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Novel Neutral and Anionic Rhodium Complexes Containing Imido Ligands.

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COMMUNICATIONS
Novel Neutral and Anionic Rhodium Complexes
Containing Imido Ligands**
P ' O '
Cristina Tejel, You-Mao Shi, Miguel A. Ciriano*,
A n d r e w J. Edwards, Fernando J. L a h o z , and
Luis A. Oro*
The interest in the chemistry of transition metal imido complexes has grown substantially in recent years."] These compounds are believed to be intermediates in many important catalytic processes such as propene amrnoxidation,['I nitrile
imide group tran~fer.1~1
and reduction and carbonylation of n i t r ~ a r e n e s , [and
~ ] they are models for the Haber
ammonia synthesis. Whereas the majority of complexes with
imido ligands contain early transition metals in high oxidation
states. few imido complexes are known for the late transition
metals in low oxidation states.[61Dinuclear amido-imido tautomers, which are stabilized by dppm bridging ligands (dppm =
methylenebis(diphenyIphosphane)), are the only examples of
such complexes with rhodium in a low oxidation state.['*] We
report here on the first neutral and anionic clusters of rhodium
bridged by imido ligands. These novel compounds, which contain diene and carbonyl groups as ancillary ligands, possess new,
interesting bonding and structural features.
Reactions of equimolar amounts of the complexes [{Rh(pCl)(diene)) with a solution of para-toluidine and butyllithium
(in a 1 : 2 molar ratio) in diethyl ether at room temperature
afforded complexes of the type [Rh,(p-N-tolyl),(diene),]
(diene = 1.5-cyclooctadiene (cod) (1). tetrafluorobenzobarrelene (tfb) (2)) as dark red crystalline solids in high yields. Characterization of the new complexes as imido clusters was based
on spectroscopic data and an X-ray crystal structure analysis.["
In the neutral tetranuclear complex 1 (Fig. 1) two parn-tolylimido ligands cap either side of a trirhodium triangle through
their nitrogen atoms, while the ring of the phenyl group of one
of these ligands coordinates an isolated [Rh(cod)] fragment.
Three remaining cyclooctadiene ligands are each bound to a
rhodium atom of the trinuclear triangular core. which consists
of two clearly bonded edges and one slightly longer, apparently
nonbonded edge. Discounting the metal -metal interactions,
each rhodium atom in the trimetallic core, is essentially squareplanar coordinated. The molecular structure of 1 found in the
crystal is also maintained in solution. The ' H N M R spectra of
1 and 2 reveal the presence of two types of phenyl rings, each
showing a well-defined A,B, pattern. one of which, as a result
of the x coordination to the fourth Rh atom, is shifted to higher
field by approximately 1 ppm. Furthermore. signals for two
types of diene ligands appear in the ratio 3: 1, which are attributed to the ligands at the trimetallic core and to that bonded to the
isolated rhodium atom, respectively. Complex 1 is the first example of an it,-iinido rhodium system. Within 1, the average
Kh --N bond lengths differ significantly (0.04 A) between the
two face-capping ligands, unlike in comparable examples such
as [OS,(NC,H~)~(CO),].[~]
where they are essentially equivalent. The ri5-cyclohexadienyl-likecoordination of the imido lig[*] Dr M . A C.triaiio. Prof 1.A Oro, Dr. C. Tejel. Dr Y.-M. Shr.
D r A .I. E d b d r . Dr. F. .I. Laho/
Dep.irt;imcntc dc Quimrca Inorg8nrc.a
In\trtuto de ('iencia de Materiales de Aragon
Unr~crsidaddc Zaragora-C.S I .C.. E-j0009-Zai-agora (Spain)
FCi.x:
I n [ . codc + (761761143
[**I
Wc t h m k the Diieccion General de Investigation fientifica y Tkcnica ( D G I ~
C'YT) for lin.incrnl support (Projects PB94-1186 and PB92-86-C2) and for a
felloL<shipt o YM
:
S. (on leave from Dalian Institute of Chemical Physics.
c'hrnc\c Acadcm) of Sciences) iind the European Community Human Capital
and ivlohilrt! I'rogrnm (CT93-0347) for a fellowship to A. J. E.
Fig. 1. Molecular structure of I . Selected Interatomic distances [A] and angles [ 1:
Rh(ZI-Rh(3) 2.765(1), Rh(2)-Rh(4) 2.774(1), Rh(3) - Rh(4) 3.108(1). Rh(Z)-N(I)
2.107(3). Rh(2)-N(2) 2.1 12(3). Rh(3)-N(1) 2.088(3). Rh(3)-h'(2) 2.058(3). Rh(4)N(1) 2.139(3). Rh(4)-N(2) 2.043(3). N(1)-C(11) 1.355(5), N(Z)-C(21) 1.422(6),
Rh(l)-C(12)jC(16) 2.224 -2.375(5). Rh(1). . -C(11) 2 576(11). Rh(3)-Rh(2)-Rh(4)
68.27(3), Rh(Z)-Rh(3)-Rh(4) 56.00(2). Rh(2)-N(I)-Rh(3) 82.5(1), Rh(2)-N(l)Rh(4) 81.6(1). Rh(3)-N(l)-Rh(4) 94 7(1), C(ll)-N(l)-Rh(2) 138.2(3). C(ll)-N(l)Rh(3) 130.8(3), C(ll)-N(l)-Rh(4) 114.1(3). Rh(2)-N(2)-Rh(3)X3.0(1). Rh(2)-N(2)Rh(41 83.8(1). Rh(3)-N(?)-Rh(4) 98.6(1). C(21)-N(?)-Rh(Z) 138.1(3).
C(21)-N(2)-Rh(3) 119.7(3). C(21)-N(2)-Rh(4) 122 2(3).
and to the fourth rhodium atom follows from the deviation of
the ifso carbon from the ring plane by 17.4(4) and from the
Rh-C,,,, distance which is 0.294 A longer than the average
R h - C distance for this ligand. Associated with this peculiar q5
coordination is a dramatic shortening of the C,,,,-N bond,
indicative of clear partial C - N double bond ~haracter.~']
These
data suggest a charge delocalization from the nitrogen atom into
the ring. Furthermore, attempts to isolate pentanuclear complexes by coordination of mononuclear cationic species such as
[Rh(cod)S,]BF, (S = solvent) at the free phenyl group have
proved unsuccessful, since 1 lacks coordination sites with sufficient electron density. However. the iniido nitrogen atom still
possesses nucleophilic character, since complexes 1 and 2 react
slowly with methanol to give the known methoxo complexes
[{Rh(p-OMe)(diene)),] and para-toluidine.
Complexes 1 and 2 can be considered, in a simplified way, to
be related to the known species [Rh(cod)BPh,], where the
trimetallic core takes the role of the BPh, ion. However, in our
case the q5 coordination of the imido ligand seems to be nonlabile when compared with xi-coordinated arene hgands in corresponding complexes of
With this in mind, the
preparation of p3-imido anionic complexes, for example [Rh,(pN-t~lyl)~(tfb),]-.requires the formation of very stable cations
such as [Rh(CNtBu),]'. Thus, reaction of 2 with excess CNtBu
leads to the rupture of the Rh-n-cyclohexadienyl interaction,
yielding the anionic imidorhodium cluster [Rh,(p-Ntolyl),(tfb),][Rh(CNtBu),l3 (Scheme 1). Complex 3 is isolated
as a yellow crystalline solid in 75 YOyield and shows the expected
spectroscopic features. Thus, the anion is detected in the negative ion FAB mass spectrum, and the para-tolylimido groups are
equivalent in the 'H and 13C{*H]N M R spectra (Table 1). Furthermore, the ortho carbon atoms give rise to quartets in the
13C{'H) N M R spectrum because of coupling with three equivalent Rh nuclei, while the lpso carbon atoms give a broad
singlet. Complex 3 is the first characterized anionic imido complex of rhodium which, despite the low oxidation state of the
COMMUNICATIONS
1-
which is isolated in 90% yield as a yellow microcrystalline solid.
Further studies on the reactivity of the electron-rich complexes
3 and 4 are in progress.
In conclusion, neutral and anionic imidorhodium(1) clusters
are feasible and stable and could possibly be intermediates in the
catalytic reduction and carbonylation of nitroarenes by Rh
complexes.
Experimental Procedure
General synthesis of I and 2: Solid [iRh(~~-Cl)(diene)],]
(0.5 mmol) was added to a
solution of para-toluidine (0.5 mmol) and butyllithium (1 .0 mmol) in diethyl ether
at room temperature to give a dark red solid. Further extraction with
dichloromethane and work up yielded the complexes 1 and 2 as crystalline solids.
Received: September 15, 1995
Revised version: December 11. 1995 [Z 8404 IE]
German version: Angeu. Chem. 1996, 108, 707-709
4
Scheme 1. Reactions of complexes 1 and 2 L L
(2, 3).
=
diene ligand: cod (1. 4). tfb
Keywords: arene complexes . clusters . complexes with nitrogen
ligands . rhodium compounds
111 D. E. Wigley. frog. 1nor-g. Chem. 1994, 42, 239. and references therein; W A.
Nugent. J. M. Mayer, Mefal-Ligand Multiple Bonds, Wiley. New York, 1988.
[2] E A. Maatta. Y. J. Du. 1 Am. Chem. SOC.1988, 110. 8249, and references
1: 'H NMR (CD2C12,298 K): 6 = 6.61 (aA, 2H. Ph). 6.32 ( b R ,JAR
= 8.4 Hz, 2H.
therein.
=7.0 Hz, 2H, Ph"), 4.18 (br. s, 4H, =CH").
Ph), 5.60 (aA. 2H, Ph"), 5.36 (aR,JAR
[3] a) M. Bakir. P. E. Fanwick. R. A. Walton, Inorg. Chem. 1988, 27. 2016;
3.54(br.s,12H. =CH),2.44(m,12H,CH,),2.33(m,4H,CH",.2.17(~,3H,Me),b) S. H. Han, G. L. Geoffroy, Pol.yhedron 1988, 7, 2331
2.08 (s, 3H, Me?, 2.01 (d, 8.24, 4H. CH;), 1.84 (d, 7.69, 12H, CH,);
[4] a) P. J. Walsh. A. M. Baranger, R. G. Bergman, J. A m . Chem. Sor. 1992, 114,
"C{'H) NMR (CD,CI,, 298 K): 6 =166.7 (br. s, ipso-C. Ph), 161.5 (br. s, ipso-C,
1708; b) D. A. Evans, M. M. Faul, M. T. Bilodeau, J. Org. Chem. 1991, 56,
Ph')), 130.0 (C4, Ph), 126.8 (C3, Ph). 125.2 (9, J(Rh,C) = 1 Hz, C2. Ph). 107.5 (d.
6744.
4Rh.C) = 2 Hz, C4. Ph"). 101.7 (d, J(Rh,C) = 3 Hz, C3. Ph"), 94.0 (m, C2, Pha),
[5] a) F. Ragaini. S. Cenini. F. Demartin, Orgunomefallics1994, 13, 1178; b) J. D.
77.0 (d, J(Rh.C) = 13 Hz, =CH), 73.4 (br. s, =CH"), 31.9 (CH,). 31.1 (CH",). 20.4
Gargulak. W. L. Gladfelter, J. A m . Chem. SOC.1994, 116, 3792.
(Me), 18.6 (Me'); MS (FAB'): m / z (Oh):1054 (M', 5). 843 ( M + - Rh(cod). 48)
[6] a) Rhodium complexes: Y-W. Ge, E Peng, P. R. Sharp, J. Am. Chem. SOC.
2: 'H NMR (CDZCl,, 298 K). 6 = 6.46 (JA, 2H, Ph). 5.96(6,. 2H, Pha). 5.82 (aR.
1990, 112. 2632: b) iridium complexes: C. Ye, P. R. Sharp, Inorg. Chem. 1995,
J,,=8.2OHz,2H,Ph).5.34(6,.J,,=7.1
Hz,2H,Pha),553(br.s.6H,HC),5.04 34, 55; D A. Dobbs. R. G. Bergman, Organometallics 1994, 13, 4594; M. K.
(br. S , 2H, HC"), 3.62 (br. s, 4H , =CH"), 3.19 (br. s, 6H, =CH), 3.06 (br. s. 6H.
Kolel-Veetil. K. J. Ahmed, Inorg. Chem. 1994,33.4945, and references therein;
c) recent ruthenium and osmium compounds: A. K. Burrel. A. J. Steedman,
=CH), 1.97 (s. 3H, Me), 1.91 (s. 3H, Me')); I9F NMR (CD,CI,. 298 K).
6 = -146.6 (m, 2F'), -148.9 (m. 6F ). -158.7 (m. 2F"). -162.1 (m, 6 F ) ; MS
J. Chem. Soc. Chem. Commun. 1995, 2109, D. L. Ramage, G. L. Geoffroy.
(FAB'): mi: (%): 1526 ( M i , 10). 1197 ( M ' - Rh(tfb). 30)
A. L. Rheingold. B. S. Haggerty, Orgunometallics 1992, I t , 1242.
[7] Crystal data for 1: C,,H,,N,Rh,. C,H,O, M, =1126.74, monoclinic, space
3. IR (Nujol): L: = 2156 (s) cm-' (CN); 'H NMR (CD'CI,. 298 K)- 6 = 6.43 (aA.
group f 2 J n (No. 14). u =17.912(4), h =12.419(2), c = 20.649(4)A, p =
4H. Ph), 6.05 (&, JAR= 8 2 Hz, 4H. Ph). 5.42 (br. s. 6H. HC), 2.95 (br. s, 12H.
105.41(3)". V = 4428(2) A', Z = 4. pcalEd
= 1.690 gcm-'. F(000) = 2288, E. =
=CH). 1.98 (s, 6H, Me). 1.53 (t. 36H, CNfBu); I9F NMR (CD,CI,, 298 K):
0.71073 8, T = 173.0(2) K, p(MoKI)= 1SO4 mm-' Data were collected on a
6 = -150.2(m,6F). -164.1 (m.6F);'3C('H)-NMR(CD,CI,,298K):6=163.7
(br.s,ipso-C,Ph),140.2(C4,Ph).137.5(m,tfb),130.5(m,tfb)129.0(m,tfb),126.9 Stoe AED diffractometer by using an oil-coated rapidly cooled crystal of dimensions 0.29 x 0.23 x 0.18 mm mounted directly from solution (T. Kottke, D.
(C3,Ph). 121.5(q,'J(Rh.C) = 1 Hz,C2,Ph),45.2(d,J(Rh.C) =10Hz. =CH. tfb).
Stalke, J Appl. Crysta//ogr. 1993, 26. 615). A total of 5665 unique reflections
39.9 (CH, tfb), 30.5 (CNtBu), 20.4 (Me); MS (FAB-): m/z (%): 1197 (anion
were collected by the 2 O/w method (3.5 c 2 0 s 45.0). The structure was solved
of 3, 78); MS (FAB'). mi; (Oh): 435 (cation of 3, 100); A , (aceton) =
by direct methods (SHELXTL PLUS, G. M. Sheldrick, Siemens Analytical
61.8 Scm'mol-'
X-ray Instruments, Inc.. Madison, WI 1990) and refined by full-matrix least4 IR (CH,CI,): L: = 2035 (m, CO), 2016 (s. CO), 1960 (s) cm-' (CO). IH NMR
squares on F' (SHELXL-93; G. M. Sheldrick, Gottingen, 1993) to R, =
(CDCI,, 298 K). 6 =7.03 ( h A , 2H, Ph), 6.79 (&,JAR= 8.3 Hz, 2H. Ph), 6.16 (a,,.
0.0264 [ F > 4u(F). for 4830 reflections] and R, = 0.0716 (all data)
2H. Ph'), 6.01 (6,, JAR =7.1 Hz. 2H, Ph"), 4.25 (m, 4H. =CHa). 2.92 (m, 2H.
=
- F:)2/xM'c}1'2.
M'=l/[u2(c)
=CH),2.66(m,2H, =CH),2.40(m,4H,H,C),2.24(m,4H,H2C),2.17(s.3H,[R,=XIIF\ - \ ~ \ l / x l &R2l s
( x P ) ~ r f ] ( u = 0.0358, 4' = 8.1612), P = (F: + 2F:)/3]. A THF molecule
Me). 2.07 (s. 3H. Me'). 2.06 (m, 4H. H,C), 1.66 (m. 4H. H,C); ''C{'H} NMR
was located and found to be disordered over two sites, these were modelled at
(CD2CI2. 298 K): 6 ~ 1 9 1 . (d,
3 J(Rh,C) = 65 Hz, CO), 191.2 (d, J(Rh.C) =71 Hz,
50% occupancy. All non-hydrogen atoms were refined anisotropically, with
CO), 160.9(br. s,ipso-C, Ph), 155.0(br. s, ipso-C. Ph'), 130.3 (C4, Ph). 127.6(C3,
the exception of disordered oxygen and carbon atoms in the TH F solvate
Ph), 124.7 (4. 'J(Rh.C) = I Hz, C2, Ph). 108 7 (d, J(Rh.C) = 3 Hz, C4. Ph"). 103.5
molecule. Ail hydrogen atoms riding on sp2 carbon atoms were located and
(d, J(Rh,C) = 3 Hz, C3, Ph"), 99.0 (dq, '4Rh.C) = 3, 'J(Rh,C) = 1 Hz, C2, Ph").
allowed to freely refine isotropically, the remaining hydrogen atoms were fixed
80.7 (d. J(Rh.C)=13Hz. =CH"). 76.9 (d. J(Rh,C)=14Hz. =CH), 75.5 (d.
in idealized positions with thermal parameters (1.2 times that of the corre4Rh.C) =12Hz. =CH). 31.9 (H2Ca),31.2 (H2C), 31.0 (H,C). 20.4 (Me). 18.4
sponding parent carbon atom). Largest peak and hole in the final difference
(Me'); MS (FAB+): rnjr (%): 950 (M +.87),922 ( M - CO, 66). 894(M + - 2CO.
map 0.528and -0.362 eA-'. Further detailsofthecrystal structure investiga17). 866 (M' - 3C 0, 20). 838 ( M ' - 4 C 0 , 70)
tion are available on request from the Director of the Cambridge Crystallographic Data Centre, 12 Union Road. GB-Cambridge, CB2lEZ (UK), on
[a] The new compounds give satisfactory C.H.N. elemental analyses; the superquoting the full journal citation.
fragment; H.H-COSY experiments,
script a denotes the ~5-(~~-N-p-tolyl)Th(diene)
[8] J. A. Smieja. W. L. Gladfelter, Inorg. Chem. 1986, 25. 2667.
and high-resolution processing of the I3C{'HI NMR spectra were used for accurate
191 R. Uson. L. A. Oro. D. Carmona, M. A Esteruelas, C. Foces-Foces. F. H.
assignments.
Cano. S. Garcia-Blanco. A. Vdzquez de Miguel, J. Organomef. Chem. 1984,
273.111.
[lo] M. Aresta. E. Quaranta. A. Albinati, Organometal/ics 1993.12,2039; R. Uson,
L. A. Oro. C. Foces-Foces. F. H. Cano. S. Garcia-Blanco. M. Valderrama, J.
metals and the high electronic density (hard-base character) of
Orgunomef. Chem. 1982, 229. 293.
Table 1. Selected physical data of complexes 1-4 pa].
+
{x.W(c
+
+
~
~~~~~~~
the imido ligand, is surprisingly stable. Substitution of the ancillary ligands in the periphery of the trinuclear core of 1 by carbon
monoxide reveals the inequivalence of the metals within this
triad. Thus, reaction of 1 with carbon monoxide at room temperature leads to [Rh,(p-N-tolyl),(CO),(cod),] (4) (Scheme I ) ,
634
VCH Verlagsgesellschufi mhH, 0-694S1 Weinheim, 1996
0570-0833/96/3506-0634$ 15.00+ ,2510
Angew. Chem. Int. Ed. Engl. 1996, 35, N o . 6
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