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Aluminabenzene-rhodium and -iridium complexes were synthesized, in which the aluminum atom played as a proximal Lewis acidic site. Based on their structural analysis, aluminabenzene ligand could coordinate to Rh and Ir as a η5-pentadienyl ligand. The Lewis acidic character of aluminum atom in aluminabenzene ligand was confirmed by treatment with 4-dimethylaminopyridine to form the corresponding Lewis acid-base complexes. In addition, the α-selective C-H borylation of triethylamine with the aluminabenzene-ligated iridium catalyst was demonstrated. [ABSTRACT FROM AUTHOR]

In this article, we report the synthesis of a tridentate carbene-centered bisphosphine ligand precursor and its complexes. The developed four-step synthetic strategy of a new PCBImP pincer ligand represents the derivatization of benzimidazole in the first and third positions by (diphenylphosphoryl)methylene synthone, followed by phosphine deprotection and subsequent insertion of a noncoordinating anion. The obtained ligand precursor undergoes complexation, with PdCl2 and [μ-OCH3Rh(COD)]2 smoothly forming the target organometallics [PCBImPPdCl][PF6] and [PCBImPRh(L)][PF6] under mild hydrogenation conditions. A more detailed study of the rhodium complexes [PCBImPRh(L)][PF6] reveals significant thermal stability of the PCBImPRh moiety in the solid state as well as in solution. The chemical behavior of 1,3-bis(diphenylphosphinomethylene)benzimidazol-2-ylrhodium acetonitrile hexafluorophosphate has been screened under decarbonylation, hydrogenation, and hydroboration reaction conditions. Thus, the PCBImPRhI complex is a sufficiently stable compound, with the potential to be applied in catalysis. [ABSTRACT FROM AUTHOR]

Controlling the relative and absolute configuration of octahedral metal complexes constitutes a key challenge that needs to be overcome in order to fully exploit the structural properties of octahedral metal complexes for applications in the fields of catalysis, materials sciences, and life sciences. Herein, we describe the application of a proline-based chiral tridentate ligand to decisively control the coordination mode of an octahedral rhodium(III) complex. We demonstrate the mirror-like relationship of synthesized enantiomers and differences between diastereomers. Further, we demonstrate, using the established pyridocarbazole pharmacophore ligand as part of the organometallic complexes, the importance of the relative and absolute stereochemistry at the metal toward chiral environments like protein kinases. Protein kinase profiling and inhibition data confirm that the proline-based enantiopure rhodium(III) complexes, despite having all of the same constitution, differ strongly in their selectivity properties despite their unmistakably mutual origin. Moreover, two exemplary compounds have been shown to induce different toxic effects in an ex vivo rat liver model. [ABSTRACT FROM AUTHOR]

Controlling the relative and absolute configuration of octahedral metal complexes constitutes a key challenge that needs to be overcome in order to fully exploit the structural properties of octahedral metal complexes for applications in the fields of catalysis, materials sciences, and life sciences. Herein, we describe the application of a proline-based chiral tridentate ligand to decisively control the coordination mode of an octahedral rhodium(III) complex. We demonstrate the mirror-like relationship of synthesized enantiomers and differences between diastereomers. Further, we demonstrate, using the established pyridocarbazole pharmacophore ligand as part of the organometallic complexes, the importance of the relative and absolute stereochemistry at the metal toward chiral environments like protein kinases. Protein kinase profiling and inhibition data confirm that the proline-based enantiopure rhodium(III) complexes, despite having all of the same constitution, differ strongly in their selectivity properties despite their unmistakably mutual origin. Moreover, two exemplary compounds have been shown to induce different toxic effects in an ex vivo rat liver model. [ABSTRACT FROM AUTHOR]

Electrophilic, cationic Rh(III) complexes of composition [(η5-C5Me5)Rh(Ap)]+, (1+), were prepared by reaction of [(η5-C5Me5)RhCl2]2 and LiAp (Ap = aminopyridinate ligand) followed by chloride abstraction with NaBArF (BArF = B[3,5-(CF3)2C6H3]4). Reactions of cations 1+ with different Lewis bases (e.g., NH3, 4-dimethylaminopyridine, or CNXyl) led in general to monoadducts 1·L+ (L = Lewis base; Xyl = 2,6-Me2C6H3), but carbon monoxide provided carbonyl-carbamoyl complexes 1·(CO)2+ as a result of metal coordination and formal insertion of CO into the Rh-Namido bond of complexes 1+. Arguably, the most relevant observation reported in this study stemmed from the reactions of complexes 1+ with H2. ¹H NMR analyses of the reactions demonstrated a H2-catalyzed isomerization of the aminopyridinate ligand in cations 1+ from the ordinary κ²-N,N' coordination to a very uncommon, formally tridentate κ-N,η³ pseudoallyl bonding mode (complexes 3+) following benzylic C-H activation within the xylyl substituent of the pyridinic ring of the aminopyridinate ligand. The isomerization entailed in addition H-H and N-H bond activation and mimicked previous findings with the analogous iridium complexes. However, in dissimilarity with iridium, rhodium complexes 1+ reacted stoichiometrically at 20 °C with excess H2. The transformations resulted in the hydrogenation of the C5Me5 and Ap ligands with concurrent reduction to Rh(I) and yielded complexes [(η4-C5Me5H)Rh(η6, (2+), in which the pyridinic xylyl substituent is 6-bonded to the rhodium(I) center. New compounds reported were characterized by microanalysis and NMR spectroscopy. Representative complexes were additionally investigated by X-ray crystallography. [ABSTRACT FROM AUTHOR]

Using a general synthetic procedure employing readily accessed terminal alkene-functionalized pro-ligands and macrocyclization by ring-closing olefin metathesis, rhodium carbonyl complexes have been prepared that contain lutidine (1a; n = 1) and pyridine (1b; n = 0) derived tridentate CNC macrocycles with dodecamethylene spacers. In solution, 1a shows temperature-invariant time-averaged C2 symmetry by ¹H NMR spectroscopy (CD2Cl2, 500 MHz), whereas in the solid-state, two polymorphs can be obtained showing different conformations of the alkyl spacer about the metal-carbonyl bond (asymmetric and symmetric). In contrast, time-averaged motion of alkyl spacer in 1b can be halted by cooling below 225 K (CD2Cl2, 500 MHz), and the complex crystallizes as a dimer with an interesting unsupported Rh···Rh bonding interaction (3.2758(6) Å). Oxidative addition reactions of 1a and 1b, using MeI and PhICl2, have been studied in situ by ¹H NMR spectroscopy, although pure Rh(III) adducts can be ultimately isolated only with the pyridine-based macrocyclic ligand. The lutidine backbone of 1a can be deprotonated by addition of K[N(SiMe3)2], and the resulting neutral dearomatized complex (5) has been fully characterized in solution, by variable-temperature ¹H NMR spectroscopy, and in the solid state, by X-ray diffraction. [ABSTRACT FROM AUTHOR]

A rhodium(II) dibenzotetramethylaza[14]annulene dimer ([(tmtaa)Rh]2) undergoes metathesis reactions with [CpCr(CO)3]2, [CpMo(CO)3]2, [CpFe(CO)2]2, [Co(CO)4]2, and [Mn(CO)5]2 to form (tmtaa)Rh-M complexes (M = CrCp(CO)3, MoCp(CO)3, FeCp(CO)2, Co(CO)4, or Mn(CO)5). Molecular structures were determined for (tmtaa)Rh-FeCp(CO)2, (tmtaa)Rh-Co(μ-CO)(CO)3, and (tmtaa)Rh-Mn(CO)5 by X-ray diffraction. Equilibrium constants measured for the metathesis reactions permit the estimation of several (tmtaa)Rh-M bond dissociation enthalpies (Rh--Cr = 19 kcal mol-1, Rh--Mo = 25 kcal mol-1, and Rh--Fe = 27 kcal mol-1). Reactivities of the bimetallic complexes with synthesis gas to form (tmtaa)Rh-C(O)H and M-H are surveyed. [ABSTRACT FROM AUTHOR]

A rhodium(II) dibenzotetramethylaza[l4]-annulene dimer ([(tmtaa)Rh]2) (l) reacts with CO and H2 in toluene and pyridine to form equilibrium distributions with hydride and formyl complexes ((tmtaa)-Rh-H (2); (tmtaa)Rh-C(0)H (3)). The rhodium formyl complex ((tmtaa)Rh-C(O)H) was isolated under a CO/H2 atmosphere, and the molecular structure was determined by X-ray diffraction. Equilibrium constants were evaluated for reactions of (tmtaa)Rh-H with CO to produce formyl complexes in toluene (K2(298 K)(tol) = 10.8 (1.0) × 103) and pyridine (K2(298 K)(py) = 2.2 (0.2) × 103). Reactions of 1 and 2 in toluene and pyridine are discussed in the context of alternative radical and ionic pathways. The five-coordinate 18-electron Rh(l) complex ([(py)-(tmtaa)Rh1]-) is proposed to function as a nucleophile toward CO to give a two-electron activated bent Rh-CO unit. Results from DFT calculations on the (tmtaa)Rh system correlate well with experimental observations. Reactions of 1 with CO and H2 suggest metal catalyst design features to reduce the activation barriers for homogeneous CO hydrogenation. [ABSTRACT FROM AUTHOR]

A monoanionic, bidentate phosphaalkenyl–phosphidoligandwas designed, synthesized, and used for the complexation of a rhodiumcarbonyl fragment. The characterization of the latter revealed delocalizedπ electrons on the phosphaalkenyl–phosphide moiety. Thecatalytic activity of this rhodium carbonyl complex has been demonstratedin a hydrosilylation reaction. [ABSTRACT FROM AUTHOR]

Rhodium(I)silylamide complexes supported by the 1,2-bis(di-tert-butylphosphino)ethane (dtbpe) ligand have been preparedand their structures and reactivity studied. Although the complexesdegrade over time to release the corresponding silylamines, they reactcleanly with silver(I) salts to transfer the amido group at ambienttemperature. The bis(trimethylsilyl)amide complex (dtbpe)Rh–N(TMS)2reacts with CO2to form a carbamate complex thatdecomposes via loss of hexamethyldisiloxane to form a bis(μ-isocyanate)dimer, suggesting that silylamides may be useful nitrene-group andnitrogen-atom sources through selective N–Si bond cleavage. [ABSTRACT FROM AUTHOR]

The C–C bond of cyclobutanones undergoes oxidative addition to a T-shape rhodium(I) complex possessing a PBP pincer ligand at room temperature. The remarkable propensity of the rhodium complex for oxidative addition is attributed to the highly electron-donating nature of the boron ligand as well as the unsaturation on the rhodium center. [ABSTRACT FROM AUTHOR]

The bis(pentalene) complexes M2(pent†)2(M = Rh (1), Pd (2); pent†= 1,4-bis(triisopropylsilyl)pentalene) have been synthesizedand structurally characterized. In both 1and 2the metals have a formal electron count in excess of 18 per metalcenter, and DFT calculations indicate antibonding metal–metalinteractions are present in 1, whereas 2involves antibonding metal–ligand interactions. [ABSTRACT FROM AUTHOR]

The neutral rhodium(I) square-planar complexes [RhX(CO)2(L)] [X = Cl (3), I (4)] bearing a nitrogen-containing ligand L [diethylamine (a), triethylamine (b), imidazole (c), l-methylpyrazole (d), pyrazole (e), l-methyipyrazole (f), 3,S-dimethyIpyrazole (g)] are straightforwardly obtained from L and [Rh(µ-X)(CO)2]2 [X = CI (1), I (2)] precursors. The synthesis is extended to the diethylsulfide ligand h for 3h and 4h. According to the CO stretching frequency of 3 and 4, the ranking of the electronic density on the rhodium center follows the order b>a≈d>c>g>f≈h>e. The X-ray molecular structures of 3a, 3d--3f, 4a, and 4d--4f were determined. Results from variable-temperature 1H and 13C{1H} NMR experiments suggest a fluxional associative ligand exchange for 4c∼4h and a supplementary hydrogen-exchange process in 4e and 4g. The oxidative addition reaction of CH3I to complexes 4c--4g affords the neutral dimeric iodo-bridged acetylrhodium(III) complexes [RhI(µ-I)(COCH3)(CO)(L)]2 (6c--6g) in very good isolated yields, whereas 4a gives a mixture of neutral 6a and dianionic [RhI2(µ-I)(COCH3)(CO)][NHMeEt2]2 and 4h exclusively provides the analogue dianionic complex with [SMeEt2]+ as the counterion. X-ray molecular structures for 6d2 and 6e reveal that the two apical CO ligands are in mutual cis positions, as are the two apical d and e ligands, whereas Isomer 6d, is centrosymmetric. Further reactions of 6d and 6e with CO or ligand e gave quantitatively the monomeric complexes [RhI2(COCH3)(CO)2(d)] (7d) and [RhI2(COCH3)(CO)(e)2] (8e), respectively, as confirmed by their X-ray structures. The initial rate of CH3I oxidative addition to 4 as determined by IR monitoring is dependent on tlie nature of the nitrogen-containing ligand. For 4a and 4h, reaction rates similar to those of the well-known rhodium anionic [RhI2(CO)2]- spedes are observed and are consistent with tlie fonnation of this intermediate species through methylation of die a and h ligands. The reaction rates are reduced significantly when using imidazole and pyrazole ligands and involve the direct oxidative addition of CH3I to the neutral complexes 4c--4g. Complexes 4c and 4d react around 5-10 times fester than 4e--4g mainly because of electronic effects. The lowest reactivity of 4f toward CH3I is attributed to the steric effect of the coordinated ligand, as supported by the X-ray structure. [ABSTRACT FROM AUTHOR]

To examine the steric effect of the phosphorus substituents in cyclodiphosphazanes, two less sterically demanding alkynyl-functionalized cis-[(μ-NtBuP)2(C=CPh)2] (1) and trans-[(μ-NtBuP)2(C=CPh)2] (2) were synthesized. The cis isomer 1, with a large subtending angle (135.8°) upon treatment with [Rh(CO)2Cl]2, afforded the first rhodium(I) cyclic pentameric macrocycle [Rh(CO)Cl{(μ-NtBuP)2(C=CPh)2}]5 (3). The crystal structure of the cyclic pentamer 3 closely resembles a classical "Ferris wheel". [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of a bimetallic conjugate (RhPt) in which an oxaliplatin derivative is tethered to a rhodium metalloinsertor through an aminomalonate leaving group ligand. The complex interacts with DNA through metalloinsertion at a base pair mismatch followed by formation of a covalent Pt-DNA adduct. Characterization of RhPt in mismatch repair-deficient HCT116O cells reveals increased cytotoxicity compared to cisplatin and oxaliplatin as well as relative to the unconjugated rhodium and platinum counterparts. Caspase and poly-ADP ribose polymerase inhibition assays indicate that RhPt induces apoptotic cell death. Inductively coupled plasma mass spectrometry (ICP-MS) experiments reveal that RhPt exhibits enhanced cellular uptake properties that contribute to its increased efficacy. [ABSTRACT FROM AUTHOR]