Synthesis of neutral and zwitterionic phosphinomethylpyrrolato complexes of nickel

Article abstract of DOI:10.1016/j.jorganchem.2009.08.033

Potassium salts of the new 2-phosphinomethyl-1H-pyrroles, K[R₂PCH₂C₄H₃N] (R = Ph, Cy) react with (η³-allyl)nickel bromide to give the chelate complexes (R₂PCH₂C₄H₃N)Ni(allyl), whereas the sterically hindered 2-diphenylphosphinomethyl-5-t-butyl-1H-pyrrole and (η³-allyl)nickel bromide afford a phosphine adduct (HNC₄H₂-5-Bu^t-2-CH₂PPh₂ )Ni(allyl)Br which is stabilized by an intramolecular NH?Br hydrogen bond. The addition of B(C₆F₅)₃ to (R₂PCH₂C₄H₃N)Ni(allyl) leads to an electrophilic attack in 5-position of the pyrrole ring, to give the thermally unstable zwitterions (η³-C₃H₅)Ni[NC₄H ₃(2-CH₂PR₂)-5-B(C₆F₅) ₃] which catalyse the isomerisation of 1-hexene. The addition of B(C₆F₅)₃ is reversible, and slow ligand rearrangement to Ni(N-P)₂ products appears to be the major catalyst deactivation pathway.

Full text of DOI:10.1016/j.jorganchem.2009.08.033

Journal of Organometallic Chemistry 694 (2009) 4084–4089
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of neutral and zwitterionic phosphinomethylpyrrolato complexes
of nickel
*
Lewis M. Broomfield, David Boschert, Joseph A. Wright, David L. Hughes, Manfred Bochmann
Wolfson Materials and Catalysis Centre, School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK
a r t i c l e i n f o
a b s t r a c t
Potassium salts of the new 2-phosphinomethyl-1H-pyrroles, K[R2PCH2C4H3N] (R = Ph, Cy) react with (g3
-
Article history:
Received 7 June 2009
Received in revised form 28 July 2009
Accepted 4 August 2009
Available online 29 August 2009
allyl)nickel bromide to give the chelate complexes (R2PCH2C4H3N)Ni(allyl), whereas the sterically hin-
dered 2-diphenylphosphinomethyl-5-t-butyl-1H-pyrrole and (g
3-allyl)nickel bromide afford a phos-
phine adduct (HNC4H2-5-But-2-CH2PPh2)Ni(allyl)Br which is stabilized by an intramolecular NHꢀ ꢀ ꢀBr
hydrogen bond. The addition of B(C6F5)3 to (R2PCH2C4H3N)Ni(allyl) leads to an electrophilic attack in
5-position of the pyrrole ring, to give the thermally unstable zwitterions (g
3-C3H5)Ni[NC4H3(2-
Keywords:
Nickel
Pyrrole ligands
Phosphinoalkyl pyrrole
Chelate ligands
Allyl
CH2PR2)-5-B(C6F5)3] which catalyse the isomerisation of 1-hexene. The addition of B(C6F5)3 is reversible,
and slow ligand rearrangement to Ni(N-P)2 products appears to be the major catalyst deactivation
pathway.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
4
Nickel(II) complexes with a variety of chelating ligands have
been much studied, mainly in connection with their activity as eth-
ylene oligomerization catalysts. Nickel P–O chelates form the basis
of the Shell Higher Olefins Process (SHOP) [1–3]. Some nickel allyl
and benzyl chelate complexes show also good polymerisation
activity [4,5]. The range of ligands has recently been extended to
include new bidentate [6–12] and tridentate [13] P–N systems.
We have recently reported the facile synthesis of the new phos-
phorylmethylpyrrolato ligands [R2P(O)–CH2pyr]ꢁ by the reaction
of sec-phosphines with pyrrole aldehydes [14]. We report here
their reduction to the corresponding phosphines, the formation
and structure of their nickel allyl complexes and their activation
to give alkene isomerisation catalysts [15].
t
Ligands with mono-substituted pyrrole rings (2a and 2c)
undergo facile deprotonation with potassium hydride to give the
corresponding potassium salts K[R2PCH2C4H3N], which react with
(g
3-allyl)nickel bromide to give the chelate complexes 3a and 3c
as orange (R = Ph) or yellow (R = Cy) solids (Eq. (2)). The 1H NMR
spectra of complexes 3a, c show five individual signals for the five
protons in the
therefore no facile
g
3-allylic group at room temperature; there is
p–r–p flipping of the allyl ligand under these
2. Results and discussion
conditions. The two syn-protons show different coupling patterns,
since the one trans to P shows coupling to P whereas the one trans
to N does not. The CH2P protons are diastereotopic and appear as
two doublets of doublets, which further corroborates the restricted
rotation of the allyl ligand in 3. The anti-H atom of the allyl ligand
in 3c is hidden by the cyclohexyl signals but was identified by
1H/1H correlation experiments.
The reduction of 2-phosphorylmethyl-1H-pyrroles (1a–c) with
LiAlH4 in THF at room temperature for a period of 24 h affords
the corresponding phosphine derivatives
2 in 45–61% yield
(Eq. (1)). Extending the reaction times to up to a week did not
result in substantial increases in yield. The compounds were
isolated as off-white to pale-yellow solids.
Crystals suitable for X-ray diffraction were grown from diethyl
ether solution at ꢁ30 °C (Fig. 1). Although some trans effect on the
Ni–C bond lengths to the allyl ligand might have been expected,
the effect is negligible within the standard deviations.
* Corresponding author. Fax: +44 1603 592044.
E-mail address: m.bochmann@uea.ac.uk (M. Bochmann).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.08.033

L.M. Broomfield et al. / Journal of Organometallic Chemistry 694 (2009) 4084–4089
4085
Fig. 2. Molecular structure of 4b showing the atomic numbering scheme. Ellipsoids
are drawn at 50 % probability. Hydrogen atoms except H(32) have been omitted for
clarity.
Fig. 1. Molecular structure of 3a, showing the atomic numbering scheme. Ellipsoids
are drawn at 50% probability. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (°): Ni(1)–N(1) 1.880(5), Ni(1)–C(18) 2.023(6),
Ni(1)–C(19) 1.979(10), Ni(1)–C(20) 2.008(8), Ni(1)–P(1) 2.1638(17); N(1)–Ni(1)–
P(1) 85.79(16), C(18)–Ni(1)–C(20) 74.0(3), N(1)–Ni(1)–C(20) 173.1(3), C(18)–Ni(1)–
P(1) 171.5(2).
The complexes 3a and 3c do not react with either ethylene or
hex-1-ene. However, with B(C6F5)3 they give the catalytically ac-
tive zwitterionic products 5a (R = Ph) and 5c (R = Cy), respectively.
Some time ago Erker et al. reported the abstraction of a pyrro-
late ligand from Cp2ZrMe(NC4H4) by B(C6F5)3 to give the
[(1-pyrrolyl)B(C6F5)3]ꢁ anion [16] and synthesized 5H-pyrrole-
B(C6F5)3 complex by acidification of (Et2O)2Li[(1-pyrrolyl)B(C6F5)3]
[17], while Resconi and co-workers undertook a detailed study of
the reaction of B(C6F5)3 with pyrroles, indoles, imidazoles and pyr-
azoles [18–20]. In all these cases, with the exception of N-alkyl
pyrroles, the boron adds to the nitrogen atom. It seemed reason-
able therefore to assume that in the case of complexes 3 attack
by B(C6F5)3 would also take place on the nitrogen of the N–P che-
late, to give a product of structure I or II (Chart 1). Failing this, the
electrophilic borane could be expected to react with one of the
nucleophilic termini of the allyl ligand, to give 14-, 16- or 18-elec-
tron zwitterions of types III–V.
However, the spectroscopic data of 5 were inconsistent with
any of these structures. The 11B NMR spectra of 5a and 5c consisted
of relatively sharp singlets with chemical shift values that are
indicative of B(C6F5)3 bonded to a carbon atom, whereas N-bonded
B shows quadrupolar broadening [21,22]. For 5a, there was a new
signal centred at d 4.75 in the 1H NMR spectrum for a methylene
group with an AB pattern and a large geminal H–H coupling con-
stant of 24.9 Hz but no coupling to phosphorus. The 13C NMR signal
which correlates with these protons (d 76.4) also did not couple to
Br
R'
+
R
½
Ni
Ni
Ni
N
P
Br
R
K
+2−
K
R2
P
H
H
THF
(2)
−78 °C to RT
N
3a c
,
Somewhat surprisingly, the more sterically hindered ligand 2b
failed to react with potassium hydride in THF and could be recov-
ered unchanged. However, treatment of 2b in diethyl ether with
(g
3-allyl)nickel bromide led to a colour change to dark brown,
and a dark-orange product 4b was isolated. Whereas 3a gave a
31P NMR chemical shift of d 42.5, 4b was clearly different and
showed a 31P singlet resonance at d 19.5. The complex was identi-
fied crystallographically as a phosphine adduct of (allyl)NiBr
(Eq. (3)). Although the crystal quality was limited and the final
R-factors were not as low as normally expected, the structure is
clear and shows a nickel atom with square-planar geometry coor-
dinated to an
g
3-allyl, a bromide and a phosphine ligand. There is
no bonding interaction to the nitrogen atom of the pyrrole ring;
instead, there is a well-defined intramolecular hydrogen bond be-
tween the pyrrole N–H group and the bromide ligand: Br–H(32)
2.61 Å, N(32)–Br 3.411(16) Å (Fig. 2).
2
2
3
3
Br
But
Ph
N
+
½
Ni
H
Ni
P
Ph
H
2b
2
2
2
Br
PPh2
Ni
Br
THF
-78 °C to RT
(3)
N
3
3
3
But
4b
Chart 1.

4086
L.M. Broomfield et al. / Journal of Organometallic Chemistry 694 (2009) 4084–4089
R2
P
R2
P
R2
P
R2
P
Ni
Ni
Ni
H
Ni
B(C6F5)3
N
N
N
H
N
H
H
B(C6F5)3
B(C6F5)3
3a c
,
B(C6F5)3
5a c
,
Scheme 1.
Table 1
Isomerisation of hex-1-ene.a
Catalyst
Time
Conversion % Z-hex-2-
% E-hex-2-
% Z-hex-3-
precursor (min) (%)b
enec
enec
enec
3a
3c
120
480
100
90
15
43
64
47
21
10
a
Conditions: 1.7 lm catalyst, 1.7 mmol hex-1-ene, Ni/B ratio 1.5, C6D6 (0.5 mL),
20 °C.
b
Determined by integrations of the 1H NMR spectra.
Product distribution calculated from the 13C NMR integrals.
c
phosphorus. These observations are consistent with the presence
of acidic sp3 protons in 5-membered N-heterocyclic compounds
[18,19]. The 1H NMR signals for the diastereotopic CH2P group
were found as two multiplets centred at d 2.51 and 2.74; the cor-
responding 13C signal appears as a doublet (JC–P = 26.6 Hz) and its
coupling pattern is, as expected, altered in the 1H{31P} NMR spec-
trum (these 1H NMR signals do not in fact become simple doublets
of doublets as a small coupling exists between this ABX system and
the AB methylene system situated on the 3-position of the pyrrole
ring, as shown by 2D COSY NMR). The carbon in 2-position of the
pyrrolyl ring can be identified as a highly deshielded doublet at d
186.57 (2JC–P = 9.2 Hz). The data therefore point to the formation
of a zwitterion with a B(C6F5)3 moiety bound to an sp2-C-atom in
5-position of the heterocycle, accompanied by an allylic 1,3-shift
of an H atom (Scheme 1).
Compounds 5 do not undergo alkene insertion chemistry but
catalyse the isomerisation of hex-1-ene to products with internal
double bonds, in the manner of acid catalysts. Complex 5a, which
contains the less basic phosphine donor, showed both improved
catalytic activity and higher selectivity for E-hex-2-ene. 5a also
yielded a higher conversion to the Z-hex-3-ene isomer, with traces
of E-hex-3-ene also present (Table 1). No such isomerisation took
place with B(C6F5)3 alone. The catalyst is recyclable. After complete
conversion of hex-1-ene by 3a/B(C6F5)3, all volatiles were removed
and a second reaction batch of solvent and substrate was added.
Although the conversion was reduced slightly (to 81% in
120 min), the product ratios remained unchanged.
Fig. 3. Molecular structure of 6aꢀC6H6 showing 50% probability ellipsoids. One
molecule of benzene and hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°): Ni(1)–N(10) 1.8791(15), Ni(1)–P(1) 2.2123(5); N(1)–
Ni(1)–P(1) 82.86(5), N(1)–Ni(1)–N(10) 176.20(9), P(1)–Ni(1)–P(1’) 168.28(3), N(1)–
Ni(1)–P(10) 97.53(5).
with t-butyl substituents in ortho-position to N proved unexpect-
edly resistant to deprotonation under the same conditions. The
complexes Ni(allyl)(j
2-R2PCH2C4H3) react with B(C6F5)3 via attack
in 5-position of the pyrrole ring, accompanied by a 1,3-hydride
shift. The resulting zwitterionic complex catalyses the isomerisa-
tion of hex-1-ene to predominantly E-hex-2-ene at room tempera-
ture in high conversions.
4. Experimental
4.1. General procedures
Syntheses were performed under nitrogen using standard
Schlenk line techniques. Solvents were distilled from sodium-
benzophenone (diethyl ether, THF), sodium–potassium alloy
(light petroleum, b.p. 40–60 °C), or CaH2 (dichloromethane).
NMR solvents (CDCl3, CD2Cl2, C6D6) were dried over activated
4 Å molecular sieves and degassed by several freeze–thaw cycles.
Hex-1-ene was dried over sodium–potassium alloy for a mini-
Leaving the reaction of 5a to stand for 3 days resulted in a black
precipitate of nickel metal, accompanied by red crystals of
Ni(Ph2PCH2-2-C4H3N)2 (6a). This suggests that the formation of
5a from 3a and B(C6F5)3 is reversible, and that under these condi-
tions 3a can slowly disproportionate into the bis-ligand complex
6a and thermally labile Ni(allyl)2. The structure of 6a is shown in
Fig. 3. The complex is square-planar, with an angle sum about
the Ni centre of 360.78(10)°.
mum of 6 h, distilled and degassed before use. [Ni(
-Br)]2 [23,24], B(C6F5)3 [25,26], 2-diphenylphosphorylmethyl-
g
3-allyl)
(l
1H-pyrrole [14], 2-diphenylphosphorylmethyl-5-t-butyl-1H-pyr-
role [14] and 2-dicyclohexylphosphorylmethyl-1H-pyrrole [14]
were synthesised using literature procedures; for the ligand pre-
cursor synthesis see also the Supporting Information. Dicyclo-
hexyl phosphine oxide was made using standard literature
procedures and reduced to the corresponding dicyclohexyl phos-
phine with LiAlH4 in THF [27]. NMR spectra were recorded using
a Bruker DPX-300 spectrometer with a 5 mm BBO probe. Chemi-
cal shifts are reported in ppm and referenced to residual solvent
resonances (1H, 13C), 19F is relative to CFCl3. Nitrogen was purified
3. Conclusion
The reduction of phosphorylmethylpyrroles R2P(O)CH2-2-
C4H3N-5-R0 gives the new N–P chelate ligands R2P(O)CH2-2-
C4H3N-5-R’ (R = Ph or Cy; R0 = H or But). The mono-substituted
pyrroles are readily deprotonated and react with (allyl)nickel
bromide to give the expected chelates (N–P)Ni(g
3-allyl). Pyrroles

L.M. Broomfield et al. / Journal of Organometallic Chemistry 694 (2009) 4084–4089
4087
by passing through columns of supported P2O5, with moisture
indicator, and activated 4 Å molecular sieves. Elemental analyses
were performed by London Metropolitan University.
added [(g
3-allyl)NiBr]2 (0.120 g, 0.33 mmol) in THF (15 cm3) at
ꢁ50 °C. The reaction mixture changed from deep-red to orange.
The mixture was allowed to reach room temperature and left to
stir for 6 h. Volatiles were removed in vacuo and the resultant
brown solid was extracted as a yellow solution in diethyl ether
(2 ꢂ 50 cm3). On concentration and cooling the product was ob-
served as yellow needles suitable for X-ray diffraction (0.170 g,
71%). Anal. Calc. for NiC20H20NP: C, 65.98; H, 5.54; N, 3.85. Found:
C, 65.71; H, 5.66; N, 3.97%. 1H NMR (300 MHz, 300 K, C6D6):
d 7.47–7.41 (m, 4H, Ph), 7.10–7.01 (m, 7H, Ph + pyrrole), 7.00
(m, 1H, pyrrole), 6.74 (m, 1H, pyrrole), 4.97–4.92 (m, 1H, allyl),
4.2. Ligand synthesis
4.2.1. Preparation of 2-diphenylphosphinomethyl-1H-pyrrole (2a)
2-Diphenylphosphorylmethyl-1H-pyrrole (1a) (5.63 g, 20.0 mmol)
was dissolved in THF (250 cm3) and slowly added to LiAlH4 (2.34 g,
61.7 mmol). The suspension was stirred for 3 d and excess LiAlH4
was hydrolysed with degassed, aqueous NH4Cl (120 cm3). The mix-
ture was agitated for 15 min and left to separate. The aqueous layer
was washed with THF (2 ꢂ 100 cm3) and the combined organic
phases dried over MgSO4 and filtered. The solvent was removed
under reduced pressure to give 3.5 g of crude product, which was
then extracted with diethyl ether (100 cm3). The solvents were
evaporated to give the product as a pale-yellow solid (2.37 g,
45%). From the reaction residue 1.13 g (20%) of the starting mate-
rial was recovered. Anal. Calc. for C17H16NP; C, 76.97; H, 6.08; N,
5.28. Found: C, 76.54; H, 5.87; N, 5.21%. 1H NMR (300 MHz,
300 K, CDCl3): d 7.92 (br s, 1H, NH), 7.73–7.38 (m, 10H, Ph), 6.61
(s, 1H, pyrrole), 6.04 (s, 1H, pyrrole), 5.87 (s, 1H, pyrrole), 3.47 (s,
2
4.15–4.12 (m, 1H, allyl CHanti), 3.67 (dd, 1H, JH–P = 9.7 Hz,
2J = 15.0 Hz, CHHP), 3.55 (dd, 1H, 2JH–P = 9.8 Hz, 2J = 15.0 Hz, CHHP),
3
3.03 (dd, 1H, JH–P = 5.2 Hz, 2J = 10.6 Hz, allyl CHsyn), 2.87–2.80 (m,
1H, allyl CHanti), 1.56 (d, 1H, 2J = 12.0 Hz, allyl, CHsyn). 13C NMR
2
(75 MHz, 300 K, C6D6): d 137.19 (d, JC–P = 8.8 Hz, pyrrole C),
133.49 (d, JC–P = 22.5 Hz, aromatic C–P), 133.49 (d, JC–P = 23.1 Hz,
2
aromatic C–P), 132.42 (d, JC–P = 12.1 Hz, Ph), 132.08 (d,
4
2JC–P = 12.1 Hz, Ph), 131.46 (d, JC–P = 2.7 Hz, pyrrole CH), 130.18
4
3
(d, JC–P = 1.7 Hz, Ph), 128.77 (d, JC–P = 6.6 Hz, Ph), 128.66 (d,
3JC–P = 7.1 Hz, Ph), 111.25 (allyl), 110.82 (pyrrole CH), 103.81 (d,
3JC–P = 10.4 Hz, pyrrole CH), 67.67 (d, JC–P = 24.4 Hz, allyl H2Ctrans),
2
2
2
2H, PCH2). 13C NMR (75 MHz, 300 K, CDCl3): d 138.71 (d, JC–
46.78 (d, JC–P = 3.8 Hz, allyl H2Ccis), 32.43 (d, JC–P = 25.8 Hz, PCH2).
P = 14.7 Hz, Ph), 134.23 (d, JC–P = 18.1 Hz, aromatic C–P), 132.91
31P{1H} NMR (121 MHz, 300 K, C6D6): d 42.47.
3
(Ph), 127.28 (Ph), 126.98 (d, JC–P = 6.7 Hz, pyrrole CH) 117.14 (d,
4
2JC–P = 7.01 Hz, pyrrole C), 108.61 (d, JC–P = 5.4 Hz, pyrrole CH),
4.3.2. Preparation of (3-C3H5)Ni(NC4H3-2-CH2PCy2) (3c)
107.33 (pyrrole CH), 27.87 (d, JC–P = 15.0 Hz, PCH2). 31P{1H} NMR
(121 MHz, 300 K, CDCl3,): d ꢁ16.28.
The compound was made as described for 3a, using the potas-
sium salt of 2-dicyclohexylphosphinomethyl-1H-pyrrole (2c). On
removal of all volatiles the crude product was observed as a yellow
solid (0.15 g, 80%). Anal. Calc. for NiC20H32NP: C, 63.86; H, 8.57; N,
3.72. Found: C, 63.75; H, 8.91; N, 3.63%. 1H NMR (300 MHz, 300 K,
C6D6): d 7.28–7.25 (m, 1H, pyrrole CH), 6.99–6.97 (m, 1H, pyrrole
CH), 6.70–6.68 (m, 1H, pyrrole CH), 5.06–4.91 (m, 1H, allyl),
4.2.2. Preparation of 2-diphenylphosphinomethyl-5-t-butyl-1H-
pyrrole (2b)
The compound was made as described for 1a, using 2-diphenyl-
phosphorylmethyl-5-t-butyl-1H-pyrrole (1b). The crude product
was extracted into petrol and volatiles were removed to give the
pure product as a white sticky solid, 0.53 g (61%). Anal. Calc. for
C21H24NP: C, 78.48; H, 7.53; N, 4.36. Found; C, 78.58; H, 7.54; N,
4.44%. 1H NMR (300 MHz, 300 K, CDCl3): d 8.65 (br s, 1H, NH),
7.43–7.35 (m, 10H, Ph), 5.77 (s, 1H, pyrrole), 5.72 (s, 1H, pyrrole),
3.41 (s, 2H, PCH2), 1.13 (s, 9H, But). 13C NMR (75 MHz, 300 K,
3
4.17–4.14 (m, 1H, allyl CHanti), 3.13 (dd, 1H, JH–P = 5.9 Hz,
2
2J = 8.9 Hz, allyl CHsyn), 2.96 (dd, 1H, JH–P = 10.6 Hz, 2J = 16.3 Hz,
2
CHHP), 2.82 (dd, 1H, JH–P = 9.9 Hz, 2J = 16.3 Hz, CHHP), 2.64–2.58
(m, 1H, allyl CHanti), 1.79–0.96 (23H, cyclohexyl + 1 allyl CHsyn).
2
13C NMR (75 MHz, 300 K, C6D6): d 138.46 (d, JC–P = 8.2 Hz, pyrrole
C), 130.85 (d, 4J = 2.2 Hz, pyrrole CH), 110.45 (pyrrole CH), 110.00
2
2
CDCl3): d 141.12 (Ph), 138.51 (d, JC–P = 15.0 Hz, Ph), 132.78 (d,
(allyl), 102.76 (d, 3J = 9.9 Hz, pyrrole CH), 68.12 (d, JC–P = 20.3 Hz,
2
JC–P = 18.2 Hz, aromatic C–P), 128.81 (Ph), 128.51 (d,
allyl H2Ctrans), 46.78 (d, JC–P = 6.0 Hz, allyl H2Ccis), 33.67
2
3JC–P = 6.6 Hz, pyrrole CH), 125.02 (d, JC–P = 7.01 Hz, pyrrole C),
(d, JC–P = 22.3 Hz, Cy), 33.43 (d, JC–P = 22.0 Hz, Cy), 28.73
4
3
3
106.61 (d, JC–P = 5.5 Hz, pyrrole CH), 102.21 (pyrrole C), 31.21
(d, JC–P = 6.5 Hz, Cy), 28.64 (d, JC–P = 7.3 Hz, Cy), 26.83 (d,
(CMe3), 30.37 (CMe3), 27.91 (d, JC–P = 15.0 Hz, PCH2). 31P{1H} NMR
(121 MHz, 300 K, CDCl3,): d ꢁ15.41.
2JC–P = 12.5 Hz, Cy) 26.77 (d, 2JC–P
=
13.3 Hz, Cy), 26.50
(d, 4JC–P = 5.7 Hz, Cy) 26.00 (d, 4JC–P = 5.0 Hz, Cy) 22.50
(d, JC–P = 22.7 Hz, PCH2). 31P{1H} NMR (121 MHz, 300 K, C6D6): d
59.35.
4.2.3. Preparation of 2-dicyclohexylphosphinomethyl-1H-pyrrole (2c)
The compound was made as described for 2a, using 2-dic-
yclohexylphosphorylmethyl-1H-pyrrole (1d). The crude product
was extracted into light petroleum and volatiles were removed
to give the title product in 90% purity (by NMR) as an off-white so-
lid, (0.45 g, 48%). 1H NMR (300 MHz, 300 K, CDCl3): d 8.27 (br s, 1H,
NH), 6.68 (s, 1H, pyrrole CH) 6.10 (br s, 1H, pyrrole.), 5.93 (br s, 1H,
pyrrole), 2.82 (s, 2H, PCH2), 1.90–1.03 (m, 22H, Cy). 13C NMR
4.3.3. Preparation of (3-C3H5)NiBr(2-Ph2PCH2(5-But)C4H2NH) (4b)
To a solution of 2b (0.20 g, 0.62 mmol) in THF was added slowly
a solution of [(g
3-allyl)NiBr]2 (0.12 g, 0.33 mmol) in THF (50 cm3)
to give a dark brown solution. Volatiles were removed in vacuo
and the product exacted as a dark-orange solution in diethyl ether.
The filtrate was cooled to ꢁ35 °C for 48 h to give 4b as orange crys-
tals suitable for X-ray diffraction, yield (0.14 g, 45%). Anal. Calc. for
NiC24H29BrNP: C, 57.53; H, 5.83; N, 2.80. Found: C, 57.79; H, 6.16;
N, 3.07%. 1H NMR (300 MHz, 300 K, C6D6): d 10.32 (br s, 1H, NH),
7.40–7.27 (m, 10H, Ph), 5.97 (br s, 1H, pyrrole CH), 5.64 (br s, 1H,
pyrrole CH), 4.84–4.79 (m, 1H, allyl), 3.78 (br s, 1H, allyl CHanti),
2
(75 MHz, 300 K, CDCl3): d 129.10 (d, JC–P = 8.4 Hz, pyrrole C),
116.21 (pyrrole CH), 114.18 (pyrrole CH), 108.28 (3JC–P = 4.2 Hz,
3
2
pyrrole CH), 33.31 (d, JC–P = 12.9 Hz, Cy), 29.81 (d, JC–P = 13.0 Hz,
4
Cy), 28.69 (d, JC–P = 8.5 Hz, Cy), 27.33 (d, JC–P = 19.2 Hz, Cy),
20.42 (d, JC–P = 18.3 Hz, PCH2). 31P{1H} NMR (121 MHz, 300 K,
CDCl3,): d ꢁ6.65.
2
3.41 (d, 2H, JH–P = 7.0 Hz, CH2P), 2.67 (br s, 1H, allyl CHsyn), 1.51
(s, 9H, But), 1.35 (m, 1H allyl CHanti), 0.97 (d, 1H, 2J = 6.6 Hz, allyl
CHsyn). 31P{1H} NMR (121 MHz, 300 K, C6D6): d 19.48.
4.3. Synthesis of complexes
4.3.1. Preparation of (3-C3H5)Ni(NC4H3CH2PPh2) (3a)
4.3.4. (3-C3H5)Ni[NC4H3(2-CH2PPh2)-5-B(C6F5)3] (5a)
To a suspension of the potassium salt of 2-diphenylphosphino-
Tris(pentafluorophenyl)borane (0.036 g, 0.07 mmol) in deuter-
methyl-1H-pyrrole (2a) (0.20 g, 0.66 mmol) in THF (25 cm3) was
ated benzene (0.2 cm3) was added to 3a (0.020 g, 0.06 mmol) in

4088
L.M. Broomfield et al. / Journal of Organometallic Chemistry 694 (2009) 4084–4089
deuterated benzene (0.4 cm3) in an NMR tube to give an orange
solution of compound 5a. The compounds could not be crystallised,
and attempted isolation resulted in a black oil. 1H NMR (300 MHz,
300 K, C6D6): d 7.43–7.09 (m, 10H, Ph) 6.72 (br s, 1H, ring CH), 4.80
(d, 1H, 2J = 24.9 Hz, one of ring CH2), 4.71 (d, 1H, 2J = 24.9 Hz, one of
ring CH2), 4.52 (m, 1H, allyl), 3.66–3.63 (m, 1H, allyl CHanti),
2.75–2.73 (m, 1H, CHHP), 2.69 (br s, 1H, allyl CHanti), 2.54–2.48
Table 2
Crystal and refinement data.
Compound
3a
4b
6aꢀC6H6
C34H30N2NiP2ꢀC6H6
Empirical
formula
Formula
weight
Temperature
(K)
Crystal size
(mm)
Crystal
C20H20NNiP
C24H29BrNNiP
364.03
120(2)
501.07
140(1)
665.36
140(2)
3
(m, 1H, CHHP), 2.23 (dd, 1H, JH–P = 5.4 Hz, 2J = 8.6 Hz, allyl CHsyn),
1.42 (d, 1H, 2J = 15.6 Hz, allyl CHsyn). 13C NMR (75 MHz, 300 K,
0.01 ꢂ 0.13 ꢂ 0.24 0.13 ꢂ 0.22 ꢂ 0.36 0.20 ꢂ 0.45 ꢂ 0.50
2
C6D6): d 185.80 (d, JC–P = 9.2 Hz, ring H2CC@N), 156.15 (CH@C),
148.14 (1JC–F = 232.0 Hz, C–F), 137.48 (1JC–F = 240.1 Hz, C–F),
134.51 (1JC–F = 256.2 Hz, C–F), 132.11–130.41 (m, Ph), 114.52 (al-
Monoclinic
Orthorhombic
Monoclinic
system
Space group
Pbca
C2/c
P1
2
lyl), 76.36 (ring CH2), 70.23 (d, JC–P = 18.8 Hz, allyl H2Ctrans),
a (Å)
b (Å)
c (Å)
8.4825(5)
9.9139(5)
11.3723(7)
108.024(3)
100.524(3)
100.965(3)
862.43(9)
2
11.5013(3)
15.2545(3)
27.0832(7)
90
90
90
12.9628(3)
14.2974(3)
17.8256(4)
90
104.097(2)
90
50.00 (allyl H2Ccis), 33.91 (3JC–P = 25.5 Hz, PCH2). 11B NMR
(96 MHz, 300 K, C6D6): d ꢁ15.25. 19F NMR (282 MHz, 300 K,
3
3
a
(°)
C6D6): d ꢁ130.05 (d, 2F, JF–F = 22.8 Hz, o-F), ꢁ160.60 (t, 1F, JF–
F = 20.6 Hz, p-F), ꢁ164.84, ꢁ164.97 (m, 2F, m-F). 31P{1H} NMR
(121 MHz, 300 K, C6D6): d 42.51.
b (°)
c
(°)
V (Å3)
4751.7(2)
8
3204.20(12)
4
Z
Number of
reflections
12 696
41 106
21 560
4.3.5. (3-C3H5)Ni[NC4H3(2-CH2PCy2)-5-B(C6F5)3] (5c)
B(C6F5)3 (0.036 g, 0.07 mmol) in deuterated benzene (0.2 cm3)
collected
Number of
unique
reflections
Rint
was added to
(g
3-C3H5)Ni(NC4H3CH2PCy2) (3d) (0.021 g,
3916
2212
3701
0.06 mmol) in deuterated benzene (0.4 cm3) in an NMR tube to give
an orange solution of 5c. 1H NMR (300 MHz, 300 K, C6D6): d 6.71 (br
s, 1H, ring CH), 4.73 (d, 1H, 2J = 24.4 Hz, one of ring CH2), 4.58 (d, 1H,
2J = 24.4 Hz, one of ring CH2), 4.45 (m, 1H, allyl), 3.63–3.61 (m, 1H,
0.100
0.092
0.090
0.112
0.247
0.032
0.033
0.092
R1 [I > 2r(I)]
wR2 (all data) 0.192
3
allyl CHanti), 2.51 (br s, 1H, allyl CHanti), 2.26 (dd, 1H, JH–P = 5.6,
2J = 8.5 Hz, allyl CHsyn), 1.97–1.90 (m, 2H, CH2P), 1.58–0.96 (m,
23H, Cy + allyl CHsyn). 13C NMR (75 MHz, 300 K, C6D6): d 186.50
Structures were determined by direct methods using SHELXS
(3a and 4b) [31] or SIR-92 (6a) [32]. In all cases refinement was
carried out by full-matrix least-squares methods using SHELXL-97
[31] within the WinGX suite [33]. Non-hydrogen atoms were re-
fined with anisotropic thermal parameters. Hydrogen atoms were
included using a riding model. Crystal and refinement data are col-
lected in Table 2.
2
(d, JC–P = 8.5 Hz, H2CC@N), 148.21 (1JC–F = 232.8 Hz, C–F), 138.48
(1JC–F = 240.8 Hz, C–F), 136.51 (1JC–F = 261.2 Hz, C–F), 128.12
2
(CH@C), 113.30 (allyl), 76.19 (ring CH2), 70.41 (d, JC–P = 18.4 Hz,
allyl H2Ctrans), 45.10 (allyl H2Ccis), 32.51 (d, JC–P = 22.4 Hz, Cy),
2
3
28.18 (d, JC–P = 10.0 Hz, Cy), 26.12 (d, JC–P = 5.5 Hz, Cy), 25.57
(Cy), 25.15 (d, JC–P = 20.5 Hz, PCH2).11B NMR (96 MHz, 300 K,
C6D6): d ꢁ15.29. 19F NMR (282 MHz, 300 K, C6D6): d ꢁ130.25
3
3
(d, 2F, JF–F = 22.2 Hz, o-F), ꢁ160.70 (t, 1F, JF–F = 20.7 Hz, p-F),
ꢁ164.92, ꢁ164.06 (m, 2F, m-F). 31P{1H} NMR (121 MHz, 300 K,
C6D6): d 59.85.
Acknowledgements
This work was supported by the Engineering and Physical Sci-
ences Research Council. We thank the EPSRC National Crystallogra-
phy Service for collection of diffraction data for compounds 3a.
4.3.6. Ni(NC4H3-2-CH2PPh2)2 (6a)
Leaving a solution of 5a and hex-1-ene in benzene for a 48 h
period caused the precipitation of the title complex as dark red
crystals suitable for X-ray crystallography. The complex was ob-
served as a mixture of trans and cis isomers (ꢃ1:1) by NMR spec-
troscopy. Anal. Calc. for NiC34H30N2P2: C, 69.54; H, 5.15; N, 4.77.
Found: C, 69.72; H, 4.89; N, 4.95%. 1H NMR (300 MHz, 300 K,
CDCl3): d 7.67–7.14 (m, 40H, Ph), 6.98–6.96 (m, 2H, pyrrole),
6.15–6.12 (m, 2H, pyrrole), 6.01–5.99 (m, 2H, pyrrole), 5.97–5.94
(m, 4H, pyrrole), 5.85–5.80 (m, 2H pyrrole), 3.69–3.65 (m, 4H,
CH2P), 3.61–3.58 (m, 4H, CH2P). 31P{1H} NMR (121 MHz, 300 K,
CDCl3): d 42.42, 31.17.
Appendix A. Supplementary data
CCDC 731719, 731720 and 731721 contain the supplementary
crystallographic data for complexes 3a, 4b and 6a. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.08.033.
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