Ethylene Insertion in Tp‘Pt(Ph)(η²-CH₂CH₂) and C−H Activation of Ethylbenzene to Form a Platinum(IV) <i>o</i><i>rtho</i>-Metalated Phenethyl Complex

Abstract

Heating Tp‘Pt(Ph)(η 2 -CH 2 CH 2 ) ( 5 ) in benzene forms an ortho -metalated phenethyl hydrido platinum(IV) complex, ( 7 ). Presumably this net reaction reflects phenyl migration to ethylene to give the insertion product, Tp‘PtCH 2 CH 2 Ph, as an unsaturated intermediate. Intramolecular C−H activation of an ortho phenyl proton from this intermediate would produce the metallacyle product. Low-temperature protonation of the phenyl ethylene complex 5 results in the formation of a cationic η 2 -ethylene phenyl complex, [κ 2 -(HTp‘)Pt(C 6 H 5 )(η 2 -CH 2 CH 2 )][BAr‘ 4 ] ( 6 ). Low-temperature protonation of the ortho -metalated phenethyl complex 7 followed by addition of acetonitrile leads to reductive coupling of the Pt−H and the alkyl methylene group to give a cationic Pt(II) 2-ethylphenyl complex, [κ 2 -(HTp‘)Pt(C 6 H 4 -2-CH 2 CH 3 )(NCCH 3 )][BAr‘ 4 ] ( 9 ). Complex 7 has also been isolated as the sole product of gentle heating of Tp‘Pt(Me) 2 (H) ( 2 ) with the Lewis acid B(C 6 F 5 ) 3 in ethylbenzene. Additional analogous Pt(IV) metallacycles, ( 11a/11b ) and ( 13 ), have also been synthesized by this route. Note that heating of the dihydride reagent Tp‘Pt(Me)(H) 2 ( 3 ) with B(C 6 F 5 ) 3 in either ethylbenzene or 2-propylbenzene gave only Tp‘Pt(Ar)(H) 2 ( 14 and 15 ) products. Attempts to isolate an η 2 -propylene phenyl complex were unsuccessful; formation of the 1,2-insertion product, ( 10 ), and 2,1-insertion products, 11a and 11b, resulted. An in situ attempt to isolate the cationic [κ 2 -(HTp‘)Pt(C 6 H 5 )(η 2 -CH 2 CH(CH 3 ))][BF 4 ] resulted in the isolation of the Pt(II) phenyl aqua complex [κ 2 -(HTp‘)Pt(C 6 H 5 )(OH 2 )][BF 4 ] ( 12 ) instead.