Synthesis Of Ruthenium (Ⅱ) Hydroxide Complexes And Their Roles In The Catalytic Hydration Of Acetonitrile And Terminal Alkynes

In organic synthesis, hydration reaction between nitrile and alkyne needs of catalyst such as mercury salt or acid catalysis, which caused serious environmental damage, so the exploration for new and efficient and environmental catalyst of hydration reaction between nitrile and alkyne has important significance. Transition metal complexes with [Ru]-OH bond has been considered to be the important intermediates in many catalytic reaction taking water as the substrate, but the number of detachable mononuclear transition metal hydroxyl complexes is not much. So the hydration reaction between nitrile and alkyne using hydroxyl complexes as catalyst is seldom reported. In this paper, two single-core transition metal ruthenium hydroxide complexes have been designed and synthetized, the reaction mechanism of hydration reaction and terminal alkyne were studied deeply in order to find efficient green catalyst.The main content can be summarized as follows:1. The hydration of acetonitrile and terminal alkynes catalyzed by TpRu(PPh₃)₂(OH) and TpRu(PPh₃)(CNCH₃)(OH) was respectively studied. (1) Catalytic hydration of acetonitrile did not occur in dried THF solution. The further study showed that added water has large effect on the catalytic hydration reaction. The catalytic mechanism is proposed that O-bonded imido complex TpRu(PPh₃)(CH₃CN)(OCMe=NH) is the key intermediate, which then undergoes nucleophilic attack at the carbon atom of nitrile ligand to form TpRu(PPh₃)(η²-N,O-NH=CMeN=CMeO). Ring-opening necleophilic attack of TpRu(PPh₃)(η²-N,O-NH=CMeN=CMeO) by water pruduces TpRu(PPh₃) (NH=C(OH)Me)(OCMe=NH). The displacement of NH=C(OH) Me ligand in the latter complex by acetonitrile forms acetamide, and regenerates TpRu (PPh₃)(CH₃CN)(OCMe=NH) to fulfill catalytic cycle. (2) The hydration of two terminal alkynes (benzene acetylene and 1-hexyne) catalyzed by TpRu(PPh₃)₂(OH) and TpRu(PPh₃)(CH₃CN)(OH) was respectively studied. The reaction results showed that catalytic hydration of terminal alkynes occurred when TpRu(PPh₃)(CH₃CN)(OH) was employed as catalyst, but it did not occur using TpRu(PPh₃)₂(OH) as catalyst. There are two reasons: phenyl ring of phenylacetylene formsπ-πconjugation with triple bond, which decreases the electronic negativity of carbon atom in C≡C so that phenylacetylene does not easily combine with ruthenium center. In addition, steric hindrance of PPh₃ ligand in TpRu(PPh₃)₂(OH) blocks the alkyne to combine with TpRu(PPh₃)2(OH), and thus influences catalytic hydration cycle.2. A novel water-soluble ruthenium hydroxide complex cis-[(bipy)₂Ru (OH)(H₂O)](OTf) was synthesized via deprotonation of [(bipy)₂Ru(H₂O)₂] (OTf)₂ (bipy = 2,2′-bipyridine, OTf- = triflate) by DBU (1,8-Diazabicyclo [5.4.0]undec-7-ene), which was conformed by IR, EA and NMR spectra. (1) The catalytic hydration of acetonitrile to form acetamide catalyzed by cis-[(bipy)₂Ru(OH)(H₂O)](OTf) was studied. O-bonded imido complex [(bipy)₂Ru(N≡CCH₃)(OCMe=NH)]⁺ is postulated to be the key intermediate, which then undergoes nucleophilic attack at the carbon atom of nitrile ligand to form [(bipy)₂Ru(η²-N,O-NH=CMeN=CMeO)]⁺. Ring-opening nucleophilic attack of [(bipy)₂Ru(η²-N,O-NH=CMeN=CMeO)]⁺ by water produces [(bipy)₂Ru(NH=C(OH)Me)(OCMe=NH)]⁺. The displacement of NH=C(OH) Me ligand in the latter complex by acetonitrile forms acetamide, and regenerates [(bipy)₂Ru(N≡CCH₃)(OCMe=NH)]⁺ to fulfill catalytic cycle. (2) The catalytic hydration of 1-hexyne to form 1-hexanal was observed. [(bipy)₂Ru(=C=CHR)(OH)]⁺ is proposed to be the key intermediate. Undergoes nucleophilic attack at the carbon atom of Ru-C to form (bipy)₂ RuC(OH)=CHR by oxygen atom of hydroxyl ligand .Finally, add water to form 1-hexanol.