METALLACYCLOHEXADIENE AND METALLABENZENE CHEMISTRY .6. CHEMISTRY OF AN (ETA-6-METALLABENZENE)METAL COMPLEX, [(ETA-6-IR-CH-C(ME)-CH-C(ME)-CH)(PET3)3]MO(CO)3

Iridabenzene, (Ir radical-anion CH radical-anion C(Me) radical-anion CH radical-anion C(Me) radical-anion CH)(PEt3)3 (1), displaces p-xylene from (eta-6-p-xylene)MO(CO)3 in tetrahydrofuran solvent, producing (eta-6-iridabenzene)MO(CO)3 (2). The solid state structure of 2 has been determined by a single-crystal X-ray diffraction study (monoclinic, P2(1)/n, a = 9.897 (i) A, b = 16.213 (3) angstrom, c = 20.937 (3) angstrom, beta = 96.68 (1)-degrees, V = 3336.7 (9) angstrom3, Z = 4, R = 0.036, R(w) = 0.042). The iridium center in 2 retains the square-pyramidal coordination geometry of parent compound 1, but the MO(CO)3 Moiety now occupies the formerly "open face" of the pyramid. In solution, the iridabenzene ring rotates with respect to the Mo(CO)3 fragment. The barrier for this process (DELTA-G double dagger) is estimated to be less than 8 kcal/mol. Treatment of 2 with PMe3 or CO (L) results in clean replacement of one basal PEt3 ligand and production of [(eta-6-Ir radical-anion CH radical-anion C(Me) radical-anion CH radical-anion C(Me) radical-anion CH)(PEt3)2(L)]Mo(CO)3 (3, L = PMe3; 4, L = CO). The solid state structure of 3 (monoclinic, P2(1)/n, a = 10.005 (2) angstrom, b = 18.012 (3) angstrom, c = 17.055 (4) angstrom, beta = 93.33 (2)-degrees, V = 3068.3 (11) angstrom3, Z = 4, R = 0.031, R(w) = 0.041) confirms the basal coordination position of the PMe3 ligand. As in 2, solution-phase arene ring rotation in 3 and 4 is facile. Treatment of 2-4 with HBF4.OEt2 leads to proto nation of the metal centers and production of the novel mu-H heterobimetallic complexes, {[eta-6-Ir radical-anion CH radical-anion C(Me) radical-anion CH radical-anion C(Me) radical-anion CH)(PEt3)2(L)(mu-H)]Mo(CO)3}+BF4- (5, L = PEt3; 6, L = PMe3; 7, L = CO). In the solid state structure of 6.tetrahydrofuran (orthorhombic, P2(1)2(1)2(1), a = 10.200 (4) angstrom, b = 16.467 (9) angstrom, c = 22.023 (7) angstrom, V = 3699 (3) angstrom3, Z = 4, R = 0.022, R(w) = 0.029), the hydride ligand resides approximately trans to the axial phosphine on iridium but bends in slightly toward molybdenum, generating a P(ax)-Ir-H angle of 173 (2)-degrees. The Ir-H and Mo-H bond lengths are 1.77 (6) and 1.97 (7) k, respectively. While solution-phase arene ring rotation still occurs in 5-7, the barrier for this process (DELTA-G double dagger) increases to approximately 13.5-15 kcal/mol.