Synthesis, structures, and reactions of manganese complexes containing diphosphine ligands with pendant amines

Article abstract of DOI:10.1021/om100668e

Addition of the pendant amine ligand PN^RP (PN^RP = Ph₂PCH₂NRCH₂PPh₂; R = Me, Ph, n-Bu) to Mn(CO)₅Br gives fac-Mn(PN^RP)(CO)₃Br. Photolysis of fac-Mn(PN^RP)(CO)₃Br with dppm [dppm = 1,2-bis(diphenylphosphino)methane] provides mixed bis(diphosphine) complexes, trans-Mn(PN^RP)(dppm)(CO)(Br). Reaction of trans-Mn(PN ^RP)(dppm)(CO)(Br) with LiAlH₄ leads to trans-Mn(PN ^RP)(dppm)(CO)(H), which has been characterized by crystallography. Mn(P₂^PhN₂^Bn)(dppm)(CO)(H) [P ₂^PhN₂^Bn = 1,5-diphenyl-3,7-dibenzyl- 1,5-diaza-3,7-diphosphacyclooctane] can be prepared in a similar manner; its structure has one chelate ring in a chair conformation and the second in a boat conformation. The boat-conformer ring directs the nitrogen of the ring toward the carbonyl ligand, and the N...C distance between one N of the P ₂^PhN₂^Bn ligand and CO is 3.171(4) A, indicating a weak interaction between the N of the pendant amine and the CO ligand. Reaction of NaBAr^F₄ (Ar^F = 3,5-bis(trifluoromethyl)phenyl) with Mn(P-P)(dppm)(CO)(Br) produces the cations [Mn(P-P)(dppm)(CO)]⁺. The crystal structure of [Mn(PN ^MeP)(dppm)(CO)][BAr^F₄] shows two very weak agostic interactions between C-H bonds on the phenyl ring and the Mn. The cationic complexes [Mn(P-P)(dppm)(CO)]⁺ react with H₂ to form dihydrogen complexes [Mn(H₂)(P-P)(dppm)(CO)]⁺ (K _eq = 1-90 atm^-1 in fluorobenzene, for a series of different P-P ligands). Similar equilibria with N₂ produce [Mn(N ₂)(P-P)(dppm)(CO)]⁺ (K_eq generally 1-3.5 atm^-1 in fluorobenzene).

Full text of DOI:10.1021/om100668e

4532 Organometallics 2010, 29, 4532–4540
DOI: 10.1021/om100668e
Synthesis, Structures, and Reactions of Manganese Complexes
Containing Diphosphine Ligands with Pendant Amines
Kevin D. Welch,† William G. Dougherty,‡ W. Scott Kassel,‡ Daniel L. DuBois,† and
R. Morris Bullock*,†
†Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, K2-57,
Richland, Washington 99352, and ‡Department of Chemistry and Biochemistry, Villanova University,
Villanova, Pennsylvania 19085
Received July 8, 2010
Addition of the pendant amine ligand PNRP (PNRP = Ph2PCH2NRCH2PPh2; R = Me, Ph, n-Bu)
to Mn(CO)5Br gives fac-Mn(PNRP)(CO)3Br. Photolysis of fac-Mn(PNRP)(CO)3Br with dppm
[dppm = 1,2-bis(diphenylphosphino)methane] provides mixed bis(diphosphine) complexes, trans-
Mn(PNRP)(dppm)(CO)(Br). Reaction of trans-Mn(PNRP)(dppm)(CO)(Br) with LiAlH4 leads to
trans-Mn(PNRP)(dppm)(CO)(H), which has been characterized by crystallography. Mn(P2PhN2Bn)-
Bn
(dppm)(CO)(H) [P2PhN2 = 1,5-diphenyl-3,7-dibenzyl-1,5-diaza-3,7-diphosphacyclooctane] can be
prepared in a similar manner; its structure has one chelate ring in a chair conformation and the second
in a boat conformation. The boat-conformer ring directs the nitrogen of the ring toward the carbonyl
Bn
ligand, and the N C distance between one N of the P2PhN2 ligand and CO is 3.171(4) A, indi-
˚
3 3 3
cating a weak interaction between the N of the pendant amine and the CO ligand. Reaction of
NaBArF (ArF = 3,5-bis(trifluoromethyl)phenyl) with Mn(P-P)(dppm)(CO)(Br) produces the
4
cations [Mn(P-P)(dppm)(CO)]þ. The crystal structure of [Mn(PNMeP)(dppm)(CO)][BArF4] shows
two very weak agostic interactions between C-H bonds on the phenyl ring and the Mn. The cationic
complexes [Mn(P-P)(dppm)(CO)]þ react with H2 to form dihydrogen complexes [Mn(H2)(P-P)-
(dppm)(CO)]þ (Keq = 1-90 atm-1 in fluorobenzene, for a series of different P-P ligands). Similar
equilibria with N2 produce [Mn(N2)(P-P)(dppm)(CO)]þ (Keq generally1-3.5atm-1 influorobenzene).
Introduction
protons.2 The presence of two positioned proton relays3
was found to lead to faster catalytic rates in Ni electrocata-
lysts for oxidation of H2 compared to catalysts with just one
positioned proton relay.4 Cobalt diphosphine complexes
with a pendant amine are electrocatalysts for production of
H2 by reduction of protons,5,6 but related catalysts lacking
the pendant amine are essentially inactive.5 Iron complexes
with diphosphines containing pendant amines have also been
studied;7-9 rapid intramolecular proton/hydride exchange
Incorporation of a pendant amine functionality1 into a
diphosphine ligand can cause large changes in reactivity. The
pendant amines are generally intended to function as proton
relays, and they are designed to be close enough to interact
with H2 or H ligands on the metal, but not close enough to
form direct M-N bonds. While the initial intent of incor-
poration of pendant amines was to facilitate intramolecular
and intermolecular proton transfer reactions, it has become
clear that pendant amines also provide additional advan-
tages, including stabilization of binding of H2 or CO ligands
to a metal, lowering the barrier for heterolytic cleavage of H2,
facilitating proton-coupled electron transfer reactions, and
lowering overpotentials in electrocatalytic reactions.
(3) Wilson, A. D.; Newell, R. H.; McNevin, M. J.; Muckerman, J. T.;
DuBois, M. R.; DuBois, D. L. J. Am. Chem. Soc. 2006, 128, 358–366.
(4) Yang, J. Y.; Bullock, R. M.; Shaw, W. J.; Twamley, B.; Fraze, K.;
Rakowski DuBois, M.; DuBois, D. L. J. Am. Chem. Soc. 2009, 131,
5935–5945.
(5) Jacobsen, G. M.; Yang, J. Y.; Twamley, B.; Wilson, A. D.;
Bullock, R. M.; Rakowski DuBois, M.; DuBois, D. L. Energy Environ.
Sci. 2008, 1, 167–174.
Incorporation of pendant amines into the diphosphine
ligand of [Ni(diphosphine)2]2þ complexes led to a decrease of
about 0.7 V in the overpotential for oxidation of H2 to
(6) Wiedner, E. S.; Yang, J. Y.; Dougherty, W. G.; Kassel, W. S.;
Bullock, R. M.; DuBois, M. R.; DuBois, D. L., Organometallics 2010,
ASAP; doi: 10.1021/om100395r.
(7) Henry, R. M.; Shoemaker, R. K.; Newell, R. H.; Jacobsen, G. M.;
DuBois, D. L.; Rakowski DuBois, M. Organometallics 2005, 24, 2481–
2491.
(8) Henry, R. M.; Shoemaker, R. K.; DuBois, D. L.; DuBois, M. R.
J. Am. Chem. Soc. 2006, 128, 3002–3010.
(9) (a) Jacobsen, G. M.; Shoemaker, R. K.; Rakowski DuBois, M.;
DuBois, D. L. Organometallics 2007, 26, 4964–4971. (b) Jacobsen, G. M.;
Shoemaker, R. K.; McNevin, M. J.; Rakowski DuBois, M.; DuBois, D. L.
Organometallics 2007, 26, 5003–5009.
*To whom correspondence should be addressed. E-mail:
morris.bullock@pnl.gov.
(1) (a) Rakowski DuBois, M.; DuBois, D. L. Acc. Chem. Res. 2009,
42, 1974–1982. (b) Rakowski DuBois, M.; DuBois, D. L. Chem. Soc. Rev.
2009, 38, 62–72. (c) Rakowski DuBois, M.; DuBois, D. L. C. R. Chim. 2008,
11, 805–817.
(2) Curtis, C. J.; Miedaner, A.; Ciancanelli, R.; Ellis, W. W.; Noll,
B. C.; DuBois, M. R.; DuBois, D. L. Inorg. Chem. 2003, 42, 216–227.
r
pubs.acs.org/Organometallics
Published on Web 09/20/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 20, 2010 4533
can be observed8 between Fe-H and N-H when structural
and thermochemical properties are appropriately matched.
We have prepared nickel complexes with two different
diphosphines, but in some cases, these nickel complexes are
difficult to obtain in pure form, since ligand redistribution
reactions occur, converting [Ni(P-P)(P0-P0)]2þ into equi-
librium mixtures that contain significant amounts of
[Ni(P-P)2]2þ and [Ni(P0-P0)2]2þ.4 In an expansion of our
studies that have previously concentrated on Ni, Co, and Fe
complexes, we have begun an investigation of Mn complexes
with two diphosphine ligands. We report here our initial
studies of the synthesis, structures, and reactivity of manga-
nese complexes that contain a diphosphine ligand with
pendant amines. The synthetic procedure reported here pro-
vides a route to complexes containing two different diphosphine
ligands. This allows the incorporation of two diphosphines that
have different electronic and steric properties.
Figure 1. Structure of Mn(PNMeP)(dppm)(CO)(Br) (30%
probability ellipsoids). Only the ipso carbons of the Ph groups
are shown.
[dppp = 1,2-bis(diphenylphosphino)propane], and trans-
Mn(P2PhN2Bn)(dppm)(CO)(Br) (eq 2) were prepared and
characterized in a similar fashion using the appropriate dipho-
sphine in place of PNMeP.
Results
Syntheses and Characterization of Mixed Diphosphine
Bromide Complexes. Addition of an excess of the pendant
amine ligand PNMeP (PNMeP = Ph2PCH2N(Me)CH2PPh2)
to Mn(CO)5Br in toluene results in the loss of two CO ligands
and addition of a single equivalent of the diphosphine,
yielding fac-Mn(PNMeP)(CO)3Br, as a yellow solid (eq 1).
Even with two equivalents of diphosphine ligand added, only
one diphosphine was incorporated into the product. The
31P NMR spectrum exhibits a singlet at δ 20.9, and three
carbonyl stretching bands are observed in the IR spectrum at
2026, 1957, and 1924 cm-1, both consistent with a facial
geometry. The symmetric complex trans-Mn(dppm)2(CO)(Br)
The structure of Mn(PNMeP)(dppm)(CO)(Br) was deter-
mined by single-crystal X-ray diffraction. Figure 1 shows the
molecular structure, and Table 1 lists bond distances and
angles for Mn(PNMeP)(dppm)(CO)(Br) and three other
complexes to be discussed later.
Syntheses and Characterization of Manganese Hydride
Complexes Mn(P-P)(dppm)(CO)(H). The reaction of the
manganese bromide complex Mn(PNMeP)(dppm)(CO)(Br)
with LiAlH4 in THF, followed by treatment with water,
results in the formation of the manganese hydride complex
trans-Mn(PNMeP)(dppm)(CO)(H), which was isolated as a
[dppm =1,2-bis(diphenylphosphino)methane] was prepared
by Reimann and Singleton by photolysis of Mn(CO)5Br with
dppm.10 We found that photolysis of a toluene solution of
Mn(PNMeP)(CO)3Br in the presence of dppm results in the
formation of the mixed bis(diphosphine) complex trans-Mn-
(PNMeP)(dppm)(CO)(Br);eq1. Thiscompoundcanbeisolated
as an orange solid. Infrared spectroscopy of Mn(PNMeP)-
(dppm)(CO)(Br) in CH2Cl2 shows a single carbonyl
absorption at 1842 cm-1, consistent with the expected
monocarbonyl species. A 31P NMR spectrum shows two
distinct, broad resonances at δ 45.5 and 15.7 (line widths of
302 and 220 Hz, respectively) with no discernible coupling.
The broad resonances observed in this and other Mn
bright yellow solid. Both 31P and 1H NMR spectra are
consistent with a trans geometry for the diphosphine ligands,
as observed in the bromide. The hydride resonance for
Mn(PNMeP)(dppm)(CO)(H) is observed in the 1H NMR
spectrum at δ -3.58 as a triplet of triplets of doublets. The
two larger couplings are due to coupling of the hydride to
1
complexes in the 31P and H NMR spectra are due to the
quadrupolar 55Mn nucleus (100% abundant, I = 5/2). The
complexes trans-Mn(PNPhP)(dppm)(CO)(Br), trans-Mn-
(PNnBuP)(dppm)(CO)(Br), trans-Mn(dppp)(dppm)(CO)(Br)
1
phosphorus (2JPH = 49.3, 34.2 Hz). A 31P-decoupled H
(10) Reimann, R. H.; Singleton, E. J. Organomet. Chem. 1972, 38,
113–119.
NMR spectrum simplifies the hydride signal to a doublet with a

4534 Organometallics, Vol. 29, No. 20, 2010
Welch et al.
Table 1. Bond Distances and Bond Angles for Mn(PNMeP)(dppm)(CO)(Br), Mn(PNMeP)(dppm)(CO)(H), Mn(P2PhN2Bn)(dppm)(CO)-
(H), and [Mn(PNMeP)(dppm)(CO)]þ
Mn(PNMeP) (dppm)(CO)(Br)
Mn(PNMeP) (dppm)(CO)(H)
Mn(P2PhN2Bn) (dppm)(CO)(H)
[Mn(PNMeP) (dppm)(CO)]þ
˚
Bond Distances, A
Mn-P1(5)
Mn-P2(6)
Mn-P3(8)
Mn-P4(7)
Mn-Br
2.2892(6)
2.2816(8)
2.3264(8)
2.3322(6)
2.5770(5)
2.2220(7)
2.2333(8)
2.2769(7)
2.2618(7)
2.1835(8)
2.1980(8)
2.2263(9)
2.2394(9)
2.2665(7)
2.2478(8)
2.2945(7)
2.3204(5)
Mn-H
1.63(3)
1.783(3)
1.170(3)
1.63(4)
1.782(3)
1.179(3)
Mn-CO
C-O
1.777(3)
1.084(3)
1.744(3)
1.169(3)
Bond Angles, deg
P1-Mn-P2
P1-Mn-P3
P1-Mn-P4
P2-Mn-P3
P2-Mn-P4
P3-Mn-P4
P1-Mn-Br
P2-Mn-Br
P3-Mn-Br
P4-Mn-Br
P1-Mn-H
P2-Mn-H
P3-Mn-H
P4-Mn-H
P1-Mn-CO
P2-Mn-CO
P3-Mn-CO
P4-Mn-CO
Br-Mn-CO
H-Mn-CO
Mn-C-O
89.54(3)
100.30(3)
170.27(3)
168.92(3)
99.15(3)
70.67(2)
85.35(2)
84.01(2)
101.73(2)
99.82(2)
89.01(3)
99.71(3)
166.16(3)
165.13(3)
97.99(3)
71.09(2)
80.51(3)
99.30(3)
163.18(3)
155.96(3)
100.26(3)
73.09(3)
88.70(3)
101.77(3)
172.54(3)
167.51(3)
98.50(2)
70.85(2)
105(1)
107(1)
59(1)
61(1)
87.78(8)
93.65(8)
98.67(8)
103.58(8)
88(1)
82(1)
74(1)
75(1)
94.19(9)
100.49(9)
103.50(9)
102.13(9)
89.96(8)
90.30(8)
84.67(8)
85.66(8)
172.64(8)
91.46(8)
92.88(8)
93.63(8)
90.15(8)
155(1)
178.4(2)
176(1)
176.3(2)
179.6(2)
179.0(2)
Figure 3. Structure of Mn(PNMeP)(dppm)(CO)(H) (30% prob-
ability ellipsoids). Only the ipso carbons of the Ph groups are
shown.
four-bond coupling between the Mn-H and one C-H on the
dppm ligand is observed (4JHH = 7.5 Hz). This is an unusually
large four-bond coupling, but the iron hydride trans-[HFe-
(PEtNMePEt)(dmpm)(MeCN)]þ (PEtNMePEt = Et2PCH2N-
MeCH2PEt2; dmpm = Me2PCH2PMe2) exhibits a 4JHH
=
4 Hz coupling between the Fe-H and one C-H on the
dmpm ligand, and JHH = 3.5 Hz was found for [HFe-
4
Figure 2. Spectra of Mn(PNMeP)(dppm)(CO)(H) in THF-d8
showing the (A) hydride and (B) methylene resonances in the
1H NMR (bottom) and with broadband 31P decoupling (top).
The peak at δ 3.58 is the residual proton signal from THF-d8.
(PEtNMePEt)(dmpm)(CO)]þ.7
Vapor diffusion of hexane into a THF solution of Mn-
(PNMeP)(dppm)(CO)(H) produced single crystals suitable
for X-ray diffraction. A drawing of the structure is presented
in Figure 3, and selected bond distances and angles are given
in Table 1. Of particular note is the significant distortion of
the hydride ligand from idealized octahedral geometry. The
coupling of 7.5 Hz. The same coupling constant is observed for
the resonance at δ 3.71, which has been assigned as one of
the protons on the CH2 group of the dppm ligand. Thus a

Article
Organometallics, Vol. 29, No. 20, 2010 4535
hydride is bent toward one C-H (H40A in Figure 3) of the
methylene group of the dppm ligand, with a H-Mn-CO
angle of 155(1)°. The distance between the hydride and the
˚
closest H of the CH2 group is 2.10(3) A. The structure of
Mn(PNMeP)(dppm)(CO)(H) was determined by X-ray dif-
fraction, so the distances and angles involving hydrogen are
subject to much more uncertainty than those determined by
neutron diffraction. The distortions due to this interaction in
Mn(PNMeP)(dppm)(CO)(H) could be less pronounced than
indicated in this X-ray structure; attempts to determine the
structure by neutron diffraction are underway.
˚
This C-H H-Mn distance of 2.10(3) A between the
3 3 3
C-H on an alkyl group and a Mn-H bond is very similar to
˚
the C-H H-Mn distance of 2.101(3) A determined by
3 3 3
neutron diffraction for the interaction of the aromatic C-H
bond of a phenyl group with the Mn-H bond in cis-HMn-
Figure 4. Structure of Mn(P2PhN2Bn)(dppm)(CO)(H) (30%
probability ellipsoids). Only the ipso carbons of the Ph groups
are shown.
(CO)4PPh3.11 The C-H H-Mn interaction in HMn-
3 3 3
(CO)4PPh3 is due to a protic-hydridic hydrogen-bonding
in a boat conformation. The boat-conformer ring directs the
nitrogen of the ring toward the carbonyl ligand. The N
C
3 3 3
Bn
distance between one N of the P2PhN2 ligand and CO is
˚
3.171(4) A. The carbonyl ligand displays a Mn-C-O angle
of 176.3(2)° with the oxygen tilting away from nitrogen. The
hydride shows a distortion from octahedral geometry in a
fashion similar to that seen in the solid state for Mn(PNMeP)-
(dppm)(CO)(H). A H-Mn-CO angle of 176.7(14)° directs
the hydride toward the dppm methylene group. The distance
interaction. An experimental charge density determination
of HMn(CO)4PPh3 showed an effective atomic charge of
-0.4e on the manganese hydride and a þ0.3e on the C-H
of the phenyl group. The electrostatic energy of this
˚
between the hydride and the closest C-H is 2.76(4) A, so the
distortions are significantly less pronounced in Mn(P2PhN2Bn)-
(dppm)(CO)(H) compared to those found in Mn(PNMeP)-
(dppm)(CO)(H).
Hδþ Hδ- interaction was calculated to be 5.7 kcal/mol.
3 3 3
Crabtree and co-workers have reported extensive studies12
Bn
The interaction of the P2PhN2 ligand with the CO in
on related interactions involving N-H H-Ir interac-
Mn(P2PhN2Bn)(dppm)(CO)(H) is similar to that observed pre-
viously in the crystal structure of [Ni(CO)(P2CyN2Bn)2]2þ (Cy=
3 3 3
tions; their experimental and computational studies resulted
in a range of 5.7-7.1 kcal/mol for the estimated hydrogen
Bn
cyclohexyl).16 The interaction of the P2CyN2 ligand with
bond strength.13 Related complexes with N-H H-Ir
3 3 3
the CO ligand on Ni is sufficiently strong to cause binding of
the CO to Ni, since Ni complexes such as [Ni(dppe)2]2þ, with
diphosphines that have no pendant amine, do not bind CO.
The crystal structure of [Ni(CO)(P2CyN2Bn)2]2þ showed that
the Ni-C-O angle was slightly nonlinear (177.5(4)°). In this
interactions were reported by Morris and co-workers.14
These unconventional H H interactions have been re-
3 3 3
ferred to as “dihydrogen bonds”.15
The hydride Mn(P2PhN2Bn)(dppm)(CO)(H) was prepared
from Mn(P2PhN2Bn)(dppm)(CO)(Br) by reaction with
LiAlH4 in an analogous fashion to Mn(PNMeP)(dppm)-
(CO)(H). This compound has a hydride resonance in the
1H NMR at δ -5.11. Like its PNMeP analogue, it is split into
a triplet of triplets of doublets (J = 46, 38, 7.3 Hz) in which
the larger couplings correspond to phosphorus coupling and
the smaller coupling matches the coupling to one of the C-H
groups on the dppm ligand.
Ni complex with two P2CyN2Bn ligands, the N C distances
3 3 3
˚
were 3.30 and 3.38 A, which is longer than the N
distance observed in Mn(P2PhN2Bn)(dppm)(CO)(H).
C
3 3 3
For comparison to our Mn complexes with diphosphines
containing pendant amines, the manganese hydride Mn-
(dppe)2(CO)(H) [dppe = 1,2-bis(diphenylphosphino)ethane]
was synthesized from Mn(dppe)2(CO)(Br) through an ana-
logous reaction with LiAlH4. A hydride resonance is ob-
served at δ -7.32 as a quintet (JPH = 44 Hz) in the 1H NMR
spectrum. Unlike hydrides Mn(PNMeP)(dppm)(CO)(H) and
Mn(P2PhN2Bn)(dppm)(CO)(H), the coupling observed on the
hydride is exclusively due to P-H coupling, as evidenced by
this resonance collapsing to a singlet in the 31P-decoupled 1H
NMR.
The structure of Mn(P2PhN2Bn)(dppm)(CO)(H) was de-
termined by X-ray diffraction of single crystals grown
through the layering of hexane on a methylene chloride
Bn
solution of the hydride. The cyclic P2PhN2 ligand orients
with one chelate ring in a chair conformation and the second
(11) Abramov, Y. A.; Brammer, L.; Klooster, W.; Bullock, R. M.
Inorg. Chem. 1998, 37, 6317–6328.
(12) Crabtree, R. H.; Siegbahn, P. E. M.; Eisenstein, O.; Rheingold,
A. L.; Koetzle, T. F. Acc. Chem. Res. 1996, 29, 348–354.
(13) Peris, E.; Lee, J. C., Jr.; Rambo, J. R.; Eisenstein, O.; Crabtree,
R. H. J. Am. Chem. Soc. 1995, 117, 3485–3491.
(14) (a) Park, S.; Ramachandran, R.; Lough, A. J.; Morris, R. H.
J. Chem. Soc., Chem. Commun. 1994, 2201–2202. (b) Lough, A. J.; Park,
S.; Ramachandran, R.; Morris, R. H. J. Am. Chem. Soc. 1994, 116, 8356–
8357.
Formation of Mn Cations [Mn(P-P)(dppm)(CO)]þ. The
reaction of 1.1 equivalents of NaBArF (ArF = 3,5-bis-
4
(trifluoromethyl)phenyl) with the mixed diphosphine bromide
complex Mn(PNMeP)(dppm)(CO)(Br) in fluorobenzene re-
sults in the formation of a deep blue solution. The reaction
mixture shows two singlets in the 31P NMR spectrum at δ 52.4
and 30.3 (with line widths of 315 and 90 Hz, respectively).
(15) (a) Richardson, T.; de Gala, S.; Crabtree, R. H.; Siegbahn,
P. E. M. J. Am. Chem. Soc. 1995, 117, 12875–12876. (b) Custelcean, R.;
Jackson, J. E. Chem. Rev. 2001, 101, 1963–1980.
(16) Wilson, A. D.; Fraze, K.; Twamley, B.; Miller, S. M.; DuBois,
D. L.; Rakowski DuBois, M. J. Am. Chem. Soc. 2008, 130, 1061–1068.

4536 Organometallics, Vol. 29, No. 20, 2010
Welch et al.
A single CO stretching band is observed at 1843 cm-1. The
characterization of this complex as the cationic [Mn(PNMeP)-
(dppm)(CO)]þ is further supported by its reactivity under
H2 or N2 (vide infra). The other bromides Mn(P-P)-
(dppm)(CO)(Br) show analogous reactivity with NaBArF
,
4
producing deep blue solutions with similar spectroscopic
Figure 5. Structure of [Mn(PNMeP)(dppm)(CO)]þ (30% prob-
ability ellipsoids).
characteristics. Kubas and co-workers17,18 prepared similar
complexes [Mn(dppe)2(CO)]þ[BArF ]- and [Mn(depe)2-
[Mn(depe)2(CO)]þ [depe = 1,2-bis(diethylphosphino)ethane],
did not locate the H atoms on the ethyl groups, but idealized
positions for them were calculated as Mn H distances of
3.30 and 3.42 A. These long distances were interpreted as
being “suggestive of van der Waals contacts with perhaps
only a small contribution from agostic bonding”.18
4
(CO)]þ[Ga(C6F5)4]- [depe = 1,2-bis(diethylphosphino)-
ethane] by analogous reactions, and their complexes were
also deep blue. These complexes appear to be 16-electron
complexes, but they have one or more weak agostic interac-
tions between a C-H bond on the ligand and the Mn.
These cationic complexes are extremely sensitive to air and
solvent impurities and are most easily studied by in situ
generation by vacuum transfer of fluorobenzene onto the
3 3 3
˚
In contrast to the deep blue solutions obtained for all the
cationic Mn complexes discussed above, the reaction of
Mn(P2PhN2Bn)(dppm)(CO)(Br) with NaBArF4 in fluoroben-
zene produces a red solution. A 31P NMR spectrum of the
reaction shows two singlets, one very broad, at δ 24.6 and
23.4 (line widths of 262 and 76 Hz, respectively), consistent
with retention of a plane of symmetry in the molecule. The
relatively upfield shift of the phosphorus signals along with
the pronounced difference in color suggests a different struc-
ture and bonding relative to the other cationic complexes
discussed above. However, the CO stretching frequency
of 1843 cm-1 is nearly identical to those found in the other
Mn cationic complexes. Initial attempts at isolation of this
complex have been unsuccessful, but further attempts are
continuing.
Formation of Manganese Complexes with H2 and N2 Ligands.
The addition of 1 atm of H2 to the deep blue solutions of the
Mn cations [Mn(P-P)(dppm)(CO)]þ described above results
in a color change to yellow rapidly upon mixing. Removal of
the H2 atmosphere by three freeze-pump-thaw cycles of
the solution returns the original blue color of the Mn cation.
31P NMR spectra of these yellow solutions under H2 show
a pair of new singlets, slightly shifted from those seen in
[Mn(P-P)(dppm)(CO)]þ (see Table 2 for spectroscopic
details). The 1H NMR spectra contain one broad singlet
resonance for each complex between δ -2.9 and -3.7 (with
line widths ranging from 44 to 97 Hz), consistent with the
presence of a dihydrogen ligand. To determine hydrogen
binding constants for these complexes, each solution was
allowed to equilibrate under 100 Torr of H2 gas. 31P NMR
spectra of the resulting green solutions show a mixture of
dihydrogen and [Mn(P-P)(dppm)(CO)]þ complexes, which
was used to calculate the binding constant, Keq(H2).
reactants in an NMR tube. Attempts to isolate the BArF
4
salts of these complexes repeatedly resulted in degradation.
Addition of hexane or pentane or prolonged exposure to the
argon atmosphere of the glovebox resulted in a visible
change of the color of the solution from deep blue to green
and the formation of multiple unidentified products in the
31P NMR spectrum. Evaporation of solvent from the reac-
tion mixture also resulted in a color change from blue to
green of the reaction solution and formation of unidentified
products.
Dark blue single crystals of [Mn(PNMeP)(dppm)(CO)]-
[BArF4] were obtained as a mixture with amorphous solids
from diffusion of hexane into a fluorobenzene reaction solu-
tion. The X-ray structure is presented in Figure 5, and selec-
ted bond lengths and angles are given in Table 1. The unit cell
of the crystal shows two unique structures with very similar
structural features. Each structure is square pyramidal with
an open coordination site trans to the carbonyl ligand; one of
the two structures is shown in Figure 5. Two ortho-hydro-
gens from phenyl groups of opposite phosphines are aligned
toward the open coordination site, creating two agostic inter-
actions. The Mn H distances are 2.7562(3) and 3.1212(4)
3 3 3
˚
A, indicating very weak agostic interactions. A similar struc-
ture with two agostic interactions from C-H bonds of a Ph
ring was previously found by Kubas and co-workers for
[Mn(dppe)2(CO)]þ.17 The Mn H distances for [Mn(dppe)2-
3 3 3
(CO)]þ were found to be 2.89(6) and 2.98(6) A, indicating
˚
weak agostic interactions. A structural study of the related
complex with Et groups on the diphosphine ligand,
(17) King, W. A.; Luo, X.-L.; Scott, B. L.; Kubas, G. J.; Zilm, K. W.
J. Am. Chem. Soc. 1996, 118, 6782–6783.
(18) King, W. A.; Scott, B. L.; Eckert, J.; Kubas, G. J. Inorg. Chem.
Exposure of each of the blue cation solutions to an atmo-
sphere of N2 results in the formation of a green solution that
shows resonances consistent with a mixture of [Mn(P-P)-
1999, 38, 1069–1084.

Article
Organometallics, Vol. 29, No. 20, 2010 4537
a
Table 2. Spectroscopic Data for Cationic Manganese Complexes and Equilibrium Constants for Binding of H2 or N2
[Mn(P-P) (P0-P0)(CO)]þ
H2 complex
N2 complex
Keq(N2)c (atm-1
)
Mn cation
31P (δ)
IR (cm-1
)
1H (δ)b
31P (δ)
Keq(H2) (atm-1
)
31P (δ)
75.3
40.7, 21.6
46.2, 22.6
46.4, 22.2
44.0, 22.1
42.4, 31.0
[Mn(dppe)2(CO)]þ
83.8
1843
1841
1842
1840
1839
1843
-7.2 (55)
-3.7 (55)
-3.4 (44)
-3.5 (97)
-2.9 (69)
-3.2 (56)
89.5
56
26
32
25
90
1.1
1.4 (58)
2.8 (74)
3.5 (78)
2.4 (71)
1.1 (52)
<0.05d
[Mn(PNMeP)(dppm)(CO)]þ
[Mn(PNPhP)(dppm)(CO)]þ
[Mn(PNnBuP)(dppm)(CO)]þ
[Mn(dppp)(dppm)(CO)]þ
[Mn(P2PhN2Bn)(dppm)(CO)]þ
52.4, 30.3
54.5, 30.3
53.5, 30.7
53.4, 29.4
24.6, 23.4
50.5, 31.9
51.4, 31.1
50.7, 31.5
52.7, 30.6
55.4, 37.4
a Data are for fluorobenzene solutions of complexes generated in situ by the reaction of NaBArF with the corresponding bromide, followed by
4
reaction with H2 or N2. b Number in parentheses is the line width in Hz. c Number in parentheses is the percentage of N2 complex observed at 1 atm of N2.
d The amount of N2 complex was too small to be quantified at 1 atm of N2.
Scheme 1
(dppm)(CO)]þ and a new complex in the 31P NMR. The
cations can be converted completely to a new compound, a
yellow solution, by the addition of N2 gas to the solution at
liquid nitrogen temperatures followed by thawing and mixing.
The 31P NMR resonances are shifted upfield by 5-10 ppm for
each of the new species. These data are all consistent with the
formation of the dinitrogen complexes, as described by Kubas
for the [Mn(dppe)2(CO)]þ 17 and [Mn(depe)2(CO)]þ 18 ca-
tions. Nitrogen binding constants, Keq(N2), were calculated
using the mixtures present at 1 atm of N2, after equilibration.
Addition of H2 (1 atm) to the red solution resulting from
the reaction of Mn(P2PhN2Bn)(dppm)(CO)(Br) with Na-
BArF4 in fluorobenzene shows no pronounced color change
upon mixing, in contrast to the reactions described above. A
31P NMR spectrum of the reaction shows a mixture of two
complexes in a 1.1:1 ratio, with the minor component identi-
fied as the starting complex. Addition of H2 at liquid nitro-
gen temperatures results in the complete conversion to the
new adduct as noted by 31P NMR, as well as the change in
color of the solution from red to yellow. The 31P NMR
resonances at δ 55.4 and 37.4 and the presence of a broad
proton resonance at δ -3.2 support the characterization of
this as the dihydrogen cation complex [Mn(P2PhN2Bn)-
(dppm)(CO)(H2)]þ.
minor species has phosphorus shifts of δ 42.4 and 31.0,
consistent with shifts of the other N2 adducts.
In all of the complexes studied here, the equilibrium
constant for binding of H2 is substantially larger than that
for N2. The same trend was found by Kubas and co-workers
in their study of [Mn(dppe)2(CO)]þ 17 and [Mn(depe)2(CO)]þ.18
Although the differences are small, the complexes that bind
H2 most strongly tend to bind N2 more weakly. The unusually
weak binding of both H2 and N2 to [Mn(P2PhN2Bn)(dppm)-
(CO)]þ is not understood and is under further study.
NMR experiments show that the H2 complexes [Mn(dppe)2-
(CO)(H2)]þ, [Mn(PNMeP)2(CO)(H2)]þ, and [Mn(P2PhN2Bn)-
(dppm)(CO)(H2)]þ can also be generated by addition of one
equivalent of bis(trifluoromethanesulfonyl)amine or pyridinium
tetrafluoroborate to the corresponding neutral hydride in fluoro-
benzene under hydrogen atmosphere. The H2 complexes formed
in this fashion slowly decompose into unidentified products,
presumably due to the presence of the anion or pyridine base.
The addition of an excess of triethylamine or diisopropylethyl-
amine to solutions of these same H2 complexes results in the
complete conversion back to the corresponding hydride as
observed by NMR.
Conclusions
The addition of an atmosphere of N2 to a solution of
[Mn(P2PhN2Bn)(dppm)(CO)]þ does not result in the appear-
ance of any new species as observed in the 31P NMR.
Addition of 3.8 atm of N2 gives a 5.6:1 mixture of complexes
with the major component remaining the starting cation. The
A series of Mn complexes were prepared that have dipho-
sphine ligands with pendant amines. The X-ray crystal
structure of Mn(PNMeP)(dppm)(CO)(H) shows a distortion
of the Mn-H toward a C-H on the dppm ligand, indicating a

4538 Organometallics, Vol. 29, No. 20, 2010
Welch et al.
protic-hydridic interaction. The structure of Mn(P2PhN2Bn)-
(dppm)(CO)(H) has a boat conformation for one ring, position-
ing the nitrogen toward the CO ligand, suggesting a weak
7.3 Hz, 2H, aromatic); 6.88 (t, J = 7.3 Hz, 1H, aromatic); 6.41
(d, J = 8.2 Hz, 2H, aromatic); 4.67 (dt, JHH = 13.6 Hz, JPH =
4.8, 2H, CH2); 4.22 (dt, JHH = 13.6 Hz, JPH = 8.5 Hz, 2H,
CH2). 31P{1H} NMR (THF-d8): δ 22.9 (s).
˚
interaction (N C distance of 3.171(4) A). The manganese
3 3 3
Mn(PNBuP)(CO)3(Br). Yield: 86%, as a pale yellow solid. 1H
NMR (benzene-d6): δ 7.95 (m, 4H, aromatic); 7.46 (m, 4H,
aromatic); 6.96-7.18 (12H, aromatic); 4.01 (dt, JHH = 13.2 Hz,
bromide complexes were converted to cationic complexes [Mn-
(P-P)(dppm)(CO)]þ with a variety of diphosphine ligands. The
crystal structure of [Mn(PNMeP)(dppm)(CO)]þ[BArF ]- shows
4
J
PH = 4.1 Hz, 2H, CH2); 3.26 (dt, JHH = 13.2 Hz, JPH = 9.0 Hz,
two very weak agostic interactions between C-H bonds on the
phenyl ring and the Mn. Dihydrogen complexes are observed
from reaction of cationic complexes [Mn(P-P)(dppm)(CO)]þ
with H2. Equilibrium constants range from 1 to 90 atm-1 in
fluorobenzene. The pendant amines are not sufficiently basic to
deprotonate the H2 ligand. Manganese complexes with dinitro-
gen ligands, [Mn(N2)(P-P)(dppm)(CO)]þ, are observed, but the
binding constants are lower for N2 than for H2. Further studies
are seeking to prepare Mn complexes with more acidic H2
ligands.
2H, CH2); 2.18 (t, J = 6.2 Hz, 2H, butyl CH2); 0.68-0.90 (4H,
butyl CH2); 0.65 (t, J = 6.0 Hz, 3H, butyl CH3). 31P{1H} NMR
(benzene-d6): δ 22.9 (s).
Mn(dppp)(CO)3(Br). Yield: 82%, as a yellow solid. 1H NMR
(benzene-d6): δ 7.78 (m, 4H, aromatic); 7.27 (m, 4H, aromatic);
7.07 (t, J = 7.4 Hz, 4H, aromatic); 7.02 (t, J = 6.9 Hz, 4H,
aromatic); 6.93 (t, J = 7.3 Hz, 4H, aromatic); 3.20 (td, JHH
13.9, 2.3 Hz, 2H, CH2); 1.81 (m, 1H, CH2); 1.26 (qt, JHH
=
=
14.0 Hz, JPH = 6.2 Hz, 1H, CH2). 31P{1H} NMR (benzene-d6): δ
29.4 (s).
Mn(PPh2NBn2)(CO)3(Br). A suspension of Mn(CO)5Br (0.705
Bn
g, 2.56 mmol) and P2PhN2 (1.78 g, 3.70 mmol) in toluene
Experimental Section
(40 mL) was stirred overnight (∼16 h), resulting in a yellow
mixture. White solids were removed by filtration through a
medium-porosity fritted funnel. The solvent was removed under
vacuum to give a yellow-orange oil. The oil was dissolved in
CH2Cl2, which was subsequently removed under vacuum to give
a yellow solid. Yield: 1.72 g (2.46 mmol, 96%). 1H NMR
(CD2Cl2): δ 7.10-7.62 (20H, aromatic); 4.26 (d, JHH = 11.7
Hz, 2H, CH2); 4.06 (s, 2H, benzyl CH2); 3.72 (s, 2H, benzyl
CH2); 3.44 (dt, JHH = 12.9 Hz, JPH = 3.6 Hz, 2H, CH2); 3.30 (d,
JHH = 12.9 Hz, 2H, CH2); 2.92 (dt, JHH = 11.7 Hz, JPH = 7.9
Hz, 2H, CH2). 31P{1H} NMR (CD2Cl2): δ 28.9 (s). IR νCO
(CH2Cl2) = 2025(s), 1959(s), 1913(s) cm-1. Anal. Calc for
C33H32BrMnN2O3P2: C, 56.51; H, 4.50; N, 3.99. Found: C,
55.96; H, 4.50; N, 4.02.
1H and 31P NMR spectra were recorded on a Varian Unity
INOVA (500 MHz for 1H) or Varian (300 MHz for 1H) spectro-
meter at 20 °C. 1H NMR chemical shifts were calibrated using
the monoprotio solvent impurities for deuterated solvents or by
addition of TMS for fluorobenzene. 31P NMR spectra were
proton decoupled, and chemical shifts were referenced using
external phosphoric acid. Infrared spectra were obtained using a
Nicolet Magna-IR 860 or Thermo Scientific Nicolet iS10 FT-IR
spectrometer.
Synthesis and Materials. Syntheses were performed using
standard Schlenk techniques under a nitrogen atmosphere or
in a glovebox under an argon atmosphere. Cation complexes
were prepared in situ using standard high-vacuum techniques.
Photolysis reactions were performed using a water-jacketed Ace
Hanovia 450 W, medium-pressure, Hg lamp. Quartz glassware
was used for all photolysis reactions. Toluene, THF, hexane,
and dichloromethane were dried using an activated alumina
column. Benzene and fluorobenzene were dried over P2O5 for
2 days and distilled under reduced pressure. Mn(CO)5Br
was prepared from Mn2(CO)10 according to a literature met-
Mn(PNMeP)(dppm)(CO)(Br). A mixture of Mn(PNMeP)-
(CO)3(Br) (1.01 g, 1.56 mmol) and dppm (0.83 g, 2.16 mmol)
in fluorobenzene (50 mL) was photolyzed under a purge of N2.
The reaction was monitored using 31P NMR until the starting
material signal was no longer observed (∼6 to 8 h). The resulting
red solution was filtered through a medium-porosity fritted
funnel, and the volume was reduced to one-quarter of its
original volume. Hexane (50 mL) was added to precipitate an
orange solid, which was collected by filtration. The product was
recrystallized from fluorobenzene. Yield: 719 mg (0.738 mmol,
21
hod.19 PNP20 and P2N2 ligands were prepared as previously
described.
Mn(PNMeP)(CO)3(Br). A solution of Mn(CO)5Br (3.22
g,11.7 mmol) and Ph2PCH2N(Me)CH2PPh2 (10.60 g, 24.80
mmol) in benzene (75 mL) was stirred overnight (∼16 h),
resulting in a mixture of a yellow precipitate in a clear solution.
The yellow solid was collected by filtration and rinsed with
hexane. Yield: 7.70 g (11.9 mmol, 98%). 1H NMR (CD2Cl2): δ
7.88 (br s, 4H, aromatic); 7.52 (br s, 4H, aromatic); 7.25-7.47
(12H, aromatic); 3.77 (dt, JHH = 13.4 Hz, JPH = 3 Hz, 2H,
CH2); 3.50 (dt, JHH = 13.4 Hz, JPH = 9 Hz, 2H, CH2); 2.56 (s,
3H, CH3). 31P{1H} NMR (CD2Cl2):δ 20.9 (s). IR νCO (CH2Cl2) =
1
47%). H NMR (CD2Cl2): δ 6.74-7.95 (40H, aromatic); 4.71
(br s, 1H, dppm CH2); 3.98 (br s, 2H, PNP CH2); 3.85 (br s, 1H,
dppm CH2); 3.18 (br s, 2H, PNP CH2); 2.40 (br s, 3H, CH3).
31P{1H} NMR (CD2Cl2): δ 45.5 (s, dppm); 15.7 (s, PNP). IR νCO
(CH2Cl2) = 1842(s) cm-1
.
Mn(P-P)(dppm)(Br). These compounds were prepared from
Mn(PNPhP)(CO)3(Br), Mn(PNBuP)(CO)3(Br), and Mn(dppp)-
(CO)3(Br) in an analogous fashion to Mn(PNMeP)(dppm)(CO)-
(Br).
2026(s), 1957(s), 1924(s) cm-1
. Anal. Calc for C30H27-
Mn(PNPhP)(dppm)(CO)(Br). Yield: 10%, as an orange solid.
1H NMR (CD2Cl2): δ 7.62 (m, 4H, aromatic); 6.97-7.32 (38H,
aromatic); 6.80 (td, JHH = 7.3, 1.0 Hz, 1H, aromatic); 6.34 (dd,
BrMnNO3P2: C, 55.75; H, 4.21; N, 2.17. Found: C, 55.84; H,
4.12; N, 2.18.
Mn(P-P)(CO)3(Br). These compounds were prepared in an
analogous fashion to Mn(PNMeP)(CO)3Br, with 1.5 to 2 equiva-
lents of the appropriate diphosphine (PNPhP, PNBuP, or dppp)
used in place of PNMeP.
J
HH = 8.5, 1.0 Hz, aromatic); 4.72 (dt, JHH = 13.1 Hz, JPH =
3.9 Hz, 2H, PNP CH2); 4.44 (dt, JHH = 14.2 Hz, JPH = 10.2 Hz,
1H, dppm CH2); 4.03 (dt, JHH = 14.2 Hz, JPH = 8.7 Hz, 1H,
dppm CH2); 3.91 (dt, JHH = 13.1 Hz, JPH = 6.1 Hz, 2H, PNP
CH2). 31P{1H} NMR (CD2Cl2): δ 44.5 (s, dppm); 17.7 (s, PNP).
Mn(PNBuP)(dppm)(CO)(Br). Yield: 44%, as a red-orange
Mn(PNPhP)(CO)3(Br). Yield: 80%, as a bright yellow solid.
1H NMR (THF-d8): δ 7.85 (m, 4H, aromatic); 7.37-7.47 (12H,
aromatic); 7.28 (t, J = 7.6 Hz, 4H, aromatic); 7.06 (dd, J = 8.2,
1
solid. H NMR (CD2Cl2): δ 7.70 (m, 4H, aromatic); 7.49 (m,
4H, aromatic); 6.93-7.28 (32H, aromatic); 4.56 (dt, JHH = 14.1
Hz, JPH = 10.6 Hz, 1H, dppm CH2); 4.06 (dt, JHH = 12.6 Hz,
(19) Reimer, K. J.; Shaver, A.; Quick, M. H.; Angelici, R. J. Inorg.
Synth. 1980, 19, 158–163.
(20) Redin, K.; Wilson, A. D.; Newell, R.; DuBois, M. R.; DuBois,
J
PH = 2.5 Hz, 2H, PNP CH2); 3.91 (dt, JHH = 14.1 Hz, JPH =
8.2 Hz, 1H, dppm CH2); 3.22 (dt, JHH = 12.6 Hz, JPH = 7.1 Hz,
2H, PNP CH2); 2.49 (t, JHH = 7.3, 2H, butyl CH2); 1.20
(quintet, JHH = 7.3, 2H, butyl CH2); (sextet, JHH = 7.3, 2H,
D. L. Inorg. Chem. 2007, 46, 1268–1276.
€
(21) Markl, V. G.; Jin, G. Y.; Schoerner, C. Tetrahedron Lett. 1980,
21, 1409–1412.

Article
Organometallics, Vol. 29, No. 20, 2010 4539
Table 3. Crystallographic Collection and Refinement Data
Mn(PNMeP)(dppm)(CO)(Br) Mn(PNMeP)(dppm)(CO)(H) Mn(P2PhPN2Bn)(dppm)(CO)(H) 2 [Mn(PNMeP)(dppm)(CO)]
3
3
3
3
1.5(C6H5F)
THF
2(CH2Cl2)
BArF
4
formula
fw
C62H56.50BrF1.50MnNOP4
1118.81
100(2)
triclinic
P1
12.8796(5)
13.5776(5)
17.9331(10)
102.992(2)
102.014(2)
112.728(2)
2662.3(2)
C57H58MnNO2P4
967.86
100(2)
monoclinic
C2/c
36.1746(7)
13.3586(3)
20.0544(4)
C58H59Cl4MnN2OP4
1120.69
120(2)
orthorhombic
Pna21
28.894(5)
C176H127B2F49Mn2N2O2P8
3612.06
100(2)
triclinic
P1
16.8661(7)
22.7560(9)
24.8001(10)
64.6560(10)
89.5880(10)
80.3940(10)
8459.6(6)
temp (K)
cryst syst
space group
˚
a (A)
˚
b (A)
13.643(2)
13.733(2)
˚
c (A)
R (deg)
β (deg)
γ (deg)
92.1980(10)
3
˚
V (A )
Z
9684.0(3)
8
3.805
1.54178
1.328
5413.6(15)
4
0.602
0.71073
1.375
2
1.167
0.71073
1.396
2
0.333
0.71073
1.418
μ (mm-1
)
˚
λ (A)
F
calc (g cm-3
)
cryst size (mm)
θ range (deg)
total no. of reflns
no. of indep reflns,
I g 3.0σ(I)
0.16 ꢀ 0.09 ꢀ 0.08
1.23 to 33.34
42 297
0.35 ꢀ 0.23 ꢀ 0.11
2.44 to 67.69
21 842
0.18 ꢀ 0.18 ꢀ 0.06
1.41 to 33.27
59 506
0.23 ꢀ 0.22 ꢀ 0.10
1.51 to 33.22
149 486
19 930 [R(int) = 0.0307]
8367 [R(int) = 0.0363]
18 255 [R(int) = 0.0966]
64 408 [R(int) = 0.0551]
no. of params
final R indices
[I >2σ(I)]a
650
R1 = 0.0506,
wR2 = 0.1089
587
635
2191
R1 = 0.0443,
wR2 = 0.1187
R1 = 0.0509,
wR2 = 0.1241
1.045
R1 = 0.0564,
wR2 = 0.1089
R1 = 0.0957,
wR2 = 0.1260
1.009
R1 = 0.0643,
wR2 = 0.1301
R1 = 0.1363,
wR2 = 0.1473
1.010
R indices (all data)a R1 = 0.0963,
wR2 = 0.1249
goodness-of-fit on F2 1.019
absorption corr
semiempirical from equivalents
P
P
P
P
a R1 =
Fo| - |Fc
/
|Fo|; wR2 = { [w(|Fo2| - |Fc2|)2]/ [w|Fo2|2]}1/2
.
butyl CH2); 0.74 (t, JHH = 7.3, 3H, butyl CH3). 31P{1H} NMR
(CD2Cl2): δ 42.0 (s, dppm); 14.4 (s, PNP).
44 Hz, 1H, hydride). 31P{1H} NMR (CD2Cl2): δ 99.5 (s). IR: νCO
(CH2Cl2) = 1814(s) cm-1. Anal. Calc for C53H49MnOP4: C,
70.27; H, 5.61. Found: C, 71.06; H, 5.30.
Mn(dppp)(dppm)(CO)(Br). Yield: 30%, as a pale orange solid.
1H NMR (benzene-d6): δ 7.81 (br s, 4H, aromatic); 6.78-7.45
(36H, aromatic); 4.36 (dt, JHH = 14.4 Hz, JPH = 9.3 Hz, 1H,
dppm CH2); 4.01 (m, 1H, dppm CH2); 3.63 (t, JHH = 10.6 Hz,
2H, dppp CH2); 2.00 (br s, 2H, dppp CH2); 1.63 (m, 1H, dppp
CH2); 1.31 (m, 1H, dppp CH2). 31P{1H} NMR (benzene-d6): δ
47.7 (s, dppm); 19.3 (s, PNP).
Mn(PNMeP)(dppm)(CO)(H). LiAlH4 (121 mg, 3.19 mmol)
was added to a stirred solution of Mn(PNMeP)(dppm)(CO)(Br)
(303.7 mg, 0.312 mmol) in THF (20 mL). After stirring over-
night (∼16 h), the reaction mixture was red-brown. The reaction
was filtered through Celite to give a yellow solution. Water
(∼0.1 mL) was added dropwise to the solution until no more
bubbling occurred upon addition. The resulting yellow mixture
was filtered through Celite to remove solids, and the solution
was evaporated to dryness to give a yellow solid. Yield: 253 mg
Mn(PPh2NBn2)(dppm)(CO)(Br). A solution of Mn(PPh2NBn2)-
(CO)3(Br) (525 mg, 0.738 mmol) and dppm (423 g, 1.10 mmol) in
fluorobenzene (45 mL) was stirred and photolyzed under a
stream of N2. The reaction was monitored by 31P NMR for
disappearance of the starting material signal (∼4 to 6 h). The
resulting red solution was evaporated under vacuum to give a
red solid. The solids were dissolved in minimal THF (∼5 mL).
Hexane (20 mL) was then added to give an oil, which was stirred
overnight in the THF/hexane mixture to yield a powder. A red
solid was collected by filtration and dried under vacuum. Yield:
1
(0.282 mmol, 90%). H NMR (CD2Cl2): δ 7.44 (m, 8H, aro-
matic); 6.90-7.20 (32H, aromatic); 4.32 (dt, JHH = 13.8 Hz,
J
PH = 10.5 Hz, 1H, dppm CH2); 3.71 (m, JHH = 13.8, 7.5 Hz,
1H, dppm CH2); 3.30 (dt, JHH = 12.7 Hz, JPH = 6.3 Hz, 2H,
PNP CH2); 3.21 (dt, JHH = 12.7 Hz, JPH = 3.7 Hz, 2H, PNP
CH2); 2.19 (s, 3H, CH3); -3.58 (ttd, JPH = 49.3, 34.2 Hz, JHH
=
=
7.5 Hz, 1H, hydride). 31P{1H} NMR (CD2Cl2): δ 65.6 (d, JPP
1
520 mg (0.505 mmol, 67%). H NMR (CD2Cl2): δ 6.75-7.50
37.3 Hz, dppm); 44.2 (d, JPP = 37.3 Hz, PNP). IR: νCO (CH2Cl2)
= 1797(s) cm-1. Anal. Calc for C53H50BrMnNOP2: C, 71.06; H,
5.63; N, 1.56. Found: C, 70.44; H, 5.81; N, 1.65.
(40H, aromatic); 4.71 (m, 1H, dppm CH2); 4.68 (m, 1H, dppm
CH2); 4.60 (dt, JHH = 10.8 Hz, JPH = 3.0 Hz, 2H, P2N2 CH2);
3.95 (s, 2H, benzyl CH2); 3.79 (s, 2H, benzyl CH2); 3.35 (dt,
Mn(PPh2NBn2)(dppm)(CO)(H). LiAlH4 (138 mg, 3.64 mmol)
was added to a stirred solution of Mn(PPh2NBn2)(dppm)(CO)-
(Br) (290 mg, 0.282 mmol) in THF (10 g). After stirring over-
night (∼16 h), the brown mixture was filtered through Celite to
give an orange solution. Water (∼0.1 mL) was added dropwise
until the reaction mixture was yellow and bubbling no longer
occurred upon water addition. Solids were removed by filtration
through Celite, and the solution was evaporated to dryness to
give a yellow solid. Yield: 269 mg (0.281 mmol, 99%). 1H NMR
(CD2Cl2): δ 6.75-7.65 (40H, aromatic); 4.15 (s, 2H, benzyl
CH2); 4.07 (ddt, JHH = 13.9, 7.3 Hz, JPH = 7.6 Hz, 1H, dppm
CH2); 3.92 (dt, JHH = 13.9 Hz, JPH = 10.3 Hz, 1H, dppm CH2);
3.60 (s, 2H, benzyl CH2); 3.07 (d, JHH = 11.2 Hz, 2H, P2N2
JHH = 10.8 Hz, JPH = 3.0 Hz, 2H, P2N2 CH2); 3.17 (d, JHH =
12.6 Hz, 2H, P2N2 CH2); 2.91 (dt, JHH = 10.8 Hz, JPH = 6.0 Hz,
2H, P2N2 CH2). 31P{1H} NMR (CD2Cl2): δ 49.2 (s, dppm): 29.8
(s, P2N2). IR: νCO (CH2Cl2) = 1835(s) cm-1
.
Mn(dppe)2(CO)(H). LiAlH4 (34 mg, 0.90 mmol) was added to
a solution of Mn(dppe)2(CO)(Br) (198 mg, 0.206 mmol) in THF
(3.10 g), and the mixture was stirred overnight (∼16 h). The
resulting red-brown mixture was filtered through Celite to give
an orange solution. Water (∼0.1 mL) was added until the color
changed to yellow and no more bubbling occurred upon water
addition. The resulting mixture was filtered through Celite to
remove all solids. The solvent was removed under vacuum to
give a yellow solid. Yield: 132 mg (0.150 mmol, 73%). 1H NMR
(CD2Cl2): δ 7.42 (t, JPH = 6 Hz, 8H, aromatic); 6.98-7.20 (32H,
CH2); 3.04 (d, JHH = 11.2 Hz, 2H, P2N2 CH2); 2.84 (d, JHH =
11.8 Hz, 2H, P2N2 CH2); 2.64 (dt, JHH = 11.8 Hz, JPH = 4.3 Hz,
2H, P2N2 CH2); -5.11 (ttd, JPH = 46.4, 38.3 Hz, JHH = 7.3, 1H,
aromatic); 2.26 (m, 4H, CH2); 1.94 (m, 4H, CH2); -7.32 (p, JPH
=

4540 Organometallics, Vol. 29, No. 20, 2010
Welch et al.
hydride). 31P{1H} NMR (CD2Cl2): δ 67.8 (dd, JPP = 30.7, 10.5
Hz, dppm); 53.5 (dd, JPP = 30.7, 10.5 Hz, P2N2). IR: νCO
allowed to warm to room temperature and shaken to give a dark
blue solution and a white precipitate. The solution was frozen in
liquid nitrogen, and maintaining liquid nitrogen temperatures, 1
atm of hydrogen gas was introduced into the tube from a 2 L
ballast. The tube was sealed and allowed to warm to room
temperature. Upon shaking, the color of the solution changed
from blue to yellow. The procedure was repeated for each
bromide and for both H2 and N2. Spectral data are provided
in Table 2.
Determination of Equilibrium Constants for Binding of H2 and
N2. In a representative reaction, a J. Young NMR tube was
charged with 20.1 mg (0.0206 mmol) of the bromide Mn-
(PNMeP)(dppm)(CO)(Br) and 25.9 mg (0.0292 mmol, 1.4 equiv-
alents) of NaBArF4 under an argon atmosphere. The tube was
evacuated, and 0.57 mL of fluorobenzene was vacuum trans-
ferred into the tube. Upon warming to room temperature and
mixing, a dark blue solution and white precipitate formed. Then
102 Torr of hydrogen gas was transferred into the tube, and the
solution was mixed for 120 s, resulting in a green solution. The
tube was sealed, and the ratio of complexes was determined by
31P NMR. The ratio was checked again after 24 h, and a second
determination of the equilibrium value was determined starting
from the H2 complex, to ensure equilibrium was achieved. This
procedure was repeated for each bromide for both H2 and N2
coordination.
(CH2Cl2) = 1811(s) cm-1
.
In Situ Formation of Cation Complexes. [Mn(PNMeP)(dppm)-
(CO)][BArF4]. A J. Young NMR tube was charged with Mn-
(PNMeP)(dppm)(CO)(Br) (14.5 mg, 0.0149 mmol) and NaBArF
4
(23.1 mg, 0.0261 mmol) in a glovebox under argon. The tube was
evacuated on a high vacuum line, and fluorobenzene (∼0.5 mL)
was vacuum transferred from P2O5. The tube was sealed. Upon
shaking a dark blue solution and a white precipitate formed.
31P{1H} NMR (C6H5F): δ 52.4 (s, dppm), 30.3 (s, PNP). IR: νCO
(C6H5F) = 1841(s) cm-1
.
[Mn(PNPhP)(dppm)(CO)][BArF4]. Prepared in an analogous
fashion to [Mn(PNMeP)(dppm)(CO)][BArF4] from Mn(PNPhP)-
(dppm)(CO)(Br), generating a dark blue solution. 31P{1H}
NMR (C6H5F): δ 54.5 (s, dppm), 30.3 (s, PNP). IR: νCO
(C6H5F) = 1842(s) cm-1
.
[Mn(PNBuP)(dppm)(CO)][BArF4]. Prepared in an analogous
fashion to [Mn(PNMeP)(dppm)(CO)][BArF4] from Mn(PNBuP)-
(dppm)(CO)(Br), generating a dark blue solution. 31P{1H}
NMR (C6H5F): δ 53.5 (s, dppm), 30.7 (s, PNP). IR: νCO
(C6H5F) = 1840(s) cm-1
.
[Mn(dppp)(dppm)(CO)][BArF4]. Prepared in an analogous
fashion to [Mn(PNMeP)(dppm)(CO)][BArF4] from Mn(dppp)-
(dppm)(CO)(Br), generating a dark blue solution. 31P{1H}
NMR (C6H5F): δ 53.4 (s, dppm), 29.4 (s, PNP). IR: νCO
(C6H5F) = 1839(s) cm-1
.
Acknowledgment. We thank the Division of Chemical
Sciences, Biosciences and Geosciences, Office of Basic
Energy Sciences, Office of Science of the U.S. Depart-
ment of Energy, for support of this work. Pacific North-
west National Laboratory is operated by Battelle for the
U.S. Department of Energy.
[Mn(P2PhN2Bn)(dppm)(CO)][BArF4]. Prepared in an analo-
gous fashion to [Mn(PNMeP)(dppm)(CO)][BArF4] from Mn-
(P2PhN2Bn)(dppm)(CO)(Br), generating a red solution. 31P{1H}
NMR (C6H5F): δ 24.6 (s), 23.7 (s). IR: νCO (C6H5F) = 1843(s)
cm-1
.
Formation of H2 and N2 Complexes. In a representative
experiment, a J. Young NMR tube was charged with 14.8 mg
(0.0152 mmol) of the bromide Mn(PNMeP)(dppm)(CO)(Br) and
18.9 mg (0.0213 mmol, 1.4 equiv) of NaBArF4 under an argon
atmosphere. The tube was evacuated, and 0.53 mL of fluoro-
benzene was vacuum transferred into the tube. The tube was
Supporting Information Available: 1H and 31P NMR spectra
for Mn bromides and hydrides. X-ray structure files in cif
format. This material is available free of charge via the Internet
at http://pubs.acs.org.