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A series of neutral and cationic Ir(III) and Rh(III) aminoquinoline-benzimidazole hybrid complexes were synthesised and their inhibitory activities evaluated against Plasmodium falciparum and Mycobacterium tuberculosis. In general, the hybrid complexes display good activity against the chloroquine-sensitive NF54 strain of P. falciparum. The neutral Ir(III)- and Rh(III)-Cp∗ complexes were the most active (IC 50  = 0.488 μM for Ir III ), maintaining activity against the multidrug-resistant K1 strain. Low to no cytotoxicity against the Chinese hamster ovarian cell line was observed for the tested complexes. Selected active hybrid complexes demonstrated significant inhibition of β-haematin formation in a cell-free NP-40 assay, suggesting an effect on the host haemoglobin degradation pathway as a potential contributing mechanism of action. When tested against M. tuberculosis H37Rv, most hybrid complexes displayed moderate to good activity. Again, the neutral complexes outperformed the cationic complexes, with the neutral Ir(III)-Cp∗ complexes proving most active (MIC 90  = 0.488-1.490 μM)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

A series of bidentate salicylaldimine ligands was prepared and reacted with either [RuCl(µ-Cl)(p-cymene)] 2 , [RhCl(µ-Cl)(Cp*)] 2 or [IrCl(µ-Cl)(Cp*)] 2 . All of the compounds were characterised using an array of spectroscopic and analytical techniques, namely, nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy and mass spectrometry. Single crystal X-ray diffraction (XRD) was used to confirm the bidentate coordination mode of the salicylaldimine ligand to the metal centre. The platinum group metal (PGM) complexes were screened against the MCF7 breast cancer cell line. The ruthenium and iridium salicylaldimine complexes showed comparable or greater cytotoxicity than cisplatin against the MCF7 cancer cells, as well as greater cytotoxicity than their rhodium counterparts. Three of the salicylaldimine complexes showed potent activity in the range 18-21 µM. Two of these complexes had a greater affinity for cancerous cells than for CHO non-cancerous cells (SI > 4). Preliminary mechanistic studies suggest that the ruthenium complexes undergo solvation prior to 5'-GMP binding, whereas the iridium complexes were inert to the solvation process.

A series of mono- and bis-salicylaldimine ligands and their corresponding Rh(i) complexes were prepared. The compounds were characterised using standard spectroscopic techniques including NMR, IR spectroscopy and mass spectrometry. The salicylaldimine ligands and complexes were screened for antiparasitic activity against two strains of Plasmodium falciparum i.e. the NF54 CQ-sensitive and K1 CQ-resistant strain as well as against the G3 isolate of Trichomonas vaginalis. The monomeric salicylaldimine quinolines exhibited good activity against the NF54 strain and the dimeric salicylaldimine quinolines exhibited no cross resistance across the two strains. The binuclear 5-chloro Rh(i) complex displayed the best activity against the Trichomonas vaginalis parasite, possibly a consequence of its enhanced lipophilicity. The compounds were also screened for cytotoxicity in vitro against WHCO1 oesophageal cancer cells. The monomeric salicylaldimine quinolines exhibited high selectivity towards malaria parasites compared to cancer cells, while the dimeric compounds were less selective.

A series of ferrocenyl- and aryl-functionalised organosilane thiosemicarbazone compounds was obtained via a nucleophilic substitution reaction with an amine-terminated organosilane. The thiosemicarbazone (TSC) ligands were further reacted with either a ruthenium dimer [(η(6-i)PrC6H4Me)Ru(μ-Cl)Cl]2 or a rhodium dimer [(Cp*)Rh(μ-Cl)Cl]2 to yield a series of cationic mono- and binuclear complexes. The thiosemicarbazone ligands, as well as their metal complexes, were characterised using NMR and IR spectroscopy, and mass spectrometry. The molecular structure of the binuclear ruthenium(ii) complex was determined by single-crystal X-ray diffraction analysis. The thiosemicarbazones and their complexes were evaluated for their in vitro antiplasmodial activities against the chloroquine-sensitive (NF54) and chloroquine-resistant (Dd2) Plasmodium falciparum strains, displaying activities in the low micromolar range. Selected compounds were screened for potential β-haematin inhibition activity, and it was found that two Rh(iii) complexes exhibited moderate to good inhibition. Furthermore, the compounds were screened for their antitrichomonal activities against the G3 Trichomonas vaginalis strain, revealing a higher percentage of growth inhibition for the ruthenium and rhodium complexes over their corresponding ligand.

The synthesis and characterisation of two new water‐soluble RhI mononuclear 1,4‐diazabutadiene (DADs) complexes of general formula: [Rh(DADs‐R)(COD)], where (DADs = sulfonated‐tagged–1,4‐diazabutadiene, COD = cyclooctadiene; and R = H or C10H8), are described. The rhodium(I) complexes were obtained via a complexation reaction of [Rh(COD)(MeCN)2]BF4 with the sulfonated α‐diimine (DAD) ligands, which were previously obtained from a Schiff base condensation reaction of 4‐aminophenol with either 1,2‐ethanedione or acenapthenequinone. All rhodium complexes and their precursor ligands were characterised using 1H NMR, 13C NMR, FT‐IR spectroscopy and mass spectrometry. Their performance as catalyst precursors in the hydroformylation of 1‐octene was assessed and compared to those of the non‐sulfonated RhI mononuclear 1,4‐diazabutadiene (DAD) complexes. Utilisation of the water soluble [Rh(DADs‐R)(COD)] lead to high conversions and regioselectivity (linear/branched aldehyde ratio) in the aqueous biphasic hydroformylation of 1‐octene. Additionally, the catalysts were recovered by phase separation and are reusable over four consecutive catalytic runs without significant loss in catalytic activity. [ABSTRACT FROM AUTHOR]

Monometallic and heterobimetallic complexes of Rh(I) bearing chelating N, O-bidentate aryl- and ferrocenyl-derived ligands have been synthesised via Schiff base condensation reactions, and characterised fully using 1H NMR, 13C{1H} NMR and Fourier transform infrared spectroscopies, elemental analysis and mass spectrometry. The new monometallic and heterobimetallic complexes were evaluated as potential catalyst precursors in the hydroformylation of 1-octene at 95°C and 40 bar. The ferrocenylimine mononuclear compounds were inactive in the hydroformylation experiments. The Rh(I) monometallic and the ferrocene-Rh(I) heterobimetallic pre-catalysts displayed good activity and conversion of 1-octene as well as outstanding chemoselectivity towards aldehydes in the hydroformylation reaction. [ABSTRACT FROM AUTHOR]

A series of rhodium(I)-1,2,3-triazol-5-ylidene (trz) complexes are described, containing either a novel triarylated trz ligand A' (N1, N3-arylated, C4-ferrocenyl) {complexes 1, [Rh(A')Cl(cod)]; 4, [Rh(A')Cl(CO)2]}, or N3-alkylated triazolylidenes with a C4-ferrocenyl {2, [Rh(B')Cl(cod)]; 5, [Rh(B')Cl(CO)2]} or C4-phenyl substituent {3, [Rh(C')Cl(cod)]; 6, [Rh(C')Cl(CO)2]}. The free mesoionic carbene (MIC) A' is structurally characterized and its electronic properties evaluated by employing the complex [Pd(Br)2(iPr2-bimy)(A')] (7) in an NMR spectroscopic analysis method. The redox activity of A' is exploited, and the chemically oxidized precursor Aox and complex 4ox are isolated. The mesoionic carbene complexes 1-3, as well as in situ oxidized 1ox, are used as homogeneous catalysts for the hydroformylation of 1-octene for the first time, and the influence of chemical oxidation of the catalyst on the activity and chemoand regioselectivity of the catalyst precursor 1 is evaluated. [ABSTRACT FROM AUTHOR]

A series of mono- and bis-salicylaldimine ligands and their corresponding Rh(i) complexes were prepared. The compounds were characterised using standard spectroscopic techniques including NMR, IR spectroscopy and mass spectrometry. The salicylaldimine ligands and complexes were screened for antiparasitic activity against two strains of Plasmodium falciparum i.e. the NF54 CQ-sensitive and K1 CQ-resistant strain as well as against the G3 isolate of Trichomonas vaginalis. The monomeric salicylaldimine quinolines exhibited good activity against the NF54 strain and the dimeric salicylaldimine quinolines exhibited no cross resistance across the two strains. The binuclear 5-chloro Rh(i) complex displayed the best activity against the Trichomonas vaginalis parasite, possibly a consequence of its enhanced lipophilicity. The compounds were also screened for cytotoxicity in vitro against WHCO1 oesophageal cancer cells. The monomeric salicylaldimine quinolines exhibited high selectivity towards malaria parasites compared to cancer cells, while the dimeric compounds were less selective. [ABSTRACT FROM AUTHOR]

Schiff base ligands obtained from the condensation of 4-aminophenylmethanol and either 2-pyridinecarboxaldehyde or salicylaldehyde were used to synthesise bidentate trimeric ester ligands. The trimeric ester ligands were used to prepare a new series of trinuclear polyester organometallic complexes by using the dimeric precursors, [Ru(η6- p- iPrC6H4Me)Cl2]2, [Rh(C5Me5)Cl2]2 or [Ir(C5Me5)Cl2]2. The Schiff base ligands act as bidentate donors to each metal. All compounds were characterised by NMR and IR spectroscopy, elemental analysis and EI/ESI mass spectrometry. Model mononuclear analogues were prepared, and the molecular structures of selected compounds were determined by single-crystal X-ray diffraction analysis. The mono- and trimeric ligands and the metal complexes were evaluated for inhibitory effects against the human ovarian cancer cell lines, A2780 (cisplatin-sensitive) and A2780 cisR (cisplatin-resistant), and the model human skin fibroblast cell line, KMST-6. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mono- and dinuclear Rh(I) complexes based on alkylated-sulfonated scaffolds have been prepared. • The complexes were characterized using several spectroscopic and analytical techniques. • The complexes were evaluated as catalyst precursors for the hydroformylation of 1-octene. • The dinuclear complex showed higher conversion rates. The synthesis of two water-soluble Rh(I) complexes, a disulfonated diimine mononuclear complex and a tetrasulfonated tetraimine binuclear complex, is reported. The reaction of the N,N -donor ligands containing the sulfonated alkyl substituents with [Rh(COD)(MeCN) 2 ]BF 4 led to the formation of the corresponding water-soluble Rh(I) complexes. The complexes were fully characterised using an array of analytical techniques such as NMR, infrared spectroscopy and mass spectrometry. The complexes were evaluated as catalyst precursors in the aqueous biphasic hydroformylation of 1-octene. Both catalyst precursors are highly active as hydroformylation precatalysts showing high conversions of 1-octene and good aldehyde chemoselectivity with no hydrogenation products (alkanes or alcohols) observed. The binuclear complex gave higher quantitative conversions compared to the mononuclear rhodium complex. Additionally, the catalysts were recovered by phase separation and reused over four catalytic runs, notably with a significant drop in conversion after each cycle. [ABSTRACT FROM AUTHOR]

A series of mono- and multivalent phosphorus-based ligands was synthesised by the lower-rim benzylation of the water-soluble ligand, 1,3,5-triaza-7-phosphaadamantane (PTA). These ligands were used to prepare mono-, bi- and trinuclear Rh(I) complexes whose catalytic activity, product selectivity and recyclability were evaluated in the aqueous biphasic hydroformylation of 1-octene. [ABSTRACT FROM AUTHOR]

Two mononuclear rhodium complexes, Rh(I)-1,5-cyclooctadiene and Rh(III)-pentamethylcyclopentadienyl, and a bimetallic Rh(I)-Rh(III) mixed-valence complex were synthesised. The complexes were fully characterised using an array of analytical techniques which included NMR and infrared spectroscopy, single-crystal X-ray diffractometry, elemental analysis, and mass spectrometry. These complexes were evaluated as catalyst precursors in the hydroformylation of olefins. All catalyst precursors were active in the hydroformylation of 1-octene under optimised conditions. The rhodium complexes generally showed chemoselectivity towards the formation of linear aldehydes. The electrochemical behaviour of the rhodium complexes was examined using cyclic voltammetry. [ABSTRACT FROM AUTHOR]

A series of fluorocarbon-containing salicylaldimine and iminophosphine Schiff base ligands and their Rh(I) complexes were synthesized. The synthesized ligands and complexes were characterized using different analytical and spectroscopic techniques including ( 1 H, 13 C{ 1 H}, 31 P{ 1 H} and 19 F{ 1 H} NMR spectroscopy), FT-IR spectroscopy, mass spectrometry (ESI and EI), and elemental analysis. In addition, single crystal X-ray diffraction was also used for characterization for complexes 1 and 2 . Consequently, the Rh(I) synthesized complexes were evaluated as catalyst precursors in the hydroformylation of 1-octene. The hydroformylation results showed that the iminophosphine and salicylaldimine-based catalyst precursors are active and selective under mild conditions, converting 1-octene to mostly aldehydes. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of poly(propyleneimine)-iminopyridyl and iminophosphine rhodium(I) metallodendrimers, with rhodium coordinated to monodentate (N-donor) and chelating, heterobidentate (P,N) moieties respectively located on the periphery, has been accomplished in order to evaluate their potential as hydroformylation catalysts. Related mononuclear complexes were obtained in a similar manner to model the multinuclear complexes. The multinuclear rhodium(I) complexes were found to be effective catalyst precursors in the hydroformylation of 1-octene, achieving higher conversions, faster reaction rates and slightly enhanced catalytic activity when compared with analogous mononuclear rhodium complexes. Hydroformylation reactions using the tetra- and octanuclear rhodium complexes generally show a chemoselective formation of aldehydes, together with a small amount of isomerisation products. [Copyright &y& Elsevier]

• Core-functionalised dendritic rhodium(I) precatalysts were evaluated for olefin hydroformylation. • Precatalysts show good yields and aldehyde chemoselectivity. • Higher generation dendritic precatalysts gave better regioselectivity, favouring linear aldehydes. • Mercury drop experiments suggest a combination of homogeneous and heterogeneous catalysis. Rhodium(I) poly(aryl ether)-based, core-functionalised alpha-diimine metallodendrimers were investigated as catalyst precursors in the rhodium-catalysed hydroformylation of terminal olefins, 1-octene and styrene. The electronic environment across the metallodendrimer series was probed using cyclic voltammetry. The electrochemical behaviour of the metallodendrimers show irreversible and quasi-reversible electrochemical behaviour in the range 0.0–2.0 V at a scan rate of 100 mV s−1. All the catalyst precursors (C1 - C6) gave excellent conversions of the respective substrates with good chemoselectivity under the investigated conditions. In general, the higher dendritic catalysts C5 and C6 gave better regioselectivity, favouring linear aldehydes. [ABSTRACT FROM AUTHOR]

• Water-soluble Rhodium(I) precatalysts were evaluated for olefin hydroformylation. • Catalysts can be recycled using an aqueous biphasic strategy. • The trinuclear precatalyst shows greater stability. • Precatalysts show good activity and aldehyde chemoselectivity. Water-soluble, sulfonated, salicylaldiminato-aryl ether mono- (7) and trimeric (8) ligands were prepared and reacted with the [Rh(μ-Cl)(η2:η2−COD)] 2 dimer to yield the corresponding water-soluble mononuclear (9) and trinuclear (10) Rh(I) complexes. These rhodium complexes were evaluated and are active as catalyst precursors in the aqueous biphasic hydroformylation of 1-octene and styrene. Optimal conditions were realised, using 1-octene as a model substrate, at 85 °C and a syngas pressure of 50 bar, where the best activity and chemoselectivity for aldehydes was obtained. Catalyst recycling was successfully conducted over 5 cycles in a biphasic medium, with a gradual loss in catalytic performance for both complexes. However, the dendrimer-stabilised trinuclear precatalyst (10) showed improved recyclability during "neat", aqueous monophasic hydroformylation experiments, while the mononuclear precatalyst (9) showed a reduced overall performance. Both precatalysts showed sustained catalytic activity (> 450 h−1) and a total bias towards aldehyde chemoselectivity during the aqueous biphasic hydroformylation of styrene. [ABSTRACT FROM AUTHOR]

• Mononuclear Rh(I) metallacycles based on alkylated-PTA scaffolds have been prepared. • The complexes were characterized using several spectroscopic and analytical techniques. • The complexes were evaluated as catalyst precursors for the aqueous biphasic (water-toluene) hydroformylation of 1-octene. • The precatalysts are chemoselective towards aldehydes but show poor recyclability. A series of rhodium(I) metallacycles based on alkylated PTA complexes were synthesised and fully characterised using a range of spectroscopic and analytical techniques. These mononuclear Rh(I) complexes were evaluated in the aqueous biphasic (water-toluene) hydroformylation of 1-octene, showing chemoselectivity to aldehydes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Rhodium(I) monometallic and heterobimetallic precatalysts evaluated for post-metathesis product 7-tetradecene hydroformylation. • High turnover numbers up to 4310 towards predominantly alkyl-branched aldehydes products. • Heterobimetallic precatalyst showed improved hydroformylation performance under mild reaction conditions. • Precatalysts remain active over at least three consecutive reaction cycles. Abstract The rhodium-catalysed hydroformylation of the post-metathesis product 7-tetradecene using aryl- (1) and ferrocenyl- (2) Schiff base derived precatalyst complexes was investigated. It was found that the reaction temperature (75–115 °C), pressure (30–60 bar, CO/H 2 = 0.5–2) and 7-tetradecene-to-precatalyst molar ratio (1000:1–6000:1) had a significant influence on the hydroformylation performance. Turnover numbers up to 4310 were observed and the selectivity data show a temperature and pressure-dependent conversion of 7-tetradecene to the primary branched aldehyde product 2-hexylnonanal and isomeric branched aldehydes. A cooperative effect between rhodium and ferrocene was observed as hydroformylation performance results obtained with the heterobimetallic precatalysts (2) differ from that achieved using the monometallic catalyst system (1) under mild reaction conditions. Both precatalysts performed optimally at a temperature of around 95 °C. Lifetime studies with the precatalysts were conducted and the precatalysts were found to remain active over at least three consecutive reaction cycles. [ABSTRACT FROM AUTHOR]

Mononuclear and trinuclear half-sandwich Rh(III) and Ir(III) complexes based on a sulfonated scaffold have been synthesised and characterised using NMR and IR spectroscopy, mass spectrometry and elemental analysis. The cytotoxicities of the compounds were evaluated against the WHC01 oesophageal cancer cell line, with a slight increase in activity observed upon coordination of the metal. [ABSTRACT FROM AUTHOR]

Water-soluble complexes based on monosodium 5-sulfonato salicylaldimine ( 3 ) and 3- t butyl-5-sulfonatosalicylaldimine have been synthesised via sulfonation and Schiff base condensation reactions. The ligand ( 3 ) and the new water-soluble mononuclear 5-sulfonatosalicylaldimine-ferrocenylimine complexes ( 4 and 5 ) have been synthesised and characterised fully using 1 H NMR, 13 C{ 1 H} NMR, and FT-IR spectroscopy, elemental analysis as well as mass spectrometry. Subsequently, the Rh(I) heterobimetallic complexes ( 6 and 7 ) were synthesised from [RhCl(COD)] 2 (COD = 1,5-cyclooctadiene) and the ferrocenylimine metalloligands ( 4 and 5 ) and characterised using various analytical and spectroscopic techniques. These complexes were applied as catalyst precursors in aqueous biphasic hydroformylation reactions. Optimal conditions were established at 95 °C (40 bar), showing the best chemoselectivity for aldehydes. The mononuclear ferrocenyl pre-catalysts ( 4 and 5 ) were inactive in the aqueous-biphasic hydroformylation of 1-octene. The heterobimetallic catalyst precursors ( 6 and 7 ) displayed good activity and could be recycled for at least 4 runs under the investigated conditions for the aqueous biphasic hydroformylation of 1-octene. [ABSTRACT FROM AUTHOR]

• A heteroleptic rhodium(III) phenylpyridyl aminoquinoline-benzimidazole hybrid complex was prepared. • Good in vitro activity as an antiplasmodial agent against Plasmodium falciparum was shown. • Selected compounds showed significant inhibition of β-haematin formation in a cell-free NP-40 assay. • Only one promising candidate was evaluated for the inhibition of β-haematin formation. A small series of cationic Rh(III) polypyridyl aminoquinoline-benzimidazole hybrid complexes were synthesised and evaluated for their in vitro antiplasmodial activity against the chloroquine-sensitive (NF54) and multi-drug resistant (K1) strains of the human malaria parasite, Plasmodium falciparum. In general, the hybrid complexes display good activity against the chloroquine-sensitive (NF54) strain of P. falciparum , maintaining activity against the multidrug-resistant (K1) strain, with low to no cytotoxicity against the Chinese hamster ovarian cell line. Selected active hybrid complexes demonstrated significant inhibition of β-haematin formation in a cell-free NP-40 assay. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of cyclometalated rhodium and iridium complexes from first- and second-generation naphthaldimine-based poly(propyleneimine) dendrimer scaffolds of the type, DAB-(NH 2 ) n (where n = 4 or 8, DAB = diaminobutane) has been accomplished. Four metallodendrimers were synthesised, viz. (Cp*MCl) 4 G n ( 1 – 4 ), by first reacting DAB-(NH 2 ) n with napththaldehyde and subsequently metallating the Schiff-base dendrimers with the dimers [Cp*MCl 2 ] 2 (where M = Rh or Ir). Related mononuclear complexes [Cp*MCl(L)] (L = naphthaldimine) ( 5 – 6 ) were obtained in a similar manner. The molecular structures of 5 and 6 have been determined by single-crystal X-ray diffraction analysis and the in vitro anticancer activities of 1 – 6 were evaluated against the A2780 and A2780cisR human ovarian carcinoma cell lines. [ABSTRACT FROM AUTHOR]

Two new di- and tripyridyl aromaticether ligands (1and 2) have been synthesizedusing the Williamson ether method. Functionalization of these ligandswith either dichlorido(p-cymene)ruthenium(II),dichlorido(pentamethylcyclopentadienyl)rhodium(III), ordichlorido(pentamethylcyclopentadienyl)iridium(III)fragments yielded three di- and three trinuclear organometallic complexes(1a–cand 2a–c). Both ligands act as monodentate donors to each metal centervia the pyridyl nitrogen atoms, and this coordination mode of thepolyaryl ether ligands has been confirmed upon elucidation of themolecular structure of the dinuclear iridium complex 1c. All of the synthesized compounds were evaluated for inhibitoryeffects on the Plasmodium falciparumstrain NF54(chloroquine-sensitive) and found to have moderate to high antiplasmodialactivities, with the trinuclear complexes displaying activities inthe nanomolar range. The most active compounds were studied for theirability to inhibit formation of synthetic hemozoin in a cell-freemedium. Against the Trichomonas vaginalisstrainG3, these aryl ether compounds were only moderately active. [ABSTRACT FROM AUTHOR]

Abstract: The development of multinuclear pentamethylcyclopentadienyl (Cp*) rhodium and iridium complexes from first- and second-generation 2-iminopyridyl and salicylaldimine based poly(propyleneimine) dendrimer scaffolds of the type, DAB-(NH2) n (n = 4 or 8, DAB = diaminobutane) has been accomplished. Eight compounds were synthesised, viz. (Cp*MCl)4 G n (1–8), by first reacting DAB-(NH2) n with either 2-pyridinecarboxaldehyde or salicylaldehyde and subsequently metallating the Schiff-base dendrimers with [Cp*MCl2]2 (where M = Rh, Ir). Related mononuclear complexes [Cp*MCl(L)] (L = iminopyridyl or salicylaldimine) (9–12) were obtained in a similar manner. The molecular structures of 9–12 have been determined by single-crystal X-ray diffraction analysis and the in vitro anticancer activities of 1–12 were evaluated against the A2780 and A2780cisR human ovarian carcinoma cell lines. [Copyright &y& Elsevier]

The use of metallodendrimers in various applications such as catalysis and biology has highlighted the potential for the development of polynuclear metal-based complexes. This review provides a more focused overview of the developments in the application of metallodendrimers as catalysts for the hydroformylation reactions involving olefins. Specific attention is drawn to the influence of these dendritic scaffolds on the activity as well as the chemo- and regioselectivity afforded by the catalyst itself. We furthermore emphasize the recyclability of the rhodium-bearing metallodendrimers via heterogenization of homogeneous catalysts. Recyclable and reusable catalyst precursors are attractive in championing the sustainable use of mineral resources, especially where rare, expensive, and fast-depleting metals such as rhodium are of prime importance. [Display omitted] • A review of metallodendrimers for hydroformylation is presented. • This covers both heterogeneous and homogeneous metallodendrimers. • Distinction is made between core- and peripheral-functionalised dendrimers. • Strategies for recycling are touted. [ABSTRACT FROM AUTHOR]

The preparation of a series of rhodium(I) complexes coordinated by various electronically tuneable Fischer carbene (FC) ligands, is reported. The Rh(I) metal complexes' electronic properties could readily be modulated by variation of a p - N,N- dimethylaniline moiety with a ruthenocenyl substituent, or alternatively, substituting the carbene O -heteroatom for an amino-group. The electronic properties of the complexes were evaluated, and it was determined from the Tolman electronic parameters that the donor-ability of the FC ligands are comparable to N -heterocyclic carbenes. Furthermore, the facile control of the electronic properties of the complexes was demonstrated by mild oxidation of a ferrocenyl aminocarbene rhodium(I) complex, yielding the corresponding ferrocenium rhodium(I) complex cation. Finally, the complexes were evaluated as catalyst precursors for the hydroformylation of 1-octene. RhI Fischer carbene complexes are evaluated in the hydroformylation of 1-octene, with tailoring of the catalyst performance allowed by the tuning of the electronic properties of the electron-donating Fischer carbene ligands. Image 1 •The manuscript describes the synthesis and spectroscopic and structural characterisation of new Fischer carbene complexes of rhodium(I), containing ferrocenyl, ruthenocenyl, or p- N,N -dimethylaniline substituents. • The catalytic performance of the rhodium(I) Fischer carbene complexes in the hydroformylation of 1-octene was evaluated. • Chemical oxidation of the ferrocenyl aminocarbene rhodium(I) complex was investigated as a possible redox-switchable catalyst. • Improved catalytic activity (turnover frequency) was observed for ruthenocenyl Fischer carbene complexes, while improved regioselectivity (linear aldehyde formation) was achieved by the dimethylaniline Fischer carbene complexes. [ABSTRACT FROM AUTHOR]

• Fréchet-type dendrons containing a chelating N,P -iminophosphine entity at the focal point have been prepared. • Neutral Rh(I) organometallic dendrons were synthesized by reacting the N,P -iminophosphine dendrons with [Rh(μ-Cl)(CO) 2 ] 2. • The complexes were characterised using several spectroscopic and analytical techniques. • The complexes were evaluated as catalyst precursors in the hydroformylation of 1-octene but showed poor conversion. Fréchet-type dendrons containing a chelating N,P -iminophosphine entity at the focal point were synthesized by reacting an N,P -iminophosphine Schiff base with the appropriate bromido-Fréchet dendron (G 0 , G 1 or G 2) via a Williamson-ether reaction. Neutral Rh(I) organometallic dendrons were synthesized by reacting the N,P -iminophosphine dendron with [Rh(μ-Cl)(CO) 2 ] 2. The ligands and complexes were characterised using NMR and IR spectroscopy, mass spectrometry, elemental analysis and the G 0 analogue was characterised using single-crystal X-ray diffraction. All complexes were evaluated as catalyst precursors for the hydroformylation of 1-octene. [ABSTRACT FROM AUTHOR]

• Rhodium-salicylaldimine precatalysts evaluated for olefin hydroformylation. • Catalysts can be reused using organic solvent nanofiltration. • Both catalysts have an activation of 62 kJ mol−1. • Observed rate constants compare favourably with a modified rate model. Rh(I)-salicylaldimine-triazole mononuclear (6) and trinuclear (7) complexes based on an aryl-ether scaffold were investigated as precatalysts in the rhodium-catalysed hydroformylation of the terminal olefin, 1-octene, and internal olefins, 7-tetradecene and 4-octene. The complexes generally show good catalytic activity in the hydroformylation of 1-octene at temperatures ranging from 75 °C to 95 °C and syngas pressures of 20 to 40 bar. The precatalysts have excellent stability and could be reused several times using organic solvent nanofiltration under optimum conditions of 85 °C and 40 bar. Kinetic studies using catalyst precursor 6 were investigated by evaluating the effect of temperature, syngas total pressure and catalyst loading on the rate of hydroformylation. The activation energy for the hydroformylation of 1-octene was calculated to be 62 kJ mol−1 and the experimental rate constants were found to be in good agreement with the predicted rate data obtained using a modified fundamental mechanism-based rate model. [ABSTRACT FROM AUTHOR]