Phosphanylborohydrides: First assessment of the relative Lewis basicities of [BH3PPh2]-, CH3PPh2, and HPPh2

Article abstract of DOI:10.1002/ejic.200501126

The compounds K[PPh₂], HPPh₂, CH₃PPh ₂, BH₃(H)PPh₂, BBr₃(H)PPh ₂, BH₃(CH₃)PPh₂, BBr ₃(CH₃)PPh₂, [H

Full text of DOI:10.1002/ejic.200501126

FULL PAPER
DOI: 10.1002/ejic.200501126
Phosphanylborohydrides: First Assessment of the Relative Lewis Basicities of
[BH3PPh2]–, CH3PPh2, and HPPh2
Franz Dornhaus,[a] Michael Bolte,[a] Hans-Wolfram Lerner,[a] and Matthias Wagner*[a]
Keywords: P Ligands / Phosphanylborohydride / Ligand design / Donor–acceptor systems / Isoelectronic analogues
The compounds K[PPh2], HPPh2, CH3PPh2, BH3(H)PPh2,
BBr3(H)PPh2, BH3(CH3)PPh2, BBr3(CH3)PPh2, [H2PPh2]I,
[CH3(H)PPh2]I, [(CH3)2PPh2]I, and K[(BH3)2PPh2] have been
investigated by NMR spectroscopy. In addition, X-ray crystal
structures have been determined for K(18-crown-6)[PPh2],
BBr3(H)PPh2, BBr3(CH3)PPh2, [H2PPh2]I, [CH3(H)PPh2]I,
clusion that dative bonds originating from ligand [BH3PPh2]–
possess a significantly higher p character than dative bonds
1
involving the ligands HPPh2 and CH3PPh2. The JPB values
obtained for BH3(H)PPh2, BH3(CH3)PPh2, and [(BH3)2PPh2]–
suggest [BH3PPh2]– to form the strongest [BH3] adduct of all
three compounds which is in agreement with the results of
[(CH3)2PPh2]I, and K(18-crown-6)[(BH3)2PPh2]. An evalu- displacement reactions employing the couples CH3PPh2/
1
ation of coupling constants (e.g. JPCi; Ci = ipso carbon atom
of a phenyl ring) augmented by an inspection of key struc-
tural parameters (e.g. the angles Ci–P–CiЈ) leads to the con-
[(BH3)2PPh2]– and [BH3PPh2]–/BH3(CH3)PPh2.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
elements, Manners and co-workers have recently employed
the compound Li[BH3PPh2] in the preparation of linear hy-
brid aminoborane/phosphanylborane chains.[7] The
same group has also reported on the synthesis of the
Introduction
Organophosphanes have been extensively studied as li-
gands to both main group Lewis acids and transition metals
in order to unveil the factors governing the stability and
reactivity of coordination complexes.[1] In the course of
these studies it soon became apparent that phosphanes may
not generally be viewed as simple σ donors because often
an intricate interplay exists between the P Ǟ M σ interac-
tion and an M Ǟ ligand π back-donation. The π acceptor
strength of PF3, for example, is comparable to that of CO,
commonly regarded as the archetypical π acceptor ligand.
If, on the other hand, electropositive substituents are at-
tached to the phosphorus atom, one would expect an in-
crease in Lewis basicity likely together with a decrease in π
acidity of the respective phosphane molecule. One way to
test this assumption is through replacement of alkyl groups
on phosphorus by borane moieties. Using parent [BH3], we
thereby arrive at a class of anionic species [BH3PRRЈ]–
which are the heavier homologues of the better-known ami-
noborohydrides [BH3NRRЈ]–.[2] Until today, phosphanyl-
borohydrides [BH3PRRЈ]– have mainly been generated in
situ and used as building blocks for the preparation of chi-
ral organophosphanes.[3–6] Moreover, aiming at the synthe-
sis of polymeric materials involving group 13 and group 15
platinum
phosphanylborohydride
complexes
trans-
[PtH(BH3PPhR)(PEt3)2] (R = H, Ph) by the regioselective
insertion of the Pt(PEt3)2 fragment into the P–H bond of
BH3(H)2PPh or BH3(H)PPh2.[8] Other examples of struc-
turally characterised phosphanylborohydride complexes in-
clude the compounds [(dppp)Pd(C6F5)(BH3PPh2)][9] and
[(C5Me5)Fe(CO)2(BH3PPh2)].[10] Finally, Müller et al. have
explored the complexation potential of [BH3P(CH3)2]– and
[BH3P(Ph)tBu]– toward lithium and aluminium.[11]
In a 1996 paper, Fu et al. described diphenylphosphido-
boratabenzene, [(BC5H5)PPh2]–, as anionic analogue of the
ubiquitous triphenylphosphane ligand and explored its co-
ordination chemistry.[12] Stimulated by their investigations,
our group embarked on a systematic study of the ligand
properties of anionic phosphanylborohydrides [BH3PRRЈ]–
in comparison to their neutral isoelectronic and iso-
structural methyl analogues CH3PRRЈ. For a start, we are
focusing on compounds in which the phosphorus atom is
exclusively engaged in σ bonds. Effects of π bonding will be
considered at a later stage. All compounds under investiga-
tion here are based on the PPh2 fragment (Figure 1). The
series of derivatives starts with the [PPh2]– ion (K[PPh2], 1)
and continues with the phosphanes HPPh2 (2) and
H3CPPh2 (3), followed by their complexes with the main
group Lewis acids [BH3], H+, and [CH3]+ (cf. 4H, 5H, and
6–8). As we were not able to grow X-ray quality crystals of
the [BH3] adducts 4H and 5H, the corresponding BBr3 ad-
[a] Institut für Anorganische Chemie, Johann Wolfgang Goethe-
Universität Frankfurt am Main,
Marie-Curie-Straße 11, 60439 Frankfurt, Germany
Fax: +49-69-798-29260
E-mail: Matthias.Wagner@chemie.uni-frankfurt.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2006, 1777–1785
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1777

F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner
FULL PAPER
ducts 4Br and 5Br were structurally characterised instead. prepared by treatment of HPPh2 (2) and CH3PPh2 (3) with
The series closes with the anionic species K[(BH3)2PPh2] excess HI in toluene; for the syntheses of [CH3(H)PPh2]Br
(9).
and [(CH3)2PPh2]I (8) see refs.[17,18] The synthesis of
K[(BH3)2PPh2] was accomplished by deprotonation of
BH3(H)PPh2 (4H) with KH and subsequent addition of
BH3·THF in THF.
In the following, all compounds under investigation will
be viewed as adducts between the Lewis bases HPPh2 (2),
CH3PPh2 (3), and [BH3PPh2]– with the Lewis acids H+,
[BH3], BBr3, and [CH3]+.
X-ray Crystallography: Single crystals of the potassium
salts 1 and 9 were obtained only after potassium complex-
ation with 18-crown-6. The compounds K(18-
crown-6)[PPh2] and K(18-crown-6)[(BH3)2PPh2] will be re-
ferred to as 1c and 9c, respectively. Selected bond lengths
and angles of compounds 1c, 4Br, 5Br, 6, 7, 8, and 9c are
compiled in Table 1.
The potassium diphenylphosphide K(18-crown-6)[PPh2]
(1c) crystallises from THF in the monoclinic space group
P21/n (Figure 2).
The asymmetric unit of 1c contains two formula units
and features diphenylphosphide anions in distinctly dif-
ferent chemical environments: The first [PPh2]– fragment
coordinates to two potassium counterions with bond
lengths P(1)–K(1) and P(1)–K(1A) of 3.347(1) Å and
3.267(1) Å, respectively (sum of the ionic radius of K+ and
the van-der-Waals radius of phosphorus: 3.55 Å[19]). Each
potassium centre is encapsulated by one crown ether ligand;
in addition, a relatively short intermolecular contact is es-
tablished between K(1A) and one phenyl ring [K(1A)···
C(25A) = 3.518(2) Å]. The bond angles around the phos-
Figure 1. The potassium phosphide 1, the phosphanes 2, 3, and the
phosphane adducts 4–9.
With this selection of molecules it is possible to study
systematic trends in NMR- and structural parameters (i)
upon increasing the coordination number of phosphorus
from two to three and four (e.g. [PPh2]– vs. HPPh2 vs.
[H2PPh2]+) and (ii) by comparing isoelectronic and iso-
structural species of different charge (e.g. [(BH3)2PPh2]– vs.
[(CH3)2PPh2]+). It is to be mentioned that some of the com-
pounds under investigation here are already known in the
literature (see below). However, crystal structure analyses
were missing and even though selected NMR spectroscopic
data have been reported, measurement conditions vary to
such an extent that a re-investigation using the same solvent
and (in the case of 6–8) counterion was inevitable, because
these can greatly influence the chemical shift values.[13]
Results and Discussion
Syntheses: K[PPh2] (1) was prepared through deproton- phorus atom P(1) cover the wide range from 84.0(1)° for
ation of HPPh2 (2) with potassium metal in THF. BH3(H)- C(21)–P(1)–K(1A) to 150.1(1)° for K(1)–P(1)–K(1A). How-
PPh2 (4H) is accessible from HPPh2 (2) and B2H6.[14] How- ever, the angle defined by the two phenyl ipso-carbon atoms
ever, we preferred to use a calibrated solution of BH3·THF and the phosphorus atom is close to the ideal tetrahedral
in THF which is more convenient to handle. BBr3(H)PPh2 angle of 109.5° [C(21)–P(1)–C(31) = 107.1(1)°]. A largely
(4Br) was synthesised from HPPh2 (2) and BBr3 following two-coordinate phosphorus atom is found in the second
a published procedure.[14] BH3(CH3)PPh2 (5H) is formed [PPh2]– ion [shortest P(1A)···K contact: 5.918 Å]. Neverthe-
similar to BH3(H)PPh2 (4H) upon treatment of CH3PPh2 less, both the P–Ci bond lengths (Ci = ipso carbon atom of
(3) with BH3·THF in THF (Manners et al. have used a phenyl ring) and the Ci–P–CiЈ bond angles of the two
BH3·SMe2 instead[7]). An alternative route to 5H employs different PPh2 fragments are almost identical within experi-
ClPPh2 as starting material which is first methylated with mental error [C(21A)–P(1A)–C(31A) = 108.3(1)°; Table 1].
MeMgI and subsequently borylated with NaBH4/I2.[15] Two other adducts of K[PPh2] have previously been charac-
BBr3(CH3)PPh2 (5Br) was synthesised from CH3PPh2 (3) terised, the N,N,NЈ,NЈЈ,NЈЈ-pentamethyldiethylenetriamine
[20]
and BBr3 following a published procedure.[16] The phospho- complex {K(pmdta)[PPh2]}n
and the 1,4-dioxane com-
nium iodide salts [H2PPh2]I (6) and [CH3(H)PPh2]I (7) were plex {K(dioxane)2[PPh2]}n.[21] Most notably, Eaborn, Smith
Table 1. Key structural parameters of compounds 1c, 4Br, 5Br, 6, 7, 8, and 9c.
P–B
P–Ci
P–CH3
Ci–P–CiЈ
1c
K(18-c-6)[PPh2]
–
–
1.811(2)/1.815(2)[a]
1.807(2)/1.817(2)[b]
1.803(4)/1.805(4)
1.801(11)/1.810(10)
1.794(2)/1.798(2)
1.796(3)/1.797(3)
1.794(3)
–
–
–
107.1(1)[a]
108.3(1)[b]
110.8(2)
106.5(5)
109.6(1)
110.8(1)
107.6(2)
100.2(1)
4Br
5Br
6
BBr3(H)PPh2
BBr3(CH3)PPh2
[H2PPh2]I
[CH3(H)PPh2]I
[(CH3)2PPh2]I
K(18-c-6)[(BH3)2PPh2]
1.965(4)
1.976(9)
–
–
1.814(11)
–
1.798(3)
1.782(3)
–
7
8[18]
9c
–
1.930(2)/1.940(2)
1.829(2)/1.831(2)
[a] Coordinated [PPh2] unit. [b] Non-coordinated [PPh2] unit.
1778
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1777–1785

Phosphanylborohydrides: Assessment of the Relative Lewis Basicities of [BH3PPh2]–, CH3PPh2, and HPPh2
FULL PAPER
Figure 3. Molecular structure and numbering scheme of compound
9c; thermal ellipsoids shown at the 50% probability level. Selected
bond lengths [Å] and bond angles [°]: P(1)–B(1) = 1.930(2), P(1)–
B(2) = 1.940(2), P(1)–C(21) = 1.829(2), P(1)–C(31) = 1.831(2),
C(34)–K(1)# = 3.372(2), K(1)–H(1A) = 2.683, K(1)···H(1B) =
3.452, K(1)–H(1C) = 3.003, B(1)···K(1) = 3.205; B(1)–P(1)–B(2) =
116.3(1), C(21)–P(1)–C(31) = 100.2(1). Symmetry transformation
used to generate equivalent atoms: x, –y + 1/2, z – 1/2 (#).
Figure 2. Molecular structure and numbering scheme of compound
1c; thermal ellipsoids shown at the 50% probability level; hydrogen
atoms omitted for clarity. Selected bond lengths [Å] and bond
angles [°]: P(1)–C(21) = 1.815(2), P(1)–C(31) = 1.811(2), P(1A)–
C(21A)
= 1.817(2), P(1A)–C(31A) = 1.807(2), P(1)–K(1) =
K(1) distance in 9c amounts to 3.205 Å, it may be con-
cluded that [(BH3)2PPh2]– acts as bidentate ligand toward
the potassium cation which is the most common binding
mode in metal borohydrides.[24] Further short contacts be-
tween the phenyl carbon atom C(34) and the neighbouring
3.347(1), P(1)–K(1A) = 3.267(1), K(1A)···C(25A) = 3.518(2);
C(21)–P(1)–K(1A) = 84.0(1), K(1)–P(1)–K(1A) = 150.1(1), C(21)–
P(1)–C(31) = 107.1(1), C(21A)–P(1A)–C(31A) = 108.3(1).
et al.[22] have determined the crystal structure of solvent- potassium ion K(1)# [C(34)–K(1)# = 3.372(2) Å] stabilize
free {K[PPh2]}n which contains seven molecules in the the molecular packing as zig-zag chains in the crystal lattice
asymmetric unit.
(Figure 4).
ORTEP drawings of the molecular structures of the
Looking at the series of compounds 1c, 4Br, 5Br, 6, 7, 8,
boron–phosphorus adducts (BBr3)HPPh2 (4Br) and and 9c, it is our goal to find out whether differences in the
BBr3(CH3)PPh2 (5Br) as well as of the phosphonium salts electron-density distribution at phosphorus can be corre-
[H2PPh2]I (6), [CH3(H)PPh2]I (7), and [(CH3)2PPh2]I (8)[18,23] lated to systematic trends in the key structural parameters
can be found in the Supporting Information. In all these of these molecules (cf. Table 1). To this end we are consider-
compounds, the phosphorus atom is surrounded by four ing the P–Ci bond lengths and the Ci–P–CiЈ bond angles
substituents. Important bond lengths and angles for com- of the PPh2 fragments first. According to Bent’s rule,[26]
a
parison are listed in Table 1. In the case of 6 and 7, the tetracoordinate atom A directs hybrids of greater p charac-
iodide ions are part of a complex network of P–H···I and ter toward more electronegative substituents S and SЈ which
Ph–H···I hydrogen bridges.
in turn leads to smaller S–A–SЈ bond angles. In this con-
The phosphanylborohydride adduct K(18-crown-6)- text, lone pairs on atoms not involved in multiple bonds are
[(BH3)2PPh2] (9c) crystallises in the monoclinic space group in a first approximation viewed as residing in tetrahedral
P21/c (Figure 3).
hybrid orbitals. Deviations from perfect sp3 hybridisation
Each K+ ion is complexed by six oxygen atoms of a that occur are in a direction that concentrates s character
crown ether molecule and establishes two short and one sig- in the lone-pair orbitals. This effect normally becomes more
nificantly longer contact to the hydrogen atoms of one pronounced as the number of unshared electron pairs about
[BH3] fragment [K(1)–H(1A) = 2.683 Å, K(1)–H(1C) = the heavy atom increases.[26]
3.003 Å, K(1)···H(1B) = 3.452 Å]. Using Edelstein’s corre-
The K+-coordinated [PPh2]– ion of 1c shows a more
lation[24] of metal–boron distances as a measure of the acute Ci–P–CiЈ angle [107.1(1)°] than the free [PPh2]– ion
denticity of borohydride groups, values of 1.6 0.1 Å and [108.3(1)°], however, the actual difference of 1.2(1)° is very
1.36 0.06 Å are estimated for the ionic radii of bidentate small. One reason for this seeming violation of Bent’s rule
and tridentate borohydride ligands, respectively. Thus, B···K could be that the interaction of P(1) with the two potassium
distances of about 3.25 Å and 3.01 Å are to be expected ions is merely electrostatic in nature and thus has no pro-
for K-µ2-BH3R and K-µ3-BH3R coordination modes (ionic nounced effect on the orbital composition of the phospho-
radius of octacoordinated K+ = 1.65 Å[25]). Since the B(1)··· rus atom. In the case of the two BBr3 adducts 4Br and 5Br,
Eur. J. Inorg. Chem. 2006, 1777–1785
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1779

F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner
FULL PAPER
not interpolate that of the doubly protonated molecule 6
and the doubly methylated compound 8. By far the most
pronounced deviation of Ci–P–CiЈ from the ideal tetrahe-
dral angle is observed in the adduct K(18-crown-6)-
[(BH3)2PPh2] (9c). In line with Bent’s rule, the value of
100.2(1)°, as compared to 107.6(2)° in [(CH3)2PPh2]I (8),
points towards a high degree of p character in the P–Ci
bond orbitals of 9c. This interpretation is supported by the
fact that the corresponding P–Ci bond lengths are signifi-
cantly elongated [cf. 9c: 1.829(2) Å/1.831(2) Å; 8:
1.794(3) Å]. In contrast to a priori expectations, they are
even longer and the Ci–P–CiЈ angle is more acute than in
the potassium phosphide 1 [1.807(2) Å to 1.817(2) Å;
average value for Ci–P–CiЈ: 107.7°].
NMR Spectroscopy: The most characteristic NMR pa-
rameters of the compounds 1–9 are compiled in Table 2.
For comparability and solubility reasons, all NMR spec-
tra were run at ambient temperature (300 K). However, as
[H2PPh2]I (6) appeared to be largely dissociated in CDCl3
solution under these conditions, the compounds 6 and 7
have also been investigated at low temperature (233 K) in
order to shift the dissociation–association equilibrium to
the adduct side (low-temperature data included in Table 2).
In order to assess the relative degree of s and p character
in the P–E bonding orbitals (E = H, C, B), we will mainly
1
rely on the corresponding JPE coupling constants. Com-
mon wisdom has it that NMR coupling constants via a
certain bond are governed by the Fermi contact term,
which increases with increasing s character of the respective
bond. We are aware of the fact that 1JPE values may change
their sign upon going from one compound to another. In
Figure 4. Crystal packing diagram of compound 9c.
1
such cases, a correlation of JPE with the s character of the
P–E bond is not possible until the signs of the coupling
we find a significantly smaller Ci–P–CiЈ angle for the methyl constants are known. We have not determined any relative
derivative [4Br: 110.8(2)°, 5Br: 106.5(5)°]. Given the well- sign data, however, it is firmly established in the literature
1
known positive inductive effect of the CH3 substituent, this that JPB coupling constants in phosphane–boranes[27] as
1
indicates a higher p character in the P–Ph bonds of 5Br well as JPH coupling constants[28] are generally positive.
than in those of 4Br. Within the series 6 Ǟ 7 Ǟ 8, only 1JPC coupling constants tend to be negative in three-coordi-
small differences between the individual Ci–P–CiЈ angles are nate phosphanes (cf. PPh3: 1JPC = –12.5 Hz) and positive in
observed, which, moreover, do not follow a systematic trend compounds containing four-coordinate phosphorus centres
since the respective angle in the mixed compound 7 does (cf. [PPh4]+: 1JPC = +88.4 Hz).[28] For a detailed description
Table 2. Selected NMR parameters of compounds 1–9; solvents: THF (1–5Br, 9), CDCl3 (6–8); upfield shifts are denoted by a minus
sign and downfield shifts by a plus sign.
Chemical shift values [ppm] (1JPX [Hz])
Nucleus
31P
11B (1JPB
)
P–1H (1JPH
)
P–13Ci (1JPC
)
P–13CH3 (1JPC
)
1
K[PPh2]
HPPh2
CH3PPh2
–9.8
–
–
–
–
157.1 (56.0)
135.4 (10.7)
140.8 (10.0)
127.6 (56.2)
121.3 (65.7)
131.9 (54.8)
124.2 (68.2)
–
–
2
–39.5
–26.1
1.7
–13.6
11.5
5.11 (215.7)
–
6.16 (380.8)
6.97 (444.4)
3
12.9 (12.0)
–
–
4H
4Br
5H
5Br
6
BH3(H)PPh2
BBr3(H)PPh2
BH3(CH3)PPh2
BBr3(CH3)PPh2
[H2PPh2]I
[CH3(H)PPh2]I
[(CH3)2PPh2]I
K[(BH3)2PPh2]
–40.0 (42)
–17.1 (142)
–37.9 (55)
–14.6 (150)
–
–
–
–
–
11.4 (40.0)
7.1 (48.7)
–
–9.2
–31.0[a]
–5.2[a]
21.9
9.91 (530.6)[a]
128.0 (83.0)[a]
115.9 (85.4)[a]
120.5 (87.6)
140.2 (38.5)
7
9.87 (521.7)[a]
7.1 (53.8)[a]
11.4 (56.4)
–
8
–
–
9
–11.1
–34.6 (64)
[a] Recorded at 233 K.
1780
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1777–1785

Phosphanylborohydrides: Assessment of the Relative Lewis Basicities of [BH3PPh2]–, CH3PPh2, and HPPh2
FULL PAPER
of the effect of electron lone pairs on nuclear spin–spin CH3 for P–H results in a general deshielding of the respec-
coupling constants, the reader is referred to the work of Gil tive 31P nucleus. The isosteric couples 4H/7, 5H/8, and 8/9
and Philipsborn.[29]
deserve special attention. The 31P NMR resonance of H–
At first, we are considering systematic changes in the P(BH3)Ph2 (4H) is shifted by 6.9 ppm to lower field as com-
NMR parameters of the three Lewis bases HPPh2 (2), pared to the resonance of [H–P(CH3)Ph2]I (7). However,
CH3PPh2 (3), and [BH3PPh2]– upon variation of the coordi- this order is reversed and the absolute difference increases
nated acid. Drake et al. have determined the P–H proton (∆δ = –10.4) in the case of CH3–P(BH3)Ph2 (5H; δ = 11.5)
chemical shifts for five series of BX3–P(H)RRЈ adducts (R/ vs. [CH3–P(CH3)Ph2]I (8; δ = 21.9). Finally, the largest shift
RЈ = H/H, CD3/H, CD3/CD3, Ph/H, Ph/Ph; X = F, Cl, Br, difference (∆δ = –33.0) is found between K[BH3–P(BH3)-
I).[14] As a general trend within any of the five groups, the Ph2] (9; δ = –11.1) and [CH3–P(CH3)Ph2]I (8; δ = 21.9).
shielding of the proton on phosphorus was found to de-
11B NMR spectroscopy reveals a slight downfield shift
crease in a manner parallel to the accepted order of Lewis of the boron nucleus upon going from 4H (δ = –40.0) to
acidity (BF3 Ͻ BCl3 Ͻ BBr3 Ͻ BI3). Consistently, we ob- 5H (δ = –37.9) and 9 (δ = –34.6). A qualitatively similar
serve a downfield shift of the P–H resonance along the effect is observed for the couple 4Br/5Br (Table 2).
series P(H)Ph2 (2; δ = 5.11) Ǟ BH3–P(H)Ph2 (4H; δ = 6.16)
In the second stage, we will now consider three groups
Ǟ BBr3–P(H)Ph2 (4Br; δ = 6.97) Ǟ [CH3–P(H)Ph2]+ (7; δ of aggregates of the ligands P(H)Ph2 (2), P(CH3)Ph2 (3),
= 9.87) Ǟ [H–P(H)Ph2]+ (6; δ = 9.91). Parallel to that, 1JPH and [P(BH3)Ph2]– in which the Lewis acid is kept constant
becomes larger, thereby indicating an increasing degree of s (Figure 5). Special emphasis is placed on the 1JDA coupling
character in the P–H bond. Moreover, the absolute value of constants (D and A = donor and acceptor nuclei, respec-
1
the coupling constant JPCi between phosphorus and the tively) because they are a property of the donor–acceptor
ipso carbon atoms of the attached phenyl rings also in- bond in question and thus likely to provide insight into the
creases in the same order: 2 (10.7 Hz) Ͻ 4H (56.2 Hz) Ͻ relative base strengths of the three phosphorus donors. The
4Br (65.7 Hz) Ͻ 7 (85.4 Hz) Ϸ 6 (83.0 Hz). A similar trend proton adducts (series a, Figure 5) show similar 1JPH values
1
in the JPC values of the P–CH3 and the P–Ph fragments is for the P(H)Ph2 and P(CH3)Ph2 ligand and a much smaller
1
evident within the series of methylphosphane adducts: 3 Ͻ value in H–P(BH3)Ph2. The same is true for JPC in the
5H Ͻ 5Br Ͻ 7 Ͻ 8 (Table 2). Thus, there is obviously an [CH3]+ adducts of series b (Figure 5).
increase in s character in the P–H and P–C bonding orbitals
of 2 and 3 upon adduct formation. Concomitantly, an in-
crease in the p character of the phosphorus lone pair has
to be postulated as it becomes involved in dative bonding.
In line with the isovalent hybridisation hypothesis,[26] the p
character of the donor-acceptor bond is more pronounced
when more Lewis acidic electrophiles are coordinated. Of
special interest is an evaluation of the characteristic NMR
parameters of the isoelectronic donors P(CH3)Ph2 (3) and
[P(BH3)Ph2]– after coordination of [BH3], H+, and [CH3]+,
respectively. As far as the 31P–13Ci coupling constants are
concerned, we obtain qualitatively similar results for both
1
1
Figure 5. Systematic trends in the JDA and JPCi coupling con-
stants along three series of [P(BH3)Ph2]–, P(CH3)Ph2, and P(H)Ph2
adducts.
1
ligands with JPCi being consistently smaller in the [BH3]
adducts as compared to the protonated or methylated deriv-
atives {cf. K[BH3–P(BH3)Ph2] (9), H–P(BH3)Ph2 (4H),
1
CH3–P(BH3)Ph2 (5H): JPCi = 38.5 Hz, 56.2 Hz, 54.8 Hz;
Thus, compared to the neutral phosphane ligands,
BH3–P(CH3)Ph2 (5H), [H–P(CH3)Ph2]I (7), [CH3–P(CH3)- [P(BH3)Ph2]– is able to provide an electron pair of higher
Ph2]I (8): JPCi = 54.8 Hz, 85.4 Hz, 87.6 Hz}.
1
p character such that the charge density is more strongly
The 31P NMR resonances within the series P(H)Ph2 (2), polarized in the direction of the acceptor orbital. This in-
BH3–P(H)Ph2 (4H), BBr3–P(H)Ph2 (4Br), and [CH3–P(H)- terpretation most likely holds also for the [BH3] adducts of
Ph2]I (7) possess chemical shift values of δ = –39.5 ppm, series c (Figure 5) even though 31P–11B coupling via the
1.7 ppm, –13.6 ppm, and –5.2 ppm, respectively (Table 2). dative bond is now larger in K[BH3–P(BH3)Ph2] (9) and
This observation is in agreement with the known fact that smaller in BH3–P(H)Ph2 (4H), and BH3–P(CH3)Ph2 (5H).
in most cases quaternisation of phosphanes leads to a Here, the decisive factor is the rehybridisation of [BH3] as
downfield shift of the 31P NMR signal as the shielding ef- it moves from a planar sp2 configuration to a tetrahedral
fect of the lone pair is removed.[13] Deshielding is most pro- sp3 arrangement. As a consequence, we are facing two op-
nounced after coordination of the isoelectronic and iso- posing trends:[14] When phosphane forms an adduct, the
steric Lewis acids [BH3] and [CH3]+. Adduct formation of phosphorus orbital involved in bond formation decreases
P(H)Ph2 with BBr3 leads to a smaller downfield shift. in s character. On the other hand, the stronger the donor-
Within the series of P(CH3)Ph2 adducts, the following 31P acceptor interaction, the more pyramidalized the coordi-
NMR shifts are observed (Table 2): 3 (δ = –26.1), 5H (δ = nated borane which in turn results in more B(2s) character
11.5), 5Br (δ = –9.2), 8 (δ = 21.9). Thus, substitution of P– being diverted into the P–B bond. Despite of the fact that
Eur. J. Inorg. Chem. 2006, 1777–1785
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1781

F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner
FULL PAPER
signal not observed, i = ipso, o = ortho, m = meta, p = para. Ele-
mental analyses were performed by the microanalytical laboratory
of the J. W. Goethe University, Frankfurt/Main, Germany.
a quantitative assessment of these two competing factors
is obviously difficult, an empirical correlation between the
magnitude of 1JPB and dative bond strength became evident
from several studies on [BH3] adducts of selected series em-
ploying smoothly varying phosphane ligands.[14,30–32] Based
Materials: Lithium and potassium metal, PPh3, CH3PPh2 (3),
BH3·THF solution (1 mol/ L in THF) and 18-crown-6 were pur-
chased from Aldrich or Fluka and used as received. HPPh2 (2) was
obtained through reductive cleavage of triphenylphosphane with
lithium powder in THF and subsequent hydrolysis and distillation
as described by Bianco and Doronzo.[35]
1
on the development of JPB coupling constants along the
sequence 4H (42 Hz), 5H (55 Hz), and 9 (64 Hz) we there-
fore confidently assign the highest Lewis basicity to the
phosphanylborohydride ligand [P(BH3)Ph2]– (note that for
1
Synthesis of K[PPh2] (1): The compound was obtained through de-
protonation of HPPh2 (2; 320 mg, 1.72 mmol) with potassium me-
tal (120 mg, 3.07 mmol) in THF (5 mL). The resulting orange solu-
tion was decanted from excess potassium and directly used for the
NMR measurements. X-ray quality crystals of 1·18-crown-6 (1c)
were grown by gas-phase diffusion of diethyl ether into a THF
solution containing K[PPh2] and an equimolar amount of 18-
crown-6. 1H NMR (THF, 250.13 MHz): δ = 6.42 (tr, 3JHH = 7.2 Hz,
Li[(BH3)2P(CH3)2] a coupling constant JPB = 107 Hz has
1
been published,[33] which is even larger than JPB of 9).
To test this hypothesis, two displacement experiments
have been carried out and monitored by 31P NMR spec-
troscopy. First, we investigated an equimolar mixture of
K[(BH3)2PPh2] (9) and CH3PPh2 (3) in THF. Even after
prolonged storage of the NMR vessel at ambient tempera-
ture, no transfer of [BH3] with formation of K[BH3PPh2]
and BH3(CH3)PPh2 (5H) was observable. The result re-
mained the same at higher temperatures. In contrast, be-
tween BH3(CH3)PPh2 (5H) and K[BH3PPh2] a reaction to
CH3PPh2 (3) and K[(BH3)2PPh2] (9) takes place already at
ambient temperature (ca. 10% conversion after 2 d). Heat-
ing of the sample to a temperature of 50 °C for 2 h leads to
ca. 50% conversion.
3
2 H, H-p), 6.73 (vtr, JHH = 7.5 Hz, 4 H, H-m) 7.40–7.49 (m, 4 H,
H-o) ppm. 13C{1H} NMR (THF, 62.90 MHz): δ = 118.6 (br., C-
3
2
p), 127.5 (d, JPC = 5.5 Hz, C-m), 129.2 (d, JPC = 18.6 Hz, C-o),
1
157.1 (br. d, JPC
=
56.0 Hz, C-i) ppm. 31P NMR (THF,
161.98 MHz): δ = –9.8 (s) ppm.
Synthesis of BH3(H)PPh2 (4H): To a solution of HPPh2 (2.53 g,
13.5 mmol) in THF (10 mL) was added a calibrated solution
(1 mol/ L) of BH3·THF in THF (13.5 mL, 13.5 mmol) at –78 °C
with stirring. After the mixture had been warmed to ambient tem-
perature overnight, all volatiles were removed in vacuo. The re-
sulting oily residue was purified by column-chromatography (50 g
silica-gel; eluent: hexane/toluene, 1:1). After evaporation of the elu-
ate, the resulting oil of 4H was triturated with pentane whereupon
it solidified to give a colourless waxy material. Yield: 2.29 g (85%).
Conclusion
Based on NMR spectroscopy (1JPB values) and displace-
ment experiments we come to the conclusion that the phos-
phanylborohydride ligand [BH3PPh2]– possesses a higher
Lewis basicity towards [BH3] than its neutral isoelectronic
and isostructural congener P(CH3)Ph2. Moreover, NMR
1
1H NMR (THF, 400.13 MHz): δ = 1.15 (q, JBH = 100 Hz, 3 H,
1
3
BH3), 6.16 (dq, JPH = 380.8 Hz, JHH = 7.1 Hz, 1 H, PH), 7.19–
7.30 (m, 6 H, H-m,p), 7.51–7.65 (m, 4 H, H-o) ppm. 11B NMR
1
1
(THF, 128.38 MHz): δ = –40.0 (dq, JPB = 42 Hz, JBH = 100 Hz)
spectroscopy (1JPB, JPH, and JPCi values) and X-ray crys- ppm. 13C{1H} NMR (THF, 62.90 MHz): δ = 127.6 (d, JPC
=
=
1
1
1
3
4
56.2 Hz, C-i), 129.3 (d, JPC = 10.1 Hz, C-m), 131.8 (d, JPC
tallography (Ci–P–CiЈ angles; Ci = ipso carbon atom of the
phenyl ring) on selected adducts of the ligands HPPh2,
CH3PPh2, and [BH3PPh2]– indicate [BH3PPh2]– to form
dative bonds of the highest p character within this series.
Consequently, [BH3PPh2]– is best suited to direct the charge
density of its electron lone pair in the direction of the ac-
ceptor orbital of a coordinated Lewis acid.
2.5 Hz, C-p) 133.3 (d, JPC = 9.3 Hz, C-o) ppm. 31P{1H} NMR
2
(THF, 161.98 MHz): δ = 1.7 (m) ppm.
Synthesis of BBr3(H)PPh2 (4Br): The compound was synthesised
from BBr3 (320 mg, 1.28 mmol) and HPPh2 (230 mg, 1.24 mmol)
in hexane (5 mL) as described in the literature.[14] Yield: 489 mg
(92%). X-ray-quality crystals were grown by gas-phase diffusion of
pentane into a solution of 4Br in toluene. Since the compound is
not stable in THF for extended periods of time, NMR measure-
ments have to be carried out immediately after sample preparation.
C12H11BBr3P (436.72): calcd. C 33.00, H 2.54; found: C 33.15, H
Experimental Section
1
1
2.50. H NMR (THF, 400.13 MHz): δ = 6.97 (d, JPH = 444.4 Hz,
1 H, PH), 7.31–7.39 (m, 4 H, H-m), 7.43–7.48 (m, 2 H, H-p), 7.76–
7.84 (m, 4 H, H-o) ppm. 11B NMR (THF, 128.38 MHz): δ = –17.1
General Considerations: All reactions and manipulations of air-sen-
sitive compounds were carried out under dry nitrogen using stan-
dard Schlenk techniques. Solvents were freshly distilled under ar-
gon from sodium/benzophenone (THF, diethyl ether, toluene) or
sodium-lead alloy (pentane, hexane) prior to use. NMR spectra
were recorded with Bruker AMX 250 or AMX 400 spectrometers.
Approximately 0.1 mL of C6D6 was added to all samples recorded
in undeuterated THF (0.6 mL) to provide a lock signal. 1H- and
13C NMR shifts are reported relative to tetramethylsilane and were
referenced against residual solvent peaks (C6D5H: δ = 7.16, C6D6:
δ = 128.06; CHCl3: δ = 7.26, CDCl3: δ = 77.16 ppm).[34] 11B NMR
spectra were referenced against external BF3·OEt2. 31P NMR spec-
tra are reported relative to external H3PO4 (85%). Abbreviations:
s = singlet, d = doublet, tr = triplet, vtr = virtual triplet, q = quar-
tet, dq = doublet of quartets, m = multiplet, br. = broad, n.o. =
(d, JPB = 142 Hz) ppm. 13C{1H} NMR (THF, 100.62 MHz): δ =
121.3 (d, JPC = 65.7 Hz, C-i), 129.7 (d, JPC = 11.7 Hz, C-m),
1
1
3
4
2
133.4 (d, JPC = 2.8 Hz, C-p), 134.6 (d, JPC = 8.2 Hz, C-o) ppm.
31P{1H} NMR (THF, 161.98 MHz): δ = –13.6 (q, JPB = 142 Hz)
1
ppm.
Synthesis of BH3(CH3)PPh2 (5H): To a solution of CH3PPh2
(270 mg, 1.35 mmol) in THF (2 mL) was added a calibrated solu-
tion (1 mol/ L) of BH3·THF in THF (1.3 mL, 1.3 mmol) at –78 °C
with stirring. After the mixture had been warmed to ambient tem-
perature overnight, all volatiles were removed in vacuo. 5H was
obtained in essentially quantitative yield as a colourless oil. 1H
2
NMR (THF, 250.13 MHz): δ = 1.03 (q, 3 H, BH3), 1.66 (d, JPH
1782
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1777–1785

Phosphanylborohydrides: Assessment of the Relative Lewis Basicities of [BH3PPh2]–, CH3PPh2, and HPPh2
FULL PAPER
= 10.0 Hz, 3 H, CH3), 7.18–7.31 (m, 6 H, H-m,p), 7.51–7.63 (m, 4
(90%). X-ray quality crystals were grown by gas-phase diffusion of
pentane into a solution of 5Br in toluene. C13H13BBr3P (450.74):
calcd. C 34.64, H 2.91; found: C 34.41, H 2.79. 1H NMR (THF,
1
H, H-o) ppm. 11B NMR (THF, 128.38 MHz): δ = –37.9 (dq, JPB
1
= 55 Hz, JBH = 99 Hz) ppm. 13C{1H} NMR (THF, 62.90 MHz):
1
3
2
δ = 11.4 (d, JPC = 40.0 Hz, CH3), 129.0 (d, JPC = 9.8 Hz, C-m),
400.13 MHz): δ = 2.11 (d, JPH = 11.9 Hz, 3 H, CH3), 7.28–7.34
4
1
131.2 (d, JPC = 2.4 Hz, C-p), 131.9 (d, JPC = 54.8 Hz, C-i), 132.2
(m, 4 H, H-m), 7.39–7.44, (m, 2 H, H-p), 7.74–7.80 (m, 4 H, H-o)
(d, JPC = 9.6 Hz, C-o) ppm. 31P{1H} NMR (THF, 161.98 MHz):
2
1
ppm. 11B NMR (THF, 128.38 MHz): δ = –14.6 (d, JPB = 150 Hz)
1
ppm. 13C{1H} NMR (THF, 100.62 MHz): δ = 7.1 (d, JPC
=
=
=
δ = 11.5 (m) ppm.
1
3
48.7 Hz, CH3), 124.2 (d, JPC = 68.2 Hz, C-i), 129.2 (d, JPC
4
2
Synthesis of BBr3(CH3)PPh2 (5Br): The compound was synthesised
from CH3PPh2 (235 mg, 1.17 mmol) and BBr3 (302 mg, 1.21 mmol)
in hexane (5 mL) following a published procedure.[16] Yield: 487 mg
10.9 Hz, C-m), 132.9 (d, JPC = 2.7 Hz, C-p), 134.3 (d, JPC
8.1 Hz, C-o) ppm. 31P{1H} NMR (THF, 161.98 MHz): δ = –9.2 (q,
1JPB = 150 Hz) ppm.
Table 3. Crystallographic data for compounds 1c, 4Br, 5Br, 6, 7, and 9c.
1c
4Br
5Br
Formula
Fw
C24H34KO6P
488.58
C12H11BBr3P
436.72
C13H13BBr3P
450.74
Colour, shape
Temperature [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
orange, block
173(2)
monoclinic
P21/n
10.5151(7)
14.8018(7)
32.593(2)
90
colourless, plate
173(2)
orthorhombic
Pbca
10.2401(3)
8.7189(3)
32.686(2)
90
colourless, block
173(2)
monoclinic
C2/c
32.935(5)
7.074(1)
13.842(2)
90
α [°]
β [°]
96.286(5)
90
5042.4(5)
8
1.287
2080
90
90
2918.3(2)
8
1.988
1664
8.378
100.25(1)
90
3173.4(8)
8
1.887
1728
γ [°]
V [Å3]
Z
Dcalcd. [g cm–3]
F(000)
µ [mm–1]
0.310
7.708
Crystal size [mm]
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
GOOF on F2
R1, wR2 [I Ͼ 2σ(I)]
R1, wR2 (all data)
0.49×0.46×0.42
20677
9044 (0.0392)
9044/0/577
0.981
0.0423, 0.1043
0.0599, 0.1122
0.688 and –0.404
0.28× 0.26×0.13
46394
3151 (0.0887)
3151/0/159
1.077
0.0391, 0.1046
0.0419, 0.1073
0.951 and –0.643
0.28×0.26×0.24
8766
2800 (0.1247)
2800/0/163
1.102
0.0839, 0.2000
0.0981, 0.2116
1.345 and –2.047
)
Largest diff. peak and hole [e·Å–3]
6
7
9c
Formula
Fw
Colour, shape
Temperature [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C12H12IP
314.09
colourless, block
173(2)
monoclinic
P21/c
8.8460(5)
14.3281(9)
9.8352(6)
90
C13H14IP
328.11
colourless, block
173(2)
orthorhombic
Pbca
16.2294(7)
9.6942(3)
17.1034(6)
90
C24H40B2KO6P
516.25
colourless, block
173(2)
monoclinic
P21/c
8.4076(10)
19.714(2)
16.867(2)
90
β [°]
99.437(5)
90
1229.7(1)
4
1.697
608
2.695
0.37×0.33×0.25
19524
90
90
2690.9(2)
8
1.620
1280
2.467
0.27×0.25×0.24
57301
96.674(10)
90
2776.7(6)
4
1.235
1104
0.284
0.48× 0.46×0.43
11881
γ [°]
V [Å3]
Z
Dcalcd. [g cm–3]
F(000)
µ [mm–1]
Crystal size [mm]
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
GOOF on F2
)
2229 (0.0363)
2229/0/136
1.087
0.0161, 0.0389
0.0175, 0.0395
0.289 and –0.439
3902 (0.0384)
3902/0/141
1.298
0.0297, 0.0706
0.0312, 0.0724
0.493 and –0.560
5347 (0.0739)
5347/0/309
0.871
0.0404, 0.0950
0.0549, 0.0982
0.611 and –0.460
R1, wR2 [I Ͼ 2σ(I)]
R1, wR2 (all data)
Largest diff. peak and hole [e·Å–3]
Eur. J. Inorg. Chem. 2006, 1777–1785
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1783

F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner
FULL PAPER
1
Synthesis of [H2PPh2]I (6): For the synthesis of 6, HPPh2 (322 mg,
1.73 mmol) was treated with excess HI in toluene (3 mL) at –78 °C.
Yield: 429 mg (80%). Crystals suitable for X-ray crystallography
formed when a concentrated CHCl3 solution of 6 was slowly cooled
to –30 °C. C12H12IP (314.09): calcd. C 45.89, H 3.85; found: C
46.16, H 3.83. 1H NMR (CDCl3, 250.13 MHz, 300 K): δ = 5.8
(very br., 2 H, PH2), 7.41–7.56 (m, 6 H, H-m,p), 7.73–7.84 (m, 4
11B{1H} NMR (THF, 128.38 MHz): δ = –34.6 (d, JPB = 64 Hz,
3
BH3) ppm. 13C{1H} NMR (THF, 62.90 MHz): 127.4 (d, JPC
=
8.2 Hz, C-m), 127.9 (d, 4JPC = 2.0 Hz, C-p), 133.4 (d, 2JPC = 7.7 Hz,
C-o), 140.2 (d, JPC = 38.5 Hz, C-i) ppm. 31P NMR (THF,
1
161.98 MHz): δ = –11.1 (m) ppm.
X-ray Structural Characterisation: Data collections were performed
on a Stoe IPDS-II two-circle diffractometer with graphite-mono-
chromated Mo-Kα radiation. Empirical absorption corrections with
the MULABS option[37] in the program PLATON[38] were per-
formed. Equivalent reflections were averaged. The structures were
solved by direct methods[39] and refined with full-matrix least-
squares on F2 using the program SHELXL-97.[40] Hydrogen atoms
bonded to carbon and boron were placed on ideal positions and
refined with fixed isotropic displacement parameters using a riding
model. H atoms bonded to phosphorus were refined isotropically.
Details of the X-ray crystal structure analyses of 1c, 4Br, 5Br, 6, 7,
and 9c are summarised in Table 3.
CCDC-290838 (for 1c), -290839 (for 4Br), -290840 (for 5Br),
-290841 (for 6), -290842 (for 7), and -290843 (for 9c) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
1
H, H-o) ppm. H NMR (CDCl3, 250.13 MHz, 233 K): δ = 7.45–
7.85 (m, 6 H, H-m,p), 7.94–8.15 (m, 4 H, H-o), 9.91 (br. d, 2 H,
PH2) ppm. 13C{1H} NMR (CDCl3, 62.90 MHz, 300 K): broad, po-
orly resolved signals. 13C{1H} NMR (CDCl3, 62.90 MHz, 233 K):
1
3
128.0 (d, JPC = 83.0 Hz, C-i), 129.2 (d, JPC = 13.2 Hz, C-m),
2
4
131.1 (d, JPC = 11.8 Hz, C-o), 133.4 (d, JPC = 1.6 Hz C-p) ppm.
31P{1H} NMR (CDCl3, 161.98 MHz, 300 K): δ = –34.2 (br. s) ppm.
31P{1H} NMR (CDCl3, 161.98 MHz, 233 K): δ = –31.0 (tr, 1JPH
=
530.6 Hz) ppm.
Synthesis of [CH3(H)PPh2]I (7): Following a published pro-
cedure,[17] CH3PPh2 (336 mg, 1.68 mmol) was treated with excess
HI in toluene (3 mL) at –78 °C. Yield: 385 mg (70%). Crystals suit-
able for X-ray crystallography formed when a concentrated CHCl3
solution of 7 was slowly cooled to –30 °C. C13H14IP (328.11): calcd.
C 47.59, H 4.30; found: C 47.82, H 4.53. 1H NMR (CDCl3,
250.13 MHz, 300 K): δ = 2.58 (d, 2JPH = 14.7 Hz, 3 H, CH3), 7.51–
7.61 (m, 4 H, H-m), 7.64–7.73 (m, 2 H, H-p), 7.91–8.03 (m, 4 H,
Supporting Information (for details see the footnote on the first
page of this article): ORTEP drawings of 4Br, 5Br, 6, 7, and 8.
1
1
H-o), 10.1 (d, JPH = 521.7 Hz, 1 H, PH) ppm. H NMR (CDCl3,
250.13 MHz, 233 K): δ = 2.57 (dd, 2JPH = 14.6 Hz, 3JHH = 5.7 Hz,
3 H, CH3), 7.47–8.01 (m, 10 H, H-o/m/p), 9.87 (d, 1JPH = 521.7 Hz,
1 H, PH) ppm. 13C{1H} NMR (CDCl3, 62.90 MHz, 300 K): δ =
Acknowledgments
1
1
7.7 (d, JPC = 54.1 Hz, CH3), 116.8 (d, JPC = 84.9 Hz, C-i), 130.3
The authors are grateful to the Deutsche Forschungsgemeinschaft
(DFG) and the Fonds der Chemischen Industrie (FCI) for financial
support.
3
2
(d, JPC = 13.2 Hz, C-m), 133.3 (d, JPC = 10.9 Hz, C-o), 135.1
4
(d, JPC = 3.1 Hz, C-p) ppm. 13C{1H} NMR (CDCl3, 62.90 MHz,
233 K): δ = 7.1 (d, 1JPC = 53.8 Hz, CH3), 115.9 (d, 1JPC = 85.4 Hz,
3
2
C-i), 130.2 (d, JPC = 13.1 Hz, C-m), 133.0 (d, JPC = 10.8 Hz,
C-o), 135.1 (br., C-p) ppm. 31P{1H} NMR (CDCl3, 161.98 MHz,
300 K): δ = –4.7 (s) ppm. 31P{1H} NMR (CDCl3, 161.98 MHz,
233 K): δ = –5.2 (s) ppm.
[1] L. H. Gade, Koordinationschemie, Wiley-VCH, Weinheim,
1998.
[2] C. T. Goralski, B. Singaram, C. J. Collins, J. R. Cuzens, M.
Lanz, in: ACS Symposium Series, vol. 783 (Eds.: P. V. Ramach-
andran, H. C. Brown), American Chemical Society, Washing-
ton, DC, 2001, pp. 18–32.
[3] J.-M. Camus, J. Andrieu, P. Richard, R. Poli, C. Darcel, S.
Jugé, Tetrahedron: Asymmetry 2004, 15, 2061–2065.
[4] B. Wolfe, T. Livinghouse, J. Org. Chem. 2001, 66, 1514–1516.
[5] T. Miura, H. Yamada, S. Kikuchi, T. Imamoto, J. Org. Chem.
2000, 65, 1877–1880.
[6] B. Wolfe, T. Livinghouse, J. Am. Chem. Soc. 1998, 120, 5116–
5117.
Synthesis of [(CH3)2PPh2]I (8): The compound was synthesised fol-
lowing a published procedure[36] via the reaction of HPPh2
(204 mg, 1.10 mmol) with ICH3 (217 mg, 1.53 mmol) in THF
(4 mL). Yield: 353 mg (94%). Crystals suitable for X-ray crystal-
lography formed when a concentrated CHCl3 solution of 8 was
slowly cooled to –30 °C. C14H16IP (342.15): calcd. C 49.15, H 4.71;
1
found: C 48.92, H 4.58. H NMR (CDCl3, 250.13 MHz): δ = 2.88
2
(d, JPH = 13.9 Hz, 3 H, CH3), 7.60–7.79 (m, 6 H, H-m,p), 7.83–
[7] C. A. Jaska, A. J. Lough, I. Manners, Inorg. Chem. 2004, 43,
7.95 (m, 4 H, H-o) ppm. 13C{1H} NMR (CDCl3, 62.90 MHz): δ =
11.4 (d, 1JPC = 56.4 Hz, CH3), 120.5 (d, 1JPC = 87.6 Hz, C-i), 130.3
1090–1099.
[8] H. Dorn, C. A. Jaska, R. A. Singh, A. J. Lough, I. Manners,
Chem. Commun. 2000, 1041–1042.
[9] A.-C. Gaumont, M. B. Hursthouse, S. J. Coles, J. M. Brown,
Chem. Commun. 1999, 63–64.
[10] W. Angerer, W. S. Sheldrick, W. Malisch, Chem. Ber. 1985, 118,
3
2
(d, JPC = 12.8 Hz, C-m), 132.3 (d, JPC = 10.7 Hz, C-o), 135.0 (d,
4JPC = 3.0 Hz, C-p) ppm. 31P{1H} NMR (CDCl3, 161.98 MHz): δ
= 21.9 (s) ppm.
Synthesis of K[(BH3)2PPh2] (9): To
a
solution of
1261–1266.
435 mg K[BH3PPh2] (1.82 mmol) in THF (5 mL) was added a cal-
ibrated solution (1 mol/ L) of BH3·THF (1.8 mL, 1.8 mol) at
–78 °C with stirring. After 30 min, the cooling bath was removed
and the reaction mixture warmed to ambient temperature with sub-
sequent stirring for another 60 min. All volatiles were removed in
vacuo and the resulting colourless solid was washed twice with pen-
tane (2 mL). Yield: 423 mg (92%). X-ray quality crystals were
grown by gas-phase diffusion of diethyl ether onto a solution con-
taining K[(BH3)2PPh2] and an equimolar amount of 18-crown-6.
C24H40B2KO6P (516.25): calcd. C 55.84, H 7.81; found C 55.38, H
[11] G. Müller, J. Brand, Organometallics 2003, 22, 1463–1467.
[12] D. A. Hoic, W. M. Davis, G. C. Fu, J. Am. Chem. Soc. 1996,
118, 8176–8177.
[13] L. D. Quin, A Guide to Organophosphorus Chemistry, John
Wiley & Sons, Inc., New York, 2000.
[14] B. Rapp, J. E. Drake, Inorg. Chem. 1973, 12, 2868–2873.
[15] M. A. Mathur, W. H. Myers, H. H. Sisler, G. E. Ryschkewitsch,
Inorg. Synth. 1974, 15, 128–133.
[16] M. L. Denniston, D. R. Martin, J. Inorg. Nucl. Chem. 1974, 36,
1461–1464.
[17] S. O. Grim, W. McFarlan, Can. J. Chem. 1968, 46, 2071–2074.
[18] F. Dornhaus, H.-W. Lerner, M. Bolte, Acta Crystallogr., Sect.
E 2005, 61, o1657–o1658.
1
7.63. 1H NMR (THF, 250.13 MHz): δ = 1.0 (q, JBH = 89 Hz, 6
H, BH3), 7.00–7.10 (m, 6 H, H-m,p), 7.74–7.85 (m, 4 H, H-o) ppm.
1784
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1777–1785

Phosphanylborohydrides: Assessment of the Relative Lewis Basicities of [BH3PPh2]–, CH3PPh2, and HPPh2
FULL PAPER
[19] A. F. Holleman, N. Wiberg, Lehrbuch der Anorganischen
Chemie, 101 ed., de Gruyter, Berlin, New York, 1995.
[20] K. Izod, W. McFarlane, B. V. Tyson, W. Clegg, R. W. Harring-
ton, S. T. Liddle, Organometallics 2003, 22, 3684–3690.
[21] O. Kühl, J. Sieler, E. Hey-Hawkins, Z. Kristallogr. 1999, 214,
496–499.
[22] A. G. Avent, D. Bonafoux, C. Eaborn, M. S. Hill, P. B. Hitch-
cock, J. D. Smith, J. Chem. Soc. Dalton Trans. 2000, 2183–
2190.
[29] V. M. S. Gil, W. von Philipsborn, Magn. Res. Chem. 1989, 27,
409–430.
[30] A. H. Cowley, M. C. Damasco, J. Am. Chem. Soc. 1971, 93,
6815–6821.
[31] R. W. Rudolph, C. W. Schultz, J. Am. Chem. Soc. 1971, 93,
6821–6822.
[32] R. Foester, K. Cohn, Inorg. Chem. 1972, 11, 2590–2593.
[33] L. D. Schwartz, P. C. Keller, Inorg. Chem. 1971, 10, 645–647.
[34] H. E. Gottlieb, V. Kotlyar, A. Nudelman, J. Org. Chem. 1997,
62, 7512–7515.
[35] V. D. Bianco, S. Doronzo, Inorg. Synth. 1976, 16, 161–163.
[36] H. J. Cristau, Y. Ribeill, Synthesis 1988, 11, 911–912.
[37] R. H. Blessing, Acta Crystallogr., Sect. A 1995, 51, 33–38.
[38] A. L. Spek, Acta Crystallogr., Sect. A 1990, 46, C34.
[39] G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467–473.
[40] G. M. Sheldrick, SHELXL-97. A Program for the Refinement
of Crystal Structures, University of Göttingen, 1997.
Received: December 20, 2005
[23] R. J. Staples, T. Carlson, S. Wang, J. P. Fackler Jr, Acta Crys-
tallogr., Sect. C 1995, 51, 498–500.
[24] N. Edelstein, Inorg. Chem. 1981, 20, 297–299.
[25] R. D. Shannon, Acta Crystallogr., Sect. A 1976, 32, 751–767.
[26] H. A. Bent, Chem. Rev. 1961, 61, 275–311.
[27] H. Nöth, B. Wrackmeyer, in: NMR Basic Principles and Pro-
gress. (Eds.: P. Diehl, E. Fluck, R. Kosfeld), vol. 14: Nuclear
Magnetic Resonance Spectroscopy of Boron Compounds,
Springer, Berlin, 1978.
[28] S. Berger, S. Braun, H.-O. Kalinowski, NMR-Spektroskopie von
Nichtmetallen; Band 3; 31P-NMR-Spektroskopie, Thieme,
Stuttgart, 1993.
Published Online: March 22, 2006
Eur. J. Inorg. Chem. 2006, 1777–1785
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1785