Department of Inorganic Chemistry, University of Oxford, Oxford, OX1 3QR, United Kingdom.
Inorg Chem. 2010 Feb 1;49(3):1111-21. doi: 10.1021/ic9020542.
Complexes formed between {Rh(P(i)Pr(3))(2)}(+) or {Rh(H)(2)(P(i)Pr(3))(2)}(+) fragments and the amine- and dimeric amino-borane sigma ligands H(3)B.NMe(3) and H(2)BNMe(2) have been prepared and their solution and solid-state structures determined: [Rh(P(i)Pr(3))(2)(eta(2)-H(3)B.NMe(3))][BAr(F)(4)] (1), [Rh(P(i)Pr(3))(2){eta(2)-(H(2)BNMe(2))(2)}][BAr(F)(4)] (2), [Rh(H)(2)(P(i)Pr(3))(2)(eta(2)-H(3)B.NMe(3))][BAr(F)(4)] (3), and [Rh(H)(2)(P(i)Pr(3))(2){eta(2)-(H(2)BNMe(2))(2)}][BAr(F)(4)] (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(F)(4)] and H(2)BNMe(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 (1)H NMR spectroscopy in solution and the Rh...B distances measured in the solid state, the P(i)Pr(3) complexes show tighter interactions with the sigma 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 interactions, 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.NHMe(2) to give the dimeric amino-borane H(2)BNMe(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(F)(4)] (with 1 and 2) and the previously reported [Rh(H)(2)(P(i)Pr(3))(2)(NCMe)(2)][BAr(F)(4)] (with 3).
{Rh(P(i)Pr(3))(2)}(+) 或 {Rh(H)(2)(P(i)Pr(3))(2)}(+) 片段与胺和二聚氨基硼烷 σ 配体 H(3)B.NMe(3)和 H(2)BNMe(2)形成的配合物已被制备，并确定了其溶液和固态结构：[Rh(P(i)Pr(3))(2)(eta(2)-H(3)B.NMe(3))][BAr(F)(4)] (1)、[Rh(P(i)Pr(3))(2){eta(2)-(H(2)BNMe(2))(2)}][BAr(F)(4)] (2)、[Rh(H)(2)(P(i)Pr(3))(2)(eta(2)-H(3)B.NMe(3))][BAr(F)(4)] (3) 和 [Rh(H)(2)(P(i)Pr(3))(2){eta(2)-(H(2)BNMe(2))(2)}][BAr(F)(4)] (4) [Ar(F) = C(6)H(3)(CF(3))(2)]。最后一种化合物仅在固态中观察到，因为在溶液中，由于配体和金属片段之间的空间位阻，它会解聚为 [Rh(H)(2)(P(i)Pr(3))(2)][BAr(F)(4)] 和 H(2)BNMe(2)。这些新配合物的结构和反应性与之前报道的三异丁基同系物进行了比较。基于溶液中的 (11)B 和 (1)H NMR 光谱以及固态中测量的 Rh...B 距离，与 P(i)Bu(3)配合物相比，P(i)Pr(3)配合物与 σ 配体的相互作用更紧密，对于 Rh(III)盐，H(2)的损失更稳定。对于 Rh(I)物种 (1 和 2)，这被认为是与 ML(2)片段弯曲相关的电子因素所致。对于 Rh(III)配合物 (3 和 4)，H(2)损失稳定性增加的根本原因尚不清楚，但据推测，空间位阻因素会影响二氢的相对稳定性，尽管其他因素，如支持的桥接相互作用，也可能起作用。这些更紧密的相互作用和较慢的 H(2)损失反映在催化剂中，与 P(i)Bu(3)配位的催化剂相比，在 H(3)B.NHMe(2)的脱氢偶联中催化剂的周转率较慢，以生成二聚氨基硼烷 H(2)BNMe(2)（TOF 4 h(-1)，分别为 15 h(-1)）。向 1、2 或 3 中添加过量的 MeCN 会导致 σ-配体取代，并形成加合物物种 trans-[Rh(P(i)Pr(3))(2)(NCMe)(2)][BAr(F)(4)]（与 1 和 2）和之前报道的 [Rh(H)(2)(P(i)Pr(3))(2)(NCMe)(2)][BAr(F)(4)]（与 3）。
