A new family of acylrhodium organometallics

Article abstract of DOI:10.1021/om980748e

The Schiff mono bases of 2,6-diformyl-4-methylphenol, 1, react with RhCl₃·3H₂O and PPh₃ in ethanol, affording dichloro[4-methyl-6-((arylimino)methyl)phenolato-C ¹,O]bis(triphenylphosphine)rhodium(III), Rh(XL_sb)(PPh₃)₂Cl₂ (5; X = H, Me, OMe, Cl). Organometallics of the type (carboxylato)[4-methyl-6-formylphenolato-C ¹,O]bis(triphenylphosphine]rhodium(III), Rh(L_al)(PPh₃)₂(RCO₂) (6; R = H, Me, Et, Ph), have been synthesized by oxidative addition of 1 to RhCl(PPh₃)₃ in the presence of dilute RCO₂H in ethanol. Replacement of RCO₂H by dilute HNO₃ has afforded the nitrate analogue Rh(L_al)(PPh₃)2(NO₃) (7). Species of type 5 are susceptible to aldiminium → aldehyde hydrolysis in a dichloromethane-acetone-water mixture with concomitant chloride dissociation, furnishing Rh(L_al)(PPh₃)₂Cl (8a), from which the N-bonded nitrite Rh(L_al)(PPh₃)₂(NO₂) (8b) has been generated metathetically. The four types of species 5-8 are interconvertible, and a possible reaction pathway involving pentacoordinate intermediates is proposed. The X-ray structures of Rh(MeL_sb)(PPh₃)₂Cl₂ (5b; bis(dichloromethane) adduct), Rh(L_al)(PPh₃)₂(MeCO₂) (6b), Rh(L_al)(PPh₃)₂(NO₃) (7), and Rh-(L_al)(PPh₃)₂(NO₂) (8b) have been determined. Among these, 5b, 6b, and 7 are pseudooctahedral - the bonds trans to the acyl function being longer by 0.2-0.4 A? compared to those trans to phenolato oxygen. Complex 8b is square pyramidal, there being no ligand trans to the acyl function. In 5b iminium-phenolato (N?O, 2.66(1) A?) and in the remaining species aldehyde-phenolato (C?O, 2.86(1) A?) hydrogen bonding is present. Internal charge balance is crucial for the stability of the present organometallics.

Full text of DOI:10.1021/om980748e

1486
Organometallics 1999, 18, 1486-1494
A New F a m ily of Acylr h od iu m Or ga n om eta llics
Sujay Pattanayak, Swarup Chattopadhyay, Kaushik Ghosh, Sanjib Ganguly,
Prasanta Ghosh, and Animesh Chakravorty*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Calcutta 700 032, India
Received September 3, 1998
The Schiff mono bases of 2,6-diformyl-4-methylphenol, 1, react with RhCl3‚3H2O and PPh3
in ethanol, affording dichloro[4-methyl-6-((arylimino)methyl)phenolato-C1,O]bis(triphenyl-
phosphine)rhodium(III), Rh(XLsb)(PPh3)2Cl2 (5; X ) H, Me, OMe, Cl). Organometallics of
the type (carboxylato)[4-methyl-6-formylphenolato-C1,O]bis(triphenylphosphine)rhodium(III),
Rh(Lal)(PPh3)2(RCO2) (6; R ) H, Me, Et, Ph), have been synthesized by oxidative addition of
1 to RhCl(PPh3)3 in the presence of dilute RCO2H in ethanol. Replacement of RCO2H by
dilute HNO3 has afforded the nitrate analogue Rh(Lal)(PPh3)2(NO3) (7). Species of type 5
are susceptible to aldiminium f aldehyde hydrolysis in a dichloromethane-acetone-water
mixture with concomitant chloride dissociation, furnishing Rh(Lal)(PPh3)2Cl (8a ), from which
the N-bonded nitrite Rh(Lal)(PPh3)2(NO2) (8b) has been generated metathetically. The four
types of species 5-8 are interconvertible, and a possible reaction pathway involving
pentacoordinate intermediates is proposed. The X-ray structures of Rh(MeLsb)(PPh3)2Cl2 (5b;
bis(dichloromethane) adduct), Rh(Lal)(PPh3)2(MeCO2) (6b), Rh(Lal)(PPh3)2(NO3) (7), and Rh-
(Lal)(PPh3)2(NO2) (8b) have been determined. Among these, 5b, 6b, and 7 are pseudoocta-
hedralsthe bonds trans to the acyl function being longer by 0.2-0.4 Å compared to those
trans to phenolato oxygen. Complex 8b is square pyramidal, there being no ligand trans to
the acyl function. In 5b iminium-phenolato (N‚‚‚O, 2.66(1) Å) and in the remaining species
aldehyde-phenolato (C‚‚‚O, 2.86(1) Å) hydrogen bonding is present. Internal charge balance
is crucial for the stability of the present organometallics.
In tr od u ction
elusive acyl intermediate incorporating the ring 3
formed via oxidative (Ru(II) f Ru(IV)) aldehyde addi-
tion. The richness of the chemistry1-5 of 2 has prompted
us to search for organorhodium species based on 1, with
special reference to the status of the acylrhodium moiety
4.
The reaction of Ru(PPh3)3Cl2 with the Schiff mono
base of 2,6-diformyl-4-methylphenol, 1, has been shown
to afford organometallics of type 2.1,2 The unusual four-
In the present work we have scrutinized the reaction
of 1 with RhCl(PPh3)3. Aldehydes are usually decarbonyl-
ated6-9 by RhCl(PPh3)3 (eq 1), a reaction that finds use
(3) Ghosh, P.; Pramanik, A.; Chakravorty, A. Organometallics 1996,
15, 4147.
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membered metallacycle has been proposed to arise from
reductive (Ru(IV) f Ru(II)) decarbonylation of an
(1) (a) Bag, N.; Choudhury, S. B.; Pramanik, A.; Lahiri, G. K.;
Chakravorty, A. Inorg. Chem. 1990, 29, 5013. (b) Bag, N.; Choudhury,
S. B.; Lahiri, G. K.; Chakravorty, A. J . Chem. Soc., Chem. Commun.
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3042.
10.1021/om980748e CCC: $18.00 © 1999 American Chemical Society
Publication on Web 03/20/1999

A New Family of Acylrhodium Organometallics
Organometallics, Vol. 18, No. 8, 1999 1487
in organic synthesis (Q ) alkyl, aryl).10,11 Acyl inter-
in the presence of dilute hydrochloric acid. The reaction
is shown in eq 2. The synthesis can be conveniently
QCHO + RhICl(PPh3)3 f
RhCl(PPh3)3 + 1 + HCl f 5 + PPh3 + H2 (2)
QH + trans-Rh(CO)Cl(PPh3)2 (1)
carried out as a single-pot process involving 1, RhCl3‚
3H2O, and PPh3, the last two generating RhCl(PPh3)3
and HCl in situ.14,15
In the absence of HCl the reaction of RhCl(PPh3)3 and
1 affords only trans-Rh(CO)Cl(PPh3)2, presumably formed
via reductive decarbonylation of a hydridoacyl interme-
diate incorporating motif 9. The acid (here HCl) is
mediates formed via oxidative (Rh(I) f Rh(III)) addition
are implicated, but these are generally very unstable
with respect to reductive (Rh(III) f Rh(I)) decarbonyl-
ation. Instances of isolation and characterization of such
intermediates are therefore rare.12,13
If decarbonylation would prevail in our reaction also,
the only products would be a salicylaldimine and trans-
Rh(CO)Cl(PPh3)2. No rhodium(I) analogue of 2 is an-
ticipated, since the low-spin d8 metal is already coordi-
natively saturated in trans-Rh(CO)Cl(PPh3)2. In practice,
the reaction of 1 with RhCl(PPh3)3 proceeded smoothly
in acidic media without decarbonylation, affording
stable acylrhodium species incorporating motif 4. The
structure and properties of the new family of organo-
metallics generated via this route are reported in this
present work.
believed to facilitate rapid proton-assisted displacement
of hydride from 9 by chloride. The acid also sustains
the cationic aldiminium moiety, which helps to stabilize
the system (vide infra). Upon using 2,6-diformyl-4-
methylphenol in place of 1 in eq 2, rapid decarbonylation
occurs and only trans-Rh(CO)Cl(PPh3)2 is isolated.
c. Rh (La l)(P P h 3)2(RCO2) (6) a n d Rh (La l)(P P h 3)2-
(NO3) (7). The reaction (eq 3) of RhCl(PPh3)3 with 1 in
the presence of dilute carboxylic acids proceeds in a
manner similar to that of eq 2 but with concomitant
hydrolysis of the aldimine function affording 6 in
excellent yields. Upon replacing RCO2H by HNO3, the
Resu lts a n d Discu ssion
A. Syn th esis. a . Th e F a m ily. The title family
consists of three pseudooctahedral and one distorted
square pyramidal acylrhodium system. These are ab-
breviated as Rh(XLsb)(PPh3)2Cl2 (5), Rh(Lal)(PPh3)2-
(RCO2) (6), Rh(Lal)(PPh3)2(NO3), (7), and Rh(Lal)(PPh3)2-
(Y) (8).
RhICl(PPh3)3 + 1 + RCO2H + H2O f
6 + PPh3 + XC6H4NH2‚HCl + H2 (3)
nitrate 7 is obtained. We have been able to isolate 6
and 7 only via this substitution-cum-hydrolysis route.
Use of 2,6-diformyl-4-methylphenol in place of the
Schiff base 1 in eq 3 leads to decarbonylation, affording
trans-Rh(CO)Cl(PPh3)2. This prompts us to propose that
in the present synthesis the cation [Rh(XLsb)(PPh3)2-
(RCO2)]+ incorporating the aldiminium function is first
formed in the same manner as 5 is formed in eq 2. It is,
however, subject to facile nucleophilic water attack
(13) Acylrhodium species have, however, been isolated by using
specialized multidentate ligands13a and via other synthetic routes such
as carbon monoxide insertion13b into the Rh-C bond and addition of
acid chlorides, acid anhydrides, and aldehydes to rhodium(I):13c-j (a)
Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Bachechi, F. Organo-
metallics 1991, 10, 820. (b) Garc´ıa, M. P.; J ime´nez, M. V.; Cuesta, A.;
Siurana, C.; Oro, L. A.; Lahoz, F. J .; Lopez, J . A. Catala´n, M. P.;
Tiripicchio, A.; Lanfranchi, M. Organometallics 1997, 16, 1026. (c)
McGuiggan, M. F.; Doughty, D. H.; Pignolet, L. H. J . Organomet. Chem.
1980, 185, 241. (d) Bennett, M. A.; J effrey, J . C.; Robertson, G. B. Inorg.
Chem. 1981, 20, 323. (e) Suggs, J . W.; Wovkulich, M. J .; Cox, S. D.
Organometallics 1985, 4, 1101. (f) Suggs, J . W.; Wovkulich, M. J .;
Williard, P. G.; Lee, K. S. J . Organomet. Chem. 1986, 307, 71. (g) Miller,
J . A.; Nelson, J . A. Organometallics 1991, 10, 2958. (h) Moloy, K. G.;
Wegman, R. W. Organometallics 1989, 8, 2883. (i) Egglestone, D. L.;
Baird, M. C.; Lock, C. J . L.; Turner, G. J . Chem. Soc., Dalton Trans.
1977, 1576. (j) Slack, D. A.; Egglestone, D. L.; Baird, M. C. J .
Organomet. Chem. 1978, 146, 71.
b. Rh (XLsb)(P P h 3)2Cl2, 5. The type 5 organometal-
lics are afforded in excellent yields upon reacting the
Schiff mono base 1 with RhCl(PPh3)3 in boiling ethanol
(14) Cotton, S. A. In Chemistry of Precious Metals; Blackie Academic
and Professional: London, 1997; pp 88-132.
(15) (a) Chatt, J .; Shaw, B. L. J . Chem. Soc. A 1966, 1437. (b)
Osborn, J . A.; J ardine, F. H.; Young, J . F.; Wilkinson, G. J . Chem.
Soc. A 1966, 1711. (c) Brown, J . M.; Lucy, A. R. J . Chem. Soc., Chem.
Commun. 1984, 914. (d) Duckett, S. B.; Newell, C. L.; Eisenberg, R. J .
Am. Chem. Soc. 1994, 116, 10548.
(10) Song, L.; Arif, A. M.; Stang, P. J . Organometallics 1990, 9, 2792.
(11) Murakami, M.; Amii, H.; Shigeto, K.; Ito, Y. J . Am. Chem. Soc.
1996, 118, 8285.
(12) Suggs, J . W. J . Am. Chem. Soc. 1978, 100, 640.

1488 Organometallics, Vol. 18, No. 8, 1999
Pattanayak et al.
1
Ta ble 1. Rin g Cu r r en t Sh ifts (p p m )a of H NMR
furnishing electroneutral 6 via rapid aldiminium f
aldehyde hydrolysis.
Sign a ls of 5b, 6b, 7, a n d 8bb
compd
3-H
5-H
4-Me
9-H
10-Me
d . Rh (La l)(P P h 3)2(Y) (8). Aldimine f aldehyde hy-
drolysis occurs in the case of 5 also upon boiling its
solution in a dichloromethane-acetone mixture with
water. The process is associated with concomitant
dissociation of a chloride ligand, affording electroneutral
8a (eq 4). In 5 the Rh-Cl bond trans to the acyl function
5b
6b
7
1.00 (0.90)
c
0.24 (0.30)
1.33 (0.90) 0.50 (0.20) 0.50 (0.20) 0.60 (0.70) 0.94 (1.35)
1.20 (1.40) 0.58 (0.53) 0.43 (0.45) 0.71 (0.68
0.91 (0.90) 0.29 (0.36) 0.44 (0.34) 0.83 (0.50)
8b
a
b
Calculated shifts are in parentheses. The atom-numbering
scheme is the same as in X-ray structures (see Figures 1-4). c Not
individually resolved; lies within a complex multiplet of aromatic
protons (7-8 ppm).
5 + H2O f 8a + XC6H4NH2‚HCl
(4)
the three nitrate vibrations4,18 in 7. and the three nitrite
vibrations18e,19 in 8b are consistent with the designated
bonding modes.
is reletively weak (vide infra), and it is this bond that
undergoes ionic dissociation. The synthesis of 8b in-
volves metathesis between 8a with NaNO2 (eq 5).
A characteristic feature of the 1H NMR spectra of the
present organometallics is the significant upfield shift
of several proton signals of chelated XLsb and Lal ligands
relative to 1 and 2,6-diformyl-4-methylphenol. The X-ray
structural results (vide infra) revealed that ring cur-
rents due to phosphine phenyl rings can be the primary
origin of such shifts. Using structural parameters and
isoshielding F-z plots20 the expected shifts due to ring
current have been estimated in the case of 5b, 6b, 7,
and 8b. These are listed in Table 1 along with the
corresponding observed shifts. The agreement is gener-
ally satisfactory. The most shifted protons are 3-H (all
cases), 9-H (6b, 7, 8b), and 10-Me21 (6b).
8a + NaNO2 f 8b + NaCl
(5)
e. Sta bility. The Rh-C(acyl) bond in the present
complexes is stabilized by chelate formation involving
phenolato oxygen. All members in the family 5-8 are
indefinitely stable in the solid state and in dry halocar-
bon (CH2Cl2, CHCl3) solutions. The type 5 complexes
are sparingly soluble in ethanol, and dissolution in
boiling ethanol is associated with reductive decarbony-
lation to trans-Rh(CO)Cl(PPh3)2. In the synthesis of 5
it is therefore necessary to optimize the reaction time
so that trans-Rh(CO)Cl(PPh3)2 remains only a minor
byproduct. In contrast to 5, 6-8 have good solubility in
ethanol and the solutions are thermally stable.
C. Str u ctu r e. a . Geom etr ica l F ea tu r es. The X-ray
structures of 5b (bis(dichloromethane) adduct), 6b, 7,
and 8b have been determined. Molecular views are
shown in Figures 1-4, and selected bond parameters
are listed in Tables 2-4. To our knowledge, instances
where acyl complexes have been isolated by the reaction
of RhCl(PPh3)3 with aldehydes followed by X-ray struc-
tural characterization are rare, probably unknown. The
present structures are of particular significance in this
context. The structures of a few rhodium acyl complexes
formed via other routes have been documented.13a-f
In 5b, 6b, and 7 the coordination spheres are severely
distorted from idealized octahedral geometry. In 5b the
Rh(MeLsb)Cl2 fragment defines a crystallographic plane
of symmetry (x, 1/4, z). The Rh(Lal) fragments in 6b and
7 constitute good planes (plane A, mean deviation e0.05
Å), and the carboxylate (6b) and nitrate (7) chelate rings
are nearly perfectly planar (plane B, mean deviation
e0.01 Å). The dihedral angle between A and B is 11.7°
in 6b and 4.0° in 7. Thus, the bulk of the equatorial
region increases in the order 5b < 7 < 6b, and this is
attended by a corresponding increase in the P-Rh-P
angle in the same order.
Internal charge balance is a crucial stabilizing factor
in this family of organometallics. In this context we note
the intimate relationship between the charge of the
anion(s) bonded to the metal and the state of the remote
side chain on the phenolato-acyl ligand. Thus, when
two chloride ligands are present, electroneutrality is
achieved in the form of 5, where the side chain is in the
aldiminium form. In 8 only one chloride ligand is
present and the side chain becomes aldehydic (6 and 7
are similar). We have not succeeded in isolating cationic
species such as [Rh(XLsb)(PPh3)2(RCO2)]+, which was
implicated as a hydrolytically unstable intermediate in
the synthesis of 6; neither have we been able to prepare
an anionic system such as [Rh(Lal)(PPh3)2Cl2]-.
The aldehyde function in 6-8 is a potential site of
further oxidative addition to RhCl(PPh3)3. In practice,
however, no reaction occurs even on prolonged boiling
in ethanol. The formyl function in 6-8 is deactivated
by the existing acyl moiety and the bulk of the neigh-
boring Rh(PPh3)2 fragment.
B. Sp ectr a . The colors of type 5 (orange-yellow) and
type 6-8 (yellow) are due to MLCT(t2fπ*) absorption
occurring near 500 and 425 nm, respectively. The acyl
CdO stretch13b,16 is observed as a strong band near 1700
cm-1. Two well-separated Rh-Cl stretch (near 320 and
350 cm-1) occur in 5, consistent with the cis-RhCl2
configuration having two Rh-Cl bonds of unequal
lengths. Significantly, the single Rh-Cl stretch in 8a
is at 350 cm-1. The two carboxyl vibrations3,13e,17 in 6,
(18) (a) Betts, C. E.; Haszeldine, R. N.; Parish, R. V. (Dick). J . Chem.
Soc., Dalton Trans. 1975, 2218. (b) Steed, J . W.; Tocher, D. A.
Polyhedron 1994, 13, 167. (c) Critchlow, P. B.; Robinson, S. D. Inorg.
Chem. 1978, 17, 1896. (d) Critchlow, P. B.; Robinson, S. D. Inorg. Chem.
1978, 17, 1902. (e) Nakamoto, K. Infrared and Raman Spectra of
Inorganic and Coordination Compounds, 4th ed.; Wiley: New York,
1986. (f) Heaton, B. T.; Lggo, J . A.; J acob, C.; Blanchard, H.;
Hursthouse, M. B.; Ghatak, I.; Harman, M. E.; Somerville, R. G.;
Heggie, W.; Page, P. R.; Villax, I. J . Chem. Soc., Dalton Trans. 1992,
2533. (g) Hursthouse, M. B.; Malik, K. M. A.; Michael, D.; Mingos, P.;
Willoughby, S. D. J . Organomet. Chem. 1980, 192, 235.
(19) (a) Muccigrosso, D. A.; Mares, F.; Diamond, S. E.; Solar, J . P.
Inorg. Chem. 1983, 22, 960. (b) J ohnson, S. A.; Basolo, F. Inorg. Chem.
1962, 1, 925. (c) Hitchman, M. A.; Rowbottom, G. L. Coord. Chem. Rev.
1982, 42, 55.
(20) J ohnson, C. E., J r.; Bovey, F. A. J . Chem. Phys. 1958, 29, 1012.
(21) The chemical shift of the acetate methyl signal in the absence
of such shielding is 1.7 ppm: J ia, G.; Rheingold, A. L.; Haggerty, B. S.;
Meek, D. W. Inorg. Chem. 1992, 31, 900.
(16) Coutinho, K. J .; Dickson, R. S.; Fallon, G. D.; J ackson, W. R.;
Simone, T. D.; Skelton, B. W.; White, A. H. J . Chem. Soc., Dalton
Trans. 1997, 3193.
(17) Kavanagh, B.; Steed, J . W.; Tocher, D. A. J . Chem. Soc., Dalton
Trans. 1993, 327.

A New Family of Acylrhodium Organometallics
Organometallics, Vol. 18, No. 8, 1999 1489
F igu r e 3. ORTEP plot (30% probability ellipsoids) and
atom-labeling scheme for 7.
F igu r e 1. ORTEP plot (30% probability ellipsoids) and
atom-labeling scheme for 5b‚2CH2Cl2.
F igu r e 4. ORTEP plot (30% probability ellipsoids) and
atom-labeling scheme for 8b.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) a n d Th eir Estim a ted Sta n d a r d Devia tion s
for 5b‚2CH2Cl2
F igu r e 2. ORTEP plot (30% probability ellipsoids) and
atom-labeling scheme for 6b.
Distances
Rh-C1
Rh-O2
Rh-Cl1
Cl-O1
1.983(9)
2.070(6)
2.552(3)
1.203(11)
Rh-Cl2
2.365(3)
2.367(2)
2.367(2)
2.663(1)
In 8b the coordination sphere has distorted-square-
pyramidal geometry. The donor atoms P1, P2, O2, and
N1 constitute an excellent equatorial plane (mean
deviation 0.02 Å), from which the metal atom is shifted
by 0.15 Å toward the acyl carbon atom. The Rh(NO2)
plane (mean deviation 0.02 Å) makes a dihedral angle
of 86.1° with the equatorial plane and 12.8° with the
Rh(Lal) plane (mean deviation 0.06 Å).
Rh-Pl
Rh-PlA
N1‚‚‚O2
Angles
C1-Rh-O2
Cl1-Rh-Cl2
Pl-Rh-P1A
O2-Rh-Cl2
P1-Rh-O2
P1-Rh-Cl2
83.8(3)
96.2(1)
173.4(1)
177.0(2)
88.2(1)
91.9(1)
O2-Rh-Cl1
Cl2-Rh-Cl
Cl-Rh-Cl1
P1-Rh-Cl
P1-Rh-Cl1
86.8(2)
93.2(3)
170.6(3)
92.6(1)
87.1(1)
b. Bon d Len gth s. The observed Rh-C(acyl), Cd
O(acyl), and Rh-P lengths fall within reported rangess
1.94-1.99 Å,13a-d 1.18-1.22 Å,13a-d and 2.30-2.40 Å,22
respectively. The Rh-N distance in 8b (1.997(5) Å) is
The structures provide an unique opportunity for
observing the strong trans influence of the acyl function.
The two Rh-Cl distances in 5b, Rh-O(acetate) dis-
tances in 6b, and Rh-O(nitrate) distances in 7 differ
by ∼0.2, ∼0.3, and ∼0.4 Å, respectively. In each case
the longer and shorter bonds lie respectively trans to
the acyl and phenolato functions.
shorter than that in Rh(NO2)6 (2.06 Å).23
3-
(22) (a) Cotton, F. A.; Kang, S. J . Inorg. Chem. 1993, 32, 2336. (b)
Hataya, K. O. K.; Yamamoto, T. Inorg. Chem. 1993, 32, 2360. (c)
Harlow, R. L.; Thorn, D. L.; Baker, T.; J ones, N. L. Inorg. Chem. 1992,
31, 993.
(23) Gronilov, S. A.; Alekseev, V. I.; Baudina, I. A.; Kharanenko, S.
P. Russ. J . Inorg. Chem. (Engl. Transl.) 1992, 37, 306.
The C-O(acetate), N-O(nitrate), and N-O(nitrite)
distances in 6b, 7, and 8b are consistent with the

1490 Organometallics, Vol. 18, No. 8, 1999
Pattanayak et al.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) a n d Th eir Estim a ted Sta n d a r d Devia tion s
for 6b a n d 7
Sch em e 1
6b
7
6b
7
Distances
Rh-C1
Rh-O2
Rh-O3
Rh-O4
Rh-P1
Rh-P2
C1-O1
1.955(5) 1.965(7) C10-O3
2.045(3) 2.038(4) C10-O4
2.089(4) 2.077(4) N1-O3
2.402(4) 2.495(6) N1-O4
2.368(2) 2.359(2) N1-O6
2.368(2) 2.370(2) C9‚‚‚O2
1.226(6) 1.194(7)
1.261(6)
1.237(7)
1.278(8)
1.246(7)
1.206(8)
2.861(1) 2.860(1)
Angles
C1-Rh-O2 82.7(2) 83.9(2) P1-Rh-O2 91.0(1) 88.4(1)
O2-Rh-O4 115.2(1) 120.2(2) P1-Rh-O4 83.0(1) 84.4(1)
O4-Rh-O3 57.3(1) 55.0(2) P1-Rh-O3 91.6(1) 91.1(1)
O3-Rh-Cl 105.3(2) 100.9(2) P2-Rh-Cl 91.2(1) 91.4(1)
P1-Rh-P2 178.2(1) 176.4(1) P2-Rh-O2 90.8(1) 89.8(1)
Cl-Rh-O4 160.4(2) 155.3(2) P2-Rh-O4 96.2(1) 93.7(1)
O2-Rh-O3 171.6(1) 175.2(2) P2-Rh-O3 86.6(1) 90.4(1)
P1-Rh-C1 89.1(1) 91.6(1)
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) a n d Th eir Estim a ted Sta n d a r d Devia tion s
for 8b
Distances
CdN stretching frequency25,26 (∼1635 cm-1) and a high-
field shift27 of the C-H proton signal (∼7.3 ppm; 8.7
ppm in 1).
The nearly perfectly planar aldehyde-phenolato moi-
ety 14 is present in 6b, 7, and 8b. All hydrogen atoms
were resolved in difference Fourier maps in the case of
8b. The C9‚‚‚O2 distance is 2.86(1) Å in all the species.
The rotameric conformations of 13 and 14 around the
C6-C9 axis differ by 180°, consistent with the presence
of hydrogen bonding.
d . In ter con ver sion . (i) Sp ecies 5-8. The four
groups of organometallics reported in this work are
readily interconvertible upon treatment with appropri-
ate reagents. Some of the interconversions centered
around 5 are shown in Scheme 1. Thus, when 5 is
reacted with excess carboxylates or free carboxylic acids,
6 is obtained in excellent yields and the reverse reaction
occurs on treating 6 with XC6H4NH2‚HCl (excess) and
HCl (eq 6).
Rh-C1
Rh-N1
Rh-P2
N1-O4
1.975(5)
1.997(5)
2.376(2)
1.334(7)
Rh-O2
Rh-P1
N1-O3
C1-O1
O9‚‚‚O2
2.059(3)
2.369(2)
1.094(8)
1.205(6)
2.860(1)
Angles
C1-Rh-O2
C1-Rh-P1
O2-Rh-N1
83.3(2)
90.1(1)
170.1(2)
C1-Rh-N1
C1-Rh-P2
P1-Rh-P2
106.5(2)
95.7(1)
173.8(1)
approximate valence-bond structures 10, 11, and 12,
respectively. The length of the shorter N-O bond (1.094-
(3) Å) in 8b approaches that of nitric oxide and the
complex is thus a potentially good candidate for oxo-
transfer activity.19a,24
5 + RCO2H + H2O {CH Cl -Me CO-H O
}
c. Ald im in iu m -P h en ola to a n d Ald eh yd e-P h e-
n ola to Moieties. The nonhydrogen atoms of the aldi-
minium-phenolato moiety 13 present in 5b define a
virtually perfect plane. The observed N1‚‚‚O2 length,
2
2
2
2
EtOH
6 + XC6H4NH2‚HCl + HCl (6)
In the conversion of 5 to the other species the reaction
medium always contains water. In view of the facile
nature of the reaction 5 f 8a , it is plausible that the
conversions of 5 to the other species proceed through
pentacoordinated 8a . For example, the reaction 5 f 6
can proceed via occupation of the vacant site by a
carboxyl oxygen followed by displacement of chloride
ligand and completion of chelate ligation (Scheme 2).
(ii) Com p a r ison w ith Ru th en iu m . The pair 5 and
6 provides a contrast to the ruthenium pair 2 and 15,
2.663(11) Å, is the same as that, 2.665(12) Å, in the
ruthenium complex 2 (Ar ) p-tolyl), where the iminium
hydrogen was directly located.2 The iminium N-H
stretch in 5 occurs near 3400 cm-1 25 and in 1H NMR
,
the iminium proton resonates near 14 ppm, giving rise
to a relatively broad signal which disappears upon
shaking with D2O. Further, the presence of the aldi-
minium function in 5 is consistent with relatively high
(25) (a) Sandorfy, C.; Vocelle, D. Mol. Phys. Chem. Biol. 1989, IV,
195. (b) Chevalier, P.; Sandorfy, C. Can. J . Chem. 1960, 38, 2524. (c)
Favrot, J .; Vocelle, D.; Sandorfy, C. Photochem. Photobiol. 1979, 30,
417.
(26) Bohme, H.; Haake, M. In Advances in Organic Chemistry;
Bohme, H., Viehe, H. G., Eds.; Interscience: New York, 1976; Part 1,
Vol. 9, p 1.
(24) Sieker, F.; Blake, A. J .; J ohnson, B. F. G. J . Chem. Soc., Dalton
Trans. 1996, 1419.
(27) Sharma, G. M.; Roels, O. A. J . Org. Chem. 1973, 38, 3648.

A New Family of Acylrhodium Organometallics
Organometallics, Vol. 18, No. 8, 1999 1491
Sch em e 2
which are also interconvertible. In the 5, 6 pair substi-
The 5, 6 pair provides a contrast with the ruthenium
pair 2, 15, where chelation by RCO2- is accommodated
by sacrificing the Ru-O(phenolato) bond. The strong
trans influence of the acyl function promotes monoden-
tate Rh-NO2 bonding in 8b, while in the nitrite
-
analogue of 15, NO2 is O,O-chelating. In view of the
large asymmetry of N-O bond lengths, we are scruti-
nizing the possible oxo transfer behavior of 8b.
Exp er im en ta l Section
Ma t er ia ls. RhCl(PPh3)3 was prepared by a reported
method.28 The purification of dichloromethane was done as
described before.29 All the other chemicals and solvents were
of analytical grade and were used as received. The Schiff bases
1 were prepared by reacting 2,6-diformyl-4-methylphenol with
the amine XC6H4NH2 in a 1:1 (in hot ethanol) ratio.
tution of chloride by carboxylate occurs in the ratio 2:1,
but in the 2, 15 pair this ratio is 1:1. Electroneutrality
thus remains unaffected by the substitution in the latter
case and there is no aldiminium hydrolysis in the
-
conversion 2 f 15, unlike in 5 f 6. Chelation by RCO2
is accommodated in 15 by sacrificing the Ru-O(pheno-
lato) bond present in 2. The process is attended with
aldiminium-phenolato f aldimine-phenol tautomer-
ization and a rotameric transformation around the Ru-
C(aryl) axis.3
P h ysica l Mea su r em en ts. Electronic and IR spectra were
recorded with Hitachi 330 and Perkin-Elmer 783 IR spectro-
1
photometers. For H NMR spectra a Bruker 300 MHz FT NMR
spectrophotometer was used (tetramethylsilane is the internal
standard). Microanalyses (C, H, N) were done by using a
Perkin-Elmer 240C elemental analyzer.
P r ep a r a tion of Com p lexes. The Rh(XLsb)(PPh3)2Cl2 (5),
Rh(Lal)(PPh3)2(RCO2) (6), Rh(Lal)(PPh3)2(NO3) (7), Rh(Lal)(PPh3)2-
Cl (8a ), and Rh(Lal)(PPh3)2(NO2) (8b) complexes were synthe-
sized by using the same general procedures. Details are given
for representative cases.
Rh (HLsb)(P P h 3)2Cl2 (5a ). a . F r om Rh Cl(P P h 3)3. To a
solution of 2-formyl-4-methyl-6-((phenylimino)methyl)phenol
(1; X ) H) (13 mg, 0.05 mmol) in hot ethanol (25 mL) was
added RhCl(PPh3)3 (50 mg, 0.05 mmol) and 2 N HCl (5 mL).
The mixture was heated to reflux for 0.5 h. Upon cooling, a
bright orange-yellow crystalline solid separated, which was
collected by filtration, washed thoroughly with cold ethanol,
and dried in vacuo. The crude product was purified by washing
with benzene (30 mL), which removes the small amount of Rh-
(CO)Cl(PPh3)2 formed as a byproduct. Yield: 45 mg (89%). Anal.
Calcd for RhC51H42NO2P2Cl2: C, 65.38; H, 4.48; N, 1.49. Found:
C, 65.30; H, 4.46; N, 1.50. 1H NMR (CDCl3; δ): 6.81 (s, 1H,
arom), 7.13-7.86 (m, 32H arom), 7.35 (d, 2H, arom, J HH ) 8.7
Hz), 7.40 (d, 2H, arom, J HH ) 8.8 Hz), 2.16 (s, 3H, CH3), 7.30
(s, 1H, -CHdN+), 14.00 (s, 1H, dN+H). IR (KBr; cm-1): ν(Cd
N) 1630; ν(CdO(acyl)) 1680; ν(Rh-Cl) 320, 350; ν(N-H,
hexachlorobutadiene) 3420. UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1
cm-1)): 500 (11 600), 310 (23 300).
The case of nitrites provides another notable rhodium-
ruthenium contrast, highlighting the qualitative effect
of the acyl trans influence on the binding of ligands. In
the case of rhodium a pentacoordinated structure, 8b,
with a strong Rh-NO2 bond is preferred to a hexaco-
ordinated situation involving O,O-chelation weakened
by acyl trans influence. For ruthenium this effect is
-
absent and nitrite is chelating (as in 15 with RCO2
replaced by NO2-).
Con clu d in g Rem a r k s
Organometallics of type 5-7 incorporating acyl-
phenolate chelation have been synthesized via oxidative
addition of the Schiff mono base 1 to RhCl(PPh3)3 in
acidic media. These are rare instances where the
aldehyde-RhCl(PPh3)3 reaction gets arrested prior to
reductive decarbonylation. In 5-7 the metal is hexaco-
ordinated, the bond trans to the acyl function being
strongly elongated (by 0.2-0.4 Å). This bond is prone
to ionization, thus providing access to square-pyramidal
species of type 8. The intermediacy of pentacoordination
forms a plausible basis for the observed interconversion
among species of types 5-8.
Internal charge balance is a crucial stabilizing factor,
and there is an intimate relationship between the
charge of the anion(s) bonded to the metal and the state
of the remote side chain of the phenolato-acyl ligand.
Thus, in 5 the side chain is aldiminium in nature and
in 6-8 it is aldehydic. The rotameric conformations of
the two functions get spontaneously adjusted to promote
NH‚‚‚O or CH‚‚‚O hydrogen bonding.
b. F r om Rh Cl3‚3H2O. To a solution of 2-formyl-4-methyl-
6-((phenylimino)methyl)phenol (45 mg, 0.18 mmol) in hot
ethanol (25 mL) was added an ethanolic solution (25 mL) of
RhCl3‚3H2O (50 mg, 0.18 mmol) and PPh3 (100 mg, 0.38 mmol).
The mixture was heated to reflux for 0.5 h. Upon cooling, a
(28) Osborn, J . A.; Wilkinson, G. Inorg. Synth. 1967, 10, 67.
(29) (a) Vogel, A. I. Practical Organic Chemistry, 3rd ed.; ELBS and
Longman Group: Harlow, U.K., 1965; Chapter 2, pp 176-177. (b)
Sawyer, D. T.; Roberts, J . L., J r. Experimental Electrochemistry for
Chemists; Wiley: New York, 1974; p 212.

1492 Organometallics, Vol. 18, No. 8, 1999
Pattanayak et al.
bright orange-yellow crystalline solid separated, which was
collected by filtration, washed with cold ethanol, and dried in
vacuo. This crude product was purified by washing with
benzene (30 mL). Yield: 155 mg (88%).
R h (MeLsb ) (P P h 3)2Cl2 (5b ). Yield: 89%. Anal. Calcd for
RhC52H44NO2P2Cl2: C, 65.68; H, 4.63; N, 1.47. Found: C, 65.62;
H, 4.61; N, 1.48. 1H NMR (CDCl3; δ): 6.80 (s, 1H, arom), 7.14-
7.86 (m, 31H, arom), 7.33 (d, 2H, arom, J HH ) 9.0 Hz), 7.38
(d, 2H, arom, J HH ) 8.9 Hz), 2.17 and 2.46 (2s, 6H, 2CH3),
7.28 (s, 1H, -CHdN+), 13.98 (s, 1H, dN+H). IR (KBr; cm-1):
ν(CdN) 1645; ν(CdO(acyl)) 1690; ν(Rh-Cl) 320, 355; ν(N-H,
hexachlorobutadiene) 3440. UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1
cm-1)): 500 (11 300), 310 (22 600).
Rh (MeOLsb) (P P h 3)2Cl2 (5c). Yield: 90%. Anal. Calcd for
RhC52H44NO3P2Cl2: C, 64.59; H, 4.55; N, 1.44. Found: C, 64.61;
H, 4.57; N, 1.42. 1H NMR (CDCl3; δ): 6.75 (s, 1H, arom), 7.11-
7.81 (m, 31H, arom), 6.93 (d, 2H, arom, J HH ) 8.7 Hz), 7.15
(d, 2H, arom, J HH ) 7.3 Hz), 2.13 (s, 3H, CH3), 3.84 (s, 3H,
OCH3), 7.28 (s, 1H, -CHdN+), 14.02 (s, 1H, dN+H). IR (KBr;
cm-1): ν(CdN) 1635; ν(CdO(acyl)) 1680; ν(Rh-Cl) 315, 350;
ν(N-H, hexachlorobutadiene) 3440. UV-vis (CH2Cl2; λmax, nm
(ꢀ, M-1 cm-1)): 505 (10 800), 315 (21 900).
Rh (ClLsb) (P P h 3)2Cl2 (5d ). Yield: 91%. Anal. Calcd for
RhC51H41NO2P2Cl3: C, 63.06; H, 4.22; N, 1.44. Found: C, 63.10;
H, 4.24; N, 1.45. 1H NMR (CDCl3; δ): 6.82 (s, 1H, arom), 7.13-
7.83 (m, 31H, arom), 7.19 (d, 2H, arom, J HH ) 7.2 Hz), 7.42
(d, 2H, arom, J HH ) 8.7 Hz), 2.17 (s, 3H, CH3), 7.34 (s, 1H,
-CHdN+), 14.01 (s, 1H, dN+H). IR (KBr; cm-1): ν(CdN) 1630;
ν(CdO(acyl)) 1685; ν(Rh-Cl) 310, 350; ν(N-H, hexachloro-
butadiene) 3440. UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)): 510
(11 600), 320 (22 400).
mmol) and 0.4 N HNO3 (10 mL). The mixture was heated to
reflux for 1 h, affording a yellow solution. The solvent was
removed under reduced pressure, leaving a yellow residue.
This was isolated by filtration, washed with water, and dried
in vacuo. Yield: 42 mg (92%). Anal. Calcd for RhC45H36NO6P2:
1
C, 63.45; H, 4.23. Found: C, 63.48; H, 4.19; N, 1.62. H NMR
(CDCl3; δ): 6.65 (d, 1H, arom, J HH ) 3 Hz), 6.93 (d, 1H, arom,
J HH ) 3 Hz), 7.33-7.51 (m, 30H, arom), 1.97 (s, 3H, CH3), 9.84
(s, 1H, -CHO). IR (KBr; cm-1): ν(CdO(acyl)) 1705; ν(Cd
O(formyl)) 1670; ν(NdO) 1500; ν(NO2) 1000 (sym), 1200
(asym). UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)): 420 (4250).
Rh (La l)(P P h 3)2Cl (8a ). To a solution of Rh(MeLsb)(PPh3)2-
Cl2 (50 mg, 0.05 mmol) in dichloromethane (20 mL) and
acetone (20 mL) was added water (15 mL). The heterogeneous
mixture was then heated to reflux for 0.5 h, affording a yellow
solution. The organic solvents were removed under reduced
pressure, leaving a suspension of the yellow residue in water.
The solid was isolated by filtration, washed with water, and
dried in vacuo. Yield: 40 mg (93%). Anal. Calcd for RhC45H36O3-
ClP2: C, 65.49; H, 4.36. Found: C, 65.51; H, 4.38. 1H NMR
(CDCl3, δ): 6.87 (d, 1H, arom, J HH ) 2.1 Hz), 7.01 (d, 1H, arom,
J HH ) 2.1 Hz), 7.33-7.51 (m, 30H, arom), 2.00 (s, 3H, CH3),
9.51 (s, 1H, -CHO). IR (KBr; cm-1): ν(CdO(acyl)) 1705; ν(Cd
O(formyl)) 1675; ν(Rh-Cl) 350. UV-vis (CH2Cl2; λmax, nm (ꢀ,
M-1 cm-1)): 425 (5200).
Rh (La l)(P P h 3)2(NO2) (8b). To a stirred solution of Rh-
(MeLsb)(PPh3)2Cl2 (50 mg, 0.005 mmol) in dichloromethane-
acetone (1:1) (30 mL) was added an aqueous solution of NaNO2
(40 mg, 0.57 mmol). Stirring was continued for 0.5 h, and the
orange color of the solution changed to yellow. The resulting
solution was evaporated under reduced pressure. A yellow
suspension of the complex was obtained, which was isolated
by filtration and then washed repeatedly with water. The
crystalline solid was dried in vacuo. Yield: 41 mg (94%). Anal.
Calcd for RhC45H36NO5P2: C, 64.67; H, 4.31; N, 1.67. Found:
C, 64.61; H, 4.40; N, 1.65. 1H NMR (CDCl3; δ): 6.94 (d, 1H,
arom, J HH ) 3.2 Hz), 7.22 (d, 1H, arom, J HH ) 2.8 Hz), 7.37-
7.65 (m, 30H, arom), 1.96 (s, 3H, CH3), 9.72 (s, 1H, -CHO).
IR (KBr; cm-1): ν(CdO(acyl)) 1705; ν(CdO(formyl)) 1670; ν(N-
O) 1280 (sym), 1310 (asym); ν(O-N-O) 830. UV-vis (CH2-
Cl2; λmax, nm (ꢀ, M-1 cm-1)): 420 (5120).
In ter con ver sion s. a . Rh (MeLsb)(P P h 3)2Cl2 (5b) to Rh -
(La l)(P P h 3)2(MeCO2) (6b). To a stirred solution of Rh-
(MeLsb)(PPh3)2Cl2 (50 mg, 0.05 mmol) in 1:1 dichloromethane-
acetone (40 mL) was added an aqueous solution of NaCO2Me‚
3H2O (50 mg, 0.36 mmol). The solution instantly changed from
orange to yellow. Stirring was continued for 0.5 h. The organic
solvents were removed under reduced pressure, leaving an
aqueous suspension of a yellow residue of 6b. This was isolated
by filtration, washed with water, and dried in vacuo. Yield:
93%.
b. Rh (La l)(P P h 3)2(MeCO2) (6b) to Rh (MeLsb)(P P h 3)2Cl2
(5b). To a stirred solution of Rh(Lal)(PPh3)2(MeCO2) (10 mg)
in ethanol (5 mL) were added MeArNH2‚HCl (10 mg) and 0.3
N HCl solution (2 mL). The solution immediately changed from
yellow to orange. Stirring was continued for another 15 min.
The solvent was then removed under reduced pressure, and
water was added to the orange residue of 5b. The suspension
was stirred, and the orange solid was collected by filtration,
washed with water, and dried in vacuo. Yield: 79%.
Rh (La l)(P P h 3)2(HCO2) (6a ). To a solution of 2-formyl-4-
methyl-6-((p-tolylimino)methyl)phenol (20 mg, 0.07 mmol) in
hot ethanol (25 mL) was added RhCl(PPh3)3 (50 mg, 0.05
mmol) and 0.3 N HCOOH (10 mL). The mixture was heated
to reflux for 1.5 h, affording a yellow solution. The solvent was
removed under reduced pressure, leaving a yellow residue.
This was isolated by filtration and washed with water and
dried in vacuo. Yield: 41 mg (92%). Anal. Calcd for
1
RhC46H37O5P2: C, 66.18; H, 4.43. Found: C, 66.02; H, 4.32. H
NMR (CDCl3; δ): 6.876 (d, 1H, arom, J HH ) 1.7 Hz), 7.01 (d,
1H, arom, J HH ) 1.9 Hz), 7.34-7.61 (m, 31H, arom and HCO2),
1.93 (s, 3H, CH3), 9.50 (s, 1H, -CHO). IR (KBr; cm-1): ν(Cd
O(acyl, formyl)) 1670; ν(OCO) 1455 (sym), 1545 (asym). UV-
vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)): 435 (6450).
Rh (La l)(P P h 3)2(MeCO2) (6b). Yield: 93%. Anal. Calcd for
1
RhC47H39O5P2: C, 66.50; H, 4.59. Found: C, 66.40; H, 4.61. H
NMR (CDCl3; δ): 6.52 (d, 1H, arom, J HH ) 1.8 Hz), 7.01 (d,
1H, arom, J HH ) 2.0 Hz), 7.31-7.56 (m, 30H, arom), 1.91 and
0.76 (2s, 6H, 2CH3), 9.89(s, 1H, -CHO). IR (KBr; cm-1): ν(Cd
O(acyl, formyl)) 1670; ν(OCO) 1450 (sym), 1550 (asym). UV-
vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)): 430 (6830).
Rh (La l)(P P h 3)2(EtCO2) (6c). Yield: 94%. Anal. Calcd for
1
RhC48H41O5P2: C, 66.82; H, 4.75. Found: C, 66.92; H, 4.82. H
NMR (CDCl3; δ): 6.48 (d, 1H, arom, J HH ) 1.8 Hz), 6.98 (d,
1H, arom, J HH ) 2.1 Hz), 7.32-7.55 (m, 30H, arom), 0.96 (q,
2H, Et), 0.17 (t, 3H, Et), 1.90 (s, 3H, CH3), 9.88 (s, 1H, -CHd
O). IR (KBr; cm-1): ν(CdO(acyl, formyl)) 1665; ν(OCO) 1450
(sym), 1550 (asym). UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)):
430 (6520).
Rh (La l)(P P h 3)2(P h CO2) (6d ). Yield: 94%. Anal. Calcd for
RhC52H41O5P2: C, 68.57; H, 4.50. Found: C, 68.63; H, 4.61. H
c. Rh (La l)(P P h 3)2Cl (8a ) to Rh (MeLsb)(P P h 3)2Cl2 (5b).
To a stirred solution of Rh(Lal)(PPh3)2Cl (10 mg) in ethanol
(20 mL) was added MeC6H4NH2‚HCl (10 mg) and 0.3 N HCl
solution (5 mL). Stirring was continued for 0.5 h. After the
organic solvent was evaporated, the residue of 5b was washed
with ethanol dried in vacuo. Yield :94%.
d . Rh (La l)(P P h 3)2Cl (8a ) to Rh (La l)(P P h 3)2(RCO2) (6b).
To a stirred solution of Rh(Lal)(PPh3)2Cl (50 mg, 0.06 mmol)
in a 1:1 dichloromethane-acetone mixture (25 mL) was added
an aqueous solution of NaCO2Me (30 mg, 0.24 mmol). Stirring
was continued for 0.5 h. After the organic solvents were
1
NMR (CDCl3; δ): 6.52 (d, 1H, arom, J HH ) 1.8 Hz), 7.02 (d,
1H, arom, J HH ) 2.0 Hz), 7.11-7.58 (m, 31H, arom), 6.66 (d,
2H, arom, J HH ) 7.8 Hz), 6.93 (t, 2H, arom, J HH ) 6.7 Hz),
1.91 (s, 3H, CH3), 9.96 (s, 1H, -CHdO). IR (KBr; cm-1): ν(Cd
O(acyl, formyl)) 1670; ν(OCO) 1457 (sym), 1555 (asym). UV-
vis (CH2Cl2;, λmax, nm (ꢀ, M-1 cm-1)): 430 (7200).
Rh (La l)(P P h 3)2(NO3) (7). To a solution of 2-formyl-4-
methyl-6-((p-tolylimino)methyl)phenol (20 mg, 0.07 mmol) in
hot ethanol (25 mL) was added RhCl(PPh3)3 (50 mg, 0.05

A New Family of Acylrhodium Organometallics
Organometallics, Vol. 18, No. 8, 1999 1493
Ta ble 5. Cr ysta l, Da ta Collection , a n d Refin em en t P a r a m eter s for 5b‚2CH2Cl2, 6b, 7, a n d 8b
5b‚2CH2Cl2
6b
7
8b
mol formula
mol wt
cryst syst
space group
a, Å
C
54H49Cl6NO2P2Rh
C47H39O5P2Rh
848.6
C45H36NO6P2Rh
851.6
C45H36NO5P2Rh
835.6
1121.5
orthorhombic
Pnma (No. 62)
18.560(7)
18.230(6)
15.182(4)
monoclinic
P21/c (No. 14)
10.967(4)
31.117(16)
11.698(6)
93.02(4)
3987(3)
4
monoclinic
P21/n (No. 14)
21.086(10)
10.216(6)
21.309(7)
118.70(3)
4026(3)
4
monoclinic
P21/c (No. 14)
17.885(10)
9.930(3)
22.060(9)
94.43(4)
3904(3)
4
b, Å
c, Å
â, deg
V, Å3
5137(3)
4
Z
λ, Å
0.710 73
7.49
1.450
22
3.79
4.36
0.710 73
5.56
1.414
22
4.10
0.710 73
5.54
1.408
22
4.12
0.710 73
5.67
1.422
22
3.63
µ, cm-1
D
calcd, g cm-3
temp, °C
R,a %
R,b %
4.99
1.32
4.58
1.06
4.22
1.03
GOFc
1.29
a
b
2
2
R ) ∑||Fo| - |Fc|/∑|Fo|. Rw ) [∑w(||Fo| - |Fc|)2/∑w|Fo| ]1/2; w-1 ) σ2|Fo| + g|Fo| . g ) 0.004 for 5b‚2CH2Cl2, 0.002 for 6b, 0.0002 for
7, and 0.0003 for 8b. c The goodness of fit is defined as [∑w(|Fo| - |Fc|)2/(no - nv)]1/2, where no and nv denote the numbers of data and
variables, respectively.
evaporated. the yellow aqueous suspension of 6b was filtered,
washed with water, and dried in vacuo. Yield: 98%.
e. Rh (La l)(P P h 3)2Cl (8a ) to Rh (La l)(P P h 3)2(NO3) (7). Use
of NaNO3 instead of NaCO2Me in the above procedure afforded
7. Yield: 94%.
f. Rh (Lal)(P P h 3)2Cl (8a ) to Rh (Lal)(P P h 3)2(NO2) (8b). Use
of NaNO2 in place of NaCO2Me in procedure d above furnished
8b. Yield: 98%.
g. Rh (La l)(P P h 3)2(NO2) (8b) to Rh (La l)(P P h 3)2Cl (8a ). To
a stirred solution of Rh(Lal)(PPh3)2(NO2) (50 mg, 0.05 mmol)
in ethanol (20 mL) was added 0.3 N aqueous HCl (5 mL). The
stirring was continued for 0.5 h. After the organic solvent was
evaporated, the residue 8a was extracted with water and
finally isolated by filtration. It was washed repeatedly with
water and dried in vacuo. Yield: 95%.
h . Rh (La l)(P P h 3)2(MeCO2) (6b) to Rh (La l)(P P h 3)2Cl (8a ).
This was achieved by using Rh(Lal)(PPh3)2(MeCO2) in place of
Rh(Lal)(PPh3)2(NO2) in procedure g. Yield: 97%.
In each case the metal atom was located from a Patterson
map; the rest of the non-hydrogen atoms emerged from
successive Fourier synthesis. The structures were refined by
full-matrix least-squares procedures. All the non-hydrogen
atoms were refined anisotropically, and the hydrogen atoms
of 5b‚2CH2Cl2, 6b, and 7 were added at calculated positions
with fixed U ) 0.08 Å2. All the hydrogen atoms of 8b were
located by difference Fourier maps and refined with a fixed U
) 0.08 Å2 using a riding model. The highest residuals were
0.33 e Å-3 (5b‚2CH2Cl2), 0.92 e Å-3 (6b), 0.94 e Å-3 (7), and
0.50 e Å-3 (8b) near the metal atom. All calculations were done
on a MicroVax II computer using the SHELXTL-PLUS pro-
gram package.31 Significant crystal data are listed in Table 5.
Com p u ta tion of Ch em ica l Sh ift Du e Rin g Cu r r en ts.
The parameters taken from the crystallographic data of 5b‚
2CH2Cl2, 6b, 7, and 8b are (i) distance of the concerned proton
from the centroid (G) of each PPh3 phenyl ring and (ii) the
angle between each distance vector and the normal to the
plane of the phenyl ring at G. From these parameters the
cylindrical coordinates32 F and z of the proton involved were
calculated in units of the radius of the benzene hexagon. With
the help of isoshielding plots20 and F, z values the shifts were
calculated. The net shifts were obtained after summation of
the individual contributions. Further details are given in a
dissertation.33
i. Rh (La l)(P P h 3)2(NO3) (7) to Rh (La l)(P P h 3)2Cl (8a ). Rh-
(Lal)(PPh3)2(NO3) was used instead of Rh(Lal)(PPh3)2(NO2) in
procedure g. Yield: 98%.
Rea ction of 1 (X ) OMe) w ith Rh Cl(P P h 3)3 in th e
Absen ce of HCl. To a solution of 2-formyl-4-methyl-6-((p-
methoxyimino)methyl)phenol (22 mg, 0.08 mmol) in hot etha-
nol (25 mL) was added RhCl(PPh3)3 (50 mg, 0.05 mmol). The
mixture was heated to reflux for 0.5 h. Upon cooling, bright
yellow crystalline trans-Rh(CO)Cl(PPh3)2 separated out. It was
collected by filtration, washed thoroughly with cold ethanol,
and dried in vacuo. Yield: 36 mg (98%). The same result was
obtained irrespective of the X substituent.
X-r a y Str u ctu r e Deter m in a tion s. Single crystals of 5b‚
2CH2Cl2 (0.40 × 0.30 × 0.25 mm3) and 6b (0.50 × 0.40 × 0.35
mm3), 7 (0.20 × 0.30 × 0.30 mm3), and 8b (0.20 × 0.20 × 0.35
mm3) were grown by slow diffusion of hexane into dichloro-
methane and benzene solutions, respectively. To avoid loss of
solvent and crystallinity 5b‚2CH2Cl2 was mounted in a sealed
capillary over mother liquor. Cell parameters were determined
by a least-squares fit of 30 machine-centered reflections (2θ
) 15-30°). Data were collected by the ω-scan technique in the
ranges 3° e 2θ e 46° for 5b‚2CH2Cl2, 3° e 2θ e 45° for 6b, 3°
e 2θ e 48° for 7, and 3° e 2θ e 45° for 8b on a Siemens R3m/V
four-circle diffractometer with graphite-monochromated Mo
KR radiation (λ ) 0.710 73 Å). Two check reflections measured
after every 198 reflections showed no significant intensity
reduction in all cases. All data were corrected for Lorentz-
polarization effects, and an empirical absorption correction30
was done on the basis of an azimuthal scan of six reflections
for each crystal.
Ack n ow led gm en t. We are thankful to the Indian
National Science Academy, New Delhi, India, the De-
partment of Science and Technology, New Delhi, India,
and the Council of Scientific and Industrial Research,
New Delhi, India, for financial support. Affiliation with
the J awaharlal Nehru Centre for Advanced Scientific
Research, Bangalore, India, is acknowledged.
Su ppor tin g In for m ation Available: For Rh(MeLsb)(PPh3)2-
Cl2‚2CH2Cl2 (5b‚2CH2Cl2), Rh(Lal)(PPh3)2(MeCO2) (6b), Rh-
(Lal)(PPh3)2(NO3) (7), and Rh(Lal)(PPh3)2(NO2) (8b ) all bond
distances (Tables S1, S6, S11, and S16) and angles (Tables
(30) North, A. C. T.; Phillips, D. C.; Mathews, F. A. Acta Crystallogr.,
Sect. A 1968, A24, 351.
(31) Sheldrick, G. M. SHELXTL-Plus Structure Determination
Software Programs; Siemens Analytical X-ray Instruments Inc.,
Madison, WI, 1990.
(32) Margenan, H.; Murphy, G. M. The Mathematics of Physics and
Chemistry; Van Nostrand: Princeton, NJ , 1956.
(33) Pattanayak, S. Chemistry of New Coordination and Organo-
metallic Compounds of d-Block Elements. Ph.D. Thesis, J adavpur
University, Calcutta, India, 1998.

1494 Organometallics, Vol. 18, No. 8, 1999
Pattanayak et al.
S2, S7, S12, and S17), anisotropic thermal parameters (Tables
S3, S8, S13, and S18), hydrogen atom positional parameters
(Tables S4, S9, S14, and S19), and non-hydrogen atomic
coordinates and U values (Tables S5, S10, S15, and S20). This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM980748E