3H-1,3-Azaphospholo[4,5-b]pyridines-novel heterocyclic P,N-bridging or hybrid ligands: Synthesis and first d8-transition metal complexes

Article abstract of DOI:10.1039/c5dt04073f

The first 3H-1,3-azaphospholo-pyridines 2a-c were synthesized as racemic mixtures in modest to medium yield by the reaction of N-(2-chloropyrid-3-yl)-trimethylacetimidoyl chloride 1 with RPLi₂ (R = Ph, n-Bu, i-Bu), generated from RPH₂

Full text of DOI:10.1039/c5dt04073f

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3H-1,3-Azaphospholo[4,5-b]pyridines – novel
heterocyclic P,N-bridging or hybrid ligands:
synthesis and first d8-transition metal complexes†
Cite this: DOI: 10.1039/c5dt04073f
Mohamed Shaker S. Adam,a,b Markus K. Kindermann,a Peter G. Jonesc and
Joachim W. Heinicke*a
The first 3H-1,3-azaphospholo-pyridines 2a–c were synthesized as racemic mixtures in modest to
medium yield by the reaction of N-(2-chloropyrid-3-yl)-trimethylacetimidoyl chloride 1 with RPLi2 (R =
Ph, n-Bu, i-Bu), generated from RPH2 and BuLi in THF at −70 °C, and studied with respect to their suit-
ability as ligands (L) in transition metal complexes. Reactions of 2a with group 6 metal(0) pentacarbonyls
led to P-coordinated LM(CO)5 complexes 3a–5a (Cr, Mo, W) and the reaction of 2c with (norbornadiene)-
Mo(CO)4 surprisingly to 4c. [Rh(1,5-COD)Cl]2 and 2a,b, in metal/ligand ratio 1 : 1, furnished LRh(1,5-COD)Cl
complexes 6a,b with P-coordination, 6b accompanied by a minor contamination by the bis-coordinated
L[Rh(COD)Cl]2 complex 7b. Reactions of 2a,b with [(allyl)PdCl]2 proceeded in THF with dismutation of
N-coordinated (allyl)PdCl and formed with 2a a labile crude product [(2a){(allyl)PdCl}1.2(PdCl2)0.8]·C4H8O,
with the composition close to L[Pd(allyl)Cl]PdCl2 THF (8a·THF), which converted during crystallization to
9a, whereas 2b directly formed the N,N’-PdCl2-bridged bis[LPd(allyl)chloride] complex 9b. Conversion of
2b with equimolar amounts of Pd(CH3CN)2Cl2 in THF, or Na2PdCl4 in methanol, gave rise to the dimeric
P,N-bridging complex 10b. Crystal structure analyses of 6a (rac), 9b·2CDCl3 (meso), 10b·4.5THF and
10b·2D6-acetone (rac) provided detailed structural information. 10b, but more efficiently complexes
formed in situ from 2a,b and Pd2(DBA)3 or Pd(OAc)2, catalysed the arylamination of 2-bromopyridine with
2,4,6-trimethylaniline.
Received 16th October 2015,
Accepted 24th November 2015
DOI: 10.1039/c5dt04073f
www.rsc.org/dalton
dibenzophosphole and a η1P-AuCl complex of the N-methyl-
Introduction
ated ligand.3 In connection with our investigations of
Various types of pyridylphosphines are known and have been pyrido[b]-anellated 1H-1,3-azaphospholes,4 we were interested
applied as hybrid or hemilabile ligands in a large number of in establishing the consequences for the coordination behaviour
mono-, di- and polynuclear transition metal complexes and in if the phosphorus is fixed within a cyclic structure, fused with
a
variety of transition-metal-catalysed organic transform- the pyridine ring. Since the dicoordinated phosphorus of the
ations.1 Even four-membered P,N-chelate complexes can be 1H-1,3-azaphospholes is a weak donor and has formed isolable
formed with 2-PR2 derivatives2 if the rotation of this group transition metal complexes so far only with M0(CO)n fragments
around the C–P bond is not hindered by a substituent in (M = Cr, Mo, W; n = 5, rarely 4 and 3)4,5 or, as shown for the
3-position of the pyridine ring. Pyrido[b]-anellated phospholes related 1H-1,3-benzazaphospholes, with electron-rich d10
or phosphinines, or partially saturated derivatives thereof with coinage metal compounds or HgCl2,6 the first pyrido[b]-anel-
the phosphino group fixed in a ring system, are, to the best lated 3H-1,3-azaphospholes were synthesized and tested with
of our knowledge, still unknown except for a single 4-aza- respect to their reactions with some transition metal com-
pounds and as ligands in a Pd-catalysed C–N cross-coupling
reaction.
aInstitut für Biochemie, Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-
Str. 4, 17487 Greifswald, Germany. E-mail: heinicke@uni-greifswald.de
bDepartment of Chemistry, College of Science, King Faisal University, P.O. Box 380,
Al Hufuf 31982, Al Hassa, Saudi Arabia
cInstitut für Anorganische und Analytische Chemie, Technische Universität
Results and discussion
Braunschweig, Hagenring 30, 38106 Braunschweig, Germany
†Electronic supplementary information (ESI) available. CCDC 1423102–1423105.
Ligands and LM(CO)5 complexes
For the synthesis of the novel P,N-ligands we exploited the
increased reactivity of 2-chloropyridines to electrophilic
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5dt04073f
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substitution compared to chlorobenzenes. The precursor N-(2- lower end of the Δδ-ranges of the M(PR3)(CO)5 complexes of
chloropyrid-3-yl)-imidoyl chloride 1, accessible by refluxing chromium, molybdenum and tungsten.7a The 13C NMR
N-(2-chloropyrid-3-yl)-pivalamide with PCl5 in toluene, was found signals of C2 and C3a, in α-position to phosphorus, are slightly
to react at −70 to 20 °C with RPLi2 species (R = Ph, n-Bu, i-Bu), downfield-shifted by coordination of the metals at phos-
1
freshly prepared from the corresponding primary phosphines phorus, with a concomitant decrease of JPC of C2 from 35–38
and two equivalents of nBuLi in THF at −70 °C, to form the in 2a–c to 3–6 Hz (or broad singlets) in 3a–5a but a strong
1
P-substituted 1,3-azaphospholo[4,5-b]pyridines 2a–c (Scheme 1). increase of JPC of C3a from 17–20 to ca. 60–72 Hz. Coordi-
These compounds were isolated in low to moderate yields nation of M(CO)5 at nitrogen was not observed, even if excess
(21–59%) as oily racemic mixtures of 3R- and 3S-enantiomers. or two equivalents of M(CO)5(THF) were used; this simply
Compound 2a solidified on storage at room temperature. The caused contamination by M(CO)6. The lack of additional
non-aromatic phosphole-type heterocycles are more sensitive N-coordination is revealed by the 13C NMR spectra, in which a
to air and to decomposition by acidic OH-groups on silica gel second set of cis-M(CO)4 and trans-M(CO) signals, clearly
than their aromatic 1H-1,3-isomers,4b but vacuum distillation recognizable in the spectra of the better soluble complexes 3a
provided the compounds in sufficient purity for reactivity and 4c, is absent. The absence of N-coordination is further
studies towards transition metal compounds.
supported by minimal downfield coordination chemical shifts
Treatment of 2a with M(CO)5(THF) (M = Cr, Mo, W) in THF, of C5 in 3a–5a and 4c (Δδ = 1.0–1.5 ppm), whereas in pyri-
prepared in situ by UV-irradiation of the corresponding M(CO)6 dine–W(CO)5 complexes the Δδ values are larger, amounting to
solution, furnished at r.t. the carbonyl complexes 3a–5a as 4.9–6.3 ppm.9 Attempts to prepare a mono- or dimeric N,P-
amorphous solids in high (Cr, W) to moderate (Mo) yield. The bridging complex by the reaction of 2c (as ligand L) with an
weak CO bands at 2068, 2076 and 2075 cm−1 (A1 mode, trans- equimolar amount of Mo(NBD)(CO)4 (NBD = norbornadiene)
CO stretching) of 3a–5a are similar or equal to the wave failed. Instead, the Mo(κ1P-L)Mo(CO)5 complex 4c was isolated
numbers published for the corresponding Ph3PM(CO)5 com- in fair yield (34%). It was unambiguously identified by its 13C
plexes (2065, 2074 and 2075 cm−1) whereas the strong CO and 31P NMR data (Δδ31P4c–2c = 40.8 ppm). Whether this is
bands of 4a and 5a at 1944 and 1936 cm−1 (in 3a super- attributable to the higher stability of 4c compared to a dimeric
imposed by the absorption of Cr(CO)6 trace impurity) are batho- [Mo(κ2P,N-L)(CO)4]2 complex, or to weak intramolecular inter-
chromically shifted relative to the E-bands (unsymmetric actions with the N-lone pair or π-density at the pyridine
stretching of four coplanar CO ligands) of the respective N-atom in a [Mo(L)(CO)4] monomer, promoting dismutation
Ph3PM(CO)5 complexes (1950 and 1942 cm−1) and comparable reactions, was not investigated during this study.
to those of (phenyldialkylphosphine)M(CO)5 complexes (1942
and 1937 cm−1).7 The one-bond 31P–183W coupling constant of
LRh(COD)Cl complexes
5a (1JPW = 225 Hz), known to correlate in a linear fashion with
Reaction of [Rh(COD)Cl]2 in THF solution with 2a,b in a
the CO(E-mode) stretching vibrations7a and the total electro-
negativity of the P-substituents,8 even adopts a value between
that of PhBu2PW(CO)5 and Bu3PW(CO)5 (1JPW = 235 and 200
Hz).7a The higher donor strengths indicated by the E- than by
the A1-mode bands might be attributable to interactions
between the cis-CO ligands and the delocalized π-system of the
phosphole-type ligand, which are lacking for the perpendicu-
larly bound trans-CO ligand. The 31P coordination chemical
shifts of 3a–5a, Δδ = 20.1, 36.8 and 60.0 ppm, are found at the
1 : 2 molar ratio led to cleavage of the weak μ2-chloro bridging
bond (Scheme 2). The higher coordination strength at
rhodium(I) of the σ3P donor compared to the imino-N-atoms,
known from early measurements of reaction enthalpies of
[Rh(COD)Cl]2 with Ph3P and pyridine10 and from the P-coordi-
nation in (2-PyPPh2)Rh(COD)Cl,11 led to the expected coordi-
nation at phosphorus. The racemic complexes 6a,b were
obtained in high yields as orange-yellow powders, and 6a also
as single crystals, providing detailed structural information.
Scheme 2 Formation of (1,3-azaphospholo[4,5-b]pyridine)Rh(COD)Cl
complexes 6a,b; possible N,P-bis-Rh(COD)Cl intermediates 7a,b and
equilibrium species in solution.
Scheme 1 Synthesis of 3H-1,3-azaphospholo[4,5-b]pyridines 2a–c and
metal(0) pentacarbonyl complexes 3a–5a and 4c.
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The triclinic unit cell (space group P1), contains one (S)- reduced downfield shifts of 13C2 and 13C3a, the characteristic
(Fig. 1) and (R)-enantiomer. The rhodium center is co- changes of the 1JPC coupling constants as mentioned above for
ordinated by the pyridoazaphosphole ligand through the phos- 3a–5a, and, in particular, by the downfield shifts of the
phorus atom, and exhibits a distorted square-planar geometry. phosphorus resonance (Δδ ≈ 29 ppm). The 31P doublets of 6a
The Rh–P bond length is shorter than in the complexes and 6b appear at δ = 27.2 and 28.2 ppm, respectively, and thus
(triarylphosphine)Rh(COD)Cl (2.297–2.3607(14) Å)12a and in lie within the signal range of (2-PyPPh2)Rh(COD)Cl and
(P-tert-butyl-2-trimethylsilyl-1,3-benzazaphospholine)RhCOD)Cl (triarylphosphine)Rh(COD)Cl complexes.11,12 The one-bond
ˉ
1
(2.3354(5) Å),13 thus implying a somewhat stronger coordi- 31P–103Rh-coupling constants, JPRh ≈ 143 (6a) and 141.7 Hz
nation. The chloride ligand and the center of the C25–C26 (6b), indicative of the sum of electronegativities of the ligands
double bond are arranged cis to phosphorus while the C21– at Rh(I),13 were smaller by ca. 10 Hz than in the aforemen-
C22 double bond is positioned cis to chloride. The angles of tioned complexes11,12 and also smaller than in the aryldialkyl-
the CvC centers to the Cl- and P-atoms in the trans-position phosphine-ligated (P-tert-butyl-1,3-benzazaphospholine)Rh-
are effectively linear (177.5, 176.7°) and the Rh-(CvC) distance (COD)Cl (1JPRh = 150.7–151.9 Hz)14 and (2-PyPiPr2)Rh(COD)Cl
trans to phosphorus is 0.09 Å shorter than the Rh-(CvC) trans complexes (1JPRh = 144.7 Hz).15 For the solution of 6a in CDCl3,
to chloride, presumably because of back bonding (trans-influ- besides the strong phosphorus doublet, a small but very broad
ence). Because the C3A–P3–C2 angle in the five-membered singlet was observed at δ31P = −1.1 ppm (integral ratios 87–83
ring (87.53(4)°) is smaller than the ideal tetrahedral angle, the to 13–17%), close to that of the free ligand (δ31P = −1.9 ppm),
opposite angle Rh–P3–C11 at the distorted tetrahedral phos- which may be caused by small equilibrium amounts of
phorus is widened (122.16(3)°). The two imino N-atoms are far N-coordinated species and/or 2a, formed by ligand dissociation
away from rhodium, both intramolecularly and also in the in solution. Such processes are known for the sterically hin-
packing (see the ESI†), where the 3R- and 3S-enantiomers each dered (o-Tol3P)Rh(COD)Cl12a and double exchange reactions of
form homochiral chains with weak intermolecular contacts (Ph3P)Rh(COD)Cl with (p-MeOC6H4)3P-ligated LRh(CO)(acac).16
(H6⋯Cl 2.79 and H7⋯Cl 2.89 Å) between the chlorine atom of The analogous dynamic behavior of 6a is further confirmed
the Rh(COD)Cl group and H6 and H7 of the pyridine ring of by rather broad aryl signals in the proton and 13C NMR
the neighbouring molecule. The chains are linked by inversion spectra and very broad signals for the COD protons and 13C
via the contact H19B⋯Cl, 2.85 Å. The intramolecular contact nuclei. An indication of involvement of pyridine nitrogen may
H20A⋯Cl, 2.74 Å, may also be a stabilizing factor. Both these be provided by the lack of equally intense vCH proton signals
latter contacts involve tert-butyl hydrogens.
for 6a in the range 3.1–3.6 and 5.2–5.7 ppm, typical of (triaryl-
The solution NMR spectra in CDCl3 confirmed the for- phosphine)Rh(COD)Cl complexes,11,12 and by the occurrence
mation of complexes 6a and 6b in terms of the slightly of a very broad signal at δ = 4.24 ppm, close to the averaged
vCH proton signal of (2-PyPPh2)Rh(COD)Cl (δ
=
4.42 ppm).11,12 An averaged 13C signal for vCH at δ =
85.8 ppm, close to that in (2-PyPPh2)Rh(COD)Cl at δ = 88 ppm
and absent in (triarylphosphine)Rh(COD)Cl complexes, consti-
tutes additional evidence in this direction. Thus, it can be
assumed that the interactions with the pyridine N-atom lead
in analogy to (2-PyPPh2)Rh(COD)Cl to trigonal bipyramidal
intermediates that allow rapid pseudorotation with the inter-
change of axial and equatorial positions and thus of the vCH
nuclei in the trans- and cis-positions to phosphorus or chlor-
ide.11 Coordination at the pyridine nitrogen within the ring
plane and at the phosphorus of 6a outside the ring plane dis-
favors intramolecular N- and P-coordination compared to pyri-
dylphosphines, where the PR2 group may rotate around the
P–C2-bond to a suitable position and even allow P,N-chelate
formation. Weak interactions with π-electrons of pyridine
nitrogen, however, and thus an intramolecular Rh(COD)Cl
migration, may not a priori be excluded, though an inter-
molecular mechanism of two molecules 6a via an intermediate
P,N-bis-Rh(COD)Cl complex 7a might be a more suitable
Fig. 1 Molecular structure of 6a the (3S)-enantiomer is depicted; ellip- pathway. Small equilibrium amounts of 2a might also cause
soids with 50% probability. Selected bond lengths (Å) and angles (°):
Rh–P3 2.2855(3), Rh–Cl 2.3547(3), Rh–C25 2.1274(11), Rh–C26 2.1364(11),
Rh–C21 2.2085(11), Rh–C22 2.2176(11), Rh–(C21vC22) 2.103,
Rh–(C25vC26) 2.013, C2–P3 1.8733(10), P3–C3A 1.8144(10), N1–C2
similar (or further) line broadening by rapid ligand exchange
reactions, long known for (Ph3P)Rh(COD)Cl in the presence of
Ph3P.12 Whether the imino group of the five-membered ring is
also involved in solution reactions is not clear. Since the be-
havior of 6a is certainly even more complicated than that of
1.2902(13), N1–C7A 1.4159(12); P3–Rh–Cl 90.624(10), C3A–P3–C2
87.53(4), C11–P3–Rh 122.16(3), N1–C2–P3 113.53(7).
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triaryl- or pyridylphosphinorhodium complexes,
a closer
investigation of the dynamic behavior is a case for specialists
in this field.
The solution NMR spectra of the P-butyl-1,3-azaphospholo-
[4,5-b]pyridine)Rh(COD)Cl complex 6b differ from those of 6a.
The proton and 13C NMR signals of the olefinic vCH nuclei
trans and cis to P or Cl, respectively, are not averaged out but
appear in a similar region as in (Ph3P)Rh(COD)Cl11 or
(2-PyPiPr2)Rh(COD)Cl) at low temperatures (≤−30 °C).15 This,
together with the only marginal changes in VT 31P NMR
spectra of 6b in the temperature range of −56 to +40 °C,
means that the ligand exchange reactions are considerably
slower than in 6a and in (2-pyridyldialkylphosphine)Rh(COD)-
Cl complexes. This may be attributed to the higher complex
stability of P-alkyl- compared to P-aryl-azaphospholopyridine–
Rh(I) complexes and to the rigidity of the bicyclic azaphos-
pholopyridine ligands. A small sharp 31P doublet signal at δ =
17.2 ppm (1JPRh = 151.1 Hz), ca. 5% by 31P-integration, may be
attributed, in accordance with the CHN values and a cationic
fragment peak for [7b-Cl]+ in the high resolution mass spec-
Fig. 2 Crystal structure of 9b·2CDCl3 (hydrogens and solvent omitted
for clarity). Ellipsoids represent 50% probability levels. Selected bond
lengths (Å) and angles (°): Pd1–P3 2.2685(5), Pd1–Cl1 2.3542(5), Pd1–
C18 2.125(2), Pd1–C17 2.157(2), Pd1–C16 2.197(2), C16–C17 1.384(4),
C17–C18 1.396(4), Pd2–N4 2.0121(15), Pd2–Cl2 2.2976(5), C2–P3
1.8506(19), P3–C3A 1.8027(18), C2–N1 1.288(2), N1–C7A 1.417(2) Å;
C16–Pd1–Cl1 100.35(7), C18–Pd1–Cl1 167.66(7), C16–Pd1–P3 165.00(8),
C18–Pd1–P3 97.89(7)°.
trum, to
a
small amount of contamination by 7b.
N-Coordinated (pyridyl)Rh(COD)Cl complexes are known17
and thus, in addition to phosphorus of 2b, the N-atom may
also undergo coordination to the transition metal.
C16 and C17 are coplanar (mean deviation 0.02 Å); the angles
P3–Pd1–C16 and Cl1–Pd1–C18 are roughly linear (165.00(8),
LPd(allyl)Cl and (LPdCl2)2 complexes
With the intention of ensuring complete conversion of the 167.66(7)°). Similarly to the Rh(COD) complex 6a, the Pd1–C16
ligands to complexes with a 1 : 1 ligand/metal ratio, reactions bond length trans to phosphorus is shorter by 0.072 Å than the
of 2a and 2b were performed with [η3-(allyl)PdCl]2 in a molar Pd1–C18 bond length trans to chloride. Despite this back-
ratio 2 : 1.5. This led in THF to orange-yellow products, soluble bonding effect, C17–C18 is still shorter than C16–C17, which
in THF and sparingly soluble in hexane. CHN analyses of the suggests a slightly increased weight of a resonance structure
yellow powder, obtained from 2a after the extraction of hexane- with the C–Pd σ-bond trans to P and the (CvC)–Pd π-bond
soluble components, were roughly consistent with a compo- trans to the Cl atom. The P3–Pd1–Cl1 angle (94.182(19)°) is
sition [(2a){(allyl)PdCl}1.2(PdCl2)0.8]·C4H8O (close to 8a·C4H8O); close to the ideal 90°, but the bite angle C18–Pd1–C16 (67.44(10)°)
those of the product formed with 2b corresponded to 9b with of the allyl group is substantially smaller and causes sig-
a composition [(2b)2{(allyl)PdCl}2(PdCl2)]. Crystals were first nificant deviations of C16 and C18 from true cis- and trans-
obtained from a solution of the crude product formed from 2a positions to Cl and P. The phosphorus atom is a distorted tetra-
in THF by overlayering with hexane. These were studied by hedral with a narrow C2–P3–C3A angle (87.36(8)°), enforced
XRD and identified as complex 9a, crystallised with THF, by the five-membered azaphosphole ring, and a concomitantly
showing that 2a reacts more slowly, but analogously to 2b to increased C12–P3–Pd1 angle (121.33(6)°). The palladium Pd1
form complexes of type 9. Severe disorder of the allyl group is coordinated 2.00 Å above the mean ligand plane (average
and unexpected peaks, possibly caused by twinning, prevented deviation 0.03 Å), and the n-butyl group is directed towards the
satisfactory refinement. However, single crystals were then opposite side, with C12 lying 1.56 Å out of the plane. In the
grown by slow concentration of an NMR sample of crude 9b in crystal packing the molecules are connected to form ribbons
CDCl3, allowing a full and satisfactory refinement of the XRD parallel to [110] by weak interactions of 2.89, 2.76 Å between
data and unambiguous identification as 9b·2CDCl3 (Fig. 2).
chlorine Cl1 of the Pd(allyl)Cl groups and H6 and H7 of the
The crystal structure analysis of 9b·2CDCl3 revealed an pyridine rings of the neighbouring molecules, in a fashion
inversion-symmetric molecule in which a central PdCl2 unit similar to that observed for 6a (an intramolecular contact
connects two (η3-allyl)(κ1P-azaphospholopyridine)palladium H5⋯Cl1, 2.71 Å across the inversion centre, is also observed).
chloride fragments by κ1N-coordination within the ring plane; In addition, short N⋯D and Cl⋯Cl contacts of 2.53 and 3.49 Å
as a consequence of symmetry, the mutual orientation of the respectively are observed between CDCl3 and the molecules of
two pyridoazaphosphole rings is trans with anti-orientation, 9b (Fig. 3).
and the configuration at phosphorus is R in one and S is in
The surprising coordination of PdCl2 as well as (allyl)PdCl
the other ring. The planes of the pyridine ring and the almost may be explained by primary formation of P- and N-bis
perfectly square planar N2Pd2Cl2 moiety are arranged perpen- (allylPdCl) azaphospholopyridine complexes, formed by the
dicularly (interplanar angle 89.9°). The atoms Pd1, P3, Cl1, association of the P,N-ligand with the weakly chloro-bridged
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To obtain information on the nature of palladium com-
plexes containing only PdCl2 units and azaphospholo[4,5-b]-
pyridines, ligand 2b was treated with bis(acetonitrile)palla-
dium dichloride in THF and in a second experiment with pot-
assium tetrachloropalladate in methanol, each in a 1 : 1 molar
ratio (Scheme 4). The rigidity of the aromatic pyridine ring,
coordinating the metal at nitrogen within the ring plane,
together with the rigid position of the tetrahedrally co-
ordinated phosphorus in the five-membered ring with the
metal outside the pyridine ring plane are inappropriate for the
formation of stable mononuclear four-membered N,P-chelate
complexes. At best, labile intermediates with some stabiliz-
ation by π-interactions with the pyridine N-atom outside the
ring plane are conceivable. These should either dimerize or
polymerize to more stable products with coordination at nitro-
gen within the ring plane. The orange-yellow and yellow com-
plexes, formed from the two different precursors, differed in
their solubility, the first being well soluble in THF or CDCl3,
the second rather sparingly soluble in these solvents and
better soluble only in more polar solvents such as methanol or
acetone. The NMR spectra indicated complex formation by
downfield shifts of the phosphorus resonance, Δδ = 33.5 and
29.2 ppm, respectively, slightly (Cq of 2-tBu) and clearly (C7a)
Fig. 3 Packing of 9b·2CDCl3 in the crystal (n- and tert-butyl groups
indicated by their α-C atoms). Dashed lines represent weak C–H⋯Cl
and C–D⋯N hydrogen bonds or Cl⋯Cl contacts.
(allylPdCl) dimer and subsequent dismutation of the less
stable N-coordinated (allyl)PdCl fragment. Since N-pyridyl-Pd-
(allyl)Cl complexes18 have not been reported to convert to
N-pyridyl-PdCl2 complexes, activation of this process is
assumed to be connected with the proximity of the P-co-
ordinated (allyl)PdCl group. A possible scenario might be a
chloro-bridging interaction, leading to a more labile penta-
coordinated Pd(allyl)Cl group that could undergo allyl-chloride
exchange reaction with a second molecule. This would lead to
8a, which together with THF and a small residual amount of
the primary product would be consistent with the composition
of the crude product formed from 2a and, after combination
with the intermediate LRh(allyl)Cl, with the formation of 9a,b
(Scheme 3). The atomic balance of the chloro atoms in 9a,b
shows that the reaction actually proceeded in a ligand/metal
ratio of 1 : 2. The assumption of an allyl-Cl exchange implies
the formation of (allyl)2Pd, removed by washing the products
with hexanes on work-up. A small shoulder (δ = 58 ppm) at the
upfield end of the allyl 13CH2 resonance (δ = 62.8 ppm) in the
13C solution NMR spectrum of [(2a){(allyl)PdCl}1.2(PdCl2)0.8]·
C4H8O, close to the upfield vCH2 signal of diallylpalladium
(δ = 54.6 in D8-toluene19), might be a hint at this species,
formed by dismutation of the residual (2a)(allylPdCl)2 complex
of the crude product. The corresponding CH2-signals of
N- and P-(allyl)PdCl compounds absorb at lower field
(δ = 61–63 ppm)18,20 and are not responsible for this shoulder.
2
increased JPC coupling constants, typically for complexes of
2b, and a somewhat downfield shifted 2-tBu proton singlet,
while the majority of the 13C and proton signals is scarcely
Scheme 4 Formation of dimeric (1,3-azaphospholopyridine-κ1P, κ1N’)-
PdCl2 complexes 10b with schematic presentation of its “twisted boat
structure”.
Scheme 3 Reaction of 2a,b with [η3-(allyl)PdCl]2 via assumed intermediates 8a,b to 9a,b.
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changed by the coordination. However, XRD analyses of crys-
tals of both products, grown by slow diffusion of hexane into
the complex solution in THF or by slow concentration of the
D6-acetone solution, respectively, revealed in both cases a
dimeric structure consisting of [cis-Cl2Pd(L-P,N′)]2 moieties
with Pd(II) bound at P and pyridine-N′ or P′ and pyridine-N,
one from each azaphospholopyridine bridging ligand. Both
structures exhibit the two ligands on the same side (syn-form)
of the connecting Cl–Pd–P axes with opposite orientation of
the five- and six-membered rings, so that they are different sol-
vates of the same dinuclear complex 10b. Neither complex dis-
plays imposed crystallographic symmetry, but the THF solvate
has approximately twofold symmetry (r.m.s. deviation 0.04 Å),
while the acetone solvate does not, because of different orien-
tations of the substituents. The ligand ring systems remain
planar (mean deviations 0.01–0.02 Å) and the interplanar
angles are 32° and 27° respectively for the THF and acetone
solvates. The square planar configuration around Pd(II), with
cis-orientation of the two chloride ligands, causes an almost
perpendicular orientation of the Cl–Pd–P axis towards the
plane of the N-coordinated pyridine ring (angles between
Cl⋯P vector and normal to the ligand plane 87–89°), while the
coordination of the distorted tetrahedral phosphorus outside
the pyridine-ring plane of the respective ligand enforces a con-
siderable mutual twisting of the N–Pd–Cl axes of the two
Cl2PdNP fragments in the dimer (angle between vectors
N4′⋯Cl1 and N4⋯Cl3: 62, 61°) and a “twisted boat structure”
for the central eight-membered ring. The mutual orientation of
the two azaphospholopyridine ligands, together with the local
twofold symmetry, implies the same configuration for the two
P atoms in the dimers and leads for both 10b·4.5THF and
10b·2D6-acetone (Fig. 4), to pairs of (3S,3′S)- and (3R,3′R)-dia-
stereoisomers, co-crystallising as racemic products. Different
packing in the crystals of 10b·4.5THF and 10b·2D6-acetone
must thus be caused by the different solvent molecules; the
large number of H⋯Cl and H⋯O contacts however makes an
exact analysis difficult. The Pd–P, Pd–N and Pd–Cl and intra-
ligand bond lengths and angles exhibit no special features and
are similar in both complexes and also in (R,S)-9b·2CDCl3. The
somewhat longer Pd–Cl bond trans to phosphorus compared
to that trans to nitrogen reflects the known stronger trans influ-
ence of P versus N donors.
Fig. 4 (a) View of the (3S,3’S)-enantiomers in the crystal of 10b·4.5THF
(above) and (b) in the crystal of 10b·2(D6-acetone) (below, alternative
view direction); solvents omitted for clarity, ellipsoids with 50% prob-
ability. Selected bond lengths (Å) and angles (°) for 10b·4.5THF: Pd1–P3
2.2397(9), Pd1–N4’ 2.048(3), Pd1–Cl1 2.2725(9), Pd1–Cl2 2.3396(8), C2–
P3 1.865(3), P3–C3A 1.808(3), P3–C12 1.821(3); N4’–Pd1–Cl1 178.70(8),
N4’–Pd1–P3 90.62(8), N4’–Pd1–Cl2 89.47(8), P3–Pd1–Cl1 88.39(3),
P3–Pd1–Cl2 176.55(3), Cl1–Pd1–Cl2 91.57(3), C2–P3–C3A 87.61(15),
C12–P3–Pd1 122.68(11), N1–C2–P3 113.7(2); bond lengths and angles of
10b·2(D6-acetone) are similar (see deposited material for details).
type, also known as Buchwald–Hartwig reactions,24 are impor-
tant tools for the production of arylamine fine chemicals.25
The coupling according to Scheme 5 was carried out using a
similar protocol to that used with the formerly applied cata-
lysts,22,23 to allow a comparison of the catalytic performance.
The reactants were heated in toluene in the presence of two
equivalents of KOtBu with 5 mol% 10b or precatalysts, pre-
pared in situ from 2a or 2b and Pd(OAc)2 or Pd2DBA3 (DBA –
dibenzoylacetone) in a 1 : 1 or 2 : 1 molar ratio. With 10b the
Catalytic tests
Pyridylphosphines1 have found wide applications in tran-
sition-metal-catalysed organic syntheses. The hemilabile pro-
perties, known also from other P,N ligands,21 might be
advantageous by enabling temporary substrate binding on
replacement of the more labile donor and catalyst stabilization
after reductive elimination by re-occupation of an empty
coordination site. For the first test of the suitability of azaphos-
pholopyridine complexes as catalysts the known N-arylation
of 2,4,6-trimethylaniline (mesitylamine) with 2-bromopyri-
dine22,23 was chosen, providing 2-mesitylaminopyridine (11) as
a potential precursor for the synthesis of N-mesityl-substituted
Scheme 5 The Pd-catalysed C–N coupling reaction of 2-bromopyri-
1,3-azaphospholo[5,4-b]pyridine.4b C–N cross-couplings of this dine with mesitylamine.
Dalton Trans.
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Table 1 Screening of 10b and in situ generated azaphospholopyridine–
Pd catalysts in the arylamination of 2-bromopyridinea
Experimental
All manipulations were carried out under an atmosphere of
dry argon or nitrogen using Schlenk techniques. Solvents were
dried over sodium ketyl and distilled before use. 3-Amino-2-
chloropyridine, primary phosphines and transition metal com-
pounds were used as purchased. NMR spectra were recorded
on a multinuclear FT-NMR spectrometer ARX300 or Avance300
(Bruker) at 300.1 (1H), 75.5 (13C), and 121.5 (31P) MHz and
298 K. The 1H, 13C and 31P chemical shifts are δ values and
given in ppm relative to Me4Si and H3PO4 (85%), respectively,
as external standards or to solvents calibrated with the afore-
mentioned standards. Coupling constants refer to H–H
(1H NMR) or P–C couplings (13C NMR) unless stated otherwise.
NMR assignment numbers follow the nomenclature, and are
illustrated in Scheme 1 for the compounds 1 and 2a–c and
used also for the coordinated ligands. For atom numbers in
crystal structures see Fig. 1–4. Mass spectra were recorded on a
single-focusing sector field mass spectrometer AMD40 (Intec-
tra, EI 70 eV); HRMS spectra were recorded on a double-focus-
ing sector field mass spectrometer MAT 95 (Fa. Finnigan, EI 70
eV) or an ion cyclotron resonance-mass spectrometer APEX IV
(Bruker Daltonik, ESI in MeOH, NH4OAc). Elemental analyses
(C, H, N) were carried out using a LECO elemental analyzer,
Model CHNS-932, under standard conditions.
Pd
Metal/ligand
ratio
Mol%
ligand
Yield
(%)
Entry
compound
Ligand
1
2
3
4
5
6
7
8
9
10b
—
2a
2a
2b
2b
2b
2b
Ph3P
(p-Tol)3P
(o-Tol)3P
1 : 1
1 : 1
1 : 2
1 : 1
1 : 2
1 : 1
1 : 2
1 : 2
1 : 2
1 : 2
5
5
10
5
10
5
10
10
10
10
26
57
43
54
42
51
33
21
23
18
Pd2DBA3
Pd2DBA3
Pd2DBA3
Pd2DBA3
Pd(OAc)2
Pd(OAc)2
Pd2DBA3
Pd2DBA3
Pd2DBA3
10
a Reaction conditions: Heating of 2-bromopyridine, mesitylamine and
KOtBu with the given amount of 10b or the given ligand and Pd-
compound in toluene for 24 h at 100 °C; yields refer to isolated
product after separation by column chromatography.
yield of 11 was rather low (Table 1, entry 1, 26%), comparable
to that obtained with catalysts for comparison generated
in situ from Pd2DBA3 and triphenyl- or tri-tolylphosphines
(1 : 2 molar ratio), whereas the catalysts formed from 2a or 2b
and Pd(OAc)2 or Pd2DBA3 gave higher yields, particularly for a
1 : 1 molar ratio of metal to ligand (Table 1, entries 2, 4 and 6).
The maximum yield of 57% (after isolation) is not high, but is
higher than the reported results with DPPE/Pd2DBA3 (51%
yield for 2 mol% catalyst and heating with 2 equiv. NaOtBu
overnight)22 and 2,3-bis(diphenyl)quinoxaline/Pd(OAc)2 or
Pd2DBA3 (36–43% yield with 2–5 mol% catalyst, conditions
as here).23
N-(2-Chloropyrid-3-yl)-trimethylacetimidoyl chloride (1)
(a) Trimethylacetylchloride (5.14 mL, 42.0 mmol) was added
dropwise to a solution of 3-amino-2-chloropyridine (4.5 g,
35.0 mmol) and triethylamine (5.85 mL, 42.0 mmol) in THF
(20 mL) and Et2O (20 mL) at 0 °C. The reaction mixture was
stirred for 1 h at 0 °C, overnight at room temperature, and
then treated with water to remove trimethylamine hydrochlo-
ride, trimethylacetic acid and pyridinium salts. The aqueous
Conclusions and outlook
The first synthesis of 3H-1,3-azaphospholo-pyridines, which phase was separated, extracted with ether, the combined
except for a single 4-aza-dibenzophosphole seem also to be the organic phase washed with a concentrated aqueous solution of
first representative of pyrido[b]-anellated five- and six-mem- NaHCO3, and then dried over MgSO4. The solvent was
bered heterocycles containing one phosphorus atom, paves the removed in a vacuum to give 6.2 g (83%) of NMR-spectroscopi-
way for investigations of transition metal complexes of these cally pure N-2-chloropyrid-3-yl-trimethylacetamide, which was
1
novel P,N ligands, closely related to 2-pyridylphosphines, used without recrystallization in step (b). H NMR (CDCl3): δ =
but with restricted flexibility and lacking free rotation around 1.36 (s, 9 H, CMe3), 7.27 (t, 3J = 8.2, 4.7 Hz, 1 H, H-5), 8.00
3
4
the C–P bond at the pyridine ring. The first examples of such (v br, NH), 8.11 (dd, J = 4.7, J = 1.7 Hz, 1 H, H-6), 8.76 (dd,
complexes, hints at dynamic properties and applicability to 3J = 8.2, 4J = 1.8 Hz, 1 H, H-4).
transition-metal-catalysed reactions were presented. The asym-
(b) Phosphorus pentachloride (5.1 g, 24.5 mmol) was added
metry at phosphorus and the potential for a wide range of to a solution of N-2-chloropyrid-3-yl-trimethylacetamide (5.1 g,
different P- and/or N-coordinated complexes, including brid- 24.0 mmol) in dry toluene (50 mL). The reaction mixture was
ging or cluster compounds as known for pyridyl phosphine refluxed for 4 h, after which the solvent and volatile by-pro-
ligands, open a wide field for coordination chemical studies ducts were removed under vacuum. The residue was distilled
with the novel ligands. If the additional imino donor of the at 10−5 mbar/96 °C to give 5.0 g (90%) of 1 as colourless oil.
five-membered ring is also involved in transition metal coordi- 1H NMR (CDCl3): δ = 1.30 (s, 9 H, CMe3), 7.08 (dd, 3J = 7.8, 4J =
nation, even a three-dimensional metal–ligand network might 1.6 Hz, 1 H, H-4), 7.14 (dd, 3J = 7.8, 4.8 Hz, 1 H, H-5), 8.08 (dd,
4
become accessible. Last but not least, electronic delocalization 3J = 4.8, J = 1.6 Hz, 1 H, H-6). 13C{1H} NMR (CDCl3): δ = 27.90
within the effectively planar imino-conjugated pyridine (CMe3), 43.97 (CMe3), 122.57 (C-5), 129.06 (C-4), 141.38, 141.49
π-system might lead to transition metal complexes with inter- (Cq-2, Cq-3), 144.70 (C-6), 160.48 (CvN). MS (EI 70 eV, 65 °C):
esting redox and/or photophysical properties.
m/z (%) = 232 (5), 230 (8) [M+], 197 (21), 195 (66), 141 (28),
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Dalton Transactions
139 (84), 57 (100). Anal. calcd for C10H12Cl2N2 (231.12): −70 °C with n-butyl lithium (7.81 mL, 1.6 M, 12.5 mmol), reac-
C 51.97, H 5.23, N 12.12; found: C 51.87, H 5.38, N 12.00.
tion with a solution of 1 (1.20 g, 5.19 mmol) in THF (80 mL) at
−70 °C to room temperature and work-up as described above
DL-2-tert-Butyl-3-phenyl-1,3-azaphospholo[4,5-b]pyridine (2a)
to give at 10−5 mbar/80–85 °C (bath) 0.81 g (33%) air sensitive
1
n-Butyl lithium solution (19.4 mL, 1.6
M
in hexane, slightly contaminated pale yellow oily 2c. H NMR (C6D6): δ =
31.4 mmol) was slowly added while stirring at −70 °C to 0.75–1.0 (m, 6 H, CHMeAB), 1.37 (s, 9 H, CMe3), 1.6–2.05 (br m,
3
phenylphosphine (1.70 mL, 15.44 mmol) dissolved in THF 2 H, PCH2), 2.10–2.30 (m, 1 H, CH), 6.72 (dd, J = 8.0, 4.8 Hz,
4
(20 mL). After 1 h a solution of 1 (2.90 g, 12.6 mmol) in THF 1 H, H-6), 7.83 (dt, 3J = 8.0, 4J = JPH = 1.5 Hz, 1 H, H-7),
4
(100 mL) was added dropwise at −70 °C to the reaction 8.40 (ddd, 3J = 4.8, 4J = 1.5, JPH = 1.0 Hz, 1 H, H-5).
mixture. Stirring was continued for 1 h at low temperature and 13C{1H} (CH-COSY, DEPT135) NMR (C6D6): δ = 24.38 (d, 3J =
then overnight at room temperature. The solvent was removed 7.3 Hz, CMeA), 24.67 (d, 3J = 8.4 Hz, CMeB), 28.17 (d, 2J =
under vacuum, the residue was extracted with Et2O (50 mL), 9.0 Hz, CH), 30.79 (d, 3J = 5.1 Hz, CMe3), 35.72 (d, 1J = 19.3 Hz,
2
and ether was evaporated. The residue was distilled at 10−5 PCH2), 40.98 (d, J = 17.3 Hz, CMe3), 123.33 (s, CH-6), 129.90
mbar/95–100 °C (bath temp.) to give 0.71 g (21%) pale yellow (s, CH-7), 147.79 (d, 3J = 10.0 Hz, CH-5), 152.26 (d, 1J = 18.6 Hz,
2
1
oily 2a, which solidified on storage at room temperature. Cq-3a), 166.17 (d, J = 17.4 Hz, Cq-7a), 201.48 (d, J = 37.8 Hz,
1H NMR (CDCl3): δ = 1.27 (s, 9 H, CMe3), 7.20–7.38 (m, 6 H, Cq-2). 31P{1H} NMR (C6D6): δ = −10.2. MS (EI 70 eV, 250 °C):
3
4
4
phenyl, H-6), 8.05 (ddd, J = 8.1, J = 1.3, JPH = 1.7 Hz, 1 H, m/z (%) = 249 (8), 248 (31) [M+], 192 (62), 191 (89), 177 (100).
H-7), 8.48 (dt, 3J = 4.8, 4J = 1.3, 4JPH = 1.2 Hz, 1 H, H-5). 13C{1H} HRMS (ESI in MeOH/NH4OAc): C14H21N2P (248.30), calcd for
NMR (CDCl3): δ = 30.09 (d, 3J = 5.3 Hz, CMe3), 40.65 (d, 2J = [M + H]+ 249.15151, found: 249.15160.
1
16.7 Hz, CMe3), 123.17 (s, C-6), 128.86 (d, J = 13.3 Hz, Cq-i),
DL-(2-tert-Butyl-3-phenyl-1,3-azaphospholo[4,5-b]pyridine-κ1P)-
pentacarbonyl chromium(0) (3a)
129.10 (d, 3J = 9.2 Hz, 2 C-m), 129.45 (s, C-7) 130.46 (d, 4J =
1.9 Hz, C-p), 135.02 (d, 2J = 20.6 Hz, 2 C-o), 147.61 (d, 3J =
9.9 Hz, C-5), 151.93 (d, 2J = 18.9 Hz, Cq-7a), 164.68 (d, 1J = A solution of Cr(CO)5(THF), prepared by irradiation of Cr(CO)6
20.3 Hz, Cq-3a), 200.64 (d, 1J = 35.1 Hz, Cq-2). 31P{1H} NMR: δ = (351 mg, 1.60 mmol) in THF (30 mL; 36 mL of CO evolved),
−1.9 (CDCl3); −4.4 (D6-DMSO). MS (EI 70 eV, 25 °C): m/z (%) = was added to a solution of 2a (214 mg, 0.797 mmol) in THF
269 (17), 268 (100) [M+], 253 (71), 212 (45), 211 (30), 139 (34), (10 ml) at −10 °C. The solution was warmed to room tempera-
57 (88). HRMS (EI, 70 eV): calcd for [M]+ 268.1124; found: ture and stirred for 2 d. The solvent was evaporated under
268.1128. Anal. calcd for C16H17N2P (268.29): H 6.39, N 10.44; vacuum, excess Cr(CO)6 was removed under high vacuum, and
found: H 6.16, N 10.27.
the residue was extracted with ether/hexane yielding 330 mg of
an air-sensitive pale brown powder with rather low solubility,
still containing some Cr(CO)6. 1H NMR (CDCl3): δ = 1.31 (s,
DL-3-n-Butyl-2-tert-butyl-1,3-azaphospholo[4,5-b]pyridine (2b)
Compound 2b was prepared in analogy to 2a by lithiation of 9 H, CMe3), 7.37–7.51 (m, 6 H, phenyl and H-6), 8.07 (ddd, 3J =
n-butylphosphine (1.47 mL, 13.1 mmol) in THF (10 mL) at 8.1, JPH = 2.4, 4J = 1.2 Hz, 1 H, H-7), 8.63 (dd, 3J = 4.3, 4J ≈
4
−70 °C with n-butyl lithium (16.4 mL, 1.6 M in hexane, 1 Hz, 1 H, H-5). 13C{1H} NMR (CDCl3): δ = 30.10 (d, 3J = 2.3 Hz,
26.16 mmol), and subsequent reaction with a solution of 1 CMe3), 41.03 (d, 2J = 18.0 Hz, CMe3), 125.05 (C-6), 129.43 (d,
(2.52 g, 10.9 mmol) in THF (80 mL) at −70 °C to room temp- 3J = 10.6 Hz, 2 C-m), 131.7, 131.8 (C-7, C-p), 133.15 (d, 2J =
erature and work-up as described above to give 1.6 g (59%) of 12.0 Hz, 2 C-o), 149.09 (d, 3J = 14.2 Hz, C-5), 215.53 (d, 2J =
an air sensitive pale yellow viscous oil, distilled at 10−5 mbar/ 11.9 Hz, 4 cis-CO); Cq signals except for cis-CO at the noise
1
3
90–96 °C (bath). H NMR (CDCl3): δ = 0.72 (t, J = 7.0 Hz, 3 H, level. 31P{1H} NMR (CDCl3): δ = 58.1. MS (EI 70 eV, 90 °C): m/z
CH3), 1.05–1.32 (m, 6 H, CH2), 1.34 (s, 9 H, CMe3), 7.21 (dd, (%) = 460 (4), 349 (5), 348 (20) [M+ − 4CO], 321 (22), 320 (100)
3J = 8.1, 4.8 Hz, 1 H, H-6), 7.91 (dt, 3J = 8.1, 4J = 1.3, JPH
=
[M+ − 5CO], 52 (98) [Cr+]. HRMS (ESI in MeOH + NH4OAc):
4
1.6 Hz, 1 H, H-7), 8.43 (dt, J = 4.8, J ≈ 4JPH = 1.2, 1.3 Hz, 1 H, C21H17CrN2O5P (460.34) calcd for: [M + H]+ 461.03530, found:
H-5). 13C{1H} NMR (CDCl3): δ = 13.10 (s, Me), 23.47 (d, J = 461.03530. IR (KBr): ν(CO) = 2068 (w) cm−1; the very strong
8.0 Hz, CH2), 24.92 (d, J = 20.2 Hz, CH2), 28.40 (d, J = 1.5 Hz, band at 1950 cm−1 is superimposed by the absorption of the
CH2), 29.32 (d, 3J = 4.8 Hz, CMe3), 39.74 (d, 2J = 17.2 Hz, Cr(CO)6 contamination.
3
4
CMe3), 122.19 (s, C-6), 128.68 (s, C-7), 146.57 (d, 3J = 9.7 Hz,
Detection of DL-(2-tert-butyl-3-phenyl-1,3-azaphospholo[4,5-b]-
C-5), 151.13 (d, 2J = 17.5 Hz, Cq-7a), 163.38 (d, 1J = 17.2 Hz,
pyridine-κ1P)pentacarbonyl molybdenum(0) (4a)
Cq-3a), 200.13 (d, 1J = 38.3 Hz, Cq-2). 31P{1H} NMR (CDCl3): δ =
−2.5. MS (EI 70 eV, 20 °C): m/z (%) = 249 (2), 248 (26) [M+], A solution of Mo(CO)5(THF), prepared by irradiation of
192 (35), 191 (100) [M − Bu+], 165 (48), 149 (28), 148 (29), 137 (21), Mo(CO)6 (208 mg, 0.79 mmol) in THF (20 mL; 18 mL of CO
136 (29), 57 (35). HRMS (ESI in MeOH, NH4OAc): C14H21N2P evolved), was added to a solution of 2a (141 mg, 0.53 mmol) in
(248.30) calcd for [M + H]+ 249.15151; found 249.15161.
THF (5 mL) at −10 °C. Filtration, removal of the solvent after
2 d at room temperature and repeated extraction of unconverted
2a from the crude product with ether/hexane afforded 105 mg
DL-2-tert-Butyl-3-isobutyl-1,3-azaphospholo[4,5-b]pyridine (2c)
Compound 2c was prepared in analogy to 2a by lithiation of (40%) of an air-sensitive pale brown powder with rather low
isobutylphosphine (0.70 mL, 6.22 mmol) in THF (10 mL) at solubility. 1H NMR (D6-acetone): δ = 1.33 (s, 9 H, CMe3),
Dalton Trans.
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7.46–7.64 (m, 6 H, phenyl and H-6), 8.19 (ddd, 3J = 8.0, Cq-3a), 195.41 (d, 2J = 2.7 Hz, Cq-2), 195.58 (d, 2J = 6.6 Hz, 4
4JPH = 2.6, 4J = 1.5 Hz, 1 H, H-7), 8.65 (ddd, 3J = 4.9, 4J = cis-CO), 197.23 (d, 1J = 22.6 Hz, 1 trans-CO). 31P{1H} NMR
4
1.5, JPH = 0.6 Hz, 1 H, H-5). 13C{1H} NMR (D6-acetone): (CDCl3): δ = 18.2 (s, satl, 1JPW = 225 Hz). IR (KBr): ν(CO) = 2075 (w),
δ = CMe3 superimposed by solvent signals, 41.66 (d, 2J = 1936 (vs, br) cm−1. MS (EI 70 eV, 80 °C): m/z (%) = 593 (30)
18.9 Hz, CMe3), 126.50 (C-6), 130.57 (d, 3J = 10.6 Hz, 2 C-m), [M(184W)
+ + − 5 CO].
H+], 453 (100%) [M(184W) H+
131.18 (C-7), 133.00 (d, 4J = 2.4 Hz, C-p), 134.38 (d, 2J = 13.5 HRMS (ESI in MeCN): calcd for [M(184W) + H+] 593.04571;
Hz, 2 C-o), 150.13 (d, 3J = 13.9 Hz, C-5), 205.52 (d, 2J = 8.2 Hz, 4 found: 593.04569 (and correct isotopic pattern). Anal. calcd
cis-CO); Cq signals except for cis-CO at the noise level. 31P{1H} for C21H17N2O5PW (592.18): H 2.89, N 4.73; found: H 3.15,
NMR (D6-acetone): δ = 34.9. IR (KBr): ν(CO) = 2076 (w), N 4.67.
1944 (vs) cm−1
.
DL-(2-tert-Butyl-3-phenyl-1,3-azaphospholo[4,5-b]pyridine-κ1P)-
(η4-cycloocta-1,5-diene)rhodium(I)chloride (6a)
DL-(2-tert-Butyl-3-isobutyl-1,3-azaphospholo[4,5-b]pyridine-κ1P)-
pentacarbonyl molybdenum(0) (4c)
[RhCl(1,5-COD)]2 (32 mg, 0.065 mmol) in THF (5 mL) was
Mo(CO)4(NBD) (117.1 mg, 0.39 mmol) and 2c (96.8 mg, added slowly at −20 °C to
a solution of 2a (35 mg,
0.39 mmol) were placed into a Schlenk flask, THF (10 mL) was 0.130 mmol) in THF (5 mL). The mixture was stirred overnight
added and the mixture heated at 40 °C for 4 h. Insoluble impu- at room temperature, resulting in a colour change from yellow
rities were filtered off and washed with ether. Removal of the to deep orange. Insoluble material was removed by filtration,
solvent under vacuum provided a yellow-brown oil. 31P NMR the solvent was evaporated under vacuum and the residue was
monitoring displayed the product (δ = 30.6) along with two washed several times with n-hexane and dried under vacuum
contaminants (δ = 29.1, −7.3). Purification by column chrom- to give ca. 60 mg (90%) of an orange-yellow solid. 1H NMR
atography on silica gel (hexane/2% ethyl acetate) furnished (CDCl3): δ = 1.61 (s, 9 H, CMe3), 1.9, 2.4 (vbr s, 8 H, CH2, COD),
61 mg (32%) of an air-sensitive pale yellow viscous oil. δ = 4.2, 4.6, 5.6 (3 vbr s, 2 H, 1 H, 1 H, vCH, COD), 7.27–7.40 (m,
3
1H NMR (CDCl3): δ = 0.49 (d, 3J = 6.4 Hz, 3 H, CHMeA), 0.86 4 H, H-6, H-p, H-o), 7.65 (vbr t, J ≈ 8.1 Hz, 2 H, H-m), 8.0 (vbr
(d, 3J = 6.8 Hz, 3 H, CHMeB), 1.54 (s, 9 H, CMe3), 1.45–1.61 d, 3J = 7.8 Hz, 1 H, H-7), 8.45 (vbr, 1 H, H-5). 13C{1H} and
(superimposed m, PCH2), 2.35 (m, 1 H, CH), 7.38 (ddd, 3J = DEPT135 NMR (CDCl3): δ = 30.21 (superimposed s, CMe3), 30.8
5
3
4
7.9, 4.9, JPH = 1.5 Hz, 1 H, H-6), 7.99 (ddd, J = 7.9, JPH = 2.3, (superimposed vbr, 4 CH2, COD), 41.42 (d, 2J = 18.4 Hz, CMe3),
4J = 1.5 Hz, 1 H, H-7), 8.64 (dd, J = 4.9, J = 1.5 Hz, 1 H, H-5). 78.7 (vbr, vCH, COD), 85.8 (vbr, vCH, COD), 105.9 (vbr,
3
4
13C{1H} and DEPT-135 NMR (CDCl3): δ = 23.52 (d, J = 5.3 Hz, 2 vCH, COD), 124.5 (superimposed d, Cq-i), 124.79 (CH-6),
3
CMeA), 24.97 (d, J = 9.3 Hz, CMeB), 28.25 (d, J = 8.0 Hz, CH), 128.80 (d, 3J = 10.6 Hz, 2 CH-m), 130.4, 131.2 (2 br s, CH-7,
3
2
29.86 (d, 3J = 2.7 Hz, CMe3), 39.52 (d, 1J = 11.9 Hz, PCH2), CH-p), 134.16 (d, J = 12.1 Hz, 2 CH-o), 148.0 (br d, J = 14 Hz,
2
3
40.43 (d, 2J = 18.6 Hz, CMe3), 124.68 (s, CH-6), 129.97 (s, CH-5), 150.08 (d, 2J = 27.6 Hz, Cq-7a), 159.56 (d, 1J = 68 Hz,
CH-7), 147.92 (d, J = 29.2 Hz, Cq-7a), 148.52 (d, J = 13.3 Hz, Cq-3a), 192.6 (br, Cq-2). 31P{1H} NMR (CDCl3): δ = 27.2 (br d,
2
3
CH-5), 160.05 (d, 1J = 65.0 Hz, Cq-3a), 195.25 (d, 1J = 9.3 Hz, half width each ≈25 Hz, 1JPRh = 139–143 Hz), −0.8 (minor solu-
2
2
Cq-2), 204.64 (d, J = 8.9 Hz, 4 COcis), 208.94 (d, J = 22.6 Hz, tion species, 13–17%). Anal. calcd for C24H29ClN2PRh (514.83):
COtrans). 31P{1H} NMR (CDCl3):
30.6. HRMS (DEI): C 55.99, H 5.68, N 5.44; found: C 55.58, H 5.43, N 5.35. Orange
δ
=
C19H21MoN2PO5 (484.29); calcd for [M(98Mo)]+ 486.0237; found crystals suitable for XRD analysis, formed by slow diffusion of
486.0230; calcd for [M(98Mo)
458.0277.
−
CO]+ 458.0287; found: hexane into a solution of the solid in a small amount of THF,
were selected from the mixture with mother liquor. Crystal
data are compiled in Table 2, and the selected bond lengths
and angles are shown Fig. 1.
DL-(2-tert-Butyl-3-phenyl-1,3-azaphospholo[4,5-b]pyridine-κ1P)-
pentacarbonyl tungsten(0) (5a)
DL-(3-n-Butyl-2-tert-butyl-1,3-azaphospholo[4,5-b]pyridine-κ1P)-
(η4-cycloocta-1,5-diene)rhodium(I)chloride (6b) and detection
of 7b
A solution of W(CO)5(THF), prepared by irradiation of W(CO)6
(160 mg, 0.455 mmol) in THF (30 mL; 10.2 mL of CO evolved),
was added to a solution of 2a (0.121 g, 0.451 mmol) in THF
(5 mL) at −10 °C. Work-up after 2 d as described for 5a [RhCl(1,5-COD)]2 (177 mg, 0.36 mmol) in THF (5 mL) was
afforded 128 mg (88%) of a pale green powder 5a, contami- added slowly at −20 °C to a solution of 2b (178 mg,
nated by a small amount of oligoethylene grease. 1H NMR 0.72 mmol) in THF (10 mL). The mixture was stirred for 1 d at
(CDCl3): δ = 1.32 (s, 9 H, CMe3), 7.38–7.47 (m, 6 H, phenyl, room temperature (colour changed from yellow to deep orange
3
4
4
H-6), 8.07 (ddd, J = 8.1, JPH = 2.6, J = 1.5 Hz, 1 H, H-7), 8.63 and brownish-yellow) and worked up as described for 6a yield-
(dd, 3J = 4.8, 4JPH = 1.5 Hz, 1 H, H-5). 13C{1H} NMR (CDCl3): δ = ing 312 mg 6b (95 mol%, corr. yield 84%) as a yellow powder,
30.25 (d, 3J = 2.5 Hz, CMe3), 40.98 (d, 2J = 18.6 Hz, CMe3), containing 5 mol% 7b. 1H NMR (CDCl3): δ = 0.77 (t, 3J = 7.2
125.23 (C-6), 126.03 (d, 1J = 35.8 Hz, Cq-i), 129.49 (d, 3J = Hz, 3 H, CH3), 1.15–1.30 (m, 4 H, CH2), 1.68 (s, 9 H, CMe3),
10.6 Hz, 2 C-m), 130.17, 131.91 (2 d, J = 2.7 Hz, C-7, C-p), 1.79–1.93 (m, 4 H, CH2, COD), 2.15–2.40 (m, 2 H, PCH2),
2
2
133.48 (d, J = 11.9 Hz, 2 C-o), 148.26 (d, J = 31.8 Hz, Cq-7a), 2.33–2.52 (m, 4 H, CH2, COD), 3.67–3.77 (m, 2 H, vCH, COD),
149.04 (d, 3J = 14.6 Hz, C-5), 162.3 (low int. d, 1J ≈ 75 Hz, 5.50–5.52 (m, 3J = 3.5 Hz, 1 H, vCH, COD), 5.6 (vbr s, 1 H,
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Table 2 Crystal data and structure refinement
Identification code
6a
9b·2CDCl3
10b·4.5THF
10b·2D6-acetone
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C
24H29ClN2PRh
C36H52D2Cl10N4P2Pd3
1280.48
100(2) K
C46H78Cl4N4O4.5P2Pd2
1175.66
100(2) K
0.71073 Å
Monoclinic
C2/c
C34H42D12Cl4N4O2P2Pd2
979.43
100(2) K
0.71073 Å
Monoclinic
P21/c
514.82
103(2) K
0.71073 Å
Triclinic
0.71073 Å
Triclinic
ˉ
P1
ˉ
P1
Unit cell dimensions
a = 9.1441(6) Å,
α = 83.875(2)°
b = 9.8885(6) Å,
β = 81.588(2)°
c = 13.5572(8) Å,
γ = 67.831(3)°
1121.25(12) Å3
2
a = 8.5594(7) Å,
α = 101.959(4)°
b = 9.6780(8) Å,
β = 92.199(4)°,
c = 16.4206(13) Å,
γ = 109.528(4)°
1245.60(18) Å3
1
a = 27.727(3) Å,
α = 90°
a = 11.9584(4) Å,
α = 90°
b = 16.625(2) Å,
β = 90.891(6)°
c = 23.302(3) Å,
γ = 90°
b = 29.4872(8) Å,
β = 115.816(5)°
c = 13.0738(4) Å,
γ = 90°
Volume
Z
10 739(2) Å3
8
4150.0(2) Å3
4
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data
collection
1.525 Mg m−3
0.965 mm−1
528
1.707 Mg m−3
1.702 mm−1
1.454 Mg m−3
0.972 mm−1
4864
1.567 Mg m−3
1.236 mm−1
1968
636
0.30 × 0.30 × 0.20 mm3
1.52 to 31.06°
0.20 × 0.20 × 0.03 mm3
2.30 to 30.58°
0.30 × 0.15 × 0.15 mm3
2.27 to 30.03°
0.14 × 0.11 × 0.06 mm3
2.70 to 28.28°
Index ranges
−13 ≤ h ≤ 13,
−14 ≤ k ≤ 14,
−19 ≤ l ≤ 19
−12 ≤ h ≤ 12,
−13 ≤ k ≤ 13,
−23 ≤ l ≤ 23
−39 ≤ h ≤ 38,
−23 ≤ k ≤ 23,
−32 ≤ l ≤ 32
−15 ≤ h ≤ 15,
−39 ≤ k ≤ 39,
−17 ≤ l ≤ 17
Reflections collected
Independent reflections
Completeness to theta
Absorption correction
61 697
38 910
153 859
76 588
7166 [R(int) = 0.0319]
= 30.00°, 99.9%
Semi-empirical from
equivalents
7630 [R(int) = 0.0307]
= 30.50°, 100.0%
Semi-empirical from
equivalents
15 352 [R(int) = 0.0490]
= 30.00°, 97.7%
Semi-empirical from
equivalents
10 287 [R(int) = 0.0800]
= 28.28°, 99.8%
Semi-empirical from
equivalents
Max. and min.
transmission
Refinement method
0.830 and 0.694
0.951 and 0.808
0.868 and 0.732
1.000 and 0.952
Full-matrix
Full-matrix
Full-matrix
Full-matrix
least-squares on F2
7166/6/281
least-squares on F2
7630/0/274
least-squares on F2
15 352/511/585
least-squares on F2
10 287/266/445
Data/restraints/
parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
1.04
1.03
1.18
0.82
R1 = 0.0166,
wR2 = 0.0422
R1 = 0.0176,
wR2 = 0.0429
R1 = 0.0248,
wR2 = 0.0572
R1 = 0.0329,
wR2 = 0.0612
2.53 and −1.59 e Å−3
R1 = 0.0409,
wR2 = 0.0803
R1 = 0.0782,
wR2 = 0.0982
1.33 and −0.68 e Å−3
R1 = 0.0304,
wR2 = 0.0481
R1 = 0.0680,
wR2 = 0.0516
0.76 and −0.47 e Å−3
R indices (all data)
Largest diff. peak and hole 0.52 and −0.32 e Å−3
3
5
vCH, COD), 7.37 (ddd, J = 8.1, 4.9, JPH = 1.6 Hz, 1 H, H-6), Detection of 8a and [meso-bis{(η3-allyl)(2-tert-butyl-3-phenyl-
3
4
4
7.93 (ddd, J = 8.1, JPH = 2.2, J = 1.2 Hz, 1 H, H-7), 8.58 (dd, 1,3-azaphospholo[4,5-b]pyridine-κ1P)palladium(II)chloride}-
3J = 4.8, 4J = 1.2 Hz, 1 H, H-5). 13C{1H} and DEPT135 NMR κ1N]palladium(II)dichloride (9a)
(CDCl3): δ = 13.45 (CH3), 23.25 (d, J = 17.5 Hz, CH2), 23.91
(d, J = 13.2 Hz, CH2), 26.44 (d, J = 6.1 Hz, CH2), 28.60, 28.97 Allylpalladium chloride dimer (146 mg, 0.40 mmol) in THF
(2 CH2, COD), 29.77 (CMe3), 32.36 (CH2, COD), 33.39 (d, J = (5 mL) was added slowly at −20 °C to a solution of 2a (145 mg,
2
2.3 Hz, CH2, COD), 40.96 (d, J = 18.6 Hz, CMe3), 68.57 (d, J = 0.54 mmol) in THF (5 mL) and stirred for 2 d at room tempera-
13.1 Hz, vCH, COD), 72.64 (d, J = 13.2 Hz, vCH, COD), ture (colour changed from pale yellow to deep orange). The
104.73 (dd, J = 10.5, 8.1 Hz, vCH, COD), 105.28 (dd, J = 12.5, insoluble material was removed by filtration, the solvent was
7.3 Hz, vCH, COD), 124.73 (s, CH-6), 129.85 (d, 3J = 2.0 Hz, evaporated under vacuum and the residue was washed several
3
2
CH-7), 147.99 (d, J = 13.2 Hz, CH-5), 150.78 (d, J = 26.6 Hz, times with n-hexane/Et2O and dried under vacuum to give
1
1
Cq-7a), 156.53 (d, J = 67.4 Hz, Cq-3a), 192.29 (d, J = 6.1 Hz, 202 mg (53% referred to as 2a, 72% ref. to Pd) of an
Cq-2). 31P{1H} NMR (CDCl3): δ = 28.2 (d, JPRh = 141.7 Hz, orange-yellow powder of crude 8a·THF with CHN analysis
1
1
95 mol% 6b), 17.2 (d, JPRh = 151.1 Hz, 5 mol% 7b). HRMS values roughly corresponding to a composition [(2a){(allyl)-
(ESI in MeCN): calcd for [6b-Cl]+ 459.1431, calcd. for [7b-Cl]+ PdCl}1.2(PdCl2)0.8]·C4H8O. 1H NMR (CDCl3): δ = 1.27 (s, 9 H,
705.1113; found 459.1431, 705.1111. Anal. calcd for 6b, CMe3), 2.8 (vbr, 2 H, allyl), 3.5, 5.5, 5.7 (vbr, 3 H, allyl), 7.45
C22H33ClN2PRh (494.84): C 53.40, H 6.72, N 5.66; calcd for 6b/ (td, J ≈ 7.6, 4J ≈ 1.6 Hz, 2 H, H-m), 7.55 (t, J = 7.8, 7.7 Hz,
3
3
3
7b (95/5 mol%): C 52.68, H 6.63, N 5.38; found: C 52.55, 1 H, H-p), 7.60 (dd, J = 8.0, 5.8 Hz, 1 H, H-6), 7.9 (vbr s, 2 H,
3
4
4
H 6.56, N 5.00.
H-o), 8.18 (dt, J = 8.2, J ≈ JPH ≈ 1.5 Hz, 1 H, H-7), 8.8 (vbr,
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1 H, H-5); THF: 1.85 (m, 4 H, CH2), 3.73 (m, 4 H, OCH2). n-hexane and drying under vacuum gave 120 mg (76%) yellow
3
1
3
13C{1H} and DEPT-135 NMR (CDCl3): δ = 30.18 (d, J = 3.5 Hz, powder. H NMR (CDCl3): δ = 0.77 (t, J = 7.2 Hz, 3 H, CH3),
2
CMe3), 41.00 (d, J = 19.3 Hz, CMe3), ca. 60 (sh, minor, C′allyl), 0.70–0.95 (superimposed m, 2 H, CH2), 1.13–1.28 (m, 2 H,
62.8 (vbr, C-αallyl), 84.7 (minor, C′allyl), 114.8 (vbr, Callyl), 118.7 CH2), 1.57 (s, 9 H, CMe3), 2.32–2.47 (m, 1 H, PCH), 3.67–3.84
3
5
(vbr, Callyl), 123.56 (d, 1J = 31.1 Hz, Cq-i), 126.6 (br, CH-6), (m, 1 H, PCH), 7.45 (ddt, J ≈ 8, 5, |5JPH + JP′H| = 3.5 Hz, 1 H,
129.76 (d, 3J = 10.9 Hz, 2 CH-m), 131.46 (s, CH-7), 132.54 (d, H-6), 7.94 (dt, J = 8.1, JPH = 2, J = 1.2 Hz, 1 H, H-7), 8.54 (tt,
3
4
4
4J = 1.9 Hz, CH-p), 134.61 (d, J = 12.1 Hz, 2 CH-o), 150.26 (d, |3J + 4JP′H| = 4.2, 4J ≈ 4JPH = 1.2, 1.4 Hz, 1 H, H-5). 13C{1H} NMR
2
2J = 27.2 Hz, Cq-7a), 151.5 (vbr, CH-5), 160 (br d, J ≈ 60 Hz, (CDCl3): δ = 13.48 (s, CH3), 23.50 (d, J = 14.1 Hz, CH2), 24.79
1
3
Cq-3a), 195.4 (br, Cq-2); THF 25.60 (CH2), 67.96 (OCH2). (d, J = 17.4 Hz, CH2), 25.39 (d, J = 10.1 Hz, CH2), 29.74 (d, J =
31P{1H} NMR (CDCl3): δ = 15.4 (vbr). Anal. calcd for 8a·THF 3.8 Hz, CMe3), 40.70 (d, 2J = 21.1 Hz, CMe3), 127.59 (CH-6),
3
(C23H30Cl3N2OPPd2, 700.67): C 39.43, H 4.32, N 4.00; calcd for 132.36 (CH-7), 150.6 (superimposed d, J = 10 Hz, CH-5), 150.7
[(2a)(allylPdCl)1.2(PdCl2)0.8]·C4H8O (C23.6H31Cl2.8N2OPPd2, 701.80): (superimposed d, 2J = 28 Hz, Cq-7a), 157.3 (partly at noise
C 40.39, H 4.45, N 3.99; found: C 40.66, H 4.18, N 3.54. Slow level, Cq-3a), 190.4 (br, Cq-2). 31P{1H} NMR (CDCl3): δ = 26.7.
diffusion of hexane into a concentrated solution of crude 8a in Anal. calcd for THF free complex C28H42Cl4N4P2Pd2 (851.26):
THF gave crystals of 9a·THF. Severe disorder of the allyl group C 39.51, H 4.97, N 6.58; found: C (incomplete combustion),
and unexpected peaks in the residual electron density (possibly H 5.25, N 6.73. Single crystals of 10b·4.5THF were obtained by
by twinning) did not allow satisfactory refinement of the XRD slow diffusion of n-hexane into the saturated solution in THF;
data, but allowed the identification of 9a·THF (Fig. S26, ESI†).
the solvent was lost rapidly in air, and the crystal had to be
handled under inert oil. Crystal data are given in Table 2, and
the selected bond lengths and angles in Fig. 4a.
(B) 10b·2D6-acetone. K2PdCl4 (120 mg, 0.368 mmol) in
MeOH (10 mL) was added slowly at −20 °C to a solution of 2b
[meso-Bis{(η3-allyl)(3-n-butyl-2-tert-butyl-1,3-azaphospholo-
[4,5-b]pyridine-κ1P)palladium(II)chloride}-κ1N]palladium(II)
dichloride (9b)
Reaction of allylpalladium chloride dimer (180 mg, (89 mg, 0.358 mmol) in MeOH (10 mL). The mixture was
0.49 mmol) in THF (10 mL) with 2b (0.162 g, 0.652 mmol) in stirred for 3 d at room temperature, filtered, and the deep
THF (15 mL) and workup as described for 8a gave 250 mg yellow precipitate was washed several times with water and
(74%) yellow powder. CHN analysis values are in accordance MeOH, and then dried under vacuum yielding 108 mg (71%)
1
with THF-free 9b. Crude powder with residual THF – H NMR of a yellow air-stable powder. This was insoluble in n-hexane
1
(CDCl3): δ = 0.80 (t, 3J = 7.2 Hz, 3 H, CH3), 1.28 (m, 3J = 7.8, 6.8 and slightly soluble in acetone. H NMR (D6-acetone): δ = 0.75
3
Hz, 4 H, CH2), 1.47 (br s, 9 H, CMe3), 2.6 (vbr s, 2 H, PCH2 (t, J = 7.3 Hz, 3 H, CH3), 1.0–1.43 (m, 4 H, CH2), 1.82 (s, 9 H,
and/or allyl), 2.7–3.4 (vbr m, 2 H, allyl and/or PCH2), 3.55–3.9 CMe3), 3.2–3.35, 3.7–3.85 (vbr m, 2 H, PCH), 7.69 (ddd, 3J = 8.2,
5
4
(superimposed by THF, vbr, Hallyl), 4.0–4.2 (vbr, Hallyl), 4.8, 5.7, JPH = 1.4 Hz, 1 H, H-6), 8.08 (dt, 3J = 8.2, 4J ≈ JPH
=
5.3–5.8 (vbr, Hallyl), 7.5 (vbr, 1 H, H-6), 8.1 (vbr d, 3J ≈ 7 Hz, 1.2 Hz, 1 H, H-7), 8.40 (dt, J = 5.6, J ≈ JPH = 1 Hz, 1 H, 5-H).
1 H, H-7), 8.7 (vbr, 1 H, H-5); ca. 0.3 THF/9b: 1.85 (m, CH2), 13C{1H} NMR (D6-acetone): δ = 14.26 (CH3), 24.64 (d, J =
3.75 (m, OCH2). 13C{1H} NMR (CDCl3): δ = 13.43 (s, CH3), 16.6 Hz, CH2), 25.59 (d, J = 22.6 Hz, CH2), 26.96 (d, J = 20.4 Hz,
3
4
4
2
23.6–23.8 (br superimposed d, 2 CH2), 26.53 (d, J = 8.2 Hz, CH2), 29 (br s superimposed with solvent, CMe3), 43.23 (d, J =
CH2), 29.68 (d, 3J = 2.9 Hz, CMe3), 40.54 (d, 2J = 19.6 Hz, 20.4 Hz, CMe3), 131.3 (vbr, CH-6), 135.2 (vbr, CH-7), 152.5 (vbr,
CMe3), 58 (vbr, C′αγ-allyl), 62.2 (vbr, Cα-allyl), 80.5 (vbr, Cγ-allyl), CH-5); Cq-signals in noise. 31P{1H} NMR (D6-acetone): δ = 31.0.
114.6 (br, C′β-allyl), 117.2, 118.8 (vbr, Cβ-allyl), 125.3 (vbr, C-6), LRMS (ESI in MeCN): calcd for most abundant fragment
130.5 (vbr, C-7), 148.5–150.5 (vbr, C-5, Cq-7a), 158.6 (br d, J ≈ [M − Cl]+ 815.00; found: 815.00 (and correct isotopic pattern).
1
72 Hz, Cq-3a), 192.4 (br, low int., Cq-2); int. Call: C′all ca. 3 : 1. Anal. calcd for C28H42Cl4N4P2Pd2 (851.26): C 39.51, H 4.97,
31P{1H} NMR (CDCl3): δ = 17 (vbr), 25 (vbr), integral ratio 3 : 1. N 6.58; found: C 40.06, H 5.06, N 6.34. Slow diffusion of
Anal. calcd for C34H52Cl4N4P2Pd3 (1039.82): C 39.27, H 5.04, n-hexane into a saturated solution in D6-acetone provided
N 5.39; found: C 38.87, H 5.12, N 5.14. Single crystals of single crystals of 10b·2D6-acetone. Crystal data are given in
9b·2CDCl3, grown by slow concentration of the CDCl3 solution, Table 2, and the structure is shown in Fig. 4b.
were selected from the mixture with mother liquor for crystal
Catalytic tests – 2-mesitylaminopyridine 11
structure determination. For selected bond lengths and angles
see Fig. 3, and for crystal data see Table 2.
A Schlenk bottle was charged with 2-bromopyridine (212 mg,
1.34 mmol), mesitylamine (269 mg, 1.99 mmol), KOtBu
(310 mg, 2.76 mmol), 10b (prepared from Pd(CH3CN)2Cl2,
29 mg) or the given amount of ligand and Pd-compound (see
DL-anti-Bis[{(3-n-butyl-2-tert-butyl-1,3-azaphospholo[4,5-b]-
pyridine)-κ1N,κ1P}cis-palladium(II)dichloride] (10b) solvates
(A) 10b·4.5THF. [Pd(CH3CN)2Cl2] (96.5 mg, 0.372 mmol) Table 1) and toluene (10 mL) and heated under nitrogen for
in THF (10 mL) was added slowly at −10 °C to a solution of 2b 24 h at 100 °C. The mixture was filtered, washed with toluene,
(92.4 mg, 0.372 mmol) in THF (10 mL). The reaction mixture the solution was transferred to a silica gel column and com-
was stirred for 2 d at room temperature (colour changed from pound 11 was separated using ethyl acetate/hexane 2 : 8. The
1
pale yellow to orange) and filtered. Removal of the solvent results are compiled in Table 1. The H and 13C NMR data of
under vacuum, washing the orange solid residue with 11 were in accordance with known values.22
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Crystal structure analysis
54; (b) M. Ghalib, L. Könczöl, L. Nyulászi, G. J. Palm,
C. Schulzke and J. W. Heinicke, Dalton Trans., 2015, 44,
1769–1774; (c) M. Ghalib, P. G. Jones, C. Schulzke,
D. Sziebert, L. Nyulászi and J. W. Heinicke, Inorg. Chem.,
2015, 2117–2127; (d) J. Heinicke, Eur. J. Inorg. Chem., 2016,
DOI: 10.1002/ejic.201500941.
7 (a) S. O. Grim, D. A. Wheatland and W. McFarlane, J. Am.
Chem. Soc., 1967, 89, 5573–5577; (b) F. A. Cotton and
C. S. Kraihanzel, J. Am. Chem. Soc., 1962, 4432–4438.
8 (a) E. O. Fischer, L. Knauss, R. L. Keiter and J. G. Verkade,
J. Organomet. Chem., 1972, 37, C7–C10; (b) F. Mercier,
F. Mathey, C. Afiong-Akpan and J. F. Nixon, J. Organomet.
Chem., 1988, 348, 361–367.
Crystals of 6a, 9b·2CDCl3, 10b·2D6-acetone and 10b·4.5THF
were mounted on glass fibres in an inert oil. Data were
recorded at low temperature on an Oxford Diffraction Xcalibur
E (10b·2(D6-acetone)) or a Bruker APEX2 diffractometer using
MoKα-radiation (λ = 0.71073 Å). Crystal data are summarized
in Table 2. The structures were refined anisotropically on F2
using the program SHELXL-97.26 Hydrogen atoms were
included using a riding model or rigid methyl groups, except
for hydrogens of coordinated allyls or coordinated double
bonds, which were refined freely. For 10b·4.5THF, one THF is
disordered over two positions and one lies on a twofold axis.
Crystallographic data for 6a, 9b·2CDCl3, 10b·4.5THF and
10b·2D6-acetone have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC 1423102, 1423105, 1423103 and 1423104 respectively.
9 (a) M. A. M. Meester, R. C. J. Vriends, D. J. Stufkens and
K. Vrieze, Inorg. Chim. Acta, 1976, 19, 95–103; (b) H. Daamen
and A. Oskam, Inorg. Chim. Acta, 1978, 26, 81–89.
10 W. Partenheimer and E. F. Hoy, Inorg. Chem., 1973, 12,
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Acknowledgements
11 E. Rotondo, G. Battaglia, C. G. Arena and F. Faraone,
J. Organomet. Chem., 1991, 419, 399–402.
A fellowship (M.S.S.A.) from the Deutscher Akademischer Aus-
tauschdienst (DAAD) and financial support by the Deutsche
Forschungsgemeinschaft (HE 1997/12-2) are gratefully
acknowledged. We thank B. Witt, G. Thede and M. Steinich for
NMR and LRMS and Dr H. Frauendorf and G. Sommer-Udvar-
noki (Georg-August-Universität Göttingen, Institut für Orga-
nische und Biomolekulare Chemie) for HRMS measurements.
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(b) M. Ghalib, P. G. Jones, S. Lysenko and J. W. Heinicke,
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