Transition Metal Complexes of PNP and PNN Ligands: Synthesis and Catalytic Applications in Hydrophosphination of Terminal Alkynes

In this study, we report the synthesis and structural characterization of a series of transition metal complexes derived from two pincer‐type ligands: {( o ‐PPh 2 )C 6 H 4 C(O)NH(C 9 H 6 N)} ( 1) and {( o ‐Ph 2 PC 6 H 4 C(O)N(H)C 6 H 4 PPh 2 ‐ o )} ( 2 ). Treatment of Ligand 1 with [Rh (acac)(CO) 2 ] afforded rhodium pincer complex [Rh (CO){( o ‐PPh 2 )C 6 H 4 C(O)N(C 9 H 6 N)}κ 3 ‐ P , N , N ] ( 3 ). Ligand 1 , upon reaction with [Ru(H)(CO)(Cl)(PPh 3 ) 3 ] in THF, yielded the ruthenium complex [Ru (PPh 3 )(CO)(Cl){( o ‐PPh 2 )C 6 H 4 C(O)N(C 9 H 6 N)}κ 3 ‐ P , N , N ] ( 4 ), while its reaction with [Ru (Cl) 2 (PPh 3 ) 3 ] in methanol afforded a Ru III complex, [Ru (CH 3 OH)(Cl) 2 {( o ‐PPh 2 )C 6 H 4 C(O) N(C 9 H 6 N)}κ 3 ‐P,N,N] (5) . Ligand 2 , when reacted with CuI in a 1:1 M ratio in a CH 2 Cl 2 /CH 3 CN (1:1 v/v) mixture, yielded the dimeric complex [CuI( o ‐PPh 2 )C 6 H 4 C(O) N(H)CH 2 C 6 H 4 ( o ‐PPh 2 )] 2 ( 6 ). Increasing the CuI to ligand ratio to 2:1 yielded the tetrameric complex [Cu 4 ( μ 2 ‐I) 2 ( μ 3 ‐I) 2 {( o ‐PPh 2 )C 6 H 4 C(O)NCH 2 C 6 H 4 ( o ‐PPh 2 )} 2 ‐ P , P ] ( 7 ). The reaction of Ligand 2 with two equivalents of [AuCl (SMe 2 )] produced a binuclear gold complex, [AuCl{( o ‐PPh 2 )C 6 H 4 C(O)N(H)CH 2 C 6 H 4 {( o ‐PPh 2 )}AuCl] ( 8 ). Furthermore, Ligand 2 underwent complexation with [Rh (acac)(CO) 2 ] and [Mn 2 (CO) 10 ] to afford PNP‐type pincer complexes [RhCO{( o ‐PPh 2 )C 6 H 4 C(O)NCH 2 C 6 H 4 ( o ‐PPh 2 )}κ 3 ‐ P , N , P ] ( 9 ) and [Mn (CO) 3 {( o ‐PPh 2 )C 6 H 4 C(O)NCH 2 C 6 H 4 ( o ‐PPh 2 )}κ 3 ‐ 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.