Electrochemistry of Some Rhodium(I) Complexes

Author: Najdzionek, Jan Stanley

Year: 1982

Degree: Dissertation (Ph.D.)

Advisor: Dervan, Peter B.

Committee Members: Anson, Fred C.; Gray, Harry B.; Janda, Kenneth C.; Dervan, Peter B.

Option: Chemistry

DOI: 10.7907/pqye-xp04

Abstract

The electrochemistry of Rh[C6H5)2P(CHx)nP(C6H5)2]2 Y where Y = CF3SO-3 or ClO-4, x = 2 with n = 1, 2, 3, 4 and x = 1 with n = 2 was examined and compared with that of Co[(C6H5)2P(CHx)2P(C6H5)2]2 where x = 1 and 2. Cyclic voltammetric (CV), chronoamperometric (CA), polarographic (including D.C., normal and differential pulse) and bulk electrolytic experiments were performed and the results show that all of these Rh(I) phosphine complexes are reduced in a two-electron process.

CV and CA measurements were used to determine the heterogeneous electron transfer rate constants for Rh[(C6H5)2P(CH2)2P(C6H5)2]2. The values determined were 0.0092 and 0.0087 cm/sec, respectively, and the results are discussed in relation to the Butler-Volmer formulation of electrode kinetics.

Fluorescence measurements were made on the above rhodium complexes for n = 1, 3 and 4 at room temperature and at 77 K. None emit under ambient conditions in solution but the compound containing ligands with a single methylene unit backbone emitted at 77 K with a lifetime of 20 microseconds. The UV-Visible spectrum of reduced Rh(DPP)+2, the most stable of the reduced complexes, displayed a very intense absorption at 450 nm which was assumed to be charge-transfer in origin.

The two-electron reduction of Rh2(2,5-dimethyl-2,5-diisocyanohexane)2+4 produced a unique species in which a CN- ion has been lost resulting in the formation of a cyclohexylimine ligand which bridges the metal atoms through the imine function. The strain imposed on the TMB ligand backbone forces the rhodium atoms to have the strongest interaction of any of the Rh(Br)+4 compounds studied [Rh(l)-Rh(2) = 2.970(1)Å]. Linear isocyanide carbon-nitrogen distances range from 1.153(9) to 1.175(9) Å while the imine carbon-nitrogen is extended slightly to 1.254(9) Å.

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