Chaplin, Adrian B. and Weller, Andrew S.. (2010) Amine− and dimeric amino−borane complexes of the {Rh(PiPr3)2}+ fragment and their relevance to the transition-metal-mediated dehydrocoupling of amine−boranes. Inorganic Chemistry, Vol.49 (No.3). pp. 1111-1121. ISSN 0020-1669

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Abstract

Complexes formed between {Rh(P(i)Pr(3))(2)}(+) Or {Rh(H)(2)(P(i)Pr(3))(2)}(+) fragments and the amine- and dimeric aminoborane sigma ligands H(3)B center dot NMe(3) and [H(2)BNMe(2)](2) have been prepared and their solution and solid-state structures determined: [Rh(P(i)Pr(3))(2)(eta(2)-H(3)B center dot NMe(3))][BAr(4)(F)] (1), [Rh(P(i)Pr(3))(2){eta(2)-(H(2)B center dot NMe(2))(2)}][BAr(4)(F)] (2), [Rh(H)(2)(P(i)Pr(3))(2)(eta(2)-H(3)B center dot NMe(3))][BAr(4)(F)](3), and [Rh(H)(2)(P(i)Pr(3))(2)][eta(2)-(H(2)BN center dot Me(2))(2)][BAr(4)(F)](4) [Ar(F) = C(6)H(3)(CF(3))(2)], The last compound was only observed in the solid state, as in solution it dissociates to give [Rh(H)(2)(P(i)Pr(3))(2)] [BAr(4)(F)] and [H(2)B center dot NMe(2)](2) due to steric pressure between the ligand and the metal fragment. The structures and reactivities of these new complexes are compared with the previously reported tri-isobutyl congeners. On the basis of (11)B and (H) NMR spectroscopy in solution and the Rh center dot center dot center dot B distances measured in the solid state, the P'Pr3 complexes show tighter interactions with the a ligands compared to the P(i)Bu(3) complexes for the Rh(I) species and a greater stability toward H(2) loss for the Rh(III) salts. For the Rh(I) species (1 and 2), this is suggested to be due to electronic factors associated with the bending of the ML(2) fragment. For the Rh(III) complexes (3 and 4), the underlying reasons for increased stability toward H(2) loss are not as clear, but steric factors are suggested to influence the relative stability toward a loss of dihydrogen, although other factors, such as supporting agostic interections, might also play a part. These tighter interactions and a slower H(2) loss are reflected in a catalyst that turns over more slowly in the dehydrocoupling of H(3)B center dot NHMe(2) to give the dimeric amino-borane [H(2)BNMe(2)](2), when compared with the P(i)Bu(3)-ligated catalyst (ToF 4 h(-1), c.f., 15 h(-1), respectively). The addition of excess MeCN to 1, 2, or 3 results in the displacement of the (sigma-ligand and the formation of the adduct species trans-[Rh(P(i)Pr(3))(2)(NCMe)(2))[BAr(4)(F)] (with 1 and 2) and the previously reported [Rh(H)(2)(P(i)Pr(3))(2)(NCMe)(2)][BAr(4)(F)] (with 3).

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry
Divisions:	Faculty of Science > Chemistry
Library of Congress Subject Headings (LCSH):	Amines, Boranes, Complex compounds, Rhodium, Transition metal catalysts
Journal or Publication Title:	Inorganic Chemistry
Publisher:	American Chemical Society
ISSN:	0020-1669
Date:	1 February 2010
Volume:	Vol.49
Number:	No.3
Page Range:	pp. 1111-1121
Identification Number:	10.1021/ic9020542
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	Engineering and Physical Sciences Research Council (EPSRC), University of Oxford
URI:	http://wrap.warwick.ac.uk/id/eprint/40525

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