56281-34-6Relevant academic research and scientific papers
QUANTITATIVE STUDIES OF CHEMICAL REACTIVITY OF TETRA- mu -BUTYRATO-DIRHODIUM(II) COMPLEXES.
Drago,Tanner,Richman,Long
, p. 2897 - 2903 (1979)
In the reported experiments, the authors have studied the thermodynamics of adduct formation for 1:1 and 2:1 adducts formed by Lewis bases with Rh//2(C//4H//7O//2)//4 in benzene solutions. Electrochemical studies of these adducts were also carried out in CH//2Cl//2. Corrections for a benzene-acid interaction were necessary to obtain solvent minimized enthalpies of acid-base adduct formation. The thermodynamic data clearly demonstrates substantial changes in the acidic and redox properties of the second metal as a result of base coordination to the first. The metal-metal bonding in the system causes this dimer to be a most unusual Lewis acid, as evidenced by deviations of the E and C predicted enthalpies from those observed. The unusual Lewis acid properties are attributed to the enhanced pi -back-bonding capability of the rhodium(II) center as a result of extensive mixing of orbitals with pi symmetry on the two metal centers. This causes the rhodium(II) center to be very effective in pi -back-bonding to the axial ligands. The reduction potentials of Rh//2(C//4H//7O//2)** plus , Rh//2(C//4H//7O//2)//4B** plus , and Rh//2(C//4H//7O//2)//4B//2** plus are analyzed, and provide further support for the extensive pi -back-bonding capabilities of this metal cluster.
EPR spectra and bonding in the 2:1 Base adducts of Rh2(carboxylate)4+
Drago, Russell S.,Cosmano, Richard,Telser, Joshua
, p. 3120 - 3124 (2008/10/08)
In this paper, EPR studies are reported on a series of 1:1 and 2:1 adducts of Rh2(butyrate)4+. The results provide a simplified interpretation of the EPR spectra of the 2:1 adducts. The key feature is the energy of the additional molecular orbital that arises when the donor lone pair is mixed into the 1:1 adduct to form the 2:1 adduct. When the donor lone pair ionization potential is low (C number is large) and the interaction strong, this σ molecular orbital becomes the HOMO and an EPR signal is detected. When the donor ionization potential is high and the interaction weak, the HOMO is π* and no EPR spectrum is seen. The EPR spectrum of the cation provides no insight into the question of π-stabilization. Clearly, in the CO adducts the π-back-bonding is slight compared to that of most metal carbonyls but it is a significant fraction of the total weak interaction of CO with this acid. The complexes formed when pyridine or N-methylimidazole is added in excess to the radical cation do not have axial symmetry.
Metal synergism in the coordination chemistry of a metal-metal bonded system: Rh2(C3H7COO)4
Drago, Russell S.,Long, John R.,Cosmano, Richard
, p. 2920 - 2927 (2008/10/08)
An earlier study on the thermodynamic and electrochemical properties of Rh2But4 (But = butyrato) led to the conclusion that π back-bonding in d14 metal dimer systems is responsible for some unusual cluster chemistry. In an attempt to more fully understand the influence that substitution on one metal center in a cluster has on a second metal center, further studies on Rh2But4 have been carried out. This problem could not be investigated in the solvent benzene, because coordination of this solvent occurred. To gain further support for benzene coordination and to investigate the influence of ΔH1:1 on ΔH2:1, we carried out analogous studies in CH2Cl2. In contrast to the results in benzene, ΔH2:1 is not as negative as ΔH1:1 for all adduct formation reactions measured in CH2Cl2. Evidence that π-back-bonding stabilization is important in adducts of the dimer is supported by the data in CH2Cl2. A mathematical model has been developed that can be used to set an upper limit of π stabilization in the 2:1 adduct for those bases which undergo a π-back-bonding interaction with Rh2But4. This permits an unprecedented comparison of the extent of π-back-bond stabilization upon coordination of sequential competitive π-acceptor ligands. A novel application of isosbestic points is presented that improves the determination of the four values for K1, K2, ε1, and ε2.
