FLUXIONAL BEHAVIOR OF TERT-BUTYL-SUBSTITUTED 2,2' 6'2''-TERPYRIDYLMOLYBDENUM(0) AND 2,2'-BIPYRIDYLMOLYBDENUM(II) COMPLEXES - ENHANCED SOLUBILITY AND EASE IN NMR-STUDY CAUSED BY THE TERT-BUTYL GROUP/

Reaction of [Mo(CO)(4)(norbomadiene)] with 4,4',4 ''-tri-tert-butyl-2, 2':6',2 ''-terpyridine afforded the complex [Mo(CO)(4)(4,4',4 ''-(t)Bu (3)terpy)] (2), which in solution shows fluxional behavior, observed b y H-1 and C-13 NMR studies at between 25 and -70 degrees C. [Mo(CO)(4) (4,4'-(t)Bu(2)bipy)] (1) reacts with I-2 and SnBr4 by oxidative additi on to give molybdenum(II) complexes, [Mo(CO)(3)(4,4'-(t)Bu(2)bipy)I-2] (3) and [Mo(CO)(3)(4,4'-(t)Bu(2)bipy)(SnBr3)Br] (4). The related comp ounds [Mo(CO)(4,4'-(t)Bu(2)bipy)X(2)] (X = Br(5) or Cl(6)) have been p repared by oxidation of 1 with two equivalents of CuX(2). The IR spect ra of 3 in different polar solvents suggest that this compound exists in solution in two isomeric forms, which are in equilibrium. The NMR s pectra of 3, 5 and 6 are temperature dependent, indicating their dynam ic behavior in solution. Delta G double dagger values for the fluxiona l process of about 47 kJ mol(-1) and about 53 kJ mol(-1) have been obt ained for 5 and 6 respectively. Low temperature C-13 NMR studies of 4 have shown that this compound in solution has a different kind of flux ional behavior.