Low-temperature N-O bond cleavage in nitrosyl ligands induced by the unsaturated dimolybdenum anion [Mo2(η5-C 2H5)2(μ-PPh2)(μ-CO) 2]-

Article abstract of DOI:10.1021/ic901120x

The unsaturated anion [Mo₂Cp₂(W-PPh ₂)(W-CO)₂]^- (1) (Na⁺ salt) reacts with the nltrosyl complexes [MCp^'(CO)₂(NO)]BF₄ (M = Mn, Re; Cp' = μ-C₅H

Full text of DOI:10.1021/ic901120x

9282 Inorg. Chem. 2009, 48, 9282–9293
DOI: 10.1021/ic901120x
Low-Temperature N-O Bond Cleavage in Nitrosyl Ligands Induced by the
Unsaturated Dimolybdenum Anion [Mo2(η5-C5H5)2(μ-PPh2)(μ-CO)2]-
†
†
,†
‡
‡
ꢀ †
ꢀ
´
´
M. Esther Garcıa, Daniel Garcıa-Vivo, Sonia Melon, Miguel A. Ruiz,* Claudia Graiff, and Antonio Tiripicchio
†
´
ꢀ
ꢀ
Departamento de Quımica Organica e Inorganica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain,
‡
ꢁ
and Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita di Parma,
Viale G. P. Usberti 17/A, I-43100 Parma, Italy
Received June 10, 2009
The unsaturated anion [Mo2Cp2(μ-PPh2)(μ-CO)2]- (1) (Naþ salt) reacts with the nitrosyl complexes
[MCp0(CO)2(NO)]BF4 (M = Mn, Re; Cp0 = η5-C5H4Me) rapidly at about 193 K. Upon warming of the resulting
mixtures up to 243 K orange solutions are obtained, shown to contain the corresponding oxo- and nitride-bridged
tetracarbonyl complexes [Mo2MCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)4] as the major product, which could be isolated only
for M = Re. Above 253 K, however, these compounds experience spontaneous decarbonylation to yield the
unsaturated tricarbonyl derivatives [Mo2MCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3] (Mo-Mo = 2.840 A for the Mn
compound, according to density functional theory (DFT) calculations). These complexes in turn react rapidly with
air to give the corresponding dioxodicarbonyl derivatives [Mo2MCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2] almost
quantitatively. The structure of the latter product (M = Re) was determined by X-ray diffraction methods (Mo-Mo =
2.763(1) A). In contrast with the N-O bond cleavage easily taking place in the above reactions, the direct
nitrosylation of 1 with N-methyl-N-nitroso-p-toluenesulfonamide induces no bond cleavage process in the nitrosyl
ligand, but just gives the electron-precise tricarbonyl derivative [Mo2Cp2(μ-PPh2)(CO)3(NO)] or, in the presence of
CNtBu, a mixture of the new isocyanide complexes [Mo2Cp2(μ-PPh2)(CNtBu)(CO)2(NO)] and [Mo2Cp2(μ-PPh2)-
(μ-η1:η2-CNtBu)(CO)(NO)]. Separate experiments indicated that these isocyanide complexes cannot be converted
one into each other, nor can they be obtained through thermal substitution reactions on the above tricarbonyl product.
Introduction
chemistry.1,2 Further interest in this molecule stems from its
biological activity,1,3 and also because nitrogen monoxide is
one of the important air pollutants requiring catalytic abate-
ment.1,4,5 The activation and cleavage of the strong N-O
bond of nitrogenmonoxide when bound to a metalatom then
is a process of particular relevance to understanding the
biological role of this molecule and also to developing better
catalysts for its abatement in diverse gas effluents. In this
context we have carried out a prospective study on this
important reaction using different binuclear carbonyl com-
plexes as potential activators of the N-O bond of the nitrosyl
ligand.
Nitrogen monoxide is a remarkable molecule able to
strongly bind to transition metal atoms both in high and
low oxidation states, thus giving rise to a wide variety of
coordination and organometallic complexes exhibiting a rich
*To whom correspondence should be addressed. E-mail: mara@uniovi.es.
(1) Ritcher-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University
Press: Oxford, U.K., 1992.
(2) (a) Hayton, T. W.; Legzdins, P.; Sharp, W. B. Chem. Rev. 2002, 102,
935. (b) Ford, P. C.; Lorkovic, I. M. Chem. Rev. 2002, 102, 993. (c) Mingos, D.
M. P.; Sherman, D. J. Adv. Inorg. Chem. 1989, 34, 293. (d) Gladfelter, W. L. Adv.
Organomet. Chem. 1985, 24, 41.
(3) (a) Franke, A.; Roncaroli, F; Rudi, v. E. Eur. J. Inorg. Chem. 2007,
773. (b) Ghosh, A. Acc. Chem. Res. 2005, 38, 943. (c) Ford, P. C.; Laverman, L.;
Lorkovic, I. M. Adv. Inorg. Chem. 2003, 54, 203. (d) Wang, P. G.; Xian, M.;
Tang, X.; Wu, X.; Wen, Z.; Cai, T.; Janczuk, A. J. Chem. Rev. 2002, 102, 1091.
(e) Butler, A. R.; Megson, I. L. Chem. Rev. 2002, 102, 1155. (f) Williams, R. J. P.
Chem. Soc. Rev. 1996, 77. (g) Clarke, M. J.; Gaul, J. B. Struct. Bonding (Berlin)
1993, 81, 147.
(4) (a) Reduction of Nitrogen Oxide Emissions; Ozkan, U. S., Agarwal, S.
K., Marcelin, G., Eds.; American Chemical Society: Washington, DC, 1995. (b)
Environmental Catalysis; Armor, J. M., Ed.; American Chemical Society:
Washington, DC, 1994. (c) Catalytic Control of Air Pollution; Silver, R. G.,
Sawyer, J. E., Summers, J. C., Eds.; American Chemical Society: Washington,
DC, 1992. (d) Energy and the Environment; Dunderdale, J., Ed.; Royal Society of
Chemistry: Cambridge, U.K., 1990. (e) Pollution: Causes, Effects and Control;
Harrison, R. M., Ed.; Royal Society of Chemistry: Cambridge, U.K., 1990.
The ability of organometallic compounds to cleave the
N-O bond of the nitrosyl ligand is known, but the electronic
and steric factors governing this fundamental reaction re-
main unclear in most cases. For example, it is not unusual
that the treatment of carbonyl clusters with several sources of
the NO ligand would lead to the corresponding nitride
(5) (a) Basu, S. Chem. Eng. Commun. 2007, 194, 1374. (b) Tayyeb, J. M.;
Naseem, I.; Gibbs, B. M. J. Environ. Manage. 2007, 83, 251. (c) Wallington,
T. J.; Kaiser, E. W.; Farrell, J. T. Chem. Soc. Rev. 2006, 35, 335. (d) McMillan,
S. A.; Broadbelt, L. J.; Snurr, R. Q. Environ. Catal. 2005, 287. (e) Curtin, T.
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r
pubs.acs.org/IC
Published on Web 09/11/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 19, 2009 9283
(rather than nitrosyl) derivatives.2c,d,6 However, even when
intermediate nitrosyl complexes are expected to be involved
in these reactions, the actual transformation of a well-defined
nitrosyl complex into the corresponding nitride derivative
has been rarely observed (eq 1).7 A few other reactions
involving the cleavage of the N-O bond by metals in well-
defined organometallic nitrosyl complexes have been re-
ported, all of these involving electron-deficient centers, either
binuclear (eq 2),8 or mononuclear ones (eq 3).9 Yet, another
reported cleavage process is the abstraction of the oxygen
atom of a terminal nitrosyl ligand by a strongly oxophilic
complex (eq 4),10 this reaction being specially favored for M
and M0 having d3 and d2 configurations respectively, accord-
ing to recent density functional theory (DFT) calculations.11
this reaction) was kinetically favored because of the close
proximity between CO and NO ligands in the intermediate
states, this being facilitated by the presence of three CO
ligands (or the equivalent) in the anionic group 6 metal
complex.12 With this precedent in mind we then considered
the possibility of using group 6 metal carbonyl anions having
fewer ligands at the metal so as to achieve an N-O bond
cleavage process without release of CO2. In this paper we
report our results on the reactions of the unsaturated anion
[Mo2Cp2(μ-PPh2)(μ-CO)2]- (1) (Naþ salt, Chart 1)13 with
the mentioned nitrosyl cations [M0Cp0(CO)2(NO)]þ, which
indeed lead to the full cleavage of the nitrosyl N-O bond to
give the corresponding oxonitride heterometallic derivatives.
The bonding in the latter complexes has been examined using
DFT methods. We next examined the direct nitrosylation
reactions of 1 to check whether the electronic and coordina-
tive unsaturation of this anion would be enough to induce the
cleavage of the nitrosyl ligand, but these reactions gave only
different nitrosyl derivatives, as it will be discussed below.
MnðNOÞðCOÞm f Mnðμ-NÞðCOÞm -1þCO2
Mðμ-NOÞM f MtN -MðOÞ
MðNOÞR f MðOÞðNRÞ
ð1Þ
ð2Þ
ð3Þ
ð4Þ
Results and Discussion
Reactions of Compound 1 with Nitrosyl Complexes. The
unsaturated anion 1 reacts in tetrahydrofuran (THF)
solution with several nitrosyl complexes susceptible to
act as sources of cationic nitrosyl metal fragments, such as
the compounds [CoCpX(NO)] (X = Cl, I) and [MCp-
Cl(NO)2] (M = Mo, W) or related species, but complex
mixtures of products were obtained in all cases, these
including the previously reported compounds [Mo2-
Cp2(μ-Cl)(μ-PPh2)(CO)2]13 and [Mo2Cp2(μ-PPh2)(CO)3-
(NO)],14 then suggesting the operation of several elec-
tron-transfer processes involving halogen and nitrosyl
transfer to the unsaturated dimolybdenum center. In
contrast, the reaction of 1 with the rhenium salt
[ReCp0(CO)2(NO)]BF4 was found to be quite selective.
The latter takes place rapidly at about 193 K, since a
black-green solution is instantaneously formed upon
mixing of the reagents at that temperature. Upon warm-
ing the mixture up to 243 K over 30 min, an orange
solution is formed, shown to contain the nitride tetra-
carbonyl complex [Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)-
(CO)4] (2a) as the major product (Scheme 1).
M;NOþM0 f MtNþM0ðOÞ
Recently we reported that the reactions of several anionic
complexes of the group 6 metals [MCp(CO)2L]- (Naþ or Kþ
salts; M = Mo, W; Cp = η5-C5H5; L = CO, P(OMe)3, PPh3)
with the electron-precise nitrosyl cations [M0Cp0-
(CO)2(NO)]þ (BF4 salts; M0 = Mn, Re; Cp0 = η5-C5H4Me)
-
take place readily at low temperatures and lead to the
heterometallic nitride-bridged derivatives [MM0CpCp0(μ-N)-
(CO)3L].12 A DFT study of the likely pathways involved in
these reactions revealed that the N-O bond cleavage process
yielding the nitride derivative follows from the orbitally
controlled nucleophilic attack of the anion to the nitrogen
atom of the nitrosyl ligand in the cation, eventually releasing
CO2 (eq 5). We should note that this reaction pathway
appears to have been not recognized previously in the
chemistry of polynuclear complexes having carbonyl or
nitrosyl ligands.
-
Compound 2a can be isolated as a solid from the
reaction mixture in the usual way, as long as the tempera-
ture is kept below 253 K. Above this temperature, how-
ever, an spontaneous decarbonylation takes place to yield
the unsaturated tricarbonyl derivative [Mo2ReCp2Cp0(μ-
N)(μ-O)(μ-PPh2)(CO)3] (3a) almost quantitatively. Ac-
cording to the EAN formalism we might formulate a
molybdenum-molybdenum double or a single bond for
this molecule, depending on the electron-donor ability of
the bridging oxygen atom, a question to be addressed
later on in the light of DFT calculations. In any case, this
complex turns out to be very air-sensitive, and it progres-
sively evolves upon manipulation (rapidly in the presence
of air) to give the dioxodicarbonyl derivative [Mo2Re-
Cp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2] (4a) in quite good
yield, presumably with evolution of CO2, as it is usually
½LnMðCOÞꢀ þ ½ON -M0Lm0 ꢀþ f LnMtN -M0Lm0 þ CO2
ð5Þ
Our calculations on the above reactions suggested that the
elimination of CO2 (a major thermodynamic driving force for
::
(6) For a recent work on this matter see: Babij, C.; Farrar, D. H.; Poe, A.
J.; Tunik, S. P. Dalton Trans. 2008, 5922.
(7) (a) Fjare, D. E.; Gladfelter, W. L. J. Am. Chem. Soc. 1984, 106, 4799.
(b) Feasey, N. D.; Knox, S. A. R.; Orpen, A. G. J. Chem. Soc., Chem. Commun.
1982, 75.
(8) Legzdins, P.; Young, M. A. Comments Inorg. Chem. 1995, 17, 239.
(9) (a) Blackmore, I. J.; Jin, X.; Legzdins, P. Organometallics 2005, 24,
4088. (b) Sharp, W. B.; Daff, P. J.; McNeil, W. S.; Legzdins, P. J. Am. Chem. Soc.
2001, 123, 6272.
(10) (a) Veige, A. S.; Slaughter, LeG. M.; Lobkovsky, E. B.; Wolczansky,
P. T.; Matsunaga, N.; Decker, S. A.; Cundari, T. R. Inorg. Chem. 2003, 42,
6204. (b) Odom, A. L.; Cummins, C. C.; Protasiewicz, J. D. J. Am. Chem. Soc.
1995, 117, 6613.
ꢀ
´
a, M. E.; Melon, S.; Ramos, A.; Riera, V.; Ruiz, M. A.; Belletti,
(11) Cavigliasso, G.; Christian, G.; Stranger, R.; Yates, B. F. Dalton
Trans. 2009, 956.
a, M. E.; Melon, S.; Ruiz, M. A.; Lopez, R.; Sordo, T.;
Marchio, L.; Tiripicchio, A. Inorg. Chem. 2008, 47, 10644.
(13) Garcı
D.; Graiff, C.; Tiripicchio, A. Organometallics 2003, 22, 1983.
(14) Garcıa, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Lanfranchi, M.;
Tiripicchio, A. J. Am. Chem. Soc. 1999, 121, 4060.
ꢀ
ꢀ
(12) Garcı
´
´
ꢁ

9284 Inorganic Chemistry, Vol. 48, No. 19, 2009
Garcıa et al.
Chart 1
Scheme 1
Figure 1. ORTEP drawing (30% probability) of the molecular structure
of compound 4a, with H atoms omitted for clarity.
Table 1. Selected Bond Lengths (A) and Angles (deg) for compound 4aa
the case in the oxidation reactions of many metal carbo-
nyls. The assignment of the intermetallic bond order in
this dioxonitride complex again is not a straightforward
matter, and this will be addressed in the light of the
structural data to be discussed below.
Mo(1)-Mo(2)
Mo(1)-P(1)
Mo(2)-P(1)
Mo(1)-O(3)
Mo(2)-O(3)
Mo(2)-O(4)
Mo(1)-N(1)
Re(1)-N(1)
Mo(2)-C(14)
Mo(1)-Ct(1)
Re(1)-Ct(3)
2.763(1)
2.379(1)
2.460(2)
1.983(3)
1.929(3)
1.702(3)
1.756(3)
1.985(3)
2.356(4)
2.090(6)
1.974(5)
Mo(2)-C(15)
Mo(2)-C(16)
Mo(2)-C(17)
Mo(2)-C(18)
Mo(1)-C(9)
Mo(1)-C(10)
Mo(1)-C(11)
Mo(1)-C(12)
Mo(1)-C(13)
Mo(2)-Ct(2)
2.382(5)
2.451(4)
2.454(4)
2.359(4)
2.446(5)
2.427(6)
2.353(6)
2.327(6)
2.365(6)
2.080(4)
The reaction of
1
with the manganese salt
[MnCp0(CO)2(NO)]BF4 was much less selective than the
one with the rhenium cation just discussed, and several
side-products were detected, these including known bi-
nuclear products such as the nitrosyl [Mo2Cp2(μ-PPh2)-
(CO)3(NO)],14 the hydride [Mo2Cp2(μ-H)(μ-PPh2)-
(CO)4],15 and the dimer [Mn2Cp02(CO)2(NO)2].16 Thus,
it is obvious that electron-transfer processes become more
prevalent in the reaction with the manganese cation.
Besides, we could detected spectroscopically the forma-
tion of an intermediate species comparable to the tetra-
carbonyl 2a, but apparently this complex is even more
unstable than its rhenium analogue, and it rapidly dis-
sociates carbon monoxide to give the tricarbonyl deriva-
tive [Mo2MnCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3] (3b),
which is the only new product that we could isolate from
the reaction mixture, even if in a modest yield (ca. 25%).
Compound 3b seems to have the same structure as the
rhenium tricarbonyl 3a, a matter to be discussed later on,
and it is also very air-sensitive, since it reacts rapidly with
air to give the corresponding dioxodicarbonyl derivative
[Mo2MnCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2] (4b) in
good yield. The structure and bonding of 3b has been
theoretically analyzed using DFT methods, as it will be
discussed later on.
Mo(1)-P(1)-Mo(2)
Mo(1)-O(3)-Mo(2)
Mo(1)-Mo(2)-O(4)
Mo(2)-Mo(1)-N(1)
Mo(1)-N(1)-Re(1)
69.63(5)
89.9(1)
112.8(1)
99.4 (1)
165.2(2)
O(4)-Mo(2)-P(1)
O(4)-Mo(2)-O(3)
N(1)-Mo(1)-P(1)
N(1)-Mo(1)-O(3)
N(1)-Re(1)-C(1)
C(1)-Re(1)-C(2)
Mo(2)-Ct(2)-C(14)
Mo(2)-Ct(2)-C(15)
Mo(2)-Ct(2)-C(16)
Mo(2)-Ct(2)-C(17)
Mo(2)-Ct(2)-C(18)
99.1(1)
105.4(2)
93.7(1)
102.1(1)
93.5(2)
88.6(2)
87.5(1)
88.8(1)
93.0(1)
93.0(1)
87.7(1)
Mo(1)-Ct(1)-C(9)
Mo(1)-Ct(1)-C(10)
Mo(1)-Ct(1)-C(11)
Mo(1)-Ct(1)-C(12)
Mo(1)-Ct(1)-C(14)
93.3(1)
91.4(1)
88.5(1)
87.5(2)
89.1(3)
a Ct are the centroids of the cyclopentadienyl rings.
viewed as made of two cyclopentadienylmolybdenum
fragments arranged in a transoid conformation and
bridged by diphenylphosphide and oxo ligands. Each
metal atom carries out one further ligand, a terminal
oxygen atom on Mo(2), and a nitride ligand acting as an
essentially linear bridge between Mo(1) and the ReCp0-
(CO)2 fragment (Re-N-Mo = 165.2(2)°). The internal
parameters in the latter fragment are unremarkable. As
for the dimolybdenum center, we note a significant
asymmetry in the bridges, with the P-Mo lengths
differing by about 0.1 A (closer to Mo(1)), this being only
partially counterbalanced by the asymmetric position-
ing of the O(3) atom (ca. 0.05 A closer to Mo(2)). The
average Mo-O(3) length of about 1.95 A is comparable
to the Mo-O bond lengths measured in related
compounds having angular oxygen bridges, such as
Solid-State Structure of the Nitride Complex 4a. The
molecular structure of this complex in the crystal is shown
in Figure 1, while the most relevant bond lengths and
angles are collected in Table 1. The molecule can be
(15) Henrick, K.; McPartlin, M.; Horton, A. D.; Mays, M. J. J. Chem.
Soc., Dalton Trans. 1988, 1083.
(16) James, T. A.; McCleverty, J. A. J. Chem. Soc (A) 1970, 850.

Article
Inorganic Chemistry, Vol. 48, No. 19, 2009 9285
ligand to effectively behave as a four-electron donor
atom, with this eventually leading to the formulation of
a single Mo-Mo bond according to the EAN formalism
(form I in Figure 2). However, we note that the elongation
effect of the terminal oxo ligand on the metal-metal bond
in 4a seems to be substantially smaller than that pre-
viously found for related cyclopentadienyl oxocomplexes
such as [Mo2Cp2(μ-PPh2)(μ-CHCHPh)(O)(CO)],21a
[Mo2Cp2(μ-PPh2)2(O)(CO)],20 and [W2Cp2(μ-PPh2)(μ-
CH2PPh2)(O)(CO)],21b which exhibit intermetallic dis-
tances in the range 2.89-2.95 A. Therefore we conclude
that the contribution of the canonical form I to the actual
electronic structure of 4a must be significant but not
dominant, in agreement with the spectroscopic data in
solution to be discussed later on.
Figure 2. Canonical forms describing the metal-ligand and metal-
metal bonding in compounds 4 and 3 (see text).
A further structural effect of the terminal oxo ligand
can be finally appreciated in the cyclopentadienyl ligand
bound to the same metal atom, since the carbon atoms
positioned in trans with respect to the O(4) atom (C(16)
and C(17)) exhibit Mo-C lengths about 0.1 A longer than
the other atoms of the ring (Table 1). This trans influence
of terminal oxo ligands on cyclopentadienyl groups has
been recognized previously,20,22 and a similar trans influ-
ence might be expected for the nitride ligand, since the
latter is also a strongly π-donor group. Indeed, the carbon
atoms positioned in trans with respect to the N atom (C(9)
and C(10)) are similarly distorted, with the corresponding
Mo-C lengths being about 0.1 A longer than those
involving the other atoms of the ring. This distortion
can be also measured in each case through the angles
defined by the metal, centroid of the ring and the corre-
sponding carbon atoms, these yielding values of about
93° for the C(9), C(10), C(16), and C(17) atoms (Table 1).
Spectroscopy and Solution Structure of Compounds 4.
The IR spectrum of 4a, when recorded in a KBr pellet, is
consistent with the crystal structure just discussed and
provides spectroscopic evidence for the presence of the
oxo and nitride ligands, a piece of information also useful
for the spectroscopic characterization of compounds 2
and 3. Thus, in addition to the C-O stretching bands at
1904 and 1844 cm-1 arising from the Re(CO)2 fragment,
this spectrum exhibits bands at 911, 897, and 837 cm-1
that can be assigned to the stretches of the MotN,
ModO, and Mo-O-Mo moieties, respectively. In fact,
the first band is very similar to those exhibited by the
related nitride-bridged complexes [MoReCpCp0(μ-N)-
(CO)3L] (913 and 908 cm-1 for L = CO and PPh3,
respectively).12 On the other hand, the bands at 897 and
837 cm-1are very close to the absorptions measured
for related dimolybdenum complexes having both
terminal and angular-bridging oxygen atoms, for in-
stance [Mo2Cp2(μ-O)(O)2{μ-C2(CO2Me)2}] (894 and
799 cm-1),17a and [Mo2Cp02(μ-NPh)(μ-O)(O)2] (885 and
823 cm-1).17b
[Mo2Cp2(μ-O)(O)2{μ-C2(CO2Me)2}]17a and [Mo2Cp02(μ-
NPh)(μ-O)(O)2].17b On the other hand, the terminal oxo
ligand exhibits a much shorter Mo(2)-O(4) length of
1.702(3) A, as usually found in organomolybdenum
complexes having terminal oxo ligands, this being indi-
cative of substantial multiplicity in the corresponding
Mo-O bonds.18 Concerning the nitride ligand, the
Mo-N and N-Re lengths of 1.756(3) A and 1.985(3) A,
respectively, are comparable to the corresponding values
recently reported by us for the dimetallic nitride-bridged
complex [WReCpCp0(μ-N)(CO)3{P(OMe)3}] (W-N =
1.81(3) A, N-Re = 1.97(3) A).12 As we noted then, these
figures can be considered respectively as slightly longer
and significantly shorter than the reference values for
triple MotN and single Re-N bonds, respectively, and
this suggests some delocalization of the π-interaction
along the Mo-N-Re framework. Actually, the structur-
al parameters of 4a can be justified using a combination of
two canonical forms (I and II in Figure 2) that imply this
delocalization. This view is also substantiated by DFT
calculations on 3b to be discussed later on.
According to the EAN formalism, a Mo-Mo double
bond might be formulated for compound 4a, if we were to
consider the terminal oxygen atom as a two-electron
donor, but as a single bond if we consider it as a four-
electron donor (forms II and I in Figure 2, respectively).
Indeed the Mo-Mo length in this compound (2.763(1) A)
is much shorter than the reference single-bond figures
usually measured for comparable structures (above ca.
2.9 A), but still is somewhat longer than the reference
values for related species having double ModMo bonds,
such as [Mo2Cp2(μ-NdCHPh)(μ-PCy2)(CO)2], (2.632(1)
A),19a [Mo2Cp2(μ-PCy2)(μ-CCO2Me)(CO)2] (2.656(1)
A),19b and [Mo2Cp2(μ-PPh2)2(CO)2] (2.716(1) A).20 We
can interpret this elongation as an indication that the oxo
ligand might be using at a significant extent an additional
electron pair for binding to the metal. Such additional
interaction, in its extreme form, would make the oxo
Spectroscopic data for compounds 4a and 4b, both in
the solid state and in solution (Table 2 and Experimental
Section) are very similar to each other, thus indicating
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(19) (a) Alvarez, M. A.; Garcıa, M. E.; Ramos, A.; Ruiz, M. A.
´
ꢀ
Organometallics 2007, 26, 1461. (b) García, M. E.; García-Vivo, D.; Ruiz, M.
A. Organometallics 2008, 27, 543.
~
(22) (a) Riera, V.; Ruiz, M. A.; Villafane, F.; Bois, C.; Jeannin, Y.
::
Organometallics 1993, 12, 124. (b) Herrmann, W. A.; Herdtweck, E.; Floel,
::
(20) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P. R.
J. Chem. Soc., Dalton Trans. 1989, 1555.
M.; Kulpe, J.; Kusthardt, U.; Okuda, J. Polyhedron 1987, 6, 1165.

9286 Inorganic Chemistry, Vol. 48, No. 19, 2009
Table 2. Selected IR and 31P{1H} NMR Data for New Compounds
compound
Garcıa et al.
ν(CO)a
ν(MotN)b
ν(ModO)b
ν(MoOMo)b
δ(P)c
[Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)4] (2a)
[Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3] (3a)
[Mo2MnCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3] (3b)
[Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2] (4a)
[Mo2MnCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2] (4b)
[Mo2Cp2(μ-PPh2)(CNtBu)(CO)2(NO)] (5)
1974 (s), 1901 (vs), 1836 (s)
1948 (m), 1896 (vs), 1832 (s)
1953 (m), 1912 (vs), 1854 (s)
1909 (vs), 1846 (s)
1926 (vs), 1869 (s)
2116 (m),e 1898 (vs), 1819 (s), 1605 (s)f
1858 (vs), 1647 (w),e 1604 (s)f
918
912
910
911
925
813
805
808
837
840
204.4d
169.2
169.1
167.3
168.3
204.9
195.3
897
894
[Mo2Cp2(μ-PPh2)(μ-η1:η2-CNtBu)(CO)(NO)] (6)
a Recorded in dichloromethane solution, unless otherwise stated; ν in cm-1 b Data recorded in KBr discs. c Recorded at 121.50 MHz in CD2Cl2
.
solutions at 290 K unless otherwise stated, δ in ppm relative to external 85% aqueous H3PO4. d Recorded at 253 K. e ν(CN). f ν(NO).
that both compounds share the same structure, and they
are also consistent with the structure found in the crystal
for 4a. Both compounds display two C-O stretching
bands with relative intensities (very strong and strong,
respectively, in order of decreasing frequencies) indicative
of the presence in each case of a M(CO)2 oscillator with a
C-M-C angle slightly below 90 degrees (cf. 88.6(2)o for
4a in the crystal), while their wavenumbers are higher for
the manganese compound as usual.23 The presence of two
different bridges connecting the Mo atoms removes any
symmetry element from the molecule, and this is reflected
in the appearance of two different carbonyl resonances
and up to four resonances for the CH(Cp0) groups in the
compounds 3) is not immediately obvious in the IR
spectrum, which exhibits just three C-O stretching
bands, but is clearly denoted by the appearance of two
deshielded resonances (apart from those of the Re-bound
carbonyls) in the carbonyl region of the 13C NMR
spectrum. The very different P-C coupling of these two
resonances (27 and ca. 0 Hz) indicates that both carbonyls
must be bound to the same metal atom, since this would
then lead to very different C-Mo-P angles for these two
ligands, a critical structural factor governing the magni-
tude of two-bond P-C couplings.24 Besides this, we note
that a similar pattern in the P-C couplings is usually
observed for the 13C resonances of the binuclear com-
plexes of type [Mo2Cp2(μ-H)(μ-PRR0)(CO)4], which lo-
cally exhibit comparable CpMo(CO)2 fragments
connected by PRR0 and hydride bridges.25 Incidentally,
we note that the observed P-C coupling for the Mo-
bound carbonyl in 3a (18 Hz) is intermediate between the
values observed for 2a, in agreement with the proposed
structures, implying C-Mo-P angles in the order 2a (cis
to P) < 3a < 2a (trans to P).
According to the EAN formalism, the tetracarbonyl
compound 2a has an electron-precise (34-electron) dimo-
lybdenum center, and a single Mo-Mo bond must be
formulated for this molecule. In contrast, the tricarbonyl
compounds 3a,b have two fewer electrons and a Mo-Mo
double bond might be formulated for them, if we were to
consider the bridging oxygen atom as a two-electron
donor (as we do for 2a). We have noted previously that
32-electron dimolybdenum compounds of the type
trans-[Mo2Cp2(μ-PRR0)(μ-X)(CO)2] (X = 3 electron-
donor group) systematically exhibit 31P chemical shifts
much lower than the corresponding electron-precise
complexes [Mo2Cp2(μ-PRR0)(μ-H)(CO)4] or [Mo2Cp2-
(μ-PRR0)(μ-X)(CO)3].25a,26 The 31P shifts in compounds
2a and 3 seems to follow this trend, with the resonances
for the unsaturated tricarbonyls (ca. 169 ppm) being
some 35 ppm more shielded than those of the electron-
precise tetracarbonyl 2a (204.4 ppm). Yet all these values
1
13C and H NMR spectra (see Experimental Section),
which of course also exhibit two distinct Cp resonances in
each case.
Structural Characterization of Compounds 2 and 3. The
structure proposed for the tricarbonyl compounds 3a,b is
based on that determined for 4a after replacement in the
latter of the terminal oxo ligand with CO, and proved to
be a true minimum in the potential energy surface of 3b, as
computed using DFT methods (see later). In fact, we trust
that the transoid arrangement of the Cp ligands around
the dimolybdenum center, usually more favored on steric
grounds, is retained all the way from the initial tetracar-
bonyl compound 2 down to the dicarbonyls 4. The
presence in compounds 3 of a carbonyl ligand terminally
bound to molybdenum is denoted by the observation of
an additional C-O stretching band at about 1950 cm-1 in
the corresponding IR spectra (in addition to the char-
acteristic bands due to the M(CO)2Cp0 fragments) and
also by the appearance of an additional NMR resonance
(δ 240.0 ppm) in the 13C NMR spectrum of 3a, substan-
tially more deshielded than the resonances of the Re-
bound carbonyls (δ 207.3, 206.5 ppm), and exhibiting a
significant coupling to the 31P nucleus (18 Hz). Finally,
the presence of the nitride ligand is denoted by the
appearance in the corresponding solid-state IR spectra
of the characteristic band at about 910 cm-1, while the
absence of additional bands in this region, coupled to the
presence of a band at about 805 cm-1, both support the
presence in compounds 3 of a bridging, rather than
terminal, oxo ligand.
(24) (a) Jameson, C. J. In Phosphorous-31 NMR Spectroscopy in Stereo-
chemical Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH: New York, 1987;
Chapter 6. (b) Wrackmeyer, B.; Alt, H. G.; Maisel, H. E. J. Organomet. Chem.
1990, 399, 125.
The solid-state IR spectrum of 2a also displays bands
)
arising from nitride (918 cm-1) and oxo (813 cm-1
ꢀ
´
(25) (a) Garcıa, M. E.; Riera, V.; Ruiz, M. A.; Rueda, M. T.; Saez, D.
Organometallics 2002, 21, 5515. (b) Alvarez, C. M.; Alvarez, M. A.; García-
bridging ligands. The presence of an extra terminal CO
ligand bound to molybdenum (compared to the tricarbonyl
ꢀ
Vivo, D.; García, M. E.; Ruiz, M. A.; Saez, D.; Falvello, L. R.; Soler, T.; Herson, P.
Dalton. Trans. 2004, 4168. (c) Alvarez, C. M.; Alvarez, M. A.; Alonso, M.;
García, M. E.; Rueda, M. T.; Ruiz, M. A. Inorg. Chem. 2006, 45, 9593.
ꢀ ꢀ
´ ´
(26) (a) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A.; Aullon, G.; Alvarez,
(23) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London, U.
K., 1975.
S. Organometallics 2007, 26, 5912. (b) Alvarez, M. A.; García, M. E.; Ramos, A.;
Ruiz, M. A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2007, 26, 5454.

Article
Inorganic Chemistry, Vol. 48, No. 19, 2009 9287
are substantially higher than those of comparable
carbonyl compounds (cf. 135.3 and 180.9 ppm for
trans-[Mo2Cp2(μ-PPh2)(μ-Cl)(CO)2]13 and [Mo2Cp2(μ-
PPh2)(μ-H)(CO)4],27 respectively). We attribute this de-
shielding effect in compounds 2 and 3 to the presence of
the strongly π-donor nitride ligand on one of the molyb-
denum atoms. Perhaps the bridging oxo ligand in 3 also
contributes to this effect. In fact, the terminal oxo ligands
(which are strong π-donor groups) have been previously
found to induce even stronger deshielding effects of about
100 ppm, as found in the pairs [Mo2Cp2(μ-PPh2)(μ-X)-
(CO)2]/[Mo2Cp2(μ-PPh2)(μ-X)(O)(CO)] (X = PPh2,20
CH2PPh2).28 In the case of the terminal oxo ligand, we
can interpret this deshielding effect as associated with
strong OfMo π-interactions, which makes the O atom
an effective donor of more than two electrons, thus
reducing the intermetallic bond order, as discussed above
for the oxocomplex 4a (represented by the canonical form
I in Figure 2). In the case of the tricarbonyls 3, our DFT
calculations on 3b, to be discussed below, have revealed
that the bridging oxygen atom is also involved in a similar
π-bonding interaction with the dimetal center, this also
leading to a reduction of the Mo-Mo bond order. The
bonding in these tricarbonyl complexes thus might be
analogously represented by two extreme canonical forms
(III and IV in Figure 2) implying Mo-Mo and Mo-O
bonds orders intermediate between 1 and 2.
Table 3. Selected DFT-Optimized Bond Lengths and Angles for Compound 3b
Mo(1)-Mo(2)
Mo(1)-O(7)
Mo(2)-O(7)
Mo(1)-P(4)
Mo(2)-P(4)
2.840 Mo(2)-C(67)
2.021 Mo(1)-N(8)
1.866 N(8)-Mn(3)
2.474 Mn(3)-C(10)
2.463 Mn(3)-C(9)
2.002
1.718
1.881
1.783
1.777
Mo(1)-O(7)-Mo(2)
Mo(1)-P(4)-Mo(2)
C(67)-Mo(2)-Mo(1)
93.8
70.2
97.7
Mo(2)-Mo(1)-N(8) 104.7
Mo(1)-N(8)-Mn(3) 168.4
C(10)-Mn(3)-C(9)
94.8
C(67)-Mo(2)-Mo(1)-N(8) 168.3
Figure 3. DFT-optimized geometry for compound 3b, with hydrogen
atoms omitted for clarity.
DFT Studies on the Tricarbonyl Complex 3b. To better
understand the nature of the Mo-Mo, Mo-O, and
Mo-N bonding in the oxonitride complexes 2-4 we
carried out DFT29 calculations on the manganese com-
pound 3b (see the Experimental Section for details). The
electronic structure and bonding in this unsaturated
molecule has been analyzed through the properties of
the relevant molecular orbitals, and also by inspection of
the topological properties of the electron density, as
managed in the AIM theory.30
The most relevant parameters derived from the geo-
metry optimization of compound 3b can be found in the
Table 3, with the corresponding view being collected in
the Figure 3. The structure is comparable to that of the
dioxocomplex 4a, if we replace the terminal oxo ligand in
the latter by a carbonyl ligand, and many of the optimized
bond lengths are comparable to those experimentally
measured for 4a, after allowing for the fact that the values
calculated for lengths involving the metal atoms with the
functionals currently used in the DFT computations of
transition metal compounds tend to be slightly longer
(less than 0.05 A) than the corresponding experimental
data.29a,31 As expected for an unsaturated molecule, a
relatively short intermetallic length (2.840 A) is computed
for 3a, slightly longer than the experimental distance in
the dioxocomplex 3a (2.763(1) A) . This distance is about
0.1 A longer than the intermetallic lengths computed at
the same level of theory for the 32-electron carbyne
complexes [Mo2Cp2(μ-COMe)(μ-PCy2)(CO)2] (2.734 A)
and [Mo2Cp2{μ-C(CO2Me)}(μ-PCy2)(CO)2] (2.699 A),
but yet substantially shorter than the values computed
for related electron-precise complexes displaying single
Mo-Mo bonds (e.g., 3.158 A for cis-[Mo2Cp2(μ-COMe)-
(μ-PCy2)(CO)3].26a Thus the intermetallic separation for
3b would be consistent with the presence of significant
multiplicity in the Mo-Mo interaction. As for the
Mo-N length, 1.718 A, it is slightly shorter than the
corresponding experimental distance in 4a (1.756(3) A),
which is suggestive of a very strong interaction, close to
the triple bond. Finally, and more surprising, even when
the Mo-O lengths for the bridging ligand in 3b are on
average only marginally shorter than the experimental
values in 4a (1.944 vs 1.956(3) A), they are quite different
from each other, with the shorter Mo(2)-O(7) length of
1.866 A being compatible with the presence of substantial
multiplicity in that bond, in agreement with the orbital
analysis shown below.
The most relevant molecular orbitals of compound 3b
are depicted in the Figure 4, along with their associated
energy and prevalent bonding character. Although there
is extensive orbital mixing, we can appreciate that the
HOMO (MO 155) has π Mo-N character (also present in
MO 139), while the orthogonal component of the triple
Mo-N bond is mainly represented by MO 138. Note that
the latter has a significant participation of a Mn d orbital,
thus giving support to the delocalization of the π Mo-N
bonding along the Mo-N-Mn path, as proposed on the
basis of the structural data and well represented by
the canonical forms III and IV in Figure 2. Incidentally,
we note that a similar delocalization is present in the
(27) Henrick, K.; McPartlin, M.; Horton, A. D.; Mays, M. J. J. Chem.
Soc., Dalton Trans. 1988, 1083.
ꢀ
´ ´
(28) Garcıa, G.; Garcıa, M. E.; Melon, S.; Riera, V.; Ruiz, M. A.;
~
Villafane, F. Organometallics 1997, 16, 624.
(29) (a) Koch, W.; Holthausen, M. C. A Chemist’s Guide to Density
Functional Theory, 2nd ed.; Wiley-VCH: Weinheim, 2002. (b) Ziegler, T. Chem.
Rev. 1991, 91, 651. (c) Foresman, J. B.; Frisch, ó. Exploring Chemistry with
Electronic Structure Methods, 2nd ed.; Gaussian, Inc.: Pittsburg, 1996.
(30) (a) Bader, R. F. W. Atoms in molecules-A Quantum Theory; Oxford
University Press: Oxford, U.K, 1990.
(31) Cramer, C. J. Essentials of Computational Chemistry, 2nd ed.; Wiley:
Chichester, U.K., 2004.

9288 Inorganic Chemistry, Vol. 48, No. 19, 2009
Garcıa et al.
Table 4. Topological Properties of the Electron Density at the Bond Critical
Points in Compound 3ba
2
bond
F
r F
Mo(2)-O(7)
Mo(1)-O(7)
Mo(2)-C(67)
Mo(1)-N(8)
Mn(3)-N(8)
Mo(1)-P(4)
Mo(2)-P(4)
Mn(3)-C(9)
Mn(3)-C(10)
1.121
0.738
0.820
1.660
0.767
0.507
0.512
1.020
1.017
17.14
12.72
10.10
18.18
13.15
2.84
3.10
13.58
12.70
a Values of the electron density at the bond critical points (F) are given
2
in e A-3; values of the laplacian of F at these points (r F) are given in
e A-5
.
Figure 5. Electron density profile along the Mo(1)-Mo(2) vector for
compound 3b.
oxygen, then the intermetallic interaction gets closer to a
single intermetallic bond. This is also well represented by
the canonical forms III and IV in Figure 2, except that the
MO picture does not easily account for the geometrical
asymmetry of the oxygen bridge.
We have shown previously that the analysis of the
electron density under the AIM theory provides valuable
information (complementary to that of the MO analysis)
for the characterization and even quantification of the
bonds present in different unsaturated dimolybdenum
complexes having carbyne, phosphide, and hydride
bridges.26a,32,33 We have therefore performed a similar
analysis on 3b, with special attention to the data relative
to the metal-metal, metal-nitrogen, and metal-oxygen
bonds. The values of electron density F and its Laplacian
2
(r F) at the most relevant bond critical points (bcp) of
these complexes are collected in Table 4.
We first note that we could not locate a Mo-Mo bcp
even by using different basis for the Mo atoms. We have
encountered this problem before for the mentioned
32-electroncomplexes[Mo2Cp2(μ-COR)(μ-PCy2)(CO)2].26a
An inspection of the values of F along the intermetallic
vector reveals a relative flat plateau near the midpoint of
the vector (Figure 5), where the mathematical conditions
of the bcp cannot be satisfied. Even so, the minimum
value of F is considerable, 0.322 e A-3, actually a value
intermediate between those computed for the above-
mentioned carbyne complexes having a double Mo-Mo
Figure 4. Selected molecular orbitals of compound 3b, with their en-
ergies and main bonding character indicated below.
nitride-bridged complexes [MM0CpCp0(μ-N)(CO)3L]
mentioned above.12 The intermetallic interaction in 3b
is mainly described by MO 154 and MO 153, which
represent an essentially σMo-Mo bond mixed with a
non-bonding electron pair on manganese. Interestingly,
at energies between those of the σMo-N and σMo-O bonds,
there are two orbitals (MO 131 and MO 130) representing
a π-donor interaction from the O atom to the Mo atoms,
this having the same phase as the π-bonding component
of the intermetallic bond in this sort of bioctahedral
molecules, and therefore being destructive in that respect.
Thus we can say on a qualitative basis that upon the
strengthening of this π-donor interaction of the bridging
ꢀ ꢀ
a, M. E.; Garcıa-Vivo, D.; Ruiz, M. A.; Aullon, G.; Alvarez, S.
´ ´
(32) Garcı
Organometallics 2007, 26, 4930.
(33) Garcıa, M. E.; Ramos, A.; Ruiz, M. A.; Lanfranchi, M.; Marchio, L.
Organometallics 2007, 26, 6197.
´

Article
Inorganic Chemistry, Vol. 48, No. 19, 2009 9289
bond (ca. 0.43 e A-3), and those computed at the same
level of theory for electron-precise complexes having
single Mo-Mo bonds such as [Mo2Cp2(μ-COMe)-
(μ-PCy2)(CO)3 (0.22 e A-3) and [Mo2Cp2(CO)6] (0.17
e A-3)].26a,32From these data, therefore, we conclude that
there is also substantial multiplicity in the Mo-Mo bond
of 3b. Incidentally, we note that the minimum of F is
reached at about 1.33 A from Mo(1), rather than at the
exact midpoint of the vector (1.42 A). This can justified by
considering that the electron density at Mo(1) is lower (by
ca. 0.4 e) than that at the carbonyl-bearing Mo(2) atom
(see Supporting Information).
Scheme 2. Proposed Steps for the N-O Bond Cleavage Reactions of
Compound 1 (M = ReCp0(CO)2 or MnCp0(CO)2)
As for the Mo-N and Mo-O bonds, although we have
no data on related compounds to be used for comparative
purposes, we note the very high value of F at the bcp of
the Mo-N bond (1.660 e A-3), consistent with its multi-
ple character, and the noticeably higher value of F at the
shorter O-Mo(2) bond (1.123 e A-3), compared to that
in the O-Mo(1) bond (0.738 e A-3). Again we take these
data as an independent indication of the π-interaction of
the bridging oxygen atom with the Mo atom bearing the
carbonyl ligand. As a result, we trust that the canonical
forms III and IV depicted in Figure 2 give a simple but
realistic description of the bonding in the tricarbonyl
compounds 3, where all the Mo-Mo, Mo-N, and
Mo-O bonds seem to have intermediate bond orders,
and the same can possibly be said of the canonical forms I
and II for compounds 4. In that case, we propose that the
π-donor interaction will be arising from the terminal
oxygen atom, rather than from the bridging one. Finally,
in the case of the tetracarbonyl complexes 2, we trust that
the π interaction from the bridging oxygen atom is
negligible, since now there is an additional carbonyl
ligand, which is an excellent donor for a soft molybdenum
atom.
Pathways for N-O Bond Cleavage in the Reactions of
Compound 1. By following the results of our previous
DFT calculation on the reactions of the anion
[WCp(CO)3]- with the nitrosyl cation [MnCp(CO)2-
(NO)]þ we can reasonably assume that the formation of
compounds 2 also proceeds under orbital control, and
thus would be initiated by the nucleophilic attack of the
anion to the nitrogen atom of the nitrosyl ligand in the
cation, strongly involved in the corresponding lowest
unoccupied molecular orbital (LUMO).12 This most
probably would involve a single Mo site of the anion
for steric reasons, even when DFT calculations on the
related anion [Mo2Cp2(μ-PCy2)(μ-CO)2]- indicate that
the suitable donor orbitals involve both metal atoms.32
The intermediate A thus formed (Scheme 2) has a nitrosyl
ligand bridging the Re atom and a highly unsaturated
dimolybdenum center, and then it would rearrange to
reduce this electronic deficiency by coordinating its oxy-
gen atom to the second Mo center. The resulting inter-
mediate B would have a μ3-nitrosyl ligand in a very
uncommon arrangement. Actually, to the best of our
knowledge all known compounds having nitrosyl ligands
bridging three metal atoms bind the metals exclusively
through the N atom. However, there are a few examples
where a nitrosyl ligand has been found coordinated
through both the N and O atoms, either to two (μ2-N:
N,O mode)34 or to four metal atoms (μ4-N:O:N:O and μ4-
N:N:N:O modes).35,36 Interestingly, in all these cases the
N-O bond of the nitrosyl ligand is considerably elon-
gated, thus suggesting a significant activation with respect
to the full cleavage of this bond. In the case of intermedi-
ate B, the progressive weakening of the N-O bond might
readily proceed first through a rearrangement rendering
double NdMo and single N;O bonds (C in Scheme 2)
and finally by full cleavage of the latter bond, also
involving the opening of the bridging carbonyl at some
stage, to finally yield the observed tetracarbonyl product
of type 2. In our view, then, the great electronic and
coordinative unsaturation of the anion 1 is a circumstance
of critical influence for the successful cleavage of the N;
O bond being observed, since this induces and/or facil-
itates the simultaneous coordination of both the N and O
atoms of the nitrosyl ligand, as required for the cleavage
of this ligand without direct participation of carbonyl
ligands (i.e., processes yielding CO2).12
Nitrosylation Reactions of Compound 1. As stated
above, we examined these reactions so as to check
whether the electronic and coordinative unsaturation of
this anionic complex would be enough to induce the
cleavage of the nitrosyl ligand. The reaction of 1 with
the strong nitrosylating agent (NO)BF4 was difficult to
control, and a mixture of several compounds was ob-
tained under all experimental conditions examined. In
contrast, the reaction of 1 with a milder reagent such as
N-methyl-N-nitroso-p-toluenesulfonamide proceeds more
(35) Beringhelli, T.; Ciani, G.; D0Alfonso, G.; Molinari, H.; Sironi, A.;
Freni, M. J. Chem. Soc., Chem. Commun. 1984, 1327.
(36) (a) Kyba, E. P.; Kashyap, R. P.; Mountzouris, J. A.; Davis, R. E. J.
Am. Chem. Soc. 1990, 112, 905. (b) Ellis, D.; Farrugia, L. J. J. Cluster Sci. 2001,
12, 243.
(34) (a) Legzdins, P.; Rettig, S. J.; Veltheer, J. E.; Batchelor, R. J.;
Einstein, F. W. B. Organometallics 1993, 12, 3575. (b) Ipaktschi, J.; Mohse-
::
ni-Ala, J.; Dulmer, A.; Steffens, S.; Wittenburg, C.; Heck, J. Organometallics
2004, 23, 4902.

9290 Inorganic Chemistry, Vol. 48, No. 19, 2009
Garcıa et al.
selectively to give the electron-precise nitrosyl derivative
[Mo2Cp2(μ-PPh2)(CO)3(NO)]. This complex has been
previously prepared by us through the reaction of the
paramagnetic complex [Mo2Cp2(μ-PPh2)(CO)4] with
NO.14 Since the observed product contains one more CO
than the starting anion, it can be guessed that a very
unstable unsaturated nitrosyl derivative is initially formed,
this then evolving through spontaneous carbonylation
rather than through any N-O bond cleavage process, as
it will be discussed later on. We then attempted to modify
this evolution by carrying out the nitrosylation reaction in
the presence of CNtBu, a ligand comparable to CO, but
with higher donor ability and steric demands, which per-
haps would open a new CO2-elimination channel for the
cleavage of the nitrosyl ligand.12 Indeed this reaction
proceeds smoothly below room temperature, and the for-
mation of the tricarbonyl complex [Mo2Cp2(μ-PPh2)-
(CO)3(NO)] is essentially suppressed, but no cleavage of
the nitrosyl ligand is induced either. Instead, a mixture of
the isocyanide complexes [Mo2Cp2(μ-PPh2)(CNtBu)-
(CO)2(NO)] (5) and [Mo2Cp2(μ-PPh2)(μ-η1:η2-CNtBu)-
(CO)(NO)] (6) is obtained in an about 1:2 ratio (Chart 2).
Although these products differ by just one CO ligand,
separate experiments indicated that compound 6 does not
react with CO under ordinary conditions, whereas com-
pound 5 neither experiences spontaneous decarbonylation
in solution, even in refluxing toluene. Thus, we must
conclude that the formation of these two products follow
from different reaction pathways, a matter to be discussed
later on. We should finally stress that, in spite of the fact
that compound 5 can be formally derived by replacement of
CO with CNtBu in the tricarbonyl complex [Mo2Cp2(μ-
PPh2)(CO)3(NO)], this substitution reaction actually does
not take place even in refluxing toluene solution, as in-
dicated by independent experiments.
Chart 2
Scheme 3. Pathways in the Nitrosylation Reactions of Compound 1
(P = PPh2; L = CO, CNtBu)
ligand, by comparison with the IR data of the related
complexes
[Mo2Cp2(μ-η1:η2-CNtBu)(CO)2(μ-dppm)]
Structural Characterization of Compounds 5 and 6. The
proposed structure of the dicarbonyl compound 5 is
based on that crystallographically determined for the
tricarbonyl complex [Mo2Cp2(μ-PPh2)(CO)3(NO)].14
The presence of the four terminal ligands is immediately
denoted by the appearance of four medium to strong
bands in the characteristic regions of the C-N, C-O, and
N-O bond stretches of the corresponding terminal li-
gands (Table 2), while the strong NMR deshielding of the
P nucleus, similar to that of the tetracarbonyl complex 2a,
is fully consistent with the electron-precise nature of this
molecule. Out of the possible arrangements of the term-
inal ligands, our proposal for 5 is derived from the P-C
couplings exhibited by the 13C NMR resonances of the
carbonyl (δ 243.5 ppm, JCP = 21 Hz and δ 234.4 ppm, JCP
∼ 0 Hz) and isocyanide (δ 169.7 ppm, JCP ∼ 0 Hz) ligands,
these denoting a positioning relative to the P atom cis,
trans, and trans, respectively.
and [Mo2Cp2(μ-η1:η2-CNtBu)(CO)3(κ1-dppm)].28,37 This
is further confirmed by the 13C NMR spectrum of 6,
which exhibits an abnormally deshielded isocyanide re-
sonance at 214.6 ppm, as found for the mentioned
compounds and related dimolybdenum complexes hav-
ing μ-η1:η2 isocyanide ligands.38 Our spectroscopic data,
however, do not allow us to define whether the carbon
atoms of the isocyanide and carbonyl ligands in 6 are
bound to the same or different metal atom, although the
second possibility seems more likely on mechanistic
grounds, next discussed. Our data do not either show
whether the CpMo moieties in 6 are positioned in a cisoid
or transoid arrangement, but the latter is the one most
commonly found in this sort of cyclopentadienyl com-
plexes, presumably favored over the cisoid isomers on
steric grounds.
Pathways in the Nitrosylation Reaction of Compound 1.
The nucleophilic attack of the unsaturated anion 1 on N-
methyl-N-nitroso-p-toluenesulfonamide is expected to
give initially an unsaturated nitrosyl-bridged derivative
[Mo2Cp2(μ-NO)(μ-PPh2)(CO)2] (D in Scheme 3) much in
the same way as the protonation reaction of 1 gives the
corresponding hydride-bridged derivative [Mo2Cp2-
(μ-H)(μ-PPh2)(CO)2].13 Apparently, this intermediate
The IR spectrum of compound 6 exhibits strong bands
at 1858 and 1604 cm-1, which are indicative of the
presence of terminal CO and NO ligands, respectively.
This spectrum shows no high-frequency band characteri-
stic of terminal isocyanide ligands, but exhibits a weak
and broadband at 1647 cm-1 suggestive of the presence
of a four-electron donor (μ-η1:η2) bridging isocyanide
~
(37) Riera, V.; Ruiz, M. A.; Villafane, F.; Bois, C.; Jeannin, Y. J.
(38) Adams, H.; Bailey, N. A.; Bannister, C.; Faers, M. A.; Fedorko, P.;
Organomet. Chem. 1990, 382, 407.
Osborn, V. A.; Winter, M. J. J. Chem. Soc., Dalton Trans. 1987, 341.

Article
Inorganic Chemistry, Vol. 48, No. 19, 2009 9291
would be very unstable, and it would partially decom-
pose, thus liberating CO that rapidly would react with
undecomposed molecules to give the electron-precise and
very stable tricarbonyl [Mo2Cp2(μ-PPh2)(CO)3(NO)].
Decomposition of D is then expectedly avoided in the
presence of isocyanide, since any ligand being present (L)
would rapidly react with D to give an electron precise
intermediate E, perhaps still retaining the nitrosyl bridge,
if we use the results of the carbonylation reactions of the
isoelectronic complexes [Mo2Cp2(μ-PCy2)(μ-X)(CO)2]
(X = alkenyl, COMe) as a model.26 The intermediate E
would easily rearrange in different ways eventually open-
ing the nitrosyl bridge, then leading to the dicarbonyl 5 or,
when L = CO, to the tricarbonyl [Mo2Cp2(μ-PPh2)-
(CO)3(NO)] as noted above. Alternatively, when L =
CNtBu the intermediate E might evolve through decar-
bonylation, perhaps induced by the presence on the same
metal atom of the relatively bulky CNtBu ligand, to give a
new unsaturated intermediate F, which then would reach
the electronic saturation by a rearrangement of the iso-
cyanide ligand, from terminal to the μ-η1:η2 bridging
mode, this being accompanied by a displacement of the
bridging nitrosyl to a terminal position, thus explaining
the formation of the isocyanide-bridged complex 6.
Concluding Remarks. The formation of the nitride-
bridged complexes 2 (which in turn are the precursors
of the nitride-bridged compounds 3 and 4) can be under-
stood as derived initially from an orbitally controlled
nucleophilic attack of a metal atom of the anion 1 to the N
atom of the nitrosyl ligand in the cations [MCp0-
(NO)(CO)2]þ. Because of the electronic and coordinative
unsaturation of the resulting trimetallic intermediate, the
system does not evolve through a CO2 elimination path-
way, as previously observed by us in the reactions of the
electron-precise anions of type [MCp(CO)2L]-, and this
gives further support to our previous hypothesis that a
close approach of the carbonyl ligands to the bridging
nitrosyl ligand in the intermediates initially formed is
essential for this particular reaction pathway to be op-
erative. Instead, we trust that the unsaturated dimolyb-
denum center derived from 1 allows and induces the
simultaneous coordination of both the N and O atoms
of the nitrosyl ligand to partially relieve this deficiency,
thus initiating a progressive weakening of the N-O bond
in the nitrosyl ligand eventually leading to its full clea-
vage, to yield metal-bound nitride and oxo ligands and
thus achieving the complete electronic saturation of the
resulting molecule. The presence of a metal initially
bound to the nitrosyl ligand is essential to the overall
process, since otherwise this ligand binds the unsaturated
dimolybdenum center in non-activated (with respect to
the N-O bond cleavage) coordination modes involving
only the nitrogen atom, as observed in the nitrosylation
reactions of the anion 1. Further work will be needed to
prove the use of the above ideas for a better understand-
ing of the ways in which transition-metal complexes can
cleave the strong bond of the NO molecule, and for the
design of polymetallic substrates able to carry out this
process in an efficient and even catalytic way.
atmosphere using standard Schlenk techniques. Solvents were
purified according to literature procedures and distilled prior to
their use.39 Petroleum ether refers to that fraction distilling in
the range 338-343 K. Compounds [MCp0(CO)2(NO)]BF4
[M = Mn (1),40 Re (2)41] and THF solutions of Na[Mo2Cp2-
(μ-PPh2)(μ-CO)2] (1)13 were prepared as described previously.
Chromatographic separations were carried out on alumina
using jacketed columns cooled by tap water (ca. 285 K) or by
a closed 2-propanol circuit, kept at the desired temperature with
a cryostat. For this purpose, commercial aluminum oxide
(Aldrich, activity I, 150 mesh) was degassed under vacuum prior
to use. The latter was mixed under nitrogen with the appropriate
amount of water to reach the activity desired. All other reagents
were obtained from the usual commercial suppliers and used as
received. IR stretching frequencies were measured in solution or
KBr discs. Nuclear Magnetic Resonance (NMR) spectra were
routinely recorded at 300.13 (1H), 121.50 (31P{1H}), or 75.47
MHz (13C{1H}) at 290 K in CD2Cl2 solutions unless otherwise is
stated. Chemical shifts (δ) are given in ppm, relative to internal
tetramethylsilane (1H, 13C) or external 85% aqueous H3PO4
(31P). Coupling constants (J) are given in hertz.
Preparation of [Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)4]
(2a). Solid [ReCp0(CO)2(NO)]BF4 (0.075 g, 0.17 mmol) was
added to a freshly prepared THF solution (10 mL) containing
about 0.17 mmol of compound 1, cooled at 193 K. The mixture
turned into black-green instantaneously and was further stirred
for 30 min while allowing it to warm up to 243 K, to yield an
orange mixture. The solvent was then removed under vacuum,
the residue was extracted with a minimum CH2Cl2, and the
extract was chromatographed on alumina (activity 3.5) at 243 K.
Elution with dichloromethane-petroleum ether (1:1) gave a
minor orange fraction containing some [Mo2(μ-PPh2)(CO)3-
(NO)]. Elution with THF-petroleum ether (1:1) gave a major
orange fraction which yielded, after removal of solvents under
vacuum at 243 K, compound 2a as a brown-orange powder
(0.095 g, 62%). This compound is thermally unstable, and it
transforms into 3a above 253 K in dichloromethane solution.
Thus satisfactory elemental analysis for this compound could
not be obtained. 1H NMR (400.13 MHz, 253 K): δ 8.3-6.7 (m,
Ph, 10H), 5.50, 5.24 (2s, 2 ꢁ 5H, Cp), 5.11, 4.99, 4.94, 4.89 (4m, 4
ꢁ 1H, C5H4), 2.11 (s, 3H, Me). 13C{1H} NMR (100.63 MHz, 253
K): δ 239.7 (d, JCP = 27, MoCO), 233.7 (s, MoCO), 206.5, 206.1
(2s, ReCO), 141.5 [d, JPC= 41, C1(Ph)], 136.5 [d, JPC = 49,
C1(Ph)], 135.5-128.7 (m, Ph), 110.5 [s, C1(C5H4)], 105.2, 97.6
(2s, Cp), 83.5, 83.4, 83.1, 82.6 [4s, C2,3(C5H4)], 13.9 (s, Me).
Preparation of [Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3]
(3a). A solution of compound 2a (0.046 g, 0.05 mmol) in
dichloromethane (20 mL) was stirred at room temperature for
2 h to give a dark green solution which was filtered through
alumina (3 ꢁ 2.5 cm, activity 3.5) at 285 K. Addition of
petroleum ether to the filtrate and removal of solvents under
vacuum gave compound 3a as an emerald-green, air-sensitive
powder (0.039 g, 88%). Anal. Calcd for C31H27Mo2NO4PRe: C,
1
42.00; H, 3.07; N, 1.58. Found: C, 41.60; H, 3.25, N, 1.70. H
NMR (200.13 MHz): δ 8.2-6.5 (m, Ph, 10H), 6.05 (s, 5H, Cp),
5.59 (d, JPH = 1, 5H, Cp), 4.96, 4.68 (2m, 2 ꢁ 1H, C5H4), 4.75
(m, 2H, C5H4), 1.71 (s, 3H, Me). 13C{1H} NMR (100.63 MHz,
253 K): δ 240.0 (d, JCP = 18, MoCO), 207.3, 206.5 (2s, ReCO),
144.1 [d, JPC= 28, C1(Ph)], 138.1 [d, JPC = 52, C1(Ph)],
135.8-128.5 (m, Ph), 110.3 [s, C1(C5H4)], 104.1, 99.4 (2s, Cp),
84.2, 84.1, 83.9, 81.6 [4s, C2,3(C5H4)], 14.0 (s, Me).
Preparation of [Mo2MnCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3]
(3b). Solid [MnCp0(CO)2(NO)]BF4 (0.052 g, 0.17 mmol) was
added to a freshly prepared THF solution (10 mL) containing
(39) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemicals,
5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003.
Experimental Section
(40) Connelly, N. G. Inorg. Synth. 1974, 15, 91.
General Procedures and Starting Materials. All manipula-
tions and reactions were carried out under a nitrogen (99.995%)
(41) Tam, W.; Liu, G. Y.; Wang, K. W.; Kiel, W. A.; Wong, V. K.;
Gladysz, J. A. J. Am. Chem. Soc. 1982, 104, 141.

9292 Inorganic Chemistry, Vol. 48, No. 19, 2009
Garcıa et al.
about 0.17 mmol of compound 1, cooled at 193 K, and the
mixture was further stirred for 3 h while allowing it to warm up
to room temperature, to yield a brown-green mixture. The
solvent was then removed under vacuum, the residue was
extracted with a minimum dichloromethane-petroleum ether
(1:1), and the extract was chromatographed on alumina (activity
3.5) at 285 K. Elution with the same solvent mixture gave a
minor orange fraction containing some [Mo2Cp2(μ-PPh2)-
(CO)3(NO)] and [Mo2Cp2(μ-H)(μ-PPh2)(CO)4] in similar
amounts. Elution with dichloromethane-petroleum ether (1:1)
gave a red-brown fraction containing [Mn2Cp02(CO)2(NO)2]
and minor amounts of other uncharacterized species. Finally,
elution with dichloromethane gave a green fraction which
yielded, after removal of solvents under vacuum, compound
3b as a green, air-sensitive microcrystalline solid (0.033 g, 26%).
Thus satisfactory elemental analysis for this compound could
not be obtained. 1H NMR: δ 8.29-6.42 (m, Ph, 10H), 6.04, 5.57
(2s, 2 ꢁ 5H, Cp), 4.19, 4.10 (2m, 2 ꢁ 1H, C5H4), 3.99 (m, 2H,
C5H4), 1.64 (s, 3H, Me).
Table 5. Crystal Data for Compound 4a
mol formula
mol wt
cryst syst
space group
radiation (λ, A)
a, A
b, A
c, A
R, deg
β, deg
C30H27Mo2NO4PRe
874.58
triclinic
P1
0.71073
11.186(4)
15.058(5)
9.851(3)
79.09(3)
64.21(2)
72.91(3)
1424.4(8)
2
2.039
5.198
293(2)
3.09 to 30.00
-13, 15; -20, 21; 0, 13
8298
8298 (0.000)
6124
γ, deg
V, A3
Z
calcd density, gcm-1
absorp coeff., mm-1
temperature, K
θ range, deg
index ranges (h, k, l)
no. of reflns collected
no. of indep reflns (Rint
)
Preparation of [Mo2ReCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2]
(4a). A solution of compound 3a (0.045 g, 0.05 mmol) in
dichloromethane (12 mL) was stirred at room temperature in
the presence of air for 30 min to give a blue solution which was
chromatographed on alumina (10 ꢁ 2.5 cm, activity 3.5) at 285
K. Elution with dichloromethane gave a dark blue fraction.
Removal of solvents under vacuum and crystallization of the
residue from dichloromethane-petroleum ether at 253 K gave
compound 4a as a blue microcrystalline solid (0.036 g, 82%).
The crystals used in the X-ray study were grown by the slow
diffusion at room temperature of a layer of diethyl ether into a
concentrated solution of the complex in toluene. Anal. Calcd for
C30H27Mo2NO4PRe: C, 41.20; H, 3.11; N, 1.60. Found: C, 41.09;
no. of reflns with I > 2σ(I)
R indexesa [data with I > 2σ(I)]
R1 = 0.0323
wR2 = 0.0707
R1 = 0.0554
wR2 = 0.0768
0.929
R indexesa (all data)
GOF
no. of restraints/parameters
0/358
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|, wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2
.
C2(Ph)], 132.2 [d, JPC= 11, C2(Ph)], 128.9-127.7 (m, Ph), 96.8,
91.1 (2s, Cp), 59.6 [s, C1(tBu)], 30.7 [s, C2(tBu)]. Data for
compound 6: Anal. Calcd for C28H29Mo2N2O2P: C, 51.87; H,
4.51; N, 4.32. Found: C, 51.68; H, 4.72; N, 4.05. 1H NMR
(200.13 MHz): δ 7.67-6.76 (m, Ph, 10H), 5.50, 5.31 (2s, 2 ꢁ 5H,
Cp), 1.45 (s, 9H, Me). 13C{1H} NMR (50.33 MHz): δ 232.5 (d,
JCP = 12, MoCO), 214.6 (d, JCP = 5, μ-η1:η2-CN), 149.5 [d,
1
H, 3.00; N, 1.75. H NMR (400.13 MHz): δ 8.18-7.28 (m, Ph,
10H), 5.68, 5.55 (2d, JPH = 1, 2 ꢁ 5H, Cp), 5.04, 5.01 (2m, 2 ꢁ 2H,
C5H4), 2.12 (s, 3H, Me). 13C{1H} NMR (100.63 MHz, 213 K): δ
205.2, 205.0 (2s, ReCO), 137.5 [d, JPC= 37, C1(Ph)], 135.7-128.3
[m, C1(Ph) and C2,3(Ph)], 109.9 [s, C1(C5H4)], 104.4, 102.4 (2s,
Cp), 84.6, 84.5, 83.7, 83.3 [4s, C2,3(C5H4)], 13.2 (s, Me).
J
PC= 23, C1(Ph)], 136.9 [d, JPC = 44, C1(Ph)], 131.6 [d, JPC
=
12, C2(Ph)], 129.1-128.1 (m, Ph), 99.9, 89.8 (2s, Cp), 62.5 [ s,
C1(tBu)], 32.2 [ s, C2(tBu)].
Preparation of [Mo2MnCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)-
(CO)2] (4b). A solution of compound 3b (0.030 g, 0.040 mmol)
in dichloromethane (10 mL) was stirred at room temperature in
the presence of air for 20 min to give a blue solution. Workup as
described for 4a yielded compound 4b as a green-black micro-
crystalline solid (0.023 g, 78%). Anal. Calcd for C30H27MnMo2-
NO4P: C, 48.47; H, 3.66; N, 1.88. Found: C, 48.35; H, 3.48; N,
1.95. 1H NMR: δ 8.13-7.29 (m, Ph, 10H), 5.71, 5.53 (2s, 2 ꢁ 5H,
Cp), 4.52, 4.39, 4.32, 4.27 (4m, 4 ꢁ 1H, C5H4), 1.82 (s, 3H, Me).
Nitrosylation of Compound 1. Solid N-methyl-N-nitroso-p-
toluenesulfonamide (0.036 g, 0.17 mmol) and neat CNtBu (20
μL, 0.17 mmol) were added to a freshly prepared THF solution
(10 mL) containing about 0.17 mmol of compound 1, cooled at
203 K, and the mixture was further stirred for 90 min while
allowing it to warm up to room temperature, to yield a brown-
orange mixture. The solvent was then removed under vacuum,
the residue was extracted with toluene (5 mL), and the extract
was chromatographed on alumina (activity 3.5) at 285 K.
Elution with toluene gave a rose-orange fraction. Removal of
the solvent and crystallization of the residue from toluene-
petroleum ether at 253 K gave compound [Mo2Cp2(μ-PPh2)-
(CNtBu)(CO)2(NO)] (5) as an orange powder (0.031 g, 27%).
Elution with dichloromethane gave a yellow-orange fraction.
Workup as above gave compound [Mo2Cp2(μ-PPh2)(μ-η1:η2-
CNtBu)(CO)(NO)] (6) as a yellow powder (0.038 g, 35%). Data
for compound 5: Anal. Calcd for C29H29Mo2N2O3P: C, 51.49; H,
4.32; N, 4.14. Found: C, 51.56; H, 4.49; N, 4.06. 1H NMR
(200.13 MHz): δ 7.60-6.83 (m, Ph, 10H), 5.12, 4.96 (2s, 2 ꢁ 5H,
Cp), 1.70 (s, 9H, Me). 13C{1H} NMR (50.33 MHz): δ 243.5 (d,
X-ray Structure Determination for Compound 4a. The inten-
sity data of compound 4a were collected at room temperature on
a Philips PW1100 single-crystal diffractometer using a graphite
monochromated Mo KR radiation. Crystallographic and
experimental details for the structure are summarized in Table 5.
A correction for absorption was made [maximum and minimum
values for the transmission coefficients were 1.000 and 0.785].42
The structure was solved by direct methods and refined by
full-matrix least-squares procedures (based on Fo2) with
SHELX-97,43 first with isotropic thermal parameters and then
with anisotropic thermal parameters in the last cycles of refine-
ment for all the non-hydrogen atoms. At the end of the isotropic
refinement the thermal parameters of the N and O bridging
atoms resulted comparable, so confirming the correct position
of the bridging atoms. An alternative refinement with the nitride
bridging the two molybdenums and the oxo bridging the one Mo
and one Re was also carried out, but the thermal parameters of
the oxygen and the nitrogen atoms resulted very different (that
of the N atom, very high, about three times higher than that of
the O atom, very low). The hydrogen atoms were introduced
into the geometrically calculated positions and refined riding on
the corresponding parent atoms. In the final cycles of refinement
2
2
a weighting scheme w = 1/σ2Fo þ (0.0403P)2] where P = (Fo
þ
2
2Fc )/3, was used. Full crystallographic data for 4a are provided
in the CIF file format.
(42) (a) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158. (b)
Ugozzoli, F. Comput. Chem. 1987, 11, 109.
(43) Sheldrick, G. M. SHELX-97. Programs for Crystal Structure Ana-
::
:: ::
J
CP = 21, MoCO), 234.4 (s, MoCO), 169.7 (s, MoCN), 147.0 [d,
lysis (Release 97-2); Institut fur Anorganische Chemie der Universitat
:: ::
Gottingen: Gottingen, Germany, 1997.
J
PC= 34, C1(Ph)], 142.6 [d, JPC = 36, C1(Ph)], 135.2 [d, JPC= 9,

Article
Computational Details. All computations described in this
Inorganic Chemistry, Vol. 48, No. 19, 2009 9293
restrictions, using initial coordinates derived from X-ray data of
comparable complexes, and frequency analyses were performed
to ensure that a minimum structure with no imaginary frequen-
cies was achieved in each case. For interpretation purposes,
natural population analysis (NPA) charges49 were derived from
the natural bond order (NBO) analysis of the data.49 Molecular
orbitals and vibrational modes were visualized using the
Molekel program.50 The topological analysis of F was carried
out with the Xaim routine.51
work were carried out using the GAUSSIAN03 package,44
in which the hybrid method B3LYP was applied with the
Becke three parameters exchange functional45 and the Lee-
Yang-Parr correlation functional.46 Effective core potentials
(ECP) and their associated double-ζ LANL2DZ basis set were
used for the molybdenum and manganese atoms.47 The light
elements (P, O, C, and H) were described with 6-31G* basis.48
Geometry optimizations were performed under no symmetry
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M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
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Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
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J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
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Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A. Gaussian 03,
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Acknowledgment. We thank the MEC of Spain and Princi-
pado de Asturias, Spain, for financial support (Projects
CTQ2006-01207 and PA-MAS94-05).
Supporting Information Available: Tables of selected molec-
ular orbitals, atomic charges and data from the AIM topological
analysis for compound 3b in pdf format, and full crystallo-
graphic data for 4a in the CIF file format. This material is
available free of charge via the Internet at http://pubs.acs.org.
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Petersson, G. A.; Al-Laham, M. A. J. Chem. Phys. 1991, 94, 6081. (c) Petersson,
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Luthi, H. P. CHIMIA 2000, 54, 766.
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