ELECTROPHILIC ATTACK ON DIPHOSPHAZANE-BRIDGED DERIVATIVES OF DIRUTHENIUM NONACARBONYL BY HALOGENS - CRYSTAL-STRUCTURE OF [RU2(MU-I)I(CO)3(MU-(PRIO)2PN(ET)P(OPRI)2)2]

Treatment of [Ru2(mu-CO)(CO)4{mu-(RO)2PN(Et)P(OR)2}2] (R = Me or Pr(i)) with halogens results in the ready formation of [Ru2X(CO)5{mu-(RO)2PN(Et)P(OR)2}2]+ (X = Cl, Br or I) with the halogen atom co-ordinating terminally. These pentacarbonyl species, isolated as their hexafluorophosphate salts, decarbonylate in solution, rapidly in the presence of trimethylamine N-oxide dihydrate but slowly in the absence of this decarbonylating agent, to produce the tetracarbonyl species [Ru2(mu-X)(CO)4{mu-(RO)2PN(Et)P(OR)2}2]+ in which the halogen bridges the two ruthenium atoms. Substitution of the carbonyl groups in these tetracarbonyl species can be effected further by halide ions, either photochemically or by promoting the process using Me3NO.2H2O and thus reaction of [Ru2(mu-X)(CO)4{mu-(RO)2PN(Et)P(OR)2}2]+ with chloride, bromide or iodide ions in the presence of Me3NO.2H2O readily affords [Ru2(mu-X)X(CO)3{mu-(RO)2PN(Et)P(OR)2}2]. Significantly, treatment of [Ru2I(CO)5{mu-(RO)2PN(Et)P(OR)2}2]I3, or [Ru2I(CO)5{mu-(RO)2PN(Et)P(OR)2}2]PF6 in the presence of iodide ions, with an excess of Me3NO.2H2O leads solely to the neutral tetracarbonyl derivative [Ru2I2(CO)4{mu-(RO)2PN(Et)P(OR)2}2]. On the basis of an X-ray crystallographic study on [Ru2(mu-I)I(CO)3{mu-(Pr(i)O)2PN(Et)P(OPr(i))2}2], the tricarbonyl derivatives have structures related to that of [Ru2(mu-X)-(CO)4{mu-(RO)2PN(Et)P(OR)2}2]+ with an axial carbonyl group having been replaced by a halide ion.