Stevens, Charlotte J., Dallanegra, Romaeo, Chaplin, Adrian B., Weller, Andrew S., Macgregor, Stuart A., Ward, B. (Bryan), McKay, D. (David), Alcaraz, Gilles and Sabo-Etienne, Sylviane (2011) [Ir(PCy(3))(2)(H)(2)(H(2)B-NMe(2))](+) as a latent source of aminoborane : probing the role of metal in the dehydrocoupling of H(3)B center dot NMe(2)H and retrodimerisation of [H(2)BNMe(2)](2). Chemistry: A European Journal, Vol.17 (No.10). pp. 3011-3020. doi:10.1002/chem.201002517 ISSN 0947-6539.

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Abstract

The Ir(III) fragment {Ir(PCy(3))(2)(H)(2)}(+) has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H(3)B center dot NMe(2)H (A) to ultimately give dimeric aminoborane [H(2)BNMe(2)](2) (D). Addition of A to [Ir(PCy(3))(2)(H)(2)(H(2))(2)][BAr(4)(F)] (1; Ar(F) =(C(6)H(3)(CF(3))(2)), gives the amineborane complex [Ir(PCy(3))(2)(H)(2)(H(3)B center dot NMe(2)H)][BAr(4)(F)] (2a), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy(3))(2)(H)(2)(H(2)B-NMe(2))][BAr(4)(F)] (3). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H(2) loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3. DFT calculations indicate that this involves metal trapping of the monomer-dimer equilibrium, 2H(2)BNMe(2) reversible arrow [H(2)BNMe(2)](2). Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy(3))(2)(H)(2)(NCMe)(2)][BAr(4)(F)] (6) liberating H(2)B-NMe(2) (B), which then dimerises to give D. This is shown to be a second-order process. It also allows on-and off-metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine-borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H(3)B center dot NMe(2)BH(2)center dot NMe(2)H (C), which ultimately was converted to D. These results indicate that the metal is involved in both the dehydrogenation of A, to give B, and the oligomerisation reaction to afford C. A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D, with 3 observed as the final organometallic product, suggesting a B-N bond cleavage mechanism. Complex 6 does not react with C, but in combination with B oligomer C is consumed to eventually give D, suggesting an additional role for free aminoborane in the formation of D from C.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Divisions:	Faculty of Science, Engineering and Medicine > Science > Chemistry
Library of Congress Subject Headings (LCSH):	Amines, Boranes, Catalysis, Density functionals, Iridium, Reaction mechanisms (Chemistry)
Journal or Publication Title:	Chemistry: A European Journal
Publisher:	Wiley - V C H Verlag GmbH & Co. KGaA
ISSN:	0947-6539
Official Date:	March 2011
Dates:	Date Event March 2011 Published
Volume:	Vol.17
Number:	No.10
Page Range:	pp. 3011-3020
DOI:	10.1002/chem.201002517
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	University of Oxford, Centre national de la recherche scientifique (France) (CNRS), France. Agence nationale de la recherche (ANR), Université de Toulouse, Engineering and Physical Sciences Research Council (EPSRC), Heriot-Watt University
Grant number:	ANR-09-BLAN-0184-01 HyBoCat (ANR), EP/E02971X/1 (EPSRC)

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