Syntheses, Structures, and Reactivity Studies of Half-Open Ruthenocenes and Their Oxodienyl Analogues

Improved synthetic routes to Cp*Ru(Pdl) complexes (Pdl = 2,4-dimethylpentadienyl and
various oxodienyl ligands) including Cp*Ru(η5-2,4-Me2-C4H3O) (1), Cp*Ru[η5-2,4-(t-Bu)2-C4H3O] (1‘), and Cp*Ru(η5-2,4-Me2-C5H5) (1‘ ‘) have been developed, and the relative
reactivities of the resulting complexes toward oxidative addition or ligand addition reactions
have been examined. Thus, the oxopentadienyl complexes 1 and 1‘ and the 2,4-dimethylpentadienyl complex 1‘ ‘ were found to undergo oxidative addition of SnCl4, Me2SnCl2, I2,
Cl2 (via CHCl3), and O2, yielding Cp*Ru[η3-CH2C(R)CHC(R)O](X1)(X2) [R = Me, X1 = Cl, X2
= SnCl3 (2); R = Me, X1 = X2 = I (3); R = t-Bu, X1 = X2 = I, (3‘); R = Me, X1 = X2 = Cl (4);
R = t-Bu, X1 = X2 = Cl (4‘)] or Cp*Ru[η3-CH2C(Me)CHC(Me)CH2](X1)(X2) [(X1) = Cl, (X2) =
SnClMe2 (2a‘ ‘); (X1) = (X2) = I2 (3‘ ‘); (X1) = (X2) = Cl2 (4‘ ‘)] and a peroxide Cp*Ru[η3-CH2C(Me)CHC(Me)O](O2) (5) readily, the oxodienyl products having η3-oxodienyl coordination
occurring preferentially through an all-carbon allylic fragment, in line with ruthenium's
soft nature. The O2 reaction was of additional interest in that it also led to a product in
which oxidation of the Cp* ligand to a C5Me4(CHO) ligand had occurred, giving (η5-C5Me4CHO)Ru[η5-CH2C(Me)CHC(Me)O] (6). In contrast to the above, reactions of the 2,4-di(tert-butyl)oxodienyl or 2,4-dimethylpentadienyl ligand complexes were much less favorable,
occurring much more slowly, if at all. For the reaction of CHCl3 with the 2,4-dimethylpentadienyl complex, a small amount of an η6-toluene complex, [Cp*Ru(η6-C7H8)][Cp*RuCl3]
(11), was formed, apparently as a result of a carbon−carbon bond activation, giving a
rearrangement of the dienyl ligand. The additions of Lewis bases to the oxodienyl complexes,
leading to Cp*Ru[η3-CH2C(Me)CHC(Me)O]L species [L = PPh3 (7), PHPh2 (8), PMe3 (9), CO
(10)], were most facile for small donors such as PMe3, while PPh3 and CO additions were
more reversible. Structural data have been obtained for representative examples of the above,
i.e., complexes 1, 1‘, 2, 5, 6, 7, and 11.