Synthesis and X-ray structures of manganese(I) and rhenium(I) formato complexes, fac-(CO)3(dppp)M-OC(H)O

Article abstract of DOI:10.1016/S0022-328X(99)00743-3

The mononuclear manganese(I) and rhenium(I) formato complexes, fac-(CO)₃(dppp)M-OC(H)O (M=Mn, 1; M=Re, 2), have been prepared from fac-(CO)₃(dppp)MH and formic acid, and their X-ray structures determined. Compounds 1 and 2 are unusual in that the formato ligands are bound in a terminal, monodentate fashion. For Mn, only multinuclear complexes containing bridging formato ligands have been characterized previously by X-ray diffraction. The M-O bond lengths and M-O-C bond angles are 2.043(2) ? and 124.2(2)°, respectively for 1 and 2.167(3) ? and 122.3(3)°, respectively for 2. Compounds 1 and 2 can also be decarboxylated at elevated temperatures with quantitative recovery of fac-(CO)₃(dppp)MH.

Full text of DOI:10.1016/S0022-328X(99)00743-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 599 (2000) 308–312
Note
Synthesis and X-ray structures of manganese(I) and rhenium(I)
formato complexes, fac-(CO)3(dppp)MꢀOC(H)O
Miyoshia T. Williams a, Christopher McEachin a, Thomas M. Becker b,
Douglas M. Ho c, Santosh K. Mandal a,*
a Department of Chemistry, Morgan State Uni6ersity, Baltimore, MD 21251, USA
b Department of Chemistry, Uni6ersity of Cincinnati, Cincinnati, OH 45221, USA
c Department of Chemistry, Princeton Uni6ersity, Princeton, NJ 08544, USA
Received 18 October 1999; received in revised form 7 December 1999
Abstract
The mononuclear manganese(I) and rhenium(I) formato complexes, fac-(CO)3(dppp)MꢀOC(H)O (M=Mn, 1; M=Re, 2), have
been prepared from fac-(CO)3(dppp)MH and formic acid, and their X-ray structures determined. Compounds 1 and 2 are unusual
in that the formato ligands are bound in a terminal, monodentate fashion. For Mn, only multinuclear complexes containing
bridging formato ligands have been characterized previously by X-ray diffraction. The MꢀO bond lengths and MꢀOꢀC bond
,
,
angles are 2.043(2) A and 124.2(2)°, respectively for 1 and 2.167(3) A and 122.3(3)°, respectively for 2. Compounds 1 and 2 can
also be decarboxylated at elevated temperatures with quantitative recovery of fac-(CO)3(dppp)MH. © 2000 Elsevier Science S.A.
All rights reserved.
Keywords: Synthesis; Manganese; Rhenium; Formato complexes; X-ray structure
tems, and describe herein the synthesis, structural and
reaction chemistry of fac-(CO)3(dppp)MnꢀOC(H)O (1)
and fac-(CO)3(dppp)ReꢀOC(H)O (2).
1. Introduction
Metallocarboxylic acids (MꢀCO2H) and their iso-
meric monodentate formato complexes (MꢀOC(H)O)
have been proposed as intermediates in the water–gas
shift reaction [1]. Formato complexes have also been
implicated in the metal-catalyzed reduction of CO2 to
HCO−2 [2], CO2–H2 reactions [3], isomerization of
methyl formate to acetic acid [4], decarboxylation of
formic acid [5], and transfer hydrogenations [6]. The
synthesis and reactivity of metallocarboxylic acid and
formato complexes are therefore of key interest to the
above and related processes. The synthesis and reac-
2. Results and discussion
2.1. Synthesis of the manganese formato complex 1
and rhenium formato complex 2
Formato complexes can be prepared from a variety
of starting materials, e.g. carbon dioxide [8], simple
formate salts [1], or from formic acid itself [9]. Since the
manganese(I) and rhenium(I) hydrido complexes fac-
(CO)3(dppp)MH were readily available [10], the synthe-
sis of 1 and 2 by the insertion of CO2 into the MꢀH
bond was first attempted. Unfortunately, the formato
complexes were not obtained. The latter formic acid
route was therefore attempted next and found to give
the desired products (Eq. (1)):
tivity
of
the
metallocarboxylic
acids
fac-
(CO)3(dppe)ReCO2H and fac-(CO)3(dppp)ReCO2H
have been reported earlier [7]. We have now completed
complementary studies on the isomeric formato sys-
* Corresponding author. Fax: +1-410-3193778.
E-mail address: smandal@morgan.edu (S.K. Mandal)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00743-3

M.T. Williams et al. / Journal of Organometallic Chemistry 599 (2000) 308–312
309
example, (h5-C5H5)Fe(CO)2OC(H)O was found to de-
carboxylate with CO dissociation [1]. However, the
rhenium formate, (h5-C5H5)Re(NO)(PPh3)OC(H)O was
found to decarboxylate without PPh3 dissociation [11].
We did not study the decarboxylation mechanism at
this time. Attempts to decarboxylate and transform 1
and 2 to metallocarboxylates were unsuccessful.
2.3. Spectral studies
(1)
The IR and NMR spectral data for 1 and 2 are given
in Section 3. Three strong IR bands observed between
2033 and 1898 cm−1 are consistent with the presence of
a facial M(CO)3 functional group in these compounds.
A medium-intensity band observed in the 1630–1610
cm−1 region is attributable to the CꢁO group of a
2.2. Decarboxylations of 1 and 2
Complexes 1 and 2 were converted to the corre-
sponding hydrides at their melting temperatures. Also
when 1 or 2 was heated to 110°C in toluene-d8, the
corresponding hydrides were obtained (Eq. (2)).
1
formate anion. The formate H- and 13C-NMR reso-
nances occur as triplets at roughly 8.4 and 169.0 ppm,
respectively. These observations are consistent with the
presence of discrete (dppp)M(h1-O2CH) moieties, the
1
formate H and 13C triplet signals being the result of
coupling with the two phosphorus atoms of the dppp
ligand. The 13C resonances for the terminal carbonyl
ligands occur as a broad signal centered at 215.8 ppm
for 1, and as two triplets at 194.3 (axial, CO) and 190.7
ppm (equatorial, 2CO) for 2.
(2)
The decarboxylation mechanism of formato com-
plexes have been reported by many research groups. It
has been suggested to proceed via b elimination of the
hydrogen atom to the metal center, followed by forma-
tion of a metal hydride species. This mechanism re-
quires a vacant coordination site on the metal. For
2.4. X-ray structures of 1 and 2
A molecular plot and selected distances and angles
for 1 are provided in Fig. 1 and Table 2, respectively.
The Mn atom is octahedrally coordinated to three
carbonyl ligands in a facial arrangement, a bidentate
Fig. 1. A thermal ellipsoid plot of compound 1.

310
M.T. Williams et al. / Journal of Organometallic Chemistry 599 (2000) 308–312
Fig. 2. A thermal ellipsoid plot of compound 2.
dppp, and a monodentate formate anion. The equato-
bonyls are eclipsed with respect to each other in this
bipy analogue, in contrast to the staggered geometry
found in 1 and 2. Finally, we mention that crystals of 1
also contain formic acid molecules of crystallization.
One formic acid molecule is hydrogen bonded to each
formate O(5) atom in the lattice with O(6)ꢀH(6),
H(6)···O(5), O(6)···O(5), and O(6)ꢀH(6)···O(5) being
,
rial MnꢀCO bonds are 0.05 A longer than the axial
MnꢀCO bond, consistent with dppp having a greater
trans influence than formate. The formate ligand is
bound to the Mn atom in a syn conformation with the
O(4)ꢀC(4)ꢀO(5) plane symmetrically bisecting the equa-
torial Mn(CO)2 moiety. The C(2)ꢀMnꢀO(4)ꢀC(4)ꢀO(5)
and C(3)ꢀMnꢀO(4)ꢀC(4)ꢀO(5) torsion angles are −
44.3(2) and 44.9(2)°, respectively. The MnꢀO(4) bond is
,
0.92(2), 1.71(4), 2.579(3) A, and 156(4)°, respectively.
Crystals of 2 did not contain formic acid.
,
2.043(2) A and is comparable to distances of 2.020–
,
2.042 A reported for manganese carboxylato complexes
[12] and fac-(CO)3(dppe)MnOC(O)OCH3 [13].
A
3. Experimental
molecular plot and selected bond distances and angles
for 2 are provided in Fig. 2 and Table 2, respectively.
The Re coordination geometry is analogous to that
described above for the Mn derivative, e.g. the equato-
All manipulations were carried out under a nitrogen
atmosphere. Reagent grade chemicals were used with-
out further purification. Formic acid (96%) was ob-
tained from Aldrich Chemical Company, Inc. IR
spectra were recorded on a Perkin–Elmer 1600 series
FTIR instrument. NMR spectra were recorded on a
,
rial ReꢀCO bonds are 0.04 A longer than the axial
ReꢀCO bond, the C(2)ꢀReꢀO(4)ꢀC(4)ꢀO(5) and
C(3)ꢀReꢀO(4)ꢀC(4)ꢀO(5) torsion angles are −45.3(3)
and 44.4(3)°, respectively, and the ReꢀO(4) bond is
1
Bruker AC 250 (250.133 MHz, H; 62.896 MHz, 13C)
,
spectrometer. Melting points were recorded on a Mel-
Temp apparatus and are uncorrected. Microanalyses
were conducted by Quantitative Technologies Inc.
2.167(3) A. The latter ReꢀO(4) distance is comparable
,
to values of 2.127(3)–2.230(10) A observed in related
carboxylato [14] and carbonato bridged complexes [15].
,
The ReꢀO(4) bond is 0.124 A longer than the MnꢀO(4)
bond in excellent agreement with an expectation value
3.1. Synthesis of the manganese formato complex 1
and rhenium formato complex 2
,
of 0.13 A based on the difference in the Re and Mn
covalent radii.
The most interesting feature in 1 and 2 is the
metalꢀformate binding mode. To our knowledge, 1 is
the first example of a monomeric manganese complex
confirmed crystallographically to contain a terminally
bound formato ligand. Compound 2 is equally uncom-
mon. The only other rhenium example is fac-
(CO)3(bipy)ReꢀOC(H)O [16]. It is interesting to note
that the axial formate and one of the equatorial car-
To 0.73–0.91 mmol of fac-M(CO)3(dppp)H (M=
Mn; Re) [10] dissolved in about 50 cm3 of
dichloromethane was added formic acid (0.15–0.17
cm3, 3.98–4.51 mmol) and the solutions were stirred for
1 h. The excess acid was removed by extraction with
water. The dichloromethane solution was concentrated
and mixed with hexane. The resultant mixture was
cooled at −5°C. Pure crystalline formato complexes 1

M.T. Williams et al. / Journal of Organometallic Chemistry 599 (2000) 308–312
311
93%; m.p. 185–188°C with decomposition. IR (cm−1
,
and 2 were collected by filtration. Data for 1: yield,
88%; m.p. 153–155°C with decomposition. IR (cm−1
CH2Cl2): w(CꢂO) 2033 vs, 1954 s, 1898 s, and w(CꢁO)
,
1
1625 m. H-NMR (l, CDCl3): 8.19 (t, 2 Hz, OꢁCꢀH),
CH2Cl2): w(CꢂO) 2027 vs, 1960 s, 1906 s, and w(CꢁO)
1617 m. 1H-NMR (l, CDCl3): 8.53 (t, 2 Hz, 1H,
OꢁCꢀH), 7.49–7.31 (m, 20H, C6H5), 2.86–2.21 (m, 6H,
CH2CH2CH2). 13C-NMR (l, CDCl3): 215.8 (s, br, CO),
169.2 (t, 6 Hz, CꢁO), 135.8–128.6 (m, C6H5), 24.9 (t, 11
Hz, CH2CH2CH2), 18.7 (18.7, s, CH2CH2CH2). Anal.
Found: C, 61.5; H, 4.6. C31H27MnO5P2 Anal. Calc.: C,
62.4; H, 4.6%. The elemental analysis done on a
crushed sample that had been evacuated to remove any
traces of dichloromethane, hexanes or formic acid,
indicates that 1 slowly decomposes. Data for 2: yield:
7.50–7.29 (m, 20H, C6H5), 2.94–2.28 (m, 6H,
CH2CH2CH2). 13C-NMR (l, CDCl3): 194.3 (t, 6 Hz,
CꢂO), 190.7 (t, 24 Hz, 2 CꢂO), 168.9 (t, 6 Hz, CꢁO),
136.1–126.57 (m, C6H5), 24.6 (t, 15 Hz, CH2CH2CH2),
19.3 (18.7, s, CH2CH2CH2). Anal. Found: C, 50.8; H,
3.7. C31H27O5P2Re Anal. Calc.: C, 51.2; H, 3.7%.
3.2. Decarboxylations of 1 and 2
About 0.015 mmol of 1 or 2 was dissolved in 0.500
cm3 of toluene-d8 at 110°C and the reaction was moni-
tored by 31P-NMR. After 2 h, the only product from 1
or 2 was the corresponding hydride. No evidence of
free dppp ligand was observed. Also when heated to
their melting points, the formato complexes 1 and 2
lose CO2 and are converted quantitatively to their
corresponding hydrides. The decarboxylations occur
slowly at lower temperatures without melting.
Table 1
Summary of crystal data for fac-Mn(CO)3(dppp)OC(H)O·HC(O)OH
(1) and fac-(CO)3(dppp)ReꢀOC(H)O
1
2
Color and habit Yellow prism
Colorless plate
Crystal size
(mm)
0.50×0.50×0.50
0.07×0.13×0.15
Chemical
formula
C32H29MnO7P2
C31H27O5P2Re
3.3. X-ray crystal structure of
fac-Mn(CO)3(dppp)OC(H)O·HC(O)OH (1)
,
a (A)
9.5216(6)
10.2134(5)
16.9567(8)
90.503(4)
94.807(5)
106.774(4)
1572.3(2)
17.8435(3)
16.5212(2)
19.8756(3)
90
90
90
5859.2(2)
0.71073
Orthorhombic
Pbca (no. 61)
8
Nonius Kappa CCD
4.295
,
b (A)
,
c (A)
Crystals of 1 were grown from CH2Cl2–hexane at
−5°C. Data were collected on a Siemens P4 diffrac-
tometer at 298(2) K and corrected for decay and
Lorentz-polarization effects, but not for absorption or
extinction. The structure was solved by heavy atom
methods and refined by full-matrix least-squares on F2
using SHELXTL. The non-hydrogen atoms were refined
anisotropically and the hydrogens were included with a
riding model and isotropic displacement coefficients
U(H)=1.2U(C) except where noted below and the
weighting scheme employed was w=1/[|2(Fo2)+
(0.0515P)2] where P=(Fo2 +2F2c)/3. The formic acid
hydrogen atom H(6) was assigned an isotropic displace-
ment coefficient U(H)=1.5U(O), and its coordinates
were free to vary. Convergence gave R=0.0356 for
4044 reflections with I\2|(I). Additional crystallo-
graphic data and results are summarized in Table 1.
h (°)
i (°)
k (°)
3
,
V (A )
,
Wavelength (A) 0.71073
Crystal system
Space group
Z
Triclinic
(
P1 (no. 2)
2
Diffractometer
v(Mo–Ka)
Siemens P4
0.566
(mm−1
)
Scan mode,
qmax (°)
Completeness
(%)
Limiting indices 05h511,
−125k511,
ꢀ, 25.00
ꢀ, 27.53
100
99.9
05h523,
05k521,
05l525
Gaussian
−205l520
None
Absorption
correction
Reflections
collected
Reflections
merged (Rint
Reflections
observed
5906
54 230
3.4. X-ray crystal structure of
fac-Re(CO)3(dppp)OC(H)O (2)
5540 (0.0197)
4044; I\2|(I)
6747 (0.0801)
4593; I\2|(I)
)
Crystals of 2 were grown from CH2Cl2–hexane at
−5°C. Data were collected on a Nonius Kappa CCD
diffractometer at 200(2) K and corrected for Lorentz-
polarization and absorption effects, but not for extinc-
tion. The structure was solved by direct methods and
refined by full-matrix least-squares on F2 using
SHELXTL. The non-hydrogen atoms were refined an-
isotropically. The hydrogen atoms were assigned
isotropic displacement coefficient U(H)=1.2U(C) and
were allowed to ride on their respective carbons. The
Variables
382
352
R (all) a
0.0356 (0.0549)
0.0849 (0.0908)
1.042 (0.940)
0.0314 (0.0652)
0.0566 (0.0658)
1.073 (1.018)
Rw (all) a
Goodness-of-fit
(all)
Refinement
method
Full-matrix least-
Full-matrix least-
squares on F2
squares on F2
a Definitions of R and Rw: R: SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ, Rw: [Swi(ꢀFoꢀ −
2
ꢀFcꢀ ) /S wiꢀF2oꢀ2]1/2
2 2
.

312
M.T. Williams et al. / Journal of Organometallic Chemistry 599 (2000) 308–312
Table 2
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336033; email: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
,
Selected bond lengths (A) and angles (°) for 1 and 2
1
2
Bond lengths
MnꢀC(1)
MnꢀC(2)
MnꢀC(3)
MnꢀO(4)
MnꢀP(1)
1.779(2)
1.826(3)
1.833(3)
2.043(2)
2.3666(7)
2.3517(7)
1.271(3)
1.223(3)
0.92(4)
ReꢀC(1)
ReꢀC(2)
ReꢀC(3)
ReꢀO(4)
ReꢀP(1)
ReꢀP(2)
C(4)ꢀO(4)
C(4)ꢀO(5)
1.898(5)
1.943(4)
1.940(5)
2.167(3)
2.4699(10)
2.4570(10)
1.277(5)
1.219(5)
References
[1] D.J. Darensbourg, M.B. Fischer, R.E. Schmidt Jr., B.J. Baldwin,
J. Am. Chem. Soc. 103 (1981) 1298.
[2] R.P.A. Sneeden, in: G. Wilkinson, F.G.A. Stone, E. Abel (Eds.),
Comprehensive Organometallic Chemistry, vol. 8, Pergamon,
New York, 1982, p. 225.
[3] K. Klier, Adv. Catal. 31 (1982) 243. For the evidence of forma-
tion of surface-bound formates, see: J.M. Basset, A. Choplin, A.
Theolier, Nouv. J. Chim. 9 (1985) 655.
MnꢀP(2)
C(4)ꢀO(4)
C(4)ꢀO(5)
O(6)ꢀH(6)
H(6)···O(5)
O(6)···O(5)
1.71(4)
2.579(3)
Bond angles
[4] R.L. Pruett, R.T. Kacmarcik, Organometallics 1 (1982) 1693.
[5] R.J. Madix, Adv. Catal. 29 (1980) 1.
[6] R. Bar, Y. Sasson, J. Blum, J. Mol. Catal. 16 (1982) 175.
[7] S.K. Mandal, D.M. Ho, M. Orchin, J. Organomet. Chem. 439
(1992) 53.
[8] (a) M.K. Whittlesey, R.N. Perutz, M.H. Moore, Organometal-
lics 15 (1996) 5166. (b) D.L. Allen, M.L.H. Green, J.A. Bandy,
J. Chem. Soc. Dalton Trans. (1990) 541. (c) P. Kundel, H. Berke,
J. Organomet. Chem. 339 (1988) 297. (d) B.P. Sullivan, T.J.
Meyer, J. Chem. Soc. Chem. Commun. (1984) 1244. (e) A.
Immirzi, A. Musco, Inorg. Chim. Acta 22 (1977) L35.
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Inorg. Chem. 23 (1984) 4022. (b) C.C. Tso, A.R. Cutler, Inorg.
Chem. 29 (1990) 471. (c) C. Pomp, K. Wieghardt, B. Nuber, J.
Weiss, Inorg. Chem. 27 (1988) 3789.
C(3)ꢀMnꢀP(2)
C(2)ꢀMnꢀP(1)
C(2)ꢀMnꢀO(4)
C(3)ꢀMnꢀO(4)
O(1)ꢀC(1)ꢀMn
O(2)ꢀC(2)ꢀMn
O(3)ꢀC(3)ꢀMn
C(4)ꢀO(4)ꢀMn
O(5)ꢀC(4)ꢀO(4)
O(6)ꢀH(6)···O(5)
176.43(7)
173.92(7)
92.03(9)
94.14(9)
173.7(2)
176.1(2)
175.8(2)
124.2(2)
126.5(2)
156(4)
C(3)ꢀReꢀP(2)
C(2)ꢀReꢀP(1)
C(2)ꢀReꢀO(4)
C(3)ꢀReꢀO(4)
O(1)ꢀC(1)ꢀRe
O(2)ꢀC(2)ꢀRe
O(3)ꢀC(3)ꢀRe
C(4)ꢀO(4)ꢀRe
O(5)ꢀC(4)ꢀO(4)
178.4(2)
171.51(13)
90.45(14)
96.9(2)
176.6(4)
179.5(4)
175.6(5)
122.3(3)
126.8(5)
weighting scheme employed was w=1/(|2(Fo2 +
(0.0246P)2+3.8979P], P=(Fo2 +2F2c)/3.
where,
Convergence gave R=0.0314 for 4593 reflections with
I\2|(I). Additional crystallographic data and results
are summarized in Table 1.
[10] S.K. Mandal, J. Feldman, M. Orchin, J. Coord. Chem. 33 (1994)
219.
[11] J.H. Merrifield, J.A. Gladysz, Organometallics 2 (1983) 782.
[12] (a) W.A. Herrmann, I. Schweizer, P.S. Skell, M. Ziegler, K.
Weidenhammer, B. Nuber, Chem. Ber. 112 (1979) 2423. (b) F.A.
Cotton, D.J. Darrensbourg, B.W.S. Kolthammer, Inorg. Chem.
20 (1981) 1287.
4. Supplementary material
[13] S.K. Mandal, D.M. Ho, M. Orchin, Organometallics 12 (1993)
1714.
[14] G. La Monica, S. Cenini, E. Forni, M. Manassero, V.G. Albano,
J. Organomet. Chem. 112 (1976) 297.
[15] S.K. Mandal, D.M. Ho, G.Q. Li, M. Orchin, Polyhedron 17
(1998) 607.
[16] J. Guilhem, C. Pascard, J-M. Lehn, R. Ziessel, J. Chem. Soc.
Dalton Trans. (1989) 1449.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 135153 for compound 1,
CCDC no. 135154 for compound 2. Copies of this
information may be obtained free of charge from: The
.