Activation of small molecules by a rhodium bis(phosphinite) pincer complex

Abstract

Rhodium hydrido chloride pincer complex RhH(Cl)[2,6 (Bu t 2 PO) 2 C 6 H 3 ] was syn thesized and used for the preparation of new complexes with labile two electron ligands Rh(L)[2,6 (Bu t 2 PO) 2 C 6 H 3 ] (L = MeCN or S(CH 2 ) 4 ) and complexes with small molecules, such as CO, O 2 , H 2 , and N 2 .

Oxidative Addition of a Mechanically Entrapped C(sp)–C(sp) Bond to a Rhodium(I) Pincer Complex

“…The decisive role of macrocyclic ligand in 1 was also confirmed by comparison to the acyclic congener 5, with Ar'(CH 2 ) 4 Ar' the only organic product observed alongside Rh I dihydrogen complex 9 on reaction with H 2 under equivalent conditions (Scheme 3, insert). [20] The remarkable reactivity of 1 presented herein can be reconciled by a pronounced "catenand effect", the name given by Sauvage for the augmentation of a metal ions reactivity due to confinement within a threaded structure, [7] and this conclusion is substantiated by comparison to the electronically similar acyclic congener 5 (Scheme 4). [9,18] Insertion of rhodium into the C(sp)-C(sp) bond of Ar'C 4 Ar' in 1 is a reversible but thermodynamically uphill reaction that is associated with a formidable activation barrier of DG°2 98K = 120 AE 3 kJ mol À1 .…”

“…This complex can be viewed as an intermediate in the associative substitution of Ar′C 4 Ar′ by CO, but dissociation of the diyne in this case appears to be arrested by the steric constraints imposed by tight confinement within the ring. For comparison, the acyclic congener of 1 , [Rh(PONOP‐ t Bu)(η 2 ‐Ar′C 4 Ar′)] 5 (see Supporting Information for full details), [18] was prepared and found to give Rh I carbonyl derivative 6 by rapid displacement of the diyne upon placing under CO (1 atm) at RT [19, 20] . Coordination of CO to 1 is reversible and analysis of the dynamic equilibrium between 1 and 4 by variable temperature UV‐vis spectroscopy (1 atm CO) enabled the associated thermodynamic parameters to be established (Δ H =−71±1 kJ mol −1 , Δ S =−223±3 J mol −1 K −1 ) [21] .…”

A Series of Pincer-Ligated Rhodium Complexes as Catalysts for the Dimerization of Terminal Alkynes

“…Pincer carbonyl complexes could also be obtained by treating the (pincer)Rh(S i Pr 2 ) complexes (7-Rh(S i Pr 2 ) and 8-Rh(S i Pr 2 )) with an atmosphere of CO to form 7-Rh(CO) and 8-Rh(CO). Complexes n-Rh(CO) (n = 5-8) were analyzed using IR spectroscopy and compared to the reported CO stretching frequencies of 3-Rh(CO), 32 4-Rh(CO), 33 10-Rh(CO) 32 to gauge the electron richness 34 of the ligand backbone (Table 1).…”

Oxidative Addition of a Mechanically Entrapped C(sp)–C(sp) Bond to a Rhodium(I) Pincer Complex

“…To exclude alternative reaction pathways commencing with hydrogenation of the diyne, the E ‐enyne derivative 8 ( δ 31P 185.1, 182.5; 2 J PP =401 Hz) was prepared by stepwise proton and hydride transfer and shown to be thermally stable under H 2 (1 atm). The decisive role of macrocyclic ligand in 1 was also confirmed by comparison to the acyclic congener 5 , with Ar′(CH 2 ) 4 Ar′ the only organic product observed alongside Rh I dihydrogen complex 9 on reaction with H 2 under equivalent conditions (Scheme 3, insert) [20] …”

“…For comparison, the acyclic congener of 1, [Rh(PONOP-tBu)(h 2 -Ar'C 4 Ar')] 5 (see Supporting Information for full details), [18] was prepared and found to give Rh I carbonyl derivative 6 by rapid displacement of the diyne upon placing under CO (1 atm) at RT. [19,20] Coordination of CO to 1 is reversible and ; Cnt = bond centroid. [22] analysis of the dynamic equilibrium between 1 and 4 by variable temperature UV-vis spectroscopy (1 atm CO) enabled the associated thermodynamic parameters to be established (DH = À71 AE 1 kJ mol À1 , DS = À223 AE 3 J mol À1 K À1 ).…”