Synthesis and reactivity of the labile dihydrogen complex [{MeC(CH2PPh2)(3)}Ir(H-2)(H)(2)]BPh4

The novel Ir(III) nonclassical tetrahydrido complex [(triphos)Ir(H-2)(H)(2)]BPh4 (4BPh(4)) has been prepared by hydrogenation of the ethene dihydride complex [(triphos)Ir(C2H4)(H)(2)]BPh4 in either the solid state (P-H2 greater than or equal to 1 atm) or CH2Cl2 solution (P-H2 greater than or equal to 3 atm) [triphos = MeC(CH2PPh2)(3)]. Complex 4BPh(4) is very labile in solution and can be isolated in the solid state exclusively from solid-gas reactions. Characterization of 4BPh(4) in solution can be achieved by high-pressure NMR and IR spectroscopies, however. Various deuterated isotopomers of [(triphos)Ir(H-2)(H)(2)](+) have been obtained in CD2Cl2 solution at low temperature by treatment of the trihydride [(triphos)IrH3] with DOSO2CF3. On the basis of a variety of NMR experiments, the complex cation [(triphos)Ir(H-2)(H)(2)](+) is assigned an octahedral structure where two terminal hydride ligands and a dihydrogen molecule are trans to the phosphorus atoms of a facial triphos ligand. Complex 4BPh(4) dissolves in THF at room temperature yielding [(triphos)IrH3], BPh3, and benzene; a similar reaction occurs in acetone, whereas in CH2Cl2 the complex loses H-2 converting to the dimers cis- and trans-[(triphos)IrH(mu-H)(2)HIr(triphos)](BPh4)(2).