Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl complexes of N-B-PTA(BH3): X-ray crystal structures of [Cp*RhCl2{N-B}-PTA(BH3)] and [Cp*Rh{N-B-PTA(BH3)}(η2-CH2 = CHPh)]

Article abstract of DOI:10.1016/j.jorganchem.2008.04.006

The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N-B-PTA(BH₃) and [Cp^*RhCl(μ-Cl)]₂ affords [Cp^*Rh{N-B-PTA(BH₃)}Cl₂] (3) or [Cp_*Rh{N-B-PTA(BH₃)}₂Cl]Cl (5) containing one or two P-bonded boronated PTA ligands. The hydride [Cp_*Rh{N-B-PTA(BH₃)}H₂] (8) was also obtained by reaction of 3 with NaBH₄ and alternatively by direct hydroboration of [Cp^*Rh(PTA)Cl₂] with excess NaBH₄. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen, H₃BO₃ and the corresponding PTA derivatives, including the water-soluble dihydride [Cp^*Rh(PTA)H₂] (9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp^*Rh{N-B-PTA(BH₃)}(η²-CH₂ = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers η²-coordinated to rhodium without affecting the N-BH₃ moiety. The X-ray crystal structures of 3 and 10 were also obtained and are here discussed.

Full text of DOI:10.1016/j.jorganchem.2008.04.006

Journal of Organometallic Chemistry 693 (2008) 2397–2406
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and reactivity of rhodium(III) pentamethylcyclopentadienyl
complexes of N–B–PTA(BH3): X-ray crystal structures of
[Cp*RhCl2{N–B–PTA(BH3)}] and [Cp*Rh{N–B–PTA(BH3)}(g2-CH2 = CHPh)]
b,
a
c
c
b
Sandra Bolaño a, , Alberto Albinati , Jorge Bravo , Maria Caporali , Luca Gonsalvi , Louise Male ,
*
*
M.a Mar Rodríguez-Rocha a, Andrea Rossin c, Maurizio Peruzzini c,
*
a Departamento de Quimica Inorganica, Facultade de Quimica, Universidade de Vigo, Campus Universitario, E-36310 Vigo, Spain
b Department of Structural Chemistry (DCSSI) and School of Pharmacy, University of Milan, 21, via G. Venezian I – 20133 Milan, Italy
c Istituto di Chimica del Composti Organometallici, Consiglio Nazionale delle Ricerche (ICCOM–CNR), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Florence, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction between 1-boranyl-1,3,5-triaza-7-phosphaadamantane ligand N–B–PTA(BH3) and
[Cp*RhCl(l-Cl)]2 affords [Cp*Rh{N–B–PTA(BH3)}Cl2] (3) or [Cp*Rh{N–B–PTA(BH3)}2Cl]Cl (5) containing
one or two P-bonded boronated PTA ligands. The hydride [Cp*Rh{N–B–PTA(BH3)}H2] (8) was also
obtained by reaction of 3 with NaBH4 and alternatively by direct hydroboration of [Cp*Rh(PTA)Cl2] with
excess NaBH4. Moderately slow hydrolysis of the N-boranyl rhodium complexes affords dihydrogen,
H3BO3 and the corresponding PTA derivatives, including the water-soluble dihydride [Cp*Rh(PTA)H2]
(9). Finally, the reaction of 8 with electron poor alkynes gives the alkene complexes [Cp*Rh{N–B–
PTA(BH3)}(g2-CH2 = CHR)] (R = Ph, 10; C(O)OEt, 11) as a mixture of rotamers g2-coordinated to rhodium
without affecting the N–BH3 moiety. The X-ray crystal structures of 3 and 10 were also obtained and are
here discussed.
Received 3 March 2008
Received in revised form 2 April 2008
Accepted 2 April 2008
Available online 10 April 2008
Keywords:
Water-soluble complexes
Rhodium
Hydrides
Boranyl phosphines
X-ray crystallography
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
remarkable binding activity towards both DNA and proteins show-
ing cytotoxicity towards selected tumour cells. More recently, re-
Water-soluble phosphines are among the preferred ligands
used to impart solubility in water to transition metal complexes
[1] and a variety of monodentate and polydentate hydrosoluble
phosphines have been used over the years to generate homoge-
neous catalysts for applications to processes in water or biphasic
water/organic solvent conditions [2].
Among monodentate phosphines, a special role is played by the
neutral cage-like ligand 1,3,5-triaza-7-phosphaadamantane (PTA)
(I) originally synthesised by Daigle et al. in 1974 [3] and used in
the following three decades to prepare an assortment of water-sol-
uble transition metal complexes to be used as homogeneous aque-
ous phase catalysts and as luminescent materials when
coordinated to gold precursors [4].
During the last few years a renewed interest for PTA and its
chemistry has been stimulated by the increasing attention to
chemical sustainable processes aimed at minimizing waste and
environmental impact [5], and by the recent findings that transi-
tion metal PTA complexes, mainly ruthenium [6,7] but also os-
mium [8], rhodium [8] and platinum [9], are endowed with
search has focused on modifications of PTA motif as subtle
changes of the electronic and steric requirements of the phospha-
adamantane skeleton may help in the tailored synthesis of efficient
catalysts for various applications.
The most straightforward modifications of PTA bottom rim have
been generally achieved by reaction with electrophiles, including
alkyl halides [10] (II) and anhydrides (III) [11]. Double quaterniza-
tion of the PTA ligand has been recently demonstrated (IV) [12],
while opening of the PTA cage has resulted in bidentate P,N- (V)
[13] and N,N-ligands (VI) [12], which, in the former case, have been
used by some of us to prepare rhodium catalysts active in biphasic
alkene hydroformylation [14]. Neutral Lewis-acids may represent
target reagents towards the functionalization of PTA and in recent
reports our group [15], Frost et al. [16] have separately shown that
borane binds PTA with up to four BH3 groups, i.e. on both nitrogen
and phosphorus atoms. In this contribution, we report findings on
the coordination chemistry of mono- and bis-boranyl PTA towards
Cp*Rh synthons forming a variety of boronated-PTA rhodium com-
plexes. These complexes can undergo different reactions resulting
in the formation of boronated-PTA rhodium hydrides and p-alkene
complexes, as demonstrated by NMR experiments and X-ray
crystallographic studies.
* Corresponding authors. Tel.: +39 0555225289; fax: +39 0555225203.
E-mail addresses: mperuzzini@iccom.cnr.it, peruz@fi.cnr.it (M. Peruzzini).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.006

2398
S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
[d = ꢀ10.55]. Noticeably, coordination to rhodium of the N-boranyl
2. Results and discussion
phosphine broadens the 11B resonance (x1/2 = 345 Hz) which does
not show any discernable coupling to BH3 protons. In keeping with
P-coordination to rhodium of the phosphaadamantane [18], the
31P{1H} NMR spectrum exhibits a doublet at ꢀ29.2 ppm with
1JPRh = 147 Hz consistent with a Rh(III) metal centre [8]. The 1H
2.1. Synthesis and characterization of rhodium PTA boranyl complexes
The straightforward reaction of the 1-boranyl-1,3,5-triaza-7-
phosphaadamantane ligand N–B–PTA(BH3) [16] with [Cp*RhCl-
(l-Cl)]2 (1) in a 2:1 mol ratio in THF affords, after work-up, the
new complex [Cp*Rh{N–B–PTA(BH3)}Cl2] (3) which was isolated
in excellent yield as an air stable orange microcrystalline solid with
analytical data in agreement with the proposed formulation
(Scheme 1). Alternatively, compound 3 can be prepared in compa-
rable yield by treatment of the known [Cp*Rh(PTA)Cl2] complex (2)
[8] in THF with a stoichiometric amount of BH3.THF. Apart from
microanalytical data, the presence of the aminoborane moiety in
3 was determined by IR and NMR spectroscopy. The IR spectrum
of 3 shows stretching vibrations ascribable [17] to both mBH at
2372, 2316, 2273 cmꢀ1 and mBN at 1176 cmꢀ1, while the 11B NMR
spectrum (CDCl3) exhibits a broad resonance at ꢀ9.85 ppm only
slightly deshielded with respect to the free N-boronated phosphine
NMR spectrum displays
a broad three protons resonance
(0.9–1.5 ppm) corresponding to the BH3 group bound to the N
atom. The other proton resonances agree with the proposed formu-
lation and do not deserve additional comment confirming the lack
of C3 symmetry for the 12 CH2 protons of the PTA backbone
(3.7–4.6 ppm) upon quaternization of one nitrogen atom (see
Scheme 2).
The solid-state structure of compound 3 proved difficult to re-
fine satisfactorily due to the poor quality of the crystals (obtained
by slow evaporation of a diluted acetone solution) and the disorder
arising from the Cp* ring (cf. Section 4). Nevertheless, there is no
question as to the overall structure of complex, confirming the
structural formulation as shown in Fig. 1. Selected bond lengths
and angles are listed in Table 1.
The coordination around the rhodium atom can be described as
a three-legged piano stool defined by the Cp* ligand, the N-boro-
nated PTA phosphine and two chloride atoms. The Rh–P bond
P
N
N
Cl
Cl
Cl
Rh
BH3
length in
3 [2.268(4) Å] is significantly longer than that in
N
Rh
Rh
Cl
[Rh(PTA){PTA(H)}3Cl]Cl2, with a Rh–P separation at 2.206(1) Å
[19], but identical to that in [Cp*Rh{P(OEt)3}Cl2] [20] [2.268(3) Å]
and similar to that found in 2 [2.286(1) Å] [8].
Cl
THF, RT
P
N
Cl
N
N
3
Compound 3 is the third transition metal complex of the re-
cently prepared 1-boranyl-PTA ligand [21] and its synthesis con-
firms that boranyl adducts of the popular phosphaadamantane
PTA may be used to obtain another class of ligands to bind transi-
tion metal fragments. Alternatively, the reaction of 2 with borane,
which also results in the formation of 3, suggests that this class of
ligands may be directly assembled via simple boronation of
P-bonded PTA ligands. As for the free 1-boranyl-1,3,5-triaza-7-phos-
phaadamantane molecule [15], 3 is unstable in water and slowly
reverts back to 2 releasing one equivalent of orthoboric acid when
water is added to a MeOH or Me2CO solution of 3 [22]. By contrast,
1
BH3
BH3.THF
CHCl3
P
H2O
-H3BO3, -H2
N
N
N
Rh
Cl
Cl
P
N
N
N
2
Scheme 1.
-
+
P
Cl
Cl
Cl
N
exc
N
BH3
N
BH3
Rh
Rh
Cl
P
Rh
Cl
N
P
CH2Cl2, reflux
P
N
Cl
N
N
N
N
4
1
BH3
CH2Cl2
reflux
N
N
N
P
THF, RT
exc
N
N
N
BH3
BH3.THF
THF, RT
H2O
Rh
Rh
- H3BO3
Cl
P
N
Cl
Cl
Cl
P
N
N
N
N
N
2
P
3
BH3
THF, RT
N
N
BH3.THF
THF, RT
-
+
N
Cl
-
+
Cl
Rh
N
P
P
Cl
Rh
H2O
N
N
N
N
N
P
N
P
N
Cl
N
BH3
N
N
- H3BO3
6
N
5
Scheme 2.

S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
2399
in refluxing dichloromethane. Monitoring of the reaction by
31P{1H} NMR spectroscopy shows the presence of pure 4 in solu-
tion without additional signals. However, work-up of the solution
at room temperature gives a yellow powder whose analytical data
do not perfectly match the proposed formula (see Section 4). On
redissolving 4 in DMSO at room temperature, 31P{1H} NMR shows
that the bis-boranyl adduct slowly reverts into 3 with loss of one
N–B–PTA(BH3) ligand, hence cannot be isolated in pure form but
rather as a mixture of 4 and 3 in the approximate 9:1 ratio. In con-
trast, the bis-PTA complex [Cp*Rh(PTA)2Cl]Cl (5) is indefinitely sta-
ble in solution [8]. At first glance, there is no simple rationale to
account for the observed instability of 4 which can hardly be
attributed exclusively to electronic factors associated with the N-
boronation of PTA. We believe that steric reasons (crowding of
the piano stool ligands) may be also important in determining
the instability of 4. Direct boronation of 5 in THF using a slight ex-
cess of BH3 ꢁ THF or reaction of 3 with excess of boronated PTA also
affords 4 in fairly good yield.
In line with the proposed formula, the 31P{1H} NMR spectrum of
1
4 displays a doublet at ꢀ32.5 ppm with a JPRh = 135 Hz. Consis-
tently, the 1H NMR spectrum shows, apart from a broad signal be-
tween 0.98 and 1.40 ppm for the six BH3 protons and the expected
uninformative multiplets (3.85–4.71 ppm) due to the PTA methy-
lene protons, a triplet at d 1.83 (4JHP = 3.3 Hz) assigned to the
methyl Cp* protons coupled to the two P atoms.
Fig. 1. ORTEP plot of complex 3 (Hydrogen atoms omitted for clarity; ellipsoids
drawn at 50% probability).
When dissolved in wet DMSO-d6, complex 4 slowly hydrolyses
to give a mixture of 5 and the mixed PTA–PTA(BH3) species
[Cp*Rh{N–B–PTA(BH3)}(PTA)Cl]+ (6) [31P{1H} NMR: dPTA = ꢀ 34.1,
Table 1
2
Selected bond lengths (Å) and angles (°) for 3
d{N–B–PTA(BH )} = 34.2; JPP = 135.7 Hz]. On standing, complex
6
3
*
a
slowly converts to 5 with release of H3BO3. No attempt was made
to isolate pure 6 in the solid state.
Rh–cp
1.80 (3)
2.391 (3)
2.268 (4)
2.13 (4)
2.07 (2)
2.21 (1)
1.64 (2)
P1–Rh1–Cl1
P1–Rh1–Cl10
Cl1–Rh1–Cl10(2)
P1–Rh1–cp*
87.3a
87.3a
Rh1–C11
Rh1–P1
Rh1–C7
Rh1–C8
Rh1–C9
N3–B1
91.4b
We have previously observed that multiple boronation of PTA is
possible and, depending on the PTA/BH3 ratio, up to 4 equiv. of bor-
ane may be coordinated to the four heteroatoms of the triaza-
phosphaadamantane molecule [15]. Attempts to incorporate more
than one BH3 unit on the same PTA molecule once coordinated to a
transition metal were however only partially successful (Scheme
3). When a THF solution of 2 was reacted at room temperature
with 2.5 equiv. of BH3 ꢁ THF and the progress of the reaction mon-
itored by 31P{1H} NMR spectroscopy, a new signal at ꢀ30.9 ppm
(d, 1JPRh = 152 Hz) was observed. This product was isolated as an or-
ange solid that slowly decomposes even if kept under inert atmo-
sphere. Although the low stability of this compound in the solid
state did not allow to obtain good analytical data, its spectroscopic
features agree with the occurrence of a double N,N0-boronation of
129.8 (7)
124.5 (6)
Cl1–Rh1–cp*
cp* refers to the centroid of the Cp* ligand.
Primed atoms are obtained by those unprimed by the symmetry operation: x,
1/2 ꢀy, z.
a
b
solutions of 3 in dry polar solvents (MeOH, Me2CO, THF, CH2Cl2)
are indefinitely stable when exposed to air.
The bis-boranyl-PTA derivative [Cp*Rh{N–B–PTA(BH3)}2Cl]Cl (4)
was obtained by reacting 1 with N–B–PTA(BH3) in a 1:4 molar ratio
Cl
Cl
Rh
Rh
Cl
Cl
P
1
N
N
THF
BH3
N
BH3
Rh
Rh
Rh
Cl
- BH3
Cl
exc BH3.THF
THF, RT
Cl
P
N
P
N
Cl
Cl
P
N
Cl
N
N
N
N
N
N
solution or
solid state
2
7
3
H3B
BH3
BH3
Scheme 3.

2400
S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
the rhodium-coordinated PTA [23]; thus, we assign the formula
[Cp*Rh{N–B–PTA(BH3)2}Cl2] (7). Once redissolved in DMSO-d6,
the 1H NMR spectrum of 7 displays a broad resonance (0.89–
1.44 ppm) for the six BH3 hydrogens, a doublet at 1.67 ppm (Cp*
Me) and several multiplets at (3.7–4.6 ppm) ascribable to the PTA
protons. All these signals coexist in solution with those of com-
pound 3, indicating that compound 7 easily undergoes partial deb-
oronation yielding the monoboronated species 3 unless an excess
of borane is maintained in the solution. The deboronation process
is faster in DMSO solution than in the solid state and is completed
in about 2 h giving 3 as the only detectable species. Addition of de-
gassed water to a DMSO solution of 7 greatly accelerates the pro-
cess which eventually affords the deboronated PTA complex 2.
In keeping with our analysis, the reaction of the dimer 1 in
CDCl3 with excess N–B–PTA(BH3)2, in NMR tube scale gave 7, indi-
cating that also the bis-boronated phosphine may behave as a
ligand.
integrating by two protons and assignable to the two hydride li-
gands (Fig. 2, right). These exhibit a T1(min) value of 532 ms at
400 MHz (acetone-d6, 193 K) confirming their classical nature
[26]. The multiplets due to the boronated PTA ligand range from
4.20 to 3.40 ppm and suggest a loss of the ternary PTA symmetry
due to the boronation of one of the nitrogen atoms. This lack of
symmetry is reflected also in the 13C{1H} NMR spectrum which dis-
plays two pairs of CH2 resonances. Computer simulation [27] of the
spectrum and a perusal of 2 D 1H,13C-HMQC, 1H,1H-COSY and
1H,1H-NOESY spectra allowed us to fully assign the proton and car-
bon resonances (see sketch VII below for the labelling scheme used
and Section 4 for details) and disclose the otherwise practically
invisible BH3 resonance. Indeed, these three protons give rise to a
very broad signal centred at 2.07 ppm extended over 400 Hz,
0
which correlates only to the Ha and the two diastereotopic Hc
and Hc protons in the 1H,1H-NOESY spectrum (Fig. 3).
00
The presence of N-bonded BH3 was eventually confirmed by the
11B NMR spectrum displaying
a
broad quartet at d = ꢀ 10.8
2.2. Synthesis and characterization of the rhodium hydrides
(1JHB = 85 Hz).
[Cp*Rh{ N–B–PTA(BH3)}H2] (8) and [Cp*Rh(PTA)H2] (9)
The N-boranyl PTA hydride is unstable in chlorinated solvents
where it quickly reverts to 3, whereas solutions of 8 in benzene,
toluene and acetone are stable for several days when stored under
an inert atmosphere.
Hydrosoluble rhodium hydride complexes are an underrepre-
sented class of organometallic complexes [24], thus we decided
to investigate the reaction of 2 with NaBH4 which is one of the
most common reagents to convert rhodium halides into the corre-
sponding hydrides [25]. However, treatment of 2 in EtOH with a
large excess of NaBH4 did not give the expected dihydride complex
[Cp*Rh(PTA)H2] (9). Instead, the dihydride [Cp*Rh{N–B–
PTA(BH3)}H2] (8) was obtained, where a BH3 ligand has been selec-
tively delivered to one of the PTA nitrogen atom (Scheme 4). Com-
pound 8 can also be obtained by reacting the N-boranyl complex 3
with NaBH4 under the same reaction conditions. The hydride 8 is a
brownish red solid, stable only if kept under inert atmosphere.
The IR spectrum of 8 shows characteristic mBH bands at 2371,
2318, 2275 cmꢀ1, a mBN band at 1170 cmꢀ1 and a medium intensity
mRhH band at 1964 cmꢀ1. The 31P{1H} NMR spectrum displays a
doublet at ꢀ18.5 ppm (1JPRh = 155 Hz) which transforms into a
doublet of triplets (JPH(residual) = 43 Hz) when an off-resonance
experiment is performed, confirming the presence of two magnet-
ically equivalent hydride ligands coordinated to the rhodium atom.
The 1H NMR spectrum displays, apart from the signals correspond-
ing to the Cp* and N–B–PTA(BH3) ligands, a high field doublet of
multiplets (d = ꢀ13.67; 2JPH = 43 Hz, 1JRhH = 27 Hz, 4JHH(Me) = 1.1 Hz)
Full deboronation of 8 takes place by adding an excess (0.4 mL,
300 equiv.) of degassed water to an acetone-d6 solution in a NMR
tube and heating to ca. 60 °C for 20 h. Hydrolytic removal of BH3
from 8 affords a slightly high field shifted doublet in the 31P{1H}
1
NMR spectrum (d = ꢀ20.2 ppm, doublet, JPRh = 147 Hz) which is
consistent with the formation of the rhodium dihydride
[Cp*Rh(PTA)H2] (9) in quantitative NMR yield. Formation of
H3BO3 (
11B NMR: d = 19.5, s) [15,22] and evolution of dihydrogen
(1H NMR: d = 4.64, s) accompany the cleavage of the NPTA–BH3bond
of 8 similarly to what shown by both 5 and the free ligand. Accord-
ingly, a new set of hydride resonances (dd) appears in the high field
2
region of the 1H NMR spectrum (d = ꢀ14.44 ppm; JHP = 42 Hz and
1JHRh = 28 Hz) replacing the multiplet of 8 (Scheme 4).
Independent synthesis of 9 (NMR tube scale) by treatment of
a solution of 2 in benzene-d6 with one equivalent of sodium
bis(2-methoxyethoxy)aluminium hydride, i.e. Red-Al, a hydrurat-
ing reagent comparable with LiAlH4 that does not contain boron
atoms (Scheme. 5), confirmed the NMR data set observed in the
previous experiment generating 9 by selective N–B hydrolysis of
8 [28].
CHCl3
Rh
exc NaBH4
Rh
Rh
Cl
H
exc NaBH4
EtOH, RT
Cl
EtOH, RT
P
N
P
N
Cl
3
H
P
N
N
N
Cl
N
N
N
N
8
2
BH3
BH3
H2O
- H3BO3
- H2
acetone-d6
Rh
H
H
P
N
N
N
9
Scheme 4.

S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
2401
H
Rh
H
H
H
P
H
H
α
H
H
H
β
N
N
BH3
γ
H
N
δ
H
H
H
H
VII
4.20
4.00
3.80
3.60
3.40
3.20
3.10
-13.50
-13.66
Fig. 2. Experimental (top) and simulated (bottom) 1H NMR spectrum of compound 8 (C6D6, 294 K, 400.13 MHz).
H
α
H
γ’
Hγ”
Hδ’+Hδ”
ppm
ppm
1.6
2.0
2.5
3.0
3.5
4.0
ppm
1.8
2.0
2.2
2.4
2.6
4.0
3.5
3.0
2.5
2.0
4.2 4.0 3.8 3.6 3.4 ppm
Fig. 3. 1H NOESY spectrum of 8 (C6D6, 294 K, 400.13 MHz). Broad NOE signals allow to assign the resonances of BH3 protons and to confirm the presence of this fragment in
the molecule.
2.3. Reactivity of 8 with alkynes: synthesis of Rh(I) complexes
[Cp*Rh{N–B–PTA(BH3)}(g2-CH2 = CHPh)] (10) and
[Cp*Rh{N–B–PTA(BH3)}{g2-CH2 = CHC(O)OEt}] (11)
tron poor alkynes are suitable reagents for electrophilic
activation of Rh–H bonds. Generally, the reaction results in the for-
mation of insertion products with different regio- and stereochem-
istry strongly depending on the electronic nature of the alkyne and
reaction conditions [29].
In order to verify whether the PTA-boranyl coordinated mole-
cule may undergo further reactivity at the ancillary ligands, we
investigated the reactions of the dihydride 8 towards typical or-
ganic substrates capable of reacting with rhodium hydrides. Elec-
The dihydride [Cp*Rh{N–B–PTA(BH3)}H2] (8) reacts with a slight
excess of activated alkynes, such as phenylacetylene or ethyl pro-
piolate HC„CC(O)OC2H5 in C6H6 to give the p-alkene complexes

2402
S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
a broad signal at d = ꢀ10.9 (10) and d = ꢀ10.4 (11). Remarkably,
Na
O
O
O
O
H
H
no differentiation of the two rotamers was evident from the boron
NMR spectra, likely reflecting the negligible difference of the two
N–B–PTA(BH3) borane atoms in the two rotamers.
Al
Rh
Rh
H
Cl
C6D6, RT
P
N
Crystals of 10 were obtained from slow evaporation of a diluted
benzene solution. An ORTEP view of this complex is shown in Fig. 4
together with the labelling scheme while selected bond distances
and angles listed in Table 2. The coordination sphere consists of
the a Cp* ligand, the P-coordinated N–B–PTA(BH3) phosphine and
the p-coordinated styrene ligand.
H
P
N
Cl
N
N
N
N
2
9
Scheme 5.
The distances Rh–C(Cp* ) are not equivalent, with two separa-
tions Rh1–C9 and Rh1–C11 (at 2.293(9) Å and 2.19(1) Å, respec-
tively) being significantly different from the others, likely caused
by the PTA-boranyl ligand. For the BH3 coordinated to one of the
three nitrogen atoms of PTA, the N–B separation at 1.61(1) Å is
comparable to that found both in the coordinated and uncoordi-
nated boronated cage [1.58(2) Å] [16]. All other distances fall in
the expected range [32].
[Cp*Rh{N–B–PTA(BH3)}(g2-CH2 = CHPh)] (10) and [Cp*Rh{N–B–
PTA(BH3)}{g2-CH2 = CHC(O)OEt}] (11), respectively (Scheme 6).
Complexes 10 and 11 are orange solids stable at room temperature
if stored under an inert atmosphere. As expected from the different
electronic properties of the two alkynes, the reaction takes place
immediately with ethylpropiolate whereas the less activated
HC„CPh reacts only after heating the solution to about 60 °C.
Although no intermediate product was observed by in situ NMR
monitoring of the process, it is likely that the reaction proceeds
via alkyne insertion across one Rh–H bond to give a Rh(hydri-
do)vinyl species. Such species have been detected in a few cases
[30],
including
for
the
related
rhodium
complexes
[Cp*Rh(PMe3)(HRC = CHR)] for which a detailed mechanistic study
was undertaken [29].
Both 31P{1H} NMR spectra of compounds 10 and 11 feature two
1
doublets in the ratio 1:4 (10) (d = ꢀ 31.6 ppm, JPRh = 206 Hz;
1
d = ꢀ 36.9 ppm, JPRh = 214 Hz) and 1:9 (11) (d = ꢀ32.4 ppm,
1JPRh = 198 Hz; d = ꢀ35.2 ppm, JPRh = 207 Hz) indicating the pres-
1
ence of two different Rh(I) species tentatively assigned as rotamers
of the g2-alkene complexes [29a,31]. Increasing the temperature to
80 °C in toluene-d8, the 31P NMR spectra did not show coalescence
of the rotamers resonances neither for 10 nor for 11, thus suggest-
ing a high-energy rotational barrier.
The 1H NMR spectra of both compounds show the disappear-
ance of the high field hydride signals and confirm the formation
of two structurally related blocked rotamers of the g2-alkene com-
plexes. Although a close superimposition of the NMR resonances of
the rotamers in both 1H and 13C NMR spectra does not allow a
complete assignment of the NMR spectrum of the less abundant
rotamers, a series of heterocorrelated 13C-1H 2D-NMR experiments
has permitted to assign the 1H and 13C{1H} NMR signals for the ma-
jor rotamers of the two compounds.
The reaction of 8 with terminal alkynes does not affect the
N-boranyl functionality of the coordinated boronated-PTA as con-
firmed by both IR spectroscopy, showing the typical absorptions
of the N–BH3 moiety, and 11B{1H} NMR spectroscopy, displaying
Fig. 4. ORTEP view of complex 10 (Hydrogen atoms omitted for clarity; ellipsoids
drawn at 50% probability).
Table 2
Rh
Bond lengths (Å) and angles (°) for 10
R
P
Rh1–P1
2.217 (2)
2.269 (9)
2.265 (9)
2.293 (9)
2.265 (9)
2.19(1)
2.098 (9)
2.143 (9)
1.90 (1)
1.836 (9)
1.61 (1)
1.40 (1)
1.47 (1)
Rh1— P1–C1
Rh1–P1–C2
Rh1–P1–C3
P1–Rh1–cp*
cp*–Rh1–C17
cp*–Rh1–C18
C17–C18–C19
B1–N3–C3
125.2 (3)
117.7 (3)
117.6 (3)
131.4 (4)
131.3 (7)
128.2 (8)
127.3 (9)
110.7 (7)
110.1 (7)
110.0 (7)
N
Rh1–C7
Rh1–C8
Rh1–C9
Rh1–C10
Rh1–C11
Rh1–C17
Rh1–C18
Rh1–cp*a
N
N
H3B
+
HC CR
Rh
H
C6H6
P
N
H
N
N
Rh
B1–N3–C5
B1–N3–C6
b
P
N
P1–Cav
N
N
BH3
B1–N3
C17–C18
C18–C19
H3B
R
8
Cp* refers to the centroid of the Cp* ligand.
a
R= Ph, 10; C(O)OEt, 11
b
P1–Cav refers to the average P–C bond length involving the P-atom and the
three methylene carbons of the PTA cage, namely C1, C2 and C3.
Scheme 6.

S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
2403
4.50 (m, CH2, 12H) ppm. 31P{1H} NMR (DMSO-d6): ꢀ29.19 (d,
1JPRh = 146.5 Hz) ppm. 13C{1H} NMR (DMSO-d6): 9.1 (s, C5CH3);
3. Conclusions
1
1
46.5 (d, CH2P, JCP = 15.5 Hz); 53.1 (d, CH2P, JCP = 18.4 Hz); 69.2
In this paper, we have described the synthesis and characteriza-
tion of a new family of rhodium complexes containing the N–bora-
nyl PTA(BH3) cage-like phosphine as a monodentate P-coordinated
ligand. The PTA-boronated complexes may be prepared either by
direct reaction of the N-boranyl PTA adduct with suitable rho-
dium(III) precursors or by in situ boronation of the PTA derivatives.
Remarkably, the N–boranyl PTA complexes tolerate a variety of
chemical transformations including the reaction with hydride
sources such as NaBH4 terminally yielding a rhodium dihydride.
As determined for the free ligand, the N–BH3 moiety does not sur-
vive hydrolytic conditions, but the hydrolysis is much slower than
that observed for the free boronated molecule.
3
3
(d, CH2N, JCP = 6.4 Hz); 76.8 (d, CH2N, JCP = 4.2 Hz); 99.2 (dd,
C5CH3, JCP = 7.1 Hz, JCRh = 2.8 Hz) ppm. 11B NMR (CDCl3): ꢀ9.85
2
1
(br, BH3) ppm.
4.3. Synthesis of [Cp*Rh{N–B–PTA(BH3)}2Cl]Cl (4)
4.3.1. Method A
A mixture of [Cp*RhCl(l-Cl)]2 (100.0 mg, 0.16 mmol) and N–B–
PTA(BH3) (123.0 mg, 0.72 mmol) in CH2Cl2 (20 mL) was refluxed
for 24 h under stirring. The solution was cooled to room tempera-
ture and the yellow solid which precipitated out, was separated
from the mother liquor by decantation, washed with cold CH2Cl2
(2 ꢂ 2 mL) and Et2O (3 ꢂ 3 mL), and dried under vacuum.
(116.0 mg, 56% yield) [35].
4. Experimental
4.1. General procedures
4.3.2. Method B
Compound 4 can also be obtained by treating a solution of
[Cp*Rh(PTA)2Cl]Cl (120.0 mg, 0.19 mmol) in THF (15 mL) with
BH3 ꢁ THF (1 M, 0.60 mmol, 600 lL) at room temperature under
stirring. The yellow solid which separated out was washed with
Et2O (2 ꢂ 3 mL) and dried under vacuum. Yield: 88.5 mg, 72%
[35].
All synthetic procedures were carried out using standard
Schlenk glassware under an inert atmosphere of dry argon. The li-
gands PTA [3] and N–B–PTA(BH3) [15] and the complexes
[Cp*RhCl(l-Cl)]2 [33], and [Cp*Rh(PTA)Cl2] [8] were prepared as de-
scribed in the literature. Other reagents were obtained from com-
mercial suppliers and used without further purification. Solvents
were distilled and degassed according to standard procedures
[34]. Infrared spectra (KBr discs) were recorded on a Bruker Vector
IFS 28 FT apparatus. 1H, 31P{1H} and 13C{1H} NMR spectra were re-
corded on a Bruker ARX-400 spectrometer operating at frequencies
of 100, 161 and 400 MHz, respectively. Peak positions are relative
to tetramethylsilane and were calibrated against the residual sol-
vent resonance (1H) or the deuterated solvent multiplet (13C).
Phosphorus chemical shifts were measured relative to external
85% H3PO4, with downfield shifts reported as positive. 11B NMR
spectra were recorded on a Bruker Avance DRX-400 spectrometer
operating at 128 MHz. The 11B chemical shifts are relative to an
external reference of BF3 in diethyl ether, with positive values
downfield from the reference. All the NMR spectra were recorded
at room temperature (20 °C) unless otherwise stated. Elemental
analyses (C, H, N) were performed using a Carlo Erba model 1106
elemental analyser by the Microanalytical Service of the Depart-
ment of Chemistry at the University of Florence.
Anal. Calc. for C22H45B2Cl2N6P2Rh (651.02 g/mol ): C, 40.59; H,
6.97; N, 12.91. Found: C, 40.41; H, 6.71; N, 12.69%. IR (KBr pel-
lets, cmꢀ1): mBH = 2361 (m), 2319 (w), 2270 (w), mBN = 1161 (m).
1H NMR (DMSO-d6): 0.98–1.40 (br s, BH3, 6H, x1/2 = 47 Hz);
4
1.83 (t, C5CH3, JHP = 3.3 Hz, 15H); 3.85–4.05 (m, CH2, 6H);
4.27–4.47 (m, CH2, 12H); 4.57–4.71 ppm (m, CH2, 6H). 31P{1H}
1
NMR (DMSO-d6): ꢀ32.47 (d, JPRh = 135.4 Hz) ppm. 13C{1H}
1
NMR (DMSO-d6): 9.9 (s, C5CH3); 47.4 (d, CH2P, JCP = 13.5 Hz);
1
53.4 (d,CH2P, JCP = 16.4 Hz); 68.7 (br s, CH2N); 76.1 (br s,
CH2N); 105.6 (m, C5CH3) ppm.
4.4. Synthesis of [Cp*Rh{N-B-PTA(BH3)2}Cl2] (7)
2.5 equiv. of BH3 ꢁ THF (1 M, 0.53 mL, 0.53 mmol) at room tem-
perature, were added to a stirred [Cp*Rh(PTA)Cl2] (100.0 mg,
0.21 mmol) solution in THF (15 mL). The formation of an orange
solid was immediately observed. The reaction was monitored by
31P{1H} NMR (DMSO-d6) and considered completed when a new
and unique signal was observed (ꢀ30.9 ppm, JPRh = 151.8 Hz). The
solid obtained was separated from the mother liquor by decanta-
tion and dried under vacuum (86.1 mg, 83.0% yield). Anal. Calc.
for C16H33B2Cl2N3PRh (493.86 g/mol ): C, 38.91; H, 6.74; N, 8.51%.
Found: C, 38.86; H, 6.77; N, 8.48%. IR (KBr pellets, cmꢀ1):
mBH = 2385 (s), 2345 (m), 2278 (m), mBN = 1164 (m). 1H NMR
(DMSO-d6): 0.89–1.44 (br s, BH3, 6H, x1/2 = 66 Hz); 1.67 (d,
4.2. Synthesis of [Cp*Rh{N–B–PTA(BH3)}Cl2] (3)
4.2.1. Method A
A red suspension of [Cp*RhCl(l-Cl)]2 (100.0 mg, 0.16 mmol) in
THF (30 mL) was treated with solid N–B–PTA(BH3) (54.7 mg,
0.32 mmol) at room temperature under stirring. An orange solu-
tion was obtained, from which an orange solid quickly precipi-
tated. The solid was separated from the mother liquor by
decantation, washed with Et2O (2 ꢂ 3 mL) and dried under vac-
uum. Yield: 123.2 mg, 80.2%.
4
C5CH3, JHP = 4.2 Hz, 15H); 3.70–4.60 (m, CH2, 12H) ppm. 31P{1H}
1
NMR (DMSO-d6): ꢀ30.87 (d, JPRh = 151.8 Hz) ppm. 11B NMR
(CDCl3): ꢀ9.85 (br, BH3) ppm.
4.5. Synthesis of [Cp*Rh{N–B–PTA(BH3)}H2] (8)
4.2.2. Method B
Compound 3 can also be obtained by treating a red suspension
of [Cp*Rh(PTA)Cl2] (100.0 mg, 0.21 mmol) in THF (15 mL) with
BH3.THF (1 M, 0.25 mmol, 250 lL) at room temperature under stir-
ring. The orange solid obtained was separated from the mother li-
quor by decantation, washed with Et2O (2 ꢂ 3 mL) and dried under
vacuum. Yield: 89.3 mg, 88.6%. Anal. Calc. for C16H30BCl2N3PRh
(480.03 g/mol): C, 40.03; H, 6.30; N, 8.75. Found: C, 40.10; H,
6.24; N, 8.79%. IR (KBr pellets, cmꢀ1): mBH = 2372 (m), 2317 (w),
2273 (w), mBN = 1176 (m). 1H NMR (DMSO-d6): 0.85–1.50 (br s,
4.5.1. Method A
[Cp*Rh(PTA)Cl2] (0.70 g, 1.50 mmol) was added to degassed
absolute EtOH (30 mL). Then an excess of solid NaBH4 (0.37 g,
9.76 mmol) was added portionwise to the solution and the mixture
was stirred for 4 h at room temperature in the dark. The solution
was concentrated to dryness and the residue was dissolved in ben-
zene (40 mL), and filtrated under argon through a celite plug. The
solvent was removed again under vacuum leaving a fine brown
solid (489 mg, 79.3% yield).
4
BH3, 3 H, x1/2 = 345 Hz); 1.64 (d, C5CH3, JHP = 4.0 Hz, 15H); 3.85–

2404
S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
4.5.2. Method B
remove the volatiles. The dark oily residue was triturated with
EtOH to give an orange solid (73.2 mg, 59.9 % yield). Anal. Calc.
for C21H38BN3O2PRh (509.24 g/mol): C, 49.53; H, 7.52; N, 8.25.
Found: C, 49.60: H, 7.68; N, 8.59%. IR (KBr pellets, cmꢀ1):
mBH = 2356 (m), 2308 (w), 2265 (w), mCO = 1680 (m), mC=C = 1440
(w), mCOC = 1378 (m), mBN = 1162 (s). 1H NMR (C6D6): (intensity ratio
Complex 8 may be prepared in comparable yield by replacing
[Cp*Rh(PTA)Cl2] with 1 in the above method. Anal. Calc. for
C
16H32BN3PRh (411.14 g/mol): C, 46.74; H, 7.85; N, 10.22. Found:
C, 46.71; H, 7.80; N, 10.26%. IR (KBr pellets, cmꢀ1): mBH = 2371
(m), 2318 (w), 2275 (w); mRhH = 1964 (m); mBN = 1170 (m). 1H
NMR (C6D6, for the labelling scheme see sketch 1 above): ꢀ13.56
3
9:1 A/B rotamers). Rotamer A: 1.08 (t, CH2CH3, JHH = 7.1 Hz, 3H);
(ddm, Rh-H,2JHP = 43.4; JHRh = 27.1; JHMe = 1.1 Hz, 2H); 2.04
1.59 (d, C5CH3, JHP = 2.0 Hz, 15H); 1.67 (m, =CH2, 1Hvinyl); 2.20
1
4
4
4
3
(C5CH3, JMeP = 2.7; JMeRh = 1.6 Hz, 15H); 2.07 (br s, BH3, 3H);
(m, =CH2, 1Hvinyl); 2.36 (m, =CH, 1Hvinyl); 3.26 (m, PCH2, 2H);
3.54 (m, NCH2, 1/2H); 3.57 (m, NCH2, 1/2H); 3.77 (m, NCH2,
4
4
3.13 (m, Hb00, JHb Hc = 1.5; JHb Hd = 2.0 Hz, 2Hb00); 3.17 (m, Hb0,
00
00
00
00
2
4
3
JHb Hb = 15.6; JHb Hc = 1.3;4 JHb Hd = 1.3;2JHbP = 1.3 Hz, 2Hb0); 3.50
PCH2, 1H+2H); 3.86 (m, PCH2, 2H); 4.05 (t, CH2CH3, JHH = 7.1 Hz,
0
00
0
0
0
0
2
4
(s, Hd00); 3.53 (m, Hd, JHd Hd = 13.7; JHd P = 1.5 Hz, Hd); 3.68 (m,
2H); 4.14 (m, NCH2, 3H); 4.23 (m, NCH2, 1H); 4.27 (m, NCH2, 2H)
ppm. Signals of rotamer B were not observed as they are likely bur-
ied under the resonances of rotamer A. 31P{1H} NMR (C6D6): Rot-
amer A: ꢀ35.17 ppm (d, 1JPRh = 206.1 Hz); Rotamer B:
0
00
0
Ha,4JHaHb = 1.2;
JHaHb = 1.2;4 JHaHc = 1.1;4 JHaHc = 1.1;2JHaP
=
4
0
00
0
00
4
1.1 Hz, 2 Ha); 3.98 (m, Hc00, JHc Hd 2.0 Hz, 2Hc00); 4.15 (m,
00
00
Hc,2JHc Hc 13.2; JHc Hd 1.3; JHc P 1.2 Hz, 2Hc) ppm. 31P{1H} NMR
4
4
0
00
0
0
0
(C6D6): ꢀ18.41 ppm (d, 1JPRh = 155.0); 31P NMR (C6D6):
ꢀ32.37 ppm (d, JPRh = 198.2 Hz). 13C{1H} NMR (C6D6): 10.20 (s,
1
ꢀ18.41 ppm (dt, JPRh = 155.0 Hz, JPH = 43.8 Hz). 13C{1H} NMR
C5CH3); 14.81 (s, CH2CH3), 31.06 (dd, =CH2, JCP = 14.8 Hz,
1
2
3
3
(C6D6, for the labelling scheme used see sketch 1): 11.59 (s,
2JCRh = 4.9 Hz); 38.68 (d, =CH, JCP = 14.8 Hz); 49.36 (d, PCH2,
1
2
3
C5CH3), 54.87 (dd, JCP = 21.0; JCRh = 2.0, Cb); 60.70 (dd,
1JCP = 9.9 Hz); 50.39 (s, CH2CH3); 70.84 (d, NCH2, JCP = 5.6 Hz);
2
3
3
3
1JCP = 13.9; JCRh = 2.0, Ca); 77.36 (d, JCP = 6.6, Cd); 77.57 (d,
77.87 (d, NCH2, JCP = 4.2 Hz); 78.13 (d, NCH2, JCP = 3.5 Hz); 96.90
(dd, C5CH3, 2JCP = 4.2 Hz, 1JCRh = 2.8 Hz); 178.01 (t, COO,
4JCP = 2.1 Hz) ppm. Signals of rotamer B were not observed as likely
masked by those of rotamer A. 11B NMR (C6D6): ꢀ10.36 ppm (br,
BH3) (both rotamers).
3JCP = 4.0, Cc); 97.47 (dd, JCP = 3.7; JCRh = 2.9, C5CH3) ppm. 11B
2
1
1
NMR (C6D6): ꢀ10.78 (br q, JBH = 85.0 Hz, BH3) ppm.
4.6. Synthesis of [Cp*Rh{N-B–PTA(BH3)}(g2-CH2 = CHPh)] (10)
To
a
stirred benzene solution (15 mL) of [Cp*Rh{N–B–
4.8. Crystallography
PTA(BH3)}H2] (100.0 mg, 0.24 mmol), 32.5 lL (0.29 mmol) of phen-
ylacetylene were added via syringe. The solution was heated to
60 °C for 1.5 h and the volatiles were removed under vacuum leav-
ing a dark oil, which was triturated with Et2O to yield an orange so-
Crystals were mounted on
a Bruker APEX diffractometer,
equipped with a CCD detector, for the unit cell and space group
determinations. Selected crystallographic and other relevant data
are listed in Table 3 and in the deposited cif file.
lid (92 mg, 74.7% yield). Anal. Calc. for
C24H38BN3PRh
(513.28 g/mol): C, 56.16; H, 7.46; N, 8.19. Found: C, 56.10; H,
7.44; N, 8.59%. IR (KBr pellets, cmꢀ1): mBH = 2363 (m), 2309 (w),
2266 (w), mC=C = 1594 (w), mBN = 1166 (m). 1H NMR (C6D6) (intensity
ratio 4:1 A/B rotamers). Rotamer A: 1.21-2.47 (br s, BH3, 3H); 1.42
Data were corrected for Lorentz and polarization factors with
the data reduction software SAINT [36] and empirically for absorp-
tion using the SADABS program [37].
4
(br, =CH2, 1Hvinyl); 1.67 (d, C5CH3, JHP = 1.7 Hz, 15H); 2.05
Table 3
2
(m, =CH2, 1Hvinyl); 2.64 (dm, PCH2, JHH = 15.1 Hz, 1 H); 2.72 (dm,
Experimental data for the X-ray diffraction study of compounds 3 and 10
2
2
PCH2, JHH = 15.4 Hz, 1H); 2.89 (dm, PCH2, JHH = 15.1 Hz, 1H);
2.99 (dm, PCH2, 2JHH = 15.4 Hz, 1H); 3.10 (dm, PCH2, 2JHH = 15.3 Hz,
1H); 3.39 (br, NCH2, 2H); 3.40 (dm, PCH2, JHH = 15.3 Hz, 1H); 3.60
3
10
2
Formula
Moleculat weight
C
16H30BCl2N3PRh
C24H38BN3PRh
513.26
4
480.02
(br, =CH, 1Hvinyl); 3.75 (dm, NCH2, JHH = 13.2 Hz, 1H); 3.82 (d,
2
Data collected T (K)
Diffractometer
Crystal system
Space group (no.)
295 (2)
Bruker APEX
Orthorhombic
Pcmn (62)
7.2370 (6)
12.510 (1)
22.120 (2)
90
295 (2)
NCH2, JHH = 13.2 Hz, 1H); 3.98 (m, NCH2, 2H); 6.95 (m, C6H5,
3
3
1H); 7.03 (t, C6H5, JHH = 7.5 Hz, 2H); 7.26 (d, C6H5, JHH = 7.5 Hz,
2H) ppm. Signals of rotamer B could not be assigned as they are
likely obscured by those of rotamer A. 31P{1H} NMR (C6D6): Rot-
Monoclinic
P21/a (14)
16.168 (1)
9.1778 (6)
17.096 (1)
90
107.91(1)
90
2413.7(3)
4
a (Å)
b (Å)
c (Å)
a (°)
b (°)
c (°)
V (Å3)
Z
1
amer A: ꢀ36.88 (d, JPRh = 213.6 Hz) ppm; Rotamer B: ꢀ31.62 (d,
1JPRh = 206.0 Hz) ppm. 13C{1H} NMR (C6D6), Rotamer A: 10.4 (s,
2
1
C5CH3), 26.7 (dd, =CH2, JCP = 14.8 Hz, JCRh = 2.8 Hz); 50.2 (d,
90
90
1
1
PCH2, JCP = 13.4 Hz); 50.3 (d, PCH2, JCP = 13.4 Hz); 50.9 (d, =CH,
2JCP = 14.1 Hz); 56.8 (d, PCH2, JCP = 9.2 Hz); 70.6 (d, NCH2,
1
2002.6 (3)
4
1.592
3JCP = 5.6 Hz); 77.6 (d, NCH2, JCP = 3.5 Hz); 77.7 (d, NCH2,
3
qcalc (g cmꢀ3
)
1.412
0.790
3JCP = 3.5 Hz); 96.6 (dd, C5CH3, JCP = 3.53 Hz, JCRh = 2.8 Hz); 125.1
2
1
l (mmꢀ1
)
1.223
3
2
(s, Cortho–C6H5); 149.8 (dd, Cipso–C6H5, JCP = 3.5 Hz, JCRh = 2.1 Hz)
ppm, (the aromatic Cpara and Cmetasignals are probably obscured
by the solvent). Rotamer B: Signals of rotamer B are partially
superimposed with those of rotamer A.10.3 (s, C5CH3), 46.5
Radiation
Mo Ka (graphite monochrom.,
k = 0.71073 Å)
h Range (°)
Number of data collected
Number of independent data
1.84 < h < 27.44
17243
2091
2.50 < h < 27.51
17130
5517
4005
2
(d, =CH, JCP = 14.1 Hz); 49.6 and 57.3 (m, PCH2); 78.0, 78.1
Number of observed reflections (no) 1618
[jFoj2 > 2.0r(jFj )]
2
(m, NCH2); 97.0 (C5CH3); 123.8 (s, Cortho–C6H5); 146.1 (Cipso–C6H5)
ppm. 11B NMR (C6D6): ꢀ10.9 (br, BH3) ppm (both rotamers).
Number of parameters refined (nv)
92
266
a
Rint
0.0986
0.0712
0.1924
1.274
0.1236
0.0831
0.1664
1.114
R (observed reflections)b
4.7. Synthesis of [Cp*Rh{N–B–PTA(BH3)}{g2-CH2CHC(O)OEt}] (11)
R2w ðobserved reflectionsÞ
c
Goodness-of-fitd
24.8 lL (0.24 mmol) of ethyl propiolate were added to a stirred
benzene solution (15 mL) of [Cp*Rh{N–B–PTA(BH3)}H2] (100.0 mg,
0.24 mmol). The solution was additionally stirred for 5 min at
room temperature, then filtered and evaporated under vacuum to
P
P
jF2oꢀ < F2o > j= F2o.
P
a
b
c
Rint
¼
P
R = (jFo ꢀ (1/k)Fcj)/ jFoj.
P
P
2
2
1=2
R2w ¼ f ½wðF2o ꢀ ð1=kÞFc2Þ ꢃ= wjF2oj ꢃg
.
P
2
1=2
GOF=[ wðF2o ꢀ ð1=kÞFc2Þ =ðno ꢀ nvÞꢃ
.
d

S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
2405
The structures were solved by direct and Fourier methods and
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.04.006.
refined by full matrix least-squares [38] (the function minimized
P
being [w(Fo ꢀ 1/kFc)2]). For all structures, no extinction correc-
tion was deemed necessary. The scattering factors used, corrected
for the real and imaginary parts of the anomalous dispersion, were
taken from the literature [32]. All calculations were carried out by
using the PC version of SHELX-97 [38], WINGX and ORTEP programs [39].
References
4.9. Structural study of [Cp*Rh{N–B–PTA(BH3)} Cl2] (3)
[1] For a review on water-soluble phosphine complexes and their applications in
homogeneous catalysis see: N. Pinault, D.W. Bruce, Coord. Chem. Rev. 241
(2003) 1–25.
[2] B. Cornils, W.A. Herrm (Eds.), Aqueous Phase Organometallic Catalysis, 2nd ed.,
Wiley–VCH, Weinheim, 2004.
The data were collected by using x scans, in steps of 0.5°. For
each of the 1363 collected frames, counting time was 20 s.
The cell constants were refined by least-squares, at the end of
the data collection, while the space group, determined from the
systematic absences, was consistent with both the orthorhombic
space group Pc21n (no. 33) or its centrosymmetric counterpart
Pcmn (no. 62). The structure could be solved in both space groups.
However, the refinement in the non-centrosymmetric space group
lead to high correlation coefficients between refined parameters
and to geometrical parameters with no physical significance
(i.e.: chemically equivalent distances, e.g. the P–C separations,
were significantly different). Thus the refinement was carried
out in the centrosymmetric space group (with only half molecule
in the independent unit). The relatively high R factors and esd’s
are due to the poor quality of the crystals and the molecular dis-
order. Indeed, the atoms of the Cp* ligand show rotational disor-
der as could be inferred by the very large displacements of the
carbon atoms in the Cp* ring plane leading to unphysical, cigar
shaped, ADP’s.
[3] (a) D.J. Daigle, A.B. Pepperman Jr., G. Boudreaux, J. Heterocyc. Chem. 11 (1974)
1085–1086;
(b) D.J. Daigle, Inorg. Synth. 32 (1998) 40–45.
[4] For a review on the PTA chemistry covering the literature up to the end of
2003, see: A.D. Phillips, L. Gonsalvi, A. Romerosa, F. Vizza, M. Peruzzini, Coord.
Chem. Rev. 248 (2004) 955–993.
[5] (a) For some general references on sustainable chemistry and catalysis, see, for
example: I.W.C.E. Arends, R.A. Sheldon, U. Hanefeld, Green Chemistry and
Catalysis, Wiley–VCH, Weinheim, D, 2007;
(b) J.P.G. Crespo, C.A.M. Afonso, Green Separation Processes: Fundamentals
and Applications, Wiley–VCH, Weinheim, D, 2006;
(c) D.J. Macquarrie, J.H. Clark, Handbook of Green Chemistry and Technology,
Blackwell Pub., Oxford, UK, 2002;
(d) M. Lancaster, Green Chemistry: An Introductory Text, RSC, Cambridge, UK,
2002.
[6] (a) A. Romerosa, M. Saoud, T. Campos-Malpartida, C. Lidrissi, M. Serrano-Ruiz,
M. Peruzzini, J.A. Garrido, F. García-Maroto, Eur. J. Inorg. Chem. (2007) 2803–
2812;
(b) A. Romerosa, T. Campos-Malpartida, C. Lidrissi, M. Saoud, M. Serrano-Ruiz,
M. Peruzzini, J.A. Garrido-Cardenas, F. Garcia-Maroto, Inorg. Chem. 45 (2006)
1289–1298;
(c) D.N. Akbayeva, L. Gonsalvi, W. Oberhauser, M. Peruzzini, F. Vizza, P.
Brüggeller, A. Romerosa, G. Sava, A. Bergamo, Chem. Commun. (2003) 264–
265.
Thus the final least-squares refinement was carried out using
isotropic displacement parameters for the atoms of the Cp* moiety
and anisotropic for the remaining non-hydrogen atoms. The contri-
bution of the hydrogen atoms, in their calculated positions, [C–H =
0.96 (Å), B(H) = 1.5 ꢂ B(Cbonded) (Å2)], was included in the refine-
ment using a riding model.
[7] (a) W.H. Ang, E. Daldini, C. Scolaro, R. Scopelliti, L. Juillerat-Jeannerat, P.J.
Dyson, Inorg. Chem. 45 (2006) 9006–9013;
(b) C. Scolaro, T.J. Geldbach, S. Rochat, A. Dorcier, C. Gossens, A. Bergamo, M.
Cocchietto, I. Tavernelli, G. Sava, U. Rothlisberger, P.J. Dyson, Organometallics
25 (2006) 756–765;
(c) A. Dorcier, P.J. Dyson, C. Gossens, U. Rothlisberger, R. Scopelliti, I. Tavernelli,
Organometallics 24 (2005) 2114–2123;
(d) C. Scolaro, A. Bergamo, L. Brescacin, R. Delfino, M. Cocchietto, G. Laurenczy,
T.J. Geldbach, G. Sava, P.J. Dyson, J. Med. Chem. 48 (2005) 4161–4171;
(e) C.S. Allardyce, P.J. Dyson, D.J. Ellis, D P.A. Salter, R. Scopelliti, J. Organomet.
Chem. 668 (2003) 35–42;
4.10. Structural study of [Cp*Rh{N–B–PTA(BH3)} (g2-CH2 = CHPh)]
(10)
(f) C.S. Allardyce, P.J. Dyson, D.J. Ellis, S.L. Heath, Chem. Commun. (2001)
1396–1397.
[8] A. Dorcier, W. Han Ang, S. Bolaño, L. Gonsalvi, L. Juillerat-Jeannerat, G.
Laurenczy, M. Peruzzini, A.D. Phillips, F. Zanobini, P.J. Dyson, Organometallics
25 (2006) 4090–4096.
[9] A. Romerosa, P. Bergamini, V. Bertolasi, A. Canella, M. Cattabriga, R. Gavioli, S.
Mañas, N. Mantovani, L. Pellacani, Inorg. Chem. 43 (2004) 905–913.
[10] (a) (R = Me) D.J. Daigle, A.B. Pepperman Jr., J. Heterocycl. Chem. 12 (1975)
579–580;
The space group was determined from the systematic absences,
while the cell constants were refined by least-squares, at the end of
the data collection. The data were collected by using x scans, in
steps of 0.5°. For each of the 1363 collected frames, counting time
was 20 s.
The least-squares refinement was carried out using anisotropic
displacement parameters for all non-hydrogen atoms, while the H
atoms were included in the refinement using a riding model
[C–H = 0.96 (Å), B(H) = aB(Cbonded) (Å2), with a = 1.5 for the CH3
groups and a = 1.2 for the remaining hydrogen atoms].
(b) (R = Et)J.M. Forward, R.J. Staples, C.W. Liu, J.P. Fackler, Acta Crystallogr. C
53 (1997) 195–197;
(c) (R = Bz)E. Fluck, J.E. Förster, J. Weidlein, E. Hädicke, Z. Naturforsch. 32
(1977) 499–506.
[11] (a) D.J. Darensbourg, C.G. Ortiz, J.W. Kamplain, Organometallics 23 (2004)
1747–1754;
(b) D.A. Krogstad, G.S. Ellis, A.K. Gunderson, A.J. Hammrich, J.W. Rudolf, J.A.
Halfen, Polyhedron 26 (2007) 4093–4100.
Acknowledgements
[12] A. Mena-Cruz, P. Lorenzo-Luis, A. Romerosa, M. Saoud, M. Serrano-Ruiz, Inorg.
Chem. 46 (2007) 6120–6128.
[13] (a) B. Assmann, K. Angermaier, H. Schmidbaur, J. Chem. Soc., Chem. Commun.
(1994) 941–942;
(b) B. Assmann, K. Angermaier, M. Paul, H. Riede, H. Schmidbaur, Chem. Ber.
128 (1995) 891–900.
[14] A.D. Phillips, S. Bolaño, S.S. Bosquain, J.-C. Daran, R. Malacea, M. Peruzzini, R.
Poli, L. Gonsalvi, Organometallics 25 (2006) 2189–2200.
[15] S. Bolaño, A. Albinati, J. Bravo, L. Gonsalvi, M. Peruzzini, Inorg. Chem. Commun.
9 (2006) 360–363.
[16] B.J. Frost, C.A. Mebi, P.W. Gingrich, Eur. J. Inorg. Chem. (2006) 1182–1189.
[17] See for example: C.A. Taylor II, S.W. Brown, V. Subramaniam, S. Kidner, S.C.
Rand, R. Clarke, Appl. Phys. Lett. 65 (1994) 1251–1253.
[18] Coordination of PTA and its derivatives through nitrogen rather than
phosphorus has been also reported see: B.J. Frost, C.M. Bautista, R. Huang, J.
Shearer, Inorg. Chem. 45 (2007) 3481–3483;
The authors would like to thank the EC for promoting this sci-
entific activity through the FP5 Research Training Network HYD-
ROCHEM (HPRN-CT-2002-00176). Thanks are also expressed to
‘‘FIRENZE HYDROLAB”, a project sponsored by Ente Cassa di Risparmio
di Firenze, for financial support. S.B. and M.R.-R. thank Xunta de
Galicia for a Parga Pondal contract and a postgraduate grant,
respectively. Dr. P. Barbaro (ICCOM CNR) is thanked for help in run-
ning 11B NMR spectra.
Appendix A. Supplementary material
Nitrogen coordination after metal coordination of the phosphorus donor is
also known. See:C. Lidrissi, A. Romerosa, M. Saoud, M. Serrano-Ruiz, L.
Gonsalvi, M. Peruzzini, Angew. Chem., Int. Ed. 44 (2005) 2568–2572.
CCDC-675447 and 675448 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of

2406
S. Bolaño et al. / Journal of Organometallic Chemistry 693 (2008) 2397–2406
[19] D.J. Darensbourg, N.W. Stafford, F. Joó, J.H. Reibenspies, J. Organomet. Chem.
488 (1995) 99–108.
abundant impurities were attributed to
a
Rh(I) species (d = ꢀ35, d,
JPRh = 207 Hz) tentatively assigned as [Cp*Rh(PTA)2] (see [Cp*Rh(CO)(PTA):
d = ꢀ37.2, d, JPRh = 187 Hz) [8] and to the deuterido perdeuterated phenyl
derivative [Cp*Rh(PTA)D(Ph-d5)] (31P NMR: d = ꢀ30, d, JPRhꢄ 170 Hz) which
likely formed from 9 via H2 reductive elimination followed by C–D oxidative
addition from C6D6 solvent.
[20] S. Ogo, T. Suzuki, Y. Ozawa, K. Isobe, Inorg. Chem. 35 (1996) 6093–6101.
[21] The ruthenium derivatives [TpRuX(PPh3){PTA(BH3)}] (X = Cl, H) and
[TpRuCl{PTA(BH3)}2][Tp = tris-(pyrazolyl)borate] have been also prepared: S.
Bolañ o, J. Bravo, J.A. Castro, M.M. Rodríguez-Rocha, M.F.C. Guedes da Silva,
A.J.L. Pombeiro, L. Gonsalvi, M. Peruzzini, Eur. J. Inorg. Chem (2007) 5523–
5532.
[29] (a) A. Selmeczy, W.D. Jones, Inorg. Chim. Acta 300/302 (2000) 138–150;
(b) C. Bianchini, A. Meli, M. Peruzzini, F. Vizza, P. Frediani, Organometallics 9
(1990) 1146–1155;
(c) B.L. Booth, A.D. Lloyd, J. Organomet. Chem. 35 (1972) 195–201.
[30] (a) G.E. Herberich, H. Mayer, J. Organomet. Chem. 347 (1988) 93–100;
(b) D.L. Reger, S.A. Klaeren, J.E. Babin, R.D. Adams, Organometallics 7 (1988)
181–189;
[22] At room temperature the hydrolysis of 3 to 2 shows an approximate t1/2 of ca.
5 h. The formation of H3BO3 when 3 is dissolved in water is confirmed by 11B
NMR monitoring of the hydrolysis process where
a singlet at 19.5 ppm
assigned to boric acid appears. See: (a) S. Hermanek, Chem. Rev. 92 (1992)
325–362;
(b) R.R. Gupta, M.D. Lechner, Chemical Shifts and Coupling Constants for
Boron-11 and Phosphorus-31 Landolt–Börnstein - Group III Condensed Matter,
vol. 35/subvolume A, Springer-Verlag GmbH, 1997.
(c) R.G. Bergman, J.M. Huggins, J. Am. Chem. Soc. 103 (1981) 3002–3011.
[31] B. Klingert, H. Werner, Chem. Ber. 116 (1983) 1450–1462.
[32] A.J.C. Wilson (Ed.), International Tables for X-ray Crystallography, vol. C,
Kluwer Academic, Dordrecht, The Netherlands, 1992 (Chapter 9.6).
[33] J.W. Kang, K. Moseley, P.M. Maitlis, J. Am. Chem. Soc. 91 (1969) 5970–5977.
[34] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemicals, 3rd ed.,
Oxford, Butterworth and Heinemann, 1988.
[23] Spectroscopic data for the N–B–PTA(BH3) and N–B–PTA(BH3)2 ligands: N–B–
PTA(BH3): 31P{1H} NMR (161 MHz, acetone-d6, 20 °C): ꢀ95.2 ppm (s); 1H NMR
1
(400 MHz, acetone-d6,20 °C): 1.23 (br q, JHB = 94 Hz, 3H, BH3), 3.67–4.04 (m,
6H, PCH2N), 4.24–4.56 (m, 6H, NCH2N). N–B–PTA(BH3)2: 31P{1H} NMR
(161 MHz, acetone-d6, 20 °C): ꢀ92.5 ppm (s); 1H NMR (400 MHz, acetone-d6,
[35] P{1H} NMR analysis (DMSO-d6) of the crude product confirms that this solid is
an approximate 9:1 mixture of 4 and 3. The formation of 3 as a contaminant in
the attempted isolation of 4 cannot be avoided even when the solution used to
precipitate the solid contained only 4 (31P{1H} NMR check).
1
20 °C): 1.40 (br q, JHB = 92 Hz, 6H, BH3), 3.66–4.63 (m, 12H, CH2).
[24] (a) A. Bakac, Dalton Trans. (2006) 1589–1596;
(b) X. Fu, B.B. Wayland, J. Am. Chem. Soc. 127 (2005) 16460–16467.
[25] R.A. Periana, R.G. Bergman, J. Am. Chem. Soc. 108 (1986) 7332–7346.
[26] V.I. Bakhmutov, Practical NMR Relaxation for Chemists, Wiley Interscience,
Chichester, UK, 2004.
[36] BrukerAXS, SAINT
Madison, WI, 1995.
[37] G.M. Sheldrick, SADABS
, Integration Software, Bruker Analytical X-ray Systems,
,
Program for Absorption Correction, University of
[27] gNMR version 4.1, Cherwell Scientific Limited, Oxford Science Park, Oxford,
UK, 1999.
[28] As the reaction of 2 with Red-Al does not afford 9 in quantitative NMR yield,
we did not attempt to isolate the dihydride 9 in pure form from this reaction.
Minor amounts of other species, summing up to less than 10 % with respect to
9, whose assignment resulted difficult, were always observed. The most
Göttingen, Göttingen, Germany, 1996.
[38] G.M. Sheldrick, SHELX-97 Structure Solution and Refinement Package, Universit
ät Göttingen, 1997.
[39] (a) L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565;
(b) L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.