Transition Metal Complexes of PNP and PNN Ligands: Synthesis and Catalytic Applications in Hydrophosphination of Terminal Alkynes
Khilesh C. Dwivedi, Gazal Sabharwal, Maravanji S. BalakrishnaABSTRACT
In this study, we report the synthesis and structural characterization of a series of transition metal complexes derived from two pincer‐type ligands: {(o‐PPh2)C6H4C(O)NH(C9H6N)} (1) and {(o‐Ph2PC6H4C(O)N(H)C6H4PPh2‐o)} (2). Treatment of Ligand 1 with [Rh (acac)(CO)2] afforded rhodium pincer complex [Rh (CO){(o‐PPh2)C6H4C(O)N(C9H6N)}κ3‐P,N,N] (3). Ligand 1, upon reaction with [Ru(H)(CO)(Cl)(PPh3)3] in THF, yielded the ruthenium complex [Ru (PPh3)(CO)(Cl){(o‐PPh2)C6H4C(O)N(C9H6N)}κ3‐P,N,N] (4), while its reaction with [Ru (Cl)2(PPh3)3] in methanol afforded a RuIII complex, [Ru (CH3OH)(Cl)2{(o‐PPh2)C6H4C(O) N(C9H6N)}κ3‐P,N,N] (5). Ligand 2, when reacted with CuI in a 1:1 M ratio in a CH2Cl2/CH3CN (1:1 v/v) mixture, yielded the dimeric complex [CuI(o‐PPh2)C6H4C(O) N(H)CH2C6H4(o‐PPh2)]2 (6). Increasing the CuI to ligand ratio to 2:1 yielded the tetrameric complex [Cu4(μ2‐I)2(μ3‐I)2{(o‐PPh2)C6H4C(O)NCH2C6H4 (o‐PPh2)}2‐P,P] (7). The reaction of Ligand 2 with two equivalents of [AuCl (SMe2)] produced a binuclear gold complex, [AuCl{(o‐PPh2)C6H4C(O)N(H)CH2C6H4{(o‐PPh2)}AuCl] (8). Furthermore, Ligand 2 underwent complexation with [Rh (acac)(CO)2] and [Mn2(CO)10] to afford PNP‐type pincer complexes [RhCO{(o‐PPh2)C6H4C(O)NCH2C6H4(o‐PPh2)}κ3‐P,N,P] (9) and [Mn (CO)3{(o‐PPh2)C6H4 C(O)NCH2C6H4(o‐PPh2)}κ3‐P,N,P] (10) respectively. Notably, the rhodium PNN pincer Complex 3 was successfully employed as a catalyst in the additive‐free hydrophosphination of phenylacetylenes, providing a more straightforward and operationally simple methodology for this transformation.