Recent Research: Some of our projects are described briefly below.

1. We prepared 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 relativeaffinity 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).

2. We 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.

3. 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: Some possible topics 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+.