16.6^◦. In molecule B the ring

planes of both mesityl (Mes) substituents lie almost normal to the

Ni(2) coordination plane (dihedral angle 85.2^◦), whereas in A the

Mes substituents at N(1) and N(2) are inclined to the mean N(4)

plane by 72^◦and 68^◦, respectively. All the N–Ni bond distances

are slightly longer in the planar complex (B) than in its puckered

counterpart (A).

2

=

Fig. 3 Molecular structure of [Ni{2-(Mes-N CH)C₄H₃N-j -N,N)₂] (16)

showing molecule A (top) and B (bottom) with the thermal ellipsoids set

at the 50% probability level. Primed atoms are generated by the inversion

centre.

A number of the corresponding bis(pyrrolato-N-alkylimine)

Ni(II) complexes have been previously prepared in a ‘one-pot’

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fashion from NiSO₄·2H₂O, 2-acetylpyrrole and an alkyl amine.⁵⁵

Their structures are entirely comparable to that of 16, with the

bulk of the N-alkyl substituent determining the extent of deviation

from square planar coordination at Ni. The palladium congeners

molecular mass polymer formation,⁵⁰and (b) what the effect of

the comparatively poor r-donor character (vide supra) of ligands

3 and 4 would be upon the rate of chain termination by b-hydride

elimination.

=

of 16 have also been prepared, e.g. [Pd{2-(aryl–N CH)C₄H₃N}₂],

Treating toluene solutions of palladium complexes 13 and

14 (5 × 10⁻⁵mol) with 500 equivalents of MAO at ambient

temperature led to initiator decomposition, as signiﬁed by the

rapid formation (minutes) of ‘palladium black’ for both systems.

The resulting suspensions showed no activity towards ethylene (1

or 10 bar, ambient temperature). These observations are consistent

with those reported for certain related bidentate phosphine-imine

scaffolds bound to Pd(II).⁶³Since it is well established that the

oligo-/poly-merisation activity of late transition metal complexes

of P–N ligands is intimately linked to the nature of the Lewis acidic

co-initiator,⁶¹an alternative activation procedure was invoked.

Despite a distinct colour change (orange to yellow) on addition

of 4.5 equivalents of EtAlCl₂to toluene solutions of 13 and 14

(5 × 10⁻⁵mol), the resulting species again proved inactive for the

polymerisation of ethylene (1 or 10 bar, ambient temperature).

However, unlike the reactions with MAO, no ‘palladium black’

was found to have formed at the end of the polymerisation

tests.

Contrastingly, activation of the corresponding Ni(II) derivatives

15 (5 × 10⁻⁵mol) by 4.5 equivalents of EtAlCl₂(in toluene) led

to the formation of initiators that rapidly convert ethylene (1 bar,

ambient temperature, 0.5 h) to mixtures of butenes and hexenes

(identiﬁed by GC-MS) as the only organic products, in initially

very exothermic reactions (reaching ca. 80 ^◦C). The alkenes are

obtained as isomeric mixtures as a result of well-established Ni-

catalysed double bond isomerisation. This behaviour is consistent

with that observed previously for Ni(II) complexes of other P–

N chelates.^61,62,64No higher molecular weight polyoleﬁn products

were formed. Degradation of the initiator systems derived from

15a–c was evident from the slow, gradual precipitation of a

brown, water-soluble solid in varying amounts. In contrast, no

decomposition was observed using proinitiator 15d over the course

of the reaction.

Notably, the substitution pattern about the imine moiety

impacts directly upon both the selectivity and the activity of the

various initiator systems derived from 15, although it is difﬁcult

to establish any conclusive structure–property correlations with

this small data set. However, it is clear that proinitiators 15a,b,d

all exhibit a very marked selectivity for the formation of butenes

(Table 5, entries 1, 2 and 4), while the mesityl-bearing derivative

15c demonstrates an inverse selectivity favouring production of

hexenes (entry 3). The levels of activity (total for all products)

of complexes 15 may be classiﬁed as ‘moderate’ on the scale

established by Gibson and co-workers.⁵⁹Both the selectivity and

activity of the systems based on 15 are comparable to that reported

previously for an isoelectronic phosphonite-derived P–N chelate

system.⁶⁵

whose structures are analogous to those of the square planar form

of 16.⁵⁶

Despite the existence of both a square planar and a distorted

form of 16 in the solid state, in solution the complex is diamag-

netic, with its NMR spectroscopic data being consistent with a

symmetrical trans structure. Relative to the parent pyrrole 2c, the

proton and carbon resonances for the CH N moiety of 16 are

shifted to lower and higher frequencies, respectively (Table 1).

=

Attempted CO/ethylene copolymerisation reactions

Previous studies have indicated that P–N-chelating phosphino-

(phenylpyridin-2-yl methylene)amine complexes of Pd(II) are

highly chemoselective proinitiators for alkene hydrocarboxylation

in methanol.¹⁰Their success has been attributed to the ﬂexible

nature of the ligand, which readily allows it to adopt 90 or 120^◦

bite-angles, as a result of its ﬂexible six-membered ring chelation.

To further explore this hypothesis, it was of interest to screen the

considerably more rigid, yet still six-membered chelate-forming

complexes 13 and 14 for CO/ethylene polymerisation activity.

◦

Methanol solutions of 13 and 14 were heated to 90 C under

a 1 : 1 CO–C₂H₄atmosphere (40 bar) in the presence of four

equivalents of methane sulfonic acid for periods of 3 h.¹⁰Although

a slight gas uptake was detected in all cases, GC-MS analysis of the

crude reaction mixtures did not reveal the formation of any new

products. After each run, initiator decomposition was apparent

from signiﬁcant deposits of ‘palladium black’ within the autoclave.

It should be noted, however, that both 13 and 14 have been shown

to be stable in methanolic solution in the presence of methane

sulfonic acid under the reaction conditions for short periods of

time.

This lack of carbonylation activity for complexes of 3 and 4

is somewhat surprising, certainly in light of successful polyke-

tone formation initiated by a range of palladium complexes

of phosphine-imine scaffolds and, in particular, those using

structurally-related chelating aza-N-indolylphosphines.^6,8,9One

possible explanation for the difference in behaviour of 3 and 4

compared with that of the aza-N-indolyl-based scaffolds could

lie in the nature of the N-donor component; aryl imine vs.

aromatic heterocyclic nitrogen, respectively. While pyridines are

both good r-donors and p-acceptors,⁵⁷non-conjugated imines

have essentially no acceptor character,⁵⁸a difference that affects

the strength of the Pd–nitrogen interaction (imines potentially

being more labile) and in turn the reactivity of the metal centre.

Ethylene oligomerisation reactions

Upon activation by 4.5 eq. EtAlCl₂the mesityl-substituted

bis(pyrrolatoaryl imine) derivative 16 exhibits a very slight activity

for the dimerisation of ethylene at 1 bar (Table 6, entry 5).

The extremely low activity of 16 for the formation of butenes

compared with the efﬁcacy of complexes 15a,b,d indicates that

under the polymerisation conditions employed, complexes 15 are

not converted to their bis(pyrrolatoimine) counterparts on the

time-scale of the catalytic tests.

Following various reports of the use of P–N ligands in oleﬁn

polymerisation, an investigation of the utility of the sterically

demanding, non-enolisable ligands 3 and 4 as metal scaffolds

in ethylene polymerisation was undertaken.^52,59–62Here, it was of

interest to explore whether (a) the tris(amino) ligand series 4

that locates signiﬁcant steric constraints close to the axial sites

of the metals’ square coordination planes, would favour high

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Table 5 Ethylene di- and tri-merisation studies^a

Selectivity (%)^d

Entry

Proinitiator^b

Activator [eq.]

P/bar

Initial T^c/^◦C

C₄

C₆

Activity^e,f

1

2

3

4

5

15a

15b

15c

15d

16

EtAlCl₂[4.5]

1

20

92

72

8

83

100

8

28

92

17

0

3.8

51.5

17.1

56.9

∼1

^aReaction conditions: toluene (50 cm³), reaction time 30 min. ^b5 × 10⁻⁵mol. ^cNo cooling applied. ^dC_nfraction deﬁned as the (amount of C_noleﬁns)/(total

amount of oleﬁns) × 100. ^eAverage productivity (two runs) expressed in g(total product) mmol (Ni)⁻¹h⁻¹bar⁻¹. ^fDetermined by quantitative GC using

nonane as internal standard.

Palladium and rhodium salts were used on loan from John-

Summary

son Matthey. Pyrrole-2-carbaldehyde and 2-acetylpyrrole were

Pyrrole-substituted in the 2-position makes a useful building

purchased from Avocado, gaseous chemicals from BOC and all

block for the straightforward preparation of various heteroditopic

other chemicals from Aldrich. All solid reagents were used as

chelating ligands with a range of substitution patterns. Here, the

synthesis of two families of N-pyrrolylphosphinoarylimines that

bear phenyl (3) or diisopropylamino (4) groups at phosphorus

have been described. Both ligand sets 3 and 4 readily form rigid

j²-P,N six-membered chelates with Rh(I) and Pd(II). In contrast,

only the [NiBr₂(3-j²-P,N)] (15) complexes could be prepared. The

use of rhodium carbonyl chloride complexes to probe the donor

character of chelating heteroditopic ligands should be used with

caution, since both steric and electronic factors can impact in an

received. Where appropriate, liquid reagents were dried, distilled

and deoxygenated prior to use. Gases were passed through a

drying column (silica/CaCO₃/P₂O₅) prior to use. The start-

ing materials (Prⁱ₂N)₂PCl,⁶⁶[PdCl₂(COD)],⁶⁷[PdCl₂(MeCN)₂],⁶⁸

[RhCl(CO)₂]₂,⁶⁹and Ph₂PNC₄H₄were prepared according to

34

literature procedures or slight modiﬁcations thereof.

Routine NMR spectra were collected on a Bruker AM250,

DPX300 or Varian Inova 500 at ambient probe temperatures

(∼290 K) unless stated otherwise, and NOE spectra on a Bruker

AMX400. Chemical shifts were referenced to residual protio

impurities in the deuterated solvent (¹H), ¹³C shift of the solvent

(¹³C), or to external aqueous 85% H₃PO₄(³¹P). Solvent proton

shifts (ppm): CDCl₃, 7.27 (s). Solvent carbon shifts (ppm): CDCl₃,

77.2 (t). In ¹H NMR spectra, ³¹P coupled resonances were veriﬁed

unpredictable manner upon the observed values of m_CO

.

Despite the structural similarity between the N-

pyrrolylphosphino-N^ꢀ-arylaldimine ligands reported here

and a variety of other P–N chelate systems that have been

reported previously, palladium dichloride complexes of 3 and

4 proved inactive for CO/C₂H₄copolymerisation. In contrast,

following activation by EtAlCl₂the Ni(II) complexes 15 afford

initiators that exhibit moderate activity for the formation of

isomeric mixtures of butenes and hexenes from ethylene under

mild conditions. Although bulky arylimine substituents (known

to support the formation of high molecular weight polyoleﬁn

products) were present in ligands 3, the comparatively unhindered

diphenylphosphino moiety proved insufﬁcient to prevent rapid

b-hydride elimination and hence permitted only ethylene di- and

tri-merisation.

31

by running ¹H { P} experiments. ¹³C NMR spectra were assigned

1

with the aid of DEPT 135 and H–¹³C correlation experiments.

Chemical shifts are reported in ppm and coupling constants in Hz.

While ¹J_SePcoupling constants are negative,⁷⁰only the magnitudes

are reported here, since direct measurements are not possible from

the ³¹P NMR spectra and only relative differences in magnitude

are of relevance.

FAB (3-nitrobenzyl alcohol matrix) and EI mass spectra were

recorded on a Kratos Concept 1H instrument, while MALDI

(dithranol matrix) were obtained on an Applied Biosystems

Voyager-DE STR instrument and are all reported in (m/z). The

isotope distributions for all parent ion peaks for metal complexes

were veriﬁed via comparison with a theoretical isotope pattern.

Elemental analyses were performed by Mr S. Boyer at the London

Metropolitan University or by Mrs J. Dostal of the Analytical

Services Department, Durham University. Infrared spectra were

collected on a Perkin Elmer 1600 spectrophotometer using KBr

discs, or a solution cell with KBr windows or via ATR-FTIR on a

Perkin Elmer Spectrum ONE instrument. GC/MS were obtained

using a Thermo Finnegan Trace instrument (Agilent HP-5MS

30 m column, internal diameter 0.25 mm, ﬁlm thickness 0.25 lm).

The utility of ligands 3 and 4 in other catalytic applications is

under active investigation.

Experimental

General considerations

All operations were conducted under an atmosphere of dry

nitrogen using standard Schlenk and cannula techniques, or in a

nitrogen-ﬁlled glove box, unless stated otherwise. All NMR-scale

reactions were conducted using NMR tubes ﬁtted with J. Young

tap valves. Solvents were freshly distilled under nitrogen from

sodium/benzophenone (Et₂O, toluene, and DME), from sodium

(hexane, pentane), from magnesium turnings (MeOH), from

calcium hydride (CH₂Cl₂) or from P₂O₅(CDCl₃) and deoxygenated

prior to use. Sonication was achieved by suspending the desired

reaction vessel in a water-ﬁlled Grant Ultrasonic Bath XB2.

Syntheses and reactions

Phenyl(1H-pyrrol-2-ylmethylene)amine 2a. A modiﬁcation of

the literature procedure was employed.³³Under air, aniline

(4.0 cm³, 43.3 × 10⁻³mol) was added to a solution of

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pyrrole-2-carbaldehyde (1) (3.80 g, 40.0 × 10⁻³mol) in toluene

(100 cm³). A catalytic quantity of p-TSA (0.1 g, 0.7 × 10⁻³mol)

was added and the mixture heated to reﬂux under Dean–Stark

conditions for 17 h. The toluene was then removed in vacuo,

replaced with CH₂Cl₂and the solution ﬁltered to remove p-

TSA. The CH₂Cl₂was removed under reduced pressure and the

resulting dark brown solid was then washed with hexane (3 ×

10 cm³) to remove excess aniline and dried in vacuo to afford

2a (4.25 g, 63%) as a dark brown crystalline solid following

recrystallisation from methanol (Anal. Calc. for C₁₁H₁₀N₂: C,

77.61; H, 5.93; N, 16.46. Found: C, 77.42; H, 6.02; N, 16.26%);

d_H(300.1 MHz, CDCl₃) 6.31 (t, ³J_HH= 3.0 Hz, 1H, H⁴), 6.76 (d,

³J_HH= 3.0 Hz, 1H, H³), 6.84 (s, 1H, H⁵), 7.15 (m, 3H, m/p-C₆H₅),

(m_CN) cm⁻¹. The product is hygroscopic and must be stored under

a dry nitrogen atmosphere to prevent degradation.

(2,6-Diisopropylphenyl)(1H-pyrrol-2-ylmethylene)amine 2d.

A

modiﬁcation to the literature procedure was used.⁷¹Under air,

2,6-diisopropylaniline (6.65 cm³, 35.3 × 10⁻³mol) was added to

a solution of 1 (3.10 g, 32.6 × 10⁻³mol) in toluene (100 cm³). A

catalytic quantity of p-TSA (0.1 g, 0.7 × 10⁻³mol) was added and

the mixture heated to reﬂux under Dean–Stark conditions for 16 h.

The toluene was then removed in vacuo, replaced with CH₂Cl₂and

the solution ﬁltered to remove p-TSA. The CH₂Cl₂was removed in

vacuo. Following recrystallisation from MeOH, 2d (4.39 g, 53%)

was obtained as a dark cream-coloured crystalline solid (Anal.

=

7.30 (m, 2H, o-C₆H₅), 8.32 (s, 1H, CH N), 10.27 (br s, m_1/2

=

Calc. for C₁₇H₂₂N₂: C, 80.25; H, 8.73; N, 11.01. Found: C, 80.43;

30.0 Hz, 1H, pyrrolyl NH); d_C(75.5 MHz, CDCl₃) 110.8 (s, C⁴),

H, 8.50; N, 11.07%); d_H(300.1 MHz, CDCl₃) 1.19 (d, J_HH

=

3

117.8 (s, C³), 121.2 (s, m-C₆H₅), 124.4 (s, p-C₆H₅), 125.9 (s, C⁵),

6.8 Hz, 12H, o-((CH₃)₂CH)₂C₆H₃), 3.20 (sept, ³J_HH= 6.8 Hz, 2H,

2

129.6 (s, o-C₆H₅), 130.8 (s, C ), 150.5 (s, CH N), 151.8 (s, i-PhC);

o-((CH₃)₂CH)₂C₆H₃), 6.06 (s, 1H, H⁴), 6.17 (s, 1H, H³), 6.66 (d,

=

MS (FAB⁺): m/z 171 (MH⁺); IR (ATR, neat): = 3221 (m_NH), 1583

(m_CN) cm⁻¹. The product is hygroscopic and must be stored under

a dry nitrogen atmosphere to prevent degradation.

³J_HH= 1.4 Hz, 1H, H⁵), 7.26 (m, 3H, m/p-C₆H₃), 8.05 (s, 1H,

1

=

CH N); d_C{ H} (62.9 MHz, CDCl₃): d 24.0 (s, o-C₆H₃), 28.4 (s,

o-C₆H₃), 110.2 (s, C⁴), 117.0 (s, C³), 123.6 (s, m-C₆H₃), 124.4 (s,

p-C₆H₃), 124.9 (s, C⁵), 130.3 (s, C²), 139.3 (s, o-C₆H₃), 148.9 (s,

+

=

i-C₆H₃), 153.0 (s, CH N); MS (FAB ) m/z 255 (MH ); IR (ATR,

neat) 3232 (m_NH), 1585 (m_CN) cm⁻¹. The product is hygroscopic

and must be stored under a dry nitrogen atmosphere to prevent

degradation.

(3,5-Dimethylphenyl)(1H-pyrrol-2-ylmethylene)amine 2b. Us-

ing conditions analogous to those for the preparation of 2a,

3,5-dimethylaniline (4.75 cm³, 38.1 × 10⁻³mol) was reacted

with 1 (3.43 g, 36.1 × 10⁻³mol) in toluene (100 cm³) in the

presence of p-TSA (0.1 g, 0.71 × 10⁻³mol) at reﬂux under Dean–

Stark conditions for 20 h. Subsequently, compound 2b (5.18 g,

72%) was isolated as a dark brown crystalline solid following

recrystallisation from methanol (Anal. Calc. for C₁₃H₁₄N₂: C,

78.74; H, 7.13; N 14.13. Found: C, 78.90; H, 7.33; N, 14.17%);

Attempted preparation of phenyl[1-(1H-pyrrol-2-yl)ethylidene]-

amine. Under air, aniline (1.81 cm³, 16.8 × 10⁻³mol) was added

to a solution of 1 (2.00 g, 18.3 × 10⁻³mol) in toluene (100 cm³).

A catalytic quantity of p-TSA (0.1 g, 0.7 × 10⁻³mol) was added

and the mixture heated to reﬂux under Dean–Stark conditions for

14 h. The toluene was removed in vacuo to afford a dark brown

crystalline solid, which following recrystallisation from methanol

afforded bright purple needles that, upon further analysis, were

shown to be predominately 1 with only traces of the desired

ketimine. Attempts were made to isolate the imine by further

recrystallisation from methanol, but without success. Similarly,

no tractable products resulted using 3,5-dimethylaniline, 2,4,6-

trimethylaniline or 2,6-diisopropylaniline.

d_H(400.1 MHz, CDCl₃) 2.39 (s, 6H, (CH₃)₂C₆H₃), 6.37 (t, ³J_HH

=

2.8 Hz, 1H, H⁴), 6.56 (s, 1H, p-C₆H₃), 6.72 (d, ³J_HH= 2.6 Hz, 1H,

3

5

=

H ), 6.84 (s, 1H, H ), 7.09 (s, 2H, o-C₆H₃), 8.25 (s, 1H, CH N),

1

9.88 (br s, m_1/242.0 Hz, 1H, pyrrolyl NH); d_C{ H} (75.5 MHz,

CDCl₃) 21.4 (s, m-C₆H₃), 110.5 (s, C⁴), 117.5 (s, C³), 118.8 (s,

o-C₆H₃), 124.4 (s, p-C₆H₃), 127.4 (s, C⁵), 130.5 (s, C²), 138.9 (s,

+

=

m-C₆H₃), 149.9 (s, CH N), 151.3 (s, i-C₆H₃); MS (FAB ) m/z 199

(MH⁺); IR (ATR, neat) 3282 (m_NH), 1585 (m_CN) cm⁻¹. The product is

hygroscopic and must be stored under a dry nitrogen atmosphere

to prevent degradation.

(1-Diphenylphosphanyl-1H -pyrrol-2-ylmethylene)phenylamine

3a. A solution of 2a (1.10 g, 6.5 × 10⁻³mol) in DME (20 cm³) was

cooled to −78 ^◦C with stirring. BuⁿLi (4.03 cm³, 6.5 × 10⁻³mol;

1.6 mol dm⁻³solution in hexanes) was added, the resulting solution

allowed to stir at −78 ^◦C for 0.5 h and then allowed to warm

slowly to RT. Ph₂PCl (1.18 cm³, 6.4 × 10⁻³mol) was added by

syringe and the mixture allowed to stir at RT for 18 h. The volatile

components were then removed in vacuo, CH₂Cl₂added and the

solution ﬁltered. The CH₂Cl₂was then removed under vacuum

and the product dried in vacuo to yield a red–brown tar. Hexane

(10 cm³) was then added, the red–black tar triturated and the

mixture ﬁltered to afford 3a (1.92 g, 84%) as a waxy dark brown

solid (Anal. Calc. for C₂₃H₁₉N₂P: C, 77.94; H, 5.41; N, 7.91. Found:

C, 78.11; H, 5.61; N, 8.11%); d_H(300.1 MHz, CDCl₃): d 6.38 (t,

³J_HH= 2.4 Hz, 1H, H⁴), 6.55 (m, 1H, H³), 7.03 (m, 3H, m/p-C₆H₅),

(2,4,6-Trimethylphenyl)(1H-pyrrol-2-ylmethylene)amine

2c.

Using conditions analogous to those for the preparation of 2a,

2,4,6-trimethylaniline (4.95 cm³, 35.2 × 10⁻³mol) was added to 1

(3.09 g, 32.5 × 10⁻³mol) in toluene (100 cm³) and p-TSA (0.1 g,

0.71 × 10⁻³mol) was added and the mixture heated to reﬂux

under Dean–Stark conditions for 16 h. Subsequently, compound

2c (4.36 g, 63%) was isolated as a mid-brown-coloured crystalline

solid following recrystallisation from methanol (Anal. Calc. for

C₁₄H₁₆N₂: C, 79.19; H, 7.61; N, 13.20. Found: C, 79.22; H, 7.51;

N, 13.27%); d_H(250.1 MHz, CDCl₃) 2.13 (s, 6H, o-(CH₃)₂C₆H₂),

2.30 (s, 3H, p-CH₃C₆H₂), 6.29 (t, ³J_HH= 2.5 Hz, 1H, H⁴), 6.61 (d,

³J_HH= 1.4 Hz, 1H, H³), 6.82 (d, ³J_HH= 1.4 Hz, 1H, H⁵), 6.89 (s,

1

=

2H, m-C₆H₂), 7.96 (s, 1H, CH N); d_C{ H} (62.9 MHz, CDCl₃)

18.6 (s, o-(CH₃)₂C₆H₂), 21.1 (s, p-CH₃C₆H₂), 110.3 (s, C⁴), 117.0

7.09 (m, 1H, H⁵), 7.16 (m, 2H, o-C₆H₅), 7.34 (m, 4H, PC₆H₅),

4

(s, C³), 124.3 (s, C⁵), 128.5 (s, o-C₆H₂), 129.2 (s, m-C₆H₂), 130.3

7.44 (m, 6H, p-C₆H₅), 8.68 (d, J_PH= 1.2 Hz, 1H, CH N); d_C

=

{ H} (75.5 MHz, CDCl₃) 112.7 (s, C⁴), 118.0 (s, C³), 121.2 (s, m-

2

1

=

(s, p-C₆H₂), 133.6 (s, C ), 148.6 (s, i-C₆H₂), 153.7 (s, CH N);

MS (FAB⁺) m/z 213 (MH⁺); IR (ATR, neat) 3131 (m_NH), 1587

5370 | Dalton Trans., 2006, 5362–5378

C₆H₅), 125.6 (s, p-C₆H₅), 129.0 (d, ³J_PC= 6.8 Hz, m-C₆H₅P), 129.3

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2

(s, p-C₆H₅P), 130.2 (s, o-C₆H₅), 130.4 (s, C⁵), 132.8 (d, J_PC

=

o-((CH₃)₂CH)₂C₆H₃), 6.38 (t, ³J_HH= 3.3 Hz, 1H, H⁴), 6.51 (m, 1H,

1

21.9 Hz, o-C₆H₅P), 137.0 (d, J_PC= 14.7 Hz, i-C₆H₅P), 137.2 (s,

H³), 7.02 (m, 1H, H⁵), 7.30 (m, 4H, PC₆H₅), 7.43 (m, 6H, PC₆H₅),

C²), 149.9 (d, J_PC= 9.8 Hz, CH N), 152.2 (s, i-C₆H₅); d_P{ H}

(121.5 MHz, CDCl₃) + 47.5 (s); MS (FAB⁺) m/z 355 (MH⁺); IR

(KBr, CH₂Cl₂) 1589 (m_CN), 897 (m_PN(pyrl)) cm⁻¹.

8.31 (d, ⁴J_PH= 1.8 Hz, 1H, CH N); d_C{ H} (75.5 MHz, CDCl₃)

3

1

=

23.7 (s, o-((CH₃)₂CH)₂C₆H₃), 27.7 (s, o-((CH₃)₂CH)₂C₆H₃), 112.1

(s, C⁴), 118.1 (s, C³), 122.8 (s, m-C₆H₃), 123.1 (s, C⁵), 123.4 (s,

3

p-C₆H₃), 129.0 (d, J_PC= 6.8 Hz, m-C₆H₅P), 130.2 (s, p-C₆H₅P),

(3,5-Dimethylphenyl)(1-diphenylphosphanyl-1H -pyrrol-2-yl-

methylene)amine 3b. Using an analogous procedure to that used

to prepare 3a, reaction of 2b (1.70 g, 8.6 × 10⁻³mol) in DME

(20 cm³) with BuⁿLi (5.40 cm³, 8.6 × 10⁻³mol; 1.6 mol dm⁻³,

solution in hexanes) followed by addition of Ph₂PCl (1.58 cm³,

8.6 × 10⁻³mol) afforded, after stirring for 23 h and appropriate

puriﬁcation, 3b (0.90 g, 27%) as a thick orange oil. Further

distillation led to decomposition of 3b, hence analytical data are

reported for the crude material. (Anal. Calc. for C₂₅H₂₃N₂P: C,

78.50; H, 6.07; N, 7.33. Found: C, 75.07; H, 5.38; N, 6.34%); d_H

2

132.9 (d, J_PC= 22.6 Hz, o-C₆H₅P), 136.0 (s, o-C₆H₃), 137.5 (d,

¹J_PC= 17.4 Hz, i-C₆H₅P), 138.5 (s, C²), 149.8 (s, i-C₆H₃), 152.3 (d,

3

1

=

J_PC= 6.8 Hz, CH N); d_P{ H} (121.5 MHz, CDCl₃) +49.1 (s);

MS (FAB⁺): m/z 439 (MH⁺); IR (KBr, CH₂Cl₂) 1588 (m_CN), 895

(m_PN(pyrl)) cm⁻¹.

(Bis(diisopropylamino)phosphanyl)(1H -pyrrol-2-ylmethylene)-

phenylamine 4a. A solution of 2a (1.12 g, 6.6 × 10⁻³mol) in DME

◦

(20 cm³) was cooled to −78 C with stirring. BuⁿLi (4.15 cm³,

6.6 × 10⁻³mol; 1.6 mol dm⁻³, solution in hexanes) was added

and the resulting solution allowed to stir at −78 ^◦C for 0.5 h and

then allowed to warm slowly to RT. A solution of (Prⁱ₂N)₂PCl

(1.76 g, 6.6 × 10⁻³mol) in DME (20 cm³) was added via cannula

and the resulting mixture allowed to stir at RT for 16 h. The

DME was then removed in vacuo, CH₂Cl₂added, and the solution

ﬁltered. Removal of CH₂Cl₂under vacuum and drying in vacuo

afford 4a (2.01 g, 76%) as a mid-brown-coloured crystalline solid

(Anal. Calc. for C₂₃H₃₇N₄P: C, 68.95; H, 9.33; N, 13.99. Found:

C, 69.02; H, 9.25; N, 13.75%); d_H(300.1 MHz, CDCl₃) 1.09 (d,

³J_HH= 6.6 Hz, 12H, ((CH₃)₂CH)₂N)), 1.28 (d, ³J_HH= 6.6 Hz, 12H,

(400.1 MHz, CDCl₃) 2.15 (s, 6H, m-(CH₃)₂C₆H₃), 6.20 (t, ³J_HH

=

3.4 Hz, 1H, H⁴), 6.39 (m, 1H, H³), 6.49 (s, 2H, o-C₆H₅), 6.65 (s,

1H, p-C₆H₃), 6.92 (s, 1H, H⁵), 7.20 (m, 4H, PC₆H₅), 7.23 (m, 6H,

PC₆H₅), 8.51 (d, ⁴J_PH= 2.4 Hz, 1H, CH N); d_C{ H} (100.6 MHz,

1

=

CDCl₃): d 21.7 (s, m-(CH₃)₂C₆H₃), 112.7 (s, C⁴), 117.5 (s, C³), 119.0

(s, p-C₆H₃), 127.3 (s, o-C₆H₃), 129.0 (d, ³J_PC= 6.6 Hz, m-C₆H₅P),

130.1 (s, C⁵), 130.2 (s, p-C₆H₅P), 132.7 (d, J_PC= 21.9 Hz, o-

2

C₆H₅P), 136.0 (d, ¹J_PC= 13.5 Hz, i-C₆H₃P), 137.2 (s, C²), 138.8 (s,

m-C₆H₃), 149.5 (d, ³J_PC= 10.3 Hz, CH N), 152.2 (s, i-C₆H₃); d_P

=

{ H} (121.5 MHz, CDCl₃) + 47.9 (s); MS (FAB⁺) m/z 383 (MH⁺);

1

IR (KBr, CH₂Cl₂) 1585 (m_CN), 897 (m_PN(pyrl)) cm⁻¹.

3

((CH₃)₂CH)₂N)), 3.55 (sept, J_HH= 6.6 Hz, 4H, (CH₃)₂CH)₂N),

6.36 (s, 1H, H⁴), 7.14 (d, ³J_HH= 3.9 Hz, 1H, H³), 7.20 (d, ³J_HH

=

(2,4,6 - Trimethylphenyl)(1 - diphenylphosphanyl - 1H - pyrrol - 2-

methylene)amine 3c. Using an analogous procedure to that used

to prepare 3a, reaction of 2c (1.11 g, 5.2 × 10⁻³mol) in DME

(20 cm³) with BuⁿLi (3.30 cm³, 1.6 mol dm⁻³, solution in hexanes)

followed by the addition of Ph₂PCl (0.96 cm³, 5.2 × 10⁻³mol)

afforded, after stirring for 14 h and appropriate puriﬁcation, 3c

(1.45 g, 70%) as a red–brown oil (Anal. Calc. for C₂₆H₂₅N₂P: C,

78.75; H, 6.37; N, 7.07. Found: C, 78.81; H, 6.77; N, 7.27%); d_H

(300.1 MHz, CDCl₃) 2.21 (s, 6H, o-(CH₃)₂C₆H₂), 2.31 (s, 3H, p-

3

7.5 Hz, 3H, m/p-C₆H₅), 7.25 (s, 1H, H⁵), 7.37 (t, J_HH= 7.5 Hz,

4

1

=

2H, o-C₆H₅), 8.99 (d, J_PH= 5.7 Hz, 1H, CH N); d_C{ H}

3

(75.5 MHz, CDCl₃) 23.8 (d, J_PC= 12.6 Hz, ((CH₃)₂CH)₂N)),

24.0 (d, ³J_PC= 12.6 Hz, ((CH₃)₂CH)₂N)), 47.0 (d, ²J_PC= 13.6 Hz,

((CH₃)₂CH)₂N)), 111.2 (s, C⁴), 113.6 (s, C³), 121.4 (s, m-C₆H₅),

125.1 (s, p-C₆H₅), 127.9 (s, C⁵), 129.2 (s, o-C₆H₅), 134.7 (s, C²),

3

1

=

152.0 (d, J_PC= 24.9 Hz, CH N), 153.0 (s, i-C₆H₅); d_P{ H}

(121.5 MHz, CDCl₃) +84.4 (s); MS (FAB⁺) m/z 400 (M⁺); IR

(KBr, CH₂Cl₂) 1589 (m_CN), 897 (m_PN(pyrl)) cm⁻¹.

CH₃C₆H₂), 6.65 (t, J_HH= 3.3 Hz, 1H, H⁴), 6.85 (m, 1H, H³),

3

6.89 (s, 2H, m-C₆H₂), 7.22 (m, 1H, H⁵), 7.59 (m, 4H, PC₆H₅), 7.71

(3,5-Dimethylphenyl)(bis(diisopropylamino)phosphanyl)(1H-

pyrrol-2-ylmethylene)amine 4b. Using an analogous procedure

to that for the preparation of 4a, derivative 2b (1.13 g, 5.7 ×

10⁻³mol) as a solution in DME (20 cm³) was reacted with BuⁿLi

(3.6 cm³, 5.8 × 10⁻³mol; 1.6 mol dm⁻³, solution in hexanes) and a

solution of (Prⁱ₂N)₂PCl (1.51 g, 5.7 × 10⁻³mol) in DME (20 cm³).

Following puriﬁcation, 4b (2.19 g, 90%) was isolated as a brown

crystalline solid (Anal. Calc. for C₂₅H₄₁N₄P: C, 70.04; H, 9.66;

N, 13.07. Found: C, 69.94; H, 9.60; N, 12.91%); d_H(300.1 MHz,

4

1

=

(m, 6H, PC₆H₅), 8.35 (d, J_PH= 3.0 Hz, 1H, CH N); d_C{ H}

(75.5 MHz, CDCl₃) 19.2 (s, o-(CH₃)₂C₆H₂), 21.3 (s, p-CH₃C₆H₂),

3

116.4 (s, C⁴), 117.9 (s, C³), 129.0 (s, p-C₆H₅P), 129.5 (d, J_PC

=

6.8 Hz, m-C₆H₅P), 130.1 (s, C⁵), 130.4 (s, o-C₆H₂), 130.6 (s, m-

C₆H₂), 132.7 (d, ¹J_PC= 12.1 Hz, i-C₆H₅P), 133.0 (s, p-C₆H₂), 133.2

(d, ²J_PC= 22.1 Hz, o-C₆H₅P), 136.5 (s, C²), 149.4 (s, i-C₆H₂), 156.6

3

1

=

(d, J_PC= 7.9 Hz, CH N); d_P{ H} (162.0 MHz, CDCl₃) +48.4

(s); MS (FAB⁺) m/z 397 (MH⁺); IR (KBr, CH₂Cl₂) 1582 (m_CN), 896

(m_PN(pyrl)) cm⁻¹.

3

CDCl₃) 1.10 (d, J_HH= 6.6 Hz, 12H, ((CH₃)₂CH)₂N), 1.27 (d,

(2,6-Diisopropylphenyl)(1-diphenylphosphanyl-1H-pyrrol-2-yl-

methylene)amine 3d. Using an analogous procedure to that used

to prepare 3a, reaction of 2d (1.01 g, 4.0 × 10⁻³mol) in DME

(20 cm³) with BuⁿLi (2.50 cm³, 4.0 × 10⁻³mol; 1.6 mol dm⁻³,

solution in hexanes) followed by Ph₂PCl (0.73 cm³, 4.0 × 10⁻³mol)

afforded, after stirring for 14 h and extraction, 3d (1.51 g, 86%) as

a beige waxy solid, that was not amenable to further puriﬁcation

and hence data are recorded for the crude material (Anal. Calc.

³J_HH= 6.6 Hz, 12H, ((CH₃)₂CH)₂N), 2.34 (s, 6H, m-CH₃C₆H₃),

3.54 (sept, ³J_HH= 6.6 Hz, 4H, ((CH₃)₂CH)₂N)₂), 6.34 (s, 1H, H⁴),

6.83 (s, 1H, p-C₆H₃), 6.84 (s, 2H, o-C₆H₃), 7.12 (d, ³J_HH= 2.9 Hz,

4

1H, H³), 7.23 (s, 1H, H⁵), 8.96 (d, J_PH= 5.6 Hz, 1H, CH N);

=

d_C{ H} (75.5 MHz, CDCl₃) 21.8 (s, m-CH₃C₆H₃), 24.1 (d, ³J_PC

=

1

13.6 Hz, ((CH₃)₂CH)₂N), 47.3 (d, ²J_PC= 13.6 Hz, ((CH₃)₂CH)₂N),

111.2 (s, C⁴), 113.5 (s, C³), 119.3 (s, o-C₆H₃), 126.9 (s, C⁵), 127.9 (s,

p-C₆H₃), 134.8 (s, C²), 138.8 (s, m-C₆H₃), 151.7 (d, ³J_PC= 24.4 Hz,

1

=

for C₂₉H₃₁N₂P: C, 79.41; H, 7.14; N, 6.39. Found: C, 77.51;

CH N), 153.4 (s, i-C₆H₃); d_P{ H} (121.5 MHz, CDCl₃) +83.2

3

H, 7.04; N, 6.93%); d_H(300.1 MHz, CDCl₃) 1.05 (d, J_HH

=

(s); MS (FAB⁺) m/z 428 (M⁺); IR (KBr, CH₂Cl₂) 1584 (m_CN), 897

(m_PN(pyrl)) cm⁻¹.

6.9 Hz, 12H, o-((CH₃)₂CH)₂C₆H₃), 2.80 (sept, ³J_HH= 6.9 Hz, 4H,

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(2,4,6 - Trimethylphenyl)(bis(diisopropylamino)phosphanyl)(1H-

pyrrol-2-ylmethylene)amine 4c. Using an analogous procedure

to that for the preparation of 4a, compound 2c (1.56 g, 7.4 ×

10⁻³mol) in DME (20 cm³) was reacted with BuⁿLi (4.6 cm³, 7.4 ×

10⁻³mol; 1.6 mol dm⁻³, solution in hexanes) and (Prⁱ₂N)₂PCl

(1.97 g, 7.4 × 10⁻³mol) in DME (20 cm³). Following puriﬁcation

4c (2.84 g, 87%) was obtained as a light brown crystalline solid

(Anal. Calc. for C₂₆H₄₃N₄P: C, 70.54; H, 9.81; N, 12.66. Found:

C, 70.31; H, 10.00; N, 12.72%); d_H(300.1 MHz, CDCl₃): d 1.04

(d, ³J_HH= 6.6 Hz, 12H, ((CH₃)₂CH)₂N), 1.23 (d, ³J_HH= 6.6 Hz,

12H, ((CH₃)₂CH)₂N), 2.13 (s, 6H, o-CH₃C₆H₂), 2.28 (s, 3H, p-

129.1 (s, p-C₆H₅P), 129.4 (d, ³J_PC= 11.5 Hz, m-C₆H₅P), 129.6 (s,

C⁵), 132.2 (s, o-C₆H₅), 133.0 (d, ²J_PC= 10.4 Hz, o-C₆H₅P), 133.1

(d, ¹J_PC= 10.8 Hz, i-C₆H₅P), 142.7 (s, C²), 152.5 (s, i-C₆H₅), 156.3

1

(d, ³J_PC= 6.1 Hz, CH N), 186.9 (d, J_CRh= 65.2 Hz, RhCO); d_P

=

1

{ H} (121.5 MHz, CDCl₃) +92.9 (d, J_RhP= 185 Hz); IR (KBr,

CDCl₃) 1586/1568 (m_CN), 2017 (m_CO) cm⁻¹.

(3,5-Dimethylphenyl)(1-diphenylphosphanyl-1H -pyrrol-2-yl-

methylene)amine rhodium carbonyl chloride 5b. Using the proce-

dure as described for 5a with 3b (0.045 g, 1.2 × 10⁻⁴mol) and

[Rh(CO)₂Cl]₂(0.023 g, 5.9 × 10⁻⁵mol): d_H(300.1 MHz, CDCl₃)

2.20 (s, 6H, m-CH₃C₆H₃), 6.42 (s, 1H, H⁴), 6.62 (s, 1H, H³), 6.68

(s, 2H, o-C₆H₃), 6.75 (s, 1H, p-C₆H₃), 7.00 (s, 1H, H⁵), 7.42 (m, 4H,

3

CH₃C₆H₂), 3.55 (sept, J_HH= 6.6 Hz, 4H, ((CH₃)₂CH)₂N), 6.36

(s, 1H, H⁴), 6.86 (s, 2H, m-C₆H₂), 7.15 (d, ³J_HH= 3.5 Hz, 1H, H³),

4

1

7.23 (s, 1H, H⁵), 8.67 (d, J_PH= 5.6 Hz, 1H, CH N); d_C{ H}

(75.5 MHz, CDCl₃) 18.8 (s, o-CH₃C₆H₂), 21.2 (s, p-CH₃C₆H₂),

24.1 (d, ³J_PC= 13.3 Hz, ((CH₃)₂CH)₂N), 47.2 (d, ²J_PC= 13.3 Hz,

((CH₃)₂CH)₂N), 110.9 (s, C⁴), 112.7 (s, C³), 127.4 (s, C⁵), 127.8 (s,

PC₆H₅), 7.50 (m, 6H, PC₆H₅), 7.87 (d, ⁴J_PH= 2.4 Hz, 1H, CH N);

=

1

d_C{ H} (100.6 MHz, CDCl₃) 21.6 (s, m-CH₃C₆H₃), 114.8 (s, C⁴),

120.0 (s, C³), 121.4 (s, o-C₆H₃), 129.0 (s, p-C₆H₃), 129.4 (d, ³J_PC

=

11.1 Hz, m-C₆H₅P), 129.6 (s, p-C₆H₅P), 131.1 (s, C⁵), 132.8 (d,

²J_PC= 14.7 Hz, o-C₆H₅P), 133.1 (s, i-C₆H₅P), 138.3 (s, m-C₆H₃),

o-C₆H₂), 128.8 (s, m-C₆H₂), 132.3 (s, p-C₆H₂), 134.4 (s, C²), 150.1

(s, i-C₆H₂), 154.5 (d, ³J_PC= 25.6 Hz, CH N); d_P{ H} (121.5 MHz,

142.6 (s, C²), 152.1 (s, i-C₆H₃), 156.1 (d, ³J_PC= 6.1 Hz, CH N),

1

=

CDCl₃) +82.8 (s); MS (FAB⁺) m/z 443 (MH⁺); IR (KBr, CH₂Cl₂)

1588 (m_CN), 896 (m_PN(pyrl)) cm⁻¹.

187.5 (d, ¹J_CRh= 67.4 Hz, RhCO); d_P{ H} (121.5 MHz, CDCl₃)

1

+92.7 (d, ¹J_RhP= 186 Hz); IR (KBr, CDCl₃) 1586/1567 (m_CN), 2013

(m_CO) cm⁻¹.

(2,6 - Diisopropylphenyl)(bis(diisopropylamino)phosphanyl)(1H-

pyrrol-2-ylmethylene)amine 4d. Following a procedure analo-

gous to that used to prepare 4a, compound 2d (1.33 g, 5.2 ×

10⁻³mol) in DME (20 cm³) was treated with BuⁿLi (3.3 cm³,

5.3 × 10⁻³mol; 1.6 mol dm⁻³, solution in hexanes) followed by

(Prⁱ₂N)₂PCl (1.40 g, 5.2 × 10⁻³mol) in DME (20 cm³). Following

work-up and puriﬁcation 4d (2.23 g, 88%) was isolated as a light

brown solid after drying in vacuo (Anal. Calc. for C₂₉H₄₉N₄P:

C, 71.84; H, 10.21; N, 11.56. Found: C, 71.97; H, 10.10; N,

11.49%); d_H(400.1 MHz, CDCl₃): d 1.18 (d, ³J_HH= 6.8 Hz, 12H,

((CH₃)₂CH)₂N), 1.31 (d, ³J_HH= 6.8 Hz, 12H, ((CH₃)₂CH)₂C₆H₃),

(2,4,6-Trimethylphenyl)(1-diphenylphosphanyl-1H -pyrrol-2-

methylene)amine rhodium carbonyl chloride 5c. Using the proce-

dure as described for 5a with 3c (0.043 g, 1.1 × 10⁻⁴mol) and

[Rh(CO)₂Cl]₂(0.021 g, 5.4 × 10⁻⁵mol): d_H(300.1 MHz, CDCl₃)

1.95 (s, 6H, o-CH₃C₆H₂), 2.15 (s, 3H, p-CH₃C₆H₂), 6.34 (t, ³J_HH

=

3.5 Hz, 1H, H⁴), 6.63 (s, 1H, H³), 6.72 (s, 2H, m-C₆H₂), 6.92

(m, 1H, H⁵), 7.41 (m, 4H, PC₆H₅), 7.47 (m, 6H, PC₆H₅), 7.68 (d,

4

1

=

J_PH= 2.7 Hz, 1H, CH N); d_C{ H} (100.6 MHz, CDCl₃) 19.5

(s, o-CH₃C₆H₂), 21.2 (s, p-CH₃C₆H₂), 114.6 (s, C⁴), 120.5 (s, C³),

128.9 (s, p-C₆H₅P), 129.0 (s, m-C₆H₂), 129.3 (d, ³J_PC= 11.9 Hz, m-

C₆H₅P), 130.4 (s, o-C₆H₂), 131.4 (s, C⁵), 132.6 (d, ²J_PC= 14.2 Hz,

3

1.37 (d, J_HH= 6.8 Hz, 12H, ((CH₃)₂CH)₂N), 3.24 (sept, J_HH

=

3

6.7 Hz, 2H, o-((CH₃)₂CH)₂C₆H₃), 3.72 (sept, J_HH= 6.8 Hz,

1

o-C₆H₅P), 133.1 (s, p-C₆H₂), 133.3 (d, J_PC= 13.7 Hz, i-C₆H₅P),

4H, ((CH₃)₂CH)₂N), 6.50 (s, 1H, H⁴), 7.23 (m, 1H, H³), 7.28 (s,

148.3 (s, C²), 152.9 (s, i-C₆H₂), 157.9 (d, ³J_PC= 6.8 Hz, CH N),

=

3

2H, m-C₆H₃), 7.29 (s, 1H, p-C₆H₃), 7.38 (d, J_HH= 3.5 Hz, 1H,

188.2 (d, ¹J_RhC= 70.0 Hz, RhCO); d_P{ H} (121.5 MHz, CDCl₃)

1

4

1

H⁵), 8.79 (d, J_PH= 5.7 Hz, 1H, CH N); d_C{ H} (100.6 MHz,

=

1

+90.9 (d, J_RhP= 185 Hz); IR (KBr, CDCl₃) 1572 (m_CN), 2018

CDCl₃): d 23.1 (d, ³J_PC= 13.2 Hz, ((CH₃)₂CH)₂N), 23.3 (d, ³J_PC

=

(m_CO) cm⁻¹.

13.2 Hz, ((CH₃)₂CH)₂N), 27.3 (s, o-((CH₃)₂CH)₂C₆H₃), 46.1 (s, o-

((CH₃)₂CH)₂C₆H₃), 46.4 (d, ²J_PC= 13.2 Hz, ((CH₃)₂CH)₂N), 110.3

(s, C⁴), 112.3 (s, C³), 122.4 (s, m-C₆H₃), 122.9 (s, p-C₆H₃), 126.7

(s, C⁵), 133.8 (s, C²), 138.0 (s, o-C₆H₃), 149.6 (s, i-C₆H₃), 152.9 (d,

(2,6-Diisopropylphenyl)(1-diphenylphosphanyl-1H-pyrrol-2-yl-

methylene)amine rhodium carbonyl chloride 5d. Using the pro-

cedure as described for 5a with 3d (0.054 g, 1.2 × 10⁻⁴mol)

and [Rh(CO)₂Cl]₂(0.024 g, 6.2 × 10⁻⁵mol): d_H(300.1 MHz,

3

1

=

J_PC= 25.9 Hz, CH N); d_P{ H} (121.5 MHz, CDCl₃): d +82.7

(s); MS (FAB⁺): m/z = 485 (MH⁺); IR (KBr, CH₂Cl₂) 1585 (m_CN),

897 (m_PN(pyrl)) cm⁻¹.

3

CDCl₃) 0.69 (d, J_HH= 6.7 Hz, 6H, o-((CH₃)₂CH)₂C₆H₃), 1.20

3

(d, J_HH= 6.7 Hz, 6H, o-((CH₃)₂CH)₂C₆H₃), 2.95 (sept, J_HH

=

3

(1-Diphenylphosphanyl-1H -pyrrol-2-ylmethylene)phenylamine

rhodium carbonyl chloride 5a. In a glove box, a Young’s tap NMR

tube was charged with 3a (0.044 g, 1.2 × 10⁻⁴mol), [Rh(CO)₂Cl]₂

(0.025 g, 6.4 × 10⁻⁵mol) and sealed before transferring to a

Schlenk line. CDCl₃(0.6 cm³) was added and the tube freeze/thaw

degassed, back-ﬁlled with nitrogen and sealed. After 0.5 h, when

gas evolution had ceased, the solution was freeze/thaw degassed,

back-ﬁlled with CO and sealed; d_H(300.1 MHz, CDCl₃): d 6.40 (t,

³J_HH= 3.0 Hz, 1H, H⁴), 6.62 (s, 1H, H³), 7.01 (s, 1H, H⁵), 7.10 (t,

6.7 Hz, 2H, o-((CH₃)₂CH)₂C₆H₃), 6.43 (t, J_HH= 3.3 Hz, H⁴),

6.63 (s, 1H, H³), 6.92 (m, 1H, H⁵), 7.01 (s, 2H, m-C₆H₃), 7.06 (s,

1H, p-C₆H₃), 7.41 (m, 4H, PC₆H₅), 7.45 (m, 6H, PC₆H₅), 7.74 (d,

4

1

=

J_PH= 2.4 Hz, 1H, CH N); d_C{ H} (100.6 MHz, CDCl₃) 23.4

(s, o-((CH₃)₂CH)₂C₆H₃), 24.6 (s, o-((CH₃)₂CH)₂C₆H₃), 28.9 (s, o-

((CH₃)₂CH)₂C₆H₃), 114.4 (s, C⁴), 123.2 (s, m-C₆H₃), 123.8 (s, C³),

3

127.0 (s, p-C₆H₃), 129.0 (s, p-C₆H₅P), 129.3 (d, J_PC= 11.5 Hz,

m-C₆H₅P), 131.6 (s, C⁵), 132.5 (d, ²J_PC= 14.3 Hz, o-C₆H₅P), 132.7

(d, ¹J_PC= 18.0 Hz, i-C₆H₅P), 133.4 (s, o-C₆H₃), 141.3 (s, C²), 147.9

³J_HH= 6.9 Hz, 1H, o-C₆H₅), 7.14 (s, 1H, p-C₆H₅), 7.22 (m, ³J_HH

=

3

1

=

(s, i-C₆H₃), 157.4 (d, J_PC= 7.0 Hz, CH N), 188.2 (dd, J_CRh=

2 1

8.1 Hz, 1H, m-C₆H₅), 7.45 (m, 4H, PC₆H₅), 7.51 (m, 6H, PC₆H₅),

61.7 Hz, J_CP= 18.6 Hz, RhCO); d_P{ H} (121.5 MHz, CDCl₃)

1

7.89 (d, ⁴J_PH= 2.4 Hz, 1H, CH N); d_C{ H} (100.6 MHz, CDCl₃):

+90.7 (d, J_RhP= 183 Hz); IR (KBr, CDCl₃) 1587/1570 (m_CN),

=

d 114.5 (s, C⁴), 122.2 (s, C³), 123.7 (s, m-PhC), 127.2 (s, p-C₆H₅),

5372 | Dalton Trans., 2006, 5362–5378

2014 (m_CO) cm⁻¹.

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(Bis(diisopropyl)aminophosphanyl)(1H -pyrrol-2-ylmethylene)-

phenylamine rhodium carbonyl chloride 6a. Using the procedure

as described for 5a with 4a (0.041 g, 1.0 × 10⁻⁴mol) and

[Rh(CO)₂Cl]₂(0.020 g, 5.1 × 10⁻⁵mol): d_H(300.1 MHz, CDCl₃)

1.35 (d, ³J_HH= 6.7 Hz, 6H, o-((CH₃)₂CH)₂C₆H₃), 1.43 (d, ³J_HH

=

3

6.6 Hz, 12H, ((CH₃)₂CH)₂N), 3.13 (sept, J_HH= 6.7 Hz, 2H, o-

((CH₃)₂CH)₂C₆H₃), 4.44 (dsept, ³J_HH= 6.7 Hz, ³J_PH= 6.7 Hz, 4H,

((CH₃)₂CH)₂N), 6.49 (t, ³J_HH= 3.0 Hz, 1H, H⁴), 6.87 (m, 1H, H³),

3

1.19 (d, J_HH= 6.3 Hz, 12H, ((CH₃)₂CH)₂N), 1.35 (d, J_HH

=

7.12 (d, J_HH= 1.5 Hz, 1H, p-C₆H₃), 7.15 (s, 2H, m-C₆H₃), 7.58

6.3 Hz, 12H, ((CH₃)₂CH)₂N), 4.40 (dsept, ³J_HH= 6.3 Hz, ³J_PH

(s, 1H, H⁵), 7.81 (d, J_PH= 2.7 Hz, 1H, CH N); d_C{ H} NMR

(100.6 MHz, CDCl₃) 23.3 (d, ³J_CP= 2.4 Hz, ((CH₃)₂CH)₂N), 24.1

(d, ³J_CP= 2.4 Hz, ((CH₃)₂CH)₂N), 24.7 (s, o-((CH₃)₂CH)₂C₆H₃),

25.0 (s, o-((CH₃)₂CH)₂C₆H₃), 47.8 (s, o-((CH₃)₂CH)₂C₆H₃), 47.9

(s, o-(CH₃)₂CH)₂C₆H₃), 49.8 (d, ²J_PC= 11.1 Hz, ((CH₃)₂CH)₂N),

4

1

=

11.7 Hz, 4H, ((CH₃)₂CH)₂N), 6.37 (t, ³J_HH= 3.3 Hz, 1H, H⁴), 6.87

(s, 1H, H³), 7.17 (m, 3H, m/p-C₆H₅), 7.29 (t, ³J_HH= 7.8 Hz, 2H, o-

4

C₆H₅), 7.49 (s, 1H, H⁵), 7.94 (d, J_PH= 2.7 Hz, 1H, CH N);

=

1

3

d_C{ H} NMR (100.6 MHz, CDCl₃) 24.1 (d, J_CP= 2.7 Hz,

2

((CH₃)₂CH)₂N), 50.2 (d, J_PC= 12.1 Hz, ((CH₃)₂CH)₂N), 112.5

112.5 (s, C⁴), 123.1 (s, m-C₆H₃), 126.9 (s, p-C₆H₃), 129.2 (s, C³),

(s, C⁴), 124.0 (s, o-C₆H₅), 126.5 (s, p-C₆H₅), 128.3 (s, m-C₆H₅),

129.2 (s, C³), 130.3 (s, C⁵), 130.4 (s, C²), 153.0 (s, i-C₆H₅), 155.8

131.0 (s, C⁵), 141.2 (s, o-C₆H₃), 148.9 (s, C²), 157.4 (d, J_PC

=

3

6.7 Hz, CH N), 153.5 (s, i-C₆H₃), 189.1 (dd, J_RhC= 73.0, ²J_PC

=

1

=

3

1

2

1

=

(d, J_PC= 6.4 Hz, CH N), 188.9 (dd, J_RhC= 79.6 Hz; J_PC

=

15.9 Hz, RhCO); d_P{ H} NMR (121.5 MHz, CDCl₃): d +117.5

21.5 Hz, RhCO); d_P{ H} (121.5 MHz, CDCl₃) +117.9 (d, ¹J_RhP

=

(d, J_RhP= 235 Hz); IR (KBr, CDCl₃) = 1587/1570 (m_CN), 2005

1

233 Hz); IR (KBr, CDCl₃) 1590 (m_CN), = 2005 (m_CO) cm⁻¹.

(m_CO) cm⁻¹.

Preparation of (1-diphenylphosphanylselenido-1H-pyrrol-2-

ylmethylene)phenylamine 7a. A Young’s Tap NMR tube was

charged with 3a (0.050 g, 0.1 × 10⁻³mol) and grey selenium

(0.056 g, 0.7 × 10⁻³mol) and sealed under an N₂atmosphere.

CDCl₃(0.6 cm³) was added and the tube heated to reﬂux for

1 h, after which time complete conversion of 3a to 7a had been

(3,5-Dimethylphenyl)(bis(diisopropyl)aminophosphanyl)(1H-pyr-

rol-2-ylmethylene)amine rhodium carbonyl chloride 6b. Using the

procedure as described for 5a with 4b (0.049 g, 1.1 × 10⁻⁴mol) and

[Rh(CO)₂Cl]₂(0.022 g, 5.7 × 10⁻⁵mol): d_HNMR (300.13 MHz,

3

CDCl₃) 1.25 (d, J_HH= 7.1 Hz, 12H, ((CH₃)₂CH)₂N), 1.40 (d,

³J_HH= 7.1 Hz, 12H, ((CH₃)₂CH)₂N), 2.31 (s, 6H, m-CH₃C₆H₃),

4.44 (dsept, ³J_HH= 7.1 Hz, ³J_PH= 12.0 Hz, 4H, ((CH₃)₂CH)₂N)),

6.42 (t, ³J_HH= 3.3 Hz, 1H, H⁴), 6.83 (s, 2H, o-C₆H₃), 6.85 (s, 1H,

1

achieved according to ³¹P{ H} NMR spectroscopy. No attempt

was made to isolate and fully characterise the phosphine selenide

7a. See Table 2.

3

p-C₆H₃), 6.92 (s, 1H, H³), 7.53 (d, J_HH= 1.8 Hz, H⁵), 7.98 (d,

4

1

=

J_PH= 2.7 Hz, 1H, CH N); d_C{ H} NMR (100.6 MHz, CDCl₃)

Preparation of selenide compounds 7b–d and 8. These com-

pounds were all prepared using a procedure exactly analogous to

that used for the preparation of 7a; each compound was examined

3

21.7 (s, m-CH₃C₆H₃), 24.1 (d, J_CP= 4.1 Hz, ((CH₃)₂CH)₂N),

3

2

25.1 (d, J_CP= 4.1 Hz, ((CH₃)₂CH)₂N), 50.2 (d, J_PC= 12.1 Hz

((CH₃)₂CH)₂N), 112.5 (s, C⁴), 121.7 (s, o-C₆H₃), 128.6 (s, p-C₆H₃),

129.2 (s, C³), 130.4 (s, C⁵), 130.8 (s, m-C₆H₃), 138.1 (s, C²), 153.4

1

by ³¹P{ H} NMR spectroscopy once the reaction had reached

completion. See Table 2.

3

1

=

(s, i-C₆H₃), 155.8 (d, J_PC= 6.4 Hz, CH N), 189.1 (d, J_RhC

=

1

1-Diphenylphosphanylselenido-1H-pyrrole

10. 1-Diphenyl-

69.0, RhCO); d_P{ H} NMR (121.5 MHz, CDCl₃) d +117.7 (d,

phosphanyl-1H-pyrrole (0.050 g, 0.2 × 10⁻³mol) was treated with

grey selenium (0.048 g, 0.2 × 10⁻³mol) in a Young’s Tap NMR

tube and sealed under an N₂atmosphere. CDCl₃(0.6 cm³) was

¹J_RhP= 233 Hz); IR (KBr, CDCl₃) 1586 (m_CN), 2000 (m_CO) cm⁻¹.

(2,4,6 - Trimethylphenyl)(bis(diisopropyl)aminophosphanyl)(1H-

pyrrol-2-ylmethylene)amine rhodium carbonyl chloride 6c. Using

the procedure as described for 5a with 4c (0.055 g, 1.2 ×

10⁻⁴mol) and [Rh(CO)₂Cl]₂(0.024 g, 6.2 × 10⁻⁵mol): d_H

1

added and the tube heated to reﬂux for 1 h. d_P{ H} (162.0 MHz,

CDCl₃) +58.4 (¹J_SeP= 812 Hz).

1-Bis(di_◦isopropylamino)phosphanyl-1H-pyrrole

11. To

a

3

NMR (300.13 MHz, CDCl₃) 1.27 (d, J_HH= 6.6 Hz, 12H,

cooled (0 C) suspension of KH (0.30 g, 7.5 × 10⁻³mol) in THF

(40 cm³) was added a solution of pyrrole (0.5 cm³, 7.5 × 10⁻³mol)

drop-wise in THF (30 cm³). The reaction mixture was then

allowed to warm to RT during which time it changed colour from

a cloudy white, to yellow, to pale green. After 3 h, the reaction

3

((CH₃)₂CH)₂N), 1.41 (d, J_HH= 6.6 Hz, 12H, ((CH₃)₂CH)₂N),

2.16 (s, 6H, o-CH₃C₆H₂), 2.36 (s, 3H, p-CH₃C₆H₂), 4.45 (dsept,

³J_HH= 6.3 Hz, ³J_PH= 12.1 Hz, 4H, ((CH₃)₂CH)₂N), 6.47 (s, 1H,

H⁴), 6.84 (s, 2H, m-C₆H₂), 6.90 (s, 1H, H³), 7.57 (s, 1H, H⁵), 7.73 (d,

4

1

=

J_PH= 2.6 Hz, 1H, CH N); d_C{ H} NMR (100.6 MHz, CDCl₃)

◦

vessel was cooled to 0 C and a solution of (Prⁱ₂N)₂PCl (2.00 g,

19.6 (s, o-CH₃C₆H₂), 21.3 (s, p-CH₃C₆H₂), 24.2 (d, ³J_CP= 3.2 Hz,

((CH₃)₂CH)₂N), 25.1 (d, ³J_CP= 3.2 Hz, ((CH₃)₂CH)₂N), 49.8 (d,

²J_PC= 11.1 Hz, ((CH₃)₂CH)₂N), 112.4 (s, C⁴), 128.6 (s, m-C₆H₂),

129.2 (s, C³), 130.6 (s, o-C₆H₂), 130.8 (s, C⁵), 135.2 (s, p-C₆H₂),

7.5 × 10⁻³mol) in THF (50 cm³) added. The mixture was then

stirred at RT for a period of 12 h. The volatile components were

then removed in vacuo and the mixture extracted with hexane

(3 × 10 cm³). Removal of solvent under reduced pressure afforded

11 as an analytically pure pale yellow solid (1.41 g, 63%), (Anal.

Calc. for C₁₆H₃₂N₃P: C, 64.60, H, 10.86; N, 14.13. Found: C,

64.78; H, 10.81; N, 14.20%); d_H(499.8 MHz, CDCl₃) 1.17 (d,

141.8 (s, C²), 152.3 (s, i-C₆H₂), 158.0 (d, ³J_PC= 7.1 Hz, CH N),

=

1

189.0 (d, J_RhC= 69.1 Hz, RhCO); d_P{ H} NMR (121.5 MHz,

CDCl₃) +117.8 (d, ¹J_RhP= 236 Hz); IR (KBr, CDCl₃) 1572 (m_CN),

2002 (m_CO) cm⁻¹.

3

³J_HH= 6.8 Hz, 12H, CH₃), 1.28 (d, J_HH= 6.8 Hz, 12H, CH₃),

3

(2,6 - Diisopropylphenyl)(bis(diisopropyl)aminophosphanyl)(1H-

pyrrol-2-ylmethylene)amine rhodium carbonyl chloride 6d. Using

the procedure as described for 5a with 4d (0.054 g, 1.1 ×

10⁻⁴mol) and [Rh(CO)₂Cl]₂(0.022 g, 5.7 × 10⁻⁵mol): d_H

3.53 (d sept, J_HH= 6.8, J_PH= 12.5 Hz, 4H, CH₂(CH₃)₂), 6.25

1

(m, 2H, H³+ H⁴), 6.94 (m, 2H, H²+ H⁵); d_C{ H} (125.7 MHz,

CDCl₃) 24.0 (d, ³J_PC= 7.5 Hz, (CH₃)₂CH), 24.4 (d, ³J_PC= 7.5 Hz,

(CH₃)₂CH), 47.0 (d, ²J_PC= 13.8 Hz, (CH₃)₂CH), 109.2 (d, ³J_PC

=

1

3

NMR (300.13 MHz, CDCl₃) 1.06 (d, J_HH= 6.7 Hz, 6H, o-

2.3 Hz, C³+ C⁴), 112.7 (d, J_PC= 11.9 Hz, C²+ C⁵), d_P{ H}

(161.9 MHz, CDCl₃) +89.7 (s); MS (ESI⁺): m/z 298 (MH)⁺.

((CH₃)₂CH)₂C₆H₃), 1.29 (d, ³J_HH= 6.7 Hz, 12H, ((CH₃)₂CH)₂N),

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1-Bis(diisopropylamino)phosphanylselenido-1H-pyrrole 12.

A

4.40; N, 4.88. Found: C, 54.22; H, 4.34; N, 4.69%); d_H(500.1 MHz,

CDCl₃) 2.11 (s, 6H, o-CH₃C₆H₂), 2.20 (s, 3H, p-CH₃C₆H₂), 6.57

(t, 1H, ³J_HH= 3.0 Hz, H⁴), 6.75 (s, 1H, H³), 6.78 (s, 2H, m-C₆H₂),

7.19 (m, 1H, H⁵), 7.49 (m, 4H, PC₆H₅), 7.61 (m, 6H, PC₆H₅),

sample of 11 (0.050 g, 0.17 × 10⁻³mol) was treated with grey

selenium (0.048 g, 0.2 × 10⁻³mol) in a Young’s Tap NMR tube

and sealed under an N₂atmosphere. CDCl₃(0.6 cm³) was added

and the tube heated to reﬂux for 1 h, during which time complete

7.79 (d, ⁴J_PH= 3.0 Hz, 1H, CH N); d_C(125.5 MHz, CDCl₃) 19.2

=

conversion of 11 to 12 had been achieved according to ³¹P{ H}

(s, o-CH₃C₆H₂), 21.2 (s, p-CH₃C₆H₂), 116.6 (s, C⁴), 127.9 (s, C³),

1

3

NMR spectroscopy. d_P{ H} (162.0 MHz, CDCl₃) +60.4 (¹J_SeP

=

128.4 (s, m-C₆H₂), 128.8 (s, p-C₆H₅P), 129.5 (d, J_PC= 12.4 Hz,

842 Hz).

m-C₆H₅P), 130.6 (s, o-C₆H₂), 130.9 (s, C⁵), 131.7 (s, p-C₆H₂), 133.0

(d, ²J_PC= 12.9 Hz, o-C₆H₅P), 133.4 (d, ¹J_PC= 12.9 Hz, i-C₆H₅P),

(1-Diphenylphosphanyl-1H -pyrrol-2-ylmethylene)phenylamine

palladium dichloride 13a. To stirred suspension of

136.3 (s, C²), 149.4 (s, i-C₆H₂), 156.7 (d, ³J_PC= 7.7 Hz, CH N); d_P

=

a

1

{ H} (121.5 MHz, CDCl₃) +64.4 (s); MS (FAB⁺) m/z 539 (M −

[PdCl₂(COD)] (0.30 g, 1.0 × 10⁻³mol) in CH₂Cl₂(10 cm³), a

solution of 3a (0.410 g, 1.2 × 10⁻³mol) in CH₂Cl₂(10 cm³)

was added via cannula and the mixture allowed to stir for

16 h. The volatile components were then removed in vacuo and

the yellow–orange oil extracted with hexane (20 cm³) before

volatile components were removed under vacuum to afford 13a

(0.40 g, 71%) as a dark yellow crystalline solid (Anal. Calc. for

C₂₃H₁₉N₂PPdCl₂: C, 51.95; H, 3.61; N, 5.27. Found: C, 52.11; H,

3.50; N, 5.04%). d_H(300.1 MHz, CDCl₃) 6.31 (s, 1H, H⁴), 6.48

(m, 1H, H³), 7.12 (m, 3H, m/p-C₆H₅), 7.21 (s, 1H, H⁵), 7.44 (m,

2H, o-C₆H₅), 7.54 (m, 4H, C₆H₅P), 7.72 (m, 6H, C₆H₅P), 8.23 (d,

Cl)⁺; IR (ATR, neat) 1590 (m_CN).

(2,6-Diisopropylphenyl)(1-diphenylphosphanyl-1H-pyrrol-2-yl-

methylene)amine palladium dichloride 13d. To a stirred solution

of [PdCl₂(COD)] (0.30 g, 1.0 × 10⁻³mol) in CH₂Cl₂(10 cm³),

a solution of 3d (0.500 g, 1.2 × 10⁻³mol) in CH₂Cl₂(10 cm³)

was added via cannula and the mixture was allowed to stir for

19 h. The volatile components were then removed in vacuo and the

yellow–orange oil extracted with hexane (20 cm³). Exposure to

vacuum afforded 13d (0.54 g, 84%) as a dark yellow crystalline

solid; prolonged standing of a CH₂Cl₂solution of 13d gave

rise to yellow cubic crystals suitable for X-ray analysis (Anal.

Calc. for C₂₉H₃₁N₂PPdCl₂: C, 56.55; H, 5.08; N, 4.55. Found:

C, 56.62; H, 4.94; N, 4.47%); d_H(300.1 MHz, CDCl₃) 0.79 (d,

³J_HH= 6.7 Hz, 6H, o-((CH₃)₂CH)₂C₆H₃), 1.27 (d, ³J_HH= 6.7 Hz,

4

1

=

J_PH= 3.2 Hz, 1H, CH N); d_C{ H} (75.5 MHz, CDCl₃) 115.0

(s, C⁴), 122.0 (s, m-C₆H₅), 128.0 (s, p-C₆H₅), 128.3 (s, C³), 128.9 (s,

p-C₆H₅P), 129.4 (d, ³J_PC= 12.1 Hz, m-C₆H₅P), 130.0 (s, o-C₆H₅),

130.7 (s, C⁵), 132.1 (d, ²J_PC= 13.2 Hz, o-C₆H₅P), 133.0 (d, ¹J_PC

=

12.8 Hz, i-C₆H₅P), 137.2 (s, C²), 150.3 (s, i-C₆H₅), 154.5 (d, ³J_PC

3

6H, o-((CH₃)₂CH)₂C₆H₃), 3.04 (sept, J_HH= 6.7 Hz, 2H, o-

1

=

7.2 Hz, CH N); d_P{ H} (121.5 MHz, CDCl₃) +66.5 (s); MS

3

((CH₃)₂CH)₂C₆H₃), 6.53 (t, J_HH= 3.3 Hz, 1H, H⁴), 6.71 (s, 1H,

(FAB⁺) m/z 495 (M − Cl)⁺; IR (ATR, neat) 1596 (m_CN).

H³), 7.04 (m, 3H, m/p-C₆H₃), 7.19 (m, 1H, H⁵), 7.47 (m, 4H,

PC₆H₅), 7.57 (m, 6H, PC₆H₅), 7.78 (d, ⁴J_PH= 3.3 Hz, 1H, CH N);

=

(3,5-Dimethylphenyl)(1-diphenylphosphanyl-1H -pyrrol-2-yl-

methylene)amine palladium dichloride 13b. A Young’s NMR tube

was charged with [PdCl₂(MeCN)₂] (0.12 g, 0.45 × 10⁻⁴mol) and

3a (0.172 g, 0.45 × 10⁻⁴mol). CDCl₃(0.6 cm³) was added and

the tube placed in an ultrasound bath for 10 min. The solution

was then ﬁltered to remove undissolved solids and the volatile

components removed in vacuo to afford 13b (0.194 g, 77%) as a

yellow crystalline solid (Anal. Calc. for C₂₅H₂₃N₂PPdCl₂: C, 53.64;

H, 4.15; N, 5.01. Found: C, 53.45; H, 4.80; N, 5.18%). Further

puriﬁcation by crystallisation was unsuccessful. d_H(250.1 MHz,

CDCl₃) 2.14 (s, 6H, m-CH₃C₆H₃), 6.45 (s, 1H, H⁴), 6.60 (s, 1H, H³),

6.70 (s, 1H, p-C₆H₃), 6.75 (s, 2H, o-C₆H₃), 7.22 (s, 1H, H⁵), 7.41

1

d_C{ H} (75.5 MHz, CDCl₃): d 23.4 (s, o-((CH₃)₂CH)₂C₆H₃), 24.6

(s, o-((CH₃)₂CH)C₆H₃), 28.9 (s, o-((CH₃)₂CH)₂C₆H₃), 116.3 (s, C⁴),

123.6 (s, m-C₆H₃), 127.8 (s, C³), 127.9 (s, p-C₆H₃), 128.6 (s, o-C₆H₃),

129.6 (d, ³J_PC= 12.5 Hz, m-C₆H₅P), 130.4 (s, C⁵), 132.1 (d, ¹J_PC

=

2

12.5 Hz, i-C₆H₅P), 133.1 (d, J_PC= 12.5 Hz, o-C₆H₅P), 134.1 (s,

p-C₆H₅P), 141.3 (s, C²), 148.6 (s, i-C₆H₃), 155.6 (d, ³J_PC= 7.9 Hz,

1

+

=

CH N); d_P{ H} (121.5 MHz, CDCl₃) +65.5 (s); MS (FAB ): m/z

579 (M − Cl)⁺; IR (ATR, neat) 1597 (m_CN).

(Bis(diisopropyl)aminophosphanyl)(1H -pyrrol-2-ylmethylene)-

phenylamine palladium chloride 14a. To a stirred solution of

[PdCl₂(COD)] (0.30 g, 1.1 × 10⁻³mol) in CH₂Cl₂(10 cm³), a

solution of 4a (0.500 g, 1.2 × 10⁻³mol) in CH₂Cl₂(10 cm³)

was added via cannula and the mixture was allowed to stir for

19 h. The volatile components were then removed in vacuo and

the yellow–orange oil extracted with hexane (20 cm³) and volatiles

removed under vacuum to afford 14a (0.41 g, 69%) as a dark yellow

crystalline solid (Anal. Calc. for C₂₃H₃₇N₄PPdCl₂: C, 47.80; H,

6.47; N, 9.70. Found: C, 47.60; H, 6.51; N, 9.50); d_H(300.1 MHz,

(m, 4H, PC₆H₅), 7.51 (m, 6H, PC₆H₅), 7.96 (d, ⁴J_PC= 2.9 Hz, 1H,

1

=

CH N); d_C{ H} (62.9 MHz, CDCl₃) 21.0 (s, m-CH₃C₆H₃), 116.2

(s, C⁴), 121.2 (s, o-C₆H₃), 127.6 (s, m-C₆H₃), 128.6 (s, p-C₆H₅P),

129.0 (d, J_PC= 12.7 Hz, m-C₆H₅P), 130.9 (s, C³), 131.9 (s, C⁵),

3

2

132.1 (s, p-C₆H₃), 132.6 (d, J_PC= 13.2 Hz, o-C₆H₅P), 133.2 (d,

¹J_PC= 12.6 Hz, i-C₆H₅P), 137.5 (s, C²), 152.5 (s, i-C₆H₃), 153.7 (d,

3

1

=

J_PC= 7.0 Hz, CH N); d_P{ H} (101.3 MHz, CDCl₃) +65.8 (s);

MS (FAB⁺): m/z 525 (M − Cl⁺); IR (ATR, neat) 1597 (m_CN).

3

CDCl₃) 1.19 (d, J_HH= 6.9 Hz, 12H, ((CH₃)₂CH)₂N)), 1.48 (d,

(2,4,6 - Trimethylphenyl)(1 - diphenylphosphanyl - 1H - pyrrol - 2-

methylene)amine palladium dichloride 13c. To a stirred solution

of [PdCl₂(COD)] (0.31 g, 1.1 × 10⁻³mol) in CH₂Cl₂(10 cm³),

a solution of 3c (0.48 g, 1.2 × 10⁻³mol) in CH₂Cl₂(10 cm³)

was added via cannula and the mixture allowed to stir for 19 h.

The volatile components were then removed in vacuo and the

yellow–orange oil extracted with hexane (20 cm³). Elimination of

solvent under vacuum afforded 13c (0.59 g, 94%) as a dark yellow

crystalline solid (Anal. Calc. for C₂₆H₂₅N₂PPdCl₂: C, 54.42; H,

³J_HH= 6.9 Hz, 12H, ((CH₃)₂CH)₂N)), 4.38 (dsept, ³J_HH= 6.9 Hz,

³J_PH= 3.0 Hz, 4H, ((CH₃)₂CH)₂N)), 6.50 (t, ³J_HH= 3.3 Hz, 1H,

H⁴), 7.07 (m, 1H, H³), 7.21 (m, 2H, o-C₆H₅), 7.26 (m, 3H, m/p-

C₆H₅), 7.57 (m, 1H, H⁵), 8.01 (d, ⁴J_PH= 3.0 Hz, 1H, CH N); d_C

=

1

{ H} (75.5 MHz, CDCl₃) 23.8 (d, ³J_CP= 6.0 Hz, ((CH₃)₂CH)₂N),

3

2

25.1 (d, J_CP= 6.0 Hz, ((CH₃)₂CH)₂N), 51.3 (d, J_PC= 9.8 Hz,

((CH₃)₂CH)₂N), 114.2 (s, C⁴), 123.7 (s, o-C₆H₅), 127.3 (s, p-

C₆H₅), 128.8 (s, m-C₆H₅), 130.4 (s, C³), 130.8 (s, C⁵), 139.4 (s,

3

1

C²), 153.6 (s, i-C₆H₅), 154.9 (d, J_PC= 7.5 Hz, CH N); d_P{ H}

=

5374 | Dalton Trans., 2006, 5362–5378

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©

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(121.5 MHz, CDCl₃) +81.3 (s); MS (FAB⁺) m/z 541 (M − Cl)⁺;

IR (ATR, neat) 1601 (m_CN).

to afford 14d (0.95 g, 85%) as a dark yellow crystalline solid

following removal of volatiles under vacuum (Anal. Calc. for

C₂₉H₄₉N₄PPdCl₂: C, 52.60, H, 7.47; N, 8.46. Found: C, 52.98;

(3,5-Dimethylphenyl)(bis(diisopropyl)aminophosphanyl)(1H-

pyrrol-2-ylmethylene)amine palladium dichloride 14b. To a stirred

solution of [PdCl₂(COD)] (1.22 g, 4.3 × 10⁻³mol) in CH₂Cl₂

(10 cm³), a solution of 4b (1.665 g, 4.7 × 10⁻³mol) in CH₂Cl₂

(10 cm³) was added via cannula and the mixture was allowed to

stir for 19 h. The volatile components were then removed in vacuo

and the yellow–orange oil extracted with hexane (20 cm³) and

solvent removed under vacuum to afford 14b (0.57 g, 88%) as

a dark yellow crystalline solid. Prolonged standing of a CH₂Cl₂

solution of 14b gave rise to yellow cubic crystals suitable for X-

ray analysis (Anal. Calc. for C₂₅H₄₁N₄PPdCl₂: C, 49.55; H, 6.83;

N, 9.25. Found: C, 49.44; H, 6.92; N, 9.05%). d_H(300.1 MHz,

3

H, 7.34; N, 8.02%); d_H(250.1 MHz, CDCl₃) 1.11 (d, J_HH

=

3

6.9 Hz, 6H, o-((CH₃)₂CH)₂C₆H₃), 1.31 (d, J_HH= 6.7 Hz, 12H,

((CH₃)₂CH)₂N), 1.42 (d, ³J_HH= 6.9 Hz, 6H, o-((CH₃)₂CH)₂C₆H₃),

3

1.47 (d, J_HH= 6.7 Hz, 12H, ((CH₃)₂CH)₂N), 3.22 (sept, J_HH

=

3

6.9 Hz, 2H, o-((CH₃)₂CH)₂C₆H₃), 4.47 (dsept, J_HH= 6.9 Hz,

³J_PH= 2.0 Hz, 4H, ((CH₃)₂CH)₂N), 6.59 (t, J_HH= 3.0 Hz, 1H,

3

H⁴), 7.01 (m, 1H, H³), 7.12 (s, 1H, p-C₆H₃), 7.15 (s, 2H, m-

C₆H₃), 7.83 (d, ⁴J_PH= 4.1 Hz, 1H, CH N); d_C{ H} (100.1 MHz,

1

=

3

CDCl₃) 22.0 (d, J_PC= 4.4 Hz, ((CH₃)₂CH)₂N), 23.2 (d, J_PC

=

4.4 Hz, ((CH₃)₂CH)₂N), 26.9 (s, o-((CH₃)₂CH)₂C₆H₃), 45.5 (s, o-

((CH₃)₂CH)₂C₆H₃), 49.1 (d, ²J_PC= 9.6 Hz, ((CH₃)₂CH)₂N), 113.8

(s, C⁴), 122.6 (s, m-C₆H₃), 126.9 (s, p-C₆H₃), 127.7 (s, o-C₆H₃),

130.2 (s, C³), 131.1 (s, C⁵), 140.6 (s, C²), 149.2 (s, i-C₆H₃), 155.4 (d,

3

CDCl₃) 1.24 (d, J_HH= 5.5 Hz, 12H, ((CH₃)₂CH)₂N), 1.54 (d,

³J_HH= 5.5 Hz, 12H, ((CH₃)₂CH)₂N), 2.32 (s, 6H, m-CH₃C₆H₃),

4.44 (d sept, ³J_HH= 5.5 Hz, ³J_PH= 2.7 Hz, 4H, ((CH₃)₂CH)₂N),

6.51 (t, ³J_HH= 3.3 Hz, 1H, H⁴), 6.88 (s, 1H, p-C₆H₃), 7.01 (s, 2H,

3

1

=

J_PC= 8.8 Hz, CH N); d_P{ H} (121.5 MHz, CDCl₃) +80.9 (s);

MS (FAB⁺): m/z 625 (M − Cl)⁺; IR (ATR, neat) 1599 (m_CN).

o-C₆H₃), 7.08 (s, 1H, H³), 7.61 (m, 1H, H⁵), 8.04 (d, ⁴J_PH= 3.0 Hz,

(Phenyl)(1-diphenylphosphanyl-1H-pyrrol-2-ylmethylene)amine

nickel dibromide 15a. To a suspension of [NiBr₂(DME)] (0.14 g,

4.7 × 10⁻⁴mol) in CH₃CN (10 cm³) was added a solution of

3a (0.29 g, 8.2 × 10⁻⁴mol) in CH₃CN (10 cm³) via cannula

and the mixture stirred vigorously for 3 h. The precipitated solid

was then isolated by ﬁltration and residual volatile components

removed in vacuo. The red–brown solid was then washed twice

with hexane (2 × 5 cm³) to afford 15a as a brown/green powder

following drying under vacuum (0.16 g, 59%) (Anal. Calc. for

C₂₃H₁₉N₂PNiBr₂: C, 48.22; H, 3.35; N, 4.89. Found: C, 48.41; H,

3.39; N, 4.81%). MS (MALDI) m/z 493 (M − Br)⁺; IR (ATR,

neat) 1596 (m_CN).

1

=

1H, CH N); d_C{ H} NMR (75.5 MHz, CDCl₃): d 21.6 (s, m-

CH₃C₆H₃), 23.9 (d, ³J_CP= 5.3 Hz, ((CH₃)₂CH)₂N), 25.2 (d, ³J_CP

=

2

5.3 Hz, ((CH₃)₂CH)₂N), 51.4 (d, J_PC= 9.8 Hz, ((CH₃)₂CH)₂N),

114.4 (s, C⁴), 121.7 (s, o-C₆H₃), 129.4 (s, p-C₆H₃), 129.5 (s, m-C₆H₃),

130.1 (s, C³), 130.7 (s, C⁵), 138.2 (s, C²), 153.7 (s, i-C₆H₃), 154.8

(d, ³J_PC= 7.6 Hz, CH N); d_P{ H} NMR (121.5 MHz, CDCl₃):

1

=

d +81.6 (s); MS (FAB⁺) m/z 571 (M − Cl)⁺; IR (ATR, neat) 1600

(m_CN).

(2,4,6-Trimethylphenyl)(bis(diisopropyl)aminophosphanyl)(1H-

pyrrol-2-ylmethylene)amine palladium dichloride 14c. To a stirred

solution of [PdCl₂(COD)] (0.60 g, 2.1 × 10⁻³mol) in CH₂Cl₂

(10 cm³), a solution of 4c (1.022 g, 2.3 × 10⁻³mol) in CH₂Cl₂

(10 cm³) was added via cannula and the mixture was allowed to

stir for 19 h. The volatile components were then removed in vacuo

and the yellow–orange oil extracted with hexane (20 cm³) and

volatiles removed under vacuum to afford 14c (0.43 g, 33%) as a

dark yellow crystalline solid (Anal. Calc. for C₂₆H₄₃N₄PPdCl₂: C,

50.36; H, 7.00; N, 9.04. Found: C, 50.25; H, 7.18; N, 9.22%); d_H

(500.0 MHz, CDCl₃) 1.29 (d, ³J_HH= 7.0 Hz, 12H, ((CH₃)₂CH)₂N),

(3,5-Dimethylphenyl)(1-diphenylphosphanyl-1H-pyrrol-2-ylmeth-

ylene)amine nickel dibromide 15b. To a solution of [NiBr₂(DME)]

(0.30 g, 9.8 × 10⁻⁴mol) in CH₃CN (10 cm³) was added a solution

of 3b (0.38 g, 9.8 × 10⁻⁴mol) in CH₃CN (10 cm³) via cannula

and then stirred vigorously for 3 h. The brown solid was then

isolated by ﬁltration and then washed twice with hexane (2 ×

5 cm³) to afford 15b (0.27 g, 47%) as a brown powder following

drying under vacuum (Anal. Calc. for C₂₅H₂₃N₂PNiBr₂: C, 49.96;

H, 3.87; N, 4.67. Found: C, 50.25; H, 3.78; N, 4.55%); MS (ES⁺):

m/z 521 (M − Br)⁺; IR (ATR, neat) 1596 (m_CN).

3

1.53 (d, J_HH= 7.0 Hz, 12H, ((CH₃)₂CH)₂N), 2.27 (s, 3H, p-

CH₃C₆H₂), 2.28 (s, 6H, o-CH₃C₆H₂), 4.40 (dsept, ³J_HH= 7.0 Hz,

³J_PH= 2.1 Hz, 4H, ((CH₃)₂CH)₂N)), 6.54 (t, ³J_HH= 3.0 Hz, 1H,

H⁴), 6.84 (s, 2H, m-C₆H₂), 7.01 (s, 1H, H³), 7.64 (s, 1H, H⁵), 7.76

To a solution of [NiBr₂(DME)] (0.16 g, 5.3 × 10⁻⁴mol) in

CH₃CN (10 cm³) was added a solution of 3c (0.21 g, 5.3 × 10⁻⁴mol)

in CH₃CN (10 cm³) via cannula and then stirred vigorously for

3 h. Volatile components were then removed in vacuo to afford a

brown solid that was then washed twice with hexane (2 × 5 cm³)

to afford 15c (0.16 g, 50%) as a brown powder following drying

under vacuum (Anal. Calc. for C₂₆H₂₅N₂PNiBr₂: C, 50.77; H, 4.11;

N, 4.56. Found: C, 51.01; H, 4.35; N, 4.39%). MS (MALDI) m/z

535 (M − Br)⁺; IR (ATR, neat) not assignable.

4

1

=

(d, J_PH= 3.8 Hz, 1H, CH N); d_C{ H} (125.5 MHz, CDCl₃)

19.4 (s, o-CH₃C₆H₂), 21.3 (s, p-CH₃C₆H₂), 24.2 (d, ³J_CP= 4.6 Hz,

((CH₃)₂CH)₂N), 25.3 (d, ³J_CP= 4.6 Hz, ((CH₃)₂CH)₂N), 51.2 (d,

²J_PC= 9.1 Hz, ((CH₃)₂CH)₂N), 114.0 (s, C⁴), 128.7 (s, m-C₆H₂),

129.0 (s, p-C₆H₂), 130.3 (s, C³), 130.6 (s, o-C₆H₂), 131.2 (s, C⁵),

132.6 (s, C²), 150.2 (s, i-C₆H₂), 156.4 (d, ³J_PC= 7.3 Hz, CH N); d_P

=

{ H} (162.0 MHz, CDCl₃) +81.4 (s); MS (FAB⁺) m/z 583 (M −

1

Cl)⁺; IR (ATR, neat) 1605 (m_CN).

(2,6-Diisopropylphenyl)(bis(diisopropyl)aminophosphanyl)(1H-

pyrrol-2-ylmethylene)amine palladium dichloride 14d. To a stirred

solution of [PdCl₂(COD)] (0.49 g, 1.7 × 10⁻³mol) in CH₂Cl₂

(10 cm³), a solution of 4d (0.89 g, 1.8 × 10⁻³mol) in CH₂Cl₂

(10 cm³) was added via cannula and the mixture was allowed

to stir for 18 h. The volatile components were then removed in

vacuo and the yellow–orange oil extracted with hexane (20 cm³)

(2,6-Diisopropylphenyl)(1-diphenylphosphanyl-1H-pyrrol-2-yl-

methylene)amine nickel dibromide 15d. To

a solution of

[NiBr₂(DME)] (0.14 g, 4.5 × 10⁻⁴mol) in CH₃CN (10 cm³) was

added a solution of 3d (0.20 g, 4.5 × 10⁻⁴mol) in CH₃CN (10 cm³)

via cannula and then stirred vigorously for 3 h. The mixture was

then ﬁltered and the volatile components removed in vacuo. The

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brown solid was then washed twice with hexane to afford 15d

(0.21 g, 70%) as a green powder following drying under vacuum

(Anal. Calc. for C₂₉H₃₁N₂PNiBr₂: C, 52.13; H, 4.85; N, 4.34.

Found: C, 51.75; H, 5.03; N, 4.58%). MS (MALDI) m/z 577 (M −

Br)⁺; IR (ATR, neat) not assignable.

129.3 (s, m-ArC), 133.2 (s, o-ArC), 136.2 (s, p-ArC), 136.9 (s, C⁵),

2

=

140.7 (s, i-ArC), 144.9 (s, C ), 162.4 (s, CH N); MS (MALDI)

m/z 482 (MH)⁺; IR (ATR, neat) 1592 (m_CN).

Ethylene polymerisation testing protocol

Alternative preparation of (3,5-dimethylphenyl)(1-diphenyl-

phosphanyl-1H-pyrrol-2-ylmethylene)amine nickel dibromide 15b.

To a solution of [NiBr₂(PPh₃)₂] (0.50 g, 0.7 × 10⁻³mol) in MeCN

(10 cm³) was added 3b (0.26 g, 0.7 × 10⁻³mol) in MeCN (10 cm³)

and the mixture allowed to stir at RT for 18 h, the solution rapidly

changing colour from green to brown. Volatile components were

removed in vacuo and the brown solid extracted with hexane (3 ×

20 cm³) and the resulting solid dried under reduced pressure to

afford 15b (0.29 g, 71%) as a dark red/brown powder.

Under the conditions described in procedures 1–3 (below) the

proinitiators NiBr₂(PPh₃)₂and PdCl₂(MeCN)₂proved inactive.

Procedure 1. In a Schlenk, toluene solutions (100 cm³) of com-

plexes 13 or 14 (5.0 × 10⁻⁵mol) were treated with 500 equivalents

of MAO (10 wt% in toluene) at ambient temperature. This led to

an immediate colour change from yellow/orange to brown. The

initiator/activator solutions were aged for a period of 10 min under

nitrogen. Subsequently, three cycles of vacuum/ethylene (1.0 bar)

were applied to the reaction vessel, before it was pressurised with

ethylene (1.0 bar) and then stirred rapidly for 0.5 h. The mixture

was then quenched by the cautious addition of aqueous 1.0 M

HCl and methanol prior to aqueous/organic extraction. GC/MS

Attempted preparation of (bis(diisopropyl)aminophosphanyl)(1H-

pyrrol-2-ylmethylene)phenylamine nickel dibromide

1

This reaction was undertaken using a procedure analogous to that

with 3 (above) using [NiBr₂(DME)] (0.30 g, 9.7 × 10⁻⁴mol) and 4b

(0.43 g, 1.1 × 10⁻³mol). Following work-up, a green paramagnetic

solid was isolated (0.17 g), whose structure could not be elucidated

from the available analytical data, together with Prⁱ₂NH₂Br.

and H NMR spectroscopic analyses of the organic phases were

undertaken.

Procedure 2. An autoclave was charged with toluene solutions

(20 cm³) of complexes 13 or 14 (5.0 × 10⁻⁵mol) under nitrogen.

Subsequently, 4.5 equivalents of EtAlCl₂(0.1 cm³, 1.8 M, in

toluene) was added under nitrogen and the mixture aged for

20 min. The reactor vessel was then pressurised with ethylene

(10 bar) for a period of 3 h at ambient temperature. On releasing

the pressure, the resulting mixtures were cautiously hydrolysed by

addition of 1.0 M HCl and methanol prior to aqueous/organic

Bis{(2,4,6-trimethylphenyl)(pyrrolato)}nickel 16. To a solu-

tion of [NiBr₂(DME)] (0.16 g, 5.3 × 10⁻⁴mol) in CH₂Cl₂(10 cm³)

was added a solution of 3c (0.21 g, 5.3 × 10⁻⁴mol) in CH₃CN

(10 cm³) via cannula and then stirred vigorously for 3 h to give

a clear red solution. Volatile components were then removed

in vacuo to afford a red solid that was then washed twice with

hexane (2 × 5 cm³) to afford 16 (0.11 g, 45%) as a brown powder

following drying under vacuum (Anal. Calc. for C₂₆H₂₅N₂PNiBr₂:

C, 69.87; H, 6.30; N, 11.64. Found: C, 69.90; H, 6.30; N, 11.83%).

d_H(300.0 MHz, CDCl₃) 2.29 (s, 3H, p-ArCH₃), 2.60 (s, 3H, o-

1

extraction. GC/MS and H NMR spectroscopic analyses of the

organic phases were undertaken.

Procedure 3. A Schlenk was charged with toluene solutions

(20 cm³) of complexes 15 or 16 (5.0 × 10⁻⁵mol) under nitrogen.

Subsequently, 4.5 equivalents of EtAlCl₂(0.1 cm³, 1.8 M, in

toluene) was added under nitrogen and the mixture aged for

20 min. The vessel was then pressurised with ethylene (1.0 bar) for a

ArCH₃), 4.75 (s, 1H, H⁴), 5.78 (s, 1H, H³), 6.59 (m, 1H, H⁵), 6.89

1

=

(s, 2H, m-ArH), 7.17 (s, 1H, CH N); d_C{ H} (100.6 MHz, CDCl₃)

19.4 (s, o-ArCH₃), 21.3 (s, p-ArCH₃) 112.6 (s, C4), 118.1 (s, C³),

Table 6 Crystallographic data for complexes 13d, 14b and 16

Compound

13d

14b

16

Formula

M

T/K

C₂₉H₃₁Cl₂N₂PPd

615.83

150(2)

Monoclinic

C2/c (15)

32.505(4)

9.9996(11)

17.8876(19)

90

102.609(2)

90

5673.9(11)

8

1.442

0.919

C₂₅H₄₁Cl₂N₄PPd·2CH₂Cl₂

775.74

150(2)

Monoclinic

P2₁/c (14)

13.742(3)

17.691(4)

14.077(3)

90

91.965(4)

90

3420.5(12)

4

1.506

1.082

C₂₈H₃₀N₄Ni

481.27

120(2)

Crystal system

Space group (no.)

Triclinic

¯

P1 (2)

˚

a/A

10.031(1)

12.921(1)

13.951(1)

92.56(1)

93.53(1)

91.99(1)

1801.7(3)

3

˚

b/A

˚

c/A

a/^◦

b/^◦

c /^◦

3

˚

U/A

Z

D_c/g cm⁻³

1.331

0.83

l/mm⁻¹

Crystal size/mm

Reﬂections collected

Independent reﬂections

R_int

R1, wR2 [I > 2r(I)]

R Indices (all data)

0.29 × 0.21 × 0.18

0.34 × 0.11 × 0.04

0.37 × 0.28 × 0.08

21726

26447

24988

5569

0.0260

0.0251, 0.0648

0.0274, 0.0660

6713

0.0643

0.0454, 0.0895

0.0665, 0.0960

9511

0.069

0.0385, 0.0881

0.0565, 0.0943

5376 | Dalton Trans., 2006, 5362–5378

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period of 30 min at ambient temperature. After 5 min, the reaction

became extremely exothermic causing the reaction mixture to

reach ca. 80 ^◦C. At the end of the test period, the pressure was

released and nonane (1.00 cm³) was added and GC/MS analysis

of the organic phases undertaken immediately.

12 K. R. Reddy, K. Surekha, G.-H. Lee, S.-M. Peng and S.-T. Liu,

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Ethylene/carbon monoxide co-polymerisation testing protocol.

An autoclave was charged with toluene solutions (50 cm³) of

complexes 13 or 14 (18.0 × 10⁻⁵mol) under nitrogen, followed

by addition of methane sulfonic acid (50 lL, 7.2 × 10⁻⁴mol).

Subsequently, the reactions were heated to 90 ^◦C under a 1 :

1 CO–C₂H₄atmosphere (40 bar) for periods of 3 h. Upon

depressurisation, the contents of the autoclave were ﬁltered and

the organic phase subject to GC-MS analysis.

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Crystallography

X-Ray diffraction data (Table 6) were collected on Bruker diffrac-

tometers equipped with Apex 2 K (for 13d and 14b) or SMART 1 K

(for 16) CCD area detectors and Oxford Cryostream N₂cooling

devices, using graphite-monochromated Mo-Ka radiation (k =

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˚

0.71073 A). Data collection and reduction were conducted using

the SMART and SAINT programs,⁷²respectively. Absorption

corrections were applied for 13d and 14b by semi-empirical

methods,⁷⁴and for 16 by numerical integration based on crystal

face-indexing.⁷³The structures were solved by Patterson (13d,

14b) or direct (16) methods and reﬁned by full-matrix least

squares based on F², using the SHELXTL package and programs

therein.⁷⁵All non-hydrogen atoms were reﬁned anisotropically,

then hydrogen atoms included at idealised positions and reﬁned

as rigid groups.

32 C. E. Anderson, M.Phil. Thesis, University of Leicester, 2003; C. E.

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Howard, Dalton Trans., 2006, 4134.

CCDC reference numbers 617735–617737.

For crystallographic data in CIF or other electronic format see

DOI: 10.1039/b611652c

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Acknowledgements

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The Royal Society and The Nufﬁeld Foundation are thanked

for grants to P. W. D. Johnson Matthey Plc. is thanked for the

generous loan of palladium salts. Financial support from Leicester

and Durham Universities (C. E. A. and P. W. D.) is gratefully

acknowledged. Mr D. Hunter (Durham University) is thanked for

his assistance with high pressure reactions.

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Chelating N-pyrrolylphosphino-N′-arylaldimine ligands: Synthesis, ligand behaviour and applications in catalysis

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