Research: Current research includes a series of square-planar d8 complexes of formula trans-Rh(PPh3)2(CO)X and determined the relative

   affinity of the Rh(I) center for a range of monoanions X- by infrared spectroscopic studies (using the carbonyl stretching bands) of equilibria such

   as the one shown below.

Rh(PPh3)2(CO)F + Cl- = Rh(PPh3)2(CO)Cl + F-

   Of particular interest was the relative affinity within the halides: X- = F- > Cl- > Br- > I-. The extent of perturbation of equilibrium of Rh(PPh3)2(CO)F

   + Br- = Rh(PPh3)2(CO)Br + F- by addition of small amounts of polar compounds (e.g., H2O, MeOH, EtOH, Me2CO, Me2SO) allowed us

   to measure their relative strengths of solvation of F-. This project involved synthesis of organometallic complexes, their spectroscopic

   characterization, and measurement of equilibrium constants in anhydrous solutions by IR and electronic spectroscopy. We are currently

   extending these studies to other trans-Rh(PR3)2(CO)X systems (including growing crystals for x-ray diffraction structures for correlation

   with those predicted in computational studies with Dr. Wierzbicki and a U. of Memphis group).

   We have also prepared the octahedral d6 fluoro complexes mer,trans-Re(CO)3(PPh3)2F and (C5H5)Ru(CO)(PCy3)F and showed by infrared

   spectroscopy (using the MCº O stretching bands) that their rates of ligand-substitution were much faster than those of their chloro and bromo

   analogs.

   Additionally, we have prepared several sets of octahedral d6 complexes to study the kinetics of ligand substitution: (i) for

   (C5H5)Ru(PPh3)2X, replacement of PPh3 by CO (X =: Cl, Br, I, NCO) and (ii) replacement of weakly coordinating anions Y- (NO3- and O2PF2-)

   in (C5H5)Ru(CO)(L)Y by uninegative ligands (e.g., Br-) as a function of the nature of L. Reactions were monitored by IR (MCº O stretches)

   and visible-UV spectroscopy.

   Prospective research projects that can be pursued are listed below. All entail organometallic synthesis, instrumental characterization

   of complexes, equilibrium and/or kinetics measurements on infrared, visible-UV, and/or NMR spectrometers, growth of crystals for

   x-ray structures, and structure computations.

1. Steric effects observed in trans-Rh(PR3)2(CO)X for especially bulky PR3 ligands.

2. Ligand-substitution equilibrium studies on the
square-planar Rh(I) carbenoid species at the right

Rh(PR3)(C)(CO)X + PR' 3 = Rh(PR' 3)(C)(CO)X + PR3

Rh(PR3)(C)(CO)X + Y- = Rh(PR3)(C)(CO)Y + X-

3. Studies of ligand effects in bonding of N- and S-aromatics (e.g., pyridine, C5H5N, and thiophene, C4H4S);

stereoelectronic effects of R and N-ligand in equilibria of square-planar d8 trans-Rh(PR3)2(CO)(L)+

and in the electrochemistry of d6 species Ru(phen)2(CO)(L)2+.

 

   Recent Publications & Collaborations:

  

   Sykora, R. E., Harris, A. G., Clements, J. W., & Hoffman, N. W. (2011). Dichlorido(η⁶-p-cymene)(4-fluoroaniline-κN)ruthenium(II). Acta

   Crystallographica Section E: Structure Reports, E67, m99-m100.

   Wicker, B. F., Seaman, R., Hoffman, N. W., Davis Jr., J. H., & Sykora, R. E. (2011). {2,6-Bis[(2,6-diphenylphosphanyl)oxy]-4-fluorophenyl-κ³P,C¹,P

   ’}(6-methyl-2,2,4-trioxo-3,4-dihydro-1,2,3-oxathiazin-3-ido-κN)palladium(II). Acta Crystallographica Section E: Structure Reports, E67, m286-m287.

   Clements, J. W., Grenga, D., & Hoffman, N. W. (2011).  Ligand Substitution Reactions of (O,N,)-dipicolinate)Palladium(II).  Poster presentation at

   the 18^th Annual University of South Alabama Research Forum, Mobile, AL.

   Clements, J. W., Forbes, D. C., Hoffman, N. W., Obiako, A. J., & South, M. S. (2011).  The Synthesis and Use of Zwitterionic Micelles for the

   Remediation of Aqueous Systems.Poster presentation at the 18^th Annual University of South Alabama Research Forum, Mobile, AL.

   Arnold, S. E., Battiste, D. R., Clements, J. W., Forbes, D. C., Hoffman, N. W., Mockel, W. D., & Oertli, C. (2011).  Microwave Assisted Diels-Alder

   Synthesis of trans-6-Methyl-3-Cyclohexene Carboxylic Acid.  Poster presentation at the 18^th Annual University of South Alabama Research

   Forum, Mobile, AL.