CRYSTAL-STRUCTURES OF NS-[RU(DPPE)(2)(CO)(CL)](BF4)CENTER-DOT-2(TOLUENE) AND TRANS-[RU(DPPM)(2)(CO)(CL)](BF4)CENTER-DOT-CH2CL2 - A STUDY OFTHE STERIC AND ELECTRONIC LIGAND EFFECTS OF TRANS-POSITIONED DIPHOSPHINE LIGANDS

Single-crystal X-ray diffraction studies were carried out on the compl exes trans-[Ru(dppe)(2)(CO)(Cl)](BF4). 2(toluene) (1) (where dppe = 1, 2-bis(diphenylphosphino)ethane) and trans-[Ru(dppm)(2)(CO)(Cl)](BF4). CH2Cl2 (2) (where dppm = bis(diphenylphosphino) methane). Complex 1 cr ystallizes in the orthorhombic space group P2(1)2(1)2 with a=14,366(3) , b=17.075(3), c=12.433(2) Angstrom, V=3049.8(10) Angstrom(3) and Z=2, The structure was refined to R=3.02% for 3233 reflections above 6 sig ma (R=4.46% for all 3991 point-group independent data); the Ru-cation lies on a site of C-2 symmetry, leading to disorder of the Cl and CO l igands. Complex 2 crystallizes in the orthorhombic space group Pna2(1) , with a=22.425(7), b=11.515(4), c=19.511(10) Angstrom, V=5038(3) Angs trom(3) and Z=4. The structure was refined toR=4.43% for 4770 reflecti ons above 6 sigma (R=7.09% for all 6631 point-group independent data). The crystal structure data suggest increased intramolecular interliga nd interactions with the trans-bis(dppe) complexes relative to the tra ns-bis(dppm) complexes, In order to further assess the steric ligand e ffects of dppm and dppe on the redox chemistry of ruthenium complexes, the electrochemical data for complexes 1 and 2 as well as for trans-R u(dppe)(2)(Cl)(2) and trans-Ru(dppm)(2)(Cl)(2) were analyzed. The E(pa ) value for the oxidation of complex 1 was more positive than the E(pa ) value for the oxidation of complex 2; similarly, the E(1/2) value fo r the oxidation of trans-Ru(dppe)(2)(Cl)(2) was more positive than the E(1/2) value for the oxidation of trans-Ru(dppm)(2)(Cl)(2). The incre ase in the redox potentials for the oxidation of the dppe complexes ma y be due to the enhanced intramolecular interligand interactions of th e dppe ligands, which is in agreement with the crystal structure data.