Hydroxyalkyl complexes and hemiaminal formation in the reaction of o-diphenylphosphinobenzaldehyde with rhodium(I) dihydrazone complexes

Article abstract of DOI:10.1021/om0006413

The diimino complex Rh(COD)(bdh)Cl (bdh: H₂NNqqC(Me)C(Me)qqNNH₂) reacts with o-diphenylphosphino(benzaldehyde) (PCHO) in the presence of PPh₃ to give acylhydrido [Rh(H)(PCO)(PPh₃)(bdh)]⁺ species. When using Rh/PCHO = 1:2 stoichiometric ratios, oxidative addition of one PCHO and P-coordination of another PCHO occurs. The aldehyde group then undergoes two competitive reactions: (i) addition of one free amino group to give a stable hemiaminal and a complex [Rh(H)(PCO)(Pbdh)]⁺ that contains a new PNN ligand coordinated via the imino nitrogens and the phosphorus atom or (ii) insertion into Rh-H to give the hydroxyalkyl complex [Rh(PCO)(PCHOH)(bdh)]⁺. The complexes have been fully characterized, and X-ray diffraction structures of both of them are reported. Some intermediates in the competitive reactions have been spectroscopically characterized, and the transformation of the hemiaminal group into imine to give a PaNN ligand in the complex [Rh(H)(PCO)(Pabdh)]⁺ has also been studied.

Full text of DOI:10.1021/om0006413

5310
Organometallics 2000, 19, 5310-5317
Hyd r oxya lk yl Com p lexes a n d Hem ia m in a l F or m a tion in
th e Rea ction of o-Dip h en ylp h osp h in oben za ld eh yd e w ith
Rh od iu m (I) Dih yd r a zon e Com p lexes
Rachad El Mail,† Mar´ıa A. Garralda,*,† Ricardo Herna´ndez,† Lourdes Ibarlucea,†
Elena Pinilla,*,‡ and M. Rosario Torres‡
Facultad de Quı´mica de San Sebastia´n, Universidad del Paı´s Vasco,
Apdo. 1072, 20080 San Sebastia´n, Spain, and Departamento de Qu´ımica Inorga´nica,
Laboratorio de Difraccio´n de Rayos X, Facultad de Ciencias Qu´ımicas,
Universidad Complutense, 28040 Madrid, Spain
Received J uly 25, 2000
The diimino complex Rh(COD)(bdh)Cl (bdh: H2NNdC(Me)C(Me)dNNH2) reacts with
o-diphenylphosphino(benzaldehyde) (PCHO) in the presence of PPh3 to give acylhydrido
[Rh(H)(PCO)(PPh3)(bdh)]+ species. When using Rh/PCHO ) 1:2 stoichiometric ratios,
oxidative addition of one PCHO and P-coordination of another PCHO occurs. The aldehyde
group then undergoes two competitive reactions: (i) addition of one free amino group to
give a stable hemiaminal and a complex [Rh(H)(PCO)(Pbdh)]+ that contains a new PNN
ligand coordinated via the imino nitrogens and the phosphorus atom or (ii) insertion into
Rh-H to give the hydroxyalkyl complex [Rh(PCO)(PCHOH)(bdh)]+. The complexes have
been fully characterized, and X-ray diffraction structures of both of them are reported. Some
intermediates in the competitive reactions have been spectroscopically characterized, and
the transformation of the hemiaminal group into imine to give a PaNN ligand in the complex
[Rh(H)(PCO)(Pabdh)]+ has also been studied.
In tr od u ction
and chelates can be formed, the corresponding acyl-
hydrido complexes may be obtained more easily.7,9
o-(Diphenylphosphino)benzaldehyde (PCHO) has been
used to add oxidatively to rhodium(I),7 iridium(I),10
platinum(0),11 or cobalt(I),12 yielding cis acylhydrido
complexes that contain acylphosphine chelates (PCO);
nevertheless, examples of complexes of these metals
containing monodentate PCHO ligand are known.13 The
reduction of aldehydes to alcohols and the conversion
of syngas to methanol or ethylene glycol may involve
either alkoxy or hydroxymethyl intermediates,14 and
both types of compounds are well known for late
transition metals.15,16 Hydrogenation of aldehydes by
rhodium phosphine complexes is believed to proceed via
hydroxyalkyl intermediates,17 though insertion of an
Organometallic rhodium complexes play an important
role in the transformation of many organic compounds.1
The most studied catalysts are those containing phos-
phine ligands, and the recent development of homoge-
neous catalysis shows an increasing interest in using
N-donor-containing complexes.2 Many transformations
affecting aldehydes are catalyzed by rhodium complexes
and may involve oxidative addition of aldehyde to
rhodium(I).3 Cleavage of C-H bonds in aldehydes and
promoted by rhodium may lead to acylhydrido species,4
and the presence of N-donors gives electron-rich metal
centers and may favor the oxidative addition reaction;5
[Rh(NP3)]+ species (NP3 ) N(CH2CH2PPh2)3) react with
aldehydes to give [Rh(H)(COR)(NP3)]+, while the iso-
electronic species [Rh(PP3)]+ does not give this re-
action.6-8 When the aldehyde is close to a donor atom
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1991, 10, 820.
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Moneti, S.; Orlandini, A. J . Chem. Soc., Dalton Trans. 1988, 1833.
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therein.
* Corresponding author. E-mail: qppgahum@sq.ehu.es.
† Universidad del Pa´ıs Vasco.
‡ Universidad Complutense.
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10.1021/om0006413 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 11/14/2000

Hydroxyalkyl Complexes and Hemiaminal Formation
Organometallics, Vol. 19, No. 25, 2000 5311
aldehyde into a M-H bond is rarely observed.16,18 The
reaction of RhH(N4) compounds (N4 ) macrocyclic or
nonmacrocyclic ligand) with RCHO gives the hydroxy-
alkyl [Rh(CH(OH)R)(N4)] derivatives,19 and chelate
assistance allows PCHO to insert into M-H of HMn-
(CO)5 to give the hydroxyalkyl derivative Mn(CO)4(PPh2-
(o-C6H4CHOH)),20 while HPt(PPh2O)(PPh2OH)2 gives a
cyclic platinum alkoxide Pt(PPh2O)(PPh2OH)(PPh2(o-
C6H4CH2O))21 and [IrH(PCO)Cl(CO)(PPh2(o-C6H4CHO))]
contains a monodentate PCHO.22
Ch a r t 1
Since its preparation by Rauchfuss,23 PCHO has been
widely used to prepare hemilabile ligands, by con-
densation of the aldehyde group with primary amines,
that are of interest in the synthesis of homogeneous
catalysts precursors.24 Complexes of the isolated biden-
tate iminophosphines PN,25 PNN ligands that can
behave as tridentates or as PN bidentates,26 or PPNN
tetradentate ligands27 have been reported. The conden-
sation reaction occurs via hemiaminal >C(OH)NHR
intermediates that lose water readily to give the imine
group. Some of these hemiaminals have been detected
spectroscopically,28 and recently it has been reported
that the coordinated amino group of glycylglycinato
Co(III) complexes reacts with formaldehyde in alkaline
aqueous solution to give a mixture of coordinated
hemiaminal and imino complexes and that the hemi-
aminal group transforms readily into imine.29
Sch em e 1
In this work we report the reactions of a rhodium(I)
compound Rh(COD)(bdh)Cl containing a bidentate di-
imine ligand such as biacetyldihydrazone (bdh)30 with
PCHO to give the oxidative addition product (Rh/PCHO
) 1:1). When using Rh/PCHO ) 1:2 stoichiometric
ratios, complexes of a new tridentate PNN ligand and
hydroxyalkyl complexes are formed in a competitive
reaction. Unexpectedly the PNN ligand contains a very
stable hemiaminal group. Some of the intermediates in
the competitive reaction have been characterized, and
the crystal structure of the two isolated compounds is
reported. Transformation of the hemiaminal group into
imine to give the PaNN ligand has also been studied.
Chart 1 shows the ligands used and the new tridentate
PNN and PaNN ligands formed.
(18) Vaughn, G. D.; Gladysz, J . A. J . Am. Chem. Soc. 1981, 103,
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Organometallics 1990, 9, 2179.
(22) Landvatter, E. F.; Rauchfuss, T. B. Organometallics 1982, 1,
506.
(23) Rauchfuss, T. B. J . Organomet. Chem. 1978, 162, C19.
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Scapacci, G. J . Chem. Soc., Dalton Trans. 1992, 3371. (b) Barbaro, P.;
Bianchini, C.; Laschi, F.; Midollini, S.; Moneti, S.; Scapacci G.; Zanello,
P. Inorg. Chem. 1994, 33, 1622. (c) Gao, J . X.; Ikariya, T.; Noyori, R.
Organometallics 1996, 15, 1087. (d) Sa´nchez, G.; Serrano, J . L.; Moral,
M. A.; Pe´rez, J .; Molins, E.; Lo´pez, G. Polyhedron 1999, 18, 3057. (e)
Brunner, H.; Fu¨rst, J . Inorg. Chim. Acta 1994, 220, 63. (f) Crociani,
B.; Antonaroli, S.; Bandolini, G.; Canovese, L.; Visentin, F.; Uguagliati,
P. Organometallics 1999, 18, 1137.
(26) (a) Bacchi, A.; Carcelli, M.; Costa, M.; Fochi, A.; Monici, C.;
Pelagatti, P.; Pelizzi, C.; Pelizzi, G.; Roca, L. M. S. J . Organomet. Chem.
2000, 593-594, 180. (b) Wehman, P.; Ru¨lke, R. E.; Kaasjager, V. E.;
Kamer, P. C. J .; Kooijman, H.; Spek, A. L.; Elsevier, C. J .; Vrieze, K.;
Van Leeuwen, P. W. N. M. J . Chem. Soc., Chem. Commun. 1995, 331.
(c) Ru¨lke, R. E.; Kaasjager, V. E.; Wehman, P.; Elsevier: C. J .; Van
Leeuwen, P. W. N. M.; Vrieze, K. Organometallics 1996, 15, 3022.
(27) (a) Marxen, T. L.; J ohnson, B. J .; Nilsson, P. V.; Pignolet, L. H.
Inorg. Chem. 1984, 23, 4663. (b) Gao, J .; Yi, X.; Xu, P.; Tang, C.; Wan
H.; Ikariya, T. J . Organomet. Chem. 1999, 592, 290.
(28) March, J . Advanced Organic Chemistry, 4th ed.; Wiley: New
York, 1992; p 896.
Resu lts a n d Discu ssion
Rh /P CHO ) 1:1 Rea ction s. The reaction of Rh-
(COD)(bdh)Cl prepared “in situ” with o-diphenylphos-
phino(benzaldehyde) (PCHO) (Rh/PCHO ) 1:1) requires
the presence of PPh3 (Rh/PPh3 ) 1:1) for all the starting
material to react and leads to the chelate-assisted
oxidative addition product, with displacement of 1,5-
cyclooctadiene, as shown in Scheme 1. The acylhydrido
complex formed contains unmodified dihydrazone ligand
and has been isolated as the tetraphenylborate salt
[Rh(H)(PCO)(PPh3)(bdh)]BPh4 (1), which behaves as 1:1
electrolyte in acetone solution.31
The IR spectrum shows the expected absorptions due
to coordinated diimines, ν(Rh-H) in the 2000-2030
cm-1 region and ν(CdO), ca. 1600 cm-1, at lower
frequencies than in the free ligand, indicating acyl
coordination.7,22 The ν(N-H) absorptions due to un-
coordinated amino groups are not displaced toward
lower frequencies with respect to the free ligands. The
31P{1H} NMR spectrum shows two doublets of doublets
corresponding to an AMX pattern. PCO shows the
characteristic low-field resonance, ca. 60 ppm (J (Rh,P)
128 Hz) due to the five-membered-ring effect.32 The
(29) Solujic, L.; Nelson, J . H.; Fisher, J . Inorg. Chim. Acta 1999,
292, 96.
(30) Bikrani, M.; El Mail, R.; Garralda, M. A.; Ibarlucea, L.; Pinilla,
E.; Torres, M. R. J . Organomet. Chem. 2000, 601, 311.
(31) Geary, W. J .Coord. Chem. Rev. 1971, 7, 81.
(32) Garrou, P. E. Chem. Rev. 1981, 81, 229.

5312 Organometallics, Vol. 19, No. 25, 2000
El Mail et al.
Sch em e 2
resonance of coordinated PPh3 appears around 40 ppm
(J (Rh,P) 120 Hz) and J (P,P) of 310 Hz, indicating trans
arrangement of the phosphorus atoms. The 1H NMR
spectrum shows a hydride resonance in the high-field
region, ca. -13 ppm, as a multiplet due to a J (Rh,H) of
19 Hz and equals a J (P,H) of 10 Hz, which agree with
both phosphines being cis to the hydride. The 13C{1H}
NMR spectrum shows the expected doublet for the acyl
group at ca. 240 ppm (J (Rh,C) 30 Hz).33 The diimine
shows two sets of resonances due to inequivalent imino
fragments trans to hydride or acyl, respectively.
Rh /P CHO ) 1:2 Rea ction s. Rh(COD)(bdh)Cl pre-
pared “in situ” reacts with o-diphenylphosphino(benz-
aldehyde) (PCHO) (Rh/PCHO ) 1:2) to undergo the
oxidative addition of one PCHO, with displacement of
1,5-cyclooctadiene, and P-coordination of the second
PCHO molecule. Its aldehyde then undergoes two
competitive reactions as depicted in Scheme 2: (i)
addition of one free amino group of the dihydrazone to
form a hemiaminal group, thus giving a new PNN
tridentate ligand and complex [Rh(H)(PCO)(Pbdh)]+ (5),
or (ii) insertion into the Rh-H bond to give hydroxyalkyl
complexes such as [Rh(PCO)(PCHOH)(bdh)]+ (7). The
reactions performed in CH2Cl2 or CH3OH gave mixtures
of almost equal amounts of hemiaminal-containing
species and hydroxyalkyl complexes. By following this
reaction in CD3OD, we have been able to detect some
of the intermediates shown in Scheme 2. At 253 K
formation of the complexes in 2-5 is observed. Both 2
and 5 contain trans P atoms, while 3 and 4 contain cis
P atoms. 2 is a precursor of 5, while 3 and 4 are involved
in the formation of the stable hydroxyalkyl complex
(vide infra).
H em ia m in a l-Con t a in in g Com p lexes. 2 contains
acylphosphine chelate (δPCO 72.8 {dd} ppm, J (Rh,P)
126 Hz), trans (J (P,P) 319 Hz) to monodentate PCHO
(δPCHO 43.8 {dd} ppm, J (Rh,P) 122 Hz; δHCO 9.42 {s}
ppm) and hydride (δH-Rh -12.6 ppm {ddd}, J (Rh,H)
18 Hz, J (PCO,H) 6 Hz, J (PCHO,H) 11 Hz) and trans-
forms at 253 K into the complex in 5, while the other
species remain unmodified. Therefore we think that
P-coordination of PCHO occurs prior to hemiaminal
formation. When performing this reaction at 293 K, 2
is not observed.
[Rh(H)(PCO)(Pbdh)]Cl precipitates almost quantita-
tively when the reaction is performed in CH2Cl2 and can
thus be separated from the reaction mixture. The
isolation of [Rh(H)(PCO)(Pbdh)]BPh4 (5) allows com-
plete characterization of the complex. To ascertain
hemiaminal formation, we have also prepared [Rh(H)-
(PCO)(Pgmh)]BPh4 (8) because gmh (MeHNNdCHCHd
NNHMe) contains secondary amino groups and cannot
undergo condensation to form imine. These compounds
behave as 1:1 electrolytes,31 and their FAB spectra show
the corresponding [M+] peak. The appearance of ν(OH)
at ca. 3500 cm-1 suggests the hemiaminal formation
confirmed by NMR spectroscopy. The 13C{1H} NMR
spectra show the resonance due to >CH(OH)NR′′-
around 85 ppm (J (P,C) {d} 8 Hz). In the 1H NMR
spectrum of 5 (R′′ ) H) the signals due to NH (5 ppm)
and CH (7 ppm) are coupled and appear as doublets
(J (H,H) 10 Hz), while OH shows a singlet at ca. 2 ppm.
(33) Adams, H.; Bailey, N. A.; Mann B. E.; Manuel, C. P. Inorg.
Chim. Acta 1992, 198-200, 111.

Hydroxyalkyl Complexes and Hemiaminal Formation
Organometallics, Vol. 19, No. 25, 2000 5313
Ta ble 1. Selected Bon d Len gh ts (Å) for th e
Com p lexes [Rh (H)(P CO)(P bd h )]BP h 4 (5) a n d
[Rh (P CO)(P CHOH)(bd h )]BP h 4 (7)
5
7
Rh(1)-P(1)
Rh(1)-P(2)
Rh(1)-N(3)
Rh(1)-N(2)
Rh(1)-C(11)
Rh(1)-C(30)
Rh(1)-H
2.299(1)
2.348(1)
2.145(5)
2.181(4)
1.990(5)
2.316(1)
2.356(1)
2.171(3)
2.211(3)
2.004(4)
2.097(4)
1.41(5)
1.815(5)
1.820(5)
1.806(5)
1.830(5)
1.816(6)
1.830(5)
1.219(6)
1.417(6)
1.122
P(1)-C(5)
1.805(4)
1.827(4)
1.832(4)
1.821(4)
1.834(4)
1.838(4)
1.219(5)
1.440(5)
0.814
1.389(5)
1.044
1.046
1.301(5)
1.305(5)
1.391(4)
0.996
P(1)-C(18)
P(1)-C(12)
P(2)-C(24)
P(2)-C(31)
P(2)-C(37)
O(1)-C(11)
O(2)-C(30)
O(2)-H(2)
N(1)-N(2)
N(1)-H(1A)
N(1)-H(1B)
N(2)-C(1)
N(3)-C(2)
N(3)-N(4)
N(4)-H(4A)
N(4)-H(4B)
1.414(6)
1.093
1.304(7)
1.288(7)
1.363(6)
0.825
F igu r e 1. ORTEP view of the cation in 5 showing the
atomic numbering (30% probability ellipsoids). The hydro-
gen atoms except one have been omitted for clarity.
0.880
0.854
These assignments agree with other reported data,34
and 8 (R′′ ) CH3) shows a singlet at 2 ppm due to OH.
The 31P resonance of the new tridentate ligand PNN in
a seven-membered metallocycle in compound 5 appears
around 25 ppm (J (Rh,P) 120 Hz). Other spectroscopic
features are similar to those of compound 1 (see
Experimental Section) and indicate the presence of only
one isomer, which, because hydride chemical shifts are
sensitive to the nature of the trans groups,35 we assign
tentatively to that containing the hydride trans to the
unreacted hydrazone group.
An X-ray diffraction study of 5 has been undertaken
and confirms hemiaminal formation and the hydride
being trans to the unreacted hydrazone group. To the
best of our knowledge, this is the first crystal structure
of a late transition metal complex containing a hemi-
aminal group. The crystal consists of [Rh(H)(PCO)-
(Pbdh)] cations and BPh4 anions held together by
electrostatic interactions. Figure 1 shows an ORTEP
view of the molecular structure of the cation; pertinent
bond distances and angles are summarized in Tables 1
and 2. The N1-C30 and C30-O2 distances, 1.485(7)
and 1.417(6) Å, respectively, along with the O2-C30-
C25 angle of 110.3(4)° show the new C-N bond forma-
tion, with C30 changing from sp2 to sp3. As expected,
the cation in 5 exhibits a distorted octahedral geometry,
due to the presence of the chelate rings, in which the P
atoms occupy trans positions and the highest deviation
of 21° corresponds to the P1-Rh1-P2 angle. Imino N2,
N3, and P2 atoms of the PNN ligand occupy three facial
positions, the hydride is trans to N3 (N3-Rh1-H,
167(1)°), and C11 of the acyl group fills the sixth
coordination site. The best least-squares plane C11,N2,
N3,H,Rh1 shows a 0.19(5) Å maximum deviation for the
H atom. The metallocycle including the acylphosphine
chelate Rh1,P1,C5,C6,C11 deviates from planarity and
Ta ble 2. Selected An gles (d eg) for th e Com p lexes
[Rh (H)(P CO)(P bd h )]BP h 4 (5) a n d
[Rh (P CO)(P CHOH)(bd h )]BP h 4 (7)
5
7
C(11)-Rh(1)-H
C(11)-Rh(1)-N(3)
N(3)-Rh(1)-H
92(2)
96.1(2)
168(2)
C(11)-Rh(1)-C(30)
C(11)-Rh(1)-N(3)
C(30)-Rh(1)-N(3) 175.3(1)
C(11)-Rh(1)-N(2) 170.5(2)
C(30)-Rh(1)-N(2) 104.2(2)
N(3)-Rh(1)-N(2)
C(11)-Rh(1)-P(1)
C(30)-Rh(1)-P(1)
N(3)-Rh(1)-P(1)
N(2)-Rh(1)-P(1)
C(11)-Rh(1)-P(2)
C(30)-Rh(1)-P(2)
N(3)-Rh(1)-P(2)
N(2)-Rh(1)-P(2)
84.8(2)
97.9(1)
C(11)-Rh(1)-N(2) 169.3(2)
N(2)-Rh(1)-H
98(2)
73.1(2)
80.0(2)
76(2)
96.9(1)
100.7(1)
91.0(2)
86(2)
N(3)-Rh(1)-N(2)
C(11)-Rh(1)-P(1)
P(1) -Rh(1)-H
72.9(1)
84.5(1)
88.1(1)
88.4(1)
92.8(1)
90.6(1)
80.4(1)
103.4(1)
93.8(1)
167.80(4)
N(3)-Rh(1)-P(1)
N(2)-Rh(1)-P(1)
C(11)-Rh(1)-P(2)
P(2)-Rh(1)-H
N(3)-Rh(1)-P(2)
N(2)-Rh(1)-P(2)
P(1)-Rh(1)-P(2)
102.0(1)
91.5(1)
159.86(5) P(1)-Rh(1)-P(2)
forms a dihedral angle of 18.3(1)° with its phenyl ring.36
The observed Rh-C(acyl), CdO(acyl), and Rh-P dis-
tances fall within reported ranges,37 and the Rh-N
distances are as expected.30 Rh1-P1 (2.299(1) Å) is
shorter than Rh1-P2 (2.348(1) Å), and this may be due
to P1 forming a five-membered chelation ring and P2
being in a seven-membered chelate ring that adopts a
boat conformation. It has been reported that acyl ligands
have slightly weaker trans-influence than hydride.38 In
5 Rh-N2 trans to the acyl group is longer than Rh-N3
trans to hydride, and this can be due to N2 being the
central atom of a tridentate ligand. The Rh-H distance
is in the short end of the 1.993-1.245 Å range found
for rhodium hydrides (CSD-Database 5.18, October
1999) and is similar to that reported for other Rh(III)
complexes.39 The BPh4 anion shows the expected angles
and distances.
(36) Nardelli, M. Parst 97; University of Parma, 1997.
(37) Pattanayak, S.; Chattopadhyay, S.; Ghosh, K.; Ganguly, S.;
Ghosh, P.; Chakravorty, A. Organometallics 1999, 18, 1486.
(38) Coe, B. J .; Glenwright, S. J . Coord. Chem. Rev. 2000, 203, 5.
(39) (a) Osakada, K.; Sarai, S.; Koizumi, T.; Yamamoto, T. Organo-
metallics 1997, 16, 3973. (b) Liou, S.; Gozin, M.; Milstein, D. J . Am.
Chem. Soc. 1995, 117, 9774.
(34) Dosta´l, J .; Marek, R.; Slav´ık, J .; Ta´borska´, E.; Pota´cek, M.;
Sklena´r, V. Magn. Reson. Chem. 1998, 36, 869.
(35) (a) Yao, W.; Crabtree, R. H. Inorg. Chem. 1996, 35, 3007. (b)
Crabtree, R. H.; Demou, P. C.; Eden, D.; Mihelcic, J . M.; Parnell, C.
A.; Quirk, J . M.; Morris, G. E. J . Am. Chem. Soc. 1982, 104, 6994.

5314 Organometallics, Vol. 19, No. 25, 2000
El Mail et al.
Sch em e 3
) 1:2) in CD3OD at 253 K gives species 3 and 4 among
others (Scheme 2). Our proposal of structures for both
complexes is based on spectroscopic evidence43 assuming
cis oxidative-addition of aldehyde.7 Both 3 and 4 contain
two phosphorus atoms mutually cis (J (P,P) 13 and 19
Hz, respectively) and no free aldehyde. 3 contains
hydride cis to both phosphines (δH-Rh -14.46 {ddd}
ppm, J (Rh,H) 18, J (P,H) 31, 13 Hz) and due to the
absence of aldehyde can contain a hemiaminal group
in a PNN ligand with P (δ 17.1 {dd} ppm) trans to an
acyl group (J (Rh,P) 67 Hz) and P of the acylphosphine
chelate (δ 76.3 {dd} ppm) trans to N (J (Rh,P) 149 Hz).
4 contains no hydride and shows a broad singlet at 6.68
ppm that can be due to CHOH of a hydroxyalkyl group
in a PCHOH chelate, with P (δ 59.8 {dd} ppm) trans to
N (J (Rh,P) 150 Hz) and P of the acylphosphine chelate
(δ 40.2 {dd} ppm) trans to hydroxyalkyl (J (Rh,P) 82 Hz).
On raising the temperature to 293 K, 4 remains
unaltered, while 3 transforms into 6, which contains no
hydride and according to its spectral features (δPCO
57.6 {dd} ppm, J (Rh,P) 148, J (P,P) 21 Hz; δPCHOH
38.6 {dd} ppm, J (Rh,P) 80 Hz; δCHOH 6.05 {s} ppm)
is an isomer of 4. These observations suggest cleavage
of the hemiaminal group in 3 and insertion of aldehyde
into the Rh-H bond to form the hydroxyalkyl group.
When performing this reaction at 293 K, a mixture of
4, 5, and 6 is formed and 3 is not observed. At room
temperature both 4 and 6 rearrange into the final
product 7, containing trans phosphines.
When performing this reaction in CH3OH, addition
of NaBPh4 gives a precipitate containing a mixture of
5 and 7. By refluxing the solid in absolute ethanol, 5
dissolves and is transformed into 10 (eq 1), while highly
unsoluble 7 remains solid and can thus be separated
from the mixture. [Rh(PCO)(PCHOH)(bdh)]BPh4 (7)
behaves as 1:1 electrolyte in acetone solution and shows
ν(OH) around 3500 cm-1. 1H and 13C{1H} NMR confirm
formation of the hydroxyalkyl group bonded to rhodi-
um.20,44 Its 13C resonance appears at 75.5 ppm (J (Rh,C)
{d} 28 Hz), the methine proton at ca. 5 {ddd} ppm is
coupled with rhodium (J (Rh,H) 2 Hz), the hydroxy
proton (J (H,H) 4 Hz), and phosphorus (J (P,H) 15 Hz),
and the hydroxy proton appears as a doublet (ca. 1.7
ppm). The dihydrazone ligand shows two sets of reso-
nances due to inequivalent imino fragments, and the
31P{1H} NMR spectrum shows two doublets of doublets
(ABX pattern) corresponding to two inequivalent phos-
phines mutually trans (J (P,P) 320 Hz).
The uncoordinated HN-CH(OH) hemiaminal group
in complex [Rh(H)(PCO)(Pbdh)]+ 5 is stable in the solid
state and also in methanol or dichloromethane solution.
Condensation reaction of these groups to afford the
corresponding imines by hydrogen transfer from N to
O is usually easy and needs both H and OH being on
the same side of the N-C bond.40 We think that the
hemiaminal in 5 is stable because it belongs to a rather
rigid seven-membered metallocycle.41 Compound 5 in
unstabilized chloroform transforms very slowly at room
temperature into 9, which contains a new tridentate
PaNN ligand (Scheme 3). The NH and OH resonances
disappear, and a new resonance at 1.43 ppm due to H2O
is observed. Addition of HCOOH accelerates the reac-
tion, most likely by protonation of the hydroxy group,
though the obtained compound is impure. Compound 9
is also a hydride, and its 13C{1H} NMR spectrum shows
three singlets due to three different CdN groups. The
31P{1H} NMR spectrum shows an AMX pattern with
PaNN in 9 at lower field than PNN in the starting
complex 5; therefore we think that 9 contains a triden-
tate ligand also forming a seven-membered PN and a
five-membered NN chelate ring. A shift toward higher
fields would be expected if opening of one arm of the
tridentate ligand42 followed by formation of two six-
membered metallocycles was to occur.32
In refluxing absolute ethanol, cleavage of the hemi-
aminal group in complex 5 to regenerate the bidentate
NN ligand occurs (eq 1), and the new species [Rh(PCO)2-
[Rh(H)(PCO)(Pbdh)]+
EtOH, reflux8
5
+ + H2 (1)
[Rh(PCO)2(bdh)]
10
(bdh)]+ 10 is formed, likely with H2 loss. According to
NMR data 10 contains equivalent phosphine-acyl
groups and equivalent imino groups and no hydride. Its
FAB spectrum shows the corresponding [M+] peak and
confirms this formulation, although the elemental analy-
sis is not in convenient agreement with the expected
values, and this can be due to bad combustion of the
sample or to the presence of NMR-silent impurities.
Hyd r oxya lk yl Com p lexes. As mentioned above, the
reaction of “Rh(COD)(bdh)Cl” with (PCHO) (Rh/PCHO
The crystal structure of 7 confirms the spectroscopic
findings. The crystal consists of [Rh(PCO)(PCHOH)-
(bdh)] cations and BPh4 anions held together by elec-
trostatic interactions. Figure 2 shows an ORTEP view
of the molecular structure of the cation; pertinent bond
distances and angles are summarized in Tables 1 and
2. The cation in 7 exhibits a distorted octahedral
geometry, in which the P atoms occupy trans positions,
the highest deviation of 13.2° corresponds to the P1-
Rh1-P2 angle, and the distortion is less severe than
that for 5. The equatorial plane is occupied by the imino
N atoms and the carbon atoms. This best least-squares
plane shows a 0.013(4) Å maximum deviation for the
(40) Hall, N. E.; Smith, B. J . J . Phys. Chem., A 1998, 102, 4930.
(41) Stable hemiaminals such as OdC-NH-CH(OH) in cyclic
molecules are known; see for example: J ournet, M.; Cai, D.; Dimichele,
L. M.; Hughes, D. L.; Larsen, R. D.; Verhoeven, T. R.; Reider, P. J . J .
Org. Chem. 1999, 64, 2411.
(42) (a) Bianchini, C.; Mazzi, D.; Meli, A.; Peruzzini, M.; Zanobini,
F. J . Am. Chem. Soc. 1988, 110, 6411. (b) Hii, K. K.; Thornton-Pett,
M.; J utand, A.; Tooze, R. P. Organometallics 1999, 18, 1887.
(43) Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition
Metal Phosphine Complexes; Springer: Berlin, 1979.
(44) Thorn, D. L.; Tulip, T. H. Organometallics 1982, 1, 1580.

Hydroxyalkyl Complexes and Hemiaminal Formation
Organometallics, Vol. 19, No. 25, 2000 5315
The hemiaminal is stable because it is included in a
seven-membered metallocycle, and its transformation
into azines is favored by acids.
Exp er im en ta l Section
Gen er a l P r oced u r es. The preparation of the metal com-
plexes was carried out at room temperature under nitrogen
by standard Schlenk techniques. [{Rh(COD)Cl}2]46 was pre-
pared as previously reported. R-Diimines47 were synthesized
according to known procedures. o-Diphenylphosphine(benz-
aldehyde) (PCHO) was purchased from Aldrich and used as
received. Microanalysis were carried out with a Leco CHNS-
932 microanalyzer. Conductivities were measured in acetone
or methanol solution with a Metrohm E 518 conductimeter.
IR spectra were recorded with a Nicolet FTIR 740 spectro-
photometer in the range 4000-400 cm-1 using KBr pellets.
NMR spectra were recorded with an XL-300 Varian spectrom-
eter; 1H and 13C (TMS internal standard) and 31P (H3PO4
external standard) spectra were measured from CDCl3, CD3OD,
or CD2Cl2 solutions. Mass spectra were recorded on a VG
Autospec, by liquid secondary ion (LSI) MS using nitro-
benzyl alcohol as matrix and a cesium gun (Universidad de
Zaragoza).
F igu r e 2. ORTEP view of the cation in 7 showing the
atomic numbering (30% probability ellipsoids) and the
intramolecular hydrogen bond. The hydrogen atoms except
three have been omitted for clarity.
[[Rh (H)(P CO)(P P h 3)(bd h )]BP h 4 (1). To a MeOH suspen-
sion of [{Rh(COD)Cl}2] (0.04 mmol) were added stoichiometric
amounts (0.08 mmol) of bdh, PPh3, and PCHO, whereupon a
brown solution was formed, which upon addition of NaBPh4
(0.08 mmol) gave a precipitate that was filtered off, washed
with MeOH, and vacuum-dried. Yield: 60%. IR (KBr, cm-1):
3394(s), 3288(s), ν(NH2); 2020(w), ν(RhH); 1612(s), ν(CdO);
1576(s), ν(CdN). ΛM (Ω-1 cm2 mol-1): 72 (acetone). FAB MS:
calcd for C41H40N4OP2103Rh, 769; observed, 769 (M+). 1H NMR
(CDCl3): δ -12.88 (m, RhH), J (Rh,H) 19, J (P,H) 10; 4.64 (s),
4.54 (s) (NH2); 0.87 (s), 0.86 (s) (CH3). 31P{1H} NMR (CDCl3):
δ 63.4 (dd, PCO), J (Rh,P) 128, J (P,P) 313; 42.3 (dd, PPh3),
J (Rh,P) 120. 13C{1H} NMR (CDCl3): δ 243.3 (d, CO), J (Rh,C)
31; 149.3 (s), 147.8 (s) (CdN); 12.6 (s), 12.9 (s) (CH3). Anal.
C30 atom, and the rhodium atom is placed out of this
plane (0.0589(3) Å).36 Both P1 and P2 are in five-
membered chelation rings. The metallocycle including
the acylphosphine chelate Rh1,P1,C5,C6,C11 is almost
planar, contrarily to 5, with a maximum deviation of
0.025(4) Å for C11, and forms a dihedral angle of 0.8(1)°
with its phenyl ring. The metallocycle including the
hydroxyalkylphosphine chelate deviates from planar-
ity as expected, and the best least-squares plane
Rh1,P2,C24,C29,C30 forms a dihedral angle of 34.0(1)°
with its phenyl ring. Also, the Rh1-C30 (2.097(4) Å)
and the Rh1-P2 (2.356(1) Å) distances are slightly
longer than the Rh1-C11 and the Rh1-P1 distances
(2.004(4) and 2.316(1) Å, respectively). These differ-
ences may be viewed as a consequence of the different
hybridization for C30 (sp3) and for C11 (sp2).45 The
different Rh1-N2 and Rh1-N3 distances (Table 1) can
reflect the suggested slightly larger trans-influence of
the acyl than of the hydroxyalkyl group45a now in the
same complex. In addition an intramolecular hydrogen
bond between O2 and N1 is observed (N1- - -O2 and
O2- - -H1A distances of 2.914(5) and 2.016(3) Å, respec-
tively, and NHO angle 142.5(2)°). Other features of the
bdh ligand30 and the BPh4 anion are as expected.
Calcd for
C65H60BN4OP2Rh: C, 71.70; H, 5.55; N, 5.15.
Found: C, 71.31; H, 5.21; N, 4.86.
[Rh (H)(P CO)(P bd h )]BP h 4 (5). To a CH2Cl2 solution of
[{Rh(COD)Cl}2] (0.04 mmol) was added
a stoichiometric
amount (0.08 mmol) of bdh, whereupon a red precipitate was
formed, which upon addition of PCHO (0.16 mmol) gave a
yellow solution, from which a yellow precipitate of [Rh(H)-
(PCO)(Pbdh)]Cl appeared that was filtered off and dried (50%
yield). [Rh(H)(PCO)(Pbdh)]Cl (0.06 mmol) was dissolved in
MeOH, and NaBPh4 (0.06 mmol) was added to give a precipi-
tate that was filtered off, washed with MeOH, and vacuum-
dried. Yield: 80%. IR (KBr, cm-1): 3535(m), ν(OH); 3401(m),
3302(m), ν(NH2); 2048(w), ν(RhH); 1607(s), ν(CdO); 1576(s),
ν(CdN). ΛM (Ω-1 cm2 mol-1): 86 (acetone). FAB MS: calcd for
C
42H40N4O2P2103Rh, 797; observed, 797 (M+). 1H NMR
(CDCl3): δ -12.86 (m, HRh), J (Rh,H) 19, J (P,H) 10; 7.34 (d,
Con clu sion s
3
HC-N), J (H,H) 10; 5.16 (d, NH); 4.72 (s, NH2); 2.27 (s, OH);
0.92 (s), 0.75 (s) (CH3). 31P{1H} NMR (CDCl3): δ 62.1 (dd,
PCO), J (Rh,P) 126, J (P,P) 311; 26.6 (dd, PNN), J (Rh,P) 120.
13C{1H} NMR (CDCl3): δ 238.6 (d, CO), J (Rh,C) 31; 148.6 (s),
148.0 (s) (CdN); 84.6 (d, COH), J (P,C) 8; 13.3 (s), 12.0 (s) (CH3).
Anal. Calcd for C66H60BN4O2P2Rh: C, 70.98; H, 5.41; N, 5.02.
Found: C, 70.59; H, 5.25; N, 5.04.
[Rh (P CO)(P CHOH)(bd h )]BP h 4 (7). To a MeOH suspen-
sion of [{Rh(COD)Cl}2] (0.12 mmol) were added stoichiometric
amounts of bdh (0.24 mmol) and PCHO (0.48 mmol). After 24
h stirring at room temperature the volatiles were removed in
a vacuum and the residue was dissolved in EtOH. Addition of
A rhodium(I) complex containing biacetyldihydrazone
undergoes readily the chelate-assisted oxidative addi-
tion of PCHO to give the cis acylhydrido complex. A
second PCHO molecule may coordinate to rhodium as
a P-monodentate ligand and may occupy a cis or a trans
site with respect to the P atom of the acylphosphine.
The trans disposition allows the reaction of the aldehyde
group with one amino group to form a hemiaminal,
while the cis disposition allows the insertion of aldehyde
into the Rh-H bond to form hydroxyalkyl complexes.
(45) (a) Clark, G. R.; Greene T. R.; Roper, W. R. J . Organomet. Chem.
1985, 293, C25. (b) Hahn, C.; Spiegler, M.; Herdtweck, E.; Taube, R.
Eur. J . Inorg. Chem. 1999, 435.
(46) Chatt, J .; Venanzi, L. M. J . Chem. Soc., A 1957, 4735.
(47) (a) Fisher, H. M.; Stoufer, R. C. Inorg. Chem. 1966, 5, 1172. (b)
Bush, D. H.; Bailar J r., J . C. J . Am. Chem. Soc. 1956, 78, 1137.

5316 Organometallics, Vol. 19, No. 25, 2000
El Mail et al.
Ta ble 3. Cr ysta l a n d Refin em en t Da ta for [Rh (H)(P CO)(P bd h )]BP h 4 (5) a n d [Rh (P CO)(P CHOH)(bd h )]BP h 4
(7)
5
7
formulas
Mr
C
66H60BN4O2P2Rh
C66H60BN4O2P2Rh
1116.84
1116.84
cryst syst
space group
a, Å
monoclinic
C2/c
22.400(1)
monoclinic
P21/c
11.0040(2)
b, Å
15.443(1)
23.7755(2)
c, Å
32.158(2)
21.5596(4)
â (deg)
95.021(2)
11082(1), 8
4640
99.713(1)
5559.7(2), 4
2320
V, Å3, Z
F(000)
D(calcd), g cm-3
temp, K
µ, mm-1
cryst dimens, mm
diffractometer
radiation
1.34
293
0.42
1.334
293
0.41
0.11 × 0.11 × 0.09
0.45 × 0.40 × 0.20
Bruker-CCD
graphite-monochromated
Mo KR (0.71073 Å)
ω and æ
(-9,-31,-28) to (14,31,27)
1.29-28.30
37 302
13 670 (Rint ) 0.059)
Patterson and Fourier
full-matrix least-squares on F2
13 670/691
0.050 (8934 obs rflns)
0.17
Bruker-CCD
graphite-monochromated
Mo KR (0.71073 Å)
ω and æ
(-23,-20,-42) to (29,17,35)
1.27-27.92
29 241
12 120 (Rint ) 0.087)
Patterson and Fourier
full-matrix least-squares on F2
12 120/694
0.048 (4709 obs rflns)
0.16
scan technique
data collected
θ
no. of reflns collected
no. of ind reflns
structure solution
refinement method
no. of data/params
R ) ∑[|Fo| - |Fc|]/∑|Fo|
a
RwF (all data)
GOF(F2)
0.75
0.47
0.72
0.43
maximum residual, e Å-3
a
2
2
2 2
[∑[w(|Fo| - |Fc| )2]/[∑[w|Fo | ]]1/2
.
NaBPh4 (0.24 mmol) gave a mixture of 5 and 7, which was
refluxed for 4 h to allow dissolution of 5. The suspension was
filtered warm, and the solid was washed with warm EtOH and
vacuum-dried. Yield: 45%. IR (KBr, cm-1): 3542(m), ν(OH);
3408(m), 3373(m), 3295(w), ν(NH2); 1626(s), ν(CdO); 1577(s),
ν(CdN). ΛM (Ω-1 cm2 mol-1): 102 (acetone). FAB MS: calcd
for C42H40N4O2P2103Rh, 797; observed, 797 (M+). 1H NMR
(CDCl3): δ 5.22 (ddd, HC-OH), 3J (H,H) 4, 2J (Rh,H) 3, 4J (P,H)
15; 5.83 (s), 5.07 (s) (NH2); 1.69 (d, OH); 1.49 (s), 1.34 (s) (CH3).
31P{1H} NMR (CDCl3): δ 57.1 (dd, PA), J (Rh,P) 128, J (P,P)
323; 49.9 (dd, PB), J (Rh,P) 132. 13C{1H} NMR (CD2Cl2): δ 236.9
(d, CO), J (Rh,C) 35; 149.5 (s), 146.5 (s) (CdN); 75.5 (d, CHOH),
1590(s), ν(CdO); 1577(s), ν(CdN). ΛM (Ω-1 cm2 mol-1): 98
(acetone). FAB MS: calcd for C42H38N4OP2103Rh, 779; observed,
779 (M+). 1H NMR (CDCl3): δ -12.92 (ddd, HRh), J (Rh,H)
20, J (PCO,H) 13, J (PaNN,H) 7; 5.14 (s, NH2); 1.47 (s), 0.59 (s)
(CH3). 31P{1H} NMR (CDCl3): δ 61.6 (dd, PCO), J (Rh,P) 128,
J (P,P) 307; 34.6 (dd, PaNN), J (Rh,P) 119. 13C{1H} NMR
(CDCl3): δ 241.5 (d, CO), J (Rh,C) 30; 157.3 (s), 151.5 (s), 145.2
(s) (CdN); 16.1 (s), 11.5 (s) (CH3). Anal. Calcd for C66H58BN4-
OP2Rh‚0.3CHCl3: C, 70.18; H, 5.18; N, 4.94. Found: C, 69.68;
H, 5.15; N, 4.99.
[Rh (P CO)2(bd h )]BP h 4 (10). A solution of [Rh(H)(PCO)-
(Pbdh)]Cl (0.09 mmol) in absolute ethanol was refluxed for 4
h. Addition of NaBPh4 (0.09 mmol) gave a brownish precipi-
tate, which was filtered off, washed with ethanol, and vacuum-
dried. Yield: 50%. IR (KBr, cm-1): 3394(m), 3295(m), ν(NH2);
1594(s), ν(CdO); 1576(s), ν(CdN). ΛM (Ω-1 cm2 mol-1): 89
(acetone). FAB MS: calcd for C42H38N4O2P2103Rh, 795; ob-
J (Rh,C) 28; 13.6 (s), 13.3 (s) (CH3). Anal. Calcd for C66H60
-
BN4O2P2Rh: C, 70.98; H, 5.41; N, 5.02. Found: C, 70.49; H,
5.29; N, 4.78.
[Rh (H)(P CO)(P gm h )]BP h 4 (8). PCHO (0.16 mmol) and
gmh (0.08 mmol) were added to a stirring solution of [{Rh-
(COD)Cl}2] (0.04 mmol) in benzene, and the resulting suspen-
sion was filtered after 3 h of stirring. The solid was dissolved
in methanol, and addition of NaBPh4 (0.08 mmol) gave a
precipitate that was filtered off, washed with MeOH, and
vacuum-dried. Yield: 65%. IR (KBr, cm-1): 3492(m), ν(OH);
3358(m), ν(NH2); 2055(w), ν(RhH); 1624(s), ν(CdO); 1579(s),
ν(CdN). ΛM (Ω-1 cm2 mol-1): 106 (acetone). FAB MS: calcd
for C42H40N4O2P2103Rh, 797; observed, 797 (M+). 1H NMR
(CDCl3): δ -13.11 (m, HRh), J (Rh,H) 21, J (P,H) 10; 5.79(s),
5.74(s) (HC-N); 6.04 (q, NHMe), 3J (H,H) 4.3; 2.0 (s, OH); 2.04
(s, CH3), 1.97 (d, MeNH). 31P{1H} NMR (CDCl3): δ 56.1 (dd,
PCO), J (Rh,P) 126, J (P,P) 311; 25.5 (dd, PNN), J (Rh,P) 118.
13C{1H} NMR (CDCl3): δ 240.1 (d, CO), J (Rh,C) 30; 139.0 (s),
138.9 (s) (CdN); 86.4 (d, COH), J (P,C) 6; 33.1 (s), 31.2 (s) (CH3).
Anal. Calcd for C66H60BN4O2P2Rh: C, 70.98; H, 5.41; N, 5.02.
Found: C, 70.44; H, 5.31; N, 4.87.
1
served, 795 (M+). H NMR (CDCl3): δ 4.70 (s, NH2); 0.74 (s,
CH3). 31P{1H} NMR (CDCl3): δ 55.2 (d), J (Rh,P) 137. 13C{1H}
NMR (CDCl3): δ 236.9 (d, CO), J (Rh,C) 32; 148.5 (s, CdN);
12.8 (s, CH3). Anal. Calcd for C66H58BN4O2P2Rh: C, 71.10; H,
5.24; N, 5.03. Found: C, 66.86; H, 4.86; N, 4.95.
X-r a y Str u ctu r e Deter m in a tion of 5 a n d 7. Prismatic
yellow single crystals of 5 and 7 were grown by layering
dichloromethane solutions with diethyl ether. A summary of
the fundamental crystal data and refinement parameters is
given in Table 3. The data were collected on a Bruker Smart
CCD diffractometer with graphite-monochromated Mo KR (λ
) 0.71073) radiation operating at 50 kV and 20 mA. Data were
collected over a hemisphere of the reciprocal space by combi-
nation of three exposure sets. Each exposure of 20 s covered
0.3 in ω. The cell parameters were determined and refined by
least-squares fit of all reflections collected. The structures were
solved by Patterson (Rh atoms, SHELXS) and conventional
Fourier techniques and refined by full-matrix least-squares
on F2 (SHELXTL).48 Anisotropic parameters were used in the
last cycles of refinement for all non-hydrogen atoms. The
hydrogen atoms were included in calculated positions and
[Rh (H)(P CO)(P a bd h )]BP h 4 (9). A solution of 5 (0.04
mmol) in CDCl3 was allowed to stir for 15 days. Addition of
diethyl ether gave a yellow precipitate that was filtered off,
washed with diethyl ether, and vacuum-dried. Yield: 51%. IR
(KBr, cm-1): 3380(m), 3295(m), ν(NH2); 2041(m), ν(RhH);

Hydroxyalkyl Complexes and Hemiaminal Formation
Organometallics, Vol. 19, No. 25, 2000 5317
refined as riding on carbon atoms with some exceptions. In
both compounds the hydrogen atoms of the amine groups, the
alcoholic group, and the hydrogen bonded to C30 were located
in a Fourier synthesis, included, and refined isotropically. For
5 the hydride atom has been located as the first peak in a
Fourier synthesis and included, and their parameters were
refined. Maximum and minimum peaks in the final difference
synthesis were 0.43 and -0.49 or 0.47 and -0.34 for 7 and 5,
respectively.
Ack n ow led gm en t. Partial financial support by
UPV and Diputacio´n Foral de Guipuzcoa is gratefully
acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of structure
refinement, atomic coordinates, bond lengths and angles,
anisotropic displacement parameters, hydrogen coordinates,
and torsion angles for complexes 5 and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.
(48) Sheldrick, G. M. SHELXTL, Program for Refinement of
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