Square planar diphosphinoazine rhodium(I) amido carbonyl complexes with an unsymmetrical PNP′ pincer-type coordination

Article abstract of DOI:10.1016/j.jorganchem.2008.02.029

A series of novel diphosphinoazine rhodium amido carbonyl complexes [{R₂PCH{double bond, long}C(Bu^t)-NN{double bond, long}C(Bu^t)CH₂PR₂}Rh(CO)] (R = Ph, Prⁱ, c-C₆H₁₁, Bu^t) was prepared by deprotonation of cationic diphosphinoazine rhodium amino carbonyl complexes. The complexes were characterized by NMR as were also their precursors. The crystal structures of two cationic and one neutral deprotonated complex were determined by X-ray diffraction showing the complexes to be essentially planar with mutual trans arrangement of phosphine groups and nitrogens trans to carbonyl ligands. Measurement of valence vibration frequencies of carbonyl groups in the complexes allowed to estimate the electron density on the rhodium centre. The ene-hydrazone ligand backbone (nitrogen covalently bonded) is more electron donating than the azine backbone (nitrogen bonded by electron pair donation) as expected. In the neutral series of complexes electron donation increases with phosphine substitution in the order Ph < Prⁱ = c-C₆H₁₁ < Bu^t with the corresponding decrease of carbonyl valence vibration frequency. The tert-butyl cationic complex undergoes in a low yield an unusual diphosphinoazine bond cleavage with simultaneous oxidation of the metal resulting in a binuclear bis(iminophosphine)dirhodium complex [{(Bu^t)₂PCH₂C(Bu^t){double bond, long}NH}Rh(Cl)₂(μ-Cl)]₂ the structure of which was also determined by X-ray diffraction.

Full text of DOI:10.1016/j.jorganchem.2008.02.029

Journal of Organometallic Chemistry 693 (2008) 1997–2003
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Square planar diphosphinoazine rhodium(I) amido carbonyl complexes with an
unsymmetrical PNP0 pincer-type coordination
a
a,
a
b
c
a
ˇ
*
´
ˇ
Martin Pošta , Jan Cermák , Jan Sykora , Pavel Vojtíšek , Ivana Císarová , Radek Fajgar
a Institute of Chemical Process Fundamentals AS CR, v.v.i., Rozvojová 135, 165 02 Prague 6, Czech Republic
b Department of Inorganic Chemistry, Faculty of Natural Science, Charles University, Hlavova 2030, 128 40 Prague, Czech Republic
c Center of Molecular and Crystal Structures, Faculty of Natural Science, Charles University, Hlavova 2030, 128 40 Prague, Czech Republic
a r t i c l e i n f o
a b s t r a c t
series of novel diphosphinoazine rhodium amido carbonyl complexes [{R2PCH@C(But)–NN@
Article history:
Received 2 January 2008
Received in revised form 19 February 2008
Accepted 25 February 2008
Available online 4 March 2008
A
C(But)CH2PR2}Rh(CO)] (R = Ph, Pri, c-C6H11, But) was prepared by deprotonation of cationic diphosphino-
azine rhodium amino carbonyl complexes. The complexes were characterized by NMR as were also their
precursors. The crystal structures of two cationic and one neutral deprotonated complex were deter-
mined by X-ray diffraction showing the complexes to be essentially planar with mutual trans arrange-
ment of phosphine groups and nitrogens trans to carbonyl ligands. Measurement of valence vibration
frequencies of carbonyl groups in the complexes allowed to estimate the electron density on the rhodium
centre. The ene-hydrazone ligand backbone (nitrogen covalently bonded) is more electron donating than
the azine backbone (nitrogen bonded by electron pair donation) as expected. In the neutral series of com-
plexes electron donation increases with phosphine substitution in the order Ph < Pri = c-C6H11 < But with
the corresponding decrease of carbonyl valence vibration frequency. The tert-butyl cationic complex
undergoes in a low yield an unusual diphosphinoazine bond cleavage with simultaneous oxidation of
the metal resulting in a binuclear bis(iminophosphine)dirhodium complex [{(But)2PCH2C(But)@NH}-
Rh(Cl)2(l-Cl)]2 the structure of which was also determined by X-ray diffraction.
Keywords:
Polydentate ligands
Diphosphinoazines
Rhodium complexes
Carbonyl complexes
Pincer complexes
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
tion [7] and later reported their catalytic activity in the Heck
reaction [8]. Previously, palladium [9a], platinum [9a], and iridium
Pincer ligands and pincer complexes are now well established
in organometallic and coordination chemistry [1]. Tridentate bond-
ing scheme (two-electron donor–covalently bonded atom–two-
electron donor) usually creates a bicyclic complex with a metal
belonging to both rings of the same size. However, unsymmetrical
pincer complexes are now also common [2], the first reported
being arguably (see below) those of Eberhard et al. [3].
The central covalently bonded monoanionic atom is usually car-
bon, but there are other possibilities. Among those, probably the
most important one is nitrogen bonded as an amide [4]. Square
planar Ni, Pd and Pt complexes with a rigid [donor–amide nitro-
gen–donor] framework are believed to show an unusual reactivity
due to the presence of a strongly electron-donating amide trans to
the potential reaction site [5].
[9b,9c] complexes of this type were reported but only with the
diphosphinoazine bearing phenyl groups on phosphorus atoms.
Rhodium diphosphinoazine amido complexes and in particular
amido carbonyl complexes are unknown. At the same time,
rhodium pincer complexes with PCP frame were thoroughly stud-
ied mainly by Milstein’s group and used in further stoichiometric
and catalytic transformations [10]. Here we report the first
synthesis and characterization including X-ray diffraction of diph-
osphinoazine rhodium(I) amido carbonyl complexes with an
unsymmetrical PNP0 pincer-type coordination.
2. Experimental
2.1. General
Rhodium PNP symmetrical pincer complexes were studied by
Ozerov et al. [4c, p. 287], but the first rhodium amido carbonyl pin-
cer complex was reported by Mayer and Kaska [6] only recently.
We published synthesis of palladium(II) diphosphinoazine ami-
do complexes with an unsymmetrical PNP0 pincer-type coordina-
All preparations were carried out under an argon atmosphere
using standard Schlenk techniques. Solvents were dried and dis-
tilled prior to use. Pentane, hexane and methanol were distilled
from sodium, tetrahydrofuran was distilled from sodium/benzo-
phenone, dichloromethane was distilled from CaCl2 and chloro-
form was purified by distillation from P2O5 and then from CaCl2.
* Corresponding author. Tel.: +42 0220390356; fax: +42 0220920661.
ˇ
E-mail address: cermak@icpf.cas.cz (J. Cermák).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.02.029

1998
M. Pošta et al. / Journal of Organometallic Chemistry 693 (2008) 1997–2003
Triethylamine was stored over KOH and distilled on the Fischer
distillation column prior to use.
13C NMR: (CDCl3) 16.65 d (1JPC = 10.4 Hz, PCH2), 25.68 d
(J = 3.7 Hz, CH2, c-C6H11), 26.24–26.74 m (CH2, c-C6H11), 27.58 s
(CH3, t-Bu), 28.43 s (CH2, c-C6H11), 28.50 s (CH2, c-C6H11), 28.62 s
(CH3, t-Bu), 29.33 d (2JPC = 2.5 Hz, CH2), 30.49 s (CH2, c-C6H11),
Complex [Rh(CO)2Cl]2 [11] and the starting diphosphinoazines
Ph2PCH2C(But)@NN@C(But)CH2PPh2 (1) [12], (C6H11)2PCH2C(But)@
N–N@C–(But)CH2P(C6H11 2
)
(2) [13], Pri2PCH2C(But)@NN@C(But)-
33.29
c-C6H11), 35.84
d d
(1JPC = 19.2 Hz, PCH2), 34.17 (1JPC = 22.2 Hz, CH,
CH2PPri2 (3) [13], and But2PCH2C(But)@NN@C(But)CH2 PBut2 (4)
[13] were prepared according to published procedures, as
indicated.
d
(1JPC = 20.4 Hz, CH, c-C6H11), 40.86
d
(3JPC = 5.6 Hz, ꢀCꢁ, t-Bu), 40.87 d (3JPC = 1.7 Hz, ꢀCꢁ, t-Bu),172,57 s
(ꢀCꢁ, ꢀC@N), 190.37 dd (2JPC = 4.7 Hz, JPC = 2.7 Hz, ꢀCꢁ, ꢀC@N),
5
1H (299.9 MHz), 13C (75.4 MHz) and 31P (121.4 MHz) NMR spec-
tra were recorded on a Varian MercuryVX 300 spectrometer in
CDCl3 solution unless stated otherwise. Chemical shifts are re-
ported in ppm (d) relative to TMS, referenced to hexamethyldisi-
194.64 m (ꢀCꢁ, CO).
IR (mCO, CHCl3, cmꢀ1) 1950.
Single crystal suitable for X-ray analysis was grown by slow
diffusion of hexane vapour to the chloroform solution at room
temperature. Structure of the complex was determined as
[{(C6H11)2PCH2C(But)@NN@C(But)CH2P(C6H11)2}Rh(CO)][(CO)2Rh-
Cl2] (6a).
lane or the solvent peak (1H, 13C) and external 85% H3PO4 31P).
(
Assignments in NMR spectra were aided by gNMR V4.1.0 [14].
IR spectra were obtained on Nicolet Impact 400 by the specular
reflection method in range 400–4000 cmꢀ1 with resolution 2 cmꢀ1
.
3.1.3. [{Pri2PCH2C(But)@NN@C(But)CH2PPri2}Rh(CO)]Cl (7)
31P NMR: (CDCl3): ABX 78. 9 (1JRhP = 115.9 Hz), 86.7 (1JRhP
=
3. Syntheses of the complexes
128.6 Hz) (2JPP = 265.7 Hz). 1H NMR (CDCl3): 1.28–1.38 m (24H,
CH3, i-Pr), 1.29 s (9H, t-Bu), 1.40 s (9H, t-Bu), 2.29 d sep. (2H,
3.1. Cationic complexes
3
2
2JPH = 2.1 Hz, JHH = 7.1 Hz, CH, i-Pr), 2.35 d sep. (2H, JPH = 2.1 Hz,
3JHH = 7.1 Hz, CH, i-Pr), 2.61 dd (2H, JPH = 10.9 Hz, JPH = 2.7 Hz,
2
4
All cationic square planar diphosphinoazine complexes of Rh(I)
of the general formula [Rh(CO)L]Cl (L = 1–4) were prepared by a
general procedure as follows. Rhodium precursor [Rh(CO)2Cl]2
(0.0500 g, 0.108 mmol) was dissolved in 5 ml of CHCl3 and an
2
4
PCH2), 3.65 dd (2H, JPH = 8.3 Hz, JPH = 4.1 Hz, PCH2).
13C NMR (CDCl3): 16.59 d (1JPC = 9.9 Hz, PCH2), 19.15 d (2JPC
=
4.3 Hz, CH3, i-Pr), 20.0 d (2JPC = 2.7 Hz, CH3, i-Pr), 24.86 ddd
(1JPC = 21.9 Hz, JRhC = 1.7 Hz, JPC = 1.8 Hz, CH, i-Pr), 25.98 ddd
2
3
appropriate amount of ligands
1
(0.121 g, 0.216 mmol),
2
(1JPC = 20.9 Hz, JRhC = 2.0 Hz, JPC = 2.4 Hz, CH, i-Pr), 27.50 s (CH3,
t-Bu), 28.50 s (CH3, t-Bu), 33.18 d (1JPC = 19.0 Hz, PCH2), 40.83 d
(3JPC = 1.7 Hz, ꢀCꢁ, t-Bu), 40.92 d (3JPC = 5.6 Hz, ꢀCꢁ, t-Bu), 172.29s
2
3
(0.126 g, 0.216 mmol), (0.093 g, 0.216 mmol),
3
4
(0.104 g,
0.216 mmol), in 5 ml of CHCl3 was added. Solution was stirred at
room temperature for 5 h. Solvent was partially removed by evap-
oration in vacuo to ca. 2 ml and product was obtained by precipita-
tion after addition of 15 ml of methanol. Mother liquor was filtered
off by cannula and the residue was washed twice with methanol
and dried in vacuo. By this method 0.122 g (78%) of yellow complex
5, 0.136 g (81%) of pale yellow complex 6, 0.078 g (61%) of yellow
complex 7 and 0.079 g (61%) of yellow–orange complex 8 was
obtained.
(ꢀCꢁ, ꢀC@N), 190.61 ddd (2JPC = 6.4 Hz, JPC = 2.7 Hz, JRhC = 1.5 Hz,
ꢀCꢁ, ꢀC@N), 192.12–192.93 m (ꢀCꢁ, CO).
IR (mCO, CHCl3, cmꢀ1) 1952.
5
2
3.1.4. [{But2PCH2C(But)@NN@C(But)CH2PBtt2}Rh(CO)]Cl (8)
Anal. Calc. for C37H42ClN2OP2Rh: C, 53.50; H, 8.98; N, 4.30.
Found: C, 52.47; H, 7.77; N, 4.13%. 31P NMR (CDCl3): ABX 93.0
(1JRhP = 116.1 Hz), 97.8 (1JRhP = 129.7 Hz) (2JPP = 256.2 Hz). 1H NMR
3
3.1.1. [{Ph2PCH2C(But)@NN@C(But)CH2PPh2}Rh(CO)]Cl (5)
Anal. Calc. for C37H42ClN2OP2Rh: C, 60.79; H, 5.79; N, 3.83.
Found: C, 60.45; H, 5.72; N, 3.77%. 31P NMR (CDCl3): ABX 54.5
(1JRhP = 123.0 Hz), 63.6 (1JRhP = 139.6 Hz) (2JPP = 310.0 Hz) 1H NMR
(CDCl3): 1.35 s (9H, t-Bu), 1.41 d (18H, JPH = 6.8 Hz, t-Bu), 1.42 s
3
(9H, t-Bu), 1.5
d
(18H, JPH = 7.0 Hz, t-Bu), 2.52 dd (2H,
2JPH = 10.0 Hz, JPH = 2.2 Hz, PCH2), 3.67 dd (2H, JPH = 6.9 Hz,
4JPH = 4.0 Hz, PCH2).
4
2
13C NMR (CDCl3): 14.30 d (1JPC = 5.5 Hz, CH2, PCH2), 28.47 s
(CH3, t-Bu), 28.99 s (CH3, t-Bu), 29.38 d (2JPC = 4.3 Hz, CH3, t-Bu),
29.53 d (2JPC = 4.9 Hz, CH3, t-Bu), 33.77 d (1JPC = 15.5 Hz, CH2,
PCH2), 35.86 d (1JPC = 18.1 Hz, ꢀCꢁ, t-Bu), 37.15 d (1JPC = 14.7 Hz,
ꢀCꢁ, t-Bu), 41.07 d (3JPC = 4.9 Hz, ꢀCꢁ, t-Bu), 41.94 d (3JPC = 2.0 Hz,
(CDCl3): 0.77 s (9H, t-Bu), 1.24
s (9H, t-Bu), 3.66 dd (2H,
4
2
2JPH = 12.3 Hz, JPH = 2.3 Hz, PCH2), 4.50 dd (2H, JPH = 10.0 Hz,
4JPH = 4.5 Hz, PCH2), 7.48–7.54 m (12H, CH, meta and para protons
Ph), 7.73–7.80 m (4H, CH, ortho protons Ph), 7.84–7.91 m (4H, CH,
ortho protons Ph).
ꢀCꢁ, t-Bu), 173.60
d
(2JPC = 1.2 Hz ꢀCꢁ, ꢀC@N), 191.33 ddd
13C NMR (CDCl3): 25.29 d (1JPC = 15.6 Hz, PCH2), 26.80 s (CH3, t-
Bu), 27.95 s (CH3, t-Bu), 39.94 d (J = 1.7 Hz, ꢀCꢁ, t-Bu), 40.36 d
(J = 5.5 Hz, ꢀCꢁ, t-Bu), 41.22 d (1JPC = 24.2 Hz, PCH2), 129.36 d
(4JPC = 10.9 Hz, CH, Ph), 129.15 d (4JPC = 10.8 Hz, CH, Ph), 129.58
5
2
(2JPC = 6.4 Hz, JPC = 3.3 Hz, JRhC = 1.81 Hz, ꢀCꢁ, ꢀC@N), 194.34
ddd (1JRhC = 71.40 Hz, JPC = 14.5 Hz, JPC = 14.5 Hz, ꢀCꢁ, CO).
2
2
IR (mCO, CHCl3, cmꢀ1) 1972.
3
dd (1JPC = 4.0 Hz, JRhC = 2.0 Hz, ꢀCꢁ, Ph), 130.15 dd (1JPC = 4.0 Hz,
Single crystal suitable for X-ray analysis was grown by slow dif-
fusion of hexane vapour to the chloroform solution at room
temperature.
3JRhC = 2.0 Hz, ꢀCꢁ, Ph), 131.57 d (5JPC = 1.9 Hz, CH, Ph), 132.86 d
(3JPC = 12.8 Hz, CH, Ph), 133.65 d (3JPC = 12.87 Hz, CH, Ph), 171.25
5
s
(ꢀCꢁ, ꢀC@N), 187.26 dd (2JPC = 5.8 Hz, JPC = 2.6 Hz, ꢀCꢁ,
3.2. Ene-hydrazone complexes
ꢀC@N),190.52 broad m (ꢀCꢁ, CO).
IR (mCO, CHCl3, cmꢀ1) 1972.
3.2.1. {Ph2PCH@C(But)–NN@C(But)CH2PPh2}Rh(CO)] (9)
3.1.2. [{(C6H11)2PCH2C(But)@NN@C(But)CH2P(C6H11)2}Rh(CO)]Cl (6)
Anal. Calc. for C37H66ClN2OP2Rh: C, 58.84; H, 8.81; N, 3.71.
Found: C, 58.72; H, 8.71; N, 3.63%. 31P NMR: (CDCl3) ABX 70.6
(1JRhP = 115.6 Hz), 78.8 (1JRhP = 128.5 Hz) (2JPP = 265.9 Hz) 1H
NMR: (CDCl3) 1.12–1.41 m (24H, CH2, c-C6H11), 1.24 s (9H, t-Bu),
1.35 s (9H, t-Bu), 1.66–2.10 m (20H, CH + CH2, c-C6H11), 2.56 d
Solution of [Rh(CO)2Cl]2 (0.0300 g, 0.065 mmol), ligand (1)
0.0726 g (0.130 mmol) and 0.6 g (11 mmol) of sodium methoxide
in 5 ml of THF was sealed under vacuum in a glass ampoule and
the reaction mixture was sonicated for 1 h. Then the reaction mix-
ture was left standing for 15 days. Dark red solution was filtered
and the product was obtained by evaporation of solvent in vacuo.
Single crystal suitable for X-ray analysis was grown by slow
evaporation of chloroform solvent at room temperature.
2
2
4
(2H, JPH = 9.6 Hz, PCH2), 3.61 dd (2H, JPH = 8.3 Hz, JPH = 4.1 Hz,
PCH2).

M. Pošta et al. / Journal of Organometallic Chemistry 693 (2008) 1997–2003
1999
31P NMR (CD2Cl2): ABX 37.1 (1JRhP = 126.8 Hz), 63.6 (1JRhP
144.9 Hz) (2JPP = 296.1 Hz). 1H NMR (CD2Cl2): 0.74 s (9H, t-Bu),
=
and 0.1 ml (0.720 mmol) of triethylamine was added. Reaction
mixture was stirred for 24 h. Dark red solution was filtered off from
a small amount of precipitate and the product was obtained by
drying in vacuo.
2
4
1.34 s (9H, t-Bu), 3.01 dd (2H, JPH = 11.4 Hz, JPH = 1.8 Hz, PCH2),
2
4
4.53 dd (1H, JPH = 2.7 Hz, JPH = 2.1 Hz, PCH), 7.32–7.35 m (6 H,
CH, Ph), 7.38–7.43 m (6H,CH, Ph), 7.66–7.73 m (8H, CH, Ph).
13C NMR (CD2Cl2): 21.86 d (1JPC = 17.3 Hz, CH2, PCH2), 28.61 s
(CH3, t-Bu), 31.10 s (CH3, t-Bu), 39.07 d (3JPC = 2.3 Hz, ꢀCꢁ, t-Bu),
39.49 d (3JPC = 15.4 Hz, ꢀCꢁ, t-Bu), 75.40 d (1JPC = 53.3 Hz, CH,
PCH), 128.77 d (JPC = 20.7 Hz, CH, Ph), 128.90 d (JPC = 20.4 Hz, CH,
Ph), 129.80 d (JPC = 2.1 Hz, CH, Ph), 131.00 d (JPC = 1.8 Hz, CH, Ph),
132.54 d (JPC = 12.1 Hz, CH, Ph), 133.78 d (JPC = 12.7 Hz, CH, Ph),
134.08 d (1JPC = 45.3 Hz, ꢀCꢁ, Ph), 137.29 d (1JPC = 49.2 Hz, ꢀCꢁ,
31P NMR (CDCl3): ABX 73.8 (1JRhP = 123.2 Hz), 91.3 (1JRhP
=
133.9 Hz) (2JPP = 267.7 Hz). 1H NMR (CDCl3): 1.22 s (9H, t-Bu),
3
1.27 s (9H, t-Bu), 1.32 d (18H, JPH = 5.6 Hz, t-Bu), 1.36 d (18H,
2
4
3JPH = 5.2 Hz, t-Bu), 2.20 dd (2H, JPH = 10.5 Hz, JPH = 2.5 Hz, CH2,
2
4
PCH2), 4.19 dd (1H, JPH = 3.5 Hz, JPH = 2.3 Hz, CH, PCH).
13C NMR (CDCl3): 10.16 d (1JPC = 9.5 Hz, CH2, PCH2), 28.70 d
(2JPC = 5.0 Hz, CH3, t-Bu), 29.18 d (2JPC = 4.9 Hz, CH3, t-Bu), 29.80 s
(CH3, t-Bu), 30.89 s (CH3, t-Bu), 35.15 d (1JPC = 21.31 Hz, ꢀCꢁ, (P–
5
Ph), 150.37 s (ꢀCꢁ, fflC–N), 190.11 dd (2JPC = 25.3 Hz, JPC = 2.67 Hz,
C(CH3)3)), 35.56 d d
(1JPC = 12.8 Hz, ꢀCꢁ, (P–C(CH3)3)), 38.30
ꢀCꢁ, ꢀC@N), 194.85–197.28 m (ꢀCꢁ, CO).
(3JPC = 14.1 Hz, ꢀCꢁ, t-Bu), 39.74 d (3JPC = 3.4 Hz, ꢀCꢁ, t-Bu), 73.66
IR (mCO, CHCl3, cmꢀ1) 1957.
d (1JPC = 42.9 Hz, CH, PCH), 143.06 s (ꢀCꢁ, fflC–N), 187.76 dd
(2JPC = 21.3 Hz, JPC = 2.8 Hz, ꢀCꢁ, ꢀC@N), 198.48 ddd (1JRhC
=
5
3.2.2. [{(C6H11)2PCH@C(But)–NN@C(But)CH2P(C6H11)2}Rh(CO)] (10)
Solution of [Rh(CO)2Cl]2 (0.0250 g, 0.055 mmol), ligand (2)
0.0605 g (0.110 mmol) and 0.6 g (11 mmol) of sodium methoxide
in 5 ml of THF was sealed under vacuum in glass ampoule and
reaction mixture was sonicated for 1 h. Then the reaction mixture
was kept at room temperature for 15 days. Dark red solution was
filtered and the product was obtained by evaporation of solvent
in vacuo.
65.1 Hz, JPC = 15.5 Hz, JPC = 15.5 Hz, ꢀCꢁ, CO).
IR (mCO, CHCl3, cmꢀ1) 1938.
2
2
3.2.5. [{(But)2PCH2C(But)@NH}Rh(Cl)2(l-Cl)]2 (13)
Complex [(But2PCH2C(But)@NN@C(But)CH2PBut2)Rh(CO)] (8)
(0.1000 g, 0.154 mmol) was dissolved in 1 ml of chloroform and
0.2 ml of 35% aqueous HCl was added. Reaction mixture was left
at room temperature for 2 months with occasional stirring. The
red product which precipitated was dried in vacuo, then dissolved
in 0.5 ml of chloroform and isolated by crystallization via slow dif-
fusion of hexane vapour to the chloroform solution at room tem-
perature. Yield 0.011 g (8%).
31P NMR: (CD2Cl2) ABX 51.3 (1JRhP = 120.9 Hz), 67.0 (1JRhP
=
130.0 Hz) (2JPP = 268.3 Hz). 1H NMR: (CDCl3): 1.14 s (9H, t-Bu),
1.26 s (9H, t-Bu), 1.19–1.44 m (24H, CH2, c-C6H11), 1.70–2.06 m
2
4
(20H, CH + CH2, c-C6H11), 2.24 dd (2H, JPH = 10.7 Hz, JPH = 1.7 Hz,
2
4
PCH2), 3.80 dd (1H, JPH = 3.6 Hz, JPH = 1.8 Hz, PCH).
Crystal suitable for X-ray analysis was grown by slow diffusion
of hexane vapour to the chloroform solution at room temperature.
31P NMR (CD2Cl2): 96.7 d (1JRhP = 121.4 Hz). 1H NMR (CD2Cl2):
13C NMR (CDCl3): 13.38 d (1JPC = 14.1 Hz, CH2, PCH2), 26.63 s
(CH2, c-C6H11), 26.85 s (CH2, c-C6H11), 27.22–27.56 m (CH2, c-
C6H11), 28.65 s (CH2, c-C6H11), 29.01 s (CH2, c-C6H11), 29.19 s
(CH3, t-Bu), 30.22 d (J = 14.2 Hz, CH2, c-C6H11), 30.25 d (J = 10.2
Hz, CH2, c-C6H11), 31.50 s (CH3, t-Bu), 35.55 d (1JPC = 18.7 Hz, CH,
2
1.38 s (18H, t-Bu), 1.57 bs (36H, t-Bu), 3.15 dd (2H, JPH = 17.0 Hz,
2JHH = 10.5 Hz, CH2), 3.45 dd (2H, 2JPH = 16.2 Hz, 2JHH = 9.1 Hz, CH2),
10.48 bs (2H, NH).
c-C6H11), 35.63
d
(1JPC = 29.9 Hz, CH, c-C6H11), 38.99
d
(3JPC = 14.7 Hz, ꢀCꢁ, t-Bu), 39.88 d (3JPC = 2.2 Hz, ꢀCꢁ, t-Bu), 71.03
d (1JPC = 43.9 Hz, CH, PCH), 145.85 s (ꢀCꢁ, fflC–N), 189.31 dd
3.3. Crystallographic data
(2JPC = 22.2 Hz, JPC = 2.7 Hz, ꢀCꢁ, ꢀC@N), 197.05–197.41 m (ꢀCꢁ,
The diffraction-quality crystals of complexes were grown as
mentioned above. The crystals were selected in mother liquor
and quickly transferred into Fluorolube oil, then mounted on glass
fibres in random orientation and cooled to 150(1) K. Diffraction
data were collected using Nonius Kappa CCD diffractometer (En-
raf-Nonius) at 150(1) K (Cryostream Cooler Oxford Cryosystem)
and analyzed using the HKL program package [15]. The structures
were solved by direct methods and refined by full matrix least-
squares techniques (SIR92 [16], SHELXL97 [17] or CRYSTALS [18]). Final
geometric calculations were carried out with the recent version
of the PLATON program [19].
5
CO).
IR (mCO, CHCl3, cmꢀ1) 1944.
3.2.3. [{Pri2PCH@C(But)–NN@C(But)CH2PPri2}Rh(CO)] (11)
Solution of [Rh(CO)2Cl]2 0.0300 g (0.065 mmol), ligand (3)
0.0660 g (0.130 mmol) and 0.6 g (11 mmol) of sodium methoxide
in 5 ml of THF was sealed under vacuum in glass ampoule and
reaction mixture was sonicated for 1 h. Then the reaction mixture
was left standing for 15 days. Dark red solution was filtered and
the product was obtained by evaporation of solvent in vacuo.
31P NMR (CD2Cl2): ABX 60.0 (1JRhP = 120.6 Hz), 76.6 (1JRhP
=
132.6 Hz) (2JPP = 268.2 Hz). 1H NMR (CD2Cl2): 1.05–1.30 bm (24H,
CH3, i-Pr), 1.17 s (9H, CH3, t-Bu), 1.28 s (9 H, CH3, t-Bu), 2.08–
3.3.1. [{(C6H11)2PCH2C(But)@NN@C(But)CH2P(C6H11)2}Rh(CO)]-
[(CO)2RhCl2] (6)
2
4
2.21 bm (4H, CH, i-Pr), 2.26 dd (2H, JPH = 10.7 Hz, JPH = 2.2 Hz,
X-ray: C39H66Cl2N2O3P2Rh2, M = 949.63 g/mol, triclinic, space
2
4
ꢀ
CH2, PCH2), 3.86 dd (1H, JPH = 3.9 Hz, JPH = 2.2 Hz, CH, PCH).
13C (CD2Cl2): 12.81 d (1JPC = 13.8 Hz, CH2, PCH2), 18.39 s (CH3, i-
Pr), 18.97 s (CH3, i-Pr), 19.64 d (2JPC = 2.2 Hz, CH3, i-Pr), 19.74 d
(2JPC = 5.4 Hz, CH3, i-Pr), 25.54 d (1JPC = 20.8 Hz, CH, i-Pr), 26.03 d
(1JPC = 29.2 Hz, CH, i-Pr), 29.30 s (CH3, t-Bu), 31.59 s (CH3, t-Bu),
39.13 d (2JPC = 14.6 Hz, ꢀCꢁ, t-Bu), 39.98 d (2JPC = 1.9 Hz, ꢀCꢁ, t-
Bu), 70.44 d (1JPC = 44.2 Hz, CH, PCH), 145.24 s (ꢀCꢁ, fflC–N),
group: P1, a = 11.7725(2) Å, b = 17.6971(3) Å, c = 22.4909(6) Å,
a = 93.954(1), b = 97.510(1), c = 109.284(1)°, Z = 4, V = 4353.3(2)
Å3, Dcalc = 1.45 g cmꢀ3, l(Mo Ka) = 0.99 mmꢀ1, crystal dimensions
of 0.1 ꢁ 0.1 ꢁ 0.2 mm. The independent part is created by two
complex molecules. The structure was refined by full matrix
least-squares on F values [18]. All heavy atoms were refined aniso-
tropically. All hydrogen atoms were localized from the expected
geometry and were not refined. This model converged to the final
R = 0.0443 and Rw = 0.0509 using 10879 independent reflections
(hmax = 27.52°).
5
190.01 dd (2JPC = 21.7 Hz, JPC = 2.5 Hz, ꢀCꢁ, ꢀC@N), 197.47 ddd
2
2
(1JRhC = 64.2 Hz, JPC = 15.5 Hz, JPC = 15.5 Hz, ꢀCꢁ, CO).
IR (mCO, CHCl3, cmꢀ1) 1943.
3.2.4. [{But2PCH@C(But)–NN@C(But)CH2PBut2}Rh(CO)] (12)
Rhodium(I) precursor [Rh(CO)2Cl]2 (0.0300 g, 0.065 mmol) and
ligand (4) 0.0750 g (0.130 mmol) were dissolved in chloroform
3.3.2. [{But2PCH2C(But)@NN@C(But)CH2PBut2}Rh(CO)]Cl (8) ꢂ 2CHCl3
X-ray:
C29H58ClN2OP2Rh ꢂ 2CHCl3(C31H60Cl7N2OP2Rh).
M =
889.81 g/mol, monoclinic, space group: P21/n, a = 11.0678(1) Å,

2000
M. Pošta et al. / Journal of Organometallic Chemistry 693 (2008) 1997–2003
b = 24.404(2) Å, c = 15.3403(2) Å, b = 100.3023(6)°, Z = 4, V =
4243.03(8) Å3, Dcalc = 1.393 g cmꢀ3, l(Mo Ka) = 0.945 mmꢀ1, crys-
tal dimension of 0.35 ꢁ 0.4 ꢁ 0.45 mm. The structure was refined
by full matrix least-squares on F values [17]. All heavy atoms were
refined anisotropically. All hydrogen atoms were localized from
the expected geometry and were not refined. This model con-
verged to the final R = 0.0299 and Rw = 0.0660 using 8240 indepen-
dent reflections (Fo > 4r(Fo); hmax = 27.50°).
4. Results and discussion
Diphosphinoazine square planar cationic complexes of Rh(I)
which are precursors to the amido carbonyl complexes were syn-
thesized by cleavage of the chloride bridges of [Rh(CO)2Cl]2 and
liberating one mole of carbon monoxide per rhodium atom. Com-
plexes containing all four ligands with variable steric demands
could be prepared. The formation of cationic complexes is very ra-
pid, complete within several minutes, except the formation of
complex 5, whereby an intermediate was observed by NMR spec-
troscopy. Two possible structures 5A and 5B were proposed for this
intermediate from the set of 31P and 1H NMR spectra (Scheme 1).
Two diphosphinoazine ligands can act either as bridging ligands
in a binuclear complex with 18–membered ring (5A), analogous
to a known platinum complex [9a], or the intermediate is mononu-
clear with the chelating ligand (5B). It was not possible to decide
between the two proposed structures from NMR spectra because
ligand 1 is in (Z,Z) configuration in both structures and groups cru-
cial for assignment are thus equivalent in both cases. In 31P NMR
spectra a characteristic doublet with an interaction constant
125 Hz was found which was attributed to two equivalent phos-
phorus nuclei that interact with rhodium. Proton spectra are con-
sistent with phosphorus spectra and with both proposed
intermediates since signals of the protons of the groups from both
halves of the diphosphinoazine moiety are equivalent as well.
Ene-hydrazone amido carbonyl complexes of Rh(I) were pre-
pared from the corresponding cationic complexes 5–8 via their
deprotonation by a base. Ene-hydrazone complexes 9–11 contain-
ing less sterically demanding ligands 1–3 were synthesized by
treating complexes 5–7, generated in situ in anhydrous tetrahydro-
furan from the starting materials, with an excess of sodium meth-
oxide. Complex 12 with the bulkiest ligand 4 was prepared
similarly from complex 8, but triethylamine was used as the base
and chloroform as the solvent (Scheme 2).
3.3.3. 2 [{Ph2PCH@C(But)–NN@C(But)CH2PPh2}Rh(CO)] (9) ꢂ CH2Cl2
X-ray: C74H84N2O2P4Rh2. CH2Cl2 (C75H86Cl2N2O2P4Rh2), M =
1476.13 g/mol, monoclinic, space group: Pc, a = 10.1220(2) AA,
b = 24.9990(4) AA, c = 18.1989(2) Å, b = 129.521(1)°, Z = 4, V =
3552.3(1) Å3, Dcalc = 1.37 g cmꢀ3, l(Mo Ka) = 0.68 mmꢀ1, crystal
dimensions of 0.2 ꢁ 0.2 ꢁ 0.4 mm. The independent part is
created by two complex molecules and one disordered solvent
molecule. The structure was refined by full matrix least-squares
on F values [18]. All heavy atoms were refined anisotropically.
All hydrogen atoms were localized from the expected geometry
and were not refined. This model converged to the final
R = 0.0357 and Rw = 0.0372 using 10558 independent reflections
(hmax = 26.06°).
3.3.4. [{(But)2PCH2C(But)@NH}Rh(Cl)2(l-Cl)]2 (13) ꢂ 2CHCl3
X-ray: C14H30Cl3NPRh ꢂ 2 CHCl3 (C15H31Cl6NPRh; dimer).
M = 571.99 g/mol, monoclinic, space group P21/c, a = 10.6868(2)
Å, b = 17.7065(4) Å, c = 12.9903(3) Å, b = 106.118(1)°, Z = 4, V =
2361.48(9) Å3, Dcalc = 1.609 g cmꢀ3, l(Mo Ka) = 1.470 mmꢀ1, crys-
tal dimension of 0.15 ꢁ 0.25 ꢁ 0.25 mm. The structure was refined
by full matrix least-squares on F values [17]. All heavy atoms were
refined anisotropically. All hydrogen atoms were localized from
the expected geometry and were not refined. This model con-
verged to the final R = 0.0530 and Rw = 0.1313 using 4614 indepen-
dent reflections (Fo > 4r(Fo); hmax = 27.49°).
2
But
But
OC
Ph2
PPh2
P
N
Rh
[Rh(CO)2Cl]2
CHCl3
N
N
But
PPh2
Rh
OC
N
2 Cl
But
N
CO
Ph2P
Ph2P
But
N
P
Ph2
CO
1
But
5A
[Rh(CO)2Cl]2
3 h
CHCl3
- CO
But
But
PPh2
Ph2
CO
CO
PPh2
P
N
N
Rh CO
PPh2
Rh
- CO
3 h
Cl
N
N
Cl
But
But
5
5B
Scheme 1.

M. Pošta et al. / Journal of Organometallic Chemistry 693 (2008) 1997–2003
2001
But
But
PR2
PR2
MeONa/THF or
Et3N/CHCl3 (R = But)
N
Rh CO
PR2
N
Rh CO
PR2
Cl
N
N
But
But
R = Ph, 9
R = Ph, 5
R = c-C6H11, 10
R = c-C6H11, 6
R = Pri, 11
R = Pri, 7
R = But, 12
R = But, 8
Scheme 2.
31P NMR spectra of complexes 5–12 were assigned as ABX spin
systems. The exact chemical shifts and interaction constants of
both phosphorus atoms were determined by computer simulation
in the gNMR [14] program. The phosphorus atoms are in trans
arrangement in diphosphinoazine square planar complexes of
Rh(I), but they are not equivalent due to coordination of one nitro-
gen atom to rhodium, which leads to the formation of two metal-
lacycles of different sizes. The value of the interaction constant
1JRhP was different for phosphorus atoms P1 and P2 of the ligand
in the square planar complexes 5–8 and was in the range typical
for such interaction (P1: 115.6–123.0 Hz, P2: 128.5–139.6 Hz). Val-
bered ring and carbons belonging to the 5-membered ring, respec-
1
tively. Values of JPC increase with increasing bulkiness of the
phosphine groups of the ligand in the series Ph < Pri < c-C6H11 < But.
Methylene and methine carbons in deprotonated complexes 9–
12 exhibit analogous interactions with phosphorus atoms as do
their cationic precursors and the signals of appropriate methylene
1
carbons are split into doublets with JPC from 9.5 to 17.3 Hz. The
signals of methine carbon are also split into doublets. In this case
1
the value of the interaction constant JPC is somewhat higher, in
the range of 42.9–53.3 Hz.
Differences in electrondonor properties of ligands with variable
substitution were studied by infrared spectroscopy by means of
the differences in the values of valence vibration of the carbonyl
group which is known to be indirectly influenced by p-donation
from the ligand to the metal atom. For this vibration a strong band
in the range of 1950–1972 cmꢀ1 for cationic complexes 5–8 and
1938–1957 cmꢀ1 for deprotonated complexes 9–12 was found.
The amide nitrogen of the ene-hydrazone ligand is a weaker p-
acceptor, therefore due to the increasing electron density on the
metal a reduction of the value of carbonyl valence vibration from
6 to 34 cmꢀ1 was observed between pairs of corresponding com-
plexes 5 and 9, 6 and 10, etc. The value of 1957 cmꢀ1 for complex
9 is close to the value of 1960 cmꢀ1 found by Mayer and Kaska [6]
for the only rhodium PNP pincer amido carbonyl complex known
1
ues of interaction constants JRhP in these complexes were very
similar to the starting cationic complexes and were in the range
from 120.6 to 126.8 Hz for P1 and from 130.0 to 144.9 Hz for P2.
All 31P NMR shifts and interaction constants are summarized in
Tab. 1. From the 31P NMR spectra it is evident that the chemical
shift of phosphorus atoms increases with increasing value of the
Tolman angle [20] of the phosphine groups, as the bulkiness in-
creases and the s-character of the free electron pair decreases
(Ph < c-C6H11 < i-Pr < t-Bu). Since phosphorus atoms are trans their
2
interaction constant JPP is relatively high, in the range of 256–
310 Hz. Diphosphinoazine complexes of Ir(I) [9b] exhibit very sim-
2
ilar JPP interaction constant (ca 308 Hz) as the discussed rhodium
complexes. Similar value of phosphorus–phosphorus interaction
constant (354–396 Hz) can be also found in rhodium(I) P,C,P pincer
complexes [10d,21] similar to complexes 5–12.
1H and 13C NMR spectra of diphosphinoazine cationic com-
plexes and deprotonated ene-hydrazone complexes are similar to
each other as far as diphosphinoazine or en-hydrazone ligand
frame is concerned. Differences were naturally stemming from dif-
ferent substituents on phosphorus P1 and P2. Ligands are in (E,Z)
configuration in all the cases as was confirmed from 1H and 13C
NMR spectra and in three cases also by X-ray diffraction. Due to
the P,N,P0 ligand coordination, five- and six-membered metallacy-
cles have formed. Therefore two different signals of methylene
protons were observed for complexes 5–8 and in complexes 9–
12 only one signal of the methylene protons and one signal of
methine proton was observed. Depending on the particular com-
plex these signals were doublets (6) or doublets of doublets (5, 7,
2
4
8) with very well resolved JPH and JPH; signal of methine proton
in complexes 9–12 was doublet of doublets in all the cases.
All signals of the protonated carbons were identified from DEPT
and qHSQC experiments, signals of quaternary carbon atoms were
assigned from gHMBC experiment. Signals of methylene carbon
atoms in complexes 5–8, which are in the proximity of phosphorus
atoms are split to doublets with interaction constants 1JPC in range of
5.5–15.5 Hz and 15.5–24.2 Hz for carbons belonging to the 6-mem-
Fig. 1. ORTEP view of 6. Hydrogen atoms are omitted for clarity.

2002
M. Pošta et al. / Journal of Organometallic Chemistry 693 (2008) 1997–2003
so far. Significant further increase of electron density on rhodium
was achieved by substituting phenyl groups on phosphorus atoms
by more electron-donating groups, the value of carbonyl valence
room temperature. The structures of 6, 8 and 9 showed that com-
plexes were square planar with ligand P,N,P0 coordinated in the ex-
pected (E, Z) configuration in all the cases. Single crystal of the
cationic complex 6 contains unexpected [Rh(CO)2Cl2]ꢀ anion while
in complex 8 the counterion is a chloride anion. We explain the
unusual counteranion by very long (1 month) crystallization of
complex 6 whereby the chloride anion was substituted by the
[Rh(CO)2Cl2]ꢀ anion, which most probably resulted from the par-
tial decomposition of the complex in solution. All the structures
exhibited only small deviations from planarity as far as atoms tak-
ing part in square planar coordination polyhedron are concerned.
However, since one of the metallarings in the complexes is a six-
membered ring, its puckering allowed pyramidal arrangement of
bonds on an amide nitrogen in compound 9. This alleviation of
strain was not possible in case of two five membered rings of an
analogous rhodium amido carbonyl complex [6]. Other important
structural features are in accordance with the analogous data for
this complex (in brackets). Nitrogen–rhodium distance 2.101 Å
(2.074 Å) confirms single bond character, P–Rh–P0 angle 168.17°
(163.8°) is a bit wider, again probably owing to less strained ligand
backbone of our complex. Rhodium–carbonyl carbon distance
1.837 Å (1.855 Å) and carbonyl bond length 1.151 Å (1.125 Å) are
similar and supporting slightly more electron-donating character
of our ligand found by IR spectroscopy.
vibration for the tert-butyl substituted complex being 1938 cmꢀ1
.
We have succeeded in growing the single crystals of cationic
complexes 6 and 8 (Figs. 1 and 2) and of the amido complex
9(Fig. 3). Single crystals of 6 and 8 were obtained by a slow diffu-
sion of hexane vapour to chloroform solutions. A single crystal of 9
was obtained by a slow evaporation of dichloromethane solvent at
It was found, that complex 8 in chloroform in the presence of HCl
undergoes splitting of the azine N–N bond and a complex of Rh(III)
(13) is formed upon oxidation in a very small yield (Scheme 3). The
X-ray structure of the complex (Fig. 4) shows that it is a dimer with
two chloride bridges connecting two metal centres. Diphosphino-
azine ligand But2PCH@C(But)–NN@C(But)CH2PBut2 is cleaved into
two symmetric parts (But)2PCH2C(But)@NH coordinated to two rho-
diums by the phosphorus and nitrogen atoms via their free electron
Fig. 2. ORTEP view of 8. Hydrogen atoms are omitted for clarity.
Fig. 3. ORTEP view of 9. Hydrogen atoms are omitted for clarity.
Fig. 4. ORTEP view of 13. Hydrogen atoms are omitted for clarity.
But
PBut2
Cl
But2P
Cl
NH
Cl
Cl
But
H+, CHCl3
N
Rh CO
PBut2
Rh
Rh
But
2
Cl
Cl
N
N
H
PBut2
Cl
But
13
8
Scheme 3.

M. Pošta et al. / Journal of Organometallic Chemistry 693 (2008) 1997–2003
2003
pairs. Structure of this complex in solution was also confirmed by 1H
and 31P NMR spectroscopy. Measurement of 13C NMR spectra was
not possible, because crystals of complex 13 are poorly soluble in
common solvents used for NMR spectroscopy.
(c) M.E. van der Boom, D. Milstein, Chem. Rev. 103 (2003) 1759;
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Wisniewski, H. Görls, R.J. Mynott, N. Theyssen, D. Milstein, W. Leitner,
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Cleavage of the N–N bond of the diphosphinoazine ligand is un-
ique and has not been published, cleavage of an azine moiety was re-
ported in several cases, however. Ketazines are cleaved giving
ketiminato mononuclear [22a], binuclear homometallic [22b] or
heterometallic [22c] complexes. Interestingly, substituted titano-
cene fragments cleave acetoneazine depending on the number of
methylsontitanocene rings, givingeithermononuclear monoketim-
inato complexormononuclearbis(amido)complex withdoubleC–H
activation [22d]. Milstein et al. [22e] reported that aldazines are
cleaved by rhodium PCP and PCN complexes in a sort of dismutation
reaction resulting in an aldimine complex (or a free unstable aldim-
ine) and a nitrile complex, ketimines were unreactive. On the basis of
calculations, the reaction is believed to avoid direct oxidative addi-
tion of N–N bond to rhodium. We believe that in our case the oxida-
tion of metal is caused by the presence of chloroform, similarly to the
oxidation of Rh(I) observed in cycloocta-1,5-diene complexes [23],
azine moiety being at the same time cleaved into two didentate
phosphine–imine ligands. The source of hydrogen for iminato to
imine transformation is unclear. It could be either HCl present in
chloroform upon long standing or added purposefully or the hydro-
gen may come from another diphosphinoazine ligand which loses a
rhodium atom entering a new complex. Owing to a low yield of the
product we were unable to identify the fate of this free diphosphino-
azine or its decomposition products.
[5] (a) J.C. Peters, S.B. Harkins, S.D. Brown, M.W. Day, Inorg. Chem. 40 (2001)
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ˇ
ˇ
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ˇ
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3311;
5. Conclusions
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1996, p. 147.
The synthesis of a series of unsymmetrical pincer-like rhodium
amido carbonyl complexes with four electronically and sterically
different diphosphinoazine ligands considerably extends the avail-
able information about trans amido carbonyl arrangement on rho-
dium including data from X-ray diffraction. The comparison with
the only known trans amido rhodium carbonyl symmetrical pincer
complex shows that our complexes have basically the same struc-
tural features as the symmetrical complex. However, the ease of
their preparation and specific features of the diphosphinoazine li-
gand backbone make them suitable candidates for future stoichi-
ometric and possibly catalytic transformations on an electron-
rich pincer-supported rhodium centre.
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ˇ
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The support of grant agencies (Grant Agency of the Czech
Republic, 203/01/0554, 203/06/0738; Ministry of Education, Youth
and Sport of the Czech Republic, LC06070) is gratefully
acknowledged.
Appendix A. Supplementary material
CCDC 671356, 665063, 671355 and 665064 contain the supple-
mentary crystallographic data for compounds 6, 8, 9 and 13. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
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