REACTIONS OF THE RHENIUM(I) FRAGMENT [(MEC(CH(2)PPH(2))(3))RE(CO)(2)](+) - SYNTHESIS AND CHARACTERIZATION OF A STABLE CATIONIC ETA(2)-H-2 COMPLEX OF RHENIUM

Reaction of Re(CO)(3)(PPh(3))(2)Cl with MeC(CH(2)PPh(2))(3) (triphos) gives (triphos)Re(CO)(2)Cl (1) which is converted to the hydride (triphos)Re(CO)(2)H (2) by treatment with LiAlH4. An X-ray diffraction analysis of 2 shows that the rhenium atom is octahedrally coordinated by triphos, which occupies a triangular face of the coordination polyhedron, by two carbonyl groups and by a terminal hydride ligand. Treatment of 2 with Me(3)OBF(4) results in the evolution of methane and formation of the unsaturated complex [(triphos)Re(CO)(2)]BF4 (4) which is stabilized by an agostic interaction between the rhenium center and a phenyl C-H bond of triphos. The eta(2)-H-2 complex [(triphos)Re(CO)(2)(H-2)]BF4 (3) is obtained either by protonation of 2 or by addition of Hz to the agostic complex 4. The presence of an intact dihydrogen ligand in 3 is unambiguosly shown by H-1 NMR spectroscopy [T-lmin = 8.6 ms (CD2Cl2, 300 MHz, -58 degrees C); J(HD) of 30.8 Hz for the monodeuteriated isotopomer [(triphos)Re(CO)(2)(HD)]-BF4 (3-d(1))]. Vinylidene derivatives of the formula [(triphos)Re(CO)(2)({C=C(H)R)]BPh(4) (R = Ph, 8; CO(2)Et, 9; C6H13, 10) are obtained by reaction of either the eta(2)-H-2 complex 3 or the agostic complex 4 with terminal alkynes in the presence of NaBPh(4). The preference for the coordination of neutral groups at rhenium in the [(triphos)Re(CO)(2)](+) fragment follows the order N-2 < C-H-(agostic) < H-2 < HC=CR < CH3CN < CO. All the reactions described have been carried out in tetrahydrofuran or dichloromethane.