C−H Activation Reactions on Rh(I)−Ethylene Complexes of the Hydrotris(3,5-dimethylpyrazolyl)borate Ligand, Tp^Me₂

Abstract

N-donor Lewis bases such as acetonitrile or pyridine react with the Rh(I) compound TpMe 2 Rh(C2H4)2 (1) to give the Rh(III) derivatives TpMe 2 Rh(CHCH2)(C2H5)(L) (2, 3) as the kinetic products of the reactions. Upon heating at 60 °C, the acetonitrile adduct 2 converts into TpMe 2 Rh(C2H4)(NCMe) (5). Under similar conditions, 2 is able to induce the activation of one of the C−H bonds of C6H6, in a process that involves the intermediacy of 1, as demonstrated by isotopic labeling studies. The phosphine adducts TpMe 2 Rh(C2H4)(PR3) (R = Me, Et) are also efficient reagents for the C−H bond activation of C6H6, py, or thiophene. In the latter case, rupture of the C−S bond is also detected, although the C−S bond activation complexes are thermodynamically disfavored with respect to those derived from the cleavage of one of the α-C−H bonds.

Rhodium Complexes in P−H Bond Activation Reactions

“…Thus, the 1 H NMR spectrum showed the diastereotopic CH 2 protons of ethyl group as two multiplets coupled to a triplet corresponding to the methyl group (Figure , in blue). In addition, the large coupling constant of the methylenic carbon to rhodium ( J (C,Rh)=24 Hz) clearly evidences the presence of a direct Rh−C bond …”

Reaction of [TpRh(C2H4)2] with Dimethyl Acetylenedicarboxylate: Identification of Intermediates of the [2+2+2] Alkyne and Alkyne–Ethylene Cyclo(co)trimerizations

“…The synthesis of the known compound [TpRh(C 2 H 4 ) 2 ] ( 1 ) was improved to excellent yields (≥95 %) by adapting the procedure reported for the synthesis of the related [Tp Rh(C 2 H 4 ) 2 ] (see the Experimental Section) . The reaction of 1 with 3 equiv of DMAD (C 6 H 6 , 25 °C, 4 h) gave a mixture of rhodium complexes 2 – 5 and C 6 (CO 2 Me) 6 ( 6 ), that is, the already known product resulting from the [2+2+2] cyclotrimerization of the alkyne, being 2 and 3 the more abundant organometallic species of this complex mixture (Scheme ).…”

“…Mechanistic studies on phosphine‐ethylene [TpRh(PR 3 )(C 2 H 4 )] complexes and their reactivity towards hydrogen have also been performed . In comparison with its Tp analogue, [Tp Rh(C 2 H 4 ) 2 ], which is only stable below −10 °C, complex 1 can be handled in air and at room temperature.…”

The Effects of Ancillary Ligands on Metal–Carbon Bond Strengths as Determined by C–H Activation

“…To generate the 16-electron fragment, Tp 0 Rh(PMe 3 )H 2 (4) was used as a photochemical precursor of the reactive intermediate [16,17] Tp'Rh(CNR')RH Tp'Rh(CNR')RH Fig. 3 Plot of relative experimental M-C bond strengths vs. C-H bond strengths.…”