Reactions of Neutral Scandium/Phosphorus Lewis Pairs with Small Molecules
journal contributionposted on 26.06.2018, 19:14 by Kejian Chang, Xiaoming Wang, Zhengning Fan, Xin Xu
Treating a scandium mixed alkyl/diaryloxide complex with phosphino-substituted alcohols resulted in the formation of scandium mixed alkoxyl/diaryloxide complexes Sc[OC(CH3)2CH2PR2][O-2,6-tBu2-C6H3]2[THF] (6, R = Ph; 8, R = tBu). The reactivity of Sc-based Lewis pair complexes 6 and 8 toward a wide range of substrates was investigated. A ligand substitution reaction occurred when complex 6 was treated with benzophenone. The reaction of complex 6 with sulfur afforded a phosphane oxidative product. Complexes 6 and 8 also exhibited typical Sc/P frustrated Lewis pair (FLP) reactivity. They added to the carbonyl group of phenyl isocyanate to form seven-membered metallacycles. Complex 6 underwent selective Sc/P 1,4-addition reactions with α,β-unsaturated carbonyl compounds to give the corresponding nine-membered metallacyclic products. The reaction of 6 with 0.5 mol of dimethyl acetylenedicarboxylate led to the formation of bicyclo[7.7.0]cetane-derived metallacycle 16 in a distinctive double 1,4-addition pattern. With benzil complex 6 underwent a 1,4-addition reaction to afford a cis-enediolate which was coordinated to the Sc/P FLP through Sc–O and P–O bonds. Treatment of complex 6 with cyclopropyl phenyl ketone afforded the 10-membered metallaheterocycle 18, in which a scandium Lewis acid added to the oxygen atom and the phosphine Lewis base attacked the cyclopropyl group with ring opening. A ring-opening reaction also took place when epoxycyclohexane was employed as a substrate. Complex 6 successfully cleaved the C–Br bond of benzyl bromide to give zwitterionic complex 20 with newly formed Sc–Br and P–C bonds. Scandium phosphazine complex 21 was generated by a Sc/P 1,1-addition to the terminal nitrogen atom of (trimethylsilyl)diazomethane. Aided by the phosphorus Lewis base, scandium Lewis acid was able to abstract chloride from (Ph3P)AuCl to produce heterobimetallic Sc/Au complexes 22 and 23. Many complexes in this study were characterized by single-crystal X-ray diffraction.
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form seven-membered metallacyclesSc-based Lewis pair complexes 6single-crystal X-ray diffractionphosphorus Lewis baseTHFC 6 H 310- membered metallaheterocycle 18bondFLPPRligand substitution reactionComplex 6phosphane oxidative productCHterminal nitrogen atomscandium Lewis acidnine-membered metallacyclic productscyclopropyl phenyl ketonephosphine Lewis base