SYNTHETIC, SPECTROSCOPIC, AND ELECTROCHEMICAL STUDIES OF THE ISOMERICALLY-RICH [M(CO)(2)(P2P')X](+ 0) (M=MN, RE X=CL, BR P2P'=ETA(3)-PH(2)P(CH2)(2)P(PH)(CH2)(2)PPH(2)) SYSTEM - STRUCTURAL CHARACTERIZATION OF ANOVEL PAIR OF DIASTEREOISOMERS OF CIS,MER-RE(CO)(2)(P2P')CL/

Reaction of Mn(CO)(5)X (X = Cl, Br) with Ph(2)P(CH2)(2)P(Ph)(CH2)(2)PP h(2) (P2P') in refluxing xylene led to the formation of isomerically p ure Cis,mer-Mn(CO)(2)(eta(3)-P2P')X. Cyclic voltammograms in dichlorom ethane (0.1 M Bu(4)NPF(6)) show a reversible one-electron oxidation (p rocess 1, E(1/2) = 0.142 V) to give cis,mer-[Mn(CO)(2)(P2P')X](+). How ever, in acetone (0.1 M Bu(4)NPF(6)) at room temperature, process 1 is not reversible and an additional redox process 4 (E(1/2) = 0.048 V) i s observed. Process 4 is not observed at low temperatures, and at high er temperatures in acetone it merges with process 1 and also a new rev ersible redox couple (process 5, E(1/2) = -0.411 V) appears. A combina tion of electrolyses, chemical oxidation, and subsequent reduction, co upled with IR and P-31 NMR spectroscopies and electrospray mass spectr ometry (ESMS), is used to show that processes 1, 4, and 5 are all asso ciated with redox and interconversion reactions of different isomers o f Mn(CO)(2)(P2P')X and [Mn(CO)(2)(P2P')X](+). Other irreversible proce sses due to oxidation of the different isomers of [Mn(CO)(2)(P2P')X]() are observed at very positive potentials. Reaction between Re(CO)(5) X and P2P' in refluxing mesitylene gives a soluble product and a small amount of precipitate. The major soluble product was identified as ci s,mer-Re(CO)(2)(P2P')X, and the oxidative chemistry is similar to that of the manganese analogues. The precipitate consists of five compound s, one of which was cis,mer-Re(CO)(2)(P2P')X. The new compounds A-D we re identified as follows: A is cis,mer-{Re(CO)(2)(P2P')X}(2), a dimeri c species with bridging P2P' ligands. The spectroscopic data for B ind icated that it was a form of cis,mer-Re(CO)(2)(P2P')X, but not the sam e as the major product. Compound C is cis,fac-Re(CO)(2)P(P2P')X, and c ompound D was shown to be fac-[Re(CO)(3)(P2P')]X. The crystal structur es of cis,mer-Re(CO)(2)(P2P')CI(I) and cis,mer-Re(CO)(2)(P2P') Cl(II) show the compounds to be diastereoisomers with the same mer geometry o f the P2P' ligand, which of necessity generates a cavity formed by thr ee phenyl rings on one side of the rhenium atom. The coordination geom etry of the two compounds differ only by the interchange of the mutual ly trans chloro and carbonyl ligands. In (I) the carbonyl ligand is wi thin the cavity and in (II) the chloro ligand is within the cavity.