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(η 5 -2,4-Me 2 -C 4 H 3 O) ( 1 ), Cp*Ruη 5 -2,4-( t -Bu) 2 -C 4 H 3 O ( 1 ‘), and Cp*Ru(η 5 -2,4-Me 2 -C 5 H 5 ) ( 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 SnCl 4, Me 2 SnCl 2, I 2, Cl 2 (via CHCl 3 ), and O 2, yielding Cp*Ruη 3 -CH 2 C(R)CHC(R)O(X 1 )(X 2 ) R = Me, X 1 = Cl, X 2 = SnCl 3 ( 2 ); R = Me, X 1 = X 2 = I ( 3 ); R = t -Bu, X 1 = X 2 = I, ( 3 ‘); R = Me, X 1 = X 2 = Cl ( 4 ); R = t -Bu, X 1 = X 2 = Cl ( 4 ‘) or Cp*Ruη 3 -CH 2 C(Me)CHC(Me)CH 2 (X 1 )(X 2 ) (X 1 ) = Cl, (X 2 ) = SnClMe 2 ( 2a ‘ ‘); (X 1 ) = (X 2 ) = I 2 ( 3 ‘ ‘); (X 1 ) = (X 2 ) = Cl 2 ( 4 ‘ ‘) and a peroxide Cp*Ruη 3 -CH 2 C(Me)CHC(Me)O(O 2 ) ( 5 ) readily, the oxodienyl products having η 3 -oxodienyl coordination occurring preferentially through an all-carbon allylic fragment, in line with ruthenium's soft nature. The O 2 reaction was of additional interest in that it also led to a product in which oxidation of the Cp* ligand to a C 5 Me 4 (CHO) ligand had occurred, giving (η 5 -C 5 Me 4 CHO)Ruη 5 -CH 2 C(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 CHCl 3 with the 2,4-dimethylpentadienyl complex, a small amount of an η 6 -toluene complex, Cp*Ru(η 6 -C 7 H 8 )Cp*RuCl 3 ( 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*Ruη 3 -CH 2 C(Me)CHC(Me)OL species L = PPh 3 ( 7 ), PHPh 2 ( 8 ), PMe 3 ( 9 ), CO ( 10 ), were most facile for small donors such as PMe 3, while PPh 3 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 .