Inorganic Chemistry
Article
Electron Mixed-Valence Photocatalyst. Science 2001, 293, 1639−
1641.
(7) Maguire, J. A.; Boese, W. T.; Goldman, A. S. Photochemical
dehydrogenation of alkanes catalyzed by trans-carbonylchlorobis-
(trimethylphosphine)rhodium: aspects of selectivity and mechanism.
J. Am. Chem. Soc. 1989, 111, 7088−7093.
whereas the SMD solvation model gives a lower BDFE(MeCN) value
of 105 kcal/mol (298 K). The SMD value is used throughout the
manuscript. See the experimental section.
(23) Mader, E. A.; Mayer, J. M. The importance of precursor and
successor complex formation in a bimolecular proton-electron transfer
reaction. Inorg. Chem. 2010, 49, 3685−3687.
(8) Kee, J. W.; Chwee, T. S.; Tan, X. Y.; Webster, R. D.; Fan, W. Y.
Significant O−H bond weakening in CpMn(CO)2(CH3OH):
Evidence for the generation of the CpMn(CO)2(CH3O) radical
upon H-atom abstraction by O2. Organometallics 2013, 32, 4359−
4365.
(9) Godemann, C.; Hollmann, D.; Kessler, M.; Jiao, H.;
Spannenberg, A.; Bruckner, A.; Beweries, T. A Model of a Closed
̈
(24) Clerk, M. D.; Copp, S. B.; Subramanian, S.; Zaworotko, M. J.
Supramolecular properties of [Mn(CO)3(μ3-OH)]4 a neutral organo-
metallic molecule that is capable of binding a variety of small and
large guest molecules. Supramol. Chem. 1992, 1, 7−9.
(25) Markle, T. F.; Darcy, J. W.; Mayer, J. M. A new strategy to
efficiently cleave and form C−H bonds using proton-coupled electron
transfer. Sci. Adv. 2018, 4, eaat5776.
Cycle of Water Splitting Using ansa-Titanocene(III/IV) Triflate
Complexes. J. Am. Chem. Soc. 2015, 137, 16187−16195.
(10) Jin, L.; Wang, J.; Ye, W.; Fang, W.; Chen, X. Electron transfer
controls the photochemical splitting of water mediated by a
titanocene transition metal complex. J. Phys. Chem. C 2018, 122,
18412−18421.
(11) Bezdek, M. J.; Guo, S.; Chirik, P. J. Coordination-induced
weakening of ammonia, water, and hydrazine X−H bonds in a
molybdenum complex. Science 2016, 354, 730−733.
(26) To rule out actual proton exchange that might cause
coalescence of both [{DBU}H]+ and [1]−, we confirmed with
solution FTIR that [{DBU}H]+ was not formed (Figure S4).
(27) Bryant, J. R.; Taves, J. E.; Mayer, J. M. Oxidations of
hydrocarbons by manganese(III) tris(hexafluoroacetylacetonate).
Inorg. Chem. 2002, 41, 2769−2776.
(28) Moran, S.; Ellis, H. B., Jr.; DeFrees, D. J.; McLean, A. D.;
Ellison, G. B. Carbanion spectroscopy: CH2CN−. J. Am. Chem. Soc.
1987, 109, 5996−6003.
(12) Margulieux, G. W.; Bezdek, M. J.; Turner, Z. R.; Chirik, P. J.
Ammonia activation, H2 evolution and nitride formation from a
molybdenum complex with a chemically and redox noninnocent
ligand. J. Am. Chem. Soc. 2017, 139, 6110−6113.
(13) Chciuk, T. V.; Li, A. M.; Vazquez-Lopez, A.; Anderson, W. R.,
Jr.; Flowers, R. A., II Secondary amides as hydrogen atom transfer
promoters for reactions with samarium diiodide. Org. Lett. 2017, 19,
290−293.
(14) (a) Tarantino, K. T.; Miller, D. C.; Callon, T. A.; Knowles, R.
R. Bond-weakening catalysis: conjugate aminations enabled by the
soft homolysis of strong N−H bonds. J. Am. Chem. Soc. 2015, 137,
6440−6443. (b) Kolmar, S. S.; Mayer, J. M. SmI2(H2O)n reduction of
electron rich enamines by proton-coupled electron transfer. J. Am.
Chem. Soc. 2017, 139, 10687−10692.
(15) Kadassery, K. J.; Dey, S. K.; Friedman, A. E.; Lacy, D. C.
Exploring the Role of Carbonate in the Formation of an Organo-
manganese Tetramer. Inorg. Chem. 2017, 56, 8748−8751.
(16) Warren, J. J.; Tronic, T. A.; Mayer, J. M. Thermochemistry of
Proton-Coupled Electron Transfer Reagents and its Implications.
Chem. Rev. 2010, 110, 6961−7001.
(17) (a) The oxidation potentials of organomanganese complexes
are often irreversible, even at high scan rates. The oxidation event for
1 does not show any reversibility with the scan rates up to 12 V/s
(Figure S1b). (b) Lacombe, D. A.; Anderson, J. E.; Kadish, K. M.
E l e c t r o c h e m i s t r y o f d i m a n g a n e s e d e c a c a r b o n y l ,
pentacarbonylmanganese(1+), pentacarbonylmanganate(1-), and
manganese pentacarbonyl. Inorg. Chem. 1986, 25, 2074−2079.
(18) See the SI for a description of the attempts to obtain [1]+ from
reactions with 1 and [NO]PF6 in DCM.
(29) (a) Other base and oxidant (e.g., [NO]+ and CeIV) pairs with
appropriate BDFE values were also used but were not informative
because of condition incompatibilities. (b) The material obtained
from the oxidation of 1 with [NO]+ in DCM does not react with
DBU (see the SI); therefore, using a pKa value of 28 and a E1/2 value
of 0.66 V, BDFEO−H of 1 can be estimated at 104 kcal/mol in MeCN.
(30) Morris, W. D.; Mayer, J. M. Separating proton and electron
transfer effects in three-component concerted proton-coupled
electron transfer reactions. J. Am. Chem. Soc. 2017, 139, 10312−
10319.
(31) (a) Thermal CO dissociation is endergonic. For instance, first-
row transition-metal carbonyl bond strengths vary from ≈15 to 45
kcal/mol. (b) Sunderlin, L. S.; Wang, D.; Squires, R. R. Bond
strengths in first-row-metal carbonyl anions. J. Am. Chem. Soc. 1993,
115, 12060−12070. (c) The DFT-computed Mn−CO dissociation
free energy in 1 is 37 kcal/mol in toluene and MeCN (298 K); see the
SI for computational methods.
(32) Eisenhart, T.; Dempsey, J. L. Photo-induced proton-coupled
electron transfer reactions of acridine orange: comprehensive spectral
and kinetic analysis. J. Am. Chem. Soc. 2014, 136, 12221−12224.
(33) Lennox, J. C.; Kurtz, D. A.; Huang, T.; Dempsey, J. L Excited-
state proton-coupled electron transfer: different avenues for
promoting proton/electron movement with solar photons. ACS
Energy Lett. 2017, 2, 1246−1256.
(34) Wenger, O. S. Proton-coupled electron transfer with photo-
excited metal complexes. Acc. Chem. Res. 2013, 46, 1517−1526.
(35) Wenger, O. S. Proton-coupled electron transfer originating
from excited states of luminescent transition-metal complexes. Chem. -
Eur. J. 2011, 17, 11692−11702.
(19) Copp, S. B.; Holman, T.; Sangster, J. O. S.; Subramanian, S.;
Zaworotko, M. J. Supramolecular chemistry of [{M(CO)3(μ3-OH)}4]
(M = Mn, Re): A modular approach to crystal engineering of
superdiamondoid networks. J. Chem. Soc., Dalton Trans. 1995, 2233−
2243.
(36) Chambers, M. B.; Kurtz, D. A.; Pitman, C. L.; Brennaman, M.
K.; Miller, A. J. M. Efficient photochemical dihydrogen generation
initiated by a bimetallic self-quenching mechanism. J. Am. Chem. Soc.
2016, 138, 13509.
(37) Vlcek, A., Jr. The life and times of excited states of
organometallic and coordination compounds. Coord. Chem. Rev.
2000, 200−202, 933−977.
(38) (a) Hummel, P.; Oxgaard, J.; Goddard, W. A., III; Gray, H. B.
Ligand-Field Excited States of Metal Hexacarbonyls. Inorg. Chem.
2005, 44, 2454−2458. (b) Hartwig, J. F. Organotransition Metal
Chemistry, From Bonding to Catalysis; University Science Books: Mill
Valley, CA, 2010.
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(20) (a) Soovali, L.; Kaljurand, I.; Kutt, A.; Leito, I. Uncertainty
estimation in measurement of pKa values in nonaqueous media: a case
study on basicity scale in acetonitrile medium. Anal. Chim. Acta 2006,
566, 290−303. (b) If the pKa value of 1 is ≈28, 10000 equiv of DBU
would be required to establish an equilibrium. Hence, for a 0.001 M
solution of 1, this would require a concentration of DBU higher than
its neat molarity (6.6 M).
(21) Waidmann, C. R.; Miller, A. J. M.; Ng, C.-W. A.; Scheuermann,
M. L.; Porter, T. R.; Tronic, T. A.; Mayer, J. M. Using combinations
of oxidants and bases as PCET reactants: thermochemical and
practical considerations. Energy Environ. Sci. 2012, 5, 7771−7780.
(22) BDFE depends on the solvation model used. For instance, the
PCM solvation model gives a BDFE(MeCN) value of 109 kcal/mol,
(39) Lian, T.; Bromberg, S. E.; Asplund, M. C.; Yang, H.; Harris, C.
B. Femtosecond Infrared Studies of the Dissociation and Dynamics of
Transition Metal Carbonyls in Solution. J. Phys. Chem. 1996, 100,
11994−12001.
(40) (a) A single photon can liberate more than one CO ligand; see
the following references: A single photon can liberate more than one
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