Synthesis, Characterization, and Theoretical Studies on Heterobinuclear (p-cymene)Os(μ-pz)2M (M = Ir, Rh; Hpz = Pyrazole) Complexes

Article abstract of DOI:10.1021/om990624h

The cationic compounds [(η⁶-p-cymene)OsCl(Hpz)₂]A (A = Cl (1), BF₄ (2)) have been prepared by treating the dimeric [{(η⁶-p-cymene)OsCl}₂(μ-Cl)₂] with pyrazole (p-cymene = p-isopropylmethylbenzene, Hpz = pyrazole). Compounds 1 and 2 are precursors to new heterobinuclear complexes of stoichiometry [(η⁶-p-cymene)OsCl(μ-pz)₂M(COD)] (M = Ir (3), Rh (4); COD = 1,5-cyclooctadiene). Carbonylation of 3 and 4 produces the dicarbonyls [(η⁶-p-cymene)OsCl(μ-pz)₂M(CO)₂] (M = Ir (5a), Rh (6)) or, in the presence of NaBPh₄, the cationic tricarbonyls [(η⁶-p-cymene)Os(CO)(μ-pz)₂M(CO) ₂]BPh₄ (M = Ir (7), Rh (8)). Complex 5a in methanol isomerizes to the metal-metal-bonded compound [(η⁶-p-cymene)Os(μ-pz)₂IrCl(CO)₂] (5b) (first-order kinetics in 5a; k_obs = 3.8 × 10^-4 s^-1 (room temperature), ΔH? = 93 kJ mol^-1, ΔS? = 7 J K^-1 mol^-1). The molecular structures of [(η⁶-p-cymene)OsCl(μ-pz)₂Rh(CO)₂] (6) and [(η⁶-p-cymene)Os(CO)(μ-pz)₂Rh(CO) ₂]BPh₄ (8) have been determined by X-ray diffraction methods. In both cases, the molecules contain (η⁶-p-cymene)Os and Rh(CO)₂ moieties bridged by two pyrazolate groups. The osmium-rhodium distances, 3.6231(5) A? (6) or 3.7012(6) A? (8), exclude any direct intermetallic interaction. The metal-metal-bonded halide carbonyl complexes [(η⁶-p-cymene)Os(μ-pz)2Ir(CO)₂] (X = Br (9), I (10)) and [(η⁶-p-cymene)Os-(μ-pz)₂RhI(CO)] (12), as well as the OsRh compound [(η⁶-p-cymene)OsBr(μ-pz)₂Rh(CO)₂] (11), have been prepared by metathetical reaction on the corresponding dicarbonyls 5a,b and 6 with sodium halides. The molecular structures of 10 and 12 have been elucidated by diffractometric means. The metal-metal distances, 2.7196(6) A? (Os-Ir, 10) and 2.6936(9) A? (Os-Rh, 12), confirm the presence of metal-metal bonds. In the solid state, complex 12 crystallizes as a dimer of two dinuclear moieties through an asymmetric diiodide bridge. A theoretical study of the related RuIr dicarbonyl chloride isomers [(η⁶-p-cymene)RuCl(μ-pz)₂Ir-(CO)₂] (13a) and [(η⁶-p-cymene)Ru(μ-pz)₂IrCl(CO)₂] (13b) is also reported.

Full text of DOI:10.1021/om990624h

798
Organometallics 2000, 19, 798-808
Syn th esis, Ch a r a cter iza tion , a n d Th eor etica l Stu d ies on
Heter obin u clea r (p-cym en e)Os(µ-p z)2M (M ) Ir , Rh ; Hp z
) P yr a zole) Com p lexes
Daniel Carmona,* J oaquina Ferrer, J ose´ M. Arilla, J osefa Reyes,
Fernando J . Lahoz, Sergio Elipe, F. J avier Modrego, and Luis A. Oro*
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-Consejo Superior de Investigaciones Cientı´ficas,
50009 Zaragoza, Spain
Received August 4, 1999
The cationic compounds [(η6-p-cymene)OsCl(Hpz)2]A (A ) Cl (1), BF4 (2)) have been
prepared by treating the dimeric [{(η6-p-cymene)OsCl}2(µ-Cl)2] with pyrazole (p-cymene )
p-isopropylmethylbenzene, Hpz ) pyrazole). Compounds 1 and 2 are precursors to new
heterobinuclear complexes of stoichiometry [(η6-p-cymene)OsCl(µ-pz)2M(COD)] (M ) Ir (3),
Rh (4); COD ) 1,5-cyclooctadiene). Carbonylation of 3 and 4 produces the dicarbonyls [(η6-
p-cymene)OsCl(µ-pz)2M(CO)2] (M ) Ir (5a ), Rh (6)) or, in the presence of NaBPh4, the cationic
tricarbonyls [(η6-p-cymene)Os(CO)(µ-pz)2M(CO)2]BPh4 (M ) Ir (7), Rh (8)). Complex 5a in
methanol isomerizes to the metal-metal-bonded compound [(η6-p-cymene)Os(µ-pz)2IrCl(CO)2]
(5b) (first-order kinetics in 5a ; kobs ) 3.8 × 10-4 s-1 (room temperature), ∆Hq ) 93 kJ mol-1
,
∆Sq ) 7 J K-1 mol-1). The molecular structures of [(η6-p-cymene)OsCl(µ-pz)2Rh(CO)2] (6)
and [(η6-p-cymene)Os(CO)(µ-pz)2Rh(CO)2]BPh4 (8) have been determined by X-ray diffraction
methods. In both cases, the molecules contain (η6-p-cymene)Os and Rh(CO)2 moieties bridged
by two pyrazolate groups. The osmium-rhodium distances, 3.6231(5) Å (6) or 3.7012(6) Å
(8), exclude any direct intermetallic interaction. The metal-metal-bonded halide carbonyl
complexes [(η6-p-cymene)Os(µ-pz)2Ir(CO)2] (X ) Br (9), I (10)) and [(η6-p-cymene)Os-
(µ-pz)2RhI(CO)] (12), as well as the OsRh compound [(η6-p-cymene)OsBr(µ-pz)2Rh(CO)2] (11),
have been prepared by metathetical reaction on the corresponding dicarbonyls 5a ,b and 6
with sodium halides. The molecular structures of 10 and 12 have been elucidated by
diffractometric means. The metal-metal distances, 2.7196(6) Å (Os-Ir, 10) and 2.6936(9)
Å (Os-Rh, 12), confirm the presence of metal-metal bonds. In the solid state, complex 12
crystallizes as a dimer of two dinuclear moieties through an asymmetric diiodide bridge. A
theoretical study of the related RuIr dicarbonyl chloride isomers [(η6-p-cymene)RuCl(µ-pz)2Ir-
(CO)2] (13a ) and [(η6-p-cymene)Ru(µ-pz)2IrCl(CO)2] (13b) is also reported.
In tr od u ction
chiometry [RuM(p-cymene)X(Pz)2(CO)2] (M ) Rh, Ir;
p-cymene ) p-isopropylmethylbenzene; X ) Cl, Br, I;
Pz ) pyrazolate (pz), 3-substituted pyrazolate).5f,6 The
RuIr chloride compounds were isolated as mixtures of
two isomers whose separation was achieved only in
some instances. The complexes were independently
In the field of organometallic chemistry the area of
bimetallic complexes bonded to flexible and firmly
binucleating anionic ligands has aroused increased
interest. Of particular interest are the very versatile
pyrazolate ligands, which can straddle an unusually
wide range of intermetallic separations to hold two
adjacent metal centers in chemically stable configura-
tions.1
While an extensive chemistry on homobinuclear rhod-
ium,2 iridium,3 and ruthenium4 complexes with pyra-
zolate bridging ligands has been thoroughly investi-
gated, heterobinuclear complexes containing platinum-
group metals have been scarcely studied.5
(2) (a) Uso´n, R.; Oro, L. A.; Ciriano, M. A.; Pinillos, M. T.; Tiripicchio,
A.; Tiripicchio-Camellini, M. J . Organomet. Chem. 1981, 205, 247. (b)
Uso´n, R.; Oro, L. A.; Ciriano, M. A.; Carmona, D.; Tiripicchio, A.;
Tiripicchio-Camellini, M. J . Organomet. Chem. 1982, 224, 69. (c) Oro,
L. A.; Carmona, D.; Lamata, M. P.; Apreda, M. C.; Foces-Foces, C.;
Cano, F. H.; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1984, 1823.
(d) Elguero, J .; Esteban, M.; Grenier-Loustalot, M. F.; Oro, L. A.;
Pinillos, M. T. J . Chim. Phys. 1984, 81, 251. (e) Oro, L. A.; Carmona,
D.; Lamata, M. P.; Foces-Foces, C.; Cano, F. H. Inorg. Chim. Acta 1985,
97, 19. (f) Oro, L. A.; Carmona, D.; Pe´rez, P. L.; Esteban, M.; Tiripicchio,
A.; Tiripicchio-Camellini, M. J . Chem. Soc., Dalton Trans. 1985, 973.
(g) Carmona, D.; Oro, L. A.; Pe´rez, P. L.; Tiripicchio, A.; Tiripicchio-
Camellini, M. J . Chem. Soc., Dalton Trans. 1989, 1427. (h) Carmona,
D.; Lamata, M. P.; Esteban, M.; Lahoz, F. J .; Oro, L. A.; Apreda, M.
C.; Foces-Foces, C.; Cano, F. H. J . Chem. Soc., Dalton Trans. 1994,
159. (i) Tejel, C.; Villoro, J . M.; Ciriano, M. A.; Lo´pez, J . A.; Eguiza´bal,
E.; Lahoz, F. J .; Bakhmutov, W. I.; Oro, L. A. Organometallics 1996,
15, 2967.
In this context, we have previously reported a series
of heterobinuclear RuM dicarbonyl complexes of stoi-
(1) (a) Trofimenko, S. Prog. Inorg. Chem. 1986, 34, 115. (b) Oro, L.
A.; Carmona, D.; Esteban, M. Trends Organomet. Chem. 1994, 1, 565.
(c) La Monica, G.; Ardizzoia, G. A. Prog. Inorg. Chem. 1997, 46, 151.
10.1021/om990624h CCC: $19.00 © 2000 American Chemical Society
Publication on Web 02/04/2000

Heterobinuclear (p-cymene)Os(µ-pz)2M Complexes
Organometallics, Vol. 19, No. 5, 2000 799
Sch em e 1. Solu tion Equ ilibr iu m for th e Ru Ir
Ru(µ-pz)2IrX(CO)2] and, in contrast, only the non-
metal-metal-bonded isomer was observed for the RuRh
chloride compounds [(η6-p-cymene)RuCl(µ-Pz)2Rh(CO)2].
Furthermore, the related C5Me5 dicarbonyl derivatives
[(η5-C5Me5)MX(µ-pz)2M′(CO)2] (M, M′ ) Rh, Ir; X ) Cl,
I, N3) only adopt nonbonded structures of the type I.5f,8
The RuIr bromide or iodide, the RuRh chlorides, nor the
C5Me5 related compounds undergo the aforementioned
isomerization process, even under more forcing condi-
tions (reflux in toluene). To shed some light on this
peculiar isomerization process, we extended our inves-
tigations to include related (p-cymene)Os complexes and
carried out a theoretical study in an attempt to establish
the influence of the M′ metal and halogen on the relative
stabilities of structures I and II. The results of our study
are described in this paper.
Com p lexes [(η6-p-cym en e)Ru Cl(µ-P z)2Ir (CO)2] a n d
[(η6-p-cym en e)Os(µ-P z)2Ir Cl(CO)2]
Resu lts a n d Discu ssion
Heter obim eta llic OsIr a n d OsRh Com p lexes. (a )
Mon on u clea r (p-cym en e)Os P r ecu r sor s. The cat-
ionic chloride [(η6-p-cymene)OsCl(Hpz)2]Cl (1) can be
quantitatively prepared by treating methanolic suspen-
sions of the dimer9 [{(η6-p-cymene)OsCl}2(µ-Cl)2] with
4 equiv of Hpz (eq 1). The addition of 2 equiv of pyrazole
characterized, and the molecular structures, determined
by diffractometric methods6a for the unsubstituted pyra-
zolate derivatives [(η6-p-cymene)RuCl(µ-pz)2Ir(CO)2] and
[(η6-p-cymene)Ru(µ-pz)2IrCl(CO)2], are schematically
represented as I and II, respectively, in Scheme 1.
Interestingly, an equilibrium of the two isomers I
and II, which implies the migration of the chloride
ligand between the metals accompanied by the re-
versible cleavage and formation of a Ru-Ir bond, is
reached in solution. This kind of isomerization, which
takes place under mild conditions, is very unusual.7 In
fact, only structures of the type II have been detected
for the bromide and iodide analogues [(η6-p-cymene)-
[{(η6-p-cymene)OsCl}2(µ-Cl)2] + 4Hpz f
2[(η6-p-cymene)OsCl(Hpz)2]Cl
(1)
1
to a dichloromethane solution of [{(η6-p-cymene)OsCl}2-
(µ-Cl)2] led to a mixture of neutral10 [(η6-p-cymene)-
OsCl2(Hpz)] and 1 in a ca. 5.5:1 ratio, along with
unreacted starting material. The formation of cationic
1 could not be avoided, even by use of less than 2 equiv
of Hpz. However, the related ruthenium5a,b,6b ([(η6-p-
cymene)RuCl2(HPz)]) and rhodium or iridium3c ([(η5-
C5Me5)MCl2(HPz)]) neutral compounds can be isolated
in good yield by starting from the corresponding dimers
and using the procedure described above. Noncoordi-
nating anions such as BF4 can metathetically replace
the ionic chloride in 1 to give [(η6-p-cymene)OsCl(Hpz)2]-
BF4 (2). Complexes 1 and 2 were characterized on the
basis of elemental analysis and NMR and IR spectros-
copy (see Experimental Section). The IR spectra in Nujol
mulls exhibit an intense11 ν(NH) band at 3321 cm-1
along with a very broad, medium-intensity ν(NH)
absorption in the 2500-3200 cm-1 region, which sug-
gests that a strong hydrogen bond is present in the solid
(3) (a) Oro, L. A.; Pinillos, M. T.; Royo, M.; Pastor, E. J . Chem. Res.,
Synop. 1984, 206. (b) Oro, L. A.; Carmona, D.; Puebla, M. P.; Lamata,
M. P.; Foces-Foces, C.; Cano, F. H. Inorg. Chim. Acta 1986, 112, L11.
(c) Carmona, D.; Oro, L. A.; Lamata, M. P.; Puebla, M. P.; Ruiz, J .;
Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1987, 639. (d) Sola, E.;
Bakhmutov, W. I.; Torres, F.; Elduque, A.; Lo´pez, J . A.; Lahoz, F. J .;
Werner, H.; Oro, L. A. Organometallics 1998, 17, 683. (e) Beveridge,
K. A.; Bushnell, G. W.; Stobart, S. R.; Atwood, J . L.; Zaworotko, M. J .
Organometallics 1983, 2, 1447. (f) Atwood, J . L.; Beveridge, K. A.;
Bushnell, G. W.; Dixon, K. R.; Eadie, D. T.; Stobart, S. R.; Zaworotko,
M. J . Inorg. Chem. 1984, 23, 4050. (g) Bushnell, G. W.; Fjeldsted, D.
O.; Stobart, S. R.; Zaworotko, M. J .; Knox, S. A. R.; Macpherson, K. A.
Organometallics 1985, 4, 1107. (h) Bushnell, G. W.; Decker, M. J .;
Eadie, D. T.; Stobart, S. R.; Vefghi, R.; Atwood, J . L.; Zaworotko, M. J .
Organometallics 1985, 4, 2106. (i) Bailey, J . A.; Grundy, S. L.; Stobart,
S. R. Inorg. Chim. Acta 1996, 243, 47. (j) Arthurs, M. A.; Bickerton,
J .; Stobart, S. R.; Wang, J . Organometallics 1998, 17, 2743.
(4) (a) Oro, L. A.; Garc´ıa, M. P.; Carmona, D.; Foces-Foces, C.; Cano,
F. H. Inorg. Chim. Acta 1985, 96, L21. (b) Cabeza, J . A.; Landazuri,
C.; Oro, L. A.; Tiripicchio, A.; Tiripicchio-Camellini, M. J . Organomet.
Chem. 1987, 322, C16. (c) Cabeza, J . A.; Landazuri, C.; Oro, L. A.;
Belletti, D.; Tiripicchio, A.; Tiripicchio-Camellini, M. J . Chem. Soc.,
Dalton Trans. 1989, 1093. (d) Carmona, D.; Mendoza, A.; Ferrer, J .;
Lahoz, F. J .; Oro, L. A. J . Organomet. Chem. 1992, 431, 87.
(5) (a) Oro, L. A.; Carmona, D.; Garc´ıa, M. P.; Lahoz, F. J .; Reyes,
J .; Cano, F. H.; Foces-Foces, C. J . Organomet. Chem. 1985, 296, C43.
(b) Garc´ıa, M. P.; Portilla, A.; Oro, L. A.; Foces-Foces, C.; Cano, F. H.
J . Organomet. Chem. 1987, 322, 111. (c) Cano, F. H.; Foces-Foces, C.;
Oro, L. A.; Pinillos, M. T.; Tejel, C. Inorg. Chim. Acta 1987, 128, 75.
(d) Garc´ıa, M. P.; Lo´pez, A. M.; Esteruelas, M. A.; Lahoz, F. J .; Oro, L.
A. J . Organomet. Chem. 1990, 388, 365. (e) Garc´ıa, M. P.; Lo´pez, A.
M.; Esteruelas, M. A.; Lahoz, F. J .; Oro, L. A. J . Chem. Soc., Dalton
Trans. 1990, 3465. (f) Carmona, D.; Ferrer, J .; Lahoz, F. J .; Oro, L.
A.; Reyes, J .; Esteban, M. J . Chem. Soc., Dalton Trans. 1991, 2811.
(g) Carmona, D.; Lamata, M. P.; Ferrer, J .; Modrego, J .; Perales, M.;
Lahoz, F. J .; Atencio, R.; Oro, L. A. J . Chem. Soc., Chem. Commun.
1994, 575.
(7) (a) J ones, R. A.; Wright, T. C.; Atwood, J . L.; Hunter, W. E.
Organometallics 1983, 2, 470. (b) Bender, R.; Braunstein, P.; Tiripic-
chio, A.; Tiripicchio-Camellini, M. Angew. Chem., Int., Ed. Engl. 1985,
24, 861. (c) Braunstein, P.; De Meric de Bellefon, C.; Bouaoud, S.-E.;
Grandjean, D.; Halet, J .-F.; Saillard, J .-Y. J . Am. Chem. Soc. 1991,
113, 5282. (d) Bender, R.; Braunstein, P.; Dedieu, A.; Ellis, P. D.;
Huggins, B.; Harvey, E.; Sappa, E.; Tiripicchio, A. Inorg. Chem. 1996,
35, 1223.
(8) Oro, L. A.; Carmona, D.; Reyes, J .; Foces-Foces, C.; Cano, F. H.
J . Chem. Soc., Dalton Trans. 1986, 31.
(9) Cabeza, J . A.; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1985,
573.
(10) [(η6-p-cymene)OsCl2(Hpz)] was characterized by 1H NMR in
CDCl3: δ 12.14 (bs, 1H, NH); 7.80 (bs, 1H, Hpz); 7.50 (bs, 1H, Hpz);
6.36 (bd, 1H, 3J (HH) ) 2.2 Hz, Hpz); 5.90, 5.72 (AA′BB′ system, J (AB)
) J (A′B′) ) 5.6 Hz, C6H4); 2.76 (sp, 1H, CHMe2); 2.24 (s, 3H, Me);
1.21 (d, 6H, 3J (HH) ) 6.9 Hz, CHMe2).
(6) (a) Carmona, D.; Ferrer, J .; Mendoza, A.; Lahoz, F. J .; Reyes, J .;
Oro, L. A. Angew. Chem., Int. Ed. Engl. 1991, 30, 1171. (b) Carmona,
D.; Ferrer, J .; Oro, L. A.; Trofimenko, S. Gazz. Chim. Ital. 1994, 124,
35.
(11) J ones, C. J .; McCleverty, J . A.; Rothin, A. S. J . Chem. Soc.,
Dalton Trans. 1986, 109.

800 Organometallics, Vol. 19, No. 5, 2000
Carmona et al.
Ch a r t 1. P r op osed Str u ctu r e for Com p lexes
state.12 The band due to the ν(OsCl)9,13 vibration was
observed at ca. 300 cm-1. The presence of the uncoor-
dinated BF4 anion in complex 2 is revealed by two
3 a n d 4
strong absorptions14 centered at ca. 1100 and 520 cm-1
.
The 1H NMR spectrum of 2 is consistent with the
presence of two coordinated Hpz ligands per cation.
Their chemical shifts and coupling constants are com-
parable to those previously reported for the homologous
ruthenium complex15 [(η6-p-cymene)RuCl(Hpz)2]BF4. All
1
the H NMR data of the chloride compound 1 are also
comparable to those of the tetrafluoroborate 2, apart
from those for the NH protons. These protons are more
deshielded than those of 2 (a difference in chemical shift
of 2.4 ppm), and more interestingly, their couplings with
the pyrazolate protons H3, H4, and H5 can be directly
measured in the spectrum, their values being 2.1, 2.1,
and 1.8 Hz, respectively. These results suggest that the
strong hydrogen bond N-H‚‚‚Cl detected by IR spec-
troscopy in the solid state is also present in chloroform
solution. Although a similar behavior has been found
in complexes with one diazole ligand,15,16 in compounds
with two diazoles15 couplings involving the NH protons
are rarely observed in solution because they are impli-
cated in rapid prototropism.
(b) Bin u clea r OsM Diolefin Com p lexes. Treat-
ment of [(η6-p-cymene)OsCl(Hpz)2]BF4 (2) with the
dimers [M(µ-OMe)(COD)]2 (M ) Ir, Rh)17 in the presence
of 1 equiv of KOH led to the neutral dinuclear com-
pounds [(η6-p-cymene)OsCl(µ-pz)2M(COD)] (M ) Ir (3),
Rh (4)) in ca. 60% (3) and 90% (4) yields, respectively.
situation that has also been found in the crystal
structures of the related carbonyl derivatives (see
below).
The preparation of the OsIr compound 3 was ac-
companied by the formation of the diiridium dimer19 [Ir-
(µ-pz)(COD)]2 and the triply bridged diosmium com-
pound20 [{(η6-p-cymene)Os}2(µ-Cl)(µ-pz)2]BF4, which
accounts for the moderate preparative yield. Scheme 2
illustrates a possible reaction path for the preparation
of these compounds. The reaction could proceed through
the common undetected intermediate A, formed by
abstraction of one of the NH protons on 2 by a methoxo
group of the iridium dimer. The cleavage of the Os-N
bond in A affords “[Os(p-cymene)Cl(Hpz)]+” and “Ir(pz)-
(COD)” moieties. Reaction of the former with KOH and
subsequent dimerization with dissociation of one chlo-
ride anion leads to the diosmium cation [{(η6-p-cymene)-
Os}2(µ-Cl)(µ-pz)2]+. The highly unsaturated “Ir(pz)-
(COD)” unit dimerizes to the observed product [Ir(µ-
pz)(COD)]2. Alternatively, the intermediate A could
directly react with KOH, thus removing the remaining
NH proton and affording 3. Comparable redistribution
reactions have been reported for binuclear RuRh and
RuIr derivatives with two pyrazolate bridging groups.5f,21
[(η6-p-cymene)OsCl(Hpz)2]BF4 +
1/2[M(µ-OMe)(COD)]2 + KOH f
[(η6-p-cymene)OsCl(µ-pz) M(COD)]
+
2
M ) Ir (3), Rh (4)
(c) Bin u clea r OsM Ca r bon yl Com p ou n d s. When
CO is bubbled through dichloromethane solutions of
complexes 3 and 4 at room temperature, the dicarbonyl
compounds [(η6-p-cymene)OsCl(µ-pz)2M(CO)2] (M ) Ir
(5a ), Rh (6)) can be isolated in good yield (eq 3).
MeOH + KBF4 + H2O (2)
Complexes 3 and 4 were characterized by elemental
1
analysis and IR and H NMR spectroscopy (see Experi-
mental Section). The IR spectra do not show the
characteristic NH, BF4, and C-O vibrations of the
starting materials and do show one absorption at 1059
cm-1, which can be assigned to the δ(CH) vibration of
the pyrazolate ligand.18 The ν(OsCl) stretching fre-
quency appears at 304 (3) and 302 (4) cm-1, as expected
[(η6-p-cymene)OsCl(µ-pz)2M(COD)] + 2CO f
[(η6-p-cymene)OsCl(µ-pz) M(CO) ]
+ COD (3)
2
2
M ) Ir (5a ), Rh (6)
1
for a terminal Os-Cl bond. The H NMR spectra are
The IR spectra of complexes 5a and 6 show two very
strong ν(CO) absorptions in the 1996-2081 cm-1 region,
and these are characteristic of cis-dicarbonyl struc-
tures.22 A weak band at ca. 300 cm-1 is also observed
consistent with the proposed formulation (Chart 1), and
they show the inequivalence of the H3 and H5 pyrazolate
protons and the presence of the p-cymene, pz, and COD
ligands in the required proportions. The two pyrazolate
groups are acting as exobidentate bridging ligands, a
(19) (a) Beveridge, K. A.; Bushnell, G. W.; Dixon, D. R.; Eadie, D.
T.; Stobart, S. R.; Atwood, J . L.; Zaworotko, M. J . J . Am. Chem. Soc.
1982, 104, 920. (b) Coleman, A. W.; Eadie, D. T.; Stobart, S. R.;
Zaworotko, M. J .; Atwood J . L. J . Am. Chem. Soc. 1982, 104, 922.
(20) The complex cation [{(η6-p-cymene)Os}2(µ-Cl)(µ-pz)2]+ was spec-
troscopically detected by 1H NMR resonance and by mass spectrometry.
1H NMR (CDCl3, δ): 7.69 (bs, 4H, pz); 6.03 (bs, 2H, pz); 5.81, 5.66
(AA′BB′ system, 8H, J (AB) ) J (A′B′) ) 5.1 Hz, C6H4); 2.64 (sp, 2H,
CHMe2); 2.32 (s, 6H, Me); 1.10 (d, 12H, 3J (HH) ) 6.8 Hz, CHMe2). MS
(FAB+): m/z 819 (M+).
(21) (a) Uso´n, R.; Oro, L. A.; Ciriano, M. A.; Pinillos, M. T.; Cabeza,
J . A. J . Organomet. Chem. 1981, 221, 249. (b) Uso´n, R.; Gimeno, J .;
Oro, L. A.; Mart´ınez de Ilarduya, J . M.; Cabeza, J . A. J . Chem. Soc.,
Dalton Trans. 1983, 1729.
(12) Oro, L. A.; Carmona, D.; Lamata, M. P.; Tiripicchio, A.; Lahoz,
F. J . J . Chem. Soc., Dalton Trans. 1986, 15, and references therein.
(13) Arthur, T.; Stephenson, T. A. J . Organomet. Chem. 1981, 208,
369.
(14) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; Wiley: New York, 1986; p 132.
(15) Carmona, D.; Ferrer, J .; Oro, L. A.; Apreda, M. C.; Foces-Foces,
C.; Cano, F. H.; Elguero, J .; J imeno, M. L. J . Chem. Soc., Dalton Trans.
1990, 1463.
(16) (a) Elguero, J .; Fruchier, A.; Pardo, M. C. Org. Magn. Reson.
1974, 6, 272. (b) Claramunt, R. M.; Elguero, J .; Marzin, C.; Seita, J .
An. Quim. 1979, 75, 701. (c) Fruchier, A.; Elguero, J . Spectrosc. Lett.
1979, 12, 809.
(17) Uso´n, R.; Oro, L. A.; Cabeza, J . A. Inorg. Synth. 1985, 23, 126.
(18) Uso´n, R.; Oro, L. A.; Esteban, M.; Cuadro, A. M.; Navarro, P.;
Elguero, J . Transition Met. Chem. 1982, 7, 234.
(22) (a) Uso´n, R.; Oro, L. A.; Claver, C.; Garralda, M. A. J .
Organomet. Chem. 1976, 105, 365. (b) Uso´n, R.; Oro, L. A.; Artigas,
J .; Sariego, R. J . Organomet. Chem. 1979, 179, 65. (c) Bonati, F.;
Wilkinson, G. J . Chem. Soc. 1964, 179, 3156.

Heterobinuclear (p-cymene)Os(µ-pz)2M Complexes
Organometallics, Vol. 19, No. 5, 2000 801
Sch em e 2. P ossible P a th for Rea ction 2a
a
Legend: (i) -MeOH; (ii) +KOH, -H2O, -KBF4; (iii) +KOH, -H2O, -KCl.
and is attributable to a terminal ν(OsCl) vibration. The
1H NMR spectra show the presence in the molecule of
the two pyrazolate groups and one p-cymene, the signals
of which have the expected chemical shifts, multiplici-
ties, and relative intensities (see Experimental Section).
The molecular structure of compound 6, determined by
X-ray crystallographic means, agrees with all these
spectroscopic data (see below).
(8)) (eq 4). Alternatively, compound 8 can be prepared
by treating methanolic suspensions of compound 6 with
CO in the presence of NaBPh4.
[(η6-p-cymene)OsCl(µ-pz) M(COD)]
+
2
M ) Ir (3), Rh (4)
3CO + NaBPh4 f
As reported for its RuIr homologue6a (see Scheme 1),
complex 5a easily isomerizes at room temperature in
methanol or chloroform, with a lower rate of isomer-
ization in the latter. The similarity of the NMR data
between the RuIr and the OsIr compounds permits us
[(η6-p-cymene)Os(CO)(µ-pz)2M(CO)2]BPh4
+
M ) Ir (7), Rh (8)
COD + NaCl (4)
Complexes 7 and 8 were characterized by elemental
1
analysis and IR and H NMR spectroscopy (see Experi-
to propose the formulation [(η6-p-cymene)Os(µ-pz)2IrCl-
(CO)2] (5b) for the new OsIr isomer, with the isomer-
ization involving the formal migration of the chloride
from the Os to the Ir with concomitant formation of an
Os-Ir bond. According to 1H NMR data, the system
reached equilibrium in methanol-d4, at room tempera-
ture (K ) [5b]/[5a ] ) 2.9 ( 0.1). Isomer 5b is less soluble
in methanol than 5a , and by taking advantage of this
property, spectroscopically pure 5b can be isolated.
Thus, pure 5b slowly separates from methanolic sus-
pensions of 5a . The progress of the isomerization 5a f
5b was monitored by 1H NMR in methanol-d4. The
reaction obeys a first-order rate law in 5a , and from the
value of the rate constant at different temperatures,23
activation parameters of ∆Hq ) 93 kJ mol-1 and ∆Sq )
7 J K-1 mol-1 were measured.24 On the other hand, we
have not observed a similar isomerization process for
the OsRh analogue [(η6-p-cymene)OsCl(µ-pz)2Rh(CO)2]
(6) even in refluxing methanol. In summary, the behav-
ior of the OsM systems closely resembles that observed
for the RuM analogues.
mental Section). Furthermore, the structure of complex
8 was determined by diffractometric methods. The IR
spectra show the characteristic bands of the terminal
CO groups in the 2000 cm-1 region and an absorption
at 1581 cm-1, which is assigned to the uncoordinated
-
BPh4 anion and reflects the ionic nature of the com-
pounds. The chemical shifts, couplings, and intensities
1
of the resonances in the H NMR spectra are in good
agreement with a molecular structure containing one
p-cymene group and two bridging, chemically equivalent
pyrazolate ligands, as found in the X-ray molecular
structure determination of complex 8.
(d ) Molecu la r Str u ctu r es of [(η6-p-cym en e)OsCl-
(µ-p z)2Rh (CO)2] (6) a n d [(η6-p-cym en e)Os(CO)(µ-
p z)2R h (CO)2]BP h 4 (8). Molecular representations of
compound 6 and of the cation of complex 8 are shown
in Figures 1 and 2, respectively, together with the atom
labeling system used. Selected bond distances and
angles are listed in Table 1. Both complexes consist of
pseudooctahedral osmium(II) and square-planar rhod-
ium(I) atoms connected by two bridging pyrazolate
ligands. The resulting OsN4Rh metallacycles adopt boat
conformations; the Cremer and Pople puckering param-
eters for these complexes are listed in Table 4. The
coordination around the osmium atom is completed by
one η6-p-cymene ligand and one terminal chloride (6)
or one terminal CO group (8). The rhodium atoms are
also bonded, in both cases, to two terminal carbonyl
ligands. The Os-Rh distances, 3.6231(5) Å (6) and
3.7012(6) Å (8), exclude any significant metal-metal
interaction. These values correlate with the relative
Bubbling of carbon monoxide through methanolic
solutions of compounds 3 and 4 in the presence of
NaBPh4 caused, besides the displacement of the coor-
dinated diolefin, the elimination of the terminal chloride
ligand and the formation of the cationic tricarbonyls [(η6-
p-cymene)Os(CO)(µ-pz)2M(CO)2]BPh4 (M ) Ir (7), Rh
(23) The k values at 5, 10, 15, and 21 °C were 4.3 × 10-5, 5.9 ×
10-5, 1.5 × 10-4, and 3.8 × 10-4 s-1, respectively.
(24) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transi-
tion Metal Complexes, 2nd ed.; VCH: Weinheim, Germany, 1991; p
87.

802 Organometallics, Vol. 19, No. 5, 2000
Carmona et al.
ligands as well as those of the BPh4 anion are not
unusual and do not warrant further comment.
In summary, carbonylation of the chloride diolefin
compounds 3 and 4 in polar media, such as methanol,
and in the presence of halogen scavangers, such as
NaBPh4, afforded the tricarbonyl compounds 7 and 8,
most probably via the dicarbonyl derivatives 5 and 6,
which are the final products in nonpolar media and in
the absence of halogen labilizers.
(e) Meta th esis w ith Na X (X ) Br , I). Mixtures of
the chloride compounds 5a and 5b, in methanol, reacted
with NaX (X ) Br, I), affording the metal-metal-bonded
OsIr dicarbonyls [(η6-p-cymene)Os(µ-pz)2IrX(CO)2] (X )
Br (9), I (10)). Under the same conditions, the OsRh
complex 6 gave the non-metal-metal-bonded bromide
compound [(η6-p-cymene)OsBr(µ-pz)2Rh(CO)2] (11) and
the metal-metal-bonded iodide monocarbonyl [(η6-p-
F igu r e 1. Molecular representation of [(η6-p-cymene)OsCl-
(µ-pz)2Rh(CO)2] (6).
cymene)Os(µ-pz)2RhI(CO)] (12).26 Complex 12 could be
quantitatively prepared by carrying out the reaction in
refluxing methanol. However, neither the OsIr com-
pounds 9 and 10 nor the OsRh bromide 11 were
converted into the corresponding monocarbonyl com-
plexes in refluxing methanol.
Again, as in the RuM (M ) Rh, Ir) chemistry,5f,6a,b
only for the OsIr-containing derivatives was it possible
to detect metal-metal-bonded species. The sole excep-
tion was the monocarbonyl OsRh iodide [(η6-p-cymene)-
Os(µ-pz)2RhI(CO)] (12), in which the elimination of one
of the two terminal carbonyls forces the formation of
the OsRh bond. Furthermore, from the analogy with the
RuM chemistry, neither the bromide nor the iodide
metal-metal bonded OsIr derivatives isomerized to the
corresponding non-metal-metal-bonded species.
F igu r e 2. Molecular structure of the cation of the complex
[(η6-p-cymene)Os(CO)(µ-pz)2Rh(CO)2]BPh4 (8).
The IR spectra of complexes 9-12 show the expected
strong ν(CO) absorption bands in the region of 2000
cm-1 (see Experimental Section). The 1H NMR data are
in good agreement with structures consisting of (p-
cymene)Os and M(CO)2 (9-11) or M(CO) (12) moieties
linked by two exobidentate pyrazolate groups. In par-
folding of the structures observed by the dihedral angles
between the two Os-N-N-Rh bridging moieties (â
angle) and between the two metal coordination planes
(R angle) (see Table 4): longer intermetallic distances
imply that both dihedral angles have higher values.2i
The Os-N (mean 2.094(4) Å (6), 2.074(4) Å (8)) and
Rh-N (mean 2.070(4) Å (6), 2.065(4) Å (8)) bond
distances compare well with the bond lengths found in
the analogous RuRh compound [(η6-p-cymene)RuCl(µ-
pz)2Rh(CO)2] (Ru-N mean 2.086(3) Å; Rh-N mean
2.062(4) Å).6a The Os-G (G ) p-cymene centroid)
separations are significantly different, with values of
1.668(5) Å in 6 and 1.764(7) Å in 8. The distance
obtained in 6 falls in the range of previously reported
Os-p-cymene bond distances, 1.63-1.72 Å,25 in related
mono- or polynuclear complexes. However, the value
determined in 8 is clearly longer, probably reflecting the
lower electron density present on the metal center in
this case. In both structures the Os-C(p-cymene)
distances are significantly different, showing that the
p-cymene ring is not completely planar but is slightly
puckered and adopts, in the case of 6, a clear boat
conformation, with atoms C(7) and C(10) at the bow and
stern. The structural parameters of CO and pyrazolate
1
ticular, the H NMR spectral data of the monocarbonyl
compound [(η6-p-cymene)Os(µ-pz)2RhI(CO)] (12) show
the chemical inequivalence of the two bridging pyra-
zolate ligands. The absence of a symmetry plane relating
these two groups renders the osmium center chiral, and
accordingly, the p-cymene ligand contains two different
aromatic AB systems, as well as two diastereotopic
methyl isopropyl groups. The characterization of these
types of compounds was completed with the X-ray
determination of the molecular structures of compounds
10 and 12.
(f) Molecu la r Str u ctu r es of [(η6-p-cym en e)Os(µ-
p z)2Ir I(CO)2] (10) a n d [(η6-p-cym en e)Os(µ-p z)2Rh I-
(CO)] (12). Molecular drawings of complexes 10 and 12
are represented in Figures 3 and 4, respectively. Se-
lected bond distances and angles for 10 and 12 are
(26) Comparison of the1H NMR data of the methyls of the p-cymene
ligand and of the pyrazolate protons of the dicarbonyl compounds 5a ,b,
9, and 11 with those of homologous compounds characterized by
diffractometric methods, [(η6-p-cymene)RuCl(µ-pz)2M(CO)2] (M ) Rh,
Ir), [(η6-p-cymene)Os(µ-pz)2IrCl(CO)2], 6, and 10, clearly distinguish
between metal-metal-bonded and non-metal-metal-bonded molecules.
(25) (a) Watkins, S. F.; Fronczek, F. R. Acta Crystallogr., Sect. B
1982, 38, 270. (b) Cabeza, J . A.; Adams, H.; Smith, A. J . Inorg. Chim.
Acta 1986, 114, L17. (c) Michelman, R. I.; Bergman, R. G.; Andersen,
R. A. Organometallics 1993, 13, 2741. (d) Bell, A. G.; Kozminski, W.;
Linden, A.; von Philipsborn, W. Organometallics 1996, 15, 3124. (e)
Burrell, A. K.; Steedman, A. J . Organometallics 1997, 16, 1203

Heterobinuclear (p-cymene)Os(µ-pz)2M Complexes
Organometallics, Vol. 19, No. 5, 2000 803
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for th e Com p lexes
[(η6-p-cym en e)OsCl(µ-p z)2Rh (CO)2] (6) a n d [(η6-p-cym en e)Os(CO)(µ-p z)2Rh (CO)2]BP h 4 (8)
6 (L ) Cl)
8 (L ) CO)
6 (L ) Cl)
8 (L ) CO)
Os-L
2.4129(12)
2.091(4)
2.097(4)
2.217(5)
2.177(5)
2.161(4)
2.227(5)
2.197(5)
2.195(5)
1.861(7)
2.073(4)
2.074(4)
2.290(6)
2.277(7)
2.272(7)
2.263(6)
2.199(6)
2.248(6)
Rh-N(2)
2.073(4)
2.066(4)
1.866(7)
1.864(6)
1.142(9)
1.139(8)
2.062(5)
2.068(4)
1.856(6)
1.871(6)
1.135(7)
1.122(8)
1.166(9)
1.362(6)
1.367(6)
Os-N(1)
Os-N(3)
Os-C(7)
Os-C(8)
Os-C(9)
Os-C(10)
Os-C(11)
Os-C(12)
Rh-N(4)
Rh-C(17)
Rh-C(18)
C(17)-O(1)
C(18)-O(2)
C(19)-O(3)
N(1)-N(2)
N(3)-N(4)
1.371(6)
1.370(6)
L-Os-N(1)
L-Os-N(3)
86.02(10)
85.60(11)
127.54(16)
83.81(16)
128.8(2)
87.8(2)
90.3(2)
N(2)-Rh-N(4)
N(2)-Rh-C(17)
N(2)-Rh-C(18)
N(4)-Rh-C(17)
N(4)-Rh-C(18)
C(17)-Rh-C(18)
Rh-C(17)-O(1)
Rh-C(18)-O(2)
88.68(16)
91.6(2)
176.1(2)
179.3(2)
88.1(2)
91.6(3)
177.4(6)
176.7(5)
89.85(17)
89.5(2)
177.7(2)
176.9(2)
90.6(2)
89.9(3)
176.0(6)
178.4(6)
L-Os-Ga
127.0(3)
85.60(17)
126.3(2)
126.9(2)
179.7(6)
N(1)-Os-N(3)
N(1)-Os-G
N(3)-Os-G
Os-C(19)-O(3)
129.6(2)
a
G represents the centroid of the p-cymene ring.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for th e Com p lex
[(η6-p-cym en e)Os(µ-p z)2Ir I(CO)2] (10)
Os-Ir
2.7196(6)
2.085(8)
2.056(9)
2.204(11)
2.178(9)
2.182(11)
2.212(11)
2.180(10)
2.172(11)
Ir-I
2.8127(10)
2.070(8)
2.034(8)
1.842(12)
1.859(11)
1.149(15)
1.130(13)
1.357(11)
1.392(12)
Os-N(1)
Os-N(3)
Os-C(7)
Os-C(8)
Os-C(9)
Os-C(10)
Os-C(11)
Os-C(12)
Ir-N(2)
Ir-N(4)
Ir-C(17)
Ir-C(18)
C(17)-O(1)
C(18)-O(2)
N(1)-N(2)
N(3)-N(4)
Ir-Os-N(1)
Ir-Os-N(3)
Ir-Os-Ga
69.8(2)
70.2(2)
140.4(3)
83.3(3)
132.8(4)
134.0(4)
177.4(6)
178.4(6)
158.71(3)
94.8(3)
I-Ir-N(2)
93.0(2)
92.4(2)
100.6(3)
97.1(4)
85.2(3)
91.1(4)
168.7(4)
166.7(4)
89.2(4)
92.1(5)
I-Ir-N(4)
I-Ir-C(17)
I-Ir-C(18)
N(1)-Os-N(3)
N(1)-Os-G
N(3)-Os-G
Ir-C(17)-O(1)
Ir-C(18)-O(2)
Os-Ir-I
N(2)-Ir-N(4)
N(2)-Ir-C(17)
N(2)-Ir-C(18)
N(4)-Ir-C(17)
N(4)-Ir-C(18)
C(17)-Ir-C(18)
Figu r e 3. Molecular diagram of [(η6-p-cymene)Ru(µ-pz)2IrI-
(CO)2] (10).
Os-Ir-C(17)
Os-Ir-C(18)
97.0(3)
a
G represents the centroid of the p-cymene ring.
tures are compared with that of the chloride parent
compound 6. Thus, while the osmium and rhodium are
separated by 3.6231(5) Å in 6, the Os-M distances are
only 2.7196(6) and 2.6936(9) Å in 10 and 12, respec-
tively. Compressions of about 1 Å in the Os-M vector
account for the formation of metal-metal bonds and
reflect the great flexibility of the pyrazolate bridging
groups.1,27 The dihedral angles R and â are consequently
smaller (Table 4). The OsN4Ir(Rh) six-membered rings
adopt boat conformations with the metals at the bow
and stern. In both complexes, the Os completes its
coordination sphere with one η6-p-cymene ligand sepa-
rated by normal distances25 of 1.666(10) and 1.670(9) Å
for 10 and 12, respectively.
F igu r e 4. Molecular representation of [(η6-p-cymene)-
Os(µ-pz)2RhI(CO)] (12).
The coordination polyhedron around the iridium atom
in 10 is a distorted octahedron, with the two pyrazolate
nitrogens and two CO groups in an ideal equatorial
plane and the metal-metal bond and the iodide ligand
in the relative apical positions. The Os-Ir-I angle of
listed in Tables 2 and 3, respectively. Both complexes
consist of “(p-cymene)Os” and “IrI(CO)2” (10) or “RhI-
(CO)” (12) moieties connected by two bridging pyrazolate
ligands and by an Os-M metal-metal bond. It is
particularly interesting that great changes are observed
in the Os-M separations when these molecular struc-
(27) Pinillos, M. T.; Elduque, A.; Oro, L. A.; Lahoz, F. J .; Bonati, F.;
Tiripicchio, A.; Tiripicchio-Camellini, M. J . Chem. Soc., Dalton Trans.
1990, 989.

804 Organometallics, Vol. 19, No. 5, 2000
Carmona et al.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for th e Com p lex
the remaining apical position and, consequently, leading
to a tetranuclear complex. The two Rh-I bond distances
are different; the distance with the iodide ligand trans
to N(2) is 2.6724(12) Å, while the bond length with the
iodine atom in a trans disposition to the Os-Rh bond
is significantly longer (2.9368(11) Å), as observed in 10.
Th eor etica l Stu d ies. The isomerization processes
between metal-metal-bonded and unbonded com-
pounds, observed both for RuIr and OsIr complexes,
prompted us to carry out a theoretical analysis of the
electronic structure of the species involved. It was
believed that such a study would shed some light on
the energy factors governing these processes and would
form the basis for the relative stabilization of the two
isomers. We carried out a detailed analysis of the nature
of the metal-metal bond in the RuIr complex [(η6-p-
[(η6-p-cym en e)Os(µ-p z)2Rh I(CO)] (12)a
Os-Rh
2.6936(9)
2.070(9)
2.058(8)
2.193(12)
2.156(11)
2.198(11)
2.206(10)
2.186(9)
2.192(10)
Rh-I
2.6724(12)
2.9368(11)
2.019(8)
Os-N(1)
Os-N(3)
Os-C(7)
Os-C(8)
Os-C(9)
Os-C(10)
Os-C(11)
Os-C(12)
Rh-I′
Rh-N(2)
Rh-N(4)
Rh-C(17)
C(17)-O(1)
N(1)-N(2)
N(3)-N(4)
2.056(9)
1.851(12)
1.107(15)
1.343(11)
1.362(10)
Rh-Os-N(1)
Rh-Os-N(3)
Rh-Os-Gb
N(1)-Os-N(3)
N(1)-Os-G
N(3)-Os-G
Rh-C(17)-O(1)
Os-Rh-I
69.7(2)
69.6(2)
138.5(3)
83.5(3)
134.6(4)
133.9(4)
177.5(11)
99.04(3)
162.02(3)
95.8(3)
I′-Rh-N(2)
98.5(2)
91.9(2)
100.1(3)
89.45(3)
84.8(3)
94.7(4)
170.2(2)
167.9(5)
89.3(2)
89.4(4)
I′-Rh-N(4)
I′-Rh-C(17)
I′-Rh-I
N(2)-Rh-N(4)
N(2)-Rh-C(17)
N(2)-Rh-I
N(4)-Rh-C(17)
N(4)-Rh-I
C(17)-Rh-I
cymene)Ru(µ-pz)2IrCl(CO)2] (13b) and of the compara-
tive stability of [(η6-p-cymene)RuCl(µ-pz)2Ir(CO)2] (13a )
and 13b and their bromide and iodide homologues. This
study can be generalized to include the OsIr-containing
analogues 5a ,b. The calculations were performed by
means of extended Hu¨ckel molecular orbital calculations
using standard programs and atomic parameters.29
On a simple electron count basis, the metal-metal
bond in 13b can be formally described as a covalent link
between two d7 centers, Ru(I)-Ir(II), or as a donor-
acceptor interaction to d6 Ru(II) from d8 Ir(I). The
coordination geometry of 13b agrees with any of these
proposals. Metal-metal-bonded species with geometries
similar to those found here are known for Ir(II)19a and
Ru(I),4c whereas donor-acceptor metal-metal interac-
tions are also known for Ir(I).30 On the other hand, the
ν(CO) stretching frequencies give information about the
electronic density at the metal center. The ν(CO)
Os-Rh-I′
Os-Rh-C(17)
Rh-I-Rh′
90.55(3)
a
Primed atoms are related to the unprimed ones by the
b
symmetry transformation -x, -y, -z. G represents the centroid
of the p-cymene ring.
Ta ble 4. Geom etr ica l P a r a m eter s of th e
Os(µ-p z)2M′ Meta lla cyclesa
6 (M ) Rh) 8 (M ) Rh) 10 (M ) Ir) 12 (M ) Rh)
Os-M, Å 3.6231(5)
3.7012(6)
76.29(16)
65.35(11)
1.070(3)
-3.5(2)
2.7196(6)
52.2(3)
89.56(18)
1.584(5)
0.4(3)
2.6936(9)
52.3(2)
89.7(2)
1.578(5)
1.8(3)
R, deg
â, deg
Q, Å
84.05(14)
71.37(10)
1.177(2)
0.56(19)
86.36(16)
Φ, deg
θ, deg
84.3(2)
89.9(2)
90.2(2)
a
R is the dihedral angle between the coordination planes of the
two metals; â is the dihedral angle between the two Os-N-N-M
planes; Q, Φ, and θ are the Cremer and Pople parameters.
absorptions observed for complex 13b (2080, 2020 cm-1
)
are slightly shifted toward higher frequencies in relation
to those found for 13a (2065, 1995 cm-1). As complex
13a contains one ruthenium(II) and one iridium(I), this
reveals a shift of electron density out of the iridium atom
in 13b, in agreement with a partially oxidized iridium
atom, either by a dative Ir(I)-Ru(II) bond or a direct
Ir(II)-Ru(I) covalent bond. This behavior has also been
observed in the osmium complexes described above:
complex 5b shows two absorptions at 2081 and 2023
cm-1 that are shifted to lower wavenumbers in 5a (2060
and 1996 cm-1).
We have carried out a set of extended Hu¨ckel calcula-
tions in order to understand the nature of the metal-
metal bond in 13b. When the direct overlap between
the two metal atoms is forced to be zero in the calcula-
tions to simulate the absence of metal-metal interac-
tion, the seven highest occupied orbitals of the complex
show a predominant d character. A Mulliken population
analysis indicates that two of these MO’s are centered
on the ruthenium atom and three on the iridium atom.
The remaining two are the result of an equal participa-
tion of the two metals. As all of them are doubly
158.71(3)° reveals the transoid disposition of the halogen
and osmium and also explains the very long Ir-I bond
distance found28 (2.8127(10) Å), which is likely to be due
to the high trans influence of the metal-metal bond.
Complex 12 crystallizes as a dimer of two dinuclear
moieties, with two iodine atoms asymmetrically bridging
the rhodium centers. As for the iridium in 10, the
coordination polyhedron around the rhodium atom is a
distorted octahedron, with ideal equatorial positions
occupied by the two pyrazolate nitrogens, the CO group,
and one iodide ligand; one apical position is occupied
by the Os atom, permitting the iodine atom of another
dinuclear moiety to coordinate to the rhodium through
(28) (a) Ciriano, M. A.; Viguri, F.; Oro, L. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M. Angew. Chem., Int. Ed. Engl. 1987, 26, 444.
(b) Maverick, A. W.; Smith, T. P.; Maverick, E. F.; Gray, H. B. Inorg.
Chem. 1987, 26, 4336. (c) Ciriano, M. A.; Sebastian, S.; Oro, L. A.;
Tiripicchio, A.; Tiripicchio-Camellini, M.; Lahoz, F. J . Angew. Chem.,
Int. Ed. Engl. 1988, 27, 402. (d) Vaartstra, B. A.; Xiao, J .; J enkins, J .
A.; Verhagen, R.; Cowie, M. Organometallics 1991, 10, 2708. (e)
Crispini, A.; De Munno, G.; Ghedini, M.; Neve, F. Inorg. Chem. 1992,
31, 4700. (f) Xiao, J .; Santarsiero, B. D.; Vaartstra, B. A.; Cowie, M. J .
Am. Chem. Soc. 1993, 115, 3212. (g) Xiao, J .; Cowie, M. Organome-
tallics 1993, 12, 463. (h) Crispini, A.; Ghedini, M.; Neve, F. Inorg. Chim.
Acta 1993, 209, 235. (i) Asseid, F.; Browning, J .; Dixon, K. R.;
Meanwell, N. J . Organometallics 1994, 13, 760. (j) Ciriano, M. A.; Dias,
A. R.; Nunes, P. M.; Oro, L. A.; Minas da Piedade, M. F.; Minas da
Piedade, M. E.; Ferreira da Silva, P.; Martinho Simoes, J . A.; Pe´rez-
Torrente, J . J .; Veiros, L. F. Struct. Chem. 1996, 7, 337. (k) Kuang, S.
M.; Xue, F.; Zhang, Z.-Z.; Xue, W.-M.; Che, C.-M.; Mak, T. C. W. J .
Chem. Soc., Dalton Trans. 1997, 3409. (l) Tejel, C.; Ciriano, M. A.;
Lo´pez, J . A.; Lahoz, F. J .; Oro, L. A. Angew. Chem., Int., Ed. Engl.
1998, 37, 1542.
(29) (a) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397. (b) Hoffmann,
R.; Lipscomb, W. N. J . Chem. Phys. 1962, 36, 2179, 2872. (c) Howell,
J .; Rossi, A.; Wallace, D.; Haraki, K.; Hoffmann, R. QCPE 1977, 11,
344.
(30) (a) Oro, L. A.; Sola, E.; Lo´pez, J . A.; Torres, F.; Elduque, A.;
Lahoz, F. J . Inorg. Chem. Commun. 1998, 1, 64. (b) Tejel, C.; Ciriano,
M. A.; Lo´pez, J . A.; Lahoz, F. J .; Oro, L. A. Organometallics 1997, 16,
4718.

Heterobinuclear (p-cymene)Os(µ-pz)2M Complexes
Organometallics, Vol. 19, No. 5, 2000 805
F igu r e 5. MO diagram showing the relationship between
the molecular orbitals of the pseudofragments [IrCl(CO)2-
(Hpz)2] and [Ru(pz)2(η6-C6H6)] and the electronic structure
of 13b.
occupied the electron count would be equivalent to a
formal d8 electron configuration for the iridium atom
and a d6 configuration for the ruthenium center. Fur-
thermore, these frontier orbitals, in which the lack of
direct metal-metal interaction has been simulated, can
be matched to the superposition of the molecular orbit-
als of the two hypothetical independent complexes [IrCl-
(CO)2(Hpz)2] and [Ru(pz)2(η6-C6H6)]. When the inter-
metallic overlap is switched on, the interaction between
the metal atoms can be described as a donor-acceptor
bond between the HOMO of the pentacoordinated
pseudofragment [IrCl(CO)2(Hpz)2] and the LUMO of
[Ru(pz)2(η6-C6H6)] (Figure 5). The rest of the orbitals,
which have a significant d character, remain basically
unaltered and have a nonbonding role with respect to
the metal-metal interaction. Although this simple
theoretical model seems to support the idea of a donor-
acceptor bond between d8 Ir(I) and d6 Ru(II), which
implies a partial oxidation of the iridium in 13b (as
indicated by the IR measurements), the possibility of a
covalent bond between two different d7 centers (Ir(II)-
Ru(I)) cannot be excluded, both theoretically and chemi-
cally. The latter view would suggest that the chlorotro-
pic shift leads to a redox tautomerism between species
13a and 13b (Ir(I)-Ru(II) and Ir(II)-Ru(I)) similar to
that recently observed for the diiridium complexes
[(CNBut)2Ir(µ-pz)2Ir(Cl)(CH2Ph)(CNBut)2] and [(CNBut)2-
(Cl)Ir(µ-pz)2Ir(CH2Ph)(CNBut)2]31 (Ir(I)-Ir(III) and
Ir(II)-Ir(II)).
The relative stability of the isomers 13a and 13b was
studied by a fragment analysis of the interaction of a
chloride anion with the cationic fragments 13a + and
13b+. The studies of both isomers showed a slightly
higher stability for 13a than for 13b, a trend in accord
with previous experimental equilibrium data. Neverthe-
less, the most stable cationic fragment is 13b+, rather
than 13a +, indicating that the origin of the difference
in stability is the distinct interaction with the chloride
ligand. Thus, in both complexes (13a and 13b) the
interaction between the chloride ligand and the metal
atoms leads to the bonding-antibonding linear combi-
nations that give rise to a stabilization of the atomic
orbitals of the chlorine atom. This is because they play
F igu r e 6. Schematic interaction diagram between two
different halide ions, X- and X′-, with the fragment 13b+.
a predominant role in the bonding combinations and
there is a major contribution of the metal orbitals in
the corresponding antibonding linear combinations. In
complex 13a the interaction between the chloride ligand
an the ruthenium atom is of a donor-acceptor type and
the antibonding orbitals remain unoccupied. On the
other hand, in complex 13b the interaction takes place
essentially between the chloride ligand and the occupied
d orbitals of the iridium atom, which generates a typical
nonstabilizing two-orbital-four-electron combination
(Figure 6). This situation would not be stable at all in
the absence of additional effects created by the mixing
with other orbitals. In fact, the admixture of the LUMO
of the pseudofragment [Ru(pz)2(η6-C6H6)] into the an-
tibonding Ir-Cl orbital has a bonding character relative
to the metal-metal interaction, and this can be traced
as the origin of the metal-metal bond of order 1. This
admixture counteracts the destabilizing effect of this
antibonding orbital and means a transfer of electronic
density from the halogen to the ruthenium atom through
the iridium center and the metal-metal bond.
The electronegativity of the halogen ligand decreases
when the chloride ligand is replaced by bromide or
iodide, and there is a better match in the energies of
the occupied orbitals on iridium and those of the orbitals
of the halogen atom. As expected, the more favorable
interaction has a stabilizing effect in the bonding linear
combinations but also should have a greater increase
in energy in the antibonding ones. Indeed, the calcula-
tions show a progressive stabilization of the bonding
linear combination, but its antibonding counterpart
hardly changes in energy. This is due to the mixing with
the LUMO of the ruthenium-containing moiety. The
global energy balance of this interaction makes the
metal-metal-bonded isomer more stable on changing
from chlorine to iodine, as the more favorable bonding
interaction is not canceled by its antibonding occupied
counterpart, which in fact remains at an almost con-
stant energy value in all the halogen complexes. The
replacement of Ru for Os has a similar effect, in this
(31) Tejel, C.; Ciriano, M. A.; Lo´pez, J . A.; Lahoz, F. J .; Oro, L. A.
Organometallics 1998, 17, 1449.

806 Organometallics, Vol. 19, No. 5, 2000
Carmona et al.
3J (H5H4) ) 1.7 Hz, H4 of pz); 6.01, 6.09 (AA′BB′ system, J (AB)
) J (A′B′) ) 5.4 Hz, C6H4); 4.01 (m, 2H, vinylic CH); 3.56 (m,
2H, vinylic CH); 2.38 m (5H, CH2 of COD and CHMe2 of
p-cymene); 1.77 (s, 3H, Me); 1.68 (m, 4H, CH2); 1.15 (d, 6H,
3J (HH) ) 6.8 Hz, CHMe2).
case owing to the more favorable metal-metal interac-
tion in the OsIr species, which is reflected in the
increased stability for the metal-metal-bonded isomers.
[(η6-p-cymene)OsCl(µ-pz)2Rh(COD] (4) was prepared in a
way similar to that given above. The reaction time was 23 h.
Yield: 89%. Anal. Calcd for C24H32ClN4OsRh: C, 40.9; H, 4.5;
N, 7.9. Found: C, 41.15; H, 4.7; N, 7.8. 1H NMR (CDCl3, δ):
7.59 (d, 2H, H3/5 of pz); 7.20 (d, 2H, H5/3 of pz); 5.98 (t, 2H,
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were carried out using
standard Schlenk techniques. All solvents were dried, distilled
under N2, and degassed prior to use. Infrared spectra were
recorded on Perkin-Elmer 783 and 1330 spectrophotometers
(range 4000-200 cm-1) using Nujol mulls between polyethyl-
ene sheets or dichloromethane solutions between NaCl plates.
3
3J (H3H4) ) J (H5H4) ) 2.1 Hz, H4 of pz); 6.11, 6.28 (AA′BB′
system, J (AB) ) J (A′B′) ) 5.2 Hz, C6H4); 4.34 (m, 2H, CH of
COD); 3.90 m (2H, CH of COD); 2.56 (m, 4H, CH2); 2.38 (sp,
1H, CHMe2); 1.91 (m, 4H, CH2); 1.78 (s, 3H, Me); 1.17 (d, 6H,
3J (HH) ) 6.9 Hz, CHMe2).
13
1H and C NMR spectra were recorded on a Varian XL-300
spectrometer (300.0 (1H) or 75.4 (13C) MHz). The chemical
shifts were measured relative to partially deuterated solvent
peaks but are reported in parts per million (ppm) relative to
tetramethylsilane. Mass spectra were measured on a VG
Autospec double-focusing mass spectrometer operating in the
FAB+ mode. Ions were produced with the standard Cs+ gun
at ca. 30 kV, and 3-nitrobenzyl alcohol (NBA) was used as a
matrix. The C, H, and N analyses were carried out with a
Perkin-Elmer 240B microanalyzer.
P r ep a r a tion of [(η6-p-cym en e)OsCl(µ-p z)2Ir (CO)2] (5a ).
Bubbling of carbon monoxide (atmospheric pressure, room
temperature) for 3 h through a CH2Cl2 (30 mL) solution of
compound 3 (0.238 g, 0.30 mmol) led to an orange solution,
which was partially concentrated under reduced pressure. The
slow addition of n-hexane gave complex 5a as a brown solid,
which was filtered off, washed with n-hexane, and air-dried.
The complex was recrystallized from diethyl ether/hexane.
Yield: 82%. Anal. Calcd for C18H20ClN4O2OsIr: C, 29.1; H, 2.7;
N, 7.55. Found: C, 29.5; H, 2.2; N, 7.5. IR (CH2Cl2): ν(CO)
P r ep a r a tion of [(η6-p-cym en e)OsCl(Hp z)2]Cl (1). To a
suspension of [{(η6-p-cymene)OsCl}2(µ-Cl)2] (0.102 g, 0.13
mmol) in MeOH (5 mL) was added Hpz (0.037 g, 0.54 mmol).
After the mixture was stirred for 30 min, the resulting solution
was concentrated under reduced pressure. The slow addition
of diethyl ether led to the precipitation of a yellow solid, which
was filtered off, washed with diethyl ether, and air-dried.
Yield: 77%. Anal. Calcd for C16H22Cl2N4Os: C, 36.2; H, 4.1;
N, 10.5. Found: C, 36.4; H, 4.15; N, 10.8. IR (Nujol mull): ν-
(NH) 3321 (s), 3200-2500 (m) cm-1. 1H NMR (CDCl3, δ): 14.45
(bs, 2H, NH); 8.01 (dt, 2H, 3J (H4H3) ) 2.1, 4J (H1H3) ) 2.1,
1
2068 (vs), 1996 (vs) cm-1. H NMR (CDCl3, δ): 7.64 (dd, 2H,
4J (H5H3) ) 0.7 Hz, H3/5 of pz); 7.45 (dd, 2H, H5/3 of pz); 6.16 (t,
2H, 3J (H3H4) ) 3J (H5H4) ) 2.3 Hz, H4 of pz); 5.88, 5.91 (AA′BB′
system, J (AB) ) J (A′B′) ) 5.9 Hz, C6H4); 2.47 (sp, 1H, CHMe2);
3
1.79 (s, 3H, Me); 1.16 (d, 6H, J (HH) ) 6.9 Hz, CHMe2).
Complex 6 was prepared in a way similar to that given
above. Yield: 85%. Anal. Calcd for C18H20ClN4O2OsRh: C,
33.1; H, 3.1; N, 8.6. Found: C, 33.1; H, 3.8; N, 8.25. IR (CH2-
Cl2): ν(CO) 2081 (vs), 2014 (vs) cm-1. 1H NMR (CDCl3, δ): 7.63
(d, 2H, H3/5 of pz); 7.33 (d, 2H, H5/3 of pz); 6.12 (t, 2H, 3J (H3H4)
3
4J (H5H3) ) 0.7 Hz, H3 of Hpz); 7.64 (ddd, 2H, J (H4H5) ) 2.2,
3J (H1H5) ) 1.8 Hz, H5 of Hpz); 6.23 (q, 2H, 4J (H1H4) ) 2.1 Hz,
H4 of Hpz); 6.15, 6.19 (AA′BB′ system, J (AB) ) J (A′B′) ) 5.8
Hz, C6H4); 2.04 (sp, 1H, CHMe2); 1.75 (s, 3H, Me); 1.03 (d, 6H,
3J (HH) ) 6.9 Hz, CHMe2). MS (FAB+): m/z 361 (M+ - 2Hpz,
20%); 393 (M+ - Cl - Hpz, 9%); 429 (M+ - Hpz, 100%); 497
(M+, 49%).
3
) J (H5H4) ) 2.1 Hz, H4 of pz); 5.90 (bs, 4H, C6H4); 2.46 (sp,
3
1H, CHMe2); 1.76 (s, 3H, Me); 1.15 (d, 6H, J (HH) ) 6.9 Hz,
CHMe2). 13C{1H} NMR (CDCl3, δ): 185.8 (d, 1J (CRh) ) 65.6
Hz, CO); 142.9 (s, C3/5 of pz), 140.6 (s, C5/3 of pz); 105.7 (s, C4
of pz); 92.6 (s,CMe of p-cymene); 93.6 (s, CCHMe2 of p-cymene);
78.0 (s, CAA′/BB′, of p-cymene); 73.1 (s, CBB′/AA′ of p-cymene); 31.0
(s, CHMe2); 22.8 (s, CHMe2); 17.8 (s, Me). MS (FAB+): m/z
493 (M+ - Cl - pz - 2CO, 84%); 559 (M+ - Cl - 2CO, 52%);
598 (M+ - 2CO, 84%); 619 (M+ - Cl, 100%); 654 (M+, 24%).
P r ep a r a tion of [(η6-p-cym en e)OsCl(Hp z)2]BF 4 (2). Hpz
(0.256 g, 3.69 mmol) and NaBF4 (93%) (0.224 g, 1.89 mmol)
were added to a suspension of [{(η6-p-cymene)OsCl}2(µ-Cl)2]
(0.728 g, 0.92 mmol) in methanol (15 mL). The suspension was
stirred for 2 h and then evaporated to dryness. The residue
was extracted with dichloromethane (3 × 20 mL) and the
resulting solution concentrated to ca. 2 mL. The slow addition
of diethyl ether led to the precipitation of a yellow solid, which
was filtered off, washed with diethyl ether, and air-dried.
Yield: 87%. Anal. Calcd for C16H22ClN4BF4Os: C, 33.0; H, 3.8;
N, 9.6. Found: C, 32.75; H, 3.9; N, 9.5. IR (Nujol mull): ν-
P r ep a r a tion of [(η6-p-cym en e)Os(µ-p z)2Ir Cl(CO)2] (5b).
A suspension of [(η6-p-cymene)OsCl(µ-pz)2Ir(CO)2] (5a ) in
MeOH (5 mL) was stirred for 24 h. The precipitate that formed
was filtered off, washed with methanol, and air-dried. Yield:
70%. Anal. Calcd for C18H20ClN4O2OsIr: C, 29.1; H, 2.7; N,
7.55. Found: C, 28.8; H, 2.8; N, 7.3. IR (CH2Cl2): ν(CO) 2081
1
(vs), 2023 (vs) cm-1. H NMR (CDCl3, δ): 7.59 (d, 2H, H3/5 of
(NH) 3321 (vs), 3200-2500 (m) cm-1
.
1H NMR (CDCl3, δ):
pz); 7.35 (d, 2H, H5/3 of pz); 5.93 (t, 2H, 3J (H3H4) ) 3J (H5H4) )
2.2 Hz, H4 of pz); 5.64, 5.77 (AA′BB′ system, J (AB) ) J (A′B′)
) 5.4 Hz, C6H4); 2.54 (sp, 1H, CHMe2); 2.21 (s, 3H, Me); 1.08
3
4
12.05 (bs, 2H, NH); 8.12 (dd, 2H, J (H4H3) ) 2.3, J (H5H3) )
0.6 Hz, H3 of Hpz); 7.56 (dd, 2H, 3J (H4H5) ) 2.8 Hz, H5 of Hpz);
6.36 (t, 2H, H4 of Hpz); 6.07, 6.17 (AA′BB′ system, J (AB) )
J (A′B′) ) 5.8 Hz, C6H4); 2.32 (sp, 1H, CHMe2); 1.86 (s, 3H,
3
(d, 6H, J (HH) ) 6.9 Hz, CHMe2).
P r ep a r a tion of [(η6-p-cym en e)Os(CO)(µ-p z)2Ir (CO)2]-
BP h 4 (7). Bubbling of carbon monoxide (atmospheric pressure,
room temperature) for 2 h through a solution of [(η6-p-cymene)-
OsCl(µ-pz)2Ir(COD)] (3; 0.101 g, 0.13 mmol) and NaBPh4 (0.053
g, 0.15 mmol) in methanol (30 mL) led to the precipitation of
a yellow solid, which was filtered off, washed with methanol,
and air-dried. Yield: 44%. Anal. Calcd for C43H40BN4O3OsIr:
C, 49.0; H, 3.8; N, 5.3. Found: C, 48.6; H, 4.3; N, 5.2. IR (CH2-
3
Me); 1.07 (d, 6H, J (HH) ) 7.0 Hz, CHMe2).
P r ep a r a tion of [(η6-p-cym en e)OsCl(µ-p z)2Ir (COD)] (3).
To a solution of [(η6-p-cymene)OsCl(Hpz)2]BF4 (0.198 g, 0.34
mmol) in acetone (30 mL), under nitrogen, was added [Ir(µ-
OMe)(COD)]2 (0.113 g, 0.17 mmol) and KOH in MeOH (1.2
mL, 0.2800 N, 0.34 mmol). After the mixture was stirred for
15 min, the resulting suspension was extracted with dichlo-
romethane (6 × 15 mL) and the solution concentrated under
reduced pressure to ca. 2 mL. The slow addition of n-hexane
led to the precipitation of an orange precipitate, which was
filtered off, washed with n-hexane, and air-dried. Yield: 62%.
Anal. Calcd for C24H32ClN4OsIr: C, 36.3; H, 4.0; N, 7.05.
Cl2): ν(CO) 2079 (vs), 2012 (br) cm-1
.
1H NMR (CD2Cl2, δ):
7.57 (d, 2H, H3/5 of pz); 7.5-6.8 (bm, 22H, H5/3 of pz and 4Ph);
3
3
6.35 (t, 2H, J (H3H4) ) J (H5H4) ) 2.4 Hz, H4 of pz); 5.74 (s,
4H, C6H4); 2.46 (sp, 1H, CHMe2); 1.67 (s, 3H, Me); 1.12 (d, 6H,
3J (HH) ) 6.9 Hz, CHMe2). MS (FAB+): m/z 649 (M+ - 3CO,
26%); 677 (M+ - 2CO, 46%); 707 (M+ - CO, 100%); 735 (M+,
69%).
1
Found: C, 36.3; H, 3.9; N, 7.0. H NMR (CDCl3, δ): 7.63 (d,
3
2H, H3/5 of pz); 7.34 (d, 2H, H5/3 of pz); 6.05 (t, 2H, J (H3H4) )

Heterobinuclear (p-cymene)Os(µ-pz)2M Complexes
Organometallics, Vol. 19, No. 5, 2000 807
Ta ble 5. Cr ysta llogr a p h ic Da ta a n d Refin em en t Deta ils for 6, 8, 10, a n d 12
6
8
10
12
cryst color, habit
cryst size, mm
chem formula
fw
yellow, irregular block
0.52 × 0.42 × 0.36
C18H20ClN4O2OsRh
652.94
orange, prismatic block
0.36 × 0.18 × 0.08
C43H40BN4O3OsRh
964.71
reddish, irregular block
0.17 × 0.15 × 0.10
C18H20IIrN4O2Os
833.68
orange, prismatic block
0.26 × 0.20 × 0.14
C17H20IN4OOsRh
716.38
cryst syst
space group
a, Å
b, Å
monoclinic
P21/n (No. 14)
11.9551(11)
14.0018(13)
12.4844(12)
90
99.183(8)
90
2063.0(4)
triclinic
P1h (No. 2)
9.7378(8)
11.2371(11)
18.8008(14)
73.716(6)
83.814(6)
78.431(7)
orthorhombic
P212121 (No. 19)
9.5321(11)
12.7061(15)
17.9660(13)
90
monoclinic
P21/c (No. 14)
9.2213(15)
13.577(2)
16.009(2)
90
102.544(12)
90
1956.5(5)
c, Å
R, deg
â, deg
90
90
γ, deg
V, Å3
1931.7(3)
2176.0(4)
Z
4
2
4
4
F(calcd), g cm-3
2.102
7.102
1.659
3.757
2.545
13.381
2.432
8.922
µ, mm-1
θ range data collecn, deg
index ranges
2.19-35.02
-1 e h e 14,
-1 e k e 22,
-20 e l e 20
5959 (Rint ) 0.0465)
0.022, 0.068
1.92-27.50
-1 e h e 12,
-13 e k e 14,
-24 e l e 24
6328 (Rint ) 0.0632)
0.377, 0.533
1.96-24.98
-11 e h e 1,
-15 e k e 0,
-21 e l e 21
3832 (Rint ) 0.0265)
0.458, 1.000d
1.99-25.02
-5 e h e 10,
0 e k e 16,
-19 e l e 9
3438 (Rint ) 0.0582)
0.035, 0.062
no. of unique rflns
min, max transmissn
factors
no. of data/
5959/0/250
6328/0/485
3832/75/250
3438/30/232
restraints/params
R(F) (F2 > 2σ(F2))a
Rw(F2) (all data)b
S (all data)c
0.0314
0.0753
0.937
0.0365
0.0769
0.900
0.0321
0.0498
1.015
0.0425
0.0675
0.973
a
b
2
R(F) ) ∑||Fo| - |Fc||/∑|Fo| for 4607, 6328, 3263, and 2381 observed reflections, respectively. Rw(F2) ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2])1/2
;
-
w-1 ) [σ2(Fo2) + (aP)2], where P ) [max(Fo2, 0) + 2Fc2]/3 (6:, a ) 0.0454; 8, a ) 0.0369; 10, a ) 0.0160; 12, a ) 0.0151). c S ) [∑[w(Fo
2
Fc2)2]/(n - p)]1/2, where n is the number of reflections and p the number of parameters. Correction factors are included.
d
P r ep a r a tion of [(η6-p-cym en e)Os(CO)(µ-p z)2Rh (CO)2]-
BP h 4 (8). Bubbling of carbon monoxide (atmospheric pressure,
room temperature) for 3 h through a suspension of [(η6-p-cymene)-
OsCl(µ-pz)2Rh(COD)] (4; 0.101 g, 0.14 mmol) in methanol (25 mL)
gave a yellow solution. The addition of NaBPh4 (0.059 g, 0.17
mmol) led to the precipitation of a yellow solid, which was filtered
off, washed with methanol, and air-dried. Yield: 64%. Anal. Calcd
for C43H40BN4O3OsRh: C, 53.55; H, 4.15; N, 5.8. Found: C, 53.3;
Com p lex 9. Yield: 66%. Anal. Calcd for C18H20BrIrN4O2-
Os: C, 27.5; H, 2.5; N,7.1. Found: C, 28.1; H, 2.15; N, 7.1. IR
(CH2Cl2): ν(CO) 2025 (vs), 2081 (vs) cm-1 1H NMR (CDCl3,
.
δ): 7.59 (d, 2H, H3/5 of pz); 7.35 (d, 2H, H5/3 of pz); 5.91 (t, 2H,
3
3J (H3H4) ) J (H5H4) ) 2.1 Hz, H4 of pz); 5.66, 5.79 (AA′BB′
system, J (AB) ) J (A′B′) ) 5.2 Hz, C6H4); 2.54 (sp, 1H, CHMe2);
3
2.22 (s, 3H, Me); 1.07 (d, 6H, J (HH) ) 6.9 Hz, CHMe2). MS
(FAB+): m/z 707 (M+ - Br, 100%); 733 (M+ - 2CO, 20%); 760
(M+ - CO, 36%); 788 (M+, 33%).
H, 4.05; N, 5.6. IR (CH2Cl2): ν(CO) 2093 (vs), 2029 (br) cm-1 1H
.
NMR (CD2Cl2, δ): 7.45 (d, 2H, H3/5 of pz); 7.4-6.8 (bm, 22H, H5/3
of pz and 4Ph); 6.30 (t, 2H, 3J (H3H4) ) 3J (H5H4) ) 2.4 Hz, H4 of
pz); 5.76 (s, 4H, C6H4); 2.45 (sp, 1H, CHMe2); 1.66 (s, 3H, Me);
1.12 (d, 6H, 3J (HH) ) 6.9 Hz, CHMe2). MS (FAB+): m/z 561 (M+
- 3CO, 13%); 619 (M+ - CO, 29%); 647 (M+, 100%).
Complex 8 can be also prepared starting from [(η6-p-
cymene)OsCl(µ-pz)2Rh(CO)2] (6) using the method described
above. Yield: 65%.
Com p lex 11. Yield: 65%. Anal. Calcd for C18H20BrN4O2-
OsRh: C, 31.0; H, 2.9; N, 8.0. Found: C, 30.8; H, 3.05; N, 7.9.
IR (CH2Cl2): ν(CO) 2014, 2081 (vs) cm-1. 1H NMR (CDCl3, δ):
7.77 (d, 2H, H3/5 of pz); 7.33 (d, 2H, H5/3 of pz); 6.11 (t, 2H,
3
3J (H3H4) ) J (H5H4) ) 2.2 Hz, H4 of pz); 5.96 (s, 4H, C6H4);
3
2.44 (sp, 1H, CHMe2); 1.73 (s, 3H, Me); 1.15 (d, 6H, J (HH) )
6.9 Hz, CHMe2). MS (FAB+): m/z ) 561 (M+ - Br - 2CO,
37%); 619 (M+ - Br, 100%); 670 (M+ - CO, 50%); 698 (M+,
24%).
P r ep a r a tion of [(η6-p-cym en e)Os(µ-p z)2Ir I(CO)2] (10).
Under nitrogen, to a solution of [(η6-p-cymene)OsCl(µ-pz)2Ir-
(CO)2] (0.102 g, 0.14 mmol) in methanol (15 mL) was added
NaI‚2H2O (0.403 g, 2.17 mmol). The solution was stirred for 2
h and then evaporated to dryness. The residue was extracted
with dichloromethane (3 × 10 mL) and the extract evaporated
to ca. 2 mL. The slow addition of n-hexane led to the
precipitation of an orange solid, which was filtered off, washed
with n-hexane, and air-dried. Yield: 57%. Anal. Calcd for
C18H20IIrN4O2Os: C, 25.9; H, 2.4; N, 6.7. Found: C, 26.4; H,
P r ep a r a tion of [(η6-p-cym en e)Os(µ-p z)2Rh I(CO)] (12).
To a suspension of [(η6-p-cymene)OsCl(µ-pz)2Rh(CO)2] (0.101
g, 0.15 mmol) in methanol (10 mL), under nitrogen, was added
NaI‚2H2O (0.154 g, 0.83 mmol). The resulting solution was
heated under reflux for 2 h. The orange precipitate that formed
was filtered off, washed with methanol, and air-dried. Yield:
67%. Anal. Calcd for C17H20IN4OOsRh: C, 28.5; H, 2.8; N, 7.8.
Found: C, 28.3; H, 2.4; N, 7.8. IR (CH2Cl2): ν(CO) 2017 (vs)
cm-1. 1H NMR (CDCl3, δ): 7.80 (d, 1H, H3/5 of pz); 7.65 (d, 1H,
H3/5 of pz); 7.48 (d, 1H, H5/3 of pz); 7.12 (d, 1H, H5/3 of pz); 6.16
(t, 1H, 3J (H3H4) ) 3J (H5H4) ) 2.0 Hz, H4 of pz); 6.10 (bm,
overlapping of the signals of two AB systems, 4H, C6H4); 5.96
1
2.0; N, 6.7. IR (CH2Cl2): ν(CO) 2025 (vs), 2079 (vs) cm-1. H
NMR (CDCl3, δ): 7.59 (d, 2H, H3/5 of pz); 7.36 (d, 2H, H5/3 of
pz); 5.88 (t, 2H, 3J (H3H4) ) 3J (H5H4) ) 2.2 Hz, H4 of pz); 5.67,
5.80 (AA′BB′ system, J (AB) ) J (A′B′) ) 5.6 Hz, C6H4); 2.54
3
3
(t, 1H, J (H3H4) ) J (H5H4) ) 2.0 Hz, H4 of pz); 2.63 (sp, 1H,
3
(sp, 1H, CHMe2); 2.22 (s, 3H, Me); 1.08 (d, 6H, J (HH) ) 6.9
CHMe2); 2.22 (s, 3H, Me); 1.20 (d, 3H, 3J (HH) ) 6.9 Hz,
CHMe2); 0.97 (d, 3H, J (HH) ) 6.9 Hz, CHMe2).
Hz, CHMe2). MS (FAB+): m/z 677 (M+ - I - CO, 13%); 707
(M+ - I, 100%); 806 (M+ - CO, 10%); 833 (M+, 11%).
3
Cr ysta l X-r a y Mea su r em en ts a n d Str u ctu r e Deter m i-
6
6
n a tion of [(η -p-cym en e)OsCl(µ-p z)2Rh (CO)2] (6), [(η -p-
[(η6-p-cymene)Os(µ-pz)2IrBr(CO)2] (9) and [(η6-p-cymene)-
OsBr(µ-pz)2Rh(CO)2] (11) were prepared in a way similar to
that given above, but with sodium bromide.
cym en e)Os(CO)(µ-p z)2Rh (CO)2]BP h 4 (8), [(η6-p-cym en e)-
Os(µ-p z)2Ir I(CO)2] (10), a n d [(η6-p-cym en e)Os(µ-p z)2Rh I-

808 Organometallics, Vol. 19, No. 5, 2000
Carmona et al.
(CO)] (12). Crystals suitable for X-ray diffraction were grown
by slow evaporation of a solution of 8 in CH2Cl2 or by slow
diffusion of pentane into a solution of 6 in Et2O and of hexane
into solutions of 10 in CH2Cl2 and 12 in CHCl3. Crystals were
glued to the end of glass fibers and mounted on a four-circle
diffractometer (Siemens P4 for 6 and 8, Siemens-Stoe AED-2
for 10 and 12), working with graphite-monochomated Mo KR
radiation and operating at 200 K. A summary of crystal data,
intensity collection procedures, and refinement parameters for
the four structural analyses is reported in Table 5. Precise
lattice parameters were determined by least-squares fits from
72 (6), 56 (10), and 47 (12) centered reflections in the region
25 e 2θ e 38° and from 50 reflections in the region 20 e 2θ e
35° (8). Three standard reflections were monitored every 97
measured reflections (6, 8) or every 55 min of measuring time
(10, 12) to check crystal and instrument stability throughout
data collection; no significant variations of the intensities were
observed. All data were corrected for Lorentz and polarization
effects, and a semiempirical absorption correction was also
applied (ψ-scan method32 for 6, 8, and 12 and ∆F method33
for 10); minimum and maximum transmission factors are
listed in Table 5. The structures were solved by Patterson and
conventional Fourier techniques and refined by full-matrix
least-squares methods on F2 (SHELXL-97)34 with initial
isotropic thermal parameters. Anisotropic thermal parameters
were used in the last cycles of refinement for all non-hydrogen
atoms. Hydrogen atoms for methyl groups were include in
calculated positions (C-H ) 0.96 Å), and the remaining
hydrogens were located in difference Fourier maps; all were
included in the refinement riding on their respective carbon
atom with different common isotropic thermal parameters for
the distinct types of H atoms. Atomic scattering factors,
corrected for anomalous dispersion for heavy atoms, were
taken from ref 35.
Ack n ow led gm en t. We thank the Direccio´n General
de Investigacio´n Cient´ıfica y Te´cnica for financial sup-
port (Projects PB96/0845 and PB95/1186). S.E. thanks
the DGICYT for a fellowship.
Su p p or tin g In for m a tion Ava ila ble: Full listings of
crystallographic data, atomic coordinates, isotropic and aniso-
tropic thermal parameters, and bond distances and angles, in
CIF format, for complexes 6, 8, 10, and 12. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM990624H
(34) Sheldrick, G. M. SHELXL-97 Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(35) International Tables For Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
(32) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.
(33) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.