Oxidative Dehydrogenation of Tris(o-isopropylphenyl)phosphines by Platinum Complexes
摘要:
The binuclear cyclometalates [Pt2Cl2{2-CMe2C6H4P(C6H4(2-Pr-i))(2)}(2)] (1a) and [Pt2Cl2{2-CMe2C6H3(4-OMe)P(C6H3(2-Pr-i)(4-OMe))(2)}(2)] (1b) react with CHCl2CHCl2 to give the corresponding mononuclear phosphine-alkene chelates [PtCl2{2-CH2=CMeC6H4P(C6H4(2-Pr-i))(2)}] (2a) and [PtCl2{2-CH2=CMeC6H3(4-OMe)P(C6H3(2-Pr-i)(4-OMe))(2)}] (2b). The product 2a can also be formed directly from [PtCl2((NCBu)-Bu-t)(2)] and L-a in CHCl2CHCl2 or by addition of SO2Cl2 to 1a. Addition of an excess of SO2Cl2 to 1b gave [PtCl2{2-CH2=CMeC6H3(4-OMe)P(C6H2(2-Pr-i)(4-OMe)(5-Cl))(2)}] (3b), a derivative of 2b featuring meta-chlorine substituents on the terminal P groups as a result of electrophilic aromatic substitution. A mechanism for the conversion of 1a,b to 2a,b is proposed involving an electrophilic alkyl C-H activation by a coordinatively unsaturated platinum(IV) species. The mechanism is supported by the isolation of the diplatinum(IV) cyclometalate [Pt2Cl2{2-CH2C6H3(4-OMe)P(C6H3(2-Me)(4-OMe))(2)}] as a mixture of syn and anti isomers 5b and 5b'. The crystal structures of 2a and 3b have been determined.