Variable hydrazine coordination modes from reactions with dichlorotris(triphenylphosphine)ruthenium(II)

Abstract

The reactivity of the prominent ruthenium(II) catalyst and precursor, RuCl2(PPh3)3, was explored with hydrazine and its derivatives. The reactions produced 6-coordinate ruthenium(II) products that bond with the hydrazine moiety in bridging (NH2NH2 or NH2NHMe), end-on (NH2NHMe, NH2NHPh, or NH2NMe2), or side-on (NH2NMe2) fashions. The products have been characterized by single crystal X-ray diffraction and 31P NMR spectroscopy. With NH2NH2, the dimeric product, [RuCl2(PPh3)2]2(μ-N2H4)2, was formed under all conditions used. For other hydrazines, the reaction stoichiometry governed product formation to yield either bimetallic or monomeric products. When the RuCl2(PPh3)3 to hydrazine derivative ratio was 1:1 or lower, bimetallic complexes were formed while a 1:2 ratio produced monomeric compounds. The exception to the latter occurs with the production of the monomeric compound, RuCl2(PPh3)2(η2-NH2NMe2), that forms employing a 1:1 ratio. In addition to stoichiometry, steric factors and hydrogen bonding played a significant role in dictating the bonding mode of hydrazines. The bimetallic complexes were further reacted to yield the corresponding monomeric products, adopting the form RuCl2(PPh3)2(L)2 (L = NH2NHMe, NH2NHPh, or NH2NMe2). Reactions utilizing less than a 1:2 ratio of RuCl2(PPh3)3 to NH2NMe2 produced a mixture of products that appear to be in equilibrium. DFT calculations were performed to gain insight into the reaction energetics and molecular stability.