New monocationic trialkylphosphine tetraphenylborate salts

Article abstract of DOI:10.1080/10426507.2010.533394

Six newmonocationic trialkylphosphines, [P(CH₂NH ₂R){CH₂N(R)CH₂N(R)CH₂}]+ (R = C ₆H₅CH₂, 4-FC₆H₄CH ₂, 4-ClC₆H₄CH

Full text of DOI:10.1080/10426507.2010.533394

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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New Monocationic Trialkylphosphine
Tetraphenylborate Salts
Allen T. Ekubo a , Mark R. J. Elsegood a & Martin B. Smith a
a Department of Chemistry , Loughborough University ,
Loughborough , Leics , UK
Published online: 25 Apr 2011.
To cite this article: Allen T. Ekubo , Mark R. J. Elsegood & Martin B. Smith (2011) New Monocationic
Trialkylphosphine Tetraphenylborate Salts, Phosphorus, Sulfur, and Silicon and the Related Elements,
186:4, 826-829, DOI: 10.1080/10426507.2010.533394
To link to this article: http://dx.doi.org/10.1080/10426507.2010.533394
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Phosphorus, Sulfur, and Silicon, 186:826–829, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.533394
NEW MONOCATIONIC TRIALKYLPHOSPHINE
TETRAPHENYLBORATE SALTS
Allen T. Ekubo, Mark R. J. Elsegood, and Martin B. Smith
Department of Chemistry, Loughborough University, Loughborough, Leics, UK
Abstract Sixnewmonocationic trialkylphosphines,[P(CH2NH2R){CH2N(R)CH2N(R)CH2}]+
(R = C6H5CH2, 4-FC6H4CH2, 4-ClC6H4CH2, 4-CH3C6H4CH2) as their Cl− (1c, 1d) or
−
1
BPh4 (2a−2d) salts, are described. All compounds have been characterized by 31P{ H}
spectroscopy, FTIR spectroscopy, and elemental analysis. A single crystal X-ray structure
determination of 2a has been performed. In contrast to recent examples reported by us, only
one intramolecular N−H···N hydrogen bond was observed in molecules of 2a; the other N
H
was involved in an N H···π intermolecular interaction to the BPh4− anion.
Keywords Anion metathesis; ligands; spectroscopy; tertiary phosphine; X-ray crystallography
INTRODUCTION
Water-soluble tertiary phosphines are widely recognized as an important class of
ligand finding uses in coordination chemistry and catalysis. One noteworthy example is
1,3,5-triaza-7-phosphaadamantane (PTA),1 which has received much recent interest for its
ease of chemical modification,2,3 diverse metal coordination,4 and cytotoxic5,6 and catalytic
properties.7,8 As part of continuing studies investigating new horizons in phosphine chem-
istry, we recently prepared the charged variants 1a/1b (Scheme 1), which are structurally
related to PTA. Moreover we showed that the diamondoid framework in 1a/1b is confor-
mationally locked, in the solid state, through two intramolecular N H···N hydrogen bonds
using the quaternary dialkylammonium/tertiary nitrogen atoms as donor/acceptor sites, re-
spectively.9 This structural motif remains unaltered, even after complexation to RuII or RhIII
metal centers. The behavior of these ligands towards PdII or PtII metal centers was also
illustrated by the formation of unusual homodinuclear zwitterionic complexes containing a
partially delocalized P{cyclo-CH2N(R)CHN(R)CH2} bridging phosphido ligand.10 In this
article, we describe the synthesis and characterization of two further derivatives of 1 and
also a series of tetraphenylborate salts 2a−2d. The single crystal X-ray structure determi-
nation of 2a revealed a new structural motif to that previously observed for 1a/1b and its
related analogues.9
Received 8 September 2010; accepted 15 October 2010.
We would like to thank Niger Delta University, Bayelsa State, Nigeria, for funding (A.T.E.). Rhodia U.K.
Ltd (Dr. Ranbir Padda) is gratefully acknowledged for the kind donation of THPC.
Address correspondence to Dr. Martin B. Smith, Department of Chemistry, Loughborough University,
Loughborough, Leics, LE11 3TU, UK. E-mail: m.b.smith@lboro.ac.uk
826

MONOCATIONIC TRIALKYLPHOSPHINE TETRAPHENYLBORATE SALTS
827
BPh4
Cl
Cl
NH2R
NH2R
CH2OH
P
(i)
(ii)
N
N
R
R
P
P
N
N
HOCH2
HOCH2
CH2OH
R
R
1a
2a
2b
2c
2d
R = C6H5CH2
R = C6H5CH2
1b
1c
1d
R = 4–FC6H4CH2
R = 4–ClC6H4CH2
R = 4–CH3C6H4CH2
R = 4–FC6H4CH2
R = 4–ClC6H4CH2
R = 4–CH3C6H4CH2
Scheme 1 (i) ∼4 equiv. 4-XC6H4CH2NH2 (X = Cl or CH3), EtOH, r.t. (ii) 1.5 equiv. Na[BPh4], MeOH.
RESULTS AND DISCUSSION
The monocationic chloride salts 1c (R = 4-ClC6H4CH2) and 1d (R = 4-
CH3C6H4CH2) were synthesized from commercially available [P(CH2OH)4]Cl (THPC)
and approx. 4 equiv. of 4-XC6H4CH2NH2 (X = Cl, CH3) according to a previously
published procedure (Scheme 1).9 Facile anion metathesis of 1a−d with Na[BPh4]
in MeOH afforded the corresponding tetraphenylborate salts 2a−d in excellent yields
1
(around 90%). In all four cases, the 31P{ H} NMR spectra revealed a predominant species
around δ(P) −55 ppm [recorded in (CD3)2SO]. All compounds were further characterized
by FT−IR spectroscopy, FAB−MS, and elemental analysis (see the Experimental section
for selected data).
Suitable crystals of 2a were obtained by vapor diffusion of diethyl ether into a
CH2Cl2 solution over the course of several days. The single crystal X-ray structure11 of 2a
has been determined (Figure 1), with selected bond lengths and angles given in Table 1. The
Figure 1 Crystal structure of 2a. All hydrogen atoms except H(1A), H(1B), and H(35) have been omitted for
clarity. Cg(1) is the centroid of the phenyl group C(20) to C(25); Cg(2) is the midpoint between atoms C(29) and
C(30).

828
A. T. EKUBO ET AL.
Table 1 Selected bond lengths (Å) and angles (◦) for 2a
P(1)−C(1)
P(1)−C(9)
P(1)−C(11)
C(1)−N(1)
C(9)−N(2)
1.8581(16)
1.8457(13)
1.8407(14)
1.4816(19)
1.4772(17)
C(11)−N(3)
1.4664(17)
100.54(6)
98.39(7)
C(1)−P(1)−C(9)
C(1)−P(1)−C(11)
C(9)−P(1)−C(11)
97.38(6)
phosphorus environment in 2a is best described as pyramidal, and the P C N C N C
six-membered ring adopts the expected chair conformation. The P−C and P−N bond
distances are broadly as expected and in keeping with values previously reported in the
literature.9 The most striking feature of 2a is the presence of a single intramolecular
N(1)−H(1A)···N(2) hydrogen bond [N(1)···N(2) 2.7393(17) Å, H(1A)···N(2) 1.887(18) Å;
N(1)−H(1A)···N(2) 148.4(16)◦] unlike the two intramolecular N−H···N contacts found
in 1b and variants (SbF6−, PF6−) thereof [N···N range 2.804(3)−2.915(5) Å].9 There are
also N(1)−H(1B)···π{Cg(2)} (2.42 Å) and C(35)−H(35)···π{Cg(1)} (3.38 Å) interactions
between the cation and the BPh4− anion.
In summary, we have shown that new monocationic trialkylphosphines, as their
tetraphenylborate salts, can be readily prepared. Further studies are currently underway
that are looking at their coordination and organometallic chemistry.
EXPERIMENTAL
Ligands 1c and 1d were prepared following a previously published procedure.9 The
following method was used for the synthesis of the tetraphenylborate compound 2a. To a
solution of 1a (0.20 g, 0.45 mmol) in HPLC grade MeOH (10 mL), Na[BPh4] (0.23 g, 0.67
mmol) was added in the minimum volume of HPLC grade MeOH. The solution was stirred
for 30 min at r.t., and the volume was concentrated to dryness under reduced pressure. The
addition of distilled water (10 mL) gave a colorless solid, which was collected by suction
filtration and dried under vacuum. Yield: 0.29 g, 89%. Compounds 2b (86%), 2c (90%),
and 2d (90%) were each prepared in a similar manner.
1
Selected data for 2a: 31P{ H} NMR [(CD3)2SO, 298 K]: δ(P) −55.1 ppm. FT−IR
(KBr): 3163, 3053, 3027, 3001, 2983, 2848, 2779 cm−1 (νNH/νCH). FAB−MS: m/z 404
[M−BPh4]+. Calcd. for C49H51BN3P: C, 81.30; H, 7.12; N, 5.81. Found: C, 80.85; H,
1
6.80; N, 5.69. Selected data for 2b: 31P{ H} NMR [(CD3)2SO, 298 K]: δ(P) −54.9 ppm.
FT−IR (KBr): 3120, 3055, 3039, 3000, 2985, 2930, 2830, 2792 (νNH/νCH), 1227 (νCF
)
cm−1. FAB−MS: m/z 458 [M−BPh4]+. Calcd. for C49H48BF3N3P·H2O: C, 73.95; H, 6.35;
1
N, 5.28. Found: C, 74.28; H, 6.06; N, 5.39. Selected data for 2c: 31P{ H} NMR [(CD3)2SO,
298 K]: δ(P) −54.5 ppm. FT−IR (KBr): 3163, 3121, 3054, 3039, 2999, 2983, 2925,
2838, 2792 (νNH/νCH), 844, 807 (νCCl) cm−1. FAB−MS: m/z 508 [M−BPh4]+. Calcd.
for C49H48BCl3N3P·H2O: C, 69.64; H, 5.98; N, 4.97. Found: C, 69.77; H, 5.75; N, 5.04.
1
Selected data for 2d: 31P{ H} NMR [(CD3)2SO, 298 K]: δ(P) −54.6 ppm. FT−IR (KBr):
3155, 3052, 2999, 2982, 2945, 2921, 2852, 2825, 2780 cm−1 (νNH/νCH). FAB−MS: m/z
446 [M−BPh4]+. Calcd. for C52H57BN3P: C, 81.54; H, 7.52; N, 5.49. Found: C, 81.22; H,
7.52; N, 5.53.
Crystal data for 2a: C49H51BN3P, M = 723.71; monoclinic, P21/c, a = 12.9954(4),
b = 19.7592(6), c = 16.6069(5) Å, V = 4049.3(2) Å3; Z = 4, ρcal 1.187 g cm−3; µ(Mo-
Kα) = 0.106 mm−1; λ = 0.71073 Å, T = 150(2) K; 48008 reflections were collected

MONOCATIONIC TRIALKYLPHOSPHINE TETRAPHENYLBORATE SALTS
829
on a Bruker APEX 2 CCD diffractometer11 using narrow ω-scans, 12372 of which were
independent (Rint = 0.0427). The structure was solved by Patterson synthesis and refined
on F2 values to give a final R1 = 0.0508 for 8920 data with F2>2σ (F2); wR2 = 0.1314
for all data.12 A complete set of X-ray crystallographic structural data for compound 2a
(CCDC no. 791781) is available at the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.ac.uk) on
request, quoting the deposition number.
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