Photochemistry of Os(dmpe)(2)H-2: Matrix, transient solution, and NMR studies of 16-electron Os(dmpe)(2) (dmpe = Me2PCH2CH2PMe2)

The complex Os(dmpe)(2)H-2 (dmpe =Me2PCH2CH2PMe2) was synthesized by reacti on of trans-Os(dmpe)(2)Cl-2 with sodium under hydrogen and was shown to con sist of cis and trans isomers in a ratio of ca. 60:1. UV irradiation in arg on and methane matrices yielded Os(dmpe)(2) with a characteristic multiband UV-vis spectrum; the lowest energy transition occurs close to 800 nm. In C O-doped matrices, Os(dmpe)(2)(CO) was generated. Laser flash photolysis exp eriments (266 nm excitation) demonstrated that the same species was produce d in cyclohexane solutions of Os(dmpe)(2)H-2 at room temperature. The initi al photoproduct, Os(dmpe)(2), is formed within 60 ns of the laser flash. Th is species reacts with hydrogen and with CO with rate constants exceeding 1 0(9) dm(3) mol(-1) s(-1), indicating that there is essentially no barrier t o its reaction with these substrates. Rate constants for reaction with ethe ne, triethylsilane, and nitrogen are all close to 10(8) dm(3) mol(-1) s(-1) . Comparison of the UV-vis spectrum of Os(dmpe)(2) with Ru-0, Rh+, and Iranalogues indicates that Os(dmpe)(2) has a structure close to square planar (local Du, symmetry). The products of photochemical reaction of Os(dmpe)(2 )H-2 in solution were also studied by NMR spectroscopy. Reaction with benze ne yields cis-Os(dmpe)(2)(Ph)H, while reaction with ethene yields cis- and trans-Os(dmpe)(2)(CH=CH2)H.