Steric Control over Arene Coordination toβ-Diiminate Rhodium(I) Fragments

Abstract

The bulky ligands L(X)- (L(X) = (2,6-C6H3X2)NC(Me)CHC(Me)N(2,6-C6H3X2), X =Cl, Me) can be used to generate fluxional mononuclear arene complexes [L(X)Rh(eta4-arene)] (arene = benzene, toluene, m-xylene, mesitylene), which for X = Me disproportionate to fluxional dinuclear complexes [[L(Me)Rh]2(anti-mu-arene)]. For both mononuclear and dinuclear complexes, steric interactions do not stop the fluxionality but govern the preferred orientation of the methyl-substituted arenes, thus allowing indirect determination of the static NMR parameters. For the mu-arene complexes, two distinct types of fluxionality are proposed on the basis of calculations: ring rotation and metal shift. In the solid state, the toluene complex has an eta4(1,2,3,4):eta4(3,4,5,6)-bridged structure; the NMR analysis indicates that the benzene and m-xylene complexes have similar structures. The mesitylene complex, however, has an unprecedented eta3(1,2,3):eta3(3,4,5)-bridged structure, which is proposed to correspond to the transition state for arene rotation in the other cases. Steric factors are thought to be responsible for this reversal of stabilities.

{Rh(PiBu3)2}+ Fragments Ligated to Arenes: From Benzene to Polyaromatic Hydrocarbons, Part I – An Experimental Approach

“…Both η 2 ‐ and η 3 ‐coordination modes have precedent in Rh I complexes. For example (C 5 Me 5 )Rh(PMe 3 )(phenanthrene) is η 2 ,10 while {LMeRh} 2 (mesitylene) is η 3 (L = 2,6‐C 6 H 3 Me 2 )NC(Me)CHC(Me)N(2,6‐C 6 H 3 Me 2 ) 42. Interestingly, this latter complex has been proposed as a model for the transition state in the fluxional pathway for movement of the metal from chemically equivalent η 4 to η 4 coordination modes.…”

Copper–Nitrene Complexes in Catalytic CH Amination

“…We reasoned that the use of chemically inert substituents at the ortho ‐aryl position of the β‐diketiminate N groups could thwart intramolecular nitrene insertion and enable the functionalization of more synthetically useful, exogenous CH bonds. [{(Cl 2 NN)Cu} 2 (μ‐benzene)] ( 3 ), having Cl substituents in the ortho positions of the β‐diketiminate N ‐aryl groups, can be prepared in 94 % yield from the reaction of the free diimine [H(Cl 2 NN)]14 and CuO t Bu in benzene. Reaction of [{(Cl 2 NN)Cu} 2 (μ‐benzene)] with N 3 Ad in chlorobenzene results in the isolation of [{(Cl 2 NN)Cu} 2 (μ‐NAd)] ( 4 ) as a green crystalline material in 63 % yield.…”

Cascade Activation of SiH, CH, and SiC Bonds at a Rhodium β‐Diiminate Complex

“…In contrast, dimethyl octadecyl silane produces two rearranged products in a ratio close to 1:1, most likely diastereomers formed by activation of SiMe bonds (entry 7); the reaction with dimethyl cyclohexyl silane proceeds with higher selectivity (about 1:2, entry 8). With dimethyl phenyl silane, the initial bis(silane) adduct is formed, but heating does not lead to the expected rearrangement product, giving instead a mixture of various mono(hydride) complexes; we tentatively ascribe this to arene coordination to Rh 22. Tris(isopropyl)silane appears to be too hindered to form a silane complex.…”