Addition of Amines to a Carbonyl Ligand: Syntheses, Characterization, and Reactivities of Iridium(III) Porphyrin Carbamoyl Complexes

Treatment of (carbonyl)chloro(meso-tetra-p-tolylporphyrinato)iridium(III), (TTP)Ir(CO)Cl (1), with excess primary amines at 23 °C in the presence of Na2CO3 produces the trans-amine-coordinated iridium carbamoyl complexes (TTP)Ir(NH2R)[C(O)NHR] (R = Bn (2a), n-Bu (2b), i-Pr (2c), t-Bu (2d)) with isolated yields up to 94%. The trans-amine ligand is labile and can be replaced with quinuclidine (1-azabicyclo[2.2.2]octane, ABCO), 1-methylimidazole (1-MeIm), triethyl phosphite (P(OEt)3), and dimethylphenylphosphine (PMe2Ph) at 23 °C to afford the hexacoordinated carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (for R = Bn: L = ABCO (3a), 1-MeIm (4a), P(OEt)3 (5a), PMe2Ph (6a)). On the basis of ligand displacement reactions and equilibrium studies, ligand binding strengths to the iridium metal center were found to decrease in the order PMe2Ph \u3e P(OEt)3 \u3e 1-MeIm \u3e ABCO \u3e BnNH2 ≫ Et3N, PCy3. The carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (L = RNH2 (2a,b), 1-MeIm (4a)) undergo protonolysis with HBF4 to give the cationic carbonyl complexes [(TTP)Ir(NH2R)(CO)]BF4 (7a,b) and [(TTP)Ir(1-MeIm)(CO)]BF4 (8), respectively. In contrast, the carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (L = P(OEt)3 (5a), PMe2Ph (6a,c)) reacted with HBF4 to afford the complexes [(TTP)Ir(PMe2Ph)]BF4 (9) and [(TTP)IrP(OEt)3]BF4 (10), respectively. The carbamoyl complexes (TTP)Ir(L)[C(O)NHR] (L = RNH2 (2a–d), 1-MeIm (4a), P(OEt)3 (5b), PMe2Ph (6c)) reacted with methyl iodide to give the iodo complexes (TTP)Ir(L)I (L = RNH2 (11a–d), 1-MeIm (12), P(OEt)3(13), PMe2Ph (14)). Reactions of the complexes [(TTP)Ir(PMe2Ph)]BF4 (9) and [(TTP)IrP(OEt)3]BF4 (10) with [Bu4N]I, benzylamine (BnNH2), and PMe2Ph afforded (TTP)Ir(PMe2Ph)I (14), (TTP)Ir[P(OEt)3]I (13), [(TTP)Ir(PMe2Ph)(NH2Bn)]BF4 (16), and trans-[(TTP)Ir(PMe2Ph)2]BF4 (17), respectively. Metrical details for the molecular structures of 4a and17 are reported

Temperature dependent CO2 behavior in microporous 1-D channels of a metal-organic framework with multiple interaction sites

The MOF with the encapsulated CO2 molecule shows that the CO2 molecule is ligated to the unsaturated Cu(II) sites in the cage using its Lewis basic oxygen atom via an angular eta(1)-(O-A) coordination mode and also interacts with Lewis basic nitrogen atoms of the tetrazole ligands using its Lewis acidic carbon atom. Temperature dependent structure analyses indicate the simultaneous weakening of both interactions as temperature increases. Infrared spectroscopy of the MOF confirmed that the CO2 interaction with the framework is temperature dependent. The strength of the interaction is correlated to the separation of the two bending peaks of the bound CO2 rather than the frequency shift of the asymmetric stretching peak from that of free CO2. The encapsulated CO2 in the cage is weakly interacting with the framework at around ambient temperatures and can have proper orientation for wiggling out of the cage through the narrow portals so that the reversible uptake can take place. On the other hand, the CO2 in the cage is restrained at a specific orientation at 195 K since it interacts with the framework strong enough using the multiple interaction sites so that adsorption process is slightly restricted and desorption process is almost clogged.ope

Photochemical dihydrogen production using an analogue of the active site of [NiFe] hydrogenase

The photoproduction of dihydrogen (H2) by a low molecular weight analogue of the active site of [NiFe] hydrogenase has been investigated by the reduction of the [NiFe2] cluster, 1, by a photosensitier PS (PS = [ReCl(CO)3(bpy)] or [Ru(bpy)3][PF6]2). Reductive quenching of the 3MLCT excited state of the photosensitiser by NEt3 or N(CH2CH2OH)3 (TEOA) generates PS•−, and subsequent intermolecular electron transfer to 1 produces the reduced anionic form of 1. Time-resolved infrared spectroscopy (TRIR) has been used to probe the intermediates throughout the reduction of 1 and subsequent photocatalytic H2 production from [HTEOA][BF4], which was monitored by gas chromatography. Two structural isomers of the reduced form of 1 (1a•− and 1b•−) were detected by Fourier transform infrared spectroscopy (FTIR) in both CH3CN and DMF (dimethylformamide), while only 1a•− was detected in CH2Cl2. Structures for these intermediates are proposed from the results of density functional theory calculations and FTIR spectroscopy. 1a•− is assigned to a similar structure to 1 with six terminal carbonyl ligands, while calculations suggest that in 1b•− two of the carbonyl groups bridge the Fe centres, consistent with the peak observed at 1714 cm−1 in the FTIR spectrum for 1b•− in CH3CN, assigned to a ν(CO) stretching vibration. The formation of 1a•− and 1b•− and the production of H2 was studied in CH3CN, DMF and CH2Cl2. Although the more catalytically active species (1a•− or 1b•−) could not be determined, photocatalysis was observed only in CH3CN and DMF

Advances in heterometallic ring-opening (co)polymerisation catalysis

Truly sustainable plastics require renewable feedstocks coupled with efficient production and end-of-life degradation/recycling processes. Some of the most useful degradable materials are aliphatic polyesters, polycarbonates and polyamides, which are often prepared via ring-opening (co)polymerisation (RO(CO)P) using an organometallic catalyst. While there has been extensive research into ligand development, heterometallic cooperativity offers an equally promising yet underexplored strategy to improve catalyst performance, as heterometallic catalysts often exhibit significant activity and selectivity enhancements compared to their homometallic counterparts. This review describes advances in heterometallic RO(CO)P catalyst design, highlighting the overarching structure-activity trends and reactivity patterns to inform future catalyst design