Barium complexes with crown-ether-functionalised amidinate and iminoanilide ligands for the hydrophosphination of vinylarenes

Article abstract of DOI:10.1039/c9dt01512d

The detailed multistep syntheses of two nitrogen-based sterically congested iminoanilidine and amidine proligands bearing a tethered 15-member aza-ether-crown macrocycle, namely {I^Acrown}H and {Amcrown}H, are reported. These proligands react with [Ba{N(SiMe2H)2}2·(thf)n] to generate the heteroleptic barium complexes [{I^Acrown}BaN(SiMe2H)2] (5) and [{Amcrown}BaN(SiMe2H)2] (6) in high yields. These complexes exhibit high coordination numbers (resp. eight and seven) and are in addition stabilised by mild Ba?H-Si interactions. Unusually for oxophilic elements such as barium, the amidinate ligand in 6 is only η1-coordinated. Complexes 5 and 6 mediate the intermolecular hydrophosphination of styrene with primary (PhPH2) and secondary (HPPh2) phosphines. Their catalytic performance compares favourably with those of other barium precatalysts for these reactions. During the course of the hydrophosphination of styrene with HPPh2 catalysed by 5, the phosphide complex [{I^Acrown}BaPPh2] (7) could be intercepted and crystallographically characterised.

Full text of DOI:10.1039/c9dt01512d

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Barium complexes with crown-ether-functionalised amidinate and iminoanilide ligands
for the hydrophosphination of vinylarenes†
(a contribution to the special issue of Dalton Transactions dedicated to nitrogen-based ligands)
Erwann Le Coz,‡ Hanieh Roueindeji,‡ Thierry Roisnel, Vincent Dorcet,
Jean-François Carpentier and Yann Sarazin*
Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) – UMR 6226, F-35000 Rennes,
France.
Corresponding author: yann.sarazin@univ-rennes1.fr
† Electronic supplementary information (ESI) available: full experimental details including NMR spectra
and crystallographic data for CCDC 1896037-1896039 and 1897231.
1

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Abstract
The detailed multistep syntheses of two nitrogen-based sterically congested iminoanilidine and amidine
proligands bearing a tethered 15-member aza-ether-crown macrocycle, namely {I^Acrown}H and
{Amcrown}H, are reported. These proligands react with [Ba{N(SiMe2H)2}2.(thf)n] to generate the heteroleptic
barium complexes [{I^Acrown}BaN(SiMe2H)2] (5) and [{Amcrown}BaN(SiMe2H)2] (6) in high yields. These
complexes exhibit high coordination numbers (resp. eight and seven), and are in addition stabilised by mild
Ba···H‒Si interactions. Unusually for oxophilic elements such as barium, the amidinate ligand in 6 is only
η1-coordinated. Complexes 5 and 6 mediate the intermolecular hydrophosphination of styrene with primary
(PhPH2) and secondary (HPPh2) phosphines. Their catalytic performance compares favourably with those
of other barium precatalysts for these reactions. During the course of the hydrophosphination of styrene
with HPPh2 catalysed by 5, the phosphide complex [{I^Acrown}BaPPh2] (7) could be intercepted and
crystallographically characterised.
2

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Introduction
The past 15 years have experienced the emergence of main group metals molecular (pre)catalysts built on
abundant metals as suitable alternatives to mainstream homogenous catalytic systems devised around late
transition metals. Amongst these, the three large alkaline earths (= Ae) calcium, strontium and barium have
been used to a great effect to fabricate a range of potent catalysts.1 Following the seminal works by the
groups of Hill and Harder, Ca, Sr and Ba complexes have been used to catalyse CN bond formation in the
intramolecular2 and intermolecular3 hydroamination of alkenes. Effective alkene hydrosilylation mediated
by Ae complexes has been known for 10 years.4 By comparison, Ae-promoted regiospecific CP (alkene5
and alkyne6 hydrophosphination) and NSi (amine/hydrosilanes heterodehydrocouplings7) bond creations
are recent addition to the arsenal of tools implementable by synthetic chemists.
Organophosphorus compounds find widespread applications, e.g. as ligands in coordination chemistry
and for metal-catalysed organic transformations,8 in industry as pest control and pesticides, and also owing
to their biological activity, e.g. such as antibiotics and antitumor agents.9 The 100% atom-efficient catalysed
addition of HP bonds across unsaturated C=C bonds is an attractive way to produce a variety of CP bonds.
Across an homologous series of complexes of large Ae metals, barium alkene hydrophosphination
precatalysts have displayed the most impressive performances, enabling addition of secondary phosphines
across activated alkenes (vinylarenes, conjugated dienes) with high anti-Markovnikov regioselectivity and
reaction rates.3c,3d It was found that reaction rates increase upon descending group according to Ca < Sr <
Ba, a trend repeated on many occasions of Ae-catalysed reactions,3-7,10 albeit not systematically.2,7a,11
The design of bulky, monoanionic ligand (= {Lig}‒) capable of sheltering the large, electropositive and
polarisable Ae2+ ions (rionic: Ca2+, 1.00 Å; Sr2+, 1.18 Å; Ba2+, 1.35 Å) has been key to the implementation of
Ae-mediated catalysis. In particular, heteroleptic precatalysts of the type {Lig}AeX (where X‒ =
‒
‒
‒
‒
N(SiMe2H)2 , N(SiMe3)2 , CH(SiMe3)2 , PPh2 , etc.) provide on the whole the best versatility and turnovers.1
In this context, nitrogen-based ligands have had the upper hand.1,12 Most prominently, the β-diketiminate
{BDIDipp2}‒ (where BDIDipp2 = CH[C(CH3)NDipp]2, Dipp = 2,6-diisopropylphenyl, Figure 1) has been most
useful, affording access to unusual or highly reactive low coordinate Ae species such as the ubiquitous
[{BDIDipp2}CaN(SiMe3)2.(thf)] (1) and its derivatives with smaller X‒ functionalities.1-7,13 Related
‒
‒
[{I^ADipp2}AeX.(thf)n] complexes (X‒ = N(SiMe3)2 or CH(SiMe3)2 , n = 1-2 Figure 1) incorporating the
hindered iminoanilide {I^ADipp2}‒ are excellent hydroamination and hydrophosphination precatalysts,
especially for Ae = Ba (2).3c,3d Besides, amidinates have been shown to constitute suitable ligand platforms
for the synthesis of original heteroleptic Ae complexes, e.g. molecular hydrides as in 3.14 Elsewhere, the
utilisation of multidentate neutral (co)ligands such as polyamines and aza-crown-ethers has also yielded
very active Ae hydrides hydrogenation catalysts4b,15 and various Ae polymerisation catalysts, e.g.
[{LONO4}BaN(SiMe2H)2] (4) bearing the multidentate aza-crown-ether-phenolate {LONO4}‒.10a,16
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N(SiMe2H)2
Ba
O
O
N
N
N
N
N
H
N
N
N(SiMe3)2
thf
CH(SiMe3)2
(thf)2
tBu
Ca
Ba
Ca
Ad
Ca
O
Ad
N
H
N
O
O
tBu
2a
3d
14a
16
1
( )
2
( )
3
( )
4
( )
Fig. 1 Examples of N-based and macrocycle-functionalised alkaline earth molecular complexes. Ad = adamantyl.
As part of our ongoing studies in the area of Ae-mediated molecular catalysis, we thought of combining
the advantages of N-based ligands and macrocycles into ligand frameworks able to stabilise barium species.
We report here on the design of new bulky iminoaniline and amidine proligands that include a tethered
macrocycle. We anticipated that the pairing of bulky iminoanilide or amidinate, which have shown their
ability to kinetically stabilise Ae complexes against ligand scrambling, with a macrocycle known for its
ability to stabilise otherwise electronically unsaturated Ae species, would deliver original ligands
particularly well suited to this chemistry. These ligands were used to generate heteroleptic barium amido
complexes that in turn display good performance in the hydrophosphination of vinylarenes. Synthetic,
structural and catalytic features of these barium compounds are discussed.
Results and Discussion
Synthesis and characterisation
The functionalised iminoaniline {I^Acrown}H and amidine {Amcrown}H proligands containing a tethered 15-
member macrocycle were constructed in convergent multistep syntheses (Scheme 1) that started with the
large scale synthesis of 2-(1-aza-15-crown-5)-ethan-1-amine (A). Condensation of A with the Dipp-N-
substituted benzaldehyde B afforded {I^Acrown}H, whereas {Amcrown}H was obtained by reacting A with the
adamantyl-substituted N-Dipp-carbimidoyl chloride C. Complete experimental details for the synthesis of
the two proligands and of the synthetic intermediates, together with pertaining analytical data, are provided
in the Supporting Information.# Note that the condensation affording {I^Acrown}H, aka step (xiv) in Scheme
1, requires several days and addition of amine A in several portions. Under optimised conditions, this
proligand was ultimately obtained in high yield as an off-white oil which solidified slowly upon standing at
room temperature. However, we found that the final yields of isolated product could vary to noticeable
extents depending on reaction times and protocol for the addition of A.
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OTs
OTs
OH
(i)
HN
Cl
O
O
O
O
ClH3N
(iii)
O
O
O
OH
(v)
O
N
HO
O
HO
O
Cl
(iv)
HN
N
(vi)
O
(ii)
O
HO
HO
O
NH
O
N
O
O
(vii)
O
O
O
O
O
O
O
O
A
(
)
N
N
(viii)
O
N
H
O
NH2
Br
O
Br
O
O
O
NH
NH
(ix)
(x)
(xi)
O
B
(
)
O
O
O
Cl
(xii)
(xiii)
N
Cl
C
)
(
N
H
O
O
O
O
H
O
N
N
N
N
(xiv)
(xv)
A
B
+
N
A
C
+
NH
O
O
O
{I^Acrown}H
{Amcrown}H
Scheme 1. Synthesis of the proligands {I^Acrown}H and {Amcrown}H. Reaction conditions: (i) NaOH, H2O, 50 °C, 4 h,
75%; (ii) Et2O, NEt3, 0 to 20 °C, 12 h, 51%; (iii) TsCl, DMAP, NEt3, CH2Cl2, 0 to 20 °C, 12 h, 85%; (iv) BnBr,
Na2CO3, acetone, reflux, 4 h, 80%; (v) NaOH, nBu4NBr, toluene, 70 °C, 10 h, 82%; (vi) H2, Pd/C, MeOH, 20 °C, 12
h, 80%; (vii) CH3CN/toluene (1:1 v/v), reflux, 24 h, 70%; (viii) H2, Pd/C, MeOH, 20 °C, 15 h, 97%; (ix)
HOCH2CH2OH, PTSA, toluene, reflux, 48 h, 61%; (x) 2,6-iPr2C6H3NH2, Pd(OAc)2, tBuOK, PtBu3, thf, reflux, 16 h;
(xi) CF3COOH, MeOH, 1 h, 20 °C, 38%; (xii) 2,6-iPr2C6H3NH2, toluene, NEt3, 70 °C, 3 h, 98%; (xiii) SOCl2, reflux,
3 h, 90%; (xiv) petroleum ether, reflux, 10 d, 90%; (xv) NEt3, CH2Cl2, 20 °C, 72 h, 32%.
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The sterically congested amidine {Amcrown}H was isolated as analytically pure pale yellow crystals in
non-optimised ca. 30% yield by reaction of compounds A and C under mild and straightforward operating
conditions (see Scheme 1). Alternatively, it was obtained in 70-80% yield as an oily material, although
NMR analysis showed in these cases the presence of trace amounts of residual impurities. Both proligands
were fully characterised by NMR, mass spectrometry and combustion analyses. They are highly soluble in
all common organic solvents, including aliphatic hydrocarbons. Single crystals of {I^Acrown}H suitable for
X-ray diffraction crystallography were grown from the oily material upon standing at room temperature. Its
molecular solid-state structure, with notable interatomic distances, are given in Figure 2. Crystals of
{Amcrown}H were also analysed, but the final refinement of the structure was high (>20%) due to high
disorder.
Fig. 2. ORTEP representation of the molecular solid-state structure of {I^Acrown}H. Ellipsoids at the 50% probability
level. Only one of the two identical molecules in the asymmetric unit is depicted. CH atoms omitted for clarity. Selected
interatomic distances (Å): C17-N18 = 1.461(4), N18-C19 = 1.268(4), N1-C16 = 1.458(3), N1-C15 = 1.469(4), N1-C2
= 1.470(4), C25-N26 = 1.369(4), N26-C27 = 1.428(4).
‒
The amido group N(SiMe2H)2 has been introduced in barium chemistry as a useful tool for the
stabilisation of barium complexes through the presence of intramolecular Ba···H–Si anagostic interactions,
as in a monometallic aminoether-phenolato complex [{LONO4}BaN(SiMe2H)2] (3)16 or in the trinuclear
cluster [Ba3{OSi(OtBu)3}3{N(SiHMe2)2}3].17 Following the same line, the stoichiometric reaction of
[Ba{N(SiMe2H)2}2.(thf)2] with the iminoaniline {I^Acrown}H returned, upon selective release of one
equivalent of HN(SiMe2)H)2, the heteroleptic complex [{I^Acrown}BaN(SiMe2H)2] (5) as an orange solid in
6

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86% yield (Scheme 2). The 1H NMR spectrum of 5 in thf-d8 is characterised by a singlet at δ 8.04 ppm for
the CH=N imine hydrogen, and a multiplet at δ 4.57 ppm for the SiH hydrogen. There is a substantial level
of fluxionality in the complex, as the resonances for OCH2, CH(CH3)2 and Si(CH3)2 moieties are somewhat
broad at room temperature. Similarly, the amidinate complex [{Amcrown}BaN(SiMe2H)2] (6) was isolated as
colourless microcrystals in 85% yield following treatment of [Ba{N(SiMe2H)2}2]∞ with one equivalent of
{Amcrown}H and release of HN(SiMe2H)2. Complexes 5 and 6 are sparingly to moderately soluble in
hydrocarbons (petroleum ether, benzene and toluene), and dissolve well in ethers. The presence of two
stretching bands for Si‒H bonds at 2052 and 1990 cm‒1 (for 5) and at 2014 and 1975 cm‒1 (for 6) in the
FTIR spectra of the two complexes recorded as Nujol mulls is consistent with Ba∙∙∙H‒Si anagostic
interactions in the solid state. This is corroborated by the 1H NMR spectrum of 6 recorded in thf-d8, where
the 1JSiH coupling constant of 160 Hz is also diagnostic of mild Ba···H‒Si interactions in solution.
O
(HMe2Si)2N
Ba
O
O
O
N
O
O
N
O
N
N
NH
N
O
– 2 thf
 HN(SiMe2H)2
5
( )
+
[Ba{N(SiMe2H)2}2.(thf)2]
O
(HMe2Si)2N
N
O
H
N
N
N
N
N
O
Ba
O
O
O
 HN(SiMe2H)2
O
O
6
( )
+
[Ba{N(SiMe2H)2}2]
Scheme 2. Syntheses of [{I^Acrown}BaN(SiMe2H)2] (5), [{Amcrown}BaN(SiMe2H)2] (6).
The molecular solid-state structure of 5 depicted in Figure 3 shows the complex to rest in an eight-
coordinate environment, with coordination of all heteroatoms on the ancillary ligand onto the metal centre
completed by the Nsilazide atom from the tetramethyldisilazide co-ligand. The Ba-O and Ba-Namine interatomic
distances to the heteroatoms in the aza-crown-ether fragment are unremarkable and compare to those in the
phenolato complex [{LO}BaN(SiMe2H)2] (3) already mentioned.16 Similarly, that Ba-Nsilazide bond length
in 5 (2.704(3) Å) matches that in 3 (2.688(2) Å). Coordination of the Nimine atom onto barium does not
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induce a significant stretching of the C=N bond compared to that in the proligand (1.287(5) Å in 5 and
1.268(4) Å in the proligand). Complex 5 exhibits a mild Ba···H‒Si anagostic interaction with H2Si,18 as
indicated by the large discrepancy between the narrow Ba1-N4-Si2 and wider Ba1-N4-Si1 angles
(104.90(14) and 126.02(16) °, respectively); this is consistent with the solution 1H NMR data of the complex
(see above). The barium atom protrudes greatly (1.76 Å) out of the mean plane formed by the atoms N2,
C13, C14, C19 and N3. Note that there is a substantial distortion of the aromatic ring in the anilido fragment,
and that the iminoanilido core made of these six carbons atoms together with C13, N2 and N3 deviates very
clearly from the planarity observed in the proligand (Figure 3).
Fig. 3. Top, ORTEP representation of the molecular solid-state structure of [{I^Acrown}BaN(SiMe2H)2] (5); bottom,
representation of the non-planar iminoanilide core in the molecular solid-state structure of 5. Ellipsoids at the 50%
probability level. CH atoms omitted for clarity. Selected interatomic distances (Å) and angles (°): Ba1-N1 = 3.025(3),
Ba1-N2 = 2.746(3), Ba1-N3 = 2.756(3), Ba1-N4 = 2.704(3), Ba1-O1 = 2.934(3), Ba1-O2 = 2.849(3), Ba1-O3 =
2.906(3), Ba1-O4 = 2.928(3), N2-C13 = 1.287(5), N2-C12 = 1.461(5); Si1-N4-Ba1 = 126.02(16), Si2-N4-Ba1 =
104.90(14).
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The molecular structure of complex 6 is given in Figure 4; it shows one of the two distinct but very
similar molecules of the complex found in the asymmetric unit. The final refinement (R1 = 16.4%) for the
structure is insufficient to enable a thorough discussion of the metric parameters, but the connectivity in the
solid state could be established without ambiguity. The barium atom is seven-coordinate, with binding of
all heteroatoms in the aza-crown-ether fragment completed by the nitrogen atom of tetramethylsilazide (N1)
and, remarkably, by only one of the N atoms (N33) in the hence η1-coordinated amidinate; the other N atom
(N35) points away from the metal centre.
Fig. 4. ORTEP representation of the molecular solid-state structure of [{Amcrown}BaN(SiMe2H)2] (6). Only one of the
two molecules in the asymmetric unit is represented. Ellipsoids at the 50% probability level. Non-interacting benzene
molecules, iPr groups and H atoms other than those interactions with barium omitted for clarity. Poor refinement (R1
= 16.4%) precludes a thorough discussion of metric parameters.
Note that counter-intuitively, the distance from the central carbon atom C34 to the metal-bound nitrogen
atom N33 (ca. 1.33 Å) seems shorter than that to the non-coordinating one N35 (ca. 1.40 Å), but the poor
refinement of the data set precludes a detailed analysis. The η1-coordination mode observed for the
amidinate in 6 is unusual. A similar one was observed in calcium-hydride amidinates, but these complexes
featured an additional pattern of stabilising Ca···C(π) interactions involving the flanking 2,6-iPr2C6H3
substituents.12e There is no such interaction in 6. On the other hand, the geometrical features of the
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tetramethyldisilazide group, notably the largely different Ba1-N1-Si1 (ca. 106 °) and Ba1-N1-Si2 (ca. 120
°) angles, militate in favour of the presence of a Ba1···Hi1 β-SiH anagostic interaction with Hi1.3,16,17,19
Interestingly, the adamantyl substituent of the amidinate is directed towards the metal, and the short
distances to the two hydrogen atoms H56a and H56b (ca. 2.80 Å) could indicate additional agostic bonding.
Barium-catalysed intermolecular hydrophosphination of vinylarenes
The catalytic performances of [{I^Acrown}BaN(SiMe2H)2] (5) and [{Amcrown}BaN(SiMe2H)2] (6) in styrene
hydrophosphination were examined in the light of earlier benchmark results obtained in our group for this
catalysis.3d,5d Two reactions were initially examined (Scheme 3), involving the secondary phosphine HPPh2
(the archetypal substrate in intermolecular hydrophosphination catalysis) and the primary phosphine PhPH2.
Ph
P
Ph
[precat]
10 mol%
Ph2PH
+
benzene-d6, 60 °C
1:1
anti-Markovnikov products
H
P
[precat]
2 mol%
+
PhPH2
Ph
Ph
Ph
benzene-d6, 25 °C
1:1
sec-P
Ph
P
+
Ph
tert-P
Scheme 3. Anti-Markovnikov hydrophosphination of styrene with HPPh2 or PhPH2 using [{I^Acrown}BaN(SiMe2H)2
(5) as the precatalyst.
A preliminary assessment in the equimolar hydrophosphination of styrene with HPPh2 (Scheme 3, top)
showed that under otherwise identical experimental conditions ([styrene]0/[HPPh2]0/[Ba]0 = 10:10:1,
benzene-d6, 60 °C, 60 min), complexes 5 (52% conversion, TOF = 0.5 h–1) and 6 (49% conversion, TOF =
0.5 h–1) both improve on the iminoanilide precatalyst [{I^ADipp2}BaN(SiMe3)2.(thf)2] (32% conversion, TOF
= 0.3 h–1) bearing two Dipp substituents reported previously by our group (Table 1).3c,3d In all cases, and
characteristically for alkaline earth precatalysts,1 the reactions are regioselective and only afford the anti-
Markovnikov addition product PhCH2CH2PPh2 (δ31P = –16.04 ppm in benzene-d6 at 60 °C); no trace of the
branched product could be detected by NMR spectroscopy. Subsequent work focused on the somewhat
more active and more soluble precatalyst 5. Monitoring of the consumption of HPPh2 during the reaction
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catalysed by 5 showed that it is zeroth-order on the concentration [HPPh2]. This is reminiscent of the
behaviour already known for [{I^ADipp2}BaN(SiMe3)2.(thf)2], and for which the following kinetic rate law
was established:3d
rate = k.[HPPh2]0.[styrene]1.[Ba]1
(1)
It is therefore probable that in hydrophosphination reactions catalysed by 5, the operative mechanism is
identical to that with [{I^ADipp2}BaN(SiMe3)2.(thf)2], with rate-limiting 2,1-insertion of the unsaturated C=C
bond in the Ba‒PPh2 bond of a catalytically active [{I^ADipp2}BaPPh2] species (vide infra).
The rate of reactions catalysed by 5 increases substantially for reactions carried out without solvent.
For instance, full conversion of 50 equivalents of HPPh2 and styrene vs 5 was quantitative at 60 °C within
15 min, corresponding to a TOF value ≥ 200 h–1. Complex 5 also mediates the regiospecific anti-
Markovnikov hydrophosphination of styrene with PhPH2 (Scheme 3, bottom). The conversion of 50
equivalents of styrene and phosphine ([styrene]0/[PhPH2]0/[5]0 = 50:50:1) performed at 25 °C in benzene-
d6 is near-quantitative within 60 min. It yields the secondary phosphine PhPHCH2CH2Ph (doublet at δ31P
=
–52.41 ppm in benzene-d6 at 60 °C) with high selectivity, as only traces of the tertiary phosphine
1
PhP(CH2CH2Ph)2 (singlet at δ31P = –24.09 ppm) were detected by H and 31P NMR spectroscopy. The
selectivity towards the secondary phosphine under these experimental conditions typically exceeds 95%.
Note that under identical experimental conditions ([styrene]0/[PhPH2]0/[5]0 = 50:50:1, 25 °C, 60 min,
[metal]0 = 11.5 mM in benzene-d6), the performance of 5 (93% conversion, TOF = 54 h–1) betters that
displayed by the divalent rare-earth precatalysts [{LONO4}YbN(SiMe3)2] (74% conversion, TOF = 37 h–1)
and [{LONO4}SmN(SiMe3)2] (63% conversion, TOF = 32 h–1) supported by the multidentate aminoether-
phenolate {LONO4}‒ (see Figure 1).5d Substrate conversion reaches near completion in the reaction of two
equivalents of styrene vs PhPH2 catalysed by 5 ([styrene]0/[PhPH2]0/[5]0 = 50:25:1, 25 °C, 60 min, [5]0 =
8.0 mM in benzene-d6), and the formation of the tertiary phosphine PhP(CH2CH2Ph)2 is then selective.
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Table 1. Comparative data for the hydrophosphination of styrene with HPPh2 and various Ba precatalysts.
Conversionb TOFc
Precatalyst
[styrene]0/[HPPh2]0/[Ba]0
[%]
[h‒1]
[{I^Acrown}BaN(SiMe2H)2] (5)
[{Amcrown}BaN(SiMe2H)2] (6)
[{I^ADipp2}BaN(SiMe3)2.(thf)2]d
10:10:1
10:10:1
10:10:1
52
49
32
0.52
0.49
0.32
a T = 60 °C, t = 60 min, benzene-d6, [Ba]0 = 10 mM. b Conversion determined by 1H NMR spectroscopy.
c Turnover frequency. d See references 3c and 3d.
On the nature of the active species in Ba-mediated intermolecular alkene hydrophosphination
During the course of the hydrophosphination of styrene with HPPh2 catalysed by 5 (see Scheme 3, top)
carried out in bznezene-d6 at 60 °C, a small crop of orange single crystals formed out of solution. The
identity of the compound, [{I^Acrown}BaPPh2] (7), was established by X-ray diffraction analysis.
The molecular structure of 7 shows the barium to rest in an eight-coordinate environment, with
coordination of all heteroatoms form the macrocycle (Figure 5). To our knowledge, it is the first structurally
authenticated heteroleptic barium-phosphide, although a number of homoleptic complexes have been
previously reported, e.g. [{([Me3Si]2CH)(C6H3-2-OMe-3-Me)P}2Ba.(thf)2],20 [Ba{P(SiMe3)2}2.(thf)4],21
[Ba(PPh2)2.(thf)5],22 and [Ba(PPh2)2.(18-crown-6)].23 The Ba‒N interatomic distances in 7 are
commensurate with those measured in the parent amido complex 5. The Ba‒P bond length (3.3686(9) Å) is
comparable to those in [Ba(PPh2)2.(thf)5] (3.328(2) and 3.345(2) Å) and [Ba(PPh2)2.(18-crown-6)]
(3.3484(7) Å).22,23
The mononuclear complex 7 is thought to have formed under catalytic conditions upon deprotonation
of the relatively acidic substrate HPPh2 by precatalyst 5, with concomitant release of HN(SiMe2H)2. An
NMR scale reaction between 5 and a stoichiometric amount of HPPh2 in thf-d8 was consistent with the
formation of a main new organometallics species assumed to be 7 (see ESI). Besides production of this new
complex, the 1H NMR spectrum indicated release of HN(SiMe2H)2 and quantitative consumption of HPPh2,
together with the presence a small amount, ca. 15%, of free {I^Acrown}H (presumably released through
hydrolysis during sample preparation). The 31P NMR spectrum confirmed full consumption of HPPh2 (δ ca.
‒41 ppm),22 and a broad resonance at ca. +5 ppm compatible with a putative [Ba]‒PPh2 species was
detected.22-23 Yet, the NMR data for the reaction between 5 and HPPh2 also showed the presence of other
unidentified species, and we failed to isolate analytically pure 7. Catalytic studies with pre-isolated 7 could
hence not be conducted. We therefore cannot assert with total confidence that 7, which could not be isolated
cleanly, is the sole active species under catalytic conditions.
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Fig. 5. ORTEP representation of the molecular solid-state structure of [{I^Acrown}BaPPh2] (7). Ellipsoids at the 50%
probability level. H atoms and non-interacting benzene molecule omitted for clarity. One component of each disordered
C6H5 moieties is depicted. Selected interatomic distances (Å): Ba1-N31 = 2.691(2), Ba1-N23 = 2.780(2), Ba1-O10 =
2.847(2), Ba1-O4 = 2.869(2), Ba1-O7 = 2.886(2), Ba1-O13 = 2.886(2), Ba1-N1 = 2.972(2), Ba1-C32 = 3.302(3), Ba1-
P1 = 3.3686(9).
Based on our earlier investigations of the mechanism of intermolecular hydrophosphination reactions,3d
7 is thought to be the catalytically active species in the catalysed hydrophosphination of styrene mediated
by 5 (Scheme 4). Considering that the reactions only generate the anti-Markovnikov products of addition,
the mechanism is proposed to involve 2,1-insertion of the polarised Ph(H)C(δ–)=C(δ+)H2 double bond into the
[Ba]–PPh2 bond in 7, resulting in the production of a transient barium alkyl species [Ba]–CH(Ph)CH2PPh2.
This intermediate is then rapidly protonated by an incoming HPPh2 to release the product PhCH2CH2PPh2
and regenerate the active species 7.
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2,1-insertion
Ph2P
Ph
O
O
O
O
(HMe2Si)2N
Ba
O
PPh2
O
N
N
N
O
O
O
Ba
N
Ba
O
O
O
N
N
N
N
N
HPPh2
 HN(SiMe2H)2
protonolysis
7
( )
5
( )
precatalyst
catalyst
HPPh2
PhCH2CH2PPh2
anti-Markovnikov
product
Scheme 4. Proposed mechanism for styrene/HPPh2 hydrophosphination catalysed by [{I^Acrown}BaN(SiMe2H)2] (5).
Conclusion
The two nitrogen-based proligands {I^Acrown}H and {Amcrown}H, respectively an iminoaniline and an
amidine bearing a tethered macrocycle side-arm prepared in multi-step procedures, enable the preparation
of the heteroleptic barium complexes [{I^Acrown}BaN(SiMe2H)2] and [{Amcrown}BaN(SiMe2H)2]. These
solvent-free complexes have been characterised in the solid state, and they both exhibit high coordination
numbers. The iminoanilide [{I^Acrown}BaN(SiMe2H)2] mediates competently the hydrophosphination of
styrene with primary and secondary phosphines. These reactions exhibit entire anti-Markovnikov
selectivity, and they also generate chemoselectively a single secondary phosphine in the reaction of PhPH2
with either one or two equivalents of styrene.
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Conflicts of interest
There are no conflicts of interest to declare.
Notes and references
‡
#
These two co-authors have contributed equally to the work.
Note that the macrocyclic 1-aza-15-crown-5, i.e. the product of reaction (vi) in Scheme 1, is
commercially available, but at prohibitive cost for large scale syntheses.
1
2
(a) S. Harder, Chem. Rev., 2010, 110, 3852; (b) M. R. Crimmin and M. S. Hill, Top. Organomet. Chem.,
2013, 45, 191; (c) M. S. Hill, D. J. Liptrot and C. Weetman, Chem. Soc. Rev., 2016, 45, 972.
(a) M. R. Crimmin, I. J. Casely and M. S. Hill, J. Am. Chem. Soc., 2005, 127, 2042; (b) M. R. Crimmin,
M. Arrowsmith, A. G. M. Barrett, I. J. Casely, M. S. Hill and P. A. Procopiou, J. Am. Chem. Soc., 2009,
131, 9670; (c) M. Arrowsmith, M. R. Crimmin, A. G. M. Barrett, M. S. Hill, G. Kociok-Köhn and P.
A. Procopiou, Organometallics, 2011, 30, 1493; (d) J. S. Wixey and B. D. Ward, Chem. Commun.,
2011, 47, 5449; (e) B. Liu, T. Roisnel, J.-F. Carpentier and Y. Sarazin, Chem. Eur. J., 2013, 19, 2784;
(f) N. Romero, S.-C. Roşca, Y. Sarazin, J.-F. Carpentier, L. Vendier, S. Mallet-Ladeira, C. Dinoi and
M. Etienne, Chem. Eur. J., 2015, 21, 4115; (g) S. Tobisch, Chem. Eur. J., 2015, 21, 6765; (h) B. Freitag,
C. A. Fischer, J. Penafiel, G. Ballmann, H. Elsen, C. Färber, D. F. Piesik and S. Harder, Dalton Trans.,
2017, 46, 11192.
3
(a) A. G. M. Barrett, C. Brinkmann, M. R. Crimmin, M. S. Hill, P. Hunt and P. A. Procopiou, J. Am.
Chem. Soc., 2009, 131, 12906; (b) C. Brinkmann, A. G. M. Barrett, M. S. Hill and P. A. Procopiou, J.
Am. Chem. Soc., 2012, 134, 2193; (c) B. Liu, T. Roisnel, J.-F. Carpentier and Y. Sarazin, Angew. Chem.
Int. Ed., 2012, 51, 4943; (d) B. Liu, T. Roisnel, J.-F. Carpentier and Y. Sarazin, Chem. Eur. J., 2013,
19, 13445; (e) S. Tobisch, Chem. Eur. J., 2014, 20, 8988.
4
5
(a) F. Buch, J. Brettar and S. Harder, Angew. Chem. Int. Ed., 2006, 45, 2741; (b) P. Jochmann, J. P.
Davin, T. P. Spaniol, L. Maron and J. Okuda, Angew. Chem. Int. Ed., 2012, 51, 4452; (c) J. Intemann,
H. Bauer, J. Pahl, L. Maron and S. Harder, Chem. Eur. J., 2015, 21, 11452.
See 2e, 3c, 3d and: (a) M. R. Crimmin, A. G. M. Barrett, M. S. Hill, P. B. Hitchcock and P. A.
Procopiou, Organometallics, 2007, 26, 2953; (b) H. Hu and C. Cui, Organometallics, 2012, 31, 1208;
(c) S.-C. Roşca, T. Roisnel, V. Dorcet, J.-F. Carpentier and Y. Sarazin, Organometallics, 2014, 33,
5630; (d) I. V. Basalov, B. Liu, T. Roisnel, A. V. Cherkasov, G. K. Fukin, J.-F. Carpentier, Y. Sarazin
and A. A. Trifonov, Organometallics, 2016, 35, 3261; (e) B. J. Ward and P. A. Hunt, ACS Catal., 2017,
7, 459; (f) I. V. Lapshin, O. S. Yurova, I. V. Basalov, V. Yu. Rad’kov, E. I. Musina, A. V. Cherkasov,
15

Dalton Transactions
Page 16 of 18
View Article Online
DOI: 10.1039/C9DT01512D
G. K. Fukin, A. A. Karasik and A. A. Trifonov, Inorg. Chem., 2018, 57, 2942; (g) I. V. Lapshin, I. V.
Basalov, K. A. Lyssenko, A. V. Cherkasov and A. A. Trifonov, Chem. Eur. J., 2019, 25, 459.
(a) T. M. A. Al-Shboul, H. Görls and M. Westerhausen, Inorg. Chem. Commun., 2008, 11, 1419; (b)
T. M. A. Al-Shboul, H. Görls, S. Krieck and M. Westerhausen, Eur. J. Inorg. Chem., 2012, 5451; (c)
F. M. Younis, S. Krieck, T. M. A. Al-Shboul, H. Görls and M. Westerhausen, Inorg. Chem., 2016, 55,
4676.
6
7
(a) M. S. Hill, D. J. Liptrot, D. J. MacDougall, M. F. Mahon and T. P. Robinson, Chem. Sci., 2013, 4,
4212; (b) C. Bellini, J.-F. Carpentier, S. Tobisch and Y. Sarazin, Angew. Chem. Int. Ed., 2015, 54,
7679.
8
9
O. I. Kolodiazhnyi, Top. Curr. Chem., 2015, 360, 161.
D. Georgiadis and V. Dive, Top. Curr. Chem., 2015, 360, 1; (b) D. Virieux, J.-N. Volle, N. Bakalara
and J.-L. Pirat, Top. Curr. Chem., 2015, 360, 39; (c) A. J. Wiemer and D. F. Wiemer, Top. Curr. Chem.,
2015, 360, 115.
10 (a) Y. Sarazin, B. Liu, T. Roisnel, L. Maron and J.-F. Carpentier, J. Am. Chem. Soc., 2011, 133, 9069;
(b) H. Bauer, M. Alonso, C. Fischer, B. Rösch, H. Elsen and S. Harder, Angew. Chem. Int. Ed., 2018,
57, 15177.
11 M. Arrowsmith, M. S. Hill and G. Kociok-Köhn, Organometallics, 2010, 29, 4203.
12 (a) M. H. Chisholm, J. Gallucci and K. Phomphrai, Chem. Commun., 2003, 48; (b) S. Datta, M.T.
Gamer and P. W. Roesky, Organometallics, 2008, 27, 1207; (c) T. D. Nixon and B. D. Ward, Chem.
Commun., 2012, 48, 11790; (d) M. Arrowsmith, M. S. Hill and G. Kociok-Köhn, Organometallics,
2014, 33, 206; (e) A. Causero, G. Ballmann, J. Pahl, H. Zijlstra, C. Färber and S. Harder,
Organometallics, 2016, 35, 3350; (f) X. Shi, C. Hou, C. Zhou, Y. Song and J. Cheng, Angew. Chem.
Int. Ed., 2017, 56, 16650.
13 (a) S. Harder and J. Brettar, Angew. Chem. Int. Ed., 2006, 45, 3474; (b) C. Ruspic, S. Nembenna, A.
Hofmeister, J. Magull, S. Harder and H. W. Roesky, J. Am. Chem. Soc., 2006, 128, 15000; (c) C. Ruspic
and S. Harder, Inorg. Chem., 2007, 46, 10426; (d) S. Nembenna, H. W. Roesky, S. Nagendran, A.
Hofmeister, J. Magull, P.-J. Wilbrandt and M. Hahn, Angew. Chem. Int. Ed., 2007, 46, 2512; (e) A. S.
S. Wilson, M. S. Hill, M. F. Mahon, C. Dinoi and L. Maron, Science, 2017, 358, 1168.
14 (a) A. Causero, H. Elsen, G. Ballmann, A. Escalona and S. Harder, Chem. Commun., 2017, 53, 10386;
(b) B. Freitag, J. Pahl, C. Färber and S. Harder, Organometallics, 2018, 37, 469; (c) C. N. de Bruin-
Dickason, T. Sutcliffe, C. Alvarez Lamsfus, G. B. Deacon, L. Maron and C. Jones, Chem. Commun.,
2018, 54, 786.
15 (a) V. Leich, T. P. Spaniol, L. Maron and J. Okuda, Angew. Chem. Int. Ed., 2016, 55, 4794; (b) D.
Schuhknecht, C. Lhotzky, T. P. Spaniol, L. Maron and J. Okuda, Angew. Chem. Int. Ed., 2017, 56,
16

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12367; (c) M. Wiesinger, B. Maitland, C. Färber, G. Ballmann, C. Fischer, H. Elsen and S. Harder,
Angew. Chem. Int. Ed., 2017, 56, 16654.
16 Y. Sarazin, D. Roşca, V. Poirier, T. Roisnel, A. Silvestru, L. Maron and J.-F. Carpentier,
Organometallics, 2010, 29, 6569.
17 O. Michel, S. König, K. W. Törnroos, C. Maichle-Mössmer and R. Anwander, Chem. Eur. J., 2011,
17, 11857.
18 H1Si and H2Si hydrogen atoms linked to silicon atoms were introduced in the structural model through
Fourier difference maps analysis.
19 (a) O. Michel, K. W. Törnroos, C. Maichle-Mössmer and R. Anwander, Chem. Eur. J., 2011, 17, 4964;
(b) O. Michel, K. W. Törnroos, C. Maichle-Mössmer and R. Anwander, Eur. J. Inorg. Chem., 2012,
44; (c) B. Liu, T. Roisnel, J.-P. Guégan, J.-F. Carpentier and Y. Sarazin, Chem. Eur. J., 2012, 18, 6289;
(d) J. P. Davin, J.-C. Buffet, T. P. Spaniol and J. Okuda, Dalton Trans., 2012, 41, 12612; (e) S.-C.
Roşca, C. Dinoi, E. Caytan, V. Dorcet, M. Etienne, J.-F. Carpentier and Y. Sarazin, Chem. Eur. J.,
2016, 22, 6505; (f) S.-C. Roşca, E. Caytan, V. Dorcet, T. Roisnel, J.-F. Carpentier and Y. Sarazin,
Organometallics, 2017, 36, 1269; (g) D. Mukherjee, S. Shirase, K. Beckerle, T. P. Spaniol, K. Mashima
and J. Okuda, Dalton Trans., 2017, 46, 8451; (h) E. Le Coz, H. Roueindeji, V. Dorcet, T. Roisnel, J.-
F. Carpentier and Y. Sarazin, Dalton Trans., 2019, DOI: 10.1039/C9DT00771G.
20 S. Blair, K. Izod, W. Clegg and R. W. Harrington, Inorg. Chem., 2004, 43, 8526.
21 M. Westerhausen and W. Schwarz, J. Organomet. Chem., 1993, 463, 51.
22 M. Gärtner, H. Görls and M. Westerhausen, Z. Anorg. Allg. Chem., 2007, 633, 2025.
23 M. R. Crimmin, A. G. M. Barrett, M. S. Hill, P. B. Hitchcock and P. A. Procopiou, Inorg. Chem., 2007,
46, 10410.
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For the Table of Contents only
Two barium-amide complexes bearing crown-ether-functionalised amidinate and iminoanilide
ligands that act as competent precatalysts for the intermolecular hydrophosphination of vinylarenes
are presented. The ligands combine features that are very effective in alkaline earth chemistry.
Hydrophosphination barium catalysis
Ph
P
Ph
Ph2PH
+
barium
precatalyst
H
P
Ph
+ PhPH2