Dirhodium Formamidinate Compounds with Bidentate Nitrogen Chelating Ligands

Chifotides, Helen T.; Catalan, Kemal V.; Dunbar, Kim R.

doi:10.1021/ic034737b

Cited by 25 publications

(15 citation statements)

References 36 publications

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“…In particular, the single‐crystal X‐ray crystallographic determination of HH cis ‐[Rh 2 (DTolF) 2 (9‐EtGuaH) 2 (NCCH 3 )](BF 4 ) 2 revealed bridging 9‐EtGuaH groups binding to equatorial sites of the dirhodium unit through N7/O6. 23 Related studies involving the reactions of cis ‐[Rh 2 (DTolF) 2 (CH 3 CN) 6 ](BF 4 ) 2 with NN chelates, which mimic the binding of two adjacent DNA bases (2,2′‐bipyridine and 1,10‐phenanthroline), demonstrated that the latter bind to the dirhodium core in a chelating fashion by substituting acetonitrile molecules in equatorial positions 24…”

Section: Introductionmentioning

confidence: 99%

Head‐to‐Head Cross‐Linked Adduct between the Antitumor Unit Bis(μ‐N,N′‐di‐p‐tolylformamidinato)dirhodium(II,II) and the DNA Fragment d(GpG)

Chifotides¹,

Dunbar²

2006

Chemistry A European J

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Reactions of the compound cis-[Rh2(DTolF)2(CH3CN)6](BF4)2, a formamidinate derivative of the class of antitumor compounds [Rh2(O2CR)4] (R=Me, Et, Pr), with 9-ethylguanine (9-EtGuaH) or the dinucleotide d(GpG) proceed by substitution of the acetonitrile groups, with the guanine bases spanning the Rh--Rh bond, in a bridging fashion, through sites N7/O6. In the case of 9-EtGuaH, both head-to-head (HH) and head-to-tail (HT) isomers are formed, whereas with the tethered bases in d(GpG), only one right-handed conformer HH1R [Rh2(DTolF)2{d(GpG)}] is present in solution. For both cis-[Rh2(DTolF)2(9-EtGuaH)2](BF4)2 and [Rh2(DTolF)2{d(GpG)}], the absence of N7 protonation at low pH and the substantial decrease of the pKa values for N1-H deprotonation, support N7/O6 binding of the bases to the dirhodium core. The N7/O6 binding of the bases is further corroborated by the downfield shift by Deltadelta approximately 4.0 ppm of the 13C NMR resonances for the C6 nuclei as compared to the corresponding resonances of the free ligands. The HH arrangement of the guanine bases in [Rh2(DTolF)2{d(GpG)}] is indicated by the intense H8/H8 ROE cross-peaks in the 2D ROESY NMR spectrum. Complete characterization of the [Rh2(DTolF)2{d(GpG)}] conformer by 2D NMR spectroscopy supports anti-orientation and N (C3'-endo) conformation for both deoxyribose residues. The N-pucker for the 5'-G base is universal in such cross-links, but it is very unusual for platinum and unprecedented for dirhodium HH cross-linked adducts to have both deoxyribose residues in the N-type conformation. The bulk, the nonlabile character, and the electron-donating ability of the formamidinate bridging groups spanning the dirhodium core affect the nature of the preferred dirhodium DNA adducts. Molecular modeling studies performed on [Rh2(DTolF)2{d(GpG)}] corroborate the structural features obtained by NMR spectroscopy.

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Section: Introductionmentioning

confidence: 99%

Head‐to‐Head Cross‐Linked Adduct between the Antitumor Unit Bis(μ‐N,N′‐di‐p‐tolylformamidinato)dirhodium(II,II) and the DNA Fragment d(GpG)

Chifotides¹,

Dunbar²

2006

Chemistry A European J

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“…The diimine-coordinated, formamidinate-bridged Rh 2 II,II dimers were synthesized via a stepwise approach to permit purification at each step. [7,19,23,34,35] As depicted in Figure 1, the final step involves refluxing 1 with two equivalents of the bridging np or bidentate chelating dap diimine ligand in CH 3 CN to afford 3 as a dark purple powder (69%) or 4 as a dark 8 maroon powder (75%), respectively. The formation of the diimine-bridged dimer was complete within 3 hr, indicating the rapid nature of the coordination of the np ligand to the dirhodium core.…”

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confidence: 99%

Electronic influences of bridging and chelating diimine ligand coordination in formamidinate-bridged Rh2(II,II) dimers

et al. 2016

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Two new formamidinate-bridged Rh 2 II,II complexes, cis-[Rh 2 II,II (µ-DTolF) 2 (µ-np) 2 ] 2+ (3; DTolF = N,N′-dip -tolylformamidinate; np = 1,8-naphthyridine) and cis-[Rh 2 II,II (µ-DTolF) 2 (κ 2-dap) 2 ] 2+ (4; dap = 1,12-diazaperylene), were synthesized from [Rh 2 II,II (µ-DTolF) 2 (CH 3 CN) 6 ](BF 4) 2 (1), and their properties were compared to those of [Rh 2 II,II (µ-DTolF) 2 (phen) 2 ](BF 4) 2 (2). Density functional theory (DFT) and electrochemical analyses support the description of the highest occupied molecular orbitals (HOMOs) of 3 and 4 as possessing contributions from the metals and formamidinate bridging ligands, with Rh 2 /form character, and lowest unoccupied molecular orbitals (LUMOs) localized on the respective diimine ligand np and dap π* orbitals. Both 3 and 4 display strong, low energy Rh 2 /formdiimine(π*) metal/ligand-to-ligand charger transfer (1 ML-LCT) transitions with maxima at 566 nm (ε = 3,600 M −1 cm −1) for 3 and at 630 nm (ε = 2,900 M −1 cm −1) for 4 in CH 3 CN. Time dependent-DFT (TD-DFT) calculations support these assignments. The ability of both the bridging np and chelating dap diimine ligands to produce strong absorption of these Rh 2 II,II complexes throughout the visible region is potentially useful for the development of new photocatalysts for H 2 production and photochemotherapeutics.

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“…The bond distances found trans to guanidinate nitrogen atoms are slightly longer than those cis to them. This lengthening trend of trans groups is similar to the trans influence of both guanidinate and formamidinate groups relative to carboxylates. ,, Meanwhile, the average N–C bond lengths were 1.357 Å for – hpp and 1.331 Å for – DAniF, which are consistent with the delocalized charge in these bonds.…”

Section: Resultsmentioning

confidence: 99%

Redox Potential Tuning of Dimolybdenum Systems through Systematic Substitution by Guanidinate Ligands

et al. 2020

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We report the synthesis and characterization of a series of dimolybdenum paddlewheel complexes of the type Mo 2 (DAniF) 4−n (hpp) n (n = 1−3), where DAniF is the anion of N,N′-di-p-anisyl-formamidine and hpp is the anion of 1, 3,4,6,7,8hexahydro-2H-pyrimido[1,2-a]pyrimidine. The effect on the electronic structure of these tetragonal paddlewheel dimolybdenum compounds was studied upon systematic substitution of formamidinate ligands by the more basic guanidinates. Mo−Mo distances in the paddlewheel structures decreased upon guanidinate ligand substitution, and were found to be 2.0844(6) and 2.0784(6), for Mo 2 (DAniF) 3 (hpp) (1 ) and trans-Mo 2 (DAniF) 2 (hpp) 2 (2), respectively. Electrochemical studies show that the half-wave potential of the Mo 2 5+ /Mo 2 4+ couple shifts cathodically upon ancillary ligand substitution ranging from −0.286 V for the tetraformamidinate complex to −1.795 V for the tetraguanidinate analogue and with redox potentials of −0.75, −1.07, and −1.14 V for 1, 2, and 3 (Mo 2 (DAniF)(hpp) 3 ), respectively. The presence of a second redox event assigned to the Mo 2 6+ /Mo 2 5+ couple was not observed until two guanidinate ligands were introduced. Raman spectroscopy shows that the v(M−M) stretch gets systematically strengthened upon formamidinate ligand substitution by the guanidinate ligand hpp. The induced delta bond destabilization by the basic hpp ligand was measured using DFT calculations by tracking the energy of the frontier orbitals. The decrease in the HOMO−LUMO energy gap was supported by the red shift in the UV−vis spectra of the compounds: 412, 442, and 450 nm for 1, 2, and 3, respectively.

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Dirhodium Formamidinate Compounds with Bidentate Nitrogen Chelating Ligands

Cited by 25 publications

References 36 publications

Head‐to‐Head Cross‐Linked Adduct between the Antitumor Unit Bis(μ‐N,N′‐di‐p‐tolylformamidinato)dirhodium(II,II) and the DNA Fragment d(GpG)

Head‐to‐Head Cross‐Linked Adduct between the Antitumor Unit Bis(μ‐N,N′‐di‐p‐tolylformamidinato)dirhodium(II,II) and the DNA Fragment d(GpG)

Electronic influences of bridging and chelating diimine ligand coordination in formamidinate-bridged Rh2(II,II) dimers

Redox Potential Tuning of Dimolybdenum Systems through Systematic Substitution by Guanidinate Ligands

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