Platinum Assisted Tandem P-C Bond Cleavage and P-N Bond Formation in Amide Functionalized Bisphosphine o -Ph 2 PC 6 H 4 C(O)N(H)C 6 H 4 PPh 2 - o : Synthesis, Mechanistic, and Catalytic Studies.

The reactions of amide functionalized bisphosphine o -Ph 2 PC 6 H 4 C(O)N(H)C 6 H 4 PPh 2 - o ( 1 ) with platinum salts are described. Treatment of 1 with [Pt(COD)Cl 2 ] yielded a chelate complex, [PtCl 2 { o -Ph 2 PC 6 H 4 C(O)N(H)C 6 H 4 PPh 2 - o } κ 2 -P,P ] ( 2 ), which on subsequent treatment with LiHMDS formed a novel 1,2-azaphospholene-phosphine complex [Pt(C 6 H 5 )Cl{ o -C 6 H 4 {C(O)N( o -PPh 2 (C 6 H 4 ))P(Ph)}} κ 2 -P,P ] ( 3 ) involving a tandem P-C bond cleavage and P-N bond formation. The same complex 3 on passing dry HCl gas afforded the dichloro complex [PtCl 2 { o -C 6 H 4 {C(O)N( o -PPh 2 (C 6 H 4 ))P(Ph)}} κ 2 -P,P ] ( 5 ). Complex 2 upon refluxing in toluene or treatment of 1 with [Pt(COD)Cl 2 ] in the presence of a base at room temperature resulted in the pincer complex [PtCl{ o -Ph 2 PC 6 H 4 C(O)N(C 6 H 4 PPh 2 - o )} κ 3 -P,N,P ] ( 4 ). Reaction of 1 with [Pt(COD)ClMe] at room temperature also afforded the pincer complex [PtMe{ o -Ph 2 PC 6 H 4 C(O)N(C 6 H 4 PPh 2 - o )} κ 3 -P,N,P ] ( 6 ). Mechanistic studies on 1,2-azaphospholene formation showed the reductive elimination of LiCl to form a phosphonium salt that readily adds one of the P-C bonds oxidatively to the in situ generated Pt 0 species to form a chelate complex 3 . The analogous palladium complex [PdCl 2 { o -C 6 H 4 {C(O)N( o -PPh 2 (C 6 H 4 ))P(Ph)}} κ 2 -P,P ] ( 7 ) showed excellent catalytic activity toward N -alkylation of amines with alcohols with a very low catalyst loading (0.05 mol %), and the methodology is very efficient toward the gram-scale synthesis of many N -alkylated amines.