Organometallics
ARTICLE
combustion, then the H O used in the overall reaction of
2
hydrolysis and combustion would then, formally be used in a
catalytic fashion. The resulting energy would therefore be produced
from the recycling of water.
’
CONCLUSIONS
In conclusion, we have demonstrated the use of unusual,
formally 14e, bis-ortho-metalated IrꢀNHC complexes as highly
active catalysts in the solvolysis of ammoniaꢀborane. The reaction
is proposed to proceed through Ir-mediated cleavage of the BꢀN
bond followed by hydrolysis of the liberated borane by the reaction
solvent. Two cationic IrꢀNH complexes have been isolated and
3
are proposed to be resting states of the active catalyst. Further
t
0
development of the ortho-metalated complexes [Ir(I Bu ) Cl]
2
t
0
2
and [Ir(I Bu ) ][PF ] as catalysts is currently underway in our
6
laboratories.
t
t
0
Figure 10. ORTEP representations of [Ir(H)(NH )(I Bu)(I Bu )]-
3
t
0
’
ASSOCIATED CONTENT
[PF
6
] (4) and [Ir(NH
3
)(I Bu )
2
][PF
6
] (5). All hydrogens except
hydride and the counterion PF6 are omitted for clarity. Ir(1)ꢀ
ꢀ
S
Supporting Information. Text giving the experimental
N(1) = 2.260(7) Å (4) and 2.233(7) Å (5).
b
section and figures, tables, and CIF files giving NMR spectra for
high-pressure experiments, data for kinetic experiments, and
crystallographic data for [B O H ][NH ], 4, and 5. This material
Scheme 1. Plausible Mechanism for the Catalytic Solvolysis
of AmmoniaꢀBorane Promoted by [Ir(I Bu ) ][PF ] (3)
5
10
4
4
t
0
2
is available free of charge via the Internet at http://pubs.acs.org.
6
’
AUTHOR INFORMATION
Corresponding Author
*
E-mail: snolan@st-andrews.ac.uk.
’
ACKNOWLEDGMENT
The ERC (Advanced Investigator Award FUNCAT) is grate-
fully acknowledged for support. S.P.N. is a Royal Society-
Wolfson Research Merit Award holder.
’
REFERENCES
(1) Staubitz, A.; Robertson, A. P. M.; Manners, I. Chem. Rev. 2010,
110, 4079–4124.
(
(
2) Smythe, N. C.; Gordon, J. C. Eur. J. Inorg. Chem. 2010, 509–521.
3) Alcaraz, G.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2010,
4
9, 7170–7179.
4) Hamilton, C. W.; Baker, R. T.; Staubitz, A.; Manners, I. Chem.
Soc. Rev. 2009, 38, 279–293.
5) Stephens, F. H.; Pons, V.; Baker, R. T. Dalton Trans. 2007,
613–2626.
(
(
2
(
(
6) Marder, T. B. Angew. Chem., Int. Ed. 2007, 46, 8116–8118.
7) (a) Kelly, H. C.; Marchelli, F. R.; Giutso, M. B. Inorg. Chem.
1964, 3, 431–437. (b) Ryschkewitsch, G. E. J. Am. Chem. Soc. 1960,
82, 3290–3294. (c) Kelly, H. C.; Marriott, V. B. Inorg. Chem. 1979,
18, 2875–2878. (d) D’Ulivo, A.; Onor, M.; Pitzalis, E. Anal. Chem. 2004,
76, 6342–6352.
(8) Chandra, M.; Xu, Q. J. Power Sources 2006, 156, 190–194.
If a significant amount of hydrogen is present, complex 5
would be converted to the dihydride complex 6. These com-
plexes would serve as the resting state of the active catalyst.
Dissociation of the weak ammonia ligand from complex 5
followed by ligation of AB completes the catalytic cycle. Likewise,
complexation of AB to 6 could result in a species similar to those
(9) Clark, T. J.; Whittell, G. R.; Manners, I. Inorg. Chem. 2007,
6, 7522–2527.
4
(10) Graham, T. W.; Tsang, C.-W.; Chen, X.; Guo, R.; Jia, W.; Lu, S.-
M.; Sui-Seng, C.; Ewart, C. B.; Lough, A.; Amoroso, D.; Abdur-Rashid,
K. Angew. Chem. Int., Ed. 2010, 49, 8708–8711.
(
11) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.;
Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516–3526.
12) Scott, N. M.; Pons, V.; Stevens, E. D.; Heinekey, D. M.; Nolan,
22
disclosed by the Aldridge group.
(
An interesting aspect of the reaction is that 3 mol of H is
2
S. P. Angew. Chem., Int. Ed. 2005, 44, 2512–2515.
(13) Cavallo, L.; Nolan, S. P.; Jacobsen, H. Can. J. Chem. 2009,
87, 1362–1368.
produced from 1 mol of AB. Half of the evolved hydrogen is
obtained from H O. If the ultimate fate of the released H is
2
2
5
491
dx.doi.org/10.1021/om2007437 |Organometallics 2011, 30, 5487–5492