Synthesis and oxidation reactions of the unsaturated anion [Mn2(CO)6(μ-Ph2PCH2 PPh2)]2-

Article abstract of DOI:10.1021/om0101590

Chemical reduction of the unsaturated dihydride [Mn₂(μ-H)₂(CO)₆(μ-dppm)] (dppm = Ph₂PCH₂PPh₂) with several reagents (Na-Hg, K, etc.) promotes dihydrogen elimination to yield the deep green

Full text of DOI:10.1021/om0101590

Organometallics 2001, 20, 3007-3016
3007
Syn th esis a n d Oxid a tion Rea ction s of th e Un sa tu r a ted
An ion [Mn 2(CO)6(µ-P h 2P CH2P P h 2)]2-†
Xiang-Yang Liu, V´ıctor Riera, and Miguel A. Ruiz*
Departamento de Quı´mica Orga´nica e Inorga´nica, IUQOEM, Universidad de Oviedo,
E-33071 Oviedo, Spain
Claudette Bois
Laboratoire de Chimie des Me´taux de Transition, UACNRS419, Universite´ P. et M. Curie,
4 Place J ussieu, 75252 Paris, Cedex 05, France
Received February 27, 2001
Chemical reduction of the unsaturated dihydride [Mn2(µ-H)2(CO)6(µ-dppm)] (dppm ) Ph2-
PCH2PPh2) with several reagents (Na-Hg, K, etc.) promotes dihydrogen elimination to yield
the deep green anion [Mn2(CO)6(µ-dppm)]2-. Oxidation of the latter with [FeCp2]PF6 (Cp )
η5-C5H5) gives the CO-bridged species [Mn2(µ-η1:η2-CO)(CO)6(µ-dppm)] or, if PR3 is present,
the related complexes [Mn2(µ-η1:η2-CO)(CO)5(PR3)(µ-dppm)] (R ) Ph, OMe). Oxidation of
the anion in the presence of nitriles or 1-alkynes gives nitrile or vinylidene-bridged derivatives
[Mn2(µ-η1:η2-L)(CO)6(µ-dppm)] with high yield (L ) NCR or CCHR). The complexes having
the (µ-η1:η2-CO) ligand display dynamic behavior in solution and react readily with CO to
give the corresponding [Mn2(CO)7L(dppm)] (L ) CO, PR3). Diazocompound CH(SiMe3)N2
also adds readily to [Mn2(µ-η1:η2-CO)(CO)6(µ-dppm)], but the C-Si bond in the initial product
is easily hydrolyzed to yield the diazomethane complex [Mn2(µ-CO)(µ-η1:κ1-CH2N2)(CO)6(µ-
dppm)]. The structure of the new complexes is analyzed in the light of their IR and variable-
temperature NMR spectra, and possible reaction pathways for the above oxidation processes
are proposed on the basis of the nature of the compounds actually isolated and that of the
detected intermediates. The structure of the new compounds [Mn2(µ-η1:η2-CO)(CO)5-
{P(OMe)3}(µ-dppm)] and [Mn2(CO)7(PPh3)(µ-dppm)] has been solved through single-crystal
X-ray diffraction studies.
Ch a r t 1
In tr od u ction
Organometallic compounds having multiple metal-
metal bonds are species of interest because of the high
reactivity they usually display toward a great variety
of molecules under mild conditions.1 Relevant examples
of this sort of molecules are the triply bonded cyclopen-
tadienyl dimers [M2Cp2(CO)4] (M ) Mo, W; Cp ) η5-
C5H5)2 or the osmium dihydride [Os3(µ-H)2(CO)10].3
Attempts to synthesize new compounds within this class
of species by using decarbonylation or other ligand
elimination reactions from suitable precursors often fail
to give the desired result. In part this is because the
primary unsaturated dimetal center being generated is
reactive enough so as to activate bonds in the surround-
ing ligands, thus relieving both coordination and elec-
tronic deficiency. For example, we have found previously
that removal of CO in the electron precise dimers [M2-
Cp2(CO)4(µ-L2)] [M ) Mo, W; L ) Ph2PCH2PPh2, dppm;
(EtO)2POP(OEt)2, tedip] can induce either C-H, P-C,
or P-O bond cleavages in the cyclopentadienyl or
phosphorus-donor ligands, depending on the complex
and reaction conditions.4 This is also the case of the
reduction of the unsaturated dihydride [Mn2(µ-H)2(CO)6-
(µ-tedip)], which yields the P-O cleavage product [Mn2-
{µ-P(OEt)2}{µ-OP(OEt)2}(CO)6]2- (Chart 1).5 By con-
trast, reduction of the dppm-bridged analogue [Mn2(µ-
H)2(CO)6(µ-dppm)] causes no cleavage in the phosphorus
ligand but yields the doubly bonded anion [Mn2(CO)6-
(µ-dppm)]2- (1) (Chart 1).6 Although previous results by
† Dedicated to Prof. R. Uso´n on the occasion of his 75th birthday.
* E-mail address: mara@sauron.quimica.uniovi.es.
(1) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms;
Oxford University Press: Oxford, U.K., 1993.
(2) (a) Curtis, M. D. Polyhedron 1987, 6, 759. (b) Winter, M. J . Adv.
Organomet. Chem. 1989, 29, 101.
(3) (a) Humphries, A. P.; Kaesz, H. D. Prog. Inorg. Chem. 1979, 25,
145. (b) Deeming, A. J . Adv. Organomet. Chem. 1986, 26, 1. (c)
D’Alfonso, G. Chem. Eur. J . 2000, 6, 209.
(4) Alvarez, M. A.; Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A.; Bois, C. Organometallics 1997, 16, 2581, and references therein.
(5) Liu, X. Y.; Riera, V.; Ruiz, M. A.; Lanfranchi, M.; Tiripicchio,
A.; Tiripicchio-Camellini, M. Organometallics 1994, 13, 1940.
(6) Liu, X. Y.; Riera, V.; Ruiz, M. A. Organometallics 1994, 13, 2925.
10.1021/om0101590 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/05/2001

3008 Organometallics, Vol. 20, No. 14, 2001
Ta ble 1. IR Da ta for New Com p ou n d sa
Liu et al.
compound
νst(CO)/cm-1
[Mn2(µ-H)2(CO)6(µ-dppm)]
2031 (s), 2000 (s), 1948 (s), 1920 (vs)
1888 (s), 1841 (vs), 1817 (s), 1787 (s)
Na2[Mn2(CO)6(µ-dppm)] (1)
[Mn2(µ-η1:η2-CO)(CO)6(µ-dppm)] (2)
[Mn2(µ-η1:η2-CO)(CO)5(µ-dppm)(PPh3)] (3a )
[Mn2(µ-η1:η2-CO)(CO)5(µ-dppm){P(OMe)3}] (3b)
[Mn2(µ-η1:η2-NCtBu)(CO)6(µ-dppm)] (4a )
[Mn2(µ-η1:η2-NCPh)(CO)6(µ-dppm)] (4b)
[Mn2(CO)7(µ-dppm)(PPh3)] (5a )
2034 (vs), 1987 (s), 1961 (s), 1934 (s, sh) 1922 (s), 1709 (w)b
1997 (s), 1939 (vs), 1919 (s), 1892 (s), 1866 (m), 1665 (w)
2006 (s), 1948 (vs), 1925 (s), 1897 (s), 1870 (m), 1669 (w)b
2018 (s), 1964 (vs), 1943 (m), 1910 (m), 1902 (m), 1886 (w)
2020 (vs), 1969 (s), 1946 (m), 1913 (m), 1907 (m), 1891 (w)
2033 (s), 1949 (vs), 1915 (m), 1873 (m)b
[Mn2(CO)7(µ-dppm){P(OMe)3}] (5b)
[Mn2(µ-CH2N2)(µ-CO)(CO)6(µ-dppm)] (6)
2034 (s), 1950 (vs), 1923 (m), 1896 (m), 1880 (m, sh)b
2032 (vs), 1995 (vs), 1962 (s), 1934 (m), 1922 (w, sh), 1871 (w)c
Recorded in tetrahydrofuran solution, unless otherwise stated. bIn dichloromethane solution. 1653 (w) cm-1 [ν(N-N)].
a
c
Ch a r t 2
us4 and others7 indicate that backbone P-C cleavage
in the dppm ligand is a thermal process facilitated by
the presence of unsaturation at a dimetallic center,
anion 1 is surprisingly stable in this respect, showing
no change even in refluxing tetrahydrofuran. This
cannot be conciliated either with recent results on
diruthenium complexes, which suggest that an increase
in electron density at the dimetallic center might
actually facilitate the backbone P-C cleavage of the
dppm ligand.8 In this context we decided to study the
oxidation reactions of dianion 1 in order to test the effect
of increasing the formal unsaturation in the molecule
while at the same time reducing its negative charge.
The results of that study, here presented, indicate that
no cleavage of the dppm is induced in this way, which
tend to force coordination of the CO ligand in a η1:η2
fashion instead. Further information on the processes
involved has been obtained by carrying out the oxidation
of 1 in the presence of ligands such as phosphines,
nitriles, or isocyanides. The latter reactions also repre-
sent a good synthetic approach to new complexes not
available through alternative, more conventional routes.
Part of this work appeared in a communication.6
of the starting dihydride (Chart 1). For example, the
IR spectrum shows four strong νst(CO) bands (Table 1),
and its 31P spectrum denotes a single environment for
both phosphorus atoms of the bridging ligand, as found
for the dihydride precursor. All this is consistent with
a C2v symmetry for the anion. Furthermore, the absence
of additional bands in the IR spectrum and the low
sensitivity of the latter to the nature of the cation (Li+,
Na+, K+) indicate that anion-cation interactions for 1
are rather weak in tetrahydrofuran solutions. This in
turn is consistent with the very low C-O stretching
frequencies exhibited by 1, with an average value (1833
cm-1) some 140 cm-1 lower than the corresponding
figure for the neutral precursor (1975 cm-1).
Resu lts a n d Discu ssion
Oxida tion of Tetr a h ydr ofu r a n Solu tion s of Com -
p ou n d 1. When 2 equiv of [FeCp2]PF6 is added to a
tetrahydrofuran solution of 1 at - 80 °C, an immediate
color change from green to orange is observed, and
within a few minutes the IR spectrum of the solution
shows almost complete formation of the new heptacar-
bonyl complex [Mn2(µ-η1:η2-CO)(CO)6(µ-dppm)] (2). The
structure of 2 (Chart 2) is firmly supported by spectro-
scopic data (Table 1 and Experimental Section). Thus,
the IR spectrum of 1 shows five strong ν(CO) bands in
the terminal carbonyl region, with a pattern similar to
that of other dimetallic complexes having two fac-Mn-
(CO)3 oscillators in a low-symmetry environment. In
addition, there is a low-frequency ν(CO) band at 1709
cm-1, which suggests the presence of a four-electron-
donor µ-η1:η2 bridging carbonyl ligand, as found in the
prototypal [Mn2(µ-η1:η2-CO)(CO)4(µ-dppm)2].10 The lat-
ter complex was found to be fluxional in solution, the
NMR data being compatible with the restricted ex-
change process depicted in Figure 1.11 That process
creates a pseudo mirror plane containing the phospho-
rus and manganese atoms and seems to be present also
in compound 2. Thus, the 13C NMR spectrum of 2 at
Syn th esis of Na 2[Mn 2(CO)6(µ-d p p m )] (1). Dihy-
dride [Mn2(µ-H)2(CO)6(µ-dppm)] reacts readily with
sodium amalgam in tetrahydrofuran at room tempera-
ture, presumably evolving hydrogen, to yield a dark
green solution of the dianion 1 (Na+ salt). The same
anion is obtained by using other reducing agents, such
as potassium or an excess of Li[HBEt3], with only minor
differences in their IR or 31P NRM spectra, surely due
to slightly different ion-pair effects.9 Removal of solvents
from a filtered solution yields compound 1 as a very air-
sensitive green powder, which readily decomposes upon
manipulation, attempts of crystallization, etc. Attempts
to exchange the cation (Na+ by AsPh4+, N(PPh3)2+, etc.)
so as to give a more stable salt were also unsuccessful.
As expected, anion 1 is readily protonated (by [NH4]PF6)
to regenerate the starting dihydride.
Spectroscopic data in solution for 1 are indicative of
a highly symmetric structure for this anion, close to that
(7) (a) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev.
1988, 86, 191. (b) Doherty, N. M.; Hogarth, G.; Knox, S. A. R.;
Macpherson, K. A.; Melchior, F.; Orpen, A. G. J . Chem. Soc., Chem.
Commun. 1986, 540. (c) Doherty, N. M.; Hogarth, G.; Knox, S. A. R.;
Macpherson, K. A.; Melchior, F.; Morton, D. A. V.; Orpen, A. G. Inorg.
Chim. Acta 1992, 198, 257.
(8) Shiu, K.-B.; J ean, S.-W.; Wang, H.-S. Organometallics 1997, 16,
114.
(9) Darensbourg, M. Y. Prog. Inorg. Chem. 1985, 33, 221.
(10) (a) Colton, R.; Commons, C. J . Aust. J . Chem. 1975, 28, 1673.
(b) Colton, R.; Hoskins, B. F. Aust. J . Chem. 1975, 28, 1663.
(11) Marsella, J . A.; Caulton, K. G. Organometallics 1982, 1, 274.

Unsaturated Anion [Mn2(CO)6(µ-Ph2PCH2PPh2)]2-
Organometallics, Vol. 20, No. 14, 2001 3009
F igu r e 1. Fluxional process proposed for [Mn2(µ-η1:η2-CO)-
(CO)4(µ-dppm)2]11 (only the plane containing the manga-
nese and carbonyl atoms is shown).
238 K exhibits seven CO resonances in the range 240-
215 ppm, in agreement with the static structure. At
room temperature, however, three resonances remain
unchanged, while the other four have coalesced pair-
wise. This is consistent with the rearrangement depicted
in Figure 1, which also implies (in the fast exchange
limit) the equivalence of the methylenic protons of the
1
dppm ligand, as observed in the room-temperature H
NMR spectrum of 2.
F igu r e 2. CAMERON drawing of the molecular structure
of [Mn2(µ-η1:η2-CO)(CO)5{P(OMe)3}(µ-dppm)] (3b). Ellip-
soids represent 30% probability.
Compound 2 has a low thermal stability. Solutions
of 2 slowly transform (even at -20 °C) into [Mn2(CO)8-
(µ-dppm)].10a,12 This corresponds to an intermediate
behavior between the stable pentacarbonyl [Mn2(µ-η1:
η2-CO)(CO)4(µ-dppm)2] and the enneacarbonyl complex
[Mn2(µ-η1:η2-CO)(CO)8], the latter being a very unstable
species detected during different photolysis studies
carried out on [Mn2(CO)10].13
Ta ble 2. 31P {1H } NMR Da ta for New Com p ou n d sa
The formation of heptacarbonyl 2 from 1 requires
some decomposition so as to liberate the extra carbon
monoxide needed at some stage of the process. In fact,
IR monitoring of the reaction mixture denotes the
presence of at least an intermediate species for which
stretching C-O bands at 1999 and 1689 cm-1 can be
assigned (others being obscured by those of 2). This
species rapidly disappears at room temperature or by
removal of tetrahydrofuran (THF) from the cold reaction
mixture and dissolution of the residue in toluene. It is
thus sensible to assume that the mentioned intermedi-
ate could be the hexacarbonylic solvate [Mn2(µ-η1:η2-
CO)(CO)5(THF)(µ-dppm)]. To check this hypothesis, we
studied the oxidation reactions of 2 in the presence of
PPh3 or P(OMe)3, two P-donor ligands with different
electronic and steric properties.
Oxid a tion of 1 in th e P r esen ce of P R3 (R ) P h ,
OMe). Anion 1 reacts with 2 equiv [FeCp2]PF6 in the
presence of stoichiometric amounts of PR3 to give in
good yields the corresponding hexacarbonyl complexes
[Mn2(µ-η1:η2-CO)(CO)5(PR3)(µ-dppm)] (3a , b) (a , R ) Ph;
b, RdOMe).
The structure of 3b‚C7H8 has been solved through an
X-ray study and is depicted in Figure 2, while Table 3
lists the most relevant bond distances and angles. The
structure is closely related to those previously found for
the pentacarbonyl complexes [Mn2(µ-η1:η2-CO)(CO)4(µ-
R2PCH2PR2)2] (R ) Ph,10 Cy14) after replacing in the
latter a diphosphine ligand by CO and P(OMe)3. Bond
distances and angles within the almost planar Mn2(µ-
δ/ppm
P2
J (PP)/Hz
compd
P1
P3
J (1,2) J (1,3) J (2,3)
1b
2
3a
3b
4a c
4bc
60.7 (s)
68.2 (d) 51.8 (d)
78.5 (dd) 49.0 (dd) 74.1 (s, br)
75.1 (dd) 50.7 (dd) 194.2 (s, br)
91
88
92
66
61
77
83
80
88
94
3
30
9
12
55.8
52.5
54.4
51.4
5a (C)d 58.5 (d) 52.7 (dd) 75.4 (d)
24
5a (T)d 57.7 (d) 72.8 (d)
70.6 (s, br)
5b (C)d 60.4 (d) 58.3 (dd) 191.0 (d)
58
40
5b (T)d 60.3 (dd) 68.7 (dd) 183.9 (dd)
9
6
51.4
48.3
a
Measured at 121.5 MHz, in CD2Cl2 solution at room temper-
ature, unless otherwise stated. Phosphorus atoms are labeled (P1
to P3) according to the figure shown, except for compounds 4 and
6, where labeling is arbitrary. bIn tetrahydrofuran: C6D6 solution
(9:1). AB multiplet. d213 K.
c
η1:η2-CO)(CO)4 moiety in 3b are similar to those found
for the bis(diphosphine) derivatives. Because of the low
accuracy of our structural determination, the small
differences in the bond lengths observed for the bridging
carbonyl [Mn(1)-C(4) longer and Mn(1)-O(4) shorter
with respect to the referenced compounds] are probably
(12) Reimann, E.; Singleton, E. J . Organomet. Chem. 1972, 38, 113.
(13) (a) Hepp, A. F.; Wrighton, M. S. J . Am. Chem. Soc. 1983, 105,
5934. (b) Dunkin, I. A.; Ha¨rter, P.; Shields, C. J . J . Am. Chem. Soc.
1984, 106, 7248. (c) Church, S. P.; Hermann, H.; Grevels, F.-G.;
Shaffner, K. J . Chem. Soc., Chem. Commun. 1984, 785. (d) Zhang, S.;
Zhang, H.-T.; Brown, T. L. Organometallics 1992, 12, 3929.
(14) Morgan, C. A.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chim. Acta
1994, 224, 105.

3010 Organometallics, Vol. 20, No. 14, 2001
Liu et al.
multiplet. The 13C spectra are also temperature-depend-
ent. At 213 K, the spectrum exhibits in the carbonyl
region three doublets of doublets and three doublets,
which is consistent with the static structure. At 293 K,
however, just two resonances remain sharp (one dd and
one d), while the other four resonances are very broad.
All this is consistent with the fluxional process depicted
in Figure 1 and allows us to identify the chemical shift
of the bridging CO as either 235.7 or 231.8 ppm on the
basis of the multiplicity and temperature-dependence
of these two resonances.
Compounds 3 are structural models for the interme-
diate species detected during the formation of hepta-
carbonyl complex 2 (see above). Indeed, the bands that
can be clearly assigned to that intermediate (1999 and
1689 cm-1) are very close to those observed for 3. Thus
we assume that this intermediate is isostructural to
complexes 3, with THF in the former occupying the
position of PR3 in the latter.
Whatever the exact nature of the intermediate result-
ing from the removal of two electrons in dianion 1, that
species effectively behaves as a source for the highly
unsaturated, 30-electron [Mn2(CO)6(µ-dppm)] fragment.
To explore the synthetic potential of this system, we
studied the oxidation reactions of 1 in the presence of
ligands able to act as 4e-donor bridging groups, such
as nitriles or 1-alkynes.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 3b
Mn(1)-Mn(2)
Mn(1)-C(1)
Mn(1)-C(3)
Mn(2)-P(2)
Mn(2)-C(4)
Mn(2)-C(6)
2.981(8)
1.80(4)
1.70(5)
2.28(1)
1.84(4)
1.66(3)
Mn(1)-P(1)
Mn(1)-C(2)
Mn(1)-C(4)
Mn(2)-P(3)
Mn(2)-C(5)
Mn(1)-O(4)
2.33(1)
1.87(5)
2.23(3)
2.20(1)
1.81(4)
2.12(3)
P(1)-Mn(1)-C(2)
C(3)-Mn(1)-P(1)
C(3)-Mn(1)-Mn(2)
C(5)-Mn(2)-C(6)
C(5)-Mn(2)-Mn(1)
175.0(14) P(2)-Mn(2)-P(3) 172.6(5)
91.0(15) C(3)-Mn(1)-C(1)
88.4(14) C(5)-Mn(2)-P(2)
94.8(19)
87.7(12)
106.5(16) C(5)-Mn(2)-C(4) 141.5(15)
93.9(11) Mn(2)-C(4)-O(4) 163.5(33)
not significant. However, the intermetallic separation
in 3b [2.981(8) Å], while compatible with the formula-
tion of a single Mn-Mn bond, is significantly longer
than the corresponding figure in the bis(diphosphine)
analogues (ca. 2.93 Å)10,14 and even longer than that for
[Mn2(CO)10] [2.904(1)].15 The large intermetallic separa-
tion in 3b cannot be obviously attributed to the presence
of a single dppm bridge in the molecule. This is more
obvious when comparing its structure with that of the
isoelectronic [Mn2(µ-η1:η2-CdCHtBu)(CO)6(µ-dppm)], a
molecule displaying a Mn-Mn bond length as short as
2.800(5) Å.16 Thus, there seems to be a genuine length-
ening effect of the 4e-donor bridging CO on the Mn-
Mn bond. The associated effect of this lengthening is
an increase of the distance between the bridgehead
carbon and the Mn atom to which it is π-bonded and a
decrease in the oxygen-metal distance. In terms of the
structural classification of the linear semibridging car-
bonyls proposed by Crabtree and Lavin,17 the (µ-η1:η2-
CO) ligand in the above dimanganese complexes, rather
than representing an entirely differentiated type of
coordination for CO ligands (class IV),17 might instead
be viewed as examples of an intermediate situation
between class I (strong O-M interaction, 4e-donors) and
class II (weak O-M interaction, 2e-donors) linear
semibridging carbonyls.
Oxid a tion of 1 in th e P r esen ce of Ter m in a l
Alk yn e or Nitr ile Liga n d s. Although the title ligands
are rather poor donors (when compared with PR3), they
are active enough when used in excess so as to compete
with solvent during oxidation of 1, thus yielding the
corresponding derivatives in good yield.
t
In the case of RCCH (R ) Ph, Bu), the products are
the corresponding vinylidene complexes [Mn2(µ-η1:η2-
CCHR)(CO)6(µ-dppm)], and these are obtained in quite
good yields (80-85%). We note that these compounds
could be obtained previously from RCCH and either
[Mn2(µ-H)2(CO)6(µ-dppm)] (slow thermal reaction) or
[Mn2(CO)8(µ-dppm)] (slow photochemical reaction), but
yields were in general much lower (ca. 30%).16 There-
fore, the present procedure is more convenient from a
synthetic point of view.
IR and 31P NMR data in solution for compounds 3 are
consistent with the solid-state structure found for 3b.
For example, the IR spectra exhibit five strong bands
in the terminal νst(CO) region and a weak absorption
at ca. 1670 cm-1, which can be assigned to the µ-η1:η2-
CO ligand. As expected, the 31P spectra of 3 exhibit
separated resonances for the inequivalent P atoms of
dppm. However, the two-bond couplings between dppm
and PR3 (J 13 in Table 2) are unusually low (3 or 30 Hz)
for mutually trans P atoms (cf. a value of 110 Hz has
been calculated for [Mn2(µ-η1:η2-CO)(CO)4(µ-dppm)2]).18
We will address this point later on.
The oxidation of 1 in the presence of excess nitrile
NCR (R ) tBu, Ph) gives the corresponding derivatives
[Mn2(µ-η1:η2-NCR)(CO)6(µ-dppm)] (4a ,b). Similar com-
pounds have been obtained from dihydride [Mn2(µ-Η)2-
(CO)6(µ-dppm)] and NCR (R ) Me, Et, Pr).19 In fact,
spectroscopic data for the latter nitrile derivatives are
very similar to those of 4 (Tables 1 and 2), so they all
must have the same structure (Chart 3), confirmed for
R ) Me through an X-ray study.19
There are several points of interest in the formation
of compounds 4. In the first place, neither 4a nor 4b
can be obtained through the reaction of dihydride [Mn2-
(µ-Η)2(CO)6(µ-dppm)] with the corresponding nitrile.
Actually, NCtBu failed to react at all, even at 330 K,
whereas NCPh gave the hydridoalkylideneimido com-
plex [Mn2(µ-H)(µ-ΝCHPh)(CO)6(µ-dppm)].19 Thus, oxi-
dation of 1 in the presence of NCR is the only synthetic
way currently available for compounds 4a ,b. The failure
of NCtBu to react with the dimanganese dihydride must
The 13C and 1H NMR spectra of compound 3b (see
Experimental Section) give clear indication of fluxional
behavior in solution. Although we have not studied this
1
in detail, we note that the room-temperature H NMR
spectrum displays just a single triplet for the methylenic
hydrogens of the bridging dppm, which is inconsistent
with the static structure of the molecule. By lowering
the temperature, however, this resonance broadens and
eventually transforms into a poorly resolved ABMX
(15) Churchill, M. R.; Amoh, K. N.; Wassermann, H. J . Inorg. Chem.
1981, 20, 1609.
(16) Garc´ıa-Alonso, F. J .; Riera, V.; Ruiz, M. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M. Organometallics 1992, 11, 370.
(17) Crabtree, R. H.; Lavin, M. Inorg. Chem. 1986, 25, 805.
(18) Caulton, K. G.; Adair, P. J . Organomet. Chem. 1976, 114, C11.
(19) Garc´ıa-Alonso, F. J .; Garc´ıa-Sanz, M.; Riera, V.; Anillo-Abril,
A.; Tiripicchio, A.; Ugozzoli, F. Organometallics 1992, 11, 801.

Unsaturated Anion [Mn2(CO)6(µ-Ph2PCH2PPh2)]2-
Organometallics, Vol. 20, No. 14, 2001 3011
Ch a r t 3
Sch em e 2. Rea ction s of (µ-η1:η2-CO) Com p lexes
w ith CO or P R3 [Mn -Mn ) Mn 2(µ-d p p m )]
Sch em e 1. P r op osed Rea ction P a th w a ys for th e
Oxid a tion Rea ction s of Dia n ion 1 [Mn -Mn )
Mn 2(µ-d p p m ); S ) Tetr a h yd r ofu r a n ]
intermediate is thermally unstable and partially de-
composes, the liberated CO completing its transforma-
tion into the heptacarbonyl 2. In the presence of L, the
corresponding hexacarbonyl structure is stable only for
L ) PR3 (cf. compounds 3). For L ) nitrile, further
isomerization to give the bridged nitrile products 4
rapidly occurs at room temperature. Finally, for L )
1-alkyne, the intermediate structure must have a
lifetime long enough so as to allow for the isomerization
of the terminally bound alkyne into a terminally bonded
vinylidene group, which displaces CO from the bridging
position afterward to yield the more stable µ-η1:η2-
vinylidene derivative. We note that this last proposal
is in full agreement with the data obtained from the
reactions of [Mn2(µ-Η)2(CO)6(µ-dppm)] with 1-alkynes.16
Ch em ica l Beh a vior of th e µ-η1:η2-CO Br id ged
Com p ou n d 2. The prototypal [Mn2(µ-η1:η2-CO)(CO)4-
(µ-dppm)2] has been shown to be quite reactive toward
a variety of reagents including CO,20 RNC,21 diazo-
methane,22 or even weaker electron donors such as SO2
or CS2.22a In all cases, the incoming molecule destroys
the π interaction between the bridging CO and the
second metal atom (eq 1), although further rearrange-
ments are possible.
[Mn2(µ-η1:η2-CO)(CO)4(µ-dppm)2] + L f
[Mn2(CO)5L(µ-dppm)] (1)
When L ) CO, eq 1 also represents a carbonylation/
decarbonylation equilibrium which has been previously
studied for several bridging diphosphines. From that
study it was concluded that steric factors were domi-
nant, with the bulkier diphosphine ligands favoring the
pentacarbonyl structure.20b On this basis, the bridging
CO ligands in compounds 2 and 3 are expected to be
much more reactive than the above bis-dppm-bridged
compounds. To explore this, we studied the reactions
of 2 or 3 with CO, PR3 (R ) Ph, OMe), and CH(SiMe3)-
N2. The results of the reactions with simple two-electron
donor ligands are summarized in Scheme 2. As stated
above, compound 2 slowly decomposes to give [Mn2-
(CO)8(µ-dppm)], and, expectedly, this transformation
occurs instantaneously in the presence of CO. Hexa-
carbonyls 3a ,b are more stable complexes, but are also
readily carbonylated in the presence of CO to yield the
have therefore a kinetic origin, as we have found that
compound 4a is in fact very stable. For example, it does
not react with CO or PPh3 at room temperature, thus
indicating that the µ-η1:η2-nitrile ligand is tightly bound
to the dimanganese center, in contrast to the µ-η1:η2-
carbonyl ligand present in compounds 2 or 3. In agree-
ment with this, we note that an intermediate species
can be detected during the formation of 4a . IR bands
clearly assignable to that intermediate species appear
at 1998 and 1707 cm-1, which suggests a structure
similar to that of compounds 3. We trust this intermedi-
ate has a terminal nitrile and bridging µ-η1:η2-CO group
and evolves at room temperature to the thermodynamic
product 4a , with terminal CO and bridging nitrile
ligands.
By considering all the results discussed so far, a
unified picture emerges for the processes occurring
during oxidation of dianion 1 (Scheme 1). Removal of
two electron from 1 gives a highly unsaturated species,
[Mn2(CO)6(µ-dppm)], which rapidly reacts with a mol-
ecule of solvent S or ligand L (if available) to give a CO-
bridged species [Mn2(µ-η1:η2-CO)(CO)5X(µ-dppm)] (X )
S, L). For S ) tetrahydrofuran, this hexacarbonyl
(20) (a) Aspinall, H. C.; Deeming, A. J . J . Chem. Soc., Chem.
Commun. 1981, 724. (b) Wolf, T. E.; Klemann, L. P. Organometallics
1982, 1, 1667.
(21) Balch, A. L.; Benner, L. S. J . Organomet. Chem. 1977, 135, 339.
(22) (a) Turney, T. W. Inorg. Chim. Acta 1982, 64, L141. (b)
Ferguson, G.; Laws, W. J .; Parvez, M.; Puddephatt, R. J . Organome-
tallics 1983, 2, 276.

3012 Organometallics, Vol. 20, No. 14, 2001
Liu et al.
Ch a r t 4
relatively bulky phosphorus ligands around Mn(2)
seems to impose some steric pressure on the structure,
as deduced from the bending of these ligands away from
each other [P(2)-Mn(2)-P(3) ) 102.0(2)°]. This might
be related with the observation that, in solution at room
temperature, compound 5a (but not 5b) reversibly
dissociates PPh3 to a small extent (Scheme 2). This
dissociation process is favored upon increasing the
temperature, and it is fully suppressed below 0 °C, as
shown by IR and NMR data.
F igu r e 3. CAMERON drawing of the molecular structure
of [Mn2(CO)7(PPh3)(µ-dppm)] (5a ). Ellipsoids represent 30%
probability.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 5a
As stated above, compounds 5 exist in solution as a
mixture of two isomers. In both isomers the methylenic
protons of dppm are chemically equivalent, as deduced
Mn(1)-Mn(2)
Mn(1)-C(1)
Mn(1)-C(3)
Mn(2)-P(2)
Mn(2)-C(5)
Mn(2)-C(7)
3.005(3)
1.73(2)
1.85(2)
2.345(5)
1.77(2)
1.85(2)
Mn(1)-P(1)
Mn(1)-C(2)
Mn(1)-C(4)
Mn(2)-P(3)
Mn(2)-C(6)
2.280(5)
1.82(2)
1.76(2)
2.285(4)
1.78(2)
1
from H NMR data (see Experimental Section). There-
fore, we conclude that the PR3 ligand must be contained
in the averaged plane defined by the dppm bridge and
manganese atoms. This leaves out just two possibilities,
labeled C and T to indicate the position of PR3 (cis or
trans) relative to dppm (Chart 4). Isomer C is that one
found in the crystal for 5a . The equilibrium ratio C/T
for compounds 5 was found to be somewhat dependent
on temperature or solvent, but we have not studied this
dependence in detail. In addition, isomers T were found
to be fluxional in solution, whereas isomers C remained
rigid on the NMR time scale.
C(4)-Mn(1)-Mn(2)
C(2)-Mn(1)-C(3)
C(6)-Mn(2)-C(7)
P(3)-Mn(2)-Mn(1)
176.6(6)
166.0(7)
173.5(7)
168.5(2)
C(4)-Mn(1)-P(1)
C(1)-Mn(1)-P(1)
C(5)-Mn(2)-P(2)
P(3)-Mn(2)-P(2)
91.2(6)
176.7(6)
162.0(6)
102.0(2)
corresponding heptacarbonyls [Mn2(CO)7(PR3)(µ-dppm)]
(5a ,b). A further proof of the stabilizing effect of PR3
(relative to CO) on the (µ-η1:η2-CO) structures is the fact
that compounds 5a ,b can be converted back to 3a ,b
through UV photolysis at -10 °C, whereas [Mn2(CO)8-
(µ-dppm)] fails to yield 2 in that way.
The high reactivity of 2 is illustrated through its facile
reaction with PR3 (R ) Ph, OMe) under ambient
conditions. As expected, the products are the heptacar-
bonyls 5a ,b, and this is in fact the preferred preparative
method for these new compounds.
Str u ctu r e an d Solu tion Dyn am ics of Com pou n ds
5. Both 5a and 5b exist in solution as an equilibrium
mixture of two isomers, which we have labeled C and T
(Table 2). The structure of the major (C) isomer for 5a
has been solved through an X-ray study and is depicted
in Figure 3, while Table 4 lists the most relevant bond
distances and angles. As expected, the structure can be
derived from that of [Mn2(CO)10] by replacing two
equatorial carbonyls by the dppm bridge and one axial
carbonyl by PPh3. The intermetallic distance 3.005(3)
Å is longer than that in [Mn2(CO)10] (2.9038(3) Å)15 but
comparable to that in [Mn2(CO)6(µ-dppm)2] (3.010(3)
Å)23 or [Mn2(CO)8(µ-Ph2AsCH2AsPh2)] (2.962(3) Å).24 As
found for the above dimanganese compounds, the bridg-
ing ligand constrains the staggering of both coordination
octahedra, so that the torsion angle defined by P(2)-
Mn(2)-Mn(1)-P(1) in compound 5a is ca. 30°, rather
than the optimum value (45°) for minimum repulsion
between both metal fragments. The presence of two
The assignment of 31P resonances (Table 2) has been
made on the basis of the expected trends in chemical
shifts: (a) Isomers C and T should display similar
chemical shifts for P1 (P trans to CO), with a value close
to that for [Mn2(CO)8(µ-dppm)] (59.7 dppm). (b) Isomer
T should have a second dppm resonance P2 (trans to
PR3) with a higher chemical shift, close to the value of
70.2 ppm reported for [Mn2(CO)6(µ-dppm)2].18 The above
assignments imply that the coupling constant between
P2 and P3 in the cis isomers exceeds by some 20 Hz the
value for the corresponding trans isomers. We recall
here that an unusually low value for trans-2J PP coupling
was also found for compounds 3. Although the usual
2
trend for J PP in octahedral geometry is |J trans| > |J cis|,
there are cases where the reverse holds, mainly because
2
2J cis tends to be negative while J trans is usually posi-
tive.25
The assignment just discussed is fully consistent with
the dynamic behavior exhibited by these isomers in
solution, as deduced from the 13C NMR data. By
recalling the fluxional behavior of [Mn2(CO)6(µ-dppm)2]11
we would expect that a similar CO scrambling process
should be possible in isomer T, but not for C because of
(25) (a) J ameson, C. J . In Phosphorus-31 NMR Spectroscopy in
Stereochemical Analysis; Verkade, J . G., Quin, L. D., Eds.; VCH:
Deerfield, 1987; Chapter 6. (b) Pregosin, P. S.; Kunz, R. W. 31P and
13C NMR of Transition Metal Phosphine Complexes; Springer-Verlag:
Berlin, 1979.
(23) Cotton, F. A.; Shin, K. B. Gazz. Chim. Ital. 1985, 705.
(24) Hoskins, B. F.; Steen, R. J . Aust. J . Chem. 1983, 36, 683.

Unsaturated Anion [Mn2(CO)6(µ-Ph2PCH2PPh2)]2-
Ta ble 5. 13C{1H} NMR Da ta a for Com p ou n d s 5
Organometallics, Vol. 20, No. 14, 2001 3013
Ch a r t 5
δ/213 K
δ/293 K
isomer
resonance
5a
5b
5a
5b
C
C
C
C
C
T
T
T
T
T
5 + 7
233.9
229.9
228.6
225.1
222.2
236.1
227.4
227.4
224.8
222.3
231.1
225.8
228.7
224.9
221.9
232.7
227.4
224.9
223.2
221.9
233.9
229.6
228.5
224.7
222.1
229.0b
229.0b
229.0b
224.7
229.0b
231.5
226.4
229.0
225.0
222.4
228.5b
228.5b
228.5b
223.4
228.5b
Spectroscopic and microanalytical data for 6 give full
support to its formulation as a diazomethane complex,
although some details of the structure cannot be de-
duced without uncertainty. In light of our data we
propose for 6 the structure depicted in Chart 5, contain-
ing a diazomethane molecule bridging the manganese
atoms through C and N and behaving as a two-electron
donor group. However, we cannot exclude completely
for 6 a structure related to that found for [Mn2{C(O)-
CH2N2}(CO)4(µ-dppm)2],22b where the diazomethane
molecule bridges the manganese atoms through a single
N atom, while the methylenic end couples to a carbonyl,
yielding a bonded acyl group (Chart 5). We favor the
first formulation on the basis of different pieces of
evidence. First, the IR spectrum of 6 exhibits five νst-
(CO) bands between 2032 and 1922 cm-1, with a pattern
characteristic of many hexacarbonylic dimanganese
compounds of general formula [Mn2(µ-X)(µ-Y)(CO)6(µ-
dppm)] (X, Y being one to three electron-donor ligands).
In addition, there is also a weak band substantially
shifted to lower wavenumbers (1871 cm-1), thus sug-
gesting the presence of a bridging or semibridging
carbonyl ligand, and a weak band at 1653 cm-1 which
could be assigned to the N-N stretch.22 In agreement
with the IR data, the 13C NMR spectrum of 6 exhibits
six different resonances in the terminal carbonyl region
and a seventh one at 279 ppm. We note here, however,
that the high chemical shift of the latter could be itself
consistent with the presence of either a bridging car-
bonyl or an acyl group.27 Unfortunately, in the absence
of 13C data on related complexes, the chemical shift of
the methylenic group of the diazo fragment (116 ppm)
cannot be used as a diagnostic for its attachment to
either C or Mn atoms. The 1H NMR spectrum of 6,
however, suggests that the CH2N2 group also binds the
metal through its C atom. This is because the methyl-
enic protons exhibit a coupling to phosphorus (4 Hz) that
6
1 + 3
4
2
5 + 7
1 + 3
6
4
2
a
Measured in CD2Cl2 solutions; chemical shifts are only given
for CO resonances. Carbonyl ligands have been labeled (1-7)
according to the figures shown. bVery broad resonance.
the presence of the PR3 ligand in the plane perpendicu-
lar to the dppm bridge, where the carbonyl scrambling
should take place. Indeed, isomer C behaves as a rigid
molecule from 213 to 293 K, exhibiting the expected five
13C carbonyl resonances (ca. 2:2:1:1:1 intensity). For
isomer T, however, the five carbonyl resonances ob-
served at low temperatures broaden on warming up and
at 293 K are observed as two broad resonances (ca. 6:1
intensity). This is consistent with the “merry-go-round”
mechanism proposed for [Mn2(CO)6(µ-dppm)2], whereby
the resonance not involved in the dynamic process can
be safely assigned to the carbonyl trans to phosphorus
in isomer T (position 4, see Table 5). Starting from this
assignment and proceeding through the expected analo-
gies in chemical shifts, all carbonyl resonances can be
assigned as shown in Table 5.
Dia zom eth a n e Der iva tive of Com p ou n d 2. The
high reactivity of compound 2 (compared with the
related pentacarbonyl [Mn2(µ-η1:η2-CO)(CO)4(µ-dppm)2])
is also illustrated through its rapid reaction with CH-
(SiMe3)N2, a stable but less reactive derivative of
diazomethane. This reaction takes place in a few
minutes, in contrast to the reaction of [Mn2(µ-η1:η2-CO)-
(CO)4(µ-dppm)2] with diazomethane, reported to be
completed in about 24 h.22b Surprisingly, however, no
SiMe3 group is incorporated into the major product
isolated from the reaction of 2 with CH(SiMe3)N2, which
instead can be formulated as the diazomethane complex
[Mn2(µ-η1:κ1-CH2N2)(µ-CO)(CO)6(µ-dppm)] (6). Monitor-
ing of the above reaction by IR and 31P NMR spectros-
copy suggests that a species similar to 6 might be
formed initially (perhaps containing a CH(SiMe3)N2
ligand), but this intermediate is rapidly decomposed
(presumably through hydrolysis) upon manipulation or
any attempts of isolation (crystallization, chromatogra-
phy, etc.) to give 6 and other unidentified products.
There are precedents of the use of CH(SiMe3)N2 as a
synthetic equivalent of diazomethane, the CH(SiMe3)
group being transformed into CH2 through hydrolysis
during workup.26
3
can be reasonably identified as a J PH figure while would
appear as too large for a four-bond coupling constant.
Con clu d in g Rem a r k s. The oxidation reactions of 1
represent a useful synthetic route to dimanganese
compounds having four-electron η1:η2 ligands (CO, NCR,
CCHR) not accessible through more conventional ther-
mal or photochemical reactions. The new η1:η2-bridged
complexes [Mn2(µ-η1:η2-CO)(CO)5L(µ-dppm)] (L ) CO,
PPh3, P(OMe)3) are species more reactive than the
pentacarbonyls [Mn2(µ-η1:η2-CO)(CO)4(µ-R2PCH2PR2)2].
The relative stability of the singly bridged dppm com-
plexes follows the order PR3 > CO and P(OMe)3 > PPh3.
(26) Chan, K. S.; Wulff, W. D. J . Am. Chem. Soc. 1986, 108, 5229.
(27) Mann, B. E.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic Press: London, U.K., 1981.

3014 Organometallics, Vol. 20, No. 14, 2001
Liu et al.
The latter suggests, in contrast to previous conclusions,20b
that π acid phosphorus-donor ligands increase the
stability of the µ-η1:η2-CO complexes when steric effects
are not to be considered.
reach room temperature for 1 h. Solvent was afterward
removed under vacuum and the orange residue chromato-
graphed on an alumina column (activity III, 15 cm) at -35
°C. Elution with THF/petroleum ether (1:5) gave a yellow
fraction containing [FeCp2]. Elution with a 1:2 mixture gave
a yellow-orange fraction, which yielded, after removal of
solvents under vacuum, compound 3a as an orange powder
(0.026 g, 45%). This compound can be recrystallized from
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations and reactions
were carried out using standard Schlenk techniques under an
atmosphere of dry, oxygen-free nitrogen. Solvents were puri-
fied according to standard literature procedures28 and distilled
under nitrogen prior to use. Petroleum ether refers to that
fraction distilling in the range 60-65 °C. Compounds [Mn2-
(µ-H)2(CO)6(µ-dppm)],16 [FeCp2]PF6,29 and Ph2PCH2PPh230 were
prepared according to literature procedures. Other reagents
were obtained from the usual commercial suppliers and used
without further purification. Filtrations were carried out using
diatomaceous earth, and alumina for column chromatography
was deactivated by appropriate addition of water to the
commercial material (Aldrich, neutral, activity I). NMR spectra
were recorded at 300.13 MHz (1H), 121.50 MHz (31P{1H}), and
75.47 MHz (13C{1H}), at room temperature unless otherwise
stated. Chemical shifts (δ) are given in ppm, relative to
internal TMS (1H, 13C) or external 85% H3PO4 aqueous solution
(31P), with positive values for frequencies higher than that of
the reference. Coupling constants (J ) are given in hertz. 13C-
{1H} NMR spectra were routinely recorded on solutions
containing a small amount of tris(acetylacetonate)chromium-
(III) as a relaxation reagent.
P r ep a r a tion of Tetr a h yd r ofu r a n Solu tion s of Na 2[Mn 2-
(CO)6(µ-d p p m )] (1). In a typical experiment, dihydride [Mn2-
(µ-H)2(CO)6(µ-dppm)] (0.035 g, 0.053 mmol) in tetrahydrofuran
(10 mL) was stirred with an excess of 1% (by weight) sodium
amalgam (ca. 1 mL, 5 mmol of Na) for 30 min, affording a dark
green solution. The latter was filtered using a cannula and
was then ready for further use. IR and 31P NMR spectroscopy
showed the presence of a single species in this solution, and
thus a 100% yield in the formation of 1 was assumed.
P r ep a r a tion of [Mn 2(µ-η1:η2-CO)(CO)6(µ-d p p m )] (2).
Solid [FeCp2]PF6 (0.033 g, 0.1 mmol) was added to a solution
of compound 1 (ca. 0.05 mmol) in THF (10 mL), previously
cooled at -80 °C. The mixture was stirred for 5 min and the
solvent then removed under vacuum from the yellow-orange
resulting solution. Toluene (10 mL) was then added to the
residue, and the mixture was further stirred for 5 min and
filtered. Removal of solvent from the filtrate and washing of
the residue with petroleum ether (3 × 5 mL, so as to remove
[FeCp2]) gave compound 2 as an essentially pure yellow powder
(0.026 g, 75%). Although this complex could be purified by
column chromatography on Florisil (Aldrich, 100-200 mesh)
at -40 °C by using dichloromethane/petroleum ether (1:1) as
elution solvent, all attempts to crystallize this complex resulted
in its progressive decomposition (to give [Mn2(CO)8(µ-dppm)]).
Anal. Calcd for C32H22Mn2O7P2: C, 55.66; H, 3.21. Found: C,
55.92; H, 3.21. 1H NMR (CD2Cl2): δ 7.6-7.0 (m, 20H, Ph), 3.45
(t, J PH ) 11, 2H, CH2). 13C{1H} NMR [THF/C6D6 (9:1)]: δ 233.2
(br, 2 × CO), 226.0 (br, 2 × CO), 223.6 (d, J PC ) 7, CO), 222.8
(d, J PC ) 26, CO), 215.3 (d, J PC ) 29, CO), 135.0-128.5 (Ph),
39.6 (t, J PC ) 19, CH2). 13C NMR [THF/C6D6 (9:1), 228 K]: δ
239.0, 231.3, 227.5 (3 × m, 3 × CO), 223.8 (s, CO), 222.7 (d,
J PC ) 27, CO), 220.0 (m, CO), 215.4 (d, J PC ) 29, CO).
P r ep a r a tion of [Mn 2(µ-η1:η2-CO)(CO)5(P P h 3)(µ-d p p m )]
(3a ). Solid [FeCp2]PF6 (0.050 g, 0.15 mmol) was added to a
THF solution (15 mL) containing compound 1 (ca. 0.075 mmol)
and PPh3 (0.021 g, 0.075 mmol) at -80 °C. The mixture was
stirred at that temperature for 10 min and then allowed to
toluene/petroleum ether at -20 °C. Anal. Calcd for C49H37
-
Mn2O6P3: C, 63.65; H, 4.03. Found: C, 63.71; H, 4.11. 1H NMR
(C6D6): δ 7.9-6.6 (complex, Ph, 35H), 3.33 (ABMX broad
multiplet, CH2, 2H).
P r ep a r a tion of [Mn 2(µ-η1:η2-CO)(CO)5{P (OMe)3}(µ-
d p p m )] (3b). The procedure is totally analogous to that
described for 3a , except that P(OMe)3 (7 µL, 0.08 mmol) was
used instead of PPh3 (reaction time 30 min), and dichlo-
romethane/petroleum ether mixtures were used in the chro-
matography on alumina (activity III, 25 cm, -35 °C). Ferrocene
was first eluted by using an 1:5 mixture. Further elution with
a 1:3 solvent mixture gave an orange fraction, which yielded,
after removal of solvents under vacuum, compound 3b as an
orange powder (0.036 g, 61%). The crystals used in the X-ray
diffraction study were grown from a toluene/petroleum ether
solution of the complex at -20 °C. Anal. Calcd for C34H31
-
Mn2O9P3: C, 51.93; H, 3.97. Found: C, 52.08; H, 4.01. 1H NMR
(CD2Cl2, 200.13 MHz): δ 7.6-6.9 (complex, 20H, Ph), 3.65 (d,
J PH ) 12, 9H, OMe), 3.20 (t, J PH ) 11, 2H, CH2). 13C{1H} NMR
(CD2Cl2): δ 236.0, 233.5, 232.0, 220.5 (4 × m, br, 4 × CO),
227.2 (dd, J PC ) 38, 29, 1 × CO), 216.2 (d, J PC ) 34, 1 × CO),
132.5-127.6 (complex, Ph), 52.2 (d, J PC ) 5, OMe), 41.6 (t, J PC
) 16, PCH2). 13C{1H} NMR (CD2Cl2/213 K): δ 235.7 (dd, J PC
) 30, 19, CO), 233.9 (d, J PC ) 22, CO), 231.8 (dd, J PC ) 34, 23,
CO), 226.8 (dd, J PC ) 40, 27, CO), 220.3 (d, J PC ) 27, CO),
215.9 (d, J PC ) 34, CO), 140.0-125.7 (complex, Ph), 52.4 (s,
Me), 41.5 (t, J PC ) 16, CH2).
P r ep a r a tion of [Mn 2(µ-η1:η2-CCHR)(CO)6(µ-d p p m )] (R
t
) P h , Bu ). Solid [FeCp2]PF6 (0.033 g, 0.1 mmol) was added
to a THF solution (10 mL) of compound 1 (ca. 0.05 mmol) and
HC2R (1 mL, excess) at - 80 °C, and the mixture was stirred
and allowed to reach room temperature for 40 min. Solvent
was then removed under vacuum and the red residue extracted
with toluene (2 × 8 mL) and filtered. Removal of solvent from
the filtrate gave a residue, which was washed with petroleum
ether (5 × 5 mL) and recrystallized from toluene/petroleum
ether at -20 °C to give red crystals of the title compounds
(0.033 g, 85% for R ) Ph; 0.030 g, 80% for R ) tBu).
Spectroscopic data for these products were identical to those
reported in ref 19.
P r epar ation of [Mn 2(µ-η1:η2-NCtBu )(CO)6(µ-dppm )] (4a).
The procedure is totally analogous to that described for 3b,
t
except that excess BuCN (1 mL) was used instead of P(OMe)3
(reaction time 2 h). Elution with dichloromethane/petroleum
ether (1:5) gave first a yellow fraction containing ferrocene and
then a yellow-orange fraction. Removal of solvents from the
latter under vacuum gave compound 4a as a yellow-orange
microcrystalline powder (0.043 g, 75%). Anal. Calcd for C36H31
-
Mn2NO6P2: C, 58.00; H, 4.19; N, 1.88. Found: C, 58.34; H,
4.03; N, 1.83. 1H NMR (CD2Cl2): δ 8.00-6.41 (m, 20H, Ph),
3.20 (dt, J HH ) 14, J PH ) 12, 1H, CH2), 2.39 (dt, J HH ) 14, J PH
) 10, 1H, CH2), 1.08 (s, 9H, Me).
P r epar ation of [Mn 2(µ-η1:η2-NCP h )(CO)6(µ-dppm )] (4b).
The procedure is totally analogous to that described for 4a ,
t
except that excess PhCN (1 mL) was used instead of BuCN
(reaction time 30 min). An orange fraction was collected when
eluting with dichloromethane/petroleum ether (1:3). Removal
of solvents from this fraction under vacuum gave compound
4b as a yellow-orange microcrystalline powder (0.038 g, 65%).
Anal. Calcd for C38H27Mn2NO6P2: C, 59.65; H, 3.53; N, 1.83.
Found: C, 59.43; H, 3.48; N, 1.81. 1H NMR (CD2Cl2): δ 7.92-
6.38 (m, 25H, Ph), 3.24 (dt, J HH ) 14, J PH ) 12.5, 1H, CH2),
2.39 (dt, J HH ) 14, J PH ) 9.5, 1H, CH2).
(28) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.
(29) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
(30) Aguiar, A. M.; Beisler, J . J . Org. Chem. 1964, 29, 1660.

Unsaturated Anion [Mn2(CO)6(µ-Ph2PCH2PPh2)]2-
Organometallics, Vol. 20, No. 14, 2001 3015
Ta ble 6. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d ies
P r ep a r a tion of [Mn 2CO)7(P P h 3)(µ-d p p m )] (5a ). A THF
solution of compound 2 was prepared in situ from ca. 0.057
mmol of anion 1 as described above. To this solution, solid PPh3
(0.015 g, 0.057 mmol) was added at -40 °C, and the mixture
was stirred at that temperature for 15 min. Solvent was
removed under vacuum and the residue chromatographed on
an alumina column (activity III, 20 cm) at -40 °C. Ferrocene
was first eluted by using a THF/petroleum ether (1:5) mixture,
while a 1:3 mixture gave a minor yellow fraction containing a
small amount of [Mn2(CO)8(µ-dppm)]. Finally, elution with a
THF/petroleum ether (1:2) mixture gave an orange fraction,
which yielded, after removal of solvents under vacuum,
compound 5a as a red-orange powder (0.036 g, 60%). The
crystals used for the X-ray study were grown by slow diffusion
of a dichloromethane solution of 5a into a layer of petroleum
ether at -20 °C. Anal. Calcd for C50H37Mn2O7P3: C, 63.04; H,
3.92. Found: C, 62.65; H, 4.12. 1H{31P} NMR (CD2Cl2, 278
K): δ 7.55-6.72 (complex, 35H, Ph), 3.93 (s, br, 2H, CH2,
isomer C), 3.88 (s, br, 2H, CH2, isomer T). Ratio C/T ) 2. 13C-
{1H, 31P} (100.63 MHz, CD2Cl2, 213 K): Isomer C: δ 233.9 (s,
2 × CO), 229.9 (s, CO), 228.6 (s, 2 × CO), 225.1 (s, CO), 222.2
(s, CO), 137.2-127.9 (Ph), 49.9 (s, CH2). Isomer T: δ 236.1 (s,
2 x CO), 227.4 (s, 3 × CO), 224.8 (s, CO), 222.3 (s, CO), 137.2-
127.9 (Ph), 47.2 (s, CH2). 13C{1H, 31P} (100.63 MHz, CD2Cl2,
295 K): Isomer C: δ 233.9 (s, 2 x CO), 229.6 (s, CO), 228.5 (s,
2 x CO), 224.7 (s, CO), 222.1 (s, CO), 51.2 (s, CH2). Isomer T:
δ 229.0 (br, 6x CO), 224.7 (s, br, CO), 48.0 (s, CH2). See Table
5 for assignment of the carbonyl resonances.
3b‚C7H8
5a
mol formula
mol wt
C41H39Mn2O9P3 C50H37Mn2P3O7
878.53
952.61
cryst syst
monoclinic
P21/n
monoclinic
P21/n
space group
radiation (λ, Å)
a, Å
Mo KR (0.71069)
12.091(2)
18.272(3)
18.589(4)
95.54(2)
4088(2)
4
13.666(7)
18.94(1)
18.52(1)
106.21(4)
4603(8)
4
b, Å
c, Å
â, deg
V, Å3
Z
calcd density, gcm-3
µ(Mo KR), cm-1
diffractometer
temperature, K
scan type
2θ range, deg
scan width
total no. of unique data
no. of unique obsd data
[I > 2.5σ(I)]
merging R factor
Ra
1.43
7.60
Nonius CAD4
293
ω/2θ
1.37
6.77
293
ω/2θ
4-50
2-38
0.8 + 0.345 tan θ
3273
707
6386
1723
0.13
0.074
0.082
0.10
0.052
0.057
0.90, 1.07
none
b
Rw
abs coeff corr (min., max.) 0.829, 1.195
secondary extinction corr
no. of variables
205 × 10-5
154
351
R ) ∑||Fo| - |Fc||/∑|Fo|. bRw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
P r ep a r a tion of [Mn 2CO)7{P (OMe)3}(µ-d p p m )] (5b). A
THF solution of compound 2 was prepared in situ from ca.
0.08 mmol of anion 1 as described above. To this solution,
P(OMe)3 (10 µL, 0.08 mmol) was added at -50 °C, and the
mixture was stirred at that temperature for 10 min. Solvent
was then removed under vacuum and the residue chromato-
graphed on an alumina column (activity III, 15 cm) at -30
°C. Ferrocene was first eluted by using a dichloromethane/
petroleum ether (1:6) mixture. Elution with a dichloromethane/
petroleum ether (1:3) mixture gave a yellow-orange fraction,
which yielded, after removal of solvents under vacuum,
compound 5b (46 mg, 70%) as a red-orange microcrystalline
solid. Anal. Calcd for C35H31Mn2O10P3: C, 51.62; H, 3.84.
Found: C, 52.03; H, 4.02. 1H NMR (CD2Cl2): Isomer C: δ
7.63-6.83 (complex, 20H, Ph), 3.84 (t, J PH ) 10, 2H, CH2), 3.38
(d, J PH ) 11, 9H, OMe). Isomer T: δ 7.63-6.83 (complex, 20H,
Ph), 3.76 (t, J PH )10, 2H, CH2), 3.47 (d, J PH ) 11, 9H, OMe).
Ratio C/T ) 0.5. 13C{1H} NMR (100.63 MHz, CD2Cl2, 238 K):
isomer C: δ 231.1 (t, J PC ) 20, 2 × CO), 228.7 (d, J PC ) 21, 2
× CO), 225.8 (m, CO), 224.9 (m, CO), 221.9 (m, CO), 131.7-
128.0 (Ph), 52.3 (d, J PC ) 7, OMe), 48.3 (t, J PC ) 21, CH2).
Isomer T: δ 232.7 (m, 2 × CO), 227.4 (d, J PC ) 23, 2 × CO),
224.9 (m, CO), 223.2 (m, CO), 221.9 (m, CO), 131.7-128.0 (Ph),
52.2 (d, J PC ) 6, OMe), 48.3 (t, J PC ) 21, CH2). 13C{1H} NMR
(100.63 MHz, CD2Cl2, 295 K): isomer C: δ 231.5 (t, J PC ) 20,
2 × CO), 229.0 (m, 2 × CO), 226.4 (m, CO), 225.0 (m, CO),
222.4 (m, CO). Isomer T: δ, 228.5 (br, 6 × CO), 223.4 (m, CO).
a
Mn2N2O7P2: C, 54.13; H, 3.31; N, 3.82. Found: C, 54.56; H,
3.67; N, 3.70. H NMR (CD2Cl2): δ 7.60-6.79 (complex, 20H,
1
Ph), 5.49, 5.19 (ABX multiplet, J HH ) 22, J PH ) 4, 2H, CH2N2),
2.46 (m, 2H, PCH2). 1H{31P} NMR (400.13 MHz, CD2Cl2): δ
5.49, 5.19 (AB multiplet, J HH ) 22, 2H, CH2N2), 2.49, 2.44 (AB
multiplet, J HH ) 13, 2H, PCH2). 13C{1H} NMR (100.63 MHz,
CD2Cl2, 213 K): δ 279.1 (d, J PC ) 20, µ-CO), 228.1 (d, J PC
)
10, CO), 223.0 (d, J PC ) 22, CO), 222.6 (d, J PC ) 20, CO), 222.5
(d, J PC ) 24, CO), 213.7 (d, J PC ) 25, CO), 211.9 (d, J PC ) 16,
CO), 135.6-128.8 (Ph), 116.0 (s, CH2N2), 17.0 (s, br, PCH2).
X-r a y Str u ctu r e Deter m in a tion for Com p ou n d s 3b‚
C7H8 a n d 5a . A selected crystal was set up on an automatic
diffractometer. Unit cell dimensions with estimated standard
deviations were obtained from least-squares refinements of the
setting angles of 25 well-centered reflections. Two standard
reflections were monitored periodically; they showed no change
during data collection. Crystallographic data and other infor-
mation are summarized in Table 6. Corrections were made for
Lorentz and polarization effects. Empirical absorption correc-
tion (Difabs)31 was applied. A secondary extinction correction
was unnecessary for 5a and was applied for 3b.
Computations were performed by using the PC version of
CRYSTALS.32 Atomic form factors for neutral Mn, P, O, C,
and (for 5a ) H were taken from ref 33. Real and imaginary
parts of anomalous dispersion were taken into account. The
structures were solved by direct methods (SHELXS)34 and
successive Fourier maps. Because of the few number of
reflections, in the case of 5a carbon atoms of the phenyl groups
were isotropically refined, and the hydrogen atoms were
theoretically located and given an overall isotropic thermal
parameter. For the same reason, in the case of 3a phenyl rings
were refined as rigid groups and all atoms were isotropically
refined, except the hydrogen atoms, not located nor introduced
P r ep a r a tion of [Mn 2(µ-η1:K1-CH2N2)(µ-CO)(CO)6(µ-
d p p m )] (6). A toluene solution (10 mL) of compound 2 was
prepared in situ from ca. 0.1 mmol of anion 1 as described
above. To this solution, CH(SiMe3)N2 (100 µL of a 2 M solution
in hexanes, ca. 0.2 mmol) was added, and the mixture was
stirred at room temperature for 30 min. Solvent was then
removed under vacuum and the residue chromatographed on
an alumina column (activity III, 20 cm) at -30 °C. Ferrocene
was first eluted by using a toluene/petroleum ether (1:4)
mixture. Further elution with a 1:1 mixture gave a yellow
fraction containing some [MnH(CO)3(dppm)], and elution with
(31) Walker, N.; Stuart, D. Acta Crystallogr., A 1983, 39, 158.
(32) Watkin, D. J .; Carruthers, J . R.; Betteridge, P. W. CRYSTALS,
An advanced Crystallographic Computer Program; Chemical Crystal-
lography Laboratory: Oxford, U.K., 1988.
(33) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV.
a
4:1 mixture gave a minor fraction containing several
unidentified species. Finally, elution with pure tetrahydrofu-
ran gave a yellow-orange fraction, which yielded, after removal
of solvent under vacuum, compound 6 (0.035 g, 50%) as an
(34) Sheldrick, G. M. SHELXS 86, Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, 1986.
orange microcrystalline powder. Anal. Calcd for
C33H24-

3016 Organometallics, Vol. 20, No. 14, 2001
Liu et al.
in calculations. In this case the unit cell also contains a toluene
molecule, of which the methyl group could not be located; this
molecule was also refined as a rigid group, with an overall
isotropic thermal parameter.
views of these compounds, with ellipsoids at 30% probability.
Tables of observed and calculated structure factors are avail-
able from the authors on request.
Refinements were carried out in three blocks by minimizing
the function ∑w(|Fo| - |Fc|)2, where Fo and Fc are the observed
and calculated structure factors. Models reached convergence
with R ) ∑(|Fo| - |Fc|)/∑|Fo| and Rw ) [∑w(|Fo| - |Fc|)2/
∑w(Fo)2]1/2 having values listed in Table 6. For 5a , the
weighting scheme was unity. For 3b, in the last stages of
refinement, each reflection was assigned a weight w ) w′[1 -
((|Fo| - |Fc|)/6σ(Fo))2]2 with w′ ) 1/∑r)1,3ArTr(X) with three
coefficients 4.41, -2.88, and 3.08 for a Chebyshev series, for
which X ) Fo/Fo(max). Figures 2 and 3 represent CAMERON35
Ack n ow led gm en t. We thank the Ministerio de
Educacio´n y Ciencia and the Ministerio de Asuntos
Exteriores of Spain for a grant (to X-Y. Liu), and the
DGICYT of Spain (Projects PB91-0678 and PB96-
0317) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of fractional
atomic coordinates, anisotropic thermal parameters, and bond
lengths and angles for compounds 3b and 5a . This material
is available free of charge via the Internet at http://pubs.acs.org.
(35) Pearce, L. J .; Watkin, D. J . CAMERON; Chemical Crystal-
lography Laboratory, Oxford, U.K., 1989.
OM0101590