Iridium Pincer Complexes with an Olefin Backbone

Abstract

Among the large variety of pincer complexes, those with carbon− carbon double bonds in the backbone have received little attention. Here, we report the reactions of complex (PCCP)IrPh (3) and its derivatives with small molecules. Compound 3 readily adds CO to give the 18e adduct (PCCP)IrPhCO (5a), which upon heating undergoes isomerization into the thermodynamically more stable isomer (PCCP)IrCO(Ph) (5b), via reversible loss of CO. Reaction of 5 with hydrogen leads to the formation of saturated carbonyl compounds (PC−CP)IrCO (9) and (PC−CP)IrH(CO)H (10). In contrast to the hydrides (PCCP)IrH 3 (6) and (PC−CP)IrH 4 (7), which are in tautomeric equilibrium via insertion of one of the hydrides into the olefin moiety, the former compounds do not isomerize into the olefin form. Protonation of 5 with CF 3 COOH gives a complex with an agostic methylene group, 11, which undergoes a rare transformation for Ir pincers, which is insertion of CO into the Ir−Ph bond with subsequent formation of (PCCP)IrOCOCF 3 (12) and Ph−CHO. The trihydride 6 reacts with CO to give 9, which can add a second molecule of CO to reversibly form the dicarbonyl 13.

An electron poor iridium pincer complex for catalytic alkane dehydrogenation

“…24 Compound 7 reacts with COE and TBE in benzene solution at room temperature forming deep red solutions of complexes 8 and 9, correspondingly (Scheme 3). 25,26 These experiments show that COE binds much stronger than TBE to compound 7. The signal from 8 agrees very well with the signal of the reaction mixture after catalysis.…”

α‐ and β‐Eliminations in Transition Metal Complexes: Strategies to Cleave Unstrained C−C and C−F Bonds

“…Reactivity of complex 68 with the olefin backbone and its derivatives towards small molecules such as CO, H 2 , CF 3 COOH, and O 2 has been presented recently, and it was suggested that such complexes were best categorized as olefin complexes with minor or no contribution of the metallacyclopropane structure, despite the fact that chemical shifts of the olefin moiety appear in the aliphatic region [11] …”

“…From a mechanistic point of view, oxidative additions and β‐eliminations are the two most common pathways for transition metal mediated C−C bond cleavage whereas there are still few reports on α‐eliminations [9–11] . For unstrained C−C‐bonds, however, oxidative additions are uncommon, particularly in a catalytic context, and this review will emphasize the use of α‐ and β‐elimination which may be better options for C−C bond cleavage and high‐light work where these mechanistic steps have been shown to operate.…”

Synthesis and Characterisation of Transition Metal Complexes of a Novel 1,5‐benzodiazepine‐Functionalised Tertiary Phosphine

“…Single crystal X-ray studies were undertaken on 2 a • Et 2 O, 2 b, 3 • 2CH 3 OH and 3' • 1 = 2 CH 3 OH. [20,21] Suitable crystals of 2 a • Et 2 O and 3 • 2CH 3 OH were obtained by vapour diffusion of Et 2 O into a CDCl 3 (for 2 a), slow diffusion of CH 3 OH into a CDCl 3 (for 2 b) or vapour diffusion of Et 2 O into a CH 3 OH (for 3 and 3') solution over several days (Figure 2, Figure 3, Figure 4, and SI). All four structures reveal classic, three-legged, piano stool geometries, with the iridium centres coordinated by an η 5 -Cp* and either two chlorides and a P-monodentate 1 or an anionic P/N amine /Cterdentate 1.…”

“…The IrÀ C(30) distance [2.212(8) Å] is slightly longer than observed in known CÀ H activated iridium (III) compounds. [8,18,21] The most remarkable feature of the molecular structures of 3 • 2CH 3 OH and 3' • 1 = 2 CH 3 OH is the unusual η 3 -P/N/C coordination mode of 1, affording an iridacycle with both IrPC 4 (or IrPC 3 N) six-membered and IrC 2 N fourmembered rings. The acute C(30 in accord with formation of a four-membered IrNC 2 ring.…”