Rhodium pincer complexes of 2,2′-bis(diphenylphosphino) diphenylamine

Article abstract of DOI:10.1016/S0022-328X(03)00776-9

The novel pincer ligand 2,2′-bis(diphenylphosphino)diphenylamine (1) has been synthesized by treatment of 2,2′-dibromodiphenylamine with n -butyl lithium and subsequent reaction with diphenylchlorophosphine. When ligand 1 is treated with RhCl₃ hydrate the dinuclear complex 1a forms which can be converted into the square planar carbonyl complex 1c upon reduction with Na/Hg in the presence of CO. Depending on the reaction conditions two different complexes were isolated when 1 reacts with [(COE)₂ RhCl]₂. In THF the hydrochloro complex 1b and with n-butyl lithium the COE complex 1d is generated. Interestingly, the formation of 1b represents a rare case of N-H oxidative addition to a late transition metal complex fragment. Compound 1c is observed upon reaction of the COE complex 1d with carbon monoxide. Quantum chemical calculations at different levels of theory are in good agreement with the experimental structure of 1c.

Full text of DOI:10.1016/S0022-328X(03)00776-9

Journal of Organometallic Chemistry 682 (2003) 149ꢀ154
/
www.elsevier.com/locate/jorganchem
Rhodium pincer complexes of 2,2?-
bis(diphenylphosphino)diphenylamine
Angelika M. Winter a, Klaus Eichele a, Hans-Georg Mack b, Suzan Potuznik c,
Hermann A. Mayer a,*, William C. Kaska c,*
a Institut fur Anorganische Chemie, Universitat Tubingen, Auf der Morgenstelle 18, 72076 Tubingen, Germany
¨
¨
¨
¨
b Institut fur Physikalische und Theoretische Chemie, Universitat Tubingen, Auf der Morgenstelle 8, 72076 Tubingen, Germany
¨
¨
¨
¨
c Department of Chemistry, University of California Santa Barbara, 93106 Santa Barbara, CA, USA
Received 17 March 2003; received in revised form 27 June 2003; accepted 27 June 2003
Dedicated to Professor H. Werner on the occasion of his 70th birthday
Abstract
The novel pincer ligand 2,2?-bis(diphenylphosphino)diphenylamine (1) has been synthesized by treatment of 2,2?-dibromodiphe-
nylamine with n-butyl lithium and subsequent reaction with diphenylchlorophosphine. When ligand 1 is treated with RhCl3 hydrate
the dinuclear complex 1a forms which can be converted into the square planar carbonyl complex 1c upon reduction with Na/Hg in
the presence of CO. Depending on the reaction conditions two different complexes were isolated when 1 reacts with [(COE)2RhCl]2.
In THF the hydrochloro complex 1b and with n-butyl lithium the COE complex 1d is generated. Interestingly, the formation of 1b
represents a rare case of NꢀH oxidative addition to a late transition metal complex fragment. Compound 1c is observed upon
/
reaction of the COE complex 1d with carbon monoxide. Quantum chemical calculations at different levels of theory are in good
agreement with the experimental structure of 1c.
# 2003 Elsevier B.V. All rights reserved.
Keywords: PNP pincer ligand; Rhodium complexes; NꢀH oxidative addition; Quantum chemical calculations
/
1. Introduction
Tridentate pincer ligand complexes [1ꢀ
reagents with promising applications in the areas of
sensors [9], catalysis [10,11], and dendrimer synthesis
[12]. Most of these compounds have a central anionic
atom (N, C, Si [13]) or functional group and a variety of
donor atoms (N, S, O, P) which coordinate the metal
atom to the ligand backbone. In this paper we report on
the synthesis of nitrogen based pincer complexes and the
X-ray structure of Rh(CO){N[(o-PPh2)C6H4]2} (1c).
The experimental structural analysis was supplemented
by the results of various density functional calculations.
The hybrid amine phosphine tridentate ligand 1 was
chosen to study the effect of an amide ligand on the
chemistry of low valent late transition metals. The amine
is positioned between two diphenylphosphine groups in
order to take advantage of the strong metal binding
properties of the phosphines. The chelate effect of the
ligand prevents the dissociation of the highly electron
rich amide from an electron rich low valent late
transition metal. Furthermore, the ortho derivatized
diphenyl amine does not contain b hydrogens which
could transfer onto the metal and lead to decomposition
of the amide.
/
8] are versatile
* Corresponding authors. Tel.: ꢁ
/
49-7071-297-6229; fax: ꢁ
/
49-7071-
295-306 (H.A.M.); tel.:
(W.C.K.).
ꢁ
/
1-805-893-2515; fax: 1-805-893-4120
ꢁ/
E-mail addresses: hermann.mayer@uni-tuebingen.de (H.A. Mayer),
kaska@chem.ucsb.edu (W.C. Kaska).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00776-9

150
A.M. Winter et al. / Journal of Organometallic Chemistry 682 (2003) 149ꢀ154
/
2. Experimental
(500.12 MHz, CD2Cl2): d 6.78 (m, 4H, PPhPh? H6), 7.01
(m, 4H, PPhPh? H5), 7.13 (t, 3JHH
7.7 Hz, 2H, PPhPh?
H7), 7.36 (m, 4H, PPhPh? H6), 7.46 (t, JHH
ꢂ
/
3
2.1. General remarks, materials, and instrumentation
ꢂ7.7 Hz,
/
2H, PPhPh? H7), 7.50 (m, 2H, H3), 7.58 (m, 2H, H4),
7.72 (m, 2H, H2), 7.93 (m, 4H, PPhPh? H5), 8.04 (m, 2H,
Reactions were performed under Ar using standard
Schlenk techniques according to previously described
procedures [14,15] unless otherwise specified.
H1), 8.30 (s, br, 1H, NH). 31P{1H}-NMR (121.4 MHz,
1
CD2Cl2): d 37.1 (d, JRhP
ꢂ115.8 Hz). MS (DCI): m/z
/
Benzene, hexane and etheral solvents were distilled
from benzophenone ketyl, CH2Cl2 from LiAlH4,
MeOH, EtOH and toluene from sodium. Deuterated
solvents were degassed and distilled from LiAlD4.
[(COE)2RhCl]2 was prepared according to the procedure
of Van der Ent and Onderdelinden [16]. 2,2?-Dibromo-
diphenylamine was prepared according to the procedure
described by Jones and Mann [17]. Note! We found that
674 (RhCl{HN[(o-PPh2)C6H4]2}ꢁ), Calc. 674.91; m/z
639 (Rh{HN[(o-PPh2)C6H4]2}ꢁ), Calc. 639.48. UVꢀ
vis
/
(CH2Cl2): o236
1530.
ꢂ
/
2.70ꢄ
/
104, o270
ꢂ
/
2.51ꢄ
/
104, o394
ꢂ
/
2.4. Synthesis of Rh(H)(Cl)(THF){N[(o-
PPh2)C6H4]2} (1b)
a temperature of 255ꢀ
Chapman rearrangement to occur.
/
265 8C was necessary for the
A suspension of 86 mg (0.02 mmol) [(COE)2RhCl]2
and 138 mg (0.26 mmol) 2,2?-bis(diphenylphosphino)di-
phenylamine (1) in 25 ml THF was stirred at r.t. for 3.5
h and refluxed for 4 h. After vacuum removal of the
solvent and dissolution in 3 ml toluene the product
precipitates as a yellow solid. Yield: 44 mg (24.7%).
Anal. Calc. for C40H37ClNOP2Rh: C, 64.28; H, 4.99; N,
2.2. Synthesis of 2,2?-
bis(diphenylphosphino)diphenylamine HN[(o-
PPh2)C6H4]2 (1)
Under a nitrogen atmosphere 58 ml (97.44 mmol) of
n-butyl lithium (1.68 M in hexane) was added dropwise
to 9.9 g (30.09 mmol) of 2,2?-dibromodiphenylamine in
50 ml Et2O at 0 8C. The reaction mixture was allowed to
stir for 1.5 h. 17.5 ml (97.48 mmol) diphenylchlorophos-
phine in 50 ml Et2O were added dropwise at 0 8C and
the solution was stirred at room temperature (r.t.)
overnight. The reaction mixture was then hydrolyzed
with 30 ml of concentrated hydrochloric acid, the
solution washed with water, and the product precipi-
tated with EtOH. The colorless 2,2?-bis(diphenylphos-
phino)diphenylamine (1) can be purified by recrystalli-
zation from CH2Cl2 and EtOH. Yield: 7.8 g (48.3%).
1.87. Found: C, 64.07; H, 5.10; N, 1.81%. 1H-NMR
1
21.77 (dt, JRhH
11.4 Hz, 1H, Rh-H), 1.64 (m, br, 4H,
(500.12 MHz, CD2Cl2): d ꢃ
/
ꢂ29.5 Hz,
/
2JPH
ꢂ
/
CH2CH2O), 3.52 (m, br, 4H, CH2CH2O), 6.61 (m, 2H,
H3), 7.06 (m, 2H, H2), 7.46 (m, 14H, H4, H6, H7), 7.64
(m, 4H, H5), 7.69 (m, 2H, H1), 7.94 (m, 4H, H5).
31P{1H}-NMR (121.4 MHz, CD2Cl2): d 35.1 (d,
1JRhP
ꢂ
108.8 Hz). 13C{1H}-NMR (125.76 MHz,
/
CD2Cl2): d 25.8 (s, CH2CH2O), 68.4 (s, CH2CH2O),
118.0 (m), 118.1 (s), 128.9 (m), 129.1 (m), 130.5 (s), 131.1
(s), 131.4 (s), 133.6 (m), 134.7 (m), 135.4 (s). MS (DCI):
m/z 674 [Mꢃ
/
{Hꢁ
THF}ꢁ], Calc. 674.89; m/z 639
/
(Rh{N[(o-PPh2)C6H4]2}ꢁ), Calc. 639.48.
m.p. 200ꢀ
/
201 8C. Anal. Calc. for C36H29NP2: C, 80.44;
H, 5.44; N, 2.61. Found: C, 80.29; H, 5.53; N, 2.62%.
2.5. Synthesis of Rh(CO){N[(o-PPh2)C6H4]2} (1c)
2
1H-NMR (500.12 MHz, C6D6): d 6.67 (dd, JHH
Hz, 7.5 Hz, 2H, H3), 7.00 (m, 16H, H1, H2, H4, H6), 7.31
ꢂ7.5
/
2.5.1. Method A
(m, 11H, NH, H5, H7). 31P{1H}-NMR (202.47 MHz,
40 mg (0.05 mmol) of Rh2Cl4{HN[(o-PPh2)C6H4]2}
(1a) were added to sodium amalgam prepared from 25
ml (1.69 mmol) mercury and 5 mg (0.23 mmol) sodium.
20 ml of THF were added and the flask was flushed with
carbon monoxide. The reaction mixture was stirred
vigorously for 18 h at r.t. The solid was allowed to
settle and the solution was filtered in air. The air stable
yellow product is obtained by removal of the solvent in
C6D6): d ꢃ
19.2 (s). IR (KBr pellet): 3340 cmꢃ1 (nNꢀH).
/
MS (DCI): m/z 538 (Mꢁ), Calc. 537.58. m/z 532 [Mꢃ
/
PPh2ꢁ], Calc. 351.39.
2.3. Synthesis of Rh2Cl4{HN[(o-PPh2)C6H4]2} (1a)
A solution of 198 mg (0.83 mmol) RhCl3 hydrate
(42.9% Rh) and 481 mg (0.89 mmol) 2,2?-bis(diphenyl-
phosphino)diphenylamine (1) in 50 ml MeOH was
refluxed under a nitrogen atmosphere for 18 h. A yellow
precipitate forms which can be isolated by filtration,
washing with hexane, and recrystallization from
vacuo, and recrystallized from CH2Cl2ꢀhexane. Yield:
/
18 mg (60%).
2.5.2. Method B
25 mg (0.03 mmol) Rh(COE){N[(o-PPh2)C6H4]2} (1d)
were dissolved in 30 ml benzene and left under one
atmosphere of carbon monoxide for several hours at r.t.
Rh(CO){N[(o-PPh2)C6H4]2}) (1c) precipitated as a yel-
low powder. Yield: 100% (based on 31P{1H}-NMR).
CH2Cl2ꢀhexane. The crystals formed quickly turn to a
/
powder when removed from the mother liquor. Yield:
316 mg (84.7%). Anal. Calc. for C36H29Cl4NP2Rh2: C,
1
48.82; H, 3.30. Found: C, 48.83; H 3.23%. H-NMR

A.M. Winter et al. / Journal of Organometallic Chemistry 682 (2003) 149ꢀ
/
154
151
Anal. Calc. for C37H28NOP2Rh: C, 66.59; H, 4.23.
Found: C, 66.30; H, 4.06%. 1H-NMR (500.12 MHz,
C6D6): d 6.43 (m, 2H, H3), 6.96 (m, 14H, H2, H6, H7),
90024. Hydrogen atoms were located in the difference
map and refined with fixed isotropic thermal parameters
(see Section 5).
3
3
7.13 (m, 2H, H4), 7.76 (ddd, JPH
ꢂ
/
12.5 Hz, JHH
ꢂ6.5
/
Hz, 4JRhH 1.5 Hz, 8H, H5), 7.81 (m, 2H, H1). 31P{1H}-
ꢂ
/
2.8. Quantum chemical calculations
NMR (121.4 MHz, C6D6): d 41.8 (d, 1JRhP
ꢂ135.1 Hz).
/
MS (DCI): m/z 667 [Mꢁ], Calc. 667.49; m/z 639
(Rh{N[(o-PPh2)C6H4]2}ꢁ), Calc. 639.48. IR (KBr pel-
Density
functional
(DFT)
calculations
for
Rh(CO){N[(o-PPh2)C6H4]2} (1c) were performed at
various levels of theory using the program Jaguar 4.1
[18]. The geometric structure was optimized at the local
density approximation (SVWN) [19,20] as well as with
let): 1960 cmꢃ1 (nCO). UVꢀ
104, o318 104, o345
1.93ꢄ
104, o580
184, o654 126.
/
vis (CH2Cl2): o240
1.67ꢄ
104, o386
ꢂ
/
3.96ꢄ
/
ꢂ
/
/
ꢂ
/
/
ꢂ
/
12.9ꢄ
/
ꢂ
/
ꢂ
/
the gradient-corrected B3LYP [19ꢀ/22] and B3GGA-II
2.6. Synthesis of Rh(COE){N[(o-PPh2)C6H4]2} (1d)
[19ꢀ24] functionals. For all calculations, the pseudo-
/
potential LACVP* basis set [25] was applied. In this
basis, Rh is described by an effective core potential,
whereas the outermost core orbitals are taken into
account explicitly. For the other atoms in the compound
considered here Pople’s 6-31G* basis set was used.
A solution of 159 mg (0.29 mmol) lithium 2,2?-
bis(diphenylphosphino)diphenylamide in 20 ml toluene
was added dropwise to a solution of 102 mg (0.14 mmol)
[(COE)2RhCl]2 in 20 ml toluene at 15 8C. The reaction
mixture was stirred at r.t. for 90 min, the volatiles were
removed in vacuo and the residue dissolved in 10 ml of
toluene. The solution was concentrated to approxi-
mately 3 ml, filtered and the filtrate dried in vacuo.
The product forms as a fine orange powder. Yield: 70
3. Results and discussion
The synthesis of HN[(o-PPh2)C6H4]2 (1) was achieved
by treatment of 2,2?-dibromodiphenylamine with n-
butyl lithium to effect halogen metal exchange followed
by the reaction of the lithio adduct with diphenylchlor-
ophosphine (Scheme 1). Because the multiplets in the
1
mg (32.9%). H-NMR (500.12 MHz, C6D6): COE: d
0.94 (m, 2H, CH2), 1.24 (m, 8H, CH2), 2.26 (m, 2H,
CH2), 3.64 (m, br, 2H, ꢁ
/
CH). N[(o-PPh2)C6H4]2: d 6.43
(m, 2H, H3), 6.85 (m, 2H, H2), 7.04 (m, 12H, H6, H7),
1
7.23 (m, 2H, H4), 7.55 (m, 2H, H1), 7.97 (m, br, 8H, H5).
31P{1H}-NMR (121.4 MHz, C6D6): d 38.8 (d, JRhP
aromatic region of the H-NMR spectrum of the pincer
ligand 1 appeared rather broad the NH proton could
1
ꢂ
/
148.3 Hz). 13C{1H}-NMR (125.76 MHz, C6D6): COE: d
26.6 (s, CH2), 31.8 (s, CH2), 32.0 (s, CH2), 68.5 (d,
not be located. A singlet in the 31P{1H}-NMR spectrum
at ꢃ19.2 ppm supports the formation of 1. The highest
/
1JRhC
117.3 (m), 128.3 (s), 128.6 (m), 129.3 (s), 129.9 (s), 131.4
ꢂ
/
11.3 Hz, ꢁ/CH), N[(o-PPh2)C6H4]2: d 115.8 (m),
molecular peak in the mass spectrum of 1 represents the
ligand, HN[(o-PPh2)C6H4]2. This and the H, C, and N
elemental analysis provide the positive information that
two and not one of the diphenylphosphine groups are
present in 1.
(s), 133.1 (s), 134.1 (m), 134.9 (m). MS (DCI): m/z 749
[Mꢁ],
Calc.
749.68;
m/z
639
(Rh{N[(o-
PPh2)C6H4]2}ꢁ), Calc. 639.48.
Upon refluxing RhCl3 hydrate with 1 in methanol
under an N2 atmosphere the air stable pale yellow
dinuclear complex Rh2Cl4{N[(o-PPh2)C6H4]2} (1a) pre-
cipitated from the reaction mixture (Scheme 1). The
NMR data are consistent with a plane of symmetry in 1a
which contains the NH unit, the two rhodium atoms,
2.7. X-ray structural analysis for Rh(CO){N[(o-
PPh2)C6H4]2} (1c)
Crystal data: C37H28NOP2Rh, Mꢂ
/
667.45, orthor-
32.643(4),
298 K, mꢂ
0.68 mmꢃ1, graphite monochromated Moꢀ
Ka radia-
orange skewed bipyramids
with dimensions ca. 0.47ꢄ0.4ꢄ0.3 mm, crystal
hombic, space group Fdd2, aꢂ18.513(2), bꢂ
/
/
3
1
˚
cꢂ
/
10.153(1), Vꢂ
/
6135.7(12) A , Zꢂ
/
8, Tꢂ
/
/
and the two bridging chlorides. Consequently the H-
/
NMR spectrum of 1a displays ten unique hydrogen
multiplets which arise from the NH hydrogen, the four
non-equivalent hydrogens on the aromatic rings of the
ligand backbone, and the two pairs of non-equivalent
phenyl groups of the diphenylphosphines. Also in
agreement with this is the observation of only one
doublet in the 31P{1H}-NMR spectrum of 1a. The
phosphorus rhodium interaction of 116 Hz is very close
to JRhP of square pyramidal 1b, a Rh(III) species, and is
˚
tion (lꢂ
/
0.71069 A), yellowꢀ
/
/
/
mounted on a glass fiber with epoxy and transferred
to a Blake Industries four-circle diffractometer, u range
for data collection 2ꢀ
I ꢀ3s(I) of 3030 collected reflections and used for
refinement of 199 parameters via least-squares method
on ½F½, final R(I ꢀ3s(I))ꢂ4.6, Rw(I ꢀ3s(I))ꢂ5.5,
GOFꢂ1.6. The structure was solved by a combination
/
32.58, 2249 unique reflections with
/
/
/
/
/
/
significantly smaller than JRhP (135ꢀ148 Hz) for the
/
of direct and Patterson methods and Fourier syntheses
using the crystallographic computing package by C.E.
Strouse, Dep. of Chemistry, UCLA, Los Angeles, CA,
square planar Rh(I) complexes 1c,d prepared with
ligand 1. Although the highest molecular weight peak
in the mass spectrum is generated by the RhCl{N[(o-

152
A.M. Winter et al. / Journal of Organometallic Chemistry 682 (2003) 149ꢀ154
/
2JPH
two equivalent phosphine groups. Also one set of
ꢂ11.4 Hz) by the interaction with rhodium and the
/
resonances due to one molecule of THF is observed in
1
the H- and 13C{1H}-NMR spectra. Furthermore the
1JRhP coupling constant of 108.8 Hz agrees well with a
Rh(III) system. The formation of 1b is a rare instance
where chelate assisted oxidative addition of the Nꢀ
bond occurs with rhodium.
The yellowꢀorange pincer complex Rh(CO){N[(o-
/H
/
PPh2)C6H4]2} (1c) was synthesized by treating
Rh2Cl4{N[(o-PPh2)C6H4]2} (1a) with Na/Hg in the
presence of carbon monoxide in THF. A second method
was direct treatment of Rh(COE){N[(o-PPh2)C6H4]2}
(1d) with CO. The yellow carbonyl product is stable in
air as a solid and in solution. The carbonyl group cannot
be removed with trimethylamine oxide or photolysis
without decomposition of the complex. Addition of
gaseous HCl decolorizes the yellow solution but removal
of solvent under vacuum gives back the starting
material.
The 1H-, 13C{1H}- and 31P{1H}-NMR spectra are
consistent with the structure represented in Scheme 1.
The structural details supported by the NMR data were
confirmed by an X-ray structural analysis illustrated in
Fig. 1 and by quantum chemical calculations.
The coordination sphere of the rhodium atom is a
slightly distorted square plane. The rhodium, nitrogen
and phosphorus atoms lie in one plane with the
phosphorus atoms pulled back toward the nitrogen
atom thus forming a Pꢀ
/
RhꢀP angle of 163.88. The
/
carbonyl group is bent slightly away from the axis
taking up one of the two possible positions related by
the 1808 rotation. The amide nitrogen atom is planar as
required by symmetry. Some relevant structural para-
meters of 1c as obtained by X-ray diffraction and
density functional calculations (SVWN/LACVP*,
B3LYP/LACVP*, B3GGA-II/LACVP*) are compared
in Table 1. The same distorted square-planar coordina-
tion geometry around rhodium as observed in the
experiment is predicted by the computational proce-
dures. The phosphorus atoms are bent away from the
carbonyl group and an envelope configuration of the
five-membered rings is obtained. The gas-phase calcula-
tions yield a C1 molecular symmetry since free rotation
of the phenyl groups is allowed, whereas in the crystal
structure the phenyl groups arrange in a C2 symmetry,
according to the space group. However, due to the
disorder of the CO ligand, the symmetry of an actual
molecule is C1. In most cases, the bond lengths obtained
using the B3GGA-II functional agree best with the X-
ray diffraction values, whereas the B3LYP bond lengths
are too long and the SVWN distances are too short. An
Scheme 1.
PPh2)C6H4]2}ꢁ fragment the elemental analysis con-
firms Rh2Cl4{N[(o-PPh2)C6H4]2} (1a).
Reaction between the ligand 1 and [(COE)2RhCl]2 in
THF generates Rh(H)(Cl)(THF){N[(o-PPh2)C6H4]2}
(1b) and requires a reaction time of 8 h for ideal product
yield. By oxidative addition of the Nꢀ
/
H bond to a
rhodium complex fragment a square pyramidal complex
is formed with the hydride located in the apical position.
In addition one molecule of THF is weakly bound to the
empty coordination site. The structure as shown in
Scheme 1 is confirmed by 1H-, 13C{1H}-, 31P{1H}-NMR
spectroscopy and mass spectrometry as well as by
exception is the C(19)ꢀ/O(1) multiple bond, which is
1
elemental analysis. A characteristic feature in the H-
predicted by all calculations to be much longer than the
experimentally observed value but within the relatively
high error limits (3 sigma) for this disordered part. The
NMR spectrum is the hydride resonance at d ꢃ
/
21.77
which is split into a doublet of triplets (1JRhH
ꢂ/29.5 Hz,

A.M. Winter et al. / Journal of Organometallic Chemistry 682 (2003) 149ꢀ
/
154
153
Fig. 1. ORTEP plot of Rh(CO){N[(o-PPh2)2C6H4]2} (1c).
comparatively large deviation between experiment and
theory observed for this distance is certainly due to the
fact, that the lengths of multiple bonds in general are
underestimated in X-ray structures. In any case, it is
expected that geometrical parameters as obtained by ab
initio calculations (which relate to the gas-phase equili-
brium structure of a molecule a 0 K) would compare
better to the results of a corresponding neutron diffrac-
tion or gas-phase electron diffraction analysis.
functional, is satisfactory. The calculations, thus, con-
firm the experimental data.
The infrared stretching frequency of the CO ligand is
1960 cmꢃ1 which suggests significant p-bonding with
the Rh atom. Although amide complexes of the early
transition metals are well known [26], compounds with
the late transition metals are not so common and
thermally less stable [27]. Moreover, p-bonding of the
filled metal orbitals with the filled 2pz nitrogen orbital is
The bond angles for the more rigid part of the
structure, as predicted by the SVWN and B3GGA-II
functionals, are in good agreement with the experiment
(within the experimental error limits). The overall
agreement between the experimental crystal structure
and the gas-phase structures as predicted by the
theoretical procedures, especially by the B3GGA-II
likely to be minimal. Single metalꢀ
distances are expected to lie within 1.95ꢀ
experimental RhꢀN bond distance of 2.074(9) A as well
as the theoretically calculated values for 1c suggest that
this bond is a single bond even though the planarity of
the amide bond does not necessarily confirm whether p-
bonding occurs between the rhodium and the nitrogen
/
nitrogen bond
˚
/
2.15 A. The
˚
/
Table 1
Relevant structural parameters of Rh(CO){N[(o-PPh)2C6H4]2} (1c) as obtained by X-ray diffraction and density functional calculations a
X-ray
SVWN/LACVP*
B3LYP/LACVP*
B3GGA-II/LACVP*
Symmetry
Bond lengths (A)
C1
C1
C1
C1
˚
Rh(1)ꢀ
Rh(1)ꢀ
Rh(1)ꢀ
Rh(1)ꢀ
C(19)ꢀ
/
C(19)
N(1)
P(1)
1.855
2.074(9)
2.292(3)
1.818
2.072
2.256
2.259
1.168
1.863
2.125
2.333
2.325
1.163
1.845
2.106
2.307
2.305
1.162
/
/
/
P(1A)
/O(1)
1.125(23)
Bond angles (8)
P(1)ꢀRh(1)ꢀP(1A)
C(19)ꢀRh(1)ꢀ
C(19)ꢀRh(1)ꢀ
C(19)ꢀRh(1)ꢀ
C(1)ꢀN(1)ꢀ
O(1)ꢀC(19)ꢀ
/
/
163.8
173.7
95.0
165.7
178.4
97.2
162.5
178.1
98.0
162.7
177.3
98.5
/
/
N(1)
P(1)
/
/
/
/
P(1A)
96.9
98.0
97.8
/
/
C(1A)
122.5(7)
167.0(40)
122.5
177.7
123.2
178.1
122.4
178.9
/
/
Rh(1)
a
For atom labeling see Fig. 1.

154
A.M. Winter et al. / Journal of Organometallic Chemistry 682 (2003) 149ꢀ154
/
atom. Some p-bonding can occur in the complex
versity of Michigan for preliminary EHMO calculations
and the Fonds der Chemischen Industrie for financial
support. A.M.W. gratefully acknowledges the DAAD
and the Studienstiftung des deutschen Volkes for a
scholarship.
Cp2Hf(H)(NHMe) [28] which shows an amide unit
˚
N bond distance of 2.027 A where
planar with the Hfꢀ
/
the amide adopts a conformation favorable for p-
bonding to the empty orbitals of the Hf atom.
Our calculations give no indications for an interaction
between the Npz orbital and the dyz orbital of the Rh
atom [29]. According to a Mulliken population analysis
[30] (B3GGA-II) both nitrogen (ꢃ
/
0.7 a.u.) and rhodium
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/
density distribution is consistent with the chemical
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reactivity of the low valent rhodium atom toward
oxidative addition reactions and the increased bond
order of the rhodium carbonyl carbon bond where
excess electron density can be channeled into the anti-
bonding orbitals of the carbon atom.
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/
IL, September 8ꢀ13, 1985] (1987) 299.
/
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Acknowledgements
[29] The z-axis lies perpendicular to the Rh, P, N, P plane; the y-axis
This work [31] was supported by the Petroleum
Research Fund administered by the American Chemical
Society and the University of California Energy Re-
search Fund. We thank Professor Dave Curtis Uni-
is parallel to the NꢀRh bond.
/
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