SYNTHESIS AND PROPERTIES OF (ETA-5-6,6-DIMETHYLCYCLOHEXADIENYL)MOLYBDENUM ((DMCH)MOLN) COMPLEXES - X-RAY STRUCTURE OF [(DMCH)(CO)2MO]2

The ancillary character of the 6,6-dimethylcyclohexadienyl ligand (dmCh) was examined via the syntheses of various (dmCh)MoLn derivatives. Treatment of (diglyme)Mo(CO)3 with K(dmCh) afforded [K(diglyme)n][dmCh)Mo(CO)3] (1, 85%), which was converted to (dmCh)Mo(CO)3I (2) by I2 in low yield. The addition of HgI2 to 2.0 equiv of 1 produced [(dmCh)Mo(CO)3]2Hg (3, 77%); iodination of 3 generated 2 in 65% yield. Photolysis of 3 provided the dimer, [(dmCh)Mo(CO)3]2 (4), which was most conveniently prepared via [Cp2Fe]PF6 oxidation of 1 (57%). Thermolysis of 4 yielded a triply bonded dimer, [(dmCh)Mo(CO)2]2 (5,80%), that contains a 2.508-Å Mo≡Mo bond and two semibridging carbonyls. Crystal data for 5: Cu Kα, triclinic, P1, a = 9.654 (1) Å, b = 8.658 (1) Å, c = 12.608 (2) Å, α = 93.44 (1)°, β = 104.80 (1)°, γ = 100.79 (1)°, Z = 2, T = 23 °C, R = 0.049, Rw = 0.036, 2518 reflections (|Fo| ≥ 3σ(Fo)). Anion 1 (Ea = +0.14 V) and singly bonded dimer 4 (Ec = -0.60 V) were observed to be electrochemically coupled via either an ECE or an ECC process; 5 displayed a reversible reduction at -1.10 V. Diazald reacted with 1 to form (dmCh)Mo(CO)2NO (6, 46%); exposure of 6 to PPh3 and PMe3 resulted in the synthesis of (dmCh)Mo(PPh3)(NO)CO (7) and (dmCh)Mo(PMe3)(NO)CO (9) in modest yield, the latter via (η1-dmCh)Mo(PMe3)2(CO)2NO (8). The characteristics of these complexes, as compared with cyclopentadienyl congeners, are consistent with an assessment of dmCh as a strong-field ligand. © 1990, American Chemical Society. All rights reserved.