High Structural Control in Metal-Mediated Synthesis of New Functionalized Diphosphines Using Diphosphinoketenimines as Precursors

The diphosphinoketenimine ligand in the neutral complexes fac-[MnI(CO)3{(PPh2)2CCNR}] (1 a: R = Ph; 1 b: R = p-tolyl) undergoes nucleophilic attack by MeLi and nBuMgCl yielding, after hydrolysis, the diphosphinoenamine-containing complexes fac-[MnI(CO)3{(PPh2)2CC(R′)NHR}] (3 a,b: R′ = Me; 4 a,b: R′ = nBu). Complex 1 a reacts under the same conditions with H2CCCHMgBr to afford fac-[MnI(CO)3{(PPh2)2CC(CH2CCCH)NHR}] (5 a), which contains a terminal alkyne group on the α-carbon atom of the diphosphinoenamine ligand. The cationic complexes fac-[Mn(CO)4{(PPh2)2CCNR}]+ (6) react with H2CCCHMgBr to afford diphosphinomethanide derivatives bearing three different types of functional groups, depending upon the substituent on the nitrogen atom of the ketenimine: cumulene in fac-[Mn(CO)4{(PPh2)2CC(CHCCH2)N-xylyl}] (7 d), internal alkyne in fac-[Mn(CO)4{(PPh2)2CC(CCCH3)NtBu}] (8), and quinoline in 9 (R = Ph), whose formation implies an unusual cyclization process. Protonation of 7 d, 8, and 9 with HBF4 occurs at the nitrogen atom to give the cationic derivatives 10 d, 11, and 12, respectively, which contain the corresponding functionalized diphosphine ligands. Irradiation of 3 a,b and 4 a,b with Vis/UV light makes it possible to isolate the free ligands (PPh2)2CC(R′)NHR (13 a,b and 14 a,b), completing the metal-assisted synthesis of these novel functionalized diphosphines. Irradiation of 12 with Vis/UV light generates free phosphinoquinoline ligand 15, which readily affords a complex 16 containing 15 as a P,N-chelating ligand when treated with [PdCl2(NCMe)2], thus demonstrating its coordination capability.