Synthesis and Reactivity of the Labile Dihydrogen Complex [{MeC(CH2PPh2)3}Ir(H2)(H)2]BPh4

The novel Ir(III) nonclassical tetrahydrido complex [(triphos)Ir(H2)(H)2]BPh4 (4BPh4) has been prepared by hydrogenation of the ethene dihydride complex [(triphos)Ir(C2H4)(H)2]BPh4 in either the solid state (PH2 g 1 atm) or CH2Cl2 solution (PH2 g 3 atm) [triphos ) MeC(CH2PPh2)3]. Complex 4BPh4 is very labile in solution and can be isolated in the solid state exclusively from solid-gas reactions. Characterization of 4BPh4 in solution can be achieved by high-pressure NMR and IR spectroscopies, however. Various deuterated isotopomers of [(triphos)Ir(H2)(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(H2)(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 4BPh4 dissolves in THF at room temperature yielding [(triphos)IrH3], BPh3, and benzene; a similar reaction occurs in acetone, whereas in CH2Cl2 the complex loses H2 converting to the dimers cis- and trans-[(triphos)IrH(í-H)2HIr(triphos)](BPh4)2.